Abstract:
A tension mechanism for a robotically-controlled medical device measures the tension applied to an actuation tendon to provide feedback to a robotic controller. In one embodiment, the device comprises an elongated instrument, an elongated member, and a base. The elongated member is coupled to the distal end of the elongated instrument, configured to actuate the distal end of the elongated instrument in response to tension in the elongated member. The base is located at the proximal end of the elongated instrument, and comprises a first redirect surface that redirects the elongated member. The first redirect surface is coupled to a lever element that is configured to exert a reactive force on a sensor in response to tension in the elongated member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of and priority to U.S. Provisional Application No. 62/184,741 filed Jun. 25, 2015, the entire contents of which are incorporated herein by reference. This application is related to U.S. patent application Ser. No. 14/523,760, filed Oct. 24, 2014, U.S. Provisional Patent Application No. 62/019,816, filed Jul. 1, 2014, U.S. Provisional Patent Application No. 62/037,520, filed Aug. 14, 2014, U.S. Provisional Patent Application No. 62/057,936, filed Sep. 30, 2014, and U.S. Provisional Patent Application No. 62/140,344, filed Mar. 30, 2015, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field of Art 
     This description generally relates to surgical robotics, and particularly to an instrument-mounted tension sensing design that may be used in conjunction with a medical robotics platform for a number of surgical procedures. More particularly, the field of the invention pertains to instrument-mounted tension sensing mechanisms that detect tension in actuation tendons, such as those used to operate robotically-controlled tools to perform diagnostic and therapeutic surgical procedures. 
     2. Description of the Related Art 
     Use of robotic technologies presents a number of advantages over traditional, manual surgery procedures. In particular, robotic surgeries often allow for greater precision, control, and access. Robotically-controlled technologies, however, sometimes create engineering challenges that require creative engineering workarounds. In the case of robotically-controlled tools, the use of actuation tendons to operate robotic laparoscopic tools and catheters gives rise to control problems that often requires very precise monitoring of the actuation tendons. Over the lifespan of an actuation tendon, the tendon may stretch and deform, and over time exhibit greater non-linearity with respect to instrument tip displacement relative to the tension applied to the tendon. Accordingly, within a robotically-controlled instrument, there is a need to measure the tension applied to the actuation tendon to provide feedback to the control robotic controller. Accordingly, there is a need for an instrument-mounted tension sensing mechanism. 
     SUMMARY 
     In general, the present invention provides for a medical device comprising an elongated instrument, an elongated member coupled to the distal end of the elongated instrument, configured to actuate the distal end of the elongated instrument in response to tension in the elongated member, and a base located at the proximal end of the elongated instrument, the base comprising redirect surface that redirects the elongated member, wherein the first redirect surface is coupled to a lever element that is configured to exert a reactive force on a sensor in response to tension in the elongated member. 
     In one aspect, the first redirect surface is low friction. In one aspect, the first redirect surface comprises a first rotatable body. In one aspect, the base further comprises a second rotatable body, wherein the elongated member is threaded around the second rotatable body. In one aspect, rotational motion of the second rotatable body is configured to cause tension in the elongated member. In one aspect, the second rotatable body comprises splines that receive rotational motion through a sterile interface from the robotic drive mechanism. In one aspect, the second rotatable body is a male connector. In one aspect, the second rotatable body is a female connector. 
     In another aspect, the lever element is constrained by a pivot point on a first location of the lever element and the sensor on a second location of the lever element. In one aspect, the pivot point of the lever element is offset from the axis of the first rotatable body. 
     In another aspect, the ratio of the tension in the elongated member to the reactive force on the sensor is fixed. In one aspect, the lever element is configured to distribute the tension in the elongated member between the pivot point and the sensor. In one aspect, the elongated instrument is flexible. In one aspect, the elongated instrument is a catheter. In one aspect, the elongated instrument is rigid. In one aspect, the base is configured to interface with a robotic drive mechanism. In one aspect, the elongated member is at least one of a wire, cable, and a tendon. In one aspect, the sensor is at least one of a load cell, a piezoresistive device, a piezoelectric device, and a strain gauge. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  illustrates a tension sensing mechanism located within a robotically-controlled instrument, in accordance with an embodiment of the present invention. 
