Abstract:
A drive device is provided having a movable part, a fixed part, and a drive part. The fixed part is provided within a movement range of the movable part. The drive part drives the movable part in a first direction so as to strike said fixed part. The drive part drives the movable part to and fro along the first direction alternately for different time intervals so as to strike the fixed part.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a drive device that drives a movable part on which, for example, an image sensor of a camera is attached. 
     2. Description of the Related Art 
     A device which is provided in a photographing device such as a digital camera and removes dust particles attached to the camera&#39;s image sensor and its cover is proposed. 
     United States Published Patent Application Publication Number 2005-0264656 A discloses a drive device which vibrates attached dust particles by striking a movable part against a fixed part for a constant interval so as to dislodge the dust particles attached to an image sensor and its cover with the impact of the strike. 
     However, dust particles vary in weight, but only a constant vibrational frequency is generated by striking a movable part against a fixed part for a constant interval. Therefore, some dust particles may not be removed from an image sensor and its cover by the impact of the strike. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a drive device which efficiently removes dust particles from an image sensor and its cover. 
     A drive device is provided having a movable part, a fixed part, and a drive part. The fixed part is provided within a movement range of the movable part. The drive part drives the movable part in a first direction so as to strike said fixed part. The drive part drives the movable part to and fro along the first direction alternately for different time intervals so as to strike the fixed part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects and advantages of the present invention will be better understood from the following description, with reference to the accompanying drawings in which: 
         FIG. 1  is a perspective view of the image-capturing device according to the embodiment of the present invention; 
         FIG. 2  is a front view of the image-capturing device; 
         FIG. 3  is a block diagram of the image-capturing device; 
         FIG. 4  is a flowchart showing a main process of the image-capturing device; 
         FIG. 5  is a flowchart showing an interrupting process; 
         FIG. 6  is a flowchart showing a dust-removal process; 
         FIG. 7  shows the trajectory of the movable part in the y-direction during the dust-removal process; 
         FIG. 8  schematically shows the trajectory of the movable part watching an imaging device from the lens side; and 
         FIG. 9  shows the trajectory of the movable part in the x-direction during the dust-removal process. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is described below with reference to the embodiment shown in the drawings.  FIGS. 1 to 3  show the construction of an image-capturing apparatus  1  which comprises a drive device according to the present embodiment. In this embodiment, the photographing apparatus  1  is a digital camera. A photographing optical system, such as a camera lens  67  etc., that captures an optical image on a photographing surface of the image sensor of the photographing apparatus  1  has an optical axis LX. In order to explain the orientation of the embodiment, an x-direction (the first direction), a y-direction (the second direction), and a z-direction are defined (refer to  FIG. 1 ). The x-direction is in the horizontal plane and perpendicular to the optical axis LX. The y-direction is perpendicular to the optical axis LX and the x-direction. The z-direction is parallel to the optical axis LX and perpendicular to both the x-direction and the y-direction. The positive x-direction is the XP-direction; the negative x-direction is the XM-direction. The positive y-direction is the YP-direction; the negative y-direction is the YM-direction. The positive x-direction is the XP-direction; the negative x-direction is the XM-direction. The positive y-direction is the YP-direction; the negative y-direction is the YM-direction. 
     The photographing apparatus  1  comprises a power button  11  which is used to turn on or off the power of the photographing apparatus, a release button  13 , an anti-shake button  14 , an LCD monitor  17 , a mirror-aperture-shutter unit  18 , a DSP  19 , a CPU  21 , an AE (automatic exposure) unit  23 , an AF (automatic focus) unit  24 , an anti-shake unit  30 , imaging unit  39   a , and a camera lens  67 . These components perform the imaging function. 
     Whether the power switch  11   a  is in the ON state or the OFF state is determined by the state of the power button  11 , so that the ON and OFF states of the photographing apparatus  1  correspond to the ON and OFF states of the power switch  11   a . The photographic subject image is captured as an optical image through the camera lens  67  by the imaging unit  39   a , and the captured image is displayed on the LCD monitor  17 . The photographic subject image can be observed through the optical finder (not depicted). 
     After the power button  11  is depressed, putting the photographing apparatus  1  in the ON state, a dust-removal operation is performed in a first period (320 ms). 
     When the release button  13  is partially depressed by the operator, the photometric switch  12   a  changes to the ON state so that the photometric operation, the AF-sensing operation, and the focusing operation are performed. When the release button  13  is fully depressed by the operator, the release switch  13   a  changes to the ON state so that the imaging operation by the imaging unit  39   a  (the imaging apparatus) is performed, and the image is captured and stored. 
     The mirror-aperture-shutter unit  18  is connected to port P 7  of the CPU  21  and performs an UP/DOWN operation of the mirror (a mirror-up operation and a mirror-down operation), an OPEN/CLOSE operation of the aperture, and an OPEN/CLOSE operation of the shutter according to the ON state of the release switch  13   a.    
     The DSP  19  is connected to the imaging unit  39 , and port P 9  of the CPU  21 . Based on a command from the CPU  21 , the DSP  19  performs calculations such as image processing, etc., on the image signal obtained by the imaging operation of the imaging unit  39   a.    
     The CPU  21  is a control apparatus that controls each part of the photographing apparatus  1  regarding the imaging operation, the dust-removal operation, and the anti-shake operation (i.e., the image stabilizing operation). The anti-shake operation includes both the movement of the movable part  30   a  and a position-detection operation. Furthermore, the CPU  21  stores the value of anti-shake parameter IS, the value of release state parameter RP, the value of dust-removal state parameter GP, and the value of dust-removal time parameter CNT. 
     Anti-shake parameter IS indicates whether the photographing apparatus  1  is in the anti-shake mode. When the anti-shake parameter IS equals one, the photographing apparatus  1  is in the anti-shake mode; when it equals zero, the photographing apparatus  1  is not in the anti-shake mode. 
     The value of the release state parameter RP changes with respect to the release sequence operation. When the release sequence operation is performed, the value of the release state parameter RP is set to one (refer to steps S 24  to S 31  in  FIG. 4 ); and when the release sequence operation is finished, the value of the release state parameter RP is set (reset) to zero (refer to steps S 13  and S 32  in  FIG. 4 ). 
     The dust-removal state parameter GP indicates whether the dust-removal operation is finished. The value of the dust-removal state parameter GP is set to one because the dust-removal operation may be considered underway from the moment immediately after the photographing apparatus  1  is set to the ON state until the first period (320 ms) has elapsed (refer to step S 14  in  FIG. 4 ). 
     The value of the dust-removal state parameter GP is set to zero because the dust-removal operation may be considered to be finished from the moment when the first period (320 ms) has elapsed after the photographing apparatus  1  is set to the ON state (refer to step S 16  in  FIG. 4 ). 
     The dust-removal time parameter CNT is used for measuring the length of time the dust-removal operation is underway. The initial value of the dust-removal time parameter CNT is substituted by zero. While the dust-removal operation is being performed, the value of the dust-removal time parameter CNT is increased by one at every time interval of 1 ms (refer to step S 701  in  FIG. 6 ). 
