Surgical Knife Assembly Interference Coupling Dissimilar Materials
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Solution Overview
Problem
Designing knife assemblies for surgical instruments that prevent deformation and ensure reliable coupling between components made of different materials, such as stainless steel and Nitinol, is challenging due to weak welds and potential failure during tissue cutting.
Innovation Solution
The knife assembly features an elongated tube and knife blade made of stainless steel, with a Nitinol shaft that includes an enlarged distal end portion, which is heated to expand and secure within the tube, preventing movement and ensuring a strong coupling, and a shaft stop to prevent retraction issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If welding is used to couple components made of different materials (stainless steel and Nitinol), then assembly strength is improved, but weld reliability deteriorates due to weak welds between dissimilar materials
Solution Approach 1:
The patent introduces an intermediary interference fit coupling mechanism between the Nitinol shaft and stainless steel tube. The shaft includes an enlarged portion that creates a mechanical interference fit within the tube, serving as a mediator that transfers loads between dissimilar materials without requiring direct welding. This intermediary mechanical coupling resolves the contradiction by providing reliable force transmission while avoiding weak welds between incompatible materials.
Solution Approach 2:
The patent segments the coupling mechanism into distinct functional zones: the enlarged shaft portion for interference fitting, the welded region for permanent attachment, and the remaining shaft length for actuation. This segmentation allows optimization of each zone for its specific function, with the enlarged portion providing mechanical interlocking and the welded region providing structural continuity, thereby resolving the reliability-strength contradiction.
2Ease of operation
If the shaft is made flexible (Nitinol material), then ease of operation is improved, but manufacturing precision deteriorates due to potential deformation
Solution Approach 1:
The patent applies local quality by creating an enlarged portion at a specific location on the Nitinol shaft. This localized geometric modification provides a rigid interference fit interface precisely where needed for coupling, while the remainder of the shaft maintains its flexible Nitinol properties for ease of operation. This local structural differentiation resolves the contradiction between flexibility and manufacturing precision.
Solution Approach 2:
The patent performs preliminary action by pre-forming the enlarged portion on the shaft before final assembly. This pre-formed geometric feature ensures precise dimensional control and proper fit within the tube before the shaft is subjected to operational stresses. The preliminary formation of the coupling interface prevents deformation during manufacturing and assembly while preserving shaft flexibility for operation.
3Reliability
If the shaft is constrained within the tube, then reliability is improved by preventing movement, but device complexity increases due to additional coupling mechanisms
Solution Approach 1:
The patent merges multiple coupling functions into a single integrated enlarged shaft portion. This unified structure simultaneously provides interference fit for mechanical coupling, defines the boundary for welding, and prevents shaft rotation or lateral movement. By combining these functions into one geometric feature rather than using separate components, the patent achieves high coupling reliability while minimizing device complexity.
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
This configuration minimizes the risk of deformation and coupling failure, ensuring the knife blade remains within the channel during use, maintaining effective tissue cutting and assembly integrity.
Implementation Method 1
an enlarged distal end portion, which is heated to expand and secure within the tube
Implementation Method 2
a knife blade having a pair of opposing lateral sides and a sharpened distal end configured to cut tissue
Data Source
AI summary
An electrosurgical instrument includes first and second jaw members each including an outer jaw housing, a tissue-treating plate, and a longitudinally-extending knife channel. The electrosurgical instrument also includes a knife actuator and a knife assembly operably coupled to the knife actuator. The knife assembly includes an elongated tube defining a longitudinal lumen and an elongated shaft having a proximal portion coupled to the knife actuator and a distal portion configured to be received through the longitudinal lumen. The distal portion of the elongated shaft includes an enlarged distal end portion configured to prevent movement of the elongated shaft relative to the elongated tube. The knife assembly also includes a knife blade having a pair of opposing lateral sides and a sharpened distal end configured to cut tissue. The elongated tube is configured to be coupled to one of the pair of opposing lateral sides of the knife blade.