JP2012124717A - Imaging apparatus and control method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus and a control method for the same capable of reducing power consumption and removing foreign objects adhering to a filter properly aligned on an optical axis.SOLUTION: An imaging apparatus includes vibration means such as a piezoelectric device for vibrating a filter disposed on an optical axis to remove a foreign object adhering to the filter. At least during a period when the adhering foreign object moves from one end to the other end on the filter, a voltage applied to the vibration means is controlled as follows. That is, the voltage is controlled to apply a first voltage to the vibration means at least at the start of voltage application to place the foreign object adhering to the filter into a movable state, and to apply a second voltage which is lower than the first voltage at the end of voltage application to allow the foreign object in a movable state to move.

Description

  The present invention relates to a technique for removing foreign substances adhering to a filter disposed on an optical axis.

  An imaging apparatus such as a digital single-lens reflex camera includes an imaging device, photoelectrically converts an optical image formed on the imaging device via an optical system such as a lens, and converts an output analog image signal to convert image data. Obtainable. The imaging device is provided with an optical low-pass filter and an infrared absorption filter on the optical axis on the subject side to reduce the effects of infrared light components contained in the optical image, false colors, moire, etc. Placed in the device.

  For example, in an imaging device with interchangeable lenses, mechanically operated members such as shutters and quick return mirrors are arranged in the vicinity of the imaging unit, and dust is adhering to the filter surface of the imaging unit when the lenses are replaced or when the members are operated. Such foreign matter may adhere. When a foreign object adheres, the image data obtained by taking a photograph appears as a black dot, for example, and causes image quality deterioration.

  In order to remove foreign substances adhering to the filter surface of the imaging unit in this way, a technique is known in which the filter surface is vibrated at a resonance frequency by a piezoelectric element such as a piezoelectric element. However, depending on the surface condition such as the temperature of the filter surface of the imaging unit, the adhering force of the adhering foreign matter differs, and a sufficiently removed result may not be obtained. Patent Document 1 discloses a technique for detecting the temperature of the filter surface and controlling the driving conditions of the vibration element applied to the filter surface.

JP 2009-165032 A

  As shown in FIG. 6, in the conventional foreign matter removal method using the vibration of the piezoelectric element as in Patent Document 1, the amplitude of the voltage applied to the piezoelectric element has a constant value from the start of application to the end of application. Had. The constant voltage value applied to the piezoelectric element is a voltage value necessary to first move the foreign matter adhering to the filter into a movable state and then remove it by moving it from the filter. However, the voltage value required to move the foreign matter once released from the adhesive force such as liquid bridging force or electrostatic attraction and moving on the filter is to make the foreign matter attached to the filter movable. Is smaller than the voltage value required for.

  In addition, the amplitude of vibration applied by the piezoelectric element to remove foreign matter attached to the filter surface of the imaging unit is inversely proportional to the square of the size of the attached foreign matter when the vibration frequency is fixed at the resonance frequency. It is known. Due to the recent increase in the number of pixels and the increase in the density of image sensors and the reduction in the distance between the image sensor and the filter due to the downsizing of the image pickup apparatus, the size of foreign objects that can be recognized by image data obtained by taking a picture tends to decrease. is there. That is, even a small foreign object causes a deterioration in image quality. Therefore, in order to remove the foreign object, it is necessary to apply a higher voltage to the piezoelectric element to increase the amplitude.

  That is, when the voltage applied to the piezoelectric element is increased in order to remove small foreign matter, the method of applying a constant voltage from the start of application to the end of application as in the prior art increases unnecessary power consumption. Will be invited.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to remove foreign matters attached to a filter appropriately disposed on the optical axis while suppressing power consumption.

In order to achieve the above object, an imaging apparatus of the present invention has the following configuration.
An imaging element; an optical member disposed in front of the imaging element; a vibrating unit that vibrates the optical member when a voltage is applied; and a control unit that controls a voltage applied to the vibrating unit. The control means applies a first voltage to the vibration means when the vibration means starts to vibrate the optical member, and after applying the first voltage to the vibration means, the first voltage is applied to the vibration means. A second voltage smaller than the voltage is applied to the vibrating means.

