Towards versatile legged robots through active impedance control

Abstract

Robots with legs and arms have the potential to support humans in dangerous, dull or dirty tasks. A major motivation behind research on such robots is their potential versatility. However, these robots come at a high price in mechanical and control complexity. Hence, until they can demonstrate a clear advantage over their simpler counterparts, robots with arms and legs will not fulfill their true potential. In this paper, we discuss the opportunities for versatile robots that arise by actively controlling the mechanical impedance of joints and particularly legs. In contrast to passive elements such as springs, active impedance is achieved by torque-controlled joints allowing real-time adjustment of stiffness and damping. Adjustable stiffness and damping in real-time is a fundamental building block towards versatility. Experiments with our 80 kg hydraulic quadruped robot HyQ demonstrate that active impedance alone (i.e. no springs in the structure) can successfully emulate passively compliant elements during highly dynamic locomotion tasks (running, jumping and hopping); and that no springs are needed to protect the actuation system. Here we present results of a flying trot, also referred to as a running trot. To the best of the authors' knowledge this is the first time a flying trot has been successfully implemented on a robot without passive elements such as springs. A critical discussion on the pros and cons of active impedance concludes the paper. This article is an extension of our previous work presented at the International Symposium on Robotics Research (ISRR) 2013.

“Leg-grope walk”: strategy for walking on fragile irregular slopes as a quadruped robot by force distribution

“…The robot keeps its attitude angles (roll and pitch angle) and never stumbles when and after the foothold of leg L 1 collapses region for the leg-grope is not so large. Recent dynamical walking strategies for legged robots [25][26][27][28][29] may outshine the proposed strategy in terms of walking speed. However, our walking strategy must be useful in a situation where scattered debris or a fragile environment should not be further compromised.…”

Electric-Pneumatic Actuator: A New Muscle for Locomotion

“…Inspired by the functional performance and neuromechanical control of biological muscles [31], appropriate design of the actuator and control strategies can largely enhance the locomotor function. If a robot without any passive compliance jumps or runs, even with precise force feedback control to have active compliance [32,33], it has to cope with energy losses and compensate delay effects [34]. Adaptable compliances as found in biological systems provide significant advantages over traditional actuation for legged robots and assistive devices (e.g., orthoses, prostheses).…”

Parameters Sensitivity Analysis of Position-Based Impedance Control for Bionic Legged Robots’ HDU

“…As a commonly used control method for compliance, the impedance control method has been widely applied to motor-driving legged robots such as the Tekken [7], Scout [8] and MIT cheetah robot [9]. In recent years, as the hydraulic-driven legged robot became the focus of increased research, impedance control was also applied to this kind of robot, as exemplified by robots such as Bigdog [10], HyQ [11], and Scalf-1 [12]. Force-based and position-based impedance control methods are often used for dynamic compliance control.…”