Method and Apparatus for Performing Real-Time Computer Animation

The invention relates generally to the field of computer animation. More specifically, the invention relates to a method and apparatus for providing real-time computer animation of physical simulation data generated by computer-aided design systems in order to model a physical phenomena.

Advancements in computer-aided design technology have led to systems that enable engineers to run simulations that test the physical properties of parts or systems. The ability to run simulations of the physical properties of the parts or systems prior to their the actual manufacture or implementation enables the engineer to identify potential design flaws or deficiencies during the design process. Simulations can be run, for example, to determine when and where a mechanical part will fail under load conditions, thereby enabling the engineer to strengthen or modify the part during the design process to improve its performance.

In addition to the analysis of completed parts, simulations of physical processes are also useful to identify potential problems in the manufacturing process. Injection molding, for example, is a physical process that would benefit by the application of computer simulation technology. The injection molding process consists of three stages; filling a mold with plastic under high pressure; holding and compressing the plastic into the mold; and solidifying the plastic in the mold. The process is particularly useful for manufacturing thin walled structures with complicated shapes. Many problems, however, can occur during the molding process such as a premature solidification of plastic in a part of the mold which blocks the flow of plastic into adjacent regions.

A detailed understanding of physical flow of the plastic through the mold is an essential element in mold design to avoid such problems. Traditionally, the mold designer had to design parts without the benefit of having data that simulated the dynamics involved in the molding process. Thus, the mold designer was required to rely on time consuming physical tests of a series of prototype molds to determine if parts manufactured by the molds were of sufficient quality. Adjustments to the mold design were made based on the results obtained from the prototype molds on a trial and error basis and mold design tended to be more of an art than science.

More recently, computer simulations of the molding process have been devised over the past fifteen years that enable the mold designer to simulate the flow of plastic through the mold during the design process. Cornell University of Ithaca, N.Y., for example, has maintained an ongoing research project in cooperation with the National Science Foundation, designated the Injection Molding Project, directed to computer-aided design of injection molds. The progress and results of the Injection Molding Project have been published in a series of progress reports. See generally, Injection Molding Project, Progress Reports Nos. 1-14, Wang et al., Cornell University, 1975-1988, the contents of which are herein incorporated by reference, and in particular Progress Report 11 entitled "Computer-Aided Design and Fabrication of Molds and Computer Control of Injection Molding", Wang et al., April 1985, NSF Grant MEA-8200743, Progress Report 12 entitled "Integration of CAD/CAM for Injection-Molded Plastic Parts:, by Wang et al., May 1986, NSF Grant DMC-8507371, and Progress Report 13 entitled "Integration of CAD/CAM for Injection-Molded Parts", by Wang et al., June 1987, NSF Grant DMC-8507371.

The results of the research project has yielded a computer aided engineering package referred to as the Cornell Injection Molding Program (CIMP) that enables the mold designer to simulate flow characteristics of the plastic through a mold design. Further development work based on the research done at Cornell has also produced commercially available software packages such as C-FLOW, an extension of the CIMP developed by Advanced CAE Technology, (See generally, Applications of Computer Aided Engineering in Injection Molding, ed. Louis T. Manzione, Hanser Publications, New York:Macmillian, 1987, the contents of which are herein incorporated by reference, and specifically Chapter 7 entitled "C-Flow: a CAE Package with High-Level Interface Graphics", by Wang et al.). With the aid of computer simulations, the mold designer is able to make modifications to the mold design during the design process without having to produce prototype molds, thereby significantly reducing the time required to finalize the mold design and produce production molds.

While computer packages have been developed that permit the mold designer to generate simulation data as noted above, the simulation data generated by such packages often contains large data sets having many parameters, i.e., multi-variable data, which is difficult to present in a format that can be readily interpreted by the mold designer. Conventional methods for presenting multi-variable data include the use of contour plots and three-dimensional surface elevation maps, for example a geological survey map, which plot elevation and surface type over a two-dimensional surface by the use of color and contour lines. Another approach is to use symbols, called glyphs, which represent data at sample points. See, Glyphs Getting the Picture, W. Sacco et al., Janson Publications, Inc., Providence, R.I., 1987.

