TW202011002A - Encoder with magnetic field shielding plate - Google Patents

Abstract

An encoder (20) includes an encoder shaft (1) having a shaft coupler provided at a lower end thereof; an encoder base member (7) having a hole for the encoder shaft (1) to penetrate; a magnet (2) disposed at an upper end of the encoder shaft (1); a circuit board (4) installed with a magnetic sensor (3) for detecting the magnetic field of the magnet (2) and a computing element (41) that calculates the rotation angle of the encoder shaft (1) based on an output of the magnetic sensor (3); a circuit board holding member (5) having a cylindrical shape with two opening ends, onto an upper end of which the circuit board (4) is fixed; and a magnetic field shielding plate (6) having a portion overlapping a cylinder portion of the circuit board holding member (5). The magnetic field shielding plate (6) is formed with a cut-off, via which the encoder base member (7) abuts the circuit board holding member (5), at a part of the portion overlapping the cylinder portion of the circuit board holding member (5) in an axial direction of a central axis of the circuit board holding member (5).

Description

Encoder with magnetic shield

The invention relates to an encoder with a magnetic field shielding plate provided with a magnetic sensor.

Encoders equipped with magnetic sensors are generally equipped with magnets fixed to the encoder shaft. By reading the magnetic field generated by the magnet with a magnetic sensor, the function of detecting the rotation angle of the motor shaft connected to the encoder shaft or detecting the multi-turn rotation position is realized. The magnetic flux leakage from the motor or electromagnetic brake will be detected as noise by the magnetic sensor, which will reduce the detection accuracy. Therefore, an encoder equipped with a magnetic sensor is provided with a magnetic field shielding element composed of a soft magnetic body, so as to reduce leakage magnetic flux that becomes noise if the magnetic sensor detects it and invade the magnetic sensor.

The detection accuracy of the encoder depends on the assembly accuracy of the rotation angle detection ruler fixed on the shaft and the rotation angle detection sensor mounted on the circuit board. Therefore, in order to obtain high detection accuracy, it is necessary to accurately assemble the rotation angle detection ruler and the sensor. Therefore, it is necessary to perform high-precision processing on the contact portion between the member supporting the circuit board and the bracket.

Patent Document 1 discloses a structure in which a magnetic field shield element entirely covers an opening of a housing member of an electromagnetic brake opposite to a load side, and reduces the noise given to the magnetic sensor by the leakage magnetic flux leaking from the electromagnetic brake. [Prior Technical Literature] [Patent Literature]

(Patent Document 1) Japanese Patent No. 5943694

[Problems to be solved by the invention]

The encoder disclosed in Patent Document 1 has a structure in which a magnetic field shielding element is sandwiched between a member supporting a circuit board and a bracket. Therefore, in order to improve the detection accuracy, it is necessary to increase the dimensional accuracy of the magnetic field shielding element itself. The soft magnetic material used for the magnetic field shielding element in the encoder disclosed in Patent Document 1 cannot be manufactured by die-cast molding or resin molding. Therefore, in order to achieve high part accuracy in the complex shape of the magnetic field shielding element disclosed in Patent Document 1, it is necessary to perform cutting processing. Therefore, the encoder disclosed in Patent Document 1 needs to perform the operation of improving the dimensional accuracy of the magnetic field shielding element, and the number of manufacturing operations will increase.

The present invention has been accomplished in view of the above-mentioned problems, and its object is to obtain an encoder with a magnetic field shielding plate that can improve detection accuracy without increasing the dimensional accuracy of the magnetic field shielding element. [Means to solve the problem]

