What triggers the "cool down" mode?

Technical
#1

The Glowforge has a way of detecting that it’s running too hot, as you know, and will pause its work while it cools down. It apparently accomplishes this through a combination of fluid pumped through the laser tube and running the fans on maximum. I say fans, plural, because I believe it runs not just the exhaust fan but also the fans connected to the head. If this is erroneous, I appreciate the correction.

What I’m looking for better understanding on is:

  1. What triggers the Glowforge to halt? There’s a sensor either in the fluid or somewhere in the case (possibly multiple) that monitors temperature. Where is this sensor?

  2. If more than one is present, which one determines “cool down” should begin? Is there a consensus of sensors needed?

  3. I’ve read that the Glowforge doesn’t care/stop the machine if the fluid pump is disconnected, which would mean it doesn’t monitor that pump while the laser is operating. Is this accurate?

  4. From my experimenting, it appears the Glowforge has the ability to enter a cool-down mode either after the job is complete, or during the job. What determines which approach it takes?

  5. Under what circumstances does the orange/amber button light come on with regard to overheating? Why does it sometimes come on when it needs to cool down, and other times does not?

  6. What is the maximum temperature the Glowforge will operate at (based on question 2)?

Thank you for your consideration and time in responding.

#2

There was a recent firmware update that activated additional sensors in the Glowforge that had previously been dormant. I believe there was some mention of using infrared sensors in the lid to detect flare-ups, although they could simply be referring to the CCD in the camera. They may also be measuring the temperature at various points inside the machine.

I operate my Glowforge in my basement where the ambient room temperature is generally in the
50s or 60s. I’ve had it be too cold to operate, but rarely too hot. I have seen reports that people who have the Glowforge in a garage have had problems starting when the temperature is in the mid-to-high 70s.

I could be wrong, but I believe many of the changes that pause a print job midway are recent.

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#3

The unit has the following fans:

  • Two Intake Fans (Delta QFR1212GHE 210.4CFM)
    These are ran at approximately 66% speed and are located in the lower right hand side of the unit.
  • Exhaust Fan (Sunon PF92381BX-000U-S99 182.4 CFM)
    This is ran at 100% (without external filter) and is located in the left rear at the exhaust port.
  • Air Assist Fan (Delta THA0142AD 20.6CFM)
    This is ran at 100% and is located at the rear of the laser head sled. This is to assist in clearing away the products of combustion and blowing out small flames during a run. It does not assist in cooling.
  • Lens Purge Fan (Sunon MC20080V1-000U-A99 1.6CFM)
    This is ran at roughly full speed and is located on the laser head assembly. This is to clear products of combustion from inside the lens assembly. It also does not assist in cooling.

For temperature sensors, there are several.

  • The accelerometers (LIS2HH12) located on the lid camera board, the control board, and the laser head each have an embedded temperature sensor.
  • The interconnect board (left side of unit) has a LM75B compatible temperature sensor.
  • The power supply
  • The coolant loop has two temperature sensors and a heating element. One sensor is upstream and the other is downstream of the heater.

That covers the “what”. The “when” seems to depend on what mode the device is in at the time.

The device sends a constant data stream (telemetry) to the mothership with all of the various sensor values. If these are showing the temp to be too high, the web interface will alert you.

If the device is in the middle of a job, the trigger points come from the job file itself. The file contains thresholds for each sensor. There appears to be a minimum and maximum value for starting a job as well as for pausing a job. I haven’t fully deciphered them all, but you can grab one for yourself, decode what is in it, and update the list if you figure out what any of them are.

From what I’ve seen, most of the values for the sensor trip points seem to be maxed out, which effectively nullifies their contribution to the shutdown. It seems that the coolant temperature is the only one that is considered (your question #2).

My guess is that the Orange light comes on when the device itself triggers the cooldown based on job settings, and it does not come on when the service detects it via telemetry.

As to what the exact temperatures are that the device will run at? Your guess is as good as mine. Glowforge gives the technical specs, but these don’t seem to align with the actual operation of the unit. Though, based on the numbers I can glean from looking at the job files, it seems to be 10-25C (50-77F).

This did seem to be the case the last time I tested it (which was a few firmware revisions ago). It is possible that this has changed, though I have not confirmed one way or the other.

There are four IR sensors on the lid LED strips. There didn’t seem to be any mention of these in previous firmware releases, and I haven’t examined the newest release to see if that changed. I’m not sure about the utility of these, and I would be impressed if GF was able to get them to operate reliably as flare-up sensors.

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#4

I’m confused. You list the intake fans as moving higher CFM than the exhaust. I thought is was the other way around to generate and maintain a negative pressure inside the machine.
Isn’t that how smoke is prevented from issuing from the openings in the enclosure?

Also, Dan mentioned a while back that they had changed the two intake fan configuration to one.