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비균일 임피던스를 갖는 변형체와 접촉하는 방향을 추정하기 위한 실험적 방법
김청준(Cheongjun Kim),이두용(Doo Yong Lee) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
Model-mediated teleoperation is a system which provides haptic sensation using environment models. Parameters of the model are estimated from the position and force information measured at the slave side. It is necessary to know the direction of contact between the slave tool-tip and the object to distinguish the viscoelastic and frictional components of the measured force. The contact direction does not coincide with the object surface when the impedance distribution of the object is inhomogeneous. An experimental method to estimate the contact direction from the measured position and force is developed. An object with inhomogeneous impedance is constructed by using two different types of silicone. A force/torque sensor is attached to the 7-axis articulated robot. The robot is controlled to move with a constant force to the object, and the position and force are measured. The object is modeled as two springs connected in series. The contact direction is derived as a function of the force and the pressing depth. The amount of changes in the contact direction varies depending on the hardness ratio of the two silicones according to the derived equation. The elastic modulus of each commercial silicone is calculated from the measurement condition of Shore hardness. It is confirmed that the changes in the contact direction vary from 15.52 deg to 31.19 deg when the inner silicone has Shore A-50 and the outer silicone has Shore OO-10 to 50.
Vision-based Identification of Soft Tissues with Different Stiffness
김경현,김청준,이두용 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.4
Palpation on soft tissues can reveal areas having different stiffness. This paper reports a preliminary result of a vision-based method to localize a region of soft tissues with stiffness different from surrounding tissues. Tissue surface neighboring a stiffer region tends to deform perpendicularly in the direction toward the stiffer region when a tool tip presses the soft tissue. The proposed method estimates relative direction between the tool tip and the stiff region by computing eigenvectors of the deformed area. Feasibility of the method is analyzed using an FEM simulation. A rigid rod-shaped tool presses a slate of soft tissues which consists of a spherical region with higher stiffness and surrounding tissues. The tissues are modeled as having linear elasticity, and the parameters are set to represent human hepatic tumors and liver tissues, respectively. Simulation result shows that the proposed method estimates the tumor position with an error of 1.52 ° average, 1.09° standard deviation when the tool presses 5 mm in depth at a point 50 mm away from the tumor.