In order to solve the above problems and achieve the object of the invention, the present invention has: an encoder shaft provided with a coupling at the lower end; an encoder base member formed with a hole through which the encoder shaft passes; and provided on the encoder shaft The magnet at the upper end of the circuit; a circuit board mounted with a magnetic sensor that detects the magnetic field of the magnet and a calculation element that calculates the rotation angle of the encoder shaft based on the output of the magnetic sensor; the shape is open at both ends A cylindrical substrate with a circuit board holding member fixed to its upper end; and a magnetic field shielding plate that overlaps the cylindrical portion of the circuit board holding member when viewed along the central axis of the circuit board holding member. The magnetic field shielding plate is formed with a notch at a part of the portion where the axial direction of the central axis of the circuit board holding member overlaps the cylindrical portion of the circuit board holding member. The encoder base member and the circuit board holding member are in contact with each other through the notch. Furthermore, a convex portion is provided, which extends from at least the upper surface of the encoder base member out of the lower end of the circuit board holding member and the upper surface of the encoder base member, in the axial direction of the central axis of the circuit board holding member In the extender, the convex portion penetrates the notch portion, whereby the encoder base member contacts the circuit board holding member. [Effect of invention]

The encoder with the magnetic field shielding plate of the present invention will produce the effect of improving the detection accuracy.

Hereinafter, the encoder with a magnetic field shielding plate according to an embodiment of the present invention will be described in detail based on the drawings. The invention is not limited by this embodiment.

Implementation form 1. Figure 1 is a perspective view of an encoder according to Embodiment 1 of the present invention. 2 and 3 are cross-sectional views showing the configuration of the encoder of Embodiment 1. The encoder 20 of the first embodiment is a magnetic encoder that magnetically detects the rotation angle of the encoder shaft 1. The encoder 20 of the first embodiment includes an encoder shaft 1 supported rotatably, a magnet 2 fixed to the upper end of the encoder shaft 1, and a magnetic sensor 3 that detects the magnetic field generated by the magnet 2. The fixing method of the magnet 2 and the encoder shaft 1 may be an adhesive method, or a method of forming the magnet 2 into a hollow cylindrical shape and then fixing it with screws. The magnetic sensor 3 is mounted on the circuit board 4. The magnetic sensor 3 adopts a Hall element or a magnetoresistive element. The circuit board 4 is also mounted with an arithmetic element 41 that processes the output voltage of the magnetic sensor 3 to calculate the rotation angle of the encoder shaft 1.

The encoder 20 of Embodiment 1 further includes a circuit board holding member 5 that supports the circuit board 4 and a magnetic field shielding plate 6. That is, the encoder 20 is an encoder provided with a magnetic field shielding plate including the magnetic field shielding plate 6. The encoder 20 of Embodiment 1 has an encoder base member 7 formed as a housing and a resin encoder cover 10. The magnet 2, the circuit board 4, the circuit board holding member 5 and the magnetic field shielding plate 6 are housed in a housing formed by the encoder base member 7 and the resin encoder cover 10. The outside of the resin encoder cover 10 is also covered with an external magnetic field shield cover 11.

The encoder base member 7 is formed of aluminum alloy or synthetic resin added with a filler. The magnetic field shielding plate 6 is formed of a soft magnetic body.

A coupling 9 is provided at the lower end of the encoder shaft 1. The encoder shaft 1 is connected to the motor shaft of the servo motor via a coupling 9.

The sealing member 12 is provided on the flat bottom surface 72 of the groove 71 provided in the encoder base member 7, and the flat portion of the peripheral portion of the resin encoder cover 10 is in contact with the sealing member 12. The screw 13 fixes the external magnetic field shield cover 11 and the resin encoder cover 10 to the encoder base member 7. The external magnetic field shield cover 11 is fixed to the encoder base member 7 with screws 13. After the screw 13 is tightened, the sealing member 12 existing between the flat portion of the resin encoder cover 10 and the flat bottom surface 72 of the groove 71 of the encoder base member 7 is compressed, and a high dustproof and waterproof effect can be obtained . The term flat here means that it is macroscopically flat, even if there are irregularities from a microscopic perspective. Since the sealing member 12 is compressed between the flat surfaces, the external magnetic field shield cover 11 and the encoder base member 7 are not processed with high accuracy, and the dustproof and waterproof effect can be obtained at low cost. The sealing member 12 is an O-ring made of nitrile rubber or silicone rubber.