         FIG. 1B  illustrates a top schematic view of the robotically-controlled instrument of  FIG. 1A , in accordance with an embodiment of the present invention. 
         FIGS. 1C, 1D, 1E, 1F, 1G  illustrate additional views of the robotically-controlled instrument from  FIGS. 1A, 1B , in accordance with an embodiment of the present invention. 
         FIG. 2A  illustrates an instrument that incorporates a tension sensing mechanism and is designed to actuate an elongated instrument, in accordance with an embodiment of the present invention. 
         FIG. 2B  illustrates the idler carriage of the instrument of  FIG. 2A  that incorporates a tension sensing mechanism, in accordance with an embodiment of the present invention. 
         FIG. 2C  illustrates the idler carriage of the instrument of  FIG. 2A  that incorporates a tension sensing mechanism, in accordance with an embodiment of the present invention. 
         FIG. 2D  illustrates a vertical cross-sectional view of the idler carriage of the instrument of  FIG. 2A  that incorporates a tension sensing mechanism, in accordance with an embodiment of the present invention. 
         FIG. 2E  illustrates an overhead view of the idler carriage of the instrument of  FIG. 2A  that incorporates a tension sensing mechanism, in accordance with an embodiment of the present invention. 
         FIG. 3  illustrates a free body diagram representing the mechanical operation of a tension sensing apparatus, in accordance with an embodiment of the present invention. 
         FIG. 4  illustrates a free body diagram representing the mechanical operation of a tension sensing apparatus, in accordance with an embodiment of the present invention. 
         FIG. 5  illustrates a free body diagram representing the mechanical operation of a tension sensing apparatus, in accordance with an embodiment of the present invention. 
       Reference will now be made in detail to several embodiments, examples of which are illustrated in the accompanying figures. It is noted that wherever practicable similar or like reference numbers may be used in the figures and may indicate similar or like functionality. The figures depict embodiments of the described system (or method) for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Although certain preferred embodiments and examples are disclosed below, inventive subject matter extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses, and to modifications and equivalents thereof. Thus, the scope of the claims appended hereto is not limited by any of the particular embodiments described below. For example, in any method or process disclosed herein, the acts or operations of the method or process may be performed in any suitable sequence and are not necessarily limited to any particular disclosed sequence. Various operations may be described as multiple discrete operations in turn, in a manner that may be helpful in understanding certain embodiments; however, the order of description should not be construed to imply that these operations are order dependent. Additionally, the structures, systems, and/or devices described herein may be embodied as integrated components or as separate components. 
     To guarantee control fidelity, it may be important to monitor the tendon tension when robotically-controlling endoscopic and laparoscopic tools that use tendon-like members, such as a catheter, endoscope, laparoscopic grasper, or forceps. While there are a number of approaches to monitoring tendon tension, direct measurement in the instrument provides a number of practical advantages, including simplifying the instrument-driver interface, and reduce friction and inefficiencies in transmission through the interface. Accordingly, the present invention provides a sensing apparatus that may be mounted within the instrument. 
       FIG. 1A  illustrates a tension sensing mechanism located within the robotically-controlled instrument, in accordance with an embodiment of the present invention. In transparent isometric view  100 , the instrument  101  provides for a series of actuating bodies, such as rotatable bodies for low friction, such as spools or pulleys  102 ,  103 , that are coupled to tendons  106  and  107  that are designed to actuate the distal end of an elongated instrument (not shown), such as a flexible catheter or rigid laparoscopic tool, in response to tension. Instrument  101  also provides for cavities  104 ,  105  for additional rotatable bodies to actuate additional tendons (now shown). Rotatable bodies  102 ,  103 , and those potentially used in cavities  104 ,  105  may be driven by a robotically-controlled instrument device manipulator as part of a larger robotic system, such as those disclosed in the aforementioned patents. While the instrument  101  is shown to be circular, other embodiments may take other shapes, such as oblong, rectangular, or square-shaped. 
     In addition to the actuating rotatable bodies, and related cavities for additional rotatable bodies, the present embodiment contemplates redirecting surfaces, represented as rotatable (body) pulleys  108  and  109  in instrument  101 , to measure tension in tendons  106  and  107  respectively. To measure tension, tendons  106  and  107  may be wound around rotatable bodies  108  and  109  in addition to rotatable bodies  102  and  103 . 
