Abstract:
Provided is a lens unit comprising an actuator that is self-supporting when at a stopped position. The lens unit comprises a holding frame that holds a lens; a movement actuator that moves the holding frame, which is connected to a moving member that moves linearly relative to a stator, when drive force is generated, and does not prevent the moving member from moving relative to the stator when the moving member is stopped; and a braking actuator that stops the moving member from moving relative to the stator, using frictional force, when the movement actuator is not generating the drive force, and decreases the frictional force when the movement actuator generates the drive force.

Description:
[0001]    The contents of the following. Japanese patent applications are incorporated herein by reference: No. 2009-135474 filed on Jun. 4, 2009, and No. 2009-135496 filed on Jun. 4, 2009. 
         [0002]    The contents of the following International patent application are incorporated herein by reference: PCT/JP2010/003742 filed on Jun. 4, 2010. 
       BACKGROUND 
       [0003]    1. Technical Field 
         [0004]    The present invention relates to a lens unit and an image capturing apparatus. 
         [0005]    2. Related Art 
         [0006]    In an optical system of an image capturing apparatus, a linear actuator is used as one type of drive source for moving the optical components. A linear actuator can be formed by arranging one of coils and a permanent magnet on a stator in a line and mounting the other of the coils and the permanent magnet on a moving member that moves along the stator, as described in Japanese Patent Application Publication No. 2004-191453, for example. 
         [0007]    In a linear actuator, the moving member has a structure enabling smooth movement. Therefore, when the moving member is stopped, power is consumed in order to hold the moving member at the stopped position using feedback control based on the position of the moving member, for example. Furthermore, when the power supply is cut off, the linear actuator cannot maintain the position of the moving member. 
       SUMMARY 
       [0008]    In order to solve the above problems, according to a first aspect related to the innovations herein, provided is a lens unit comprises a holding frame that holds a lens; a movement actuator that moves the holding frame, which is connected to a moving member that moves linearly relative to a stator, when drive force is generated, and does not prevent the moving member from moving relative to the stator when the moving member is stopped; and a braking actuator that stops the moving member from moving relative to the stator, using frictional force, when the movement actuator is not generating the drive force, and decreases the frictional force when the movement actuator generates the drive force. 
         [0009]    According to a second aspect related to the innovations herein, provided is an image capturing apparatus comprising the lens unit. 
         [0010]    The summary clause does not necessarily describe all necessary features of the embodiments or the present invention. The present invention may also be a sub-combination of the Features described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a schematic cross-sectional view of the overall image capturing apparatus  99 . 
           [0012]      FIG. 2  is a perspective view of the linear movement drive section  300 . 
           [0013]      FIG. 3  is a cross-sectional view of the linear movement drive section  300 . 
           [0014]      FIG. 4  is a cross-sectional view of the linear movement drive section  300  during operation. 
           [0015]      FIG. 5  is a perspective view of most of the configuration of the stator  120 . 
           [0016]      FIG. 6  is a schematic view of the electrical configuration of the linear movement drive section  300 . 
           [0017]      FIG. 7  is a block diagram of the control system  301  of the linear movement drive section  300 . 
           [0018]      FIG. 8  shows another configuration of the lens unit  100 . 
           [0019]      FIG. 9  shows yet another configuration of the lens unit  100 . 
           [0020]      FIG. 10  is a schematic cross-sectional view of another image capturing apparatus  499 . 
           [0021]      FIG. 11  is a perspective view of the linear movement drive section  700 . 
           [0022]      FIG. 12  is a cross-sectional view of the linear movement drive section  700 . 
           [0023]      FIG. 13  is a perspective view of most of the configuration of the stator  520 . 
           [0024]      FIG. 14  is a schematic view of the electrical configuration of the linear movement drive section  700 . 
           [0025]      FIG. 15  is a block diagram of the control system  701  of the linear movement drive section  700 . 
           [0026]      FIG. 16  shows another configuration of the lens unit  500 . 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0027]    Hereinafter, some embodiments of the present invention will be described. The embodiments do not limit the invention according to the claims, and all the combinations of the features described in the embodiments are not necessarily essential to means provided by aspects of the invention. 
         [0028]      FIG. 1  is a schematic cross-sectional view of an overall configuration of an image capturing apparatus  99 . The image capturing apparatus  99  is formed by combining a lens unit  100  and an image capturing section  200 . 
         [0029]    The lens unit  100  includes a lens barrel  110 , a stator  120 , a moving member  130 , a guide axle  140 , a guided portion  150 , a holding frame  160 , a diaphragm apparatus  170 , and a plurality of lens groups  102 ,  104 , and  106 . The lens groups  102 ,  104 , and  106  are arranged on a common optical axis C, thereby forming an optical system  101 . 
         [0030]    The lens barrel  110  is formed integrally with the image capturing section  200  by being connected to a mount section  260  of the image capturing section  200 , which is described further below. The stator  120  and the guide axle  140 , which are shaped as axles, are fixed within the lens barrel  110  to be parallel to each other and oriented in the longitudinal direction of the lens barrel  110 . 
         [0031]    The lens groups  102 ,  104 , and  106  are each held independently by the holding frame  160 . The holding frame  160  holds the lens group  104  and the diaphragm apparatus  170 . 
         [0032]    All or a portion of the holding frame  160  is supported to be moveable in the longitudinal direction of the lens barrel  110  from the stator  120  and the guide axle  140 , via the moving member  130 , the braking actuator  136 , and the guided portion  150 . The focal distance and focal position of the optical system  101  can be adjusted by moving the lens groups  102 ,  104 , and  106 . The braking actuator  136  is described in detail in relation to  FIGS. 3 and 4 . 
         [0033]    The image capturing section  200  includes an optical system having a main mirror  240 , a secondary mirror  242 , a pentaprism  270 , and an ocular optical system  290 , and a control system having a focal point detecting section  230 , a main control section  250 , and a photometric unit  280 . The main mirror  240  moves between a standby position, in which the main mirror  240  is oriented diagonally in the optical path of incident light through the optical system  101  of the lens unit  100 , and an image capture position, which is shown by the dotted line in  FIG. 1  and in which the main mirror  240  is raised out of the optical path of the incident light. 
         [0034]    A secondary mirror  242  is disposed on the back surface of the main mirror  240  in the standby position. The secondary mirror  242  guides a portion of the incident light passing through the main mirror  240  to the focal point detecting section  230  positioned therebelow. Therefore, when the main mirror  240  is in the standby position, the focal point detecting section  230  detects a focal state of the optical system  101 . When the main mirror  240  moves to the image capture position, the secondary mirror  242  also moves out of the optical path of the incident light. 
