A constant-force or recoil spring is a strip spring wound around itself that can store a large amount of energy over a long travel.
It offers several specific advantages:
- The stored force is released at an almost constant level throughout the travel.
- Very long travel is possible.
- Installation space is limited because the metal strip winds onto itself.
These springs are used in mechanisms requiring controlled return, safety systems such as seat belts and fall-arrest harnesses, and everyday products such as cable reels and tape measures.