GB1499812A - Machine tools - Google Patents

Abstract

1499812 Machine tool control system CRANFIELD INSTITUTE OF TECHNOLOGY 9 April 1975 [10 April 1974] 16039/74 Heading G3N A control system controls the position of a tool, e.g. a grinder 22, acting on a rotating workpiece 10, e.g. a cam ring or an external cam, forming part of a fuel injection pump for an internal combustion engine, and compensates for wear of the grinder. The grinder 22 is mounted on the spindle of a grinding head 1 movable at right angles to the cam axis using electric servo controlled motor 2 with tacho 4. Datum sensor 35 defines a data position for head 1 from which grinder movement units are defined by photosensors and the head (wheel) position is sensed by optical linear transducer 5, phase divider 6 and counter 7 to feed one input of comparator 8. The other comparator input receives a desired grinder position from mini computer 18 and the comparator output (difference) is converted to analog in unit 9 and used to reduce the difference. The workpiece 10 is rotated by motor 11 controlled by servo-amplifier 12 using velocity feedback from tacho 13. The angular position of spindle 15 (supporting the cam) is sensed by transducer 16 controlling circuit 17 which compensates for spindle eccentricity. The spindle is advanced rightwards from a rest position, defined by sensor 27, on carriage 26 using servomotor tacho drive 28 and photosensors 29, 30 sense the grinding stroke limits. Sensors 32, 33 are used for grinder dressing with vane 34 and swinging arm 45 carrying tool 46 and sensor 47. The computer 18 holds the desired cam shape data and cam follower 20 measures actual cam profile and feeds it to computer 18. The computer selects the signal to comparator 8 in depedence on the cam angular setting and the machined profile measured by follower 20 and shuts down the machine using logic 24 if the grinder wear exceeds a predetermined limit. A datum face 43 is provided with follower 20, controls 40, 37 and sensors 38-42. D/A converter 25 compensates for velocity lag errors. A computer program for controlling the system Figs. 3-6 (not shown), together with the mathematics of the grinding operation, are described in some detail.