stepping motor

Abstract

A stepping motor of the present invention includes a stator, and a rotor disposed opposite to the stator and movable in a prescribed moving direction. The stator has a plurality of main poles, windings for the respective main poles, a plurality of stator teeth disposed at intervals in a circumferential direction on the respective main poles, and stator slots formed between adjacent stator teeth. The rotor has a plurality of rotor teeth disposed at intervals in the moving direction, and rotor slots formed between adjacent rotor teeth. In at least one of the stator slots and the rotor slots, a slot magnet composed of a hard magnetic insert magnetized in a depth direction of the slot is disposed. A width of the slot magnet in the moving direction is 60% to 80% of a width of the slot in the moving direction.

Description

Technical Field

[0001] This invention relates to stepper motors. Background Technology

[0002] A hybrid stepper motor includes a rotor, which is constructed by holding a disk-shaped magnet between a pair of rotor segments with multiple rotor teeth formed at intervals on their outer circumference. A stator is disposed around the rotor. The stator has multiple main poles, each with multiple stator teeth arranged opposite to the rotor. The multiple stator teeth are arranged circumferentially at substantially the same intervals as the rotor teeth. The maximum torque of the hybrid stepper motor is limited by magnetic saturation between the stator and rotor teeth.

[0003] Patent document 1 discloses a stepper motor with a structure in which permanent magnets are inserted into slots formed between adjacent rotor teeth and / or adjacent stator teeth. This structure provides a magnetic structure that reduces magnetic saturation and effectively utilizes the generated magnetic flux, thereby increasing the maximum torque. In other words, the permanent magnets embedded in the slots suppress magnetic flux leakage, concentrating the gap flux between the stator and rotor teeth, thus contributing to increased torque.

[0004] Patent document 1 describes a relationship between the holding force of the permanent magnet inserted into the slot and the ratio of the slot depth to the slot width (width-depth ratio), and states that there exists an optimal width-depth ratio (page 6, left column, line 37 to right column, line 18).

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Publication No. 7-8126 Summary of the Invention

[0008] The technical problem that the invention aims to solve

[0009] When manufacturing a stepper motor with a structure like that in Patent Document 1, the basic design principle is to cram permanent magnets into the slots with as little clearance as possible. This is because maximizing magnetic flux is considered effective in increasing torque.

[0010] However, during a detailed analysis of the magnetic flux flow near the gap between the rotor and stator, the inventors of this invention noted that the existing basic design principles may not be optimal from the perspective of maximizing torque. Specifically, the inventors observed that a portion of the magnetic flux generated from the magnets in the slots of one of the rotor and stator flows back without reaching the other. Such flux is ineffective and does not contribute to torque.

[0011] One embodiment of the present invention provides a stepper motor with a structure that effectively increases torque, based on the unsolved discovery described above.

[0012] Technical solutions adopted to solve technical problems

[0013] One embodiment of the present invention provides a stepper motor, comprising: a stator, and a mover disposed opposite to the stator and movable relative to the stator along a predetermined movement direction. The stator includes a plurality of main poles, windings for each main pole, a plurality of stator teeth spaced apart along the movement direction and opposite to the mover on each main pole, and stator slots formed between adjacent stator teeth. The mover has a plurality of mover teeth spaced apart along the movement direction and opposite to the stator, and mover slots formed between adjacent mover teeth. In at least one of the stator slots and the mover slot, a slot magnet composed of a hard magnetic insert (an insert of hard magnetic material) magnetized along the depth direction of the slot is disposed. The width of the slot magnet in the movement direction is preferably 60% to 80% of the width of the slot in the movement direction.

[0014] The moving tooth may be a protrusion extending in a transverse direction intersecting the direction of movement. The stator tooth may be a protrusion extending in the transverse direction intersecting the direction of movement. The moving tooth and the stator tooth may extend parallel to each other. The moving tooth and the stator tooth may be positioned opposite each other, spaced apart in a relative direction orthogonal to the direction of movement and the transverse direction. This relative direction may be parallel to the depth direction of the groove.

[0015] The moving element can be a rotor that rotates about a predetermined axis of rotation. In this case, the direction of movement can be circumferential about the axis of rotation.

[0016] The slot magnets may include stator slot magnets, which are composed of hard magnetic inserts disposed within the stator slots and magnetized along the depth direction of the stator slots. Furthermore, the slot magnets may include mover slot magnets, which are composed of hard magnetic inserts disposed within the mover slots and magnetized along the depth direction of the mover slots. The stator slot magnets and the mover slot magnets may be magnetized such that, when opposite to each other, their opposing magnetic poles have opposite polarities (opposite polarities).

