Part size, resolution, and other tid bits.

[Jon Watson]

So. I wanted to brainstorm ideas about how we will achieve 1:1 part
size on out 3d printers. Will it be a function of the distance between
the projector and the build plane? (Lets call the bottom of the tank
or vat the "build plane" this is where the light actually touches the
resin and where the magic happens)

I've been thinking a lot about this and wanted everyone to chime in on
this issue. There are factors here that need to be taken into
consideration.

1. the distance from projector to build plane (or focal distance)
2. The resolution of the full screen projection (i.e. 1024 x 768)
3. The pixel aspect ratio and if remains consistent between all the
software the slices will be processed through.
4. The image aspect ratio. Are the slices centered or stretched to fit
a square bitmap image or rectangle.
5. Does the bitmapped image represent the full XY build dimensions
(i.e. 1024 x 768 projected at 8" x 6" = 128 x 128 pixels per inch)
6. Calibrating the software to output the slices 1:1 at 128 ppi (per
example resolution)
7. Using a calibration card with a grid to lay at the build plane and
project the same grid onto the build plane and register the two by
adjusting the focal length. Even this would not be accurate within a
few thou's. Once you figure out your own grid spacing at your
particular resolution, you can start at the there & work your way back
through the software to keep sizes consistent.

So, if you establish that your build area is 8"x6", and your projector
output is 1024 x 768,(and you match the entire output into the 8x6
area)

then you know your slices need to be output at 128 pixels per inch to
be 1:1.

Some people might not care about exact sizes. Close enough might be
good enough, especially for experimenting and creating action
figures,lol.

I just know that I want functional parts that work in the real world.
If I want to print my own custom Lego pieces, I want them to play nice
with real Lego's.

Anyone else have any thoughts on this matter, please chime in.

Jon

[John]

I agree, for most, close is probobly good enough. I think it will be
difficult to get an exact 1:1 stricly from the math. If we eyeball it
then make a cube, we can get the calipers and make fine adjustments
using the zoom on the projector. Print a cube/ measure/ adjust/
repeat. It should be possible to dial in a pretty accurate 1:1, at
least as close as is possible on that particular machine.

John

[tj]

> 1. the distance from projector to build plane (or focal distance)

I made the model shaper modular so when you decide what type of
models you are going to build you set your image size first then the
focus then you can calibrate into square and scale.Different
individuals have different needs. I am a jewelry designer so my scale
is 3 x 2 cube inch.This is to my favor because I can have extremely
high resolution in a 3 x 2" footprint.

Now to make matters even more complicated,if I use my zoom (image size
adjust ,it opens a whole new can of worms too....lol

> 2. The resolution of the full screen projection (i.e. 1024 x 768)

I hope mine to be 1900 x 1080 .Roberto put me on this new toy that I
just bought, its a USB UGA MULTI DISPLAY ADAPTER here

http://www.excheap.com/product_info.php?products_id=4714

thats usb2 AND goes DVI to HDMI and hopefully will give me a full
1900 x 1080 native.on a VIEWSONIC PRO 8200.

> 3. The pixel aspect ratio and if remains consistent between all the
> software the slices will be processed through.

This is something I honestly do not know much about. I guess it is
very much monitor and graphics card bound??? I am going to leave this
one to Roberto.
It is a big issue especially because there is so much different
systems and displays.

> 4. The image aspect ratio. Are the slices centered or stretched to fit
> a square bitmap image or rectangle.

Again the same as point 4# ..???. I would think centered would be the
only way to go, I can't see how streched would work.

> 5. Does the bitmapped image represent the full XY build dimensions
> (i.e. 1024 x 768 projected at 8" x 6" = 128 x 128 pixels per inch)

In fullscreen mode It should, I think??....ROBERTO!!!!!!!!!!!!!!!!!!

> 6. Calibrating the software to output the slices 1:1 at 128 ppi (per
> example resolution)

explain more please??

> 7. Using a calibration card with a grid to lay at the build plane and
> project the same grid onto the build plane and register the two by
> adjusting the focal length. Even this would not be accurate within a
> few thou's.  Once you figure out your own grid spacing at your
> particular resolution, you can start at the there & work your way back
> through the software to keep sizes consistent.

I have been thinking about the same lines too, I was thinking of
making a scale/ abberation calibration plate with 8 tiny holes and 8
photo sensors on top to to do a scale calibration with a
corresponding 8 dot image. When all the 8 dots is on the holes 8 leds
will light up . If the white little dot is off the led will be
off., .this would only be done once every time the focal distance is
adjusted to accomodate a bigger or smaller model size. This is at
least my hypothesis.

> So, if you establish that your build area is 8"x6", and your projector
> output is 1024 x 768,(and you match the entire output into the 8x6
> area)
>
> then  you know your slices need to be output at 128 pixels per inch to
> be 1:1.
>
> Some people might not care about exact sizes. Close enough might be
> good enough, especially for experimenting and creating action
> figures,lol.

You're exactly right. or quadruple your resolution to a 4 x 3".

