Robotic infrared thermographic inspection for unitized composite structures

A system and method for nondestructive inspection of a unitized composite structures is provided. The system includes an infrared thermographic camera and a carriage that can be mounted on, for example, adjacent frames of the unitized composite structure. The carriage can move along the length of the frames while the infrared thermographic camera collects and analyzes thermographic images of the frame, skin, and stiffeners. The carriage can be moved to other frames and the inspection continued until the entire unitized composite structure has be inspected.

FIELD

The present disclosure generally relates to methods and systems for nondestructive inspection of composite structures.

BACKGROUND

A composite structure can be fabricated either as a single unitized composite structure or in multiple parts that must subsequently be assembled. Fabrication of a unitized composite structure, for example an integrally stiffened skin panel, provides several advantages. For example, shorter cycle times and fewer labor requirements reduce manufacturing costs. In addition, manufacturing the unitized composite structure avoids the cost and time associated with use of numerous and varied fasteners.

A unitized composite structure, however, can present inspection challenges. A composite structure needs to be inspected, typically by nondestructive ultrasonic methods. Prior to assembly, ultrasonic transducers have access to all surfaces of the multiple composite parts. With a unitized composite structure, it can be difficult for the transducer to gain access to all surfaces, for example, those near corners. Custom transducers to inspect these areas can be complex and costly. Furthermore, ultrasonic inspection requires the transducer to have access to the exposed surface of the unitized composite structure to transmit and detect ultrasonic waves. Depending on the size and shape of the composite structure, this can be time consuming process.

A cost effective and efficient system and method to nondestructively inspect unitized composite structures would be desirable.

SUMMARY

According to the present teachings, an infrared thermographic inspection system for inspection of a unitized composite structure is provided. The system can include a thermography camera, one or more lights, and a carriage. The carriage can include a carriage body, wherein the thermography camera and the one or more lights are secured to the carriage body. The carriage can further include a first support disposed on the carriage body and a second support disposed on the carriage body, wherein the first support and the second support are spaced apart at a distance for the first support to rest on an edge of a first frame and the second support to rest on an edge of a second frame of the unitized composite structure.

Various optional features of the infrared thermographic inspection system for inspection of a unitized composite structure can include a robot configured to lift and place the carriage on the edge of the first frame and the edge of the second frame of the unitized composite structure. Additional optional features include the first support and the second support each comprising one or more wheels contacting the edge of the first frame and the edge of the second frame, respectively; a motor configured to propel the carriage along a length of the first frame and the second frame; a robot configured to slide the carriage along a length of the first frame and the second frame; a processor configured to provide instructions to the motor; and a mount that extends, retracts and/or swivels to reposition the thermography camera. Additional optional features can further include the carriage being able to position the thermography camera at a distance from the unitized composite structure to permit the thermography camera a field of view of two or more of a plurality of stiffeners disposed between the first and second frames; the first mount and the second mount being shaped to mount the carriage on a straight frame edge, an L shaped frame edge, or a T shaped frame edge; and the processor being configured to provide instructions the thermography camera and synchronizes movement of the carriage with capture of infrared thermography images by the camera.

According to the present teachings, a method for infrared thermographic inspection of a unitized composite structure is provided. The method can include placing an infrared thermographic inspection system on a first frame edge and a second frame edge of the unitized composite structure, wherein the infrared thermographic inspection system comprises a first carriage support and a second carriage support attached to a carriage, the first carriage support and the second carriage support disposed at a distance apart to removably mount on the first frame edge and second frame edge, respectively, and wherein the infrared thermographic inspection system further comprises one or more light sources and a thermography camera. The method further includes directing light from one or more light sources at a first inspection area of the unitized composite structure, capturing a first thermographic image of the first inspection area by the thermography camera mounted on the carriage, and moving the carriage in a direction lengthwise relative to the first frame edge and the second frame edge. Light from one or more light sources can be directed at a second inspection area and a second thermographic image of the second inspection area can be captured by the thermography camera mounted on the carriage.

