Patent Publication Number: US-10313590-B2

Title: Drive device and method for controlling the drive device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2017-005085, filed Jan. 16, 2017 the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a drive device and a method for controlling the same. 
     2. Description of the Related Art 
     In digital cameras or the like, blur correction is known as a function to suppress image blurring which occurs in a video signal generated by an imaging element due to camera shake when the imaging element or a lens is moved. To perform this kind of blur correction function, a drive device is known, in which a movable frame including a lens or an imaging element is configured to be moved relative to a fixed frame by a voice coil motor (VCM) using a drive coil and a driving magnet. 
     In the VCM, a Hall element is used as a detector to detect a position of the movable frame relative to the fixed frame. For example, a driving magnet and another magnet, that is, a position detecting magnet are placed in the fixed frame, and a Hall element is placed in the movable frame. In this placement, a position of the movable frame relative to the fixed frame is detected based on a change of a flux from the position detecting magnet detected by the Hall element in accordance with a movement of the movable frame relative to the fixed frame. 
     To downsize the drive device, in some configurations, a single magnet is used for both driving and position detecting, or a driving magnet and a position detecting magnet are placed in proximity. In those configurations, a drive coil and a Hall element are also placed in proximity. Therefore, the Hall element detects not only a magnetic flux from the position detecting magnet but also a magnetic flux from the drive coil. Due to the magnetic flux from the drive coil, a detection signal from the Hall element may include a false position signal. If position detection is performed on the basis of the detection signal including a false position signal, a position detection error may occur. Jpn. Pat. Appln. KOKAI Publication No. 2015-088956 proposes an imaging device, in which, to cancel a position detection error due to a magnetic flux from a drive coil as described above, a correction signal for a detection signal is generated using a time constant and a field noise factor that was determined in advance to correct a detection signal of a Hall element in accordance with a drive current. 
     BRIEF SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, there is provided a drive device comprising: a fixed frame on which one of a drive coil and a magnet facing the drive coil is disposed; a movable frame on which another one of the drive coil and the magnet is disposed and which is movable relative to the fixed frame; a detector that is disposed on one of the fixed frame and the movable frame on which the drive coil is disposed, and that detects and outputs a detection signal corresponding to a magnetic flux of the magnet; a noise signal calculation unit that calculates a noise signal corresponding to a magnetic flux generated from a current flowing through the drive coil; a signal correction unit that corrects the detection signal detected by the detector based on the noise signal; and a drive controller that controls, based on a corrected signal obtained from correction by the signal correction unit, a drive signal to be applied to the drive coil and that drives the movable frame to a position corresponding to the corrected signal, wherein from the detection signal detected by the detector when a drive signal, in which a high-frequency drive signal is superimposed on a drive current to drive the movable frame, is applied to the drive coil, the noise signal calculation unit acquires an amplitude of a predetermined frequency band including a frequency of the high-frequency drive signal, and calculates the noise signal included in the detection signal based on the acquired amplitude. 
     According to a second aspect of the invention, there is provided a method for controlling a drive device comprising: a fixed frame on which one of a drive coil and a magnet facing the drive coil is disposed; a movable frame on which another one of the drive coil and the magnet is disposed and which is movable relative to the fixed frame; and a detector that is disposed on one of the fixed frame and the movable frame on which the drive coil is disposed, and that detects and outputs a detection signal corresponding to a magnetic flux of the magnet, the method comprising: applying a drive signal, in which a high-frequency drive signal is superimposed on a drive current to drive the movable frame, to the drive coil; acquiring an amplitude of a predetermined frequency band including a frequency of the high-frequency drive signal from the detection signal detected by the detector; calculating a noise signal included in the detection signal based on the acquired amplitude; correcting the detection signal detected by the detector based on the noise signal; and controlling, based on a corrected signal obtained from the correcting, a drive signal to be applied to the drive coil and driving the movable frame to a position corresponding to the corrected signal. 
     Advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a schematic diagram showing a configuration of an imaging device according to an embodiment of the present invention. 
         FIG. 2  is a schematic diagram showing a configuration of a camera shake correction unit as an example of a drive device according to the embodiment of the present invention. 
         FIG. 3  is a diagram showing a configuration of a fixed frame. 
         FIG. 4  is a diagram showing a configuration of a movable frame. 
         FIG. 5  is a diagram showing a configuration of a yoke. 
         FIG. 6  is a diagram showing a fundamental configuration of a voice coil motor (VCM). 
         FIG. 7  is a diagram showing a configuration of a modification of a VCM. 
         FIG. 8  is a diagram showing a generation principle of a false position signal. 
         FIG. 9  is a diagram showing an amount of a false position signal output from a Hall element relative to an amount of current applied to a drive coil. 
         FIG. 10  is a diagram showing a detection deviation of a position due to generation of a false position signal. 
         FIG. 11  is a diagram showing a relationship among a magnet, a drive coil, and a Hall element in a state where the movable frame has been shifted in XY directions from the fixed frame. 
         FIG. 12  is a diagram showing a dependence of the amount of a false position signal on a shift amount. 
         FIG. 13  is a diagram showing an amount of a false position signal output from a Hall element relative to an amount of a current applied to a drive coil in consideration of the shift amount of the movable frame. 
         FIG. 14  is a diagram showing a relationship among a magnet, a drive coil, and a Hall element in a state where a gap misalignment of the movable frame relative to the fixed frame occurs. 
         FIG. 15A  is a diagram for explaining the gap misalignment. 
         FIG. 15B  is a diagram for explaining the gap misalignment. 
         FIG. 16  is a diagram showing a dependence of an amount of a false position signal on a gap amount. 
         FIG. 17  is a diagram showing a drive characteristic (transmission characteristic) of a motor (VCM). 
         FIG. 18A  is a diagram showing (1) a drive current in a low-frequency band, (2) a drive current in a mid-frequency band, and (3) a drive current in a high-frequency band. 
         FIG. 18B  is a diagram showing displacements of the movable frame when the drive currents shown in  FIG. 18A  are applied to the motor. 
         FIG. 19  is a block diagram showing a configuration of a position control system of the camera shake correction unit of the imaging device according to the embodiment. 
