electric machine

Abstract

A motor includes a rotor having a plurality of magnetized magnetic poles and rotating around a rotation axis, and a stator including a plurality of stator teeth. Then, when the number of the plurality of magnetic poles is defined as Nm, the number of the plurality of stator teeth is defined as the number of teeth Ns, an angle of a gap between the magnetic poles on a circumference of a circle centered on the rotation axis and having a facing surface reference radius rd is defined as Pm [degrees], an angle occupied by the magnetic poles on the circumference of the circle centered on the rotation axis and having the facing surface reference radius rd is defined as m [degrees], and an angle occupied by the stator teeth on the circumference of the circle centered on the rotation axis and having the facing surface reference radius rd is defined as s [degrees], Pm is set so as to minimize a difference between a maximum value and a minimum value of L(ω) represented by the following formula (1). Here, x(k, ψ) in formula (1) is represented by formula (2), and a and b in formula (2) are represented by formula (3). Formula (1)

Description

Technical Field

[0001] This technology relates to an electric motor, and more particularly to technology related to axial clearance motors. Background Technology

[0002] In related art, an axial gap motor is known, wherein a magnet disposed in a rotor and stator teeth disposed in a stator are arranged to face each other axially (e.g., see PTL 1). In the stator for an axial gap motor, a plurality of stator teeth are arranged circumferentially at equal intervals, projecting toward a surface side of the stator base, and coils are mounted on each stator tooth.

[0003] Reference List

[0004] Patent documents

[0005] PTL 1: JP 2011-24291A Summary of the Invention

[0006] Technical issues

[0007] In axially backlash motors, when no drive current is supplied to the coils, an attractive force is generated between the magnets and the stator teeth due to the magnetic force of the magnets. This attractive force results in cogging torque when the rotor rotates without a drive current supply to the coils. Cogging torque causes vibration and noise in the motor drive itself. Therefore, there is a need to reduce cogging torque in axially backlash motors.

[0008] Therefore, it is necessary to reduce cogging torque with a simple construction.

[0009] Solution to the problem

[0010] An electric motor according to an embodiment of the present technology includes a rotor and a stator, the rotor having a plurality of magnetized poles and configured to rotate about a rotation axis, and the stator including a plurality of stator teeth.

[0011] The magnetic poles and stator teeth are separated from each other in a first direction, which is parallel to the axis of rotation. The plurality of magnetic poles are arranged at equal intervals on a first circumference centered on the axis of rotation, and the plurality of stator teeth are arranged at equal intervals on a second circumference centered on the axis of rotation.

[0012] When the number of the plurality of magnetic poles is defined as Nm and the number of the plurality of stator teeth is defined as Ns, when the rotor and stator are viewed in a plan view from a first direction, and when the distance from the rotation axis to the midpoint of the area where the magnetic poles and stator teeth overlap in a second direction perpendicular to the first direction is defined as the opposing surface reference radius rd, the angle of the circumferential spacing between the magnetic poles is defined as Pm [degrees], and the angle occupied by the magnetic poles on the circumference of a circle centered on the rotation axis and having the opposing surface reference radius rd is defined as... When m [degrees], the angle occupied by the stator teeth on the circumference of a circle centered on the rotation axis and having a reference radius rd of the opposing surface is defined as s[degree], Pm is set such that the difference between the maximum and minimum values ​​of L(ω) as expressed by equation (1) is minimized.

[0013] [Expression 1]

[0014] Here, 0 ≤ ψ ≤ 360 / Nm [degrees] is satisfied, ω is the rotation angle of the rotor, x(k, ψ) in expression (1) is represented by expression (2), and a and b in expression (2) are represented by expression (3).

[0015] [Expression 2]

[0016] [Expression 3] Attached Figure Description

[0017] Figure 1 This is a cross-sectional view of an axial clearance motor.

[0018] Figure 2 This is an exploded 3D view of an axial clearance motor.

[0019] Figure 3 It is a diagram showing the definitions of various dimensions related to magnets and stator teeth.

[0020] Figure 4 This is a graph showing the relationship between Ps(θ) and x(k, ψ).

[0021] Figure 5 This is a diagram showing the number of effective stator teeth relative to the phase of the magnet.

[0022] Figure 6 This shows how to change ω and A graph of the length L obtained from m.

[0023] Figure 7 This is a diagram showing the configuration of the rotor according to a variant.

[0024] Figure 8 This is a diagram showing the structure of a stator tooth based on a variant.

[0025] Figure 9 This is a diagram showing the structure of a stator tooth based on a variant. Detailed Implementation

[0026] The embodiments will be described below in the following order.

