electric machine

Abstract

Embodiments provide an electric machine, comprising: a shaft; a rotor coupled to the shaft; and a stator disposed between the shaft and the rotor, wherein the rotor comprises a yoke engaged with the shaft and a drive magnet and a sense magnet engaged with the yoke. The sense magnet comprises a first sense magnet and a second sense magnet, wherein the first sense magnet has first poles and second poles alternately disposed on a first circumference, and the second sense magnet is disposed on a second circumference and comprises first poles and second poles, a radius of the second circumference is different from a radius of the first circumference, and a length of the second poles of the second sense magnet in a circumferential direction is different from a length of the first poles of the second sense magnet in the circumferential direction.

Description

TECHNICAL FIELD

[0001] The present embodiment relates to an electric motor. BACKGROUND

[0002] The electric motor can include a rotor, a stator, and a shaft. The shaft is coupled to the rotor. The rotor can be disposed outside the stator. The rotor rotates due to electromagnetic interaction between the rotor and the stator, and the shaft rotates when the rotor rotates.

[0003] Such an electric motor can be used as a driving source configured to rotate a sensor device (e.g., a light detection and ranging (LDAR) device). The shaft of the electric motor is connected to the sensor device. In this case, constant speed driving of the electric motor can be an important factor in ensuring performance of the sensor device. The constant speed driving of the electric motor can be determined by detecting a position of the rotating rotor. To detect the position of the rotor, the electric motor can include a Hall sensor configured to detect a change in magnetic flux of a driving magnet disposed on the rotor. However, when the electric motor used in the sensor device requires a high constant speed condition, there is a problem in that it is difficult to satisfy the constant speed condition of the electric motor only by detecting a change in magnetic flux due to a general driving magnet.

[0004] Accordingly, to improve resolution, a separate multi-pole magnetized sensing magnet can be used. For example, a first sensing magnet and a second sensing magnet can be disposed on two circumferences concentric to each other. Since it is difficult to magnetize one first sensing magnet to have a plurality of poles, a second sensing magnet can be additionally provided to more accurately detect the position of the rotor. One example thereof is to use an induced signal generated by the second sensing magnet as an index signal to identify one rotation of the electric motor.

[0005] However, it is very difficult and cumbersome to simultaneously magnetize the first sensing magnet and the second sensing magnet disposed on the two circumferences to have a plurality of poles. SUMMARY

[0006] TECHNICAL PROBLEM

[0007] Accordingly, the present application aims to provide an electric motor capable of accurately identifying a position of a rotor using a sensing magnet having a simple structure.

[0008] The problems to be solved by the present application are not limited to the above-mentioned problems, and other problems not mentioned herein will be clearly understood by those skilled in the art through the following description.

[0009] TECHNICAL SOLUTION

[0010] One aspect of the present application provides an electric motor including a shaft, a rotor coupled to the shaft, and a stator disposed between the shaft and the rotor, wherein the rotor includes a yoke coupled to the shaft, and a drive magnet and a sense magnet coupled to the yoke, the sense magnet including a first sense magnet and a second sense magnet, first poles and second poles being alternately disposed on a first circumference of the first sense magnet, the second sense magnet being disposed on a second circumference and including first poles and second poles, a radius of the second circumference being different from a radius of the first circumference, a length in a circumferential direction of the second poles of the second sense magnet being different from a length in a circumferential direction of the first poles of the second sense magnet.

[0011] Another aspect of the present application provides an electric motor including a base and a sense magnet disposed on the base, wherein the sense magnet includes a first sense magnet disposed on a first circumference and a second sense magnet disposed on a second circumference, first poles and second poles being alternately disposed in the first sense magnet, the second sense magnet including first poles and second poles, a length in a circumferential direction of the first poles of the second sense magnet being longer than a length in a circumferential direction of the first poles of the first sense magnet, a length in a circumferential direction of the second poles of the second sense magnet being longer than a length in a circumferential direction of the first poles of the second sense magnet.

[0012] The length in the circumferential direction of the first poles of the second sense magnet can be longer than the length in the circumferential direction of the first poles of the first sense magnet.

[0013] The length in the circumferential direction of the first poles of the second sense magnet can be longer than the length in the circumferential direction of the second poles of the second sense magnet.

