JP7499131B2 - Manufacturing method of shield member - Google Patents

Description

The present invention relates to an encoder and a motor.

In a motor in which a stator and rotor are housed in a motor case, an encoder-equipped motor is used in which an encoder case is fixed to the axial end of the motor case and an encoder that detects the rotation of the rotor is housed inside the encoder case. Patent Document 1 discloses this type of motor.

The motor in Patent Document 1 includes a motor housing (motor case) in which a first bearing holder and a second bearing holder are fixed to both ends of a cylindrical case that houses a stator and a rotor, and a cover (encoder case) is fixed to the axial end of the motor housing. An encoder is configured inside the cover. The encoder includes a permanent magnet fixed to the end of the rotating shaft via a magnet holder, and a magnetic sensor mounted on a sensor board facing the permanent magnet. The sensor board is fixed to the first bearing holder via a resin board holder. The encoder is surrounded by a shield member (shield plate) fixed to the inside of the cover.

JP 2016-86557 A Japanese Patent Application Laid-Open No. 11-275795

The encoder mounted on the motor is subject to various types of noise, and output may change depending on the product's operating environment, resulting in possible angle errors. For example, angle errors may occur due to the influence of external magnetic fields. As a measure against such noise, Patent Document 1 uses a metallic shielding member surrounding the sensor board and permanent magnet as a magnetic shield.

The magnetic shield of an encoder is generally made of materials such as soft magnetic iron, permalloy, silicon steel, and magnetic stainless steel, but these materials are expensive. Magnetic annealing has been used as a technique for improving the magnetic properties of a magnetic shield. For example, in Patent Document 2, magnetic annealing is performed on a shield tube that covers a stepping motor to improve the magnetic properties and reduce the diffusion of noise generated by the motor. This makes it possible to obtain a magnetic shielding effect similar to that of a magnetic shield made of an expensive material, even though the magnetic shield is made of a low-cost material.

However, magnetic annealing has the problem that the magnetic properties are not stable depending on the conditions and the number of times it is performed. Patent Document 2 describes that the noise reduction effect is enhanced by magnetic annealing, but does not verify the variation in magnetic properties depending on the conditions and number of times it is performed. In addition, the magnetic shield of the encoder may have hysteresis due to the influence of the permanent magnet placed inside. Therefore, the reduction and stabilization of the coercive force is required as a magnetic property, but Patent Document 2 does not verify the effect of reducing the coercive force.

In view of the above problems, the objective of the present invention is to provide an encoder equipped with a magnetic shield that is low cost and has good magnetic properties.

In order to solve the above problems, the present invention provides an encoder for detecting the rotation of a motor having a rotor with a rotating shaft and a stator radially opposed to the rotor, the encoder comprising a magnet holder fixed to one end of the rotating shaft in the axial direction, a magnet held by the magnet holder, a magnetic sensor opposed to the magnet from one side in the axial direction, a sensor board on which the magnetic sensor is disposed, and a shielding member surrounding the magnet and the magnetic sensor, the shielding member being formed from a cold-rolled steel plate and having been subjected to magnetic annealing at least twice.

According to the present invention, the magnet and the magnetic sensor are surrounded by a shielding member, which can shield the magnetic field and reduce the effect of the magnetic field on the detection angle of the encoder. The shielding member is made of cold-rolled steel plate and has been subjected to magnetic annealing at least twice. Cold-rolled steel plate is easy to procure, has low cost, and is easy to process. In addition, when the magnetic annealing process is performed to reduce the coercive force of the cold-rolled steel plate and improve its magnetic properties as a magnetic shield, the magnetic properties are not stable after one magnetic annealing process, but a low coercive force can be stably obtained by repeating the magnetic annealing process two or more times. Therefore, the encoder of the present invention is provided with a shielding member that is low cost and has good magnetic properties, so that the deterioration of detection accuracy due to the magnetic field can be suppressed.

