Note: Descriptions are shown in the official language in which they were submitted.
"` ~ lL¢~6~41
This application is a divisional of our copending
Application Serial No. 291,377 filed November 21, 1977 and entitled
Method and Apparatus for Cutting Sheet Material with Improved
Accuracy.
The present invention relates to a method and apparatus
for cutting sheet material by means of a cutting blade such as
a reciprocating blade. More particularly, the present invention
resides in an automatically controlled cutting machine that can
be optionally programmed at the machine or operator's discretion
to cause special cutting techniques to be utilized by the blade
during the cutting operation. The optional programs are selected
based on knowledge, testing and prior experience and take into
consideration such factors as the type of sheet material being
cut, the special features or contours of the patterns or array
of patterns being cut, the proximity of adjacent lines of cut,
the depth of the sheet material and the desired accuracy of the
finished product.
The techniques of controlling the motions of a cutting
blade as it advances along a cutting path through a layup of
sheet material are based partly on technical reasoning and partly
on experience in the art. For example, in U.S. Patents 3,855,887
and 3,864,997 issued to Pearl and Robison and having the same
assignee as the present invention, a yawing technique is disclosed
and claimed for in controlling a reciprocating cutting blade as
it advances along a cutting path in close proximity to adjacent
cuts. Such technique comprises rotating the cutting blade slightly
out of a position tangent to the cutting path and away from a
previous adjacent cut to prevent the cutting blade from jumping
into the previous cut as a point of tangency is approached.
The special techniques for controlling motions of a
cutting blade cause the blade to track a desired cutting path
with minimal error in spite of the complex loading of the blade
which affects its cutting operation, particularly in multi-ply
layups of sh~et material. Stress and strain within the blade
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cause the blade to deviate from a desired cutting path in spite
of the accuracy with which servomechanisms or other positioning
mechanisms locate the blade, and without the special techniques,
the deviations are often sufficient to produce cuttins errors
which are too significant to be ignored.
Several objects are achieved by the special techniques
of controlling blade motions. First of all, it is highly desirable
to have uniformity among pattern pieces which are cut at different
positions in a multi-ply layup of sheet material. Such uniformity
enables pattern pieces to be interchanged and assembled in a
finished product such as an item of upholstery or a garment with
greater ease and consistent quality.
Secondly, with greater assurance that the cutting blade
will track a desired cutting path, pattern pieces may be more
closely packed in the marker or array of pattern pieces cut from a
piece of sheet material. Closer packing conserves material and
since the material is a significant factor in the cost of a
finished product, the product can be manufactured at a lower cost.
It has been found from experience that the special
cutting techniques are not always needed. Some sheet materials
or markers can be cut quite satisfactorily without adapting the
machine to use special techniques and, in fact, if the techniques
are employed, the resulting pattern pieces may be less accurate
because of different material behaviors and cutting conditions.
On the other hand, the special techniques may be employed
advantageously in other situations and, it is desirable to have
the option of employing the techniques.
In the prior art patents 3,855,887 and 3,864,997 refer-
ence above, the special cutting techniques are integrated into
the cutting program at the digitizing stage. Therefore, it was
not possible for the operator or the cutting machine to be select-
- ive in the employment of the techniques after the contours were
set in the digitized data.
Furthermore, the special cutting techniques disclosed
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in the referenced patent were employed only in limited circum-
stances. It has been determined, however, that a more general
application of special techniques is needed if discretion to use
the techniques is to be allowed. Accordingly, new techniques
have been conceived which have broader application, and it is
these techniques that form the basis of the optional programs of
the present invention.
Accordingly, it is a general object of the present
invention to provide method and apparatus for cutting sheet
material by introducing special cutting techniques into a cutting
operation when needed or desired. It is a further object of the
invention to disclose new cutting techniques which are suitable
for general application to the cutting of pattern pieces, espec-
ially when the techniques are offered as optional cutting programs.
The present invention resides in a method and apparatus
for cutting pattern pieces from sheet material with special
cutting techniques or blade maneuvering.
