manufacture a prototype for a NON LINEAR EXTENSION SPRING, for which i have attached the Load - displacement characteristics, data and representational photograph.
Though i'm providing the dimensions, you have the liberty to tweak it as per the design constraint. You can use any type of spring for the same, namely barrel, helical or conical, it does not matter.
length - 7 cm
dia -- 1 cm
max. extensible length - 3 cm