Abstract:
A lens apparatus is disclosed, which can control the position of a lens unit driven by an actuator such as a vicecoil motor in a non-energizing state of the actuator easily. The lens apparatus comprises: a first lens unit and second lens unit moving in an optical axis direction, respectively; a first actuator driving the first lens unit; and a second actuator driving the second lens unit. The first lens unit is driven by the second lens unit that is driven by the second actuator in a nonenergized state of the first actuator, and a member is provided in one of the first and second lens units. The member contacts the other lens unit in the nonenergized state.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a lens apparatus used for an image-taking apparatus such as a digital camera and video camera. 
     BACKGROUND OF THE INVENTION 
     A collapsible lens barrel is used in an image-taking apparatus such as a digital still camera. The collapsible lens barrel changes its length in an image-taking state in which the distance between a plurality of lens units changes to perform zooming and focusing, and in a housed (collapsed) state in which the distance between the plurality of lens units and the distance from between the plurality of lens units to an image-pickup plane reduce to a predetermined distance. Such a collapsible lens barrel is driven by a driving mechanism such as a cam and a helicoid gear. 
     Miniaturization of the lens barrel is required with miniaturization of the image-taking apparatus, and quiet drive of the lens barrel is required for reduction of the volume and weight of the lens barrel. For this purpose, in Japanese Patent Laid-Open Application No. H05-150152, a lens driving mechanism is disclosed, in which a lens unit is driven in the optical axis direction thereof by a voicecoil motor including a magnet arranged around the lens unit, and a coil and yoke arranged around the magnet. 
     However, since a voicecoil motor does not have a stable stop position (for example, a magnetic stable position in a stepping motor) in a nonenergized state, the position of the lens unit driven by the voicecoil motor in the optical axis direction is not held in the nonenergized state such as a nonuse state of the image-taking apparatus. Therefore, there is a problem that the lens unit moves in its movable range in the nonuse state. 
     When the lens unit having no stable stop position collides a mechanical end of the movable range, deterioration of the optical accuracy of the lens barrel and a collision sound will occur. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide a lens apparatus and an image-taking apparatus, which can control the position of a lens unit driven by an actuator such as a voicecoil motor in a nonenergized state of the actuator easily. 
     A lens apparatus that is one aspect of the present invention comprises: a first lens unit and second lens unit moving in an optical axis direction, respectively; a first actuator driving the first lens unit; and a second actuator driving the second lens unit. The first lens unit is driven by the second lens unit that is driven by the second actuator in the nonenergized state of the first actuator, and a member is provided in one of the first and second lens units. The member contacts the other lens unit in the nonenergized state. 
     A lens apparatus that is another aspect of the present invention comprises: a first lens unit, which moves in an optical axis direction; a second lens unit, which is located on an object side further than the first lens unit and moves in the optical axis direction; a first actuator, which drives the first lens unit; and a second actuator, which drives the second lens unit. The lens apparatus has a first state in which the first lens unit is driven in the optical axis direction by the first actuator at the time of image-taking, and a second state in which the first lens unit is driven in the optical axis direction by the second actuator in response to an instruction for stowing. 
     A lens apparatus that is still another aspect of the present invention comprises: a first lens unit, which moves in an optical axis direction; a second lens unit, which is located on an object side further than the first lens unit and moves in the optical axis direction; a first actuator, which drives the first lens unit; and a second actuator, which drives the second lens unit. The first lens unit is driven in the optical axis direction by the first actuator at the time of image-taking, and is driven in the optical axis direction by contacting the second lens unit in response to an instruction for stowing. 
     Other objects and further features of the present invention will become readily apparent from the following description of the preferred embodiments with reference to accompanying drawings 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view showing the structure of a lens barrel that is an embodiment of the present invention in a collapsed state. 
         FIG. 2  is a sectional view showing the structure of the lens barrel of the embodiment in an image-taking state. 
         FIG. 3  is an exploded perspective view of a second lens unit in the lens barrel of the embodiment. 
