Latest Papers

ASME Journal of Mechanisms and Robotics

  • Stable Inverse Dynamics for Feedforward Control of Nonminimum-Phase Underactuated Systems
    on January 25, 2023 at 12:00 am

    AbstractAn enhanced inverse dynamics approach is here presented for feedforward control of underactuated multibody systems, such as mechanisms or robots where the number of independent actuators is smaller than the number of degrees of freedom. The method exploits the concept of partitioning the independent coordinates into actuated and unactuated ones (through a QR-decomposition) and of linearly combined output, to obtain the internal dynamics of the nonminimum-phase system and then to stabilize it through proper output redefinition. Then, the exact algebraic model of the actuated sub-system is inverted, leading to the desired control forces with just minor approximations and no need for pre-actuation. The effectiveness of the proposed approach is assessed by three numerical test cases, by comparing it with some meaningful benchmarks taken from the literature. Finally, experimental verification through an underactuated robotic arm with two degrees of freedom is performed.

A Distribution Method of Driving Torque for a Novel 3UPS-RR Redundant Solar Tracker

Abstract

This paper proposes a novel two-axis solar tracker with a redundant parallel mechanism and investigates the distribution method of driving torque. In view of the difference between the singular configuration of the redundant parallel mechanisms and that of the corresponding non-redundant ones, an index related to the minimum singular value of the Jacobian matrix is used to indicate the position of the singular configuration relative to the boundaries of the required workspace. The driving torque and energy consumption can be optimized with this index. Based on the fact that the direction of driving torque is opposite to that of rotor in most of the running processes, a distribution method of driving torque with the minimum energy consumption for the redundant parallel solar tracker is proposed. The distribution method is compared with the minimum norm solution which is adopted by the conventional redundant parallel mechanism. And energy consumption can be significantly reduced by adopting this method. In addition, the workspace and energy consumption of the redundant solar tracker and its non-redundant counterpart are compared. The results show that the redundant solar tracker has a larger workspace and lower energy consumption.
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