         FIG. 20A  is a diagram showing drive signals output from a motor driver. 
         FIG. 20B  is a diagram showing a displacement of the movable frame when the drive currents shown in  FIG. 20A  are applied to the motor. 
         FIG. 20C  is a diagram showing outputs of an analog amplifier when the drive currents shown in  FIG. 20A  are applied to the motor. 
         FIG. 21  is a diagram showing a configuration of an example of a high frequency detection unit. 
         FIG. 22  is a diagram showing a frequency characteristic of a BPF. 
         FIG. 23  is a diagram showing a relationship between a BPF output and a distance from a magnet to a drive coil. 
         FIG. 24  is a flowchart of a process for calculating a false position signal gain. 
         FIG. 25  is a flowchart of feedback control in the imaging device shown in  FIG. 19 . 
         FIG. 26  is a flowchart of a process for calculating a current position. 
         FIG. 27  is a flowchart of a process for correcting a false position signal. 
         FIG. 28  is a block diagram showing a configuration of a position control system of a camera shake correction unit in an imaging device of prior art. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention will be described with reference to the accompanying drawings.  FIG. 1  is a schematic diagram showing a configuration of an imaging device according to an embodiment of the present invention. The imaging device  1  shown in  FIG. 1  includes an interchangeable lens  10  and a main body  20 . The interchangeable lens  10  is attached to the main body  20  via a mount  21  mounted on the main body  20 . The interchangeable lens  10  and the main body  20  are communicatably connected by the attachment of the interchangeable lens  10  to the main body  20 . As a result, the interchangeable lens  10  and the main body  20  operate in cooperation. The imaging device  1  is not necessarily a lens-exchangeable type imaging device. For example, the imaging device  1  may be a lens-integrated type imaging device. Furthermore, the imaging device shown in  FIG. 1  maybe of various types of imaging devices, such as a digital camera, that includes a camera shake correction unit  23 . 
     The interchangeable lens  10  includes an optical system  11 . The optical system  11  includes, for example, a plurality of lenses and an aperture, and causes an optical beam from an object (not shown) to be incident on the camera shake correction unit  23  of the main body  20 . The optical system  11  shown in  FIG. 1  is comprised of a plurality of lenses; however, the optical system  11  may be comprised of one lens. The optical system  11  may include a zoom lens in addition to a focus lens. In these cases, at least a part of the lenses of the optical system  11  is freely movable in a z direction along an optical axis O. 
     The main body  20  includes a shutter  22 , the camera shake correction unit  23 , a monitor  24 , an operation unit  25 , and a control circuit  26 . 
     The shutter  22  is a focal plane shutter disposed, for example, in front of the camera shake correction unit  23  (referred to as a positive side in the z direction). Opening of the shutter  22  causes the camera shake correction unit  23  to be exposed. Closure of the shutter  22  causes the camera shake correction unit  23  to be shielded from light. 
     The camera shake correction unit  23 , as an example of the drive device, includes an imaging element and images an object (not shown) thereby to generate a video signal relating to the object. Furthermore, the camera shake correction unit  23  moves a movable frame relative to a fixed frame by a voice coil motor (VCM) using a coil and a magnet, thereby to correct an object light incident on the imaging element and to correct image blurring, which occurs in the video signal due to a camera shake or the like. Configurations of the camera shake correction unit  23  will be detailed later. 
     The monitor  24  is, for example, a liquid crystal display, and displays an image based on a video signal generated by the camera shake correction unit  23 . The monitor  24  also displays a menu window that allows a user to perform various settings of the imaging device  1 . The monitor  24  may include a touch panel. 
     The operation unit  25  includes, for example, a release button. The release button is a button that allows the user to provide an instruction to start imaging by the imaging device  1 . The operation unit  25  includes various operation parts in addition to the release button. 
     The control circuit  26  includes, for example, a CPU and a memory, and controls all operations of the imaging device  1 , such as an imaging operation in the imaging device  1 . 
     The camera shake correction unit  23  will be further explained.  FIG. 2  is a schematic diagram showing a configuration of the camera shake correction unit  23  as an example of a drive device according to the embodiment of the present invention. A left part of  FIG. 2  is a front view of the camera shake correction unit  23 , and a right part is a side view of the same. The camera shake correction unit  23  shown in  FIG. 2  is a device to correct an object light incident on the imaging element. This is a drive device that performs blur correction drive to drive the imaging element in directions parallel to an image surface (XY directions in  FIG. 1 ) to prevent noise from being caused in a video signal due to image blurring. In this configuration, it is assumed that the front of the camera shake correction unit  23  is a surface which faces the positive side in a Z direction in  FIG. 1 . Furthermore, when the camera shake correction unit  23  is placed as shown in  FIG. 2 , the horizontal direction is an X direction in  FIG. 1 , and the vertical direction is a Y direction in  FIG. 1 . 
     Broadly, the camera shake correction unit  23  shown in  FIG. 2  includes a fixed frame  102 , a movable frame  104 , and a yoke  106 . The fixed frame  102  is fixed to the main body  20  of the imaging device  1 . As shown in the side view, the yoke  106  is fixed to the fixed frame  102  at a predetermined distance from the fixed frame  102 . The movable frame  104  is interposed between the fixed frame  102  and the yoke  106 , and attached to the fixed frame  102  with urging force toward the fixing fixed frame  102  by urging springs  108 . Three balls  110  are arranged on a rear surface of the movable frame  104 . The movable frame  104  is configured to smoothly move on the surface of the fixed frame  102  by the three balls  110 . 
       FIG. 3  is a diagram showing a configuration of the fixed frame  102 . In  FIG. 3 , a left part is a front view of the fixed frame  102 , and a right part is a side view of the same. As shown in  FIG. 3 , three magnets  112   a ,  112   b , and  112   c  are disposed on the fixed frame  102 . 
     The magnet  112   a  is disposed on an upper left corner in the front surface of the fixed frame  102 . The magnet  112   a  includes a first magnet and a second magnet. The first magnet is disposed so that the longitudinal direction coincides with the Y direction, and a north pole faces the movable frame  104 . The second magnet is disposed so that the longitudinal direction coincides with the Y direction, and a south pole faces the movable frame  104 . 
