Smart Identification Method for B-Axis and Tool-Nose Center Misalignment in Ultra-Precision Lathe Using Servo-Based Contact Detection

In recent years, B-axis rotary motion has often been utilized in ultra-precision turning operations, where it is essential to align the tool-nose center precisely with the center of the B-axis rotation and compensate for the residual misalignment that usually remains. Conventionally, this alignment relies on time-consuming, low-accuracy manual operations, resulting in the need for compensation machining after measurement and a reduction in both machining accuracy and overall efficiency. To overcome this issue, this study proposes a smart B-axis and tool-nose center misalignment identification method using servo-based tool–workpiece contact detection. In this paper, the thrust command signal of the Z-axis linear servo motor is used as the servo signal. By using this method, an external-sensorless, automatic, and high-precision alignment is expected to be realized. This paper presents the concept of the developed B-axis and tool-nose center misalignment identification method, and experiments are conducted to evaluate its effectiveness. The results show that the tool–workpiece contact position is identified with a repeatability of about 0.05 µm, and that the B-axis and tool-nose center misalignment identified by the proposed method is reduced from 6.2 µm to 0.34 µm by a single compensation.