JP5020649B2 - Stepping motor and camera diaphragm device - Google Patents

Description

  The present invention relates to a stepping motor that generates a rotational driving force by an electromagnetic force and a camera diaphragm device using the stepping motor.

As a conventional stepping motor, a rotor magnetized with four poles, a first stator having a pair of magnetic pole portions formed in a substantially U shape and opposed to the rotor at both ends thereof, and for excitation wound around the first stator A first stator having a pair of magnetic poles opposed to the rotor at both ends thereof, a second coil for excitation wound around the second stator, or further facing the rotor A device having a pair of complementary electrodes is known (for example, see Patent Document 1 and Patent Document 2).
In these stepping motors, stability in a non-energized state, ease of assembly work, improvement of assembly accuracy, and the like are achieved.
However, since the rotor is magnetized with four poles, it has been difficult to achieve high resolution and to obtain high-precision and smooth operation. In particular, there has been a limit to application as a drive source for a camera diaphragm device or the like that requires high-precision and fine drive control.

In addition, as a conventional stepping motor, a rotor magnetized to 8 poles, a first stator having three magnetic pole portions formed in a substantially E shape and facing the rotor at each tip, and a central portion of the first stator A wound first coil for excitation, a second stator formed in a substantially E shape and having three magnetic pole portions facing the rotor at the respective tips, and an excitation coil wound around the central portion of the second stator What is equipped with the 2nd coil etc. is known (for example, refer to patent documents 3).
This stepping motor employs a rotor magnetized to eight poles and two stators having three magnetic pole portions to increase torque.
However, in this stepping motor, since the coil is wound around the central portion (central pole teeth) of the stator having a substantially E shape, an attempt to secure a predetermined number of turns or more leads to an increase in the size of the stator. On the other hand, when trying to reduce the size of the stator, there is a problem that the number of turns of the coil is reduced due to the restriction on the distance between the both side portions (pole teeth on both sides), and the driving torque is reduced.

JP 9-224365 A JP 2003-32991 A JP-A-2-269594

  The present invention has been made in view of the above-mentioned problems of the prior art. The object of the present invention is to realize a high resolution while achieving a reduction in size and cost with a simple structure, and a high resolution. An object of the present invention is to provide a stepping motor that can operate accurately and smoothly and that can prevent noise and the like, and a camera diaphragm using the stepping motor.

The stepping motor of the present invention has a cylindrical rotor that defines an outer peripheral surface by a magnet magnetized with eight poles at equal intervals in the circumferential direction, a magnetic pole portion facing the outer peripheral surface of the rotor, and an exciting coil And a second stator having a magnetic pole portion facing the outer peripheral surface of the rotor and having an exciting coil wound thereon, the magnetic pole portion of the first stator and the magnetic pole of the second stator parts is a stepping motor which is arranged in line symmetry with respect to a straight line extending from the center of rotation of the rotor in the radial direction, the magnetic pole portion of the upper Symbol first stator, the first magnetic pole portion and the second may result in different magnetic poles from each other A first magnetic pole portion having two magnetic pole portions, the magnetic pole portion of the second stator being arranged in line symmetry with the first magnetic pole portion and the second magnetic pole portion of the first stator with respect to a straight line, and generating different magnetic poles. Magnetic pole part and second Have a magnetic pole portion, the first magnetic pole portion, when the angle .theta.1 away from the said straight line relative to the center of rotation, it is formed so as to satisfy 2 ° ≦ θ1 ≦ 5 °, the second magnetic pole portion, the rotation When the angle away from the straight line with respect to the center is θ2, it is formed so as to satisfy 137 ° ≦ θ2 ≦ 140 °, and the central angle of the first magnetic pole part and the second magnetic pole part is θp, It is characterized by being formed so as to satisfy 18.5 ° ≧ θp ≧ 12.5 ° .
According to this configuration, when the coils of the first stator and the second stator are energized as appropriate (for example, by two-phase excitation or 1-2 phase excitation), the eight magnetic poles of the rotor (four N poles and four Two S poles) and the magnetic attraction and repulsion between the first and second magnetic poles of the first and second stators to generate a rotational driving force with high accuracy and smoothness. . In this way, with a simple structure, high resolution can be realized while achieving miniaturization and cost reduction, and high precision and smooth operation can be achieved, and generation of noise and the like can be prevented.
Further, when the angle at which the first magnetic pole portion is separated from the straight line with respect to the rotation center is θ1, the first magnetic pole portion is formed so as to satisfy 2 ° ≦ θ1 ≦ 5 °, and the second magnetic pole portion is linear with respect to the rotation center. 1θ ° ≧ θp, where θ2 is an angle that is spaced apart from the first magnetic pole portion and θp is the center angle of the first magnetic pole portion and the second magnetic pole portion, and θ1 Since it is formed so as to satisfy ≧ 12.5 °, a more reliable magnetic attraction force between the magnetic pole portions of the first stator and the second stator and one magnetic pole (N pole or S pole) of the rotor. And a repulsive force can be obtained, and a rotor can be rotated smoothly.