[0017] The stator slot magnet and the mover slot magnet can form a gap when they are facing each other. This gap can be smaller than the gap between the mover tooth and the stator tooth.

[0018] The slot magnet may contain samarium magnets.

[0019] The slot magnet may contain neodymium magnets.

[0020] Other objects, features, and effects of the present invention, whether above or further, will become more apparent from the description of the embodiments set forth below with reference to the accompanying drawings. Attached Figure Description

[0021] Figure 1 This is a perspective view illustrating the structure of a stepper motor according to one embodiment of the present invention.

[0022] Figure 2 It is an exploded perspective view used to illustrate the structure of the stator and rotor.

[0023] Figure 3 It is a magnified partial cross-sectional view showing the rotor teeth and stator teeth.

[0024] Figure 4 An example of the results of analyzing the flow of magnetic flux near the rotor and stator teeth is shown.

[0025] Figure 5A The analysis results of the torque generated when using neodymium magnets are shown as a function of the magnet width ratio.

[0026] Figure 5B The analysis results show the variation of torque relative to the magnet width ratio when using other neodymium magnets.

[0027] Figure 5C The analysis results of the torque generated when using samarium magnets are shown as a function of the magnet width ratio.

[0028] Figure 6 The analysis results show the changes in torque relative to the magnet width ratio when another aspect ratio is set.

[0029] Figure 7 The measurement results of the current torque characteristics of one embodiment are shown.

[0030] Figure 8 Measurement results of the current torque characteristics of another embodiment are shown. Detailed Implementation

[0031] Figure 1 This is a perspective view illustrating the structure of a stepper motor according to one embodiment of the present invention. The stepper motor 1 includes a stator 2, a rotor 3 (as an example of a mover), a motor flange 4, a bracket 5, and a pair of bearings 6 and 7.

[0032] The stator 2 includes a stator core 21 and windings 22. The motor flange 4 and the bracket 5 are respectively fixed to both ends of the stator core 21, and they constitute the motor housing 8.

[0033] Inside the motor housing 8, the rotor 3 is rotatably configured about a rotation axis 10. The rotor 3 includes a rotation shaft 30 configured along the rotation axis 10 and a rotor core 31 supported by the rotation shaft 30. The rotation shaft 30 is rotatably supported by a pair of bearings 6 and 7. One bearing 6 is mounted on the motor flange 4, and the other bearing 7 is mounted on the bracket 5.

[0034] Figure 2 This is an exploded perspective view used to illustrate the structure of stator 2 and rotor 3.

[0035] On the outer circumferential surface of the rotor core 31, rotor teeth 33, as an example of mover teeth, are formed at equal intervals in the circumferential direction 11 with a predetermined tooth pitch. Each rotor tooth 33 extends parallel to the rotation axis 10. However, the rotor teeth 33 may be inclined relative to the rotation axis 10.

[0036] Rotor slots 34 are formed between adjacent rotor teeth 33. Rotor slot magnets 35, as an example of mover slot magnets, are inserted into the rotor slots 34. The rotor slot magnets 35 are hard magnetic inserts (typically permanent magnet sheets) extending in a rod shape along the rotor slots 34. The rotor slot magnets 35 are fixed to the rotor slots 34, for example, by an adhesive.

[0037] The stator core 21 includes a frame-shaped back yoke 27 and a plurality of main poles 28. The plurality of main poles 28 extend from the back yoke 27 toward the rotor core 31 and are arranged circumferentially spaced around the rotor core 31. Thus, the plurality of main poles 28 divide the generally cylindrical rotor housing space 32 centered on the rotation axis 10. Winding 22 (see reference) Figure 1 . Figure 2 (Illustration omitted) It is wound around each of the main poles 28.

