JP3422981B2 - Stepping motor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stepping motor, and more particularly to a technique effective when applied to a geared motor having a plurality of gears for transmitting the rotational motion of a rotor (rotor) while decelerating the rotational motion. It is effective when used to drive the pointer of a measuring instrument.

[0002]

2. Description of the Related Art In recent years, with the progress of electronic devices such as semiconductors and the progress of digital control technology using microcomputers (microcomputers) and the like, the drive control of pointers in in-vehicle indicating instruments such as speedometers has been the same as before. Digital control by microcomputers is becoming mainstream instead of mechanical control.

The indicating instrument is suitable for intuitively and easily displaying an analog amount such as a speed according to the deflection position of the pointer, but a stepping motor has come to be used for digitally controlling the deflection position of the pointer. Came. In this case, the stepping motor is used for positioning the pointer by open loop control. That is, by giving a forward or reverse rotation drive pulse to the stepping motor whose rotary output shaft is connected to the pointer, the pointer can be moved in both directions and the number of the rotation drive pulses can be changed. The amount of movement of the pointer can be controlled. Since the rotation amount (rotation angle) of the stepping motor can be uniquely determined by the number of the drive pulses, the pointer or the like can be positioned without complicated feedback control using the position sensor.

This type of stepping motor has a rotor having permanent magnets magnetized in multiple poles so that magnetic poles are alternately inverted along the circumferential direction, and a two-phase rotor arranged around the outer periphery of the rotor. Two or more stator yokes forming the above multi-phase field and an exciting coil for exciting the stator yokes are provided, and the magnetic pole portion of the stator yoke is closely opposed to the magnetic pole passage surface of the permanent magnet. Are located (eg, US Pat. No. 5,959,378). This stepping motor is usually used in the above-mentioned indicating instrument or the like in combination with a speed reduction mechanism composed of a plurality of gears.

[0005]

In the stepping motor described above, a magnetic attraction force is generated between the permanent magnet and the stator yoke. This magnetic attraction force is generated even in the non-excited state when de-energized, and the magnetic attraction force is further increased. It greatly depends on the rotational position (angle) of the rotor. That is, a magnetic attraction force that greatly changes depending on the relative positions of the magnetic poles of the permanent magnets forming the rotor and the magnetic pole portions of the stator yoke is generated. This magnetic attraction force produces a so-called detent torque that tends to pull the rotor into a specific rotational position even in a non-excited state (when not energized). For this reason, there is a problem that the rotation output of the stepping motor has a large torque ripple, and it is difficult to obtain continuous and smooth rotation.

Therefore, when the stepping motor is used, for example, for driving the pointer of the above-mentioned indicator, the pointer does not move smoothly, and the analog amount such as speed cannot be accurately instructed. The problem arises. Further, since the torque ripple causes vibration and noise, there is a problem that it is not suitable for use where quietness is required.

Further, this type of stepping motor is often used together with a plurality of gears that transmit the rotation of the motor rotation shaft while decelerating the rotation. In this case, noise due to the vibration of the torque ripple is generated by the gears. As the vibration increases, the problem that the gear biting state becomes unstable due to the vibration occurs.

As a conventional technique for reducing the above-mentioned detent torque, in US Pat. No. 5,959,378, the shape of the magnetic pole of the stator yoke, in particular, the surface of the permanent magnet forming the rotor, which is close to and opposed to the magnetic pole passage surface, is used. There is provided a technique of forming the magnetic pole passing surface at unequal intervals. However, to sufficiently reduce the detent torque only by the magnetic pole shape of the stator yoke,
It turned out to be difficult in reality. Moreover, when the magnetic pole shape of the stator yoke is formed as described above, another problem such as an increase in the effective gap between the magnetic pole of the permanent magnet and the magnetic pole of the stator yoke and a decrease in rotational torque may occur. There was found.

As a countermeasure against the noise, it is effective to assemble the entire motor including the gear into a resin casing. The resin casing is suitable for mass production by molding and is advantageous in cost reduction, and in the case of an electrically insulating resin casing, it is possible to obtain the advantage that the insulation structure of the motor energizing terminal can be simplified. it can. However, the resin casing has more difficult dimensional accuracy than the metal casing, and because the degree of deformation due to thermal expansion is large, the pitch distance of the gears easily fluctuates, and abnormal gear engagement such as play occurs in the gear. Therefore, the rotation may not be smoothly transmitted, and in some cases, the rotation may not be accurately transmitted, or the gear may be disengaged to make the rotation impossible.

