Patent Publication Number: US-2007106116-A1

Title: Endoscope-shape monitoring system

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a system or to an apparatus that is used for monitoring the shape of an insertion portion or a flexible tube of an endoscope that is inserted inside a cavity or a hollow of an inspection object.  
      2. Description of the Related Art  
      It is beneficial for an endoscopic operator to grasp the shape of a flexible tube of an endoscope that is inserted inside a body. In particular, the visualization of the endoscope shape inside the body has a significant advantage when operating a lower intestinal endoscope, such as a colonoscope, since insertion of the flexible tube into a tortuous intestine is difficult. As a result, various types of endoscope-shape monitoring systems have been proposed.  
      A system that uses an alternating magnetic field for detecting the shape of a flexible tube of an endoscope is conventionally known. In this system, a plurality of coils are disposed along the longitudinal direction of the flexible tube, and a three-dimensional position and a direction for each of the coils are detected by using electromagnetic interactions between the alternating magnetic field and the coils. For example, the shape of the flexible tube is represented by a three-dimensional spline curve, which is obtained from positional data of measurement points where the coils are placed, and the result is displayed on a monitor.  
     SUMMARY OF THE INVENTION  
      However, the coils that are provided inside the insertion portion have significant size so that the coils are repeatedly subjected to bending stress when the insertion portion is bent. Further, signal wires are wired between the coils and the operating portion of the endoscope, so that the signal wires are also subjected to bending stress and tensile stress. Therefore, the conventional endoscope-shape monitoring system has issues of durability.  
      Therefore, an object of the present invention is to improve the durability of an endoscope-shape monitoring system.  
      According to the present invention, an endoscope shape monitoring system that is used to grasp the shape of a flexible insertion portion is provided. The endoscope shape monitoring system includes a plurality of coils. The coils are used as a magnetic sensor. The coils are disposed on a flexible portion of the insertion portion. The plurality of coils are arranged at positions where the coils are not subjected to a bending stress that is induced when the flexible portion is bent.  
      According to another aspect of the present invention, an endoscope used in an endoscope shape monitoring system is provided. The endoscope shape monitoring system is used to grasp the shape of a flexible insertion portion that includes a bendable portion and a flexible portion. The endoscope includes a plurality of coils, and a plurality of rigid sections.  
      The coils are used as a magnetic sensor, and are disposed on the flexible portion of the insertion portion. The rigid sections have rigidity against the bending of the flexible portion. The rigid sections are arranged along the axis of the flexible portion at predetermined intervals, and the coils are disposed inside the rigid sections, so that the coils are protected from bending stress.  
      According to another aspect of the present invention, an endoscope used in an endoscope shape monitoring system is provided. The endoscope shape monitoring system is used to grasp the shape of a flexible insertion portion that includes a bendable portion and a flexible portion. The endoscope comprises a plurality of coils and a spiral band member.  
