Patent Publication Number: US-2009227841-A1

Title: Endoscope

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an endoscope for use in medical and other fields, and more specifically, to an endoscope having a bending portion provided near a distal end of an insertion section. 
     As is also well known, an endoscope includes an insertion section to be inserted into the human body, a manipulating section by which the insertion section is manipulated and the endoscope is manipulated for air insufflation/water feeding, a connector (LG—light guide-connector) that is connected to an air insufflation source, a suction pump, etc., and a universal cord (supply hose) for connecting the connector to the manipulating section and the insertion section. 
     As disclosed in JP 11-47082 A, JP 2000-229061 A, JP 2001-346756 A, and the like, a bending portion (angle portion), which can be bent in four directions, up and down and to the right and left, by turning a manipulative knob provided to the manipulating section, is typically provided near the distal end of the insertion section of the endoscope. 
     The bending portion is generally bent by being pulled with wires. Specifically, the bending portion has a configuration in which great number of rings is arrayed and linked in a tubular-form, where each ring is alternately linked to be swingable in the up or down direction and the left or right direction (two orthogonal directions). A total of four wires including a pair of wires spaced apart in the up down direction and a pair of wires spaced apart in the left and right direction, are inserted into the great number of rings, and the distal ends of such wires are fixed to the ring positioned on the most distal end side. 
     With respect to the manipulative knob, an UD (Up Down) knob for bending the bending portion to up or down, and an LR (Left Right) knob for bending the bending portion to left or right are provided to the manipulating section. 
     The basal ends of the two wires spaced apart in the up and down direction inserted to the rings of the bending portion is connected to each other to form one wire, and are wounded around a pulley that integrally rotates with the UD knob. Similarly, the basal ends of the two wires spaced apart in the left and right direction is connected to each other to form one wire, and are wounded around a pulley that integrally rotates with the LR knob. 
     Therefore, by turning the manipulative knob, one of the wires of each pair linked to the ring on the most distal end side of the bending portion is pulled while the other wire is advanced, whereby the bending portion can be bent. The bending portion can be bent to an arbitrary direction, up or down or to the right or left, by manipulating both the UD knob and the LR knob. 
     In the bending portion of the endoscope, the straight state in which the bending portion is not bent is normally set as the neutral point, which means the normal state. 
     Thus, when the manipulative knob is turned to bend the bending portion, the counter force acts so as to return the bending portion to the straight state, and the bending portion automatically returns to the straight state when the hand is released from the manipulative knob. Further, the counter force becomes larger as the amount of bending becomes larger, that is, greater force is required to further manipulate the bend (to turn the manipulative knob). 
     Therefore, the load on doctors, who are operators of the endoscope, becomes very large depending on the type of examinations to be conducted with the endoscope. 
     For instance, as conceptually illustrated in  FIG. 12 , the gastric fundus is examined by rotating the insertion section about its axis with the bending portion being greatly bent. 
     In other words, the doctor who manipulates the endoscope needs to hold the manipulating section having weight and rotate the insertion section while holding the manipulative knob so as not to return against the strong counter force, and thus the load becomes very large. If the doctor carelessly releases the hand from the manipulative knob, the bending portion returns to the straight state at once by the strong counter force, which may damage the human body as the target of examination. 
     In this regard, an endoscope equipped with a so-called brake mechanism for fixing the bending portion in the bent state has been proposed as described in JP 11-47082 A, JP 2000-229061 A, and JP 2001-346756 A. 
     The brake mechanism normally holds the bending portion in the bent state by stopping the turning of the manipulative knob with the frictional force, and puts the manipulative knob into a fixed state in which the manipulative knob does not move at all and a half-braking state in which the bent state of the bending portion is maintained but the angle (amount of bending) of the bending portion can be changed by turning the manipulative knob in accordance with the difference in the frictional force. 
     Therefore, the load of rotating the insertion section while holding the manipulative knob with the hand can be eliminated by using the brake mechanism. However, in order to adjust the angle of the bending portion in a half-brake applied state, the manipulative knob needs to be turned/manipulated with a force beyond the frictional force for maintaining the half-braking state, and thus force is required in the manipulation, and the load on the doctors is still large. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to solve the above-mentioned problem of the conventional technology, that is, for example, to provide an endoscope capable of greatly reducing the load of the operator and allowing easy and safe operation even when the rotation of the insertion section or the adjustment of the amount of bending need to be carried out with the bending portion greatly bent such as in the gastric fundus examination. 
     An endoscope according to a first aspect of the present invention includes an insertion section having a bending portion near its distal end, a state where the bending portion is not bent being set as a neutral point, the endoscope including: a bending mechanism for bending the bending portion; a manipulating section for bending the bending portion through the bending mechanism on the basis of a manipulative force applied by an operator; a driving means that applies a driving force on the bending mechanism; resetting means that inputs an instruction to reset a state where the bending portion is bent as a new neutral point; and control means that controls the driving means so as to maintain the state where the bending portion is bent corresponding to the neutral point reset on the basis of the instruction input by the resetting means. 
     An endoscope according to a second aspect of the present invention includes an insertion section having a bending portion near its distal end, a state where the bending portion is not bent being set as a neutral point, the endoscope including: a bending mechanism for bending the bending portion; a manipulating section for bending the bending portion through the bending mechanism on the basis of a manipulative force applied by an operator; a driving means that applies a driving force on the bending mechanism; a manipulative force detection means that detects a manipulative force applied on the manipulating section by the operator; and a control means that controls, when the manipulative force detected by the manipulative force detection means changes to be zero from a value other than zero, the driving means so as to apply to the bending mechanism a driving force corresponding to the value before the change. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a perspective view showing an entire structure of an endoscope according to a first embodiment of the present invention; 
         FIG. 2  is a partial cross-sectional view illustrating a manipulating section of the endoscope according to the first embodiment; 
         FIG. 3  is a partial cross-sectional view illustrating the manipulating section of the endoscope according to a modification example of the first embodiment; 
         FIG. 4  is a diagram conceptually illustrating the bending mechanism of the angle portion of the endoscope according to the first embodiment; 
         FIG. 5  is a plan view conceptually illustrating the angle portion of the endoscope according to the first embodiment; 
         FIG. 6A  is a diagram describing the resetting of the neutral point of the angle portion in the endoscope according to the first embodiment; 
         FIGS. 6B and 6C  are graphs for describing the manipulation when the neutral point of the angle portion is reset in the endoscope according to the first embodiment, respectively; 
         FIG. 7A  is a diagram for describing a method of resetting the neutral point of the angle portion in the endoscope according to another modification example of the first embodiment; 
         FIG. 7B  is a diagram conceptually illustrating the bending mechanism of the angle portion of the endoscope according to yet another modification example of the first embodiment; 
         FIGS. 8A and 8B  are graphs for describing another example of the operation in the endoscope according to the first embodiment; 
         FIG. 9  is a perspective view illustrating an entire structure of an endoscope according to a second embodiment; 
         FIG. 10  is a view conceptually illustrating the bending mechanism of the angle portion in the endoscope according to the second embodiment; 
         FIG. 11A  is a conceptual view for describing the manipulative force exerted on the manipulative knob of the endoscope according to the second embodiment; 
         FIGS. 11B to 11E  are conceptual views for describing a pseudo-brake in the endoscope according to the second embodiment; and 
         FIG. 12  is a conceptual view for describing the gastric fundus examination by the endoscope. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     On the following pages, an endoscope of the present invention is described in detail with reference to the preferred embodiments illustrated in the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a view illustrating an entire structure of an endoscope  10  according to a first embodiment. The endoscope  10  is inserted into a part such as a body cavity (e.g. digestive tract or ears, nose, or larynx) to be examined and is used to observe the part, take a still or moving picture of the part, or even collect a tissue of the part. 
     The endoscope  10  is basically the same as a known conventional endoscope (endoscopic apparatus) other than that a neutral point resetting function allowing a neutral point of an angle portion  24  (stationary state in which bending is not manipulated with a manipulative knob) to be set to a desired bent state. 
     The endoscope  10  includes an insertion section  12 , a manipulating section  14 , a light guide (LG) connector  16 , and a universal cord  18 . 
     The insertion section  12  is an elongated part that is to be inserted into a part to be examined such as a body cavity, and has a distal end portion  22  at the distal end (distal end which is to be inserted and away from the manipulating section  14 ), the angle portion  24 , and a flexible portion  26 . 
