Abstract:
A system and method for automatic digital radiographic inspection of round aerospace parts ( 18 ) and irregularly shaped aerospace parts ( 19 ) includes a radiation source ( 14 ) and a radiation detector ( 16 ) located on opposite sides of the aerospace part to receive the radiation from the radiation source. In operation the radiation source and the radiation detector are manipulated by a robot ( 10 ) in six independent axes of motion. The aerospace part is rotated by a part manipulator ( 20 ) to provide the seventh axis of motion and the aerospace part is tilted to provide the eighth axis of motion. This allows every portion of the aerospace part to be examined. The radiation detector converts the impinging radiation into electrical signals and the system generates the radiographic images and archives these images.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of provisional patent application Ser. No. 60/906,579, filed 2007 Mar. 13 by the present inventors. 
     
    
     FEDERAL SPONSORED RESEARCH 
       [0002]    Not Applicable 
       SEQUENCE LISTING OR PROGRAM 
       [0003]    Not Applicable 
       BACKGROUND OF THE INVENTION 
     Field of Invention 
       [0004]    This invention relates to automatic radiographic inspection and automated image acquisition of aerospace engine parts that are hollow and round such as engine fan frames, combustion housings and stators as well as irregularly shaped aerospace parts such as turbine blades. The round parts typically range from two to six feet in diameter and the irregular parts are usually smaller with complex geometries and undercuts. 
         [0005]    Aerospace engine parts require non destructive inspection in order to ensure that the product is safe for use in a jet engine. These parts need to be free of all flaws; such as porosity flaws and other internal voids remaining from the aerospace part manufacturing process to ensure that the parts are safe for use in the aircraft. These flaws are internal and are detectable only by radiographic techniques such as x-ray inspection. 
         [0006]    In order to completely inspect these parts there may be multiple views (in the hundreds) required in order to provide for 100 percent inspection of each portion of the aerospace part. 
         [0007]    The current state of the art involves putting the aerospace part into a radiation shielded x-ray vault and then imaging the part in a manual and slow fashion. Only a single area covering approximately 14″×17″ of a given part can be x-rayed at a single time. The aerospace part is placed in the vault with a single piece of film located in a specific position. The vault is closed and the film exposed to the x-ray; the vault is opened the film removed and the part manipulated to allow for the next image. A typical operation will complete only six to ten images in an hour. Because there may be hundreds of images required the current state of the art is time consuming and expensive. After the film is removed the film needs to be taken to a dark room and further processed to develop the image and then read against a light box. This manual process takes approximately ten minutes per image adding to time and cost of the process as it is currently practiced. The inspectors enter and exit the vault to set up and remove every exposure. 
         [0008]    Accordingly, there is a need for a method and a system to automate the process and to ensure reliable and efficient inspection of every portion of the aerospace part as is provided by this invention. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The above mentioned need is met by the present invention, which according to one aspect provides a system for automatic digital radiographic inspection of aerospace parts; including a supporting means for the radiation source and the radiation detector such that the radiation source and the radiation detector are located on opposite sides of the wall of the round aerospace part. Means are provided to pivotably hold the aerospace part and a computer controls the movement of the supporting means and the holding means to provide seven independent axes of motion. Means are provided to tilt the aerospace part to provide an eighth independent axis of motion. An imaging unit is provided to receive the data from the radiation detector. 
         [0010]    According to another aspect of the invention, a method for automatic digital radiographic inspection of aerospace parts includes providing a radiation source and radiation detector mounted on a c-arm support such that the radiation source and the radiation detector are situated on the opposite sides of the wall of the aerospace part, providing robot manipulation of the c-arm in six independent axes of movement; providing a seventh independent axes of motion by rotating the aerospace part; providing an eighth independent axes of motion via a tilting mechanism; subjecting the robot to teach-learn sequence using pendant control; manipulating the c-arm and the aerospace part in eight independent axes of motion such that every portion of the aerospace part is inspected and collecting the digital signals from the radiation detector. 
         [0011]    According to another aspect of the invention a system of automatic digital inspection of aerospace parts includes: a radiation source attached to one prong of a c-arm and a radiation detector situated directly opposite on the other prong of the c-arm; a robot with six independent axes of motion attached to the c-arm; a part manipulator used to mount the aerospace part as well as rotate the aerospace part in the seventh independent axis of motion; a tilt mechanism to tilt the part manipulator and provide the eight independent axis if motion; a computer to control the movement of the robot and the part manipulator; and means for collect the image data from the radiation detector. 
     