In the present invention, it is preferable that a corrosion prevention layer is provided on the surface of the shielding member. For example, it is preferable that the corrosion prevention layer is a high-phosphorus electroless nickel plating layer with a phosphorus content of 10% or more. In this way, the corrosion prevention layer becomes non-magnetic and has more stable magnetic properties than low-phosphorus or medium-phosphorus type electroless nickel plating layers. Therefore, since the encoder is provided with a shielding member that has good magnetic properties, high environmental resistance, and is resistant to changes over time, the durability of the encoder can be improved.

In the present invention, the corrosion prevention layer may be a zinc plating layer. Alternatively, the corrosion prevention layer may be an electrocoating layer. These corrosion prevention layers are non-magnetic, and therefore have good magnetic properties and can increase the durability of the shielding member. Therefore, the durability of the encoder can be increased.

In the present invention, the magnetic annealing is preferably performed under heat treatment conditions that satisfy the following conditions 1 to 4. By performing the magnetic annealing process two or more times under such heat treatment conditions, a stable coercive force reduction effect can be obtained.
Condition 1: Heating time 60 minutes Condition 2: Annealing time 40 minutes or more Condition 3: Annealing temperature 850°C ± 10°C
Condition 4: Furnace cooling time 120 minutes

In the present invention, it is preferable that the shielding member has a bottom portion covering one axial side of the magnet and the sensor board, and a sidewall portion extending from the outer periphery of the bottom portion to the other axial side and surrounding the outer periphery of the magnet and the sensor board. In this way, the side not shielded by the stator can be covered by the shielding member, so that disturbance magnetic fields can be effectively shielded. Therefore, the effect of disturbance magnetic fields on the detection angle of the encoder can be reduced.

Next, the present invention is a motor having the above-mentioned encoder. In this way, it is possible to provide a motor with an encoder in which the effect of disturbance magnetic fields on the angle detected by the encoder is minimal.

According to the present invention, since the encoder is provided with a shielding member that surrounds the magnet and the magnetic sensor, it is possible to shield the external magnetic field, and the influence of the external magnetic field on the detection angle of the encoder can be reduced. In addition, the shielding member is formed of cold-rolled steel plate and has been subjected to magnetic annealing at least twice. Cold-rolled steel plate is easy to procure, has low cost, and has excellent workability. In addition, the inventors have confirmed that, in reducing the coercive force by magnetic annealing and improving the magnetic properties as a magnetic shield, the magnetic properties are not stable with one magnetic annealing process, but a low coercive force can be stably obtained by repeating the magnetic annealing process two or more times. Therefore, since the encoder of the present invention is provided with a shielding member that is low cost and has good magnetic properties, it is possible to suppress the deterioration of detection accuracy due to the external magnetic field.

1 is a cross-sectional view of a motor equipped with an encoder according to the present invention. 3A and 3B are a perspective view and a plan view of a shield member. 1 is a graph showing changes in magnetic properties due to magnetic annealing processing.

(overall structure)
An embodiment of a motor to which the present invention is applied will be described below with reference to the drawings. Fig. 1 is a cross-sectional view of a motor 1 equipped with an encoder 10 according to the present invention. The motor 1 includes a rotor 2 equipped with a rotating shaft 20, a stator 3 arranged on the outer periphery of the rotor 2, a cylindrical motor case 4 that houses the stator 3, a first bearing holder 5 fixed to one end of the motor case 4, a second bearing holder 6 fixed to the other end of the motor case 4, and an encoder 10 that detects the rotation of the rotor 2. The encoder 10 is housed in an encoder case 7.

The rotor 2 comprises a rotating shaft 20 and a rotor magnet 21 fixed to the outer circumferential surface of the rotating shaft 20. The rotating shaft 20 is made of a magnetic material. The rotating shaft 20 is rotatably held by a first bearing 22 held in a recess formed in the center of the first bearing holder 5, and a second bearing 23 held in a recess formed in the center of the second bearing holder 6. In this embodiment, the first bearing 22 and the second bearing 23 are ball bearings.

