Stepping motor

Abstract

To provide a stepping motor which can easily and accurately position the pole teeth of a yoke and has high stopping accuracy SOLUTION: A stator yoke 20 including an outer yoke 2 in which a plurality of pole teeth 2a formed in a comb-tooth shape are disposed in a circumferential direction and an inner yoke 4 which is provided inside the outer yoke 2 and in which a plurality of pole teeth 4a formed in a comb-tooth shape are disposed in the circumferential direction, an excitation coil 3 which excites the stator yoke 20, and a shaft 6 to which a rotor magnet 5 disposed inside the stator yoke 20 and having an outer peripheral surface magnetized to a plurality of poles is attached, wherein the outer yoke 2 has a cutout portion 2b on an outer periphery, the inner yoke 4 has a projection side 2b fitted to the notch side 4b, and the inner yoke 4 is joined to the outer yoke 2 in a state where the projection side 2b is abutted on a reference surface side 2c provided on the circumferential inside 4b of the notch side wall.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a stepping motor, and more particularly to the structure of a stator yoke thereof. [Background technology]

[0002] A conventional stepping motor includes a cylindrical rotor magnet whose circumferential surface is magnetized with different poles alternately, and a pair of stator yokes arranged to surround the rotor magnet.

[0003] Each of the pair of stator yokes consists of an inner yoke and an outer yoke in which a plurality of comb-like pole teeth are intertwined in a staggered manner in the circumferential direction, and the comb-like pole teeth are positioned by fitting the inner yoke and outer yoke together.

[0004] In a stepping motor, in order to drive the rotor magnet in steps at equal intervals, the pole teeth of the inner and outer yokes must be arranged at equal intervals. As in Patent Document 1, there is a configuration in which positioning protrusions are provided on a cylindrical frame yoke and fitted into positioning notches on the periphery of the stator yoke, thereby arranging the pole teeth at equal intervals. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-78419 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the conventional stepping motor described above, the frame yoke and stator yoke are positioned by fitting the convex portion on the periphery of the frame yoke into the notch in the stator yoke, so play due to tolerances affects the positioning and makes it impossible to position with high precision. [Means for solving the problem]

[0007] In order to solve the above problems, the stepping motor of the present invention comprises: a stator yoke including an outer yoke having a plurality of comb-shaped pole teeth arranged in the circumferential direction, and an inner yoke provided inside the outer yoke and having a plurality of comb-shaped pole teeth arranged in the circumferential direction; an excitation coil for exciting the stator yoke; a shaft on which a rotor magnet is attached, the outer circumferential surface of which is magnetized with multiple poles and is disposed inside the stator yoke; Equipped with The outer yoke has a notch on its outer periphery, the inner yoke has a protrusion that fits into the notch, The inner yoke is joined to the outer yoke in a state in which the protrusion abuts against a reference surface provided on the inner wall of the cutout portion in the circumferential direction. [Effects of the Invention]

[0008] According to the present invention, the pole teeth of the inner yoke and the outer yoke can be positioned at equal intervals with high precision, thereby realizing a highly accurate stepping motor. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an exploded perspective view of a stepping motor according to a first embodiment of the present invention; [Figure 2] Enlarged view of outer yoke 2 (9) and inner yoke 4 (7) in Figure 2 [Figure 3] Stator diagram [Figure 4] 1 is a diagram showing the main part of the present invention; [Figure 5] FIG. 10 is a diagram showing a main part of a stepping motor according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Embodiment 1) DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Fig. 1 shows an exploded perspective view of a stepping motor 100 according to a first embodiment of the present invention.

[0011] Stators 20 and 30 are arranged side by side along the axial direction of the stepping motor 100. Since the stators 20 and 30 have the same structure, the following explanation will focus on the configuration of stator 20, and the components corresponding to stator 30 will be written in parentheses.

