3D and 2D finite element analysis in soft tissue cutting for haptic display

ICAR '05. Proceedings., 12th International Conference on Advanced Robotics, 2005. Pub Date : 2005-07-18 DOI:10.1109/ICAR.2005.1507436

T. Chanthasopsephan, J. Desai, A. Lau

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引用次数: 9

Abstract

Real-time medical simulation for robotic surgery planning and surgery training requires realistic yet computationally fast models of the mechanical behavior of soft tissue. This paper presents a study to develop such a model to enable fast haptics display in simulation of soft-tissue cutting. An apparatus was developed and experiments were conducted to generate force-displacement data for cutting of soft tissue such as pig liver. The force-displacement curve of cutting pig liver revealed a characteristic pattern: the overall curve is formed by repeating units consisting of a local deformation segment followed by a local crack-growth segment. The modeling effort reported here focused on characterizing the tissue in the local deformation segment in a way suitable for fast haptic display. The deformation resistance of the tissue was quantified in terms of the local effective modulus (LEM) consistent with experimental force-displacement data. An algorithm was developed to determine LEM by solving an inverse problem with iterative finite element models. To enable faster simulation of cutting of a three-dimensional (3D) liver specimen of naturally varying thickness, three levels of model order reduction were studied. Firstly, a 3D quadratic-element model reduced to uniform thickness but otherwise haptics-equivalent (have identical force-displacement feedback) to a 3D model with varying thickness matching that of the liver was used. Next, haptics-equivalent 2D quadratic-element models were used. Finally, haptics-equivalent 2D linear-element models were used. These three models had a model reduction in the ratio of 1.0:0.3:0.04 but all preserved the same input-output (displacement, force) behavior measured in the experiments. The values of the LEM determined using the three levels of model reduction were close to one another. Additionally, the variation of the LEM with cutting speed was determined. The values of LEM decreased as the cutting speed increased

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触觉显示中软组织切割的三维和二维有限元分析

机器人手术计划和手术训练的实时医学模拟需要真实且计算速度快的软组织力学行为模型。为了在软组织切割仿真中实现快速的触觉显示，本文对该模型的开发进行了研究。研制了一种装置，并进行了实验，以生成用于猪肝等软组织切割的力-位移数据。切割猪肝的力-位移曲线呈现出一种特征模式:整体曲线由局部变形段和局部裂纹扩展段组成的重复单元组成。本文报道的建模工作主要集中在以适合快速触觉显示的方式表征局部变形段中的组织。组织的变形抗力用局部有效模量(LEM)来量化，与实验力-位移数据一致。提出了一种利用迭代有限元模型求解逆问题来确定LEM的算法。为了能够更快地模拟自然变化厚度的三维(3D)肝脏标本的切割，研究了三个级别的模型阶降。首先，将三维二次元模型简化为均匀厚度，但在触觉上等效(具有相同的力-位移反馈)，与具有与肝脏相匹配的不同厚度的三维模型相匹配。其次，采用触觉等效二维二次元模型。最后，采用触觉等效二维线性元模型。这三种模型的模型缩小比例为1.0:0.3:0.04，但都保持了实验中测量到的相同的输入输出(位移、力)行为。利用三个层次的模型缩减确定的LEM值彼此接近。此外，还确定了LEM随切削速度的变化规律。LEM值随切削速度的增加而减小

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ICAR '05. Proceedings., 12th International Conference on Advanced Robotics, 2005.

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