Image capturing apparatus, control method therefor, and program regarding foreign substance removal

This invention can more efficiently remove, at a more effective timing, a foreign substance such as dust adhering on an optical member inserted on the image capturing optical axis. An image capturing apparatus having an image sensor which photo-electrically converts an object image includes an optical element arranged on the image sensor on a side close to an object, a foreign substance removing unit which removes a foreign substance adhering to the surface of the optical element, an instruction unit which issues instructions to power on and power off the image capturing apparatus, and a control unit which controls the foreign substance removing unit to execute a foreign substance removing operation in accordance with the instruction to power off the image capturing apparatus by the instruction unit.

TECHNICAL FIELD

The present invention relates to a technique for removing a foreign substance such as dust adhering to the surface of an optical member inserted on the image capturing optical axis in an image capturing apparatus.

BACKGROUND ART

An image capturing apparatus such as a digital camera which captures an image by converting an image signal into an electrical signal receives an image capturing light beam using an image sensor, converts the photo-electrically converted signal output from the image sensor into image data, and records the resultant image data on a recording medium such as a memory card. A CCD (Charge Coupled Device) or C-MOS (Complementary Metal Oxide Semiconductor) is known as the image sensor.

In such an image capturing apparatus, an optical low-pass filter and infrared cut filter are arranged on the object side of the image sensor. It has been known that when foreign substances such as dust adhere to the surfaces of these filters or a cover glass of the image sensor, the adhesion portion is seen in a captured image as a black point to result in degradation in its quality.

Especially in a interchangeable single-lens reflex digital camera, since mechanical actuating units such as a shutter or quick return mirror are set near the image sensor, foreign substances such as dust produced from these actuating units sometimes adhere on the image sensor or low-pass filter. Also, dust or the like sometimes enters the camera main body from the opening of the lens mount and adheres on it (what is it?) during lens interchange.

As a prior art for solving the above problem, Japanese Patent Laid-Open No. 2002-204379 discloses a technique for providing, on the object side of the image sensor, a dustproof curtain which transmits an image capturing light beam, to cause a piezoelectric element to vibrate the dustproof curtain, thereby removing the foreign substance such as dust adhering to the surface of the dustproof curtain.

Japanese Patent Laid-Open No. 2003-330082 discloses a technique for executing the vibration operation for removing a foreign substance such as dust after activating the system upon power ON, upon attaching/detaching the lens or accessory unit, or prior to a release (image capturing) operation.

Japanese Patent Laid-Open No. 2004-264580 discloses a technique for changing the vibration mode of the vibration operation for removing a foreign substance such as dust, between a timing synchronized with a release (image capturing) operation and a timing corresponding to manual operation or lens attachment/detachment.

To remove the foreign substance adhering to the surface of the dustproof curtain, Japanese Patent Laid-Open No. 2002-204379 described above applies a voltage to the piezoelectric element which connects to the dustproof curtain, to vibrate the dustproof curtain by driving the piezoelectric element. In this case, removal of the foreign substance adhering to the dustproof curtain requires scattering the foreign substance from the dustproof curtain by applying a force stronger than the adhesion force of the foreign substance to it, so large energy is necessary. However, Japanese Patent Laid-Open No. 2002-204379 does not consider any method of efficiently driving the piezoelectric element to effectively remove the foreign substance when vibrating the dustproof curtain. This leads to high power consumption.

Japanese Patent Laid-Open No. 2003-330082 executes the vibration operation for removing a foreign substance such as dust not only when vibrating the dustproof curtain after activating the system upon power ON and when attaching/detaching the lens or accessory unit but also for every release operation. Therefore, the influence of power supply energy consumed by vibrating the dustproof curtain on the number of photographable images is not negligible.

Japanese Patent Laid-Open No. 2004-264580 executes the vibration operation for removing a foreign substance such as dust in a low power consumption mode only at a slow shutter speed or only for the valve in a release operation at a timing other than that corresponding to manual operation or lens attachment/detachment. However, the vibration operation with low power consumption, i.e., the vibration operation with low foreign substance removal capability sometimes fails to sufficiently remove the dust. This may only result in wasteful power consumption.

Both of the above-described prior arts execute the vibration operation for removing a foreign substance such as dust in lens interchange. Actually, a foreign substance such as dust in the outside air can readily enter the mirror box in lens interchange because the mount opens and the interior of the mirror box is exposed to the outside air.

However, even when a foreign substance such as dust enters the mirror box at this time, it merely adheres to the wall surface or structure in the mirror box in many cases. Therefore, the foreign substance rarely enters the region beyond the shutter curtain while it is closed. That is, while the shutter curtain is closed, a foreign substance rarely adheres to the surface of the optical member such as a filter which covers the image sensor unit. It is not always good to execute the vibration operation for removing a foreign substance such as dust in lens interchange.

Various references reveal that the foreign substance such as dust adhering on the optical member such as a filter strongly produces an adhesion force using, e.g., Van der Waals force, liquid cross-linking force, and electrostatic force. As measures against the adhesion due to an electrostatic force, there have been known a variety of techniques for, e.g., making the surface of the optical member such as a filter fall to GND to drop the surface potential, thereby removing the charges of the surface and preventing charging of the surface.

Various kinds of foreign substances such as dust adhere on the optical member such as a filter. It has been clarified by experiments that when a foreign substance is left adhered for a long period of time, its adhesion force generally increases and makes it hard to remove the foreign substance. This phenomenon occurs because the adhesion force such as a liquid cross-linking force increases as the foreign substance condenses upon a change in environment, i.e., temperature/humidity, or because the foreign substance gets stronger adhesion as the dirt repeatedly swells and dries upon a change in temperature/humidity. Also, an elastic material such as rubber gets stronger adhesion because fat and oil contained in itself bleed over time.

