CHAPTER 4. EQUIPMENT USED IN VISUAL INSPECTION
400. GENERAL. The following chapter describes the various aids to vision used in visual inspection. In general, they consist of mirrors, magnifiers, and various schemes for conveying images from inaccessible sources to where they may be seen.
a. Inspection Mirrors. Inspection mirrors are used to view areas that are not in the normal line of sight. Table 4-1 shows some of the typical types of inspection mirrors that are available for inspection of hidden areas.
TABLE 4-1. TYPICAL INSPECTION MIRRORS (Courtesy of McMaster-Carr Supply Company) (Sheet 1 of 2) Ball-Joint Telescoping Inspection Mirror.
This inspection mirror has tempered spring steel'image or magnifying) to move 360° for double ball-joint links to allow mirror viewing in any position. Nonrotating inner hex rods on telescoping models prevent mirrors from swinging out of alignment. Replacement mirrors are available.
b. Spring-Loaded Inspection Mirror. This inspection mirror has a spring-loaded plunger to tilt the mirror 90°. The mirror is returned to the straight position by tripping a locking device. Single-handed operation allows inspection without removing the mirror from the work area.
Telescoping Inspection Mirror with Magnet.
This inspection mirror can be used to find lost nuts, bolts, and other small parts then pick them up with the magnet in the handali-joint to hold glass mirror at any angle. the telescoping handle has a double Electrical Component Inspection Mirror.
This inspection mirror is extra thin so it can be used to inspect under and around small electrical components. The 90-degree mirrors have beveled edges to match inspection surfaces. Handles are spring-mounted.
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TABLE 4-1. TYPICAL INSPECTION MIRRORS (Courtesy of McMaster-Carr Supply Company) (Sheet 2 of 2)
e. Electrically Insulated Inspection Mirror.
This inspection mirror is electrically insulated to prevent dangerous shocks or shorts when inspecting near sources of electricity.
İ . Adjustable Angle Illuminated Inspection Mirror. This inspection mirror has a light and adjustable mirror at the tip that can be controlled with the thumb.
Magnetic Base Inspection Mirror. This inspection mirror has magnets in a molded nylon base that allows mounting in the work area.
Two ball joints allow adjustment of the glass mirror.
Long Reach Extension Inspection Mirror.
This inspection mirror has a nonconducting handle which extends from five to sixteen feet and it has a nine- by nine-inch glass mirror with light.
Suction Cup Inspection Mirror. This telescoping arm inspection mirror attaches with three suction cups to any hard smooth surface.
The telescoping arm can be extended up thirty inches. The four-inch-diameter unbreakable mirror is true image on one side and magnified image on the other.
Illuminated Inspection Mirror. This penlight inspection mirror has a Lucite rod that directs light on an adjustable plastic frame mirrOr.
b. Simple Magnifiers. A single converging lens, the simplest form of a microscope, is often referred to as a simple magnifier. Magnification of a single lens is determined by the equation M = 10/f, where M is the magnification, f is the focal length in inches, and 10 represents the average minimum distance at which objects can be distinctly seen by the unaided eye.
example, using this equation, a lens with a focal length of 5 inches has a magnification of 2, or is said to be a two-power lens (sometime written 2X). Table 4-2 shows some of the typical types of simple magnifiers that are available.
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TABLE 4-2. TYPICAL SIMPLE MAGNIFIERS (Courtesy of McMaster-Carr Supply Company) Folding Case Magnifiers.
magnifiers single glass or acrylic plastic lenses which can be combined for magnification from 3 to 20 The lenses swing out when needed and the plastic case acts as a Focal lengths vary from 1/2 to 1/2 inches depending on lens combina- Pocket Magnifiers. These magnifiers contain single glass or acrylic plastic lenses mounted in a case that slides open and locks shut to protect the lens when placed in the pocket.
Overall size is 1 5/8 inches by 2 1/4 in 3X and 5X with focal length of 3.3 inches and 2 inches.
Round and Rectangular Magnifiers.
These magnifiers have a sculptured plastic handle and lens frame and are available with glass or scratch resistant acrylic plastic lenses. The glass lenses have 2X magnification, lens diameters from 2.75 to 5.32 inches and focal lengths from 6 to 13 inches.
acrylic lens have 2.5% to 3X (with a 5X bifocal insert), lens diameters are from 2 inches and focal lengths from 10 to 2 inches.
d. Attached Case Magnifiers. These magnifiers have an all in one case that protects the lens and serves as a handie. A 2X model has a glass and vinyl case; 3X model has an acrylic lens and plastic case. Lens diameters are 2 inches and 1.5 inches and focal lengths are 5 inches and 2.5 inches.
Working Distance. The focal length of a simple magnifier and its working distance are approximately the same.
example, suppose that it is desired to examine a part without removing it and the magnifier cannot be placed nearer than 3 inches. Therefore, a magnifier with a working distance (focal length) of at least 3 inches is required. From the equation M = 10/f, a three-power lens is required.
(2) Field of View. The field of view is the area seen through the simple magnifier. The diameter of the field of view Chap 4 Par 400 Page 119
of a simple magnifier is less than its focal length. Selection of a magnifier with proper field of view is important. For example, if a large object is to be examined, the time involved using a 20-power magnifier (with a field of view slightly greater than 3/8 inch) would be prohibitive.
(3) Depth of Field. Depth of field is the term used to indicate the distance a magnifier can be moved toward or away from an object, with the object remaining in good focus. At other distances the object is out of focus and not sharply defined. Depth of field varies with the power of the lens and is comparatively greater in lower-power magnifiers, decreasing as the power of the lens increases.
nifiers with single and multiple lenses jeweler's eye loupes, use in conducting visual inspections include: hand-held maii- MAGNIFYING DEVICES. Some magnifying devices recommended luminated magnifiers, pocket/desk type microscopes, toolmaker's nicroscopes, rigid/flexible borescopes, and video imaging systems. These devices are available with numerous features, such as 1 to 2000 power, self-contained illumination, adjustable varible magnification (zoom), stereo viewing, data storage/ trans.
nission, computer generated electronic alignment targets, anc measuring capability.
a. Selecting Magnification Power. Magnification power and field of view are interrelated, and, in general, as magnification power is increased, the field of view is reduced. Therefore, it is important to select a magnification power that will provide the proper field of view for the part being inspected. when inspecting a large area, the time involved could be prohibitive if high power magnification (with a small field of view) is used.
Therefore, the recommended procedure is to first use low power nagnification (with a large field of view), mark questionable areas, and then examine marked areas using high power magnification. The precise relationship between magnification power and field of view of a product is usually specified by the manufac-
nifier depends on its light collecting ability, which depends on its diameter and focal ratio (focal length divided by diameter).
monitor or a photograph allowe inspectors to share analysis, de- cisions, knowledge, and skills when making visual inspections. PHOTOGRAPHIC AND VIDEO SYSTEMS. An image on a video Photographic and video systems are available which attach to the eyepieces of borescopes, fiberscopes, and microscopes for documentation and analysis of visual inspection images. Video systems are also available that have a charge-coupled device (CCD) image sensor at the probe end of the borescope or microscope, which allows wire rather than fiber optic transmission of the image.
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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.
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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