Electromagnetic drive device and light quantity adjustment device using the same

An electromagnetic drive device includes a coil frame with a hollow tubular shape, a magnet rotor rotatably disposed in the coil frame through a rotational shaft, a transmission member for transmitting a rotation of the magnet rotor, and a coil wound around an outer periphery of the coil frame. The coil frame is formed of two coil frame halves divided vertically along the rotational shaft of the rotor, and the coil is wound in a direction crossing connection faces (joint faces) of the two coil frame halves on upper and lower end surfaces thereof.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to an electromagnetic drive device in which a magnet rotor formed of a permanent magnet is rotatably accommodated in a coil frame with a coil wound around on an outer periphery thereof so that the magnet rotor rotates when a direct current is supplied to the coil, and a light quantity adjustment device for adjusting a light quantity of an optical image pick-up device through a torque generated in the magnet rotor.

Generally, as disclosed in Japanese Utility Model No. 2541274, in an optical device such as a camera, an opening/closing blade member is provided at an image pick-up lens part on an optical axis of image light so that the blade member shields light under a so-called shutter control or adjusts the quantity of light under a so-called exposure control. Such a blade member is connected to a magnet rotor through a transmission member, and arranged to open and close when a current is supplied to a coil wound around the magnet rotor. In such an electromagnetic drive device comprising the magnet rotor and the coil, the magnet rotor is rotatably supported in a coil frame having a hollow tubular shape and formed of a resin and the like, and the coil is wound around an outer periphery of the coil frame. A yoke (magnetic induction member) covers an outer surface of the coil frame.

Conventionally, such a coil frame has a structure divided laterally (up and down) or vertically (left and right) with respect to a rotational shaft of the magnet rotor. The magnet rotor is disposed inside the coil frame, and the coil is wound around the outer periphery thereof, thereby integrally assembling the device. When the coil frame is divided laterally, it is necessary to provide a taper for easy molding. Also, it is sometimes difficult to smoothly rotate the magnet rotor due to a positional misalignment between upper and lower bearing portions when the magnet rotor is supported inside the coil frame, thereby causing a problem in manufacture.

The present invention relates to an improved structure of the coil frame divided vertically, thereby reducing a size of the device. Conventionally, a tubular (cylindrical) coil frame is divided vertically at the center thereof into two portions, and a magnet with a rotational shaft is disposed inside the coil frame. A transmission member protruding outwardly from the coil frame is attached to a rotational shaft of the magnet rotor. The coil is wound on concave grooves individually formed in each of the two divided coil frame halves, respectively. The two coil frame halves are joined at a center portion from which the rotational shaft of the magnet rotor protrudes, and are integrated with an adhesive tape.

In the structure of the conventional electromagnetic device, the coil frame halves with the coil wound around thereon are joined at the center portion where the rotational shaft is located, so that the tubular coil frame has a large diameter in a radial direction. When the coil has, for example, 200 turns, it is necessary to provide a winding margin such as the concave groove in each of the coil frame halves for winding 100 turns. Further, it is necessary to provide bearing portions for supporting the shaft at the center of the coil frame and thick wall portions for forming the bearing portions, thereby increasing a size of the device in the radial direction.

As disclosed in Japanese Utility Model No. 2606159, in an optical image pick-up device such as a video camera and still camera, a shutter blade for shielding light or a stop blade for adjusting light is disposed in a lens-barrel provided with an image pick-up lens to control a quantity of light. The blade member is disposed on an image pick-up optical axis in the lens-barrel to be rotatable or slidable, and an electromagnetic drive device drives and controls the blade member. In such an electromagnetic drive device, a magnet rotor is rotatably accommodated inside a coil frame with a conductive coil wound around an outer periphery thereof. A rotation of the magnet rotor is transmitted to the blade member for opening and closing or adjusting a photographing optical axis to increase and decrease an aperture diameter. Such a structure has been widely used in which the magnet rotor is polarized in two poles N and S, and a magnetic field is generated in the coil to rotate the rotor when a direct current is supplied to the coil.

In the electromagnetic drive device, the magnet rotor is rotatably supported in the coil frame having a hollow tubular shape and formed of a resin and the like, and a torque is transmitted to the blade member from the rotational shaft through a transmission arm. Accordingly, the coil frame has a structure divided into two portions for accommodating the magnet rotor inside. After the rotor is disposed inside the coil frame, the two portions are joined and the coil is wound around an outer periphery of the coil frame. The coil frame is divided vertically into two portions along the rotational shaft of the magnet rotor or divided laterally into two portions in a direction perpendicular the rotational shaft.

When the coil frame is divided vertically, even if a diameter of the coil frame is reduced to make the device small, since the two coil frame halves are joined (connected) vertically in a longitudinal direction, it is possible to join the two halves with little misalignment, thereby making it easy to install the magnet rotor. However, when the coil frame is divided vertically along the rotational shaft of the magnet rotor, it is necessary to provide bearing portions. Conventionally, as disclosed in Japanese Utility Model No. 2606159, a bearing concave portion is formed in each of the coil frame halves, and the coil frame halves are joined to support the rotational shaft.

When the bearing concave portion is formed in each of the coil frame halves and the coil frame halves are joined to support the rotational shaft of the magnet rotor, it is difficult to smoothly rotate the magnet rotor if the concave portions have low dimensional accuracy so that a positional misalignment occurs when the coil frame halves are joined. Recently, the device has been made small, and it is necessary to accurately form a bearing portion to support a rotational shaft of a rotor having a diameter of only about 1 mm. In view of electric power consumption, it is necessary to provide a bearing portion of a rotational shaft with a low mechanical loss such as friction.