The present invention has been made in consideration of the above problems, and has as its object to more efficiently remove, at a more effective timing, a foreign substance such as dust adhering on an optical member inserted on the image capturing optical axis.

DISCLOSURE OF INVENTION

In order to solve the above problems and to achieve the object, according to a first aspect of the present invention, there is provided an image capturing apparatus including an image sensor which photo-electrically converts an object image, characterized by comprising an optical element arranged on the image sensor on a side close to an object, foreign substance removing means for removing a foreign substance adhering to a surface of the optical element, instruction means for issuing instructions to power on and power off the image capturing apparatus, and control means for controlling the foreign substance removing means to execute a foreign substance removing operation in accordance with the instruction to power off the image capturing apparatus by the instruction means.

According to a second aspect of the present invention, there is provided a method of controlling an image capturing apparatus including an image sensor which photo-electrically converts an object image and an optical element arranged on the image sensor on a side close to an object, characterized by comprising a foreign substance removing step of removing a foreign substance adhering to a surface of the optical element, an instruction step of issuing instructions to power on and power off the image capturing apparatus, and a control step of controlling to execute a foreign substance removing operation in the foreign substance removing step in accordance with the instruction to power off the image capturing apparatus in the instruction step.

EFFECTS OF THE INVENTION

According to the present invention, it is achieved to more efficiently remove, at a more effective timing, a foreign substance such as dust adhering on an optical member inserted on the image capturing optical axis.

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment

The schematic arrangement of a camera according to the first embodiment of the present invention will be explained first.

FIG. 1is a block diagram showing the schematic arrangement, mainly, the electrical arrangement of the camera according to the first embodiment of the present invention.

A plurality of circuit substrates are arrayed in a camera1001and form various kinds of electrical circuits. As shown inFIG. 1, the electrical arrangement of the camera1001includes a CPU1041, image signal processing circuit1016a, work memory1016b, storage medium1043, storage medium interface1042, display unit1046, display circuit1047, battery1045, power supply circuit1044, dustproof filter driving unit1048, and USB and IEEE1394 serving as a communication interface1049. The CPU1041serves as a control means, i.e., control circuit for systematically controlling the overall camera1001. The image signal processing circuit1016aexecutes various kinds of signal processes such as a signal process for converting an image signal acquired by an image sensor1027into a signal in a format compatible to recording. The work memory1016btemporarily records the image signal and image data processed by the image signal processing circuit1016a, and various types of information associated with them. The storage medium1043records the image data for recording in a predetermined format, which is generated by the image signal processing circuit1016a. The storage medium interface1042electrically connects the storage medium1043to the electrical circuits of the camera1001. The display unit1046includes a liquid crystal display (LCD) which displays an image. The display circuit1047electrically connects the display unit1046to the camera1001, receives the image signal processed by the image signal processing circuit1016a, and generates an image signal for display that is optimal for display using the display unit1046. The battery1045includes a secondary battery such as a dry cell. The power supply circuit1044receives power from an external power supply (AC), which is provided by the battery1045or a predetermined connecting cable (not shown), controls the power to be suitable for operating the camera1001, and distributes the power to the electrical circuits. The dustproof filter driving unit1048includes an oscillator and serves as an electrical circuit (driving circuit) for driving and controlling a piezoelectric element1022in accordance with a control signal output from the CPU1041to vibrate a dustproof filter1021included in an image capturing unit1015. The communication interface1049transfers a dust profile and captured image to the PC. Reference numeral1012ais a lens; and1014, a shutter unit.

The dust removing operation of the digital image capturing apparatus will be explained next with reference toFIG. 2. As the power supply is turned on (S201), it is determined whether a predetermined time has elapsed from when an active sweep (the vibration operation of the dustproof filter1021) is executed at the previous time (S202). If the predetermined time has elapsed (YES in step S202), it is determined whether the active sweep has been executed a predetermined number of times (S203). If the active sweep has not been executed the predetermined number of times (NO in step S203), the active sweep starts again (S204). If the predetermined time has not elapsed (NO in step S202), it is detected whether the power supply has been turned off (S205). If the power supply has been turned off (YES in step S205), it is determined whether the active sweep has been executed the predetermined number of times (S206). If the active sweep has not been executed the predetermined number of times (NO in step S206), the active sweep starts again (S207). If the power supply is ON (NO in step S205), the process waits until the predetermined time elapses again (S202).

As has been described above, according to the first embodiment, since it is hard to clean the dust that has been left adhering on the dustproof filter for a predetermined time in the digital image capturing apparatus, the vibration operation is executed after the elapse of the predetermined time. This makes it possible to facilitate cleaning of the dust.

When the digital image capturing apparatus is powered off, the dustproof filter is vibrated to clean the dust. This prevents the dust from being left adhering on the dustproof filter for a long period of time even when the user leaves the digital image capturing apparatus unused after power OFF.

Second Embodiment

FIGS. 3 and 4are perspective views showing the outer appearance of a single-lens reflex digital camera according to the second embodiment of the present invention. More specifically,FIG. 3is a front perspective view of the camera while a photographing lens unit is detached, andFIG. 4is a rear perspective view of the camera.

Referring toFIG. 3, reference numeral1denotes a camera main body having a gripping portion1awhich extends forward such that the user can easily, stably grip the camera in image capture. Reference numeral2denotes a mount portion which fixes a detachable photographing lens unit210(seeFIG. 5) to the camera main body1. Mount contacts21have a function of communicating, e.g., a control signal, status signal, and data signal between the camera main body1and the photographing lens unit210, and supplying power to the photographing lens unit210side. The mount contacts21may be able to execute not only electrical communication but also optical communication, speech communication, and the like.

