Magnetic azimuth detector

A magnetic sensor including an annular iron core, an annular hollow bobbin for a primary winding which incorporates therein the annular iron core, the bobbin having a plurality of protruded portions which are arranged along a circumference of the annular bobbin with an equal distance, each of the protruded portions being extended in a direction parallel to a center axis of the annular iron core, the primary winding being wound on the annular bobbin at respective portions between adjacent protruded portions with an equal number of turns, a bobbin for a secondary winding having a positioning means for the primary winding in association with the protruded portions of the bobbin for the primary winding when the bobbins for the primary and secondary windings are assembled, the secondary winding being wound on the bobbin to form more than two pairs of winding groups.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a magnetic sensor. 
2. Description of the Prior Art 
Generally, the magnetic sensor to which the present invention is directed 
includes an exciting primary winding wound in one direction around an 
annular iron core and a secondary winding located, relative to the exited 
magnetic flux generated by the primary winding, such that the interlinking 
magnetic flux becomes substantially zero. This kind of magnetic sensor 
serves as a magnetic azimuth director in a system disclosed for example, 
in U.S. Pat. No. 3,678,593, issued July 25, 1972 to Baker et al. If a 
magnetic field is applied in a certain diametric direction of the iron 
core, across the secondary winding, a secondary higher harmonic voltage 
(hereinafter referred to as a secondary voltage) is generated which 
corresponds to the magnitude and the direction of the input axis direction 
component of the secondary winding of the magnetic flux within the iron 
core generated by the magnetic field. If a plurality of secondary windings 
are simultaneously located with different input axes, it is possible to 
detect the direction of the applied magnetic field, that is the magnetic 
azimuth, from the secondary voltage appearing on each of the secondary 
windings. 
However, since the magnetic sensor of this kind is overexcited, the 
non-uniform winding of the primary winding causes a non-uniform excited 
magnetic flux within the annular iron core. As a result, the intensity of 
the excited magnetic field, corresponding to the secondary windings, 
becomes different and this causes a magnetic azimuth error to occur. 
Also, it is natural that the angular error between the input axes of the 
plurality of secondary windings becomes the magnetic azimuth error. 
In the prior art magnetic sensor of this kind, the primary winding is wound 
around the annular iron core over the whole periphery thereof as uniformly 
as possible. The resulting primary winding is inserted into the bobbin of 
the secondary winding so that the inner diameter or other diameter of the 
primary winding is taken as the guide member and the secondary winding is 
wound around the resulting winding. However, according to this prior art 
method, it is difficult to wind the primary winding uniformly around the 
annular iron core over its whole periphery. Further, a significant defect 
occurs in that the winding around the annular iron core can not provide an 
accurate outer dimension which can be used as a reference to guide the 
primary winding into the bobbin of the secondary winding. 
Further, in the magnetic sensor of this kind, if the winding distribution 
in the several secondary windings is not uniform, the directions of the 
input axes of the secondary windings are displaced from the desired 
direction with the result that a magnetic azimuth error occurs. 
In order to obtain a high magnetic azimuth accuracy, it has been proposed 
that an area on an annular iron core around which a secondary winding is 
wound be precisely determined and that the secondary winding be wound as 
uniformly as possible within this area and then a magnetic sensor having a 
desired accuracy is selected by inspection and test. However, in this 
prior art method, there is a serious defect that when a magnetic sensor is 
found which can not provide the desired accuracy, and if the cause thereof 
lies in the manner in which the winding is wound, the winding is removed 
and must be wound again around the annular iron core with great care. 
OBJECTS AND SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide an improved 
magnetic sensor which can remove the defects encountered with the prior 
art magnetic sensors. 
Another object of this invention is to provide an improved magnetic sensor 
which can position both a primary winding and a secondary winding with 
high accuracy. 
Further object of this invention is to provide an improved magnetic sensor 
which can correct the direction of the input axis of the secondary winding 
and which can provided a high magnetic azimuth accuracy. 
Still further object of this invention is to provide an improved magnetic 
sensor which can afford a uniform scale factor of a magnetic sensor 
without the scattering. 
Yet a further object of this invention is to provide an improved magnetic 
sensor which can reduce the number of steps in the manufacturing process 
and which can also reduce the manufacturing cost. 
