Design and characterization of an instrumented hand-held power tool to capture dynamic interaction with the workpiece during manual operations

In recent years, robots have contributed extensively to the automation of repetitive tasks for which position control-based approaches represent effective solutions. However, other contact tasks such as finishing, deburring and grinding require both position and force control. To date, despite the availability of cost-effective robotic solutions, such tasks are still carried out manually by skilled operators mainly because programming is time consuming and not sufficiently flexible to be readapted to product or task changes. An alternative approach is teaching by demonstration, by instrumenting hand-held tools for capturing both the force and the contact point while an expert operator performs tooling tasks. This paper presents a novel approach for instrumenting hand-held tools for polishing/grinding used in monitoring the performance of skilled human operators which can be, in future work, translated into planning strategies for robot programming and control. More specifically, the instrumented tool is designed to monitor interaction forces with the workpiece and point of contact, where these interaction forces arise. The key element in our design is a flexible coupler which, ideally, only transmits rotation torques to spin the polishing/grinding wheel while all the remaining torque and force components are transmitted through a parallel structure and sensed by a 6-axis loadcell. Sensing torques, in addition to forces, also allows for a dynamic estimation of the point of contact.