Patent Publication Number: US-2022211456-A1

Title: Surgical tool

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present international application claims the benefit of the Japanese patent application No. 2019-045601 filed on Mar. 13, 2019 with the Japan Patent Office, the entire disclosure of the Japanese patent application No. 2019-045601 is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a surgical tool. 
     BACKGROUND ART 
     In regard to master-slave type surgical robots, there have been demands for a technique to transmit external forces acting on robot forceps, which are a type of surgical tool, to operators who operate the robots in isolated places in order to improve safety and shorten the time for doctors to learn the operation. The external forces to be transmitted to the operators are estimated based on information such as the position of actuators and driving forces. 
     Known methods for driving surgical tools of robots include a method in which a driving force generated by a driving source, such as an actuator, is transmitted to a surgical tool through a wire to drive the surgical tool (see, for example, Patent Document 1). The wire is arranged between the driving source and the surgical tool, and the tension thereof is adjusted to within a specified range. 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: Japanese Patent No. 4938753 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In the technique described in Patent Document 1, part of the wire is wound around a columnar or cylindrical adjusting member. The tension of the wire is adjusted by controlling a torque that is a force applied in the direction to reel in the wire on the adjusting member. 
     It is difficult, however, to make fine adjustment of the wire in the method in which the torque of the adjusting member is controlled to adjust the tension of the wire. It is also difficult to maintain the adjusted tension and fix the tension at the adjusted tension. 
     The tension of the wire is considered to influence the magnitude of the frictional force generated when the driving force is transmitted to the surgical tool. If more than one wires are provided, the tensions of the wires are different, and thus likely to cause variations in tension. That is, the frictional force generated when the surgical tool is driven is different from one wire to another, for example, different for each movement of the surgical tool. On the other hand, with regard to external force estimation for transmitting the external force acting on the surgical tool, the accuracy of the external force estimation tends to decrease due to changes in the frictional forces generated when the external force is transmitted. 
     It is desirable that one aspect of the present disclosure provides a surgical tool that can enhance the accuracy of the external force estimation. 
     Means for Solving the Problems 
     The present disclosure provides the following means. 
     One aspect of the present disclosure provides a surgical tool comprising a driven portion, a cord-shaped element, a rotor, a first and a second supporting portion, a rotational shaft, and a securing portion. To the driven portion, a driving force is transmitted from an external portion. The cord-shaped element transmits a movement of the driven portion to a working portion. The rotor has a circumferential surface around which the cord-shaped element extending from the driven portion to the working portion is wound. The first and second supporting portions are arranged such that the rotor is interposed therebetween, and support the rotor such that the rotor is movable in an approaching and separating manner in relation to at least one of the driven portion and the working portion. The rotational shaft includes a first end securable to the first supporting portion, and supports the rotor such that the rotor is rotatable about a rotational axis thereof. The securing portion is arranged between a second end of the rotational shaft and the second supporting portion. A position of the securing portion relative to the rotational shaft is changeable in a rotational axis direction. The securing portion is securable to the second supporting portion. 
     In the surgical tool according to the present disclosure, the arrangement position of the rotor can be changed in the approaching and separating manner in relation to at least one of the driven portion and the working portion, and thereby the tension of the cord-shaped element can be adjusted. In comparison with, for example, the tension adjustment method described in Patent Document 1, it is easy to finely adjust the tension and to maintain the adjusted tension. Moreover, it is possible to reduce the variation in tension to stabilize the tension. Thus, the frictional force acting between the driven portion and the working portion is also stabilized. This facilitates improvement in accuracy of external force estimation. 
     Furthermore, the rotational shaft and the securing portion are configured such that the relative positions thereof in the rotational axis direction can be changed. Thus, the rotation of the rotor is less likely to be inhibited. In the case, for example, where the rotational shaft is secured to the first supporting portion and the securing portion is secured to the second supporting portion, which is the other supporting portion, the length of the combination of the rotational shaft and the securing portion is adjusted by changing the relative positions even when the length of the combination is different from the distance between the first and second supporting portions. Accordingly, the influence of the securing does not easily reach the rotor supported by the rotational shaft, and the rotation is less likely to be inhibited. 
     In the case where two or more rotors are provided, it is easy to change the arrangement position of each of the rotors in the approaching and separating manner. In other words, even after fixing the arrangement position of one rotor, the arrangement positions of other rotors can be easily changed in the approaching and separating manner. 
