Motor and light amount adjusting apparatus

A motor having a short axial length and a large torque, including a disk-shaped rotor having at least one plane magnetized in a plurality of different poles in a rotational direction thereof, a coil arranged such that an inner circumferential surface of the coil faces an outer circumferential surface of the rotor, or an outer circumferential surface of the coil faces an inner circumferential surface of the rotor, a first magnetic pole portion that faces a plane of the rotor, is formed with teeth extending in a radial direction of the rotor, and can be excited by the coil, and a second magnetic pole portion that is provided on a side of the rotor opposite the first magnetic pole portion such that the first and second magnetic pole portions sandwich the rotor, and can be excited by the coil.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motor in which rotor length in the direction of a rotation axis is shortened, and a light amount adjusting apparatus in which this motor is used as a driving force for a blade member such as a shutter or an f-stop number adjusting mechanism.

2. Related Background Art

In general, operation concerning the exposure of a digital camera is performed as follows.

First of all, a main power source is turned on before taking a picture, a shutter blade is held in an open position when an image pickup element becomes a working condition, and the luminous flux of an objective field reaches the image pickup element. The image pickup element that receives the luminous flux of the objective field performs photoelectric conversion and repeats the accumulation of electric charges, and the emission and transmission of the accumulate charges. Then, an image monitor displays an image of the objective field on the basis of the transmitted signal. When a release button is pushed, an f-stop number and exposure time are determined according to an output of the image pickup element at that time, and the aperture blade is driven according to the determined f-stop number. Next, the image pickup element discharging the accumulated charges is made to start the accumulation of electric charges, and at the same time, an exposure time controlling circuit is started while making an accumulation start signal a trigger signal. When predetermined exposure time elapses, the shutter blade is moved to and held in a closed position for the luminous flux of the objective field to reach the image pickup element. Thereafter, the accumulated electric charges are transferred, and image information is recorded in a recording medium by an image recording apparatus. The reason why exposure to the image pickup element is prevented during transferring the electric charges is to prevent the electric charges from changing during transferring the electric charges by extra light.

A small motor is used as a drive unit that operates these shutter blade and aperture blade. There is a brushless type motor as a suitable form for a small motor, and further, there is a stepper motor, shown inFIG. 9, as the brushless type motor.

This is constituted by coaxially winding a coil105around a bobbin101, and the bobbin101is axially held and fixed with two stator yokes106. In addition, stator teeth106aand106bare staggered in an inner circumferential face of the bobbin101in the stator yoke106. In a housing103, a stator102is constituted by fixing the stator yoke106that is integrated with the stator teeth106aor106b. In one of two housings103, a flange115and a bearing108are fixed, and in another housing103, another bearing108is fixed. A rotor109consists of rotor shaft110and a rotor magnet111fixed to this, and there is a gap between the rotor magnet111and stator yoke106aof the stator102. Then, the rotor shaft110is supported rotatably by two bearings108.

However, since such a type of motor that is shown inFIG. 9is provided while centering on an output shaft, the motor does not have hollow structure. Therefore, when this motor is used as a driving force that drives an aperture blade, a shutter, a lens, or the like, this motor is arranged so that this motor may become parallel to an optical axis outside the lens in a body tube of a camera. Hence, the radius of the body tube becomes a value obtained by adding the diameter of the motor to the radius of the lens and the radius of an aperture opening.

Therefore, this applicant proposed a motor that was lessened in the radial direction of the rotor in U.S. Pat. No. 5,831,356. Since this motor was miniaturized in the radial direction of the rotor, it was possible to make the diameter of the body tube small enough even if the motor was arranged in the outer circumferential face of the lens.

On the other hand, another motor is proposed, the motor that has a hollow shape and is constituted so that the luminous flux of an objective field can pass the hollow portion. Since the luminous flux of the objective field passes a core of the motor, this is more suitable for the miniaturization in the radial of the body tube than the structure that the motor is arranged in parallel with the lens. Moreover, if motor length in the direction of a rotation axis of the rotor is shortened, it is possible to constitute the lens body tube very compactly.

In addition, motors with short total length in the rotation axis of the rotor are proposed in Japanese Patent Application Laid-Open No. 7-213041, Japanese Patent Application Laid-Open No. 2000-50601, and the like. Though the motors described in the above-mentioned two gazettes are not hollow, it will be possible to modify them into hollow motors by providing each ring rotor, making this rotor an output member, and providing a hole in a central portion of its housing.

The simplified structure of the motors described in the above-mentioned gazettes is shown inFIGS. 10 and 11. A motor having the simplified structure is constituted by a plurality of coils301,302, and303, and a disc-like magnet304, a coil has a thin coin shape as shown in figure, and a pivot of the coil is arranged in parallel to a magnet shaft. The disc magnet is magnetized in the axial direction of the disk, and is arranged so that a magnetized side of the magnet may face the coil. The magnet304is rotated by energizing a plurality of coils301to303sequentially and generating magnetic flux. Since the coils301to303and magnet304are formed thinly together, it is possible to lessen the size in the direction of the rotation axis of the motor.

Nevertheless, in the motors proposed in Japanese Patent Application Laid-Open No. 7-213041, Japanese Patent Application Laid-Open No. 2000-50601, and the like, as shown inFIG. 11, the magnetic flux generated in each coil did not necessarily effectively go to the magnet304, but some magnetic flux went in the direction out of the magnet. Therefore, torque was not so large for the size of the entire motor.

