Spring-Mass Walking With ATRIAS in 3D: Robust Gait Control Spanning Zero to 4.3 KPH on a Heavily Underactuated Bipedal Robot

Abstract

We present a reduced-order approach for dynamic and efficient bipedal control, culminating in 3D balancing and walking with ATRIAS, a heavily underactuated bipedal robot. These results are a development toward solving a number of enduring challenges in bipedal locomotion: achieving robust 3D gaits at various speeds and transitioning between them, all while minimally draining on-board energy supplies. Our reduced-order control methodology works by extracting and exploiting general dynamical behaviors from the spring-mass model of bipedal walking. When implemented on a robot with spring-mass passive dynamics, e.g. ATRIAS, this controller is sufficiently robust to balance while subjected to pushes, kicks, and successive dodge-ball strikes. The controller further allowed smooth transitions between stepping in place and walking at a variety of speeds (up to 1.2 m/s). The resulting gait dynamics also match qualitatively to the reduced-order model, and additionally, measurements of human walking. We argue that the presented locomotion performance is compelling evidence of the effectiveness of the presented approach; both the control concepts and the practice of building robots with passive dynamics to accommodate them.

ATRIAS: Design and validation of a tether-free 3D-capable spring-mass bipedal robot

“…First, the passive dynamics already approximate a spring-mass model, likely requiring much less control effort to formally match the target model. (Rezazadeh et al, 2015), the robot continually steps in place to hold position. Batteries and computers are all mounted onboard, with no communication cables or connection to the experiment boom.…”

“…A strategy that works within the framework of spring-mass locomotion may help maximally leverage the machine's passive dynamics to achieve speed and efficiency. In fact, policies adapted from spring-mass studies, in combination with other components, are now exhibiting successful 3D locomotion with ATRIAS in simulation (Martin et al, 2015) and experiment (Rezazadeh et al, 2015).…”

“…For our general controller, we define a simple PD control law that regulates the position of each motor angle (Rezazadeh et al, 2015) experiment. In general form, θ des m is the solution to the system of equations: ] defines the target value of the quantity.…”

“…These are the characteristic dynamics of spring-mass gaits, as defined by groundreaction forces: a "double-humped" profile for walking and a "single-humped" profile for running and hopping. the same policies, or structurally similar policies (Martin et al, 2015;Rezazadeh et al, 2015), as those developed in the literature.…”

A Control Framework for Anthropomorphic Biped Walking Based on Stabilizing Feedforward Trajectories

“…Although several successful attempts on the implementation of dynamic locomotion on the bipedal robots have been reported in the past years [2–5], still a fully dynamic and human-like locomotion of an anthropomorphic robot has yet to be achieved. The highly stable, robust, dynamic, efficient, and natural-looking walking achieved with ATRIAS in 3D [5] motivated us to extend the method to a more human-like system.…”