Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1998-09-14
2001-10-30
Grant, William (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S186000
Reexamination Certificate
active
06311100
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to computer aided manufacturing (CAM) and more particularly to the automated generation of tool paths for CAM applications.
BACKGROUND OF THE INVENTION
Machining is used extensively for producing prototypes, partially completed or roughed parts and finished parts in laboratory, industry, and other environments. However, since it takes considerable intelligence and manual skill to both plan and operate tools like milling machines and lathes to perform machining operations, particularly for complex parts, automatic machining involving computer aided manufacturing (CAM) has become increasingly popular over the years.
Current CAM systems require as inputs shape primitives, defined in terms of access directions and paremetrized cutting paths, and generate low level cutting instructions from such inputs. Such systems work reasonably well for three-axis machining such as end milling, face milling and drilling, but cannot efficiently capture the tool paths required for machining in four or more axis. Further, these techniques do not make tool paths for machining various features directly available from the received inputs, and these paths must be extracted with manual input from the user. Thus, for these systems, the onus of feature extraction is on the manufacturing engineer, making the processes time consuming and expensive. The resulting output may also frequently require considerable operator skill, something which is difficult to come by. This results in the laying out of a CAM job representing a significant fraction of the total cost of the entire project.
One problem when laying out tool paths, particularly for workpieces or parts having hidden surfaces, is to assure that contact by the workpiece with the tool is only at the tool's cutting/working surface and that spurious collisions do not occur between the workpiece and other parts of the tool, which collisions could interfere with tool operation and could result in defects in the resulting parts, rendering them unusable. Existing systems do not guarantee that the tool paths generated will be collision free and the onus of avoiding collisions between the tool and workpiece again falls on the manufacturing engineer and/or system operator. Difficulties in performing collision avoidance is a significant reason for the high cost in laying out complex CAM jobs.
A need therefore exist for an improved methodology for providing tool paths, particularly for complex parts or workpieces having at least partially hidden surfaces, and particularly where the CAM systems has four or more axis which may be utilized to facilitate access to such complex workpieces. Such a methodology should permit collision free tool paths to be automatically and rapidly generated, without requiring substantial time and effort on the part of the manufacturing engineer or other person laying out the job, and without requiring significant skill on the part of the machine operator. Such methodology would thus significantly speed the process of laying out CAM projects, facilitating the use of CAM for generating laboratory prototypes and the like, and would also significantly reduce the skill level of personnel required both to lay out jobs and to operate CAM machines. It would also result in more optimal paths for such systems, would significantly reduce the total cost involved in a CAM project, particularly ones involving short runs of parts, and would significantly reduce the time required to set up a CAM project, permitting users to more rapidly respond to parts requirements from customers and others.
SUMMARY OF THE INVENTION
In accordance with the above, this invention provides a method for utilizing a computer system to generate tool paths for computer aided machining in at least four-axis of a selected workpiece or part from a stock, which method includes the steps of (a) storing in the computer system both a surface point representation of the workpiece, which representation contains a unique code for each of the surface points, and a representation of a tool for which paths are to be generated; (b) viewing the workpiece surface from a discrete number of orientations and generating a map of surface points visible from each such discrete orientations; (c) utilizing said map to obtain selected most promising access directions; (d) performing collision detection for the tool along each of the most promising access directions for each most promising access direction; and (e) connecting the legal directions into tool paths. The method may also include the steps, performed either during or after step (e), of performing collision detection on the tool paths and adjusting the tool paths to avoid detected collisions. Step (e), the connection of legal directions into tool paths, may be performed by interpolating both between legal directions and the orientations of the legal directions for the successive points. The generation of the tool paths thus involves two levels of interpolation.
The surface segmented representation of the workpiece may be a tesselated representation, with each point being a triangular segment, and the tool may be represented as a series of triangulated slabs. Collision detection may be performed by positioning the tool at a most promising access direction previously determined, performing collision detection between the tool and the workpiece for each such access direction, computing a correction if a collision is detected and rotating the tool by the correction angle. The performance of collision detection may be repeated, with the collisions corrected in each instance, until either a collision is not detected during collision detection or a selected number of iterations of collision detection and correction have been performed. The tool may alternatively be represented as an implicit equation, and the representation of the tool used during collision detection may be wider than the tool, at least in the nonworking or in active areas thereof. Further, the code assigned to each segment on the workpiece surface may be a color code, with the map generated of visible surface points being a color map.
Step (c) may include forming a visibility “cone” for each segment to be operated on by the tool, the segments being voxels for a roughing operation and surface points (triangles for preferred embodiments) for a finishing operation. The visibility cones can be utilized to determine the most promising access direction. For preferred embodiments, this is accomplished by selectively thinning the visibility cone. Where there are angular limits on at least one of the axis, the thinning step is restricted so that each most promising access direction is within the angular limits of such axis. For a preferred embodiment, the selective thinning is performed by removing outer visibility paths of the visibility cone.
Step (c) may also include the generation of a voxel visibility map for each surface point which includes voxels in a delta volume of the stock to be removed. In this case, the most promising access direction would be obtained for each such voxel. The delta volume containing the voxels may be divided into slices, with the tool paths being generated for each slice.
The invention also includes a machine readable storage media containing representations of tool paths for the computer aided machining in at least four axis of a workpiece from stock, which tool paths are generated utilizing the method described above.
Finally, the invention includes a computing machine which receives both a surface point representation of the workpiece, which representation contains a unique code for each surface point, and a representation of a tool, the machine utilizing the representations to generate tool paths for the computed aided machining in at least four axis of the workpiece from a stock. The machine includes a machine readable storage media having the workpiece and tool representation stored therein. The machine also includes a means for viewing the workpiece surface from a discrete number of orientations; mea
Balasubramaniam Mahadevan
Laxmiprasad Putta
Sarma Sanjay E.
Gain, Jr. Edward F
Grant William
Mass. Institute of Technology
Wolf Greenfield & Sacks P.C.
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