Design and Instrumentation of Force Feedback in Telerobotics

The design and instrumentation of force feedback (FF) is presented for a networked telerobotic system that consists of a master arm client station (MACS) and a slave arm server station (SASS). A motion coordination system maps the operator hand at the MACS to a user-defined floating tool frame at the SASS. Variational analysis for a wrist force sensor (FS) allows evaluation of the force at a floating point of the tool frame. Force is streamed from the SASS to the MACS, where it is displayed on the operator hand. Performance evaluation of contact with the environment is presented. First, a user-controlled teleoperation with FF is described. Contact instabilities are observed in the pre- and postcontact phases. Second, a programmed compliance loop is implemented at the SASS by selectively converting sensed forces into corrective motion, which allows minimization of contact forces. Third, a supervisory mechanism based on a user-controlled active compliance (AC) is presented. High FF gain improves operator sensitivity but may cause instability in case of contact with a stiff environment. Motion mapping minimizes the number of trials to set up the tool configuration. Light and stiff arms are highly recommended to reduce the degradation in telerobotic synchronization caused by elasticity in linkage transmission and by the network delays. The AC at the slave arm improved contact stability and provided an effective supervisory control.