Bob Ammerman wrote:
>
> How's this:
>
> 1. Build a table that can move a PC board in one dimension in 1/300"
> increments with no cumulative error.
> [Old plotter anybody?]
>
> 2. Create a UV LED bar containing LED's on 0.1" centers. Over the LEDs is a
> mask containing 1/300"+ holes on 0.1" +/- 0.0005" centers [this is the
> tricky part :-)]. The holes need to be a bit oversize so that consecutive
> stripes will overlap a bit.
>
> 3: Mount the LED bar over the PC board on the table. The mask can almost be
> in contact with the board.
>
> 4: Attach the LED bar to an indexing mechanism that allows it to move
> perpendicular to the direction the PC board in 1/300" +/- 0.0005 steps (with
> no cumulative error).
>
> Now, to plot the board:
>
> repeat until done:
>
> Run the board from one end to the other.
> Index the LED bar one step.
> Run the board back.
> Index the LED bar one step.
>
> I figure you should be able to move the board a good 1" (300 steps) per
> second.
> Reversing direction should be about 1/10 of a second, which should give you
> plenty of time to index the  LED bar.
>
> It only takes 300/0.1 = 30 passes to do the entire board.
>
> Thus, a 5" board would take about:
>
> 30 passes/board * 5 " * 1"/second        ; for scanning
> + 30 passes/board * 0.1 second           ; for reversing
>
> This comes to 150 seconds + 3 seconds = 153 seconds.
>
> That's pretty fast.


Here's an idea Bob, how about use a laser to "scan" across
the board, with a spinning mirror. Sould be easy enough to index.
Then just move the board through in one pass, and the laser
scans across it and obviously turning laser on and off will
give the exposure. This system only has one axis motor to
move the board (less junk for me to fix later) and the spinning
mirror can be stepper/flywheel driven for easy indexing and very
low mechanical wear. Yes there will be some compensation needed
for the different laser "angle" from board centre to board edge,
but simply using a very high-res mirror indexing system with
software compensation would work.

Since this would scan the entire board it would work just
as well with pos/neg emulsions. Should be pretty quick, and
only one main expense for the board traverse axis, ie, rails,
linear bearings etc.

Hey, just thought, laser printers use a rotating lens and
laser that is probably suitable for photo emulsions since
it is suitable for the laser drum... You could kill an old
laser printer and apart from running it slower and using rails
for the board traverse (I wouldn't trust rollers) you would have
a real fine and reliable system...
-Roman

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