     The CPU  21  moves the movable part  30   a  to a predetermined initial position in the dust-removal operation before the anti-shake operation. This operation is named the centering operation (refer to step S 84  in  FIG. 7 ). In this embodiment, the predetermined position is the center of the movement range (where the coordinate values in the x-direction and in the y-direction are both 0). 
     Then, the center of mass of the movable part  30   a  is kept at a certain position relative to the x-direction by the CPU  21 . The XP-side of the movable part  30   a  is driven in the YP-direction of the y-direction, and the XM-side of the movable part  30   a  is driven in the YM-direction at the same time. Therefore, the movable part  30   a  swings relative to a given axis, so that the XP-end of the YP-side of the movable part  30   a  strikes the upper boundary  34   a  of the movable range and the XM-end of the YM-side of the movable part  30   a  strikes the lower boundary  34   b  of the movable range. 
     Then, the XP-side of the movable part  30   a  is driven in the YM-direction of the y-direction, and the XM-side is simultaneously driven in the YP-direction, while the movable part  30   a  is kept at a certain position concerning to the x-direction. Therefore, the movable part  30   a  swings in the direction opposite to last swing, so that the XM-end of the YP-side strikes the upper boundary  34   a  of the movable range and the XP-end of the YM-side strikes the lower boundary  34   b  of the movable range. After repeating these processes, the dust-removal operation ends. 
     The dust particles on the imaging unit  39   a  of the movable part  30   a  (the image sensor and the low-pass filter) are removed by the shock of the impact of the movable part  30   a  against the boundary of said movable range. After the dust-removal operation is completed, the anti-shake operation begins. 
     Next, the CPU  21  stores the values of a first digital angular velocity signal Vxn, a second digital angular velocity signal Vyn, a first digital angular velocity VVxn, a second digital angular velocity VVyn, a first digital displacement angle Bxn, a second digital displacement angle Byn, the coordinate of position Sn in the x-direction, Sxn; the coordinate of position Sn in the y-direction, Syn; the first driving force, Dxn; the second driving force, Dyn; the coordinate of position Pn after A/D conversion in the x-direction, pdxn; the coordinate of position Pn after A/D conversion in the y-direction, pdyn; a first subtraction value, exn; a second subtraction value, eyn; a first proportional coefficient, Kx; a second proportional coefficient, Ky; a sampling cycle θ of the anti-shake operation; a first integral coefficient, Tix; a second integral coefficient, Tiy; a first differential coefficient, Tdx; and a second differential coefficient, Tdy. 
     The AE unit  23  (an exposure calculating unit) performs the photometric operation and calculates the photometric values, based on the subject being photographed. The AE unit  23  also calculates the aperture value and the duration of the exposure, with respect to the photometric values, both of which are needed for imaging. The AF unit  24  performs the AF-sensing operation and the corresponding focusing operation, both of which are also needed for imaging. In the focusing operation, the camera lens  67  is moved along the optical axis LX. 
     The anti-shake part (the anti-shake apparatus) of the photographing apparatus  1  comprises an anti-shake button  14 , an anti-shake switch  14   a , an LCD monitor  17 , a CPU  21 , an angular velocity detection unit  25 , a driver circuit  29 , an anti-shake unit  30 , a hall-element signal-processing unit  45  (a magnetic-field change-detecting element), and the camera lens  67 . 
     When the anti-shake button  14  is depressed by the operator, the anti-shake switch  14   a  is set to the ON state. When the anti-shake switch  14   a  is in the ON state, the photographing apparatus  1  is in the anti-shake mode, and the anti-shake parameter IS is set to one (IS=1). When the anti-shake switch  14   a  is not in the ON state, the photographing apparatus  1  is in the non-anti-shake mode, and the anti-shake parameter IS is set to zero (IS=0). In the anti-shake mode, the anti-shake operation is executed. In the anti-shake operation, the angular velocity detection unit  25  and the anti-shake unit  30  are driven for the second period independent of other operation, such as the photometry operation. In this embodiment, the value of the predetermined time interval is set to 1 ms. 
     The CPU  21  controls the various output commands corresponding to the input signals from these switches. The port P 12  of the CPU  21  receives a 1-bit digital signal indicating whether the photometric switch  12   a  is in the ON state or the OFF state. The port P 13  of the CPU  21  receives a 1-bit digital signal indicating whether the release switch  13   a  is in the ON state or the OFF state. The port P 14  of the CPU  21  receives a 1-bit digital signal indicating whether the anti-shake switch  14   a  is in the ON state or the OFF state. The AE unit  23 , the AF unit  24 , and the LCD monitor  17  are respectively connected to port P 4 , P 5  and P 6  of the CPU  21  for I/O. 
     Next, the details of the angular velocity detection unit  25 , the driver circuit  29 , the anti-shake unit  30 , and the hall-element signal-processing unit  45  are described. 
     The angular velocity detection unit  25  has a first angular velocity sensor  26   a , a second angular velocity sensor  26   b , a first high-pass filter circuit  27   a , a second high-pass filter circuit  27   b , a first amplifier  28   a  and a second amplifier  28   b.    
     The first angular velocity sensor  26   a  detects the angular velocity of a rotary motion (the yawing) of the photographing apparatus  1  about the axis of the y-direction, i.e., it detects the velocity component in the x-direction of the angular velocity of the photographing apparatus  1 . The first angular velocity sensor  26   a  is a gyro sensor that detects the yaw angular velocity. 
     The second angular velocity sensor  26   b  detects the angular velocity of a rotary motion (the pitch) of the photographing apparatus  1  about the axis of the x-direction i.e., detects the velocity component in the y-direction of the angular velocity of the photographing apparatus  1 . The second angular velocity sensor  26   b  is a gyro sensor that detects a pitch angular velocity. 
     The first high-pass filter circuit  27   a  reduces a low-frequency component of the signal output from the first angular velocity sensor  26   a , because the low-frequency component of the signal output from the first angular velocity sensor  26   a  includes signal elements that are based on a null voltage and panning motion, neither of which are related to camera shake. The second high-pass filter circuit  27   b  reduces a low-frequency component of the signal output from the second angular velocity sensor  26   b , because the low-frequency component of the signal output from the second angular velocity sensor  26   b  includes signal elements that are based on a null voltage and panning motion, neither of which are related to camera shake. The processes performed by the first and second high-pass filter circuit  27   a  and  27   b  are analog high-pass filter processes. 
     The first amplifier  28   a  amplifies a signal related to the yawing angular velocity, whose low-frequency component has been reduced, and outputs the analog signal to the port A/D 0  of the CPU  21  as a first angular velocity vx. The second amplifier  28   b  amplifies a signal relating to the pitch angular velocity, whose low-frequency component has been reduced, and outputs the analog signal to the port A/D 1  of the CPU  21  as a second angular velocity vy. 