The application of glyphs to present injection mold simulation data is discussed in detail in an article entitled "Visualization of Injection Molding", by R. Ellson and D. Cox, Simulation, Vol. 51, No. 5, November, 1988, incorporated herein by reference. A multi-layer glyph is used to represent the simulation data at various points in the mold during the molding process. The shape of the glyph is modified to reflect changes in the flow rate of the plastic. The temperature of the plastic is represented by the coloring of various layers of the glyph. The pressure of the plastic is represented by the coloring of a base plane of the glyph. The simulation data is processed to generate a plurality of image frames illustrating, through the use of the glyphs, the flow of the plastic through the mold. Once all of the frames are generated, a moving animation of the plastic flow can be generated by displaying the plurality of image frames in sequence.

The presentation of simulation data in the forms of glyphs as described above represents a vast improvement over conventional two-dimensional graphical presentation methods. Unfortunately, the mold designer is not able to view the animation of the plastic flow in real-time as a significant amount of processing capacity and time is required to generate pictorial representations, i.e., image frames, of the multi-variable data in easily comprehensible forms such as glyphs. For example, the system described by Ellson and Cox cited above requires about eight minutes to generate the image data for a single frame using a mini-supercomputer. A typical animation may includes one hundred animation frames. Accordingly, the generation of the image data for the animation frames alone takes between 13 and 14 hours. Additional time is required to generate a moving animation by linking the frames together. Thus, the mold designer must run the simulation program and wait several days before a moving animation of the physical phenomena can be viewed.

The primary drawbacks to achieving real-time animation are found in the basic approach taken by conventional systems to generate and display the simulation data. Conventional injection mold simulation programs as mentioned above, for example, divide the mold into a number of geometric elements represented by floating point data and characterize the flow of plastic through the geometric elements with variables, such as velocity, temperature, pressure, etc., that are also represented as floating point data. Animation processes of the type described above have centered on the generation of a list of polygons, based on the geometrical and variable floating point data, that are used to create an image frame of the physical process for each step in time.

Each image frame generated by the animation process may contain over a hundred thousand polygons. The polygons are represented by a number of vertices (3 or 4) having three-dimensional coordinates that relate to the location of the polygon within the mold cavity. The shear volume and complexity of processing the floating-point data used to generate the tens of thousands of polygons required to construct each image frame in real-time is beyond the capability conventional computer processing equipment, such as stand alone engineering workstations, that are available to the average mold designer.

Real-time animation is technically possible, of course, if large dedicated supercomputers were used to perform the processing of the floating-point data in the above-described manner. The average mold designer, however, does not have access to such computing power. Thus, even after the generation of the simulation data is complete, the mold designer must wait a significant period of time to view the simulation data in a comprehensible form.

In view of the above, it is an object of the invention to provide a method and apparatus for performing real-time computer animation that would enable the mold designer to view the animation of the simulation data in real-time, thereby enabling the mold designer to analyze the simulation data and make required corrections to modify the mold design in an efficient manner.

It is a further object of the invention to provide a method and apparatus for performing real-time computer animation that is economical and therefore readily available to the average designer.

It is an additional object of the invention to provide a method and apparatus for performing real-time computer animation of a physical phenomena that permits a user to modify the animation display.

The present invention provides a method and apparatus for performing real-time computer animation of data used to simulate physical phenomena. More specifically, a real-time animation system is provided that generates floating point geometrical element simulation data and byte width variable simulation data with a processing unit. The floating point geometrical simulation data is supplied to a graphics processor which generates element transformation matrices. The variable simulation data is applied to each of the element transformation matrices by the graphics processor to generate a plurality of layer transformation matrices. The layer transformation matrices are then applied to a stock piece-wise polygonal surface to generate a plurality of layer elements. The layer elements are displayed on a graphics display unit in real-time in the form of glyphs which animate the physical phenomena.

The animation system also includes a direct user interface that permits a user of the system to vary the presentation of the animation display. For example, the user may alter the viewpoint or perspective from which an observer views the animation display by rotating and translating the glyph representation presented on the graphics display unit. The user can also utilize the user interface to recall the specific data that was used to generate a particular glyph, thereby enabling the user to view the quantitative scalar values of the variable data. In addition, the user interface is employed to permit the user to define certain characteristics of the animation display including the size and aspect ratio of the glyphs and the frame rate at which the animation display runs. The user may also utilize the user interface to select variable ranges so that the animation display reflects only information regarding the physical phenomena that is within the selected variable ranges.

