Why is there so much head movement with no aparent reason?

Bambu Lab P1 Series
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1

There are many times when I observe the print head moving to various locations, but there is no obvious reason.

For example: during bed calibration the print head moves to various spots on the bed and that makes sense.

When I press filament load, the print head moves all around for no apparent reason.
To me it seems like to unload filament the print head doesn’t need to move at all, and to load filament it just needs to move to the purge location to purge the old filament.

There are many other times during operation that I notice the print head moving with no obvious purpose. What are the reasons that print head movement is required when not

  • homing
  • bed leveling
  • purging and wiping nozzle
  • printing
    ??

I am no expert and I just want to understand and learn. I also have a Prusa and I don’t see this kind of behavior from it.

2

I’m pretty sure that Bambu Lab has a good reason WHY it does this movements.

3

I wasn’t claiming that there wasn’t a good reason. I was just asking what the reason was so that I can learn more about printers.

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4

Press filament cutter lever front left so filament can be extracted, purge remaining filament in the rear left, wipe nozzle in the rear center.

The remaining movement is things like scanning QR code on print bed, scanning printed calibration lines, scanning first layer print. While doing these scans, the nozzle temp drops so that liquid filament doesn’t ooze out, so that means that has to be purged again before resuming the print, so more movement.

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5

I don’t know all of the reasons but do know the purpose of some locations.

Viewed from the front, the left front corner is where the cutter is located. It may always do a cut move before purging as it may not know if there is filament in the path. The right front corner is the home position, it will drive the print head into the corner in both the X and Y directions when setting home, and may do both twice to dial the home position in. On the right half way back is the calibration area for the lidar and camera built into the print head. At the front edge of the build sheet is the QR code for which type of sheet it is. There are the 36 bed leveling points across the build sheet. It will also scan the intended print area before beginning a print if you have a plate that is not textured installed, probably so that it can build a map to compare with when doing the first layer check. This will compensate for any damage or glue build up that may exist. It will skip this step with the textured plate. Then there’s the nozzle wipe at the wiper near the chute after a purge plus the nozzle wipe on the build plate itself just before the leveling procedure. There may be a few what look like random moves when it is checking the head for ease of movement. It can determine if the carbon rods need cleaning based on either the current draw or maybe missed steps if it has that capability.

So yes, it does move around quite a lot but I think every move has a purpose even if it’s not obvious.

6

You don’t need to understand why it does this things.

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7

But I want to, and that is more important that what you think.

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8

What I notice the most are moves to the front right corner, which is for homing purposes. Any time the motors are idle/powered down the printer loses track of their position, so in order to make sure that they end up going to the right place next time they’re moved, it homes first.

There are “closed-loop” motors that can tell where they are at all times but I’ve never seen them in a printer and only started hearing about them in the 3D printing world recently. I suppose even those probably need to be homed at least once after being idle (I imagine they can only keep track of their position while powered).

Aside from the constant need to home, I think @lasermike has most of the other moves covered. Would be neat if Bambu outlined everything in the manual/wiki, though