Patent GB-837817-A (GB)
Title: Improvements relating to automatic machine tool control
IPC: G05B19/23
Filed: 1956-12-06
Abstract: 837,817. Lathes. GENERAL ELECTRIC CO. Dec. 6, 1956 [Dec. 6, 1955], No. 37357/56. Class 83 (3). Apparatus for automatically controlling the motion of a machine-tool part 7 comprises a pulse generator 42 for producing sequential electric pulses correspondingly with motion of the part, a pulse-counter 47, correlating means 48 for comparing the instantaneous pulse count with a reference number recorded to represent a position of the part at which its motion is required to be modified, and command means 54 responsive to a predetermined relationship between the pulsecount and the recorded number for appropriately modifying the motion when said relationship pertains. A turret-lathe has a chuck 4, rotated at a speed determined by a lever 6, and a turret-saddle 7 traversed by a main D.C. motor 30 at a high or low speed in either direction, by a shaft 9 or 15 according to the setting of levers 11, 16. The saddle can be crosstraversed by a capstan 17, and the turret is indexed by hand or power. The control apparatus determines the direction and speedof-traverse of the saddle by controlling the energy supplied to the motor 30. Each of the shafts 9, 15 carries a perforated disc 20, 22 co-operating with photo-electric pick-up means 21, 23 to measure the movement of the saddle. (Such devices may also be employed to measure the rotary movement of the turret or spindle and/or the cross-movements of the turret.) In a typical circuit, which may include transistors, current is supplied from lines 37, 38 to the main motor 30, through a device 34 comprising a double-throw, double-pole switch to determine the direction of rotation of the motor, and a rheostat or potentiometer to determine the speed. The pulse generator 42 supplies electric pulses to the binary-counter 47, consisting of a number of cascade connected bi-stable trigger stages. The coincidence circuit 48 correlates the pulse input with the pulses read from a punched tape 49 by pickup 50, and passes signals to the command circuit 54, which controls the machine tool through the outputs 55-57, and advances the tape through a ratchet device 53. The tape has thirty channels, and the holes are " read " by a series of contacts 72a-77a connected-to an electrical source 79 and contacts 72b-77b, each of which completes a circuit when it coincides with a hole. Fifteen channels are used for denoting numbers up to 32,000 in the binarycode, so giving a slide travel of 32 inches in 1/1000ths. Of the other channels, one is used for switching the motor 30 on-or-off, one for directing the counter 47 to add or subtract, four for selecting resistances to determine the speed of rotation of the motor 30, and one for determining the direction of rotation of the motor 30. If desired, other channels control the direction and speed of the spindle and turret rotation. The four motor speeds are used for fast approach to a workpiece, a slower approach prior to the cut, a cutting-speed, and a slow feed when the end-of-a-cut is approached, to prevent over-shooting. An over-shoot after a fast-retraction movement is not important as the counter maintains its count. The circuit may be arranged so that one counter serves several drive-motors.