Reference numeral4denotes a lens lock cancel button to be pressed in detaching the photographing lens unit. Reference numeral5denotes a mirror box which is accommodated in the camera housing and to which the image capturing light beam having passed through the photographing lens200is guided. A quick return mirror6is placed in the mirror box5. The quick return mirror6can be held at 45° with respect to the image capturing optical axis to guide the image capturing light beam to a pentagonal prism22(seeFIG. 5), or held at a position retreated from the image capturing light beam to guide it to an image sensor33(seeFIG. 5).

On the gripping side at the upper portion of the camera, a shutter button7serving as an activation switch for starting image capture, a main operation dial8for setting the shutter speed and lens F-number in accordance with the operation mode in image capture, and a set button10for setting the operation mode of the image capturing system are provided. An LCD display panel9displays parts of the operation results of these operation members.

The shutter button7turns on a switch SW1denoted by reference numeral7a(to be described later) by the first stroke (when pressed halfway), and turns on a switch SW2denoted by reference numeral7b(to be described later) by the second stroke (when pressed fully).

The set button10serves to, e.g., set whether to execute continuous shooting or image capture of one frame when the shutter button7is pressed once, and set a self image capture mode. The LCD display panel9displays these setting statuses.

At the center of the upper portion of the camera, an electronic flash unit11which pops up from the camera main body, a shoe groove12for electronic flash attachment, and an electronic flash contact13are arranged. An image capture mode setting dial14is arranged on the right side of the upper portion of the camera.

An openable/closable external terminal lid15is arranged on the side surface opposite to the gripping side. A video signal output jack16and USB output connector17are accommodated as external interfaces inside the external terminal lid15.

Referring toFIG. 4, a viewfinder eyepiece window18is mounted at the upper portion of the camera on its rear side, and a color liquid crystal monitor19which allows image display is set around the center of the rear surface. A sub operation dial20juxtaposed to the color liquid crystal monitor19plays an auxiliary role of the function of the main operation dial8, and is used to, e.g., set the exposure compensation amount relative to an appropriate exposure value calculated by an automatic exposure unit, in an AE mode of the camera. In a manual mode in which the user sets the shutter speed and lens F-number by his/her will, the main operation dial8sets the shutter speed and the sub operation dial20sets the lens F-number. The sub operation dial20is also used to display and select captured images to be displayed on the color liquid crystal monitor19.

Reference numeral43denotes a main switch for activating or deactivating the operation of the camera.

Reference numeral44denotes a cleaning instruction operation member for activating the cleaning mode and instructing to shake off the dirt adhering on the low-pass filter. Details of the cleaning instruction operation member44will be described later.

FIGS. 5A and 5Bare block diagrams showing the major electrical arrangement of the single-lens reflex digital camera according to the second embodiment. The same reference numerals as inFIGS. 3 and 4described above denote the common constituent components inFIG. 5.

Reference numeral100denotes a central processing unit (to be referred to as an MPU hereinafter) which includes a microcomputer built in the camera main body1. The MPU100executes various kinds of processes and instructions for the constituent components to control the operation of the camera.

Reference numeral100adenotes an EEPROM which is built in the MPU100and can store time measurement information of a time measurement circuit109and other information.

The MPU100connects to a mirror driving circuit101, focus detection circuit102, shutter driving circuit103, video signal processing circuit104, switch sense circuit105, photometry circuit106, LCD driving circuit107, battery check circuit108, the time measurement circuit109, a power supply circuit110, and piezoelectric element driving circuit111. These circuits operate under the control of the MPU100.

The MPU100communicates, via the mount contacts21, with a lens control circuit201built in the photographing lens unit210. The mount contacts21also have a function of transmitting a signal to the MPU100upon being connected to the photographing lens unit210. With this operation, the lens control circuit201communicates with the MPU100to be able to drive a photographing lens200and aperture stop204in the photographing lens unit210via an AF driving circuit202and aperture stop driving circuit203.

Although the photographing lens200is shown as one lens in the second embodiment for convenience, it is formed from a large number of lenses in practice.

The AF driving circuit202includes, e.g., a stepping motor, and focuses the image capturing light beam on the image sensor33by changing the focus lens position in the photographing lens200under the control of the lens control circuit201. The aperture stop driving circuit203includes, e.g., an auto iris, and obtains the optical F-number by changing the aperture stop204using the lens control circuit201.

The quick return mirror6guides the image capturing light beam passing through the photographing lens200to the pentagonal prism22, and partially transmits and guides it to a submirror30. The submirror30guides the transmitted image capturing light beam to a focus detection sensor unit31.

The mirror driving circuit101serves to drive the quick return mirror6to a position at which the object image is observable via the viewfinder and to a position retreated from the image capturing light beam. At the same time, the mirror driving circuit101drives the submirror30to a position at which the image capturing light beam is guided to the focus detection sensor unit31and to a position retreated from the image capturing light beam. More specifically, the mirror driving circuit101includes, e.g., a DC motor and gear train.

Reference numeral31denotes the focus detection sensor unit of a known phase difference scheme, which includes a field lens and reflecting mirror that are arranged near the imaging plane (not shown), a secondary imaging lens, an aperture stop, and a line sensor including a plurality of CCDs. The signal output from the focus detection sensor unit31is supplied to the focus detection circuit102and converted into an object image signal. The resultant signal is transmitted to the MPU100. The MPU100executes a focus detection arithmetic operation using a phase difference detection method on the basis of the object image signal. The MPU100calculates the defocus amount and defocus direction. On the basis of the calculated defocus amount and defocus direction, the MPU100drives the focus lens in the photographing lens200to the in-focus position via the lens control circuit201and AF driving circuit202.

Reference numeral22denotes the pentagonal prism which serves as an optical member for converting the image capturing light beam reflected by the quick return mirror6into an erect image and reflecting it. The user can observe the object image from the viewfinder eyepiece window18via the finder optical system.

