FORM 2
THE PATENTS ACT, 1970
(39 of& 1970) THE PATENTS RULES, 2003 COMPLETE SPECIFICATION
[See section 10, Rule 13] ENCODER;
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED
AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 1008310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

DESCRIPTION
Field
[0001] The present invention relates to an encoder
including a magnetic shield and a magnetic sensor.
Background
[0002] In a magnetic encoder with a magnetic sensor
mounted on a substrate, a permanent magnet is located on a
shaft about its axial center, and generates a magnetic flux
to operate the magnetic sensor. The magnetic sensor
detects a magnetic flux generated from the permanent magnet.
However, when there is a device or a power line generating
a magnetic field around the encoder, this leads to a
problem in that an external magnetic field interferes with
a magnetic flux generated from the permanent magnet, which
causes the magnetic sensor to operate improperly.
Therefore, it is necessary to place a magnetic shield to
shield the magnetic sensor from the external magnetic field.
[0003] Patent Literature 1 discloses a magnetic encoder
in which a magnetic cover is placed in such a manner that a
soft magnetic portion is located at a position where the
soft magnetic portion does not affect the operating
magnetic field of a magnetic sensor.
Citation List
Patent Literature
[0004] Patent Literature 1: Japanese Patent Application
Laid-open No. 2015-169439

Summary
Technical Problem
[0005] However, in the structure of the encoder
disclosed in Patent Literature 1, an external magnetic
field, applied in a direction that is the same as the
detection direction in which the magnetic sensor detects a
magnetic flux generated from the permanent magnet, may
possibly enter the magnetic cover through a non-magnetic
portion. Therefore, there is a problem in that an external
magnetic field applied in a direction that is the same as
the detection direction of the magnetic sensor may enter
the magnetic cover through the non-magnetic portion, which
increases a noise component of the detection result of the
magnetic sensor and accordingly decreases accuracy in
detecting the rotational angle.
[0006] The present invention has been achieved to solve
the above problems, and an object of the present invention
is to provide an encoder that prevents or reduces a
decrease in accuracy in detecting a rotational angle caused
by an external magnetic field.
Solution to Problem
[0007] In order to solve the above problems and achieve
the object, the present invention includes: a magnetic
sensor having directional detection sensitivity to a
magnetic field, the magnetic sensor having higher detection
sensitivity to a magnetic field applied in a reading
direction, while having lower detection sensitivity to a
magnetic field applied in a direction forming a greater
angle with respect to the reading direction; an encoder
substrate having the magnetic sensor mounted thereon; a
magnetic shield to shield against a magnetic field, the
magnetic shield including a side portion covering sides of
the magnetic sensor and a top-side portion covering a top
of the magnetic sensor; a permanent magnet located to face
the encoder substrate; a shaft having the permanent magnet
attached to a tip end of the shaft; and a bracket to
support the shaft in a rotatable manner. On the side
portion of the magnetic shield, a notch or a hole is
provided to serve as a connector insertion portion through
which a connector is inserted. The connector insertion
portion is located at a position where the connector
insertion portion does not overlap an extended area that is
obtained by extending the magnetic sensor in the reading
direction.
Advantageous Effects of Invention
[0008] The encoder according to the present invention
has an effect where it is possible to prevent or reduce a
decrease in accuracy in detecting a rotational angle caused
by an external magnetic field.
Brief Description of Drawings
[0009] FIG. 1 is a perspective view of an encoder
according to a first embodiment of the present invention.
FIG. 2 is a perspective view of a magnetic shield of
the encoder according to the first embodiment.
FIG. 3 is a diagram illustrating a positional relation
between a magnetic sensor and the magnetic shield of the
encoder according to the first embodiment.
FIG. 4 is a diagram illustrating a positional relation
between the magnetic sensor and the magnetic shield of the
encoder according to the first embodiment.
FIG. 5 is a perspective view of an encoder according
to a second embodiment of the present invention.
FIG. 6 is a diagram illustrating a positional relation
between magnetic sensors and a magnetic shield of the
encoder according to the second embodiment.
FIG. 7 is a diagram illustrating a positional relation
between the magnetic sensors and the magnetic shield of the
encoder according to the second embodiment.
FIG. 8 is a diagram illustrating a positional relation
between the magnetic sensors and the magnetic shield of the
encoder according to the second embodiment.
FIG. 9 is a perspective view of an encoder according
to a third embodiment of the present invention.
FIG. 10 is a perspective view of the encoder according
to the third embodiment.

Description of Embodiments
[0010] An encoder according to embodiments of the
present invention will be described in detail below with
reference to the accompanying drawings. The present
invention is not limited to the embodiments.
[0011] First embodiment.
