Motor

Abstract

To provide a motor that is simple in structure and capable of equalizing cogging torque and output torque.SOLUTION: The motor has a stator including a coil and a stator core, a rotor rotatable relative to the stator, and a bearing disposed between the stator and the rotor. On the surface facing the stator core of the rotor, S poles and N poles are arranged alternately so that a first group of magnets and a second group of magnets are arranged along the circumferential direction. The center of the first group of magnets in the axial direction is displaced in the axial direction with respect to the center of the second group of magnets in the axial direction.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a motor. [Background technology]

[0002] For example, a direct drive motor is a motor that uses a drive method that transmits rotational force directly to a rotating body without the use of transmission mechanisms such as gears, belts, and rollers, and rotates the rotating body in a specified direction relative to the rotated body.

[0003] Patent Document 1 discloses a motor in which ten magnets are arranged circumferentially around a rotor core. The ten magnets are arranged at constant intervals in the circumferential direction (arrangement direction), and the height of the ten magnets relative to the mounting surface is also constant. If the axial position of the rotor core can be fixed accurately relative to the stator, the magnetic field generated by the magnets and the position of the stator can be optimally set by making the height of the magnets relative to the mounting surface constant. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2023-122945 A Summary of the Invention [Problem to be solved by the invention]

[0005] In a typical motor, a rolling bearing is placed between the rotor and the housing that supports the stator. The rolling bearings have variations in the shapes of their components and also have assembly errors, which can cause the stator and rotor to deviate from their reference positions. If such a deviation occurs, even if the height of the magnet relative to the mounting surface is constant, the magnetic field generated by the magnet and the position of the stator will not have an appropriate relationship, which will lead to non-uniform cogging torque and non-uniform output torque.

[0006] The present invention has been made in consideration of the above problems, and has an object to provide a motor that can achieve uniform cogging torque and uniform output torque while having a simple structure. [Means for solving the problem]

[0007] The motor of the present invention comprises: a stator having a coil and a stator core; a rotor rotatable relative to the stator; a bearing disposed between the stator and the rotor; A first group of magnets and a second group of magnets are arranged along a circumferential direction on a surface of the rotor facing the stator core such that S poles and N poles are arranged alternately, The magnets of the first group are characterized in that the axial centers of the magnets are arranged displaced in the axial direction relative to the axial centers of the magnets of the second group. Effect of the Invention

[0008] According to the present invention, it is possible to provide a motor that can achieve uniform cogging torque and uniform output torque while having a simple structure. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of a direct drive motor according to this embodiment. [Diagram 2] FIG. 2 is an enlarged cross-sectional view showing the vicinity of the motor unit of the direct drive motor according to this embodiment. [Diagram 3] FIG. 3(a) is a diagram showing the outer peripheral surface of the outer cylindrical portion to which the magnet is attached in this embodiment in an expanded state, and FIG. 3(b) is a graph showing an example of the waveform of the back electromotive force generated in the stator circuit when the stator core is displaced relative to the magnet shown in FIG. 3(a) in the direction of motor rotation. [Figure 4]FIG. 4(a) is a diagram showing the outer peripheral surface of the outer cylindrical portion to which the magnet is attached in this embodiment in an expanded state, and FIG. 4(b) is a graph showing an example of the waveform of the back electromotive force generated in the stator circuit when the stator core is displaced relative to the magnet shown in FIG. 4(a) in the direction of motor rotation. [Diagram 5] FIG. 5(a) is a diagram showing the outer peripheral surface of the outer cylindrical portion to which a magnet is attached in a comparative example in an expanded state, and FIG. 5(b) is a graph showing an example of the waveform of the back electromotive force generated in the stator circuit when the stator core is displaced relative to the magnet shown in FIG. 5(a) in the direction of motor rotation. [Figure 6] FIG. 6(a) is a diagram showing the outer peripheral surface of the outer cylindrical portion to which a magnet is attached in a comparative example in an expanded state, and FIG. 6(b) is a graph showing an example of the waveform of the back electromotive force generated in the stator circuit when the stator core is displaced relative to the magnet shown in FIG. 6(a) in the direction of motor rotation. [Figure 7] FIG. 7 is a view similar to FIG. 3(a) showing an arrangement of magnets according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a cross-sectional view of a direct drive motor 1 according to the present embodiment, which is an example of a motor. Fig. 2 is an enlarged cross-sectional view of the direct drive motor 1 and its vicinity.