    
     
       DRAWINGS 
       Figures 
         [0012]      FIG. 1  shows a perspective view of the main components of the system including the robot, c-arm, part manipulator, the aerospace part to be examined and the computer station. 
           [0013]      FIG. 2  shows a perspective view of the c-arm with the x-ray source and detector mounted on the two arms. 
           [0014]      FIG. 3  shows a perspective view of the part manipulator for large round parts. 
           [0015]      FIG. 4  shows the top view and the side view of the fixture that is mounted on the part manipulator for inspection of smaller parts. 
           [0016]      FIG. 5  shows the complete system for automated digital radiographic inspection of large round aeronautical parts. 
           [0017]      FIG. 6  shows the complete system for automated digital radiographic inspection of small parts and non round parts that utilizes a fixture to hold these parts. 
       
    
    
     DRAWINGS 
     Reference Numerals 
       [0000]    
       
         
           
               10  robot 
               12  c-arm 
               14  x-ray Source 
               16  x-ray Detector 
               18  large round part 
               19  small parts 
               20  part manipulator 
               22  three jaw chuck 
               24  raised base 
               26   a ,  26   b ,  26   c  arms 
               27   a ,  27   b ,  27   c  set of rollers 
               28  fixture 
               29  servo motor 
               30  computer station 
               32  tilt control 
               40  system for automated radiographic inspection of large round parts. 
               50  system for automated radiographic inspection of small parts. 
             In the drawings identical reference numerals denote the same elements throughout the various views. 
           
         
       
