Learn About Stepper Motors
A stepper motor is a DC motor that moves in discrete steps. The coils are organized into phases. When the phases are energized in sequence the motor will rotate in precise increments.
Types of Stepper Motors
Permenent Magnet Stepper Motor
The rotor is permanently magnetized. A voltage is applied in sequential order to the stator windings. The magnetized stator coils then attract the rotor.
Variable Reluctance Stepper Motor
This type of motor uses a non-magnetized iron rotor with 'teeth' that are offset from the stator. As the stator coils are activated the rotor moves.
Hybrid Synchronous Stepper Motor
This motor type is a combination of the two previous designs. The rotor has magnetized teeth whose polarities are offset from each other. Two stator windings are activated with different polarities to move the rotor. This type of motor can offer higher torque and more precise stepping.
Controlling a Stepper Motor
Open loop control is used on stepper motors. Utilizing a synchronized series of outputs stepper motors can be moved by single steps, half steps, micro-steps
Single Step control
Activating one stator coil at a time, or a pair of adjacent coils a stepper motor will cause the motor to rotate 1/4 of an electrical cycle.
Half-Step
Activating 2 stator coils at a phase of 90 degrees will cause the rotor to take 8 half-steps for each electrical rotation.
Mirco-step
Outputting a sinusoidal signal on adjacent stator coils, with the same phase as a half step, will cause to rotor to move in what is referred to as micro-steps.
Advantages and Disadvantages of Stepper Motors
Advantages
- Precise positioning
- High torque at low speed.
- Ideally suited for high-precision applications such as printers and CNC.
Disadvantages
- Low torque at high speed
- No inherent feedback, external circuits are required to gain position feedback.
- Electrically inefficient