Hydraulic cylinder device for platen spacing indication and control

Abstract

A press has upper and lower platens which can be moved towards and away from one another. Four hydraulic leveling cylinders are mounted in a vertical orientation on the lower platen for purposes of platen parallelism control. In preferred form, each cylinder has a piston rod which engages an associated post on the upper platen as the platens approach one another. The piston rod and associated piston are formed with a longitudinal bore open at the upper piston rod end, and a rigid shaft is mounted in the bore with a lower end extending through the bottom of the cylinder housing. A coil spring in the interior of the piston rod urges the rigid shaft upwardly until a collar formed on the shaft engages a stop surface, the upper shaft end then being flush with the upper piston rod end. The associated post is fixed to the upper press platen in-line with the piston rod and has an internal passage in which is located a stud-like shaft that engages the rigid shaft mounted in the piston rod. Changes in the spacing between platens, including changes attributable to axial contraction and expansion of the post and piston rod with varying applied loads, are consequently manifested as axial displacement of the lower end of the rigid shaft relative to the lower platen. A sensor detects this relative displacement, producing a signal indicating platen spacing at the leveling cylinder. Sensor signals from the four cylinders are used to control the cylinders so as to maintain platen parallelism.