Abstract:
A system and method using a touch probe device for eddy current inspection. The touch probe provides a simple approach for coming within close contact of the specimen while maintaining a normal angle and pressure at the right positions. The use of the touch probe further reduces the total time for the eddy current inspection. The touch probe aligns the probe to a specimen to be inspected, for the purpose of reducing measurement errors and increasing productivity.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Provisional Application No. 60/744,693 filed Apr. 12, 2006, the complete disclosure of which is incorporated herein by reference. 
     
     FIELD OF THE INVENTION 
       [0002]    The present invention is directed to a method of automatic alignment for eddy current inspection using a Touch probe (TP). 
       BACKGROUND OF THE INVENTION 
       [0003]    Eddy current (EC) inspection is commonly used to detect flaws in material properties such as residual stress, density, and degrees of heat treatment, as well as detect any cracks, pings, dings, or raised material on surfaces of manufactured components such as gas turbine engine components. EC inspection is required for most aircraft engine components on which abnormal indications are detected to ensure the engine&#39;s integrity until the next maintenance schedule. During this type of inspection, electromagnetic induction is used to induce eddy currents in the component being inspected. An array of coils inside an eddy current probe generates alternating magnetic fields, which induce the eddy currents when the probe is moved near the component. When flaws are present in the component, the flow of eddy currents is altered, thereby indicating the flaw to the inspector. The altered eddy currents produce changes in a secondary magnetic field, which are detected by the array of coils inside the eddy current probe. The array generates an electrical signal in response to the altered secondary magnetic field, where the amplitude of the electrical signal is generally proportionate to the size of the flaw. 
         [0004]    In order to effectively inspect the surface and maintain the integrity of the EC signal, smaller sized coils are used to enable maneuvering around the surface of the component. A small coil typically used is around 0.02 inches, and is effective at detecting any imperfections in the surface of the component, however these small coils are also extremely sensitive to the inspection equipment. Further, the coil has to travel with a constant pressure in relation to the specimen. To enable easier inspection of the components with the probes, the probes are often designed smaller, so they can fit into the smaller areas of the component surface. Changes in the probe shape prevent the probe from being positioned a uniform distance from the inspected component. Further, due to variations in size and shape of the component being inspected, gaps sometimes occur between the probe and the component surface, which also prevents the probe from being positioned at a uniform distance from the component. For years it has been a challenge to place a moving probe in close proximity with the component while maintaining a normal angle and normal pressure at positions sufficient for accurate readings. Even with the current, more sophisticated methods and probes available on market, the procedure to align the probe for inspection can be very time consuming, where the small features of the components are particularly difficult to align with the probe. 
         [0005]    One current method for EC inspections uses an alignment template for each individual inspection feature. The EC probe is aligned with the alignment template, which results in an accurate inspection, assuming the template is correctly aligned with the component. This alignment template method requires the construction of a precise template, repeating the steps of realigning the template to the component, aligning the probe to template, detaching the template, and finally checking the probe alignment with the component. This current method adds the unnecessary high cost of producing the templates as well as high labor costs and delays timely delivery. 
         [0006]    Another method for EC inspection, described in “Eddy current inspection Method” U.S. Pat. No. 6,907,358, improves the alignment process and increases productivity. However, this method is a manual process that is slow and cumbersome. Because the alignment of the EC touch probe for EC inspection is visually or audibly checked manually by a technician to ensure that no gap existed between the probe and the component surface, the component was required to be re-inspected due to the changes in the various technician&#39;s perception. Also, this method is dangerous, as to effectively hear or see the probe touching the component surface, the technician often has to dangerously place his or her head near the moving parts, or bend and twist into uncomfortable positions to ensure that the alignment is correct. Further, some areas that require inspection are small and located between engine blades or in unreachable cavities. Since these areas are difficult and often impossible to reach, the manual alignment method cannot effectively inspect those areas. Lastly, since the manual alignment method is time consuming and often consumes a significant amount of a technician&#39;s time. Because so much of a technician&#39;s time is dominated by the alignment method, the method is costly as well. 
