Install Air Compressor on Shaft in Rotation

Define:

1. "fluidic muscles"

2. Does "5,5 inches in radius" mean 11 inches in diameter?

3. "install an air compressor on the outside wall of that shaft"

4. "that application"?

5. If a lubricated seal "generates too much friction and overheats" why would a dry one survive?

Can you send a picture?

Hoe are you going to get power to this compressor? An electrical commutator may have as many issues as a fluid commutator. A small rotary union at the center of one end of the shaft is likely to be the best bet.

How much flow at what pressure do you need ?

Design a compressor to fit inside the rotating shaft. use the shaft axis of rotation versus the shaft exterior to create your torques to generate compression. the compressor becomes totally internal and needs no power supply other than the rotation of the shaft itself.

Send my cheque to : XXXXXXXXXXX@XXXXXXX.com lol

I would mount an injector to the center of a 11" bearing and seal combination, and just inject the air into the cylinder...in fact I would reduce the size required by welding a plate with an insert in it, to a popular size seal bearing combination....

Aha....

Which of these look like they might work for you.

What pressure do you need for the (I think Festo ) muscles ?

Can you drill in your shaft axial, centered, hole ? If yes there are rotating connectors working at such rpm or even higher available of the shelf. This being the simplest solution !!!

If not there is a possibility to use magnetic fluids to build up a seal with almost no friction and use a compressor of classical design out of your machine. The success of this solution depends on the pressure level.

The idea of building a rotating piston compressor (since I think you will need such a design) is the most complex and difficult way to solve your problem. It is of course possible and you can do it with radial pistons and an eccentric bearing to make the stroke but you will have a lot of problems to solve, lubrication being the least.

"because the size and speed of it, it generates too much friction and overheats."

Size, It only has to be big enough to handle the air flow need to the devices. If they are trying to design it to the size of the shaft just because they have all that shaft is a mistake.

Speed I've seen rotary seals for air that handle 90 thousand rpm. At that speed it's a non contact seal. Where clearance between spinning shaft and the stationary shaft are so small that there is minimum air leakage. What air that does leak cools the packing.

Search for rotating unions, they're used in expanding mandrels for turning lathes (and other machine tools), I never measured the volume, but the ones I've found in lathes work at around 100 PSI, from 0 to a couple thousand RPMs, and at about 80% duty cycle (you know, part loading/unloading).

This way you can use your existing air supply lines and save the task of designing a built-in compressor.

I know it is emotionally hard to drop a custom designed part, but sometimes you have no choice.

Regards

Yes, the shaft is 11 inches in diameter (5,5 x 2). The fluidic muscles are in fact Festo muscles that become shorter or longer depending on the air pressure that's into them (0 to 8 bar). The flow needed in these is practically zero, since it's a closed loop system. The little air we lose through leaks would be about 2-3 SCFM max in my opinion.

It's more complicated than just putting a rotary union right at the end of the shaft because there is a steel wire traveling in the centre of it. Also, there are a few other traveling steel wires around the one in the centre placed to make a circle of about 7 inches of diameter, so there is pratically no room inside the shaft to put anything there.

One of the solutions I thought, and I know it exists because I have seen it, is to design a one piece structure that is dynamically ballanced (with one small compressor or more in the design) that slides on the shaft and is screwed on it.

The more I think about it, the more I realize that it will be long and costly to bring that solution from paper to reality.

That's why I am currently looking for a rotary seal that will run dry at speeds of ~4 m/s for about 2 hours and that can survive its own heat produced by friction and trapped inside a small space... I want to do something like SolarEagle's idea, without reducing the size of the bearing (because I can't). We already have a design of a slipring with a physical channel inside of it to get air inside the shaft between 2 rotary seals. I also need to be able to sustain the pressure of the air at 90 psig between the seals when the shaft is not rotating.

I am doing my own homework to find the perfect seal, but any cue or share of knowledge will be very appreciated.

(BTW, thanks alot nick name, Deublin has the best solution out there, (slipring+bore union assembly), but unfortunetaly their delivery time and cost is too long and too much for us...)

You need a CONTINUOUS compressed air source ONLY if the operation takes a long time.

If it is short in time you could use a "pneumatic battery" i.e. one or more air bottles filled at high pressure before every operation. A pressure reducing valve and a 3 ways/2 positions valves will allow the muscle control. Bottles and valves are fastened on the shaft and rotate with it. I presume you already have the slip rings for the electrical control so that this part of communication is solved.