Design of Ultra-Precision CNC Grinding Machine and Its Application in Machining Large Aspheric Mirrors

Large aspheric mirrors are needed for the remote sensing and ground based telescope optical systems,these mirrors are made of hard and brittle materials which require ultra-precision grinding process to guarantee the high profile accuracy and machining efficiency. The ultra-precision aspheric CNC grinding machine( UAG900) is presented by this paper,as well as its grinding capability. The hydrostatic bearings of high accuracy and stiffness are adopted by the linear and rotary motions to guarantee the mirror accuracy,material removal rate and subsurface damage. Disk type grinding wheel with arc edge is used. The material removal rate can be up to 360 mm3/ min to guarantee the machining efficiency during rough grinding using D180 diamond grinding wheel while the fine grinding is performed using D15 grinding wheel. It indicates that the grinding wheel radius measuring error is proportional to the profile error induced by the grinding path. The grinding step size is better to be 0. 01 mm for the reduction of the grinding movement accelerations and program length. The grinding path is planned and expressed based on the grinding mode according to the mirror shape. One540 mm×450 mm× 100 mm zerodur mirror is ground and re-ground using the measuring data acquired by the Leitz CMM. The final surface accuracy of P-V value is less than 5 μm after compensation grinding.

Large Aperture Mirror Surface Test

The large aperture mirror surface test is the basis of optical processing and alignment, and is also the key to the development of remote sensing device. The simulation results show that the RMS values of 1.07 m primary mirror with multi-point support and sling support are 1.86 nm and 3.28 nm respectively. Using 36 point unloading device, sponge 36 point free support and sling support to test the mirror surface, the results are basically consistent, RMS is better than 0.02λ (λ = 632.8 nm).