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Mohammad M. Aref

Possible papers associated with this exact author name in Arrow. This page groups case-insensitive exact name matches and is not a full identity disambiguation profile.

8 papers
1 author row

Possible papers

8

ICRA Conference 2021 Conference Paper

Neural Network Controller for Autonomous Pile Loading Revised

  • Wenyan Yang
  • Nataliya Strokina
  • Nikolay Serbenyuk
  • Joni Pajarinen
  • Reza Ghabcheloo
  • Juho Vihonen
  • Mohammad M. Aref
  • Joni-Kristian Kämäräinen

We have recently proposed two pile loading controllers that learn from human demonstrations: a neural network (NNet) [1] and a random forest (RF) controller [2]. In the field experiments the RF controller obtained clearly better success rates. In this work, the previous findings are drastically revised by experimenting summer time trained controllers in winter conditions. The winter experiments revealed a need for additional sensors, more training data, and a controller that can take advantage of these. Therefore, we propose a revised neural controller (NNetV2) which has a more expressive structure and uses a neural attention mechanism to focus on important parts of the sensor and control signals. Using the same data and sensors to train and test the three controllers, NNetV2 achieves better robustness against drastically changing conditions and superior success rate. To the best of our knowledge, this is the first work testing a learning-based controller for a heavy-duty machine in drastically varying outdoor conditions and delivering high success rate in winter, being trained in summer.

ICRA Conference 2016 Conference Paper

A multistage controller with smooth switching for Autonomous Pallet Picking

  • Mohammad M. Aref
  • Reza Ghabcheloo
  • Antti Kolu
  • Jouni Mattila

This paper addresses the problem of pallet picking by an Articulated-Frame-Steering (AFS) hydraulic machine. We propose a macro-micro visual mobile manipulation architecture, where a smooth switching logic navigates the robot to pick an object. The state space is divided into several regions depending on the accuracy of the vision and robot's degrees of freedom. The control architecture benefits from the following phenomena: at distance, when the location of the object of interest is detected, its orientation may not be reliably estimated; at some closer distances, orientations also become available; and because pallets are wide with small height, yaw angle estimation are more accurate than pitch is. The switching logic is devised to control the corresponding degree of freedom of the mobile manipulator in each region. Moreover, in different regions, we employ different coordinate frames, namely an earth-fixed frame or an object-local frame, which is more natural for the problem in that region. We show that the architecture accomplishes the following: 1) it eliminates the need for replanning as the accuracy of pose estimation improves; and 2) it provides the mobile base with a longer corridor to steer toward the pallet and align its heading. We also incorporate a robust, accurate solution based on fiducial markers for object manipulation in unstructured outdoor environments and unfavorable weather conditions, which relies solely on a monocular camera for pallet detection. The presented experimental results demonstrate the superiority of the method, as the model starts following the target even when the pallet is still 6m away from the vehicle.

ICRA Conference 2014 Conference Paper

A macro-micro controller for pallet picking by an articulated-frame-steering hydraulic mobile machine

  • Mohammad M. Aref
  • Reza Ghabcheloo
  • Jouni Mattila

This paper addresses the macro-micro configuration of a mobile manipulation problem for a forklift; specifically, it investigates pallet picking with visual feedback. A manipulator with limited degrees of freedom and differential constraint mobility, together with the large dimensions of the machine, requires reliable visual feedback (pallet pose) and navigation from relatively large distances. It has been shown that the problem can be divided into two parts in order to solve the related issues based on path following theories and visual servoing. Moreover, visual pallet detection is non-real-time and unreliable, especially due to large distances, unfavorable vibrations, and fast steering. To address these issues, we introduce a simple and efficient method that integrates the vision output with odometry and realizes a smooth and nonstop transition from global navigation to visual servoing. Real-world implementation on a small-sized forklift demonstrates the efficacy of the proposed macro-micro architecture.

