Patent Publication Number: US-2022233261-A1

Title: Surgical robot system, external force estimation device, and computer readable storage medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Application is a Continuation Application of International Application No. PCT/JP2020/035626 filed on Sep. 18, 2020, which is based on Japanese patent application No. 2019-190341 filed on Oct. 17, 2019 with the Japanese Patent Office, the entire contents of each of which are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     The present disclosure relates to a surgical robot system, an external force estimation device, and a computer readable storage medium. 
     In recent years, endoscopic surgery using a surgical robot system is becoming widespread. Various surgical instruments, e.g., a laparoscope, an endoscope, a forceps, and so on, each of which are attached to an arm of the surgical robot system are used in endoscopic surgery. 
     SUMMARY 
     It is an aspect to provide a surgical robot system in which a size of a distal end of the surgical instrument is reduced and in which accuracy in measurement of an external force acting on the surgical instrument is improved, and that enhances comfort and safety for the subject. 
     According to an aspect of one or more embodiments, there is provided a surgical robot system comprising a surgical instrument including a shaft that is configured to be inserted through a trocar placed in a subject; an arm device configured to hold the surgical instrument and to move the surgical instrument with respect to the subject; a detector arranged at the arm device and configured to detect values of forces and torques acting on the surgical instrument; and a controller configured to calculate a value of a first external force that the surgical instrument receives from the trocar and a value of a second external force that is received from an object other than the trocar and that is abuttable on the surgical instrument, based on the values of the forces and torques, and based on a value of a resistance force acting between the trocar and the shaft, and configured to control the arm device to move the surgical instrument, based on the value of the first external force and the value of the second external force. 
     According to another aspect of one or more embodiments, there is provided an external force estimation device comprising at least one central processing unit configured to at least receive values of forces and torques detected by a detector provided at an arm device, the arm device being detachably connected to a surgical instrument having a shaft that is inserted through a trocar placed in a subject; calculate a value of a first external force that the surgical instrument receives from the trocar and a value of a second external force that is received from an object other than the trocar and that is abuttable on the surgical instrument, based on the values of the forces and torques, and based on a value of a resistance force acting between the trocar and the shaft; and transmit, to the arm device, control signals to control the arm device to move the surgical instrument, based on the value of the first external force and the value of the second external force. 
     According to another aspect of one or more embodiments, there is provided a non-transitory computer readable storage medium that stores program code which, when executed by one or more processors, causes the one or more processors to at least receive values of forces and torques detected by a detector provided at an arm device, the arm device being detachably connected to a surgical instrument having a shaft that is inserted through a trocar placed in a subject; calculate a value of a first external force that the surgical instrument receives from the trocar and a value of a second external force that is received from an object other than the trocar and that is abuttable on the surgical instrument, based on the values of the forces and torques, and based on a value of a resistance force acting between the trocar and the shaft; and transmit, to the arm device, control signals to control the arm device to move the surgical instrument, based on the value of the first external force and the value of the second external force. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects will become apparent from the following description of various embodiments and with reference to the following drawings, in which: 
         FIG. 1  is a schematic diagram explaining an example of a configuration of a surgical robot system according to various embodiments; 
         FIG. 2  is a diagram explaining a coordinate system, forces, and torques in the surgical robot system in  FIG. 1 ; 
         FIG. 3  is a block diagram explaining an example of a configuration of a controller of the surgical robot system in  FIG. 1 , according to various embodiments; 
         FIG. 4  is a schematic diagram explaining another example of a configuration of a surgical robot system according to various embodiments; 
         FIG. 5  is a block diagram explaining an example of a configuration of a controller of the surgical robot system in  FIG. 4 , according to various embodiments; 
         FIG. 6  is a schematic diagram explaining another example of a configuration of a surgical robot system according to various embodiments; and 
         FIG. 7  is a block diagram explaining an example of a configuration of a controller of the surgical robot system in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     A trocar (or a port) through which a surgical instrument is inserted is placed in a subject (e.g., through an abdominal wall of the subject) to be subjected to endoscopic surgery. It is advantageous to reduce a load, specifically a force, applied to the subject by the surgical instrument during the endoscopic surgery. 
     Examples of the force applied may include a force applied to the abdominal wall of the subject via the trocar, and a force applied directly to the subject by a part of the surgical instrument not at a position corresponding to the trocar (e.g., a distal end of the surgical instrument or a shaft of the surgical instrument), i.e., by a part of the surgical robot system that is inserted into the subject. 
     In a related art method for detecting a force applied by the distal end of the surgical instrument, in other words a force applied to the distal end of the surgical instrument, a sensor arranged in the neighborhood of the distal end may measure the force applied and/or an external force applied to a joint of the distal end based on a driving force may be estimated. 
     However, the related art method of measuring the force by a sensor arranged in the neighborhood of the distal end of the surgical instrument makes it necessary to attach the sensor for measurement directly to the neighborhood of the distal end of the surgical instrument. Such an arrangement position of the sensor causes a problem in that the size of the distal end of the surgical instrument is increased and a problem in that the difficulty in sterilizing and washing the surgical instrument is increased. This increase in size and difficulty in sterilization results in further problems, such as increased costs for manufacture and use of the surgical instrument and thus the surgical robot system, as well as additional discomfort to and decrease in safety for the subject undergoing the surgery. 
     The related art method of estimating an external force applied to the joint has problems such as variability of accuracy in estimating the external force under the influence of, for example, friction within a mechanism of the surgical instrument and so on, and the inability to detect a force direction depending on arrangement of degrees of freedom of the surgical instrument. 
     Moreover, in the related art methods, a force applied to the shaft of the surgical instrument in a middle area of the surgical instrument cannot be measured or estimated, respectively. Thus, an estimated value of the external force could result in being smaller than an actual value of the external force. 
     It is an aspect to provide a surgical robot system in which a size of a distal end of the surgical instrument is reduced and in which accuracy in measurement of an external force acting on the surgical instrument is improved, and that enhances comfort and safety for the subject. 
