# Patent

## Title
Apparatus for searching for and detecting defects in parts by endoscopy

## Abstract

Apparatus for searching for and detecting defects on parts that are substantially inaccessible, being located behind a wall, the apparatus comprising a first endoscope for illumination in visible light and for observation, the first endoscope and pipes for feeding and spraying penetration test substances being housed together in a rod which can be passed through an orifice in the wall in order to examine a part, the apparatus further comprising a second endoscope independent of the first endoscope and the rod for illuminating in ultraviolet light and for observing the portion of the part that has been treated by the penetration test substances.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is a Divisional Application of U.S. Ser. No. 10/880,502, filed Jul. 1, 2004, which is hereby incorporated herein by reference in its entirety, and claims the benefit of priority from the French patent application No. 03 08156 filed Jul. 4, 2003.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to endoscopic apparatus for searching for and detecting defects in parts that are substantially inaccessible, being located behind a wall.
2. Description of the Background
It is already known to inspect internal components of equipment or a machine by means of an endoscope, i.e. an elongate optical instrument of small diameter that is passed through a small orifice in a wall in order to examine the appearance of components that are located on the other side of the wall. This makes it possible in particular to inspect the blades of a turbomachine such as an airplane turbojet or turboprop, without dismantling the turbomachine.
Nevertheless, the ability to detect defects is limited by the resolution of the optical system of the endoscope, by the illumination, by the orientation of the endoscope relative to the surface under observation, and by the nature of the defects, amongst other things.
It is also known to seek defects on machine components by using a penetration test technique, which consists in depositing organic substances on the surface under examination of a component and in observing the results under ultraviolet illumination. It is thus possible to detect surface discontinuities such as cracks or fissures that are of very small dimensions, and that are invisible under normal illumination, by depositing a fluorescent dye on the component, which dye penetrates into the surface discontinuities, and then by washing and baking or drying the corresponding surface of the component, and subsequently depositing a developer to reveal the fluorescent dye that has infiltrated into the surface discontinuities. The component is then illuminated in ultraviolet radiation which excites the fluorescent dye, which responds by emitting radiation at some other wavelength, for example of a green color in the visible spectrum.
This penetration test technique generally requires the machine under examination to be disassembled more or less completely.
Proposals have already been made, in document U.S. Pat. No. 4,273,110, to combine the techniques of endoscopy and of penetration testing in a single instrument which comprises, in an elongate cylindrical sheath of small diameter, a quartz tube for transmitting ultraviolet light and visible light towards an end of the instrument that is close to the component under examination, a light pipe containing lenses to observe an illuminated zone of the component, and three pipes for feeding and spraying penetration test substances onto the component under examination. An optical filter that stops visible light is removably mounted at the other end of the instrument between the quartz tube and a light source that emits in the visible and in the ultraviolet, so as to enable the component to be illuminated alternately in visible light and in ultraviolet light. The outside diameter of the sheath of the instrument is small enough to enable it to pass through an endoscope orifice having a diameter of about 9 millimeters (mm).
That prior art instrument presents several drawbacks:
The illumination of the component in ultraviolet light takes place via an axial outlet in order to avoid using reflecting mirrors which are excessively penalizing 30 in terms of size and light absorption. The outlets of the spray pipes are necessarily axial, as are the outlets for illumination and for the observation means, thereby greatly restricting the use of the instrument. In addition, the section of the observation light pipe is very small, since said pipe must leave sufficient space inside the sheath to enable the quartz tube and the pipes for feeding and spraying penetration test substances to be installed, such that when the instrument is used with ultraviolet illumination, it can pick up only a small fraction of the light emitted by the penetration test substances, and therefore does not enable observation to be performed reliably.