         [0035]    When in the standby position, the main mirror  240  is inclined relative to the incident light and guides a majority of the incident light to a focusing screen  272  arranged thereabove. The focusing screen  272  is arranged at the focal position of the optical system  101 , and displays the image formed by the optical system  101 . 
         [0036]    The image formed by the focusing screen  272  can be seen from the ocular optical system  290  via the pentaprism  270 . Therefore, the image on the focusing screen  272  can be seen as a normal image from the ocular optical system  290 . 
         [0037]    A half mirror  292  is arranged between the pentaprism  270  and the ocular optical system  290 . The half minor  292  superimposes the display image formed by the finder LCD  294  onto the image of the focusing screen  272 . As a result, the image seen at the output end of the ocular optical system  290  is a combination of the image of the focusing screen  272  and the image of the finder LCD  294 . The finder LCD  294  displays information concerning image capturing conditions, setting conditions, and the like of the image capturing apparatus  99 . 
         [0038]    A portion of the light output from the pentaprism  270  is guided to the photometric unit  280 . The photometric unit  280  measures the intensity of the incident light and a distribution or the like thereof, and these measurement results are referenced when determining the image capturing conditions. 
         [0039]    The image capturing section  200  includes a shutter  220 , an optical filter  212 , and an image capturing element  210  that are arranged in the stated order on the optical axis C behind the main minor  240  in a direction of the incident light from the lens unit  100 . When the release switch of the image capturing section  200  is pressed, the main mirror  240  moves to the image capture position, and so the incident light is directed toward the shutter  220 . When the shutter  220  is opened, the incident light progresses to be incident to the image capturing element  210 . As a result, the image formed by the optical system  101  is converted into an electrical signal by the image capturing element  210 . 
         [0040]    The image capturing section  200  is provided with a main LCD  296  facing away from the lens unit  100 . The main LCD  296  displays various types of setting information concerning the image capturing section  200 , and can also display the image formed by the image capturing element  210  when the main mirror  240  is in the image capture position. Furthermore, the main LCD  296  may be used when showing the images generated by the image capturing element  210 . 
         [0041]    The main control section  250  performs overall control of the various operations described above. Furthermore, the main control section  250  controls an auto-focus mechanism that drives the lens unit  100  while referencing information concerning the distance to a subject as detected by the focal point detecting section  230  of the image capturing section  200 . 
         [0042]      FIG. 2  is a perspective view of a linear movement drive section  300  in the lens unit  100 .  FIG. 2  shows one lens group  106  and the components for driving the holding frame  160  holding the lens group  106  extracted from the lens unit  100 . In  FIG. 2 , components that are the same as components in  FIG. 1  are given the same reference numerals, and redundant descriptions are omitted. 
         [0043]    In the linear movement drive section  300 , the holding frame  160  holding the lens group  106  is supported by the moving member  130  and the guided portion  150 , which are formed integrally at symmetrically opposite positions on a frame having a substantially circular shape. The moving member  130  couples with the holding frame  160  via the braking actuator  136 . The stator  120  is inserted into the moving member  130 , and the moving member  130  moves in the direction in which the stator  120  extends. The guide axle  140  is inserted into the guided portion  150 , and the guided portion  150  moves along the guide axle  140 . 
         [0044]    The drive force that moves the holding frame  160  is generated between the stator  120  and the moving member  130 , as will be described further below. Therefore, a cable  121  that supplies power is coupled to the stator  120 . 
         [0045]    The holding frame  160  and the guided portion  150  move together with the moving member  130 . The stator  120  and the guide axle  140  are arranged parallel to the optical axis C of the optical system  101 , and therefore the lens group  106  held by the holding frame  160  moves along the optical axis C. 
         [0046]      FIG. 3  is a cross-sectional view of the linear movement drive section  300 .  FIG. 3  shows the linear movement drive section  300  when the moving member  130  is not moving. 
         [0047]    The stator  120  includes an outer barrel  122 , a core  128 , and a plurality of coils  124 . The moving member  130  includes a moving member body  138 , and also a bearing  132 , a permanent magnet  134 , and a braking actuator  136  that are attached to the moving member body  138 . 
         [0048]    In the stator  120 , the outer barrel  122  and the core  128  are arranged to be coaxial. Each coil  124  is wrapped around the core  128  inside the outer barrel  122 , and the coils  124  are arranged in the longitudinal direction of the stator  120 . In order to improve the control of the linear movement drive section  300 , the outer barrel  122  and the core  128  are preferably non-magnetic. 
         [0049]    In the moving member  130 , the moving member body  138  has an inner diameter that is greater than the outer diameter of the stator  120 . A bearing  132  is disposed on the inner surface of the moving member  130  that is toward the bottom of  FIG. 3 , and in the state shown in  FIG. 3 , the bottom inner surface of the moving member  130  is separated from the stator  120 . On the other hand, the top inner surface of the moving member  130  serves as a braking surface  137  that contacts the top surface of the stator  120 . As a result, movement of the moving member  130  relative to the stator  120  can be stopped. 
         [0050]    The guided portion  150  has an inner diameter that is greater than the outer diameter of the guide axle  140 , and the inner surface of the guided portion  150  is distanced from the surface of the guide axle  140 . A pair of bearings  152  are disposed on the inner surface at each end of the guided portion  150 , and the guided portion  150  is supported by the guide axle  140  via the bearings  152 . Therefore, the guided portion  150  can slide along the guide axle  140 . 
         [0051]    The permanent magnet  134  is shaped as a ring that surrounds the stator  120  in the middle of the moving member body  138 . The permanent magnet  134  is magnetized such that the polarity is inverted at the ends thereof in the longitudinal direction of the stator  120 . However, the magnetism of the permanent magnet  134  is not particularly limited, and the permanent magnet  134  may be arranged to have a polarity in the longitudinal direction of the stator  120  that is opposite the polarity shown in  FIG. 3 . 
         [0052]    The top surface of the braking actuator  136  is coupled to the bottom surface of the moving member body  138 , and the bottom surface of the braking actuator  136  is coupled to the holding frame  160 . As a result, the holding frame  160  is connected to the moving member body  138 . When the braking actuator  136  operates according to a drive voltage supplied from the outside, the thickness of the braking actuator  136  increases, and the resulting state is shown in  FIG. 4 . 
