Stepper motor: moving by fixed angles
Energise the coils in sequence to move 1.8° at a time. Full step, microstepping, lost steps and constant-current drivers.
Principle
The rotor magnets (teeth) are pulled towards the energised stator coils. Change the current in coils A and B in sequence and the rotor turns one step at a time. A typical hybrid stepper has 200 steps per revolution = 1.8°.
Drive methods
| Method | Characteristics |
|---|---|
| Full step | Simple, strong vibration |
| Half step | Twice the resolution |
| Microstepping (1/16, 1/256) | Splits the A and B currents as sine and cosine for smooth motion. Less vibration and noise |
Microstepping increases position resolution but does not increase accuracy by the same ratio. Under load the intermediate positions shift.
RoadmapSee where this note sits in Motor Control→The open-loop trap: lost steps
Steppers are usually run without a position sensor (open loop). Accelerate too fast or exceed the torque with the load and the motor loses steps, and the controller does not know. So you use acceleration profiles (trapezoid, S-curve) and find the origin with a limit switch at start-up.
Drivers
Drivers such as the A4988, DRV8825 and TMC2209 hold the coil current constant with a constant-current chopper. Raising the supply voltage improves torque at high speed. The TMC family offers a silent mode and load detection (something like lost-step detection).