JP6192788B2 - Stepping motor, lens device, and imaging device - Google Patents

Description

  The present invention relates to a stepping motor.

  A stepping motor is used as a drive source for a movable member of various devices, and in particular, as a drive source for an optical adjustment member such as a lens that requires position control accuracy. In recent years, with the miniaturization design of cameras and lenses, stepping motors are required to have a small size and high driving torque performance with further improved space efficiency. Such a stepping motor is required not only to improve driving torque characteristics, but also to be quiet enough to capture a moving image by a camera. For this reason, various proposals for reducing the noise of the stepping motor itself have been made.

  In Patent Document 1, by extending one of the bearing portions at both ends so as to contact the rotor magnet, the contact surface between the coil bobbin and the coil bobbin and the axial center surface of the rotor magnet are displaced by a necessary amount. A stepping motor is disclosed. In the stepping motor of Patent Document 1, the magnetic center between the rotor magnet and the coil bobbin is displaced in advance by a necessary amount. For this reason, even if the magnetic balance between the rotor magnet and the coil bobbin is lost depending on the individual difference of the parts, the rotor is prevented from being displaced in the axial direction. For this reason, the striking sound generated by the rotor magnet and the bearing can be reduced.

JP-A-8-149780

  However, in the stepping motor disclosed in Patent Document 1, the magnetic center between the rotor magnet and the coil bobbin is displaced in order to prevent the rotor from being displaced in the axial direction due to the loss of the magnetic balance between the rotor magnet and the coil bobbin. Yes. For this reason, compared with the case where the magnetic center of a rotor magnet and a coil bobbin is made to correspond, the drive torque of a motor becomes small. On the other hand, in order to secure a desired driving torque in the configuration of Patent Document 1, it is necessary to extend the entire length of the motor by an amount necessary to compensate for the decrease in the facing area between the rotor magnet and the coil bobbin by extending the bearing. There will be an increase in the size of the stepping motor.

  Therefore, the present invention provides a stepping motor with high noise reduction in which the impact sound of the rotor magnet and the bearing portion is reduced while maintaining the driving torque characteristics. In addition, a lens apparatus and an imaging apparatus provided with such a stepping motor are provided.

A stepping motor according to one aspect of the present invention includes a rotor having a rotor magnet fixed to a rotation shaft, a plurality of coil bobbins each having a coil wound thereon, and each of the plurality of coil bobbins in the axial direction of the rotation shaft. And a stator yoke group having a plurality of stator yokes each having pole teeth that are enclosed in the radial direction and alternately arranged in the circumferential direction around the rotation axis so as to face the side surface of the rotor magnet, and the rotation A first bearing and a second bearing for supporting the shaft; a first case sheet metal for supporting the first bearing; a second case sheet metal for supporting the second bearing; the rotor magnet; It includes a washer provided between the second bearing, and the magnetic member for attracting the rotor magnet on the side of the second bearing, the said Rotamagune' And the axial direction of the mind in the and the center of the said axial direction of the stator yoke group coincide with each other, wherein the thickness T _M of said axial magnetic member, one side end surface of the rotor magnet and The distance T _A between the one end face of the second case sheet metal satisfies the relationship T _M ≦ T _A , and the washer is in contact with the rotor magnet and the second bearing .

  A lens apparatus according to another aspect of the present invention includes the stepping motor.

  An imaging apparatus as another aspect of the present invention includes the stepping motor.

  Other objects and features of the present invention are illustrated in the following examples.

  According to the present invention, it is possible to provide a stepping motor with high noise reduction in which the striking sound between the rotor magnet and the bearing portion is reduced while maintaining the driving torque characteristics. In addition, it is possible to provide a lens apparatus and an imaging apparatus provided with such a stepping motor.

It is sectional drawing of the stepping motor as a comparative example. It is a wave form diagram of the drive current of a stepping motor. It is a schematic diagram which shows the positional relationship of the rotor magnet of a stepping motor, and the pole teeth of a stator yoke. It is operation | movement sectional drawing of the stepping motor as a comparative example. 1 is a cross-sectional view of a stepping motor in Embodiment 1. FIG. It is sectional drawing of the stepping motor in Example 2. FIG. It is sectional drawing of the stepping motor in Example 3. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same members are denoted by the same reference numerals, and redundant description is omitted.

  First, a stepping motor as a comparative example for comparison with the present invention will be described with reference to FIG. FIG. 1 is a sectional view of a stepping motor (two-phase PM type stepping motor) as a comparative example.

