Abstract
A non-contact method for precisely detecting the tip position of micro-tools is proposed in this paper. The tip position of a micro-tool must be detected for milling work pieces precisely. Conventional detectors for the tip position of micro-tools can break the tip of the micro-tool by contact force or fail to detect all three axes. Therefore, the tip position of a micro-tool must be detected precisely without contact. An optical set-up to detect the position is composed of a microscope and optical devices. A CCD camera in the set-up produces magnified images of the tip of the micro-tool, and contrasts between the tip images are calculated. The shallower the depth of focus of an objective lens, the smaller the width of the contrast peak. The tip position of micro-tools is detected without contact by the repeatability of the contrast peak position of images. Experiments are conducted to confirm that a highly repetitive detection accuracy is obtained by this method. In the experiments, two parameters are used: the calculating range of the contrast and the direction of the detecting line of light intensity distribution obtained by the CCD camera. The two parameters are optimized from the experimental results. The parameter called the contrast calculating range has the highest precision repetitive detecting position, provided that it is longer than 3μm. Fringes with a high spatial frequency and a detecting position with a high repetitive precision are obtained when the direction of the detecting line is at a right angle to the direction of the cut made in the micro-tool. Considering the circumstances mentioned above, the degrees of precision in the repetitive detecting position were 2σ=±0.036μm (φ0.04mm Square endmill) and 2σ=±0.019μm (Nose R0.05mm Ball endmill). These experimental results show a higher level of precision than tool position detectors currently in use. The proposed method has sufficiently high performance to allow detection of the position of the micro-tool.
