In-process vision detection of flaw and FOD characteristics

An inspection system (9) includes an idler wheel (61) that is coupled to a fabrication system (8) and is in contact with a backing layer (65) of an applied material (64). A rotation sensor (63) monitors the idler wheel (61) and generates a rotational signal. A controller (24) is coupled to the rotation sensor (63) and determines a characteristic of one or more flaws and FOD (19) on a composite structure (12) in response to the rotation signal.

RELATED APPLICATIONS

TECHNICAL FIELD

The present invention relates generally to the fabrication of composite structures and to material placement machines. More particularly, the present invention relates to systems and methods of detecting flaws and foreign object debris (FOD) and characteristics thereof during the fabrication of a composite structure.

BACKGROUND OF THE INVENTION

Composite structures have been known in the art for many years. Although composite structures can be formed in many different manners, one advantageous technique for forming composite structures is a fiber placement or automated collation process. According to conventional automated collation techniques, one or more ribbons of composite material, known as composite strands or tows, are laid down on a substrate. The substrate may be a tool or mandrel, but more conventionally, is formed of one or more underlying layers of composite material that have been previously laid down and compacted.

Conventional fiber placement processes in the formation of a part utilize a heat source to assist in the compaction of the plies of composite material at a localized nip point. In particular, the ribbons or tows of the composite material and the underlying substrate are heated at the nip point to increase resin tack while being subjected to compressive forces to ensure adhesion to the substrate. To complete the part, additional strips of composite material can be applied in a side-by-side manner to each layer and can be subjected to localized heat and pressure during the consolidation process.

Unfortunately, defects can occur during the placement of the composite strips onto the underlying composite structure. Such defects can include tow gaps, overlaps, dropped tows, puckers, and twists. Additionally, foreign objects and debris (FOD), such as resin balls and fuzz balls, can accumulate on a surface of the composite structure. Resin balls are small pieces of neat resin that build up on the surfaces of the fiber placement head as the pre-impregnated tows pass through the guides and cutters. The resin balls become dislodged due to the motion and vibration of the fiber placement machine, and drop on to the surface of the ply. Subsequent courses of applied layers cover the resin ball and a resultant bump is created in the laminate whereat there may be no compaction of the tows. The fuzz balls are formed when fibers at the edges of the tows fray and break off as the tows are passed through the cutter assembly. The broken fibers collect in small clumps that fall onto the laminate and are covered by a subsequent layer.

Composite structures fabricated by automated material placement methods typically have specific maximum allowable size requirements for each flaw, with these requirements being established by the production program. Production programs also typically set well-defined accept/reject criteria for maximum allowable cumulative defect width-per-unit-area.

Composite laminates fabricated by fiber placement processes are typically subjected to a 100% ply-by-ply visual inspection for both defects and FOD. Typically, these inspections are performed manually during which time the fiber placement machine is stopped and the process of laying materials halted until the inspection and subsequent repairs, if any, are completed. In the meantime, the fabrication process has been disadvantageously slowed by the manual inspection process and machine downtime associated therewith.

Current inspection systems are capable of identifying defects in a composite structure during the fabrication process without requiring machine stoppage for manual inspections. The inspection systems are capable of detecting, measuring, marking, and identifying FOD “in-process” or during the fabrication of a composite structure. This, in turn, eliminates the need for manual FOD inspections and the machine downtime associated therewith.

It is desirable that an inspection system be capable of determining characteristics of flaws and FOD, including size, location, type, density-per-unit area, and cumulative defect width-per-unit area. Thus, there exists a need for an improved inspection system and method of detecting, identifying, and determining characteristics of flaws and FOD within and during the fabrication of a composite structure.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides an inspection system that includes an idler wheel. The idler wheel is coupled to a fabrication system and is in contact with a backing layer of an applied material. A rotation sensor monitors the idler wheel and generates a rotational signal. A controller is coupled to the rotation sensor and determines a characteristic of one or more flaws and FOD on a composite structure in response to the rotation signal.

