Patent GB-1188096-A (GB)
Title: Method and Apparatus for Controlling the Motion of a Reciprocable Tool Element or the like
IPC: B23B47/20
Filed: 1968-09-12
Abstract: 1,188,096. Programmed control of machine tools. GIDDINGS & LEWIS Inc. Sept.12, 1968 [Oct. 16, 1967], No.43416/68. Heading G3N. Engagement of a machine tool with a workpiece 14 is detected by the change in traverse speed of the tool during engagement. As shown, the cutter 12 is traversed rapidly towards the workpiece 14 by a reversible motor 28 through a rack and pinion 16, 18, and the traverse speed is measured by a pulse generator 35 driven in response to movement of the cutter to produce an output signal 35b having a frequency proportional to the speed. When the cutter 12 engages the work the frequency of signal 35b drops abruptly to lie outside the normal range of frequencies and a second signal is consequently produced which is used to change the traverse speed to a lower feed speed. The pulse generator comprises an apertured or notched disc driven by rack 16 and positioned between a light source and a photo-cell whose output is fed to an amplifier and pulse shaper. The pulses 35b so produced are fed to an engagement sensor 50 which comprises an R-C integrator which produces an output voltage substantially proportional to the pulse frequency. The output voltage is compared with a set voltage on a voltage divider or Schmitt trigger which produces an output signal, only when the frequency drops on engagement of cutter and workpiece to set a flip-flop and produce a 1 level output signal E. The 1 level signal resets a flip-flop FF2 and sets a flip-flop FF3 so that servomotor 28 changes from traverse to a lower feed-speed. The machine tool is tape controlled and the tape reader 74 is started by an initiation signal applied to its terminal ST. The block of data is read from tape 70 and produces a position command signal PC which causes the servo 29 to bring workpiece 14 into a desired position whereupon it will produce an in position signal 1P. Signal 1P sets flip-flop FF2 to produce a "1" level signal TD which conditions the servo 28 to drive cutter 12 at the traverse speed. An artificial high velocity signal is impressed on the capacitor in the R-C integrator circuit by a one-shot device triggered by the setting of signal TD to the "1" level and thereby prevents the generation of a false engagement signal. The switching of signal TD to the "1" level also resets a counter in depth controller 76 to zero and resets the flip-flop of the engagement sensor 50. When the cutter 12 engages the workpiece the engagement signal E from sensor 50 resets flip-flop FF2, and sets flip-flop FF3. The output signal FD from FF3 therefore conditions the servo 28 to advance the cutter at a feed speed set by a feed signal FC from decoder 75 and opens a gate 80 so that the pulses from the pulse generator 35, which represent a specific travel e.g. 0.001", are fed to depth counter 76. The cutter 12 continues feeding into the workpiece until the number of pulses fed into controller 76 equals the number stored therein by the depth control signal DC produced from the tape. When the counter 76 is empty a hole complete signal HC is generated which resets flip-flop FF3 and sets a flip-flop FF4. The output signal TU of flip-flop FF4 now conditions servo 28 to retract the cutter 12 at a high traverse speed. The upward traverse is terminated by a limit switch LS which produces an upper limit signal UL which resets flip-flop FF4, restores signal HC of controller 76 to the "0" level and is applied to the terminal ST of tape reader 74 so that it commences reading the next block of data. Once the engagement signal E is generated and flip-flop FF2 reset, its output signal TD at the "0" level is used to maintain the capacitor of the R-C integrator fully charged until the cutter 12 is arrested at its upper position. The spindle speed drive 19 is controlled in accordance with a set signal SC from the tape.