Variable-Velocity Surgical Instrument Control for Flexing Limits
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Solution Overview
Problem
Minimally invasive surgical instruments face challenges with limited stiffness, leading to flexing and splaying during grasping, clamping, and stapling operations due to size constraints, resulting in potential failed operations and irregular velocity profiles.
Innovation Solution
A surgical instrument with a computer-assisted medical device that adjusts the velocity set point of the actuator based on applied force or torque thresholds, using a state machine to manage the operation of the end effector, transitioning through states to maintain optimal velocity and torque levels, thereby reducing flexing and improving operation precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the end effector size is kept small to minimize damage to healthy tissue, then the instrument can be inserted through small openings, but the limited stiffness causes flexing and splaying during operations
Solution Approach 1:
The system dynamically adjusts the velocity setpoint of the actuator based on real-time torque measurements. When torque exceeds a threshold (indicating flexing or splaying), the velocity setpoint is reduced to allow the end effector to stabilize, preventing operational failures while maintaining small size for minimally invasive access
2Productivity
If the velocity set point is maintained at a constant high level, then productivity is improved, but flexing and splaying occur leading to failed operations
Solution Approach 1:
The control system continuously monitors torque applied by the actuator and uses this feedback to adjust the velocity setpoint. When torque indicates flexing or splaying, the system reduces velocity to prevent operational failure, thereby maintaining high reliability while achieving high productivity during stable operations
3Reliability
If the velocity set point is reduced to prevent flexing, then reliability is improved, but productivity decreases due to slower operations
Solution Approach 1:
The system dynamically adjusts the velocity setpoint based on real-time torque measurements rather than using a fixed low velocity. This allows high velocity during stable operations for productivity while reducing velocity only when torque indicates flexing or splaying, maintaining reliability without unnecessary speed reduction
Data Source
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.