GB2130742A

GB2130742A - Optical sensor

Info

Publication number: GB2130742A
Application number: GB08321607A
Authority: GB
Inventors: Douglas Scott Steele
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1982-11-18
Filing date: 1983-08-11
Publication date: 1984-06-06
Also published as: FR2536532A1; GB8321607D0; JPS5992310A; DE3329375A1; IT8322826A0

Abstract

An optical sensor is disclosed in which a first optical wave-guide 12 receives light and transmits the light to a target zone and in which a second optical wave-guide 31 receives an image reflected at the target zone for transmission to a remote location. Lens 9 focusses the laser beam 4 (which may sporadically deviate as shown at 15, 16, 17). <IMAGE>

Description

SPECIFICATION Optical sensor A light source which is utilized to illuminate an object for optical examination commonly produces heat. The heat produced by be deleterious to other apparatus used in conjunction with the optical examination, apparatus such as cameras or photodiode arrays as well as integrated circuitry utilized in signal processing.

Thus, it can be desirable to keep the light source and the other apparatus physically separate from each other. Further, the optical examination is frequently undertaken in the environment of a factory machine shop. Such an environment subjects equipment in its presence to extremes of temperature, dirt and debris, electrical noise, and vibration. It is desired to protect sensitive equipment from these extremes. Still further, when the light source comprises a laser, it is found that the light beam projected by the laser can sporadically deviate from its intended path and thus the light beam can illuminate unintended portions of an object under study. Thus, it is desirable to minimize the effect of the sporadic deviation.

Objects of the invention It is an object of the present invention to provide a new and improved optical sensor.

It is an object of the present invention to provide a new and improved optical sensor which separates a heat-producing source of illumination from heat-sensitive signal-processing circuitry.

It is a further object of the present invention to provide a new and improved optical sensor which locates its source of illumination and signalprocessing equipment at a position remote from the hostile environment in which the optical sensing is undertaken.

It is a further object of the present invention to provide a new and improved optical sensor which reduces the effects of sporadic changes in light beam position resulting from the use of a laser as a source of illumination.

Summary of the invention In one form of the invention, a first optical wave-guide receives a light beam at a remote location and projects the light beam to a target zone. Light reflected from the target zone is transmitted to a second optical wave-guide and is transmitted thereby to another remote location.

Brief description of the drawings Figure 1 illustrates one embodiment of the present invention.

Figure 2 illustrates a light beam of large diameter used to illuminate an optic fibre of the invention.

Figure 3 illustrates reflection of a light beam by an object located at two different positions.

Detailed description of the invention As shown in Figure 1, a source of illumination, which preferably is a collimated light source such as a laser 3, projects a light beam 4 to an electro optical attenuator 6 and thence to a lens means 9 which focuses light beam 4 onto the receiving end face 11 of a first optical wave-guide means such as an optical fiber 12. Generally, the light beam 4 produced by laser 3 can sporadically shift in position so that it may unpredictably occupy any of the paths shown as 15,16, or 17. The effects of these shifts in position are reduced by the dispersing properties of the optical fiber 12.

That is, as the light beam 4 travels through the optical fibre 12, it is reflected internally so that the transmitting end face 21 of the optical fiber 12 will be substantially uniformly illuminated irrespective of whether light beam 4, 1 5, 16, or 17 strikes the receiving end face 1 1.The uniformly illuminated end face 21 reprojects a light beam 23 which has many of the properties, such as coherence and low dispersion, of the laser light beam 4. The light beam 23 travels to a target zone indicated as dotted block 25 for reflection by the surface of an object, such as object 27 present within the target zone 25. The light beam 23 is shown as following a path which is not perpendicular (that is, non-normal) to the surface of object 27.

The light beam 4 is shown in Figure 1 to be of a diameter smaller than that of the optical fiber 1 2. However, this need not be the case. A light beam 4A of a larger diameter can be used, as shown in Figure 2. In this case, random shifts in beam position will not similarly affect the position of light beam 23 projected to the target zone 25, so long as the incoming beam 4A does not shift to a position which causes the incoming beam 4A to substantially fail to enter the optical wave-guide 12.

With reference to Figure 1, light beam 23 will be reflected in the target zone 25 in directions which are determined by the surface characteristics of the object 27 and these characteristics include such factors as smoothness and roughness, shininess and dullness, the composition of the material, and the presence of flaws in the surface of the material. In general, however, a reflected light beam 29 will be projected toward a second optical wave-guide 31. A second lens means 34 is preferably located between the second optical wave-guide 31 and the target zone 25 in order to focus the light reflected from the surface of the object 27 onto an image plane 36. Since the reflected light contains information concerning this surface, the reflected light is considered to contain an image of this surface.The second optical wave-guide 31 is positioned at the image plane 36 to receive the image and to transmit the image to a remote location where an optical sensor such as a camera means 38 is located. Associated with the camera means 38 is a signal processing means 41 which is utilized to analyze the image.