     The magnet  112   b  is disposed on a lower left corner in the front surface of the fixed frame  102 . The magnet  112   b  includes a first magnet and a second magnet. The first magnet is disposed so that the longitudinal direction coincides with the Y direction, and a north pole faces the movable frame  104 . The second magnet is disposed so that the longitudinal direction coincides with the Y direction, and a south pole faces the movable frame  104 . 
     The magnet  112   c  is disposed on a bottom center portion in the front surface of the fixed frame  102 . The magnet  112   c  includes a first magnet and a second magnet. The first magnet is disposed so that the longitudinal direction coincides with the X direction, and a north pole faces the movable frame  104 . The second magnet is disposed so that the longitudinal direction coincides with the X direction, and a south pole faces the movable frame  104 . 
     The magnet  112   a  and the magnet  112   b  are magnets to drive the movable frame in the X direction in  FIG. 3 , and the magnet  112   c  is a magnet to drive the movable frame in the Y direction in  FIG. 3 . 
       FIG. 4  is a diagram showing a configuration of the movable frame  104 . In  FIG. 4 , a left part is a front view of the movable frame  104 , and a right part is a side view of the same. As shown in  FIG. 4 , the movable frame  104  includes an imaging element  114 , three drive coils  116   a ,  116   b , and  116   c , and three detectors, namely, Hall elements  118   a ,  118   b , and  118   c.    
     The imaging element  114  is mounted in an opening in a central portion of the movable frame  104 . The imaging element  114  images an object and generates an image signal concerning the object. The imaging element  114  converts an image signal to a digital signal and outputs the digital signal. 
     The drive coil  116   a  is disposed on an upper left corner in the front surface of the movable frame  104  so as to correspond to the magnet  112   a  disposed on the fixed frame  102 . The drive coil  116   a  generates a magnetic flux by a current applied thereto. 
     The drive coil  116   b  is disposed on a lower left corner in the front surface of the movable frame  104  so as to correspond to the magnet  112   b  disposed on the fixed frame  102 . The drive coil  116   b  generates a magnetic flux by a current applied thereto. 
     The drive coil  116   c  is disposed on a bottom center portion in the front surface of the movable frame  104  so as to correspond to the magnet  112   c  disposed on the fixed frame  102 . The drive coil  116   c  generates a magnetic flux by a current applied thereto. 
     The Hall element  118   a  is disposed in a nearly central portion of a winding, which is a point of application of a driving force of the drive coil  116   a . The Hall element  118   a  outputs a detection signal in accordance with the magnetic flux from the magnet  112   a  as a position signal indicative of a position of the movable frame  104  relative to the fixed frame  102 . 
     The Hall element  118   b  is disposed in a nearly central portion of a winding, which is a point of application of a driving force of the drive coil  116   b . The Hall element  118   b  outputs a detection signal in accordance with the magnetic flux from the magnet  112   b  as a position signal indicative of a position of the movable frame  104  relative to the fixed frame  102 . 
     The Hall element  118   c  is disposed in a nearly central portion of a winding, which is a point of application of a driving force of the drive coil  116   c . The Hall element  118   c  outputs a detection signal in accordance with the magnetic flux from the magnet  112   c  as a position signal indicative of a position of the movable frame  104  relative to the fixed frame  102 . 
       FIG. 5  is a diagram showing a configuration of the yoke  106 . In  FIG. 5 , a left part is a front view of the yoke  106 , and a right part is a side view of the same. As shown in FIG.  5 , the yoke  106  has an almost L shape that faces the magnets  112   a ,  112   b , and  112   c  of the fixed frame  102  shown in  FIG. 3 . The yoke  106  is formed of a ferromagnetic material, such as iron, and forms a magnetic circuit among the magnets  112   a ,  112   b , and  112   c . Thus, the yoke  106  functions to increase the magnetic flux that the drive coils  116   a ,  116   b , and  116   c  receive. 
       FIG. 6  is a diagram showing a fundamental configuration of a voice coil motor (VCM).  FIG. 6  shows a VCM comprised of the magnet  112   a  and the drive coil  116   a . A VCM comprised of the magnet  112   b  and the drive coil  116   b  and a VCM comprised of the magnet  112   c  and the drive coil  116   c  are the same as the VCM comprised of the magnet  112   a  and the drive coil  116   a  in a basic configuration, except for a difference in placement of the magnetic poles of the magnets. Therefore, in  FIG. 6 , the magnets  112   a ,  112   b , and  112   c  are collectively indicated as the magnet  112 , the drive coils  116   a ,  116   b , and  116   c  are collectively indicated as the drive coil  116 , and the Hall elements  118   a ,  118   b , and  118   c  are collectively indicated as the Hall element  118 .  FIG. 6  shows placement of the magnet  112 , the drive coil  116 , and the Hall element  118  in the VCM in an initial state, when driving has not started, for example, immediately after the power is turned on. 
     In the initial state, as shown in  FIG. 6 , the central portion of the winding of the drive coil  116  is placed above a boundary line between the first magnet  1121  and the second magnet  1122  of the magnet  112 , and in a central position that halves the boundary line. In this case, the Hall element  118  is also placed in a central position of the boundary line between the first magnet  1121  and the second magnet  1122 . With this configuration, the magnet  112  functions as not only a driving magnet that generates a magnetic flux to move the drive coil  116 , but also a position detecting magnet that generates a magnetic flux to detect a position by the Hall element  118 . 
