Abstract:
There is provided a light control apparatus that maintains the overall apparatus size small, increases the number of stop stages, and is suitable for both the shutter and stop actions. A light control apparatus includes a first actuator, a second actuator, a first light shielding member driven by the first actuator, and a second light shielding member driven by the second actuator, wherein in a stop adjusting action, the first and second actuators drive the first and second light shielding members and adjust an aperture formed by the first and second light shielding members, and wherein in a shutter action, the second actuator drives the second light-shielding member for a light shielding action.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a light control apparatus for a stop-cum-shutter to be mounted in an optical apparatus, such as a still camera, a video camera and an interchangeable lens. 
   As an optical apparatus, such as a digital camera, has been made smaller, a smaller shutter unit and a smaller stop unit are required to be mounted on it. A light control apparatus (shutter-cum-stop unit) is known which serves as both a shutter and a stop, and makes the optical apparatus smaller than a combination of a shutter unit and a stop unit separately. 
   Japanese Patent Application, Publication No. 2002-55375 discloses a stop-cum-shutter unit that includes a pair of motors, and a pair of stop-cum-shutter blades driven by these motors. As one motor is electrified, the stop-cum-shutter unit drives both stop-cum-shutter blades to a position that forms a predetermined aperture. As the other motor is electrified while the stop state is maintained, both stop-cum-shutter blades acts as a shutter. The disclosed stop-cum-shutter unit switches actions of these two motors, and sets the apertures to two predetermined apertures and release aperture. In other words, the unit acts as a shutter as well as selecting plural apertures. 
   However, the above conventional stop-cum-shutter unit in which one motor drives two stop-cum-shutter blades and forms an aperture has difficulties in making the aperture shape circular and making the stop multistage. In other words, the above conventional stop-cum-shutter unit provides only three apertures, a release aperture, an aperture driven by one motor, and another aperture driven by the other motor. 
   One known method for increasing the number of stop stages and make circular the stop shape is that a stepping motor drives plural stop blades using another component, such as a ring member. However, use of the ring member increases the number of components, and makes the apparatus large. In addition, the stepping motor is unsuitable for quick shutter actions of plural stop blades connected to the ring member. The high-speed shutter action needs a dedicated shutter blade and a motor. 
   Moreover, the above conventional stop-cum-shutter unit uses the same type of actuators that enable each of the two motors to drive the stop and the shutter. It is therefore difficult to form a suitable structure for both the stop action and the shutter action. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention is directed to a light control apparatus that maintains the overall apparatus size small, increases the number of stop stages, and is suitable for both the shutter and stop actions. 
   A light control apparatus according to one aspect of the present invention includes a first actuator, a second actuator, a first light shielding member driven by the first actuator, and a second light shielding member driven by the second actuator, wherein in a stop adjusting action, the first and second actuators drive the first and second light shielding members and adjust an aperture formed by the first and second light shielding members, and wherein in a shutter action, the second actuator drives the second light-shielding member for a light shielding action. 
   A light control apparatus according to another aspect of the present invention includes a first actuator, a second actuator, a first light shielding member driven by the first actuator, and a second light shielding member driven by the second actuator, and driven by the first light shielding member driven by the first actuator, wherein in a stop adjusting action, the first actuator drives the first and second light shielding members and adjusts an aperture formed by the first and second light shielding members, and wherein in a shutter action, the second actuator drives the second light-shielding member for a light shielding action. 
   An optical apparatus according to another aspect of the present invention includes the above light control apparatus and an image-pickup device for photoelectrically converting a subject image that passes an aperture formed by said first and second light shielding members. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematic structure of a digital still camera according to a first embodiment of the present invention. 
       FIG. 2  is a schematic perspective view of a light control apparatus according to the first embodiment. 
       FIG. 3  is a front view of the light control apparatus in a release state according to the first embodiment. 
       FIG. 4  is a front view of the light control apparatus in an intermediate stop state according to the first embodiment. 
       FIG. 5  is a front view of the light control apparatus in an intermediate stop state according to the first embodiment. 
       FIG. 6  is a front view of the light control apparatus in an intermediate stop state according to the first embodiment. 
       FIG. 7  is a front view of the light control apparatus in an intermediate stop state according to the first embodiment. 
       FIG. 8  is a front view of the light control apparatus that finishes the shutter action according to the first embodiment. 