In addition, since the coils301to303, and the magnet304are abreast arranged in the direction of the rotation axis of the motor, the length of the motor in the axial direction becomes the length obtained by adding the height of the coil to the height of the magnet at lowest. When this motor was used as an adjustment mechanism of the shutter blade or the aperture blade, the total length of the apparatus did not become so short, and hence, this motor was not so suitable for the structure that an image-taking lens is arranged near the aperture blade or the shutter blade. Therefore, in order to provide a motor where the total length in the direction of the rotation axis is further shortened and torque is improved, it is preferable to further improve the motor.

SUMMARY OF THE INVENTION

The present invention provides a motor comprising: a rotor that is formed into a hollow disk shape, and has at least one plane of the disk magnetized in a plurality of different poles in the rotational direction; a coil that is arranged in a position where its inner circumferential surface faces an outer circumferential surface of the rotor or, a position where its outer circumferential surface faces an inner circumferential surface of the rotor; a first magnetic pole portion that faces one plane of the rotor, is formed with teeth extending in the radial direction of rotor, and is excited by the coil; and a second magnetic pole portion that is provided in an opposite side of the first magnetic pole portion while sandwiching the rotor, and is excited by the coil.

According to this structure, it becomes possible to provide a motor whose total length in the direction of a rotation axis is shortened and which has large torque.

In addition, it is desirable that the first magnetic pole portion is formed in a plate-like shape extending in parallel to the faced side of the rotor.

Another aspect of the present invention provides a light amount adjusting apparatus comprising: a rotor that is formed into a hollow disk shape, and has at least one plane of the disk magnetized in a plurality of different poles in the rotational direction; a coil that is arranged in a position where its inner circumferential surface faces an outer circumferential surface of the rotor or, a position where its outer circumferential surface faces an inner circumferential surface of the rotor; a first magnetic pole portion that faces one plane of the rotor, is formed with teeth extending in the radial direction of the rotor, and is excited by the coil; a second magnetic pole portion that is provided in an opposite side of the first magnetic pole portion while sandwiching the rotor, and is excited by the coil; a base plate member that has an opening; and a blade member that moves on the opening while interlocking with the rotation of the rotor.

According to this structure, it is possible to provide the light amount adjusting apparatus that is equipped with a shutter, an f-stop number adjusting mechanism, etc., and is short in the axial direction.

In addition, it is desirable that the light amount adjusting apparatus further comprises a regulator that drives a lever member by the rotation of the rotor, and regulates the quantity of light that passes the opening of the base plate member by the opening or a filter portion that is provided in the lever member.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, the present invention will be explained on the basis of drawn embodiments.

FIGS. 1to4andFIGS. 5Ato5C show a shutter drive unit that is an embodiment according to a light amount adjusting apparatus of the present invention.FIG. 1is an exploded perspective view of the shutter drive unit,FIG. 2is a sectional view of the shutter drive unit in the direction of its rotation axis in the state of assembly completion,FIG. 3is a sectional view of a one-way clutch described later,FIG. 4is a plan view showing the relation between a ratchet member14and an output member13that is described later, andFIGS. 5A,5B and5C are drawings for explaining the rotational operation of a magnet of the shutter drive unit.

InFIGS. 1to4andFIGS. 5Ato5C, a magnet1that is a rotor is formed in a hollow disk shape (ring shape) and is rotatably held while centering on a center of a circle, wherein at least a surface1eperpendicular to the rotation axis (i.e., a plane in one direction of the disk) is divided into a plurality of pieces in the rotational (circumferential) direction to be alternately magnetized in different polarities. In this embodiment, as shown inFIGS. 5Ato5C, the surface1eof the magnet1is divided into 10 pieces in the rotational direction while centering on the rotation axis, and S and N poles are alternately magnetized. A surface1fopposite to the surface1eof the magnet1is dividedly magnetized in a polarity opposite to the surface1e, or, is not magnetized at all. Alternatively, it is no problem that the surface1eof the magnet1is not magnetized and only the surface if is divided and magnetized. The magnet1is formed by injection-molding plastic magnet material. According to injection-molding, it is possible to easily form the short length of magnet1in the thickness direction, that is, the short length of magnet1in the axial direction of the disk-shaped magnet1.

Dowels1b,1cand1dthat project in the direction parallel to the rotation axis are formed in the magnet1, a central fitting portion1afits with a fitting portion6bof a fitting ring6described later, and the magnet1is supported rotatably. Since the magnet1is formed by injection-molding a plastic magnet, production is easy even if the magnet1has a shape having the dowels1b,1cand1d. In addition, since the fitting portion1ais molded in one piece with the magnet1, the axial accuracy of a magnet portion to a center of rotation improves.

In addition, since a thin resin film is formed on each surface of the injection-molded magnet, rust is greatly little generated in comparison with a compression magnet, and hence, rust proofing such as coating can be abolished. Furthermore, there is no adhesion of magnetic powder that becomes a problem in the compression magnet, and also no swelling of a surface that easily arises at the rust proofing coating.

