Abstract:
A method of converting a program, such as a graphic database, representing the geometry of a workpiece, into numeric control code in order to program a numeric machine control to operate a machine, such as a router. The machine control receives and processes the program according to a set of machine-specific attributes, including axis configuration and worktable size and layout. Operational attributes, such as feed rate and tool assignments, are specified. Optionally, multiple components or workpieces are nested into a cluster, and available off-fall sheets are matched to the cluster, so as to maximize the efficient use of material. Numeric code is then generated to permit the machine control to operate the machine.

Description:
[0001]    The present invention relates to Computer Numerical Control (CNC) machines and more particularly to a method and system for converting graphic based computer programs from various sources into numeric control (NC) code in order to control the operation of a CNC based machine.  
         BACKGROUND OF THE INVENTION  
         [0002]    In a typical CNC machine installation, workpiece processing programs are generated at a location separate from the machine, generally in an office environment. This type of programming is commonly referred to as “off-line” programming. While it is possible to generate programs at the machine, doing so can be economically prohibitive. Two factors contribute to such result. First, the CNC machine is an integrated production tool. In order to serve in a programming capacity, the CNC machine must be removed from production. Second, generating programs at the machine control requires the operator either to enter each axis movement as a line of NC code or to generate cut paths with a hand-held pendant as the machine executes each axis movement. Because they often consume a considerable number of hours per program, neither of these methods is more efficient than off-line methods.  
           [0003]    A typical off-line process begins with the generation of a workpiece program using computer aided manufacturing (CAM) software. The program is then post-processed. Post-processing typically includes selection of tooling, assignment of various feed rates, nesting of cutting profiles into patterns that provide for maximum material utilization, and configuring the program into a specific machine format suitable for use by a CNC machine control. After the program has been completely processed off-line, it may be loaded into the control of a CNC machine center from magnetic storage media or sent directly to the machine through a local area network or a direct NC (DNC) link.  
           [0004]    While off-line programming provides several significant advantages over the older, more conventional method of generating programs at the machine, it has certain shortcomings. For instance, the process is rather inflexible. Parameters such as tool selection and feed speeds, generated off-line, cannot be modified at the CNC control without great difficulty. When a program is conventionally post-processed, it is configured for a specific machine format and cannot be used on any other machine without going through the complete post-processing procedure again. It would be decidedly advantageous to have the ability to post process a program, to input and modify program parameters, and to configure the program automatically for the proper machine format at the machine control. This would allow a wide variety of off-line generated programs to be used on a diverse group of machines more efficiently.  
           [0005]    Accordingly, the principal object of the present invention is to provide an improved method of converting a diverse group of off-line-generated computer programs into numeric control code in order to control a CNC machine system.  
           [0006]    Another object of the invention is to provide method of programming a CNC machine control in such a way as to combine the benefits of off-line programming with the flexible selection of operational attributes at the machine control.  
           [0007]    A further object of the invention is to provide a method of nesting at the machine control, workpieces and individual components of workpieces into clusters in order to maximize the use of available material.  
           [0008]    A still further object of the invention is to provide a method of recording, tracking and matching off-fall sheets to nested clusters in order to optimize the use of available material.  
           [0009]    A more specific object of the invention is to provide a system for carrying out at the central of a CNC machines the conversion of off-line generated computer programs into numeric control code in order to control such system, including means for nesting workpieces and components of workpieces into clusters and means for recording, tracking and matching off-fall sheet to nested clusters.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention addresses the above-described problem by disclosing a method of converting off-line-generated component geometry programs into NC code in the CNC machine control. A program is presented to the machine control, where it is automatically configured for machine-specific attributes such as axis configuration and worktable size and layout. Control over various operational attributes such as tool selection and feed rates are assigned to the machine operator. The invention also provides for the utilization of off-fall (material left over from previous cutting operations) by recording and tracking off-fall as it is generated, automatically selecting suitably sized off-fall sheets, then nesting multiple workpieces or components of workpieces thereon for maximum material utilization. The use of off-fall, which frequently consists of sizable sheets of material, presents an economically beneficial and environmentally conscious alternative to wasting the material through disposal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a perspective view of a computer numeric controlled (CNC) machining system embodying the present invention;  
         [0012]    [0012]FIG. 2 is a diagram illustrating the interconnection and data flow between the various software modules comprising an NC code generating and processing scheme utilized in the embodiment shown in FIG. 1; and  
         [0013]    [0013]FIG. 3 is a flow diagram illustrating the conventional method of inputting NC code into a CNC machine control. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]    Referring to FIG. 1 of the drawings, there is illustrated a computer numeric controlled (CNC) machining system, which generally includes a base member  101 , a worktable  102 , a gantry  103 , a toolhead support assembly  104  and a toolhead assembly  105  provided with a spindle in the lower end thereof. The gantry consists of a pair of leg members  106  and  107 , rigidly secured at their lower ends to base member  101 , and a transversely disposed section  108  supported on the leg sections and spanning above the worktable. The base member is formed of steel sections welded together to provide a rigid and stable foundation. Worktable  102  is mounted horizontally with the surface parallel to the plane formed by the x and y axes and is adapted to be displaced longitudinally relative to the base member or along a y axis. Worktable  102  may be of any number of sizes and layouts depending on the type of work to be performed using the machine. The front face of transverse section  108  is provided with a pair of vertically spaced, transversely disposed rails  109  and  110  on which toolhead support assembly  103  is mounted and displaceable transversely or along an x-axis. Toolhead assembly  104  is mounted on support assembly  105  and is adapted to be displaced vertically or along a z-axis by such assembly. Each of worktable  102 , toolhead support assembly  104  and toolhead assembly  105  is displaceable along its respective axis by a feed screw arrangement driven by an AC servomotor. The operation of such servomotors is controlled by a programmable computer-numeric controller (CNC)  111  to provide for movement of a tool mounted on the toolhead assembly along a motion path to perform a work function such as routing, shaping, drilling and the like on a workpiece mounted on the worktable. Taken together, the axes of motion of worktable  102 , toolhead support assembly  104  and toolhead assembly  105  can be said to form the axes configuration of the machine.  
