Machine Cutting 1 - 2mm short semi frequently

Good Day all,
I hope I selected the correct category.

We have a simple 1 axis machine with 2 limit switches. The axis is a ball screw that moves an arm up and down according to user input. The machine's computer runs on Linuxcnc with our own front end software. The linux software is Debian 12. The motor is driven by a Wantai DQ860HA drive and the drive is controlled by a DB25-1205 breakout board.

We recently upgraded the machine to the latest linuxcnc and debian 12 from a previous linuxcnc and ubuntu install. The machine is about 8 to 10 years old with the original motherboard and processor that was installed when the machine was manufactured. 

Since the software upgrade, every 4 or 5th movement is short by 1-2mm. This shortness is not temporary and the machine stays out of calibration(every movement after is short by the same amount) until the machine is recalibrated through the software. The machine will then operate as normal until it gets the fault again and needs to be re-calibrated.

We have added more noise reduction such as running limits through a relay module and adding a better cable with ferrite cores to the step and direction signals as we initially thought it was a noise issue. We have also tried lowering the BASE_PERIOD and the machine's feed speeds and velocities as we thought there might be a timing miscommunication between the new software and old hardware.

None of this has removed the fault and we are at a loss as what to try next.

Any help or recommendations will be greatly appreciated, should you need more information please let me know.

Hi Tommy.

I implemented the changes you suggested except for those done on the Bios as I do not have access to it over AnyDesk.
After implementing the machine would home correctly as normal, but when running to a set distance the arm would halt after moving about 20 mm and give an error, "joint 0 following error" and this process of moving slightly and giving error happens every time any distance is entered. I also received latency warnings for 100000. I have attached a picture of the errors.

I reverted the settings back one by one and machine ran as it did before only after all changes were reverted. These were the changes I made:

• Base_Period = 100000 >>> set back to 500
• Drive microstepping = 1600 >>> set back to 2000 pul/rev 
• Parport reset time = 10000 >>> set back to 500
• I added STEP_SPACE and STEP_TIME to the "EMCMOT" section as I did not already have it in the ini file. STEP_SPACE & STEP_TIME = 0.00001 >>> I removed these two settings after.

Any thoughts on how to proceed? Thank you for your input so far.
 

Thank you very much, I will try those fixes and get back to you.

I also wanted to mention that when we manufacture this machine with new pc hardware and this new software we get the latency warnings but the machine performs without issues. I don't know if that is relevant or not.

Hi Tommy.

I implemented the changes you suggested except for those done on the Bios as I do not have access to it over AnyDesk.
After implementing the machine would home correctly as normal, but when running to a set distance the arm would halt after moving about 20 mm and give an error, "joint 0 following error" and this process of moving slightly and giving error happens every time any distance is entered. I also received latency warnings for 100000. I have attached a picture of the errors.

I reverted the settings back one by one and machine ran as it did before only after all changes were reverted. These were the changes I made:

• Base_Period = 100000 >>> set back to 500
• Drive microstepping = 1600 >>> set back to 2000 pul/rev 
• Parport reset time = 10000 >>> set back to 500
• I added STEP_SPACE and STEP_TIME to the "EMCMOT" section as I did not already have it in the ini file. STEP_SPACE & STEP_TIME = 0.00001 >>> I removed these two settings after.
  
  Any thoughts on how to proceed? Thank you for your input so far

If you have errors with a base period (not frequency) of 100000 reducing it will not fix it, it will only make the issue worse.

What you will need to do is run a latency test and see how things are going.
The first error that shows in your picture is a latency error, that need addressing first, you will need to set a very high base period and slowly work backwards.

A base period of 500 would yield a base frequency of about 2Mhz, a 250000 base period would yield a base frequency of 40kHz. The larger the base period the slower the base frequency.

If you were getting errors at at base period of 100000 i would double this to see how things are, you may reach a stage where the base period is so high that the machine may not be usable with the hardware\OS combo.

At some stage you may have to get access to the BIOS.

Be aware that when timings are talked about they are in nano seconds, it does make things easier if that convention is kept.