Patent Publication Number: US-2011054252-A1

Title: Endoscope having optical fibers

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an endoscope having optical fibers. More particularly, the present invention relates to an endoscope having optical fibers in which an elongated tube can have a reduced diameter, images of high image quality can be produced, and a head assembly of the elongated tube can be protected effectively. 
     2. Description Related to the Prior Art 
     An endoscope is an important medical instrument used in the field of the clinical medicine. Examples of the endoscope include primitive models such as a fiberscope or stomach camera, an electronic endoscope containing a CCD, and a capsule endoscope which is orally swallowed by a patient to retrieve an image. 
     In the field of endoscopic examination, extreme thinning of a tube for a reduced diameter to produce an ultra thin tube is desired very seriously for an elongated tube of the endoscope. Various ideas for the extreme thinning for a reduced diameter have been suggested for the purpose of imaging of various body parts in a narrow lumen, such as a pancreatic duct, bile duct, breast duct, terminal bronchioles, and the like. 
     The fiberscope is structurally suitable for the extreme thinning for a reduced diameter, because the image can be retrieved only by having a fiber optic image guide and an illuminating light guide. The fiber optic image guide transmits image light of the image of a body part or object of interest. The illuminating light guide applies light to the body part. However, cladding of an optical fiber bundle constituting the fiber optic image guide does not contribute to the transmission of the image light. There occurs a problem in that a pattern of mesh of a loss region due to the cladding appears locally within the image, and the image quality of the image will be low. 
     In view of this problem, U.S. Pat. No. 4,618,884 (corresponding to JP-A 60-053919) discloses the fiberscope. In a first embodiment of the document, a focusing lens system is disposed at a distal tip of the fiber optic image guide for focusing of image light on the distal tip. A piezoelectric actuator vibrates the focusing lens system to remove light component of a pattern of mesh from the image. The piezoelectric actuator vibrates the focusing lens system horizontally and vertically at a predetermined amount according to a pixel pitch of the pixels of the CCD or the optical fibers in the fiber optic image guide. 
     In a second embodiment of U.S. Pat. No. 4,618,884, the CCD is disposed at a distal end of the elongated tube without the fiber optic image guide. The focusing lens system in front of the CCD is vibrated in the same manner as its first embodiment. During the vibration, image light of the image is received on pixels of the CCD in a time division manner. Data are obtained, and written to a frame memory sequentially, to produce one frame of the image. Thus, high definition of the image can be obtained. 
     The focusing lens system has a larger diameter than the fiber optic image guide to ensure high brightness in the image. In U.S. Pat. No. 4,618,884, the focusing lens system is vibrated by the piezoelectric actuator. Even with the focusing lens system having the larger diameter than the fiber optic image guide, a further space is required for positioning a frame or retention mechanism for supporting the focusing lens system in a pivotally movable manner. The elongated tube must have a larger size in the radial direction. It follows that vibrating the focusing lens system with the piezoelectric actuator is inconsistent to the extreme thinning for a reduced diameter. A space required for positioning such a frame or retention mechanism is a serious problem in view of the extreme thinning for a reduced diameter of an order from tens of microns to a number of millimeters. 
     Although high definition of an image can be obtained from the second embodiment of U.S. Pat. No. 4,618,884, the extreme thinning for a reduced diameter is still impossible because the CCD is disposed in front of the elongated tube in addition to the focusing lens system. 
     Therefore, development of an endoscope system has been suggested in which a distal tip of a fiber optic image guide is displaced periodically by a piezoelectric actuator, and an object is imaged for plural times in synchronism with the displacement. One synthesized image is created from plural output images and also in consideration of information of shift amounts. This is for meeting purposes of achieving an ultra thin tube and obtaining images of high quality. 
     However, the suggestion of the development of the endoscope system lacks an air/water supply channel for washing the distal tip of the endoscope with air or water. This is for the reason of an ultra thin tube. For advance of the endoscope in a body, particles may stick on an imaging window of the elongated tube. Those will obstruct the imaging, and cannot be removed acceptably. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing problems, an object of the present invention is to provide an endoscope having optical fibers in which an elongated tube can have a reduced diameter, images of high image quality can be produced, and a head assembly of the elongated tube can be protected effectively. 
     In order to achieve the above and other objects and advantages of this invention, an endoscope for image pickup of an object by receiving image light with an image sensor is provided. An objective lens system is incorporated in an elongated tube, for entry of the image light from the object. A fiber optic image guide includes a plurality of optical fibers being bundled, and has a distal tip, is inserted through the elongated tube, for transmitting the image light focused on the distal tip by the objective lens system in a proximal direction. A piezoelectric actuator is disposed on an outer side of the distal tip, for periodically displacing the distal tip, wherein the image sensor picks up the image light from the fiber optic image guide for plural times in synchronism with displacement, to form one synthesized image. A hood device is mounted on a head assembly of the elongated tube, and shiftable between a closed position for covering a distal end face of the head assembly and an open position for revealing the distal end face. A moving mechanism moves the hood device from the closed position to the open position. 
     The hood device includes a transparent cover portion for covering the distal end face. 
     The cover portion is a resilient cap portion including an end opening. The hood device includes a sleeve, disposed about the distal tip to extend from the resilient cap portion in the proximal direction, moved between the open and closed positions by the moving mechanism, for narrowing the end opening in front of the distal end face when in the closed position, and for widening the end opening by pushing open the resilient cap portion with the distal end face when in the open position. 
     In a preferred embodiment, the cover portion is a cover door, and is moved by the moving mechanism for opening and closing. 
     Furthermore, a calibration chart is secured to a surface of the cover door directed in the proximal direction, for calibrating a shift amount of the fiber optic image guide. 
     The calibration chart includes plural stripe areas extending in a predetermined direction. The distal tip is displaced back and forth in a shift direction extending across the predetermined direction, and picks up an image of the calibration chart to form a test image, the shift amount being calibrated according thereto. 
     The distal tip is displaced by application of a driving voltage to the piezoelectric actuator. The test image is evaluated for calibration so as to determine an adjusted driving voltage for displacement of imaging. 
     The moving mechanism includes a control wire secured to the hood device. A wire moving device is disposed on a side of the proximal direction, for winding or unwinding the control wire. 
     The control wire is embedded partially in the elongated tube. 
