Motor

Abstract

This motor comprises: a rotor that has a plurality of magnetized magnetic poles and rotates about a rotation axis; and a stator that has a plurality of stator teeth. When the number of the plurality of magnetic poles is denoted by Nm, the number of the plurality of stator teeth is denoted by Ns, the angle of the interval of the magnetic poles on the circumference of a circle having a facing surface reference radius rd about the rotation axis is denoted by Pm [deg], the angle occupied by each magnetic pole on the circumference of the circle having the facing surface reference radius rd about the rotation axis is denoted by φm [deg], and the angle occupied by each stator tooth on the circumference of the circle having the facing surface reference radius rd about the rotation axis is denoted by φs [deg], the angle of the interval has Pm at which the difference between the maximum value and the minimum value of L (omega) represented by the following formula (1) is minimized. In formula (1), x (k, psi) is represented by formula (2), and a and b in formula (2) are represented by formula (3).

Description

Motor

[0001] The present technology relates to a motor, and more particularly to a technology relating to an axial gap type motor.

[0002] Conventionally, there has been known an axial gap motor in which a magnet provided on a rotor and stator teeth provided on a stator are arranged axially opposite each other (see, for example, Patent Document 1). The stator used in an axial gap motor is configured such that a plurality of stator teeth protruding from one side of a stator base are arranged at equal intervals in the circumferential direction, and a coil is attached to each of the stator teeth.

[0003] JP 2011-24291 A

[0004] In an axial gap motor, when no drive current is supplied to the coil, an attractive force is generated between the magnet and the stator teeth due to the magnetic force of the magnet. This attractive force generates cogging torque when the rotor rotates in an axial gap motor when no drive current is supplied to the coil. Cogging torque causes vibrations and abnormal noise in the motor drive itself. Therefore, there is a demand for reducing the cogging torque in axial gap motors.

[0005] Therefore, an object of the present technology is to reduce the cogging torque with a simple configuration.

[0006] A motor according to the present technology includes a rotor having a plurality of magnetized magnetic poles and rotating about a rotation axis, and a stator having a plurality of stator teeth, wherein the magnetic poles and the stator teeth are spaced apart from each other in a first direction parallel to the rotation axis, the plurality of magnetic poles are arranged at equal intervals on a first circumference centered on the rotation axis, and the plurality of stator teeth are arranged at equal intervals on a second circumference centered on the rotation axis. When the number of the plurality of magnetic poles is Nm, the number of the plurality of stator teeth is Ns, and when the rotor and the stator are viewed in a plane from the first direction, a distance from the rotation axis to a midpoint in a second direction that is perpendicular to the first direction of an area where the magnetic poles and the stator teeth overlap is defined as an opposing surface reference radius rd, an angle between the magnetic poles on the circumference of a circle of the opposing surface reference radius rd that is centered on the rotation axis is defined as Pm [deg], an angle occupied by the magnetic poles on the circumference of the circle of the opposing surface reference radius rd that is centered on the rotation axis is defined as φm [deg], and an angle occupied by the stator teeth on the circumference of the circle of the opposing surface reference radius rd that is centered on the rotation axis is defined as φs [deg], then Pm has a value that minimizes the difference between the maximum and minimum values ​​of L(ω) expressed by the following equation (1): Here, 0≦ψ≦360 / Nm [deg], ω is the rotation angle of the rotor, x(k, ψ) in equation (1) is expressed by equation (2), and a and b in equation (2) are expressed by equation (3).

[0007] FIG. 1 is a cross-sectional view of an axial gap type motor. FIG. 2 is an exploded perspective view of an axial gap type motor. FIG. 3 is a diagram showing definitions of various dimensions related to magnets and stator teeth. FIG. 4 is a diagram showing the relationship between Ps(θ) and x(k, ψ). FIG. 5 is a diagram showing the number of effective stator teeth with respect to the phase of the magnet. FIG. 6 is a diagram showing the length L when ω and φm are changed. FIG. 7 is a diagram showing the configuration of a rotor in a modified example. FIG. 8 is a diagram showing the structure of stator teeth in a modified example. FIG. 9 is a diagram showing the structure of stator teeth in a modified example.

