1. To exert nearly constant torque during entire stroke. 2. It has better performance than power spring in more revolution designs. 3. All revolutions are almost useful revolutions. Itˇ¦s high efficiency.
Variable force spring is not restricted to Hookˇ¦s Law for compression springs that the load increases proportionally with stroke. According to your request, you can have a multi-load design. Here are some relations between load and stroke that can be used on specific occasion.