     In the case, for example, where there are no securing portions and only the rotational shafts are provided, in response to the arrangement position of one of the rotors being fixed, each end of the rotational shaft of the one rotor comes into contact with the first supporting portion or the second supporting portion. At this time, the first and second supporting portions come close to each other and the distance therebetween becomes equal to the length of the rotational shaft. That is, each end of the rotational shafts of the other rotors also comes into contact with the first supporting portion or the second supporting portion. Then, despite an attempt to change the arrangement positions of the other rotors in the approaching and separating manner, the ends of the rotational shafts of the other rotors cannot be easily moved in the approaching and separating manner since the frictional force acting on the surfaces in contact with the first and second supporting portions tends to large. 
     In contrast, in the case where the relative positions of the rotational shafts and the securing portions can be changed, the first and second supporting portions do not come close to each other even after fixing the arrangement position of one rotor. That is, the frictional force acting on the contacting surfaces between the rotational shafts of the other rotors and the supporting portion, and the contacting surfaces between the securing portions and the supporting portion is less likely to be large. Accordingly, even after fixing the arrangement position of one rotor, it is easy to change the arrangement positions of other rotors in the approaching and separating manner. 
     Furthermore, the length of the combination is adjusted by changing the relative positions. Thus, a load is less likely to be imposed on the first and second supporting portions. In the case, for example, where the first and second supporting portions are plate-shaped members extending in a direction intersecting the rotational shafts, the load may cause deformation or breakage of the first and second supporting portions. Even in such a case, it is easy to inhibit deformation and breakage of the first and second supporting portions since the load is less likely to be imposed thereon. 
     In one aspect of the present disclosure, the first supporting portion and the second supporting portion may comprise an elongated hole extending in an approaching and separating direction of the rotor. A stator inserted in the elongated hole may be provided to facilitate pressing of the rotational shaft and the securing portion respectively against the first supporting portion and the second supporting portion. 
     Pressing the rotational shaft against the first supporting portion and pressing the securing portion against the second supporting portion using the elongated hole and the stator in this way enables fixation of the arrangement position of the rotor in relation to at least one of the driven portion and the working portion. Increasing the pressing force enables more reliable fixation of the arrangement position, and reducing the pressing force facilitates changes in the arrangement position. 
     In one aspect of the present disclosure, one of the rotational shaft and the securing portion may comprise a projection extending in the rotational axis direction that is a direction of the rotational axis, and another may comprise a recess that engages with the projection. 
     Use of the projection extending in the rotational axis direction and the recess engaged with the projection as described above allows changes in the position of the rotational shaft relative to the securing portion in the rotational axis direction. Moreover, it is possible to maintain the relative position in the direction intersecting the rotational axis direction. 
     In one aspect of the present disclosure, the driven portion may be moved linearly in a reciprocating manner by the driving force transmitted. The rotor may be arranged such that the driven portion is interposed between the rotor and the working portion. Of ends of the cord-shaped element wound around the rotor, a first end of the cord-shaped element may be arranged to extend toward the driven portion, and a second end of the cord-shaped element may be arranged to extend toward the working portion. 
     Arrangement of the driven portion between the rotor and the working portion and transmission of the reciprocating movement of the driven portion to the working portion through the cord-shaped element wound around the rotor facilitate adjustment of the tension of the cord-shaped element. 
     Effects of the Invention 
     In the surgical tool according to the present disclosure, the arrangement position of the rotor can be changed in the approaching and separating manner in relation to at least one of the driven portion and the working portion, and the rotational shaft and the securing portion are configured such that the relative positions thereof in the rotational axis direction can be changed. Accordingly, the surgical tool achieves an effect of enhancing the accuracy of the external force estimation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a configuration of a surgical tool according to one embodiment of the present disclosure. 
         FIG. 2  is a partial sectional view illustrating a state of the surgical tool in  FIG. 1  engaged with an adapter. 
         FIG. 3  is a perspective view illustrating arrangement positions of a first housing portion and a second housing portion of the surgical tool in  FIG. 1 . 
         FIG. 4  is a top view illustrating a configuration inside of a housing in 
         FIG. 1 . 
         FIG. 5  is a partial sectional view illustrating the configuration inside of the housing in  FIG. 1 . 
         FIG. 6A  is a diagram illustrating configurations of grooves and cut-out portions formed on a pulley, and  FIG. 6B  is a schematic diagram illustrating an arrangement of a wire extending from the pulley to a shaft. 
         FIG. 7A  is a schematic diagram illustrating a movement of the wire in the present embodiment, and  FIG. 7B  is a schematic diagram illustrating a movement of the wire in a spiral groove. 
