Permanent magnet inductor tachometer

Claim 1

In a mechanical apparatus having an output shaft supported by an output bearing for driving belted loads, the improvement in combination therewith of a tachometer located inboard of the output bearing for maintaining the belted load capacity of the apparatus and adapted to provide an electric signal indicative of the rotary speed of the output shaft, the tachometer comprising: (a) a rotor mounted inboard of said bearing on said shaft for rotation therewith and having a plurality of projections protruding along the rotor periphery; and (b) a stator assembly mounted inboard of said bearing and having: (i) a plurality of opposed stator segments, each having stator teeth, (ii) windings on said stator teeth for providing the electric speed signal, (iii) flux establishing means for establishing magnetic flux in said stator segments, and (iv) flux return path means connecting said stator segments exterior of said rotor for providing a magnetic flux return path between said stator segments in the stator; wherein said rotor projections and said stator teeth form a plurality of flux transmission paths whose magnetic flux varies in response to rotation of said shaft; and wherein said flux return path means receives substantially all the flux from said flux transmission paths so that the total machine flux in said return path is substantially constant.