Simultaneous control signal and power transmission through mechanical rotary joint without wiring connection

This paper describes a transmission system which can simultaneously transmit both the control signal and power through a rotary joint by optical signals and RF wireless coupling in place of wiring connection. The system consists of a control signal transmission subsystem and a power transmission subsystem. The power transmission subsystem consists of a MOSFET inverter, a pair of power transmission coils and a rectifier. Based on the magnetic coupling, the RF transmission system has a capability to transmit the power without any electrical contact. The control signal transmission subsystem consists of a signal sender and a signal receiver. The control signal is transmitted via an air gap by using a light emitting diode (LED) and a photodiode (PD). The signal transmission subsystem can transmit 7 function (3-bit) signals. An experiment was successful when the modulation center frequency was set at 520 kHz and the air gap was 9.5 cm. The power conversion efficiency of the power transmission subsystem was 40% with a 50 ohm resistive load when the air gap was set st 2.88 mm. The diameter of each transmission coil in the power transmission subsystem was 25 mm. The LED and PD are concentrically placed at the center of the coil, so the transmission system volume is compact and suitable for industry applications.