Abstract:
In a drive mechanism which displaces a movable lens to be displaced, a shape memory element which is displaced due to heating. A displaceable range of a movable lens is restricted between a first position and a second position. With the shape memory element in a heated state upon applying a predetermined amount of heat to the shape memory element, the movable lens is displaced to the first position, and when the shape memory element is not heated, the movable lens is displaced to the second position. During a normal observation, a time for which the movable lens is displaced to the second position is longer than a time for which the movable lens is displaced to the first position.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2006-196441 filed on Jul. 19, 2006; the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an endoscope. 
         [0004]    2. Description of the Related Art 
         [0005]    In an endoscope which includes an image pick-up unit at a front end portion, and which is provided with a flexible tube having a bent portion, generally, for observing an endoscope image in an optimum state, it is necessary to adjust a focal point by moving a focusing lens and an image pick-up element. 
         [0006]    As an endoscope apparatus for solving this problem, an image pick-up apparatus for endoscope described in Japanese Patent Application Laid-open Publication No. 2004-129950 has been proposed. In the image pick-up apparatus for endoscope according to this proposal, at a front end portion of the endoscope, a shape memory alloy is let to be a variable means of relative positions of an optical element and an image pick-up element. 
         [0007]    However, when a shape memory element is used in an actuator which drives a lens as in a conventional technology, generally, when the shape memory alloy is held for a long time with a load exerted thereon, in a heated state, a lattice defect is developed inside, and a function as an actuator is declined. 
         [0008]    Since this developing becomes remarkable when a shape memory treatment having a substantial displacement due to heating is carried out, there is a problem that it has been difficult to achieve a substantial displacement for using stably for a long period of time. 
         [0009]    Moreover, for restricting a movable range of a lens accurately, it is desirable to restrain mechanically the movable range of the lens. However, in such structure in which a movement margin is taken into consideration, a substantial stress is exerted on a shape memory alloy at the time of heating. Therefore, the abovementioned problem is particularly remarkable. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention is made in view of these points, and an object of the present invention is to provide an endoscope in which a stable range operation is possible over a long period of time while achieving a comparatively substantial displacement of the lens, by optimizing a structure with respect to a state frequency of an actuator in an actual working condition. 
         [0011]    To solve the abovementioned problems, and to achieve the object, according to the present invention, it is possible to provide an endoscope which includes 
         [0012]    a front end portion, at which an image pick-up unit which has an optical system which changes an image-formation range by focusing by displacing at least a part of a lens group, is disposed. 
         [0013]    In a driving mechanism which displaces the range group to be displaced, a shape memory element which is displaced by heating is let to be a driving force, and a displaceable range of the lens group is restricted between a first position and a second position. 
         [0014]    With the shape memory element in a heated state by imparting a predetermined amount of heat to the shape memory element, the lens group to be displaced is displaced to the first position, and when the shape memory element is not heated, the lens group to be displaced is displaced to the second position. 
         [0015]    During a normal observation, a time for which the position of the lens group to be displaced is displaced to the second position is longer than a time for which the position of the lens group to be displaced is displaced to the first position. 
         [0016]    Moreover, according to a preferable aspect of the present invention, it is desirable that an image-formation range of focusing when a position of the lens group to be displaced is the second position is wider than an image-formation range of focusing when the position of the lens group to be displaced is the first position. 
         [0017]    Furthermore, according to a preferable aspect of the present invention, it is desirable that the position of the lens group to be displaced is restricted by constraining mechanically between the first position and the second position. 
         [0018]    According to a preferable aspect of the present invention, it is desirable that a bias spring which exerts a force on the lens group to be displaced, toward the second position is fitted into the drive mechanism which displaces the lens group to be displaced. 
         [0019]    According to a preferable aspect of the present invention, it is desirable that the endoscope includes a bending tube which can be bent, and which is connected to the front end portion, and the shape memory element is interpolated into a tube member which can be bent, and the shape memory element and the tube member are extended to the bending portion, and the tube member and the shape memory element are coupled at an end portion of the tube member, toward the bending tube, and the other end of the tube member is fixed to a predetermined part of the front end portion, and the other end of the shape memory element is fixed to the lens group to be displaced. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a diagram showing a schematic structure of an entire endoscope apparatus according to an embodiment of the present invention; 
           [0021]      FIG. 2  is a diagram showing a front-view of the endoscope apparatus according to the embodiment; 
           [0022]      FIG. 3  is a diagram showing a cross-sectional view of the endoscope apparatus according to the embodiment; and 
           [0023]      FIG. 4  is a diagram showing a cross-sectional view of the endoscope apparatus according to the embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    An embodiment of an endoscope according to the present invention will be described below by referring to the accompanying diagrams. However, the present invention is not restricted to this embodiment. 
