Design of the Telecentric Lens for Dual Side Imaging of the Small Size Particles with Equal Optical Path

Due to the industrial automation requirements, a machine vision is widely used in the industrial production and detection. Compared with the traditional artificial, it has the advantages of high speed and high accuracy, especially to the small-size granular products. It is difficult to detect the surfaces of the small-size granular products quickly and accurately by artificial vision due to the limitations of human eyes. Therefore, the machine vision system with large magnification and high resolution often being used. For the products that need to detect multiple surface, it is often necessary to configure multiple sets of machine vision systems, which are very complex. In order to realize the multi-surfaces detection of small-size granular products, a two-sided imaging telecentric optical lens is designed in this paper, which can image the adjacent surfaces of the product simultaneously using one set of machine vision system. The lens consists of five prisms for double-sided image conversion and splitting and six spherical lenses. It has 1 times magnification, high resolution and the telecentricity was less than 0.01 °， the working distance is 36.84mm. Because there is an inclined angle of the glass wedge in the meridian plane, which makes the meridian plane asymmetric, when the MTF value is 0.3, the Nyquist frequency of the meridian surface is 65 lp/mm, and the Nyquist frequency of the sagittal surface is 125 lp/mm. The maximum distortion of the system is controlled within 0.2%, and it is suitable for 2 / 3 "CCD. Through tolerance analysis, the lens has good tolerance compatibility, high cost performance, and can be mass produced.