Focal plane shutter and optical apparatus

This application is based upon and claims priority to Japanese Patent Application No. 2013-129949 filed on Jun. 20, 2013, subject matter of this patent document is incorporated by reference herein in its entirety.

(i) Technical Field

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

(ii) Related Art

There is known a focal plane shutter equipped with a buffering member absorbing the impact caused by stopping of a shutter. For example, the buffering member is provided to abut a drive arm driving the shutter or the shutter at a stop position thereof. Such a focal plane shutter is disclosed in Japanese Unexamined Patent Application Publication No. 2011-170226.

During the stopping of the shutter, the shutter or the drive arm is maintained in abutment with such a buffering member. Therefore, variation in size of the buffering member might cause variation in stop position of the shutter, so that the positional accuracy of the stop position of the shutter might not be ensured.

Further, in a case where the shutter or the drive arm is maintained in abutment with the buffering member for a long time, the shutter or the drive arm might adhere to the buffering member and might be difficult to be spaced therefrom, as depending on a material thereof. Furthermore, the shutter or the drive arm might be deformed.

It is therefore an object to provide a focal plane shutter and an optical apparatus capable of suppressing problems caused by a buffering member provided for absorbing impact caused by stopping of a shutter.

According to an aspect of the present invention, there is provided a focal plane shutter includes: a board including an opening; a shutter opening and closing the opening; a drive source driving the shutter; a drive lever driven by the drive source; a drive arm connected to the drive lever and driving the shutter; a restriction portion defining a stop position of the drive lever; and a buffering member elastically deformable, wherein, when the drive lever drives, abuts the restriction portion, and stops, at least one of the drive arm and the shutter temporarily abuts the buffering member, is spaced from the buffering member, and stops.

FIG. 1 is a front view of a focal plane shutter according to the present embodiment;

FIG. 2 is a block diagram of a camera including the focal plane shutter;

FIGS. 3A and 3B are respective explanatory views of a leading shutter actuator and a trailing shutter actuator;

FIG. 4 is an explanatory view of an operation of the focal plane shutter;

FIG. 5 is an explanatory view of an operation of the focal plane shutter;

FIG. 6 is an explanatory view of an operation of the focal plane shutter; and

FIGS. 7A and 7B are enlarged views of a buffering member and an arm when the trailing shutter stops.

In the following, the embodiment will be described with reference to drawings. FIG. 1 is a front view of a focal plane shutter 1 according to the present embodiment. FIG. 2 is a block diagram of a camera including the focal plane shutter 1 . FIGS. 3A and 3B are respective explanatory views of a leading shutter actuator 70 a and a trailing shutter actuator 70 b . The focal plane shutter 1 includes: a board 10 including an opening 11 ; a leading shutter 20 A and a trailing shutter 20 B opening and closing the opening 11 ; an arm 31 a and an assist arm 32 a for driving the leading shutter 20 A; and an arm 31 b and an assist arm 32 b for driving the trailing shutter 20 B. The arm 31 a and the assist arm 32 a are an example of a leading drive arm. The arm 31 b and the assist arm 32 b are an example of a trailing drive arm.

The board 10 is made of a synthetic resin, and includes the opening 11 having a rectangular shape. Although the leading shutter 20 A and the trailing shutter 20 B each include plural blades, blades 21 a and 21 b are only illustrated and other blades are omitted in FIG. 1 . Each of the blades 21 a and 21 b is made of a synthetic resin, and is formed into a thin shape. Further, each of the arms 31 a and 31 b and assist arms 32 a and 32 b is made of a synthetic resin and has a thin plate shape. These arms are swingably supported by the board 10 .

The focal plane shutter 1 includes a leading shutter actuator 70 a (hereinafter, referred to as actuator) and a trailing shutter actuator 70 b (hereinafter, referred to as actuator) as respective drive sources driving the leading shutter 20 A and the trailing shutter 20 B. The actuators 70 a and 70 b respectively include rotors 71 a and 71 b that are rotatable within a predetermined range in both directions. The actuators 70 a and 70 b will be described later in detail. The rotors 71 a and 71 b are respectively secured with a leading shutter drive lever (hereinafter referred to as a drive lever) 40 a and a trailing shutter drive lever (hereinafter referred to as a drive lever) 40 b serving as drive members.

