Friday, November 2, 2018

Four types of waveforms and sequences drive for stepper motors

There are four types of waveforms, or sequences, through which stepper motors are driven. These are:

1. Wave drive;

2. Full step drive;

3. Half step drive;

4. Micro stepping – we will present this method and when it is employed in another article.

Wave drive
By using this method, a single phase of a cheap stepper motor is energized at a time. If we refer to figure 1 below we can see how a stepper motor is driven. We can observe that there are 3 phases (f=3), AA’, BB’ and CC’ and 2 teeth (z=2) North and South. The rotor will perform full steps, with the angle: Theta=360/(f*z)=60 degrees.

Full step drive
When the rotor of the motor depicted in figure 1 reaches position 3 we can see that the motor can also be driven by having two phases energized at the same time. The rotor will perform full steps, according to the formula above, aligning itself exactly in the middle of the angle between the stator poles, North and South. This drive method provides full torque of the motor.

The sequence will be:


Half step drive
This method implies alternately powering either one phase or two phases at a time. The rotor will align itself either with stator poles, as in wave drive, or between them, as in full step drive. In this case the rotor will have 30 degree step angles.

The sequence is:

The direction of rotation in either case is determined on how the sequence is started. Sequences presented above assume clockwise rotation when applied starting from the first row and counter-clockwise rotation when started from back to front.

So, if we look at figure 1, depicting a 2-phase bipolar stepper motor like the one we want to control, we can determine the control sequences for each method mentioned above. It can be observed that such a motor has 4 leads, corresponding to 4 pins of an output controller or interface. So the sequences will be:

• Wave drive: 1000 0100 0010 0001;

• Full step drive: 1100 0110 0011 1001;

• Half step drive: 1000 1100 0100 0110 0010 0011 0001 1001.

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