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Yangsheng Xu

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111 papers
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111

EAAI Journal 2024 Journal Article

Incorporating syntax and semantics with dual graph neural networks for aspect-level sentiment analysis

  • Pengcheng Wang
  • Linping Tao
  • Mingwei Tang
  • Liuxuan Wang
  • Yangsheng Xu
  • Mingfeng Zhao

Aspect-level sentiment analysis is a more fine-grained task that aims to determine the sentiment polarity of specific aspects. Recent studies have employed graph attention networks and graph convolutional networks to model dependency trees, effectively establishing explicit associations between aspects and opinions, yielding promising performance. However, these methods have limitations in capturing complex linguistic features and the intricate dependencies between aspects and their contexts, resulting in suboptimal performance. In this paper, we propose a dual graph neural network that incorporates syntax and semantics, called IDGNN. Specifically, we utilize the relational graph attention network (RGAT) to encode the syntactic dependency tree and obtain syntactic information, while incorporating dependency labels to enhance aspect representation. Additionally, the semantic graph convolutional network (SemGCN) is employed to encode the self-attention matrix and capture semantic information, with the inclusion of orthogonal regularization to enhance semantic association. Furthermore, we introduce two fusion strategies based on gate mechanisms: the syntax fusion module (SYF) and the semantic fusion module (SEF). SYF combines contextual and syntactic representations to obtain global syntactic features, while SEF fuses semantic information with global syntactic features to obtain the final feature representation. Experimental results demonstrate that our proposed model achieves state-of-the-art performance on several benchmark datasets.

ICRA Conference 2022 Conference Paper

A User-customized Automatic Music Composition System

  • Fan Mo
  • Xiaoqiang Ji 0001
  • Huihuan Qian
  • Yangsheng Xu

This paper introduces an intelligent system which composes music following the users' instructions. Current auto-matic music generation models are lack of stability. Meanwhile, they cannot satisfy the preference of different people. To overcome these challenges, we train a Transformer-based neural network to generate short music segments using a dataset. A user can compose music pieces by interacting with a well-trained generator. Our system collects the user's feedback during the interactions, and fine-tunes the neural network to optimize the generator. After a large number of interactions, our system can learn the musical taste of the user and customize a personal automatic music composer for him or her. Our work enhances the application value of generative models significantly, which enables people to compose music with the assistance of artificial intelligence.

IROS Conference 2021 Conference Paper

BORM: Bayesian Object Relation Model for Indoor Scene Recognition

  • Liguang Zhou
  • Jun Cen
  • Xingchao Wang
  • Zhenglong Sun 0001
  • Tin Lun Lam
  • Yangsheng Xu

Scene recognition is a fundamental task in robotic perception. For human beings, scene recognition is reasonable because they have abundant object knowledge of the real world. The idea of transferring prior object knowledge from humans to scene recognition is significant but still less exploited. In this paper, we propose to utilize meaningful object representations for indoor scene representation. First, we utilize an improved object model (IOM) as a baseline that enriches the object knowledge by introducing a scene parsing algorithm pretrained on the ADE20K dataset with rich object categories related to the indoor scene. To analyze the object co-occurrences and pairwise object relations, we formulate the IOM from a Bayesian perspective as the Bayesian object relation model (BORM). Meanwhile, we incorporate the proposed BORM with the PlacesCNN model as the combined Bayesian object relation model (CBORM) for scene recognition and significantly outperforms the state-of-the-art methods on the reduced Places365 dataset, and SUN RGB-D dataset without retraining, showing the excellent generalization ability of the proposed method. Code can be found at https://github.com/FreeformRobotics/BORM.

IROS Conference 2021 Conference Paper

Design of an SSVEP-based BCI Stimuli System for Attention-based Robot Navigation in Robotic Telepresence

  • Xingchao Wang
  • Xiaopeng Huang
  • Yi Lin
  • Liguang Zhou
  • Zhenglong Sun 0001
  • Yangsheng Xu

Brain-computer interface (BCI)-based robotic telepresence provides an opportunity for people with disabilities to control robots remotely without any actual physical movement. However, traditional BCI systems usually require the user to select the navigation direction from visual stimuli in a fixed background, which makes it difficult to control the robot in a dynamic environment during the locomotion. In this paper, a novel SSVEP-based BCI stimuli system is proposed for robotic telepresence. The novel system utilized the live video streamed from the robot onboard camera as the input. By altering and flickering the detected objects in the scene with different frequencies predefined based on their relative positions on the screen, the robot can be navigated based on the user’s attention in a dynamic manner. In order to better differentiate multiple objects (more than the number of frequencies predefined), the task-related component analysis (TRCA) model was trained with a priori offline experimental data to select the front objects with priority. Experiments were conducted to validate the proposed system. Using the system, four human subjects are able to control a humanoid robot to navigate through multiple objects to reach the desired goal. The success rate reaches 87. 5% in average.

ICRA Conference 2021 Conference Paper

Long-Range Hand Gesture Recognition via Attention-based SSD Network

  • Liguang Zhou
  • Chenping Du
  • Zhenglong Sun 0001
  • Tin Lun Lam
  • Yangsheng Xu

Hand gesture recognition plays an essential role in the human-robot interaction (HRI) field. Most previous research only studies hand gesture recognition in a short distance, which cannot be applied for interaction with mobile robots like unmanned aerial vehicles (UAVs) at a longer and safer distance. Therefore, we investigate the challenging long-range hand gesture recognition problem for the interaction between humans and UAVs. To this end, we propose a novel attention-based single shot multibox detector (SSD) model that incorporates both spatial and channel attention for hand gesture recognition. We notably extend the recognition distance from 1 meter to 7 meters through the proposed model without sacrificing speed. Besides, we present a long-range hand gesture (LRHG) dataset collected by the USB camera mounted on mobile robots. The hand gestures are collected at discrete distance levels from 1 meter to 7 meters, where most of the hand gestures are small and at low resolution. Experiments with the self-built LRHG dataset show our methods reach the surprising performance-boosting over the state-of-the-art method like the SSD network on both short-range (1 meter) and long-range (up to 7 meters) hand gesture recognition tasks.

IROS Conference 2021 Conference Paper

Object-to-Scene: Learning to Transfer Object Knowledge to Indoor Scene Recognition

  • Bo Miao
  • Liguang Zhou
  • Ajmal Mian
  • Tin Lun Lam
  • Yangsheng Xu

Accurate perception of the surrounding scene is helpful for robots to make reasonable judgments and behaviours. Therefore, developing effective scene representation and recognition methods are of significant importance in robotics. Currently, a large body of research focuses on developing novel auxiliary features and networks to improve indoor scene recognition ability. However, few of them focus on directly constructing object features and relations for indoor scene recognition. In this paper, we analyze the weaknesses of current methods and propose an Object-to-Scene (OTS) method, which extracts object features and learns object relations to recognize indoor scenes. The proposed OTS first extracts object features based on the segmentation network and the proposed object feature aggregation module (OFAM). Afterwards, the object relations are calculated and the scene representation is constructed based on the proposed object attention module (OAM) and global relation aggregation module (GRAM). The final results in this work show that OTS successfully extracts object features and learns object relations from the segmentation network. Moreover, OTS outperforms the state-of-the-art methods by more than 2% on indoor scene recognition without using any additional streams. Code is publicly available at: https://github.com/FreeformRobotics/OTS.

ICRA Conference 2014 Conference Paper

A geometric approach to stroke extraction for the Chinese calligraphy robot

  • Yuandong Sun
  • Huihuan Qian
  • Yangsheng Xu

Known as “the art of strokes”, Chinese calligraphy expresses its aesthetic through the strokes. A calligraphy learner practise the strokes and compose a calligraphic character by the strokes thereafter. Following the same process, the calligraphy robot, Callibot [2] needs to extract the strokes from a character. Therefore, we propose an approach to extract strokes using the geometric properties on the contour(s) of a character. A key discovery is that if two strokes intersect, the contour is concave; otherwise it is convex. The curvature vector defined in [1] is used to locate the vertexes whose interior angles are greater than 180° (these vertexes are named as C-points). C-points separate the contours into sub-contours. The corresponding sub-contours then form the basic strokes (i. e. dot stroke, horizontal stroke, vertical stroke, left-falling stroke and right-falling stroke). The experimental results show that this approach is feasible of extracting strokes from characters. This research is also useful for Chinese character recognition and calligraphic styles classification.

IROS Conference 2014 Conference Paper

Design and implementation of a low-cost and lightweight inflatable robot finger

  • Ronghuai Qi
  • Tin Lun Lam
  • Yangsheng Xu

In this paper, mechanical design and implementation of a low-cost and lightweight inflatable robot finger are proposed. The proposed soft inflatable robot finger is different from traditional designs. It uses a common and low cost inflatable material and can be easily and massively manufactured. The proposed soft inflatable finger only weighs 0. 8 grams, but can well realize swift movement which is actuated by low pressure air. Numerous analyses and experiments have been conducted for key parameters selection of the mechanical design. The performances of the proposed finger including flexing and extending have also been evaluated, and results are satisfactory.

ICRA Conference 2014 Conference Paper

Kinematic modeling and control of a multi-joint soft inflatable robot arm with cable-driven mechanism

  • Ronghuai Qi
  • Tin Lun Lam
  • Yangsheng Xu

In this paper, the kinematic modeling and control for a multi-joint inflatable robot arm with cable-driven mechanism are proposed. The soft inflatable robot arm is capable of imitating human arms to realize remote interaction. The weight of the arm is only about 50 grams, and collision safe. To solve the challenge problems of kinematics of the soft inflatable arm, new approaches are proposed, including redundant rigid arm and soft inflatable joint models. The approaches have a good advantage of applying to muti-joint arms. As our knowledge it is the first time to solve the kinematics of muti-joint soft inflatable arm in Three-Dimensional coordinate space. Numerous experiments have been conducted, including movement space and positioning accuracy. The workspace and velocity are close to an adult's arm movement space and normal motion speed.

ICRA Conference 2014 Conference Paper

Longitudinal wheel-slip control for four wheel independent steering and drive vehicles

  • Tin Lun Lam
  • Huihuan Qian
  • Yangsheng Xu

In this paper, a longitudinal wheel-slip controller for four wheel independent steering and drive (4WISD) vehicles is proposed to suppress longitudinal wheel slip in varying road conditions. Different from conventional methods that consider single driving source and zero steering angle, the proposed controller considers all independent traction sources from each driving wheel and omnidirectional steering command so as to eliminate slip detection errors in 4WISD vehicles. The proposed controller requires low cost sensing equipment, including merely wheel speed sensor and accelerometer, which makes the system practical to be utilized. The proposed wheel-slip controller can be applied to vehicles with arbitrary quantity of driving wheels and different steering configurations such as traditional two-front-wheel steering and two-rear-wheel steering. Numerical simulation results are presented to demonstrate the efficiency of the proposed longitudinal wheel-slip controller.

ICRA Conference 2014 Conference Paper

Mechanical design and implementation of a soft inflatable robot arm for safe human-robot interaction

  • Ronghuai Qi
  • Tin Lun Lam
  • Yangsheng Xu

In this paper, a novel soft inflatable arm is proposed for telepresence robots. It is capable of imitating human arms to realize remote interaction. The new proposed arm using a very common and low cost inflatable material, and it is very light, which weight is only about 50 grams, but can well realize agile movement by driving three tiny cables installed in shoulder joint and elbow joint, respectively. Meanwhile, the proposed cable driven mechanism also allows connecting numbers of joints easily. The soft inflatable can work just by pumping air with very low pressure (7. 32 ± 3. 45 kPa), and allows human directly and safely contact without any external sensors. Moreover, to solve the challenge problems of soft joint deformation, the kinematic modeling of the joint with deformation compensation is also developed. Experimental results show that the soft inflatable arm can agilely move for remote interaction. The workspace and velocity are also close to an adult's arm movement space and normal motion speed.