         [0053]    In this way, when the braking actuator  136  is not operating, the moving member body  138  contacts the stator  120  and the resulting frictional force holds the moving member  130  in place. Accordingly, the holding frame  160  and the lens group  106  held by the holding frame  160  are held in place relative to the stator  120 . 
         [0054]    The braking actuator  136  is formed of a piezoelectric element whose thickness changes when voltage is applied thereto. In other words, a piezoelectric element is used to form the braking actuator  136  with a thickness that decreases when a drive voltage is applied thereto. As a result, when the linear movement drive section  300  is not driving the moving member  130 , the linear movement drive section  300  is in the state shown in  FIG. 4 . 
         [0055]      FIG. 4  is a cross-sectional view of the linear movement drive section  300  during operation. When the linear movement drive section  300  operates, the drive voltage is applied to the braking actuator  136  as well. Therefore, the thickness, i.e. height, of the braking actuator  136  increases and the moving member body  138  is raised upward, i.e. toward the top of  FIG. 4 . 
         [0056]    As a result, as shown in  FIG. 4 , the braking surface  137  of the moving member body  138  is moved away from the surface of the stator  120 . Furthermore, the bearing  132  of the moving member body  138  contacts the stator  120 . The bearing  132  decreases the sliding resistance between the moving member body  138  and the stator  120 , and so the moving member  130  can move smoothly on the stator  120 . The driving of the moving member  130  relative to the stator  120  is described further below in relation to  FIGS. 5 to 7 . 
         [0057]    The braking actuator  136  operating as described above can be formed of a bimetal that is deformed when heated. As another example, the braking actuator  136  can be formed of a shape memory alloy that returns to the remembered shape when heated to a transition temperature. 
         [0058]    The bimetal or shape memory alloy can be combined with a heater, for example, and controlled by turning the power supply ON and OFF. By transferring the heat generated by the coils  124  in the stator  120  to the braking actuator  136 , the operation of the linear movement drive section  300  is automatically performed simultaneously with the releasing of the brake on the moving member  130  by the braking actuator  136 . 
         [0059]    In the above example, one end of the holding frame  160  is driven by the moving member  130  and the other end serves as the guided portion  150  that follows on the moving member  130 . However, a pair of moving members  130  may be provided such that the holding frame  160  is driven simultaneously at both ends. In this case, it is obvious that a stator  120  is used in place of the guide axle  140 . 
         [0060]      FIG. 5  is a perspective view of the linear movement drive section  300 , in which the internal structures of the stator  120  and the moving member  130  are exposed. Components that are the same as components shown in  FIGS. 1 to 3  are given the same reference numerals, and redundant descriptions are omitted. 
         [0061]    The stator  120  includes the plurality of coils  124  arranged along the core  128 . Each coil  124  independently generates a magnetic field when a drive current is applied thereto. In the moving member  130 , the permanent magnet  134  surrounds the coils  124  from the outer surface of the outer barrel  122 . Furthermore, in the moving member  130 , the braking actuator  136  is arranged on the outer surface of the moving member  130  in the radial direction of the stator  120  and the moving member  130 . 
         [0062]      FIG. 6  is a schematic view of the electrical configuration of the linear movement drive section  300 . Components that are the same as components shown in other Figures are given the same reference numerals, and redundant descriptions are omitted. 
         [0063]    Each coil  24  is independently wrapped around the core  128 , and as shown by the dotted lines in  FIG. 6 , three phases (U, V, and W) are created. In this example, the three phases U, V, and W are used, but it is obvious that the configuration is not limited to three phases, and these phases can be set according to the desired distance over which the moving member  130  is to move. The connections of the coils  124  are not limited to three phases of connections, and the number of phase connections may be two, or greater than three. 
         [0064]      FIG. 7  is a block diagram showing the control system  301  of the linear movement drive section  300 . The control system  301  includes a position calculating section  320 , a drive circuit  330 , and a switch control section  340 . The control system  301  is included in the control section  250  of the image capturing section  200 . 
         [0065]    The position calculating section  320  references the position of the moving member  130  detected by the encoder  310  disposed in the linear movement drive section  300 , and turns ON the drive circuit  330  when moving the moving member  130 . The drive circuit  330  includes a three-phase command issuing section  332  and a DC voltage generating section  334 . The three-phase command issuing section  332  generates a drive current to be supplied to the coils  124 . The DC voltage generating section  334  generates the drive voltage to be applied to the braking actuator  136 . The switch control section  340  couples the three-phase command issuing section  332  and the DC voltage generating section  334  to the coils  124  or the braking actuator  136  in response to instructions from the position calculating section  320 . 
         [0066]    When the switch SW 0  is connected, the drive voltage of the braking actuator  136  is applied to the braking actuator  136  via the amplifier  350 . As a result, the thickness of the braking actuator  136  increases and the moving member body  138  moves in the radial direction of the stator  120 . Therefore, the braking surface  137  moves away from the stator  120 , and the moving member body  138  contacts the stator  120  via the bearing  132 . Accordingly, the moving member  130  can move smoothly along the stator  120 . 
         [0067]    Concerning the drive current supplied to the coils  124 , when the control section  250  indicates a target position for the moving member  130 , the position calculating section  320  references the encoder  310  and calculates a drive amount for the linear movement drive section  300  corresponding to the direction and distance to the target position. The three-phase command issuing section  332  generates the drive current for each of the U-phase, the V-phase, and the W-phase, according to the calculation results, and supplies a three-phase command value to the corresponding current amplifiers. 
         [0068]    The switch control section  340  turns a plurality of switches SW 1  to SW 9  of the switching section S ON and OFF according to the calculation results of the position calculating section  320 . In this way, the linear movement drive section  300  can be operated by causing currents Iu, Iv, or Iw to flow through the coils  124 . The current amplifiers may be provided with serial resistors that sense excessive current, in order to protect against excessive current. 
         [0069]    The supply schedule of the drive current to the coils  124  is shown below in Table 1. In Table 1, a switch number for the switches SW 1  to SW 9  corresponding to the coils  124  is recorded in each row, and a distance in millimeters to the target position of the moving element is recorded in each column. Furthermore, each ∘ mark in Table 1 indicates that the corresponding coil is being powered, and each X mark indicates that the corresponding coil is not being powered. The numerical value for the magnet position indicates the length of one coil  124 , in millimeters, in the movement direction of the moving member  130 . Each coil  124  has a length of 10 millimeters. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 COIL 
                 MOVING MEMBER POSITION 124 La (mm) 
               