     Consequently, an elongated tube can have a reduced diameter, images of high image quality can be produced, and a head assembly of the elongated tube can be protected effectively, because the hood device can operate for protecting the head assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become more apparent from the following detailed description when read in connection with the accompanying drawings, in which: 
         FIG. 1  is a perspective view illustrating an endoscope system; 
         FIG. 2A  is a perspective view illustrating a hood device in an endoscope; 
         FIG. 2B  is a perspective view illustrating the same as  FIG. 2A  but in an open position; 
         FIG. 3  is a front elevation illustrating a head assembly of an endoscope of the endoscope system; 
         FIG. 4  is a vertical section illustrating the head assembly; 
         FIG. 5  is a perspective view illustrating a displacing device; 
         FIG. 6  is a front elevation illustrating a bundle of optical fibers of a fiber optic image guide; 
         FIG. 7  is a block diagram illustrating relevant elements in the endoscope system; 
         FIG. 8  is an explanatory view in a front elevation illustrating a relationship between an image transmitted by the core and a pixel of a CCD; 
         FIG. 9  is an explanatory view illustrating one example of displacement; 
         FIG. 10A  is an explanatory view in a front elevation illustrating a two-dimensional path of a distal tip of one of the cores; 
         FIG. 10B  is an explanatory view in a front elevation illustrating another two-dimensional path of the distal tip; 
         FIG. 11  is a block diagram illustrating relevant circuits for operation upon designating a composite imaging mode; 
         FIG. 12  is a timing chart illustrating a relationship between driving of the CCD, a piezoelectric control signal and an image synthesis signal; 
         FIG. 13  is a flow chart illustrating operation of the endoscope system; 
         FIG. 14  is a perspective view illustrating one preferred embodiment including a calibration chart inside a cover door; 
         FIG. 15  is a front elevation illustrating the cover door; 
         FIG. 16  is an explanatory view in elevations, illustrating the calibration chart; 
         FIG. 17  is an explanatory view illustrating a sequence of displacement of each of the cores in the calibration; 
         FIG. 18  is a graph illustrating a relationship between black density and a shift amount; 
         FIG. 19  is a table illustrating part images transmitted by cores in a reference position and set positions. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) OF THE PRESENT INVENTION 
     In  FIG. 1 , an endoscope system  2  includes an endoscope  5 , a processing apparatus  6  and a light source apparatus  7 . The endoscope  5  is used for imaging of various body parts in narrow lumens, for example, a pancreatic duct, bile duct, breast duct, terminal bronchioles, and the like. The endoscope  5  includes an elongated tube  8  or insertion tube, a handle  9 , a first connector  10 , a second connector  11  or coupler, and a universal cable  12 . The elongated tube  8  is flexible and entered in a patient&#39;s body. The handle  9  is disposed at a proximal end of the elongated tube  8 . The first connector  10  is plugged in the processing apparatus  6 . The second connector  11  is plugged in the light source apparatus  7 . The universal cable  12  extends from the handle  9  to the first connector  10  and the second connector  11 . 
     The elongated tube  8  has a thickness of 50 microns and outer diameter of 0.9 mm, and is formed from flexible material such as a Teflon (trade name), namely tetrafluoroethylene. A recording button  13  or release button among various buttons is disposed on the handle  9  for recording an endoscopic still image of a body part. An instrument opening  14  or forceps opening is formed on a side of the handle  9 , and receives passage of an electrosurgical knife or other instruments for treatment. A head assembly  15  is disposed at a distal end of the elongated tube  8 . An instrument opening  26  or forceps opening (See  FIG. 3 ) is formed in the head assembly  15 . A working channel  46  or forceps channel (See  FIG. 4 ) is formed through the elongated tube  8 , and extends from the instrument opening  14  to the instrument opening  26 . 
     A hood device  16  or protection device or cover is secured to the head assembly  15 . In  FIG. 2 , the hood device  16  includes a sleeve  21  and a resilient cap portion  20  with an easy open end. 
     The resilient cap portion  20  has a decreasing width. An end opening  22  is formed in the resilient cap portion  20 . Its size can be enlarged at the easy open end. Examples of materials of the resilient cap portion  20  are silicone rubber, polyurethane rubber and the like being transparent and colorless, and having biocompatibility and resiliency. A thickness of the sleeve  21  is very small. An inner bore of the sleeve  21  is substantially equal to an outer diameter of the head assembly  15 . Its length is slightly larger than that of the head assembly  15 . The sleeve  21  has a surface extending from that of the resilient cap portion  20  smoothly in a seamless manner, and can be handled together with the resilient cap portion  20 . Examples of materials for the sleeve  21  are fluorocarbon resins and the like having biocompatibility and sufficient rigidity. Note that the material for the sleeve  21  maybe the same as that for the resilient cap portion  20 . 
     Two control wires  23  are secured to a proximal end of the sleeve  21  and positioned at an interval of 180 degrees. An example of the control wires  23  is plural coiled filaments of metal or the like having sufficient rigidity and sufficient flexibility. An intermediate portion of the control wires  23  is embedded in a sealing hole (not shown) formed in the elongated tube  8  of the endoscope  5 . A length of an uncovered portion of the control wires  23  before the embedment is substantially equal to that of the resilient cap portion  20 . A wall of the sealing hole is formed from flexible material, and has a slightly smaller diameter than an outer diameter of the control wires  23 , to avoid entry of water or fluid into the elongated tube  8 . 
     A winder  17  of  FIG. 1  is incorporated in the elongated tube  8  and positioned near to the instrument opening  14 . The control wires  23  are connected with the winder  17 . The winder  17  is a reel mechanism or moving mechanism, and includes a spool and a spiral spring. Proximal ends of the control wires  23  are secured to the spool. The spiral spring biases the spool in a winding direction for the control wires  23 . Also, a lock device is incorporated in the winder  17  for blocking rotation of the spool against the bias of the spiral spring. A winding button  18  is disposed near to the instrument opening  14 , and depressed for disabling the lock device and releasing the spool from the regulation. 
     When the winding button  18  is operated manually, the lock device becomes unfastened. The bias of the spiral spring rotates the spool to wind the control wires  23 . An amount of winding the control wires  23  about the spool is as much as a length of an uncovered portion of the control wires  23  before embedment in the sealing hole, namely the length of the resilient cap portion  20 . In  FIG. 2A , a distal end face  15   a  of the head assembly  15  is covered by the resilient cap portion  20  (closed position). The resilient cap portion  20  becomes peeled off in the proximal direction by enlarging the end opening  22  in  FIG. 2B , to reveal the distal end face  15   a  (open position). When the resilient cap portion  20  is moved in the distal direction from the state of  FIG. 2B , the spool rotates in an unwinding direction against the spiral spring until the lock device starts actuation. The control wires  23  are unwound from the winder  17  for return to the state of  FIG. 2A . Note that an additional device can be installed for advancing and pressing the control wires  23  in the distal direction, to return from the state of  FIG. 2B  to the state of  FIG. 2A  in a semi-automatic manner. 
     For imaging, at first a doctor or operator enters the elongated tube  8  in a body by keeping the hood device  16  in the closed position. Upon reach to an object of interest, the control wires  23  are operated to peel off the resilient cap portion  20  to reveal the distal end face  15   a  of the head assembly  15  for the open position. After the imaging, the elongated tube  8  is moved back while the hood device  16  is in the open position. Thus, a mechanism for moving the hood device  16  from the open position of  FIG. 2B  to the closed position of  FIG. 2A  is unnecessary. Furthermore, it is possible to utilize contact of the hood device  16  with a wall in the patient&#39;s body with friction, and to pull the elongated tube  8  in the proximal direction to move the hood device  16  relatively in the distal direction for return to the closed position. 
     In  FIG. 1 , the processing apparatus  6  is connected with the light source apparatus  7  electrically, and controls operation of the constituents of the endoscope system  2 . A connection cable  45  of  FIG. 4  is inserted through the universal cable  12  and the elongated tube  8 , and supplies the endoscope  5  with power from the processing apparatus  6 . A displacing device  32  of  FIG. 4  is also controlled by the processing apparatus  6 . A fiber optic image guide  31  and a CCD group  58  are contained in the processing apparatus  6 . The CCD group  58  includes CCDs  58 B,  58 G and  58 R or image pickup devices. See  FIG. 7 . Image light of an image of a body part is transmitted by the fiber optic image guide  31 , and received by the CCD group  58 , which generates an image signal. The processing apparatus  6  processes the image signal in image processing, to create an image. A monitor display panel  19  is connected by use of a cable, and displays the image created by the processing apparatus  6 . 
     The head assembly  15  has a wall constituted by a pipe of a stainless steel and has a thickness of 25 microns and an outer diameter of 0.8 mm. In  FIG. 3 , the distal end face  15   a  of the head assembly  15  is illustrated after removing the hood device  16 . An imaging window  25  is disposed in an upper portion of the distal end face  15   a.  The instrument opening  26  is open in the distal end face  15   a  and disposed under the imaging window  25 . A plurality of light guide devices  27  or illumination fiber optics are contained in the head assembly  15 . Ends of the light guide devices  27  are positioned beside the imaging window  25  and the instrument opening  26  without bundling and packed randomly in a tube lumen inside the head assembly  15 . 