IROS Conference 2014 Conference Paper

Robot learns Chinese calligraphy from Demonstrations

  • Yuandong Sun
  • Huihuan Qian
  • Yangsheng Xu

Chinese calligraphy is a unique form of art in the world, whose aesthetic is mainly created by the proper manipulation of the brush. However, it is impossible for a person to figure out the 6-D motion of the brush from calligraphy images, if he has no experience of writing calligraphy. In this paper, we propose a Learning from Demonstration approach for our calligraphy robot, Callibot, to acquire calligraphy skills. We first propose a new stroke parametrization approach. Then we apply Locally Weighted Linear Regression to map from the stroke parameters to the trajectory of the brush. The training data are obtained from several demonstrations. Thereafter, Callibot is capable of writing a new stroke, if the stroke's parameters are given. The resulting motion is as natural as human writing. Experimental results prove the feasibility of our proposed approach. This approach is independent of the robot and is compatible with any robot with six or more degrees of freedom. This approach can be further integrated with our previous research, i. e. stroke extraction, so that Callibot will be able to replicate calligraphy from images.

IROS Conference 2013 Conference Paper

A novel hand posture recognition system based on sparse representation using color and depth images

  • Dan Xu 0006
  • Yen-Lun Chen
  • Xinyu Wu 0001
  • Wei Feng 0009
  • Huihuan Qian
  • Yangsheng Xu

Hand posture is a natural and effective human robot interaction way. In this paper, an user-independent hand posture recognition system using depth and color images captured from an RGB-D camera is presented. To recognize hand posture against complicated background conditions, we propose a novel method for automatic and accurate hand posture segmentation which detects the hand with Chamfer matching, tracks the hand with Kalman filter and segments the hand with region growing algorithm only in the depth space. A new hand posture descriptor invariant to scale, shift and in-plane rotation is constructed with the combination of local contour Fourier descriptor and global Bag-of-Features (BoF) descriptor based on Scale Invariance Feature Transform (SIFT). The sparse representation-based classification (SRC) is applied to perform the hand posture recognition task in the system. Experiments with a self-built large scale hand posture database collected online show the robustness and effectiveness of the proposed system.

ICRA Conference 2013 Conference Paper

A robot for classifying Chinese calligraphic types and styles

  • Yuandong Sun
  • Ning Ding 0003
  • Huihuan Qian
  • Yangsheng Xu

As one of the most unique types of art in Chinese culture, nowadays Chinese calligraphy is attracting increasing interests from researchers. It will be a big step if we have a robot to write Chinese calligraphy, especially in various styles, and it will form a bridge to combine science with art directly. However, there are so many different types and styles in Chinese calligraphy, and to distinguish them is the most basic quality to a green hand, but it is a big challenge for a robot to do so. For the lack of exploration about this, we conduct a lot of experiments to help the robot to accomplish it automatically. We first propose a parametric representation of calligraphic characters, and then adopt the Mahalanobis distance for similarity measurement and classification. The average accuracies of classifying types and styles of the Chinese calligraphy are 96. 36% and 95. 61% respectively. During the experiments, some interesting phenomena are discovered through similarity measure. Meanwhile, the parametric representation also has some potential applications, such as defining aesthetic grading standards of calligraphy and synthesizing calligraphy. Based on our research, the calligraphy robot can tell which style of calligraphy it sees for mimicking.

IROS Conference 2013 Conference Paper

Identifying the singularity conditions of Canadarm2 based on elementary Jacobian transformation

  • Wenfu Xu
  • Jintao Zhang
  • Huihuan Qian
  • Yongquan Chen
  • Yangsheng Xu

The Canadarm2, also named Space Station Remote Manipulator System (SSRMS), is a 7-joint redundant manipulator. Without spherical wrists, the singularity analysis and avoidance of these manipulators are very difficult. In this paper, a method is presented to analytically identify its singular configurations based on the elementary transformation of Jacobian matrix. Firstly, we constructed a general kinematics model to describe them in a united manner. Correspondingly, the differential kinematics equation and the modified form are derived. Secondly, the singularity conditions are isolated and collected in a 3×4 sub-matrix by several times row transformation of the modified Jacobian matrix, which is partitioned into a block-triangle matrix. Finally, all the singularity configurations are determined by analyzing the rank degeneracy conditions of the 3×4 sub-matrix. The proposed method isolates the singularity conditions, and collects them in a 3×4 sub-matrix, largely reducing the computation workload.

IROS Conference 2013 Conference Paper

Rubbot: Rubbing on flexible loose surfaces

  • Guangchen Chen
  • Yuanyuan Liu
  • Ruiqing Fu
  • Jianwei Sun
  • Xinyu Wu 0001
  • Yangsheng Xu

This paper presents a newly-designed robot named “Rubbot” dedicated to climbing on soft flexible clothes. Equipped with novel grippers which grip and rub on clothes, Rubbot is able to climb on flexible clothes and control how much fabric to grasp by feedback from infrared sensor. Rubbot also has a frame which has three passive folders which adjust the climbing posture of Rubbot. This not only makes Rubbot quite functional with clothes of different thicknesses and curved surfaces, but also makes Rubbot's motion more flexible. A theory of the deformation of cloth is then presented based on an analysis of creases created while Rubbot is climbing, this leads to a more reliable method to climb flexible surfaces. Finally experiments have verified that Rubbot is effective on flexible surfaces, as it can climb on 95% of the surfaces human clothes and still perform well on non-rigidly backed cloth.

ICRA Conference 2013 Conference Paper

Traction/braking force distribution algorithm for omni-directional all-wheel-independent-drive vehicles

  • Tin Lun Lam
  • Jingyu Yan 0001
  • Huihuan Qian
  • Yangsheng Xu

In this paper, a traction/braking force distribution algorithm for omni-directional all-wheel-independent-drive vehicles is proposed as a tool to enhance driving stability. In the proposed algorithm, the amount of the traction or braking force on each driving wheel can be determined so as to generate a desired tangential force, yaw moment and centripetal force independently. The algorithm considers omni-directional steering command and is capable of handling both traction and braking force commands. The algorithm is applicable on vehicles with at least three independent driving wheels. Simulations have been conducted to illustrate the use of the proposed force distribution method in enhancing vehicles stability.

IROS Conference 2012 Conference Paper

A novel design of Tri-star wheeled mobile robot for high obstacle climbing

  • Yong Yang
  • Huihuan Qian
  • Xinyu Wu 0001
  • Guiyun Xu
  • Yangsheng Xu

This paper proposed a novel Tri-star wheeled robot called “Tribot”, which targets on high obstacle performance in unstructured environments, especially at the performance for climbing vertical obstacles. Tribot equips with six Tri-star wheels and each wheel can be driven independently. The chassis of the Tribot is divided into two parts which are connected by an articulated mechanism, making the Tribot has a remarkable obstacle performance to adapt changing environments mechanically, without any interpolate complex control. Numerous experiments have been conducted for vertical obstacle performance tests. Although the diameter of the wheel of the Tribot is only 220 mm, the robot can climb over vertical obstacle of 450 mm high, twice more of the wheel diameter. All results show that Tribot has excellent vertical climbing performance in unstructured environments.

IROS Conference 2012 Conference Paper

Collision avoidance of industrial robot arms using an invisible sensitive skin

  • Tin Lun Lam
  • Hoi Wut Yip
  • Huihuan Qian
  • Yangsheng Xu

Collision avoidance of industrial robot arms in varying environment is a challenging task which has been a tough problem for decades. It often requires a large number of sensors and high computational power. Moreover, since the sensors are often mounted on the surface of robot arms, they may affect the appearance of the robot arms and may be vulnerable to damage. This video presents a cost-effective invisible sensitive skin that can cover a large area without utilizing a large number of sensors and it is built inside the robot arm. By using only 5 contactless capacitive sensors and specially designed antennas, collision avoidance of a 6-DOF industrial robot arm is attained.

ICRA Conference 2012 Conference Paper

Direct yaw moment control for four wheel independent steering and drive vehicles based on centripetal force detection

  • Tin Lun Lam
  • Huihuan Qian
  • Yangsheng Xu

In this paper, a deterministic yaw moment controller for four wheel independent steering and drive vehicles is proposed to enhance driving stability and controllability. Different to conventional methods that track a desired yaw rate, the proposed controller stabilizes a vehicle by additionally tracking the heading angle of a vehicle which is more efficient and robust. The heading angle of a vehicle is obtained by a novel method which is based on centripetal force detection. It eliminates the prerequisite knowledge of the characteristics between wheels and road surface which are time varying and difficult to be measured in real time. The proposed system only requires low cost sensing equipment such as wheel speed sensor and accelerometer that makes the system practical to be utilized. The proposed heading angle detection method can be generally applied to any kind of vehicle. The deterministic yaw moment controller is also applicable to any type of four wheel independent drive vehicles.

IROS Conference 2012 Conference Paper

Path planning for clothes climbing robots on deformable clothes surface

  • Yuanyuan Liu
  • Xinyu Wu 0001
  • Dezhen Song
  • Ruiqing Fu
  • Duan Zheng
  • Yangsheng Xu

This paper proposes a novel path planning method for a robot to climb on the deformable clothes surface. Based on the deformable characteristic of the clothes, the tension force of clothes is analyzed and the model of tension degree is established. A clothes climbing robot called Clothbot is composed of a two-wheeled gripper and a 2 Degrees of Freedom (DOF) tail. Based on the locomotion of this robot, the weights of tension degree and the locomotion characteristic are added into the A* algorithm. Combined with the two weights applied, the optimal path to the target for the Clothbot is obtained. The Clothbot has been developed to evaluate the algorithm. The simulation and the experiments have verified the feasibility of this method. In addition, The error state of the movement of the robot which is called side tumbling has been corrected by the motion of the 2-DOF tail.

ICRA Conference 2012 Conference Paper

System and design of Clothbot: A robot for flexible clothes climbing

  • Yuanyuan Liu
  • Xinyu Wu 0001
  • Huihuan Qian
  • Duan Zheng
  • Jianquan Sun
  • Yangsheng Xu

This paper presents a novel climbing robot called Clothbot which has high maneuverability on flexible clothes. It has a novel gripper consisting of two parallel wheels that can grip continuously and stably on various kinds of clothes. Clothbot also has an omni-directional tail of two DOFs so that it can change its center of gravity to control the moving direction on complex and undeterminate clothes. Consequently, Clothbot is able to access most positions of the clothes by moving straight and turning around with only four motors. It is compact, small and light-weighted but has a load capacity six times its own weight. A series of experiments validate its high performance on flexible clothes.

ICRA Conference 2011 Conference Paper

A flexible tree climbing robot: Treebot - design and implementation

  • Tin Lun Lam
  • Yangsheng Xu

This paper proposed a novel tree climbing robot "Treebot" that has high maneuverability on an irregular tree environment and surpasses the state of the art tree climbing robots. Treebot's body is a novel continuum maneuver structure that has high degrees of freedom and superior extension ability. Treebot also equips with a pair of omni-directional tree grippers that enable Treebot to adhere on a wide variety of trees with a wide range of gripping curvature. By combining these two novel designs, Treebot is able to reach many places on trees including branches. Treebot can maneuver on a complex tree environment, but only five actuators are used in the mechanism. As a result, Treebot can keep in compact size and lightweight. Although Treebot weighs only 600 grams, it has payload capability of 1. 75 kg which is nearly three times of its own weight. On top of that, the special design of the gripper permits zero energy consumption in static gripping. Numerous experiments have been conducted on real trees. Experimental results reveal that Treebot has excellent climbing performance on a wide variety of trees.

