Abstract:
An endoscopic apparatus comprises: a movable lens that is movably built in an objective optical system arranged at an tip of an insert part of an endoscope; a piezoelectric-element drive mechanism that causes the movable lens to move forward and backward in an optical axis direction due to driving of a piezoelectric element; a control circuit that provides a drive pulse to the piezoelectric element; and a storage section that stores respective ones of drive-pulse count data for moving the movable lens forward and backward equally in amount, wherein the control circuit performs control of providing a drive-pulse count, different in between forward and backward movement, to the piezoelectric element of the piezoelectric-element drive mechanism so as to move the movable lens forward and backward equally in amount depending upon drive-pulse count data read out of the storage section.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to endoscopic apparatuses and more particularly to piezoelectric-element drive mechanism control to drive the movable lens, arranged in an objective optical system, through expansion and contraction of a piezoelectric element for the purpose of auto-focusing and zooming functions. 
         [0003]    2. Description of the Related Art 
         [0004]    For example, the electronic endoscopic apparatus has an electronic endoscope (scope), a processor unit, a light source, a monitor and so on. In the tip of the electronic endoscope, there are arranged an objective optical system (lenses), a CCD (charge coupled device) serving as a solid-state imager, and so on. Depending upon the illumination of from the light source, the CCD takes an image of a subject-of-observation. The image signal is video-processed in the processor unit, to thereby display a video image of the subject-of-observation on the monitor. The objective optical system is built therein with a movable lens for the purpose of zooming and focusing functions. It is a recent practice to use a piezoelectric-element drive mechanism in order to drive such a movable lens. 
         [0005]    In the piezoelectric-element drive mechanism, the drive shaft coupled to a piezoelectric element is frictionally engaged with a moving body so that the moving body can be moved slightly by delivering the expansion/contraction of the piezoelectric element to the moving body through the drive shaft (JP-B-4-52070 and Japanese Patent No. 3,635,525). By controlling the waveform, etc. of a drive voltage to be supplied to the piezoelectric element, the moving body can be moved in forward and backward directions. Such a piezoelectric-element drive mechanism is advantageously arranged in the tip of an endoscope having a reduced diameter because of its easiness to reduce the size. 
         [0006]    However, in the movable lens movement control based on the conventional piezoelectric-element drive mechanism, when drive signals are provided in pulse count to drive the lens forward and backward equally in amount in the optical-axis direction, there encounters a difference of movement amount in between forward and backward movements thus resulting in a problem of the lowed accuracy of movement amount control. Namely, a difference occurs in moving amount in between the forward and backward due to the structure of the piezoelectric-element drive mechanism, such as a piezoelectric element as a drive source, a drive shaft coupled to the drive shaft, a frictional engagement state of between the drive shaft and the moving body. The difference depends also upon the characteristic unique to the piezoelectric-element drive mechanism, i.e. individual difference. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention has been made in view of the foregoing problem, and it is an object thereof to provide an endoscopic apparatus that the forward and backward moving amount of the movable lens can be placed under control with accuracy due to a piezoelectric-element drive mechanism even where there is a difference in the movement amount of the movable lens in between the forward and backward or such a difference is based on an individual difference. 
         [0008]    In order to achieve the foregoing object, the invention is an endoscopic apparatus comprising: a movable lens that is movably built in an objective optical system arranged at an tip of an insert part of an endoscope; 
         [0009]    a piezoelectric-element drive mechanism (a piezoelectric-element drive actuator) that causes the movable lens to move forward and backward in an optical axis direction due to driving of a piezoelectric element; a control circuit that provides a drive pulse to the piezoelectric element; and a storage section that stores respective ones of drive-pulse count data for moving the movable lens forward and backward equally in amount, wherein the control circuit performs control of providing a drive-pulse count, different in between forward and backward movement, to the piezoelectric element of the piezoelectric-element drive mechanism so as to move the movable lens forward and backward equally in amount depending upon drive-pulse count data read out of the storage section. 
