Resolution of motors
Resolution and accuracy of position control motors depend on several factors.
Contents
Servo motor
Resolution
Servo motor resolution is determined by feedback device of motor. I.e. 1000 PPR (pulses per revolution) quadrature encoder yields 1/4000 revolutions because 1000 PPR equals 4000 counts per revolution after standard 4X decoding.
Accuracy
In most cases accuracy is more important value than resolution. Accuracy is more difficult to measure because it largely depends on mechanical load characteristics and dynamics. In ideal conditions the accuracy is very close to resolution but in most of practical cases the accuracy is 5 to 10 times less than resolution. I.e. 1000 PPR encoder can be expected to provide 1/400 to 1/800 revolutions accuracy.
If feedback device has very high resolution, such as 1/1000000, then limiting factor of accuracy will be other error sources than feedback device alone.
Stepping motor
Resolution
Stepper resolution depends on number of magnetic steps per revolution and drive's electrical step angle size. Most modern drives implement microstepping to increase resolution and motion smoothness. Most common stepper resolution is 200 full steps per revolution but when driven for example with 16-microstep drive, the resulting resolution is 1600 steps per revolution (1/1600 revolutions).
Accuracy
Because steppers don't usually have feedback devices, the accuracy depends on motor load torque and motor linearity. Most stepping motor manufacturers quote angular accuracy of ±0.9° or 1/400 revolutions. Stepper accuracy can't be increased by increasing microstepping resolution.
See also
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