Figure 6.6-3 - Phase Timing Diagram; Figure 6.6-4 - Energizing Two Phases Simultaneously - Newport ESP6000 User Manual

Section 6 — Motion Control Tutorial
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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 motor moves one step forward.
If, on the other hand, the next energized phase is D, the closest rotor tooth
is in the opposite direction, thus causing the motor to move in reverse.
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 (see Figure 6.6-3):
A
B
C
D
Figure 6.6-3 — Phase Timing Diagram
One phase is energized after another, in a sequence. To advance one full
rotor tooth we need to make a complete cycle of four steps. To make a full
rotor revolution, we need a number of steps four times the number of rotor
teeth. These steps are called full steps. They are the largest motion incre-
ment the stepper motor can make. Running the motor in this mode is called
full-stepping.
Figure 6.6-4 demonstrates the effect if we energize two neighboring phases
simultaneously.
Figure 6.6-4 — Energizing Two Phases Simultaneously
Both phases will pull equally on the motor but will move the rotor only half
of a full step. If the phases are always energized two at a time, the motor
still makes full steps. But, if we alternate one and two phases being acti-
vated simultaneously, the result is that the motor will move only half a step
at a time. This method of driving a stepper motor is called half-stepping.
The advantage is that we can get double the resolution from the same
motor with very little effort on the driver's side. The timing diagram for
half-stepping is shown in Figure 6.6-5.
A B C D A
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