IROS Conference 2010 Conference Paper

Explicit dynamics formulation of Stewart-Gough platform: A Newton-Euler approach

  • Reza Oftadeh
  • Mohammad M. Aref
  • Hamid D. Taghirad

Dynamic analysis of parallel manipulators plays a vital role in the design and control of such manipulators. Closed-chain kinematic structure affects the dynamics formulations by several constraints. Therefore, especially for higher degrees of freedom manipulators, manipulation of implicit and bulky dynamics formulation looses the tractability of the analysis. In this paper, a methodology and some simplification tools are introduced to achieve explicit dynamics formulation for parallel manipulators. This methodology is applied for the dynamics analysis of the most celebrated parallel manipulator, namely Stewart-Gough platform. By avoiding any recursive or component-wise derivations, the resulting dynamics formulation provides more insight for designers, and can be much easier used in any model-based control of such manipulators. In order to verify the resulting dynamics equations, Lagrange method is used to derive and compare the manipulator mass matrix. This methodology can be further used to formulate the explicit dynamics of other parallel manipulators.

IROS Conference 2010 Conference Paper

Forward kinematic analysis of a planar cable driven redundant parallel manipulator using force sensors

  • Reza Oftadeh
  • Mohammad M. Aref
  • Hamid D. Taghirad

Newly developed cable driven redundant parallel manipulators (CDRPM) have numerous advantages compared to that of the conventional parallel mechanisms. However, there exist some challenging issues in over-constrained mechanisms like CDRPMs. In contrast to serial manipulators, complexity of parallel manipulator forward kinematics (FK) is one of the main issues being under study in the control of such manipulators. Moreover, using extra sensory data is a common approach in the FK solution of rigid-linked parallel manipulators, which is considered by fewer researchers for CDRPMs. In this paper, tension force sensors of the cables are used as an extra sensor to simplify analytical solution of the FK for a planar CDRPM. To find a suitable solution, geometrical and physical characteristics of the robot are analyzed. It is shown that the proposed method provides the required accuracy and significantly improves the process time compared to the conventional methods.

ICRA Conference 2010 Conference Paper

Integrated controller for an over-constrained cable driven parallel manipulator: KNTU CDRPM

  • Alaleh Vafaei
  • Mohammad M. Aref
  • Hamid D. Taghirad

This paper presents an approach to the control of the KNTU CDRPM using an integrated control scheme. The goal in this approach is achieving accurate trajectory tracking while assuring positive tension in the cables. By the proposed controller, the inherent nonlinear behavior of the cable and the target tracking errors are simultaneously compensated. In this paper asymptotic stability analysis of the close loop system is studied in detail. Moreover, it is shown that the integrated control strategy reduces the tracking error by 80% compared to that of a single loop controller in the considered manipulator. The closed-loop performance of the control topology is analyzed by a simulation study that is performed on the manipulator. The simulation study verifies that the proposed controller is not only promising to be implemented on the KNTU CDRPM, but also being suitable for other cable driven manipulators.

IROS Conference 2008 Conference Paper

Geometrical workspace analysis of a cable-driven redundant parallel manipulator: KNTU CDRPM

  • Mohammad M. Aref
  • Hamid D. Taghirad

KNTU CDRPM is a cable driven redundant parallel manipulator, which is under investigation for possible high speed and large workspace applications. This newly developed mechanisms have several advantages compared to the conventional parallel mechanisms. Its rotational motion range is relatively large, its redundancy improves safety for failure in cables, and its design is suitable for long-time high acceleration motions. In this paper, collision-free workspace of the manipulator is derived by applying fast geometrical intersection detection method, which can be used for any fully parallel manipulator. Implementation of the algorithm on the Neuron design of the KNTU CDRPM leads to significant results, which introduce a new style of design of a spatial cable-driven parallel manipulators. The results are elaborated in three presentations; constant-orientation workspace, total orientation workspace and orientation workspace.

IROS Conference 2008 Conference Paper

On the control of the KNTU CDRPM: A cable driven redundant parallel manipulator

  • Pooneh Gholami
  • Mohammad M. Aref
  • Hamid D. Taghirad

This paper is devoted to the control of a cable driven redundant parallel manipulator, which is a challenging problem due the optimal resolution of its inherent redundancy. Additionally to complicated forward kinematics, having a wide workspace makes it difficult to directly measure the pose of the end-effector. The goal of the controller is trajectory tracking in a large and singular free workspace, and to guarantee that the cables are always under tension. A control topology is proposed in this paper which is capable to fulfill the stringent positioning requirements for these type of manipulators. Closed-loop performance of various control topologies are compared by simulation of the closed-loop dynamics of the KNTU CDRPM, while the equations of parallel manipulator dynamics are implicit in structure and only special integration routines can be used for their integration. It is shown that the proposed joint space controller is capable to satisfy the required tracking performance, despite the inherent limitation of task space pose measurement.

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