In view of the problems described above, the present invention has been made, and an object of the present invention is to provide an electromagnetic drive device with a compact size and easy to manufacture, and a light quantity adjustment device using the same, wherein a coil is wound around a coil frame divided vertically into two portions along a rotational shaft of a rotor without dividing the coil, and it is possible to prevent a breakage of the coil wire by a groove at a joint line of the coil frame.

Another object of the present invention is to provide an electromagnetic drive device in which it is easy to form a coil frame for supporting a magnet rotor with a small mechanical loss at a bearing portion of a rotational shaft, thereby rotating the magnet rotor smoothly.

SUMMARY OF THE INVENTION

In order to achieve the objects described above, according to a first aspect of the present invention, an electromagnetic drive device includes a coil frame with a hollow tubular shape, a magnet rotor rotatably disposed in the coil frame through a rotational shaft, a transmission member for transmitting a rotation of the magnet rotor, and a coil wound around an outer periphery of the coil frame. The coil frame is formed of two coil frame halves divided vertically along the rotational shaft of the rotor, and the coil is wound in a direction crossing a connection line (joint line) on upper and lower end surfaces of the two coil frame halves.

In the first aspect of the invention, the coil frame is formed of the coil frame halves divided vertically along the rotational shaft of the magnet rotor. The coil is wound around an outer periphery of the coil frame in a direction crossing a line or groove formed by connection surfaces of the coil frame halves at the upper and lower end surfaces thereof, so that a coil wire is not broken at the connection line when the coil is wound or in use. Accordingly, as compared with a conventional device in which a coil is wound on each of coil frame halves divided vertically, it is possible to increase a space for winding the coil and decrease a size of the device. Further, as compared with the conventional device in which the coil is wound in each of the coil frame halves divided separately, it is possible to wind just a single coil on the coil frame.

According to a second aspect of the present invention, in the electromagnetic drive device of the first aspect of the invention, the transmission member is disposed in a direction approximately perpendicular to a winding direction of the coil. An opening is formed in a part of connection surfaces of the coil frame halves for allowing the transmission member to rotate by a predetermined angle. Accordingly, the coil is wound in a direction approximately perpendicular to the transmission member, so that the transmission member such as an arm member is arranged approximately perpendicular to the coil wound around the outer periphery of the coil frame. As a result, it is possible to rotate the transmission member in left and right directions by a predetermined angle (usually about 60 degrees), thereby increasing an area for winding the coil around the coil frame.

According to a third aspect of the present invention, in the electromagnetic drive device in the first aspect of the invention, the coil is wound in a direction approximately perpendicular to the connection line on the upper and lower end surfaces of the two coil frame halves, and the transmission member is disposed in a direction approximately perpendicular to the winding direction of the coil. Accordingly, the coil is wound in a direction approximately perpendicular to the groove formed by the connection surfaces of the two coil frame halves in the upper and lower end surfaces thereof, thereby preventing a breakage of the coil by the groove.

According to a fourth aspect of the present invention, in the electromagnetic drive device in the first aspect of the invention, one of the bearing portions for supporting the rotational shaft of the magnet rotor is formed in one of the two coil frame halves. Accordingly, the rotational shaft of the magnet rotor is supported on the one of the two coil frame halves, so that the bearing portions located vertically are not shifted relative to each other.

According to a fifth aspect of the present invention, in the electromagnetic drive device in the first aspect of the invention, one of the bearing portions for supporting the rotational shaft of the magnet rotor is formed in one of the coil frame halves, and the other of the bearing portions is formed in the other of the coil frame halves. Accordingly, the pair of the bearing portions for supporting the rotational shaft of the magnet rotor is formed in the divided two coil frame halves, so that the magnet rotor can be easily disposed to the bearing portions when the coil frame halves are joined, thereby making the manufacture of the device easy.

According to a sixth aspect of the present invention, in the electromagnetic drive device in the first aspect of the invention, a bearing concave portion is provided in one of the coil frame halves for supporting one end of the rotational shaft of the magnet rotor, and a bearing concave portion is provided in the other of the coil frame halves for supporting the other end of the rotational shaft, so that the two coil frame halves are joined to form the coil frame.

In the sixth aspect of the invention, an electromagnetic drive device includes a coil frame having a hollow tubular shape; a cylindrical magnet rotor rotatably disposed in the coil frame and having a rotational shaft at a center thereof; a transmission member attached to the rotational shaft for transferring a rotation of the magnet rotor to an outside of the coil frame; and a coil wound around an outer periphery of the coil frame. The coil frame is formed of two coil frame halves divided vertically along the rotational shaft of the magnet rotor. A bearing concave portion is formed in one of the coil frame halves for supporting one end of the rotational shaft, and a bearing concave portion is formed in the other of the coil frame halves for supporting the other end of the rotational shaft, respectively. Accordingly, it is possible to join the two coil frame halves at connection surfaces thereof in an axial direction without misalignment. The bearing concave portions for supporting the rotational shaft are formed individually in the coil frame halves, thereby preventing a bite phenomenon of a conventional device in which bearing concave portions are connected. As a result, it is easy to make a compact device.