       FIG. 7  is a diagram showing a configuration of a modification of a VCM. The magnet  112  of the modification shown in  FIG. 7  includes a third magnet  1123  in addition to the first magnet  1121  and the second magnet  1122 . The third magnet  1123  is disposed so that the pole opposite to that of the second magnet  1122  faces the movable frame  104 ; that is, in the case of the magnet  112   a , the north pole of the third magnet  1123  faces the movable frame  104 . In the initial state, as shown in  FIG. 7 , the central portion of the winding of the drive coil  116  is placed in a central position of a boundary line between the first magnet  1121  and the second magnet  1122  of the magnet  112 . On the other hand, the Hall element  118  is placed in a central position of the boundary line between the second magnet  1122  and the third magnet  1123 , not the central portion of the winding of the drive coil  116 . With this configuration, a set of the first magnet  1121  and the second magnet  1122  of the magnet  112  function as driving magnets that generate a magnetic flux to move the drive coil  116 . In addition, a set of the second magnet  1122  and the third magnet  1123  of the magnet  112  function as position detecting magnets that generate a magnetic flux to detect a position by the Hall element  118 . Thus, in the example shown in  FIG. 7 , the second magnet  1122  serves as a magnet for both driving and position detecting. 
     In the configuration shown in  FIG. 6  or  FIG. 7 , when the drive coil  116  is energized, a magnetic flux and driving force corresponding to the amount and direction of a current flowing through the drive coil  116  are generated. The drive coil  116  moves in accordance with the driving force generated in the drive coil  116 . When the drive coil  116  moves, the positional relationship between the Hall element  118  and the position detecting magnet changes. Accordingly, the amount of the magnetic flux received by the Hall element  118  changes, and the amount of the detection signal output by the Hall element  118  also changes. Thus, a relative position between the drive coil  116  and the Hall element  118  can be detected from the detection signal output by the Hall element  118 . 
     The operations described above are performed for the VCM comprised of the magnet  112   a  and the drive coil  116   a , the VCM comprised of the magnet  112   b  and the drive coil  116   b , and the VON comprised of the magnet  112   c  and the drive coil  116   c  in the same manner. At that time, the movable frame  104  moves or rotates relative to the fixed frame  102  by appropriately setting the amounts of drive currents applied to the drive coils  116   a ,  116   b , and  116   c . A position of the movable frame  104  relative to the fixed frame  102  is detected from detection signals output by the Hall elements  118   a ,  118   b , and  118   c.    
     In the VCM shown in  FIG. 6 , the Hall element  118  is placed in a central portion of the winding of the drive coil  116 . In this case, the third magnet  1123  shown in  FIG. 7 , which is a position detecting magnet, need not be placed; therefore, the VOM can be compact. On the other hand, since the Hall element  118  is placed in the central portion of the winding of the drive coil  116 , the Hall element  118  actually receives a magnetic flux from the drive coil  116 , not only magnetic fluxes from the first magnet  1121  and the second magnet  1122 , as shown in  FIG. 8 . Therefore, the detection signal output from the Hall element  118  includes a false position signal corresponding to the magnetic flux from the drive coil  116  as a noise signal. 
       FIG. 8  shows a generation principle of a false position signal in the configuration shown in  FIG. 6 . However, even in the configuration including the position detecting magnet as shown in  FIG. 7 , if the drive coil  116  and the Hall element  118  are placed at a short distance, the detection signal output from the Hall element  118  includes a false position signal corresponding to the magnetic flux from the drive coil  116  as in the configuration shown in  FIG. 6 . 
       FIG. 9  is a diagram showing an amount of a false position signal output from a Hall element relative to an amount of current applied to a drive coil. Generally, it is known that the amount of a magnetic flux generated in a coil is proportional to the amount of a current applied to the coil. Therefore, the amount of a false position signal is also proportional to the amount of a current, as shown in  FIG. 9 . For example, if the amount of a current applied to the coil is 100 mA, the Hall element outputs a false position signal corresponding to 100 mA. 
       FIG. 10  is a diagram showing a detection deviation of a position due to generation of a false position signal. The horizontal axis in  FIG. 10  represents a position of the movable frame  104  detected from a detection signal. The vertical axis in  FIG. 10  represents an amount of the detection signal. As shown in  FIG. 9 , the detection signal output from the Hall element  118  includes a false position signal corresponding to the amount of current flowing through the drive coil. Therefore, with regard to the same position of the movable frame  104 , when the current flowing through the drive coil  116  is 100 mA, the detection signal includes a false position signal corresponding to 100 mA in addition to the detection signal generated when the current flowing through the drive coil  116  is 0 mA. Similarly, when the current flowing through the drive coil  116  is −100 mA, the detection signal includes a false position signal corresponding to −100 mA in addition to the detection signal generated when the current flowing through the drive coil  116  is 0 mA. If position detection is performed on the basis of the detection signal including a false position signal, the detected position includes a deviation from the actual position. Therefore, to accurately detect a position of the movable frame  104 , the false position signal must be removed from the detection signal output from the Hall element  118 . 
       FIG. 28  is a block diagram showing a configuration of a position control system of a camera shake correction unit  23  in an imaging device  1  of prior art. As shown in  FIG. 28 , the imaging device  1  includes a controller  202 , a motor driver  204 , a motor (VCM)  206 , a position detecting magnet  208 , a Hall element  212 , an analog amplifier  214 , a low-pass filter (LPF)  216 , an AD converter  218 , a false position signal calculation block  220 , a subtractor  222 , a position correction block  224 , and a subtractor  226 . A part of these components may be configured by software. The configuration shown in  FIG. 28  is provided for each of a number of VCMs, although  FIG. 28  shows the configuration for only one of the VCMs. Furthermore,  FIG. 28  indicates one of the VCMs (each formed of a drive coil and a driving magnet) in the camera shake correction unit  23  as the motor  206 , one of the position detecting magnets of the VCM (which also functions as a driving magnet in  FIG. 6 ) as the magnet  208 , and one of the Hall elements as the Hall element  212 . 
     The controller  202  is a drive controller that performs feedback control about the position of the movable frame  104  by, for example, PID control. Specifically, the controller  202  includes an IIR filter, performs a filtering process for a deviation signal input from the subtractor  226  to generate a signal indicative of a value of a drive current for driving the motor  206 , and outputs the value of the generated drive current to the motor driver  204 . 
     The motor driver  204  displaces the movable frame  104  by applying a drive signal, corresponding to the value of the drive current input from the controller  202 , to the motor  206  (actually, the drive coil  116 ). 
