| Summary: | Hydraulic system has been widely used in many mechatronic systems. Accurate identification of the hydraulic stiffness is critical to the design and control of such kind of system. It is widely recognized that the nonlinear hydraulic stiffness is influenced by many factors such as the compressibility of the fluid, the flexibility of the fluid supply circular tube, and the working status of the system. It is very difficult to accurately formulate the hydraulic stiffness due to the complex coupling effects. In this article, the concept of the volume modulus is first introduced to characterize the flexibility of the structure as a container. A hydraulic cylinder consisting of flexible circular tubes is used as an example to illustrate the relationship between the volume modulus and Young’s modulus of the circular tube. A novel formulation of the hydraulic stiffness is then proposed by taking into account the structural flexibility via the volume modulus of the circular tube. Finally, the influences of the circular tube parameters on the hydraulic stiffness are analyzed. Experiments are also carried out to verify the presented formulation. The proposed method can be used to design hydraulic system for achieving desired static and dynamic performances.
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