     The distal end portion  22  is provided with a lighting glass for performing illumination with a light guide, air insufflation and water feeding nozzles through which air is typically withdrawn from the part under examination or air or water is fed to the part, and a forceps port through which forceps are inserted into the part under examination, typically to collect a tissue. 
     By way of example, the illustrated endoscope  10  is a so-called electronic scope for photographing the part under examination using an image sensor such as a CCD sensor, in which a photographing objective lens, a CCD sensor, a substrate for processing an image signal of an image photographed by the CCD sensor, and the like are attached to the distal end portion  22 . The endoscope of the present invention is not limited to the electronic scope, and may be a so-called fiber scope with which the part under examination can be directly observed using an optical fiber. In this case, a viewing lens, a viewing window, and the like are attached to the distal end portion  22 . 
     The angle portion (bending portion)  24  is a region which can be bent by manipulating the manipulating knobs (LR knob  36  and UD knob  38 ), to be described later, of the manipulating section  14 , up and down or from right to left and vice versa (in two orthogonal directions) in order to insert the distal end portion  22  into a desired position or locate it in a desired position. 
     The flexible portion  26  is a part that connects the distal end portion  22  and the angle portion  24  to the manipulating section  14 , and is an elongated member that is sufficiently flexible to allow the distal end portion  22  to be inserted into the part to be examined. The flexible portion  26  (and the angle portion  24 ) accommodates a forceps channel (tube) into which forceps are to be inserted, air insufflation and water feeding channels that are to be connected to the air insufflation and water feeding nozzles, a light guide for illuminating the part to be examined, and a cable for transferring an image (image signal) photographed by a CCD sensor. 
     The manipulating section  14  is a part for manipulating the endoscope  10 . The manipulating section  14  is provided with a forceps port  28  through which forceps are to be inserted, a suction button  30  for performing suction through the air insufflation and water feeding nozzles at the distal end portion  22 , and as well as an air insufflation/water feeding button  32  for performing air insufflation and water feeding through the air insufflation and water feeding nozzles at the distal end portion  22 . If the endoscope  10  is an electronic scope, a variety of manipulating means for photographing the part to be examined such as a zooming switch and an imaging switch are attached to the manipulating section  14 . 
     The manipulating section  14  is provided with manipulating knobs (bent manipulating means) for bending the angle portion  24  of the insertion section  12 . Specifically, an LR knob  36  for bending the angle portion  24  to the left or right direction and a UD knob  38  for bending the angle portion  24  up and down in directions perpendicular to the above-mentioned left and right directions are provided in the manipulating section  14 . In the endoscope  10 , the LR knob  36  is turned to bend (flex) the angle portion  24  of the insertion section  12  to left or right direction whereas the UD knob  38  is turned to bend the angle portion  24  up and down (directions perpendicular to the right and left directions). 
     The manipulating section  14  is also provided with an LR brake manipulating section  40  which fixes the angle portion  24  being bent to the left or right direction by manipulating the LR knob  36 , and a UD brake manipulating section  42  which fixes the angle portion  24  being bent up or down by manipulating the UD knob  38 . 
     Furthermore, the manipulating section  14  is provided with a reset switch  44  for resetting the neutral point of the angle portion  24  from the normal straight state to the desired bent state, and a cancel switch  46  for returning the reset neutral point to the stationary straight state. 
     The configuration of the manipulative knob and the brake mechanism of the manipulating section  14 , the configuration of the angle portion  24 , the action of bending, and further, the reset switch  44  and the cancel switch  46  are described in more detail afterwards. 
     The LG connector  16  is a part that connects the endoscope  10  to water feeding means, air insufflation means, suction means, and the like installed in an endoscope processor (not shown), and the connector  16  is provided with a suction connector  50  for connecting the endoscope  10  to the suction means, a water feeding connector for connecting the endoscope  10  to the water feeding means, a ventilating connector for connecting the endoscope  10  to the air insufflation means, and the like. 
     The connector  16  is also provided with an LG rod  52  for connecting the illuminating light guide to a light source to be provided to the endoscope processor, and an S terminal  54  to which an S cord is connected to provide a path for diverting the leakage current to the endoscope  10  in the process of using an RF treating tool (so-called electrical scalpel such as electrical snare or knife). 
     The connector  16  is also connected with a video connector  56 , which connects the endoscope  10  and a video processor for processing and displaying images, and the like photographed by the endoscope  10  (CCD sensor thereof). 
     The universal cord (LG flexible section)  18  is a part that connects the connector  16  to the manipulating section  14 . 
     The lightguide, air insufflation and water feeding channels, etc. extending from the connector  16  pass through the universal cord  18  to be connected to the manipulating section  14 , and the light guide, air insufflation and water feeding channels, etc. extending from the manipulating section  14  pass through the flexible portion  26  of the insertion section  12  to be connected to the distal end portion  22  as described above. 
       FIG. 2  illustrates a configuration of the LR knob  36 , the UD knob  38 , the LR brake manipulating portion  40 , and the UD brake manipulating portion  42  in the manipulating section  14 . The endoscope of the present invention is not limited to such a configuration, and all known configurations used in various types of endoscopes can be used. 
     A housing  60  of the manipulating section  14  has a cylindrical insertion portion  60   a  that is erected to penetrate the wall of the housing  60 , and a substabtially C-shaped fixing portion  60   b  is provided at the lower end of the insertion portion  60   a  (in the inner side end portion of the housing  60 ). 
     The fixing portion  60   b  has a columnar central shaft  62  that is erected to pass through the insertion portion  60   a  to project outward from the housing  60 . 
     A linking tube (rotating shaft)  64  is fixed to the underside of the LR knob  36  and a pulley  68  is fixed to the lower end of the linking tube  64 . Two wires  70  and  72  for bending the angle portion  24  are connected to each other and wounded around the pulley  68  (alternatively, the ends of the wires  70  and  72  are respectively fixed to the pulley  68 ). 
     The wires  70  and  72  are adopted to bend the angle portion  24  to the left or right direction (angle wire/manipulating wire), and are inserted to the angle portion  24  while being spaced apart from each other in the left and right direction by a wire guide and the like, the ends of the wires on the distal end portion  22  side being fixed to a distal end ring  112  of the angle portion  24 , as described later. 
     In the pulley  68 , there is also coaxially formed a gear that rotates by a LR motor  74  for resetting the neutral point in the left and right direction of the angle portion  24 . 
     The linking tube  64  is a cylindrical member, through which the central shaft  62  passes, so as to be rotatably supported about the central shaft  62 . Hence, both the LR knob  36  and the pulley  68  are also supported in a rotatable manner about the central shaft  62 . When the LR knob  36  is turned by the operator, the pulley  68  is rotated by the same amount as that of the LR knob  36  so that any one of the wires  70  and  72  is pulled and the other wire is advanced. 
     The topside of the LR knob  36  is recessed to receive the lower part of the LR brake manipulating portion  40 . Provided on the underside of the LR brake manipulating portion  40  is an LR brake member  76  for locking the LR knob  36  against turning. 
     The LR brake manipulating portion  40  is axially supported in a manner capable of turning with respect to the central shaft  62 . On other hand, the LR brake member  76  is a cylindrical member, through which the central shaft  62  passes, so as to be supported by the central shaft  62  in such a manner that the LR brake member  76  cannot turn with respect to the central shaft  62  but can move along the length of the central shaft  62 . 
     When the LR brake manipulating portion  40  is turned about the central shaft  62 , the LR brake member  76  moves along the length of the central shaft  62  depending on the direction of turning by known means such as a cam mechanism or a screw mechanism. 
     As illustrated in  FIG. 2 , the LR brake member  76  is fully spaced apart from the LR knob  36  when being positioned on the LR brake manipulating portion  40  side. However, when the LR brake member  76  moves along the length of the central shaft  62  according to the turning of the LR brake manipulating portion  40 , the LR brake member  76  is brought into contact with the LR knob  36  to be capable of depressing the LR knob  36 . The LR brake member  76  is supported by the central shaft  62  to be incapable of turning, and hence, if the LR brake member  76  depresses the LR knob  36 , frictional force develops to stop the turning of the LR knob  36 , that is, put a brake on the LR knob  36 . In addition, the LR brake member  76  does not turn with respect to the central shaft  62 , and hence the above-mentioned braking action by no means causes the LR knob  36  to turn. 
