Patent Publication Number: US-2020275981-A1

Title: Optical force sensor for robotic surgical system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is continuation of U.S. patent application No. 15,768,342, filed on Apr. 13, 2018, which is a U.S. National Stage Application filed under 35 U.S.C. § 371(a) of International Patent Application Serial No. PCT/US2016/062138, filed Nov. 16, 2016, which claims the benefit of and priority to U.S. Provisional Patent Application Ser. No. 62/257,564, filed Nov. 19, 2015, the entire disclosure of which is incorporated by reference herein. 
    
    
     BACKGROUND 
     Robotic surgical systems have been used in minimally invasive medical procedures. During a medical procedure, the robotic surgical system is controlled by a surgeon interfacing with a user interface. The user interface allows the surgeon to manipulate an end effector that acts on a patient. The user interface includes an input controller that is moveable by the surgeon to control the robotic surgical system. 
     The robotic surgical system includes a surgical robot that is associated with the user interface. The surgical robot includes linkages that support a surgical instrument. The surgical instrument can include one or more jaw members that act on tissue of the patient during a surgical procedure. As the clinician manipulating the end effector is remote to the patient, it is important to accurately determine the forces exerted on the tissue by the jaw members. 
     Accordingly, there is a need for accurately determining forces exerted on or by the jaw members of the surgical instrument during a surgical procedure. 
     SUMMARY 
     This disclosure relates generally to optical force sensors that are disposed in one or more jaw members of a surgical instrument of a robotic surgical system. The optical force sensors directly measure the deflection of the respective jaw member in one or more directions to determine force exerted on or by the respective jaw member. The direct measurement of the deflection of the respective jaw member has been shown to provide an accurate measure of the force exerted on or by the respective jaw member. 
     The measured force can be used to provide feedback to a clinician engaged with the user interface of the robotic surgical system. In addition, the measured force can be used to enhance the function of a variety of instruments including, but not limited to, a grasper, a stapler (monolithic or two-part fasteners), electrosurgical forceps, and an endoscopic suturing device. For example, when the surgical instrument is a grasper, the measured force can be used to determine a force exerted on tissue by the grasper or to determine if an item (e.g., a suture) is slipping between two graspers. Additionally, when the instrument is a stapler, the measured force can be used to determine a force exerted to clamp tissue between the jaw members to prevent under or over clamping of the tissue before application of a one or two-part staple. Further, when the instrument is an electrosurgical forceps, the measured force can be used to optimize sealing, cutting, and/or coagulating of tissue between the jaw members. In addition, when the instrument is an endoscopic suturing device the measured force can be used to optimize the force exerted on a suture. 
     According to an aspect of the present disclosure, a surgical instrument is provided and includes a housing; an elongate shaft extending from the housing; and a tool assembly supported by a distal portion of the elongate shaft, the tool assembly including first and second jaw member. The at least one of the first and second jaw members is moveable relative to the other jaw member between a neutral configuration in which the first and second jaw members are spaced apart relative to one another; and a clamping configuration in which the first and second jaw members are approximated relative to one another with tissue grasped therebetween, the first jaw member defining a cavity. 
     The surgical instrument further includes an optical force sensor configured to determine a force exerted to tissue. The optical force sensor includes a light source; a reflector disposed within the cavity of the first jaw member and configured to reflect light emitted from the light source; a light receiver configured to sense an amount of light reflected from the light source; and a processor in communication with the light receiver and configured to determine deflection of the first jaw member from the amount of sensed light, the deflection of the first jaw member correlated to a force exerted by the first jaw member to tissue. 
     The light source may be disposed within the housing. 
     The optical force sensor may include a light guide extending between the light source and the cavity. 
     The light receiver may be disposed within the housing and in communication with the light guide such that light reflected from the reflector passes through the light guide. 
     In use, light reflected from the reflector may have at least one property different than light emitted towards the reflector, the at least one property is at least one of a phase or a wavelength. 
     The light receiver may be disposed within the cavity. 
     The first jaw member may have a tissue contacting surface opposing the second jaw member and an outer surface opposite the tissue contacting surface. The first and second jaw members may have a distracting configuration in which the outer surface of the first jaw member is engaged with tissue. 
     In the clamping configuration, the first jaw member may be deflected in a first direction, and in the distracting configuration, the first jaw member may be deflected in a second direction opposite the first direction. The processor may be configured to determine a direction of deflection of the first jaw member from the amount of light received by the light receiver. 
     The reflector may be disposed orthogonal to an axis of transmittance of light emitted from the light emitter. 
     The reflector may be disposed at an angle relative to an axis of transmittance of the light emitted from the light emitter in a range of about 5° to about 85°. 
     The reflector may be concave. The concavity of the reflector may be configured to direct the entire amount of light emitted from the light source towards the light detector when the first jaw member is in the neutral configuration. 
     The light source may be at least one of a microLED or a laser diode. 
     According to a further aspect of the present disclosure, a tool assembly is provided and includes a jaw member defining a cavity; and an optical force sensor configured to determine a force exerted to tissue by a jaw tool assembly, the tool assembly defining a cavity. The optical force sensor includes a first light source; a reflector disposed within a cavity of the tool assembly and configured to reflect light emitted from the first light source; a light receiver configured to sense an amount of emitted by the first light source and reflected by the reflector; and a processor in communication with the light receiver and configured to determine deflection of the first jaw member from the amount of sensed light, the deflection of the first jaw member correlated to a force exerted by the first jaw member to tissue. 
     The optical force sensor may include a second light source. The reflector may be configured to reflect light emitted from the second light source. The light receiver may be configured to sense an amount of light emitted by the second light source and reflected by the reflector. 
     The cavity may be defined by a first sidewall and a second sidewall perpendicular to the first sidewall. The first light source may be configured to emit light through an opening in the first sidewall and the second light source may be configured to emit light through an opening in the second sidewall. 
     The first light source may be configured to emit light having a first property and the second light source is configured to emit light having a second property different from the first property, the light detector differentiating between sensed light from the first light source and sensed light from the second light source. 