OBJECTS AND SUMMARY OF THE INVENTION
A particular object of the invention is to provide a solution to this problem which is simple, satisfactory, and inexpensive.
The invention seeks to provide apparatus combining the techniques of endoscopy and penetration testing, while avoiding the drawbacks of known means.
To this end, the invention provides apparatus for searching for and detecting defects on parts that are substantially inaccessible, being located behind a wall, the apparatus comprising a rigid tubular cylindrical rod of small diameter for passing through an endoscope orifice in the wall, pipes received in the rod for depositing penetration test substances on a portion of the part under examination, and light guide and image transmission means received in the rod to illuminate and observe said portion of the part under examination, wherein the light guide and image transmission means are constituted by a first endoscope that operates with visible light mounted axially in the rod and surrounded by pipes for air and penetration test substances, said endoscope having a tube that is rectilinear in which the visible light guide means and the image transmission means are mounted in parallel, and wherein the apparatus further comprises a second endoscope that operates with ultraviolet light, independent of the first endoscope and of the above-mentioned rod for observing the portions of the part that has been treated by the penetration test substances.
In the apparatus of the invention, it is the visible light endoscope that is housed together with the pipes for penetration test substances in the cylindrical rod, which is used solely for observation in visible light of the portion of the part onto which the test substances have been sprayed. The effects of these substances are then observed by means of the second endoscope whose optical performance is not restricted by its cross-section being reduced because of the presence of pipes for feeding test substances being housed in a tube of dimensions that are small enough to allow it to be passed through an endoscope orifice.
Illuminating the portion of the part that is to be treated in visible light suffices to ensure that the test substances are properly deposited, and illuminating said portion of the part in ultraviolet light by means of the second endoscope makes it possible to observe clearly the effects of the test substances, thereby optimizing detection of defects in the parts under examination.
According to another characteristic of the invention, the light guide means of the first endoscope comprise an optical fiber cable extending from one end to the other of the tube, the cable having a bent outlet end that is oriented obliquely relative to the axis of the tube and that is for bringing into the vicinity of a portion of a part that is to be examined. The illumination outlet is thus not axial, but is 25 perpendicular to the axis of the tube, for example, so turning the rod about its own axis, and moving said rod in translation along its axis makes it possible to illuminate and observe large areas of the parts.
The image transmission means of the first endoscope comprise a rectilinear set of optical components, comprising an image-forming objective lens and image-transferring lenses, said set extending from one end of the tube to the other and also comprising light reflector means mounted at the end of said set of components on its optical axis and oriented obliquely relative to said optical axis.
These optical reflector means and the bent outlet end of the illuminating cable are close together and are oriented in corresponding manner so as to illuminate and observe the same portion of the part.
Preferably, the optical reflector means are formed by a prism.
The reflecting face of the prism is advantageously oriented at 45° relative to the optical axis of the image transmission means and the bent end of illuminating cable extends perpendicularly to the axis of the tube.
The pipes which are received in the rod around the first endoscope comprise an air pipe, a powder pipe, and a liquid pipe, extending from one end of the rod to the other, and each having a first end for connection to feed means. The second ends of the powder and liquid pipes open out at the corresponding end of the rod in the same direction as the illuminating means and the image transmission means of the first endoscope, whereas the second end of the air pipe opens out axially at the end of the rod in order to protect the first endoscope and prevent powder and liquid becoming deposited on its end.
In a particular embodiment of the invention, the tube of the first endoscope has a diameter of about 4 millimeters (mm) and the rod has a diameter of about 8 mm.
The second endoscope for illuminating in ultraviolet light can have an outside diameter that is substantially equal to that of the above-mentioned rod, thus ensuring good performance in terms of illumination in ultraviolet light and observation of defects in the part.



BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and other characteristics, details, and advantages thereof will appear more clearly on reading the following description made by way of example with reference to the accompanying drawings, in which:
FIG. 1 is a diagrammatic view of the apparatus of the invention for illuminating with visible light and depositing penetration test substances onto the part to be examined;
FIG. 2 is a diagrammatic view of the second endoscope for illuminating the part under examination in ultraviolet light;
FIGS. 3 and 4 are diagrammatic plan views of the rod for illuminating in visible light and for depositing penetration test substances; and
FIG. 5 is a diagrammatic axial section view of the visible light endoscope used in this rod.



MORE DETAILED DESCRIPTION
In FIG. 1, reference 10 designates a wall such as 15 a turbomachine casing behind which there are parts 12 for examination such as the rotor blades of the turbomachine.
The wall 10 includes an endoscope orifice 14 of small size (typically having a diameter of 9 mm), through which it is possible to insert a rod 16 for illuminating with visible light and for spraying penetration test substances, one end of the rod being provided with a block 18 for connection to means for supplying penetration test substances and compressed air, and its other end 20 being designed to be brought up to face a surface of the part 12 for examination.
The rod 16 is shown in greater detail in FIGS. 3 and 4. The rod is a rigid tubular cylinder, e.g. made of metal, and contains a first endoscope 22 for illuminating and observing in visible light, a pipe 24 for feeding and spraying a powder on the surface of the part 12 to be examined, a pipe 26 for feeding compressed air, and a pipe 28 for feeding and spraying a liquid which may be in succession acetone, a penetrating agent, an emulsifier, and water. The first endoscope 22 and the pipes 24, 26, and 28 extend longitudinally in the rod 16 from one end thereof to the other, the endoscope lying on the axis of the rod 16 and the pipes 24, 26, and 28 being disposed around the endoscope.
As shown diagrammatically in FIGS. 1 and 3, the first endoscope 22 has a first end 30 for connection to a source of visible light and a second end which is described in greater detail below and which opens out at the end 20 of the rod 16.
The pipes 24 and 28 for feeding penetration test substances have first ends 32 for connection to tanks 34 containing the substances, themselves connected to a compressed air feed 36, and having second ends 38 which open out at the end 20 of the rod 16 perpendicularly to the axis of said rod.
The compressed air feed means and the sources of 15 visible and ultraviolet light are preferably grouped together in a feed module 40, itself including electrical power supply means and compressed air supply means.
The end 30 of the first endoscope 22 includes an eyepiece 42 enabling an observer to view directly the surface of the part 12 under examination facing the end 20 of the rod.
The endoscope 22 is shown in greater detail in FIG. 5, and it essentially comprises a rigid cylindrical tube 44, e.g. made of metal having disposed therein an optical fiber cable 46 for guiding visible light from one end of the endoscope to the other, the cable 46 having a first end for connection to the visible light source provided in the feed module 40, and a second end 48 through which light is delivered and extending for example perpendicularly to the axis of the tube 44 at the end of the endoscope that is remote from the end fitted with the eyepiece 42. Image transmission means 50 are also disposed inside the tube 44 and extend therein longitudinally from one end to the other, said image transmission means 50 being constituted by a rectilinear assembly of optical components comprising, in particular: an image-forming objective lens 52 and one or more transfer lenses 54. Reflector means 56 are placed in the tube 44 close to the objective lens 52, between said lens and the second end 48 of the light guide means 46, the optical reflector means 56 being formed by a prism which is placed on the optical axis of the image transmission means 50 and which has a reflecting face inclined at 45° relative to said axis, for example, in order to observe in a direction that is perpendicular to said optical axis and parallel to the direction in which the end 48 of the light guide 46 extends.
As can be seen clearly in FIG. 5, the light guide 46 extends along the wall of the tube 44, and the image transmission means 50 occupy practically all of the remainder of the tube, thus making it possible to use a section that is as large as possible for the image transmission means 50 in order to improve observation.
In a particular embodiment, given herein by way of example, the rigid tube 44 has an outside diameter of about 4 mm and a length of about 40 centimeters (cm). It is designed to aim at 90° relative to its axis and to have a field of observation of 55°.
The apparatus of the invention comprises a second endoscope 60 shown diagrammatically in FIG. 2, which second endoscope is independent from the rod 16 and the first endoscope 22 and is designed to be inserted through the endoscope orifice 14 in the wall 10 in order to observe the surface of the part 12 once it has been treated with the penetration test substances.
This endoscope 60 has a first end provided with an eyepiece 62 and means 64 for connection to a source of ultraviolet light and forming part of the feed module 40, and a second end 66 having a light outlet perpendicular to the axis of the endoscope for illuminating the treated surface of the part 20 in ultraviolet light and for observing it.
This endoscope 60 may be of conventional type, or preferably it is of the type described in another patent application in the name of the Applicant. Since this endoscope 60 is used on its own, it may have transverse dimensions that are larger than would be possible if it were used together with or instead of the first endoscope 22 in the rod 16, which in general means that it is possible to illuminate the surface of the part 12 better in ultraviolet light and to observe the results of the penetration test better.
The apparatus of the invention is used as follows:
Initially, the rod 16 is inserted through the orifice 14 in the wall 10 and its end 20 is moved in axial translation and by being turned about said axis, facing the surface of a part 12 to be examined.
In order to verify whether an apparent defect of the part 12 is or is not a real defect such as a crack or a fissure, penetration test substances are sprayed in succession onto the corresponding portion of the part 12, these substances including a fluorescent liquid which penetrates into surface discontinuities, a washing liquid, and a developer powder for revealing the presence of the penetrating substance that has infiltrated into a surface discontinuity, even if the discontinuity is of very small dimensions.
Examination of the part 12 and observation of the spraying of penetration test substances onto said part are performed using visible light, with the surface of the part 12 being illuminated by the light flux leaving the angled end 48 of the light guide 46 of the first endoscope, this light being reflected and/or backscattered by the surface of the part and being picked up by the mirror 56 which returns it along the axis of the image transmission means 50 to the eyepiece 42 mounted at the other end of the first endoscope.
The rod 16 is then withdrawn from the endoscope 35 orifice 14 and the second endoscope 60 connected to the source of ultraviolet light in the feed module 40 is inserted in turn through the orifice 14 and its end 66 is brought to face the treated surface of the part 12. Illuminating the treated surface of the part 12 in ultraviolet light causes the penetration test substance that has infiltrated into a surface discontinuity and which diffused into the developer to be excited, with the penetrating substance responding to said excitation by fluorescing, e.g. with a green color, which can clearly be seen in the dark and which the user can observe by means of the eyepiece 62.
In general, the separation in accordance with the invention of illumination with ultraviolet light and illumination with visible light makes it possible to improve the performance of both illumination operations and to improve observation of the corresponding results.