             
          
           
               
                 124 
                 SW 
                 −35 TO −25 
                 −25 TO −15 
                 −15 TO −5 
                 −5 TO 5 
                 5 TO 15 
                 15 TO 25 
                 25 TO 35 
               
               
                   
               
               
                 U1 
                 SW1 
                 ∘ 
                 x 
                 x 
                 x 
                 x 
                 x 
                 x 
               
               
                 V1 
                 SW4 
                 ∘ 
                 ∘ 
                 x 
                 x 
                 x 
                 x 
                 x 
               
               
                 W1 
                 SW7 
                 ∘ 
                 ∘ 
                 ∘ 
                 x 
                 x 
                 x 
                 x 
               
               
                 U2 
                 SW2 
                 x 
                 ∘ 
                 ∘ 
                 ∘ 
                 x 
                 x 
                 x 
               
               
                 V2 
                 SW5 
                 x 
                 x 
                 ∘ 
                 ∘ 
                 ∘ 
                 x 
                 x 
               
               
                 W2 
                 SW8 
                 x 
                 x 
                 x 
                 ∘ 
                 ∘ 
                 ∘ 
                 x 
               
               
                 U3 
                 SW3 
                 x 
                 x 
                 x 
                 x 
                 ∘ 
                 ∘ 
                 ∘ 
               
               
                 V3 
                 SW6 
                 x 
                 x 
                 x 
                 x 
                 x 
                 ∘ 
                 ∘ 
               
               
                 W3 
                 SW9 
                 x 
                 x 
                 x 
                 x 
                 x 
                 x 
                 ∘ 
               
               
                   
               
             
          
         
       
     
