Force and torque sensing for surgical instruments

Abstract

An apparatus, system, and method for improving force and torque sensing and feedback to the surgeon performing a telerobotic surgery are provided. Groups of axially oriented strain gauges are positioned on a distal end of an instrument shaft proximate a moveable wrist of a robotic surgical instrument to sense forces and torques at the distal tip of the instrument. Advantageously, errors due to changes in the configuration of the tip or steady state temperature variations are eliminated. Other advantageous configurations and methods are disclosed.

1 - 41 . (canceled) 
     
     
         42 . A method of sensing a force exerted on an end portion of a surgical instrument comprising:
 receiving sensed strains from a plurality of strain gauges, the plurality of strain gauges being mounted on a distal end portion of a shaft of the surgical instrument adjacent to a distal end of the shaft, the shaft including a proximal end coupled to a housing portion of the surgical instrument, the distal end portion of the shaft extending proximally from the distal end, a lengthwise axis of the shaft being defined from the proximal end of the shaft to the distal end of the shaft, an articulatable wrist joint being coupled to the distal end of the shaft, the end portion being coupled to the distal end of the shaft by the articulatable wrist joint, and the receiving being by a processor;   combining arithmetically two or more of the sensed strains from the plurality of strain gauges to determine a force exerted on the end portion, the combining being by the processor; and   transmitting an indication of the force to a servo control, the transmitting being by the processor.   
     
     
         43 . The method of  claim 42 , wherein the force is selected from a group consisting of a side force, an axial force, and a torque. 
     
     
         44 . The method of  claim 42 , wherein the force is independent of uniform temperature changes. 
     
     
         45 . The method of  claim 42 , wherein the force is independent of variations in distance between the distal end of the shaft and a distal end of the end portion. 
     
     
         46 . The method of  claim 42 , the force being a side force F x , and the combining arithmetically two or more of the sensed strains to determine a force comprising:
     F   x =(ε 1 −ε 2 −ε 3 +ε 4 ) EI/ 2 lr,  
   ε 1 , ε 2 , ε 3 , and ε 4  being select sensed strains received from the plurality of strain gauges, E being a material modulus of elasticity, in the axial direction, of the shaft, I being a section moment of inertia of the shaft, l being a distance between two inline strain gauges of the plurality of strain gauges, and r being a radius from the lengthwise axis of the shaft to the acting planes of the strain gauges of the plurality of strain gauges providing the select sensed strains.   
     
     
         47 . The method of  claim 42 , the force being a side force F y , and the combining arithmetically two or more of the sensed strains to determine a force comprising:
     F   y =(ε 5 −ε 6 −ε 7 +ε 8 ) EI/ 2 lr,  
   ε 5 , ε 6 , ε 7 , and ε 8  being select sensed strains received from the plurality of strain gauges, E being a material modulus of elasticity, in the axial direction, of the shaft, I being a section moment of inertia of the shaft, l being a distance between two inline strain gauges of the plurality of strain gauges, and r being a radius from the lengthwise axis of the shaft to the acting planes of the strain gauges of the plurality of strain gauges providing the select sensed strains.   
     
     
         48 . The method of  claim 42 , the force being an axial force F z , and the combining arithmetically two or more of the sensed strains to determine a force comprising:
     F   z =(ε 1 +ε 2 +ε 3 +ε 4 +ε 5 +ε 6 +ε 7 +ε 8 ) EA/ 8,
   ε 1 , ε 2 , ε 3 , ε 4 , ε 5 , ε 6 , ε 7 , and ε 8  being select signals sensed strains received from the plurality of strain gauges, E being a material modulus of elasticity, in the axial direction, of the shaft, and A being a cross-sectional area of the shaft.   
     
     
         49 . The method of  claim 54 , the torque being a torque T y , the combining arithmetically two or more of the sensed strains from the plurality of strain gauges to determine a torque comprising:
     T   y =(ε 1+ ε 2 −ε 3 −ε 4 ) EI/ 4 r,  
   ε 1 , ε 2 , ε 3 , and ε 4  being select sensed strains received from the plurality of strain gauges, E being a material modulus of elasticity, in the axial direction, of the shaft, I being a shaft section moment of inertia of the shaft, and r being a radius from the lengthwise axis of the shaft to the acting planes of the strain gauges of the plurality of strain gauges providing the select sensed strains.   
     
     
         50 . The method of  claim 54 , the torque being a torque T x , the combining arithmetically two or more of the sensed strains from the plurality of strain gauges to determine a torque comprising:
     T   x =(−ε 5 −ε 6 +ε 7 +ε 8 )/ EI/ 4 r,  
   ε 5 , ε 6 , ε 7 , and ε 8  being select sensed strains received from the plurality of strain gauges, E being a material modulus of elasticity, in the axial direction, of the shaft, I being a section moment of inertia of the shaft, and r being a radius from the lengthwise axis of the shaft to the acting planes of the strain gauges of the plurality of strain gauges providing the select sensed strains.   
     
     
         51 . The method of  claim 42 , further comprising calibrating the surgical instrument by applying combinations of forces and torques to the end portion serially, simultaneously, or in combinations while correction factors and offsets are determined. 
     
     
         52 . The method of  claim 51 , wherein the correction factors and offsets are determined directly or via a neural network. 
     
     
         53 . The method of  claim 42 , further comprising:
 receiving a sensed strain from a force sensor proximate the housing position, the sensed strain being responsive to an axial force along the lengthwise axis of the shaft.   
     
     
         54 . The method of  claim 42 , further comprising:
 combining arithmetically two or more of the sensed strains from the plurality of strain gauges to determine a torque exerted on the end portion, the combining being by the processor.