According to a seventh aspect of the present invention, in the electromagnetic drive device in the sixth aspect of the invention, the bearing concave portion formed in the one of the coil frame halves protrudes toward the other of the coil frame halves, so that it is easy to locate the bearing concave portions at the center of the two coil frame halves. Especially, when the coil frame halves are formed in a tubular shape with a same diameter, it is possible to form the bearing concave portions at the center of the coil frame halves according to an external dimension of the tubular shape, thereby making the manufacture easy.

According to an eighth aspect of the present invention, in the electromagnetic drive device in the sixth aspect of the invention, the rotational shaft has pointed ends. The bearing concave portions are formed of pivot bearings, so that the magnet rotor is supported pivotally and rotates smoothly. At the same time, the bearing concave portions are individually formed in the coil frame halves, thereby making is easy to form.

According to a ninth aspect of the present invention, in the electromagnetic drive device in the first aspect of the invention, the coil is wound in a direction crossing the connection line on the upper and lower end surfaces of the two coil frame halves. The two coil frame halves are joined to form the coil frame, and the groove is formed by the connection surfaces. Accordingly, it is possible to prevent a breakage of the coil wire when the coil is wound in the direction crossing the connection surfaces (groove).

According to a tenth aspect of the present invention, an electromagnetic drive device includes a cylindrical magnet rotor having a rotational shaft and a pair of magnetic poles formed along a direction perpendicular to the rotational shaft; a transmission member extending in a radial direction of the magnet rotor approximately perpendicular to a direction of the magnetic poles; a coil frame with a hollow tubular shape for retaining the magnet rotor and the transmission member to be rotatable through the rotational shaft; and a coil wound around an outer periphery of the coil frame. The coil frame is formed of two coil frame halves divided vertically along the rotational shaft in a direction crossing the direction of the magnetic poles. An opening is formed in connection surfaces of the coil frame halves for allowing the transmission member to rotate by a predetermined angle, and the coil is wound in a direction approximately identical to the direction of the magnetic poles.

In the tenth aspect of the invention, the coil frame is divided in the direction perpendicular to the direction of the magnetic poles of the magnet rotor, and the coil is wound in the direction approximately identical to the direction of the magnetic poles and approximately perpendicular to the groove formed by the connection surfaces of the coil frame halves, thereby preventing a breakage of the coil wire.

According to an eleventh aspect of the present invention, in the electromagnetic drive device in the tenth aspect of the invention, the coil frame is formed of the coil frame halves divided vertically along the rotational shaft of the magnet rotor. An opening is formed in the connection surfaces of the coil frame halves for allowing the transmission member to protrude to an outside of the coil frame. A pivot bearing portion is formed in one of the coil frame halves for supporting one end of the rotational shaft, and a pivot bearing portion is formed in the other of the coil frame halves for supporting the other end of the rotational shaft, respectively. It is possible to obtain advantages similar to the first aspect of the invention.

According to a twelfth aspect of the present invention, a light quantity adjustment device includes a base plate having an optical axis aperture; a blade member for adjusting a quantity of light passing through the optical axis aperture of the base plate; a coil frame with a hollow tubular shape attached to the base plate; a magnet rotor rotatably disposed in the coil frame through a rotational shaft; a transmission member for transmitting a rotation of the magnet rotor to the blade member; and a coil wound around an outer periphery of the coil frame. The coil frame is formed of two coil frame halves divided vertically along the rotational shaft of the rotor, and the coil is wound in a direction intersecting connection surfaces of the two coil frame halves on upper and lower end surfaces thereof. Accordingly, it is possible to reduce a size of the light quantity adjustment device such as a shutter device and a light quantity stop device to be incorporated in an image pick-up lens-barrel of a camera and the like, thereby reducing a size of the camera lens-barrel.

According to a thirteenth aspect of the present invention, in the light quantity adjustment device in the twelfth aspect of the invention, the coil frame is formed of the two coil frame halves divided vertically along the rotational shaft of the magnet rotor. A bearing concave portion is formed in one of the coil frame halves for supporting one end of the rotational shaft, and a bearing concave portion is formed in the other of the coil frame halves for supporting the other end of the rotational shaft, respectively. Accordingly, the coil frame retaining the magnet rotor with the coil wound around is easy to manufacture in a small size, thereby reducing a size and cost of an optical device using the light quantity adjustment device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, embodiments of the invention will be explained with reference to the accompanying drawings.FIG. 1is a vie showing a shutter device for a camera according to an embodiment of the invention, in which MO denotes an electromagnetic drive device according to the invention, and SH denotes a light quantity adjustment device. As shown inFIG. 1, the light quantity adjustment device SH includes two blades3and4rotatably accommodated between a pair of plate-like base plates1and2with a pin5, so that the blades3and4open and close an optical axis aperture6formed in the base plates1and2. The base plate1is formed of a synthetic resin including polycarbonate as a main component with a resin molding, and the optical axis aperture is formed at a center of the base plate1for passing light of a camera device.

The base plate1is integrally provided with the pin5for supporting the blades3and4and hook protrusions7for fixing the electromagnetic drive device MO (described later). The base plate1is also provided with protrusions8at suitable positions on a peripheral edge thereof to form a predetermined gap when the base plate2is attached to the protrusions8. The blades3and4are supported between the pair of the base plates1and2to open and close freely. The base plate2is formed of a thin metal plate and the like, and is integrally attached to the base plate1by fixing means such as a small screw. The base plate2has the optical axis aperture6at a center thereof.