[0014] One end of the second sense magnet and one end of the first sense magnet can be disposed on a first straight line in a radial direction, the other end of the second sense magnet and the other end of the first sense magnet can be disposed on different straight lines in the radial direction.

[0015] The first straight line can correspond to a reference position of a rotation angle of the rotor.

[0016] The second sense magnet can have one first pole and one second pole.

[0017] The first straight line can correspond to the reference position of the rotation angle of the rotor.

[0018] The yoke can include a base, a magnet receiving portion protruding from the base, and a column portion protruding from the magnet receiving portion.

[0019] The sensing magnet can be mounted on the base.

[0020] The circumferential length of the first pole of the second sensing magnet may be shorter than the sum of the circumferential length of the first pole and the circumferential length of the second pole of the first sensing magnet.

[0021] The first sensing magnet and the second sensing magnet can be arranged concentrically.

[0022] The first sensing magnet and the second sensing magnet may overlap along the radial direction.

[0023] The motor may include a substrate spaced apart from the yoke, the substrate may include a first sensor and a second sensor, the first sensor at least partially overlapping the first sensing magnet in the axial direction, and the second sensor at least partially overlapping the second sensing magnet in the axial direction.

[0024] The sensing magnet may include a non-magnetized region, which may be disposed between the first sensing magnet and the second sensing magnet along the radial direction.

[0025] The motor may include a substrate spaced apart from the yoke, the substrate may include a third sensor, the third sensor partially overlapping the first sensing magnet in the axial direction and partially overlapping the second sensing magnet in the axial direction.

[0026] Beneficial effects

[0027] According to the embodiments described, beneficial effects are provided in satisfying high constant speed drive conditions.

[0028] According to the embodiment described, it has the advantage of simplifying the structure of the second sensing magnet.

[0029] According to the embodiment, it has the advantage of accurately identifying the position of the rotor by using a second sensing magnet to generate an index signal.

[0030] According to the embodiment described, there is an advantage in using a single sensor to accurately identify the rotor position. Attached Figure Description

[0031] Figure 1 This is a perspective view showing the motor according to an embodiment;

[0032] Figure 2 It is shown Figure 1 An exploded perspective view of the motor shown;

[0033] Figure 3 It shows along Figure 1 A side sectional view of the motor taken by line AA;

[0034] Figure 4 is a plan view showing a sensing magnet;

[0035] Figure 5 is a plan view showing a length in a circumferential direction of a first pole and a length in a circumferential direction of a second pole in a sensing magnet;

[0036] Figure 6 is a view showing a first sensor, a second sensor, and a sensing magnet;

[0037] Figure 7 is a view showing a control unit, a first sensor, and a second sensor;

[0038] Figure 8 is a plan view showing a sensing magnet according to a modification example;

[0039] Figure 9 is a plan view showing a sensing magnet according to another modification example.

[0040] Figure 10 is a plan view showing a sensing magnet according to still another modification example;

[0041] Figure 11 is a view showing a sensing signal generated by a change in magnetic flux sensed by a first sensor of Figure 10 ;

[0042] Figure 12 is a view showing a yoke;

[0043] Figure 13 is a side cross-sectional view of the yoke taken along a line B-B of Figure 12 ; DETAILED DESCRIPTION

[0044] A direction parallel to a longitudinal direction (up-down direction) of the shaft is referred to as an axial direction, a direction perpendicular to the axial direction of the shaft is referred to as a radial direction, and a direction around a circumference of a circle having a radius in the radial direction around the shaft is referred to as a circumferential direction.

[0045] Figure 1 is a perspective view showing a motor according to the embodiment, Figure 2 is an exploded perspective view of the motor shown in Figure 1 , Figure 3 is a side cross-sectional view of the motor taken along a line A-A of Figure 1 . Hereinafter, the term "inner side" refers to a direction toward the shaft 100, and the term "outer side" refers to a direction opposite to the "inner side".

[0046] Referring to Figures 1 to 3 , the motor according to the embodiment can include a shaft 100, a rotor 200, and a stator 300.

[0047] The shaft 100 is coupled to the yoke 210 of the rotor 200. The shaft 100 can be coupled to the yoke 210 in a press-fit manner. Alternatively, the shaft 100 can be integrally formed with the yoke 210. The shaft 100 rotates together with the rotor 200. The shaft 100 is rotatably supported by a bearing disposed inside the bearing housing 500.