      The coils are used as a magnetic sensor, and are disposed on the flexible portion of the insertion portion. The spiral band member configures the flexible portion. The coils are integrally provided on the spiral band member, whereby the coils are not subjected to bending stress induced by bending of the flexible portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The objects and advantages of the present invention may be better understood from the following description, with reference to the accompanying drawings in which:  
       FIG. 1  is a general view of an endoscope to which an endoscope shape monitoring system as a first embodiment of the present invention is applied;  
       FIG. 2  schematically illustrates an arrangement of coils provided inside an insertion portion;  
       FIG. 3  is a partially magnified schematic perspective view, where one of the coils is detailed to illustrate the arrangement of the magnetic sensor coils;  
       FIG. 4  is a block diagram that shows overall electrical structures of the electronic endoscope system;  
       FIG. 5  schematically illustrates the structure of an insertion portion that is wound by a spiral band member;  
       FIG. 6  indicates a situation where the bendable portion is slightly bent;  
       FIG. 7  indicates a situation where the bendable portion is bent, where the end face of the distal end portion is turned around approximately 180 degrees;  
       FIG. 8  illustrates an example of an image representation of the shape of the insertion portion where the points P 1 -P 8  are connected by segments (a linear interpolation);  
       FIG. 9  illustrates an example of an image representation of the shape of the insertion portion, where the points P 1 -P 8  form the basis of a Bézier curve or a spline curve;  
       FIG. 10  schematically illustrates an example of structures of a bendable portion and a flexible portion;  
       FIG. 11  schematically illustrates another example of structures of the bendable portion and the flexible portion;  
       FIG. 12  schematically shows the shape of the bendable portion that is bent by a plurality of curvatures;  
       FIG. 13  indicates the positions of the points P 1 -P 4  and the representation of the linear interpolation thereof, where the bendable portion  12 B is bent in a narrow arc;  
       FIG. 14  schematically illustrates actual shapes of the bendable portion in several bending situations and relations of the positions between the point P 1  and the point P 2  in each of the bending situations; and  
       FIG. 15  schematically illustrates the relations between the positional coordinate data (X 1 , Y 1 , Z 1 ) -(X 9 , Y 9 , Z 9 ) and the bendable portion in situations where the point P 1  is positioned at P 1 ( 0 ), P 1 ( 4 ), and P 1 ( 8 ),  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The present invention is described below with reference to the embodiments shown in the drawings.  
       FIG. 1  is a general view of an endoscope to which a first embodiment of an endoscope-shape monitoring system of the present invention is applied. In this embodiment, an electronic endoscope is employed as an example of the endoscope.  
      The electronic endoscope  10  has an operating portion  11 , which an endoscopic operator manipulates. An insertion portion (a flexible tube)  12  and a light-guide cable  13  are both connected to the operating portion  11 . A connector  13 A is provided at the distal end of the light-guide cable  13 . The connector  13 A is detachably attached to a processor apparatus (not depicted), for example, in which a light source and an image-signal processing unit are integrally installed. Namely, illumination light from the light source inside the processor apparatus is supplied to a cavity or a hollow viscus through the connector  13 A of the electronic endoscope  10  and the light-guide cable  13 . Further, image signals from the electronic endoscope  10  are supplied to the image-signal processing unit inside the processor apparatus.  
      The insertion portion  12  comprises of a flexible portion  12 A, a bendable portion  12 B, and a distal end portion  12 C. Most of the insertion portion  12  is occupied by the flexible portion  12 A that is formed of a flexible tube, which is freely bendable, and the flexible portion  12 A is directly connected to the operating portion  11 . The bendable portion  12 B is provided between the distal end portion  12 C and the flexible portion  12 A, and is bended in accordance with a rotational operation of an angle lever  11 A that is provided on the operating portion  11 . For example, the bendable portion  12 B can be bended as far as if the distal end portion  12 C is rotated 180 degrees. Further, as is detailed later, the distal end portion  12 C is provided with an imaging optical system, an imaging device, an illuminating optical system, and other components.  
       FIG. 2  schematically illustrates an arrangement of magnetic sensor coils installed inside the insertion portion  12 . Further,  FIG. 3  is a partially magnified schematic perspective view where one of the coils is detailed to illustrate the arrangement of the magnetic sensor coils. Note that, in  FIG. 2 , five magnetic sensor coils S 1 -S 5  are shown as an example.  
      The distal end portion  12 C of the insertion portion  12  is formed as a rigid section. Inside the distal end portion  12 C, an imaging device  15  and the front end  16 A of a light guide (optical fiber bundle)  16  are disposed. Further, an illuminating optical system  16 B for emitting light from the light guide  16 , and an imaging optical system  15 A for projecting an object image onto the imaging device  15 , are also provided in the distal end portion  12 C of the insertion portion  12 .  
