Patent Publication Number: US-2023157778-A1

Title: Medical manipulator system and access device

Description:
This is a continuation of International Application PCT/JP2020/029654 which is hereby incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a medical manipulator system and an access device. 
     BACKGROUND ART 
     A known access device in the related art is attached to the outside of an endoscope and guides a treatment tool (for example, see PTLs 1 and 2). 
     In the case of a treatment tool having a flexible shaft with high flexibility, a doctor needs to hold an operation part of the treatment tool with one hand and support the flexible shaft with the other hand in order to prevent the flexible shaft from bending. Hence, it is difficult for one doctor to operate two flexible treatment tools simultaneously. 
     PTL 2 discloses a rigid shaft provided at the proximal end of a treatment tool and a rigid sheath provided at the proximal end of an access device and supporting the rigid shaft. Because the combination of the rigid shaft and the rigid sheath eliminates the need for a doctor to support the flexible shaft with the other hand, the aforementioned disadvantage is eliminated. 
     CITATION LIST 
     Patent Literature 
     {PTL 1} Publication of Japanese Patent No. 3806518 
     {PTL 2} U.S. Patent Application Publication No. 2018/0021060 
     SUMMARY OF INVENTION 
     According to an aspect of the present invention, there is provided a medical manipulator system including: a treatment tool having a long flexible shaft and a rigid shaft connected to a proximal end of the flexible shaft; an access device that guides the treatment tool and that has a long flexible tube, into which the flexible shaft is inserted, and a rigid sheath, which is connected to a proximal end of the flexible tube and into which the flexible shaft and the rigid shaft are inserted; and a resistance generating part that is provided on at least one of the rigid shaft and the sheath and that generates resistance to advancing of the rigid shaft through the sheath. The resistance generated by the resistance generating part increases when a distal end of the advancing treatment tool passes through a distal end of the flexible tube or a vicinity of the distal end of the flexible tube inside the flexible tube, and the resistance generated by the resistance generating part decreases after the distal end of the advancing treatment tool passes through the distal end of the flexible tube or the vicinity. 
     According to another aspect of the present invention, there is provided an access device that guides a treatment tool, the access device including: a long flexible tube; a sheath that is connected to a proximal end of the flexible tube; and a resistance generating part that generates resistance when the treatment tool is inserted. The resistance generated by the resistance generating part increases when a distal end of the advancing treatment tool passes through a distal end of the flexible tube or a vicinity of the distal end of the flexible tube inside the flexible tube, and the resistance generated by the resistance generating part decreases after the distal end of the advancing treatment tool passes through the distal end of the flexible tube or the vicinity. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram showing an example of surgery using a medical manipulator system according to an embodiment of the present invention. 
         FIG.  2    shows the overall configuration of a treatment tool according to the embodiment of the present invention. 
         FIG.  3    shows the overall configuration of an access device according to the embodiment of the present invention. 
         FIG.  4 A  is a diagram for explaining the operation of the medical manipulator system. 
         FIG.  4 B  is a diagram for explaining the operation of the medical manipulator system. 
         FIG.  4 C  is a diagram for explaining the operation of the medical manipulator system. 
         FIG.  5    is a diagram for explaining design values of the treatment tool and the access device. 
         FIG.  6 A  is a diagram showing a modification of a resistance generating part. 
         FIG.  6 B  is a diagram showing another modification of the resistance generating part. 
         FIG.  6 C  is a diagram showing another modification of the resistance generating part. 
         FIG.  7    is a partial side view of a modification of a rigid shaft of the treatment tool. 
         FIG.  8 A  is a partial longitudinal sectional view of a modification of the access device. 
         FIG.  8 B  is a partial longitudinal sectional view of the access device in  FIG.  8 A  in a state in which a telescopic structure is contracted. 
         FIG.  9    is a partial longitudinal sectional view of another modification of the access device. 
         FIG.  10    is a partial longitudinal sectional view of another modification of the access device. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A medical manipulator system  100  according to an embodiment of the present invention will be described below with reference to the drawings. 
       FIG.  1    shows an example of use of the medical manipulator system  100  according to this embodiment. The medical manipulator system  100  is used in combination with an endoscope  30  and, as shown in  FIGS.  1  to  3   , includes a treatment tool  1  and an access device  10  that is externally attached to the endoscope  30  and guides the treatment tool  1 . The treatment tool  1  and the access device  10  are inserted together with the endoscope  30  into the anus of a patient A lying on an operating table  110 . The treatment tool  1  is operated by a doctor B, and the endoscope  30  is operated by a scopist C. 
     As shown in  FIG.  2   , the treatment tool  1  includes a long flexible shaft  2  having flexibility, an end effector  3  connected to the distal end of the flexible shaft  2 , a rigid shaft  4  connected to the proximal end of the flexible shaft  2 , and an operation unit  5  connected to the proximal end of the rigid shaft  4 . 