[0048] The rotor 200 can include the yoke 210, a driving magnet, and a sensing magnet.

[0049] The yoke 210 is joined to the shaft 100. The shaft 100 can be located at the center of the yoke 210.

[0050] The driving magnet 220 serves to rotate the yoke 210. The driving magnet 220 can be disposed on the inner surface of the yoke 210. The driving magnet 220 can be disposed to face the stator 300 in the radial direction of the rotor 200. When an electrical interaction occurs between the driving magnet 220 and the coil of the stator 300, the yoke 210 rotates. The driving magnet 220 can be formed by combining a plurality of unit magnets. Alternatively, the driving magnet 220 can be a single member having a ring shape.

[0051] The sensing magnet 230 serves to accurately identify the position of the rotor 200. The sensing magnet 230 can be disposed on the inner surface of the yoke 210. In addition, the sensing magnet 230 can be disposed to face the substrate 400 in the axial direction.

[0052] The stator 300 can be disposed between the shaft 100 and the yoke 210. The stator 300 can be fixed to the outer surface of the bearing housing 500. The stator 300 includes a core of the stator 300 having a plurality of teeth, and a coil can be wound around the teeth. The teeth can include an insulator that insulates the coil from the core of the stator 300.

[0053] The substrate 400 is disposed at one side of the yoke 210. The substrate 400 can include a first sensor 410 and a second sensor 420. The first sensor 410 can be a Hall integrated circuit (IC) configured to detect a change in magnetic flux of the sensing magnet 230. The second sensor 420 can be an encoder IC. The first sensor 410 and the second sensor 420 can each be disposed to face the sensing magnet 230 in the axial direction.

[0054] The bearing housing 500 is a member for accommodating a bearing 700 therein. The bearing housing 500 can include an area of a cylindrical member or the like disposed to extend in the axial direction.

[0055] The bearing housing 500 is fixed to the plate 600. Although the plate 600 and the bearing housing 500 are shown as separate components, the plate 600 and the bearing housing 500 can be integrally formed. The substrate 400 can be placed on one surface of the plate 600.

[0056] The bearings 700 can be installed inside one end portion of the bearing housing 500 and the other end portion of the bearing housing 500 in the axial direction. The bearings 700 rotatably support the shaft 100. The bearings 700 can be disposed not to overlap the stator 300 in the radial direction of the motor. For example, in the axial direction, any one of the two bearings 700 can be disposed above the stator 300, and the other of the two bearings 700 can be disposed below the stator 300. In addition, any one of the two bearings 700 can be disposed above the driving magnet 220 in the axial direction.

[0057] The bushing 800 is a member for coupling the yoke 210 and the holder 900. The bushing 800 is disposed between the yoke 210 and the holder 900 in the axial direction and couples the yoke 210 and the holder 900. A hole in which a screw tap is formed in the axial direction can be formed in the bushing 800. The coupling member 10 passing through a partial area of the holder 900 and coupled thereto is coupled to the hole disposed in the bushing 800 to couple the yoke 210 and the holder 900. When the yoke 210 rotates, the bushing 800 rotates, and the holder 900 also rotates therewith. The bushing 800 can be a cylindrical member. In the axial direction, one surface of the bushing 800 can be in contact with the yoke 210, and the other surface of the bushing 800 can be in contact with the holder 900.

[0058] The holder 900 fixes the mirrors 1000 and 1100. In addition, the holder 900 is coupled to the bushing 800 and rotates with the yoke 210. The holder 900 can be a member having a frame with an H-beam shape in cross section. The holder 900 having the above-described shape has the advantages of high bending resistance and significant weight reduction. The first mirror 1000 and the second mirror 1100 can be disposed on one surface and the other surface of the holder 900 to face each other.

[0059] The mirrors 1000 and 1100 are used to reflect laser light emitted to the detection target. The mirrors 1000 and 1100 can include a first mirror 1000 disposed on one surface of the holder 900 and a second mirror 1100 disposed on the other surface of the holder 900. When the yoke 210 is rotated, the holder 900 is rotated, and the mirrors 1000 and 1100 are also rotated according to the rotation of the holder 900. The mirrors 1000 and 1100 can be plate-shaped members extending in the axial direction. The mirrors 1000 and 1100 and the holder 900 can be coupled by an adhesive.

