Question

A 3-phase stepping motor is to be used to drive a linear axis for a robot. The motor output shaft will be connected to a screw thread with a screw pitch of 1 mm. We want to be able to have a spatial control of at least 0.05 mm. a)How many poles should the motor have?

Answer 1

Answer:

The  number of poles is 12.

Explanation:

The step angle is given by

$\phi=\frac{360^{\circ}}{N}$

Where

$\phi_1$ is the step angle

To Find the Step angle of the Stator

$\phi_1=\frac{360^{\circ}}{N_s}$

Where

$\phi_1$  is the step angle

$N_s$ is the number of poles or teeth on stator

To Find the Step angle of the Rotor

$\phi_2=\frac{360^{\circ}}{N_r}$

where

$\phi_2$  is the step angle

$N_r$ is the number of poles or teeth on rotor

In the question it is stated that

$N_s+ N_r = \frac{1}{0.05}$

$N_s+ N_r = 20$

Selecting $N_s$= 12 and $N_r$= 8  

$\phi = \phi_2 -\phi_1$  

$=\frac{(360^{\circ})}{8}- \frac{(360^{\circ})}{12}$

=$45^{\circ}-30^{\circ}$  

=$15^{\circ}$