The external magnetic field shield cover 11 is formed of a soft magnetic body. The material of the external magnetic field shielding cover 11 may be iron-nickel alloy called permalloy with high magnetic field shielding effect, or it may be used for general structure which is inferior to iron-nickel alloy, but cheaper than iron-nickel alloy. Rolled steel or cold rolled steel.

Since the encoder 20 of Embodiment 1 can increase the size of the screw 13 used for fixing the external magnetic field shielding cover 11, the dustproof and waterproof performance caused by insufficient force for fixing the external magnetic field shielding cover 11 can be suppressed reduce. In addition, since the encoder 20 of the first embodiment compresses the sealing member 12 between flat surfaces, it is possible to obtain waterproof and dustproof performance without processing the external magnetic field shield cover 11 and the encoder base member 7 with high accuracy .

On the inner periphery of the hole through which the encoder shaft 1 of the encoder base member 7 passes, an inner periphery protrusion 73 protruding in a rib-like shape toward the center axis of the hole is formed. The inner peripheral protrusion 73 abuts on the outer ring 81 of the bearing 8. In addition, a bearing pressing rib 1 a protruding in a flange shape in the outer diameter direction is formed on the encoder shaft 1. The inner ring 82 of the bearing 8 on the magnet 2 side abuts on the bearing pressing rib 1 a. Therefore, the bearing 8 on the magnet 2 side is fixed by being sandwiched between the inner peripheral protrusion 73 and the bearing pressing rib 1a. In addition, the inner ring 82 of the bearing 8 on the side opposite to the magnet 2 is in contact with the coupling 9. Therefore, the bearing 8 on the side opposite to the magnet 2 is sandwiched and fixed by the inner peripheral protrusion 73 and the coupling 9.

FIG. 4 is a diagram schematically showing magnetic field induction by the external magnetic field shielding cover of the encoder of Embodiment 1. In addition to blocking the external magnetic field in the use environment of the motor, the external magnetic field shielding cover 11 also has a function of inducing the magnetic field induced from the servo motor or electromagnetic brake to the magnetic field shielding plate 6 away from the magnetic sensor 3. The specific gravity of the soft magnetic body used as the material of the magnetic field shielding plate 6 is generally larger than that of the aluminum alloy used as the material of the encoder base member 7 or the synthetic resin with filler added. The encoder 20 of the first embodiment achieves a magnetic field shielding effect, and achieves lighter weight than the case where the encoder base member 7 is formed entirely of soft magnetic materials.

FIG. 5 is an exploded perspective view of the circuit board, the circuit board holding member, and the magnetic field shielding plate of the encoder of Embodiment 1. FIG. The circuit board holding member 5 has a cylindrical cylindrical portion, that is, the cylindrical body 51, and both ends thereof are opened. The circuit board 4 is adhesively fixed to the upper end of the circuit board holding member 5. A convex portion 52 is formed on the lower end portion of the circuit board holding member 5. The convex portion 52 is formed with a hole through which the screw 14 passes, and the screw 14 is used to fix the circuit board holding member 5 to the encoder base member 7. FIG. 5 shows that the part of the screw 14 for fixing to the encoder base member 7 penetrates the structure of the convex part 52, but the part of the screw 14 penetrating the circuit board holding member 5 may be a part other than the convex part 52. That is, in the portion where the screw 14 penetrates the circuit board holding member 5, the circuit board holding member 5 and the encoder base member 7 may not be in contact.

The magnetic field shielding plate 6 is provided between the circuit board 4 and the encoder base member 7 and is fixed to the encoder base member 7 with screws 15. The method of fixing the magnetic field shielding plate 6 to the encoder base member 7 is not limited to locking with screws, but can also be fixed by means of adhesion or concave-convex fitting.

The magnetic field shielding plate 6 is formed with two notch portions 61 in a part of the portion overlapping the cylindrical body 51 when viewed from the direction along the central axis of the circuit board holding member 5. The notch portion 61 is in the form of a notch that opens up to the edge of the magnetic field shielding plate 6 or does not reach the edge of the magnetic field shielding plate 6. In Embodiment 1, the notch 61 has a circular hole shape. However, the shape of the hole is not limited to a circle. Moreover, the number of notch portions 61 is not limited to two.