     According to an aspect of various embodiments, a surgical robot system may comprise a surgical instrument used in surgery on a subject, the surgical instrument including a shaft formed in a long shape, the shaft being inserted through a trocar placed in the subject; an arm portion configured to grasp the surgical instrument in a movable manner with respect to the subject; a detector arranged at a position not where the shaft is present but where the arm is present and configured to detect values of forces and torques acting on the surgical instrument, the detector detecting the values of a length-direction force acting in a length direction of the shaft, a length-direction torque acting about the length direction, a first intersecting-direction force acting in a first intersecting direction that intersects with the length direction, a first intersecting-direction torque acting about the first intersecting direction, a second intersecting-direction force acting in a second intersecting direction that intersects with the length direction and with the first intersecting direction, and a second intersecting-direction torque acting about the second intersecting direction; and a calculator configured to calculate a value of a first external force that the surgical instrument receives from the trocar and a value of a second external force that is received from an object other than the trocar and that abuts the surgical instrument, based on the values of the length-direction force, the first intersecting-direction force, the second intersecting-direction force, the length-direction torque, the first intersecting-direction torque, and the second intersecting-direction torque, and on a value of a resistance force acting between the trocar and the shaft. 
     According to additional aspect of various embodiments, an external force estimation device and a non-transitory computer readable storage medium consistent with the surgical robot system are also provided. 
     The surgical robot system according to various embodiments make it possible to calculate the value of the first external force that the surgical instrument receives from the trocar and the value of the second external force that is received from an object other than the trocar and that abuts the surgical instrument, based on values of various external forces and torques detected by the detector and on the value of the resistance force acting between the trocar and the shaft. 
     Further, since the detector for detecting the values of the various external forces and torques is arranged at a position not where the shaft is present but where the arm is present, a size of the surgical instrument is facilitated, as compared with a related art device in which a sensor is arranged at a distal end of the surgical instrument. 
     A drive portion configured to drive a distal end of the shaft of the surgical instrument may be provided, the arm portion may comprise a holder configured to hold the surgical instrument, and the detector may be arranged between the drive portion and the holder. 
     Such an arrangement of the detector between the drive portion and the holder makes it less likely for the detector to detect a force and a torque caused by operation of the drive portion, as compared with a related art case in which, for example, the detector is arranged closer to the distal end than the drive portion is. Such an arrangement therefore improves the accuracy of detection by the detector. 
     A distal end external force detector configured to detect a value of a distal end external force, which is an external force that the distal end receives, may be provided, and the calculator may calculate a value of a shaft external force, which is an external force in the shaft received from an object other than the treatment tool and the trocar and that is abuttable on the surgical instrument, based on the value of the second external force and the value of the distal end external force. 
     Such provision of the distal end external force detector enables the calculator to calculate the value of the shaft external force, which is an external force in the shaft received from an object other than the treatment tool and the trocar and that is abuttable on the surgical instrument. Examples of the shaft external force may include a force applied by contact of a midsection of the shaft with an organ or the like of the subject, caused by relative movement of the surgical instrument with respect to the subject. 
     A storage may be provided which stores values of resistance forces each acting between the trocar of a different type and the shaft are stored in association with types of the trocar and a selector used to select the type of the trocar may be provided, and the calculator may acquire, from the storage, the value of the resistance force for the type of the trocar selected by the selector and may calculate the first external force and the second external force using the value of the resistance force acquired. 
     Such provision of the storage and the selector makes it easier to inhibit deterioration in accuracy of the calculated values of the first external force and the second external force, even when the trocar to be used is changed to a different trocar in which the resistance force acting between the trocar and the shaft is different. 
     The value of the first external force that the surgical instrument receives from the trocar and the value of the second external force that is received from an object other than the trocar and that abuts the surgical instrument may be calculated based on the values of the various external forces and torques detected by the detector and on the value of the resistance force acting between the trocar and the shaft. This calculation makes it possible to reduce the size of the distal end of the surgical instrument and to increase the accuracy in measurement of an external force acting on the surgical instrument, and thus enhance the safety of the surgical robot system. 
       FIGS. 1-3  illustrate an example of a configuration of a surgical robot system according to various embodiments. A surgical robot system  1  is a surgery assisting robot or the like used in endoscopic surgery. As shown in  FIG. 1 , the surgical robot system  1  comprises a surgical instrument  10 , an arm device  30 , and a controller  50 . The arm device  30  and the controller  50  each correspond to one example of an arm portion and an external force estimation device, respectively. 
     According to various embodiments, the surgical instrument  10  may be a treatment tool of any kind, such as, for example, a laparoscope, an endoscope or forceps, or other treatment tool used in endoscopic surgery. For ease of illustration, an explanation will be given of an example in which the surgical instrument  10  is a forceps. As shown in  FIG. 1 , the surgical instrument  10  comprises a shaft  11  and a main body  16 . 
     The shaft  11  is a member extending in a tubular shape or a rod shape, and is inserted through a trocar  75  to thereby be inserted inside an abdominal wall  71  of a patient  70 . The shaft  11  is provided with a forceps  12  at a distal end thereof, and a bend portion  13 . 
     The trocar is hereinafter also referred to as a port. The patient  70  corresponds to one example of a subject. 
     The forceps  12  is a part at a distal end of the shaft  11 , which is an end of the shaft  11  to be inserted into the patient  70 . The forceps  12  is provided with an element for gripping an object. 
     The bend portion  13  has a shape of a cylinder or a column, with a first end thereof arranged on the forceps  12  and a second end thereof arranged on the shaft  11 . The bend portion  13  has a configuration capable of bending laterally with respect to a direction in which the shaft  11  extends.  FIG. 1  shows an example in which the bend portion  13  is configured with two rotating portions  14  and  15 , rotation axes of which intersect with each other. In some embodiments, the rotation axes may intersect perpendicularly with each other. The configuration of the bend portion  13  is not particularly limited to this configuration. 
     The main body  16  is a part, in the surgical instrument  10 , to be attached to and detached from the arm device  30 . The main body  16  has a configuration through which a driving force to drive the forceps  12  and the bend portion  13  is transmitted from the arm device  30 . A specific configuration of the main body  16  is not particularly limited. 
     The arm device  30  supports the surgical instrument  10  such that a position and an attitude thereof are changeable. The arm device  30  is controlled so that the surgical instrument  10  passes through a pivot position  75   p , which is a specified relative position with respect to the arm device  30 , even when the position and/or the attitude of the surgical instrument  10  are/is changed. The pivot position  75   p  is hereinafter also referred to as an immovable position. In some embodiments, the arm device  30  may move the surgical instrument  10  with six degrees of freedom. 