     According to still another aspect of the present disclosure, a method is provided for determining a force applied to tissue by a jaw member of a tool assembly. The method includes engaging tissue with a jaw member of a tool assembly such that the jaw member is deflected; emitting light from a light source towards a reflector disposed within a cavity defined in within the jaw member; sensing an amount of light from the first light source reflected by the reflector with a light detector; and determining the force applied to the tissue by the jaw member from the amount of sensed light. 
     The engaging tissue with the jaw member may include at least one of engaging tissue with a tissue contacting surface of the jaw member in a clamping configuration or engaging tissue with an outside surface of the jaw member opposite the tissue contacting surface in a distracting configuration. 
     The determining of the force applied to tissue by the jaw member may include a configuration of the jaw member based on the amount of sensed light. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various aspects of the present disclosure are described hereinbelow with reference to the drawings, which are incorporated in and constitute a part of this specification, wherein: 
         FIG. 1  is a schematic illustration of a user interface and a robotic system in accordance with the present disclosure; 
         FIG. 2  is a schematic illustration of a surgical instrument of the robotic system inserted into a body cavity of a patient; 
         FIG. 3  is a schematic illustration of an optical force sensor of the surgical instrument of  FIG. 2  provided in accordance with the present disclosure; 
         FIG. 4  is a schematic illustration of the first jaw member of the surgical instrument of  FIG. 2  including the optical force sensor of  FIG. 3  in a neutral configuration; 
         FIG. 5  is a schematic illustration of the optical force sensor of  FIG. 4  in a closing configuration; 
         FIG. 6  is a schematic illustration of the optical force sensor of  FIG. 4  in an opening configuration; 
         FIG. 7A  is a schematic illustration of the first jaw member of the surgical instrument of  FIG. 2  including another optical force sensor provided in accordance with the present disclosure in a neutral configuration; 
         FIG. 7B  is a schematic illustration of the optical force sensor of  FIG. 7A  in a closing configuration; 
         FIG. 7C  is a schematic illustration of the optical force sensor of  FIG. 7A  in an opening configuration; 
         FIG. 8A  is a schematic illustration of the first jaw member of the surgical instrument of  FIG. 2  including another optical force sensor provided in accordance with the present disclosure in a neutral configuration; 
         FIG. 8B  is a top view of a cavity of the first jaw member of  FIG. 8A ; 
         FIG. 9A  is a schematic illustration of the first jaw member of the surgical instrument of  FIG. 2  including another optical force sensor provided in accordance with the present disclosure in a neutral configuration; 
         FIG. 9B  is a top view of a cavity of the first jaw member of  FIG. 9A ; 
         FIG. 10A  is a schematic illustration of the first jaw member of the surgical instrument of  FIG. 2  including another optical force sensor provided in accordance with the present disclosure in a neutral configuration; 
         FIG. 10B  is a schematic illustration of the optical force sensor of  FIG. 7A  in a closing configuration; 
         FIG. 10C  is a schematic illustration of the optical force sensor of  FIG. 7A  in an opening configuration; 
         FIG. 11  is a side view of two end effectors of two surgical instruments each including an optical force sensor provided in accordance with the present disclosure; and 
         FIG. 12  is a flowchart illustrating a method of generating force feedback for a robotic surgical system in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are now described in detail with reference to the drawings in which like reference numerals designate identical or corresponding elements in each of the several views. As used herein, the term “clinician” refers to a doctor, a nurse, or any other care provider and may include support personnel. Throughout this description, the term “proximal” refers to the portion of the device or component thereof that is closest to the clinician and the term “distal” refers to the portion of the device or component thereof that is farthest from the clinician. 
     This disclosure relates generally to optical force sensors that are disposed in one or more jaw members of a surgical instrument of a robotic surgical system. The optical force sensors directly measure the deflection of the respective jaw member in one or more directions to determine force exerted on or by the respective jaw member. The optical force sensor includes a light source, a light guide, a reflector, and a light receiver. The light guide is in communication with the light source to transmit light produced by the light source into a cavity defined within a jaw member of the surgical instrument. An amount of the transmitted light is reflected off of the reflector and returned into the light guide. The light receiver measures an amount of light returned into the light guide to determine the deflection of the jaw member. The reflector is supported within the cavity such that as the jaw member is deflected, the amount of light returned into the light guide varies. 
     Referring to  FIG. 1 , a robotic surgical system  1  is shown generally as a robotic system  10 , a processing unit  30 , and a user interface  40 . The robotic system  10  generally includes linkages  12  and a robot base  18 . The linkages  12  moveably support an instrument  20  which is configured to act on tissue. The linkages  12  may be in the form of arms or links each having an end  14  that supports an instrument  20  which is configured to act on tissue. In addition, the ends  14  of the linkages  12  may include an imaging device  16  for imaging a surgical site “S”. The user interface  40  is in communication with robot base  18  through the processing unit  30 . 
     The user interface  40  includes a display device  44  which is configured to display three-dimensional images. The display device  44  displays three-dimensional images of the surgical site “S” which may include data captured by imaging devices  16  positioned on the ends  14  of the linkages  12  and/or include data captured by imaging devices that are positioned about the surgical theater (e.g., an imaging device positioned within the surgical site “S”, an imaging device positioned adjacent the patient “P”, imaging device  56  positioned at a distal end of an imaging linkage  52 ). The imaging devices (e.g., imaging devices  16 ,  56 ) may capture visual images, infra-red images, ultrasound images, X-ray images, thermal images, and/or any other known real-time images of the surgical site “S”. The imaging devices transmit captured imaging data to the processing unit  30  which creates three-dimensional images of the surgical site “S” in real-time from the imaging data and transmits the three-dimensional images to the display device  44  for display. 
