Possible hole fix - Drip those holes away!

[NoctumSolis]

Unfortunately, this little revelation adds parts that need machining and I can't for the life of me figure out how you can get it so the end user can calibrate a multi-step attenuator easily, since you have to aim the laser exactly through both of the holes.

I'm showing my ignorance here, but... wouldn't it just be a matter of extra snap-together parts designed to hold the pre-machined parts in position? If the emitter is mounted to the circuit board then its position, along with all dimensions, are known quantities.

I realise there are plenty of fiddly, moving parts to calibrate, but wouldn't a static attenuator be easy enough to ensure consistent placement for?

[Feign]

Maybe, maybe not. Basically, you have a disk with a small hole through it that you have to shoot the laser through without touching the edge of the hole (or else you get the scattering all over again.) There's about 0.01mm of leeway for the second disk if there is good separation between the first and second apertures and the laser diode is lined up just right. I'm not sure how tight a tolerance the snap fit can make.

Here's a good picture of what the scattered light looks like for the red spectrum, as wavelength goes down, the spacing of the rings also decreases.
pinhole2.jpgWhat you really want is the beam to be on-center enough that the edge is in the first dark region between rings. However this picture was probably taken in a dark room at about five feet from the wall. Trying to find the rings at 10cm in UV wavelength would take a microscope.

However, if the second aperture is two or three times the size of the first, and you don't have it exactly lined up, you only get a few pairs of points on the second aperture where light is getting re-scattered, and they are from the rings, which have much less light in them anyway. It all boils down ti where the magic "good enough region" lays. In any case, it's a thing that would need calibration. Not something that I would trust to laser cut acrylic tolerances.

[Feign]

Just found the formula for it! The distance between the rings of light (y) is based on the equation y=D((mλ)/d) Where D is the distance from the aperture and d is the diameter... m is a constant whos origin I don't know...

Here's a handy little calculator (physics department websites are quite handy): Circular Aperture Diffraction Plugging in the numbers, for a .5mm first aperture diameter and a 10cm spacing between the first and second apertures, the minima (dark space between rings) has .01cm of wiggle room to calibrate the placement of the second aperture.

But like I said, you don't have to get it exact to get the scatter down significantly.

[erikk]

... m is a constant whos origin I don't know...

m = 1 for the first ring, 2 for the second... etc.
Its means the 10th ring is 10 times the angle from center as the first ring
Edit: maybe m isn't exactly nice numbers but there's an m for every minimum/maximum ring

[jsondag]

What if you used a pump like this. http://www.ebay.com/itm/6v-dc-Dosing...item2ed1c1d0d1
You can reverse the direction. Pump in some water, pump out some of it, and repeat. You can raise the resin over the print and back down. All it takes is a little attiny85/45 or something, which are a dollar or two, and a small H-bridge chip. You could integrate it into your board fairly cheaply, or let people use an arduino or similar. This would solve your drip inconsistency, as well as a number of other problems.

[Aztecphoenix]

What if you used a pump like this. http://www.ebay.com/itm/6v-dc-Dosing...item2ed1c1d0d1
You can reverse the direction. Pump in some water, pump out some of it, and repeat. You can raise the resin over the print and back down. All it takes is a little attiny85/45 or something, which are a dollar or two, and a small H-bridge chip. You could integrate it into your board fairly cheaply, or let people use an arduino or similar. This would solve your drip inconsistency, as well as a number of other problems.

I'm not so sure about using the reverse feature, but make sure you use varable speed otherwise you can't adjust the flow depending on the size of your print

[User_Defined]

Feign Thank you so much for the suggestion ... ive been using a bunch of razor blades stuck to a hollowed out magnet, by sliding the blads up to the beam scatter I can reduce it, but i love the threaded hole idea.... i have a piece of solid graphite ( quite black ) im going to try threading that now.

I have been theorizing exactly the scatter reduction technique you speak of on our white board, good to know with some confidence that multiple apertures is worth trying.

Easy fix for this:

Make some kind of foil holder mechanism that will attach onto the laser diode module. Inside this foil holder will be three discs of aluminum foil (basically like your instructional video, except with three foils within it).

Then perform the same hole making action but pierce through all three foils at once. The only thing is that it would need to be very straight.

You could probably try it easily with some big washers for spacers, with foil folded between them and crumpled on the sides to hold it all together.

For the actual implementation, have the foil holder as part of the peachy frame, and use 4 laser cut plastics before the first foil to line up and guide the hole piercing probe and ensure it being straight. This should keep everything aligned with the laser cut frame and reduce human errors.

Or, make an alignment tool with 4 laser cut plastics for when you need to pierce the triple hole.



- UD

[jsondag]

I'm not so sure about using the reverse feature, but make sure you use varable speed otherwise you can't adjust the flow depending on the size of your print

You can use PWM from the attiny to control the speed. The H-bridge is what reverses the direction. It's just an input line on the H-bridge to reverse the polarity, and thus, direction of the motor.

[jsondag]

What if you used a pump like this. http://www.ebay.com/itm/6v-dc-Dosing...item2ed1c1d0d1
You can reverse the direction. Pump in some water, pump out some of it, and repeat. You can raise the resin over the print and back down. All it takes is a little attiny85/45 or something, which are a dollar or two, and a small H-bridge chip. You could integrate it into your board fairly cheaply, or let people use an arduino or similar. This would solve your drip inconsistency, as well as a number of other problems.

Thinking about this, it actually makes sense as an external add on. It would have an output for the pump motor, and an output to the sound card to simulate drips. One adjustment knob to change drip rate independently for calibration to container size, and another main knob to change motor speed. The main knob would adjust speed, and drip pulses linearly.

If anyone were interested in this as an add on, once I get my peachy, I could easily draw up a PCB, make it a kit, and open source it.

[Aztecphoenix]

You can use PWM from the attiny to control the speed. The H-bridge is what reverses the direction. It's just an input line on the H-bridge to reverse the polarity, and thus, direction of the motor.

I meant, I don't really see the point in using the reverse, I don't feel as though it could be precise enough to pump out exactly enough water to bring the level back to proper height to resume the print or even whether it could pump out fast enough so the prints don't take hree times as long, but I do agree with the PWM for speed control