Various optional features of the method for infrared thermographic inspection of a unitized composite structure can include placing the carriage on the first frame edge and the second frame edge by a robot; and moving the carriage lengthwise along the first frame edge and the second frame edge by a robot. Other optional features can include moving the carriage lengthwise along the first frame edge and the second frame edge by rolling the carriage; engaging a motor to roll the carriage; adjusting a field of view of the infrared camera to include at least two or more stiffeners, wherein the at least two or more stiffeners are part of a plurality of stiffeners disposed in a row between two frames of the unitized composite structure; moving the carriage in a lengthwise direction along the first frame edge and the second frame edge to capture additional thermographic images to inspect an entire row of stiffeners between the first frame and the second frame; and placing the carriage on a third frame edge and a fourth frame edge of the unitized composite structure to inspect stiffeners disposed between the third frame and the fourth frame. Additional optional features can include using a robot to place the carriage on a third frame edge and a fourth frame edge; and using a secondary heat source to locally heat corners of the unitized composite structure.

DESCRIPTION

Reference will now be made in detail to exemplary implementations of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. In the following description, reference is made to the accompanying drawings that form a part thereof, and in which is shown by way of illustration specific exemplary implementations in which the present disclosure may be practiced. These implementations are described in sufficient detail to enable those skilled in the art to practice the present disclosure and it is to be understood that other implementations may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, merely exemplary.

Implementations of the present disclosure address the need for a cost effective and efficient system and method to nondestructively inspect unitized composite structures. The disclosed infrared thermographic inspection system can be mounted on top of two frames and move in a lengthwise direction to inspect the frame, skin, and an entire row of stiffeners between the two frames. It can then be mounted on another two frames of the unitized composite structure. In this manner, inspection of the entire unitized composite structure can be completed. The disclosed infrared thermographic inspection system reduces inspection times and provides inspection of all surfaces without the need for customized ultrasonic transducers. Moreover, the disclosed method can be advantageously automated so that it can move along the top of a pair of frames in a lengthwise direction and move to another pair of frame with little or no need of assistance from a technician. While the examples below disclose systems and methods for infrared thermography in the context of a unitized composite aerospace structure, one of ordinary skill in the art will understand that the exemplary systems and methods can be used on any unitized composite structure. Examples include, but are not limited to, composite boat hulls and cylindrical vessels.

FIG. 1Ashows a perspective view of an exemplary unitized composite structure100. For example, unitized composite structure100can form a portion of aircraft10. Composite structure can range in size, for example, from 10 ft.×15 ft. to 40 ft.×60 ft. or larger.FIG. 1Bshows a side view of unitized composite structure100. Unitized composite structure100includes a skin101and a plurality of frames120oriented generally perpendicular to skin101. A plurality of stiffeners103(also referred to as “continuous stiffeners” or “stringers”) are disposed in rows between adjacent frames120. Although plurality of stiffeners103are depicted with a blade or inverted “T” configuration, one of ordinary skill in the art will understand that implementations of the present teachings encompass other configurations. They include, but are not limited to, open shapes such as an “I” or inverted “J” or closed shapes such as a “hat shaped,” trapezoidal, rounded hat or rectangular cross sections. During manufacturing, fabric performs of skin101, frames120, and stiffeners103are stitched together to make a single preform that is then infused with resin and cured. Alternatively, the frames120, skin101, and stiffeners103can be individually made with pre-impregnated carbon or other fibers and assembled prior to cure to form the unitized composite structure. After curing, all surfaces of unitized composite structure100must be inspected. As is evident, inspection of corners, for example the inside or interior corners, formed by a frame and a stiffener or corners formed by a frame and the skin are difficult to inspect ultrasonically. Ultrasonic inspection can also be time consuming due to the size of unitized composite structure100.

FIG. 2shows an exemplary infrared thermographic inspection system250. Infrared thermographic inspection system250includes a carriage260, a thermography camera270(also referred to herein as an “infrared thermography camera’), and one or more lights280. Examples of thermography camera270include, but are not limited to, FLIR X8000sc series (FLIR Systems, Wilsonville, Oreg.) and Indigo Merlin Mid (Indigo Systems, Goleta, Calif.). Thermography camera270can also include software and hardware to capture, store, manipulate, and or display thermographic images taken during inspection. Examples of lights280that provide heat include, but are not limited to, Xenon flash tubes, quartz flash lamps, and photographic flash lamps. In implementations, infrared thermographic inspection system250can include a processor (not shown) to control movement of one or all of carriage260, camera270, and lights280. The processor can also store, manipulate and display thermographic images captured during inspection. The processor can be part of a computer connected to the infrared thermographic inspection system or incorporated into the infrared thermography camera.