[0027] 1. Motor configuration

[0028] 2. The relationship between the magnet and the stator teeth

[0029] 3. Usage Example

[0030] 4. Variation

[0031] 5. Overview of the Implementation Examples

[0032] 6. This technology

[0033] 1. Configuration of Motor 1

[0034] Figure 1 This is a cross-sectional view of the axial clearance motor 1. Figure 2 This is an exploded perspective view of the axial clearance motor 1. Hereinafter, the direction along the rotation axis of the rotor 3 is referred to as the axial direction. The direction orthogonal to and passing through the rotation axis of the rotor 3 is defined as the radial direction. The direction along the circumference surrounding the rotation axis of the rotor 3 is defined as the circumferential direction.

[0035] like Figure 1 and Figure 2 As shown, motor 1 is an axial gap type brushless motor, including housing 2, rotor 3 and fixed part 4. The rotor 3 is rotatably arranged relative to housing 2, and the fixed part 4 is fixed to housing 2.

[0036] The housing 2 is formed by integrating a cylindrical portion 2a, an inner flange portion 2b, and an outer flange portion 2c. The cylindrical portion 2a is cylindrical. The inner flange portion 2b is continuously formed to one end of the cylindrical portion 2a. The inner flange portion 2b is annular and extends radially inward from one end of the cylindrical portion 2a. The outer flange portion 2c is annular and extends radially outward from a midpoint along the axial direction of the cylindrical portion 2a.

[0037] The rotor 3 is rotatably supported inside the cylindrical section 2a via bearings 5 ​​and 6. The rotor 3 includes a shaft 11, a rotor yoke 12, and a plurality of magnets 13.

[0038] The shaft 11 is cylindrical. The outer diameter of the shaft 11 is smaller than the inner diameter of the inner flange 2b, and one end of the shaft 11 is inserted into a hole drilled at the center of the inner flange 2b. Viewed from one end of the shaft 11, the shaft 11 integrally forms a flange 11a with an annular shape, which extends radially outward on the other end side in the axial direction. Furthermore, the shaft 11 integrally forms a stepped portion 11b with an outer diameter larger than the shaft 11, and the stepped portion 11b is located closer to one end than the flange 11a. The flange 11a and the stepped portion 11b are continuously formed in the axial direction of the shaft 11.

[0039] The rotor yoke 12 contacts the surface of the flange portion 11a on the side opposite to the housing 2. The rotor yoke 12 is formed as a ring and is fixed to the flange portion 11a by fastening members 8 such as screws. Therefore, the rotor yoke 12 rotates integrally with the shaft 11.

[0040] The rotor yoke 12 is formed to be longer in the radial direction than the flange portion 11a, and a plurality of magnets 13 are attached to the opposing surface 12a facing the fixed portion 4. Viewed axially, the magnets 13 are formed in a generally trapezoidal shape, wherein the circumferential length of the magnets 13 increases radially outward. Furthermore, the magnets 13 are arranged on the circumference of a first circle centered on the rotation axis of the rotor 3, and are spaced apart from each other at equal intervals in the circumferential direction. Note that each of the plurality of magnets 13 is formed to have approximately the same dimensions.

[0041] Between adjacent magnets 13, different magnetic poles are arranged facing the fixed portion 4. In other words, multiple magnets 13 are arranged such that different magnetic poles are arranged alternately circumferentially. Therefore, magnets 13 can be described as magnetic poles, and this also applies to the following description.

[0042] The fixing part 4 is attached to the opposing surface 2d of the outer flange 2c of the housing 2, and the opposing surface 2d faces the magnet 13. The fixing part 4 includes a stator 21, a plurality of coils 22 and a flexible printed circuit board 23.

[0043] The stator 21 is formed by integrating a stator base 31 and a plurality of stator teeth 32. The stator base 31 is formed in an annular shape and contacts the opposing surface 2d. The stator base 31 is then fixed to the outer flange portion 2c by fastening members 9 such as screws.

[0044] A plurality of stator teeth 32 protruding axially are formed on the surface of the stator base 31 facing the magnet 13. The stator teeth 32 are formed of a magnetic material and, when viewed axially, have a generally trapezoidal shape in which the circumferential length of the stator teeth 32 increases radially outward. Furthermore, the stator teeth 32 are arranged at equal intervals along the circumferential direction of a second circle centered on the rotation axis of the rotor 3. Note that each of the plurality of stator teeth 32 is formed to have substantially the same dimensions. Furthermore, the second circle may have the same dimensions as the first circle, or it may have different dimensions.

