High-precision concave spherical artifact for accuracy evaluation of a measuring instrument for an internal gear

The vibration and noise from internal gears is an important issue in mechanical devices such as automobiles. The characteristics of the vibration and noise of internal gears are markedly influenced by micrometer-order manufacturing errors of the tooth flank form. Therefore, quality control using a measuring instrument is required. The accuracy of a gear measuring instrument is usually evaluated using a master gear. However, it is difficult to manufacture master gears with high accuracy because the reference surface of a master gear for an internal gear has a geometrically complicated form. This limits the accuracy of the evaluation and calibration of measuring instruments for internal gears. In order to address this problem, the present paper proposes a novel artifact with a concave spherical surface for the evaluation of the accuracy of measuring instruments for internal gears. A concave spherical surface can be manufactured with high accuracy because of its simple features. As such, a highly accurate artifact can be developed using this surface. In the present paper, the concept for the proposed artifact is described, and a mathematical model for the measurement conditions of the artifact is constructed. The design of the artifact is described, and an evaluation method for the measuring instrument is developed. The artifact is then manufactured, and its accuracy is calibrated. A measurement experiment using the proposed artifact is carried out, and the effectiveness of the evaluation method is verified.