Cross-Entropy Optimization of Physically Grounded Task and Motion Plans

Andreu Matoses Gimenez1 Nils Wilde2 Chris Pek1 Javier Alonso-Mora1

Abstract

Autonomously performing tasks often requires robots to plan high-level discrete actions and continuous low-level motions to realize them. Task and Motion Planning (TAMP) algorithms solve these hybrid problems together. Previous TAMP algorithms have focused mainly on computational performance, completeness, or optimality by making the problem tractable through simplifications and abstractions. However, this comes at the cost that the resulting plans may not adequately account for the dynamics or complex contacts necessary to reliably perform the task when manipulation of objects is required. Additionally, approaches that ignore effects of thelow-level controllers may not obtain optimal or feasible plan realizations for the real system. We investigate the use of a GPU-parallelized physics simulator to compute realizations of plans with a motion controller, explicitly accounting for dynamics, and considering contacts with the environment. Using cross-entropy optimization, we sample the parameters of the controllers, or actions, to obtain low-cost solutions. Since our approach uses the same controllers as the real system, the robot can directly execute the computed plans. We demonstrate our approach for a set of tasks where the robot is able to exploit the environment's geometry to move an object.