This paper presents a computational-based kinetostatic synthesis method for realizing nonlinear stiffness characteristics. The significance of this method is that it provides a solution to achieve nonlinear translational stiffness with a spring four-bar mechanism (S4M) featuring a simple structure. The kinetostatic model of the S4M is developed by adopting the free-body diagram method. The link dimensions and spring parameters of the mechanism are computationally determined by using particle swarm optimization (PSO) that minimizes the output force error with consideration of practical spring constraints. The applications of the proposed method are demonstrated through different scenarios in which nonlinear translational stiffnesses are required. Theoretical studies show that the force errors of S4Ms can be less than 1%. This work also presents experimental studies to validate the design feasibility and high performance of the mechanisms.