[0008] The embodiments will be described below in the following order: <1. Motor configuration> <2. Relationship between magnet and stator teeth> <3. Usage example> <4. Modification example> <5. Summary of the embodiment> <6. Present technology>

[0009] 1. Configuration of Motor 1 Fig. 1 is a cross-sectional view of an axial gap motor 1. Fig. 2 is an exploded perspective view of the axial gap motor 1. In the following, the direction along the rotation axis of the rotor 3 is referred to as the axial direction. Furthermore, the direction perpendicular to the rotation axis of the rotor 3 and passing through the rotation axis of the rotor 3 is referred to as the radial direction. Furthermore, the direction along the circumference centered on the rotation axis of the rotor 3 is referred to as the circumferential direction.

[0010] As shown in FIGS. 1 and 2 , the motor 1 is an axial gap type brushless motor that includes a housing 2 , a rotor 3 that is rotatable relative to the housing 2 , and a fixed portion 4 that is fixed to the housing 2 .

[0011] The housing 2 is integrally formed with a cylindrical portion 2a, an inner flange portion 2b, and an outer flange portion 2c. The cylindrical portion 2a is formed in a cylindrical shape. The inner flange portion 2b is formed continuous with one end of the cylindrical portion 2a. The inner flange portion 2b is formed in a ring shape extending radially inward from one end of the cylindrical portion 2a. The outer flange portion 2c is formed in a ring shape extending radially outward from the middle of the axial direction of the cylindrical portion 2a.

[0012] A rotor 3 is rotatably supported inside the cylindrical portion 2a via bearings 5 ​​and 6. The rotor 3 includes a shaft 11, a rotor yoke 12, and a plurality of magnets 13.

[0013] The shaft 11 is formed in a cylindrical shape. The outer diameter of the shaft 11 is smaller than the inner diameter of the inner flange portion 2b, and one end of the shaft 11 is inserted into a hole formed in the center of the inner flange portion 2b. A ring-shaped flange portion 11a extending radially outward is formed integrally with the shaft 11 on the other end side in the axial direction as viewed from one end of the shaft 11. In addition, a step portion 11b having an outer diameter larger than the shaft 11 is formed integrally with the shaft 11 on the one end side of the flange portion 11a. The flange portion 11a and the step portion 11b are formed continuously in the axial direction of the shaft 11.

[0014] A rotor yoke 12 abuts against the surface of the flange portion 11a opposite to the housing 2. The rotor yoke 12 is formed in an annular shape 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.

[0015] The rotor yoke 12 is formed to be radially longer than the flange portion 11a, and a plurality of magnets 13 are attached to an opposing surface 12a that faces the fixed portion 4. When viewed from the axial direction, the magnets 13 are formed in a generally trapezoidal shape whose circumferential length increases toward the radially outer side. The magnets 13 are also arranged at equal intervals in the circumferential direction on the circumference of a first circle whose center is the rotation axis of the rotor 3. The plurality of magnets 13 are formed to be approximately the same size.

[0016] Adjacent magnets 13 are arranged with different magnetic poles facing the fixed portion 4. In other words, the magnets 13 are arranged with their magnetic poles staggered along the circumferential direction. Therefore, the magnets 13 can be interchanged with magnetic poles, and the same applies hereinafter.

[0017] The fixed part 4 is attached to an opposing surface 2d of the outer flange part 2c of the housing 2 that faces the magnet 13. The fixed part 4 includes a stator 21, a plurality of coils 22, and a flexible printed circuit board .

[0018] The stator 21 is integrally formed with a stator base 31 and a plurality of stator teeth 32. The stator base 31 is formed in an annular shape and abuts against the opposing surface 2d. The stator base 31 is fixed to the outer flange portion 2c with fastening members 9 such as screws.

[0019] A plurality of stator teeth 32 protruding in the axial direction are formed on the surface of the stator base 31 facing the magnet 13. The stator teeth 32 are made of a magnetic material and formed into a generally trapezoidal shape whose circumferential length increases radially outward when viewed from the axial direction. The stator teeth 32 are arranged at equal intervals along the circumferential direction on the circumference of a second circle whose center is the rotational axis of the rotor 3. The plurality of stator teeth 32 are formed to be generally the same size. The second circle may be the same size as the first circle, or may be a different size.