[0060] Figure 4 is a plan view showing a sensing magnet.

[0061] Referring to Figure 4 The sensing magnet 230 can include a first sensing magnet 231 and a second sensing magnet 232.

[0062] The first sensing magnet 231 is disposed on a first circumference O1. For example, the first sensing magnet 231 can be disposed such that a center in a radial direction of the first sensing magnet 231 is disposed on the first circumference O1. The second sensing magnet 232 is disposed on a second circumference O2. For example, the second sensing magnet 232 can be disposed such that a center in a radial direction of the second sensing magnet 232 is disposed on the second circumference O2. The first circumference O1 and the second circumference O2 are concentrically disposed with respect to a center C of the sensing magnet 230. That is, the first sensing magnet 231 and the second sensing magnet 232 can be concentrically disposed. In addition, the first sensing magnet 231 and the second sensing magnet 232 can be disposed to overlap in the radial direction. A radius of the first circumference O1 is smaller than a radius of the second circumference O2. Accordingly, the second sensing magnet 232 can be disposed outside the first sensing magnet 231.

[0063] The first sensing magnet 231 is a member configured to generate a sensing signal for accurately detecting a position of the rotor 200. The first sensing magnet 231 can include a plurality of first poles P1 and a plurality of second poles P2. The first poles P1 and the second poles P2 can be alternately disposed along a circumferential direction of the sensing magnet 230. A polarity of the first poles P1 is different from a polarity of the second poles P2. For example, hereinafter, the first poles P1 can be N poles, and the second poles P2 can be S poles.

[0064] The second sensing magnet 232 is a member configured to generate a sensing signal for detecting one rotation of the rotor 200. The second sensing magnet 232 can include a first pole P3 and a second pole P4. For example, the second sensing magnet 232 can include one first pole P3 and one second pole P4. The second pole P4 is disposed at both sides of the first pole P3 to more accurately detect a magnetic flux change at a boundary of the first pole P3.

[0065] Figure 5 is a plan view showing the length in the circumferential direction of the first pole P1 and the length in the circumferential direction of the second pole P2 of the sensing magnet 230.

[0066] Referring to Figure 5 In the second sensing magnet 232, the length L3 in the circumferential direction of the first pole P3 is different from the length L4 in the circumferential direction of the second pole P4. Hereinafter, the length in the circumferential direction can be the length on the first circumference O1 or the length on the second circumference O2. In the second sensing magnet 232, the length L3 in the circumferential direction of the first pole P3 can be shorter than the length L4 in the circumferential direction of the second pole P4. In the first sensing magnet 231, the length L1 in the circumferential direction of the first pole P1 and the length L2 in the circumferential direction of the second pole P2 can be the same. In addition, the length L3 in the circumferential direction of the first pole P3 of the second sensing magnet 232 can be longer than the length L1 in the circumferential direction of the first pole P1 of the first sensing magnet 231.

[0067] The length L3 in the circumferential direction of the first pole P3 of the second sensing magnet 232 can be shorter than the sum of the length L1 in the circumferential direction of one first pole P1 and the length L2 in the circumferential direction of one second pole P2 of the first sensing magnet 231. This is because the position of one end or the other end of the first pole P3 of the second sensing magnet 232 in the circumferential direction of the sensing magnet 230 is an important position for recognizing one rotation of the rotor 200, which is considered to limit the length L3 in the circumferential direction of the first pole P3. When the length L3 in the circumferential direction of the first pole P3 of the second sensing magnet 232 is longer than the sum of the length L1 in the circumferential direction of one first pole P1 and the length L2 in the circumferential direction of one second pole P2 of the first sensing magnet 231, it is difficult to accurately recognize one rotation of the rotor 200.

[0068] One end of the second sensing magnet 232 can be disposed on the first straight line H1 in the radial direction, together with one end of the first sensing magnet 231. The other end of the second sensing magnet 232 can be disposed on the second straight line H2 in the radial direction. The other end of the first sensing magnet 231 can be disposed on a straight line different from the second straight line H2. The first straight line H1 can correspond to a reference position of the rotation angle of the rotor 200. That is, the position in the circumferential direction of the first straight line H1 can be a reference position for recognizing one rotation of the rotor 200.

[0069] Figure 6 is a view showing the first sensor 410, the second sensor 420, and the sensing magnet 230.

