Flexible Videoscopes With CCD Probes. Flexible videoscopes have CCD imaging sensors at the distal tip to electronically transmit color or black and white images to a video moni- The fiber-optic image bundle inside the insertion tube is replaced by a wire assembly to carry video information. Videoscopes with CCD imaging sensors produce images with spatial resolutions on the order of those described in Figure 4-20.
90° FIELD OF VIEW 60° FIELD OF VIEW 30> FIELD OF VIEW UMM LIN. UMM LIM. UMM LIN.
102 T - USEABLE 4020 USEABLE ISEABLE - RESOLUTION 300 RESOLUTION 300 RESOLUTION 300 200 200 100 100
• ~ 20 80 100 40 6D 10%
OBJECT DISTANCE MM OBJECT DISTANCE MM OBJECT DISTANCE MM WIN. = Lines per inch UMM = Lines per millimeter SHARP FOCUS FIGURE 4-20. TYPICAL CCD VIDEOSCOPE RESOLUTION (Courtesy of Welch Allyn, Inc.)
The resolution of videoscopes, like rigid borescopes and flexible fiberscopes, depends on the object-to-lens distance and the field of view, since these two factors affect the amount of magnification. Generally, videoscopes produce higher resolution than fiberscopes, although riberscopes with smaller diameter fibers can be competitive with the resolution of videoscopes. A primary advantage of videoscopes is their longer working length. with a given amount of illumination at the distal tip, videoscopes can return an image over a greater length than fiberscopes.
features of videoscopes include (1) the display can help reduce eye fatigue (but does not allow the capability of direct viewing through an eyepiece); (2) there is no honeycomb pattern or irregular picture distortion as with some fiberscopes (see Figure 4-21); (3) the electrical image signal allows digital image enhancement and the potential for integration with automatic inspection systems; and (4) the display allows the generation of reticles on the viewing screen for point-to-point measurements.
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• FIGURE 4-21. COMPARISON BETWEEN VIDEOSCOPE AND FIBERSCOPE IMAGES (Courtesy of Welsh Allyn, Inc.)
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Borescopes With Special Features. Borescopes, fiberscopes, video systems, and related equipment are being used for more purposes, more complex inspections, and even some limited repair applications. Some of the borescope products briefly described are measuring borescopes and fiberscopes, working channels, flying probe, VideoHook Probe, power blending borescope, and ShadowProbe™.
(1) Measuring Borescopes and Fiberscopes. Measuring borescopes and fiberscopes contain a moveable cursor that allows measurements during viewing (see Figure 4-22). When the object under measurement is in focus, the movable cursor provides a reference for dimensional measurements in the optical plane of the This capability eliminates the need to know the objectto-lens distance when determining magnification factors. Measuring borescopes and fiberscopes can be used in aircraft maintenance for measuring cracks in aircraft turbine liners, blade damage, etc.
FIGURE 4-22. VIEW THROUGH A MEASURING FIBERSCOPE (Courtesy of Olympus Corporation) Working Channels. Working channels are used in borescopes and fiberscopes to pass working devices to the distal Figure 4-23 shows a retrieval tool in a working channel picking up a screw inside a machine. Table 4-3 shows some typical devices for use in working channels. working channels are presently used to pass measuring instruments, retrieval devices, and hooks for aiding the insertion of thin, flexible fiberscopes.
working channels are used in flexible fiberscopes with diameters Chap 4 Par 404 Page 147
as small as 0.106 inch. Working channels are also under consideration for the application and removal of dye penetrants and for the passage of wires and sensors in eddy current measurements.
Retrieval tools are typically used in aircraft maintenance for removing objects from aircraft turbines and appliances that may have been dropped during maintenance and repair work.
FIGURE 4-23. RETRIEVAL DEVICE IN BORESCOPE WORKING CHANNEL (Courtesy of Olympus Corporation) Chap 4 Page 148 Par 404
TABLE 4-3. TYPICAL WORKING CHANNEL DEVICES (Sheet 1 of 2) (Courtesy of Olympus Corporation)
TYPE DIAGRAM COMMENT
SAMPLING FORCEPS Standard Round jaws for normal grasping.
(Fenestrated 20 . Ellipsoid Longer jaws in order to grasp more (Fenestrated) than the standard type.
3. Alligator Designed for scooping with side opening jaws.
4. Crescent For lassoing foreign objects.
5. Hexagonal For lassoing foreign objects.
6. Oval For lassoing foreign objects.
B. GRASPING FORCEPS Tripod Good for gripping larger solid ob- Jects
2. Hooked Jaws Good for clenching into softer objects.
3. "W" Shaped collects flat foreign objects,
e.g., coins.
4. Alligator Jaws Designed to prevent slipping, grip well.
5. Rat Tooth Jaws hinge together to provide good grip.
6. Pelican Type Useful for awkward foreign objects.
7. Basket Type Basket tightens up on an object for removal, e.g., ball bearings.
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TABLE 4-3. TYPICAL WORKING CHANNEL DEVICES (Sheet 2 of 2) (Courtesy of Olympus Corporation) B. GRASPING FORCEPS (Continued)
8. Rubber Tipped Jaws Good for grasping smooth surfaces.
c. MAGNETIC EXTRACTORS Cylindrical Shape Good for retrieving ferromagnetic foreign objects.
