Patent GB-902821-A (GB)
Title: Improvements in or relating to the control of individual movements of mechanical devices
IPC: G05B19/425
Filed: 1958-11-19
Abstract: 902,821. Programmed electric control systems. MASCHINENFABRIK HEID A.G. Nov. 19, 1958 [Nov. 20, 1957], No. 37170/58. Class 38 (6). [Also in Group XXXV] The rotation of a shaft is recorded on a magnetic tape as a series of incremental pulses of alternating current, two frequencies being used alternately for successive increments of movement in one direction, and two different frequencies for movements in the opposite direction, so that on play-back the frequency appropriate to the position of the shaft and the particular frequency from the record can be compared and the shaft and record kept in synchronizm by varying the speed of one or the other. If the two fall seriously out of step the system is shut down. The object to be controlled (not shown) is driven by a motor (not shown) through reversing magnetic clutches 15, 20 controlled by valves 10, 11 and 16, 17 through relays 13, 14 and 18, 19 respectively. Movement of the object also rotates a switch arm 6 over contact segments 1<SP>1</SP>, 1<SP>11</SP>, 2<SP>1</SP> and 2<SP>11</SP>. Recording.-The grid circuits of valves 1 ... 4 are disconnected from the output circuit of the tape recorder 5 by switch 7. The valves 1 ... 4 4 then form oscillators and supply the selected one of the four different frequency control signals to the input of the tape recorder 5 when relay contacts 13<SP>11</SP>, 14<SP>11</SP>, 18<SP>11</SP> or 19<SP>11</SP> are closed. According to whether switch 7<SP>1</SP> has been placed manually in its upper or lower position (depending upon the direction of movement to be recorded) and assuming switch 12 to be closed, the rotating switch arm 6 applies negative bias in turn to either valves 10, 11 or valves 16, 17 to de-energize their relays in turn, so that pulses of the appropriate frequency are recorded. Playback.-The output of the tape recorder 5 is connected to the valves 1 ... 4 by switch 7, the output circuit of the recorder being of such a low impedance that the valve circuits do not oscillate but act as tuned amplifiers to selectively control the relays 13, 14 or 18, 19 as appropriate and so cause the unspecified motor to move the unspecified object through either clutch 15 or clutch 20. The selected relay also closes contact 13<SP>111</SP>, 14<SP>111</SP>, 18<SP>111</SP>, or 19<SP>111</SP> as appropriate so that as the object moves and the contact 6 moves round the segments 1<SP>1</SP>, 1<SP>11</SP>, 2<SP>1</SP>, 2<SP>11</SP>, polarized relays 22, 23 are connected in turn to a battery 21 (the switch 7<SP>1</SP> has been manually moved to its central position), but the circuit is normally interrupted by the open contacts 13<SP>111</SP>, 14<SP>111</SP>, 18<SP>111</SP>, 19<SP>111</SP>. If, however, the record lags the contact 6 then one of the contacts, e.g. 13<SP>111</SP> will be closed when the contact 6 reaches segment 2<SP>11</SP> and relay 22 will be energized to energize a relay 25, which opens contact 25<SP>1</SP> to disengage the clutch 15 or 20 and so slow down the movement of the object. Similarly, a record advance causes relay 23 to be energized and this controls a braking relay 24 to slow down the recorder. In addition, two stepping switches are provided, Figs. 2 and 3 (not shown), which detect phase errors exceeding one step and shut down the system. Among the many variations mentioned are (a) the use of perforated tapes or photographic tapes instead of magnetic, (b) the use of multi- or single-track recording, (c) the use of different amplitude recorded signals instead of different frequency, (d) the use of capacitative or inductive switches instead of the rotor arm 6, (e) slowing the tape for a prolonged period until it actually lags behind the controlled object, (f) providing more than 4 segments for the contact arm 6, (g) making the arm 6 bridge the segments and using the resulting mixed frequencies as additional control steps, (h) simultaneously changing the speed of both record and controlled object to bring them into step.