Just to add this one

Can’t figure out what is different with your machines and the PRU I have. Never have to move the head. Haven’t had a head crash for many months, though it did it a couple times in the beginning Which is an indicator to me that our mechanical design is similar enough. Since the head location is unknown without the lid camera it leads me to speculate a lot of possibilities but truth is we just don’t understand. I would think Support has figured it out with this many reports.

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I haven’t had to do a manual positioning since the first week of with my production unit. I don’t use it every day, but it gets turned on and off frequently enough throughout the week. It is puzzling.

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Mine had been doing the same. What bothers me is you can tell it’s in a pretty good bind when it does it. Been trying to get a video of it but if I pull my phone out it works fine :wink:

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Ditto. My PRU did it occasionally, but my Basic had only done this once.

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If we could see a raw lid camera image it would probably reveal what goes wrong. Can the camera actually see the head when it is top left?

I don’t know why it doesn’t assume the head is in park the position and go right and forwards by default.

Also seems to be a mechanical issue when the head is on the left. Does it rub on the Y rail?

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My hypothesis: the startup homing procedure first has to determine where the head currently is, which it seems to do with a couple of pictures and a small jog. It then tries to move it to approximately the center, in a single diagonal motion. If it incorrectly “sees” the head over on the right, it tries to move down and to the left, continuously crunching against the end of travel.

I would imagine the lid camera can’t see the corners very well, and a bit of shadow or reflection, especially if the bed isn’t empty, might throw off the algorithm enough to cause this. Most other machines have you-know-whats for this purpose, but they’re unreliable if you break them, so GF has had the courage to think different.

Perhaps feedback from the accelerometers during this process could detect that something has gone wrong and stop it.

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Apple flashback < shudder >

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The displayed camera image does not show the head. Might be cropped. The head does not hit the Y-rail or anything on the left side. It hits a hard stop on the gantry a full 3/4" away from anything on the left side. When it happens it just looks like something is scraping down the left side. It’s not. Just being driven against the stops while simultaneously moving forward.

Yeah, I know. You would never design it that way.

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The ironic thing is if it is happy to head bang on the left it could simply move left 20" and then right 10" (or whatever the exact measurements are) and be bang under the head.

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Yeah, I know you have a quick and easy solution.

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Some 3D printers actually use that method to home X and Y although I wouldn’t advocate it.

Since the current is programmable it could do it gently. Just drop the current and slowly drive left. Since it parks back left it can bump off the end stops very quickly and then zoom to under the head for fine registration with the camera.

With the accelerometers in the head it could even detect the bump and stop without grinding

With modern computer vision it would be easy to locate the head logo unless the camera is dazzled by something.

So I really don’t know why after two years of development it can’t home reliably and why when there are daily reports of it they don’t roll out a fix post-haste.

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ding ding ding…back to your corner now.

Mine has done this so consistently that I’m wired on moving the head every time. I initially read the others posts about moving it below the camera, but I’ve found moving it even just a couple of inches to the right is enough to fix the issue.

To clarify, this is only ever the case when the machine has been off and I turn it back on, but I have never experienced the issue if I do more than one print in a session.

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OK. I spent some time trying to figure out why so many people are having problems with the head bumping into the left stops. My machine does not normally have this issue but I was able to reproduce the problem. I power cycled my machine and moved the head to maybe 50 different positions for calibration tests. The following is speculation on my part but seems to give consistent results.

Edit: I had to edit the rest of this post because I’ve done additional tests. Hope it doesn’t confuse the topic flow

It seems that when the head scrapes down the side of the machine during calibration it is because the S/W has lost track of the head. When the S/W gets confused the head could be driven into hard stops on the gantry. (stepper motor assembly) Can only speculate as to the cause. The camera might not be able to see the head clearly or maybe cutouts in the material on the bed may confuse the camera. Might not be one reason. Either way, the solution seems to be to move the head to a position where the camera can easily recognize the head before power on and calibration.

I had originally thought that the camera alignment accuracy could be part of the problem. Now I don’t think so but can’t rule it out.

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That has been my experience, too.

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Finally an explanation, thanks. I wonder why it wants to move left 1/2" before it can see where it is.

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Has to be a reason but can’t think what it might be.

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I think you might be on to something.

On this PRU, the place where the head gets parked after a print is normally about half an inch to the right of the stop. I also think that’s the natural home position for it.

The only time I’ve had the whacky-whacky happen is when I have accidentally moved the head all the way to the left against the stop. I think it’s just expecting to start about half an inch further over to the right. (I move it during cleaning, or if I have to stop a print for any reason.)

The whacky-whacky will continue though until the whole shebang gets reset by turning off the machine, centering the head under the lid camera, and letting it reset itself once. After that, I can turn off the machine normally, and it starts itself back up properly over on the left side of the bed.

Like I said, I don’t see it often, but I also don’t move the head by hand, even with the machine turned off. If I just don’t mess with it, it’s not usually a problem for me.

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Ok, folks. I’m posting what I’m going to call the definitive recording of the Glowforge startup and homing procedure. Including a variety of tests which may debunk some of the theories posed earlier in this and other topics. I didn’t go into this expecting to prove anything, but I think the evidence suggests that my earlier guess is still the most plausible.

I’m very curious why rpegg’s machine apparently does an initial move down and to the left, when mine moves toward the center on both axes.

Anyway, it’s all here for the record. Pixels don’t lie:

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Everything you showed mine does also. It doesn’t always move straight down the left side. Mine does both motion paths. The one where it moves directly toward the head camera and the one where it moves almost in a straight line down the left side but also moves toward the left stops. The one that moves toward the center never scrapes. The one I described always scrapes. Don’t know why it takes one path or the other. Might be light interference, the lid camera might see the head but be confused by cutouts in used material. It clearly has lost track of the head. Doesn’t matter to my description. When it scrapes down the left side it is hitting the stop on the gantry motor assembly which creates the sound everyone is complaining about. I can also give you a setup where it will always hit hard stops on the right side. Nothing I said conflicts with your video or your earlier statements.

BTW: you can feel the ticking noise you described in the head so doubt it is the pump.

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