Robots Driven by Compliant Actuators: Optimal Control Under Actuation Constraints

Abstract

Abstract-Anthropomorphic robots that aim to approach human performance agility and efficiency are typically highly redundant not only in their kinematics but also in actuation. Variableimpedance actuators, used to drive many of these devices, are capable of modulating torque and impedance (stiffness and/or damping) simultaneously, continuously, and independently. These actuators are, however, nonlinear and assert numerous constraints, e.g., range, rate, and effort limits on the dynamics. Finding a control strategy that makes use of the intrinsic dynamics and capacity of compliant actuators for such redundant, nonlinear, and constrained systems is nontrivial. In this study, we propose a framework for optimization of torque and impedance profiles in order to maximize task performance, which is tuned to the complex hardware and incorporating real-world actuation constraints. Simulation study and hardware experiments 1) demonstrate the effects of actuation constraints during impedance control, 2) show applicability of the present framework to simultaneous torque and temporal stiffness optimization under constraints that are imposed by real-world actuators, and 3) validate the benefits of the proposed approach under experimental conditions.

Spatio-temporal optimization of multi-phase movements: Dealing with contacts and switching dynamics

“…6. Hybrid dynamics of a hopping robot model and locomotion phases during one cycle force applied in the leg N u 3 hip joint stiffness Nm/rad u 4 leg stiffness N/m applied to achieve multiple hopping cycles of locomotion on event based switching dynamics. Robustness of the obtained optimal feedback controller will be evaluated by applying external disturbances during the multiple hopping cycles to demonstrate the feasibility of the optimized controller.…”

“…VSAs are composed of mechanically adjustable compliant mechanisms with the capability of simultaneous modulation of stiffness and output torque. In previous studies, benefits of variable stiffness actuation such as energy storage capability in explosive movements have been demonstrated, leading to an improvement of task performance [2], [3], and exploitation of passive dynamics in periodic movements [4], [5] and in brachiation tasks [6]. However, traditional approaches have focused on the optimal control formulation over a predetermined time horizon with smooth, continuous plant dynamics.…”

A universal algorithm for sensorless collision detection of robot actuator faults

“…1 There is some research work in that direction. Automatic collision avoidance is achieved by the control design at the kinematic level exploiting the joint space redundancy.…”

Time-Optimal Control of Variable-Stiffness-Actuated Systems

“…The advantages of this type of robots compared to the traditional rigid ones are discussed in [3]. While researchers continue to work on ingenious mechanical designs for variable impedance actuation [4]- [8], the control of these systems started to attract more attention [9]- [12]. Task planning and control of these robots are daunting problems due to the highlyconstrained and nonlinear nature of these systems.…”