| 摘要 |
PURPOSE:To maintain the amount of magnetic flux affecting on the focusing characteristics at a constant level, by forming a gap containing a bimetal at a part of a magnetic path which embraces a permanent magnet and changing the gap in accordance with temperature. CONSTITUTION:Each face of an annular permanent magnet 1 in a focusing magnet device is provided with a magnetic path member 10 consisting of a bimetal, which is formed by a magnetic metal with a low thermal expansion coefficient and containing iron and nickel as main components and a metal bonded to the magnetic metal and having a high thermal expansion coefficient, in such a manner that the magnetic metal is brought into contact with the permanent magnet 1. The upper peripheral edge of the magnetic path member 10 terminates in an outwardly flared portion 14 so as to make a gap between the magnet 1 and magnetic path member 10. The outwardly flared portion 14 defines a number of a notches 15. The magnetic resistance of the magnetic path can be changed by using temperature deformations of the bimetal. It is therefore possible to maintain the amount of the magnetic flux affecting on the focusing characteristics at a constant level, irrespective of changes in temperature. |