     The instrument opening  26  has an outer diameter of 0.34 mm and an inner bore of 0.3 mm, and is an exit opening of the working channel  46 . See  FIG. 4 . An example of material of a wall of the working channel  46  is polyimide. An example of the light guide devices  27  is an optical fiber having a diameter of 50 microns. The light guide devices  27  are inserted through the elongated tube  8  and the universal cable  12 , and have a proximal end located in the second connector  11  or coupler. Light is entered through the proximal end of the light guide devices  27 , is transmitted, and is applied to an object of interest through a distal end of the light guide devices  27  positioned within the distal end face  15   a.    
     For the light guide devices  27 , a plurality of optical fibers without bundling are inserted in the elongated tube  8 . Adhesive agent in a fluid form is supplied into the head assembly  15  for adhesion of the light guide devices  27 . It is possible according to requirements to polish the surface of the distal end of the light guide devices  27  after the adhesion, or to dispose a lighting window in front of the distal end of the light guide devices  27  to cover the same. Also, a coating of phosphor or other materials may be applied to the lighting window to diffuse the light. 
     In  FIG. 4 , the elements are depicted after removal of the hood device  16  in the same manner as  FIG. 3 . An objective lens system  30  is disposed behind the imaging window  25  together with the fiber optic image guide  31  and the displacing device  32 . The displacing device  32  shifts the fiber optic image guide  31 . A lens barrel  33  contains the objective lens system  30 . A distal tip  48  for receiving light is positioned on a plane where image light of an image from an object is in focus. A diameter of the objective lens system  30  is 0.35 mm. An outer diameter of the lens barrel  33  is 0.4 mm. A length of the lens barrel  33  in the axial direction is 3.2 mm. 
     The fiber optic image guide  31  is a bundle of optical fibers with a diameter of 0.2 mm. See  FIG. 5 . The fiber optic image guide  31  extends through the elongated tube  8  and the universal cable  12 , and has a proximal tip contained in the first connector  10 . The fiber optic image guide  31  transmits image light of an object received from the objective lens system  30  through the distal tip  48  toward its proximal tip. 
     In  FIG. 5 , the displacing device  32  includes a support casing  34 , a piezoelectric actuator material  35  and electrodes  36 . The support casing  34  is a barrel or pipe of stainless steel, and has an outer diameter of 0.26 mm and an inner bore of 0.2 mm. The fiber optic image guide  31  is inserted in and fixed on the support casing  34 . The piezoelectric actuator material  35  has a thickness of 15 microns, and is a coating applied to an outer surface of the support casing  34  in a cylindrical form. The electrodes  36  have a thickness of 5 microns, and are a coating about the piezoelectric actuator material  35 . 
     The displacing device  32  is contained in a wall of the head assembly  15 . A lumen  37  is defined between the outside of the displacing device  32  and the inside of the wall of the head assembly  15 , and has a width of approximately 0.1 mm. 
     The displacing device  32  includes a shift mechanism  38  and a stationary section  39 . The shift mechanism  38  is a portion of the displacing device  32  free from the wall of the head assembly  15  without fixing. The fiber optic image guide  31  is displaceable within the lumen  37  with respect to the stationary section  39 . Adhesive agent  40  is used in the stationary section  39 , and attaches the displacing device  32  to the inner wall of the head assembly  15 . An area of the adhesive agent  40  extends from a proximal point of the displacing device  32  where the fiber optic image guide  31  appears to a point near to a distal end of the elongated tube  8 . Lengths of the shift mechanism  38  and the stationary section  39  are respectively 4 mm and 1.9 mm in the axial direction. A length of filling of the adhesive agent  40  in the axial direction is 3.2 mm inclusive of the stationary section  39  and a distal portion of the elongated tube  8 . 
     The electrodes  36  are arranged in the circumferential direction regularly at an angle of 90 degrees. The electrodes  36  are oriented with an inclination of 45 degrees relative to the vertical or horizontal direction of  FIG. 3 . Four grooves  41  are formed to extend in parallel with the axial direction, and define the electrodes  36  of two pairs. The electrodes  36  have a locally large width in the shift mechanism  38 , as an interval between the electrodes  36  is only as great as the width of the grooves  41 . In contrast, recesses  42  are defined with the electrodes  36  in the area of the stationary section  39 , and extend in a symmetrical manner from the grooves  41 . A narrow portion  43  of the electrodes  36  is defined by the recesses  42 . The narrow portion  43  extends to the vicinity of the proximal end of the piezoelectric actuator material  35 . The grooves  41  and the recesses  42  are formed by etching after applying a coating of the electrode material to the entire surface of the piezoelectric actuator material  35 . 
     Pads  44  are disposed at proximal ends of the narrow portion  43 . The connection cable  45  is connected with each of the pads  44 . Also, the end of the support casing  34  has another one of the pads  44 , with which the connection cable  45  is connected. Consequently, the support casing  34  operates as a common electrode for the piezoelectric actuator material  35 . 
     The connection cable  45  has a cable diameter of 15 microns and an outer jacket diameter of 20 microns. The connection cable  45  is extended about the fiber optic image guide  31 , inserted in the elongated tube  8  and the universal cable  12 , and connected by the first connector  10  with the processing apparatus  6 . 
     The two pairs of the electrodes  36  are supplied with voltages of opposite polarities with reference to a voltage applied to the support casing  34  as a common electrode. For example, let the support casing  34  have a potential of 0 V. An upper one of the electrodes  36  is supplied with +5 V. A lower one of the electrodes  36  is supplied with −5 V. The piezoelectric actuator material  35  under the electrodes  36  expands and contracts axially. In response to this, a portion of the shift mechanism  38  in front of the stationary section  39  displaces in the lumen  37  together with the distal tip  48  of the fiber optic image guide  31 . It is possible to displace the shift mechanism  38  at a predetermined angle and amount by changing a combination of the electrodes  36  for powering and levels of the voltages. 
     In  FIG. 6 , the fiber optic image guide  31  has plural optical fibers  52 , for example 6,000 fibers, bundled with extreme tightness in an equilateral hexagonal form. Each of the optical fibers  52  includes a core  50  and a cladding  51 . A diameter of the core  50  is 3 microns. A diameter of the cladding  51  is 6 microns. A pitch P of arrangement of the optical fibers  52  is 6 microns. 
     In  FIG. 7 , the processing apparatus  6  includes an enlarging lens system  55  and a three-CCD assembly  56 . The enlarging lens system  55  is opposed to the proximal tip of the fiber optic image guide  31  extending to the outside of the first connector  10 . The enlarging lens system  55  enlarges the object image from the fiber optic image guide  31  with a suitable magnification, and directs its image light to the three-CCD assembly  56 . 
     The three-CCD assembly  56  is an image sensor disposed behind the enlarging lens system  55 . A color separation prism  57  is combined with the CCD group  58  to constitute the three-CCD assembly  56  as well-known in the art. The color separation prism  57  includes three prism blocks and two dichroic mirrors disposed on optical faces of the prism blocks. The color separation prism  57  separates image light of a body part from the enlarging lens system  55  into light components of red, blue and green colors, which are directed to the CCD group  58 . The CCD group  58  outputs an image signal according to light amounts of the light components from the color separation prism  57 . Note that a CMOS image sensor may be used instead of the CCD. 
