Delta MMC120 - Manual (Page 19)

19
PROPORTIONAL GAIN affects the responsiveness of the system. Low gains make the
system sluggish and unresponsive. Gains that are too high make the axis oscillate or
vibrate. You can adjust the PROPORTIONAL GAIN by slowly increasing it and moving
the axis. When you see a tendency to oscillate as the axis moves or stops, reduce the gain
by 10 to 30 percent.
Many hydraulic systems do not require
INTEGRAL GAIN or DIFFERENTIAL GAIN .
However, it is usually desirable to have some INTEGRAL GAIN (5 to 50 counts) to help
compensate for valve null drift or changes in system dynamics. Some systems may
require larger INTEGRAL GAIN , in particular if they are moving a large mass or are
nonlinear. Too much INTEGRAL GAIN will cause oscillations.
DIFFERENTIAL GAIN is used mainly on systems that have a tendency to oscillate.
This happens when heavy loads are moved with relatively small cylinders.
DIFFERENTIAL GAIN will tend to dampen out oscillations and help the axis track
during acceleration and deceleration. If you use DIFFERENTIAL GAIN , you may be
able to increase the PROPORTIONAL GAIN somewhat without causing the system to
oscillate.
A disadvantage to
DIFFERENTIAL GAIN is that it amplifies position measurement
noise which can cause the system to chatter or oscillate if the gain is too high or there is
too much noise.
The
ACCELERATION FEED FORWARD terms are particularly useful for axes which
move large masses with relatively small cylinders. This combination delays the start of
movement, and the ACCELERATION FEED FORWARD terms can help compensate
for this delay. ACCELERATION FEED FORWARDS are easiest to adjust with the PID
gains set low and the VELOCITY FEED FORWARDS adjusted properly. After
commanding a move, plot the move using the monitor program and look for a following
error during the acceleration. Increase the ACCELERATION FEED FORWARD until
the error disappears. For large masses the ACCELERATION FEED FORWARD can be
in the tens of thousands.
If the axis hunts around the set point, you can increase the
DEAD BAND ELIMINATOR
value slowly until the hunting stops or the axis starts to oscillate. If it oscillates, reduce
the DEAD BAND ELIMINATOR value.
If the axis gets no following errors, reduce the FOLLOWING ERROR until errors start to
occur then adjust the FEED FORWARD gains.
Increase the SPEED and ACCELERATION values gradually while making long moves.
Use the monitor program to plot the moves and look for following errors, overshoot, or
oscillations. Eventually, when the SPEED and ACCELERATIONS are too high, the
moves will cause an error on the axis.
If an overdrive error occurs, there is not enough drive capacity to drive the axis at the
requested SPEED . Should this occur, reduce the SPEED . If a following error occurs, the
appropriate FEED FORWARD must be increased. If the FOLLOWING ERROR occurs
on an extend move, increase the EXTEND FEED FORWARD ; it the error occurs on a
retract move, increase the RETRACT FEED FORWARD . If this doesn't solve the
problem, the ACCELERATION and DECELERATION ramps are too steep for the
response of the system. Their values can be reduced, or the ACCEL FEED FORWARD
terms can be increased. After the problem which caused the error has been corrected,