JP2007135318A - Stepping motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stepping motor which shortens the interval between an A phase magnetic circuit and a B phase magnetic circuit, shortens the whole length in the axial direction by controlling a detent torque at low values, restrains the detent torque caused by the magnetic connection between the A phase and B phase, and also shorten the whole length in the axial direction even further by obtaining the increased capacity of the magnetic connection between the A phase and B phase. <P>SOLUTION: In this stepping motor, inductors 3 are radially arranged in a rotor 2, and a plurality of magnetic poles 6 are arranged so as to surround the outer circumference of the inductors 3, thereby forming a field magnet. The stators 1a, 1b of the A and B phases are respectively lined with coils 7 in the axial direction as opposed to the field magnet. The inductors 3a, 3b of respective phases form the shapes of the surfaces opposing to the magnetic poles in roughly triangular shapes. The tips in the narrower width sides of the inductors 3a, 3b protrude and overlap one another in the predetermined position. A third inductor 8 is mounted between the inductors of the A and B phases so as to magnetically be spaced in a roughly middle position between both stators. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a stepping motor. More specifically, the present invention relates to a two-phase structure in which an inductor is arranged in a rotor, and two phase A and phase B stators each have a coil axially connected to a field magnet. It relates to the improvement of the magnetic circuit in the structure.

  In recent years, digital cameras and mobile phones with small cameras have become widespread, and these products are particularly demanded for development of small size and light weight. For this reason, a small drive motor is required for a drive source such as a lens drive. Yes.

  In a small stepping motor suitable for reducing the diameter, as disclosed in, for example, Patent Document 1 and Patent Document 2, each component on the stator side is sequentially arranged in the axial direction, and is positioned on the outer periphery of the rotor. There are proposals to reduce the number of components. For example, the structure shown in FIGS. 1 and 2 is adopted. This figure is a configuration example shown in Patent Document 2, and in order to reduce the diameter of the motor structure, inductors 217 and 218 are provided on the rotor side, and the permanent magnets 215 and 216 are arranged on the stator side to provide a magnetic circuit. Configure. The two magnetic circuits of the first magnetic circuit and the second magnetic circuit including the drive solenoid windings 213 and 214 are arranged opposite to each other on both sides in the axial direction of the magnetic circuit.

  1 and 2, 207 is a cylindrical outer yoke forming a first magnetic circuit, 208 is a cylindrical inner yoke forming a first magnetic circuit, and 209 is a magnetic coupling between the outer yoke 207 and the inner yoke 208. 210 is a cylindrical outer yoke that forms a second magnetic circuit, 211 is a cylindrical inner yoke that forms a second magnetic circuit, and 212 is a magnetic coupling between the outer yoke 207 and the inner yoke 208. These annular plate yokes are made of a soft magnetic material.

Permanent magnets 215 and 216 are divided into n pieces in the circumferential direction and are alternately magnetized to different poles. The inductors 217 and 218 are made of a soft magnetic material, and are coupled to the rotating shaft 220 via a shaft connecting member 219 made of a nonmagnetic material. The two permanent magnets 215 and 216 are set so that the magnetization positions in the circumferential direction are shifted so that both the first and second magnetic circuits are armatures having a phase difference of 90 degrees in electrical angle. is doing. A yoke coupling member 221 made of a non-magnetic material maintains the distance between the first and second magnetic circuits together with the shaft connection member 219 and reduces magnetic coupling.
JP-A-11-41902 JP-A-2005-204453

  However, such conventional stepping motors have the following problems. The stepping motors described in Patent Document 1 and Patent Document 2 are suitable for reducing the diameter because there are few components located on the outer periphery of the rotor, but the components such as the drive coil are connected in the axial direction. Therefore, there is a problem that the total length in the axial direction becomes long.

  Further, since the A-phase and B-phase magnetic circuits are connected in the axial direction, there is a problem that both are magnetically coupled, and there is interference due to this coupling, resulting in deterioration of output characteristics. For this reason, as seen in Patent Document 2, for example, a magnetic coupling is reduced by arranging a non-magnetic spacer between the A-phase magnetic circuit and the B-phase magnetic circuit or by setting a large interval. The structure made to do will be taken. However, in that case, the total length in the axial direction is further increased, which is not a solution for downsizing.

