Surgical Instrument Pretension Control for Backlash and Compliance
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Solution Overview
Problem
Surgical robotic systems face challenges in precise control of end effectors due to compliance, backlash, and internal friction in the transmission between tool drives and end effectors, especially under varying external loads, which affects the accuracy and reliability of robotic surgical tools.
Innovation Solution
The implementation of multiple actuators that establish static pretension by operating in opposition to each other, reducing compliance and backlash, and transitioning to position control mode to maintain precise movement and control of the end effector while driving the tool.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple actuators are operated in opposition to each other under torque control, then static pretension is established and compliance is reduced, but device complexity increases
Solution Approach 1:
The system performs preliminary action by establishing static pretension through opposing torque control of multiple actuators before actual positioning operations. This preliminary tensioning of the transmission mechanism eliminates compliance and backlash, creating a rigid mechanical foundation for subsequent precise position control movements.
Solution Approach 2:
The system dynamically switches between two control modes: torque control mode for establishing static pretension, and position control mode for precise end effector positioning. This dynamic mode transition allows the system to optimize performance by applying the appropriate control strategy at each stage of operation.
2Ease of operation
If transmission components are made more compliant to reduce friction, then ease of operation improves, but control precision deteriorates
Solution Approach 1:
The system applies preliminary action by pre-tensing the transmission mechanism through opposing actuator torques before positioning operations. This preliminary tensioning eliminates compliance and backlash in the transmission, ensuring that subsequent position commands are transmitted accurately without the negative effects of friction or play.
3Manufacturing precision
If static pretension is maintained during position control, then backlash is reduced, but energy consumption increases
Solution Approach 1:
The system employs periodic action by alternating between torque control mode (for establishing static pretension) and position control mode (for precise positioning). During position control, the system maintains pretension but optimizes energy consumption by coordinating actuator movements and utilizing the already-tensed transmission mechanism rather than continuously applying maximum opposing torques.
Data Source
AI summary
For control of a surgical instrument in a surgical robotic system, multiple actuators establish a static pretension by actuating in opposition to each other in torque control. The static pretension reduces or removes the compliance and elasticity, reducing the backlash width. To drive the tool, the actuators are then moved in cooperation with each other in position mode control so that the movement maintains the static pretension while providing precise control.