     The user interface  40  also includes input devices or handles attached to gimbals  70  which allow a clinician to manipulate the robotic system  10  (e.g., move the linkages  12 , the ends  14  of the linkages  12 , and/or the instruments  20 ). Each of the gimbals  70  is in communication with the processing unit  30  to transmit control signals thereto and to receive feedback signals therefrom. Additionally or alternatively, each of the gimbals  70  may include control interfaces or input devices (not shown) which allow the surgeon to manipulate (e.g., clamp, grasp, fire, open, close, rotate, thrust, slice, etc.) the instruments  20  supported at the ends  14  of the linkages  12 . 
     Each of the gimbals  70  is moveable to move the ends  14  of the linkages  12  within a surgical site “S”. The three-dimensional images on the display device  44  are orientated such that movement of the gimbals  70  moves the ends  14  of the linkages  12  as viewed on the display device  44 . It will be appreciated that the orientation of the three-dimensional images on the display device may be mirrored or rotated relative to view from above the patient “P”. In addition, it will be appreciated that the size of the three-dimensional images on the display device  44  may be scaled to be larger or smaller than the actual structures of the surgical site “S” permitting the surgeon to have a better view of structures within the surgical site “S”. As the gimbal  70  is moved, the instruments  20  are moved within the surgical site “S”. Movement of the instruments  20  may also include movement of the ends  14  of the linkages  12  which support the instruments  20 . 
     For a detailed discussion of the construction and operation of a robotic surgical system  1 , reference may be made to U.S. Pat. No. 8,828,023, the entire contents of which are incorporated herein by reference. 
     With reference to  FIG. 2 , an instrument  20  is inserted into a body cavity “C” of a patient “P” through a port or trocar  80  to access the surgical site “S”. The instrument  20  includes a housing or body  110 , an elongate shaft  120 , and an end effector  130 . The body  110  includes an interface  112  that couples to an instrument drive unit (IDU)  90  which provides mechanical energy or input for manipulating the instrument  20 . The IDU  90  may also provide electrical and/or optical energy to the instrument  20  through the interface  112 . In addition, the instrument  20  may provide feedback signals, electrical, mechanical, and/or optical, to IDU  90 . The IDU  90  is in communication with the processing unit  30  ( FIG. 1 ) to receive signals for manipulating the instrument  20  and to provide feedback signals from the instrument  20  and the IDU  90  to the processing unit  30  as described in detail below. 
     The elongate shaft  120  extends from the body  110  and is articulable in three degrees of freedom (DOF) relative to the body  110 . It will be appreciated that the body  110  is moveable into and out of the trocar  80  to provide a fourth DOF. The body  110  includes an articulation mechanism (not explicitly shown) to articulate the elongate shaft  120  in response to mechanical input from the IDU  90 . 
     The end effector  130  is supported at a distal end  128  of the elongate shaft  120  and includes a first jaw member  140  and a second jaw member  150  that are moveable relative to one another between an open position and a closed position. As shown, each of the first and second jaw members  140 ,  150  pivot relative to one another about a pin  134  ( FIG. 3 ) of the end effector  130 ; however, one of the first or second jaw members  140 ,  150  may be fixed relative to the elongate shaft  120  with the other one of the first or second jaw members  140 ,  150  moveable relative to the fixed jaw member. The IDU  90  includes a motor  94  that is associated with the end effector  130  to transition the first and second jaw members  140 ,  150  between the open and closed positions. Some IDUs  90  may include two or more motors  94  that may actuate one or more features of instrument  20 . One or more of the motors  94  may be associated with respective cables to actuate one or more features of the instrument  20 . These features may include, for example, articulation of the jaws  140 ,  150  or end effector  130  in one or more degrees of freedom. As detailed below, the IDU  90  includes a torque or force sensor  96  that generates a direction signal indicative of whether the motor  94  is transitioning the first and second jaw members  140 ,  150  towards the closed position or towards the open position. 
     Referring to  FIGS. 3 and 4 , the first jaw member  140  defines a cavity  142  that includes an optical force sensor  200  in accordance with the present disclosure. The optical force sensor  200  includes a light source  210 , a light guide  220 , a reflector  230 , and a light receiver  240 . As shown, the light source  210  is disposed in the body  110  ( FIG. 2 ); however, it is contemplated that the light source  210  (e.g., a microLED or laser diode) may be disposed in the elongate shaft  120  or the end effector  130  (e.g., a yoke  132  of the end effector  130  or the first or second jaw member  140 ,  150 ). The light guide  220  may be in the form of an optical fiber (e.g., fiber optic cable) that extends from the body  110 , through the elongate shaft  120 , and into the end effector  130 . The light guide  220  includes a proximal end  222  that is in optical communication with the light source  210  to receive light provided by the light source  210  and a distal end  228  disposed in the cavity  142  defined within the first jaw member  140 . 
     The reflector  230  is supported by the first jaw member  140  within the cavity  142 . The walls defining the cavity  142  may be treated with light absorbing material, a non-reflective material, or a diffusing material to increase the sensitivity of the optical force sensor  200 . The reflector  230  is aligned with the distal end  228  of the light guide  220  such that light transmitted through the distal end  228  of the light guide  220  is in a light cone “LC” having a transmittance axis “T” that is directed towards the reflector  230 . It will be appreciated that the amount of light at the transmittance axis “T” is greater than an amount of light at a point within the light cone “LC” a distance away (e.g., a radial distance) from the transmittance axis “T”. The reflector  230  is a flat mirror that is disposed substantially orthogonal to the transmittance axis “T” such that light transmitted through the distal end  228  of the light guide  220  is reflected off of the reflector  230  back towards the distal end  228  of the light guide  220  in a reflected light cone “RLC” having a reflectance axis “R”. It will be appreciated that an amount of light at the reflectance axis “R” is greater than an amount of light at a point within the reflected light cone “RLC” spaced apart (e.g., a radial distance) from the reflectance axis “R”. 
     The light receiver  240  is disposed within the body  110  of the surgical instrument  100  in optical communication with the proximal end  222  of the light guide  220 . The light receiver  240 , which may in some instances be a photocell, may be configured to sense an amount of light reflected through the light guide  220  from the reflector  230 . 