      Although they are not shown in  FIG. 2 , a plurality of bending frame links that are linked together in a series are provided inside the bendable portion  12 B. On the other hand, although the flexible portion  12 A is wound with a spiral band member, a rigid section that shows rigidity against bending is not usually provided inside the flexible portion  12 A. Therefore, the coils S 2  to Sn (only S 2 -S 5  are shown), which are provided inside the flexible portion  12 A, are directly subjected to bending of the flexible portion  12 A. In particular, the axis of the coils is conventionally arranged in parallel with the axis of the insertion portion, so that, in prior art, the coils tend to be subjected to a bending stress when the insertion portion is bended.  
      Therefore, in the first embodiment, rigid sections  12 D that show rigidity against the bending are provided inside the flexible portion  12 A at predetermined intervals. The coils S 2 -Sn are disposed, respectively, inside the rigid sections  12 D and can be, for example, integrated with the rigid sections  12 D. The number of rigid sections  12 D may correspond to the number of the coils S 2 -Sn installed inside the flexible portion  12 A.  
      For example, as shown in  FIG. 3 , the rigid sections  12 D comprise hollow cylindrical members with a predetermined width W, and are formed of material, such as resin, having sufficient rigidity against banding of the flexible portion  12 A. Further, material for the rigid sections  12 D is selected from materials that do not affect the magnetic field around the magnetic sensor coils; in the present embodiment, hard plastic is used for the rigid sections  12 D.  
      In the present embodiment, the coils S 2 -Sn are arranged inside the rigid sections  12 D, so that the axis of the coil Si (where i=2, . . . , n) and the axis or the longitudinal direction of the insertion portion  12  are related by skew lines. In the present embodiment, the axis of the coil Si (where i=2, . . . , n) is disposed in a plane perpendicular to the central axis X of the insertion portion  12  (which comprises the cylindrical rigid sections  12 D).  
      By arranging the coil Si as described above, the width W of the rigid sections  12 D can be made narrower than the length “d” of the coil Si. Namely, obstruction or resistance against bending of the flexible portion  12 A due to rigidity of the rigid sections  12 D can be prevented by reducing the width W of the rigid sections  12 D. In the present embodiment, the coil S 1  disposed inside the distal end portion  12 C is arranged in parallel with the central axis X, but this arrangement is only an example, and the arrangement is not restricted to this embodiment.  
       FIG. 4  is a block diagram that shows an electrical structure of the electronic endoscope system of the present embodiment. The electronic endoscope system of the present embodiment includes an insertion-portion-shape monitoring system that detects positions of the insertion portion  12  and indicates the shape thereof, and a capturing-image indicating system that captures an endoscopic image at the distal end of the insertion portion  12  and indicates the captured image.  
      The capturing-image indicating system generally includes the imaging device  15  and the light guide  16  that are provided inside the insertion portion  12 , a processor unit  30 , and an image-indicating device (not shown) for representing an image captured by the imaging device  15 . The processor unit  30  supplies illumination light to the light guide  16 , drives the imaging device  15 , and processes the image signals from the imaging device  15 .  
      On the other hand, the insertion-portion-shape monitoring system generally includes the plurality of coils S 1 -Sn, which are used as a magnetic sensor and are provided inside the insertion portion  12  of the endoscope, an insertion-portion-shape monitoring unit  40 , an image-indicating device  41  for indicating the shape of the insertion portion  12 , and a magnetic field generator  42 .  
      In the present embodiment, the processor unit  30  and the insertion-portion-shape monitoring unit  40  are provided inside the processor apparatus to which the connector  13 A (see  FIG. 1 ) is detachably attached. Namely, the signal wires of the imaging device  15 , the light guide cable  16 , and the signal wires of the coils S 1 -Sn lead to the processor apparatus via the light guide cable  13  and the connector  13 A.  
      The light guide  16  and the signal wires of the imaging device  15  are connected to the processor unit  30 , provided inside the processor apparatus. The imaging device  15  is driven by an imaging device driver  300 , provided inside the processor unit  30 , and the image signals from the imaging device  15  are fed to a pre-signal processing circuit  301  of the processor unit  30 .  
