Patent Publication Number: US-2007106114-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 magnetic sensor coils are disposed along the longitudinal direction of the flexible tube, and the three-dimensional position and the 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.  
      The insertion portion of the endoscope generally includes a bendable portion that is connected with a distal end portion, and a flexible portion that connects the bendable portion with an operating portion. The bendable portion is a portion that is bent in connection with an operation of an angle lever provided on the operating portion. On the other hand, the flexible portion is a portion that is flexibly bended.  
      As schematically illustrated in  FIG. 11 , the flexible portion  120 A is structured from a spiral band member  123 , which forms a flexible tube, and the bendable portion  120 B is structured from a plurality of bending frame links  121 . Each of the neighboring bending frame links  121  is connected together with a hinge section  122 , whereby the bendable portion  120 B is structured so as to be bendable. Further, an alternative structure of the bendable portion  120 B′ is schematically shown in  FIG. 12 . In the example of  FIG. 12 , the bendable portion  120 B′ includes two types of bending frame links  121 A and  1218 . In  FIG. 12 , the bending frame links  121 A, which have a narrower width than those of the bending frame links  121 B, are applied to the distal end side of the bendable portion  120 B′. Therefore, the distal end side of the bendable portion  120 B′ can be bent in a wide arc compared to the flexible portion side.  
      From the structures indicated in  FIGS. 11 and 12 , the curvatures of the bendable portions  120 B and  120 B′ when the bendable portions  120 B and  120 B′ are factitiously bent by an operation of the angle lever  11 A are significantly larger than the curvature of the flexible portion  120 A, which is due to a flexible bend. Further, the bending manners of the bendable portions  1208  and  120 B′ are also quite dissimilar from that of the flexible portion  120 A. For example, as shown in  FIG. 13 , when the bendable portion  120 B ( 120 B′) is bent, the bendable portion  120 B ( 120 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 portions  120 B or  120 B′ by applying the same method as used in the representation of the flexible portion  120 A.  
      For the above problems, a system that increases the number of the coils provided on the bendable portion, and densely disposes the coils therein, is provided, so that the shape of the bendable portion is precisely represented.  
     SUMMARY OF THE INVENTION  
      However, when a large number of the coils are provided inside the bendable portion, the permissible range of the bendable portion&#39;s curvature becomes limited, so that durability of the bendable portion deteriorates. Further, the number of components and the size of the bendable portion increases.  
      Therefore, an object of the present invention is to provide an endoscope-shape monitoring system that is able to reproduce the shape of an insertion portion with a relatively simple structure.  
      According to the present invention, an endoscope-shape monitoring system is provided that is used to grasp the shape of a flexible insertion portion.  
      The endoscope-shape monitoring system includes a position detecting system, the bending determinator, and a bendable-portion-shape reproducing processor.  
      The position detecting system detects positions of both sides of a bendable portion of the insertion portion. The bending determinator determines a bending situation of the bendable portion. The bendable-portion-shape reproducing processor reproduces the shape of the bendable portion in accordance with the positions and the bending situation.  
      According to another aspect of the present invention, an endoscope shape monitoring system that is used to grasp a shape of a flexible insertion portion is provided that includes a distance detector and a memory.  
      The distance detector detects the distance between both ends of a bendable portion of the insertion portion. The memory stores bendable-portion shape data for reproducing the shape of the bendable portion in accordance with the distance. 
