Fabrication of Off-Axis Aspherical Mirrors with Loose Abrasive Point-Contact Machining

In order to rapidly manufacture aspherical mirrors used for infrared reconnaissance and security cameras, a new fabrication technique, called as loose abrasive point- contact machining, is introduced in detail. The new technique is based on computer-controlled optical surfacing (CCOS). It has the features of conventional loose abrasive machining with the characteristics of a tool having multiple degrees of freedom moving in a planar mode. A new CNC machining system with two kinds of moving coordinate systems and dual tool activities is presently developed based on the new concept. The relationship between the motions of the tool and the workpiece during machining was analyzed on the basis of the Preston hypothesis followed by simulating the effect of the contact pressure. Experiments were carried out on the developed CNC system. The results indicated that the required convergent speed and precision could be achieved with high efficiency by utilizing the new technique. The accuracy of the aspherical mirror improved from the initial form error of 8.28μm to the final one of 1.71μm after machining for 70 hours.