The encoder base member 7 and the circuit board holding member 5 are brought into contact with each other by the projection 52 of the circuit board holding member 5 passing through the notch 61 of the magnetic field shielding plate 6. Among them, the cylindrical body 51 of the circuit board holding member 5 is not in contact with the magnetic field shielding plate 6.

When the motor shaft rotates, the rotation is transmitted to the encoder shaft 1 via the coupling 9, and the magnet 2 fixed to the encoder shaft 1 rotates. Therefore, the output voltage output by the magnetic sensor 3 changes as the rotation angle of the motor shaft changes. The arithmetic element 41 processes the output voltage of the magnetic sensor 3 to calculate the rotation angle of the encoder shaft 1 connected to the motor shaft.

In the above description, although the encoder 20 is an example of a magnetic encoder, the encoder 20 may be an optical encoder that optically detects the rotation angle of the encoder shaft 1. FIG. 6 is a cross-sectional view showing a modification of the encoder of Embodiment 1. FIG. The circuit board 4 is provided with a light emitting element 42 and a light receiving element 43. In addition, a reflective optical scale 21 is attached to the magnet 2. When the light emitted from the light-emitting element 42 is reflected by the reflective optical scale 21, the light intensity is modulated by the rotation of the encoder shaft 1 before entering the light-receiving element 43. The output voltage output from the light receiving element 43 is processed by the arithmetic element 41 mounted on the circuit board 4, and the rotation angle of the encoder shaft 1 connected to the motor shaft of the servo motor can be detected.

In the encoder 20 of the modification of Embodiment 1, the magnetic sensor 3 uses a composite magnetic wire that can obtain the Barkhausen effect. When the direction of the magnetic field changes with the change of the rotation angle of the encoder shaft 1 to which the magnet 2 is fixed, a power generation pulse is output from the magnetic sensor 3 which is a composite magnetic wire due to the Barkhausen effect. By performing calculation on the power generation pulse output by the magnetic sensor 3, the calculation element 41 can measure the rotation direction and the number of rotations of the encoder shaft 1.

Since the encoder 20 of Embodiment 1 is the circuit board holding member 5 fixed to the encoder base member 7 through the notch 61 of the magnetic field shielding plate 6, the magnetic shielding plate 6 can be improved even if the magnetic field shielding plate 6 is not processed with high accuracy The position accuracy of the sensor 3 is set. Therefore, the encoder 20 is not easily affected by an external magnetic field, and the detection accuracy can be improved.

In addition, since the encoder 20 of the embodiment 1 is fixed in such a manner that the magnetic field shielding plate 6 is not sandwiched between the encoder base member 7 and the circuit board holding member 5, in the axial direction of the encoder shaft 1 The size of the encoder 20 does not increase due to the thickness of the magnetic field shielding plate 6.

Implementation type 2. The encoder 20 of Embodiment 2 of the present invention is the same as the encoder 20 of Embodiment 1 except that the shapes of the circuit board holding member 5, the magnetic field shielding plate 6 and the encoder base member 7 are different. FIG. 7 is an exploded perspective view of a circuit board, a circuit board holding member, and a magnetic field shielding plate of an encoder according to Embodiment 2 of the present invention. The notch portion 61 formed in the magnetic field shielding plate 6 is opened to the open edge of the magnetic field shielding plate 6. A convex portion 74 is provided on the upper surface of the encoder base member 7. The convex portion 74 of the encoder base member 7 passes through the notch portion 61, and the circuit board holding member 5 and the encoder base member 7 abut in this way. The encoder base member 7 and the circuit board holding member 5 are fixed by screws 14 penetrating through the convex portion 74. Among them, the cylindrical body 51 of the circuit board holding member 5 is not in contact with the magnetic field shielding plate 6.

The encoder base member 7 is formed into a rough shape by aluminum die-casting, and the parts requiring high dimensional accuracy are further cut. The part of the encoder base member 7 that is in contact with the circuit board holding member 5 needs to be cut, but the encoder 20 of the embodiment 2 only needs to cut the convex part 74, so the encoder base can be reduced The manufacturing cost of the component 7.

