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.

Hierarchical Sliding Mode Control for the Trajectory Tracking of a Tendon-Driven Manipulator

Abstract

The tracking control of tendon-driven manipulators has recently become a hot topic. However, the flexible elastic tendon introduces greater residual vibration, making it more difficult to control the trajectory tracking of the manipulator. In this paper, a dynamics model of the elastic tendon-driven manipulator (ETDM) that considers motion coupling is established. A hierarchical sliding mode control (HSMC) method is proposed to realize the trajectory tracking control of the ETDM. On the basis of the Lyapunov design method, the actuator subsliding manifold is defined as the first sliding manifold. The first sliding manifold is then used to construct the joint side subsliding manifold. Furthermore, the total sliding manifold is established based on the joint side sliding manifold and the actuator’s sliding manifold. The stability of the proposed HSMC is proved using the Lyapunov stability theory. Finally, simulations and experiments are performed on a two-degree-of-freedom ETDM tracking desired trajectories to demonstrate the effectiveness of the proposed HSMC method. The proposed HSMC exhibits higher tracking accuracy compared with proportional–integral–derivative, and adaptive second-order fast nonsingular terminal sliding mode (SOFNTSM) controls in the simulations. The introduction of different disturbances reveals that HSMC has better robustness than proportional–integral–derivative control. Experimental results show that the maximum error of trajectory tracking is less than 0.025 rad.

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