      The image signals that are subjected to predetermined image-signal processes at the pre-signal processing circuit  301  are temporarily stored in an image memory  302 , and then successively fed to a latter signal processing circuit  303 . At the latter signal processing circuit  303 , the image signals are subjected to predetermined image-signal processes, and then the image signals are encoded as video signals. The video signals are fed to an output device, such as the image-indicating device.  
      Note that the imaging device driver  300  and the image memory  302  are driven by control signals from a timing controller  304 , and a system controller  305  controls the timing controller  304 .  
      Further, the imaging device  15  captures images inside the body, while emitting illumination light from the light guide  16 . The illumination light is supplied from the light source unit inside the processor apparatus to the light guide  16 . The light source unit includes a lamp  306 , and white light from the lamp  306  is concentrated upon the end face of the light guide  16 , which is inserted inside the processor apparatus, via a shutter  307  and a condenser lens  308 .  
      The lamp  306  receives electric power from a lamp power source  309 . A motor  310  that is controlled by a motor driver  311  drives the shutter  307 . The lamp power source  309  and the motor driver  311  are controlled by the system controller  305 .  
      Note that the system controller  305  is connected to a front panel  312 , which includes switches that are operated by a user. The system controller  305  is able to change various types of preset parameters and modes according to operations of the switches on the front panel  312 .  
      Further, a ROM  130  is provided inside the connector  13 A of the electronic endoscope  10 . When the connector  13 A is attached to the processor apparatus, the ROM  130  is connected to the system controller  305 , so that electronic endoscope identification information stored in the ROM  130  is transmitted to the system controller  305 . Namely, the ROM  130  stores information relating to the electronic endoscope  10 , such as the type of the scope and parameters used in the image processing and the information acquired by the system controller  305 .  
      On the other hand, the signals from the coils (magnetic sensors) S 1 -Sn are amplified by a predetermined gain, and converted from analog signals to digital signals at an amplifier A/D  400 . The signals of the coils S 1 -Sn, is which are converted to digital signals at the amplifier A/D  400 , are input to a microprocessor  401 , and the position of each coil S 1 -Sn is calculated.  
      Image data for representing the entire shape of the insertion portion  12  are generated at an image-indicating controller  402 , based on the positions of the coils S 1 -Sn, which are calculated by the microprocessor  401 , and output to the image-indicating device  41 . The image data may represent the shape of the insertion portion  12  by using an interpolation curve line that connects the positions of the coils S 1 -Sn.  
      The positions of the coils S 1 -Sn are obtained by detecting the effects of electromagnetic interactions to the coils S 1 -Sn, where the effects are induced by the alternating magnetic field. For example, as is known in the art, the magnetic field generator  42  generates alternating magnetic fields in turn for each of the X, Y, and Z coordinates of an orthogonal coordinate system XYZ. The magnetic field generator  42  is controlled by a magnetic field generator driver  403 . Further, the microprocessor  401 , the image-indicating controller  402 , and the magnetic field generator driver  403  are controlled by the timing controller  404 .  
      As described above, according to the first embodiment of the present invention, the rigid sections are disposed in the flexible portion, where the magnetic sensor coils are disposed, and each coil is provided inside the rigid sections. Thereby, the coils are released from the stresses induced by the bending of the flexible portion; thus, the durability of the coils is improved.  
      Further, in the first embodiment, the width required for each rigid section is reduced by arranging the magnetic sensor coils in the plane perpendicular to the central axis of the insertion portion. Thereby, the rigid sections can be provided for the flexible portion without decreasing the flexibility.  
      Next, with reference to  FIG. 5 , a second embodiment of the present invention is explained below. Although the structures of the second embodiment are dissimilar from those of the first embodiment in the aspect of mounting the magnetic sensor coils on the insertion portion, the remaining structures are the same as those in the first embodiment. The explanations will only be given for the dissimilar structures. Note that  FIG. 5  schematically illustrates the structures of the insertion portion, which is wound with a spiral band member.  