The present invention has been made in view of the above background, and its main purpose is to cause a torque ripple in a rotation output in a stepping motor without significantly impairing motor performance such as rotation torque. The purpose is to effectively reduce the detent torque and obtain a smooth rotation output.

Another object of the present invention is to solve various problems such as a decrease in precision caused by the use of an electrically insulating resin casing, to reduce noise and cost, and to simplify the structure of a current-carrying terminal. In addition to being advantageous to, it is possible to surely obtain a smooth and stable operation.

Other objects and features of the present invention will be apparent from the description of the present specification and the accompanying drawings.

[0013]

In order to solve the above problems, the present invention provides the following means. A first means is a rotor having a permanent magnet that is magnetized in multiple poles so that the magnetic poles are alternately inverted along the circumferential direction, and a multi-phase rotor having two or more phases arranged around the outer periphery of the rotor. Stepping provided with two or more stator yokes that form a field and an exciting coil that excites the stator yoke, and is arranged such that the magnetic pole portion of the stator yoke closely faces the magnetic pole passage surface of the permanent magnet. In the motor, the permanent
The magnet has 3 to 6 poles, and the stator yoke is 1
Two are provided to form a pair of two-pole magnetic pole, and two of them are provided.
The intermediate magnetic body magnetically independent of the stator yokes on both sides is arranged at a predetermined position on the side where the angle between the stator yokes is small .

The inventor has clarified that the intermediate magnetic body has a function of significantly reducing the detent torque generated by the magnetic attraction between the permanent magnet and the stator yoke. Regarding the mechanism, for example, (1) the intermediate magnetic body magnetically separated from the stator yoke suppresses the generation of detent torque due to the magnetic influence from the stator yoke, and (2) between two adjacent stator yokes. By flattening the state of magnetic distribution at the above-mentioned intermediate magnetic body, the magnetic attraction force, that is, the detent torque for pulling the rotor to a specific rotation angle is reduced. (3) In addition to between the permanent magnet and the stator yoke In addition, a magnetic attraction force is also generated between the permanent magnet and the intermediate magnetic body, and the magnetic attraction force acts to cancel or reduce the detent torque. In any case, the present inventor has found that the intermediate magnetic body is very effective in reducing the detent torque without significantly impairing motor performance such as rotation torque.

The second means is the same as the first means,
A plurality of gears transmitting the rotational movement of the rotor are rotatably supported on a support substrate made of a magnetic material, and the intermediate magnetic material is integrally formed on the support substrate. The stepping motor is often configured with a plurality of gears that transmit the rotation output of the motor,
By forming the intermediate magnetic body using the supporting substrate that supports the gear, the detent torque can be reduced without increasing the number of parts, and the positioning of the gear and the intermediate magnetic body can be accurately and accurately reproduced. You can do it with good sexuality.

A third means is the same as the second means,
The entire motor including the gear is assembled in an electrically insulating resin casing, and the supporting substrate is formed of a magnetic material having a linear expansion coefficient with temperature smaller than that of the resin casing. This solves various problems such as a decrease in precision that occurs with the use of an electrically insulating resin casing, which is advantageous in reducing noise and cost and simplifying the motor terminal structure, and also is smooth and stable. It is possible to achieve the purpose of surely obtaining various movements.

In a fourth means, in any one of the first to third means, at least one shaft of a plurality of gears for transmitting the rotational movement of the rotor is made of a magnetic material, and the shaft of the magnetic material is used. The intermediate magnetic body is formed. This makes it possible to arrange the intermediate magnetic body for obtaining the effect of reducing the detent torque without increasing the number of parts.

A fifth means is the method according to any one of the first to fourth means, wherein the thickness width of the magnetic pole passing surface of the permanent magnet is
The width of the portion of the intermediate magnetic body that closely opposes the magnetic pole passing surface is set to 1/2 or less. According to the knowledge of the present inventor, the effect of reducing the detent torque varies depending on the positional relationship between the magnetic pole passing surface of the permanent magnet and the intermediate magnetic body. It turned out that it can be effectively reduced.

