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

我们研究了去年研制的一种形状测量设备的测量精度，并开发了一个咬合接触计算机分析系统，用激光束截面法测量形状的测量精度不仅取决于物体的材料，而且取决于光斑所在的表面点的形状。为了阐明这种相互作用，我们研究了曲面点的曲率和法线方向对测量误差的影响。作为测试对象，我们使用了一个石膏球从轴承球的精确印象产生。每个表面点数据的测量误差通过距球的估计中心的距离与球的直径之间的差来评估。使用直径约为3.1 mm和1.5 mm的两个球进行两次试验，结果如下：1）两个测试球之间的测量误差没有差异，2）当法向量方向与激光束方向之差小于50 °时，误差小于10 μ m它由三个子系统组成：1）分析系统，3）显示系统和4）数据文件管理系统。将获得的数据传送到微型计算机（MX5600，Mitsubishi Electric）。然后，计算机进行诸如消除不必要的数据，缺失数据的插值，对牙齿之间的牙尖间距的计算和接触区域的识别。显示系统将牙尖间距数据和牙外形数据在CRT显示器上显示出来。

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.