       FIG. 1B  illustrates a top schematic view of the instrument  101 , in accordance with an embodiment of the present invention. As shown in view  110 , tendon  106  may be wound around pulley  102  and pulley  108 . Similarly, tendon  107  may be wound around pulley  103  and pulley  109 . Even though pulleys  102 ,  103 ,  108 ,  109  are shown to have parallel axes in instrument  101 , they may not be parallel in other embodiments. 
     Pulley  108  is coupled to a lever element  111 , which is configured to exert a reactive force in response to tension in tendon  106 . The resulting reactive force from tension in tendon  106  may be resolved through contact between lever  111 , constrained by a pivot point such as pivot axis  112 , and sensor  113 . While the instrument  101  contemplates the pivot axis  112  and sensor  113  positioned at opposite ends of the level element  111 , they may be positioned at a number of positions along the lever element in other embodiments. The relative position of the sensor and pivot point may provide for a known, fixed ratio between the tension and the reactive force on the sensor. Identical structural relationships exist with respect to pulley  109 , lever element  114 , pivot axis  115 , and sensor  116 . 
     In some embodiments, the sensors  113  and  116  may be force sensors, piezoelectric sensors, piezoresistive sensors, or load cells to measure the reactive force exerted by levers  111  and  114  respectively. In some embodiments, it may be desirable for the sensors to be low cost, particularly if the instrument is intended to be recyclable or disposable. 
     In some embodiments, such as instrument  101 , the pivot point may be offset from the axis of the corresponding rotatable body, e.g., the axis of pulley  108  relative to the pivot axis  112  in instrument  101 . As shown in instrument  101 , while the pivot point may be a pivot axis  112 , which reduces friction resulting from any bending moments, the pivot point may be non-axial element in other embodiments, such as a flexure. 
     Tension on tendon  106  may be the consequence of a number factors, including rotation of pulley  108  or external pressure on the elongated member in which tendon  106  resides. Regardless of its source, when wound around pulley  108 , tension on tendon  106  may be imparted equally around pulley  108 . As the pulley  108  is operatively coupled to lever  111 , the resulting reactive force may be transmitted through the lever  111  and measured based on the force exerted on sensor  113 . The positioning of the lever  111 , in contact with sensor  113 , allows measurement of the reactive force from the tension in tendon  106 . 
     Offsetting the axis of the pivot point such as pivot axis  112  at fixed distance from the axis of pulley  108  allows the force from lever  111  to be smaller or larger in magnitude based on the length of the lever and the fixed offset. Using these measurements, combined with the measured force at the sensor  113 , the tension in tendon  106  may be calculated. Allowing for differences in the magnitude of the lever force based on the length of the lever may be useful to bring the measured force within the range and tolerances of the sensor. This may be particularly useful for inexpensive sensors designed for a specific range of forces. Identical operational relationships exist with respect to pulley  109 , lever element  114 , pivot axis  115 , and sensor  116 . 
     Among other advantages, this method of direct measurement of the tendon tension bypasses the complexity and efficiency losses that may be associated with measuring force further down the drivetrain. 
       FIGS. 1C, 1D, 1E, 1F, 1G  illustrate additional views of instrument  101  from  FIGS. 1A, 1B , in accordance with an embodiment of the present invention. Side view  117  from  FIG. 1C  illustrates a side perspective of instrument  101  and the alignment of the tendons, spools, levers, and sensors within instrument  101 , according to one embodiment. Front view  118  from  FIG. 1D  illustrates a frontal perspective of instrument  101  and the alignment of the spools and sensors within instrument  101 , according to one embodiment. Partial cutaway view  119  from  FIG. 1E  illustrates a rear perspective of instrument  101  and the alignment of the spools and levers within instrument  101 , according to one embodiment. Rear view  120  from  FIG. 1F  illustrates a rear perspective of instrument  101  and the alignment of the spools and levers, and their respective axes, without the exterior shell of instrument  101 , according to one embodiment. Bottom cutaway view  121  from  FIG. 1G  illustrates a bottom-up perspective of instrument  101  and the alignment of the spools, levers, sensors within instrument  101 , according to one embodiment. In addition, view  121  illustrates placement of magnets  122  that may be configured to couple instrument  101  to an interface or an instrument driving mechanism/instrument device manipulator. 