ICRA Conference 2011 Conference Paper

A novel design of Movable Gripper for non-enclosable truss climbing

  • Wingkwong Chung
  • Jiangbo Li
  • Yongquan Chen
  • Yangsheng Xu

In this paper, we present a novel Movable Gripper (MovGrip) which targets on climbing non-enclosable rectangular trusses such as bridges and space stations. It is designed with a transformation mechanism which provides the features of parallel grippers, rotatory grippers, and active wheels. For truss climbing, MovGrip acts as a parallel gripper which allows the change in gripping width according to different size of trusses. Since MovGrip is equipped with active wheels, fast climbing motion can therefore be realized. Moreover, MovGrip can be transformed into a mobile platform which is suitable for the navigation on ground. It weighs only 500 grams with a climbing speed of 3 cm/s. To maintain the climbing stability, we steer the rotation axis of wheels. By this, a directional pulling force (from MovGrip to truss surface) can be distributed from the drive force of wheels which pulls MovGrip towards the truss while climbing. Experimental results show that tilting of MovGrip can be auto-adjusted based on the proposed design. Also, it is shown that the load carrying capability of MovGrip is approximately 1 kg which is 2 times of its weight.

IROS Conference 2011 Conference Paper

Mechanical design of a tree gripper for miniature tree-climbing robots

  • Tin Lun Lam
  • Yangsheng Xu

In this paper, an novel tree gripping mechanism has been proposed for miniature tree-climbing robots. It is capable of attaching on a wide variety of trees with a wide range of gripping curvature. In addition, it is lightweight and simple in control. The gripper is simple in control as it is actuated by one actuator only. In addition, the omni-directional gripping ability also simplifies the use of the gripper as there is no extra actuator needed for orientation control. The special mechanism and optimized settings make the gripper able to attach on different sizes of tree tightly. The mechanism also allows zero energy consumption in static gripping. Numerous on-tree experiments of the proposed mechanism have been conducted and the results are satisfied.

ICRA Conference 2011 Conference Paper

Treebot: Autonomous tree climbing by tactile sensing

  • Tin Lun Lam
  • Yangsheng Xu

This paper proposed an autonomous tree climbing algorithm for a novel tree climbing robot named Treebot. Making a robot realize an environment and climb on a tree autonomously is a challenging task as the shape of tree is complex and irregular. To our best knowledge, this is the first paper dealing with the autonomous climbing problem in an unknown tree environment. The proposed method is aimed to use minimal sensing resources to achieve autonomous climbing. It reconstructs the shape of tree by using tactile sensors and guides the robot to climb along an optimal path. Numerous experiments have been carried out and the results are satisfactory.

IROS Conference 2010 Conference Paper

A space robotic system used for on-orbit servicing in the Geostationary Orbit

  • Wenfu Xu
  • Bin Liang 0001
  • Dai Gao
  • Yangsheng Xu

The failures of GEO (Geostationary Orbit) spacecrafts will result in large economic cost and other bad impacts. In this paper, we propose a space robotic servicing concept, and present the design of the corresponding system. The system consists of a 7-DOF redundant manipulator, a 2-DOF docking mechanism, a set of stereo vision and general subsystems of a spacecraft platform. This system can serve most existing GEO satellites, not requiring specially designed objects for grappling and measuring on the target. The serving tasks include: (a) visual inspecting; (b) target tracking, approaching and docking; (c) ORUs (Orbital Replacement Units) replacement; (d) un-deployed mechanism deploying; (e) extending satellites lifespan by replacing its own controller. As an example, the servicing mission of a malfunctioned GEO satellite with three severe mechanical failures is presented and simulated. The results show the validity and flexibility of the proposed system.

IROS Conference 2010 Conference Paper

Energy management for four-wheel independent driving vehicle

  • Huihuan Qian
  • Guoqing Xu
  • Jingyu Yan 0001
  • Tin Lun Lam
  • Yangsheng Xu
  • Kun Xu

The promising electric vehicle (EV) technology is a direction to tackle the global non-renewable energy problem. However, the efficiency to use the electric energy still needs deliberate research. Traditional EV has no choice to manage its energy flow, because it has only one traction motor. With the robotic research in 4 wheel independent drive (4WID), the driving task of the single traction motor can be shared by 4 independent in-wheel motors. By exploring the motor efficiency map, we propose the energy management strategy based on optimal driving torque distribution (ODTD). The total input power of the 4 motors can be minimized while the driving performance is still maintained, and electric energy consumption can be reduced compared with traditional single motor driving EV. Simulation results validate the proposed strategy. The energy management strategy can also be applied to multi-driving-wheel mobile robots.

IROS Conference 2010 Conference Paper

Linear-time path and motion planning algorithm for a tree climbing robot - TreeBot

  • Tin Lun Lam
  • Guoqing Xu
  • Huihuan Qian
  • Yangsheng Xu

This paper proposes a path and motion planning algorithm for a tree climbing problem. This problem is challenging as the shape of tree is complex and irregular. To our best knowledge, this is the first paper dealing with the path planning problem on natural tree environment. Different from conventional motion planning approach that requires constructing a complex configuration space, this paper divides the planning problem into two parts, i. e. , path and motion planning problem so as to reduce the dimension of the problem. An intuitive method to represent a climbing space is proposed that highly simplifies the path planning problem. With the use of a dynamic programming algorithm, an optimal path to reach a target position can be acquired in linear time. In addition, an efficient motion planning algorithm for a tree climbing robot named TreeBot is developed to make TreeBot follow the planned path.

IROS Conference 2010 Conference Paper

On stability region analysis for a class of human learning controllers

  • Yongsheng Ou
  • Huihuan Qian
  • Xinyu Wu 0001
  • Yangsheng Xu

In this paper, we study the stability region for a set of intelligent controllers developed by learning human expert control skills using support vector machines (SVMs). Based on the discrete-time system Lyapunov theory, a Chebychev points based estimation approach is proposed to evaluate the stability region, a key property of this set of SVM-based human learning controllers. One of such learning controllers has been implemented in vertical balance control of a dynamically stable, statically unstable single wheel mobile robot - Gyrover. The experimental results validate the proposed scheme for estimation of the stability region.

IROS Conference 2009 Conference Paper

Gait pattern classification with integrated shoes

  • Meng Chen 0004
  • Jingyu Yan 0001
  • Yangsheng Xu

In this paper, we aim to study and classify gait patterns among flat walking, descending stairs, and ascending stairs using inertial measurement unit (IMU) including triaxial accelerometers and gyroscopes. Six subjects were invited to gather gait data of flat walking, descending stairs, and ascending stairs wearing the shoe-integrated system with free speeds. The design of the classifier for identifying gait patterns based on continuous kinematic signals is composed of three steps. In the first step, we separate gait signals of the six sensors in the same period into gait segments which are further used as the units for pattern feature analysis. Secondly, based on discrete wavelet transform (DWT), the average sum of squares of wavelet coefficients of each segment for anteroposterior acceleration, vertical acceleration, and sagittal plane angular rate are demonstrated and selected as the common features for gait pattern classification. At the last step, the fuzzy logic based classifier is proposed according to the distribution of the common features of different gait patterns. Experimental results demonstrate the proposed methodology is efficient for classifying gait patterns during humans' daily activity.

ICRA Conference 2009 Conference Paper

Omni-directional steer-by-wire interface for four wheel independent steering vehicle

  • Tin Lun Lam
  • Huihuan Qian
  • Yangsheng Xu
  • Guoqing Xu

In this paper, an omni-directional steer-by-wire interface for four wheel independent steering vehicle is presented. The proposed steering interface is an extension of a traditional steering interface that provides three steering inputs. By combination of which, driver can control the vehicle in traditional way or omni-directionally without any mode switching operation. The reservation of the conventional steering behavior makes driver easy to adapt the novel steering interface. The force feedback controller is designed to synchronize the extended steering interface and the orientations of wheels so as to improve vehicle handling. Hardware-in-the-loop simulations are conducted to verify the hardware prototype and examine the proposed algorithms.

ICRA Conference 2009 Conference Paper

Traction force distribution on omni-directional four wheel independent drive electric vehicle

  • Tin Lun Lam
  • Yangsheng Xu
  • Guoqing Xu

This paper proposes an optimal traction force distribution for omni-directional four wheel independent steering (4WIS) and four wheel independent drive (4WID) vehicle. The proposed force distribution algorithm is aimed to enhance the vehicle stability with minimum cost. The algorithm avoids the use of any feedback information of vehicle motion such as linear velocity as this information is difficult to measure accurately and the price of the measuring equipment is very high. As a result, the implementation cost can be reduced and at the same time avoid improper force distribution due to the inaccurate measured information. Moreover, the proposed algorithm does not involve any parameter tuning. It makes the algorithm easy to implement. The proposed algorithm can also be applied to any steering types of 4WID vehicle such as typical two wheel steering (2WS) as 4WIS is the general case of any steering configuration. Simulation results reveal that the performance of the proposed force distribution is superior to the uniform force distribution which is commonly used in 4WID vehicle.

ICRA Conference 2008 Conference Paper

Intelligent shoes for abnormal gait detection

  • Meng Chen 0004
  • Bufu Huang
  • Yangsheng Xu

In this paper we introduce a shoe-integrated system for human abnormal gait detection. This intelligent system focuses on detecting the following patterns: normal gait, toe in, toe out, oversupination, and heel walking gait abnormalities. An inertial measurement unit (IMU) consisting of three-dimensional gyroscopes and accelerometers is employed to measure angular velocities and accelerations of the foot. Four force sensing resistors (FSRs) and one bend sensor are installed on the insole of each foot for force and flexion information acquisition. The proposed detection method is mainly based on Principal Component Analysis (PCA) for feature generation and Support Vector Machine (SVM) for multi-pattern classification. In the present study, four subjects tested the shoe-integrated device in outdoor environments. Experimental results demonstrate that the proposed approach is robust and efficient in detecting abnormal gait patterns. Our goal is to provide a cost-effective system for detecting gait abnormalities in order to assist persons with abnormal gaits in the developing of a normal walking pattern in their daily life.

ICRA Conference 2008 Conference Paper

Postural kyphosis detection using intelligent shoes

  • Meng Chen 0004
  • Bufu Huang
  • Yangsheng Xu

Postural kyphosis as one of the most common kinds of kyphosis is usually diagnosed in adolescents and young adults. Long-term kyphosis will not only affect the persons' appearance, but also result in thoracic deformity accompanied by pain. In this paper, we introduce a cost-effective shoe-integrated system which mainly consists of 8 force sensing resistors (FSRs) for gathering the pressure information under the 8 bony prominences. Based on the gathered plantar pressure information, the methodology of cascade neural networks with node-decoupled extended Kalman filtering (CNN-NDEKF) is applied for training the model of detecting the gait pattern associated with postural kyphosis. Experimental results demonstrate that the proposed approach is efficient. This device is of particular significance to provide feedback in the application of postural kyphosis rectification.

