Ball joint design

[EngPhil]

Hi,

I'm currently designing a ball joint. It will be used on a medical device, which means that it needs to be stainless steel and has to be sterilized frequently. This implies: no plastics, no springs, no lubricants, no sealed housing, etc.

I would like to achieve an adjustable holding force. Basically, using a lever of sorts, the clamping force should be changed thereby gradually changing the friction on the ball joint and changing its holding force. Ultimately, I'd like to be able to adjust the force so that the ball joint will "slip" (ie, adjust) at a desired applied force.

I'm worried that a stainless on stainless design will be fairly "on/off" in the amount of friction. What are the characteristics of stainless on stainless in that regard? Are there surface coatings / finishes that will help? Is there a good mechanism to allow variable force?

Thanks,
Phil

 

[hydtools]

Why do you say no plastics? UHMW polyethelene is often used where sterilization is required.

Ted

 

[vc66]

Your main problem is going to be wear on the sliding surfaces. With more force, there will be more wear. There are plenty of combinations in use today of materials in sliding medical devices. Any motion preserving spinal implants come to mind.

V

 

[zzag]

Here are some example medical device patents that employ ball joints: 3,017,887 and application 20030040753. They both have adjustable friction on the ball. You can get copies here:

http://www.pat2pdf.org/