Proximity Sensing and Reactive Control for Safe Manipulation

Abstract

This paper presents a new proximity sensing algorithm, and a real-time reactive control for collision avoidance and preparation for safe collision for robots which have passive safety components such as variable stiffness joints or mechanical joint torque limiters. Although passive safety components make robot safe under accidental collision, they cannot work at or around specific poses of robots. In order to detect obstacles, we get depth images from a RGBD image sensor (Kinect TM for Windows R ) and convert them into sets of point clouds. The points in the clouds are classified into ‘robot’, ‘obstacle’ and ‘ignored’. The reactive controller, which shares its basic principle with that of potential field method, calculates virtual forces on the robot by the points identified as ‘obstacle’, and avoids collision between them. Simultaneously, the controller also prepares soft (safe) collision by changing the pose of the robot so that the passive safety components function effectively. We implement the algorithm on Safeand-Speedy Arm I (SS-Arm I), and successfully demonstrate it with a task that has a constraint on the orientation of the end-effector.