Capture point trajectories for reduced knee bend using step time optimization

Abstract

Traditional force-controlled bipedal walking utilizes highly bent knees, resulting in high torques as well as inefficient, and unnatural motions. Even with advanced planning of center of mass height trajectories, significant amounts of knee-bend can be required due to arbitrarily chosen step timing. In this work, we present a method that examines the effects of adjusting the step timing to produce plans that only require a specified amount of knee bend to execute. We define a quadratic program that optimizes the step timings and is executed using a simple iterative feedback approach to account for higher order terms. We then illustrate the effectiveness of this algorithm by comparing the walking gait of the simulated Atlas humanoid with and without the algorithm, showing that the algorithm significantly reduces the required knee bend for execution. We aim to later use this approach to achieve natural, efficient walking motions on humanoid robot platforms.

Straight-Leg Walking Through Underconstrained Whole-Body Control

“…We implemented the proposed method on the Atlas robot, and conducted both simulations and physical experiments. Using the combination of step adjustment from [18], step time optimization from [19], and the presented strategies for straight leg walking and toe-off control, the robot was able to walk over both flat ground and varying terrain with straight legs. For the physical experiments presented here, a The ICP is able to be tracked fairly well using the ICP control framework in [18].…”

“…In our approach, we utilize a step adjustment strategy based on that presented in [18] to increase the control authority of the robot when walking with straight legs. We also guarantee the feasibility of the dynamic trajectories for walking with straight legs using the approach presented in [19]. This is executed using the instantaneous capture point (ICP) planner in a whole-body controller framework, as presented in section II.…”

The NAO Robot in Slippery Scenarios: A Strategy

“…Balance and disturbance adaptation in bipedal/humanoid robots are challenges that have been tackled since the first generations of humanoid robots (Abrams, 2005;Akhtaruzzaman and Shafie, 2010). Starting in 1968, the concept of ZMP was introduced by Miomir Vukobratović (Sardain and Bessonnet, 2004;Vukobratovic and Borovac, 2004;Vukobratović and Juričić, 1968), which paved the way to the basics of robot balance, leading to balance recovery techniques, like inverted pendulum and center of mass balancing, ankle compensation, hip compensation, hip and ankle compensation, capture point, or a combination of them (Elhasairi and Pechev, 2015;Ferreira et al, 2010;Gouaillier et al, 2010;Griffin et al, 2017;Pratt et al, 2006;Semwal and Nandi, 2013;Wei et al, 2009). Despite these advancements, many bipedal robots still have problems maintaining balance when walking on slippery surfaces due to sudden disturbances caused by an unexpected slip of the supporting foot.…”

Energy-Efficient Bipedal Walking: From Single-Mass Model to Three-Mass Model

“…In addition to the ZMP movement, body height variation (BHV) is another effective way to reduce energetic cost 36,37 and recent years have seen efforts in bipedal walking with time-varying CoM height trajectory or with a straight leg. [38][39][40] Although some of the above work tried to analyze the energy efficiency of BHV qualitatively, they could not either provide an explicit proof.…”