Closed Loop Motor Velocity Control for Surgical Stapler
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Solution Overview
Problem
Existing motorized surgical stapling and cutting instruments face challenges in accurately controlling the velocity of the cutting member, leading to potential system errors between the commanded velocity and the actual measured velocity.
Innovation Solution
A method is provided for adjusting the velocity of a motorized surgical instrument by using a control circuit to set a directed velocity, determine the actual velocity, calculate the error between the two, and then adjust the actual velocity based on the magnitude of the error.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If open loop control is used to control motor velocity, then the control system is simpler, but velocity accuracy deteriorates due to system errors between commanded and actual velocity
Solution Approach 1:
The patent implements closed-loop feedback control by continuously measuring the actual velocity of the cutting member using a position sensor and timer circuit, comparing it to the commanded velocity, and adjusting the motor velocity based on the error. This feedback mechanism eliminates the velocity accuracy issues inherent in open-loop control while maintaining reasonable system complexity through integrated sensor and control circuitry.
2Measurement precision
If closed loop feedback control is implemented, then velocity accuracy is improved, but device complexity increases due to additional sensors and control circuits
Solution Approach 1:
The patent uses a position sensor and timer circuit to measure actual velocity and feeds this information back to the control circuit, which adjusts motor velocity accordingly. This feedback approach achieves accurate velocity control by continuously monitoring and correcting deviations between commanded and actual velocity.
Solution Approach 2:
The control system automatically adjusts motor velocity based on real-time feedback from the position sensor without requiring external intervention. The system self-corrects velocity errors by comparing actual measured velocity with commanded velocity and making automatic adjustments through the control circuit.
3Manufacturing precision
If velocity control adjustments are made based on error magnitude, then tissue handling precision is improved, but response time increases due to continuous monitoring and adjustment
Solution Approach 1:
The control circuit continuously monitors the error between commanded and actual velocity and makes real-time adjustments based on the magnitude of the error. This feedback mechanism ensures precise tissue handling by adapting velocity to actual tissue conditions while maintaining efficient response through continuous rather than intermittent adjustment.
Data Source
AI summary
A surgical stapler is presented which includes an end effector, a firing drive electric motor, and a control circuit. The motor is configured to translate a firing bar to deploy staples from the end effector during a staple firing stroke. The control circuit is configured to provide a pulse width modulated (PWM) electrical signal to the firing drive electric motor, compare an actual velocity of the firing bar to a directed velocity, and adjust a duty cycle of the PWM electrical signal based at least in part on the comparison. The control circuit can adjust the duty cycle based on one or more of a short term error (S), cumulative error (C), change error (R), a number of overshoots (N) calculated based on the comparison of the actual velocity to the directed velocity.