According to one aspect of the invention, with which
the present application is particularly concerned, a method of
cutting pattern pieces along a closed cutting path defined
by the periphery of the pieces with a cutting blade having
a leading cutting edge comprises: moving the sheet material
and cutting blade relative to one another to cause the leading
cutting edge of the blade to advance through the sheet material
along the defined cutting path f driving the cutting blade
generally perpendicularly through the sheet material as the
blade advances to cause the sheet material to be cut by the
leading edge; and rotating the cutting blade about an axis
extending perpendicular to the plane of the sheet material at
each point along the cutting path as the material is cut to turn
the cutting blade at all times incrementally out of a position
in alignment with the cutting path and toward the inside of the
pattern piece periphery.
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Pattern pieces are cut from sheet material with an
automatically controlled cutting machine in accordance with data
defining the contours of the pattern pieces and their positional
relationship with one another and the boundaries of *he sheet
material from which they are cut. The data are used in a data
processor or other device to generate machine command signals
for translating a cutting blade and the sheet material relative
to one another along a cutting path which corresponds to the
contours of the pattern pieces. The data processor also
provides blade rotation signals which rotate the cutting blade
into a position generally aligned with the cutting path at each
point.
In implementing the present invention, one or more
optional programs are established and stored in a memory device
associated with the data processor, and these programs are called
upon when special cutting techniques are desired or needed by
the machine. In such cases, the optional program is selected and
activated to generate machine command signals which, for example,
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41
maneuver or yaw the cutting blade slightly out of a position in
alignment with the cutting path. In inst~nces where special yawing
techniques are desired, the optional program produces yaw signals
which are combined with calculated blade rotation sisnals to
produce modified blade rotation signals. Accordingly, the cutting
blade and sheet material are advanced relative to one another
along a cutting path in accordance with modified machine command
' signals to produce slightly different and improved results.
Since it is not always desirable to employ special
cutting techniques or the same cutting t~chnique, the cutting
machine is provided with program selector means to give the
machine or operator the option of selecting a program that most
suitably adapts the cutting machine to a particular situation.
The selector means includes means for adjusting the degree of
signal modification as well as the type of modification.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view illustrating an automatic-
all,y controlled cutting machine in which the present invention is
employed.
Fig. 2 is a schematic diagram illustrating in operational
relationship the principal components which are employed in an
automatic cutting process.
Fig. 3 is a front view of a program selector panel
forming part of the computer of the present invention.
Figs.4a and 4b are a flow chart illustrating the
0-channel subxoutine in the computer which generates machine
command signals controlling blade orientation during cutting.
Fig. 5 is a fragmentary plan view of a sheet material
layup and illustrates schematically a special cutting technique
for controlling blade orientation in accordance with one aspect
of the present invention.
Fig. 6 (third sheet of drawings) is a schematic plan
view of a layup and illustrates a cutting blade advancing
through a woven, anisotropic sheet material having fibers of
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different strength in different directions.
Fig. 7 (third sheet of drawings) is a diagram
illustrating a schedule of yaw compensation in one optional
program of the present invention.
Fig. ~ (third sheet of drawings) is a fragmentary plan
view of a sheet material layup and illustrates schematically the
effect of the program shown in Fig. 7.
Fig. 9 (second sheet of drawings) is a fragmentary side
elevation view illustrating a reciprocating cutting blade and a
transducer for dynamic control of the blade.
Fig. 10 (second sheet of drawings) is a front elevation
view of the cutting blade in Fig. 9, and illustrates blade bending
resulting from lateral blade loading.
Fig. 11 (first sheet of drawings) is a diagram illustra-
ting the characteristic transfer function of another optional yaw
program employing blade loading feedback.
Fig. 12 (sixth sheet of drawings) is another fragmentary
plan view of the sheet material layup and illustrates the offset
cutting technique.
Fig. 13 (sixth sheet of drawings) is a fragmentary plan
view of a layup and illustrates a cutting path produced when
dither is applied to the cutting blade.
Fig. 14 (sixth sheet of drawings) is a diagram illustra-
ting a schedule of command pulses producing the blade dither in
Fig. 13.
Fig. 15 is a perspective view of an automatically
controlled cutting machine in which a line follower is utilized
to generate data defining the desired cutting paths.
Fig. 16 is an elevation view of the cutting machine
including the line follower in Fig. 15.
Fig. 17 is a schematic diagram illustrating the controls
of the cutting machine in Fig. 15.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
_ _ .
