Balancing a humanoid robot with a prioritized contact force distribution

Humanoid robots propel themselves and perform tasks by interacting with their environment through contact forces. Typically, nonuniqueness of these forces is dealt with by distributing them evenly between the contacts. In the present paper, we introduce strict prioritization in contact force distribution, to reflect situations when an application of certain contact forces should be avoided as much as possible, for example, due to a fragility of the support. We illustrate this by designing a whole body motion controller for a setting with multiple noncoplanar contacts, where application of an optional contact force is allowed only if it is necessary to maintain balance and execute a task. Balance preservation is addressed by imposing a capturability constraint based on anticipation with a linear model adapted to multiple noncoplanar contacts. The controller is evaluated in simulations.