The blades3and4are formed of a polyester film plate or a metal thin plate (two blades structure), and are disposed in the optical axis aperture6such that tip portions of the semicircular plates close and open the optical axis aperture6. The blades3and4are provided with slits9and10for engaging a drive device (described later) at base end parts thereof, respectively.

The blades3and4are fitted to the pin5on the base plate1to rotate around the pin5, and the slits9and10of the two blades3and4are arranged with an angle in opposite directions as shown inFIG. 1. One of the blades3and4rotates in a direction opposite to a direction that the other rotates, i.e. one rotates clockwise and the other rotates counterclockwise, through a transmission pin11of the drive device (described later). Incidentally, in the embodiment, the blades are formed of the two blades, and may be formed of one piece or three or more pieces. In a case of one piece, a blade moves in left and right directions inFIG. 1, i.e. so-called focal-plane shutter. In a case of three or more pieces, blades are disposed around the optical axis aperture with a predetermined gap, and pins are provided in a ring-like operation member disposed at an outer periphery of the optical axis aperture, so that the pins are fitted to slits formed in the blades. The ring-like operation member rotates through the transmission pin11of the drive device (described later) by a predetermine angle to open and close the optical axis aperture.

The electromagnetic drive device MO drives the light quantity adjustment device SH as follows.FIG. 2is an exploded perspective view of the electromagnetic drive device MO, andFIG. 3is a longitudinal sectional view thereof. The electromagnetic drive device MO comprises a magnet rotor12formed of a permanent magnet, a coil frame13for retaining the magnet rotor12to be rotatable, a coil14wound around the coil frame13, and a yoke15fitted around the coil14. The magnet rotor12rotates when a current is supplied to the surrounding coil14.

The magnet rotor12comprises a permanent magnet16, a rotational shaft17, and a transmission member18(described later). The permanent magnet16with a cylindrical shape is formed of a magnetic material such as a plastic including a rare earth metal. The rotational shaft17is inserted into a center hole in the permanent magnet16and firmly fixed with an adhesive. The rotational shaft17is integrally provided with the transmission member18with a resin molding. The magnet16and the rotational shaft17may be integrally formed of a same material. In this embodiment, the rotational shaft17is inserted and firmly fixed to the through-hole at the center of the magnet16. Alternatively, a magnet may be installed in a synthetic resin holder having a rotational shaft without providing a center hole in a magnet.

In this manner, the magnet rotor12having the rotational shaft17is rotatably disposed in the coil frame13, and the coil14is wound around the coil frame13. The coil frame13is formed of two coil frame halves13aand13bdivided into two portions at the rotational shaft17of the rotor12, so that the coil frame13retains the magnet rotor12with the tubular magnet16.

As shown inFIG. 2, the coil frame13is usually formed in a hollow tube body, and includes a cavity19for accommodating the magnet rotor12; bearings20and21for supporting the rotational shaft17of the rotor12; an opening22for allowing the transmission member18to protrude outwardly; and a bobbin part23for winding the coil14. The coil frame13is divided into the two coil frame halves13aand13balong an axial direction (refer toFIG. 2), and is formed of a synthetic resin. When the two coil frame halves13aand13bare joined, the magnet rotor12is accommodated in the coil frame13, and both end portions of the rotational shaft are supported on the bearings20and21formed in the cavity19. The opening22extending from connection surfaces24aand24bof the two coil frame halves13aand13bis formed at a peripheral side of the coil frame13for allowing the transmission member18of the rotor12to protrude outwardly.

The coil frame13has the hollow tube body having upper and lower end surfaces and divided in a longitudinal direction as shown inFIG. 2. Each of the coil frame halves13aand13bis integrally provided with the cavity19for accommodating the magnet rotor12, the bobbin part23for winding the coil14, one of the connection surfaces24aand24b, the opening22extending from the connection surfaces, and one of the bearing portions20and21for supporting the rotational shaft17.

The connection surfaces24aand24bare provided with positioning pins25for engaging fitting holes26formed in the coil frame halves at suitable places (four pins in the embodiment). The coil frame13is also provided with protrusions27to be fixed to the base plate1of the light quantity adjustment device.

In the magnet rotor12, the rotational shaft17is fixed to the center axis hole of the cylindrical permanent magnet16with the adhesive, and the arm-like (bar-like) transmission member18is integrated with the rotational shaft17to protrude outside of the magnet16in a radial direction. The magnet16is formed of a magnetic material such as a rare earth synthetic resin as described above. The rotational shaft17is formed of a synthetic resin such as polycarbonate with a resin molding, and the transmission member18is integrated with the rotational shaft17. The magnet16is polarized in two poles N and S, so that the two poles N and S are located in a direction approximately perpendicular to the transmission member18. The transmission member18is arranged in a direction perpendicular to the direction of the N and S magnetic poles of the magnet16, so that the transmission member18is arranged in a direction approximately perpendicular to the coil14winding in a direction same as that of the N and S magnetic poles.