With the above as background, reference should now be made to the following detailed description of the preferred embodiment and the accompanying drawings, wherein:

FIG. 1 is a basic block diagram of an animation system in accordance with the present invention;

FIG. 2 illustrates a glyph that is used by the animation system illustrated in FIG. 1 to represent the physical characteristics of plastic as it flows through a mold cavity;

FIG. 3 is a block diagram representation of the generation of element transformation matrices from data contained in a geometry file;

FIG. 4 is a block diagram representation of the generation of layer transformation matrices from the element transformation matrices and the generation of layer elements based on the layer transformation matrices;

FIG. 5 is an illustration of a single image frame generated by the animation system illustrated in FIG. 1;

FIG. 6 is a general flow diagram of the operation of the animation system illustrated in FIG. 1;

FIGS. 7A and 7B illustrate a detailed flow diagram of an animation program run on the workstation of the animation system illustrated in FIG. 1;

FIG. 8 illustrates a glyph "navigator" option window that is displayed on the user interface display of the animation system illustrated in FIG. 1;

FIG. 9 illustrates a view option window that is displayed on the user interface display of the animation system illustrated in FIG. 1;

FIG. 10 illustrates a display option window that is displayed on the user interface display of the animation system illustrated in FIG. 1;

FIG. 11 illustrates a glyph scaling option window that is displayed on the user interface display of the animation system illustrated in FIG. 1;

FIG. 12 illustrates a traces option window that is displayed on the user interface display of the animation system illustrated in FIG. 1;

FIG. 13 illustrates a saved setting option window that is displayed on the user interface display of the animation system illustrated in FIG. 1;

FIG. 14 illustrates a time option window that is displayed on the user interface display of the animation system illustrated in FIG. 1;

FIG. 15 illustrates how the option windows shown in FIG. 9-14 can be overlayed on a single frame displayed on the user interface display of the animation system illustrated in FIG. 1; and

FIGS. 16A and 16B illustrate a detailed flow diagram of the gly.sub.-- pixel routine that is run on the graphics processor of the animation system illustrated in FIG. 1.

The invention is based on the recognition that data handling and processing in an animation system to generate an animation display of a physical phenomena can be greatly enhanced by defining a complex geometrical shape as a plurality of geometrical elements represented by floating point data, defining variations in the physical phenomena as it relates to the geometrical elements as byte width variable data, using a graphics processor to generate transformation matrices, and applying the transformation matrices to a standard geometrical display element to generate a plurality of glyphs which--when displayed on a graphics monitor--animate the physical phenomena. The invention is useful in modeling any type of physical phenomena that includes multi-variable data that is associated with complex geometrical configurations. It should therefore be understood, that while the invention will be discussed in detail with reference to its application to the animation of injection molding processes, the invention is not limited to the specific application set forth below.

Referring now to FIG. 1, a basic block diagram of a real-time animation system in accordance with the present invention is shown including a workstation 10 (for example a SUN 3/260 workstation available from Sun Microsystems Inc.), a graphics processor 12 (for example an AT&T PXM 900 Series Pixel Machine) coupled to the workstation 10 via a VME bus 14, and a high resolution graphics display monitor 16 coupled to the graphics processor 12. The workstation 10 includes a host processor 18, a user interface 20 (such as a keyboard, mouse, etc.), and a user interface display monitor 22. The host processor 18 and graphics processor 12 include memory units (not shown) in which operating programs and data files are stored. As will be described in greater detail below, the illustrated real-time animation system takes advantage of the ability of the graphics processor 12 to perform matrix additions and multiplications extremely rapidly.

In operation, a standard CAD/CAM software package is run on the workstation 10 to permit a user to define a mold cavity utilizing the user interface 20. The CAD/CAM package divides the defined mold cavity into a plurality of geometric elements in a conventional manner. A simulation program is then run on the workstation 10 to simulate the flow of plastic through each of the geometric elements. Simulation data generated by the simulation program is stored as a geometry file that contains floating-point data for each geometric element and a time step file that includes only variable data associated with changes in the physical properties of the plastic (such as temperature, pressure, speed, etc.) as it flows through the geometric elements.