  By the way, a typical configuration example according to the present invention shown in FIG. 6 will be described with reference to this type of stepping motor, that is, an inductor 3 arranged in a rotor 2 and two stators (A phase and B phase). In the configuration employing the two-phase structure in which the coil 7 is connected to the field magnet (permanent magnet 5) in the axial direction, both the magnetic pole 6 of the permanent magnet 5 and the inductor 3 on the rotor 2 side opposed thereto. The face-to-face relationship is important as an element that correlates with the torque characteristics, and the face-to-face relation between the two is defined as a ratio (pole-to-face ratio Z) as described later, and is used as a parameter for analyzing the torque characteristics.

When analytical calculation is performed using the pole-to-face ratio Z as a parameter to obtain the detent torque, the characteristics shown in FIG. 3 are obtained. FIG. 3 is an analysis of single-phase operation assuming that phase A and phase B exist independently, and the detent torque is
Z = 0.6
It is known that it becomes a small value in the vicinity and becomes almost zero. At this time, the magnetization distribution of the permanent magnet 5 is almost sinusoidal with respect to the rotation angle on the surface of the magnetic pole 6 and can be said to be close to the magnetization distribution actually obtained by multipolar magnetization. In FIG. 3, the detent torque is graphically displayed in standardized units.

  Next, according to the analysis of the single-phase operation, the magnetic flux flowing through the inductor 3 and interlinking with the coil 7 has a characteristic that does not change so much with respect to the change in the pole-to-face ratio Z, as shown in FIG. . The interlinkage magnetic flux shown in FIG. 4 is its amplitude, and this interlinkage magnetic flux amplitude is also expressed in a standardized unit for analysis.

  If the electrical angle is 360 degrees, the detent torque is only an even harmonic component from the symmetry condition of the magnetic circuit, and the second and fourth harmonic components can have a relatively large amplitude. A large impact. According to the analysis of the single-phase operation, the secondary component and the fourth component of the detent torque have the characteristics as shown in FIG. 5, and the change of the amplitude of the fourth component with respect to the pole-to-face ratio Z is small. As for the amplitude of, the pole-to-face ratio Z changes greatly in the vicinity of 0.6, and there is a zero point of torque.

  Therefore, the pole-to-face ratio Z is set by paying attention mainly to the secondary component of the detent torque. In a normal design, if the pole-to-face ratio Z is set to about 0.6, the secondary component of the detent torque can be suppressed to the minimum value, and the interlinkage magnetic flux can be obtained well, which is preferable. However, since this is an analytical solution assuming that the permanent magnet 5 is ideally magnetized, in reality, such magnetization cannot be performed, and a transition region is formed in the middle when the magnetic pole 6 is magnetized. As a result, the pole-to-face ratio Z changes such that the secondary component of the detent torque becomes zero, which is about 0.5 to 0.6.

  The quaternary component of the detent torque acts to hold its own stop position when the drive coil is not excited, and becomes a holding torque. In order to utilize this positively, it is necessary to make the other harmonic components other than the fourth-order component sufficiently small, so that the stop position of the inductor 3 is at an electrical angle interval of 90 degrees. It is. In addition, in order to smoothly rotate the stepping motor, it is also necessary to consider that the quaternary component of the detent torque needs to be sufficiently small.

  In the structure of the two-phase motor, the A-phase and B-phase are shifted by 90 degrees in the electrical direction in the circumferential direction. Therefore, in the theoretical ideal state, the secondary component of the detent torque is exactly opposite in both phases. Since the waveforms are similar to each other with the same value, they cancel each other and the secondary component of the detent torque does not appear on the output shaft. However, in practice, there is a magnetic coupling between the A-phase and B-phase magnetic circuits, and a detent torque is generated by the magnetic flux surrounding them.

  Further, if each phase has a secondary component of detent torque, a “torsion torque” is generated between both the A phase and the B phase, thereby causing a problem of causing unnecessary vibration. For this reason, it is desirable to design the secondary component of the detent torque to be zero in each phase in order to reduce vibration.

  The present invention solves the above-mentioned problems, and a first object is to reduce the interval between the A-phase and B-phase magnetic circuits in the configuration in which the A-phase and B-phase inductors are arranged in a row on the rotor, and the detent. An object of the present invention is to provide a stepping motor that can suppress the torque to a low value and shorten the overall length in the axial direction.

  The second object is to suppress the detent torque caused by the magnetic coupling of the A-phase and B-phase magnetic circuits in the configuration in which the A-phase and B-phase inductors are arranged in a row on the rotor. It is an object of the present invention to provide a stepping motor capable of obtaining a large allowable amount of magnetic coupling between both magnetic circuits and further shortening the overall axial length.

