Patent GB-1496344-A (GB)
Title: Multi-phase stepping motor controller
IPC: H02P8/32
Filed: 1974-11-20
Abstract: 1496344 Stepping motor control RICOH CO Ltd 20 Nov 1974 [20 Nov 1973] 50214/74 Heading H2J Method of and apparatus for driving a multiphase stepping motor, the motor having excitation means to sequentially excite the motor phases and a pulse generator operatively connected to the motor shaft to generate pulses indicating the shaft position, comprises sensing the position pulses to determine the motor shaft speed whereby a timing pulse of a predetermined duration is generated and initiated after one position pulse is terminated and before the next position pulse is initiated and the interval of coincidence of the timing pulse and the next position pulse indicates the speed of the motor shaft, and controlling the excitation means to change the phase excitation of the motor .to impart reverse torque to decelerate the shaft, at a position before a desired stopping step, during the interval of coincidence of the timing pulse and the next position pulse. A four phase stepping motor 10 is controlled by the circuit shown in Fig. 5 to execute a required number of steps in a desired direction as determined by a member 30, which sets a counter C1 and emits direction commands CW or CCW and a starting pulse A, after which the motor is controlled by pulses B produced by a photoelectric shaft position senser, Fig. 1 (not shown) and applied to control the circuit comprising logic gates, monostable multivibrators Ml to M6, flip-flops F1, F2, F3, counter C2, drivers D1-D4 for the motor windings and control unit 50 to provide high and normal energization thereof, a typical sequence of a seven step operation being as follows:- (1) The motor windings are energized (two phases at a time) in a driving mode at high power for the first three steps and at normal power for the next two steps to give acceleration and constant speed periods, Fig. 4 (not shown). (2) During the last two steps the sequence of energization of the winding pairs is such that the motor is sequentially driven at normal power and braked at normal and then at high power to produce a deceleration dependent on the motor speed and hence a completion of the stepping operation without hunting. The total time of the operation is also reduced. When the connector Cl is decremented to 2, the monostable multivibrator M1 provides a timing pulse (E) Fig. 2 (not shown) during the interval between position pulses 5 and 6 and of a duration proportional to motor speed and this causes a retardation in the phase sequence of 1-step to retard the rotor, the correct sequence being resumed at the end of the pulse. The multivibrator M2 is triggered simultaneously with M1 to provide a longer timing pulse (F) of a predetermined duration and a retardation by 2 steps in the phase sequence is provided during the interval of coincidence of this timing pulse (F) with the next position pulse. The multivibrator M3 is triggered at the start of this next position pulse, which decrements the counter to 1, and a retarding torque is applied for the duration of the coincidence between this monostable timing pulse (G) and the gap between position pulses at the end of the next position pulse. At the end of this position pulse a retardation is provided via the multivibrator M4 which is of a duration coincident with the overlap of the timing pulse with the last position pulse which decrements the counter to zero. The final two multivibrators M5, M6 are triggered at the end of this last pulse to provide a stop pulse. High power is provided during the last 2 retardation pulses and the stop pulse. The effect of the variation of the length of pulses B as the speed varies during a stepping operation is also discussed, Fig. 3 (not shown).