A sixth means is characterized in that, in any one of the first to fifth means, a magnetic material having a magnetic permeability equal to or lower than that of the stator yoke is used as a material of the intermediate magnetic body. It is considered that the intermediate magnetic body has an effect of suppressing the detent torque by forming an independent magnetic buffer between the two status yokes. However, if the magnetic permeability of the intermediate magnetic body is higher than necessary, the The effective magnetic flux that contributes to the rotation torque is collected more than necessary, and further, the detent torque may be generated due to the magnetic attraction force generated on the intermediate magnetic body. In order to avoid such a concern, it has been proved effective to set the magnetic permeability of the intermediate magnetic body as described above.

A seventh means is any one of the above-mentioned first to sixth means, wherein the permanent magnet has a magnetic pole of 3: 6 poles and the stator yoke has two magnetic poles of 1: 2 poles. Two stator yokes are provided such that the angle formed by both magnetic poles is 60 degrees, and one magnetic pole of the first stator yoke and one magnetic pole of the second stator yoke are provided. And 90 degrees, and the intermediate magnetic body is arranged at a predetermined position between the 90 degrees. For example, in the case of a stepping motor used to drive a pointer of an indicating instrument, it is known that the configuration having the magnetic pole arrangement as described above is effective in optimizing the motor size and the rotation efficiency. However, in such a structure, the means of the present invention using the above-mentioned intermediate magnetic body can exert a particularly excellent effect in reducing the detent torque.

An eighth means is characterized in that, in any of the above-mentioned first to seventh means, the stator yoke has a magnetic pole shape such that the stator yoke closely opposes the magnetic pole passage surface of the permanent magnet in parallel and at equal intervals. And As a result, the effective gap width between the magnetic pole passing surface of the permanent magnet and the magnetic pole formed by the stator yoke can be minimized, and the rotational torque performance due to the magnetic attraction force acting between the two can be secured.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an upper side view showing a main part of a stepping motor according to the present invention.

The stepping motor shown in FIG.
A rotor (rotor) 3 is formed by an annular permanent magnet 2 that is coaxially attached to the rotating shaft 1. The permanent magnet 2 is multi-pole magnetized so that the magnetic poles are alternately inverted at a pitch of 60 degrees along the circumferential direction, and has 3 to 6 poles (3 pole pairs). Two stator yokes 5a and 5b are arranged outside the rotor 3.

Each of the stator yokes 5a and 5b has a substantially U-shaped plane shape, and both ends of the U-shape are magnetic pole portions 6.
a1, 6a2, 6b1 and 6b2 are formed. That is,
The motor has a stator yoke 5 that forms one-to-two poles.
Two a and 5b are provided. The two stator yokes 5a and 5b have the same plane shape and are symmetrically opposed to each other, and the magnetic pole portions 6a1, 6a2, 6b1 and 6 are formed.
b2 is arranged so as to closely face the magnetic pole passage surface of the permanent magnet 2.

Each magnetic pole portion 6a1, 6a2, 6b1, 6b2
Each of the front end faces of is formed in an arc shape along a concentric circle so as to closely face the outer peripheral surface of the permanent magnet 2, that is, the magnetic pole passing surface, at equal intervals. Magnetic poles 6a1 and 6a
In order to match the magnetic pole pitch of the permanent magnet 2, 2 and 6b1 and 6b2 are respectively arranged so as to be located at both ends of a fan-shaped arc having a central angle of 60 degrees about the rotation axis 1. Further, the magnetic poles 6a1 and 6b1 are arranged so as to be located at both ends of a fan-shaped arc having a central angle of 90 degrees about the rotating shaft 1 in order to prevent a phase difference of 90 degrees in electrical angle. That is, it is clearly shown in Figure 1.
One of the two stator yokes 5a and 5b
Magnetic poles 6a1 and 6b1 are fan-shaped arcs with a central angle of 90 degrees
It is placed at both ends of the and has a narrow space,
The center angle between the other magnetic poles 6a2 and 6b2 is 360 degrees.
-90 degrees -2 x 60 degrees = 150 degrees on both ends of a fan-shaped arc
They are arranged and have wide intervals.

A bobbin 7 is attached to one of the U-shaped leg pairs of each of the stator yokes 5a and 5b.
An exciting coil 8 is wound around the bobbin 7 in advance. As a result, the one stator yoke 5a (or 5b) side is in the A phase, and the other stator yoke 5b (or 5
A two-phase salient pole type stepping motor having a phase B on the side a) is formed.

