Parallelogram load cell

Abstract

A device includes a first member ( 120 ) and a second member ( 122 ) disposed in series along a longitudinal axis. The device also includes links coupling first joints ( 124, 126 ) of the first member to second joints of the second member ( 128, 130 ). The first and second members and the links arranged to define a planar parallelogram linkage. The devices also include a resilient element ( 142 ) disposed between the first member and the second member, the first member and the second member preloaded against the resilient element. The first member and the second member are preloaded to provide an arrangement of the first and the second joints in which a motion of the first joints with respect to the second joints is constrained to a direction substantially parallel to the longitudinal axis. The devices further include a sensor ( 140 ) for generating a signal indicating a separation between the first member and the second member.

1 . A device, comprising:
 a first member and a second member disposed in series along a longitudinal axis, the first member comprising first joints and the second member comprising second joints;   a plurality of links mechanically coupling the first member to the second member via the first and the second joints; and   at least one sensor for generating at least one signal indicating a separation between the first member and the second member,   wherein the first member, the second member, and the plurality of links are arranged to define at least one substantially planar parallelogram linkage and having a constrained range of motion substantially along the longitudinal axis.   
     
     
         2 . The device of  claim 1 , further comprising:
 a pre-load element for biasing the first member towards the second member; and   a resilient element for biasing the first member away from the second member.   
     
     
         3 . The device of  claim 2 , wherein the preload element comprises at least one spring-loaded shoulder bolt. 
     
     
         4 . The device of  claim 2 , wherein the preload element comprises at least one tension spring. 
     
     
         5 . The device of  claim 2 , wherein the resilient member is disposed between the first member and the second member. 
     
     
         6 . The device of  claim 2 , wherein the at least one resilient element comprises at least one layer of elastomeric material. 
     
     
         7 . The device of  claim 2 , wherein the at least one resilient element comprises at least one compression spring. 
     
     
         8 . The device of  claim 1 , wherein the plurality of links comprise first and second substantially rigid links. 
     
     
         9 . The device of  claim 1 , wherein the plurality of links comprise first and second resilient links, each of the first and second resilient links configured to resist substantially any force not substantially parallel to a plane of the planar parallelogram linkage. 
     
     
         10 . The device of  claim 1 , wherein the at least one sensor comprises:
 at least one generating element disposed on a first of the first member and the second member and configured for generating a magnetic field;   at least one detecting element disposed on a second of the first member and the second member and configured for generating the at least one signal based on a magnetic field variation.   
     
     
         11 . The device of  claim 10 , wherein the at least one generating element is a magnet. 
     
     
         12 . The device of  claim 10 , wherein the at least one generating element is an induction loop. 
     
     
         13 . The device of  claim 1 , wherein the at least one sensor comprises:
 a first capacitive plate on or in the first member;   a second capacitive plate one or in the second member;   at least one detecting element coupled to the first and the second capacitive plates and configured for detecting capacitance variation and generating the at least one signal based on the capacitance variation.   
     
     
         14 . The device of  claim 1 , further comprising a controller, wherein the controller is configured for:
 calculating a current separation between the first member and the second member based on the at least one signal;   computing a load along the longitudinal axis based at least on the separation.   
     
     
         15 . The device of  claim 1 , wherein the plurality of links are coupled to the first member and the second member using a plurality of torsion springs. 
     
     
         16 . A powered leg device, comprising:
 a shank extending substantially along a shank axis and comprising a first member comprising first joints, a second member comprising second joints and disposed in series with the first member along the shank axis, a plurality of links mechanically coupling the first member to the second member via the first and the second joints, and at least one sensor for generating at least one signal indicating a separation between the first member and the second member,   a foot extending along a foot axis and comprising a resilient toe portion and a resilient heel portion;   a powered ankle joint coupling the foot portion to the shank portion; and   a controller for controlling at least the powered ankle joint based on the at least one signal,   wherein the first member, the second member, and the plurality of links are arranged to define at least one substantially planar parallelogram linkage having a plane of motion substantially parallel to the foot axis and a constrained range of motion, wherein a component for the motion in the constrained range parallel to the shank axis is substantially greater than a component for the motion in the constrained range perpendicular to the shank axis.   
     
     
         17 . The powered leg device of  claim 16 , wherein the at least one resilient element comprises at least one of at least one layer of elastomeric material and at least one spring. 
     
     
         18 . The powered leg device of  claim 16 , wherein the plurality of links comprise first and second substantially rigid links. 
     
     
         19 . The powered leg device of  claim 16 , wherein the plurality of links comprise first and second resilient links, each of resilient links configured to resist substantially any force not substantially parallel to a plane of the planar parallelogram linkage. 
     
     
         20 . The powered leg device of  claim 16 , wherein the at least one sensor comprises:
 at least one generating element for generating a magnetic field disposed on a first of the upper member and the lower member;   at least one detecting element disposed on a second of the upper member and the lower member, the at least one detecting element configured for detecting magnetic field variation and generating the at least one signal based on the magnetic field variation.   
     