     
       DETAILED DESCRIPTION 
     FIG.  1 —Preferred Embodiment 
       [0036]    A preferred embodiment of the invention to hold; manipulate and x-ray the part is shown in  FIG. 1 . It shows a perspective view of the robot  10 , c-arm  12 , x-ray source  14 , x-ray detector  16  and the part manipulator  20  holding the large round part  18  to be examined. The robot  10  is a conventional six-axis robot such as ABB™ Robot Model 660-225/2.55 that has a load capability to allow for manipulation of the c-arm  12  at full extension. The robot  10  is used to manipulate the c-arm  12  in the six primary axes of movement. The x-ray source  14  is mounted on one branch of the c-arm via conventional mechanical clamping device and the x-ray detector  16  is connected to the opposite branch of the c-arm  12  with a conventional mechanical clamping device.  FIGS. 1 &amp; 2  show the positioning in the c-arm  12  such that the radiation emitted by the x-ray source  14  irradiates the large part  18  or the small parts  19  held in the part manipulator  20  and then impinges on the x-ray detector  16 . The opening of the C-arm  12  is adjustable to create a separation between the x-ray source  14  and the x-ray detector  16 . A skilled x-ray technician can make the adjustment to create the desired sharpness of the x-ray image. Typically, a distance between 46 inches (1150 mm) and 60 inches (1524 mm) is used. 
         [0037]    The x-ray source  14  in the preferred embodiment is a typical fractional focus x-ray source capable of an energy level necessary to penetrate the wall of the aerospace part such as Comet™ MXR-225/21 that is a 225 kV tube with dual focal spots and an overall power rating of 1200 W. This source is interchangeable and the system can be configured with both larger energy sources for thicker parts and materials of greater density as well as micro-focus sources for fine resolution inspection. The detector  16  is a typical amorphous silicon digital panel x-ray detector such as Thales™ Model Flash  23 . It is capable of converting the photons received through the inspection part and, through the software and associated electronic hardware, converting the density of those photons into an image which can be inspected by the operator. 
         [0038]      FIG. 3  shows the part manipulator  20  that provides the seventh rotational axis of movement. It utilizes a three jaw chuck  22  attached to a raised base  24 . The three jaw chuck  22  holds three arms  26   a ,  26   b  and  26   c  each equipped with a set of rollers  27   a ,  27   b  and  27   c . The rollers are set on springs. The large round part  18  to be inspected is placed on top of the sets of rollers  27   a ,  27   b  and  27   c  and clamped by jaw chuck  22 . Thereby, the large round part  18  is securely held in the part manipulator  20 . Large round parts typically range in diameter from 24 inches to 72 inches. Parts that are smaller than 24 inches or parts that are non-circular in shape will require special fixtures whose design will depend on the particular shape of the part to be examined. 
         [0039]    A conventional servo motor  29  such as Baldor™ operates roller  27   a  and is controlled by the computer station  30  via robot  10 . The base of the part manipulator  20  can be tilted with tilt control  32 . The tilt control  32  allows for manual screw based tilting of the inspection base. The tilt control  32  provides the eight independent axis and permits inspection of areas of the large part  18  that otherwise would be inaccessible. By tilting the inspection base the system is capable of allowing complex angles of entry for the c-arm and inspection devices. The base is tilted with a typical industrial wheel mounted to a screw drive on a small gearbox. 
         [0040]      FIG. 4  shows the part manipulator  20  adapted by using a fixture  28  capable of holding a multiple of small parts  19 . The fixture  28  is attached to the part manipulator  20  in the same manner as used for the large part  18 . 
       Operation 
       [0041]    The system shown in  FIG. 1  enables automation of X-Ray inspection in a single step capturing x-ray images of every portion of the part to be inspected. The system is comprised of the robot  10  holding a c-arm  12  which carries the X-ray source  14  and the x-ray detector  16 . The robot manipulates the c-arm to position the x-ray source  14  and the x-ray detector  16  in various positions around the large round part  18 . The x-ray source  14  is positioned by the c-arm outside the large round part to be inspected  18  and the x-ray detector  16  is positioned by the c-arm inside the large round part  18  such that the x-ray radiation can pass through the large part  18  and strike the detector  16 . The part manipulator  20  holds the large round part to be inspected  18  and is controlled by the robot  10  to allow for a total of eight independent axes. Six of the axes are provided by the robot  10 ; the seventh axis is the rotation axis provided by the part manipulator  20  and the eighth axis is provided by the tilt control  32 . The system is programmed such that six axes provided by the robot  10  works in conjunction with the seventh axis provided by the part manipulator  20 . This combination of the six axes provided by the robot  10  with the seventh axis provided by the part manipulator  20  creates the unique ability in combination with the computer software program (not described here) to create a complete inspection sequence that moves the c-arm  6  around the large round part  18  capturing x-ray images of every portion of the part. The part manipulator  20  operates in a manner intended to augment the part inspection capabilities of the system. As described earlier, the part manipulator  20  utilizes a three jaw chuck  22  attached to a raised base  24 . The three jaw chuck  22  holds three arms  26   a ,  26   b  and  26   c  each equipped with a set of rollers  27   a ,  27   b  and  27   c . The rollers are set on springs. The large round part  18  to be inspected is placed on top of the sets of rollers  27   a ,  27   b  and  27   c  and clamped by jaw chuck  22 . Thereby, the large part  18  to be examined is securely held in the part manipulator  20 . Roller  27   a  is powered by the motor  29 , which is controlled by the robot  10  and allows the large part  18  to be rotated while the robot is moving the c-arm  12  around it. The raised base  24  of the part manipulator  20  is capable of being tilted using tilt control  32 , which allows the large round part to be examined in segments that would otherwise have been inaccessible to the radiation because of limitations of movement of the robot  10 . 