That is, the coil14is wound in a direction approximately identical to the magnetic poles N and S of the magnet16to obtain high output. The transmission member18is arranged in a direction approximately perpendicular to the coil14, so that the transmission member rotates left and right by a predetermined angle, for example, 30 degrees and 60 degrees in total. Such an arrangement is preferred. Accordingly, it is necessary to wind the coil14on the coil frame13over a range as wide as possible except a moving range of the transmission member18rotating left and right by a predetermined angle, thereby increasing an output torque or reducing an outer diameter of the coil frame. At this time, the transmission member18is arranged to rotate left and right by a predetermined angle with a direction approximately perpendicular to the coil14as a center point, thereby obtaining a large space (bobbin part23) of the coil frame for winding the coil in a case that a rotational angle of the transmission member is constant.

With the configuration, when the coil frame13has a same diameter, it is possible to obtain a higher torque, and when the output torque is constant, the diameter of the coil frame13can be reduced.

As shown inFIG. 4, the N and S magnetic poles of the magnet16is aligned with a winding direction of the coil14on line Y—Y, and the transmission member18attached to the magnet is arranged to rotate with a center point on line X—X approximately perpendicular to the line Y—Y. The transmission member18rotates to both sides by a predetermined angle with the X—X line as the center point (intermediate position) of the rotation.

Incidentally, the bobbin part23is formed in a concave groove at an outer periphery of the coil frame13as a winding margin of the coil14. The bearing portions20and21are formed in the coil frame13as notches formed in the coil frame halves13aand13bfor inserting the rotational shaft17of the magnet rotor12. One of the coil frame halves is provided with an arc-like notch20afor fitting the rotational shaft17, and the other of the coil frame halves is provided with a U-shaped notch20b(refer toFIG. 5), so that one end of the rotational shaft17is supported when the notches are joined. Incidentally, although not shown in the drawing, the rotational shaft17has the other end same as the one end.

The rotational shaft17is supported on the arc-like notch joined to the U-shaped notch. If the both notch are formed in a circular shape, the rotational shaft17does not rotate smoothly when a positional misalignment of the two coil frame halves13aand13boccurs, or a dimension error in manufacturing and a so-called bite phenomenon occur. In the embodiment, the rotational shaft17fits in the arc-like notch part20aformed in the one of the two coil frame halves13aand13b, and the U-shaped notch part20bformed in the other pushes the shaft17with a plane, thereby preventing the bite phenomenon.

Accordingly, in the embodiment, the coil frame has the divided coil frame halves, and the coil frame halves have the connection surfaces at the upper and lower ends thereof along a direction intersecting a winding direction of the coil.

As a result, a linear groove is generated between the connection surfaces24aand24bat the upper and lower ends of the two coil frame halves13aand13bformed in the cylindrical tube body, and the coil14is wound in a direction intersecting the linear groove. As shown inFIG. 5, the two coil frame halves13aand13bare joined long X—X line, and the bobbin part23is formed in a concave groove around the coil frame halves13aand13b, so that the coil is wound in a Y—Y direction. In this case, the X—X line formed by the connection surfaces24aand24bis aligned with a direction approximately perpendicular to the Y—Y line formed by the coil14.

It is possible to arrange the X—X line formed by the connection surfaces24aand24bbetween X1—X1line and X2—X2line inFIG. 5(positions deviating from ridgelines of the bobbin part), or arrange the X—X line at a position outside the range. When the connection surfaces are located between the X1—X1and X2—X2lines, the coil always crosses the linear groove formed by the connection surfaces in an intersecting direction, so that the coil wire does not enter the groove and is not damaged. Even when the connection surfaces are somewhat away from the range between the X1—X1and X2—X2lines, the groove formed by the connection surfaces is shallow, and the groove becomes deeper as the connection surfaces away from the range. That is, when the groove formed by the connection surfaces at ridges28and29of the coil frame is in an allowable range relative to a diameter of the coil wire, the connection surfaces may be located at a position outside the range.

Next, a positional relation between the connection surfaces24aand24bof the two coil frame halves13aand13band the transmission member18will be explained. It is necessary to provide the opening22in the peripheral surfaces of the coil frame halves13aand13bfor allowing a rotation of the transmission member18. It is also necessary to form the opening22to extend from the connection surfaces located at the peripheral surfaces of the coil frame halves13aand13b, so that the magnet16integrated with the transmission member18is accommodated in the coil frame.

As shown inFIG. 2, the coil frame halves13aand13bare divided in the longitudinal direction, and the opening22is a notch formed in the peripheral surfaces of the two coil frame halves13aand13band extending from each of the two coil frame halves13aand13b. With this configuration, when the two coil frame halves13aand13bare joined, the magnet rotor12is installed and the transmission member18protrudes outwardly.

As described above, the magnet rotor12is installed in the coil frame halves13aand13b, and the coil frame halves13aand13bare joined. Then, the coil14is wound around the outer periphery of the coil frame13in the direction intersecting the connection surfaces24aand24bat the upper and lower ends of the coil frame halves13aand13b. Lastly, the yoke15is attached to the outer peripheries of the coil frame halves13aand13b, thereby obtaining the electromagnetic drive device MO. The coil frame halves13aand13bare formed of a polycarbonate-base resin with a resin molding, and the magnet rotor12is formed of a rare earth resin with sintering. An outer diameter of the coil frame13is 5 mm, and a copper wire with a diameter of 0.004 mm is wound 200 times to form the coil. A width of the bobbin part of the coil frame is 3 mm.

