Stepper motor power stages operating with electronic measures to raise the physical resolution of the stepper motor are called micro step, mini step or fine step power stages. Concerning Phytron, that means the power stage can resolve to 1/512 of a full step. The selectable step resolution is, depending on the type of power stage, enhanced by a factor of 2 to 512. Converted into steps per revolution, a resolution of 1/512 for a 200 step motor results in: 102400 Micro steps per motor revolution or 0.0035° at the shaft.
From Full Step ...
With a 2 phase stepper motor operating in the full step mode, the exact physical resolution of the motor is reached. For a 200 step motor that means an obtainable resolution of 200 steps per revolution at the motor shaft. The full step position of the rotor is characterized when both phases 1 and 2 are fully powered. In the full step mode there only exists phase patters with both phases 1 and 2 fully powered. Never is only one phase powered.
... to Micro Step
By special circuit design, the physical, that means full step, resolution can be enhanced. If you multiply, for example, the resolution by a factor of 2, this is called half step mode. This way the 200 step motor can resolve 400 steps at the motor shaft. Additional to the advantage of a larger number of steps per revolution, this operating mode stimulates smoother motor run and reduces resonance behavior, which is more pronounced in the full step mode. When the resolution is further enhanced, this is called quarter step, eigth step, ... or simply mini step or micro step.
Advantages of the Micro Step Mode:
A higher step resolution includes the following advantages:
- The obtainable resolution is enhanced.
- The torque ripple decreases with the rising number of fine steps.
- Owing to the smoother operation, the lifetime of the stepper motor is remarkably elevated, especially with solid or dry lubricated ball bearings.
- Resonances and oscillations are considerably reduced; the motor runs near resonance-free.
- The acoustic noises are also reduced with rising step resolution.
- Improved torque thanks to lower energy dissipation that is caused by oscillations.
Micro Step Operation vs. Resolution:
It should be noted that setting a high step resolution only does not absolutely mean that the motor can actually execute such a fine step. Internal friction, system faults, tolerances, inhomogeneous grease allocation in the ball bearings etc. might be reasons that the motor cannot react to the control signal. Up to a resolution of about 1/20 step (frictionless) these effects are normally negligible. For positioning more exactly than 1/20 of a full step, or in systems with high static moments, it is recommended to close the control loop by an encoder, a resolver or an adequate measuring system to enforce the execution of the micro steps.
Linear power stages achieve, as a general rule, a higher accuracy of the current settings than choppered power stages. Therefore, for very fine positioning it is recommended to apply linear power stages and stepper motors with encoder or resolver systems.