Editing Stepper motor (section)

==Phase current waveforms==
[[Image:Drive.png|thumb|Different drive modes showing coil current on a 4-phase unipolar stepper motor.]]
A stepper motor is a polyphase [[electric motor#Three-phase AC synchronous motors|AC synchronous motor]] (see Theory below), and it is ideally driven by sinusoidal current. A full-step waveform is a gross approximation of a sinusoid, and is the reason why the motor exhibits so much vibration. Various drive techniques have been developed to better approximate a sinusoidal drive waveform: these are half stepping and microstepping.

===Wave drive (one phase on) ===
In this drive method only a single phase is activated at a time. It has the same number of steps as the full-step drive, but the motor will have significantly less torque than rated. It is rarely used. The animated figure shown above is a wave drive motor. In the animation, rotor has 25 teeth and it takes 4 steps to rotate by one tooth position. So there will be {{val|25|×|4}} = 100 steps per full rotation and each step will be {{frac|360|100}} = {{val|3.6 |ul=deg}}.

=== Full-step drive (two phases on) ===
This is the usual method for full-step driving the motor. Two phases are always on so the motor will provide its maximum rated torque. As soon as one phase is turned off, another one is turned on. Wave drive and single phase full step are both one and the same, with same number of steps but difference in torque.

===Half-stepping===
When half-stepping, the drive alternates between two phases on and a single phase on. This increases the angular resolution. The motor also has less torque (approx 70%) at the full-step position (where only a single phase is on). This may be mitigated by increasing the current in the active winding to compensate. The advantage of half stepping is that the drive electronics need not change to support it. In animated figure shown above, if we change it to half-stepping, then it will take 8 steps to rotate by 1 tooth position. So there will be 25×8 = 200 steps per full rotation and each step will be 360/200 = 1.8°. Its angle per step is half of the full step.

===Microstepping===
What is commonly referred to as microstepping is often ''sine–cosine microstepping'' in which the winding current approximates a sinusoidal AC waveform. The common way to achieve sine-cosine current is with chopper-drive circuits. Sine–cosine microstepping is the most common form, but other waveforms can be used.<ref>[http://www.zaber.com/wiki/Tutorials/Microstepping zaber.com], microstepping</ref> Regardless of the waveform used, as the microsteps become smaller, motor operation becomes smoother, thereby greatly reducing resonance in any parts the motor may be connected to, as well as the motor itself. Resolution will be limited by the mechanical [[stiction]], [[backlash (engineering)|backlash]], and other sources of error between the motor and the end device. Gear reducers may be used to increase resolution of positioning.

Step size reduction is an important step motor feature and a fundamental reason for their use in positioning.

Example: many modern hybrid step motors are rated such that the travel of every full step (example 1.8 degrees per full step or 200 full steps per revolution) will be within 3% or 5% of the travel of every other full step, as long as the motor is operated within its specified operating ranges. Several manufacturers show that their motors can easily maintain the 3% or 5% equality of step travel size as step size is reduced from full stepping down to 1/10 stepping. Then, as the microstepping divisor number grows, step size repeatability degrades. At large step size reductions it is possible to issue many microstep commands before any motion occurs at all and then the motion can be a "jump" to a new position.<ref>{{cite web|url=http://www.micromo.com/media/wysiwyg/Technical-library/Stepper/6_Microstepping%20WP.pdf|title=Microstepping: Myths and Realities - MICROMO|website=www.micromo.com|access-date=2024-10-07|archive-date=2016-12-06|archive-url=https://web.archive.org/web/20161206092700/http://www.micromo.com/media/wysiwyg/Technical-library/Stepper/6_Microstepping%20WP.pdf|url-status=bot: unknown}}</ref> Some stepper controller ICs use increased current to minimise such missed steps, especially when the peak current pulses in one phase would otherwise be very brief.