     Note here that the LR brake manipulating portion  40  is adapted so as to be capable of adjusting, by controlling the amount of its turning, the force by which the LR brake member  76  depresses the LR knob  36 , and the brake being exerted upon the LR knob  36  can take a fixed state or a half-braking state. 
     The fixed state is a state in which the LR brake member  76  depresses the LR knob  36  with such a great force that the LR knob  36  is incapable of turning. In contrast, the half-braking state is a state in which the LR knob  36  is sufficiently depressed with the LR brake member  76  to be prevented from automatic turning due to the counter force of the bent angle portion  24  but it is actually possible to turn the LR knob  36  though turning of the LR knob  36  requires an increased power due to the frictional force. 
     The LR motor  74  is fixed to the housing  60  of the manipulating section  14  by a stay (not shown) or the like, and a gear  78  is attached to the rotating shaft of the LR motor  74 . A gear  80  is axially supported on the housing  60 , and the gear  80  meshes with the gear  78  and the gear formed on the pulley  68 . 
     Consequently, when the LR motor  74  is driven, the rotating force is transmitted to the pulley  68 , thereby pulling one of the wires  70  and  72  and advancing the other wire, and bending the angle portion  24  to the left or right direction. In addition, the angle portion  24  can be held in the bent state by exerting torque on the pulley  68 . Further, the LR knob  36  that is directly coupled to the pulley  68  also turns by driving the LR motor  74 . 
     The manipulation of the LR knob  36  that is coupled to the pulley  68  through an intermediation of the linking tube  64 , namely, the manipulation of the bending of the angle portion  24  to the left or right direction can be assisted. 
     The UD knob  38  is provided between the LR knob  36  and the housing  60 . The UD knob  38  has a recess formed on its underside, in which the linking tube (rotating shaft)  84  is fixed to the ceiling of the recess and the pulley  86  is fixed to the lower end of the linking tube  84 . The pulley  86  has two wires  88  and  90  wounded thereto, the wires being connected to the angle portion  24  so as to pull the angle portion  24  thereby to bend the same up and down (alternatively, the ends of the wires  88  and  90  are respectively fixed to the pulley  86 ). The wires  88  and  90  are provided to bend the angle portion  24  up and down, and are inserted to the angle portion  24  while being spaced apart in the up and down direction by the wire guide, the ends of the wires  88  and  90  on the distal end portion  22  side being fixed to the distal end ring  112  of the angle portion  24 . 
     In the pulley  86 , there is also coaxially formed a gear that rotates by a UD motor  92  for assisting the bending of the angle portion  24  in the up and down direction. 
     The linking tube  84  is a cylindrical member inserted into the insertion portion  60   a  of the housing  60 , in which the linking tube  64  fixed to the LR knob  36  passes through the linking tube  84  such that the linking tube  84  is axially supported by the linking tube  64  in a rotatable manner. The pulley  86  at the lower end of the linking tube  84  is located on top of the pulley  68  at the lower end of the linking tube  64  fixed to the LR knob  36 . 
     Hence, both the UD knob  38  and the pulley  86  are supported in a rotatable manner about the linking tube  64 . When the UD knob  38  is turned by the operator, the pulley  86  is rotated by the same amount as that of the UD knob  38  so that one of the wires  88  and  90  is pulled and the other wire is advanced. 
     As described above, the linking tube  64  and the LR knob  36  rotate about the central shaft  62 . As a result, the linking tube  84  and the UD knob  38  also rotate about the central shaft  62 , and hence the LR knob  36  and the UD knob  38  that cause the angle portion  24  to bend rotate coaxially with each other. 
     The UD brake manipulating portion  42  is formed of a manipulating lever  42   a  and a cylindrical portion  42   b.  The cylindrical portion  42   b  is a cylindrical member through which the insertion portion  60   a  of the housing  60  passes in such a way that its upper part is inserted into the recess in the UD knob  38 , and this cylindrical portion  42   b  is axially supported by the insertion portion  60   a  to be capable of rotation. The manipulating lever  42   a  has one end fixed to the cylindrical portion  42   b  and the other end projecting to the outside of the UD knob  38 , and the cylindrical portion  42   b  can be rotated by manipulating the other end and swinging the manipulating lever  42   a.    
     Provided on the upper side of the cylindrical portion  42   b  of the UD brake manipulating portion  42  is a UD brake member  94  for locking the UD knob  38  against turning. The UD brake member  94  is a cylindrical member that has the same inner and outer diameters as those of the cylindrical portion  42   b  and through which the insertion portion  60   a  of the housing  60  passes. Like the previously described LR brake member  76 , the UD brake member  94  is supported by the insertion portion  60   a  so that the UD brake member  94  cannot be turned with respect to the insertion portion  60   a  but can move along the length of the insertion portion  60   a.    
     When the UD brake manipulating portion  42  (cylindrical portion  42   b ) is turned about the insertion portion  60   a,  the UD brake member  94  moves along the length of the insertion portion  60   a  by known means such as a cam mechanism or a screw mechanism depending on the direction of turning. 
     As illustrated in  FIG. 2 , the UD brake member  94  is fully spaced apart from the UD knob  38  when being positioned on the cylindrical portion  42   b  side. However, when moving along the length of the insertion portion  60   a  depending on the turning of the UD brake manipulating portion  42 , the UD brake member  94  is brought into contact with and depresses the UD knob  38 , whereby frictional force develops to put a brake on the turning of the UD knob  38 . 
     The UD brake manipulating portion  42  is adapted so as to be capable of adjusting, by controlling the amount of its turning, namely, the manipulating amount the manipulating lever  42   a,  the force by which the UD brake member  94  depresses the UD knob  38 , and the brake being exerted upon the UD knob  38  can take a fixed state or a half-braking state. 
     The UD motor  92  is fixed to the housing  60  of the manipulating section  14 , and a gear  96  is fixed to the rotating shaft of the UD motor  92 . A gear  98  is axially supported on the housing  60 , and the gear  98  meshes with the gear  96  and the gear formed on the pulley  86 . 
     Consequently, when the UD motor  92  is driven, the rotating force is transmitted to the pulley  86 , thereby pulling one of the wires  88  and  90  and advancing the other wire, and bending the angle portion  24  up or down. In addition, the angle portion  24  can be held in the bent state by exerting torque on the pulley  86 . 
     In addition, the manipulation of the UD knob  38  that is coupled to the pulley  86  through an intermediation of the linking tube  84 , namely, the manipulation of the bending up or down of the angle portion  24  can be assisted. 
     As illustrated in  FIG. 2 , the manipulating section  14  has a torque sensor  100  positioned in the hatched area of the linking tube  64  for sensing the torque exerted on the linking tube  64 . The torque sensor  100  senses the manipulative force (rotational torque) exerted on the LR knob  36  because the LR knob  36 , the linking tube  64 , and the pulley  68  integrally rotate. 
     A torque sensor  102  is provided at a position in the hatched area of the linking tube  84  for sensing the torque exerted on the UD knob  38 . The torque sensor  102  senses the manipulative force exerted on the UD knob  38  because the UD knob  38 , the linking tube  84 , and the pulley  86  integrally rotate. 
     As described later in detail, in the endoscope  10  of the illustrated example, the manipulative force exerted on the manipulative knobs  36 ,  38  is sensed in response to the input instruction from the reset switch  44  at the time, and the motors  74 ,  92  are driven (motor exerts torque on the pulley) so that the pulleys  68 ,  86  rotate at the same force as the manipulative force to thereby reset the neutral point of the angle portion  24 . 
     In other words, in the manipulating section  14  of the illustrated example, the torque sensor  100 ,  102  is arranged at part of the cylindrical linking tube  64 ,  84  which is directly coupled to the manipulative knob  36 ,  38  and which rotates integrally with that manipulative knob  36 ,  38 , and hence the manipulative force exerted on the manipulative knob  36 ,  38  to bend the angle portion  24  is directly sensed. 
     Various known types of torque sensors including a torque sensor that uses a strain gage and a magnetostrictive torque sensor may be utilized as the torque sensors  100 ,  102 . 
     In the present invention, the manipulative force for bending the angle portion  24  is not limited to being sensed at the linking tubes  64 ,  84 , and the manipulative force for bending the angle portion  24  may be directly or indirectly sensed at various positions and parts by, for example, sensing of torque at the pulleys  68 ,  86  or sensing of torque at the gears  80 ,  98 . Further, various types of force sensing means other than the torque sensor may be utilized for the manipulative force sensing means. 