     The analog amplifier  214  receives a detection signal output from the Hall element  212 , and analog-amplifies the received detection signal within an AD conversion range in the AD converter  218 . As described above, the detection signal output from the Hall element  212  includes not only a signal based on a magnetic flux from the magnet  208  but also a false position signal  210  based on a magnetic flux from the motor  206  (actually, the drive coil  116 ). The analog amplifier  214  analog-amplifies the detection signal including a false position signal. 
     The LPF  216  performs LPF processing for removing a high-frequency component of the detection signal to suppress aliasing that occurs when a detection signal output from the analog amplifier  214  is AD converted. 
     The AD converter  218  converts a detection signal output from the LPF  216  to a digital signal. 
     The false position signal calculation block  220  calculates the amount of a false position signal included in a position signal. As described above, a false position signal is proportional to the amount of a current flowing through the drive coil constituting the motor  206 . Therefore, the false position signal calculation block  220  calculates the amount of a false position signal by multiplying the value of a drive current, which is calculated by the controller  202 , by a false signal gain, which is a predetermined proportionality coefficient determined by characteristics of the drive coil etc. 
     The subtractor  222  subtracts the value of the false position signal calculated by the false position signal calculation block  220  from an AD value of the detection signal input from the AD converter  218  (including the false position signal). The subtractor  222  outputs the subtraction result to the position correction block  224  as a corrected AD value. 
     The position correction block  224  generates a current position signal to perform digital correction to control the movable frame  104  to be located at a correct position based on the corrected AD value input from the subtractor  222 . The position correction block  224  outputs the generated current position signal to the subtractor  226 . The Hall element  212  or the like has temperature characteristics, and can output different detection signals with respect to the same position of the movable frame  104 . The position correction block  224  may correct an error due to the temperature characteristics or the like by using a temperature sensor (not shown). 
     In this embodiment, the position correction block  224  performs software processing; however, a part or all of the block may be constituted by an analog circuit. 
     The subtractor  226  outputs to the controller  202  a deviation signal corresponding to a difference between a drive target position signal indicative of a drive target position of the movable frame  104  input from, for example, the control circuit  26 , and a current position signal generated by the position correction block  224 . The controller  202  calculates a drive current based on the deviation signal. As a result, the position of the movable frame  104  moves closer to the drive target position. 
     Some of the magnetic flux generated in the drive coil  116  is directly received by the Hall element  118 , and some is received via the driving magnet  112 . 
     Both the drive coil  116  and the Hall element  118  are disposed on the movable frame  104 , and their relative positions are not variable. Therefore, it is considered that the amount of the magnetic flux directly received by the Hall element  118  from the drive coil  116  is almost invariable. Therefore, the false position signal output from the Hall element  118  based on the amount of magnetic flux that the Hall element  118  directly received from the drive coil  116  can be calculated by multiplying the drive current by the constant false position signal gain, as described above. 
     On the other hand, the position of the magnet  112  relative to the drive coil  116  and the Hall element  118  may vary. Due to a change in relative position, the amount of the magnetic flux received from the drive coil  116  via the driving magnet  112  is variable. The false position signal due to the change in magnetic flux cannot be calculated by multiplying the drive current by the constant false position signal gain. 
       FIG. 11  is a diagram showing a relationship among the magnet  112 , the drive coil  116 , and the Hall element  118  in a state where the movable frame  104  has been shifted in XY directions from the fixed frame  102 . As described before, when the drive coil  116  is energized, the movable frame  104  moves relative to the fixed frame  102 . Even in this case, the relative position between the drive coil  116  and the Hall element  118  in the movable frame  104  does not vary. On the other hand, the position of the magnet  112  on the fixed frame  102  relative to the drive coil  116  and the Hall element  118  varies in accordance with the amount of movement (the shift amount) of the movable frame  104  relative to the fixed frame  102 . At this time, the magnetic flux received by the magnet  112  from the drive coil  116  decreases. 
       FIG. 12  is a diagram showing a dependence of the amount of a false position signal on a shift amount. In  FIG. 12 , the horizontal axis represents a shift amount of the drive coil  116  relative to the magnet  112 . The shift amount corresponds to the amount of a shift from the central position  0  of the boundary line between the first magnet  1121  and the second magnet  1122  of the magnet  112  shown in  FIG. 11 . The vertical axis in  FIG. 12  represents an amount of a false position signal per unit of current. As shown in  FIG. 12 , even if the amount of a current applied to the drive coil does not change, the amount of a false position signal output from the Hall element  118  increases as the shift amount increases and the magnetic flux from the drive coil  116  received by the magnet  112  decreases. For example, when the shift amount is A, the amount of the false position signal is SA, which is greater than SO of a false position signal generated when the shift amount is 0. 
       FIG. 13  is a diagram showing an amount of a false position signal output from a Hall element relative to an amount of a current applied to the drive coil  116  in consideration of the shift amount of the movable frame  104 . As shown in  FIG. 9 , the amount of a false position signal from the drive coil  116  is proportional to the amount of current. However, if the shift amount varies, even if the same current is applied to the drive coil  116 , the amount of a false position signal output from the Hall element  118  varies. 
       FIG. 11  shows a change in false position signal in accordance with movement of the movable frame  104  relative to the fixed frame  102  in the XY directions. Actually, a deviation in the Z direction (gap misalignment) may arise between the fixed frame  102  and the movable frame  104 . If a gap misalignment as shown in  FIG. 14  arises, the gap misalignment may also arise between the magnet  112  and the drive coil  116  or the Hall element  118 . 
     A concept about a gap will be explained below.  FIG. 15A  illustrates a gap. The fixed frame  102  and the movable frame  104  are disposed to be spaced at a predetermined gap via balls  110  interposed therebetween, and the movable frame  104  is urged toward the fixed frame  102  by the urging springs  108  attached to the fixed frame  102 . Thus, the gap is basically configured so that the balls  110  are always in contact with the fixed frame  102  and the movable frame  104  by the urging force of the urging springs  108 . Strictly, however, it is difficult to attach the movable frame  104  to the fixed frame  102  in parallel. For example, when the fixed frame  102  and the movable frame  104  are produced, the surface on which the movable frame  104  is in contact with the ball  110  and the surface on which the fixed frame  102  is in contact with the ball  110  may be inclined with respect to each other as shown in  FIG. 15B . Because of the inclination, the gap between the fixed frame  102  and the movable frame  104  may be nonuniform from place to place. Since the amount of the gap between the fixed frame  102  and the movable frame  104  is not uniform, the amount of the magnetic flux from the drive coil  116  received by the magnet  112  varies. The variance of the magnetic flux appears as a false position signal output from the Hall element  118 . 