         FIG. 4  is a front view of a shutter unit in the lens barrel of the embodiment in an opened state. 
         FIG. 5  is a front view of a shutter unit in the lens barrel of the embodiment in a closed state. 
         FIG. 6  is a front view of a stop unit in the lens barrel of the embodiment in an opened state. 
         FIG. 7  is a front view of the stop unit in a small aperture state. 
         FIG. 8  is a perspective view of a third lens unit and a base member for an image-pickup element in the lens barrel of the embodiment. 
         FIG. 9  is a sectional view of the third lens unit and the base member. 
         FIG. 10  is a partially sectional view of the third lens unit and the base member in  FIG. 9 . 
         FIG. 11  is a perspective view of an image-taking apparatus equipped with the lens barrel of the embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description will now be given of the preferred embodiments of the present invention by referring to the accompanying drawings. 
       FIG. 1  shows the structure of a lens barrel that is a lens apparatus of an embodiment of the present invention in a collapsed (housed) state.  FIG. 2  shows the structure of the lens barrel in an image-taking state. This lens barrel  101  is provided integrally in an image-taking apparatus  100  such as a digital still camera and a video camera as shown in  FIG. 11 . 
     In  FIG. 11 , reference numeral  102  denotes a shutter button,  103  a power on/off switch,  104  a finder window,  105  a photometry window, and  106  a flash unit. 
     As shown in  FIGS. 1 and 2 , the lens barrel of the present embodiment is a double-collapsible and four-unit lens barrel. The lens barrel includes, in order from an object side (left in the figure) to an image side, a front lens unit  1  comprising a compensator lens  1   a  held by a lens holding member  18   a  and a first holding barrel  18  holding the lens holding member  18   a , a variator lens unit (second lens unit)  2  comprising a variator lens  2   a  and a second holding barrel  14  holding the variator lens  2   a , a focusing lens unit (first lens unit)  3  comprising a focusing lens  3   a  and a third holding barrel  19  holding the focusing lens  3   a , and a relay lens unit  4  comprising a relay lens  4   a  and a fourth holding barrel holding the relay lens  4   a.    
     Reference numeral  6  denotes an image-pickup element such as a CCD sensor and a CMOS sensor. The image-pickup element photoelectrically converts an object image formed by the above-mentioned four lens units  1  to  4  to a electric signal. Reference numeral  5  denotes an element base member holding the image-pickup element  6 . 
     Reference numeral  7  denotes an optical low-pass filter,  8  a cover barrel having a substantially cylindrical shape and being fixed with a screw to the element base member  5 . 
     Reference numeral  9  denotes a driving gear engaging with a gear portion that is provided on the outer circumference of a driving barrel  10 , and transmitting the rotational power of a zoom motor  20  to the driving barrel  10 . The driving gear  9  is rotatably held by the cover barrel  8  and the element base member  5 . 
     Inside the driving barrel  10 , a fixed barrel  11  fixed to the cover barrel  8  and element base member  5  is arranged. Three taper cams  11   a  are formed on the fixed barrel  11  equiangularly. Moreover, three cams  11   b  having a through-groove shape are formed on the fixed barrel  11  equiangularly. 
     The driving barrel  10  has a cylindrical shape, and three straight grooves  10   b  extending in the optical axis direction are formed on the inner circumferential surface of the driving barrel  10  equiangularly. Moreover, a moving cam barrel  12  is arranged inside the fixed barrel  11 . The moving cam barrel  12  has a cylindrical shape, and three follower pins  12   a  that are cam followers are provided on the outer circumferential surface of the moving cam barrel  12  equiangularly. Furthermore, three driving pins  12   b  are fixed with nuts  12   c  on the outer circumferential surface of the moving cam barrel  12  equiangularly. The driving pins  12   b  are located at positions on the image-plane side further than the follower pins  12   a.    
