Abstract:
An apparatus for the ultrasonic testing of internal areas of prefabricated composite assemblies as described. The composite assemblies have one or more internal areas formed therein. The apparatus includes at least one receive transducer, at least one transmit transducer, a vertical member, a support member slidably attached to the vertical member, a pair of substantially parallel hollow rods, and an ultrasonic testing system. Each rod comprises a transducer attachment end with receive transducers attached to the transducer attachment end of a first rod, and transmit transducers attached to the transducer attachment end of a second rod. The rods are slidably attached to the support member and manually movable with respect to a composite assembly to be tested. The ultrasonic testing system is coupled to the receive transducers through the first rod, and coupled to the transmit transducers through the second rod.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to ultrasonic inspection of composite assemblies and more specifically, to methods and systems for inspection of composite assemblies that may include cavities. 
   More and more structures are fabricated utilizing composite materials. For example, airframes currently being developed incorporate more composite parts than previous airframes. However, utilization of more composite parts results in additional requirements for ultrasonic inspection to provide information with regard to the integrity of these additional composite parts. 
   Most facilities that fabricate composite materials, and thus composite parts, have limited capabilities for providing a fast, thorough ultrasonic inspection of these composite parts. One example of such a composite part is a movable trailing edge wing component. Traditionally, such a part was fabricated from metallic materials. In new generation aircraft, this component will be fabricated from composite material. As such, ultrasonic inspection will need to be utilized for this component, and the information provided by such an ultrasonic inspection will be utilized in the manufacturing process. Specifically, the ultrasonic inspection information will be utilized in adjusting the manufacturing process to ensure that quality parts are being produced for such an airframe component. 
   At least some composite components will be fabricated to include deep recessed cavities, for example, up to 30 inches deep. These cavities limit current ultrasonic technologies from performing a fast and thorough inspection. While computer controlled, gantry based, ultrasonic inspection systems are known to exist, for many inspection applications, such systems are prohibitively expensive to implement, and may not include flexibility for the inspection of many different composite assemblies. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In one aspect, an apparatus for the ultrasonic testing of internal areas of prefabricated composite assemblies is provided. The apparatus includes at least one receive transducer, at least one transmit transducer, a vertical member, a support member slidably attached to the vertical member, and a pair of substantially parallel hollow rods. Each rod includes a transducer attachment end. The receive transducer is attached to the transducer attachment end of a first rod, and the transmit transducer is attached to the transducer attachment end of a second rod. The rods are slidably attached to the support member and manually movable with respect to a composite assembly to be tested. The apparatus further includes an ultrasonic testing system coupled to the receive transducer through the first rod, and the ultrasonic testing system is coupled to the transmit transducer through the second rod. 
   In another aspect, a method for operator controlled ultrasonic inspection of prefabricated composite assemblies is provided. The method includes engaging the assembly to be inspected with transmit and receive transducers, the transmit and receive transducers mounted opposite one another on substantially parallel rods, the portion of the assembly to be inspected in the space between the transmit transducers and the receive transducers. The method further includes outputting ultrasonic inspection signals from the transmit transducers, receiving the ultrasonic inspection signals at the receive transducers, providing for planar, operator assisted movement of the rods during the outputting and receiving steps, and analyzing the signals received at the receive transducers to determine a condition of the assembly being inspected. 
   In still another aspect, a device enabling operator assisted ultrasonic inspection of composite assemblies is provided. The device includes a vertical member, a support bracket slidably attached to the vertical member, an air cylinder attached to the support bracket and the vertical member, a pair of rods slidably attached to the support bracket and substantially perpendicular to the vertical member, and transmit and receive transducers. The air cylinder is configured for operator assisted movement of the support bracket with respect to the vertical member. The pair of rods are slidably attached to the support bracket and substantially perpendicular to the vertical member. The rods are manually movable with respect to the support bracket, and each rod includes a transducer attachment end. The transmit and receive transducers are mounted to respective transducer attachment ends and are oriented such that a composite assembly may be inserted into a space between the transmit transducers and the receive transducers and between the rods. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram illustrating a movable trailing edge wing component fabricated from composite materials and having one or more deep cavities formed therein. 