ICRA Conference 2007 Conference Paper

A New Solder Paste Inspection Device: Design and Algorithm

  • Xinyu Wu 0001
  • Wingkwong Chung
  • Hang Tong
  • Jun Cheng 0002
  • Yangsheng Xu

In this paper, we present an innovative design of a solder paste inspection device which can be practically integrated into existing solder paste printing machines. Since solder paste inspection systems usually occupy a large space in vertical direction, we designed a mirror box that can re-direct the transmission of fringe pattern. In this way, a new parallel solder paste inspection device with a significant reduction in the vertical constraint is developed. We also developed a hybrid weighting algorithm that applied the distance and fringe contrast to acquire the height of solder pastes. Furthermore, we developed an algorithm that generates the 2-D image from the fringe pattern images during the 4-steps algorithm. It gives benefit (time for solder paste inspection) to traditional approach that uses some special lighting systems to create the 2-D image. Experimental results show our device can inspect the 20mm times 20mm PCB area within 2 seconds and the maximum standard deviation for the average height is 3 mum.

IROS Conference 2007 Conference Paper

A novel power control strategy of series hybrid electric vehicle

  • Zhancheng Wang
  • Weimin Li
  • Yangsheng Xu

Because of the inherent advantages of increased fuel economy, reduced harmful emissions and better vehicle performance, hybrid electric vehicles (HEV) powered by internal combustion engine (ICE) and energy storage, are being given more and more attention. In this paper, we present a novel approach to the problem of power control strategy for series hybrid electric vehicles (SHEVs). We define 3 different SHEV operation modes and a cost function. After the support vector machine (SVM) training process, we generate a classifier to determine which operation mode should be chosen during driving cycles based on the road situation data, battery state of charge (SOC) data and vehicle speed data. The approach does not need models of SHEV devices, costs less computationally and is more efficient. These distinguished advantages make the approach more practicable in real-time operation. Simulation study proves the feasibility of the approach.

ICRA Conference 2007 Conference Paper

Gait Modeling for Human Identification

  • Bufu Huang
  • Meng Chen 0004
  • Panfeng Huang
  • Yangsheng Xu

Human gait is a kind of dynamic biometrical feature which is complex and difficult to imitate, it is unique and more secure than static features such as password, fingerprint and facial feature. Analyzing people walking patterns, their "step-prints", can lead to the recognition of personal identity. In this paper, we propose to design, build, calibrate, analyze, and use wearable intelligent shoes; then focus on classifying the wearers into authorized ones and unauthorized ones by modeling their individual gait performance. Firstly the intelligent shoes for collecting and modeling human gait to measure an unprecedented number of parameters relevant to gait are presented. Then we introduce cascade neural networks with node-decoupled extended Kalman filtering (CNN-NDEKF) from the paper by Nechyba and Xu (1997) to apply for modeling and classifier generation. Finally, the experimental results of learning algorithms and comparison are described and verify that the proposed method is valid and useful for human identification.

IROS Conference 2006 Conference Paper

A Novel On-board Temperature Monitoring Approach in the Reflow Soldering Process

  • Zhancheng Wang
  • Weimin Li
  • Hang Tong
  • Yangsheng Xu

The goal of this paper is to monitor in-process on-board data as a means of indicating product quality and to be able to respond quickly to unexpected process disturbances. Due to pending environmental legislation and market requirements, lead-free soldering is widely used by the electronics industry. As the margin between the higher melting temperatures of lead-free solders and the heat-resistant temperatures of electronic components becomes narrower than lead solders, a more precise control of the temperature is required. Traditionally, the control processes of the on-board temperature are open loop because it is difficult to monitor the temperature on a PCB board. In this paper, we establish a method to determine the real process temperatures at any point on a PCB board in the furnace. We develop the method based on support vector machines (SVM) with multiple-input single-output strategies to learn relationship between the temperatures near the PCB board and the on-board temperature. The method is the only one which has been commercially utilized to predict the on-board temperature because of its low cost and high accuracy

IROS Conference 2006 Conference Paper

Multi-agent Based Surveillance

  • Yufeng Chen
  • Zhi Zhong
  • Ka Keung Lee
  • Yangsheng Xu

Taking as reference the concept of agent in the artificial intelligence, this paper proposes a new multi-agent approach which can be employed in the surveillance for a people group in public places rather than a single person. The agent embodies the state and logic relationship between the person which the agent represents and the others in the same group. It does not merely stand for such individual information of persons as given by the existing surveillance systems. The results of experiments show that by using our multi-agent approach to compute and analyze the relationship between a number of agents, we can well perform real-time surveillance for the group and the related events so as to enhance the applicability and intelligence level of surveillance systems

IROS Conference 2006 Conference Paper

Multi-Objective Genetic Algorithm for Hybrid Electric Vehicle Parameter Optimization

  • Bufu Huang
  • Zhancheng Wang
  • Yangsheng Xu

As a typical multi-objective optimization problem, parameter optimization of HEV power control strategy must deal with the conflict between objectives, as fuel consumption and emissions. Classical methods define the HEV parameter optimization as a single objective problem to minimize the fuel consumption. In this paper, the multi-objective genetic algorithm (MOGA) is generalized for parameter optimization of power control strategy of series hybrid electric vehicle. Using a single unified formulation, a number of design objectives can be simultaneously optimized through searching in the parameter space. Compared with two main strategies, as Thermostatic and single-objective genetic algorithm (SOGA), the computation procedures of MOGA are discussed. Simulation results based on the model of series hybrid electric vehicle illustrate the optimization validity of MOGA

IROS Conference 2005 Conference Paper

A detection system for human abnormal behavior

  • Xinyu Wu 0001
  • Yongsheng Ou
  • Huihuan Qian
  • Yangsheng Xu

This paper introduces a real-time video surveillance system which detects human abnormal behaviors. We present two approaches to such a problem. The first one employs principal component analysis for feature selection and support vector machine for classification of human behaviors. The proposed feature selection method is based on the border information of four consecutive blobs. The second approach computes optical flow to obtain the velocity of each pixel for determining whether a human behavior is normal or not. Both algorithms are successfully implemented in crowded environments for detecting the human abnormal behaviors, such as (1) running people in a crowded environment, (2) bending down movement while most are walking or standing, (3) a person carrying a long bar and (4) a person waving hand in the crowd. Experimental results demonstrate the two methods proposed are robust and efficient in detecting human abnormal behaviors.

ICRA Conference 2005 Conference Paper

A Wearable Translation Robot

  • Xi Shi
  • Yangsheng Xu

In this paper, we introduce an intelligent glasses, which can automatically translate multiple languages in real-time, called wearable translation robot. This paper proposes the concept of the system and demonstrates the advantages of the device over other existed systems. The paper presents the system architecture and the functions of components in the system. We then focus on the most crucial technical component, text detection. The paper proposes a novel algorithm based on the fundamental characteristics of all the characters in common use called CIC-based text detection algorithm. We show the effectiveness of the proposed methods, and define some future works.

IROS Conference 2005 Conference Paper

Contact and impact dynamics of space manipulator and free-flying target

  • Panfeng Huang
  • Yangsheng Xu
  • Bin Liang 0001

In this article, we discuss the dynamics characteristics of contact and impact when the hand of space manipulator captures the free-flying target (FFT). We establish the dynamics model of contact and impact between a space manipulator and FFT. The pre-impact, post-impact effect and condition of the space robot system and the FFT system are analyzed when there are any differences between the speed of the end-effector of the space manipulator and that of the contact and impact point on the surface of FFT. We present the relationship between the speed varieties of the space base and that of the FFT. If the impact force is kept constant, the speed varieties of the space base are different when the space robot system is at different configuration. Those methods can be used to analyze the contact and impact problem of the space robot.

IROS Conference 2005 Conference Paper

Shoe-Mouse: an integrated intelligent shoe

  • Weizhong Ye
  • Yangsheng Xu
  • Ka Keung Lee

In this paper, we developed a sensor-integrated shoe as an information acquisition platform to sense the foot motion. The system is small, portable and wearable. The platform is mainly composed of four parts including a sensing module, a computing module, a wireless communication module, and a data visualization module. Based on this platform, we developed a novel input device called Shoe-Mouse, which can be used by people who have difficulties in using their hands to operate computers or devices. We evaluated the performance of Shoe-Mouse, and the initial experimental results demonstrated the function. The platform can be also used for applications such as gait recognition, human identification, and motion monitoring.

ICRA Conference 2004 Conference Paper

A Real-time Monitoring and Diagnosis System for Manufacturing Automation

  • Yangsheng Xu
  • Ming Ge
  • Ruxu Du

Condition monitoring and fault diagnosis in modern engineering practices is of great practical significance for improving the quality and productivity, preventing the machinery from damages. In general, this practice consists of two parts: extracting appropriate features from sensor signals and recognizing possible faulty patterns from the features. In order to cope with the complex manufacturing operations and develop a feasible system for real-time application, we proposed three approaches. By defining the marginal energy, a new feature representation emerged, while by real-time learning algorithms with support vector techniques and hidden Markov model representations, a modular software architecture and a new similarity measure were developed for comparison, monitoring, and diagnosis. A novel intelligent computer-based system has been developed and evaluated in over 30 factories and numerous metal stamping processes as an example of manufacturing operations. The real-time operation of this system demonstrated that the proposed system is able to detect abnormal conditions efficiently and effectively resulting in a low-cost, effective approach to real-time monitoring in manufacturing. The related technologies have been transferred to industry, presenting a tremendous impact in current automation practice in Asia and the world.

ICRA Conference 2004 Conference Paper

Boundary Modeling in Human Walking Trajectory Analysis for Surveillance

  • Ka Keung Lee
  • Yangsheng Xu

Surveillance of public places has become a world-wide concern in recent years. The ability to classify human behaviors in real-time is fundamental to the success of intelligent surveillance systems. The recognition of different human walking trajectory patterns is an important step towards the achievement of this goal. In this research, we utilize the approach of Longest Common Subsequence (LCSS) in determining the similarity between different types of walking trajectories. In order to establish the position and speed boundaries required for the similarity measure, we compare the performance of a number of approaches, including fixed boundary values, variable boundary values, learning boundary by support vector regression, and learning boundary by cascade neural networks. The LCSS similarity approach is also compared with a similarity measure based on hidden Markov model. We found that the boundary establishing method based on learning by support vector regression gives the best results using real-life data during testing.

ICRA Conference 2004 Conference Paper

Convergence Analysis for a Class of Skill Learning Controllers

  • Yongsheng Ou
  • Yangsheng Xu

This paper studied convergence conditions for a class of intelligent controllers. We formulated conditions to verify that the learned closed-form control system is strongly stable under perturbations (SSUP). We developed an approach to evaluate the convergence quality of this class of controllers with representation of support vector machine. It has been implemented in a balance control of a dynamically stable, statically unstable single wheel robot. The experimental results verified the proposed convergence conditions and the theory upon which it is based.

ICRA Conference 2004 Conference Paper

Intelligent Diagnosis in Electromechanical Operation Systems

  • Shui Yuan
  • Ming Ge
  • Hai Qiu
  • Jay Lee
  • Yangsheng Xu

The real-time fault detection and diagnosis are critical for healthy operation of electromechanical systems, of which the complex characteristics affect the performance of current shop floor fault diagnosis methods. Aiming to overcome the drawbacks, this paper presents a new fault diagnosis method using a newly developed method, support vector machines (SVM). First, the basic theory of SVM is briefly introduced and new intelligent fault diagnosis system is presented. Next, three common SVM algorithms - v-SV, Lagrangian, and hyper-kernel - are employed for the proposed multiple faults diagnosis system. In comparison, the trade-offs among these three methods are discussed resulting in a general guideline of selecting appropriate learning algorithm for various applications. Then, the methods are applied for diagnosing vibration signals of a typical electromechanical system, elevator door. The real-time tests on 10 faulty conditions demonstrate that the proposed method is effective and efficient. In addition, the method requires only few training samples and permits fast calculation, giving it a big potential in real-world applications.

