Planar Assembly Scale

Jim Moore asked how small it would be useful to go with planar assembly.

A bit of background: When Eric Drexler proposed, back in 1992, that molecular manufacturing should be done in tabletop factories rather than vats with floating robots, his proposal had nanoscale sub-components being made and then put together in larger and larger assemblies by converging assembly lines. This design made a lot of sense, and variations of it were studied over the next decade.

Then, just a few years ago, John Burch and Eric Drexler came out with a new nanofactory architecture: one that made medium-small components, and then stuck them directly onto the surface of a product under construction, building it up block by block. This works because, as long as the machinery handling the block can scale down in proportion to the block (and scale up accordingly in operation speed), the linear deposition rate does not change.

So how small can planar assembly go? Well, the machinery to handle feedstock molecules will probably be quite a bit bigger than the molecules. So planar assembly probably doesn't work all the way down.

But it can go pretty far. The smallest number Jim asked about is 100 nm - the size of a smallish bacterium. Well, you can fit a lot of machinery into a block of that size. In my Primitive Nanofactory paper, I suggested 200 nm blocks - only eight times the volume.

It seems to me that the lower bound on size is set by the interfaces between blocks. If the blocks are intended to be functional - to include nanomachinery - then there will have to be interconnections between each block. If the interconnection systems are 10 nm thick, then almost 50% of a 100-nm block will be used up in connection hardware. A 200 nm block would use only a bit over 25% of its volume for interconnects.

There's not necessarily any upper bound on block size, but I don't see any reason to make them bigger than 200 nm. One nice feature about 200 nm blocks is that there's a fairly low chance per block of background radiation damage. You can pretty much design the machinery in a single block without worrying about fault-tolerance, and do your fault-tolerant design at a higher level. If your block was a micron or bigger, you'd have to assume that something inside it would probably be hit by background radiation in less than a year, so each block design would have to include some fault tolerance.

Jim's question included the suggestion that planar assembly might be used at small scales to make parts that could be assembled into the final product. To a first approximation, I don't think this is necessary, since the final product can be made directly with the small blocks. Rather than building a part and then fitting it into place, just build the part by planar assembly in its final position. That means you'll be building lots of fractional parts in layers at the same time, but I don't see a problem with that. The block-joining mechanisms should work the same in either case.

One more advantage to building the entire product directly out of small blocks: you never have to handle parts that are big enough to be heavy. In other words, you don't have to worry about gravity.

So planar assembly is an extremely flexible approach to building products, and should save a lot of volume and design complexity in nanofactories.

Chris Phoenix

Comments

[marie]

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[Tom Craver]

Just a nit - any "loose" part (not bonded to neighbors) couldn't be reliably made "in place" unless you make them embedded in some sort of removable scaffolding.

E.g. how would you make chain link or a chain mesh?

Since planar assembly should otherwise be quite general, I think we can speculate that removable scaffolding will be part of planar assembly.

[jim moore]

Assembly Ribbon Mill
ARM - the brainless assembler

This design is an attempt to simplify and extend the Planer Assembler design for Fabricating objects. The big advantage of this method is that the assembly ribbon contains the information and provides scaffolding for making an object. (it also effectively disconnects your assember system from the internet)

Basic Parts:
Building Blocks- 10 microns per side pre made and nano precise.
Assembly Ribbon- The ribbon is made of graphene and is~10 nm thick, ~250 nm wide and a ~1.1 meters long. The ribbons have patterns of holes along the length that code for particular types of building blocks or empty space.
Deposition Stations - sense the pattern of holes in the assembly ribbon and deposit blocks.
Housing - holds the deposition stations and provides structure for the flow of the assembly ribbons.

So the process looks like this:
For a cubic meter Fabers you will need ~10 billion assembly ribbons to code for the blocks and the empty space that make up the fabricated object. All together the assembly ribbons would make an instruction tape ~1 mm thick, ~25 mm wide and ~ 1.1 meters long. (maybe roll it up in a reel to keep it free of contamination)

The Assembly Ribbons are separated and move through a series of building block specific disposition stations (one station per type of building block) that sense the patterns of holes in the ribbon. If they code for the stations block type a block is deposited on the ribbon. The blocks (in an unassembled state) have on one side a grove ~250 nm wide and ~15 nm deep. In the grove there are pattern of rods that can be extended or retracted The rods fit into the holes in the ribbon. There is at least a ~1 micron empty space between blocks on the ribbon.

After the assembly ribbons move through the deposition stations they are simultaneously guided by the housing so that the blocks come together in the X-Y plane. Once the blocks attach to their neighbors (in the X-Y plane) the rods that are inserted into the holes in the assembly ribbon are retracted. The X-Y slices of the object are then pulled together as the ribbon is pulled through the groves in the blocks and rewound on a reel. After the assembly ribbons are pulled through the object the rods in the grove on the blocks are extended to fill in the grove.

( one kind of retro future aspect to this design is the ARM could be powered by a hand crank----- pull a reel down off the shelf, feed it to the ARM, crank the handle for a minute or two and out pops a new cell phone, electric bike or what ever.)