The pentagonal prism22also partially guides the image capturing light beam to a photometry sensor37. Upon receiving the output from the photometry sensor37, the photometry circuit106converts it into a luminance signal in each area on the observation plane, and outputs the luminance signal to the MPU100. The MPU100calculates the exposure value from the obtained luminance signal.

Reference numeral32denotes a mechanical focal plane shutter which shields the image capturing light beam while the user observes the object image via the viewfinder. In image capture, the focal plane shutter32obtains a predetermined exposure time from the traveling time difference between front vanes and rear vanes (not shown) in accordance with a release signal. The shutter driving circuit103controls the focal plane shutter32upon receiving the command from the MPU100.

Reference numeral33denotes the image sensor which uses a CMOS serving as an image capturing device. The image capturing device may take various forms such as a CCD, CMOS, and CID.

Reference numeral34denotes a clamp/CDS (Correlated Double Sampling) circuit which can execute a fundamental analog process before A/D conversion and change the clamp level. Reference numeral35denotes an AGC (Automatic Gain Controller) which can execute a fundamental analog process before A/D conversion and change the AGC basic level. Reference numeral36denotes an A/D converter which converts the analog output signal from the image sensor33into a digital signal.

Reference numeral410denotes an optical low-pass filter which is formed by bonding and stacking a plurality of phase plates and a plurality of birefringent plates made of quartz and further bonding them to an infrared cut filter.

Reference numeral430denotes a stacked piezoelectric element which vibrates in accordance with a voltage signal supplied from the piezoelectric element driving circuit111that has received the command from the MPU100. The piezoelectric element430conducts the vibration to the optical low-pass filter410.

Reference numeral400denotes an image capturing unit which is obtained by unitizing the optical low-pass filter410, piezoelectric element430, and image sensor33together with other components (to be described later). The detailed structure of the image capturing unit400will be described later.

Reference numeral104denotes the video signal processing circuit which executes general image processes such as a gamma/Knee process, a filter process, and an information composition process for monitor display for the digital image data. Via a color liquid crystal driving circuit112, the color liquid crystal monitor19displays the image data for monitor display from the video signal processing circuit104.

The video signal processing circuit104can even store image data in a buffer memory37via a memory controller38in accordance with the instruction from the MPU100. The video signal processing circuit104also has a function of executing an image data compression process such as JPEG. In continuous image capture such as continuous shooting, it is also possible to temporarily store image data in the buffer memory37and sequentially read out unprocessed image data via the memory controller38. The video signal processing circuit104can sequentially execute an image process and compression process irrespective of the rate of image data input from the A/D converter36.

The memory controller38also has a function of causing a memory39to store image data input from an external interface40(equivalent to the video signal output jack16and USB output connector17shown inFIG. 3), and a function of causing the external interface40to output the image data stored in the memory39. The memory39is, e.g., an electronic flash memory detachable from the camera main body.

Reference numeral105denotes the switch sense circuit which transmits an input signal to the MPU100in accordance with the operation status of each switch. Reference numeral7adenotes the switch SW1which is turned on by the first stroke (half pressing) of the shutter button7. Reference numeral7bdenotes the switch SW2which is turned on by the second stroke (full pressing) of the shutter button7. As the shutter button7turns on the switch SW2, an image capture start instruction is transmitted to the MPU100. The switch sense circuit105connects to the main operation dial8, sub operation dial20, image capture mode setting dial14, main switch43, and cleaning instruction operation member44.

Reference numeral107denotes the LCD driving circuit which drives the LCD display panel9or a viewfinder liquid crystal display unit41in accordance with the instruction from the MPU100.

Reference numeral108denotes the battery check circuit which checks the battery for a predetermined period of time in accordance with the signal from the MPU100, and transmits the detection output to the MPU100. Reference numeral42denotes a power supply unit which supplies necessary power to the constituent components of the camera.

Reference numeral109denotes the time measurement circuit which measures the date and the time from when the main switch43is turned off until it is turned on at the next time. The time measurement circuit109can transmit the measurement result to the MPU100in accordance with the command from the MPU100.

The detailed structure of the image capturing unit400will be explained with reference toFIGS. 6 to 12.

FIG. 6is an exploded perspective view of the schematic internal structure of the camera to show the holding structure around the low-pass filter and image sensor.

The focal plane shutter32, a main body chassis300serving as the framework of the camera main body, and the image capturing unit400are housed in the mirror box5in this order from the object side. The image capturing unit400is fixed such that the image sensing plane of the image sensor33becomes parallel to the attachment surface of the mount portion2, that serves as a reference with which the photographing lens unit is to be attached, at a predetermined distance.

FIG. 7is a front view showing parts of the constituent members of a low-pass filter holding unit470.FIG. 8is a sectional view taken along a line A-A inFIG. 7.

Referring toFIGS. 7 and 8, reference numeral510denotes a plate-like image sensor holding member which has a rectangular opening and fixes the image sensor33into the opening so as to expose the image sensor33. The image sensor holding member510has, at its periphery, three arm portions for fixing itself to the mirror box5with screws. Referring toFIG. 8, reference numeral520denotes a rubber sheet (to be described later); and530, a stepped screw (to be described later).

Reference numeral420denotes a low-pass filter holding member which is made of a resin or metal and has a frame portion420athat surrounds the periphery of the optical low-pass filter410, and an arm portion420bthat extends to left and right and holds the attachment. An accommodation unit421for accommodating the piezoelectric element430is formed on one side of the frame portion420a. The one end face of the piezoelectric element430is fixed to the frame portion420aby, e.g., bonding.