     Image light of a part image  80  is transmitted by the core  50  of the fiber optic image guide  31 . There are pixels  81  arranged on the image pickup surface of the CCD group  58 . In  FIG. 8 , the part image  80  is viewed in a state projected to the image pickup surface of the CCD group  58 . A center of the part image  80  substantially coincides with the center of a set of nine of the pixels  81 . The proximal tip of the fiber optic image guide  31  is positioned relative to the color separation prism  57  and the CCD group  58  so as to correlate the part image  80  with the pixels  81  in the depicted state. 
     In  FIG. 7 , an analog front end  59  or AFE is supplied with the image signal from the CCD group  58 . The analog front end  59  includes a correlated double sampling circuit or CDS circuit, an automatic gain control circuit or AGC circuit, and an A/D converter. The CDS circuit processes the image signal from the CCD group  58  in the correlated double sampling, and eliminates noise generated by the CCD group  58 , such as reset noise, amplification noise and the like. The AGC circuit amplifies the image signal with a predetermined signal gain after noise elimination in the CDS circuit. The A/D converter converts the amplified image signal from the AGC circuit into a digital signal with a predetermined number of bits. A digital signal processor  65  or DSP has a frame memory (not shown) to which the digital form of the image signal from the A/D converter is written. 
     A CCD driver  60  generates drive pulses for the CCD group  58  and a sync pulse for the analog front end  59 . The drive pulses include a vertical/horizontal scan pulse, electronic shutter pulse, reading pulse, reset pulse and the like. The CCD group  58  responds to the drive pulses from the CCD driver  60 , takes an image, and outputs an image signal. Components included in the analog front end  59  are operated according to the sync pulse from the CCD driver  60 . Note that the CCD driver  60  and the analog front end  59  are connected with the CCD  58 G in the drawing, but also connected with the CCDs  58 R and  58 B. 
     A piezoelectric driver  61  is connected by the connection cable  45  with the electrodes  36  and the support casing  34 . A CPU  62  controls the piezoelectric driver  61  to supply the piezoelectric actuator material  35  with voltage. 
     The CPU  62  controls the entirety of the processing apparatus  6 . The CPU  62  is connected with various elements by a data bus (not shown), address bus, control lines and the like. A ROM  63  stores data (such as graphic data) and programs (operation system and application programs) for controlling the processing apparatus  6 . The CPU  62  reads the program and data required for the purpose from the ROM  63 . A RAM  64  is a working memory with which the CPU  62  performs tasks with data for operation by running the program. An input interface  68  is also associated with the CPU  62 . The CPU  62  is supplied with information related to the examination by the input interface  68  or the LAN (local area network) or other networks, the information including a date and time of the examination, personal information of a patient, doctor&#39;s name, other text information, and the like. The CPU  62  writes the information to the RAM  64 . 
     The digital signal processor  65  reads an image signal produced by the analog front end  59  from the frame memory. The digital signal processor  65  processes the image signal in processing of various functions, such as color separation, color interpolation, gain correction, white balance adjustment, gamma correction and the like, and produces an image of one frame. Also, the digital signal processor  65  has an image synthesizing unit  65   a.  See  FIG. 11 . When a composite imaging mode (to be described later) is selected, the image synthesizing unit  65   a  outputs one synthesized image of a high definition by combining plural images obtained in one two-dimensional shift sequence. To this end, plural frame memories are incorporated in the digital signal processor  65 . A digital image processor  66  includes a frame memory (not shown) , to which the image or synthesized image from the digital signal processor  65  is written. 
     The digital image processor  66  is controlled by the CPU  62  for image processing. The digital image processor  66  reads images from the frame memory after processing in the digital signal processor  65 . Examples of functions of the image processing in the digital image processor  66  are electronic zooming, color enhancement, edge enhancement and the like. A display control unit  67  is supplied with data of the image processed by the digital image processor  66 . 
     The display control unit  67  has a VRAM for storing the processed image from the digital image processor  66 . The display control unit  67  receives graphic data read by the CPU  62  from the ROM  63  and the RAM  64 . Examples of the graphic data include data of a mask for display of an active pixel area by masking an inactive area in the endoscopic image, text information such as an examination date, patient&#39;s name, and doctor&#39;s name, and data of graphical user interface (GUI), and the like. The display control unit  67  processes the image from the digital image processor  66  in various functions of display control, the functions including superimposition of the mask, the text information and the GUI, graphic processing of data for display on the display panel  19 , and the like. 
     The display control unit  67  reads an image from the VRAM, and converts the image into a video signal suitable for display on the display panel  19 , such as a component signal, composite signal or the like. Thus, the endoscopic image is displayed by the display panel  19 . 
     The input interface  68  is a well-known input device, of which examples are an input panel on a housing of the processing apparatus  6 , buttons on the handle  9  of the endoscope  5 , mouse, keyboard, or the like. The CPU  62  operates relevant elements in the processing apparatus  6  in response to an input signal from the input interface  68 . 
     The processing apparatus  6  also includes an image compression device, a media interface and a network interface. The image compression device compresses images in a format of compression, for example JPEG format. The media interface operates in response to an input from the recording button  13 , and records the compressed images to a recording medium such as a CF card, MO (optical magnetic disk), CD-R and other removable media. The network interface transmits or receives various data by use of the LAN or other networks. Those are connected to the CPU  62  by a data bus or the like. 
     A light source  70  is incorporated in the light source apparatus  7 . Examples of the light source  70  are a xenon lamp, white LED and the like which generate light of a broad band of the wavelength from red to blue, for example, with a wavelength of 480-750 nm. A light source driver  71  drives the light source  70 . An aperture stop device  72  is disposed in front of the light source  70 , and adjusts an amount of incident light. A condenser lens  73  condenses the light passed through the aperture stop device  72 , and directs the light to the distal end of the light guide devices  27 . A CPU  74  communicates with the CPU  62  of the processing apparatus  6 , and controls the light source driver  71  and the aperture stop device  72 . 
     There are two imaging modes including a normal imaging mode without operating the displacing device  32  and a composite imaging mode in operation of the displacing device  32 . In the composite imaging mode, the number of shift events is changeable between four and nine. The input interface  68  can be operated to change over the imaging modes and set the number of shift events. 
     When the composite imaging mode is selected to set the four shift events, the piezoelectric driver  61  drives the shift mechanism  38  of the displacing device  32  to displace the distal tip  48  of the fiber optic image guide  31  as illustrated in  FIG. 9 . At first, the shift mechanism  38  displaces the distal tip  48  laterally from the initial position of (a) leftwards and downwards with an inclination of 30 degrees, and with an amount half as much as the pitch P of arrangement of the optical fibers  52 . The shift mechanism  38  sets the distal tip  48  in a set position of (b) with a first shift event. Then the distal tip  48  is displaced at the same amount in the rightward and downward direction, and set in a set position of (c) with a second shift event. In sequence, the distal tip  48  is displaced at the same amount in the rightward and upward direction, and set in a set position of (d) with a third shift event. Then the distal tip  48  is displaced at the same amount in the leftward and upward direction, and set in an initial position of (a) with a fourth shift event by way of the initial position. The shift mechanism  38  is stopped in the set positions stepwise by the piezoelectric driver  61 . Note that the solid line in the drawing indicates an actual position of the core  50  at the distal tip  48 . The broken line indicates a previous position of the core  50  before the actual position. 
     The core  50  in the distal tip  48  of the fiber optic image guide  31  repeatedly displaces in a composite sequence from the initial position of (a) to the set positions of (b), (c) and (d) then to the initial position of (a). The distal tip  48  shifts in a two-dimensional path of a polygonal shape of a rhombus of  FIG. 10A  to compensate for a loss region due to the cladding  51  in transmitting image light according to the initial position of (a). 