     The reduction of the low-frequency signal component is a two-step process; the primary part of the analog high-pass filter process is performed first by the first and second high-pass filter circuits  27   a  and  27   b , followed by the secondary part of the digital high-pass filter process that is performed by the CPU  21 . The cut-off frequency of the secondary part of the digital high-pass filter process is higher than that of the primary part of the analog high-pass filter process. In the digital high-pass filter process, the value of a time constant (a first high-pass filter time constant hx and a second high-pass filter time constant hy) can be easily changed. 
     The supply of electrical power to the CPU  21  and all parts of the angular velocity detection unit  25  begins after the power switch  11   a  is set to the ON state (i.e., the main power supply is set to the ON state). The calculation of a camera-shake value begins after the power switch  11   a  is set to the ON state and the dust-removal operation is finished. 
     The CPU  21  converts the first and second angular velocities vx and vy, which are respectively input to the ports A/D 0  and A/D 1 , to a first and second digital angular velocity signals Vxn and Vyn. It then calculates first and second digital angular velocities VVxn and VVyn by reducing a low-frequency component of the first and second digital angular velocity signals Vxn and Vyn (the digital high-pass filter process) because the low-frequency component of the first and second digital angular velocity signals Vxn and Vyn include signal elements that are based on a null voltage and panning motion, neither of which are related to camera shake. Moreover, it calculates a camera-shake displacement angle (the first and second digital displacement angles Bxn and Byn) by integrating the first and second digital angular velocities VVxn and VVyn (the integration process). 
     The CPU  21  and the angular velocity detection unit  25  use a function to calculate the camera-shake value. 
     “n” is an integer greater than zero and indicates the length of time (ms) from the commencement of the timer interruption process, (t=0; refer to step S 12  in  FIG. 4 ), to the point when the latest anti-shake operation is performed (t=n). 
     In the digital high-pass filter process regarding the x-direction, the first digital angular velocity VVxn is calculated by dividing the summation of the first digital angular velocities VVx 0  to VVxn−1 (calculated by the timer interruption process before the 1 ms predetermined time interval; i.e., before the latest anti-shake operation was performed), by the first high-pass filter time constant hx, and then subtracting the resulting quotient from the first digital angular velocity signal Vxn (VVxn=Vxn−(ΣVVxn−1)÷hx). In the digital high-pass filter process regarding the y-direction, the second digital angular velocity VVyn is calculated analogously to VVxn to give (VVyn=Vyn−(ΣVVyn−1)÷hy). 
     In this embodiment, the angular velocity detection operation in (a portion of) the timer interruption process includes the processing by the angular velocity detection unit  25  and the process of inputting the first and second angular velocities vx and vy from the angular velocity detection unit  25  to the CPU  21 . 
     In the integration process regarding the x-direction, the first digital displacement angle Bxn is calculated by summing from the first digital angular velocity VVx 0  at the point when the timer interruption process commences (t=0; refer to step S 12  in  FIG. 4 ), to the first digital angular velocity VVxn at the point when the latest anti-shake operation is performed (t=n; Bxn=ΣVVxn). 
     Similarly, in the integration process regarding the y-direction, the second digital displacement angle Byn is calculated by summing from the second digital angular velocity VVy 0  at the point when the timer interruption process commences, to the second digital angular velocity VVyn at the point when the latest anti-shake operation is performed (Byn=ΣVVyn). 
     The CPU  21  calculates the position Sn where the imaging unit  39   a  (the movable part  30   a ) should be moved, corresponding to the camera-shake value (the first and second digital displacement angles Bxn and Byn) that is calculated for the x-direction and the y-direction on the basis of a position conversion coefficient zz (a first position conversion coefficient zx for the x-direction and a second position conversion coefficient zy for the y-direction). 
     The coordinate of position Sn in the x-direction is defined as Sxn, and in the y-direction as Syn. The movement of the movable part  30   a , which includes the imaging unit  39   a , is performed using electromagnetic force, and is described later. 
     The driving force Dn drives the driver circuit  29  in order to move the movable part  30   a  to the position Sn. The coordinate of the driving force Dn in the x-direction is defined as the first driving force Dxn (after D/A conversion: a first PWM duty dx). The coordinate of the driving force Dn in the y-direction is defined as the second driving force Dyn (after D/A conversion: a second PWM duty dy). A first driving coil  31   a  is driven according to the value of the first driving force Dxn. A second driving coil  32   a  is driven according to the second driving force Dyn. 
     The first PWM duty dx is the duty ratio of the driving pulse corresponding to the first driving force Dxn. The second PWM duty dy is the duty ratio of the driving pulse corresponding to the second driving force Dyn. 
     The value of second driving force Dyn is represented by +DD or −DD. +DD indicates that the movable part  30   a  is driven in the positive y-direction (YP-direction), i.e., towards the upper end of the fixed part  30   b . −DD indicates that the movable part  30   a  is driven in the negative y-direction (YM-direction), i.e., towards the bottom end of the fixed part  30   b.    
     However, the position Sn, where the imaging unit  39   a  (the movable part  30   a ) should be moved in the first period (320 ms) for the dust-removal operation before the anti-shake operation is performed, is set to “a” value that does not correspond to the camera shake value (refer to step S 704  in  FIG. 6 ). 
     For example, the position Sn is set on the center of the fixed part  30   b  in the “a” trajectory of the dust-removal operation. Therefore, the movable part  30   a  is set on the center of the fixed part  30   b . In the “b” to “d” trajectories of the dust-removal operation, the x-direction component of the position Sn is set at a certain value, but in the y-direction, only the PWM duty is set and the y-direction component of the position Sn is not set. Thus, the movable part  30   a  is moved towards the top or bottom of the fixed part  30   b  by constant force, and strikes it. 
     In a positioning operation along the x-direction, the coordinate of position Sn in the x-direction is defined as Sxn, and is the product of the latest first digital displacement angle Bxn and the first position conversion coefficient zx (Sxn=z×Bxn). 
     In a positioning operation along the y-direction, the coordinate of position Sn in the y-direction is defined as Syn, and is the product of the latest second digital displacement angle Byn and the second position conversion coefficient zy (Syn=zy×Byn). 
     The anti-shake unit  30  corrects for camera shake by repeatedly moving the imaging unit  39   a  to position Sn. This stabilizes the photographing subject image displayed on the imaging surface of the image sensor during the exposure time when the anti-shake operation is performed (IS=1). 
     The anti-shake unit  30  has a fixed part  30   b  that forms the boundary of the movement range of the movable part  30   a , and the movable part  30   a  which includes the imaging unit  39   a  and can be moved on the xy plane. The movement range is wider than the shake-correction area in which the movable part  30   a  is moved during the anti-shake operation. 
     During the exposure time when the anti-shake operation is not performed (IS=0), the movable part  30   a  is held in the predetermined position. The predetermined position is the center of the movement range. 
     In the first period (320 ms), after the photographing apparatus  1  is set to the ON state, the movable part  30   a  is driven to the predetermined position (i.e., the center of the movement range). Next, the movable part  30   a  is driven against the boundary of the movement range in the y-direction. 