  In FIG. 1, 10 is a rotating shaft. Reference numeral 20 denotes a rotor magnet, which is fixed to the rotary shaft 10. 31 and 32 are thrust washers, which are provided at both ends of the rotor magnet 20 so as to be sandwiched and fixed in the axial direction of the rotary shaft 10. The rotating shaft 10, the rotor magnet 20, and the thrust washers 31, 32 constitute a rotor of a stepping motor. These portions constituting the rotor rotate integrally when the stepping motor is excited.

  Reference numeral 40a denotes an A-phase stator yoke, and 40b a B-phase stator yoke (collectively referred to as a “stator yoke group”). Each of the stator yoke groups encloses each of the plurality of coil bobbins in the axial direction and the radial direction of the rotating shaft 10, and the pole teeth alternately arranged in the circumferential direction around the rotating shaft 10 are arranged on the rotor magnet 20. A plurality of stator yokes are provided to face the side surfaces. The A-phase stator yoke 40a and the B-phase stator yoke 40b are alternately arranged in the circumferential direction (circumferential direction) of the rotor magnet 20 so as to face the side surface (cylindrical outer diameter side surface) of the rotor magnet 20, respectively. Stator (pole teeth). Each of the A-phase stator yoke 40a and the B-phase stator yoke 40b has a yoke that forms the outer shape of the stepping motor. The A-phase stator yoke 40a and the B-phase stator yoke 40b are stacked in two stages in the axial direction of the rotary shaft 10, and are fixed by welding or the like.

  50a is an A-phase coil bobbin, and 50b is a B-phase coil bobbin (these are collectively referred to as “coil bobbin”). The A-phase coil bobbin 50a and the B-phase coil bobbin 50b are surrounded in the axial direction and the radial direction (direction orthogonal to the axial direction and the circumferential direction) by the A-phase stator yoke 40a and the B-phase stator yoke 40b, respectively. A phase coil 60a and B phase coil 60b (collectively referred to as “coils”) are wound around the A phase coil bobbin 50a and the B phase coil bobbin 50b, respectively. A terminal for excitation in the coil is omitted.

  Reference numeral 71 denotes a bearing (first bearing), which is fixed to a case sheet metal 81 (flange sheet metal). Reference numeral 72 denotes a bearing (second bearing), which is fixed to the case sheet metal 82. The case metal plates 81 and 82 are fixed to the A-phase stator yoke 40a and the B-phase stator yoke 40b, which are fixed in two stages, by welding or the like on both sides in the axial direction of the rotary shaft 10. That is, the case metal plates 81 and 82 are fixed by fixing the bearings 71 and 72 and sandwiching the A-phase stator yoke 40a and the B-phase stator yoke 40b on both sides in the axial direction. Accordingly, the rotor is disposed so as to be sandwiched between the case metal plates 81 and 82. By arranging in this way, the bearings 71 and 72 support the rotary shaft 10 (both ends in the axial direction of the rotary shaft 10) in the radial direction. Further, when the rotor rotates by being excited by the stepping motor, the thrust washers 31, 32 are provided between the bearings 71, 72 and the rotor magnet 20 in order to prevent interference between the bearings 71, 72 and the rotor magnet 20. Are intervening. Thereby, the movement of the rotor magnet 20 in the axial direction (thrust direction) is restricted.

  Next, the principle of operation of the stepping motor (two-phase PM type stepping motor) will be described with reference to FIGS. FIG. 2 is a waveform diagram of the driving current of the stepping motor, in which the horizontal axis indicates the electrical angle and the vertical axis indicates the current value. In FIG. 2, 100a is a cosine waveform that excites the A-phase coil 60a, and 100b is a sine waveform that excites the B-phase coil 60b. FIG. 3 shows the rotor magnet 20 of the stepping motor and the pole teeth of the A-phase stator yoke 40a and the B-phase stator yoke 40b that generate magnetic poles by supplying current to the A-phase coil 60a and the B-phase coil 60b. It is a schematic diagram which shows a positional relationship.