[0045] Coil 22 is wound around stator teeth 32. Flexible printed circuit board 23 is connected to coil 22 and generates a rotating magnetic field by supplying drive current input from a control device (not shown) to coil 22 via flexible printed circuit board 23. In motor 1, rotor 3 rotates by the generated rotating magnetic field.

[0046] Note that the flexible printed circuit board 23 is arranged circumferentially further outward than the location where the stator teeth 32 are formed at the stator base 31, and is sandwiched between the stator base 31 and the coil 22.

[0047] Bearings 5 ​​and 6 are sandwiched between shaft 11 and cylindrical portion 2a. Bearings 5 ​​and 6 are separated from each other along the axial direction, and a pressure-applying assembly 7 is sandwiched between bearings 5 ​​and 6 in the axial direction.

[0048] Bearings 5 ​​and 6 are radial ball bearings, each comprising an inner ring, an outer ring, and a plurality of balls. Bearing 5 includes an inner ring that contacts the shaft 11 radially and an outer ring that contacts the cylindrical portion 2a radially and the inner flange portion 2b axially. Bearing 6 includes an inner ring that contacts the shaft 11 radially and the stepped portion 11b axially and an outer ring that contacts the cylindrical portion 2a radially.

[0049] The pressure-applying assembly 7 includes a spring and a washer. The pressure-applying assembly 7 applies force to the inner rings of bearing 5 and bearing 6 in a direction in which their inner rings are separated from each other. Furthermore, the pressure-applying assembly 7 applies force to the outer rings of bearing 5 and bearing 6 in a direction in which their outer rings are separated from each other.

[0050] The rotor 3 and housing 2 are subjected to a force acting in the direction that brings the rotor 3 and housing 2 closer together due to the attraction between them (i.e., the attraction between the magnet 13 and the stator teeth 32). At this time, the inner ring of bearing 6 is pressed against the inner flange 2b by the stepped portion 11b, and the inner ring of bearing 5 is also pressed against the inner flange 2b by the pressure-applying assembly 7. In addition, the outer ring of bearing 5 is pressed against the rotor yoke 12 by the inner flange 2b, and the outer ring of bearing 6 is also pressed against the rotor yoke 12 by the pressure-applying assembly 7.

[0051] Therefore, in each of bearings 5 ​​and 6, an axial force is applied to the inner ring from the rotor yoke 12 toward the inner flange 2b, and an axial force is applied to the outer ring from the inner flange 2b toward the rotor yoke 12. As a result, in each of bearings 5 ​​and 6, shear force is applied to the balls, and thus the clearance between the inner ring, balls, and outer ring is reduced.

[0052] The retaining ring 10 is attached to the shaft 11 on the side opposite to the bearing 5, with the inner flange 2b sandwiched between them, and prevents the rotor 3 from falling off the housing 2.

[0053] 2. The relationship between magnet 13 and stator teeth 32

[0054] In motor 1, when no drive current is supplied to coil 22, an attractive force is generated between magnet 13 and stator teeth 32 due to the magnetic force of magnet 13. Therefore, in motor 1, when rotor 3 rotates without drive current supplied to coil 22, cogging torque is generated that causes a sticking sensation.

[0055] Cogging torque causes vibration and noise during the rotation of rotor 3, and therefore it is desirable to reduce cogging torque. Therefore, in this embodiment, cogging torque is reduced by adjusting the spacing between magnets 13.

[0056] Figure 3 This is a diagram illustrating the definitions of various dimensions associated with magnet 13 and stator teeth 32. In the following text, the axis of rotation of rotor 3 may be referred to as axis of rotation O. Figure 3 As shown, when the magnet 13 and stator teeth 32 are viewed in a plan view from the axial direction, the distance from the rotation axis O to the radial midpoint of the area where the magnet 13 and stator teeth 32 overlap is defined as the opposing surface reference radius rd. Furthermore, a circle centered on the rotation axis O and having the opposing surface reference radius rd is defined as the intermediate circle Cm.

[0057] Then, the angle occupied by a magnet 13 on the circumference of the intermediate circle Cm is defined as the magnetic pole angle. m [degrees]. The angle between magnets 13 on the circumference of the intermediate circle Cm is defined as the pitch angle Pm [degrees]. The angle occupied by a stator tooth 32 on the circumference of the intermediate circle Cm is defined as the tooth angle. s[degree].

[0058] Furthermore, the number of magnets 13 is defined as the number of magnetic poles Nm, and the number of stator teeth 32 is defined as the number of teeth Ns.