One of the features of the surface of object 27 which may be analyzed by the above-described apparatus is the displacement of all or part of the surface from a known position. For example, when the surface of the object 27 is present at the position indicated by the solid outline 27A in Figure 3, the reflected light beam 29 follows the path as shown. However, if the surface of the object 27 is displaced to a position indicated by the dotted outline 27B, the reflected light beam will then follow a path indicated as 29B. In this case, the image projected onto image plane 36 will be similarly displaced with the result that the image seen by camera means 38 will also be displaced. The signal processing means 41 detects such a displacement.Thus, the displacement of the surface of the object 27 away from a predetermined position is registered by the camera means 38 as a displacement of the image of the surface. If only part of the surface of the object 27 is displaced, as in the case of a crack or pit occurring in the surface, then the corresponding part of the image received by the second wave-guide means 31 will be similarly displaced and registered by the camera means 38. Such examination of objects is commonly called optical triangulation.

The first and second optical wave-guide 12 and 31 can be supported at a predetermined distance and in a predetermined angular relation between themselves by a support 44 shown in Figure 1. The support 44 positions the transmitting end face 21 to thereby fix the path of light beam 23. The support 44 is positioned in the environment in which the object 27 to be examined is located. Optical wave-guides 12 and 31 extend from the environment to protected environments such as temperature-controlled, dust-free enclosures 46 and 48 which contain the illumination source 3 in the former and camera means 38 and signal processing circuitry 41 in the latter.The enclosures 46 and 48 are shown in Figure 1 to be spatially adjacent, but, as mentioned above, they are preferably positioned so that the heat produced by the light source 3 does not interfere with the camera means 38 or the signal processor 41.

The optical wave-guides described above can be constructed of single light pipes composed of transparent materials, or of many relatively small optical glass fibers packed into bundles. For example, between two and five thousand fibers can be packed into a bundle having a diameter of 1/2 inch (1.27 cm). Preferably, the optical waveguide 21 consists of a single optical fiber approximately .005 in. (0.13 cm) diameter. Thus, the distance 75 between the points of support 44A and 44B on support 44 can be as small as 2 inch (5.08 cm). Accordingly, the optical wave guides 12 and 31 can be used to examine the interiors of holes of a correspondingly small diameter. The optical wave-guides should have low-loss properties, that is, they should be nondegrading. In certain applications, it may be desirable to utilize nonmode-dispersing wave guides.The camera means described above can inciude a flying spot scanning camera, a vidicontype camera, a photodiode array or other types of photosensitive devices.

A second form of the present invention is shown in Figures 4 and 5. In Figure 5, the first and second optical wave-guides 1 2 and 31 are shown supported by a support 44, the arms 44A-B of which are hinged at points 200, 202, and 204 to allow support 44 to be collapsed or folded from the larger form shown in Figure 1 to the smaller form shown in Figure 5. In its collapsed form, the support 44, as shown in Figure 4, can be inserted through a small opening such as a hole 206 in the cowling 207 of a gas turbine engine containing a rotor 207A.The support 44 can be fastened to a series of arms 208A-C which are connected by articulating joints 21 OA-C, thus providing an articulating means for manipulating the support 44 into otherwise inaccessible locations to perform tasks such as the examination of a turbine engine blade 214 which is fastened to the rotor 207A.

As mentioned earlier, laser 3 (not shown in Figure 4) can be contained within enclosure 46 and the camera means 38 together with the signal processor 41 (neither shown in Figure 4) can be contained within enclosure 48 for protection from the environment and for protection of the contents of enclosure 48 from the heat of the laser 3 contained in enclosure 46.

For further protection of the contents of enclosure 48, that enclosure can be confined to a temperature and humidity controlled environment represented by chamber 21 8 at a location remote from enclosure 46 for further protection of the signal processor 41. Thus, the contents of enclosure 48 can be thermally isolated from the laser 3 as well as from the environment in which the enclosure 48 is situated.

Accordingly, an invention has been described which provides an optical sensor in which the heat producing source of illumination is spatially removed from heat-sensitive components.

Delicate components are removed from the environment in which the optical sensor is to operate, and thus are protected. Thus, these components can be tuned to greater sensitivity and accuracy by virtue of being in a controlled environment. There appears to be no theoretical limit to the lengths of the optical fibers used, and thus to the distance limit between the controlled environment and the sensor, but, in practice, this distance is seen as being of the order of magnitude of one hundred feet or less. Further, the embodiment described reduces the effects of sporadic changes in light beam position which are encountered when a laser is utilized as a source of illumination.