  In the two-phase PM type stepping motor, the rotor magnet 20 has a total of 20 poles, and N poles and S poles are alternately magnetized in the circumferential direction (8 poles in FIG. 3). For example, when driven by the 1-2 phase driving method, the rotation angle per step is 4.5 °. The A-phase stator yoke 40a and the B-phase stator yoke 40b are arranged so as to wrap around the side surface (outer periphery) of the rotor magnet 20 and with a phase shift of about 90 ° when the same shape is taken as one cycle. . When current is supplied to the excitation coils of each phase, magnetic poles are generated in the A-phase stator yoke 40a and the B-phase stator yoke 40b, attracting the magnetic poles of the rotor magnet 20, and the rotor magnet 20 stops at an angle that balances the magnetic force. .

  FIG. 3A shows the positional relationship between the rotor magnet 20, the A-phase stator yoke 40a, and the B-phase stator yoke 40b in the excitation state of FIG. 2 when the electrical angle is P0. FIG. 3B shows the positional relationship between the rotor magnet 20, the A-phase stator yoke 40a, and the B-phase stator yoke 40b in the case of the electrical angle P2 in the excited state of FIG. FIG. 3C shows the positional relationship between the rotor magnet 20, the A-phase stator yoke 40a and the B-phase stator yoke 40b in the case of the electrical angle P4 in the excited state of FIG. FIG. 3D shows the positional relationship between the rotor magnet 20, the A-phase stator yoke 40a, and the B-phase stator yoke 40b in the excitation state of FIG. 2 when the electrical angle is P6. In this way, the rotor magnet 20 as the rotor rotates (ie, the stepping motor is driven to rotate) by exciting the respective currents in the two-phase exciting coils.

  Next, the operation in the axial direction of the rotating shaft 10 during excitation of the stepping motor will be described with reference to FIG. FIG. 4A is a cross-sectional view of the stepping motor in a state where only the A-phase stator yoke 40a is excited in the case of the electrical angles P0 and P4 in FIG. At this time, since the B-phase stator yoke 40b is not excited, no magnetic force is generated in the B-phase stator yoke 40b. Therefore, the magnetic center (axial center) of the rotor magnet 20 and the magnetic center (axial center) of the A-phase stator yoke 40a are attracted to each other, so that the bearing 71 and the thrust washer 31 come into contact with each other.

  On the other hand, FIG. 4B is a sectional view of the stepping motor in a state where only the B-phase stator yoke 40b is excited in the case of the electrical angles P2 and P6 of FIG. At this time, since the A-phase stator yoke 40a is not excited, no magnetic force is generated in the A-phase stator yoke 40a. For this reason, the magnetic center (axial center) of the rotor magnet 20 and the magnetic center (axial center) of the B-phase stator yoke 40b attract each other, so that the bearing 72 and the thrust washer 32 come into contact with each other.

  Since the stepping motor operates by the A-phase current and the B-phase current (drive current) shown in FIG. 2, the excitation states of FIGS. 4 (a) and 4 (b) are repeated. As a result, the collision between the bearing 71 and the thrust washer 31 and the collision between the bearing 72 and the thrust washer 32 are repeated, and a hitting sound is generated by these collisions. Since this hitting sound is recognized by the user as an unintentional abnormal sound when a moving image is taken with an imaging device (camera), the quality of the camera may be impaired. Therefore, the present embodiment provides a stepping motor, a lens device, and an imaging device that reduce such a collision. A specific configuration will be described in Examples 1 to 3 below.

  First, with reference to FIG. 5, the stepping motor in Example 1 of this invention is demonstrated. FIG. 5 is a cross-sectional view of the stepping motor in this embodiment.

  The basic configuration of the stepping motor of this embodiment is the same as the stepping motor of the comparative example described with reference to FIG. For this reason, only the numbers necessary for explanation are shown in FIG. 5, and other numbers are omitted. In the stepping motor of the present embodiment, 90 is a magnetic washer (SUS steel) as a magnetic attraction force generating member made of a magnetic material. The magnetic washer 90 is provided in order to reduce a hitting sound generated when a stepping motor as a comparative example is rotationally driven. The magnetic washer 90 is fixed to the case sheet metal 82 by welding or the like.

The magnetic washer 90 of the present embodiment has a donut shape with an outer diameter D _M1 and an inner diameter D _M2 . Preferably, the inner diameter _{D M2} of the magnetic washer 90 is the outer diameter _{D B} more bearings 72, i.e. the outer diameter _{D B} of the inner diameter _{D M2} and the bearing 72 of the magnetic washer 90 is set so as to satisfy the relation of _{D M2} ≧ _{D B} The More preferably, the outer diameter _{D M1} of the magnetic washer 90 is less outer diameter _{D R} of the rotor magnet 20, i.e. the outer diameter _{D R} of the outer diameter _{D M1} and the rotor magnet 20 of the magnetic washer 90 the relation _{D R} ≧ _{D M1} Set to meet. By setting so as to satisfy such a relationship, the stepping motor can be reduced in size.