ICRA Conference 2004 Conference Paper

Learning and Transferring Human Navigational Skill to Wheelchair

  • Hon Nin Chow
  • Yangsheng Xu

In practice, the environments in which mobile robots operate are usually modelled in highly complex forms, and as a result autonomous navigation can be difficult. A novel navigation learning methodology is presented to abstract and transfer the human sequential navigational skill to a robotic wheelchair by showing the platform how to respond in different local environments along a demonstrated, designated route using a lookup-table representation. This method utilizes limited on-board range sensing information to concisely model local unstructured environments, with respect to the robot, for navigation along the learned route in order to achieve good performance with low on-line computational demand and low-cost hardware requirements. Experimental study demonstrates the feasibility of this method and some interesting characteristics of navigation and its associated localization and environmental modelling problems. Analysis is also conducted to investigate performance evaluation, advantages of the approach, choices of lookup-table inputs and outputs, and potential generalization of this study.

ICRA Conference 2004 Conference Paper

Learning Human Tracking and Intercepting Skill

  • Jun Cheng 0002
  • Yangsheng Xu
  • Ronald Chung

Robot tracking and intercepting fast-maneuvering object is a classical and important issue. Many research results were published in recent years. Most of them employed model-based methods which require robot's model in advance. However, it is difficult and time-consuming to obtain robot's mathematical model. In this paper, we present a novel approach which needs no mathematical model. The proposed approach is based on learning tracking strategy from human beings. With human's demonstrations, the robot can learn and abstract human tracking and intercepting skill using cascade neural network. Preliminarily simulation results attest the feasibility of this novel approach. Furthermore, experiment is done on a real-time human face tracking system and the results verify the validity and efficiency of the approach.

IROS Conference 2004 Conference Paper

Modeling human actions from learning

  • Ka Keung Lee
  • Yangsheng Xu

Human action understanding is crucial to the success of many human-machine interfaces based on vision. In this research, we apply artificial intelligence and statistical techniques towards observation of people, leading to modeling of their actions, and understanding of their intentions. In order to actualize the paradigm of learning from demonstration, a tracking system that is capable of locating the head and hand positions of moving humans has been developed. We propose to classify the motion trajectories of humans in the scene by using support vector classification. Since the data size of human motion trajectories is large, we apply principal component analysis (PCA) and independent component analysis (ICA) for data reduction. We have successfully applied the developed technique on two different applications: action recognition of table tennis players, and detection of human fighting motions.

IROS Conference 2004 Conference Paper

Piecewise human learning control for dynamically stable systems

  • Yongsheng Ou
  • Yangsheng Xu

The purpose of this work is to design a piecewise human learning control strategy for the autonomous control of dynamically stable systems in the following two cases. One case is in a single control process, the learning model is built up by combining some local neural networks. The other is that a desirable control target consists of some small control tasks which can be realized by human learning controllers individually. By estimating the stability region, we can guarantee the successful switch between two connected control pieces.

ICRA Conference 2003 Conference Paper

A service-based network architecture for wearable robots

  • Ka Keung Lee
  • Ping Zhang 0015
  • Yangsheng Xu

We are developing a network architecture for our novel robot concept of wearable robot. Wearable robots are mobile information devices capable of supporting remote communication and intelligent interaction between networked entities. In this paper, a service-based wearable robot network architecture that involves extensions to the Jini network model is presented. We discuss three extensions to the original Jini model. The first extension involves the incorporation of a task coordinator service such that the execution of the services can be managed using a priority queue. The second extension enables the system to automatically push the required service proxy to the client intelligently based on certain system-related conditions. In the third extension, we allow the system to automatically deliver the services based on contextual information. Using a fuzzy-logic-based decision making system, the matching service can determine whether the service should be automatically delivered utilizing the information provided by the service, client, lookup service and context sensors. An application scenario has been implemented to demonstrate the feasibility of this distributed service-based robot architecture.

IROS Conference 2003 Conference Paper

Input selection for learning human control strategy

  • Yongsheng Ou
  • Yangsheng Xu

In this paper, we study the input selection in reducing the problem of the high dimension of input variables severely affecting the learning control performance of artificial neural networks. We first locally transform a nonlinear mapping problem into a nearly linear one by using the first-order derivatives of it. Then, we performed a local measure of the sensitivity of each of the model inputs (state variables) with respect to model outputs (human control inputs) under the least square error standard. Finally, based on voting, we defined a determination-rule to decide the importance order of the system state variables globally. By abstracting a human expert skill for controlling a dynamically stabilized robot: Gyrover, we validated the proposed approach.

ICRA Conference 2003 Conference Paper

Learning human control strategy for dynamically stable robots: support vector machine approach

  • Yongsheng Ou
  • Yangsheng Xu

In this paper, we discuss the problem of how human control strategy can be represented as a parametric model using a Support Vector Machine (SVM), and how an SVM-based controller can be used to effectively control a dynamically stable system. We formulate the learning problem as a support vector regression and develop a new SVM learning structure to better implement human control strategy learning in control. The approach is fundamentally valuable in dealing with problems that normally dynamically stable robots experience, such as small sample data and local minima, and therefore is extremely useful in abstracting human controller for dynamic systems. The experimental study on the SVM approach with respect to other approaches clearly demonstrated the superiority of the SVM approach in terms of fidelity, efficiency and effectiveness in implementation.

IROS Conference 2003 Conference Paper

Modeling of human walking trajectories for surveillance

  • Ka Keung Lee
  • Maolin Yu
  • Yangsheng Xu

Surveillance of public places has become a world-wide concern. The ability to identify abnormal human behaviors in real-time is fundamental to the success of intelligent surveillance systems. The recognition of abnormal and suspicious human walking patterns is an important step towards the achievement of this goal. In this research, we have developed an intelligent visual surveillance system that can classify normal and abnormal human walking trajectories in outdoor environments by learning from demonstration. It takes into account both the local and global characteristics of the observed trajectories and be able to identify their normality in real-time. By utilizing support vector learning and a similarity measure based on hidden Markov models, the developed system has produced satisfactory results on real-life data during testing.

ICRA Conference 2003 Conference Paper

On learning control with limited training data

  • Yongsheng Ou
  • Yangsheng Xu

In this paper, we study the interpolation approach in reducing the problem of small training sample sizes severely affecting the learning control performance of artificial neural networks when the dimension of the input variables is high. We use the local polynomial fitting approach to individually rebuild the time-variant functions of system states. Based on these functions, we can effectively produce new unlabelled training samples. We show that by using additional unlabelled samples, the learning control performance can be improved and, therefore, the overfitting phenomenon can be mitigated. Furthermore, experimental results verified these claims.

ICRA Conference 2003 Conference Paper

Real-time estimation of facial expression intensity

  • Ka Keung Lee
  • Yangsheng Xu

Changing facial expressions is a natural and powerful way of conveying personal intention, expressing emotion and regulating interpersonal communication. Automatic estimation of human facial expression intensity is an important step in enhancing the capability of human-robot interfaces. In this research, we have developed a system which can automatically estimate the intensity of facial expression in real-time. Based on isometric feature mapping, the intensity of expression is extracted from training facial transition sequences. Then, intelligent models including cascade neural networks and support vector machines are applied to model the relationship between the trajectories of facial feature points and expression intensity level. We have implemented a vision system which can estimate the expression intensity of happiness, anger and sadness in real-time.

IROS Conference 2002 Conference Paper

A cap as interface for wheelchair control

  • Cedric Kwok-ho Law
  • Martin Yun-yee Leung
  • Yangsheng Xu
  • S. K. Tso

Many disabled people do not have the dexterity necessary to use a joystick or other hand interface for controlling a standard robotic wheelchair. In many cases, they suffer from diseases which have damaged most of the nervous and muscular system in their body, but leave the brain and eye movement unimpaired. To this end, we developed an interface which enables the user to guide a robotic wheelchair by eye-gaze, using a minimal number of electrodes attached on the head. The device can measure the electro-oculographic potential of the eye-gaze movement together with the electromyographic signals from the jaw muscle motion. By coupling these simple actions, one is able to navigate a wheelchair solely by the eye and jaw movements, which provides an aid to mobility for severely disable people.

IROS Conference 2002 Conference Paper

A prototype virtual haptic bronchoscope

  • Qi Wang
  • Yongsheng Ou
  • Yangsheng Xu

In this paper, we describe the design of the hardware and software for a virtual bronchoscope with force feedback. A haptic interface allows surgeons to feel the reaction force of virtual pneumonic surgery as if they were touching the area directly. We present novel algorithms for haptic force rendering, and examine its ability to display force. The rendering algorithms have been interfaced with a force-reflecting device. This virtual haptic bronchoscope is of significance in training inexperienced doctors in pneumonic diagnosis and surgery.

IROS Conference 2002 Conference Paper

Balance control of a single wheel robot

  • Yongsheng Ou
  • Yangsheng Xu

The single wheel, gyroscopically stabilized robot, Gyrover, is dynamically stable but statically unstable, with both first-order and second-order nonholonomic constraints. In this paper, based on the dynamic model of the robot, we first study the two classes of nonholonomic constraints associated with the system. We then propose control laws for balance control in different cases.

IROS Conference 2002 Conference Paper

Learning human navigational skill for smart wheelchair

  • Hon Nin Chow
  • Yangsheng Xu
  • S. K. Tso

In practice, the environments in which mobile robots operate are usually modeled in highly complex geometric representations, and as a result real-time autonomous navigation can be difficult. Such difficulty is even exacerbated for robots with limited but more realistic on-board computational resources since this paradigm of environmental modeling requires enormous computational power. Inspired from human daily life experience, we propose in this paper a new direction for practical robotics navigation system with locally sensed non-geometric environmental modeling. With human-guided demonstrations, the robot can learn and abstract human navigational skill in the form of reactive sensor-motor mapping to navigate in the demonstrated route with simultaneous obstacle avoidance, localization, path and trajectory planning. Learning in a cascade neural network with node-decoupled extended Kalman filtering is adopted as the basis for such reactive mapping. Preliminarily experimental results show the feasibility of this practical approach.

ICRA Conference 2002 Conference Paper

Shared Control for Navigation and Balance of a Dynamically Stable Robot

  • Cedric Kwok-ho Law
  • Yangsheng Xu

We developed a semi-autonomous control for a dynamically stable robot, Gyrover, by combining machine intelligence and human operating behaviors into a shared control environment. In this system, the entire control task is shared between the autonomous module and the human operator: the robot itself maintains local balancing, while the operator is responsible for the global navigation. The autonomous module consists of two unique and essential behaviors: lateral balancing and fall recovery. These behaviors are modeled by a machine learning algorithm. We developed a method enabling the system to make a reasonable decision in shared control, and addressed the implementation issues in the paper. Experiments demonstrated that this shared control scheme provides an efficient way to control a dynamically stable system, such as Gyrover.

ICRA Conference 2002 Conference Paper

Stabilization and Line Tracking of the Gyroscopically Stabilized Robot

  • Yongsheng Ou
  • Yangsheng Xu

The single-wheel gyroscopically-stabilized robot, Gyrover, is dynamically stable but statically unstable, with both first-order and second-order nonholonomic constraints. In this paper, based on the dynamic model of the robot, we first study the two classes of nonholonomic constrains associated with the system. We then propose control laws for the stabilization in Cartesian space and tracking line segments, while keeping its balance laterally.

