How does this work and how to scale it? 1

[DistressedNerd]

Anyone know how the mechanism behind these flip open calculators work (see link):

Link

Link

I think the same mechanism would work well for my intended purpose, assuming it can be scaled up to moving a collapsible arm many times the weight of the plastic housing on these calculators. Details on where to buy parts or how to create a scaled up version would be a godsend!

"We are all here on earth to help others; what on earth the others are here for I don't know." - Tesla

 

[3DDave]

There's a torsion spring, much like in roll-up blinds or a conventional mouse trap. There is probably a damping fluid as well to add some viscous friction to slow the deployment so it's more appealing and doesn't damage itself when it gets to the limit stop. That stop cushion is supplied by the mouse in a mouse trap.

 

[DistressedNerd]

Thanks for pointing me in the right direction I think we can agree it's a spring.

How do we know it's not a constant force (or torque) spring?

Here is one in action: Link

Specifically I am led to believe it is a Extension Constant Force Spring - it is cable of providing constant torque throughout a range of motion.

Extension Constant Force Spring for 90 degree deflections: Link

General Info on Constant Force Springs: Link

 

[ornerynorsk]

rotary dashpot.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[MikeHalloran]

Like Ornerynorsk suggested, 'rotary dashpot' should lead your search.

Last time I had a sample in my hands, they comprised a small gear that reluctantly rotated around a small adjacent housing. The whole thing was engineered to easily fit inside a calculator, a cassette recorder door, or whatever consumer product you wanted to build.

They could have been incredibly complex inside, or not; I never had reason to take one apart, and I'm not sure it was possible. They were produced in the millions, maybe billions, and were (20 yr ago) selling for about $250 per thousand.

Try to find a couple examples, dissect them, and figure out how they work.

I'm not convinced they'll scale well. I remember a linear damper of somewhat larger size, sold for electronic cabinet doors. It was based on squeezing a possibly greased rubber tube. The samples I got worked erratically, even when not exposed to temperature excursions.

Alternatives keep appearing, but successful applications still tend toward linear dampers using oil displaced through orifices by a piston.

I was once involved in a product where we built a rotary quarter-turn damper for laboratory equipment. It was expensive and fussy to build, and had a number of odd ways of not performing well enough for long enough in the field.

I'd strongly suggest finding a linear damper that's in volume production and using it as is, or negotiating for a slightly customized version, rather than building your own.





Mike Halloran
Pembroke Pines, FL, USA

 

[DistressedNerd]

Ornerynorsk - thanks for the reply.

Rotary damper, specifically dashpot. It looks like a rotary dashpot just slows down the movement and makes it smooth; it would still require a torsion spring to provide the force correct?

 

[racookpe1978]

How heavy?

Look at a catalog for woodworkers suppliers - they have many counter-balanced hinges and cabinet-door-openers that may work for 10- 150 lb doors.

 

[tbuelna]

DistressedNerd-

I looked at your other post regarding this topic and it seems like your device requires a mechanism that in one mode of operation will release, deploy, and position two counter-rotating arms with a controlled velocity, after a foot pedal is depressed. And in the other mode of operation will release, retract, and latch the two counter-rotating arms with a controlled velocity, back in their initial position when the same foot pedal is depressed. Is that correct?

The springs, dampeners, position stops, and synchronizing mechanism seem pretty straightforward. But the double acting foot pedal mechanism might require a bit of work. The arm release function is easy enough, but incorporating the ability of the foot pedal to provide a retract and latch function every other cycle will be difficult, but not impossible.

 

[DistressedNerd]

tbuelna

You are spot on! The catch is can the "two mode" foot pedal be made in a cost effective design or can even a "one mode" foot pedal be made in a cost effective design?

Ranked in order of priority (Mode 1 is more important for function than Mode 2)
1st - Mode 1 - release, deploy, and position two counter-rotating arms with a controlled velocity, after a foot pedal is depressed.
2nd - Mode 2 - release, retract, and latch the two counter-rotating arms with a controlled velocity, back in their initial position when the same foot pedal is depressed.

"The springs, dampeners, position stops, and synchronizing mechanism seem pretty straightforward." Concise and again spot on and provides affirmation to what I thought would be the required components. My questions is what is the best configuration of these components, especially the synchronizing mechanism. The torsional spring and rotary dampener seem pretty straight forward they work together as a pair and one of each is would be placed at the pivot point for each of the 2 arms. However, I am lost when it comes to how a synchronizing mechanism might be designed?

It seems like if you have a synchronizing mechanism - something linking both arms together then you may be able to incorporate the dampener & torsional spring into the synchronizing mechanism. Then you would only 1 pair instead of 2 pair (one in each of the pivot points of the arms). Is this worth pursuing, again it needs to be able to be mass manufactured?

 

[rb1957]

why a foot pedal ? why not a hand control (left stop does one op, right the other) ?

you'll only do operation 2 after you've done operation 1, so that sounds like you can build in something to sense what you've done, and what you want to do ? (maybe something as simple as a two position cam ?)

"cost effective" is something we can't measure. how many are you making ? 1 or 1,000,000 ?

another day in paradise, or is paradise one day closer ?