     As shown in  FIG. 1 , the arm device  30  comprises a rotating portion  31 , a first arm rotating portion  33 , a first arm  34 , a second arm rotating portion  35 , a second arm  36 , a gimbal portion  41 , a holder  45 , a detector  46 , a rotation support portion  47 , a drive portion  48 , and an attachment/detachment portion  49 . In some embodiments, the arm device  30  is configured such that all of the rotating portion  31 , the first arm rotating portion  33 , the first arm  34 , the second arm rotating portion  35 , the second arm  36 , the gimbal portion  41 , the holder  45 , the detector  46 , the rotation support portion  47 , the drive portion  48 , and the attachment/detachment portion  49  are controlled so that the surgical instrument  10  passes through the pivot position  75   p . However, it suffices if the surgical instrument  10  at least passes through the pivot position  75   p , and thus, the arm device  30  does not necessarily have to be configured such that all of the rotating portion  31 , the first arm rotating portion  33 , the first arm  34 , the second arm rotating portion  35 , the second arm  36 , the gimbal portion  41 , the holder  45 , the detector  46 , the rotation support portion  47 , the drive portion  48 , and the attachment/detachment portion  49  are controlled actively. 
     The pivot position  75   p  may be predetermined or may be determined experimentally. In other words, the pivot position  75   p  may be a position provided in advance, or may be a position obtained based on a value measured by a sensor. In some embodiments, the pivot position  75   p  may be a position estimated based on behavior of the arm device  30 . 
     The pivot position  75   p  generally coincides with a positon of an insertion hole in the abdominal wall  71  of the patient  70  who is subjected to endoscopic surgery. The trocar  75  through which the shaft  11  of the surgical instrument  10  is inserted is placed in the insertion hole. 
     In some embodiments, the trocar  75  comes into contact with the shaft  11  of the surgical instrument  10  inserted, and is not coupled and fixed to the arm device  30 . That is, the trocar  75  is not held by the arm device  30 . 
     In other words, the trocar  75  is used together with the arm device  30  that has no need for pivot positioning. That is, the arm device  30  has no need for alignment with an immovable point or position. Since the trocar  75  and the arm device  30  are not coupled and fixed to each other, the accuracy of a calculation of a first external force Fp and a second external force Fr may be improved as compared with a case in which the trocar  75  and arm device  30  are coupled and fixed to each other. 
     The rotating portion  31 , the first arm rotating portion  33 , the second arm rotating portion  35 , the first joint  42  and the second joint  43  of the gimbal portion  41  are driven based on control signals from the controller  50 . In some embodiments, the rotation support portion  47  and the drive portion  48  of the surgical instrument  10  may also be driven based on control signals from the controller  50 . 
     The rotating portion  31  is a joint arranged in a portion where the arm device  30  is fixed to a base  32 . The rotating portion  31  is provided with a sensor  31   s , shown in  FIG. 3 , used to detect a phase of the rotating portion  31 . The rotating portion  31  may have a configuration capable of being rotationally driven about a vertically extending rotation axis. However, the specific configuration is not particularly limited as long as the rotating portion  31  may be rotationally driven about the vertically extending rotation axis. 
     In some embodiments, the rotating portion  31  may be provided with an actuator  31   a  that generates a driving force using pressure of a gas, such as air, to cause the rotating portion  31  to move rotationally. The rotating portion  31  is rotationally driven by the driving force generated by the actuator  31   a , based on a control signal from the controller  50 . 
     The first arm rotating portion  33  is arranged between the rotating portion  31  and the first arm  34 . The first arm rotating portion  33  has a configuration capable of being rotationally driven about a horizontally extending rotation axis. The first arm rotating portion  33  is provided with a sensor  33   s , shown in  FIG. 3 , used to detect a phase of the first arm rotating portion  33 . 
     In some embodiments, the first arm rotating portion  33  may be provided with an actuator  33   a  that generates a driving force using pressure of a gas, such as air. The first arm rotating portion  33  is rotationally driven by the driving force generated by the actuator  33   a , based on a control signal from the controller  50 . 
     Although the first arm rotating portion  33  is provided with the actuator  33   a , in some embodiments, the actuator  33   a  may be omitted. 
     As shown in  FIG. 1 , the first arm  34  is arranged between the first arm rotating portion  33  and the second arm rotating portion  35 . In some embodiments, the first arm  34  has a shape extending like a rod; however, the shape of the first arm  34  is not particularly limited to this shape. 
     The second arm rotating portion  35  is arranged between the first arm  34  and the second arm  36 . The second arm rotating portion  35  has a configuration capable of being rotationally driven about a horizontally extending rotation axis. The second arm rotating portion  35  is provided with a sensor  35   s , shown in  FIG. 3 , used to detect a phase of the second arm rotating portion  35 . 
     In some embodiments, the second arm rotating portion  35  is provided with an actuator  35   a  that generates a driving force using pressure of a gas, such as air. The second arm rotating portion  35  is rotationally driven by the driving force generated by the actuator  35   a , based on a control signal from the controller  50 . 
     Although the second arm rotating portion  35  is provided with the actuator  35   a , in some embodiments, the actuator  35   a  may be omitted. 
     As shown in  FIG. 1 , the second arm  36  is arranged between the second arm rotating portion  35  and the gimbal portion  41 . In some embodiments, the second arm  36  has a shape extending like a rod; however, the shape of the second arm  36  is not particularly limited to this shape. 
     The gimbal portion  41  is arranged between the second arm  36  and the holder  45 . The gimbal portion  41  comprises the first joint  42  and the second joint  43 , rotation axes of which intersect with each other. In some embodiments, the rotation axes may intersect perpendicularly with each other. 
     The first joint  42  is arranged on a side, of the gimbal portion  41 , closer to the second arm  36 . The first joint  42  is arranged in an attitude such that a rotation axis thereof extends in a direction in which the second arm  36  extends. The first joint  42  is provided with a sensor  42   s , shown in  FIG. 3 , used to detect a phase of the first joint  42 . 
     The second joint  43  is arranged on a side, of the gimbal portion  41 , closer to the holder  45 . The second joint  43  is arranged in an attitude such that a rotation axis thereof extends in a direction intersecting with the direction in which the second arm  36  extends. In some embodiments, the rotation axis of the second joint  43  may extend in a direction intersecting perpendicularly with the direction in which the second arm  36  extends. The second joint  43  is provided with a sensor  43   s , shown in  FIG. 3 , used to detect a phase of the second joint  43 . 
     In some embodiments, the first joint  42  and the second joint  43  are respectively provided with an actuator  42   a  and an actuator  43   a  that generate a driving force using pressure of a gas, such as air, based on respective control signals from the controller  50 , to cause the first joint  42  and the second joint  43 , respectively, to move rotationally. However, in some embodiments, one or both of the actuator  42   a  and the actuator  43   a  may be omitted. 
     The holder  45  is arranged between the gimbal portion  41  and the rotation support portion  47 . The holder  45  may have a configuration capable of holding the rotation support portion  47  and the drive portion  48 . However, the specific configuration of the holder  45  is not particularly limited as long as the holder  45  is capable of holding the rotation support portion  47  and the drive portion  48 . 
     The detector  46  is arranged between the holder  45  and the drive portion  48  held by the holder  45 . The detector  46  is a force/torque sensor for detecting a force Fw acting on the surgical instrument  10  or on the holder  45  and a torque Mw acting on the surgical instrument  10  or on the holder  45 , based on one or more control signals from the controller  50 . The torque Mw is also referred to as a “moment”. In some embodiments, a force torque sensor for detecting a force and a moment may be used as the detector  46 , and a detection method and so on are not particularly limited. 
     The force Fw detected by the detector  46  comprises a component of a length-direction force acting in a length direction of the shaft  11 , a component of a first intersecting-direction force acting in a first intersecting direction that intersects with the length direction, and a component of a second intersecting-direction force acting in a second intersecting direction that intersects with the length direction and with the first intersecting direction. The torque Mw comprises a component of a length-direction torque acting about the length direction, a component of a first intersecting-direction torque acting about the first intersecting direction, and a component of a second intersecting-direction torque acting about the second intersecting direction. In other words, the detector  46  is a force/torque sensor with six degrees of freedom. 
