Siemens SIMATIC FM 353 Manual page 267

Software limit switches
Software limit switches MD21 and MD22 are used to limit the working area (see
Section 9.9). The value of MD21 must be less than the value of MD22 at all times.
MD
21 Software limit switch, be-
ginning
22 Software limit switch, end
1) see Section 5.3.1, Dependencies
MSR stands for measurement system raster (see Section 5.3.1)
Backlash compensation
Mechanical drive elements generally have a certain amount of backlash (play).
MD30 provides compensation of mechanical reversal backlash. With each reversal
of direction, the mechanical backlash runs through before any axis movement
takes place. This results in positioning errors.
A backlash figure entered in the MD30 is calculated, with correction, by the stepper
motor control as a factor of the current traversing direction of the axis. The result
is an approximate compensation of backlash during positioning.
In MD31, the "backlash-free" traversing direction of the axis is identified. When
MD31 = 0, that direction is considered to be "backlash-free" which corresponds to
the direction of the axis movement at the time synchronization is begun. This cor-
responds to the following correspondence, as a factor of MD18:
MD18 = 0,2,4,8: Plus direction is backlash-free
MD18 = 1, 3, 5, 9: minus-direction backlash-free
MD
30 Backlash compensa-
tion
31 Directional reference
backlash
The backlash is traversed at a speed of 1% of the maximum possible speed
(MD23).
FM 353 Stepper Drive Positioning Module
6ES7 353-1AH01-8BG0
Designation
−1 000 000 000...<+
1 000 000 000
−
+
Reversal play or backlash
Designation
0 to 10,000
0 = as with reference point ap-
proach
Description of Functions
Value/Meaning
1)
Spindle
Value/Meaning
Unit
[MSR]
Unit
[MSR]
−
9-67