Patent GB-881722-A (GB)
Title: Hydraulic servo systems
Inventor: SCHEIB RICHARD
IPC: F15B21/00
Filed: 1958-02-28
Abstract: 881,722. Electric correspondence control systems. SPERRY RAND CORPORATION. Feb. 28, 1958, No. 6530/58. Class 40 (1). [Also in Group XXIX] in an hydraulic servomotor system for the actuation of an element subject to variable external loads means is provided for varying the output pressure of the hydraulic pump of the system in response to load variations to eliminate the effects of such variations on the response of the controlled element to the controlling member. The invention is described as applied to a system for stabilizing a ship-borne radar aerial 23 the base 10 of which is is movable in a gimbal mounting about pitch and roll axes by hydraulic motors 24, 29. The motors 24, 29 have similar control circuits and only that for the motor 24 is shown. A gyro-vertical 39 is geared to a coarse synchro generator 43 and to a fine synchro generator 44, these generators being connected to corresponding synchro control transformers 45, 46 geared to the mounting of the base 10 so that any positional control error results in a signal being sent through an automatic coarse and fine selector 47 to an amplifier 49 and thence to an amplifier 52 which controls a motor 53 operating a control valve 34 through gearing 54 and a screw and nut mechanism 55. The valve 34 controls supply of pressure fluid from a pump 70 to the motor 24. A generator 56 driven by the motor 53 provides a feedback signal for the amplifier 49 whereby the angular velocity of the motor 53 is made proportional to the error signal. This arrangement provides that the instantaneous acceleration of the base 10 is proportional to the angular deviation between the base 10 and the gyro-vertical 39. An error rate signal is also fed to the amplifier 49, being derived from a differential synchro generator 57 which is connected to a synchro control transformer 59 the output of which is fed to an amplifier 60 controlling the motor 61 which drives an A.C. tachometer 63 the output of which is fed to the amplifier 49. A generator 62 driven by the motor 61 provides a feedback to the amplifier 60. For further reducing errors in the system a D.C. tachometer 64 driven from the shaft of the generator 44 feeds a signal to a differentiating circuit 66 which provides an error signal substantially proportional to gyrovertical acceleration. This signal is then modulated by a balanced phased-sensitive modulator 67 and applied to the amplifier 49. The delivery of the pump 70 is controlled by a servopiston 76 which tilts the housing of the pump in response to variations in the delivery pressure in a conduit 32, a conduit 74 leading to a spring- loaded valve 80 for this purpose. To detect variations of external load applied to the aerial 23 and to make compensatory adjustment to the delivery pressure of the pump 70 according as to whether the external loads are assisting or resisting motion of the aerial conduits 94, 95 leading from opposite ends of the motor 24 are connected through a valve 96 to a piston 85 which adjusts the loading of the spring 82 acting on the control valve 80 of the servopiston 76. The valve 96 is moved in one direction or the other by solenoids 97, 98 energized from a differential relay 102 connected through an amplifier 99 to the generator 64 whereby the connections 94, 95 to the two sides of the piston 85 are reversed each time the direction of pitching of the ship is reversed. Specifications 604,349 and 636,679 are referred to.