Supernumerary robotic limbs for human augmentation in overhead assembly tasks

Abstract

Manufacturing tasks are highly demanding of work, and there is an especially high prevalence of injury associated with overhead tasks which are taxing to the shoulder and upper body. To assist workers completing these tasks, and to increase overall productivity, safety and effectiveness, we introduce a novel design of Supernumerary Robotic Limb (SRL). This is a robotic arm worn on the shoulder of the technician/- worker which extends the human capability with implicit force control algorithms that allow for intuitive control and interface of the extra robot arm. Affectionately dubbed Aucto, the robotic arm 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.