     It is contemplated that the reflector  230  may include a fluorescing material such that light emitted from the reflector  230  has a different wavelength than light striking the reflector  230 . For example, the reflector  230  may be a scintillator mirror. 
     It is envisioned that the second jaw member  150  may also include an optical force sensor  200  disposed within a cavity  152  defined within the second jaw member  150 . The optical force sensor  200  disposed within the second jaw member  150  may share the first light source  210  with the optical force sensor  200  disposed within the first jaw member  140 . The optical force sensor  200  disposed within the second jaw member  150  functions in a similar manner to the optical force sensor  200  disposed within the first jaw member  140  as described below and will not be described in further detail herein. 
     With reference to  FIGS. 4-6 , the first jaw member  140  has a rest or neutral configuration ( FIG. 4 ), a clamping configuration ( FIG. 5 ), and a distracting configuration ( FIG. 6 ). In the neutral configuration, the first jaw member  140  is subject to little or no force (e.g., transverse force) such that the reflectance axis “R” is substantially aligned with the transmittance axis “T”. The most amount of light may be reflected back to the light receiver  240  when the reflectance axis “R” is aligned with the transmittance axis “T”. 
     In the clamping configuration, the first and second jaw members  140 ,  150  are moving towards the closed configuration. As shown in  FIG. 5 , the first jaw member  140  is in the clamping configuration moving in a first or closing direction as represented by arrow “CD” in  FIG. 5 . In the clamping configuration, the first and second jaw members  140 ,  150  may engage an obstruction “O” (e.g., tissue, bone, vessel, another surgical instrument, etc.) such that the first jaw member  140  is deformed or deflected by a deflection force. The deflection of the first jaw member  140  moves the reflector  230  within the cavity  142  of the first jaw member  140  which misaligns the reflectance axis “R” from the transmittance axis “T”. When the reflectance axis “R” is misaligned with the transmittance axis “T”, the amount of light returned through the light guide  220 , and thus sensed by the light receiver  240 , is less than when the first jaw member  140  is in the neutral configuration (i.e., when the reflectance axis “R” is aligned with the transmittance axis “T”). The difference (e.g., reduction) in the amount of light received by the light receiver  240  from the neutral configuration is indicative of the deflection of the first jaw member  140 . With the deflection of the first jaw member  140  from the neutral configuration known, the deflection force exerted by the first jaw member  140  on the obstruction “O” can be determined. 
     In the distracting configuration, the first and second jaw members  140 ,  150  are moving towards the open configuration. As shown in  FIG. 6 , with the first jaw member  140  in the distracting configuration, the first jaw member  140  moves in a second or opening direction as represented by arrow “OD” in  FIG. 6 . In the distracting configuration, the first jaw member  140  is engaged with an obstruction “O” (e.g., tissue, bone, vessel, another surgical instrument, etc.) on an outer surface of the first jaw member  140  such that the first jaw member  140  is deflected by a deflection force. The deflection of the first jaw member  140  moves the reflector  230  within the cavity  142  of the first jaw member  140  which misaligns the reflectance axis “R” from the transmittance axis “T” as the first jaw member  140 . When the reflectance axis “R” is misaligned with the transmittance axis “T”, the amount of light returned through the light guide  220 , and thus sensed by the light receiver  240 , is less than when the first jaw member  140  is in the neutral configuration (i.e., when the reflectance axis “R” is aligned with the transmittance axis “T”). The difference (e.g., reduction) in the amount of light received by the light receiver  240  from the neutral configuration is indicative of the deflection of the first jaw member  140 . With the deflection of the first jaw member  140  from the neutral configuration known, the deflection force exerted by the first jaw member  140  on the obstruction “O” can be determined. It is contemplated that the first jaw member  140  may include cuts or reliefs (not explicitly shown) in the walls to promote deflection of the first jaw member  140  and/or to increase sensitivity of the optical force sensor  200 . 
     The optical force sensor  200  may include a processor  202  ( FIG. 3 ) that receives a signal from the light receiver  240  indicative of the amount of light received and correlates or calculates the amount of light received into a deflection force exerted by or on the first jaw member  140 . The processor  202  may be calibrated at the time of manufacture to associate a change in an amount of light received by the light receiver  240  with a deflection force of the first jaw member  140 . Additionally or alternatively, the processor  202  may be calibrated before or during a surgical procedure to compensate for changes in the jaw member  140  (e.g., a permanent deformation, obstructions in the cavity “C”, or conditions at the light source  210  or the light receiver  240 ). 
     As detailed above, the difference between the amount of light received by the light receiver  240  in the neutral configuration and the amount of light received by the light receiver  240  when the first jaw member  140  is deflected, in either the clamping or distracting configuration, is reduced. To differentiate between the clamping configuration and the distracting configuration, the processor  202  or the processing unit  30  receives a direction signal from the torque sensor  96  of the motor  94  indicative of a direction of movement of the first jaw member  140  (i.e., towards the open position or towards the closed position) to determine the configuration of the first jaw member  140 , and thus, the direction of the deflection of the first jaw member  140 . The processor  202  or the processing unit  30  may utilize the direction signal to calculate the deflection force as the first jaw member  140  may deflect asymmetrically in response to a given deflection force. 
     In aspects, the optical force sensor  200  may include a light receiver  240 ′ disposed within the cavity  142  of the first jaw member  140  that sends a signal to the processor  202  indicative of an amount of light received by the light receiver  240 ′. The light receiver  240 ′ is offset from the reflectance axis “R” and is disposed within a reflected light cone “RLC” of light transmitted through the distal end  228  of the light guide  220  and reflected off of the reflector  230 . As shown in  FIG. 5 , when the first jaw member  140  is in the clamping configuration, the light receiver  240 ′ receives an amount of light less than an amount of light received in the neutral configuration. When the first jaw member  140  is in the distracting configuration, the light receiver  240 ′ receives an amount of light greater than an amount of light received in the neutral configuration as shown in  FIG. 6 . By offsetting the light receiver  240 ′ from the reflectance axis “R” in the neutral configuration, the direction of the deflection of the first jaw member  140  and, thus, the direction of the force exerted by or on the first jaw member  140  can be determined from the increase or decrease in the amount of light received by the light receiver  240 . Thus, the extent and the direction of the deflection force can be determined without the need for a direction signal from the torque sensor  96 . It will be appreciated that by placing the light receiver  240 ′ within the cavity  142 , light may be continually transmitted through the distal end  228  of the light guide  220  without interfering with light reflected off of the reflector  230  to the light receiver  240  through the light guide  220 . 
