Date of Original Version



Conference Proceeding

Abstract or Description

Biomechanical models of human standing balance in the sagittal plane typically treat the two ankle joints as a single degree of freedom. They describe the sum of the torques produced by the ankles, but do not predict what the contribution of each ankle will be. Similarly, balance algorithms for bipedal robots control the location of the overall center of pressure, but do not consider the individual centers of pressure under each foot. We present theoretical and experimental results showing an optimal solution to the problem of producing a single desired torque with redundant actuators, resulting in alignment of the individual centers of pressure under each foot. This produces a feedback gain structure not addressed in the biomechanics literature and a balance controller that is potentially more robust to unexpected changes in the region of support. We show that the feedback gain matrix of this controller has an unexpected structure — large off-axis integral gain elements indicate that the ankle torque that equalize the position of the center of pressure is determined primarily by information from the other foot. We also demonstrate controllers based on this design using the Sarcos Primus hydraulic biped.


"©2006 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE." "This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder."

Included in

Robotics Commons