Abstract:
A system for laser peening a workpiece. The system comprises a world coordinate frame, a robot operatively connected to the world coordinate frame for moving the workpiece relative, a calibration tool operatively connected to the robot for determining a multiplicity of data points of the workpiece, a computer for storing and using the multiplicity of data points of the workpiece, and a laser system for laser peening the workpiece using the multiplicity of data points.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Patent Application No. 60/555,184 filed Mar. 22, 2004 and titled “Inspection System for Laser Peening.” U.S. Provisional Patent Application No. 60/555,184 filed Mar. 22, 2004 and titled “Inspection System for Laser Peening” is incorporated herein by this reference. 
     
    
       [0002]     The United States Government has rights in this invention pursuant to Contract No. W-7405-ENG-48 between the United States Department of Energy and the University of California for the operation of Lawrence Livermore National Laboratory. 
     
    
     BACKGROUND  
       [0003]     1. Field of Endeavor  
         [0004]     The present invention relates to laser peening and more particularly to a calibration system for laser peening.  
         [0005]     2. State of Technology  
         [0006]     The state of laser peening technology is illustrated in part by the following patents and patent applications owned by Metal Improvement Company, Inc.: European Patent No. EP1478062; United Kingdom Patent No. GB2401719; and U.S. Patent Application No. 2004/0228376. For example, United States Patent Application No. 2004/0228376 to Metal Improvement Company, Inc. and the Regents of the University of California, for self-seeded single-frequency solid-state ring laser, for a single-frequency laser peening method and system using same, published Nov. 18, 2004, provides the following state of technology information: “The use of mechanical shocks to form metals and to improve their surface properties has been realized for ages. In current industrial practice, a peening treatment of metal surfaces is accomplished by using high velocity shot. Treatment improves surface properties and very importantly for many applications, results in a part displaying significantly improved resistance to fatigue and corrosion failure. A wide range of components are shot peened in the aerospace and automotive industries. However, for many applications, shot peening does not provide sufficiently intense or deep treatment or cannot be used because of its detrimental effect on the surface finish. With the invention of the laser, it was rapidly recognized that the intense shocks required for peening could be achieved by means of a laser-driven tamped plasma. B. P. Fairand, et al., “Laser Shot Induced Microstructural and Mechanical Property Changes in 7075 Aluminum,” Journal of Applied Physics, Vol. 43, No. 9, p. 3893, September 1972. Typically, a plasma shock of 10 kB to 30 kB is generated at metal surfaces by means of high energy density (about 200 j/cm  2 ), short pulse length (about 30 nanoseconds) lasers.” (Paragraphs [0006] and [0007], United States Patent Application No. 2004/0228376).  
         [0007]     The state of laser peening technology is illustrated in part by the following patents owned by the Regents of the University of California: U.S. Pat. Nos. 6,410,884; 6,657,160; 6,805,970; and 6,818,854. For example, U.S. Pat. No. 6,805,970, for laser peening of components of thin cross-section, issued Jan. 19, 2004 to Lloyd A. Hackel, John M. Halpin, and Fritz B. Harris, Jr. and assigned to the Regents of the University of California, provides the following state of technology information: “The system for laser peening a part is shown. The near field output of a beam from a laser is image relayed by the optical imaging system to the part to be peened . . . . The part is peened with an acoustic coupling material, shock absorbing layer. The laser beam output comprises a rectangular beam that allows precise and uniform overlap of pulses and hence highly uniform compressive stress from front to back side within the part. This minimizes distortion of the peened part. The part is positioned within the system by the part manipulator.” (Col. 5, lines 16-37, U.S. Pat. No. 6,805,970).  
