Driving device

A stepping motor includes a magnet having a magnetized portion, first and second coils, a first yoke having a first-magnetic-pole portion, a second yoke having a second-magnetic-pole portion, and a rotating yoke having a third-magnetic-pole portion fixed to the single surface of the magnet. The first coil is disposed outside of the outer-circumferential surface of the magnet, and the second coil is disposed inside of the inner-circumferential surface of the magnet so as to have the same concentricity as the magnet. The first and second magnetic-pole portions and the magnetized portion face each other across a certain gap. The cylindrical portion of the first yoke and the outermost-diameter portion of the rotating yoke face each other across a gap in the radial direction, and the cylindrical portion of the second yoke and the flat surface portion of the rotating yoke face each other across a gap in the shaft direction. Thus, an easy-to-assemble low-cost driving device having a thin shape in the shaft direction, and high output with small torque loss is provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a driving device to be applied to a thin-disc-shaped stepping motor or actuator.

2. Description of the Related Art

Heretofore, a brushless motor can be cited as a model suitable for a small motor. Examples of a brushless motor of which the driving circuit is simple include a small cylindrical stepping motor which uses a permanent magnet, such as that shown inFIG. 16.

FIG. 16is a cross-sectional view illustrating the internal configuration of a stepping motor according to a known example.

InFIG. 16, a stator coil105is wound around a bobbin101concentrically, and the bobbin101is sandwiched and fixed with two stator yokes106from the shaft direction. With the stator yoke106, stator gear teeth106aand106bare alternately disposed in the circumferential direction of the inside diameter surface of the bobbin101. A stator102is configured in a case103by the stator yoke106integrated with the stator gear tooth106aor106bbeing fixed.

Of the two cases103, one case103is fixed with a flange115and a shaft bearing108, and the other case103is fixed with another shaft bearing108. A rotor109is made up of a rotor magnet111fixed to a rotor shaft110. The rotor magnet111makes up an air gap portion in a radial pattern together with the stator yoke106of the stator102. The rotor shaft110is supported between the two shaft bearings108so as to be rotated.

As for a modification of a stepping motor having the above configuration, an optical control device has been proposed (see Japanese Patent Publication No. 1978-2774, for example). An optical control device is for controlling the passage amount of light by opening/closing a shutter blade to be coupled with a stepping motor in stages. Also, as for another modification, a hollow motor has been proposed (see Japanese Patent Laid-Open No. 1982-166847, for example). A hollow motor is a stepping motor having a ring-shaped configuration, which allows light or the like to pass through the cavity of the center portion thereof.

Also, with the shutter or diaphragm adjustment mechanism of a camera or the shutter of a digital camera, or a camera which employs a silver halide film, upon attempting to subject a photographing lens to downsizing and reduction in shaft length, the photographing lens needs to be positioned before and after the shutter or diaphragm adjustment mechanism. Accordingly, thinning in the light path i.e. axial direction of the shutter or diaphragm adjustment mechanism is desired as well as high-outputting of a motor.

However, with the known small cylindrical stepping motor shown inFIG. 16, the case103, bobbin101, stator coil105, and stator yoke106are disposed concentrically on the outer circumference of the rotor109. Accordingly, this provides a disadvantage wherein the outer dimension of the stepping motor becomes large. Also, the magnetic flux generated by electric power being supplied to the stator coil105principally passes through the end surface106a1of the stator gear tooth106aand the end surface106b1of the stator gear tooth106b, as shown inFIG. 17. Accordingly, the magnetic flux does not act upon the rotor magnet111effectively, resulting in a disadvantage wherein the output power of the stepping motor is low.

Also, with the above optical control device described in Japanese Patent Publication No. 1978-2774, and the above hollow motor described in Japanese Patent Laid-Open No. 1982-166847, as with the above description, a stator coil and a stator yoke are disposed on the outer circumference of a rotor magnet. Accordingly, the outer dimension of the motor becomes great, and also the magnetic flux generated by electric power being supplied to the stator coil does not act upon the rotor magnet effectively.

In general, a camera employs a mechanism for driving a diaphragm blade, shutter, photographing lens, or the like using a motor. However, in the event that a type of motor such as shown inFIG. 16is disposed so as to be parallel to the light axis within the lens barrel of a camera, and it is attempted to be used for driving a diaphragm blade, shutter, photographing lens, or the like, this type of motor has a solid cylindrical shape, the following problems may be encountered. The radial dimension of the lens barrel is a value obtained by adding the radial dimension of the motor to the radial dimension of the photographing lens or the radial dimension of the diaphragm opening portion, so it is difficult to suppress the diameter of the lens barrel to a sufficient small value. Also, with this type of motor, the dimension in the light axial direction is long, so it is difficult to dispose the photographing lens near the diaphragm blade or shutter blade.

On the other hand, a thin motor of which the dimension in the shaft direction is short such as shown inFIGS. 18 and 19has been proposed (see Japanese Patent Laid-Open No. 1995-213041, and Japanese Patent Laid-Open No. 2000-50601, for example).

FIG. 18is a perspective view illustrating the configuration of a known brushless motor, andFIG. 19is a cross sectional view illustrating the internal configuration of the same brushless motor.

InFIGS. 18 and 19, the brushless motor comprises multiple coils301,302, and303, a disc-shaped magnet304, and so forth. The coils301through303have a thin coin shape, and the axis thereof is disposed in parallel with the axis of the magnet304. The magnet304is magnetized in the shaft direction of the disc, and the magnetized surface and the axes of the coils301through303are disposed so as to face the magnet304.

In this case, the magnetic flux to be generated from the coils301through303, as shown in the arrow inFIG. 19, does not act completely effectively upon the magnet304. Also, the rotational force which the magnet304generates acts at the center position of each of the coils301through303, a distance L from the outer diameter of the motor. Accordingly, in spite of the size of the motor, the torque generated is small. Also, the coils301through303occupy up to near the center portion of the motor, so it is difficult to dispose another part within the motor.

Further, it is necessary to provide multiple coils301through303, so this provides disadvantages such as complicating power supply control to the coils301through303, and increases costs. Also, the coils301through303and the magnet304are disposed so as to be overlapped in the parallel direction as to the rotating shaft. Accordingly, in the event of employing this motor as a shutter or a diaphragm adjustment mechanism, the dimension in the light axial direction of the motor is long, so it is difficult to dispose the photographing lens near the diaphragm blade or shutter blade.

The present applicant has proposed a motor such as the following to solve such problems (see Japanese Patent Laid-Open No. 2003-219623 (U.S. Pat. No. 6,897,579), for example).

This motor comprises a magnet, first and second coils, and first through fourth magnetic-pole portions. The magnet is formed in a hollow disc shape, and is made up of a first flat surface orthogonal to a center virtual shaft, a second flat surface orthogonal to the virtual shaft, an outer circumferential surface, and an inner circumferential surface. Also, the magnet is retained so as to be rotated with the center thereof serving as a rotational center, and also at least a surface perpendicular to the rotational center virtual shaft is divided in the angular direction (circumferential direction) centered on the virtual shaft to be magnetized to a different polarity alternately. The first coil is disposed outside of the outer circumferential surface of the magnet, and the second coil is disposed inside of the inner circumferential surface of the magnet.

The first magnetic-pole portion faces one of the surfaces perpendicular to the virtual shaft of the rotational center of the magnet with a predetermined gap, and is magnetized by the first coil. The second magnetic-pole portion faces the other surface perpendicular to the virtual shaft of the rotational center of the magnet with a predetermined gap, and is magnetized by the first coil. The third magnetic-pole portion faces one of the surfaces perpendicular to the virtual shaft of the rotational center of the magnet with a predetermined gap, and is magnetized by the second coil. The fourth magnetic-pole portion faces the other surface perpendicular to the virtual shaft of the rotational center of the magnet with a predetermined gap, and is magnetized by the second coil. Let us say that this type of motor is referred to as a first past example for the sake of facilitating description.

