Compact Torque Sensing Articulation Axis for Robotic Catheters
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Solution Overview
Problem
Robotic catheter systems face challenges in accurately predicting and controlling catheter tip movement due to unmodeled constraints and external forces, leading to inaccuracies in kinematic modeling, and lack of precise torque sensing, which affects the precision and safety of minimally invasive procedures.
Innovation Solution
A compact robotic surgical system with an instrument driver that includes a reactive torque sensor coaxial with the motor and gearbox, which measures output shaft torque using strain gauges, allowing for precise torque measurement and control without increasing the system's size, and a method for determining output torque using a torque sensor disposed in surrounding relation to the motor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a rotary encoder is used to determine rotational position of the output shaft, then the rotational position can be determined, but the torque applied at the output shaft cannot be precisely calculated due to variations in transmission efficiency and external forces
Solution Approach 1:
The patent combines the torque sensor with the motor assembly, integrating the torque sensing function into the existing motor structure. The torque sensor is positioned to measure torque on the motor shaft, which is then used to calculate output shaft torque, merging multiple functions (motor operation and torque sensing) into a unified system that reduces overall complexity.
Solution Approach 2:
The patent uses an intermediary calculation approach where torque sensor readings from the motor shaft are combined with gearbox parameters (gear ratio, efficiency) to derive output shaft torque. This intermediary method allows torque measurement at a more accessible location while still obtaining the required output shaft torque information.
2Measurement precision
If a torque sensor is added to the motor assembly, then precise torque sensing is achieved, but the height of the articulation drive assembly increases
Solution Approach 1:
The torque sensor is nested within the motor assembly structure, with the sensor positioned to measure torque on the motor shaft. The sensor is integrated into the motor housing or mounting structure, allowing it to be contained within the existing spatial envelope of the motor rather than adding external height to the assembly.
Solution Approach 2:
The patent positions the torque sensor radially rather than axially, measuring torque on the motor shaft in a radial direction. This dimensional change allows torque sensing without increasing the axial height of the assembly, as the sensor operates in a different spatial dimension (radial vs. axial).
3Reliability
If pullwire displacement is monitored alone, then the system is simple to operate, but inaccuracies occur in predicting catheter tip movement due to unmodeled constraints and external forces
Solution Approach 1:
The patent implements feedback by continuously monitoring torque sensor readings and using this information to adjust control commands. The torque information provides feedback on the actual load conditions, allowing the control system to compensate for unmodeled constraints and external forces, thereby improving prediction accuracy of catheter tip movement.
Solution Approach 2:
The torque sensor serves multiple functions: it measures torque for control purposes, detects external forces, identifies unmodeled constraints, and provides information for both open-loop and closed-loop control modes. This multi-functionality improves reliability without proportionally increasing system complexity.
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
The system achieves precise control of catheter movement and torque sensing, enhancing the accuracy and safety of robotic catheter systems by minimizing differences between predicted and actual kinematic functions and providing essential torque information without increasing the instrument driver's size.
Implementation Method 1
measuring, with the torque sensor, the output shaft torque
Data Source
AI summary
A compact height torque sensing articulation axis assembly is disclosed herein having a torque sensor, an assembly mounting flange, a motor, a motor gearbox, a gearbox output shaft, an encoder, and a cable. The assembly may sense tension on robotic catheter pullwires in an articulating catheter and/or torque on a robotic output axis using the torque sensor. Disclosed embodiments may advantageously be used to achieve small, lightweight robotic catheter systems.