(3) Flying Probe. In the so called Flying Probe, a flexible video borescope uses an air jet microthruster to help position a flexible video probe in an area to be viewed (see Figure 4-24). The air jet force can be used to pull the distal tip of the flexible video borescope through cavities to locations previously unreachable by traditional borescope techniques. The air jet microthruster system is particularly suitable for aircraft engine and structural inspections that would otherwise require the use of guide tubes.
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8/14/97 AC 43-204 FIGURE 4-24. FLYING PROBE FLEXIBLE BORESCOPE (Courtesy of Welch Allyn, Inc.)
(4) VideoHook Probe. This probe consists of a special hook attachment at the distal tip of a flexible video probe (see Figure 4-25). The special hook attachment can be hooked onto the first stage turbine blade of a Pratt & Whitney JT8D series engine for more complete viewing of the second-stage, high-pressure turbine vanes. After hook attachment, the engine rotor is slowly rotated manually to allow viewing of the full second-stage vanes.
The hook attachment can be slipped onto the distal tip of the Chap 4 Par 404 Page 151
VideoHook Probe, with no special tools or working channel required, and can be easily removed when the inspection is completed. The hook is made of special soft aluminum that will reduce damage should it be left behind in the engine.
FIGURE 4-25. VIDEOHOOK PROBE ATTACHMENT FOR A FLEXIBLE BORESCOPE (Courtesy of Welch Allyn, Inc.)
(5) Power Blending Borescope Kit. A combined borescope and blending system can detect and repair (i.e., blend) foreign object damage on the 7th-stage compressor blades of JT8D-200 series engines (see Figure 4-26). The power blending borescope allows engine repair with the engine installed on the aircraft and without engine disassembly. The power blending procedure is ac- Chap 4 Page 152 Par 404
8/14/97 AC 43-204 complished with a specially designed borescope and working chan- A rotary file or stone is connected to a drive cable that passes through the working channel and a drive motor connected to this cable rotates the cutter/stone, with speed controlled by a variable-rate foot pedal. The technician operates the tool to blend damaged blades while viewing the work process on a video monitor. A video micrometer is also incorporated into the system to allow measurements to be taken.
FIGURE 4-26. POWER BLENDING BORESCOPE KIT (Courtesy of Machida, Inc.)
(6) ShadowProbe™. The ShadowProbe™ measuring fiberscope system measures cracks, defects, and small objects while conducting remote inspections (see Figure 4-27). The Shadow- Probe™ system is designed to make measurements without comparison to reference objects by casting a shadow pattern across the system image, which is used by a system on-board computer to de- Chap 4 Par 404 Page 153
termine magnification, distance, object size and dimensions. Operators manipulate a cursor on a video screen to locate the shadow and objects to be measured. The video screen is electronically corrected for lens distortion and has built-in automatic calibration for magnification from near or far away, over a full 85-degree viewing field.
there is keyboard access to three different measurement modes to allow measurement of linear distance, depth, or objects at skewed angles.
TREM BIRDANCE
LEN OF CATE REACHER PARLAN FIGURE 4-27. SHADOWPROBE™ MEASURING SYSTEM (Courtesy of Welch Allyn, Inc.)
g. Borescope Selection Questions. By answering the following questions and reviewing the information in this document and borescope manufacturers' literature, a prospective borescope user can determine which borescope offers advantages over another for Chap 4 Page 154 Par 404
8/14/97 AU 43-204 a specific inspection. The answers to these questions can also be used as a guide for selecting or purchasing the most effective borescope for a particular application.
(1) Access Opening Inside Diameter (i.d.). How wide is the borescope entry point and what is the smallest i.d. that the borescope should pass through?
(2) Travel Path Geometry. Is the travel path geometry straight or curved? If a guide tube is required, what is the most severe bend the guide tube should negotiate and what is the
i.d. at this point?
(3) Guide lube. is a guide tube needed to racilitate borescope insertion? Is it offered with the borescope? Will it have to be custom manufactured or formed on site?
Borescope Length. What is the minimum length needed to travel to reach the inspection site? Is additional length needed for protection of the eyepiece or safety of the inspector using the borescope? Is a drawing available to study and lay out the access path requirements? The length of the borescope insercion probe should be well thought out, since it is related to costs and a longer insertion tube can be difficult to control ir an inspection with a shallow travel path. In many circumstances, two separate borescopes for different inspections will be more economical than using one scope for multiple purposes. The probability of damage and cost of repair increases with increased borescope working length.
Target Inspection Area Location. Where is the target inspection area in relation to the distal tip when the borescope reaches the target? If a flexible borescope is being considered, is there room in the work piece channel for articulating the bending section to face the target inspection area directly? How far from the target inspection area will the borescope tip be during the inspection? will variable magnification and direction of view tip adapters be required now or later?
(6) Resolution. What is the smallest dimension needed to be seen? Can the defect be large or are microscopic defects also harmful? What will happen if a microscopic defect is missed?
Frequency of Borescope Use. How often will the borescope be used? How long will the borescope be used for each inspection? How many inspections will be made for each use?
many people will use the borescope?
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Documentation. Will photo or video documentation of the inspection/defect be needed?
(9) Verification of Borescope Specifications. Can the borescopes specifications be verified independent of the supplier?
(10) Borescope Operation. Is an operating manual provided with the borescope that is adequate for the user's needs?
Is training available to improve inspection results and reduce wear and tear on borescopes?
405. LIST OF EQUIPMENT USED IN VISUAL INSPECTION. Appendix G provides a partial listing of equipment useful in accomplishing visual inspections.
406.-499. RESERVED.
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