Abstract:
A self propelled scanning device is disclosed. The device includes a self propelled chassis that is locomotive across a surface to be scanned, a translator attached to the chassis, and a carriage attached to the translator and adapted to receive a scanner. The translator selectively moves the carriage in at least one dimension across the surface to be scanned.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of U.S. Provisional Patent Application No. 61/048,349 entitled “CONTINUOUS AUTONOMOUS TESTER,” filed Apr. 28, 2008, the contents of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This disclosure relates to ultrasonic testing in general and, more specifically, to automated ultrasonic testing. 
     BACKGROUND OF THE INVENTION 
     As an aircraft ages, it becomes necessary to perform non-destructive testing on various exterior surfaces of the aircraft. This is a Federal Aviation Administration (FAA) requirement that ensures continued airworthiness. Presently, this is a labor intensive process that requires a mechanic to traverse the specified section of the aircraft with a hand held ultra sonic device. Minor fluctuations in pressure on the device or slippage can cause inaccurate readings that require a second scan. It will be appreciated that similar problems arise in testing of other structures. 
     Examples of automated non-destructive testing have been demonstrated. However, they are restrictive in that a frame or other form of external reference is needed to identify the location of the fasteners for the sensors. 
     What is needed is a system and method that addressees the above, and related, issues. 
     SUMMARY OF THE INVENTION 
     The invention disclosed and claimed herein, in one aspect thereof, comprises a self propelled scanning device. The device includes a self propelled chassis that is locomotive across a surface to be scanned, a translator attached to the chassis, and a carriage attached to the translator and adapted to receive a scanner. The translator selectively moves the carriage in at least one dimension across the surface to be scanned. 
     In some embodiments, the self propelled chassis provides a pair of slip resistant tracks in contact with the surface to be scanned, for providing locomotion across the surface. The self propelled chassis may provide a platform for a portable control computer. The device may include the portable control computer secured to the chassis and configured to selectively control the movement of the chassis on the surface to be scanned. The control computer may also control the translation of the carriage on the translator. 
     In some embodiments, the carriage is attached to the translator by a shock dampening suspension. The shock dampening suspension may comprise a coil-over-shock suspension. The carriage may have at least one rolling caster interposing the surface to be scanned and the carriage. The carriage may be configured to pivot about an axis orthogonal to a direction of translation. 
     The invention disclosed and claimed herein, in another aspect thereof, comprises an automated wing scanning device for operation upon an upper surface of an aircraft wing having a surface skin with a plurality of fasteners thereon connecting the skin to an airframe. The device has a track propelled chassis, the tracks having rubber treads and a sufficient base area to allow the chassis to operate on a slope of up to at least fifteen degrees when the surface skin is wet. A translation table is connected to the chassis and provides a suspended carriage that is selectively rastered across the surface skin. An ultrasonic scanner is secured within the suspended carriage for selectively scanning the wing surface. A control system controls the chassis to follow a predetermined scan path across the wing surface, controls the translation table to translate the carriage and scanner across the wing surface, and accepts readings from the ultrasonic scanner. The device may also comprise a camera mounted to the chassis with a view of the wing surface and interfaced to the control system to allow the control system to correct deviations from the predetermined path on the wing surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is perspective view of one embodiment of an autonomous tester according to the present disclosure. 
         FIG. 2  is a frontal view of a translation table and ultrasonic transducer of the autonomous tester of  FIG. 1 . 
         FIG. 3  is a schematic diagram of the control system of the autonomous tester of  FIG. 1 . 
         FIG. 4  is a superior view of portion of an aircraft wing upon which various embodiments of the autonomous tester of the present disclosure may operate. 
         FIG. 5  is a close up superior view of a portion of an aircraft wing illustrating skin fasteners. 
         FIG. 6  is a perspective view of an aircraft wing with one embodiment of an autonomous tester of the present disclosure operating a testing sequence thereon. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1 , a perspective view of one embodiment of an autonomous tester according to the present disclosure is shown. The autonomous tester  100  in the present embodiment is a robotic design intended to perform ultrasonic testing on the wing of an aircraft. As will be described herein, the autonomous tester  100  will be able to complete ultrasonic testing of fasteners along the surface of an aircraft with minimal user input. The autonomous tester  100  is generally of a modular design to allow easy replacement and upgrade of components. 
     One of the major components of the tester  100  is the robotic chassis  102 . One function of the chassis  102  is to provide a base upon which the remaining components may be attached. The chassis may be constructed of lightweight metals or alloys that are sufficiently strong and lightweight enough to allow the chassis to carry the various additional components of the tester  100 . In one embodiment, the completed tester  100  will be movable by a single person. 