     In the case illustrated in  FIG. 2 , the rpm caused by the motors  74  and  92  for maintaining the bent state of the angle portion  24  is reduced by the gear, but this is not the sole case of the present invention, and a planetary gear or a harmonic drive may be provided to reduce the rpm caused by the motors  74  and  92 . Alternatively, this mechanism may be combined with a gear to reduce the rotational speed. 
     Instead of applying the rotational force on the pulleys  68 ,  86  by reducing the rpm of the motors  74 ,  92 , the pulleys  68 ,  86  may be directly rotated using a direct drive motor (DD motor). 
     For example, as illustrated in  FIG. 3 , a DD motor with an inner rotor is used as an LR motor  106  whose rotor is in engagement with the cylindrical portion  68   a  formed at the lower part of the pulley  68  for bending the angle portion  24  to right or left direction. The torque is directly applied on the pulley  68  by the LR motor  106 . 
     Similarly, a DD motor with an inner rotor is used as a UD motor  108  whose rotor is in engagement through passing with the linking tube  84  linked to the pulley  86  for bending the angle portion  24  up or down. The torque is directly applied on the pulley  86  by the UD motor  108 . 
       FIG. 4  conceptually illustrates the configuration of a mechanism by which the LR knob  36  is turned to bend the angle portion  24  to the left or right direction in the case illustrated in  FIG. 2 . 
     The angle portion  24  is similar to the angle portion of a known endoscope in that the angle portion  24  has a number of circular rings connected together, and is bent to the left or right direction by the wires  70  and  72  manipulated by the LR knob  36 . The angle portion  24  is also bent up or down by the wires  88  and  90  manipulated by the UD knob  38  (not shown in  FIG. 4 ). 
       FIG. 5  is a plan view illustrating a schematic construction of the angle portion  24 . 
     Note that the construction of the angle portion  24  in the endoscope of the present invention is by no means limited to the illustrated case and that all designs that are adopted in a variety of endoscopes can be utilized. 
     In the illustrated case, the angle portion  24  includes a total of nine rings connected together, which consist of eight circular rings  110  and one distal end ring  112 . 
     Each circular ring  110  has a shape as if a ring-shaped member is slightly curved at one diameter portion, in which both surfaces in the axial direction are formed by a convex surface and a concave surface, respectively. The distal end ring  112  is a substantially cylindrical member, and is arranged at the most distal end portion  22  side of the angle portion  24 . 
     The circular rings  110  and the distal end ring  112  are linked to each other by linking pins  114   a  and linking pins  114   b.    
     Eight circular rings  110  are arranged in such a way that their curving directions (directions of curved convex and concave) alternate along the length of the insertion section  12 . Each linking pin  114   a  circularly links the convex portions of the convex surfaces of the pair of circular rings  110  facing each other in such a way that the circular rings  110  can rotate (swing) from right to left and vice versa (in the direction indicated by two-headed arrow a). In contrast, each linking pin  114   b  links the concave portions of the concave surfaces of the pair of circular rings  110  facing each other in such a way that the circular rings  110  can rotate (swing) up and down (in the direction indicated by two-headed arrow b). Similarly, the distal end ring  112  and the circular ring  110  facing thereto are also linked in such a way that the distal end ring  112  and the circular ring  110  can rotate (swing) up and down (in the direction indicated by two-headed arrow b) by the pair of linking pins  114   b.    
     The linking pins  114   a  and the linking pins  114   b  are alternately arranged, and a plurality of circular rings  110  are linked so as to be capable of turning in two alternate directions, one being vertical and other horizontal. 
     The wires  70  and  72  for bending the angle portion  24  to the left or right direction are guided by the wire guide (not shown), and spaced apart in the horizontal direction (vertical to the paper on which  FIG. 5  is drawn) to pass through the plurality of circular rings  110 . The distal end of the wire  70  is secured to the inner right side of the distal end ring  112  whereas the distal end of the wire  72  is secured to the inner left side of the distal end ring  112 . 
     Though not illustrated in  FIG. 5 , the wires  88  and  90  for bending the angle portion  24  up and down are guided by the wire guide, and spaced apart in the vertical direction (perpendicular to the paper on which  FIG. 5  is drawn) to pass through the circular rings  110 . The distal end of the wire  88  is secured to the inner upper side of the distal end ring  112  whereas the distal end of the wire  90  is secured to the inner lower side of the distal end ring  112 . 
     As described above, the pulley  68  is fixed to the LR knob  36  through an intermediation of the linking tube  64 , and the wires  70  and  72  are wounded around the pulley  68 . 
     Therefore, the linking tube  64  and the pulley  68  rotate by turning the LR knob  36 , and one of the wires  70  and  72  is pulled and the other wire is advanced depending on the direction of rotation of the pulley  68 . 
     The plurality of circular rings  110  of the angle portion  24  are linked in such a way that the circular rings  110  can turn to the left or the right, or up and down alternately by the linking pins  114   a  and  114   b,  and hence when the pulley  68  is rotated through the LR knob  36 , the angle portion  24  is bent to the left or the right with the pulled wire being on the inner side. 
     The greater the amount by which the wire  70  or  72  is pulled, namely, the greater the amount of rotation of the pulley  68 , the greater the degree by which the angle portion  24  is bent. Therefore, the angle (amount of bending) of the angle portion  24  can be adjusted by controlling the amount by which the LR knob  36  is turned. 
     When bent, the angle portion  24  attempts to return to a linear state in which it is not bent, or a straight state, by the counter force it generates, and automatically returns to the straight state by such counter force when the hand is released from the LR knob  36 . The counter force of the angle portion  24  is stronger the larger the angle. Therefore, a large force is required to bend the angle portion  24  the larger the angle. 
     Similarly, the pulley  86  is fixed to the UD knob  38  through an intermediation of the linking tube  84 , and the wires  88  and  90  are wounded to the pulley  86 . When the UD knob  38  is turned, either of the wires  88  or  90  is pulled, and the other wire is advanced depending on the direction of rotation of the pulley  86 , and the angle portion  24  is bent up or down with the pulled wire on the inner side. 
     The angle of the angle portion  24  bent upward or downward can be adjusted by controlling the amount by which the UD knob  38  is turned. The counter force to return to the straight state is stronger the larger the angle with respect to the bend upward or downward, and a large force is required to bend the angle portion  24 . 
     Therefore, by manipulating the LR knob  36  and the UD knob  38 , the doctor who is the operator of the endoscope can bend the angle portion  24  by a desired angle (less than or equal to the limit of bending) up or down, to the left or the right, and in any direction that is a combination of the up or down direction and the right or left direction, whereby the operator can observe or take a picture of the part under examination, or collect a tissue from that part. 
     Note that the mechanism by which the angle portion of the endoscope is bent is by no means limited to the illustrated case and one may utilize various means (mechanisms) for bending the angle portion adopted in various types of endoscopes. 
     As described above, the rotating shaft of the LR motor  74  is coupled to the pulley  68  through an intermediation of the gears  80  and  78 , and the wires  70  and  72  are moved back to bend the angle portion  24  to the left or the right by rotating the pulley  68  by means of the LR motor  74 . 
     Similarly, the rotating shaft of the UD motor  92  is coupled to the pulley  86  by way of the gears  98  and  96 , where the wires  88  and  90  are moved back to bend the angle portion  24  up or down by rotating the pulley  86  by means of the UD motor  92 . 
     Here, the linking tube  64  that is linked to the pulley  68  is provided with the torque sensor  100 , and the linking tube  84  that is linked to the pulley  86  is provided with the torque sensor  102 , and the detection results of the torque sensors  100  and  102  are input to a control means  118 , shown in  FIG. 4 , for controlling the drive of the LR motor  74  and the UD motor  92 . 
     A signal corresponding to the input instruction of the reset switch  44  and the cancel switch  46  is also supplied to the control means  118 . The reset switch  44  is a switch for resetting the neutral point of the angle portion  24  from the normal straight state to the desired bent state. On the other hand, the cancel switch  46  is a switch for returning the reset neutral point to the stationary straight state. 
     The operation of the control means  118  is described below taking the bend of the angle portion  24  to the left or the right through the manipulation of the LR knob  36  by way of example. 
     When the reset switch  44  is operated, the control means  118  input the sensed value of the torque sensor  100  and drives the LR motor  74  so that a torque of the same amount as the sensed value is exerted on the pulley  68 . The LR motor  74  thus exerts on the pulley  68 , that is, on the linking tube  64  a torque of the same amount as the torque exerted on the linking tube  64  at the point the reset switch  44  is operated. 