Of the sides of the frame portion420a, on the side opposing the side having the accommodation unit421, an accommodation unit422for accommodating a biasing member440having a spring force is formed to bias the optical low-pass filter410against the piezoelectric element430.

That is, the optical low-pass filter410is set to be clamped between the piezoelectric element430and the biasing member440within the same plane of the low-pass filter holding member420. With this arrangement, the optical low-pass filter410can move while following the expansion/contraction motion of the piezoelectric element430.

The biasing member440may be a plate spring or coil spring made of a metal or a high-molecular polymer such as rubber or plastic as long as it is an elastic body. In the second embodiment, the biasing member440is a separate member. However, the low-pass filter holding member420may have a spring force so that the optical low-pass filter410moves while following the expansion/contraction motion of the piezoelectric element430.

A frame-like elastic member450as shown inFIGS. 8 and 9are inserted in the gap between the low-pass filter holding member420and the four sides of the optical low-pass filter410.

FIG. 9is a view showing details of the elastic member450.

The elastic member450includes an arm portion450aextending in the expansion/contraction direction of the piezoelectric element430, and an arm portion450bextending in a direction perpendicular to the expansion/contraction direction. The arm portion450aand arm portion450bhave different rigidities. That is, to allow the optical low-pass filter410to swing while following the expansion/contraction of the piezoelectric element430, the arm portion450bwhich receives an expansion/contraction action has a lower rigidity than the arm portion450ain the elastic member450. More specifically, the arm portion450ahas a rectangular cross section B-B, while the arm portion450bhas a cross section C-C with a partially hollow rectangular shape.

The arrangement which changes the rigidity between the arm portion450aand the arm portion450bis not limited to this. For example, arm portions formed from different members may be integrated by, e.g., coinjection molding.

On the four sides around the optical low-pass filter410, the piezoelectric element430and elastic member450seal the low-pass filter holding member420not to form any gap.

In the second embodiment, the piezoelectric element430uses a stacked piezoelectric element in which generally known piezoelectric bodies and internal electrodes are alternately stacked. The piezoelectric element430also adopts a d33type stacked piezoelectric element which applies a voltage in the stacking direction of the piezoelectric body. This makes it possible to obtain a larger amplitude (displacement) in the stacking direction. That is, it is possible to largely displace the optical low-pass filter410in the vibration direction. It is also possible to use various other kinds of piezoelectric elements as long as the optical low-pass filter410is displaced in its in-plane direction, i.e., a direction perpendicular to the optical axis.

In the second embodiment, the piezoelectric element430has a cross section perpendicular to its stacking direction (the vibration direction of the optical low-pass filter410) with a dimension in the optical axis direction, which is almost equal to the thickness of the optical low-pass filter410. The cross section has a longer dimension in a direction perpendicular to the optical axis direction and vibration direction to increase the area of piezoelectric bodies to be stacked. This prevents an increase in dimension of the camera along the optical axis direction while attaining a larger force.

Forming the piezoelectric element430to have the above-described cross section increases the allowable buckling stress with respect to its rotation within a plane perpendicular to the optical axis. This makes it possible to prevent the buckling fracture of the piezoelectric element even when the optical low-pass filter410vibrates with a rotational component within a plane perpendicular to the optical axis.

An additional explanation of this mechanism will be given with reference toFIG. 10.

Letting L be the length of the piezoelectric element430in a direction perpendicular to its expansion/contraction direction (vibration direction), a force which is produced by a moment M generated upon rotation of the optical low-pass filter410within a plane perpendicular to the optical axis and acts at the edge of the piezoelectric element430is given by:
forceF=M/(L/2)

As is obvious from the above equation, the force F acting at the edge of the piezoelectric element changes depending on a dimension perpendicular to the expansion/contraction direction. Maximizing this dimension makes it possible to reduce the force acting at the edge of the piezoelectric element and to increase the allowable buckling stress by the moment M.

If a thickness T2of the piezoelectric element430in the optical axis direction is equal to the length L, the piezoelectric element430interferes with the image sensor33on the eyepiece side and the focal plane shutter32on the objective side. Elimination of this interference requires widening the gap between the image sensor33and the focal plane shutter32to result in an increase in size of the camera. Preferably, the thickness T2of the piezoelectric element430is smaller than the length L. Referring toFIG. 10, reference symbol T1denotes the thickness of the optical low-pass filter410.

Although the optical low-pass filter410directly abuts against the piezoelectric element430in the second embodiment, a spacer may be inserted between them. When a spacer is inserted between the optical low-pass filter410and the piezoelectric element430, the piezoelectric element430needs only apply vibration to the spacer. This makes it possible to relax restriction on the layout.

As described above, the piezoelectric element430is held in a direction (the vertical direction of the camera) in which the direction of expansion/contraction due to voltage application becomes perpendicular to the optical axis. The piezoelectric element430is bonded and fixed to the low-pass filter holding member420, but is merely in contact with the optical low-pass filter410without being bonded to it. That is, the vibration surface of the piezoelectric element430with respect to the optical low-pass filter410is not fixed to it.

The elastic member450supports the optical low-pass filter410to allow the optical low-pass filter410to move not only in the expansion/contraction direction of the piezoelectric element430but also in the image capturing optical axis direction by a predetermined amount. That is, the optical low-pass filter410is allowed to incline with respect to a plane perpendicular to the image capturing optical axis to some extent upon receiving vibration conducted from the piezoelectric element430. With this arrangement, the foreign substance adhering on the optical low-pass filter410can be accelerated even in the image capturing optical axis direction to result in more preferable foreign substance removal. However, if the optical low-pass filter410is allowed to incline with respect to a plane perpendicular to the image capturing optical axis, and the piezoelectric element430is bonded to the optical low-pass filter410, a shearing stress acts on the piezoelectric element430. Especially, the above arrangement is not preferable for a stacked piezoelectric element as in the second embodiment because it fractures due to such a shearing stress.