     
    
    
     EXPLANATION OF REFERENCE NUMERALS 
     
         
         
           
               1  . . . surgical tool,  3  . . . motive power transmitter (external portion),  12  . . . forceps (working portion),  21  . . . first housing portion (supporting portion),  22  . . . second housing portion (supporting portion),  23  . . . elongated hole for pulley (elongated hole),  31  . . . drive element (driven portion),  35  . . . wire (cord-shaped element),  41  . . . pulley (rotor),  46  . . . pulley&#39;s rotational shaft (rotational shaft),  49  . . . leading end (projection),  51  . . . securing block (securing portion),  52  . . . recess,  56  . . . securing screw (stator) 
           
         
       
    
     MODE FOR CARRYING OUT THE INVENTION 
     A surgical tool  1  according to one embodiment of the present disclosure will be described with reference to  FIGS. 1 to 7 . The surgical tool  1  of the present embodiment is applied to a master-slave type surgical robot. The surgical tool  1  of the present embodiment is used for surgery. As shown in  FIG. 1 , the surgical tool  1  comprises a shaft  11  with forceps  12  arranged at its leading end, and a housing  20  to be attached to the surgical robot. The forceps  12  correspond to the working portion. 
     The shaft  11  is a rod-shaped member extending from the housing  20 . In the present embodiment, the shaft  11  is a rod-shaped member extending along the Z-axis direction. The forceps  12 , which are the working portion, are provided at the leading end of the shaft  11  that is the end remote from the housing  20 . Inside the shaft  11 , a space is provided extending from the housing  20  toward the forceps  12 . A wire  35 , which will be described later, can be arranged in this space. 
     Hereinafter, the end of the shaft  11  remote from the housing  20  is the end on the positive side of the Z axis, and the direction from the housing  20  toward the forceps  12  is the positive direction of the Z-axis. 
     As shown in  FIG. 2 , the housing  20  is attachable to and detachable from an adapter  2  of the surgical robot. To the housing  20 , a driving force that drives the forceps  12  is transmitted from a power device  4  via a motive power transmitter  3  of the adapter  2 . The motive power transmitter  3  corresponds to the external portion. 
     As shown in  FIGS. 3 to 5 , the housing  20  comprises a first housing portion  21 , a second housing portion  22 , drive elements  31 , the wire  35 , pulleys  41 , pulleys&#39; rotational shafts  46 , securing blocks  51 , and securing screws  56 . 
     The first and second housing portions  21 ,  22  respectively correspond to the first and second supporting portions. The drive elements  31 , the wire  35 , the pulleys  41 , the pulleys&#39; rotational shafts  46 , the securing blocks  51 , and the securing screws  56  respectively correspond to the driven portion, the cord-shaped element, the rotor, the rotational shaft, the securing portion, and the stator. 
     As shown in  FIGS. 4 and 5 , the first and second housing portions  21 ,  22  are plate-shaped members that form at least part of the body of the housing  20 . In the present embodiment, the first housing portion  21  is arranged on the surface of the housing  20  facing the adapter  2 , and the second housing portion  22  is arranged on the surface of the housing  20  remote from the adapter  2 . Moreover, the first and second housing portions  21 ,  22  are arranged parallel to the X-Z plane. 
     In the housing  20 , the surface facing the adapter  2  is the surface on the negative side of the Y-axis, and the surface remote from the adapter  2  is the surface on the positive side of the Y-axis. 
     As shown in  FIGS. 4 and 5 , at least the wire  35 , guide pulleys  26 , the pulleys  41 , the pulleys&#39; rotational shafts  46 , and the securing blocks  51  are arranged between the first and second housing portions  21 ,  22 . 
     Elongated holes  23  for pulleys that are used for arranging the pulleys  41  are provided in the areas of the first and second housing portions  21 ,  22  located near the ends remote from the shaft  11 , that is, in the areas near the ends on the negative side of the Z-axis. 
     Each elongated hole  23  for pulley is a through-hole extending to the positive side of the Z-axis, which is toward the shaft  11  in the first and second housing portions  21 ,  22 . In other words, each elongated hole  23  for pulley is an elongated hole extending along the Z-axis direction. In the present embodiment, three elongated holes  23  for pulleys are arranged side by side at intervals in the X-axis direction. The number of the elongated holes  23  for pulleys to provide is not limited to three, and may be more or less than three. 
     The first housing portion  21  is provided with elongated holes  24  for driving in which the drive elements  31  are arranged. Each of the elongated holes  24  for driving allows the movement of the drive element  31  in the direction along the first housing portion  21 , and restricts the movement in the direction away from the first housing portion  21 , that is, in the Y-axis direction. 