[0038] Each main pole 28 has a support portion 28a coupled to the back yoke 27 and a corresponding portion 28b coupled to the front end side of the support portion 28a. The corresponding portion 28b faces the rotor receiving space 32 and is therefore opposite to the rotor core 31. The corresponding portion 28b extends on both sides of the support portion 28a in the circumferential direction 11. Therefore, winding slots 29 are formed between each main pole 28 and another main pole 28 adjacent in the circumferential direction 11. Windings 22 are disposed in these winding slots 29. The corresponding portion 28b has a facing surface opposite to the rotor core 31. A plurality of stator teeth 23 protruding toward the rotation axis 10 are formed on this facing surface. The plurality of stator teeth 23 are arranged at equal intervals along the circumferential direction 11 with a predetermined tooth pitch. Each stator tooth 23 extends along the rotation axis 10 in a manner that matches the rotor teeth 33. When the rotor teeth 33 are arranged at an angle relative to the rotation axis 10, the stator teeth 23 are also arranged at an angle relative to the rotation axis 10 accordingly.

[0039] Stator slots 24 are formed between adjacent stator teeth 23. Stator slot magnets 25 are inserted into stator slots 24. Stator slot magnets 25 are hard magnetic inserts (typically permanent magnet sheets) extending in a rod shape along stator slots 24. Stator slot magnets 25 are fixed in stator slots 24, for example, by adhesive.

[0040] The rotor slot magnet 35 and the stator slot magnet 25 are magnetized along a radial direction from the rotation axis 10. The radial direction from the rotation axis 10 refers to a direction orthogonal to the rotation axis 10. Therefore, the rotor slot magnet 35 is magnetized along the depth direction of the rotor slot 34. Furthermore, the stator slot magnet 25 is magnetized along the depth direction of the stator slot 24. Regarding the radial direction from the rotation axis 10, the magnetization direction of the rotor slot magnet 35 is the same as that of the stator slot magnet 25. Therefore, when the rotor slot magnet 35 and the stator slot magnet 25 are facing each other, the magnetic poles of the opposing rotor slot magnet 35 and the stator slot magnet 25 are magnetic poles of opposite polarity.

[0041] Figure 3 This is a magnified partial cross-sectional view showing the rotor teeth 33 and stator teeth 23.

[0042] Rotor teeth 33 are protrusions extending in a transverse direction through the circumferential direction 11, which is the direction of movement. The rotor teeth 33 protrude outwards (away from the rotation axis 10) with a substantially constant width in a radial direction within a cut plane orthogonal to the rotation axis 10. The rotor teeth 33 have a top surface 33a facing away from the rotation axis 10. The top surface 33a is along the circumferential direction 11 surrounding the rotation axis 10. In the cut plane orthogonal to the rotation axis 10, a plurality of rotor teeth 33 have substantially overlapping cross-sectional shapes and are equally spaced with a constant rotor tooth pitch Pr. Rotor slots 34 formed between adjacent rotor teeth 33 are defined by a pair of substantially parallel side surfaces 34b, 34c defined by these rotor teeth 33, and a bottom surface 34a formed between these side surfaces 34b, 34c, having a substantially rectangular cross-sectional shape. The bottom surface 34a is along the circumferential direction 11 surrounding the rotation axis 10.

[0043] In the outer peripheral surface (top surface 33a) of the rotor teeth 33, the length (circumferential width) of the circumferential direction 11 around the rotation axis 10 is called the "rotor tooth width Tr". On the other hand, in an imaginary cylindrical surface defined by connecting the outer peripheral surfaces (top surface 33a) of the multiple rotor teeth 33, the length (circumferential width) of the rotor slot 34 associated with the circumferential direction 11 around the rotation axis 10 is called the "rotor slot width Sr". Furthermore, the distance from the bottom surface 34a of the rotor slot 34 to the top surface 33a of the rotor teeth 33, i.e., the height of the rotor teeth 33, is called the "rotor tooth height Hr".

[0044] The rotor slot magnet 35 is made of a hard magnetic material and is a rod-shaped insert (typically a permanent magnet plate) extending along the rotation axis 10. In this embodiment, the rotor slot magnet 35 has a generally rectangular cross-section orthogonal to the rotation axis 10. The rotor slot magnet 35 has a bottom surface 35a opposite to the bottom surface 34a of the rotor slot 34, a top surface 35d (opposite surface) located on the opposite side of the rotation axis 10 relative to the bottom surface 35a, and a pair of side surfaces 35b, 35c formed between the bottom surface 35a and the top surface 35d. The bottom surface 35a and the top surface 35d are chamfered with respect to the side surfaces 35b, 35c to form an arc-shaped cross-section. The bottom surface 35a of the rotor slot magnet 35 is bonded (fixed) to the bottom surface 34a of the rotor slot 34, for example, by an adhesive.

