A study of the tool change timing in turning micro V-grooves roller

摘要

The diamond tools have been employed in industry in turning micro V-grooves of mirror surface on a large diameter roller for the fabrication of brightness enhancement film (BEF) required in the backlight unit (BLU) of flat panel display by imprint process. They are expensive consumables and should be retired only when necessary, and hence determination of tool retirement timing is essential. Currently it is achieved by visual inspecting the mould surfaces at the production line. No automatic mechanism is available yet. In addition, the replaced new tools must be aligned with cumbersome procedures before turning can be resumed. An approach to determine if the tool is still useful by machine vision strategy is proposed and implemented. The image of the mould surface under a LED white light source is captured by a CCD camera. The brightness of the surface is obtained by algorithm of color space conversion. A threshold value is established experimentally to determine the acceptable brightness of the roller mould surface. It was found that tools must be replaced when surface of workpiece is not mirror like and its brightness value is less than 240. By using the same setup, the amount of tool shrinkage is determined by an image processing algorithm. This can be used not only as tool tip compensation along turning direction but also as an alignment measures after tool replacement. As a result, the new tool can be accurately positioned and matched with the old tool such that the turning process can be continued successfully.