Patent GB-937178-A (GB)
Title: A lapping machine
IPC: B24B49/00
Filed: 1961-08-28
Abstract: 937,178. Surface and outline gauges. CRANE PACKING CO. Aug. 28, 1961 [March 6, 1961], No. 30897/61. Class 106 (2). [Also in Group XXIII] A lapping machine comprises a rotatable lap plate having a working surface adapted to produce a predetermined contour upon an article, rotatable means co-operable with the working surface and means for shifting the position of the rotatable means on the working surface to change the shape of the surface, and control means for the shifting means comprising a sensing head having radially spaced supports which are adapted to rest on the surface, a probe carried by the head intermediate the radially spaced supports, the probe being movable relative to the head and adapted to contact the working surface, and means operable as a function of the position of the probe relative to the head for operating the shifting means. A lapping machine comprises a frame 20 on which is mounted, for rotation about a vertical axis, a lap plate 21 having an annular lap surface 23 which is kept free of scratches and its contour maintained true by wear rings 25, 26, 27 resting loosely on the surface 23 and restrained from travelling round with the lap plate by yokes 28, 29, 30, each having spaced rollers 31, 32 against which the rings bear. The yokes have pins 33, 34, 35 extending upwardly into bearings 36, 37, 38 formed in a spider bar having three arms 40, 41, 42 radiating from a hub 43 and supported above the lap surface 23 by posts 44, 45 and a bracket 46, all secured to the frame 20. Arms 49, 50, 51 fixed to the yokes extend radially inwards under the spider arms and terminate in slots 52, 53, 54 engaged by pins 55, 56, 57 depending from a disc 58 secured to a shaft 59 driven, through epicyclic gearing, by a motor 69. Operation of the motor thus effects simultaneous radial shift of the wear rings. A lap surface contour sensing device comprises a head 71 in the form of a bar 72 having a leg 73 secured to one end and legs 74, 75 secured to the other end, the legs forming a triangle. For fine vertical adjustment of the legs 74, 75, relative to the bar 72, they are mounted in an arm 80 horizontally pivoted at 81 on the bar 72; an adjusting screw 82 and a lock screw 83 are provided. Equidistantly spaced from the legs is a vertically displaceable probe 76. The legs and the probe have hardened metal or jewelled inserts 78 to resist abrasion by the lap. The probe 76 has a notch 90 in which closely fits the end of a lever 91 pivoted at 92 to a cylindrical housing 79, the lever 91 being urged by a spring 93 against an adjustable stop 94. The probe 76 also has a notch 88 bearing against the short arm 85 of a bell-crank pivoted at 85a to the housing 79 and biased by a spring 89. The long arm 84 of the bell-crank co-operates with fixed electric contacts 86, 87. Spring 93 is stronger than spring 85 so that the lever 91 normally rests against the stop 94 which is adjusted so that the arm 84 then makes with the contact 87. The housing 79 is received in an opening 112 in the head 71 and has a hollow stem 113 extending through a smaller opening 114 and held by a clamp 115. For raising and lowering the head 71 relative to the lap surface 23 the head has an opening 95 through which passes a rod 96 having a head 97 and a tapered shoulder 98 co-operating with the chamfered end 99 of the opening 95. The rod 96 extends through an opening 100 in the yoke 28 and pin 33 by which it is guided and has secured to its upper end a piston 101 operating in a cylinder 108 and urged upwardly by a spring 110. For disposing the head 71 along a radius of the lap surface 23 to obtain maximum sensitivity, a pin 104 extends through the rod 96 into axial slots 105 in the pin 33 and a pin 106 extends through the head 71 into an axial slot 107 in the rod 96. The diameter of the rod 96 is less than the diameter of the opening 95 in the head 71 by more than the usual manufacturing tolerances so that the head 71, when lowered upon the lap surface 23, is free to move universally with respect to the rod 96 an amount sufficient to enable, the head to adjust itself to the lap surface throughout the expected variations in lap contour. The controls are conveniently arranged physically in groups for ease of operation, servicing or assembly and comprise the lapping machine standard controls 116, the lap surface sensing control chassis 118, the yoke arm operating controls 119, the solenoid-operated air valve control 120 and the sensing head 122. The lapping machine standard controls 116 include a timer switch 117 which is manually operated to initiate operation of the laprotating motor 146 and which has a timing mechanism incorporated therein set to stop the motor after the lapse of a predetermined time. The lap surface sensing control chassis 118 may be located at the control panel of the machine but may be located at a remote point if the machine has been automated so that a number of machines