An ultraprecision grinding machine for non-axisymmetric aspheric mirrors

For the purposes of grinding non-axisymmetric aspheric surfaces, a large five-axis controlled ultraprecision grinding machine has been developed for the first time in the world. As the machine is equipped with a profile measurement system, profile accuracy can be improved by feedback of profile error. A toroidal surface of 500 mm x 100 mm made of CVD-SiC has been machined. It has always been hard to grind CVD-SIC in the ductile mode with metal-bonded grinding wheels because of its hard and brittle properties, but grinding in the ductile mode has been accomplished by an improved truing and dressing method. As a result, surface roughness of less than 5.0 nm RMS was attained. By correcting profile error with the profile measurement system, profile accuracy of about 0.5 mu m was obtained after four corrections.