Photography – Camera detail – Shutter
Reexamination Certificate
2002-06-26
2004-08-31
Gray, David M. (Department: 2851)
Photography
Camera detail
Shutter
C396S489000
Reexamination Certificate
active
06783287
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a focal-plane shutter for a digital camera wherein to photograph, two blades consisting of a first blade and a second blade are operated in order in the same direction and the light reception face of an image pickup device is exposed to light through a slit formed by the first and second blades.
Generally, with a focal-plane shutter adopted for a conventional camera using a silver-salt film, first blades electromagnet and second blades electromagnet are previously energized before the light exposure operation of a first blade and a second blade. Then, the electromagnets is shut off in order at a predetermined timing by an output signal of a light exposure time control circuit, and a first blades drive member and a second blades drive member are rotated by the urging forces of a first blade drive spring and a second blade drive spring, thereby causing the first blade and the second blade to perform the light exposure operation.
Two types of configuration for holding the first blades drive member and the second blades drive member at the set position to the next photographing are known, usually called direct type and retention type. In the direct type, at the set position, the first blades drive member and the second blades drive member are brought into contact with the first blade electromagnet and the second blade electromagnet respectively, and when a release button of the camera is pressed at the next photographing, the electromagnets are energized and at the stage at which the drive members are reliably attracted by the magnetic forces of the electromagnets, a set member is restored to the initial position before the set operation.
In the retention type, the first blades drive member and the second blades drive member are retained at the set position by retention members and when a release button of the camera is pressed at the next photographing, the retention is released by the electromagnets. Therefore, in the retention type, a set member may be restored to the initial position immediately after completion of setting the drive members, or may be restored to the initial position before photographing in association with release as with the direct type described above.
By the way, a digital camera for photographing a subject by an image pickup device of a CCD, etc., for converting photograph light formed by a photographing lens into electric data adopts a focal-plane shutter of a similar type to the type described above, in which a first blade and a second blade are operated in order at a predetermined timing and continuous light exposure is conducted from one side of a light reception face of the image pickup device to an opposite side through a slit formed by the first and second blades.
Some of the digital cameras using a shutter of such a configuration are of the type in which an optical finder is provided as with the conventional camera and the light reception face is covered with at least either of the first and second blades except that photographing is conducted, and of the type in which a subject can be displayed by an electronic viewfinder implemented as a liquid crystal display, etc., for making it possible to view image data output from the image pickup device with the image pickup device exposed to photograph light even when photographing is not conducted. Therefore, in the latter type, to photograph, the first blade is operated to the position covering the light reception face before light exposure operation is performed.
FIG. 5
shows a related art as disclosed in JP-A-62-128675. The related art discloses a shutter of the direct type described above. When the camera power is turned on, as a motor lever
107
(operation member) is turned clockwise, a set lever
109
(set member) is turned counterclockwise from the initial position. Thus, an open blade drive lever
101
(first blades drive member) and a closed blade drive lever
104
(second blades drive member) are turned clockwise against the urging forces of a spring
103
(first blade drive spring) and a spring
106
(second blade drive spring) and the set completion state is entered. At this time, only the closed blade drive lever
104
is attracted to an electromagnet on the closed vane side (second blade electromagnet). After this, as the set lever
109
is restored to the initial position, the open blade drive lever
101
is operated to the open position, but the closed blade drive lever
104
is already attracted to the electromagnet and thus an aperture (opening) is opened by an open vane (first blades) and a closed vane (second blades) and it is made possible to display a subject through an electronic viewfinder.
When release operation is performed, the electromagnet on the closed vane side is demagnetized and thus the closed blade drive lever
104
is turned counterclockwise by the tension of the spring
6
for moving the closed vane to the position closing the aperture. After this, in a state in which both an electromagnet on the open vane side (first blade electromagnet) and the electromagnet on the closed vane side are excited as the set lever
109
is turned counterclockwise, the open blade drive lever
101
and the closed blade drive lever
104
are operated to the set completion position and are attracted to their respective electromagnets. After the open blade drive lever
101
and the closed blade drive lever
104
are thus attracted and held, when the set lever
109
is restored to the initial position by the urging force of a spring
111
, the electromagnet on the open vane side and the electromagnet on the closed vane side are demagnetized in order, whereby the blades start the light exposure operation.
In such a control method, when the camera is not used, the shutter blade is closed to protect the image pickup device from direct sunlight and as the power is turned on, the aperture is opened; this point is desirable. On the other hand, however, from the time when the power is turned on, the closed blade drive lever
104
must be kept at the open position to display a subject on the electronic viewfinder and thus an electric current must be continuously supplied to the closed vane electromagnet and power consumption is noticeable; this is an extreme problem.
If the open position is kept by the attraction force of the closed vane electromagnet, when vibration or a shock is applied to the camera, it is transmitted to the shutter, whereby the closed blade drive lever
104
is not kept at the open position and is brought away from the open position and a malfunction of closing the aperture may occur. Thus, a countermeasure of increasing the electric current applied to the electromagnet for enlarging the attraction force is taken; however, also in this case, a power consumption problem occurs. Particularly, with the digital camera, the camera size is made small as compared with that of the conventional camera and thus the power supply volume is limited and photoelectric conversion of the image pickup device, display on the electronic viewfinder, image recording, and the like also consume power and thus there is strong demand to suppress power consumption as much as possible. Further, to suppress costs, the focal-plane shutter of the conventional camera may be used as that of the digital camera. In such a case, however, it is large demand to suppress change in the shutter configuration and change in the parts accompanying the change in the shutter configuration as much as possible for reducing costs together with suppression of power consumption described above.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a focal-plane shutter for a digital camera for exposing the light reception face of an image pickup device to light through a slit formed by first and second blades, the focal-plane shutter being suited for a camera comprising an electronic view finder and appropriate for lower power consumption and cost reduction.
To the end, according to the invention, there is provided a focal-plane shutter for a digital camera,
Eguro Tohru
Kudo Kouichi
Gray David M.
McGinn & Gibb PLLC
Nidec Copal Corporation
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