TITLE OF THE INVENTION

[0001] Fixturing Device for Holding Sheet Type Material

FIELD OF INVENTION

[0002] The present invention relates in general to the fixturing of flexible sheet type materials such as leather for shape cutting on a computer controlled cutting table.

BACKGROUND

[0003] Computer controlled cutting tables are well known machines for cutting shapes from flexible sheet type work materials such as leather, foam and fabric, and are commonly used in the manufacture of clothing, upholstery and composites. Cutting is typically done by a knife that is computer controlled in the plane of the cutting table to follow the outline of the desired shapes. The knife may either reciprocate or drag. [0004] The flexible sheet work material is typically partially fixtured to the cutting table using vacuum. However, flexible materials held by vacuum are often easily disturbed. If counter measures are not taken, the cutting forces generated by the knife will usually locally break the vacuum hold, and shapes will be cut inaccurately. A presser foot is commonly used in conjunction with vacuum fixturing to reduce disturbance, and is a component that provides a surface that presses down on the flexible sheet work material in the immediate area surrounding the knife. However, the presser foot rubs against the material, and this generates a friction force that disturbs it, but to a lesser extent than the knife alone.

[0005] Current cutting machines in the art also do not allow the cutting of the sheet type material to the edge. This limitation is caused by the rolling or bunching up of material as the cutter approached the edge of the material. The supplemental use of

overlay plastic sheeting and vacuum technology to hold down the sheet type material as currently used in the art still does not allow the edge of the sheet type material to be cut due to rolling or bunching up of material. In addition, the use of plastic sheeting is cumbersome to use in current cutting machines.

[0006] Therefore, there remains a need in the art to eliminate the need for the overlay film while having an apparatus that is tolerant of height variations in the flexible sheet work material.

BRIEF SUMMARY OF THE INVENTION

[0007] An object of the invention is to eliminate the need for the overlay film in a cutting apparatus for sheet type material while having an apparatus that is tolerant of height variations in the flexible sheet work material.

[0008] Another object of the invention is to allow the cutting of the sheet type material closest to the edge or on the edge of the sheet type material without the sheet type material rolling or bunching up.

[0009] Another object of the invention is to allow the use of a fixturing device to hold down material of any type device that generates friction across the material and causes the material to undesirably roll or bunch up.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: [0011] FIG. 1 is a partial front view of the prior art, and is of an apparatus for knife cutting of flexible material.

[0012] FIG. 2 is a partial front view of the prior art, and shows an apparatus that helps prevent the disturbance shown in FIG. 1.

[0013] FIG. 3 is a partial front view showing the preferred embodiment of the invention.

[0014] FIG. 4 is a bottom view of the preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0015] This application is related to pending U.S. application serial no.

11/382,242 filed on May 8, 2006, Publication Number US2007-0256530A1, published

November 8, 2007, which the entirety of this application is hereby incorporated in toto by reference.

[0016] A device for use with sheet type material provides the elimination of the need for the overlay film in a cutting apparatus for sheet type material while having an apparatus that is tolerant of height variations in the flexible sheet work material. In an apparatus for cutting pattern pieces or in any apparatus that requires sheet type material to be held down, the device comprising a conforming material disposed about a movable arm of the apparatus.

[0017] The conforming material can be any type of soft material, such as soft bristles comprised of fine diameter filaments of nylon, which offer the benefits of excellent bend recovery and abrasion resistance. The material can be a solitary unit or comprise of many units such as in the soft bristles form of a brush. The device can be of any geometrical shape such as a circle square, rectangle or triangle or any other shape desirable to the application.

[0018] During operation the device produce axial forces in such a way as to resist the material from rolling up or bunching up when the device is moved over the sheet type material. The device also allows a cutting apparatus to cut close to the edge or on the edge of the sheet type material without having the material roll or bunch up. [0019] Adverting to the figures, Figure 1 shows a prior art device disturbing a flexible sheet work material. The disturbance is manifested as a wave (see reference numeral 8) in front of the moving presser foot. Such waves most frequently occur near the edges of the flexible sheet work material. One prior art method for preventing such disturbances is to place an overlay film, which is usually a thin (e.g., .001 inches thick) sheet of plastic, over the edges of the flexible sheet work material. This increases the vacuum hold down about the edges. The overlay film is consumed in the cutting process, and is therefore undesirable because it adds cost to the process and causes waste. [0020] Figure 2 shows another example of prior art. This apparatus is like the one in Figure 1 but adds a large flat ring of rigid material that ideally distributes a light uniform force to a large area surrounding the knife. However, some flexible sheet work materials, particularly natural leather, are not of uniform thickness. Furthermore, these materials can have irregularities such as wrinkles that form large and sudden height variations, and these render the apparatus of Figure 2 ineffective. [0021] The present invention eliminates the need for the overlay film while having an apparatus that is tolerant of height variations in the flexible sheet work material. FIG. 3 shows one embodiment of the invention, and is comprised of a work surface 1, a knife 3, a presser foot 7, a computer-controlled servo means (not shown) for commanding the knife 3 to follow the trajectory necessary for cutting two dimensional

