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Stepper Motor Microstepping

Micro-stepping is an advanced techniques for controlling bipolar stepper motors to achieve better resolution

Micro-stepping a Stepper Motor

Micro-stepping is an advanced techniques for controlling bipolar stepper motors to achieve better resolution, accuracy and torque.

A bipolar stepper motor driver excites the two windings of the stepper motor such that current in each winding is varied in order to rotate the stepper motor. It is the relative current in each winding that determines the angular position of the motor and of course the motor torque. There are many modes of operation like full stepping, half stepping and micro-stepping along with the amount of current by chopper or PWM methods.

Full Stepping
Simple stepper motor controllers drive the motor winding with full positive current, no current, or full negative current. In full stepping operation, the current required in each winding is either -Imax or +Imax. A step sequence of 4 full steps makes up one complete step cycle. Another variation of it is wave stepping where only one coil is energized at a time with current in each winding either -Imax, 0 or +Imax.

Half stepping
In a half stepping operation, the current required in each winding is either -Imax, 0, or +Imax making up sequence of 8 half steps to makes complete step cycle, motor move half of that what it moves in Full Stepping cycle.

Micro stepping
To implement micro-stepping the driver must be able to deliver variable amount of current to motor winding at any given time, this require a chopper or PWM type driving so is more complex to implement than Fuller/Half micro-steppers. Motor winding current is sine / cosine of peak current with sine cosine table dived in a specific steps (called micro-steps), in turn motor is made to move through equal small micro-steps before it can complete a full step. This is possibly the best method of driving a stepper motor as there is no low speed resonance / vibration if micro steps are carefully chosen and implemented with chopper or PWM.
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