[0059] Here, the magnitude of the attractive force of the magnet 13 is simplified to be equal to the area of ​​the magnet 13 and the stator tooth 32 facing each other, that is, the area of ​​the magnet 13 and the stator tooth 32 overlapping each other when viewed from the axial direction in a plan view.

[0060] Furthermore, since the arc length L of the overlap between the magnet 13 and the stator tooth 32 on the circumference of the intermediate circle Cm is proportional to the area of ​​the magnet 13 and the stator tooth 32 facing each other, the magnitude of the attractive force of the magnet 13 can be evaluated using the length L.

[0061] The method for calculating the length L will be described below. Here, the function Fs(θ) indicating whether stator teeth 32 exist on the circumference of the intermediate circle Cm is represented by expression (4).

[0062] [Expression 4]

[0063] Here, θ is the circumferential angle.

[0064] The range in which Fs(θ) becomes 1 is the range in which stator teeth 32 exist on the circumference of the intermediate circle Cm. On the other hand, the range in which Fs(θ) becomes 0 is the range in which stator teeth 32 do not exist on the circumference of the intermediate circle Cm.

[0065] Furthermore, the function Fm(θ′,t) indicating whether there is a magnet 13 on the circumference of the intermediate circle Cm is represented by expression (5).

[0066] [Expression 5]

[0067] Here, g(t) is a function representing the time t of the angle change of rotor 3.

[0068] The range in which Fm(θ′,t) becomes 1 is the range in which magnet 13 exists on the circumference of the intermediate circle Cm. On the other hand, the range in which Fm(θ′,t) becomes 0 is the range in which magnet 13 does not exist on the circumference of the intermediate circle Cm.

[0069] Then, the length L to be calculated is obtained by integrating within the range of 0 ≤ θ ≤ 360 [degrees] where both Fs(θ) and Fm(θ′,t) become 1. Here, the calculation becomes complicated because many cases need to be analyzed in order to calculate the product of the rectangular waves represented by Fs(θ) and Fm(θ′,t). Therefore, considering the symmetrical configuration of magnet 13 and stator teeth 32, the length L is expressed by expression (1) as a function of the rotation angle ω of rotor 3.

[0070] [Expression 6]

[0071] Here, 0 ≤ ψ ≤ 360 / Nm [degrees] is satisfied, and ω is the rotation angle of rotor 3. In addition, x(k,ψ) in expression (1) is represented by expression (2), and a and b in expression (2) are represented by expression (3).

[0072] [Expression 7]

[0073] [Expression 8]

[0074] Figure 4 This is a graph showing the relationship between Ps(θ) and x(k,ψ). Figure 4 An example is shown where the number of magnetic poles Nm = 10 and the number of teeth Ns = 12. Figure 4 A is a schematic diagram showing Fs(θ). Figure 4 B is a schematic diagram showing x(k,ψ).

[0075] Figure 4 The colored region in A represents stator tooth 32. Therefore, the tooth region is the region satisfying the function Fs(θ) = 1, and the region between adjacent tooth regions is the region satisfying Fs(θ) = 0. Note that in the following text, Figure 4 The colored area in A is called the tooth region.

[0076] exist Figure 4 In the example shown in A, the number of teeth Ns is 12, so there are 12 tooth regions. In addition, k in expression (1) corresponds to the number of stator teeth 32 in the clockwise direction, and the predetermined number of stator teeth 32 is 0.

[0077] exist Figure 4 In A, the area between adjacent tooth regions represents the area where stator teeth 32 do not exist.

[0078] Figure 4 The length of the arc depicted by the thick line in A corresponds to the tooth angle. s[degree]. In Figure 4 In A, corresponding to the tooth angle The thick arc of s[degree] is shown as shifting sequentially in a clockwise direction to become radially further away starting from k=0.

[0079] Then, in expression (3), a represents the starting point of the arc drawn by the thick line, and b in expression (3) represents the ending point of the arc drawn by the thick line.

[0080] also, Figure 4 The region enclosed by the dashed line in A, that is, the sector-shaped region separated by straight lines extending radially from the axis of rotation, is represented by the angular range obtained by dividing 360 [degrees] by the number of magnetic poles Nm. In the following text, the sector-shaped region is referred to as the magnetic region. Note that in Figure 4 In A, only one of the multiple magnet regions is indicated by a dashed line.

[0081] exist Figure 4 In the example shown in A, the number of magnetic poles Nm is 10, therefore there are 10 magnetic regions. The central angle of the magnetic region corresponds to the magnetic pole angle. The sum of m [degrees] and pitch angle Pm [degrees].