In the stepping motor having the above configuration, when the outer diameter of the rotor is φD and the gap between the first magnetic pole portion of the first stator and the first magnetic pole portion of the second stator is G1, 0.04 × φD ≦ G1 ≦ 0.06 A configuration formed so as to satisfy × φD can be employed.
According to this configuration, the gap G1 between the first magnetic pole portion of the first stator and the first magnetic pole portion of the second stator is formed so as to satisfy the above-described conditional expression, thereby obtaining a strong and reliable rotational driving force. be able to.

In the stepping motor having the above configuration, when the outer diameter of the rotor is φD and the gap between the first magnetic pole portion and the second magnetic pole portion and the outer peripheral surface of the rotor is G2, 0.06 × φD ≦ G2 ≦ 0.10 × A configuration formed so as to satisfy φD can be adopted.
According to this configuration, the magnetic field lines generated by forming the gap G2 between the first magnetic pole portion and the second magnetic pole portion of the first stator and the second stator and the outer peripheral surface of the rotor so as to satisfy the above-described conditional expression. Can be used effectively, and a strong and reliable rotational driving force can be obtained.

In addition, the diaphragm device for a camera of the present invention performs a diaphragm operation of the opening by cooperating with a substrate having an opening of a predetermined aperture and a substrate that is rotatable around the opening and around the opening. A plurality of aperture blades, a drive ring provided to be rotatable with respect to the substrate to drive the plurality of aperture blades, and a drive source that exerts a drive force on the drive ring, the drive source having the above-described configuration The stepping motor is any one of the stepping motors.
According to this configuration, when the coil of the stepping motor is energized, the rotor generates a rotational driving force with high accuracy and smoothly without causing noise and vibration. As a result, the drive ring is driven with high accuracy, and the plurality of diaphragm blades stably perform the diaphragm operation and the non-diaphragm (open) operation of the opening.

  As described above, according to the stepping motor of the present invention, high resolution can be realized with a simple structure while achieving downsizing, cost reduction, etc., and high accuracy without causing noise or the like. And a smooth rotational driving force can be generated. Further, according to the camera diaphragm device of the present invention, the above stepping motor is used as a drive source, so that the rotor rotates stably, and the plurality of diaphragm blades are fine and stable diaphragm operation and non-diaphragm operation. Can be performed.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
1 to 7 show an embodiment of a stepping motor according to the present invention. FIG. 1 is a plan view showing a schematic configuration thereof, FIG. 2 is an enlarged plan view thereof, and FIG. 3 is a plan view thereof. FIG. 4 and FIG. 5 are operation diagrams, and FIG. 6 and FIG. 7 are time sequence diagrams for explaining the operation.

  As shown in FIG. 1 and FIG. 3, the stepping motor includes a base 10, a rotor 20 that is rotatably supported by the base 10, a first stator 30 that is formed in a substantially U shape and is fixed to the base 10, A first coil 40 for excitation wound around the first stator 30, a second stator 50 formed in a substantially U shape and fixed to the base 10, and a second excitation coil wound around the second stator 50. A coil 60 and the like are provided.

