Note: Descriptions are shown in the official language in which they were submitted.
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PERPENDICULAR MODE r~NElIC TR~SDUCER HEAD
B.~CKGROUN~ OF THE INVENTION
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Field of the Invention
Ihe present invention relates generally to a
magnetic transducer head and is directed more particularly
to a magnetic transducer head for use with a so-called
perpendicular or vertical magnetization mode recording.
Description of the Prior Art
To record a high frequency (short wavelength)
signal on a magnetic recording tape, it is known that a
so-called perpendicular or vertical magnetization mode
recording is more advantageous than a so-called longitudinal
magnetization mode recording, in which the former utilizes
a magnetization along a direction perpendicular tc a major
plane o~ the magne~ic recording tape, while the latter utilizes
a magnetization along a major plane of a magnetic tape. This
is because a self-demagnetizing field in a magnetic layer of
the magnetic recording tape becomes smaller in the perpendicular
magnetization mode recording when a wavelength of a recording
signal becomes shorter, while the self-demagneti2ing field
becomes larger in the longitudinal magnetization mode recording.
For the magnetic transducer head utilized for this
vertical magnetization mode recording, various ones have been
proposed. T~ perform its recording ~or magnetizing the
magnetic recording layer of the magnetic tape) ideally or
perfectly in the vertical magnetization mode recording, a main
component of the magnetic field originated from the magnetic
transd~cer head has to be as vertical as possible to a
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magnetic recording medium such as a ~u~.
One example of the magnetic transducer head is
shown as h in Fig. 1 in which a main magnetic pole 2 formed
of a thin film of magnetic material having high permeability
such as permalloy and an auxiliary magnetic pole 3 are
provided across a magnetic recording medium 1 so as to
oppose to each ~ther. A coil 4 is wound around this auxili-
ary magnetic pole 3.
In this case, however, the auxiliary magnetic pole
3 has to be placed at the opp~site side from the main magnetic
pole 2 with respect to the magnetic recording medium 1 and
adjacent to the magnetic recording medium, which, as a result,
causes difficulties in assembling and handling such as loading
of the magnetic recording medium 1 between the main magnetic
pole 2 and the auxiliary magnetic pole 3.
To avoid these drawbacks, it is proposed to use a
magnetic recording medium 1, as shown in Fig. 2, which is
formed of a non-magnetic base 5 and a layer of high permea-
bility material 6 formed on the non-magnetic base 5 and a
magnetic recording layer 7 formed on the layer of high
permeability material 6. In this case, when a single pole
type magnetic head h formed of a thin film of soft magnetic
material is provided to oppose the magnetic recording layer
7 and a signal is applied to the winding 4 wound around the
pole 2 so as to record the signal, satisfactory recording
sensitivity and excellent recording characteristic can be
achieved.
The main magnetic pole 2 of the magnetic transducer
head h of this kind is formed of a thin film of ferromagnetic
mate~ia~ such as per~loy, Fe-A~-Si system alloy, a so-called
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Sendust alloy of about 0.5 to 3 ~m thick. The coil 4 to
magnetically excite the thin film main magnetic pole 2,
namely, the recording winding can be formed of a thin
film coil which is bonded through an insulating film such
as SiO2, AQ2O3, Si3N4 or the like around the vicinity of
the top of the thin film magnetic pole 2. In this case, to
excite the main magnetic pole 2 through the use of the coil
4 efficiently, it is desirable that the front end of the
coil 4 is placed so as to coincide with the top of the main
magnetic pole 2 which faces the sliding surface of the
magnetic recording medium 1. But, when the coil 4 is
located at the front end thereof facing the sliding surface
of the magnetic recording medium 1, the coil 4 will be short
-circuited by the magnetic recording medium 1 when the
magnetic recording layer 7 has conductivity. Even if the
surface of the magnetic recording layer is formed of an
insulating material, there is a substantial chance of short
-circuit of the coil 4, since the coil is usually formed of
a relatively soft material such as copper, aluminum, silver,
gold and so on, then the coil is apt to be extended to bridge
between turns of the coil with each other by rubbing of the
magnetic recording medium. Also, when the coil 4 closely
faces the magnetic recording medium 1 as described above, a
magnetic field produced from the coil 4 is directly given
to the magnetic recording medium 1 in addition to the recording
magnetic field applied through the main magnetic pole 2. The
range or area of the magnetic field macle by the coil 4 is so
widely spread that the recording magnetic field, which will
be applied to the magnetic recording medium 1, is forced to
be spread thus the high density recording being obstructed.
