Has anyone ever used living hinges for fine mechanisms?

[paboar]

I am designing a medical measuring instrument and I thought that I could reduce tolerances by using living hinges. This mechanism must be able to move from 1-15mm with steps of 1mm in between. But I am not so sure how accurate it would be. Has anyone ever used living hinges for fine mechanisms, or has some tips on the use of living hinges?

 

[MikeHalloran]

A hinge resists radial and axial loads while allowing angular excursion. Presumably your linear motion occurs at the end of a lever of unspecified length, so we can't deduce the corresponding angular excursion for the linear displacements given.

It may not matter. Plastic disposable forceps have long been sold into the medical market. At their core is a trapezoid with four living hinges. They don't really work very well for anything, especially as forceps, so they may have created enough negative goodwill for living hinges that you would not be well served to be caught using the same mechanism.

The actual problem with the forceps has to do with flexibility of the levers at the working end. Trajectory error due to the living hinges' flexibility in nominally rigid directions is a secondary problem. Durability is not an issue.



Mike Halloran
Pembroke Pines, FL, USA

 

[plasgears]

Living hinges are another example of meaningful parts count reduction in plastics design. I encourage you to pursue this.

Make a prototype using your best analytical tools (not guesswork) and fatigue test the assy. Tough neat nylons would be your first best choice.

I have use plastic cantilevers in ratchet assys, snap fits, one way clutches, etc. Good luck.