[0082] Here, the magnet 13 and the stator teeth 32 are arranged symmetrically. Therefore, as... Figure 4 As shown in B, by taking into account the symmetrical arrangement of magnet 13 and stator teeth 32, the domain of Fs(θ) 0≤θ≤360[degrees] is transformed into a magnet region 0≤ψ≤360 / Nm[degrees], thereby obtaining the function x(k,ψ).

[0083] In other words, when Figure 4 When the ten magnet regions shown in A are overlapped to form one region, the following is obtained: Figure 4 The colored region in B.

[0084] Therefore, the function x(k,ψ) is a function that indicates 1 when the kth stator tooth 32 exists at a specific phase ψ and indicates 0 when the kth stator tooth 32 does not exist at a specific phase ψ.

[0085] At this time, when a stator tooth 32 exists in a magnet region, a < b is satisfied in the range where the stator tooth 32 exists, and therefore the relation in the upper part of expression (2) is satisfied, and the relation in the lower part of expression (2) is satisfied in the range where the stator tooth 32 does not exist.

[0086] On the other hand, when a stator tooth 32 exists across different magnet regions, since b < a, the relationship in the middle part of expression (2) is satisfied within the range where the stator tooth 32 exists, and the relationship in the lower part of expression (2) is satisfied within the range where the stator tooth 32 does not exist.

[0087] Expression (1)

[0088] [Expression 9]

[0089] This indicates the number of stator teeth 32 present at a specific phase ψ. Figure 4 In phase ψ shown in B, six stator teeth 32 exist in the magnet region. Note that, in the following text, the stator teeth 32 present at a specific phase ψ may be referred to as effective stator teeth 32.

[0090] Figure 5 This is a diagram showing the number of effective stator teeth 32 relative to phase ψ. Figure 5 In the diagram, the horizontal axis represents the phase ψ, and the vertical axis represents the number of effective stator teeth 32. Furthermore, in... Figure 5In the example shown, since the number of magnetic poles Nm = 10 and 0 ≤ ψ ≤ 36 [degrees], the number of effective stator teeth 32 is shown in the range of 0 [degrees] to 36 [degrees].

[0091] In addition, Figure 5 In the middle, the range in which magnet 13 exists, that is, the range corresponding to the magnetic pole angle. The range of m [degrees] is colored. The colored range moves as the rotor 3 rotates.

[0092] like Figure 5 As shown, the number of effective stator teeth 32 varies depending on the phase ψ. Figure 5 In the example shown, for instance, when the phase ψ is 0 [degrees], the number of effective stator teeth 32 is six, and when the phase ψ is 5 [degrees], the number of effective stator teeth 32 is four.

[0093] Although the number of effective stator teeth 32 within the magnet range has been described above, the actual length L(ω) of the mutual attraction between the magnet 13 and the stator teeth 32 is obtained by integration. Figure 5 The value is obtained by coloring the range in the code.

[0094] In other words, expression (1) produces by integration Figure 5 The value is obtained by measuring the number of effective stator teeth 32 within the coloring range.

[0095] Here, as mentioned above, the magnet range corresponds to the magnetic pole angle. The magnetic pole angle is the sum of m (degrees) and the pitch angle Pm. Therefore, the magnetic pole angle can be changed by changing the pitch angle Pm. m [degrees].

[0096] The rotation of rotor 3 corresponds to the change in phase ψ over the integration range.

[0097] Figure 6 This illustrates how changing the rotation angle ω and the magnetic pole angle... A graph of the length L(ω) obtained from m. Figure 6 The horizontal axis represents the rotation angle ω of rotor 3, and Figure 6 The vertical axis represents the length L(ω).

[0098] also, Figure 6 According to magnetic pole angle The increments of m from 28 degrees to 36 degrees in 1 degree increments indicate the length L(ω).

[0099] Here, although only the range of rotation angle ω from 0 degrees to 6 degrees is shown, due to the symmetrical geometry, the number of magnetic poles Nm and the number of teeth Ns repeat every 6 degrees, so only this range is shown.

[0100] In addition, when the magnetic pole angle When m is 29 degrees or greater, only a portion of the range of the rotation angle ω is shown for the length L(ω), but the range showing the maximum and minimum values ​​is plotted.