The embodiments of the present invention provide several advantages. One such advantage is the provision of a composite structure in-process fabrication inspection technique that accurately determines flaw and FOD characteristics.

Another advantage provided by an embodiment of the present invention, is the provision of a composite structure in-process fabrication inspection technique that accurately determines flaw and FOD characteristics without actually communicating with a material placement machine to obtain location coordinates.

Yet another advantage provided by an embodiment of the present invention, is the provision of a composite structure in-process fabrication inspection technique that determines the density of flaws and FOD per unit area and the width of the flaws and FOD per unit area.

Furthermore, another embodiment of the present invention identifies areas of a composite structure for further analysis in view of processing parameters, such as placement speed and programmed gap information, and flaw and FOD trends. In analyzing processing parameters and flaw and FOD trends one can adjust fabrication processes to prevent future flaw and FOD occurrences.

Moreover, the present invention allows for the in-process repair of a composite structure upon detection of a flaw or FOD.

The present invention itself, together with further objects and attendant advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying drawing.

DETAILED DESCRIPTION

In each of the following Figures, the same reference numerals are used to refer to the same components. While the present invention is described with respect to systems and methods of detecting flaws and foreign object debris (FOD) and characteristics thereof during the fabrication of a composite structure, the present invention may be adapted for various applications and systems, such as fabrication of structures and components, production line applications, or other applications and systems known in the art. The present invention may be applied to both the fabrication of aeronautical and non-aeronautical systems and components.

In the following description, various operating parameters and components are described for one constructed embodiment. These specific parameters and components are included as examples and are not meant to be limiting.

Also, in the following description the term “foreign object debris (FOD)” refers to any resin ball, fuzz ball, impurity, backing paper, backing film, or other foreign or undesirable object contained within or on a composite structure. FOD may refer to one or more of the stated objects.

In addition, the term “flaw” refers to any defect within a composite structure or structure under fabrication. A flaw may refer to a tow gap, an overlap of material, a dropped tow, a pucker, a twist or any other flaw known in the art.

Referring now toFIG. 1, a side schematic view of a fabrication system8is shown incorporating a flaw and FOD detection and inspection system9in accordance with an embodiment of the present invention. The fabrication system8includes a lamination system10, as best seen inFIGS. 2 and 3, that may utilize an automated collation process to form a composite structure12, as shown. The inspection system9is positioned proximate the composite structure12and includes one or more illumination devices or light sources13(only one is shown) and one or more detectors14(only one is shown). The light sources13generate light arrays16that are directed at a portion18of the composite structure12to reveal flaws and FOD19within that portion18. The inspection system9also includes a flaw and FOD position detection system20, which determines the position of the flaws and FOD19. A controller24is coupled to the detectors14and the position detection system20and interprets data received therefrom. The collected data may be used to adjust the operation of the fabrication system8, the inspection system9, and the lamination system10, and to indicate, detect, and allow for the correction of the flaws and FOD19. The controller24may store the received data and/or related information in the memory or storage device26. System parameters and operation may be adjusted via the user interface28.

During the fabrication of the composite structure12, the composite structure12may be formed of adjacent tows or strips of composite tape (not shown) to form layers29. The strips include multiple fibers that are embedded in a resin or other material, which becomes tacky or flowable upon the application of heat. The strips are arranged on a work surface30of a table, mandrel, or tool32, and compacted with a compaction roller to form the composite structure12. A compaction roller34can be seen inFIG. 2. The automated collation process includes guiding the composite strips from material creels (not shown) to an automated collation or fiber placement machine, such as a machine made by Cincinnati Milacron and Ingersoll Milling Machines. In particular, the composite strips are guided to a head unit or assembly36, which may be best seen inFIG. 3, and fed under the compaction roller34. Focused heat energy is then applied to adhere the incoming material and the underlying previously laid material. With the combination of pressure and heat, the composite strips are consolidated into a previous applied layer to form an additional layer on the composite structure12.

An example of an automated collation technique that may be used is described in U.S. Pat. No. 6,799,519 B2, entitled “Composite Material Collation Machine and Associated Method for High Rate Collation of Composite Materials.” The contents of U.S. Pat. No. 6,799,519 B2 are incorporated herein by reference.