Then, two adjacent stator yokes 5
An intermediate magnetic body 9 which is magnetically independent is arranged at a position just in the middle of the magnetic poles 6a1 and 6b1 of a and 5b without contacting any magnetic pole of the two stator yokes 5a and 5b. In other words, the central angle is 90 degrees and the intervals are small.
The intermediate magnetic body 9 is arranged at the intermediate position on the side. As described above, the intermediate magnetic body 9 has the stator yokes 5a and 5a.
Generation of detent torque due to magnetic influence from b is suppressed.

FIG. 2 is a detailed sectional view of the vicinity of the intermediate magnetic body 9. In the figure, (a) is the direction A (arrow) in FIG.
The section from is shown. The magnetic body 9 is formed by bending a thin rectangular plate-shaped magnetic steel plate piece into a modified U-shape having a pair of leg portions having different lengths. The outer surface of the shorter leg portion is a magnetic action surface 10 that closely faces the magnetic pole passage surface of the permanent magnet 2. The magnetic action surface 10 is placed upright in the thickness width direction (height direction) of the magnetic pole passage surface of the permanent magnet 2 and is closely opposed to the magnetic pole passage surface in parallel with the magnetic pole passage surface.

Further, the magnetic action surface 10 is overlapped in the thickness direction (height direction) by a width (t2) that is ½ or less of the thickness width (t1) of the magnetic pole passing surface of the permanent magnet 2. It is located (t2 ≦ t1 / 2). That is, with respect to the thickness width (t1) of the magnetic pole passage surface of the permanent magnet 2, the width (t) of the portion where the intermediate magnetic body 9 closely faces the magnetic pole passage surface.
2) is set to 1/2 or less. Needless to say, in the present invention, it is more desirable to reduce the thickness to 1/2 or less, and the thickness width (t
1) It may be larger.

FIG. 2B shows another embodiment of the positional relationship between the intermediate magnetic body 9 and the permanent magnet 2. In this case, the thickness width (t1) of the magnetic pole passing surface of the permanent magnet 2 is also shown. As opposed to
The width (t2) of the portion of the intermediate magnetic body 9 that closely faces the magnetic pole passage surface is configured to be 1/2 or less.

FIG. 3 is a graph showing the detent torque characteristic of the above stepping motor. In the graph of the figure, the solid line characteristic curve is the detent torque change state with respect to the rotation angle when the intermediate magnetic body is provided, and the broken line characteristic curve is the detent torque change state with respect to the rotation angle without the intermediate magnetic body. Are shown respectively. As can be seen from the comparison graph in the figure, the variation of the detent torque due to the rotation angle of the permanent magnet is significantly reduced in the case where the intermediate magnetic body is provided (solid line) compared to the case where it is not (dashed line). Has been done. In the characteristic graph of the same figure, the detent torque on the vertical axis represents the torque on the rotation output shaft whose gear is decelerated.

FIG. 4 is a graph showing the relationship between the state in which the permanent magnet and the intermediate magnetic body are close to each other and the effect of reducing the detent torque. In the graph of the same figure, the horizontal axis represents the ratio (t2 / t1) of the width (t1) of the permanent magnet to the thickness (t1) of the permanent magnet. The vertical axis shows the size of the detent torque ratio (width of change in detent torque depending on the rotation angle)
Is a relative value with 100% when the intermediate magnetic material is not present. As shown in the graph of the figure, the detent torque ratio is clearly reduced by providing the intermediate magnetic body. The effect of the reduction is the thickness width (t
The ratio (t) of the close facing width (t2) of the intermediate magnetic body to 1)
It is better to make 2 / t1) smaller to some extent. In particular, the ratio (t2 / t1) is 0.5 or less, that is, with respect to the thickness width (t1) of the magnetic pole passing surface of the permanent magnet 2, the width (the width of the portion where the intermediate magnetic body 9 closely opposes the magnetic pole passing surface ( It can be read from the graph in the figure that the effect of reducing the detent torque becomes remarkable when t2) becomes 1/2 or less. Table 1 shows the difference in detent torque ratio depending on the material of the intermediate magnetic body.