[0070] Referring to Figure 6At least a portion of the first sensor 410 can be disposed to overlap the first sensing magnet 231 in the axial direction. The first sensor 410 detects a change in magnetic flux corresponding to rotation of the first sensing magnet 231. At least a portion of the second sensor 420 can be disposed to overlap the second sensing magnet 232 in the axial direction. The second sensor 420 detects a change in magnetic flux corresponding to rotation of the second sensing magnet 232. For example, the second sensor 420 can detect a change in magnetic flux due to one of the first poles P1 in the second sensing magnet 232.

[0071] The first sensor 410 and the second sensor 420 can be disposed on the substrate 400.

[0072] Figure 7 is a view illustrating the control unit 1, the first sensor 410, and the second sensor 420.

[0073] Referring to Figure 7 The control unit 1 receives information about a change in magnetic flux detected by the first sensor 410. When the first sensor 410 detects the first pole P1, the control unit 1 can generate a first sensing signal S1 having a pulse waveform of an ON state with a voltage of 5 V, and when the first sensor 410 detects the second pole P2, the control unit 1 can generate a second sensing signal S2 having a pulse waveform of an Off state with a voltage of 0 V. In this case, the first sensing signal S1 and the second sensing signal S2 can have a phase difference.

[0074] The control unit 1 receives information about a change in magnetic flux detected by the second sensor 420. When the second sensor 420 detects the first pole P3, the control unit 1 can generate a third sensing signal S3 having a pulse waveform of an ON state with a voltage of 5 V, and when the second sensor 420 detects the second pole P4, the control unit 1 can generate a third sensing signal S3 having a pulse waveform of an Off state with a voltage of 0 V. The third sensing signal S3 has one index pulse waveform I because it has one first pole P3. A point in time at which the index pulse waveform I is generated can become a reference for one rotation of the rotor 200.

[0075] Figure 8 is a plan view illustrating the sensing magnet 230 according to a modified example.

[0076] Referring to Figure 8 In the sensing magnet 230 according to the modified example, the second sensing magnet 232 can be disposed inside the first sensing magnet 231. Accordingly, the first sensor 410 can be disposed on the opposite outer side of the second sensor 420.

[0077] Figure 9 is a plan view illustrating the sensing magnet 230 according to another modified example.

[0078] Referring to Figure 9 , the sensing magnet 230 according to another modification example can include a non-magnetized region 233. The non-magnetized region 233 can be disposed between the second sensing magnet 232 and the first sensing magnet 231 in the radial direction.

[0079] Figure 10 is a plan view illustrating the sensing magnet 230 according to still another modification example.

[0080] Referring to Figure 10 , the change in the magnetic flux of the first sensing magnet 231 and the change in the magnetic flux of the second sensing magnet 232 can be detected by one first sensor 410. A portion of the first sensor 410 can be disposed to overlap the first sensing magnet 231 in the axial direction. Another portion of the first sensor 410 can be disposed to overlap the second sensing magnet 232 in the axial direction. That is, the first sensor 410 can be disposed to span the first sensing magnet 231 and the second sensing magnet 232 in the radial direction. The first sensing signal S1 and the second sensing signal S2 can be generated using only the first sensor 410, the position of the rotor 200 can be detected by the first sensing signal S1 and the second sensing signal S2, and one rotation of the rotor 200 can be detected by the third sensing signal S3.

[0081] Figure 11 is a view illustrating a sensing signal generated due to the change in the magnetic flux detected by Figure 10 the first sensor 410.

[0082] Referring to Figure 11 , when the second sensing magnet passes through the first sensor 410, an irregular pulse waveform N is formed in the first sensing signal S1 and the second sensing signal S2. This is because, when the first pole P1 of the second magnet passes through the first sensor 410, the regular change in the magnetic flux due to the first pole P1 and the second pole P2 of the first sensing magnet is affected. An index signal for identifying one rotation of the rotor 200 can be extracted by using the irregular pulse waveform N. The width of the irregular waveform is different from the width of the regular pulse waveform due to the first sensing magnet 231.

[0083] The control unit 1 can generate the third sensing signal S3 having an index pulse waveform I at the time point of the rising edge T1 at which the irregular pulse waveform N starts in the first sensing signal S1 and the second sensing signal S2.