According to one aspect of the present invention, there is provided a 
magnetic sensor comprising an annular iron core and an annular hollow 
bobbin surrounding the core. The bobbin has a plurality of protrusions 
uniformly spaced about the circumference of the bobbin and extending in a 
direction parallel to the central axis of the core and define a plurality 
of circumferential sectors. A primary winding is wound on the annular 
bobbin having equal number of turns and uniform direction in each of the 
sectors. A bobbin shell surrounds the primary winding and has means for 
receiving the primary winding and the protrusions. A secondary winding is 
wound on the bobbin shell. The secondary winding comprises at least two 
pair of winding, each winding having an equal number of turns and each 
pair being uniformly spaced about the bobbin shell. Mounted on the bobbin 
shell between selected adjacent secondary windings, are means for 
adjusting the azimuth error related to the secondary winding. 
These and other objects, features and advantages of the present invention 
will become apparent from the following detailed description of the 
preferred embodiments taken in conjunction with the accompanying drawings, 
throughout which like reference numerals designate like elements and parts 
.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the attached drawings, a magnetic sensor according to the 
present invention will hereinafter be described in detail. 
FIG. 1 is an exploded perspective view of one embodiment of the magnetic 
sensor according to the present invention and FIG. 2 is a cross sectional 
view thereof taken along a plane perpendicular to a central axis O--O in 
the assembled state of the magnetic sensor. In FIG. 1 and 2, reference 
numeral 1 generally designates an annular primary winding assembly. 
Reference numerals 21 and 21' designate secondary winding bobbins of 
cylindrical shell shape which are used to secure the primary winding 
assembly 1 therebetween. Both of the secondary winding bobbins 21 and 21' 
are symmetrical relative to the primary winding assembly member 1. 
The primary winding assembly 1 comprises an annular iron core 110 secured 
within an annular primary winding bobbin 121 having a C-shaped cross 
section. This primary winding bobbin 121 is provided with a plurality of 
protrusions, for example, six members 141 to 146 each having the same 
dimension and the same shape. These protrusions 141 to 146 are 
respectively located on the circumference of the primary winding bobbin 
121 with an equal spacing such that they are arranged in parallel to the 
central axis O--O and that they extend to the right-hand side direction in 
FIG. 1. A bobbin lid 122, for the primary winding bobbin 121, is formed as 
an annular shape similar to that of the bobbin 121 being also provided 
with six protruding portions 141' to 146' each having the same dimension 
and the same shape as protrusions 141-146. These protruding portions 141' 
to 146' are located, spaced uniformly about the circumference of the 
bobbin lid 122, in such a manner that they are arranged in parallel to the 
central axis O--O and that they extend in the left-hand side direction of 
FIG. 1 
The bobbin lid 122 is attached to the primary winding bobbin 121 in such a 
fashion that its extending portions 141' to 146' and the extending 
portions 141 to 146 of the primary winding bobbin 121 coincide with one 
another as shown in FIG. 1. Primary windings 131 to 136 are wound around 
the bobbin 121 and the bobbin lid 122 as a unitary body between the pairs 
of protruding portions with the equal number of turns and in the same 
direction. Thus, the primary winding assembly member 1 is formed. 
Both of the secondary winding bobbins 21 and 21' are respectively provided 
with concentrically annular grooves 210 at their bottoms. The diameters of 
the annular groove 210 and its annular side walls 211 and 212 are selected 
such that when the primary winding assembly 1 is secured between both of 
the secondary winding bobbins 21 and 21', the arc section of the 
protruding portions 141 to 146 and 141' to 146' of the primary winding 
assembly 1 are each placed in contact with at least one of the annular 
side walls 211 and 212 of the annular grooves 210 of both the bobbins 21 
and 21'. It is not particularly necessary to provide a side wall which 
does not contact with the above mentioned arc section. Further, a depth 
h.sub.1 of each annular groove has a depth h.sub.1 ; each of the 
protruding portions 141 to 146 of the primary winding bobbin 121 has a 
length l; parallel to the central axis O--O, and, each of the protruding 
portions 141' to 146' of the bobbin lid 122 has a protruding length 
l.sub.2 parallel to the central axis O--O.sub.0 l.sub.1 =l.sub.2, are 
selected to be larger than the thickness of the primary winding, taking 
the diameter of the conductive lines of the primary winding 1 and the 
number of layers of the winding into consideration. Further, the depth 
h.sub.2 from an opening end face 220 of each of the secondary winding 
bobbins 21 to 21' to the bottom of each annular groove 210 is selected to 
be slightly smaller than one half of a length between both end faces of 
each pair of protruding portions 141 to 146 and 141' to 146' respectively 
in the direction of the central axis O--O. 
