My newest article in the International Journal of Robotics was just published:

Constrained Stochastic Optimal Control with Learned Importance Sampling: A Path Integral Approach
Jan Carius, René Ranftl, Farbod Farshidian, Marco Hutter
The International Journal of Robotics Research (IJRR), 2021

Here is the abstract of the publication:

Modern robotic systems are expected to operate robustly in partially unknown environments. This article proposes an algorithm capable of controlling a wide range of high-dimensional robotic systems in such challenging scenarios. Our method is based on the path integral formulation of stochastic optimal control, which we extend with constraint-handling capabilities. Under our control law, the optimal input is inferred from a set of stochastic rollouts of the system dynamics. These rollouts are simulated by a physics engine, placing minimal restrictions on the types of systems and environments that can be modeled. Although sampling-based algorithms are typically not suitable for online control, we demonstrate in this work how importance sampling and constraints can be used to effectively curb the sampling complexity and enable real-time control applications. Furthermore, the path integral framework provides a natural way of incorporating existing control architectures as ancillary controllers for shaping the sampling distribution. Our results reveal that even in cases where the ancillary controller would fail, our stochastic control algorithm provides an additional safety and robustness layer. Moreover, in the absence of an existing ancillary controller, our method can be used to train a parametrized importance sampling policy using data from the stochastic rollouts. The algorithm may thereby bootstrap itself by learning an importance sampling policy offline and then refining it to unseen environments during online control. We validate our results on three robotic systems, including hardware experiments on a quadrupedal robot.

The full article is freely available online.

This work was supported by Intel Labs, the Swiss National Science Foundation (SNSF) [project number 188596], and the Swiss National Centres of Competence in Research (NCCR Robotics). Moreover, this work has been conducted as part of ANYmal Research, a community to advance legged robotics.