On-line coaching of robots through visual and physical interaction: Analysis of effectiveness of human-robot interaction strategies

Continuous and on-line adaptation of robotic trajectories is one of the key properties of robotic control policies that make robots useful in unstructured environments, where the conditions of the external world are not predefined or stationary. Modification of robotic trajectories through human intervention, in order to make them more suitable to the user, is often termed as robotic coaching. In the manner of a tutor, the user shows to the robot which part of the motion to change and how. Predefined gestures acquired with visual systems and direct physical interaction are two possibilities to realize robotic coaching. In this paper we study what are the desired user features and which of the three tested coaching methods is deemed most favorable by a group of 7 subjects. The three methods we explore all build on on-line coaching of dynamic motion primitives, but are based on different feedback signals, i. e., visual or force feedback, and different low-level robot control approaches, i. e., a stiff or a compliant robot. The experiment required coaching of a KUKA LWR-4 robot arm while wiping a flat surface, so that it followed two simple patterns. The survey presented in this paper aims at providing the designers of human-robot coaching interfaces with answers on the feasibility, advantages and drawbacks of the three methods for on-line coaching analyzed in this paper: 1. visual feedback, 2. force feedback with a stiff robot, and 3. position feedback with a compliant robot.