[0020] Coils 22 are wound around the stator teeth 32. Flexible printed circuit boards 23 are connected to the coils 22, and a rotating magnetic field is generated when a drive current input from a control device (not shown) is supplied to the coils 22 via the flexible printed circuit board 23. In the motor 1, the generated rotating magnetic field causes the rotor 3 to rotate.

[0021] The flexible printed circuit board 23 is disposed along the circumferential direction radially outward from the position where the stator teeth 32 are formed on the stator base 31 , and is interposed between the stator base 31 and the coil 22 .

[0022] Between the shaft 11 and the cylindrical portion 2a, there are interposed a bearing 5 and a bearing 6. The bearing 5 and the bearing 6 are arranged apart in the axial direction, and a pressurizing part 7 is interposed between the bearing 5 and the bearing 6 in the axial direction.

[0023] Bearings 5 ​​and 6 are radial ball bearings having an inner ring, an outer ring, and multiple balls. The inner ring of bearing 5 abuts radially against shaft 11, and the outer ring abuts radially against cylindrical portion 2a and axially against inner flange portion 2b. The inner ring of bearing 6 abuts radially against shaft 11 and axially against stepped portion 11b, and the outer ring abuts radially against cylindrical portion 2a.

[0024] The pressure applying part 7 includes a spring and a washer. The pressure applying part 7 biases the inner ring of the bearing 5 and the inner ring of the bearing 6 in a direction separating them from each other. The pressure applying part 7 also biases the outer ring of the bearing 5 and the outer ring of the bearing 6 in a direction separating them from each other.

[0025] The rotor 3 and housing 2 are pulled toward each other by the attractive force, i.e., the force of attraction, between the magnets 13 and the stator teeth 32. At this time, the inner ring of bearing 6 is pressed toward the inner flange 2b by the stepped portion 11b, and the inner ring of bearing 5 is also pressed toward the inner flange 2b via the pressurizing part 7. The outer ring of bearing 5 is pressed toward the rotor yoke 12 by the inner flange 2b, and the outer ring of bearing 6 is also pressed toward the rotor yoke 12 via the pressurizing part 7. As a result, in bearings 5 ​​and 6, a force is applied to the inner ring in the axial direction from the rotor yoke 12 toward the inner flange 2b, and a force is applied to the outer ring in the axial direction from the inner flange 2b toward the rotor yoke 12. As a result, a shearing force is applied to the balls in bearings 5 ​​and 6, making it possible to reduce rattle of the inner ring, balls, and outer ring.

[0026] A retaining ring 10 is attached to the shaft 11 on the opposite side of the bearing 5 across the inner flange portion 2 b to prevent the rotor 3 from coming off the housing 2 .

[0027] 2. Relationship Between Magnet 13 and Stator Teeth 32 Incidentally, in the motor 1, when no drive current is supplied to the coil 22, an attractive force is generated between the magnet 13 and the stator teeth 32 due to the magnetic force of the magnet 13. Therefore, in the motor 1, when the rotor 3 rotates while no drive current is supplied to the coil 22, a cogging torque is generated, which causes a sense of resistance.

[0028] It is desirable to reduce the cogging torque because it causes vibration and abnormal noise during rotation of the rotor 3. Therefore, in this embodiment, the cogging torque is reduced by adjusting the spacing between the magnets 13.

[0029] FIG. 3 is a diagram showing definitions of various dimensions related to the magnets 13 and the stator teeth 32. Hereinafter, the rotation axis of the rotor 3 may be referred to as the rotation axis O. As shown in FIG. 3 , when the magnets 13 and the stator teeth 32 are viewed axially in a plan view, the distance from the rotation axis O to the radial midpoint of the area where the magnets 13 and the stator teeth 32 overlap is defined as the opposing surface reference radius rd. Furthermore, a circle having the opposing surface reference radius rd and centered on the rotation axis O is defined as an intermediate circle Cm. The angle occupied by one magnet 13 on the circumference of the intermediate circle Cm is defined as the magnetic pole angle φm [deg]. The angle between the magnets 13 on the circumference of the intermediate circle Cm is defined as the pitch angle Pm [deg]. The angle occupied by one stator tooth 32 on the circumference of the intermediate circle Cm is defined as the tooth angle φs [deg]. 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.