## Claims

1. A method of detecting defects in a turbojet part by endoscopy comprising:
providing a rod with a first diameter and including
at least one pipe, and
a first endoscope including a visible light guide received in the rod and a first image transmission assembly received in the rod, the first endoscope being free of any means for producing ultraviolet light;

providing a second endoscope with a second diameter, the second endoscope being free of any pipes configured to feed gas or fluid and free of any means for producing visible light, the second endoscope including an ultraviolet light guide and a second image transmission assembly;
inserting the rod through an orifice in a wall of the turbojet;
after inserting the rod through the orifice and while the first endoscope is disposed within the orifice, exposing the turbojet part to visible light transmitted via the visible light guide and produced by a dedicated visible light source, and applying a penetration test substance to a surface of the turbojet part by sending the penetration test substance through the at least one pipe;
withdrawing the rod from the orifice after applying the penetration test substance to the turbojet part;
inserting the second endoscope through the orifice after withdrawing the rod;
exposing the turbojet part to ultraviolet light with the ultraviolet light guide while the second endoscope is in the orifice; and
viewing the turbojet part exposed to ultraviolet light through the second image transmission assembly while the second endoscope is in the orifice.

2. The method according to claim 1, wherein the turbojet is mounted on an airplane.

3. The method according to claim 1, further comprising configuring the second diameter to be substantially equal to the first diameter.

4. The method according to claim 3, further comprising configuring the first diameter to be about 8 mm.

5. The method according to claim 1, further comprising configuring the orifice in the wall of the turbojet to have a diameter of about 9 mm.

6. The method according to claim 1, further comprising reflecting light received from the turbojet part with a prism that is included in the first image transmission assembly.

7. The method according to claim 1, further comprising reflecting light received from the turbojet part with a prism that is included in the second image transmission assembly.

