Here’s a simple, easy to understand, overview of what a step motor is, how a step motor controller works, and how the step motor and step motor controller work together to provide maximum efficiency for your project.
Step Motor Basics
A generator is designed to convert mechanical energy into electricity. A stepper motor does the opposite, converting electrical pulses into rotating mechanical energy. These pulses are directed by a step motor controller. The rotor rotates according to discrete increments, measured in degrees and called steps. This is where the name “step motor” comes from. The speed and direction in which the rotor rotates in the step motor is dependent upon the action of the step motor controller on the motor’s windings. The direction of the motor’s rotation is dependent on how the controller sequences the electrical pulses. The motor’s speed is dependent on the frequency of the controller pulses. And the length of the rotation is dependent on how long the controller keeps sending electrical pulses to the motor.
Benefits of a Step Motor
The benefits of a step motor are many. For one, these motors work well with open loop control. Open loop control means that there is no feedback from the step motor to the step motor controller. Most step motors are used with a consistent, low to moderate load at a constant speed; therefore, motor controller feedback is not necessary, as no major adjustments need to be made based on what is happening with the motor. Since systems with feedback, called closed loop systems, tend to be rather expensive, many people find this to be a big benefit of the step motor.
Another advantage of a step motor with a step motor controller is its accuracy. There is a direct relationship between the rotation angle and the input pulse, so you can “stop on a dime.” In other words, you can get the motor to stop almost exactly where you want at any time, or you can get it to reverse direction at exactly where you want. For applications that require great precision, step motors are therefore ideal.
Yet another very big advantage to the step motor is the fact that it is brushless. Other types of motors often have a physical commutator and electrical contacts called brushes that work to spin the rotor. These brushes tend to wear out and require replacement, in addition to the fact that they cause sparks and noise. Since stepper motors are electronically commutated, there are no brushes.
Types of Step Motors
There has been some evolution in step motors over the years, and there are three basic types of step motors, each a little superior to the last, although all are currently still in use.
The Variable Reluctance Motor
In a VR motor, the rotor has soft iron “teeth” that are magnetically attractive. When the stator windings are energized with electricity via the step motor controller, the poles become magnetized and attract the teeth, moving the rotor.
The PM motor has rendered the VR motor almost obsolete. These motors use permanent magnets, powerful rare earth magnets, to move the rotor so that no teeth are required. The result is improved torque characteristics versus the variable resistance motor. This fact has made PM motors some of the most popular step motors on the market.
Slightly more expensive, but also more effective in many ways, is the hybrid step motor. This type of step motor provides the best of both worlds, combining the teeth of the variable reluctance motor with the magnet action of the permanent magnet motor. The result is a motor that offers better torque, speed and step resolution than either the permanent magnet motor or the variable reluctance motor.
Using Step Motors
Step motors are useful for a wide range of jobs, from computer applications like DVD players and CD-ROM drives to hobbies like turntable building and robot construction. Step motors offer great accuracy, especially for low and medium power and speed operations, and can be quite affordable. Whether you opt for the permanent magnet motor or upgrade to the hybrid motor, there’s a good chance that a step motor will provide exactly what you need.