[0045] A pair of side surfaces 35b and 35c are respectively opposite to a pair of side surfaces 34b and 34c of the rotor slot 34. One or both of these side surfaces 35b and 35c form a gap 36 between the opposite side surfaces 34b and 34c of the rotor slot 34. Therefore, the distance between the pair of side surfaces 35b and 35c of the stator slot magnet 25, i.e., the magnet width (rotor magnet width) MWr, is less than the rotor slot width Sr.

[0046] The top surface 35d of the rotor slot magnet 35 is the opposing surface to the stator 2. In this embodiment, the top surface 35d is located backward toward the axis of rotation 10 compared to the imaginary cylindrical surface defined by the outer peripheral surface (top surface 33a) connecting the plurality of rotor teeth 33. That is, the distance between the bottom surface 35a and the top surface 35d, i.e., the magnet thickness (rotor magnet thickness) MTr, is less than the depth of the rotor slot 34 (= rotor tooth height Hr). Therefore, the entire rotor slot magnet 35 is accommodated within the rotor slot 34. The top surface 35d is substantially parallel to this imaginary cylindrical surface. Strictly speaking, the top surface 35d can be a plane, which can be parallel to the plane formed by connecting the opening edges of the corresponding rotor slot 34. In this embodiment, the plurality of rotor slot magnets 35 inserted into the plurality of rotor slots 34 respectively have substantially the same shape and size.

[0047] Stator teeth 23 are protrusions extending in a transverse direction through the circumferential direction 11, which is the direction of movement. Stator teeth 23 extend parallel to rotor teeth 33. Stator teeth 23 protrude inward with a substantially constant width (closer to the direction of rotation axis 10) in a radial direction within a cut plane orthogonal to the rotation axis 10. Stator teeth 23 have a top surface 23a facing the rotation axis 10. Top surface 23a is along the circumferential direction 11 surrounding the rotation axis 10. In the cut plane orthogonal to the rotation axis 10, a plurality of stator teeth 23 have substantially overlapping cross-sectional shapes and are equally spaced with a constant stator tooth pitch Pr. Stator slots 24 formed between adjacent stator teeth 23 are defined by a pair of substantially parallel side surfaces 24b, 24c defined by these stator teeth 23 and a bottom surface 24a formed between these side surfaces 24b, 24c, and have a substantially rectangular cross-sectional shape. Bottom surface 24a is along the circumferential direction 11 surrounding the rotation axis 10.

[0048] In the inner circumferential surface (top surface 23a) of the stator tooth 23, the length (circumferential width) of the circumferential direction 11 around the rotation axis 10 is called the "stator tooth width Tr". On the other hand, in the imaginary cylindrical surface defined by connecting the inner circumferential surfaces (top surfaces 23a) of the multiple stator teeth 23, the length (circumferential width) of the stator slot 24 related to the circumferential direction 11 around the rotation axis 10 is called the "stator slot width Ss". Furthermore, the distance from the bottom surface 24a of the stator slot 24 to the top surface 23a of the stator tooth 23, i.e., the height of the stator tooth 23, is called the "stator tooth height Hs".

[0049] The stator slot magnet 25 is made of a hard magnetic material and is a rod-shaped insert (typically a permanent magnet sheet) extending along the rotation axis 10. In this embodiment, the cross-section of the stator slot magnet 25 orthogonal to the rotation axis 10 is generally rectangular. The stator slot magnet 25 has a bottom surface 25a opposite to the bottom surface 24a of the stator slot 24, a top surface 25d (opposite surface) located on the side of the rotation axis 10 opposite to the bottom surface 25a, and a pair of side surfaces 25b, 25c formed between the bottom surface 25a and the top surface 25d. The bottom surface 25a and the top surface 25d are chamfered with respect to the side surfaces 25b, 25c to form an arc-shaped cross-section. The bottom surface 25a of the stator slot magnet 25 is bonded (fixed) to the bottom surface 24a of the stator slot 24, for example, by an adhesive.

[0050] A pair of side surfaces 25b and 25c are respectively opposite to a pair of side surfaces 24b and 24c of the stator slot 24. One or both of these side surfaces 25b and 25c form a gap 26 between the opposite side surfaces 24b and 24c of the stator slot 24. Therefore, the distance between the pair of side surfaces 25b and 25c of the stator slot magnet 25, i.e., the magnet width (stator magnet width) MWs, is less than the stator slot width Ss.

