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Add an illustration of a plain arc scan.

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hzeller committed Jun 17, 2017
1 parent 670a2c0 commit f9e1ea8ff6728d176741759670db2bf9884ec2a9
Showing with 23 additions and 15 deletions.
  1. +2 −1 README.md
  2. +21 −14 design.md
  3. BIN img/anim-plain-arc-scan.gif
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@@ -109,7 +109,7 @@ access to a laser cutter (hint: your local Hackerspace might have one).
Here, all electronics is mounted on the top for easier measurements and
such. The final version will fit everything inside.
![Case](./img/sample-case.jpg)
[![Case][case-pic]](./hardware)
Above is current status of the case, which went through some refinements (here
an [earlier case](./img/intermediate-case.jpg) which better shows
@@ -143,3 +143,4 @@ issues seen up to the point where it starts to be usable for PCB work.
[resolution-thumb]: ./img/line-resolution-small.jpg
[resolution]: https://plus.google.com/u/0/+HennerZeller/posts/a8taHWeL5CC
[design]: ./design.md
[case-pic]: ./img/sample-case.jpg
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@@ -35,12 +35,18 @@ in fact, in an early experiment for LDGraphy I was doing exactly that:
[![Early experiment][early-experiment]][arc-project-vid]
There are advantages for this set-up: we use a large angle range, so
essentially can utilize the full laser on-time. Also, the laser is always
in focus where it hits the board because it always is the same distance from
the lens. The disadvantages is that the laser dot hits the
photo resist at a shallow angle. This of course increases the size of the
exposure point seen by the photoresist.
There are advantages for this set-up: we can utilize a large fraction of the
laser on-time by covering the majority of the available scan range.
Also, the scanning laser is almost in focus for the scan range where it hits
the board.
Here is a simulation of such a scanning in which we use 105 out of 120 degrees
(the laser is off only for 15 degrees). In the exaggerated laser thickness, we
can see that the laser dot is a little bit oval in the extreme angles: in
places where we are not quite in focus, the shallow angle deforms the larger
'focus' circle to an oval.
![](./img/anim-plain-arc-scan.gif)
This could be fixed, if we had a mirror that points the laser-arc downwards, so
that it hits the resist perpendicularly. The mirror would need to be a circular
@@ -87,22 +93,23 @@ So let's review our options
* Build a scanner by pointing the laser at a shallow angle at the polygon
mirror:
* :thumbsup: very simple; full use of the laser; No light losses.
* :thumbsdown: hitting photo resist at a shallow angle; Large build.
* :thumbsup: fewest parts needed; almost full use of the laser; No light losses.
* :thumbsdown: not always in focus; hitting photo resist at a shallow angle.
* Build a scanner with a 45 degree cone mirror:
* :thumbsup: full use of laser; no light losses; hitting resist
perpendicularly.
* :thumbsup: almost full use of laser; no light losses; hitting resist
perpendicularly; always in focus.
* :thumbsdown: Hard to build.
* Build an f-theta lens and use a straight scanning projection:
* :thumbsup: Full use of the laser; hitting resist perpendicularly.
* :thumbsdown: hard to build. Might have optical losses in the material.
* :thumbsup: Almost full use of the laser; hitting resist perpendicularly.
* :thumbsdown: hard to build; might have optical losses in the material if
not transparent enough for near UV light.
* Only use part of the scanning range and use a straight mirror:
* :thumbsup: easy to build.
* :thumbsdown: we need longer exposure time because we only have a limited
on-time.
* :thumbsdown: we need longer exposure time because we only use a fraction
of available on-time.
Since ease-of-build for everyone with limited access to tools is a priority,
we use the last variant for this first version of LDGraphy.
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