a . System Capabilities. Video systems permit video images to be recorded and stored on print or slide film, video cassette recorders, or computer disks. Microprocessors can be used to digitize video images for storage on a computer disk, or for transfer to other sites by modem and telephone lines. Photographic or video recording provides verifiable data for training purposes and for trend monitoring.
o. lypical Systems. Figure 4-1 shows a typical 35-mm camera and adapter installed on a rigid borescope that has a mounting kit to provide a platform for vibration-free photography. Figure 4-2 shows a typical video adapter system for converting a standard flexible or rigid borescope to a video inspection and documentation system. Figure 4-3 shows a block diagram of a typical video inspection, documentation, storage, and transmission sys- FIGURE 4-1. TYPICAL 35-MM CAMERA AND CAMERA ADAPTER INSTALLATION
ON A RIGID BORESCOPE (Courtesy of Olympus Corporation) Chap 4 Par 402 Page 121
FIGURE 4-2. TYPICAL BORESCOPE VIDEO ADAPTER SYSTEM (Courtesy of Optronics Engineering Corporation) Chap 4 Page 122 Par 402
Rigid Flexible Borescope Borescope Microscope Video Camera Adapter TV Monitor and Video Microscope with a CCD Borescope or Recording Assembly Image Processor at the Probe End Computer Image Digitizing, Processing, and Data Management Modes Telephone Line Modes Remote Computer System GSC.0059.95-1 FIGURE 4-3. BLOCK DIAGRAM OF A TYPICAL VIDEO INSPECTION SYSTEM
c. Hand-Held Video Microscope Imaging System. In some video microscope inspection equipment, the camera, lens, and lighting are all integrated into a flexible, hand-held probe that is taken to the item to be inspected (see Figure 4-4). A solid-state CCD sensor is located in the end of the camera head, and various Chap 4 Par 402 Page 123
lenses can be attached to the camera head to provide the user with magnifications from 0.7 to 800 power and working distances from contact to 600 mm. The instrument provides a high resolution, full color video image; records the image for later use; is portable; and can be customized for a specific application.
instrument is particularly useful in areas where it is difficult to hold a flashlight and mirror while trying to focus a magnifying glass. Some typical uses for the hand-held video microscope in aircraft maintenance are inspection of aircraft seat tracks for cracks (it is a one-hand operation of placing the video microscope head on the tracks and viewing the screen, where previously a mirror and flashlight were required); inspection of composite-material helicopter rotor leading edges for delamination/ damage; inspection of aircraft turbine honeycomb seal rings for defects; and inspection of aircraft rear pressure bulkhead, engine pylon, spar, and main landing gear aft trunnion for defects.
PAI FIGURE 4-4. SCOPEMAN HAND-HELD VIDEO MICROSCOPE IMAGING SYSTEM (Courtesy of Moritex USA, Inc.)
d. Video Measuring Microscope. Video measuring microscopes (see Figure 4-5) are also available. They use a high-quality Chap 4 Page 124 Par 402
zoom microscope (magnification from 8 to 1630 power) with joystick control in conjunction with a high-resolution color video and computer. The SmartScope system contains a set of computergenerated electronic targets and charts for superimposing on the color video image to match the feature being measured. A graphics model that looks like a blueprint of the part is built by SmartScope software as each measurement is completed. The graphics model is stored on a hard disk and can be displayed or printed at any time. Some examples of the use of video measuring microscopes for aircraft maintenance are measurement of hole diameter and locations on castings after they have been reworked and measurement of dimensions of used mechanical parts to determine if they are still serviceable.
FIGURE 4-5. SMARTSCOPE VIDEO MEASURING MICROSCOPE SYSTEM (Courtesy of Optical Gaging Products, Inc.)
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AG 43-204 8/14/97
103. OPTICAL COMPARATORS. Optical comparators are devices that project a magnified silhouette of a small part onto a large projection screen, which is then compared against a magnified outline drawing of the part being inspected. They are used in aircraft maintenance for assessing parts conformity. Figure 4-6 shows a typical schematic of an optical comparator. Optical comparators are available with numerous options, such as screen sizes from 14 to 30 inch diameter, magnifications from 5 to 500 power, computerized control of measurement and movement, computer statistical analysis of data, part programming from blueprint (off-line or pantograph, 0.00005-inch measurement and one minute or arc resolution), and automatic centerline system for detection of shadow edges. Parts with recessed contours can also be measured on optical comparators by using a pantograph. One arm of the pantograph is a stylus that traces the recessed contour of the part, and the other arm carries a follower that is visible in the light path. As the stylus moves, the follower projects a contour on the screen. Optical comparators typically are used to measure threads, gear teeth, hole diameters, distance between holes, angles, and tapers. Figure 4-7 shows a typical optical comparator. Some examples of the use of an optical comparator for aircraft maintenance are measuring dimensions on grinding wheels that are used to rework aircraft turbine blades (if contact type measurements were made in this application, the measuring tools would be damaged by the grinding wheel abrasive); measurement of hole diameter and locations on gearbox castings rework; and measurement of radii on used constant-speed drive shafts to verify that the shear sections would meet new part requirements.
