backlash-compensator

Modifies G-Code to compensate for backlash in the Z axis

Installation

• Make sure you've got Python 3 installed and python is in your PATH
• Clone/download and unzip the repo into the desired location
• Adjust the BACKLASH variable at the top of the script as necessary (it's in millimeters)
• In Slic3r, place the absolute path to backlash_compensator.py in the "Post-processing Scripts" box inside the "Output options" panel inside the "Print Settings" tab. Cura and Simplify3D should work similarly.

Theory

The script loops through the generated g-code looking for every instange of a G0 or G1 command with a Z component to it. Whenever a Z movement is found, it's pushed into a queue of Z moves (which also stores the g-code line number and z height of the movement). Once the queue has three movements, it can be checked for an inflection point in the middle point. If the inflection point...

• Is above the two outer points, then we need to soak up the backlash for the impending downwards movement. Insert a G1 Z{z_move.height - BACKLASH} after the middle point in the g-code to reel in the slack, then insert a G92 Z{z_move.height} afterwards to update the system with the actual coordinates.
• Is below the two outer points, then we need to soak up the backlash for the impending upwards movement. Insert a G1 Z{z_move.height + BACKLASH} after the middle point in the g-code to reel in the slack, then insert a G92 Z{z_move.height} afterwards to update the system with the actual coordinates.

However, if the inflection point doesn't exist, then don't do anything as there isn't a direction change that'll need the backlash to be dealt with.

Why?

I've been working on a low-cost CNC project that uses a 28byj-48 geared stepper to control the Z axis. Unfortunately it has a TON of slop in the gearing which made it impossible to get anything even remotely accurate out of it, hence this script.