GB1372376A - Servo-control apparatus - Google Patents

Abstract

1372376 Servo-positioning apparatus; MOOG Inc 9 Dec 1971 [29 Jan 1971] 57151/71 Headings G3P and G3R Lever 38 operating a control surface of an aircraft is moved by three similar independent retroactive position control servosystems, Fig. 11; Figs. 11A, 11B (not shown), having no interconnecton between them, each having an equalizing feedback loop including unit 42 having an input/output characteristic, Fig. 15, with hysteresis to ensure load sharing by the actuators 31 (31a, 31b). Position control system. At summing junction 21, command signal 20 is combined with actual position feedback signal 41 derived from a linear differential transformer 40 connected to the output shaft 39 of actuator 31 to provide a normal position error signal 22, which in turn is combined at junction 23 with an equalization voltage 48, LVDT, Fig. 15, dirived from a linear differential transformer 46 coupled to output member 45 of equalizer 42, in dependence upon the differential pressure between fluid lines 43, 44. The resultant signal 24, via amplifier 25 controls the torque motor of an electro-hydraulic flow control valve 28 controlling piston 33 of actuator 31. Hydraulic equalizer 42, Fig. 12 Pistons 59 60 are biased apart by preloaded spring 61, and pressure differential between lines 43, 44 provides thrust on both pistons in the same sense, depending on the sign of pressure differential. Output shaft 76, provided with friction packing 91 between glands 92, 93 is provided with collars 82, 83, 84 around which fluid can pass freely, and such that, in the absence of pressure, collars 82, 84 engage surfaces 63, 85, collar 83 being equidistant between surfaces 67, 89, (whose spacing represents twice the lost motion of the equalizer), of the respective pistons. As pressure differential increases, in either sense, no motion takes place until spring preload is overcome B59, or B60 Fig. 15, whence one or other piston moves inwardly without movement of shaft 76, until collar 83 engages it B59-L59 B60-L60, followed by movement of the piston and output shaft 76, L59-P59 or L60-P60. Subsequent reduction of pressure differential causes no output shaft movement until collar 84, or 82 is engaged by the piston, P59-E59 or P60-F60, hence providing a hysteresis characteristic. Electric equalizer, Fig. 16 (not shown). Pressure transducer (95) provides an output voltage proportional to the pressure differential, which is fed to hysteresis circuit (96) including anti-parallel diode pair (101) and integrator (100) to output a parallelogram form hysteresis characteristic, which, after passage through threshold circuit (97) including anti-parallel diode pair (104) provides a hysteresis characteristic (e,#P) Fig. 16A (not shown) having substantially the form of Fig. 15. The output of equalizer 42 may be mechanically applied to servovalve 28, and it can be responsive to the actuator force, derived from a strain gauge in the load drive.