Galil DMC-2X00 - Manual (Page 124)

method splits the filter function between the two encoders. It applies the KP (proportional) and KI
(integral) terms to the position error, based on the load encoder, and applies the KD (derivative) term
to the motor encoder. This method results in a stable system.
The dual loop method is activated with the instruction DV (Dual Velocity), where
DV 1,1,1,1
activates the dual loop for the four axes and
DV 0,0,0,0
disables the dual loop.
Note that the dual loop compensation depends on the backlash magnitude, and in extreme cases will
not stabilize the loop. The proposed compensation procedure is to start with KP=0, KI=0 and to
maximize the value of KD under the condition DV1. Once KD is found, increase KP gradually to a
maximum value, and finally, increase KI, if necessary.
Sampled Dual Loop
In this example, we consider a linear slide which is run by a rotary motor via a lead screw. Since the
lead screw has a backlash, it is necessary to use a linear encoder to monitor the position of the slide.
For stability reasons, it is best to use a rotary encoder on the motor.
Connect the rotary encoder to the A-axis and connect the linear encoder to the auxiliary encoder of A.
Assume that the required motion distance is one inch, and that this corresponds to 40,000 counts of the
rotary encoder and 10,000 counts of the linear encoder.
The design approach is to drive the motor a distance, which corresponds to 40,000 rotary counts. Once
the motion is complete, the controller monitors the position of the linear encoder and performs position
corrections.
This is done by the following program.
Instruction Interpretation
#DUALOOP Label
CE 0
Configure encoder
DE0 Set initial value
PR 40000 Main move
BGA Start motion
#CORRECT Correction loop
AMA Wait for motion completion
v1=10000-_DEA Find linear encoder error
v2=-_TEA/4+v1 Compensate for motor error
JP#END,@ABS[v2]<2 Exit if error is small
PR v2*4 Correction move
BGA Start correction
JP#CORRECT Repeat
#END
EN
Motion Smoothing
The DMC-2x00 controller allows the smoothing of the velocity profile to reduce the mechanical
vibration of the system.
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• Chapter 6 Programming Motion
DMC-2X00