Medical Robotic Control System Actuator Joint Linkage Compensation
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Solution Overview
Problem
Medical robotic systems face challenges in precise control due to non-ideal actuator-to-joint linkage characteristics, such as cable friction and compliance, leading to excessive estimation errors and diminished control capability, especially in fine motor tasks like suturing.
Innovation Solution
A control system that generates distal joint commands and actuator feedback to accurately move end effectors, using sensors to compensate for non-idealities in the linkage, ensuring precise position and force control through multiple control loops and sensor feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If rigid linkages are used to couple actuators to joints, then position estimation is improved, but control precision deteriorates due to cable friction and compliance
Solution Approach 1:
The patent implements a feedback mechanism where sensors detect actual joint positions and the control system compares these with expected positions based on actuator commands. The difference (error) is used to generate compensatory commands that account for friction and compliance effects, thereby maintaining control precision despite non-ideal linkage characteristics
Solution Approach 2:
The control system dynamically adjusts control parameters including feedforward torque compensation and feedback gain values to account for varying friction and compliance conditions. By changing these parameters based on operational state, the system maintains accurate control across different operating conditions
2Device complexity
If simple kinematic transforms are applied to estimate tool positions, then computational complexity is reduced, but estimation error increases due to linkage non-idealities
Solution Approach 1:
The patent replaces direct mechanical measurement at the end effector with a computational approach using sensors at the actuator and mathematical models (kinematic transforms enhanced with friction and compliance compensation). This substitution maintains relatively simple system architecture while significantly improving position estimation accuracy
3Ease of manufacture
If cable transmission is used for actuator linkage, then mechanical simplicity is improved, but control capability deteriorates due to friction and compliance
Solution Approach 1:
The control system acts as an intermediary between the simple cable-driven mechanical linkage and the desired precise control. By introducing computational compensation for friction and compliance effects, the system bridges the gap between the mechanically simple but imprecise cable transmission and the requirement for fine control capability
Data Source
AI summary
A medical robotic system having non-ideal actuator-to-joint linkage characteristics, includes a control system including a proximal control loop with actuator sensor feedback to control dynamic response of an actuator coupled to a distal joint which in turn, is coupled to an end effector to provide a degree of freedom movement of the end effector, a distal control loop with distal joint sensor feedback and feedforward to the actuator to ensure steady-state convergence of the distal joint position, and an end effector control loop with end-point sensor feedback to control the end effector position to reach a commanded end effector position.