Abstract:
An imaging device for picking up an image of an object via an optical system and recording image information in a recording medium, a driving system for the optical system being controlled according to a position of an operating unit, includes a motor driving an object to be controlled by the driving system, a driver driving the motor, an absolute position detector detecting a relatively-low-resolution absolute position of the operating unit, a relative position detector detecting a relatively-high-resolution relative position of the operating unit, a position generator, and a controller. The position generator generates a position output corresponding to a position in a restricted range of movement of the operating unit using a combination of the detected absolute position and the detected relative position. The controller controls the motor via the driver to drive the object to be controlled according to the generated position output of the operating unit.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
   The present invention contains subject matter related to Japanese Patent Application JP 2004-250733 filed in the Japanese Patent Office on Aug. 30, 2004, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an imaging device in which a lens driving system is controlled during imaging, and to a method for driving an optical system. 
   2. Description of the Related Art 
   Recently, camera drive systems of the open-loop control method in which a stepping motor serves as an actuator have been widespread. Such a control mechanism provides high positioning resolution and achieves high positioning accuracy on the order of several micrometers (μm). 
   In one known camera drive system, when a motor drives a lens, an operation control unit detects the state of an operating member and controls the motor according to the detected state or the calculated amount. The operating member is implemented as, for example, a lever/ring the middle of whose operating range is the natural restoration point (see Japanese Unexamined Patent Application Publication No. 59-216111) or a rotating ring (see Japanese Unexamined Patent Application Publication No. 63-177118). Such control performed by the operation control unit improves the positioning accuracy with which the lens is controlled; and the need for rings that allow for a higher-resolution operation has increased. 
   In lens mechanisms (typically used for business purposes, etc.) in which a ring and a lens are mechanically connected and the lens moves forward or backward in a lens barrel depending on the amount of rotation of the ring, the angle of rotation of the ring is limited in association with the maximum forward or backward position of the lens in the lens barrel. In addition, the angle of rotation of the ring and the lens position are in one-to-one correspondence. Such lens mechanisms are therefore intuitive and easy-to-operate. 
   Lens position detection systems with a resolution as high as operating rings also have been demanded. 
   Existing lens position determination methods include the following types. 
   A first type is the type in which the absolute position is determined using a hall sensor, a potentiometer, or the like. 
   A second type is the type in which with the use of a reset sensor for detecting a reference position and a frequency generator (FG) pulse counter for counting pulses from the reference position, or the reset sensor and a magnetoresistive (MR) sensor, or the like, the relative position from the reference position is determined using the reset sensor/encoder combination (see Japanese Unexamined Patent Application Publication No. 59-216111, noted above). 
   A third type is the in which that a plurality of reference positions are detected using a plurality of reset sensors, e.g., two reset sensors, three reset sensors, etc. 
   SUMMARY OF THE INVENTION 
   When the above-described lens mechanism in which a ring and a lens are mechanically connected is applied to an inner focusing lens, the complexity in structure increases, and it is difficult to provide a one-to-one correspondence between the movable range of the ring and the movable range of the lens. It is therefore difficult to determine intuitively whether the object to be controlled (i.e., the inner focusing lens) has reached the movable end. 
   In the second lens-position determination method, a relative position sensor detects the amount of rotation of the operating ring using a displacement sensor, such as a two-phase pulse encoder. This relative position sensor has a problem in that when the angle of rotation of the operating ring is limited, it is difficult to determine the ring position immediately after the camera is turned on. In order to overcome this problem, the amount of relative movement is determined based on the state immediately after the camera is turned on, and the ring allows infinite rotation. Thus, it is difficult to provide a one-to-one correspondence between the movable range of the ring and the movable range of the lens, and it is therefore difficult to determine intuitively the amount of control. 
   In the first lens-position determination method, it is possible to determine the amount of rotation of the operating ring using the output of an absolute position sensor, such as a potentiometer. However, due to its typical restrictions, such as low resolution and high susceptibility to noise, the absolute position sensor is not suitable for smooth or fine movement of the lens. 