     The end effector  3  is a portion that acts on a biological tissue and is, for example, a high-frequency knife or grasping forceps. 
     The flexible shaft  2  is a portion to be inserted into the body, and a bending portion  2   a  is provided at the distal end of the flexible shaft  2 . The rigid shaft  4  extends coaxially with the flexible shaft  2 , and the rigid shaft  4  and the operation unit  5  are disposed outside the body of the patient A. 
     The rigid shaft  4  includes a cylindrical shaft body  41  and a tapered portion  42  connected to the distal end of the shaft body  41 . The rigid shaft  4  is formed of a hard material, such as a hard resin or a metal. 
     The outer diameter of the shaft body  41  is uniform and is larger than the outer diameter of the flexible shaft  2 , and an outer circumferential surface (parallel surface)  41   a  of the shaft body  41  is parallel to the longitudinal axis of the shaft body  41 . 
     The tapered portion  42  has a truncated cone shape whose diameter gradually decreases toward the side of the distal end, and an outer circumferential surface (inclined surface)  42   a  of the tapered portion  42  is inclined so as to be gradually displaced radially outward from the side of the distal end toward the side of the proximal end with respect to the longitudinal axis of the rigid shaft  4 . The outer diameter of the proximal end of the outer circumferential surface  42   a  is equal to the outer diameter of the outer circumferential surface  41   a,  and the outer circumferential surface  41   a  extends from the proximal end of the outer circumferential surface  42   a  toward the side of the proximal end of the rigid shaft  4 . The tapered portion  42  may have a shape other than a truncated cone and may have, for example, a hemispherical shape or a stepped shape. 
     The operation unit  5  includes an operation handle  51  to be held by a hand of the doctor B. The doctor B can advance the entire treatment tool  1  by pushing the operation handle  51  toward the side of the distal end and can retract the entire treatment tool  1  by pulling the operation handle  51  toward the side of the proximal end. 
     The operation handle  51  is supported by a ball joint structure  52  between the rigid shaft  4  and the operation handle  51  so as to be tiltable in any direction with respect to the longitudinal axis of the rigid shaft  4 . The operation handle  51  is connected to the bending portion  2   a  by a wire passing through the inside of the shafts  2  and  4 , and the bending portion  2   a  is configured to bend in accordance with the tilting direction and tilting angle of the operation handle  51 . 
     The operation unit  5  may be further provided with a rotation operation part  53  for integrally rotating the end effector  3 , the flexible shaft  2 , and the rigid shaft  4  about the longitudinal axes of the shafts  2  and  4 . 
     The operation unit  5  may be further provided with a structure correspond in to the type of the end effector  3 . For example, when the end effector  3  is grasping forceps, a slider  54  for opening and closing the grasping forceps may be provided. 
     As shown in  FIG.  3   , the access device  10  includes a long tubular flexible tube  11  having flexibility and a rigid tubular holder (sheath)  12  connected to the proximal end of the flexible tube  11 . 
     The distal end of the flexible tube  11  is fixed to an attachment part  13  attached to the distal end of the endoscope  30 . The attachment part  13  is, for example, an annular or cylindrical cap fitted to the outside of the distal end of the endoscope  30 . By attaching the attachment part  13  to the distal end of the endoscope  30 , the access device  10  is attached to the endoscope  30  such that the flexible tube  11  is parallel to the endoscope  30 . As in the example in  FIG.  1   , when two treatment tools  1  are to be inserted into the body together with one endoscope  30 , the access device  10  may have two flexible tubes  11  connected to one attachment part  13 . 
     The holder  12  extends coaxially with the flexible tube  11 , and the inner hole of the flexible tube  11  and the inner hole of the holder  12  form a treatment tool channel  10   a  (see  FIG.  5   ), which extends from the proximal end face of the holder  12  to the distal end face of the flexible tube  11  and into which the treatment tool  1  is inserted. The inner diameter of the flexible tube  11  is larger than the outer diameter of the flexible shaft  2 , so that the flexible shaft  2  can be inserted through the flexible tube  11 . The inner diameter of the holder  12  is larger than the outer diameter of the rigid shaft  4 , so that the flexible shaft  2  and the shaft  4  can be inserted through the holder  12 . 
     A fixing portion  14  for fixing the holder  12  to the operating table  110  is fixed to the holder  12 . By inserting the rigid shaft  4  into the holder  12  fixed to the operating table  110  at the fixing portion  14 , the treatment tool  1  is supported by the holder  12 , and the rigid shaft  4  is guided by the holder  12  in the longitudinal direction of the holder  12 . Accordingly, it is possible for one doctor to easily operate two treatment tools  1 . 