are supervised by one operator. The chassis includes a selector switch 121 and a motor-driven sequence timer 125. The yoke arm operating controls 119 are mounted under the motor 69 which comprises two motors 129, 130, one designed to rotate in one direction only and the other designed to rotate only in the opposite direction and both connected to the shaft 68. Limit switches 131, 132 automatically stop the rotation of the motors upon a predetermined angular movement of the shaft 68. A control 133 determines the degree of rotation of shaft 68 upon successive sensing cycles. The air valve solenoid 120 controls the admission of pressure air to cylinder 108 to lower the sensing head relative to the lap surface and also admits air to another cylinder co-operating with the control 133. The sequence timer 125 has a motor 159 driving cams 166-169 operating switch arms 162-165. Cam 166 controls the circuit through motor 159. Cam 167 controls the energization and consequent latching of a relay and the application of 6V. power to sensing head 122. Cam 168 controls a signal light 171 and the application of power to the latching coil of the relay to restore the relay to its released condition. Cam 169 applies 110V. power to sensing head 122 and to motors 129, 130. The surface of the lap plate may deviate from the desired contour by various amounts. It is desirable that the deviation be corrected in the shortest possible time. The time required to effect a correction is a function of the displacement of a wear ring from the position at which it is found when a measurement is made. Since measurements of lap surface contour cannot be made except when the lap plate is stationary and since it is not desirable to interrupt a lapping operation in progress, such measurements are therefore made between lapping cycles. It is possible that after the wear rings have been displaced radially to make a correction, measurement of the surface will indicate that the surface has been brought to the desired contour but continued operation with the wear rings in the same location will cause the lap surface to become oppositely contoured. To meet the foregoing conditions it is necessary to take into consideration the condition of the surface at the next preceding measurement and to correlate that condition with a present condition before effecting a corrective movement of a wear ring. Thus, the control for the wear rings 25-27 is designed to move the rings radially inwardly or outwardly by increments of “ inch. This movement is modified so that if the yokes 28-30 are moved in one direction an increment of “ inch and the sensing head upon the next measurement indicates that the desired contour has been effected, then instead of remaining in such position the yokes will be moved back toward their previous position by # inch since to remain in the same position would cause over-correction. If upon the next measurement it is again found that the surface has the desired contour then there will be no radical movement of the yokes. The necessary " memory " is supplied by the control 133 and associated relays. The control 133 comprises a brass switch arm 206 mounted on horizontal pivots 207, 208 extending outwardly from a hub 209 keyed to the shaft 59. The hub 209 is of hard non-conducting material and has secured to its sides spring fingers 212, 213 converging to form jaws 214, 215 within which is retained an axially disposed pin 216. The clamping pressure of the jaws is adjustable. The pin 216 extends downwardly from a disc 221 freely rotatable on shaft 59. The cylindrical outer surface of the disc is frictionally engageable by the end of a radially disposed pin 223 urged away from the disc by a spring 227 and towards the disc by air pressure on a piston 226. Thus the spring fingers 212, 213 acting upon pin 216 tend to rotate disc 221 with hub 209 and will do so when the braking effect of the pin 223 is not exerted. The disc 221 is of hard non-conductive material and carries contacts 188, 189, 228, 229 co-operating with a contact 230 on switch arm 206. The sensing head 71 is lowered upon the lap surface simultaneously with movement of the pin 223 to hold the disc 221 against rotation, the pistons 101, 226 being jointly controlled by the solenoid-operated valve 120. At the end of a lapping cycle, set up by the timer 117, the sequence timer motor 159 is energized. Subsequently cam 167 makes a circuit to energize solenoid of valve 120, thereby lowering sensing head 71 upon the lap surface and holding disc 221 against rotation. Head 71 may require a second or two after it is lowered to settle upon the lap surface and to avoid starting a correction during this period cam 169 is designed to interpose a five-second delay in energizing sensing head 122 and making power available to motors 129, 130. With the head 122 energized and resting upon the lap surface, if the latter is convex the arm 84 will make with contact 86. Consequently 6V. supply is connected to contact 229 of the control 133.