Understanding the Types of Stepper Motors and Operating Modes to Control Motion
Stepper motors can be a very important part of a motion control system. Stepper motors can be described as being similar to AC-induction motors of the past in that they both have a stator, and a rotating rotor. However, this is only a small part of their similarities. Stepper motors can be described as a DC synchronous motor. A stepper motor's rotation is much more controllable than an induction motor. Stepper motors can generate full, instantaneous torque even at a standstill. They are ideal for motion control applications where precision, repeatability, power, and power are essential.
Types Of Stepper Motors
There are three types of stepper motors.
Permanent Magnet Stepper. Permanent magnet stepper. These rotors are made with permanent magnets. They interact with the electromagnets to create torque and rotation. PM steppers are able to produce more torque per unit power and have low power requirements.
Variable Reluctance stepper. Permanent magnets are not used to build VR stepper rotors. They are made of plain iron and look like a gear with protrusions (or "teeth") around the circumference. VR steppers with teeth have very high angular resolution, but this often comes at the cost of torque.
Hybrid Syncronous Stepper. The best features of both VR and PM steppers are combined in HS stepper motors. An HS motor's rotor has a permanent magnet core. The circumference, however, is made from plain iron with teeth. The hybrid synchronous motor has high angular resolution as well as high torque.
Three main modes of operation are available for stepper motors. The operating modes of a rotor having 200 teeth are an example.
Full Step Mode. The rotor goes through 200 steps for each 360deg rotation. Each step is exactly 1.8deg. Two phases of the stator must be energized during full step operation. This gives maximum torque but limits angular resolution due to the number of teeth on rotor.
Half-step Mode. The rotor goes through 400 steps for each 360deg rotation. Each step is exactly 0.9deg. Half-step operation allows for an alternation of having one or two phases of the stator energized. This gives twice the level of accuracy for positioning accuracy, but at the cost of torque.
Micro Step Mode. The rotor goes through 51,200 steps for each 360deg rotation. Each step is exactly 0.007deg. The micro-step operation allows phases on the stator to be energized, partially energized, or de-energized. This mode can be used for applications that require precise positioning. However, torque rating can be decreased by up to 30%.
It is crucial to examine the torque-speed curve of the stepper motor before you choose one. The manufacturer should have this data. It is a graphic representation of the motor's torque at given speeds. If the torque-speed curve for a motor does not match the application requirements, then the system's performance will be less than expected.Tags: stepper motor