Abstract:
A lens device comprises a movable compensation lens holding member holding a blur compensation lens, two blur compensation actuators for driving the movable compensation lens holding member to move in a direction orthogonal to an optical axis of the lens device to compensate for image blur, a movable lens holding member holding a movable lens, and an axial lens driving actuator for driving the lens holding member to move in the axial direction; an optical equipment comprises an optical system including such optical elements, a light amount adjusting member and an imaging element. The axial lens driving actuator includes a magnet magnetized vertically in the direction of the optical axis, a yoke, and a coil mounted on the movable lens holding member at a predetermined distance from the magnet, where the coil is movable in the direction of the optical axis by application of current in the direction orthogonal to a magnetic flux generated by the magnet. The axial lens driving actuator is disposed at a position symmetrical to one of the two blur compensation actuators with respect to the optical axis when viewed in the direction of the optical axis.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lens device and optical equipment using the same, such as a video camera or a digital still camera. 
     2. Description of the Related Art 
     It is known to prevent image blur due to handshake that tends to occur during a hand-held photo-taking operation using an image blur compensation unit, where the image blur compensation unit detects the state of blurring of a camera with a blur detecting unit and shifts a compensation lens in a direction orthogonal to the optical axis in accordance with the detected results. 
     In a camera provided with such an image blur compensation unit, displacement of an imaging position due to shake (blurring) is compensated for by movably supporting a compensation lens constituting at least a part of a photo-taking lens system and moving the compensation lens in a direction within a plane orthogonal to the optical axis of the main optical system so as to compensate for the shake (image blur). 
     In such an image blur compensation unit, an electromagnetic actuator is constructed of a coil and a magnet. One of the coil and the magnet is attached to a fixed portion (e.g., a fixed lens barrel) and the other one is attached to a lens holding frame for holding the compensation lens, so that relative movement of the lens holding frame may be directly achieved. When considering downsizing and power saving of the unit, it is advantageous to attach the magnet, which is heavier in weight, to the fixed portion and to attach the coil, which is lighter in weight, to the lens holding frame. In this configuration, wiring from the fixed portion to the coil mounted on the lens holding frame may be provided by a flexible printed board. 
     The position of a movable lens group for zooming or focusing is adjusted by rotating a screw portion provided on an output shaft of a stepping motor, so that a lens carrier frame connected to a rack member, which moves in conjunction with the screw portion, is moved in the direction of the optical axis. 
     In the case of the above-described related art, a stepping motor for driving the movable lens group for zooming and focusing controls the movable lens group so as to move and stop at a predetermined position by rotating a feed screw by an angle corresponding to a predetermined number of pulses. 
     In order to enhance resolution of the stop position of the movable lens group, it is necessary to reduce the pitch of the feed screw of the stepping motor. On the other hand, in order to increase the speed of movement of the movable lens group, the stepping motor may be rotated at a higher speed; in order to further increase the speed, it is necessary to increase the pitch of the feed screw. Therefore, simultaneous pursuit of increase in speed and improvement in accuracy is limited. 
     In particular, a simultaneous pursuit of stoppage with a high-degree of accuracy and movement of a focus lens at a high-speed is required due to the recent increase in pixel count of imaging elements and an increase in zoom ratio. Hence, a system realizing simultaneous pursuit of accurate control of lens stop positions and an increase in lens speed has been proposed, wherein a linear actuator including a coil and a magnet is used for moving the focus lens instead of a conventional stepping motor. 
     Such a linear actuator, however, has a lower generated torque than a driving mechanism using a stepping motor. Thus, the actuator cannot be disposed at a position too remote from the center of gravity of the movable lens group. Rather, the linear actuator must be disposed near the lenses in accordance with the amount of movement of the movable lens group. Consequently, in a construction in which an image blur compensation unit that drives a compensation lens in a direction orthogonal to the optical axis using an electromagnetic actuator and a linear actuator that drives a movable lens in a direction of the optical axis are disposed in a lens barrel, the effective arrangement of those actuators is an important issue. 
