Stepper Motors: Step Operation

Stepper motors can

  • execute a stepwise operation, moving a defined angle and then stopping again
  • hold a fixed position

A driver circuitry must provide an appropriate current sequence to the different windings of the motor.

Total moving angle is = step angle • number of steps.

JE stepper motors are of claw pole design, step angle is 7.5° … 18° at full step operation mode.

Stepper motors can be controlled in a simple open loop system, without any feedback information of the position.
There is no need to implement an optical or magnetical encoder.
However, if the motor is overloaded or the acceleration being commanded is too fast, it looses steps.
Information of actual rotor position is lost, the system must be reinitialized.

 

Execution of one step:

New angle position is reached after time t.
But then the rotor makes some oscillations, stable new position
is not reached before time T.

stepper motors 
 Execution of several steps:  
 stepper motors Picture left shows step operation at low clock (e.g. 10Hz).
Each step causes an oscillation, no smooth rotation.
This can be improved by applying half step or microstep operation (see section below).
 stepper motors With increasing step frequency, the rotation gets smoother (e.g. 100 Hz).