Non-linear springs, specifically "constant" force springs

[Howard]

Are there any coil springs that are constant force or near-constant force? Most coil springs follow Hooke's Law.

 

[Unitary]

If the spring gave the same force, no matter its displacement from equilibrium, it would be a linear spring as its force would be F_s=C. As for the physicality of a spring with these characteristics I think it would be hard to really call it a "spring".

 

[PsiStar]

google is your friend ... http://en.wikipedia.org/wiki/Constant-force_spring

 

[Howard]

google is your friend ... http://en.wikipedia.org/wiki/Constant-force_spring

I need further details on that conical spring.