     Let a number of shift events be nine (9). In  FIG. 10B , a two-dimensional path according to the nine shift events is illustrated. The number of shift events in each of the directions is one larger than that according to the mode of the four shift events. Note that a lateral direction from the seventh set position to the eighth set position is downward in contrast with the upward direction from the sixth set position to the seventh set position. A lateral direction from the eighth set position to the initial position or the ninth set position is upward with an angle of 90 degrees. In a manner similar to the mode of the four shift events, the two-dimensional path according to the nine shift events is in a shape to compensate for a loss region of the cladding  51  in transmitting image light according to the initial position. Furthermore, the distal tip  48  is displaced to the positions of the second, fourth and sixth set positions, which are the same as initial positions of three adjacent cores among the cores  50 . 
     In  FIG. 11 , the composite imaging mode is designated. A sync control unit  62   a  and a piezoelectric control unit  62   b  are started in the CPU  62  of the processing apparatus  6 . According to displacement information  85 , the image synthesizing unit  65   a  of the digital signal processor  65  cooperates with the sync control unit  62   a  and the piezoelectric control unit  62   b  to perform various tasks. 
     The displacement information  85  is data related to shift events of the shift mechanism  38  of the displacing device  32 . Examples of the data are a number of shift events, shift direction, shift pitch, relative positions of the pixels  81  of the CCD group  58  and the part image  80  transmitted through the core  50  of the fiber optic image guide  31  of  FIG. 8 . The data of the number of shift events is generated by the input interface  68 . The ROM  63  stores basic datasets of the shift direction, shift pitch, relative positions of the pixels  81  and the part image  80 . Any of those is read from the ROM  63  to the image synthesizing unit  65   a,  the sync control unit  62   a  and the piezoelectric control unit  62   b.    
     The sync control unit  62   a  receives information of the drive pulses for the CCD group  58  from the CCD driver  60 , and sends the piezoelectric control signal Sa to the piezoelectric control unit  62   b  and the image synthesis signal Sb to the image synthesizing unit  65   a.  The piezoelectric control unit  62   b  controls the piezoelectric driver  61  for fine displacement in synchronism with the piezoelectric control signal Sa. Similarly, the image synthesizing unit  65   a  performs a task of image synthesis in synchronism with the image synthesis signal Sb. Pixels of images G 0 , G 1 , G 2  and G 3  obtained from the set positions (in the mode of the four shift events) are mapped in accordance with the set positions, to create one synthesized image Gc. 
     In  FIG. 12 , a mode of the four shift events is illustrated. Immediately after completing storing of the charge in the CCD group  58 , the sync control unit  62   a  generates a piezoelectric control signal Sa. This is when the signal charge of one frame is read to a vertical transfer path from the pixels  81  of the CCD group  58  (or when a reading pulse is output by the CCD driver  60  to the CCD group  58 ). Also, the sync control unit  62   a  generates an image synthesis signal Sb upon completion of reading the charge of the CCD group  58  in correspondence with the image G 3  obtained at the third set position. The operation of reading the charge is a sequence of CCD operation inclusive of reading the signal charge from the pixels  81  of the CCD group  58  to the vertical path, and vertical transfer, horizontal transfer and an output of an image signal of one frame. 
     The piezoelectric driver  61  in response to the piezoelectric control signal Sa supplies the piezoelectric actuator material  35  with a predetermined voltage, to displace the shift mechanism  38  from a previous set position to a present set position. Shift time from an output of the piezoelectric control signal Sa from the sync control unit  62   a  to the piezoelectric driver  61  until shift of the shift mechanism  38  to a succeeding set position is shorter than clearing time from completion of previous storing of charge in the CCD group  58  until a start of succeeding storing of charge. Thus, succeeding storing of charge is always started while the shift mechanism  38  is kept set in the succeeding set position by the piezoelectric driver  61 . 
     The image synthesizing unit  65   a  in response to the image synthesis signal Sb reads images G 0 -G 3  obtained from the set positions of displacement. The image synthesizing unit  65   a  maps pixels of the images G 0 -G 3  according to the set positions of displacement, and outputs a synthesized image Gc. It is further possible to interpolate the pixels to process the images G 0 -G 3  or synthesized image Gc in the course of the synthesis. 
     In the synthesized image Gc, a loss region due to the cladding  51  in transmitting image light can be compensated for in a visible manner. Pixel values of the pixels of the portions are directly derived from the object image without approximation or interpolation of adjacent pixels within one frame. Consequently, the number of pixels is higher than that in images obtained from the normal imaging mode or according to each one of the set positions of displacement, to produce the image in a very fine quality. Note that the image quality is higher in images obtained according to the nine shift events than images of the four shift events. 
     It is to be noted that the images G 0 -G 3  are different part images  80  with differences in the set position by displacement. The part image  80  at the distal tip  48  is only shifted by keeping a proximal tip of the fiber optic image guide  31  stationary. No change occurs in the relative position between the proximal tip of the fiber optic image guide  31  and an image pickup surface of the CCD group  58 . There are no apparently distinct feature between data output according to the pixels  81  even with the various set positions. For example, the part image  80  of a position in the image GO is different from the part image  80  of the same position in the image G 1  in relation to the set position. However, those are recorded commonly by the pixels  81  on the CCD group  58 . Accordingly, the image synthesizing unit  65   a  determines original pixels of pixel values of the images among the pixels  81  by mapping on the basis of the relative position of the part image  80  of the displacement information  85  and the pixels  81 , to carry out the pixel interpolation. 
     The operation of the endoscope system  2  of the above construction is described now. To observe a body part of a patient endoscopically, a doctor or operator connects the endoscope  5  to the processing apparatus  6  and the light source apparatus  7 , which are turned on and powered. The input interface  68  is manually operated to input information related to the patient, to start examination. 
     After instructing the start, the doctor or operator enters the elongated tube  8  in the body. Light from the light source apparatus  7  is applied to body parts, while he or she observes an image on the display panel  19  from the CCD group  58  of the image sensor. 
     To introduce the elongated tube  8  in the body, the resilient cap portion  20  of the hood device  16  covers the distal end face  15   a  as illustrated in  FIG. 2A . Particles or foreign material present in the body will not stick on the distal end face  15   a  because of the closed position of the resilient cap portion  20  for protection. As the resilient cap portion  20  is formed from colorless transparent material, an object can be imaged safely through the same. When fine imaging of the object of interest starts upon reach of the head assembly  15  thereto, the doctor or operator depresses the winding button  18  to actuate the winder  17 . The hood device  16  is moved in a proximal direction as illustrated in  FIG. 2B  to peel off the resilient cap portion  20  for the open position. The distal end face  15   a  is revealed to ensure a field of view with more clarity than in the closed position of  FIG. 2A  of covering of the resilient cap portion  20 . 
     An image signal is generated by the CCD group  58 , processed by the analog front end  59  for various functions of processing, and input to the digital signal processor  65 . The digital signal processor  65  processes the image signal for various functions of signal processing, to produce an image. The image from the digital signal processor  65  is output to the digital image processor  66 . 
     The digital image processor  66  is controlled by the CPU  62  and processes the image from the digital signal processor  65  for various functions of image processing. The image is input by the digital image processor  66  to the display control unit  67 . According to the graphic data from the CPU  62 , the display control unit  67  carries out control for display. Thus, the image is displayed on the display panel  19  as an endoscopic image. 
     In  FIG. 13 , a composite imaging mode is designated (yes at the step S 10 ). The sync control unit  62   a  and the piezoelectric control unit  62   b  are ready in the CPU  62  in the processing apparatus  6 . According to the displacement information  85  and information of drive pulses from the CCD driver  60  for the CCD group  58 , the sync control unit  62   a  sends the piezoelectric control signal Sa to the piezoelectric control unit  62   b,  and sends the image synthesis signal Sb to the image synthesizing unit  65   a.    
