The variable here is actually the means with which they are homing the head of the laser. From what we know the lid camera looks to see if the logo on top of the laser head is in the correct spot. However, being at the edge of the cameras viewable area and it using a wide angle lens, the ability for it to be as accurate as we might need has come into question. And as the machine does not use limit switches there is no secondary means of verifying that the location is exactly the same as it was last time.
Problems that I can see arising from this approach are:
- camera can shift or become physically moved over time by accident. (Materials hitting it when removing them etc), and/or slight manufacturing differences in placement
- lid doesn’t close at the exact angle it did when purchased
- resolution of camera isn’t high enough to accurately determine location within an acceptable margin of error
- smoke or other contaminants causing visibility of lens to change
- discoloration or distortion of homing logo on laser head
I think you get the idea. Without some way of making sure the head starts at the exact same position every time, any thing being permanently attached to the laser bed as a reference will also be inaccurate.