Difference between revisions of "ReChain tensioner"

Latest revision as of 08:00, 15 August 2024

(wiki-TODO: Add illustrativve image: https://en.wikipedia.org/wiki/File:Highfield_lever.png)

Purpose

In ReChain Frame Systems tensioners are needed to stiffen the loosely pre-assembled structures
by introducing tension into the ReChain force circuit.

It seems important to keep tensioners conceptually separate from ReChain length adjusters.
In practice the lines can blur a bit.

Development progress

For concrete design attempts see page: ReChain tensioner design attempts.
Getting to a compact design that does not friction-self-lock is still an open challenge.

Ideally we want tensioning functionality strictly separate from locking functionality.
Especially locking from friction is undesired.
This may be unachievable for some macroscale designs.
At the nanoscale inherent slipperiness of atomically precise surfaces and thermal motion help.

Tensioner - categorization / classification

centerspanners & endspanners

Tensioners can be placed either at a center position or an end position of a ReChain strut.

hullpushers & chainpullers

Tensioners can either push the ReChain hull segments apart or pull the ReChain core chain together. Tensioners may effect length change due to tensioning and resulting mechanical properties in different ways. (locally concentrated length change in hull may be undesirable - due to misaligned alignment structures)

(wiki-TODO: Add illustrative image: chain-core-reinforcement-details.svg)

Factoring tensioners and length adjusters apart

Intermixing of tensioning and length adjusting issue:
Conceptually (for the sake of separation of concerns) it makes sense to
separate tensioners from ReChain coarse length adjusters.
Practically their effect of operation can overlap.
and separation of concerns in this regard may not be practical.
(especially for compact designs)

Concrete example:
Using a nut to tension a ReChain core chain naively means that
the nut rubs on a ReChain hull segment with a force that is
proportional to the tension so far (scaled by friction coefficient).
Factoring tensioning apart form length adjustment means that …

• one first pulls on the thread with the dedicated tensioning mechanism
  thereby lifting the nut away from the contact to the ReChain hull segment
• one screws the nut in without load till it touches the ReChain hull segment again
  
• one releases the load (this allows to reset a nonlinear tensioning mechanism in position, more on that later)

Factoring tensioners out of the frame system (take 1)

Keeping tensioners in the final frame structure is …
★ wasting space
★ adding weight
=> Factor tensioners out into the tools for assembly (possibly a robotic end-effector)
See page: RepRec tensioning end-effector

ReChain frame systems shall be designed such that tensioning and detensioning operations
can be done at dedicated ReChain force hydrant locations.
These can be spaced out from sterically congested areas ☺.
That is: E.g. away from ReChain nodes where many ReChain struts converge and thus
not much space is present (especially for a robotic end-effector)

Factoring tensioners out of the ReChain core system (take 2)

There is no need to keep tensioners within the frame system once
they have fulfilled their purpose and tensioned the system.
With a design that allows such a [:TensionerRemoval](./TensionerRemoval.md) after tensioning
is should be possible to save a significant amount of
size and mass in the final structure.
Total design complexity is preserved if not increased.
The now separate tensioning mechanism still needs to be designed.

Many Tensioner designs ( See: ReChain tensioner design attempts though
are not removable after tensioning the system since they themselves form part of the tensioned system.
That is: They can not be decoupled without de-tensioning the system.
This is especially the case for ReChain center tensioners (tensioners in the middle of a strut)
instead of a ReChain turn around point.
To have ReChain center tensioner removable despite their position in the middle of a ReChain force circuit
there is the need for the introduction of a ReChain plugged T junction.

(wiki-TODO: add new thought here - converting "chain bound tensioners" into seperable tensioner tools)

Resulting factors after the factorization

When making the tensioners removable after tensioning (factoring that functionality out)
then one ends up with two things:

① ReChain force hydrants. That is …
Spots where the ReChain core chain is accessible from the outside
and temporarily (or permanently) extendable: ReChain force hydrants.
These may be ReChain extensible turnaround points or ReChain plugged T junctions.

② ReChain tensioner tool. That is …
A special tensioner device that can be used:
★ either as a special hand tool
★ or as a special end-effector for robotic tensioning

Nonlinear tensioning mechanism in assembly-tool / end-effector

Nonlinear tensioners have the advantage of high leverage ratios.
That in combination with low frictive self holding forces.
But ultimately once the load is high the travel is low.
So the amount of tension they can put into the system when used naively is low.
Linear tensioning mechanisms like screws on the other hand
tend to have high frictive self folding forces (undesired).

The trick: With …
– having tensioner and length adjuster functionalities factored apart and …
– having tensioners factored out of the frame system …
one can alternate between …
– tensioning with high nonlinear leverage and …
– length adjusting under no load.
One gets both …
– arbitrary long range to tension and
– no or little frictive self holding forces

Related

• Up: ReChain ReChain frame systems

• ReChain tensioner design attempts
• ReChain positive locking mechanism

• ReChain length adjuster

• Tensioning mechanism design
• Static rebar profile force circuit

• RepRec tensioner

External links

Existing tensioners to learn from:

• en https://en.wikipedia.org/wiki/Turnbuckle ( de https://de.wikipedia.org/wiki/Spannschloss )
• en https://en.wikipedia.org/wiki/Differential_screw ( de https://de.wikipedia.org/wiki/Differenzgewinde )
• toggle (joint) clamp https://commons.wikimedia.org/wiki/File:SceneryWagonBrake.jpg
• ( https://en.wikipedia.org/wiki/Highfield_lever — good illustrative conceptual picture)

Page history before migration to this wiki

Created Monday 20 February 2017