         [0070]    By sequentially supplying the drive current to the coils  124  in this way, the moving member  130  on which the permanent magnet  134  is mounted can be moved. Furthermore, by supplying the drive current to the coil  124  in the reverse order, the movement direction of the moving member  130  can be reversed. 
         [0071]    Furthermore, while the drive current is being supplied to one of the coils  124 , the braking actuator  136  does not perform braking of the moving member  130 . Therefore, the moving member  130  receiving this drive force can slide, thereby moving the holding frame  160 . 
         [0072]    When none of the coils  124  are supplied with the drive current, the switch control section  340  causes all of the switches SW 1  to SW 9 , but not the switch SW 0 , to be in the connected state. As a result, the linear movement drive section  300  enters a coil short mode, and the linear movement drive section  300  is stopped by the counter electromotive current generated by the relative movement of the permanent magnet  134  and the coils  124 . 
         [0073]    Furthermore, when none of the coils  124  are supplied with the drive current, the drive voltage is not supplied to the braking actuator  136 . As a result, the braking actuator  136  moves the moving member body  138  such that the bearing  132  is moved away from the stator  120 , the braking surface  137  contacts the stator  120 , and the movement of the moving member  130  is stopped by the stator  120 . 
         [0074]    This braking is maintained without drive power being received from the outside, and therefore the position at which the moving member  130  is stopped is maintained regardless of whether the power supply is ON or OFF. Furthermore, no power is consumed by stopping the moving member  130 . 
         [0075]      FIG. 8  shows another configuration of the lens unit  100 . Components that are the same as components shown in other Figures are given the same reference numerals, and redundant descriptions are omitted. Furthermore, aside from the portion described below, this lens unit  100  has the same configuration as the embodiment shown in  FIGS. 1 to 7 . 
         [0076]    In the lens unit  100 , the moving member body  138  and the guided portion  150  are each supported by the holding frame  160  via a hinge portion  135 . One end of each hinge portion  135  is formed integrally with the outer surface of the holding frame  160 , and the other end is formed integrally with the corresponding moving member body  138  or guided portion  150 . 
         [0077]    Each hinge portion  135  biases the corresponding moving member body  138  or guided portion  150  toward the optical axis C of the lens group  106 . As a result, the braking surface  137  of the moving member body  138  generates a braking force by being pressed against the stator  120 . Furthermore, the braking surface  137  on the inner surface of the guided portion  150  contacts the guide axle  140 . As a result, the braking force is further increased, and the lens group  106  can be reliably held in position. 
         [0078]    A pair of braking actuators  136  are disposed respectively between the holding frame  160  and the moving member body  138  and between the holding frame  160  and the guided portion  150 . When operating, each braking actuator  136  causes the corresponding moving member body  138  or guided portion  150  to move away from the optical axis of the lens group  106 . Accordingly, when the braking actuators  136  operate, the braking surfaces  137  of the moving member body  138  and the guided portion  150  move away from the stator  120  and the guide axle  140 , and the braking force of the braking surfaces  137  is thereby removed. 
         [0079]    As a result, the moving member body  138  and the guided portion  150  are able to slide along the stator  120  and the guide axle  140 . With the operation described above, the bearing  152  on the inner surface of the guided portion  150  further from the optical axis C is omitted. With this configuration, the positions of the moving member body  138  and the guided portion  150  are fixed relative to the holding frame  160  by the hinge portions  135 , and therefore remain in the same positions regardless of deformation of the braking actuators  136 . 
         [0080]    Furthermore, the hinge portions  135  are disposed to be symmetrically opposite each other with respect to the optical axis C of the lens group  106 . The movement of the hinge portions  135  when the braking actuators  136  operate is also symmetric with respect to the optical axis C. Therefore, the optical axis C does not move no matter the operational state of the braking actuators  136 , and so the optical performance of the lens unit  100  can be ensured. 
         [0081]      FIG. 9  is a cross-sectional view of another configuration of the lens unit  100 .  FIG. 9  shows a cross-sectional plane orthogonal to the optical axis C. In  FIG. 9 , components that are the same as components shown in other Figures are given the same reference numerals, and redundant descriptions are omitted. This lens unit  100  has a unique configuration in which the braking actuator  136  is arranged between the moving member body  138  and the lens barrel  110  of the lens unit  100 . 
         [0082]    The braking actuator  136  is the same as the braking actuator  136  described in relation to  FIG. 3 , and when a drive voltage is not supplied thereto, one surface of the braking actuator  136  is fixed on the moving member body  138  and the other surface presses against the inner surface of the lens bagel  110 . As a result, the moving member body  138  is pressed down, and the braking surface  137  is pressed against the stator  120 . Accordingly, the moving member  130  is prevented from moving relative to the stator  120 . 
         [0083]    When the moving member  130  is to be moved relative to the stator  120 , the braking actuator  136  is driven such that the thickness thereof decreases in the radial direction of the lens barrel  110 . As a result, the moving member  130  is no longer prevented from moving relative to the lens barrel  110 , and can slide along the stator  120  or the guide axle  140 . 
         [0084]    A piezoelectric element, bimetal, or a shape memory alloy may be used for the braking actuator  136 , in the same manner as in the other embodiments. Furthermore, aside from the arrangement of the braking actuator  136 , the configurations of the stator  120  and the moving member  130  are the same as in the other embodiments. 
         [0085]      FIG. 10  is a schematic cross-sectional view of the overall configuration of another image capturing apparatus  499 . The image capturing apparatus  499  is formed by combining a lens unit  500  and an image capturing section  600 . 
         [0086]    The lens unit  500  includes a lens barrel  510 , a stator  520 , a moving member  530 , a guide axle  540 , a guided portion  550 , a holding frame  560 , a diaphragm apparatus  570 , and a plurality of lens groups  502 ,  504 , and  506 . The lens groups  502 ,  504 , and  506  are arranged on a common optical axis C, thereby forming an optical system  501 . 