IROS Conference 2001 Conference Paper

Input reduction in human sensation modeling using independent component analysis

  • Ka Keung Lee
  • Yangsheng Xu

We model human sensations in virtual reality applications using cascade neural networks. In the modeling process, the dimension of inputs presented to the humans and the sensation systems may be very high. In this research we propose using the independent component analysis (ICA) to achieve input reduction. We obtain human sensation data from a full-body motion virtual reality interface - "motion-based movie". A fixed-point ICA algorithm is applied to achieve feature extraction and input selection for reducing the dimension of the environmental stimulus data. The fidelity of the sensation models trained using the reduced inputs is verified by the hidden Markov model based similarity measure. The performance of input reduction using ICA is compared with that using the principal component analysis. Experimental results showed that the input selection scheme based on ICA is capable of improving the modeling performance of the computational sensation systems and reducing the input dimension by 60%.

IROS Conference 2000 Conference Paper

Dynamics of a rolling disk and a single wheel robot on an inclined plane

  • Yangsheng Xu
  • Loi Wah Sun

The dynamics of a rolling disk and a single wheel robot on an incline are derived and established respectively. The condition of rolling up is addressed. If the condition of rolling up is violated, a methodology of tracking is proposed. The system is stabilized around the position perpendicular to the surface. Simulation results are also provided.

IROS Conference 2000 Conference Paper

Human sensation modeling in virtual environments

  • Ka Keung Lee
  • Yangsheng Xu

This paper aims to study human-machine integration in the human sensation aspect. We propose using cascade neural networks to model human sensation during the interaction, between humans and machines. The fidelity of the sensation models is verified using a hidden Markov model (HMM)-based similarity measure scheme. We applied this modeling technique in a full-body motion virtual reality interface-"motion-based movie". The sensation levels of the human participants in this application were modeled effectively by the cascade neural networks and the fidelity of the models were revealed by the HMM similarity measure scheme.

ICRA Conference 2000 Conference Paper

On Tracking Control of Mobile Manipulators

  • Wenjie Dong
  • Yangsheng Xu
  • Qi Wang

This paper studies the tracking control problem of mobile manipulators with consideration of the interaction between the mobile platform and the manipulator. A global tracking controller is proposed based on the dynamics of the defined tracking error and the extended Barbalat's lemma. The proposed controller ensures that the full state of the system asymptotically track the given desired trajectory globally in the presence of the system coupling. Extensive simulations presented in the paper show the effectiveness of the proposed approach.

ICRA Conference 2000 Conference Paper

Path Following of a Single Wheel Robot

  • Kwok Wai Samuel Au
  • Yangsheng Xu

A single wheel, gyroscopically stabilized robot was developed to provide a dynamic stability for rapid locomotion. It is a sharp-edged wheel actuated by a spinning flywheel for steering and a drive motor for propulsion. The spinning flywheel acts as a gyroscope to stabilize the robot and it can be tilted to achieve steering. In this paper, we present a path following controller for the robot. We first describe the robot motion by a set of configurations using the path curvature. We present a controller for tracking any desired straight line without falling over. For the controller, we first design the linear and steering velocities for driving the robot to the desired straight line through controlling the path curvature. The controller then applies the linear state feedback to stabilize the robot to the predefined lean angle such that the resulting steering velocity of the robot converges to the given steering velocity.

ICRA Conference 2000 Conference Paper

Stabilization of a Gyroscopically Stabilized Robot on an Inclined Plane

  • Yangsheng Xu
  • Loi Wah Sun

The dynamics of a single wheel robot rolling without slipping on an inclined plane are investigated. The motion of a single wheel robot is analyzed using Lagrangian dynamics with no assumption that the robot is constrained to remain vertical. We linearized the dynamic model around the position perpendicular to the surface and proposed a state feedback controller for preventing the robot falling over. The backstepping control was designed to stabilize the robot following a straight path with a general heading angle. The feasibility and efficiency of the method are then validated by simulation study.

ICRA Conference 2000 Conference Paper

Trajectory Fitting with Smoothing Splines using Velocity Information

  • Christopher Lee 0001
  • Yangsheng Xu

We present a derivation for a spline smoother which takes into account local velocity information. This smoother is well suited for finding a best-fit trajectory from multiple example trajectories and is thus useful in applications such as programming by demonstration and online gesture recognition for teleoperation. Currently available smoothers are designed to consider only position information and not local velocity information, and are thus less suited for smoothing trajectories over time of dynamic systems.

IROS Conference 1999 Conference Paper

Decoupled dynamics and stabilization of single wheel robot

  • Kwok Wai Samuel Au
  • Yangsheng Xu

Gyrover is a single wheel, gyroscopically stabilized robot. It is a single wheel connected to a spinning flywheel through a two-link manipulator at the wheel bearing. The nature of the system is nonholonomic, nonlinear and underactuated. In this paper, we first develop a dynamic model and decouple the model with respect to the control inputs. We then study the effect of the flywheel dynamics on stabilizing the single wheel robot via simulation and experiment study. Finally, we design a linear state feedback control law that stabilizes the single wheel robot toward/in different lean angles, so as to control the precession rate. Simulation and experiment study validated the proposed controller as well as the developed dynamic model.

IROS Conference 1999 Conference Paper

Modeling human strategy in controlling a dynamically stabilized robot

  • Yangsheng Xu
  • Wai-Kuen Yu
  • Kwok Wai Samuel Au

We present a method to model human operator's strategy in controlling a dynamically stabilized robot, Gyrover, which is a single-wheel gyroscopically stabilized robot. We first select the relevant state variables for training from kinematic and dynamic equations. Then, we defined a measure of the sensitivity of each of the state variables with respect to operator's control input by a sensitivity function in order to reduce the number of the state variables required in the model. We experimentally implemented the method and demonstrated that the robot can be automatically controlled using the learned human control model. The work is of significance in abstracting operator's skill for controlling a dynamically stabilized system in generating an automatic control input.

ICRA Conference 1999 Conference Paper

Modeling of Human Strategy in Controlling Light Source

  • Jiong Zhang
  • Yangsheng Xu

In this paper, we present a method of modeling human strategy in controlling light source in dynamic environment. We take a simple example of how to control the light source to avoid a shadow and maintain appropriate illumination condition on the target area of attention to illustrate the procedure and method. The work is valuable to various applications of automatic light control from surgical room and space applications to inspections.

ICRA Conference 1999 Conference Paper

Transfer of Human Control Strategy Based on Similarity Measure

  • Jingyan Song
  • Yangsheng Xu
  • Michael C. Nechyba
  • Yeung Yam

We address the problem of transferring human control strategies (HCS) from an expert model to an apprentice model. The proposed algorithm allows us to develop useful apprentice models that incorporate some of the robust aspects of the expert HCS models. We first describe our experimental platform, a real-time graphic driving simulator, for collecting and modeling human control strategies. Then, we discuss an adaptive neural network learning architecture for abstracting HCS models. Next, we define a hidden Markov model (HMM) based similarity measure which allows us to compare different human control strategies. This similarity measure is combined subsequently with simultaneously perturbed stochastic approximation to develop our proposed transfer learning algorithm. In this algorithm, an expert HCS model influences both the structure and the parametric representation of the eventual apprentice HCS model. Finally, we describe some experimental results of the proposed algorithm.

IROS Conference 1998 Conference Paper

Analysis of actuation and dynamic balancing for a single-wheel robot

  • Yangsheng Xu
  • Kwok Wai Samuel Au
  • Gora C. Nandy
  • H. Benjamin Brown

We develop a dynamic model of the steering and actuation mechanism of Gyrover, a single-wheel robot which can be considered as a single wheel, actuated through a spinning flywheel attached through a two-link manipulator at the wheel bearing and a drive motor. The spinning flywheel acts as a gyroscope to stabilize the robot, and at the same time it can achieve steering. We develop a dynamic model, investigate its motion equation, and nonholonomic constraints, and present a simulation study. The work is significant in understanding this type of dynamically stable but statically unstable system, and in developing automatic control of the system.

IROS Conference 1998 Conference Paper

Control of underactuated free floating robots in space

  • Hai-Long Pei
  • Yangsheng Xu

The underactuated free floating robot in space is a nonlinear system where velocity and acceleration constraints are both nonintegrable, therefore it is a second-order nonholonomic system. Some of the existing nonholonomic control methods will not be directly applicable to such systems as it is extremely difficult, if not impossible, to find the control Lie brackets. In this paper, by investigating the system dynamics in depth, we propose a simple velocity-based method to control the unactuated joints and a multistep composite strategy to implement orientation tracking tasks. The proposed algorithm is of significance in controlling of space robots when some joints fail to function, or they are intentionally set to be passive for energy efficiency and safety purposes.

ICRA Conference 1998 Conference Paper

Dynamic Model of a Gyroscopic Wheel

  • Gora C. Nandy
  • Yangsheng Xu

We develop a dynamic model of a gyroscopic wheel, an important component of Gyrover, a single-wheel robot developed at Carnegie Mellon University. The Gyrover robot consists of a single wheel, and is actuated through a spinning flywheel attached through a two-link manipulator at the wheel bearing. The flywheel can be tilted to achieve steering, and can be driven forwards and backwards to accelerate the robot. This paper focuses on developing a 3D model of the wheel part of the Gyrover. We first describe the Gyrover robot. We then develop the dynamic model of the wheel through the Lagrangian constrained generalized formulation. Finally, we implement the resulting equations of motion and present simulation results for the unactuated Gyrover in the different gravitational environments of Earth, the Moon, and Mars.

ICRA Conference 1998 Conference Paper

Message-Based Evaluation for High-Level Robot Control

  • Christopher Lee 0001
  • Yangsheng Xu

In this paper, we present a method for high-level control of robots whose low-level software is based on dynamically reconfigurable, reusable real-time software modules. Our approach is to use an embedded interpreter for a general-purpose programming language to direct the operation of the low-level modules toward meeting the task-level goals of the robot. To this end, we present RSK, a virtual-machine kernel implementing a scheme interpreter capable of hard real-time operation, and employing a method of code execution we call "message-based evaluation" (MBE). MBE is a novel combination of a traditional code execution model and a message-passing architecture, which simplifies the process of writing code for managing the robot's reconfigurable subsystem.

ICRA Conference 1998 Conference Paper

On Discontinuous Human Control Strategies

  • Michael C. Nechyba
  • Yangsheng Xu

Models of human control strategy (HCS), which accurately emulate dynamic human behavior, have far reaching potential in areas ranging from robotics to virtual reality to the intelligent vehicle highway project. A number of learning algorithms, including fuzzy logic, neural networks, and locally weighted regression exist for modeling continuous human control strategies. These algorithms, however, may not be well suited for modeling discontinuous human control strategies. Therefore, we propose a new stochastic discontinuous modeling framework, for abstracting human control strategies, based on hidden Markov models. In this paper, we first describe the real-time driving simulator which we have developed for investigating human control strategies. Next, we demonstrate the shortcomings of a typical continuous modeling approach in modeling a discontinuous human control strategy. We then propose an HMM-based method of modeling discontinuous human control strategies, and show that the proposed controller overcomes these shortcomings and demonstrates greater fidelity to the human training data. We conclude the paper with further comparisons between the two competing modeling approaches.