As shown in FIG. 3, the base 10 integrally includes a support shaft 11 that rotatably supports the rotor 20, a fixing portion 12 that fixes the first stator 30, a fixing portion 13 that fixes the second stator 50, and the like. I have.
Here, the support shaft 11 defines a rotation center (line) C of the rotor 20 described later.

As shown in FIGS. 1 to 3, the rotor 20 has eight magnetic poles (that is, four N poles and four S poles each having a central angle of 45 degrees arranged alternately at equal intervals in the circumferential direction. A cylindrical magnet 21 that defines an outer peripheral surface 21a having a predetermined outer diameter φD, and the magnet 21 is externally fitted and fixed, and is rotatably fitted to the support shaft 11 of the base 10. A shaft member 22 having a through-hole, a gear 23 formed on the distal end side of the shaft member 22 and outputting a rotational driving force to the outside is provided.
The support shaft 11 is inserted into the through hole of the shaft member 22, and the rotor 20 is supported so as to be rotatable around the rotation center (line) C.

As shown in FIGS. 1 to 3, the first stator 30 is formed in a substantially U shape so as to define the two arm portions 31 and 32, and is fixed to the fixing portion 12 of the base 10.
The tip of the arm portion 31 is formed so as to demarcate the first magnetic pole portion 31a facing the outer peripheral surface 21a of the rotor 20, and the tip of the arm portion 32 is the second magnetic pole portion 32a facing the outer peripheral surface 21a of the rotor 20. Are defined.
The first magnetic pole portion 31a forms an arcuate surface 31a ′ that delimits the outer peripheral surface 21a of the rotor 21 and a predetermined gap G2.
The second magnetic pole portion 32a forms an arcuate surface 32a ′ that delimits the outer peripheral surface 21a of the rotor 21 and a predetermined gap G2.

  The first coil 40 is wound around the arm portion 32 of the first stator 30 via the bobbin 40a. Therefore, by switching the energization direction flowing through the first coil 40, the N pole (or S pole) is generated in the first magnetic pole portion 31a, and the S pole (or N pole) is generated in the second magnetic pole portion 32a. it can.

As shown in FIGS. 1 to 3, the second stator 50 is formed in a substantially U shape so as to define two arm portions 51 and 52, and is fixed to the fixing portion 13 of the base 10.
The tip of the arm portion 51 is formed so as to define a first magnetic pole portion 51 a that faces the outer peripheral surface 21 a of the rotor 20, and the tip of the arm portion 52 is a second magnetic pole portion 52 a that faces the outer peripheral surface 21 a of the rotor 20. Are defined.
The first magnetic pole portion 51a forms an arcuate surface 51a 'that defines the outer peripheral surface 21a of the rotor 21 and a predetermined gap G2.
The second magnetic pole portion 52a forms an arcuate surface 52a 'that defines the outer peripheral surface 21a of the rotor 21 and a predetermined gap G2.

  The second coil 60 is wound around the arm portion 52 of the second stator 50 via the bobbin 60a. Therefore, by switching the energization direction flowing through the second coil 60, the N pole (or S pole) is generated in the first magnetic pole portion 51a, and the S pole (or N pole) is generated in the second magnetic pole portion 52a. it can.

Here, the 1st stator 30 and the 2nd stator 50 are formed in the same shape by the magnetic material which lets a magnetic force line pass, and as shown in Drawing 1 and Drawing 2, it is a diameter from rotation center (line) C of rotor 20. The rotor 20 is disposed so as to sandwich the rotor 20 in a state of being line symmetric with respect to the straight line L extending in the direction.
More specifically, as shown in FIG. 2, the first magnetic pole portion 31 a of the first stator 30 is formed starting from a position that is separated from the straight line L by the angle θ <b> 1 clockwise around the rotation center C of the rotor 20. The first magnetic pole portion 51a of the second stator 50 is formed starting from a position separated from the straight line L by the same angle θ1 about the rotation center C of the rotor 20 as a center.