     Otherwise (except for the first period and the exposure time), the movable part  30   a  is not driven. 
     The anti-shake unit  30  does not have a fixed-positioning mechanism that maintains it in a fixed position when it is not being driven (i.e., the drive OFF state). 
     The driving of the movable part  30   a  of the anti-shake unit  30 , including the movement to a predetermined fixed position, is performed by the electromagnetic force of the coil and magnetic units for driving, by action of the driver circuit  29  which has first PWM duty dx input from the PWM 0  of the CPU  21  and second PWM duty dy input from the PWM 1  of the CPU  21 . 
     The movable part  30   a  of the anti-shake unit  30  is driven by the electromagnetic force created by the coil and magnet units. The electromagnetic force is generated when the driver circuit  29  energizes the coil units. The driver circuit  29  energizes a first driving coil  31   a  when receiving first PWM duty dx output by the PWM 0  of the CPU  21 , and a second driving coil  32   a  when receiving second PWM duty dy output by the PWM 1 . 
     The position Pn of the movable part  30   a , either before or after the movement effected by the driver circuit  29 , is detected by the hall element  44   a  and the hall-element signal-processing unit  45 . 
     Information regarding the first coordinate of the detected position Pn in the x-direction, in other words the first detected position signal px, is input to the A/D converter A/D 2  of the CPU  21  (refer to ( 2 ) in  FIG. 6 ). The first detected position signal px is an analog signal that is converted to a digital signal by the A/D converter A/D 2  (A/D conversion). Through the A/D conversion, analog px becomes digital pdxn. 
     Similarly, regarding the y-direction, py is input to the A/D converter A/D 3  of the CPU  21 . Through the A/D conversion, analog py is becomes digital pdyn. 
     The PID (Proportional Integral Differential) control procedure calculates the first and second driving forces Dxn, Dyn on the basis of the coordinate data for the detected position Pn (pdxn, pdyn) and the position Sn (Sxn, Syn) following movement. 
     The calculation of the first driving force Dxn is based on the first subtraction value exn, the first proportional coefficient Kx, the sampling cycle θ, the first integral coefficient Tix, and the first differential coefficient Tdx (Dxn=Kx×{exn+θ÷Tix×Σexn+Tdx÷θ×(exn−exn−1)}). The first subtraction value exn is calculated by subtracting the first coordinate of the detected position Pn in the x-direction after the A/D conversion, pdxn, from the coordinate of position Sn in the x-direction, Sxn (exn=Sxn−pdxn). 
     The calculation of the second driving force Dyn is based on the second subtraction value eyn, the second proportional coefficient Ky, the sampling cycle θ, the second integral coefficient Tiy, and the second differential coefficient Tdy (Dyn=Ky×{eyn+θ÷Tiy×Σeyn+Tdy÷θ×(eyn−eyn−1)}). The second subtraction value eyn is calculated by subtracting the second coordinate of the detected position Pn in the y-direction after the A/D conversion, pdyn, from the coordinate of position Sn in the y-direction, Syn (eyn=Syn−pdyn). 
     The value of the sampling cycle θ is set to the predetermined time interval of 1 ms (the second period). 
     The movable part  30   a  is driven to the position Sn (Sxn, Syn) by the anti-shake operation of the PID control procedure, when the photographing apparatus  1  is set to the anti-shake mode (IS=1) by the setting of the anti-shake switch  14   a  to the ON state. The position Sn is determined by the PID control procedure comprised in the anti-shake operation. 
     When the anti-shake parameter IS is zero, the PID control procedure not comprised in the anti-shake operation is performed so that the movable part  30   a  is moved to the center of the movement range (the predetermined position). 
     In the dust-removal operation, from the point when the photographing apparatus  1  is set to the ON state until the anti-shake operation commences, the movable part  30   a  is first moved to the center of the movement range. After that, the movable part  30   a  is driven according to the processes described herein before. 
     The movable part  30   a  has a coil unit for driving that is comprised of a first driving coil  31   a , a second driving coil  32   a , an imaging unit  39   a  that has the image sensor, and a hall element  44   a  acting as a magnetic-field change-detecting element. In the first embodiment, the image sensor is a CCD; however, the image sensor may be another image sensor such as a CMOS etc. 
     The rectangular form of the imaging surface of the image sensor has two sides parallel to the x-direction and two sides parallel to the y-direction that are shorter than those of the x-direction. Accordingly, the movement range of the movable part  30   a  in the x-direction is greater than in the y-direction. 
     The fixed part  30   b  has a magnetic unit for driving that is comprised of a first position-detecting and driving magnet  411   b , a second position-detecting and driving magnet  412   b , a first position-detecting and driving yoke  431   b , and a second position-detecting and driving yoke  432   b.    
     The fixed part  30   b  movably supports the movable part  30   a  in the x-direction and in the y-direction. 
     The fixed part  30   b  has a buffer member that absorbs the shock at the point of contact the movable part  30   a  (at the boundary of the movement range). 
     The hardness of the buffer member is chosen such that the part making contact, such as the movable part  30   a , is not damaged by the shock of the impact, but any dust on the movable part  30   a  will be removed by the shock of the impact with the buffer member. 
     In the first embodiment, the buffer member is attached to the fixed part  30   b ; however, the buffer member may be attached to the movable part  30   a.    
     When the movable part  30   a  is positioned at the center of its movement range in both the x-direction and the y-direction, the center of the image sensor intersects the optical axis LX of the camera lens  67 , and the full imaging range of the image sensor may be utilized. 
     The rectangle shape, which is the form of the imaging surface of the image sensor, has two diagonal lines. In the first embodiment, the center of the image sensor is at the intersection of these two diagonal lines. 
     The first driving coil  31   a , the second driving coil  32   a , and the hall element  44   a  are attached to the movable part  30   a.    
     The first driving coil  31   a  is formed in a sheet and a spiral and has magnetic field lines in the y-direction, thus creating the first electromagnetic force for moving the movable part  30   a  which includes the first driving coil  31   a , in the x-direction. 
     The first electromagnetic force occurs on the basis of the current direction of the first driving coil  31   a  and the magnetic-field direction of the first position-detecting and driving magnet  411   b.    
     The second driving coil  32   a  is formed in a sheet and a spiral and has magnetic field lines in the x-direction, thus creating the second electromagnetic force for moving the movable part  30   a  which includes the second driving coil  32   a  in the y-direction. 
     The second electromagnetic force occurs on the basis of the current direction of the second driving coil  32   a  and the magnetic-field direction of the second position-detecting and driving magnet  412   b.    
     The first and second driving coils  31   a  and  32   a  are connected to the driver circuit  29  which drives the first and second driving coils  31   a  and  32   a  through a flexible circuit board (not depicted). The first PWM duty dx is input to the driver circuit  29  from the PWM 0  of the CPU  21 . Similarly, the second PWM duty dy is input to the driver circuit  29  from the PWM 1  of the CPU  21 . The driver circuit  29  supplies power to the first driving coil  31   a  corresponding to the value of the first PWM duty dx, and to the second driving coil  32   a  that corresponding to the value of the second PWM duty dy in order to drive the movable part  30   a.    