The cylindrical coil2is wound around a bobbin3that is made of insulating material. The coil2is arranged outside the magnet1coaxially with the magnet1, and an inner circumferential surface of the coil2is made to face an outer circumferential surface of the magnet1. In addition, the thickness of the coil2in the direction of the rotation axis is made to be approximately the same as the thickness of the magnet1in the direction of the rotation axis (i.e., the thickness of the magnet1). That is, the magnet1and coil2are constituted so that they may be arranged on the same plane perpendicular to the rotation axis, and may become the same position in the direction of the rotation axis.

A stator4is made of soft magnetic material, and has first magnetic pole portion members4a,4b,4c,4dand4eexcited by energizing the coil2. These magnetic pole portion members4ato4eface the surface1eof the disk-shaped magnet1while having a predetermined gap, and is constituted by comb-like teeth extending to the radial direction of the magnet1. Then, by letting a magnetized division number of the magnet1be n, a number of these extending comb teeth is n/2 (five in this embodiment). All the magnetic pole portion members4ato4eare mutually excited in the same polarity by energizing the coil.

Here, let a magnetized division number of the surface1eof the magnet1be n. The magnetic pole portion members4ato4eare formed by equally dividing a circumference by 720/n (72° in this embodiment). These magnetic pole portion members4ato4eare formed in a plate-like shape extending in parallel to the faced surface of the rotor. In this manner, by constituting the first magnetic pole portion, it becomes possible to further thin the thickness of the entire shutter drive unit. Supposing the magnetic pole portion is formed by concave and convex portions extending in parallel to the axial direction, the thickness of the stator increases only by the difference between the concave and convex portions. Nevertheless, by making the magnetic pole portion comb-shaped like this embodiment, it is possible to form the stator from which this differential thickness is omitted.

A blade pressure plate9described later is arranged in a position facing the magnetic pole portion members4ato4ewhile sandwiching the magnet1, and forms a second magnetic pole portion to be excited by the coil2in the polarity opposite to the magnetic pole portion members4ato4e. The blade pressure plate9is made of soft magnetic material, and is magnetically connected to the stator4in a position different from the magnetic pole portion members4ato4eto constitute a magnetic circuit with the coil2, and stator4. In this embodiment, as shown inFIG. 2, the stator4is connected to the blade pressure plate9in a position4fwhere an outside diameter of the coil2is covered.

The blade pressure plate9is constituted by a plane parallel to the surface1fof the magnet1, and faces the surface1fwith a predetermined gap. Though being constituted in a simply plate-like shape in this embodiment, the blade pressure plate9may be also constituted in a comb-like shape that has teeth the same number as that of the magnetic pole portion members4ato4eof the stator4. However, when the blade pressure plate9is constituted in the comb-like shape, respective comb teeth of the blade pressure plate are made to face the comb teeth4ato4eof the stator4. In this case, if the surface1fof the magnet1is dividedly magnetized in the polarity opposite to the surface1e, it is possible to further enlarge a rotation output of the rotor. If the blade pressure plate9is constituted in the simply plate-like shape like this embodiment, the magnetic flux that is generated by the coil2passes between the comb-like magnetic pole portion members4ato4eof the stator4and positions where the shapes of these magnetic pole portion members4ato4eare projected on a plane of the blade pressure plate9. Hence, it is acceptable that the shape of the blade pressure plate9that is a second magnetic pole portion facing the magnetic pole portion members4ato4eof the stator4is merely tabular. In addition, it is also acceptable to constitute the second magnetic pole portion with another member (soft magnetic material) without making the blade pressure plate9serve as the second magnetic pole portion combinedly. In this case, since another member functions as the second magnetic pole portion, the blade pressure plate9need not be made of soft magnetic material. In this embodiment, since the blade pressure plate9doubles as the magnetic poles facing the magnetic pole portion members4ato4eof the stator4, it is possible to constitute the shutter drive unit more thinly.

The coil2and bobbin3are fixed between the stator4and blade pressure plate9by bonding and the like. A rib3bof the bobbin3is constituted so as to regulate a position of the surface1eof the magnet1, and secures a gap between the magnet1and magnetic pole portion members4ato4eof the stator4only by a predetermined quantity.

The magnetic pole members4ato4eof the stator4that are the first magnetic pole portion, and the magnetic pole of the blade pressure plate9that is the second magnetic pole portion are provided so as to sandwich the magnetization portion1eof the magnet1while keeping a predetermined gap. Hence, the magnetic flux generated by energizing the coil2crosses the magnet1between the magnetic pole members4ato4eof the stator4and the magnetic pole of the blade pressure plate9. Hence, the magnetic flux effectively acts on the magnet1that is the rotor, and improves an output of the rotor. Moreover, since it is possible to constitute the magnet1in the length in the direction of the rotation axis of the magnet1, that is, in the thickness direction of the magnet1very thinly as described above, it is possible to quite lessen the gap between the magnetic pole portion members4ato4eof the stator4and the magnetic pole of the blade pressure plate9. Therefore, it is possible to constitute the magneto-resistance of a magnetic circuit formed with the coil2, stator4, and blade pressure plate9in small size. Owing to this, since it is possible to make a lot of magnetic flux arise by a small current, it is possible to provide a motor achieving the improvement of a rotor output, reduction of power consumption, and miniaturization of the coil.

