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.

Modeling and Design Exploration of a Tensegrity-Based Twisting Wing

Abstract

This paper presents a modeling and design exploration study of a novel twisting wing whose motion is enabled by a tensegrity mechanism. The aerodynamic characteristics of the twisting wing, which does not require control surfaces to modulate its shape, are compared with those of a conventional wing having a control surface. It is shown via computational fluid dynamics analyses that the twisting wing displays higher lift-to-drag ratio than the conventional wing and hence the twisting wing is more aerodynamically efficient. Subsequently, the torsional tensegrity mechanism, composed of multiple tensegrity cylindrical cells forming a column along the wingspan, is described. A finite element model of the wing incorporating this mechanism is developed. Using the model, a design of experimental study of the influence of the topological parameters of the torsional tensegrity mechanism on the twist angle, mass, and stress in different components of the wing is performed. A wingspan of 142.24 cm and a chord length of 25.31 cm are assumed, corresponding to those of the Carl Goldberg Falcon 56 Mk II R/C unmanned aerial vehicle. For a wing of such dimensions, the maximum achievable twist angle from root to tip per unit mass without any component exceeding their allowable stress is 5.93 deg/kg, which is sufficiently large to allow for effective modulation of the aerodynamic characteristics of the wing. The torsional tensegrity mechanism for this design consists of eight cylindrical cells and four sets of actuator wires along the circumference of each cell.
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