[0030] Here, the strength of the attractive force of magnet 13 is simply considered to be equivalent to the area where magnet 13 faces stator teeth 32, that is, the area where magnet 13 overlaps stator teeth 32 in a plan view from the axial direction. Furthermore, because the length L of the arc where magnet 13 overlaps stator teeth 32 on the circumference of intermediate circle Cm is proportional to the area where magnet 13 faces stator teeth 32, it is possible to evaluate the strength of the attractive force of magnet 13 using length L.

[0031] The following describes a method for calculating the length L. Here, a function Fs(θ) indicating the presence or absence of stator teeth 32 on the circumference of the intermediate circle Cm is expressed by equation (4). where θ is a circumferential angle. The range where Fs(θ) is 1 is the range where stator teeth 32 exist on the circumference of the intermediate circle Cm. On the other hand, the range where Fs(θ) is 0 is the range where stator teeth 32 do not exist on the circumference of the intermediate circle Cm.

[0032] Furthermore, a function Fm(θ′, t) indicating the presence or absence of the magnet 13 on the circumference of the intermediate circle Cm is expressed by equation (5). where g(t) is a function of time t that indicates the change in angle of the rotor 3. The range where Fm(θ', t) is 1 is the range where the magnet 13 exists on the circumference of the intermediate circle Cm. On the other hand, the range where Fm(θ', t) is 0 is the range where the magnet 13 does not exist on the circumference of the intermediate circle Cm.

[0033] The length L to be found is obtained by integrating the range in which both Fs(θ) and Fm(θ', t) are 1 over the range 0≦θ≦360 [deg]. Since finding the product of the square waves expressed by Fs(θ) and Fm(θ', t) requires many case distinctions and is complicated, the length L is expressed as a function of the rotation angle ω of the rotor 3 in equation (1), taking into account the symmetry of the arrangement of the magnet 13 and the stator teeth 32. Here, 0≦ψ≦360 / Nm [deg], and ω is the rotation angle of the rotor 3. Furthermore, x(k, ψ) in equation (1) is expressed by equation (2), and a and b in equation (2) are expressed by equation (3).

[0034] Fig. 4 is a diagram showing the relationship between Ps(θ) and x(k, ψ). Fig. 4 shows an example in which the number of magnetic poles Nm = 10 and the number of teeth Ns = 12. Fig. 4A is a diagram showing Fs(θ) in a simplified manner. Fig. 4B is a diagram showing x(k, ψ) in a simplified manner.

[0035] The colored areas in Figure 4A represent stator teeth 32. Therefore, a teeth area is an area that satisfies the function Fs(θ) = 1, and the area between adjacent teeth areas is an area that satisfies Fs(θ) = 0. Note that hereinafter, the colored areas in Figure 4A will be referred to as teeth areas. In the example of Figure 4A, the number of teeth Ns = 12, so there are 12 teeth areas. Also, k in equation (1) corresponds to the number of stator teeth 32 in the clockwise direction, with a specific stator tooth 32 being numbered 0. In Figure 4A, the area between adjacent teeth areas represents an area where no stator teeth 32 exist.

[0036] The length of the thick arc in Fig. 4A corresponds to the teeth angle φs [deg]. In Fig. 4A, the thick arc corresponding to the teeth angle φs [deg] is shown shifted clockwise from k = 0, increasing radially. In equation (3), "a" represents the start point of the thick arc, and "b" represents the end point of the thick arc.

[0037] In addition, the area surrounded by dashed lines in Figure 4A, i.e., the sector-shaped area delimited by straight lines extending radially from the rotation axis, is an area represented by an angular range obtained by dividing 360 [deg] by the number of magnetic poles Nm. Hereinafter, this sector-shaped area will be referred to as a magnet area. Note that in Figure 4A, only one of the multiple magnet areas is shown by a dashed line. In the example of Figure 4A, the number of magnetic poles Nm = 10, so there are 10 magnet areas. The central angle of a magnet area corresponds to the sum of the magnetic pole angle φm [deg] and the pitch angle Pm [deg].