Such a drive device MO is made small with a diameter of 5 mm, and the winding margin of the coil14is 3 mm. In this constitution, the coil winding margin (bobbin part) is a single piece, and the coil14is wound in the direction intersecting the connection surfaces24aand24bof the coil frame halves13aand13b, thereby reducing a size of the device. In the drive device MO, the coil frame halves13aand13bare provided with the protrusions27at four places, and the protrusion27is formed in a hook shape with a reverse L-shape section. The protrusion27is fitted in the protrusion7formed in the base plate1of the light quantity adjustment device SH, so that the drive device MO is attached to the base plate1.

The light quantity adjustment device with this configuration is incorporated into, for example, a photographing lens of a camera, and the blades3and4are urged in closing directions (arrow directions inFIG. 1) by a spring (not shown). A current is supplied to the coil14from a power source upon a release operation of the camera. As a result, the coil14generates a magnetic field to rotate the magnet rotor12clockwise inFIG. 1, so that the blades3and4open the optical axis aperture6. Accordingly, the exposure for photographing starts. When the camera receives a signal of an exposure completion, a reverse current is supplied to the coil14to rotate the magnet rotor12counterclockwise, and the blades3and4close the optical axis aperture6. Accordingly, it is possible to adjust the light quantity in a shutter operation of various camera devices.

Next, a light quantity adjustment device will be explained with reference to an exploded perspective views ofFIGS. 6 and 7and a longitudinal sectional view ofFIG. 8. The light quantity adjustment device is a stop device for adjusting a quantity of light passing through a photographing optical axis according to a photographing condition.

As shown inFIG. 6, EX denotes the light quantity adjustment device as the stop device, and MO denotes the electromagnetic drive device. The light quantity adjustment device EX is arranged such that stop blades53and54are slidably incorporated between a pair of flat base plates51and52, and a diameter of an optical axis aperture55provided in the base plates51and52is adjusted by the blades53and54. The base plate51is formed of a synthetic resin such as polycarbonate with a resin molding, and an optical axis aperture55is formed at a center of the base plate51. A rib (not shown) is formed around the optical axis aperture55for guiding the blades53and54.

The base plate52is formed of a thin metal plate and the like, and is attached to protrusions56provided on the base plate51to form a gap between the base plate51for allowing the blades to slide. The stop blades53and54are provided with slits57ato57dat four places for inserting pins (not shown) formed in the base plate51, so that the stop blades53and54are supported and move left and right inFIG. 6.

The blade53is provided with a slit58at a base end thereof, and the blade54is provided with a slit59at a base end thereof. Transmission pins60and61of the electromagnetic drive device (described later) engage the slits58and59, so that the blades53and54move mutually in different directions by the transmission pins to change a diameter of the optical axis aperture55.

A hook protrusion62with a reverse L-shape section is integrated with the base plate51for fixing the electromagnetic drive device MO. A slit63is formed in the base plate51as an escape groove for not hindering motions of the transmission pins60and61. Incidentally, in the embodiment, the blade member is formed of the two blades, and may be formed of one piece or three or more pieces. In a case of one piece, the blade has an aperture with a diameter smaller than the optical axis aperture, and moves between a position facing the optical axis aperture of the base plate and a position away from the optical axis aperture to adjust the light quantity. In a case of three or more pieces, the blades are disposed around the optical axis aperture with a predetermined gap, and pins are provided in a ring-like operation member arranged at an outer periphery of the optical axis aperture for inserting into slits formed in the blades. The ring-like operation member rotates by a predetermined angle through transmission pins of the drive device (described later) to adjust a diameter of the optical axis aperture.

Next, the electromagnetic drive device MO will be explained with reference to an exploded perspective view ofFIG. 7and a longitudinal sectional view ofFIG. 8. The same reference numerals denote components same as those inFIG. 2. The electromagnetic drive device MO comprises the magnet rotor12formed of a permanent magnet, the coil frame13for retaining the magnet rotor12to be rotatable, the coil14wound around the coil frame13, and the yoke15fitted around the coil14, so that the magnet rotor12rotates when a current is supplied to the surrounding coil14.

The magnet rotor12comprises the magnet16, the rotational shaft17, and a transmission member64(described later). The magnet16has a cylindrical shape and is formed of a magnetic material such as a rare earth plastic. The rotational shaft17is inserted into a center hole of the cylindrical magnet16and firmly fixed with an adhesive. The rotational shaft17is integrally provided with the transmission member64with a resin molding of a synthetic resin.

The transmission member64is an arm member extending left and right with the rotational shaft17at a center, and is integrally provided with transmission pins60and61at tips thereof for engaging slits58and59formed in the stop blades53and54. Accordingly, when the rotor12rotates, the transmission pins60and61swing in opposite directions, respectively.

The coil frame13is formed of the coil frame halves13aand13bdivided into two portions at the rotational shaft17of the rotor12, so that the coil frame13retains the magnet rotor12with the tubular magnet16. Similar to the structure shown inFIG. 2, the coil frame13is formed in a hollow tube body, and includes the cavity19for accommodating the magnet rotor12; the bearings20and21for supporting the rotational shaft17of the rotor12; openings65for allowing the transmission member64to protrude outwardly; and the bobbin part23with the coil14wound thereon.

The coil frame13is divided into the coil frame halves13aand13balong the axial direction, and is formed of a synthetic resin. When the coil frame halves13aand13bare joined, the magnet rotor12is accommodated in the coil frame13, and both end portions of the rotational shaft are supported on the bearings20and21formed in the cavity19. A pair of the openings65extending from the connection surfaces24aand24bof the two coil frame halves13aand13bis formed at left and right peripheral sides of the coil frame13for allowing the transmission member64of the rotor12to protrude outwardly.

