Patent GB-1176561-A (GB)
Title: Contour Tracing and Tracking System
IPC: G05B19/42
Filed: 1967-03-30
Abstract: 1,176,561. Programmed control of machine tools. UNITED AIRCRAFT CORP. March 30, 1967 [April 5, 1966], No. 14696/67. Heading G3N. In a contour tracing and tracking system the contour is tracked at a speed which is independent of variations in the speed of tracing the contour by feeding sampled tracing position signals and velocity signals to a storage device which is read and drive signals for a tracking member are produced which are a function of the difference between the stored position signals and signals related to the actual position of the tracking member, a sealing circuit being responsive to the stored tracing velocity signals to modify the drive signals whereby the tracking speed is made independent of the tracing speed. As shown, Fig. 1, a prototype 12 on a table 10 is moved by X and Y co-ordinate velocity servos 18, 20 under control of an operator observing the prototype through an eyepiece 14. The operator determines the tracing speed by a foot-pedal 22 coupled to a circuit 24 producing a velocity dependent signal which is applied to a sinecosine potentiometer 26. The operator steers the table 10 by a wheel 16 positioning wiper arms 26a, 26b connected to the inputs of the servos 18, 20. Signals representative of instantaneous position of the table, determined by X and Y position digitizers 28, 30, and a digital velocity signal from the circuit 24 are stored in circuits 32, 34 and sampled, in parallel or sequentially, by a record control circuit 38 controlled by timing signals from a recording rate generator 36. The sampled signals are fed to a tape punch 40 producing a paper tape 42. Auxiliary data, such as tape or machine identification is fed to a second input of circuit 34. The prepared tape representing movements during equal time intervals at varying velocities is employed in an automatic machine tool control system, Fig. 2, wherein the relative movement of a tool 54 and table 50 is carried out at a constant velocity manually set in a speed control 78. The tape 42 is parallel or sequentially read by a reader 56 and the signals stored in a circuit 58. The read position signals are fed to positioning systems 60, 62 and the read velocity signal to a scale control circuit 64 and a counter 66. The systems 60, 62 are similar and for the X co-ordinate system the output of a digitizer 70 is subtracted from the position signal in a circuit 68 and the digital difference inserted in a shift register 72 which is shifted by pulses from the circuit 64, corresponding in number to the tracing speed, whereby the digital difference is divided by the sealed tracing speed. The shift register is emptied into a digital to analog converter 74 which, under control of the playback speed from circuit 78, develops a co-ordinate analogue signal which controls the velocity servo 76. A signal on lead 78b is applied to the circuit 66 which counts this signal until it reaches the previously set read velocity signal when a carry pulse is generated. The carry pulses, through a read control circuit 82, determine the times at which the tape is read and stored in circuit 58, the sampling of the position digitizers and the emptying of the shift registers. In a modification, by appropriate switching, the record and playback arrangements are combined in one circuit.