Further, the first magnetic pole portion 31a of the first stator 30 and the first magnetic pole portion 51a of the second stator 50 are arranged so as to form a gap G1 in a direction perpendicular to the straight line L, as shown in FIG.
Here, the value of the gap G1 is preferably set to a dimension (0.04 × φD ≦ G1 ≦ 0.06 × φD) in the range of 4% to 6% of the outer diameter φD of the rotor 20. According to this, since the gap G1 between the first magnetic pole portion 31a of the first stator 30 and the first magnetic pole portion 51a of the second stator 50 is formed so as to satisfy the above-described conditional expression, strong and reliable rotational drive is achieved. You can gain power.

  As shown in FIG. 2, the second magnetic pole portion 32a of the first stator 30 is formed starting from a position separated from the straight line L by an angle θ2 about the rotation center C of the rotor 20. The second magnetic pole portion 52a of the second stator 50 is formed starting from a position separated from the straight line L by the same angle θ2 around the rotation center C of the rotor 20.

Here, the value of the angle θ1 regarding the first magnetic pole portion 31a of the first stator 30 and the first magnetic pole portion 51a of the second stator 50 is set in a range of 2 ° to 5 ° (2 ° ≦ θ1 ≦ 5 °). The angle θ2 regarding the second magnetic pole portion 32a of the first stator 30 and the second magnetic pole portion 52a of the second stator 50 is preferably in the range of 137 ° to 140 ° (137 ° ≦ θ2 ≦ 140 °) is preferable.
According to this, the first magnetic pole portions 31a and 51a and the second magnetic pole portions 32a and 52a of the first stator 30 and the second stator 50 are formed so as to satisfy the above-described conditional expressions, whereby each magnetic pole portion 31a. , 32a, 51a, 52a and one magnetic pole (N pole or S pole) of the rotor 20, more reliable magnetic attractive force and repulsive force can be obtained.

Further, the first magnetic pole portion 31a and the second magnetic pole portion 32a of the first stator 30 and the central angle of the first magnetic pole portion 51a and the second magnetic pole portion 52a of the second stator 50 (that is, opposite to the outer peripheral surface 21a of the rotor 20). The angle (θ) defining the width of the circular arc surfaces 31a ′, 32a ′, 51a ′, 52a ′) θp is formed so as to be able to be opposed with a width smaller than half of the circular arc surface of one magnetic pole (N pole or S pole). Yes.
Here, the value of the central angle θp is preferably set in the range of 12.5 ° to 18.5 ° (12.5 ° ≦ θp ≦ 18.5 °). When the angle θ1 is 2 °, the central angle θp corresponds to 18.5 °, and when the angle θ1 is 5 °, the central angle θp corresponds to 12.5 °.
According to this, by forming the central angle θp of the first magnetic pole portions 31a and 51a and the second magnetic pole portions 32a and 52a of the first stator 30 and the second stator 50 so as to satisfy the above-described conditional expressions, More reliable magnetic attractive force and repulsive force can be obtained between the magnetic pole portions 31a, 32a, 51a, 52a and one magnetic pole (N pole or S pole) of the rotor 20.

Furthermore, the value of the gap G2 between the first magnetic pole portions 31a and 51a and the second magnetic pole portions 32a and 52a of the first stator 30 and the second stator 50 and the outer peripheral surface 21a of the rotor 20 is 6 of the outer diameter φD of the rotor. It is preferably set to a dimension in the range of percent to 10 percent (0.06 × φD ≦ G2 ≦ 0.10 × φD).
According to this, the gap G2 between the first magnetic pole portions 31a and 51a and the second magnetic pole portions 32a and 52a of the first stator 30 and the second stator 50 and the outer peripheral surface 21a of the rotor 20 satisfies the above-described conditional expression. By being formed, the generated magnetic lines of force can be used effectively, and a strong and reliable rotational driving force can be obtained.

