Endoscope Optical Unit Brazing for Thermal Stress Relief
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Solution Overview
Problem
The existing optical units in endoscope apparatuses are prone to airtightness failure when exposed to high-temperature autoclaving due to thermal stress caused by non-uniform cylindrical member thickness, leading to peeling of the transparent cover glass, especially when the optical axis is deviated from the center line.
Innovation Solution
An optical unit with a cylindrical member of varying thickness, where a joining member with a thicker radial thickness at the thick portion of the cylindrical member is used to secure the transparent cover glass, and the assembly is brazed using a vacuum brazing process with the cylindrical member inclined to reduce thermal stress concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the optical axis is deviated from the center line of the cylindrical member to enable fine-adjustment of the optical unit position, then the positioning accuracy is improved, but the airtightness reliability deteriorates due to thermal stress concentration in autoclaving
Solution Approach 1:
The joining member is designed with non-uniform thickness that corresponds to the non-uniform thickness distribution of the cylindrical member. Specifically, the joining member has a thicker portion at the location where the cylindrical member is thickest, creating a localized reinforcement that compensates for thermal stress concentration in that specific region while maintaining the overall deviated optical axis configuration.
Solution Approach 2:
Both the cylindrical member and the joining member exhibit asymmetric thickness distributions. The cylindrical member has a thick portion and a thin portion in the circumferential direction, and the joining member mirrors this asymmetry with its own thick and thin portions. This asymmetric design allows the optical axis to be deviated from the center line for positioning accuracy while the thick portions provide stress concentration relief for airtightness reliability.
2Adaptability or versatility
If the cylindrical member has non-uniform thickness in the circumferential direction to accommodate deviated optical axis, then the positioning flexibility is improved, but the thermal stress resistance deteriorates leading to cover glass peeling
Solution Approach 1:
The joining member provides localized reinforcement at the thick portion of the cylindrical member where thermal stress concentrates during autoclaving. This local quality enhancement ensures that the weakest point (thick portion) is strengthened to match the stress distribution, preventing cover glass peeling while preserving the non-uniform thickness configuration needed for positioning flexibility.
Solution Approach 2:
The optical unit employs a composite structure combining the cylindrical member (metal material such as stainless steel) with the joining member (different material properties) and the cover glass (transparent member). This composite design allows each material to contribute its advantageous properties: the metal cylindrical member provides structural integrity and thermal expansion characteristics, while the joining member provides stress distribution and bonding functionality.
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 solution ensures the optical unit remains airtight and durable against high-temperature environments, preventing the cover glass from peeling off and maintaining watertightness even when the optical axis is deviated from the center line, thus allowing for effective autoclaving sterilization.
Implementation Method 1
the cylindrical member is made from a metal material such as stainless steel and its thermal expansion coefficient is much different from that of the transparent member made from glass or the like. Therefore, when the optical unit is put in a high-temperature atmosphere of autoclaving, stress is concentrated in the thick portion of the cylindrical member
Implementation Method 2
a joining member which joins the transparent member to the cylindrical member and thereby seals the cylindrical member at the one end in the axial direction
Data Source
AI summary
An optical unit includes: a cylindrical member whose thickness varies in a circumferential direction; a transparent member disposed at one end, in an axial direction, of the cylindrical member; and a joining member which joins the transparent member to the cylindrical member and thereby seals the cylindrical member at the one end in the axial direction, and a portion, joining a side surface of the transparent member to an inner circumferential surface of the cylindrical member, of the joining member is thicker at a position where the cylindrical member is thick than at a position where the cylindrical member is thin.