The Overtool: A Proposed Universal Assembler
By Forrest Bishop
Copyright (c) 1996 All Rights
Reserved
(0) Abstract
A proposed method of constructing a Drexler Universal Assembler is outlined.
The essential features include an "MNT Active Cell", and a manipulator
mounted on an active cell. An aggregate of these devices provides the
necessary functionality, variability, and means of transport to form the
core of a general assembler, for macroscopic assembly as well as for diamondoid
mechanosynthesis.
The active cells and manipulators are further broken down into
a set of standardized parts. The assembler should be capable of making
and assembling all of these parts, and thereby replicating itself. Figures:
(1) Introduction
Some observers, including this author, think the putative Drexler Universal
Assembler would be the most important new tool since the stone ax. In
addition to replicating itself with atomic precision, this kind of machine
would be able to construct many other atomically perfect products, and
in effect displace most current manufacturing methods [refs]. These new
products would have properties and capabilities so far beyond contemporary
machinery as to be unrecognizable as human artifacts [refs]. The ramifications
of this are qualitatively different from those of any other technological
advance to date, hence the name "Overtool"[refs].
Much progress has been made in the last few years toward specifying the
requirements of such a device [refs], yet many issues are still unresolved
[refs]. Some of these problems involve designing a machine with enough
variability in its permitted degrees of freedom to perform the immense
number of different tasks needed, as well as proving out a reliable algorithm
for the assembly process.
The essence of this proposal is to reduce the number of individual parts
(the cells) to a small set of identical components governed by a few simple
rules of interaction. A collection, or aggregate, of these cells then
form a device of arbitrary size which can change its configuration to
fit the desired task. These "active cells" are essentially cubicle,
and thus constrained to relative movement in only one of the three perpendicular
directions at a time [refs].
A second type of cell has much the same functionality as the "standard
cell", except that one of the faces of the cube holds an "XYZ
gantry", similar to a contemporary Coordinate Measuring Machine [ref],
to permit the fine control and generate the forces needed for diamondoid
mechanosynthesis [ref]. This simple type of three-dimensional manipulator
may seem to be too restricted in its motion to perform the many necessary
maneuvers. It will be shown that when incorporated in an active cell aggregate,
and programmed to work in concert with others of its kind, this machine
can indeed execute a large class of rotational and translational movements
of interest to the mechanosynthesist.
The tip of this mechanical arm may have a holder for interchangeable
tools, or perhaps a dedicated tool [ref]. As there are six faces on a
cube, there are six possible orientations for this "Gantry Cell".
This means a number of Gantry Cells can be simultaneously engaged in a
particular process. Some of the cells can be holding, straining, and rotating
an arbitrary workpiece, while others fetch reactive species or perform
abstraction reactions [ref].
Although is not strictly necessary to use the XYZ gantry, a number of
advantages incur. Its geometry is quite compatible with the cubicle active
cell, simplifying the design. In addition, the Cartesian kinematics are
trivial, for both forward and backward solutions [Ref]. This means the
development time, as well as the real-time computation, are significantly
less than what would be required for a more elaborate robot arm.
A secondary feature is the "Moiety Palette", which is based
on an active cell "passive faceplate". What would be the interior
surface of this component is made flat, with receptors incorporated for
the desired molecules. These may be as simple as a single crystal Au(111)
surface, for self assembling monolayers[Ref], or more specifically tailored
receptors. A similar device is used for waste removal.
(2) Active Cells (Figure "Assembled XY Cube", "Interior
View")
The design presented in ("A Proposed MNT Active Cell") is used
here as the basic unit of the assembler. This standard active cell is
composed of six individual faceplates, which are designed in a manner
that permits omitting any one of the faceplates (and its associated "busbar")
without seriously compromising the integrity and functionality of the
cell. The remaining five faceplates can be assembled in several different
sequences to form an open ended box. It is necessary to adhere to the
various 'XY' faceplate orientations used for a full, six-sided cell to
maintain compatibility with the aggregate.In the case of omitting the
passive faceplate that holds the motor, another of the two remaining passive
faceplates can be used for this. This same strategy applies to any special
structures mounted on the interior surfaces of the faceplates, and so
good design precludes depending on absolute orientations of these internal
components.
(3) XYZ Gantry Cells (Figure "Gantry Cell")
The second major assembly is an "XYZ Gantry" with a base
configuration that allows mating to the open side of the otherwise standard
active cell. There are six possible gross orientations for this gantry
(+-('x','y','z')). Additionally, since the faceplate joints are four-fold
symmetrical, two or four 'XY' orientations are possible, depending on
the symmetry of the gantry itself. It may be possible to allow a portion
of the 'Z' axis actuator to extend into the included volume of the active
cell, depending on the arrangement of the internal parts of the five-faced
standard cell. This is not strictly necessary. A Gantry Cell can be two
or more times the standard cell edge length in its local '-Z' direction
without putting undue constraints on its versatility. The gantry cell
of figure (Gantry Cell #1) is designed to fit within a volume of two standard
cells without interfering with the interior components of its active cell
base. The gantry cell of figure (Gantry Cell #2) fits into a three-cell
volume, and can extend further in the 'Z' direction.