     In some aspects, the light receiver  240 ′ may be used in conjunction with the light receiver  240  to provide a direction signal to the processor  202  and/or provide a verification of the extent of the deflection force. 
     Referring now to  FIGS. 7A-C , another optical force sensor  1200  is provided in accordance with the present disclosure. The optical force sensor  1200  is similar to the optical force sensor  200 , as such, only the differences will be detailed below with like structures represented with a similar label including a “1” preceding the previous label. 
     The optical force sensor  1200  includes a light source  1210 , a light guide  1220 , a reflector  1230 , and a light receiver  1240 . The reflector  1230  is supported within the cavity  142  of the first jaw member  140  at an angle offset from a plane “P” orthogonal to the distal end  1228  of the light guide  1220  in the neutral configuration of the first jaw member  140 . The angle may be in a range of about 5° to about 85° (e.g., about 15°). In the neutral configuration of the first jaw member  140 , the reflectance axis “R” is offset from the transmittance axis “T” with the distal end  1228  of the light guide  1220  within the reflected light cone “RLC” of light transmitted through the distal end  1228  of the light guide  1220 . 
     In use, when the first jaw member  140  is in the neutral configuration, an amount of light is reflected into the distal end  1228  of the light guide  1220  which is transmitted through the light guide  1220  and onto the light receiver  1240 . The amount of light transmitted onto the light receiver  1240  is measured by the light receiver  1240 . When the first jaw member  140  is in the clamping configuration, as shown in  FIG. 7B , an amount of light is reflected off of the reflector  1230  into the distal end  1228  of the light guide  1220 , and thus onto the light receiver  1240 , is less than the amount of light reflected into the distal end  1228  when the first jaw member  140  is in the neutral configuration. When the first jaw member  140  is in the dissecting configuration as shown in  FIG. 7C , an amount of light reflected into the distal end  1228  of the light guide  1220 , and thus onto the light receiver  1240 , is greater than the amount of light reflected into the distal end  1228  when the first jaw member  140  is in the neutral configuration. 
     As detailed above, by disposing the reflector  1230  within the cavity  142  of the first jaw member  140 , at an angle relative to the distal end  1228  of the light guide  1220 , such that the reflectance axis “R” is offset from the transmittance axis “T”, when the first jaw member  140  is in the neutral configuration, the optical force sensor  1200  senses the extent and direction of the deflection of the first jaw member  140 . 
     In aspects, the optical force sensor  1200  includes a light receiver  1240 ′ disposed within the cavity  142  of the first jaw member  140  that sends a signal to a processor  1202  of the optical force sensor  1200  indicative of an amount of light received by the light receiver  1240 ′. The light receiver  1240 ′ is offset from the reflectance axis “R” and is disposed within a reflected light cone “RLC”. As shown in  FIG. 7B , when the first jaw member  140  is in the clamping configuration, the light receiver  1240 ′ receives an amount of light less than an amount of light received in the neutral configuration. When the first jaw member  140  is in the distracting configuration, the light receiver  1240 ′ receives an amount of light greater than an amount of light received in the neutral configuration as shown in  FIG. 7C . By offsetting the light receiver  1240 ′ from the reflectance axis “R”, the extent and the direction of the deflection of the first jaw member  140  is determined by the amount of light measured by the light receiver  1240 ′. 
     In some aspects, the light receiver  1240 ′ is disposed within the cavity  142  and is aligned with the reflectance axis “R” when the first jaw member  140  is in the neutral configuration. Similar to the optical force sensor  200  detailed above, when the light receiver  1240 ′ is aligned with the reflectance axis “R”, when the first jaw member  140  is in either the clamping or distracting configurations, the amount of light received by the light receiver  1240 ′ is less than when the first jaw member  140  is in the neutral configuration. In such aspects, the optical force sensor  1200  includes a processor  1202  that receives a direction signal from a torque sensor  96  ( FIG. 2 ) associated with the motor  92  to determine the direction of the deflection of the first jaw member  140 . 
     It is contemplated that the optical force sensor  1200  may utilize the light receiver  1240  to determine the direction of the deflection of the first jaw member  140  and the light receiver  1240 ′ to determine the extent of the deflection of the first jaw member  140 . Alternatively, the optical force sensor  1200  may utilize the light receiver  1240  to determine the direction and the extent of the deflection of the first jaw member  140  and utilize the light receiver  1240 ′ to verify the extent of the deflection of the first jaw member  140 . 
     Referring to  FIGS. 8A-B , another optical force sensor  2200  is provided in accordance with the present disclosure. The optical force sensor  2200  is similar to the optical force sensor  200 , as such, only the differences will be detailed below with like structures represented with a similar label including a “2” preceding the previous label. 
     The optical force sensor  2200  includes a light source  2210 , a light guide  2220 , a reflector  2230 , and a light receiver  2240 . The reflector  2230  is supported within the cavity  142  of the first jaw member aligned with the plane “P” orthogonal to a distal end  2228  of the light guide  2220 . The reflector  2230  is concave in a first direction and flat in a second direction aligned with the opening and closing directions “OD”, “CD” which is orthogonal to the first direction. The concavity of the reflector  2230  focuses light transmitted through the distal end  2228  of the light guide  2220  on the distal end  2228  of the light guide  2220  in a direction substantially parallel to the opening and closing directions “OD”, “CD”. As such, the reflected light cone “RLC” is substantially linear at the distal end  2228  of the light guide  2220  in a direction substantially parallel to the opening and closing directions “OD”, “CD”. 
