This could work

[mike_biddell]

How about this idea to overcome laser intensity and focus problems, due to distance from print to peachy changing as the print progresses. Dump the upper tank completely and in the lower tank have a telescopic platform, say 8 inches in diameter and with nesting cylinders with a weight and an O ring. Place a valve at the base of the cylinder and open it as the print starts. the cylinders are full of saline and fully extended to contact the floating resin. When the valve is open, the weight pushes the top cylinder downwards and expels the saline into the tank, thru the orifice (so the level in the tank never varies). The platform will fall under gravity in an entirely deterministic way for a given orifice. So once calibrated, Z is deterministic. The cost of two nesting cylinders with an O ring is minimal and hence we could have a very cheap lowering platform, with a decent print size, and peachy would remain at a fixed distance from the print. This idea overcomes problems associated with floating solutions with the wobble factor and overcomes focus problems.

[Anuvin]

I think I see where you are going with this idea, and I do like it, but I am having a hard time conceptualizing it. Any chance you could doodle up a design?

[mike_biddell]

I think I see where you are going with this idea, and I do like it, but I am having a hard time conceptualizing it. Any chance you could doodle up a design?

two cylinders nest into each other and are sealed with an O ring. The top cylinder orifice is to allow the cylinders to be full of saline and is closed when printing starts (using a small bung). The shaky rectangle on the top cylinder is a weight. You simply pull the cylinders apart until the top cylinder just touches the resin, then close the top orifice. The platform descends, expelling saline out of the bottom orifice, back into the tank. The descent of the top cylinder for a given orifice size and weight should be reliable and reproducible, as long as the O ring is not too worn. Sorry for the rubbish sketch.

[Slatye]

Build_platform.jpg

Something like this? So the green cylinder slowly displaces the water in the blue one, at a rate determined by how far open the valve is (and obviously the Peachy's water drop sensor gets attached to the valve).

There might be some issues getting the friction low enough on the O-rings; you might have to grease them before each job to keep them sliding nicely.

[mike_biddell]

Build_platform.jpg

Something like this? So the green cylinder slowly displaces the water in the blue one, at a rate determined by how far open the valve is (and obviously the Peachy's water drop sensor gets attached to the valve).

There might be some issues getting the friction low enough on the O-rings; you might have to grease them before each job to keep them sliding nicely.

slatye.... your drawing is a million times better than mine....but the bottom cylinder must also be contained in the tank such that the when the saline is expelled it leaves the volume in the tank unchanged. If the weight is large, the O ring friction becomes a negligible factor. But thanks for grasping the concept so quickly as it is difficult to describe.

[Slatye]

Hmm, not quite sure that I fully understand that bit. I was assuming that you'd have an O-ring around the bottom of the main tank so that the "printing water" (in that tank) is completely separated from the "support water" (in the lower cylinder). You use up the support water, but the printing water remains fixed so you've got a constant volume of that. This should just result in the green cylinder/piston moving down, lowering the print bed into the printing water and resin.


Regarding the weight, there are two problems with making it really heavy. One is obviously that it'll be a pain to ship it - you might have to ask end users to attach big steel bolts or something to make it heavy enough. The other is that there'll be a lot of pressure in the support cylinder which makes it difficult to find a suitable valve setting. Still, it might be that this is just what has to be done to make it work. It'd be a small price to pay to get a nice printing platform.

[mike_biddell]

Hmm, not quite sure that I fully understand that bit. I was assuming that you'd have an O-ring around the bottom of the main tank so that the "printing water" (in that tank) is completely separated from the "support water" (in the lower cylinder). You use up the support water, but the printing water remains fixed so you've got a constant volume of that. This should just result in the green cylinder/piston moving down, lowering the print bed into the printing water and resin.


Regarding the weight, there are two problems with making it really heavy. One is obviously that it'll be a pain to ship it - you might have to ask end users to attach big steel bolts or something to make it heavy enough. The other is that there'll be a lot of pressure in the support cylinder which makes it difficult to find a suitable valve setting. Still, it might be that this is just what has to be done to make it work. It'd be a small price to pay to get a nice printing platform.

slatye..... there is no problem with the user adding the weight, so it is not shipped. You will see with your sketch that the volume in the tank will drop as the platform drops.... the whole concept is that the level in the tank does not drop.... therefore the expelled volume must be into the tank, so that the level in the tank does not change. The heavy weight takes friction out of the equation, and to compensate, the orifice is quite small.

[masterada]

Hey guys!
What about this sollution?
printersketch.jpg
If the size of the 2 containers is right, the resin should stay in place, while the inner container floats down (didnt do the math). The z-speed remains measurable the same way it was before.
The sketch misses some stuff (like some supporter rods or something for the inner container so it wont float randomly in the x-y plane, and a plug from the inner container to reset the setup).
The laser is in a fixed position above the whole setup.

[Feign]

Masterada, I actually really like that one. It allows your outer tank to be vary heavily built up to hold the hydrostatic pressure of a really deep resivoir and the inner tank doesn't need much structure at all.

Looks like a good alternative to the floating laser base that was talked about in earlier threads.

[mike_biddell]

Masterada, not quite sure how the fluid gets from the outer container into the inner. If it's syphonic action, how do you start the syphon? I believe your solution would work if you just retain the upper tank and drip from that. Your inner tank should have arms which touch the outer tank, to prevent relative movement of the inner tank, with respect to the outer tank.