Difference between revisions of "Mechanical computation"

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= Why nanomechanical logic =
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{{stub}}
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{{todo|add info about Macromechanical computation}}
  
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* It can be built smaller than nanoelectronics (bound atoms practically do not tunnel away like electrons)
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As it became apparent that computers can be useful tools (to a few privileged individuals in the past)
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* It is easier to do [[exploratory engineering]] about nanomechanics than nanoelectronics. (See: [[non mechanical technology path]]).
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electronics was still immature (compared to the "silicon transistor age")
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So there where attempts to build computers in a purely mechanical approach.
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Electronics quickly majored though and mechanical computers turned out to be vastly inferior to electronic ones.
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As a result serious attempts at mechanical computers design are limited to only a brief but fascinating episode of history.
  
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= Basic elements =
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With the coming advent of atomically precise gem-gum nanosystems
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mechanical computation might experience some revival due to several reasons.
  
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=== Differentials ===
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= Benefits of mechanical computation over electronic computation at the nanoscale =
  
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One of the most important things in any computer are wires and forks of them.
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* Speed: making things smaller makes them faster (a [[scaling law]]) - up to low GHz range is reasonable for nanomechanical computing
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* Friction: while crudely etched micro-electro-mechanical systems (MEMS) have huge problems with friction the polar opposite is the case for atomically precise [[mechanosynthesis|mechanosynthesized]] nano-electro-mechanical systems (AP-NEMS). See: "[[Superlubrication]]" 
  
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The mechanical elements that correspond to simple electrical connections (solder points) are
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* Nanomechanics in general features [[Nanomechanics is barely mechanical quantummechanics|near classical behavior at the nanoscale]]. This makes design easier and more straightforward. Sharp corners in conductive nano-wires can create unexpected high resistances for electric currents due to ballistic transport effects. There's a lot of experience from todays silicon wafer technology though.
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mechanical differentials (that includes planetary gear assemblies and linear versions).
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The angular speed (corresponding to electrical current) distributes proportional to the loads ([[http://en.wikipedia.org/wiki/Current_divider current divider]). (Simple splitups of geartrains act like [http://en.wikipedia.org/wiki/Voltage_divider Voltage divider]s)
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=== Testing element (gate) ===
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* Highly compact design: Nanomechanic computing systems can likely be built more compact (in gate density) than nanoelectronic computing systems. In case of nanoelectronic systems electrons tunnel through isolators with a thickess of several atoms (especially at higher voltages) which can lead to unwanted dissipation losses.
  
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As in electronic computation a single [http://en.wikipedia.org/wiki/NOR_logic universal type of logical gate] is sufficient to create any 'programmable logic arrays'.
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* In an advanced productive nanosystem like a [[nanofactory]] relatively slow mechanical motion (MHz range) is needed anyway for the [[mechanosynthesis core]]s and further up assembly robotics. So making low performance local logic purely mechanical too makes sense.
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[http://en.wikipedia.org/wiki/Programmable_Logic_Array (PLA)] can be made. See: disjunctive or conjunctive normal form ([http://en.wikipedia.org/wiki/Disjunctive_normal_form DNF] / [http://en.wikipedia.org/wiki/Conjunctive_normal_form CNF])
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In a clocked gate the input moves a blocking part in the way of the output (or not). Both are spring loaded.
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* Nanomechanic computation has inherent robustness against electromagnetic interference. Even hard against the worst case: EMP (electromagnetic pulse)
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(Instant chain logic gates work differently)
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* Nanomechanic computation has robustness against ionizing radiation (in case too filigree structure are avoided like e.g. single bonded ethyne chains). Note that with this design decision one looses the benefit of '''highly compact design''' though.
  
