Looking for a part, does it exist?

[turbo]

You might want to make a prototype block, using a small solenoid to apply the clamping force. Drill a hole through the block and mount the solenoid so that when activated, its ram presses radially inward. The brake shoe could be as simple as a cylinder of teflon threaded onto the ram with a bit of rubber epoxied to the end. When power is discontinued, the solenoid retracts and the block slides freely. If I'm imagining this correctly, you will want the block to actuate a switch that shuts off power to the solenoid when the block hits its lower limit, then the solenoid ram will retract and the spring will pull the block back to the upper limit. If you have a machine shop and can prototype this block, you will have a chance to refine it before contracting for a production run.

Note: I said production run, because what you're asking for probably does not exist in a form that you would find usable. Your best bet is to prototype it, then get bids for a production run large enough to fill your needs and large enough to keep the per-unit cost down.

 

[Danger]

Okay, I'm back in.
The main thing that I see as a problem is that you're going to have to do some kind of fabrication just to make whatever you find fit into your system. No way will you find something 'off the shelf' that is exactly the right size and shape and has the mounting holes in the right place and etc..
I have an 'iffy' idea about a component that already exists, but you'd still have to build mounting brackets. What I'm thinking of is the fast-idle solenoid from a carbeurator. You could just cram a chunk of rubber (maybe a vacuum cap) onto the end of the plunger and have it poke the side of the rod. There's some good force in those things.
The other thing that I might suggest would be an iris diaphram that encircles the rod. They're pretty expensive, but you can get them at optical houses (maybe even camera stores). If I'm not mistaken, they can be had with actuator motors or solenoids already attached. I have no idea what kind of clamping force you could get out of one, though.

 

[RainmanAero]

As a prof of systems engineering, I feel I should address some fallacies and typical causes of problems down the road:

Everyone please concentrate on this instead of questioning what I'm doing, what this is for, suggesting better ways to do it, etc. This sort of thing just adds confusion to the thread.

Knowledge is a tricky thing. Passing on knowledge is even trickier if your media for doing so is limited. The fact that we are asking questions (to try to visualize) means WE are the ones who are already confused. Your saying this adds confusion to the thread is not borne-out by the fact that you "forgot about the spring" initially, and who knows if that may have not come out but for our questioning. "Forgetting" about key requirements or elements is quite common. It is why systems engineering (up-front) is so crucial to success. That is why we call it "requirements DISCOVERY".

I believe the descriptions I've written thus far in the thread should be enough to get my point across. If not, I'm very sorry.

One of the greatest tests for a systems engineer who derives & writes technical requirements is this: Take it to THREE other engineers, each of differing speciality disciplines. Ask them to give their interpretation of what is wanted. If all three give reasonably similar interpretations, you have at least an adequate requirement.

I do not plan on writing any kind of specs until I get a sample part in my hand.

MAJOR caution. This kind of thinking results in airplanes crashing, shuttles exploding, and much less severe (although not necessarily less costly) hazards. We live in a business environement where everyone wishes to make somethign with "off the shelf" components... before they have ever even studied their needs, modeled them, or analyzed them in detail. Sometimes, there is no "shelf". How do you think some of us write specs when there IS no part we can hold in our hands?

I have some flexibility in the devices size and orientation. Writing specs for something that is not available off the shelf that I have no intention of manufacturing myself or having someone else manufacture is a complete waste of my time.

I don't often speak this frankly, but you are completely wrong. I deal with this attitude with students and with professional engineers who should know better. Ignorance of requirements and how they are developed is THE SINGLE MOST-CITED "lesson learned" on any failed program. There is at least one spec (I know there are more) which is certainly not a waste of your time... and I have asked you about it and you have not answered. Loading. In fact, this is the MOST IMPORTANT question with regard to size of the device you are looking for, its holding force, and if it is E/M actuated, the power required to hold said load.

I fully realize that the engineering world works in drawings and specs but my situation is comparable to me asking General Motors if they have anything in flying cars and they ask me to write up a spec for it.

I'm not buying that analogy. I think you are making an excuse to be lazy. (Just my opinion). I see it all the time in students.

Like I said, I am willing to help. But if you are going to not answer questions and insist that your way is adequate enough (even though more people than me seem to be confused) then you have not learned enough about engineering to succeed. Sorry, but I call 'em as I see 'em.

Rainman

 

[AlephZero]

Amen!

Actually I would go a one step further than RainmanAero. I could easily think of 10 or 20 questions I would want to know about this device before I could make any rational suggestions about how to design it, but those questions are not the ones to ask first. The first question is very simple, but given the way this thread is going I doubt we will get an answer to it.

The question is: What is the FUNCTION of this device? If we knew that, I bet somebody could come up with a different way of implementing the function that WAS available off the shelf.

 

[FredGarvin]

What I am envisioning is a linear bearing that is a standard, off the shelf item. However, this bearing would have some kind of electronic capability that when energized, the bearing locks in place so it, or the rail in this case, can not move. The electromagnetic equivilent to brake shoes.

