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Liao Wu

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11 papers
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11

IROS Conference 2024 Conference Paper

Effects of fiber number and density on fiber jamming: Towards follow-the-leader deployment of a continuum robot

  • Chen Qian
  • Tangyou Liu
  • Liao Wu

Fiber jamming modules (FJMs) offer flexibility and quick stiffness variation, making them suitable for followthe-leader (FTL) motions in continuum robots, which is ideal for minimally invasive surgery (MIS). However, their potential has not been fully exploited, particularly in designing and manufacturing small-sized FJMs with high stiffness variation. Although existing research has focused on factors like fiber materials and geometry to maximize stiffness variation, the results often do not apply to FJMs for MIS due to size constraints. Meanwhile, other factors such as fiber number and packing density, less significant to large FJMs but critical to smallsized FJMs, have received insufficient investigation regarding their impact on the stiffness variation for FTL deployment. In this paper, we design and fabricate FJMs with a diameter of 4mm. Through theoretical and experimental analysis, we find that fiber number and packing density significantly affect both absolute stiffness and stiffness variation. Our experiments confirm the feasibility of using FJMs in a medical FTL robot design. The optimal configuration is a 4mm FJM with 0. 4mm fibers at a 56% packing density, achieving up to 3400% stiffness variation. A video demonstration of a prototype robot using the suggested parameters for achieving FTL motions can be found at https://youtu.be/7pI5U0z7kcE.

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IROS Conference 2024 Conference Paper

Hardware-Based Time Synchronization for a Multi-Sensor System

  • Yueqi Wang
  • Tangyou Liu
  • Licheng Feng
  • Jinze Wang
  • Yang Yang
  • Jianjun Bao
  • Binghao Li
  • Liao Wu

Accurate time synchronization is crucial for multisensor fusion, which is widely used in mobile robotics, autonomous driving, and virtual reality. Despite many advancements, precise multi-sensor synchronization is still challenging due to the sensors’ internal characteristics, data filtering, disjointed clock reference, and transmission delay caused by operation system scheduling. This paper proposes a novel hardware-based synchronization solution to achieve synchronization in microsecond-level precision. By introducing a Sensor Adaptor board that provides a unified clock reference, the proposed hardware architecture enables high-precision synchronization across multiple sensors. Furthermore, we develop a method for Visual-Inertial time synchronization that actively controls the exposure duration using an ambient light sensor. By managing the IMU clock signal and exposure trigger, we align the camera’s sampling moment with the authentic IMU sampling time and significantly reduce the time discrepancy in the Visual-Inertial system. Experiments are conducted to evaluate the efficiency of the proposed method and system, including comparisons with previous work. The results indicate that our method can achieve precise time synchronization and be successfully implemented in multi-sensor systems.

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IROS Conference 2021 Conference Paper

A Static Model for a Stiffness-Adjustable Snake-Like Robot

  • Di Shun Huang
  • Jian Hu
  • Liuchunzi Guo
  • Yi Sun 0008
  • Liao Wu

In minimally invasive surgery, miniaturisation and in situ adjustable stiffness of robotic manipulators are desired features. Previous research proposed a simple and effective tendon-driven curve-joint manipulator design using a variable neutral-line mechanism, which highly satisfies both criteria. A kinematic model was developed for such a manipulator based on the geometry of the structure. However, such a model assumes that joint angles are all equal between disks without a rigorous derivation, and fails if not all the shapes of the disks are identical. Moreover, the model does not involve an analysis of the tension of each tendon. This paper suggested a static model for predicting the articulation of such a manipulator given the applied tensions on driving tendons. It validates the assumption of equally distributed joint angles and works for manipulators with more general configurations of disks and tendons. It also sets a foundation for further development of tension based control and external force estimation. Simulations on Adams were conducted to prove the correctness of the proposed model. A video demonstrating the simulation results can be found via https://youtu.be/MXhL1LGwLtw

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IROS Conference 2021 Conference Paper

SnakeRaven: Teleoperation of a 3D Printed Snake-like Manipulator Integrated to the RAVEN II Surgical Robot

  • Andrew Razjigaev
  • Ajay K. Pandey
  • David Howard 0001
  • Jonathan Roberts 0001
  • Liao Wu