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Such drawbacks can be avoided by p~oviding the
exciting coil4remote from the end of the main pole 2 which
faces the magnetic recording medium, that is, a spacing is
provided between the top of the exciting coil and the end
of the main magnetic pole. By providing the spacing, direct
contact of the exciting coil to the magnetic recording
medium can be avoided. In addition, the magnetic field qenerated
by the exciting coil at the magnetic recording medium
decreases abruptly as the spacing increases.
On the contrary, if the exciting coil 4 is provided
at a spacing from the magnetic recording medium, although
the portion of the main magnetic pole 2 around which the
winding 4 is provided is strongly magnetized, the magnetization
level at the end of the main magnetic pole 2 protruded from
the portion around which the winding of the coil 4 is provided
is rapidly decreased. This is mainly because the exciting
coil 4 is wound nearly tight around the main magnetic pole 2,
the diameter of the coil 4 wound therearound is relatively
selected to be small, then the magnetic field originated by
the coil is decreased suddenly at the portion remote from the
end of the coil, and the main magnetic pole 2 is formed of
the thin film having magnetic resistance and so on.
~ig. 3 shows the relationship between a position
in the main magnetic pole 2, and the magnetic flux density By
along an axis of the main magnetic pole, in which the abscissa
represents the position along a direction y,that is,the axis
of the main magnetic pole 2, and the ordinate represents the
magnetic flux density By along the direction y. The solid
line ~ indicates a distribution of By of the magnetic trans-
3~ ducer head in which the exciting coil is so wound nearly tight
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on the main magnetic pole that the main magnetic pole is
protruded from the top of the exciting coil for 50~. The
broken line 9 indicates the magnetic flux density By when
the main magnetic pole is excited in a parallel magnetic
field instead of the exciting coil 4 wound on the pole.
As apparent from the curve 8, the magnetization
at the top of the main magnetic pole 2 protruded from the
coil 4 is decreased abruptly. Whereas, as shown by the curve
9 in Fig. 3, the main magnetic pole 2 is excited fully up to
its end by the parallel magnetic field. Accordingly, it is
desired that the main magnetic pole 2 is excited based upon
the parallel magnetic field. To achieve such parallel
magnetic field, the winding diameter of the coil 4 must be
enlarged. But, if the winding diameter of the coil 4 is
enlarged as described above, the recording efficiency is
deteriorated and large recording current is required.
To improve such disadvantage, as shown in Fig. 4,
it is considered that an auxiliary core 10 formed of high
permeability material may be placed so as to be attached to
one surface or both surfaces of the thin film main magnetic
pole 2 so as to protrude the main magnetic pole, in other
words, the auxiliary cores are provided remote from the
sliding surface with the magnetic recording medium 1. ~n
this case, it is apparent tha-t the recording efficiency will
be enhanced more when the exciting coil 4 is wound around
the vicinity of the top of the auxiliary core 10 as near as
possible to the top.
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OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present
invention to provide a magnetic transducer head for use
with vertical magnetization mode recording.
lt is another object of the present invention to
provide a magnetic transducer head for use with vertical
magnetization mode recording of high recording efficiency.
It is a further object of the present invention
to provide a magnetic transducer head structure to efficiently
magnetize a single pole magnetic core.
