Estimation Method for Maximum Injection Pressure by Motion Analysis in the Needle-free Injector

A needle-free injector designed to inject medicinal fluids into skin using only fluid pressure is gaining popularity. This paper has considered the estimation method for maximum injection pressure of the needle-free injector. A model of the needle-free injector was created taking into account the movement of the internal parts, such as a piston, a plunger and a spring, which were derived on the basis of mechanical modeling and motion analysis. The elastic or viscoelastic deformation of the internal parts of a syringe and a gasket was calculated based on FEM and replaced by equivalent spring constant. The consumption of energy for injecting the fluid was expressed by the damping coefficient. The experimental results showed that maximum injection pressure and the transition of injection pressure are affected by the elastic spring force and the impact gap. The estimation results of the maximum injection pressure were in good agreement with the experimental results under the same design parameters. As a result, it was clarified that the maximum injection pressure of the needle free injector can be estimated by using the motion analysis.