Latest Papers

ASME Journal of Mechanisms and Robotics

  • Statically Balancing a Reconfigurable Mechanism by Using One Passive Energy Element Only: A Case Study
    by Kuo C, Nguyen V, Robertson D, et al. on April 19, 2021 at 12:00 am

    AbstractThis paper presents the static balancing design of a special reconfigurable linkage that can switch between two one-degree-of-freedom (DoF) working configurations. We will show that the studied dual-mode linkage only requires one mechanical spring or one counterweight for completely balancing its gravitational effect in theory at both modes. First, the theoretical models of the spring-based and the counterweight-based designs are derived. The proposed design concepts were then demonstrated by a numerical example and validated by software simulation. Experimental tests on both designs were also performed. The result of this study shows that a reconfigurable mechanism with N working configurations can be completely statically balanced by using less than N passive energy elements.

  • Multiparameter Real-World System Identification Using Iterative Residual Tuning
    by Allevato A, Pryor M, Thomaz AL. on April 19, 2021 at 12:00 am

    AbstractIn this work, we consider the problem of nonlinear system identification using data to learn multiple and often coupled parameters that allow a simulator to more accurately model a physical system or mechanism and close the so-called reality gap for more accurate robot control. Our approach uses iterative residual tuning (IRT), a recently developed derivative-free system identification technique that utilizes neural networks and visual observation to estimate parameter differences between a proposed model and a target model. We develop several modifications to the basic IRT approach and apply it to the system identification of a five-parameter model of a marble rolling in a robot-controlled labyrinth game mechanism. We validate our technique both in simulation—where we outperform two baselines—and on a real system, where we achieve marble tracking error of 4% after just five optimization iterations.

  • Exploiting Redundancies for Workspace Enlargement and Joint Trajectory Optimization of a Kinematically Redundant Hybrid Parallel Robot
    by Wen K, Gosselin C. on April 19, 2021 at 12:00 am

    AbstractIn this paper, possibilities for workspace enlargement and joint trajectory optimization of a (6 + 3)-degree-of-freedom kinematically redundant hybrid parallel robot are investigated. The inverse kinematic problem of the robot can be solved analytically, which is a desirable property of redundant robots, and is implemented in the investigations. A new method for detecting mechanical interferences between two links which are not directly connected is proposed for evaluating the workspace. Redundant degrees-of-freedom are optimized in order to further expand the workspace. An approach for determining the desired redundant joint coordinates is developed so that a performance index can be minimized approximately when the robot is following a prescribed Cartesian trajectory. The presented approaches are readily applicable to other kinematically redundant hybrid parallel robots proposed by the authors.

Inertial Measurement Unit-Based Optimization Control of a Soft Exosuit for Hip Extension and Flexion Assistance

Abstract

The optimization of the assistive force of a soft exosuit is crucial to the assistive effect. In this paper, an inertial measurement unit (IMU)-based optimization controller was designed to provide effective hip extension and flexion assistance for a soft hip-assistive exosuit. The parameters of the assistive profiles that were defined by two functions were approximatively estimated based on an analysis of biological hip power, and then optimized in real time using the hip angles measured by two IMUs bound to the thighs of the wearer. The peak and offset timings were determined using the parameters of the previous gait, while the start and stop points were determined from those of the current gait. Confirmation experiment was conducted in which four subjects were tested to demonstrate the validity of the optimization by applying the optimized parameters to the soft exosuit developed by the authors’ group. Two of the subjects completed the outdoor walking test at a self-determined pace while carrying a load of 15 kg. All the subjects conducted the walking test on a treadmill at a constant speed of 1.53 m/s with the same load. The results showed that the proposed optimization controller worked well without considering individual differences. In the outdoor walking test, the wearer’s natural gait could be maintained by applying the optimized assistive forces. In the treadmill walking test, metabolic rate with assistance turned on was reduced by 8.53 ± 2.65% (average ± SEM) compared with the result of assistance turned off.
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