From Motors and Drives

Specialty Motors

General Principles of Operation-Stepper
A step or stepper motor is one in which electrical pulses are converted into mechanical movements. A standard DC motor, for example, rotates continuously; but a stepper motor rotates in fixed increments whenever it is pulsed on. A standard DC motor would be considered an analog device, while a stepper motor would be considered digital.

The size of the step, or the step angle, is determined by the motor construction or by the type of controller connected. (Note: The step angle is determined in fractions of 360°, which is one complete shaft rotation.) For example, the step resolution of 90° would be four steps per rev (revolution). A 15° resolution would indicate 12 steps per rev, and 1.8° would indicate 200 steps per rev. Microstep motors are capable of thousands of steps per rev.

Because of their exactness of rotation, stepper motors are used, "openloop" in control systems where position is critical. In many high-accuracy applications, an encoder or position feedback device is used to confirm the actual position of the motor shaft.

Stepper motors require a drive package with an electronic controller, power supply, and feedback device, if needed. Figure 3-42...


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Products & Services
Motor Controllers
Motor controllers receive supply voltages and provide signals to motor drives that are interfaced to motors. They include a power supply, amplifier, user interface, and position control circuitry.
Linear Motors
Linear motors generate force only in the direction of travel. They are capable of extremely high speeds, quick acceleration, and accurate positioning.
Stepper Motor Drives
Stepper motor drives power unipolar and bipolar stepper motors in full step, half step, and microstep motion control applications.
AC Motor Drives
AC motor drives interface controllers to AC motors. They match the control signals (voltage and power levels) as well as the signal type (analog or digital). They also provide power conversion, amplification, and the sequencing of waveform signals.

Topics of Interest

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The shaft of a stepper motor moves between discrete rotary positions typically separated by a few degrees. Because of this precise position controllability, stepper motors are excellent for...