The industrial lens is an important part of the machine vision acquisition system. The telecentric lens is a relatively young member of the lens family and is becoming the most kind star with its unique performance. However, due to the relatively short introduction time of the telecentric lens, many of its features have not been widely known by people. The following Swiss Vision Technologies will introduce the principles of the basic knowledge of telecentric lenses, from the principle of telecentric lenses to the scope of application. Three aspects of the selection method, to comprehensively expound on it, reveal the secret art journey experienced by the secret light in the telecentric system.
First, the principle of telecentric lens
First of all, we start with a few questions about non-telecentric lenses. The first problem, the general lens in the imaging process, when the working distance changes, the resulting image size will change accordingly, the result is the same focal length lens, corresponding to different object distance, there will be different The magnification is similar to that of the human vision system.
This problem can be ignored or even used in some applications, but this feature can be a great obstacle when our vision system is used to perform precise measurement tasks. The second problem is that ordinary shots have a certain range of depth of field. When the measured object is not within the depth of field of the lens, the image becomes blurred and the focus cannot be clearly focused. For this reason, the designers designed the ordinary lens. Focus ring, when the working distance changes, you can adjust the focus area to see clearly the area of ​​interest.
The problem is that if the depth of the measured object itself exceeds a certain range, the lens has no way to see both ends at the same time. This problem must be resolved through other means. The third problem is that with the ever-increasing resolution of imaging chips, users are increasingly demanding the measurement accuracy. Ordinary lenses are subject to the principles of optical imaging, and the best is only about 10um. The field of vision inspection requires more accurate imaging products.
Double telecentric lens is to solve these problems came into being. Double-telecentric lens By placing an aperture stop in the middle of the optical system, the chief ray must pass through the center point of the aperture, and the principal ray of the object side and the imaging side must enter the lens parallel to the optical axis. Incident parallel light ensures a sufficiently large range of depth of field. The parallel light coming out of the lens ensures that the working distance changes drastically within the depth of field, and the height of the image, ie the magnification, does not change. The specific light path diagram is as follows:
Second, the use of telecentric lens
Under what circumstances should we choose a telecentric lens? According to the experience of dimension image in the selection of machine vision products for many years, the following conditions, it is recommended to choose dual telecentric lens.
1. When the object to be inspected has a large thickness and needs to detect more than one plane, typical applications are food boxes, beverage bottles, etc.
2. When the position of the measured object is uncertain, it may be at a certain angle with the lens.
3. When the measured object jumps up and down in the process of being detected, such as when the working distance changes due to vibration on the production line.
4. When the measured object has an aperture or a three-dimensional object.
5, when the need for low distortion rate, the brightness of the image is almost exactly the same.
6, when the need to detect defects can only be detected in the same direction parallel lighting.
7, when the need to exceed the detection accuracy, such as the allowable error is 1um.
Third, the telecentric lens selection method
The telecentric lens selection method is actually similar to the lens in ordinary optical systems. The following points need attention:
1. Compatible CCD target surface size. This is similar to the selection of a normal lens, which requires that the telecentric lens compatible CCD target surface is greater than or equal to the matching camera target surface, otherwise it will result in a waste of resolution.
2, the interface type. Currently, the type of interface provided by the telecentric lens is similar to that of ordinary lenses. There are C-ports, F-ports, etc., as long as they are compatible with the camera.
3, magnification, or imaging range. When the magnification and CCD target surface are determined, the imaging range is determined, and vice versa.
4, working distance. In the general case of the above three points selected, the working distance has been determined within a range, which is determined by its imaging light path. It should be noted that this working distance meets the actual use requirements. When using the telecentric system for detection, we recommend selecting the lens first and designing other mechanical structures based on their working distance.
5, depth of field. Under the premise of satisfying the previous conditions of use, the larger the depth of field, the better the optical properties of the telecentric system, and can be used as a reference when selecting the type.
Because these characteristics of the telecentric lens, resulting in very high production process requirements, so the current major manufacturers are abroad, Swiss Vision as the leading domestic optical brand of telecentric self, its BT series of double telecentric lens products with its High accuracy, stability and cost-effectiveness are gaining recognition from more and more customers. We hope that we can accompany you to grow up on the road of telecentric optics and contribute to the construction of this family of machine vision. power.
Modular Ups,Hot-Swappable Modularity,Pure Sinusoidal,Parallel Redundant Ups
Shenzhen Unitronic Power System Co., Ltd , https://www.unitronicpower.com