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.

Design and Control of SLPM-Based Extensible Continuum Arm

Abstract

As an important branch of reconfigurable robots, extensible continuum robots are soft and light, with the flexibility of movement and high adaptability in complex environments. These robots have very broad applications in a variety of fields, including military reconnaissance, geological exploration and rescue operations. In this paper, a high folding ratio, flexible, and compact extensible continuum arm is designed using a novel combination of parallel and deployable mechanisms. We present the spherical-linkage parallel mechanism (SLPM) as a flexure hinge. The analysis suggests that the SLPM is highly flexible and meets the requirements for many DoFs (degrees-of-freedom) needed in various fields. The folding ratio of the SLPM was 72.73. Following this, we present an SLPM compliant module powered by a set of embedded shape memory alloy (SMA) springs. These can change the internal elasticity of the module as temperature changes, thereby varying the stiffness. Moreover, the control system is designed to enable real-time cooperation between multiple motors and carries out simulations for deployable motion. The extensible continuum arm prototype was manufactured and its performance was tested in complex environments. From the results, it is shown that the arm can be utilized for rescue during disasters as well as investigation and repair of aircraft engines.

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