Fig. 1 illustrates an automatically controlled cutting
41
machine, generally designated 10, of the type shown and described
in greater detail in U.S. Patent 3,495,492 having the same
assignee as the present invention. The cutting machine 10 is
utilized to cut a marker of pattern pieces from sinqle or multi-
ply layups L of sheet material such as woven and non-woven fabrics,
paper, cardboard, leather, rubber, synthetics and others. A
marker is a closely packed array of pattern pieces as they are cut
from the material. The illustrated machine 10 is a numerically
controlled machine having a controller or computer 12 serving the
function of a data processor and a cutting table 22 which performs
the cutting operation on sheet material in response to machine
command signals transmitted to the table from the computer through
the control cable 14. The computer 12 reads digitized data from
a program tape 16 defining the contours of the pattern pieces to
be cut and generates the machine command signals guiding a recip-
rocating cutting blade 20 as the cutting operation is carried out.
The present invention, however, is not limited to the disclosed
numerical control system and has utility with other real time or
preprocessed data systems including line followers and analog
systems.
The cutting table 22 as disclosed has a penetrable bed
24 defining a flat surface supporting the layup L during cutting.
The bed may be comprised of a foamed material or preferably a bed
of bristles which can be penetrated by the reciprocating cutting
blade 20 without damage to either as a cutting path P is traversed.
The bed may also employ a vacuum system such as illustrated and
described in greater detail in the above-referenced patent
3,495,492 for compressing and rigidizing the layup firmly in
position on the table.
The cutting blade 20 is suspended above the support
surface of the bed 24 by means of an X-carriage 26 and a Y-
carriaqe 28. The X-carriage translates back and forth in the
illustrated X-coordinate direction on a set of racks 30 and 32.
The racks are engaged by pinions driven by an X-drive motor 34
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41
in response to command signals from the computer 12. The Y-
carriage 28 is mounted on the X-carriage 26 for movement relative
to the X-carriage in the Y-coordinate direction and is translated
by the Y-drive motor 36 and a lead screw 38 connected between the
motor and carriage. Like the drive motor 34, the drive motor 36
is energized by command signals from the computer 12. Coordinated
movements of the carriages 26 and 28 are produced by the computer
in response to the digitized data taken from the program tape 16
and guide the reciprocating cutting blade 20 along a cutting path
P. Thus, the cutting blade is utilized to cut pattern pieces
over any portion of the table supporting the sheet material.
The cutting blade 20 is suspended in cantilever fashion
from an adjustable platform 40 attached to the projecting end of
the Y-carriage 28. The adjustable platform elevates the sharp,
leading cutting edge of the blade into and out of cutting engage-
ment with the sheet material. The blade i5 reciprocated by means
of a drive motor 42 supported on the platform 40. Another motor
(not shown) on the platform rotates or orients the blade about a
~-axis perpendicular to the sheet material and generally aligns
the blade with the cutting path at each point. For a more
detailed description of the blade driving and supporting mechanism,
reference may be had to U.S. Patent 3,955,458 issued May 11, 1976
to the assignee of the present invention. Of course, other types
of cutting blades such as band blades shown in U.S. Patent
3,350,969 and rotary cutting blades shown in U.S. Patent 3,776,072
may be used. Furthermore, the cutting blade need not be completely
cantilevered from the platform 40 for penetration into the bed 24,
but can cooperate with a blade guide and foot which travels under
the layup as shown in U.S. Patents 1,172,058 or 3,245,295.
Fig. 2 illustrates the major components employed by the
machine 10 in an automatic cutting process. The primary input
data for the machine are the contours of the pattern pieces 46.
An automatic marker generator 48 may be utilized to arrange the
pattern pieces in positional relationships which correspond with
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41
the relationships of the pieces when they are cut from the sheet
material. The marker generator 48 may be an automatic computerized
type disclosed in U.S. Patent 3,596,068. Computerized marker
generators which are fully automated include a packing subroutine
that in effect shifts and bumps the pattern pieces together within
the boundaries of a marker until the amount of material required
to cut the pieces is a minimum. As would be expected, the pattern
pieces in the marker after packing contact one another and have
points of tangency, points of close approach, common contour
segments between adjacent pieces and closely spaced parallel seg-
ments. It is these conditions and others which require special
cutting techniques as described below.