In the center of a base plate5, an opening5ais formed, dowels5band5cprojecting in the direction parallel to an optical axis are formed, and slots5dand5ewith which the dowels1cand1dof the magnet1contact are formed. A rotatable angle of the magnet1is regulated by contacting the dowels1cand1dof the magnet1with the slots5dand5e. In addition, let this rotatable angle be θ°. In addition, the thickness of an outer circumferential edge portion of the base plate5is larger than that of other portions of the base plate5to form an outside wall.

A fitting ring6is fixed by fitting a portion6awith a fitting hole9aof the blade pressure plate9. In the fitting ring6, a surface6bthat is a sliding surfaces with the magnet1fits rotatably with an inner diameter portion1aof the magnet1, and the rib6cregulates the position of the surface1fof the magnet1to secure a gap between the blade pressure plate9, which is the second magnetic pole portion, and the magnet1by predetermined distance.

In shutter blades7and8, a round hole7aprovided in the shutter blade7fits with the dowel5cof the base plate5rotatably, and the round hole7bfits with the dowel id of the magnet1slidably. In addition, a round hole8aprovided in the shutter blade8fits with the dowel5bof the base plate5rotatably, and a round hole8bfits with the dowel1cof the magnet1slidably.

A maximum opening9athat regulates maximum aperture size is formed in the center of the shutter blade pressure plate9. The predetermined distance of gap is formed between the shutter blade pressure plate9and base plate5by contacting an outer circumferential portion of the shutter blade pressure plate9with an outside wall of the base plate5. In addition, the shutter blade7and shutter blade8are arranged in this gap. In addition, the shutter blade pressure plate9also serves as a supporting member that prevents the shutter blade7and shutter blade8from coming off axially.

When the coil2is energized and the magnet1rotates, the round hole7bof the shutter blade7is pushed by the dowel1cof the magnet1, the shutter blade7rotates while centering on the round hole7a, the round hole8bof the shutter blade8is pushed by the dowel1dof the magnet1, and the shutter blade8rotates while centering on the round hole8a. By rotating the magnet1within a rotatable angle, the shutter blades7and8move between a shading position where the maximum opening9aof the shutter blade pressure plate9and the opening5bof the base plate5are covered, and an exposure position where the passing of light is allowed. That is, while interlocking with the rotation of the magnet1, the shutter blades7and8perform opening and closing drive. In addition, it is also possible to use these shutter bladed7and8as aperture blades by modifying their shapes.

In an ND filter plate10, a hole portion10afits with the dowel5fof the base plate5rotatably. An ND filter portion10bwith small optical transmittance moves between a position where an opening9aof the shutter blade pressure plate9is covered, and a position where the ND filter portion evacuates from opening9aby the rotation of the ND filter plate10to adjust the light amount passing the opening9a.

In an interlock lever11, a hole11afits with the dowel3aof the bobbin3rotatably. A groove portion11bfits with the dowel1bof the magnet1slidably, and when the magnet1rotates, the interlock lever11rotates by an angle corresponding to the rotation of the magnet1while centering on the hole11a.

In an input gear12, a gear portion12aengages with a gear portion11cof the interlock lever11, and a portion12bfits rotatably with a pin from the base plate that is not shown. This input gear12constitutes a one-way clutch with an output member13, and a ratchet member14.

FIG. 3is a sectional view of the one-way clutch, andFIG. 4is a plan view showing the relation between the ratchet member14and output member13.

In the output member13of the one-way clutch, a pin13bfits with a slot10cof the ND filter plate10slidably. According to the rotation of the output member13, the ND filter10moves between a position where the opening9aof the shutter blade pressure plate9is covered, and a position where the ND filter10evacuates from the opening9a. The output member13is installed onto a pin15from the base plate, not shown, rotatably at a13cportion as shown inFIG. 4, and a ratchet gear13dis formed in its inner diameter portion.

A ratchet member14shown inFIG. 4has a claw portion14bthat has an elasticity, and the claw portion14bfits with a ratchet gear13dof the output member13. The ratchet member14rotatably fits with the pin15from the base plate, not shown, at a portion14a. When the ratchet member14rotates in the direction shown by an arrow A inFIG. 4, the claw portion14bis caught by the ratchet gear13dfor the output member13to rotate. However, when the ratchet member14rotates in the direction opposite to the direction shown by the arrow A, the claw portion14bslides on the ratchet gear13dby its bending, and hence the output member13never rotate. As shown inFIG. 3, in the ratchet member14, a pin14cis provided. Since this pin14cfits with a hole12cof an input gear12, the ratchet member14and input gear12rotate always as one body.

In addition, the interlock lever11and input gear12are constituted so that the input gear12rotates by 180° when the magnet1rotates by θ°.

FIGS. 5A,5B and5C are drawings for explaining the rotation operation of a magnet of the shutter drive unit, and are drawings at the time of viewing the shutter drive unit from the upper side of the drawing shown in FIG.2.FIGS. 5A and 5Cshow the state that the dowels1cand1dof the magnet1contact with edges of the slots5dand5eof the base plate5and the counterclockwise rotation of the magnet1is regulated.FIG. 5Bshows the state that the dowels1cand1dof the magnet1contact with edges of the slots5dand5eof the base plate5and the clockwise rotation of the magnet1is regulated. The rotational position of the magnet1inFIGS. 5A and 5Cis different from the rotational position of the magnet1inFIG. 5Bby θ°.