[0101] exist Figure 6 In the example shown, when the magnetic pole angle is satisfied... When m = 30 degrees, the difference between the maximum and minimum values ​​of length L is minimized. In this way, motor 1 is designed with magnetic pole angles... m and pitch angle Pm, in the magnetic pole angle The difference between the maximum and minimum values ​​of length L at pitch angle Pm and m is minimized. Therefore, in motor 1, even when rotor 3 rotates, the change in the attractive force between magnet 13 and stator teeth 32 is minimized. Thus, motor 1 can reduce cogging torque. In this case, there is no need to complicate the shapes of magnet 13 and stator teeth 32.

[0102] 3. Usage Example

[0103] The motor 1 described above can be used as a drive device to move the camera along the panning direction. In this case, the motor 1 rotates the camera along the panning direction within a predetermined angle range. Then, it is conceivable to arrange the motor 1 and the camera such that the cogging torque becomes maximum at the end of the camera's panning direction. Therefore, when the camera moves to the end along the panning direction, the cogging torque of the motor 1 can act as a pseudo-damper. As a result, a mechanical damper can be omitted in the camera. Note that the motor 1 described above is not limited to moving the camera along the panning direction, but can also be used, for example, as a drive device to move the camera along the tilt direction.

[0104] 4. Variations

[0105] It should be noted that this embodiment is not limited to the specific example described above, and various modifications can be made.

[0106] Figure 7 This is a diagram showing the configuration of rotor 3A according to a modified example.

[0107] For example, in the above embodiment, the rotor 3 has multiple magnetic poles generated by multiple magnets 13. However, as Figure 7 As shown, rotor 3A has multiple magnetic poles generated by a magnet 13A.

[0108] In this configuration, magnet 13A can be magnetized into positive pole 41 and negative pole 42, which are alternately arranged circumferentially and spaced apart from each other. The angle occupied by the positive pole 41 and negative pole 42 on the intermediate circle Cm is the magnetic pole angle. m [degrees], and the angle between the positive electrode 41 and the negative electrode 42 on the intermediate circle Cm is the pitch angle Pm.

[0109] Figure 8 This is a diagram showing the structure of stator tooth 32A according to a modified example. Figure 9 This is a diagram showing the structure of stator tooth 32B according to a modified example.

[0110] Although the detailed shape of the stator teeth 32 is not described in the above embodiments, the shape may be as follows: Figure 8 The stator teeth 32A shown and as shown Figure 9 The stator teeth shown are in the shape of 32B.

[0111] like Figure 8 As shown, the stator tooth 32A includes a bottom surface 51, a side surface 52, and a connecting surface 53. The bottom surface 51 faces the magnet 13. The side surface 52 is a surface that extends axially from the stator base 31 to the bottom surface 51. The bottom surface 51 and the side surface 52 are then connected by the connecting surface 53. The connecting surface 53 is provided on each of the two radially arranged sides and on each of the two circumferentially arranged sides.

[0112] The radial connecting surface 53 is chamfered into a concave shape, with the circumferential center recessed. Similarly, the circumferential connecting surface 53 is chamfered into a concave shape, with the radial center recessed.

[0113] Therefore, when the rotor 3 rotates and the magnet 13 approaches the stator teeth 32A, the radial connecting surface 53 faces the magnet 13, and then the bottom surface 51 faces the magnet 13. This allows for a smooth change in the attractive force between the magnet 13 and the stator teeth 32A caused by the rotation of the rotor 3.

[0114] like Figure 9 As shown, the stator tooth 32B includes a bottom surface 61, a side surface 62, and a connecting surface 63. The bottom surface 61 faces the magnet 13. The side surface 62 is a surface extending axially from the stator base 31 to the bottom surface 61. The bottom surface 61 and the side surface 62 are connected by the connecting surface 63. The connecting surface 63 is provided on each of the two radially arranged sides and on each of the two circumferentially arranged sides.

[0115] The radial connecting surface 63 is chamfered to a convex shape, such that the circumferential center bulges outward. Similarly, the circumferential connecting surface 63 is chamfered to a convex shape, such that the radial center bulges outward.

[0116] Therefore, when the rotor 3 rotates and the magnet 13 approaches the stator teeth 32B, the radial connecting surface 53 faces the magnet 13, and then the bottom surface 51 faces the magnet 13. This allows for a smooth change in the attractive force between the magnet 13 and the stator teeth 32B caused by the rotation of the rotor 3.

[0117] 5. Summary of Examples

[0118] The motor 1 includes a rotor 3 and a stator 21. The rotor 3 has multiple magnetized magnetic poles and rotates about a rotation axis. The stator 21 includes multiple stator teeth.