Implementation pattern 3. The encoder 20 of Embodiment 3 of the present invention is the same as the encoder 20 of Embodiment 1 except that the shapes of the circuit board holding member 5, the magnetic field shielding plate 6, and the encoder base member 7 are different. FIG. 8 is an exploded perspective view of a circuit board, a circuit board holding member, and a magnetic field shielding plate of an encoder according to Embodiment 3 of the present invention. In the encoder 20 of the third embodiment, three notches 61 are formed in the magnetic field shielding plate 6. The notch portion 61 of the magnetic field shielding plate 6 of the encoder 20 of Embodiment 3 is an arc-shaped notch formed by partially removing the outer peripheral side of the ring. Therefore, the magnetic field shielding plate 6 is formed to include a ring portion 62 smaller than the end surface of the circuit board holding member 5 and a radial direction from the outer edge of the ring portion 62 away from the center axis of the circuit board holding member 5 The shape of a plurality of protruding pieces 63 protruding.

At the lower end portion of the circuit board holding member 5, a convex portion 52 having a shape extending downward from the cylindrical body 51 is provided. The convex portion 52 of the circuit board holding member 5 penetrates the notch portion 61 of the magnetic field shielding plate 6 and comes into contact with the encoder base member 7. Among them, the cylindrical body 51 of the circuit board holding member 5 is not in contact with the magnetic field shielding plate 6. The convex portions 52 of the circuit board holding member 5 are formed as concave portions 53 having a larger thickness than the protruding pieces 63 of the magnetic field shielding plate 6. Therefore, when the encoder base member 7 is in contact with the circuit board holding member 5, interference between the magnetic field shielding plate 6, the circuit board holding member 5 and the encoder base member 7 is prevented.

The encoder 20 of the embodiment 3 can prevent the external magnetic field from causing the detection accuracy of the magnetic sensor 3 to decrease, and at the same time can suppress the size of the vertical direction from becoming larger. Furthermore, since the contact area between the circuit board holding member 5 and the encoder base member 7 can be enlarged, vibration resistance and shock resistance can be improved.

Implementation pattern 4. The encoder 20 of Embodiment 4 of the present invention is the same as the encoder 20 of Embodiment 1 except that the shapes of the circuit board holding member 5, the magnetic field shielding plate 6 and the encoder base member 7 are different. 9 is an exploded perspective view of a circuit board, a circuit board holding member, and a magnetic field shielding plate of an encoder according to Embodiment 4 of the present invention. In the encoder 20 of the fourth embodiment, three notches 61 are formed in the magnetic field shielding plate 6. The notch 61 of the magnetic field shielding plate 6 of the encoder 20 of Embodiment 4 is an arc-shaped notch formed by partially removing the outer peripheral side of the ring. Therefore, the magnetic field shielding plate 6 is provided with a ring portion 62 that is smaller than the end surface of the circuit board holding member, and protruding radially from the outer edge of the ring portion 62 in a direction away from the central axis of the circuit board holding member 5 The shape of a plurality of protruding pieces 63.

FIG. 10 is an exploded perspective view of the encoder of Embodiment 4. FIG. The encoder base member 7 is formed with a concave portion 75 that accommodates the magnetic field shielding plate 6. The depth of the recess 75 is greater than the thickness of the magnetic field shielding plate 6. Therefore, in a state where the magnetic field shielding plate 6 is accommodated in the concave portion 75, the upper surface of the magnetic field shielding plate 6 is located below the upper surface of the encoder base member 7. Therefore, the cylindrical body 51 of the circuit board holding member 5 is not in contact with the magnetic field shielding plate 6. Therefore, when the encoder base member 7 is in contact with the circuit board holding member 5, interference between the magnetic field shielding plate 6, the circuit board holding member 5 and the encoder base member 7 is prevented.

