Patent GB-816951-A (GB)
Title: Improvements relating to apparatus for automatically controlling machine tools
Inventor: WOLFENDALE FREDERICK CALEB
IPC: G05B19/4105
Filed: 1954-10-13
Abstract: 816,951. Programming for machine-tools; drilling; copy-milling. ELECTRIC & MUSICAL INDUSTRIES Ltd. Sept. 29, 1955 [Oct. 13, 1954], No. 29446/54. Class 83 (3). [Also in Group XXXVIII] Apparatus for controlling a machine tool comprises means for effecting a relative displacement between a tool holder 10 and a work holder 12, and means responsive to an applied signal for causing one of said holders to describe a circle with reference to the other holder, said circle having a radius determined by said signal. A jig-borer may thus bore a number of holes of different radii, the smallest radius being that of the cutter. The tool 11 on the head 1 is vertically adjustable by a screw 3 rotated by a servomotor 4 controlled by a circuit 6 comparing the signal from a temporary store 7 deriving information from a punched tape 30, and a tap 8 of a potentiometer 9 giving a feedback signal. The work-table 12 is traversed on a slide 20 by a screw 14 rotated by a motor 15, controlled similarly to the motor 4 from a temporary store 18 and a potentiometer 19. Similarly, a motor 21, controlled by a temporary store 27 and a potentiometer 28, moves the slide 20. The motors 4, 15, 21 thus provide movements respectively in z, x and y directions. The instructions from the decimal binary code tape 30 may be applied to the stores, which may be as described in Specification 796,993, [Group XXXVIII], by a programme unit 32 as described in Specification 807,643, [Group XXXVIII]. A signal for controlling the radius of the bore is applied by the programme unit, following each group of three co-ordinate signals, to a store 33, the output of which is applied across an auto-transformer 34. The transformer tap 35 is rotated by a motor 39 driving, through a shaft 36, a friction-drive 37, 38 and a clutch 60, the friction-drive being adjusted by a lever 40, preset to represent the radius of the cutter 11. The clutch 60 is energized wherever any voltage-analogue is stored in the store 33. The voltage picked up by the tap 35 is applied across a transformer primary winding 41 associated with rotating secondary windings 42, 43, the generated voltages of which are proportional to A sin #t and A cos #t, and are injected in series with the output of the stores 18, 27 by transformers 44, 45. The speed of the motor 39 is determined by the output of a variable-gain amplifier 46, the input signal for which is derived from a potentiometer 47, set according to the maximum permissible speed of the shaft 36. The gain of the amplifier is controlled by a bridge circuit, one arm of which is a strain gauge 49 in the tool-holder 10. The rate of working is thus controlled to keep the strain on the tool within a certain limit. When it is desired to bore a hole of greater radius than the cutter, the tool is positioned in the x, y and z co-ordinates, and the signal representing the radius of the hole is applied from the tape 30 to the store 33. Thereupon the shaft 36 and tap 35 rotate to move the tool in a spiral path, the lever 40 having been adjusted so that, for each revolution of the shaft 36, the increase A in the path dimension is not greater than the cutter diameter. At the required radius, the tap 35 closes a contact 62 and de-energizes the clutch 60, the rotation of the shaft 36 being stopped manually or automatically. All the x, y, z displacements may be applied to the tool and may be controlled by signals from interpolating means as described in Specifications 796,994, [Group XXXVI], and 807,643, [Group XXXVIII].