       FIG. 2  is a schematic block diagram of a multi-channel, multiplexed, through-transmission ultrasonic inspection system. 
       FIG. 3  is a schematic block diagram of a multi-channel, multiplexed, through-transmission ultrasonic inspection system connected to a remote processor using an Ethernet connection. 
       FIG. 4  is a plan view of a mechanical device for the attachment of transducers which allow for the through-transmission ultrasonic inspection of composite assemblies that include one or more deep cavities. 
       FIG. 5  is an illustration of rods of the mechanical device of  FIG. 3  moving ultrasonic transducers within the wing component of  FIG. 1  as part of an inspection process. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Herein described is a rapid inspection technique and system that can protrude deep into the cavities of a composite component, for example, a movable trailing edge wing component to instantly provide a user with C-scan data resulting from the inspection of the composite component. Inspection of such components is facilitates the manufacture and production of both the herein described composite component and other composite components that also may include cavities. 
   The described inspection system provides the ability to rapidly inspect large recessed composite areas without the added complexity of motion control hardware and software. Specifically, the system is operated manually with the aid of air cylinders. The air cylinders minimize the exerted force necessary for a user to apply to accurately control placement of transmit and receive transducers. The air cylinders help to control movement of the transducers by countering the effects of gravity. Therefore, the operator/user can make directional changes for the transmit and receive transducers with little applied force, for example, three pounds of force. The small amount of applied force required of a user provides for a manual ultrasonic inspection with minimal impact on the human operator. As further described herein, adjustments that can be made with respect to a pedestal also provide a safe ergonomic operating zone that can be easily adjusted for a wide variety of inspection locations and operator variables, for example, the height of an operator. 
   The use of fast, multi-channel ultrasonic electronics and positional feedback to a computer system having a visual user interface, provides the operator with the ability to see the inspection results at updating rates in excess of seven square inches/second. An analogy is the operator painting a picture of the part under inspection on the computer screen as they are moved rods up and down, and back and forth, with minimal effort. Easy manual manipulation of the transmit and receive transducers eliminates the need for motors, motion control hardware and software, while still maintaining a respectable inspection speed and area coverage. 
     FIG. 1  is a diagram of a movable trailing edge wing component  10 . Wing component  10  includes an underside  12 , a top surface  14 , and a plurality of web components  16  that extended between and are affixed to underside  12  and top surface  14 . Web components  16  are substantially perpendicular to the respective underside  12  and top surface  14  at the locations where web components  16  are affixed. Web components  16  provide stability and strength to wing component  10  and help to maintain relative positioning between underside  12  and top surface  14  of wing component  10 . In the production of wing component  10 , web components  16  need to be inspected. One system for inspecting of composite components is an ultrasonic inspection system. An ultrasonic inspection system provides a C-scan image on a computer screen as a user is taking ultrasonic data with the inspection system. 
     FIG. 2  is a schematic block diagram of one embodiment of an ultrasonic inspection system  100 . Ultrasonic inspection system  100  is a thirty-two channel multiplexed through-transmission ultrasonic (TTU) inspection system. Specifically, system  100  includes thirty-two pairs of corresponding transducers. Of the sixty-four transducers, thirty-two transducers are transmitting transducers  102  or pulsing transducers on one side of a component or structure (for example, wing component  10  shown in  FIG. 1 ) under inspection. The other thirty-two transducers are receiving transducers  104  on the opposing side of the structure under inspection. Thus, thirty-two channels are provided for thirty-two transmit transducers  102  and thirty-two channels are provided for thirty-two receive transducers  104 . As used herein, a “channel” refers to the communication link to a transducer. The transducers may be included in one device or probe. Alternatively, the plurality of channels may be divided in such a manner as to function as an array of probes, such as a sixty-four probe array with thirty-two transmitting probes and thirty-two receiving probes, where each probe includes one transducer. Each transmit or receive channel corresponds with an individual piezoelectric crystal transducer. The individual transducers, as described, may be arranged as in a single probe or a number of probes functioning in an array. 