         [0008]     The state of measuring probe technology is illustrated in part by the following patents and patent applications owned by Renishaw plc: U.S. Pat. Nos. 4,819,491; 5,402,981; 5,435,072; 6,275,053; 6,301,796; 6,633,051; 6,810,597; 6,839,563; RE37,030; and United States Patent Application No. 2004/0219886. For example, U.S. Pat. No. 5,402,981 for a workpiece measuring machine, issued Jan. 19, 2004 to David R. McMurtry and assigned to Renishaw plc provides the following state of technology information: “A variety of forms of measuring machine are currently in use each of which is more or less suited to carry out measurements on workpieces as diverse as small engineering piece parts, and large scale parts such as car bodies or aircraft wings. These have conveniently been classified into ten categories in a report commencing on page 11 of the ASME standard reference ASME B89.1.12M-1990, the categories including the well-known bridge machines, gantry machines, or cantilever machines. The machines may have either fixed or moving tables on which the workpiece is carried. The philosophy behind the design of the machines has always been that the table used for supporting the workpiece has to be relatively massive, (traditionally a large granite slab) in order to avoid distortions occurring when heavy workpieces are mounted on the table. This has been particularly so in the moving bridge machines in which the tracks on which the bridge moves are formed on the table. Thus the table also has to be rigid enough to avoid distortions due to the movements of the bridge, which itself is a relatively massive structure in order to support the other moving parts of the machine.” (Col. 1, lines 9-32, U.S. Pat. No. 5,402,981).  
       SUMMARY  
       [0009]     Features and advantages of the present invention will become apparent from the following description. Applicants are providing this description, which includes drawings and examples of specific embodiments, to give a broad representation of the invention. Various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this description and by practice of the invention. The scope of the invention is not intended to be limited to the particular forms disclosed and the invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims.  
         [0010]     The present invention provides a system for laser peening a workpiece. The system utilizes a world coordinate frame, a calibration tool for determining a multiplicity of data points of the workpiece, a robot operatively connected to the world coordinate frame for moving the calibration tool relative to the workpiece for determining the multiplicity of data points, a computer for storing and using the multiplicity of data points, and a laser system for laser peening the workpiece using the multiplicity of data points.  
         [0011]     In another embodiment, a system for laser peening a workpiece utilizes a world coordinate frame, a calibration tool for determining a first multiplicity of data points of the workpiece, a touch-trigger probe for determining a second multiplicity of data points of the workpiece, a robot operatively connected to the world coordinate frame for moving the calibration tool relative to the workpiece for determining the first multiplicity of data points and moving the workpiece relative to the touch-trigger probe for determining a second multiplicity of data points of the workpiece, a computer for storing and using the first and second multiplicity of data points, and a laser system for laser peening the workpiece using the first and second multiplicity of data points.  
         [0012]     The system for laser peening a workpiece has use in situations where a robot or machine tool manipulates a workpiece and uses a fixed tool. The tool can be, for example, a point in a laser beam, a cutting tool or an EDM electrode. For example, the system for laser peening a workpiece can be used for laser peening for jet engine components.  
         [0013]     The invention is susceptible to modifications and alternative forms. Specific embodiments are shown by way of example. It is to be understood that the invention is not limited to the particular forms disclosed. The invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     The accompanying drawings, which are incorporated into and constitute a part of the specification, illustrate specific embodiments of the invention and, together with the general description of the invention given above, and the detailed description of the specific embodiments, serve to explain the principles of the invention.  
         [0015]      FIG. 1  is a schematic illustration of one embodiment of an inspection system for laser peening constructed in accordance with the present invention.  
         [0016]      FIG. 2  is a schematic illustration of the laser peening portion of the system for laser peening constructed in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     Referring to the drawings, to the following detailed description, and to incorporated materials, detailed information about the invention is provided including the description of specific embodiments. The detailed description serves to explain the principles of the invention. The invention is susceptible to modifications and alternative forms. The invention is not limited to the particular forms disclosed. The invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims.  
         [0018]     Referring now to the drawings and in particular to  FIG. 1 , a schematic illustration of one embodiment of an inspection system for laser peening incorporating the present invention is shown. The inspection system of this embodiment is designated generally by the reference numeral  100 . The inspection system  100  for laser peening includes the following structural components: a touch-trigger probe  101 , a stylus  102 , a probing sphere  103 , a robot  105 , a robot wrist  106 , a calibration tool  107 , a high-precision sphere  108 , a workpiece holder  109 , a robot wrist  110 , a computer  111 , and a world coordinate frame  112 .  
         [0019]     The inspection system  100  for laser peening comprises hardware and software to determine the coordinate frame transformation between a workpiece  104  and the robot  105  that will subsequently be used for laser peening the workpiece  104 . The touch-trigger probe  101  and the robot  105  are rigidly mounted in fixed relation to the world coordinate frame  112 . The touch-trigger probe  101 , the stylus  102 , and the probing sphere  103  are rigidly mounted in fixed relation to the world coordinate frame  112 . The robot  105 , the robot wrist  106 , the calibration tool  107 , and the high-precision sphere  108  are also rigidly mounted in fixed relation to the world coordinate frame  112 . Also, the robot  105 , the robot wrist  110 , the workpiece holder  109 , and the workpiece  104  are rigidly mounted in fixed relation to the world coordinate frame  112 .  
         [0020]     The first set of hardware components are the calibration tool  107  that mounts to the robot  105  by robot wrist  106 . This tool has a larger, high-precision sphere  108  on it and the relationship between the robot wrist  106  and high-precision sphere  108  is known.  
         [0021]     The second set of hardware components of the system  100  are the touch-trigger probe  101  that has a stylus  102  with a probing sphere  103  at its end. The probe  101  can detect when the probing sphere  103  is displaced from its nominal position by very small amounts. That is, it detects when something contacts the probing sphere  103 . The probe  101  is mounted in a fixed position in the world coordinate frame  112 .  
         [0022]     The structural components of the inspection system  100  for laser peening having been described and illustrated in  FIG. 1 , the construction and operation of the inspection system for laser peening  100  will now be described. The inspection system for laser peening  100  comprises a system to determine the coordinate frame transformation between the workpiece  104  attached to the robot wrist  110  of the robot  105  and the coordinate system comprising (1) the robot  105 , the robot wrist  106 , the calibration tool  107 , and the high-precision sphere  108 ; and (2) the touch-trigger probe  101 , the stylus  102 , and the probing sphere  103 .  
         [0023]     The position of the probing sphere  103  relative to the world coordinate frame  112  is measured. The workpiece  104  is gripped by the robot  105  and the workpiece  104  is moved so that the probing sphere  103  contacts several datum surfaces of the workpiece  104 . The position of the probing sphere  103  in the coordinate system is determined for each contact point and a first set of data points are obtained. The information is stored in computer  111  for further use.  
         [0024]     The calibration tool  107  is used to determine a second set of data points. The high-precision sphere  108  is used to contact several datum surfaces of the workpiece  104 . The first data points and the second data points are used to compute a full six degrees of freedom coordinate transformation between the robot  105  and the workpiece  104 . In addition, the known geometric characteristics of the workpiece  104  can be used to compute a full six degrees of freedom coordinate transformation between the robot  105  and the workpiece  104 . The information is stored in computer  111  for further use.  
         [0025]     The software portion of the system  100  in the computer  111  comprises a procedure to find the center of the probing sphere  103  of the touch trigger probe  101 , procedures to both manually and automatically acquire the first set of data points where the probing sphere  103  contacts the workpiece  104 , procedures to both manually and automatically acquire the second set of data points where the high-precision sphere  108  contacts the workpiece  104 , and a workpiece specific set of calculations to determine the coordinate frame transformation. Enough data points are acquired to fully constrain the workpiece in six degrees of freedom. The coordinate transformation between the workpiece, the world coordinate frame  112 , and the robot  105  is computed from the recorded contact data points by computer  111 . The coordinate transformation between the workpiece  104  and the world coordinate frame  112 , and robot  105  is used for further processing where the workpiece  104  is acted on by the laser peening system illustrated in  FIG. 2 .  
