Views: 0 Author: Site Editor Publish Time: 2022-09-14 Origin: Site
Video measuring instrument is a new type of high-efficiency precision measuring instrument developed based on computer vision detection technology in recent years. It is widely used in machinery manufacturing, electronics, automobiles, aerospace and other industries. It can be used for online inspection of the size, shape and mutual position of components, and can also be applied to scribing, centering holes, lithography integrated circuit alignment, etc. Because of its strong versatility, large measurement range, high precision, good performance, strong real-time performance, and the ability to connect with flexible manufacturing systems, it is widely used.
The measurement error of the image measuring instrument refers to the error inherent in the image measuring instrument itself. The errors caused by the instrument are multi-faceted, and errors may occur at various stages of the design, manufacture and use of the instrument, which are called the principle error, manufacturing error, and operation error of the measuring instrument.
1. Principle error
The principle errors that belong to the image measuring instrument are: the errors caused by the distortion of the CCD camera and the errors caused by different measurement methods. Due to the manufacturing and process of the camera, the refraction error of the incident light passing through each lens and the position error of the CD lattice, etc., the optical system has nonlinear geometric distortion, which makes the target image point and the theoretical image point. There are various types of Geometric distortion: radial distortion, eccentric distortion, thin prism distortion, etc., and the radial distortion is large, the tangential distortion and thin prism distortion are small, and the distortion in the central area of the image is small, and the edge distortion is large. Using a high-quality lens can reduce the influence of distortion error, but in precision measurement, it is necessary to take into account the influence of distortion and correct the measurement results.
The errors caused by different measurement methods mainly refer to the identification and quantification errors caused by different image processing techniques. The edge of the image is the basic feature of the image, and it is the reflection of the outline of the object or the boundary between different surfaces of the object in the image. Edge contour is an important factor for humans to recognize the shape of objects, and it is also an important processing object in image processing.
In the process of image processing, edge extraction needs to be carried out, and there are many different methods of edge extraction in digital image processing technology. The selection of different extraction methods will cause a lot of changes in the edge position of the same test piece, so it will affect the final edge position. 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 change accordingly. It can be seen that in the process of image processing, the image processing algorithm has a very important influence on the measurement accuracy of the instrument, and is the focus of image measurement.
2. Manufacturing error
The manufacturing errors of the image measuring instrument are: errors generated by the guiding mechanism, installation errors, etc. The error generated by the guiding mechanism is mainly the linear motion positioning error in the mechanism error for the image measuring instrument. Image measuring instrument is an orthogonal coordinate system measuring instrument. The orthogonal coordinate system measuring instrument has three mutually perpendicular axes, namely X, Y, and Z axes, and three moving parts move along these three axes, so that the CCD moves in a three-dimensional straight line relative to the measured workpiece. The use of high-quality motion guides can reduce the effects of such errors.
The installation error mainly lies in the relative relationship between the camera and the work surface. When the measurement platform and the lens of the CCD camera present a certain angle H, the error calculation formula can be obtained according to the knowledge of geometry: D =L(1- cosH)
If the level performance of the measuring platform of the image measuring instrument and the installation of the CCD camera are excellent, the included angle between them is within the range, and this error is very small.
3. Running Error
The operating errors of the image measuring instrument are: errors caused by changes in the measurement environment and conditions (such as temperature changes, voltage fluctuations, changes in lighting conditions, mechanism wear, etc.), and dynamic errors. Due to the change of temperature, the size, shape, mutual positional relationship and some important characteristic parameters of the components of the image measuring instrument change, thus affecting the accuracy of the instrument. Changes in temperature may also cause changes in electrical parameters and changes in instrument characteristics, resulting in temperature sensitivity drift and temperature zero drift.
Changes in voltage and lighting conditions will affect the brightness of the upper and lower light sources of the image measuring instrument, resulting in uneven illumination of the system, resulting in image edge extraction errors caused by shadows on the edge of the captured image. Abrasion makes the parts of the image measuring instrument produce size, shape and position errors, and the matching clearance increases, which reduces the stability of the working accuracy of the instrument. Therefore, improvements in measurement operating conditions can effectively reduce the effects of such errors.
