The bending section of the endoscope is the most core moving part of the flexible endoscope. Relying on the internal artinged part and the traction steel wire, the lens can be turned up and down, left and right, which determines whether the endoscope can reach the narrow cavity smoothly, which directly affects the operation feel, service life and product stability. Whether it is new product research and development, or old mirror repair and replacement, the selection of bending sections needs to be comprehensively evaluated from multiple dimensions of structure, specifications, materials, processes and test indicators.

I. Clarify the application scenario first and lock in the basic specifications.

The first step of selection is to determine the use scenario and size boundary to avoid specification mismatch.

1. Outer diameter and inner diameter: The outer diameter determines the minimum aperture diameter of the channel. OD0.9/1.2/1.6/2.0/2.35mm and other micro-small bending parts specifications, from 9.2/11.5/12.5/14.5mm medical large size. The inner diameter needs to reserve the assembly space of optical fiber, image harness, instrument channel and traction wire. Insufficient inner diameter will cause wire harness compression and steering jam.

2. Effective bending length: The longer the effective activity length of the bending section, the better. In the scene of narrow cavity, the short bending section is more accurate; in the scene that requires large-angle bending, it is necessary to match the longer effective bending section.

3. Degree of freedom and bending angle: divided into two-way bending and four-way bending. Medical endoscopes mostly use four-way (up, down, left and right); small industrial endoscopes and disposable endoscopes can choose two-way. At the same time, check the maximum bending angle. If the angle is not enough, there will be a blind area of vision; if it is too large, it is easy to get stuck in the joints and the outer sheath will tear.

4. Adaptation method: the riveting bending part has strong stability and durability for reuse, and is mostly used for repeatable medical endoscopes; laser cutting integrated snake bone, compact structure, suitable for disposable minimally invasive endoscopes.

II. Material selection, balance toughness, strength and corrosion resistance

The material directly determines the fatigue life and environmental adaptability. The mainstream materials are divided into two categories:

• Medical stainless steel: strong versatility, mature processing, corrosion resistance, controllable cost, the most commonly used snake bone tube material, suitable for conventional endoscopy. But there is an upper limit to the fatigue life of repeated bending.

• Nickel-titanium alloy (memory alloy): good elasticity, excellent fatigue resistance, not easy to plastic deformation after bending, suitable for high-frequency repeated operation of high-end endoscopes; the disadvantage is that the processing is difficult and the cost is higher. At the same time, pay attention to the materials of rivets and pins. The supporting connectors need to be matched with the body material of the bending part to prevent electrochemical corrosion.

III. Focus on evaluating the structure and processing technology

The bend of the reusable endoscope is made of a joint joint, and the details of the process determine the feel and reliability.

1.Joint hinging accuracy: The hole tolerance of the joint and rivet hole of the joint must be precise. If the tolerance is too large, there will be gaps and jitter in the steering, and the control position will be large; if it is too tight, the bending resistance will be large, and the operation will be difficult. High-quality products rotate smoothly between single sections, without jamming and space.

2. Traction wire guide groove: The steel wire guide groove inside the joint is the key. The guide groove is smooth and burr-free, which can reduce the wear of the traction wire and greatly extend the life of the whole machine; the rough edge will continue to cut and grind the wire, and it is very easy to break the wire.

3. Surface treatment: metal surface deburring and polishing. The burrs will not only cut the outer rubber sheath, but also produce stress concentration under repeated bending, causing joint fracture.

4. Concentricity: The concentricity of the whole snake bone should meet the standard, and it should not be eccentric when bending, so as to avoid uneven force on the traction wire after assembly and unilateral overload.

IV. Must-see performance test indicators to screen qualified products

In the procurement or sample stage, several core tests need to be verified:

• Bending fatigue test: continuous back and forth bending to assess the anti-fatigue life. Medical endoscopes have extremely high requirements for the number of fatigues, and the curved part of the disposable endoscope can be selected according to the low fatigue index.

• Bending torque and return neutrality: Under the same bending angle, the torque is uniform and moderate. After release, it can return to the positive smoothly, and there is no rebound jam.

• Anti-torsion performance: under torsion conditions, the joints will not be unritted or dispersed. Disintegration cannot occur when the endoscope is rotated in the cavity.

• Sealing adaptability: The bend of the endoscope itself is not waterproof, but the outer layer needs to be covered with a sheath. When selecting, it is confirmed that the outer contour of the bending part is smooth, does not cut the sheath, and meets the overall waterproof requirements of the endoscope.

V. Key points to avoid buying pitfalls

1. Only look at the appearance without testing: the brightness of the surface does not mean that the internal hole position and the guide groove are qualified. Many samples look smooth statically, and the wire is broken after dozens of fatigue tests.

2. Blindly pursue super-large bending angles: super-large angles will sacrifice structural strength, and joint collapse and sheath breakage are more likely to occur in clinical/industrial use.

3. Ignoring assembly matching: snake bone, wave tube, traction wire and sheath are the whole set of systems. If the snake bone is purchased separately, it is easy for the whole set of control to be uncoordinated.

4. Confusing disposable and reusable structures: disposable snake bone lightweight design, which cannot be used for repeated operations, is extremely easy to damage quickly.

Conclusion

The bending section of the endoscope is the "joint" of the endoscope. The core of the selection is scene priority, specification matching, process bottoming, and fatigue verification. The four elements of outer diameter, bending angle, material and hinging process are indispensable. Only by completing the fatigue, torque and jam test in the sample stage, and then purchasing in bulk, can we ensure the stability of the endoscope product and reduce the risk of later maintenance and failure.