    
    
     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 and a bending sensor provided inside an insertion portion, in the first embodiment;  
       FIG. 3  is a block diagram that shows overall electrical structures of the electronic endoscope system of the first embodiment;  
       FIG. 4  indicates a situation where the bendable portion is slightly bent;  
       FIG. 5  indicates a situation where the bendable portion is bent, where the end face of the distal end portion is turned around by approximately 180 degrees;  
       FIG. 6  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. 7  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. 8  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. 9  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;  
       FIG. 10  is a graph that schematically represents the relations between the curvature “ρ” and the resistance “R”, as a example;  
       FIG. 11  schematically illustrates an example of prior art structures of a bendable portion and a flexible portion;  
       FIG. 12  schematically illustrates another example of prior art structures of the bendable portion and the flexible portion;  
       FIG. 13  schematically shows the shape of the prior art bendable portion that is bent by a plurality of curvatures;  
       FIG. 14  schematically illustrates an arrangement of coils and bending sensors provided inside the insertion portion, in a second embodiment;  
       FIG. 15  is a partially magnified view of a cross section of the bending frame link, in a plane perpendicular to the axis of the bending frame link;  
       FIG. 16  is a block diagram that shows overall electrical structures of the electronic endoscope system of the second embodiment;  
       FIG. 17  schematically illustrates positions P 1 -P 5  of the coils S 1 -S 5  and an interpolation curve, when the bendable portion is bent, in which the end face of the distal end portion is turned around by approximately 270 degrees;  
       FIG. 18  schematically illustrates structures of a sensor unit used in the endoscope-shape monitoring system of the third embodiment;  
       FIG. 19  is a block diagram that schematically illustrates the endoscope-shape monitoring system of the third embodiment; and  
       FIG. 20  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 ), PT( 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 for 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 and 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 to 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  is comprised 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 such that the direction of the distal end portion  12 C is rotated by 180 degrees. Further, as will be 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  is a partially magnified view that schematically illustrates the configuration around the bendable portion  12 B of the insertion portion  12 .  
      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  1 SA 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 .  
      Further, a first coil S 1  is provided in the distal end portion  12 C, and a second coil S 2  is provided near the boundary between the bendable portion  12 B and the flexible portion  12 A. In the present embodiment, the second coil S 2  is provided in the flexible portion  12 A at a position near the bendable portion  12 B. A third coil S 3 , a fourth coil S 4 , a fifth coil S 5 , . . . , and an n-th coil Sn, are successively arranged along the axis of the flexible portion  12 A at predetermined intervals “A”, from the side of the coils S 2  to the side of the operating portion  11 . The first coil Si to the n-th coil Sn are used as magnetic sensors. In  FIG. 2 , only the coils S 1 -S 3  are indicated as examples. Further, although the bending frame links, as is present in conventional structures, are not depicted in  FIG. 2 , a suitable bending frame link mechanism is applied to the embodiment.  
      Further, the bendable portion  12 B is provided with a bending sensor  20  that extends along the axis of the bendable portion  12 B from the flexible portion  12 A to the distal end portion  12 C. The bending sensor  20  is a sensor that detects the degree of bending of the bendable portion  12 B. In the present embodiment, a strain gauge is adopted. Note that, one end of the strain gauge  20  is fixed to the end of the flexible portion  12 A, which is connected to the bendable portion  12 B, by a fixing member  20 A, while the other end is fixed to the distal end portion  12 C.  
       FIG. 3  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 an 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 indicating 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 magnetic sensors and 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  16 , the signal wires of the coils S 1 -Sn, and the signal wires of the strain gauge  20  are led to the processor apparatus via the light guide cable  13  (see  FIG. 1 ) 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 is 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 in the pre-signal processing circuit  301  are temporarily stored in an image memory  302 , and are then successively fed to a latter signal processing circuit  303 . In 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 control: ed 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 is acquired by the system controller  305 .  
      For example, signals from the coils (magnetic sensors) S 1 -Sn are fed to a multi-channel A/D converter  400  inside the insertion-portion-shape monitoring unit  40  via a multi-channel amplifier  131 , and amplified by a predetermined gain. Signals from the coils S 1 -Sn, which are converted from analog signals to digital signals at the multi-channel A/D converter  400 , are input to a microprocessor  401 , and the position of each coil S 1 -Sn is calculated.  
      On the other hand, variation in electrical resistance in the strain gauge  20  is detected by a strain gauge circuit  132  that is provided inside the connector  13 A. Signals that represent the variation in resistance are fed to an A/D converter  402  inside the insertion-portion-shape monitoring unit  40 , via a buffer  133  provided inside the connector  13 A. Namely, the signals from the strain gauge  20  are converted to digital signals at the A/D converter  402 , and are then input to the microprocessor  401 .  