     In the present embodiment, the chassis is of a tracked design, having two tracks  104 . The tracked design allows the tester  100  to have complete freedom of movement across two dimensions. Where design constraints allow, the tester  100  could be equipped with wheels or other locomotion devices. The tracks  104  may be rubber, rubber coated, or equipped with rubber pads to allow the tester  100  to operate with sure footedness across various surfaces. In some forms of ultrasonic testing, the surface upon which the tester  100  operates will be wet and therefore slick. Since aircraft wings are seldom perfectly level, the tester  100  also is required to be able to operate on varying slopes. In some embodiments, the tester  100  will be required to operate on slopes of up to 15 degrees, and the present design has been found to exceed this threshold. 
     In the present embodiment, the power for the locomotion of the tester  100  is provided by a pair of electric motors  106 . As can be seen, the electric motors  106  will interact with the tracks  104  by a pair of sprockets  108 . In other embodiments, other devices may be used to transfer torque from the motors  106  to the tracks  104 . 
     In one embodiment, a pair of sprockets  110  (only one visible in the present view) will be provided near the base of the tracks  104 , creating a triangular configuration on each side of the chassis  102 . This configuration will allow the motors  106  to be away from the base of the chassis  102  while giving the tracks  104  an increased amount of stability. In other embodiments, a traditional track configuration (e.g., non-triangular) may be used. It is understood that various idlers and shock absorbers may be part of the track system. This will allow the tracks to contour to the surface being scanned, enhancing the stability of the tester  100 . 
     The chassis  102  may also have a platform  103  for mounting a control computer  112 . In the present embodiment, the control computer  112  is a personal laptop computer, but in other embodiments, the control computer could be built into the body of the chassis  102  and could be a purpose-built machine. As will be explained in greater detail below, the control computer  112  will control the operation of the electric motors  106  and thus the speed and direction of the tester  100 . The various motors of the present disclosure may be open loop AC or DC motors, stepper motors, servo motors, or other motors that satisfy the particular application. In one embodiment, the tester  100  will have a maximum forward speed of about 1 inches per second. This maximum speed may be the same in reverse, although it is understood that, in operation the tester  100  may not travel this fast. 
     The tester  100  may also provide a translation table  114 . The translation table  114  provides for movement (e.g., translation or rastering) of a carriage  116  in a direction lateral to the direction of travel of the tester  100 . In the present embodiment, the translation table  114  is belt driven and electrically powered by a motor  107 . 
     The attachment point between the translation table  114  and the chassis  102  may also provide a pivot point, allowing self adjustment of the slope of the translation table  114  to account for uneven surfaces on the scanned surface. 
     The carriage  116  may provide a suspension system which may comprise a set of coil over shocks  118 . An ultrasonic sensor (shown as  206  in  FIG. 2 ) may be carried in the carriage  116  and the suspension system will allow the sensor to remain the appropriate distance from the surface being scanned while also absorbing impact. Ball casters  120  may also be provided on the carriage  116  to aid in keeping the ultrasonic sensor held in the appropriate location. In another embodiment, a combination lens and bumper, possibly made from a polymer, may be provided instead of, or in addition to, the ball casters  120 . The use of a lens may also focus ultrasonic energy and enhance scanning. Ball casters  122  may be provided at various points along the translation table  114  to aid in allowing the translation table  114  to self rotate to follow contours of the scanned surface. In other embodiments, various replaceable bumpers may be used in place of the ball casters  122 . 
     The carriage  116 , in addition to securing the scanner, may provide for power and/or data cables to reach to and interface with the scanner. In the present embodiment, this is accomplished via a port or opening  124  in the carriage  116 . Another possible location  126  for the port is shown in dotted line. 
     As will be described more fully below, the tester  100  may also be equipped with a camera  128  used for tracking the progress of the tester  100  along the testing surface. The camera  128  is shown in the present embodiment mounted on the platform  103 , but it is understood that the camera  128  may be located in a number of locations on the chassis  102  and still be able to capture images or moving pictures of the surface. 
     Referring now to  FIG. 2 , a frontal view of a translation table and ultrasonic transducer of the autonomous tester of  FIG. 1  is shown. From the viewpoint of  FIG. 2 , it can be seen that the translation table  114  of the present embodiment provides two ball casters  122  as previously described. In the present embodiment, the translation table  114  provides a rail-mounted, motor-driven system for moving the carriage  116  in a lateral direction for scanning purposes. However, it is understood that, in other embodiments, other types of translation tables may be used. Additionally, in some embodiments, an array of carriages  116  may be utilized, each containing an ultrasonic scanner. In such an embodiment, the carriages would be arrayed across the front of the chassis  102 , obviating the need for a translation table to move a single carriage  116  in a lateral direction for scanning. 