[0051] The top surface 25d of the stator slot magnet 25 is the opposing surface to the rotor 3. In this embodiment, the top surface 25d is located in a position receding away from the rotation axis 10 compared to the imaginary cylindrical surface defined by the inner circumferential surface (top surface 23a) connecting the plurality of stator teeth 23. That is, the distance between the bottom surface 25a and the top surface 25d, i.e., the magnet thickness (stator magnet thickness) MTs, is less than the depth of the stator slot 24 (= stator tooth height Hs). Thus, the entire stator slot magnet 25 is accommodated within the stator slot 24. The top surface 25d is substantially parallel to this imaginary cylindrical surface. Strictly speaking, the top surface 25d can be a plane, which can be parallel to the plane formed by connecting the opening edges of the corresponding stator slot 24. In this embodiment, the plurality of stator slot magnets 25 inserted into the plurality of stator slots 24 respectively have substantially the same shape and size.

[0052] The rotor slot magnet 35 and the stator slot magnet 25 may have substantially the same shape and size.

[0053] When rotor teeth 33 and stator teeth 23 are opposite each other, a fixed gap (void) is formed between them in relation to their relative direction, i.e., the radial direction (the depth direction of slots 34 and 24). This gap is called the "iron gap ΔF". When rotor slot 34 and stator slot 24 are opposite each other, a fixed gap is formed between rotor slot magnet 35 and stator slot magnet 25 in relation to their relative direction, i.e., the radial direction (the depth direction of slots 34 and 24). This gap is called the "magnet gap ΔM".

[0054] When the iron clearance ΔF is sufficiently small, the stator tooth pitch Ps and the rotor tooth pitch Pr are essentially equal, the rotor tooth width Tr and the stator tooth width Ts are essentially equal, and correspondingly, the rotor slot width Sr and the stator slot width Ss are essentially equal. Therefore, the stator tooth pitch Ps and the rotor tooth pitch Pr are sometimes referred to as "tooth pitch P", the rotor tooth width Tr and the stator tooth width Ts are referred to as "tooth width T", and the rotor slot width Sr and the stator slot width Ss are referred to as "slot width S".

[0055] In this embodiment, the rotor tooth height Hr and the stator tooth height Hs can be substantially equal to each other. Therefore, the rotor tooth height Hr and the stator tooth height Hs are sometimes referred to as "tooth height H" below. Furthermore, in this embodiment, the rotor slot magnet 35 and the stator slot magnet 25 can be constructed from hard magnetic inserts (typically permanent magnet sheets) of substantially the same shape and size. Therefore, the rotor magnet width MWr and the stator magnet width MWs are sometimes referred to as "magnet width MW" below. Additionally, the rotor magnet thickness MTr and the stator magnet thickness MTs are sometimes referred to as "magnet thickness MT".

[0056] In addition, rotor slot magnet 35 and stator slot magnet 25 are sometimes collectively referred to as "slot magnets". Rotor slot 34 and stator slot 24 are sometimes collectively referred to as "slots".

[0057] Figure 4 An example of the results of analyzing the magnetic flux flow near rotor tooth 33 and stator tooth 23 is shown.

[0058] The magnetic flux across rotor 3 and stator 2 contributes to the torque that rotates rotor 3. This magnetic flux includes the flux exiting stator teeth 23 and entering rotor teeth 33, the flux exiting stator teeth 23 and entering rotor slot magnets 35, the flux exiting stator slot magnets 25 and entering rotor teeth 33, and the flux exiting stator slot magnets 25 and entering rotor slot magnets 35.

[0059] On the other hand, magnetic flux circulating through the stator teeth 23 and stator slot magnets 25 but not through the rotor teeth 33 or rotor slot magnets 35, i.e., magnetic flux returning in the stator 2, does not contribute to torque. Similarly, magnetic flux circulating through the rotor teeth 33 and rotor slot magnets 35 but not through the stator teeth 23 or stator slot magnets 25, i.e., magnetic flux returning in the rotor 3, also does not contribute to torque.

[0060] The inventors of this application focus on the backflow of magnetic flux and believe that if the backflow of magnetic flux can be suppressed, the magnetic flux that contributes to torque can be increased, thereby increasing torque.

[0061] The basic design principle of stepper motors using slot magnets in the past was that maximizing torque could be achieved by inserting the slot magnet (hard magnetic material) into the slot without gaps. However, as the above analysis shows, in the structure where the slot magnet is inserted into the slot without gaps, the magnetic flux return increases, and ensuring a gap between the slot side and the slot magnet is more conducive to increasing torque.

