Surgical Robotic Arm Torque Sensing for External Force Compensation
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Solution Overview
Problem
Surgical robotic arms are affected by various external forces during minimally invasive medical procedures, necessitating effective monitoring and compensation to improve their operation.
Innovation Solution
The surgical robotic arm incorporates a joint torque sensor to measure torque imparted on its links, a controller to calculate input motor torque commands, determine estimated and environmental torque values, and detect collisions by comparing these values. The controller adjusts the motor torque command to prevent oversaturation and compensate for friction, gravity, and inertia.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a joint torque sensor is added to measure torque imparted on the robotic arm links, then measurement precision of external forces is improved, but device complexity increases
Solution Approach 1:
The patent introduces a joint torque sensor as an intermediary device that measures torque at the joint level. This sensor acts as a mediator between the robotic arm's internal actuation system and the external forces acting on it, providing indirect but accurate measurement of external torques without requiring direct sensing of all external force vectors.
Solution Approach 2:
The patent replaces complex mechanical force sensing systems with a simpler torque measurement approach. Instead of using multiple force sensors to directly measure external forces, the system uses a single joint torque sensor combined with dynamic modeling to infer external forces, substituting mechanical complexity with computational analysis.
2Stability of the object's composition
If the controller continuously monitors and adjusts motor torque commands to compensate for external forces, then stability of the robotic arm is improved, but use of energy increases
Solution Approach 1:
The patent implements a feedback control mechanism where the controller continuously monitors joint torque sensor data, compares it with expected torque from motion commands, detects deviations indicating external forces, and adjusts motor torque commands accordingly. This closed-loop feedback system maintains robotic arm stability by dynamically compensating for external disturbances.
Solution Approach 2:
The patent applies preliminary compensation by calculating and applying counter-torques before external forces can significantly disrupt the robotic arm's intended motion. The system proactively adjusts motor commands based on detected external torques, preventing instability rather than reacting to it after occurrence.
3Reliability
If the controller adjusts the input motor torque command to prevent oversaturation, then reliability of the actuator is improved, but productivity of the robotic arm decreases
Solution Approach 1:
The patent employs dynamic torque adjustment where the controller continuously adapts the motor torque command based on real-time conditions. The system dynamically balances between applying sufficient torque for rapid motion and limiting torque to prevent actuator saturation, optimizing both response speed and reliability through real-time parameter adjustment.
Solution Approach 2:
The patent changes the torque parameter dynamically based on operational conditions. The controller adjusts the input motor torque command magnitude according to the difference between estimated and measured torques, modifying this key parameter to prevent actuator oversaturation while maintaining optimal performance across varying operational demands.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables precise monitoring and compensation of external forces, enhancing the robotic arm's stability and safety during procedures by effectively detecting collisions and adjusting motor torque accordingly.
Implementation Method 1
a joint torque sensor disposed within the first joint and configured to measure torque imparted on at least one of the first link or the second link to obtain a measured torque value
Implementation Method 2
The controller is further configured to determine a frictional loss for the first actuator and a frictional loss for the first joint
Implementation Method 3
The controller is further configured to determine a gravity effect on at least one of the first link or the second link
Implementation Method 4
a motor torque sensor configured to measure the output torque imparted by the first actuator
Data Source
AI summary
A surgical robotic arm includes a first link; a second link coupled to the first link at a first joint such that at least one of the first link or the second link is movable relative to each other; and a first actuator configured to move at least one of the first link or the second link. The surgical robotic arm also includes a joint torque sensor disposed within the first joint and configured to measure torque imparted on at least one of the first link or the second link to obtain a measured torque value. The surgical robotic arm further includes a controller configured to: determine an estimated joint torque value; compare the estimated joint torque value to the measured torque value; and determine an environmental torque value based on a comparison of the estimated joint torque value and the measured torque value.