Ovalized Cannula Reduces Friction During Instrument Insertion
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Solution Overview
Problem
Current minimally invasive robotic surgical systems face challenges in performing single port access surgeries due to high friction and stiction between surgical instruments and cannulas, leading to difficulty in instrument insertion and potential patient injury.
Innovation Solution
A curved cannula with an ovalized cross section is designed, where the major axis aligns with the cannula's radius of curvature, increasing the contact patch area and reducing friction and stiction by distributing contact stress over a larger area, and markings on the cannula assist in correct orientation during insertion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a circular cross-section cannula is used, then the structure is simple and easy to manufacture, but friction and stiction between the instrument and cannula are high, making instrument insertion difficult
Solution Approach 1:
The cannula cross-section is changed from a symmetric circular shape to an asymmetric oval shape, where the major axis aligns with the radius of curvature. This asymmetric geometry creates a larger contact patch area on the inner wall, distributing contact stress and reducing friction and stiction forces during instrument insertion while maintaining structural simplicity
Solution Approach 2:
The geometric parameters of the cannula cross-section are modified by ovalizing it along the radius of curvature direction. This parameter change increases the contact patch area between the instrument and cannula inner wall, thereby reducing the friction and stiction forces that oppose instrument insertion
2Ease of operation
If the contact patch area is increased to reduce friction, then instrument insertion is easier, but the cannula structure becomes more complex
Solution Approach 1:
The cannula cross-section is changed from a symmetric circular shape to an asymmetric oval shape, where the major axis aligns with the radius of curvature. This asymmetric geometry creates a larger contact patch area on the inner wall, distributing contact stress and reducing friction and stiction forces during instrument insertion while maintaining structural simplicity
Data Source
AI summary
The cross section of a curved portion of a curved cannula is oval shaped. The oval is oriented such that a major axis of the oval is generally aligned with the curved portion's bend radius. In one aspect, the cannula tube is ovalized so that the radius of curvature of an interior wall approaches the outer radius of an instrument component that contacts the curved portion during instrument insertion. In this first aspect, a wider contact patch area between the instrument component and the cannula results, which reduces friction and stick-slip during insertion. In another aspect, the cannula tube is ovalized so that the radius of curvature of an interior wall is less than the outer radius of an instrument component that contacts the curved portion during instrument insertion. In this second aspect, two contact patches are established between the instrument component and cannula, which also reduces friction and stick-slip during instrument insertion. Also disclosed is a cannula orientation marking that changes circumferential orientation along a length the curved cannula to help a person who is inserting the cannula to properly twist the cannula during insertion.