Rockwell Automation 999 IMC S Class Compact Motion Controller (Cat. No. 4100-999-122) - Manual (Page 106)

5-26 Understanding IMC-S/23x Setups
Publication 999-122 - January 1997
Unwind
If the axis is configured as a rotary Axis in the application setup menu,
a value for the Unwind constant is requested. This is the value used to
perform electronic unwind of rotary axes. Electronic unwind allows
infinite position range for rotary axes by subtracting the unwind value
from both the actual and command position every time the axis makes
a complete revolution. To avoid accumulated error due to roundoff with
irrational conversion constants, the unwind value is requested in units
of encoder or feedback counts per axis revolution. Enter the appropriate
value using up to 9 digits and press ENTER.
For example, suppose this axis is configured as a rotary axis using
position units of Degrees and 10 feedback counts per degree. It is
desired to unwind the axis position after every revolution. In this case,
the IMC-S/23x might display:
Enter 3600 since there are 3600 feedback counts
(10
x 360 ) per revolution of the axis and press ENTER.
Unwind Reference Point
If the axis is configured as a rotary axis in the Application Setup menu,
a value for the Unwind Reference Point is requested. This value is used
when an unwind is performed on a rotary axis. The Unwind Reference
Point is the position to which the axis rolls during an unwind. The
position to which an axis rotates to before it unwinds to the Unwind
Reference Point is equal to the Unwind Reference Point plus the
Unwind. The total distance traveled before the axis unwinds remains
constant and is not affected by the Unwind Reference Point.
For example, if the Unwind is 4 position units and the Unwind
Reference Point is -1 position units, the axis rotates up to 3 position
units and unwinds back to -1 position units.
Unwind (Counts/Rev) = 4000.000000000
Counts
Degree
-------------------
De gree s
R ev
----------------------
TIP: The unwind constant must be an integer. Because the number is
in encoder counts, you cannot have a fraction of a count.