BACKGROUND

1. Field

[0001] The present disclosure generally relates to the field of non-destructive evaluation of articles of manufacture by stimulating an article with electromagnetic energy, then imaging and evaluating a resulting topography of differential inductive heating on a surface of the article.

2. Description of the Related Art

[0002] Active thermography is a non-destructive evaluation (NDE) technique in which a non-destructive stimulation such as acoustic or electromagnetic energy is applied to a test object. The applied energy induces mechanical vibrations or electromagnetic currents (respectively) in the object, thereby producing an uneven temperature distribution in the object. Structure features and flaws in the object generate localized heat under such stimulation. A resulting temperature topography on a surface of the object is imaged with an infrared camera. Information about defects and the inner structure of the object can be obtained by evaluating the images individually or a time series of such images. Each image may be digitized into picture elements, or pixels, with each pixel representing a small unit area on the surface. These digitized images can then be used for digital displays and for computer analyses, in which a temperature/time series may be processed and analyzed by pixel over time and in patterns of pixels over time and/or space. Time series information improves overall sensitivity of the technique and facilitates the determination of geometric quantities like local coating thickness, wall thickness, or depth of a defect.

[0003] Stationary inspection systems are generally used to test articles of manufacture during their production. Mobile systems are often used for field inspections of operational apparatus such as aircraft, power plant equipment, transportation equipment, and the like. Currently NDE techniques such as dye penetrant, magnetic particle coatings, ultrasonic stimulation, and eddy current stimulation have various disadvantages in speed, flexibility and/or potential contamination to the articles tested. Improved NDE devices and techniques are thus desired.

SUMMARY

[0004] Briefly described, aspects of the present disclosure relate to a hand-held thermography system and a method for using the hand-held thermography system.

[0005] A disclosed embodiment is directed to a hand-held thermography system. The hand-held thermography system includes a housing to enclose the components of the thermography system, the housing configured to be hand-held. Within the housing an electric current generator, a digital infrared camera, and a processor are disposed. An induction coil is disposed within a slot in a wall of the housing so that the induction coil faces outward from an exterior of the housing. The electric current generator produces an alternating current that is provided to the induction coil through control by the processor. The digital infrared camera includes a lens having a field of view directed through an opening in the first wall so that the lens includes a field of view outward from the exterior of the housing and effective to capture images. The processor is connected to both the current generator and the digital infrared camera. The processor controls the imaging from the digital camera and stores the captured images.

[0006] A further disclosed embodiment is directed to a method for using the hand held thermography system. The method may include positioning the induction coil adjacent to an area on a surface of the test object and pressing a triggering to activate the electric current from the electric current generator to the induction coil and to start imaging from the infrared camera. At least one image may be captured by the infrared camera. The at least one image may be evaluated for anomalies.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Fig. 1 illustrates an exterior perspective view of a hand-held thermography system according to an embodiment, [0008] Fig. 2 illustrates a schematic view of the hand-held thermography system according to an embodiment,

[0009] Fig. 3 illustrates a schematic view of a hand-held thermography system according to another embodiment, and [0010] Fig. 4 illustrates a method of operation of the hand-held thermography system.

DETAILED DESCRIPTION

[0011] To facilitate an understanding of embodiments, principles, and features of the present disclosure, they are explained hereinafter with reference to implementation in illustrative embodiments. Embodiments of the present disclosure, however, are not limited to use in the described systems or methods.

[0012] The components and materials described hereinafter as making up the various embodiments are intended to be illustrative and not restrictive. Many suitable components and materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of embodiments of the present disclosure.

[0013] Testing a component for damage in the field and in situ is often a challenge and may require expensive, bulky, and advanced technologies. Typical NDE techniques that are implemented in the field either require a specialized technician, are lengthy in time to complete, and/or are often unreliable. A proposed handheld induction thermography system provides a platform for testing parts in real time that can be easily interpreted. The system may also be modified for multiple testing scenarios and may be implemented in the field. [0014] Figure 1 illustrates a perspective view of an exterior of a hand-held, portable thermography system 10 according to an embodiment. The housing 15 may comprise a plurality of walls in a box shape configured to be hand held. For example, the housing 15 may include measurements such as 6 in. by 4 in. by 4 in. (1 x w x h) so that the system 10 may be hand held. In an embodiment, the housing may comprise an ergonomic design, such as by including two handles 20 on opposing walls to further enable it to be hand held. Within a first wall 17 of the housing 15, an opening 25 may be disposed to accommodate a lens of an infrared camera. A material of the housing 15 may comprise a plastic material. Plastic is chosen because it is light weight and inexpensive. In an embodiment, the housing 15 may be produced by a 3D printing device.