[0062] On the other hand, if the magnet width MW is too small, the concentration efficiency of the magnetic flux on the teeth may be reduced, and the magnetic flux across the stator 2 and rotor 3 may be reduced.

[0063] Therefore, there should be an appropriate range for maximizing the torque, for the gaps 26 and 36 that need to be ensured between the sides of slots 24 and 34 and the sides of slot magnets 25 and 35.

[0064] Based on this concept, the inventors of this application studied the relationship between the magnet width MW and the torque in order to investigate the relationship between the aforementioned gaps 26 and 36. The results are explained below.

[0065] In this explanation, the following terms are defined. First, "magnet width ratio" refers to the ratio of magnet width MW to slot width S. Second, "tooth width ratio" refers to the ratio of tooth width T to tooth pitch P (= slot width S + tooth width T). Third, "tooth height ratio" refers to the ratio of tooth height H to tooth width T. These are summarized below.

[0066] Magnet width ratio = Magnet width MW / Slot width S

[0067] Tooth width ratio = Tooth width T / Tooth pitch P = Tooth width T / (Slot width S + Tooth width T)

[0068] Tooth width-to-height ratio = Tooth height H / Tooth width T

[0069] Figures 5A-5C The results of torque analysis using FEM (finite element method) for various magnet thicknesses MT and magnet widths MW are shown, with the iron gap ΔF set to 40 μm, the tooth width ratio T / P set to 39%, and the tooth height ratio H / T set to 1.0. Furthermore, empirically, it is known that in stepper motors, the torque reaches its maximum at a tooth width ratio H / T of approximately 40% (e.g., 30%–45%).

[0070] Figure 5A The analysis results show the results of using a strong neodymium sintered magnet with an energy product of 49 MGOe and a residual magnetic flux density of 1.4 T as a slot magnet. Figure 5B The analysis results are shown when a weakly sintered neodymium magnet with an energy product of 42 MGOe and a residual magnetic flux density of 1.3 T is used as a slot magnet. Figure 5C The analysis results are shown when a samarium-based magnet (e.g., a samarium-cobalt magnet) with an energy product of 26 MGOe and a residual magnetic flux density of 1.0 T is used as a slot magnet. Neodymium sintered magnets are an example of neodymium-based magnets, including, for example, neodymium-iron-boron alloys.

[0071] exist Figures 5A-5C In the figure, curves L100, L300, L400, L600, and L800 represent the variation of the generated torque with respect to the magnet width ratio MW / S. Curves L100, L300, L400, L600, and L800 represent the analysis results when the magnet thickness MT is adjusted and the magnet gap ΔM is set to 100μm, 300μm, 400μm, 600μm, and 800μm, respectively.

[0072] A comparison of curves L100, L300, L400, L600, and L800 shows that as the magnet thickness MT increases, the top surfaces 25d and 35d (gap surfaces) of the slot magnet approach the top surfaces 23a and 33a (tooth surfaces) of teeth 23 and 33, respectively, leading to a tendency for increased torque. Furthermore, it can be seen that regardless of the magnet gap ΔM, the torque reaches its maximum at a specific magnet width MW. Therefore, as shown by the dashed line L1, it is preferable to have a smaller magnet gap ΔM and a smaller magnet width MW for achieving the maximum torque design.

[0073] In addition, from Figures 5A-5C The comparison also shows that if the residual magnetic flux density is about 1T (e.g., 1.0T to 1.4T), even if magnets with different magnetic flux densities are used, the torque will not change when the torque reaches its maximum at a specific magnet width MW.

[0074] exist Figure 5A In the example, it can be seen that in order to achieve a design with maximum torque, the magnet width ratio MW / S can be set within the range of 60% to 75% (preferably 62% to 72%). Figure 5B In the example shown, it can be seen that in order to achieve the maximum torque design, the magnet width ratio MW / S can be set in the range of 63% to 76% (preferably 65% ​​to 73%). In the example shown in Figure 5c, it can be seen that in order to achieve the maximum torque design, the magnet width ratio MW / S can be set in the range of 73% to 80% (preferably 75% to 80%).

[0075] Moreover, it is known that regardless of the type of magnet or the magnet gap ΔM, a design that generates large torque can be achieved by setting the magnet width ratio MW / S within the range of 60% to 80%.