     
         21 . The powered leg device of  claim 16 , wherein the determining by the controller further comprises:
 calculating a current separation between the upper member and the lower member based on the at least one signal; and   computing a current axial load along the shank based at least on the separation.   
     
     
         22 . The powered leg device of  claim 16 , wherein the controller is configured for determining the load on each of the resilient toe portion and the resilient heel portion; and wherein the determining by the controller further comprises estimating the load on each of the toe portion and the heel portion based on the current axial load, a current torque of the powered ankle joint, and relative distances of each of the toe portion and the heel portion with respect to the powered ankle joint at equilibrium. 
     
     
         23 . A method of controlling a powered leg device comprising a shank extending substantially along a shank axis with a first member comprising first joints, a second member comprising second joints and disposed in series with the first member along the shank axis, a plurality of links mechanically coupling the first member to the second member via the first and the second joints, at least one sensor for generating at least one signal indicating a separation between the first member and the second member, a foot extending along a foot axis with a resilient toe portion and a resilient heel portion, a powered ankle joint coupling the foot portion to the shank portion, and a controller for controlling at least the powered ankle joint based on the at least one signal, wherein the first member, the second member, and the plurality of links arranged to define at least one planar parallelogram linkage having a plane of motion substantially parallel to the foot axis, and wherein the first member, the second member, and the plurality of links are arranged to define at least one substantially planar parallelogram linkage and having a constrained range of motion substantially along the longitudinal axis, the method comprising:
 calculating a current separation between the first member and the second member based on the at least one signal;   computing a current axial load along the shank axis based at least on the current separation; and   estimating a toe load for the resilient toe portion and a heel load for the resilient heel portion based on at least the current axial load, a current torque of the powered ankle joint, and a relative distance of each of the resilient toe portion and the resilient heel portion with respect to the powered ankle joint.   
     
     
         24 . The method of  claim 23 , further comprising:
 adjusting a configuration of the powered ankle joint based on at least one of the toe load, the heel load, and the current axial load.   
     
     
         25 . The method of  claim 24 , wherein the powered leg device further comprises a powered knee joint, and wherein the method further comprises:
 adjusting a configuration of at least one of the powered knee joint and the powered ankle joint based on at least one of the toe load, the heel load, and the current axial load.   
     
     
         26 . The method of  claim 23 , further comprising:
 selecting the relative distance for the resilient toe portion with respect to the powered ankle joint to be a distance between the resilient toe portion and the powered ankle joint along the foot axis when the spring in the toe portion is at equilibrium, and   selecting the relative distance for the resilient heel portion with respect to the powered ankle joint to be a distance between the resilient heel portion and the powered ankle joint along the foot axis when the spring in the heel portion is at equilibrium.   
     
     
         27 . The method of  claim 26 , wherein the estimating further comprises evaluating: 
       
         
           
             
               
                 
                   F 
                   toe 
                 
                 = 
                 
                   
                     
                       
                         
                           
                             F 
                             shank 
                           
                           * 
                           
                             d 
                             heel 
                           
                         
                         + 
                         
                           τ 
                           ankle 
                         
                       
                       
                         
                           d 
                           toe 
                         
                         - 
                         
                           d 
                           heel 
                         
                       
                     
                      
                     
                         
                     
                      
                     and 
                      
                     
                         
                     
                      
                     
                       F 
                       heel 
                     
                   
                   = 
                   
                     
                       
                         
                           F 
                           shank 
                         
                         * 
                         
                           ( 
                           
                             
                               d 
                               toe 
                             
                             - 
                             
                               d 
                               heel 
                             
                           
                           ) 
                         
                       
                       - 
                       
                         τ 
                         ankle 
                       
                     
                     
                       
                         d 
                         toe 
                       
                       - 
                       
                         d 
                         heel 
                       
                     
                   
                 
               
               , 
             
           
         
       
       where F shank  is the force along the shank axis, d toe  is the distance between the resilient toe portion and the powered ankle joint along foot axis at equilibrium, d heel  is the distance between the resilient heel portion and the powered ankle joint along the foot axis at equilibrium, and τ ankle  is the torque at powered ankle joint. 
     
     
         28 . A method, comprising:
 providing a device comprising a first member and a second member disposed in series along a longitudinal axis, the first member comprising first joints and the second member comprising second joints; a plurality of links mechanically coupling the first member to the second member via the first and the second joints; at least one resilient element disposed between the first member and the second member; and at least one sensor for generating at least one signal indicating a separation between the first member and the second member, wherein the first member, the second member, and the plurality of links are arranged to define at least one substantially planar parallelogram linkage, and wherein the first member and the second member maintain contact with the resilient element to provide an arrangement of the first and the second joints in which a motion of the first joints with respect to the second joints is constrained primarily in a direction substantially parallel to the longitudinal axis.   calculating a current separation between the first and the second members based on the at least one signal; and   computing a current axial load along the longitudinal axis based at least on the current separation.   
     
     
         29 - 33 . (canceled)