Are high microstep resolutions > 32/1 advisable?
Support » FAQ » Stepper motor positioning controls
The temptations to purchase a stepper motor drive that enables as high a microstep setting as possible in order to achieve a high resolution and hence also a high accuracy are often irresistible. The aim is certainly tempting to order a drive with a resolution of 1/128 (in a 1.8 stepper motor mathematically = 0.0140625 /step = 25600 steps/rev), for example, only to suffer a heavy setback in terms of accuracy when testing.
The torque reserve in the microstep at the current load angle or at the current position (the smaller the torque reserve, the greater the variation in the microstep) is decisive.
Without microstep current compensation the holding torque or the torque reserve is reduced compared to the full step 1/1 = 100%, half step ½ = 70.7%, quarter step ¼ = 38%, 1/8 = 19.5%, 1/16 = 10%, 1/32 = 5%, 1/64 = 2.5%, 1/128 = 1.25%.
At a microstep of 1/64 or 1/128, this means that the current only varies by 2.5% or 1.25% from the nominal current. Without current compensation this small current change causes hardly any angular change to the motor shaft because the pole sensitivity (static holding torque) is already greater than the magnetic flux change brought about by the differential current or the force field in the stator field.
When changing or reserving the direction of rotation, the error is even greater because here many microsteps are required before the motor shaft begins to rotate backwards at all only to then make a big jump when the microsteps move to approx. 1/8 or ¼ step values.
Without current compensation microstep operation is also still reproducible to some extent with good accuracy up to ½ and possibly ¼ step operation; beyond that it is actually only used for reducing resonance and running noise as well as improved operating behavior at low speeds where also here no significant advantages over 1/16 and 1/32 step operation are detectable.
First of all, economical suppliers of microstep drives with high resolution should be asked whether this positioning control contains integrated current compensation in order to save money and, above all, time.
In addition to the current compensation, the stepper motors themselves do not generate a true sinus curve over 360°. The distorted sinus curves of the motors (neither a true nor real sinusoid, nor are they exactly dephased by 90° from one another) also impair the accuracy of the step angle and this, above all, in the microstep.
Nanotec has suitably adapted the current curves of its new drive to the somewhat distorted sinus curves of its motors and, thus, a reduced step angle error of < 3% can be reached. In the Plug & Drive motors even the step angle errors (also those in the microstep) can be further improved because the current curve is adapted to the sinus curve of the motor as they form a single unit.
