Patent GB-1196635-A (GB)
Title: Machine Control System
IPC: G05B19/23
Filed: 1967-06-23
Abstract: 1,196,635. Positioning machine tools. STEWART-WARNER CORP. 23 June, 1967 [24 June, 1966], No. 5400/70. Divided out of 1,196,634. Heading G4H. [Also in Division G3] A machine too] is controlled by a punched tape responsive system contained in a console and a workpiece is positioned with respect to a tool by carriages driven by D.C. shunt wound feed motors. The control system enables positioning for drilling, and straight milling cuts along directions parallel to the X and Y axes. The control system. Fig. 2, is responsive to a punched tape providing plus and minus X and Y dimension programming in four axes with respect to an adjustable or floating zero reference and the direction of tool offset. The tape is read by a reader 112 and set in co-ordinate command registers 200, 200a and combined with tool offset data from digital thumb-wheel switches forming control 202. The actual position of carriages 108, 110 is determined for each axis by the count in a register such as 204 responsive to the output of a wheel 206, driven by the feed motor 104, which produces a pulse for each increment of movement of the carriage. The position pulses are synchronized with the control system clock pulses by a circuit 207 and added or subtracted to the data in the register 204 by a circuit 108 in accordance with the direction of movement detected by a circuit 210 responsive to the phase-relationship of pulses from a pair of photo-cells spaced around the periphery of the pulse wheel. The data contained in the command register 200 is compared with the data in the position register 204 by a subtractor circuit 212. The difference output of the subtracter circuit is transmitted through a detector 214, which slips the carriage when the difference falls to zero, and a detector 216, which reduces the programmed feed rate at a predetermined minimum output, to a motor drive amplifier 218 providing a driving voltage to the motor 104. A reverse detector 220 controls the direction of movement of the carriage in dependence on the sign detected by the subtractor 212. The feed rate signal is fed from the reader 112 to a feed speed generator 222 which determines the magnitude of the driving voltage from the amplifier 218. The tool offset dimensions are set into the control system by the thumb-wheel switches in decimal form and converted digit-by-digit to a parallel sequence binary-coded decimal form which is combined with the corresponding digit read from the tape, as determined by the direction of offset data, and the result converted to binary rotation and stored in the command register 200. Actual position data read-in, Fig. 18.-The actual carriage position is derived by a pulse wheel 206, Fig. 21 (not shown), having photocell outputs D, E, of which output D only is used to determine carriage position and both outputs are used in the direction detector 210. The pulse signal D is attenuated by calibration potentiometer 1802 and transmitted through NAND gates 1804, 1806, 1808 to a pulse shaping circuit 1810 providing a 10 microsecond low pulse to the first input of a NAND gate 1812 for a pulse rise. Since both inputs to gate 1812 are normally high a 10 microsecond high pulse is fed to a NAND gate 1814. A pulse shaping 1810a, fed from NAND gate 1806, provides a 10 microsecond pulse to the second input of NAND gate 1812 for a pulse fall indicating the next increment of pulse wheel movement. The pulses from gate 1812 are synchronized with the control system logic sequence by the pulse wheel and logic synchronizing circuit 207. The output of gate 1812 and the clock pulses C1 are fed to the inputs of a NAND gate 1814 so that a single low-going pulse, synchronized with the clock pulse, is provided at the output. This low-going pulse sets a R-S flip-flop 1820 to provide a high signal to a second input of a NAND gate 1822, having as a first input the C11 pulse from a divide by sixteen counter, not shown. The gate 1822 provides an input count pulse to the full adder-subtractor 208. This pulse is added to the count in the position storage register 204 which is circulated through circuit 208 by the clock pulses. The flip-flop 1820 is reset after each pulse from the pulse wheel from a circuit including NAND gate 1828, flip-flop 1830 and NAND gate 1832. The direction detector 210 determines whether the pulses from the pulse wheel are to be added or subtracted from the contents of the position register 204 in dependence on the time sequence of pulses on lines D and E. When the pulse wheel 206 is moving in a clockwise direction the photo-cell output D lags by 90 degrees the photo-cell output E and vice versa for counter-clockwise movement. The output signals D, E, together with inverse signals D, E, are combined by NAND gates 1842, 1844, 1846, 1848 to control a flip-flop 1850 and set it to a clockwise or counter-clockwise determining state to condition the adder-subtractor circuit 208 so that the contents of the position register 204 are correctly up-dated. The register 204 is set to all zeros at the start of the tape programme by a signal, from a reference zero switch, on a line 1824 to the adder-subtraotor 208. The maximum repetition frequency of the pulse wheel signals is lower than the repetition frequency of the 16 count timing cycles so that each pulse wheel pulse is entered only once into the position storage register 204.