   The third lens-position determination method using a plurality of reset sensors has the drawback of low resolution due to mechanical restrictions, such as installation positions of the plurality of reset sensors. 
   It is therefore desirable to provide an imaging device that easily determines the amount of control and that performs control to smoothly drive an object to be controlled and to provide a method for driving an optical system. 
   An imaging device according to an embodiment of the present invention includes the following elements. A motor drives an object to be controlled by a driving system. A driver drives the motor. Absolute position detecting means detects a relatively-low-resolution absolute position of an operating unit. Relative position detecting means detects a relatively-high-resolution relative position of the operating unit. Position generating means generates a position output corresponding to the position of the operating unit using a combination of the absolute position detected by the absolute position detecting means and the relative position detected by the relative position detecting means; control means controls the motor via the driver to drive the object to be controlled according to the generated position output of the operating unit. 
   Therefore, with the use of both the absolute position detecting means with low resolution and the relative position detecting means with high resolution, with respect to the operating unit whose angle of rotation (movable range) is physically restricted, both detection of the absolute angle of rotation and high-resolution detection of the amount of rotation can be achieved. 
   The position generating means may initialize a value in a storage region storing the generated position output based on the absolute position detected by the absolute position detecting means. After the initialization, the position generating means may increase or decrease the value in the storage region based on a signal from the relative position detecting means. 
   The position of components of the optical system, such as a zoom lens and a focus lens or an iris of the imaging device, also may be controlled based on the value in the storage region in the position generating means. 
   A method for driving an optical system according to an embodiment of the present invention includes the steps of detecting a relatively-low-resolution absolute position of an operating unit, detecting a relatively-high-resolution relative position of the operating unit, generating a position output corresponding to a position of the operating unit using a combination of the absolute position detected in the step of detecting the absolute position and the relative position detected in the step of detecting the relative position, controlling a motor via a driver to drive an object to be controlled by a driving system according to the generated position output of the operating unit, and driving the object to be controlled by the driving system using the motor. 
   Therefore, with the processing using both steps of detecting the relatively-low-resolution absolute position and detecting the relatively-high-resolution relative position, with respect to the operating unit whose angle of rotation (movable range) is physically restricted, both detection of the absolute angle of rotation and high-resolution detection of the amount of rotation can be achieved. 
   In the step of generating a position output, a value in a storage region storing the generated position output may be initialized based on the absolute position detected in the step of detecting the absolute position, and, after the initialization, the value in the storage region may be increased or decreased based on a signal output in the step of detecting the relative position. 
   The positions of components of the optical system, such as a zoom lens and a focus lens or an iris of an imaging device, also may be controlled based on the value in the storage region in the step of generating a position output. 
   According to an embodiment of the present invention, therefore, the position of an operating ring whose angle of rotation is physically restricted can be determined using a sensor for detecting the absolute position and a sensor for detecting the amount of relative movement in order to achieve a determination of the absolute angle of rotation and a high-resolution detection of the position of the ring. 
   Therefore, with respect to a ring whose angle of rotation is restricted, of which the amount of control can be determined intuitively, fine and smooth manual operation of a lens, etc., can be performed. Moreover, even if the ring is rotated when applying no current, the angle of rotation of the ring can be detected when the imaging device is turned on. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of an imaging device according to an embodiment of the present invention; 
       FIG. 2  is a diagram of a lens driving system to show the lens driving operation of a ring position generator; 
       FIG. 3  is a diagram showing an iris driving system to show the iris driving operation of the ring position generator; 
       FIG. 4  is a diagram showing a MR encoder output; 
       FIG. 5  is a diagram showing a linear potentiometer output; 
       FIG. 6  is a diagram showing a non-linear potentiometer output; 