The rotation of the rotor 71 a causes the drive lever 40 a to swing within a predetermined range. The drive lever 40 a is formed with a drive pin 43 a at its end. The drive pin 43 a is fitted into a fitting hole of the arm 31 a . Further, the board 10 is formed with an escape slot 13 a releasing the drive pin 43 a and having an arc shape. The abutment of the drive pin 43 a with end portions 13 a 1 and 13 a 2 of the escape slot 13 a restricts the swingable range of the drive lever 40 a . Additionally, the end portion 13 a 1 is provided with a buffering member (not illustrated) such as a rubber, but may not be provided.

Additionally, the board 10 is provided with a positioning portion 13 a 3 , and the drive pin 43 a abuts the end portion 13 a 2 and the positioning portion 13 a 3 . The positioning portion 13 a 3 protrudes from the front surface or the rear surface of the board 10 , and has a thickness thicker than another portion. The drive pin 43 a abuts both the end portion 13 a 2 and the positioning portion 13 a 3 , thereby ensuring an area of the drive pin 43 a abutting the board 10 when the drive pin 43 a stops. Thus, the drive pin 43 a is prevented from being tilted when the drive pin 43 a abuts the board 10 and stops.

In the state where the leading shutter 20 A recedes away from the opening 11 , the drive pin 43 a of the drive lever 40 a abuts the end portion 13 a 1 . In the state where the leading shutter 20 A closes the opening 11 , the drive pin 43 a of the drive lever 40 a abuts the end portion 13 a 2 .

Likewise, the drive lever 40 b includes a drive pin 43 b fitting into a fitting hole of the arm 31 b , and the drive pin 43 b abuts end portions 13 b 1 and 13 b 2 of an escape slot 13 b to restrict the swinging range of the drive lever 40 b . Additionally, a buffering member such as a rubber (not illustrated) is provided at the end portion 13 b 1 , but it may not be provided. In the state where the trailing shutter 20 B recedes from the opening 11 , the drive pin 43 b of the drive lever 40 b abuts the end portion 13 b 2 . In the state where the trailing shutter 20 B closes the opening 11 , the drive pin 43 b of the drive lever 40 b abuts the end portion 13 b 1 . Likewise, the board 10 is provided with a positioning portion 13 b 3 , and the drive pin 43 b abuts the end portion 13 b 2 and the positioning portion 13 b 3 . The positioning portion 13 b 3 protrudes from the front surface or the rear surface of the board 10 , and has a thickness thicker than smother portion. The escape slots 13 a and 13 b , the positioning portions 13 a 3 and 13 b 3 are examples of a restriction portion defining the stop positions of the drive levers 40 a and 40 b.

With the above configuration, the rotation of the rotor 71 a causes the drive lever 40 a to swing, thereby enabling the arm 31 a to swing. Therefore, the leading shutter 20 A moves to open or close the opening 11 . Likewise, the rotation of the rotor 71 b causes the drive lever 40 b to swing, thereby enabling the arm 31 b to swing. Therefore, the trailing shutter 20 B moves to open or close the opening 11 .

A rubber G is provided in the board 10 . The rubber G does not abut the arm 31 b in the finished state of the charging operation of the trailing shutter 20 B. However, the rubber G is provided in such a position as to temporarily abut the arm 31 b to absorb the impact thereof at the time when the trailing shutter 20 B drives and stops in the charging operation. It is therefore possible to, for example, prevent damage to the arm 31 b due to abutment of the drive pin 43 b with an edge of a fitting hole of the arm 31 b into which the drive pin 43 b is fitted. For example, it is possible to prevent a gap between the drive pin 43 b and the fitting hole of the arm 31 b near the opening 11 . The rubber G is an example of a buffering member. The buffering member is not limited to be made of rubber, and may be made of another material with elasticity such as silicone.