Of course, the marker can also be generated manually or
semi-automatically. In the manual process, cardboard representa-
tions of the patterns are shifted on a table until the most compact
array is obtained. In the semi-automatic process, an interactive
graphics system is employed. In this system, the pattern pieces
are displayed on a tablet or the screen of a cathode ray tube (CRT)
connected to a data computer which generates the display. An
indexing instrument such as an electrical wand or light pen inter-
acts with the tablet or CRT and permits the pieces to be shifted
to various positions. By a trial-and-error process resembling the
entirely manual process, the closely packed array is obtained and
when the final grouping is arrived at, the array is frozen.
Regardless which process is utilized, the marker 50 or
data defining the marker becomes the input of the automatically
controlled cutting machine. The marker for the numerically con-
trolled cutting machine must be reduced to digital data which can
come from the marker generator itself, and in this case the data
is supplied directly to a pattern memory 54. The pattern memory
can be a deck of punched cards or magnetic or perforated tape
such as the tape 16 illustrated in Fig. 1.
If digitized data identifying the contours and positions
of the pattern pieces has not already been generated in the course
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of generating the marker 50, then the digitizer 52 is operated to
reduce the pattern contours in the marker to point data. The
digitizer may be a manually operated digitizer or a line follower
which outputs the data automatically and places it in the pattern
memory 54. Thus, the contours of the pattern pieces are defined
in the memory as a series of digital commands representing straight
or curved line segments identified by the X- and Y-coordinates
associated with end points of each segment.
The principal components of the computer 12 and the
basic inputs supplied to the computer are also shown in Fig. 2.
The principal input, of course, is pattern data from the memory
54. The computer also receives a cutting program which is com-
prised of standard servo and curve algorithms. Such algorithms
define machine command calculations peculiar to the cutting table
22 and take into consideration limitations such as the maximum
rate of acceleration. The algorithms also determine when to lift
or plunge the blade along a cutting path and determine other
functions which in summary comprise all the routine operations
performed by a cutting blade and any accessories during a cutting
operation. In accordance with the present invention, the computer
also receives optional programs, as explained in greater detail
below.
The pattern data stored in the memory 54 are acted upon
by computing circuits 60 within the computer to reduce the data
to machine commands that are output in real time in a form
intelligible to servomotor drivers on the cutting table. The
pattern data enters the computer through a buffer 62 and the
computing circuits read the data as needed. In the course of a
computing operation, the circuits are controlled by the cutting
pxogram which is stored in a memory 64. The machine commands are
output from the computer in the form of electrical signals and
may be applied directly to the cutting table 22 at a controlled
rate or the signals may be stored in a buffer 66 for use on demand.
With the exception of the optional program memory 70, the program
6~1
selector 72, and associated circuits described below, the system
illustrated in Fig. 2 is conventional and well known in the
numerical control cutting field.
The basic or fundamental machine command signals gener-
ated from the digitized pattern data by the computing circuits
include X and Y displacement signals applied to the servomotors
34 and 36 in Fig. 1 to cause the cutting blade 20 to be translated
relative to the sheet material along the cutting path. ~n order
to raise and lower the cutting blade in and out of cutting engage-
~ent with the sheet material, "blade up" or "blade down" signalsare also generated. In the present embodiment of the invention,
a blade rotation signal is calculated in the computer from the
digitized data to orient the cutting blade about the ~-axis
tangent to the cutting path at each point along the path. Thus,
the displacement signals, the "up" or "down" signals and the
rotation signals completely define the basic motions of the
cutting blade which cause the blade to traverse a specific path
in cutting relationship with the sheet material.
A principal feature of the present invention is the
inclusion of an optional program memory 70 and a program selector
panel 72 in the computer. The optional memory ~70 is connected
with the computing circuits, and the computing circuits utilize
the optional programs when selected by the machine operator to
modify the basic of fundamental machine command signals. By
providing a number of optional programs in the memory 70, the
machine operator or other person is given the choice of that
program which according to his knowledge, testing and prior
experience produces the most accurate pieces with the least diffi-
culty and minimum expenditure of time. Some of the factors taken
into consideration are the type of material being cut, the special
features or contours of the patterns or array of patterns, the
proximity of adjacent lines of cut, the depth of the layup and
the permissible tolerances of the cut pattern pieces. The auto-
matically controlled cuttiny machine with the optional program -`
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memory 70 and selector panel 72 is more versatile because marker
patterns can be cut from sheet material with or without special
cutting techniques defined in the optional programs. Giving the
operator discretion in controlling the cutting blade constitutes
a significant improvement in the art, since previously cutting
has been restricted by the fixed program generated from the
digitized data in the memory 64.
