Hydraulic Actuation for Surgical Robotic End Effector Force Sensing
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Solution Overview
Problem
In minimal-invasive surgical robotic systems, Bowden cables used for actuating end effectors introduce friction and interference with contact force measurements due to manufacturing tolerances and material properties, complicating force transmission and assembly in miniaturized mechanics.
Innovation Solution
A hydraulic drive system is employed, using a hydraulic cylinder and line connected to the end effector, which minimizes friction and interference, allowing for precise force measurement and high reduction ratios with a simple design, and utilizing a metallic bellows for sealing and isotonic sterile saline fluid to ensure safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If Bowden cables are used to drive the end effector, then the actuator can transmit driving forces, but frictional forces and interference with contact force measurements occur due to manufacturing tolerances and material properties
Solution Approach 1:
The patent replaces the Bowden cable mechanical transmission system with a hydraulic drive system. The hydraulic cylinder (20) with hydraulic line (36) transmits driving forces through hydraulic fluid, which is virtually free of friction. This eliminates the frictional forces and interference with contact force measurements that plague Bowden cable systems, particularly in miniaturized surgical robotic applications.
Solution Approach 2:
The patent substitutes the mechanical Bowden cable transmission system with a hydraulic system. The hydraulic drive (cylinder 20, line 36) replaces the cable-based mechanical transmission, eliminating friction and manufacturing tolerance issues inherent in mechanical systems while maintaining the ability to transmit driving forces to the end effector.
2Volume of moving object
If miniaturization is pursued to reduce the size of surgical robotic systems, then the system fits better for minimal-invasive surgery, but manufacturing and assembly become increasingly difficult and complex
Solution Approach 1:
The hydraulic drive system provides a compact actuation mechanism that maintains functional performance while reducing size. The hydraulic cylinder and line configuration allows for compact integration into the end effector, avoiding the complexity of miniaturized mechanical transmission components while achieving the required size reduction for minimal-invasive surgery.
3Power
If Bowden cables are used in miniaturized systems, then driving forces can be transmitted, but friction and energy loss increase due to manufacturing tolerances and material properties
Solution Approach 1:
The hydraulic transmission system eliminates the frictional losses inherent in Bowden cable mechanical transmission. Hydraulic fluid transmission is virtually friction-free, maintaining driving force efficiency while avoiding the energy losses that occur in miniaturized mechanical cable systems due to manufacturing tolerances and material properties.
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 hydraulic drive system enhances the accuracy of contact force detection by reducing parasitic forces, enabling high force transmission with minimal hydraulic pressure changes and maintaining sterility, thus improving mechanical decoupling and reducing interference with force sensor readings.
Implementation Method 1
The actuator of the end effector is formed by a hydraulic cylinder (20) which is used for driving the end effector element (24, 25). The robotic arm (12) is provided with a hydraulic line (36) which is connected to the hydraulic cylinder (20).
Implementation Method 2
The hydraulic line (36) can be run within narrow radii or within decoupling loops. The free length of the hydraulic line between the robotic arm and the end effector can be made large enough to allow only negligibly small forces to be transmitted between the robotic arm and the end effector.
Data Source
AI summary
A surgical robotic system includes a robotic arm, an end effector movably connected thereto and provided with a movable end effector element driven by an actuator, and a force sensor arranged between the robotic arm and the end effector. The actuator is formed by a hydraulic cylinder. The robotic arm is provided with a hydraulic line connected to said hydraulic cylinder of the end effector.