GB1174655A - Device for the Positioning of an Endless Belt - Google Patents

Abstract

1,174,655. Automatic edge guiding. GEVAERT-AGFA N.V. April 11, 1967 [Oct. 26, 1966], No. 16457/67. Heading G3R. Lateral deviations of the edge position of an endless belt are detected and signals dependent on the average deviation and the rate of change of the average deviation are utilized to restore the edge to a desired position automatically. As applied to an endless motor-driven metal belt, e.g. for casting film, the edge of the belt passes between the plates of a condenser arranged in an A.C. bridge circuit the output of which is rectified and compared with an adjustable reference voltage so that as the belt wanders laterally from a desired position a D.C. error signal is produced which is applied through a switch S 1 , Fig. 4, to two integrating amplifiers 30, 40. An inverting amplifier 34 ensures that the error signal is applied in opposite senses to the two integrators and a switch 16, camoperated at each revolution of the belt, changes over switches S 5 S 6 so that each integrator receives error signals alternately in opposite senses. Since, by virtue of different resistors R d , R dp , the time constants are different for integration in each sense, the outputs of the integrators are not only dependent on the average error but also on the rate of change of the average error. Cam-operated switch 16 also causes a switch S 3 to close at the end of each integrating period so that the integrator outputs, selected alternately by a switch S 7 operated with switches S 5 , S 6 , are applied to two Schmitt trigger circuits (not shown), one or other of which operates a reversible servomotor in the appropriate direction to move the belt to its desired position by adjusting one end of a skew roll over which the belt passes. The operated trigger circuit also closes a switch S 8 or S 9 so that a voltage of corresponding polarity is applied through a cam-operated switch S 2 and a resistor R o to discharge the appropriate integrator, thereby causing the servomotor to run for periods dependent on the magnitude of integrator outputs. Cam-operated switch S 1 ensures that error signals are not applied to the control system during these periods. The Specification also refers to pneumatic, photo-electric or inductive edge detectors, the use of two servomotors, limit switches, and a belt tension responsive strain gauge controlling belt tension by adjusting roll position.