      As described in the previous part of this specification, the insertion portion  12 , including the flexible part, is wound with the spiral band member that forms a flexible tube. The spiral band member  50  is configured from a long band member, which is helically wound. The spiral band member  50  has a certain degree of rigidity in the lateral direction of the band, so that the insertion portion is bent or curved by a continuous subtle twist along the longitudinal direction of the band.  
      In the prior art, the magnetic sensor coils S 2 -Sn are disposed inside the flexible portion  12 A, separate from the spiral band member  50 , so that the coils S 2 -Sn may be arranged between neighboring band sections, or may come into contact with the other members provided inside the flexible tube or the spiral band member  50 ; thus, the coils S 2 -Sn can be affected by bending stress induced when the flexible portion  12 A is bent. Further, the signal wires are connected to the coils S 2 -Sn, while the distances between each of the coils S 2 -Sn varies according to the manner of bending of the flexible portion  12 A, so that the signal wires may be subjected to tensile stress when the insertion portion  12 A is bent.  
      Therefore, in the second embodiment, as shown in  FIG. 5 , the magnetic sensor coils S 1 -Sn are integrally provided on the spiral band member  50 , and the signal wires  51  are wired along the spiral band member  50 . For example, coils S 1 -Sn and the signal wires  51  are previously attached to the spiral hand member  50  and integrated thereto. The flexible tube of the insertion portion  12  is configured by spirally winding the spiral band member  50 , in which the coils S 1 -Sn are integrally provided. The coils S 1 -Sn may be arranged in the lateral direction of the spiral band member  50 .  
      As described above, according to the second embodiment, the magnetic sensor coils and the signal wires are released from the stress induced by the flexible portion&#39;s bending; thus, the durability is improved as well as in the first embodiment.  
      With reference to  FIGS. 6-14 , the processes for indicating the shape of the insertion portion are described below.  
       FIGS. 6 and 7  schematically illustrate the shapes of the endoscope insertion portion  12  around the distal end portion, when the angle lever  11 A is operated and the bendable portion  12 B is bent.  FIG. 6  indicates a situation where the bendable portion  12 B is slightly bent.  FIG. 7  indicates a situation where the bendable portion  12 B is bent in which the end face of the distal end portion  12 C is turned around approximately 180 degrees.  
      In the present embodiment, the coil S 1  (the first magnetic sensor) is provided in the distal end portion  12 C of the insertion portion  12 . The coil S 2  (the second magnetic sensor) is disposed at an end of the bendable portion  12 B, on the side close to the operational portion  11 . Further, the coil S 2  is separated from the coil S 1  by a distance “B” along the axis. As it is described in the first and the second embodiments, the coils S 3 , . . . , Sn are successively arranged at the predetermined intervals A, from the side of the coils S 2  to the side of the operational portion  11 .  
      In the insertion-portion shape-indicating process, the shape of the insertion portion  12  is reproduced on the screen of the image-indicating device  41  by connecting the points P 1 -Pn that correspond to the positions of the coils S 1 -Sn, where the positions are obtained by using the alternative magnetic field. In  FIG. 8 , an example of image representation where the points P 1 -Pn are connected by segments (a linear interpolation) is illustrated. In  FIG. 9 , an example of image representation where the points P 1 -Pn are connected or fitted by a Bézier curve or a spline curve is illustrated.  
      However, the structures of the bendable portion  12 B are generally different from those of the flexible portion  12 A. Further, the way force acts on the bendable portion  12 B is also different from the way that force acts on the flexible portion  12 A, since the bendable portion  12 B is affected by the force of the angle wires. Therefore, the manner of bending of the bendable portion  12 B is quite different from that of the flexible portion  12 A, so that if the same interpolation method were used for the flexible portion  12 A and for the bendable portion  12 B, in the conventional way, the reproduced shape of the bendable portion  12 B could be quite different from the actual shape.  
