Hydraulic Micro Device with Force Sensing for Measurement of Mechanical Characteristics

Abstract

The medical and bio-engineering fields have been increasingly using information and communication technology. To introduce robots into surgical procedures, data on surgical operations are required. Several studies have tried the creation of data on living tissues for mechanical actions, which makes determining the mechanical characteristics of living tissues vital, but few have been commonly used. Therefore, we previously developed a sensing system that uses a hydraulic-driven micro mechanism to measure the force applied to an object when it is touched. Micro force sensors are necessary for various manipulations requiring careful operation. Unfortunately, the measurement accuracy of sensors tends to reduce with the reduction in sensor size. The proportional output in conventional force sensors, such as piezoelectric sensors, also decreases when the size of the sensor is reduced. However, a micro force sensor using a hydraulic-driven micro mechanism can obtain a large output even when it is small. Our system uses Pascal’s principle to measure small forces acting on the end effector. We propose methods for identifying the mechanical characteristics of certain viscoelastic materials similar to those used in a living organ. A hydraulic-driven micro device pushes an object and measures the reaction force and its displacement. We have used two types of micro devices, micro cylinder and micro bellows. Its stiffness and viscosity coefficient are obtained through calculations using Kelvin-Voigt and Zenner models. Discrete displacement and load data are applied to the estimated model, and the mechanical characteristics of the materials are identified as a minimized value between the estimated value and experimental one. We conducted experiments using the proposed identification methods on viscoelastic materials, and the results indicate that the value provided from the Kelvin-Voigt model was near the truth value.