Data-Efficient Reinforcement Learning for Variable Impedance Control

Abstract

One of the most crucial steps toward achieving human-like manipulation skills in robots is to incorporate compliance into the robot controller. Compliance not only makes the robot's behaviour safe but also makes it more energy efficient. In this direction, the variable impedance control (VIC) approach provides a framework for a robot to adapt its compliance during execution by employing an adaptive impedance law. Nevertheless, autonomously adapting the compliance profile as demanded by the task remains a challenging problem to be solved in practice. In this work, we introduce a reinforcement learning (RL)-based approach called DEVILC (Data-Efficient Variable Impedance Learning Controller) to learn the variable impedance controller through real-world interaction of the robot. More concretely, we use a modelbased RL approach in which, after every interaction, the robot iteratively learns a probabilistic model of its dynamics using the Gaussian process regression model. The model is then used to optimize a neural-network policy that modulates the robot's impedance such that the long-term reward for the task is maximized. Thanks to the model-based RL framework, DEVILC allows a robot to learn the VIC policy with only a few interactions, making it practical for real-world applications. In simulations and experiments, we evaluate DEVILC on a Franka Emika Panda robotic manipulator for different manipulation tasks in the Cartesian space. The results show that DEVILC is a promising direction toward autonomously learning compliant manipulation skills directly in the real world through interactions. A video of the experiments is available in the link: https://youtu.be/_uyr0Vye5no INDEX TERMS Model-based reinforcement learning, Variable impedance learning control, Gaussian processes, Covariance matrix adaptation.