Thus, the escape slots 13 a and 13 b respectively restrict the swinging ranges of the drive levers 40 a and 40 b . In other words, the escape slots 13 a and 13 b respectively restrict the rotational ranges of the rotors 71 a and 71 b . This restricts the reciprocating ranges of the leading shutter 20 A and the trailing shutter 20 B. In the fully opened state in FIG. 1 , the drive pin 43 a and 43 b of the drive levers 40 a and 40 b respectively abut the end portions 13 a 2 and 13 b 2 , so that the escape slot 13 a restricts the drive lever 40 a and the rotor 71 a from swinging clockwise from the fully opened state in FIG. 1 . The escape sloe 13 b restricts the drive lever 40 b and the rotor 71 b from swinging counterclockwise from the fully opened state in FIG. 1 . Thus, in the fully opened state in FIG. 1 , the leading shutter 20 A and the trailing shutter 20 B are restricted from further moving away from the opening 11 .

A description will be given of a configuration of a camera equipped with the focal plane shutter 1 . As illustrated in FIG. 2 , the camera includes: the focal plane shutter 1 ; a control portion 300 ; and an image pickup element 400 . The control portion 300 controls an operation of the whole camera and includes a CPU, a ROM, and a RAM. Additionally, the camera includes lenses, not illustrated in FIG. 2 , for adjusting a focal length.

The control portion 300 controls energization states of the coils of the actuators 70 a and 70 b . The control portion 300 is an example of a drive control portion. The light enter the image pickup element 400 through the opening 11 , and the image pickup element 400 changes an object image formed by the entered light into electric signals. The image pickup element 400 is, for example, a CCD or a CMOS.

Additionally, there is not provided a set member for respectively positioning the leading shutter 20 A and the trailing shutter 20 B at charging positions. This is because the leading shutter 20 A and the trailing shutter 20 B can be positioned at the charging positions by the rotors 71 a and 71 b that are rotatable in both directions.

The actuators 70 a and 70 b are supported on the board 10 . The actuators 70 a and 70 b respectively drives the drive levers 40 a and 40 b . The actuator 70 a includes a rotor 71 a rotatably supported by the board 10 , a stator 74 a excited to generate magnetic force between the stator 74 a and the rotor 71 a , and a coil 76 a for exciting the stator 74 a . The rotor 71 a is a permanent magnet that is energized to have different polarities in the circumferential direction. A rotation axis of the rotor 71 a is connected to the spindle of the drive levers 40 a . Accordingly, energization to the coil 76 a causes the rotor 71 a to rotate so that the drive lever 40 a rotates. The rotation of the drive lever 40 a causes the leading shatter 20 A to drive. And also, opposite energization to the coil 76 a causes the rotor 71 a to rotate in the reverse direction so that the leading shutter 20 A drive in the direction opposite to the direction described above. Likewise, as for the actuator 70 b , the energization to the coil 76 b causes the rotor 71 b of the actuator 70 b , whereby the drive lever 40 b rotates, so that the trailing shutter 20 B moves. Also, opposite energization to the coil 76 b causes the trailing shutter 20 B to move in the direction opposite to the direction mentioned above. Additionally, the rotor 71 a and the drive lever 40 a may be indirectly connected through a gear or the like. That is, the drive lever 40 a has only to rotate in response to the rotation of the rotor 71 a.

Next, a description will be given of the operation of the focal plane shutter 1 . FIG. 1 illustrates an initial state of the focal plane shutter 1 . In the initial state, as illustrated in FIG. 1 , the leading shutter 20 A and the trailing shutter 20 B recedes away from the opening 11 .

A release button of the camera is pushed to start a charging operation. When the charging operation starts, the coil 76 a of the actuator 70 a is energized, so the leading shutter 20 A moves to close the opening 11 .

After that, the energization of the coils 76 a and 76 b of the actuators 70 a and 70 b is stopped in the state where the leading shutter 20 A closes the opening 11 and the trailing shutter 20 B are positioned away from the opening 11 . In such a way, the charging operation is finished. FIG. 4 illustrates the focal plane shutter 1 in the state where the charging operation is finished. Further, in the present embodiment, even after the energization is stopped, the charging finished state is maintained by the detent torque of the rotors 71 a and 71 b.

