Patent ID: 6018970
Filing Date: 2000-02-01
Classification: B21D

Abstract:
In a stretch-forming machine of the type wherein a pair of opposed curving jaws grips opposing ends of a metal sheet to be stretch-formed in a curved configuration, each of said jaws being formed of an array of adjacent grippers movable relative to each other by respective hydraulic cylinders to define a part of the curve of the jaw, the improvement comprising a closed-loop servo-controller for moving each one of said grippers into a predetermined position relative to each other, each of said servo-controllers comprising:(a) a hydraulic cylinder position controller carried by the hydraulic cylinder of said one gripper for controlling hydraulic fluid flow to said hydraulic cylinder responsive to stored data representing the desired predetermined position of one of the grippers;(b) said position controller comprising:i. circuit means for summing a signal representing the desired predetermined position of one of the grippers, and said signal representing the position of the hydraulic cylinder to said position controller and outputting a signal representative of any variance between the desired and actual position of said hydraulic cylinder; andii. valve means cooperating with blind and rod sides of said hydraulic cylinder for moving said hydraulic cylinder by hydraulic fluid flow.