     The follower pin  12   a  has a taper portion on its tip, the taper portion engaging with the taper cam  11   a . The driving pin  12   b  engages with the cam  11   b , and penetrates it to engage with the straight groove  10   b.    
     When the driving barrel  10  is rotated around the optical axis of the lens barrel by the driving power from the zoom motor  20 , the moving cam barrel  12  rotates around the optical axis with the driving barrel  10  because of the engagement of the driving pin  12   b  and straight groove  10   b . At this time, since the follower pin  12   a  of the moving cam barrel  12  engages with the cam  11   b  of the fixed barrel  11 , the moving cam barrel  12  is moved in the optical axis direction by the lift of the taper cam  11   a.    
     A straight-proceeding barrel  13  is arranged inside the moving cam barrel  12 . The straight-proceeding barrel  13  has a cylindrical shape, and three protruding portions  13   e  are formed in the rear end on the outer circumferential surface of the straight-proceeding barrel  13  equiangularly. The three protruding portions  13   e  engage with three straight grooves  11   c  that are formed on the inner circumferential surface of the fixed barrel  11  equiangularly so as to extend in the optical axis direction. Therefore, the straight-proceeding barrel  13  is movable with respect to the fixed barrel  11  in the optical axis direction, but its rotation around the optical axis is prevented. 
     Three protruding portions  13   a  are formed in the vicinity of the rear end on the outer circumferential surface of the straight-proceeding barrel  13  equiangularly. The protruding portion  13   a  engages with a groove  12   c  formed on the inner circumferential surface of the moving cam barrel  12  so as to extend in the circumferential direction. Therefore, the movement of the moving cam barrel  12  in the optical axis direction moves the straight-proceeding barrel  13  in the same direction. At this time, the moving cam barrel  12  rotates, but the straight-proceeding barrel  13  does not rotate. 
     Three straight grooves  13   b  extending in the optical axis direction and having a through-groove shape are formed in the straight-proceeding barrel  13  equiangularly. Moreover, three taper cams  12   d  are formed on the inner circumferential surface of the moving cam barrel  12  equiangularly. 
     Furthermore, three follower pins  14   a  are provided on the outer circumferential surface of the second holding barrel  14  equiangularly. The follower pin  14   a  penetrates the straight groove  13   b  and engages with the taper cam  12   d  at a taper portion formed at its tip. Therefore. the second holding barrel  14  is moved by the lift of the taper cam  12   d  in the optical axis direction in synchronization with the movement in the optical axis direction and rotation of the moving cam barrel  12 . 
     The second holding barrel  14  holds the variator lens unit  2   a , a shutter unit  15  and a stop unit  16 . Hereinafter, these are collectively referred to as the second lens unit, and the detailed explanation thereof will be given later. 
     Three taper cams  13   c  having a through-groove shape are formed at the front portion of the straight-proceeding barrel  13  equiangularly. Moreover, three cams  13   d  are formed at the front portion on the inner circumferential surface of the straight-proceeding barrel  13  equiangularly. 
     The first holding barrel  18  is arranged inside the straight-proceeding barrel  13 . Furthermore, three straight grooves  12   e  extending in the optical axis direction are formed at the front portion on the inner circumferential surface of the moving cam barrel  12  equiangularly. Inside the first holding barrel  18 , the lens holding member  18   a  is joined with the first holding barrel  18 ; the lens holding member  18   a  holds the compensator lens  1   a.    
     Three follower pins  18   b  that are cam followers are provided on the outer circumferential surface of the first holding barrel  18  equiangularly, and three driving pins  18   c  are fixed with nuts  18   d  to the first holding barrel  18  equiangularly. 
     A taper portion formed at the tip of the follower pins  18   b  engages with the taper cam  13   c . The driving pin  18   c  penetrates the cam  13   d  formed in the straight-proceeding barrel  13  and engages with a straight groove  12   e  formed on the inner circumferential surface of in the moving cam barrel  12  and extending in the optical axis direction. Thereby, when the moving cam barrel  12  is rotated, the first holding barrel  18  is rotated around and moved in the optical axis direction by the lift of the taper cam  13   c  of the straight-proceeding barrel  13 . 
     By the structure described above, the lens barrel is driven so as to change its whole length between the collapsed state shown in  FIG. 1  and the image-taking state shown in  FIG. 2 . Zooming is preformed by the change of the distances in the optical axis direction of the four lens units by the driving power of the zoom motor  20 . Focusing is preformed by the change of the position in the optical axis direction of the third holding barrel  19  (focusing lens  3   a ) by the driving power of the voicecoil motor that will be described later. 
     Control of energization for the zoom motor  20  and voicecoil motor (coil  51 ), that is, control of the positions of the second lens unit  2  and third lens unit  3  is performed by a controller  70  shown in  FIG. 1 . 
     Next, the second lens unit  2  will be explained using  FIGS. 3 to 5 . In  FIG. 3 , reference numeral  30  denotes a driving source of the shutter unit  15 . The driving source  30  comprises a coil  31  wound around a bobbin. Magnetic flux generated by the energization to the coil  31  passes through yokes  32  and  33 , and generates magnetic torque in a magnet  34   b  integrally provided on an arm  34 . The rotation angle of the arm  34  is limited by the contact between a pin  34   a  formed on the arm  34  and the ends of an opening  35   a  formed in a shutter base member  35 . 
     The pin  34   a  is inserted into openings  36   a  and  37   a  respectively formed in two shutter blades  36  and  37  as shown in  FIGS. 4 and 5 . Therefore, when the arm  34  is rotated, the shutter blades  36  and  37  are rotated in their open/close direction along rails formed on the shutter base member  35  by the driving power received at the openings  36   a  and  37   a  from the pin  34   a . A pin  35   b  formed on the shutter base member  35  is inserted into openings  36   b  and  37   b  respectively formed in the shutter blades  36  and  37 . The pin  35   b  becomes the rotation center of the shutter blades  36  and  37 ; the shutter blades  36  and  37  rotate between the open state shown in  FIG. 4  and the close state shown in  FIG. 5 . 
     In the states shown in  FIGS. 4 and 5 , the magnet  34   b  stops at the rotation position where a magnetic attracting force acts between its magnetic poles and the yokes  32  and  33 . Therefore, the shutter blades  36  and  37  are held in each state after stopping the energization to the coil  51 . 
     In  FIG. 3 , reference numeral  38  denotes a shutter top board holding the shutter blades  36  and  37  so that they may not drop out of the shutter base member  35 . 
     Next, the stop unit  16  will be explained using  FIGS. 3 ,  6  and  7 . The stop unit  16  in this embodiment is an iris stop having six stop blades. A stop base member  40  is provided on the object side of the second holding barrel  14 . A stepping motor  41  for driving the stop blades is fixed to the stop base member  40 . A gear  41   a  attached to the output shaft of the stepping motor  41  protrudes from a hole  40   a  formed in the stop base member  40 . The gear  41   a  engages with a gear  42   a  provided on the outer circumferential portion of the stop-driving ring  42 . 
     Six pins  42   b ,  42   c ,  42   d ,  42   e ,  42   f  and  42   g  are formed on the object-side surface of the stop-driving ring  42 . These pins  42   b  to  42   g  engage with cam grooves formed in the stop blades  43 ,  44 ,  45 ,  46 ,  47  and  48 , respectively. On the other hand, six pins  40   b ,  40   c ,  40   d ,  40   e ,  40   f  and  40   g  are formed on the object-side surface of the stop base member  40 . These pins  40   b  to  40   g  are inserted into holds formed in the stop blades  43  to  48 , respectively. 
       FIG. 6  shows the stop unit  16  in the open state, and  FIG. 7  shows the stop unit  16  in a small aperture state. The rotation of the stepping motor  41  rotates the stop-driving ring  42 , which is arranged in a concave portion  40   h  (see  FIG. 3 ) formed around an aperture (light-passing opening) that is formed at the center of the stop base member  40  The gear  42   a  of the stop-driving ring  42  has a circular arc shape; the rotation amount of the stop-driving ring  42  is limited by a circular arc hole  40   a  formed in the stop base member  40 . 
