GB1347297A - Multiplex actuator - Google Patents

Abstract

1347297 Controlling aircraft E-SYSTEMS Inc 19 April 1971 [2 Feb 1970] 20881/71 Heading B7G [Also in Divisions G1 and H2] A redundant channel, velocity summing, multiplex actuator for adjusting the position of a control surface 56 of an aircraft comprises four servomotors, Fig. 2 (not shown), each having a respective control amplifier receiving the same control signal 11 ... 14, which may be derived from the pilot's control stick or the autopilot, stability or navigation controls, two sets of differential gearing coupling respective pairs of motor shafts to a third differential gear set whose rotary motion is converted to linear movement of a rod 16, a dual tandem servovalve 18 responsive to movement of the rod 16 to vary the fluid pressure flow signals to a dual tandem power ram 20 connected by members 52, 54 to the surface 56, and a linear voltage differential transformer 57 responsive to movement of the piston-rod 52 to generate separate but equal position feedback signals 59 ... 62 which are applied to the control amplifiers to balance the signals 11 ... 14. Fig. 4 shows a pair of the servomotors which are combined with respective tachometer and brake members to form units 150, 160 mounted on a housing 152. The motor shafts are coupled to a differential 158 by gears 154, 156, 164, 166, the differential 158 being coupled to a differential 176 by gears 172, 174. Another gear 178 of the differential 176 is coupled to a third differential (not shown) receiving the drives from units (not shown) similar to the units 150, 160. The shaft 182 of the differential 176 rotates with a speed equal to the velocity sum of the four units and engages the lead-screw 186 of a ball-screw assembly, whose ball nut 192 is restrained from rotation by retaining pins 194, 196 and is fixed to an extension shaft 198 terminating in a rod end 200 coupled to the rod 16 in Fig. 1. The rod end 200 is moved to a neutral position, in the event of failure of the actuator, by means of a centring assembly including a carriage 202 fastened to extension 198 by a nut 204, the carriage 202 moving with the nut 192 during normal operation. Upon actuator failure a spring 206, maintained in a housing 208 by spring guides 210, 212, forces the nut 192 to a centre position. To allow spring 206 to act on the actuator output, at least one brake must be released to allow back-driving the mechanism. Connectors 214, 216 transmit the control, feedback and velocity signals in the respective motor, amplifier and tachometer circuits. Operation of an arrangement, Fig. 3 (not shown), similar to Fig. 4, is discussed for failure of one, two or three of the servomotors, the or each failed motor preferably being stopped by its brake to prevent it being dragged by the remaining operative motor of the affected pair. Another similar arrangement, Fig. 5 (not shown) is discussed with respect to gear ratios, velocities and variation of the number of servomotors and gears. Gearing other than differential may be used to couple the servomotors which may be odd instead of even in number.