Patent GB-907954-A (GB)
Title: Apparatus for automatically maintaining a predetermined contour on the rotatable lapdevice of a lapping machine
IPC: B24B37/10
Filed: 1961-04-07
Abstract: 907,954. Control of motors. CRANE PACKING CO. April 7, 1961 [April 12, 1960], No. 12531/61. Class 38 (3). [Also in Groups XXIII and XXXV] A lapping machine has means adapted to co-operate with the surface of a rotatable lap device to sense deviations thereof from a predetermined contour and motor means controlled by the sensing means for altering the wearing effect of a correcting device upon the surface to restore the surface to its predetermined contour. A lapping machine comprises a frame 10 having a table-like top 11 with an opening 12 through which projects a rotating lap 13 having an annular lapping surface 14 to which lapping compound, in paste or liquid form, is applied. Articles to be lapped are placed within cast iron wear rings 19, 20, 21 resting on the lapping surface 14 and engaged by yokes permitting the rings to rotate about their own axes but preventing the rings from revolving about the axis of the lap. The yoke for at least one of the wear rings, e.g. 19, comprises a slotted bar 23 secured to a guard plate 24 secured to the frame 10. The wear ring is located by a roller 26 on one end of bar 23 and a roller 28 on one end of an arm 27 pivoted at 29 to the bar 23. The other end of arm 27 has a slot 34 engaged by a pin 33 carried by a plate 32 rotatable, through a speed reducer, by a motor 30. The hub 36 of the plate 32 carries stops 37, 38 co-operating with the operating lever 39 of a limit switch 40 controlling the motor 30. Operation of the motor 30 moves the wear ring 19 to one or other of two radial positions relative to the lap. A lap surface contour sensing mechanism comprises a base-plate 46 to which is secured a flange 47 secured by a clamping device 48 to a bar 43 supported on standards 44, 45 affixed to table top 11 and guard plate 24. The bar 43 is removable from the standards to allow servicing of the lap 13 and its removal and replacement when worn. Probes 41, 42 lie on a radius of the lap. The probe 41 comprises a vertical rod 49 to the lower end of which is secured a foot 50, preferably of abrasion-resistant material such as tungsten carbide, having a forward end 51 which is shorter than the rearward end 52 so as to be self-aligning or castering when the foot contacts the lapping surface 14. The rod 49 extends through a bearing 54 in a tube 55, downward movement of the rod relative to the tube being limited by engagement of a stop collar 64 secured to the upper end of rod 49 with a shoulder provided by a counterbore 63 in the upper end of the tube 55. The tube 55 is slidable in a block 65 secured to the base-plate 46. A U-shaped plate 59 secured to the upper end of the tube 55 carries a microswitch 58, the actuator 57 of which is close to the upper end of rod 49. The probe 42 is identical with probe 41; block 77, plate 80 and microswitch 100 are counterparts of block 65, plate 59 and microswitch 58. The upper limbs 78, 79 of the plates 59, 80 rest on rollers 81, 82 at the ends of a rod 69 passing through bearings 70, 71 pivotally mounted on plates 73, 72 secured to a secondary base-plate 74. The latter is free to slide or to turn to a limited extent relative to base-plate 46 with which it is held in contact by guide rollers 76, 75 mounted on blocks 65, 77. Dials 91, 92 having hubs 83, 94 resting on flange 47 are secured to screws 85, 86 passing through apertures 89, 90 in the flange 47 and through threaded openings 87, 88 in the plates 73, 72. Tension springs 83, 84 are secured to the shafts of guide rollers 76, 75 and to plates 73, 72. By turning the dials 91, 92 the axis of the rod 69 is set parallel to the ideal lapping surface 14; this is preferably done empirically, using a lapping surface which is known to be true, or some other test surface. The rod 69 rests on a cam 66. The probes are normally held raised so that the feet 50, 50 do not engage the lapping surface 14. By rotating the cam 66 the probes are lowered so that their feet engage the lapping surface and are then raised. During the descent the microswitches 53, 100 are closed and during the ascent they are opened. If the lapping surface is not parallel to the axis of rod 69, the microswitches do not open simultaneously and this, by means of the control system shown in Fig. 7, causes rotation of the motor 30 in the appropriate direction to effect the necessary wear ring adjustment. Checking of the lapping surface is automatically effected periodically; a constantly running motor 102, mounted on secondary base-plate 74, drives a disc 103 having a notch 104. When the end of a contact arm 106 of a switch 105 enters the notch 104, the switch 105 is closed and energizes motor 68 for cam 66 through a time delay relay 108 working in conjunction with a limit switch 109 having an arm 110 riding on rod 69. Specifications 652,655 and 676,284 are referred to.