Design and manufacturing technology of ultrashort-throw projectors with freeform mirrors

Ultrashort-throw projectors allow large screens in very limited space and without concerns about shadows that obstruct the image, which is the development trend of the projector industry. However, the technical problems of image distortion and uneven illumination restrict its industrialization development. The freeform mirror is the core component of the ultrashort-throw projection system, and the high-performance design method and corresponding manufacturing technology are the key factors of ultrashort-throw projectors to achieve rapid development. In this paper, the initial shape of the freeform mirror is designed by geometric construction with energy mapping. The ultrashort-throw projection imaging system model is established. After optimization, the throw ratio is 0.2, the projection screen is 80 inches, the total length of the projection lens is 155 mm, the field of view is 152 deg, and the edge illumination of the system is 97% of the center illumination. The assembly and adjustment method of the lens and the processing and coating method of the mirror are studied, and the experimental prototype is assembled and tested. This paper aims to establish the theory of freeform surface design and provide theoretical and technical support for the construction and system design of off-axis complex freeform surface.