| 摘要 |
<p>A guide cylinder (10) having a box-shaped section and made of a non-magnetic material is disposed inside a braking drum (7) coupled to a rotary shalt (1). A large number of ferromagnetic plates (15) are connected to an outer peripheral wall (10a) of the guide cylinder (10) equidistantly in a peripheral direction. Magnets (14A) facing the ferromagnetic plates (15) are connected to a magnet support cylinder (14) which is rotatably supported inside an inner space of the guide cylinder (10). A recess (26) is formed near the center of the outer peripheral surface of each magnet (14A) in the peripheral direction. When the magnet support cylinder (14) is rotated by a half arrangement pitch of the ferromagnetic plates (15), the ferromagnetic plates (15) are changed over to braking positions at which they entirely superpose with the magnets (14A) of the magnet support cylinder (14) and to non-braking positions at which each ferromagnetic plate (15) is so positioned as to bridge between two magnets (14A) having different polarities, and a short-circuit magnetic circuit is formed between the ferromagnetic plate (15) and the magnet support cylinder (14). Since each magnet (14A) is equipped with the recess (26) at the central portion in the peripheral direction, a magnetic field leaking from the magnet (14A) to the braking drum (7) through a mutual gap between the ferromagnetic plates (15) becomes weaker, and a drag torque can be suppressed. <IMAGE></p> |
