Surgical Instrument Velocity Control Under Tissue Torque Variation
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Solution Overview
Problem
Minimally invasive surgical instruments face issues with flexing and splaying due to limited stiffness, leading to failed operations and ragged velocity profiles during tasks like grasping, clamping, and stapling, especially when subjected to varying tissue conditions.
Innovation Solution
A computer-assisted surgical instrument with an end effector and actuator system that adjusts velocity set points based on applied force or torque thresholds, using a state machine to transition between clamp states and a wait state to maintain consistent operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the end effector is kept small to minimize invasive damage, then the stiffness is reduced, but the instrument becomes susceptible to flexing and splaying during grasping, clamping, and stapling operations
Solution Approach 1:
The system dynamically adjusts the velocity set point of the actuator based on real-time torque measurements. When torque exceeds a threshold (indicating tissue engagement), the velocity is reduced to prevent excessive flexing and splaying. This dynamic control allows the small end effector to maintain stability during critical operations without requiring increased physical stiffness.
2Speed
If a simple torque limit is applied to the actuator, then the operation speed is maintained, but the velocity profile becomes ragged and operations may fail due to tissue variations
Solution Approach 1:
The system continuously monitors torque applied by the actuator and uses this feedback to adjust the velocity set point in real-time. When torque approaches the threshold, velocity is reduced smoothly; when torque decreases, velocity can be increased again. This closed-loop feedback control eliminates ragged velocity profiles and adapts to tissue variations, significantly improving operational reliability while maintaining overall speed.
Data Source
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Figure 3A~3D
AI summary
A system and method of variable velocity control of a surgical instrument in a computer-assisted medical device including an end effector located at a distal end of the instrument, an actuator, and drive mechanisms for coupling force or torque from the actuator to the end effector. To perform an operation with the instrument, the computer-assisted medical device sets a velocity set point of the actuator to an initial velocity, monitors force or torque applied by the actuator, reduces the velocity set point when the applied force or torque is above a first threshold, increases the velocity set point when the applied force or torque is below a second threshold, decreases the velocity set point to zero when the applied force or torque is above a maximum threshold, and drives the actuator based on the velocity set point. The first and second thresholds are lower than the maximum threshold.