Device for driving a transfer beam

Device for driving a transfer beam, notably for handling relatively heavy loads, in which the reciprocating transfer beam is rigid with a rack meshing with a pinion driven by a motor in either direction for imparting to and fro movements to said beam, said device further comprising in the transmission from said motor to said pinion a clutch and a brake both controlled by electro-magnetic means, servo means for supplying electric current to each electro-magnetic control of said clutch and brake, said system comprising a comparator having one input supplied with current from a tachometric generator coupled to the transmission member operatively connected to said pinion for supplying real velocity data, and another input for the reference velocity data, the output of said comparator being coupled via amplifiers responsive to the polarity of the output signal on the one hand to a stage supplying electric power to the electro-magnetic clutch control means and on the other hand to another stage supplying electric power to the electro-magnetic brake control means, and a pair of servo generators, one servo generator adapted to monitor the acceleration phase of the transfer beam from the standstill condition thereof and the other the deceleration phase of said transfer beam before stopping said beam, said pair of servo generators being coupled to the reference velocity data input via switching means putting one or the other servo generator into service in response to predetermined positions of said transfer beam and means responsive to the positions of said beam being provided to monitor said other servo generator.