Rockwell Automation 1784-PM16SE SoftLogix Motion Card Setup and Configuration Manual - Manual (Page 341)

Publication 1784-UM003A-EN-P – June 2003
Motion Object Attributes 333
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. Another common
case is when performing certain motion. -. When the Integrator Hold Enable
attribute is set, the servo loop automatically disables the integrator during
commanded motion.
While the Pos I Gain, if employed, is typically established by the automatic
servo tuning procedure, 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. Refer to Output Scaling attribute
description for an explanation of how the Output Scaling factor can be
calculated. 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 = 0.25 * 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
.
Velocity Proportional Gain When configured for a torque (current) loop servo drive, the servo module’s
digital velocity loop provides damping without the requirement for an analog
tachometer. The 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 the damping
effect. Thus, increasing the Velocity Proportional Gain results in smoother
motion, enhanced acceleration, reduced overshoot, and greater system
stability. The velocity loop also allows higher effective position loop gain
values to be used, however, too much Velocity Proportional Gain leads to high
frequency instability and resonance effects. Note that units for Velocity
Proportional Gain are identical to that of the Position Proportional Gain
making it easy to perform classic inches/min/mil calculations to determine
static stiffness or damping.
GSV/SSV Access Attribute Name Data Type Values
SSV/GSV Position Integral Gain REAL 1/mSec-Sec
GSV/SSV Access Attribute Name Data Type Values
SSV/GSV Velocity Proportional Gain REAL 1/Sec