A. NEG'ATOR® CONSTANT FORCE SPRINGS
1.0 INTRODUCTION
The NEG'ATOR spring is a prestressed strip of fiat spring stock which coils
tightly around a bushing or around successive layers of itself as shown in
Figure 1.
Figure 1 The Constant-Force Extension Spring In Relaxed Position
Resembles a
Tight Roll
of Metal Tape. It Is Usually Made of Stainless
Steel or High-Carbon Spring
Steel.
When this spring is deflected
by pulling out the outer end of the coil, see Figure 2, the following occurs:
(1) a resisting force "P" results; (2) force P has a line of action
through "Z";(3) force P does not increase with Increasing deflection
(extension) as In a conventional extension spring; (4) the change from the
original curvature of the material to a straightened condition occurs in the
short zone X" in Figure 2; (5) after passing through zone X, the material
flattens (though not completely) in the direction of pull; (6) the straightened
material, "L", stores the energy converted but adds nothing further to
the force; (7) force P results from the tendency of the material to recoil
around the bushing, this high recoiling force being related to the configuration
in zone X; (8) there is no friction inherent in the spring, the only evidence of
friction is in the bearing of bushing Z.
Figure 2 The Constant-Force Spring Develops Its Resisting Force
Incrementally
Rather Than Cumulatively.
A convenient way to highlight
the capabilities of the NEG'ATOR spring is by comparison with a conventional
extension spring. Such a comparison is shown in Figure 3.
*Registered trademark of Ametek Inc.
*The material in this section is presented with the permission of
Hunter Spring,
a Division of
AMETEK Corp.
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