Authors: Zack Bright, H. Harry Asada
Design and control of a novel extra robotic arm attached to the shoulder of a worker for performing tasks in the overhead area are presented. The wearable robot, called Supernumerary Robotic Limbs (SRL), can lift an object and hold it while the wearer is securing the object using a tool with both hands. The worker does not have to take a laborious posture for a long time, reducing fatigue and injuries. Furthermore, a single worker can execute the task, which would otherwise require two workers. Two technical challenges and novel solutions are presented. One is to make the wearable robot simple and lightweight with use of a new type of granular jamming gripper that can grasp diverse objects from an arbitrary direction. This eliminates the need for orienting the gripper against the object with three-axis wrist joints, reducing the number of degrees of freedom (DOF) from 6 to 3. The other is an effective control algorithm that allows the wearer to move freely while the robot on the shoulder is holding an object. Unlike a robot sitting on a floor, the SRL worn by a human is disturbed by the movement of the wearer. An admittance-based control algorithm allows the robot to hold the object stably and securely despite the human movement and changes in posture. A 3 DOF prototype robot with a new granular jamming gripper and an ergonomic body mounting gear is developed and tested. It is demonstrated that the robot can hold a large object securely in the overhead area despite the movement of the wearer while performing an assembly work.