The rotating shaft 20 extends in the axial direction L at the radial center of the motor 1. In this specification, one side in the axial direction L is designated as L1, and the other side in the axial direction L is designated as L2. The first bearing holder 5 is fixed to an end of the motor case 4 on one side L1 in the axial direction L, and the second bearing holder 6 is fixed to an end of the motor case 4 on the other side L2 in the axial direction L. The rotating shaft 20 includes an output shaft 20A that protrudes from the first bearing holder 5 to the other side L2 in the axial direction L. Therefore, in this embodiment, the other side L2 in the axial direction L is the output side, and the one side L1 in the axial direction L is the anti-output side.

The motor case 4 is made of a non-magnetic metal such as aluminum. The stator 3 includes a stator core 30 made of a laminated core, and coils 33 wound around each of a number of salient poles 31 provided on the stator core 30 via insulators 32. The stator core 30 is fixed to the inside of the motor case 4 by shrink fitting or press fitting. An annular wiring board 34 is disposed on one side L1 of the stator 3. The wiring board 34 is electrically connected to the coils 33 via terminal pins 35 protruding from the insulator 32.

A lead wire holder 41 is fixed to the side of the motor case 4, covering a notch 40 formed in the motor case 4. A lead wire (not shown) for supplying power to the coil 33 is routed inside the lead wire holder 41, and is pulled into the inside of the motor case 4 through the notch 40 and connected to the wiring board 34.

The motor 1 is an AC servo motor, and the stator 3 is equipped with a three-phase coil 33. In this embodiment, the number of slots in which the coils 33 are arranged is 12. The rotor magnet 21 is an 8-pole magnetized magnet with N poles and S poles magnetized alternately in the circumferential direction on the outer circumferential surface. In other words, the motor 1 in this embodiment has 8 poles and 12 slots. Note that the number of poles and the number of slots of the motor 1 may be different from those described above.

The encoder case 7 is made of a non-magnetic material such as resin. The encoder case 7 has a bottom 71 that faces the second bearing holder 6 in the axial direction L, and a side wall 72 that rises from the outer periphery of the bottom 71 to the other side L2 toward the second bearing holder 6. The gap between the tip of the side wall 72 and the second bearing holder 6 is sealed with a sealing material 8. The side wall 72 is provided with an encoder wiring outlet 73 for pulling out the encoder wiring 19 connected to the encoder 10 to the outside.

(Encoder)
The encoder 10 is a magnetic encoder. The encoder 10 includes a magnet 12 fixed to a rotating shaft 20 via a magnet holder 11, and a magnetic sensor 13 facing the magnet 12 from one side L1 in the axial direction L. The magnet 12 is magnetized with one N pole and one S pole on the magnetized surface facing the magnetic sensor 13. A sensor board 14 on which the magnetic sensor 13 is disposed is fixed to the second bearing holder 6 via a board holder 15. The magnet 12 and the sensor board 14 are surrounded on the outer periphery and one side L1 by a cup-shaped shield member 16 fixed to the inside of the encoder case 7.

In the encoder 10, the magnet 12 rotates with the rotation of the rotating shaft 20, and the magnetic sensor 13 detects the change in the magnetic field caused by the rotation of the magnet 12. The magnetic sensor 13 is a magnetic sensing element such as a Hall element. The detected angle based on the output of the magnetic sensor 13 is output to the outside via the encoder wiring 19 connected to the connector 17 on the sensor board 14.

Figure 2 shows an oblique view and a plan view of the shield member 16. The shield member 16 has a circular bottom 161 and a cylindrical side wall 162 that rises from the outer periphery of the bottom 161 to the other side L2. The bottom 161 has a fitting hole 163 that fits into the protrusion 74 provided on the bottom 71 of the encoder case 7, and two positioning holes 164 are provided on both sides of the fitting hole 163. The side wall 162 also has a cutout 165 for passing the encoder wiring 19 through.

