Electromagnetic braking device

An electromagnetic braking device for braking movement of a rotation shaft of a braking target, the electromagnetic braking device comprising:

• a brake disk rotatable integrally with the rotation shaft and slidable along a central axis of the rotation shaft;
• a fixed disk disposed facing one side of, and coaxially with, the brake disk;
• an armature disposed facing another side of, and coaxial with, the brake disk, and slidable along the central axis;
• a biasing member for biasing the armature in a direction in which the brake disk is disposed;
• and
• a stator disposed with respect to the armature on a side opposite to a side where the brake disk is disposed, and capable of generating a magnetic force for attracting the armature in a direction away from the brake disk, wherein
• the stator includes a coil and a stator magnetic circuit member, which includes a first yoke, a permanent magnet, and a second yoke,
• the stator magnetic circuit member has a substantial U shape that surrounds the coil in a cross-sectional view of a surface obtained by cutting by a plane including the central axis, and is disposed so that one end surface on one end side, and another end surface on another end side, of the U shape face the armature,
• elements of the stator magnetic circuit member are arranged, from one end to another end of the U shape, in order of the first yoke, the permanent magnet, and the second yoke,
• at least one of the one end side and the another end side of the U shape stator magnetic circuit member includes a first portion having a first width and a second portion having a second width which is narrower than the first width of the first portion when viewed in the cross-sectional view of the surface obtained by cutting by the plane including the central axis of the stator,
• a portion between the first portion and the second portion of the stator magnetic circuit member is stepped on a portion closer to the armature than a center of the coil,
• the permanent magnet is in the first portion, and
• the electromagnetic braking device is configured so that
• in a rotatable state in which the rotation shaft is rotatable, a magnitude of a force attracting the armature by a magnetic circuit that uses the permanent magnet as a magnetomotive force source exceeds a magnitude of a biasing force biasing the armature by the biasing member,
• when transitioning from the rotatable state to a rotation braking state in which rotation of the rotation shaft is braked, the magnitude of the force attracting the armature by the magnetic circuit with the permanent magnet and the coil as the magnetomotive force source is smaller than the magnitude of the biasing force,
• in the rotation braking state, the magnitude of the force attracting the armature by the magnetic circuit that uses the permanent magnet as the magnetomotive force source is smaller than the magnitude of the biasing force, and
• when transitioning from the rotation braking state to the rotatable state, the magnitude of the force attracting the armature by the magnetic circuit that uses the permanent magnet and the coil as the magnetomotive force source exceeds the magnitude of the biasing force.