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.

Algorithmic Selection of Sliding–Sticking Contacts in Robotic In-hand Manipulation


The paper describes a kinematic method for robotic in-hand manipulation of objects. The method focuses on repositioning the object using a combination of sticking and sliding robotic contacts. Two fingertips with sliding contacts are fixed in space while the remaining two fingertips actively manipulate the object without a change in the point of contact with the object. When sliding over two fixed contacts, the object is constrained to a “three-parameter twist space” if it is not programmed to rotate about the line joining the two fixed contacts. A gradient-descent-based kinematic algorithm is developed to project the desired twist to the allowable twist space, generating a movement sequence of robotic fingertips. The transition from fixed support vis-á-vis the sticking contacts for manipulating the object also emerges from the algorithm.

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