Next, the operation of this stepping motor will be described with reference to FIGS. Here, as shown in FIG. 6, the case where the first coil 40 and the second coil 60 are energized and driven by two-phase excitation will be described.
First, at an initial position (a state in which the first coil 40 and the second coil 60 are each energized in a predetermined direction), as shown by S1 in FIG. 4, the first magnetic pole portion 31a has an S pole and the second magnetic pole portion 32a. N pole, N pole in the first magnetic pole part 51a, and S pole in the second magnetic pole part 52a are generated, respectively, and the rotor 20 is stopped at a predetermined angular position by the magnetic attractive force.

  Subsequently, when the energization direction of the first coil 40 is switched to the opposite direction, an N pole is generated in the first magnetic pole portion 31a and an S pole is generated in the second magnetic pole portion 32a, as indicated by S2 in FIG. The rotor 20 rotates clockwise by a predetermined angle Δθ (22.5 degrees ((360 degrees / 8) / 2), as indicated by S3 in FIG.

  Subsequently, when the energization direction of the second coil 60 is switched to the opposite direction, an S pole is generated in the first magnetic pole portion 51a and an N pole is generated in the second magnetic pole portion 52a, as indicated by S4 in FIG. The rotor 20 rotates clockwise by a predetermined angle Δθ (22.5 degrees ((360 degrees / 8) / 2), as indicated by S5 in FIG.

  Subsequently, when the energization direction of the first coil 40 is switched to the opposite direction, an S pole is generated in the first magnetic pole portion 31a and an N pole is generated in the second magnetic pole portion 32a, as indicated by S6 in FIG. The rotor 20 rotates clockwise by a predetermined angle Δθ (22.5 degrees ((360 degrees / 8) / 2), as indicated by S7 in FIG.

Subsequently, when the energization direction of the second coil 60 is switched to the opposite direction, an N pole is generated in the first magnetic pole portion 51a and an S pole is generated in the second magnetic pole portion 52a, as indicated by S8 in FIG. The rotor 20 rotates clockwise by a predetermined angle Δθ (22.5 degrees ((360 degrees / 8) / 2), as indicated by S9 in FIG.
Thereafter, the operation from S2 in FIG. 4 to S9 in FIG. 5 is repeated.

That is, according to this stepping motor, the rotor 20 advances or continuously rotates in response to the power pulses applied to the first coil 40 and the second coil 60, and is proportional to the number of input pulses. The rotation angle changes, and the rotation speed changes in proportion to the input frequency.
Therefore, by performing the two-phase excitation as shown in FIG. 6 or the 1-2 phase excitation as shown in FIG. 7 and appropriately controlling the direction of the power pulse and the rotating magnetic field, the high step angle is small. A stepping motor with resolution can be realized, and with this stepping motor, a high-precision and smooth rotational driving force can be obtained, and since it is smooth, generation of noise and the like can be prevented.

  8 to 10 show an embodiment of a camera diaphragm device provided with the above-described stepping motor as a drive source. FIG. 8 is a plan view of the device, and FIG. 9 is a plan view showing the inside of the device. FIG. 10 is a sectional view of the apparatus.

  As shown in FIGS. 8 to 10, this apparatus is provided with a plurality of (here, a plurality of) base plates 110 and back plates 120 serving as substrates having openings 110 a and 120 a having a predetermined diameter, which are rotatable with respect to the base plate 110. , Six) diaphragm blades 130, a drive ring 140 for driving a plurality of diaphragm blades 130, a two-stage gear 150 integrally including a large gear 151 and a small gear 152, and a drive ring 140 via the two-stage gear 150. A stepping motor M or the like as a driving source that exerts a driving force on is provided.

The stepping motor M has the same configuration as described above, and includes a rotor 20, a first stator 30, a first coil 40, a second stator 50, and a second coil 60, as shown in FIGS.
As described above, the rotor 20 is integrally provided with a magnet 21, a shaft member 22, a gear 23, and the like.
As described above, the first stator 30 and the second stator 50 include first magnetic pole portions 31a and 51a and second magnetic pole portions 32a and 52a, respectively.