When the coil2is not energized, the magnet1is held in any one of rotational positions inFIGS. 5Ato5C. This aspect will be explained by usingFIGS. 5Ato5C, and FIG.6.

FIG. 6is a graph showing an aspect of cogging torque, and shows the relation between the rotational position of the magnet1and the attraction that the magnet1receives from the first magnetic pole portion members4ato4ein the state of not energizing the coil2.

Specifically, the vertical axis denotes the magnetism generated between the magnet1and stator4, and the horizontal axis does the rotation phase of the magnet1. At points shown by an E1point and an E2point, when the magnet starts normal rotation, a counterrotating force is generated to return the magnet1to the former position. On the other hand, when starting reverse rotation, a normal rotating force is generated to return the magnet1to the former position. That is, in the magnet, a cogging force that tries to stably position the magnet at either of the E2point or the E2point is generated. In addition, when being located at either of phases at an F1point, an F2point, or an F3point phase, the magnet1stops. However, when a phase shifts from these positions even a little, a force of rotating to the E1point or the E2point before or after the shifted position is generated. That is, it can be said that the F1point, F2point, and F3point are stopping positions in unstable balance.

This embodiment has the structure that, when the coil2is not energized, the magnet1stably stops when a central portion of each pole of the magnet1is in the E1point or the E2point. However, by modifying shapes of the first magnetic pole portion members4ato4e, this embodiment can also have the structure that the magnet1stably stops when a boundary of poles of the magnet1is at the E1point or the E2point.

The central portion of a magnetic pole of the magnet1does not stop at either of the F1point, F2point, or F3point since there arise vibration, a change of posture, etc. in the state of not energizing the coil2, and hence, the magnet1stops at the E1point or the E2point with stability.

Stable points of the cogging like the El point and the E2point exist at a cycle of 360/n while letting a magnetized division number of the magnet1be n, and their intermediate positions become unstable points like the F1point, F2point, and F3point.

In this embodiment, the E1point and the E2point correspond to the centers of the first magnetic pole portion members4ato4e. That is, when the centers of the poles of the magnet1faces the centers of the first magnetic pole portion members4ato4e, the magnet1stably stops. However, even if the magnetic pole portion members4ato4eare excited from the state that the centers of the poles of the magnet1face the centers of the first magnetic pole portion members4ato4eby energizing the coil2, a turning force is not generated in the magnet1. Then this embodiment is set as shown inFIG. 5Aso that the dowels1cand1dare made to contact with edges of the slots5dand5e, and when the coil2is not energized, an angle between the centers of the poles of the magnet1and the centers of the first magnetic pole portion members4ato4emay become α°. Owing to this, when the magnetic pole portion members4ato4eare excited by energizing the coil2from the state shown inFIG. 5A, a turning force toward the E2point from the E1point, that is, the turning force in the clockwise direction is generated in the magnet1. In addition, the state shown inFIG. 5Acorresponds to a G point in FIG.6. Cogging torque (attraction that is generated between the magnet1and stator4and acts on the magnet1) in this position is T2, and a minus force returning the magnet to the E1point (a counterclockwise force inFIGS. 5Ato5C) acts. That is, the holding power of the position where the dowels1cand1dof the magnet1contact with the slots5dand5eof the base plate5becomes T2. Therefore, the magnet1stably stops in the position shown inFIG. 5Aby the holding power T2at the time of not energizing the coil2.

Similarly, in regard to the rotation of the magnet1in the clockwise direction of magnet1, as shown inFIG. 5B, it is set that the dowels1cand1dare made to contact with edges of the slots5dand5e, and when the coil2is not energized, an angle between the centers of poles of the magnet1and the centers of the first magnetic pole portion members4ato4ebecomes β°.

That is, the rotation of the magnet1is regulated by the slots5dand5eof the base plate5so that its rotation quantity may become smaller than the distance between the centers of S and N poles adjacent to each other in the magnet1.

When the magnetic pole portion members4ato4eare excited by energizing the coil2from the state shown inFIG. 5A, a turning force toward the E1point from the E2point, that is, the turning force in the counterclockwise direction is generated in the magnet1. In addition, the state shown inFIG. 5Bcorresponds to an H point in FIG.6. Cogging torque in this position is T1, and a plus force advancing the magnet to the E2point (a clockwise force inFIGS. 5Ato5C) acts. That is, the holding power of the position where the dowels1cand1dof the magnet1contact with the slots5dand5eof the base plate5becomes T1. Therefore, the magnet1stably stops in the position shown inFIG. 5Bby the holding power T1at the time of not energizing the coil2. A turning angle of the magnet1from the state shown inFIG. 5Ato the state shown inFIG. 5Bis θ° mentioned above.

Next, the aspect of the rotary operation of the magnet1and ND filter plate10will be explained by usingFIGS. 5Ato5C.

Suppose that the magnet1stably stops in the position shown inFIG. 5Awhen the coil2is not energized. At this time, the ND filter portion10bis held by a pin13bof the output member13in the position where the ND filter portion10bevacuates from the opening9aof the shutter blade pressure plate9. This state is assumed to be a first exposure state.