       FIG. 7  is a diagram showing a pulse encoder output; 
       FIG. 8  is a diagram showing an absolute encoder output; 
       FIG. 9  is a PAD diagram showing the lens driving operation; and 
       FIGS. 10A and 10B  are illustrations of a MR encoder and a potentiometer, respectively. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An embodiment of the present invention will be described in detail hereinbelow with reference to the drawings. 
     FIG. 1  is a block diagram schematically showing the structure of an imaging device according to an embodiment of the present invention. 
   In  FIG. 1 , an imaging lens and iris block  1  serves as an optical system, and the system includes an iris  12  that is adjustable to control the amount of light with respect to an objective lens and a lens housing accommodating a focus lens  13  in a manner capable of performing a focusing operation and a zoom lens  11  in manner capable of performing zoom-in and zoom-out operations. 
   An imaging element  2  is disposed along the optical axis of the imaging lens and iris block  1 . An image signal that is photoelectrically converted by the imaging element  2  is sampled and held at a predetermined timing by a sample-hold circuit  14  in a sample-hold and analog-to-digital conversion block  3 , and it is then converted into digital image data by an analog-to-digital conversion circuit  15 . 
   The digital image data is amplified by an amplification circuit  16  in a camera signal processor block  4  to a level capable of signal processing, and the amplified digital image data is subjected to luminance and chrominance signal processing by a luminance and chrominance signal processing circuit  17 . The resulting data is output to a video output unit  8  or a recorder  9 . 
   The digital image data amplified by the amplification circuit  16  to the level capable of signal processing also is supplied to a luminance signal detection circuit  18  to detect a luminance signal level and a high-frequency luminance signal component. In a camera control block  5 , an automatic exposure control unit  23 ′ performs exposure control depending on the luminance signal level, and an automatic focus control unit  23  performs focus control depending on the high-frequency luminance signal component. 
   Specifically, the amount of light passing through the iris  12 , the photoelectric conversion timing for the imaging element  2  from a timing generation circuit  7 , and the amplification level of the amplification circuit  16  are controlled based on an exposure control signal from the automatic exposure control unit  23 ′. 
   Based on a focus control signal from the automatic focus control unit  23 , the position of the focus lens  13  is controlled by a lens control unit  19  and a lens driving unit  20 . 
   In response to an input to a user interface control block  6  by a user operation of an operating ring, a displacement detector  24  and an absolute position detector  25  detect an amount of relative displacement and an absolute position, respectively, as described below. The amount of relative displacement and the absolute position output from the displacement detector  24  and the absolute position detector  25  are supplied to a ring position generator  26 . The ring position generator  26  generates a ring position output by combining the amount of relative displacement and the absolute position. 
   The ring position output is supplied to the lens control unit  19  in the camera control block  5 , and the lens control unit  19  generates a lens control signal based on the ring position output. The lens control signal is supplied to the lens driving unit  20 , and the lens driving unit  20  drives the focus lens  13  and the zoom lens  11  based on the lens control signal. 
     FIG. 2  is a diagram of a lens driving system using an operating ring, showing the lens driving operation of a ring rotation position generator. 
   In  FIG. 2 , a ring  27  has an angle of rotation that is restricted to a range of movement from 0 degrees to about 90 degrees. For convenience of illustration, the upper end and the lower end of the ring  27  are 0° and 90°, respectively. When the ring  27  is rotated by a user operation, a rotary MR encoder  28  and a rotary potentiometer  29  rotate about the rotation axes via gears followed by the ring  27 . 
   An output of the MR encoder  28  is processed in the displacement detector  24 . The output of the MR encoder  28  is represented by, for example, 90° out-of-phase two-phase sine waves  41  and  42 , as shown in  FIG. 4 . The displacement detector  24  determines the amount of movement and the movement direction from voltage outputs of a series of linear portions of the sine waves  41  and  42  with respect to the angle on the basis of the voltage of each phase and the phase relation. The output of the MR encoder  28  largely changes even with a slight rotation of the ring  27 . The displacement detector  24  therefore can provide high-resolution detection of the amount of rotation. 
   For the convenience of illustration, the MR encoder  28  has a resolution of 0.001°. If the amount of displacement of the MR encoder  28  detected by the displacement detector  24  is indicated by ΔR and the amount of displacement of the ring  27  is indicated by Δθ, the relationship between the values ΔR and Δθ is determined by Eq. 1:
 