In order to achieve the first object described above, a stepping motor according to the present invention has a field magnet in which inductors are arranged radially on a rotor, and a large number of magnetic poles made of permanent magnets are arranged around the circumference of the inductors. And the A-phase and B-phase two stators are stepping motors in which coils are connected to the field magnet in the axial direction,
In the plane perpendicular to the center of rotation, the ratio of the angle α formed by the magnetic pole to the center of rotation and the angle β formed by the surface of the inductor and the center of rotation is defined as the pole-to-face ratio Z, and the pole-to-face ratio Z is Z = β / α.
When defining
Z <0.5
Set as follows.

  In addition, as the inductor, the surface shape opposite to the magnetic pole may be a stepped shape having protrusions asymmetrically in the circumferential direction, or alternatively, an inclined shape inclined obliquely in the circumferential direction, It is also possible to make the narrow side face in both the A phase and the B phase as a convex shape or a substantially triangular shape with one end edge being narrow as viewed along.

  The A phase inductor and the B phase inductor are set to have a positional relationship in which the facing ends of the A phase inductor and the B phase inductor protrude from each other at adjacent shift positions and overlap each other.

  In order to achieve the second object, the stepping motor according to the present invention is provided with a third inductor in the rotor, and the third inductor is magnetic with respect to both the A-phase and B-phase stators. It is preferable to arrange at a position where the general interval is substantially in the middle.

With this configuration, in the present invention, since the facing relationship between the magnetic pole and the inductor is defined as a ratio (pole-to-face ratio Z), it is easy to analyze the torque characteristics, and the pole-to-face ratio Z is set to Z <0. 5
By setting to, the width of the inductor in the circumferential direction can be narrowed. For this reason, the A-phase inductor and the B-phase inductor can be set in a positional relationship in which the facing ends of the two protrude from each other at adjacent shift positions and overlap each other at a predetermined position. It doesn't matter. Therefore, the total length of the permanent magnet can be shortened by the amount that the inductors overlap between the A phase and the B phase, and the total length of the motor in the axial direction can be shortened. Further, since the pole-to-face ratio Z is set appropriately, the torque characteristics can be kept good, and the detent torque can be suppressed to a low value.

  Therefore, as the A-phase and B-phase inductors, it is only necessary that the adjacent ends protrude from each other and overlap each other in a form that avoids mechanical contact between the two adjacent ones. Therefore, the surface shape of the inductor may be a stepped shape having a protruding portion asymmetrically in the circumferential direction, or may be an inclined shape that is inclined obliquely in the circumferential direction, or one edge when viewed along the axis. As a convex shape or a substantially triangular shape, the narrow side may be faced in both the A phase and the B phase.

  Further, by providing the third inductor, the third inductor shares a permanent magnet with both the A-phase and B-phase magnetic circuits, and constitutes a new third magnetic circuit. The B phase is magnetically coupled to each other. For this reason, a magnetic field can be generated in a direction that cancels the detent torque due to magnetic coupling of the A-phase and B-phase magnetic circuits, and the detent torque that appears as an output can be reduced to a small value as a result.

  In the stepping motor according to the present invention, the surface shapes of the A-phase and B-phase inductors can be set appropriately, so that their orientation can be overlapped while avoiding mechanical contact, and the interval can be reduced. it can. As a result, the total length of the permanent magnet can be shortened by the amount of overlapping of the inductors between the A phase and the B phase, and the total length in the axial direction can be shortened as the diameter is reduced. Since the pole-to-face ratio Z is set appropriately, the torque characteristics can be kept good, and the detent torque can be suppressed to a low value.

  Second, since the rotor is provided with a third inductor, a new third magnetic circuit is formed in a form sharing a permanent magnet, and the A phase and the B phase are magnetically coupled to each other. The magnetic field can be generated in a direction that cancels the detent torque due to the magnetic coupling of the phase and B phase magnetic circuits, and the detent torque that appears as an output can be reduced to a small value as a result. Therefore, the detent torque caused by the magnetic coupling of the A-phase and B-phase magnetic circuits can be suppressed, and in terms of design, the allowable amount of magnetic coupling between both the A-phase and B-phase magnetic circuits is increased. Obtainable. As a result, the axial length of the permanent magnet can be further shortened, and the axial length of the motor can be further reduced.

