67
Single Channel Stepper Motor Controller
F.2.5 Power Saving
The current needed to hold a motor in a fixed position is much smaller than the current
needed to move it, and it is advantageous to reduce the current through a stationary
motor in order to reduce heating. Although this heating does not harm the motor or
stage, it i s often undesirable because it ca n cause thermal movements through
expansion of the metal of the stage.
For this reason, power saving is implemented by default from the software drivers.
When a motor is moving, the ‘Move Power’ is applied. When a motor is stationary, the
‘Rest Power’ is applied. See ‘Phase Powers’ in Section 5.3.3. for more d etails on
these power settings.
F.3
Error Correction
F.3.1 Backlash correction
The term
backlash
refers to the tendency of the stage to reach a different position
depending on the direction of approach.
Backlash can be overcome by always making the last portion of a move in the same
direction, conventionally the positive direction. Consider the situation in Fig. 6.6, a
positive
move, from 10 to 20 mm, is carried out as one simpl e move, whereas a
negative
move, from 20 to 10 mm, first causes the stage to oversho ot the target
position and then move positively through a small amount.
Fig. 6.6 Backlash correction
The controller has this type of ‘backlash correction’ enabled as its defau lt mode of
operation, but it can be overridden if the overshoot part of the move is unacceptable
for a particular application.
See Chapter 5 for details on setting the backlash correction.
negative move
positive move
10mm
20mm
position
