TRS&TRA Iterpolation Troubleshooting.PDF

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TRS/TRA Servo System
TRS/TRA Interpolation Problems
USA-E99321-001-*
MITSUBISHI ELECTRIC AUTOMATION
USA
List of Past Revisions
Suffix
*
Date of Revision
06/09/01
Detail
First edition created
INTERPOLATION PROBLEM ON TRS/A SERVO DRIVE
Interpolation problems could be a result of a few things. One, the actual servo drive could be out of
adjustment. These adjustments are made on the drive with variable resistors (VR2-VR9). Two, the pitch
error or backlash compensation could need adjustment. Three, there could be an actual mechanical
problem with the machine. The following diagrams give a possible solution to the related interpolation
problem.
1. When the interpolation is slightly rotated to either the left or right from the center point. The position
loop gain (VR2) is misadjusted. Depending on what direction you are cutting changes which axis needs
adjustment. Both axis may need to be adjustmed. But only adjust one axis at a time. Adjust VR2 until you
find the best point that the circle is centered to 0 degrees. Then try to adjust the other axis to see if it can be
improved. If it can not be improved, then the adjustment is done. The goal is to make the position loop
gain the same for both axis if possible.
a) The following diagrams indicates that the position loop gain in X axis < Y axis.
Y
0 degrees
Y
0 degrees
X
X
cutting
CW
cutting
CCW
b) The following diagrams indicates that the position loop gain in X axis >Yaxis.
Y
0 degrees
Y
0 degrees
X
X
cutting
CCW
cutting
CCW
2. When there is a dimple in the mid point in either axis. This indicates that the speed loop gain ( VR9)
may need adjustment. Adjust the axis that shows the dimple. The cutting direction does not matter in this
case.
a) In the following diagrams indicates that the speed loop gain needs to be adjusted for that specific axis.
Y
Y
X
X
adjust Y
adjust X
3. When doing a interploation cut and a very rough surface is present. Then the speed loop gain
(VR3 & VR9) need adjustment. The best method of adjustment is to cut a 45 degree line. If steps are seen
through out the cut adjust VR3 & VR9 until the line is smooth. Adjust one axis at a time, and one pot at a
time.
a) In the following diagram indicates that the speed loop gain needs adjustment.
Y
Y
X
VR3 & VR9
needs
adjustment
X
Doesn’t
need
adjustment
4. There may also be a mechanical problem causing the interpolation problem. There is only so much we
can do with the adjustment on the drives. The other possibilites are pitch error and backlash.
a) In the following diagram indicates a problem with backlash in the machine.
Y
Y
X
X
b) In the following diagram indicates a problem with pitch error in the machine. Although VR9 ( speed
loop gain) can be adjusted to see if it helps. But usually it is a pitch error problem.
Y
Y
X
X

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