Stiff yet Bendy: Tubular Transmissions for Driving Surgical Robots through Flexible Endoscopes

Area of Science:

• Robotics
• Mechanical Engineering
• Biomedical Devices

Background:

• Flexible endoscopes require concentric push-pull robots with transmission tubes exhibiting high axial stiffness, high torsional stiffness, and low bending stiffness.
• Existing laser-cut tube designs often focus on bending/torsional stiffness ratios, neglecting simultaneous optimization of all three stiffness properties.
• A trade-off exists in current designs, making it challenging to achieve high axial stiffness concurrently with low bending stiffness due to their strong correlation.

Purpose of the Study:

• To address the simultaneous design of axial, torsional, and bending stiffness in laser-cut transmission tubes for endoscopic robots.
• To overcome the inherent correlation between axial and bending stiffness in existing laser-cut patterns.
• To propose and validate a novel laser material removal pattern that enables independent control over all three stiffness values.

Main Methods:

• Proposed a new laser material removal pattern utilizing local stiffness asymmetry in discrete bending segments.
• These segments are separated by solid tube sections and rifled along the tube to achieve global stiffness symmetry.
• Employed finite-element analysis for design parameterization and property study, including interference effects between misaligned tubes.
• Experimentally validated the design using manufactured Nitinol tube prototypes.

Main Results:

• The proposed discrete asymmetric segment design effectively breaks the correlation between axial and bending stiffness.
• Achieved superior high axial and torsional stiffness compared to previous laser patterns while maintaining low bending stiffness.
• Experimental validation confirmed the design's predicted properties and actuation performance in a prototype endoscopic robot system.

Conclusions:

• The novel discrete asymmetric segment pattern offers a viable solution for optimizing transmission tube stiffness in endoscopic robots.
• This design enables independent control over axial, torsional, and bending stiffness, enhancing robotic system capabilities.
• The findings have significant implications for the development of more effective and precise endoscopic robotic tools.