     As shown in  FIGS.  4 A to  4 C , the medical manipulator system  100  further includes resistance generating parts  20  that are, provided on the holder  12  of the access device  10  and that generate resistance to the advancing of the rigid shaft  4  through the holder  12 . 
     The resistance generating parts  20  are spring plungers protruding radially inward from the inner circumferential surface of the holder  12 . The resistance generating parts  20  include movable bodies  21 , such as balls or pins, and elastic members  22 , such as springs, that urge the movable bodies  21  inward in the radial direction of the holder  12 . The elastic members  22  are accommodated in recesses formed in the inner circumferential surface of the holder  12 . The ends of the movable bodies  21  are spherical. 
     As shown in  FIG.  4 A , while the elastic members  22  are in a natural state, the distance from the longitudinal axis of the holder  12  (or the longitudinal axis of the treatment tool channel  10   a ) to the end of a resistance generating part  20  is larger than the radii of the end effector  3  and the flexible shaft  2  and is smaller than the radius of the shaft body  41 . Accordingly, the resistance generating parts  20  do not come into contact with the outer circumferential surfaces of the end effector  3  and the flexible shaft  2  but come into contact with the outer circumferential surfaces  41   a  and  42   a  of the rigid shaft  4 . 
     Specifically, the positions of the resistance generating parts  20  satisfy the following relationship: 
         D 1&gt; d 1&gt; D 2×2&gt; d 2,
 
     where D 1  is the inner diameter of the holder  12 , D 2  is the distance from the longitudinal axis of the holder  12  to a resistance generating part  20  in the radial direction when the elastic member  22  is in a natural state, d 1  the outer diameter of the shaft body  41  of the rigid shaft  4 , and d 2  is the outer diameter of the flexible shaft  2 . 
     The resistance generating parts  20  generate resistance to the advancing of the rigid shaft  4  through the holder  12  by making contact with the outer circumferential surface  42   a  of the tapered portion  42 . Specifically, the movable bodies  21  are pressed outward in the radial direction of the holder  12  by the outer circumferential surface  42   a,  and the elastic members  22 , which elastically contract in the radial direction of the holder  12 , generate an elastic restoring force. Because the outer circumferential surface  42   a  is inclined with respect to the longitudinal axis of the rigid shaft  4 , a component force of the elastic restoring force is generated in the longitudinal direction of the rigid shaft  4 , and this component force serves as resistance. Furthermore, the friction between the movable bodies  21  and the outer circumferential surface  42   a  also serves as resistance. 
     A doctor operating the treatment tool  1  feels the force generated in the resistance generating parts  20  through the rigid shaft  4  and the operation unit  5 , which are made of a rigid material. Hence, the resistance generated in the resistance generating parts  20  is efficiently transmitted to the hand of the doctor holding the operation handle  51 , and the doctor can clearly feel resistance. 
     The resistance generating parts  20  may also be configured to come into light contact with the outer circumferential surfaces of the end effector  3  and the flexible shaft  2 . 
     As shown in  FIG.  4 B , in the longitudinal direction of the holder  12 , the resistance generating parts  20  are provided at such positions that the tapered portion  42  of the rigid shaft  4  passes through the resistance generating parts  20  when the distal end of the treatment tool  1  advancing through the treatment tool channel  10   a  passes through the distal end of the flexible tube  11  or the vicinity of the distal end of the flexible tube  11  inside the flexible tube  11 . 
     Specifically, the resistance generating parts  20  generate large resistance based on the elastic restoring force and the friction when the distal end of the treatment tool  1  advancing through the treatment tool channel  10   a  passes through the distal end or the vicinity of the distal end of the flexible tube  11 . Meanwhile, the resistance generating parts  20  do not generate resistance until the distal end of the treatment tool  1  advancing through the treatment tool channel  10   a  reaches the distal end or the vicinity of the distal end of the flexible tube  11 . Hence, the doctor can recognize that the distal end of the treatment tool  1  has reached the distal end of the flexible tube  11  or the vicinity thereof on the basis of an increase in the resistance felt by the hand gripping the operation handle  51 . 
     As shown in  FIG.  5   , the dimensions of the treatment tool  1  and the access device  10  in the longitudinal direction have the following relationship: 
       ( L 3− L 1)≥ L 4&gt; L 5≥ L 2,
 
     where L 1  is the distance from the distal end of the treatment tool  1  to the proximal end of the bending portion  2   a,  L 2  is the distance from the distal end of the treatment tool  1  to the proximal end of the tapered portion  42  (the distal end of the shaft body  41 ), L 3  is the distance from the distal end of the treatment tool  1  to the proximal end of the rigid shaft  4 , L 4  is the distance from the distal end of the flexible tube  11  to the proximal end of the holder  12 , and L 5  is the distance from the distal end of the flexible tube  11  to the resistance generating parts  20 . 
