Layer shift on Y axis

Hi,

My printer used to work well but since I added a peice glass on top of my dibond printbed I sometimes have a layer shift on the Y axis, usualy in the middle of the print. Im guessing its because of the added weight.

What do I need to adjust exactly to fix this? speed, jerk, accel, stepper voltage??? im kinda lost.

I tried to fix it myself and I just made things worst, could use some pointers.

Thank you.

Turn up the stepper driver slightly, if it still happens reduce the acceleration setting in the firmware.

Thank you I will try that.

If anyone else drops by, could someone explain to me what the acceleration and jerk settings do exactly?

Tried to find some kind of marlin fw manual but wasnt lucky.

Jerk is the instantaneous change in velocity, i.e. it's the initial speed the printer starts to move at.
The acceleration is the rate of change of velocity above that point, how quickly it speeds up to the requested velocity.

The term Jerk is actually supposed to refer to the rate of change of acceleration. I donk know if it is implemented in firmware that way though.

I agree what's called Jerk ought to be named Impulse.
I haven't looked at the code either, but it's in mm/s which to me implies instantaneous change.

Thanks for clarifying that.

But if im reading this properly does this mean our printers don't slow down before changing direction? They just interrupt the move they were doing with another move at "jerk" speed and then accelerates from there?

It's not that simple the firmware maintains a buffer of commands, and there is a path planner reads ahead in the buffer to determines how fast the head should be moving at any point. As far as I can tell just watching the printers, the planners don't use exact position, but rather allow some epsilon and try to maintain velocity.

Stops aren't instantaneous, for a long move you can see the print head both accelerate and decelerate, I assume it starts at the jerk velocity and ends at it.

The source code is all ion git-hub if your really interested.