     The elongated holes  24  for driving are provided near the shaft  11  as compared with the elongated holes  23  for pulleys in the first housing portion  21 . For example, the elongated holes  24  for driving are provided in the central area of the first housing portion  21  in the Z-axis direction. 
     Each of the elongated holes  24  for driving is a through-hole linearly extending toward the shaft  11 , that is, to the positive side of the Z-axis. In other words, each of the elongated holes  24  for driving is an elongated hole extending along the Z-axis direction. In the present embodiment, the three elongated holes  24  for driving are arranged side by side at intervals in the X-axis direction. The number of the elongated holes  24  for driving to provide may correspond to the number of the elongated holes  23  for pulleys, may be more than three, or may be less than three. 
     In the present embodiment, the three elongated holes  24  for driving are equal in length in the Z-axis direction. The lengths of the three elongated holes  24  for driving in the Z-axis direction may be equal as mentioned above, or may be different. 
     The guide pulleys  26  guide the wire  35 , extending from the drive elements  31  to the shaft  11 , to the internal space of the shaft  11 . More specifically, the guide pulleys  26  guide the wire  35 , extending from the drive elements  31  arranged on the positive side or the negative side of the shaft  11  in the X-axis direction away from the shaft  11 , to the shaft  11 . 
     As shown in  FIGS. 4 and 5 , the guide pulleys  26  are arranged between the first and second housing portions  21 ,  22  and adjacent to the shaft  11 , that is, in the end area on the positive side of the Z-axis. In other words, the guide pulleys  26  are arranged in the space between the first and second housing portions  21 ,  22  and between the elongated holes  24  for driving and the shaft  11 . 
     The guide pulleys  26  are attached to at least one of the first and second housing portions  21 ,  22 , and are rotatable about the axes extending in the Y-axis direction. The shape and configuration of the guide pulleys  26  are not particularly limited. 
     As shown in  FIGS. 4 and 5 , in response to transmission of the driving force from the motive power transmitter  3  of the adapter  2 , each of the drive elements  31  sends the transmitted driving force to the wire  35 . Each of the drive elements  31  reciprocates along the elongated hole  24  for driving due to the driving force transmitted from the motive power transmitter  3 . 
     On the surface of each drive element  31  facing the elongated hole  24  for driving, an uneven shape is formed to allow a relative movement of the drive element  31  along the first housing portion  21  and to restrict a movement of the drive element  31  in a direction to be disengaged from the first housing portion  21 . Each of the elongated holes  24  for driving is provided with an uneven shape formed to be joined with the uneven shape of the drive element  31 . The shape of this uneven shape is not particularly limited. 
     A further uneven shape used for transmitting the driving force is formed in the area of each drive element  31  facing the motive power transmitter  3 . This uneven shape formed on each drive element  31  is also a shape that allows the drive element  31  and the motive power transmitter  3  to be engaged and separated in the Y-axis direction. The shape of this uneven shape is not particularly limited. 
     The wire  35  transmits the driving force, sent to the drive elements  31 , to the forceps  12 . In other words, the wire  35  transmits the movements of the drive elements  31  to the forceps  12 . The material and shape of the wire  35  are not particularly limited. 
     The wire  35  extending from the drive elements  31  in the negative direction of the Z-axis is wound around the pulleys  41 . The wire  35 , after being wound around the pulleys  41 , extends in the positive direction of the Z-axis to be guided into the shaft  11 . Of the ends of the wire  35 , the end extending toward the drive elements  31  corresponds to the first end of the cord-shaped element, and the end arranged to extend toward the shaft  11  corresponds to the second end of the cord-shaped element. 
     The wire  35  extending from the drive elements  31  in the positive direction of the Z-axis is wound around the guide pulleys  26  and guided into the shaft  11  in the case, for example, where the drive elements  31  are arranged on the positive side of the shaft  11  in the X-axis direction away from the shaft  11 . 
     The wire  35  guided into the shaft  11  transmits the driving force to the forceps  12 . The configuration for transmitting the driving force may be, for example, a configuration in which each end of the wire  35  guided into the shaft  11  is attached to the forceps  12 , or each end of the wire  35  is connected to the other end to form a loop and wound around a pulley provided to the forceps  12 . 
     The pulleys  41  are members formed in a cylindrical shape having a circumferential surface around which the wire  35  is wound, and change the direction of the wire  35  extending from the drive elements  31  in the negative direction of the Z-axis to the positive direction of the Z-axis. 
     Each of the pulleys  41  is placed in the elongated hole  23  for pulley using the pulley&#39;s rotational shaft  46 , the securing block  51 , and the securing screws  56 . In other words, each of the pulleys  41  is arranged at a position where the drive element  31  is interposed between the shaft  11 , provided with the forceps  12 , and the pulley  41 . 
     Each of the pulleys  41  is formed in a cylindrical shape. The cylindrical pulley  41  is formed having a length in the direction of its central axis smaller than the distance between the first and second housing portions  21 ,  22 . In other words, the cylindrical pulley  41  is formed having a height in the Y-axis direction smaller than the distance between the first and second housing portions  21 ,  22 . 
     The internal space of the cylindrical pulley  41  is a space where the pulley&#39;s rotational shaft  46  is arranged, and bearings  44  that support the pulley  41  such that the pulley  41  is rotatable about the rotational axis L are arranged between the pulley  41  and the pulley&#39;s rotational shaft  46 . The central axis of the pulley  41  and the rotational axis L coincide with each other. 
     As shown in  FIG. 6A , the circumferential surface of the cylindrical pulley  41  is provided with three annular grooves  42  next to each other in an equidistant manner in the direction of the central axis of the pulley  41 , that is, along the Y-axis direction. In the present embodiment, each of the three grooves  42  has a width equal to the length of two wires  35  arranged side by side. The width of each of the three grooves  42  may be larger or smaller than the length of the two wires  35  arranged side by side. 
     Moreover, each of the pulleys  41  is provided with two cut-out portions  43  connecting the adjacent grooves  42 . Each of the two cut-out portions  43  is formed by scraping off part of a ridge-shaped protrusion that partitions the adjacent grooves  42 , and have a width in which the wire  35  can be arranged from one groove  42  to another groove  42 . In the present embodiment, the two cut-out portions  43  are provided side by side in the same phase of the circumferential surface of the pulley  41 . The two cut-out portions  43  may be provided side by side in the same phase, or may be provided in different phases. 
     As shown in  FIG. 5 , the pulleys&#39; rotational shafts  46  are cylindrical or columnar members that support the pulleys  41  such that pulleys  41  are rotatable. Each of the pulleys&#39; rotational shafts  46  comprises an insertion portion  47  inserted into the bearings  44  arranged in the internal space of each pulley  41 , and an enlarged-diameter portion  48  provided at one end of the insertion portion  47 . A leading end  49  of the insertion portion  47  is inserted into a recess  52  of the securing block  51 , which will be described below. The leading end  49  of the insertion portion  47  corresponds to the projection. 
     The enlarged-diameter portion  48  has a shape with a diameter larger than the inner diameter of the bearings  44  into which the insertion portion  47  is inserted. Each of the pulleys&#39; rotational shafts  46  has a length such that the end of the insertion portion  47  and the end of the enlarged-diameter portion  48  protrude from the corresponding pulley  41  when the insertion portion  47  is inserted into the bearings  44  and the enlarged-diameter portion  48  is in contact with the bearing  44 . 
     Each of the pulleys&#39; rotational shafts  46  is provided, on the end surface that is where the enlarged-diameter portion  48  is located, with a screw hole  50  with which the securing screw  56  threadedly engages. The screw holes  50  are provided on the central axes of the cylindrical or columnar pulleys&#39; rotational shafts  46 . The screw holes  50  may be holes penetrating the pulleys&#39; rotational shafts  46 , or holes with closed ends. 
     The securing blocks  51  are cylindrical or columnar members that support the pulleys  41  together with the pulleys&#39; rotational shafts  46 . Each securing block  51  is provided, at the end thereof adjacent to the pulley&#39;s rotational shaft  46 , with the recess  52  into which the leading end  49  of the insertion portion  47  is inserted, and, at the opposite end thereof, a screw hole  53  with which the securing screw  56  threadedly engages. 
     In the present embodiment, the securing block  51  is provided with the recess  52 , and the leading end  49  of the insertion portion  47  is inserted into the recess  52 ; the configuration, however, may be such that the insertion portion  47  is provided with a recess, and a projection that the securing block  51  is provided is inserted into the recess. 
     Each of the securing blocks  51  is arranged between the leading end  49  of the pulley&#39;s rotational shaft  46  and the second housing portion  22 . The securing blocks  51  are movable in the Z-axis direction relative to the second housing portion  22  and are securable to the second housing portion  22 . The position of each of the securing blocks  51  relative to the pulley&#39;s rotational shaft  46  can be changed along the Y-axis direction, and the movements thereof relative to the pulley&#39;s rotational shaft  46  in the X-axis and Z-axis directions are restricted. 
