Latest Papers

ASME Journal of Mechanisms and Robotics

  • Discrete Cosserat Method for Soft Manipulators Workspace Estimation: An Optimization-Based Approach
    by Walid A, Zheng G, Kruszewski A, et al. on August 11, 2021 at 12:00 am

    AbstractThis article investigates the workspace estimation of soft manipulators. Given a configuration of such a soft robot, with the bounded actuators, the discrete Cosserat method is adopted to deduce the mathematical model of soft manipulators, based on which an optimization-based approach is proposed to estimate the workspace. Implemented to various soft manipulators’ configurations, numerical simulations are provided to highlight the feasibility of the proposed methodology.

  • Design Control and Performance of a Cable-Driving Module With External Encoder and Force Sensor for Cable-Driven Parallel Robots
    by An H, Zhang Y, Yuan H, et al. on August 11, 2021 at 12:00 am

    AbstractCable-driven parallel robots (CDPRs) have the characteristic of easy deployment, which endows CDPRs with flexible workspace, freely configurable degrees-of-freedom (DOFs), and various configurations, greatly expanding their range of applications. Modular design provides excellent convenience and feasibility for deployment, which is a crucial issue of CDPR design. A highly integrated cable-driving module is designed in this paper, which includes the winding bobbin, servo motor, force sensor, external encoder, electromagnetic brake, as well as other devices. Experiments show that the maximum cable length control error is less than 0.16%, and the maximum cable tension control error is less than 8% in the back-and-forward rotation test. Furthermore, a CDPR with eight cables and six DOFs is constructed rapidly using the proposed module, whose dimension is 850 × 850 × 650 mm3. Results show that the robot’s trajectory errors are all less than 4.5 mm, and the root-mean-square-error (RMSE) is 2.1 mm. Besides, the compliance control experiments show that the robot’s tracking error in an impedance control mode is less than 2 mm, and the RMSE is 0.95 mm. Moreover, the dragging force in a teaching mode is less than 2.5 N. The proposed integrated cable-driving module could be helpful for the modular design and deployment of CDPRs.

  • A Modular Method for Mechanical Error Analysis of Planar Linkages Composed of Class II Assur Group Kinematic Chains
    by Hsu K, Chung J. on August 11, 2021 at 12:00 am

    AbstractThis paper presents a modular method for the mechanical error analysis of complex planar linkages. The topology of the linkage under investigation is decomposed into several class II Assur group kinematic chains (AGKCs) combined in a given sequence. Therefore, the mechanical error of the whole linkage can be analyzed by investigating the error propagations of adopted AGKCs in successive order. Because class II AGKCs are first served as modules, the mechanical error equations of these AGKCs in terms of each error in link lengths and joint variables can be pre-formulated and embedded in form of subroutines in any programmable language. Once the AGKCs constituting the linkage topology are identified, the corresponding subroutines are introduced to compute the error propagations in the linkage. Therefore, the presented modular approach can facilitate the analysis by concentrating on the topology decomposition instead of the algebraic derivation. Numerical examples are provided to illustrate the advantage and flexibility of the modular approach.

Flexible-Joint Humanoid Balancing Augmentation via Full-State Feedback Variable Impedance Control

Abstract

This paper attempts to address the quandary of flexible-joint humanoid balancing performance augmentation, via the introduction of the Full-State Feedback Variable Impedance Control (FSFVIC), and Model-Free Compliant Floating-base VIC (MCFVIC) schemes. In comparison to rigid-joint humanoid robots, efficient balancing control of compliant bipeds, powered by Series Elastic Actuators (or harmonic drives), requires the design of more sophisticated controllers encapsulating both the motor and underactuated link dynamics. It has been demonstrated that Variable Impedance Control (VIC) can improve robotic interaction performance, albeit by introducing energy-injecting elements that may jeopardize closed-loop stability. To this end, the novel FSFVIC and MCFVIC schemes are proposed, which amalgamate both collocated and non-collocated feedback gains, with power-shaping signals that are capable of preserving the system’s stability/passivity during VIC. The FSFVIC and MCFVIC stably modulate the system’s collocated state gains to augment balancing performance, in addition to the non-collocated state gains that dictate the position control accuracy. Utilization of arbitrarily low-impedance gains is permitted by both the FSFVIC and MCFVIC schemes propounded herein. An array of experiments involving the COmpliant huMANoid reveals that significant balancing performance amelioration is achievable through online modulation of the full-state feedback gains (VIC), as compared to utilization of invariant impedance control.
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