  6 and 7 show a first embodiment of the present invention. In the present embodiment, the stepping motor is configured such that the inductors 3 are arranged radially on the rotor 2, and the two stators (A phase, B phase) respectively connect the coil 7 to the field magnet (permanent magnet 5) in the axial direction. Adopt a two-phase structure. In other words, the A-phase stator 1a and the B-phase stator 1b are assembled together in a cylindrical housing 10 (outer yoke), the rotor 2 having the inductor 3 is disposed in the center of the housing, and the brackets 11 are fitted in the front and rear. In addition, the rotation shaft 4 is supported.

  The A phase and the B phase have the same configuration except that the electrical angle is shifted by 90 degrees in the rotation direction, and a plurality of projecting pieces project radially on the rotating shaft 4. The magnetic poles 6 formed by the cylindrical permanent magnets 5 located on the outside face each other to become the inductors 3, and the coils 7 arranged in the respective phase stators 1 are energized to sequentially magnetize the N and S poles.

  The permanent magnet 5 has a cylindrical inner peripheral surface divided into n parts in the circumferential direction and is magnetized into alternating poles of N poles and S poles. In this embodiment, the magnetic pole 6 is set to 5 to 10 poles, whereas the inductor 3 is set to 5 poles. FIG. 7 shows only the portion related to the inductor 3 of one set of A phase and B phase. It shows. The magnetic pole 6 may be formed from a single magnet, and the cylindrical permanent magnet 5 may be formed by connecting them together.

  The housing 10 and the bracket 11 are made of a soft magnetic material such as iron, and the front and rear brackets 11 are integrally assembled with a cylindrical bearing 12 at the center of a circular plate. In the state where the front and rear brackets 11 are fitted to the housing 10, the coils 7 are positioned on the back side of each bracket 11, whereby the housing 10 forms an outer yoke, the circular plate portion of the bracket 11 is an end surface yoke, and a cylindrical shape. These bearings 12 serve as inner yokes, and these serve as a yoke for the motor as a whole.

  Therefore, on the A phase side, the permanent magnet 5 serves as a field magnet, the coil 7a serves as a magnetic flux source, and the closed magnetic circuit surrounding each yoke and the inductor 3a encloses them as an A phase magnetic circuit. Similarly, on the B phase side, the permanent magnet 5 serves as a field magnet, the coil 7b serves as a magnetic flux source, and the closed magnetic circuit surrounding each yoke and the inductor 3b surrounding them constitutes a B phase magnetic circuit.

Here, regarding the magnetic field analysis, the relationship between the magnetic pole 6 of the permanent magnet 5 and the inductor 3 facing the magnetic pole 6 is defined as follows. When the angle formed by the magnetic pole 6 and the rotation center O on the plane perpendicular to the rotation axis 4 is α and the angle formed by the surface of the inductor 3 facing the magnetic pole 6 and the rotation center O is β, these ratios are As the facing ratio Z,
Z = β / α
It is defined as

  In this embodiment, since the magnetic pole 6 is 10 poles, the angle α formed with the rotation center O is 36 degrees, and since the inductor 3 is 5 poles, the mechanical angle of the magnetic circuit that is 1/5 in the circumferential direction is 72 degrees. . The mechanical angle of 72 degrees is set to 360 degrees in terms of electrical angle, and description will be made using the electrical angle.

  The inductor 3 has a surface shape opposite to the magnetic pole 6 formed in a substantially triangular shape with one end having a narrow width, and the narrow side faces in both the A phase and the B phase. As shown in the figure, the positional relationship is such that the facing ends of the two protrude from each other at adjacent shift positions and overlap each other by a predetermined amount. In FIG. 8, the magnetic pole 6 is shown expanded in the horizontal axis direction with an electrical angle. The inductor 3 is located at 0 degrees and 360 degrees in terms of electrical angles on the A phase side, and on the B phase side in terms of electrical angles. Those located at 90 degrees and 450 degrees are shown respectively.

This inductor 3 has a pole-to-face ratio Z,
Z = 0.6
The inclined surface of the other example 4 which will be described later is formed in a substantially triangular shape obtained by dividing the inclined shape from the substantially central portion in the axial direction and folding one side.