The flow of the plastic through the geometric elements is actually broken down into a number of element layers. The data for the element layers of a given geometric element will be used to generate a corresponding multi-layer glyph of the type illustrated in FIG. 2. The glyph in FIG. 2 conveys information on the pressure, temperature and velocity of the plastic as it moves through a defined geometric element. Direction of flow is illustrated by the orientation of the glyph. The length of each glyph layer illustrates the speed of the plastic through that layer of the geometric element. The temperature of the plastic is illustrated by the coloring of the glyph layers. The pressure of the plastic is illustrated by the coloring of the base plane of the glyph. The data structure for the time step files which determine the shape, color and size of layers (n) of the glyphs (g) at various points in time (t) can be represented as follows:

The variable data representing each physical property is scaled to a single byte (an integer value between 0-255).

Floating-point numbers are not used to define the variable data, but are used to define the geometrical information in the geometry file for each of the elements (e) as illustrated below:

The real-time animation system generates image frames in real-time through the use of transformation matrices constructed from the floating point data in the geometry and the byte width data in the time step files. At initialization of an animation program, the floating point data in the geometry file for each geometric element is multiplied by standard factors in order to generate a plurality of element transformation matrices that relate the data to a local coordinate system. More specifically, as illustrated in FIG. 3, the host processor 18 of the workstation 10 passes the floating point data in the geometry file corresponding to each of the elements to the graphics processor 12 over the VME bus 14. The graphics processor 12 performs matrix computations on the floating point geometry data to generate element transformation matrices that corresponds to each the geometric elements.

A layer transformation matrix is then generated for each layer of the geometric elements. Referring now to the block diagram representation illustrated in FIG. 4, the host processor 18 recalls and passes the byte length variable data related to the first layer of the first geometric element, i.e, the data for Glyph 1, layer 1, to the graphics processor 12. The graphics processor 12 uses the variable data to modify the previously generated element transformation matrix for the first element to produce a layer transformation matrix for the first layer of the first element. The host processor 18 then sends a data representation of a stock piecewise-polygonal surface to the graphics processor 12. The graphics processor 12 applies the layer transformation matrix to the data representation of the stock piecewise-polygonal surface. The layer transformation matrix modifies the stock piecewise-polygonal surface to generate the first glyph layer of the glyph that corresponds to the first element and the first glyph layer is displayed on the graphics display monitor 16. The process is repeated until each layer of the first glyph has been generated and displayed. The graphics processor 12 then retrieves the element transformation matrix corresponding to the second element and the process is continued, i.e., the host processor 18 supplies the variable data for the first layer of the second element, the graphics processor 12 modifies the second element transformation matrix based on the variable data to form a first layer transformation matrix for the second element, and the host processor 18 supplies the stock polygon piece to the graphics processor 12 which modifies the stock polygon based on the first layer transformation matrix to generate the first layer of the second glyph. The overall process is continued until all of the glyphs for a given frame are generated and displayed. The process is then repeated for the next image frame.

An example of one image frame that is displayed on the graphics display monitor 16 is shown in FIG. 5 (FIG. 5 is a representation of the color illustration of the image frame published as FIG. 2 of the article entitled "Visualization of Injection Molding" incorporated by reference above). The image frame represents a mold having two thicknesses. Temperature (T) and pressure (P) color bar graphs are provided above the mold animation. The back portion of the mold is the thicker portion and fills first. The filling of the thinner front portion of the mold produces high shear and the plastic flows along a curved path. The plastic flow is illustrated by the elongated glyphs.

After the initial display of several animation frames, the user may desire to change certain aspects of the animation display including the scaling of the glyphs or the view presented to the user. In addition, the user may wish to delete certain information from the animation display to more clearly illustrate certain aspects of the physical phenomena being modeled. For example, it may be desirable to animate only the plastic flow that is above certain temperatures or pressures. The illustrated animation system permits the user to enter certain user variables to change the aspect ratio, view presented to the user, etc., via the user interface 20. The user variables are supplied to the graphics processor 12 and are used to modify each of the element transformation matrices thereby changing the animation display.