According to one aspect of the present invention,
there is provided a magnetic transducer head having a main
magnetic pole formed of a thin film magnetic material having
a major surface and facing to a magnetic recording medium at
one end t~ereof, an auxiliary magnetic core provided adjacent
to the major surface of the thin film magnetic material
having a thickness a along a direction perpendicular to the
major surface, an end of the auxiliary magnetic core being
spaced from the end of the main magnetic pole with a distance
Q, a coil wound around the main magnetic pole and the auxiliary
magnetic core and at the end of the auxiliary magnetic core,
the coil having a thickness b, wherein the a, b and Q are
selected for satisfying that a value (a + b2)/Q is not less
than 0.5~ ~ut not more than 2.4.
The other objects, features and advantages of the
present invention will become apparent from the following
description taken in conjunction with the accompanying drawings
thro~h which t~e like references designate the same elements
and parts.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figs. 1, 2 and 4 are respectively diagrams each
schematically showing a prior art magnetic transducer head
for use with vertical magnetization mode recording;
Fig. 3 shows a relationship between a magnetic
flux density in a main magnetic pole and a position in the
pole;
Figs. 5, 6 and 10 are respectively diagrams each
schematically showing examples of a magnetic transducer head
according to the present invention;
Figs. 7, 8 and 9 are graphs to explain the present
invention; and
Figs. 11 through 17 are schematic illustrations
showing manufacturing steps of the magnetic transducer head
of the present invention.
DESCRIPTION OF THE PREFERRED RMBODIMENTS
The inventors clarified that in the magnetic -trans-
ducer head having such auxiliary core, a magnitude of magnetic
field for the recording a-t the -top portion of the main
magnetic pole depended upon a magnitude of the exci-ting
magnetic field at -the top of the main maynetic pole, in other
words, a magnitude of a magne-tic field at the top of the main
magnetic pole when the main magnetic pole was removed but
instead, the auxiliary core around which the coil is wound
exists alone.
Therefore, to record the signal on the magnetic
recording medium most efficiently, it should be arranged to
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generate the strongest magnetic field at the top of the
main magnetic pole, when a predetermined current is applied
to the exciting coil. Generally, as the diameter of the
coil wound becomes large, the attenuation of the magnetic
field at the position remote from the coil on the central
axis of the coil becomes small. On the other hand, the
magnetic field on the central axis of the coil becomes
smaller when the winding diameter of the coil becomes larger.
Accordingly, it is necessary to consider the arrangement of
the coil, the position of the coil wound on -the core, the
diameter of the coil and so on properly, to maximize the
exciting magnetic field.
On the basis of the above-mentioned consideration
and clarification and further with various experiments and
discussious, the inventors propose a magnetic transducer head
for use in vertical magnetization mode recording with high
recording efficiency.
Now, embodiments of the magnetic transducer head
according to the present invention will be described with
reference to Fig. 5 and the following drawings in which like
references corresponding to those of Figs. 1,2 and 4 designate
the same elements and parts.
In the figures, reference letter H denotes an
overall arrangement of a magnetic transducer head according
to the present invention.
In the embodiment of the present invention, as
shown in Fig. 5 or 6 by way of example, there is provided
the main magnetic pole 2 formed of a thin film of magnetic
material made of, for example, permalloy, Sendust alloy and
so on of about 0.5 to 3 ~m thick, a thickness of which is
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represented by letter t in the figure. On both surfaces or
one surface of the main magnetic pole 2 is magnetically
bonded tight an auxiliary core or cores 10 formed of high
permeability material such as Mn- Zn ferrite, Ni- Zn ferrite
or the like. This auxiliary core 10 is placed in such a
manner that the top thereof may be located at the position
farther back from the top of the main magnetic pole 2 facing
the slidiny surface of the magnetic recording medium (not
shown) along which the main magnetic pole 2 slides by a
distance Q.
The coil 4 is placed on this auxiliary magnetic
core 10 in such a manner as to wrap both the auxiliary
magnetic core 10 and the main magnetic pole 2 sandwiched
therebetween. ~ore precisely, the coil 4 is placed on the
auxiliary magnetic core 10 as near as possible to the end of
the auxiliary core, so that the top surface thereof may be
coincident with the top surface of the auxiliary magnetic
core 10, which is then wound therearound by, for example, a
winding of a conductive wire.