Carriage260can include, for example, a carriage body262, a mount264for thermography camera270and/or lights280, first support265and second support267. Carriage body262can be any shape or configuration from which first support265and second support267can extend. Carriage body262also securely supports mount264, thermography camera270, and/or lights280. Mount264serves to attach thermography camera270to carriage body262and can be, for example, a pole, a gimbal, turntable or a screw. It can be sized to mount thermography camera270a sufficient distance from the unitized composite structure to be inspected. In other words, mount264can be any shape or size that secures thermography camera270to carriage body262and provides a desired field of view for thermography camera270to inspect the unitized composite structure. For example, a gimbal can attach thermography camera270to carriage body262and allow thermography camera270to move in a vertical direction closer or further away from the unitized composite structure and rotate to further change the field of view of thermography camera270.

First support265and second support267serve to support and stabilize infrared thermographic inspection system250as it sits on the frames of the unitized composite structure being inspected. First support265and second support267can be aluminum, or composite, for example, fiberglass/epoxy or carbon/epoxy. The supports can vary in size and shape depending on a number of factors including, but not limited to, with width of the frame edges, the distance between frames, and the size and weight of the thermography camera and lights. Although shown extending out from carriage body262, first support265and second support267can be, for example, grooves in carriage body262spaced apart to match the distance between frames. For reference purposes,FIG. 2also shows a unitized composite structure200including a skin201, a plurality of stiffeners203, a first frame220, and a second frame222. As shown, infrared thermographic inspection system250rests on a top of first frame220and a top of a second frame222. Although depicted resting on adjacent frames220and222, one of ordinary skill in the art will understand that infrared thermographic inspection system250can rest on non-adjacent frames, if desired. First support265and second support267can also include low friction features that facilitate sliding of first support265and second support267along tops of first frame220and the second frame222. The low friction features can include, but are not limited to, coatings deposited on the first and second supports, pieces of low friction materials attached to first and second supports, and air bearings.

The infrared thermographic inspection system can further include one or more wheels, also referred to herein as “rollers.” As shown inFIG. 3A, a first wheel296and a second wheel298can be mounted to allow carriage body262to roll along a top of first and second frames220and222in a direction along a length of the frames. Partial views of unitized composite structure200and carriage360are also shown. For example, first wheel296and second wheel298can be secured to carriage body262, first and second supports265and267, or to any other location to allow carriage360to roll along the top of two frames. Wheels can be mounted in pairs and more than one pair can be used to provide stability to carriage360as it rolls. In various implementations, wheels can be made of a soft rubber to avoid damaging the frames.

AlthoughFIGS. 2 and 3Ashow frames with straight edges, infrared thermographic inspection system250can be used to inspect unitized composite structures with other frame edge shapes. As used herein, “frame edge” refers to an end of the frame opposite an end of the frame adjacent to the skin. For, example,FIG. 3B, shows first and second frames220and222with an L-shaped frame edge223. Partial views of unitized composite structure200and carriage361are also shown.FIG. 3C, shows first and second frames220and222with a T-shaped frame edge225. Partial views of unitized composite structure200and carriage362are also shown. One of ordinary skill in the art understands that the disclosed infrared thermographic inspection systems can be used to inspect unitized composite structures with other frame edge shapes and that the shape, size, and number of supports can vary in order to securely mount the infrared inspection system on other frame edges.

In an implementation, the infrared thermographic inspection system can further include a robot. Referring to infrared thermographic inspection system250shown inFIG. 2, robot290can move carriage260, attached infrared thermography camera270, and lights280to another location along a length of first and second frames220and220to inspect other stiffeners in a same row of stiffeners. For example, after capturing a thermographic image of two or more stiffeners, robot290can mount infrared thermographic inspection system250at a different location on the frames by picking up or sliding infrared thermographic inspection system250lengthwise along the top of the frames. Robot290can also mount carriage260, infrared thermography camera270, and lights280on a different set of frames, for example, adjacent to first and second frames220and222to inspect another row of stiffeners.

Referring toFIGS. 3A-C, robot290can be used to roll carriage360,361, or362and their associated infrared thermography cameras and lights to another location along the length of first and second frames220and222to inspect other stiffeners in a same row of stiffeners. Robot290can also be used to pick up carriage360,361, or362, and their associated infrared thermography cameras and lights, and mount the carriage on another pair of frames.

In another implementation, infrared thermographic inspection system250can include a motor. A motor295shown inFIGS. 3A-Ccan be used in conjunction with first and second wheels296and298to roll carriage360,361, or362and their associated infrared thermography cameras and lights along the top of first frame220and second frame222. Motor295can be, for example, a small stepper motor typically used for equipment positioning, such as ElectroCraft TorquePower motors (ElectroCraft, Inc., Gallipolis, Ohio).