Referring now to the inspection system9, the light sources13are positioned to emit light arrays at the selected portion18of the composite structure12. The light sources may be positioned at various angles as known in the art, depending on the application. Any number of light sources may be utilized even though a specific number is shown.

The light sources13are positioned relative to the composite structure12via a mounting apparatus40. The mounting apparatus40includes a main shaft42, a secondary shaft44, and a locking clamp46for adjusting the position of the light sources13. The mounting apparatus40, in turn, can be attached to the frame48, to the detectors14, to the bracket50, or to some other object that defines a common position for both the light sources13and the detectors14to maintain a constant spatial relationship relative to one another.

The light sources13may be selected from an infrared light or another type of light having an infrared component, such as a halogen light source or other incandescent light sources. In other embodiments, the light sources13are in the form of a fluorescent light source (e.g., white light LEDs, a low pressure/mercury filled phosphor glass tube, etc.), a strobe or stroboscopic light source, a noble gas arc lamp (e.g., xenon arc, etc.), a metal arc lamp (e.g., metal halide, etc.), or a laser (e.g., pulsed laser, solid state laser diode array, infrared diode laser array, etc.). The light from the light sources13may pass through optical fibers to the point of delivery, an example of which is shown inFIG. 5. The light sources13may include LEDs arranged in an array or cluster formation. In one specific embodiment, the light sources13include twenty-four LEDs mounted in an array upon a three-inch square printed circuit board.

In some embodiments, the light sources13are operated at a power level that increases the infrared (IR) component of the light arrays, which aids in the inspection of dark tow material, such as carbon. In this regard, exemplary power levels in the range of approximately one hundred fifty watts (150 W) and in the wavelength range of about seven hundred nanometers to one thousand nanometers (700 nm-1000 nm) may be used. However, the particular power levels and wavelengths for the light sources13depends at least in part on the speed and sensitivity of the detectors14, the speed at which the material is being laid, the light delivery losses, and the reflectivity of the material being inspected.

The detectors14may be of various types and styles. A wide range of detectors may be used including commercially available cameras capable of acquiring black and white images. In one embodiment, the detectors14are in the form of a television or other type of video camera having an image sensor (not shown) and a lens13through which light passes when the cameras are in operation. Other types of cameras or image sensors can also be used, such as an infrared-sensitive camera, a visible light camera with infrared-pass filtration, a fiber optic camera, a coaxial camera, a charge coupled device (CCD), or a complementary metal oxide sensor (CMOS). The detectors14may be positioned proximate the composite structure12on a stand (not shown) or mounted to the frame48or a similar device. In embodiments of the present invention that do not include a reflective surface, the detectors14may be positioned approximately six inches from the top surface52of the composite structure12, and mounted to the frame48by way of the bracket50and associated connectors54. Also, any number of detectors may be utilized.

The controller24may be microprocessor based such as a computer having a central processing unit, memory (RAM and/or ROM), and associated input and output buses. The controller24may be a portion of a central main control unit, be divided into multiple controllers, or be a single stand-alone controller as shown.

The connectors54may be rivets, screws, or the like and used to mount the detectors14to the frame48in a stationary position. Alternatively, the connectors54may be a hinge-type connector that permits the light sources13, the detectors14, and associated assembly to be rotated away from the composite structure12. This embodiment is advantageous in situations when there is a desire to access parts of the material placement device that are located behind the detectors14and associated assembly, such as during maintenance, cleaning, or the like.

The inspection system9may also include filters56(only one is shown), which may be utilized in conjunction with the lens58for filtering the light passing therethrough. In one embodiment, the filters56are designed to filter the light such that the infrared component of or a certain infrared wavelength or range of wavelengths of the light is able to pass into the detectors14. Thus, the filters56may prevent ambient visible light from entering the detectors14and altering the appearance of the captured image.

