Mapping Human Muscle Force to Supernumerary Robotics Device for Overhead Task Assistance

Supernumerary Robotics Device (SRD) or Supernumerary Robotic Limbs (SRL) is an ideal solution to provide robotic assistance in overhead manual manipulation, especially the tasks including supporting a panel and fitting it in the ceiling in limited space such as compartment. Since two arms are occupied for the overhead task, it is desired to have additional arms to assist us in achieving other subtasks such as supporting the far end of a long panel and actively pushing it upward to fit in the ceiling. In this study, a method that maps human muscle force to SRD for overhead task assistance is explored. Our idea is to utilize redundant DoFs such as the idle muscles in the leg to control the supporting force of the SRD. A sEMG device is worn on the operator’s shank where muscle signals are measured, parsed, and transmitted to SRD for control. In the control aspect, we adopted stiffness control in the task space of the SRD. The sEMG signals detected from human muscles are extracted, filtered, rectified, and parsed to estimate the muscle force. The muscle force estimated by sEMG is mapped to the desired force in the task space of the SRD. This force information is taken as the intent of the operator for proper overhead supporting force. Through tuning the stiffness and equilibrium point, the supporting force of SRD in task space can be easily controlled. The desired force is transferred into stiffness or equilibrium point to output the corresponding supporting force. In the preliminary test, we demonstrated the muscle force estimation using sEMG signals from shank, active stiffness control in SRD task space and supporting force control through mapping sEMG to equilibrium point of stiffness in SRD task space. A SRD prototype is integrated with a sEMG device, a 6-axis force sensor, and a visual odometry camera. Experiment results in the preliminary tests are presented to prove the feasibility of the proposed method.