     As shown in  FIG. 2 , in a case where an orthogonal coordinate system { 5 } is set on the surgical instrument  10 , the length direction, the first intersecting direction, and the second intersecting direction described above correspond respectively to an x-direction, a y-direction, and a z-direction in the coordinate system { 5 }. 
     Referring back to  FIG. 1 , a position where the detector  46  is arranged may be between the holder  45  and the drive portion  48  as described above, or may be a position further closer to the shaft  11  of the surgical instrument  10 . When an arrangement position of the detector  46  is closer to the shaft  11 , a calculation accuracy of the first external force Fp and the second external force Fr may be improved as compared with a case where the arrangement position is farther from the shaft  11 . 
     The rotation support portion  47  rotatably supports the drive portion  48  about a central axis of the shaft  11  of the surgical instrument  10 . In the state where the surgical instrument  10  is attached to the attachment/detachment portion  49 , the rotation support portion  47  rotatably supports the drive portion  48  and the surgical instrument  10  about the central axis. The rotation support portion  47  is provided with an actuator  47   a  that generates a driving force to control rotation of the rotation support portion  47 , based on a control signal from the controller  50 . 
     The drive portion  48  is rotatably supported by the rotation support portion  47 , and generates the driving force to drive at least one of the forceps  12  at the distal end of the shaft  11  or the bend portion  13  of the surgical instrument  10 . 
     In some embodiments, a gas-pressure actuator for generating the driving force using pressure of a gas, such as air, may be arranged in the drive portion  48 . In this case, the generated driving force is transmitted to the main body  16  of the surgical instrument  10  via the attachment/detachment portion  49 , and is transmitted to at least one of the forceps  12  at the distal end of the shaft  11  or the bend portion  13  via a wire passed through the shaft  11 . 
     A configuration of the drive portion  48  is not particularly limited to a specific configuration. Moreover, in some embodiments, a method of generating the driving force may be a method using pressure of a gas as described above or in other embodiments may be a method using an electric motor. However, these methods are only exemplary, and in other embodiments, other methods may be used. 
     The attachment/detachment portion  49  is arranged between the drive portion  48  and the surgical instrument  10 . The attachment/detachment portion  49  has a configuration allowing for attachment/detachment of the main body  16  of the surgical instrument  10 , and also has a configuration allowing for transmission of the driving force from the drive portion  48  to the main body  16 . A specific configuration of the attachment/detachment portion  49  is not particularly limited. 
     The controller  50  calculates the first external force that the surgical instrument  10  receives from the trocar  75  and the second external force that is received from an object other than the trocar  75 , the object being abuttable on the surgical instrument. For example, in some embodiments, the object other than the trocar that is abuttable on the surgical instrument may be a subject or may a portion other than the surgical instrument. For example, in some embodiments, the object other than the trocar that is abuttable on the surgical instrument may be a portion of the surgical robot system other than the surgical instrument. In addition, the controller  50  obtains positions and attitudes of the arm device  30  and the surgical instrument  10  by kinematic calculation, based on information detected by the sensor  31   s , the sensor  33   s , the sensor  35   s , the sensor  42   s , and the sensor  43   s . The controller  50  outputs controls signals including respective drive commands to the actuator  31   a , the actuator  33   a , the actuator  35   a , the actuator  42   a , the actuator  43   a  and the actuator  47   a  based on the obtained positions and attitudes. External force information, such as a value of an external force calculated by a calculator  53  may be incorporated into the drive command to be outputted. 
     As shown in  FIG. 1  and  FIG. 3 , the controller  50  may be implemented in hardware, firmware, or a combination of hardware and software. The controller  110  may be an information processor, such as a computer, which comprises at least one central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), an input/output interface, and so on. Program code stored in a storage device, such as the ROM or the RAM, causes the CPU, the ROM, the RAM, and the input/output interface to work cooperatively to function as at least an inputter  51 , a storage section  52 , and the calculator  53 . In some embodiments, the controller  50  may include one or more controllers capable of being programmed to perform a function. The controller may include a memory such as the RAM, the ROM, and/or another type of dynamic or static storage device (e.g., a flash memory, a magnetic memory, and/or an optical memory) that stores information and/or instructions for use by controller  50 . The memory stores information and/or software related to the operation and use of the surgical robot system  1 . In some embodiments, the memory may include a hard disk (e.g., a magnetic disk, an optical disk, a magneto-optic disk, and/or a solid state disk), a compact disc (CD), a digital versatile disc (DVD), a floppy disk, a cartridge, a magnetic tape, and/or another type of non-transitory computer-readable medium, along with a corresponding drive. The memory may store program code which when read and executed by the controller  50 , causes the controller  50  to perform the various functions of the controller  50 . 
     The inputter  51  (e.g., the information processor) receives input of information on the force Fw and the torque Mw that are detected and outputted by the detector  46 . Specifically, values of the length-direction force, the first intersecting-direction force, and the second intersecting-direction force, and values of the length-direction torque, the first intersecting-direction torque, and the second intersecting-direction torque are received from the detector  46 . The inputter  51  also receives detection signals from the sensor  31   s , the sensor  33   s , the sensor  35   s , the sensor  42   s , and the sensor  43   s.    
     The storage section  52  (e.g., the information processor in combination with RAM) stores in advance a value of a resistance force 5Fpx acting between the trocar  75  and the shaft  11  of the surgical instrument  10 , and a value of a gravity W acting on the surgical instrument  10 . A value of weight or mass may be used as the value of the gravity W. The resistance force takes a different value depending on combination of the trocar  75  and the shaft  11 . When the trocar  75  and the surgical instrument  10  to be used in the surgical robot system  1  are known, the resistance force is measured or calculated, and is stored in advance in the storage section  52  (e.g., the RAM or the ROM). 
     The calculator  53  (e.g., the information processor in combination with RAM) calculates a value of the first external force and a value of the second external force based on the information on the force Fw and the torque Mw inputted to the inputter  51  (i.e., received from the detector  46 ) and on the value of the resistance force stored in advance in the storage section  52  (e.g., the RAM or the ROM). Specific details of the calculation of the value of the first external force and the value of the second external force will be described below. 
     Next, an explanation will be given of calculation of the value of the first external force and the value of the second external force in the surgical robot system  1  having the above-described configuration. First, derivation of equations for calculating the value of the first external force and the value of the second external force will be described with reference to  FIG. 2 . 
     To begin with, an equation (1) of equilibrium of a translational force as seen from the coordinate system { 5 } shown in  FIG. 2  and an equation (2) of equilibrium of moment about the detector  46  are obtained. The equation (1) and the equation (2) are provided below. Here, the coordinate system { 5 } is an orthogonal coordinate system set on the surgical instrument  10 , and the direction in which the shaft  11  extends is set as the x-direction. 
       [Mathematical Expression 1] 
         F   r   +F   p   +W+F   w =0  (1)
 