         [0010]    According to the above structure, the storage section in the emdoscopic apparatus is stored with drive-pulse count data for forward and backward movements each per unit amount (distance) [or predetermined amount (distance)], for example. When operating the piezoelectric-element drive mechanism, the drive-pulse count data is read out, based on which control is effected to move the movable lens a predetermined amount based on the pulse count different in between forward and backward movements. For example, to the piezoelectric element is supplied pulses in the number of 1200×9=(10800) as drive pulse count for a forward movement over a distance of 0.5 mm, and of 1200×7=(8400) as drive pulse count for a backward movement over the same distance. This makes it possible to move the movable lens forward and backward the same distance of 0.5 mm. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a diagram showing a main configuration of an electronic endoscopic apparatus according to an embodiment of the present invention; 
           [0012]      FIG. 2  is a sectional view showing an interior structure of an endoscopic tip portion in the embodiment; 
           [0013]      FIG. 3  is a view showing the overall exterior arrangement of the electronic endoscopic apparatus; 
           [0014]      FIGS. 4A to 4D  are figures showing drive-pulse examples (I, II) of forward and backward movements formed in the example. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]      FIG. 1  shows a main arrangement of an electronic endoscopic apparatus according to an embodiment,  FIG. 2  an interior construction of an endoscopic tip region, and  FIG. 3  an exterior appearance of the electronic endoscopic apparatus. In  FIG. 3 , the electronic endoscopic apparatus includes an electronic endoscope (scope)  11  made up by an insertion part  11 A as a portion to be inserted into a subject-of-observation and having an objective optical system at the tip and a solid-state imager, such as a CCD, an operation part  11 B having an angular-operation knob, various switches, etc., a cable part  11 C having a light-source connector  11 D and an electric connector  11 E, a light source  12  to which the electronic endoscope  11  is connected through the light-source connector  11 D, a processor unit  14  to which the electronic endoscope  11  is connected through the electric connector  11 E, and a not-shown monitor. 
         [0016]    In  FIG. 2 , the insertion part  11 A, at its tip, is arranged therein with an objective optical system that includes a fixed lens  16   a  including a viewing window, first and second movable lenses  17   a ,  17   b  for power change arranged as a variable-focal lens, a fixed lens  16   b  and a third movable lens  17   c  for focal adjustment, in the order closer to the front. In rear of the third movable lens  17   c , there are arranged a prism  19  and, through a cover glass  20 , a CCD  21  serving as a solid-state imager. The signal, taken at the CCD  21 , is delivered to the processor unit  14  by way of a circuit board  22  and a signal line  23 . 
         [0017]    The first movable lens  17   a  is held by a support (holder frame)  25  having an engagement hole  25 A while the second movable lens  17   b  is by a support  26  having an engagement hole  26 A. In the state the engagement holes  25 A,  26 A fit over an outer periphery of a cylindrical camshaft  27 , the lenses  17   a ,  17   b  are arranged on the camshaft  27 . A cam pin  29  is arranged projecting for the engagement hole  25 A while a cam pin  30  is for the engagement hole  26 A. Meanwhile, in the camshaft  27 , cam grooves  31 ,  32  are formed different in inclination direction with respect to the axis thereof so that the cam pin  29  engages in the cam groove  31  while the cam pin  30  in the cam groove  32 . 
         [0018]    The camshaft  27  is coupled with a linear-transmission member  34  formed by a multi-coiled spring or the like. The linear-transmission member  34  has the other end connected to a motor provided in the operation part  11 B. Accordingly, by rotating the camshaft  27  due to motor driving through the linear-transmission member  34 , the first and second movable lenses  17   a ,  17   b  are moved back and forth in the optical-axis direction through the engagement of the camshaft  31 ,  32  and the cam pin  29 ,  30 . This causes a change of optical power. Namely, the first and second movable lenses  17   a ,  17   b  constitute a variable-focal optical system, to cause a change of optical power (made variable in observation distance, observation depth, focal length, etc.) while being moved back and forth. 
         [0019]    Meanwhile, a small-sized piezoelectric-element drive mechanism (piezoelectric actuator) in order to drive the focusing, or third, movable lens  17   c . The piezoelectric-element drive mechanism is arranged with a support (moving body)  36  serving as a holder frame sustaining the third movable lens  17   c  and formed with (cylindrical member having) an engagement hole  36 A in the upper portion thereof, a cylindrical drive shaft (body)  37  frictionally engaged in the engagement hole  36 A of the support  36 , and a piezoelectric element  38  coupled (fixed) to the drive shaft  37 . The piezoelectric element  38  is supplied with a drive pulse through the drive line  39 . With the piezoelectric-element drive mechanism, by longitudinally moving the drive shaft  37  due to expansion/contraction driving of the piezoelectric element  38 , the third movable lens  17   c  can be moved forward or backward. 
         [0020]    Meanwhile, stoppers  41   a ,  41   b  are provided to bring the focusing, or third, movable lens  17   c  into stop at a start end (start point) and a termination end (termination point). In the embodiment, the start or termination point where the drive shaft  37  is restricted by the stopper  41   a ,  41   b  is detected by not-shown detecting means, such as a optical or magnetic sensor, e.g. photo-interrupter. This makes it possible to control the moving amount of the third movable lens  17   c , from the start or termination point. 
