sliding joint question

[maker9876]

I have two 14mm plastic cylindrical bearings (in yellow in the left photo below) mounted horizontally, 10cm above each other.

In the horizontal plane they are separated, perpendicular to their axes, by 5mm so that a vertical 5mm plate (one face of the L-shaped angle iron in the below photo) can just slide up and down between them.

The plate is then connected to a platform which extends off to one side such that the upper bearing acts as a fulcrum and the lower bearing contains the plate.

My question is how to assemble this joint?

I can select the vertical plate as a joint surface. 

But how can I select a the outside of a cylinder so that the vertical plate will form a joint with it and move in the desired way? (And then do the same thing for the second cylinder?)

I'd like to assemble the whole thing and then, amongst other things, perform a stress analysis with the mechanism in a couple of different positions!

[maker9876]

No, that would be a mistake.

I have not succeeded in assembling it and certain measurements were just guesses during sketching in an earlier document!

[Beyondforce]

This is how it looks lik:

[maker9876]

Great!

So I need to modify the sketch for the platform to make it wider.

Still, most worried about getting the basic movement to work....

Sent from my iPhone

[Beyondforce]

Don't worry, we gonna figure out something 🙂
Do you want me to send you back the file with the position change?

[maker9876]

Sounds good! 😉

[Beyondforce]

Here you go and send it back to me when you done 🙂

[maker9876]

Here we are.

Moved the L-bars further apart and shortened the bolts.

btw. I notice you grounded the "front sheet"? That's just the front wood cover... perhaps better to ground the "Frame" which is the entire welded metal structure?

[Beyondforce]

what happen to the yellow bearings? There are only screws!

[maker9876]

Odd. Sorry!

Now they are back....

[Beyondforce]

If you don't mind, could you tell me more about this design, what is it exactly for, and how do you want this part to behave?

[maker9876]

It will be a piece of furniture to help in the presentation and service of food.

There will be two platforms, one next to the other.

Each platform will have a linear actuator to push it up / down. (The body of the linear actuator is 450mm long and the shaft can extend 300mm further.)

Each platform will have food (in a container weighing less than 20kg) placed on it.

The height of the platform will adapt so that the top of the food container (sometimes they are tall, sometimes they are short) is at the same height as the top of the frame.

Because the big frame and the platforms are both welded they will not be precise so various adjustment points are necessary.

One adjustment point will be the feet at the bottom of the main frame.

Another adjustment point will be the wheels that support the platform and adjust it's precise angle.

The idea is that, after assembly and after adjusting the feet so that the whole structure is horizontal, then we will adjust the wheels so that the platform is horizontal.

Perhaps it is only necessary to have adjustable wheels EITHER at the top OR at the bottom, but I've put them top and bottom for now... That would allow even more adjustment...

[Beyondforce]

Okay, so if I understand it correctly, the bearings are there for support, is that correct?

[maker9876]

Yes, that's right.

The idea is that the space under the platform should not contain any mechanisms, so that it can be used for storing things in.

That means we must support the platform from just one end with a relatively strong structure (right now the platform is in steel but may change to aluminium - after some stress calculations! - to save weight).

[Beyondforce]

If the platform is going to slide up/down 90 degrees, then why did you make the bearing rolling unevenly?

[Beyondforce]

Before we continue, I think we should add the Actuator, because the platform is going to be attached to the actuator and the actuator is responsible for the Up/Down movement.
So, what you need to do is, position the actuator where is should be and use the Rigid joint to connect between the platform and the actuator hand that moves U/D.

[maker9876]

Because I'm convinced that:

a) the two "legs" of the platform MIGHT not be perfectly parallel;

b) the holes, together MIGHT not create a perfectly vertical line;

c) the holes on the left side of the platform MIGHT not be perfectly aligned with the holes on the right side of the platform;

Why? 

Because it will not be built by CNC, 3D printing, lasercutting..... but rather by welding bars of steel together.

I'll build some kind of jig to align them but even after that there will be some distortion / misalignment.

If it's difficult to model these special nuts with bolts placed asymmetrically, we could just put "normal" wheels in for the purposes of creating a model that "works".

Then in reality there will be the special bolts which I'll adjust so that the platform works as if everything were perfect! 😉

[maker9876]

OK I'll take a look at the actuator problem.

[Beyondforce]

I was thinking, we could talk on Skype, it will help to speed up our communication 🙂

[maker9876]

Nice to talk to you Ben.

I've made some progress.

There's now a linear actuator in position.

It has an arm that can be pulled out 300mm.

There's a pin at the bottom attached to the frame but not yet to the actuator.

The actuator arm is not yet attached at the top.

[Beyondforce · Accepted solution]

Here you go: