Robotic Wrist Jaw Grip Force Limiting Feedback Control
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Solution Overview
Problem
In robotic surgical systems, there is a need for precise control of grip force to prevent tissue damage and ensure precise manipulation, particularly during transitions between positional and force control modes to avoid accidental drops of grasped objects.
Innovation Solution
A feedback control system that limits the maximum grip force during jaw closure in position mode and maintains a minimum jaw opening force in position mode, using a debouncing strategy to ensure smooth transitions between control modes, thereby preventing tissue damage and maintaining object grasp.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the jaws operate in position control mode with high grip force to ensure secure grasping, then the reliability of object grasp is improved, but the tissue may be damaged due to excessive force
Solution Approach 1:
The system dynamically switches between position control mode and force control mode based on the desired jaw angle. In position control mode, the jaws are commanded to a desired angle for secure grasping. When the desired jaw angle falls below a threshold indicating contact with tissue, the system transitions to force control mode where grip force is limited to a pre-specified maximum threshold, thereby preventing tissue damage while maintaining grasp reliability
Solution Approach 2:
The control system changes the grip force parameter based on the operating mode. In position control mode, high grip force is applied for secure grasping. When transitioning to force control mode (when jaw angle < threshold), the grip force parameter is constrained to a maximum threshold value, preventing excessive force application to tissue while maintaining adequate grasp force
2Reliability
If the system transitions smoothly between position mode and force mode to prevent accidental drops, then the reliability of object grasp is improved, but the control system complexity increases
Solution Approach 1:
The system uses feedback from the desired jaw angle to determine the operating mode. When the desired jaw angle is above the threshold, position control mode is active. When the desired jaw angle falls below the threshold, force control mode is activated. This feedback mechanism ensures smooth transitions between modes, preventing accidental drops of grasped objects while maintaining a relatively simple control architecture
Solution Approach 2:
The system pre-specifies a maximum grip force threshold and a jaw angle threshold to govern mode transitions. These pre-defined parameters enable smooth transitions between position and force control modes without requiring complex real-time decision algorithms, thereby maintaining control system simplicity while ensuring reliable object grasp during transitions
Data Source
AI summary
Disclosed are systems and methods for limiting the grip force generated by closing robotic wrist jaws while operating in position mode in which the jaws are commanded to a desired jaw angle prior to being commanded to generate a grip force. In the positional mode, the desired jaw angle is above a threshold that corresponds to an angle at which both jaws are just simultaneously in contact with an object between the jaws or, if there is no object to grasp, when the jaws begin to touch each other. A feedback loop may analyze the desired jaw angle and the measured grip force to determine if the jaws are closing in the position mode and if the measured grip force exceeds a maximum grip force threshold. If so, the feedback loop may calculate a grip force error to limit the measured grip force to the maximum grip force threshold.