A Variable Stiffness Actuator Module With Favorable Mass Distribution for a Bio-inspired Biped Robot

Abstract

Achieving human-like locomotion with humanoid platforms often requires the use of variable stiffness actuators (VSAs) in multi-degree-of-freedom robotic joints. VSAs possess 2 motors for the control of both stiffness and equilibrium position. Hence, they add mass and mechanical complexity to the design of humanoids. Mass distribution of the legs is an important design parameter, because it can have detrimental effects on the cost of transport. This work presents a novel VSA module, designed to be implemented in a bio-inspired humanoid robot, Binocchio, that houses all components on the same side of the actuated joint. This feature allowed to place the actuator's mass to more proximal locations with respect to the actuated joint instead of concentrating it at the joint level, creating a more favorable mass distribution in the humanoid. Besides, it also facilitated it's usage in joints with centralized multi-degree of freedom (DoF) joints instead of cascading single DoF modules. The design of the VSA module is presented, including it's integration in the multi-DoFs joints of Binocchio. Experiments validated the static characteristics of the VSA module to accurately estimate the output torque and stiffness. The dynamic responses of the driving and stiffening mechanisms are shown. Finally, experiments show the ability of the actuation system to replicate the envisioned human-like kinematic, torque and stiffness profiles for Binocchio.

Design and Analysis of a Linear Digital Variable Stiffness Actuator

“…To reduce control complexity, the equilibrium position of the elastic elements is utilized. Based on this, MACCEPA tunes the spring pretension through a ball screw mechanism [10], [11]. Another way is to change the effective turns of a linear spring or adjust the angle between the spring deflection direction and the main driving force direction [12], [13].…”

A Configurable Architecture for Two Degree-of-Freedom Variable Stiffness Actuators to Match the Compliant Behavior of Human Joints

“…One limitation of physically compliant VSAs is that one mechanical implementation corresponds to one embedded passive behavior. Although there are devices that are humanlike in terms of shapes and dimensions, and are able to perform activities of daily living (ADL) (Grebenstein et al, 2011;Weckx et al, 2014;Koganezawa, 2017;Stoeffler et al, 2018;Rodriguez-Cianca et al, 2019), there is, for now, no multi-DoF VSA embedding a compliant behavior that matches human joints. It is worth mentioning that there are alternatives to design compact 2 DoF joints with inherent compliance (not necessarily with variable stiffness in the following examples).…”

“…Nevertheless, the performances of PMs are very sensitive to their geometric parameters ( Siciliano and Khatib, 2007 ). Alternative works explored the independent setup approach, consisting mainly of a serial arrangement of position motor units with several DoF in position (using either SMs or PMs) and an additional motor unit dedicated solely to the control of the stiffness ( Weckx et al, 2014 ; Barrett et al, 2017 ; Tan et al, 2017 ; Rodriguez-Cianca et al, 2019 ). Finally, other works draw inspiration from the antagonistic arrangements of the musculoskeletal system ( Koganezawa, 2017 ; Stoeffler et al, 2018 ; Malosio et al, 2019 ).…”

Motion and Trajectory Constraints Control Modeling for Flexible Surgical Robotic Systems

“…Nonetheless, the high complexity and computation cost of each variant are common cons when used for high-DoF flexible robots [16,17]. Since joint forces are dependent on the physical limits of their actuators [18], the motion and force profiles of unique joints are investigated for point-to-point convergence of the robot during operation.…”