Focal plane shutter and optical apparatus

A focal plane shutter includes: a board including an opening; blades capable of opening and closing the opening; a drive lever swingably supported, holding a movable iron piece and driving the blades; a self-holding type solenoid capable of adsorbing to the movable iron piece by a given attraction force in a non-energized state, and reducing the given attraction force in an energized state; a biasing member biasing the drive lever to move the drive lever away from the self-holding type solenoid; and a set member moving the drive lever to abut the drive lever with the self-holding type solenoid, wherein the self-holding type solenoid is energized to reduce the given attraction force when the drive lever is swung by the set member to abut the movable iron piece with the self-holding type solenoid.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims priority to Japanese Patent Application No. 2010-265797 filed on Nov. 29, 2010, subject matter of these patent documents is incorporated by reference herein in its entirety.

BACKGROUND

(i) Technical Field

The present invention relates to focal plane shutters and optical apparatuses.

(ii) Related Art

There is known a focal plane shutter using a self-holding type solenoid for driving blades. In addition to the self-holding type solenoid, such a focal plane shutter is equipped with a drive lever, a biasing member, and a set member. The drive lever holds a movable iron piece and drives the blades. The self-holding type solenoid is capable of adsorbing to the movable iron piece by a given attraction force in a non-energized state, and reduces the attraction force in an energized state. The biasing member is provided for biasing the drive lever such that the movable iron piece moves away from the self-holding type solenoid. The set member drives the drive lever to abut the movable iron piece with the self-holding type solenoid. Japanese Patent Unexamined Application Publication No. 2010-152000 discloses the focal plane shutter employing the self-holding type solenoid.

The set member drives the movable iron piece to abut the movable iron piece with the self-holding type solenoid in the non-energized state. After that, the set member recedes from the drive lever. A wait state where the self-holding type solenoid is adsorbed to the movable iron piece is maintained. After a given period elapses from when a release button is pushed, the self-holding type solenoid is energized. This reduces the attraction force of the self-holding type solenoid, whereby the drive lever recedes from the self-holding type solenoid in accordance with the biasing force of the biasing member. This drives the blades. Subsequently, the set member moves the drive lever, and a wait state where the self-holding type solenoid is adsorbed to the movable iron piece is maintained again.

Herein, a state where the self-holding type solenoid is adsorbed to the movable iron piece may be maintained for a long period, while a portion where the movable iron piece of the drive lever and a yoke of the self-holding type solenoid abut each other is attached with a lubricant oil applied in producing the focal plane shutter and impure substances such as dusts or metal powders by generated in driving the focal plane shutter. This tends to fix the movable iron piece of the drive lever and the yoke of the self-holding type solenoid. This may result in variations in the period from when energization of the self-holding type solenoid starts to when the drive lever recedes from the self-holding type solenoid after the release button is pushed again. This may result in variations in the timing of driving the blades.

SUMMARY

It is therefore an object to provide a focal plane shutter and an optical apparatus having the same suppressing a variation in the timing of driving blades.

According to an aspect of the present invention, there is provided a focal plane shutter including: a board including an opening; blades capable of opening and closing the opening; a drive lever swingably supported, holding a movable iron piece and driving the blades; a self-holding type solenoid capable of adsorbing to the movable iron piece by a given attraction force in a non-energized state, and reducing the given attraction force in an energized state; a biasing member biasing the drive lever to move the drive lever away from the self-holding type solenoid; and a set member moving the drive lever to abut the drive lever with the self-holding type solenoid, wherein the self-holding type solenoid is energized to reduce the given attraction force when the drive lever is swung by the set member to abut the movable iron piece with the self-holding type solenoid.

DETAILED DESCRIPTION

In the following, the present embodiment according to the present invention will be described with reference to the drawings.

FIG. 1is a front view of a focal plane shutter according to the present embodiment.FIGS. 2 and 3are front views of a part of the focal plane shutter. Additionally, reference numerals are given to some of the parts inFIGS. 1 to 3.