Now, let us take a thickness of the auxiliary core
as _, that is, a distance from one surface of the main
magnetic pole to which a surface of the auxiliary magnetic
pole abut to the inner surface of the coil, and a winding
thickness of the coil 4 as b. In this invention the above
defined dimensions, Q, a and _ are selected to satisfy a
relation that (a + b2 )/Q is not more than 2.4 but not less
than 0.55 under the practical dimension of Q ranging from
10 to 200 ~Im. The reason why the distance Q is selected as
described above is based upGn the results shown in Figs. 7
and 8 in which the magnetic field in the axial direction
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component at the top of the main magnetic pole 2 is examined
when the value of (a + 2 )/Q is changed in the magnetic
transducer head, a construction o~ which is shown in Figs.
5 and 6. In Figs. 7 and 8, the magnetic field is expressed
as a relative value when the maximum value thereof is taken
as 100% . In Fig. 7, curves 11, 12 and 13 each describe
the case where the positions of the tops of the paired auxi-
liary magnetic cores 10, which are located symmetrically to
grip the main magnetic pole 2 therebetween as shown in Fig. 5,
are selected such that the distance Q between the tops of the
main magnetic pole 2 and the auxiliary magnetic core 10 may
change as 30 ~m, 50 ~m and 100 ~m, respectively. Also, curves
14, 15 and 16 of E`ig. 8 describe the case in which the
position of the top of the auxiliary magnetic core 10 located
at one side of the main magnetic pole 2 as shown in Fig. 6 is
selected such that the distance Q between the tops of the
main magnetic pole 2 and the auxiliary core 10 may change as
30 ~m, 50 ~m and 100 ~m, respectively. In this case, Fig. 8
shows a distribution of the magnetic field in which the
spacing _ where no auxiliary magnetic core is provided is
selected equal to the distance a.
Turning back to Fig. 7, it is understood that the
magnetic field becomes strongest when (a + b2 )/Q is 1.3, the
magnetic field decreases by about ~2 % (+1 %)of the maximum
value when (a+ b2 )/Q,is in a range from 0.8 to 2.0 and it
decreases by -4 ~ (~2 %) of -the maximum value when (a + b )/Q
is in a range from 0.65 to 2.4. Also, with reference to Fig.
8, the magnetic field becomes strongest when (a+ b2 )/Q is
1.22, it decreases by about - 2 % (+1 %) of the maximum value
when (a + 2 )/Q is in a range from 0.7 to 2.0 and it decreases
7~
by -4 ~ ( ~ 2%) of the maximum value when ta ~ b2 )/~ is in
a range from 0.55 to 2.42. Comparing the representations
in Fig. 7 with those of Fig. 8, an tendency of how the top
of the main magnetic pole 2 influences the magnetic field
is nearly equal in both cases where the auxiliary magnetic
core 10 is provided at both surfaces of the main magnetic
pole 2 and where it is provided on the one surface thereof
as shown in Figs. 5 and 6. From Figs. 7 and 8, it is
understood that the magnetic field at the top of the main
1~ magnet~c pole 2 is effectively enhanced if (a+ b2 )/~ is in
the range from 0.55 to 2.4, which is why the range of
(a+ b2 )/Q is selected to be from 0.55 to 2.4.
In the case, as shown in Fig. 6, when the auxiliary
core 10 is placed at one side surface of the main magnetic
15 . pole 2, the similar magnetic field at the top of the main
magnetic pole 2 is measured while the distance d from the
other side surface of the main magnetic pole 2, which the
auxiliary core 10 is not attached to, to the inner surface of
the coil 4 opposing thereto is selectively changed with the
results shown in Fig. 9. In this case, Q is selected as 50 ~m,
a is selected as 50 ~m and _ is selected as 20 ~m. In
addition, the length c of the coil 4 is selected as 50 ~m.
As it will be clear from Fig. 9, the magnetic field
at the top of the main magnetic pole 2 becomes larger if d > b
is established. Thus, when the auxiliary magnetic core 10 is
placed on one side of the main magnetic pole 2, it is desired
to select the relationship between the lengths d and _ so as
to satisfy d ~ b.