   Each of the thirty-two transmit channels  102  may be sequentially pulsed, such as a pulser board pulsing channels 1 through thirty-two, one channel every 200 microseconds (us), at a 5 kHz repetition rate to cycle through the thirty-two channels  102  once every 6.4 milliseconds (ms). A pulser board pulsing channels refers to the pulser board providing a transmit signal to a transmit channel for a transducer. An example pulser board, or interface board or receiver board, may be a printed circuit board (PCB) with electrical connections or communication paths. An interface board  106 , and/or a processor or microcontroller of an attached computer (not shown), may be used to control the sequential pulsing of the thirty-two transmit channels  102  and coordination of the sequence of received signals. The repetition rate for the cycling of channels is typically selected, and limited, in part due to the time for an ultrasonic signal to propagate from a transmitting transducer crystal through a couplant to the surface of the part, through the part under inspection, and from the surface of the part through a couplant to a receiving transducer crystal. The repetition rate may also be dependent upon such factors as the communication bandwidth to transmit the processed signals from the multiplexing receiver board to a computer controlling and/or processing the inspection. 
   The embodiment illustrated in  FIG. 2  shows two sixteen channel pulser boards  120 ,  122 , each connected to an interface board  106  and each providing sixteen of the thirty-two transmit channels  102 . A pulser board typically is a PCB board which can independently provide signals intended for the sixteen different transducers from an interface board to the sixteen corresponding channels using corresponding pulsers of the pulser board. The corresponding pulsers provide electronic pulse signals for the digital or electronic signals from the interface board. Also included are two sixteen channel receiver boards or RF amplifier and A/D boards  124 ,  126 , each coupled to the interface board  106  and each receiving sixteen of the thirty-two receive channels  104 . 
   A thirty-two channel multiplexed TTU system as shown in  FIG. 2  may also include an encoder interface  130  to provide an interface between positional encoders  1 thirty-two of a scanning system and an interface board  106  of the thirty-two channel multiplexed TTU system. An encoder interface  130  may include two counter chips, such as L87266R1 counter chips manufactured by LSI Computer Systems, Inc., of Melville, N.Y. The counter chips have internal registers which hold the current value as an encoder on the scanning system moves back and forth with a scanning probe. The counter chips will count up and down from a reference value to provide different values for the internal registers of the counter chips. Such information is typically referred to as position information of the scanning system. The position information is relative to the position of the transducers in some physical manner because the encoders are mechanically tracking the movement of the transducers. Thus, the position information provided by an encoder is synchronous to the movement of a scanning probe, but the transducer signals are asynchronous to the scanner movement. Thus by combining the position information of the encoder through an encoder interface, a microprocessor is capable of tying the two pieces of information together to establish the position of a transducer for a particular ultrasonic signal. For example, a microprocessor may combine positional information from the counter chips of the encoder interface into the same data packet as the corresponding ultrasonic data. Additional software may then be able to analyze the particular data packet as having an ultrasonic data value at a specific position which occurred during the scan. Although encoders are typically used to provide position information, encoders may additionally or alternatively be used to provide such data as speed data, velocity data, and distance data. 
   A receiver board  124 ,  126  may include a tuned filter  142  for each receive channel  104 . For example, a tuned filter  142  may include a base amplifier and a tank circuit. A tunable capacitor of a tuned filter  142  may be adjusted to filter the received signal to a specific frequency, such the frequency of a piezoelectric crystal oscillating at 5 MHz. After filtering each of the received signals, all sixteen signals are provided to a first layer of multiplexing switches  146 , referred to as a first multiplexing chip. As a non-limiting example, a multiplexing chip may be a MAX31OCPE multiplexing chip manufactured by Maxim Integrated Products, Inc., of Sunnyvale, Calif., which permits a signal voltage input range of 15 volts peak-to-peak (Vpp). The first layer of multiplexing switches  146  may provide 60 dB of isolation between the sixteen signals. A second layer of multiplexing switches  148 , also referred to as a second multiplexing switch may provide an additional 10 dB) of isolation between the channels. The second layer of multiplexing switches  148  may also use MAX3I OCPE multiplexing switches. Using two layers of multiplexing switches  148  can achieve 70 dB) of isolation between the channels. With 70 dB of isolation between channels, one channel can be 3000 times greater than another channel without affecting the smaller input as provided by 70 dB=20×Log (difference) where (difference) is equal to 3000 for 70 dB. For example, one channel can have a 5 MHz signal with a strength of one millivolt (mV) and another channel can have a 5 MHz signal with a three volt (V) strength without affecting the 1 mV signal. Also, by separating the multiplexing switches into two layers, the capacitance is decreased so as not to degrade the RF signal. Different combinations of channel switching may be used with the two layers of multiplexing switches. For example, a single 60 dB multiplexing chip used to switch between sixteen channels may be used with two 10 dB multiplexing chips to switch between eight channels each. By selecting corresponding channels in the first layer of multiplexing switches  146  and the second layer of multiplexing switches  148 , a single receive channel may be selected. 
