How to set the lens parameters in the machine vision system?

The lens is an important component in the machine vision system and plays a key role in the imaging quality of visual inspection. Its main parameters include: focal length, aperture coefficient, field of view, working distance, depth of field, etc. The following quaternion numerical control will introduce some of the main parameters of the machine vision system. The focal length (field angle) not only describes the refractive power of the lens, but also serves as a reference for image quality. Generally, the lens distortion increases with the decrease of the focal length (or the increase of the angle of view), so choose a measuring lens instead of a lens with a small focal length (less than 8mm) or a large angle of view. Aperture factor is an important internal parameter of the lens. It is the reciprocal of the relative aperture of the lens. Normal manufacturers will use the F number to represent this parameter. For example, if the relative aperture of the lens is 1:2, then its aperture is also F2.0. This indicator will be written on the lens of the camera. Since the aperture factor is the reciprocal of the relative aperture, if the number of the nominal value of the aperture factor is larger, it means that the actual aperture is smaller. Generally speaking, the order of the aperture of the lens is: 1, 1.4, 2.0, 2.8, 3.5, 4.0, 5.6, 8.0, 11, 16, 22, 32 and so on. As the value increases, the actual aperture size also decreases, and its luminous flux within the same shutter time also decreases. Of course, in order to increase the reliability of the lens and reduce the cost, some machine vision systems adopt a fixed aperture design. When the aperture cannot be changed, the brightness of the image needs to be adjusted by adjusting the light source intensity or camera gain. The image field of view (that is, the size of the supported CCD chip) is also an important internal parameter of the lens. The size of the CCD chip is usually 1/3”, 1/2”. Different chip specifications require corresponding lens specifications. The lens design specifications must be equal to or greater than the chip specifications, otherwise black bars will appear at the edges of the field of view. Especially in the measurement, it is best to use a slightly larger lens, because the lens tends to have the greatest distortion at its edges. Working distance is often very important in vision applications. It is proportional to the size of the field of view. Some systems have a small working space and require a small working distance for the lens, but some systems may need to install a light source or other working devices in front of the lens. There must be a larger working distance to ensure space. Generally, compared with a surveillance lens, a small working distance is an important difference between FA lenses. Depth of field is another important external parameter of the lens. It represents the difference between the farthest position and the nearest position that meets the requirements of image clarity. The calculation of the depth of field may be relatively troublesome. It is related to the lens focal length, aperture value, working distance and the maximum diameter of the allowable diffuse spot. Since the maximum diameter of the permissible diffuse spot is a relative quantity, its acceptable diameter largely depends on the application, so in actual vision applications, the reference value given by the experiment and the reference lens is the main one. Simply put, the smaller the aperture, the deeper the depth of field; the shorter the focal length, the deeper the depth of field; the longer the focusing distance (working distance), the deeper the depth of field. There are also many application cases in the measurement algorithm, including excellent corner detection algorithms. Quaternion is committed to the development and application of industrial automation technologies such as motion control, image and vision sensing. Its products are widely used in printing equipment, die-cutting equipment, laminating equipment, multi-axis numerical control equipment, manipulators, electronic processing and testing equipment, Laser processing equipment, polishing machinery production automation and other industrial control fields.