Latest Papers

ASME Journal of Mechanisms and Robotics

  • Measurement Configuration Optimization and Kinematic Calibration of a Parallel Robot
    by Huang C, Xie F, Liu X, et al. on December 10, 2021 at 12:00 am

    AbstractThis paper presents the kinematic calibration of a four-degrees-of-freedom (4DOF) high-speed parallel robot. In order to improve the calibration effect by decreasing the influence of the unobservable disturbance variables introduced by error measurement, a measurement configuration optimization method is proposed. Configurations are iteratively selected inside the workspace by a searching algorithm, then the selection results are evaluated through an index associated with the condition number of the identification Jacobian matrix; finally, the number of optimized configurations is determined. Since the selection algorithm has been shown to be sensitive to local minima, a meta-heuristic method has been applied to decrease this sensibility. To verify the effectiveness of the algorithm and kinematic calibration, computation validations, pose error estimations, and experiments are performed. The results show that the identification accuracy and calibration effect can be significantly improved by using the optimized configurations.

Design and Prototyping of Rotational Bi-Stable Mechanism Using Permanent Magnets

Abstract

Diverse applications including switches, deployable structures, and reconfigurable robots can benefit from bi-stability characteristics. However, the complexity of the implementation and the limitation of the structural configuration makes it difficult to apply conventional bi-stable mechanisms to the structures that require rotational bi-stability. In this paper, an implementation method using cylindrical magnets for the rotational bi-stable mechanism is proposed. The proposed bi-stable mechanism consists of a revolute joint with two links. It has rotational bi-stability through the magnetic force relationship between the array of magnets on each link. To identify the characteristics of the proposed bi-stable mechanism, a cylindrical permanent magnet is considered as an electromagnet model that consists of one ring with a virtual electric current. The magnetic field of the cylindrical permanent magnet can be calculated using the Biot–Savart law. Similarly, the magnetic force between two cylindrical permanent magnets is calculated using the Lorentz force law. The criteria of the magnet array for symmetric bi-stability are described and the potential energy diagram of the rotation link is considered as the performance criterion to identify the stable state. The proposed bi-stable mechanism was applied to the prototype of a deployable structure consisting of two links. The load testing of the structure against external torque was performed and it was obtained that the rotation link can stay within 5 deg angle to the maximum load applied and was experimentally verified with good agreement.
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