The shield member 16 is made of a magnetic material having electrical conductivity. In this embodiment, the shield member 16 is formed by pressing a cold-rolled steel plate (SPCC), and is subjected to magnetic annealing. The magnetic annealing is performed twice under heat treatment conditions that satisfy all of the following conditions 1-4. The magnetic annealing may be performed more than twice.
Condition 1: Heating time 60 minutes Condition 2: Annealing time 40 minutes or more Condition 3: Annealing temperature 850°C ± 10°C
Condition 4: Furnace cooling time 120 minutes

FIG. 3 is a graph showing the change in magnetic properties due to magnetic annealing. The inventors compared the magnetic properties of materials that have been used as magnetic shields in the past, such as electromagnetic soft iron (pure iron), permalloy, silicon steel, and electromagnetic stainless steel, with the magnetic properties of cold-rolled steel sheet (SPCC). In this case, the magnetic properties of materials that have been subjected to magnetic annealing once or twice or more were compared. As a result, as shown in FIG. 3, it was confirmed that even when cold-rolled steel sheet (SPCC) is used, if magnetic annealing is performed twice or more, magnetic properties (coercive force) equivalent to those of pure iron that has been subjected to magnetic annealing only once can be obtained. When used as a magnetic shield for the encoder 10, materials are selected with the goal of achieving a coercive force of about 1.0 A/cm or less, but it was confirmed that even low-cost cold-rolled steel sheet (SPCC) can be used as a magnetic shield with good magnetic properties by performing magnetic annealing at least twice.

The shield member 16 has a corrosion prevention layer on its surface. The process of forming the corrosion prevention layer is performed after magnetic annealing. The corrosion prevention layer may be a general zinc plating layer, but is preferably an electroless nickel plating layer. More preferably, it is an electroless nickel plating layer of a high phosphorus type (e.g., phosphorus content of 10% or more). Alternatively, electrocoating may be selected.

(Main effects of this embodiment)
As described above, the motor 1 of this embodiment includes the rotor 2 having the rotating shaft 20, the stator 3 radially facing the rotor 2, and the encoder 10 that detects the rotation of the rotor 2. The encoder 10 of this embodiment includes the magnet holder 11 fixed to an end of one side L1 in the axial direction L of the rotating shaft 20, the magnet 12 held by the magnet holder 11, the magnetic sensor 13 facing the magnet 12 from the one side L1 in the axial direction L, the sensor board 14 on which the magnetic sensor 13 is disposed, and the shield member 16 that surrounds the magnet 12 and the magnetic sensor 13. The shield member 16 is formed of a cold-rolled steel plate (SPCC) and has been subjected to magnetic annealing at least twice.

In this embodiment, the magnet 12 and the magnetic sensor 13 are surrounded by a shielding member 16, so that the disturbance magnetic field can be shielded by the shielding member 16. The shielding member 16 is made of cold-rolled steel plate (SPCC) and has been subjected to magnetic annealing at least twice. Cold-rolled steel plate (SPCC) is easy to procure, has low cost, and has excellent workability. In addition, cold-rolled steel plate (SPCC) cannot stably obtain a low coercive force by a single magnetic annealing process, and has unstable magnetic properties. However, when the magnetic annealing process is repeated two or more times, a low coercive force can be stably obtained. Therefore, the encoder 10 of this embodiment is provided with a shielding member 16 that is low cost and has good magnetic properties, and can suppress the deterioration of detection accuracy due to disturbance magnetic fields.