  By adopting such a surface shape, the inductor 3a of the A-phase magnetic circuit and the inductor 3b of the B-phase magnetic circuit have a positional relationship in which the directions of both overlap in the axial direction. The cylinder length can be shortened, the overall length of the motor in the axial direction can be shortened, and the amount of magnet material used is reduced, which is advantageous in terms of cost reduction. In other words, by forming the shape of the inductor 3 in a substantially triangular shape with one edge being narrow, both the A phase and the B phase can be overlapped while avoiding mechanical contact, Since the positional relationship is partially overlapped in the axial direction, the total axial length of the motor can be shortened.

  In this case, the inductor 3 has an area corresponding to the pole-to-face ratio Z of 0.6. Therefore, as can be seen from the torque characteristics described above, the detent torque can have a substantially zero value for the secondary component for each phase alone. Further, when the substantially triangular base edge is set to 90 degrees in electrical angle, the inductor 3 has a substantially triangular base edge, and the phase difference of the quaternary component of the detent torque when viewed at the rotational angle position. For this reason, generation | occurrence | production of a quaternary component can be suppressed.

  The shape of the inductor 3 is not limited to a substantially triangular shape as in the present embodiment. For example, FIGS. 9 to 12 are schematic diagrams for explaining other examples 1 to 4 of the inductor 3. 9 to 12, similarly to FIG. 8, the magnetic pole 6 is shown expanded in an electric angle in the horizontal axis direction, and the inductor 3 has an electric angle of 0 degrees and 360 degrees on the A phase side. Those located and those located on the B phase side at 90 degrees and 450 degrees in electrical angle are respectively illustrated.

(Other example of inductor 3 1: narrow shape)
The inductor 3 shown in FIG. 9 is formed in a narrow shape by narrowing the axial width. That is, in this other example 1, the inductor 3 has a pole-to-face ratio Z,
Z <0.5
This is a narrow shape as shown in the figure.

  By adopting such a surface shape, the inductor 3a of the A-phase magnetic circuit and the inductor 3b of the B-phase magnetic circuit are set in a positional relationship in which the orientations of the two protrude from each other at adjacent shift positions and overlap a predetermined amount. it can. Therefore, the cylinder length of the permanent magnet 5 can be shortened by the amount that the inductors 3a and 3b overlap between the A phase and the B phase.

  The magnetic flux interlinking with the coil 7 changes with an electrical angle of 360 degrees as one cycle, and the pole-to-face ratio Z is correlated with the torque characteristics. When the pole-to-face ratio Z is set to a small value, the decrease in the amplitude of the interlinkage magnetic flux is not so large as shown in FIG. 4 described above. The decrease in the interlinkage magnetic flux can be compensated for by slightly increasing the axial length of the narrow-shaped inductor 3. Further, the secondary component of the detent torque is slightly increased as can be seen from FIG. 5 described above, but since it has a two-phase structure, the secondary component cancels out in the motor, which is not inconvenient in practical use.

(Other example 2 of inductor 3: step shape)
The inductor 3 shown in FIG. 10 is formed in a step shape by providing protrusions asymmetrically in the circumferential direction. That is, in this other example 2, the inductor 3 has a pole-to-face ratio Z,
Z = 0.6
The surface area is divided into two equal parts in the circumferential direction, and a step shape is formed by shifting each other in the direction by a shift amount γ.

  By adopting such a surface shape, the inductor 3a of the A-phase magnetic circuit and the inductor 3b of the B-phase magnetic circuit are set in a positional relationship in which the orientations of the two protrude from each other at adjacent shift positions and overlap a predetermined amount. it can. Therefore, the cylinder length of the permanent magnet 5 can be shortened by the amount that the inductors 3a and 3b overlap between the A phase and the B phase.

  In this case, since the inductor 3 has an area corresponding to the pole-to-face ratio Z of 0.6, the detent torque can have a substantially zero value for the secondary component for each phase alone. Also, when the amount of deviation γ is set to approximately 45 degrees in electrical angle, the inductor 3 is shifted in phase with respect to the quaternary component of the detent torque when viewed from the position of the rotational angle when the portions of the step shape are displaced, For this reason, generation | occurrence | production of a quaternary component can be suppressed.