With the above configuration, the length in the shaft direction of the stepping motor is determined by the thickness of the magnet, and the magnetic-pole portion facing the thickness direction of the magnet, so the dimension in the shaft direction of the stepping motor can be reduced to be very small. Also, the magnetic flux to be generated by the first coil traverses the magnet present between the first magnetic-pole portion and the second magnetic-pole portion, so acts effectively. The magnetic flux to be generated by the second coil traverses the magnet present between the third magnetic-pole portion and the fourth magnetic-pole portion, so acts effectively. Thus, a high-outputting motor can be provided.

Also, an actuator employing the same method as the motor described in the above Japanese Patent Laid-Open No. 2003-219623 (U.S. Pat. No. 6,897,579) has been proposed (see Japanese Patent Laid-Open No. 2004-45682 (U.S. Pat. No. 6,781,772), for example). This actuator comprises a magnet, a coil, and first and second magnetic-pole portions. The magnet is formed in a hollow disc shape, and is made up of a first flat surface orthogonal to a center virtual shaft, a second flat surface orthogonal to the virtual shaft, an outer circumferential surface, and an inner circumferential surface. Also, the magnet is retained so as to be rotated with the center thereof serving as a rotational center, and also at least a surface perpendicular to the rotational center virtual shaft is divided in the angular direction (circumferential direction) centered on the virtual shaft to be magnetized to a different polarity alternately. The coil is disposed outside of the outer circumferential surface of the magnet.

The first magnetic-pole portion faces one of the surfaces perpendicular to the virtual shaft of the rotational center of the magnet with a predetermined gap, and is magnetized by the coil. The second magnetic-pole portion faces the other surface perpendicular to the virtual shaft of the rotational center of the magnet with a predetermined gap, and is magnetized by the coil. Let us say that this type of actuator is referred to as a second past example for the sake of facilitating description.

Also, the following configuration can be conceived wherein a coil is disposed on the inner circumferential side of a magnet as an actuator similar to the actuator described in the above Japanese Patent Laid-Open No. 2004-45682 (U.S. Pat. No. 6,781,772). This actuator comprises a magnet, a coil, and first and second magnetic-pole portions. The magnet is formed in a hollow disc shape, and is made up of a first flat surface orthogonal to a center virtual shaft, a second flat surface orthogonal to the virtual shaft, an outer circumferential surface, and an inner circumferential surface. Also, the magnet is retained so as to be rotated with the center thereof serving as a rotational center, and also at least a surface perpendicular to the rotational center virtual shaft is divided in the angular direction (circumferential direction) centered on the virtual shaft to be magnetized to a different polarity alternately.

The coil is disposed inside of the inner circumferential surface of the magnet. The first magnetic-pole portion faces one of the surfaces perpendicular to the virtual shaft of the rotational center of the magnet with a predetermined gap, and is magnetized by the coil. The second magnetic-pole portion faces the other surface perpendicular to the virtual shaft of the rotational center of the magnet with a predetermined gap, and is magnetized by the coil. Let us say that this type of actuator is referred to as a third past example for the sake of facilitating description.

However, the motor of the above first past example (Japanese Patent Laid-Open No. 2003-219623 (U.S. Pat. No. 6,897,579)) is a rotating member serving as output means, i.e., the magnet faces the first through fourth magnetic-pole portions with a gap. Accordingly, the thickness in the shaft direction of the motor is the dimension of sum of at least the first magnetic-pole portion, the gap between the magnet and the first magnetic-pole portion, the magnet, the gap between the magnet and the second magnetic-pole portion, and the second magnetic-pole portion. Or else, this is the dimension of sum of the third magnetic-pole portion, the gap between the magnet and the third magnetic-pole portion, the magnet, the gap between the magnet and the fourth magnetic-pole portion, and the fourth magnetic-pole portion.

Also, the rotational output of the magnet needs to be extracted from between the first magnetic-pole portion and the third magnetic-pole portion, or between the second magnetic-pole portion and the fourth magnetic-pole portion using a pin or the like. Extracting the output as a rotational shaft, such as a normal motor, further needs a member such as a disc or the like engaged with the above pin, and this makes the thickness of the motor further great in some cases.

Also, the actuator of the above second past example (Japanese Patent Laid-Open No. 2004-45682 (U.S. Pat. No. 6,781,772)) is also a rotating member serving as output means, i.e., the magnet faces the first and second magnetic-pole portions with a gap. Accordingly, the thickness in the shaft direction of the motor is the dimension of sum of at least the first magnetic-pole portion, the gap between the magnet and the first magnetic-pole portion, the magnet, the gap between the magnet and the second magnetic-pole portion, and the second magnetic-pole portion.

Also, the actuator according to the above third past example is a rotating member serving as output means, i.e., the rotational output of the magnet needs to be extracted from between the teeth of the first magnetic-pole portion and the second magnetic-pole portion, or from the outer circumferential side of the magnet using a pin or the like. Accordingly, the position for extracting the rotational output is stipulated, and the degree of freedom in the case of employing an actuator are restricted in some cases. Also, the magnet is fit to a member such as the bobbin outside of the coil or the like, so friction therebetween is great, it is sometimes difficult to obtain stable performance.

SUMMARY OF THE INVENTION

The present invention provides an easy-to-assemble low-cost driving device having a thin shape wherein the dimension in the shaft direction is very small, and high output wherein torque loss due to friction is small.

A first aspect of the present invention provides a driving device, comprising: a magnet having an annular shape, retained so as to be rotated in a plane about an axis passing through substantially the center of the annulus, with at least one of the surfaces of the magnet being substantially perpendicular to the axis of rotation and having adjacent areas magnetized to different polarities; a concentric coil disposed outside and overlapping said magnet in the plane of rotation; a yoke including a first magnetic-pole portion facing said at least one of the surfaces of said magnet with a predetermined first gap therebetween, and including magnetic-poles having a tooth shape extending in the diameter direction of said magnet, and also magnetized by said coil, and a cylindrical portion covering the outer circumferential portion of said coil; and a rotating yoke including a second magnetic-pole portion fixed to the opposite surface of said magnet, and rotatable integrally with said magnet, and also magnetized by said coil; wherein the cylindrical portion of said yoke and said rotating yoke face each other across a second gap in the radial direction.

A second aspect of the present invention provides a driving device, comprising: a magnet having an annular shape, retained so as to be rotated in a plane about an axis passing through substantially the center of the annulus, with at least one of the surfaces of the magnet being substantially perpendicular to the axis of rotation and having adjacent areas magnetized to different polarities; a concentric coil disposed inside and overlapping said magnet in the plane of rotation; a yoke including a first magnetic-pole portion facing said at least one of the surfaces of said magnet with a predetermined first gap therebetween, and including magnetic-poles in a tooth shape extending in the diameter direction of said magnet, and also magnetized by said coil, and a cylindrical portion covering the inner circumferential portion of said coil; and a rotating yoke including a second magnetic-pole portion fixed to the opposite surface of said magnet, and rotatable integrally with said magnet, and also magnetized by said coil; wherein the cylindrical portion of said yoke and said rotating yoke face each other across a second gap in the axial direction.

A third aspect of the present invention provides a driving device, comprising: a magnet having an annular shape, retained so as to be rotated in a plane about an axis passing through substantially the center of the annulus, with at least one of the surfaces of the magnet being substantially perpendicular to the axis of rotation and having adjacent areas magnetized to different polarities; a first coil disposed outside and overlapping said magnet in the plane of rotation, and also having the same concentricity as said magnet; a second coil disposed inside and overlapping said magnet in the plane of rotation, and also having the same concentricity as said magnet; a first yoke including a first magnetic-pole portion facing said at least one of the surfaces of said magnet with a predetermined gap therebetween, and having magnetic-poles in a tooth shape extending in the inside diameter direction of said magnet, and also magnetized by said first coil, and a cylindrical portion covering the outer circumferential portion of said coil; a second yoke including a second magnetic-pole portion facing said one of the surfaces of said magnet with a predetermined gap, and having magnetic-poles in a tooth shape extending in the outside diameter direction of said magnet, and also magnetized by said second coil, and a cylindrical portion covering the inner circumferential portion of said coil; and a rotating yoke including a third magnetic-pole portion fixed to the opposite surface of said magnet, and rotatable integrally with said magnet, and also magnetized by said first or second coil; wherein the cylindrical portion of said first yoke and said rotating yoke face each other across a gap in the radial direction, and the cylindrical portion of said second yoke and said rotating yoke face each other across a gap in the direction of the axis of rotation.