In this embodiment, the magnetic annealing process for the cold-rolled steel sheet (SPCC) is performed under heat treatment conditions that satisfy the following conditions 1 to 4. The present inventors have verified that a stable coercive force reduction effect can be obtained by performing the magnetic annealing process two or more times under such heat treatment conditions.
Condition 1: Heating time 60 minutes Condition 2: Annealing time 40 minutes or more Condition 3: Annealing temperature 850°C ± 10°C
Condition 4: Furnace cooling time 120 minutes

The shield member 16 has a corrosion prevention layer on its surface. For example, in this embodiment, the corrosion prevention layer is a high-phosphorus electroless nickel plating layer with a phosphorus content of 10% or more. High-phosphorus electroless nickel plating layers are non-magnetic and have more stable magnetic properties than low-phosphorus or medium-phosphorus electroless nickel plating layers. Therefore, it can be used as a shield member 16 with good magnetic properties, high environmental resistance, and resistance to aging, resulting in high durability of the encoder 10.

The corrosion prevention layer may be a zinc plating layer or an electrodeposition coating. Even when these corrosion prevention layers are used, the durability of the shield member 16 can be increased.

The shield member 16 in this embodiment has a bottom portion 161 that covers one side L1 of the magnet 12 and the sensor board 14 in the axial direction L, and a side wall portion 162 that extends from the outer periphery of the bottom portion 161 to the other side L2 in the axial direction L and surrounds the outer periphery of the magnet 12 and the sensor board 14. By using this shape, directions other than the side shielded by the stator 3 and the second bearing holder 6 (the other side L2 in the axial direction L) can be covered by the shield member 16, and disturbance magnetic fields can be effectively shielded. Therefore, the effect of disturbance magnetic fields on the detection angle of the encoder 10 can be reduced.

1...motor, 2...rotor, 3...stator, 4...motor case, 5...first bearing holder, 6...second bearing holder, 7...encoder case, 8...sealing material, 10...encoder, 11...magnet holder, 12...magnet, 13...magnetic sensor, 14...sensor board, 15...board holder, 16...shield member, 17...connector, 19...encoder wiring, 20...rotating shaft, 20A...output shaft, 21...rotor magnet, 22...first Bearing, 23...second bearing, 30...stator core, 31...salient pole, 32...insulator, 33...coil, 34...wiring board, 35...terminal pin, 40...notch, 41...lead wire holder, 71...bottom, 72...side wall, 73...encoder wiring outlet, 74...projection, 161...bottom, 162...side wall, 163...fitting hole, 164...positioning hole, 165...notch, L...axial direction, L1...one side in the axial direction, L2...other side in the axial direction

Claims (6)

A method for manufacturing a shield member that surrounds a magnet that is held via a magnet holder at one end of a rotating shaft of a motor in an axial direction, and a magnetic sensor that is disposed on a sensor substrate that faces the magnet from one side in the axial direction, comprising the steps of:
A step of manufacturing a pressed product by pressing a cold-rolled steel plate into the shape of the shield member;
and performing a magnetic annealing process at least twice on the pressed product under heat treatment conditions that satisfy the following conditions 1 to 4.
Condition 1: Heating time 60 minutes
Condition 2: Annealing time 40 minutes or more
Condition 3: Annealing temperature 850°C ±10°C
Condition 4: Furnace cooling time 120 minutes 2. The method for manufacturing a shielding member according to claim 1, further comprising the step of forming a corrosion prevention layer on the surface of the shielding member after the magnetic annealing process . 3. The method for manufacturing a shielding member according to claim 2, wherein the corrosion prevention layer is a high-phosphorus electroless nickel plating layer having a phosphorus content of 10% or more. The method for manufacturing a shielding member according to claim 2, wherein the corrosion prevention layer is a zinc plating layer. The method for manufacturing a shielding member according to claim 2, wherein the corrosion prevention layer is an electrodeposition coating. A method for manufacturing a shielding member described in any one of claims 1 to 5, characterized in that the shielding member comprises a bottom portion covering one side of the magnet and the sensor board in the axial direction, and a side wall portion extending from the outer periphery of the bottom portion to the other side in the axial direction and surrounding the outer periphery of the magnet and the sensor board .

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