Design of a six-axis high precision machine tool and its application in machining aspherical optical mirrors

Abstract The paper presents the design of a six-axis machining system and its application in fabricating large off-axis aspherical mirrors with sub-aperture lapping techniques. The new system is based on computer-controlled optical surfacing (CCOS), which combines the faculties of grinding, polishing, and on-machine profile measuring, has the features of conventional loose abrasive machining with the characteristics of a tool having multiple degrees of freedom moving in planar model. And a novel dual touch-trigger probe profiler is designed, which is composed of a probe, model METRO-MT60 made by HEIDENHAIN Co., is integrated into the system for measuring the shape accuracy of the tested aspherical surface, another probe modeled METRO-MT12 is designed as a calibrating device for minimizing the cosine error caused by assembly inaccuracy. The new CNC machining system with two kinds of moving coordinate systems, dual tool activities and on-machine measuring is presently developed based on the new concept. The general material removal function during machining is analyzed on the basis of the Preston hypothesis. Further, an alignment test of the measuring profiler is carried out using a leveling rule as a specimen. The accuracy of the optical surfaces measured by the dual probe profiler is found to be within 1 μm PV after removing cosine error and error compensating, achieves to the resolving power of the profiler is about 0.2–0.5 μm, so the developed system can be applied to the shape accuracy measuring of aspheric fabrication with micro precision during fine grinding process according to the calibrating results. Finally, the manufacturing experiments are carried out by virtue of an off-axis oblate ellipsoid mirror with rectangular aperture as 770 mm×210 mm and centered 127 mm. The accuracy of the aspherical mirror improved from the initial form error of 17.648 μm rms to the final one of 0.728 μm rms after grinding for 200 h.

[1]  Harvey M. Pollicove.  Next-generation optics manufacturing technologies , 2000, International Symposium on Advanced Optical Manufacturing and Testing Technologies (AOMATT).

[2]  Greg Paula.  Sensors give chip makers a new edge , 1997 .

[3]  M. Negishi,et al.  Studies of super-smooth polishing on aspherical surfaces , 1995 .

[4]  G. Doughty,et al.  Microcomputer-controlled polishing machine for very smooth and deep aspherical surfaces. , 1987, Applied optics.

[5]  D. R. Baselt,et al.  Float-polishing process and analysis of float-polished quartz. , 1994, Applied optics.

[6]  Y. Mori,et al.  Computer numerically controlled plasma chemical vaporization machining with a pipe electrode for optical fabrication. , 1998, Applied optics.

[7]  Victor Rupp.  The Development of Optical Surfaces during the Grinding Process , 1965 .

[8]  Hirofumi Suzuki,et al.  Study on Aspherical Surface Polishing Using a Small Rotating Tool. Development of Polishing System. , 1993 .

[9]  R. A. Jones,et al.  Optimization of computer controlled polishing. , 1977, Applied optics.

[10]  Robert A. Jones,et al.  Rapid optical fabrication with computer-controlled optical surfacing , 1991 .

[11]  W Rupp.  Loose abrasive grinding of optical surfaces. , 1972, Applied optics.

[12]  Bernd Harnisch,et al.  Off-axis telescopes: the future generation of Earth observation telescopes , 1998, Optics + Photonics.

[13]  Kazuto Yamauchi,et al.  Mechanism of atomic removal in elastic emission machining , 1988 .

[14]  Y. Mori,et al.  Elastic Emission Machining , 1987 .