Patent Document

BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to machine cutting tools, and more particularly, to control systems for machine cutting tools. 
     2. Description 
     Within the automotive manufacturing industry, die parts are used to stamp sheet metal into automotive parts. The die parts themselves are manufactured from an iron-based material being casted via a Styrofoam® pattern. Since the die part usually has intricate slots and precisely positioned holes and other physical features, the Styrofoam® pattern must be accurately shaped to allow the cooling cast iron material to assume the desired shape for stamping the sheet metal. 
     The Styrofoam® pattern is cut from a Styrofoam® stock piece by a numerical control (NC) tool cutting machine. Tool path data is fed into the NC tool cutting machine to indicate how the NC machine is to cut the Styrofoam® pattern from the Stryrofoam® stock piece. 
     Present approaches include without limitation time-intensive and trial-and-error Computer-Aided Manufacturing (CAM) approaches to generate the correct tool path data to be fed into the NC tool cutting machine. Within this type of approach, the user of the CAM tool is usually closely involved in examining the physical characteristics of the die part to be produced. With the die part having been examined by the user via the CAM tool, the user determines a set of tool paths to cut the Styrofoam® pattern. This type of an approach may consume as much as three days to generate the correct data to cut the Styrofoam® pattern due to, among other reasons, the user being so closely involved in examining the die part and in determining the tool paths. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the aforementioned disadvantages and other disadvantages. The present invention is a computer-implemented apparatus and method for generating tool paths for cutting a physical part. The present invention includes storing geometric data indicative of the geometric configuration of the part. A plurality of planes are used to slice the geometric data. Micro features of the part are recognized based upon the sliced geometric data. Macro features of the part are determined based upon groupings of the recognized micro features. Tool path data is generated based upon the determined macro features of the part, and the tool path data is used for cutting the physical part. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a block diagram depicting the inventive computer system for generating tool paths for cutting a physical part; 
     FIG. 2 is an x-y-z graph illustrating an exemplary z-map model; 
     FIG. 3 is a flow chart depicting the steps for constructing a z-map model; 
     FIG. 4 a  is a flow chart depicting the steps for recognizing machining features; 
     FIG. 4 b  is a grid depicting layer numbers of the sliced z-map model shown in FIG. 4 a;    
     FIG. 5 a  is a diagrammatic prospective view depicting an exemplary die part model; 
     FIG. 5 b  is a diagrammatic prospective view depicting identified machining features; 
     FIG. 5 c  is a top view of FIG. 5 b  which depicts identified machining features; 
     FIGS. 5 d ,  5   e  and  5   f  are diagrammatic perspective views depicting various machining features; 
     FIG. 6 is a flow chart depicting the steps for generating a process plan; 
     FIGS. 7 a ,  7   b  and  7   c  are respective views of different tool paths on part; 
     FIG. 8 a  is a flow chart depicting the steps for generating tool path data files; 
     FIG. 8 b  is a tool path diagram depicting an offset region boundary situation; and 
     FIGS. 9 a ,  9   b  and  9   c  are diagrammatic prospective views of an exemplary part with tool paths as determined by the present invention being depicted therewith. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a system block diagram depicting the manner in which tool path data  42  is generated for die part  20  for determining numerical control (NC) tool paths. Solid model data  22  and surface model data  24  are generated for die part  20 . Solid model data  22  and surface model data  24  are indicative of the geometric characteristics of die part  20 . Solid model data  22  includes information regarding the planar surfaces of die part  20 . Surface model data  24  includes information of the non-planar surfaces of die part  20 . 
     A z-map model builder  26  constructs z-map model data for use in the present invention based upon the solid model data  22  and surface model data  24 . Z-map model builder  26  utilizes a merger module  28  in order to properly combine data from solid model data  22  and surface model data  24 . 
     Based upon the resulting z-map model from z-map model builder  26 , machining feature recognizer  30  classifies features first into micro features and then into macro features. The micro and macro features classification process allows the present invention to analyze the z-map model at different levels of detail in order to produce optimal cutting paths for die part  20 . 
     A process plan generator module  34  uses machining sequence rules  36  and feature-tool path mapper rules  38  in order to calculate which tool paths are needed for the recognized features. Machining sequence rules  36  provide a prioritized scheme for which features should be cut first. Feature-tool path mapper rules  38  provides what type of tool path should be utilized for a particular recognized macro feature. 
     Tool path generator module  40  produces NC tool path data  42  based upon the process plan generated by module  34 . In the preferred embodiment, the present invention utilizes the CATIA computer program in order to verify the NC tool path data  42 . The CATIA computer program is available from the following company: Dassault Systemes located in France. NC tool path data  42  is used by NC machine  44  to cut a stock part (typically made of Styrofoam®) which is then used to help construct die part  20 . 
     FIG. 2 depicts an exemplary z-model  60 . The z-axis is depicted at reference numeral  62  and the x-y plane is depicted at reference numeral  64 . For a general discussion of the z-map model mathematical technique, please consult the following reference: B. K. Choi,  Surface Modeling for CAD/CAM , Elsevier, 1991, pp. 360-361. 
     FIG. 3 depicts the steps to construct a z-map model for subsequent use by the other computer-implemented modules of the present invention to generate tool path data. Process block  70  constructs a first z-map model  72  from solid model data  22 . An exemplary z-value of the first z-map model  72  is depicted at reference numeral  74 . Process block  80  constructs a second z-map model  82  from the surface model  24 . An exemplary z-value is indicated at reference numeral  84 . 
     Process block  90  offsets in an upward manner second z-map model  82  from the surface by the casting stock allowance in order to produce an offset second z-map model  92 . The casting stock allowance is utilized by the present invention in order to account for shrinkage of casting stock. In the preferred embodiment, typical casting stock allowance values include, but are not limited to, such values as generally ten to twelve millimeters. 
     Process block  100  merges the first z-map model  72  and the second z-map offset model  92  by taking the maximum value between the first z-map model  72  and the offset z-map model  92  at each position in order to produce the resulting z-map model  102 . 
     FIG. 4 a  depicts the processing steps for recognizing such machining features as, but not limited to, bolt slot features or open pocket features. Process block  120  slices z-map model  102  by a predetermined number of horizontal x-y planes ( 122   a ,  122   b ,  122   c , and  122   d ). The horizontal x-y planes ( 122   a ,  122   b ,  122   c , and  122   d ) partition z-map model into various levels. For example, horizontal x-y planes  122   b  and  122   c  partition the z-map model  102  into a level # 2 . 
     Z-points are associated with a particular level number. For example, the points as depicted by reference numeral  124  are associated with a level value of four. Moreover, z points as depicted by reference numeral  126  are associated with a level value of one. Process block  130  marks each grid point (e.g., points  124  and  126 ) by the layer number to which it belongs in order to produce grid  132 . Grid  132  is a top view of the z points of the z-map model  102 . Grid  132  contains the z-points  124  with the level value of four. FIG. 4 b  provides an enlarged view of grid  132 . 
     It should be understood that the present invention is not limited to the number of horizontal x-y planes depicted in FIG. 4 a  but includes an appropriate number of planes that will yield the desired level of resolution for a given application. 
     With reference made to FIG. 4 a , process block  140  constructs micro features by grouping the adjacent grid points which have the same level number. For example, z points  124  of grid  132  are grouped together as micro feature  142 . 
     Process block  150  constructs macro features by merging the micro features which have similar geometric characteristics. For example, micro features  144  and  146  which correspond to a gradual sloping surface in z-map model  102  are merged to form macro feature  152 . The present invention includes considering such geometric characteristics as slope and gap values of the micro features. For example, if the maximum vertical gap between two adjacent micro features is less than five millimeters, then those two micro features are merged into a macro feature. 
     Process block  160  classifies the macro features into predetermined machining feature types  162 . The predetermined machining feature types include, but are not limited to, profile features, pocket features, and special features which further decompose into the following feature subclasses: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                        Feature Class 
                 Feature Subclass 
               
