In recent years, there has been demand for the increased adoption of electric vehicles and further efficiency improvement of internal combustion engines for environmental purposes. The cylindrical shapes of motor cases and cylinders are machined by boring; however, the cylindrical portions are often distorted owing to differences in the conditions during machining and after machining. The solution is to perform non-axisymmetric and non-circular inner cylinder machining in anticipation of this distortion. In this study, we developed a machine tool spindle with a mechanism that can control the rotational speed and position of the tool tip in the radial direction using a special motor. The rotational trajectory of the tool tip is controlled by precessing and nutating the spindle shaft in synchronization with the rotation angle. In this study, a disturbance observer was added to the radial position control system to improve the accuracy of the rotational trajectory control against the cutting force by estimating the cutting force. Non-circular machining tests using the proposed spindle and test workpieces were performed to evaluate the effectiveness of this function. In this paper, we report the feasibility of non-circular machining and the effectiveness of the disturbance observer based on the measurement of a machined workpiece.

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