     SUMMARY OF THE INVENTION 
     In one aspect, the present invention relates to a lens device in which two actuators for driving a compensation lens in a direction orthogonal to the optical axis and an actuator for driving a movable lens in a direction of the optical axis are efficiently disposed in a space of the lens device, whereby downsizing of the lens device (lens barrel) and shortening of the length of the lens device (lens barrel) in the direction of the optical axis are achieved, the range of movement of the movable lens that moves in the direction of the optical axis is efficiently increased, and detection of the position of the movable lens in the direction of the optical axis is detected with a high-degree of accuracy. 
     In another aspect, the present invention related to an optical equipment using the same. 
     The in above-described drawbacks of the related art are overcome by a lens device of the present invention, which includes: 
     a blur compensation lens holding frame holding a blur compensation lens; 
     two blur compensation actuators that drive the blur compensation lens holding frame to move in a direction orthogonal to an optical axis of the lens device; 
     a movable lens holding member holding a movable lens; and 
     an axial driving actuator that drives the movable lens holding member in the direction of the optical axis; 
     wherein the axial driving actuator includes a magnet magnetized vertically in the direction of the optical axis, a yoke, and a coil mounted on the movable lens holding frame at a predetermined distance from the magnet and is movable in a direction of the optical axis by application of current in a direction orthogonal to a magnetic flux generated by the magnet, and 
     wherein the driving actuator is disposed at a position symmetrical to one of the two blur compensation actuators with respect to the optical axis when viewed in the direction of the optical axis. 
     In the lens device described above, the two blur compensation actuators are provided at respective positions in two different directions orthogonal to the optical axis (e.g., horizontal and vertical directions). 
     In this manner, the two actuators for driving the compensation lens in a direction orthogonal to the optical axis and the actuator for driving the movable lens in the direction of the optical axis efficiently may be arranged in a space of the lens device, thereby reducing a size of the lens device, shortening the length of the lens device in the direction of the optical axis, and efficiently and securely increasing the range of movement of the movable lens in the direction of the optical axis. 
     Optical equipment of the present invention includes: 
     an optical system including a movable lens axially movable in the direction of the optical axis, and a blur compensation lens that compensates for image blur by moving in a direction orthogonal to the optical axis; 
     two compensation actuators that drive the blur compensation lens holding frame in a direction orthogonal to the optical axis; 
     a driving actuator for driving the moving lens holding frame in the direction of the optical axis; 
     a light amount adjusting member that adjusts the amount of light passing through the optical system; and 
     an imaging element for imaging the optical image from the optical system; 
     wherein the driving actuator includes a magnet magnetized vertically in the direction of the optical axis, a yoke, and a coil mounted on a member holding the movable lens at a predetermined distance from the magnet and is movable in the direction of the optical axis by application of current in the direction orthogonal to the magnetic flux generated by the magnet, and 
     wherein the driving actuator is disposed at a position symmetrical to one of two blur compensation actuators that drive the blur compensation lens with respect to the optical axis when viewed in the direction of the optical axis. 
     In the optical equipment described above, the two blur compensation actuators are provided at respective positions in two different directions orthogonal to the optical axis. In addition, in the optical equipment described above, the one blur compensation actuator and the driving actuator are disposed between the light amount adjusting member and the imaging element. 
     In this arrangement, the two blur compensation actuators for driving the blur compensation lens in a direction orthogonal to the optical axis and the actuator for driving the movable lens in the direction of the optical axis efficiently may be arranged in a space of the optical equipment, thereby reducing the size of the optical equipment, shortening the length of the optical equipment in the direction of the optical axis, and effectively and securely increasing the range of movement of the movable lens in the direction of the optical axis. 
     According to the present invention, the optical system described above may employ a rear focus zoom lens constructed of four lens groups, with a first lens group including fixed positive lenses, a second lens group including negative variable power lenses for effecting zooming by moving in the direction of the optical axis, a third lens group including positive compensation lenses that compensate for image blur by moving a part of or all of the lenses in a direction orthogonal to the optical axis, and a fourth lens group including focus lenses movable in the direction of the optical axis that compensate for variations of image surface in association with the movement of the variable power lenses (the second lens group) and perform focus adjustment. The driving actuator described above may be used to move movable lenses, such as the variable power lens and the focus lens, in the direction of the optical axis. 
     Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional side view showing a construction of a zoom lens device of optical equipment according to an embodiment of the invention. 
     FIG. 2 is a view of the device of FIG. 1 from the object side, with the first lens group omitted. 
     FIG. 3 is a view of the device of FIG. 1 from the image surface, with a holder barrel omitted. 
     FIG. 4 is a cross-sectional side view showing an image blur compensation unit of the device of FIG.  1 . 
     FIG. 5 is a view of the unit of FIG. 4 from the image surface side (image blur compensation lens L 3   b  side). 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 to  5  illustrate one embodiment of a lens device (lens barrel) of the present invention applied to optical equipment including an imaging element, such as a video camera or a digital still camera. FIG. 1 is a cross-sectional side view showing a zoom lens barrel of optical equipment according to an embodiment of the present invention; FIG. 2 is a view of the device of FIG. 1 from the object side with the first lens group omitted; and FIG. 3 is a view of the device of FIG. 1 from the image surface side (from a CCD  21 ) with a holder barrel omitted. 
     A zoom optical system in the zoom lens barrel is a rear focus zoom optical system respectively including four groups of convex lenses, concave lenses, convex lenses and convex lenses (positive, negative, positive and positive) arranged in sequence from the object side. 
     In FIGS. 1 to  3 , a first lens group barrel  1  holds a fixed lens group L 1  belonging to the first lens group. The first lens group barrel  1  is fixed to a fixed lens barrel  2 . A second lens group holding frame (holding member)  3  holds a zoom lens group L 2  belonging to the second lens group accommodated in the fixed lens barrel  2 . The second lens group holding frame  3  is formed with a sleeve portion  3   a  and a U-shaped groove portion  3   b , as shown in FIG.  2 . The sleeve portion  3   a  and the U-shaped groove portion  3   b  movably engage guide bars  8  and  9  provided on the fixed lens barrel  2  along the optical axis, whereby the second lens group holding frame  3  is guided by the guide bars  8  and  9  for movement substantially along the optical axis. 
     An aperture unit  4  includes a drive unit  4   a  that controls the amount of light passing through the optical system by driving an aperture blade (not shown). The amount of light also is controlled by a drive unit  4   d  that drives a filter frame with an ND filter adhered thereon (both not shown). 
     An image blur compensation unit  5  includes an afocal lens group, belonging to the third lens group, that is separated into a lens group L 3   a  (which is fixedly held), and an image blur compensation lens group L 3   b  (which is movable). 
     A fourth lens group holding frame (holding member)  6  holds a focus lens group L 4 , belonging to the fourth lens group, and serves as a compensator and as focusing means. The fourth lens group holding portion  6  includes a sleeve portion  6   a  and a U-shaped groove portion  6   b , as shown in FIG.  3 . The sleeve portion  6   a  and the U-shaped groove  6   b  movably engage guide bars  10  and  11  provided on a holder barrel (rear side fixed lens barrel)  7  along the optical axis, whereby the fourth lens group holding frame  6  is guided by the guide bars  10  and  11  for movement substantially along the optical axis. 
     As shown in FIG. 2, a rack  12  is mounted to the second lens group holding frame  3 . The rack  12  meshes with an output screw portion (not shown) of a zoom motor  13  (FIG. 2 shows a state in which the zoom motor  13  and the output screw portion are separated from one another). In this case, a stepping motor is used as the zoom motor  13 . When the zoom motor  13  rotates, the second lens group holding frame  3  is driven in the direction of the optical axis by the actions of the output screw portion and the rack  12 . 
     Positional control of the movement of the second lens group holding frame  3  is performed by determining an initial position at which a light-shielding wall  3   c  of the second lens group holding frame  3  shields light incident on a photo interrupter  14 , and thereafter by controlling the position of the lenses in the second lens group holing frame  3  by counting pulses of the stepping motor, which constitutes the zoom motor  13 . 
