Improving Safety and Accuracy of Impedance Controlled Robot Manipulators with Proximity Perception and Proactive Impact Reactions

Abstract

We present a system which improves the safety and accuracy of impedance controlled robotic manipulators with proximity perception. Proximity servoed manipulators, which use proximity sensors attached to the robot’s outer shell, have recently demonstrated robust collision avoidance abilities. Nevertheless, unwanted collisions cannot be avoided entirely. As a fallback safety mechanism, robots with joint force/torque sensing rely on impedance controllers for impact attenuation and compliant behavior. However, impedance controllers induce undesired deflections of the robot from its trajectory when it is not in contact. These deviations are more pronounced at soft configurations and when the robot grasps objects of unknown weight distribution, thus a compromise must be made between high positional accuracy and softness (safety). The proximity information allows the robot to react to anticipated impacts proactively for attenuation and damage reduction of unavoidable collisions, while still maintaining high accuracy during regular operation. This is achieved through variations of impedance parameters according to proximity measurements and motions towards safe joint configurations during the preimpact phase.