[0076] Figure 6 The diagram shows that, except for the face-to-height ratio H / T being 0.65, in relation to... Figure 5A Under the same conditions, the same analytical results were obtained when using a neodymium sintered magnet with an energy product of 49 MGOe and a residual magnetic flux density of 1.4 T. Curves L100, L200, and L300 represent the changes in torque relative to the magnet width ratio MW / S when the magnet thickness MT is adjusted and the magnet gap ΔM is set to 100 μm, 200 μm, and 300 μm, respectively. The dashed line L2 represents the relationship between the magnet gap and the magnet width used to maximize the torque.

[0077] and Figure 5A Compared to the previous analysis example, even with the same magnet gap ΔM, the smaller the tooth height H (i.e., the groove depth), the thinner the magnet thickness MT. Specifically, Figure 6 When the magnet gap ΔM = 100 μm (curve L100), the magnet thickness MT is equal to Figure 5A The magnet thickness MT when the magnet gap ΔM = 800 μm (curve L800).

[0078] like Figures 5A-5C As illustrated in the analysis example, stepper motors typically use a tooth width-to-height ratio of around 1. However, from... Figure 6 The analysis example shows that even when the tooth width-to-height ratio H / T decreases, the torque still reaches its maximum at a specific magnet width ratio MW / S.

[0079] exist Figure 6 In the example, it can be seen that in order to achieve a design that maximizes torque, the magnet width ratio MW / S can be set within the range of 63% to 84% (preferably 68% to 76%). Moreover, it can be seen that regardless of the type of magnet gap ΔM, a design that generates a large torque can also be achieved by setting the magnet width ratio MW / S within the range of 60% to 80%.

[0080] The magnet gap ΔM is preferably 800 μm or less, more preferably 400 μm or less, and even more preferably 200 μm or less. The magnet gap ΔM is preferably iron gap ΔF (e.g., 40 μm or more), but may also be 100 μm or more.

[0081] As an example, a motor with an installation angle of 60mm, a motor length of 40mm, and a rotor moment of inertia of 370×10⁻⁶ was prepared. -7 kgm 2 A two-phase slot magnet stepper motor with 50 rotor teeth, a tooth width ratio T / P = 39%, and a tooth width-to-height ratio H / T = 1.0 was constructed. Furthermore, the magnet width ratio MW / S was set to 75%, and the magnet thickness MT was increased, thereby narrowing the magnet gap ΔM. Neodymium sintered magnets with a residual magnetic flux density of 1.4T were used for the slot magnets. The current-torque characteristics of the stepper motor in this embodiment were measured under two-phase excitation. Figure 7 The measured values ​​are shown in curves L200, L400, and L800. As a comparative example, the measured values ​​of a hybrid stepper motor with the same size, motor length, and winding specifications are represented by curve Lh.

[0082] Curves L200, L400, and L800 correspond to magnet gap ΔM values ​​of 200 μm, 400 μm, and 800 μm, respectively. These curves show that the torque changes significantly with respect to the magnet gap ΔM. Furthermore, it can be observed that when the magnet gap ΔM is 200 μm (curve L200), approximately twice the torque is obtained compared to the hybrid type (curve Lh).

[0083] As another embodiment, a motor with an installation angle of 42mm, a motor length of 52mm, and a rotor moment of inertia of 55×10⁻⁶ was prepared. -7 kgm 2 A two-phase slot magnet stepper motor with 50 rotor teeth, a tooth width ratio T / P = 39%, and a tooth width-to-height ratio H / T = 1.0. Furthermore, the magnet gap ΔM = 200 μm, and the magnet width ratio MW / S = 76%–70%. Neodymium sintered magnets with a residual magnetic flux density of 1.4 T were used for the slot magnets. The current-torque characteristics of the stepper motor in this embodiment were measured under two-phase excitation. Figure 8 The measured values ​​are shown in curves L70, L73, and L76. As a comparative example, the measured values ​​of a hybrid stepper motor with the same size, motor length, and winding specifications are represented by curve Lh.

[0084] Curves L70, L73, and L76 correspond to magnet width ratios (MW / S) of 70%, 73%, and 76%, respectively. According to... Figure 7 and Figure 8 The comparison confirmed that even among motors with different mounting angle dimensions, slot magnet stepper motors have a torque advantage over hybrid stepper motors. Furthermore, actual measurements confirmed that the torque reaches its maximum when the magnet width ratio MW / S is 73% (curve L73).

