Blade drive device and optical device

A blade drive device includes: a board having an opening; a blade for adjusting an amount of the opening; and first and second drive rings having a support structure for commonly supporting the blade for swinging, rotating in an identical direction with a given speed difference, and being arranged in a same plane.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to blade drive devices and optical devices.

2. Description of the Related Art

Conventionally, there has been known a blade drive device having a drive ring for applying a drive force to a blade, which adjusts an opening amount of an opening formed on a board (see Japanese Examined Patent Application Publication No. 07-92580).

In such a blade drive device, it is preferable to reduce and transmit the drive force from a drive source to the blade, in order to improve the positional accuracy of the blade. However, in order to reduce a speed of the drive force from the drive source, it is necessary to transmit the drive force to the drive ring via plural gears. There is a problem in which the blade drive device is increased in size due to the presence of such gear for reducing the speed.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a blade drive device in which the positional accuracy of a blade is improved and an increase in its size is suppressed.

According to an aspect of the present invention, there is provided a blade drive device including: a board having an opening; a blade for adjusting an amount of the opening; and first and second drive rings having a support structure for commonly supporting the blade for swinging, rotating in an identical direction with a given speed difference, and being arranged in a same plane.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given, with reference to the accompanying drawings, an embodiment of the present invention.FIG. 1is a perspective view of a blade drive device in a fully opened state,FIG. 2is a perspective view of the blade drive device in a small aperture state, andFIG. 3is a partially cross-sectional view of the blade drive device.

Referring toFIGS. 1 to 3, the blade drive device according to the present embodiment includes: a board10having an opening12at its center portion; plural blades20adjusting the opening amount of the opening12; drive rings30and40rotatably supported on the board10and transmitting a drive force to the plural blades20; an electromagnetic actuator50serving as a drive source; a pinion gear60; and a blade retaining board70having an opening72. The drive rings30and40respectively serve as first and second drive rings.

The board10, the blades20, the drive rings30and40, the pinion gear60, and the blade retaining board70are made of synthetic resins. The drive rings30and40are arranged concentrically with the opening12. Further, plural drive pins32are arranged at even intervals on the drive ring30. Plural spindle portions42are arranged at even intervals on the. drive ring40. The drive pins32and the spindle portions42serve as a support structure for commonly supporting the blades20for swinging. The number of the drive pins32is identical to that of the blades20. The number of the spindle portion42is identical to that of the blades20. The drive pins32are arranged closer to the opening12than the spindle portions42. The spindle portion42is engaged with a hole formed on the blade20, so that the blade20is swingably supported. Further, the drive pin32is engaged with a cam hole22having a circular shape. Furthermore,FIGS. 1 and 2are views of the blade drive device when viewed from the blade retaining board70side. The blade retaining board70is omitted inFIGS. 1 and 2. Moreover, the electromagnetic actuator50is partially omitted inFIG. 3.

Additionally, the drive rings30and40are provided with teeth portions36and46at their peripheral portions in the given ranges, respectively. The teeth portions36and46respectively correspond to first and second teeth portions. The range where the teeth portion36is arranged is larger than the range where the teeth portion46is arranged. As illustrated inFIG. 3, the teeth portion36is located at a radially outward position with respect to a step portion35. The teeth portions36and46are arranged in line in the optical axis direction. Further, the pinion gear60, which transmits the drive force to the drive rings30and40, has gears63and64directly meshing with the teeth portions36and46, respectively. The teeth portion36and the gear63meshing with the teeth portion36serve as a first engagement portion, whereas the teeth portion46and the gear64meshing with the teeth portion46serve as a second engagement portion. Further, the pinion gear60is made of a resin and press fitted onto a rotary shaft52of a rotor51included in the electromagnetic actuator50. This allows the gears63and64and the rotor51to integrally rotate. As illustrated inFIG. 3, the gears63and64are arranged in line in the optical axis direction, that is, in the axial direction of the rotary shaft52. The gears63and64are integrally formed. The pitch circle radius of the gear63is larger than that of the gear64. The gears63and64are identical to each other in the number of teeth.

