Assembly from atomically precise nanoscale and microscale parts

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Nanoscale specialized end-effector exploiting nanoscale physics (van der Waals sticking force) for not needing to resort to complex gripper mechnanisms. (CLICK IMAGE TO SEE ANIMATION)

This is about assembly from smaller base parts (already bigger than atoms) to larger composite structures. Like e.g.:

This page shall focus less on a particular size scale,
and more on the relevant physical forces and design consequences in the context of assembly.

Relevant Nanoscale physics for assembly at smaller scales

Related: Intercrystolecular forces

Change of dominant forces

For part manipulation and assembly context:
At the macroscale the dominant fundamental physical forces are:

  • (1) unavoidably only downward directed gravity (excluding in space of course) and
  • (2) avoidably omnidirectional magnetic forces

At the nanoscale the dominant fundamental physical forces are instead:

  • (1) unavoidably omnidirectional van der Waals forces (and avoidably electrostatic forces) and
  • (2) unavoidably omnidirectional thermal motions (to lesser degree) (also less of a "fundamental force")

Van der Waals force replacing gravity in importance

The (mostly) attractive van der Waals forces between atomically precise flat surfaces …

  • … are very strong. While they are more than 100 times weaker than covalent forces, covalent forces are enormous, thus they are still huge.
  • … are proportional to surface area.
  • … would be strong at the macroscale too but one rarely encounters flat enough surfaces meeting each other.
  • … are dominant over gravity due to down masses becoming so small relative to surface areas. Well known scaling law.

Dominance of van der Waals forces means that everything sticks together.
(Related but less applicable here due to already being bigger than atoms: Sticky finders problem)

This van der Waals force sticking …

  • can be exploited in assembly in various ways, in particular simplifying the end effectors for part manipulation.
  • preventing random thermal motions jolts from making parts flying off (evaporate/sublimate like gas molecules)

For more details see main pages:
Van der Waals force & nonbonded interactions

Change of relevant effects

Not fundamental forces, but highly relevant phenomena/principles/effects as holding methods and connection methods there is:

  • (1) Friction forces, these do not translate well to the nanoscale, conservatively better assume absence of it.
  • (2) Form closure working perfectly totally scale invariantly across all scales.
  • (3) Energy barriers by deformation (i.e. bending)

The last (3) latter combined with the preceding (2) gives sort of snap fit clip connectors.
These should work well at the nanoscale with some energy efficiency caveats.
(1) and (2) sort of blur. More on that later.

stick-n-place ~vs~ pick-n-place

Grippers style end-effectors may be unnecessary and mostly redundant.

Omnipresent omnidirectional attractive van der Waals force i.e.
everything sticking to everything should be exploitable to
simplify the structural complexity of part manipulating endeffectors.

What (sort of) replaces friction at the nanoscale is commensural interdigitation of atomic corrugation.
So static friction at the macroscale (sort of) converts to a special case of form closure at the nanoscale.
This does not constitute dynamic friction which is an other story that is …
… less relevant here in the context of parts assembly by end-effector and
… more relevant in the context of moving bearings in the robotics behind the end-effector.

pick-n-place – nanoscale physics abiding assembly

Macroscale: (Avoiding having magnets in all parts)
one usually desires something like parallel acting grippers that feature:
– either sufficient friction to the gripped parts
– or sufficient fully enclosing shape complementarity to the gripped parts.
'What one inherits from naively copy pasting over to the nanoscale:

Static friction related NEUTRAL/PRO:
– Given static friction (sort of) becomes commensural interdigitation form closure
an advantage of gripper style end effector design might be that
pressing force can raise the corrugation energy barriers
an thus exponentially reduce the likelihood of slipping due to accidental slip notch jumping.

Static friction related NEUTRAL/CON:
– Always the risk of one-off corrugation misgrippings.
– Shoving the part all the way back may work for some parts.
– parts with surfaces incommensurate to the grippers surfaces may be superlubric and be sucked back by van der Waals forces

Undercutting form closure related CLEAR CONs:
– A possibly non-trivial clasping motion is needed preferably keeping brackets parallel.
– An undercut is needed to prevent slide-out of parts thus one gets stronger constraints on shape complementarity.
– Form closure induced shape constraints distribute to the parts site and gripper style end-effectors side.
– A larger number of standard gripper end-effectors may be needed.

stick-n-place – nanoscale physics exploiting assembly

End-effector manipulators designed for exploiting nanoscale physics:

Van der Waals force (and partial form closure) CLEAR PROs:
– No clasping motion is needed, just a means to push off the stuck on parts is needed
– Much weaker constraints on shape complementarity. No need for undercuts in shape complementary pickup.

Static friction related:
– Intentional design for superlubtic suck-up leading to reliable larger scale self centering
… possibly less placement accuracy needed


Static friction related NEUTRAL/CON:
– For non-superlubcric cases: Always the risk of one-off corrugation misgrippings.
– commensural interdigitation sticking might be weak to jolts from bending snaps
and even thermal motions for the very smallest small surface contact areas and high temperatures
– accidental slip notch jumping

Unintentional misplacements

Going down from the strongest and most likely pertorbation (shock) to the weakest and least likely.
This qualitatively foruses on external influences not insuffieciencies in the driving robotics. At last not directly.

Van der Waals force combined with commensural interdigitation causes static friction
– energy barriers against sliding
– force barriers against sliding
Referred to as notches in the following.

Slip-notch-jumps and even full-fly-off due to off-site snap induced shocks

Violent shocks from bending snaps acoustically transmitted elsewhere
(and not yet fully thermalized) may not only lead to slips but even full fly-off.

There are non-thermal shock motions but
with thermal speeds (~ speed of sound) and larger amplitudes. See pages:

Slip-notch-jumps due to thermal motions (unclear)

But the energy barriers against sliding are much smaller tha the ones for full ripp-off
and thus more amenable to be overcome by mere thermal motion energies.
I.e. high temperatures may be able to supply sufficient energy to
cause unintentional slips across commensural interdigitation energy barriers.
Especially when nearing more incommensural cases with
zero static friction as the limit in the case of superbubricity.

Full-fly-off due to thermal motions (unlikely)

Van der Waals force more or less suppress thermal motion based undesired disassembly.
Due to van der Waals force being so surprisingly strong
even rather small contact areas already suffice to prevent a full separation fly-off event and that
even at the highest temperatures materials can endure before decomposing/melting/…

Small crystolecules

– Small parts feature small surfaces so binding energies can't be very high for these. Lower vdW sticking force.
– Small parts can't have many atomic grooves and thus can't be very incommensural. Raising the (low) force against sliding a notch.

Summarizing hypothesis and related questions

(TODO: Prove / corroborate following hypothesis and answer subsequent questions.)

Hypothesis:
To do assembly of crystolecules
one can rely on attractive van der Waals forces,
thereby avoiding the complexity of grippers that
constrain part position via undercutting form closure.

❓Q: How big are binding energies and
maximal attractive forces per area more precisely
i.e. beyond existing models?
=> Intercrystolecular interactions

❓Q: How likely do snaps yields undesired outcomes?
Snaps of similar or greater energy to
binding / "holding" energy.
Misplacement / fly-off to stick elsewhere / …
=> Intercrystolecular snapping modes

❓Q: What are the snapping modes? And …
❓Q: In how far need can and need these
snapping modes be avoided
in crystolecule assembly?
=> Intercrystolecular snapping modes

❓Q: Are there furthe ropportunities?
=> Intercrystolecular levitation

Related

External links

  • Snap fit
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