The above configurations can provide an easy-to-assemble low-cost driving device having a thin shape wherein the dimension in the shaft direction is very small, and high output wherein torque loss due to friction is small.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, the present invention will be described in detail based on the drawings.

The stepping motor and driving device according to the present invention are as shown in the following first through third embodiments.

First Embodiment

FIG. 1is an exploded perspective view illustrating the configuration of a stepping motor serving as a driving device according to a first embodiment of the present invention.FIG. 2is a cross-sectional view illustrating the internal configuration in the shaft direction in an assembled state of the stepping motor.FIGS. 3 through 6are diagrams for describing the rotational action of a magnet in this embodiment.

InFIGS. 1 through 6, the stepping motor includes a magnet1, a first coil2, a first bobbin3, a second coil4, a second bobbin5, a first yoke7, a rotating yoke8, a second yoke9, a base11, and a shaft bearing12.

The magnet1is formed in a flat annular or toric shape, comprising first and second flat surfaces orthogonal to a center virtual shaft (i.e. an axis of rotation), an outer circumferential surface, and an inner circumferential surface, and also is retained with the virtual shaft serving as the rotational center so as to be rotated. Also, as shown inFIG. 3throughFIG. 6, with the magnet1, a surface (first flat surface or second flat surface)1eorthogonal to the virtual shaft is divided into n divisions (10 divisions in the present embodiment) in the angular direction (circumferential direction) centered on the virtual shaft, which are magnetized with the south polarity and north polarity alternately. Note that the other surface1fof the magnet1may be divided and magnetized with the reverse polarity of the one surface1e(hereinafter, referred to as magnetized portion1e), or may not be magnetized at all.

Also, the magnet1is made up of a plastic magnet material which is formed by injection molding. Thus, the thickness direction of the disc-shaped stepping motor, i.e., the length in the shaft direction can be configured very thin. With the magnet formed with injection molding, a thin resin film is formed on the surface thereof, so occurrences of rust are extremely low as compared with a magnet formed with compression molding, such that antirust processing such as paint application can be eliminated. Further, the magnet formed with injection molding has no adhesion of magnetic powder which provides a problem when employing magnets formed with compression molding, and no swelling of the surface which readily occurs at the time of antirust coating, and can achieve improvement of quality.

As for the materials of the magnet1, Nd—Fe—B rare-earth magnetic powder, and a plastic magnet material formed by subjecting a mixture with a thermoplastic resin binder material such as a polyamide resin to injection molding are employed. Thus, while bending strength in the case of the magnet formed with compression molding is around 5000 N/cm2, bending strength of 8000 N/cm2or more can be obtained in the case of employing a polyamide resin as a binder material of the magnet formed with injection molding. As a result, the magnet1can be formed in a thin toric shape which can not be formed with compression molding.

The magnet1is formed in a thin toric shape, whereby the gap between the first magnetic-pole portion of the first yoke7and the third magnetic-pole portion of the rotating yoke8, and the gap between the second magnetic-pole portion of the second rotating yoke9and the third magnetic-pole portion of the rotating yoke8, which will be described later, can be set to be reduced, and the magnetic circuit of which the magnetic resistance therebetween is small can be provided. Thus, in the event of electric power being supplied to the first coil2and the second coil4, many magnetic fluxes can be generated even with small magnetomotive force, thereby improving the performance of the stepping motor.

The first coil2is formed in a toric shape, and is wound around the first bobbin3made up of an insulating material. The first coil2is disposed in the position overlapped in the direction perpendicular to the virtual shaft outside of the outer circumferential surface of the magnet1so as to have the same concentricity as the magnet1. The length in the shaft direction of the first coil2is set to generally the same dimension as the length in the shaft direction (toric thickness) of the magnet1.

The second coil4is formed in a toric shape, and is wound around the second bobbin5made up of an insulating material. The second coil4is disposed in the position overlapped in the direction perpendicular to the virtual shaft outside of the inner circumferential surface of the magnet1so as to have the same concentricity as the magnet1. The length in the shaft direction of the second coil4is set to generally the same dimension as the length in the shaft direction (toric thickness) of the magnet1.

The first yoke7is formed of a soft magnetic material, and includes first magnetic-pole portions7a,7b,7c,7d, and7ewhich are magnetized by electric power being supplied to the first coil2. The first magnetic-pole portions7athrough7eare disposed in a state facing the magnetized portion1eof the magnet1with a predetermined gap, and also comprise magnetic-poles in a tooth shape extending in the inside diameter direction of the magnet1, as shown inFIG. 2. The number of the magnetic-pole teeth of the first magnetic-pole portions7athrough7eis set to “the number of n magnetized divisions of the magnet ½” (five teeth in the present embodiment), and these are equally disposed by 720/n degrees (72 degrees in the present embodiment). The first magnetic-pole portions7athrough7eare all magnetized so as to mutually have the same polarity by electric power being supplied to the first coil2.

The second yoke9is formed of a soft magnetic material, and has second magnetic-pole portions9a,9b,9c,9d, and9ewhich are magnetized by electric power being supplied to the second coil4. The second magnetic-pole portions9athrough9eare disposed in a state facing the magnetized portion1eof the magnet1with a predetermined gap as shown inFIG. 2, and also comprise magnetic-poles in a tooth shape extending in the outside diameter direction of the magnet1. The number of the magnetic-pole teeth of the second magnetic-pole portions9athrough9eis set to “the number of n magnetized divisions of the magnet ½” (five teeth in the present embodiment), and these are equally disposed by 720/n degrees (72 degrees in the present embodiment). The second magnetic-pole portions9athrough9eare all magnetized so as to mutually have the same polarity by electric power being supplied to the second coil4.

The rotating yoke8is formed of a soft magnetic material, and comprises a disc flat surface portion8a, and a shaft8b. The rotating yoke8is supported with a shaft bearing12so as to be rotated integrally with the magnet1as well as the surface1fof the magnet1being firmly fixed to the disc flat surface portion8a. With the rotating yoke8, the portions facing the first magnetic-pole portions7athrough7eof the first yoke7are magnetized to the reverse polarities of the first magnetic-pole portions7athrough7eby electric power being supplied to the first coil2. Hereinafter, these portions are referred to as a 3-1st magnetic-pole portion. Also, with the rotating yoke8, the portions facing the second magnetic-pole portions9athrough9eof the second yoke are magnetized to the reverse polarities of the second magnetic-pole portions9athrough9eby electric power being supplied to the second coil4. Hereinafter, these portions are referred to as a 3-2nd magnetic-pole portion.

With the present stepping motor, the above first coil2, first yoke7, and rotating yoke8make up a first magnetic circuit, and also the above second coil4, second yoke9, and rotating yoke8make up a second magnetic circuit.

As shown inFIG. 2, the first yoke7and the rotating yoke8are magnetically coupled at the reverse side positions of the respective magnetic-pole portions, i.e., between the cylindrical portion7fsection of the first yoke7and the outermost diameter portion8fsection of the rotating yoke8which cover the outside diameter portion of the first coil2with a small gap L1being provided in the radial direction. Also, the second yoke9and the rotating yoke8are magnetically coupled at the reverse side positions of the respective magnetic-pole portions, i.e., between the cylindrical portion9fsection of the second yoke9and the flat surface portion8gsection of the rotating yoke8which cover the inside diameter portion of the second coil4with a small gap L2being provided in the shaft direction.

The first magnetic-pole portions7athrough7eof the first yoke7and the second magnetic-pole portions9athrough9eof the second yoke9are formed in a tooth shape extending in the radial direction along the magnetized portion1eof the magnet1, whereby the magnetic-pole portions can be formed while suppressing the thickness of the stepping motor to the minimum. That is to say, upon the magnetic-pole portions being formed with concavity and convexity extending in parallel to the shaft direction, the stepping motor becomes thick by just that much. On the other hand, with the present embodiment, the magnetic-pole portions are formed in the above tooth shape, so the dimension in the shaft direction of the stepping motor, i.e., the thickness can be minimized.

