Control system for film processing and rewinding equipment

Abstract

Film type materials often have to be processed. A reel of film is unwinded, the film passes over several rollers along the processing units and is rewinded. Since the diameters of both reels vary in time, one or more dancing rollers are used to cope with imperfect matching of unwinding and rewinding speeds. This research aims at an alternative control system for the motors driving the reels. The new control system should avoid the numerous disadvantages of dancing rollers and should be cheap and compact. The film passes over a fixed roller equipped with a force measuring system on its axis. This force is used either to control the speed of the unwinding motor or the torque of the rewinding motor.This new control system has been compared to the more conventional control using a dancing roller: the maximum achievable line speed for a specific film type is higher and moreover the line speed accuracy is better. Moreover the force based control allows to compensate for less than perfect alignment of the rollers along the processing line and results in visually perfect rewinding of the film. Since there is no need to measure the actual diameter of both reels, practical difficulties to measure these diameters are avoided. Although further tests using different types of film are required, the new control system is very promising for film processing equipment.