This paper is focused on developing a compensation module for reducing the thermal errors of a computer numerical control (CNC) milling machine. The thermal induced displacement variations of machine tools are a vital problem that causes positioning errors to be over than 65%. To achieve a high accuracy of machine tools, it is important to find the effective methods for reducing the thermal errors. To this end, this study first used 14 temperature sensors to examine the real temperature fields around the machine, from which four points with high sensitivity to temperature rise were selected as the major locations for creating the representative thermal model. With the model, the compensation system for controlling the displacement variation was developed. The proposed model has been applied to the milling machine. Current results show that the displacement variations on the x-and y-axes and the position error at the tool center were controlled within 20 µm when the compensation system was activated. The feasibility of the compensation system was successfully demonstrated in application on the milling operation.

Active hybrid aerodynamic and aerostatic bearing system has gradually become more valued in recent years for its application in the precision machine field, especially for precision instruments and mechanisms that require high rotational speed, high precision, and high rigidity support. In this system, air lubricated bearing is mainly used for support. Although the carrying capacity is not as high as oil film bearings, air lubricated bearings can provide a work environment where the rotor (spindle) will not experience axial deformation at high rotational speed and low heat generation. In practice, spindle system dynamic problems include critical speed, spindle imbalance, and improper bearing design, which can cause the spindle system to produce aperiodic motion, instability, and even chaotic motion under certain parameters and conditions during its operation. If severe, these irregular motions may cause machine damage or delay production. In order to understand what type of work situation can produce aperiodic phenomenon, and to prevent irregular vibration and reduce instantaneous air hammer effect, the finite difference method and mixed method are used to explore the related characteristics for spindle system. Meanwhile, relevant theories including bifurcation diagram, Poincare map, spectrum response phenomenon, and maximum Lyapunov exponents are applied to analyze rotor non-linear dynamic behavior. In addition, we verified the non-linear motion parameter conditions to prevent spindle system from falling into the instable status during design. The objective is to lower the probability of chaotic phenomenon in the system and reduce damage caused by irregular vibrations in the system. The result of this study can serve as a reference when designing precision spindle systems or mechanisms.

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For improving the defects in milling processes caused by traditional spindle bearings, e.g., the dimensional discrepancy of a finished workpiece due to bearing wear or oil pollution by lubricant, a novel embedded cylindrical-array magnetic actuator (ECAMA) is designed for milling applications. Since ECAMA is a non-contact type actuator, a control strategy named fuzzy model-reference adaptive control (FMRAC) is synthesized to account for the nonlinearities of milling dynamics and magnetic force. In order to ensure the superior performance of spindle position regulation, the employed models in FMRAC are all constructed by experiments. Based on the experimental results, the magnetic force by ECAMA is much stronger than that by the traditional active magnetic bearing (AMB) design under the same test conditions and identical overall size. The efficacy of ECAMA to suppress the spindle position deviation with the aid of FMRAC has been verified as well via numerical simulations and practical metal cutting.