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=== Sequencing mechanism ===
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== A note on ternary (3-valued) logic ==
  
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The analog power-source must somehow be converted in a digital sequence.
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Mechanical computing systems may make ternary logic more easy to implement. The benefits of ternary logic are questionable though.
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Too harsh jumps in acceleration may increase power-dissipation.
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While in principle ternary has a better '''radix economy''' than binary in adder circuits (a very core component of most computing systems) the gained benefit in the adding logic seems to be lost with the carry bit logic. {{todo|add link to relevant web-pag(es)}}
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There are more possible ternary logic gates than binary ones. This may sometimes make design more complicated and less intuitive. Automated design tools can help.
  
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Quantum dispersion through anharmonic potential (see: [http://en.wikipedia.org/wiki/Coherent_states coherent states]) is probably not to expect even at low temperatures [To investigate!]. A connected nanomechanical system will have a quite high mass in daltons.
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== A note on analog logic ==
  
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= Reversible mechanical logic =
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There is a very good reason why we switched to digital systems.
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'''noise error margins''' and '''error correction''' allow for scaling up many many orders of magnitude with ridiculous levels of reliability.
  
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[[Reversible data processing|Reversible]] mechanics means: whenever an elastic element (a spring) is de-tensioned it must feed back its stored energy into the energy source.
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In fact thats exactly the same reason why a nanofactory for physical production is more desirable than being content with the current day chemistry that is adding up errors with growing product size.
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'''Stiffness is the key for suppression of thermal fluctuations.'''
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It keeps atom deposition at the right place well apart from atom deposition at the wrong place.
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Just as it keeps bits from being in the wrong state due to charge fluctuations.
  
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Testing a clocked reversible mechanical gate is done via pulling pushing turning twisting or whatever against a potential steric hindrance obstacle
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* s = (1/k) * F ... to keep position fluctuations low stiffness (= "inverse mechanical capacity") must be kept high
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that was put in place (or not) by the precedent gate .
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* Q = C * U ... to keep charge fluctuations low capacity (= "inverse electrical stiffness") must be kept low<br> {{todo|Something is reverse here. Usually there are voltage margins not charge margins. What's going on?}}
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As long as the outputs are in use the inputs cannot be removed. If they would be removed all consecutive outputs would snap back - BAD.
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Thus the testing clock signal must rise like a bar graph display.
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This is best done till an appropriate computation result is reached that has way viewer bits than the intermediate computation steps that lead there.
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While analog in pure form is unsuitable here's an idea how some form of pseudo-analog computing mechanisms may be useful in the nanoscale:
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This result can then be copied into a storage register and the output deleted. Meaning a view testing springs snap back irreversible and release their energy into the background heat bath.
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Finally one let the bar graph clock signal stepwisely recede letting go of the testing gates in reverse order and pushing back the energy into the energy source (e.g. a flywheel).
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=== Subatomic pseudo-analog mechanical computation ===
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One could say one un-computes the intermediate data garbage.
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This hole process is called a '''retractile cascade'''
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{{speculativity warning}}
  
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The energy swings back and forth between the energy storage and the many logic gates.
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What will be referred to as "pseudo-analog" in the following is analog with forbidden levels separating allowed ones.
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Tree like distributed though mechanical differenials.
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----
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In nanomechanical digital logic it seems one is fundamentally limited with the size of atoms.
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But (using rotating mechanics as an example) a torsionally stiff rotating axle can actually can resolve angular steps fine enough such that
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the circumference arc-length steps are of a size way below the size of an atom.
  
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In a programmable logic array (PLA) first the gates in the AND-plane and then the gates in the OR-plane must be evaluated in sequence.
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To tap this space one could try a strategy like this:
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The results may be fed back into other yet unevaluated parts of the PLA for a second and further rounds.
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* convert to pseudo analog
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* use analog mechanical computing mechanisms
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* convert back to digital before the levels blur to the point of unreliable separability
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* do re-amplification / error correction in the usual digital fashion
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* recurse
  