      For example, as shown in  FIG. 10 , the flexible portion  12 A is structured by a spiral band member  123 , while the bendable portion  12 B is structured by a plurality of bending frame links  121 . Each of the neighboring bending frame links  121  is connected together with a hinge section  122 , whereby to configure the bendable structure. Further, as an example, another structure of the bendable portion  12 B is schematically shown in  FIG. 11 . In the example of  FIG. 11 , the bendable portion  12 B includes two types of bending frame links  121 A and  121 B. In the example of  FIG. 11 , the bending frame links  121 A, which have a narrower width than that of the bending frame links  121 B, are arranged on the distal end side of the bendable portion  12 B. Therefore, the distal end side of the bendable portion  12 B can be bent by a relatively large curvature compared to the flexible portion side.  
      From the structures indicated in  FIGS. 10 and 11 , the curvature of the bendable portion  12 B when the bendable portion  12 B is factitiously bent by an operation of the angle lever  11 A, is significantly larger than the curvature of the flexible portion  12 A, which is due to a free bend. Further, the manner of bending of the bendable portion  12 B is also quite dissimilar from that of the flexible portion  12 A. For example, as shown in  FIG. 12 , when the bendable portion  12 B is bent, the bendable portion  12 B includes a plurality of curvatures, whose values are different from one another. Therefore, it is difficult to precisely represent the shape of the bendable portion  12 B by applying the same method as used in the representation of the flexible portion  12 A.  
      Referring to  FIG. 13 , the positions of the points P 1 -P 4  and the representation of the linear interpolation thereof, when the bendable portion  12 B is bent in a narrow arc, are indicated. Namely, the reproduced shape of the insertion portion  12 , which is represented by the linear interpolation (where the points P 1 -P 4  are connected by the segments), is described by the solid line Ls. On the other hand, the actual shape of the insertion portion  12  is described by the phantom line Lb.  
      As shown in  FIG. 13 , since the flexible portion  12 A forms a gentle curve when it is bent, the reproduced shape (Ls) approximates the actual shape (Lb) for the intervals between the points P 2 -P 4  that correspond to the flexible portion  12 A. However, for the interval between the point P 1  and the point P 2  that corresponds to the bendable portion  12 B, the reproduced shape is far from the actual shape. As an example of an extreme case,  FIG. 13  represents the linear interpolation case. However, even by applying a Bézier curve or a spline curve for the interpolation, it would be difficult suitably to represent the shape of the bendable portion  12 B when the bendable portion  12 B is bent in a narrow arc, if the same interpolation method were used to represent the flexible portion  12 A and the bendable portion  12 B.  
      In order to reproduce the shape of the bendable portion  12 B accurately, a plurality of magnetic sensor coils may be disposed inside the bendable portion  12 B. However, a bending operation due to the manipulation of the angle lever  11 A would be obstructed if a coil were disposed inside the bendable portion  12 B, and the coil could also be damaged or destroyed. Accordingly, in the present embodiments, the coil S 1  and the coil S 2  are disposed on both ends of the bendable portion  12 B.  
      In general, the bending properties of the bendable portion  12 B are specific for each product. The actual shapes of the bendable portion  12 B in several bending situations, and relations of the positions between the point P 1  and the point P 2  in each of the bending situations are schematically illustrated in  FIG. 14 . In  FIG. 14 , nine types of bending situations of the bendable portion  12 B are illustrated in stages from the non-bending situation to the situation where the bendable portion  12 B is approximately turned around in the opposite direction.  