The positions where the first magnetic-pole portions7athrough7eof the first yoke7face the magnet1are on the outer circumferential surface side of the magnet as to the positions where the second magnetic-pole portions9athrough9eof the second yoke9face the magnet1. If we say that the distance from the rotational center of the position on the magnet which electromagnetic force generated by the first magnetic-pole portions7athrough7ebeing magnetized acts upon is R1, and the distance from the rotational center of the position on the magnet which electromagnetic force generated by the second magnetic-pole portions9athrough9ebeing magnetized acts upon is R2, the relation between R1and R2is R1>R2.

If we say that the area where the first magnetic-pole portions7athrough7eface the magnet1is S1, and the area where the second magnetic-pole portions9athrough9eface the magnet1is S2, the relation between S1and S2is set so as to satisfy S1<S2. Thus, the electromagnetic force generated by the second magnetic-pole portions9athrough9ebeing magnetized is greater than the electromagnetic force generated by the first magnetic-pole portions7athrough7ebeing magnetized. The value of (electromagnetic force)×(radius which electromagnetic force acts upon), i.e., rotational torque is the same in the case of being generated by the first magnetic-pole portions7athrough7ebeing magnetized, and in the case of being generated by the second magnetic-pole portions9athrough9ebeing magnetized. Thus, the stepping motor of which positioning performance is improved can be provided.

The phase where the first magnetic-pole portions7athrough7eface the magnetized portion1eof the magnet1and the phase where the second magnetic-pole portions9athrough9eface the magnetized portion1eof the magnet1are set in a state shifted by (180/N) degrees (18 degrees in the present embodiment).

The shift bearing12is fitted and fixed to the inside diameter portion9gof the second yoke9, and retains the shaft8bof the rotating yoke8so as to be rotated.

The base11is formed of a nonmagnetic material, and fixes both the first yoke7and the second yoke9while magnetically isolating both.

With the above rotating yoke8, the amount of wobbling in the axial direction due to tilt as to the shaft direction is great at the outside diameter portion as compared with the wobbling in the radial direction, and description will be made regarding the influence to the magnetic circuit caused by the wobbling.

With the present embodiment, as shown in the above, the first yoke7and the rotating yoke8are configured so as to be magnetically coupled at the reverse side positions of the respective magnetic-pole portions, i.e., between the cylindrical portion7fsection of the first yoke7and the outermost diameter portion8fsection of the rotating yoke8which cover the outside diameter portion of the first coil2with a small gap L1(seeFIG. 2) being provided in the radial direction. Accordingly, the first magnetic circuit is, so to speak, a magnetic circuit which is stable without receiving the influence due to wobbling caused by the tilt as to the shaft direction.

Also, as described above, the second yoke9and the rotating yoke8are configured so as to be magnetically coupled at the reverse side positions of the respective magnetic-pole portions, i.e., between the cylindrical portion9fsection of the second yoke9and the flat surface portion8gsection of the rotating yoke8which cover the inside diameter portion of the second coil with a small gap L2being provided in the shaft direction. The cylindrical portion9fsection of the second yoke9has a small diameter, so the amount of change of the above gap L2due to the wobbling caused by the tilt as to the shaft direction is small. Accordingly, the second magnetic circuit is, so to speak, a magnetic circuit which is stable without receiving the influence of the tilt as to the shaft direction.

Next, the action of the stepping motor according to the present embodiment having the above configuration will be described in detail with reference toFIGS. 3 through 6.

FIG. 3illustrates a magnetized state in which electric power is supplied to the first coil2and the second coil4so as to set the first magnetic-pole portions7athrough7eof the first yoke7, the second magnetic-pole portions9athrough9eof the second yoke9, and the 3-1st and 3-2nd magnetic-pole portions to the following polarities. That is to say, the first magnetic-pole portions7athrough7eof the first yoke7are set to the north polarity, and the portions of the rotating yoke8facing the first magnetic-pole portions7athrough7e, i.e., the 3-1st magnetic-pole portion is set to the south polarity. The second magnetic-pole portions9athrough9eof the second yoke9are set to the south polarity, and the portions of the rotating yoke8facing the second magnetic-pole portions9athrough9e, i.e., the 3-2nd magnetic-pole portion is set to the north polarity.

The electric power supplying direction to the second coil4is switched from the state inFIG. 3to a magnetized state in which the second magnetic-pole portions9athrough9eof the second yoke9are set to the north polarity, and the 3-2nd magnetic-pole portion of the rotating yoke8is set to the south polarity while keeping the electric power supply to the first coil2as it is. Thus, the magnet1rotates 18 degrees in the counterclockwise direction, and becomes the state shown inFIG. 4.

Next, magnetization is made so as to set the first magnetic-pole portions7athrough7eof the first yoke7to the south polarity, and the 3-1st magnetic-pole portion of the rotating yoke8to the north polarity by inverting the electric power supply to the first coil2. Thus, the magnet1further rotates 18 degrees in the counterclockwise direction, and becomes the state shown inFIG. 5.

Next, magnetization is made so as to set the second magnetic-pole portions9athrough9eof the second yoke9to the south polarity, and the 3-2nd magnetic-pole portion of the rotating yoke8to the north polarity by inverting the electric power supply to the second coil4. Thus, the magnet1further rotates 18 degrees in the counterclockwise direction, and becomes the state shown inFIG. 6.

Hereinafter, the magnet1serving as a rotor rotates to a position according to an electric power supply phase by switching the electric power supply direction to the first coil2and the second coil4sequentially.

Next, it will be described that the stepping motor according to the present embodiment having the above configuration is the most appropriate configuration to realize high output and also microminiaturization.

The basic configuration of the stepping motor according to the present embodiment is as follows:(1) The magnet1is to be formed in a toric shape.(2) The surface perpendicular to the virtual shaft of the rotational center of the magnet1is to be divided in the angular direction (circumferential direction) centered on the virtual shaft so as to be magnetized to a different polarity alternately.(3) The first coil2is to be disposed in a position overlapped in the direction perpendicular to the virtual shaft outside of the outer circumferential surface of the magnet1so as to have the same concentricity as the magnet1, and the second coil4is to be disposed in a position overlapped in the direction perpendicular to the virtual shaft inside of the inner circumferential surface of the magnet1so as to have the same concentricity as the magnet1.(4) The first magnetic-pole portions7athrough7eof the first yoke7, the second magnetic-pole portions9athrough9eof the second yoke9, and the 3-1st and 3-2nd magnetic-pole portions of the rotating yoke8, which are magnetized by the first and second coils2and4, are each to face the surface perpendicular to the shaft direction of the magnet1, i.e., the flat surface in a toric shape.(5) The first magnetic-pole portions7athrough7eof the first yoke7are to be formed in a tooth shape extending in the radial direction.(6) The rotating yoke8having the 3-1st and 3-2nd magnetic-pole portions is to be employed as an output member for extracting rotational output without any modification.

The stepping motor according to the present embodiment provides the following advantages by using the above configuration.

The magnetic flux generated by electric power being supplied to the first coil2traverses the magnet1present between the first magnetic-pole portions7athrough7eof the first yoke7and the 3-1st magnetic-pole portion of the rotating yoke8, so acts effectively.

The magnetic flux generated by electric power being supplied to the second coil4traverses the magnet1present between the second magnetic-pole portions9athrough9eof the second yoke9and the 3-2nd magnetic-pole portion of the rotating yoke8, so acts effectively.

The first coil2is disposed in a position overlapped in the direction perpendicular to the virtual shaft outside of the outer circumferential surface of the magnet1so as to have the same concentricity as the magnet1, and the second coil4is disposed in the position overlapped in the direction perpendicular to the virtual shaft inside of the inner circumferential surface of the magnet1so as to have the same concentricity as the magnet1. Also, the first magnetic-pole portions7athrough7eof the first yoke7and the second magnetic-pole portions9athrough9eof the second yoke9are formed in a tooth shape extending in the radial direction. Thus, the dimension in the shaft direction can be reduced as compared with a magnetic-pole portion made up of concavity and convexity extending in parallel to the shaft direction, whereby a stepping motor in a very thin disc shape can be provided.