[0012] 1, the stepping motor 100 includes a cylindrical rotor magnet 5 made of a plastic magnet or the like with different magnetic poles magnetized alternately on its outer periphery, a shaft 6 made of a non-magnetic material such as stainless steel that penetrates the rotor magnet 5 in the axial direction and is formed integrally with it, an outer yoke 2 (9) made of a soft magnetic material with multiple pole teeth 2a (9a) arranged circumferentially, an inner yoke 4 (7) made of a soft magnetic material and having multiple pole teeth 4a (7a) arranged circumferentially inside the outer yoke 2 (9), an excitation coil 3 (8) sandwiched between the inner yoke 4 (7) and the outer yoke 2 (9) to excite these yokes, and a sintered oil-impregnated bearing 1 (10) that rotatably supports the shaft. The inner yoke 4 (7) and the outer yoke 2 (9) form a stator yoke that is excited by the excitation coil 3 (8). The stator 20 (30) is composed of an inner yoke 4 (7) and an outer yoke 2 (9) arranged so that the pole teeth 2a (9a), 4a (7a) are spaced apart and mesh with each other, and an excitation coil 3 (8). The rotor magnet 5 is provided at the center of the joined inner yokes 4, 7, and is rotatably arranged in a central hole that passes through the stators 20, 30 with a gap between them and the pole teeth 2a, 4a, 7a, 9a.

[0013] The rotor magnet 5 is a molded plastic magnet, but it may also be one formed by cutting a sintered magnet, for example. In the above configuration, when the exciting coils 3, 8 are energized, the inner yokes 4, 7 and outer yokes 2, 9 are excited, and the pole teeth 2a, 4a, 7a, 9a are magnetized. As a result, they repel / attract the magnetized poles of the rotor magnet 5, generating a rotational torque, which rotates the rotor magnet 5 as the exciting coils 3, 8 are energized, and the driving force is transmitted from the shaft 6 to the outside.

[0014] Figure 2 is an enlarged view of the outer yoke 2 (9) and inner yoke 4 (7) of Figure 1, shown in Figures 2(a) and 2(b), respectively. The outer yoke 2 (9) is provided with a positioning notch 2b (9b), which is a feature of the present invention, and a reference surface 2c (9c) on its circumferential inner wall, which serves as a reference for assembly. The inner yoke 4 (7) is provided with a positioning protrusion 4b (7b), which is a feature of the present invention, and a reference surface 4c (7c) on its circumferential side wall, which serves as a reference for assembly.

[0015] Figure 3 is an explanatory diagram illustrating the structure of the stator 20 (30). Figure 3(a) is a view of the stator 20 (30) viewed from the inner yoke 4 (7) side. The inner yoke 4 (7) and the outer yoke 2 (9) are assembled by butting the reference surface 4c (7c) that serves as the reference for assembling the inner yoke 4 (7) against the reference surface 2c (9c) that serves as the reference for assembling the outer yoke 2 (9). At this time, the positioning notch 2b (9b) of the outer yoke 2 (9) is set wider than the width of the positioning protrusion 4b of the inner yoke 4 (7) so that a gap d is formed.

[0016] Figure 3(b) is a development view of the pole teeth of the stator 20 (30). In conventional assembly, the pole teeth 4a (7a) of the inner yoke 4 (7) and the pole teeth 2a (9a) of the outer yoke 2 (9) could not be accurately positioned due to play in the fit, but by assembling the inner yoke 4 (7) so that the reference surface 4c (7c) of the inner yoke 4 (7) abuts against the reference surface 2c (9c) of the outer yoke 2 (9), the play can be eliminated. This allows the pole teeth 4a (7a) and the pole teeth 2a (9a) to be positioned at equal intervals with high precision, as shown in Figure 3(b), making it possible to achieve a stepping motor with high stopping accuracy.

[0017] Figure 4 shows the main components of the present invention. The relative positions of the inner yokes 4 and 7 are determined by fitting the protrusions 4d and 7d into the holes 7e, as shown in Figure 2. The outer yoke 2 is attached to the inner yokes 4 and 7 so that the reference surface 2c abuts against the reference surface 4c, and the outer yoke 9 is attached so that the reference surface 9c abuts against the reference surface 7c. The outer periphery joint surfaces and positioning protrusions 4b and 7b are fixed in place by welding or other methods. By making the inner yokes 4 and 7 and the outer yokes 2 and 9 the same component, when the stators 20 and 30 are butted together, the reference surfaces 4c and 7c of the inner yokes 4 and 7 and the reference surfaces 2c and 9c of the outer yoke 29 are offset vertically and horizontally. By making the inner yokes 4 and 7 and the outer yokes 2 and 9 the same component, a stepping motor with high stopping accuracy can be realized while minimizing mold investment.