[0085] In addition, the tooth pitch P of the rotor and stator can take various values, but the torque can be increased by using magnets (slot magnets) of appropriate width corresponding to the tooth pitch P.

[0086] The above describes one embodiment of the present invention, but the present invention can also be implemented in other ways. For example, in the above embodiment, a stepper motor with a rotor 3 rotating about a rotation axis 10 was mainly described, but the present invention can also be applied to a stepper motor having the form of a linear motor. That is, it can be configured such that the stator is arranged along a linear path and the mover moves along the stator.

[0087] Furthermore, in the above embodiment, a structure including stator slot magnet 25 and rotor slot magnet 35 is shown. However, it is possible to omit stator slot magnet 25 and only include rotor slot magnet 35, or to include only stator slot magnet 25 and omit rotor slot magnet 35.

[0088] The embodiments of the present invention have been described in detail, but these are merely specific examples used to clarify the technical content of the present invention. The present invention should not be construed as being limited to these specific examples, and the scope of the present invention is defined only by the appended claims.

[0089] This application claims priority based on Japanese Patent Application No. 2020-77740, filed on April 24, 2020, and all contents of that application are incorporated herein by reference.

[0090] Label Explanation

[0091] 1 stepper motor

[0092] 2 stators

[0093] 3. Rotor (Motor)

[0094] 10 Rotation axis

[0095] 11. Circumferential direction (movement direction)

[0096] 23 stator teeth

[0097] 24 stator slots

[0098] 25 stator slot magnets

[0099] 26 gaps

[0100] 28 main poles

[0101] 33 rotor teeth

[0102] 34 rotor slots (moving element slots)

[0103] 35 rotor slot magnets (moving slot magnets)

[0104] 36 gaps

[0105] Pr rotor tooth pitch

[0106] Tr rotor tooth width

[0107] Sr rotor slot width

[0108] Hr rotor tooth height

[0109] MWr rotor magnet width

[0110] MTr rotor magnet thickness

[0111] Ps stator tooth pitch

[0112] Ts stator tooth width

[0113] Ss stator slot width

[0114] Hs stator tooth height

[0115] MWs stator magnet width

[0116] MTs stator magnet thickness

[0117] ΔF iron gap

[0118] ΔM magnet gap.

Claims

1. A stepper motor, characterized in that, It includes a stator and a mover disposed opposite to the stator and movable relative to the stator in a predetermined direction of movement. The stator includes a plurality of main poles, windings for each main pole, a plurality of stator teeth spaced apart along the moving direction and opposite to the mover, and stator slots formed between adjacent stator teeth. The mover has a plurality of mover teeth arranged at intervals along the moving direction and opposite to the stator, and mover slots formed between adjacent mover teeth. Within the stator slot and the mover slot, slot magnets are disposed, consisting of hard magnetic inserts magnetized along the depth direction of the slot. The width of the slot magnet in the direction of movement is 60% to 80% of the width of the slot in the direction of movement. The slot magnet includes: a stator slot magnet, which is composed of a hard magnetic insert disposed within the stator slot and magnetized along the depth direction of the stator slot; and a mover slot magnet, which is composed of a hard magnetic insert disposed within the mover slot and magnetized along the depth direction of the mover slot. The tooth width of the stator tooth in the moving direction is 30% to 45% of the tooth pitch of the stator tooth in the moving direction, and the magnet thickness of the stator slot magnet is less than the depth of the stator slot. The width of the moving tooth in the moving direction is 30% to 45% of the tooth pitch in the moving direction, and the thickness of the moving slot magnet is less than the depth of the moving slot.

2. The stepper motor as described in claim 1, characterized in that, The moving element is a rotor that rotates around a predetermined axis of rotation, and the direction of movement is circumferential around the axis of rotation.

3. The stepper motor as described in claim 1, characterized in that, The stator slot magnet and the mover slot magnet are respectively magnetized such that when they are opposite to each other, their opposing magnetic poles have opposite polarities.

4. The stepper motor as described in claim 2, characterized in that, The stator slot magnet and the mover slot magnet are respectively magnetized such that when they are opposite to each other, their opposing magnetic poles have opposite polarities.

5. The stepper motor as described in any one of claims 1 to 4, characterized in that, The slot magnet comprises a samarium magnet.

6. The stepper motor as described in any one of claims 1 to 4, characterized in that, The slot magnet contains neodymium magnets.

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