When a predetermined rest period elapses after the charging operation, an exposure operation starts. When the exposure operation starts, the coil 76 a of the actuator 70 a is energized, and the leading shutter 20 A moves to open the opening 11 . After a predetermined period elapses from the time when the coil 76 a of the actuator 70 a is energized, the coil 76 a of the actuator 70 b is energized, so the trailing shutter 20 B moves to close the opening 11 . When the leading shutter 20 A moves fully away from the opening 11 and the trailing shutter 20 B fully closes the opening 11 , the energization of the coils 76 a and 76 b of the actuators 70 a and 70 b are stopped. In such a way, the exposure operation is finished. A period from the time when the reading shutter 20 A starts moving to open the opening 11 to the time when the trailing shutter 20 B fully closes the opening 11 is referred to as an exposure period. FIG. 5 illustrates the state of the focal plane shutter 1 after the exposure operation is finished.

After the exposure operation is finished, the data are read from the image pickup element 400 by the RAM of the control portion 300 or memory of the camera side. Next, the coil 76 b of the actuator 70 b is energized, and the trailing shutter 20 B moves away from the opening 11 . Thus, the state returns to the initial state illustrated in FIG. 1 .

Herein, when the trailing shutter 20 B moves away from the opening 11 , the arm 31 b temporarily abuts the rubber G as illustrated in FIG. 6 . FIG. 7A is an enlarged view when the arm 31 b abuts the rubber G. After that, the arm 31 b is spaced from the rubber G. FIG. 7B is an enlarged view when the arm 31 b is spaced from the rubber G.

Just when the drive pin 43 b of the drive lever 40 b swings and abuts the end portion 13 b 2 and the positioning portion 13 b 3 , the arm 31 b tends to further swing by its inertial force and the trailing shutter 20 B tends to further move away from the opening 11 , Therefore, just when the drive lever 40 b is stopped by the abutment of the drive pin 43 b thereof with the end portion 13 b 2 and the positioning portion 13 b 3 , the arm 31 b temporarily abuts the rubber G in accordance with the inertial force. Thus, the impact of the arm 31 b is absorbed by the rubber G. After the arm 31 b abuts the rubber G, the arm 31 b is spaced from the rubber G in the state where the drive pin 43 b is kept stopped. For example, this is because that there is some gap between the drive pin 43 b and the fitting hole of the arm 31 b through which the drive pin 43 b penetrates, and that the arm 31 b is positionally displaced with respect to the drive lever 40 b by the gap while the inertial force exerts on the arm 31 b . Further, when the inertial force exerts on the arm 31 b , the arm 31 b might be temporarily deformed since the arm 31 b has a thin plate shape. For this reason, while the inertial force exerts on the arm 31 b after the drive lever 40 b swings and stops, the arm 31 b abuts the rubber G. After the inertial force on the arm 31 b disappears, the arm 31 b returns to an original state and is spaced from the rubber G. In other words, the position of the rubber G is set such that the arm 31 b temporarily abuts the rubber G when the drive lever 40 b is quickly stopped by abutting the end portion 13 b 2 and the positioning portion 13 b 3 in the state where the drive lever 40 b swings in a constant speed. Additionally, the drive pin 43 b of the drive lever 40 b is maintained in abutment with the end portion 13 b 2 and the positioning portion 13 b 3 by the detent torque of the rotor 71 b after the energization of the actuator 70 b is cut.

In this way, just when the drive pin 43 b of the drive lever 40 b abuts the end portion 13 b 2 and the positioning portion 13 b 3 , the arm 31 b tends to further swing by its inertial force. However, in this case, since the arm 31 b abuts the rubber G, this suppresses the damage to the arm 31 b due to the abutment of the drive pin 43 b with the edge of the fitting hole of the arm 31 b into which the drive pin 43 b fits. For example, this suppresses the increased gap between the drive pin 43 b and the fitting hole of the arm 31 b near the opening 11 .

