Patent GB-546081-A (GB)
Title: Improvements in control systems
IPC: G05D1/02
Filed: 1940-11-25
Abstract: 546,081. Fluid-pressure servomotor-control systems. FOTHERGILL, H. Nov. 25, 1940, No. 16898. [Class 135] [Also in Group XXXV] Consists in apparatus for maintaining an instrument-supporting or other frame in a predetermined position, wherein the frame is provided with a floating " chopperblock " from which the cut pressure operates a diaphragm &c. which restores the block to its normal position in relation to the chopper or interceptor, such diaphragm &c. also actuating a valve, switch, or other means controlling a servomotor effecting movement of the frame. A frame 1, Fig. 1, is to be moved in accordance with movements of a light member 2 which may be the gimbal ring of a gyroscope or other delicate device. The " chopper block " consists of the interceptor 3 carried by the member and a block 4 carried on a spindle 5 which, under the action of a spring 6 holds the valve 7 of a servomotor against a diaphragm 8. Low pressure air from a pipe 9 crosses the block 4 and enters a pipe 10 leading to the underside of a diaphragm 8. The casing 11 of the valve 7 has a port 13 for entry of pressure air and ports 12, 14 leading to a motor 15 connected to the frame 1. With the interceptor stationary, the pressure on the diaphragm just balances the spring 6 and about half the volume of air from pipe 9 is intercepted. If now the frame 1 moves downwards, less air is intercepted and the pressure on diaphragm 8 is increased thus lifting valve 7 to admit air to port 12 and cause the piston 16 and frame 1 to rise, at the same time bringing the block 4 to its former position relative to the interceptor 3. The pressure on the diaphragm is then reduced and the valve 7 will return to normal central position. With a suitable strength of the spring 6, oscillation of the spindle 5 and valve 7 can be obtained resulting in a more sensitive control. Air pressure may be applied to the upper surface of the diaphragm. The valve casing 11 is adjustably mounted on a part 17 of the frame 1 by a screwed spindle 18 and locking screws 19. Fig. 2 shows the application of this device for stabilizing the position of an instrument 20 relatively to the plane of spin of a gyro 26. The instrument is attached to an inner gimbal frame 21 pivoted at 22 in an outer frame 23 in turn pivoted at 24 in the frame 25. The gyro rotor in inner and outer gimbals 27, 28 is supported by an extension 29 from the inner frame 21. This extension also supports two valve casings 11, 11a controlling the air supply from a pipe 30 to motors 15, 15a supported respectively on the main frame 25 and from the gimbal 23. The " chopper blocks for the two directions of tilt are shown at 4 and 4a. To stabilize the instrument in azimuth, the gyro, servomotor and control gear are mounted on the inner gimbal frame 21. In Fig. 3, the servomotor 15 of Fig. 1 is replaced by a reversible electric motor 31 having two separate oppositely wound fields connected to contacts 32, 33 which alternately touch central contact 34 carried by the spindle 5, the shaft of the motor being connected to the frame 1 by screw mechanism 35. By suitably proportioning the spring 6, diaphragm 8 and the air pressure, the spindle 5 can be made to oscillate, and the motor kept in a state of dither. Alternatively, the motor 31 can be made to hunt the frame 1. In a further modification, Fig. 4, the diaphragm 8 instead of being connected directly to the block 4, is arranged to control the latter by means of a reversible motor 31 through worm and screw gearing 36, 35 which moves the spindle 5a. The operation of the motor is controlled by contacts 32 ... 34 as described with reference to Fig. 3. The motor can be geared to any device the position of which relative to the member 2 is to be controlled. Reference has been directed by the Comptroller to Specification 572,631.