影像测量仪的测量误差分析

    影像测量仪的测量误差是指影像测量仪本身固有的误差。引起的误差的原因是多方面的，在仪器设计、制造和使用的各个阶段都可能出现误差，称为测量仪的原理误差、制造误差和运行误差。

   1.原理误差。

   属于影像测量仪的主要误差有：CCD摄像机畸变引起的误差和不同测量方法引起的误差。相机的制造和工艺，入射光的折射误差和CCD在通过各个透镜时的位置误差等。目标像点和理论像点：径向畸变、偏心畸变、薄棱镜畸变等, 并且径向畸变大，切向畸变和薄棱镜畸变小，图像中心区域畸变小，边缘畸变大，使用优质镜头可以减少畸变误差的影响，但在精密测量中需要考虑畸变的影响，对测量结果进行修正。

  不同测量方法引起的误差主要是指不同图像处理技术引起的识别和量化误差。图像的边缘是图像的基本特征，是图像中物体轮廓或物体不同表面之间的边界的反映。边缘轮廓是人类识别物体形状的重要因素。也是图像处理中重要的处理对象。在图像处理过程中，需要进行边缘提取。在数字图像处理技术中，边缘提取的方法有很多种，使用的提取点也不同。这是一个不小的变化，因此会影响最终的测量结果。例如，在测量圆形工件的半径和圆心时，当圆的轮廓发生变化时，其半径值和圆心位置也会随之变化。可见，图像处理算法在图像处理过程中对仪器的测量精度有着非常重要的影响，是影像测量的重点。

   2.制造误差。

  影像测量仪的制造误差有：导向机构产生的误差、安装误差等。导向机构产生的误差主要是影像测量仪机构误差中的直线运动定位误差。影像测量为正交坐标系测量仪器。直角坐标系测量仪有3个相互垂直的轴，X、Y和Z轴。有3个运动部件沿这三个轴运动，使CXIED2可以相对于被测工件做三维直线运动。 选择高质量的运动引导机构可以减少此类错误图像。安装错误是主要当测量平台与CCD相机的运动差计算公式为如角度E时，根据几何知识可以得到误差计算公式，如果测量仪的测量平台级性能和CCD相机的安装都非常出色。它们之间的夹角都在015b以内，误差就会很小。

  3.运行误差。

  影像测量仪的运行误差有：测量环境和条件变化（如温度变化、电压波动、光照条件变化、机构磨损等）引起的误差和动态误差。由于温度放置关系和一些重要的特性参数发生了变化。从而影响仪器的精度，温度的变化会影响成像测量。测量仪器上下光源灯的亮度导致系统照明不均匀，从而导致捕获图像边缘出现阴影导致图像边缘提取误差。磨损使影像测量仪的零件产生尺寸、形状和位置误差，配合间隙增大，降低了仪器工作精度的稳定性。因此，改善测量操作条件可以有效降低此类误差的影响。

The measurement error of image measuring instrument refers to the inherent error of image measuring instrument itself. The causes of the error are various, in the instrument design, manufacture and use of each stage may appear error, known as the principle of the measuring instrument error, manufacturing error and operation error.

1. Principle error.

The main errors of image measuring instrument are: CCD camera distortion error and error caused by different measurement methods. Camera manufacturing and technology, refraction error of incident light and CCD position error when passing through each lens. Image point target image point and theory: the radial distortion, eccentric distortion and thin prism distortion, etc., and radial distortion, tangential distortion and thin prism distortion is small, the image distortion center area is small, the edge distortion, using high quality lens can reduce the influence of the distortion error, but need to consider the effect of distortion in the precision measurement, the measurement results are corrected.

The errors caused by different measurement methods mainly refer to the recognition and quantization errors caused by different image processing techniques. The edge of an image is the basic feature of the image, which is the reflection of the contour of the object or the boundary between different surfaces of the object. Edge contour is an important factor for human to recognize the shape of objects. It is also an important object in image processing. In the process of image processing, edge extraction is needed. In digital image processing technology, there are many methods of edge extraction, and different extraction points are used. This is not a small change, so it affects the final measurement. For example, when measuring the radius and center of a circular workpiece, when the contour of the circle changes, its radius value and center position will also change. It can be seen that the image processing algorithm has a very important influence on the measurement accuracy of the instrument in the process of image processing, which is the focus of image measurement.

2. Manufacturing error.

The manufacturing errors of the image measuring instrument include the errors generated by the guiding mechanism and installation errors. The error produced by the guiding mechanism is mainly the linear motion positioning error in the mechanism error of the image measuring instrument. Image measurement is an orthogonal coordinate system measuring instrument. A cartesian coordinate system has three perpendicular axes, X, Y and Z. There are three moving parts moving along these three axes, so that CXIED2 can make three-dimensional linear motion with respect to the workpiece under test. Choosing a high quality motion guide can reduce such false images. Installation error is mainly when the calculation formula of motion difference between the measuring platform and CCD camera is such as Angle E, error calculation formula can be obtained according to geometric knowledge, if the measuring platform level performance of the measuring instrument and the installation of CCD camera are very good. They're all within 015B, so the error is going to be small.

3. Operation error.

The operating errors of the image measuring instrument include the errors and dynamic errors caused by the changes of measuring environment and conditions (such as temperature change, voltage fluctuation, illumination condition change, mechanism wear loss, etc.). Due to temperature placement and some important characteristic parameters have changed. Thus affecting the accuracy of the instrument, temperature changes will affect the imaging measurement. The brightness of the upper and lower light source of the measuring instrument leads to uneven illumination of the system, which leads to the shadow at the captured image edge and leads to the error of image edge extraction. Wear causes the size, shape and position error of the parts of the image measuring instrument, and increases the fit clearance, which reduces the stability of the instrument's working accuracy. Therefore, improving the measurement operating conditions can effectively reduce the impact of such errors.