Eddy current deceleration device
The disclosed is a deceleration device including a cylindrical brake member fixed to a rotary shaft, a plurality of permanent magnets arrayed in a circumferential direction of a circle around the rotary shaft, a cylindrical magnet holder holding the permanent magnets, and a switching mechanism that switches between a braking state and a non-braking state. The plurality of permanent magnets include primary magnets and secondary magnets that are arrayed alternatively in the circumferential direction. When viewed on a surface facing the brake member, north poles of the primary magnets are circumferentially adjacent to and in contact with north poles of the secondary magnets, and south poles of the primary magnets are circumferentially adjacent to and in contact with south poles of the secondary magnets. The magnetic holder is ferromagnetic.
1. An eddy current deceleration device comprising:
a cylindrical brake member fixed to a rotary shaft;
a plurality of permanent magnets arrayed in a circumferential direction of a circle around the rotary shaft to face an outer peripheral surface or an inner peripheral surface of the brake member with a gap;
a cylindrical magnet holder holding the permanent magnets; and
a switching mechanism that switches between a braking state and a non-braking state, wherein:
the plurality of permanent magnets are located between the brake member and the magnet holder;
the plurality of permanent magnets include primary magnets and secondary magnets that are arrayed alternatively in the circumferential direction;
the primary magnets are laid such that magnetic poles of each of the primary magnets are arranged in a radial direction from an axis of the rotary shaft and such that two circumferentially adjacent ones of the primary magnets have opposite magnetic pole arrangements;
the secondary magnets are laid such that magnetic poles of each of the secondary magnets are arranged in the circumferential direction;
when viewed on a surface facing the brake member, north poles of the primary magnets are circumferentially adjacent to north poles of the secondary magnets, and south poles of the primary magnets are circumferentially adjacent to south poles of the secondary magnets; and
the magnetic holder is ferromagnetic.
2. The eddy current deceleration device according to claim 1 , wherein
a non-magnetic member is provided between each of the secondary magnets and the magnet holder.
3. The eddy current deceleration device according to claim 2 , wherein:
a space is made between each of the secondary magnets and the magnet holder; and
the non-magnetic member is atmospheric air in the space.
4. The eddy current deceleration device according to claim 3 , wherein
the non-magnetic member has a rounded-off corner on a side farther from the brake member.
5. The eddy current deceleration device according to claim 4 , wherein
each of the secondary magnets has a dimension in the circumferential direction that decreases with decreasing distance from the brake member.
6. The eddy current deceleration device according to claim 3 , wherein
each of the secondary magnets has a dimension in the circumferential direction that decreases with decreasing distance from the brake member.
7. The eddy current deceleration device according to claim 2 , wherein
the non-magnetic member has a rounded-off corner on a side farther from the brake member.
8. The eddy current deceleration device according to claim 7 , wherein
each of the secondary magnets has a dimension in the circumferential direction that decreases with decreasing distance from the brake member.
9. The eddy current deceleration device according to claim 2 , wherein
each of the secondary magnets has a dimension in the circumferential direction that decreases with decreasing distance from the brake member.
10. The eddy current deceleration device according to claim 1 , wherein
each of the secondary magnets has a dimension in the circumferential direction that decreases with decreasing distance from the brake member.
11. The eddy current deceleration device according to claim 1 , wherein:
the array of primary and secondary magnets is divided into a first row and a second row, each of the rows extending in the circumferential direction, and the magnet holder is divided into a first section and a second section holding the first row of primary and secondary magnets and the second row of primary and secondary magnets, respectively;
in the gap between the brake member and the primary magnets, a plurality of plate-like ferromagnetic switches are arrayed in the circumferential direction to be positioned at same placement angles as placement angles of the primary magnets;
either the first section or the second section of the magnet holder is rotatable around the rotary shaft; and
the switching between the braking state and the non-braking state is carried out by a rotation of the first section of the magnet holder or the second section of the magnet holder.
12. The eddy current deceleration device according to claim 11 , wherein:
in the non-braking state, the permanent magnets are positioned such that two axially adjacent ones of the primary magnets have opposite magnetic pole arrangements and such that two axially adjacent ones of the secondary magnets have opposite magnetic pole arrangements; and
in the braking state, the permanent magnets are positioned such that two axially adjacent ones of the primary magnets have a same magnetic pole arrangement and such that two axially adjacent ones of the secondary magnets have a same magnetic pole arrangement.
13. The eddy current deceleration device according to claim 11 , wherein
a dimension in the circumferential direction of each of the plate-like switches is equal to a dimension in the circumferential direction of each of the primary magnets.
14. The eddy current deceleration device according to claim 1 , wherein:
the array of primary and secondary magnets is divided into a first row, a second row and a third row, each of the rows extending in the circumferential direction, and the magnet holder is divided into a first section, a second section and a third section holding the first row of primary and secondary magnets, the second row of primary and secondary magnets, and the third row of primary and secondary magnets, respectively;
in the gap between the brake member and the primary magnets, a plurality of plate-like ferromagnetic switches are arrayed in the circumferential direction to be positioned at same placement angles as placement angles of the primary magnets;
either the first and the third sections or the second section of the magnet holder is rotatable around the rotary shaft; and
the switching between the braking state and the non-braking state is carried out by a rotation of the first and the third sections of the magnet holder or the second section of the magnet holder.
15. The eddy current deceleration device according to claim 1 , wherein
the magnet holder is movable in the axial direction along the axis of the rotary shaft; and
the switching between the braking state and the non-braking state is carried out by a movement of the magnet holder.
16. The eddy current deceleration device according to claim 1 , wherein
a dimension in the circumferential direction of each of the primary magnets is 1.5 to 9 times a dimension in the circumferential direction of each of the secondary magnets.