     The operation of the piezoelectric driver  61  is controlled by the piezoelectric control unit  62   b  upon receiving the piezoelectric control signal Sa. The piezoelectric driver  61  applies a predetermined voltage to the piezoelectric actuator material  35 . Thus, the shift mechanism  38  displaces at a predetermined angle and pitch according to the designated number of the shift events. See the step S 11 . At each time that the shift mechanism  38  is retained in one of the set positions, charge is stored in the CCD group  58 . The part image  80  of a body part is picked up by the pixels  81  through the fiber optic image guide  31  in the step S 12 . A sequence including the steps S 11  and S 12  is repeated (no at the step S 13 ) until the end of one two-dimensional shift sequence by shift of the shift mechanism  38  from the initial position and again to the same position. 
     When one two-dimensional shift sequence is terminated (yes at the step S 13 ), image synthesis is carried out by the image synthesizing unit  65   a  upon receiving the image synthesis signal Sb, to produce a synthesized image at the step S 14  from the images obtained according to the set positions of fine displacement. After data of the synthesized image is processed in the digital image processor  66  and the display control unit  67 , the synthesized image is displayed on the display panel  19  at the step S 15 . In contrast, when the normal imaging mode is designated, an image is picked up in the step S 12  but without carrying out the sequence of the steps S 11  and S 14 . Those steps are repeated until a command signal for terminating the examination is input (yes at the step S 16 ). 
     As described heretofore, the distal end face  15   a  is covered and protected in the course of advance of the elongated tube  8 . The distal end face  15   a  is revealed by displacing the hood device  16  for imaging of an object of interest endoscopically. Thus, the head assembly  15  can be kept clean without depositing of foreign material or particles in the course of advance of the elongated tube  8 . A field of view in the imaging can be maintained. 
     It is possible to extend the sleeve  21  to the vicinity of the root of the handle  9  and in a form of a bag or tube. No embedment of the control wires  23  in the elongated tube  8  is required. The control wires  23  are inserted through a groove or channel formed in the sleeve  21 . See a groove  95  or channel in  FIG. 14 . This makes it unnecessary to forma sealing hole in the elongated tube  8  for the control wires  23 . The elongated tube  8  can be protected by the sleeve  21 . 
     Another preferred hood device  90  or protection device or cover is illustrated in  FIG. 14 . A cover door  91  is included in the hood device  90  instead of the resilient cap portion  20 . Examples of materials of the cover door  91  are various transparent colorless materials in the manner of the resilient cap portion  20 . The hood device  90  includes a sleeve  92  and a hinge  93  for securing the cover door  91  to the sleeve  92 . The cover door  91  is movable pivotally about the hinge  93  between open and closed positions in the arrow direction. A torsion coil spring (not shown) is incorporated in the hinge  93  and biases the cover door  91  in an opening direction. In the drawing, the cover door  91  is in the closed position against the bias of the torsion coil spring. 
     A control wire  94  as moving mechanism is secured to a rear surface  91   a  of the cover door  91  opposite to the hinge  93 . See  FIG. 15 . The control wire  94  has coiled filaments of metal similar to the control wires  23 . The groove  95  or channel is formed in the sleeve  92 . The control wire  94  extends through the groove  95 , appears in a proximal end of the sleeve  92  to the outside, and is embedded in a sealing hole of the elongated tube  8 . As the control wire  94  passes through the elongated tube  8 , its proximal end is secured to a spool of a winder (not shown) disposed near to the instrument opening  14 . 
     The winder includes an operation button in addition to the above-described elements in the winder  17 , the operation button for freely rotating the spool by release from the bias of the spiral spring. The force of the bias of the spiral spring is higher than that of the torsion coil spring of the hinge  93 . When the lock device is disabled by a setting of the winding button  18 , rotation of the spool pulls the control wire  94  in a proximal direction, to close the cover door  91  against the bias of the torsion coil spring. 
     When the operation button for free rotation of the spool is depressed, application of pulling force to the control wire  94  is discontinued, to open the cover door  91  with the bias of the tension coil spring. When the lock device is actuated while the cover door  91  is open or closed, the cover door  91  becomes stopped during the actuation. The maximum opening angle of the cover door  91  is 90 degrees or larger than 90 degrees. A length of the control wire  94  and an amount of winding of the control wire  94  about the spool are adjusted for setting the maximum opening angle. 
     To enter the elongated tube  8  in a patient&#39;s body, a doctor or operator depresses the winding button  18  to close the cover door  91 . The distal end face  15   a  is covered by the cover door  91  as depicted in the drawing. To start imaging of an object of interest, he or she depresses the operation button for freely rotating the spool. The cover door  91  is opened to reveal the distal end face  15   a.  Accordingly, the same effect as the first embodiment can be obtained. 
     Note that the cover door  91  may be directly secured to the head assembly  15  except for the sleeve  92 . Also, it is possible to dispose the hinge  93  close to the instrument opening  26 , and dispose a portion of the control wire  94  for attachment to the rear surface  91   a  of the cover door  91  close to the imaging window  25 . Also, a portion of the control wire  94  for attachment to the rear surface  91   a  of the cover door  91  can be defined near to the hinge  93  or the like for the purpose of keeping the control wire  94  out of the field of view upon opening the cover door  91 . 
     In  FIG. 15 , a calibration chart  101  for a shift amount is secured to a part, for example central part, of a rear area  100  (indicted by the phantom line) of the rear surface  91   a  of the cover door  91  opposed to an imaging window. Black and white areas  110   a  and  110   b  as stripe areas are arranged on the calibration chart  101  as will be described later. The hood device  90  is fixedly secured to the head assembly  15  by aligning a shift direction of the fiber optic image guide  31  with the width direction of the black and white areas  110   a  and  110   b.  There is a positioning structure for positioning the hood device  90 . Examples of the positioning structure can include a combination of a groove in an inner surface of the sleeve  92  in the hood device  90  and a projection on the head assembly  15  for engagement with the groove in the sleeve  92 , and a combination of a projection on an inner surface of the sleeve  92  in the hood device  90  and a groove in the head assembly  15  for engagement with the projection in the sleeve  92 , and a combination of a male thread on the head assembly  15  and a female thread in the sleeve  92 . 
     Due to specificity in the fiber optic image guide  31  and the piezoelectric actuator material  35  for shifting the fiber optic image guide  31 , failure may occur in shifting of the distal tip  48  of the fiber optic image guide  31  at a predetermined shift amount even if the piezoelectric actuator material  35  is driven properly. An error in the image registration will occur in forming the synthesized image Gc, which will have an artifact. To prevent such a problem, calibration of the shift amount is carried out by use of the calibration chart  101 . 
     In  FIG. 16 , the calibration chart  101  has a multi-stripe pattern of the black and white areas  110   a  and  110   b  arranged alternately as stripe areas, in parallel and with an equal width dh. The black areas  110   a  are hatched in the drawing in contrast with the white areas  110   b.  A pitch width 2dh as a sum of widths of one of the black areas  110   a  and one of the white areas  110   b  is a constant value times the constant shift amount Hs, namely the shift amount in the direction of 30 degrees. In short, 2dh=kh.Hs where kh is the constant value. The constant value kh is determined according to the magnification of the objective lens system  30  and a distance between the distal end face  15   a  and the rear surface  91   a  of the cover door  91  in the closed position. The constant value kh is so defined that the pitch width 2dh of the black and white areas  110   a  and  110   b  on the plane of the CCD group  58  becomes equal to the shift amount Hs when the rear surface  91   a  of the cover door  91  in the closed position is opposed to the distal end face  15   a.    