     As shown in  FIG. 5 , each of the securing screws  56  is a male screw that is inserted into the elongated hole  23  for pulley and threadedly engages with the pulley&#39;s rotational shaft  46  or the securing block  51 . The securing screw  56  threadedly engaged with the screw hole  50  of the pulley&#39;s rotational shaft  46  holds the first housing portion  21  together with the pulleys&#39; rotational shafts  46 . Moreover, the securing screw  56  threadedly engaged with the screw hole  50  of the pulley&#39;s rotational shaft  46  presses the pulley&#39;s rotational shaft  46  against the first housing portion  21  to secure the pulley&#39;s rotational shaft  46 . The securing screw  56  threadedly engaged with the screw hole  53  of the securing block  51  holds the second housing portion  22  together with the securing block  51 . The securing screw  56  threadedly engaged with the screw hole  53  of the securing block  51  presses the securing block  51  against the second housing portion  22  to secure the securing block  51 . 
     Next, the operation of the surgical tool  1  having the above configuration will be described. 
     As shown in  FIG. 2 , the driving force that drives the forceps  12  of the surgical tool  1  is transmitted from the power device  4  to the drive elements  31  via the motive power transmitter  3  of the adapter  2 . As shown in  FIGS. 2 and 4 , the drive elements  31  reciprocate relative to the housing  20  along the Z-axis direction along the elongated holes  24  for driving. 
     The movement of each of the drive elements  31  is transmitted to the wire  35 . The wire  35  reciprocates along its extending direction. The wire  35  extending from the drive elements  31  toward the forceps  12 , that is, to the positive side of the Z-axis direction reciprocates in the direction guided by the guide pulleys  26 . The wire  35  extending from the drive elements  31  to the side where the pulleys  41  are arranged, that is, to the negative side of the Z-axis direction reciprocates along the direction guided by the pulleys  41  and the guide pulleys  26 . 
     The wire  35  extends through the internal space of the shaft  11  to the forceps  12 , and the reciprocating movement of the wire  35  is transmitted to the forceps  12 . The forceps  12  open/close based on the reciprocating movement of the wire  35 . Although the forceps  12  open/close based on the reciprocating movement of the wire  35  in the present embodiment, the forceps  12  may also make other movements, such as bending, in order to change the direction of the forceps  12 . 
     Next, a method for tensioning the wire  35 , that is, adjusting the tension of the wire  35  will be described with reference to  FIGS. 4 and 5 . First, tensioning of the wire  35  is performed by changing the positions of the pulleys  41  relative to the housing  20 . Specifically, the tension is adjusted by moving the pulleys  41  along the elongated holes  23  for pulleys along the Z-axis direction. For example, the tension is increased as the pulleys  41  are moved in the direction away from the shaft  11 , that is, in the negative direction of the Z-axis, and the tension is reduced as the pulleys  41  are moved in the direction approaching the shaft  11 , that is, in the positive direction of the Z-axis. 
     When the pulleys  41  are moved along the elongated holes  23  for pulleys, the securing screws  56  threadedly engaged with the pulleys&#39; rotational shafts  46  are loosened, and the securing screws  56  threadedly engaged with the securing blocks  51  are loosened. In other words, the force pressing the pulleys&#39; rotational shafts  46  against the first housing portion  21  is reduced, and the force pressing the securing blocks  51  against the second housing portion  22  is reduced. 
     As a result, the pulleys&#39; rotational shafts  46  and the securing blocks  51  can come relatively close to each other in the Y-axis direction. Accordingly, gaps can be formed between the pulleys&#39; rotational shafts  46  and the first housing portion  21 , and between the securing blocks  51  and the second housing portion  22 . 
     Subsequently, the pulleys  41  are moved in relation to each other to positions where the tension of the wire  35  is at a desired value. When the relative positions of the pulleys  41  are determined, the securing screws  56  threadedly engaged with the pulleys&#39; rotational shafts  46  are tightened, and the securing screws  56  threadedly engaged with the securing blocks  51  are tightened. At this time, the pulleys&#39; rotational shafts  46  and the securing blocks  51  are separated in a relative manner in the Y-axis direction. 
     In other words, the force pressing the pulleys&#39; rotational shafts  46  against the first housing portion  21  is increased, and the force pressing the securing blocks  51  against the second housing portion  22  is increased. This increases the frictional force between the pulleys&#39; rotational shafts  46  and the first housing portion  21 , and between the securing blocks  51  and the second housing portion  22 . That is, the arrangement positions of the pulleys  41  are fixed. 
     Next, the winding of the wire  35  around the pulley  41  will be described with reference to  FIGS. 6A to 7B . In the case, for example, where the wire  35  guided into the shaft  11  is arranged side by side in the Y-axis direction as shown in  FIG. 6B , the wire  35  is wound around the pulley  41  as shown in  FIG. 6A . 