The length in the shaft direction of the present stepping motor is determined with the dimension of sum of the first magnetic-pole portions7athrough7eof the first yoke7, the gap between the magnet1and the first magnetic-pole portions7athrough7e, the magnet1, and the third magnetic-pole portion of the rotating yoke8. Or else, the length in the shaft direction of the present stepping motor is determined with the dimension of sum of the second magnetic-pole portions9athrough9eof the second yoke9, the gap between the magnet1and the second magnetic-pole portions9athrough9e, the magnet1, and the third magnetic-pole portion of the rotating yoke8. Thus, the stepping motor according to the present embodiment is thinner than the above first past example (Japanese Patent Laid-Open No. 2003-219623 (U.S. Pat. No. 6,897,579) by the dimension of the gap between the magnet1and the third magnetic-pole portion.

The third magnetic-pole portion of the rotating yoke8made up of a soft magnetic material is fixed to the surface1fperpendicular to the virtual shaft of the rotational center of the magnet1, so the mechanical integrity of the magnet1increases. Thus, the magnet1even in a thin toric shape can be prevented from cracking.

The third magnetic-pole portion of the rotating yoke8serves as back metal, and the permeance coefficient of the magnetic circuit is set high. Thus, magnetic deterioration due to demagnetization can be reduced even in the event of employing the present stepping motor under a high-temperature environment.

The rotating yoke8is retained at the small-diameter shaft8bby the shaft bearing12so as to be rotated, so the shaft support configuration is smaller than the above first past example, whereby the torque loss due to friction can be reduced.

The first yoke7and the rotating yoke8are magnetically coupled between the cylindrical portion7fsection of the first yoke7and the outermost diameter portion8fsection of the rotating yoke8with a small gap L1being provided in the radial direction. Thus, the rotating yoke8can retain a suitable rotational state without abutting the first yoke7, and also can form a stable magnetic circuit.

The second yoke9and the rotating yoke8are magnetically coupled between the cylindrical portion9fsection of the second yoke9and the flat portion8gsection of the rotating yoke8with a small gap L2being provided in the shaft direction. Thus, the rotating yoke8can retain a suitable rotational state without abutting the second yoke9, and also can form a stable magnetic circuit.

Also, the rotating yoke8is employed as an output member for extracting rotational output without any modification, so additional parts for extracting rotational output are unnecessary, and consequently the number of parts and cost can be reduced.

As described above, the present embodiment can provide an easy-to-assemble low-cost stepping motor having a thin shape wherein the dimension in the shaft direction is very small, and high output wherein torque loss due to friction is small.

Second Embodiment

The second embodiment of the present invention is different from the above first embodiment in that when citing an actuator serving as a driving device for example, the actuator has the configuration shown inFIGS. 7 and 8. With the present embodiment, the components appended with the same reference numerals as the above first embodiment (FIGS. 1 and 2) are the same as those inFIGS. 1 and 2, so the description thereof will be simplified or omitted.

FIG. 7is an exploded perspective view illustrating the configuration of an actuator serving as a driving device according to the present embodiment, andFIG. 8is a cross-sectional view illustrating the internal configuration in the shaft direction in an assembled state of the actuator.FIG. 9andFIG. 10are diagrams for describing the rotational action of a magnet.FIG. 11is a diagram illustrating the relation between the force and rotational phase generated at the magnet.

InFIGS. 7 through 11, the actuator is for reciprocating by disposing a coil outside of a magnet, and comprises a magnet1, a coil2, a bobbin3, a yoke7, a rotating yoke18, a base13, and a shaft bearing12. Hereinafter, description will be made primarily regarding the differences as to the first embodiment.

The magnet1includes a dowel1c. As with the above first embodiment, which is divided into n divisions (10 divisions in the present embodiment) in the angular direction (circumferential direction) centered on the virtual shaft of the rotational center of a magnetized portion1e, and these divisions are magnetized with the south polarity or the north polarity alternately. The magnet1is formed in a thin toric shape, whereby the later-described gap between the first magnetic-pole portions of the yoke7and the second magnetic-pole portion of the rotating yoke18can be set to be reduced, and the magnetic circuit of which the magnetic resistance therebetween is small can be provided. Thus, in the event of electric power being supplied to the coil2, many magnetic fluxes can be generated even with small magnetomotive force, thereby improving the performance of the actuator.

The coil2is wound around the bobbin3. The coil2is disposed in the position overlapped in the direction perpendicular to the virtual shaft outside of the outer circumferential surface of the magnet1so as to have the same concentricity as the magnet1. Note that the coil2may be disposed in the direction perpendicular to the shaft direction of the magnet1on the inside of the inner circumferential surface of the magnet1so as to have the same concentricity as the magnet1. With the present embodiment, description will be made regarding the former case.

The yoke7comprises first magnetic-pole portions7a,7b,7c,7d, and7e. The first magnetic-pole portions7athrough7eare all magnetized so as to mutually have the same polarity by electric power being supplied to the first coil2.

The rotating yoke18is formed of a soft magnetic material, and comprises a disc flat surface portion18a, and a shaft18b. The rotating yoke18is supported with a shaft bearing12so as to be rotated integrally with the magnet1as well as the surface1fof the magnet1being firmly fixed to the disc flat surface portion18a. With the rotating yoke18, the portions facing the first magnetic-pole portions7athrough7eof the yoke are magnetized to the reverse polarities of the first magnetic-pole portions7athrough7eby electric power being supplied to the first coil2. Hereinafter, these portions are referred to as a second magnetic-pole portion.

With the present actuator, the above coil2, yoke7, and rotating yoke18make up a magnetic circuit.

As shown inFIG. 8, the yoke7and the rotating yoke18are magnetically coupled at the reverse side positions of the respective magnetic-pole portions, i.e., between the cylindrical portion7fsection of the yoke7and the outermost diameter portion18fsection of the rotating yoke18which cover the outside diameter portion of the coil2with a small gap L1being provided in the radial direction.

The first magnetic portions7athrough7eof the yoke7are formed in a tooth shape extending in the radial direction along the magnetized portion1eof the magnet1, whereby the magnetic-pole portions can be formed while minimizing the thickness of the stepping motor. That is to say, upon the magnetic-pole portions being formed with concavity and convexity extending in parallel to the shaft direction, the stepping motor becomes thick by just that much. On the other hand, with the present embodiment, the magnetic-pole portions are formed in the above tooth shape, so the dimension in the shaft direction of the stepping motor, i.e., the thickness can be minimized.

The shaft bearing12, which is stored on the inside diameter side of the magnet1and also fitted and fixed to the inside diameter portion of the base13, retains the shaft18bof the rotating yoke18so as to be rotated.

The base13is formed of a nonmagnetic material, and fixes the yoke7and the shaft bearing12. Also, the base13includes a slot13d. The rotation of the magnet1is restricted by the dowel1cof the magnet1abutting on the slot13din the base13. That is to say, the magnet1can rotate between the positions restricted by the slot13dof the dowel1c. Let us say that this rotational angle is θ degrees.

With the above rotating yoke18, the amount of wobbling due to tilt as to the shaft direction is great at the outside diameter portion as compared with the wobbling in the radial direction, and description will be made regarding the influence to the magnetic circuit caused by the wobbling.

With the present embodiment, as described above, the yoke7and the rotating yoke18are magnetically coupled at the reverse side positions of the respective magnetic-pole portions, i.e., between the cylindrical portion7fsection of the yoke7and the outermost diameter portion18fsection of the rotating yoke18which cover the outside diameter portion of the coil2with a small gap L1being provided in the radial direction. Thus, a magnetic circuit which is stable without influence due to wobbling caused by the tilt as to the shaft direction can be provided.

Next, it will be described that the actuator according to the present embodiment having the above configuration is the most appropriate configuration to realize high-output and also microminiaturization.