[0084] Because the second sensing signal S2 for detecting one rotation of the rotor 200 can be generated using only one first sensor 410 without a separate second sensor 420, there is an advantage of reducing the number of components.

[0085] Figure 12 is a view showing the yoke 210, Figure 13 is a side sectional view of the yoke 210 showing a line B-B of Figure 12 .

[0086] Referring to Figure 3 , Figure 12 and Figure 13 , the yoke 210 can include a base 211, a magnet accommodation portion 212, and a column portion 213. The yoke 210 can be a substantially cylindrical member that is open at one side and the other side. The magnet accommodation portion 212 can protrude from the base 211. The column portion 213 can protrude from the magnet accommodation portion 212. The inner diameters of the base 211, the magnet accommodation portion 212, and the column portion 213 can be different from each other. The inner diameter of the base 211 can be greater than the inner diameter of the magnet accommodation portion 212. The inner diameter of the magnet accommodation portion 212 can be greater than the inner diameter of the column portion 213.

[0087] The sensing magnet 230 is disposed at the inner side of the base 211. The driving magnet 220 is disposed inside the magnet accommodation portion 212. A portion of the bearing housing 500 can be disposed inside the column portion 213. One end surface of the column portion 213 and one end surface of the sleeve 800 are in contact in the axial direction. A hole 213a through which the shaft 100 and the coupling member 10 pass can be disposed in one surface of the column portion 213.

[0088] The column portion 213 can be disposed to overlap the retainer 900 in the radial direction. The column portion 213 can be disposed to overlap the first mirror 1000 and the second mirror 1100 in the radial direction. The yoke 210 is disposed in the above-described shape in consideration of the characteristics of the shaft 100, the first mirror 1000, and the second mirror 1100, which are disposed to extend in the axial direction.

[0089] The present application can be applied to various devices such as vehicles or home appliances, etc.

Claims

1. An electric motor, comprising: axis; Rotor, which is engaged with the shaft; as well as The stator is disposed between the shaft and the rotor. The rotor includes a yoke that engages with the shaft, and a drive magnet and a sensing magnet that engage with the yoke. The sensing magnet includes a first sensing magnet and a second sensing magnet. A first pole and a second pole are alternately arranged on the first circumference of the first sensing magnet. The second sensing magnet is disposed on a second circumference and includes a first pole and a second pole. The radius of the second circumference is different from the radius of the first circumference, and the circumferential length of the second pole of the second sensing magnet is different from the circumferential length of the first pole of the second sensing magnet. Wherein, one end of the first pole of the second sensing magnet and one end of the first pole of the first sensing magnet are arranged along a first straight line in the radial direction; and the other end of the second pole of the second sensing magnet and the other end of the second pole of the first sensing magnet are arranged along different straight lines in the radial direction. Wherein, the circumferential length of the first pole of the first sensing magnet is the same as the circumferential length of the second pole of the first sensing magnet. Wherein, the circumferential length of the first pole of the second sensing magnet is longer than the circumferential length of the first pole of the first sensing magnet. Wherein, the length of the first pole of the second sensing magnet in the circumferential direction is shorter than the sum of the length of the first pole of the first sensing magnet in the circumferential direction and the length of the second pole of the first sensing magnet at the circumferential position.

2. The motor according to claim 1, wherein, The length of the first pole of the second sensing magnet in the circumferential direction is shorter than the length of the second pole of the second sensing magnet in the circumferential direction.

3. The motor according to claim 2, wherein, The first straight line corresponds to the reference position of the rotation angle of the rotor.

4. The motor according to claim 1, wherein, The second sensing magnet has a first pole and a second pole.

5. The motor according to claim 1, wherein, The yoke includes: Base; A magnet receiving portion, the magnet receiving portion protruding from the base; and A column portion that protrudes from the magnet receiving portion.

6. The motor according to claim 5, wherein, The sensing magnet is mounted on the base.

7. The motor according to claim 1, wherein, The motor includes a substrate spaced apart from the yoke, the substrate including a first sensor and a second sensor, at least a portion of the first sensor overlapping the first sensing magnet in the axial direction, and a portion of the second sensor overlapping the second sensing magnet in the axial direction.

8. The motor according to claim 1, wherein, The sensing magnet includes a non-magnetized region, which is disposed between the first sensing magnet and the second sensing magnet in the radial direction.

Images