When the coil2is energized from the state shown inFIG. 5Ato excite the magnetic pole portion members4ato4eof the stator4into S poles, the magnet1receives an electromagnetic force in the rotary direction, and the magnet1that is the rotor starts rotation in the clockwise direction smoothly. Then, when the turning angle becomes θ° (i.e., the state shown in FIG.5B), energizing of the coil2is shut off. Since the state shown inFIG. 5Bcorresponds to the H point inFIG. 6, the magnet1is stably held in this position by the cogging torque T1as mentioned above.

Though the input gear12rotates in the clockwise direction in connection with the clockwise rotation of the magnet1, the output member13does not rotate since the claw portion14bof the ratchet member14that rotates as one body with the input gear12is bent and slides on the ratchet gear13das explained inFIGS. 3 and 4. Hence, the position of the pin13bof the output member does not move, and the ND filter portion10bkeeps the position where the ND filter portion10bevacuates from the opening9aof the shutter blade pressure plate9.

Here, when the coil2is energized in the direction opposite to the former direction to excite the magnetic pole portion members4ato4eof the stator4into N poles, the magnet1that is the rotor starts rotation in the counterclockwise direction smoothly. Then, when the turning angle becomes θ° (i.e., the state shown in FIG.5C), energizing of the coil2is shut off. Since the state shown inFIG. 5Ccorresponds to the G point inFIG. 6similarly toFIG. 5A, the magnet1is stably held in this position by the cogging torque T1as mentioned above.

InFIGS. 5A and 5C, though the rotational position of the magnet1is the same, positions of the pin13bof the output member13are different. Input gear12rotates by 180° (i.e., a half turn) in the counterclockwise direction when the magnet1rotates from the position, shown inFIG. 5B, in the counterclockwise direction by θ°. The claw portion14bof the ratchet member14rotating with the input gear12as one body engages with the ratchet gear13dof the output member13to rotate the output member13by 180° in the counterclockwise direction. Therefore, the ND filter portion10brotates by the pin13bof the output member to the position where the ND filter portion10bcovers the opening9aof the shutter blade pressure plate9. The light amount that passes the opening9ain this state decreases in comparison with the state inFIG. 5A, and this state is made to be a second exposure state.

When the coil2is energized again to excite the magnetic pole portion members4ato4eof the stator4into S poles, the magnet1that is the rotor starts rotation in the clockwise direction. When the energizing of the coil2is reversed after the magnet1rotates at θ° to excite the magnetic pole portion members4ato4eof stator4into N poles and to rotate the magnet1in the counterclockwise direction again, the state returns to the first exposure state shown in FIG.5A.

In this manner, the ND filter portion10bmoves by the movement of the magnet1in the counterclockwise direction between the position where the ND filter portion10bevacuates from the opening9aof the shutter blade pressure plate9, and the position where the ND filter portion10bcovers the opening9a. Owing to this, it is possible to switch the first exposure state and the second exposure state that are mentioned above.

In this manner, by switching the direction where the coil2is energized and rotating the magnet1, it becomes possible to control positions of the shutter blade7and shutter blade8in the open position and the closed position. Hence, it is possible to control the quantity of light passing the opening9aof the shutter blade pressure plate9and the opening5bof the base plate5. Moreover, at the time of not energizing the coil2, each position is kept by the attraction between the magnet1and the magnetic pole portion members4ato4e. Therefore, even if the coil2is not energized, the positions of the shutter blade7and shutter blade8never change by vibration etc., and hence, it is possible to improve the reliability of the shutter and to save energy. Hence, this apparatus acts as a shutter apparatus that can be stably held even in the opening position or the closing position at the time of being not energized.

It is possible to perform two types of shuttering operations: an operation of making a state from the first exposure state that the ND filter portion10bshown inFIG. 5Ais in the position, where the ND filter portion10bevacuates from the opening9aof the shutter blade pressure plate9, to a shuttering position where the maximum opening9aof the blade pressure plate9and the opening5bof the base plate5are covered with the shutter blade7and shutter blade8by exciting the magnetic pole portion members4ato4eof the stator4into S poles by energizing the coil2and rotating the magnet1in the clockwise direction at θ°; and an operation of making a state from the second exposure state, where the ND filter portion10bshown in theFIG. 5Cis in the position where the ND filter portion10bcovers the opening9aof the shutter blade pressure plate9, to a shuttering position where the maximum opening9aof the blade pressure plate9and opening5bof the base plate5are covered with the shutter blade7and shutter blade8by exciting the magnetic pole portion members4ato4eof the stator4into S poles by energizing the coil2, and rotating the magnet1in the clockwise direction at θ°.

That is, it is possible to make it as a lens with two kinds of f-stop numbers as a taking lens. If an objective field is dark, it is possible to perform exposure from the first exposure state, and exposure can be also performed from the second exposure state when the objective field is bright.

In addition, it is possible that only one shutter drive unit drives them, and moreover, it is not necessary to keep energizing so as to keep a maximum aperture. Since the transmitted light amount is adjusted by putting the ND filter in and out, the diffraction phenomenon of light does not arise.

The size of the entire shutter drive unit in the direction of the rotation axis of the rotor is only the thickness of the disk-shaped magnet and the thickness of stator facing this magnet. Since the thickness of the stator itself is thin, it is possible to make the shutter drive unit microminiature so long as the magnet and the coil contained in the stator are made thin. Moreover, since it is sufficient to provide only one coil, an energization control circuit also becomes simple, and hence, it is possible to perform constitution in low cost.