         M   w +( P   r   −P   w )× F   r +( P   p   −P   w )× F   p +( P   g   −P   w )× W= 0  (2)
 
     In the equations (1) and (2) above, Fr represents an external force when the second external force to be obtained acts concentratedly on the forceps  12  at the distal end of the shaft  11 . In other words, the second external force to be obtained is assumed to act concentratedly on the forceps  12  at the distal end of the shaft  11  as a resultant force obtained by combining a shaft external force acting also on other portions. Pr represents a position vector of the forceps  12  at the distal end of the shaft  11 . Fp represents an external force acting on a portion of the shaft  11  facing the insertion hole, and Pp represents a position vector of the insertion hole. W represents the gravity acting on the surgical instrument  10 , and Pg represents a position vector of the center of gravity of the surgical instrument  10 . Fw represents a force acting on the holder  45 , and is a force detected by the detector  46 . Mw represents a moment acting on the holder  45 , and is a moment detected by the detector  46 . The external force acting on the portion of the shaft  11  facing the insertion hole corresponds to one example of the first external force. 
     Here, unknowns are only Fp and Fr. Other values may be measured by the sensors or estimated by calculation based on robot forward kinematics. Eliminating Fr from the above equations (1) and (2) yields the following equation (3). 
       [Mathematical Expression 2] 
       ( P   p   −P   r ) x F   p =−( P   g   −P   r )× W −( P   w   −P   r )× F   w   −M   w   (3)
 
     As shown in  FIG. 2 , a coordinate system {0} is set on the arm device  30 . The equation (3) is considered in the coordinate system {5}, and an attitude matrix of the coordinate system {0} as seen from the coordinate system {5} is created as described below in Mathematical Expression 3. Using this attitude matrix, the equation (3) may be expressed as the following equation (4). 
         0   5   R   [Mathematical Expression 3]
 
       [Mathematical Expression 4] 
       { 0   5   R ( P   p   −P   r )}×( 0   5   RF   p )=−{ 0   5   R ( P   g   −P   r )}×( 0   5   RW )−{ 0   5   R ( P   w   −P   r )}×( 0   5   RF   w )− 0   5   RM   w   (4)
 
     Given that the equation (4) is expressed using the following mathematical expression and that the right side of the equation (4) is M, the equation (4) may be expressed as an equation (5). 
         0   5   RF   p = 5   F   p   [Mathematical Expression 5]
 
       [Mathematical Expression 6] 
         0   5   R ( P   p   −P   r )× 5   F   p   =M   (5)
 
     When the equation (5) is expressed using the following mathematical expression, the equation (5) is expressed as an equation (6). 
     
