A Convex Model of Momentum Dynamics for Multi-Contact Motion Generation
This work addresses the challenge of online motion planning for humanoid robots in complex environments, such as uneven terrain, by providing a computationally efficient method, though it is incremental as it builds on existing momentum dynamics models.
The authors tackled the problem of generating multi-contact motions for humanoid robots by developing a convex relaxation of the non-linear momentum dynamics model, enabling efficient optimization as a QCQP and real-time contact location adaptation, with experimental results showing tight relaxation and applicability in scenarios like push recovery.
Linear models for control and motion generation of humanoid robots have received significant attention in the past years, not only due to their well known theoretical guarantees, but also because of practical computational advantages. However, to tackle more challenging tasks and scenarios such as locomotion on uneven terrain, a more expressive model is required. In this paper, we are interested in contact interaction-centered motion optimization based on the momentum dynamics model. This model is non-linear and non-convex; however, we find a relaxation of the problem that allows us to formulate it as a single convex quadratically-constrained quadratic program (QCQP) that can be very efficiently optimized. Furthermore, experimental results suggest that this relaxation is tight and therefore useful for multi-contact planning. This convex model is then coupled to the optimization of end-effector contacts location using a mixed integer program, which can be solved in realtime. This becomes relevant e.g. to recover from external pushes, where a predefined stepping plan is likely to fail and an online adaptation of the contact location is needed. The performance of our algorithm is demonstrated in several multi-contact scenarios for humanoid robot.