Research On The Design Method Of Free-form Surface Prism Based On The Ultra-precision Machining

After forty years development, the technology of Head Mounted Display (HMD)has progressed greatly. With the development of the high resolution micro display andvirtual reality technology, the HMD will have a broad application prospect, and it hasdeveloped gradually from military field to civil field, such as industry, medicaltreatment and education. The system of HMD contains three parts, include image,optical system and support system. The optical system is the most important in HMD,but the traditional optical system can’t achieve all features of the ideal optical systemat the same time, such as light weight, small volume, and large field of view.Recently ten years, with the development of optical design methods and theultra-precision machining technology, the free-form surface prism was used in theoptical system of HMD gradually, achieving the requirements of ideal optical system,that is, light weight, small volume, and large field of view, etc. However, thefree-form surface prism has strict requirements on the structural tolerance and surfacetolerance, leading to the processing more difficultly, at last brought about thefree-form surface prism has not been used widely.In response to this situation and characteristics of the free-form surface prism,this paper dose a series research on the design and processing of the free-form surfaceprism with large field of view based on the actual processing angle. In addition, thepaper introduces the optimization design method based on tolerance analysis. Specificresearch contents are as follows:1. Elaborates the design steps and design methods of free-form surface prism inHMD, establishes the appropriate initial model and determines the appropriateoptimal control conditions and the surface upgrade strategy to get the design proposalof the free-form surfaces prism which has high imaging quality.2. Based on the analysis about the affect of surface tolerance on the imagingquality for the processing, this paper proposes the surface tolerance about free-formsurface prism, which can guide the actual processing and also provide a strong basisfor the analysis of the prism imaging.3. For the problem of strict tolerances of prism and difficult processing, thepaper proposes a tolerance optimization and constraint method, which can improve the structure tolerance of the free-form surface prism, reduce the difficulty ofprocessing, all of those can ensure that the image quality after processing..Finally, this paper tests and verifies the high-quality imaging performance andthe tolerance optimization of the free-form surface prism by processing andexperiments, In addition, analyses the free-form surface prism after processing andverifies the design method and steps are reasonable, which can make a direction forfurther optimization design.