     In use, the optical force sensor  2220  functions in a manner similar to the optical force sensor  200  for detecting deflection of the first jaw member  140  towards and away from the second jaw member  150  (i.e., in the opening direction “OD” or in closing direction “CD”). By reflecting light transmitted through the distal end  2228  of the light guide  2220  in a substantially linear reflected light cone “RLC”, the concavity of the reflector  2230  isolates deflection of the first jaw member  140  in the opening and closing directions “OD”, “CD” from deflection of the first jaw member  140  in a first transverse direction “TD 1 ” or a second transverse direction “TD 2 ”. Thus, the concavity of the reflector  2230  may increase the accuracy of the optical force sensor  2220  for detecting an extent of the deflection of the first jaw member  140  in the opening and closing directions “OD”, “CD”. It is contemplated that the reflector  2230  concave in both the first and second directions such the reflector  2230  focuses light transmitted through the distal end  2228  of the light guide  2220  to a point or a focused spot. 
     In aspects, the optical force sensor  2200  includes a light receiver  2240 ′ disposed within the cavity  142  of the first jaw member  140 . The light receiver  2240 ′ is positioned offset from a transmittance axis “T” of the light cone “LC” of light transmitted through the distal end  2228  of the light guide  2220  and aligned with the distal end  2228  of the light guide  2220  such that the light receiver  2240 ′ receives a substantially linear reflected light cone “RLC”. In use, the light receiver  2240 ′ functions substantially similar to the light receiver  240 ′ and may have increased accuracy for detecting an extent of the deflection of the first jaw member  140 . 
     Referring to  FIGS. 9A and 9B , another optical force sensor  3200  is provided in accordance with the present disclosure. The optical force sensor  3200  is similar to the optical force sensor  1200 , as such, only the differences will be detailed below with like structures represented with a similar label replacing the first numeral “1” with a numeral “3”. 
     The optical force sensor  3200  includes a light source  3210 , a light guide  3220 , a reflector  3230 , and a light receiver  3240 . The reflector  3230  is supported within the cavity  142  of the first jaw member  140  at an angle offset from a plane “P” orthogonal to a distal end  3228  of the light guide  3220 . The reflector  3230  is concave in a first direction and flat in a second direction aligned with the opening and closing directions “OD”, “CD” which is orthogonal to the first direction. The concavity of the reflector  3230  focuses light transmitted through the distal end  3228  of the light guide  3220  on the distal end  3228  of the light guide  3220  in a direction substantially parallel to the opening and closing directions “OD”, “CD”. As such, the reflected light cone “RLC” is substantially linear at the distal end  3228  of the light guide  3220  in a direction substantially parallel to the opening and closing directions “OD”, “CD”. 
     In use, the optical force sensor  3220  functions in a manner similar to the optical force sensor  1200  for detecting deflection of the first jaw member  140  towards and away from the second jaw member  150  (i.e., in the opening direction “OD” or in closing direction “CD”). By reflecting light transmitted through the distal end  3228  of the light guide  3220  in a substantially linear reflected light cone “RLC”, the concavity of the reflector  3230  isolates deflection of the first jaw member  140  in the opening and closing directions “OD”, “CD” from deflection of the first jaw member  140  in a first transverse direction “TD 1 ” or a second transverse direction “TD 2 ”. Thus, the concavity of the reflector  3230  may increase the accuracy of the optical force sensor  3220  for detecting an extent of the deflection of the first jaw member  140  in the opening and closing directions “OD”, “CD”. 
     In aspects, the optical force sensor  3200  includes a light receiver  3240 ′ disposed within the cavity  142  of the first jaw member  140  that sends a signal to a processor  3202  of the optical force sensor  3200  indicative of an amount of light received by the light receiver  3240 ′. The light receiver  3240 ′ is offset from the reflectance axis “R” and is disposed within a reflected light cone “RLC” of light transmitted through the distal end  3228  of the light guide  3220 . When the first jaw member  140  is in the clamping configuration, the light receiver  3240 ′ receives an amount of light less than an amount of light received in the neutral configuration. When the first jaw member  140  is in the distracting configuration, the light receiver  3240 ′ receives an amount of light greater than an amount of light received in the neutral configuration. By offsetting the light receiver  3240 ′ from the reflectance axis “R”, the extent and the direction of the deflection of the first jaw member  140  is determined by the amount of light measured by the light receiver  3240 ′. 
     In some aspects, the light receiver  3240 ′ is disposed within the cavity  142  and is aligned with the reflectance axis “R” when the first jaw member  140  is in the neutral configuration. Similar to the optical force sensor  200  detailed above when the light receiver  3240 ′ is aligned with the reflectance axis “R”, when the first jaw member  140  is in either the clamping or distracting configurations, the amount of light received by the light receiver  3240 ′ is less than when the first jaw member  140  is in the neutral configuration. In such aspects, the optical force sensor  3200  includes a processor  3202  that receives a direction signal from a torque sensor  96  ( FIG. 2 ) associated with the motor  92  to determine the direction of the deflection of the first jaw member  140 . 
     Referring now to  FIGS. 10A-C , another optical force sensor  4200  is provided in accordance with the present disclosure. The optical force sensor  4200  is similar to the optical force sensor  200 , as such, only the differences will be detailed below with like structures represented with a similar label including a “4” preceding the previous label. 
     The optical force sensor  4200  includes a first light source, a second light source, a first light guide  4220 , a second light guide  4224 , a reflector  4230 , and a light receiver  4246 . The reflector  4230  is supported within the cavity  142  of the first jaw member  140  at an angle offset from the plane “P” that is orthogonal to the distal end  4228  of the first light guide  4230 . 
     In use, the first light source, the first light guide  4220 , and the light receiver  4246  function in a similar manner to the similar components of the optical force sensor  1200  detailed above. As such, only the differences will be described below for reasons of brevity. 