(Other example 3 of the inductor 3: the center is convex)
The inductor 3 shown in FIG. 11 is formed in a convex shape at the center. That is, in the other example 3, the center where one projecting portion is shifted in the axial direction from the step shape of the other example 2 has a convex shape. And like the other example 2, the inductor 3 has a pole-to-face ratio Z,
Z = 0.6
The surface area is equivalent to

  By adopting such a surface shape, the inductor 3a of the A-phase magnetic circuit and the inductor 3b of the B-phase magnetic circuit are set in a positional relationship in which the orientations of the two protrude from each other at adjacent shift positions and overlap a predetermined amount. it can. Therefore, the cylinder length of the permanent magnet 5 can be shortened by the amount that the inductors 3a and 3b overlap between the A phase and the B phase.

  In this case as well, since the inductor 3 has an area corresponding to the pole-to-face ratio Z of 0.6, the detent torque can have a substantially zero value for the secondary component for each phase alone. Further, when the width γ of the convex shoulder is approximately 45 degrees in electrical angle, the inductor 3 has an inverse with respect to the fourth component of the detent torque when the convex shoulders are viewed at the rotational angle. Therefore, the generation of quaternary components can be suppressed.

(Other example 4 of the inductor 3: an inclined shape inclined obliquely)
The inductor 3 shown in FIG. 12 is formed in an inclined shape inclined obliquely in the circumferential direction. In other words, in this other example 4, the inductor 3 has a pole-to-face ratio Z,
Z = 0.6
The surface area is inclined in the circumferential direction so as to have a predetermined inclination.

  By adopting such a surface shape, the inductor 3a of the A-phase magnetic circuit and the inductor 3b of the B-phase magnetic circuit can be set to a positional relationship in which the orientation of the two protrudes from each other at adjacent shift positions and overlaps with each other. . Therefore, the cylinder length of the permanent magnet 5 can be shortened by the amount that the inductors 3a and 3b overlap between the A phase and the B phase.

  In this case as well, since the inductor 3 has an area corresponding to the pole-to-face ratio Z of 0.6, the detent torque can have a substantially zero value for the secondary component for each phase alone. Also, when the inclined edges are 90 degrees in electrical angle, the inductors 3 are opposite in phase with respect to the quaternary component of the detent torque when the inclined edges of the inductor 3 are viewed at the rotational angle position. Therefore, generation of the quaternary component can be suppressed.

  Thus, similarly in any of the other examples 1 to 4, both the A phase and the B phase can be overlapped in a state avoiding mechanical contact, and the positional relationship partially overlapping in the axial direction can be obtained. Therefore, the total axial length of the motor can be shortened. Since the pole-to-face ratio Z is set appropriately, the torque characteristics can be kept good, and the detent torque can be suppressed to a low value.

  FIG. 13 shows a second embodiment of the present invention. In the present embodiment, the stepping motor is configured such that the inductors 3 are arranged radially on the rotor 2, and the two stators (A phase, B phase) respectively connect the coil 7 to the field magnet (permanent magnet 5) in the axial direction. The A-phase and B-phase magnetic circuits have the same configuration as that of the first embodiment, but the rotor 2 has a third inductor between the A-phase and the B-phase. 8 is provided.

  In other words, a plurality of third inductors 8 are provided radially projecting substantially at the center of the rotating shaft 4, which respectively face the magnetic poles 6 formed by the permanent magnets 5 located on the outside, and each phase stator. When the coil 7 arranged at 1 is energized, it is magnetized in order of N and S poles. Since the magnetic pole 6 of the permanent magnet 5 is 5 to 10 in this embodiment, the inductor 8 is provided with 5 poles, and the surface shape facing the magnetic pole 6 is formed in a small rectangular shape.

  The inductor 8 is positioned approximately in the middle of the A-phase inductor 3a and the B-phase inductor 3b, and is arranged at a position where the magnetic spacing is approximately in the middle between the A-phase and B-phase stators. Specifically, as shown in FIG. 14, in the circumferential direction, the electrical angle is arranged at 0 degree on the A phase side and -135 degree with respect to the 90 degree side on the B phase, and 360 degrees on the A phase side and 450 degrees on the B phase side. In contrast, it is arranged at 225 degrees. Therefore, the inductor 8 shares the permanent magnet 5 with both the A-phase and B-phase magnetic circuits to form a new third magnetic circuit, which is magnetically coupled to the A-phase and B-phase. Will do.

  Since this new third magnetic circuit shares the permanent magnet 5 with the A-phase and B-phase magnetic circuits, it is not necessary to change the total length of the permanent magnet 5 in the axial direction. Conversely, when the overlap between the inductor 3a and the inductor 3b is increased, the magnetic coupling between both the A-phase and B-phase magnetic circuits becomes dense, and this coupling increases the detent torque. The detent torque that acts as an output canceling out the magnetic field generated by the third magnetic circuit around the inductor 8 can be made small as a result.