         [0015]    Those having ordinary skill in the art will recognize that several different arrangements of the elements of the machine as described are possible. As an example, instead of the worktable being displaceable and the gantry being stationary as described, the worktable can be stationary and the gantry may be displaceable along the y-axis to provide displacement between the gantry and the worktable. Because there are many possible variations on these machine-specific attributes, information about these attributes is necessary in order to generate the correct NC code for control of the machine.  
         [0016]    Programming the machine, whether performed as part of a conventional method or in accordance with the present invention, makes use of two essential elements: A computer software system that generates cut-path geometry based on user-entered data, generally referred to as a Computer Aided Manufacturing (CAM) program, and a means of processing the cut-path data into usable NC code format. In perhaps its simplest form, an off-line-generated program may consist of nothing more than a data interchange file (DXF) from a computer aided drafting (CAD) program. Some of the more complex CAM software systems utilize a two-part parametric graphic software which allows for designing a specific type of end product, then converting the data into cut-path geometry for the individual components. However, regardless of the system being used, the cut-path geometry must be converted into usable NC code through post-processing. The post processing software program (post-processor) is usually a separate module from the CAM program. The post-processor, aside from converting the CAM program into NC code, also provides a means whereby the user may input operational attributes, such as feed speeds, tool selection, as well as machine-specific attributes, such as axis configuration and worktable size and layout.  
         [0017]    The preferred embodiment of the present invention is carried out by means of software submodules embedded within the CNC machine control, which provide for the processing of off-line generated cut-path programs according to machine-specific attributes, the selection by the machine operator of operational attributes, and the generation of NC code, all with the CNC machine control. For example, program attributes such as tool assignments and feed speeds can be selected and entered by the operator based on conditions unique to a specific application. The software is also configured to process the program based on machine-specific attributes such as axis configuration and worktable size and layout.  
         [0018]    A further important feature of the present invention is carried out by software that nests workpieces or components of workpieces onto appropriately sized sheets of material. A Workpiece may consist, for instance, of several individual components to be cut from the same material. Nesting is a process whereby the individual components within a workpiece program are assembled into a pattern that allows for the optimum number of components to be cut from the smallest possible amount of material. Algorithms for nesting are well known in the art. However, performing post-processing at the machine control further permits the use of off fall material that is available to a particular machine. Off-fall material may be material that has been left on the worktable from the preceding cutting cycle or that has been saved from previous cutting cycles and identified and stored for future use. Off-fall material is recorded and tracked in the software according to geometric shape and surface area, then matched to nested component clusters based on the amount of material required to execute the program. This method reduces the amount of wasted material by recapturing and using material that would otherwise be discarded, which reduces production costs and is more environmentally compatible.  
         [0019]    Because post-processing is accomplished at the machine control, it is possible to next substantially complementary components from multiple workpieces, or from multiple instances of the same workpiece, in order to improve nesting efficiency even further. The method disclosed herein permits multiple databases to be inputted, processed, and nested onto the same sheet of material. Such a feature is a valuable asset in terms of material conservation.  
         [0020]    [0020]FIG. 2 is a conceptual diagram that demonstrates the interconnection and data flow between the various software modules that accomplish the NC code generating method described herein. Program data, originating from a basic CAD software system  201  or from other graphic-based software systems  202  are loaded directly into databases  203  and  210  respectively. While only two graphic databases are exemplified herein, it should be understood that numerous databases may be created, depending on the number of programs entered. The program data, as represented by the database, contain information about workpiece geometry. CNC control software module  206  is located within CNC machine control  209 , which generally comprises a central processing unit, a memory, electronic storage, a display and one or more input devices, and is connected to and controls a CNC machine y executing code  208 . Those skilled in the art will recognize that many different embodiments for CNC machine control  209  are possible. The data are loaded into CNC control software module  206  by any number of means for transferring data electronically, such as magnetic or optical data storage or local area network connection. The machine operator or programmer may then enter operational attributes  205 , which may include tool assignments and feed speeds. Machine-specific attributes  204 , such as worktable size and layout and axis configuration, are provided to CNC control software module  206 . Program nesting and matching of appropriately sized new material or off-fall is performed based on recorded and tracked geometric shape and surface area data  211 . NC control code  207  is generated based on the program data and on the attributes, which include machine-specific attributes  204 , operational attributes  205  and material-specific attributes  211 , such as geometric shape and surface area data for a piece of material. NC control code is then executed ( 208 ) as a workpiece processing program by the CNC machining system.  
         [0021]    [0021]FIG. 3 exemplifies the flow of data in a conventional off-line programming scheme. An NC code program  301  originating from one of various sources is entered into the CNC machine control  302  where it is stored in machine memory to be retrieved at later time for program execution  303 . The code must be post-processed with all parameter assignments before being loaded into a CNC control.  
         [0022]    From the foregoing detailed description, it will be evident that there are a number of changes, adaptations and modifications of the present invention which come within the province of those persons having ordinary skill in the art to which the aforementioned invention pertains. However, it is intended that all such variations not departing from the spirit of the invention be considered as within the scope thereof as limited solely by the appended claims.