Δθ=Δ R×α   Eq. (1)
 
where α denotes a constant.
 
   The value Δθ is set as the output of the displacement detector  24 . 
   An output of the potentiometer  29  is processed in the absolute position detector  25 . For example, when the output of the potentiometer  29  has a linear characteristic  51  shown in  FIG. 5 , if the voltage with respect to an angle of 0° is indicated by V1 and the voltage with respect to an angle of 90° is indicated by V2, the angle of rotation θ of the ring  27  with respect to an output voltage V is determined by Eq. (2):
 
θ=90×( V−V 1)/( V 2 −V 1)  Eq. (2)
 
   When the output of the potentiometer  29  has a non-linear characteristic  61 , as shown in  FIG. 6 , the non-linear output  61  is corrected using a linear correction function g(x) and the angle of rotation θ is determined by Eq. (3):
 
θ=90×( g ( V )− g ( V 1))/( g ( V 2)− g ( V 1))  Eq. (3)
 
   The function g(x) is configurable using a function expressed as a polynomial or a table including the correspondence between the output and the angle of rotation. The determined angle of rotation θ is set as the output of the absolute position detector  25 . 
   The resolution with which the absolute position detector  25  detects the absolute position using the output of the potentiometer  29  is substantially not high because the amount of voltage change due to the noise, etc., of the potentiometer  29  directly affects the position accuracy. For the convenience of illustration, the resolution of the potentiometer  29  is 0.5°. 
   The lens driving operation performed with this configuration will be described hereinbelow. 
     FIG. 9  is a PAD diagram showing a flow of lens driving operation steps that are executed by microcomputers in the user interface control block  6  and the camera control block  5  shown in  FIG. 1 . 
   In  FIG. 9 , first, it is determined whether or not initialization is completed (step S 1 ). If it is determined in step S 1  that initialization is not completed, the ring position is set as the absolute position detector output (step S 2 ), and initialization is completed (step S 3 ). Specifically, the ring position generator  26  has a storage region  32  when the ring position generator  26  generates a value corresponding to the angle of rotation of the ring  27 . Thus, the storage region  32  stores the value corresponding to the angle of rotation of the ring  27 . If the storage region  32  is not defined, for example, when the imaging device is turned on, an absolute value initialization unit  30  in the ring position generator  26  initializes the storage region  32  using the angle of rotation detected by the absolute position detector  25 . 
   If it is determined in step S 1  that initialization is completed, the displacement detector output is added to the ring position (step S 4 ). Specifically, for example, the angle of rotation detected by the absolute position detector  25  in step S 2  is 45°. When initialization is completed in step S 3 , the amount of rotation of the ring  27  that is offset from 45° is calculated using the output of the displacement detector  24 . For example, when the ring  27  is rotated by 0.5°, the displacement detector  24  outputs the amount of rotation, i.e., 0.5°, and a relative value addition unit  31  in the ring position generator  26  adds 0.5° to 45° stored in the storage region  32 , and generates a value of 45.5. In this way, the relative value addition unit  31  in the ring position generator  26  adds an output of the displacement detector  24  to a value stored in the storage region  32  to generate a ring position. 
   The lens control unit  19  outputs a control value based on the generated ring position (step S 5 ), and the lens driving unit  20  moves a lens  34  to the corresponding position via a lens drive motor  33  (step S 6 ). For the convenience of illustration, if one movable end of the lens  34  is indicated by a value of 0 and the other movable end is indicated by a value of 100, a lens position L (0≦L≦100) with respect to a ring position θ (0≦θ≦90°) is given by Eq. (4):
 
 L=θ _to —   L (θ)=(100−0)×θ/(90−0)  Eq. (4)
 
