Update: Cameras and Calibration Tool

A project log for Tool Switching - Multi Extrusion

A scaleable approach to multi extrusion, easy to adopt in most CoreXY/H-Bot printer designs.

rolmie 09/24/2017 at 20:300 Comments

Only a brief update, as it is late already, but I'm eager to get a few news out.

I just uploaded CAD and STL (case, diffuser) files for the inspection camera. The cover is a dual extrusion print with transparent PLA used as light diffuser. I'll add detailed instructions in the next days.

The case is compatible with these two cameras (amazingly PCB dimensions, mount hole distances etc are the same). The first one is available for about $12. It features an 720P chip with support for MJEPG compression, which allows for 30fps in all situations.

This one is available for about $6, but only supports 640x480. The frame rate sometimes drops down to about 5 fps and the overall image quality is blurry. It is good enough for the job, but not convenient to work with.

The calibration tool is also slowly progressing towards being feature complete. The UI is now much cleaner an easier to work with. It keeps a reference image of each nozzle after registration which is later used to estimate the offset after a reload and to estimate the resolution of the camera (µm/pixel).

A few TODO's are left, eg. nozzle types are still hard coded, significant offsets in are Z difficult to work with, offset measurements are given in pixel instead of µm ... 

My favorite feature is the repeatability measurement job. All tools are loaded repeatedly and the reference image is used to estimate the XY offset. The plots below are in pixel, the camera resolution is about 4.5µm per pixel, each tool was loaded 50 times. "Tool 3" is a reference point on the carriage, unaffected by tool changes.

It is very useful while tuning, eg. I figured that my printer was loosing steps in Y because I pushed the carriage to hard. I'm a still a bit concerned about the trend in the Y offset of tool 0 and tool 2, investigation is ongoing.