Further, the thickness _{T M} of the axial direction of the magnetic washer 90, the distance _{T A} between one side end face 82a of the one side end face 20a and the case sheet metal 82 in the axial direction of the rotor magnet 20, the _{T M} ≦ _{T A} Set to satisfy the relationship. By setting so as to satisfy such a relationship, interference between the rotor magnet 20 and the magnetic washer 90 can be prevented when the rotor magnet 20 rotates by excitation.

  Next, a mechanism in which the magnetic washer 90 works as a magnetic attraction force generating member will be described. First, the magnetization in the rotor magnet 20 of the stepping motor of this embodiment is applied not only to the side surface facing each excitation stator but also to the bottom surface (one end surface 20a of the rotor magnet 20) facing the magnetic washer 90. . For this reason, the bottom surface of the rotor magnet 20 has a constant magnetic flux density. That is, by arranging the magnetic washer 90 so as to face the bottom surface of the rotor magnet 20, a magnetic attractive force is generated between the rotor magnet 20 and the magnetic washer 90. With such a configuration, the magnetic washer 90 can attract the rotor magnet 20 in the axial direction by a magnetic attraction force. For example, when exciting only in the A phase or the B phase in the stepping motor as a comparative example, the magnetic force acting in the axial direction of the rotating shaft 10 with respect to the rotor magnet 20 is 1.1 gf at the maximum. On the other hand, in the stepping motor of this embodiment, the magnetic attractive force of the magnetic washer 90 is set to exceed 1.1 gf.

  With the above configuration, even when a magnetic force is generated in the axial direction of the rotary shaft 10 with respect to the rotor magnet 20 in a state where only the A phase or the B phase is excited, the magnetic force (magnetic) applied to the rotor magnet 20 by the magnetic washer 90 It can be attracted with a magnetic force greater than (attractive force). For this reason, during the rotational drive of the stepping motor, the rotor magnet 20 is always attracted to the bearing 72 side, and the thrust washer 32 and the bearing 72 are kept in contact with each other. Therefore, the collision between the bearing 71 and the thrust washer 31 and the collision between the bearing 72 and the thrust washer 32 are reduced, and as a result, the generation of impact sound can be reduced.

  In the stepping motor of this embodiment, the axial center surface 22 of the rotor magnet 20 and the axial center surface of the stator yoke group (A-phase stator yoke 40a, B-phase stator yoke 40b) coincide with each other. Here, the term “match” means not only a strict match but also includes a case where it is evaluated that a match substantially exists, that is, a case of a substantially match. In the stepping motor of this embodiment, it can be said that the magnetic centers of the rotor magnet 20 and the stator yoke group coincide with each other. The magnetic center of the rotor magnet 20 is the central surface 22 in the axial direction of the rotor magnet 20. The magnetic center of the stator yoke group is the contact surface 42 (center plane of the stator yoke group) of the A-phase stator yoke 40a and the B-phase stator yoke 40b, and the current is simultaneously supplied to the phase coils 60a and 60b. Means the magnetic center at Further, “matching magnetic centers” means not only a case where the magnetic centers are exactly matched but also a state where it is evaluated that they are substantially matched, that is, a case where they are substantially matched. In the present embodiment, the stator yoke group has a two-stage configuration of an A-phase stator yoke 40a and a B-phase stator yoke 40b, but is not limited to this, and may have a plurality of stages. For example, in the case of a three-stage configuration, the magnetic center of the stator yoke group corresponds to the center plane of the stator yoke located at the center (second stage) of the three stages.

  In the stepping motor of the present embodiment, the magnetic washer 90 is arranged in a space-efficient manner without reducing the facing area between the rotor magnet 20 and each phase stator (stator yoke). For this reason, even when the magnetic washer 90 is provided and a countermeasure against noise is taken, good driving torque characteristics can be maintained. Further, in the stepping motor of this embodiment, the space efficiency is taken into consideration without increasing the outer shape of the stepping motor, so that the stepping motor can be reduced in size. In this embodiment, the magnetic washer 90 is disposed on the bearing 72 side (case sheet metal 82 side), but is not limited thereto. The magnetic washer 90 may be disposed on the bearing 71 side (case sheet metal 81 side).