The basic configuration of the actuator according to the present embodiment is as follows:(1) The magnet1is to be formed in a toric shape.(2) The surface perpendicular to the virtual shaft of the rotational center of the magnet1is to be divided in the angular direction (circumferential direction) centered on the virtual shaft so as to be magnetized to a different polarity alternately.(3) The coil2is to be disposed in a position overlapped in the direction perpendicular to the virtual shaft outside of the outer circumferential surface of the magnet1so as to have the same concentricity as the magnet1.(4) The first magnetic-pole portions7athrough7eof the yoke7, and the second magnetic-pole portion of the rotating yoke18which are magnetized by the coil2are each to face the surface perpendicular to the shaft direction of the magnet1, i.e., the flat surface portion in a toric shape.(5) The first magnetic-pole portions7athrough7eof the yoke7are to be formed in a tooth shape extending in the radial direction.(6) The rotating yoke18having the second magnetic-pole portion is to be employed as an output member for extracting rotational output without any modification.

The actuator according to the present embodiment provides the following advantages by using the above configuration.

The magnetic flux generated by electric power being supplied to the coil2traverses the magnet1present between the first magnetic-pole portions7athrough7eof the yoke7and the second magnetic-pole portion of the rotating yoke18, so acts effectively.

The coil2is disposed in a position overlapped in the direction parallel to the virtual shaft outside of the outer circumferential surface of the magnet1so as to have the same concentricity as the magnet1. Also, the first magnetic-pole portions7athrough7eof the yoke7are formed in a tooth shape extending in the radial direction. Thus, the dimension in the shaft direction can be reduced as compared with a magnetic-pole portion made up of concavity and convexity extending in parallel to the shaft direction, whereby the actuator in a very thin disc shape can be provided.

The length in the shaft direction of the present actuator is determined with the dimension of the sum of the first magnetic-pole portions7athrough7eof the yoke7, the gap between the magnet1and the first magnetic-pole portions7athrough7e, the magnet1, and the second magnetic-pole portion of the rotating yoke18. Thus, the actuator according to the present embodiment is thinner than the above second past example (Japanese Patent Laid-Open No. 2004-45682 (U.S. Pat. No. 6,781,772)) and the above third past example by the dimension of the gap between the magnet1and the second magnetic-pole portion.

The second magnetic-pole portion of the rotating yoke18made up of a soft magnetic material is fixed to the surface1fperpendicular to the virtual shaft of the rotational center of the magnet1, so the mechanical integrity of the magnet1increases. Thus, the magnet1even in a thin toric shape can be prevented from cracking.

The second magnetic-pole portion of the rotating yoke18serves as back metal, and the permeance coefficient of the magnetic circuit is set high. Thus, magnetic deterioration due to demagnetization can be reduced even in the event of employing the present actuator in a high-temperature environment.

The rotating yoke18is retained at the small-diameter shaft18bby the shaft bearing12so as to be rotated, so the shaft support configuration is smaller than the above third past example, whereby the torque loss due to friction can be reduced.

The yoke7and the rotating yoke18are magnetically coupled between the cylindrical portion7fsection of the yoke7and the outermost diameter portion18fsection of the rotating yoke18with a small gap L1being provided in the radial direction. Thus, the rotating yoke18can retain a suitable rotational state without abutting the yoke7, and also a stable magnetic circuit can be formed.

Also, the rotating yoke18is employed as an output member for extracting rotational output without any modification, so parts for extracting rotational output are unnecessary, and consequently the number of parts and cost can be reduced.

FIG. 9shows a state in which the dowel1cof the magnet1abuts one of the end surfaces of the slot13din the base13, and rotation in the counterclockwise direction is restricted. Also,FIG. 10shows a state in which the dowel1cof the magnet1abuts the other end surface of the slot13dof the base13, and rotation in the clockwise direction is restricted. The rotational position of the magnet1shown inFIG. 9differs by θ degrees from the rotational position of the magnet1shown inFIG. 10.

The rotational position of the magnet1is retained in each state shown inFIGS. 9 and 10when no electric power is supplied to the coil2. This situation will be described with reference toFIGS. 9 through 11.

FIG. 11illustrates the situation of cogging torque. That is to say,FIG. 11illustrates a situation in which the rotational position of the magnet1, and the magnet1is sucked in by the first magnetic-pole portions7athrough7eof the yoke7when no electric power is supplied to the coil2. The vertical axis inFIG. 11represents the magnetic force generated between the magnet1and the yoke7, which affects the magnet1, and the horizontal axis inFIG. 11represents the rotational phase of the magnet1.

At points E1and E2, upon the magnet1attempting to perform positive rotation, negative force acts thereupon to return to the original position, and upon the magnet1attempting to perform counter-rotation, positive force acts thereupon to return to the original position. That is to say, the points E1and E2are cogging positions where the magnet1is positioned at the point E1or E2in a stable manner by the magnetic force between the magnet1and the magnetic-pole portions7athrough7eof the yoke7.

Points F1, F2, and F3are stopping positions in an unstable balanced state in which upon the phase of the magnet1deviating from a normal position, rotating force acts upon the position of the forward or backward point E1or E2of the magnet1. In a state in which no electric power is supplied to the coil2, the magnet1does not stop at the point F1, F2, or F3by vibration or change in attitude, but stops at the position of the point E1or E2.

Cogging stable points such as the point E1or E2are present in the cycle of 360/n degrees if we say that the number of magnetized poles of the magnet1is n, and the intermediate position thereof becomes an unstable point such as the point F1, F2, or F3.

With the present embodiment, in a state in which no electric power is supplied to the coil2, the size of the first magnetic-pole portions7athrough7eis set such that the center of a pole of the magnet1stops at the position facing the center of the first magnetic-pole portions7athrough7eof the yoke7in a stable manner. However, even if the first magnetic-pole portions7athrough7eare magnetized by electric power being supplied to the coil2from this state, no rotating force is generated at the magnet1.

Accordingly, with the present embodiment, the relation between the dowel1cof the magnet1and the slot13dof the base13is set such that the magnet1is in the state shown inFIG. 9. That is to say, the rotational position of the magnet1in the counterclockwise direction is set such that the angle between the center of a pole of the magnet1and the center of the first magnetic-pole portions7athrough7eof the yoke7is α degrees by the dowel1cof the magnet1abutting the end surface of the slot13dof the base13.

Thus, upon the first magnetic-pole portions7athrough7eof the yoke7being magnetized by electric power being supplied to the coil2from the state shown inFIG. 9, rotating force is generated at the magnet1, and consequently, the stepping motor is activated in a stable manner.

Also, upon the state shown inFIG. 9being applied toFIG. 11, the position of a point G is obtained. The cogging torque (suction force generated between the magnet1and the yoke7which affects the magnet1) at this position is T2. This means that negative force (force in the counterclockwise direction inFIG. 9) affects the rotational direction where the magnet1attempts to return to the point E1. That is to say, the holding force at the position where the dowel1cof the magnet1abuts the slot13dof the base13is T2. Accordingly, when no electric power is supplied to the coil2, the magnet1stops at this position (position shown inFIG. 9) in a stable manner.

Similarly, with the present embodiment, the rotation in the clockwise direction of the magnet1is set such that the position of the magnet1is the position shown inFIG. 10, and the end surface of the slot13dof the base13abuts the dowel1cof the magnet1. The position of the magnet1in this case is set such that the angle between the center of a pole of the magnet1and the center of the first magnetic-pole portions7athrough7eof the yoke7is β degrees.

Thus, upon the first magnetic-pole portions7athrough7eof the yoke7being magnetized by electric power being supplied to the coil2from the state shown inFIG. 10, rotating force is generated at the magnet1, and consequently, the stepping motor is activated in a stable manner.

Also, upon the state shown inFIG. 10being applied toFIG. 11, the position of a point H is obtained. The cogging torque at this position is T1. This means that positive force (force in the clockwise direction inFIG. 10) affects the rotational direction where the magnet1attempts to proceed to the point E2. That is to say, the holding force at the position where the dowel1cof the magnet1abuts the end surface of the slot13dof the base13is T1. Accordingly, when no electric power is supplied to the coil2, the magnet1stops at this position (position shown inFIG. 10) in a stable manner.

In the state shown inFIG. 9and the state shown inFIG. 10, the magnet1is set so as to have been rotated θ degrees.

Next, the situation of rotational action of the magnet1will be described with reference toFIGS. 9 and 10.

