Fabrication of microlens array mold by indentation method with height control of the indenter

摘要

In the general fabrication process of a microlens array mold, considerable time and labor are required for the shaping of optical surfaces; a numerical control machine tool is used in the shaping step, in which each element is shaped individually by feeding the tool precisely. To efficiently produce lens array molds, in a previous study, we proposed a method for forming microlens elements by indentation. In this method, a flat sintered porous metal plate is used as a workpiece, which is indented by an indenter having a lens element profile. The repetition of the indentation process enables a number of impressions, i.e., lens elements, to be rapidly produced on the mold surface. In the previous study, each indentation was terminated when the indentation load reached specific value to obtain the target depth of the impression. However, it was found that the depth of the impressions was not constant even though the indentation load was constant for each indentation. This was probably because the porosity of the workpiece was heterogeneous, which resulted in the variation of the depth of the impressions generated by setting the load of the indentation. In the present study, we terminate each indentation when the height displacement of the indenter is a specific value. To set the displacement in this manner, it is important to determine the start position of the height of the indenter. Thus, in the present method, the start position is determined by detecting electrical conduction between the indenter and the workpiece. As a result, the repeatability of the depth of the impressions is improved as compared with that of the previous method.