STEPPER MOTORS (part 3)
Till now I showed you how is that a stepper motor is compossed, how it works basically and the main 2 types of motors.
Now I would like to talk a little bit about half step, full step and micro stepping. I mentioned some of it before and it would be a little interesting to go a bit further.
The condition to have the motor working in full step is to always have only one winding energized. So the torque and holding force are gone be directly related to the energy in one winding.
As shown in the image the magnetic forces align the poles in the stator and the rotor producing a holding torque and when windings are switched it will attract the rotor poles to the new stator poles. This will produce a rotation and a torque.
When working in half step mode the stepping sequence is gone be: only one winding energized and in the next step another winding is energized having now two windings energized simultaneously. To keep the rotation of the motor the next step in the sequence is to keep the last winding energized while turning OFF the first one. So that is the sequence 1 winding ON then 2 ON, 1 and 2 and so on.
But by doing this, as you see from the image it will generate different levels of force depending whether one or two windings are energized. This will also result in an uneven torque transmited to the load. The good thing is that using half step doubles the amount of pulses per turn in the motor.
This is a technique that is a bit far from the typical stepper motor use but I'm going to mention it here.
Basically it a half stepping technique with the added feature to control the current in the windings. By doing this it allows to position the rotor in any position between two poles.
How this works?, simply by applying less current to one of the windings it will generate a smaller force and the composition of forces will result in an angle that is not in the middle from the two poles
By using this technique it means a more complex sequence and control.
If you want more information on stepper motors take a look at Control of Stepping Motors