Patent GB-834439-A (GB)
Title: Improvements relating to positional control systems
IPC: G05D3/12
Filed: 1956-10-05
Abstract: 834,439. Machine positioning devices. GENERAL ELECTRIC CO. Oct. 5, 1956 [Oct. 5, 1955], No. 30441/56. Class 40 (1). [Also in Groups XXXV and XXXVII] In a positioning control system an error voltage is derived from the relative positioning of a position director on one hand and a position indicator on the other. A bias is applied to this error voltage and the resultant signal is used to control a motor used to bring the indicator into alignment with the director. Due to the bias voltage a false position of correspondence is established. As the bias always has the same magnitude and polarity this false position is always a displacement of a given magnitude and in a given sense from the true position of correspondence. When the false position has been reached the bias is slowly removed and the motor slowly drives the position director into a position of true correspondence. Hence effects due to backlash may be eliminated. The apparatus as shown in Fig. 1 comprises selsyn devices 2 and 4 which act as position directors and position indicators respectively; an error detector 5 which gives a D.C. output at 28b indicative of both magnitude and phase of any error signal from the coil 4a; a motor control circuit 6 which drives a reversible D.C. motor in accordance with the error signal fed in at 28c; a dropper resistance 42 and a condenser 45; a divider network 46, 47 and 75 for supplying a bias to 42a by means of diode 79 when the terminals 44c are closed; and a double triode 71 whose input is the error signal at 42 and whose output controls another double triode 72 the output of which controls a relay 43 in such a manner that the relay is energized whenever an error signal occurs at 42a. A triode 60 controls a relay 61 to operate in accordance with the state of charge of condenser 45. An interlocking relay circuit is also provided for controlling the apparatus. In operation the apparatus may be used to control the positioning of a machine tool for example a Wiedermann punch to which the position indicator is connected and the position of the director may be determined by feeding in a punched card to a suitable feed and read device. The card feed and read cycle begins simultaneously with the machine operating cycle. The former finishes first and leaves the position director set. On completion of this cycle a relay switch closes the circuit which energizes the selsyn device and causes an error signal to appear eventually at 42a which in turn causes the energization of relay 43. On completion of the machine operating cycle the energizing circuit to the motor 3 is completed and the bias mentioned above is applied to 42a by closing switch 44c. The motor then drives the machine until the indicator 4 is in its false position of correspondence. When this happens the error signal at 42a momentarily disappears causing relay 43 to fall out which in turn causes relay 44 to fall out and hence removes the bias signal. The bias therefore slowly leaks away as the condenser 45 slowly discharges through resistors 46 and 47. Hence a small error signal again appears at 42a causing relay 43 to be energized and motor 3 to drive the machine until the indicator 4 takes up a position of true correspondence. Relay 43 then falls out. Condenser 45 continues to charge via 46 and 47 and eventually causes valve 60 to conduct hence exciting relay 61. This indirectly through other relay initiates the card feed and read cycle and also the machine operating cycle and the whole procedure is then repeated. A full account of the operation of the relays is given in the Specification. Specification 801,472 is referred to.