There are several possible layouts and actuator types for the drive mechanisms
for this robot arm. A molecular mechanical version of a screw drive is
perhaps the most obvious. The mechanical power is provided by the logic
engine motor in the active cell base.
Moiety Palette (Figure Moiety Palette)
This device is a flat, square plate formed from a standard passive faceplate.
One side has the standard passive t-post layout,the other side is flat
and contains receptors for the desred molecules. They are then able to
be moved around by active-faced cells without needing any extra components
onboard themselves. The edges of the palette can be brought out to the
edge of the cell, such that the edge length equals the cell metric. This
would allow a number of palettes to be brought together to form a flat
surface of any size, which can then be treated with a bulk process, if
desired.
There are only three gross orientations available for these types
of palettes (say -('x','y','z')).
(4) Working together (Figures "14 Gantry Cells", "Strained
Shell")
With the above specifications, as many as 14 gantry cells of the six
possible orientations can be brought together such that their working
tips are confined to the same small volume (say 1000 nm^3, depending on
the tip geometry). For example, four each of +-'z', two each of +-'y',
and one each of +-'x', are brought together as depicted in (figure 14
gantry cells). One of the 'z' cells is shown with a different 'XY' orientation
than the other three, as mentioned above.
This configuration, or some part of it, would be useful in straining
a bearing sleeve such as the one depicted in [1], Figure 1.1. The +-'x'
tips are brought together to form a mandrel. Some portion of the remaining
12 available gantry cells then bring a pre-assembled flat strip up to
the mandrel and wrap (and strain) the strip around it. While these cells
hold the strip in place, another available gantry cell(s) performs the
necessary abstractions and reactions needed to finish the joining. The
+-x tips then retract, freeing the finished part.
Handing Off Parts
Caterpillar (ref Peter Will)
Gantry Attachments
{1} Reaction tools
(a) Carbyne Tool
(b) C2 Tool
(c) Abstraction tool
{2} Part Handling Tools
(a) cones- positive and negative
(b) faceplate fixture
(c) Mandrel
(d) Flat or grooved plate
Abstraction [refs]
Reaction [refs]
"Dynamic" reaction
When a perpendicular force is not suitable for the reaction, the angle
can be made to vary by moving both workpiece and reactive species in coordination.
The simplest example is 45 degrees: both manipulators approach the intended
reaction coordinates at the same rate. A net relative twisting motion
can be superposed on the general velocity vectors, if need be. This method
also eliminates the need for a rotating joint on the manipulator, in most
pertinent cases.
Torqueing a Pi bond [ref]
Translating and Rotating the workpiece.
AFM topography [ref] for QC.
In this mode the gantry cell is functioning exactly like a coordinate
measuring machine. A force feedback system is required for the 'Z'-axis
arm.
Parts assembly.
Active cells form grippers for larger pieces. Dedicated jigs in
the usual sense are generally not required: the active cell aggregate
can emulate any required shape, and apply net forces of any magnitude
(up to the breaking strength of the active cell) and direction to exterior
points of the workpeice. The required force is generated by engaging the
drive systems of a number of cells connected in parallel. The direction
of the net force vector is then controlled by the number of connected
cells engaged in each of the three perpendicular directions, i. e. the
vector components.
(5) Reactive surfaces, manufacturing environment, transport in
and out of. (Figures "Assembly Line Model", "Eutactic Space"
Transport- active cells with moiety palettes form arbitrary conveyor belt.
Bulk processing
A group of similarly oriented moiety palettes (figure Moiety Palette)
can be brought together to form a flat surface of an arbitrary size. The
Palette can be a square with an edge length equaling the cell metric,
so that the arranged palettes form a continuous surface. Although this
would interfere with 'Z' translation in the usual sense, active cells
could be made to move out of the way to permit this movement.
A "top down" bulk process can now be used to impregnate the
receptor surfaces, or to remove waste products [refs].
Forming an eutactic environment as in Nanosystems
(6) Large Structures
The architecture of an active cell aggregate is eminently scaleable,
from the assembly of mesoscopic systems, to the mechanosynthesis and assembly
of quite large structures using the same cell family. The diameter of
the shell in figure ("Strained Shell") is intentionally omitted.
It may be 1700 nanometers, or perhaps 1700 kilometers (space-based) [ref].
It would be necessary to build such a large structure of something very
strong and cheap, like diamond.
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