     In addition to translating the carriage  116  and scanner  206  laterally, the arrows A indicate how the translation table itself may be allowed to rotate or tilt. This may be accomplished in the manner in which the translation table  114  is mounted to the chassis  102 . For example, a rotating mount using a ball bearing or sleeve bearing could be utilized. 
     From the viewpoint of  FIG. 2 , it can be seen that in the present embodiment, the carriage  116  comprises an outer carriage  202  and an inner carriage  204 . The carriage  116  is designed to allow displacement of the inner carriage  204  into the outer carriage  202 . This configuration works in conjunction with the coil over shocks  118  to properly suspend a scanner  206  (shown in dotted line) over, or in contact with, the surface to be scanned. It is understood that, in other embodiments, the scanner  206  may be properly located relative to the surface by other configurations. 
     In one embodiment, the scanner  206  is a phased array ultrasonic transducer (PAUT) from Ultrasonix. Data from the ultrasonic scanner  206  may be provided to a computer by a data link  208 . This may be a serial connection, a universal serial bus (USB) connection or another type of connection with sufficient bandwidth and durability. 
     Referring now to  FIG. 3 , a schematic diagram of the control system of the autonomous tester of  FIG. 1  is shown. Here, one possible way of connecting the control computer to the various components of the tester  100  is shown. As previously described, the control computer  112  may be a personal computer or could also be a purpose-built computer designed specifically to operate the tester  100 . The control computer may interact with the various other components of the scanner  100  in a variety of ways. In one embodiment, the control computer  112  will be running the commercially available control software LabView. 
     The control computer  112  may interface directly with the camera  128 . The camera  128  may connect to the control computer  112  via a universal serial bus (USB) cable or an IEEE 1394 (Firewire) connection. Implemented in the control computer  112  may be an algorithm that accepts images from the camera  128  of the surface being scanned and uses such images to correct for displacement errors when the scanner  100  is scanning a surface. Additionally, some embodiments of the tester  100  may provide for data gathering by the camera  128  instead of, or in addition to, the ultrasonic scanner  206 . In some applications, the camera may be utilized to capture video or composite still images that may be used for evaluation of the surface being scanned. 
     In one embodiment, the control computer  112  may interface with data acquisition (DAQ) hardware  308 . In one example, the DAQ  308  is a USB DAQ  6216  from National Instruments. This device is powered via a USB connection with the control computer  112 . The DAQ  308  provides a way for the control computer  112  to control the motors  106 ,  107  as well as obtain information back form the motors that can be used to determine the distance traveled or rotated by the tester  100 . In some embodiments, various other sensors can be connected through the DAQ  308 , such as the optional IR sensors  310 ,  312  that may be mounted to the tester  100  to determine, for example, when the tester  100  has neared the edge of a surface or other obstacle. 
     The DAQ  308  may interact with the motors  106 ,  107  through one or more drive boards  304 . The drive boards  304  may be connected to a power supply (not shown) to deliver a predetermined amount of power to the motors  106 ,  107  based on one or more control signals from the DAQ  308 . In one embodiment, the drive boards are Syren 25 devices from Dimension Engineering. In other embodiments, other devices, such as electronic speed controllers, could be used to provide power to the boards based on control signals from the DAQ  308  and/or control computer  112 . 
     In the present embodiment, the ultrasonic scanner  206  interacts with a separate scan computer  302  that powers the scanner  206  and collects the scan data as well. The scan computer may be located remotely and connected to the scanner  206  by the data link  208 . In cases where the scan computer  302  is located remotely from the tester  100 , the scan computer  302  may interface with the control computer  112  to provide start and stop sequences and other data to the control computer. This allows the scan computer to operate as a remote control for the tester  100 . In other embodiments, the scan computer is located on the tester  100 . In some embodiments, the control computer  112  will accept scan data from the scanner  206 , obviating the need for the scan computer. In this case, the data link  208  will connect directly to the control computer  112  as shown in dotted line. 
     Referring now to  FIG. 4 , a superior view of a portion of an aircraft wing upon which various embodiments of the autonomous tester of the present disclosure may operate is shown. It is understood that the tester  100  of the present disclosure is described in an exemplary fashion as being utilized to scan the surface, particularly the fasteners, on an aircraft wing. However, it is also understood that the various embodiments of the tester  100  of the present disclosure may be readily utilized or adapted to scan or test many surfaces, whether on an aircraft or otherwise. Moreover, even when utilized in the context of an aircraft wing, the tester  100  may test for corrosion and other defects whether they occur on or near a fastener or otherwise. 
