Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1997-12-22
2001-03-06
Grant, William (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S136000, C700S137000, C700S181000, C700S182000, C700S183000, C112S470050, C112S475180, C112S254000
Reexamination Certificate
active
06198983
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to textile manufacturing. More specifically, this invention relates to a software architecture for a computer numerically controlled stitching system.
Large aircraft structures such as wing covers are now being fabricated from textile composites. The textile composites are attractive because of their potential for lowering the cost of fabricating the large aircraft structures. Cutting pieces of fabric and stitching the fabric pieces together have the potential of being less expensive then cutting sheets of aluminum, drilling holes in the aluminum sheets, removing excess metal and assembling metal fasteners.
The wing cover can be made from a carbon-fiber textile composite. Sheets of knitted carbon-fiber fabric are cut out into pieces having specified sizes and shapes. Fabric pieces having the size and shape of a wing are laid out first. Several of these pieces are stacked to form the wing cover. Additional pieces are stacked to provide added strength in high stress areas. After the fabric pieces are arranged in their proper positions, the pieces are stitched together to form a wing preform. Secondary details such as spar caps, stringers and intercostals are then stitched onto the wing preform. Such a wing preform might have a thickness varying between 0.05 inches and 1.5 inches. The wing preform is quite large, and its surface is very complex, usually a compound contoured three-dimensional surface.
The stitched wing preform is transferred to an outer mold line tool that has the shape of an aircraft wing. Prior to the transfer, a surface of the outer mold line tool is covered with a congealed epoxy-resin. The tool and the stitched wing preform are placed in an autoclave. Under high pressure and temperature, the resin is infused into the stitched preform and cured. Resulting is a cured wing cover that is ready for assembly into a final wing structure.
For textile composite technology to be successful, two barriers must be addressed: cost and damage tolerance. Damage tolerance is achieved by making high quality, closely-spaced stitches on the wing preform. The high quality, closely-spaced stitches add a third continuous column of material to the wing preform. If thread tension is not proper, a large number of stitches on the preform will not be of sufficient quality and will reduce the damage tolerance. Improper thread path geometry might also degrade the quality of the stitches and, therefore, reduce the damage tolerance.
Even though the stitches are made by a stitching machine that is computer numerically controlled (“CNC”), it is difficult to make stitches having the high quality required for the wing preform. On a compound, contoured three-dimensional surface, thread tension and thread path geometry must be constantly adjusted for an exceedingly large number of stitches. The CNC stitching machine might make eight to ten stitches per inch, in rows that might be spaced 0.1 inches to 0.5 inches apart, over a surface that might be longer than forty feet and wider than eight feet. The total number of stitching points on the wing preform might exceed 1.5 million.
Much manual labor is required. Because the wing preform has many regions of differing thickness, a machine operator must constantly stop the stitching machine when a new region is about to be stitched, adjust the thread tension and possibly the thread path geometry, and restart the stitching machine. Of course, the CNC stitching machine has multiple stitching heads. At any given time, two or more stitching heads might be stitching different regions having different thicknesses. Whenever one of the stitching heads enters a new region, the stitching machine must stopped and the thread tension and perhaps the thread path geometry of the stitching head entering the new region must be adjusted. Resulting is a large number of instances in which the stitching machine must be stopped, the thread tension and thread path geometry adjusted, and the stitching machine restarted.
Additionally, the operator must know when to stop the machine and make the adjustments, or the operator must be prompted to stop the stitching machine and make the adjustments. Either way, the operator must pay constant attention while the wing preform is being stitched. That too is difficult, considering the large number of stitches that must be made.
Moreover, generating the code for the CNC stitching machine would take a programmer thousands of hours. Not only would generating the code take a long time, but it would also be subject to human error.
The manual labor increases the time and cost of manufacturing the wing preform, and it potentially reduces damage tolerance. Based on the foregoing, it can be appreciated that there presently exists a need for a software architecture that allows for complete operation, from path generation to control of the stitching process. As will become apparent hereinafter, the present invention fulfills this need.
SUMMARY OF THE INVENTION
The invention can be regarded as a method of using a computer to generate native code for a stitching machine. The method comprises the steps of using the computer to generate a geometry model; using the computer to generate tool paths from the geometry model, the tool paths including a first plurality of instructions for making stitches; and using the computer to generate a second plurality of instructions indicating thickness values. The instructions of the second plurality are inserted between the instructions of the first plurality.
The invention can also be regarded as a computer system for generating native code for a CNC stitching machine. The system comprises means for generating a geometry model; means for generating tool paths from the geometry model, the tool paths including a first plurality of instructions for making stitches; a zone table for determining thickness values; and means for accessing the zone table to generate a second plurality of instructions indicating the thickness values. The instructions of the second plurality are inserted between the instructions of the first plurality.
The invention can also be regarded as a method of using a processor to automatically adjust thread tension in a stitching head of a stitching machine. The stitching head includes a servo for setting the thread tension. The method comprises the steps of: using the processor to access data indicating a thickness value; using the processor to determine a thread tension value corresponding to the thickness value; and commanding the servo to the thread tension value.
The invention can also be regarded as an article of manufacture comprising computer memory; and data encoded in the computer memory. The data includes instructions for instructing a computer to access a lookup table for thickness values, access thread tension values corresponding to the thicknesses values, and generate servo commands corresponding to the thread tension values.
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Codos Richard
Collan William
Fox Rhoda
Korolev Alexandre
Korte Mike
Grant William
Marc McDieunel
McDonnell Douglas Corporation
Powell, Jr. Raymond H. J.
Westerlund Robert A.
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