         [0025]      FIG. 1  shows a schematic structure of an endoscope  1 . As shown in  FIG. 1 , the endoscope  1  includes an operating section  2  which performs a bending operation, and a control of a pipe conduit system, an inserting section  3  which is inserted into a body cavity of an object to be examined, and a rear-end side of which is connected to the operating section  2 . 
         [0026]    The inserting section  3  includes a flexible tube  4  having, a bending section  5  which can be bend and which is provided at a front end side of the flexible tube  4 , and a front end section  6  which is hard and which is provided at a front end side of the bending section  5 . An image pick-up element unit  32  which picks up an image of a part to be observed inside the body cavity, and which will be described later is built-in in the front end section  6 . 
         [0027]      FIG. 2  shows a front view of a front end portion to be inserted of the endoscope in  FIG. 1 . As shown in  FIG. 2 , in a front-end surface  21  of the front end section  6 , an observation window  22 , an illumination window  23 , an endoscopic instrument inserting channel aperture section  24 , a gas-water supply nozzle  25 , and a front water supply channel aperture section  26  are disposed. The observation window  22  functions as a lens which forms the image pick-up unit  32  which will be described later. The illumination window  23  functions as a lens which forms each of light guide units, the endoscopic instrument inserting channel aperture section  24  is an aperture section of a channel for inserting an endoscopic instrument. The gas-water supply nozzle  25  is an aperture section of a gas-water supply channel  25   a  which is for washing the observation window  22 . The front water supply channel aperture section  26  is an aperture section of front water supply channel for washing a liquid such as mucus and blood of a patient subjected to examination. 
         [0028]      FIG. 3  and  FIG. 4  show a cross-sectional view of a front end section along a line A-A in  FIG. 2 . As shown in  FIG. 4 , the front end section  6  is provided with a hard front end section body which is not described. Built-in components such as the image pick-up unit  32  corresponding to the observation window  22  and a light guide unit  33  corresponding to the illumination window  23  are disposed in the front end section main body. Moreover, the front end section main body is covered by a front end cover  31 . 
         [0029]    The image pick-up unit  32  includes the observation window  22 , an objective optical system  32   a,  an image pick-up element  32   c,  and a circuit substrate  32   d,  and is held by a lens barrel  7 . The objective optical system  32   a  is provided at a rear end side of the observation window  22 , and is formed by a plurality of lens groups. The image pick-up element  32   c  which is a solid image pick-up element such as a CCD (charge coupled device) is disposed at a rear end side of the objective optical system  32   a.  The circuit substrate  32  to which, the image pick-up element  32   c  is connected carries out various processes such as signal amplification. 
         [0030]    A signal cable  32   e  which is extended from the circuit substrate  32   d  is inserted through the inserting section  3 , in the image pick-up unit  32 . The objective optical system  32   a  includes a movable lens  34 . The movable lens  34  is supported by a movable lens frame  35 . 
         [0031]    One end of a shape memory element  41  which is in the form of a wire is fixed to the movable lens frame  35 , and the shape memory element  41  is accommodated in a tube  51  which can be bent, and which is fixed to a tube fixing member  36  of the lens barrel  7 . 
         [0032]    The structure is such that the tube  51  which accommodates the shape memory element  41  is inserted through the bending section  5  which is formed to be tapered shaped such that a side from inside of the front end section  6  up to a side of the front end section  6  is thick, inside the flexible tube  4 , one end of the tube  51  is clamped to one end of the shape memory element  41  by a caulking for fixing  52 , and one end of the shape memory element  41  is fixed. 
         [0033]    The shape memory element  41  has a property of getting displaced, or getting contracted in particular when heated up to a transformation temperature, and getting slackened when cooled down to the transformation temperature. A shape memory element in the form of a wire which expands and contracts according to the temperature is to be used. One end of a coiled spring for bias  61  is fixed to the tube fixing member  36 . The other end of the coiled spring for bias  61  is fixed to the movable lens frame  35 . 