         [0007]    Therefore what is needed is a method and system that is directed to an accurate and efficient EC inspection process that can reduce errors, alleviate safety concerns, and lower production costs. 
       SUMMARY OF THE INVENTION 
       [0008]    A method for aligning a probe for eddy current inspection of a component includes characterizing a touch probe with a calibration plate to find a probe radius and a probe offset of the touch probe, aligning a component to be inspected with the touch probe to locate and place a virtual zero point of a model of the component to a virtual zero point of the component and transferring a virtual zero point of the touch probe to a virtual zero point of the eddy current probe. The probe radius and the probe offset are entered into coordinates that are transferred to the eddy current probe to compensate for a plurality of offsets between the touch probe and the eddy current probe during the step of aligning the component with the touch probe. 
         [0009]    A method for eddy current inspection of a component includes aligning an eddy current probe for eddy current inspection of the component using a touch probe, initializing a scan plan of the component and completing the eddy current inspection of the component. The touch probe is used with the scan plan to reduce time and errors associated with eddy current inspection. 
         [0010]    One advantage of the present invention is the elimination of the alignment template, which results in a more efficient and cost effective inspection. 
         [0011]    Another advantage of the present invention is reduced errors and increased accuracy because the amount of user set-up is reduced. 
         [0012]    Yet another advantage of the present invention is that the touch probe itself is the alignment tool and does not require any parameter adjustments. The elimination of the parameter adjustment reduces the inspection time greatly compared to past methods, in which adjustments were repeated several times to gain the desired accuracy for the inspection. 
         [0013]    Another advantage of the present invention is the use of an industrial type touch probe, which produces accurate repeatability with inspections, to reduce errors and time consumption. 
         [0014]    An additional advantage of the present invention is that the positioning accuracy at the component surface is improved, thereby reducing errors. 
         [0015]    Another advantage of the present invention is the pressure between the probe and component is consistent, thereby producing a clean and precise EC signal for the inspection. 
         [0016]    Another advantage of the present invention is the reduction of human errors and an increase of safety because the probe performs the alignment automatically. 
         [0017]    Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is an illustration of the of the eddy current probe performing an eddy current inspection of a component. 
           [0019]      FIG. 2  is a schematic of eddy current inspection of the inside of a component using an EC probe. 
           [0020]      FIG. 3A  is an illustration of the characterization of a touch probe. 
           [0021]      FIG. 3B  is an illustration of the probe radius and probe alignment. 
           [0022]      FIG. 4A  is a schematic of the alignment of the touch probe for the coordinate transfer from the touch probe to the eddy current probe. 
           [0023]      FIG. 4B  is a schematic of the alignment of the eddy current probe for the coordinate transfer from the touch probe to the eddy current probe. 
           [0024]      FIG. 5  is a flow chart of the alignment of the touch probe with the component. 
           [0025]      FIG. 6  is an illustration of the characterization of the touch probe with the component. 
           [0026]      FIG. 7  is an illustration of the auto-alignment of the touch probe and the component. 
           [0027]      FIG. 8  is an illustration of eddy current inspection of a component with the eddy current probe. 
       
    
    
       [0028]    Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    A touch probe is used to align the EC probe for eddy current inspection of manufactured components such as gas turbine engine components.  FIG. 1  illustrates the eddy current inspection of an oil drain hole  8  of a component. While  FIG. 1  is shown and described as the feature being inspected, any feature or surface requiring inspection may be utilized. The eddy current probe  6  is placed inside the oil drain hole  8  as shown in  FIG. 2 , or near the component for inspection. An alternating current through the probe coil  14  (not shown) produces eddy currents in the component surface  4 . The reaction of the eddy currents in the component surface  4  are monitored by the probe  6  and are sent to a computer to process. Before the inspection can be initiated, however, several steps must be performed by using a touch probe to correctly align the eddy current probe  6  to ensure accurate results. Lift-off, the gap between the EC probe  6  and the component surface  4 , must be eliminated during inspection. Even a lift-off as small as 0.001 inch could affect the results of the inspection, therefore, there must be direct contact between the probe  6  and the component surface  4  during the entire inspection process. The alignment of the probe  6  with the component surface eliminates the lift-off effect during inspection, and helps to maintain consistent probe pressure on the component  10  during the inspection process, which produces accurate results. 
