Patent GB-777952-A (GB)
Title: Improvements in and relating to systems for magnetically recording a programme of sequential operations
IPC: G05B19/42
Filed: 1954-03-29
Abstract: 777,952. Electric control systems. GENERAL ELECTRIC CO. March 29, 1954 [March 30, 1953], No. 9138/54. Class 40 (1). A system for recording movements of a tracer element comprises means for producing on a magnetizable tape on parallel tracks a trace representing a sinusoidal reference voltage and two traces representing voltages, the instantaneous phase relationships of which, relative to the reference voltage, correspond respectively to the position along two Cartesian co-ordinate axes of the tracer, wherein the drives of the tape and the reference voltage generator are coupled to that of the tracer to maintain the reference voltage frequency at a fixed ratio to the speeds of the element and tape, so that the number of reference voltage cycles per unit length of tape stays constant while the tracer speed may vary. The motion of tracer element 5, which is driven across drawing 1 by a friction wheel 18, the direction of heading and speed of which are under manual or automatic control, is resolved into two co-ordinate motions at right angles by mounting on a carriage 4 movable transversely on a further carriage 3 which is movable longitudinally on racks 12, 13. The motor driving friction wheel 18 also drives shaft 21, the motion of which is communicated through wheel 25 to the capstan 29 driving the tape 30. Tension in the tape is maintained by a torque motor driving take-up reel 32, and a braking generator mechanically connected to unwinding reel 31. The reference signal impressed on recording coil 33 is derived from sine wave potentiometer 36 driven in correspondence with the tape by gears 44, 45, while the X component control signal is generated by sine wave potentiometer 46 driven through differential 47, which has inputs from shaft 48 corresponding to tape speed and via gears 15, 50 and coupling 59 corresponding to X component of velocity. The Y component control signal is generated in sine wave potentiometer 51 driven through differential 52, which has inputs corresponding to tape speed from gear-box 24 and to Y component of velocity via gear 55. The X and Y signals are supplied to recording coils 34, 35 respectively. The tracing element 5 which is a transparent disc in the shape of the tool which is to execute the work, is guided round the drawing at a speed varying with the operator's ability to maintain it on the curve, but the number of voltage cycles in the recorded signals per unit length of tape is constant, so that when the tape is driven at constant speed during the playback operation, the tool may execute motions corresponding to those of the tracer element at optimum speed throughout the operation. The tool has appreciable inertia and at the start of the machining operation cannot instantaneously attain the speed corresponding to that of the recorded motion, and it is therefore necessary to modify the recording so that at the beginning of that record rate of change of phase between the control and reference voltages rises continuously from zero to the optimum working rate at a rate with which the tool driving motor can keep pace. This is effected by a skilled operator allowing progressively decreasing slip when the friction wheel first engages the drawing by restraining motion of gimbol 19, so obtaining a smooth rate of change of phase of X and Y voltages to the optimum value. Copies of X and Y voltage traces obtained in this way or by other methods may be grafted and matched on to the start of all records for use with the same tool. More accurate reproductions are obtained by using a large scale drawing which is cut up into sections which are placed successively on the board. Tracing is carried out normally until the trace leaves the section when clutches 58, 59 communicating motion of the co-ordinate carriages 4, 5 to counter 56, 57 are disengaged, the drawing section replaced by the next one, and carriages 4, 5 moved until the tracer coincides with the continuation of the trace from the earlier sheet, the clutches are re-engaged and tracing continued. The above process is repeated until the trace has been followed back to the starting point. Specification 671,136 is referred to.