Screen Condensing Reflecting lens mirror Light Magnifying source lens Object FIGURE 4-6. SCHEMATIC OF AN OPTICAL COMPARATOR Chap 4 Page 126 Par 403
FIGURE 4-7. TYPICAL OPTICAL COMPARATOR (Courtesy of Optical Gaging Products, Inc.)
BORESCOPES. A borescope is a long, tubular, precision optical instrument, with built-in illumination, designed to allow remote visual inspection of internal surfaces, or otherwise inac- The tube, which can be rigid or flexible with a wide variety of lengths and diameters, provides the necessary optical connection between the viewing end and an objective lens at the distant, or distal, tip of the borescope. Rigid and flexible borescopes are available in different designs for a variety of standard applications, and manufacturers also provide custom designs for specialized applications. Figure 4-8 shows three typical designs of borescopes.
Chap 4 Par 403 Page 127
Eyepiece lens Relay lens Objective lens Incandescent lamp (a} Eyepiece lens Focusing ring Control handles for lour-way to articulation Interchangeable . Image guide lIOS Objective lens Diopter ring Light guide Protective sheath Light guide exit Light source Projection lamp.
Field of Orbital scan Focus VISW control control Shaft rotation for orbital scan Working lengin - Light guide connector (Inside handle) Light guide To light source (integral or separate (€ ) hree typical designs of borescopes. (a) A rigid borescape with a lamp at the distal end. (b) A flexibl barscope wim a light source. (c) A rigid borescope with a light guide bundle in the shal FIGURE 4-8. THREE TYPICAL DESIGNS OF BORESCOPES (Courtesy of ASM International)
a. Borescope Uses. Borescopes are used in aircraft/engine maintenance programs to reduce or eliminate the need for costly teardowns. Aircraft turbine engines have access ports that are specifically designed for borescopes. Borescopes are also used extensively in a variety of aviation maintenance programs to ensure the airworthiness of difficult-to-reach components.
Borescopes typically are used to inspect interiors of hydraulic cylinders and valves for pitting, scoring, porosity, and tool Chap 4 Page 128 Par 404
marks; inspect for cracked cylinders in aircraft reciprocating engines; inspect turbojet engine turbine blades and combustion cans; verify the proper placement and fit of seals, bonds, gaskets, and subassemblies in difficult-to-reach areas of aircraft and aeronautical equipment; and assess Foreign Object Damage (FOD) in aircraft, airframe, and powerplants. Borescopes may also be used to locate and retrieve foreign objects in engines and airframes.
Optical Designs. Typical designs for the optical connection between the borescope viewing end and the distal tip are as follows: rigid tube with a series of relay lenses, flexible or rigid tube with a bundle of optical fibers, and flexible or rigid tube with wiring that carries the image signal from a CCD imaging sensor at the distal tip. These designs can have either fixed or adjustable focusing of the objective lens at the distal tip. The distal tip also has prisms and mirrors that define the direction and field of view (Figure 4-9). A fiber-optic light guide with white light is generally used in the illumination system, but ultraviolet light can also be used to inspect surfaces treated with liquid fluorescent penetrant or to inspect for contaminants that fluoresce. Some videoscopes with long working lengths use lightemitting diodes at the distal tip for illumination.
55° Bottoming 55* 55° Right angle Circumference 55° p Forward oblique Retrospective FIGURE 4-9. TYPICAL DIRECTIONS AND FIELD OF VIEW OF RIGID BORESCOPES (Courtesy of ASM International) Borescope Selection. Flexible and rigid borescopes are available in a wide variety of standard and customized designs, and several factors can influence the selection of a scope for Chap 4 Par 404 Page 129
particular application. These factors include focusing and resolution, illumination, magnification and field of view, working length, direction of view, and environment.
(1) Focusing and Resolution. In general, the optical quality of a rigid borescope improves as the size of the lens increases; consequently, a borescope with the largest possible diameter should be used. If portions of long objects are at different planes, the borescope should have sufficient focus adjustment to achieve an adequate depth of field. If the borescope has a fixed focal length, the object will be in focus only at a specific lens-to-object distance. To allow the observation of surface detail at a desired size, the optical system of a borescope should also provide adequate resolution and image contrast. If resolution is adequate, but contrast is lacking, detail cannot be observed. For fiberscopes, the resolution is dependent on the accuracy of alignment and the diameter of the fibers in the image bundle. Smaller diameter fibers provide more resolution and edge contrast when combined with good geometrical alignment of the fi-
(2) Illumination. The amount of illumination depends on the diameter of the light guide bundle; therefore, it is desirable to use the largest diameter possible. The required intensity of the light source is determined by the reflectivity of the surface, the area of surface to be illuminated, and the transmission losses over the length of the scope. Rigid borescopes with a lamp at the distal end provide the greatest amount of illumination over the widest area at working lengths greater than 20 feet; however, the heat generated by the light source can damage some materials. Fiber-optic illumination is usually brighter than a lamp at the distal end with scope working lengths less than 20 feet and is suitable for heat-sensitive applications when filters are used to remove infrared wavelengths.