         [0030]    There are three steps to accomplish the EC probe alignment with the component  10  as described in  FIG. 5 . In summary, the three steps include a touch probe  12  (not shown) used to reduce any errors once the EC probe  6  (not shown) is used. First, the touch probe  12  is characterized with the calibration plate  26  to find the probe radius  18  and the probe offset  20 . The radius  18  and offset  20  of the probe are necessary to compensate for any physical bending or imperfection in the probe during the alignment and inspection. The probe radius  18  and offset  20  values are inserted into coordinates and eventually transferred to the EC probe  6  to compensate for any imperfections during the inspection process. These compensations further eliminate lift-off effect during inspection. 
         [0031]    The first step is shown schematically in  FIG. 3A , where the touch probe  12  is configured to find the probe radius  18 , the probe offset  20  relative to the center of rotation of the component  10  and the angle  22  of the touch point with the component  10 . This step requires additional alignment when the component  10  contains features such as dovetails, oil drain holes, or Lock&amp;Load slots, a generic term or abbreviation for locking slot and loading slot. Referring back to  FIG. 2 , when the component  10  contains features such as dovetails, oil drain holes, or Lock&amp;Load slots, the EC probe  6  must be aligned for those features to ensure accurate inspection of the component  10 . The EC probe  6  follows an exact scan path, or the exact feature shape. This exact path or feature shape is obtained from the part drawings. A UniGraphics (UG) model of the component  10  is composed based on the part drawings before the actual inspection begins so the EC probe coil  14  can be placed in the desired position of the component  10  without having to calibrate the coil  14  numerous times before the probe  12  is in the desired location. A UG model is used for ease of data extraction and easier viewing of the part, and further eliminates the time consuming alignment procedures previously used for EC Inspection. Before the EC probe  6  is placed for inspection, the inspection path is obtained from the UG model by overlaying the model on the component  10 . The probe  6  is aligned to the UG model of the component  10 , which is an overlay of the component  10 , thus during inspection, the probe  6  follows the same path that was determined during inspection with the overlay. 
         [0032]    As part of the touch probe configuration, the touch probe  12  is configured to interrupt the computer process when the stylus  24  contacts the calibration plate  26 . Contact occurs during the first step, when the probe  12  is obtaining axis positions. As shown in  FIG. 3A , the axis is found by rotating the touch probe  12  to zero degrees  16  and moving the touch probe  12  towards the calibration (CAL) plate  26 . The next axis position is found at ninety degrees  17 , then at one hundred and eighty degrees  19 , and lastly at two hundred and seventy degrees  21 . The existing flat surface of the CAL plate  26  is used for measuring the radius and angle of the TP stylus  24 . The information of the TP radius and angle is needed to rotate the same TP stylus  24  to each alignment touch point of the component. When the probe  12  touches the calibration plate  26 , the displacement axis position  20  is recorded. As shown in  FIG. 3B , the probe radius  18  (TP_Radius) and the probe&#39;s angle of alignment  22  (TP_TiltAngle) is computed by using the following equations: 
         [0000]        TP _Radius=(( Posit   — 0- Posit   — 180)*( Posit   — 0- Posit   — 180)+( Posit   — 90- Posit   — 270)*( Posit   — 90- Posit   — 270))/2+ TP   —   dia/ 2  Equation 1 
         [0000]        TP _TiltAngle= RadToDeg*ATAN ( Posit   — 90- Posit   — 270)/( Posit   — 0- Posit   — 180))  Equation 2 
       The characterization of the touch probe  12  is shown in FIG. 6, where the probe  12  is calibrating the radius  18  and the angle  22  for accurate EC inspection of the component  10 . 