[0038] Here, the magnets 13 and stator teeth 32 are arranged symmetrically. Therefore, as shown in Fig. 4B, the function x(k, ψ) is obtained by converting the domain of Fs(θ), 0≦θ≦360 [deg], into one magnet region, 0≦ψ≦360 / Nm [deg], taking into account the symmetry of the arrangement of the magnets 13 and stator teeth 32. In other words, the ten magnet regions shown in Fig. 4A are overlapped into one region, which is the shaded region in Fig. 4B.

[0039] Therefore, the function x(k, ψ) is a function that indicates 1 when the kth stator tooth 32 is present at a specific phase ψ and indicates 0 when the kth stator tooth 32 is not present. In this case, when one stator tooth 32 is present in one magnet region, a < b holds in the range where the stator tooth 32 is present, and the relationship in the upper part of equation (2) holds in the range where the stator tooth 32 is not present. On the other hand, when one stator tooth 32 is present across different magnet regions, b < a holds in the range where the stator tooth 32 is present, and the relationship in the middle part of equation (2) holds in the range where the stator tooth 32 is present, and the relationship in the lower part of equation (2) holds in the range where the stator tooth 32 is not present.

[0040] In formula (1), indicates how many stator teeth 32 are present at a specific phase ψ. At the phase ψ shown in FIG. 4B, six stator teeth 32 are present in the magnet region. Note that hereinafter, the stator teeth 32 present at a specific phase ψ may be referred to as effective stator teeth 32.

[0041] Fig. 5 is a diagram showing the number of effective stator teeth 32 with respect to the phase ψ. In Fig. 5, the horizontal axis represents the phase ψ, and the vertical axis represents the number of effective stator teeth 32. In the example of Fig. 5, the number of magnetic poles Nm = 10, and 0 ≤ ψ ≤ 36 degrees, so the number of effective stator teeth 32 is shown in the range from 0 degrees to 36 degrees.

[0042] 5, the range in which the magnet 13 exists, i.e., the range corresponding to the magnetic pole angle φm [deg], is shown in color. This colored range moves as the rotor 3 rotates.

[0043] As shown in Fig. 5, the number of effective stator teeth 32 varies depending on the phase ψ. In the example shown in Fig. 5, for example, when the phase ψ is 0 [deg], the number of effective stator teeth 32 is six, and when the phase ψ is 5 [deg], the number of effective stator teeth 32 is four.

[0044] So far, we have explained the number of effective stator teeth 32 within the magnet range, but the actual length L(ω) of attraction between magnet 13 and stator teeth 32 is the value obtained by integrating the range shown in color in Fig. 5. In other words, equation (1) is the value obtained by integrating the number of effective stator teeth 32 within the range shown in color in Fig. 5.

[0045] As described above, the magnet range corresponds to the sum of the magnetic pole angle φm [deg] and the pitch angle Pm. Therefore, it is possible to change the magnetic pole angle φm [deg] by changing the pitch angle Pm. Furthermore, the rotation of the rotor 3 corresponds to changing the phase ψ of the integral range.

[0046] Fig. 6 is a diagram showing the length L(ω) when the rotation angle ω and the magnetic pole angle φm are changed. The horizontal axis of Fig. 6 represents the rotation angle ω of the rotor 3, and the vertical axis of Fig. 6 represents the length L(ω). Fig. 6 also shows the length L(ω) in 1 degree increments for magnetic pole angles φm ranging from 28 degrees to 36 degrees.

[0047] Here, the rotation angle ω is shown only in the range of 0 [deg] to 6 [deg], but this time the number of magnetic poles Nm and the number of teeth Ns are shown in the range of 6 [deg] because of the symmetry of the figure. Furthermore, when the magnetic pole angle φm is 29 [deg] or more, only a part of the range of the rotation angle ω for the length L(ω) is shown, but the range showing the maximum and minimum values ​​is plotted.