  With such a configuration, according to the present invention, it is possible to remove foreign substances attached to a filter appropriately disposed on the optical axis while suppressing power consumption.

1 is a block diagram illustrating a functional configuration of a digital camera according to an embodiment of the invention. FIG. 3 is an exploded perspective view illustrating the imaging unit according to the embodiment. The figure which illustrated the voltage applied in the foreign substance removal processing concerning an embodiment. The figure which illustrated the voltage applied in the foreign substance removal processing concerning modification 1. The figure which illustrated the voltage applied in the foreign substance removal process concerning the modification 2. The figure which showed the voltage applied in the foreign material removal process of a prior art.

(Embodiment)
Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. Note that, in the embodiment described below, an example in which the present invention is applied to a digital camera capable of removing foreign matter attached to an imaging surface of an imaging unit having an imaging element as an example of an imaging apparatus will be described. However, the present invention can be applied to any optical apparatus that can remove foreign matters attached to a filter disposed on the optical axis.

FIG. 1 is a block diagram showing a functional configuration of a digital camera 100 according to an embodiment of the present invention.
A microcomputer (hereinafter referred to as MPU) 101 is, for example, a central processing unit, and controls the operation of each block included in the digital camera 100. The MPU 101 is connected to a mirror drive circuit 102, a focus drive circuit 103, a shutter drive circuit 104, an image signal processing circuit 105, a switch sensor circuit 106, a photometry circuit 107, and a piezoelectric element drive circuit 111. The circuit controls the MPU 101. It works by.

  The MPU 101 communicates with the lens control circuit 202 in the imaging lens unit 200 via the mount contact 21. When the imaging lens unit 200 is connected, the MPU 101 receives a signal via the mount contact 21 to determine that the lens control circuit 202 of the imaging lens unit 200 is communicable. The lens control circuit 202 receives the control signal from the MPU 101 to drive the imaging lens 201 and the diaphragm 205 in the imaging lens unit 200 via the AF driving circuit 203 and the diaphragm driving circuit 204. In FIG. 1, only one image pickup lens 201 is shown for convenience, but it is actually constituted by a large number of lens groups such as a focus lens.

  The AF driving circuit 203 includes, for example, a stepping motor, and changes the focus lens position in the imaging lens 201 under the control of the lens control circuit 202 to focus the imaging light flux on the imaging element 33. The aperture driving circuit 204 is an aperture mechanism such as an auto iris, and changes the aperture amount of the aperture 205 under the control of the lens control circuit 202.

  The main mirror 6 guides the photographic light flux passing through the imaging lens 201 to the pentaprism 22 while being held at an angle of 45 degrees with respect to the photographic optical axis shown in FIG. Lead to 30. The sub mirror 30 guides the photographic light beam transmitted through the main mirror 6 to the focus detection sensor unit 31.

  The mirror drive circuit 102 is constituted by, for example, a DC motor and a gear train, and drives the main mirror 6 to a position where the subject image can be observed by the finder and a position where the subject image is retracted from the photographing light flux. When the main mirror 6 is driven, the sub mirror 30 is simultaneously moved to a position for guiding the photographing light beam to the focus detection sensor unit 31 and a position for retracting from the photographing light beam.

  The focus detection sensor unit 31 is composed of a field lens, a reflection mirror, a secondary imaging lens, a diaphragm, a line sensor composed of a plurality of CCDs, etc. arranged in the vicinity of an imaging surface (not shown), and a phase difference type focus detection. I do. A signal output from the focus detection sensor unit 31 is supplied to the focus drive circuit 103, converted into a subject image signal, and then transmitted to the MPU 101.

  The MPU 101 performs focus detection calculation by the phase difference detection method based on the subject image signal. Specifically, the MPU 101 calculates the defocus amount and direction using the subject image signal, and in accordance with the calculated defocus amount and direction, the focus in the imaging lens 201 is obtained via the lens control circuit 202 and the AF drive circuit 203. The lens is driven to the in-focus position.

