404LXR Series Product Manual
Chapter 4 - Performance
32
If your application requires absolute accuracy, the slope factor must be incorporated into the
motion program. This is a matter of either assigning variables for motion positions and using the
slope correction in the variable equation, or if your controller has floating decimal scaling (with high
enough precision) the slope correction can be accounted for in scaling.
NOTE: The zero position (or starting point) of the error plots are at the extreme NEGATIVE end of
travel (refer to Chapter 2,
Dimensional Drawing
, for Negative end location).
Below is a sample program showing how to correct for slope error using variables. This example
program will work with the 6K as well as the 6000 Series Parker Controllers.
Step 2 through 3 of this program should be made a subroutine. This subroutine can then be
executed for each distance.
………………………………………………………………………………………………………..
•
Step #1
VAR
1 = 880; IN
THIS CASE THE DESIRED DISTANCE IS 880mm.
•
Step #2
DEL
SLCORR ;
DELETE SLCORR PROGRAM
DEF
SLCORR ;
DEFINE SLCORR PROGRAM
VAR
2 = (VAR1/1000)* (0.085);
VAR2 EQUALS DESIRED DISTANCE (IN METERS) TIMES THE
SLOPE FACTOR (mm/meter)
•
Step #3
VAR
3 = (
VAR
1-
VAR
2);
SUBTRACT SLOPE ERROR FROM DESIRED DISTANCE
•
Step #4
D
(
VAR
3);
SET DISTANCE AS VAR3
END ;
END SUBROUTINE
………………………………………………………………………………………………………..
In the example above, the required move distance is 880 mm. But the LXR has a slope error of
0.085mm per meter. This is a positive slope error meaning that if uncorrected the LXR will move
0.085 mm too far for every meter it travels. To correct we must command a smaller position.
•
Step #1: The required move distance is set as variable #1.
•
Step #2: In this step, we first convert 880 mm to 0.88 meters my dividing by 1000. Next we
multiply by the slope factor to calculate the slope error distance of this move (0.88 * 0.085) =
0.0748 mm.
Non-Slope Corrected
Error Plot, Total error
48 microns
Note: Slope Factor is 200 micron / meter in this
example.
Slope Corrected
Error Plot, Total error
8.5 microns
Non-Slope Corrected Error Plot
0
10
20
30
40
50
60
0
20
40
60
80
100
120
140
160
180
200
220
240
Positions (mm)
E
rr
o
r
(M
ic
ro
n
s
)
Slope Corrected Error Plot
-4
-2
0
2
4
6
0
20
40
60
80
100
120
140
160
180
200
220
240
Positions (mm)
E
rr
o
r
(M
ic
ro
n
s
)