In addition to the use of glyphs to convey data for each time step of the molding process, it is desirable to obtain information on the status of key scalar variable quantities such as material flow rate or pressure during the animation. The animation system permits the user, through the user interface 20, to select a specific glyph and display the variable quantities in the form of simple line graphs. Specifically, a cursor is displayed on the graphics display monitor 16 that the user utilizes to select a specific glyph. The variable information is displayed in the form of line graphs on the user interface display 22 simultaneously with the display of the animation on the graphics display monitor 16. A vertical line sweeps through the graphs as the animation progresses to give the user a time reference as well. While the animation of the plastic flow through the use of glyphs provides a convenient method to observe the dynamics of the process, the ability to see plots of key variables allows the user to observe time dependent variables as an aggregate.

A detailed explanation of a preferred implementation of the animation system in accordance with the present invention will now be discussed with reference to FIG. 6 which illustrates a general flow diagram of the operation of the animation system. As shown in FIG. 6, a routine called "flow" is run on the workstation 10. The flow routine displays a window of options that can be selected by the user via the user interface 20. The gly.sub.-- simulate option permits the user to run a simulation program using a selected data file. The simulation program can be a modified version of the CIMP program which produces a geometry file containing floating point data and a time step file containing byte width variable data. Alternatively, a commercially available program, such as C-Flow, can be used to run the simulation and a conversion routine can then be used to convert the output files from the commercially available program to the desired geometry and time step files. The details of the conversion routine would depend, of course, on the particular simulation software that is selected. The output files generated by the simulation program are stored in a directory called gly.sub.-- data in the memory unit of the workstation 10.

In order to increase the number of simulation output files that can be stored in the memory unit of the workstation, the user is also able to select a data compression option, gly.sub.-- compress, which uses a conventional data compression routine to compress the simulation output files. The simulation output files must be uncompressed, however, before a real-time animation of the simulation data can be run. Thus, an option is provided, called gly.sub.-- uncompress, that permits the user to uncompress previously compressed files.

A real-time animation of the simulation data is run by selecting the gly.sub.-- animate option which permits the user to select and run an animation on one of the simulation output files stored in the gly.sub.-- data directory. As shown in greater detail in FIGS. 7A and 7B, selection of the gly.sub.-- animate option causes the workstation 10 to run the main animation program called gly.sub.-- animate.c. Upon activation, the gly.sub.-- animate.c routine establishes a link with the graphics processor 12 by running a routine called anim.sub.-- link.c. A glyph "navigator" window is generated on the user interface display 22 by a routine called anim.sub.-- navigator.c which calls a make window routine named anim.sub.-- globals.c. The glyph navigator window, illustrated in FIG. 8, displays a series of options that can be selected by the user with the user interface 20. The anim.sub.-- globals.c routine contains a number of subroutines that generate a series of option windows which correspond to the options listed in the glyph navigator window. Selection of an option causes the corresponding option window to be displayed on the user interface display 22.

Selection of the "view" option causes the subroutine anim-view.c to generate and display a view option window (See FIG. 9) on the user interface display 22. The user utilizes the view option window to enter user variable data that defines how the glyph animation of a mold is to be displayed on the graphics display monitor 16 with respect to the viewer. Specifically, a series of sliders are displayed in the view option window that are used to define the coordinates (X,Y,Z) of a view point, the distance of the viewer's eye from the viewpoint, and tilt, pan and twist angles. The user selects the sliders using the user interface 20 and adjusts the listed variables as desired.

The "display" option controls and limits the simulation data that is included in the animation display. The anim.sub.-- display.c subroutine generates the display option view window illustrated in FIG. 10. Two sliders, velocity and temperature, are included in the display option view window. The user can select a desired temperature and velocity range, for example, so that only plastic flow at between a certain temperature and velocity range is included in the animation display. This allows the user to highlight particular areas of interest. Two check boxes are also included in the display option view window that permit the user to select the display of an empty mold or a transparent mold wall (outline) that is superimposed on the glyph animation.