     Specifically, the wire  35  extending from the drive elements  31  or the shaft  11  is wound in the groove  42  on the positive side or the negative side of the Z-axis direction of the pulley  41 . In the cut-out portion  43 , the wire  35  wound in the groove  42  is led to the groove  42  provided in the middle of each pulley  41 , and wound in the middle groove  42 . Further, the wire  35  is wound through the cut-out portion  43  in the groove  42  on the negative side or the positive side of the Z-axis direction of the pulley  41 , and then extends to the shaft  11  or the drive elements  31 . 
     On the other hand, in the case where the wire  35  guided into the shaft  11  is arranged side by side at the same position in the Y-axis direction with a clearance therebetween as shown in  FIG. 6B , the wire  35  is wound only in the groove  42  provided in the middle of the pulley  41 . 
     When the wire  35  around the pulley  41  shown in  FIG. 6A  reciprocates with the movement of the drive element  31 , the pulley  41  rotates with reciprocating movement of the wire  35  as shown in  FIG. 7A . Moreover, the phase of the pulley  41  changes with reciprocating movement of the wire  35 . At this time, the wire  35  moves while keeping its positions in the Y-axis direction within a specified range. 
     In other words, since the wire  35  is wound in the grooves  42  formed along the X-Z plane, it is easy, despite rotation of the pulley  41 , to keep the positions in the Y-axis direction where the wire  35  enters the grooves  42  and the positions in the Y-axis direction where of the wire  35  exits the grooves  42  within the specified range. The pulley  41  does not rotate to the positions where the wire  35  enters the grooves  42  and the positions where the wire  35  exits the grooves  42  coincide with the cut-out portions  43 . 
     In contrast, as shown in  FIG. 7B , in the case, for example, where a pulley  141  is provided, on its circumferential surface, with a spiral groove  142  in which the wire  35  is wound, the positions of the wire  35  in the Y-axis direction change with the reciprocating movement of the wire  35 . That is, when the pulley  41  rotates with the reciprocating movement of the wire  35 , the position where the wire  35  enters the spiral groove  142  and the position where the wire  35  exits move in the Y-axis direction. With this movement, the positions of the wire  35  in the Y-axis direction change. 
     In the surgical tool  1  configured as described above, the arrangement positions of the pulleys  41  can be changed in an approaching and separating manner in relation to the drive elements  31  and the forceps  12 , and thereby adjustment of the tension of the wire  35 , that is, tensioning is possible. In comparison with, for example, the tension adjustment method described in Patent Document 1, it is easy to finely adjust the tension and to maintain the adjusted tension. Moreover, it is possible to reduce the variation in tension to stabilize the tension. Thus, the frictional force acting between the drive elements  31  and the forceps  12  is also stabilized. This further facilitates improvement in accuracy of external force estimation as compared with the method in which the frictional force acting between the drive elements  31  and the forceps  12  is unstable. 
     Increasing the accuracy of the external force estimation in this way enables safer surgery using the surgical tool  1  and surgery with few complications. This furthermore facilitates improvement in QOL of patients and reduction in burden on doctors during surgery, and contributes to improvement on the learning curve of the surgical robot. The term QOL used herein is an abbreviation for quality of life and will be written in the same manner below. 
     Moreover, the pulleys&#39; rotational shafts  46  and the securing blocks  51  are configured such that the relative positions thereof in the direction of the rotational axis L can be changed. Thus, the rotations of the pulleys  41  are less likely to be inhibited. In the case, for example, where the pulleys&#39; rotational shafts  46  are secured to the first housing portion  21  and the securing blocks  51  are secured to the second housing portion  22 , the lengths of the combinations of the pulleys&#39; rotational shafts  46  and the securing blocks  51  are adjusted by changing the relative positions even when the lengths of the combinations are different from the distance between the first and second housing portions  21 ,  22 . Accordingly, the influence of the securing does not easily reach the pulleys  41  supported by the pulleys&#39; rotational shafts  46 , and the rotations are less likely to be inhibited. 
     In the case where three pulleys  41  are provided as in the present embodiment, it is easy to change the arrangement position of each of the three pulleys  41  in the approaching and separating manner. In other words, even after fixing the arrangement position of one pulley  41 , the arrangement positions of the other pulleys  41  can be easily changed in the approaching and separating manner. 
