A robot arm temporarily stops when a contact detector detects contact. The chain disk locking mechanism includes a chain disk, an engaging rotary block, a stationary shaft and a plurality of moving pins. Using a mixture of SF6 gas and fluorocarbon gas, there is a step mainly for the progression of dry etching of the etching ground surface. When a quantity of the exhaust gas discharged from each cylinder is less than another predetermined value, an intake air quantity is increased and ignition timing is delayed before the determination of presence or absence of the abnormality. In one embodiment, propagation delays of received signals within the frame are determined and provided to other communication units allowing one or more communication units to calculate locations of the communication units. The control device comprises a unit for storing at least one control profile giving a plurality of values of the excitation current varying as a function of time, and a drive unit receiving at its input an external close command and delivering at its output the said excitation current following the said control profile during the closing of the power circuit.