Rockwell Automation 8520-ARM2 9/Series CNC AMP Reference Manual Documentation Set - Manual (Page 182)

Servo Parameters
Chapter 7
7-36
Function
This parameter specifies the servo loop gain at speeds below the gain
break speed.
Gain is a function of the drives, servo motors, and machine. For example,
many machines are sized with drives and motors so that the axes can run at
a gain of 1 (0.001mm of following error for each 1 mmpm of feedrate) up
to the machine’s specified maximum cutting speed.
Typical values for the Initial Gain are between 0.5 and 2.0 (most CNC
machines use a value of 1).
Smaller values produce a “loose” system (characterized by large, heavy, or
underpowered axes). The benefits of smaller gains are improved control
over surface finish and reduced stress on the machine.
Larger values produce a “tight” system (characterized by small, light,
quick axes). The benefits of higher gains are faster response and increased
rigidity.
The relationship between following error and system gain is shown in the
following equation:
Feedrate (mmpm or ipm)
Gain = --------------------------------
Following Error (0.001 mm or in)
Gain is sometimes discussed in units of inverse milliseconds. It is often
necessary to know the Initial Gain of Position Loop in units of inverse
milliseconds when making comparisons to other parameters in this section.
To represent the value entered here in inverse milliseconds:
60
gain (in inverse milliseconds) = -------------------------
Initial Gain Position Loop
Table 7.A
Examples of Initial Gain Values and the Resulting Following Error
Initial Gain Following Error per mmpm of Velocity Initial Gain in inverse msec
0.25 0.0040 mm 240 invrs msec
0.50 0.0020 mm 120 invrs msec
1.00 0.0010 mm 60 invrs msec
2.00 0.0005 mm 30 invrs msec
7.2.8
Initial Gain of Position Loop