Still further, the optical sensor of the present invention can be structurally simplified by repiacing the lens 34 by a lens (not shown) affixed or integrally molded to the end of the optical wave-guide 31. Further still, the optical sensor described is small, rugged, and light in weight. Its small dimensions and the mobility afforded by the use of fiber optics allow the sensor to be inserted into small spaces and thus allow the examination of sharp curvatures contained therein.

One form of the invention has been described.

Numerous modifications and substitutions can be undertaken without deparing from the true spirit and scope of the invention as defined in the following claims. In particular, a single optical transmitting wave-guide (first wave-guide 12 in Figure 1) has been disclosed in connection with a single receiving wave-guide (second waveguide 31). However, the use of a single transmitting wave-guide together with more than one receiving wave-guide which view the image of the object's surface from different positions is contemplated.

What is desired to be secured by Letters Patent is the following.

Claims

1. An optical sensor, comprising: (a) a first optical wave-guide means for receiving light at a remote location and for projecting the light as a substantially nondiverging beam following a substantially predetermined and substantially nondeviating path to a target zone for reflection thereat; (b) a first lens means positioned in the path of light reflected from the target zone for focusing the reflected light onto a predetermined image plane for generation of an image; and (c) a second optical wave-guide means for receiving the image and for transmitting it to a remote location.

2. Apparatus in accordance with claim 1 in which the first optical wave-guide means is flexible.

3. Apparatus in accordance with claim 2 and further comprising a source of collimated light which supplies light to the first optical waveguide means.

4. Apparatus in accordance with claim 3 in which the source of collimated light is a laser.

5. Apparatus in accordance with claim 4 and further comprising support means for supporting the first and second wave-guide means in a predetermined nonparallel relationship with each other.

6. Apparatus in accordance with claim 5 in which the first optical wave-guide means comprises optical fibers.

7. Apparatus in accordance with claim 6 in which the second optical wave-guide means comprises optical fibers.

8. Apparatus in accordance with claim 7 in which the optical fibers are substantially nonmode dispersing.

9. Apparatus in accordance with claim 8 in which the wave-guide means each comprise at least one thousand optical fibers.

10. Apparatus in accordance with claim 9 in which the first wave-guide means consists of an optical fiber of diameter under .005 inch.

11. A method of optical sensing, comprising the steps of: (a) projecting a substantially nondiverging light beam along a nonpredetermined path among a plurality of possible paths, (b) reprojecting the light beam along a predetermined path nonnormal to the surface of an object for generation of an image of part of the surface, and (c) projecting the image onto a detector at a position on the detector indicative of the position of the image when generated.

12. A method according to claim 11 in which the light beam is reprojected by means of an optic fiber.

13. A method according to claim 12 in which the image is projected by means of a plurality of optical fibers.

14. An optical sensor comprising: (a) a first wave-guide comprising an optic fiber of diameter less than .005 in. for receiving a laser beam and projecting it as a substantially nondiverging beam to the surface of an object along a nonnormal path, (b) a lens means for focusing an image reflected by the surface of the object, and (c) a second wave-guide comprising a bundle of optical fibers for receiving the image and transmitting it to a camera means for production of an image at a position indicative of the position of the reflection of the image on the surface.

1 5. In an optical triangulation system of the kind utilizing a laser to project a light beam through a first optical wave-guide to a target zone and a camera means to generate signals in response to light reflected to a second optical wave-guide by an object in the target zone, the improvement comprising:: (a) attenuator means positioned in the path of the laser light beam for attenuating the light beam; (b) a first lens means positioned in the path of the laser light beam for focusing the light beam onto a receiving end face of the first optical wave-guide; (c) a support fastened to a transmitting end face of the first optical wave-guide for supporting the transmitting end face in a predetermined position for projecting therefrom a projected light beam derived from the laser light beam to a target zone along a predetermined path which path is substantially determined by the position of the transmitting end face and substantially independent of the path of the laser light beam; and (d) the second lens means for focusing onto the second optical wave-guide some of the light of the projected light beam which is reflected by an object present in the target zone and for reprojecting the reflected light to the camera means.

1 6. Apparatus according to claim 1 5 and further comprising articulating means for supporting the support of (c).

1 7. Apparatus according to claim 1 5 in which the support comprises respective arms for supporting the transmitting end face and the receiving end face and further comprising hinging means for foldling the arms.

18. Apparatus according to claim 15 in which the laser is contained in a first protective enclosure and the camera means is contained in a second protective enclosure which is thermally isolated from the first protective enclosure.

1 9. An optical sensor or triangulation system substantially as hereinbefore described with reference to and as illustrated in the drawings.

20. An optical sensing method substantially as hereinbefore described with reference to the drawings.