Surgical Instrument Actuator Velocity Control Under Tissue Resistance
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Solution Overview
Problem
Minimally invasive surgical instruments face challenges with limited stiffness, leading to flexing and splaying during procedures like stapling, due to size constraints and varying tissue resistance, resulting in potential operation failures and irregular velocity profiles.
Innovation Solution
A surgical instrument system with a computer-assisted medical device that sets a velocity set point for the actuator, monitors force or torque, and adjusts the operation based on predefined conditions to maintain optimal force and torque levels, pausing or adjusting the actuator movement to ensure smooth and effective stapling operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the size of the end effector 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 stapling operations
Solution Approach 1:
The system dynamically adjusts the velocity of the actuator based on real-time force feedback. When force exceeds a threshold during stapling, the velocity is automatically reduced, allowing the instrument to adapt its mechanical behavior to maintain stability without changing its physical structure. This resolves the contradiction by making the instrument's performance characteristics variable rather than fixed.
Solution Approach 2:
The control system changes the velocity parameter of the actuator in response to force conditions. By adjusting the velocity set point based on force feedback, the system optimizes the balance between operational speed and mechanical stability, allowing the small end effector to perform reliably despite its limited stiffness.
2Productivity
If the velocity of the actuator is increased to improve productivity, then stapling operations are faster, but flexing and splaying increase due to varying tissue resistance
Solution Approach 1:
The system continuously monitors force during stapling operations and uses this feedback to adjust the actuator velocity in real-time. When force increases indicating tissue resistance or instability, the velocity is reduced to maintain consistent performance. This closed-loop control ensures both high productivity and stable velocity profiles by adapting to actual operating conditions.
Solution Approach 2:
The actuator velocity transitions from a fixed parameter to a dynamic one that automatically adjusts based on force conditions. The system can operate at high speeds when conditions are favorable while automatically slowing down when tissue resistance causes instability, maintaining both productivity and velocity consistency.
3Stability of the object's composition
If force limits are imposed on the actuator to reduce flexing and splaying, then stability improves, but operation may pause or fail due to inadequate force for stapling
Solution Approach 1:
Rather than imposing a static force limit that could prevent successful stapling, the system dynamically adjusts velocity in response to force conditions. This allows the actuator to apply sufficient force for stapling while maintaining stability through speed modulation, resolving the contradiction between stability and operational reliability.
Solution Approach 2:
The system changes the velocity parameter rather than imposing hard force limits. This approach maintains reliability by allowing force to reach necessary levels for stapling while using velocity adjustment to prevent excessive flexing and splaying that would compromise stability.
Data Source
AI summary
A system and method of variable velocity control of a surgical instrument in a computer-assisted medical device includes a surgical instrument having an end effector located at a distal end of the instrument, an actuator, and one or more 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 is configured to set a velocity set point of the actuator to an initial velocity and monitor force or torque applied by the actuator. When the applied force or torque is above a first force or torque limit it is determined whether a continue condition for the operation is satisfied. When the continue condition is satisfied the operation is paused and when the continue condition is not satisfied it is determined whether forced firing of the actuator should take place.