Rockwell Automation GMLC Reference Manual - Manual (Page 104)

Publication GMLC-5.2 - November 1999
Defining Feedback 67
For example, suppose this axis utilizes a 1000 line encoder in a motor
coupled directly to a 5 pitch lead screw (5 turns per inch). With position
units of Inches, the conversion constant is calculated as shown below:
K = 1000 lines/Rev * 4Counts/Line * 5Revs/inch = 20000 Counts/Inch
For the imaginary axis, the conversion constant is essentially arbitrary,
but does affect the smoothness of gearing and position-lock cams which
use the imaginary axis as their master. In general, a value between 4000
and 10,000 counts per position unit should provide adequate resolution.
Unwind
If the axis is configured as a rotary Axis at the General screen of
Configure Axis Use, an Unwind value is requested. This is the value used
to perform electronic unwind of rotary axes. Electronic unwind allows
infinite position range for rotary axis by subtracting the unwind value
from both the actual and the command position every time the axis makes
a complete revolution.
The Unwind value is made up of the Unwind Constant (integer portion)
and the Unwind Fraction.
Unwind Constant
If the axis is configured as a rotary Axis at the General screen of
Configure Axis Use, a value for the Unwind constant is requested. This is
the integer portion of the Unwind Value used to perform electronic
unwind of rotary axes. The Unwind Constant plus the Unwind Fraction
comprises the Unwind Value that determines the Unwind.
The unwind value is requested in units of encoder or feedback counts per
axis revolution. Enter the appropriate value using up to 10 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
Unwind value would be 3600.
10 Counts/Degrees * 360 Degrees/Rev = 3600 Counts/Rev