The primary winding assembly 1 is assembled to the secondary winding 
bobbins 21 and 21' in such a manner that the centers of the protruding 
portions 141 to 146 to 141' to 146' provided in the primary winding bobbin 
121 and the bobbin lid 122 coincide with centers of the same number of 
secondary winding partitioning protrusions 241 to 246 and 241' to 246' 
provided in the secondary winding bobbins 21 to 21'. The secondary 
windings 261 to 266 are wound around compartment 231 to 236 and 231' to 
236', each being defined between the adjacent protrusions of the secondary 
winding bobbins 21 to 21', with an equal number of turns (see FIG. 3). The 
pairs of opposing secondary windings 261, 264; 262, 265; and 263, 266 are 
respectively connected with opposite polarity to the excited magnetic flux 
and each of the three pairs of the secondary winding 261, 264; 262, 265; 
and 263, 266 in a star (wye) or delta circuit fashion. The lengths of the 
secondary winding compartments 231 to 236 and 231' to 236' on the 
circumferences of the bobbins 21 and 21', that is, the lengths of the arcs 
thereof are selected to be equal to one another and also arranged with an 
equal spacing therebetween. FIG. 3A is a side view of the magnetic sensor 
constructed as described above and FIG. 3B is a cross-sectional view taken 
along a line B--B in FIG. 3A. 
While in the above mentioned embodiment the magnetic sensor of the present 
invention is a 3-phase winding structure in which the secondary windings 
opposed to each other across the central axis O--O are connected with 
opposite polarity to the excited magnetic flux as one pair and the 
secondary winding is wound around the primary winding, the present 
invention is not limited to the above mentioned embodiment. It is needless 
to say that this invention can be applied to a magnetic sensor having a 
plurality of phases, such as a 2-phase or more than 4-phases and the 
invention is not limited to a magnetic sensor in which the above mentioned 
opposing two windings are paired as the secondary windings, but also can 
be applied to a magnetic sensor in which a single winding is wound around 
the diameter of the annular iron core as the secondary winding. 
Alternately, the present invention can be applied to a magnetic sensor of a 
type in which the primary winding is provided outside the secondary 
winding with the same effect. 
According to the first embodiment of the present invention, each annular 
primary winding bobbin and bobbin lid, incorporating therebetween the 
annular iron core and around which the primary winding is wound is divided 
by the plurality of equally spaced protrusions and the primary winding is 
uniformly wound around each of the divided portions. It is easy to 
uniformly wind the winding around such small portions except the whole 
periphery of the annular iron core. Accordingly, as a series of 
connections thereof, the primary winding can be uniformly wound around the 
whole periphery of the annular iron core, that is, the primary winding 
bobbin. As a result, the azimuth error of the magnetic sensor can be 
reduced. 
Further, since the primary winding assembly and the secondary winding 
bobbin can be assembled with the predetermined positional relation 
therebetween, the plurality of secondary windings can be wound around not 
only the primary winding, but also each of the secondary winding bobbins 
with the accurate positional relation. Thus, in respect of such aspect, it 
is possible to reduce the error of the magnetic sensor. 
Furthermore, since the distance from the bottom of the annular grooves 210 
of both the secondary winding bobbins 21 and 21' to its opening end face 
220, (ie: the depth 2.h2), is selected to be slightly smaller than the 
length between both the free ends of the respective protrusions of the 
primary winding bobbin 121 and the corresponding protrusions of the bobbin 
lid 122, then if the secondary winding is wound around both the secondary 
winding bobbins, the primary winding assembly member can be more 
positively supported by both of the secondary winding bobbins. 
FIG. 4 is an exploded perspective view showing another embodiment of the 
magnetic sensor according to the present invention and FIG. 5 is a 
cross-sectional view taken along a plane vertical to the central axis O--O 
of the magnetic sensor shown in FIG. 4 when it is assembled. FIG. 6A is a 
side view of the magnetic sensor when it is assembled and further FIG. 6B 
is a cross-sectional view taken along a line B-B in FIG. 6A. Throughout 
FIGS. 4 to 6, like parts corresponding to those of FIGS. 1 to 3 are marked 
with the same references and the overlapping explanations thereof will be 
omitted. 