The depth oi ~he coil 4, namely, the size represented
3ti by the letter c in Figs. 5 and ~ does not influence the recordin~
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efficiency so much. But, if the depth c is too much large
as compared with the thickness _, this is not preferable
because it causes the recording efficiency to be lowered.
Therefore, the value of c/b must be selected to be 5 or
below, particularly, for example, less than about 2 to 3.
While in the auxiliary core 10, the distance a is
selected at its top side where the coil 4 is wound such that
(a + b2 )/Q becomes in a range from 0.55 to 2.4, the thickness
at its rear end side later than the por-tion around which the
coil 4 is wound can be increased in consideration of its
mechanical s-trength.
Fig. 10 illustrates an example of such case in which
each of reinforcing members 17 formed of non magnetic material
such as Zn ferrite is further bonded to the top of the auxi-
liary magnetic core 10 so as to extend to and grip the top of
the main magnetic pole 2 to thereby enable the top of the main
magnetic pole 2 to be reinforced.
IE the auxiliary core 10 is formed on one side of
the main magnetic pole 2, the reinforcing member 17 provided
on the side where the auxiliary magnetic core 10 is not
provided is extended backward or downward so as -to uni-te it
with the main magnetic pole 2, whereby the coil 4 can be wound
around both this reinforcing member 17 extended and the auxi-
liary magnetic core 10 on the other side of the main magnetic
pole 2.
sy way of example, the sizes of the respective parts
of the magnetic transducer head H whose structure is shown in
Fig. 10 are enumerated below. _ is 100 ~Im, a is 150 ~m, b is_
50 ~m and _ is 1.5 mm. In addition, the thickness of the
rear par-t of the auxiliary magnetic core 10, the thickness of
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which is large and shown by e in Fig. 10 can be selected
as 1 mm and the length thereof, which is designated by f,
can be selected as 4 mm.
In this case, the magnetic recording medium 1
whose layer of high permeability material 6 is formed of
permalloy layer of 0.5 ~m thick and whose magnetic recording
layer 7 is formed of Co - Cr alloy layer of 0.5 ~m thick may
be utiliæed.
An example of a method for producing a magnetic
transducer head according to the present invention will next
be described in detail with reference to Fig. 11 and the
following drawings.
First, as shown in Fig. 11, a joint body 30 is
prepared by bonding a rectangular shape block of magnetic
material 20 and a plate shape block of non-magnetic material
270 The block of magnetic material 20 may be formed of Mn - Zn
ferrite or Ni - Zn ferrite, and the block of non-magnetic
material may be formed of glass, ceramics, non-magnetic Zn
ferrite and so on. However, it is desired that both of the
magnetic and the non-magnetic materials have similar thermal
expansion coefficient with each other, thus it is preferred
that the magnetic and non-magnetic blocks 20, 27 are formed
of magnetic and non-magne-tic ferrite, respectively. The
magnetic material block 20 and the non-magnetic material
block 27 can be bonded together through the use of melt
bonding of glass, water glass, organic adhesive, such as
epoxy resin, or inorganic adhesive.
Next, the joint body 30 made of the magnetic
material block 20 and the non-magnetic material block 27 is
cut out along surfaces shown by two-dots chain lines ml, m2,
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m3, in Fig. 11 to provide a plurali-ty of plate members
31, each having a predetermined thickness as illustrated in
Fig. 12.
In Fig. 12, a major surface 31a which stretches
over the magnetic material memher 20 and -the non magne-tic
member 27 composing the plate member 31 is polished to have
a mirror finish. An insulating layer 32 made of such as SiO2,
Si3N4, AQ2O3 or the like is formed on this major surface
31a on which a thin film magne-tic material layer 22 made of,
for example, permalloy, Sendust alloy and so on of 0.5 to
3 ~m thick is formed by vacuum evapolation, sputtering or
the lik~.