Other methods of filtering light can also be used to achieve the same, or at least used to provide a similar result. For example, the detectors14may be designed to include a built-in filter of equivalent optical characteristics. In addition, the filter56may be located between the lens58and the detectors14. Alternatively, the detectors14may include image sensors that are sensitive in the infrared spectrum (i.e., an infrared-sensitive camera), thus eliminating the need for the filters56.

The inspection system9may also include a marking device60for marking the location of the defects and the FOD on the composite structure12. The marking device60may be attached to the frame48and be triggered by the controller24or similar device when a flaw or FOD is detected. The marking device60may deposit ink, paint, or the like onto the composite structure12in areas where flaws and FOD have been detected. The markings on the composite structure12enable the location of the flaws and FOD to be subsequently and readily identified either automatically or manually. The marking device60may also be adapted to mark flaws with different colored ink than that used to mark FOD. Alternatively, other marking or indicating methods can also be used, such as markings utilizing a pump-fed felt-tip marker or a spring-loaded marking pen, indications via audio or visual alerts, and the like.

Referring now also toFIG. 2, a block diagrammatic and perspective view of the position detection system20and components of a material placement machine are shown in accordance with an embodiment of the present invention. The position detection system20includes a material collection device61, an idler wheel62, and an idler wheel rotation sensor63. The composite material64having a backing layer65is directed around the compaction roller34and adhered to the composite structure12. As the composite material64reaches the compaction roller34it is heated and adhered to the composite structure12. As the composite material64adheres to the composite structure12the backing layer65is pulled from the composite material64, rolled around the compaction roller34, around the return roller66, over the idler wheel62, and into the material collection device61. The backing layer65may be in the form of a backing paper, as shown, or may be in some other form known in the art. The compaction roller34and the return roller66are part of a material placement machine or lamination system10, the entirety of which is not shown. The lamination system10may be separate from the inspection system9and the position detection system20.

The material collection device61may be in the form of a collection retainer, as shown, may be in the form of a material collection wheel, a take-up reel, a combination thereof, or may be in some other form known in the art.

The idler wheel62rests against the backing layer65and rotates as the backing layer65passes thereon. Motion of the backing layer65indicates that placement of the composite material64is in progress. The idler wheel62is free to rotate and may apply little to no pressure on the backing layer65. The idler wheel62is coupled to the lamination system15and is suspended via an idler arm67. The idler arm67may be position adjustable and pressure adjustable relative to the backing layer65. The idler wheel may be keyed, such that the controller24may capture an image of the composite material64as it is applied for a predetermined number of idler wheel revolutions.

The rotation sensor63is proximate the idler wheel62and is coupled to the idler arm67. The rotation sensor63monitors the rotation of the idler wheel62and generates a rotation signal indicative thereof. The rotation sensor may be in the form of an encoder, an infrared sensor, a rotary potentiometer, or other sensor known in the art that is capable of detection rotative position and velocity of the idler wheel62.

The position detection system20may also include a collection roller68and a second rotation sensor or collection sensor69. The collection roller is coupled to the collection device61. The backing layer65is passed over the collection roller and into the collection device61. The second rotation sensor69is proximate the collection roller68and detects the rotational position and velocity of the collection roller68.

Although a return roller66is shown, this is intended as one possible example. A material placement machine may include a moveable compaction roller or a stationary show, as known in the art.

Referring now toFIGS. 3 and 4, a perspective view of an application portion of a fabrication system8′ incorporating a flaw and FOD inspection system9′ and a perspective view of light sources13′ are shown in accordance with another embodiment of the present invention. The inspection system9′ includes two light sources13′ (only one is shown) positioned relative to the composite structure12and the compaction roller34on either side of a reflective surface70and a detector14′.FIG. 3illustrates an alternative embodiment of the hinge-type connector54that mounts the light sources13′, the detector14′, the reflective surface70, and associated head assembly36to the frame48by way of the bracket50.

The light sources13and13′ and the detectors14and14′, ofFIGS. 1 and 3, may be translated or moved relative to a composite structure, such as the composite structure12. The adjustability and moveability of the light sources13and13′ and detectors14and14′ provides flexibility in the capture of images of a composite structure. Sample systems including moveable cameras and light sources are described in detail in previously referred to U.S. patent application Ser. No. 10/217,805.

