Within the optical system of rigid endoscopes, double-sided cemented rod lenses undertake sophisticated image transmission tasks with cemented interfaces on both sides, imposing stringent requirements on cementing precision and surface cleanliness.In instances the place debonding happens on each cemented surfaces of a double-cemented rod lens, all residual adhesive should be utterly eliminated prior to re-cementing each aspects sequentially.
Tools and Materials Preparation
· Round tweezers with a 1.2 mm opening: capable of clamping rod lenses with a diameter of 1.2 mm without scratching or damaging the lens body
· 0.25 mm-diameter needle tool: the tip is cut flat, ground, chamfered and polished to form a smooth flat cross-section of 0.25 mm diameter with zero burrs on the surface; used for picking up and applying UV adhesive
· Wooden toothpicks and polishing compound: for grinding off residual adhesive
· Cotton swabs: for cleaning rod lens surfaces
· Special UV optical cement for endoscope optical lenses: compliant with high-temperature high-pressure resistance, high light transmittance and other critical performance indicators[learn more about...]
· 250 W Yokohama UV curing lamp equipped with a single 1/4 output head for UV curing
· Clean acrylic positioning sliders: auxiliary fixture for centering alignment
· Head-mounted high-magnification magnifier: for surface inspection and alignment verification during cleaning; magnification ranges from 20× to 40× according to operator preference; binocular or trinocular repair microscopes are also acceptable alternatives
Removal of bonded head and residual adhesive cleanup
Various factors can lead to yellowing, iridescent fringes, whitening and blurred imaging on cemented joints, which makes disassembly and reconditioning necessary. A hot air gun shall be used to apply even heating to the cemented area, so as to soften the original aged UV adhesive or accelerate its thermal degradation. After the heating process, use a rubber pad to grip both ends of the rod lens, and separate the bonded segments gently through lateral offset dislocation. This separation method based on dislocation can achieve uniform stress distribution and avoid chipping or cracking on lens edges that result from direct axial pulling.
Dip toothpicks in polishing compound to grind and polish cemented surfaces to eliminate residual UV adhesive and surface contaminants. Short lens segments can be fixed onto acrylic blocks for polishing. For the middle section of the rod lens with two planar cemented surfaces, secure the lens with the 1.2 mm-opening round tweezers before polishing. Special attention shall be paid to edge regions of cemented surfaces; incomplete residue removal will result in uneven adhesive layer thickness after re-cementing and directly degrade imaging performance.
Residual adhesive appearing as purple striped deposits or patchy agglomerates on fracture surfaces must be fully cleared. If hard particulate contaminants remain on cemented surfaces after wiping with alcohol-moistened cotton swabs, gently scrape them off with toothpicks. Proceed to subsequent operations only after confirming perfectly clean surfaces free of foreign attachments.
First-side bonding operation
Dip the flat cross-section of the processed 0.25 mm needle tool with an extremely tiny volume of UV cement and dispense a droplet at the center of the target cemented surface. Excessive adhesive leads to an overlarge glue layer, impairing thermal resistance and altering the effective refractive index. Place the mating rod lens directly onto the dispensed adhesive after dotting.
Place the assembled rod lens onto the acrylic slider for automatic centering positioning. Inspect coaxial alignment under high magnification; misalignment can be corrected by gently rolling the lens body until the central optical axes are perfectly collimated, then set upright promptly. Leverage the flat opposite surface of the rod lens to stand the assembly vertically on a clean acrylic plate; gravity drives uniform spreading of the adhesive, with excess glue flowing outward toward peripheral edges naturally. Allow a 5-minute dwell time before UV irradiation curing for 5 minutes using the UV lamp. After curing, wipe off extraneous adhesive around the lens periphery and recheck coaxiality and light transmittance.
Second-side bonding operation
Thoroughly clean all previously used tools before starting the second cementing cycle to avoid cross-contamination. Since one side of the rod lens has already been permanently cemented into an integrated curved assembly, stable planar placement as implemented in the first cementing step is unfeasible, increasing operational difficulty accordingly.
Discard the previously retrieved UV adhesive which has been contaminated by prolonged ambient exposure; extract fresh UV cement and perform dotting and assembly following identical procedures as the first side. Without a flat supporting base, manually hold the lens assembly steady post-assembly and rely on molecular interfacial tension to level the adhesive layer while continuously monitoring coaxial alignment. Peripheral adhesive exudation indicates adequate uniform spreading of the glue layer.
Conduct preliminary UV curing for 10–20 seconds to lock relative lens positions stably, then lay the assembly flat for full curing over another 5 minutes. Upon completion of curing, swab excess edge adhesive with alcohol-dampened cotton swabs and re-inspect flatness and coaxiality of the cemented interface.
Post-repair thermal conditioning is implemented to stabilize mechanical performance of the cured adhesive layer. Final tests on imaging clarity and optical transmission quality are carried out to validate compliance with optical path performance specifications.
We will release follow-up detailed operation guidelines and practical repair case studies covering optical component refurbishment processes and repair solutions for various endoscope models. Stay tuned for updates.
