GB675116A - Improvements relating to remote position control systems - Google Patents

Abstract

675,116. Correspondence control. BRITISH THOMSON-HOUSTON CO., Ltd., STOKES, J. A., and LUDBROOK, L. C. Oct. 6, 1950. [Oct. 7, 1949] No. 25811/49. Class 40 (i). Overshooting and hunting due to a large error in positional correspondence in a motor driven remote position control system of the type described in Specification 576,117 are avoided by use of a relay operated by excessive velocity or acceleration of the controlled device whereby the response characteristic of the system is altered until positional correspondence is re-established. A controlled device 10 is driven into positional correspondence with a controlling device 11 by means of a D.C. motor 12 fed from a generator 13 whose field is supplied by the amplifier and demodulator 15 from the error voltage induced at device 11 by the selsyn system 14. A negative feed-back circuit comprising resistance 17 and capacitance 16 is connected to be responsive to the back E.M.F. of motor 12 (and hence the velocity of the controlled device), the armature drop I.R. being balanced out by a tapping on resistance 20 connected across the generator output terminals.. The D.C. feedback is applied via modulator 18 to modify the input to amplifier and demodulator 15 and will be proportioned to the rate of change of the back E.M.F. of motor 12, i.e. its acceleration. A relay 19 is connected in series with the resistance 17 such that at a given value of acceleration it will operate and close contacts 19a, thereby converting the "transient" negative feedback to "direct" negative feedback and preventing the motor 12 from actually attaining a velocity sufficient to cause overshoot and hunting. When the misalignment has been reduced to a small value, the relay 19 will "drop out" and restore normal circuit conditions. A resistance 23 may be connected across the capacitance 16 so that the relay will also operate if the velocity exceeds a certain limit. In order to avoid excessive acceleration lag when the circuit is functioning normally, a further resistance 22 and capacitance 21 may be inserted in the feedback line as shown by broken lines, and further contacts 19b on the relay provided to short this capacitance when the relay operates. Instead of using the back E.M.F. of motor 12 a tachometer generator driven from the motor 12 may supply the required voltage proportional to velocity.