[0011] The direct drive motor 1 is used in, for example, inspection equipment, machine tools, semiconductor manufacturing equipment, and the like, to drive an object.

[0012] 1, the direct drive motor 1 includes a motor section 2 for generating power, a rotation detector 3 for detecting the rotation of the motor section 2, a housing 4 for accommodating and holding the motor section 2 and the rotation detector 3, and lead wires 10 connected to the motor section 2. Although not shown in the figure, the lead wires 10 drawn from a connector (not shown) are connected to a control device that controls the direct drive motor 1.

[0013] The motor unit 2 has a stator 21 and a rotor 22 that is rotatable relative to the stator 21. The rotor 22 rotates about a rotation axis X.

[0014] The direct drive motor 1 of this embodiment is an inner rotor type. The stator 21 is disposed around the rotor 22. That is, the stator 21 is disposed radially outward of the rotor 22 with respect to the rotation axis X.

[0015] 1, the stator 21 has a stator core 25 including a plurality of teeth 23 and a yoke connecting the plurality of teeth 23, and a coil 26 supported by the stator core 25. The teeth 23 are arranged around the rotation axis X, and the coil 26 is supported by each of the plurality of teeth 23.

[0016] The coil 26 includes concentrated winding 14. The coil 26 formed by concentrated winding of the winding 14 is supported by the teeth 23. One coil 26 is disposed on one tooth 23. Here, concentrated winding refers to winding in which a winding is wound multiple times around one tooth 23, in other words, winding of one phase around one tooth 23.

[0017] 1, the winding 14 is wound around a bobbin 28, which is supported by the teeth 23. That is, the coil 26 is made up of the winding 14 concentratedly wound around the bobbin 28 and the bobbin 28 supported by the teeth 23. The coil 26 is covered by a protective cover member 6 attached to the housing 4.

[0018] A plurality of coils 26 formed by concentrically winding the winding 14 around a bobbin 28 are inserted into each of the teeth 23 .

[0019] The rotor 22 has a plurality of permanent magnets (hereinafter referred to as magnets) 13 arranged at equal intervals around the rotation axis X. The magnets 13 are attached to the outer periphery of an outer cylindrical portion 42a of a second housing 42. The outer cylindrical portion 42a constitutes a cylindrical member having a stepped surface on the outer periphery. The stator 21 and the rotor 22 face each other in the radial direction with a gap therebetween.

[0020] 1, the direct drive motor 1 has a rotation detector 3. The rotation detector 3 includes an absolute resolver and can detect the rotation of the rotor 22 of the motor unit 2 relative to the housing 4. It is preferable that the rotation detector 3 detects at least one of the rotation speed, rotation direction, and rotation angle of the rotor 22. Note that the rotation detector 3 may include not only an absolute resolver but also an incremental resolver.

[0021] The housing 4 that holds the motor unit 2 and the rotation detector 3 includes a stator housing 4A and a rotor housing 4B. The stator housing 4A has a first housing 41 and a first support member 11. The rotor housing 4B has a second housing 42 and a second support member 12.

[0022] In this embodiment, the first housing 41 and the second housing 42 are members such as double cylinders whose lower or upper ends are connected in the radial direction, the first support member 11 is a cylindrical member, and the second support member 12 is an annular member. The first housing 41 and the first support member 11 are connected by bolts (not shown) to form the stator housing 4A. The second housing 42 and the second support member 12 are connected by bolts (not shown) to form the rotor housing 4B. The central axis of the stator housing 4A, the central axis of the rotor housing 4B, and the rotation axis X are coaxial.

[0023] The stator 21 is connected to the first housing 41 constituting the stator housing 4A via the bolts BT1. As described above, the rotor 22 is configured by assembling a plurality of magnets 13 to the second support member 12 constituting the rotor housing 4B. The arrangement of the magnets 13 will be described later.