 

[DaveC426913]

It sounds like what you want is an electromagnetic actuator (isn't that what they're called?).

Apply voltage and the piston moves. Bolt the thing in place on the block, and the piston will pop out and bind on the rod, stopping the block.

You could set up the switch any way you want, toggle on/off, pushbutton mometary on, momentary off, etc.


These should be available sold by the kilogram in your local electronics surplus store.

 

[RainmanAero]

Hi Dave,

It sounds like what you want is an electromagnetic actuator (isn't that what they're called?).

I was told an electromagnetic actuator was "not even close" (see above).

I guess as long as we are shooting in the dark (or at least dusk), then I should also mention the magnetic brake which operates on Lenz's Law. It does not even require power, but depending upon the details of how this device has to FUNCTION (kudos to AlephZero who certainly understands systems engineering) it may not be the right part. In any event, here are some details (and diagrams) of one type of magnetic brake.

http://www.cst.com/Content/Articles/article115.aspx

Rainman

 

[AlephZero]

Well, those suggestions might be the answer or they might not. We don't know what speed this thing is supposed to work at - does it move with accelerations of 0.0001G or 10,000G? What's force spectrum (noise, vibration, acceleration of the device that it's built into) it will feel when it's supposed to be "locked"? What envionment is it supposed to work in (temperature, pressure, lubrication, corrosion? What's the failsafe condition? Etc, etc...

Without a spec (which we have been told we are not going to get) we are just p*ssing in the wind here.

 

[FredGarvin]

Given the circumstances here, I think we can safely assume that it's not going to be in a nuclear environment experiencing 1000 g's.

Honestly, I saw this as a question as to whether anything like this existed prepackaged. I didn't see any requests to help with the design or anything else. It's not improper for someone to ask if something exists and then to look at the item's specs to see if it fits their needs. If detailed design criteria is not presented at the beginning then the OP is taking on the responsibility of deciding what is important information to pass along.

 

[Danger]

I agree with Fred on this. It's just a matter of throwing a bunch of ideas at the wall and seeing what sticks.

 

[Averagesupernova]

Thank you Fred and Danger. I haven't posted recently because I don't want to get into some kind of p!ssing contest with some of the other posters. Sometimes I have a hard to from keeping my mouth shut when it's in my best ineterest so I have decided to let this ride for a few days. I have had some ideas on my own that could possibly make this piece a lot easier to manufacture than I had originally envisioned. In the meantime though, something prepackaged and off the shelf would be welcome. There really is no requirement that the device needs to slide along a rod. Envision a brake caliper sliding along a flat rail. I still prefer the rod because the would be device inherently surounds the rod completely and cannot move sideways. Naturally it is assumed I will have to fabricate something to mount to it to make it interact with the rest of the machine.

 

[Danger]

Well, it not having to be a rod makes a world of difference. There is such a thing as you're looking for that works on flat material. Unfortunately, I can't remember what the hell it is. I can picture it in my mind, but not in the context in which it's used. Some sort of a maniplator claw...
I'll keep thinking on it.

 

[turbo]

Well, it not having to be a rod makes a world of difference. There is such a thing as you're looking for that works on flat material. Unfortunately, I can't remember what the hell it is. I can picture it in my mind, but not in the context in which it's used. Some sort of a maniplator claw...
I'll keep thinking on it.

Are you thinking of a cam-actuated gripper, similar to those used to hoist large sheets of iron?

 

[Averagesupernova]

Grippers, clamps, etc. you can name a whole bunch of things but they are all pneumatic.

 

[Danger]

No, but I did just remember what it was. Some old-style jukeboxes used something like that to pick a record from the rack and put it on the turntable.

edit: Just saw your post, Average. These things were not pneumatic.

 

[Averagesupernova]

LOL I don't suppose they had air compressors in jukeboxes.
-
Seriously though, check out this site: "www.solenoidcity.com"[/URL]

Very informative. I think they will have a solenoid I can use with minimal fabrication to go along with it. And yes, my current thinking will have the device grip a rod and not work like a brake caliper.

 

[Danger]

Ooohhhh, goodie! Another site for my 'favourites' list.

 

[Dreamedideas]

Maybe you can use some type of horse shoe clamping device that is actuated by magnetics within the block. i.e. using a small battery to activate two small electromagnets on either side of the U-clamp which would pull the clamp over the bar.

You may even be able to employ a remote switch to it.

 

[Q_Goest]

Hi ASNova. You might find some ideas at http://www.wmberg.com/" .

I'd also suggest calling these companies directly and talking to a sales rep. If they don't make what you're looking for, they can probably point you in the right direction. Note also that many of these companies will go through distributors, so you may find they want you to call someone else about their products. Distributors of bearings and machine components is another great source of information if you don't know where to look. Look in the yellow pages for bearings, machine parts, or something along those lines to locate distributors.