     In  FIG. 17 , calibration of a shift amount is illustrated. The piezoelectric driver  61  is controlled by the CPU  62  and drives the piezoelectric actuator material  35  cyclically at a driving voltage V of a default value and at a driving voltage m/n.V, for example, ¼.V, ½.V, ¾.V and the like. The piezoelectric actuator material  35  is returned to the state before the shift (state of zero (0) indicated by the broken line) at each time. The default driving voltage V is as high a voltage level as to displace the distal tip  48  of the fiber optic image guide  31  with a predetermined shift amount by driving the piezoelectric actuator material  35 . The distal tip  48  of the fiber optic image guide  31  is caused by the piezoelectric actuator material  35  with the driving voltage V to displace at the shift amount Hs in a direction of 30 degrees. When the driving voltage m/n.V is applied to the piezoelectric actuator material  35 , the distal tip  48  displaces at a shift amount m/n.Hs. If there is failure of driving the piezoelectric actuator material  35 , the shift amount of the distal tip  48  becomes different from the shift amount m/n.Hs. 
     The distal tip  48  of the fiber optic image guide  31  moves back and forth by a stepwise increase in the shift amount between a reference position of the broken line and one of the positions distant at each of shift amounts from the reference position. The time required for return from the previous set position to the reference position and for shift to a new set position is equal to the time required for shift from the previous set position to a new set position in the above described composite imaging mode. In short, the distal tip  48  of the fiber optic image guide  31  is displaced at a driving frequency equal to that in the composite imaging mode. 
     The CCD group  58  picks up an image of the calibration chart  101  initially in the reference position for one time and then in each of the set positions, as indicated by a sign of a camera. The CPU  62  detects black density of a local area or an entire area of a test image obtained by the CCD group  58  from the calibration chart  101 . According to the black density, a shift amount or the driving voltage for the piezoelectric actuator material  35  is calibrated. Light generated by the light source  70  in the light source apparatus  7  is used in a manner similar to the imaging. 
     As the hood device  90  is positioned relative to the head assembly  15 , a shift direction of the fiber optic image guide  31  is disposed with a width direction of the black and white areas  110   a  and  110   b  on the calibration chart  101 . In  FIG. 18 , the black density changes according to the shift amount. The black density becomes the maximum when one of the black areas  110   a  is located at the center of the part image  80  transmitted by only one of the cores  50 , and becomes the minimum when one of the white areas  110   b  is located at the center of the part image  80 . If the black and white areas  110   a  and  110   b  are captured to appear in the part image  80  equally to one another, the black density becomes a medium value. As a frequency of the change of the black density is 2dh=kh.Hs, the shift amount is equal to the shift amount Hs. Although the part images  80  obtained with the cores  50  do not necessarily change equally to one another by way of test images, results of changes in the black density are approximately the same with minor local fluctuations. 
     When the piezoelectric actuator material  35  is driven appropriately, the part images  80  of the set positions and synthesized images of the part images  80  of the reference position and the set positions are in the forms of  FIG. 19 . In the example of the drawing, the black and white areas  110   a  and  110   b  appear equally in the part image  80  in the reference position. When the piezoelectric actuator material  35  is driven with the driving voltage ¼.V and the distal tip  48  of the fiber optic image guide  31  is shifted by the shift amount ¼.Hs, one of the white areas  110   b  is located at the center of the part image  80 . One of the black areas  110   a  extends largely in the synthesized image except for a local part on the right side near to the center. In the case of driving with the driving voltage ½.V and shift amount ½.Hs, the black and white areas  110   a  and  110   b  appear equally and symmetrically in the part image  80  in the reference position. One of the black areas  110   a  extends fully in the synthesized image. In the case of driving with the shift amount ¾.Hs, one of the black areas  110   a  is located at the center of the part image  80  in contrast with the result according to ¼.Hs. One of the black areas  110   a  extends largely in the synthesized image except for a local part on the right side near to the right end. In the case of driving with the shift amount Hs, the same black or white pattern as the part image  80  of the reference position is obtained. The same black or white pattern in the synthesized image is obtained. If the shift amount becomes two times, three times and so on as much as Hs, the same black or white pattern as the part image  80  of the reference position is obtained. The same black or white pattern in the synthesized image is obtained. 
     The black density of the synthesized image is the maximum when the shift amount is ½.Hs for a full black area, and is the minimum when the shift amount is Hs (2Hs, 3Hs and so on) in the reference position. The black density of the synthesized image fluctuates periodically on a curve according to the shift amount at a period of Hs. Even though black and white areas in the part image  80  of the reference position do not appear equally to one another, the black density of the synthesized image in the reference position becomes equal to that of the synthesized image with the shift amount Hs only with a phase difference. 
     The CPU  62  detects black density in each of the test image according to the reference position and a synthesized image (not the synthesized image Gc) of the test image of the respective set positions. When the piezoelectric actuator material  35  is driven by the default driving voltage V, the distal tip  48  of the fiber optic image guide  31  is found to have been shifted at the shift amount Hs if the black density of the synthesized image is found equal to that of the test image according to the reference position. It is unnecessary to adjust the driving voltage of the piezoelectric actuator material  35 . 
     If the black density of the synthesized image is unequal to that of the test image of the reference position, the distal tip  48  of the fiber optic image guide  31  does not displace with the constant shift amount Hs even upon driving the piezoelectric actuator material  35  with the default driving voltage V. The CPU  62  determines the driving voltage of the piezoelectric actuator material  35  to calibrate the shift amount. Specifically, the driving voltage is changed stepwise by 1/10.V near to the default driving voltage V, while the distal tip  48  of the fiber optic image guide  31  is moved back and forth from the reference position (for example, is moved with 8/10.V from the reference position, returned to the reference position, and moved with 9/10.V, and returned to the reference position in a repeated manner). The calibration chart  101  is captured by the CCD group  58  to determine a driving condition of the piezoelectric actuator material  35  with the driving voltage upon coincidence of the black density of the synthesized image with that of the test image of the reference position. 
     When the piezoelectric actuator material  35  is driven at the default driving voltage V, black density of the synthesized image may not be equal to that of the test image of the reference position. Then the CPU  62  writes information of a first driving voltage to a ROM  47  in the endoscope  5  such as an EEPROM or other rewritable storage (See  FIG. 7 ), the first driving voltage being obtained by finely changing the voltage above and below the voltage V and by retrieving a level upon coincidence in the black density. At first, the ROM  47  stores the default driving voltage V as a driving condition. If the driving voltage is changed to a level different from V by the calibration, the CPU  62  rewrites the voltage in the ROM  47 . The voltage is read by the CPU  62  of the processing apparatus  6  from the ROM  47  for use, and applied to the piezoelectric driver  61 . 
     In conclusion, the shift amount of the fiber optic image guide  31  can be calibrated in the course of endoscopic examination as the calibration chart  101  is attached to the rear surface  91   a  of the cover door  91  for the calibrating operation. Occurrence of artifacts of the synthesized image Gc can be prevented. 
     In one preferred example of the endoscope, a light control mirror or dimming mirror is disposed on a rear surface of the cover door in place of or in addition to the calibration chart. The light control mirror, when the cover door is closed, is transparent, and when the cover door is open, is set reflective. A component of image light, which would not be transmitted only in the field of the imaging window  25 , is conducted to the imaging window  25  by the light control mirror. Thus, it is possible to maintain the field of view when the cover door is closed, and to widen the field when the cover door is open. 