As illustrated inFIG. 1, the focal plane shutter1includes a board10, blades21a,21bto24b, arms31a,32a,31b, and32b, an electromagnet70a, and a self-holding type solenoid70b. The board10is formed of a resin. The board10is provided with a rectangular opening11.

Trailing blades20B includes four blades21bto24b. Also, reading blades20A includes four blades. However, only one blade21ais illustrated inFIGS. 1 and 2.FIGS. 1 to 3illustrate the reading blades20A in an overlapped state and the trailing blades20B in an expanded state. InFIGS. 1 to 3, the reading blades20A recede from the opening11and the trailing blades20B close the opening11.

As illustrated inFIG. 2, the reading blades20A are connected to the arms31aand32a. The trailing blades20B are connected to the arms31band32b. Each of the arms31a,32a,31b, and32bis swingably supported by the board10. The arms31aand31bare respectively provided with fitting holes33aand33b.

As illustrated inFIG. 3, the board10is provided with a leading-blades drive lever40aand a trailing-blades drive lever40bthat drive the arms31aand31b, respectively. The leading-blades drive lever40aand the trailing-blades drive lever40bare respectively provided with spindles45aand45b. The spindles45aand45bare rotatably supported by the board10. Thus, each of the leading-blades drive lever40aand the trailing-blades drive lever40bis swingably supported in a given range by the board10. The leading-blades drive lever40aand the trailing-blades drive lever40bare respectively provided with drive pins43aand43b. The board10is provided with escape holes13aand13bthat escape the movements of the drive pins43aand43b, respectively. Each of the escape holes13aand13bhas an arc shape. The drive pins43aand43bare respectively fitted into the fitting hole33aof the arm31aand the fitting hole33bof the arm31b. Swinging the leading-blades drive lever40acauses the arm31ato swing and to move the reading blades20A. Likewise, swinging the trailing-blades drive lever40bcauses the arm31bto swing and to move the trailing blades20B.

The leading-blades drive lever40aand the trailing-blades drive lever40brespectively include movable iron pieces47aand47b. The leading-blades drive lever40ais swingable from a position where the movable iron piece47aabuts the electromagnet70ato a position where the movable iron piece47arecedes from the electromagnet70a. The configuration of the trailing-blades drive lever40bis the same. The spindles45aand45bare respectively fitted with the bias springs60aand60beach having a coil shape. The bias spring60abiases the leading-blades drive lever40ain such a direction that the movable iron piece47amoves away from the electromagnet70a. Likewise, the bias spring60bbiases the trailing-blades drive lever40bin such a direction that the movable iron piece47bmoves away from the self-holding type solenoid70b.

The spindles45aand45brespectively engage ratchet gears50aand50b. The ratchet gear50aengages one end of the bias spring60a. The other end of the bias spring60aengages the leading-blades drive lever40a. The rotational degree of the ratchet gear50ais adjusted, so that the biasing force of the bias spring60acan be adjusted. The ratchet gear50bhas the same function of the ratchet gear50a.

When being energized, the electromagnet70ais capable of adsorbing to the movable iron piece47a. The electromagnet70aincludes: a yoke; a coil bobbin attached to the yoke; and a coil wounded around the coil bobbin. The energization of the coil excites the yoke, and then the magnetic attraction force is generated between the yoke and the movable iron piece47a.

The self-holding type solenoid70bis capable of adsorbing to the movable iron piece47bby a given attraction force in a non-energized state, and reduces the attraction force in an energized state. The self-holding type solenoid70bincludes: a yoke; a coil bobbin attached to the yoke; a coil wounded around the coil bobbin; and a permanent magnet71secured to the yoke. Since the permanent magnet71is provided in the yoke, the yoke also functions as a magnet. Therefore, the self-holding type solenoid70bis capable of adsorbing to the movable iron piece47bin the non-energized state.