      The positions of the point P 1  in each of the above nine bending situations are represented by P 1 ( 0 )-P 1 ( 8 ). Further, the direction of the distal end portion  12 C when the bendable portion  12 B is being bent is represented by an angle “θ”, where the angle “θ” represents an angle against the direction of the distal end portion  12 C, when the bendable portion  12 B is directed straight forward and is not bent. Thus, the bending situation is represented by the angle “θ”. Namely, when the bendable portion  12 B is not bent and the point P 1  is positioned at P 1 ( 0 ), the angle θ=0°. Further, when the bendable portion  12 B is bent such that the distal end portion  12 C faces the opposite direction, and when the point P 1  is positioned at P 1 ( 8 ), the angle θ=180°. Moreover, the angles “θ” for each of the positions P 1 ( 0 )-P 1 ( 8 ) are represented by θ 0 -θ 8 .  
      In general, the distance “D” between the point P 1  and the point P 2  and the angle “θ” have a one-to-one correspondence (i.e., D=D(θ), θ=D −1 (D)). Further, when the distal end portion  12 C is directed in a certain direction “θ”, the bendable portion  12 B generally describes the same shape. Therefore, when the distance “D” is determined from the positions of the points P 1  and P 2 , the shape of the bendable portion  12 B can be determined.  
      In the present embodiments, information representing the correspondence between the distance “D” (the relative distance between the points P 1  and P 2 ) and the shape of the bendable portion  12 B is stored in a memory, such as the ROM  130  (see  FIG. 4 ), as bendable-portion shape data. Note that the shapes of the bendable portion  12 B that correspond to the distances “D” are measured before hand. Examples of the bendable-portion shape data are shown in Table 1.  
                                                                      P1 (0)   X1, Y1, Z1   X2, Y2, Z2   X3, Y3, Z3   X4, Y4, Z4   X5, Y5, Z5   X6, Y6, Z6   X7, Y7, Z7   X8, Y8, Z8   X9, Y9, Z9       P1 (1)   X1, Y1, Z1   X2, Y2, Z2   X3, Y3, Z3   X4, Y4, Z4   X5, Y5, Z5   X6, Y6, Z6   X7, Y7, Z7   X8, Y8, Z8   X9, Y9, Z9       P1 (2)   X1, Y1, Z1   X2, Y2, Z2   X3, Y3, Z3   X4, Y4, Z4   X5, Y5, Z5   X6, Y6, Z6   X7, Y7, Z7   X8, Y8, Z8   X9, Y9, Z9       P1 (3)   X1, Y1, Z1   X2, Y2, Z2   X3, Y3, Z3   X4, Y4, Z4   X5, Y5, Z5   X6, Y6, Z6   X7, Y7, Z7   X8, Y8, Z8   X9, Y9, Z9       P1 (4)   X1, Y1, Z1   X2, Y2, Z2   X3, Y3, Z3   X4, Y4, Z4   X5, Y5, Z5   X6, Y6, Z6   X7, Y7, Z7   X8, Y8, Z8   X9, Y9, Z9       P1 (5)   X1, Y1, Z1   X2, Y2, Z2   X3, Y3, Z3   X4, Y4, Z4   X5, Y5, Z5   X6, Y6, Z6   X7, Y7, Z7   X8, Y8, Z8   X9, Y9, Z9       P1 (6)   X1, Y1, Z1   X2, Y2, Z2   X3, Y3, Z3   X4, Y4, Z4   X5, Y5, Z5   X6, Y6, Z6   X7, Y7, Z7   X8, Y8, Z8   X9, Y9, Z9       P1 (7)   X1, Y1, Z1   X2, Y2, Z2   X3, Y3, Z3   X4, Y4, Z4   X5, Y5, Z5   X6, Y6, Z6   X7, Y7, Z7   X8, Y8, Z8   X9, Y9, Z9       P1 (8)   X1, Y1, Z1   X2, Y2, Z2   X3, Y3, Z3   X4, Y4, Z4   X5, Y5, Z5   X6, Y6, Z6   X7, Y7, Z7   X8, Y8, Z8   X9, Y9, Z9                  
 
      As shown in Table 1, the bendable-portion shape data, for example, include coordinates (x, y, z) of positions that are allocated along the central axis of the bendable portion  12 B per a predetermined interval for each of the relative positions P 1 ( 0 )-P 1 ( 8 ). As for the examples shown in Table 1, the positional coordinate data for the bendable portion  12 B between the points P 1  and P 2  are given so as the interval between the points P 1  and P 2  is evenly divided into ten intervals. For each of the points P 1 ( 0 )-P 1 ( 8 ), nine positional coordinate data (X 1 , Y 1 , Z 1 )-(X 9 , Y 9 , Z 9 ) are stored. The correspondence between the positional coordinate data (X 1 , Y 1 , Z 1 )-(X 9 , Y 9 , Z 9 ) and the bendable portion  12 B is schematically illustrated in  FIG. 15  for the situations where the point P 1  is positioned at P 1 ( 0 ), P 1 ( 4 ), and P 1 ( 8 ).  