[0015] Referring now to Figure 2, a schematic view of the thermography system 10 is presented. The components of the system 10 may be enclosed within the housing 15. The thermography system 10 includes an electric current generator 30 electrically connected to a digital controller embodied as a processor 35. Control circuitry 60, such as a relay circuit, enables the controller 35 to control the current generator or current oscillator. The electric current generator 30 generates an alternating current in a range of up to 30 amps which it provides via a connection 42 to an induction coil 50. A digital infrared camera (IR camera) 40 may also be enclosed within the housing 15 and may be electrically connected via connection 38 to the processor 35. The IR camera 40 includes a lens 45 having a field of view directed through the opening 25 in the first wall 17 so that the lens 45 includes a field of view outside of the housing 15 in order to capture images of test objects within its field of view.

[0016] The induction coil 50 may be disposed within a slot in the first wall 17 and surrounding the opening 25 so that the coil 50 is generally coplanar with the first wall 17. The induction coil 50 is positioned on the exterior of the housing 15 so that it faces outward. A trigger 55 connected to the control circuit 60 residing inside the housing enclosure 15 may be utilized to commence the flow of current from the current generator 30 to the induction coil 50. The trigger 55 may also be used to start imaging from the IR camera 40. A user simply presses the trigger 55 to energize the induction coil 50 as well as start an imaging sequence.

[0017] In operation, the electric current generator 30 may generate an alternating current that induces eddy currents in an electrically conducting object located a short distance from the thermography system 10, for example in a range such as 0 to 5 inches away, and preferably 3 inches or less away. The induced current is highest in the area of the test object closest to the induction coil 50 and decreases with increased distance from the coil. The effective test area is a function of many variables, such as the amount of current in the coil, the properties of the test object, and the sensitivity of the camera. Material properties of the test object, especially the conductivity of the material effect how much the material heats up. Typically, the resistive heating only occurs in a top surface layer of the test object, for example, a few micrometers deep from the exposed surface for magnetic materials. The IR camera 40 may then be used to capture the infra-red radiation emitted by the test object to form a thermographic image. Internal anomalies in the object, such as voids, inclusions, delamination, moisture, or changes in thickness or density cause changes in the cooling rate at the surface of the test object. These internal anomalies may be visible in the thermographic image.

[0018] Previous designs of hand-held thermography devices, for example the hand-held thermography system described in US Patent 7,485,882, included power supplies that are separate from the hand-held device mostly because the power supply was large, such as the size of a washing machine. These power supplies typically produce power in the range of 2-10 kW and source between 40-50 amps. Besides being large, disadvantages of this type of thermographic system are that it cannot be used in a large metal enclosure, such as inside a gas turbine engine, and that the high power generated poses a risk of electrocution to the user of the device.

[0019] In the proposed hand-held thermographic system 10, a low-voltage power supply such as a battery may be used. The low-voltage power supply may provide power in the range of 50-lkW, significantly lower than the previous designs of hand held thermographic systems. In an embodiment, a low voltage power supply 65 is electrically connected to the electric current generator 30 providing DC power to the electric current generator 30 via a wired connection 80 (see Fig. 3). Thus, the power supply 65 may be incorporated inside the enclosure of the housing 15 along with the other components of the system. In alternate embodiments, the low-voltage power supply 65 may be separated from the hand-held device and connected to the device by cabling. To accommodate the low voltage power supply inside the housing enclosure 15, an alternate housing configuration as shown in Fig. 3 may be utilized. This housing configuration incorporates the low-voltage power supply 65 slightly separated from the other enclosed components of the system. In order to provide a comfortable grip for the user, the housing 15 of the alternate configuration includes a long thin portion that may be used as a handle 75.

[0020] Figures 1-3 show a generally planar circularly wound induction coil 50. In the shown embodiment, the induction coil 50 is positioned around an opening 25 in the first wall 17 of the housing enclosure 15 in which a lens 45 of the IR camera is directed through. While this orientation of the induction coil 50 has been illustrated, other coil orientations may also be used. The coil geometry may be chosen to better correspond to the geometry of the test object. For curved test objects a bending of the coil may be appropriate. In some embodiments, the induction coil 50 can be embodied as a solenoid, for example. In order to heat an object with a more complex geometry, the solenoid may be disposed on a tether that can be extended to a desired position adjacent to the test object so that images properly depict the characteristic of the material desired to be analyzed. Similarly, the IR camera 40 may be tethered so that it may extend outside of the housing in order to get images in hard to reach areas.