The positioning pins25are formed in the connection surfaces24aand24bfor engaging the fitting holes26formed in the coil frame halves at suitable places (four places in this embodiment). The hook-shaped protrusions27with a reverse L-shape section are fixed to the base plate51of the light quantity adjustment device, so that the drive device MO is fixed to the base plate51through the engagement between the hook-shaped protrusions62and the base plate51.

The magnet16is polarized in the two poles N and S, so that the two poles N and S are located in a direction approximately perpendicular to the transmission member64for the reason explained previously.

Accordingly, the connection surfaces are generated at the upper and lower ends of the divided coil frame halves in the direction intersecting the direction that the coil is wound. Such a stop device is incorporated into, for example, a photographing lens of a camera, and the blades53and54are urged in closing directions (arrow directions inFIG. 6) by the spring (not shown).

When an exposure start signal is transmitted to a stop control part upon a tuning-on operation of the camera, a photoelectric conversion element in the camera measures the light quantity passing through the optical axis aperture55. When the light quantity is insufficient, a signal is sent to the stop control part and the current is supplied to the coil of the electromagnetic drive device from the power source. The magnetic field is generated in the coil14to rotate the magnet rotor12counterclockwise inFIG. 6, and the blades53and54move to open the optical axis aperture55of the base plate51.

When the photoelectric conversion element detects an appropriate light quantity, a predetermined current is supplied to the coil14to hold the blades. Conversely, when the photoelectric element detects an excessive light quantity, a reverse direction current is supplied to the coil14to thereby rotate the magnet rotor18clockwise, so that the blades53and54move to reduce a diameter of the optical axis aperture55. When the photoelectric conversion element detects the appropriate light quantity, the predetermined current is supplied to the coil14, thereby holding the blades. In this manner, it is possible to provide the light quantity adjustment device for performing the stop operation of various camera devices.

FIG. 9is a perspective view of an electromagnetic drive device according to another embodiment of the invention.FIG. 10is an exploded perspective view thereof.FIG. 11is an end view of a coil frame, andFIG. 12a longitudinal sectional view of a device shown inFIG. 9.

The electromagnetic drive device comprises the coil frame13formed in a hollow shape, the magnet rotor12rotatably supported in the inside cavity19of the coil frame13, the coil14wound around the outer periphery of the coil frame13, the transmission member18attached to the magnet rotor12for transmitting the rotation of the magnet rotor12to an outside, and the yoke15covering an outer periphery of the coil frame13.

The coil frame13is formed of a synthetic resin with a resin molding, and is provided with the cavity19for retaining the magnet rotor12and the winging margin for winding the coil14. The coil frame13has a hollow circular cylinder shape, and is formed of the two coil frame halves13aand13bdivided left and right in an axial direction. The coil frame is constituted in this manner in order to facilitate a work of forming the cavity19and an operation of incorporating the magnet rotor12into the cavity19.

Further, the coil frame13is divided left and right in the axial direction in order to reduce the positional misalignment of the coil frame halves13aand13bin the axial direction, when a size of the coil frame13is reduced in a radial direction to make the device small.

That is, in order to reduce a diameter of a lens-barrel part of a camera device, it is necessary to reduce a diameter of the light quantity adjustment device such as shutter blades and stop blades located on the photographing optical axis, and it is necessary to reduce a size of the drive device of the light quantity adjustment device not to protrude in an outer diameter direction from the photographing optical axis.

The coil frame13has a compact outer shape with a diameter of 4 mm and an axial length of 8 mm. The coil frame13is divided in the axial direction, so that the coil frame halves13aand13bare joined at the large connection surfaces, thereby reducing the positional misalignment therebetween.

The coil frame half13ahas the connection surface24aat the peripheral sidewall end thereof, and the connection surfaces24bat the upper and lower ends. Similarly, the coil frame half13bhas the connection surfaces24cand24d, so that the connection surface24acontacts the connection surface24c, and the connection surfaces24bcontact the connection surfaces24d.

Incidentally, the positioning bosses25(protrusion) are provided in the connection surface24c, and the corresponding holes are provided in the connection surface24a. Also, the positioning holes26are provided in the connection surface24c, and the corresponding protrusions are provided in the connection surface24a.

The magnet rotor12has the permanent magnet16and the rotational shaft17provided at the center of the permanent magnet16. The permanent magnet16is formed in a circular cylinder shape by sintering a magnetic material, and is polarized in the two poles N and S. As shown inFIG. 10, the permanent magnet16is magnetized such that the N pole and S pole face the cylindrical peripheral surfaces and are spaced by 180 degrees, and the rotational shaft17is inserted into the through-hole at the center of the magnet and bonded with the adhesive.

The rotational shaft17is a bar member formed of a synthetic resin, and the tip parts17aand17bare supported on bearing concave portions (described later) formed in the cavity19of the coil frame13. In the rotational shaft17, the transmission member18is integrally formed in the direction perpendicular to the axial direction, so that the rotation of the magnet rotor12is transmitted to the outside through the transmission member18.

Incidentally, the transmission member18may be integrated with the rotational shaft17with the resin molding and the like, or may be individually formed and joined with the adhesive or a method such as press fitting. The transmission member18is provided with the transmission pin11, and the transmission pin11engages the light quantity adjustment blades (shutter blades or stop blades).