  Therefore, the provision of the third inductor 8 can suppress the detent torque caused by the magnetic coupling between the A-phase and B-phase magnetic circuits. From a design standpoint, between the A-phase and B-phase magnetic circuits. Thus, a large allowable amount of magnetic coupling can be obtained. As a result, the total axial length of the permanent magnet 5 can be made shorter than that of the first embodiment, the total axial length of the motor can be further reduced, and further miniaturization can be achieved.

  In order to verify the effect of the present invention, magnetic field analysis was performed on the second embodiment shown in FIG. 13 to verify the torque characteristics. The inductor 8 of the third magnetic circuit sets the surface shape opposite to the magnetic pole 6 as appropriate, thereby exerting a magnetic field action in a direction to cancel out the detent torque generated by the A phase magnetic circuit and the B phase magnetic circuit. The detent torque that can be adjusted and expressed as an output is set to a minimum value.

  Therefore, assuming that the magnetization distribution of the permanent magnet 5 is in an ideal state, an analytical calculation is performed using the pole-to-face ratio Z as a parameter, and the second and fourth components of the detent torque generated by the inductor 8 are obtained. As a result, the characteristics shown in FIG. 15 were obtained. At this time, the magnetization distribution of the permanent magnet 5 is almost sinusoidal with respect to the wraparound angle on the surface of the magnetic pole 6 and can be said to be close to the magnetization distribution actually obtained by multipolar magnetization. In FIG. 15, the detent torque is displayed as a graph in a standardized unit as an amplitude, and the sign of the detent torque amplitude is defined as the sign of the torque at an electrical angle of 0 degrees.

  As a result, as shown in FIG. 15, it was confirmed that the secondary component of the detent torque has a characteristic that the polarity changes from positive to negative in the vicinity of the pole-to-face ratio Z of 0.5.

  By the way, in the configuration in which the inductor 8 is not provided, the detent torque generated by the A-phase magnetic circuit and the B-phase magnetic circuit exhibits characteristics as shown in FIG. That is, in the magnetic coupling of the A-phase and B-phase magnetic circuits, the secondary component D2 is generated in addition to the quaternary component D4 that originally exists as a waveform along the detent torque D0, and the phase of the secondary component D2 is generated. Is a characteristic that the electrical angle advances about 45 degrees with respect to the pole-to-face ratio Z of 0.6. In order to reduce the amplitude of the secondary component D2, it is necessary to widen the gap between both the A-phase inductor 3a and the B-phase inductor 3b, and this is the reason why the total axial length of the stepping motor cannot be shortened. It has become.

  Therefore, since the secondary component D2 of the detent torque due to magnetic coupling of the A-phase and B-phase magnetic circuits is negative when converted to amplitude, the detent can be generated by generating a torque with an appropriate positive amplitude by the third magnetic circuit. Torque can be canceled out. In particular, as apparent from FIG. 15, the amplitude of the fourth-order component DW4 is almost zero in the vicinity of the pole-to-face ratio Z of 0.28. It is possible to cancel with only the next component DW2 as a target.

  From the above, next, the pole-to-surface ratio Z was set to 0.28, and the torque generated by the third magnetic circuit with respect to the rotor rotation angle expressed in electrical angle was obtained. As a result, the torque characteristic shown in FIG. 17 was obtained. In this case, it was confirmed that the secondary component D2 of FIG. Therefore, the secondary component DW2 in FIG. 15 can be canceled out.

  That is, by appropriately setting the value of the pole-to-face ratio Z, the third magnetic circuit can generate a detent torque that is opposite in phase to the detent torque generated by the A-phase and B-phase magnetic circuits. What is necessary is just to adjust the surface shape of the 3rd inductor 8, the clearance gap with the opposing magnetic pole 6, a position in the circumferential direction, etc. suitably.