As described above, let us say that the magnet1stops at the position shown inFIG. 9in a stable manner at the beginning when no electric power is supplied to the coil2. Upon the first magnetic-pole portions7athrough7eof the yoke7being magnetized to the south polarity by electric power being supplied to the coil2from the state shown inFIG. 9, the magnet1serving as a rotor receives magnetic force in the rotational direction, and starts to rotate in the clockwise direction smoothly. Subsequently, power supply to the coil2is cut off at the timing when reaching the state shown inFIG. 10in which the rotational angle of the magnet1reaches θ degrees.

The state shown inFIG. 10is the point H inFIG. 11, so the magnet1retains this position in a stable manner by the holding force (cogging torque) T1as described above. Upon electric power supply to the coil2being inverted from the state shown inFIG. 10, the first magnetic-pole portions7athrough7eof the yoke7being magnetized to the north polarity, and the magnet1being rotated in the counterclockwise direction, the magnet1returns to the state shown inFIG. 9.

As described above, the magnet1serving as a rotor switches to the state shown inFIG. 9or the state shown inFIG. 10by switching the electric power supplying direction to the coil2. Accordingly, the present actuator is capable of driving between two positions (the state shown inFIG. 9, and the state shown inFIG. 10), and acts as an actuator capable of retaining each position in a stable manner even at the time of no electric power supply.

As described above, the present embodiment can provide an easy-to-assemble low-cost actuator having a thin shape wherein the dimension in the shaft direction is very small, and high output wherein torque loss due to friction is small.

Third Embodiment

The third embodiment of the present invention is different from the above first embodiment in that when citing an actuator serving as a driving device for example, the actuator has the configuration shown inFIGS. 12 and 13. With the present embodiment, the components appended with the same reference numerals as the above first embodiment (FIGS. 1 and 2) are the same as those inFIGS. 1 and 2, so the description thereof will be simplified or omitted.

FIG. 12is an exploded perspective view illustrating the configuration of an actuator serving as a driving device according to the present embodiment, andFIG. 13is a cross-sectional view illustrating the internal configuration in the shaft direction in an assembly completion state of the actuator.FIGS. 14 and 15are diagrams for describing the rotational action of a magnet.

InFIGS. 12 through 15, the actuator is for reciprocating by disposing a coil on the inside diameter side of a magnet, and comprises a magnet1, a coil22, a bobbin23, a yoke17, a rotating yoke18, and a shaft bearing12. Hereinafter, description will be made primarily regarding differences as to the first embodiment.

The magnet1includes a dowel1c, as with the above first embodiment, and a magnetized portion1eis divided into n divisions (10 divisions in the present embodiment) in the angular direction (circumferential direction) centered on the virtual shaft of the rotational center so as to be magnetized with the south polarity or the north polarity alternately. The magnet1is formed in a thin toric shape, whereby the later-described gap between the first magnetic-pole portions of the yoke17and the second magnetic-pole portion of the rotating yoke18can be set to be reduced, and the magnetic circuit of which the magnetic resistance therebetween is small can be provided. Thus, in the event of electric power being supplied to the coil22, many magnetic fluxes can be generated even with small magnetomotive force, thereby improving the performance of the actuator.

The coil22is wound around the bobbin23made up of an insulating material. The coil22is disposed in the position overlapped in the direction parallel to the virtual shaft inside of the inner circumferential surface of the magnet1so as to have the same concentricity as the magnet1. The length in the shaft direction of the coil22is set to generally the same dimension as the length in the shaft direction (toric thickness) of the magnet1.

The yoke17is formed of a soft magnetic material, and includes first magnetic-pole portions17a,17b,17c,17d, and17e, which are magnetized by electric power being supplied to the coil22. The first magnetic-pole portions17athrough17eface the magnetized portion1eperpendicular to the shaft direction of the magnet1with a certain gap, and are made up of a magnetic-pole in a tooth shape extending in the outside diameter direction of the magnet1. The number of the magnetic-pole teeth of the first magnetic-pole portions17athrough17eis set to “the number of n magnetized divisions of the magnet×½” (five teeth in the present embodiment), and these are equally disposed by 720/n degrees (72 degrees in the present embodiment). The first magnetic-pole portions17athrough17eare all magnetized so as to mutually have the same polarity by electric power being supplied to the coil22.

The rotating yoke18is formed of a soft magnetic material, and comprises a disc flat surface portion18a, and a shaft18b. The rotating yoke18is supported with a shaft bearing12so as to be rotated integrally with the magnet1as well as the surface1fof the magnet1being firmly fixed to the disc flat surface portion18a. With the rotating yoke18, the portions facing the first magnetic-pole portions17athrough17eof the yoke17are magnetized to the reverse polarities of the first magnetic-pole portions17athrough17eby electric power being supplied to the coil22. Hereinafter, these portions are referred to as a second magnetic-pole portion.

With the present actuator, the above coil22, yoke17, and rotating yoke18make up a magnetic circuit.

The yoke17and the rotating yoke18are magnetically coupled at the reverse side positions of the respective magnetic-pole portions, i.e., between the cylindrical portion17fsection of the yoke17and the flat surface portion18gsection of the rotating yoke8which cover the inside diameter portion of the coil22with a small gap L2being provided in the shaft direction. The cylindrical portion17fsection of the yoke17has a small diameter, so the amount of change of the above gap L2due to the wobbling caused by the tilt as to the shaft direction is small. Accordingly, this magnetic circuit is, so to speak, a magnetic circuit which is stable without receiving the influence of the tilt as to the shaft direction.

The first magnetic portions17athrough17eof the yoke17are formed in a tooth shape extending in the radial direction along the magnetized portion1eof the magnet1, whereby the magnetic-pole portions can be formed while minimizing the thickness of the stepping motor. That is to say, upon the magnetic-pole portions being formed with concavity and convexity extending in parallel to the shaft direction, the stepping motor becomes thick by just that much. On the other hand, with the present embodiment, the magnetic-pole portions are formed in the above tooth shape, so the dimension in the shaft direction of the stepping motor, i.e., the thickness can be minimized.

The shaft bearing12is fitted and fixed to the inside diameter portion of the yoke17, and retains the shaft18bof the rotating yoke18so as to be rotated.

The rotation of the magnet1is restricted by the dowel1cof the magnet1abutting the end surfaces of the first magnetic-pole portions17dand17eof the above yoke17. That is to say, the magnet1can rotate between the positions where the dowel1cis restricted by the end surfaces of the first magnetic-pole portions17dand17eof the yoke17. Let us say that this rotational angle is θ degrees.

Next, it will be described that the actuator according to the present embodiment having the above configuration is the most appropriate configuration to realize high-output and also microminiaturization.

The basic configuration of the actuator according to the present embodiment is as follows:(1) The magnet1is to be formed in a toric shape.(2) The surface perpendicular to the virtual shaft of the rotational center of the magnet1is to be divided in the angular direction (circumferential direction) centered on the virtual shaft so as to be magnetized to a different polarity alternately.(3) The coil22is to be disposed in a position overlapped in the direction perpendicular to the virtual shaft outside of the outer circumferential surface of the magnet1so as to have the same concentricity as the magnet1.(4) The first magnetic-pole portions17athrough17eof the yoke17, and the second magnetic-pole portion of the rotating yoke18which are magnetized by the coil22are each to face the surface perpendicular to the shaft direction of the magnet1, i.e., the flat surface portion in a toric shape.(5) The first magnetic-pole portions17athrough17eof the yoke17are to be formed in a tooth shape extending in the radial direction.(6) The rotating yoke18having the second magnetic-pole portion is to be employed as an output member for extracting rotational output without any modification.

The actuator according to the present embodiment provides the following advantages by using the above configuration.

The magnetic flux generated by electric power being supplied to the coil2traverses the magnet1present between the first magnetic-pole portions17athrough17eof the yoke17and the second magnetic-pole portion of the rotating yoke18, and accordingly acts effectively.

The coil22is disposed in the position overlapped in the direction parallel to the virtual shaft outside of the outer circumferential surface of the magnet1so as to have the same concentricity as the magnet1. Also, the first magnetic-pole portions17athrough17eof the yoke17are formed in a tooth shape extending in the radial direction. Thus, the dimension in the shaft direction can be reduced as compared with a magnetic-pole portion made up of concavity and convexity extending in parallel to the shaft direction, whereby the actuator in a very thin disc shape can be provided.