   The single receive channel signal, filtered and multiplexed, is provided to a logarithmic amplifier  150  which provides logarithmic amplification for 70 dB of dynamic range, such as a voltage range of −67 dB to +3 dB, although logarithmic amplification can be centered around different dynamic ranges. Thus, the layered multiplexing chips  146 ,  148  provide the fill dynamic range of the capabilities of the logarithmic amplifier  150 . Logarithmic amplification follows the formula Gain log =20×Log(V out /V in ). After logarithmic amplification, the signal may be linearly amplified by a linear amplifier  154 , such as to provide 20 dB of linear amplification to adjust the logarithmically amplified signal to the full range of an analog to digital converter. Linear amplification follows the formula Gain lin =(V out /V in ). The signal may then be converted from analog to digital using an analog to digital chip  158  (A/D converter), such as an analog to digital converter with an input range of 0 to 10 volts. An envelope (peak) detector  156  and a diode  155  may be used between the linear amplification and the conversion from analog to digital such that the peak value is converted to a digital signal by the A/D converter. The diode  155  can isolate the positive voltage of the amplified signal to permit the envelope (peak) detector  156  to capture the peak amplitude of the signal. Only the peak amplitudes of a signal are required for TTU inspection to identify flaws from changing amplitudes. For example, the logarithmic amplifier  150  may output a signal with 1.4 volts peak-to-peak (Vpp) centered around 0 volts; the linear amplifier  154  may increase the signal to a 20 Vpp signal (−10 V to +10 V); the diode  155  may isolate the +10 V peak range (0 V to +10 V); the envelope peak detector  156  may capture the peak amplitudes of the signal ranging from 0 V to +10 V; and the analog to digital chip  158  may convert the 0 V to 10 V signal to a digital signal with a 12 bit resolution. 
   The use of the large 70 dB dynamic range logarithmic amplification assists in the identification of small changes or imperfections in a part under inspection. For example, 70 dB of dynamic range maybe required to find a piece of foreign material located 68 plys (layers) into a half inch thick piece of graphite composite material under inspection, where one ply, or one layer, is seven thousandths of an inch thick. The foreign piece of material may be almost on the bottom edge of the piece of graphite under inspection as viewed through the part from the transmitting transducer to the receiving transducer. Sound, or specifically an ultrasonic signal, diminishes as it propagates through a part under inspection. 
   For example, in the inspection of the half inch thick piece of graphite, the ultrasonic signal may have dropped by as much as 60 dB in through transmission before it reaches the 68 th  ply where the piece of foreign material is located and for which 2 dB of change may be necessary to detect the presence of the piece of foreign material. In order to detect the 2 dB of change, the noise must not be so great as to mask the 2 dB change for the piece of foreign material. The dynamic range must be large enough to detect the flaw in the structure under inspection, the piece of foreign material in the graphite. By using a large logarithmic gain, a scanning system may be capable of resolving a high level of detail in a part under inspection. Using logarithmic amplification amplifies the small changes more than large changes in the signal. Typically, large changes in a signal include noise. By comparison, when using linear amplification, the noise is amplified just as much as the signal. And by using a large dynamic range, a system is capable of scanning thick parts. 
   In addition to accounting for a high dynamic range, the system  100  multiplexes the high dynamic range without acquiring crosstalk, or noise between the channels. In order to switch or multiplex the large dynamic range signals without introducing noise or crosstalk between the channels, the multiplexing may be performed by layering multiplexing chips, such as described by using an initial 60 dB range and a second layer of 10 dB range multiplexing chips. 