  The pentaprism 22 converts and reflects the photographing light beam reflected by the main mirror 6 into an erect image. Thereby, the photographer can observe the subject image from the viewfinder eyepiece window 18 through the viewfinder optical system. The pentaprism 22 also guides a part of the photographing light flux to the photometric sensor 37. The photometric circuit 107 converts the photometric value output from the photometric sensor 37 into a luminance signal for each area on the observation surface and outputs the luminance signal to the MPU 101. The MPU 101 calculates an exposure value based on the luminance signal.

  The shutter unit 32 is, for example, a mechanical focal plane shutter. When the photographer observes a subject image through the viewfinder eyepiece window 18, the shutter front curtain is in the light shielding position and the shutter rear curtain is in the exposure position. It becomes. Further, at the time of shooting, the shutter front curtain passes through the imaging light flux by performing exposure running in which the shutter front curtain moves from the light shielding position to the exposure position, and the imaging element 33 described later performs imaging by photoelectrically converting the formed subject image. After the set shutter time elapses, the shutter rear curtain performs light-shielding travel that moves from the exposure position to the light-shielding position, thereby completing the photographing for one image data. The shutter unit 32 is controlled by a shutter drive circuit 104 that receives a control command from the MPU 101.

  The image signal processing circuit 105 performs A / D conversion processing on the analog image signal output from the image sensor 33, and performs various processes such as noise removal processing and gain adjustment processing on the obtained digital image data. Perform image processing. The switch sensor circuit 106 transmits to the MPU 101 an input signal that is input when a photographer operates a user interface provided in the digital camera 100 such as the main SW 43 and the cleaning SW 44. The cleaning SW 44 is a user interface for instructing the removal of foreign matters such as dust adhering to the surface of the optical low-pass filter 410, and the photographer manually removes foreign matters on the filter by operating the cleaning SW 44. be able to.

  The imaging unit 400 is a block in which components including the optical low-pass filter 410, the piezoelectric element 430, and the imaging element 33 are unitized. The imaging device 33 is an imaging device such as a CMOS sensor or a CCD, for example, and outputs an analog image signal by photoelectrically converting the optical image of the imaged subject as described above. The piezoelectric element 430 is a single-plate piezoelectric element such as a piezoelectric element, and is configured to be vibrated by the piezoelectric element driving circuit 111 that has received a control signal from the MPU 101 and to transmit the vibration to the optical low-pass filter 410.

  Here, the imaging unit 400 according to the present embodiment, which removes foreign matters on the filter by vibrating the optical low-pass filter 410, will be described in more detail with reference to FIG. FIG. 2 is an exploded perspective view schematically showing the configuration of the imaging unit 400.

  The optical low-pass filter 410 disposed in front of the image sensor 33 is a single birefringent plate made of quartz and has a rectangular shape. The effective imaging area 411 on the surface of the optical low-pass filter 410 is provided with optical coating such as infrared cut and antireflection. In the present embodiment, the optical low-pass filter 410 will be described as a member to which foreign matter adheres, but the present invention is not limited to this. In other words, the present invention can be applied to an optical component that can be removed on the optical axis, such as an infrared absorption filter, which can remove foreign matter attached by vibration in an imaging unit including an imaging device.

  The piezoelectric element 430 has a single-plate strip shape, and the long side of the piezoelectric element is parallel to the short side (side edge) of the optical low-pass filter 410 at one peripheral portion 412 outside the effective imaging area of the optical low-pass filter 410. It arrange | positions so that it may become, and is adhere | attached and hold | maintained (attached). That is, the piezoelectric element 430 is optically attached so as to have a plurality of nodes parallel to the sides of the optical low-pass filter 410 when the digital camera 100 is in the normal position. The low-pass filter 410 is oscillated in a standing wave. In addition, although this embodiment demonstrates the example which uses only one piezoelectric element for the removal of a foreign material, a piezoelectric element may be affixed on both the right and left sides of the above-mentioned optical low-pass filter 410. FIG.