         [0042]    The operation begins with the operator establishing an initial inspection position using the robot  10  that is operated via the computer station  30 . The large part to be inspected  18  is loaded on the part manipulator  20  and the robot is subjected to a teach-learn sequence using a pendant control. The use of teach-learn and pendant control is common in robotics and easily understood by a person skilled in the art. Once the sequence is established the robot  10  sends the information to the computer station  30  where the software develops a program for inspection of the large part  18 . The program used controls the movement of the robot  10 , positions the c-arm  12  and controls the movement of the part manipulator  20 . The x-ray exposure for each position of the part manipulator  20  as it is moved through the inspection sequence is controlled by the software program operating the computer station  30 . The x-rays emitted by the x-ray source  14  irradiate the large round part  18  and then is measured by the x-ray detector  16 . The x-ray exposures are controlled by the software program operating in the computer station that allows automated control of the output parameters such as kV and mA of the x-ray source  14  and the control parameters such as frames of averaging, dwell times and other exposure parameters of the x-ray detector  16 . Image data output from the x-ray detector are fed to the computer station  30 , which processes these signals and displays them as a computer image on its monitor for the operator to inspect for any defects. Once the program is established a completely repeatable inspection is conducted on the large round part  18  and a series of programmed images are presented to the operator at the computer station  30 . The computer station  30  is capable of providing many other functions (not covered here) that allows the operator to view each image in a controlled and cataloged fashion that meets the stringent requirements of the aerospace manufacturing community. It also allows for digital archiving of the images. 
         [0043]    In addition to being able to inspect large round part  18 , the system is capable of inspecting smaller components such as turbine blades. A number of the small parts  19  are loaded onto the fixture  28  that is itself mounted on the part manipulator  20 . The part manipulator is programmed using the previously mentioned teach-learn process to rotate the parts in front of the c-arm  12  in order to create x-ray images of each of the small parts  19  that have been loaded on to the fixture  28 . The fixture design is dependant on the shape and size of the small part  19  to be examined. At the same time the c-arm  12  is moved by the robot  10  around the smaller parts in order to obtain a variety of x-ray views of these parts. 
         [0044]    The robot  10  is used to manipulate the c-arm  12  in the six primary axes of movement. The part manipulator  20  provides the seventh rotational axis of movement and the tilt control  32  provides the eight independent axis and permits inspection of areas of the small parts  19  with undercuts that otherwise would be inaccessible. 
         [0045]    Using the teach and learn mode via manipulation of the c-arm  12 ; the part manipulator  20  and the tilt control  32 , the operator is able to complete the entire inspection of a the aerospace parts with a single load into the x-ray vault. The software program used (not described here) allows the computer station  30  to program every step of the operation from the positioning of the robot  10  to the control settings of the x-ray source  14  to the image settings of the x-ray detector  16  to the digital storage of these images. Once the teach and learn mode is completed the software program automates the process for rapid inspection that is completely repeatable. 
         [0046]    The radiation source  14  is preferably, but not necessarily a standard X-ray such as Comet™ MXR-225/21, but alternative radiation sources such as an isotopic radiation source producing gamma rays could be used as well. 
       DESCRIPTION AND OPERATION OF ALTERNATIVE EMBODIMENTS 
       [0047]    While the system in the preferred embodiment is equipped with a 225 kV energy level, the c-arm  6  is designed to accommodate up to 450 kV tubes and tubes as small as 130 kV micro-focus tubes. The current system design with a digital panel x-ray detector  16  can also be modified to accommodate both different sizes and types of digital flat panels as well as, linear diode arrays and other x-ray detection devices which can be mounted on the c-arm  6 . The detector  16  in the preferred embodiment is a typical amorphous silicon digital panel x-ray detector, but it can be any means that is capable of processing radiation emitted by the radiation source  14  into a viewable image. It is preferred that that the radiation detector  16  be of the type that converts impinging radiation into an electric output signal although x-ray film could also be used. The preferred embodiment for manipulating parts  18  and  19  as described above uses the robot  10  to provide the six independent axes. Another method to provide the six axes of independence would be to build a mechanical manipulator held by a device such as a crane. It would be clear to a person skilled in the art to design such a device to provide a similar function as provided by the robot  10 . It is also possible to use a different type of motor or a mechanical device to rotate the part manipulator  20  that provides the seventh independent axis. It is also possible to provide a motorized means for operating the tilt control  32  rather than the manually operated mechanical control showed in the preferred embodiment. 
         [0048]    The foregoing has described a method and apparatus for digital radiographic inspection of aerospace parts that permits automated x-ray inspection in a single step capturing x-ray images of every portion of the part to be inspected without using the multi step process as described previously in the Background section. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the scope of the invention as defined in the claims below.