       FIG. 16  is a diagram showing a dependence of an amount of a false position signal on a gap amount. The horizontal axis in  FIG. 16  represents an amount of a gap between the magnet  112  and the drive coil  116 . The vertical axis in  FIG. 16  represents an amount of a false position signal per unit of current. As shown in  FIG. 16 , the greater the amount of the gap between the magnet  112  and the drive coil  116 , the less the amount of the false position signal. 
       FIG. 17  is a diagram showing a drive characteristic (transmission characteristic) of the motor (VCM)  206 . In  FIG. 17 , the horizontal axis represents a frequency of a current applied to the drive coil  116 , and the vertical axis represents a displacement of the movable frame  104  per unit of current. The characteristic shown in  FIG. 17  is represented by a transfer function that is expressed in a formula (1). In the formula (1), X(s)/I(s) represents a displacement (one dimensional) per unit of current, s represents a Laplace operator, ζ an attenuation coefficient, and ω n  a frequency. The actual displacement of the movable frame  104  also depends on the amplitude of a drive current. Specifically, the actual displacement of the movable frame  104  is a product of the displacement per unit of current and the amplitude of a drive current. 
     
       
         
           
             
               
                 
                   
                     
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     As shown in  FIG. 17 , the motor  206  has different drive characteristics respectively in (1) a low-frequency band, (2) a mid-frequency band, and (3) a high-frequency band. In the low-frequency band, the displacement of the movable frame  104  per unit of current is large. In the mid-frequency band, the displacement of the movable frame  104  per unit of current is moderate. In the high-frequency band, the displacement of the movable frame  104  per unit of current is small. 
       FIG. 18A  is a diagram showing (1) a drive current in the low-frequency band, (2) a drive current in the mid-frequency band, and (3) a drive current in the high-frequency band. In  FIG. 18A , amplitudes of the respective drive currents are the same.  FIG. 18B  is a diagram showing displacements of the movable frame  104  that respectively occur when the drive currents shown in  FIG. 18A  are applied to the motor  206  (the drive coil  116 ). 
     In the low-frequency band, since the displacement per unit of current is large as shown in  FIG. 17 , when the drive current of the amplitude shown in  FIG. 18A  is applied to the motor  206 , a large displacement as shown in  FIG. 18B  occurs. Similarly, in the mid-frequency band, since the displacement per unit of current is moderate as shown in  FIG. 17 , when the drive current of the amplitude shown in  FIG. 18A  is applied to the motor  206 , a moderate displacement as shown in  FIG. 18B  occurs. However, in the high-frequency band shown in  FIG. 17 , the motor  206  cannot follow the drive current. Therefore, in the high-frequency band, even if the amplitude of the drive current is increased, the displacement is negligible as shown in  FIG. 18B . As will be described in detail later, in this embodiment, a false position signal in accordance with the shift or gap misalignment between the fixed frame  102  and the movable frame  104  is detected using a drive current in a high-frequency band. At this time, it is not desirable that the displacement of the movable frame  104  due to the drive current to detect a false position signal affects an image produced via the imaging element  114 . Therefore, “the high frequency” in this embodiment is preferably a frequency in which the displacement of the movable frame  104  does not affect an image produced via the imaging element  114 . Specifically, “the high frequency” in this embodiment is preferably a frequency in which the displacement of the movable frame  104  falls within a range of one pixel of the imaging element  114 . 
       FIG. 19  is a block diagram showing a configuration of a position control system of the camera shake correction unit  23  of the imaging device  1  according to the embodiment. Configurations that are the same as those shown in  FIG. 28  are specified by the same reference symbols as those in  FIG. 28 , and explanations thereof are omitted as appropriate. 
     The motor driver  204  of this embodiment includes a high frequency superimposing unit  204   a  The high frequency superimposing unit  204   a  includes, for example, a high frequency oscillator, and applies to the motor  206  a drive signal in which a high-frequency drive current (high-frequency drive signal) is superimposed on a drive current corresponding to a drive signal from the controller  202 .  FIG. 20A  is a diagram showing drive signals output from the motor driver  204  in this embodiment. A broken line in  FIG. 20A  represents a drive current that flows before superimposition of a high-frequency drive current. A solid line in  FIG. 20A  represents a drive current that flows after superimposition of a high-frequency drive current. As described before, the drive current to drive the motor  206  is the drive current in the low-frequency band indicated by (1) in  FIG. 17 , and the high-frequency drive current is the drive current in the high-frequency band indicated by (3) in  FIG. 17 . In this embodiment, (1) the drive current in the low-frequency band is assumed to be several tens of Hz or lower; (2) the drive current in the mid-frequency band is assumed to be from several tens of Hz to 1 kHz; and (3) the drive current in the high-frequency band is assumed to be a value that is higher than 1 kHz and that suppresses the displacement of the movable frame  104  to a range smaller than the pixel pitch (that is, the displacement of the movable frame  104  is negligible). However, since the frequencies in the low, mid, and high frequency bands are relative values, they are not limited to the numerical values mentioned above. 
     The motor  206  is driven in accordance with a drive signal on which a high-frequency drive current is superimposed. As described above, the high-frequency drive current affects almost nothing on the displacement of the movable frame  104 .  FIG. 20B  is a diagram showing a displacement of the movable frame  104  that occurs when the drive currents shown in  FIG. 20A  are applied to the motor  206 . A broken line in  FIG. 20B  represents a displacement of the movable frame  104  that occurs when the drive current before superimposition of the high-frequency drive current is applied to the motor  206 . A solid line in  FIG. 20B  represents a displacement of the movable frame  104  that occurs when the drive current after superimposition of the high-frequency drive current is applied to the motor  206 . Since the high-frequency drive current affects almost nothing on the displacement of the movable frame  104  as described above, the displacement of the movable frame  104  is almost the same before and after the superimposition of the high-frequency drive current. 