8. The method according to claim 1, wherein the turbojet part is not exposed to visible light via the second endoscope during said exposing the turbojet part to ultraviolet light with the ultraviolet light guide while the second endoscope is in the orifice.

9. The method according to claim 1, wherein the applying a penetration test substance includes applying a fluorescent liquid.

10. The method according to claim 9, wherein the applying a penetration test substance includes applying a washing liquid after applying the fluorescent liquid.

11. The method according to claim 9, wherein the applying a penetration test substance includes applying a developer powder that reveals the presence of penetrating test substance that has infiltrated into a surface discontinuity in the turbojet part.

12. The method according to claim 1, wherein the at least one pipe includes a first pipe through which air is supplied, a second pipe through which liquid is supplied, and a third pipe through which powder is supplied.

13. A method of detecting defects in a turbojet part by endoscopy comprising:
inserting a first endoscope through an orifice in a wall of the turbojet, the first endoscope being free of any means for producing ultraviolet light;
while the first endoscope is disposed within the orifice, exposing the turbojet part to visible light transmitted via a visible light guide while the first endoscope is coupled to a dedicated visible light source;
while the first endoscope is disposed within the orifice, applying a penetration test substance to a surface of the turbojet part by sending the penetration test substance through at least one pipe coupled to the first endoscope;
withdrawing the first endoscope from the orifice after applying the penetration test substance;
inserting a second endoscope, free of any pipe for depositing substances on the turbojet part and free of any means for producing visible light, through the orifice after withdrawing the first endoscope;
exposing the turbojet part to ultraviolet light with an ultraviolet light guide while the second endoscope is in the orifice and is coupled to a dedicated ultraviolet light source; and
viewing the turbojet part exposed to ultraviolet light through an image transmission assembly while the second endoscope is in the orifice.

14. The method of detecting defects in a turbojet part according to claim 13, further comprising reflecting an image of the turbojet part with a prism while the turbojet part is exposed to ultraviolet light; and
viewing the reflected image of the turbojet part after the image is reflected with the prism.

15. The method according to claim 13, wherein the turbojet is mounted on an airplane.

16. The method according to claim 13, further comprising configuring the orifice in the wall of the turbojet to have a diameter of about 9 mm.

17. The method according to claim 13, further comprising
reflecting light received from the turbojet part with a prism that is included in the first endoscope; and
viewing the reflected image.

18. The method according to claim 13, further comprising
reflecting light received from the turbojet part with a prism that is included in the second endoscope; and
viewing the reflected image.

19. The method according to claim 13, wherein the applying a penetration test substance includes applying a fluorescent liquid.

20. The method according to claim 19, wherein the applying a penetration test substance includes applying a washing liquid after applying the fluorescent liquid.

21. The method according to claim 19, wherein the applying a penetration test substance includes applying a developer powder that reveals the presence of fluorescent liquid that has infiltrated into a surface discontinuity in the turbojet part.

22. The method according to claim 13, further comprising configuring the first and second endoscopes to each have an outside diameter of about 9 mm.

23. A method of detecting defects in a turbojet by endoscopy including inserting first and second endoscopes in sequence, one after another, through an orifice in a wall of the turbojet, the method comprising:
inserting a first endoscope through an orifice in a wall of the turbojet, the first endoscope being free of any means for producing ultraviolet light;
while the first endoscope is disposed within the orifice, exposing the turbojet part to visible light transmitted via a visible light guide while the first endoscope is coupled to a dedicated visible light source;
while the first endoscope is disposed within the orifice, applying a penetration test substance to a surface of the turbojet part by sending the penetration test substance through at least one pipe coupled to the first endoscope;
withdrawing the first endoscope from the orifice after applying the penetration test substance;
inserting a second endoscope, free of any pipe for depositing substances on the turbojet part and free of any means for producing visible light, through the orifice after withdrawing the first endoscope;
exposing the turbojet part to ultraviolet light with an ultraviolet light guide while the second endoscope is in the orifice and is coupled to a dedicated ultraviolet light source; and
viewing the turbojet part exposed to ultraviolet light through an image transmission assembly while the second endoscope is in the orifice.