Further, the coil is energized to cancel a polarity generated in the yoke by the permanent magnet71, thereby reducing the magnetic attraction force effecting between the yoke and the movable iron piece47b. Thus, the coil is energized to cancel the polarity generated in the yoke by the permanent magnet71while the movable iron piece47bis abutting the yoke of the self-holding type solenoid70b, thereby reducing the magnetic attraction force between the yoke and the movable iron piece47b. Therefore, the trailing-blades drive lever40bis swung by the biasing force of the bias spring60b. In such a way, the movable iron piece47bmoves away from the self-holding type solenoid70bafter being adsorbed thereto.

A set member90is provided for positioning the leading-blades drive lever40aand the trailing-blades drive lever40bat desirable positions. The set member90has a spindle portion95rotatably supported by the board10. The set member90is attached with a returning spring80for returning the set member90to an initial position. The returning spring80is fitted onto the spindle portion95. One end of the returning spring80abuts a projection portion18formed in the board10. The other end of the returning spring80abuts a projection portion98formed in the set member90. The returning spring80biases the set member90counterclockwise.

A thin plate P is arranged coaxially with the trailing-blades drive lever40b. The thin plate P has a thin plate shape. An engagement pin48bis formed in the trailing-blades drive lever40band fitted into the thin plate P. Therefore, the thin plate P and the trailing-blades drive lever40bswing together. Further, a sensor S is arranged near the trailing-blades drive lever40b. The sensor S is a sensor capable of detecting a position of the thin plate P. The sensor S detects the position of the thin plate P to detect a position of the trailing blades20B.

FIGS. 4A and 4Bare explanatory views of the sensor S. The sensor S is arranged on the board10. The sensor S has a light emitting element S2and a light receiving element S3that are arranged to face each other. The light receiving element S3receives the light emitted from the light emitting element S2. As illustrated inFIGS. 4A and 4B, the thin plate P moves to be positioned between the light emitting element S2and the light receiving element S3in response to the swinging of the trailing-blades drive lever40b. When being positioned between the light emitting element S2and the light receiving element S3, the thin plate P interrupts the light emitted from the light emitting element S2. At this time, whether or not the thin plate P is positioned between the light emitting element S2and the light receiving element S3can be detected based on output signals from the light receiving element S3, thereby detecting the position of the trailing-blades drive lever40b. This can result in detecting the position of the trailing blades20B.

Additionally, the sensor S is not limited to the above configuration. For example, the sensor S may include: a light emitting element; a mirror reflecting the light emitted from the light emitting element; and a light receiving element receiving the light reflected by the mirror. The thin plate P is positioned between the light emitting element and the mirror, or between the light receiving element and the mirror, thereby detecting the position of the thin plate P.

A description will be given of a configuration of a camera equipped with the focal plane shutter1.FIG. 5is a block view of the camera equipped with the focal plane shutter1. The camera includes: the focal plane shutter1; a drive mechanism150; a control portion300; and an image pickup element400. The control portion300controls an operation of the whole camera and includes a CPU, a ROM, and a RAM. Additionally, the camera includes lenses, not illustrated, for adjusting a focal length.

The control portion300controls energization states of the coils of the electromagnet70aand the self-holding type solenoid70b. The image pickup element400changes an object image into electric signals. The image pickup element400is, for example, a CCD or a CMOS. The drive mechanism150drives the set member90in response to the instruction from the control portion300. The control portion300controls the energization of the coil of the self-holding type solenoid70bin response to output signals from the sensor S, as will be described later.

The drive mechanism150includes: a lever100driving the set member90; and a motor120capable of linearly reciprocating the lever100by a known technique, and rotatable in forward and reverse directions. The motor120is a stepping motor, and drives the lever100via gears not illustrated. The control portion300controls the driving of the motor120to control the lever100. This controls the rotation of the set member90. The control portion300controls the rotational speed of the motor120to control the driving speed of the lever100. This controls the rotational speed of the set member90.

Next, an operation of the focal plane shutter1will be described.FIG. 6is a timing chart of the focal plane shutter1.FIGS. 7 to 13are explanatory views of the operation of the focal plane shutter1. Additionally, some parts are omitted inFIGS. 7 to 13.FIGS. 1 to 3illustrate a state just after an exposure operation is finished.