     Because L 5  is larger than or equal to L 2 , the resistance generating parts  20  come into contact with the outer circumferential surface  42   a  of the tapered portion  42  inside the holder  12  to generate resistance before the distal end of the treatment tool  1  advancing through the flexible tube  11  protrudes from the distal end of the flexible tube  11 . 
     Because L 4  is larger than L 5 , the resistance generating parts  20  come into contact with the outer circumferential surface  42   a  of the tapered portion  42  after the rigid shaft  4  is inserted into the holder  12  in the process of inserting the treatment tool  1  into the access device  10 . As a result, the rigid shaft  4  is supported by the holder  12 , stabilizing the position of the treatment tool  1 , and thus, the operability of advancing/retracting operations of the treatment tool  1  is improved. 
     Because L 3 −L 1  is larger than or equal to L 4 , the end effector  3  and the bending portion  2   a  completely protrude from the distal end of the flexible tube  11  in a state in which the entire rigid shaft  4  is inserted through the holder  12 . Hence, the end effector  3  can be moved without being restricted by the access device  10 , and the treatment performance is stabilized. 
     Next, the operation of the medical manipulator system  100  will be described. 
     In order to treat the affected area in the body of the patient A using the medical manipulator system  100  according to this embodiment, a doctor attaches the attachment part  13  of the access device  10  to the distal end of the endoscope  30 , inserts the treatment tool  1  into the treatment tool channel  10   a  from the opening at the proximal end of the holder  12 , and advances the treatment tool  1  through the treatment tool channel  10   a  from the proximal end of the holder  12  toward the distal end of the flexible tube  11  by operating the operation handle  51  held in his/her hand. 
     As shown in  FIG.  4 A , the end effector  3  and the flexible shaft  2  pass through the holder  12  without touching the resistance generating parts  20 . Hence, until the tapered portion  42  of the rigid shaft  4  reaches the resistance generating parts  20 , the resistance to the advancing of the treatment tool  1  inside the treatment tool channel  10   a  is only the relatively small friction between the inner circumferential surface of the flexible tube  11  and the outer circumferential surface of the flexible shaft  2 . The doctor B can smoothly advance the treatment tool  1  through the treatment tool channel  10   a.    
     Then, as shown in  FIG.  4 B , when the distal end of the treatment tool  1  approaches the distal end of the flexible shaft  2 , the outer circumferential surface  42   a  of the tapered portion  42  comes into contact with the resistance generating parts  20 , and the resistance generating parts  20  generate resistance to the advancing of the rigid shaft  4 . The doctor B feels an increase in the resistance to the advancing of the treatment tool  1  in his/her hand. While the resistance generating parts  20  are in contact with the outer circumferential surface  42   a,  the amount of compression and the elastic restoring force of the elastic members  22  gradually increase as the treatment tool  1  is advanced, and thus, the resistance further gradually increases. From an increase in the resistance, the doctor B can intuitively recognize the approach of the distal end of the treatment tool  1  to the vicinity of the distal end of the flexible tube  11 . 
     As shown in  FIG.  4 C , the tapered portion  42  passes through the resistance generating parts  20  at the same or substantially the same time at which the distal end of the treatment tool  1  protrudes from the distal end of the flexible tube  11 . Subsequently, the outer circumferential surface  41   a  of the shaft body  41  comes into contact with the resistance generating parts  20 , and the treatment tool  1  advances while maintaining contact between the outer circumferential surface  41   a  and the resistance generating parts  20 . 
     Also in a state in which the resistance generating parts  20  are in contact with the outer circumferential surface  41   a , the elastic members  22  in the contracted state continue to generate the elastic restoring force. Note that, because the outer circumferential surface  41   a  is parallel to the longitudinal axis of the rigid shaft  4 , a component force of the elastic restoring force is not generated in the longitudinal direction of the rigid shaft  4 , and the resistance generated by the resistance generating parts  20  is only the friction between the movable bodies  21  and the outer circumferential surface  41   a.  Furthermore, because the amount of elastic compression of the elastic members  22  is constant, the magnitude of the friction is constant. Hence, after the distal end of the treatment tool  1  protrudes from the distal end of the flexible tube  11 , the resistance generated by the resistance generating parts  20  decreases, and only small resistance having a certain magnitude is generated to the advancing of the treatment tool  1 . The doctor can recognize that the end effector  3  at the distal end of the treatment tool  1  has protruded from the distal end of the flexible tube  11  from the decrease in the resistance felt by his/her hand. 
     As described above, in a state in which the end effector  3  is disposed outside the distal end of the flexible tube  11 , the resistance generated by the resistance generating parts  20  is small. Hence, the doctor B can advance or retract the end effector  3  almost without feeling resistance, by advancing or retracting the treatment tool  1 . 
