INTERFERENCE FIT ADVICE FOR DESIGN OF A MICROSCOPE ARM 2

[vishguru]

Hi,

I am working on my first assignment- Designing a 2 axis microsope holding robotic arm. I need some advice in choosing a bearing or sleeve which would help me acheive a tight sliding fit between arms.

I am planning to connect the two alumnum rectangular bars using a partially threaded 3/8" HHCS and tighten it at the at screw end using a hex nut and thrust bearing.

Is there a better way to do this? can I use a plastic sleeve with some tight tolerence to make an intereference fit? I am bit confused after I ordered my parts, anyone please throw some light on this.

Thanks!

 

[Tmoose]

Does tight mean 0.002 inch radial clearance or zero clearance? How about friction? I'm thinking system stiffness is pretty important too. Hanging it on rubber straps would be zero clearance, but so soft as to be useless.

Preloaded tapers or spherical joints might be appropriate.
Or metallic flex joints.

 

[Pressed]

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http://www.eng-tips.com/viewthread.cfm?qid=138270

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[RotoP25]

I am not clear on the arrangement of the arm. But if you are looking for Y _ Z axes movement, try Linear slide guides, you can build required stiffness with them.

 

[vishguru]

Tmoose: Coz of the unavailablility of the material I ruled out ball and socket joints, but yes, by tight I mean stiffness and the ball-socket joint is one way of holding on to a particular position.
RotoP25: I am lookin for y-z axes movements but again I cannot use the linear guides because of place constraints.
I am trying to mimic the traditional arm for a display screen. Traditionally they use either ball and socket joints or tight-fit/friction fits to sustain the position once the display is moved according to ergonomic convinence.
Pressed: the link you sent is does not help me in this aspect. I am not worried about revoloving these arms at speed at all. To make my problem sound simple, I am looking at a joint probably as simple as a screw and washer joint or a bolt and a liner kind of joint which will hold the two arms and also will be able to hold the load(display device in my case) at any point in 3d space.

I appreciate your responses, I will be glad to hear more from you. Links and reading material are welcome.

 

[unclesyd]

You might want to take a look at these. We use this type pivot on some of our inspection machine arms.

http://www.flexpivots.com/index.asp

 

[vishguru]

Yep! I think the flex pivot is exactly what I was looking for, i never knew what it was called.

Thanks unclesyd

 

[unclesyd]

Thanks for the response.

If you have time let us know how it works out.