      Further, in the present embodiment, an angle lever sensor  11 B for detecting a direction of the angle lever operation (a rotational direction) is provided on the angle lever  11 A, which is mounted on the operating portion  11 . The angle lever sensor  11 B is connected to the microprocessor  401  via signal wires that are wired inside the light guide cable  13  and the connector  13 A, so that the signals that are detected by the angle lever sensor  11 B are input to the microprocessor  401 .  
      Image data for representing the entire shape of the insertion portion  12  are generated at an image-indicating controller  405 , based on the positional data of the coils S 1 -Sn, which are calculated by the microprocessor  401 , the data detected by the strain gauge  20 , and the signal from the angle lever sensor  11 B. The signals of the image data are then fed 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.  
      As is known in the prior art, the positions of the coils S 1 -Sn are obtained by detecting the effects of electromagnetic interactions with the coils S 1 -Sn, where the effects are induced by the alternating magnetic field. For example, 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  405 , and the magnetic field generator driver  403  are all controlled by the timing controller  404 .  
      With reference to  FIGS. 4-9 , the processes for indicating the shape of the insertion portion, in the present embodiment, are described below.  
       FIGS. 4 and 5  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. 4  indicates a situation where the bendable portion  123  is slightly bent.  FIG. 5  indicates a situation where the bendable portion  12 B is bent such that the end face of the distal end portion  12 C is turned around approximately 180 degrees.  
      In the present embodiment, the first coil S 1  is provided in the distal end portion  12 C of the insertion portion  12 . The second coil S 2  is disposed in the flexible portion  12 A, next to the bendable portion  12 B. Further, the second coil S 2  is separated from the coil S 1  by a distance “B” along the axis. In addition, the coils S 3 , . . . ,Sn are successively arranged at the predetermined intervals “A”, from the side of the coil S 2  to the side of the operating 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. 6 , an example of image indication where the points P 1 -Pn are connected by segments (a linear interpolation) is illustrated. In  FIG. 7 , an example of image indication 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  123  are generally different from those of the flexible portion  12 A. Further, the way force acts on the bendable portion  123  is also different from the way 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 the bendable portion  12 B, as is done conventionally, the reproduced shape of the bendable portion  123  could result in a quite different shape from the actual shape.  
      Referring to  FIG. 8 , 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 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. 8 , 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. 8  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  128 .  
      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 embodiment, the coil S 1  and the coil  32  are disposed on both ends of the bendable portion  123 , and the strain gauge  20  is disposed in 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  123  in several bending situations, and the relation of the positions between the point P 1  and the point P 2  in each of the bending situations, are schematically illustrated in  FIG. 9 . In  FIG. 91  nine types of bending situations of the bendable portion  12 B are illustrated in stages from the non-bending situation to the situation when the bendable portion  12 B is approximately turned around in the opposite direction.  
      In  FIG. 9 , 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 troll 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 in 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 .  
      For example, if the curvature of the bendable portion  123 , the positions of the points P 1  and P 2 , and the direction in which the bendable portion  12 B is bent are all determined, the shape of the bendable portion  12 B can be precisely reproduced. Therefore, in the present embodiment, the positions of the coils S 1  and S 2  (the points P 1  and P 2 ) are calculated as described above, and the curvature of the bendable portion  123  is derived from the data obtained by the strain gauge (the bending sensor)  20 . Further, the bending direction is detected by the signals from the angle lever sensor  11 B provided on the angle lever  11 A, so that the precise shape of the bendable portion  123  is reproduced and indicated.  
      Note that, as is well known in the art, the strain gauge  20  generally is structured such that a resistor element, such as a wire gauge, is attached to a base (a thin plate of electrical insulating material). Namely, deformation of a measurement object is detected by detecting variation in the resistor element&#39;s electrical resistance induced by the deformation.  
      For example, in the present embodiment, the correspondence between the electrical resistance “R” of the strain gauge  20  and the curvature “ρ” of the bendable portion  12 B is measured beforehand, and the information thereof is stored in a ROM  130  (see  FIG. 3 ), which is provided inside the connector  13 A of the electronic endoscope  10 , before shipment. Namely, when the connector  13 A of a certain electronic endoscope is attached to the processor apparatus, the above data are transmitted from the ROM  130 , with the identification number of the endoscope, to the microprocessor  401 .  