       FIG. 9  shows a schematic structure of a digital still camera according to a second embodiment of the present invention. 
       FIG. 10  is a front view of the light control apparatus in a release state according to the second embodiment. 
       FIG. 11  is a front view of the light control apparatus in an intermediate stop state according to the second embodiment. 
       FIG. 12  is a front view of the light control apparatus in an intermediate stop state according to the second embodiment. 
       FIG. 13  is a front view of the light control apparatus in an intermediate stop state according to the second embodiment. 
       FIG. 14  is a front view of the light control apparatus in an intermediate stop state according to the second embodiment. 
       FIG. 15  is a front view of the light control apparatus that finishes the shutter action according to the second embodiment. 
       FIG. 16  is a flowchart showing a stop adjusting action and a shutter action in the light control apparatus according to the first embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. 
   Processes, techniques, apparatus, and materials as known by one of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the enabling description where appropriate. 
   Exemplary embodiments will be described in detail below with reference to the drawings. 
   First Embodiment 
     FIG. 1  shows a schematic structure of a digital still camera having a light control apparatus according to a first embodiment of the present invention. In  FIG. 1 ,  100  denotes a camera body, and  110  denotes an image-taking optical system. The light control apparatus  120  is provided in the image-taking optical system  110 .  130  denotes an image-pickup device or an image sensor, such as a CCD sensor and a CMOS sensor, and photoelectrically converts a subject image formed by the image-taking optical system  110 . An image processing control circuit  140  performs various processes for an output signal from the image-pickup device  130 , and generates a shot image. The data of the shot image is recorded in a recording medium (not shown), such as a semiconductor memory, a magnetic disc, and an optical disc. 
     FIGS. 2 and 3  show a light control apparatus  120  as a stop-cum-shutter apparatus according to this embodiment. 
     1  denotes a base plate having a release opening  1   a  at its center thereof. A stepping motor (or first actuator)  2  is held above the base plate  1  and changes a stop position in accordance with a current value. A rotation of the stepping motor  2  is transmitted to blades (or first light shielding members)  4  and  5  via a driving lever  3 . As the stepping motor  2  rotates in an A direction in  FIG. 3 , the blades  4  and  5  rotate around shaft parts  1   b  and  1   c  provided on the base plate  1 , and close an opening formed by the blades  4  and  5 . As the stepping motor  2  rotates in a B direction in  FIG. 3 , the blades  4  and  5  rotate around the shaft parts  1   b  and  1   c  and open the opening formed by the blades  4  and  5 . 
   A bipolar moving magnet type electromagnetic motor (second actuator)  6  is held under the base plate  1 . A rotation of the electronic motor  6  is transmitted to the driving lever  7  to the blades (second light shielding members)  8  and  9 . As the electromagnetic motor  6  rotates in a C direction in  FIG. 3 , the blades  8  and  9  rotate around the shaft parts  1   d  and  1   e  provided on the base plate  1 , and close the opening formed by the blades  8  and  9 . When the electromagnetic motor  6  rotates in a D direction in  FIG. 3 , the blades  8  and  9  rotate around the shaft parts  1   d  and  1   e , and open the opening formed by the blades  8  and  9 . 
   A description will be given of an arrangement among the blades  4 ,  5 ,  8  and  9 . The blade  5  is arranged closest to the base plate  1 , and the blades  8 ,  4  and  9  arranged on the blade  5  in this order. The tips of the blades  5  and  8  and peripheral parts of the shaft parts  1   c  and  1   d  as rotational centers always overlap each other. 
   The above overlapping order of the four blades  4 ,  5 ,  8  and  9  maintains irrespective of their rotational states, and no interference occurs which would otherwise preclude the operations among the blades. In addition, overlapping of these blades can make the light control apparatus  120  small in a plane orthogonal to the optical axis. 
   A cover plate (not shown) is attached to the base plate  1  and covers the blades  4 ,  5 ,  8  and  9  so as to rotatably house these blades  4 ,  5 ,  8  and  9  in a space along a predetermined optical-axis direction. 
     FIG. 3  shows that all of the blades  4 ,  5 ,  8  and  9  rotate to the fully open positions, and the aperture at this state is a release aperture corresponding to the release opening  1   a . In this state, both the stepping motor  2  and the electromagnetic motor  6  are not electrified. 