If the gap near the opening 11 is increased, the moving distance of the drive pin 43 b required to abut the fitting hole of the arm 31 b is increased when the rotor 71 b rotates such that the trailing shutter 20 B moves toward the opening 11 . Thus, the timing when the trailing shutter 20 B starts moving is delayed, so that the variation in the exposure period by the trailing shutter 20 B is increased. However, the present embodiment suppresses the increase in the gap between the drive pin 43 b and the fitting hole, thereby suppressing the increase in the variation in the exposure period by the trailing shutter 20 B.

Further, in the present embodiment, the arm 31 b does not abut the rubber G in the state where the inertial force on the arm 31 b disappears. This can solve problems caused by the long-term abutment of the arm 31 b with the rubber G. For example, this suppresses the arm 31 b from being difficult to be separated from the rubber G, and suppresses the warp or the deformation of the arm 31 caused by urging the arm 31 b against the rubber G.

Further, since the arm 31 b does not abut the rubber G, the positional accuracy of the arm 31 b is ensured in the state where the trailing shutter 20 B stops. This is because there is some variation in size of the rubber G by forming and that the positional accuracy of the arm 31 b is difficult to be ensured if the arm 31 b always abuts the rubber G. Since the arm 31 b is connected to the trailing shutter 20 B, the positional accuracy of the arm 31 b is ensured, and the trailing shutter 20 B of the positional accuracy is also ensured. Specifically, in the present embodiment, the position where the trailing shutter 20 B recedes from the opening 11 is also the position where the trailing shutter 20 B starts moving in the charging operation. Therefore, the positional accuracy of the trailing shutter 20 B in the position to start in the charging operation is ensured, thereby suppressing the variation in the exposure period by the trailing shutter 20 B.

In addition, the rubber G may be provided in such a position that both the trailing shutter 20 B and the arm 31 b temporarily abut the rubber G, and may be provided in such a position that only the trailing shutter 20 B abuts the rubber G. Further, a buffering member may be provided so as to be temporarily abutted by at least one of the trailing shutter 20 B and the assist arm 32 b when the trailing shutter 20 B closes the opening 11 and stops.

Furthermore, a buffering member may be provided so as to be temporarily abutted by at least one of the leading shutter 20 A and the assist arm 32 a when the leading shutter 20 A closes the opening 11 and stops. Moreover, a buffering member may be provided so as to be temporarily abutted by at least one of the leading shutter 20 A and the arm 31 a when the leading shutter 20 A stops away from the opening 11 .

In addition, the focal plane shutter 1 according to the present embodiment is a normally open type that maintains the closed state of the opening 11 in the initial state. Thus, as for the camera in the present embodiment, movie output from the image pickup element 400 can be displayed on a monitor or the like in real time.

The focal plane shutter may be a normally closed type that maintains the opened state of the opening 11 in the initial state. In this case, the exposure operation is performed from the state where the opening 11 is closed. After the exposure operation, the leading shutter 20 A and the trailing shatter 20 B move to the initial state while maintaining the closed state of the opening 11 .

In the present embodiment, the actuators 70 a and 70 b respectively drive the leading shutter 20 A and the trailing shutter 20 B. However, the present invention is not limited to this arrangement. For example, an electromagnet and a spring may function as driving the drive lever and the shutter. In this case, the drive lever is provided with an iron piece absorbed to the electromagnet, and the drive lever is biased by the spring to move sway from the electromagnet. In the state where the iron piece of the drive lever is absorbed to the electromagnet, the energization state of the electromagnet is changed. As a result, the iron piece moves away from the electromagnet and the drive lever swings away from the electromagnet in accordance with the biasing force of the spring.

While the preferred 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.

Also, although the blades and the arms that are made of a synthetic resin have been described in the present embodiment, they may be made or a thin-shaped metal. In the above embodiment, the leading shutter and the trailing shutter are each composed of four blades. However, the leading shutter and the trailing shutter are not limited to these arrangements. The leading shutter and the trailing shutter may be each composed of two to five blades.