       FIG. 10  is an example of a graph that schematically represents the relation between the curvature “ρ” and the electrical resistance “R”. Further, in  FIG. 10 , whether the curvature “ρ”, is positive or negative is determined by a signal from the angle lever sensor  11 B.  
      As described above, according to the first embodiment, the shape of the insertion portion  12  is reproduced by applying the different methods for the bendable portion  12 B and the flexible portion  12 A, respectively, so that the entire shape of the insertion portion  12  is more accurately reproduced 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 way. On the other hand, as for the bendable portion  12 B and the distal end portion  12 C, the shape is reproduced based on the positions of the first and second coils S 1  and S 2  (both end positions of the bendable portion), the bending direction of the bendable portion  12 B is detected by the angle lever sensor  11 B, and the curvature of the bendable portion  12 B is obtained from the data of the strain gauge  20 .  
      Note that, when the Bézier curve or the spline curve is used to represent 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, for the interpolation curve selected for the bendable portion  12 B.  
      As described above, according to the first embodiment, the shape of a bendable portion can be reproduced more precisely with a simple structure, so that the entire shape of the insertion portion can be represented more precisely.  
      Although the number of the bending sensors (e.g., the strain gauges) is one in the first embodiment, the number of the bending sensors may be a plurality.  
      Next, with reference to  FIG. 14  to  FIG. 17 , an endoscope, to which a second embodiment of an endoscope-shape monitoring system of the present invention is applied, is explained below. Although the structures of the second embodiment are dissimilar from those of the first embodiment regarding structures relating to a bending detection, the remaining structures are the same as those in the first embodiment. Therefore, the explanations will mainly be given for the dissimilar structures, and the same reference numerals will be used for the same structures, as those in the first embodiment.  
       FIG. 14  is a partially magnified view that schematically illustrates the configuration around the bendable portion  200  of the insertion portion  12  of the second embodiment.  
      As shown in  FIG. 14 , a ring-shaped rigid section  201  is provided at the boundary between the bendable portion  200  and the flexible portion  12 A. A plurality of bending frame links  202  are provided inside the bendable portion  200 , as is known in the prior art, so that the bending frame links  202  are successively connected with each other from the distal end portion  12 C to the rigid section  201  as a chain.  
      Further, the coil S 1  is provided in the distal end portion  12 C, and the coil S 2  is provided in a bending frame link  202 A (a bending frame link that is hatched in  FIG. 14 ) that is positioned approximately at the midsection of the bendable portion  200 . Further, the coil S 3  is provided in the rigid section  201 . The coils S 4 , S 5 , S 6 , . . . , Sn, are successively arranged along the axis of the flexible portion  12 A at predetermined intervals, from the side of the coils  83  to the side of the operating portion  11 . In  FIG. 14 , only the coils S 1 -S 3  are indicated as an example.  
      In the second embodiment, bending sensors  220  and  221 , which are used to detect a bending state of the bendable portion  200 , are provided inside the bendable portion  200  along the axis thereof. The bending sensors  220  and  221  is are sensors that detect a bending degree of the bendable portion  200 , and in the present embodiment, a strain gauge is used, as in the first embodiment. Note that one end of the strain gauge  220  is fixed to the distal end portion  12 C by a fixing member  220 A, and one end of the strain gauge  221  is fixed to the rigid section  201 .  
      On the other hand, the other end  220 B of the strain gauge  220 , which is on the side opposite from the fixing member  220 A, and the other end  221 B of the strain gauge  221 , which is on the side opposite from the fixing member  221 A, both extend to the bending frame link  202 A. Further, the ends  220 B and  2213  engage with the bending frame link  202 A through a guide member  223 , whereby the ends  220 B and  2212  are only slideable along the axis of the bendable portion  200 .  