(3) Magnification and Field of View. Magnification and field of view are interrelated, and as magnification is increased, the field of view is reduced. The precise relationship between magnification and field of view is generally specified by the product manufacturer. The degree of magnification in a particular application is determined by the field of view and the distance from the objective lens to the object. The magnification increases when either the field of view or the lens-toobject distance decreases.
(4) Working Length. The working length can sometimes dictate the use of a particular type of borescope. For example, a rigid borescope with a long working length may be limited by the need for additional supports. In general, videoscopes allow a longer working length than fiberscopes.
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8/14/97 AU 43-204 Direction of View. The selection of a viewing direction is influenced by the location of the access port in relation to the object to be observed. Flexible fiberscopes or videoscopes, because of their articulating tip, are often adequate with either a side or forward viewing tip. Circumferential or panoramic heads are designed for the inspection of tubing or other cylindrical parts. A centrally located mirror permits right angle viewing of an area just scanned by the panoramic The forward viewing head permits the inspection of the area directly ahead of the viewing head and is commonly used when examining facing walls or the bottoms of blind holes and cavities. Forward-oblique heads bend the viewing direction at an angle to the borescope axis, permitting the inspection of corners at the end of a bored hole. Retrospective viewing heads bend the cone of view at a retrospective angle to the borescope axis, providing a view of the area just passed by the advancing borescope and are especially suited for inspecting the inside corners of valve body and actuating cylinder castings.
Environment. Flexible and rigid borescopes can be manufactured to withstand a variety of environments. Although most borescopes can operate at temperatures from -30 to 150 degrees F, specially designed borescopes can be used at temperatures to 3500 degrees F. Borescopes can also be manufactured for use in liquid media. Special borescopes are required for use at pressures above ambient and in atmospheres exposed to radiation.
Radiation can cause lenses and fiber-optic bundles to turn brown.
when a borescope is used in atmospheres exposed to radiation, quartz fiberscopes are generally used. Scopes used in a gaseous environment should be made explosion-proof to minimize the potential of an accidental explosion.
Rigid Borescopes. Rigid borescopes are generally used in aircraft maintenance applications where there is a straight line access path to the area to be inspected. Some typical uses for rigid borescopes in aircraft maintenance are inspection of landgear actuators and struts for corrosion; cracks and scratches on bore walls; inspection for corrosion and cracks of wing stringers, wing attachment fittings, spars, and other aircraft structural members; inspection of engine cylinder sleeves, pistons, and valves for damage; and inspection of aircraft turbines for cracks, corrosion, damage by foreign objects, and erosion.
Rigid borescope sizes range in lengths from 2 inches to over 100 feet and in diameters from 0.035 to 2.75 inches. Magnification is usually 3 to 4 power, but powers up to 50 are available. They are available with fixed and adjustable focus eyepiece. The illumination system is either an incandescent lamp located at the distal end or a light-guide bundle made from optical fibers that conducts light from an external source. The fiber-optics, lightguide bundle has no electrical contacts at the distal end and produces cold light to minimize explosion hazards. Rigid borescopes are available with a variety of viewing heads for se- Chap 4 Par 404 Page 131
AC 43 - 204 8/14/97 lection according to the application. They generally have a 55- degree field of view although fields of view can range from 10 to 90 degrees. The distal tips are generally not interchangeable, bility to rotate the optical shaft from 120 to 370 degrees for scanning purposes, and others have movable prisms at the tip for longitudinal scanning.
(1) Basic Design. The rigid borescope typically has a series of achromatic relay lenses in the optical tube.
lenses preserve the resolution of the image as it travels from the objective lens to the eyepiece. The tube diameter of these borescopes ranges from 0.035 to 2.75 inches. The illumination system can be either a distal lamp or a light-guide bundle, and the various features may include rotating optical shait, various viewing heads, and adjustable focusing of the objective lens.
(2) Micro-borescopes. Micro-borescopes are smalldiameter borescopes having an integral light-guide bundle and a one-piece rod lens for maximum resolution with a minimum diameter. Some typical uses for micro-borescopes in aircraft maintenance are inspection for damage within fuel nozzles, electronic components, instruments, hydraulic components, castings, and other miniature equipment. The lengths of micro borescopes range from 2 to 32 inches, and the diameters range from 0.020 to 0.125 inch. They are available with forward, forward oblique, and right angle views; support stands with micrometer adjustable fixturing; photo and video adapters; up to 30-power magnification;
and fixed or ocular focus. Figure 4-10 shows a typical microborescope.
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