     The angle portion  24  can be maintained in the bent state by driving the LR motor  74  such that the torque of the same amount as the manipulative force at which the LR knob  36  is turned in order to bend the angle portion  24 , that is, the torque exerted on the linking tube  64  is exerted on the pulley  68 . In other words, the counter force of the angle portion  24  and the torque exerted by the LR motor  74  are balanced to each other, and hence the angle portion  24  can be maintained in the same bent state as when the reset switch  44  is operated. 
     Further, the counter force of the angle portion  24  generated by the bending of when the reset switch  44  is operated and the torque exerted on the pulley  68  by the LR motor  74  are in an equilibrium state. Therefore, if the LR knob  36  is further turned from such equilibrium state in a direction of bending the angle portion  24 , the angle portion  24  attempts to return to the reset neutral point by the counter force that increased by the increase in angle, whereas if the LR knob  36  is turned in a direction of returning the bending of the angle portion  24 , the counter force generates from the torque exerted on the pulley  68  from the LR motor  74  and the angle portion  24  attempts to return to the reset neutral point. 
     As conceptually illustrated in  FIG. 6A , the neutral point of the angle portion  24  normally in the straight state can be reset to a bent state. 
     The relationship between the angle and the torque for bending (load by endoscope) is in a state illustrated on the left side of  FIG. 6B  at the neutral point of the normal straight state. If the torque is exerted by the LR motor  74  (middle of  FIG. 6B ) in order to reset the state of angle θ of the angle portion  24  as the neutral point, both torques are added, and the relationship between the angle and the torque (total load on the manipulation of the LR knob  36 ) becomes a state illustrated on the right side of  FIG. 6B . In other words, the load shifts upward by the torque from the LR motor  74 . 
     Therefore, when changing the angle of the angle portion  24  from the state of angle θ by an angle ±α, the manipulation needs to be carried out in a range of large load, as illustrated on the left side of  FIG. 6C , in a state the neutral point is not reset. If the neutral point is reset at the angle θ, on the other hand, the manipulation can be carried out, as illustrated on the right side of  FIG. 6C , in a range of small load (same load as manipulation at the neutral point of normal straight state), and the load of the doctor can be reduced. In particular, greater force is required for the manipulation as the angle becomes larger, as described above, the manipulative force can be greatly reduced when manipulating in the direction of increasing the amount of bending. 
     Therefore, according to the endoscope of the present invention, the insertion section can be rotated with the hand being released from the manipulative knob by resetting the neutral point even when the insertion section needs to be rotated with the bending portion being greatly bent such as in the gastric fundus examination. Further, unlike the state in which the half-brake is applied, manipulation can be carried out with a small force similarly to the manipulation at the neutral point of the normal straight state even when adjusting the angle from the reset neutral point. 
     The angle portion  24  can be held in a bent state by resetting the neutral point. Therefore, it is possible to prevent accidents such as damaging the human body by the angle portion  24  suddenly returned to the straight state by the counter force that occur when the hand is carelessly released from the manipulative knob with the angle portion  24  being in the bent state. 
     The manipulating section  14  is also provided with the cancel switch  46  for canceling the once reset neutral point, and returning the neutral point to the normal straight state. When the cancel switch  46  is operated, the control means  118  stops driving the LR motor  74  and releases the torque exerted on the pulley  68 . The neutral point of the angle portion  24  then returns to the normal straight state. 
     Preferably, the control means  118  gradually reduces the output of the LR motor  74 , that is, the torque exerted on the pulley  68  from the LR motor  74  and stops the drive of the LR motor  74  so that the angle portion  24  gradually returns to the straight state instead of immediately stopping the drive of the LR motor  74  in response to the signal from the cancel switch  46 . As a result, the damage of the human body and the like that occurs when the angle portion  24  suddenly returns to the straight state can be prevented. 
     In the first embodiment described above, the torque sensor  100  senses the torque exerted on the linking tube  64  (manipulative force on the LR knob  36 ) in response to an instruction input by the reset switch  44 , and the LR motor  74  is driven to exert the torque of the amount same as the sensed torque on the pulley  68  to reset the neutral point of the angle portion  24 . However, this is not the sole case of the present invention, and the neutral point of the angle portion  24  can be reset with various types of means. 
     By way of example, using the relationship between the displacement of the bending means by the manipulation of the manipulative knob and the force necessary for bending at the angle the displacement is produced, the force necessary for resetting the neutral point may be calculated from the displacement at the point the resetting of the neutral point of the angle portion  24  is instructed, and the angle portion  24  may be bent with the necessary force to reset the neutral point of the angle portion  24 . 
     In  FIG. 4 , when the angle portion  24  is bent by manipulating the LR knob  36 , the position of a predetermined point of the wire  70  (or wire  72 ) changes depending on the angle of the angle portion  24 , and the pulley  68  rotates thereby changing the rotating position. 
     The relationship between the angle of the angle portion  24  and the manipulative force necessary for realizing the angle such as the torque that needs to be exerted on the linking tube  64  (pulley  68  and LR knob  36 ) by turning the LR knob  36  can be known in advance. 
     Therefore, as illustrated in  FIG. 7A , a displacement-torque conversion table illustrating the relationship between the amount of displacement from the manipulation of the LR knob  36  to bend the angle portion  24  (wire position or pulley rotating position) and the torque exerted on the linking tube  64  in correspondence to the amount of displacement is formed in advance, and stored beforehand in, for example, the memory of the control means  118 . 
     In other words, the displacement-torque conversion table is a table illustrating the relationship between the displacement of the wire or the pulley when a certain angle is obtained, and the torque necessary for realizing such angle. 
     In this arrangement, as shown in  FIG. 7B , a displacement sensor  69  for sensing the rotational displacement of the pulley  68  or a displacement sensor for sensing the displacement of the wire  70  or  72  is provided in place of the torque sensor  100 . Known displacement sensors can be used for such displacement sensors. 
     When the reset switch  44  instructs the resetting of the neutral point of the angle portion  24 , the control means  118  inputs the displacement corresponding to the bending of the angle portion  24  at the time sensed by the displacement sensor, and calculates the torque exerted on the pulley  68  in correspondence to the displacement using the displacement-torque conversion table. In other words, the torque (necessary torque) necessary for realizing the angle that causes such displacement is calculated. 
     The control means  118  then drives the LR motor  74  such that the calculated necessary torque is exerted on the pulley  68 . As a result, the necessary torque is then exerted on the pulley  68 , and the angle portion  24  is maintained at the bent state, namely, the neutral point of the angle portion  24  is reset. 
     As a method of resetting the neutral point in the present invention other than the above, the neutral point of the angle portion  24  may be reset to the input instructed angle. 
     With reference to  FIG. 4 , the relationship between the angle of the angle portion  24  and the manipulative force necessary for realizing such angle, such as the torque that needs to be exerted on the pulley  68  by turning the LR knob  36  is known in advance. 
     The relationship between the angle and the torque that needs to be exerted on the pulley  68  is found and tabulated for various angles, and an input function of the angle such as 60°, 90°, and 180° is provided to the reset switch  44  in addition to the function of instructing the reset of the neutral point. Alternatively, the angle may be arbitrarily set using a dial and the like. 
     When the resetting of the neutral point and the angle are instructed (input), the control means  118  reads out the torque necessary for the instructed angle from the table, and drives the LR motor  74  such that the torque necessary for realizing such angle is exerted on the pulley  68  to thereby reset the neutral point of the angle portion  24 . 
     The resetting mechanism of the neutral point having the input means of the angle may be simultaneously used with a mechanism of sensing the torque exerted on the linking tube  64  and resetting the neutral point of the angle portion  24  according to the sensed result, and a mechanism of sensing the displacement of the bending means and resetting the neutral point of the angle portion  24  according to the sensed result. 
     The description above is made on an example of resetting and canceling the neutral point in the left and right direction, which correspond to the manipulation of the LR knob  36 , but the resetting of the neutral point and the canceling of the reset neutral point are carried out on the bend in the up and down direction by the UD knob  38  in the exact same manner. 
     Further, the resetting of the neutral point and the canceling of the reset neutral point are carried out on the bending in both the left and right, and the up and down directions if the angle portion  24  is bent by turning both the LR knob  36  and the UD knob  38 . 