     The aircraft wing  400  may comprise an airframe or skeleton covered by an aircraft skin or skins. The skin may be lightweight aluminum or other materials having sufficient strength to withstand the aerodynamic forces of flight, yet lightweight enough to actually be used on an aircraft. In order to function properly, the various skins covering the airframe may be fastened to the airframe with hundreds or thousands of discrete fasteners. In some cases, these fasteners will be placed in an orderly fashion corresponding to the underlying airframe. The grid  402  is illustrative of one possible fastener pattern on a portion of the wing  400 . 
     Referring now also to  FIG. 5 , a close up superior view of a portion of the aircraft wing  400  is shown. Here, it can be seen that along each line of the grid  402  may be a plurality of fasteners  502 . These fasteners may proceed from the outside of the aircraft wing through the skin  400  and into the airframe. It is these discrete fasteners which may be scanned by the tester  100  of the present disclosure. A line B is shown to indicate a direction of travel for the tester. As the test progresses, an ultrasonic scan may be taken of each fastener  502  and possibly the surrounding area. The translation table  114  may be used to move the scanner  206  to an adjacent row of fasteners. The translation table  114  allows the scanner to scan an entire area of fasteners as the tester moves rather than limiting the tester to a single row of fasteners per pass. As previously described, an array of scanners could also be utilized in this regard and translation or rastering may not be needed. 
     Referring now also to  FIG. 6 , a perspective view of an aircraft wing with an autonomous tester  100  in a starting position is shown. A user of the scanner  100  may be prompted to enter wing specifications (e.g., on the control computer) that may include horizontal distance and a width to be traveled by the tester  100  after being placed on the wing  400 . After entering scanning details by the user, the tester  100  may travel forward the distance specified by the user, pausing at a user-specified scan distance so that the translation table may move the carriage  116  and consequently the scanner  206  to the appropriate location over the correct fastener. The control computer  112  will collect scans and may be able to build a damage map of the wing fasteners in a manner similar to that seen in C-scans. 
     Because the surface of the wing  400  may not be level and may be wet, errors may occur in the travel of the tester  100  that cannot be compensated for merely by adjustments of the carriage on the translation table  114 . These errors may be detected by the onboard camera, based on captured images of the fasteners and other wing features as the tester  100  moves along the wing surface. This information may be utilized by the control computer  112  to correct the path of the tester  100  by controlling the electric motors  106  that provide power to the tracks  104 . 
     For visual tracking, various algorithms could be utilized, such as a neural network algorithm. This may be utilized in conjunction with image capture to allow the computer to learn the features of the aircraft wing as the tester progresses. As features are identified moving into the field of view of the camera  128 , they may be tracked across the field of view as the tester  100  progresses. The computer  112  may determine an incorrect displacement of features across the camera&#39;s field of view to determine if the tester  100  is beginning to veer off course. This information can then be utilized by the control computer  112  to determine a course correction for the tester  100 . 
     In one possible neural network suitable for guiding the tester  100 , gradient based features are extracted from targets and non-targets for input to the neural network. The gradient features are sensitive to edge and texture information. 
     The objective is to automatically assign initial targets based on features and allow the tester  100  to traverse over them autonomously. In one embodiment, targets are selected while the translation table  114  is active (tester  100  is paused). However, real-time tracking and 30 fps video from the camera  128  allows automated selection of targets at speed. Due to slipping or uneven wing surfaces, the tester  100  may need to correct steering while moving the prescribed distance. Additionally, small corrections may be implemented in the scanner software accounting for minor overlap between ultrasonic scans. Targets, such as fasteners, vary in terms of texture, contrast, sharpness of edge, and size. 
     Various feature extractors exhibit tradeoffs in terms of sensitivity and processing requirements as related to the characteristics of candidate target classes. Each target may be processed by a feature extractor selected for optimal representation in the neural network. Optimal feature selection can be automated by observing features over multiple frames. 
     The vision software may also facilitate the recognition of locations being scanned in an absolute coordinate system. For example, within a test section on an aircraft panel, a particular position may have unique characteristics typically associated with fastener positions. These characteristics can be used by a neural network or other similar software to provide a positional reference in translation and rotation for the camera with respect to the panel. Such recognition can be calibrated. Hence, it becomes unnecessary to measure by hand the starting position of the robot connected to the camera. Such global position sensitivity can be trained for specific airframes. 
     Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the claims.