   A description will be given of the stop adjusting action and shutter action of the thus configured light control apparatus  120 , with reference to a flowchart shown in  FIG. 16 . 
   In step (“S”)  1  in  FIG. 16 , the controller  140  commands a photometry unit  150  in the camera body  100  to start a photometric action after the camera is powered on and a photographer presses a photographing ready switch. In step  2 , the controller  140  electrifies the stepping motor  2  and the electromagnetic motor  6  so that the aperture having an aperture in accordance with the photometric result from the release state shown in  FIG. 3 . Thereby, a polygonal aperture in accordance with the photometric result is formed approximately around the optical axis. 
   The controller  140  shown in  FIG. 1  sequentially supplies the stepping motor  2  with the necessary number of pulsed signals to form the aperture determined based on the photometric result by changing a current value. In accordance with the photometric result, the electromagnetic motor  6  is similarly supplied with the drive signal having a current value necessary to form the determined aperture. As the controller  140  controls the current values of the pulsed signal and the drive signal, the multistage (or substantially continuous) aperture can be set as shown in  FIGS. 4 to 7 . 
   The electromagnetic motor  6  has a rotational area of about 30°, and its rotational position is held at its both ends by the holding power as the magnetic force of the motor coil. The rotational position of the electromagnetic motor  6  is controlled by a balance between the magnetic field generated in the motor coil in accordance with a current value and the magnetic field of the bipolar magnetized moving magnet that rotates with the driving lever  7 . 
   In the stop states shown in  FIGS. 4 to 7 , the blades  4  and  5  are held in place by maintaining the stepping motor  2  not electrified. The blades  8  and  9  are held in place when the electromagnetic motor  6  is supplied with a drive signal having a current value to obtain an intermediate stop state. 
   In step  3 , when a photographer presses a shot switch (not shown), the controller  140  starts resetting the electric charges stored in the image-pickup device  130  and taking in the electric charges. At approximately the same time, a shutter close signal is supplied to the electric motor  6 . The shutter close signal is supplied by further increasing the current value necessary for the drive signal to hold the electronic motor  6  at that stop state. Thereby, the electronic motor  6  further rotates in a C direction shown in  FIG. 3  irrespective of a stop position the stepping motor  2  (blades  4  and  5 ), and the blades  8  and  9  rotate and close the opening.  FIG. 8  shows that the shutter action ends. 
   In step  4 , when taking in and transfers of the electric charges from the image-pickup device  130  end, the controller  140  resets the current value of the drive signal to be supplied again to the electromagnetic motor  6  to the value before the shutter action. Thereby, the procedure returns to the stop state before the shutter action. 
   The present invention is not limited to this embodiment that sets an electromagnetic driving source that drives the blades  4  and  5  to the stepping motor and an electromagnetic driving source that drives the blades  8  and  9  to the moving magnet type electromagnetic motor. As long as a driving source can rotate each blade to a predetermined position, the driving source may be one, such as a plunger, which controls the blades&#39; rotational drive amounts by controlling the current value. 
   The aperture does not necessarily have to be close to a circle: The rotational driving amounts of the blades  8  and  9  are made different from those of the blades  4  and  5  so that the aperture has an elongated cat-eyed shape. 
   Second Embodiment 
     FIGS. 9 and 10  show a structure of the light control apparatus  220  as a stop-cum-shutter unit according to a second embodiment of the present invention. The light control apparatus  220  of this embodiment is provided in an image-taking optical system in the camera, as in the first embodiment. 
     11  denotes a base plate having a release opening  11   a  at its center thereof. A stepping motor (or first actuator)  12  is held above the base plate  11 , and a rotation of the stepping motor  12  is transmitted to blades (or first light shielding members)  14  and  15  via a driving lever  13 . 
   The blade  14  has two contact parts  14   a  and  14   b . The contact part  14   a  has such a convex shape at the side of the base plate  11  that the contact part  14   a  contacts an outer circumference part of the blade  18 . The contact part  14   b  has such a convex shape at a side opposing to the base plate  11  that the contact part  14   b  contacts an outer circumference part of the blade  19 . This embodiment that provides one blade  14  with two contact parts  14   a  and  14   b  has higher positional precision of each of the contact parts  14   a  and  14   b  than a configuration that provides each of plural blades with a contact part 
   As the stepping motor  12  rotates in an E direction in  FIG. 10 , the blades  14  and  15  rotate around shaft parts  11   b  and  11   c  provided on the base plate  11 , and close an opening formed by the blades  14  and  15 . When the contact parts  14   a  and  14   b  push the blades  18  and  19  as the blade  14  rotates, the blades  18  and  19  rotate around the shaft parts  11   d  and  11   e . Thus, the blades  14 ,  15 ,  18  and  19  form an aperture. 
