Exploiting the Kinematic Redundancy of a Backdrivable Parallel Manipulator for Sensing During Physical Human-Robot Interaction

Robots need to adapt their behaviour while physically interacting with an operator to guarantee safety and provide intuitiveness. Inferring the intentions of the operator is a challenging problem that can be addressed by introducing sensors, in addition to motor encoders. Also, kinematic redundancy can be used to avoid issues such as singularities or mechanical interference, and the redundant coordinates can be controlled freely. In this work, we propose to use the redundant degrees of freedom to infer the intentions of an operator interacting with a backdrivable kinematically redundant parallel robot, without introducing any additional sensors. The proposed approach is based on the fact that, in mechanically backdrivable robots, the operator can control the redundant degrees of freedom, and this can be sensed using solely motor encoders through the solution of the forward kinematics. This approach is implemented to switch between a position controller and a controller that allows the operator to guide the robot freely thanks to gravity compensation. Experiments are carried out to compare this approach with an existing one and show that it improves intuitiveness during interaction by reducing false mode change detections.