A stepper motor is a small powered motor designed for tracking and positioning. The electromechanical actuator converts digital inputs into analog motion through the controller electronics. The normal stepper has accuracy 3-5% of step value without error accumulation. Most step motors are used in an open-ended system configuration, which can result in oscillations.
As compared with the other electric drive, the step drive is possessed the structural simplicity, the board speed range, and the small static error within the single step. Because of the sensorless, gearless and brushless construction, this drive is high reliability.
Other advantages concern the possibility of the very low-speed development upon the loads directly connected to the motor shaft because unlike the collector motor, the step motors produce the maximum torque at the low speeds and do not operate at overspends. Its energy does not depend on the load.
At the same time, stepper open-ended system speed of response is limited because of the possible stability lost in transients. Such drive has high sensitivity to oscillations of the moment of inertia and static torque.
Commutation:
The stepper motor rotates in the strong concordance with the number of the set-point pulses and stops at over torque. The ration between the step and the teeth numbers are selected in the way that the small shift occurs between the stator teeth and non-excited pole teeth. As the voltage is applied to the winding, the rotor seeks the closed flux position and its teeth stop opposite the current-flowing poles. Therefore to rotate the rotor the motor phases must be switched alternately.
The 2-, 3- and 4 – phase stepper are supplied from the pulse controller which includes the pulse communicator and the winding power amplifier. The resulting rotor angle corresponds to the number of commutation of the stator winding whereas the rotation direction is defined by the commutation order and the angular speed depends on the switching frequency.