[0024] A bearing 5 is disposed between the stator housing 4A and the rotor housing 4B. As shown in Figs. 1 and 2, the bearing 5 has an inner ring 5a, an outer ring 5b, and rolling elements (balls) 5c disposed between the inner ring 5a and the outer ring 5b. The inner ring 5a of the bearing 5 is disposed by fitting onto the outer periphery of the first support member 11, and is sandwiched and held between an upper outer periphery step portion of the first support member 11 and the upper surface of the cylindrical portion of the first housing 41. That is, the inner ring 5a of the bearing 5 is fixed to the stator housing 4A.

[0025] On the other hand, the outer ring 5b of the bearing 5 is disposed by fitting onto the inner periphery of the cylindrical outer cylindrical portion 42a of the second housing 42, and is sandwiched and held between an inner periphery step portion of the outer cylindrical portion 42a and the upper surface of the second support member 12. That is, the inner ring 5a of the bearing 5 is fixed to the rotor housing 4B. The bearing 5 supports the rotor housing 4B rotatably about the rotation axis X with respect to the stator housing 4A.

[0026] In the direct drive motor 1 configured in this manner, the coil 26 supplied with power from an external source is excited within the magnetic field of the magnets 13A, 13B, and the electromagnetic force generated thereby rotates the rotor 22 relative to the stator 21, and rotates the rotor housing 4B relative to the stator housing 4A about the rotation axis X.

[0027] When a workpiece (not shown) is connected to the rotor housing 4B, the workpiece rotates together with the rotation of the rotor housing 4B. Therefore, the rotor housing 4B functions as an output shaft that rotates about the rotation axis X when the motor unit 2 is operated.

[0028] In this embodiment, the multiple magnets 13 (generic term for magnets in this embodiment) each have a common rectangular plate shape, but are divided into a first group of magnets 13A and a second group of magnets 13B, which are arranged alternately along the circumferential direction. The S pole of magnet 13A faces the stator side, and the N pole of magnet 13B faces the stator side, that is, the S poles and N poles of the magnets are arranged alternately in the circumferential direction. The magnetic forces of magnets 13A and 13B are equal to each other.

[0029] 2, the upper ends of the first group of magnets 13A are attached in contact with a stepped lower surface (also called a step surface) 42b that continues in the circumferential direction of the outer cylindrical portion 42a, and the lower ends of the second group of magnets 13B are attached in contact with an upper surface (also called a holding surface) 12a of the second support member 12 that abuts on the lower surface of the outer cylindrical portion 42a. Here, the stepped lower surface 42b is at a reference upper end position on a plane perpendicular to the axial direction, and the upper surface 12a is at a reference lower end position on a plane perpendicular to the axial direction, and the two face each other in the axial direction.

[0030] In other words, the upper end of the first group of magnets 13A is displaced in the axial direction relative to the upper end of the second group of magnets 13B, and the lower end of the first group of magnets 13A is displaced in the same axial direction relative to the lower end of the second group of magnets 13B. It can also be said that the axial center of the first group of magnets 13A is disposed displaced in the axial direction relative to the axial center of the second group of magnets 13B.

[0031] In this way, the magnets 13A of the first group and the magnets 13B of the second group are arranged to be shifted in the axial direction by a distance C. It is preferable that the distance C is equal to or greater than the maximum amount of axial relative positional deviation between the rotor 22 and the stator 21.

[0032] 3(a) and 4(a) are views showing the outer peripheral surface of the outer cylindrical portion 42a to which the magnets 13A and 13B are attached in a developed state, with the horizontal direction being the circumferential direction and the vertical direction being the axial direction. The relative axial positions of the rotor and the stator are different between FIG. 3(a) and FIG. 4(a). In FIG. 3(a) and FIG. 4(a), the trajectory of the upper end position of the stator core 25 relative to the outer cylindrical portion 42a is shown by a dotted line UP, and the trajectory of the lower end position of the stator core 25 is shown by a dotted line LP. Here, the distance L1 between the step lower surface 42b of the outer cylindrical portion 42a and the upper surface 12a of the second support member 12 is greater than the distance L2 between the upper and lower ends of the stator core 25.

