A small linear actuator with a very long stroke

[gabrieldom]

TL;DR Summary

I am looking for a linear actuator very short when it's folded, but very long when it's deployed.

Hello,

I am working on a mechanics project, on which I encounter a problem that I am sure others have faced before. I have tried to find answers here and there by typing keywords, but I can't find what I am looking for.

Here is the context: Two horizontal plates are separated by a mechanical system of articulated bars (a double scissor, like a laboratory scissor jack or like an aerial work platform). The bottom plate does not move, while the second can move vertically.

The top plate needs to be able to lift 10 kg to 50 cm high.
Initially, the mechanical system is completely folded between the two plates: bars are almost horizontal (2° angle between bars and the plates), so that the system is as thin as possible.

I thought installing a linear actuator to power the system, but I often come close to having the actuator almost horizontal when the system is folded (draw 1 and 2), therefore requiring a very strong force to lift the charge, due to a very important lever effect.

Ideally, I'd like to find a linear actuator that I could place vertically (so as to maximize its force) (draw 3), so with a great course (50 cm) but very small when folded (maximum is 5 cm) so that the plates can be as close as possible.

A telescopic cylinder with approximately 10 stages would be a good idea, but I am not familiar with hydraulic and pneumatic solutions, and I assume it would be much more complex to install and command.

Are there some solutions that exist to solve such kind of problem? I guess I am not the first to face this issue.

Do not hesitate if it is not clear.

Thanks!

 

[jrmichler]

A good place to start is to look at how other people have solved the same problem. Search term scissor lift on both search engine and Amazon will find many scissor lifts for laboratory use and lifting motorcycles. A large manufacturer of scissor manlifts is JLG. Their website has many photos, such as one example below:

You can see how a standard actuator gets a large lift. Another source of good information is by searching patents. A quick search of patents assigned to JLG Industries finds U.S. Patent 4,194,723, which has the following figure:

It shows another way to get large extension from standard actuator. That patent references 14 earlier patents. It is likely that some of those will have some good ideas.

All patents that are more than 20 years old are expired, so it is both legal and ethical to use anything in them.

 

[Baluncore]

Are there some solutions that exist to solve such kind of problem? I guess I am not the first to face this issue.

You have two quite separate problems.
1. Keeping the surfaces parallel and positioned in X and Y.
2. An actuator to set position in Z, with a high ratio length change.
I think you realize that solving both with one mechanism is unlikely.

Start by familiarising yourself with similar high ratio systems.

A spiral or tapered coil spring can have a high ratio of length change because it can nest as a flat spiral within it's material diameter.

An aneroid barometer employs a short cylinder with circular corrugated end(s). That is an equivalent to a multistage hydraulic cylinder. Similar corrugated rubber boots are used to environmentally seal gear change levers.

A concertina has a rectangular volume with a high volume ratio, where it is not the ends, but it is the sides that flex and extend.

A hydraulic jigger employs multi-fall pulley blocks to multiply the length of hydraulic movement.
https://en.wikipedia.org/wiki/Hydraulic_jigger

 

[Tom.G]

Take a look at an oridnary automotive scissors jack.

Also see: https://www.physicsforums.com/threa...quired-for-telescopic-cable-mechanism.1000504

 

[Lnewqban]

Please, see:
https://www.researchgate.net/figure/Evolution-of-main-actuation-mechanisms-for-scissors-lifting-tables-courtesy-1_fig6_305444519

https://www.vestil.com/product.php?FID=198

https://www.ezcarlift.com/ezcarlift_features.html