     The first and second position-detecting and driving yoke  431   b  and  432   b  are made of a soft, magnetic material, and provided on the fixed part  30   b.    
     The first position-detecting and driving yoke  431   b  prevents the magnetic-field of the first position-detecting and driving magnet  411   b  from dissipating to the surroundings, and raises the magnetic-flux density between the first position-detecting and driving magnet  411   b  and the first driving coil  31   a , and between the first position-detecting and driving magnet  411   b  and the horizontal hall element hh. 
     Similarly, the second position-detecting and driving yoke  432   b  prevents the magnetic-field of the second position-detecting and driving magnet  412   b  from dissipating to the surroundings, and raises the magnetic-flux densities between the second position-detecting and driving magnet  412   b  and the second driving coil  32   a , between the second position-detecting and driving magnet  412   b  and the first vertical hall element hv. 
     The first position-detecting and driving magnet  411   b  is attached to the movable part side of the fixed part  30   b , where the first position-detecting and driving magnet  411   b  faces the first driving coil  31   a  and the horizontal hall element hh in the z-direction. In detail, the first position-detecting and driving magnet  411   b  is attached to the first position-detecting and driving yoke  431   b . The first position-detecting and driving yoke  431   b  is attached to the fixed part  30   b  on the side of the movable part  30   a  in the z-direction. The N pole and S pole of the first position-detecting and driving magnet  411   b  are arranged in the x-direction. 
     Similarly, the second position-detecting and driving magnet  412   b  is attached to the movable part side of the fixed part  30   b , where the second position-detecting and driving magnet  412   b  faces respectively the second driving coil  32   a  and the vertical hall element hv in the z-direction. In detail, the second position-detecting and driving magnet  412   b  is attached to the second position-detecting and driving yoke  432   b . The second position-detecting and driving yoke  432   b  is respectively attached to the fixed part  30   b  on the side of the movable part  30   a  in the z-direction. The N pole and S pole of the second position-detecting and driving magnet  412   b  are arranged in the y-direction. 
     The hall element  44   a  comprises a horizontal hall element hh which detects the coordinate of the position Pn of the movable part  30   a  in the x-direction, and a vertical hall element hv which detects the coordinate of the XM-side of the movable part  30   a  in the y-direction. Each hall element are single-axis units that contain magneto-electric converting elements (magnetic-field change-detecting elements) utilizing the Hall Effect. The horizontal hall element hh outputs the first detected position signal px which indicates the present position Pn of the movable part  30   a . Similarly, the vertical hall element hv respectively output the second detected position signal py. 
     The horizontal hall element hh is attached to the movable part  30   a  where the horizontal hall element hh faces the first position-detecting and driving magnet  411   b  in the z-direction. Similarly, the vertical hall element hv is attached to the movable part  30   a  where is faces the second position-detecting and driving magnet  412   b  in the z-direction. 
     When the center of the image sensor is intersecting the optical axis LX, it is desirable to have the horizontal hall element hh positioned on the hall element  44   a  facing an intermediate area between the N pole and S pole of the first position-detecting and driving magnet  411   b  in the x-direction, as viewed from the z-direction. In this position, the horizontal hall element hh utilizes the maximum range in which an accurate position-detecting operation can be performed based on the linear output change (linearity) of the single-axis hall element. Similarly, when the center of the image sensor is intersecting the optical axis LX, it is desirable to have the vertical hall element hv positioned on the hall element  44   a  facing an intermediate area between the N pole and S pole of the second position-detecting and driving magnet  412   b  in the y-direction, as viewed from the z-direction. 
     The hall-element signal-processing unit  45  has a first hall-element signal-processing circuit  450 , and a second hall-element signal-processing circuit  460 . 
     The first hall-element signal-processing circuit  450  detects a horizontal potential difference x 10  between the output terminals of the horizontal hall element hh. The horizontal potential difference x 10  is detected with an output signal of the horizontal hall element hh. The first hall-element signal-processing circuit  450  outputs the first detected position signal px, which specifies the first coordinate of the position Pn of the movable part  30   a  in the x-direction, to the A/D converter A/D 2  of the CPU  21 , on the basis of the horizontal potential difference x 10 . 
     Similarly, the second hall-element signal-processing circuit  460  detects a vertical potential difference y 10  between the output terminals of the vertical hall element hv. The vertical potential difference y 10  is detected with an output signal of the vertical hall element hv. After that, the second hall-element signal-processing circuit  460  outputs the second detected position signal py to the A/D converter A/D 3  of the CPU  21 . 
     Next, the main process of the photographing apparatus  1  in the first embodiment is explained using the flowchart of  FIG. 4 . 
     When the photographing apparatus  1  is set to the ON state, electrical power is supplied to the angular velocity detection unit  25  so that the angular velocity detection unit  25  is set to the ON state in step S 11 . 
     In step S 12 , the timer interruption process at the predetermined time interval (1 ms) commences. In step S 13 , the value of the release state parameter RP is set to zero. The detail of the timer interruption process is explained later using the flowchart of  FIG. 5 . 
     In step S 14 , the value of the dust-removal state parameter GP is set to one; the value of the dust-removal time parameter CNT is set to zero; and the channel parameter is set to a. 
     In step S 15 , it is determined whether the value of the dust-removal time parameter CNT is greater than 320 ms. Step S 15  is provided to wait until the end of the timer interruption process. The dust-removal time parameter CNT is the time that is need so that the timer interruption process is finished. In this embodiment, in consideration of the completion time of the timer interruption process and individual differences in anti-shake units  30 , 320 ms is used. 
     In step S 15 , it is determined whether the value of the dust-removal time parameter CNT is greater than 320 ms. When it is determined that the value of the dust-removal time parameter CNT is greater than 320 ms, the process continues to step S 16 ; otherwise, the process in step S 15  is repeated. 
     In step S 16 , the value of the dust-removal state parameter GP is set to 0. 
     In step S 17 , it is determined whether the photometric switch  12   a  is set to the ON state. When it is determined that the photometric switch  12   a  is set to the ON state, the process continues to step S 18 ; otherwise, the process in step S 17  is repeated. 
     In step S 18 , it is determined whether the anti-shake switch  14   a  is set to the ON state. When it is determined that the anti-shake switch  14   a  is not set to the ON state, the value of the anti-shake parameter IS is set to zero in step S 19 ; otherwise, the value of the anti-shake parameter IS is set to one in step S 20 . 
     In step S 21 , the AE sensor of the AE unit  23  is driven, the photometric operation is performed, and the aperture value and exposure time are calculated. 
     In step S 22 , the AF sensor and the lens control circuit of the AF unit  24  are driven to perform the AF sensing and focusing operations, respectively. 