     In this regards, the assistance of bending by the motor is similarly carried out as hereinafter described in detail. 
     The endoscope  10  of the illustrated example can reset the neutral point with respect to four directions, up and down, and left and right as a preferred embodiment, but this is not the sole case of the present invention. 
     In other words, in the endoscope of the present invention, the neutral point may be set only in one direction such as only the upward bend and the rightward bend, or may be set in two directions such as only the upward and downward bend, and only the leftward and rightward bend. However, in the endoscope of the present invention, the neutral point is preferably reset for at least the upward bend (so-called up angle). More preferably, the neutral point is reset for the bending in at least both upward and downward directions, and in particular, the neutral point is most preferably reset for the bending in four directions of up and down, and left and right, as in the illustrated example. 
     In the endoscope  10  of the illustrated example, a motor is used as a driving means for resetting the neutral point of the angle portion  24 , but this is not the sole case of the present invention, and various other kinds of driving means may be utilized, as exemplified by solenoids that depend on a fluid pressure or an electromagnetic force to assist in traction of wires. 
     As described above, the endoscope  10  includes the LR motor  74  for exerting torque on the pulley  68  in correspondence to the bending of the angle portion  24  to the left or the right, the UD motor  92  for exerting torque on the pulley  86  in correspondence to the bending of the angle portion  24  up or down, the torque sensor  100  for sensing the torque exerted on the linking tube  64 , and the torque sensor  102  for sensing the torque exerted on the linking tube  84 . The manipulation for bending the angle portion  24  may be assisted using the motors  74 ,  92  and the torque sensors  100 ,  102 . 
     The assistance of bending the angle portion  24  by the LR motor  74  is described with reference to  FIG. 4  using the manipulation of the LR knob  36  for bending the angle portion  24  to the left or the right by way of example. 
     When the LR motor  74  assists the bending of the angle portion  24 , the control means  118  constantly monitors the torque which is exerted on the linking tube  64  and sensed by the torque sensor  100  (i.e., manipulative force exerted on the LR knob  36 ). 
     The control means  118  drives the LR motor  74  such that the torque of a predetermined proportion with respect to the torque sensed by the torque sensor  100  is exerted on the pulley  68  and the linking tube  64 . As a result, part of the turning force of the LR knob  36  necessary for bending the angle portion  24  is thus assisted by the LR motor  74 , and hence the turning of the LR knob  36 , namely, the manipulation of bending the angle portion  24  can be performed with a small manipulative force. 
     For instance, the control means  118  drives the LR motor  74  such that the torque which is exerted on the linking tube  64  and sensed by the torque sensor  100 , namely, the torque of constantly equal amount (100%) with respect to the manipulative force of the LR knob  36  is exerted on the pulley  68  and the linking tube  64 . 
     In other words, when torque is exerted on the LR knob  36 , the LR motor  74  exerts on the linking tube  64  the torque of equal amount to the torque exerted on the LR knob  36 . For instance, if the operator manipulates the LR knob  36  with the force of “50”, the LR motor  74  also exerts the same force of “50” on the linking tube  64 , whereby the manipulation of bending the angle portion  24  is performed with a total force of “100”. In other words, the turning of the LR knob  36  is assisted by the torque of half (50%) of the torque (force) necessary for the bending. 
     Accordingly, the manipulative force necessary for the operator to bend the angle portion  24  is the manipulative force obtained by subtracting the assisting force from the manipulative force actually required for the target angle, and the LR knob  36  merely needs to be turned with half the torque (manipulative force), and thus the angle portion  24  can be bent with a very small force. 
     In this case, the LR motor  74  is not limited to assisting with the torque of 100% of the torque exerted on the linking tube  64 , and the bending of the angle portion  24  may be assisted in various proportions, as exemplified by such a design that 30% or 80% of the torque that is exerted on the linking tube  64  is supplied by the LR motor  74 . 
     As another assisting method, there is exemplified a method of controlling the assisting force such that the LR motor  74  assists in the bending of the angle portion  24  by supplying an assisting force that is equal to the torque exerted on the linking tube  64  (i.e., manipulative force exerted on the LR knob  36  by the manipulation of the bend) as multiplied by a predetermined coefficient. 
     Write, for example, W for the force (load) necessary for bending the angle portion  24 , F for the torque exerted on the linking tube  64  by the manipulation of the LR knob  36 , and T for the assisting force exerted by the LR motor  74  on the linking tube  64 . Then, those three forces are related by: 
     
       
      
       W=T+F  
      
     
     if the coefficient (gain) of assisting is written as k, the drive of the LR motor  74  is controlled in such a way that T=kF. 
     In this case, 
         F (1+ k )= W    
         F=W /(1+ k ); 
     thus, torque F exerted on the linking tube  64  by the manipulation of the LR knob  36  can accordingly be reduced to be 1/(1+k) times the force that is actually necessary for bending the angle portion  24 . If coefficient k is set as 1, the case under consideration is equivalent to the case where 50% of the manipulative force is supplied by the LR motor  74 . 
     In a state the neutral point of the angle portion  24  is not reset, the relationship of the angle and the torque for bending is as indicated by a dotted line in  FIG. 8A . When a constant torque as indicated by a chain dashed line is supplied by the LR motor  74  in order to reset the neutral point to the angle θ, the relationship between the angle and the torque necessary for manipulating the LR knob  36  becomes the state indicated by a solid line in  FIG. 8A . 
     In contrast, when assisting by the LR motor  74  at a predetermined proportion according to the manipulative force of the LR knob  36 , the torque by the LR motor  74  becomes tilted diagonally right up with the torque of the LR motor  74  at the angle θ as the center as indicated by a chain dashed line in  FIG. 8B  when the neutral point is reset at the angle θ. As a result, the relationship between the angle and the torque necessary for manipulating the LR knob  36  becomes the state indicated by a solid line in  FIG. 8B , and the manipulative force can be reduced. 
     Therefore, when the operator performs the basic bending manipulation, and when the traction of the wire  70  or  72 , namely, the bending of the angle portion  24  is assisted by the auxiliary means such as the LR motor  74  according to the torque at which the operator turns the LR knob  36  (manipulative force exerted on the manipulation means), the insertion section  12  can be extracted in a safe manner by appropriately turning the LR knob  36  to control the bending of the angle portion  24  even if blackout or a machine trouble such as one in the LR motor  74  occurs. In addition, the bending of the angle portion  24  is basically performed by pulling the wire  70  or  72  with the aid of the manipulation means such as the LR knob  36 , and hence the operator can perform the operation of bending the angle portion  24  while feeling the counter force exerting on the angle portion  24  from the part under examination. Thus, an accident such as perforation can be effectively prevented to permit a safe operation for bending the angle portion  24 . What is more, the manipulation of the LR knob  36  and other members allows the angle portion  24  to be bent rapidly enough to enable a subtle operation for bending it. 
     The assisting in bending by the motor  74  is performed in accordance with the torque (manipulative force) applied to the LR knob  36  and other members of the manipulating means. Therefore, if the manipulative force on the LR knob  36  and the like by the operator increases, the pulling of the wires  70  or  72  is assisted in accordance thereto. Thus, even in the case where the manipulative force required by the bending operation is increased due, for example, to aging or deterioration that depends on the situation in which the endoscope has been used such as an increase in the force of friction that develops on the wires  70  and  72  or in the case where, due to the condition of the part under examination, the state of the endoscope at the part under examination or other factors, a great manipulative force is required even for the small amount of bending, the manipulation of the LR knob  36  and other members (force required for their manipulation) can be supplied consistently in accordance with the manipulative force required to bend the angle portion  24 . 
     In this case, in order to ensure that the manipulative force exerted on each of the manipulative knobs for bending the angle portion  24  is detected accurately, the manipulative force exerted on each manipulative knob has to be sensed in a position somewhere between the motor that assists in bending and the manipulative knob (upstream of the motor in the direction in which the manipulative force is transmitted from the manipulative knob toward the assist motor). 
     In order to meet this need, the manipulating section illustrated in  FIGS. 2 and 3  has a torque sensor  100  positioned in the hatched area of the linking tube  64  for sensing the manipulative force (torque) exerted on the LR knob  36 , and a torque sensor  102  positioned in the hatched area of the linking tube  84  for sensing the manipulative force exerted on the UD knob  38 . 