As shown in FIGS. 8 to 10, the base plate 110 is formed in a disc shape, and has an opening 110 a having a predetermined diameter at the center, a support shaft 111 that rotatably supports the rotor 20, and the first stator 30. A fixed shaft 112 for fixing, a fixed shaft 113 for fixing the second stator 50, a support shaft 114 for rotatably supporting the gear 150, and six support holes 115 for swingably supporting the six diaphragm blades 130 are provided. ing.
The back plate 120 is formed so as to define an opening 120a having a predetermined aperture, and is connected to the base plate 110 at a predetermined interval as shown in FIG. A blade chamber W that accommodates etc. is defined.

Each of the diaphragm blades 130 is formed to have the same contour, and as shown in FIGS. 9 and 10, the support pins 131 and the support pins 131 formed at one end to be inserted into the support holes 115 are predetermined. The engagement pin 132 that engages with a cam groove 141 (described later) of the drive ring 140 is provided at a position separated by a distance of.
As shown in FIGS. 9 and 10, the six diaphragm blades 130 are rotatably supported with respect to the base plate 110 by inserting the respective support pins 131 into the support holes 115 of the base plate 110. Each engaging pin 132 is inserted into the cam groove 141 of the drive ring 40 and guided along the cam groove 141.
That is, as shown in FIG. 9, the six diaphragm blades 130 are located at the non-throttle position where the respective parts overlap in the non-throttle state and retreat from the openings 110a and 120a. Facing the inside of 120a, the openings 110a and 120a are narrowed down to a predetermined diameter in cooperation with each other (overlapping).

  The drive ring 140 is configured to cause the six diaphragm blades 130 to perform a diaphragm operation or a non-diaphragm operation by its rotational operation, and is formed in an annular shape as shown in FIGS. , The opening 140a having a slightly larger diameter than the opening 110a of the main plate 110, a plurality of (here, six) cam grooves 141 arranged at substantially equal intervals in the circumferential direction, and a two-stage gear at a part of the outer periphery A tooth row 142 that meshes with 150 small gears 152 is provided.

Here, the operation of the driving ring 140 will be described. When the driving ring 140 rotates in one direction from the throttle state in which the six aperture blades 130 cooperate to squeeze the openings 110a and 120a to a predetermined aperture, When the coupling pin 132 moves radially outward along the cam groove 141 and the drive ring 140 reaches its rotational end, as shown in FIG. 9, the six diaphragm blades 130 open the openings 110a and 120a. It is positioned in the fully unopened state.
On the other hand, when the drive ring 140 rotates in the reverse direction from the non-throttle state, the engagement pin 132 moves inward in the radial direction along the cam groove 141, and the six diaphragm blades 130 throttle the openings 110a and 120a. Positioned in the state.
That is, when this diaphragm device is applied to a camera, it is driven smoothly and with high precision by the stepping motor M, so that a desired amount of light can be obtained and noise can be prevented, especially in a camera having a recording function. preferable.

In the above-described embodiment, the case where the rotor 20 of the stepping motor has the gear 23 that outputs the rotational driving force has been described. However, the present invention is not limited to this, and the output unit is provided at a position deviated from the rotation center. A drive pin or the like may be provided.
In the above-described embodiment, the configuration in which the rotor 20 is rotatably supported by the support shafts 11 and 111 has been described. However, the present invention is not limited to this, and a shaft that rotates integrally with the rotor is provided. You may insert in the shaft hole of a base or a board | substrate, and may support it rotatably.

  As described above, the stepping motor of the present invention can achieve high resolution while achieving low cost, etc. with a simple structure, and can rotate smoothly with high accuracy without causing noise or the like. Since a driving force can be generated, it can be applied as a driving source for a camera diaphragm device, and is also useful as a driving source for other optical systems or as a driving source in other fields.