     In step S 23 , it is determined whether the release switch  13   a  is set to the ON state. When the release switch  13   a  is not set to the ON state, the process returns to step S 17  and the process in steps S 17  to S 22  is repeated; otherwise, the process continues to step S 24  and the release-sequence operation commences. 
     In step S 24 , the value of the release state parameter RP is set to one. In step S 25 , the mirror-up operation and the aperture closing operation corresponding to the aperture value that is either preset or calculated, are performed by the mirror-aperture-shutter unit  18 . 
     After the mirror-up operation is finished, the opening operation of the shutter (the movement of the front curtain of the shutter) commences in step S 26 . 
     In step S 27 , the exposure operation, or in other words the electrical charge accumulation of the image sensor (CCD etc.), is performed. After the exposure time has elapsed, the closing operation of the shutter (the movement of the rear curtain of the shutter), the mirror-down operation, and the opening operation of the aperture are performed by the mirror-aperture-shutter unit  18  in step S 28 . 
     In step S 29 , the electrical charge which has accumulated in the image sensor during the exposure time is read. In step S 30 , the CPU  21  communicates with the DSP  19  so that the imaging process is performed based on the electrical charge read from the image sensor. The image, on which the image process is performed, is stored in the memory of the photographing apparatus  1 . In step S 31 , the image that is stored in the memory is displayed on the LCD monitor  17 . In step S 32 , the value of the release state parameter RP is set to zero, and the release sequence operation is finished. After that, the process then returns to step S 17 . In other words, the photographing apparatus  1  is set to a state where the next imaging operation can be performed. 
     Next, the timer interruption process, which commences in step S 12  in  FIG. 4  and is performed at every 1 ms time interval, is described with reference to the flowchart in  FIG. 5 . 
     When the timer interruption process commences, it is determined whether the value of the dust-removal state parameter GP is set to one in step S 50 . When it is determined that the value of the dust-removal state parameter GP is set to one, the process continues to step S 51 ; otherwise, the process proceeds directly to step S 52 . 
     In step S 51 , the dust-removal process is performed. The detail of the dust-removal process is explained later using the flowchart of  FIG. 6 . 
     In step S 52 , the first angular velocity vx, which is output from the angular velocity detection unit  25 , is input to the A/D converter A/D 0  of the CPU  21  and converted to the first digital angular velocity signal Vx n . The second angular velocity vy, which is also output from the angular velocity detection unit  25 , is input to the A/D converter A/D 1  of the CPU  21  and converted to the second digital angular velocity signal Vy n  (the angular velocity detection process). 
     The low frequencies of the first and second digital angular velocity signals Vx n  and Vy n  are reduced in the digital high-pass filter process (the first and second digital angular velocities VVx n  and VVy n ). 
     In step S 53 , it is determined whether the value of the release state parameter RP is set to one. When it is determined that the value of the release state parameter RP is not set to one, the driving control of the movable part  30   a  is set to the OFF state. In other words, the anti-shake unit  30  is set to a state where the driving control of the movable part  30   a  is not performed in step S 54 ; otherwise, the process proceeds directly to step S 55 . 
     In step S 55 , the first and second detected position signals px and py are input to the CPU  21  thorough the A/D converters A/D 2  and A/D 3 , and also converted to digital signals. The CPU  21  determines the present position Pn (pdxn, pdyn) of the movable part  30   a  with the input signals. 
     In step S 56 , it is determined whether the value of the anti-shake parameter IS is zero. When it is determined that the value of the anti-shake parameter IS is zero, (in other words when the photographing apparatus is not in anti-shake mode), the position Sn (Sxn, Syn) where the movable part  30   a  (the imaging unit  39   a ) should be moved is set to the center of the movement range of the movable part  30   a , in step S 57 . When it is determined that the value of the anti-shake parameter IS is not zero (IS=1), (in other words when the photographing apparatus is in anti-shake mode), the position Sn (Sxn, Syn) where the movable part  30   a  (the imaging unit  39   a ) should be moved is calculated on the basis of the first and second angular velocities vx and vy, in step S 58 . 
     In step S 59 , the first driving force Dxn (the first PWM duty dx), and the second driving force Dyn (the second PWM duty dyl) of the driving force Dn that moves the movable part  30   a  to the position Sn are calculated on the basis of the position Sn (Sxn, Syn) that was determined in step S 57  or step S 58 , and the present position Pn (pdxn, pdyn). 
     In step S 60 , the first driving coil unit  31   a  is driven by applying the first PWM duty dx to the driver circuit  29 , and the second driving coil unit  32   a  is driven by applying the second PWM duty dy to the driver circuit  29 , so that the movable part  30   a  is moved to position Sn (Sxn, Syn). 
     The process of steps S 59  and S 60  is an automatic control calculation that is used with the PID automatic control for performing general proportional, integral, and differential calculations. 
     Next, the dust-removal process, which commences in step S 51  in  FIG. 5 , is explained using the flowchart in  FIGS. 6 to 9 . 
     When the dust-removal process commences, the value of the dust-removal time parameter CNT is increased by one in step S 701 . 
     In step S 702 , the hall element  44   a  detects the position of the movable part  30   a , and the first and second detected position signals px and py are calculated by the hall-element signal-processing unit  45 . The first detected position signal px is then input to the A/D converter A/D 2  of the CPU  21  and converted to a digital signal pdx n , while the second detected position signal py is input to the A/D converter A/D 3  of the CPU  21  and also converted to digital signal, whereupon the CPU  21  determines the present position Pn (pdx n , pdy n ) of the movable part  30   a  with the input signal. 
     In step S 703 , it is determined whether the value of the dust-removal time parameter CNT is less than or equal to 65 ms. In the case that the value of the dust-removal time parameter CNT is less than or equal to 65 ms, steps S 704  to S 706  are commenced. In the case that the value of the dust-removal time parameter CNT is not less than or equal to 65 ms, the process proceeds to step S 710 . 
     Steps S 704  to S 706  process the “a” trajectory which drives the movable part  30   a  to the center of the fixed part  30   b.    
     In the step S 704 , the position Sn (Sxn, Syn) where the movable part  30   a  (the imaging unit  39   a ) should be moved is set to the center of the movement range of the movable part  30   a.    
     In step S 705 , the driving force Dn that moves the movable part  30   a  is calculated using the position Sn (Sxn, Syn) that was determined in step S 704  according to the present position Pn (pdxn, pdyn). This calculation is the same as the one in step S 59  in the timer interruption process. 
     In step S 706 , the movable part  30   a  is moved by executing the same process as in step S 60  in the timer interruption process. Then, the dust-removal process ends, and the process returns to the timer interruption process (subroutine return). 
     The timer interruption process is executed every millisecond (the second periods). Therefore, the dust-removal process is also repeatedly executed until the dust-removal state parameter GP is set to zero in step S 16  of the main process. 
     When the dust-removal process commences again, the value of the dust-removal time parameter CNT is increased by one, making it two, in step S 701 . Then, steps S 702  and S 703  are executed. In the step S 703 , it is determined whether the value of the dust-removal time parameter CNT is less than or equal to 65 ms. At this point, the value of the dust-removal time parameter CNT is two. Therefore, the process proceeds to step S 704 , and then ends after commencing steps S 704  to S 706  (subroutine return). After that, the dust-removal process is executed again in the timer interruption process. 