     Thus, the illustrated manipulating section  14  adopts such a preferred embodiment in which the torque sensor is positioned at part of the cylindrical linking tube which is directly coupled to a knob for manipulating the angle portion  24  to bend and which rotates integrally with that manipulative knob, whereby the manipulative force exerted on the manipulative knob to bend the angle portion  24  is directly sensed. 
     When assisting the manipulation of bending by the motor for resetting the neutral point of the angle portion  24 , various variations can be utilized other than assisting the manipulative force detected as in the example described above at a constant proportion. 
     For instance, the manipulative force necessary for bending the angle portion  24  generally becomes larger as the angle (amount of bending) becomes larger. In correspondence thereto, the proportion of the assistance by the LR motor  74  may be increased continuously or in a step-wise manner according to the increase in the manipulative force exerted on the LR knob  36 . 
     In a range where the amount of bending the angle portion  24  is small, the control system tends to easily oscillate with respect to change in the assisting angle, and the angle portion  24  requires a very small amount of force to be bent, which means that the motor has no need to assist in the bending of the angle portion  24 . Therefore, if the manipulative force exerted on the LR knob  36  is smaller than or equal to a predetermined value, the LR motor  74  need not assist in the bending of the angle portion  24 . In other words, a region that may be called “an insensitive zone” may be provided in the region where only a small amount of manipulative force is applied and no assisting may be performed in such insensitive zone but when a manipulative force beyond the insensitive zone is applied, assisting may be performed in accordance with the applied manipulative force. 
     Alternatively, a region where the manipulative force applied is smaller than a predetermined value may be assigned as a region where an assisting force is produced in a smaller proportion to the applied manipulative force than in the other regions. For instance, the insensitive zone may be replaced by a low-sensitivity range which is the region where the manipulative force applied is smaller than a predetermined value and where the response (sensitivity) to the applied manipulative force is low; in this low-sensitivity range, the proportion of the assisting force that is produced by the LR motor  74  as relative to the applied manipulative force may be adjusted to be smaller than in the other regions (where the applied manipulative force exceeds the predetermined value). 
     Conversely, if the manipulative force applied to the LR knob  36  becomes very large, there is high possibility that the angle portion  24  (distal-end portion  22 ) may have gotten stuck within the human body or may be exerting a strong compressive force within the human body. If, in this case, the angle portion  24  is further forced to bend, an accident such as perforation might even occur to damage the human body. Therefore, if the manipulative force being exerted on the LR knob  36  exceeds a predetermined value, the assisting by the motor  74  may be turned off (suspended). 
     Alternatively, if the manipulative force being applied to the LR knob  36  exceeds a predetermined value, the assisting force produced by the motor  74  may not be further increased but held constant. In other words, depending on the manipulative force applied to the LR knob  36 , a limit may be set on the assisting force that is produced by the motor  74 . 
     The UD motor  92  may assist the bending similarly to the assisting by the LR motor  74 . 
     In the present invention, the embodiments are not limited to being implemented individually when assisting the bending (manipulation) by the motor, and a plurality of embodiments may be combined to assist the bending. 
     For instance, the embodiment of providing the insensitive zone in the region where only a small amount of manipulative force is applied, and the embodiment of suspending the assistance by the motor in the region where the manipulative force exceeds the predetermined value or the embodiment of setting a limit on the assisting force may be combined. 
     The embodiment of providing the insensitive zone and the embodiment of providing a low-sensitivity region may be combined so that, with the region up to the first manipulative force being set as the insensitive zone, and the region beyond the first manipulative force up to the second manipulative force being set as the low-sensitivity region, the assisting force of high proportion is applied when exceeding the second manipulative force. 
     The embodiment of setting a limit on the assisting force and the embodiment of suspending the assisting may be combined so that assisting is carried out with a force of a predetermined proportion corresponding to the manipulative force up to the first manipulative force, the assisting force is set constant with the assisting force in the first manipulative force set as the limit from beyond the first manipulative force up to the second manipulative force, and assisting is not carried out when exceeding the second manipulative force. 
     In the endoscope of the present invention, the assisting of the bending of the angle portion by the motor for resetting the neutral point may always be performed, or may be performed only when the neutral point is not reset or only when the neutral point is reset. Alternatively, the necessity of assistance may be arbitrarily selected by the operator using an assistance select switch. 
     Second Embodiment 
       FIG. 9  illustrates an entire structure of an endoscope  10 A according to a second embodiment. In the endoscope  10  of the first embodiment, the endoscope  10 A, in place of the neutral point resetting function, has a function (hereinafter referred to as pseudo-brake function) of maintaining the manipulation of the manipulative knob immediately before the manipulative force becomes zero, that is, the bent state of the angle portion  24 . In the endoscope  10  of the first embodiment illustrated in  FIG. 1 , the endoscope  10 A includes, in place of the manipulating section  14 , a manipulating section  14 A omitted with the reset switch  44  and the cancel switch  46 , and includes, as illustrated in  FIG. 10 , a pseudo-brake switch  120  connected to the control means  118 . 
     The pseudo-brake switch  120  includes a foot switch, and serves as a selection means for selecting/switching whether or not to apply the pseudo-brake. The pseudo-brake is switched to the pseudo-brake mode ON (apply pseudo-brake) and the pseudo-brake mode OFF (cancel pseudo-brake) every time the pseudo-brake switch  120  is pressed. 
     The LR motor  74  and the UD motor  92  used as the driving means for resetting the neutral point of the angle portion  24  in the first embodiment are used as a driving means for applying the pseudo-brake for maintaining the angle portion  24  in the bent state in the second embodiment. 
     In the endoscope  10 A, when the manipulative force of the manipulative knob changes to be zero from a value other than zero, the LR motor  74  and the UD motor  92  are driven to bend the angle portion  24  at the manipulative force same as such manipulative force according to the value before the change, whereby the pseudo-brake is applied so as to maintain the angle portion  24  in the bent state without returning to the straight state or the neutral point even when the manipulative force becomes zero, namely, when the operator releases the hand from the manipulative knob. 
     In other words, when the torque sensed by the torque sensor  100  and the torque sensor  102  changes to be zero from a value other than zero, the LR motor  74  and the UD motor  92  are driven so as to apply such torque on the linking tube  64  and the linking tube  84  according to the value measured immediately before the change. As a result, the pseudo-brake is applied and the manipulative knob is prevented from returning to the neutral point, namely, the angle portion  24  is prevented from returning to the straight state and is maintained in the bent state. 
     The action of the pseudo-brake is described using the bending of the angle portion to the left or the right in correspondence to the manipulation of the LR knob  36  by way of example. When the pseudo brake switch  120  is switched to the pseudo-brake mode ON, the control means  118  continuously detects the torque measured by the torque sensor  100 , namely, the manipulative force for bending exerted on the LR knob  36  at a predetermined timing (sampling rate), and stores the latest sensed torque in the memory. 
     In addition, the control means  118  reads out from the memory the sensed torque sensed immediately before and stored in the memory when the torque sensed by the torque sensor  100  (i.e., manipulative force of the manipulative knob) becomes zero, and drives the LR motor  74  so that the torque of the same amount as the sensed torque is exerted on the pulley  68  and the linking tube  64 . 
     In other words, as conceptually illustrated in  FIG. 11A , at time t 0  at which the operator releases the hand from the LR knob  36  and the manipulative force becomes zero, the LR motor  74  is driven such that the torque same as the torque immediately before (manipulative force applied immediately before by the operator) is exerted on the pulley  68  and the linking tube  64 , as illustrated in  FIG. 11B . In other words, the torque of 100%, with respect to the torque immediately before at which the manipulative force of the LR knob  36  becomes zero, is applied on the pulley  68  and the linking tube  64  by driving the LR motor  74 . Therefore, the turning position of the LR knob  36 , that is, the bent state of the angle portion  24  when the wires  70  and  72  advance and retreat maintained. 
     Therefore, even if the operator releases the hand from the LR knob  36  and the manipulative force becomes zero, the LR knob  36  maintains the turning state corresponding to the angle of the angle portion  24 , or the angle portion  24  remains in the bent state without returning to the straight state by the counter force as if the brake is applied on the LR knob  36  (pseudo-brake state), similarly to the state immediately before the manipulative force becomes zero. 
