[R] Contact Image Sensor for coating detection

A project log for SecSavr Suspense [gd0105]

The best of resin with the best of filament; is such a 3D printer possible?

kelvinakelvinA 07/31/2022 at 21:310 Comments

I was actually looking at a project that desired to 3D print by scanning a laser dot over the vat when I thought that I should see if I could implement some kind of sensor to scan the applied layer on the PET film. This is to allow the printer to detect a coating issue so that it can recoat. If there are consecutive fails, it means there's an issue such as an empty cartridge.

I still can't figure out what module Bambu Labs uses in their new printer, considering even the "micro LIDAR" modules I found on Aliexpress start sensing at 10cm and cannot get Bambu's 7um accuracy.

I wanted to see if I could get both a scan of an opaque+transparent layer and a measurement of the thickness. If both features were in the same sensor, that would be even better. I looked to the research papers with search terms like "thin film coating measurement" and "non contact thickness detection" and a process called interferometry came up a few times.

The papers seemed a bit over my mental compute budget, so I went back to just thinking about getting a scan of a layer. The area to scan is 17cm and most scanners are for 21cm A4 paper, so I looked for a "scanner sensor". I found out that they're called "contact image sensors" and I've always wondered what they were called ever since 2017 when I found out about handheld A4 document scanners (that are still at the same £30 I remember).

It seemed that there's no off-the-shelf sensor and the only sensors are understandably repair parts for old all-in-one printers. Thus, the requirements for my search were that the sensor was cheap and abundant. I think I've found something: Q8100-60002

I've looked into some of the printers listed and they all seem to be over a decade old, so I'm suprised that there's still so much part stock today.

Anyway, when it comes to interfacing with something proprietary from a manufacturer, there's likely going to be all sorts of hurdles. I've found this log on but haven't looked into it in detail. I'm just going to design the Suspense with this in mind and deal with the complications at a later time. Regarding the light source, I'm thinking of possibly using a yellow tape like Kapton to reduce the blue light hitting the UV resin. I hear daylight LEDs cure the resin extremely slowly though, so perhaps this wouldn't be needed.