         [0087]    The lens barrel  510  is formed integrally with the image capturing section  600  by being connected to a mount section  660  of the image capturing section  600 , which is described further below. The stator  520  and the guide axle  540 , which are shaped as axles, are fixed within the lens barrel  510  to be parallel to each other and oriented in the longitudinal direction of the lens barrel  510 . 
         [0088]    The lens groups  502 ,  504 , and  506  are each held independently by the holding frame  560 . The lens group  504  is held by both the holding frame  560  and the diaphragm apparatus  570 . All or a portion of the holding frame  560  is supported to be moveable in the longitudinal direction of the lens barrel  510  from the stator  520  and the guide axle  540 , via the moving member  530  or the guided portion  550 . The focal distance and focal position of the optical system  501  can be adjusted by moving the lens groups  502 ,  504 , and  506 . 
         [0089]    The image capturing section  600  includes an optical system having a main mirror  640 , a secondary minor  642 , a pentaprism  670 , and an ocular optical system  690 , and a control system having a focal point detecting section  630 , a main control section  650 , and a photometric unit  680 . The main minor  640  moves between a standby position, in which the main mirror  640  is oriented diagonally in the optical path of incident light through the optical system  501  of the lens unit  500 , and an image capture position, which is shown by the dotted line in  FIG. 10  and in which the main minor  640  is raised out of the optical path of the incident light. 
         [0090]    A secondary mirror  642  is disposed on the back surface of the main mirror  640  in the standby position. The secondary mirror  642  guides a portion of the incident light passing through the main minor  640  to a focal point detecting section  630  positioned therebelow. Therefore, when the main mirror  640  is in the standby position, the focal point detecting section  630  detects a focal state of the optical system  501 . When the main mirror  640  moves to the image capture position, the secondary mirror  642  also moves out of the optical path of the incident light. 
         [0091]    When in the standby position, the main mirror  640  is inclined relative to the incident light and guides a majority of the incident light to a focusing screen  672  arranged thereabove. The focusing screen  672  is arranged at the focal position of the optical system  501 , and displays the image formed by the optical system  501 . 
         [0092]    The image formed by the focusing screen  672  can be seen from the ocular optical system  690  via the pentaprism  670 . Therefore, the image on the focusing screen  672  can be seen as a normal image from the ocular optical system  690 . 
         [0093]    A half mirror  692  is arranged between the pentaprism  670  and the ocular optical system  690 . The half mirror  692  superimposes the display image formed by the finder LCD  694  onto the image of the focusing screen  672 . As a result, the image seen at the output end of the ocular optical system  690  is a combination of the image of the focusing screen  672  and the image of the finder LCD  694 . The finder LCD  694  displays information concerning image capturing conditions, setting conditions, and the like of the image capturing apparatus  499 . 
         [0094]    A portion of the light output from the pentaprism  670  is guided to the photometric unit  680 . The photometric unit  680  measures the intensity of the incident light and a distribution or the like thereof, and these measurement results are referenced when determining the image capturing conditions. 
         [0095]    In the image capturing section  600 , a shutter  620 , an optical filter  612 , and an image capturing element  610  are arranged in the stated order on the optical axis C behind the main mirror  640  in a direction of the incident light from the lens unit  500 . When the release switch of the image capturing section  600  is pressed, the main mirror  640  moves to the image capture position, and so the incident light is directed toward the shutter  620 . When the shutter  620  is opened, the incident light progresses to be incident to the image capturing element  610 . As a result, the image formed by the optical system  501  is converted into an electrical signal by the image capturing element  610 . 
         [0096]    The image capturing section  600  is provided with a main LCD  696  facing away from the lens unit  500 . The main LCD  696  displays various types of setting information concerning the image capturing section  600 , and can also display the image formed by the image capturing element  610  when the main minor  640  is in the image capture position. Furthermore, the main LCD  696  may be used when showing the images generated by the image capturing element  610 . 
         [0097]    The main control section  650  performs overall control of the various operations described above. Furthermore, the main control section  650  controls an auto-focus mechanism that drives the lens unit  500  while referencing information concerning the distance to a subject as detected by the focal point detecting section  630  of the image capturing section  600 . 
         [0098]      FIG. 11  is a perspective view of a linear movement drive section  700  in the lens unit  500 .  FIG. 11  shows one lens group  506  and the components for driving the holding frame  560  holding the lens group  506  extracted from the lens unit  500 . In  FIG. 11 , components that are the same as components in  FIG. 10  are given the same reference numerals, and redundant descriptions are omitted. 
         [0099]    In the linear movement drive section  700 , the holding frame  560  holding the lens group  506  is supported by the moving member  530  and the guided portion  550 , which are formed integrally at symmetrically opposite positions on a frame having a substantially circular shape. The stator  520  is inserted into the moving member  530 , and the moving member  530  moves in the direction in which the stator  520  extends. The guide axle  540  is inserted into the guided portion  550 , and the guided portion  550  moves along the guide axle  540 . 
         [0100]    The drive force that moves the holding frame  560  is generated between the stator  520  and the moving member  530 , as will be described further below. Therefore, a cable  521  that supplies power is coupled to the stator  520 . 
         [0101]    The holding frame  560  and the guided portion  550  move together with the moving member  530 . The stator  520  and the guide axle  540  are arranged parallel to the optical axis C of the optical system  501 , and therefore the lens group  506  held by the holding frame  560  moves along the optical axis C. 
         [0102]      FIG. 12  is a cross-sectional view of the linear movement drive section  700 . The stator  520  includes an outer barrel  522 , a core  528 , and a plurality of coils  524 . The moving member  530  includes a moving member body  538 , and also bearings  532 , a permanent magnet  534 , and braking actuators  536  that are attached to the moving member body  538 . 