The length in the shaft direction of the present actuator is determined with the dimension of sum of the first magnetic-pole portions17athrough17eof the yoke17, the gap between the magnet1and the first magnetic-pole portions17athrough17e, the magnet1, and the second magnetic-pole portion of the rotating yoke18. Thus, the actuator according to the present embodiment is thinner than the above second past example and third past example by the dimension of the gap between the magnet1and the second magnetic-pole portion.

The second magnetic-pole portion of the rotating yoke18made up of a soft magnetic material is fixed to the surface1fperpendicular to the virtual shaft of the rotational center of the magnet1, so the mechanical integrity of the magnet1increases. Thus, the magnet1even in a thin toric shape can be prevented from cracking.

The second magnetic-pole portion of the rotating yoke18serves as back metal, and the permeance coefficient of the magnetic circuit is set high. Thus, magnetic deterioration due to demagnetization can be reduced even in the event of employing the present actuator in a high-temperature environment.

The rotating yoke18is retained at the small-diameter shaft18bby the shaft bearing12so as to be rotated, so the shaft support configuration is smaller than the above third past example, whereby the torque loss due to friction can be reduced.

The yoke17and the rotating yoke18are magnetically coupled between the cylindrical portion17fsection of the yoke17and the flat surface portion18gsection of the rotating yoke8with a small gap L2being provided in the shaft direction. Thus, the rotating yoke18can retain a suitable rotational state without abutting the yoke17, and also a stable magnetic circuit can be formed.

Also, the rotating yoke18is employed as an output member for extracting rotational output without any modification, so parts for extracting rotational output are unnecessary, and consequently the number of parts and cost can be reduced.

Further, the rotational restriction of the magnet1is performed at the end surfaces of the first magnetic-pole portions17dand17eof the yoke17, so a thin disc-shaped actuator of which the dimension in the shaft direction is even thinner can be provided as compared with the actuator of which rotational restriction is performed at the base shown in the above second embodiment.

FIG. 14shows a state in which the dowel1cof the magnet1abuts the end surface of the first magnetic-pole portion17eof the yoke17, and rotation in the counterclockwise direction is restricted.FIG. 15is in a state in which the dowel1cof the magnet1abuts the end surface of the first magnetic-pole portion17dof the yoke17, and rotation in the clockwise direction is restricted. The rotational position of the magnet1shown inFIG. 14differs by θ degrees from the rotational position of the magnet1shown inFIG. 15.

The rotational position of the magnet1is retained in each state shown inFIGS. 14 and 15when no electric power is supplied to the coil2. The state shown inFIG. 14is the same state as the state shown inFIG. 9in the above second embodiment, and the state shown inFIG. 15is the same state as the state shown inFIG. 10in the above second embodiment.

With the present embodiment, as with the above second embodiment, an arrangement is made wherein the magnet1can move between the state shown inFIG. 14and the state shown inFIG. 15by switching electric power supply to the coil22, and also each state is maintained even in a state in which electric power supply to the coil22is cut off.

Also, with the present embodiment, in a state in which no electric power is supplied to the coil22, the size of the first magnetic-pole portions17athrough17eis set such that the center of a pole of the magnet1stops at the position facing the center of the first magnetic-pole portions17athrough17eof the yoke17in a stable manner. However, even if the first magnetic-pole portions17athrough17eare magnetized by electric power being supplied to the coil22from this state, no rotating force is generated at the magnet1.

Accordingly, with the present embodiment, the relation between the end surface of the first magnetic-pole portion17eof the yoke17and the dowel1cof the magnet1is arranged so as to be in the state shown inFIG. 14. That is to say, in the state in which rotation in the counterclockwise direction is restricted by the dowel1cof the magnet1abutting the end surface of the first magnetic-pole portion17eof the yoke17, the angle between the center of a pole of the magnet1and the center of the first magnetic-pole portions17athrough17eof the yoke17is set so as to be α degrees. Thus, upon the first magnetic-pole portions17athrough17eof the yoke17being magnetized by electric power being supplied to the coil2from the state shown inFIG. 14, rotating force is generated at the magnet1, and consequently, the stepping motor is activated in a stable manner.

Also, upon the state shown inFIG. 14being applied toFIG. 11, the position of a point G is obtained. The cogging torque at this position is T2. This means that negative force (force in the anti-clockwise direction inFIG. 9) affects upon the rotational direction where the magnet1attempts to return to the point E1. That is to say, the holding force at the position where the dowel1cof the magnet1abuts on the first magnetic-pole portion17eof the yoke17is T2. Accordingly, when no electric power is supplied to the coil22, the magnet1stops at this position (position shown inFIG. 14) in a stable manner.

Similarly, with the present embodiment, rotation in the clockwise direction of the magnet1is set such that the position of the magnet1is the position shown inFIG. 15, and the end surface of the first magnetic-pole portion17dof the base17abuts the dowel1cof the magnet1. The position of the magnet1in this case is set such that the angle between the center of a pole of the magnet1and the center of the first magnetic-pole portions17athrough17eof the yoke17is β degrees. Thus, upon the first magnetic-pole portions17athrough17eof the yoke17being magnetized by electric power being supplied to the coil2from the state shown inFIG. 15, rotating force is generated at the magnet1, and consequently, the stepping motor is activated in a stable manner.

Also, upon the state shown inFIG. 15being applied toFIG. 11, the position of a point H is obtained. The cogging torque at this position is T1. This means that positive force (force in the clockwise direction inFIG. 15) affects the rotational direction where the magnet1attempts to proceed to the point E2. That is to say, the holding force at the position where the end surface of the first magnetic-pole portion17dof the yoke17abuts on the dowel1cof the magnet1is T1. Accordingly, when no electric power is supplied to the coil22, the magnet1stops at this position (position shown inFIG. 15) in a stable manner.

In the state shown inFIG. 14and the state shown inFIG. 15, the magnet1is set so as to have been rotated θ degrees.

Next, the situation of rotational actions of the magnet1will be described with reference toFIGS. 14 and 15.

As described above, let us say that the magnet1stops at the position shown inFIG. 14in a stable manner at the beginning when no electric power is supplied to the coil2. Upon the first magnetic-pole portions17athrough17eof the yoke17being magnetized to the south polarity by electric power being supplied to the coil22from the state shown inFIG. 14, the magnet1serving as a rotor receives magnetic force in the rotational direction, and starts to rotate in the clockwise direction smoothly.

Subsequently, electric power supply to the coil22is cut off at the timing when reaching the state shown inFIG. 15in which the rotational angle of the magnet1reaches θ degrees. The state shown inFIG. 15is the point H inFIG. 11, so the magnet1retains this position in a stable manner by the cogging torque T1as described above. Upon electric power supply to the coil2being inverted from the state shown inFIG. 15, the first magnetic-pole portions17athrough17eof the yoke17being magnetized to the north polarity, and the magnet1being rotated in the counterclockwise direction, the magnet14returns to the state shown inFIG. 14.

As described above, the magnet1serving as a rotor switches to the state shown inFIG. 14or the state shown inFIG. 15by switching the electric power supplying direction to the coil2. Accordingly, the present actuator is capable of driving at between two positions (the state shown inFIG. 14and the state shown inFIG. 15), and acts as an actuator capable of retaining each position in a stable manner even at the time of no electric power supply.

As described above, the present embodiment can provide an easy-to-assemble low-cost actuator having a thin shape wherein the dimension in the shaft direction is very small, and high output wherein torque loss due to friction is small.

Other Embodiments

Description has been made regarding the stepping motor simple substance in the above first embodiment, and the actuator simple substance in the above second and third embodiments, but the present invention is not restricted to applications to the stepping motor simple substance and the actuator simple substance. The present invention can be applied to a case in which the diaphragm blade, shutter, and photographing lens of an imaging device are driven by a stepping motor or actuator.

This application claims the priority of Japanese Application No. 2005-159857 filed May 31, 2005, which is hereby incorporated by reference herein in its entirety.