       [0033]    As shown in  FIG. 7 , the second step of the alignment is to align the component  10  with the touch probe  12  in order to locate and place the UG model&#39;s virtual zero point with the component&#39;s virtual zero point automatically. As shown in  FIG. 4A , to find the virtual zero point  31  of the touch probe  12  (not shown), the touch probe  12  touches the component  10  sequentially beginning at the top-center  28 , then moving to the top-left  30  of the component  10 , then to the top-right  32 , moving to the bottom  34 , bottom-left  36 , and lastly, the bottom-right  38  of the component  10 . By having contact with the left and right, or top and bottom of the component  10 , a true center of the component  10  is calibrated depending upon where the center of rotation  33  is located at each touch point  28 ,  30 ,  32 ,  34 ,  36 ,  38 .  FIG. 4B  illustrates how the EC probe  6  then follows the same path the touch probe completed in  FIG. 4A , touching the top-center  28 , then moving to the top-left  30  of the component  10 , then to the top-right  32 , moving to the bottom  34 , bottom-left  36 , and lastly, the bottom-right  38  of the component  10 . The virtual zero point  33  of the touch probe is transferred to the EC probe  6  and becomes the virtual zero point  35  of the EC probe  6 . One embodiment of the invention requires approximately three minutes to align the touch probe  12  to the component  10 , and may be repeated more than 3 times if a higher accuracy is required or desired. The alignment process is shown in  FIG. 7 , where the probe is aligned for the component&#39;s virtual zero point with the UG model&#39;s virtual zero point. 
         [0034]    The third step in the alignment process of the probe  12  and the component  10  before actual inspection of the component  10  is to transfer the virtual zero  31  aligned with the touch probe  12  to virtual zero  35  of EC probe  6  as shown in  FIGS. 4 and 4A . The EC probe&#39;s virtual zero point  35  is adjusted by the offset values calculated from the following equations: 
         [0000]        REL   —   X _ZERO=−1*( TP _Radius)*Cos  U   Equation 3 
         [0000]        REL   —   Y _ZERO=(ProbeOffset/2)  Equation 4 
         [0000]        REL   —   Z _ZERO=( TP _Radius)*Sin  U , Where U is angle for vertical rotation axis, to EC Probe virtual zero  Equation 5 
       After the coordinates are transferred from the touch probe  12  to the EC probe  6 , the EC probe  6  is placed at the UG model virtual zero point (not shown). The EC probe  6  follows scan points derived from UG model, as shown in FIG. 8. 
       [0035]      FIG. 5  shows the process of the three steps to initialize the EC inspection process by aligning the touch probe  12  with the component  10 . First, in Step  42 , an EC scanplan is started for inspection. A scan plan, for example, is when the touch probe  12  is placed inside the oil hole of a gas turbine engine, searching for stresses or areas of weakness that could cause errors or component failures. The touch probe  12  is characterized in Step  44  as described in greater detail above. Step  46  locates the virtual zero  33  position of the touch probe  12  with the component  10 , also as described above in greater detail. Step  48  involves configuring the six-point alignment with the component. The alignment is checked for completeness in Step  50 . If the alignment is complete, then the coordinates are transferred in Step  54  to the eddy current probe  6  from the touch probe  12 . Then in Step  56  the inspection is ready and can be initiated, as illustrated in  FIG. 8 . If the alignment is not complete in Step  50 , then the virtual zero  33  position is adjusted in Step  52 . Then step  46  is repeated to find the actual virtual zero  33  position, and Step  48  is also repeated to check the alignment once again. 
         [0036]    While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.