  The optical low-pass filter holding member 420 is a member that holds the optical low-pass filter 410 and is screw-fixed to the image sensor holding member 510, and is formed of resin or metal. The urging member 440 urges the optical low-pass filter 410 toward the image sensor 33 and is locked to the optical low-pass filter holding member 420. The biasing member 440 and the imaging effective area 411 are grounded to the ground of the digital camera 100 body, and electrostatic adhesion of dust and the like to the imaging effective area 411 on the surface of the optical low-pass filter 410 can be suppressed.

  The elastic member 450 is a frame-like elastic member having a substantially circular cross section, and is sandwiched between the optical low-pass filter 410 and the optical low-pass filter holding member 420 and held in close contact therewith. The adhesion force 450 is determined by the urging force of the urging member 440 in the direction of the image sensor 33. The elastic member 450 may be rubber, for example, or may be a high molecular polymer such as poron or plastic.

  The wave plate 460 is an optical member in which a birefringence plate having a refraction direction different by 90 degrees is bonded to the phase plate (depolarization plate), the infrared cut filter, and the optical low-pass filter 410, and the optical low-pass filter holding member 420. Adhered and fixed to.

  The flexible printed circuit board 470 is, for example, a flexible printed circuit board, and is bonded to the piezoelectric element 430 with a conductive adhesive. When a periodic voltage is applied from the piezoelectric element driving circuit 111 to the piezoelectric element 430 via the flexible printed circuit board 470, the piezoelectric element 430 periodically expands and contracts to vibrate the optical low-pass filter 410. That is, when the piezoelectric element 430 expands and contracts, the optical low-pass filter 410 is periodically bent and deformed to be bent standing wave vibration in a steady state.

  Note that the amplitude of vibration generated in the optical low-pass filter 410 can be increased by setting the frequency of the voltage applied to the piezoelectric element 430 to be close to the resonance frequency of the natural mode of the optical low-pass filter 410. That is, by causing the optical low-pass filter 410 to resonate, it is possible to remove foreign matter even with a small applied voltage. The resonance frequency varies depending on the shape, thickness, material, and the like of the optical low-pass filter 410. For example, when the digital camera 100 is shipped from the factory, information on the resonance frequency of the optical low-pass filter 410 is stored in the EEPROM 108.

  The image sensor holding member 510 is a plate-like member having a rectangular opening, and the image sensor 33 is fixed so that the image sensor 33 is exposed in the opening, and is screwed to the digital camera 100 main body. The mask 520 is a mask for preventing extra light from outside the imaging optical path from entering the image sensor 33, and is held in close contact with the optical low-pass filter holding member 420 and the image sensor 33. The imaging element urging member 530 is a pair of left and right leaf spring-like urging members, fixed to the imaging element holding member 510 by screws, and presses the imaging element 33 against the imaging element holding member 510.

  As described above, in the imaging unit 400, the optical low-pass filter 410 is sandwiched between the urging member 440 and the elastic member 450, and is supported so as to freely vibrate. Then, by being vibrated by the piezoelectric element 430, the foreign matter adhering to the surface of the optical low-pass filter 410 can be shaken off.

(Foreign substance removal processing)
Hereinafter, the foreign substance removal processing executed in the imaging unit 400 according to the present embodiment will be described in detail. Note that this foreign matter removal process will be described as being executed when the MPU 101 detects that the photographer has operated the cleaning SW 44 via the switch sensor circuit 106, but the foreign matter removal process is performed at an arbitrary timing. It may be done automatically.

FIG. 3 shows voltage control applied to the piezoelectric element 430 from the piezoelectric element drive circuit 111 under the control of the MPU 101 in this embodiment. When the MPU 101 starts the foreign substance removal processing, in this embodiment, as shown in FIG. 3, during the period (T _all ) during which at least the adhered foreign substance moves from one end to the other end of the optical low-pass filter 410, the piezoelectric element drive circuit 111 A voltage is applied to 430. The voltage applied to the piezoelectric element 430 is a rectangular wave that switches the presence or absence of output at a frequency f near the resonance frequency of the optical low-pass filter 410, and the frequency is constant from the start of application to the end of application.

