The steppers do not have position encoders, so they use “dead reckoning”. Traditionally, the current position would be known by keeping track of how many steps they moved in each direction. If it misses a step, or there is a glitch in the code that keeps track of the current position, it doesn’t know and this causes alignment “drift”.
On the Glowforge, it works only slightly differently. The device itself does not keep count. It just plays back the steps it receives in the file it gets from the cloud (the cloud’s motion planner does all the math).
The GF stepper drivers have a home indicator (these are not limit switches, just internal step counters that can be set when the head is at the home position) that will give feedback to the processor to tell it they think the head has reached home. I don’t know if the current GF firmware verifies that the drivers indicate the head at the home position when the program finishes, though it is capable. Of course, neither would know if there were missed steps, so it wouldn’t make much difference.
All that being said, it should only experience alignment “drift” when it is actually moving. Sitting still shouldn’t cause any issues unless you bump the head.
EDIT: It appears my statement “The device itself does not keep count” was incorrect. The device does appear to keep count, as the return to home steps are not coming from the cloud.