The drive ring30is housed within a space defined between the board10and the blade retaining board70. Further, a blade support board81is attached to the board10on its surface opposite the blade retaining board70, and a blade support board82is attached to the blade retaining board70on its surface opposite the board10. The blade support board81has an opening smaller than the opening12in diameter, although the opening does not have its reference number. This opening defines the maximum amount of the opening in the fully opened state. The blade support board82functions to prevent an operational failure of the blades20due to static electricity within the space defined between the board10and the blade retaining board70. Further, the diameter of the opening72is substantially identical to or slightly larger than that of the opening12. Furthermore, the blade retaining board70has receiving holes73and74which respectively permit the movements of the drive pins32and the spindle portions42, as illustrated inFIG. 3. Moreover, the board10is formed with a sliding portion13which slidably contacts the drive ring30to restrict the play thereof in the optical axis direction and the radial direction. Also, the board10is formed with a slidable portion, not illustrated, which contacts the drive ring40to restrict a play of thereof in the optical axis direction and the radial direction.

Herein, a description will be given of an operation of the blades20. The rotary shaft52rotates from the fully opened state illustrated inFIG. 1to mesh the gear63with the teeth portion36and to mesh the gear64with the teeth portion46, thereby transmitting the drive force from the electromagnetic actuator50to the drive rings30and40. Herein, a speed reduction ratio of the gear63to the teeth portion36is different from that of the gear64to the teeth portion46. More specifically, the speed reduction ratio of the gear64and the teeth portion46is larger than that of the gear63and the teeth portion36. That is, a rotational angle of the drive ring30is larger than that of the drive ring40, under the condition that the rotor51rotates the same number of times. Therefore, the drive rings30and40rotate with a given speed difference.

When the drive rings30and40rotate clockwise from the fully opened state illustrated inFIG. 1, the blade20swings to reach the opening12from a position where the blade20recedes from the opening12, due to a change of the positional relationship between the drive pin32and the spindle portion42which supports the blade20to swing. Moreover, the drive pin32and the spindle portion42, which support the blade20move away from each other. Thus, the drive pin32moves within the cam hole22, so that the blade20swings to reach the opening12, thereby shifting to the small aperture state illustrated inFIG. 2.

In this way, the drive rings30and40rotate in the same direction with a given speed difference. In this manner of rotation, the relative speed between the drive rings30and40is reduced, as compared with a case where any one of the drive rings30and40is fixed. Therefore, unlike a conventional blade drive device, the drive force from the electromagnetic actuator50can be decelerated and transmitted to the blades20without the provision of plural gears for speed reduction. The blades20are decelerated, thereby improving their positional accuracies. Specifically, in the blade drive device in which the blades20are stopped at given positions to adjust an aperture amount of the opening12, the control accuracy of the aperture amount is improved. Additionally, it is unnecessary to provide plural gears for speed reduction, thereby suppressing an increase in the number of the parts and an increase in the size of the blade drive device.

Also, since the gears63and64are arranged in line in the axial direction of the rotary shaft52so as to rotate in conjunction with the rotor51, the space can be effectively used and the aperture amount of the opening12can be controlled with the single electromagnetic actuator50. Furthermore, since the gears63and64are integrally formed, the number of the parts can be reduced, and the increasing of the size and the cost of the blade drive device can be suppressed.

Further, the drive rings30and40are arranged in the same plane, and the teeth portions36and46are arranged in different planes. That is, the teeth portions36and46are arranged in line in the optical axis direction. Therefore, the interference of the teeth portions36and46are prevented. Further, the teeth portion36faces a surface, of the drive ring40, opposite the surface where the spindle portions42are provided, thereby also preventing the interference of the drive ring30and the spindle portion42. Such a configuration can provide the blade drive device in which its size is reduced without increasing the space in the optical axis direction.

