Hydraulics & Pneumatics
Pneumatic compensating roller control
By Mary Del
The electro-pneumatic pressure regulator from Rexroth’s ED series adjusts deviations in the compensating roller when working with paper and foil webs. To keep the web tension on a printing and processing machine constant, a vertically mobile compensator is hung onto the material web. A web tension regulator maintains the position of the compensator in the centre. The compensator position is recorded via a potentiometer. The material web tension must be kept constant to avoid operating problems. If the web tension is too high, the material may tear. If the web tension is too low, the material may flutter, leading to a disturbance in the process or a torn web. A pneumatic cylinder supports the compensating roller in its function. Despite drive control, changes in tension through a reel change or out-of-roundness in the material reels move the compensating roller, which then displaces the pneumatic cylinder. The increased or decreased pressure created in the pneumatic system is recognized by the controller. An ED02 electro-pneumatic pressure regulator creates a change in output pressure via a set/actual point comparison, which then adjusts the pressure on the compensating roller so that the web tension remains constant. The ED02 is the smallest pressure regulator of the Rexroth ED series. In the ED series valves, the manufacturer has combined the control electronics, a pressure sensor and a direct drive via proportional solenoids in a compact unit.