       
         
           
             
               
                 
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     The equation (6) is an equation of an equilibrium of a moment about Pr. The equation (6) is a system of simultaneous equations from a skew-symmetric matrix. Three variables 5Fpx, 5Fpy, and 5Fpz cannot be solved independently by the equation (6) alone. 
     Here, 5Fpx is a resistance force acting between the trocar  75  and the shaft  11  of the surgical instrument  10 . Thus, a value of 5Fpx can be set in advance as an appropriate condition or value in consideration of a structure of the trocar  75 , external force compensation performance of the arm device  30 , and so on. Examples of the value of 5Fpx may include the following three conditions. In the following conditions, f represents a constant, and μ represents a coefficient of friction. 
         5   F   px =0 
     
       
      
       5 
       F 
       px 
       =f  
      
     
         5   F   px   =μN   [Mathematical Expression 9]
 
     where N=√{square root over ( 5 F px   2 + 5 F pz   2 )} 
     For example, when the condition 5Fpx=0 is used, solving for 5Fpy and 5Fpz of the equation (6) yields the following equations (7) and (8). 
     
       
         
           
             
               
                 
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     Further, solving for Fry and Frz using a relation between the above equations (7) and (8) and the equation (1) results as shown in the following equations (9) and (10). 
       [Mathematical Expression 11] 
         F   ry   =−F   py   −W   y   −F   wy   (9)
 
         F   rz   =−F   pz   −W   z   |F   wz   (10)
 
     An external force Frx parallel to the shaft  11  generated at the forceps  12  at the distal end of the shaft  11  may be obtained from the following relational equation (11) of a resultant force in terms of an x-direction component of the detector  46 . The equation (11) shows an equation with the term of Fpx on the left, so as to facilitate understanding when a condition other than 5Fpx=0 is used. 
       [Mathematical Expression 12] 
         F   wx   =−F   rx   −F   px   −W   x   (11)
 