       FIG. 20C  is a diagram showing outputs of the analog amplifier  214  that are output when the drive currents shown in  FIG. 20A  are applied to the motor  206 . As described above, the Hall element  212  detects not only a change in magnetic flux based on the displacement of the movable frame  104  relative to the fixed frame  102  but also a magnetic flux from the drive coil  116 . Although the displacement of the movable frame  104  is negligible when the high-frequency drive current is applied to the motor  206 , a magnetic flux based on the high-frequency drive current occurs in the drive coil  116 . The Hall element  212  outputs a detection signal including a detection signal based on the magnetic flux that is generated in the drive coil  116  by application of a high-frequency drive current. The analog amplifier  214  amplifies a detection signal output from the Hall element  212  including the high-frequency component of the signal. A broken line in  FIG. 20C  represents an output that is output from the analog amplifier  214  when the drive current before superimposition of the high-frequency drive current is applied to the motor  206 . A solid line in  FIG. 20C  represents an output that is output from the analog amplifier  214  when the drive current after superimposition of the high-frequency drive current is applied to the motor  206 . 
     The output of the analog amplifier  214  is input to the LPF  216 . The LPF  216  removes the high-frequency component from the output of the analog amplifier  214  and outputs a filtered output. 
     The output of the analog amplifier  214  is also input to a high frequency detection unit  228 .  FIG. 21  shows a configuration of an example of the high frequency detection unit  228 . As shown in  FIG. 21 , the high frequency detection unit  228  includes a band pass filter (BPF)  228   a  and an AD converter  228   b . The BPF  228   a  is a filter to which a frequency characteristic is set to allow passage of a signal having a frequency of the high-frequency drive current as shown in  FIG. 22 . In other words, the BPF  228   a  acquires, from the output of the analog amplifier  214 , a predetermined high-frequency signal corresponding to the frequency of the high-frequency drive current superimposed on a low-frequency wave or a mixed wave of a low-frequency wave and a mid-frequency wave. The AD converter  228   b  converts the high-frequency signal output from the BPF  228   a  to a digital signal. The AD converter  228   b  outputs an AD value of the high-frequency signal to a false position signal gain calculation block  230 . 
     The false position signal gain calculation block  230 , together with the false position signal calculation block  220 , functions as a noise signal calculation unit. The false position signal gain calculation block  230  calculates a false position signal gain to correct the false position signal from the AD value of the high-frequency signal extracted by the high frequency detection unit  228 . The value of the gain of the false position signal is 1 at maximum. The false position signal calculation block  220  calculates a false position signal in accordance with the false position signal gain calculated in the, false position signal gain calculation block  230  and the amount of the drive current, that is, the drive signal output from the controller  202 . The subtractor  222  as a signal correction unit subtracts a value of the false position signal calculated in the false position signal calculation block  220 . The subtractor  222  outputs the subtraction result to the position correction block  224  as a corrected AD value. 
     The configurations shown in  FIG. 19  are the same as those shown in  FIG. 28  except those described above. Therefore, explanations thereof are omitted. 
     A method for calculating a false position signal gain in this embodiment will be described below. As described above, the displacement of the movable frame  104  is negligible even when the high-frequency drive current is applied to the motor  206 . Therefore, the detection signal in the frequency band of the high-frequency drive current does not depend on the displacement of the movable frame  104 , but depends on the amount of the drive current flowing through the drive coil  116  and the distance between the driving magnet  112  and the drive coil  116  (the shift amount and the gap amount). As shown in  FIG. 23 , the amplitude of the signal output from the BPF  228   a  varies depending on the distance between the driving magnet  112  and the driving coil  116 , even if the amount of the driving current does not vary. A false position signal gain can be calculated from the amplitude of the signal. 
       FIG. 24  is a flowchart showing a process for calculating a false position signal gain. The processing of  FIG. 24  is executed at a frequency of twice or higher than the frequency of the high-frequency drive current. This is because the sampling frequency of the AD converter  228   b  must be twice or higher than the frequency of the high-frequency drive current in order to correctly AD convert the high-frequency component of the detection signal by the AD converter  228   b.    
     In step S 1 , the high frequency detection unit  228  detects a high-frequency component of the detection signal output from the Hall element  212  and amplified by the analog amplifier  214 . More specifically, in the high frequency detection unit  228 , the BPF  228   a  acquires a high-frequency component corresponding to the frequency of the high-frequency drive current in the detection signal, and the AD converter  228   b  converts the acquired high-frequency component of the detection signal to a digital signal and outputs the digital signal to the false position signal gain calculation block  230 . 
     In step S 2 , the false position signal gain calculation block  230  determines whether or not acquisition of the high-frequency component for one cycle has completed. If it is determined that acquisition of the high-frequency component for one cycle has not completed in step S 2 , the processing is ended. If it is determined that acquisition of a high-frequency component for one cycle has completed in step S 2 , the processing proceeds to step S 3 . 
     In step S 3 , the false position signal gain calculation block  230  calculates a false position signal gain. A false position signal gain G as a false position signal coefficient is calculated from a formula (2) below, where A represents a drive current amplitude of a high-frequency drive signal generated by the high frequency superimposing unit  204   a  of the motor driver  204 , and H represents an AD value of the amplitude of the detection signal output from the high frequency detection unit  228 . The drive current amplitude A is set to be predetermined amplitude; it may be a fixed value. From the formula (2), it is considered that the high-frequency component of the detection signal is a false position signal itself, and does not depend on the displacement of the movable frame  104 . Therefore, a false position signal gain can be calculated from the amplitude of the high-frequency component of the detection signal. After the calculation of the false position signal gain, the processing is ended.
