  Nonlinear systems exist widely in nature, however, how to construct systems
with accurate expected non-linearity artificially is still a problem, which
greatly limits their experimental study and engineering application. In this
paper, we present a general nonlinear mechanical model (GNMM) based on
special-shaped cam-spring mechanism (SCSM). GNMM consists of a mass, a roller,
a track and a novel general spring model (GSM). Firstly, the equation of motion
is derived and compared with that of SCSM. Then, the roller trajectory
functions for arbitrary given continuous force are derived. Finally, Duffing
system with softening non-linearity is constructed as a design example. The
results presented herein show that GNMM has a more general restoring force than
SCSM, and prove that there are at least six independent mechanical
configurations for a given nonlinear system with continuous restoring force.