     When the condition 5Fpx=f is used or when the condition 5Fpx=μN is used, solving for 5Fpy and 5Fpz of the equation (6) yields equations for obtaining respective values. As for Fry, Frz, and Frx, equations for obtaining respective values are yielded in a manner similar to the above and a repeated description thereof is omitted for conciseness. 
     The methods of obtaining the values of 5Fpy, 5Fpz, Fry, Frz, and Frx may be those using an analytical approach based on deformation of the equations as described above, or may be those using simultaneous equations approach, such as a numerical analysis method using a computer. 
     Next, an explanation will be given of calculation of the value of the first external force and the value of the second external force in the surgical robot system  1 . Here, Fp as described above corresponds to the first external force, and Fr as described above corresponds to one example of the second external force. The calculator  53  (i.e., the information processor in combination with the RAM) in the controller  50  performs an operation of calculating the above-described Fp and Fr. 
     The controller  50  acquires, from the storage section  52 , the value of the gravity W acting on the surgical instrument  10  to be used in calculating Fp and Fr, and also performs a process of acquiring, from the detector  46 , the force Fw acting on the holder  45  and the moment Mw acting on the holder  45 . 
     Further, the controller  50  performs an operation of obtaining position vectors of Pr, Pp, Pg, and Pw to be used in calculating Fp and Fr. When performing the operation, the controller  50  performs an arithmetic process for acquiring detection signals to be used in calculating the position vectors and control signals for controlling an attitude of the bend portion  13 . The detection signals are outputted from the sensor  31   s , the sensor  33   s , the sensor  35   s , the sensor  42   s , and the sensor  43   s.    
     Additional information such as mathematical equations used in obtaining the position vectors and size information including the length and the shape of the first arm  34  and the other components of the arm device  30  are stored in advance in the storage section  52  and are used by the controller  50 . 
     In the embodiment of  FIGS. 1-3 , in obtaining the position vectors of Pr, Pp, Pg, and Pw, the sensor  31   s , the sensor  33   s , the sensor  35   s , the sensor  42   s , and the sensor  43   s  for detecting the respective phases are used. However, the control signals for controlling the attitude of the arm device  30  may be used instead of outputs of the sensors for detecting the respective phases. 
     Similarly, although the control signals for controlling the attitude of the bend portion  13  are used in the embodiment of  FIGS. 1-3 , outputs of the sensors for detecting the attitude of the bend portion  13  may be used instead of the control signals. 
     As for the equations used in obtaining the position vectors and as for parameters included in the mathematical equations, various equations and parameters may be used according to the types and the shapes of the arm device  30  and the surgical instrument  10 , and limitation to those described above with reference to the embodiment illustrated in  FIGS. 1-3  is not intended. 
     Subsequently, the calculator  53  in the controller  50  performs an operation of calculating Fp and Fr using the position vectors of Pr, Pp, Pg, and Pw, the gravity W, the force Fw, the moment Mw, the above-described equations (7), (8), (9), (10), and (11), and so on. 
     The surgical robot system  1 , the controller  50 , and the program configured as described above, make it possible to calculate the value of the first external force Fp that the surgical instrument  10  receives from the trocar  75  and the value of the second external force Fr that is received from an object other than the trocar  75  and that is abuttable on the surgical instrument, based on values of various external forces and torques detected by the detector  46  and on the value of the resistance force 5Fpx acting between the trocar  75  and the shaft  11 . 
     Since the detector  46  for detecting the values of various external forces and torques is arranged at a position not where the shaft  11  is present but where the arm device  30  is present (i.e., at a positon between the holder  45  and the drive portion  48 ), the size of the surgical instrument  10  may be reduced as compared with a case in which a sensor or detector is arranged on the surgical instrument  10 , e.g., at the forceps or on the distal end of the surgical instrument  10 . 
     As compared with a case where, for example, the detector  46  is arranged closer to the forceps  12  than the drive portion  48  is, arranging the detector  46  between the drive portion  48  and the holder  45  makes it less likely for the detector  46  to detect a force and a torque caused by operation of the drive portion  48 . In other words, accuracy of detection by the detector  46  is improved. 
     Each component of the external force may be obtained independently based on various information from the detector  46 , which is the force/torque sensor with six degrees of freedom. Thus, theoretically speaking, there occurs no case where the external force acting on the forceps  12  at the distal end of the shaft  11 , and/or on the trocar  75  is undercalculated. 
     The surgical robot system  1  is controlled using the calculated value of the first external force Fp and the calculated value of the second external force Fr. For example, at least one actuator of the actuator  31   a , the actuator  33   a , the actuator  35   a , the actuator  42   a , the actuator  43   a  and the actuator  47  is controlled according to control signals from the controller  50 , based on the calculated value of the first external force Fp and/or the calculated value of the second external force Fr. This control permits using the first external force Fp and/or the second external force Fr to provide force feedback and to improve safety by, for example, appropriately setting thresholds for the control of the surgical robot system  1  even when some uncertainty is contained in the gravity W acting on the surgical instrument  10 , a frictional force Fpx of the trocar  75 , and so on. 
     For example, it becomes possible to achieve an operation such as maintaining the position and the attitude of the forceps  12  at the distal end of the shaft  11  without yielding to the external force acting on the shaft  11  of the surgical instrument  10  while suppressing the first external force Fp that the surgical instrument  10  receives from the trocar  75  below a certain level. 
     It is possible to detect the first external force Fp that the surgical instrument  10  receives from the trocar  75  and the second external force Fr that is received from an object other than the trocar  75  and that is abuttable on the surgical instrument in a significantly distinguishable manner. Thus, enhancement of the safety in and out of the visual field during surgery is facilitated by presenting the first external force Fp and the second external force Fr to a manipulator of the surgical robot system  1 . For example, the first external force Fp and/or the second external force Fr may be displayed on a display of the controller  50  or an audible alert may be provided such that a surgeon manipulating the surgical robot system  1  may be given feedback during a surgical operation using the surgical robot system  1 . 
       FIGS. 4-5  illustrate another example of a configuration of a surgical robot system according to various embodiments. A basic configuration of the surgical robot system illustrated in  FIGS. 4-5  is similar to that of the embodiment illustrated with reference to  FIGS. 1-3  and like reference numbers refer to like elements/components and repeated description thereof will be omitted for conciseness. However a method for obtaining the external force received by the forceps at the distal end of the shaft of the surgical instrument is different from that of the embodiment illustrated with respect to  FIGS. 1-3 . Thus, an explanation will be given of the method for obtaining the external force received by the forceps at the distal end of the shaft  11  of the surgical instrument with reference to  FIG. 4  and  FIG. 5 . 
     As shown in  FIG. 4 , a surgical robot system  101  comprises the surgical instrument  10 , an arm device  130 , and a controller  150 . The controller  150  corresponds to one example of an external force estimation device. 
     The arm device  130  comprises the rotating portion  31 , the first arm rotating portion  33 , the first arm  34 , the second arm rotating portion  35 , the second arm  36 , the gimbal portion  41 , the holder  45 , the detector  46 , the rotation support portion  47 , the drive portion  48 , the attachment/detachment portion  49 , and a distal end external force detector  148 . The distal end external force detector  148  is a sensor for detecting a value of a distal end external force Ft, which is an external force received by the forceps  12  at the distal end of the shaft  11  of the surgical instrument  10 . 
     In a case where the drive portion  48  comprises a gas-pressure actuator for generating a driving force that drives the forceps  12  at the distal end of the shaft  11  and the bend portion  13  using pressure of a gas, such as air, the distal end external force detector  148  includes a sensor for detecting a displacement of a piston and so on in the gas-pressure actuator and a sensor for detecting the pressure of gas within a cylinder of the piston. 
     A position and a detection method of the distal end external force detector  148  is not particularly limited as long as the distal end external force detector  148  may detect the external force Ft acting on the forceps  12  at the distal end of the shaft  11 . For example, in some embodiments, the distal end external force detector  148  may be a sensor that is arranged in a neighborhood of the forceps  12  at the distal end of the shaft  11  in the surgical instrument  10  to detect the external force Ft acting on the forceps  12  at the distal end of the shaft  11 . 
     As shown in  FIG. 4  and  FIG. 5 , the controller  150  is an information processor, such as a computer, which comprises a central processing unit (CPUO, a ROM, a RAM, an input/output interface, and so on. 
     Program code stored in a storage device, such as the ROM or the RAM, causes the CPU, the ROM, the RAM, and the input/output interface to work cooperatively to function as at least an inputter  151 , the storage section  52 , and a calculator  153 . 
     As compared with the inputter  51 , the inputter  151  further receives information on the distal end external force Ft from the distal end external force detector  148  that is applied to the forceps  12  at the distal end of the shaft  11  and detected by the distal end external force detector  148 . 
     The calculator  153  calculates a value of the first external force Fp and a value of the second external force Fr based on the information on the force Fw and the torque Mw inputted to the inputter  151 , based on the information on the distal end external force Ft, and on the value of the resistance force stored in advance in the storage section  52 . 
     The calculator  153  performs an operation similar to that of the calculator  53  when calculating the value of the first external force Fp and the value of the second external force Fr. When calculating a value of the distal end external force Ft acting on the forceps  12 , the calculator  153  performs an operation based on the information on the distal end external force Ft detected and outputted by the distal end external force detector  148 . Furthermore, calculation of the shaft external force, which is an external force received from an object other than the forceps  12  and the trocar  75  and that is abuttable on the surgical instrument, is performed using the calculated second external force Fr and the calculated distal end external force Ft acting on the forceps  12 . Given that a resultant force of the shaft external force is Fs, Fs may be obtained using the following equation. 
         F   s   =F   r   −F   t   [Mathematical 13]
 
