CNC Router with Clearpath Servos - X axis fault

I recently purchased a used 4 x 4 cnc router of unknown brand (DIY?) It has Clearpath Servos. Every was running great, I did 3 or 4 signs without any issues. Then halfway through on the 2nd of 2 identical signs, it faults (yellow light on clearpath) on the x axis (across the gantry). I reset it and it jogs fine...sometimes. It faults again sometimes right away when I'm jogging it back and forth and then other times not until 15 minutes after I restart the program. It is running Mach3.

In trying to diagnose the problem, I have:

1. Swapped the wires on x and y and its still faults on the original x axis.

2. Swapped x and y servos, it faulted on the y axis with the original x axis motor.

3. Bought a new motor for x axis and after autotuning it, this new motor faults as well.

It always faults within 12" or so from the left side limit of the gantry.

I'm not sure what to check next? Any help would be appreciated!

Thanks!
Geoff

Hi,
if I'm not mistaken you can plug into the servo with a programming cable and view the error message log. That would give you a better idea of what the
fault is. At a guess I would say you have the 'following error window' programmed too tightly.

Craig

Check for a mechanical problem - see if the axis slides freely when disengaged, and carefully inspect any couplers for slippage.

Thanks!

So I did hook it to a laptop and using the Clearpath software I got "RMS torque limit - Possible causes: excessive friction, mechanical misalignment, duty cycle to high, undersized motor".

It could be a mechanical issue. Now I just need to figure out how to diagnose that. It doesn't seem to bind or turn hard. It has supported round rails and a ball screw. I've tried to measure all the distances between but haven't figured out how to do it accurately yet.

I've attached a picture of similar rails.....question - should they be lubricated?? My other CNC router has rectangular rails with zerk fittings. Should these round rails have zerks as well. There are tapped holes in the bearings but there are set screws in them.

Hi,
try disconnecting the ballscrew, and run several programs.

If the load of the ballscrew is causing the 'RMS torque Limit' fault then it rather looks like you have an undersized motor.

Craig

I'm really hoping it's not an undersized motor. It faults while just jogging and only at the last 12" of travel (out of 48") and only sometimes. I'm starting to think my rails or the ballscrew aren't aligned properly.

And now that I'm really thinking about it.....why did the fault move to the other axis when I swapped the servos? That's why I thought it was the motor.

Now I'm confused again, I thought we were onto something!

Geoff

Hi,
then try putting an ammeter in the power supply line and observe the current as it moves. If you did that to both the faulty axis and a known good axis the amount of
current that each consumes may well tell you something about the load on each motor.

Craig

If it's always faulting at a certain spot 12" from the end of travel in X, it does sound like an issue with those linear slides. If they're misaligned, that can cause this. Try loosening the bolts that hold it down and running it and see if the fault goes away. And yes, lubrication can help. Check for rust spots as well.

But if the fault is consistently following the motor, and not the physical axis, it points to an issue somewhere up the line, especially if changing the motor didn't help. It could be that you've got a bad servo drive, or even a bad cable.

Hi,

Quote:

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It could be that you've got a bad servo drive,

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In a Clearpath servo the drive is incorporated into the servo.

Craig

I'm going to swap the x and y motors again tonight and see what happens. I'm so confused again, I swear when I swapped the motors before, the fault followed the motor.

I have Clearpath SDSK servos, I believe they still need drivers to get step and direction??

Thank You!

Please forgive my lack of knowledge....I've had my other router for 10 years and it's always just worked!

Hi,

Quote:

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I have Clearpath SDSK servos, I believe they still need drivers to get step and direction??

---

Clearpath servos have the servo drive built-in. All they require is Step/Direction signals from a motion controller and a power supply to operate.

Craig

I turned the ballscrew by hand and did notice that it turned slightly harder in the last 12" of travel (where I was getting faults). I loosened the bolts and ran the spindle over and retightened the bolts. This seems to have helped, I have run several programs with no issue. Fingers crossed that that has fixed it.

It only turned "slightly" harder by hand, is this enough to cause the motor to fault?

Should I be lubricating these round rails? Putting a zerk on the bearings?