     As shown in FIG. 1, the holder barrel  7  fixedly holds an imaging element (e.g., a CCD  21 ) and a filter  22 , which cuts infrared light and functions as a low-pass filter. Image signals from the CCD  21  are supplied to a signal processing system and a signal recording system of a camera unit. The holder barrel  7  includes a boss (not shown). The holder barrel  7  positions the image blur compensation unit  5  and the fixed lens barrel  2  using the boss (not shown). A frame portion  5   a  of the image blur compensation unit  5  is interposed between the fixed lens barrel  2  and the holder barrel  7 . The fixed lens barrel  2  and the holder barrel  7  are fixed by a machine screw (not shown), and thus the fixed lens barrel  2 , the holder barrel  7 , and the frame portion  5   a  of the image blur compensation unit  5  are integrally constructed as a single unit. 
     As shown in FIGS. 1 and 3, a hollow coil  15  arranged in a substantially rectangular column shape is fixed to the fourth lens group holding frame  6 . The coil  15  is provided on the side of the sleeve portion  6   a  through which a guide bar  10  of the fourth lens group holding frame  6  passes. The hollow portion (hole) of the coil  15  is formed along the optical axis. Yokes  16  and  17  and a magnet  18  fixedly held by the frame portion  5   a  of the image blur compensation unit  5  and the holder barrel  7  are provided between the frame portion  5   a  of the image blur compensation unit  5  and the holder barrel  7 . The yoke  16  is formed into a square C-shape with one side open and extending along the optical axis, with the magnet  18  held therein. The yoke  16  is inserted into the hollow portion of the coil  15  described above, and the coil  15 , the yoke  16 , and the magnet  18  are spaced apart from one another by a predetermined distance. The magnet  18  is magnetized in a direction orthogonal to the optical axis and extends along the optical axis. The yoke  17  is held by the yoke  16  on the side of the distal ends on the opened side of the square C-shape. An actuator (driving actuator)  100  as a voice coil motor is constructed of the above-described coil  15 , the yokes  16  and  17 , and the magnet  18 . When the coil  15  is energized, the fourth lens group holding frame  6  is driven in a direction of the optical axis by the magnetic action of a circuit formed by the yokes  16 ,  17  and the magnet  18  held by the image blur compensation unit  5  and the holder barrel  7 . An encoder magnet  19  having opposite magnetic poles arranged alternately at predetermined pitches in the direction of the optical axis is held by the fourth lens group holding frame  6  on the side surface of the sleeve portion  6   a  through which the guide bar  10  is to be inserted, as shown in FIG.  3 . At a position opposing the encoder magnet  19 , there is provided an MR sensor  20  held by the holder barrel  7 , and the encoder magnet  19  and the MR sensor  20  are disposed a predetermined distance apart, sufficient for detecting variations of magnetic poles. 
     The initial position of the fourth lens group holding frame  6  is determined in a state in which the fourth lens group holding frame  6  abuts against the image surface side (CCD  21  side) of the holder lens barrel  7 , and thereafter, positional detection and drive control of the fourth lens group holding frame  6  are performed based on output signals supplied from the MR sensor  20  in accordance with magnetic variations (or variations in intensity of magnetism) acting on the MR sensor  20  in association with movement of the encoder magnet  19  held by the fourth lens group holding frame  6  in position with respect to the MR sensor  20 . The MR sensor  20  outputs two-phase sinusoidal waves having a phase difference of 90 degrees, and the amount and direction of movement of the encoder magnet  19  (that is, the fourth lens group holding frame  6 ) can be determined from such two-phase outputs. Alternatively, the output of the MR sensor may be three-phase or more. Also, the phase difference may be an angle other than 90 degrees. 
     The construction of the image blur compensation unit  5  shown in FIG. 1 will be described referring to FIG.  4  and FIG.  5 . 
