Patent GB-1281866-A (GB)
Title: Positioning control system
IPC: B23Q5/22
Filed: 1970-09-03
Abstract: 1281866 Grinding INTERNATIONAL BUSINESS MACHINES CORP 3 Sept 1970 42092/70 Heading B3D [Also in Division G3] A control system for positioning a member relative to a surface being worked by the member comprises two transducers responsive to different physical variables and each producing a respective signal representing the position of the member relative to the surface, two comparison means generating respective control signals when the transducer signals differ from a reference representing the desired position of the member, control means responsive to one control signal to move the member in a direction to reduce this signal, and correction means responsive to an inconsistency between the two control signals. In the described embodiment the surface comprises a web 11 of cardstock which is advanced around a die drum 16 to pass an abrading wheel 19 whose depth of cut is maintained within a desired range by a servo-motor 44 which adjusts the position of the wheel 19 relative to the drum 16. To this end the shaft 31 driving the wheel 19 is supported in a bearing (36), Fig. 3 (not shown), eccentrically disposed in an annular housing 37 supported by a further bearing (38) carried by a fixed collar 39. Gearing 43, 45 couples members 37, 44 to provide the required adjustment. The current taken by the motor 32 driving the wheel 19 is sensed by a transformer 51, 52 to provide a signal indicative of the depth of cut, which signal is supplied to comparator circuits 56, 57 also supplied with reference signals from rheostats 58, 58a respectively representative of the maximum and minimum desired depth of cut. The comparators 56, 57 control the servo-motor 44 through relays 66, 69 so that the motor is energized to adjust the wheel 19 whenever the current signal is outside the range set by rheostats 58, 58a. The depth of cut is also sensed by an optical transducer 83 comprising two fixed and movable, vertically-spaced grills of which the movable one is connected to a roll 86 riding on the surface of the web 11 to control the amount of light passing through shutters between the grills to a photoelectric cell. The signal from the transducer 83 is supplied to comparator circuits 80, 81 also supplied with desired maximum and minimum depth of cut signals from rheostats 89, 89a set to correspond with the rheostats 58, 58a. The outputs of the comparators 80, 81 are passed to exclusive position OR gates 97, 98 which also receive the outputs of comparators 56, 57 via delay units 93, 94 to delay their signals by a time dependent on the velocity of the web and the distance between members 19, 86. In the event of a deviation from normal of the relationship between motor current and depth of cut, e.g. caused by the wheel 19 loading up, the gate 97 or 98 produces a signal to energize a relay 101 whose contacts 102, 103, 104 de-energize the motor 32 and whose contact 105 de-energizes a motor 106 driving the various drums and rolls associated with the web. The various fault conditions producing energization of relay 101 are discussed. Operation of the monitor circuit 80, 81, 83 is prevented during start up and/or calibration of the apparatus by opening a switch 100. The calibration operation is described and involves operation of a switch 110 to its X and Y positions to energize the motor 44 to set the wheel 19 at its maximum and minimum depth of cut positions. Instead of de-energizing the motor 32 when the wheel 19 loads up, a dressing unit (not shown) may be actuated to dress the wheel 19 until correct control is restored. An additional abrading wheel 111, oppositely rotated to the wheel 19, is provided to perform a coarse manually-controlled operation prior to that performed by the servo-controlled wheel 19. To minimize the amount of variation in the tension of pulley belt 34, the axis of pulley 33 is located so that a line through the axes of pulleys 33, 35 bisects the angle subtending the predetermined limits of angular movement of the shaft 31. The wheel 19 may be replaced by a grinding wheel and the die 18 eliminated.