The lever100illustrated inFIG. 3is driven from the exposure operation finished state illustrated inFIGS. 1 to 3, and then the set member90is rotated clockwise against the biasing force of the returning spring80. Therefore, the set member90abuts a roller49aof the leading-blades drive lever40aand a roller49bof the trailing-blades drive lever40bto swing the leading-blades drive lever40aand the trailing-blades drive lever40bcounterclockwise. Thus, the leading blades20A expand and move to close the opening11. The trailing blades20B move to recede from the opening11. The trailing-blades drive lever40bswings counterclockwise, and then the thin plate P also swings counterclockwise.

The swinging of the thin plate P counterclockwise allows the sensor S to detect the thin plate P.FIG. 7illustrates the focal plane shutter1in a state where the sensor S starts detecting the thin plate P. Before the trailing blades20B fully recede from the opening11and before the movable iron piece47babuts the self-holding type solenoid70b, the sensor S detects the thin plate P. Referring toFIG. 7, the blade21bpartially covers the opening11when the sensor S detects the thin plate P. When the sensor S detects the thin plate P, the control portion300energizes the coil of the self-holding type solenoid70bto cancel the polarities generated in the yoke by the permanent magnet71. As mentioned above, the control portion300energizes the coil of the self-holding type solenoid70bin response to the output from the sensor S.

Further, when the set member90rotates clockwise, the leading-blades drive lever40aand the trailing-blades drive lever40bfurther swing counterclockwise. As illustrated inFIG. 8, the leading blades20A close the opening11, and the trailing blades20B recede from the opening11. In this state, the movable iron pieces47aand47babut the electromagnet70aand the self-holding type solenoid70b, respectively.

When the movable iron piece47babuts the self-holding type solenoid70b, the above mentioned state where the coil of the self-holding type solenoid70bis energized to cancel the polarities generated in the yoke by the permanent magnet71is maintained. Further, the energization of the coil of the self-holding type solenoid70bis stopped before the set member90recedes from the trailing-blades drive lever40bas will be described later. The energization of the coil of the self-holding type solenoid70bcan reduce the magnetic attraction force that effecting on the movable iron piece47bwhen the movable iron piece47babuts the self-holding type solenoid70b. A reason to reduce the attraction force of the self-holding type solenoid70bwhen the movable iron piece47babuts the self-holding type solenoid70bwill be described later.

The control portion300stops the energization of the coil of the self-holding type solenoid70b, after the coil of the self-holding type solenoid70bis energized to abut the movable iron piece47bwith the self-holding type solenoid70bbefore the set member90recedes from the trailing-blades drive lever40b. After that, the control portion300causes the lever100to recede from the set member90. Therefore, the set member90swings counterclockwise in accordance with the biasing force of the returning spring80to recede from the leading-blades drive lever40aand the trailing-blades drive lever40b. Since the energization of the coil of the self-holding type solenoid70bhas already been stopped, the movable iron piece47bis kept being adsorbed to and held by the yoke of the self-holding type solenoid70b. In contrast, since the electromagnet70ais not energized, the leading-blades drive lever40aswings clockwise in accordance with the biasing force of the bias spring60a. Therefore, the leading blades20A and the trailing blades20B recede from the opening11to make the opening11in an opened state as illustrated inFIG. 9. The focal plane shutter1is brought into a wait state illustrated in the timing chart ofFIG. 6. Additionally, the wait state is a non-energized holding state, in the opened state, where neither the electromagnet70anor the self-holding type solenoid70bare energized.

Subsequently, in shooting, a release button of the camera is pushed, and then the lever100rotates the set member90clockwise again to swing the leading-blades drive lever40acounterclockwise. Therefore, the opening11is closed by the leading blades20A as illustrated inFIG. 10. Further, the energization of the electromagnet70astarts, whereby the movable iron piece47ais adsorbed to and held by the electromagnet70a.

After that, the lever100recedes from the set member90as illustrated inFIG. 11. Since the electromagnet70ais energized, the state where the leading blades20A close the opening11is maintained for a given period.

