GB980133A - Improvements relating to servo systems - Google Patents

Abstract

980,133. Automatic control. FERRANTI Ltd. April 11,1963 [April 17,1962], No. 14804/62. Heading G3R. In a servo-system, two servomotors mechanically coupled in series are. so arranged that when either motor reaches a limiting position in either direction, operation of a switch biases the position of the other motor so as to prevent that motor from taking up a limiting position. In Fig. 1 identical electrical control signals, e.g. in-an aircraft autostabilizer, are applied through amplifiers 9, 8 and 11, 10 to position hydraulic servomotors 1 and 4 which are mechanically coupled in series to actuate an aircraft control surface. Follow-up signals are fed back to amplifiers 9 and 11 from potentiometers 31 and 32 the sliders of which are adjusted by cups 23 and 24 moving with pistons 2 and 4 of servomotors 1 and 4. If, due to a fault, one servomotor piston is moved to a limiting position the other servomotor would move to its opposite limiting position in an attempt to compensate. This is prevented by cups 23, 24 which actuate limit switches 12-15 so that bias signals from sources 25, 28 are applied to amplifiers 9,11 of such polarity that the servomotor which is working properly is moved to a central position. At the same time further limit switches double the gain of the system controlling the effective servomotor so that autostablization is maintained by this servomotor. The error due to the faulty servomotor may either be taken up by the pilot moving his control or, as in a modification applied to an automatic pilot, the error may be eliminated automatically by a further auxiliary servomotor, having a slower response, controlled by additional limit switches. This auxiliary servomotor is automatically maintained in a central position during normal operation. Fault indicators may be provided.