Although the light sources13′ are shown in the form of four halogen light bulbs74, other quantities, types, and styles of illumination sources may be utilized. A light reflection element76is located near the light sources13′. The reflection element76includes a series of light reflecting surfaces78that redirect the light towards the desired area to be illuminated. This levels the illumination across the top surface of a composite structure and eliminates, or at least substantially reduces, the areas of intense light (i.e., hotspots) created by the brightest portion of the light source. Hotspots can lead to errors during the processing of images. The light reflection elements78are particularly advantageous for illuminating the curved/contoured surfaces of the composite structures because the redirection of the light permits a larger portion of a composite structure to be evenly illuminated.

The reflection element76is curved around the light sources13′, such as in a parabolic shape. The reflection elements78are in the form of curved steps that are substantially parallel to the light source13′. The distance between and the curvature of the reflection elements78may be selected for sufficient and even illumination generated from the sum of the two light sources13′. This enables more consistent illumination of the composite structure12, which prevents, or at least reduces, the image-processing errors due to inconsistent illumination of the composite structure12. Alternatively, the shape and/or surface configuration of the reflection elements78may be modified using other techniques known in the art to produce consistent illumination and scattering of light.

In an exemplary embodiment, seventeen reflection elements are utilized and have an overall parabolic shape and a range of widths from about 0.125 inches at the outer edge of the reflection elements to about 0.250 inches at the center of the reflection elements. The reflection elements also have a uniform step height of about 0.116 inches. In other embodiments, however, the reflection elements78may be provided with different numbers of steps having different uniform or varying widths and different uniform or varying step heights.

Furthermore, the reflection elements78may be adjusted in order to direct the light produced by the light sources13′ and scattered by the reflection elements78toward the selected portion of a composite structure. For example, as shown inFIG. 4, the reflection elements78are mounted to the mounting apparatus40with fasteners80. The fasteners80, when loose, are capable of being slid within slots82to correspondingly adjust the angle of the reflection elements78relative to a composite structure. Once the reflection elements78are positioned appropriately, the fasteners80are tightened to secure the reflection elements78in the desired position. Adjustments of the reflection elements78can also be enabled by other methods, such as by electronic means that permit remote adjustment of the reflection elements78.

The detectors14are positioned near the composite structure12and when in the form of cameras are positioned to capture images of the selected illuminated portion, which is typically immediately downstream of the nip point at which a composite tow is joined with the underlying structure.

The light sources13, the detectors14, the reflective surface16, and any reflection elements78, may be mounted on the head unit23to allow for continuous capture of real-time data of the composite structure12. The real time data may be captured as the head unit36is transitioned across the composite structure12and as the composite strips are laid down or applied.

The bracket50may be fastened to the hinge type connector54via a suitable fastener, such as a thumbscrew or any other fastener that may be utilized and inserted through hole72and then tightened to secure the assembly in place for operation. The fastener may be loosened or removed, for example, to rotate the light source and detector assembly away from the compaction roller34and other parts of the fabrication system.

The reflective surface70may be positioned near the composite structure12, and angled such that the reflective surface70reflects an image of the illuminated portion to the detectors14. In one embodiment, the angle of the reflective surface70to the composite structure is about sixty-five degrees, but the reflective surface16can also be positioned at any appropriate angle in order to reflect images of the illuminated portion to the detectors14. The detectors14may be positioned to point toward the reflective surface70in order to capture the close-range images of the illuminated portion from the reflective surface70. More than one reflective surface70may also be utilized in further embodiments of the present invention in which the reflective surface70cooperate in order to direct the images of the illuminated portion to the detectors14.

The reflective surface70may be in various positions relative to a selected portion, such as portion18. Reflective surface70can also be utilized to allow the detectors14to be placed in an advantageous positions, which might otherwise be blocked by portions of the compaction roller34and/or other parts of the fabrication system.