       FIG. 2A  illustrates an instrument that incorporates a tension sensing mechanism and is designed to actuate an elongated instrument, in accordance with an embodiment of the present invention. In isometric view  200 , instrument  201  receives rotational motion from an instrument device manipulator via coaxial drive shafts  202  to actuate tendons that are wound around redirect surfaces (i.e., idlers) that are located on an idler carriage  203 , consistent with U.S. Provisional Patent Application No. 62/134,366, the entire contents of which are incorporated by reference. 
       FIG. 2B  illustrates the idler carriage  203  from instrument  201  that incorporates a tension sensing mechanism, in accordance with an embodiment of the present invention. As shown in view  204 , the idler carriage  203  generally comprises four rotatable bodies for redirecting tendons, i.e., pulleys  205 ,  206 ,  207 ,  208 , where each of the pulleys is coupled to an individual lever element, such as levers  209 ,  210 ,  211 ,  212  respectively. Each lever  209 ,  210 ,  211 ,  212  includes a pivot axis, such as  213 ,  214 ,  215 ,  216  respectively, which is offset from the axes of pulleys  205 ,  206 ,  207 ,  208  respectively. In some embodiments, the axial offsets may be consistent and common to all the pulleys and levers in the idler carriage. In other embodiments, the axial offset between the levers and pulleys may vary within the idler carriage. 
     Consistent with previously disclosed embodiments, each lever in instrument  201  may be configured to provide reactive force to a corresponding sensor, such as sensor  217 , which is configured to detect force exerted by lever  209  in response to tension on pulley  205 . Similarly, sensor  218  is configured to detect force exerted by lever  211  in response to tension on pulley  207 . Additional sensors are similarly situated relative to levers  210  and  212 . 
       FIG. 2C  illustrates the idler carriage  203  from instrument  201  that incorporates a tension sensing mechanism, in accordance with an embodiment of the present invention. In contrast to view  204  from  FIG. 2B , frontal view  219  from  FIG. 2C  provides a different perspective of the orientation of pulleys  205 ,  206 ,  207 ,  208 , levers  209 ,  210 ,  211 ,  212  and pivot axes  213 ,  214 ,  215 ,  216  relative to each other. 
     Consistent with previously disclosed embodiments, each lever in instrument  201  may be configured to provide reactive force to a corresponding sensor, such as sensor  217 , which is configured to detect force exerted by lever  209  in response to tension on pulley  205 . Similarly, sensor  218  is configured to detect force exerted by lever  211  in response to tension on pulley  207 . 
       FIG. 2D  illustrates a vertical cross-sectional view of idler carriage  203  from instrument  201  that incorporates a tension sensing mechanism, in accordance with an embodiment of the present invention. As shown in cross-sectional view  220 , pulleys  205 ,  206 ,  207 ,  208  may wrap around levers  209 ,  210 ,  211 ,  212  respectively to capture tension in the tendons that may be redirected around them. Additionally, the distal ends of the lever elements may be directed towards the center of the carriage where the sensors (not shown) are located. 
       FIG. 2E  illustrates an overhead view of idler carriage  203  from instrument  201  that incorporates a tension sensing mechanism, in accordance with an embodiment of the present invention. As shown in top view  221 , lever elements  209 ,  211  may be directed towards sensors  217 ,  218  respectively, located towards the center of the idler carriage  203 , from opposite sides of idler carriage  203 . Sensors  217 ,  218  may be configured to detect any force generated by levers  209 ,  211  respectively based on tension around pulleys  205 ,  207  respectively. 
       FIG. 3  illustrates a free body diagram representing the mechanical operation of a tension sensing apparatus, in accordance with an embodiment of the present invention. As shown in view  300 , the embodiment may generally comprise a tendon  301 , a pulley  302  with a pulley axis  303 , a lever element  304  with a pivot axis  305 , and a sensor  306 . Tension forces (represented as arrows  307  and  308 ) in tendon  301  exert equal and opposite forces along tendon  301  as it winds around pulley  302 . 
