Patent ID: 7132774

Claim:
A stepping motor comprising: a rotor assembly shaped cylindrical, having a rotary shaft fixedly attached to its center, and having a plurality of magnetic poles arranged at its outer circumference; a first yoke formed of a soft-magnetic plate, having an opening for rotatably letting the rotor assembly through, and having a plurality of pole teeth formed at a circumference thereof defined by the opening so as to oppose the plurality of magnetic poles with a predetermined clearance in-between; a second yoke formed of a soft-magnetic plate, disposed to oppose the first yoke, having an opening for rotatably letting the rotor assembly through, and having a plurality of pole teeth formed at a circumference thereof defined by the opening so as to oppose the plurality of magnetic poles with a predetermined clearance in-between; a magnetic path means to magnetically connect the first and second yokes; and a bobbin including a middle body section shaped hollow-cylindrical, a first lateral body section shaped hollow-cylindrical and having a larger bore diameter and a larger outside diameter than the middle body section, a second lateral body section shaped hollow-cylindrical and having a larger bore diameter and a larger outside diameter than the middle body section, a first joining section to connect one end of the first lateral body section to one end of the middle body section in a coaxial manner, a second joining section to connect one end of the second lateral body section to the other end of the middle body section in a coaxial manner, a first flange formed at the other end of the first lateral body section so as to radially extend outward, and a second flange formed at the other end of the second lateral body section so as to radially extend outward, the bobbin having a magnet wire wound around the first lateral body section, the middle body section, and the second lateral body section, the bobbin having a distance between an outer face of the first flange and the first joining section larger than the length of the plurality of pole teeth of the first yoke and a distance between an outer face of the second flange and the second joining section larger than the length of the plurality of pole teeth of the second yoke such that the plurality of pole teeth of the first and second yokes are housed inside of the first and second lateral body section respectively.