To solve the above problem, in the second embodiment, the vibration surface of the piezoelectric element430with respect to the optical low-pass filter410is not bonded to the optical low-pass filter410but is merely in contact with it. Even when the optical low-pass filter410inclines with respect to a plane perpendicular to the image capturing optical axis, no shearing stress acts on the piezoelectric element430. That is, as the optical low-pass filter410inclines with respect to a plane perpendicular to the image capturing optical axis, the vibration surface of the piezoelectric element430relatively shifts from the contact surface of the optical low-pass filter410. The piezoelectric element430never directly receives the rotation force.

At the same time, as the vibration surface of the piezoelectric element430is not bonded to the optical low-pass filter410, the followability of the optical low-pass filter410with respect to the vibration of the piezoelectric element430suffers. As described above, this problem is dealt with by arranging the optical low-pass filter410to be clamped between the piezoelectric element430and the biasing member440within the same plane. That is, the optical low-pass filter410is biased using, e.g., a spring from the opposite side. This makes it possible to always bring the optical low-pass filter410into contact with the piezoelectric element430even when the piezoelectric element430is driven in the contraction direction.

With this arrangement, preferable followability of the optical low-pass filter410with respect to the vibration is ensured while avoiding the fracture of the piezoelectric element430due to a shearing stress.

FIG. 11is an exploded perspective view for further explaining the constituent components of the image capturing unit400described with reference toFIGS. 6 and 7.

Reference numeral500denotes an image sensor unit which includes at least the image sensor33and image sensor holding member510. Reference numeral470denotes the low-pass filter holding unit which includes at least the optical low-pass filter410, low-pass filter holding member420, piezoelectric element430, biasing member440, elastic member450, and a regulating member460.

The regulating member460and low-pass filter holding member420clamps the optical low-pass filter410at predetermined gaps in the image capturing optical axis direction. This regulates the movement of the optical low-pass filter410in the image capturing optical axis direction. Such regulation prevents the optical low-pass filter410from inclining with respect to a plane perpendicular to the image capturing optical axis at a predetermined angle or more.

The regulating member460also has an opening portion for regulating the opening of the optical low-pass filter410to shield the image capturing light beam which enters portions other than the opening portion. This prevents the image capturing light beam from entering the image sensor from the peripheral portion of the optical low-pass filter410so that the reflected light does not cause any ghost.

Reference numeral520denotes the elastic rubber sheet. A stepped screw530locks the arm portion420bof the low-pass filter holding member420to the image sensor holding member510through the rubber sheet520to lock the low-pass filter holding unit470to the image sensor unit500.

FIG. 12is a view for explaining details of the rubber sheet520. As shown inFIG. 12, the rubber sheet520is configured by integrally forming a frame portion520aand two arm portions520b. The two arm portions520beach have a support portion for supporting the stepped screw530and oppose each other.

The surface of the frame portion520aon the image sensor33side is in tight contact with the image sensor holding member510, while the surface of the frame portion520aon the optical low-pass filter410side is in tight contact with the frame portion420aof the low-pass filter holding member420. With this arrangement, the rubber sheet520seals the interval between the low-pass filter holding member420and the image sensor33, while the piezoelectric element430and elastic member450seal the interval between the optical low-pass filter410and the low-pass filter holding member420. The space between the optical low-pass filter410and the image sensor33becomes an enclosed space for preventing the entrance of a foreign substance such as dirt.

Even when the piezoelectric element430vibrates, the vibration of the low-pass filter holding unit470is hardly conducted to the image sensor33because the rubber sheet520forms a floating support structure using its elasticity.

Although a rubber sheet has exemplified the constituent component520in the second embodiment, the present invention is not limited to this as long as the constituent component520is made of a member which has an airtightness high enough to prevent the entrance of a foreign substance, and a vibrational absorbability high enough not to conduct the vibration of the optical low-pass to the image sensor33. For example, a member such as a gel sheet or a double-sided tape made of sponge having a predetermined thickness is applicable to the constituent component520.

The vibration of the optical low-pass filter410will be explained.

When the MPU100serving as a control means instructs the piezoelectric element driving circuit111for driving the piezoelectric element430to apply a predetermined cycle voltage to the piezoelectric element430, the piezoelectric element430vibrates while expanding/contracting in a direction almost perpendicular to the optical axis (the vertical direction of the camera). The optical low-pass filter410is located to be clamped between the piezoelectric element430and the biasing member440in almost the same in-plane direction. Since the optical low-pass filter410and piezoelectric element430are held to be always in contact with each other, the vibration of the piezoelectric element430is conducted to the optical low-pass filter410.

As described above, the rubber sheet520seals the interval between the low-pass filter holding member420and the image sensor33, while the piezoelectric element430and elastic member450seal the interval between the optical low-pass filter410and the low-pass filter holding member420. The space between the optical low-pass filter410and the image sensor33is an enclosed space free from any entrance of dirt or the like. At the same time, the image sensor unit500and the low-pass filter holding unit470including, e.g., the optical low-pass filter410clamp the rubber sheet520. The rubber sheet520absorbs the vibration of the low-pass filter holding unit470. The vibration of the low-pass filter holding unit470is hardly conducted to the image sensor33.

With this arrangement, the vibration of the piezoelectric element430, if any, hardly affects the image sensor33. This makes it possible to limit the structure which receives vibration and, especially, to selectively vibrate the optical low-pass filter410to be vibrated. It is therefore possible to minimize the total mass of the structure which receives vibration. The piezoelectric element430can be driven with smaller energy.

The vibration of the optical low-pass filter410is hardly conducted to the image sensor33. This makes it possible to prevent damage such as bond removal of the image sensor33. When an impact acts on the camera, it is hardly conducted to the piezoelectric element430. This makes it possible to prevent the piezoelectric element430from being damaged upon an impact applied to the camera.