[0048] In the example of Figure 6, the difference between the maximum and minimum values ​​of length L is smallest when the magnetic pole angle φm = 30 degrees. In this way, motor 1 is designed to have magnetic pole angle φm and pitch angle Pm that minimize the difference between the maximum and minimum values ​​of length L. As a result, in motor 1, the change in the attractive force between magnet 13 and stator teeth 32 is minimized even when rotor 3 rotates. This makes it possible for motor 1 to reduce cogging torque. In this case, there is no need to complicate the shapes of magnet 13 and stator teeth 32.

[0049] <3. Usage Example> The motor 1 described above can be used as a drive device for moving a camera in the pan direction. In this case, the motor 1 rotates the camera in the pan direction over a predetermined angle. The motor 1 and the camera can be positioned so that the cogging torque is maximized at the end of the camera's pan direction. This allows the cogging torque of the motor 1 to function as a pseudo-damper when the camera is moved to the end in the pan direction. This makes it possible to omit a mechanical damper in the camera. Note that the motor 1 described above is not limited to applications for moving a camera in the pan direction, and may also be used as a drive device for moving a camera in the tilt direction, for example.

[0050] 4. Modifications Note that the embodiment is not limited to the specific example described above, and various modifications may be made.

[0051] FIG. 7 is a diagram showing the configuration of a rotor 3A in a modified example. For example, in the above embodiment, the rotor 3 has multiple magnetic poles due to multiple magnets 13. However, as shown in FIG. 7, the rotor 3A has multiple magnetic poles due to a single magnet 13A. In this case, the magnet 13A may be magnetized so that the positive poles 41 and negative poles 42 are alternately spaced apart in the circumferential direction. In this case, the angle occupied by the positive poles 41 and negative poles 42 on the intermediate circle Cm is the magnetic pole angle φm [deg], and the angle between the positive poles 41 and negative poles 42 on the intermediate circle Cm is the pitch angle Pm.

[0052] Fig. 8 is a diagram showing the structure of a modified stator tooth 32A. Fig. 9 is a diagram showing the structure of a modified stator tooth 32B. Although the detailed shape of stator teeth 32 is not described in the above embodiment, shapes such as stator teeth 32A shown in Fig. 8 and stator teeth 32B shown in Fig. 9 may be used.

[0053] As shown in FIG. 8 , each stator tooth 32A has a bottom surface 51, side surfaces 52, and a connecting surface 53. The bottom surface 51 faces the magnet 13. The side surfaces 52 extend axially from the stator base 31 to the bottom surface 51. The bottom surface 51 and the side surfaces 52 are connected by connecting surfaces 53. The connecting surfaces 53 are provided on two radial sides and two circumferential sides. The radial connecting surfaces 53 are chamfered to have a concave shape with a recessed center in the circumferential direction. Similarly, the circumferential connecting surfaces 53 are chamfered to have a concave shape with a recessed center in the radial direction. As a result, when the rotor 3 rotates and the magnet 13 approaches the stator tooth 32A, the radial connecting surfaces 53 face the magnet 13, and then the bottom surface 51 faces the magnet 13. This allows for smooth changes in the attractive force between the magnet 13 and the stator tooth 32A due to the rotation of the rotor 3.

[0054] As shown in FIG. 9 , each stator tooth 32B has a bottom surface 61, side surfaces 62, and a connecting surface 63. The bottom surface 61 faces the magnet 13. The side surfaces 62 extend axially from the stator base 31 to the bottom surface 61. The bottom surface 61 and the side surfaces 62 are connected by a connecting surface 63. The connecting surfaces 63 are provided on two radial sides and two circumferential sides. The radial connecting surfaces 63 are chamfered to have a convex shape with a circumferential center bulging. Similarly, the circumferential connecting surfaces 63 are chamfered to have a convex shape with a bulging center. As a result, when the rotor 3 rotates and the magnet 13 approaches the stator tooth 32B, the radial connecting surfaces 53 face the magnet 13, and then the bottom surfaces 51 face the magnet 13. This allows for smooth changes in the attractive force between the magnet 13 and the stator tooth 32B due to the rotation of the rotor 3.

