open loop stop

So I have been using open loop for reasons. I was using the quick move and at the end there was some position hunting going on. So I am trying to do rate (10) then stop (2). speed 7, Halt has been from 3.5 to 7. The same move over and over stops anywhere within 4 inches? Why if told to ramp stop at a certain position, I get random end positions.

I am actually using (RMC150) command 15, but sending command 2 before the closed loop decell happens.

Is it possible that my wanting to use an absolute command is affecting my stop point?

In open loop, it is very difficult to get accurate final positions. There are other ways to prevent hunting, such as using the Deadband Tolerance. If you post some plots, I can probably give some more detailed direction.

Jacob, what kind of plots to do you want? Just quick moves?

My biggest problem with this axis is there is something like 8 ton being pulled back and forth with a hydraulic motor, and to tune there is a certain amount of slack to gather before the work happens.

There a possibly a few things to try, such as output deadband or differential gain. Both open loop plots and closed-loop plots would be useful.

Plot1.rmcplots (1.57 MB)

This is quick move… Ugly

It appears that your resolution is only 0.1 in. (assuming the feedback is in inches). This seems to be a major source of your problems. I would try some fairly heayy feedback filtering. Set the Velocity and Accel Filter Types to Low Pass, then set the Actual Position, Velocity and Acceleration filters to the same value. Try 30 Hz or so to begin with. You may need to decrease it.

Oh shoot I thought I had it set to 1 inch. Thanks I’ll make the changes.

Retrieve.rmcplots (3.83 MB)
Much better. I can’t get it to stop over shooting or quickly recover from it. Any more I add to the Prop, Int or Der Causes back and forth hunting.

Can you lower the decel rate? Sometimes that can help.

Decel is right now at 144. That is starting at 12 inches right? I’m just not sure it means to set the value at PU squared?

Decel is right now at 144. I changed the pu to 1.0 inch. So decel is starting at 12 inches right? I’m just not sure what it means to set the value at PU squared?

I am going to be in the Delta house in May. I will stay over to get truly get it. If you will do it let me know.

I think CharlesM has it right. Try setting the command deceleration to 10 and see what happens.

I set it to 10. It overshot by about a foot, then over corrected past by 8 inches the back past by about 6 inches until it hit the mark.

Hmmm… If you attach plots, it makes it easier for me to say something coherent.

Have you tried using the Output Filter (grouped with the gains)? Your system responds quite slowly, so I think using the Output Filter will reduce the chatter problems you get when increasing the gains. Try setting the Output Filter to 5.

decel 10.rmcplots (4.07 MB)

filter at 5 delel at 10.

It appears that you are sending some commands repeatedly. Motion works best if you send a motion command once, not many times in a row. You can see that the Target Velocity is starting over many times, and that, coupled with the noise ont he system , is causing the Target Position to do do strange things.