Specific optional programs considered desirable in
improving the cutting accuracy involve yawing of the cutting blade.
Yaw refers to the difference between the blade angle relative to
some reference line and the velocity vector, or an angular
rotation or biassing of the cutting blade out of a position
generally aligned with or tangent to the cutting path, the angular
amount of such yawing generally not exceeding 10 (although values
as high as 25J or more may be used) and more frequently falling
within the range of 0-5. While it may appear inconsistent to
rotate the blade out of a position in alignment with the cutting
path in order to improve accuracy, such practice is uselul for
this purpose because of lateral forces that are applied to the
blade and cause the blade to track a path different from that in
which the blade is headed.
Since blade yawing is fundamentally a rotation of the
blade, the incorporation of an optional yawing program with the
conventional cutting program consists of combining yaw commands
with the conventional blade rotation commands that normally
establish alignment with the direction of the cutting path at each
point. Fig. 4, accordingly, illustrates in a flow diagram the
~-channel subroutine of the computer 12 associated with the
determination of the blade rotation command signals, such signals
defining rotation of the blade about the ~-axis perpendicular to
the table bed 24. Illustrated in Fig. 4 are a number of optional
yaw programs that are stored in the memory 70. Each of these
programs is described below in connection with the operation of
the subroutin~.
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As each data point is processed by the computer 12,
the ~-channel subroutine is entered at 80 and in conjunction
with data defining adjacent line segments of the desired cutting
path, the angle at the point in question between the adjacent
line segments is calculated at 82. Such angle is then added to
the existing blade rotation value at 84 so that under normal
circumstances and in the absence of any special yaw commands,
the cutting blade is commanded to move along the programmed
cutting path in alignment with the path.
In accordance with the present invention, however, the
blade rotation signal is then processed through an interrogation
gate 86 in the computing circuits 60 or the optional program
memory 70 shown in Fig. 2. The gate 86 is controlled by the
program selector panel 72 shown in Fig. 2 and in greater detail
in Fig. 3. The panel has a "fixed" switch 88 and when the switch
88 is depressed by the machine operator, the gate 86 activates
the fixed yaw program.
The fixed yaw program adds a predetermined amount of
yaw bias or compensation to the rotation calculated at 84, and
the angular amount is constant or the same at each point on the
cutting path but can be adjusted by the operator by means of the
adjustment dial 90 on the selector panel. The amount selected
can be read from the indicator meter 92 adjacent the dial. The
sense or direction of the yaw bias is also established by the
dial 90 and, thus, it is apparent that the bias may rotate the
cutting blade slightly to one side of the line of cut or the
other. Preferably, the bias is adjusted to rotate the cutting
blade inwardly of the pattern piece so that closely adjacent
pattern pieces will not inadvertently be cut as the cutting blade
passes points of tangency or closest-approach. If a pattern
piece is digitized in the clockwise direction, then the cutting
blade traverses the pattern piece periphery in the same direction.
I~ the cutting blade is to be yawed toward the inside of the
pattern piece r the blade must be rotated cloc~wise about its axis
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of reciprocation, which is designated a positive bias as shown by
the meter 92 in ~ig. 3. However, if a pattern piece has been
digitized in a counterclockwise direction, the operator is advised
of this fact by means of the indicator light 94 which responds to
information stored in the digitized pattern data. In such case,
the sense of the bias must be reversed in order to maintain a yaw
bias toward the inside of the pattern.