In this second embodiment as shown in FIGS. 4 to 6, reference numerals 251 
to 256 and 251' to 256' respectively designate slots which are formed on 
the side surfaces of the respective protrusions 241 to 246 and 241' to 
246' of the annular secondary winding bobbins 21 to 21' at their 
substantially central portions. After the primary winding assembly 1 is 
incorporated between both the secondary winding bobbins 21 and 21' and the 
secondary windings 261 to 266 are wound therearound as described above, 
correcting windings 271, 272, . . . 276 are wound around the corresponding 
slots 251, 251'; 252, 252'; . . . 256, 256' of both the secondary winding 
bobbins 21 and 21'. 
The three parts of the secondary windings 261, 264; 262, 265; and 263, 266 
connected with the opposite polarity as set forth above to the excited 
magnetic flux, are respectively taken as the secondary windings A, B, and 
C. Assuming that the input axis of the secondary winder A is displaced in 
the clockwise direction, relative to the desired direction in, for 
example, FIG. 6A, then the azimuth accuracy of the magnetic sensor cannot 
satisfy its required value. Then, according to the prior art method, the 
second winding A must be wound again. 
However, according to the present invention, the secondary winding A or the 
secondary windings 261 and 264, may be respectively connected to a pair of 
opposing correction windings 276 and 273 located at one side thereof in 
the counter-clockwise direction, resulting, for example, in the 
displacement of the input axis direction of the secondary winder A in the 
counter-clockwise direction from the initial direction. In this simple 
manner the input axis of the secondary winding A may be corrected. When, 
on the contrary, the input axis of the secondary winding A is displaced in 
the counter-clockwise direction relative to the desired direction, the 
correction windings 271 and 274 are respectively connected to the 
secondary windings 261 and 264. The input axis direction of the secondary 
winding A is displaced to the clockwise direction from the direction 
before the correction winding is connected thereto. Thus, the input axis 
direction of the secondary winding A can be corrected similarly as 
described above. With respect to other secondary windings B and C, by 
properly selecting the adjacent correction windings and connecting them 
thereto, it is possible to correct the input axis directions thereof. 
Although not shown, the secondary windings 261 to 266 in this case are 
respectively provided with intermediate taps, and the positions thereof 
are selected so that the effective number of turns of the secondary 
windings are not changed before and after the connection of the correction 
windings 271 to 276 thereto. 
By selecting the number of turns of the correction windings 271 to 276 in 
relation to the number of turns of the secondary windings 261 to 266 so as 
to base the displacement of the magnetic azimuth on the resulting 
displacement of the input axis of the secondary winding twice the 
tolerable magnetic azimuth error, the tolerable magnetic azimuth error 
becomes three times its equivalent. Consequently, according to the 
magnetic sensor of the invention, the yield thereof can be increased 
considerably as compared with the prior art magnetic sensor of this kind. 
Further, the above-mentioned intermediate taps provided at the secondary 
windings can be used to adjust the sensitivity of each of the secondary 
windings (to correct the unbalance of the sensitivity among the secondary 
windings A, B, and C, etc.). Furthermore, if the correction windings are 
connected properly, it is possible to adjust the sensitivity of the 
secondary winding without displacing the input axis thereof substantially. 
In addition, the intermediate taps provided at the secondary windings and 
the correction windings can also be used as the balance adjustment (zero 
adjustment) of the respective secondary windings A, B, and C. 
Referring to FIGS. 7 and 8, further embodiment of the magnetic sensor 
according to the present invention will be described hereinafter. 
FIG. 7 is a circuit diagram of a main portion of the third embodiment of 
the magnetic sensor according to the present invention. 
In FIG. 7, reference numerals 281, 282, and 283 respectively designate 
secondary windings connected in a star-fashion and corresponding to the 
secondary winding pairs 261, 264; 262, 265; and 263, 266 of the magnetic 
sensor shown, for example, in FIG. 3. The secondary windings 281 to 283 
are each connected to a common point 0.sub.1. In the third embodiment of 
the invention, instead of the correction windings 271 to 276 of the 
magnetic sensor shown in FIGS. 4 to 6, gain adjusting means 291, 292, and 
293 such as variable resistors and the like are connected in parallel to 
the secondary windings 281 to 283, respectively. Sliding contacts 291a, 
292a, and 293a of the respective connected to free ends of resistors 301, 
302 and 303 which are connected in a star fashion in order to provide a 
neutral point O' and the sliding contacts 291a, 292a, and 293a are also 
connected to output terminals a, b, and c. A common connection point 
O.sub.2 of the resistors 301 and 303 becomes the above mentioned neutral 
point O'. The total resistance value of each of the gain adjusting means 
291 to 293 are made equal to one another, and the resistance values of the 
resistors 301 to 303 are made equal to one another. 