[0018] 4, the reference surfaces 7c (4c), 9c (2c) of the other stators are positioned within the range of the gap d in the circumferential direction between the positioning protrusion 4b (7b) of the upper stator 20 and the inner wall of the positioning cutout 2b (9b). However, the present invention is not limited to this, and the reference surfaces 7c, 9c of the other stators may be positioned at positions shifted in the circumferential direction from the gap d.

[0019] However, it is more preferable to set the positioning protrusions 4b and 7b at the same circumferential position or the positioning notches 2b and 9b at the same circumferential position. That is, the outer yokes 2 and 9 are typically welded at several locations along their outer periphery. These welds reduce leakage magnetic flux from the boundary when the stepping motor 100 is in operation. It has been found that keeping non-welded areas as short as possible more effectively reduces leakage magnetic flux from the non-welded areas. Alternatively, magnetic flux reaching the radially outer ends of the positioning protrusions 4b and 7b directly becomes leakage magnetic flux. Therefore, by aligning the circumferential positions of the positioning notches 2b and 9b (placing them in the same position) or the positioning protrusions 4b and 7b (placing them in the same position), the circumferential length of the non-welded areas can be shortened, thereby reducing leakage magnetic flux from the non-welded areas. The alignment of the circumferential positions can be selected based on the most effective method for each actual product.

[0020] (Embodiment 2) 5 is a diagram showing the main parts of a stepping motor according to embodiment 2 of the present invention. Note that the components of this embodiment are the same as those described in embodiment 1, and components having similar structures will be described using the same reference numerals, and their description will be omitted.

[0021] Although the basic configuration is the same as in embodiment 1, in embodiment 2 the reference surfaces 2c, 9c of the stator 20 (30) are aligned on one circumferential side (left in the example of FIG. 5) of the upper and lower stators. In this embodiment, the spacing between the pole teeth 4a, 7a of the inner yokes 4, 7 is set in this assembled state, and in this case, by using inner yokes 4, 7 and outer yokes 2, 9 with different shapes on the upper and lower sides, it is possible to align the reference surfaces 2c, 9c of the stator 20 (30).

[0022] In the stepping motor of embodiment 2, as in embodiment 1, by assembling the motor by butting the reference surfaces together, it is possible to eliminate backlash and position the pole teeth at equal intervals with high precision, thereby realizing a stepping motor with high stopping precision. [Explanation of symbols]

[0023] 1, 10 Bearings 2, 9 outer yoke 2a, 9a pole teeth 2b, 9b Positioning notch 2c, 9c Abutting reference surface 3, 8 coils 4, 7 inner yoke 4a, 7a pole teeth 4b, 7b Positioning protrusions 4c, 7c Abutting reference surface 5 rotor magnet 6 shafts 20, 30 Stator

Claims

1. a stator yoke including an outer yoke having a plurality of comb-shaped pole teeth arranged in the circumferential direction, and an inner yoke provided inside the outer yoke and having a plurality of comb-shaped pole teeth arranged in the circumferential direction; an excitation coil for exciting the stator yoke; a shaft on which a rotor magnet is attached, the outer circumferential surface of which is magnetized with multiple poles and is disposed inside the stator yoke; Equipped with The outer yoke has a notch on its outer periphery, the inner yoke has a protrusion that fits into the notch, a stepping motor in which the inner yoke is joined to the outer yoke with the protrusion abutting against a reference surface provided on an inner wall of the cutout in the circumferential direction.

2. 2. The stepping motor according to claim 1, wherein the stator, which is a set of the stator yoke and the excitation coil, is a first stator and a second stator arranged vertically side by side along the axis of the shaft.

3. 3. The stepping motor according to claim 2, wherein the stators are arranged so that the inner yokes are joined together.

4. 3. The stepping motor according to claim 2, wherein the outer yoke and the inner yoke of the first stator and the second stator are respectively formed from the same part.

5. the first stator and the second stator are welded together along their outer peripheries, 3. The stepping motor according to claim 2, wherein the notches of the first stator and the second stator are located at the same circumferential position.

6. the first stator and the second stator are welded together along their outer peripheries, 3. The stepping motor according to claim 2, wherein the protrusions of the first stator and the second stator are located at the same circumferential position.

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