Hypertherm V9 Series Phoenix Rev.11 - Manual (Page 212)

212 Phoenix 9.76.0 Installation and Setup Manual 806410
9 – Motion Control
Velocity Gain
When using a current loop amplifier, the internal velocity loop in the control can provide dampening without an external
tachometer.
Using the internal velocity loop with a current loop amplifier can result in higher static stiffness, smoother machine motion,
and less overshoot.
Tuning Procedures
Using the information previously provided as a core understanding of the position loop process, we can now look at
tuning motion for the desired motion performance. Due to potential safety hazards and the potential possibility for
machine damage from incorrect tuning, it is recommended that this operation be performed by trained and experienced
personnel.
Prior to performing motion tuning, values for DAC polarity, encoder polarity and maximum machine speed should be
calculated and entered into control setups. Servo Error Tolerance for the axes should be set to maximum (5 inch max for
X/Y motion).
Initially, you should start basic tuning with the motors disengaged from the machine to allow you to confirm controlled
motion and the response of the motion axes. An initial acceleration rate of 10 Mg can be used to begin the motion tuning.
It is important to remember that after the motors are engaged to the machine for motion, the load requirements for each
axis will change and require additional tuning. Additionally, if the acceleration rate is increased after the initial tuning,
additional adjustments to gain tuning may be required for proper machine motion.
Tuning for Velocity Drives
You should tune the system by performing manual moves at a slow speed with all gains set to zero with the exception of
proportional gain. Proportional gain should start with a small value of 10. Engage the motors to the machine frame and
beginning raising the proportional gain to allow movement. If the axes start to vibrate or oscillate, this indicates the
selected gain value is too high and should be lowered. It may also require de-tuning the response of the drive amplifier.
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 cut the Test Pattern simple shape from the shape library in trial mode. 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 in the preview window.
Systematically increase the value for proportional gain until it has little or no effect on the following error or until instability
becomes noticeable. Then reduce the value for 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. You do not have to
eliminate following error but you should ensure that following error for each axis is similar.
 Feed forward gain reduces 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, vary the size and trial speed to observe the mark of the pen.