Rockwell Automation 1784-PM16SE SoftLogix Motion Card Setup and Configuration Manual - Manual (Page 145)

Publication 1784-UM003A-EN-P – June 2003
Naming & Configuring Your Motion Axis 137
Output tab of this dialog box). 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 only for external drives configured for
Torque loop operation in the Servo tab of this dialog box.
Velocity Error is multiplied by the Velocity Proportional Gain to produce a
component to the 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.
Vel P Gain = Bandwidth (Hertz) / 6.28
The typical value for the Velocity Proportional Gain is ~250 mSec-1.
Integral (Velocity) Gain
Note: This parameter is enabled only for external drives configured for
Torque loop operation in the Servo tab of this dialog box.
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 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.