Redundant Strain Measurement of Link Structures for Improved Stability of Light Weight Torque Controlled Robots

Abstract

Robots that perform useful heavy-duty tasks are gaining attention in the field of construction, mining, and disaster recovery. For robust accomplishment of such tasks, control of interaction force is important fundamental functionality. Use of joint torque sensors is the most common method for robots that realize physical interaction. However, torque sensors add weight and reduce joint stiffness which result in loss of mobility performance. In this paper, joint torque sensing using link structure strain measurement is presented. Redundant strain gauges, placed in unstructured manner, are used to measure link deformation, which are then used to estimate all 6 components of the wrench acting on a link structure. Joint torque is then extracted from this wrench, which minimizes the cross-talks of the force measurement. Redundancy enhances the measurement accuracy and realizes fault tolerant force measurement. Simulation and experimental results of the measurement concept together with the fault recovery method are presented.