The fixed yaw program stored in the optional program
memory 70 is illustrated in detail in Fig. 4a under the "yes"
branch of the interrogation gate 86. Since it is desirable to
know the direction in which the cutting blade traverses the
pattern piece, gate 98 is provided. If the blade traverses the
pattern clockwise, then the fixed yaw angle determined by dial
gO is algebraically added at 100 to the blade rotation angle
calcu'ated at 84 and the subroutine is exited at 102. If blade
motion is counterclockwise, then the fixed yaw angle is algebra-
ically subtracted from the calculated angle at 104, and the sub-
routine is exited at 106.
If a fixed yaw program has not been selected by the
operator at gate 86, then a proportional yaw program is examined
at interrogation gate 110. The proportional yaw program is
illustrated more clearly by the fragmentary plan view of the
layup L in Fig. 5 where the cutting blade 20 is shown at
different points along the cutting path P.
In general, the proportional yaw program establishes
a yaw angle which is calculated to be proportional to the
curvature of the cutting path at the point in question. As
shown in the solid-line position of the blade 20, the blade is
rotated to an angle a relative to the tangent of the cutting
path at that point. The angle a is greatly exaggerated for
clarity and normally would not exceed the 10 limitation discussed
above. At the next point illustrating the cutting blade 20 in
phantom, the angle between the cutting path and the blade is some-
what less due to the smaller curvature of the path at that point.
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41
At the last position of the cutting blade also illustrated in
phantom, the cutting path P is strai~ht and thus, the yaw angle is
zero so that the blade appears generally aligned with the cutting
path. The control of yaw bias in proportion to curvature of the
path is regarded to be useful because the blade rotation tends to
redirect the blade in the new direction which the blade is
expected to assume after some finite displacement. Thus, the blade
tends to anticipate its next position, and the effects of lateral
forces which are produced on the blade are reduced if not elimin-
ated. Since a greater response is needed with increased curvatureof the path, the yaw bias of this program is made proportional to
curvature. The proportionality factor may be established by a
number of factors such as the material being cut, the blade con-
figuration and the depth of the layup, and it is advantageous to
be able to vary the factor accordingly.
Proportional yaw bias is selected by the machine operator
by means of the "proportional" switch 112 on the selector panel
of Fig. 3. When the switch is depressed, the gate 110 in Fig. 4a
activates the proportional program routine associated with the
"yes" branch of the gate. As each digitized data point along the
pattern piece periphery is processed, the path curvature at the
point is calculated at 114. Such calculations are well known in
the prior art since the velocity profile of the cutting blade
movement is also based upon path curvature. The yaw bias or angle
proporational to curYature is then calculated at 116. If cutting
is determined to be clockwise at gate 118, the proportional yaw
angle is algebraically added at 120 to the blade rotation cal-
culated at 84 and the subroutine is exited at 122. If cutting is
counterclockwise, then the proportional yaw is algebraically
subtracted at 120 from the calculated blade rotation and the
subroutine is exited at 126. Alternatively, blade rotation could
be calculated with a multiplying or other factor which is varied
as a function of path curvature.
If proportional yaw has not been selected by the machine
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41 - -
operator, the interrogation gate 130 is examined to determine
if a scheduled yaw program has been selected. The gate 130 is
energized by the machine operator from the "scheduled" switch 132
on the selector panel in Fig. 3. A scheduled yaw program is a
program in which yaw angles are empirically determined or set at
preselected values which have proven to be particularly effective
under given cutting conditions.
As an example, Fig. 6 illustrates in plan view a cutting
blade 20 advancing through a sheet of woven material having
anisotropic strength characteristics. In particular, the matrix
of fibers which form the woven material are comprised of one set
of fibers S extending in one direction and being particularly
stronger than another set of fibers W extending perpendicular to
the fibers S. Such anisotropic characteristics are found in many
fabrics such as denim and fabrics in which synthetic fibers are
mixed with natural fibers. It has been found that the amount of
yaw needed to maintain the cutting blade on the cutting path when
the blade is traveling in one direction relative to the fibers
is different from the amount needed when the blade is traveling in
another direction. It is believed that the explanation for such
differing values is the fact that the stronger fibers encounteriny
the sharp, leading cutting edge of the blade have a different
influence on the cutting action of the blade than the weaker fibers.
Also the strong and weak fibers may possess different spring and
cutting characteristics which cause the fibers to deflect away or
recede from the angularly oriented blade in different fashion.
