Stepper motors are the one of the most commonly used motor types by modern engineers due to their ease of use and precision position control capabilities. This article provides an overview of the anatomy of variable reluctance stepper motor and hybrid stepper motors.
NEMA sizes are a series of standardised housing dimensions set in place by the US National Electrical Manufacturers Association, commonly abbreviated to NEMA.
The NEMA number of a given motor represents the motor housing’s face width in inches, increased by a factor of 10. For instance, a NEMA 14 motor is 1.4 inches, a NEMA 17 is 1.7 inches, and a NEMA 23 is 2.3 inches. Though all motors within a NEMA classification will have the same face size, the length of motor bodies is not a constant dimension, and can vary dramatically.
The stator of a Stepper Motor is the outer section of the internal mechanism, which remains stationary during operation. The stator is made up of several electromagnetic phases, each of which is made up of multiple solenoid windings.
Windings or coils are the basic electromagnetic components of a stepper motor. An electromagnet coil is made up of only two parts, a tightly wound conductive wire, and a magnetic core. Directing current through a solenoid coil creates a magnetic field, which, in turn, pulls the teeth of the rotor into position.
A phase is the name given to a collection of several windings, wired in sequence to allow them to magnetise in unison. Phases can be seen as the number of different combinations in which the coils of a stepper motor can be energised.
The central rotor of a Stepper Motor is a vital component that allows the motor shaft to engage with the magnetic fields created by the motor’s coils. The rotor of a hybrid Stepper Motor is a permanently ferromagnetised column with a large number of evenly spaced teeth. The teeth of a rotor are arranged into multiple misaligned toothed rings known as laminations. This misalignment encourages the rotor to rotate smoothly and continuously – without it, a stepper motor would move in sharp, jumpy steps, or worse, simply lock up during operation.
The central shaft of a Stepper Motor is held in place by one of more Rotary Bearings. Bearings are used to centralise the Motor's shaft and reduce friction during rotation. Reducing friction improves the operating efficiency and the operating life of a motor. Because Stepper Motors are a brushless construction with very few internal sources of friction, the Bearings are usually the only part of a Stepper Motor which will become 'worn out' after a long operating life.
A Stepper Motor Driver can be a moderately simple or highly complex circuit that acts as a control system and an amplifier for a Stepper Motor’s input current. A driver is programmed to direct current to each phase of a motor in rapid succession or alternation – potentially thousands of times per second. By directing current and engaging each motor phase in precisely timed steps, a stepper motor can be controlled to run at precisely maintained speeds or achieve pinpoint positioning.
How A Stepper Motor Works
We love this video from Learn Engineering which demonstrates how a stepper works with clean animations and also explains the concept of 'half stepping':