IROS Conference 1998 Conference Paper

Optimization of human control strategy with simultaneously perturbed stochastic approximation

  • Jingyan Song
  • Yangsheng Xu
  • Yeung Yam
  • Michael C. Nechyba

Modeling the dynamic human control strategy (HCS) is becoming an increasingly popular paradigm in a number of different research areas, ranging from robotics to intelligent vehicle highway systems. Usually, HCS models are derived empirically, rather than analytically, from real human input-output data. While these empirical models offer an effective means of transferring intelligent behaviors from humans to robots and other machines, the models are not explicitly optimized with respect to potentially important performance criteria. We therefore propose an iterative algorithm for optimizing an initially stable HCS model with respect to an independent, user-specified performance criterion. We first collect driving data from different individuals through a real-time graphic driving simulator. Next, we describe how we model each individual's control strategy through flexible cascade neural networks. Once we have initially stable HCS models, we propose simultaneously perturbed stochastic approximation (SPSA) to optimize these models with respect to a chosen performance criterion. Finally, we describe and discuss some experimental results with the proposed algorithm.

IROS Conference 1998 Conference Paper

Reduced-dimension representations of human performance data for human-to-robot skill transfer

  • Christopher Lee 0001
  • Yangsheng Xu

Despite the large amount of research currently directed toward programming robots by demonstration, a significant problem with this method of human-to-robot skill transfer has not yet been addressed: developing representations of human performances which isolate the intrinsic dimensions of the performances (and thus the skills which guide them) within high-dimensional, raw human performance data. In this paper we propose the use of three methods for representing high-dimensional human performance data within lower-dimensional spaces: principal component analysis (PCA), nonlinear principal component analysis (NLPCA), and sequential nonlinear principal component analysis (SNLPCA). We compare the appropriateness of these methods for modeling a simple human grasping operation.

IROS Conference 1998 Conference Paper

Robust control of cooperative underactuated manipulators

  • Marcel Bergerman
  • Yangsheng Xu
  • Yun-Hui Liu 0001

We propose in this work the first model-based robust control method for a team of underactuated manipulators jointly manipulating a load. The method is based on feedback linearization of the nonlinear dynamic coupling between the torques applied at the actuated joints and the Cartesian acceleration of the load, combined with a variable structure controller. Singularities in the control method are addressed, and a sufficient condition for a singularity-free controller implementation is obtained. Simulation and experimental results are presented to validate the theory presented.

ICRA Conference 1998 Conference Paper

Two Performances Measures for Evaluating Human Control Strategy

  • Jingyan Song
  • Yangsheng Xu
  • Michael C. Nechyba
  • Yeung Yam

In the last few years, modeling dynamic human control strategy (HCS) is becoming an increasingly popular paradigm in a number of different research areas, such as the intelligent vehicle highway system, virtual reality and robotics. Usually, these models are derived empirically, rather than analytically, from real human input-output control data. As such, there is a great need to develop adequate performance criteria for these models, as few guarantees exist about their theoretical performance. It is our goal in this paper to develop several such criteria. In this paper, we first collect driving data from different individuals through a real-time graphic driving simulator. We then model each individual's control strategy through the flexible cascade neural network learning architecture. Next, we develop two performance measures for evaluating the resulting HCS models, one dealing with obstacle avoidance, the other with tight-turning behavior. Finally, we evaluate the relative skill of different HCS models through the proposed performance criteria.

ICRA Conference 1997 Conference Paper

Cooperation of multiple manipulators with passive joints

  • Yun-Hui Liu 0001
  • Yangsheng Xu

A single manipulator with passive joints is most likely nonholonomic systems, but multimanipulator systems may not. This paper investigates this issue by presenting a smooth feedback stabilization controller when the number of passive joints is not more than that of motion constraints associated to cooperations. This controller is a variation of the classical PD plus gravity compensation scheme and its asymptotic stability is guaranteed by LaSalle theorem. On the basis of this controller, we further discuss holonomy and nonholonomy conditions of multi-manipulator systems with passive joints. In addition, we propose a trajectory tracking controller which gives rise to asymptotic convergence of position errors and bounded interaction forces. Finally, we demonstrate asymptotic convergences of the proposed controllers with simulation study.

ICRA Conference 1997 Conference Paper

Dynamically equivalent manipulator for space manipulator system. 1

  • Bin Liang 0001
  • Yangsheng Xu
  • Marcel Bergerman

In this paper, we discuss the problem of how a free-floating space manipulator (SM) can be mapped to a conventional, fixed-base manipulator which preserves its dynamic and kinematic properties, and thus is called dynamically equivalent manipulator (DEM). The DEM concept allows one to use a conventional manipulator system to simulate a free-floating space manipulator connected to a space station, spacecraft, or satellite, without complicated experimental set-ups. This paper presents the theoretical development of the DEM concept, and demonstrates its dynamic and kinematic equivalence to the SM.

IROS Conference 1997 Conference Paper

Dynamically equivalent manipulator for space manipulator system. 2

  • Bin Liang 0001
  • Yangsheng Xu
  • Marcel Bergerman
  • Gengtian Li

We propose the concept of the dynamically equivalent manipulator (DEM) of a free-floating space manipulator (SM) system. The dynamically equivalent manipulator can be physically built and used as an experimental testbed for the study of the dynamic performance and task execution of space robots. As it is a fixed-base manipulator, there is no need to resort to complex mechanisms to simulate the space environment. In this paper, we discuss two important issues associated with the DEM concept. First, we demonstrate the property of conservation of angular momentum and verify the validity of the DEM under free-flying conditions (i. e. , when the SM base attitude is controlled via reaction wheels). Next, we investigate the effect of model uncertainty in the space manipulator and how it maps as errors in the parameters of the DEM. We derive explicit expressions for the error mapping and present a case study.

ICRA Conference 1997 Conference Paper

Force characterization and commutation of planar linear motors

  • Arthur E. Quaid
  • Yangsheng Xu
  • Ralph L. Hollis

This work examines force modeling and software-based commutation for closed-loop control of planar linear motors, motivated by the need for a robust and versatile planar robot for precision assembly. The approach taken is to make measurements of the static and dynamic force capabilities of the motor as directly as possible, and determine the applicability of simple models commonly used. Measurements of force ripple, linearity with current, force reduction with skew angle, and eddy current damping forces are presented. The high-frequency current changes required for high-speed motion are shown to make the system sensitive to both the latency and update rate of the commutator and to limit the force generation capabilities at high velocities. Although this effect is caused by multiple sources, it is shown that it is well modeled as a scalar with units of time.

ICRA Conference 1997 Conference Paper

Planning collision-free motions for underactuated manipulators in constrained configuration space

  • Marcel Bergerman
  • Yangsheng Xu

We propose a method to drive an underactuated manipulator among obstacles in its workspace. The method allows for collision-free trajectories to be generated from the dynamic equations of the manipulator. When the passive joints are locked, these trajectories lie on surfaces parallel to the axes of the active joints. When the passive joints are free, the trajectories lie on surfaces determined by the nonholonomic constraints imposed by the lack of actuation at the passive joints. By switching the joint brakes on and off, we obtain a sequence of trajectories that connect the start and the goal configurations. A robust controller is utilized to ensure that the manipulator follows the pre-planned trajectories closely despite modeling errors and external disturbances. Simulation and experimental studies demonstrate the validity of the proposed theory.

ICRA Conference 1997 Conference Paper

Stochastic similarity for validating human control strategy models

  • Michael C. Nechyba
  • Yangsheng Xu

Modeling dynamic human control strategy (HCS), or human skill through learning is becoming an increasingly popular paradigm in many different research areas, such as intelligent vehicle systems, virtual reality, and space robotics. Validating the fidelity of such models requires that we compare the dynamic trajectories generated by the HCS model in the control feedback loop to the original human control data. To this end we have developed a stochastic similarity measure-based on hidden Markov model (HMM) analysis-capable of comparing dynamic, multi-dimensional trajectories. In this paper, we first derive and demonstrate properties of the proposed similarity measure for stochastic systems. We then apply the similarity measure to real-time human driving data by comparing different control strategies for different individuals. Finally, we show that the similarity measure outperforms the more traditional Bayes classifier in correctly grouping driving data from the same individual.

ICRA Conference 1996 Conference Paper

A separable combination of wheeled rover and arm mechanism: (DM) 2

  • Yangsheng Xu
  • Christopher Lee 0001
  • H. Benjamin Brown

We present a novel mobile manipulator concept called the dual-use mobile detachable manipulator, or (DM)/sup 2/, for early construction and maintenance tasks in lunar stations. The robot consists of a wheeled rover, or mobile base and a detachable manipulator arm. The arm is symmetric, with a gripper at each end. When the arm attaches to the mobile base by grasping a handle with one of its grippers, the robot becomes a mobile manipulator and can perform exploration tasks such as collecting soil samples, surveying the lunar surface, and transporting tools and supplies. When the robot nears a lunar center structure such as a manufacturing center or a fuel tank, the manipulator arm can detach from the base and walk hand-over-hand, by grasping a series of handles on the structure, to perform tasks such as structure inspection, parts delivery, and simple assembly tasks. The paper discusses the concept and its advantages, the system under development, and its software architecture.

ICRA Conference 1996 Conference Paper

A single-wheel, gyroscopically stabilized robot

  • H. Benjamin Brown
  • Yangsheng Xu

We are developing a novel concept for mobility, and studying fundamental research issues on dynamics and control of the mobile robot. The robot, called Gyrover, is a single-wheel vehicle with an internal gyroscope that provides mechanical stabilization and steering capability. This configuration conveys significant advantages over multi-wheel, statically stable vehicles, including good dynamic stability and insensitivity to attitude disturbances; high manoeuvrability; low rolling resistance; ability to recover from falls; and amphibious capability. In this paper we present the design, analysis and implementation of the robot, as well as the associated research issues and potential applications.

ICRA Conference 1996 Conference Paper

On the fidelity of human skill models

  • Michael C. Nechyba
  • Yangsheng Xu

Modeling dynamic human control strategy, or human skill, in response to real-time sensing is becoming an increasingly popular paradigm in many research areas. These models are learned from experimental data, and as such can be characterized despite the lack of a good physical model. Unfortunately, learned models presently offer few, if any, guarantees in terms of model fidelity to the source data. As such, we propose an independent, post-training model validation procedure based on hidden Markov models (HMMs). The proposed method generates a stochastic similarity measure comparing system trajectories for the source process and the learned models. Using this method, we are able to verify model fidelity. We demonstrate the proposed method in the validation of neural-network models for real-time human driving skill.

ICRA Conference 1996 Conference Paper

Online, interactive learning of gestures for human/robot interfaces

  • Christopher Lee 0001
  • Yangsheng Xu

We have developed a gesture recognition system, based on hidden Markov models, which can interactively recognize gestures and perform online learning of new gestures. In addition, it is able to update its model of a gesture iteratively with each example it recognizes. This system has demonstrated reliable recognition of 14 different gestures after only one or two examples of each. The system is currently interfaced to a Cyberglove for use in recognition of gestures from the sign language alphabet. The system is being implemented as part of an interactive interface for robot teleoperation and programming by example.

ICRA Conference 1996 Conference Paper

Optimal control sequence for underactuated manipulators

  • Marcel Bergerman
  • Yangsheng Xu

Considers the problem of controlling an underactuated manipulator with less actuators than passive joints. The control methodology consists of dividing the passive joints in several groups, and of controlling one group at a time via its dynamic coupling with the actuators. Among the many possible control sequences for a given robot, we choose the optimal one based on the dynamic programming method. The optimization is based on a control cost defined as the reciprocal of the coupling index, a measure of the dynamic coupling available between the active and the passive joints of the manipulator. The detailed theory, computational procedures, simulation results, and experimental results are presented.