     As described above, according to this embodiment, in the process of inserting the treatment tool  1  into the access device  10 , the magnitude of the resistance generated by the resistance generating parts  20  changes with time in accordance with the position of the distal end of the treatment tool  1  with respect to the distal end or the flexible tube  11 . Specifically, when the distal end of the treatment tool  1  is away from the distal end of The flexible tube  11 , the resistance is zero, and when the distal end of the treatment tool  1  is near the distal end of the flexible tube  11 , the resistance gradually increases, and the resistance becomes maximum when or immediately before the distal end of the treatment tool  1  protrudes from the distal end of the flexible tube  11 . The resistance generated by the resistance generating parts  20  is efficiently transmitted by the rigid shaft  4  and the operation unit  5  to the hand of the doctor gripping The operation handle  51  near the resistance generating parts  20 . Hence, the doctor who is operating the treatment tool  1  can reliably recognize the timing at which the distal end of the treatment tool  1  protrudes from the distal end of the flexible tube  11 . 
     Furthermore, after the distal end of the treatment tool  1  has protruded from the distal end of the flexible tube  11 , the resistance decreases to a certain magnitude. Hence, the end effector  3  disposed outside the flexible tube  11  can be moved smoothly. 
     Furthermore, the resistance generated by the resistance generating parts  20  to the retraction of the rigid shaft  4  inside the holder  12  is only the friction between the resistance generating parts  20  and the outer circumferential surfaces  41   a  and  42   a,  which is sufficiently small. Hence, when the treatment tool  1  is removed from the body through the treatment tool channel  10   a,  the doctor B can retract the treatment tool  1  almost without feeling resistance. 
     In this embodiment, the resistance generating parts  20  may have such shapes that they make point contact with the outer circumferential surface  41   a  and surface contact or line contact with the outer circumferential surface  42   a.  This can further increase the resistance when the resistance generating parts  20  are in contact with the outer circumferential surface  42   a  and can further reduce the resistance when the resistance generating parts  20  are in contact with the outer circumferential surface  41   a.    
     For example, the movable bodies  21  may have a cone shape with a spherical end, and the side surfaces of the movable bodies  21  may be conical surfaces that make line contact with the outer circumferential surface  42   a  or may have concave surfaces that make surface contact with the outer circumferential surface  42   a.    
     Although the resistance generating parts  20  are spring plungers having the elastic members  22  in this embodiment, instead, another form is also possible. For example, the entire resistance generating parts  20  may be elastic members that are made of an elastic material. The elastic material is, for example, a resin material having elasticity. The resin material may be rubber or a plastic having high lubricity, such as polyacetal or monomer-cast nylon. 
       FIGS.  6 A to  6 C  show examples of the resistance generating part  20 , the entirety of which is an elastic member. The resistance generating part  20  is elastically deformed in at least one of the longitudinal direction and the radial direction of the holder  12  by contact with the inclined surface  42   a.  The resistance generating parts  20  in  FIGS.  6 A and  6 B  are bent and laid down by contact with the outer circumferential surfaces  41   a  and  42   a.  The resistance generating part  20  in  FIG.  6 C  is elastically compressed in the longitudinal direction of the resistance generating part  20 , which corresponds to the radial direction of the holder  12 , by contact with the outer circumferential surfaces  41   a  and  42   a.    
     Although the rigid shaft  4  has the tapered portion  42  in this embodiment, the rigid shaft  4  may have no tapered portion  42 . In that case, the resistance generating parts  20  may generate resistance by another means, instead of generating resistance by contact with the inclined surface  42   a.    
     For example, as shown in  FIG.  7   , the resistance generating parts  20  may be configured to generate resistance by being fitted into a groove  43  in the outer circumferential surface  41   a.    
     With this configuration, the resistance generating parts  20  generate a click feeling, serving as resistance, to both advancing and retraction of the rigid shaft  4  inside the holder  12 . Hence, the doctor B can also recognize The timing at which the distal end of the treatment tool  1  retracted in the treatment tool channel  10   a  is retracted into the distal end of the flexible tube  11 . Accordingly, in the process of removing the treatment tool  1 , the doctor B can intuitively recognize that the end effector  3  has been completely stored in the flexible tube  11  from the click feeling. 