Telerobotic systems combined with miniaturised snake-like or elephant-trunk robotic arms can improve the ergonomics and accessibility in minimally invasive surgical tasks such as knee arthroscopy. Such systems, however, are usually designed in a specific and integral approach, making it expensive to adapt to various procedures or patient anatomies. 3D printed instruments with a detachable design can bring the benefits of patient-specific customisation, affordability, and adaptability to new clinical scenarios. However, the integration of such snake-like instruments to standard telerobotic systems can be challenging in terms of design and control. In this study, a teleoperation system is developed to control and steer the pose of SnakeRaven: a 3D printed, customisable snake-like end-effector attached to the RAVEN II platform for the application of fibre-optic knee arthroscopy. Algorithms for the parametric inverse kinematics and mapping between the RAVEN II joint space to the coupled tendon-driven rolling joints are developed. The controller is tested and validated on the physical prototype interfacing with the RAVEN II platform in a teleoperation experiment. A video demonstrating the main results of this paper can be found via https://youtu.be/ApJjR853kIQ

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ICRA Conference 2020 Conference Paper

A Novel Articulated Soft Robot Capable of Variable Stiffness through Bistable Structure

  • Yong Zhong
  • Ruxu Du
  • Liao Wu
  • Haoyong Yu

Soft robot has demonstrated promise in unstructured and dynamic environments due to unique advantages, such as safe interaction, adaptiveness, easy to actuate, and easy fabrication. However, the highly dissipative nature of elastic materials results in small stiffness of soft robot which limits certain functions, such as force transmission, position accuracy, and load capability. In this paper, we present a novel articulated soft robot with variable stiffness. The robot is constructed by rigid joints and compliant bistable structures in series. Each joint can be independently locked through triggering the bistable structure to touch the mechanical constrain. Thus, the bending stiffness of the joint can be magnified which increases the stiffness of the articulated soft robot. Through this construction method, even driven by only one servomotor, the robot demonstrates variable workspace and stiffness which have the potential of dexterous manipulation and maintaining shape under tip load.

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ICRA Conference 2019 Conference Paper

Geometric interpretation of the general POE model for a serial-link robot via conversion into D-H parameterization

  • Liao Wu
  • Ross Crawford
  • Jonathan Roberts 0001

While Product of Exponentials (POE) formula has been gaining maturity in modeling the kinematics of a serial-link robot, the Denavit-Hartenberg (D-H) notation is still the most widely used due to its intuitive and concise geometric interpretation of the robot. This paper has developed an analytical solution to automatically convert a POE model into a D-H model for a robot with revolute, prismatic, and helical joints, which are the complete set of three basic one degree of freedom lower pair joints for constructing a serial-link robot. The conversion algorithm developed can be used in applications such as calibration where it is necessary to convert the D-H model to the POE model for identification and then back to the D-H model for compensation. The equivalence of the two models proved in this paper also benefits the analysis of the identifiability of the kinematic parameters. It is found that the maximum number of identifiable parameters in a general POE model is 5h+4r+2t+n+6 where h, r, t, and n stand for the number of helical, revolute, prismatic, and general joints, respectively. It is also suggested that the identifiability of the base frame and the tool frame in the D-H model is restricted rather than the arbitrary six parameters as assumed previously.

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IROS Conference 2019 Conference Paper

Model-less Active Compliance for Continuum Robots using Recurrent Neural Networks

  • David Jakes
  • Zongyuan Ge
  • Liao Wu

Endowing continuum robots with compliance while it interacts with the internal environment of the human body is essential to prevent damage to the robot and the surrounding tissues. Compared with passive compliance, active compliance has the advantages in terms of increasing the force transmission ability and improving safety with monitored force output. Previous studies have demonstrated that active compliance can be achieved based on a complex model of the mechanics combined with a traditional machine learning technique such as a support vector machine. This paper proposes a recurrent neural network (RNN) based approach that avoids the complexity of modeling while capturing nonlinear factors such as hysteresis, friction and delay of the electronics that are not easy to model. The approach is tested on a 3-tendon single-segment continuum robot with force sensors on each cable. Experiments are conducted to demonstrate that the continuum robot with an RNN based feed-forward controller is capable of responding to external forces quickly and entering an unknown environment compliantly.