As described above, the optical low-pass filter410and piezoelectric element430are not bonded, i.e., connected. Even when the piezoelectric element driving circuit111applies a predetermined cycle voltage to the piezoelectric element430to expand/contract it, a force in a direction in which the piezoelectric element430pushes out the optical low-pass filter410only acts on the piezoelectric element430, and no force in a direction in which the optical low-pass filter410pulls the piezoelectric element430acts on the piezoelectric element430by an inertia force. This makes it possible to prevent damage such as removal of a stacked portion because an excessive tensile force never acts on the piezoelectric element430even when a high-frequency voltage in an ultrasonic range is applied to the piezoelectric element430.

An operation for removing the foreign substance such as dust adhering to the surface of the optical low-pass filter410according to the second embodiment will be explained with reference to the flowchart shown inFIG. 13.

The power supply is turned on via the main switch43in step S1to activate the camera in step S2. More specifically, the MPU100controls the power supply circuit110to supply power to each circuit, initializes the camera, and executes a camera ON operation which allows an image capturing operation.

It is determined in step S3whether the user has operated the cleaning instruction operation member44. If the user has operated the cleaning instruction operation member44(YES in step S3), the process advances to step S4; otherwise (NO in step S3), the process advances to step S5.

Although the cleaning instruction operation member44is provided in the second embodiment, the present invention is not limited to this. The operation member for issuing an instruction to shift the camera main body1to a cleaning mode is not limited to a mechanical button. For example, there is available a method of issuing an instruction using a cursor key or instruction button from a menu displayed on the color liquid crystal monitor19.

Upon receiving the cleaning mode start command, the MPU100shifts the camera main body1to a cleaning mode in step S4. The cleaning mode is a mode for causing the piezoelectric element430to vibrate the optical low-pass filter410to shake off the foreign substance adhering to the surface of the optical low-pass filter410.

As the cleaning mode starts, the power supply circuit110supplies power necessary for the cleaning mode to the units in the camera main body1as needed. Parallel to this operation, the remaining battery level of the power supply unit42is detected to transmit the detection result to the MPU100.

Upon receiving the cleaning mode start signal, the MPU100sends a driving signal to the piezoelectric element driving circuit111. Upon receiving the driving signal from the MPU100, the piezoelectric element driving circuit111generates a cycle voltage for driving the piezoelectric element430, and applies it to the piezoelectric element430. The piezoelectric element430expands/contracts in accordance with the applied voltage. As the piezoelectric element430expands, the optical low-pass filter410moves in a direction perpendicular to the optical axis (in-plane direction) upon being pushed out by the piezoelectric element430, and the biasing member440contracts by the movement amount of the optical low-pass filter410. As the piezoelectric element430contracts, the optical low-pass filter410is biased against the piezoelectric element430by the biasing member440to move while following the contraction motion of the piezoelectric element430. As the piezoelectric element driving circuit111applies a cycle voltage to the piezoelectric element430, the above-described motion repeats itself so that the optical low-pass filter410vibrates in a direction perpendicular to the optical axis, i.e., the in-plane direction while following cyclic expansion/contraction of the piezoelectric element430.

When the cleaning mode is complete, the process advances to step S5.

Upon receiving signals from the SW17a, SW27b, main operation dial8, sub operation dial20, image capture mode setting dial14, and other switches, the MPU100executes a camera operation such as image capture/setting of the camera in step S5. Since this operation is generally known, a detailed description thereof will be omitted.

It is determined in step S6whether the camera has been powered off via the main switch43in a camera standby state. If the camera has been powered off (YES in step S6), the process advances to step S7; otherwise (NO in step S6), the process returns to step S3.

In step S7, the same operation in the cleaning mode as that in step S4is executed. The process then advances to step S8.

In the cleaning mode in step S7, the piezoelectric element430may be driven by changing its parameters such as the driving frequency, driving time, and control method from those used in step S4in consideration of the power consumption and operation time of the camera.

In step S8, the MPU100of the camera main body1controls to shut down each circuit, store necessary information and the like in the EEPROM100a, and control the power supply circuit110to execute a power OFF operation for shutting off power supply to desired circuits.

As described above, according to the second embodiment, the cleaning mode is executed to remove the foreign substance adhering on the optical low-pass filter410, not only at a timing intended by the user but also when the camera is powered off. Subsequently, the camera is powered off.

Various kinds of foreign substances adhere on the optical low-pass filter410. The present applicant and others have clarified by experiments that when a foreign substance is left adhering for a long period of time, it is hardly removed even by vibration in the cleaning mode. This phenomenon is supposed to occur because the adhesion force such as a liquid cross-linking force increases as the foreign substance condenses upon a change in environment, i.e., temperature/humidity, or because the foreign substance gets higher adhesion as the dirt repeatedly swells and dries upon a change in temperature/humidity. Also, an elastic material such as rubber gets higher adhesion because fat and oil contained in itself bleed over time.

Executing the cleaning mode at the power OFF operation timing, after which the user leaves the camera unused for a long period of time at a high probability, makes it possible to more efficiently/effectively remove the foreign substance. This operation can be said to be more efficient/effective than foreign substance removal at the power ON operation timing before which the user has left the camera unused for a long period of time, and it has become hard to remove the dirt at a high probability. Note that the power OFF operation timing does not indicate the power OFF moment, but implies a case in which the foreign substance is removed with a slight time lag from power OFF.

The second embodiment has been described with reference to the case in which the foreign substance is removed upon the power OFF operation via the main switch43. However, even in a camera OFF operation similar to power OFF after the elapse of a predetermined period of time in an ON state, the same effect can be produced as long as the cleaning mode (foreign substance removal) is executed in advance. For example, the cleaning mode may be done at the timing for shifting to a sleep state in which power supply to the system is temporarily limited to save power.