     Because the inner diameter D 1  of the holder  12  is substantially equal to the outer diameter d 1  of the rigid shaft  4 , the clearance between the holder  12  and the flexible shaft  2  is large. Hence, in the process of inserting the treatment. tool  1  into the access device  10 , the flexible shaft  2  may meander in the holder  12 . More specifically, due to the friction between the flexible shaft  2  and the flexible tube  11 , the flexible shaft  2  is caught in the flexible tube  11 , and a compressive force is applied to the flexible shaft  2  in the holder  12 , making the flexible shaft  2  meander. However, because the doctor B cannot observe the flexible shaft  2  in the opaque holder  12 , the doctor B may not notice the meandering of the flexible shaft  2 . When the operation unit  5  is further pushed in with a strong force in a state in which the flexible shaft  2  meanders, buckling of the flexible shaft  2  occurs. Such meandering and buckling of the flexible shaft  2  are particularly likely to occur with the flexible shaft  2  having a small diameter and high flexibility. Meanwhile, in order to facilitate the ease of insertion of the flexible shaft  2  into a complexly curved body cavity, such as the large intestine, the flexible shaft  2  preferably has a small diameter and high flexibility. 
     In this embodiment, in order to prevent buckling of the flexible shaft  2  in the holder  12 , a telescopic structure  15  including two or more pipes may be provided in the holder  12 , as shown in  FIGS.  8 A and  8 B . The two or more pipes have different inner and outer diameters, are concentrically arranged, and are telescopically extendable in the longitudinal direction of the holder  12 .  FIGS.  8 A and  8 B  show, as an example, the telescopic structure  15  including three pipes  15   a,    15   b,  and  15   c.    
     The outer pipe  15   a,  which has the largest outer diameter and is disposed on the outermost side, is disposed at the distal end of the holder  12  and is fixed to the holder  12 . The other two pipes,  15   b  and  15   c,  are movable relative to the outer pipe  15   a  in the longitudinal direction of the holder  12 . In a state in which the telescopic structure  15  is extended to the maximum, the proximal end of the inner pipe  15   c,  which has the smallest outer diameter and is arranged innermost, is disposed at or near the proximal end of the holder  12 . The inner diameter of the inner pipe  15   c  is substantially equal to the outer diameter of the flexible shaft  2  and is smaller than the outer diameter of the rigid shaft  4 . 
     A spring  16   a  for urging the intermediate pipe  15   b  toward the proximal end of the holder  12  is disposed between the pipes  15   a  and  15   b,  and a spring  16   b  for urging the inner pipe  15   c  toward the proximal end of the holder  12  is disposed between the pipes  15   b  and  15   c.  In a state in which no pressing force in the longitudinal direction is applied to the inner pipe  15   c,  the pipes  15   a,    15   b,  and  15   c  are arranged in the fully extended state by the urging force of the springs  16   a  and  16   b,  as shown in  FIG.  8 A . 
     The flexible shaft  2  of the treatment tool  1  is inserted into the inner pipe  15   c  of the telescopic structure  15  in the fully extended state, and then, the rigid shaft  4  is inserted into the holder  12  while pressing the inner pipe  15   c  with the distal end of the rigid shaft  4  against the urging force of the springs  16   a  and  16   b.  When the telescopic structure  15  is in a fully contracted state, as shown in  FIG.  8 B , the end effector  3  and the bending portion  2   a  are disposed at positions outside the distal end of the flexible tube  11 . 
     In this case, because the flexible shaft  2  is supported by the inner pipe  15   c  of the telescopic structure  15 , meandering and buckling of the flexible shaft  2  in the holder  12  can be prevented. In particular, meandering and buckling are likely to occur at the proximal end portion of the flexible shaft  2 , where the outer diameter sharply changes and the rigidity sharply changes. Hence, by supporting the proximal end portion of the flexible shaft  2  with the inner pipe  15   c,  meandering and buckling of the flexible shaft  2  can be effectively prevented. 
     In a state in which the rigid shaft  4  is inserted through the holder  12 , the rigid shaft  4  is subjected to an urging force in a direction in which the rigid shaft  4  is retracted from the compressed springs  16   a  and  16   b.  The urging force of the springs  16   a  and  16   b  is preferably set to be smaller than the friction between the flexible shaft  2  and the flexible tube  11 . By doing so, the rigid shaft  4  can be held at a fixed position against the urging force of the springs  16   a  and  16   b  when the doctor B releases his/her hand from the treatment tool  1  in a state in which the rigid shaft  4  is disposed in the holder  12 . 
     In order that the flexible shaft  2  is supported not only by the inner pipe  15   c  but also by the intermediate pipe  15   b  and the outer pipe  15   a,  the diameters of through-holes  15   d  and  15   e  at the ends of the pipes  15   a  and  15   b,  respectively, are preferably substantially equal to the outer diameters of the flexible shaft  2 . With this configuration, it is possible to control the shape of the flexible shaft  2  in the holder  12  to a linear shape with the through-holes  15   d  and  15   e  and to more reliably prevent meandering and buckling of the flexible shaft  2 . 