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If the negated bits are always computated in parallel the the energy stored in the springs in the gates when in evaluated state is always the same.
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The main problem here is that the gain in the compactness from the pseudo-analog part might be lost with the size of the conversion circuitry.
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Swing overshoot can be made minimal. ['''Todo:''' explain in more detail]
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Note that for every additional bit encoded in the pseudo analog value the number of levels doubles.
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So the number of encodable bits is quickly reached. To extend the number of encodable bits a bit one could cool the system to reduce thermal noise.
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But at some point one runs into eigen-modes excitated by zero point energy.
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Regaring quantum superposition of axle states for mechanically based quantum computation: the decoherence time may be way too short.
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{{todo|Inverstigate whether this has been investigated or not.}}
  
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=== Drive for retractile cascade ===
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Note: Some macroscale analog mechanical computing devices would not work at the nanosacle since they heavily rely on friction.
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A good example is the ball and disk integrator mechanism (see: "fire control computers" link).
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(Maybe related: fundamental impossibility of continuously adjustable mechanical gain chain transmission)
  
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Assuming rotative logic a possible method to generate the "bar graph display clock signal" may be like follows:
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== Related ==
  
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A binary tree of differentials to a locked chain of gears (blocked gears or geneva drives may be usable).
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* [[nanomechanical computation]]
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All gears are spring loaded and only the first one is unlocked. the torque propagates through the differential tree and turns the first gear till the endstop. This in turn unlocks the second gear. Then comes the third and so on and so forth.
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* Analogy between electrical and mechanical quantities <br>See: [[The mechanoelectrical correspondence]]
  
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= Concrete implementations =
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== External links ==
  
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* rod logic
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* Wikipedia: [https://en.wikipedia.org/wiki/Mechanical_computer Mechanical_computer]
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* rotative logic (lower maximum density of logic devices)
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----
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* pure flexture logic
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* Wikipedia: [https://en.wikipedia.org/wiki/Analytical_Engine Analytical_Engine] (Charles Babbage; base 10; never built in full)
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* ...
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* Wikipedia: [https://en.wikipedia.org/wiki/Z1_(computer) Z1_(computer)] (Konrad Zuse; base 2; rebuilt after destruction; unreliable but in a reproducible way)
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----
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= Benefits of low friction =
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* Video: [https://www.youtube.com/watch?v=s1i-dnAH9Y4 Mechanical Computer (All Parts) - Basic Mechanisms In Fire Control Computers ]
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Mechanical logical gates can either be elements that form '''instantaneous chains''' or elements that must be by a '''testing clock signal'''.
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Due to the [[superlubrication|exceptionally low friction]] of nanomechanical bearings it should be no problem to make instantaneous chains quite long.
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Also Differential gear trees with log(n) depth shouldn't pose a problem out of this reason.
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= Usage as analogous devices =
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* differentials act as analog adders
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* gear ratios act as fixed ratio multiplication
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* there's a linkage mechanism for continuous multiplication
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= External links =
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* [http://www.zyvex.com/nanotech/mechano.html Two Types of Mechanical Reversible Logic]
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[[Category:Information]]

Latest revision as of 14:27, 2 February 2022

This article is a stub. It needs to be expanded.

(TODO: add info about Macromechanical computation)

As it became apparent that computers can be useful tools (to a few privileged individuals in the past) electronics was still immature (compared to the "silicon transistor age") So there where attempts to build computers in a purely mechanical approach. Electronics quickly majored though and mechanical computers turned out to be vastly inferior to electronic ones. As a result serious attempts at mechanical computers design are limited to only a brief but fascinating episode of history.

With the coming advent of atomically precise gem-gum nanosystems mechanical computation might experience some revival due to several reasons.

