Cutting – Processes – Cutting of interdigitating products
Reexamination Certificate
2001-03-16
2004-11-02
Choi, Stephen (Department: 3724)
Cutting
Processes
Cutting of interdigitating products
C083S049000, C083S056000, C700S134000
Reexamination Certificate
active
06810779
ABSTRACT:
FIELD OF INVENTION
This invention relates to a system and method for numerically controlled cutting of pieces from sheet material, and more specifically for accurately cutting pieces from a closely packed marker.
BACKGROUND OF THE INVENTION—DESCRIPTION OF PRIOR ART
Numerically controlled cutting machines are widely used in various industries for cutting various limp sheet materials such as woven and non-woven fabrics, vinyl and other plastics, paper, cardboard, leather, etc., as well as solid materials like sheet metal, lumber, glass, etc. The cutting tool cuts either a single sheet of material or a stack of multiple sheets (multi-ply layups) under the control of a microprocessor, which is called a numerical controller. An example of such a system for cutting limp sheet material, as disclosed in the U.S. Pat. No. 4,327,615 to Heinz Gerber et al is discussed in the preferred embodiment section of the current invention (see FIG.
1
). The numerical controller converts data, written in a specific format, into signals that moves the cutting tool with the given speed along the given tool path, defined by the X, Y and Z coordinates of some reference point of the cutting tool. The numeric control (NC) data define the so-called nesting or layout of pattern pieces, that is the shape and location of the pattern pieces in a marker, the marker being a set of pattern pieces, or templates.
In order to save material, pieces in the marker are routinely positioned closely to each other; frequently touching or even slightly overlapping each other, as shown in FIG.
2
. Referring now to
FIG. 2
, a number of templates
7
are nested together to form a marker
8
, which represents the pieces to be cut out of the sheet material.
It is well known in the art that closely nested pieces are much more difficult to cut compared with loosely packed pieces. Situations that create problems when cutting are called “critical” situations; regions within the marker that give rise to critical situations are called “critical”, or “sensible” regions; and portions of the tool path (straight line segments and/or points) that are difficult to cut properly are called “critical” or “sensitive” lines, or portions, or segments, or points.
It is well known in the art that cutting problems are most profound near the points of tangency or close approach (
FIGS. 3A-3C
) and near common lines (FIGS.
4
A-
4
D). The major difference between these two “critical” situations is the magnitude of the angle between the “critical” lines and the length of the portion of a “critical” line that is so close to another “critical” line that cutting this portion of the first line after the previous line has been cut presents a problem (FIG.
5
).
To be classified as common lines, the angle between “critical lines” should generally be small, no more than several degrees, while according the U.S. Pat. No. 4,327,615 the angle between tangent lines can be as great as 30 degrees. The “critical” portion of each common line must be, as a rule, much longer, typically several inches or more, while for two tangent lines lengths in the order of tenths of an inch might be enough. It should be mentioned that the common lines geometry could vary from “external” common lines between neighboring pieces, as shown in
FIG. 4A
to “internal” common lines between overlapping pieces, as shown in FIG.
4
B. Referring to
FIG. 4A
, two templates,
41
and
43
, have two sides,
42
and
44
, which are in proximity to each other, but do not actually touch. If these sides are within a few tenths of an inch from each other, they may be treated in the same way as if they were common sides. Referring to
FIG. 4
b
, two templates,
51
and
53
, contain sides
52
and
54
, which overlap. Side
52
may be considered internal to template
51
, but if the overlap is within the order of a tenth of an inch, this situation may be treated as if the two sides were common. There may exist similar varieties in between these conditions, as shown in
FIG. 4C
, in which template
61
has side
62
which is actually common with side
63
of template
64
for most of its length. Referring now to
FIG. 4D
, template
71
contains side
72
which is common with side
74
of template
73
, except that in this case the length of commonality is only about one half the length of the longer side
74
.
The tangency geometry could vary as well: it can be an “unidirectional” (“one-sided”) “tangent” point (FIG.
3
A), or a “bi-directional” (“two-sided”) “tangent” point (FIG.
3
B), both considered in U.S. Pat. No. 3,864,997 to Pearl and Robison, or a point of close approach (not a classical tangent point at all, but in spite of that usually called a “tangent” point anyway), discussed in U.S. Pat. No. 4,327,615 to Gerber (FIG.
3
C). In further discussion we usually use the terms “common line” and “tangency” to describe all those varieties, though sometimes, when confusion is possible, we call them “generic common line” and “generic tangent point” (“generic” meaning any variety).
Cutting “critical” lines may result in reduced cut quality and/or even in damaging the cutter. For example, when cutting a limp sheet material a cutting blade severs the limp material as it advances along the cutting path but does not remove the material. As a result, the material is pushed aside by the advancing blade and generally flows around the cutting blade in pressing engagement. This pressure, combined with the ability of the layers of limp material to move against each other, forces the blade to deviate from the programmed line of cut toward the direction of “less resistance”. According to Heinz Gerber (U.S. Pat. No. 4,327,615), “when a cutting blade passes in close proximity to an adjacent pattern piece that was cut at an earlier stage in the operation, the kerf created by the previous cut interrupts the continuity of the limp sheet material and allows the material at one side of the knife blade to yield more easily to the blade than at the opposite side. As a result, the blade experiences unbalanced lateral loading”. Apparently, the closer the cutting path approaches the previous cut, the greater the unbalanced loading and the blade bending will be. The blade may eventually break up or jump completely into the kerf of the previous cut. Inaccuracies or damage to the machine are the ultimate consequences.
It is believed that the above-described condition arises for tangent points (including points of close approach) as well as for common lines. That is why it is difficult to cut all of them properly. Cutting one of common lines after the other common line has been cut can also result in frying of the material along the cut, thus resulting in a more severe cutting problem than in the tangency situation, especially when the two common lines are strictly coincident.
Similar problems, though for different reasons, arise when cutting solid materials. For example, cutting a sheet metal may produce extra internal tension, create extra defects, change the planar form of the sheet, and/or modify its elastic properties, etc., depending on the given type of the metal and the chosen cutting tool. All these changes may (and usually do) propagate within some region around the cut. Therefore cutting the metal within this area second time may (and does) result in various cutting problems, specific for each material type/cutting tool combination.
Several approaches have been suggested to overcome the difficulties associated with tangencies and/or points of close approach (
FIG. 3
) between closely packed pieces.
In U.S. Pat. Nos. 3,855,887 and 3,864,997 Gerber reveals that in such a “critical” cutting area a reciprocal knife blade may be slowed down with reduced feed rate signals and/or rotated out of tangent position with yaw signals, the signals being introduced manually by the cutter operator. In U.S. Pat. No. 4,327,615 Gerber proposes to add slow down and/or yaw command(s) to the NC data with the so-called preprocessing means that is with the help of a computer before feeding the data into the cutter. In addition, the ab
Feldman Vitaly J.
Manevich Sergio
Choi Stephen
White Mark P.
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