   At this time, since the rotor of the electromagnetic motor  16  is connected to the blades  18  and  19  via the driving lever  17 , as described later, the rotor rotates as the contact parts  14   a  and  14   b  of the blade  14  move the blades  18  and  19  in the closing direction. 
   The blades  18  and  19  contact the contact parts  14   a  and  14   b  of the blade  14  outside the light control apparatus  220  in the radial direction. Therefore, when the blades  18  and  19  rotate in the opening direction and the blades  14  and  15  rotate in the closing direction, the contact parts  14   a  and  14   b  contact the blades  18  and  19 . On the contrary, when only the blades  18  and  19  rotate in the closing direction, the blades  18  and  19  separate from the contact parts  14   a  and  14   b.    
   When the stepping motor  12  rotates in an F direction in  FIG. 10 , the blades  14  and  15  rotate around the shaft parts  11   b  and  11   c  and open the opening formed by the blades  14  and  15 . 
   A bipolar moving magnet type electromagnetic motor (second actuator)  16  is held under the base plate  11 . A rotation of the electronic motor  16  is transmitted to the driving lever  17  to the blades (second light shielding members)  18  and  19 . 
   The electromagnetic rotor  16  includes a rotor and a yoke, and has a weak holding (or cogging) power enough to open the blades  18  and  19  and enable them to contact the contact parts  14   a  and  14   b  of the blade  14 . In other words, when the electronic motor  16  is not electrified, the blade  18  always contacts the contact part  14   a  of the blade  14  while the blade  19  always contacts the contact part  14   b  of the blade  14 . 
   As the electromagnetic motor  16  rotates in a G direction in  FIG. 10 , the blades  18  and  19  rotate around the shaft parts  11   d  and  11   e  provided on the base plate  11 , and close the opening formed by the blades  18  and  19 . As the electromagnetic motor  16  rotates in an H direction in  FIG. 10 , the blades  18  and  19  rotate around the shaft parts  11   d  and  11   e , and open the opening formed by the blades  18  and  19 . 
   The electronic motor  16  has a holding power to open the blades  18  and  19 , as discussed above, and the stepping motor  12  should drive the blades  14  and  15  with a larger driving power than the holding power in order to close the blades  14  and  15 . However, the holding power of the electromagnetic motor  16  is as large as one to restrain the saccadic movements between the contact part  14   a  of the blade  14  and blade  18  and between the contact part  14   b  of the blade and the blade  19 , and is not an excessively large load in driving the blades  14  and  15 . 
   A description will be given of an arrangement among the blades  14 ,  15 ,  18  and  19 . The blade  15  is arranged closest to the base plate  11 , and the blades  18 ,  14  and  19  arranged on the blade  15  in this order. The tips of the blades  15  and  18  and peripheral parts of the shaft parts  11   c  and  11   d  as rotational centers always overlap each other. The above overlapping order of the four blades  14 ,  15 ,  18  and  19  maintains irrespective of their rotational states, and no interference occurs which would otherwise preclude the operations among the blades. 
   A cover plate (not shown) is attached to the base plate  11  and covers the blades  14 ,  15 ,  18  and  19  so as to rotatably house these blades  14 ,  15 ,  18  and  19  in a space along a predetermined optical-axis direction. 
     FIG. 10  shows that all of the blades  14 ,  15 ,  18  and  19  rotate to the fully open positions, and the aperture at this state is a release aperture corresponding to the release opening  11   a . In this state, both the stepping motor  12  and the electromagnetic motor  16  are not electrified. 
   A description will be given of the stop adjusting action and shutter action of the thus configured light control apparatus  220 . 
   Initially, the controller  140  commands the photometry unit  150  in the camera body  100  to start a photometric action after the camera is powered on and a photographer presses a photographing ready switch (not shown). The controller  140  electrifies the stepping motor  12  so that the aperture in accordance with the photometric result from the release state shown in  FIG. 10 . Thereby, a polygonal aperture in accordance with the photometric result is formed approximately around the optical axis. 
