A borescope (or borescope) is a endoscope which fulfills the same function as the corresponding medical devices, but is especially applicable in workshops and in industry automotive, naval Y aeronautics to inspect inaccessible areas, such as the interior of engines, turbines, machines and installations. In fact, the basic principle of a borescope and an endoscope are identical in that it involves directing clear, cool light through the instrument into hard-to-reach internal cavities to enable clear vision and, at the same time, objective documentation through image transfer.
In World War II, borescopes primitive to examine the interior orifices of large firearms for defects. Over time, technology perfected the instrument as we know it today.
In the general sense, the borescope is a low magnification optical instrument (3x to 4x), usually small in diameter (<20 mm) and relatively large in terms of overall length, often 50 to 100 times its diameter. The optical design of a borescope It is influenced by these dimensional limitations, by the precision requirements of optical components, and by the high level of image quality that is generally required.
Traditionally, a borescope consists of three major optical components: the objective lens, a optical image relay system (known as “Relay”) and the ocular, as we see in the figure below. The objective lens forms an internal image of the illuminated object and the eyepiece magnifies that image that it presents to the observer’s eyes.
The configuration of the objective lens it is determined by the final specifications of the instrument, such as field of view, lens speed (f / number), distortion, and image quality. The configuration of the image relay system is given by the allowable diameter of the lens, the required length of the instrument, the allowable reduction in brightness or saturation at the periphery of the image (Vignetting) and image quality. The selection of ocular It is usually done on the basis of the overall magnification required, the apparent field of view, and the comfort to the eye.
In today’s market there are several types of borescope, from the simplest and most economical to the most sophisticated, equipped with image or video devices that offer the best resolution.
Let’s see in detail what are the types of borescope and its main uses.
They are comparable to a periscope, with a stem or sheath and a special crystal tip that in addition to providing the borescope Highly resistant to damage and wear, it guarantees great protection for the optical system.
Depending on the way they transmit the image, the rigid borescopes They are subdivided into two types:
- Oscillating prism borescopes: they use a lens system for image transfer and consist of an oscillating prism at the tip of the stem. With the help of a targeting handle, the visual direction can be progressively adjusted between 0 ° and 140 ° and the stem can be rotated 400 °. It is the one shown in the figure above.
- Semi-rigid borescopes: they use a fiber optic bundle housed on a rigid stem and, therefore, its diameter is smaller than that of the oscillating prism borescopes. The advantage is that, unlike the previous one, they allow the inspection of winding zones.
The rigid borescopes with oscillating prism They have the limitation that the access to what you want to observe must be in a straight line, therefore, they are more suitable for certain tasks such as the inspection of automobile cylinders, fuel injectors, hydraulic manifold bodies and weapon manufacturing.
The criteria for selecting a borescope are generally image clarity and accessibility. If we have two instruments of similar quality, the rigid borescope from larger diameter and shorter length will provide the better picture.
A flexible borescope includes a fiber optic bundle housed in a flexible sheath that divide the image into pixels. The difference with the semi-rigid borescope What we cited above is that it lacks a rigid stem. It is also known as fiberscope and it can be used to access cavities that surround a curve, such as a combustion chamber, in order to observe the state of compressed air inlets, turbine blades and seals without the need to disassemble the engine.
The flexible borescopes they experience pixelation and crosstalk due to the fiber optic image guide. Depending on the number of fibers and the construction used in the fiber image guide, the image quality varies widely between the different models of flexible borescopes.
The components of the articulation mechanism, the width of the articulation, the field of view and the viewing angles of the objective lens are important parameters in a flexible borescope, as is the flexible image retransmission system to offer the best possible resolution to the observer. The minimum quantity for this is 10,000 pixel beams, while in larger diameter borescopes the best images are obtained with a greater number of fibers in beams of 15,000 to 50,000 pixels. The ability to control the light at the end of the insertion tube allows the user to make adjustments that can greatly improve the clarity of video or still images.
A video borescope is similar to flexible borescope, but at the end of the flexible tube uses a miniature video camera that makes it possible to capture video or still images in the depths of equipment, engines and other dark spaces.
As a remote visual inspection tool, the ability to capture video or still images for later inspection is a huge benefit. A display on the handle shows the camera view and the viewing position can be changed via a joystick or similar controls. Since the optical guide complex is replaced with a low-cost electrical cable, the videoboroscopes they can be much less expensive and, depending on the camera’s specifications, can have better resolution.
The costs of videoboroscopes High-end can range from $ 10,000 to $ 50,000, depending on the manufacturer, options, and specifications. The videoboroscopes Battery-powered, easy-to-use, 3-inch 320 x 240-pixel or larger LCD screens range from $ 100 to $ 400. In many of these models, the video camera and hose are submersible.
In the following video we see an example of a video borescope and its employment in an automotive workshop.
Other uses of the borescope
The borescopes have also found application in nondestructive testing techniques in welding, for example, for the recognition of surface defects, imperfections, porosities, cracks, corrosion, delaminations, protrusions, leaks, losses of protective coatings, deformations and wear.
They are also used borescopes in machined or cast part fabrication to inspect critical interior surfaces for burrs, surface finish, or complete through holes. Other common uses include forensic applications in law enforcement and building inspection, as well as weapon manufacturing to inspect the interior bore of a firearm.
The wide range of borescopes of all kinds is completed with a series of accessories not only to adapt them to monitors, computers, digital cameras, conventional cameras and camcorders, but also to optimize performance. In addition to these adapters and the corresponding cables (USB, composite video or S-video, etc.) the variety of accessories ranges from light sources, mounting tripods and instrument holding clips to wide angle and x2 magnification accessories for better vision.
All this is complemented by various types of software in order to combine, when necessary, visual inspection with computer analysis, which facilitates monitoring and planning work thanks to the storage of information and images in databases. Teams that collect and analyze data, update standards, and expand certification programs allow the visual inspector to focus solely on data collection, leaving all calculations to the computer.
Video of a borescope inspecting an engine block