The description that the foreign substance is removed upon the power OFF operation via the main switch43indicates that the OFF operation signal from the main switch43is transmitted to the MPU100and the MPU100issues a command to cause the piezoelectric element driving circuit111to remove the foreign substance. The description that the cleaning mode is executed at the timing for shifting to a sleep state also indicates that the MPU100issues a command at the timing for shifting to a sleep state to cause the piezoelectric element driving circuit111to remove the foreign substance.

Third Embodiment

Another form of the apparatus which removes a foreign substance adhering on an optical element such as an optical low-pass filter will be explained with reference toFIGS. 14 and 15.

An image capturing device600comprises an optical element611such as an optical low-pass filter, a holding member612for holding the optical element611, and a solid-state image capturing unit613which includes a solid-state image sensor613band a cover member613afor protecting the solid-state image sensor613b. The image capturing device600also comprises a seal member614for sealing the interval between the optical element611and the cover member613aof the solid-state image capturing unit613.

Reference numeral621denotes a lever which connects to a driving unit (not shown) and can travel in a direction indicated by an arrow D inFIG. 14in parallel to the surface of the optical element611. The lever621comprises an abrasion-resistant fiber622(e.g., Dyneema manufactured by Toyobo Co. Ltd.). The abrasion-resistant fiber622serves as a cleaning brush.

Reference numeral623denotes a foreign substance adhering on the optical element611. The abrasion-resistant fiber622has a length adjusted to come into contact with the optical element611.

The lever621is positioned at the upper portion ofFIG. 14and travels downward as the operation in the cleaning mode starts. Along with this, the abrasion-resistant fiber622also travels downward. When the abrasion-resistant fiber622travels downward while being in contact with the optical element611, the foreign substance623adhering on the optical element611is shaken off. After scanning the surface of the optical element611downward, the abrasion-resistant fiber622returns to the upward original position.

Also in the third embodiment, the operation in the cleaning mode is done at the camera power OFF operation timing. That is, executing the cleaning mode at the power OFF operation timing, after which the user leaves the camera unused for a long period of time at a high probability, makes it possible to more efficiently/effectively remove the foreign substance.

Fourth Embodiment

Another form of the apparatus which removes a foreign substance adhering on an optical element such as an optical low-pass filter will be explained with reference toFIGS. 16 and 17.

An image capturing device700comprises an optical element711such as an optical low-pass filter, a holding member712for holding the optical element711, and a solid-state image capturing unit713which includes a solid-state image sensor713band a cover member713afor protecting the solid-state image sensor713b. The image capturing device700also comprises a seal member714for sealing the interval between the optical element711and the cover member713aof the solid-state image capturing unit713.

Reference numeral721denotes an insulating portion which is made of polyimide and can travel in a direction indicated by an arrow E inFIG. 16in parallel to the surface of the optical element711. A coil (not shown) can switch the insulating portion721between a charged state and a charge-removed state. Reference numeral723denotes a foreign substance adhering on the optical element711.

The insulating portion721is positioned at the upper portion ofFIG. 16. As the operation in the cleaning mode starts, a predetermined voltage is applied to the coil (not shown). The insulating portion721is charged and travels downward.

As the insulating portion721is charged, if the charged foreign substance723is adhering to the surface of the optical element711, the charged foreign substance723and insulating portion721produce an electrostatic force between themselves. The insulating portion721attracts by the electrostatic force (electrostatic attraction force) the foreign substance723against its adhesion force acting on the surface of the optical element711. The foreign substance723attracted to the insulating portion721by the electrostatic force remains on the surface of the insulating portion721. When the insulating portion721completes downward travel, the coil (not shown) applies, to the insulating portion721, a voltage having a charge opposite to that applied in charging. The insulating portion721is then charge-removed. With this charge removing operation, the foreign substance723adhering to the surface of the insulating portion721by the electrostatic force separates and falls from the surface of the insulating portion721by gravity.

After that, the insulating portion721returns to the upward original position.

Also in the fourth embodiment, the operation in the cleaning mode is done at the camera power OFF operation timing. That is, executing the cleaning mode at the power OFF operation timing, after which the user leaves the camera unused for a long period of time at a high probability, makes it possible to more efficiently/effectively remove the foreign substance.

Other Embodiment

The object of each embodiment is achieved even by the following method. That is, a storage medium (or recording medium) which records software program codes for implementing the functions of the above-described embodiments is supplied to the system or apparatus. The computer (or CPU or MPU) of the system or apparatus reads out and executes the program codes stored in the storage medium. In this case, the program codes read out from the storage medium implement the functions of the above-described embodiments by themselves, and the storage medium which stores the program codes constitutes the present invention. In addition to the case in which the functions of the above-described embodiments are implemented when the readout program codes are executed by the computer, the present invention incorporates the following case. That is, the functions of the above-described embodiments are implemented when the operating system (OS) running on the computer performs part or all of actual processing on the basis of the instructions of the program codes.

The present invention also incorporates the following case. That is, the program codes read out from the storage medium are written in the memory of a function expansion card inserted into the computer or a function expansion unit connected to the computer. After that, the functions of the above-described embodiments are implemented when the CPU of the function expansion card or function expansion unit performs part or all of actual processing on the basis of the instructions of the program codes.

When the present invention is applied to the storage medium, the storage medium stores program codes corresponding to the above-described procedures.

This application claims the benefit of Japanese Patent Application No. 2006-063978, filed Mar. 9, 2006, and Japanese Patent Application No. 2006-198709, filed Jul. 20, 2006, which are hereby incorporated by reference herein in their entirety.