      Namely, as shown in  FIGS. 14 and 15 , the guide member  223  that extends along the axis of the bending frame link  202 A is provided on the inner side face of the bending frame link  202 A, whereby movement of the ends  220 B and  221 B other than the movement along the axis of the bendable portion is restricted. On either side of the guide member  202 A, in the longitudinal direction, there is provided an opening into which the corresponding end  220 B or  221 B is inserted. Namely, the ends  220 B or  221 B are each inserted into the corresponding side of the guide member  202 A. Further, in the second embodiment, the ends  220 B and  221 B are separately disposed at a predetermined distance, whereby they do not come into contact with each other. Note that  FIG. 15  is a partially magnified view of a cross section of the bending frame link  202 A, in a plane perpendicular to the axis of the bending frame link  202 A. Namely,  FIG. 15  schematically illustrates the relations between the ends  2203 ,  221 B, and the guide member  223 .  
       FIG. 16  is a block diagram that shows the electrical structure of the electronic endoscope system of the second embodiment.  
      Signals from the magnetic sensor coils S 1 -Sn are fed to a signal selector  234  that is provided inside the connector  13 A (see  FIG. 1 ) via the multi-channel amplifier  131 . Further, variations in the electrical resistance of the strain gauges  220  and  221  are detected by strain gauge circuits  232  and  233  that may be provided inside the connector  13 A. The signals from the strain gauge circuits  232  and  233  are then fed to the signal selector  234  as well as the signals from the coils S 1 -Sn. Further, signals from the angle lever sensor  111  are also fed to the signal selector  234 , inside the connector  13 A, via the light guide cable  13  (see  FIG. 1 ).  
      The signals selector  234  is a circuit that is for selectively outputting the signals from the coils S 1 -Sn, the signals from the strain gauges  220  and  221 , and the signals from the angle lever sensor  11 B, in a predetermined sequence. The signals output from the signal selector  234  are then fed to the A/D converter  400  inside the insertion-portion-shape monitoring unit  40 , so that the signals are converted from analog signals to digital signals and then input to the microprocessor  401 . The selection of signals that are output from the signal selector  234 , and the timing of switching the selection, are controlled by control signals from the microprocessor  401  of the insertion-portion-shape monitoring unit  40 .  
      In the microprocessor  401 , the positions of the coils S 1 -Sn are calculated from the signals from the coils S 1 -Sn, as in the first embodiment. Further, the degree of strain generated in the strain gauges  220  and  221  is calculated based on the signals from the strain gauges  220  and  221 .  
      Image data for representing the entire shape of the insertion portion  12  are generated at an image-indicating controller  402 , based on the positional data of the coils S 1 -Sn, which are calculated by the microprocessor  401 , the data detected by the strain gauges  220  and  221 , and the signal from the angle lever sensor  11 B. The signals of the image data are then fed to the image-indicating device  41 , and the shape of the insertion portion  12  is represented on the image-indicating device  41  in the same way as in the first embodiment.  
       FIG. 17  schematically illustrates positions P 1 -P 5  of the coils S 1 -S 5  and an interpolation curve suitably applied to the positions PI-P 5 , when the angle lever  11 A is operated and the bendable portion  200  is bent in a narrow arc, such that end face of the distal and portion  12 C is turned around by approximately 270 degrees.  
      In  FIG. 17 , sections that correspond to the bendable portion  200  are indicated by a solid line, and sections that correspond to the flexible portion  12 A are indicated by a phantom line. As described in the first embodiment, the flexible portion  12 A can be accurately represented by connecting the points P 3 -Pn, which correspond to the flexible portion  12 A, with a Bézier curve or a spline curve, while the bendable portion  200  cannot be appropriately represented in the same way.  
      In the second embodiment, positions of both ends of the bendable portion  200  and at least one position of a point within the bendable portion  200  are detected. Further, the degree of bending, which is defined in intervals between the above-detected points for each section is detected per section. Based on the above positional data and bending information, the shape of the bendable portion  200  is more precisely determined, and the precise shape of the bendable portion  200  is represented by the image-indicating device  41 , as shown in  FIG. 17 .  