               
                   
                   
               
             
             
               
                   
                 Special Feature 
                 Slot/Step on Rib Feature 
               
               
                   
                 Special Feature 
                 Bolt Slot Feature 
               
               
                   
                 Profile Feature 
                 Periphery Profile Feature 
               
               
                   
                 Profile Feature 
                 Through-Pocket (Hole) Profile 
               
               
                   
                   
                 Feature 
               
               
                   
                 Pocket Feature (with 
                 Open Pocket Feature 
               
               
                   
                 curved or planar bottom) 
               
               
                   
                 Pocket Feature (with 
                 Closed Pocket Feature 
               
               
                   
                 curved or planar bottom) 
               
               
                   
                   
               
             
          
         
       
     
     Process block  160  performs the feature classification by examining the geometric characteristics of the macro features, such as, but not limited to, shape of boundary curves associated with the macro features. For example, if the bottom of a macro feature is at the lowest layer, it is classified as a periphery feature or a hole feature. As another example, if all neighboring grids are higher than the grids on the boundary curve of a macro feature, and the bottom faces inside of the boundary curve is planar, it is classified as a planar closed pocket feature. 
     FIG. 5 a  depicts a graphical representation of an exemplary die part  20 . Die part  20  illustrates several machining feature types which are recognized by the present invention in order to produce data for determining tool paths. For example, the through-pocket profile feature is indicated at reference numeral  180 . 
     FIG. 5 b  is a graphical representation of machining features which have been recognized through the techniques of the present invention. Top surface  190  depicts the upper model surface of the die part. Bottom surface  194  depicts the base portion of the die part. For example, through-pocket profile feature  180  of the die part  20  is shown by reference numeral  184 . 
     FIG. 5 c  is a top view of the identified machining features of FIG. 5 b . As illustrated in FIG. 5 c , the present invention has recognized various machining features of the die part. For example, the present invention has recognized the periphery profile feature  200 . The present invention has also recognized the through-pocket profile feature as depicted by cross hatched section  204 . Moreover, the present invention has recognized the open pocket feature  208 . 
     FIGS. 5 d - 5   f  depict additional machining features. FIG. 5 d  depicts an example of a special machining feature known as the bolt slot feature  91 . FIG. 5 e  depicts a special machining feature known as the slot rib feature  92 . FIG. 5 f  depicts a special machining feature known as the step on rib feature  93 . 
     Once the present invention has recognized the machining features from the model data of a die part, then the process plan is generated. The process plan is preferably generated via the steps depicted in the flow chart of FIG.  6 . 
     With reference to FIG. 6, process block  220  determines the optimal machining sequence for each of the recognized machining features by predefined rules. The predefined rules associate machining features with machining priority numbers. The preferred embodiment utilizes the following feature-priority scheme: 
     