[0033] 3(b) and 4(b) are graphs showing examples of the waveform of the back electromotive force generated in the stator circuit when stator core 25 is displaced relative to magnets 13A and 13B shown in Figures 3(a) and 4(a) in the direction of motor rotation, with the vertical axis representing the back electromotive force and the horizontal axis representing the relative positions of magnets 13A and 13B and stator core 25. The waveform of the back electromotive force changes like a sine curve, reaching a maximum value when the center of stator core 25 coincides with the circumferential center of N-pole magnet 13B and a minimum value when the center of stator core 25 coincides with the circumferential center of S-pole magnet 13A.

[0034] (Comparison with comparative examples) The effects of this embodiment will be described below with reference to a comparative example. Figures 5(a) and 6(a) are views showing the outer peripheral surface of the outer cylindrical portion 42a to which magnets 13A' and 13B' according to the comparative example are attached in a developed state, with the horizontal direction being the circumferential direction and the vertical direction being the axial direction. The relative axial positions of the rotor and stator are different between Figures 5(a) and 6(a).

[0035] 5(a) and 6(a), the upper ends of the first group of magnets 13A' and the second group of magnets 13B' are both attached in contact with the step lower surface 42b of the outer cylindrical portion 42a, and the lower ends of the first group of magnets 13A' and the second group of magnets 13B' are attached in contact with the upper surface 12a of the second support member 12. Therefore, the first group of magnets 13A' and the second group of magnets 13B' are disposed at the same position in the axial direction, and there is no relative misalignment. The magnets 13A and 13B of this embodiment are the same as the magnets 13A' and 13B' of the comparative example.

[0036] 5(a) and 6(a), the trajectory of the upper end position of stator core 25 relative to outer cylindrical portion 42a is indicated by dotted line UP, and the trajectory of the lower end position of stator core 25 is indicated by dotted line LP. Distance L1' between step lower surface 42b of outer cylindrical portion 42a and the upper surface of upper surface 12a of second support member 12 is equal to distance L2' between the upper and lower ends of stator core 25.

[0037] Figures 5(b) and 6(b) are graphs showing examples of waveforms of back electromotive force generated in the stator circuit when the stator core 25 is displaced relative to the magnets 13A', 13B' shown in Figures 5(a) and 6(a) in the direction of motor rotation.

[0038] Here, since there is variation in the shapes of the components in the bearing 5 of the direct drive motor 1, the center position of the inner ring 5a and the center position of the outer ring 5b of the bearing 5 may be misaligned in the axial direction, which may cause the axial center of the magnets 13A', 13B' to be misaligned with the axial center of the stator core 25, resulting in a malfunction.

[0039] In the comparative example, when the axial center of magnets 13A', 13B' coincides with the axial center of stator core 25 as shown in FIG. 5(a), a back electromotive force waveform as shown in FIG. 5(b) is obtained, and the total amplitude at that time is TA3.

[0040] In contrast, when the axial center of magnets 13A', 13B' is misaligned with the axial center of stator core 25 as shown in Fig. 6(a), a back electromotive voltage waveform as shown in Fig. 6(b) is obtained, the total amplitude at that time is TA4, and TA3>TA4. This is because the misalignment of the axial center of magnets 13A', 13B' with the axial center of stator core 25 reduces the magnetic field strength received by stator core 25, and therefore reduces the back electromotive voltage.

[0041] 5(a) can be maintained, a back electromotive force waveform with the highest total amplitude can be obtained, thereby improving the efficiency of the direct drive motor 1. However, in reality, axial misalignment occurs between the rotor and the stator due to variations in the shape of the bearing 5, etc., and the magnetic field strength received by the stator core 25 is significantly reduced, which leads to non-uniformity in the cogging torque and also in the output torque.

[0042] (Action of this embodiment) In contrast, according to this embodiment, the upper ends of the first group of magnets 13A are attached at the upper end reference position by abutting against the step lower surface 42b of the outer cylindrical portion 42a, and the lower ends of the second group of magnets 13B are attached at the lower end reference position by abutting against the upper surface 12a of the second support member 12. In other words, the axial center positions of the first group of magnets 13A and the second group of magnets 13B are relatively shifted in the axial direction by a distance C, and as a result, the magnetic fields generated by the magnets 13A and 13B are formed with a deviation in the axial direction.