   The controller  140  shown in  FIG. 1  sequentially supplies the stepping motor  12  with the necessary number of pulsed signals to form the aperture determined based on the photometric result by changing a current value. As the controller  140  controls the current values of the pulsed signal, the multistage (or substantially continuous) aperture can be set as shown in  FIGS. 11 to 14 . 
   For example, when the stepping motor  12  operates the blades  14 ,  15 ,  18  and  19  through predetermined pulse driving, the state shown in  FIG. 12  is obtained and maintained when the stepping motor  12  is powered off. Although the electronic motor  16  is not also electrified at this time, the holding power of the electronic motor  16  moves the blades  18  and  19  in the opening direction and allows them to contact the contact parts  14   a  and  14   b  of the blade  14 . 
   The contact part  14   b  provided onto the blade  14  is not necessary for the stop adjusting action, and the contact part  14   a  may operate the blade  18  and the blade  19  via the driving lever  17 . 
   When the photographer presses a shot switch (not shown), the controller  140  starts resetting the electric charges stored in the image-pickup device  130  and taking in the electric charges. At approximately the same time, a shutter close signal is supplied to the electric motor  16 . The shutter close signal is supplied by further increasing the current value necessary for the drive signal to hold the electronic motor  16  at that stop state. Thereby, the electronic motor  16  further rotates in a G direction shown in  FIG. 10  irrespective of a stop position the stepping motor  12  (blades  14  and  15 ), and rotates so that the blades  18  and  19  close the opening.  FIG. 15  shows that the shutter action ends. 
   When taking in and transfers of the electric charges from the image-pickup device  130  end, the controller  140  resets the current value of the drive signal to be supplied again to the electromagnetic motor  16  to the value before the shutter action. A single photographing sequence is completed by stopping the electrification to the electronic motor  16 . 
   The light control apparatus of this embodiment adjusts the stop only by driving the stepping motor  12 , and facilitates control over the aperture. In addition, the light control apparatus can execute the shutter action only by driving the electromagnetic motor  16 . 
   In the shutter action, the blades  18  and  19  in the specific stop state rotate to close the opening, and no unnecessary operational areas for the blades  18  and  19  enable the high-speed shutter action. The blades  18  and  19  rotate to close the opening at the same time when the electromagnetic motor  16  is electrified, restraining the delays of mechanical actions and scattering of exposure time. 
   The present invention is not limited to this embodiment that sets an electromagnetic driving source that drives the blades  14  and  15  to the stepping motor and an electromagnetic driving source that drives the blades  18  and  19  to the moving magnet type electromagnetic motor. As long as a driving source can rotate each blade to a predetermined position, the driving source may be one, such as a plunger, which controls the blades&#39; rotational drive amounts by controlling the current values. 
   A reduction gear mechanism may be provided between the stepping motor  12  and the driving lever  13  for precise control over the aperture. Thereby, a rotational force of the stepping motor  12  can be amplified, the number of stop stages increases, and the positional precision improves. 
   While this embodiment uses the holding power of the electromagnetic motor  16  to maintain the blades  18  and  19  in contact with the contact parts  14   a  and  14   b  of the blade  14 , the present invention is not limited to this embodiment. For example, a spring is coupled to the driving lever  17  or the blades  18  and  19  so as to force the blades  18  and  19  in the opening direction. The plunger and the non-electrification holding power via the spring may be used to maintain the blades  18  and  19  in contact with the contact parts  14   a  and  14   b , instead of the electromagnetic motor  16 . 
   On the other hand, the contact parts  14   a  and  14   b  provided on the blade  14  may be formed as separate members or integrally formed by using plastic, etc. 
   While the above embodiments discuss an arrangement of the light control apparatus in the image-taking optical system in the integrated lens camera, the present invention is applicable to an arrangement of the light control apparatus of each embodiment in a lens unit in a camera system that includes the lens unit and the camera body mounted with the lens unit. In this case, a controller in the lens unit as well as a controller in the camera body can execute the driving control of the light control apparatus. 
   While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures and functions. 
   This application claims foreign priority benefits based on Japanese Patent Application No. 2004-296908, filed on Oct. 8, 2004, which is hereby incorporated by reference herein in its entirety as if fully set forth herein.