         [0103]    In the stator  520 , the outer barrel  522  and the core  528  are arranged to be coaxial. Each coil  524  is wrapped around the core  528  inside the outer barrel  522 , and the coils  524  are arranged in the longitudinal direction of the stator  520 . In order to improve the control of the linear movement drive section  700 , the outer barrel  522  and the core  528  are preferably non-magnetic. 
         [0104]    In the moving member  530 , the moving member body  538  has an inner diameter that is greater than the outer diameter of the stator  520 , and the inner surface of the moving member  530  is distanced from the stator  520 . A pair of bearings  532  are disposed on the inner surface at each end of the moving member  530 , and the moving member  530  is supported by the stator  520  via the bearings  532 . Therefore, the moving member  530  can slide along the stator  520 . 
         [0105]    The guided portion  550  has an inner diameter that is greater than the outer diameter of the guide axle  540 , and the inner surface of the guided portion  550  is distanced from the surface of the guide axle  540 . A pair of bearings  552  are disposed on the inner surface at each end of the guided portion  550 , and the guided portion  550  is supported by the guide axle  540  via the bearings  552 . Therefore, the guided portion  550  can move smoothly along the guide axle  540 . 
         [0106]    The permanent magnet  534  is shaped as a ring that surrounds the stator  520  in the middle of the moving member body  538 . The permanent magnet  534  is magnetized such that the polarity is inverted at the ends thereof in the longitudinal direction of the stator  520 . However, the magnetism of the permanent magnet  534  is not particularly limited, and the permanent magnet  534  may be arranged to have a polarity in the longitudinal direction of the stator  520  that is opposite the polarity shown in  FIG. 12 . 
         [0107]    The top surface of each braking actuator  536  is coupled to the bottom surface of the moving member body  538 , and the bottom surface of each braking actuator  536  contacts the outer surface of the stator  520 . As a result, the surfaces of the braking actuators  536  serve as braking sections, and the frictional force generated thereby fixes the moving member  530  relative to the stator  520 . 
         [0108]    The thickness of each braking actuator  536  decreases when operating according to control from the outside. Therefore, one surface of each braking actuator  536  moves away from the surface of the stator  520 , and so the braking actuators  536  do not impede the movement of the moving member  530  along the stator  520 . 
         [0109]    In this way, when the moving member  530  is moving relative to the stator  520  in the linear movement drive section  700 , the braking actuators  536  do not stop the movement of the moving member  530  relative to the stator  520 . Furthermore, when the movement of the moving member  530  relative to the stator  520  in the linear movement drive section  700  is stopped, the moving member  530  is fixed relative to the stator  520 . Therefore, when the moving member  530  is stopped, it is held in position. 
         [0110]    For example, each braking actuator  536  may be formed of a piezoelectric element whose thickness changes when voltage is applied thereto. In other words, a piezoelectric element is used to form each braking actuator  536  with a thickness that decreases when a drive voltage is applied thereto. As a result, when the linear movement drive section  700  is not driving the moving member  530 , the braking actuators  536  serve as a braking section that holds the moving member  530  in place. 
         [0111]    As a result, when the moving member  530  is not moving in the linear movement drive section  700 , the moving member  530  is automatically held at the position where it stopped, without power being supplied. Furthermore, when driving the moving member  530  in the linear movement drive section  700 , the drive voltage is applied to the braking actuators  536  in parallel so that the braking actuators  536  no longer operate to brake the moving member  530 , and therefore the moving member  530  moves smoothly. 
         [0112]    The braking actuators  536  performing the operation described above can be formed of a bimetal that is deformed when heated. As another example, the braking actuator  536  can be formed of a shape memory alloy that returns to the remembered shape when heated to a transition temperature. 
         [0113]    The bimetal or shape memory alloy can be combined with a heater, for example, and controlled by turning the power supply ON and OFF. By using the heat generated by the coils  524  to operate the stator  520 , the operation of the linear movement drive section  700  is automatically performed simultaneously with the releasing of the brake on the moving member  530  by the braking actuator  536 . 
         [0114]    In the above example, one end of the holding frame  560  is driven by the moving member  530  and the other end serves as the guided portion  550  that follows on the moving member  530 . However, a pair of moving members  530  may be provided such that the holding frame  560  is driven simultaneously at both ends. In this case, it is obvious that a stator  520  is used in place of the guide axle  540 . 
         [0115]      FIG. 13  is a perspective view of the linear movement drive section  700 , in which the internal structures of the stator  520  and the moving member  530  are exposed. Components that are the same as components shown in  FIGS. 10 to 12  are given the same reference numerals, and redundant descriptions are omitted. 
         [0116]    The stator  520  includes the plurality of coils  524  arranged along the core  528 . Each coil  524  independently generates a magnetic field when a drive current is applied thereto. In the moving member  530 , the permanent magnet  534  surrounds the coils  524  from the outer surface of the outer barrel  522 . Furthermore, in the moving member  530 , the braking actuators  536  are arranged respectively in front of and behind the permanent magnet  534  in the direction in which the moving member  530  moves. 
         [0117]      FIG. 14  is a schematic view of the electrical configuration of the linear movement drive section  700 . Components that are the same as components shown in other Figures are given the same reference numerals, and redundant descriptions are omitted. 
         [0118]    Each coil  524  is independently wrapped around the core  528 , and as shown by the dotted lines in  FIG. 14 , three phases (U, V, and W) are created. In this example, the three phases U, V, and W are used, but it is obvious that the configuration is not limited to three phases, and these phases can be set according to the desired distance over which the moving member  530  is to move. The connections of the coils  524  are not limited to three connections, and the number of phase connections may be two, or greater than three. 
         [0119]      FIG. 15  is a block diagram showing the control system  701  of the linear movement drive section  700 . The control system  701  includes a position calculating section  720 , a drive circuit  730 , and a switch control section  740 . The control system  701  is included in the control section  650  of the image capturing section  600 . 