While the exemplary embodiments of the present invention have been illustrated in detail, the present invention is not limited to the above-mentioned embodiments, and other embodiments, variations and modifications may be made without departing from the scope of the present invention.

Additionally, the support structure may includes: a spindle which is supporting the blade20and is provided in the drive ring30; and a drive pin which engages with the cam hole22and is provided in the drive ring40.

Moreover, the blade20may be provided with a spindles portion, and the drive ring30or40may be provided with a spindle hole engaged with the spindle portion. In addition, the blade20may be provided with a drive pin, and the drive ring30or40may be provided with a cam hole engaged with the drive pin. Also, the blade20may be provided with a spindle portion for supporting the blade20, and the drive ring may be provided with a hole engaged with the spindle portion.

Further, the teeth portions36and46may be formed on the inner peripheral portions of the drive rings30and40, respectively. Furthermore, the rotational angle of the drive ring40may be larger than that of the drive ring30, under the condition that the rotor51rotates the same number of times.

Finally, several aspects of the present invention are summarized as follows.

According to an aspect of the present invention, there is provided a blade drive device including: a board having an opening; a blade for adjusting an amount of the opening; and first and second drive rings having a support structure for commonly supporting the blade for swinging, rotating in an identical direction with a given speed difference, and being arranged in a same plane.

The first and second drive rings rotate in the same direction with a given difference in speed. This reduces the relative speed of the first and second drive rings, as compared with a case where any one of the first and second drive rings is fixed. Therefore, the relative speed of the first and second drive rings can be reduced. Consequently, the blade speed can be reduced without the intervention of a gear for reducing speed, so the blade can be controlled with high accuracy. Additionally, since the first and second drive rings are arranged in the same plane, the blade drive device that has been reduced in size can be provided without increasing the space in the optical axis direction.

In the above configuration, the blade drive device may include a drive source for exerting a drive force to the first and second drive rings, first and second engagement portions may respectively engage the drive source with the first and second drive rings, and the first and second engagement portions may be arranged in different planes.

This provides the blade drive device that has been reduced in size, without increasing the space in the optical axis direction.

In the above configuration, the first and second drive rings may respectively have first and second teeth portions, the first and second teeth portions may respectively mesh with first and second gears integrally rotating, and a speed reduction ratio of the first teeth portion to the first gear may be different from a speed reduction ratio of the second teeth portion to the second gear.

With such a configuration, the first and second drive rings rotate in the same direction with a given difference in speed, thereby reducing the relative speed of the first and second drive rings. Therefore, the blade speed can be reduced and controlled with high accuracy without the intervention of gears for speed reduction.

In the above configuration, the blade drive device may include a drive source exerting a drive force to the first and second drive rings and including a rotor, and the first and second gears may integrally rotate with the rotor.

With such a configuration, since the first and second drive rings are rotated by a single drive source, the blade is controlled with high accuracy while the device's size or cost is reduced.

In the above configuration, the first and second gears may be arranged in line in an axial direction of the rotor.

With such a configuration, since the first and second drive rings are driven by the single drive source, the blade is controlled with high accuracy while the device's size or cost is reduced.

In the above configuration, the first and second teeth portions may be arranged in different planes. This can provide the blade drive device having been reduced in size without increasing the space in the optical axis direction.

In the above configuration, the first and second gears may be integrally formed. This can reduce the number of the parts, thereby providing the blade drive device at low cost.

In the above configuration, the support structure may include: a spindle provided in one of the blade and the first drive ring; and a hole provided in the other of the blade and the first drive ring, and engaging with the spindle.

In the above configuration, the support structure may include: a drive pin provided in one of the blade and the second drive ring; and a cam hole provided in the other of the blade and the second drive ring, and engaging with the drive pin.

Additionally, the above mentioned object is also achieved by an optical device having any one of the shutter drive devices as mentioned above.