 
 G=H/A    formula (2)
 
     Operations of the position control system shown in  FIG. 19  will be described below.  FIG. 25  is a flowchart of feedback control in the position control system shown in  FIG. 19 . During the processing shown in  FIG. 25 , the processing for calculating a false position signal gain shown in  FIG. 24  is performed. The processing of  FIG. 25  need not be performed at such a high speed as in the processing of  FIG. 24 . For example, the processing of  FIG. 25  can be performed at such a frequency that allows feedback control to be performed. 
     In step S 11 , a target position is acquired. The target position is input to the subtractor  226  from, for example, the control circuit  26 . For example, the target position is set in accordance with the amount of camera shake. 
     In step S 12 , the current position calculation processing is performed. In the following, the current position calculation processing will be described with reference to  FIG. 26 . 
     In step S 21 , the subtractor  222  acquires the AD value that was LPF-processed in the LPF  216 . As described before, the AD value is an AD value of a detection signal that does not include a detection signal component based on a high-frequency drive signal. 
     In step S 22 , false position signal correction processing is performed. In the following, the false position signal correction processing will be described with reference to FIG.  27 . 
     In step S 31 , the false position signal gain calculation block  230  calculates a false position signal gain. The processing in step S 31  is the processing shown in  FIG. 24 . 
     In step S 32 , the false position signal calculation block  220  acquires the false position signal gain calculated in the false position signal gain calculation block  230 . In step S 32 , the latest one of the false position signal gains successively calculated in step S 31  is acquired. Then, the false position signal gain calculation block  230  determines whether or not the acquired false position signal gain falls within a predetermined range. If it is determined that the acquired false position signal gain does not fall within the predetermined range in step S 32 , the processing proceeds to step S 33 . If it is determined that the acquired false position signal gain falls within the predetermined range in step S 32 , the processing proceeds to step S 34 . 
     When the false position signal gain exceeds the predetermined range in step S 32 , the variation of the amplitude of the false position signal is too large or too small. Generally, the variation of the amount of shift or gap occurs within a certain range. Therefore, when the variation of the amplitude of the false position signal is too large or too small, it is considered that the cause of the variation of the amplitude of the false position signal is not the variation of the amount of shift or gap; for example, the cause may be a malfunction of the motor  206  itself. In such a case, the processing proceeds to step S 33 , and an error notification is made using, for example, the monitor  24 . After the error notification, the processing proceeds to step S 34 . The error notification includes a message to the effect that, for example, a camera shake correction cannot be performed or a drive current correction cannot be performed. Furthermore, the feedback control itself may be stopped instep S 33 . In this case as well, it is desirable to make an error notification. 
     In step S 34 , the false position signal calculation block  220  calculates a false position signal. The false position signal F is expressed by the following formula (3), where I represents the amount of a drive current:
 
 F=I×G    formula (3)
 
     In step S 35 , the subtractor  222  calculates the corrected AD value. The corrected AD value H′ is calculated from the following formula (4) using the AD value B, namely, the AD value that was LPF-processed and output from the AD converter  218 . Then, the processing is ended.
 
 H′=B−F    formula (4)
 
     Referring back to  FIG. 26 , after the false position signal correction in step S 22 , the position correction block  224  corrects the corrected AD value in step S 23 . Then, the processing is ended. The position correction block  224  corrects an error due to a temperature characteristic or the like in the corrected AD value, and generates a current position signal. 
     Referring back to  FIG. 25 , after the current position signal is calculated in step S 12 , the subtractor  226  calculates a deviation between the target position and the current position in step S 13 . The deviation signal output from the subtractor  226  is input to the controller  202 . In step S 14 , the controller  202  generates a drive signal indicative of a value of the drive current to drive the motor  206 . In step S 15 , the drive signal is input to the motor driver  204  from the controller  202 . As a result, the amount of the drive current in the motor driver  204  is set, and the motor  206  (actually, the drive coil  116 ) is driven in accordance with the amount of the drive current. The feedback control shown in  FIG. 25  is repeated, so that the movable frame  104  reaches the target position. 
     As described above, according to the embodiment, the motor  206  is driven by the drive current of the motor  206  on which the high-frequency drive current is superimposed. The detection signal output from the Hall element  212  includes a detection signal generated from the drive coil  116  in addition to the detection signal due to a change in magnetic flux based on the displacement of the movable frame  104 . However, in the high-frequency band of the detection signal, the influence of the detection signal generated from the drive coil  116  becomes dominant. Therefore, by acquiring an amplitude component of the detection signal in the high-frequency band, even if the distance (the amount of shift and gap) between the magnet  112  and the drive coil  116  varies, an accurate false position signal can be detected. Accordingly, an accurate false position signal gain including a variation of the distance (the amount of the shift and gap) between the magnet  112  and the drive coil  116  can be calculated. Thus, the position signal can be corrected adaptively and accurately in consideration of the variation of the distance (the amount of the shift and gap) between the magnet  112  and the drive coil  116 . 
     In the embodiment, the frequency of the high-frequency drive current is a frequency in which the displacement of the movable frame  104  falls within a range of one pixel of the imaging element  114 . Because of this frequency, the image quality is not affected by superimposing the high-frequency drive current on the drive current. 
     Although the present invention has been described based on the embodiment, the invention is not limited to the embodiment, and various modifications or applications may be made without departing from the spirit or scope of the general inventive concept of the present invention. For example, the configuration of the camera shake correction unit  23  described above is a mere example, but can be modified as appropriate. For example, the VCM may have a different configuration. In the example described above, the magnets are disposed on the fixed frame and the Hall elements are disposed on the movable frame. Instead, the magnets may be disposed on the movable frame and the Hall elements may be disposed on the fixed frame. Furthermore, the camera shake correction unit  23  may be configured to move the optical system  11  instead of the imaging element  114 . Moreover, the camera shake correction unit  23  may be used for a purpose other than the camera shake correction processing. For example, the camera shake correction unit  23  may be used for super-resolution processing. 
     Each of the processes of the embodiment described above may be stored as a program that can be executed by the CPU or the like as a computer. Alternatively, that can be stored and distributed in a storage medium of an external storage device, such as a memory card, a magnetic disk, an optical disk, and a semiconductor memory. The CPU or the like can read the program stored in the storage medium of the external storage device, and controls operations in accordance with the read program, so that the processing described above can be executed. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.