Design of series-parallel combined resonant circuit with rotary transformer used for ultrasonic spindle drive

The ultrasonic spindle is well-known as one of the processing equipment and has high-machining performances. An ultrasonic transducer used for the ultrasonic spindle drive is usually driven by high-frequency sinusoidal voltage. To supply this sinusoidal voltage to the ultrasonic transducer attached to the rotary axis, a rotary transformer, instead of the voltage transfer method using a brush and a slip ring is utilized to realize maintenance-free. However, the rotary transformer cannot be transferred the required voltage to drive the ultrasonic transducer because the coupling coefficient of the rotary transformer is not sufficiently high. Therefore, the leakage inductances in the rotary transformer are needed to cancel equivalently by utilizing LC cancellation techniques. This paper proposes two series-parallel combined resonant circuits. The one is a circuit which a series resonant circuit is buried in a parallel-resonant circuit, on the primary side of the transformer. The other is a circuit which a parallel-resonant circuit is buried in a series resonant circuit. In addition, the design methods for both circuits are proposed, and these circuits are compared from theoretical analysis and simulation point of views.