     Steps S 701  to S 706  are repeatedly executed until the dust-removal time parameter CNT becomes greater than 65 ms. In the case that the dust-removal time parameter CNT becomes greater than 65 ms in step S 703 , the process proceeds to step S 710 . Note that the movable part  30   a  is placed in the center of the fixed part  30   b.    
     The maximum time interval which is needed to move the movable part  30   a  from the present position to the center of the fixed part  30   b  is 65 ms. In other words, the time interval calculated by adding the average time interval which is needed to move the movable part  30   a  from the corner to the center of the fixed part  30   b  and the error time interval of the individual difference of the anti-shake unit  30  is 65 ms. Therefore, the threshold value of the dust-removal time parameter CNT is set to 65 ms. In the case the dust-removal time parameter CNT is less than or equal to 65 ms, there is a possibility that movable part  30   a  has not yet arrived the center of fixed part  30   b . When the dust-removal time parameter CNT is greater than 65 ms, the movable part  30   a  is in the center of fixed part  30   b.    
     In step S 710 , it is determined whether the dust-removal time parameter CNT is less than or equal to 115 ms. In the case that the dust-removal time parameter CNT is less than or equal to 115 ms, steps S 711  to S 715  is commenced. In the case that the dust-removal time parameter CNT is not less than or equal to 115 ms, the process proceeds to step S 720 . 
     Next, the process of steps S 711  to S 714  is described. Steps S 711  to S 714  process the “b” trajectory which strikes the movable part  30   a  against the lower boundary of the fixed part  30   b.    
     In step S 711 , the value of the second PWM duty dyl is set to −DD. The value DD, i.e., the absolute value |+DD| and |−DD| is set so that the acceleration of the movable part  30   a  at the point in time when the movable part  30   a  is moved to and struck against the boundary of the movement range of the movable part  30   a  is increased to the degree where the dust on the movable part  30   a  can be removed by the shock of the impact. 
     In step S 712 , the coordinate of position Sn in the x-direction, Sxn, where the movable part  30   a  should be moved in the x-direction, is set to the center of the movement range of the movable part  30   a  in the x-direction. 
     In step S 713 , the first driving force Dxn (the first PWM duty dx) is calculated on the basis of the coordinate of position Sn in the x-direction, Sxn, determined in step S 712 , and the coordinate of the present position Pn in the x-direction, pdxn. The first driving force Dxn, i.e., the driving force Dn which moves the movable part  30   a  in the x-direction, is needed to move the movable part  30   a  by providing current to the first driving coil unit  31   a.    
     In step S 714 , the first and second driving coil units  31   a  and  32   a  are respectively driven by applying the first and second PWM duties dx and dy to the driver circuit  29 , so that the movable part  30   a  is moved. The movable part  30   a  is moved towards the center of the movable range along the x-direction, and fixed on the center of the movable range along the x-direction (refer to  FIG. 9 ). Additionally, the movable part  30   a  is moved towards the bottom of the fixed part  30   b , i.e., along the positive y-direction. After that, the process ends (subroutine return), and the dust-removal process is executed again in the timer interruption process. 
     When the dust-removal process commences again, the value of the dust-removal time parameter CNT is increased by one so as to become 67, in step S 701 . Then, steps S 702 , S 703 , and S 710  to S 714  are executed. Thus, steps S 701  to S 703  and S 701  to S 714  are executed until the value of the dust-removal time parameter CNT is greater than 115 ms. In the case that the value of the dust-removal time parameter CNT is greater than 115 ms in step S 710 , the process proceeds to step S 720 . 
     By iterating steps S 701  to S 714 , the movable part  30   a  is fixed so as to contact the bottom side of the fixed part  30   b  after the movable part  30   a  strikes the bottom side of the fixed part  30   b.    
     Next, the reason why the threshold value of the dust-removal time parameter CNT is set to 115 ms, is described. The maximum time interval from the moment that the movable part  30   a  starts moving from the present position to the moment that bounce from the collision of the movable part  30   a  against the top or bottom of the fixed part  30   b  settles is 50 ms. Specifically, the maximum time interval calculated by adding: the average time interval from the moment that the movable part  30   a  starts moving at the center of the fixed part  30   b  to the moment that it arrives at the top or bottom of the fixed part  30   b , the error time interval of the individual difference of the anti-shake unit  30 , and the time interval that bounce created by striking the movable part  30   a  against the fixed part  30   b  is settled, is 50 ms. The threshold value 115 ms is calculated by adding the maximum time interval 50 ms and the time interval from the moment that the dust-removal process starts to the moment that the “b” trajectory is started. In the case the dust-removal time parameter CNT is less than or equal to 115 ms, there is a possibility that movable part  30   a  has not yet reached top or bottom side of fixed part  30   b . When the dust-removal time parameter CNT is greater than 115 ms, the movable part  30   a  is at the top or bottom side of fixed part  30   b.    
     In the next step, S 720 , it is determined whether the dust-removal time parameter CNT is less than or equal to 165 ms. In the case that the dust-removal time parameter CNT is less than or equal to 165 ms, steps S 721 , and S 712  to S 714  are commenced. In the case that the dust-removal time parameter CNT is not less than or equal to 165 ms, the process proceeds to step S 730 . 
     Next, the process of steps S 721 , and S 712  to S 714  is described. These steps process the “c” trajectory which strikes the movable part  30   a  against the bottom of the fixed part  30   b.    
     In step S 721 , the value of the second PWM duty dy is set to +DD. 
     Processes similar to those described above commence in steps S 712  to S 714 , so that the movable part  30   a  is returned to the center of the movable range along the x-direction after it is moved towards the center of the movable range along the x-direction (refer to  FIG. 9 ). Additionally, the movable part  30   a  is moved towards the top of the fixed part  30   b . After that, the process ends (subroutine return), and the dust-removal process is executed again in the timer interruption process. 
     When the dust-removal process commences again, the value of the dust-removal time parameter CNT is increased by one so as to become 117 ms, in step S 701 . Then, steps S 702 , S 703 , S 720 , S 721 , and S 712  to S 714  are executed. Thus, these steps are iterated until the value of the dust-removal time parameter CNT is greater than 165 ms. In the case that the value of the dust-removal time parameter CNT is greater than 165 ms in step S 720 , the process proceeds to step S 730 . 
     By executing these steps, the movable part  30   a  is fixed so as to contact the top side of the fixed part  30   b  after the movable part  30   a  strikes the top side of the fixed part  30   b.    
     The reason why the dust-removal time parameter CNT is set to 165 ms is omitted because it was described above. In the case the dust-removal time parameter CNT is less than or equal to 165 ms, there is a possibility that movable part  30   a  has not yet arrived at the top side of fixed part  30   b . In the case the dust-removal time parameter CNT is greater than 165 ms, the movable part  30   a  is fixed so as to contact the top side of fixed part  30   b.    
