One of the most essential parts of a motion control system is a stepper motor, an electromechanical tool that transforms electrical power into mechanical power. Similar to a switched reluctance motor or a legacy AC induction-type motor, the rotation of a stepper motor can be easily controlled with a certain degree of precision. This gives the motion control system the potential to break up a complete rotation into various steps.
Known as a type of DC synchronous motor, a stepper motor has the power to immediately produce complete rotation, even when not running. This is why they are largely used in motion control applications. What’s adding to their popularity further are dedicated stepper motor driver cards that enable interfacing to PC-based systems.
In this post, we will examine the different types of stepper motors, as well as the different operating modes. You can choose from different types based on your requirements, including:
1. Permanent Magnet
Using a rotor’s permanent magnet (PM), this type of a stepper motor runs on magnetism and repulsion between the PM and stator electromagnets. Also known as the tin-can or can-stack motor, PM motor is one of the most common motor control types of stepper motors, which has 48 to 24 steps for every revolution. What makes this kind of stepper motor popular is its low cost of manufacturing.
2. Variable Reluctance
Variable reluctance is a basic type of stepper motor, which makes it easier to understand the principle of operation from an organizational angle. This type of motor control works on the principle of “minimum reluctance comes with minimum gap,” and has a plain iron rotor.
These types of motors are named “variable reluctance” because the rotor’s position varies according to the reluctance of the motor circuit, which forms between the stator teeth and rotor teeth.
3. Hybrid Synchronous
The most accepted form of a stepper motor is a hybrid synchronous stepper motor. It uses the best of both permanent magnet and variable reluctance stepper motors. A hybrid synchronous stepper has a permanent magnet core rotor and a circumference made of plain iron, which also has teeth.
Having high angular resolution and high rotation, a hybrid synchronous motor offers improved performance over a permanent magnet in terms of industrial motor control and step resolution.
Now that you understand the different types, let’s look at the operating modes:
1. Full Step Mode
The rotor moves through 200 steps during each rotation of 360° of the motor channel. Each degree measures 1.8°, to be precise. Two stator phases get energized during full-step operation, which ensures maximum torque. However, the number of rotor teeth may affect the angular resolution.
2. Half Step Mode
In this case, the rotor moves through 400 steps during each rotation of 360°, where each step equals 0.9°. Either one or two phases on the stator get energized to offer almost two-fold improved angular resolution, which brings higher accuracy in position and affects torque.
3. Micro Step Mode
In the micro-step mode, the rotor moves through 51,200 steps and each step accurately measures 0.007°. A stator phase may get energized, de-energized or partially energized. The micro-step operation is required in case of applications that demand accurate positioning. You can reduce the torque rating by up to 30%.
Selecting a stepper motor for motion control requires proper analysis of the torque-speed curve of the motor. It’s important for the torque-speed curve to match the application requirements, in the absence of which the system will not deliver its best performance.