The stepper motor advantages to a new stable position by means of
several stator phases that have the teeth slightly offset from each
other. To illustrate this, (
Figure 5.32) shows a stepper motor with
four phases and, to make it easier to follow, it is drawn in a linear
fashion (as a linear stepper motor).
If, on the other hand, the next energized phase is D, the closest rotor
tooth is in the opposite direction, thus making the motor to move in
reverse.
One phase is energized after another, in a sequence. To advance one
full rotor tooth the user needs to make a complete cycle of four steps.
To make a full revolution, the user needs a number of steps four times
the number of rotor teeth. These steps are called full steps. They are
the largest motion increment the stepper motor can make. Running the
motor in this mode is called full-stepping.
Figure 5.32: Four-Phase Stepper Motor
ABCDA
The four phases, from A to D, are energized one at a time (phase A is
shown twice). The rotor teeth line up with the first energized phase,
A. If the current to phase A is turned off and B is energized next, the
closest rotor tooth to phase B will be pulled in and the more moves
one step forward.
Phase C cannot be energized immediately after A because it is exactly
between two teeth, so the direction of movement is indeterminate.
To move in one direction, the current in the four phases must have the
following timing diagram (
Figure 5.33).
A
B
C
D
Figure 5.33: Phase Timing Diagram
What happens if the user energizes two neighboring phases
simultaneously (
Figure 5.34).
Section 5 – Motion Control Tutorial 5-27
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