     FIG. 4 is a cross-sectional side view showing the image blur compensation unit  5 , and FIG. 5 illustrates the image blur compensation unit of FIG. 4 when viewed from the image surface side (image blur compensation lens L 3   b  side). In FIG. 4, only a blur compensation actuator  500   a  that drives a movable frame holding member  505  in the vertical direction orthogonal to the optical axis is shown; a blur compensation actuator  500   b  for driving the movable frame (holding member)  505  in the horizontal direction orthogonal to the optical axis (see FIG. 3) is substantially similar in structure and function, and therefore is not shown for ease of viewing. In FIG. 5, both the blur compensation actuator  500   a  that drives the movable frame  505  in the vertical direction orthogonal to the optical axis, and the blur compensation actuator  500   b  for driving the movable frame  505  in the horizontal direction orthogonal to the optical axis are shown. The blur compensation actuator  500   a  and the blur compensation actuator  500   b  are disposed so as to be orthogonal with respect to each other. In the following description, members constituting the vertical blur compensation actuator  500   a  are represented by reference numerals including a suffix “a”, and members constituting the horizontal blur compensation actuator  500   b  are represented by reference numerals including a suffix “b”. Although components of the horizontal blur compensation actuator  500   b  are not shown in FIG. 4, since they are structurally and functionally the same as like components of the vertical blur compensation actuator  500   a , those components are represented with the suffix “b”. 
     As shown in the drawings, a fixed frame  501  fixedly holds the fixed lens group L 3   a  of a third afocal lens group. A movable frame  505  holds an image blur compensation lens group L 3   b  of the third afocal lens group. Upper yoke members  507   a  and  507   b  are fixed to the fixed frame  501  together with sensor holding members  508   a  and  508   b  with machine screws (not shown). 
     A coil spring  511  held by a spring holding ring  512  fixed to the sensor holding members  508   a  and  508   b  with a machine screw urges movable frame  505  toward the fixed frame  501 , and is capable of moving freely in a direction orthogonal to the optical axis by disposing steel balls  504  between three flat portions  505   c  on the fixed frame  501  and three flat portions  505   c  formed on the movable frame  505 , respectively. The movable frame  505  is fixed with coils  506   a  and  506   b , which are used for driving movement in the vertical direction and in the horizontal direction, respectively. Magnets  503   a ,  503   b  are magnetized with two poles. The magnets  503   a  and  503   b  are attracted to lower yokes  502   a  and  502   b  formed of a material such as iron. The lower yokes  502   a  and  502   b  are fixedly held on the shoulder (not shown) of the fixed frame  501  by a magnetic force attraction between the upper yoke members  507   a  and  507   b  and the magnets  503   a  and  503   b . In this arrangement, a magnetic circuit for vertical and horizontal movement is formed. Specifically, for vertical movement, a magnetic circuit is formed by magnet  503   a , lower yoke  502   a  and upper yoke member  507 , and the coil  506   a  is inserted into a space among them. On the other hand, for horizontal movement, the magnetic circuit is formed by the magnet  503   b , the lower yoke  502   b  and the upper yoke member  507 , and the coil  506   b  is inserted into a space among them. In this manner, two electromagnetic actuators employing a moving coil system (blur compensation actuators  500   a  and  500   b  for compensating for image blur) for the vertical and horizontal movements are provided. 
     Light emitting elements  509   a ,  509   b , such as IREDs, and corresponding light receiving elements  510   a ,  510   b , such as PSDs, together constitute position sensors for the blur compensation lens. The light emitting elements  509   a ,  509   b  and the light receiving elements  510   a ,  510   b  are fixedly bonded to the sensor holding members  508   a  and  508   b , respectively. 
     When the movable frame  505  formed with slits  505   a  and  505   b , each in the shape of an elongated hole being formed integrally therewith, are inserted between the light emitting elements  509   a ,  509   b  and light receiving elements  510   a ,  501   b , only a portion of infrared light emitted from the light emitting elements  509   a  and  509   b  that passes through the slits  505   a  and  505   b  is received by the light receiving elements  510   a  and  510   b , which enables detection of vertical and horizontal positions of the movable frame  505 . The light emitting elements  509   a  and  509   b , the light receiving elements  510   a  and  510   b , and the coils  506   a  and  506   b  are connected to a flexible printed board  513  (See, FIG.  5 ), and are connected to a microcomputer (not shown) in the camera unit (see, FIG.  1 ). 