The piezoelectric element drive circuit 111 first applies the voltage V ₁ (first voltage) to the piezoelectric element 430 for a predetermined period T _const from the start of application. The voltage V ₁ is a voltage necessary for the foreign matter adhering to the surface of the optical low-pass filter 410 to move away from the influence of the adhesive force and change from a stationary state to a movable state. The voltage V ₁ is determined from, for example, the amplitude of the vibration that gives the calculated acceleration by solving the equation of motion for the adhesion force experimentally determined by the surface state of the optical low-pass filter 410 and the type and size of the adhered foreign matter. That's fine. The adhesion force is a force that acts between the foreign substance and the optical low-pass filter 410 due to, for example, a liquid bridging force or an electrostatic force. Needs to be added to the foreign object.

In addition, since the surface state of the optical low-pass filter 410 may be different for each region or may be entirely different depending on the environmental temperature and the charged state, all the adhering to the filter is applied by applying the voltage V ₁ for a predetermined period. The foreign matter can be moved.

Further, after a predetermined period of time has elapsed since the start of application, the piezoelectric element drive circuit 111 applies a voltage V ₂ (second voltage) lower than the voltage V ₁ to the piezoelectric element 430. The voltage V ₂ is a voltage at which the foreign matter made movable on the surface of the optical low-pass filter 410 can move without returning to the stationary state, that is, without stopping. As compared with the case where the foreign matter made to move is attached and is in a stationary state, the distance between the foreign matter and the optical low-pass filter 410 is increased, so that the adhesive force is smaller than before the application is started. In other words, since the moving foreign object may be moved by gravity or the like acting in the moving direction without being affected by the adhesion force, the voltage V ₂ is a vibration that gives a force greater than the adhesion force, for example, before the start of application. The voltage V ₂ lower than the voltage V ₁ is sufficient.

The parameters such as the voltages V ₁ and V ₂ , the predetermined period T _const and the voltage application period Tall are values experimentally obtained with respect to possible foreign substances. Specifically, for example, sand particles of various sizes, plastic cutting pieces, cotton dust, and the like are used as foreign material samples, and parameters necessary for removing the samples are varied in the surface state of the optical low-pass filter 410. To measure. Then, the maximum value of each parameter is stored in the EEPROM 108 so that the removal of foreign matters can be achieved for all possible foreign matters, and the MPU 101 may read and use the parameters in the foreign matter removal processing.

  As described above, the imaging apparatus according to the present embodiment can appropriately remove foreign matter on the imaging surface while suppressing power consumption. Specifically, the imaging device is a filter included in an imaging unit including an imaging element, and a piezoelectric element that vibrates the filter to remove foreign matter attached to the filter disposed on the optical axis of the imaging element. The vibration means is provided. And the voltage applied with respect to a vibration means is controlled as follows at least for the period when the adhering foreign material moves from one end to the other end on the filter. That is, at least at the start of voltage application, a first voltage is applied to make the foreign matter attached to the filter movable, and at the end of application, a second voltage lower than the first voltage at which the movable foreign matter can move is applied. Control is applied to the vibration means.

  In this way, by controlling the voltage required to remove the foreign matter depending on whether the foreign matter is in a movable state, the foreign matter can be removed with the minimum power consumption necessary for removing the foreign matter. It becomes possible.

(Modification 1)
In the above-described embodiment, the method of applying two kinds of voltages V ₁ and V ₂ to the piezoelectric element 430 in the voltage application period T _all of the foreign substance removal processing has been described, but the embodiment of the present invention is not limited thereto. . In the present invention, a voltage for moving the attached foreign matter into a movable state is applied for a predetermined period from the start of application, and at the end of application, a second voltage lower than the first voltage at which the foreign matter made movable is movable is applied. As long as voltage control is performed as described above.