[0033]

[Table 1]

In Table 1, SUY is electromagnetic soft iron often used for the stator yoke and the like, and magnetic annealing was performed after processing into the shape of the intermediate magnetic body. This material exhibits a relatively high magnetic permeability. SUS was electromagnetic stainless steel, and magnetic annealing after processing into the shape of the intermediate magnetic body was not performed. This material has a magnetic permeability lower than that of SUY.

As can be seen from Table 1, it is effective to reduce the detent torque by using a magnetic material having a magnetic permeability equal to or lower than that of the stator yoke as the material of the intermediate magnetic body.

FIG. 5 is an upper side view in the case showing a state in which the stepping motor according to the present invention is incorporated in an electrically insulating resin casing together with a reduction gear. In the figure, the rotation output of the stepping motor is taken out from the rotation shaft 1 of the permanent magnet 2. The rotation of the rotating shaft 1 is connected to the first pinion 12b connected to the rotating shaft 1, the first gear 13a meshing with the first pinion 12b, and the same rotating shaft 13 as the first gear 13a. Second pinion 13
b and the second gear 14a meshing with the second pinion 13b, the speed reduction transmission is performed, and finally the second gear 1
It is adapted to be taken out from the rotary shaft 14 of 4a.

FIG. 6 is a sectional view of the essential parts of the stepping motor with gear shown in FIG. As shown in the figure, the rotary shafts 1, 13, 14 of a plurality of gears (pinions 12b, 13b and gears 13a, 14a) transmitting the rotational motion of the rotor 3 (permanent magnet 2) are made of a magnetic material. It is rotatably supported on the shaft 15. Furthermore, this supporting substrate 1
The intermediate magnetic body 9 is integrally formed on the member 5 by bending a part of the member 5 with a press or the like. Then, the support substrate 15 and the gear (12
b, 13a, 13b, 14a), the entire motor is incorporated in an electrically insulating resin casing 11. The support substrate 15 is made of a magnetic material whose coefficient of linear expansion due to temperature is smaller than that of the resin casing 11.

With the above structure, various problems such as a decrease in accuracy caused by the use of the resin casing 11 such as deviation of the gear distance due to temperature change can be solved, and noise and cost can be reduced, and the motor terminal structure can be reduced. In addition to being advantageous in simplifying the above, smooth and stable operation can be surely obtained.

FIG. 7 is a top side view showing another embodiment of the present invention. The difference between the above-described embodiment will be focused on, and in this embodiment, the stator yokes 5a and 5b will be described.
The magnetic pole arrangement of is inverted upside down from that shown in FIG. 1 or 5. Further, in this embodiment, the rotor 3
A plurality of gears (12b, 13a, 1) that transmit the rotational movement of the
The rotating shaft 13 of at least one of the gears 3b and 14a) is made of a magnetic material, and the shaft 13 of the magnetic material forms the intermediate magnetic material 9. That is, the gear (13a, 1
The shaft 13 of 3b) and the intermediate magnetic body 9 are constituted by one component. According to the above configuration, it is possible to dispose the intermediate magnetic body 9 for obtaining the effect of reducing the detent torque without increasing the number of parts.

Although the embodiments of the present invention have been described with respect to the stepping motor for the indicating instrument, which is the main application of the embodiments, the technique of the present invention is not limited to the above-mentioned embodiments. For example, a timepiece or an instrument. It can also be used as an actuator other than the intended purpose. Also, with respect to the number of poles of the motor and the like, a multi-pole structure other than the above is possible.

[0041]

As described above, according to the present invention, a rotor having permanent magnets magnetized in multiple poles so that the magnetic poles are alternately inverted along the circumferential direction, and the rotor. Two or more stator yokes that are arranged on the outer periphery to form a multi-phase field of two or more phases and an exciting coil that excites the stator yokes are provided, and the magnetic pole portion of the stator yoke is the magnetic pole of the permanent magnet. In a stepping motor arranged so as to closely face the passage surface, the permanent magnet
The stone has 3 to 6 poles, and the stator yoke is 1 pair.
Two are provided to form a two-pole magnetic pole.
By arranging an intermediate magnetic material that is magnetically independent of the stator yokes on both sides at a predetermined position on the side where the angle between the stator yokes is small , torque ripple can be generated in the rotation output without significantly impairing motor performance such as rotation torque. It is possible to effectively reduce the detent torque that causes the torque, and obtain a smooth rotation output.