   For example, the lens  34  may be a zoom lens with the “wide” end having a value of 0 and the “tele” end having a value of 100 or with the “tele” end having a value of 0 and the “wide” end having a value of 100. The lens  34  may be a focus lens with the “far” end having a value of 0 and the “near” end having a value of 100 or with the “near” end having a value of 0 and the “far” end having a value of 100. A selector allows the relation between the rotation direction of the ring  27  and the movement direction of the lens  34  to change over, as desired by the user. 
   It is determined further whether or not the amount of displacement is discontinuous and a value jump occurs (step S 7 ). Specifically, the ring position generator  26  monitors outputs of the displacement detector  24 , and determines that a value jump occurs when the amount of displacement becomes discontinuous. 
   If it is determined in step S 7  that the amount of displacement is discontinuous, the initialization processing is performed again (step S 8 ). Specifically, the ring position generator  26  sets the angle of rotation detected by the absolute position detector  25  in step S 2  as the initial position, and initialization is completed in step S 3 . 
   If it is determined in step S 7  that the amount of displacement is not discontinuous, the lens driving processing of step S 6  is performed continuously (step S 9 ). 
   The ring rotation position generator according to the present embodiment also may be used for an iris drive control operation, described below, in addition to the lens drive control operation described above. 
     FIG. 3  shows the iris driving operation of the ring rotation position generator. 
   The system shown in  FIG. 3  is the same as that shown in  FIG. 2 , except for an iris control unit  21  and an iris driving unit  22  in place of the lens control unit  19  and the lens driving unit  20 , and an iris drive motor  37  and an iris  38  in place of the lens drive motor  33  and the lens  34 . 
   The iris driving operation of the ring rotation position generator shown in  FIG. 3  will be described by referring again to the  FIG. 9 . 
   In  FIG. 9 , first, it is determined whether or not initialization is completed (step S 1 ). If it is determined in step S 1  that initialization is not completed, the ring position is set as the absolute position detector output (step S 2 ), and initialization is completed (step S 3 ). Specifically, the ring position generator  26  includes the storage region  32  when the ring position generator  26  generates a value corresponding to the angle of rotation of the ring  27 . Thus, the storage region  32  stores the value corresponding to the angle of rotation of the ring  27 . If the storage region  32  is not defined, for example, when the imaging device is turned on, the absolute value initialization unit  30  in the ring position generator  26  initializes the storage region  32  using the angle of rotation detected by the absolute position detector  25 . 
   If it is determined in step S 1  that initialization is completed, the displacement detector output is added to the ring position (step S 4 ). Specifically, for example, the angle of rotation detected by the absolute position detector  25  in step S 2  is 45°. When initialization is completed in step S 3 , the amount of rotation of the ring  27  that is offset from 45° is calculated using the output of the displacement detector  24 . For example, when the ring  27  is rotated by 0.5°, the displacement detector  24  outputs the mount of rotation, i.e., 0.5°, and the relative value addition unit  31  in the ring position generator  26  adds 0.5° to 45° stored in the storage region  32 , and generates a value of 45.5. In this way, the relative value addition unit  31  in the ring position generator  26  adds an output of the displacement detector  24  to a value stored in the storage region  32  to generate a ring position. 
   The iris control unit  21  outputs a control value based on the generated ring position (step S 5 ), and the iris driving unit  22  moves the iris  38  to the corresponding opening/closing position via the iris drive motor  37  (step S 6 ). For convenience of the illustration, if the opening/closing position of one movable end of the iris  38  is indicated by a value of 0, and the opening/closing position of the other movable end is indicated by a value of 100, an iris opening/closing position L (0≦L≦100) with respect to a ring position θ (0≦θ≦90°) is given by Eq. (4) noted above. The calculation and the control methods in this case are the same as those described with reference to  FIG. 2 , except that the object to be controlled changes from the lens  34  to the iris  38 . 
   It is further determined whether or not the amount of displacement is discontinuous and a value jump occurs (step S 7 ). Specifically, the ring position generator  26  monitors outputs of the displacement detector  24 , and determines that a value jump occurs when the amount of displacement becomes discontinuous. 
   If it is determined in step S 7  that the amount of displacement is discontinuous, the initialization processing is performed again (step S 8 ). Specifically, the ring position generator  26  sets the angle of rotation detected by the absolute position detector  25  in step S 2  as the initial position, and initialization is completed in step S 3 . 
   If it is determined in step S 7  that the amount of displacement is not discontinuous, the iris driving processing of step S 6  is performed continuously (step S 9 ). 
     FIGS. 10A and 10B  are illustrations of the MR encoder  28  and the potentiometer  29 , respectively. 
   When an object to be detected that is magnetized, moves with respect to a MR detector  101 , the MR encoder  28  detects a change in position based on a change in resistance of the MR detector  101  due to the magnetoresistance effect. 
   When an object to be detected having a fixed movable end  104  moves with respect to a resistor  103  that is pulled up by a voltage Vcc, the potentiometer  29  detects a change in position based on a change of a divided voltage as the resistance of the resistor  103  changes. 
   The MR encoder  28  and the potentiometer  29  are merely examples, and other sensors may be used. 
   As a modification, instead of the MR encoder  28 , for example, a pulse encoder that provides the two-phase pulse outputs  71  and  72  shown in  FIG. 7  may be used as a displacement sensor. 
   Instead of the potentiometer  29 , an absolute encoder that provides a plurality of outputs  81 ,  82 ,  83 , and  84  having different detection accuracies, as shown in  FIG. 8 , may be used as an absolute position sensor.  FIG. 8 , shows an absolute encoder that provides 4-bit output. 
   While the control mechanism for the lens driving system and the iris driving system has been described, this control mechanism also may be applied to other objects to be controlled that are driven by a motor. 
   This control mechanism also may be applied not only to an operating unit driven rotatably but also to a wide variety of operating units driven linearly by linear stepping motors. In this case, instead of a rotary encoder, a linear encoder may be used with the intervention of a mechanism for converting a rotation of the ring into a linear movement. 
   Other than the structure with the intervention of gears or link mechanisms, for example, it also can be conceived that resistors are disposed along the curve of the ring and the potentiometer function is embedded in the resistors. The objects to be driven may include optical components other than lenses. 
   It should be understood by those skilled in the art that various modifications, combinations, subcombinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.