In addition, by making the shape of the shutter drive unit be a doughnut, it becomes possible to arrange a lens therein, and to use a central portion of the shutter drive unit as an optical path.

Furthermore, the magnet1is made of a plastic magnet formed by injection-molding a mixture of Nd—Fe—B based rare earth magnetic powder and thermoplastic resin binder material such as polyamide. Owing to this, though the flexural strength of a compression-formed magnet is about 500 Kgf/cm2, it is possible to obtain the flexural strength of 800 Kgf/cm2or more, when, for example, a polyamide resin is used as binder material. Hence, it becomes possible to form the magnet in a thin cylindrical shape that compression molding cannot make. The thin cylindrical formation makes it possible to set a gap between the magnetic pole portion of stator4and the magnetic poles of the blade suppression plate9to be short and to constitute a magnetic circuit having small magneto-resistance between those. Owing to this, since it is possible to generate a lot of magnetic flux even by a small magnetomotive force when energizing the coil2, the performance of the actuator is enhanced.

FIG. 7is a perspective view of a shutter drive unit in another embodiment. In the figure, instead of the ND filter plate10in the embodiment shown inFIGS. 1,2and5A to5C, a diaphragm aperture plate20that changes a diaphragm aperture is put in and out.

The dowel5fof the base plate fits with a hole20aof the diaphragm aperture plate rotatably, and a dowel13bfits with a slot20cof the diaphragm aperture plate20slidably. An opening20bis an aperture formed less than that of an opening9aof the shutter blade pressure plate9, and is made of shading material excluding the opening9a. The diaphragm aperture plate20goes into the opening9aof the shutter blade pressure plate9according to the rotation of output member13, and moves between a position where aperture diameter is lessened and a position where the diaphragm aperture plate20evacuates from the opening9ato adjust the quantity of light passing the opening9a.

Since the material of this diaphragm aperture plate20is plastic with shading capability, or metal, it is possible to constitute the diaphragm aperture plate20in the cost lower than that of the ND filter plate in the embodiment shown inFIGS. 1,2and5A to5C.

In addition, this embodiment adopts the structure that the input gear12rotates by 180° by the magnet rotating at θ°, and according to this, the pin13bof the output member13moves between two rotational positions. However, for example, if the input gear12rotates by 120° by the magnet rotating at θ°, it is possible to have the structure that the pin13bof the output member13moves between three rotational positions. Owing to this, it becomes possible to set three kinds of f-stop numbers, but the number of f-stop numbers that can be set doesn't limit this invention.

In this embodiment, though the coil is arranged outside the magnet, the coil can be also arranged inside the magnet. In this case also, the thickness of the coil2in the direction of the rotation axis is approximately equal to the thickness of the magnet1in the direction of the rotation axis (i.e., the thickness of the magnet1). A section of the shutter drive unit at this time is shown in FIG.8. Here, by focusing on the structure different from that of the embodiment shown inFIGS. 1,2and5A to5C, description will be performed.

InFIG. 8, a magnet51that is the rotor is formed into a hollow disk shape (ring shape), and is held rotatably by centering on a center of a circle. Furthermore, a surface51ein the vertical direction at least to the rotation axis is divided in the rotational direction to be alternately magnetized into different polarities. Similarly to the magnet1in the embodiment shown inFIGS. 1,2and5A to5C, in this embodiment, the surface51eof the magnet51is divided into 10 pieces in the rotational direction while centering on the rotation axis, and S and N poles are alternately magnetized. A surface51fopposite to an opposite surface of the surface51eof the magnet51is dividedly magnetized in a polarity opposite to the surface51e, or, is not magnetized at all. Alternatively, it is no problem that the surface51eof the magnet51is not magnetized and only the surface51fis divided and magnetized. The magnet51is formed by injection-molding plastic magnet material. In addition, dowels51b,51c, and51dthat project in the direction parallel to the rotation axis, and a fitting portion51ain a central portion are formed in the magnet51, the central fitting portion51afits with a fitting portion56bof a fitting ring56described later, and the magnet51is supported rotatably.

The cylindrical coil52is wound around a bobbin53that consists of insulating material. The coil52is arranged inside the magnet51, and an outer circumferential surface of the coil52is made to face an inner circumferential surface of the magnet51. In addition, the thickness of the coil52in the direction of the rotation axis is made to be approximately the same as the thickness in the direction of the rotation axis of the magnet51(i.e., the thickness of the magnet51).

A stator54is made of soft magnetic material, and has first magnetic pole portion members54a,54b,54c,54dand54eexcited by energizing the coil52similarly to the embodiment shown inFIGS. 1,2and5A to5C. These magnetic pole portion members54ato54eface the surface51eof the disk-shaped magnet51while having a predetermined gap, and is constituted by comb-like teeth extending to the radial direction of the magnet51. Then, let a magnetized division number of the magnet1be n, a number of these extending comb teeth is n/2 (five in this embodiment). All the magnetic pole portion members54ato54eare mutually excited in the same polarity by energizing the coil.

The magnetic pole portion members54ato54eare formed by equally dividing a circumference by 720/n (72° in this embodiment). These magnetic pole portion members54ato54eare formed in a plate-like shape extending in parallel to the faced surface of the rotor.

