How does the measurement error of the image measuring instrument occur?

How does the measurement error of the image measuring instrument occur? Image measuring instrument is the rapid development of geometric optical measuring instrument in the past ten years. It is based on the principle of optical projection, combined with the application of modern optoelectronic technology and computer processing technology. A two-dimensional plane coordinate position measuring instrument has been completed, which is aligned with the edge profile of the sample to achieve length measurement. The instrument can detect the profile, surface shape, size, angle and position of various complex shapes. It is suitable for product development and reverse engineering. , Quality inspection and other fields, compared with traditional tool microscopes and projectors, CCD camera sensors, digital grating position output devices and automatic positioning servo control systems have been added to the hardware. For measurement or software functions, with automatic focusing, automatic aiming and various complex automatic calculation processing functions, the development and application of electronic and image processing technology, it provides the key to the multi-function, high-precision and automation of image measuring instruments Technical Support. The image measuring instrument used for factory site measurement usually has a resolution of 0.001mm and a measurement uncertainty of 3 + L/200μm. Among them, L is the measurement length in mm, which is used in the field of high-precision measurement in image measuring instruments, such as precision measurement and measurement value transmission. The measurement uncertainty is usually better than 1.0 + L /300μm. The structural composition and optical principle characteristics of the image measuring instrument, the image measuring instrument usually consists of six parts: machinery, lighting, length measurement, image acquisition, computer and measurement software. The optical principle of image measuring instrument is very similar to that of ordinary projector. The difference is that the measurement part of the image of the former is received by the CCD sensor and collected and processed by the computer. The latter projects the image directly on the projection observation screen. The contour is completed by the operator’s sight line, resulting in a gap between the measurement accuracy and the degree of automation. There is a big difference. The image measuring instrument usually has a larger measuring range, and is usually equipped with a 0.7x~4.5x zoom object lens. In addition to ordinary bottom lights and top lights, the lighting source also has ring lights, which are suitable for applications where neither bottom lights nor top lights can effectively illuminate. The error source of the image measuring instrument, the measurement on the image measuring instrument is a single-axis or two-dimensional plane coordinate measurement. When measuring, first focus, then align, then read and count, and then calculate and process. The reading comes from the ruler, that is, the grating system. Focusing and alignment depend on the optical microscope and an illuminating light source which directly affects the measurement effect and accuracy. Because if the measuring instrument is based on the image method, if the measured object cannot be illuminated effectively and correctly, the measurement result will obviously deviate from its true size. In addition to the above factors, environmental conditions are also non-negligible factors that limit measurement accuracy. Based on the above analysis, the following error sources can be summarized: a. Error of grating counting scale; b. Straightness and swing angle of the worktable when moving Error; c. The perpendicularity error of the two measuring axes of the worktable; d. The error of the microscope's optical axis is not perpendicular to the working surface; e. The error caused by the temperature of the measurement chamber; f. The focus and the focus caused by the change of the lighting conditions. Alignment error. Among these factors, the first four errors are hardware errors that are formed and repaired during the manufacturing process of the instrument and usually cannot be changed; the latter one is often ignored, and in actual measurement, when lighting under lighting conditions, it is usually Ignore errors caused by temperature effects. The change of the light source will directly affect the lighting effect and image quality of the tested workpiece. The main reason is that the image of the image measuring instrument is received by the CCD. Although the CCD has the function of automatically adjusting the gain, when the brightness is too high, the adjustment function will be lost.