FIG. 1 is a perspective view of an encoder according
to a first embodiment of the present invention. An encoder
50 according to the first embodiment includes a permanent
magnet 4 that rotates along with a shaft 5, a magnetic
sensor 1 having directional detection sensitivity to a
magnetic field, the magnetic sensor 1 having higher
detection sensitivity to a magnetic field applied in a
reading direction, while having lower detection sensitivity
to a magnetic field applied in a direction forming a
greater angle with respect to the reading direction, an
encoder substrate 3 having the magnetic sensor 1 mounted
thereon, a bracket 6 formed of non-magnetic material to
support the shaft 5 in a rotatable manner, a magnetic
shield 2 to cover the encoder substrate 3, a spacer 7
located between the bracket 6 and the magnetic shield 2,
and a substrate holding member 8 placed on the bracket 6 to
support the encoder substrate 3. While the spacer 7
illustrated in FIG. 1 has a ring shape and is interposed
only between the bracket 6 and the magnetic shield 2, it is
allowable that the spacer 7 has a dome shape covering the
encoder substrate 3.
[0012] FIG. 2 is a perspective view of the magnetic
shield of the encoder according to the first embodiment.
The magnetic shield 2 includes a side portion 2a covering
the sides of the magnetic sensor 1 and a top-side portion
2b covering the top of the magnetic sensor 1. On the side
of the magnetic shield 2, a notch 21 is formed to serve as
a connector insertion portion through which a connector is
inserted to be connected to the encoder substrate 3. It is
allowable that a hole is formed on the side of the magnetic
shield 2 to serve as the connector insertion portion. The
magnetic shield 2 is formed of magnetic material such as
cold-rolled steel or carbon steel.
[0013] The permanent magnet 4 is located such that the
permanent magnet 4 and the encoder substrate 3 face each
other. The permanent magnet 4 is placed at the tip end of
the shaft 5. The permanent magnet 4 is a magnet of
neodymium series, samarium series, or ferrite series. It
is allowable that the permanent magnet 4 is fixed directly
to the shaft 5 or is fixed to the shaft 5 through a member
(not unillustrated).
[0014] FIG. 3 is a diagram illustrating a positional
relation between the magnetic sensor and the magnetic
shield of the encoder according to the first embodiment.
The magnetic sensor 1 has directional detection sensitivity
to a magnetic field. The magnetic sensor 1 has higher
detection sensitivity to a magnetic field applied in a
direction illustrated by an arrow D in FIG. 3, while having
lower detection sensitivity to a magnetic field applied in
a direction closer to the direction perpendicular to the
arrow D. Hereinafter, the direction illustrated by the
arrow D is referred to as "the reading direction of the
magnetic sensor 1". The magnetic shield 2 covers the
magnetic sensor 1 in a state in which the notch 21 is
located at a position where the notch 21 does not overlap
an extended area 11 that is obtained by extending the
magnetic sensor 1 in the reading direction. In a case
where an external magnetic field is applied from a
direction where the notch 21 is located, a magnetic flux
enters the magnetic shield 2 from the notch 21. However,
the direction of the magnetic flux is perpendicular to the
reading direction of the magnetic sensor 1, and accordingly
the magnetic sensor 1 has lower detection sensitivity to
the external magnetic field. This results in a smaller
noise component. Further, in a case where an external
magnetic field is applied from the reading direction of the
magnetic sensor 1, because the magnetic shield 2 covers the
location that overlaps the extended area 11, this reduces
or prevents the external magnetic field from entering the
magnetic shield 2. Therefore, although the magnetic shield
2 is formed with the notch 21, when an external magnetic
field is applied from a radial direction of the shaft 5, a
noise component included in the detection result of
magnetic field detected by the magnetic sensor 1 can be
reduced.
[0015] Because the spacer 7 is interposed between the
bracket 6 and the magnetic shield 2, the bracket 6 and the
magnetic shield 2 are not in direct contact with each other,
but are held spaced apart from each other by the thickness
30 of the spacer 7. The spacer 7 is interposed between the
bracket 6 and the magnetic shield 2, and thereby the
bracket 6 and the magnetic shield 2 are thermally separated
from each other. Providing a thermal gap between the
bracket 6 and the magnetic shield 2 can prevent or reduce
thermal transmission from the shaft 5 during driving of a
motor that rotates the shaft 5. Particularly, a distance
between the bracket 6 and the magnetic shield 2 is set
equal to or shorter than 5 mm. This setting can prevent a
magnetic flux from entering the inner side of the magnetic
shield 2, and thus can reduce a noise component included in
the detection result of magnetic field detected by the
magnetic sensor 1.