Infrared thermographic inspection system250can also include a processor that provides instruction to motor295. Instructions can include, for example, when to move carriage360,361, or362to a new location along the top of a pair of frames and how far to move the carriage. For example, the processor can provide instructions to the motor and to the camera for image capture and analysis. The processor can be incorporated into a system that includes a software package for data acquisition and analysis, and archives and displays the images in sequence to show coverage of a complete area. Control of the robot and platform motion would be integrated with and slaved to the camera for image capture and analysis in order to retain that sequential acquisition and display of images. For example, the processor can provide instructions to continuously move the carriage while the thermography camera inspects and collects images. Alternatively, the processor can provide instructions to move the carriage to a fixed location so the thermography camera can inspect and collect images before the processor provides instructions to move the carriage to another fixed location to be inspected.

FIG. 4shows an exemplary method400for infrared thermographic inspection of a unitized composite structure. Although the exemplary method is described with respect to inspection of a unitized composite structure during fabrication of, for example, a vehicle, one of ordinary skill in the art will understand that the disclosed method can be used for in-service inspection.

At410, an infrared thermographic inspection system is mounted on a first frame edge and a second frame edge of a unitized composite structure. The unitized composite structure can include, for example, skin, frames, and stiffeners as shown inFIGS. 1A-Band2. Referring toFIG. 2, an exemplary infrared thermographic inspection system250can include a carriage260including a thermography camera270, and one or more lights280. Carriage260can include, for example, carriage body262, mount264for thermography camera270and/or lights280, and first support265and second support267. First support265and second support267can be attached to carriage body262at a distance apart that matches the distance between a first frame220and a second frame222. In an implementation, the distance between first support265and second support267can be adjustable. Thus, infrared thermographic inspection system250can be placed on an edge of first frame220and an edge of second frame220of unitized composite structure200such that first support265is removably mounted on top of first frame220and second support267is removably mounted on top of second frame edge222.

At420, light from one or more light sources can be directed at a first inspection area of the unitized composite body. For example, a first inspection area571is represented by the enclosed area inFIG. 5and can include two or more stiffeners. In this example, first inspection area571includes stiffeners503a,503b, and503cfrom the row of stiffeners503, portions of the inside surface of frames520and522, and portions of skin501. One of ordinary skill in art understands that the depicted inspection area can be larger or smaller and include or exclude other features of unitized composite structure500. In an embodiment where the unitized composite structure includes tight corners where light and the subsequent heat pulse at the surface would be inadequate, localized application of heat from a secondary heat source such as a heat gun, can be used. The secondary heat source can be retractably mounted on carriage260and operated manually by an inspector. The secondary heat source can also be mounted on carriage260using a mechanism that automatically extends and retracts the heat gun.

At430, a first thermographic image of the first inspection area can be captured with an infrared camera mounted on the carriage. For example, referring again toFIG. 5, infrared thermography camera570can be positioned by the carriage and its mount at a distance and/or angle from unitized composite structure500to provide field of view that encompasses a first inspection area571. In particular, first inspection area571can include stiffeners503a,503band503c, portions of the inside surface of frame520and522located near the stiffeners, and portions of skin501. Corners formed by the frame and stiffeners, and corners formed by the frame/stiffeners and skin are also included in first inspection area571. The field of view, however, can be larger or smaller and include more or less of the unitized composite structure as desired.

At440, the carriage is moved. Referring toFIG. 2, carriage260can be moved in a direction lengthwise along frames220and222(into or out of the page as depicted inFIG. 2). Movement of carriage260can be continuous or intermittent. Mount264, camera270, and one or more lights280, attached to carriage260, are also moved with carriage260. Carriage260can be moved, for example, by robot290. Robot290can lift and place the carriage or slide the carriage along the top the two frames in a lengthwise direction. In implementations where the carriage includes wheels or rollers, it can be moved by rolling it along the top of two frames by robot290or using a motor. As shown inFIGS. 3A-C, carriages360,361, and362can be moved by engaging motor295to drive wheels296and298to roll on the top of frames220and222in a lengthwise direction. Control of the motor and wheels can be manual or use a computer and/or processor.