The "scaling" option controls the dimensions of the glyphs incorporated in the animation display. The anim.sub.-- gly.sub.-- scale.c subroutine generates a glyph scaling option window (FIG. 11) that includes sliders which are used to set the length width and height of the glyphs. The scaling option permits emphasis of small flows while preventing large flows or fine meshes from becoming obscured.

The "traces" option displays two-dimensional graphs of scalar values such as gate pressure and flow rate. The anim.sub.-- trace.c subroutine generates the traces option window illustrated in FIG. 12. The graphs are displayed on the user interface display 22 of the workstation 10.

The "saved settings" option permits the user to save a particular set of adjustments for future use or recall a previously saved set of adjustments. This permits the user, for example, to save preferred settings so that the same animation display can be run on simulation data based on a modified mold design. The anim.sub.-- save.c subroutine generates the saved settings option window illustrated in FIG. 13.

The "time" option controls the running of the animation display. The anim.sub.-- time.c subroutine generates the time option window illustrated in FIG. 14. The time option window displays a set of "buttons" similar in arrangement to the operating controls of a VCR, that permit the user to continuously play the animation in forward or reverse modes, jump to the beginning or end, or step a single frame forward (+) or a single frame backward (-). The current simulation time and frame number are also displayed and can be changed via the user interface 20.

Each of the above-described option windows can be activated while the animation display is running, thereby enabling the user to alter the presentation of the animation display and the information contained therein in real-time. The windows for each of the options can also be overlayed in a conventional manner on a single display frame as shown in FIG. 15.

A detailed flow diagram of the operation of the graphics processor 12 is illustrated in FIGS. 16A and 16B. A routine called gly.sub.-- pixel.c is used to receive information from the workstation 10 and generate the animation frames to be displayed on the graphics display monitor 16. The gly.sub.-- pixel.c routine calls a screen initialization routine called pix.sub.-- int.c that reads previously stored color files to generate temperature and pressure bar graphs that appear on the top of the animation frame (See FIG. 5). The colors for the time and pressure bar graphs are selected so that slight variations are easily detected by the human eye. A routine called pix.sub.-- geometry.c reads the geometry file data from the workstation 10 and performs and generates the element transformations matrices. The generation of the layer transformation matrices and their application to the stock piece-wise polygon surface is accomplished with a routine called pix.sub.-- draw.c.

As was stated previously, it is also desirable to select a particular glyph that is displayed in the animation display an in order to view the scalar variable data associated therewith. The selection and highlighting of a desired glyph is accomplished with a routine called pix.sub.-- pick.c. Basically, an "element" option is displayed in the glyph "navigator" window. Selection of the window option generates a "joy-stick" window on the user interface display monitor 22. When the cursor for the workstation 10 is in the joy-stick window a cursor appears on the graphics display monitor. The cursor on the graphics display monitor is used to select a particular glyph. The scalar variable data associated with the selected glyph is then displayed on the user interface display monitor 22.

A specific example of a software implementation of the routines discussed written in the programming language "C" is provided in Appendix A which forms part of this specification. The specific program employs standard matrix computation routines that are provided on an AT&T 900 Series Pixel Machine. The matrix commands used in the animation program listed in Appendix A are described in the PIClib Users Guide, Version 1.2, AT&T Pixel Machines, Holmdel, N.J., 1990.

The invention is applicable to modeling any physical phenomena in which multi-variable data must be presented with respect to a complicated geometrical structure including the modeling of natural phenomena (such as weather patterns) in addition to industrial processes (such as plastic injection molding). The real-time animation of the multi-variable data with the use of glyphs that is enabled by the invention is particularly useful in allowing users to quickly and efficiently analyze the physical phenomena being studied. Because the animation operates in real-time, the user is able to easily make adjustments to the animation display to emphasis particular areas of interest without wasting time. Although the invention has been described with particular reference to certain preferred embodiments thereof, it will be understood that modifications and variations are possible within the spirit and scope of the appended claims. For example, the invention can be implemented using different hardware components and different software than those specifically set forth above.

It should also be noted that a portion of this specification contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of this specification as it appears in the files of the United States Patent and Trademark Office, but otherwise reserves all copyrights whatsoever. ##SPC1##