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 of an Ankle Rehab Robot With a Compliant Parallel Kinematic Mechanism

Abstract

In this article, we present the design of a novel ankle rehabilitation robot (ARR), called the Flex-ARR, that employs a compliant parallel kinematic mechanism (PKM) with decoupled degrees-of-freedom. While multiple ARRs have been developed and commercialized, their clinical adoption has been limited primarily because they do not emulate the natural motion of the ankle. Based on a review of existing ARRs and their limitations, this article defines functional requirements and design specifications for an optimal ARR. These are then used to develop a design strategy followed by conceptual and detailed design of a novel ARR. The proposed Flex-ARR is designed to collocate the biological center of rotation of the ankle with that of the robot’s center of rotation to allow natural ankle motion. The strategic use of a compliant PKM in the Flex-ARR not only absorbs any residual misalignment between these two centers but also helps inherently accommodate variations in user foot sizes with minimal adjustments. Detailed design includes the ARR structure with adjustable features, compliant PKM optimization, sensor and actuator selection, and an alignment tool.
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