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ICRA Conference 2017 Conference Paper

The ACRV picking benchmark: A robotic shelf picking benchmark to foster reproducible research

  • Jürgen Leitner
  • Adam W. Tow
  • Niko Sünderhauf
  • Jake E. Dean
  • Joseph W. Durham
  • Matthew Cooper 0005
  • Markus Eich
  • Chris Lehnert

Robotic challenges like the Amazon Picking Challenge (APC) or the DARPA Challenges are an established and important way to drive scientific progress. They make research comparable on a well-defined benchmark with equal test conditions for all participants. However, such challenge events occur only occasionally, are limited to a small number of contestants, and the test conditions are very difficult to replicate after the main event. We present a new physical benchmark challenge for robotic picking: the ACRV Picking Benchmark. Designed to be reproducible, it consists of a set of 42 common objects, a widely available shelf, and exact guidelines for object arrangement using stencils. A well-defined evaluation protocol enables the comparison of complete robotic systems - including perception and manipulation - instead of sub-systems only. Our paper also describes and reports results achieved by an open baseline system based on a Baxter robot.

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IROS Conference 2016 Conference Paper

Towards hybrid control of a flexible curvilinear surgical robot with visual/haptic guidance

  • Liao Wu
  • Keyu Wu 0001
  • Hongliang Ren 0001

Comprised of multiple telescoptic precurved tubes that can independently rotate and translate, concentric tube robots (CTRs) are favorable in minimally invasive surgeries thanks to their small size and considerable dexterity along with curvilinear accessibility. However, there is a lack of investigation on improvement of the surgeons' perception which in turn can be used to guide the telemanipulation. In this work, we proposed an eye-in-hand configuration for the concentric tube robot by adding an endoscope to the tip of the inner tube, which provides direct and intuitive visual sensing ability for the operator. Based on this visual feedback, we further developed two frameworks for the hybrid control of CTR, namely Teleoperation Before Visual Servoing (TBVS) and Teleoperation During Visual Servoing (TDVS). The structures of these two frameworks were elaborated with key algorithms derived. The effectiveness of the proposed methods were demonstrated through a series of experiments both in free space and in a confined environment (inside a skull model). The results manifested that the visual guidance had the potential of assisting the operator to control the CTR more efficiently.

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IROS Conference 2015 Conference Paper

Motion planning of continuum tubular robots based on centerlines extracted from statistical atlas

  • Keyu Wu 0001
  • Liao Wu
  • Hongliang Ren 0001

Continuum tubular robots, which are constructed by telescoping pre-curved elastic tubes, are capable of balancing the force application and steerability during minimally invasive surgeries. These devices are able to reach the desired surgical sites in body cavities without colliding with critical blood vessels, nerves and tissues. However, the motion planning of continuum tubular robots is quite challenging because of their complicated kinematics as well as the high dimensional configuration space. In this paper, a sampling-based motion planning method is proposed based on the Rapidly-exploring Random Tree (RRT) algorithm for continuum tubular robots in 3D environments, such as medullary cavities. The proposed motion planner enables a continuum tubular robot to maneuver roughly along the central axis of the statistical humerus atlas in an approximate follow-the-leader manner. The experiment results have demonstrated the effectiveness and superiority of the proposed motion planning algorithm.

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IROS Conference 2014 Conference Paper

Towards simultaneous coordinate calibrations for cooperative multiple robots

  • Jiaole Wang
  • Liao Wu
  • Max Q. -H. Meng
  • Hongliang Ren 0001

Tasks that are too hard for single robot can be easily carried out by multiple robots in a cooperative manner. If some/all robots have mobile bases, the cooperation is subjected to great uncertainties in both the robotic system and environment. Therefore, the relationships among all the base frames (robot-robot calibration) and the relationships between the end-effectors and the other devices such as cameras and tools (hand-eye and tool-flange calibrations) have to be calculated to enable the robots to cooperate. To address these challenges, in this paper, we propose a simultaneous hand-eye, tool-flange and robot-robot calibration method. Thorough simulations are conducted to show the superiority of the proposed simultaneous method under different noise levels and various numbers of robot movements. Furthermore, the comparison to two non-simultaneous calibration methods has also been carried out to show the efficiency and robustness of the proposed simultaneous method.

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