     Given the known relationships between the location of the pulley  302 , lever  304 , and sensor  306 , the tension in tendon  301  may be determined based on the measurement of force at sensor  306 . Mathematically, the statistics equilibrium may be expressed as:
 
Σ M   Pivot =0=( l   1   +r ) F   Tension +( l   1   −r ) F   Tension   −l   2   F   Sense   (Equation 1)
 
     where ΣM Pivot  represents the sum of moments of lever  304  about the pivot axis  305 , F Tension  represents the tension force on the tendon  301 , l 1  represents the distance from the pulley axis  303  pivot axis  305 , l 2  represents the distance from pivot axis  305  to the point where the lever element  304  contacts the force sensor  306 , r represents the radius of the pulley  302 , and F Sense  represents the force on the sensor  306 . 
     With some algebraic manipulation, the expression may be reduced to determine the specific relationship between F Tension  and F Sense : 
     
       
         
           
             
               
                 
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     where l 1  and l 2  are fixed constants based on the physical arrangement of the pulley  302 , lever  304 , and sensor  306 . This mathematical relationship may also be applied with respect to the previously disclosed embodiments. 
     The takeoff angle of the tendons is the angle at which the tendon comes off the pulley relative to the lever. The takeoff angle of the tendons in the example of  FIG. 3  is 90 degrees. Where the takeoff angle of the tendons differs, the algebraic relationship described above may differ, but it still follows the same general principles.  FIG. 4  illustrates a free body diagram representing the mechanical operation of a tension sensing apparatus, in accordance with an embodiment of the present invention. As shown in view  400 , the embodiment may generally comprise a tendon  401 , a pulley  402  with a pulley axis  403 , a lever element  404  with a pivot axis  405 , and a sensor  406 . In view  400 , tension forces F Tension  (represented as arrows  407  and  408 ) in tendon  401  exert equal and opposite forces along tendon  401  as it winds around pulley  402 . Unlike  FIG. 3 , however, the direction of the tendon  401  off of the pulley  402  is not orthogonal to the lever  404 . As a result, the vector component of F Tension  that runs parallel to F Sense , represented as arrow  409  is calculated. Algebraic manipulation could then be used to derive the precise relationship between F Tension  and F Sense . 
     The present invention also contemplates other embodiments where the takeoff angle differs for different tendons.  FIG. 5  illustrates a free body diagram representing the mechanical operation of a tension sensing apparatus, in accordance with an embodiment of the present invention. As shown in  FIG. 5 , tension sensing may make use of an alternative arrangement of a tendon  501 , a pulley  502  with a pulley axis  503 , a lever element  504  with a pivot axis  505 , and a sensor  506 . For the embodiment of  FIG. 5 , where the tendon  501  “takes off” from the pulley  502  at different angles relative to the lever element  504 , the vector components, if any, of F Tension  that runs parallel to F Sense  is evaluated to determine the relationship between those forces. 
     The aforementioned embodiments of the present invention may be designed to interface with an instrument drive mechanism and robotics platform such as those disclosed in the aforementioned patent applications that are incorporated by reference. For example, the embodiments in  FIGS. 1A and 1B  may be configured to be driven by an instrument drive mechanism or an instrument device manipulator that is attached to the distal end of a robotic arm through a sterile interface such as a drape. The driving elements may be shafts (male) or shaft receptacles (female) with spline interfaces to transfer rotational motion from the instrument drive mechanism to the instrument. As part of a larger robotics system, robotic control signals may be communicated from a remotely-located user interface, down the robotic arm, and to the instrument device manipulator to control the embodiment (instrument) of the present invention. 
     For purposes of comparing various embodiments, certain aspects and advantages of these embodiments are described. Not necessarily all such aspects or advantages are achieved by any particular embodiment. Thus, for example, various embodiments may be carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other aspects or advantages as may also be taught or suggested herein. 
     Elements or components shown with any embodiment herein are exemplary for the specific embodiment and may be used on or in combination with other embodiments disclosed herein. While the invention is susceptible to various modifications and alternative forms, specific examples thereof have been shown in the drawings and are herein described in detail. The invention is not limited, however, to the particular forms or methods disclosed, but to the contrary, covers all modifications, equivalents and alternatives thereof.