[0055] 5. Summary of the embodiment The motor 1 includes a rotor 3 having a plurality of magnetized magnetic poles and rotating about a rotation axis, and a stator 21 having a plurality of stator teeth. The magnetic poles and the stator teeth are spaced apart from each other in a first direction parallel to the rotation axis. The plurality of magnetic poles are arranged at equal intervals on a first circumference centered on the rotation axis. The plurality of stator teeth are arranged at equal intervals on a second circumference centered on the rotation axis. Let Nm be the number of magnetic poles, Ns be the number of stator teeth, and rd be the distance from the rotation axis to the midpoint in a second direction perpendicular to the first direction of the area where the magnetic poles and the stator teeth overlap when the rotor 3 and the stator 21 are viewed in a plane from a first direction. Let Pm [deg] be the angle between the magnetic poles on the circumference of a circle of opposing surface reference radius rd centered on the rotation axis, let φm [deg] be the angle occupied by the magnetic poles on the circumference of the circle of opposing surface reference radius rd centered on the rotation axis, and let φs [deg] be the angle occupied by the stator teeth on the circumference of the circle of opposing surface reference radius rd centered on the rotation axis. Then, Pm has the smallest Pm at which the difference between the maximum and minimum values ​​of L(ω) expressed by the following equation (1) is smallest. Here, 0≦ψ≦360 / Nm [deg], ω is the rotation angle of the rotor, x(k, ψ) in equation (1) is expressed by equation (2), and a and b in equation (2) are expressed by equation (3). Here, the magnetic poles correspond to the magnets 13, or the positive poles 41 and negative poles 42. The stator teeth correspond to the stator teeth 32, 32A, and 32B. The first direction corresponds to the axial direction. The second direction corresponds to the radial direction. With this configuration, the change in the force of attraction between the magnetic poles and the stator teeth is minimized. Therefore, the motor 1 can reduce the cogging torque generated by rotating the rotor 3 when no drive current is supplied to the coils 22 with a simple configuration and without reducing the output of the motor 1.

[0056] The stator teeth 32A, 32B each have a bottom surface 51, 61, a side surface 52, 62, and a connecting surface 53, 63. The bottom surfaces 51, 61 face the magnetic poles of the rotor 3, and the bottom surfaces 51, 61 are connected to the side surfaces 52, 62 by the connecting surfaces 53, 63. This makes it possible to smooth out changes in the attractive forces between the magnetic poles and the stator teeth 32A, 32B caused by the rotation of the rotor 3. As a result, the cogging torque of the motor 1 can be further reduced.

[0057] The range of the rotor rotation angle ω is from 0 to the least common multiple of the number of magnetic poles Nm and the number of stator teeth Ns. Because the arrangement of the magnetic poles and stator teeth is symmetric, the length L calculated by equation (1) results in a loop when the rotation angle ω is changed. Therefore, by calculating the length L(ω) within the range of the rotation angle ω from 0 to the least common multiple of the number of magnetic poles Nm and the number of teeth Ns, the amount of calculations can be reduced, and the design load can also be reduced.

[0058] The pitch angle Pm is set to minimize the difference between the maximum and minimum values ​​of the length L(ω) obtained by changing the magnetic pole angle φm and the rotation angle ω. As shown in Figure 6, the amount of calculation can be reduced by calculating the pitch angle Pm at which the difference between the maximum and minimum values ​​of the length L(ω) obtained by changing the magnetic pole angle φm [deg] is minimized.

[0059] The camera can be moved in a specific direction, and the magnetic poles and stator teeth are arranged so that the cogging torque is maximized at the end of the camera in the specific direction. Here, the specific direction corresponds to the pan direction or tilt direction. This allows the cogging torque to be treated as a pseudo-damper, thereby reducing the number of camera parts.

