Force Torque Limit Compensation for Surgical Instruments
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Solution Overview
Problem
Minimally invasive surgical instruments with articulated arms face challenges in maintaining effective force and torque control, particularly when a default or home position is required, as existing return-to-home mechanisms can hinder the instrument's operation by requiring excessive force or torque to overcome the restraining mechanism.
Innovation Solution
The implementation of a force or torque limit compensation system that adjusts the operational limits based on the current position of the degree of freedom, using a torque limit compensation model and lookup table to optimize torque limits, ensuring the instrument can return to a home position without negatively impacting its functionality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a return-to-home mechanism is implemented to ensure the instrument returns to a default position, then safety and control are improved, but the force or torque required to operate the instrument increases due to the restraining mechanism
Solution Approach 1:
The system dynamically adjusts torque limits based on the current position of the degree of freedom. A torque limit compensation model calculates position-dependent compensation values that are applied to the operational torque limits. This allows the restraining mechanism to be weaker overall while providing sufficient holding force when needed, resolving the contradiction between reliability and required force.
Solution Approach 2:
The torque limits are not fixed but dynamically adjusted based on the instrument's current position. The control system continuously monitors position and modifies torque limits accordingly, allowing the system to adapt the restraining force characteristics in real-time. This dynamic adjustment enables the instrument to return to home reliably while reducing the force barrier during normal operation.
2Ease of operation
If torque limits are increased to overcome the restraining mechanism, then ease of operation is improved, but the precision and control of force application deteriorates
Solution Approach 1:
The system implements position-dependent torque limit adjustments where the compensation values are calculated based on the current degree of freedom position. This ensures that torque limits are optimized for each position, allowing smooth operation while maintaining precise force control. The lookup table provides pre-calculated compensation values that balance ease of operation with control precision.
Solution Approach 2:
The control system uses feedback from position sensors to continuously monitor the degree of freedom position and adjust torque limits accordingly. This closed-loop control ensures that the instrument operates smoothly while maintaining precise force application, as the torque limits are dynamically adapted to the current operational state rather than being fixed high values.
3Reliability
If a restraining mechanism is used to control the degree of freedom, then safety is improved, but the operational margin and flexibility of the instrument deteriorates
Solution Approach 1:
The system uses position-dependent torque limit compensation to maintain safety while preserving operational flexibility. The torque limits are adjusted based on the current position, allowing the instrument to operate with sufficient freedom within safe parameters. This dynamic adjustment maintains the operational margin while ensuring safety through the restraining mechanism.
Solution Approach 2:
The restraining mechanism operates dynamically with position-adjusted torque limits rather than static fixed limits. This dynamic operation allows the system to adapt to different operational scenarios while maintaining safety. The control system continuously adjusts torque limits based on position feedback, preserving operational margin while ensuring safety control.
Data Source
AI summary
Techniques for force and torque limit compensation include a computer-assisted device including a drive unit configured to operate a degree of freedom of an instrument supported by the computer-assisted device and a control unit. The control unit is configured to determine an expected amount of restraining or return to home force or torque applied to the degree of freedom; determine a force or torque limit compensation based on the expected amount of restraining or return to home force or torque; alter one or more force or torque limits based on the force or torque limit compensation; and adjust, using the drive unit, the degree of freedom subject to the one or more altered force or torque limits.