New DLP build started! / Pico-projector part 3

I keep saying this, but it's been too long a time since I updated my project blog. It's not for the lack of progress mind you. Things have been very busy for me lately. I'm not sure if I mentioned it before, but I started a new forum dedicated to all things DLP/SLA www.buildyourownsla.com . I have to say, never expected the explosion of interest! It's only been up for less than 2 months, but there are hundreds of active users (and about 1000 spammers).

Creation Workshop http://www.envisionlabs.net/ continues to advance rapidly, largely due to the herculean efforts of the co-programmer Shai (Thanks man!) . I've had a lot of interest with DLP/SLA printer manufacturers wanting to distribute Creation Workshop along with their printers, and I've been signing them on rapidly. I've devised a plug-in system that allows me to create vendor plug-ins to completely customize the GUI and code for each machine. It also allows me to distribute custom machine and slicing profiles tailored to each machines unique capabilities.

I've been talking with a bunch of groups/ start-ups/ companies about their machines for months, and I'm in a pretty unique position to see exactly what's going to be coming out on the market this upcoming year. I'm under NDA with a few of them, so let's just say that 2014 will be the rise of the SLA machine in the 3d printing world.

That all being said, I've been giving some thought as to how to create the 'Best' machine possible. 'Best' is an arbitrarily chosen words really. 'Balanced' would be a better descriptor. As I noted elsewhere http://www.buildyourownsla.com/forum/viewtopic.php?f=17&t=149 , there will always be tradeoffs between build size, resolution, and print speed. I think I've come upon a good balance between the 3.

What I came up with is a pico-projector mounted on an x/y linear assembly. The projector can expose smaller image tiles on a much larger vat bottom. This allows the pico-projector to maintain a 25micron (or greater) x/y resolution. The vat can be arbitrarily large. This is a good trade-off between size and print speed.

I'm still in the early stages of the build, but it's all coming along nicely.

New parts for the build

Shown above are a few parts I'm using for the build. Here's an incomplete BOM of items so far:

• 12v 6A power supply
• 5x Nema 17 steppers (I'll probably use 4)
• 12x LMU88 linear bearings
• 6 meters of GTK belt and 4 pulleys
• 10W UV LED 405nm on an alum heatsink
• Modified AAXA P2JR DLP projector
• 3' of 1/8 hose for the resin pump
• 3 prong outlet
• Mains switch
• Printed 3 way corner brackets for the 80/20 construction
• 4 printed feet

A bunch of 350mm and 300mm 25mm 80/20 aluminum.

The constructed bottom portion of the machine. Measures 350x350mm.

I'm still waiting on a few more parts in mail:

• Arduino 2560 with RAMPs board
• 8mm hardened steel rails
• 8mm threaded rod
• UV transmissive plexiglass for the vat
• UV blocking plexiglass for the outer casing/window
• Other things I forgot

I'm probably going to do a bit more construction today. Look for the next part of this build soon.
-Steve

UV DLP Pico Projector Experiments Part 1

      I briefly mentioned in one of my last posts about ordering and receiving a pico projector to experiment with. I obtained a re-furbished  AAXA P2JR directly from their webite http://www.aaxatech.com/products/p2jr_pico_projector.html  . 

The victim

      It came with the usual accessories, power adapter, micro-VGA to VGA adapter, composite cables, etc... My intent in ordering this is to see if I can adapt it for use in a bottom-up (or top-down) UV DLP 3d printer. I was a little nervous for several reasons. Normally, I don't just purchase new pieces of technology for the sole purpose of ripping them apart, but I figured I needed to break a few eggs to make an omelet.

       I was hoping that this projector would 'just work' and be able to cure resin without any modifications, but I pretty much figured it was going to need some mods. After powering it up, connecting it to my computer, and projecting silly images across my walls, cats, and girlfriend, I decided to get down to business. I ran my latest development code of 'Creation Workshop', sliced up a model, and chose a nice slice to test with.

Initial resin test

      I put a few drops of UV resin in a plastic sandwich bag, laid it flat, and projected an image slice. It went pretty much how I figured. After about 30 seconds, I checked the bag, and to my disappoint (but not surprise) I saw that it had failed to cure the resin in the slightest. 

      Now, I have it on good source that at least one person in the community has been able to modify a pico-projector for UV DLP purposes, so I wasn't ready to give up yet. I began to prep the patient for surgery.

Back cover off

The green and blue cable goes to the DLP unit's LEDs

A flat ribbon cable connects the DLP to the main board

     I was kinda nervous taking this all apart. What if I break it? What if I nick off a resistor? Am I about to lose 169$ bucks? Well, I hit my stride, and decided to make some progress in the name of science. I was able to completely dis-assemble the projector into it's essential components, the case, the speaker, the battery, the main board, and the DLP unit which was attached to a hefty heat sink.

I gently lifted the little bar that held down the ribbon cable to remove the DLP. After freeing the DLP from the main board, I had a better chance to examine the actual DLP projector without fear of tearing the ribbon cable.

Note the blue/green wires, L-bracket and copper heatsink

Initially, I was a little puzzled by the 2 sets of 4 wires. 

A good view of the optic-path

At the bottom/left of the picture, you can see the L-Bracket, each side has a 4-wire lead. Light is being projected in from 2 sides - each at a 90 degree angle from each other. Notice the funny-looking bluish glass (it's important later).

I figured that the L-Bracket contained the LEDs, and that I was probably going to have to replace them with a better UV source. I carefully sliced through the black rubbery epoxy holding the LED L-Bracket to the side of the DLP Unit.

The removed Led bracket 

I examined the LED L-bracket and noted that 1 led was marked R/B and the second was marked G. Without getting TOO much in theory about how DLP projectors work, I wanted to make a few comparisons between Color-wheel types and LED types.

In a Color-wheel type of DLP projector, a light source is projected through a spinning color wheel. The wheel has an encoder mechanism that tells the control electronics which color the light is currently projecting through. The appropriate color mask is displayed on the DLP micro-mirror array.

In a LED-type projector, either 1, 2, or 3 LEDs are used. Since LEDs can quickly turn on/off, the control electronics will turn on a single color, the DLP chip will display the appropriate mask-image for that color, and the process is repeated for all colors.

An image I found that explains the optic path 

The above image is NOT a picture of my DLP device, but serves to show the portions of the optic path. My optic path is a little different, but has very similar elements. 

Light from LEDs shine through collumnating optics. Dichroic mirrors (http://en.wikipedia.org/wiki/Dichroic_filter) reflect a specific frequency of light through a fish-eye lens, reflect on a right angle, then pass through the DLP portion and out the projection lens.

I knew that the dichroic mirrors were going to be a problem. They only allows a very narrow bandwidth of light through. 

I went ahead and took out the dichroic mirror reflectors and replaced it with a single FSM (Front surface mirror). This essentially blocked off 1 light path, which was alright, because I'm only going to use 1 light path for a UV led.

I've got a bit more to say about this and a few more results, but I'm going to save it for part 2.

Stay tuned.

-Steve