Next, the energization of the electromagnet70ais stopped to swing the leading-blades drive lever40aclockwise by the biasing force of the bias spring60a. Therefore, the leading blades20A recede from the opening11as illustrated inFIG. 12. Further, the state where the trailing blades20B recede from the opening11is maintained. Thus, the opening11is brought into the opened state.FIG. 12illustrates the exposure state.

After a predetermined period lapses since the release button is pushed, the coil of the self-holding type solenoid70bis energized to reduce the magnetic attraction force effecting between the self-holding type solenoid70band the movable iron piece47b, and then the trailing-blades drive lever40bis rotated clockwise by the biasing force of the bias spring60b. Thus, the trailing blades20B close the opening11as illustrated inFIG. 13.FIG. 13illustrates the state just after the exposure operation is finished. The state illustrated inFIG. 13is the same as the states illustrated inFIGS. 1 to 3. In such a way, one cycle of shooting is finished. The energization of the coil of the self-holding type solenoid70bis stopped after a given period lapses since the energization starts. Additionally, the trailing-blades drive lever40bswings counterclockwise, and then the thin plate P recedes from the sensor S to change its output value. The fully opened state of the opening11as illustrated inFIG. 12is formed not only in photo shooting but also in movie shooting.

Herein, a description will be given of the reason to reduce the attraction force of the self-holding type solenoid70bwhen the movable iron piece47babuts the self-holding type solenoid70b. As mentioned above, the set member90swings the trailing-blades drive lever40bto abuts the movable iron piece47bwith the yoke of the self-holding type solenoid70b. In cases where the coil of the self-holding type solenoid70bis not energized before the movable iron piece47babuts the self-holding type solenoid70b, that is, in cases where the magnetic attraction force of the self-holding type solenoid70bis large, the movable iron piece47bis attracted to the yoke of the self-holding type solenoid70bjust before the movable iron piece47babuts the self-holding type solenoid70b. This increases the speed of the movable iron piece47bmoving toward the self-holding type solenoid70bjust before the movable iron piece47babuts the self-holding type solenoid70b. On the contrary, in cases where the coil of the self-holding type solenoid70bis energized before the movable iron piece47babuts the self-holding type solenoid70b, that is, in cases where the magnetic attraction force of the self-holding type solenoid70bis small, this magnetic attraction force hardly influences the speed of the movable iron piece47bmoving toward the self-holding type solenoid70b. Thus, the speed of the movable iron piece47bmoving toward the self-holding type solenoid70bis greater in the cases where the magnetic attraction force is large than in the cases where the magnetic attraction force is small.

Herein, a period from when the energization of the coil of the self-holding type solenoid70bstarts to when the movable iron piece47bis detached from the yoke tends to be longer in cases where metal powders generated in operating the focal plane shutter are adhered to a portion where the yoke of the self-holding type solenoid70band the movable iron piece47babut each other than in cases where the metal powders are not adhered thereto. Lubricating oil applied in production acts as adhesion bond with minute impure substances such dusts or the metal powders adhered between the movable iron piece47band the yoke. Abutment surfaces constantly press each other in accordance with the attraction force of the permanent magnet71. It is thus conceivable that the movable iron piece47band the yoke of the self-holding type solenoid70bfix each other for the above reason. Further, the adhesion effect between the movable iron piece47band the yoke increases as the speed of the movable iron piece47bwhen abutting the yoke increases. This results in variations in the period from when the energization of the coil of the self-holding type solenoid70bstarts to when the movable iron piece47bis detached from the yoke, in association with the amount of the dusts or the metal powders adhered to the yoke, or in association with the amount of the lubricating oil applied thereto.