The configuration illustrated inFIG. 3aids in the capturing of images of curved/contoured surfaces of a composite structure since the reflective surface70is positioned close to the composite structure. In addition, this configuration permits the detectors14to be positioned away from a composite structure, to prevent interference between the detectors14and components of the fabrication system8′. Further, the reflective surface70can also provide a “square on” view of the selected portion being inspected, which, in turn, can improve the ability to dimension the two gaps for pass/fail decisions.

Referring now toFIG. 5, a perspective view of a fabrication system8″ incorporating a flaw and FOD inspection system9″ in accordance with another embodiment of the present invention is shown. The inspection system9″ includes lights sources (not shown) that are at a remote location. The light sources generate light rays, which are passed through linear optical fiber arrays or fiber optic cable90to point of transmission92via light emitting heads94. Light arrays are emitted from the fiber optic cable90toward the selected portion18′ of the composite structure12′ to detect flaws and FOD19′. The use of fiber optic cables simplifies the number of components mounted on the head assembly.

Referring now toFIGS. 6 and 7, a logic flow diagram illustrating a method of determining flaw and FOD characteristics during the fabrication of a composite structure and a ply layout illustrating course and frame locations are shown in accordance with an embodiment of the present invention.

In step95, strips of the composite material64are applied to the tool32to form the composite structure12.

In step96, as the strips are applied, the backing layer65is removed from the composite material64in turn causing the idler wheel62to rotate.

In step97, the rotation sensors63and69generate the rotation signals that are indicative of the rotational position and velocity of the idler wheel62and the collection roller68. The rotational signals are also indicative of any cessation in the backing layer, such as when the lamination system10or the application position of the composite material64is laterally transitioned to form another column or course. Cessation of motion indicates that material lay-down for the current course has stopped and that a new course may be started. The rotational signals may be compared, averaged, and utilized to accurately determine position of the lamination system10. The rotational signals may also be utilized to determine when the backing layer is “bunching up” or not passing through the fabrication system appropriately.

FIG. 7illustrates a sample single ply98of a rectangular composite structure99with frame rows100and courses101. Seven rows of sixteen courses are shown. Of course, any number of rows and courses may be created. Also each ply, such as ply98, may be of various shape, another example of which is shown inFIG. 8. The ply98is divided into multiple unit areas102, each of which corresponding to an image frame. Each unit area102may have a width w greater than the width of the strips (not shown) of the composite material being applied and a height h that corresponds to a determined number of revolutions of the idler wheel62. In one embodiment, the unit area width w is approximately equal to seven inches, the width of the composite material plus a half of an inch for each side of the material. In another embodiment, the height h is approximately seven inches corresponding to the circumference of the idler wheel62. The frame numbers may be sequentially assigned even when the course number changes.

In step104, the portion18of concern is selected. The portion18may include the entire composite structure under formation or may include a discrete segment or area of the composite structure. In step105, the light sources13are activated to illuminate the selected portion18. The light rays16, which may be in the form of arrays, are generated such that both the flaws and FOD19may be detected simultaneously within the selected portion18. The light sources may be activated throughout the material placement process.

In step106, detectors, such as detectors14and14′, monitor the portion18and generate status signals in response to the reflection of the light rays16off of the portion18. The status signals contain information regarding the existence of flaws and FOD in the portion18. The detectors14and14′ detect light reflection characteristics of the flaws and FOD.

In step107, the controller24determines one or more flaw and FOD characteristics in response to the rotation signal and the division of the current ply. The characteristics may be determined during the application of the composite material64. The flaw and FOD characteristics may include size, location, position, type, density-per-unit area, cumulative defect width-per-unit area, and any other flaw and FOD characteristic known in the art. Width information of flaws and FOD provides gap and density information. Manufacturing specifications that govern automated material placement have acceptance requirements for various types of defects. For gaps there is a maximum allowable width for a single gap and a maximum allowable total width for of all of the gaps existing within a defined area. Likewise, for FOD there is a maximum allowable number of occurrences with a defined area. Thus, the detector14and/or the controller24may track the area that has been inspected and the number and total width of flaws that have been detected.

