Rockwell Automation 1784-PM16SE SoftLogix Motion Card Setup and Configuration Manual - Manual (Page 139)

Publication 1784-UM003A-EN-P – June 2003
Naming & Configuring Your Motion Axis 131
Proportional (Position) Gain
Position Error is multiplied by the Position Loop Proportional Gain, or Pos P
Gain, to produce a component to the Velocity Command that ultimately
attempts to correct for the position error. Too little Pos P Gain results in
excessively compliant, or mushy, axis behavior. Too large a Pos P Gain, on the
other hand, can result in axis oscillation due to classical servo instability.
To set the gain manually, you must first set the appropriate output scaling
factor (either the Velocity Scaling factor or Torque Scaling factor) in the
Output tab of this dialog. Your selection of External Drive Configuration type
– either Torque or Velocity – in the Servo tab of this dialog determines which
scaling factor you must configure before manually setting gains.
If you know the desired loop gain in inches per minute per mil or millimeters
per minute per mil, use the following formula to calculate the corresponding P
gain:
Pos P Gain = 16.667 * Desired Loop Gain (IPM/mil)
If you know the desired unity gain bandwidth of the position servo in Hertz,
use the following formula to calculate the corresponding P gain:
Pos P Gain = Bandwidth (Hertz) * 6.28
The typical value for the Position Proportional Gain is ~100 Sec-1.
Integral (Position) Gain
The Integral (i.e., summation) of Position Error is multiplied by the Position
Loop Integral Gain, or Pos I Gain, to produce a component to the Velocity
Command that ultimately attempts to correct for the position error. Pos I Gain
improves the steady-state positioning performance of the system. Increasing
the integral gain generally increases the ultimate positioning accuracy of the
system. Excessive integral gain, however, results in system instability.
In certain cases, Pos I Gain control is disabled. One such case is when the
servo output to the axis’ drive is saturated. Continuing integral control
behavior in this case would only exacerbate the situation. When the Integrator
Hold parameter is set to Enabled, the servo loop automatically disables the
integrator during commanded motion.