Patent GB-610029-A (GB)
Title: Improvements in control systems of the correspondence kind for movable members
IPC: G05D3/14
Filed: 1945-04-25
Abstract: 610,029. Electric control systems. BELSEY, F. H., BROADBENT, D. T., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. April 25, 1945, No. 10457. [Class 40 (i)] [Also in Group XXXV] In a system for maintaining positional correspondence between a control member and a controlled member, control of motive equipment for the controlled member is influenced by backlash or resilience in the drive between the motive equipment and the controlled member, whereby there is less stiffness of control for movement of the motive equipment away from the position corresponding with the required position of the controlled member than for the movement of the motive equipment and controlled member together away from such a position. Fig. 1 shows a modification of the system described in Specification 592,208 for automatically maintaining a movable body 2, driven through reduction gearing 25 by a D.C. motor 3, in positional correspondence with the setting of a hand-wheel 1, a transmitter selsyn 13, the rotor of which is supplied with A.C. and driven by the hand-wheel is interconnected with a reset selsyn 16 the rotor of which is driven by the motor. and suppresses a thermionic valve amplifier 8, an A.C. voltage, the amplitude and sense of which is dependent on the magnitude and sense of any misalignment between motor and handwheel. Amplifier 8 controls the field excitation of a metadyne generator 6 supplying the motor which operates until the misalignment is corrected. The modification is the introduction of an additional reset selsyn 26, the rotor of which is driven by the movable body and supplies an A.C. voltage, the amplitude and sense of which is dependent on the magnitude and sense of misalignment between the movable member and the hand-wheel. This voltage is combined with the voltage from reset selsyn 16 to constitute the input to amplifier 8. The two voltages are normally additive during correction, but under certain conditions, due to backlash they oppose each other and reduce motor torque. This reduction permits a greater sensitivity or stiffness of control to be employed over the major portion of the correcting period without instability due to backlash. Potentiometers 35 and 36 controlling the ratio of the voltages from selsyns 16 and 26 are preset for optimum conditions and may be ganged so that, for a given misalignment, the voltage ratio may be adjusted without altering the total voltage input to amplifier 8. As in Specification 592,208, a further selsyn system may be provided to give coarse control and/or amplifier 8 may introduce a first derivative component of control. The following alternative modifications are described : (a) The reset selsyn driven by the movable member is connected in cascade between the transmitter selsyn and the reset selsyn driven by the motor. The output of the latter only, is then applied to the amplifier but it contains components respectively dependent on the misalignment of the motor and movable member relative to the hand-wheel. The ratio of these components is determined by the gear ratios chosen for the drives to the selsyn units; (b) In a system for the automatic levelling of a platform about a single axis on a ship the transmitter selsyn is mounted on the platform with a gyro vertical so that its rotor is adjusted by the gyro and its stator moves with the platform to provide reset. Two other selsyn units are mounted on the deck and transmitter selsyn and its amplifier, one driven by levelling motor and the other by the platform. In the absence of backlash the effects of these two additional selsyns cancel but as a result of backlash a component of control is added in the desired sense. Alternatively, the gyro may be mounted on the deck; (c) as an alternative to the cascade connection in (b) above, the two additional selsyns driven by the motor and the platform respectively are arranged to produce a voltage dependent on backlash which is applied through an adjustable potentiometer as input to the amplifier in combination with a voltage obtained from a selsyn or other inductive unit responsive to movement between the platform or motor and a gyro vertical on the deck or platform.