Modeling and Control of a Novel Variable-Stiffness Regenerative Actuator

Abstract

This paper focuses on the design, modeling and basic control of a variable stiffness actuator to be used in combination with a regenerative electromechanical drive system. Due to the use of a flexible beam, the actuator has the ability to store and return elastic potential energy. Also, an ultracapacitor is used in the electromechanical drive, which allows electrical energy storage and return. Moreover, elastic and electrostatic energies can be exchanged, resulting in a highly efficient and lightweight design which will be beneficial for robotic prostheses, exoskeletons and other orthotic devices. The paper presents a model and calculation method for large beam deflections and the integrated electromechanical actuator model. A semiactive virtual control strategy is used to decouple the mechanical dynamics from the charge dynamics and achieve position control of the actuator. Simulation results are presented to illustrate the control system and the energy exchange features.

Simulation of Stand-to-Sit Biomechanics for Design of Lower-Limb Exoskeletons and Prostheses with Energy Regeneration

“…Analogous to electric and hybrid electric vehicles [13][14], regenerative braking can extend the operating durations of robotic lower-limb prostheses and exoskeletons by converting the otherwise dissipated joint biomechanical energy during negative work movements into electrical energy via backdriving the onboard actuator-transmission system. Whereas previous investigations have focused exclusively on level-ground walking [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][33][34][35], this research computed the lower-limb joint biomechanical energy available for electrical regeneration during stand-to-sit movements. The sitting and standing movement biomechanics of nine participants were experimentally measured.…”

“…Although the hip performed the most net negative mechanical work, the knee joint should instead be considered for regenerative powertrain system designs given the increased structural complexity of the biological hip (i.e., more degrees-of-freedom). Coincidentally, most lower-limb biomechatronic devices with energy regeneration have involved knee-centered designs [5,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][33][34][35]. Using previously published maximum energy regeneration efficiencies (i.e., approximately 37 %) [16], robotic knee prostheses and exoskeletons could theoretically regenerate 0.06 ± 0.03 J/kg of electrical energy per stand-to-sit movement.…”

“…regenerative powertrains have focused exclusively on level-ground walking [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][33][34][35]. However, geriatric and rehabilitation patients often exhibit slower walking speeds (e.g., 24 % speed reduction from 25 to 75 years age) and take fewer steps/day (e.g., 75 % reduction from 60 to 85 years age) [3], therein limiting the potential for energy regeneration during level-ground walking.…”

“…Analogous to electric and hybrid electric vehicles [13][14], several biomechatronic knee designs have incorporated regenerative powertrains to convert the otherwise dissipated joint biomechanical energy during legged locomotion into electrical energy for recharging the onboard batteries while providing negative mechanical work for controlled system deceleration [5,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. These energy-efficient powertrains can enable lighter onboard batteries and/or extend the operating durations between recharging.…”