     As apparent from the above description, according to the endoscope  10 A of the second embodiment, the operator can safely release the hand from the manipulative knob for bending while bending the angle portion  24 , for example, the required manipulation can be carried out with the hand released from the manipulative knob even when performing the manipulation necessary for rotating the insertion section, with the angle portion  24  being greatly bent as in the gastric fundus examination. When further increasing the angle with the angle portion  24  being greatly bent, the operator may once release the hand from the manipulative knob and re-grip the manipulative knob to again manipulate the knob. 
     Since the half-brake for stopping the turning of the manipulative knob by the frictional force is not applied in this state, the operator can manipulate the bending of the angle portion  24  using the manipulative knob with a normal force without performing the operation of canceling the brake even after the pseudo-brake is applied. 
     Further, examinations and treatments by the endoscope can be safely performed because the angle portion  24  does not suddenly return to the straight state even if the operator carelessly releases the hand from the manipulative knob, with the angle portion  24  being bent. 
     In other words, according to the endoscope  10 A of the second embodiment, the degree of freedom of various manipulations of the endoscope  10 A greatly enhances, the load on the operator who manipulates the endoscope  10 A greatly reduces, and the safety of the endoscope further enhances. 
     In this endoscope  10 A, various modes can be utilized for the drive of the LR motor  74  after applying the pseudo-brake (manner of applying the pseudo-brake). 
     For instance, as illustrated in  FIG. 11B , the state in which the pseudo-brake is applied is maintained (output of the LR motor  74  is maintained constant) after applying the pseudo-brake at time t 0 , and the output of the LR motor  74  is set to zero and the pseudo-brake is canceled when the LR knob  36  is again manipulated at time t 1 , namely, when the torque sensed by the torque sensor  100  is changed. In this case, the pseudo-brake mode may be automatically switched from ON to OFF (cancel pseudo-brake). 
     Alternatively, as illustrated in  FIG. 11C , once the pseudo-brake is applied at time t 0 , the state in which the pseudo-brake is applied may be maintained as long a cancel instruction using the provided cancel switch and the like is appropriately issued. 
     The state in which the pseudo-brake is applied by the LR motor  74  is the state in which the counter force of the angle portion  24  by the bending and the torque exerted by the LR motor  74  are balanced. Therefore, when the LR knob  36  is turned in the direction of further bending the angle portion  24 , the angle portion  24  attempts to return to the bent state by the pseudo-brake due to the counter force that increases with increase in angle. Conversely, when the LR knob  36  is turned in the direction of returning the bending of the angle portion  24  by the pseudo-brake, the counter force generates from the torque exerted on the pulley  68  by the LR motor  74 , and the angle portion  24  attempts to return to the bent state by the pseudo-brake. In other words, a state similar to when resetting the neutral point of the angle portion  24 , which is normally in the straight state, to the bent state is obtained. 
     The cancel switch for canceling the pseudo-brake may be arranged independently of the pseudo-brake switch  120 , or the bent state by the pseudo-brake may be canceled by switching the pseudo-brake mode to OFF. 
     After applying the pseudo-brake, the LR knob  36  is manipulated so that such manipulation corresponds to the angle smaller than the angle of the angle portion  24  by the pseudo-brake, as indicated by a dotted line in  FIG. 11A , namely, the LR knob  36  may be manipulated to bend the angle portion  24  in the direction opposite to the bending direction by the LR motor  74 . In this case, in the method illustrated in  FIG. 11C , the subsequent pseudo-brake, namely, the torque exerted by the LR motor  74  on the pulley  68  and the linking tube  64  may also be an amount corresponding to the angle in accordance with the manipulation of the LR knob  36 , as indicated by a dotted line in  FIG. 11C . 
     Alternatively, a method of maintaining the pseudo-brake and a method of changing the bend by the pseudo-brake according to the manipulation by the LR knob  36  may be selectable with a selection switch and the like. 
     Further, instead of maintaining the angle by the pseudo-brake constant, the output of the LR motor  74  may be gradually reduced to gradually decrease the angle of the angle portion  24 , as illustrated in  FIG. 11D  after applying the pseudo-brake. In this method, the angle portion  24  ultimately returns to the straight state or the neutral point unless the LR knob  36  is manipulated. 
     In  FIG. 11D , while such pseudo-brake is used for the pseudo-brake illustrated in  FIG. 11B , the method of gradually decreasing the angle may be utilized in the pseudo-brake illustrated in  FIG. 11C . 
     Further, two or more methods of the methods illustrated in  FIGS. 11B to 11D  may be set in advance so that the operator can arbitrarily select the manner of applying the pseudo-brake with the selection switch and the like. 
     The operator can also choose whether or not to apply the pseudo-brake with the selection switch and the like. 
     The above description is made using the pseudo-brake corresponding to the bending of the angle portion to the left or the right by the LR knob  36  by way of example. However, but the pseudo-brake is applied in exactly the same manner with respect to the bending of the angle portion up or down by the UD knob  38  at the point the manipulative force becomes zero, namely, at the point the torque sensed by the torque sensor  102  becomes zero. 
     Further, if the angle portion  24  is bent by both the LR knob  36  and the UD knob  38 , the pseudo-brake is applied at the point the manipulative force becomes zero for the bend in both directions. 
     While in the endoscope  10 A of the illustrated example, the motor is used as a driving means for applying the pseudo-brake, this is not the sole case of the present invention. For example, various other kinds of driving means may be utilized, as exemplified by solenoids that depend on a fluid pressure or an electromagnetic force to assist in traction of wires. 
     In the second embodiment, the pseudo-brake switch  120  is not limited to a foot switch, and may be a selection or switching switch appropriately arranged in the manipulating section  14  of the endoscope  10 . 
     Further, in the endoscope  10 , whether the pseudo-brake is turned ON or OFF may be output by displaying on a monitor of the endoscope processor or a display arranged in the manipulating section  14 , or audio outputting in the endoscope processor or the manipulating section  14 , to enable the operator to easily check the ON/OFF of the pseudo-brake mode. 
     The endoscope  10  of the illustrated example enables ON/OFF (whether or not to apply pseudo-brake) of the pseudo-brake mode to be selectable as a preferred embodiment. However, this is not the sole case of the present invention, and the pseudo-brake may always be in an applied state. 
     Similarly to the first embodiment, the manipulation of bending the angle portion  24  can be assisted using the motors  74 ,  92  and the torque sensors  100 ,  102  in the second embodiment. 
     For instance, the control means  118  drives the LR motor  74  such that the torque of half (50%) of the torque applied on the linking tube  64  sensed by the torque sensor  100 , namely, the manipulative force of the LR knob  36  is constantly exerted on the pulley  68  and the linking tube  64 , as illustrated in  FIG. 11E . 
     In other words, when the torque is applied on the LR knob  36 , the LR motor  74  applies the torque of half of such torque on the linking tube  64 . For instance, if the operator manipulates the LR knob  36  with a force of “100”, the LR motor  74  applies the force of “50”, which is half of “100”, on the linking tube  64 , and thus the angle portion is bent at a force of a total of “150”. In other words, the turning of the LR knob  36  is assisted by the torque of ⅓ of the torque (force) necessary for bending the angle portion  24 . 
     Therefore, the manipulative force necessary for the operator to bend the angle portion  24  is the manipulative force obtained by subtracting the assisting force from the manipulative force actually necessary for the target angle, and the LR knob  36  merely needs to be turned at a torque (manipulative force) of ⅔, whereby the angle portion  24  can be bent with a very small force. 
     The output of the LR motor  74  is changed at the point the manipulative force of the LR knob  36  becomes zero, namely, at the point the torque which is applied on the linking tube  64  and sensed by the torque sensor  100  becomes zero such that the torque similar to the torque sensed by the torque sensor  100  immediately before the point is applied on the linking tube  64 . 
     In this case, the LR motor  74  is not limited to assisting at the torque of 50% of the torque applied on the linking tube  64 , and the bending of the angle portion  24  can be assisted at various proportions such as assisting at 30% or 100% of the torque applied on the linking tube  64  with the LR motor  74 . 
     Further, in the endoscope  10 A of the second embodiment, the assist of the bending by the motor may be always performed, may be performed only when the pseudo-brake is not applied, or may be performed only when the pseudo-brake is applied; any of which can be selected by the selection switch. Further, the operator may arbitrarily select the necessity of assistance. 
     Note that the UD motor  92  may assist the bending of the angle portion similarly to that of the LR motor  74 . 
     While the endoscope of the present invention has been described above in detail, the present invention is by no means limited to the first and second embodiments and various improvements and modifications may of course be made without departing from the gist of the present invention.