Patent GB-1349072-A (GB)
Title: Control systems
IPC: G05D1/00
Filed: 1971-04-26
Abstract: 1349072 Electric correspondence control SPERRY RAND CORP 26 April 1971 [27 April 1970] 11314/71 Heading G1N A control system for positioning an element 14, which element is movable in either of two opposite directions, in response to an analogue position-error signal (from source 1) of which the algebraic magnitude is representative of the magnitude and the direction of a desired positional change of the movable element, the system including a stepping motor 12 energizable to drive the element selectively in either of the two opposite directions, and means 4-8 responsive to the sense of the algebraic difference of the position-error signal and an analogue feedback signal (from pulse to analogue memory element 11) to provide (from threshold device 5) a first enabling signal if the sense is positive and corresponds to a demand for movement of the element in one of the opposite directions and a second enabling signal (from threshold device 6) if the sense is negative and corresponds to a demand for movement of the element in the other of the opposite directions, a pulse generator 9 responsive to the first or second enabling signal to provide (from gate 7) first pulses to energize the stepping motor to drive the element in steps in one of the opposite directions and second pulses (from gate 8) to energize the stepping motor to drive the element in steps in the other of the opposite directions, and feedback means (e.g. pulse to analogue memory element 11) responsive to the first and second pulses to derive the analogue feedback signal of which the algebraic magnitude is representative of the magnitude and direction of the accumulated positional change demanded of the element by the first pulses and the second pulses. In an alternative embodiment, Fig.2, the feedback means is a pulser 17' responsive to the movement of the motor 12 to generate third pulses corresponding to the steps, and a pulse to analogue memory 16 which is supplied with the third pulses to derive the analogue feedback signal of which the algebraic magnitude is representative of the magnitude and direction of the accumulated positional change of the element. The feedback signal is fed to the summing junction 4 for combination with the analogue position-error signal and fed to a comparator 15 with a signal from pulse to analogue memory 11; if the signals from memories 11 and 16 are identical, that is if the actual and demanded positions of the element are identical, an output signal is applied to AND gate 20 to which another input signal comes from gate 7 or 8 via monitor 19 and from which an output signal is fed to enable a gate 7 or 8. If the signals to the comparator 15 are not identical an output signal is fed to OR gate 18 which acts via clamp 21 to lock the stepping motor and via circuit 22 associated with the pulse generator 9 of a second and identical channel to double the speed of the stepping motor 23 of that channel and the motors 12 and 23 are intercoupled through a differential gear train to provide a constant torque output upon failure of one of the channels. If a failure should occur in device 5 or 6 or gate 7 or 8 so that pulses are emitted simultaneously to the sequencer 10 and the memory 11 then pulses are present simultaneously at both inputs to the monitor 19 which provides a pulse to the OR gate 18 which locks the motor. In the embodiment of Fig.3 (not shown) a three-channel system uses a multiplexing unit. A trim tab 36 is driven by a similar system to that of Fig. 1 utilizing input signals from an integrator 3 and representing long term aircraft attitude errors.