     FIG. 3  is a schematic block diagram  170  of a thirty-two channel multiplexed through-transmission ultrasonic inspection system  100  connected to a remote processor  172  using an Ethernet connection  174 . As illustrated in  FIG. 3 , thirty-two transmit channels  102  may be coupled to thirty-two transducers which are used to inspect a part  180 . thirty-two receive channels  104  may be coupled to thirty-two receive transducers to receive signals transmitted through a part under inspection  180  from thirty-two corresponding transmitting transducers. The multiplexed through-transmission ultrasonic inspection system may be connected to a remote processor  182 , such as a computer with a microprocessor for further processing, analyzing, and displaying results of the inspection, through a communication connection or a link, such as Ethernet connection  174  or a serial communication connection. 
   The above described ultrasonic inspection system  100 , while electrically configured for the ultrasonic testing of composite materials such as graphite composites, has mechanical limitations. Specifically, known mechanical mounting configurations of transducers  102  and  104  include prohibitively expensive gantry-based systems that may be best utilized in the inspection of large sheets of such material. Therefore, ultrasonic inspection system  100  has not been utilized for the inspection of three-dimensional assemblies fabricated from composite materials, such as, wing component  10  (shown  FIG. 1 ). 
     FIG. 4  is a plan view of a mechanical device  200  which provides for ultrasonic inspection of composite assemblies that include one or more deep cavities. Mechanical device  200  includes a pedestal frame  202  having a horizontal base  204  and a vertical member  206  extending vertically therefrom. Coupled to vertical member  206  are a plurality of movable rods  208  having multiple channel ultrasonic inspection probes  210  mounted thereon providing a capability to reach into cavities of preassembled parts allowing for their ultrasonic inspection. The probe and rod assembly provides a user with the capability of quickly inspecting internal areas of composite assemblies by pushing rods  208  back and forth and up and down into cavities formed by pre-assembled composite assemblies. 
   Inspection probes  210  form a part of, and are electrically connected to, a system, for example, ultrasonic inspection system  100  (shown in  FIG. 2 ). As described above, ultrasonic inspection system  100  includes ultrasonic testing electronics and software that provide a C-scan image on a computer screen as a user is utilizing system  100  along with mechanical device  200  to gather ultrasonic test data. By this manner, the user can inspect the internal web  16 , for example, of a wing component  10  (shown in  FIG. 1 ) in roughly one minute. 
   Referring still to  FIG. 4 , attached to vertical member  206  is a movable supporting bracket  220 . Movable supporting bracket  220  moves up and down to vertical member  206  by use of wheels  222  attached to movable supporting bracket  220 . Wheels  222  are run inside a grooved notch  224  in vertical member  206 . Air cylinders  230  are attached to the movable support bracket  220  and also vertical member  206 . Air cylinders  230  provide for easy movement of the support bracket by a user in the up and down direction and also counter the effects of gravity to allow a user to easily move rods  208  in a back-and-forth direction. In this manner, air cylinders  230  provide up and down movement with very little externally applied force in either direction needed from a user. 
   Movable rods  208  slide back and forth through supporting bracket  220 . Movable rods  208  have a handle  240  on one end and the inspection probes  210  on the other end. The user manipulates the location of inspection probe  210  by moving handle  240  back and forth and movable supporting bracket  220  up and down. The pedestal frame  204  has wheels  242  to provide portability and also has the ability to lock in place during an inspection. In one embodiment, inspection probes  210 , are through-transmission ultrasonic inspection probes. Therefore, inspection probes  210  include the two halves, transmit transducers and receive transducers, and the composite part to be inspected is inserted in between the two halves at slot  250 . Transmit transducers of inspection probe  210  are mounted on a first of movable rod  208 , and receive transducers are mounted on a second of movable rods  208 . In one embodiment, magnets are utilized in the inspection probe halves to keep the halves of the probe aligned properly. In an embodiment which utilizes a pulse echo testing methods, a single rod  208  is utilized to which both transmit and receive transducers are mounted, enabling testing of an assembly from a single surface. 