     In the case, for example, where there are no securing blocks  51  and only the pulleys&#39; rotational shafts  46  are provided, in response to the arrangement position of one of the pulleys  41  being fixed, each end of the pulley&#39;s rotational shaft  46  of the one pulley  41  comes into contact with the first housing portion  21  or the second housing portion  22 . At this time, the first and second housing portions  21 ,  22  come close to each other and the distance therebetween becomes equal to the length of the pulley&#39;s rotational shaft  46 . That is, each end of the pulleys&#39; rotational shafts  46  of the other pulleys  41  also comes into contact with the first housing portion  21  or the second housing portion  22 . Then, despite an attempt to change the arrangement positions of the other pulleys  41  in the approaching and separating manner, the ends of the pulleys&#39; rotational shafts  46  of the other pulleys  41  cannot be easily moved in the approaching and separating manner since the frictional force acting on the surfaces in contact with the first and second housing portions  21 ,  22  tends to be large. 
     In contrast, in the case where the relative positions of the pulleys&#39; rotational shafts  46  and the securing blocks  51  can be changed, the first and second housing portions  21 ,  22  do not come close to each other even after fixing the arrangement position of one of the pulleys  41 . That is, the frictional force acting on the contacting surfaces between the pulleys&#39; rotational shafts  46  of the other pulleys  41  and the first housing portion  21 , and the contacting surfaces between the securing blocks  51  and the second housing portion  22  is less likely to be large. Accordingly, even after fixing the arrangement position of one pulley  41 , it is easy to change the arrangement positions of the other pulleys  41  in the approaching and separating manner. 
     Furthermore, the lengths of the combinations are adjusted by changing the relative positions. Thus, a load is less likely to be imposed on the first and second housing portions  21 ,  22 . In the case of the first and second housing portions  21 ,  22 , for example, the load may cause deformation or breakage of the first and second housing portions  21 ,  22 . Even in such a case, it is easy to inhibit deformation and breakage of the first and second housing portions  21 ,  22  since the load is less likely to be imposed thereon. 
     Pressing the pulleys&#39; rotational shafts  46  against the first housing portion  21  and pressing the securing blocks  51  against the second housing portion  22  using the elongated holes  23  for pulleys and the securing screws  56  enables fixation of the arrangement positions of the pulleys  41  in relation to at least one of the drive elements  31  and the forceps  12 . Increasing the pressing force enables more reliable fixation of the arrangement positions, and reducing the pressing force facilitates changes in the arrangement positions. 
     Use of the leading ends  49  of the pulleys&#39; rotational shafts  46 , extending in the direction of the rotational axis L, and the recesses  52  of the securing blocks  51 , engaged with the leading ends  49 , allows changes in the positions of the pulleys&#39; rotational shafts  46  relative to the securing blocks  51  in the direction of the rotational axis L. Moreover, it is possible to maintain the relative positions in the direction intersecting the direction of the rotational axis L. 
     Arrangement of the drive elements  31  between the pulleys  41  and the forceps  12  and transmission of the reciprocating movements of the drive elements  31  to the forceps  12  through the wire  35  wound around the pulleys  41  facilitate adjustment of the tension of the wire  35 . 
     In comparison with the pulley  141  provided with the spiral groove  142 , it is easy, despite changes in the phase of the pulley  41 , to inhibit changes in the positions of the wire  35  in the Y-axis direction and to stabilize the tension of the wire  35 . That is, changes in the positions of the wire  35  in the Y-axis direction are inhibited, and thereby it is easy to inhibit changes in length of the path where the wire  35  is arranged, and to stabilize the tension of the wire  35 . 
     Accordingly, it is also easy to stabilize the frictional force acting between the drive elements  31  and the forceps  12 , and to improve the accuracy of the external force estimation as compared with a method in which the frictional force, acting between the drive elements  31  and the forceps  12 , is unstable. Improving the accuracy of the external force estimation in this way enables safer surgery with the surgical tool  1  and surgery with few complications. Furthermore, this facilitates improvement in QOL of patients and reduction in burden on doctors during surgery, and contributes to improvement on the learning curve of the surgical robot. 
     In comparison with the pulley  141  provided with the spiral groove  142 , it is easy to inhibit changes, due to the phases of the pulleys  41 , in the positions in the Y-axis direction where the wire  35  enters the grooves  42  and the positions in the Y-axis direction where the wire  35  exits the grooves  42 . Thus, it requires less attention to the phases of the pulleys  41  when the wire  35  is wound therearound. In other words, it is easier to wind the wire  35  around the pulleys  41 . 
     The technical scope of the present disclosure is not limited to the above embodiment. Moreover, the technical scope of the present disclosure can be modified in various ways without departing from the spirit of the present disclosure. For example, the surgical tool  1  is provided with the forceps  12  in the above embodiment; this, however, should not limit the present invention, and the surgical tool  1  may be provided with other instruments used for surgery.