       
         
               
               
               
             
           
               
                   
               
               
                  Priority No. 
                 Feature Class 
                 Feature Subclass 
               
               
                   
               
             
             
               
                 1 
                 Special Feature 
                 Slot/Step on Rib Feature 
               
               
                 2 
                 Special Feature 
                 Bolt Slot Feature 
               
               
                 2 
                 Profile Feature 
                 Periphery Profile Feature 
               
               
                 2 
                 Profile Feature 
                 Through-Pocket (Hole) Profile 
               
               
                   
                   
                 Feature 
               
               
                 3 
                 Pocket Feature (with 
                 Open Pocket Feature 
               
               
                   
                 curved or planar bottom) 
               
               
                 3 
                 Pocket Feature (with 
                 Closed Pocket Feature 
               
               
                   
                 curved or planar bottom) 
               
               
                   
               
             
          
         
       
     
     These predefined rules are used to determine the priority of which features are to be machined first. For example, the through-pocket profile feature has a higher priority number than the open pocket feature  208 . Accordingly, the present invention would indicate in its output tool path data files that the through-pocket profile feature is to be cut et feature  208 . For machining features which have the same priority present invention selects as the feature which minimizes the travel distance nearest one from the current tool position. 
     Process block  224  assigns machining parameters for each macro feature. These parameters include, but are not limited to, tool path step over and feed rate parameter. Process block  228  determines the tool path type and tool path direction for each feature. The following table provides the preferred embodiment for associating the machining feature type with a tool path type: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                             Feature Subclass 
                 Tool Path Type 
               
               
                   
                   
               
             
             
               
                   
                 Periphery Profile Feature 
                 Profile 
               
               
                   
                 Through-Pocket (Hole) Profile Feature 
                 Profile 
               
               
                   
                 Open Pocket Feature 
                 Direction Parallel 
               
               
                   
                 Closed Pocket Featute 
                 Contour Parallel 
               
               
                   
                 Bolt Slot Feature 
                 Profile 
               
               
                   
                 Slot/Step on Rib Feature 
                 Direction Parallel 
               
               
                   
                   
               
             
          
         
       
     
     FIGS. 7 a - 7   c  illustrate without limitation different tool path types of the preferred embodiment. FIG. 7 a  illustrates a profile tool path  229 . FIG. 7 b  illustrates a direction parallel tool path type  230 . FIG. 7 c  illustrates a contour parallel tool path type  231 . 
     FIG. 8 a  addresses the operations associated with the tool path generator which generates NC tool path data files based upon the process plan. Iteration block  250  and iteration termination block  262  indicate that process blocks  254  and  258  are to be performed for each recognized macro feature. Process block  254  finds the gouge-free region. Within the field of the present invention, the term “gouge-free” refers to not allowing overcutting to be done on a feature. Process block  258  offsets the region boundary in order to confine the tool center location. When the tool center  261  is in the offset region  263 , the entire tool  265  resides in the original region  267  (as shown in FIG. 8 b ). 
     With reference back to FIG. 8 a , process block  266  generates the NC tool path data files in order to provide indication to the NC machine which cutting paths and parameters are to be used. The preferred embodiment uses the CATIA software in order to analyze tool path data against the die part. 
     FIGS. 9 a - 9   c  depict tool paths as determined by the present invention in order to cut the Styrofoam® stock which is then used to produce die part  20 . The white lines on FIG. 9 a  depict the tool path as represented, for example, by reference numeral  280 . 
     FIG. 9 b  depicts the NC tool paths as determined by the present invention for the cutting of the pocket feature. Tool path  280  is depicted for establishing a reference point between FIGS. 9 a  and  9   b.    
     FIG. 9 c  depicts the NC tool paths as determined by the present invention for the boundary and hole features. An exemplary tool path is depicted by reference numeral  290 . 
     The embodiments which have been set forth above were for the purpose of illustration and were not intended to limit the invention. It will be appreciated by those skilled in the art that various changes and modifications may be made to the embodiments discussed in this specification without departing from the spirit and scope of the invention defined by the appended claims.

Technology Category: 3