Rockwell Automation 1784-PM16SE SoftLogix Motion Card Setup and Configuration Manual - Manual (Page 140)

Publication 1784-UM003A-EN-P – June 2003
132 Naming & Configuring Your Motion Axis
While the Pos I Gain, if employed, is typically established by the automatic
servo tuning procedure (in the Tuning tab of this dialog), the Pos I Gain value
may also be set manually. Before doing this it must be stressed that the Output
Scaling factor for the axis must be established for the drive system. Once this
is done, the Pos I Gain can be computed based on the current or computed
value for the Pos P Gain using the following formula:
Pos I Gain = .025 * 0.001 Sec/mSec * (Pos P Gain)2
Assuming a Pos P Gain value of 100 Sec-1 this results in a Pos I Gain value of
2.5 ~0.1 mSec-1 - Sec-1.
Proportional (Velocity) Gain
Note: This parameter is enabled for all loop types except Torque loop.
Velocity Error is multiplied by the Velocity Proportional Gain to produce a
component to the Servo Output or Torque Command that ultimately attempts
to correct for the velocity error, creating a damping effect. Thus, increasing the
Velocity Proportional Gain results in smoother motion, enhanced acceleration,
reduced overshoot, and greater system stability. However, too much Velocity
Proportional Gain leads to high frequency instability and resonance effects.
If you know the desired unity gain bandwidth of the velocity servo in Hertz,
you can use the following formula to calculate the corresponding P gain.
Velocity P Gain = Bandwidth (Hertz) / 6.28
The typical value for the Velocity Proportional Gain is 250.
Integral (Velocity) Gain
Note: This parameter is enabled for all loop types except Torque loop.
At every servo update the current Velocity Error is accumulated in a variable
called the Velocity Integral Error. This value is multiplied by the Velocity
Integral Gain to produce a component to the Servo Output or Torque
Command that attempts to correct for the velocity error. The higher the Vel I
Gain value, the faster the axis is driven to the zero Velocity Error condition.
Unfortunately, I Gain control is intrinsically unstable. Too much I Gain results
in axis oscillation and servo instability.
In certain cases, Vel 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.