      As mentioned above, when the distance “D” is calculated, the position of the point P 1  with respect to the point P 2  is uniquely determined (the degree of freedom about the axis is not considered). Thereby, one of the positions P 1 ( 0 )-P 1 ( 8 ) is selected in accordance with the determination, and the shape of the bendable portion  12 B is reproduced based on the positional coordinate data (X 1 , Y 1 , Z 1 )-(X 9 , Y 9 , Z 9 ) corresponding to the selected position.  
      The bendable-portion shape data in the present embodiments can be positional information relating to any predetermined positions between the points P 1  and P 2 , and the information may also include a curvature of the bendable portion  12 B for each situation. Further, an interpolation function or parameters thereof may also be used for reproducing the shape of the bendable portion  12 B, so that the information of the interpolation function and the parameters may be stored in the memory for each of the distances “D”. Moreover, any combinations of the above methods may also be adopted.  
      Namely, in the insertion-portion shape-indicating process of the present embodiments, different interpolation methods are applied for each of the bendable portion  12 B and the flexible portion  12 A, so that the entire shape of the insertion portion  12  is represented by the combination thereof. Namely, as for the flexible portion  12 A, each position of the coils is connected together with a Bézier curve or a spline curve, in the same way as conventionally. On the other hand, as for the bendable portion  12 B and the distal end portion  12 C, the shape is represented by the interpolation based on the given insertion-portion shape data and the relative positional relationship between the coils S 1  and S 2 , which are provided on both ends of the bendable portion  12 B, such as on the flexible portion  12 A side and on the distal end portion  12 C side.  
      Note that, when the Bézier curve or the spline curve is used for representing the flexible portion  12 A, a control point for the point P 2  of the interpolation curve of the flexible portion  12 A is determined from the geometrical parameters, such as for the tangential line and the curvature, selected for the bendable portion  12 B.  
      As described above, according to the present embodiment, in addition to the effects mentioned in the first and second embodiments, the shape of the bendable portion can be more accurately represented by a simple structure; thereby, the entire shape of the insertion portion can be reproduced accurately.  
      Further, in the present embodiments, the situations of the bendable portion is assumed to be uniquely determined by the distance between the coils S 1  and S 2 , so that only the above distance is used to determine the condition or shape of the bendable portion, and the corresponding bendable-portion shape data are referenced. However, the directions of the coils may also be used for determining the situation of the bendable portion, if differences among the above distances are not sufficient to determine the situation.  
      In the present embodiment, the alternating magnetic field is generated outside the endoscope, by the magnetic field generator disposed outside an inspection object, and the coils and the magnetic sensors are disposed inside the insertion portion. However, the coils for generating a magnetic field can be disposed inside the insertion portion, and magnetic sensors can be disposed outside the insertion portion.  
      Although the embodiments of the present invention have been described herein with reference to the accompanying drawings, obviously many modifications and changes may be made by those skilled in this art without departing from the scope of the invention.  
      The present disclosure relates to subject matter contained in Japanese Patent Application No. 2005-324533 (filed on Nov. 9, 2005), which is expressly incorporated herein, by reference, in its entirety.