Though not shown in FIG. 7, the winding method of the primary winding 
assembly, the secondary winding and so on in the illustrated example of 
FIG. 7 are similar to those of the examples shown in FIGS. 1 to 6. In this 
embodiment of the present invention the correction windings and the slots 
used therefor shown in FIGS. 4 to 6 are not provided, respectively. 
FIG. 8 is a schematic representation used to explain that the output 
signals of the above-mentioned secondary windings 281 to 283 can be 
equivalently made as a 3-phase output signal spatially balanced by the 
adjustment of the gain adjusting means 291 to 293. 
In the circuit arrangement shown in FIG. 7, the gains and the input axis 
directions of the secondary windings 281, 282, and 283 are expressed by 
the lengths and the directions of O'.sub.1 A, O'.sub.1 B and O'.sub.1 C in 
FIG. 8, respectively. In this case, the gains thereof and so on are 
displaced from the desired values. If, therefore, the gains of the 
secondary windings 281 to 283 are made to O'.sub.1 a, O'.sub.1 b and O'hd 
1c by the adjusting means 291 to 293, it is possible to obtain O'.sub.2 a, 
O'.sub.2 b and O'.sub.2 c which are the same in magnitude and different in 
direction by 102.degree. each. This is the equivalent to the case in which 
three secondary windings having an equal gain are located such that their 
input axes are located with an angular spacing of 102.degree. (equal 
angular spacing) between adjacent ones. In FIG. 8, the point O'.sub.1 is 
equal to the common connection point 0.sub.1 of the secondary windings 281 
to 283 in potential, while a point O'.sub.2 is a virtual and neutral point 
which is equal to the point O.sub.2 shown in FIG. 7 in potential. 
Further, in the prior art system, since the scattering of the magnetization 
characteristic of the iron core becomes the scattering of the scale factor 
of the magnetic sensor, the iron core must be selected strictly in 
accordance with the way that the magnetic sensor is used. However, 
according to the third embodiment of the invention, even if the 
magnetization characteristic of the iron core is a little scattered, it is 
possible to afford a uniform scale factor of the magnetic sensor without 
the scattering. 
While in the above-mentioned embodiments the magnetic sensor has a 3-phase 
winding structure, it is needless to say that this invention is not 
limited to a 3-phase structure but can be applied to a magnetic sensor in 
which a secondary winding has a 2-phase winding structure or even more 
than a 4-phase structure. Further, the circuit arrangement of the 
secondary winding is not limited to a connection in star (wye) fashion, 
but an annular connection may be used. Also, the connection of the gain 
adjusting means is not limited to the star fashion connection, but the 
annular connection method may be used, similarly. The secondary winding is 
connected in an annular fashion, and the gain adjusting means is connected 
in a star fashion with the similar effect being achieved. Further, the 
neutral point can be removed but may be provided by the use if necessary. 
Furthermore, as the gain adjusting means, in addition to the variable 
resistor, there can be used a potentiometer or a combination of a fixed 
resistor, a variable resistor and the like. In addition, an amplifier with 
a gain adjusting function and the like can be used as the gain adjusting 
means. 
According to the third embodiment of the invention as set forth above, by 
the adjustment of the gain adjusting means provided at each secondary 
winding, the output signal of the secondary winding can be equivalently 
made as a multi-phase output signal which is balanced in space, the 
magnetic azimuth error can be corrected, and the high magnetic azimuth 
precision can be obtained. 
According to the former embodiments of the present invention, there are 
required very cumbersome and complex means for separating the causes of 
the magnetic azimuth error into a cause made by the input axis (angle 
between the input axes) and a cause made by the difference of gains of the 
respective windings and further. There is a significant defect in that the 
amount of the magnetic azimuth error which can be corrected by the prior 
art is discontinuous (discrete) and so on. However, according to the third 
embodiment of the present invention, it is not necessary to separate the 
causes of error, and also the amount of error to be corrected is 
successive so that the adjustment having a high accuracy can be carried 
out with ease. 
The above-mentioned effects achieved by the invention brought about the 
reduction of the manufacturing process. 
Furthermore, the correction winding becomes unnecessary, and, hence, this 
can reduce the manufacturing cost considerably. 
In addition, it is possible to afford a uniform scale factor of the 
magnetic sensor without scattering. 
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.