Force Control for Compliant Medical Instrument Linkages
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Solution Overview
Problem
Current robotic medical instruments with compliant mechanical linkages face challenges in precise control due to the non-negligible compliance between joints and actuators, making it difficult to accurately model the relationship between actuator positions and joint positions, especially when tendons stretch under working loads.
Innovation Solution
Implementing a control system that uses distal position feedback to determine and control the forces applied by proximal actuators via mechanical linkages, allowing for precise instrument operation and independent control of joint stiffness, regardless of actuator position, by measuring joint positions and calculating the required actuator forces to converge on desired positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If compliant mechanical linkages are used in robotic medical instruments, then the instrument can safely interact with tissue and adapt to anatomical structures, but the relationship between actuator positions and joint positions becomes difficult to model accurately
Solution Approach 1:
The patent implements a feedback control system where sensors measure the actual position of distal joints and this measurement is fed back to the control system. The control system uses this feedback to calculate the actual relationship between actuator positions and joint positions in real-time, compensating for the compliance of mechanical linkages. This allows accurate position control despite the non-rigid connection between actuators and joints.
2Measurement precision
If tendons are made extremely rigid to ensure accurate position control, then the relationship between motor position and effector position can be directly modeled, but the instrument cannot safely interact with tissue or adapt to anatomical structures
Solution Approach 1:
The patent makes the mechanical linkages dynamically adjustable in terms of their stiffness characteristics. The control system can actively modulate the stiffness of tendon-driven linkages to match the requirements of different surgical tasks. During insertion or when navigating anatomical structures, the linkages can be made more compliant for safety, while during precise manipulation tasks, they can be stiffened for accuracy.
3Device complexity
If a fixed relationship between actuator control signals and effector position is assumed, then control calculations are simplified, but accurate control cannot be achieved when the mechanical structure has high compliance
Solution Approach 1:
The control system continuously measures actual joint positions and uses this feedback to update the model of the mechanical structure in real-time. This allows the system to adapt to changes in compliance and maintain accurate control without requiring an overly complex pre-programmed model of all possible compliance states.
Solution Approach 2:
The control system automatically characterizes the mechanical structure's compliance through sensor measurements and uses this self-acquired information to improve its control accuracy. The system serves itself by using its own operational data to refine its understanding of the mechanical linkages, eliminating the need for complex external calibration procedures.
4Reliability
If distal position feedback is implemented to achieve precise control, then accurate position and stiffness control can be achieved, but the control system complexity increases
Solution Approach 1:
The control system uses distal position feedback from sensors to continuously monitor the actual state of the instrument. This feedback is processed through a control algorithm that calculates the required actuator forces or torques to achieve the desired position and stiffness. The feedback loop runs at controlled frequencies to ensure stability while maintaining precision.
Data Source
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AI summary
Control systems and methods for a remote joint use position measurements to determine and control the force that an actuator applies to the joint through a linkage. The use of force and feedback allows control of a medical instrument having a linkage that provides non-negligible compliance between the joint and a proximal actuator and particularly allows precise instrument operation even when the position of the distal joint cannot be directly related to the proximal motor position.