Medical Robotic Control System for Cable Friction 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 includes an end effector controller generating a distal joint command, a distal controller for actuator command generation, and a proximal controller for feedback loop closure, with a feed-forward command to compensate for residual errors in cable transmission non-idealities, ensuring accurate movement of the end effector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If cable transmission linkages are used to couple actuators to distal joints, then the mechanical structure can achieve compact design and flexible manipulation, but cable friction and compliance cause excessive estimation errors in end effector positions and diminish control capability
Solution Approach 1:
The patent implements feedback control by measuring actual distal joint positions and using these measurements to update the estimated end effector positions. The system continuously monitors the discrepancy between kinematically transformed positions and actual positions, then compensates for this discrepancy through feedback mechanisms that account for cable friction and compliance effects.
Solution Approach 2:
The patent changes the control parameters by transitioning from open-loop kinematic transformation to closed-loop control that incorporates measured joint positions and compensates for cable non-idealities. The system dynamically adjusts control parameters based on actual system state to maintain accuracy despite cable friction and compliance.
2Reliability
If cable friction and compliance are present in the transmission system, then the mechanical linkage can tolerate non-ideal conditions, but torque propagation from motors to end effectors becomes unpredictable and fine control capability is diminished
Solution Approach 1:
The patent uses feedback control to continuously monitor and adjust torque commands based on actual system response. By measuring distal joint positions and comparing them with commanded positions, the system can compensate for unpredictable torque propagation caused by cable friction and compliance, maintaining fine control capability despite non-ideal transmission conditions.
Solution Approach 2:
The patent replaces pure mechanical torque transmission with a hybrid control approach that uses sensors and computational algorithms to compensate for mechanical non-idealities. Instead of relying solely on mechanical precision, the system uses electronic feedback and software-based compensation to achieve accurate torque control at the end effector.
3Device complexity
If simple kinematic transforms are applied to sensed actuator positions, then the control system remains simple and computationally efficient, but excessive estimation errors occur in end effector positions
Solution Approach 1:
The patent introduces feedback control that uses measured distal joint positions to correct kinematic transformation errors. The system maintains the simplicity of kinematic transforms for real-time control while adding a feedback layer that compensates for accuracy errors, achieving high precision without excessive computational complexity.
Solution Approach 2:
The patent performs preliminary compensation by pre-calculating correction factors for cable friction and compliance effects based on measured joint positions. This preliminary action allows the system to maintain simple real-time control logic while incorporating accuracy improvements through pre-computed compensation values.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The control system achieves accurate position control and refined force/torque control of surgical tools, enhancing the surgeon's capability to perform precise medical procedures by compensating for non-ideal linkage characteristics.
Implementation Method 1
when linkages are characterized by non-idealities such as cable friction
Implementation Method 2
when linkages are characterized by non-idealities such as cable friction, hysteresis and compliance
Data Source
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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.