Apparatus for synchronizing cylinder position in a multiple cylinder hydraulic press brake

In a press brake having a bed supporting a forming die, a vertically movable ram mounting a punch for cooperating with the die to bend a workpiece positioned on said die, at least two pistons connected to said ram at horizontally spaced locations, a hydraulically operated cylinder associated with each of said pistons for vertically moving said ram, and flow control means associated with each of said cylinders and responsive to an electrical command signal for its respective cylinder to control the flow of hydraulic fluid to and from its respective cylinder, the improvement comprising a ram position encoder is association with each of said cylinders each producing a digital pulse for each increment of vertical ram travel in the form of a ram position signal, control means for generating said command signal for each of said flow control means, said control means including programmed means for generating an electrical speed signal representative of the desired speed of the ram, said control means including means to produce a digital re ference signal proportional to the desired speed of said ram, and means to compare said ram position signals to said digital reference signal and to produce an error signal for each flow control means, and means to sum each error signal with said speed signal to produce said command signal for each of said flow control means whereby to control the speed of said ram and to control the vertical position of all parts of said ram during vertical movement thereof at least just before and during ram reversal.