A new rotary ultrasonic machining (RUM) spindle is proposed. It adopts contactless rotary transformer replacing the well-established slip ring technology to supply power for the transducer. Owing to the large leakage inductances, the capacitive piezoelectric transducer and the variable mechanical load, the circuit compensation is crucial for efficient and reliable power transfer. In this study, the mathematical models are presented to identify the power transfer efficiency and capability of the rotary transformer used in RUM. A general optimisation method of compensation for maximum transfer efficiency is proposed. The mechanical load dependencies of the transfer efficiency, transfer capability and power factor are researched and discussed. The efficiency has been found to be dependent of the secondary compensation elements. The series-series (SS) topology is applicable to a wide range of mechanical load variations, followed by parallel-series (PS) topology. For a varying load in RUM, the contactless energy transfer is possible to achieve high efficiency, high power factor and appropriate output power that adapts to load variations.
In rotary ultrasonic machining (RUM), the contactless energy transfer (CET) system based on the rotary transformer can replace the well-established slip ring technology to supply power for the revolving ultrasonic vibrator. However, the transfer efficiency and power output capability of the CET system is usually a pair of contradictions. The high voltage of the compensation element is prone to occur, especially in high power applications, which is dangerous. In this paper, for four basic compensation topologies, the mathematical models of the transfer efficiency, the load impedance and the compensation elements' voltages are presented. The compensation elements are optimized for improving the transfer efficiency. The effects of coil turns on the transfer efficiency, the load impedance and the compensation elements' voltages are researched. The coil turns are optimized to control the load impedance of the power supply and the voltages of the compensation elements. The experimental results basically agree with the theoretical results. The optimized CET system not only has high transfer efficiency, but also has high power output capability. At the same time, the high voltages of compensation elements are avoided effectively and the safety of the system is guaranteed. INDEX TERMS Rotary ultrasonic machining (RUM), contactless energy transfer (CET), transfer efficiency, power output capability, local high voltage, coil turns optimization.
Femtosecond (fs) laser ablation has been recognized as an effective and promising technique for high-precision processing of natural and synthesized diamond. In this work, a study of femtosecond laser polishing for nanopolycrystalline diamond (NCD) films by chemical vapor deposition (CVD) is reported. The laser irradiation is induced by 200-fs laser pulses with a repetition frequency of 50[Formula: see text]MHz, and various laser fluences are employed to investigate their polishing effectiveness. The results show that the optimal laser fluence is 0.7[Formula: see text]J/cm2, at which the nanodiamond grains on top of the cauliflower-like clusters of NCD films can be ablated. With such laser fluence, the mean surface roughness of NCD films reduces from 73.84[Formula: see text]nm to 31.88[Formula: see text]nm, which presents a 57% reduction. Nevertheless, when the laser fluence rises beyond 0.7[Formula: see text]J/cm2, large amount of amorphous carbon (a-C) balls and porous lava-like morphology would come into being, resulting in severe degradation of the NCD surface.
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