softmotion

[mfi.edu.my]

Dear all,

Who has any experience with National instrument soft motion. Try to
design my own controller on the motion system. Starting with PID. I ve
try the available program. It seems rather straight forward. At first,
I can not get my motor to work. Then problem settled when I adjust the
bit of my fielpoint. My biggest problem now, the motor is jerking when
it try to meet the target position. Mine is position control on torque
mode.

TQ

[Jasper S]

Sadiah,

Does your motor constantly "jerk" or do you just see this behavior when it starts or stops a move?  Are you moving in a straight line, contour, doing a blend?  Have you set up the timing correctly?  You will need to configure your SoftMotion timing settings to correlate with the rates that both your RT and FPGA VIs are running. 

Finally, you may want to make sure your PID rates have been set up correctly.

Regards,

Jasper S

[mfi.edu.my]

Dear Jasper,

Hear my answer to your questions. Hope your answer will help me going with the project.

1.  Does your motor constantly "jerk" or do you just see this behavior when it starts or stops a move? 

The motor is constantly jerking, but finally get to the set position.

2.  Are you moving in a straight line, contour, doing a blend? 

I am still starting with a straight line.

3. Have you set up the timing correctly? 

How do I go about this?

4.  You will need to configure your SoftMotion timing settings to correlate with the rates that both your RT and FPGA VIs are running. 

I am using FP2000, FPAIO610, FPQUAD560. How do I go about this

5. Finally, you may want to make sure your PID rates have been set up correctly.

Is there any good reference on this?

I am still a novice in thisfield of automation. So many things to catch up.

Thanks.

SADIAH

[Jasper S]

Sadiah,

From the looks of your reply, it appears you are just using the PID toolkit with FieldPoint hardware.  Is this the case?  Or are you using SoftMotion as well?

Regards,

Jasper S

[mfi.edu.my]

Atually there are two things that I am doing.

1. System identification using open loop excitation todetermine the dynamic model of the plant. My model does not seem accurate since log data does not match with the simulated data using Sys. Identification toolkits. Why? Does it anything to do with the system model eg. ARX, ARMAX or State space. Then the design the controller for the system using control design toolkits.

2. Secondly, I am using the softmotion to for the system motion tracking. The motor runs in "jerk" mode eventhough it reach the final position. Then would like to implement fuzzy logic controller.

Please advice.

SADIAH

[Jasper S]

Sadiah,

I apologize for the suggestion of changing the loop rates, I did not realize you were using a FieldPoint RT target.

Are you using the example from the LabVIEW example finder, Multiple Axes Straight Line Move?  And using the VIs cFP Motion Loop and cFP Main?  What did you adjust the fieldpoint controller that enabled the example to work?

Thanks,

Jasper S

[mfi.edu.my]

And using the VIs cFP Motion Loop and cFP Main? 

Yes

What did you adjust the fieldpoint controller that enabled the example to work?

The gain 20V/2^12  instead of 20V/2^16 as the original program. At high or low voltage input, the motor is still jerking. At high torque the motor did not meet the setpoint distance but at lower speed it does, but the output profile is very poor. I do not know whaT else to do. Does it mean, some adjusment needed on the program.

When I did my system identification (torque mode), the motor is not jerking, but the logged output (position) does not agree with the simulated model output.

SADIAH

[Jasper S]

Sadiah,

Have you modified the example program to include system identification code?  If so, you may have a situation where the timed loop is not executing in the time requested.  The timed loop has a boolean output that indicates whether or not it executed in the allotted time.

You should also ensure that your PID control values are set up appropriately.  PID Theory Explained is a wonderful resource on this topic.

Regards,

Jasper S

[mfi.edu.my]

Dear Jasper,

How do  I check on the time loop?

Can you assure me here, that I should not have problems with fieldpoint with ac servomotor control.

I have used the program by Mr Finn Haugen of Teachtech co on the system identification.

TQ.

[Jasper S]

TQ,

The timed loop structure has an output (within the loop) called finished late?  This boolean will indicate to you whether or not the previous

iteration of the loop finished within the requested time.