         [0034]    The movable lens frame  35  is in a state of being pushed by a stress of the coiled spring for bias  61 . When the shape memory element  41  is not deformed by the stress of the coiled spring for bias  61 , the movable lens  34  is in a state of being held at a fixed position. When the movable lens  34  is in the state of the position held by the stress of the coiled spring for bias  61 , without being affected by a force from the shape memory element  41 , the objective optical system  32   a  is set such that an image-formation range formed by the objective optical system  32   a  becomes wide. 
         [0035]    Since the position of the movable lens  34  is held by the stress of the coiled spring for bias  61 , the movable lens  34  is held at a fixed position at each movement, without being affected by the shape memory element  41 . Therefore, the image-formation range formed by the objective optical system  32   a  becomes constant. Moreover, since the shape memory element  41  has a structure extended up to the inside of the bending section  4 , it is possible to achieve a substantial amount of displacement of the movable lens  34 . 
         [0036]      FIG. 4  shows a state when the movable lens  34  is driven by deforming the shape memory element  41  from a state shown in  FIG. 3 . By a power supply which is not shown in the diagram, an electric voltage is applied to both ends of the shape memory element  41 , and the shape memory element  41  is heated up to a temperature beyond the transformation temperature. By heating the shape memory element  41  beyond the transformation temperature, the shape memory element  41  is contracted. 
         [0037]    Since a contraction generating force is larger than the stress of the coiled spring for bias  61 , when the shape memory element becomes shorter than a distance between one end fixed to the one end of the tube  51 , and a connecting point with the movable lens frame  35 , the movable lens  34  moves. An amount of contraction of the shape memory element  41  is determined by a length of the shape memory element  41 , and according to the amount of contraction of the shape memory element  41 , the movable lens  34  assumes a state of being held at a fixed position. 
         [0038]    Moreover, a member which stops the movable lens  34  upon being struck when the shape memory element  41  is contracted may be disposed in a movable area of the movable lens  34  (an area in which the movable lens  34  moves), and the movable lens  34  may be held at a fixed position by constraining mechanically. It is particularly preferable, since in this case, it is possible to let the position of the movable lens  34  fixed at the time of heating irrespective of unevenness in the amount of contraction of the shape memory alloy  41 , and bending of the endoscope. 
         [0039]    When the movable lens  34  is in the state of being held by a contraction force of the shape memory alloy  41 , the image-formation range formed by the objective optical system  32   a  is narrow as compared to the image-formation range in  FIG. 3 , and the objective optical system  32   a  is set such that an observation of an image which is enlarged further, is possible. The state in  FIG. 3  corresponds to a second position. The state in  FIG. 4  corresponds to a first position. 
         [0040]    As a usage of an endoscope which is capable of changing the image-formation range, an object to be examined is observed in a state of wide field of view, and when a part which is suspected of having a pathologic change is found, an enlarged observation of the narrow field of view is assumed to be carried out temporarily. 
         [0041]    Moreover, since a state in which the observation of the wide field of view is possible at the time of inserting or taking out the endoscope from an object to be examined is desirable, in a normal usage, it is common that the time of carrying out the observation of the wide field of view is quite longer than the time of carrying out the enlarged observation of the narrow field of view. 
         [0042]    Therefore, since the image-formation range of an image formed by the objective optical system  32   a  when the shape memory element  41  is not heated is wider than the image-formation range of an image formed by the objective optical system  32   a  when the shape memory element  41  is in a heated state, in the usage of the endoscope, a frequency of the state in which the shape memory element  41  is not heated becomes very high as compared to a frequency of the heated state of the shape memory element  41 . Therefore, since a life of the shape memory element  41  becomes long by shortening of a time for which the stress is exerted on the shape memory element  41  upon being heated, it is possible to have a stable operation over a long period of time. 
         [0043]    In this manner, the endoscope according to the present invention is useful as an endoscope which displaces the lens. 
         [0044]    According to the present invention, an effect is shown that by optimizing a structure with respect to for a frequency of a state of an actuator in an actual state of use, it is possible to provide an endoscope in which a stable range operation is possible over a long period of time while obtaining a comparatively substantial displacement of the lens.