     The stop-driving ring  42  is rotated according to the step-rotating angle of the stepping motor  41 , and the six stop blades  43  to  48  are rotated in the open/close direction around the pins  40   b  to  40   g  along the cam grooves thereof, respectively. Thereby, the area of the stop aperture formed by the six stop blades  43  to  48  is changed. 
     Next, the structure of the third lens unit  3  including the focusing lens  3   a  and third holding barrel  19 , and a driving mechanism thereof for focusing will be explained. 
       FIGS. 8 and 9  show the third lens unit  3  and the element base member  5 . As shown in the figures, the third holding barrel  19  holds the focusing lens  3   a . A coil  51 , yoke  52  and permanent magnet  53  constitute the voicecoil motor. 
     Reference numeral  54  denotes a first guide bar guiding the third holding barrel  19  in the optical axis direction, and  55  a metal member for fixing the yoke  52  and first guide bar  54 . Reference numeral  56  denotes a second guide bar restraining the rotation of the third holding barrel  19  in a plane orthogonal to the optical axis direction. 
     The principal of the drive of the voicecoil motor in the present embodiment is the same as that of well-known voicecoil motors. The coil  51  is wound around the third holding barrel  19  so as to encircle the yoke  52 . The permanent magnet  53  is magnetized in the optical axis direction. The magnetic flux from the permanent magnet  53  is generated radially with respect to the optical axis from the outside of the yoke  52  to the inside thereof; the direction of the magnetic flux is orthogonal to the winding direction of the coil  51 . 
     Therefore, when applying a current to the coil  51 , the third holding barrel  19  receives a driving power in the optical axis direction, and is moved along the first and second guide bars  54  and  56 . Moreover, the change of the direction of the current applied to the coil  51  switches the moving direction of the third holding barrel  19 . 
     The controller  70  detects the movement amount of the third holding barrel  19  by the following detecting structure that is used a magnetic sensor  57 . In bottom portion of the third holding barrel  19  in  FIGS. 8 and 9 , a magnetic scale  58  is provided. North poles and south poles are alternately magnetized at a predetermined pitch in the magnetic scale  58 . The magnetic sensor  57  that faces the magnet scale  58  with a predetermined gap is provided on the element base member  5 . The length of the magnetic scale  58  is set so as to be able to face the magnetic sensor  57  in the whole moving range of the third holding barrel  19  for focusing. 
     The magnetic sensor  17  outputs a signal with a near-sinusoidal waveform according to the movement of the magnetic scale  58  with the movement of the third holding barrel  19 . The controller  70  shapes the signal into a pulse signal, and counts the number of its pulse to detect the movement amount of the third holding barrel  19 . The detection of the movement amount is always performed after the power of the image-taking apparatus is turned on. 
     The controller  70  controls the drive of the third holding barrel  19  for focusing by controlling the amount and direction of the current applied to the coil  51 . The control is performed so that the detected movement amount may become substantially equal to a target movement amount that is stored in a memory (not shown in the figure) or calculated for a predetermined reference position. In other words, the control is performed so that the detected movement amount may become equal to the target movement amount or fall in a permissible range for the target movement amount, in which there is no influence on focusing. A method for setting the above-mentioned reference position will be explained later. 
     Next, the operation of the third holding barrel  19  at the time of the collapsing operation of the lens barrel will be explained using  FIGS. 1 ,  2  and  10 . When the power is turned off in the image-taking state shown in  FIG. 2 , the zoom motor  20  rotates in a direction in which the lens barrel will be collapsed. Thereby, the first holding barrel  18  and second holding barrel  14  are moved toward the image-pickup element  6 . 