[0043] As shown in FIG. 3(a), when the axial center of the upper end reference position and the lower end reference position coincides with the axial center of the stator core 25 (the distance between the step lower surface 42b and the upper end position UP is equal to the distance between the upper surface 12a and the lower end position LP), a back electromotive voltage waveform as shown in FIG. 3(b) is obtained, and the total amplitude at that time is TA1. At this time, TA1 <TA3である。

[0044] 4(a), when the rotor and stator are misaligned in the axial direction, the axial center of magnet 13A and the axial center of stator core 25 move away from each other, but the axial center of magnet 13B and the axial center of stator core 25 move closer to each other. Obviously, when the rotor and stator are misaligned in the opposite direction, the axial center of magnet 13B and the axial center of stator core 25 move away from each other, but the axial center of magnet 13A and the axial center of stator core 25 move closer to each other. Therefore, even if the magnetic field strength of the N (or S) pole that stator core 25 receives decreases, the magnetic field strength of the S (or N) pole that stator core 25 receives increases, and the output of direct drive motor 1 changes very little.

[0045] As a result, a back electromotive force waveform as shown in FIG. 4(b) is obtained, and the total amplitude at this time is TA2, and the numerical difference between TA2 and TA1 is almost equal or relatively small.

[0046] From the above, the relational expression |TA1-TA2|<(TA3-TA4) is obtained. This relational expression means that the change in the back electromotive force with respect to the misalignment between the rotor and the stator is smaller in this embodiment than in the comparative example. In other words, even if the rotor and the stator are misaligned in the axial direction, this embodiment can suppress the output reduction of the direct drive motor 1, and therefore, even with a simple structure, it is possible to achieve uniform cogging torque and uniform output torque.

[0047] (Modification) Fig. 7 is a diagram similar to Fig. 3(a) showing the arrangement of magnets 13M (generic term for magnets of modified examples) according to a modified example. The magnets 13M are composed of a first group including a plurality of magnet units UT1 each consisting of a magnet 13A with its S pole facing the stator and a magnet 13C with its N pole facing the stator, and a second group including a plurality of magnet units UT2 each consisting of a magnet 13B with its S pole facing the stator and a magnet 13D with its N pole facing the stator. The magnet units UT1 and magnet units UT2 are arranged alternately in the circumferential direction, and the magnets with S poles and the magnets with N poles are arranged alternately in the circumferential direction.

[0048] The upper ends of magnets 13A and 13C of magnet unit UT1 are attached in contact with the stepped lower surface 42b of the outer cylindrical portion 42a, and the distance between their lower ends and the upper surface 12a of the second support member 12 is C. The lower ends of magnets 13B and 13D of magnet unit UT2 are attached in contact with the upper surface 12a of the second support member 12 (FIG. 2), and the distance between their upper ends and the stepped lower surface 42b is C.

[0049] In this way, the same effect as in this embodiment can be obtained by treating multiple magnets as one magnet unit, positioning the upper end of the magnet at the upper end reference position for each magnet unit, and positioning the lower end of the magnet at the lower end reference position.

[0050] The present invention is not limited to the above-mentioned embodiment, and the configurations of the embodiment may be combined with each other, and modifications and applications by those skilled in the art based on the description in the specification and well-known techniques are also contemplated by the present invention and are included in the scope of protection sought. For example, the present invention is not limited to direct drive motors, and can be applied to general motors and rotation sensors with similar arrangements. When applied to a rotation sensor, the magnetic field received by the windings becomes more uniform in order to detect the rotation position and rotation speed, and stable detection accuracy can be obtained.

[0051] As described above, the present specification discloses the following: (1) a stator having a coil and a stator core; a rotor rotatable relative to the stator; a bearing disposed between the stator and the rotor; A first group of magnets and a second group of magnets are arranged along a circumferential direction on a surface of the rotor facing the stator core such that S poles and N poles are arranged alternately, The axial centers of the magnets of the first group are axially displaced from the axial centers of the magnets of the second group. A motor characterized by: According to this configuration, it is possible to achieve uniform cogging torque and uniform output torque with a simple structure.