Further, the wait state illustrated inFIG. 9is a state when the power supply of the camera is turned on. That is, in cases where the release button is pushed in shooting after power is applied to the camera in the wait state where neither the electromagnet70anor the self-holding type solenoid70bare energized, the shooting operation mentioned above of the focal plane shutter1is also performed. That is, after the lever100rotates the set member90clockwise again to swing the leading-blades drive lever40acounterclockwise and the leading blades20A close the opening11, the energization of the electromagnet70astarts, and then the movable iron piece47ais adsorbed to and held by the electromagnet70a, and the lever100recedes from the set member90. Next, the energization of the electromagnet70ais stopped, whereby the leading-blades drive lever40acauses the leading blades20A to recede from the opening11. After a given period lapses from when the release button is pushed, the coil of the self-holding type solenoid70bis energized to reduce the magnetic attraction force effecting between the self-holding type solenoid70band the movable iron piece47b, and then the trailing-blades drive lever40bcauses the trailing blades20B to close the opening11. Therefore, the adhesion effect between the movable iron piece47band the yoke may be great when the camera is not operated for a long period. In particular, at a first time shooting after the power is on, the period from when the energization of the coil of the self-holding type solenoid70bstarts to when the movable iron piece47bis detached from the yoke may be long.

In the present embodiment, the coil is energized to reduce the magnetic attraction force of the yoke when the movable iron piece47babuts the self-holding type solenoid70b. This can suppress the speed of the movable iron piece47babutting the yoke. It is therefore possible to reduce the adhesion effect between the movable iron piece47band the yoke caused by lubricating oil applied in production and impure substances such as metal powders or dusts attached between the movable iron piece47band the yoke. Also, even at a first-time shooting after power is applied to the camera, that is, even when the state where the movable iron piece47babuts the self-holding type solenoid70bis maintained for a long period, the adhesion effect between the movable iron piece47band the yoke can be reduced. It is thus possible to suppress the variations in the period from when the energization of the coil of the self-holding type solenoid70bstarts to when the movable iron piece47bis detached from the yoke. This can result in suppressing the variations in the timing of driving the blades and the variations in the exposure period.

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.

The focal plane shutter according to the present embodiment can be employed in an optical apparatus such as a still camera or a digital camera.

Although the blade made of a synthetic resin has been described in the present embodiment, the blade having the thin shape may be made of a metal.

In the above embodiment, the leading blades and the trailing blades are each composed of four blades. However, the leading blades and the trailing blades are not limited to these arrangements. The leading blades and the trailing blades may be each composed of two to five blades.

A self-holding type solenoid may be used instead of the electromagnet70afor driving the leading blades20A.

The sensor S detects the position of the trailing-blades drive lever40bin response to the thin plate P interrupting the light from the light emitting element S2toward the light receiving element S3. However, the sensor S is not limited to this configuration. For example, a sensor may be provided at a position such that the blade21binterrupts the light emitted from the light emitting element S2toward the light receiving element S3in accordance with the traveling of the trailing blades20B.

In the above embodiment, the energization of the self-holding type solenoid70breduces the magnetic attraction force thereof. In cases where the magnetic attraction force of the self-holding type solenoid70bin the energized state is smaller than that of the self-holding type solenoid70bin the non-energized state, any magnitude of the magnetic attraction force of the self-holding type solenoid70bin the energized state may be employed. Thus, the self-holding type solenoid70bmay be energized such that its magnetic attraction force is substantially zero, or such that its magnetic attraction force is slightly smaller in the energized state than in the non-energized state.

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

According to an aspect of the present invention, there is provided a focal plane shutter including: a board including an opening; blades capable of opening and closing the opening; a drive lever swingably supported, holding a movable iron piece and driving the blades; a self-holding type solenoid capable of adsorbing to the movable iron piece by a given attraction force in a non-energized state, and reducing the given attraction force in an energized state; a biasing member biasing the drive lever to move the drive lever away from the self-holding type solenoid; and a set member moving the drive lever to abut the drive lever with the self-holding type solenoid, wherein the self-holding type solenoid is energized to reduce the given attraction force when the drive lever is swung by the set member to abut the movable iron piece with the self-holding type solenoid.

This can suppress variations in the period from when an energization of a coil of the self-holding type solenoid starts from when the movable iron piece recedes from the self-holding type solenoid. It is thus possible to suppress variations in the timing of driving blades.

According to another aspect of the present invention, there is provided an optical apparatus including the above focal plane shutter.