Help With a Mechanism

Is pneumatic drive an option?

Not really, we have no air supply close, if pneumatics were the only way it would have to run off of a bottle.

I have something with maybe what you need, but look around the site, hope this helps.

http://www.flying-pig.co.uk/mechanisms/pages/recipro.html

since my first post, out of curisity I google and there are alot of sites.

this one is cool, (as in more interactive)

http://www.mekanizmalar.com/index.shtml

That's a great site, I can see me spending some time exploring.

You might like to download an evaluation copy of Graficalc from inventbetter:-

http://www.inventbetter.com/demos.php

I'm having trouble visualizing your proposition. Is the work piece held stationary? You mentioned dimensions and low mass. Or is it something that is moving versus the working apparatus? Oh, BTW...

"...might save me from madness..."

I don't recall that being one of the options here, it seems more likely to work the other way 'round...

Going back to my description, the 'bottle' is fixed & I need to move the 2 different 'lids' into position. The lids will be part of the test set-up & the whole apparatus is inside a sealed box.

I'm sort of thinking that I need a cylindrical cam with a pin running in a groove so that it moves axially, then hits a stop so that it rotates.

You're right about the madness, it seems to go with the job.

Does this make any sense:-

The back (right) cylinder is a cog driven by a motor. The two large cylinders are also cogs which engage with the first. The two "bottle tops" are at the front (left).

I can see where you're going with this but I can't get away with the 'lid' moving through an arc as it gets placed on the 'bottle', it has to be a linear movement. This is the part giving me the biggest headache.

In my sketch, the blue 'bottle' is fixed & I imagine the brown & orange 'lids' are fixed to the yellow arm. The arm has retracted to remove the brown lid then needs to rotate about the hole in the bottom of the tee before moving forward to place the orange lid in position.

So what's needed is a pivot point at the crossbar of the T at the upright. I can see this now, maybe as a pneudraulic setup - but you said pneumatics wasn't practical...

It could pivot about the centre of the horizontal bar as you say, I hadn't been thinking about it that way. So now I'm wondering if I could have a lead-screw through that pivot point to give the axial movement with a stop at the retracted end of the travel to persuade the arm to rotate with the lead-screw.

I don't see why not. To me, the problem is how to induce the motion. I don't fancy a bunch of bitty electric motors throughout the apparatus, too cluttered, too hard to repair (I'd think...).

A bit like one of those ball point pen bayonet type mechanisms? That way the two caps would keep rotating round each other: do you need to make any wiring connections to them?

Much food for thought, I don't need any connections, all purely mechanical.

I won't be around again until next week, I will mull this lot over until then.

How about opposed lids and cams with a floating motor drive see pic.

That's neat, unfortunately I have to move the 'lids' completely out of the way of the 'bottle'.

I started to think before see the site Phoenix suggested us, "Geneva stop" i think was the ingenious mechanism he thought useful for this.Anyway...

Sorry,to be be a little clearer...

This has some posibilities, I only need 2 'lids' so the face cam would be fairly simple.

Hello Nigh

As a few others here have stated, a small reciprocating 2 position Geneva indexer capable of being mounted horizontally would work well. I have an idea that's similar but a little different; a compound cam. Pardon the 2D as I don't have an easy 3D modeler here...

Two cam followers. One follows the inside slot to move the arm side-to-side and the other moounted parrallel to the arm follows the face of the cam to move the arm in-and-out. The standoff mount for the 2nd follower has to be long enough to prevent the high lobes of the cam face from running into the arm.

The block the arm is attached to contains linear bearings and the shaft has a stop to prevent the inner follower from bottoming out on the back of the cam.

Just a silly idea, but might get the brain juices flowing in a different direction.

Not at all silly, I've been having similar thoughts but had been working on a cylindrical face cam to provide the linear movement. The idea of using a 3D cam is worth exploring.

I've had a complete rethink about this & come up with the following set-up. Essentially it's a simple XY table but it nicely constrains the lids to a straight path when being fitted or removed & means that my drive is just a disc being rotated backwards & forwards through about 240°.

There's a video here <iframe scrolling="no" marginheight="0" marginwidth="0" frameborder="0" style="width:240px;height:66px;margin:3px;padding:0;border:1px solid #dde5e9;background-color:#ffffff;" src="http://cid-901e3968acb40de5.skydrive.live.com/embedrowdetail.aspx/Public/Mech%202.wmv"></iframe>, you have to double click the icon a couple of times to get to it. Sorry about the quality but I couldn't persuade Inventor to do any better.

Conceptual is understandable, So hopefully you don't mind me criticizing as I sit on the fence here.

- The linkage to the disc seems small as compared to length (your answer maybe concept I know)

- Also how does it reset. can one make it reset by keeping the disc rotating.

Thanks for the development feed back, so far.

phoenix911

I think you are wright but is easy to correct using mechanisms those i saw in site yourselve suggested:the "disc" does a pendulum movement thru a bar fixed on its simmetry axe and at the end a mechanism "pendulum-rotative disc transformer" like "sucker rod..." you get in mekanizmalar.com site offered us by you.-

I wasn't going to bother with any drive mechanism, the action needs to stop for a long time at either end of it's movement so I might gear it down to a motor drive then simply drive the motor through a fixed number of revolutions forwards or backwards.

It is now looking like I will have to add another pause at the mid position so the geared motor drive will work OK for that as well.

Electronic programmable driver for the electric motor? Not only mechanics?...Treason!.Out of jokes i'd like to know at the end what this is for...CD's changer? a robot toy?...

I know, but we have electronic engineers here & I like to make them feel useful.

The use is for a piece of test equipment. We make photon detectors & as part of the test and qualification we have to map the outputs. This is done by scanning across the device with a laser with different reference patterns placed between the laser & the detector. The 'lids' in my design are cylinders with a foil mask over one end & a pattern of 10µm holes in the foil.

This test has to take place inside a light proof box hence the need to change the masks remotely.

Thanks to everyone for your contributions, they sparked off ideas that I might not have had otherwise and, as always, left me with some extra knowledge.

You remind me the orthicon and vidicon cameras of the recent past.Don't waste your patient trying to explain what a photon detector is useful for.Being a little more serious if is about real job:I found a little problem:the system needs,following you said before,stops and remain stoped a while:so you will need a brake system since the motor dont stop when you switch it off.Becomes harder in case it needs to be exactly in both extremes of the cam-goove on the disc.

Would be nice for all of us,see at the end, some picture of your realized machine.-

I was thinking of using a stepper motor so that it can rotate to a precise stop position. If that won't work I could maybe build in a mechanical stop & over run the motor but incorporate a friction clutch to allow the drive to slip once it hits the stop.

Hello Nigh,

Looks like your solution is a good one!

Like Ferquiza said, if you are going to use a geared motor you'll need a clutch/brake set-up to stop at exact locations and the use of a prox switch at each end-of-stroke location will help with control.

You may also want to look into a small geared servo to control the motion as they can be stopped quickly and easily take care of bi-directional motion.

Good luck with your project and I hope it works out well.

Jeff

It is a bit out of proportion, I drew it all freehand without trying to match the real dimensions so, if I go with this, I will adjust all the sizes to suit the real life application.

Nice solution Nigh