[0016] An opening width A of the notch 21 of the
magnetic shield 2 is made smaller than a dimension B of the
magnetic sensor 1 in the reading direction. This
configuration can prevent a magnetic flux from entering the
inner side of the magnetic shield 2, and thus can enhance
the effect of reducing a noise component included in the
detection result of magnetic field detected by the magnetic
sensor 1.
[0017] FIG. 4 is a diagram illustrating a positional
relation between the magnetic sensor and the magnetic
shield of the encoder according to the first embodiment.
As illustrated in FIG. 4, the magnetic shield 2 is located
in such a manner that the direction of the normal to an
opening plane 21a of the notch 21 of the magnetic shield 2
is perpendicular to the reading direction of the magnetic
sensor 1. This can further reduce a noise component
included in the detection result of magnetic field detected
by the magnetic sensor 1 when an external magnetic field is
applied.
[0018] As illustrated in FIG. 2, the notch 21 does not
reach the top-side portion 2b of the magnetic shield 2.
This can also reduce a noise component included in the
detection result of magnetic field detected by the magnetic
sensor 1, even when an external magnetic field in the axial
direction of the shaft 5 is applied to the encoder 50.
[0019] Even when the magnetic shield 2 is provided with
the notch 21 serving as the connector insertion portion,
the encoder 50 according to the first embodiment can still
reduce a noise component included in the detection result
of magnetic field detected by the magnetic sensor 1 when an
external magnetic field is applied. In a case where the
encoder 50 according to the first embodiment is applied
with an external magnetic field from a direction crossing
the opening plane 21a of the notch 21, a magnetic flux
enters the magnetic shield 2 through the notch 21. However,
due to the magnetic flux in a direction crossing the
reading direction of the magnetic sensor 1, a smaller noise
component is included in the detection result of magnetic
field detected by the magnetic sensor 1. Further, in a
case where the encoder 50 according to the first embodiment
is applied with an external magnetic field from the reading
direction of the magnetic sensor 1, because the notch 21 is
located at a position where the notch 21 does not overlap
the extended area 11, this can reduce a noise component
included in the detection result of magnetic field detected
by the magnetic sensor 1. Therefore, the encoder 50
according to the first embodiment is highly resistant to an
external magnetic field, and can increase accuracy in
detecting the rotational angle of the shaft 5. Furthermore,
the encoder 50 does not need to be covered in its entirety
including the connector with the magnetic shield 2, and
thus it is possible to downsize the encoder 50.
[0020] Second embodiment.
FIG. 5 is a perspective view of an encoder according
to a second embodiment of the present invention. The
encoder 50 according to the second embodiment is different
from the encoder 50 according to the first embodiment in
that a plurality of magnetic sensors 1 are mounted on the
encoder substrate 3.
[0021] FIG. 6 is a diagram illustrating a positional
relation between the magnetic sensors and the magnetic
shield of the encoder according to the second embodiment.
As illustrated in FIG. 6, the magnetic shield 2 covers the
location that overlaps the extended area 11 of one of the
magnetic sensors 1 which is positioned nearest the notch 21.
[0022] FIG. 7 is a diagram illustrating a positional
relation between the magnetic sensors and the magnetic
shield of the encoder according to the second embodiment.
As illustrated in FIG. 7, the magnetic shield 2 is located
in such a manner that the direction of the normal to the
opening plane 21a of the notch 21 of the magnetic shield 2
is perpendicular to the reading direction of the magnetic
sensor 1. This can further reduce a noise component
included in the detection result of magnetic field detected
by the magnetic sensor 1 when an external magnetic field is
applied.
[0023] FIG. 8 is a diagram illustrating a positional
relation between the magnetic sensors and the magnetic
shield of the encoder according to the second embodiment.
The opening width A of the notch 21 of the magnetic shield
2 is made smaller than the dimension B of the magnetic
sensor 1 in the reading direction. This configuration can
prevent a magnetic flux from entering the inner side of the
magnetic shield 2, and thus can enhance the effect of
reducing a noise component included in the detection result
of magnetic field detected by the magnetic sensor 1.
[0024] The encoder 50 according to the second embodiment has the magnetic sensors 1 mounted on the encoder substrate
3, thereby reducing or preventing failure to detect a
magnetic field. Therefore, it is possible for the encoder
to ensure its functional safety.
[0025] Third embodiment.
FIG. 9 is a perspective view of an encoder according to a third embodiment of the present invention. The encoder 50 according to the third embodiment is different from the encoder 50 according to the first embodiment in that a magnetic shield plate 9 is located closer to the bracket 6 relative to the permanent magnet 4.
