Patent GB-715745-A (GB)
Title: Improvements in electric remote control systems
Inventor: STOKES JOHN ARTHUR
IPC: B23Q15/00
Filed: 1951-01-02
Abstract: 715,745. Control of motors. BRITISH THOMSON-HOUSTON CO., Ltd. Dec. 7, 1951 [Jan. 2, 1951], No. 159/51. Class 38(3) The direction of rotation and the speed of a motor 6 are determined by the polarity or phase and the magnitude of a direct or alternating control voltage applied at terminals 1, 2. and supplied to an amplifier 3 through resistors 4 and 5. The armature current of the motor is limited by restricting the value of the input voltage applied to the amplifier, the voltage-limiting circuit comprising diode valves 8, 9, connected across resistors 10-13 and a battery 14 which is so poled that the valves do not normally pass current. A voltage proportional to the motor current is applied through con nection 20 to the junction of resistors 11. 12, sc that, when the input voltage of the amplifier 3 tends to exceed a pre-determined value one of the diode valves is rendered conductive to prevent further increase of the input voltage. Rapid deceleration of the motor 6 is obtained when the motor approaches its limit of travel in either direction, relays 16, 17, actuated by the respective limit switches being provided for this purpose. If contacts 16 are operated, the cathode of diode 9 is connected through resistor 18 to the junction of resistors 12, 13, and through resistor 19 to a point 21 at which there is developed a potential to earth proportional to the speed of the motor, the anode of the diode 9 being connected to the left-hand terminal of the resistor 5. Assuming a positive control potential at point 1 resulting in a negative potential at points 20, 21, the cathode of diode 9 becomes negative to earth, and the resulting current through resistor 4 produces for the anode of the valve 9 a potential negative to earth which overcomes the positive potential at the terminal 1 to cause the motor to decelerate rapidly. The armature current of the motor is limited during deceleration by the action of valve 8 which becomes conductive at a value of the armature current determined by the bias voltage across resistors 10. 11. As the motor slows down the negative potential at point 21 decreases and the decelerating signal is removed for the motor to operate at a low constant speed until it comes to a mechanical stop. The potential at 21 then falls to zero and the motor current is increased so as to hold the motor against the stop, the stalled motor current being limited to a value determined by the voltage-drop in the resistor 12. When the motor is made to leave the stop by the application of an appropriate control signal the diode 9 is cut off and the diode 8 limits the armature current, as before. Operation at the other limit switch is similar to that described. The motor may be supplied from a generator the excitation of which, is determined by the control voltage through the intermediary of valve or valves, or the control voltage, after amplification. may be applied to a transductor. The voltage applied to the terminals 1, 2, may be indicative of the angular misalignment between a motor-driven element and a controlling device so that the motor is driven to remove such misalignment.