Delta MMC120 User Manual download pdf (Page 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,youmaybe

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

toomuchnoise.

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.Ifafollowing 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,

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Delta MMC120 User Manual Page 19

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