For example, the controller may determine longitudinal and lateral position of a flaw or FOD in response to the number of frames captured in a given row and the number of detected cessations per ply. The detector14or the controller24may store an image after a preset number of revolutions of the idler wheel62. The number of revolutions remains constant and establishes the image frame height. This along with the constant width of the material course being placed establishes a constant rectangle, referred to as a frame. The frames are tracked by assigning a discrete number to each frame.

In step107A, the controller24generates an image count for each of the flaws and FOD to determine a linear distance to each of the flaws and FOD. The image count provides a course measurement of longitudinal position. In step107B, the controller24generates a revolution count indicative of the revolutions of the idler wheel62, which is indicative of the position of the lamination system and any detected flaws and FOD in that position. The revolution count provides a fine measurement of longitudinal position within an image frame. In step107C, the controller24generates a cessation count for each of the flaws and FOD. In step107D, the controller24may also generate an applied layer or ply count indicative of the number of currently applied plies. In step107E, the controller24determines the position of the flaws and FOD in response to the image count, the revolution count, the cessation count, and the ply count.

In step107F, the controller24determines the flaw areal density. In step107F1, the controller24counts the flaws and FOD in a current frame to generate a current flaw and FOD frame count. In step107F2, the controller24sums the current flaw and FOD frame count with flaws and FOD of two adjacent frames of a previous course to generate a resultant sum. In step107F3, the controller24determines flaw areal density for the portion in response to the resultant sum. The flaw areal density is equal to the resultant sum divided by the area of the portion.

In step107G, the controller24determines size of the flaws and FOD. In step107H, the controller24determines cumulative gap width per unit area in response to the portion18, the frame, or a current set of frames and the size.

In step108, the detected flaws and FOD19as well as the related characteristics thereof are indicated to a user via a display, such as that shown with respect toFIG. 9.

In step109, the flaw and FOD characteristics as detected may be stored in an archival error file within the memory26, such as in an error file. The characteristics may include the ply, course, and frame number associated with each flaw and FOD. Also, after a preset number of revolutions the detectors14or the controller24may store images of the portion18within the memory26. Since the frame size is constant it is possible to establish the location of a defect on the surface by counting frames from an initial starting point. The detector14, the controller24, or other device that has access to the stored information may determine approximate location of each flaw and FOD therefrom separate from and without being hard-wired to the fabrication system8and/or the material placement machine, stated with respect toFIG. 2.

Referring now toFIG. 8, a top view of a sample irregularly shaped ply110is shown. The length of the courses111vary over the ply110and thus the image frames, corresponding to unit areas112, are staggered. When a course ends in an angular cut, the last frame in that course may be assumed to be fully rectangular in shape for the purpose of designating a unit area. Flaw and FOD characteristics may be determined in response to the frame stagger. In the example embodiment, the unit areas112and thus the frames are in a 50% stagger. Each unit area is bordered by half portions of two adjacent unit areas. The unit areas and the frames may be oriented at any staggered percentage.

When determining flaw areal density, the number of flaws in any affected frame (diagonally cut frame) is summed with those in two adjacent frames of a previous course instead of one. Cumulative gap width is determined by measurement across a designated area in a direction perpendicular to the direction of material placement on a tool. For summation purposes the gaps may be assumed or assigned to extend an entire length of the affected image frames, such that location within a frame of gap location is unnecessary.

Positions of the flaws and FOD may be determined utilizing information from archived positions and engineering disposition and may be resolved utilizing known in-process flaw and FOD marking techniques.

Referring now toFIG. 9, a front view of a user display screen120and user controls122illustrating the detection of flaws and FOD124and indication of flaws and FOD characteristics in accordance with an embodiment of the present invention is shown. Although the operation and use of the display120is primarily described with respect to the embodiment ofFIG. 1, it may be easily modified for and applied to other embodiments of the present invention. The user interface28includes the display120, such as that on a computer monitor, and can also include an input device, such as a keyboard and mouse (not shown), for permitting an operator to move a cursor about the display120and input various system settings and parameters. The display120may be touch-sensitive for permitting the operator to input the desired settings by manually touching regions of the display screen.

