Development of a Three-Dimensional Shape Measurement System for Occlusal Surfaces Using a Laser Beam Section Method

我们研究了去年开发的形状测量设备的测量精度，并开发了一个计算机化的咬合接触分析系统。众所周知，激光光束截面法形状测量的精度不仅与物体的材料有关，还与物体表面光斑所在点的形状有关。为了澄清这种相互作用，我们研究了多少曲率和表面点的法线方向反射测量值。作为测试对象，我们使用了一个由轴承球精确印模而成的石膏球。每个表面点数据的测量误差由估计的球中心距离与球直径之差来评估。使用直径分别为3.1和1.5mm的两个球进行了两次测试，结果表明：1)两个测试球的测量误差没有差异；2)当法向量方向与激光束方向的差值小于50度时，测量误差小于10 μ m。分析系统由以下三个子系统组成：1)分析系统，3)显示系统，4)数据文件管理系统。获得的数据被传输到一台微型计算机（MX5600，三菱电机）。然后计算机进行不必要数据的剔除、缺失数据的插值、对齿间牙距的计算和接触面积的识别。显示系统将形状数据和齿间距离数据可视化显示在CRT显示器上。

We investigated the measurement accuracy of a shape measurement equipment which was developed last year, and developed a system for a computerized analysis of occlusal contact.Measurement accuracy of shape measurement using Laser-beam-section method is known to depend on not only material of the object but shape of its surface point where the light spot is located. To clarify this interaction, We investigated how much curvature and the normal direction of the surface point reflect measurement eroor. As a test object, we used a plaster ball produced from the precise impression of bearing ball. Measurement error of each surface point data was evaluated by the difference between the distance from an estimated center of the ball and diameter of the ball. This test was carried out twice using two balls with different diameters about 3.1 and 1.5mm, yielding the results as follows : 1) there was no difference between the two test balls in the measurement error and 2) the error was less equal than 10 mum when the difference between the direction of normal vector and that of Laser beam was less equal than 50 degrees.The analyzing system consists of the following three subsystems : 1) an analytical system, 3) a display system and 4) a data-file management system. The obtained data are transferred to a mini-computer (MX5600, Mitsubishi Electric). The computer then carries out such takes as the elimination of unnecessary data,interpolation of missing data,computation of intercuspal distance between opposing teeth and recognition of contact area. The display system visualizes the shape data and the intercuspal distance date on CRT display.