Rev B Apr 2018
Appendix C Stepper Motor Operation
Page 38
C.2.4 Minimum and Maximum Positions
These positions are dependent upon the stage or actuator to which the motors are
fitted, and are defined as the minimum and maximum useful positions of the stage
relative to the ‘Home’ position - see Fig. C.4.
The distance from the Minimum position to the Maximum position is the ‘useful travel’
of the stage. It is often the case that the Minimum position is zero. The Home and
Minimum positions then coincide, with movement always occurring on the positive
side of the Home position.
Rotary stages have effectively no limits of travel. The Minimum and Maximum
positions are conventionally set to 0 and 360 degrees respectively. When the position
of a rotary stage is requested, the answer will be reported as a number between 0 and
360 degrees, measured in the positive direction from the Home position.
Fig. C.4 Minimum and Maximum Positions
C.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 is often undesirable because it can cause thermal movements through
expansion of the metal of the stage.
For this reason, power saving is implemented by default from the software drivers.
Travel
Min. position (zero)
(home)
Max. position
Offset
-ve limit switch
SW positive limit
SW negative limit