[0052] (2) The magnets of the first group and the magnets of the second group have a common shape. The motor described in (1) is characterized in that According to this configuration, it is possible to more efficiently achieve uniformity of the cogging torque and uniformity of the output torque.

[0053] (3) one end of the first group of magnets is displaced axially relative to one end of the second group of magnets; The other end of the first group of magnets is displaced in the same axial direction relative to the other end of the second group of magnets. The motor according to (1) or (2), characterized in that According to this configuration, the axial installation positions of the first group of magnets and the second group of magnets can be easily and reliably aligned.

[0054] (4) The rotor has a cylindrical member having a stepped surface on the outer periphery thereof, the one end of the first group of magnets abuts against a stepped surface of the cylindrical member, the other end of the second group of magnets faces the step surface and abuts against a holding surface of a support member attached to the cylindrical member; The motor according to (3) above. According to this configuration, the first group of magnets and the second group of magnets can be smoothly provided at predetermined positions.

[0055] (5) The magnets of the first group are arranged so that their south poles face the stator core, The second group of magnets has a north pole facing the stator core, the magnets of the first group are disposed between the magnets of the second group, and the magnets of the second group are disposed between the magnets of the first group; The motor according to any one of (1) to (4) above. According to this configuration, even if the rotor and the stator are misaligned in the axial direction, a decrease in the output of the motor can be suppressed.

[0056] (6) The first group of magnets includes a plurality of first magnet units including a magnet with an S pole facing the stator core and a magnet with an N pole facing the stator core, the second group of magnets includes a plurality of second magnet units including a magnet with an S pole facing the stator core and a magnet with an N pole facing the stator core, The first magnet units are disposed between the second magnet units, and the second magnet units are disposed between the first magnet units. The motor according to any one of (1) to (4) above. According to this configuration, even if the rotor and the stator are misaligned in the axial direction, a decrease in the output of the motor can be suppressed. [Explanation of symbols]

[0057] 1 Direct Drive Motor 2 Motor section 3 Rotation detector 4A stator housing 4B rotor housing 5. Bearings 6 Protective cover material 11 First support member 12 Second support member 13 Permanent magnets 14 Windings 21 Stator 22 Rotor 23 Teeth 41 1st Housing 42 Second Housing

Claims

1. a stator having a coil and a stator core; a rotor rotatable relative to the stator; a bearing disposed between the stator and the rotor; A first group of magnets and a second group of magnets are arranged along a circumferential direction on a surface of the rotor facing the stator core such that S poles and N poles are arranged alternately, The axial centers of the magnets of the first group are axially displaced from the axial centers of the magnets of the second group. A motor characterized by:

2. The magnets of the first group and the magnets of the second group have a common shape.

2. The motor according to claim 1 .

3. one end of the first group of magnets is axially displaced relative to one end of the second group of magnets; the other end of the first group of magnets is displaced in the same axial direction relative to the other end of the second group of magnets; 2. The motor according to claim 1 .

4. The rotor has a cylindrical member having a stepped surface on an outer circumferential side, the one end of the first group of magnets abuts against a stepped surface of the cylindrical member, the other end of the second group of magnets faces the step surface and abuts against a holding surface of a support member attached to the cylindrical member; 4. The motor according to claim 3.

5. The first group of magnets has a south pole facing the stator core, The second group of magnets has a north pole facing the stator core, the magnets of the first group are disposed between the magnets of the second group, and the magnets of the second group are disposed between the magnets of the first group; The motor according to any one of claims 1 to 4.

6. the first group of magnets includes a plurality of first magnet units including a magnet with an S pole facing the stator core and a magnet with an N pole facing the stator core, the second group of magnets includes a plurality of second magnet units including a magnet with an S pole facing the stator core and a magnet with an N pole facing the stator core, the first magnet units are disposed between the second magnet units, and the second magnet units are disposed between the first magnet units. The motor according to any one of claims 1 to 4.

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