[0119] The magnetic poles and stator teeth are spaced apart from each other in a first direction parallel to the axis of rotation. Multiple magnetic poles are arranged at equal intervals on a first circle centered on the axis of rotation. Multiple stator teeth are arranged at equal intervals on the circumference of a second circle centered on the axis of rotation.

[0120] The number of the plurality of magnetic poles is defined as Nm, and the number of the plurality of stator teeth is defined as Ns. When viewing the plan view of the rotor 3 and stator 21 from the first direction, and when the distance from the rotation axis to the midpoint of the area where the magnetic poles and stator teeth overlap in the second direction perpendicular to the first direction is the opposing surface reference radius rd, the angle between the magnetic poles on the circumference of a circle centered on the rotation axis and having the opposing surface reference radius rd is Pm [degrees], and the angle occupied by the magnetic poles on the circumference of a circle centered on the rotation axis and having the opposing surface reference radius rd is... m [degrees], and the angle occupied by the stator teeth on the circumference of a circle centered on the rotation axis and having a reference radius rd of the opposing surface is s[degree], Pm is set to minimize the difference between the maximum and minimum values ​​of L(ω) as expressed by equation (1).

[0121] [Expression 10]

[0122] Here, 0≤ψ≤360 / Nm[degrees] is satisfied, ω is the rotation angle of the rotor, x(k,ψ) in expression (1) is represented by expression (2), and a and b in expression (2) are represented by expression (3).

[0123] [Expression 11]

[0124] [Equation 12]

[0125] Here, the magnetic poles correspond to magnet 13, or to positive pole 41 and negative pole 42. The stator teeth correspond to stator teeth 32, 32A, and 32B. The first direction corresponds to the axial direction. The second direction corresponds to the radial direction.

[0126] With this construction, the variation in the attractive force between the magnetic poles and the stator teeth is minimized. Therefore, using a simple construction and without reducing the output of the motor 1, the motor 1 can reduce the cogging torque generated by the rotation of the rotor 3 when no drive current is supplied to the coil 22.

[0127] In addition, stator teeth 32A and 32B include bottom surfaces 51 and 61, side surfaces 52 and 62, and connecting surfaces 53 and 63. Bottom surfaces 51 and 61 face the magnetic poles of rotor 3, and bottom surfaces 51 and 61 and side surfaces 52 and 62 are connected by connecting surfaces 53 and 63.

[0128] Therefore, the change in the attractive force between the magnetic poles and the stator teeth 32A and 32B caused by the rotation of the rotor 3 can be smoothed out. As a result, the cogging torque in the motor 1 can be further reduced.

[0129] The rotation angle ω of the rotor ranges from 0 to the least common multiple of Nm and Ns, where Nm is the number of magnetic poles and Ns is the number of stator teeth.

[0130] Since the arrangement of the magnetic poles and stator teeth is symmetrical, the length L calculated by equation (1) will cycle when the rotation angle ω changes. Therefore, by calculating the length L(ω) within the range of rotation angle ω, which is the least common multiple of the number of magnetic poles Nm and the number of teeth Ns, the amount of calculation can be reduced, thereby reducing the design load.

[0131] Pm is set such that by changing the magnetic pole angle Minimize the difference between the maximum and minimum values ​​of the length L(ω) obtained by m and rotation angle ω.

[0132] like Figure 6 As shown, it can be calculated that by changing the magnetic pole angle... To reduce computation, the pitch angle Pm is minimized by minimizing the difference between the maximum and minimum values ​​of the length L(ω) obtained by m[degrees].

[0133] The camera can move in a specific direction, and the magnetic poles and stator teeth are arranged such that the cogging torque is maximized at the end of the camera in that specific direction.

[0134] Here, a specific direction corresponds to the panning direction or the tilting direction.

[0135] Therefore, cogging torque can be used as a pseudo-damper, thereby reducing the number of camera components.

[0136] 6. This technology

[0137] It should be noted that this technology can also be configured as follows.