1 is a plan view showing an embodiment of a stepping motor according to the present invention. It is the fragmentary top view which expanded a part of stepping motor shown in FIG. It is sectional drawing of the stepping motor shown in FIG. It is an operation | movement diagram which shows operation | movement of the stepping motor shown in FIG. It is an operation | movement diagram which shows operation | movement of the stepping motor shown in FIG. FIG. 2 is a time sequence diagram for driving the stepping motor shown in FIG. 1 by two-phase excitation. It is a time sequence diagram which drives the stepping motor shown in FIG. 1 by 1-2 phase excitation. It is a top view which shows one Embodiment of the aperture_diaphragm | restriction apparatus for cameras which concerns on this invention. It is a top view which shows the inside of the diaphragm | throttle device for cameras shown in FIG. It is sectional drawing of the aperture_diaphragm | restriction apparatus for cameras shown in FIG.

Explanation of symbols

L straight line C rotor center of rotation 10 base 11 support shafts 12 and 13 fixed portion 20 rotor 21 magnet 22 shaft member 23 gear 30 first stator 31 and 32 arm portion 31a first magnetic pole portion 31a 'arcuate surface 32a second magnetic pole portion 32a ′ Arc surface 40 First coil 50 Second stator 51, 52 Arm portion 51a First magnetic pole portion 51a ′ Arc surface 52a Second magnetic pole portion 52a ′ Arc surface 60 Second coil 110 Ground plate (substrate)
110a Opening 111 Support shaft 112, 113 Fixed shaft 114 Support shaft 115 Support hole 120 Back plate (substrate)
120a Opening portion 130 Plural diaphragm blades 131 Support pin 132 Engagement pin 140 Drive ring 141 Cam groove 142 Tooth row 150 Two-stage gear M Stepping motor (drive source)

Claims (4)

A cylindrical rotor that delimits an outer peripheral surface by a magnet magnetized with eight poles at equal intervals in the circumferential direction, a magnetic pole portion that faces the outer peripheral surface of the rotor, and an excitation coil is wound around 1 stator and a second stator having a magnetic pole portion opposed to the outer peripheral surface of the rotor and wound with an exciting coil, and the magnetic pole portion of the first stator and the magnetic pole portion of the second stator are A stepping motor arranged symmetrically with respect to a straight line extending in the radial direction from the rotation center of the rotor ,
Pole portion before Symbol first stator has a first magnetic pole portion and the second magnetic pole portion obtained produce different magnetic poles,
The magnetic pole portions of the second stator are arranged in line symmetry with the first magnetic pole portion and the second magnetic pole portion of the first stator with respect to the straight line, respectively, and can generate different magnetic poles. have a magnetic pole portion,
The first magnetic pole portion is formed so as to satisfy 2 ° ≦ θ1 ≦ 5 °, where θ1 is an angle away from the straight line with respect to the rotation center,
The second magnetic pole portion is formed to satisfy 137 ° ≦ θ2 ≦ 140 °, where θ2 is an angle away from the straight line with respect to the rotation center, and
When the central angle of the first magnetic pole part and the second magnetic pole part is θp, it is formed so as to satisfy 18.5 ° ≧ θp ≧ 12.5 °.
Stepping motor characterized by that. When the outer diameter of the rotor is φD and the gap between the first magnetic pole portion of the first stator and the first magnetic pole portion of the second stator is G1, 0.04 × φD ≦ G1 ≦ 0.06 × φD is satisfied. Is formed as
The stepping motor according to claim 1 . When the outer diameter of the rotor is φD and the gap between the first and second magnetic pole portions and the outer peripheral surface of the rotor is G2, 0.06 × φD ≦ G2 ≦ 0.10 × φD is satisfied. Formed,
The stepping motor according to claim 1 , wherein the stepping motor is provided. A substrate having an opening with a predetermined aperture, a plurality of aperture blades arranged to be rotatable with respect to the substrate and arranged around the opening to cooperate with each other to perform the aperture operation of the opening, and the plurality A drive ring that is rotatably provided with respect to the substrate to drive the diaphragm blades, and a drive source that exerts a drive force on the drive ring,
The drive source is a stepping motor according to any one of claims 1 to 3 .
An aperture device for a camera.

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