Hypertherm Phoenix 8.0 - Manual (Page 372)

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Under a proportional loop control, the drive system applies a restoring torque to the
motor in proportion to the position error of the axis.
If proportional gain too high, the system and axis become unstable. During cutting, the
torch can overshoot the path. This is also called a “hot” control loop.
If proportional gain too low, the system response is not precise. This can be seen in the
test pattern when the outside corners become rounded and not all the circle segments
meet in the center.
Integral Gain
Integral gain improves the positioning accuracy of the control loop. Integral gain can be
used to compensate for static friction or gravity. Excessive integral gain can result in
system instability.
For most shape cutting machines, this parameter should be set to zero (0).
Derivative Gain
Derivative gain helps to minimize sudden changes in velocity. The higher the derivative
gain, the slower the response time to the control loop. For most velocity loop drives, this
parameter is set to zero (0).
Feedforward Gain
Feedforward gain can be used to drive the following error to zero during machine motion.
In all digital control loops there is a finite amount of error that is introduced by the
velocity command. Increasing feedforward gain can reduce this introduced error.
Velocity Gain
When you use a current loop amplifier, you can use the internal velocity loop in the CNC
to provide dampening without an external tachometer.
Use of the internal velocity loop with a current loop amplifier can result in higher static
stiffness, smoother machine motion, and less overshoot.
Servo Error Tolerance
Allows the user to program the amount of servo loop following error to be allowed prior
to display an error message. The parameter is limited to a maximum value of five inches.
Encoder Counts per inch
Enter a value that is the number of encoder edges per inch of machine travel. It is
possible to enter fractional encoder units and the CNC will keep track of these fractions
automatically. Encoder counts per inch are equal to the resolution of the encoder,
multiplied by the encoder revolutions per inch or mm (based on the machine drive
gearing).