  Next, with reference to FIG. 6, the stepping motor in Example 2 of this invention is demonstrated. FIG. 6 is a cross-sectional view of the stepping motor in this embodiment. The stepping motor of the present embodiment is different from the bearing 72 of the first embodiment in that a bearing 73 having an axial bearing shape (thrust receiving shape) at one end (lower end) of the rotary shaft 10 is provided. This is different from the stepping motor. Other configurations are the same as those of the first embodiment described with reference to FIG.

  Thus, by providing the bearing 73 having the axial bearing shape of the rotating shaft 10, the air gap between the rotor magnet 20 and the magnetic washer 90 can be set with higher accuracy. For this reason, the magnetic attraction force required for the magnetic washer 90 can be reduced. As a result, since the size of the magnetic washer 90 can be reduced, the stepping motor can be reduced in size. Further, regarding the shape of the contact portion of the rotating shaft 10 with the bearing 73, the tip R shape can be freely set in order to reduce the contact loss and drive loss.

In this embodiment, as in the first embodiment, preferably, the inner diameter _{D M2} of the magnetic washer 90 is the outer diameter _{D B} more bearings 73, i.e. the outer diameter _{D B} of the inner diameter _{D M2} and the bearing 73 of the magnetic washer 90 It is set so as to satisfy the relationship of D _M2 ≧ D _B. More preferably, the outer diameter _{D M1} of the magnetic washer 90 is less outer diameter _{D R} of the rotor magnet 20, i.e. the outer diameter _{D R} of the outer diameter _{D M1} and the rotor magnet 20 of the magnetic washer 90 the relation _{D R} ≧ _{D M1} Set to meet. Preferably, the thickness T _M in the axial direction of the magnetic washer 90 and the distance T _A between the one end surface 20a in the axial direction of the rotor magnet 20 and the one end surface 82a of the case sheet metal 82 are T _M ≦ T It is set so as to satisfy the relationship of _A.

  Next, with reference to FIG. 7, the stepping motor in Example 3 of this invention is demonstrated. FIG. 7 is a cross-sectional view of the stepping motor in this embodiment. The stepping motor of this embodiment is provided with a case metal plate 83 having an axial receiving shape (thrust receiving shape) at one end of the rotating shaft 10 in place of the case metal plate 82 of the first embodiment. Different from stepping motor. Other configurations are the same as those of the first embodiment described with reference to FIG.

  Thus, by providing the case sheet metal 83 having the axial receiving shape of the rotating shaft 10, the air gap between the rotor magnet 20 and the magnetic washer 90 can be set with higher accuracy. For this reason, the magnetic attraction force required for the magnetic washer 90 can be reduced. As a result, since the size of the magnetic washer 90 can be reduced, the stepping motor can be reduced in size. Further, with respect to the shape of the contact portion of the rotating shaft 10 with the case sheet metal 83, the tip R shape can be freely set in order to reduce the contact area and drive loss.

In this embodiment, as in the first embodiment, preferably, the magnetic inner diameter _{D M2} of the washer 90 bearing 72 outer diameter _{D B} above, namely outer diameter _{D B} of the inner diameter _{D M2} and the bearing 72 of the magnetic washer 90 It is set so as to satisfy the relationship of D _M2 ≧ D _B. More preferably, the outer diameter _{D M1} of the magnetic washer 90 is less outer diameter _{D R} of the rotor magnet 20, i.e. the outer diameter _{D R} of the outer diameter _{D M1} and the rotor magnet 20 of the magnetic washer 90 the relation _{D R} ≧ _{D M1} Set to meet. Preferably, the thickness T _M in the axial direction of the magnetic washer 90 and the distance T _A between the one end surface 20a in the axial direction of the rotor magnet 20 and the one end surface 83a of the case metal plate 83 are T _M ≦ T It is set so as to satisfy the relationship of _A.

