Development of a High Precision Machining Center and its Motion Accuracy

Abstract

In the fabrication of parts and components using dies and molds for optical and/or medical use instruments, there are standing requirements that the accuracy of the form of the final products be maintained within a tolerance of 1.0μm or less and that the roughness of the machined surface be held to 0.2μm Ra or less while high production efficiency is maintained. The required accuracy of form, smoothness of the machined surface, and efficiency of production stated above can be achieved by high precision machine tools, but are beyond the performance properties expected of conventional, general-use machining centers, both of which are readily available on the open market. The authors (hereinafter collectively referred to as “the group”) who did this research agreed to refer to the machining centers that can satisfy both of the above-mentioned performance requirements as “Subject Machining Centers,” or “Subject MC,” while the other machining centers are referred to as “Conventional Machining Centers” or “Conventional MC.” This research includes a structural study of a Subject MC, followed by the actual designing and manufacturing processes of such a Subject MC, It was then subjected to an appraisal of its accuracy of motion from the data obtained through actual measurements, and a verification of the precision attained in the manufacturing process of the lens molds it produced. Through the combined use of a frictionless drive train using a hydrostatic guide and linear motor drive, together with the overall enhancement of the rigidity of the structure of the Subject MC, the following results were achieved.1.Straight line motion accuracy with a deviation of 0.2μm/100 mm or less was attained. Also, the roundness of 0.36μm of the arc interpolation movement was achieved, confirmed with a grid encorder. (“Roundness” in this study is defined as the magnitude of the deviation of either an arc or a circle as measured against their geometrically correct counterparts.)2.As a position loop gain as high asKp= 140/s was attained with the servo mechanism adopted, it was confirmed that the actual use of the micro step feed at uniform separations of 10 nanometers had become possible.3.It became possible to mold a lens with a roundness of 0.53μm and a surface roughness of 0.05μm Ra after machining. (“Ra” denotes the arithmetical average of surface roughness after machining.)