      Note that the bending properties of the bendable portion  200  are usually specific for each product. Therefore, in the second embodiment, correspondences between the output from the strain gauges  220  and  221  and information that represents the bending shape of the corresponding section, such as the curvature, are stored in the ROM  130  for each endoscope, for example, in a lookup table.  
      In the microprocessor  401 , the degree of bending of each section, such as the curvature, is obtained by signals from the strain gauges  220  and  221 , based on data stored in the ROM  130 . Namely, the curvatures of the sections S 1 -S 2  and S 2 -S 3  of the bendable portion  200 , the positions of the points P 1 , P 2 , and P 3 , and the bending direction of the bendable portion  200  are determined, so that the shape of the bendable portion  200  can be reproduced accurately.  
      As in the first embodiment, the correspondence between the electrical resistance R of the strain gauges  220  and  221  and the curvature ρ of the bendable portion  200  are measured beforehand, and the information thereof is stored in the ROM  130  before shipment.  
      As described above, according to the second embodiment, the same effect as in the first embodiment is  15  obtained. Further, in the second embodiment, since the plurality of bending sensors and at least one position within the bendable portion are detected, the shape of the bendable portion can be more precisely determined.  
      Note that in the second embodiment, the number of coils provided within the bendable portion may also be a plurality. Further, the number of bending sensors (strain gauges) may also be greater than two.  
      In the first and second embodiments, although the correspondence between the electrical resistances of the strain gauges and the curvatures is provided in a memory inside the endoscope connector, it may also be stored in the memory provided inside the processor apparatus or a computer system combined with the endoscope system. In such a case, the data may be stored in the memory based on the type (for every model number) of the endoscope. The model numbers of the endoscope may be listed on the screen, and the data may be obtained by selecting a corresponding model number from the list. Further, the model number may be stored in the memory of the endoscope, and the data, which correspond to the model number, may be automatically selected from the memory provided on a device other than the endoscope.  
      Next, with reference to  FIGS. 18-20 , a third embodiment of the endoscope-shape monitoring system of the present invention is explained below. The explanations will mainly be given for the structures that are dissimilar from the first and second embodiments. Further, the same reference numerals will be used for the same structures, as those in the first and second embodiments.  
       FIG. 18  schematically illustrates structures of a sensor unit used in the endoscope-shape monitoring system of the third embodiment.  
      In the third embodiment, the sensor unit is formed as a detachable type unit. The sensor unit  500  comprises a flexible tube  21  and a connector  22  that is attached on a proximal end of the flexible tube  21 .  
      For example, the length of the flexible tube  21  is approximately equal to the sum of the length of an insertion portion  12 , of an endoscope and the length of the light guide cable  13  (see  FIG. 13 . The distal end  21 A of the flexible tube  21  is inserted into an instrument channel of the endoscope through the instrument channel opening  11 C (see  FIG. 1 ), so that the distal end  21 A of the flexible tube  21  is arranged at the distal end of the instrument-channel, which is positioned in the distal end portion  12 C of the endoscope.  
      Here, the instrument-channel is a conduit that is formed inside the insertion portion  12 ′, from the operating portion  11  to the distal end portion  12 C. Namely, the instrument channel opening  11 C is provided on the operating portion  11 .  
      The first coil S 1  is provided on the distal end  21 A of the flexible tube  21 . The second coil S 2  is disposed inside the flexible tube  21  at a position separated from the coil  31  by a distance “B” along the axis of the flexible tube  21 . Further, the coils S 3 , S 4 , S 5 , . . . , Sn are successively arranged at the predetermined intervals A, from the side of the coils S 2  to the side of the connector  22 . The coils S 1 -Sn are electrically connected to the connector  22 .  
       FIG. 19  is a block diagram that schematically illustrates the endoscope-shape monitoring system of the third embodiment. The endoscope-shape monitoring system of the third embodiment comprises the detachable sensor unit  500 , a position detector  23  (corresponding to the insertion-portion-shape monitoring unit  40 ), the magnetic field generator  42 , and the image-indicating device  41  In  FIG. 19 , the flexible tube  21  of the detachable sensor unit  500  is suitably installed in the instrument channel of the endoscope. Namely, the detachable sensor unit  500  is inserted into the instrument channel  14  of the insertion portion  12 ′ through the instrument channel opening  11 C, and the distal end of the flexible tube  21  is positioned at the distal end portion  12 C of the insertion portion  12 ′. Therefore, the coil S 1  is disposed at the distal end portion  12 C.  