  According to each of the above-described embodiments, it is possible to provide a stepping motor with high noise reduction in which the striking sound of the rotor magnet and the bearing portion is reduced while maintaining the driving torque characteristics. Further, since it is suitable for space efficiency, the stepping motor can be downsized. Furthermore, according to each of the above embodiments, it is possible to provide a lens apparatus and an imaging apparatus provided with such a stepping motor. For example, in the lens apparatus, the stepping motor of each embodiment is used to drive the diaphragm.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

For example, instead of the magnetic washer 90 and the bearing 72 (bearing 73), the same effect as in the above embodiments can be obtained even if a radially expanded bearing made of a magnetic material is used as the magnetic attractive force generating member. . Further, in place of the magnetic washer 90 and the case metal plate 82 (the case metal plate 83), a case metal plate in which these two parts made of a magnetic material are integrated can be used as the magnetic attractive force generating member. Can be obtained. Further, the outer diameter D _M1 of the magnetic washer 90 and the outer diameter D _R of the rotor magnet 20 may be set to D _R <D _M1 , that is, the magnetic washer 90 may be sandwiched between the B-phase stator yoke 40b and the case metal plate 82. .

DESCRIPTION OF SYMBOLS 10 Rotating shaft 20 Rotor magnet 31, 32 Thrust washer 40a, 40b Stator yoke 50a, 50b Coil bobbin 60a, 60b Coil 71, 72, 73 Bearing 81, 82, 83 Case sheet metal 90 Magnetic washer

Claims (10)

A rotor having a rotor magnet fixed to a rotating shaft;
A plurality of coil bobbins wound with coils;
Each surrounds each of the plurality of coil bobbins in the axial direction and the radial direction of the rotating shaft, and the pole teeth alternately arranged in the circumferential direction around the rotating shaft face the side surface of the rotor magnet. A stator yoke group having a plurality of stator yokes,
A first bearing that supports the rotating shaft and is provided on the output side;
A second bearing that supports the rotating shaft and is provided on a side opposite to the output side;
A first case sheet metal that supports the first bearing;
A second case metal plate for supporting the second bearing;
A washer provided between the rotor magnet and the second bearing;
A magnetic member for attracting the rotor magnet toward the second bearing ,
And heart in the axial direction of the shaft the heart and stator yoke group in the direction of the rotor magnet are coincident with each other,
The axial thickness T _{M of the} magnetic member, and the distance T _A between the one end surface of the rotor magnet and the one end surface of the second case sheet metal are:
T _M ≦ T _A
Satisfy the relationship
The stepping motor according to claim 1, wherein the washer is in contact with the rotor magnet and the second bearing . A rotor having a rotor magnet fixed to a rotating shaft;
A plurality of coil bobbins wound with coils;
Each surrounds each of the plurality of coil bobbins in the axial direction and the radial direction of the rotating shaft, and the pole teeth alternately arranged in the circumferential direction around the rotating shaft face the side surface of the rotor magnet. A stator yoke group having a plurality of stator yokes,
A first bearing and a second bearing for supporting the rotating shaft;
A first case sheet metal that supports the first bearing;
A second case metal plate for supporting the second bearing;
A washer provided between the rotor magnet and the second bearing;
A magnetic member for attracting the rotor magnet toward the second bearing,
The axial center of the rotor magnet and the axial center of the stator yoke group coincide with each other,
The axial thickness T of the magnetic member _M And a distance T between one end face of the rotor magnet and one end face of the second case sheet metal _A Is
T _M ≦ T _A
Satisfy the relationship
The washer is in contact with the rotor magnet and the second bearing;
The washer is the distance T _A And the thickness T _M The stepping motor is characterized in that the difference between the stepping motor and the washer is smaller than the thickness of the washer. Outer diameter _{D B} of the inner diameter _{D M2} before Symbol magnetic member and the second bearing,
D _M2 ≧ D _B
Stepping motor according to claim 1 or 2, characterized in relationship full plus that of. Outer diameter _{D R} of the rotor magnet and the outer diameter _{D M1} of the magnetic member,
D _R ≧ D _M1
The stepping motor according to any one of claims 1 to 3, wherein the relationship is satisfied. Said second bearing is a stepping motor according to any one of claims 1 to 4, characterized in that an axial receiving shape of one end of the rotary shaft. The second case sheet metal, a stepping motor according to any one of claims 1 to 4, characterized in that an axial receiving shape of one end of the rotary shaft. An output side washer provided between the first bearing and the rotor magnet;
The stepping motor according to claim 1, wherein the output washer is not in contact with the first bearing. Lens apparatus characterized by having a stepping motor according to any one of claims 1 to 7. The lens apparatus according to claim 8, further comprising a diaphragm driven by the stepping motor. Imaging apparatus characterized by having a stepping motor according to any one of claims 1 to 7.