In brief
A stepper motor is an electric motor whose rotor turns in fixed angular steps driven by controlled current pulses, positioning without an encoder.
Contents
What is Stepper motor?
In a stepper motor, driver electronics generate a magnetic field in the windings that advances step by step, and the rotor follows it. Each pulse moves the rotor through a fixed angle. The number of pulses gives the position, and the pulse frequency gives the speed. A stepper motor can therefore be operated in open loop without feedback, as long as it is not overloaded and does not lose steps.
Hybrid stepper motors are widespread, often with 200 steps per revolution, i.e. 1.8 degrees per step. Half-step and microstep operation of the driver makes the motion finer and smoother. Key ratings are step angle, holding torque, phase current, winding resistance, number of phases, flange size and shaft design. The available torque drops significantly as speed increases. Versions with an encoder or closed-loop control detect lost steps and correct them.
Stepper motors are found in dosing and labelling machines, laboratory equipment, format adjustment systems, valve drives and small positioning axes. Typical problems are lost steps due to overload or resonance, heating, bearing wear and cable breakage. Bearing noise often gives early warning of wear.
In practice: maintenance and procurement
For a replacement, flange size, overall length, shaft diameter and length, holding torque, phase current and winding connection matter, so that the existing driver still fits. A motor with a different phase current can only be used if the driver is set accordingly.
Synonyms and abbreviations: stepping motor · step motor · hybrid stepper motor
Frequently asked questions
How does a stepper motor work?
The driver energises the windings in a fixed sequence. Each time, the magnetic field jumps on a little, and the rotor aligns itself with it. Each pulse corresponds to one step. The controller counts the pulses and thus knows the position without measuring it. The prerequisite is that the load torque stays below the available motor torque.
What is microstep operation?
In microstep operation, the driver divides each full step into many small intermediate steps by varying the currents in the windings in fine increments. This makes the motor run more smoothly, reduces resonance and increases resolution. However, the actual positioning accuracy still depends on the motor, load and mechanics.
What information is needed to replace a stepper motor?
The type designation or, failing that, flange size, overall length, step angle, holding torque, phase current, winding resistance or inductance, number of connecting leads and shaft dimensions are needed. It is also important whether a brake, encoder or gearbox is fitted and which driver controls the motor.
Why does a stepper motor lose steps?
Lost steps occur when the load torque exceeds the available motor torque, when acceleration is too fast or when mechanical resonance occurs. A current set too low on the driver or a supply voltage that is too low at high speeds are also possible causes. Without an encoder, the controller does not notice the position error.