Linear Motion System Cable Elimination Via Multiphase Capacitive Power Transfer Through Sliding Journal Bearings

Electrical loads that slide on moving gantries or rails are common in industry and automation, e.g. assembly lines, spindle heads, x-y tables, etc. These systems often use insulated linear bearings to support mechanical movement during the intended process and a flexible wire-way or cable track provides an electrical connection to power moving parts. This paper proposes eliminating the cable connection by using the capacitance of the linear bearings to transfer power between stationary and moving parts, i.e. the bearings/rails form the coupling of a capacitive power transfer system. This is enabled by a 3 -5 MHz, 3 phase, resonant inverter capable of driving AC current through the bearing-rail capacitance where it is ultimately rectified on a carriage for final use. The high switching frequency enables smaller bearing coupling capacitance to be used with lower developed voltages. The inverter uses 650V Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs) in a 3 phase configuration to extend switching frequencies to multi-MHz, thus enabling power transfer levels towards 10(2)-10(3) watt levels. The brushless and wireless excitation of a sliding electrical load, using linear plain bearings sliding on conventional 1 inch diameter anodized shafting serves as a demonstration application. Experimental tests at 3.66 MHz demonstrate 111.9W power transfer to a sliding carriage load.