| 摘要 |
PROBLEM TO BE SOLVED: To prevent the occurrence of molding defects that are caused by deteriorated circulation of molten resin in the injection molding of a rotating body, and to enhance positional accuracy at maximal stroke of a drive shaft. SOLUTION: A passing hole 22 is formed, in which at least two stripes of female screws are tapped on is inside circumferential surface in the direction toward the inside shaft of the rotating body 21 that, made of a synthetic resin, is provided inside an electromagnetic coil 2, in such a way as to rotate freely and that has a permanent magnet 4 encased solidly in its outside circumference. The drive shaft 23, on the outside circumferential surface of which at least two stripes of male screws 12 that are engaged with the female screws are threaded, is passed and arranged inside the through-hole. As the rotating body 21 rotates, the female and male screws are engaged with each other to make the drive shaft perform linear stroke movements. A stripe of spiral clearance grooves 24, on which a stopper pin 27 provided protrusively on the driving shaft slides at stroke movement, is formed on the inside circumferential surface of the through-hole. These spiral clearance grooves allows spiral thickness to be formed on the circumferential wall of the rotating body.
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