     As the amount of insertion of the rigid shaft  4  into the holder  12  increases, the amount of contraction of the springs  16   a  and  16   b  increases. When the elastic restoring force of the springs  16   a  and  16   b  increases in accordance with the amount of contraction, the rigid shaft  4  needs to be inserted with a greater amount of operation force as the rigid shaft  4  is advanced through the holder  12 . 
     In order to prevent the change in the amount of operation force like this, the springs  16   a  and  16   b  are preferably constant-load springs, which generate a constant elastic restoring force regardless of the amount of contraction. By using the constant-load spring, the rigid shaft  4  can be inserted into the holder  12  with a constant amount of operation force, regardless of the amount of insertion of the rigid shaft  4 . 
     The extension means for extending the telescopic structure  15  may be a mechanism for fixing the inner pipe  15   c  to the treatment tool  1 , instead of the springs  16   a  and  16   b . For example, as shown in  FIG.  9   , the extension means may include magnets  17   a  and  17   b,  which are provided at the proximal end of the inner pipe  15   c  and the distal end of the rigid shaft  4  and generate a magnetic attractive force therebetween. 
     Although the resistance generating parts generate resistance by means of an elastic restoring force generated by elastic deformation of at least a portion of the resistance generating parts in this embodiment, instead, resistance may be generated by another method. For example, the resistance generating parts may be provided on at least one of the outer circumferential surface of the rigid shaft  4  and the inner circumferential surface of the holder  12  and may include a high-friction material that generates friction as resistance. 
     When the telescopic structure  15  is provided in the holder  12 , the resistance generating parts  20  may be provided on the telescopic structure  15 . 
     For example, as shown in  FIG.  10   , the resistance generating parts  20  may be provided on the outer pipe  15   a  and may be configured to elastically contract by contact with the intermediate pipe  15   b.  With this configuration, the doctor B can feel resistance when the advancing intermediate pipe  15   b  goes over the resistance generating parts  20  protruding from the inner surface of the outer pipe  15   a.  Accordingly, the doctor B can intuitively recognize the approach of the distal end of the treatment tool  1  to the vicinity of the distal end of the flexible tube  11 . 
     The springs  16   a  and  16   b  may be made to function as resistance generating parts by differentiating the spring constants of the springs  16   a  and  16   b  from each other. 
     More specifically, the spring  16   a  in the outer pipe  15   a  has a greater spring constant than the spring  16   b  in the intermediate pipe  15   b.  As the rigid shaft  4  is advanced, the spring  16   b  is preferentially compressed first, and after the spring  16   b  is compressed to some extent, the spring  16   a.  is compressed. The compression of the spring  16   a  increases the resistance. By setting the spring constant of the spring  16   a  to such an extent that the doctor B can recognize an increase in the resistance, the doctor B can intuitively recognize the approach of the distal end of the treatment tool  1  to the vicinity of the distal end of the flexible tube  11 . 
     The following aspects can be derived from the embodiments. 
     According to an aspect of the present invention, there is provided a medical manipulator system including: a treatment tool having a long flexible shaft and a rigid shaft connected to a proximal end of the flexible shaft; an access device that guides the treatment tool and that has a long flexible tube, into which the flexible shaft is inserted, and a rigid sheath, which is connected to a proximal end of the flexible tube and into which the flexible shaft and the rigid shaft are inserted; and a resistance generating part that is provided on at least one of the rigid shaft and the sheath and that generates resistance to advancing of the rigid shaft through the sheath. The resistance generated by the resistance generating part increases when a distal end of the advancing treatment tool passes through a distal end of the flexible tube or a vicinity of the distal end of the flexible tube inside the flexible tube, and the resistance generated by the resistance generating part decreases after the distal end of the advancing treatment tool passes through the distal end of the flexible tube or the vicinity. 
     The flexible tube of the access device is inserted into the body, and the rigid sheath of the access device is disposed outside the body. Accordingly, a path for the treatment tool from the outside of the body to the target position inside the body is ensured inside the access device. An operator, such as a doctor, inserts the flexible shaft into the flexible tube until the rigid shaft is disposed inside the sheath. In this state, the rigid shaft is stably supported and guided by the rigid sheath of the access device. Hence, the operator can easily perform advancing/retracting operations of the treatment tool. 
     In this case, when the distal end of the treatment tool advancing through the flexible tube passes through the distal end of the flexible tube or the vicinity thereof, in other words, when or immediately before the distal end of the treatment tool protrudes from the distal end of the access device, the resistance generated by the resistance generating part provided on at least one of the rigid shaft and the sheath increases. The increase in the resistance is efficiently transmitted, via the rigid shaft, to the hand of the operator gripping the treatment tool at or near the rigid shaft. Accordingly, the operator who is operating the treatment tool can reliably recognize the timing when the distal end of the treatment tool protrudes from the distal end of the access device. 
