Control and operational aspects of the Mascot 4 force feedback servomanipulator of JET

The telemanipulator developed for maintenance of the JET (Joint European Torus) tokamak (Mascot 4) is a microprocessor-controlled unit based on bilateral position servosystems. The main objective of this type of force-feedback servomanipulator is to give the operator, as nearly as possible, the tactile sensations of actually doing the job. Servomanipulator sensitivity, stiffness, time response and low reflected inertia characteristics are achieved by using low-friction AC motors, high-resolution R/D converters, fast sampling time, and short delays in the signal transmissions. There is a 16-bit Z8001 CPU and a servo amplifier for each servo system, and a global CPU with 16+16 I/O for general supervision. For the advanced function an auxiliary CPU with 256 Kb of RAM is used. Communication between master and slave is via a high-speed full duplex serial link at 1 MHz. The digital system has permitted a reduction of the cabling required and the introduction of advanced aids to the operator: teach and repeat, tool weight compensation, and constraint of the trajectory on given planes or lines