HP blue light

  • Thread starter Thread starter geo
  • Start date Start date
During printhead allignment there is a blue light.
Does anybody know how it works?
Click to expand...

It's simply a blue LED. There is a sensor next to it to read the
reflection. I think the main reason blue is used is because it's 'cool
looking.' At work, we have a DesignJet 650C, which uses green.

By monitoring the refelection while scanning across the special
patterns, the printer can determine the correct cartridge offsets.
Yellow is used for the color cartridge alignment because it looks black
under blue light.
 
geo said:
During printhead allignment there is a blue light.
Does anybody know how it works?
Click to expand...

The alignment page prints a series of black and yellow blocks, as well as
pattern of black and yellow lines. There is a blue LED and an associated
sensor that measures the offset between the black and yellow blocks in the X
and Y dimensions and then corrects appropriately. Later versions (starting
with the DeskJet 990?) also examine the reflectance from the paper to detect
paper types automatically.

Regards,
Bob Headrick, not speaking for my employer HP
 
1-2 weeks ago the color cart had a bad clog.I ran a cleaning cicle and then
an allignment .On the printed A4 i could clearly see that the cart was still
cloged but the allign procedure was (for HP) perfect.,with the green arrows
on the left(that i could barely distinguish).
So i decided to clean manually the cart ,with success.I ran a new head
allignment but this time i tried to fool him.I printed on a A4 Dark Grey
(almost black) pre-printed paper.The results....Again perfect (for HP).I
doubt that the sensor could "see" the printed patterns.The printer just put
a green arrow again and the allignment was finished.
I don't believe that this procedure works.
Does anybody know how to test it?

Thanks for the replies !!!
 
The alignment page prints a series of black and yellow blocks, as well as
pattern of black and yellow lines. There is a blue LED and an associated
sensor that measures the offset between the black and yellow blocks in the X
and Y dimensions and then corrects appropriately. Later versions (starting
with the DeskJet 990?) also examine the reflectance from the paper to detect
paper types automatically.
Click to expand...
And, the light is used to align the paper. From the 990Cxi onwards
(another good workhorse printer from HP - but I won't be buyi9ng any
more because I know that, as soon as the next MS OS comes out, I won't
be able to run the printer and HP won't produce a driver for at least
a year).
 
geo said:
So i decided to clean manually the cart ,with success.I ran a new head
allignment but this time i tried to fool him.I printed on a A4 Dark Grey
(almost black) pre-printed paper.The results....Again perfect (for HP).I
doubt that the sensor could "see" the printed patterns.The printer just put
a green arrow again and the allignment was finished.
I don't believe that this procedure works.
Does anybody know how to test it?
Click to expand...

The alignment does work. If the sensor could not see the pattern there would
not be a checkmark on the last line. You may notice the sensor first checks
the blank paper to get a nominal reading before it starts the alignment. It is
rather immune to paper types, although it may fail on yellow paper or
transparency.

If you want to test the alignment try making a black box in Photoshop (about 1"
on a side) with sides 1 pixel wide. Now replace a bit of the side and top with
a color strip. An alternate pattern would be a thin cross of black (or color)
with extensions of color (or black). Print in plain paper normal mode.

Regards,
Bob Headrick, not speaking for my employer HP
 
I don't own an HP printer, but I have watched the alignment process on
them on occasion.

From what I can see, the alignment requires a certain amount of yellow
and black printing. If the "damaged" cartridge you speak of was able to
provide enough black and yellow information printed onto the paper, the
alignment process should work. I suspect if very little or no yellow
and or black ink was printing, then the alignment process would not have
enough printed information to make the necessary adjustments, but it
certainly is possible the alignment process doesn't require fully
functional printheads to do so. The heads may well be aligned and still
be partially clogged or "damaged", if that be the case.

Anyway, the image is either aligned or it isn't... unaligned heads would
show up with off-registered color.

Art
 
Andrew Rossmann said:
It's simply a blue LED. There is a sensor next to it to read the
reflection. I think the main reason blue is used is because it's 'cool
looking.' At work, we have a DesignJet 650C, which uses green.

By monitoring the refelection while scanning across the special
patterns, the printer can determine the correct cartridge offsets.
Yellow is used for the color cartridge alignment because it looks black
under blue light.
Click to expand...

Also the LED is used to determine the paper type (assuming you have auto paper
type selected in the driver).
 
By monitoring the refelection while scanning across the special
I wonder why more printers don't use this, for example they could create a
servo system that could be used to print better photos on color paper or could
be used to clean the head repeatedly until there are no clogs. Remember the 3
head cassette decks?? It could work like that.
 
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