The coil frame halves13aand13bare provided with the cavity19for accommodating the magnet rotor12, and bearing concave portions10aand21afor supporting the rotational shaft17of the magnet rotor12.

Conventionally, when the coil frame with a cylindrical shape is divided left and right in an axial direction through a center axis, coil frame halves are respectively provided with U-shaped notch grooves at end surfaces thereof, and the coil frame halves are joined to support a rotational shaft. However, when the device is made small, the coil frame has a diameter of 5 mm or less and the rotational shaft has a diameter of about 1 mm. In this case, it is difficult to form the coil frame halves13aand13bso that the rotational shaft17is supported on the left and right U-shape grooves. In addition to such a problem, in a case where a pivot bearing structure is designed to reduce a mechanical loss at the bearing portion, it is difficult to construct the conventional structure.

That is, in a case where a tip of the rotational shaft is sharpened to 60 degrees, the bearing concave portion must be formed in a triangular pyramid shape to support the tip of the rotational shaft. It is difficult to form the triangular pyramid shape by joining two concave grooves formed individually. Accordingly, in the embodiment, the bearing concave portion10ais formed in the coil frame half13afor supporting one end17aof the rotational shaft17, and the bearing concave portion21ais formed in the coil frame half13bfor supporting the other end17bof the rotational shaft17.

A bulge part10is formed at an upper end of the coil frame half13a, and the bearing concave portion10aconsisting of a through-hole is formed in the bulge part10. A concave part20corresponding to the bulge part10is formed at an upper end of the coil frame half13b. The one end17aof the rotational shaft17of the magnet rotor12is supported on the bearing concave portion10aof the coil frame half13a.

Similarly, a bulge part21and the bearing concave portion21aare formed at a lower end of the coil frame half13b, and a concave part (not shown) corresponding to the bulge part21is formed at a lower end of the coil frame half13a.

In this manner, the bearing concave portion10ais formed in the coil frame half13afor supporting the one end17aof the rotational shaft17, and the bearing concave portion21ais formed in the coil frame half13bfor supporting the other end17bof the rotational shaft17, so that the two coil frame halves13aand13bare easily joined and the magnet rotor12is easily installed.

The coil14is wound around the coil frame13in the direction perpendicular (intersecting) to a polarization direction (peripheral direction) of the permanent magnet16of the magnet rotor12. The concave groove23is formed at the outer periphery of the coil frame13as the winding margin of the coil. Further, the opening22is provided in the peripheral side surface of the coil frame13, so that the transmission member18protrudes outwardly. The opening22is formed of a slit-like opening22anotched in the connection surface24aof the coil frame half13aand a slit-like opening22bnotched in the connection surface24cof the coil frame half13b.

As shown inFIG. 11, the groove24is formed between the connection surfaces of the two coil frame halves13aand13baround the whole outer periphery of the coil frame13, and the coil14is wound around the outer periphery of the coil frame13.

Conventionally, the coil is wound while avoiding the groove generated by the connection surfaces, so that a coil wire is not broken by the groove. Accordingly, the coil is individually wound around each of the coil frame halves13aand13b, and wire ends of the two coils are connected to form a single coil. As a result, a band connection part is formed at a center of the coil frame13where the coil is not wound. Due to the band connection part, it is necessary to increase the coil frame diameter for providing a large margin of winding the coil to obtain a predetermined output, thereby making it difficult to reduce a size of the device.

In the embodiment, the coil is wound in the direction intersecting the linear groove generated by the connection surfaces, so that the coil can be wound over the whole area of the coil frame without breaking the wire. Accordingly, it is possible to obtain a high output with the coil frame having a same diameter, or it is possible to reduce a diameter of the coil frame with the same output, thereby reducing a size of the device.

In this manner, the concave groove23is provided on the outer periphery of the coil frame13in the direction intersecting (or perpendicularly) the connection surfaces of the coil frame halves13aand13b, and the coil14is wound around the concave groove23. The yoke15with a ring shape is formed of a soft magnetic material, and is fitted to the coil frame13for covering the outer periphery of the coil frame13and shielding a leakage magnetic flux.

As described above, according to the embodiments of the invention, the coil frame is formed of the two coil frame halves divided left and right in the axial direction along the rotational shaft of the magnet rotor. The magnet rotor is installed in the coil frame, and the coil is wound around the outer periphery of the coil frame. The coil is wound in the direction intersecting the connection surfaces of the two coil frame halves, i.e. the coil wire is wound while intersecting the groove generated between the connection surfaces of the coil frame halves, so that it is possible to wind the coil wire over the whole area of the coil frame without breaking. Accordingly, it is possible to reduce a size of the device and increase the output of the device.

Further, according to the embodiments of the invention, the coil frame is formed of the two coil frame halves divided left and right through the rotational shaft of the magnet rotor, so that the magnet rotor is installed therein and the coil is wound around the outer periphery thereof. The bearing concave portion is provided in one of the coil frame halves for supporting one end of the rotational shaft of the magnet rotor, and the bearing concave portion is provided in the other of the coil frame halves for supporting the other end of the rotational shaft. Accordingly, as compared with the conventional structure where the shaft is supported on the notch formed in each of the coil frame halves, it is not necessary to accurately form the bearing portion, so that the molding of the coil frame is easy.

Further, it is possible to reduce a frictional load on the rotational shaft of the magnet rotor at the bearing portion due to the positional misalignment of the two coil frame halves.