IROS Conference 1995 Conference Paper

Experimental study of an underactuated manipulator

  • Marcel Bergerman
  • Christopher Lee 0001
  • Yangsheng Xu

Underactuated manipulators are a class of robotic mechanisms where passive joints are present. By controlling only the motion of the active joints, it is possible to control the entire system. Our goal is to develop control schemes using both classical nonlinear and modem learning techniques for underactuated manipulators. To examine the validity of the approaches, we developed an experimental setup known as U-ARM, or underactuated robot manipulator. In this paper we present the hardware development, dynamic parameters, control software and experimental results of real-time control of the U-ARM.

IROS Conference 1995 Conference Paper

Human skill transfer: neural networks as learners and teachers

  • Michael C. Nechyba
  • Yangsheng Xu

Much work in recent years has focused on transferring human skill to robots by abstracting that skill into a machine-understandable, computational model. Such skill models, however, can be used not only for transferring human control strategy to robots, but also for helping less-skilled human operators improve their performance. The authors propose a two-step approach for transferring skill from human expert to human apprentice. An expert's relevant control strategies or skills are first abstracted into a sensory-based computational model. Afterwards, this trained computational model is used to generate on-line advice for less-skilled operators who need to improve their skill. This advice can take advantage of many different sensor modalities, thereby potentially improving both the quality and speed of learning for the apprentice. Furthermore, this approach allows for the efficient transfer of skill from a single expert to many apprentices, as well as from many experts to a single apprentice. In this paper, the authors first describe a flexible neural-network-based method for modeling human control strategy and provide motivation for its use. The authors then present a case study for teaching control strategy from one person to another in this two-step approach of transferring skill.

ICRA Conference 1994 Conference Paper

Gesture Interface: Modeling and Learning

  • Jie Yang 0001
  • Yangsheng Xu
  • C. S. Chen

This paper presents a method for developing a gesture-based system using a multidimensional hidden Markov model (HMM). Instead of using geometric features, gestures are converted into sequential symbols. HMMs are employed to represent the gestures and their parameters are learned from the training data. Based on "the most likely performance" criterion, the gestures can be recognized by evaluating the trained HMMs. We have developed a prototype to demonstrate the feasibility of the proposed method. The system achieved 99. 78% accuracy for a 9 gesture isolated recognition task. Encouraging results were also obtained from experiments of continuous gesture recognition. The proposed method is applicable to any multidimensional signal representation gesture, and will be a valuable tool in telerobotics and human computer interfacing. >

ICRA Conference 1994 Conference Paper

SM 2 for New Space Station Structure: Autonomous Locomotion and Teleoperation Control

  • Michael C. Nechyba
  • Yangsheng Xu

The self-mobile space manipulator (SM/sup 2/) has evolved to adapt to the new pre-integrated I-beam structure of the Space Station Freedom (SSF). In this paper, we first briefly overview the update of the robot configuration and testbed. The new robot is capable of projecting cameras anywhere interior or exterior of SSF, and will be an ideal tool for inspecting connectors, structures, and other facilities on SSF. Experiments have been performed under two gravity compensation systems and a full-scale model of a segment of the SSF. This paper then presents a real-time shared control architecture that enables the robot to coordinate autonomous locomotion and teleoperation input for reliable walking on SSF. Autonomous locomotion can be executed based on a CAD model and off-line trajectory planning, or can be guided by a vision system with neural network identification. Teleoperation control can be specified by a real-time graphical interface and a free-flying hand controller. SM/sup 2/ will be a valuable assistant for astronauts in inspection and other EVA missions. >

IROS Conference 1993 Conference Paper

An active Z gravity compensation system

  • Gregory C. White
  • Yangsheng Xu

To perform simulations of partial or microgravity environments on earth requires some method of compensation for the earth's gravitational field. The paper discusses an active compensation system that modulates the tension in a counterweight support cable in order to minimize state deviation between the compensated body and the ideal weightless body. The system effectively compensates for inertial effects of the counterweight mass, viscous damping of all pulleys, and static friction in all parts of the gravity compensation system using a hybrid PI (proportional plus integral)/fuzzy control algorithm. The dynamic compensation of inertia and viscous damping is performed by PI control, while static friction compensation is performed by the fuzzy system. The system provides a very precise gravity compensation force, and is capable of non-constant gravity force compensation in the case that the payload mass is not constant. The only additional hardware requirements needed for the implementation of this system on a passive counterweight balance system are: a strain gauge tension sensor, and a torque motor with encoder.

IROS Conference 1993 Conference Paper

Fuzzy inverse kinematic mapping: rule generation, efficiency, and implementation

  • Yangsheng Xu
  • Michael C. Nechyba

Inverse kinematics is computationally expensive and can result in significant control delays in real time. For a redundant robot, additional computations are required for the inverse kinematic solution through optimization schemes. Based on the fact that humans do not compute exact inverse kinematics, but can do precise positioning for heuristics, an inverse kinematic mapping using fuzzy logic is developed. The implementation of the scheme has demonstrated that it is feasible for both redundant and nonredundant cases, and that it is very computationally efficient. The result provides sufficient precision, and transient tracking error can be controlled based on a fuzzy adaptive scheme proposed in the paper.

IROS Conference 1993 Conference Paper

Implementing model-based variable-structure controllers for robot manipulators with actuator modelling

  • S. K. Tso
  • P. L. Law
  • Yangsheng Xu
  • Harry Shum

A model-based control scheme for robot manipulators employing a variable structure control law has been found to perform well, provided that the design parameters are carefully chosen. A refinement of the system model of this original scheme in which the actuator dynamics is taken into consideration is studied. Practical experiments are carried out on a commercial revolute-joint robot manipulator.

IROS Conference 1993 Conference Paper

Real-time shared control system for space telerobotics

  • Alexander Douglas
  • Yangsheng Xu

A shared control system is a modular real-time system which is designed to execute complex tasks through the intelligent coordination of task modules. A state machine is used to control task sequencing and, due to the automatic switching, the accuracy and reliability with which tasks are executed is greatly improved. Tasks consist of sets of independent, modular and reusable subtasks whose outputs are combined to create the robot control. This system has proved itself useful for rapid development of reliable high-level, multiple sensor-based manipulation and control tasks. Additionally, an extensible neural network-based visual servoing system, semi-compliant Cartesian trajectory-following heuristics, and a real-time graphical user interface have been developed. The shared control system was developed for the Self-Mobile Space Manipulator to handle a range of tasks associated with locomotion, manipulation, and material transportation on Space Station Freedom.

ICRA Conference 1992 Conference Paper

Adaptive control of space robot system with an attitude controlled base

  • Yangsheng Xu
  • Harry Shum
  • Ju-Jang Lee
  • Takeo Kanade

The authors discuss adaptive control of a space robot system with an attitude-controlled base on which the robot is attached. An adaptive control scheme in joint space is proposed. Since most tasks are specified in inertia space, instead of joint space, the authors discuss the issues associated to adaptive control in inertia space and identify two potential problems, unavailability of the joint trajectory (since mapping from inertia space trajectory is dynamics-dependent and subject to uncertainty), and nonlinear parameterization in inertia space. For a planar system, the linear parameterization problem is investigated, the design procedure of the controller is illustrated, and the validity and effectiveness of the proposed control scheme are demonstrated. >

ICRA Conference 1992 Conference Paper

Control system of Self-Mobile Space Manipulator

  • Yangsheng Xu
  • H. Benjamin Brown
  • Mark Friedman
  • Takeo Kanade

Self-Mobile Space Manipulator (SM/sup 2/) is a simple, 5-DOF (degree-of-freedom), 1/3-scale, laboratory version of a robot designed to walk on the trusswork and other exterior surfaces of Space Station Freedom. It will be capable of routine tasks such as inspection, parts transportation, and simple maintenance procedures. The authors have designed and built the robot and gravity compensation system to permit simulated zero-gravity experiments. They have developed the control system for the SM/sup 2/ including control hardware architecture and operating system, control station with various interfaces, hierarchical control structure, multiphase control strategy for step motion, and various low-level controllers. The system provides operator-friendly real-time monitoring, and robust control for 3D locomotion movements of the flexible robot. >

IROS Conference 1991 Conference Paper

Modeling and control strategy of a 3-D flexible space robot

  • Hiroshi Ueno
  • Yangsheng Xu
  • Tetsuji Yoshida

Problems of modeling and controlling the 3D motion of a flexible space robot is discussed. By concentrating the mass at the joint and neglecting the link mass, the model of the flexible robot is derived based on Lagrange dynamics and rigid and flexible coordinates transformation. For further frequency analysis, the obtained linear model is modified so that state variables of the model are independent. The model has been verified by simulation results and experiments using the laboratory robot. The resultant model is simple and easy to be executed efficiently in the real-time control. Control problems are then discussed based on the derived model. A control scheme for adaptation to variations of dynamics due to configuration changes is presented and has been implemented in a space flexible robot. >

ICRA Conference 1991 Conference Paper

Variable structure model reference adaptive control of robot manipulators

  • S. K. Tso
  • Yangsheng Xu
  • Harry Shum

An adaptive control scheme combining the variable structure and model reference methods is presented. With the variable structure technique, all known parameters of the robot system are fully used while the unknown parameters are adaptively adjusted. The overall control system maintains the basic structure of the computer torque controller, but incorporates adaptive components in the system. The method removes the requirement for persistent excitation, essential to traditional adaptive schemes for satisfactory operation. The control algorithm ensures the robustness of the controlled system with respect to disturbance, since the tracking error always converges to zero theoretically, rather than to an ill-defined residual set as in other adaptive schemes. Using this method, the transient response can be prescribed in advance. Thus, all the outstanding issues in adaptive control are directly treated. Simulation analysis for a two-degree-of-freedom robot is conducted to compare the method with the classical model reference method and computed torque method. >

ICRA Conference 1990 Conference Paper

A robot compliant wrist system for automated assembly

  • Yangsheng Xu
  • Richard P. Paul

A compliant wrist combining passive compliance and a displacement sensor has been developed for a robot manipulator to be used in assembly operations. The wrist provides the necessary flexibility to accommodate transitions as the robot makes contact with the workpiece, to correct positioning error, and to avoid high impact forces in automatic assembly. Sensing from the device makes it possible to actively control the contact forces or to compensate the positioning error during motion and contact. The design features of two prototypes of the device are described. A hybrid position force control scheme using the device and incorporating the passive compliance in the design is presented. Two basic primitives in the assembly process, edge tracking and insertion operation with the compliant wrist, are investigated. A fuzzy controller is presented to assign velocity instead of evaluating force zones in insertion. The experimental results show that the system provides a feasible and economical solution to the provision of necessary compliance in automated assembly and manufacturing. >

ICRA Conference 1988 Conference Paper

On position compensation and force control stability of a robot with a compliant wrist

  • Yangsheng Xu
  • Richard P. Paul

A compliant wrist instrumented between a robot and its end effector provides a necessary compliance for assembly operations, and the displacement and force information generated from the wrist sensor can be utilized to actively control the end effector. The authors discuss the position compensation for the detection of the compliant wrist due to the gravity load and other external forces at the unconstrained space, and the force control as the robot is constrained with the environment. The system stability problem and dynamic performance are investigated for the different control laws, wrist parameters, and environment models. By analysis and simulation, some meaningful conclusions are obtained. The results are useful for design of the compliant wrist device and determination of the compensator law in the feedback loop. >

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