Patent GB-826167-A (GB)
Title: Improvements in or relating to electromechanical control systems
Inventor: BAILEY CHRISTOPHER EDMUND GERV
IPC: H02P8/14
Filed: 1956-11-08
Abstract: 826,167. Electric motors. SOLARTRON ELECTRONIC GROUP Ltd. Nov. 1, 1957 [Nov. 8, 1956], No. 34203/56. Class 35. A step-by-step motor which may be used in a servo-system comprises a permanent magnet rotor 12, and a six-pole stator 11 having pairs of exciting windings brought out to terminals TA, TB, TC, the sequential energization of which in six different patterns, causing the rotor to step in one direction or the other. The relay circuit in Fig. 2 provides an energization sequence for clockwise or anti-clockwise rotation on closure of either switch SC or SA, and when both are opened, the pattern of excitation remains static and so holds the rotor still. The circuit consists of three relays RA, RB, RC, each with five sets of contacts, and each having two stable states. In one state the respective motor terminal is connected to one supply line (LT+), and in the other state the motor terminal is connected to the other supply line (earth, in this case). In addition the other contacts of each relay serve to energize the control circuit for cyclically switching the three relays. The contacts are arranged so that any two units being in the same stable state causes the preceding or succeeding relay to reverse its condition, depending on whether SC or SA is closed, thus causing an energizing sequence giving clockwise or anti-clockwise rotation. A modification capable of high-speed operation is described in which the three cyclically connected relays (or transistors) are controlled by a transistor or electronic valve, the control electrode of each of which is connected to the centre of a pair of resistors whose free ends are connected to the motor energizing terminals associated with the other two relays, so that unless these are both energized in the same sense they have no effect on the control electrode. Two other pairs of resistors are provided, whose free ends are respectively connected to its own motor terminal and to one and the other, respectively, of the other terminals. The centres are connected through resistors to the control electrode and optionally earthed or freed through one or other of two four-diode clamps each having a diagonally connected control switch which may be opened to provide clockwise or anti-clockwise rotation of the motor, respectively. These switches, like control switches SA, SC in Fig. 2, may be operated by a control voltage, and a two stage differential amplifier integrator 35, 36 may be used to operate them selectively in response to the control voltage. As shown in Fig. 5, an integrating circuit generates an output signal to the amplifier representative of the integral of control signals applied at terminal 37, means being provided for feedback from the output relays P, Q to the integrating circuit at a rate proportional to the motor speed, and in the correct sense to reduce the output signal from the integrating circuit. The pentode 33 and capacitor 34 form a Miller integrator circuit, controlling the first stage triode 35 of the twostage differential amplifier controlling the relays P, Q. When a control signal is applied at terminal 37 it is stored in capacitor 34, and consequent rotation of the motor causes the repeated charging and discharging of a capacitor 38 through cam-operated change-over contacts 39. The capacity of capacitor 38 is <SP>1</SP>/ 50  that of capacitor 34, and it is charged in a sense depending on the direction of rotation of the motor and such as to give feed-back pulses to successively reduce the charge on capacitor 34.