Capacitively commutated brushless dc servomotors

Abstract From the Canadian patent

There are disclosed both one- and two-dimensional high resolution, brushless DC servomotors that are linear rotary, planar and cylindrical in nature. All of these employ a capacitive method for deriving the required position and motorcommutation information. In suitable circumstances particularly two-dimensionalplanar motors on air bearings the method allows the use of the motor ferromagnetic cores themselves as the capacitive position sensing elements. This leads to a particularly simple and compact type of servomotor design. In addition since such, motors can move at high speed there are also disclosed two transformer coupled methods for handling the current drive to the motor windings. …