Patent GB-827207-A (GB)
Title: Automatic force balance device for use in computing, controlling and regulating systems
Inventor: CLARKE CYRIL WILLIAM
IPC: G06G3/04
Filed: 1956-09-19
Abstract: 827,207. Fluid-pressure servomotor-control systems. FOXBORO-YOXALL Ltd. Sept. 16, 1957 [Sept. 19, 1956], No. 28703/56. Class 135. An automatic force balance device comprises a first lever formed with a curved face and mounted to rock on a fulcrum, a second lever carrying the said fulcrum and pivoted about an axis on the concave side of the face, means for applying two variable forces to the first lever to exert opposed turning moments thereon and for applying a variable force to control the position of the second lever, and negative feedback means, sensitive to movements of the first lever about its fulcrum, for so determining one of the said three forces as to restore equilibrium of the system after the equilibrium has been disturbed by variation of one or both of the other forces, the fulcrum or the point of application of one of the said two forces being arranged to travel along the curved face of the first lever when the second lever turns about its axis. In the first example, Fig. 1, the two variable forces are fed as fluid pressures to the bellows 7 and 8 respectively to rock the lever 1 about its line of contact with a roller 12 carried by a double-armed lever 9 connected by links 13 to a plate 14 forming the movable base of a third bellows 16. The lever 1 carries a baffle 19 which co-operates with a nozzle 18 the back pressure of which is fed to the bellows 16 via a relay 21 and to a gauge 25 which indicates the ratio of the two forces. If one of the two variable forces is fed to either of bellows 7 or 8 and the other force to the bellows 16, the nozzle back pressure fed to the third bellows 8 or 7 via the relay 21 and to the gauge 25 is indicative of the product of the two forces. In another example, Fig. 3, the bellows 7 and 8 act on the underside of the lever 1 which determines the position of the baffle 19. The nozzle backpressure is fed via the relay 21 to the bellows 16 which is connected to the lever 9 by a link 51, the lever 9 being connected by linkage to a ratio indicating pointer 52. If a pneumaticallyoperated receiving indicator or controller is to be operated in dependence of the position of the lever 9 then the lever 9 may position a second baffle with respect to a second nozzle the back pressure of which is fed via a relay to the receiver and to a stabilizing bellows of the second baffle. Instead of acting against springs the bellows 7 and 8 may be opposed by evacuated bellows and so reflect absolute pressures. A linearizing cam may be located in the transmission from the lever 9 to the second baffle. In another example, Fig. 6, one of the two variable forces is applied to the bellows 7 and the other to the bellows 8 which acts directly on the lever 1. The bellows 7 and 8 are opposed by evacuated bellows 69 and 67 respectively. The bellows 7 positions a baffle 90 with respect to the nozzle 91 the back pressure of which is transmitted via a relay 93 to a bellows 92 acting on the lever 9 connected by a link 98 to the baffle 90. The lever 1 locates the baffle 19 and the back pressure of the associated nozzle 18, indicative of the product of the two variable forces, is transmitted via the relay 21 to an indicator or recorder 68 and to the bellows 16 which acts on the lever 1. A linearizing cam may be located between the link 98 and the baffle 90. In still another example, Fig. 8, the lever 1 is fixed to the pivoted lever 9 at a pivot 104. The bellows 7 acts directly on the lever 1 but the bellows 8 acts on a pivoted lever 108 carrying a roller 106 which rides the curved surface of the lever 1. The lever 108 carries the baffle 19 and the back pressure of the associated nozzle 18 is transmitted via a relay 21 to the bellows 16 which acts on an extension 111 of the lever 9. The extension 111 is connected by a link 83 to a baffle 80 and the back pressure of the associated nozzle 79, indicative of the ratio of the two forces, is transmitted to a receiver (not shown) and to a stabilizing bellows 85 of the baffle 80. If the product of the two forces is desired the locations of the bellows 8 and 16 are reversed and the appropriate changes in the pneumatic circuit is made, Fig. 9 (not shown). It is stated that the forces may be produced by electromagnetic means. Specification 670,427 is referred to.