     In next step S 730 , it is determined whether the dust-removal time parameter CNT is less than or equal to 215 ms. In the case that the dust-removal time parameter CNT is less than or equal to 215 ms, steps S 711  to S 714  are commenced. In the case that the dust-removal time parameter CNT is not less than or equal to 215 ms, the process proceeds to step S 740 . 
     The descriptions concerning steps S 711  to S 714  are omitted because they are described above. Steps S 711  to S 714  process the “d” trajectory which strikes the movable part  30   a  against the bottom side of the fixed part  30   b . By executing these steps, the movable part  30   a  is fixed so as to contact the bottom side of the fixed part  30   b  after the movable part  30   a  strikes the bottom side of the fixed part  30   b.    
     The reason why the dust-removal time parameter CNT is set 215 ms is omitted because it is described above. In the case the dust-removal time parameter CNT is less than or equal to 215 ms, there is a possibility that movable part  30   a  is not yet put in the bottom side of fixed part  30   b . In the case the dust-removal time parameter CNT is greater than 215 ms, the movable part  30   a  is fixed so as to contact the bottom side of fixed part  30   b.    
     In next step S 740 , it is determined whether the dust-removal time parameter CNT is less than or equal to 245 ms. In the case that the dust-removal time parameter CNT is less than or equal to 245 ms, steps S 721  and S 712  to S 714  are commenced. Therefore, the “c 2 ” trajectory which strikes the movable part  30   a  against the top side of the fixed part  30   b  is processed. 
     The time interval from the moment of completion of the “d 1 ” trajectory to the moment of the completion of the “c 2 ” trajectory is set to 30 ms which is shorter than the 50 ms is omitted in the “d 1 ” trajectory. The vibration frequency of the movable part  30   a  can be changed by shortening the time interval from the moment of completion of the “d 1 ” trajectory to the moment of the completion of the “c 2 ” trajectory. It is necessary to shake the movable part  30   a  at a vibration frequency corresponding to the weight of the dust particles so as to efficiently remove them from an image sensor and its cover. By changing the vibrational frequency of the movable part  30   a , the drive device can remove not only dust particles which can be removed by 30 ms of vibration, but also dust particles which can be removed by 50 ms of vibration frequency. 
     In the next step, S 750 , it is determined whether the dust-removal time parameter CNT is less than or equal to 275 ms. In the case that the dust-removal time parameter CNT is less than or equal to 275 ms, steps S 711  to S 714  are commenced. Therefore, the “d 2 ” trajectory which strikes the movable part  30   a  against the bottom side of the fixed part  30   b  is processed so that the movable part  30   a  contacts the bottom side of the fixed part  30   b . The time interval from the moment of completion of the “c 2 ” trajectory to the moment of the completion of the “d 2 ” trajectory is set 30 ms. In the case the dust-removal time parameter CNT is not less than or equal to 275 ms, the process proceeds to step S 760 . 
     In next step S 760 , it is determined whether the dust-removal time parameter CNT is less than or equal to 290 ms. In the case that the dust-removal time parameter CNT is less than or equal to 290 ms, steps S 721  and S 712  to S 714  are commenced. Therefore, the “c 3 ” trajectory which strikes the movable part  30   a  against the top side of the fixed part  30   b  is processed, so that the movable part  30   a  contacts the top side of the fixed part  30   b . In the case the dust-removal time parameter CNT is not less than or equal to 290 ms, the process proceeds to step S 770 . 
     The time interval from the moment of completion of the “d 2 ” trajectory to the moment of the completion of the “c 3 ” trajectory is set to 15 ms, which is shorter than the 30 ms taken in the “d 2 ” trajectory. According to change the vibration frequency of the movable part  30   a , the drive device can remove not only dust particles which can be removed by 15 ms of vibration, but also dust particles which can be removed by 50 ms and 30 ms of vibration. 
     In next step S 770 , it is determined whether the dust-removal time parameter CNT is less than or equal to 305 ms. In the case that the dust-removal time parameter CNT is less than or equal to 305 ms, steps S 711  to S 714  are commenced. The time interval from the moment of completion of the “c 3 ” trajectory to the moment of the completion of the “d 3 ” trajectory is set 15 ms. Therefore, the “d 3 ” trajectory which strikes the movable part  30   a  against the bottom side of the fixed part  30   b  is processed, so that the movable part  30   a  contacts the bottom side of the fixed part  30   b . In the case the dust-removal time parameter CNT is not less than or equal to 305 ms, the process proceeds to step S 780 . 
     In the next step S 780 , the movable part  30   a  is in the drive OFF state. Therefore, driving force is not applied to the movable part  30   a , so that the movable part  30   a  settled on the bottom of the fixed part  30   b  by gravity. 
     According to this embodiment, the vibrational frequency of the movable part  30   a  may be changed, so that the drive device can effectively remove dust particles of various weights. 
     Additionally, the time interval required to execute the dust-removal process may be shortened because the time interval from the moment of striking the movable part  30   a  against the fixed part  30   b  to the moment of moving the movable part  30   a  the next time shortens. 
     Note that the dust-removal time parameter CNT is increased in steps, or in random order (in regular order if the dust-removal time parameter CNT is shortened in steps), in the present embodiment. 
     Note that the impact of the movable part  30   a  and the fixed part  30   b  is not limited to three times, but may be any number of times greater than or equal to one. In that case, steps S 710  to S 770  are executed according to the number of impacts. 
     The movable part  30   a  does not strike the top and the bottom of the fixed part  30   b  alternately, but may strike repeatedly either the top or bottom of the fixed part  30   b.    
     In the dust-removal operation, the movable part  30   a  may be held at the center in the y-direction and moved in the x-direction. The movable range of the movable part  30   a  in the x-direction is longer than in the y-direction. 
     Furthermore, the position to which the movable part  30   a  is moved when the dust-removal operation commences is not limited to the center of the movement range of the movable part  30   a , but may be any position where the movable part  30   a  does not make contact with the boundary of the movement range of the movable part  30   a.    
     Moreover, it is explained that the hall element is used for position detection as the magnetic-field change-detecting element. However, another detection element, an MI (Magnetic Impedance) sensor such as a high-frequency carrier-type magnetic-field sensor; a magnetic resonance-type magnetic-field detecting element; or an MR (Magneto-Resistance effect) element may be used for position detection purposes. When one of either the MI sensor, the magnetic resonance-type magnetic-field detecting element, or the MR element is used, the information regarding the position of the movable part  30   a  can be obtained by detecting the magnetic-field change, similar to using the hall element. 
     Although the embodiment of the present invention has been described herein with reference to the accompanying drawings, obviously many modifications and changes may be made by those skilled in the art without departing from the scope of the invention. 
     The present disclosure relates to subject matter contained in Japanese Patent Application No. 2008-055969 (filed on Mar. 6, 2008), which is expressly incorporated herein, by reference, in its entirety.