Patent GB-524875-A (GB)
Title: Improvements in and relating to the electrical control of copy milling machines
IPC: B23Q35/123
Filed: 1939-02-09
Abstract: 524,875. Milling-machines. BRITISH THOMSON-HOUSTON CO., Ltd. Feb. 9, 1939, No. 4306. Convention date, Feb. 8, 1939. [Class 83 (iii)] [Also in Group XXXVIII] In a control system for a copy-milling machine of the type wherein the feeling finger and the tool are moved line by line with respect to the pattern and workpiece respectively, the feeler finger transmits adjusting impulses to the auxiliary motors controlling the speed-regulating devices of the feed motors as well as the normal switching impulses for the feed motors, the resultant feed movement running in the direction of the incline of the copied surface. The pattern and the workpiece are carried on a slide-rest 1 displaceable vertically by a motor 6 and in the depth direction by a motor 5, the feeler, cutter and milling motor 7 being mounted on a slide-rest 3 displaceable by a motor 4. Limit switches 30 ... 35 and changeover switches 10, 11 are provided. The feeler finger comprises a universally mounted member arranged to displace armatures Al, A2 axially and laterally, to unbalance impedance bridges having output transformers 48, 49 arranged in the grid circuits of gas discharge tubes. Upon the feeler being progressively axially displaced relays 19, 20 and 21 pull up in succession, their associated gas discharge tubes being correspondingly biased. In a similar manner, when laterally displaced to the position a relay 80 pulls up, in 1 and 1<SP>1</SP> relays 66 or 67 pull up according to the condition of relay 68, and in positions 2, 2<SP>1</SP> relay 18 operates. A motor M drives a generator G3 Fig. 3, and the armatures of generators G4, G5 and G6 arranged with motors 4, 5 and 6 to run in a Ward-Leonard system. The speed-regulating resistances R1 R2 and R3 are adjusted by a step-by-step motor operated by magnets M1, M2. Operation. It is assumed that the feeler is in the position shown in Fig. 4 and copying is to be performed by horizontal traverses. Main switch 1 is closed, switch 25 moved to the " Horizontal " position, completing the circuits for the motor fields, and switch 16 rotated to the " Forward " position. Relay 12 pulls up and the field of generator G5 is energized so that motor 5 runs to bring the feeler and pattern together. Starter button 22 is pressed, relay 8 locking up so that the field of generator G4 is fully energized and the feeler moves sideways relative to the pattern. Upon the feeler impacting the pattern, armature A1 passes to position 1, relay 19 pulling up and releasing 12 whereupon motor 5 stops. Sideways motion continues until the feeler contacts a slope, Fig. 6, and armature A2 passes to position 1 (the energizing of relay 80 in position a having no effect due to the shorting of contact bars on the regulating resistance -R2 by the control arm this relay only being effective when the arm passes the 50 degrees position), relay 67 energizes, stepping forward the regulating resistances and causing relays 13 and 28 to pull up so that motor 5 runs back and motor 4 is stopped and the feeler assumes the position of Fig. 7. Relay 67 releases, connecting condenser 71 in the grid bias circuit of tube 38 so that relay 19 is energized and since 13 has fallen away, motor 5 runs slowly backward, also 28 having released and relay 102 being energized, motor 4 runs so that the feeler moves in the indicated direction R. The valve of condenser 71 is chosen so that tube 38 remains ignited until the feeler again contacts the slanting surface, which corresponds to the position of Fig. 6, when the operation of relays and magnet M1 are repeated. In this manner the speeds of motors 4, 5 are adjusted until the feeler travels along the incline, Fig. 11. When travelling up a slope and meeting an abrupt change to an angle above 50 degrees, armature A2 passes to position, 1 causing 67 to pull up, followed by 13 and 28 so that motor 5 runs back and motor 4 stops, and the feeler passing to the point 2. Relay 67 releases followed by 13 and 28, 19 remaining operated due to condenser 71. As armature A2 is alone deflected on slopes above 50 degrees and A1 alone on slopes of lesser angle, when 71 is charged, 19 will release, stepping back the speed regulating resistance over M2 and energizing 12 so that G5 runs forward. The feeler makes contact again, and 67 again operates and energizes M1 which slips the regulator to its previous position. In order to avoid steps when copying slopes greater than 50 degrees, relay 80 is provided. When laterally deflected, armature A2 passes to position a and since the slope is steep the arm of regulator R2 will be near its end position so that relay 80 is effective. Magnet M2 cannot now operate with the result that the feed movement becomes progressively more parallel to the copied surface, and no downward movement takes place. In a manner similar to that described above when the feeler passes over the top of the slope to a horizontal part of the pattern it describes saw-tooth motion of decreasing amplitude until it finally runs parallel to the surface.- When descending a slope, relay 66 is energized to perform the functions corresponding to those of relay 67. At the end of a line, switch 10 passes to position II relay 8 releasing and 9 pulling up to reverse the field of generator G4 and energize relay 68 to reverse the connections to relays 66, 67. G6 is energized under the control of relay 29, the slide rest 1 being moved down one line prior to the next right to left movement. Vertical lines are milled by throwing switch 25 to the " vertical " position whereby the functions of G4 and G6 are interchanged, the reversing relays 14, 15 of G6 operating in the same way as the corresponding relays 8, 9 of G4.