> I just know that I want functional parts that work in the real world.
> If I want to print my own custom Lego pieces, I want them to play nice
> with real Lego's.

I think in the end this matter will and never be written in stone.
Everyone will have different needs for scale and accuracy. I am with
you Jon ,Mine needs to be high resolution small and to a accurate
scale. I definitly need to build to a e few thousands of a mm to
scle.. and will probably be custom calibrated accordingly. but
someone else like a anatomy sculpter might not care about any of the
above.
One thing I have a much bigger problem with is the projection angle of
mine . Because my DLP is designed to project upward the bottom of the
image is at 90 right angle to the stage and the top is about 30
degrees so difraction is another problem to sort out. Due that the
bottom of my image is much better than the top ??.

So there is still a lot l to sort out....lol .....very
interesting...thread

XGA eXtended Graphics Array 4:3 1024 768 5.64%
XGA+ eXtended Graphics Array Plus 4:3 1152 864 1.10%
WXGA Widescreen eXtended Graphics Array 5:3 (15:9) 1280 768 0.61%
WXGA Widescreen eXtended Graphics Array 8:5 (16:10) 1280 800 4.21%
SXGA (UVGA) Super eXtended Graphics Array 4:3 1280 960 1.02%
SXGA Super eXtended Graphics Array 5:4 1280 1024 13.24%
WXGA Wide XGA resolution 16:9 1360 768 1.39%
WXGA Wide XGA resolution 16:9 1366 768 5.48%
WSXGA Widescreen Super eXtended Graphics Array 8:5 (16:10) 1440 900
9.31%
HD+ High Definition Plus 16:9 1600 900 3.88%
UXGA Ultra eXtended Graphics Array 4:3 1600 1200 0.95%
WSXGA+ Widescreen Super eXtended Graphics Array Plus 8:5 (16:10) 1680
1050 19.64%
FullHDTV Full High Definition Television 16:9 1920 1080 21.14%
WUXGA Widescreen Ultra eXtended Graphics Array 8:5 (16:10) 1920 1200
7.60%
Other 4.78%




TJ.

Interesting links I read :

http://www.dpiphoto.eu/dpi.htm

http://en.wikipedia.org/wiki/Pixels_per_inch

http://en.wikipedia.org/wiki/Dots_per_inch

http://en.wikipedia.org/wiki/Display_resolution

[Jon Watson]

Tj, on the projection angle issue. Cant you just rotate your projector
a few degrees to compensate for the off axis projection angle? Or is
it not that simple?

> 6. Calibrating the software to output the slices 1:1 at 128 ppi (per
> example resolution)

I'm using the words pixels per inch (ppi) but it's really the same as
dots per inch (dpi)

This is only when you've decided on a set output or build size (like
8" x 6") If you decide to stay with a particular build size, then you
can go back into your slicing software and make sure that your slices
are output at 128 dpi. Or..if your software outputs at 300 dpi, then
you can always do a batch process in Photoshop to re-sample all the
slides to 128 dpi which should bring them to exact 1:1 size.

Of course, every slicer probably has different output options and
formats. I know for Viscam RP, I can specify my XY build size and
output the slices in relation to that size. So if I set my platform
size to 8" x 6" in VisCAM, then I know my slices are at scale within
that 8 x 6 area. There is still much to experiment with.

[John]

TJ,
On the projection angle,
If yoyu don't mind hacking that $1000 projector of yours, you might be
able to reposition the projection lens so that the image comes out the
center of the lens. I noticed that when I look into the lens of my
projector the image is only comming out the top half of the lens
leading me to believe the lens is mounted higher than the centerline
of the dlp chip. I think if you were to line the centerline of the
lens with the chip then the throw would be straight and eliminate the
difraction you get near the edges of the lense. Since you've already
taken your projector completely apart I know your'e not afraid to take
a look and see how the lens is lined up with the chip.

John

[Jon Watson]

Wow! Thanks for that link. I will study it for ideas. It's amazing
that even a "commercial" printer has to go through such an intense set
up procedure. Calibrating will be a challenge but it will get easier
once it's dialed in.

[tj]

Yes it is a pretty serious calibration ,If you have ever seen some of
the models coming of the ENVISIONTECH It is awesome! nothing like it.
and the resolution is very, very hight! Thats why it cost what it
cost!

[tj]

Jon and John
I will definitely look into that.Thats a whole project by itself.The
optic train is extremely sensitive and fragile as far as adjustments
goes,and dont even know if it possible with this lenses.I am not
afraid of hacking it,its just the time.
Coming closer to the end of this project all my ducks are somewhat in
order,so that would be just another issue to create a variable for
(that I don't need to open that can of worms right now) . I have to
get this machine to shape something soon so we can start
troubleshooting everything together.

I am on the instalation of all the pc boards and power supplies right
now,and that's way overdue (timewise). I had to master that PCB
etching technique first.That was a thorn in the flesh for a while
now ,but I won !! and the outcome was way above expectations , So our
project is moving again, we are going on! . Read up on it here:
http://www.chemshapes.com/?cat=27
TJ.