Next, as illustrated in Fig. 13, the thin film
magnetic material 22 is selectively removed by using a
photolithography technique to leave band-shaped portions 22',
22", , which are placed in parallel to each other with a
predetermined width and spacing. The portions between the
band shape thin film 22, 22" are filled in with non
-magnetic material 34 to form a flush surface with the surface
of thin film bands of magnetic material. In addition, materials
such as SiO2, Si3N4 and AQ2O3 or -the like may be formed
thereon.
On the other hand, as shown in Fig. 14, other plate
member 31', which is cut away Erom the same joint body 30 as
described previously in Fig. 11 whic}l is formed of the
maynetic material member 20 and the non-magnetic member 27, is
prepared. A major surface 31a' thereof is likewise polished
to make a mirror finish and as shown in Fig. 14, this major
surface 31a' is bonded to the surface side of the plate
member 31 on which the thin film maynetic material 22 and the
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non-magnetic layer 34 are formed as shown in Fig. 13. In
this case, a recess or notch 35 is formed in advance on the
major surface 31a' of the plate member 31' by, for example,
etching and an adhesive 36 is filled or charged into this
S notch 35, both the plate members 31 and 31' can be bonded
with one another strongly.
If necessary, as illustrated in Fig. 15, the
external surfaces of both the plate members 31 and 31' are
cut away at the side of the non magnetic member 27, the
respective thicknesses of which are selected to be smaller
than those of the remaining parts. As shown by two-dots
chain lines nl, n2, , in Fig. 15, the bonded plates 31
and 31' are cut away to include the respective band-shaped
thin film of magnetic materials 22', 22", , the top
surfaces each are ground or polished so as to construct a
sliding surface S with the magnetic recording medium (not
shown) as illustrated in Fig. 16.
Thus, the magnetic transducer head H according to
the present invention can be manufactured in which the thin
film main magnetic pole 2 made of thin film magnetic material
22 is provided to abut the sliding surface S for the magnetic
recording medium, the reinforcing members 17 formed of the
non magnetic member 27 are placed on both sides of the main
magnetic pole 2 at the vicil~ity of the top thereof and the
auxiliary cores 10 formed of the magnetic recording member
20 are placed behind the reinforcing member 17.
In this case, when the non-ma~netic material 3~ arc
located adjacent to -the main magnetic pole 2, a spacing or
gap between both of the reinforcing members 17 on both sides
of the main magne-tic pole 2 abutting against the sliding
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surface s ~or the magnetic recording medium is almost filled
by the non-magnetic material 34 so that an amount of adhesive
which will be filled into the aforesaicd gap is made less, in
other words, the area abutting the sliding surface S for the
magnetic recording medium in which the adhesive is used is
reduced to be less than that of the case where the non-magnetic
material 34 is not provided. Thus, an occurrence of head
clogging caused by the fact that much adhesive abuts against
the sliding surface S can be reduced.
This magnetic transducer head lI is wound by -the
coil 4 around its thin portion in the position at which it is
moved farther back than the sliding surface S. In this case,
even in the magnetic transducer head H thus constructed, a
relationship for dimension and arrangement between the re-
spective parts thereof is selected as described previously.
Also, this magnetic transducer head H is attached
to, as, for example, shown in Fig. 17, a head holder 43 through
which each of apertures 41 is bored to attach the same on a
rotary drum of a VTR (video tape recorder) and on which each
of conductive terminal patterns 42 is bonded. Each terminal
end of the coil 4 a-t the magnetic transducer head H is con-
nected electrically to each conductive terminal pattern 42
through soldering, by way of example.
~s described above, according -to the magnetic
transducer head of the present invention, although the coil 4
is placed farther bac~ than the sliding surface S for the
magnetic recording medium, the recording efficiency is high.
~lso, it is obvious that the same effect can be
achieved if the magnetic transducer head according to the
present invention is also applied for a magnetic transducer
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head of a multi-elements type in which a plurality oE main
magnetic poles 2 are placed.
The above description is given on the preferred
embodiments of the invention, but it will be apparent that
many modifications and variations could be effected by one
skilled in the art without departing from the spirits or
scope of the novel concepts of the invention, so that the
scope of the invention should be determined by the appended
claims only.
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