      In the third embodiment, the distance B is slightly greater than the length of the bendable portion  12 B′, so that when the installation of the sensor unit  500  into the instrument channel completes, the sensor S 1  is disposed at the distal end portion  12 C, the sensor S 2  at the front end of the flexible portion  12 A′, and the sensors S 3 -Sn in the flexible portion  12 A′.  
      The connector  22  of the sensor unit  500  is detachably connected to the position detector  23 . Signals from the coils S 1 -Sn of the sensor unit  500  are fed to a signal processor  24  inside the position detector  23 . At the signal processor  24 , the signals from the coils S 1 -Sn are subjected to amplification, detection, and A/D conversion, and are fed to the microprocessor  401  of the position detector  23 , Further, a non-volatile memory  22 M is provided in the connector  22 . When the connector  22  is attached to the position detector  23 , the memory  22 M is electrically connected to the microprocessor  401 . As is detailed below, data (bendable-portion shape data) that are used for representing the shape of the bendable portion  12 B′, when the insertion-portion shape-indicating process is carried out, are stored in the memory  22 M. The bendable-portion shape data are transmitted from the memory  22 M to the microprocessor  401  when the endoscope-shape monitoring system is powered on, and the connector  22  is attached to the position detector  23 .  
      As shown in  FIG. 9 , 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 in 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 third embodiment, a sensor unit  500  is provided that is adjusted for each endoscope. Information representing the correspondence between the distance IDC, (the relative distance between the points P 1  and P 2 ) and the shape of the bendable portion  12 B′ is stored in the memory  22 M inside the connector  22  of the sensor unit  500 , as bendable-portion shape data. Note that the shapes of the bendable portion  12 B′ that correspond to the distances “D” are measured beforehand and the distance “D” is calculated (determined) by the microprocessor  401  in accordance with the positions of the points P 1  and P 2 . Examples of 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 that 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. 20 , 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 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 may be positional information relating to any predetermined positions between the points P 1  and P 2 , and the information may also include the 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, regarding the flexible portion  12 A′, each position of the coils is represented by a Bézier curve or a spline curve, in the same way as conventionally. On the other hand, regarding 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 to represent 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 third embodiment, in addition to the effects mentioned in the first and second embodiments, the shape of the bendable portion can be accurately obtained without using a bending sensor. Further, since the separate sensor unit, which is detachable from the instrument channel, is used, the system of the third embodiment can be applied for any conventional endoscope.  
      In the third embodiment, the position detector is used to obtain the data for representing the shape of the insertion portion, and the image-indicating device is directly connected to the position detector. However, the positional data of the coils may be transmitted to an external computer system, and the shape of the insertion portion may be represented on a screen of the computer system.  
      Further, in the third embodiment, the situation 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 to determine the situation of the bendable portion, if differences among the above distances are not sufficient to determine the situation.  
      In the third embodiment, although the bendable-portion shape data are stored in the memory inside the connector of the sensor unit, it may also be stored in a memory provided inside the processor apparatus or a computer system combined with the endoscope system. In such a case, the data may be stored in the memory based on the type (for every model number) of the sensor unit or the endoscope. The model numbers of the sensor unit or the endoscope may be listed on the screen, and the data may be obtained by selecting a corresponding model number from the list. Further, the model number may be stored in the memory of the sensor unit, and the bendable-portion shape data, which correspond to the model number, may be automatically selected from a memory provided on a device other than the sensor unit.  
      In the present embodiments, an 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 may be disposed inside the insertion portion, and magnetic sensors may be disposed outside the insertion portion.  
      Although the embodiment of the present invention has 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 Applications Nos. 2005-324805, 2005-325226, and 2005-324935 (each filed on Nov. 9, 2005), which are expressly incorporated herein, by reference, in their entirety.