Optimal Stiffness Design for an Exhaustive Parallel Compliance Matrix in Multiactuator Robotic Limbs

Abstract

Comparatively slow growth in energy density of both power storage and generation technologies has placed added emphasis on the need for energy-efficient designs in legged robots. This paper explores the potential of parallel springs in robot limb design. We start by adding what we call the exhaustive parallel compliance matrix (EPCM) to the design. The EPCM is a set of parallel springs, which includes a parallel spring for each joint and a multijoint parallel spring for all possible combinations of the robot's joints. Then, we carefully formulate and compare two performance metrics, which improve various aspects of the system performance. Each performance metric is analyzed and compared, their strengths and weaknesses being rigorously presented. The performance benefits associated with this approach are dramatic. Implementing the spring matrix reduces the sum of square power (SSP) exerted by the actuators by up to 47%, the peak power requirement by almost 40%, the sum of squared current by 55%, and the peak current by 55%. These results were generated using a planar robot limb and a gait trajectory borrowed from biology. We use a fully dynamic model of the robotic system including inertial effects. We also test the design robustness using a perturbation study, which shows that the parallel springs are effective even in the presence of trajectory perturbation.

Minimizing torque requirements in robotic manipulation through elastic elements optimization in a physics engine

“…Chevallereau et al 16 have already combined both in a robotic leg, but only the placement of the actuators and the best actuation scheme have been optimized, and not the springs' characteristics (stiffness, equilibrium angle, etc.). Cahill et al 17 and Morizono et al 18 have optimized the springs' characteristics for a robotic leg and a robotic arm but not in terms of actuator torque requirements.…”

Optimization of Mono- and Bi-Articular Parallel Elastic Elements for a Robotic Arm Performing a Pick-and-Place Task

“…[20] has already combined both in a robotic leg, but only the placement of the actuators and the best actuation scheme have been optimized, and not the springs' characteristics (stiffness, equilibrium angle, etc.). [21] and [22] have optimized the springs' characteristics for respectively a robotic leg and a robotic arm, but not in terms of actuator torque requirements. To the best of the authors' knowledge, an optimal configuration of PEA and BA in terms of actuator torque requirements in a single robotic arm has only been investigated in [17].…”

Biomechanical effects of passive hip springs during walking

“…However, so far, springs across the hip joint have been primarily described as part of simulation studies (e.g. Cahill et al (2018)), in studies with a clinical focus that did not include a biomechanical analysis (Carda et al, 2012, Sutliff et al, 2008, or as part of multi-joint orthoses (e.g. Schmidt et al (2017), Walsh et al (2007)).…”