Patent GB-638179-A (GB)
Title: Improvements in or relating to electric integrating or control apparatus
Inventor: COOPER GEORGE RONALD
IPC: G05B5/01
Filed: 1947-09-06
Abstract: 638,179. Automatic speed control systems. MINISTER OF SUPPLY. Sept. 6, 1947, No. 24590. [Class 38 (iv)] [Also in Group XXXVIII] In apparatus for controlling a dynamo electric machine to run at a speed corresponding to a direct signal voltage, or to position a controlled member in accordance with such a signal, the control voltage and a feedback voltage dependent on the machine speed and/or the position of the controlled member are applied to a comparison circuit which is intermittently switched to produce a square wave dependent in phase and amplitude on the polarity and magnitude of the difference between the control and feedback voltages. The square wave is applied to the input of an A.C. amplifier, the output of which is switched synchronously with the input to apply unidirectional half waves, corresponding as above to the difference between control and feedback voltages to drive the dynamo-electric machine. In Fig. 1 the control voltage is applied to terminal 16 connected through the resistances 18, 19 to fixed contact 21 of one section of a vibrator, the opposite contact of which is earthed. The armature voltage depending on the speed of the controlled D.C. machine 13 is also connected to contact 21 through resistances 23, 24, and the resistance chains are earthed through condensers 25, 26 to reduce hunting. The square wave developed by moving contact 20, depends in amplitude and phase on the magnitude and polarity of the difference between the control voltage and the feedback voltage, and is fed to A.C. amplifier 11, the output of which is connected to fixed contact 32 of a second vibrator section synchronous with the first, having fixed contact 31 blank and moving contact 30 connected to drive the controlled machine 13 with unidirectional half waves depending similarly on the difference voltage, so that the speed of the machine is determined by the control voltage. In Fig. 2 (not shown), the control voltage is connected to vibrator contact 21, the feedback voltage to contact 22, the amplifier output to vibrator contact 31, and contact 32 is blank, so that the square wave is produced by the alternate application of control voltage and feedback voltage to the amplifier. In Fig. 3, an input potentiometer is battery energized and centre tapped to earth, and its slider 41 is operated by a controlling member (not shown) to produce a control voltage which is applied through resistance 61 to vibrator contact 21 together with a positional feedback voltage applied through resistance 62 from a similar output potentiometer whose slider 51 is driven with the controlled member (not shown) by the D.C. machine 13. The difference voltage is applied to vibrator contact 21 where it is chopped to a square wave which is fed through A.C. amplifier 11 to vibrator contact 32 and converted to unidirectional half waves which drive the machine to move the controlled member into correspondence with the controlling member, when the voltages from the output and input potentiometers cancel out. To avoid hunting, the normally unused vibrator contacts 22, 31 are respectively earthed through resistance . 65 and condenser 64, and interconnected through box 63 containing a differentiating or like circuit, so that a velocity signal from the machine armature is fed back to the amplifier input alternatively with the positional difference signal. The contact 22 may alternatively be connected direct to the machine armature through box 63. An A.C. machine controlled directly from the amplifier output may be used, having an output potentiometer operated by armature speed responsive means to provide the feedback voltage, and the A.C. may be derived from additional vibrator contacts.