         [0021]    In  FIG. 1 , in addition to the CCD  21  arranged at the tip of the insertion part  11 A, the endoscope  11  is arranged with a piezoelectric-element drive circuit  41  that provides a drive pulse for forward or backward movement to the piezoelectric element  38 , and a memory (e.g. EEPROM) that stores drive-pulse count data (drive pulse count per unit amount or predetermined amount) for moving the third movable lens  17   c  forward and backward equally in amount. Namely, the drive pulse count per unit amount (unit distance) can be determined by operating [drive pulse count required for movement over the overall travel]÷[overall travel of the third movable lens  17   c  from its start end to termination end]. 
         [0022]    Meanwhile, the processor unit  14  is provided with a focus-control circuit  44  that places the piezoelectric-element drive circuit  41  under auto-focus control, and an image-processing circuit  45  that performs an image processing depending upon the output signal from the CCD  21  and outputting a signal representative of an image clarity for use in auto-focusing to the focus-control circuit  44 . 
         [0023]    The embodiment is structured as described so far. When the electronic endoscope  11  at its insertion part  11 A is inserted in a subject-of-observation, the subject-of-observation is imaged by the CCD  21  through the objective optical system. Based upon the output signal from the CCD  21 , a video image is formed in the image-processing circuit  45 . Due to the video signal, a video image of the subject-of-observation is displayed on a monitor. Meanwhile, the image-processing circuit  45  extracts the signal representative of an image clarity and supplies the relevant signal to the focus-control circuit  44 . From the signal representative of a clarity, the focus-control circuit  44  forms a control signal for focal adjustment, i.e. a signal regulating the forward or backward movement (distance) of the focusing, or third, movable lens  17   c  (i.e. moving direction-and-amount signal). The control signal is supplied to the piezoelectric-element drive circuit  41 . 
         [0024]    At this time, in the focus control circuit  44 , there is read, out of the memory  42 , the data of drive pulse count per unit or predetermined amount for forward or backward movement (drive pulse count for equal amount of movement). Depending upon the drive-pulse count data, a control signal of forward/backward-movement amount is supplied to the piezoelectric-element drive circuit  41 . Incidentally, such drive-pulse count data may be inputted from the memory  42  directly to the piezoelectric-element drive circuit  41 . The piezoelectric-element drive circuit  41  forms a drive pulse corresponding to the control signal of forward/backward-movement amount. The drive pulse is given as shown in  FIGS. 4A and 4B . 
         [0025]      FIGS. 4A and 4B  show a drive pulse in a control example I. For a signal of forward movement amount of a distance of 5 mm, nine blocks are formed each including 1200 pulses (p) of signals at a frequency of 370 kHz (at a desired frequency), to thereby output drive pulses in the number of 1200×9=10800. For a signal of backward movement amount of the same distance 5 mm, seven blocks are formed each including 1200 pulses (p) of signals at a frequency of 370 kHz, to thereby output drive pulses in the number of 1200×7=8400. With such drive pulses, movement can be accurately effected over the same distance though movement rate is different due to the different number of drive pulses in between forward and backward directions. 
         [0026]      FIGS. 4C and 4D  show a drive pulse in a control example II wherein there is a difference in the number of one block from the control example I. This control example forms, as a signal of forward movement amount of a distance 5 mm, eleven blocks each including 1000 pulses (p) of signals at a frequency of 370 kHz, to output drive pulses in the number of 1000×11=11000. For a signal of backward movement amount of the same distance, nine blocks are formed each including 1000 pulses (p) of signals at a frequency of 370 kHz, to output drive pulses in the number of 1000×9=9000. 
         [0027]    In this manner, in the piezoelectric-element drive mechanism of the electronic endoscope  11  of this embodiment, movements can be accurately effected forward and backward over the equal distance by means of the number of drive pulses. However, in the piezoelectric-element drive mechanism arranged in other electronic endoscope, drive pulses are formed and outputted in the number for forward and backward movements depending upon the drive-pulse count data for other electronic endoscope stored in the memory. Due to this, the movable lens for auto-focusing can be placed under movement control with accuracy even where there is an individual difference in the piezoelectric-element drive mechanism. 
         [0028]    The embodiment explained the case of placing the focusing, or third, movable lens  17   c  under movement control. Besides, the piezoelectric-element drive mechanism in the invention may be arranged to drive first and second movable lenses  17   a ,  17   b  for variable power provided in the insertion part  11 A. 
         [0029]    According to the endoscopic apparatus of the invention, there is an effect that can place the forward and backward moving amount of the movable lens with accuracy due to a piezoelectric-element drive mechanism even where there is a difference in the movement amount of the movable lens in between forward and backward movements or such a difference is based on an individual difference. 
         [0030]    The entire disclosure of each and every foreign patent application from which the benefit of foreign priority has been claimed in the present application is incorporated herein by reference, as if fully set forth.