     The second light source may be positioned within the body  110  ( FIG. 2 ); however, it is contemplated that the second light source may be disposed in the elongate shaft  120  or the end effector  130  (e.g., the first or second jaw member  140 ,  150 ). The second light guide  4224  may be in the form of an optical fiber (e.g., fiber optic cable) that extends from the body  110 , through the elongate shaft  120 , and into the end effector  130 . The second light guide  4224  includes a proximal end  4225  that is in optical communication with the second light source to receive light provided by the second light source and a distal end  4226  disposed in the cavity  142  defined within the first jaw member  140 . The distal end  4226  of the second light guide  4224  is shaped such that light transmitted through the distal end  4226  defines a second transmittance axis “2T” orthogonal to the transmittance axis “T” of light transmitted through a distal end  4228  of a first light guide  4220 . As shown, the distal end  4226  of the second light guide  4224  is disposed at about a 45° angle to transmit a light cone “LC” towards the reflector  4230 ; however, the second light guide  4224  may curve adjacent the distal end  4226  such that the distal end  4226  is flat, similar to the distal end  4228  of the first light guide  4220 . The distal end  4226  of the second light guide  4224  is positioned offset from the reflectance axis “2R” of light transmitted through the distal end  4226 . Light received at the distal end  4226  of the second light guide  4224  is transmitted through the second light guide  4224  to the light receiver  4246 . The light receiver  4246  may be disposed within the body  110  of the surgical instrument  100  and is configured to sense an amount of light reflected from the reflector  4230  and returned through the second light guide  4224 . 
     The first and second light sources may produce light having properties different from one another such that the light transmitted from one of the first and second light sources and ultimately reflected from the light reflector  4230  may be differentiated from light produced by the other one of the first and second light sources. For example, the light sources may be time or frequency modulated to differentiate the light from each source. Other differentiation techniques may also be used. In some instances the light sources may be selected to emit a specific wavelength of light in a range of about 10 −16  m to about 1 m in length. The light receiver  4246  may be configured detect the differentiated light emitted from each of the light sources so that the amount of light reflected to the receiver  4246  from each of the sources may be measured. 
     In aspects, the distal end  4228  of the first light guide  4220  is offset from the reflectance axis “R” and within the reflected light cone “RLC” of light transmitted through the distal end  4226  of the second light guide  4224 . Similarly, the distal end  4226  of the second light guide  4224  is offset from the reflectance axis “R”, and is within the reflected light cone “RLC” of light transmitted through the distal end  4228  of the first light guide  4220 . The light receiver  4246  may be positioned in optical communication with a proximal end  4215  of the second light guide  4224  to measure an amount of light transmitted through the distal end  4228  of the first light guide  4220 , reflected off of the reflector  4230 , and into the distal end  4226  of the second light guide  4224 . The amount of light measured by the light receiver  4246  is indicative of the deflection of the first jaw member  140  in the opening or closing direction “OD”, “CD”. The light receiver  4246  may also be positioned in optical communication with a proximal end  4222  of the first light guide  4220  to measure an amount of light transmitted through the distal end  4226  of the second light guide  4224 , reflected off of the reflector  4230 , and into the distal end  4228  of the first light guide  4220 . By each of the first and second light sources producing light having different properties, the light sources can continuously produce light and the light receiver  4246  can continuously measure an amount of light from each of the light sources. 
     The first and second light signals are transmitted to a processor  4202  or the processing unit  30  ( FIG. 1 ) which calculates the direction and extent of deflection of the first jaw  140 . The processor  4202  or the processing unit  30  calculates deflection of the first jaw  140  in the opening or closing direction “OD”, “CD” from the first light signal and calculates deflection of the first jaw  140  in the first or second transverse direction “1TD”, “2TD” from the second light signal. 
     In some aspects, the optical force sensor  4200  includes third light receiver  4246  disposed within the cavity  142  of the first jaw member  140 . The third light receiver  4246  is positioned between the distal end  4228  of the first light guide  4220  and the distal end  4226  of the second light guide  4224  offset from the reflectance axes “R”, “2R” and within the reflected light cone “RLC” of light transmitted through the distal end  4228  of the first light guide  4220  and the distal end  4226  of the second light guide  4224 , respectively. The light receiver  4246  may be configured to differentiate light produced by the first light source from light produced by the second light source such that the light receiver  4246  can measure an amount of light received that is produced by the first light source and an amount of light received that is produced by the second light source. The light receiver  4246  generates a first light signal indicative of the amount of light received that is produced by the first light source and a second light signal indicative of the amount of light received that is produced by the second light source. 
     In particular aspects, the distal end  4228  of the first light guide  4220  may be shaped such that the reflected light cone “RLC” of light transmitted through the distal end  4228  of the first light guide  4220  in the clamping, distracting, and neutral configurations does not contact the distal end  4226  of the second light guide  4224 . Similarly, the distal end  4226  of the second light guide  4224  may be shaped such that the reflected light cone “RLC” of light transmitted through the distal end  4226  of the second light guide  4224  does not contact the distal end  4228  of the first light guide  4220  in response to deflection of the first jaw  140 . 
     As detailed and shown above, the optical force sensors (i.e., optical force sensors  200 ,  1200 ,  2200 ,  3200 ,  4200 ) are associated with the first jaw member  140  of the end effector  130 ; however, it is contemplated, as mentioned above, that second jaw member  150  may also include an optical force sensor to determine a force exerted on or by the second jaw member  150  as represented by optical force sensor  200 ′ as shown in  FIG. 3 . Additionally or alternatively, the instrument  20  may include an optical force sensor  200 ″ in the yoke  132  of the end effector  130  to measure forces exerted on or by the yoke  132 . 