   One or more encoders  260  (similar to encoders 1 thirty-two shown in  FIG. 2 ) are mounted on vertical member  206 . Encoders  260  keep track of the position of the inspection probes  210  by electronically providing pulses to through-transmission ultrasonic inspection system  100  when rods  208  move with respect to support bracket  220  or support bracket  220  moves with respect to vertical member  206 . If rods  208  are moved, encoders  260  are used to monitor movement back or forth (X direction) and send electronic pulses indicative of movement in the X direction. If support bracket  220  moves up or down, encoders  260  are used to monitor this movement (Y movement) and send electronic pulses indicative of movement in the Y direction. Through-transmission ultrasonic inspection system  100 , as described above, includes counters that keep track of the electronic pulses and provide count information to the system software as directional information that is required for C-scan ultrasonic testing and inspection. The system software receives ultrasonic test data and positional data from inspection system  100  electronics. This ultrasonic test data is mapped real time to an X &amp; Y C-scan image for the user to view on a monitor. 
     FIG. 5  illustrates an ultrasonic inspection being performed on wing component  10  utilizing mechanical device  200 . One rod  208  is extending into cavity  300  and the other rod  208  is extending onto the other side of web component  16  for the inspection of web component  16 . Water is injected into rods  208 , which are hollow, at the end having handle  240  and the water runs through the hollow chamber within rods  208 , and couples the transducer signals to the part being inspected. In one specific embodiment, seven channels of ultrasonic data are utilized to provide inspection of wing component  10 . Each channel contains a transmit transducer and a receive transducer. The transmit transducers are on one side of web component  16  and the receive transducers are on the other side of web component  16 . Electronics associated with inspection system  100  drive the transmit transducers and receive signals from the receive transducers through one or more coaxial cables also located inside rods  208 . In this manner, the electronics of the through-transmission ultrasonic inspection system  100  send a pulse to the transmit transducers which generate an ultrasonic radio frequency (RF) that is coupled to web complement  16  by the water. 
   The RF signal is sent through web component  16 , and received by the receive transducer on the other side of web component  16 , the receive transducer also being water coupled to web component  16 . The received signal is routed back to the electronics of the through-transmission ultrasonic inspection system  100  via another one are more coaxial cables inside rods  208 . If there is a defect internal to web component  16 , the RF signal reveals a change in magnitude and the electronics of through-transmission ultrasonic inspection system  100  sense this amplitude change. 
   Mechanical device  200  and ultrasonic inspection system  100  provides the capability to a quasi-manually inspect large recessed composite areas without the aid of motion control and the overhead associated with motion control. The air cylinders described herein are positioned on mechanical device  200  to minimize the user exerted force necessary to control movement of the transmit and receive transducers by countering the effects of gravity. The result is a manual inspection system that imposes a minimal impact to a human operator. The use of fast, multi-channel, ultrasonic electronics and positional feedback to the software of inspection system  100 , provide the operator with the ability to see inspection results at rates in excess of seven inches/second. The result is that mechanical device  200  provides means for easy manual manipulation, respectable inspection speed, and area coverage, while still eliminating any need for motors, motion control hardware and software. 
   The above described inspection method utilizing mechanical device  200  is not limited to through-transmission ultrasonic inspection. Pulse echo and array ultrasonic inspection system components may also be mounted on the rods  208 . As described above, in one pulse echo testing embodiment, the pulse echo components are mounted on a single rod  208 . The combination of mechanical device  200  and through-transmission ultrasonic inspection system  100  is practical and the capabilities of mechanical device  200  result in an ultrasonic inspection system that is very portable. Such an inspection system provides flexible C-scanning areas which results in a testing and inspection capability for a large variety of components that, when fabricated, include one or more cavities. In addition, such as system need not be limited to cavity scans but may be used to inspect any type of flat surface in a small amount of time. 
   The combination of mechanical device  200  and through-transmission ultrasonic inspection system  100  facilitates performing fast C-scan ultrasonic test inspection without robotic or gantry systems, and these inspections may be performed in areas that are extremely hard to access utilizing known C-scan ultrasonic testing and inspection systems. The system also provides quick feedback for a manufacturing process by providing a real-time display of an inspection area helping to ensure product quality. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.