The above-mentioned embodiment 3 shows the structure in which the magnetic field shielding plate 6 is accommodated in the recess 53 on the side of the circuit board holding member 5, and the embodiment 4 shows the structure in which the magnetic field shielding plate 6 is accommodated in the recess 75 of the encoder base member 7 However, the circuit board holding member 5 and the encoder base member 7 may be provided with recesses to prevent interference between the magnetic field shielding plate 6 and the circuit board holding member 5 or the encoder base member 7.

The encoder 20 of the embodiment 4 can prevent the external magnetic field from causing the detection accuracy of the magnetic sensor 3 to decrease, and at the same time can suppress the size of the vertical direction from becoming larger. Furthermore, since the contact area between the circuit board holding member 5 and the encoder base member 7 can be enlarged, vibration resistance and shock resistance can be improved.

The lower end portion of the circuit board holding member 5 of the encoder 20 of the embodiment 4 has no irregularities, and the strength of the circuit board holding member 5 is not impaired. Therefore, the encoder 20 of the embodiment 4 is easier to improve the vibration resistance and the shock resistance than the encoder 20 of the embodiment 3.

The configuration disclosed in the above embodiments reveals an example of the content of the present invention, and in addition, it can be combined with other well-known technologies or a part of the configuration without departing from the gist of the present invention. Omission, change, etc.

1: encoder shaft 1a: Bearing pressed rib 2: magnet 3: Magnetic sensor 4: Circuit board 5: Circuit board holding member 6: magnetic field shielding plate 7: Encoder base member 8: Bearing 9: Coupling 10: resin encoder cover 11: External magnetic field shield cover 12: Sealing member 13, 14, 15: screws 20: Encoder 21: reflective optical ruler 41: Calculation components 42: Light emitting element 43: light receiving element 51: cylinder 52, 74: convex part 53, 75: recess 61: Notch 62: Circle 63: Protruding piece 71: Groove 72: underside 73: Inner peripheral protrusion 81: Outer ring 82: inner ring

Figure 1 is a perspective view of an encoder according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view showing the configuration of the encoder of Embodiment 1. FIG. FIG. 3 is a cross-sectional view showing the configuration of the encoder of Embodiment 1. FIG. FIG. 4 is a diagram schematically showing the induction of the magnetic field caused by the external magnetic field shielding cover of the encoder of Embodiment 1. FIG. FIG. 5 is an exploded perspective view of the circuit board, the circuit board holding member, and the magnetic field shielding plate of the encoder of Embodiment 1. FIG. FIG. 6 is a cross-sectional view showing a modification of the encoder of Embodiment 1. FIG. FIG. 7 is an exploded perspective view of a circuit board, a circuit board holding member, and a magnetic field shielding plate of an encoder according to Embodiment 2 of the present invention. FIG. 8 is an exploded perspective view of a circuit board, a circuit board holding member, and a magnetic field shielding plate of an encoder according to Embodiment 3 of the present invention. 9 is an exploded perspective view of a circuit board, a circuit board holding member, and a magnetic field shielding plate of an encoder according to Embodiment 4 of the present invention. FIG. 10 is an exploded perspective view of the encoder of Embodiment 4. FIG.

1: encoder shaft

1a: Bearing pressed rib

2: magnet

3: Magnetic sensor

4: Circuit board

5: Circuit board holding member

6: magnetic field shielding plate

7: Encoder base member

8: Bearing

9: Coupling

10: resin encoder cover

11: External magnetic field shield cover

12: Sealing member

13: Screw

20: Encoder

41: Calculation components

71: Groove

72: underside

73: Inner peripheral protrusion

81: Outer ring

82: inner ring

Claims (10)

