Hypertherm Phoenix 8.0 - Manual (Page 450)

Motion Overview
443
Now that you have some basic control of the system, set up the Watch Window to display
Position and Following Error for the selected Axes. Load and automatically “Trial” the
Test Pattern simple shape from the shape library. You will be able to follow the response
of the system by watching the performance of the Motor /Encoder feedback and its ability
to maintain path on the control preview screen.
Systematically increase Proportional Gain until it has little or no effect on the following
error or until instability becomes noticeable. Then reduce Proportional Gain to eliminate
instability. Derivative Gain may be used to provide a dampening effect. For a Velocity
Loop Servo Drive, Integral Gain should be set to zero. After tuning for the best response,
increase Feed Forward Gain systematically to further reduce following error if necessary.
It is not required that you eliminate following error but it is wise to ensure that Following
Error for each axis is similar. Please Note: Feed Forward Gain will reduce steady state
following error, but may cause overshoot.
It is important to note that some following error is desirable, following error terms should
be nearly the same from one axis to another, and the polarity of the following error term
must be the same as the direction of travel.
Finally, check the system tuning by placing a pen on the system. “Draw” the test pattern
provided in the simple shape library and observe the cornering capability, arc/ circle
contouring and the ability to position at the center crossings. When troubleshooting
tuning issues, varying the size and trial speed can often provide valuable information
through observations of the pen tracing.
After the system has been successfully tuned, adjust the Servo Error Tolerance to equal
twice the normal Following Error for the axes (note: This is a common approach to
setting the Servo Error Tolerance but is up to the discretion of the service agent) . This is
allows the system to operate without nuisance faults caused by temporary resistance to
the motion, such as dirt on motion rails or temporary tension from motor cabling, etc.
Procedure for Current Type Drives
Similar to tuning for Velocity Type Drives, the recommended tuning procedure focuses
on response of the motion. The process begins with low initial values that are increased
to get a desired response. If the axes start to vibrate or oscillate, this indicates the
selected gain value is too high and should be lowered. It is recommended that basic
tuning start with the motors disengaged from the machine to allow the user to confirm
controlled motion and response of the motion axes. Motors can then be engaged to fine
tune for desired performance.
Set up the Watch Window to display Position and Following Error for the selected Axes.
Load and automatically “Trial” the Test Pattern simple shape from the shape library.
You will be able to follow the response of the system by watching the performance of the
Motor /Encoder feedback and its ability to maintain path on the control preview screen.