That is, the power consumption can be reduced by controlling the voltage so that a voltage lower than the first voltage and higher than the second voltage is applied after the elapse of a predetermined period from the start of application until the end of application. be able to. Therefore, as shown in FIG. 4, the piezoelectric element driving circuit 111 according to the present modification applies the voltage V ₁ for a predetermined period from the start of application, and after the predetermined period elapses until the end of application. Voltage control is performed so as to gradually decrease from voltage V ₁ to voltage V ₂ at each cycle.
It goes without saying that the same effects as in the above-described embodiment can be achieved by doing in this way.

(Modification 2)
In the above-described embodiment and Modification 1, it is assumed that the surface state of the optical low-pass filter 410 is different for each region or may be entirely different depending on the environmental temperature and the charged state, and the first voltage is set to a predetermined value. It demonstrated as what applies only for a period. However, for example, when the imaging unit 400 includes a sensor that detects the surface state of the optical low-pass filter 410, the environmental temperature, and the like, and each parameter of the foreign substance removal processing corresponding to the detected state is stored in the EEPROM 108, the following is performed. It may be.

In the state of the detected optical low-pass filter 410, when a sufficient voltage for making all possible foreign substances movable is experimentally determined, the voltage applied by the piezoelectric element drive circuit 111 to the piezoelectric element 430 is as shown in FIG. 5 may be controlled. That is, at the start of application, a sufficient voltage V ₁ is applied to move at least all foreign matter in a movable state, and during the voltage application period, the voltage V ₁ gradually decreases from voltage V ₁ to voltage V ₂ every cycle until the end of application. Voltage control may be performed.
By doing in this way, the same effect as the above-mentioned embodiment and modification 1 can be produced.

  In the embodiment and the modification described above, the waveform of the voltage applied to the piezoelectric element 430 has been described as using a rectangular wave. However, a sin wave or a sawtooth wave may be used instead of the rectangular wave. Further, although the optical low-pass filter 410 has been described as a quartz birefringent plate, lithium niobate may be used as the material of the birefringent plate. Further, the optical low-pass filter 410 may be configured by bonding a birefringent plate, a phase plate, and an infrared absorption filter, and may be directly excited. Moreover, the structure which excites the glass plate arrange | positioned in front of a birefringent plate may be sufficient.

  In addition, although preferred embodiment which implements this invention was mentioned above, this invention is not limited only to this embodiment, In the range which implement | achieves the meaning of this invention, it can change suitably. In the embodiment described above, an example in which the present invention is applied to a digital camera has been described, but the present invention can also be applied to an optical apparatus such as a liquid crystal projector. That is, even in an optical apparatus such as a liquid crystal projector, when a foreign substance such as dust adheres to the surface of a filter arranged on the optical axis of the projection optical system, a shadow of the foreign substance is projected, and thus the same as in the present invention. It is clear that foreign matter can be removed by this method.

(Other embodiments)
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

Claims (4)

An image sensor;
An optical member disposed in front of the image sensor;
Vibration means for vibrating the optical member by applying a voltage;
Control means for controlling the voltage applied to the vibration means,
The control means applies a first voltage to the vibration means when the vibration means starts to vibrate the optical member, and after applying the first voltage to the vibration means, the first voltage is applied to the vibration means. An image pickup apparatus, wherein a second voltage smaller than a voltage is applied to the vibrating means.   The control means applies the first voltage to the vibration means for a predetermined period after the vibration means starts to vibrate the optical member, and then continues the second operation until the vibration of the optical member is finished. The imaging apparatus according to claim 1, wherein a voltage is applied to the vibration unit.   The control means controls the second voltage to gradually decrease from when the second voltage is applied to the vibration means until the vibration of the optical member is finished. The imaging device according to claim 2. An imaging device comprising: an imaging device; an optical member disposed in front of the imaging device; a vibrating unit that vibrates the optical member when a voltage is applied; and a control unit that controls a voltage applied to the vibrating unit. An apparatus control method comprising:
When starting the vibration of the optical member by the vibration means, a first voltage is applied to the vibration means,
A method for controlling an imaging apparatus, comprising: applying a second voltage smaller than the first voltage to the vibrating unit after applying the first voltage to the vibrating unit.

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