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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.
Motion Smoothing
The CDS-3310 controller allows the smoothing of the velocity profile to reduce the mechanical
vibration of the system.
Trapezoidal velocity profiles have acceleration rates which change abruptly from zero to maximum
value. The discontinuous acceleration results in jerk which causes vibration. The smoothing of the
acceleration profile leads to a continuous acceleration profile and reduces the mechanical shock and
vibration.
Using the IT Command:
When operating with servo motors, motion smoothing can be accomplished with the IT command.
These commands filter the acceleration and deceleration functions to produce a smooth velocity
profile. The resulting velocity profile, has continuous acceleration and results in reduced mechanical
vibrations.
The smoothing function is specified by the following command:
The command, IT, is used for smoothing independent moves of the type JG, PR, PA.
CDS-3310
Instruction
#DUALOOP
CE 0
DE0
PR 40000
BGA
#CORRECT
AMA
v1=10000-_DEA
v2=-_TEA/4+v1
JP#END,@ABS[v2]<2
PR v2*4
BGA
JP#CORRECT
#END
EN
IT a,b,c,d
Interpretation
Label
Configure encoder
Set initial value
Main move
Start motion
Correction loop
Wait for motion completion
Find linear encoder error
Compensate for motor error
Exit if error is small
Correction move
Start correction
Repeat
Independent time constant
Chapter 6 Programming Motion
i
11
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