Key technologies in high efficiency and ultra precision grinding of large aperture and complex aspheric lens

Abstract

Thanks to the advantages of improving the focusing precision and reducing the energy loss in the beam focusing, complex and off-axis aspheric mirrors are widely used in the field of aviation, aerospace, national defense and other large optical systems. Ultra-precision grinding is an important technology to manufacturing large aperture aspheric optics in enormous quantities. In order to fabricate large aperture aspheric optics high efficiently and precisely, several key technologies when parallel grinding were proposed in this article. First, the computer aided programming system was developed, which could compute the coordinates of aspheric surface and diamond wheel when grinding and generate the CNC programs automatically, which can be directly executed by the grinder. On the premise of waviness controlling, the raster grinding trajectory was optimized to improve the material removal efficiency. To acquire the radius and form error of diamond wheel, the measurement of diamond wheel based on corkscrew spin trajectory was proposed, which could detect the 3-D geometric morphology of wheel. By precision tool setting using displacement sensor, the definitive position between wheel and element was established, which avoided the error correction in subsequent grinding process. Through on-machine measurement using non-contact displacement sensor, the 3-D form error of optics was acquired, which was combined with the theoretical coordinates of aspheric to compensation grinding. In the end the grinding experiment was carried out. The material removal rate of rough grinding, semi-fine grinding and fine grinding were about 520mm3/s, 26 mm3/s and 1.6 mm3/s, respectively. The P-V of form error after fine grinding was about 3.21μm. The destination of highly active and ultra-precision grinding of large aperture and complex aspheric lens was achieved.