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« New Molecular Building Block? | Main | Unwise Use of Nanoparticles? »

September 17, 2009

Comments

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Baughn

While I understand that this is only if the parts have previously been stockpiled, the "one meter per second" number is considerably more than I expected.

If you don't mind, could you point me at some reference for that?

todd

Agreed

So you can use very small blocks - sub-micron, even - and still "extrude" your product on the order of a meter per second.

I do not recall this production rate noted before although I like that number :) .

Chris Phoenix

Well, that's my own estimate, and I don't really have a lot of calculation to back it up.

To tell the truth, I did the thinking about this a while ago, and it's possible that I misremembered my conclusion. It might be a centimeter per second or a meter per minute.

I'm thinking of snap-fit fastening and conveyor-belt placement. Automated factory machines can move things around at much higher rates of speed - but the things are smaller. Picture a belt with decimeter cubes - the end of the belt scans across the product face and slaps the cubes into place - each belt end covers maybe 2 square meters, the cubes are spaced a few decimeters apart on the belt, moving at say 2 meters per second...

So you're delivering maybe 1 cube per second, and you need 400 cubes to make a decimeter layer - that's 4000 seconds for a meter. Ugh, 3 orders of magnitude off! OK, I'd better do more thinking about this. Of course, if you can pack the belts more closely or move the cubes faster, you can probably save an order of magnitude or more.

I'll adjust the post after lunch. Thanks for raising the question.

Chris

JJ

Agree with Baughn, thanks for post.

Chris Phoenix

JJ, I don't understand - Baughn's comment no longer applies - I've corrected the number he questioned. See my comment, above, from Sept. 18.

Chris

jim moore

The main problem I see with the Planar Assembly technique is that the plane of assembly is a bottle neck and a place with very limited redundancy.

But a Scaffold Assembly Technique would able to extrude an obeject at the speed of the conveyor belt plus a fixed amount of time because the system is bigger. It is also easier to add redundancy to this system. The scaffold can be very simple - an array of ribbons all in tension.

(To model your example)
You have 100 ribbons 2 cm wide 1 mm thick.
Each ribbon moves past a series of cube deposition stations at 2 meters per second.
The 3 d array of deposition stations is 3 x 3 x 8 meters.
As the ribbons (covered with cubes) funnel down to a one cubic meter box, the cubes snap together forming the object.
Total distance traveled ~12 meters or 6 seconds to extrude a 1 cubic meter sized object.

Tom Craver

I'd guess that either stuff doesn't stick enough to secure it while the deposition workstation applies pressure (i.e. it might rock or twist) and has to be held in place - or it sticks enough and thereby makes the parts essentially bonded instead of freely moving. For some materials, that'll be OK - eg a rubbery material.

Deposition workstations could probably hold the product in place - however, that adds a new dimension of complexity. For a non-moving product, you just had to create a static design and fill it in, maybe picking the right type of block for each position. Now you need to compute the forces needed at each step to maintain the product in position, OR have a process that always holds the product in position.

Figure you need at least three points of contact to lock the product against roll/pitch/yaw. And their positioning needs to be programmable (not necessarily dynamically so) to adapt to products with different hole positions. I.e. visualize the difference between pinning down a ring shaped product and a spherical product that would fit through the ring, but both of a size that a single or few deposition workstations would produce them.

I'm thinking that there may be a fuzzy "design limit" on complexity, and if the overall design has a lot of mobility (e.g. cloth, rubber-like) it probably has a highly repetitive design that allows a handful of pinning processes to suffice.

Chris Phoenix

Answers to both Jim and Tom...

Tom, there will definitely be a fuzzy "design limit" on complexity - just as there is for software.

As to things sticking together by surface forces: we should distinguish what happens during construction from what happens once each part is constructed. During construction, the part will be held by the deposition machinery, and will probably be either in close contact with neighboring parts, or sufficiently separate from neighboring parts that surface forces aren't very strong. Everything that's constructed will have to be held by the construction machinery, so I don't see added complexity from having multiple parts that don't apply much force to each other.

Once the part is constructed, and released by the construction machinery, it may flop sideways if it's not already in contact with another part. As long as this motion does not interfere with the handling of other parts that are still under construction, then there likely won't be a problem. But this is something to be determined for each class of product and/or part. Of course, if the part was fabricated in contact with another part, it won't move when released, and there's no problem.

Jim, I suspect that there's a topological equivalence between the scaffold assembly you're picturing, and the planar assembly that I'm picturing. If you deform the plane into an elongated pyramid, don't you basically get a scaffold assembly system?

And if you folded the belts over so that instead of running parallel to the product path, they simply deposited the blocks as the belt did a U-turn, wouldn't you be able to place them all in a plane?

It may be that stretching out the plane is a good way to deal with fault tolerance issues. There are at least two other ways to deal with these issues. One is to build the machinery big enough that each workstation can have fault tolerance built in. This probably means the blocks have to be quite a bit larger than a micron, which would then require two stages of assembly as in the Burch/Drexler animation. Another approach is to make the machinery flexible enough that adjacent workstations can fill in for a non-functional workstation.

Chris

Tom Craver

Chris - if you haven't seen it - this is kind of cool and sort of relevant :

Lego Digital Designer"

Now they just need to provide a way to automate assembly... And maybe work with the Play-doh folks to let you automatically extrude your own custom blocks around a Lego blank...

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