Appeal No. 2004-1072 Page 4
Application No. 09/868,150
electromagnetic coil 5. The outer yoke 6 is provided with an adequate gap 4a for
preventing the flux of the permanent magnet 4 from leaking directly to the inner
yoke 3 through a flange portion 6b of the outer yoke 6. The electromagnetic coil 5
is constructed so as to be excited by an electric current in a first direction or an
electric current in a second direction opposite to the first direction. When the
electric current in the first direction is applied to the coil 5, the disc-shaped
armature 2 is attracted by the electromagnetic force of the coil. Subsequently,
when the disc-shaped armature 2 reaches the movement terminating position
shown by solid lines in FIG. 1 and the current in the first direction is discontinued,
only the magnetic force of the permanent magnet 4 holds the disc-shaped
armature 2 at such position. On the contrary, when the electric current in the
second direction or in the direction opposite to the first direction is applied to the
electromagnetic coil 5, the electromotive force of the electromagnetic coil 5 and
the electromotive force by the permanent magnet 4 cancel each other out so as
to thereby maintain the disc-shaped armature 2 in a magnetically released state.
Uemura further teaches (column 3, lines 3-64) that:
When the electric current in the first direction is applied to the
electromagnetic coil 5, the magnetic flux generated thereby flows in the outer
yoke 6, the flat and conical portions 2a and 2b, respectively, of the disc-shaped
armature 2, the gap 7 and the inner yoke 3, whereby the magnetic attraction of
the electromagnetic coil 5 is largely generated at the tapered portion 3a of the
inner yoke 3. At this time, the magnetic flux generated by the permanent magnet
4 is added to on the magnetic flux generated by the electromagnetic coil 5 to
increase the magnetic attraction thereof. However, the magnetomotive force of
the permanent magnet 4 is far smaller than the electromotive force of the
electromagnetic coil 5.
The disc-shape armature 2 is attracted until it reaches the movement
terminating position shown by solid lines in FIG. 1 at which the flat portion 2a of
the disc-shaped armature 2 abuts against a ring-shaped projection 6a of the
outer yoke 6 and the flat portion 3b of the inner yoke 3, and the magnetic
reluctance of the magnetic path is rapidly reduced to a state of magnetic
saturation. In this state, when the first direction current is cut off, the
electromotive force of the electromagnetic coil 5 disappears and only the
electromotive force of the permanent magnet 4 remains. However, since the
reluctance of the magnetic path is, as mentioned above, a very small value, the
disc-shaped armature 2 can be held at the movement terminating position shown
by solid lines in FIG. 1 only by the magnetic force of the permanent magnet 4.
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