Canon Automatic Print Head Alignment... How?

[Nifty]

I've had this question for a while and thought I'd ask.... how does the Canon do an automatic print head alignment?

I see the paper advance and then pull back as thought it is printing and then examining what it just printed. Any ideas?

 

[Grandad35]

Nifty-Stuff,

I opened the printer cover, held down the "cover closed" switch and watched as it did the automatic portion of the head alignment procedure. My i9900 has a light on the left rear corner of the head assembly, and there must be an associated pickup that senses the presence or absence of ink from the light that is reflected from the white paper. During the automatic head alignment, ink rectangles are printed and the head then scans the light over the edges of the squares to see where they were printed.

 

[Nifty]

GD, you're a genius. I just did the same (I bent a paperclip and taped it so it would depress the cover switch). Sure enough there is a tiny red LED on the left of the printhead that "scans" the paper after it prints. I wonder what that little LED scanner could be programmed to do... scan B/W 2 color images???

I wonder if printing on black paper would mess up the scanner as I assume it is looking for reflections (or absence of) on the paper.

Also, when mine runs in seems to only print cyan and black. I've not seen it print any of the other colors during auto, but prints them all during manual alignment.

Well I thought this was so cool that I took a video. It is grainy, dark and shaky, but still cool! AVI 1.8 mb.:
http://www.nifty-stuff.com/gallery/albums/inkjet-refill-1/canon_head_alignment.avi

 

[BlasterQ]

Yeah, when I did the auto print head alignment, it printed only black and cyan, and I thought I had a clogged printhead, because I was expecting it to use all the cartridges.