     The configuration illustrated in  FIGS. 4-5  with the distal end external force detector  148  provided enables the calculator  153  to calculate a value of the shaft external force, which is an external force in the shaft  11  received from an object other than the forceps  12  and the trocar  75  and that is abuttable on the surgical instrument. Examples of the shaft external force may include a force applied due to contact of a midsection of the shaft  11  with an organ or the like of the patient  70 , which is caused by relative movement of the surgical instrument  10  with respect to the patient  70 . 
     In addition, use of the distal end external force Ft obtained by the distal end external force detector  148  as a reference signal facilitates further improvement in accuracy of the first external force Fp and the second external force Fr to be calculated, as compared with a case where the distal end external force detector  148  is omitted. 
       FIGS. 6-7  illustrate another example of a configuration of a surgical robot system according to various embodiments. A basic configuration of the surgical robot system of  FIGS. 6-7  is similar to that of the embodiment described with reference to  FIGS. 1-3  and like reference numbers are used for like elements/components and repeated description thereof is omitted for conciseness. The surgical robot system illustrated in  FIGS. 6-7  is adaptable to a different type of trocar. Thus, an explanation will be given of details of the adaptability to a different type of trocar with reference to  FIG. 6  and  FIG. 7 , and explanation of other configuration and so on will be omitted for conciseness. 
     As shown in  FIG. 6 , a surgical robot system  201  comprises the surgical instrument  10 , the arm device  30 , and a controller  250 . The controller  250  corresponds to one example of an external force estimation device. 
     As shown in  FIG. 6  and  FIG. 7 , the controller  250  is an information processor, such as a computer, which comprises a central processing unit (CPU), a ROM, a RAM, an input/output interface, and so on. Program code stored in a storage device, such as the ROM or the RAM, causes the CPU, the ROM, the RAM, and the input/output interface to work cooperatively to function as at least the inputter  51 , a selector  251 , a storage section  252 , and a calculator  253 . 
     The selector  251  is used to identify the trocar  75  to be used in the surgical robot system  1 . In some embodiments, multiple types of the trocar  75  may be used in the surgical robot system  1 , and information for identifying the trocar  75  of each type is acquired from the storage section  252 . 
     Examples of such a case may include a case where the selector  251  displays on a display of the controller  250  the types of the trocar  75  used in the surgical robot system  1  and stored in the storage section  252  and performs identification by designating a type of the trocar  75  to be used from among the displayed types of the trocar  75 , according to an input by a manipulator. 
     in another example, the trocar  75  to be used may be identified by inputting a model number, a serial number, or the like indicated on the trocar  75  to the selector  251  by a manipulator. A specific method of performing identification is not particularly limited. 
     The storage section  252  stores in advance information for identifying the trocar  75  to be used in the surgical robot system  1 , a value of the resistance force 5Fpx acting between the trocar  75  and the shaft  11  of the surgical instrument  10 , and a value of the gravity W acting on the surgical instrument  10 . A value of weight may be used as the gravity W. The information for identifying the trocar  75  and the value of the resistance force 5Fpx in the trocar  75  are stored in an associated manner. 
     The calculator  253  calculates a value of the first external force Fp and a value of the second external force Fr based on the information on the force Fw and the torque Mw inputted to the inputter  51  and based on the value of the resistance force stored in advance in the storage section  252 . The calculation in the calculator  253  differs from that in the calculator  53  in that the information for identifying the trocar  75  selected by the selector  251  and the value of the resistance force 5Fpx associated therewith are acquired from the storage section  252  to thereby perform an operation. The calculation other than this point is similar to that of the calculator  53 . 
     The above-described configuration with the storage section  252  and the selector  251  provided thereto makes it possible to calculate the value of the first external force Fp and the value of the second external force Fr using the resistance force 5Fpx corresponding to the trocar  75  to be used, even when the trocar  75  to be used is changed to the trocar  75  different in the resistance force 5Fpx acting between the trocar  75  and the shaft  11 . This ability to calculate based on the specific trocar  75  being used results in a reduction of deterioration in accuracy of the value of the first external force Fp and the value of the second external force Fr to be calculated, as compared with a case where the resistance force 5Fpx corresponding to the trocar  75  is not used. 
     The technical scope of the present disclosure is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present disclosure. For example, the present disclosure may be applied to an embodiment that is an appropriate combination of the above-described embodiments, without being limited to that obtained by applying the present disclosure to the above-described embodiments, and no particular limitation is intended. 
     For example, in the above-described embodiments, the forceps  12  is provided at the distal end of the shaft  11 . However, in other embodiments, other instruments used in endoscope surgery may be provided at the distal end of the shaft  11 , etc. 
     Examples of the endoscopic surgery to which the surgical robot system, the external force estimation device, and the computer readable medium of the present disclosure are applied may include endoscopic surgeries in general in which the surgical instrument  10  is inserted into the body of the patient  70 . From among the endoscopic surgeries, gastroenterological surgeries on a large organ, such as a digestive organ, in which an external force is likely to be applied to the surgical instrument  10 , thoracic surgeries in which the surgical instrument  10  is inserted in between costal bones, and surgeries for obese patients with a thick abdominal wall are examples of endoscopic surgeries in which the surgical robot system of the present disclosure may be used. 
     It should be understood that the inventive concept is not limited to the above embodiments, but various other changes and modifications may be made therein without departing from the spirit and scope as set forth in appended claims.