An encoder with a magnetic field shielding plate has: The encoder shaft is provided with a coupling at the lower end; The encoder base member is formed with a hole through which the encoder shaft passes; The magnet is arranged at the upper end of the aforementioned encoder shaft; The circuit board is equipped with a magnetic sensor and a calculation element that detects the magnetic field of the magnet, and the calculation element calculates the rotation angle of the encoder shaft based on the output of the magnetic sensor; The circuit board holding member has a cylindrical shape with both ends open, and the circuit board is fixed to its upper end; and The magnetic field shielding plate is provided with a portion overlapping with the cylindrical portion of the circuit board holding member when viewed along the central axis of the circuit board holding member; The magnetic field shielding plate is formed with a notch in a part of a portion of the portion of the circuit board holding member that overlaps the cylindrical portion of the circuit board holding member, The encoder base member and the circuit board holding member are in contact with each other through the notch, The encoder is provided with a convex portion which is held only by the circuit board from at least the upper surface of the encoder base member among the lower end of the circuit board holding member and the upper surface of the encoder base member The central axis of the member extends in the axial direction, and the convex portion penetrates the notch portion, whereby the encoder base member is in contact with the circuit board holding member. An encoder with a magnetic field shielding plate as described in item 1 of the patent scope, wherein, At least one of the encoder base member and the circuit board holding member is formed with a concave portion that houses the magnetic field shielding plate. An encoder with a magnetic field shielding plate as described in item 1 of the patent scope, wherein, The cylindrical portion of the circuit board holding member is not in contact with the magnetic field shielding plate system. An encoder with a magnetic field shielding plate as described in item 2 of the patent application scope, wherein, The cylindrical portion of the circuit board holding member is not in contact with the magnetic field shielding plate system. The encoder with a magnetic field shielding plate as described in item 1 of the scope of patent application includes: bearings with inner and outer rings; In addition, an inner peripheral protrusion that protrudes in a rib shape toward the central axis is formed on the inner periphery of the hole of the encoder base member, A bearing pressing rib protruding in a flange shape in the outer diameter direction is formed on the encoder shaft system, The outer ring system is fixed to the inner peripheral protrusion, The inner ring is fixed to the bearing pressing rib, The encoder base member supports the encoder shaft rotatably via the bearing. The encoder with a magnetic field shielding plate as described in item 2 of the scope of patent application includes: bearings with an inner ring and an outer ring; In addition, an inner peripheral protrusion that protrudes in a rib shape toward the central axis is formed on the inner periphery of the hole of the encoder base member, A bearing pressing rib protruding in a flange shape in the outer diameter direction is formed on the encoder shaft system, The outer ring system is fixed to the inner peripheral protrusion, The inner ring is fixed to the bearing pressing rib, The encoder base member supports the encoder shaft rotatably via the bearing. The encoder with a magnetic field shielding plate as described in item 3 of the scope of patent application includes: bearings with an inner ring and an outer ring; In addition, an inner peripheral protrusion that protrudes in a rib shape toward the central axis is formed on the inner periphery of the hole of the encoder base member, A bearing pressing rib protruding in a flange shape in the outer diameter direction is formed on the encoder shaft system, The outer ring system is fixed to the inner peripheral protrusion, The inner ring is fixed to the bearing pressing rib, The encoder base member supports the encoder shaft rotatably via the bearing. The encoder with a magnetic field shielding plate as described in item 4 of the scope of patent application includes: bearings with an inner ring and an outer ring; In addition, an inner peripheral protrusion that protrudes in a rib shape toward the central axis is formed on the inner periphery of the hole of the encoder base member, A bearing pressing rib protruding in a flange shape in the outer diameter direction is formed on the encoder shaft system, The outer ring system is fixed to the inner peripheral protrusion, The inner ring is fixed to the bearing pressing rib, The encoder base member supports the encoder shaft rotatably via the bearing. The encoder with a magnetic field shielding plate as described in any one of items 1 to 8 of the patent application scope is provided with: a light sensor that optically detects the rotation of the magnet; The magnetic sensor is a composite magnetic wire with a Barkhausen effect. The calculation element calculates the rotation angle of the encoder shaft within one turn based on the output of the optical sensor, and according to the magnetic sensor Calculate the number of turns of the encoder shaft. The encoder with a magnetic field shielding plate as described in any one of items 1 to 8 of the patent application scope, wherein, The calculation element calculates the rotation angle of the encoder shaft within one revolution based on the output of the magnetic sensor.

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