[0026] The spacer 7 is interposed between the magnetic shield plate 9 and the magnetic shield 2. Accordingly, a gap is formed between the bracket 6 and the magnetic shield
2, the gap having a thickness in which the thickness of the
magnetic shield plate 9 and the thickness of the spacer 7
are added. The spacer 7 is interposed between the magnetic shield plate 9 and the magnetic shield 2, and thereby the magnetic shield plate 9 and the magnetic shield 2 are
thermally separated from each other. Therefore, the bracket 6 and the magnetic shield 2 are also thermally separated from each other. A thermal gap is provided between the magnetic shield plate 9 and the magnetic shield
2 so that while thermal transmission from the shaft is prevented or reduced during driving of the motor that rotates the shaft 5, a noise component included in the detection result of magnetic field detected by the magnetic
sensor 1 can be reduced. Particularly, a distance between the bracket 6 and the magnetic shield 2 is set equal to or
shorter than mm. This setting can prevent a magnetic
flux from entering the inner side of the magnetic shield 2,
and thus can reduce a noise component included in the detection result of magnetic field detected by the magnetic
sensor 1.
[0027] Even in a case where the encoder 50 according to the third embodiment is applied with an external magnetic
field in the axial direction of the shaft 5, the encoder 50 can still reduce a noise component included in the detection result of magnetic field detected by the magnetic
sensor 1.
[0028] FIG. 10 is a perspective view of the encoder according to the third embodiment. It is also possible to employ such a configuration that the magnetic shield plate
9 is added to the encoder 50 according to the second embodiment, the encoder 50 having the plurality of the magnetic sensors 1 mounted on the encoder substrate 3.
Similarly to the encoder 50 illustrated in FIG. 9, even in a case where the encoder 50 illustrated in FIG. 10 is applied with an external magnetic field in the axial direction of the shaft 5, this encoder 50 can still reduce a noise component included in the detection result of magnetic field detected by the magnetic sensor 1.
[0029] The configurations described in the above
embodiments are only examples of the content of the present invention. The configurations can be combined with other well-known techniques, and part of each of the configurations can be omitted or modified without departing
from the scope of the present invention.
Reference Signs List
[0030] 1 magnetic sensor, 2 magnetic shield, 2a side
portion, 2b top-side portion, 3 encoder substrate, 4 permanent magnet, 5 shaft, 6 bracket, 7 spacer, 8
substrate holding member, 9 magnetic shield plate, 11 extended area, 21 notch, 21a opening plane, 50 encoder.

We Claim:
1. An encoder comprising:
a magnetic sensor having directional detection
sensitivity to a magnetic field, the magnetic sensor having higher detection sensitivity to a magnetic field applied in a reading direction, while having lower detection sensitivity to a magnetic field applied in a direction forming a greater angle with respect to the reading direction; an encoder substrate having the magnetic sensor
mounted thereon; a magnetic shield to shield against a magnetic field,
the magnetic shield including a side portion covering sides of the magnetic sensor and a top-side portion covering a top of the magnetic sensor; a permanent magnet located to face the encoder substrate; a shaft having the permanent magnet attached to a tip
end of the shaft; and a bracket to support the shaft in a rotatable manner,
wherein on the side portion of the magnetic shield, a notch or
a hole is provided to serve as a connector insertion portion through which a connector is inserted, and the connector insertion portion is located at a position where the connector insertion portion does not overlap an extended area that is obtained by extending the
magnetic sensor in the reading direction.
2. The encoder according to claim 1, wherein a direction of a normal to an opening plane of the connector insertion portion is perpendicular to the reading direction.
3. The encoder according to claim 1 or 2, wherein an opening width of the connector insertion portion is smaller than a dimension of the magnetic sensor in the reading direction.
4. The encoder according to claim 1, wherein
a plurality of the magnetic sensors are mounted on the encoder substrate, and
the connector insertion portion is located at a
position where the connector insertion portion does not overlap an extended area that is obtained by extending one
of the magnetic sensors in the reading direction, the one of the magnetic sensors being located nearest the connector
insertion portion.
5. The encoder according to claim 4, wherein a direction of a normal to an opening plane of the connector nsertion
portion is perpendicular to the reading direction of the one of the magnetic sensors which is located nearest the connector insertion portion.
6. The encoder according to claim 4 or 5, wherein an opening width of the connector insertion portion is smaller than a dimension of, in the reading direction, the one of the magnetic sensors located nearest the connector insertion portion.
7. The encoder according to any one of claims 1 to 6, wherein the connector insertion portion does not reach the top-side portion.
8. The encoder according to any one of claims 1 to 7, wherein the encoder includes a magnetic shield plate to shield against a magnetic field, the magnetic shield plate
being located closer to the bracket relative to the permanent magnet.9. The encoder according to any one of claims 1 to 8,wherein the magnetic shield and the bracket are thermally
separated from each other.