         [0120]    The position calculating section  720  references the position of the moving member  530  detected by the encoder  710  disposed in the linear movement drive section  700 , and turns ON the drive circuit  730  when moving the moving member  530 . The drive circuit  730  includes a three-phase command issuing section  732  and a DC voltage generating section  734 . The three-phase command issuing section  732  generates a drive current to be supplied to the coils  524 . The DC voltage generating section  734  generates the drive voltage to be applied to the braking actuators  536 . The switch control section  740  couples the three-phase command issuing section  732  and the DC voltage generating section  734  to the coils  524  or the braking actuators  536  in response to instructions from the position calculating section  720 . 
         [0121]    When the switch SW 0  is connected, the drive voltage of the braking actuator  536  is inverted by the inverting amplifier  750  and applied to the braking actuators  536 . As a result, the thickness of each braking actuator  536  decreases and one surface of each braking actuator  536  moves away from the surface of the stator  520 . Therefore, the moving member  530  can move smoothly while the drive voltage is supplied to one of the coils  524 , as described further below. 
         [0122]    Concerning the drive current supplied to the coils  524 , when the control section  650  indicates a target position for the moving member  530 , the position calculating section  720  references the encoder  710  and calculates a drive amount for the linear movement drive section  700  corresponding to the direction and distance to the target position. The three-phase command issuing section  732  generates the drive current for each of the U-phase, the V-phase, and the W-phase, according to the calculation results, and supplies a three-phase command value to the corresponding current amplifiers. 
         [0123]    The switch control section  740  turns a plurality of switches SW 1  to SW 9  of the switching section S ON and OFF according to the calculation results of the position calculating section  720 . In this way, the linear movement drive section  700  can be operated by causing currents Iu, Iv, or Iw to flow through the coils  524 . The current amplifiers may be provided with serial resistors that sense excessive current, in order to protect against excessive current. 
         [0124]    The supply schedule of the drive current to the coils  524  may be the same as shown in Table 1 above. 
         [0125]    By sequentially supplying the drive current to the coils  524  in this way, the moving member  530  on which the permanent magnet  534  is mounted can be moved. Furthermore, by supplying the drive current to the coil  524  in the reverse order, the movement direction of the moving member  530  can be reversed. 
         [0126]    Furthermore, while the drive current is being supplied to one of the coils  524 , the braking actuators  536  do not perform braking of the moving member  530 . Therefore, the moving member  530  receiving this drive force can move smoothly, thereby moving the holding frame  560 . 
         [0127]    When none of the coils  524  are supplied with the drive current, the switch control section  740  causes all of the switches SW 1  to SW 9 , but not the switch SW 0 , to be in the connected state. As a result, the linear movement drive section  700  enters a coil short mode, and the linear movement drive section  700  is stopped by the counter electromotive current generated by the relative movement of the permanent magnet  534  and the coils  524 . 
         [0128]    Furthermore, when none of the coils  524  are supplied with the drive current, the drive voltage causing the braking actuator  536  to release the brake is not supplied thereto. As a result, the braking actuator  536  contacts the moving member  530  and the stator  520 , thereby stopping the movement of the moving member  530 . This braking is maintained without drive power being received from the outside, and therefore the position at which the moving member  530  is stopped is maintained regardless of whether the power supply is ON or OFF. Furthermore, no power is consumed by stopping the moving member  530 . 
         [0129]      FIG. 16  is a cross-sectional view of another configuration of the lens unit  500 .  FIG. 16  shows a cross-sectional plane orthogonal to the optical axis C. In  FIG. 16 , components that are the same as components shown in other Figures are given the same reference numerals, and redundant descriptions are omitted. This lens unit  500  has a unique configuration in which the braking actuators  536  of the moving member  530  are arranged respectively between the moving member body  538  and the lens barrel  510  and between the guided portion  550  and the lens barrel  510 . 
         [0130]    The braking actuators  536  are the same as the braking actuators  536  described in relation to  FIG. 12 , and when a drive voltage is not supplied thereto, one surface of each braking actuator  536  is fixed on the moving member body  538  or the guided portion  550  and the other surface presses against the inner surface of the lens barrel  510 . As a result, the moving member  530  and the guided portion  550  are pressed against the lens barrel  510  over a large area, thereby stopping the movement of the moving member  530  and the guided portion  550 . 
         [0131]    When the moving member  530  is to be moved relative to the stator  520 , the braking actuators  536  are driven such that the thickness thereof decreases in the radial direction of the lens barrel  510 . As a result, the moving member  530  and the guided portion  550  are no longer prevented from moving relative to the lens barrel  510 , and can move smoothly along the stator  520  or the guide axle  540 . 
         [0132]    A piezoelectric element, bimetal, or a shape memory alloy may be used for the braking actuators  536 , in the same manner as in the other embodiments. Furthermore, aside from the arrangement of the braking actuators  536 , the configurations of the stator  520  and the moving member  530  are the same as in the other embodiments. 
         [0133]    While the embodiments of the present invention have been described, the technical scope of the invention is not limited to the above described embodiments. It is apparent to persons skilled in the art that various alterations and improvements can be added to the above-described embodiments. It is also apparent from the scope of the claims that the embodiments added with such alterations or improvements can be included in the technical scope of the invention. 
         [0134]    The operations, procedures, steps, and stages of each process performed by an apparatus, system, program, and method shown in the claims, embodiments, or diagrams can be performed in any order as long as the order is not indicated by “prior to,” “before,” or the like and as long as the output from a previous process is not used in a later process. Even if the process flow is described using phrases such as “first” or “next” in the claims, embodiments, or diagrams, it does not necessarily mean that the process must be performed in this order.