A blade pressure plate59is arranged in a position facing the magnetic pole portion members54ato54ewith sandwiching the magnet51, and forms a second magnetic pole portion to be excited by the coil52in the polarity opposite to the magnetic pole portion members54ato54e. The blade pressure plate59is made of soft magnetic material, and is magnetically connected to the stator4in a position different from the magnetic pole portion members54ato54eto constitute a magnetic circuit with the coil52, and stator54. In this embodiment, as shown inFIG. 8, the stator54is connected to the blade pressure plate59in a position (inside an inner circumference of the coil) where an inner diameter of the coil2is covered.

The blade pressure plate59is parallel to the surface51fopposite to the surface51eof the magnet51, and faces the surface51fwith a predetermined gap. Though being constituted in a simply plate-like shape, the blade pressure plate59may be also constituted in a comb-like shape that has the same number of teeth as that of the magnetic pole portion members54ato54eof the stator54. However, when the blade pressure plate59is constituted in the comb-like shape, respective comb teeth of the blade pressure plate are made to face the comb teeth54ato54eof the stator54. In this case, if the surface51fof the magnet51is dividedly magnetized in the polarity opposite to the surface51e, it is possible to further enlarge a rotation output of the rotor.

The coil52and bobbin53are fixed between the stator54and blade pressure plate59by bonding and the like. A rib53bof the bobbin53is constituted so as to regulate a position of the surface51eof the magnet51, and secures a gap between the magnet51and magnetic pole portion members54ato54eof the stator54only by predetermined quantity.

The magnetic pole members54ato54eof the stator54that are the first magnetic pole portion, and the magnetic pole of the blade pressure plate59that is the second magnetic pole portion are provided so as to sandwich the magnetization portion51eof the magnet51while keeping a predetermined gap. Hence, the magnetic flux generated by energizing the coil52crosses the magnet51between the magnetic pole members54ato54eof the stator54and the magnetic pole of the blade pressure plate59. Owing to this, since it is possible to make a lot of magnetic flux arise by a small current, it is possible to provide a motor achieving the improvement of a rotor output, reduction of power consumption, and miniaturization of the coil.

In a base plate55, an opening55ais formed, dowels55band55cprojecting in the direction parallel to an optical axis are formed as one body, and slots55dand55ewith which the dowels51cand51dof the magnet51contact are formed. A rotatable angle of the magnet51is regulated by contacting the dowels51cand51dof the magnet51with the slots55dand55e. In addition, let this rotatable angle be θ°. Furthermore, the thickness of an outer circumferential edge portion of the base plate55is larger than that of other portions of the base plate55to form an outside wall.

A fitting ring56is fixed by fitting a portion56awith a fitting hole59aof the blade pressure plate59. In the fitting ring56, a face56bthat is a sliding surface with the magnet51fits rotatably with an inner diameter portion51aof the magnet51, and the rib56cregulates the position of the surface51fof the magnet51to secure a gap between the blade pressure plate59, which is the second magnetic pole portion, and the magnet51by predetermined distance.

In shutter blades57and58, a round hole57aprovided in the shutter blade57fits with the dowel55cof the base plate55rotatably, and the round hole57bfits with the dowel51dof the magnet51slidably. In addition, a round hole58aprovided in the shutter blade58fits with the dowel55bof the base plate55rotatably, and a round hole58bfits with the dowel51cof the magnet51slidably.

A maximum opening59athat regulates maximum aperture size is formed in the center of the shutter blade pressure plate59. The predetermined distance of gap is formed between the shutter blade pressure plate59and base plate55by contacting an outer circumferential portion of the shutter blade pressure plate59with an outside wall of the base plate55. In addition, the shutter blade57and shutter blade58are arranged in this gap. Furthermore, the shutter blade pressure plate59also serves as a supporting member that prevents the shutter blade57and shutter blade58from coming off axially.

When the coil52is energized and the magnet51rotates, the round hole57bof the shutter blade57is pushed by the dowel51cof the magnet51, the shutter blade57rotates while centering on the round hole57a, the round hole58bof the shutter blade58is pushed by the dowel51dof the magnet51, and the shutter blade58rotates while centering on the round hole58a. By rotating the magnet51within a rotatable angle, the shutter blades57and58move between a shading position where the maximum opening59aof the shutter blade pressure plate59and the opening55aof the base plate55are covered, and an exposure position where the passing of light therethrough is allowed. That is, while interlocking with the rotation of the magnet51, the shutter blades57and58perform opening and closing drive. In addition, it is also possible to use these shutter bladed57and58as aperture blades by modifying their shapes.

Moreover, the magnet has a hollow disk shape in the above-mentioned embodiment since it is used as the shutter drive unit, but it is no care that the magnet has a mere disk shape when using it as only an ultra flat motor. However, it is needless to say that, since it is not possible to arrange the coil so as to face inner circumference of the magnet like the embodiment shown inFIG. 8because the magnet is not a hollow shape, it is necessary to arrange the coil so as to face the outer circumference of the magnet like the embodiment shown inFIGS. 1,2and5A to5C.

In addition, it is possible to drive the shutter blade similarly to the above-mentioned embodiment even in the structure that one set of N pole and S pole is provided in a magnet and only a first magnetic pole is provided in a stator though rotating torque drops. In this case, since it is sufficient just to arrange only two magnetic poles in the circumference of the magnet, it is possible to freely set θ° that is a rotatable angle of the magnet.