shapes in the plane of the work surface 1, and a brush or brush-like material 9. Brush 9 is not so limited to being a brush, although in its preferred embodiment brush 9 contains at least one bristle, bristles are not the only embodiment. It is within the scope of the invention for brush 9 to include materials that function similarly to that of bristles. The advantage found for having bristles in brush 9 is that any irregularities are easily compensated for in the material being cut and bristles tend to have better wear resistance properties than a solid material. The work surface 1 is typically the air permeable surface of a vacuum table, although not so limited to such a surface, and is used to vacuum fixture a flexible sheet work material 2. The combination of the brush 9, and elements just cited yield an unexpected result of eliminating the need for an overlay film. Overlay film as previously recited is typically needed with the prior art shown in FIG. 1. [0022] The brush 9, depending on the embodiment, is comprised of a rigid backing plate 20, a conforming material 10, and a means to couple the brush 9 to surround and follow the knife 3. The coupling means may be comprised of a first annular groove 11 in the presser foot 7, a second annular groove 13 in the backing plate 20, and a torus shaped spring 12. However, those skilled in the necessary arts will recognize other ways of attaching the brush 1 so that it surrounds and follows the knife 3, and it need not directly attach to the presser foot 7. Best shown in FIG. 4, the brush 9 preferably has a ring shape such to produce a symmetrical region of hold down pressure about the knife. [0023] The conforming material 10 may consist of a plurality of soft bristles, or other pliable material such as foam or sponge that would conform to height variations of the flexible sheet work material 2. hi the preferred embodiment the conforming material

10 are soft bristles comprised of fine diameter filaments of nylon, which offer the benefits of excellent bend recovery and abrasion resistance.

[0024] One example of a conforming material 10 that is in the right range of softness to be suitable for many cutting applications including the cutting of natural leather hides has an overall diameter of nominally 4.25 inches and has bristles of .004 inch diameter nylon filaments that are nominally 0.625 inches long and extend nominally 0.015 inches below the presser foot 7. These bristle groups are spaced about 0.25 inches apart and are secured in 0.156-inch diameter tuft holes using standard brush- manufacturing techniques.

[0025] A person skilled in the art of mechanics of materials will recognize after reading this disclosure of the invention that related to the softness of the conforming material 10 is a pressure that acts on the flexible sheet work material 2. It is within the scope of the invention that other designs of other dimensions and other materials, including non-bristle materials such as foam, and other like designs would produce an equivalent pressure that would yield an equivalent hold down effect. [0026] The conforming material 10 should have as a property a low coefficient of friction to minimize the traction force generated when it rubs against the flexible sheet work material 2. A coating or laminate layer may be added to the conforming material 10 to decrease the coefficient of friction. For example, the conforming material 10 may be comprised of open-cell polyurethane foam and to which may be bonded a thin flexible laminate of Teflon® (Dupont's trademark for polytetrafluoroethylene) or other low friction material to decrease the coefficient of friction where it contacts the flexible sheet work material 2.

[0027] Other variations of the invention are possible. The presser foot 7 may be eliminated by contracting the inner diameter 15 of the brush 9 to closely surround the knife 3. The work surface 1 need not be part of a vacuum table; for example, a tacky substance may be used instead. In some applications gravity and friction may provide sufficient hold down. The work surface 1 need not be planer; it could have the shape of a drum or any other shape, and cutting would be done on its cylindrical surface. [0028] Although the invention has been described in conjunction with specific embodiments, many alternatives and variations can be apparent to those skilled in the art in light of this description and the annexed drawings. Accordingly, the invention is intended to embrace all of the alternatives and variations that fall within the spirit and the scope of the appended claims.