following error goes to 32767 before motion is even commanded!

[RVallieu]

I had everything working yesterday on this motion stage:

PCI-7356

LV233 stepper

US Digital encoder

Primatics Drive

Now today when I connected everything using Phoenix Contact varioconnectors - the following error is going to the maximum amount as soon as the board is initialized and the loop control set to Closed.

I triple checked my connections and the encoder is wired properly - why would the following error go to maximum before any motion is even commanded?

[Jochen]

So far I have seen this behavior only with servo motors where the direction of the encoder feedback was reversed to the move direction. In fact I can't imagine how this problem should occurr with a stepper motor as there is no PID control running.

Have you tried to reset the board? Have you powered down the PC and does this issue occurr after rebooting?
What about the motor's position? Does it move?

Best regards,

Jochen Klier
National Instruments Germany

[RVallieu]

I have powered down the PC and rebooted.

I rewired this morning again.  Still the same issue.

I am programmatically resetting the controller, enabling the axes, loading the steps and counts, setting the polarity of the encoders (just tried adding this morning to the code), enabling the encoders.

The Load Steps Load Counts VI is working (no errors returned).  Is there a way to read the card to make sure that these values ARE in fact being stored?

It's driving me crazy since I ran 2000 cycles on the rotary axis from 0-90 degrees 2 days ago.  I come back the next day - use connectors to connect the wires in the same patterns and now it doesn't work.  Just this morning I took the connectors out of the equation again and am looking at the Primatics cabling guide and the encoder cabling just to quintuple check my connections....

[RVallieu]

Something else strange is happening when I try to use MAX to interactively control an axis - it won't let me change the following error!!  I can change the setting in the Following Error field, then click save, initialize the controller, go to the interactive tab for that axis and it still shuts off at the OLD following error limit of 100.

[Jochen]

Which version of NI-Motion are you using? I'm not aware of bugs that could cause exactly this behavior but still it makes sense to install the latest version which is 7.4.

I hope that helps,

Jochen

[RVallieu]

7.4.0.3002

Updated the firmware when the board was installed in the PC.

[Jochen]

I'd wish to be able to see what's going on with your system!
I'm sure you have checked the settings in MAX a hundred times by now but please have a look at this link and verify that you have configured everything correctly for closed loop operation.
Maybe it's a good idea to create new settings for your board in MAX and configure everything again from the scratch.

You also should try to do all tests in MAX exclusively without using your own software until your motor is moving correctly.

By the way: Does the motor move correctly in open loop mode?

[RVallieu]

Yes the motor moves perfectly in open loop mode, it goes exactly where commanded, in the directions expected.

My limit and home search VI's work perfectly - it's just when commanding to move in feedback mode starting yesterday...

I am reinstalling the NI-Motion driver, and I will try reconfiguring the board from scratch.

If this was a system that was not for a customer - I would be tempted to just run in open loop mode - but they want to use closed loop feedback 😉

[RVallieu]

Even though the system is supposed to account for the number of motor steps/revolution and encoder counter/revolution - is there a limit to the amount of micro-stepping that can be applied?

My drive is set-up for micro-stepping the 1.8 degree stepper motors at 50,000 micro-steps per revolution.

[Jochen]

As the motion control board doesn't care about the microstepping it doesn't limit this value. Still 50,000 steps per revolution is quite tough in terms of physical limitations of the motor and the drive. I have seen a lot of drive/motor combinations that allow extremely high microstepping settings like this one and none of them has been able to reach the angular resolution that the microstepping value suggests.

We have done some measurements with a laser interferometer and the results showed that within the distance of a full step the microsteps were distributed in a highly non-linear way. In general more expensive systems did better than cheap systems but in general it's a good idea not to believe that you really can reach the theoretical accuracy of extremely high microstepping rates.

Jochen