| 主权项 |
1. A magnet, comprising:
a body that comprises a first, a second, a third and a fourth sections, wherein the first and the second sections are made of magnetic material for directing magnetic flux to an object to be attached, the first and the second section being separated and attached to the third section of the body, which third section is made of non-magnetic material, and a slide that comprises a permanent magnet, and a first and a second pole piece attached to opposite magnetic pole surfaces of the permanent magnet, and the slide being arranged to be movable relative to the body between a first and a second position in order to alter path of the magnetic flux generated by the permanent magnet; wherein: the first section comprises a through hole having a first and a second end and a first and a second through hole portion, both through hole portions having a diameter, and the diameter of the first through hole portion being smaller than the diameter of the second through hole portion, the first end of the through hole being closed by the fourth section of the body and the second end of the through hole being closed by the second and the third sections of the body, so that a cavity consisting of a first and a second cavity portion is formed inside the body, the slide being arranged inside the cavity so as to be movable in longitudinal direction of the through hole, the first pole piece being directed towards the first end of the through hole, and the magnet comprises means for transferring a medium into and out of the first and the second cavity portions in order to move the slide;and wherein at the first position of the slide, the permanent magnet, at least part of the first pole piece and at least part of the second pole piece are located inside the first through hole portion, and at the second position of the slide, at least part of the first pole piece is located inside the first through hole portion and the second pole piece is located outside the first through hole portion. |
