Measurement of mechanical characteristics using micro devices with force sensing

Treating living organisms requires careful work in microscopic surgery and bio-engineering. However, the measurement accuracy of sensors tends to decrease as they are made smaller. Therefore, we developed a new sensing system that uses a hydraulic-driven micro device to measure the force applied to an object when it is held. This system can measure small forces acting on the tips of the end effector as the internal pressure changes. Generally speaking, pathological changes in living organisms can cause mechanical characteristics such as stiffness and viscosity to change. The palpations that a medical doctor performs are an example of this. Trained doctors can distinguish the state of an organ during an operation through touch. For robotic surgical systems such as da Vinci, the capability of distinguishing the state of the organ through touch will enable such a system to palpate. However, the relationship between mechanical characteristic changes and pathological changes must be explored for this to become a reality. We identified the mechanical characteristics of some viscoelastic materials similar to those used in a living organ. The hydraulic-driven micro device pushes an object and measures the reaction force and its displacement. Its stiffness and viscosity coefficient were obtained in calculations using Kelvin-Voigt and Zener models. Discrete displacement and load data were applied to the estimated model, and the mechanical characteristics of the materials were identified as a minimised value between the estimated value and the experimental one. In our experiment on viscoelastic materials, the value provided in the Kelvin-Voigt model was near the truth value. This report describes the identification methods and measurement results using these methods.