     It is possible to finish the resilient cap portion  20  or the cover door  91  in the hydrophilic surface finish for the anti-fogging purpose in a condition of high humidity in a human body. Examples of materials for the hydrophilic surface finish are a synthetic resin coating containing fine particles of hydrophilic polymer, and photocatalytic coating of titanium oxide, and the like. 
     The hood device or protection device or cover of the invention can be used repeatedly by washing periodically, or can be used only one time and discarded. In a case of a single use type of hood device, a removing mechanism is associated with the control wire. The hood device is exchanged at each time of the use. 
     Although the winder  17  is used in the above embodiment, other moving mechanisms can be used. For example, a pull ring may be formed on an end of the control wire for an operator manually to pull the same. Also, a moving mechanism may include a wheel for unwinding and pulling the control wire in a manner similar to a well-known steering wheel disposed in an endoscope for bending up or down a steering portion of the elongated tube. Furthermore, a MEMS motor as a microactuator can be used in place of the control wire to move the hood device from the closed position to the open position. 
     In the above embodiment, the resilient cap portion  20  and the cover door  91  for covering the distal end face  15   a  are formed from transparent material. However, the resilient cap portion  20  or the cover door  91  can be formed from colored material or opaque material. Although an object cannot be imaged in the course of advance of the endoscope, it is possible to guide the advance of the endoscope by monitoring a location of the endoscope by use of other imaging system, such as an X ray imaging system or the like. 
     A displacing device may be shaped in a form other than the rod form, for example, in a form of a quadrilateral prism. A fiber optic image guide is inserted in and attached to a support casing by an adhesive agent (not shown) or the like. A piezoelectric actuator material is overlaid on four faces of the support casing by way of electrodes. The fiber optic image guide is shifted together with the support casing up and down and to the right and left. For example, the displacing device displaces from the initial position in the leftward direction by 90 degrees at an amount of (3 1/2 )/4.P to come to the set position with a first shift event. After this, the displacing device is returned to the initial position, and displaces in the downward direction at an amount of ¼.P to come to the set position with a second shift event. The displacing device is returned from the set position of the second shift event to the initial position, and displaces to the right and upwards, and then is returned to the initial position again. Thus, the core  50  displaces in the two-dimensional path of a crossed shape by fine displacement. For the calibration, two calibration charts can be prepared for vertical and horizontal directions. A width of each of black and white areas can be set a constant value times the shift amount in the vertical and horizontal directions from an initial position. 
     However, there is a characteristic of the hysteresis in the piezoelectric actuator materials, of which the set position may be offset upon driving the piezoelectric actuator materials without a patterned manner. Thus, the displacing device is caused to displace with the same two-dimensional path and in the same sequence. In short, a sequence of driving the piezoelectric actuator materials for actuating the displacing device is set equal for every event. Also, a sequence of supplying electrodes with voltage on a couple of the right and left sides is kept the same. To calibrate the shift amount, the displacement is carried out with the same path in the same sequence. 
     As the fiber optic image guide is displaced by tilt of a root portion of the shift mechanism, the fiber optic image guide is likely to vibrate and stop with lag in the set positions without immediate stop. Thus, it is preferable with a piezoelectric driver to drive the piezoelectric actuator material or to use other anti-vibration methods in order to tilt the shift mechanism instantaneously in reverse to the displacing after a stop of the displacing device. Specifically, reaction force is previously measured by simulation or experimentally. An offset voltage for the piezoelectric actuator material is stored in a ROM. The piezoelectric control unit reads the information of the offset voltage from the ROM and sets the information in the piezoelectric driver. Furthermore, non-conductive fluid with high viscosity can be charged in a lumen for an anti-vibration structure by utilizing damping effect. 
     In the above embodiment, shift time for the shift mechanism to displace to a succeeding set position is shorter than clearing time from previous completion of storing charge of the CCD until a succeeding start of storing charge. However, the shift time may be longer than the clearing time for the reason of various factors, which include a length, material or shift amount of the shift mechanism, performance of the piezoelectric actuator material, or the like. In considering that the weight of the fiber optic image guide is relatively large, the shift time is very likely to be longer than the clearing time. 
     While the shift mechanism is set in the set position, the CCD driver is controlled by the CPU of the processing apparatus and supplies the CCD with an electronic shutter pulse. A start of storing charge is delayed. When the shift mechanism stops in the set position, storing charge is started. Otherwise, the light source is turned off while the shift mechanism is set in the set position, and then turned on when the shift mechanism stops in the set position. 
     In order to drive the CCD with reference to time required for shift to a succeeding one of the set positions, the frame rate must be set small should the shift time be longer than the clearing time. However, it is possible without blur to obtain an image even with the presently high frame rate by sweeping out charge with an electronic shutter pulse, or by turning off the light source, or by other methods. 
     In the above embodiment, the image synthesizing unit synthesizes the image only when the composite imaging mode is designated. However, it is possible to synthesize an image also in the normal imaging mode. This is effective in compensating for a loss region of the cladding even though an image for reflecting an object image positioned in association with the cladding cannot be obtained. Image quality can be high. 
     In the above embodiment, the image synthesizing unit carries out synthesis for one two-dimensional shift sequence, to output one synthesized image. However, a problem occurs in that a frame rate of the composite imaging mode is lower than the normal imaging mode. To solve this problem, it is preferable to raise a frame rate to four times as high a level as the frame rate for the normal imaging mode, namely change over the frame rate in response to designating the composite imaging mode. 
     Specifically, frequency of the clock signal of the system clock in the CPU  62  is changed to change frequency of a drive signal of the CCD driver  60 . Otherwise, it is possible in the CCD driver  60  to dispose a clock divider without changing the clock signal. The clock signal can be divided by the clock divider to change the frequency. 
     In another variant of the embodiment of the four shift events, the images G 0 -G 3  of one two-dimensional shift sequence is used to create a synthesized image Gc. Then the images G 0 -G 3  and one image GO according to a second two-dimensional shift sequence can be used to create a synthesized image Gc. Similarly, a combination of images G 0 -G 3  for one two-dimensional shift sequence can be changed by one image. An earliest one of the images G 0 -G 3  is replaced with a newest one of images G 0 -G 3  so as to create a series of synthesized images Gc. This is effective in preventing complexity in the control by changing a period of a clock signal. A drop of the frame rate can be prevented. 
     Elements of the hardware can be incorporated in a housing separate from the processing apparatus, or may be incorporated in the endoscope, the hardware including the three-CCD assembly, the input interface for setting the imaging mode and the number of shift events, and electronic circuits to constitute the image synthesizing unit, sync control unit and piezoelectric control unit. 
     One preferred light source apparatus can include a blue laser light source, which may have a characteristic with a central wavelength of 445 nm. A wavelength conversion device is disposed on an exit side of the light guide devices  27  at its distal end. The wavelength conversion device contains plural phosphors which partially absorb the laser light from the blue laser light source, to emit converted light with colors from green to yellow by excitation. The laser light from the blue laser light source and the excitation light from green to yellow after the conversion are coupled together, to produce white light of high brightness. It is possible to obtain sufficiently bright light with a small number of light guide devices, namely one or two, because white light can be delivered with higher brightness than the former embodiment. The diameter of the endoscope can be reduced more effectively for an ultra thin tube. 
     Note that a single CCD assembly may be used instead of a three-CCD assembly. In the above embodiments, the first connector  10  is used commonly for the connection of the fiber optic image guide and the connection cable to the processing apparatus. However, two separate connectors may be used and may contain the fiber optic image guide and the connection cable discretely. 
     Although the present invention has been fully described by way of the preferred embodiments thereof with reference to the accompanying drawings, various changes and modifications will be apparent to those having skill in this field. Therefore, unless otherwise these changes and modifications depart from the scope of the present invention, they should be construed as included therein.