[0138] (1) An electric motor, comprising: a rotor having a plurality of magnetized magnetic poles and configured to rotate about a rotation axis; and a stator including a plurality of stator teeth. The magnetic poles and stator teeth are spaced apart from each other in a first direction parallel to the rotation axis, the plurality of magnetic poles being arranged at equal intervals on a first circumference centered on the rotation axis, and the plurality of stator teeth being arranged at equal intervals on a second circumference centered on the rotation axis. When the number of the plurality of magnetic poles is defined as Nm and the number of the plurality of stator teeth is defined as Ns, when the rotor and stator are viewed in a plan view from the first direction, and when the distance from the rotation axis to the midpoint of the area where the magnetic poles and stator teeth overlap in a second direction perpendicular to the first direction is defined as the opposing surface reference radius rd, the angle between the magnetic poles on the circumference of the circle centered on the rotation axis and having the opposing surface reference radius rd is defined as Pm [degrees], and the angle occupied by the magnetic poles on the circumference of the circle centered on the rotation axis and having the opposing surface reference radius rd is defined as... m[degrees], and the angle occupied by the stator teeth on the circumference of a circle centered on the rotation axis and having the reference radius rd of the opposing surface is defined as m[degrees]. At s[degrees], Pm is set to minimize the difference between the maximum and minimum values ​​of L(ω) as expressed by the following equation (1): [Equation 13]

[0139] Here, 0 ≤ ψ ≤ 360 / Nm [degrees] is satisfied, ω is the rotation angle of the rotor, x(k, ψ) in equation (1) is represented by equation (2), and a and b in equation (2) are represented by equation (3). [Formula 14]

[0140] [Formula 15]

[0141] (2) In the motor according to (1) above, the stator teeth include a bottom surface, a side surface and a connecting surface, the bottom surface is opposite to the magnetic pole of the rotor, and the bottom surface and the side surface are connected by the connecting surface.

[0142] (3) In the motor according to (1) or (2) above, the rotation angle ω is in the range from 0 to the least common multiple of Nm and Ns, where Nm is the number of the plurality of magnetic poles and Ns is the number of the plurality of stator teeth.

[0143] (4) In the motor according to any one of (1)-(3) above, Pm is set to minimize the difference between the maximum and minimum values ​​of L(ω), and L(ω) is changed by It is obtained by m and rotation angle ω.

[0144] (5) In the motor according to any one of (1)-(4) above, the camera is configured to move in a specific direction, and the magnetic poles and stator teeth are arranged such that the cogging torque is maximized at the end of the camera in the specific direction.

[0145] List of reference numerals

[0146] 1. Motor

[0147] 3 rotors

[0148] 13 Magnets

[0149] 21 Stator

[0150] 32 stator teeth

Claims

1. An electric motor, comprising: The rotor has multiple magnetized magnetic poles and is configured to rotate about a rotation axis; as well as The stator comprises multiple stator teeth, among which... The magnetic poles and stator teeth are spaced apart from each other in a first direction that is parallel to the axis of rotation. The plurality of magnetic poles are arranged at equal intervals on a first circle centered on the axis of rotation. The plurality of stator teeth are arranged at equal intervals on a second circumference centered on the rotation axis, and When the number of the plurality of magnetic poles is defined as Nm and the number of the plurality of stator teeth is defined as Ns, when the rotor and stator are viewed in a plan view from a first direction, and when the distance from the rotation axis to the midpoint of the area where the magnetic poles and stator teeth overlap in a second direction perpendicular to the first direction is defined as the opposing surface reference radius rd, the angle between the magnetic poles on the circumference of a circle centered on the rotation axis and having the opposing surface reference radius rd is defined as Pm [degrees], and the angle occupied by the magnetic poles on the circumference of a circle centered on the rotation axis and having the opposing surface reference radius rd is defined as... m[degrees], and the angle occupied by the stator teeth on the circumference of a circle centered on the rotation axis and having the reference radius rd of the opposing surface is defined as m[degrees]. At s[degrees], Pm is set to minimize the difference between the maximum and minimum values ​​of L(ω) as expressed by the following equation (1): [Formula 1] Here, 0 ≤ ψ ≤ 360 / Nm [degrees] is satisfied, ω is the rotation angle of the rotor, x(k, ψ) in equation (1) is represented by equation (2), and a and b in equation (2) are represented by equation (3). [Equation 2] [Formula 3] 。 2. The motor according to claim 1, wherein, Stator teeth include a bottom surface, a side surface, and a connecting surface. The bottom surface is opposite to the magnetic poles of the rotor, and The bottom and side surfaces are connected by a connecting surface.

3. The motor according to claim 1, wherein, The rotation angle ω is in the range from 0 to the least common multiple of Nm and Ns, where Nm is the number of the plurality of magnetic poles and Ns is the number of the plurality of stator teeth.

4. The motor according to claim 1, wherein, Pm is set to minimize the difference between the maximum and minimum values ​​of L(ω), and L(ω) is changed by... It is obtained by m and rotation angle ω.

5. The motor according to claim 1, wherein, The camera is configured to move in a specific direction, and The magnetic poles and stator teeth are arranged to maximize the cogging torque at the end of the camera in a specific direction.

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