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 . fig1 a 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 . fig1 b 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 . fig1 c , 1d , 1e , 1f , 1g illustrate additional views of instrument 101 from fig1 a , 1b , in accordance with an embodiment of the present invention . side view 117 from fig1 c 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 fig1 d 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 fig1 e 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 fig1 f 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 fig1 g 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 . fig2 a 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 . fig2 b 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 . fig2 c 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 fig2 b , frontal view 219 from fig2 c 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 . fig2 d 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 . fig2 e 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 . fig3 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 : 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 fig3 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 . fig4 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 fig3 , 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 . fig5 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 fig5 , 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 fig5 , 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 fig1 a 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 .
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 .