     Here, in the image-taking state, the coil  51  of the voicecoil motor that drives the third holding barrel  19  is always energized for holding the position of the third holding barrel  19 . However, the energization to the coil  51  (voicecoil motor) is stopped after the power is turned off. This saves the power of the image-taking apparatus. 
     However, since the voicecoil motor has no stable stop position in the nonenergized state as described above, the third holding barrel  19  can move freely in the optical axis direction after the energization to the coil  51  is stopped. 
     To solve the problem, in the present embodiment, impact absorption members  14   b  and  14   c , which are made of elastic material such as rubber, are provided at the image-plane side portion of the second holding barrel  14 . 
     When the second holding barrel  14  is moved toward the image-pickup element  6  by the driving power of the zoom motor  20 , the impact absorption members  14   b  and  14   c  contact the object-side surface of the third holding barrel  19  to push and move the third holding barrel  19 . Moreover, when each of the second and third holding barrel  14  and  18  reaches the collapsed position, stoppers  19   f  and  19   g  formed at the image-plane side portion of the third holding barrel  19  contact stoppers  5   a  and  5   b  formed on the element base member  5 , respectively. As a result, the third holding barrel  14  is pressed against the element base member  5 ; thereby the position of the third holding barrel  14  is held. 
     As described above, in this embodiment, the third holding barrel  19  that becomes movable freely after the energization to the voicecoil motor is stopped is driven by the second holding barrel  14  that is driven to the collapsed position. Moreover, the third holding barrel  19  is held by sandwiching it between the second holding barrel  14  and the element base member  5  after reaching the collapsed position, thereby stopping free movement of the third holding barrel  19 . As a result, it is possible to avoid a problem that deterioration of the optical accuracy of the lens barrel and a collision sound will occur because of the collision between the third holding barrel  19  movable freely and the second holding barrel  14  or element base member  5 . 
     In other words, in the nonenergized state of the first actuator, it is possible to control the position of the first lens unit by using the driving power of the second lens unit. Therefore, unintended movement of the first lens unit and collision of the first lens unit and a mechanical end of the movable range are prevented in the nonenergized state of the first actuator. In addition, driving the second actuator with stopping the energization to the first actuator makes it possible to save the power. 
     Here, it is possible to set the third holding barrel  19  to a predetermined position (collapsed position) in the optical axis direction with little play by providing the impact absorption members  14   b  and  14   c  on portions that contact the third holding barrel  19  in the second holding barrel  14 , and by raising the accuracy of the distance from the image-pickup element  6  to the stoppers  5   a  and  5   b  provided on the element base member  5  to some extent. 
     Therefore, if a movement-amount-counter counting the number of pulses in the controller  70  is reset when the power is turned on, it is possible to set this position to the reference position for controlling the movement amount (position) of the third holding barrel  19 . 
     As a result, the accuracy for driving the third holding barrel  19  to an optimal focus position corresponding to the above-described target movement amount according to an object distance obtained by distance measurement is guaranteed every time the power is turned off. Therefore, resetting the movement-amount-counter every power-off makes it possible to eliminate the necessity of a reset operation at the time of power-on and a sensor for detecting the reference position. Thereby, it is possible to achieve the miniaturization of the image-taking apparatus and the simplification of lens control. 
     In the above-described embodiment, the focusing lens unit driven by the voicecoil motor originally is driven by the variator lens unit that is driven by the zoom motor in the nonenergized state of the voicecoil motor. However, the present invention can be applied to any case where a first lens unit driven by a voicecoil motor originally is driven by a second lens unit that is driven by another actuator in the nonenergized state of the voicecoil motor. 
     In addition, in the above-described embodiment, the voicecoil motor was explained as an actuator having no stable stop position in its nonenergized state. However, the present invention can be applied to any case where an actuator other than a voicecoil motor and having no stable stop position in its nonenergized state is used. 
     This application claims priority from Japanese Patent Application No. 2004-083736, filed on Mar. 22, 2004, which is hereby incorporated by reference herein.