         [0026]     The inspection system for laser peening  100  was developed to improve the Laser Peening process. The inspection system for laser peening  100  was first used in a laboratory on a low pressure fan blade workpiece  104  for a jet engine. A problem with laser peening of fan blades  104  is that the aerofoil geometry can vary due to manufacturing or use. Thus, when the blade  104  is gripped by the robot  105  on the aerofoil section the relationship between the treatment area at the blade root and the robot wrist  110  can also vary. These variations can be large enough to significantly affect the placement of the spot pattern onto the workpiece.  
         [0027]     Referring now to  FIG. 2 , a schematic illustration of the laser peening portion of the system incorporating the present invention is shown. The laser peening portion of the system is designated generally by the reference numeral  200 . The laser peening portion  200  of the system includes the following structural components: a laser  201  for laser peening, a laser beam control system  202 , a laser peening beam  203 , the workpiece  104 , the computer  111 , the workpiece holder  109 , the robot wrist  110 , and the world coordinate frame  111 . Also shown in  FIG. 2  are the robot  105 , the robot wrist  106 , the high-precision sphere  108 , and the calibration tool  107  that were used to obtain data points for the laser peening operation.  
         [0028]     The laser peening system  200  comprises the structural components listed above and software. The software comprises a procedure to find the center of the high-precision sphere  108 , procedures to both manually and automatically acquire the points where the high-precision sphere  108  contacts the surfaces of the workpiece  104 , and a workpiece specific set of calculations to determine the coordinate frame transformation.  
         [0029]     The structural components of the laser peening portion  200  of the system having been described and illustrated in  FIG. 2 , the construction and operation of the laser peening portion system  200  will now be described. As described above, the coordinate transformation information between the workpiece  104  and the high-precision sphere  108  has been stored in the computer  111  and is used by the laser peening system  200  to laser peen the workpiece  104 .  
         [0030]     Given that the high-precision sphere  108  is in a know/position in space relative to the world coordinate frame  111  and the robot  105 , the coordinate transformation information that has been stored in the computer  109  is used by the laser peening system  200  to provide instructions to the laser  201  to laser peen the workpiece  104 . The computer  109  implements the procedure that has tracked the high-precision sphere  108  and the workpiece  104  to laser peen the workpiece  104 . With the location of the high-precision sphere  108  known, the workpiece is gripped by the robot  105  and moved so that the laser  201  laser peens the workpiece  104  as instructed by the computer  111 . The laser  201  focuses the laser peening beam  203  onto the workpiece  104  using the laser beam control system  202 . The laser peening beam  203  can be used to increase the surface hardness of the workpiece  104  using shock propagation induced by laser pulses or to accomplish other operations on the workpiece  104 .  
         [0031]     In another embodiment, the information obtained by the probing sphere  103  of the touch trigger probe  101  is used to by the laser peening system  200  to laser peen the workpiece  104 . The software comprises a procedure to find the center of the probing sphere  103 , procedures to both manually and automatically acquire the points where the probing sphere  103  contacts the surfaces of the workpiece  104 , and a workpiece specific set of calculations to determine the coordinate frame transformation. Given that the probe  101  is fixed in space relative to the world coordinate frame  111 , the coordinate transformation information that has been stored in the computer  109  is used by the laser peening system  200  to provide instructions to the laser  201  to laser peen the workpiece  104 . The computer  109  implements the procedure that has tracked the probing sphere  103  of the touch trigger probe  101  and the workpiece  104  to laser peen the workpiece  104 . With the location of the probe sphere center  103  known, the workpiece is gripped by the robot  108  and moved so that the laser  201  laser peens the workpiece  104  as instructed by the computer  109 . The laser  201  focuses the laser peening beam  203  onto the workpiece  104  using the laser beam control system  202 . The laser peening beam  203  can be used to increase the surface hardness of the workpiece  104  using shock propagation induced by laser pulses or to accomplish other operations on the workpiece  104 .  
         [0032]     While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.