The interface28includes an image window126in which an image128, of the composite structure12, is displayed for viewing by an operator or other user. The image128may be in the form of an unprocessed or processed camera image. When processed the image128or a portion thereof may be binarized. During binarization, all shades of gray above a predetermined threshold value may be changed to white, while all gray shades below the threshold value may be changed to black to heighten the contrast of defects and improve the accuracy of defect detection. As an alternative or in addition to binarization, rates of light level change in the raw image and color changes in the images may be used to identify the defects and FOD.

The interface28also includes a position window129, which may display the ply number, course number, and frame number of the lamination system in a current state as is related to a currently viewed image.

The controls122allow for various user inputs to the system. The controls122may be used to adjust the binarization threshold. Generally, the setting of the binarization threshold involves a tradeoff between the sensitivity with which defects are detected and the resolution with which the defects are depicted. In one embodiment, the binarization threshold is set to about 128, which corresponds to the mid-point on the 8-bit digitizing range of 0 to 255. However, other binarization threshold values may be employed depending at least in part on the particular application, available lighting, camera settings, and other factors known in the art.

The controls122also allow the user to adjust or shift the viewing area within the window126. During operation, the window126displays real-time moving video images of the illuminated portion of the composite structure12as the detectors14and/or the reflective surface18are moved relative to the composite structure12. The controls122may be such to allow the user to input the maximum allowable dimensional parameters, the acceptable tolerances, as well as other known parameters for the flaws and FOD.

In addition to displaying images of the composite structure12, the display screen80may also include a defect table128, which lists the discovered flaws and FOD and provides related information thereof, such as location, size, and the like. The display120can further include status indicators130that notify the user whether a particular image area is acceptable or not acceptable based on predefined criteria, such as the maximum allowable dimensional parameters and tolerances.

Referring now toFIG. 10, a logic flow diagram illustrating a method of fabricating a composite structure in accordance with an embodiment of the present invention is shown. Although the logic flow diagram ofFIG. 10is primarily described with respect to the embodiment ofFIG. 1, it may be easily modified to apply to other embodiments of the present invention.

In step150, the fabrication system8applies the strips to form the layers29on the substrate32to form the composite structure12. In step152, the inspection system9illuminates selected areas of or the entire composite structure12during the application of the strips to detect the flaws and FOD19as described above with respect to the method ofFIG. 5. Flaws and FOD may be detected continuously throughout the material placement process and continuously over selected portions or the entire composite structure12.

In step154, the inspection system9distinguishes, identifies, and determines characteristics of the flaws and FOD19and the location thereof and generates a composite structure defect signal. Examples regarding systems and methods for identifying defects in a composite structure during fabrication thereof are included in U.S. patent application Ser. No. 09/819,922, filed on Mar. 28, 2001, entitled “System and Method for Identifying Defects in a Composite Structure” and in U.S. patent application Ser. No. 10/217,805, filed on Aug. 13, 2002, entitled “System for Identifying Defects in a Composite Structure”. The contents of U.S. patent application Ser. Nos. 09/819,922 and 10/217,805 are incorporated herein by reference as if fully set forth herein.

In step156, the fabrication system8may in response to the composite structure defect signal alter the operation thereof. The fabrication system8may cease further application of the strips until one or more portions of the composite structure12are repaired, may alter the manner in which the strips are applied, may adjust parameters of the fabrication system8or inspection system9, or may perform other tasks known in the art.

At any time upon or after the generation of the status signals and/or the defect signals the controller24may store data or images in the storage device26for future or off-line analysis and/or processing. Future analysis may be based on processing parameters, such as material placement speed and programmed gap information, and flaw and FOD trends.

The above-described steps in the methods ofFIGS. 5 and 8, are meant to be illustrative examples, the steps may be performed synchronously, continuously, or in a different order depending upon the application.

The present invention provides systems and methods for the simultaneous detection of flaws and FOD using a single illumination level. The present invention simplifies the detection of the flaws and FOD and allows for efficient identification and repair thereof.