Telecentric lens in object space

by lyonOP
Last updated December 16, 2021 Copy

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The invention can be used in devices for monitoring objects by the shadow optical method. The lens contains six lenses and an aperture diaphragm, located sequentially on the optical axis: a plano-convex lens located with the plane to the aperture diaphragm, a positive meniscus with an aspherical convex surface facing the space of objects, a weakly negative meniscus, facing the convex side to the aperture diaphragm, aperture consisting of a biconcave and biconvex lenses and located with the concave side to the aperture diaphragm, a biconvex lens and a weakly negative meniscus facing the convex side of the aperture diaphragm. The technical result is the expansion of the field of application, improvement of technical characteristics and enhancement of manufacturability.

The invention relates to the field of optical instrumentation, namely to optical systems of control and measuring devices, and can be used in devices for controlling objects by the shadow optical method.

One of the most urgent and frequently occurring tasks in measuring technology is the control of the geometric dimensions of products. To solve these problems, various optoelectronic control methods have become widespread. One of the most commonly used methods is the shadow method, which has high performance and low measurement error. The use of standard lenses for the shadow optical system introduces a significant additional error due to the large influence of object positioning on the linear magnification of the system. In this regard, to implement the control of products by the shadow method, it is necessary to use a telecentric lens in the space of objects, which should be practically free from distortion (less than 0.02%), field curvature and astigmatism (less than 0.1 mm), have high telecentricity in the space of objects. In this case, due to the parallel path of the main rays in the space of objects, the diameter of the first lens, and hence the field of view of the objective, must exceed the linear size of the measured object. Most of the existing lenses do not quite meet these requirements.

The telecentric lens is used in the control system of the geometric parameters of ceramic rings and provides the formation of images of a large range of products. However, this lens has the following disadvantages.

Firstly, the lens has a small field of view (less than 50 mm), which limits the use of the presented lens for a wide range of products.

Secondly, the lens has significant astigmatism (about 0.2 mm) in combination with insufficient telecentricity of the rays in the object space (maximum non-telecentricity 0.12 °), which degrades the technical characteristics of the telecentric lens and shifts the center of mass in the image of the edge beams.

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