GB821413A - Improvements in or relating to the control of electrically-driven rectilinear actuators - Google Patents

Abstract

821,413. Control of D.C. motors; controllers. HOOVER, V. A. Jan. 31, 1956, No. 5114/58. Divided out of 821,411. Class 38 (3). An actuator for controlling the wing-flaps of an aircraft, which are adapted to be stopped in a half-extended position as well as in extended and retracted positions, comprises a rotatable nut 222 for driving a non-rotatable screw 223. A motor 226 is coupled to the nut through magnetic clutch and brake unit 227 and reduction gearing 228. A load-limiting switch 232 is adapted to be short-circuited by switch 233 so as to render it effective only when the screw has approached the inner limit of its travel. A ring cam 234 moves with the screw 223 and has an adjustable collar 236. An " intermediate " limit switch 240 and an " extend " light switch 241 are operated by the cam-parts 236 and 237 respectively. The motor 226 is of the split series field type, Fig. 2 (not shown), with manual switches for driving the motor to a selected one of its three stopping-positions. Closure of a first selector switch energizes a relay for exciting one of the motor field windings and driving the screw to an extended position. Operation of switch 241 de-energizes the relay and so disconnects the motor and the clutchcoil as well as applying the brake. Movement to the intermediate and retracted positions is similarly effected, except that the motor is arrested in the retracted position by means of the load-responsive switch 232. Actuator units may be mechanically cross-connected so that both are driven by the motor of one actuator in the event of failure of the other motor. Each actuator has an auxiliary brake-releasing coil adapted to be energized through the circuit of the other actuator, and resistances are provided to prevent substantial current-flow through the field windings of the disabled motor. An actuator for an aircraft canopy, Fig. 5, comprises means for limiting the thrust exerted by screw 336 during both extension and retraction, a nut 332 being supported for limited axial movement and centred between opposed sets of springs which yield when a predetermined load has been exceeded. The resulting movement of nut 332 causes axial movement of the outer race of bearing 333, and this motion is utilized to open limit switches 366, 367, by means of arm 370 and slidable plunger 375. Because the intermediate position may be approached from either the extended or retracted positions, four limit switches 380-383 are provided and are operated by plungers 385-388. A ring cam 389 is adapted to engage followers 390, 391, so as to operate shaft 394 and cams 400-402, or shaft 395 and cam 403, respectively.