Homebrew PCBs

Alan King wrote:

> Stefan Trethan wrote:
>
> >
> > I did execute the described experiment.
> >
> > i taped a stripe of aluminium foil on one half ot the page.
> > then i printed a page with X all over.
> > cut the power as it was halfway through.
> >
> >
> > Inspection of the srum shows just what i thought.
> >
> > before point of contact:
> > clear image, thick.
> >
> > after point of contact on paper half:
> > very faint residue, if you don't know what it is you couldn't read it.
> >
> > on aluminium half:
> > about half the amount of toner still on the drum.
> > image printed on aluminium foil but not as dense as on paper (holes 
> too).
> >
> >
> > for me this shows my guess with "charge shorted but some toner still
> > transferring"
> > was very close, even the 50/50 is about what i see here.
> >
>
>
>    After reading through the HowStuffWorks, the copper/aluminum being 
> conductive
> is the problem.  The paper isn't oppositely charged from the drum.  
> The toner is
> positive, the drum is negative to pick up, and the paper is then more 
> negative
> to attract the toner from the drum.  The paper has first the charging 
> corona and
> then another discharging after to unstick the paper from the drum.  
> The paper
> underneath will keep the copper from directly shorting the 
> charge/discharge
> wires as long as they are on the underside, but the copper on top will 
> equalize
> the charge on that side or short if they're on top, so once it gets to 
> the detac
> wire it'll have both neg and pos and be whatever shade of neutral the 
> relative
> charges on the wire make.  50% less sounds about right, they may not 
> need as
> much opposite on the detac just to unstick the paper.
>
>    Note with a copper board there would be no tendency to wrap around 
> the drum,
> you could remove the detac wire and possibly get an excellent print 
> with a fully
> charged copper plate, just watch out for the static charge near any 
> electronics
> afterwards since it's not being discharged during the printing.
>
>    Now I really want to find a good upright printer as in their 
> drawing that has
> a straight mechanical path with a little case modification.  I'm now 
> fairly sure
> the direct to copper can be made to work, and the fusing part is just 
> a matter
> of heat and slower speed to get that working so should be easy 
> enough.  As good
> as toner transfer is damn it'd still be nice to not mess with the 
> paper.  The
> amount of toner etc on a normal page would be fine if it were all on 
> the copper
> and fused well, so I don't think other mods would really be necessary.
>
> Alan
>
>
>
>
>
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>
> Basic operation, in most laser printers, is based on electrostatics a 
> old art, thanks to zerox.  The drum or image roll is coated with a 
> photoconductive coating.  Which is charged with a high voltage as it 
> rotates.  The laser beam is modulated with the data image and shot 
> onto the drum.  That beam causes the photoconductor on the drum to 
> conduct and discharge thru the coating to the drum ground.  The next 
> step in the drums path is the developer which lightly dusts the drum 
> surface with toner.  While there are several  styles  in this  
> operation, the end result is the toner sticks to the drum where it is 
> held by the remaining charge.   Then next step is the image transfer.  
> Or whats known as the transfer station in the drums path.   The drum 
> now meets up with the paper, both moving at the same speed so the 
> image remains stable and clear.  With the paper between the drum and a 
> high voltage charge on a corona wire, the toner jumps off the drum 
> thru the air toward the charge and ends up landing on the paper.   The 
> paper then travels to the preheater and into the fuser area of the 
> printer and is pressed into the paper using a hot roll along with a 
> backup roll.  The hot toner melts into the paper.   What us home pc 
> makers are trying to do is keep the toner from sticking to the paper 
> so well.   Fuser oil or coatings on the paper  keep the toner from 
> locking down.   Getting that  drum  image  transfered to a  sheet of 
> copper will be a feat.  The copper has to be moving at the same speed 
> as the paper would be.  The electrostatics for image transfer are 
> critical for focus.  The sheet of copper will be like a brick wall to 
> the corona wire charge.  After transfer takes place  the left over 
> toner and charge have to be removed.  Sometimes another corona wire 
> with a diffrent charge is in the drums path, some times a cleaner 
> station to brush the left overs of the image off the drum.  Then the 
> drum is ready for a repeat for the next scan from the laser.   While I 
> don't know how to get that image on to a pc blank, I do know that is 
> won't be easy or quick. 




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