Further, it solves various problems such as a decrease in accuracy caused by the use of the electrically insulating resin casing, is advantageous in reducing noise and cost, and simplifies the structure of the current-carrying terminal. It is also possible to obtain an effect that a smooth and stable operation can be surely obtained.

[Brief description of drawings]

FIG. 1 is an upper side view showing a main part of a stepping motor according to the present invention.

FIG. 2 is a detailed cross-sectional view near the intermediate magnetic body in FIG.

FIG. 3 is a graph showing a detent torque characteristic of a stepping motor according to the present invention.

FIG. 4 is a graph showing a relationship between a state in which a permanent magnet and an intermediate magnetic body are closely opposed to each other and a detent torque reduction effect.

FIG. 5 is an upper side view in the case showing a state in which the stepping motor according to the present invention is incorporated in a resin casing.

6 is a cross-sectional view of essential parts of the geared stepping motor shown in FIG.

FIG. 7 is an upper side view showing a main part of another embodiment of the present invention.

[Explanation of symbols]

1 Rotor shaft 2 permanent magnet 3 rotors 5a, 5b stator yoke 6a1, 6a2 Magnetic pole part of stator yoke 5a 6b1, 6b2 Magnetic poles of the stator yoke 5b 7 bobbins 8 coils 9 Intermediate magnetic material 10 Magnetically active surface of intermediate magnetic material 11 Electrically insulating resin casing 12b pinion 13 Gear shaft (intermediate magnetic body) 13a gear 13b pinion 14 Gear rotation shaft (rotation extraction shaft) 14a gear 15 Support substrate

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-6-38497 (JP, A) JP-A-52-61719 (JP, A) JP-A-2002-51527 (JP, A) JP-A-2002-142432 ( JP, A) Actual development Sho 60-141683 (JP, U) US Patent 5959378 (US, A) International publication 02/13357 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02K 37/00 H02K 7/10

Claims (8)

(57) [Claims] 1. A rotor having permanent magnets magnetized in multiple poles such that magnetic poles are alternately inverted along the circumferential direction, and a multiphase field of two or more phases arranged around the outer periphery of the rotor. A stepping motor that includes two or more stator yokes that form a magnet and an exciting coil that excites the stator yoke, and that is arranged such that the magnetic pole portion of the stator yoke closely faces the magnetic pole passing surface of the permanent magnet. At
The permanent magnet has magnetic poles of 3 to 6 poles, and
Two pieces are provided to form one to two poles,
Predetermined position on the smaller angle between the two stator yokes
The stepping motor is characterized in that an intermediate magnetic body that is magnetically independent of the stator yokes on both sides is arranged in the table. 2. The method according to claim 1, wherein a plurality of gears for transmitting the rotational movement of the rotor are rotatably supported on a support substrate made of a magnetic material, and the intermediate magnetic material is integrated with the support substrate. A stepping motor characterized in that 3. The motor according to claim 2, wherein the entire motor including the gear is assembled in an electrically insulating resin casing, and the supporting substrate is made of a magnetic material having a linear expansion coefficient due to temperature smaller than that of the resin casing. A stepping motor characterized by being formed. 4. At least one of a plurality of gears for transmitting the rotational movement of the rotor according to claim 1.
A stepping motor characterized in that one shaft is formed of a magnetic material, and the shaft of the magnetic material forms the intermediate magnetic material. 5. The width of a portion of the intermediate magnet, which closely faces the magnetic pole passing surface, is 1/2 or less of a thickness width of the magnetic pole passing surface of the permanent magnet according to any one of claims 1 to 4. A stepping motor characterized by the above. 6. The stepping motor according to claim 1, wherein a magnetic material having a magnetic permeability equal to or lower than that of the stator yoke is used as a material of the intermediate magnetic body. 7. The permanent magnet according to claim 1, wherein the permanent magnet has a magnetic pole of 3: 6 poles, and the stator yoke is provided with two magnetic poles of 1: 2 poles. Two stator yokes are formed such that the angle formed by both magnetic poles is 60 degrees, and between the one magnetic pole of the first stator yoke and the one magnetic pole of the second stator yoke. Is arranged so as to be 90 degrees, and the intermediate magnetic body is arranged at a predetermined position between the 90 degrees. 8. The stepping motor according to claim 1, wherein the stator yoke has a magnetic pole shape such that the stator yoke closely opposes the magnetic pole passage surface of the permanent magnet in parallel and at equal intervals. .