Optimal control for whole-body motion generation using center-of-mass dynamics for predefined multi-contact configurations

Abstract

Multi-contact motion generation is an important problem in humanoid robotics because it generalizes bipedal locomotion and thus expands the functional range of humanoid robots. In this paper, we propose a complete solution to compute a fully-dynamic multi-contact motion of a humanoid robot. We decompose the motion generation by computing first a dynamically-consistent trajectory of the center of mass of the robot and finding then the whole-body movement following this trajectory. A simplified dynamic model of the humanoid is used to find optimal contact forces as well as a kinematic feasible center-of-mass trajectory from a predefined series of contacts. We demonstrate the capabilities of the approach by making the real humanoid robot platform HRP-2 climb stairs with the use of a handrail. The experimental study also shows that utilization of the handrail lowers the power consumption of the robot by 25% compared to a motion, where only the feet are used.

Trajectory Optimization With Implicit Hard Contacts

“…Such behavior can, in theory, be expected from using the iLQR state feedback controller (10). Still, even though small angular offsets in hip and knee propagate to an error in base height and there may be calibration errors in the draw wire encoder, the overall motion is followed very closely.…”

“…For example if base height was paramount in the OC problem, it would automatically sacrifice hip and knee joint tracking to keep the height deviation at a minimum. However, there are no theoretical guarantees that (10) stabilizes the system under model error and disturbances and we experience that the gains are too aggressive for a jumping motion on the real system. For a fair comparison, we, therefore, use a hand-tuned PD controller (11) in all of our experiments.…”

A Newton method with always feasible iterates for Nonlinear Model Predictive Control of walking in a multi-contact situation

“…Finally, external forces and torques are also bounded. We follow here the approach proposed in [7] and consider constraints:…”

“…Hand contacts with the environment can be important however, to improve stability, energetic efficiency, to interact with the environment, or to simply realize otherwise infeasible motions [4], [5], [6], [7], [8]. In this case, the constraint (1) is generally nonlinear, and we have to resort to a Newton method to obtain a solution, a potentially time-consuming and uncertain procedure involving iterative linearizations.…”

An Inverse Optimal Control Approach for the Transfer of Human Walking Motions in Constrained Environment to Humanoid Robots

“…joint angles [21,20]. To accomplish all those tasks, it is desirable to observe humans themselves and prolongate the gained knowledge to the robotic complements.…”