Benefits of mechanical computation over electronic computation at the nanoscale

  • Speed: making things smaller makes them faster (a scaling law) - up to low GHz range is reasonable for nanomechanical computing
  • Friction: while crudely etched micro-electro-mechanical systems (MEMS) have huge problems with friction the polar opposite is the case for atomically precise mechanosynthesized nano-electro-mechanical systems (AP-NEMS). See: "Superlubrication"
  • Nanomechanics in general features near classical behavior at the nanoscale. This makes design easier and more straightforward. Sharp corners in conductive nano-wires can create unexpected high resistances for electric currents due to ballistic transport effects. There's a lot of experience from todays silicon wafer technology though.
  • Highly compact design: Nanomechanic computing systems can likely be built more compact (in gate density) than nanoelectronic computing systems. In case of nanoelectronic systems electrons tunnel through isolators with a thickess of several atoms (especially at higher voltages) which can lead to unwanted dissipation losses.
  • In an advanced productive nanosystem like a nanofactory relatively slow mechanical motion (MHz range) is needed anyway for the mechanosynthesis cores and further up assembly robotics. So making low performance local logic purely mechanical too makes sense.
  • Nanomechanic computation has inherent robustness against electromagnetic interference. Even hard against the worst case: EMP (electromagnetic pulse)
  • Nanomechanic computation has robustness against ionizing radiation (in case too filigree structure are avoided like e.g. single bonded ethyne chains). Note that with this design decision one looses the benefit of highly compact design though.

A note on ternary (3-valued) logic

Mechanical computing systems may make ternary logic more easy to implement. The benefits of ternary logic are questionable though. While in principle ternary has a better radix economy than binary in adder circuits (a very core component of most computing systems) the gained benefit in the adding logic seems to be lost with the carry bit logic. (TODO: add link to relevant web-pag(es)) There are more possible ternary logic gates than binary ones. This may sometimes make design more complicated and less intuitive. Automated design tools can help.

A note on analog logic

There is a very good reason why we switched to digital systems. noise error margins and error correction allow for scaling up many many orders of magnitude with ridiculous levels of reliability.

In fact thats exactly the same reason why a nanofactory for physical production is more desirable than being content with the current day chemistry that is adding up errors with growing product size. Stiffness is the key for suppression of thermal fluctuations. It keeps atom deposition at the right place well apart from atom deposition at the wrong place. Just as it keeps bits from being in the wrong state due to charge fluctuations.

  • s = (1/k) * F ... to keep position fluctuations low stiffness (= "inverse mechanical capacity") must be kept high
  • Q = C * U ... to keep charge fluctuations low capacity (= "inverse electrical stiffness") must be kept low
    (TODO: Something is reverse here. Usually there are voltage margins not charge margins. What's going on?)

While analog in pure form is unsuitable here's an idea how some form of pseudo-analog computing mechanisms may be useful in the nanoscale:

Subatomic pseudo-analog mechanical computation

Warning! you are moving into more speculative areas.

What will be referred to as "pseudo-analog" in the following is analog with forbidden levels separating allowed ones.

In nanomechanical digital logic it seems one is fundamentally limited with the size of atoms. But (using rotating mechanics as an example) a torsionally stiff rotating axle can actually can resolve angular steps fine enough such that the circumference arc-length steps are of a size way below the size of an atom.

To tap this space one could try a strategy like this:

  • convert to pseudo analog
  • use analog mechanical computing mechanisms
  • convert back to digital before the levels blur to the point of unreliable separability
  • do re-amplification / error correction in the usual digital fashion
  • recurse

The main problem here is that the gain in the compactness from the pseudo-analog part might be lost with the size of the conversion circuitry. Note that for every additional bit encoded in the pseudo analog value the number of levels doubles. So the number of encodable bits is quickly reached. To extend the number of encodable bits a bit one could cool the system to reduce thermal noise. But at some point one runs into eigen-modes excitated by zero point energy. Regaring quantum superposition of axle states for mechanically based quantum computation: the decoherence time may be way too short. (TODO: Inverstigate whether this has been investigated or not.)

Note: Some macroscale analog mechanical computing devices would not work at the nanosacle since they heavily rely on friction. A good example is the ball and disk integrator mechanism (see: "fire control computers" link). (Maybe related: fundamental impossibility of continuously adjustable mechanical gain chain transmission)

Related

External links

  • Wikipedia: Analytical_Engine (Charles Babbage; base 10; never built in full)
  • Wikipedia: Z1_(computer) (Konrad Zuse; base 2; rebuilt after destruction; unreliable but in a reproducible way)
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