Stepper Motors & Drives Selection

What is a Step Motor?

A Step Motor is constructed with windings in the stator and magnets attached to the rotor. A step motor gets its name due to the fixed mechanical motion increments it provides, referred to as “steps.” These steps are generally specified in degrees. A step motor and stepper drive rotate in pre-defined angles proportional to the stepper pulses. A typical full-step system will achieve 200 steps per revolution, equating to about 1.8 degrees per full step.

Advantages of Step Motors

Step motors are able to provide acceleration torque that is equal to running torque and do not require maintenance. They also allow for speed to be easily determined with a simple formula (speed = steps per revolution ÷ pulse rate). Additionally, they can make fine incremental moves without a feedback encoder, with fast acceleration capabilities. Furthermore, they can be used to hold loads stationary without overheating and have excellent low speed/high torque characteristics.

What is a Stepper Drive?

A stepper drive works in conjunction with a step motor to allow for rotation in pre-defined angles. There are several different types of stepper drives.

  • Microstep Drivers: Microstepping Drives apply power to the step motor winding to produce torque. It positions the step motor at smaller increments between full steps, providing higher resolution with less torque. While this doesn’t increase step accuracy, it can allow a motor to run with less noise, in addition to minimizing low speed resonance effects and producing smooth rotation. Microstepping and microstepping drives are typically used to increase a motor’s resolution.
  • Drivers with Oscillators: An oscillator is used to produce pulses to drive a step motor at a preset speed. Oscillators can be integrated into the hardware construction of a microstepper drive.
  • Full/Half Step Drivers: Full/Half step drivers allow for both full step operation (1.8° per full step) and half step operation (0.9° per full step).

Step Motor Systems

Step motor systems, that is a step motor and a stepper drive, can be either open or closed loop systems.

  • Open Loop: open loop systems do not use feedback to verify that the desired output has been obtained. Open loop is the most common type of step motor system.
  • Closed Loop: in contrast to an open loop system, closed loop systems do use feedback to verify the desired result has been reached. Closed loop systems are traditionally achieved through use of an encoder.

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