     In this embodiment, as shown in FIGS. 1,  3  and  5 , the coil  15 , the yoke  16 , the yoke  17  and the magnet  18  constituting the magnetic circuit (driving actuator  100 ) for driving the fourth lens group movable frame  6  holding the above-described focus lens group L 4  are disposed at almost the same distance from the optical axis, and are symmetric to one of the two image blur compensation magnetic actuators (blur compensation actuators  500   a  and  500   b ) with respect to the optical axis when viewing the coil  506   a , the lower yoke  502   a  and driving magnet  503   a  constituting the magnetic circuit (blur compensation actuator  500   a ) for vertical movement of the image blur compensation unit  5  and the coil  506   b , the lower yoke  502   b  and the drive magnet  503   b  constituting the magnetic circuit (blur compensation actuator  500   b ) for horizontal movement of the image blur compensation unit  5  in the direction of the optical axis. Accordingly, as shown in FIG. 1, the position for disposing the driving actuator  100  constructed of the coil  15 , the yoke  16 , the yoke  17  and the magnet  18  for moving the focus lens group L 4  is a space in which the two actuators  500   a  and  500   b  of the image blur compensation unit  5  are not disposed, and thus the length of the yoke  16 , the yoke  17  and the magnet  18  in the direction of the optical axis may be increased, whereby a wide range of movement is ensured for coil  15  (focus lens group L 4 ). 
     The magnetic circuits (driving actuator  100  and the two blur compensation actuators  500   a  and  500   b ) are disposed between an aperture unit  4  and the CCD  21  that corresponds to an imaging element, respectively. 
     Therefore, in the embodiment described above, the two blur compensation actuators  500   a  and  500   b  for driving the blur compensation lens in a direction orthogonal to the optical axis and the actuator  100  for driving the movable lens (focus lens) L 4  in the direction of the optical axis efficiently may be disposed in a space of the lens barrel, thereby reducing a size of the lens barrel, shortening the length of the lens barrel in the direction of the optical axis, and effectively and securely increasing the range of movement of the movable lens L 4  in the direction of the optical axis. 
     By disposing the coil  15 , the yoke  16 , the yoke  17  and the magnet  18  constituting the magnetic circuit (driving actuator  100 ) for driving the fourth lens group movable frame  6  holding the focus lens group L 4  on the side (in the vicinity) of the sleeve portion  6   a  of the fourth lens group movable frame  6 , or by disposing the magnetic actuator in the vicinity of the center of gravity of the movable lens group L 4 , a torque generated by the actuator (driving force) may be effectively utilized so that high-efficiency drive is achieved. In addition, since the encoder magnet  19  for detecting the position of the focus lens group L 4  is disposed on the side surface of the sleeve portion  6   a  of the fourth lens group movable frame  6  and the MR sensor  20  is disposed so as to oppose the encoder magnet  19 , the encoder magnet  19  is positioned in the vicinity of the point of action of drive, and thus the position of the movable lens (focus lens) L 4  in the direction of the optical axis may be detected with a high degree of accuracy. 
     Although a construction in which a magnetic sensor using an encoder magnet  19  and an MR sensor  20  is employed as a sensor for detecting the position of the focus lens L 4  in the embodiment described above, an optical sensor alternatively may be used. In this case, a reflecting member formed with a grid of a predetermined cycle is provided on the side of the movable frame holding the focus lens, and an optical sensor is disposed on the side of the fixed lens barrel opposing the reflecting member. In this arrangement, the optical sensor emits light toward the reflecting member, receives light reflected therefrom, and outputs two-phase sinusoidal waves having a phase difference of 90 degrees, as in the case of the above-described MR sensor  20 . 
     As described thus far, according to the embodiment described above, the two blur compensation actuators for driving the blur compensation lens in a direction orthogonal to the optical axis, and the actuator for driving the movable lens in the direction of the optical axis efficiently may be disposed in a space of the optical system, thereby reducing the size of the lens barrel, shortening the length of the lens barrel in the direction of the optical axis, and efficiently and securely increasing the range of movement of the movable lens in the direction of the optical axis. Furthermore, the position of the movable lens in the direction of the optical axis may be detected with a high degree of accuracy. 
     While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.