Rockwell Automation 1784-PM16SE SoftLogix Motion Card Setup and Configuration Manual - Manual (Page 348)

Publication 1784-UM003A-EN-P – June 2003
340 Motion Object Attributes
The servo output limit may also be used if the drive cannot accept the full ±10
Volt range of the servo output. In this case, the servo output limit value
effectively limits the maximum command sent to the amplifier. For example, if
the drive can only accept command signals up to ±7.5 Volts, set the servo
output limit value to 7.5 volts.
Servo Offsets This section covers the various servo attributes that provide offsets to
real-time servo loop operation.
Friction Compensation It is not unusual for an axis to have enough static friction, so called “sticktion”,
that even with a significant position error, refuses to budge. Of coarse, integral
gain can be used to generate enough output to the drive to correct the error,
but this approach may not be responsive enough for the application. An
alternative is to use Friction Compensation to break sticktion in the presence
of a non-zero position error. This is done by adding, or subtracting, a fixed
output level, called Friction Compensation, to the Servo Output value based
on its current sign.
The Friction Compensation value should be just under the value that would
break the sticktion. A larger value will result in the Axis to “dither”, a
phenomena describing a rapid back and forth motion of the axis centered on
the commanded position.
Velocity Offset Velocity Offset compensation can be used to correct to provide a dynamic
velocity correction to the output of the position servo loop. Since this value is
updated synchronously every Coarse Update Period, the Velocity Offset can
be tied into custom outer control loop algorithms using Function Block
programming.
GSV/SSV Access Attribute Name Data Type Values
SSV/GSV Output Limit REAL Volts
Range: 0.0 - 10.0
GSV/SSV Access Attribute Name Data Type Values
SSV/GSV Friction Compensation REAL %
Range: - 0% to 100%
GSV/SSV Access Attribute Name Data Type Values
SSV/GSV Velocity Offset REAL Position Units per sec.