     Briefly referring back to  FIG. 2 , a pair of optical force sensors  1200 ′,  1200 ″ may be disposed within the elongate shaft  120  of the instrument  20  to determine the force exerted between the elongate shaft  120  and the trocar  80 . Specifically, an optical force sensor  1200 ′ is disposed in a portion of the elongate shaft  120  disposed within the trocar  80  and optical force sensor  1200 ″ is disposed in a portion of the elongate shaft  120  of the instrument  20  outside of the trocar  80 . The difference between a force measured by the optical force sensor  1200 ′ and a force measured by the optical force sensor  1200 ″ is indicative of the force exerted between the elongate shaft  120  and the trocar  80 . 
     Referring now to  FIG. 11 , a method of detecting suture slippage is described in accordance with the present disclosure. The method includes grasping a suture  300  with a first end effector  130  and a second end effector  130 ′. Each of the first and second end effectors  130 ,  130 ′ has a first jaw member  140  and a second jaw member  150 . Each first jaw member  140  includes an optical force sensor (e.g., optical force sensor  200 ,  1200 ,  2200 ,  3200 , or  4200 ), as detailed above. 
     The suture  300  is grasped between the first jaw members  140  of the first and second end effectors  130 ,  130 ′. The first and second end effectors  130 ,  130 ′ are in a closed position such that the second jaw member  150  of each of the first and second end effectors  130 ,  130 ′ also engages the suture  300 . Additionally or alternatively, the first jaw members  140  and/or the second jaw members may include grasping structures  148 ,  158  (e.g., teeth) that cooperate to engage the suture  300 . 
     With the suture  300  grasped between the first jaw members  140  of the first and second end effectors  130 ,  130 ′, the end effectors  130 ,  130 ′ are drawn apart to apply a tension force “TF” to the suture  300 . 
     To determine if the suture  300  is slipping with respect to one or both of the end effectors  130 ,  130 ′, the force applied by each of the first jaw members  140  to the suture  300  is determined by the optical force sensor disposed in the first jaw members  140 . The forces applied by each of the first jaw members  140  are summed together and compared to the tension force “TF” applied to the end effectors  130 ,  130 ′. If the sum of the forces applied by the first jaw members  140  is substantially equal to the tension force “TF” applied to the end effectors  130 ,  130 ′, the suture  300  is not slipping relative to the end effectors  130 ,  130 ′. Alternatively, if the sum of the forces applied by the first jaw members  140  is less than the tension force “TF” applied to the end effectors  130 ,  130 ′, the suture  300  is slipping relative to at least one of the end effectors  130 ,  130 ′. It will be appreciated, that the force applied to the suture by the first jaw members  140  may be the sum of forces applied in more than one axes (e.g., in the opening or closing direction and in the first or section transverse directions as detailed above) of the respective first jaw member  140 . 
     By comparing the forces applied by each of the first jaw members  140 , it may be determined which of the end effectors  130 ,  130 ′ the suture  300  is slipping relative to. If the force applied by one of the first jaw members  140  is significantly less than the force applied by the other one of the first jaw members  140 , the suture  300  is slipping relative to at least the first jaw member  140  applying the lower force to the suture  300 . In response to the slippage of the suture  300 , a closure force of the respective end effector  130 ,  130 ′ may be increased to engage the suture  300  between the first and second jaw members  140 ,  150  of the respective end effector  130 ,  130 ′ to prevent the slippage. The slippage of the suture  300  can then be redetermined as detailed above. The end effectors  130 ,  130 ′ may be repositioned on the suture  300  before redetermining the slippage of the suture  300 . 
     Referring to  FIGS. 1 and 12 , a method  500  for generating force feedback for a robotic surgical system is described in accordance with the present disclosure. Initially, a clinician engages an input device attached to a gimbal  70  of the user interface  40  to actuate an instrument  20  associated with the input device and the gimbal  70 . To engage the input device, the clinician may move the input device, and thus the gimbal  70 , or move a control (e.g., a button, a lever, an arm) of the input device. The input device and/or gimbal  70  generates and sends an actuation signal indicative of the actuation of the input device and/or gimbal  70  to the processing unit  30  (Step  510 ). The processing unit  30  analyzes the actuation signal and generates an actuation control signal which is transmitted to the IDU  90  associated with the instrument  20  (Step  520 ). 
     In response to the actuation control signal, the IDU  90  activates the motor  92  to actuate the instrument  20  (e.g., to actuate the end effector  130  to move the first and second jaw members  140 ,  150  towards the closed position) (Step  530 ). During actuation of the instrument  20 , an optical force sensor disposed in one of the first or second jaw members  140 ,  150  (e.g., optical force sensor  200 ,  1200 ,  2200 ,  3200 ,  4200 ) is periodically or continuously measuring the deflection of one of the first or second jaw members  140 ,  150  to determine the force exerted by one of the first or second jaw members  140 ,  150 . The optical force sensor generates and transmits a force signal to the processing unit  30  in response to the measured deflection of one of the first or second jaw members  140 ,  150  (Step  540 ). In response to the force signal, the processing unit  30  generates and transmits a feedback signal to a feedback controller  41  of the user interface  40  (Step  550 ). In response to the feedback signal, the feedback controller  41  activates a feedback motor  49  to provide feedback to the clinician engaged with the input device (Step  560 ). 
     As detailed above, the optical force sensor generates a force signal including an extent and a direction of the force exerted by one of the first or second jaw members  140 ,  150 . When the optical force sensor generates a force signal that is only indicative of the extent of the force exerted by one of the first or second jaw members  140 ,  150  (e.g., when the optical force sensor is optical force sensor  200 ), the processing unit  30  receives a direction signal from the torque sensor  96  associated with the motor  92  (Step  534 ). The processing unit  30  receives and analyzes both the force signal and the direction signal to generate the feedback signal. Alternatively, the direction signal may be transmitted to a processor  202  of the optical force sensor (Step  536 ) which combines the direction signal with the extent of the deflection of one of the first or second jaw members  140 ,  150  to generate the force signal (Step  540 ). 
     While several embodiments of the disclosure have been shown in the drawings, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Any combination of the above embodiments is also envisioned and is within the scope of the appended claims. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope of the claims appended hereto.