[0021] In an embodiment, a ferrite shield 70 may be disposed within the slot in the first wall 17 so that it may be disposed in between the IR camera 40 and the induction coil 50. In order to attach the induction coil 50 to the ferrite shield 70, it may be bonded by an adhesive, however, other techniques may also be used. The ferrite shield 70, as may be seen in both Figs. 2 and 3, blocks any stray electromagnetic radiation from the generated electromagnetic fields in the induction coil 50 that may damage any sensitive electronics within the IR camera 40 and/or may produce noise in the captured image. Additionally, the ferrite material of the shield 70 may increase the magnetic permeability of the induction coil 50 with the result that more heat may be produced in the test object.

[0022] In an embodiment, the processor 35 of the thermography system may be an embedded computer, or system on a chip (SOC). The embedded computer 35 could be utilized for control of the IR camera 40 as well as to store and transmit image data. New technology advances have developed low cost and low power computing, low cost sensing, and low-cost digital data transmission. Most of these devices also have the added advantage of being small, such as in the millimeter (or smaller) range. The embedded computer 35 may be as small as a postage stamp allowing it to be disposed within the housing 15. The embedded computer 35 may store the images for later retrieval or be configured to transmit the images via wireless communication in real time to a server. The server may be located offsite. In a further embodiment, the system 10 may be connected to an external computer by a cable or wirelessly so that the images may be accessed remotely in real time. In some embodiments, the process may utilize computer vision algorithms to detect the anomalies in the infrared images. From the detection, the processor 35 may generate a statistical and descriptive representation of the indication.

[0023] Certain embodiments may utilize sensors to enhance the system 10. For example, inductance sensors may be used to detect when a test object is in front of the induction coil 50. The induction sensing may also be used to predetermine how much power the induction coil 50 needs to pull from the power supply 65 before the induction heating process is initiated. Temperature sensors may also be used to detect when the test object reaches an ideal temperature or when the environment is becoming too hot for the electronics associated with the thermography system 10. Current shunts may be used for sensing how much power is being drawn. As an example, the current shunts may be used to detect the voltage on the low voltage power supply 65 and determine if the battery voltage is too low or too high. Light proximity sensors may be used to detect if the test object is close enough for testing. Accelerometers, gyroscopes and magnetometers may also assist in tracking the position of the test object in order create a mapping of the results to a surface of the test object.

[0024] In an embodiment, the system may include a touch screen monitor for real time display of the testing. The touch screen may be the interface for the user to operate the device alternatively to utilizing a trigger on the device.

[0025] Referring now to Fig. 4, a method for using the hand-held thermography system 10 described above is presented. In order to operate the thermography system 10 to inspect an object, such as a turbine blade 100, a user places the induction coil 50 of the system 10 adjacent to a surface of the test object to be tested and presses the trigger 55. In an embodiment, the induction coil 50 is positioned less than 3 inches from the surface of the test object. The induction coil 50 is positioned from the test object a specific distance to enable sufficient induced currents in the test object for thermographic imaging. This specific distance may be dependent on the material of the test object as well as the sensitivity of the IR camera. The trigger 55 may then be pressed to start the current flow from the electric current generator 35 to the induction coil 50 In some embodiments, the current to the induction coil 55 may be user selected as different materials require different current strength to heat up to the required degree for thermographic imaging. The trigger 55 may also initiate control of IR camera 40 to capture at least one image of the heated surface in the field of view of the camera during the excitation of the eddy currents due to the electromagnetic induction. In an embodiment where further imaging is desired, the user may move the hand-held device 10 to view another area of the test object and repeat the described steps. The image may then be evaluated manually or by a computer utilizing computer vision techniques. Images may then be stored within the processor 35 or transmitted to a digital memory device such as a disc drive.

[0026] In an embodiment, the method may include a calibration step in which the image is scanned for any high temperature spots. The pixel values of the whole image or just in areas of the image having high temperatures spots may then be zeroed in order to make the whole image one color before starting the induction heating. The purpose of this calibration step would be to enhance the contrast that will be shown from the indications.

[0027] The acquired data in the images may be analyzed in order to assess the condition of the test object. Assessing the condition of the test object may include determining defects on the component such as delaminations. Defects or discontinuities will show up in a thermographic image as a different temperature change than normal surface or subsurface conditions. Various techniques may be utilized to analyse the acquired images such as background subtraction and pulse- phase analysis for example.

[0028] The disclosure describes a self-contained portable device that can detect damage on a test object in real time. The system is relatively low cost and does not take much training to operate. The size of the device allows it to be used in tight spaces and can potentially be used to inspect parts in hard to reach areas. The compactness is attainable by reducing the size and power consumption of the electric current generator. Furthermore, the design of the induction coil of the thermography system may be adapted to fit the geometry of the test object. [0029] While embodiments of the present disclosure have been disclosed in exemplary forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions can be made therein without departing from the spirit and scope of the invention and its equivalents, as set forth in the following claims.