At450, light from the one or more light sources is directed at a second inspection area. As shown inFIG. 5, after the carriage is moved lengthwise along frames520and522, a second inspection area572will be in the field of view of camera570. Second inspection area572is represented by the enclosed area inFIG. 5. In this example, second inspection area572includes stiffeners503d,503e, and503ffrom the row of stiffeners503, portions of frames520and522adjacent to the stiffeners, and portions of the skin. Corners formed by the frame and stiffeners, and corners formed by the frame/stiffeners and skin are also included in second inspection area572. Field of view of second inspection area572can also be adjusted by moving the camera and/or changing the focal point of the thermography camera lens.

In implementations, light from the one or more light sources can be continuous, pulsed, or flashed. When using light that is flashed, movement of the carriage, the flashed lighting and image capture by the infrared thermography camera can be synchronized.

At460, a thermographic image of the second inspection area can be captured with the infrared camera mounted on the carriage. Referring toFIG. 5, moving the carriage can allow infrared thermography camera570to capture a second thermographic image represented by field of view572.

Once the carriage has been moved along length of the pair of frames and infrared thermographic images of the entire row of stiffeners captured, it can then be moved to another pair of frames to inspect another row of stiffeners. Moving the carriage to another pair of frames can be accomplished, for example, using robot290or manually by a technician. Referring toFIG. 5, once inspection of stiffeners between a first frames520and second522has been completed, the carriage, camera, and lights can be moved to rest on top of second frame522and third524to inspect the stiffeners disposed between second frame522and third frame524. This process can be repeated on third frame524and fourth frame525and so on until inspection of the unitized composite structure is completed.

Some or all of the disclosed method can be advantageously automated. As shown inFIG. 6, an exemplary infrared thermography inspection system650can include carriage660, thermography camera670, lights680, and a first robot690. For example, first robot690can mount infrared thermography inspection system650on top of a first frame620and a second frame622of unitized composite structure600. Carriage660can include a motor and wheels to move carriage660along the top of first frame620and second frame622. For example, after a thermographic image is captured of a first field of view, the motor can direct rolling of carriage660, thermography camera670, and lights680along the top of frames620and622to provide thermography camera670a second field of view. This can continue until completion of the inspection of the inside of frames620and622, skin601, and row of stiffeners603. First robot690can then move infrared thermography inspection system650to rest on top of another pair of frames622and624. This can be accomplished by robot690moving to retrieve infrared thermography inspection system650or by infrared thermography inspection system650moving back across the top of frames620and622to robot690.

In another implementation, infrared thermography inspection system650can include additional robots, for example, a second robot695to move infrared thermography inspection system650to rest on top of frames622and624. For example, first robot690can mount infrared thermography inspection system650on frames620and622. After infrared thermography inspection system650completes inspection of row of stiffeners603, moving from right to left as depicted by the arrow, second robot695can move infrared thermography inspection system650to rest on frames622and624. Infrared thermography inspection system650can then continue inspection by moving from left to right as depicted inFIG. 6. Upon completion of the inspection of the stiffeners between frames622and624, first robot690can move infrared thermography inspection system650to another pair of frames and inspection can continue, in a direction back towards second robot695. Inspection can continue in this manner until unitized composite structure600is completely inspected. Exemplary infrared thermography inspection system including more than one robot minimizes travel distance of the robots and reduces inspection time.

In implementations where a width of unitized composite structure600is larger than the reach of robots690and695, a plurality of robots can installed on the sides of unitized composite structure600so that infrared thermography inspection system650can be moved to inspect the entirety of unitized composite structure600.

In other implementations, the mount for the infrared thermography camera can swivel and/or extend. Referring toFIG. 6, mount664can be articulated to allow it to extend and retract. Mount664can also swivel to position camera to inspect a row of stiffeners adjacent to the row of stiffeners over which carriage660rests. For example, infrared thermography inspection system650can move on frames620and622to inspect row of stiffeners603, as well as the skin and frames620and622. When completed, mount664can extend and swivel to position thermography camera670to inspect an adjacent row of stiffeners, for example row of stiffeners604, as well as the skin and frames associated with row of stiffeners604.

Terms of relative position as used in this application are defined based on a plane parallel to the conventional plane or working surface of a workpiece, regardless of the orientation of the workpiece. The term “horizontal” or “lateral” as used in this application is defined as a plane parallel to the conventional plane or working surface of a workpiece, regardless of the orientation of the workpiece. The term “vertical” refers to a direction perpendicular to the horizontal. Terms such as “on,” “side” (as in “sidewall”), “higher,” “lower,” “over,” “top,” and “under” are defined with respect to the conventional plane or working surface being on the top surface of the workpiece, regardless of the orientation of the workpiece.