     Furthermore, because the resistance decreases after the distal end of the treatment tool protrudes from the distal end of the access device, in a state in which the distal end of the treatment tool protrudes from the distal end of the access device, the treatment tool can be smoothly advanced. 
     In the above aspect, it is preferable that the resistance generated by the resistance generating part gradually increase as the distal end of the advancing treatment tool approaches the distal end of the flexible tube or the vicinity, and become maximum when a distal end of the treatment tool passes through the distal end of the flexible tube or the vicinity. 
     With this configuration, the operator can more reliably recognize the timing when the treatment tool protrudes from the distal end of the access device on the basis of a change in the magnitude of the resistance. 
     In the above-described aspect, the rigid shaft may have a parallel surface extending parallel to a longitudinal axis of the sheath, and the resistance generated by the resistance generating part may decrease to a constant magnitude after the distal end of the advancing treatment tool passes through the distal end of the flexible tube or the vicinity. 
     With this configuration, the resistance decreases after the distal end of the treatment tool protrudes from the distal end of the access device, and the magnitude of the resistance is maintained constant by the interaction between the resistance generating part and the parallel surface. Hence, in a state in which the distal end of the treatment tool protrudes from the distal end of the access device, the treatment tool can be advanced with a constant force. 
     In the above aspect, the resistance generating part may protrude radially inward from an inner circumferential surface of the sheath, at least a portion of the resistance generating part may be an elastic member that is elastically deformed by contact between the resistance generating part and the rigid shaft, and the resistance generating part may be provided at such a position that a distal end of the rigid shaft passes through the resistance generating part when the distal end of the advancing treatment tool passes through the distal end of the flexible tube or the vicinity. 
     With this configuration, when the distal end of the advancing treatment tool passes through the distal end of the access device or the vicinity thereof, the resistance generating part comes into contact with the rigid shaft, and the elastic member is elastically deformed, generating an elastic restoring force, serving as resistance. Furthermore, friction, serving as resistance, is generated between the resistance generating part and the rigid shaft. In this way, the resistance can be mechanically generated with a simple structure. 
     In the above-described aspect, an end face of the resistance generating part may be a spherical surface, and the resistance may be a component force, in a longitudinal direction of the rigid shaft, of an elastic restoring force with which the resistance generating part presses the rigid shaft in a radial direction. 
     With this configuration, in which the end face of the resistance Generating part comes into point contact with the cuter surface of the rigid shaft after the distal end of the treatment tool protrudes from the distal end of the access device, the friction, serving as resistance, can be reduced to substantially zero. 
     In the above-described configuration, the rigid shaft may have an inclined surface inclined so as to be gradually displaced radially outward from a side of the distal end toward a side of a proximal end with respect to a longitudinal axis of the rigid shaft, the inclined surface may be connected, on a side of a proximal end of the inclined surface, to a distal end of a parallel surface extending toward the side of the proximal end of the rigid shaft, and the resistance may be a component force, in a longitudinal direction of the rigid shaft, of an elastic restoring force with which the resistance generating part presses the rigid shaft in a radial direction. 
     With this configuration, the resistance generating part comes into contact with the inclined surface and then comes into contact with the parallel surface. The resistance generating part is elastically deformed by contact with the inclined surface and generates a component force of an elastic restoring force, serving as resistance. Because the inclined surface is gradually displaced radially outward from the distal side toward the proximal side, the amount of elastic deformation and the elastic restoring force of the elastic member increase, and thus the resistance increases, as the rigid shaft advances through the sheath. Thus, the resistance can be gradually increased as the treatment tool is advanced. Furthermore, when the resistance generating part is in contact with the parallel surface, a component force of the elastic restoring force is not generated, and, because the amount of elastic deformation of the resistance generating part is constant, the magnitude of the friction is constant. Hence, after the distal end of the treatment tool passes through the distal end of the access device or the vicinity thereof, the resistance can be decreased, and the magnitude of the resistance can be made constant. 
     In the above-described configuration, the resistance generating part may be formed of a resin material and may be elastically deformed in at least one of a longitudinal direction and a radial direction of the rigid sheath by contact with the rigid shaft. 
     With this configuration, when the resistance generating part is elastically deformed in the longitudinal direction of the sheath, an elastic restoring force in the longitudinal direction of the rigid shaft, serving as resistance, can be generated. Furthermore, when the resistance generating part is elastically deformed in the radial direction of the sheath, friction, serving as resistance, can be generated. 
     REFERENCE SIGNS LIST 
       1  treatment tool 
       2  flexible shaft 
       4  rigid shaft 
       41   a  outer circumferential surface (parallel surface) 
       42   a  outer circumferential surface (inclined surface) 
       10  access device 
       11  flexible tube 
       12  holder (sheath) 
       20  resistance generating part 
       22  elastic member, spring