Patent ID: 7173352
Filing Date: 2007-02-06
Classification: H02K

Abstract:
1. A stepping motor comprising: a magnet ring whose outer peripheral surface is circumferentially divided to form radial protrusions and recesses and whose outer peripheral surface is made of a cylindrical permanent magnet magnetized to the same polarity; a first cylindrical coil and a second cylindrical coil that are concentric with the magnet ring and arranged so as to hold the magnet ring therebetween with respect to an axial direction; a first outer magnetic pole portion opposed to one outer peripheral surface side of the magnet ring with a predetermined distance therebetween and excited by the first coil; a second outer magnetic pole portion opposed to the other outer peripheral surface side of the magnet ring with a predetermined distance therebetween and excited by the second coil; and an output shaft formed of a soft magnetic material and fixed to an inner peripheral portion of the magnet ring, the output shaft being opposed to at least one of the first outer magnetic pole portion and the second outer magnetic pole portion in a predetermined axial range and equipped with an inner magnetic pole portion excited by at least one of the first coil and the second coil, wherein the magnet ring is formed of a sheet-like flexible material whose one side has protrusions and recesses, and is wound around and fixed to an outer peripheral surface of the inner magnetic pole portion formed on the output shaft such that the outer peripheral surface has protrusions and recesses to form a cylindrical configuration, and wherein winding-start and winding-end portions of the sheet-like flexible material with respect to the outer peripheral surface of the inner magnetic pole portion are recessed portions.