[0060] 6. The present technology may also have the following configuration: (1) A rotor having a plurality of magnetized magnetic poles and rotating about a rotation axis, and a stator having a plurality of stator teeth, wherein the magnetic poles and the stator teeth are spaced apart from each other in a first direction parallel to the rotation axis, the plurality of magnetic poles are arranged at equal intervals on a first circumference centered on the rotation axis, and the plurality of stator teeth are arranged at equal intervals on a second circumference centered on the rotation axis, a motor having Pm such that a difference between a maximum value and a minimum value of L(ω) expressed by the following equation (1) is smallest, where Nm is the number of the plurality of magnetic poles, Ns is the number of the plurality of stator teeth, when the rotor and the stator are viewed in a plane from the first direction, rd is the distance from the rotation axis to the midpoint in a second direction that is perpendicular to the first direction of an area where the magnetic poles and the stator teeth overlap, Pm [deg] is the angle between the magnetic poles on the circumference of a circle of the opposing surface reference radius rd that is centered on the rotation axis, φm [deg] is the angle occupied by the magnetic poles on the circumference of the circle of the opposing surface reference radius rd that is centered on the rotation axis, and φs [deg] is the angle occupied by the stator teeth on the circumference of the circle of the opposing surface reference radius rd that is centered on the rotation axis: Here, 0≦ψ≦360 / Nm [deg], ω is the rotation angle of the rotor, x(k, ψ) in equation (1) is expressed by equation (2), and a and b in equation (2) are expressed by equation (3). (2) The motor according to (1), wherein the stator teeth have a bottom surface, a side surface, and a connecting surface, the bottom surface facing a magnetic pole of the rotor, and the bottom surface and the side surface being connected by the connecting surface. (3) The motor according to (1) or (2), wherein the range of the rotation angle ω is from 0 to the least common multiple of Nm, the number of the plurality of magnetic poles, and Ns, the number of the plurality of stator teeth. (4) The motor according to any of (1) to (3), wherein Pm is such that the difference between the maximum and minimum values ​​of L(ω) obtained by changing φm and the rotation angle ω is minimum. (5) The motor according to any of (1) to (4), wherein a camera can be moved in a specific direction, and the magnetic poles and the stator teeth are arranged so that cogging torque is maximized at an end of the camera in the specific direction.

[0061] 1 Motor 3 Rotor 13 Magnet 21 Stator 32 Stator teeth

Claims

1. A rotor having a plurality of magnetized magnetic poles and rotating around a rotation axis; and a stator having a plurality of stator teeth, wherein the magnetic poles and the stator teeth are spaced apart from each other in a first direction parallel to the rotation axis, the plurality of magnetic poles are arranged at equal intervals on a first circumference centered on the rotation axis, and the plurality of stator teeth are arranged at equal intervals on a second circumference centered on the rotation axis, a motor having Pm such that a difference between a maximum value and a minimum value of L(ω) expressed by the following equation (1) is smallest, where Nm is the number of the plurality of magnetic poles, Ns is the number of the plurality of stator teeth, when the rotor and the stator are viewed in a plane from the first direction, rd is the distance from the rotation axis to the midpoint in a second direction that is perpendicular to the first direction of an area where the magnetic poles and the stator teeth overlap, Pm [deg] is the angle between the magnetic poles on the circumference of a circle of the opposing surface reference radius rd that is centered on the rotation axis, φm [deg] is the angle occupied by the magnetic poles on the circumference of the circle of the opposing surface reference radius rd that is centered on the rotation axis, and φs [deg] is the angle occupied by the stator teeth on the circumference of the circle of the opposing surface reference radius rd that is centered on the rotation axis: Here, 0≦ψ≦360 / Nm [deg], ω is the rotation angle of the rotor, x(k, ψ) in equation (1) is expressed by equation (2), and a and b in equation (2) are expressed by equation (3).

2. The motor according to claim 1, wherein the stator teeth have a bottom surface, a side surface, and a connecting surface, the bottom surface faces a magnetic pole of the rotor, and the bottom surface and the side surface are connected by the connecting surface.

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

4. The motor according to claim 1, wherein Pm is such that the difference between the maximum and minimum values ​​of L(ω) obtained by changing φm and the rotation angle ω is minimized.

5. The motor according to claim 1, wherein the camera can be moved in a specific direction, and the magnetic poles and the stator teeth are arranged so that the cogging torque is maximized at the end of the camera in the specific direction.

Images