TECHNICAL REFERENCE
MOTION PROGRAMMING
CONTOURING, DUAL LOOP
The contour mode bypasses the DMC motion profiler
and prescribes an arbitrary position trajectory. Position
increments (CD) over a time interval (DT) are specified
for each axis. The contour mode is useful when complex
and computer-generated trajectories must be followed. An
automatic data recording feature allows the DMC to
"learn" a path then follow it in the contour mode.
CONTOURING
DUAL LOOP
INSTRUCTION
INTERPRETATION
#RECORD
Begin program to record
DM XPOS[501]
Dimension array
RA XPOS[ ]
Specify automatic data record
RD_TPX
Specify X position for capture
MOX
Turn motor off for teach
RC2
Begin recording every 4 msec
#A;JP#A,_RC=1
Continue until done recording
#COMPUTE
Compute program
DM DX[500]
Define new array
C=0
Initialize array counter
#L
Loop label
D=C+1
DELTA=XPOS[D]-XPOS[C] Compute difference
DX[C]=DELTA
Store difference in array
C=C+1
Increment counter
JP #L,C<500
Loop until done
#PLAYBK
Playback program
SHX
Turn motor on
CMX
Contour mode on X
DT2
Specify time interval
I=0
Initialize array counter
#B
Loop label
CD DX[I];WC
Specify contour distance
I=I+1
Increment counter
JP #B,I<500
Loop until done
EN
End program
Example--Contouring
The sampled dual loop performs the correction at the end of
the move, as illustrated by the example. Consider a linear
slide driven by a leadscrew. The slide is equipped with a lin-
ear encoder having a resolution of 1 micron and a rotary
encoder which provides 4 counts per micron. The control
method is to close the loop with the rotary encoder and
monitor the linear encoder by the auxiliary encoder input.
To perform a move of 10,000 microns, the motor is driven
40,000 counts. Once the motion is complete, the linear
encoder is observed with the DE command and the position
error of the load is monitored. The motor is then required to
perform a correction move.
INSTRUCTION
INTERPRETATION
#DUAL
Label
DE 0
Set load position load to zero
PR 40000
Distance
BGX
Start first move
AMX
Wait for completion
WT 20
Wait for settling if necessary
PR 4*(10000-_DEX) Correction move
BGX
Start correction
EN
End program
Example--Dual Loop
The dual-loop encoder feature enables the DMC to com-
pensate for backlash. There are two compensation methods:
continuous dual loop which performs the correction along
the move; and sampled dual loop which performs the cor-
rection at the final point.
In both cases, two encoders are used for each axis: one
mounted on the motor and the other on the load. The
continuous dual loop, which is activated with the instruc-
tion DV1, closes the position loop with the load encoder
and derives the damping terms from the motor encoder.
This method provides backlash compensation along the
motion path.
92
·
Galil Motion Control, Inc.
·
www.galilmc.com
