Patent GB-826964-A (GB)
Title: Improvements in or relating to apparatus for controlling the movement of a body
Inventor: HANNA CLINTON RICHARDS
IPC: G05D3/12
Filed: 1956-03-29
Abstract: 826,964. Fluid-pressure servomotor-control systems. WESTINGHOUSE ELECTRIC CORPORATION. March 29, 1956, No. 9824/56. Class 135. [Also in Group XXXV] Apparatus for controlling the movement of a body, e.g. the control surface of an aircraft comprises an hydraulic actuator A with a movable part (the cylinder 6) connected to the body, valve means MV for controlling the fluid pressure in the hydraulic actuator, automatic control means for controlling the valve means and manually operated link means 20, 26, 27 coupled to the movable part 6 and operable to control the valve means directly independently of the automatic control means during an initial free movement of the link means and thereafter to effect direct operation of the movable part. In Fig. 1, a rate of turn gyroscope G controls an aircraft about its yaw axis. The actuator A comprises a piston pivoted to a fixed part 2 of the aircraft and slidable relative to a movable cylinder 6 connected to a rudder R pivoted at 5. The pilot's control operates through a link 27 and a bell-crank 26 on a rod 20 having a resilient lost-motion connection with the cylinder 6. This connection comprises a pre-loaded spring 25 confined between spring mounts 22 engaging pins 23, 24 on the rod 20 and also the ends of a frame 21 on the cylinder 6. A prod 19 on the rod 20 is adapted to engage one or the other of two groups of conducting spring fingers 17, 18 and thereby progressively shunt tapped portions of one or other of resistors 15, 16. The resistors 15, 16 form with coils C 3 , C 4  a Wheatstone bridge supplied from the direct current conductors L 1 , L 2 . The coils C 3 , C 4  form part of the automatic control means for actuating the valve means MV and are associated with two further coils C 1 , C 2  which are selectively energized from the conductors L 1 , L 2  by the engagement of a movable contact 11 with one or other of the stationary contacts 12, 13. The contact 11 is rigid with the gimbal 31 of the rate gyroscope G. The latter is biased by an electromagnetic system comprising linear pull magnets 35, 36 as described in Specification 698,032, [Group XXXV]. The magnet 35 comprises an armature 39 between coils 37, 38 of a Wheatstone bridge of which the other arms are formed by a potentiometer 42. Any unbalance in this bridge due to the movement of the armature 39 energizes one or other of the field windings PM1, PM2 of a pilot motor PM depending on which of the contacts 12, 13 is engaged by the movable contact 11. The windings PM1, PM2 are in series with the armature of the motor PM across the conductors L 1 , L 2 . The motor PM when energized operates through low gearing RG on the movable contact of a potentiometer 49 which forms with the coils 45, 46 of the magnet 36 a further Wheatstone bridge. Variations in the rate of yaw, other than transient ones, act through the motor PM with time delay to unbalance the last-mentioned bridge and apply a degree of self-bias to the gyroscope. The valve means MV, Fig. 3, has a high-pressure connection 59, a low-pressure connection 64, and connections 60, 61 leading through passages 7, 8 to opposite sides of the actuator A. The two latter connections are differentially controlled by an open-centre valve comprising shuttle lift closure members 53, 54 operating in valve chambers 51, 52 and mounted on a common spindle for actuation of pistons 65, 66. These pistons are under the control of leak-off valve 71, 72 at the end passages 69, 70, communicating with passages leading to the connection 64 through restricted orifices 77, 78. The valves 71, 72 are operated differentially by an armature pivoted at 82 on the centre leg of a three-legged magnetic core. The coils C 1 , C 3  and C 2 , C 4  are arranged on the outer legs 83, 84 of this core. " Damping " valves 9, 10 of the form shown in Fig. 2 are arranged in the passages 7, 8. These allow free flow in one direction, i.e. from the connection 86 to the connection 85 due to the check valve 87 raised from its seat 89 against a light spring 88. Large flows in the opposite direction due for instance to buffeting of the control surface are damped out bv a fixed orifice 92 and a variable orifice 91. The pressure drop across the orifice 92 is proportional to the square of the rate of flow through it and that across the orifice 91 to two-thirds power of the rate of flow through it. The orifices 91, 92 are therefore designed so that the effective pressure drop across the two is linearly proportional to the aggregate flowthrough them. The craft is normally maintained on a fixed course with the manual control centred by the spring 25. On the occurrence of a yaw velocity, the rate gyroscope acts on the valve means MV through one or other of the coils C 1 , C 2  to readjust the rudder until the yaw velocity disappears. A turn initiated by the pilot causes movement of the rod 20 against the centring spring 25 so that the coils C 3 , C 4  are differentially excited and the valve means MV causes the rudder to be adjusted in the appropriate direction. If the pilot wishes to add his control to that of the gyroscope, he must first overpower the spring 25 the force of which gives him a sense of feel. An additional resistor may be arranged at 95 in the circuit to modify the sense of feel at high air speeds. In the case of either electric or hydraulic power failure the rod 20 displaces the movable part of the actuator directly, such displacement, being permitted by the opencentre valve. The self-biased rate gyroscope may be replaced by the turn rate gyroscope of an automatic pilot or by the bank and pitch rate gyroscopes in the case of the ailerons and elevators respectively.