Delta MMC120 - Manual (Page 115)

115
DIFFERENTIAL GAIN
Default: 0
Range: 0 to 65535
The DIFFERENTIAL GAIN field is used to minimize the error between the TARGET
POSITION and the ACTUAL POSITION . The change in error is multiplied by the
DIFFERENTIAL GAIN value to get the differentiator drive term. DIFFERENTIAL
GAIN is defined as:
DIFFERENTIAL GAIN = 0.1 millivolts per change in Position Error
Differential Drive is defined as:
Differential Drive = (E0 - E1) x DIFFERENTIAL GAIN / 10
where E0 is the position error ( TARGET POSITION – ACTUAL POSITION ) in the first
time period and E1 is the position error in the second time period. (E0 - E1) is the change
in position error between the two time periods.
NOTE: The actual drive output may be reduced based on the values of the Extend Feed
Forward and Retract Feed Forward .
CAUTION: To avoid oscillation during initial tuning start with values below 10.
Why Bother?
The differentiator field should usually be set to a value of 0. This is because noise in the
MDT signals causes the speed calculations to be noisy.
EXTEND FEED FORWARD
Default: 100
Range: 0 to 65535
TIP: After the axis has made a complete move without oscillations or overdrive errors,
use the 'F' command to automatically set the FEED FORWARD value.
FEED FORWARD is an open loop compensation that is proportional to the TARGET
SPEED of the axis. This value is expressed in terms of millivolts per 1,000 Position
Units per second. EXTEND FEED FORWARD drive is added to the output only when
the axis is extending. The drive output provided by the EXTEND FEED FORWARD is
determined as follows:
Feed Forward Drive = EXTEND FEED FORWARD x TARGET
SPEED
1,000
You can find the appropriate value for EXTEND FEED FORWARD by making a move