It is a perspective view which decomposes | disassembles and shows an example of the conventional stepping motor. It is sectional drawing of the stepping motor shown in FIG. It is an analysis of single-phase operation on the assumption that an A phase and a B phase exist independently, and is a graph showing detent torque characteristics. It is an analysis of single-phase operation on the assumption that an A phase and a B phase exist independently, and is a graph showing the characteristics of interlinkage magnetic flux. It is an analysis of a single phase operation on the assumption that an A phase and a B phase exist independently, and is a graph showing characteristics of harmonic components of detent torque. It is sectional drawing which shows 1st Embodiment of the stepping motor which concerns on this invention. FIG. 7 is a perspective view showing the stepping motor shown in FIG. 6 cut in the vertical direction, and shows only a portion related to an inductor of a set of A phase and B phase. FIG. 8 is a schematic diagram for explaining the positional relationship with respect to the magnetic pole shown by expanding the inductor of FIG. 7 with an electrical angle in the horizontal axis direction. It is a schematic diagram explaining the positional relationship with respect to the magnetic pole shown about the other example 1 of an inductor expand | deployed by the electrical angle in the horizontal axis direction. It is a schematic diagram explaining the positional relationship with respect to the magnetic pole shown about the other example 2 of an inductor expand | deployed by the electrical angle in the horizontal axis direction. It is a schematic diagram explaining the positional relationship with respect to the magnetic pole shown about the other example 3 of an inductor expand | deployed by the electrical angle in the horizontal axis direction. It is a schematic diagram explaining the positional relationship with respect to the magnetic pole shown about the other example 4 of an inductor expand | deployed by the electrical angle in the horizontal axis direction. It is a perspective view which cuts and shows the 2nd Embodiment of the stepping motor which concerns on this invention to the vertical direction, and has shown and cut out only the part which concerns on the inductor of 1 set of A phase and B phase. It is a schematic diagram explaining the positional relationship with respect to the magnetic pole which expand | deploys with the electrical angle to the horizontal axis direction about the inductor of FIG. It is the graph which computed the 2nd order component and 4th order component of detent torque about the analysis model which provided the 3rd magnetic circuit. It is the graph which computed the detent torque which generate | occur | produces by the magnetic coupling | bonding of an A phase and B phase magnetic circuit. It is the graph which computed the torque characteristic about the analysis model which provided the 3rd magnetic circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Stator 2 Rotor 3 Inductor 4 Rotating shaft 5 Permanent magnet 6 Magnetic pole 7 Coil 8 Third inductor 10 Housing 11 Bracket 12 Bearing

Claims (6)

Inductors are arranged radially on the rotor, and a large number of magnetic poles made of permanent magnets are arranged around the circumference of the inductors to form field magnets. Each of the two A-phase and B-phase stators has a coil as an axis for the field magnets. A stepping motor linked to the direction,
In the plane perpendicular to the center of rotation, the ratio of the angle α formed by the magnetic pole to the center of rotation and the angle β formed by the surface of the inductor and the center of rotation is defined as a pole-to-face ratio Z, and the pole-to-face ratio Z is Z = β / α
When defining
Z <0.5
A stepping motor characterized by the following setting. Inductors are arranged radially on the rotor, and a large number of magnetic poles made of permanent magnets are arranged around the circumference of the inductors to form field magnets. Each of the two A-phase and B-phase stators has a coil as an axis for the field magnets. In stepping motors that run in the direction,
The stepping motor is characterized in that the inductor has a stepped shape having a protruding portion asymmetrically in the circumferential direction with respect to the magnetic pole. Inductors are arranged radially on the rotor, and a large number of magnetic poles made of permanent magnets are arranged around the circumference of the inductors to form field magnets. Each of the two A-phase and B-phase stators has a coil as an axis for the field magnets. In stepping motors that run in the direction,
The stepping motor according to claim 1, wherein the inductor has a surface shape opposite to the magnetic pole, which is inclined obliquely in a circumferential direction. Inductors are arranged radially on the rotor, and a large number of magnetic poles made of permanent magnets are arranged around the circumference of the inductors to form field magnets. Each of the two A-phase and B-phase stators has a coil as an axis for the field magnets. In stepping motors that run in the direction,
The inductor has a surface shape opposite to the magnetic pole, a convex shape or a substantially triangular shape whose one edge is narrow when viewed along the axis, and faces the narrow side in both the A phase and the B phase. Stepping motor characterized by that.   The A-phase inductor and the B-phase inductor are set to have a positional relationship in which the opposite ends of the A-phase inductor and the B-phase inductor protrude from each other at adjacent shift positions and overlap each other in a predetermined manner. Stepping motor described in 1.   The rotor is provided with a third inductor, and the third inductor is arranged at a position where the magnetic interval is substantially intermediate with respect to both the A-phase and B-phase stators. The stepping motor according to any one of 5.

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