Need help troubleshooting a Linux CNC problem

Linux
1

I recently encountered an issue with my Linux CNC setup while running a project. Everything was working fine until I executed a specific G-code, at which point the machine suddenly stopped responding. I’m unsure of what went wrong and how to fix it. Any insights or troubleshooting tips would be greatly appreciated.

2

When LinuxCNC suddenly stops responding during specific G-code execution, it usually points towards a couple of potential issues. You might encounter this due to:

  1. Bad G-code Instructions: Certain commands, if not supported or incorrectly formatted, can cause LinuxCNC to halt. Make sure your G-code is correctly written and free from any syntax errors. Tools like NC Validator can help verify your G-code for errors.

  2. Hardware Limits:

    • Soft Limits: If your machine is set up with software limits, make sure no commands inadvertently move beyond these bounds.
    • Hard Limits: Similar to soft limits, actual physical switches or sensors can stop the CNC if any axis moves beyond its capability.

  3. Buffer Overruns: If the G-code contains too many commands in quick succession, it might overflow the buffer, causing a freeze. Ensure there are no excessive rapid movements or complex instructions that the buffer cannot handle.

  4. Real-time Kernel Issues: LinuxCNC relies on a real-time kernel for precise control. Check your CPU usage during CNC operation. If you’re maxing out your processor, it might affect real-time performance. Running unnecessary services or GUI-heavy applications in the background can drag performance down.

  5. Subsystem or HAL Misconfiguration: Look into your HAL (Hardware Abstraction Layer) configuration. Misconfigured pins might lead to stalling the machine when certain operations are activated.

Troubleshooting Steps:

  1. Review the G-code: Starting from the point where the machine stops, inspect for any non-standard commands, or switch operations that could be causing the hiccup. Check that all syntax adheres to the required G-code regulations.

  2. Simulation Software: Run the G-code through a simulator such as Available CNC Simulators, which would tell you if there are any issues without physically risking the machine.

  3. Check Limits:

    • Verify if any soft/hard limits are being reached during the problematic section of the G-code. You may need to reconfirm the machine XYZ limits in your LinuxCNC configuration and ensure they are accurate.
    • Use the Show HAL Configuration feature in Linux CNC to verify signals and ensure limit switches are functioning correctly.

  4. Examine System Logs: LinuxCNC logs typically record errors and warnings to help diagnose issues. Check /var/log/linuxcnc.log or run dmesg for real-time kernel errors.

  5. Kernel Performance:

    • Ensure the system is providing adequate real-time performance. Run latency-test to see if your system has good real-time characteristics.
    • If using a multitasking environment, dedicate core(s) to LinuxCNC if possible.

Specific Checks:

  • Floating Points & Decimal Errors: A misformatted float or unexpected decimal point can create issues for the machine’s parser.
  • M Commands: Pause (M0 or M1), Stop (M30), or any custom M commands that interact with fixtures, tools, or the coolant system might create unpredictable stopping.

If these steps don’t resolve the problem, you might also need to dig deeper:

  • Scope Control Panel Signals and Logs: Look at the signals in the Hal scope, which can tell you what was going on just before the failure.
  • Increase Step Times or Pulse Lengths: Occasionally timing mismatches can cause unresponsive states.
  • Update Stack or BIOS Settings: Ensure hardware-specific settings are tuned correctly, especially if the CNC machine firmware has any updated recommendations.

Lastly, if all else fails, consider reaching out to the LinuxCNC community or forums with specific log excerpts and detailed machine behavior. More minds on this might uncover something you’ve missed.

Feel free to share the exact lines of G-code causing issues, as community members might spot something which a general check might not reveal.

3

If your CNC machine stops during a certain G-code segment, another aspect to consider is EMI (Electromagnetic Interference). @byteguru provides solid advice, but don’t overlook how EMI might negatively affect your setup, especially if your machine’s control cables aren’t shielded properly or run close to power cables. This can create transient errors during specific, power-heavy commands.

Another angle worth investigating could be power supply fluctuations. If your machine demands more power at certain points and your power supply isn’t stable, this might cause it to halt unexpectedly. Inspect your power supply unit for consistency, and consider using an uninterruptible power supply (UPS) to smooth out any irregularities.

You should also take a look at:

  • Grounding Issues: Improper grounding can cause various unpredictable behaviors in CNC machines. Ensure your machine, control board, and computer all share a common ground.

Some additional tips:

  1. Control Software Updates: Make sure your version of LinuxCNC is up to date. Updates often contain bug fixes that can resolve obscure issues.

  2. Environment Control: Heat buildup can affect components like stepper drivers and microcontroller boards. Verify the cooling system is working properly or consider additional cooling.

  3. Physical Inspection: Sometimes physical wear or debris can affect sensors and limit switches. Do a thorough check of the machine to ensure everything is clean and free from obstructions or damage.

Moreover, one less mentioned option is alternative control software. If the issue persists, you could try running your G-code on different control software (within a controlled test environment) to see if the problem persists. Software like Mach3 or GRBL can serve as a comparison point to rule out software-centric bugs.

As someone who’s faced similar issues, I remember a case where a faulty USB cable was causing intermittent disruptions during operation. Swapping out basic components can sometimes solve what appears to be complex issues.

All in all, a holistic approach is often essential—focusing on one troubleshooting angle can lead you to overlook another subtle cause. Given how finicky these systems can be, patience and systematic checks can ultimately save you from more frustration down the line.

Hope this gives you a few more angles to investigate!

4

I don’t know about @codecrafter and @byteguru’s suggestions, some seem overly complicated. In my experience, the most common issue with a CNC machine freezing is often something super simple and overlooked. Have you checked your wiring? Even a slightly loose wire can cause intermittent connections leading to your machine freezing.

And honestly, all this talk about real-time kernel and HAL config might be overkill unless you’re really certain the machine is otherwise perfect. Sometimes it’s just a matter of cleaning your machine and ensuring all connections are solid and no debris is interfering with sensors or switches.

And one more thing - have you considered electromagnetic interference (EMI)? With the amount of electronics involved in these setups, I’ve seen EMI cause issues with commands not properly being executed. Shielding your cables or rerouting them can sometimes make a huge difference.

Sure, simulators are great, but at the end of the day, nothing beats actually manually running a simpler version of your G-code to see where it fails. @byteguru’s idea about grounding issues is spot on too - improper grounding can seriously mess with your setup.

But honestly, if the problem persists, software like Mach3 or Fusion 360 could be used to isolate if it’s strictly a LinuxCNC issue. It’s not perfect, but diversifying your tools makes it easier to pinpoint the real problem.