Patent GB-874486-A (GB)
Title: Improvements in servo systems
Inventor: FEARNSIDE KENNETH
IPC: G05D1/00
Filed: 1958-07-25
Abstract: 874,486. Automatic control-systems for aircraft elevators. SMITH & SONS (ENGLAND) Ltd., S. July 23, 1959 [July 25, 1958], No. 24112/58. Class 38 (4). [Also in Group XXXIII] An automatic, control-system for an elevator of an aircraft wherein the elevator is divided into a number of sections each of which is normally controlled over one channel of the system by a signal common to all the channels has means whereby should one elevator section become slightly misaligned with the others the signal controlling it is modified according to the mean position of the other elevator sections and further means whereby should one section become greatly misaligned with the other sections-due to a failure of its control channelthe section is removed from the control of the common signal and is thereafter controlled in accordance with the positions of the other sections. The elevator of an aircraft is divided into four sections each of which is operated by an hydraulic pump 25 and actuator 26 and which is connected to a member 30 by a spring strut 29 or 29a, 29b, 29c each of which struts includes a switch 33 which is closed when the strut is stressed below a limiting value. When the switch 33 is closed relays 21, 24 are energized such that clamp 20 is free and clamp 23 is held. A signal, common to all four channels, is applied at 1 and fed to an amplifier 14 the output of which is applied to an electro-mechanical transducer 18 the output of which, since clamp 20 is free and clamp 23 held, controls the hydraulic pump 25 and actuator 26 by way of a differential 19. The rate of movement of the elevator section provides a rate signal by means of a tachogenerator 35 and a displacement signal is obtained by means of a second tachogenerator 36. These signals are combined and fed to the amplifier 14 together with the command signal 1. Displacement signals from the other three elevator sections are fed to a device 37 which derives the mean of these signals and should the first elevator section become misaligned with the other three sections-within a predetermined range-the signal 1 controlling the first section is modified by means of a motor 7 and a potentiometer 5 for datum errors and a motor 16 and a potentiometer 15 for gain errors. When the system is under automatic control as described above the position of the piston 27 of the actuator 26 is transmitted to the manual control member 31 by means of a differential 28 and the spring strut 29. Should the elevator section become greatly misaligned with the remainder, due, say, to a failure of its control channel, the spring strut will be stressed beyond the predetermined limit thus opening switch 33. Relays 21, 24 will then be de-energized such that clamp 23 is freed whilst clamp 20 will now be held. The hydraulic pump 25 and the actuator 26 will now be controlled in accordance with the position of the remaining three elevator sections by way of the spring strut 29, and differentials 28, 19. Closure of the switch 33 when the strut 29 resumes its normal condition does not re-energize relays 21, 24; these require to be re-set. Manual over-ride of the automatic control is obtained by applying force to the control member 31 to cause all the struts 29 to open their switches 33 when the elevator sections may then be controlled by way of member 30 the spring struts 29 and differentials 28, 19. Manual control of the elevator sections with automatic damping may be obtained by arranging that all the clamps 20, 23 are free. In a further embodiment the datum and gain controls in the four sections may be equalized by the use of a further force-responsive device between the spring struts 29 and the member 30, these devices providing the signals to be applied to the datum and gain circuits.