When the blade is travelling at an angle to the stronger fibers
with the tapered forward side of the blade almost parallel with
the stronger fibers as shown in Fig. 6, the stronger fibers are
first pushed and exert greater diverting forces on the one side
of the leading edge than the weaker fibers on the other side and,
consequently, greater yaw compensation is required. On the other
hand, when the blade moves transverse to the stronser fibers, the
effect on the one side of the cutting edge is substantially the
i41
same as that on the other side and no compensation is required.
The same is true when the blade is travelling transverse to the
weaker fibers. A similar effect can be observed with knitted
materials.
Such a theory is confirmed by cutting test lines or
patterns of given shape such as shown in the plan view of Fig. 8
and orienting the lines or patterns at different angles to the
fibers in different tests. This testing and cutting procedure is
described in greater detail in our United States Patent No.
4,140,037, dated February 20, 1979 entitled Method of Cutting
Sheet Material with Scheduled Supplementation.
As the cutting blade 20 traverses the test pattern in
Fig. 8, the lateral forces generated between the woven material
and the cutting blade are measured or the cuts are checked after-
ward. The angle of the blade is then adjusted by introducing a
certain amount of yaw and the test is continued or repeated until
the yaw angles that counteract and null out the lateral forces
or produce accurate cuts are established. It is noted from the
yaw compensation angles shown in the example of Fig. 8 that for
a null loading and maximum accuracy or identity of patterns, the
same yaw bias or compensation angle is required along parallel
sides of the test pattern, but each pair of parallel sides re-
quires different compensation. Such compensation can be related ;
to the strength and orientation of fibers in the material.
When the lines or test pattern are rotated to a slightlydifferent angle relative to the fibers, another test is performed
to establish other values of yaw for null loading. At the con-
clusion of a number of tests, a schedule of yaw angles for
finitely different cutting directions has been determined and by
interpolation, a complete schedule of angles can be had for all
directions. Fig. 7 is a diagram illustrating an exemplary schedule
of yaw angles as a function of the angle 0 or the direction in
which a cutting path extends through anisotropic material. It
will be observed that the schedule varies through a 180 cycle as
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implied by the yaw angles illustra~ed in Fig. 8. It should, how-
ever, be understood that other schedules of yaw compensation may
be established for other types of cloth and cutting conditions.
A particular schedule of yaw angle values may be readily
programmed in the optional program memory 70 or for ease of
programming a separate memory taking the form of a tape reader
133 and exchangeable tape cartridges 135 may be placed in the
selector panel as shown in Fig. 3. When the interrogation gate
130 has activated the scheduled program, the yaw value is
determined at 134 from the appropriate memory. The value is then
added at 136 to the blade rotation value calculated at 84 and the
subroutine is exited at 138. It will be readily appreciated that
the number of scheduled yaw programs stored in the memory 70 is
limited only by the memory capacity provided that a suitable
selecting switch on the program selector panel 72 is provided. If
exchangeable tape cartridges are utilized, the number of programs
is unlimited.
If the gate 130 has not been energized, a dynamically
derived yaw program may be selected by the machine operator
through the interrogation gate 140 in Fig. 4b by means of the
"derived" switch 142 in Fig. 3. The yaw program in this instance
is obtained from cutting parameter signals fed back to the
computer 12 from a sensor or transducer monitoring the cutting
operation as it progresses. The feedback signals produced by the
transducer are then converted into yaw signals as shown at 144 in
Fig. 4b. The yaw signal derivéd in this fashion is then added at
146 to the blade rotation calculated at 84 and the subroutine is
exited at 148. The procedure utilizing cutting parameter feedback
is the subject of our United States Patent No. 4,133,235, dated
January 9, 1979 entitled Closed Loop Method and Apparatus for
Cutting Sheet Material referenced above.
As an example of apparatus for monitorins cutting
parameters while the cutting operation progresses, reference is
made to Figs. 9-11. In Figs. 9 and 10, the generally flat cutting
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~1~6~4~
blade 20 having a sharp leading edge 150 and a parallel trailing
edge 152 is mounted in a rod 154 reciprocated within a carriage-
mounted sleeve 156 by means of the drive motor 42. A strain
gauge transducer 160 is mounted on the side of the sleeve 156
to measure lateral loading on the cutting blade. As shown in
Fig. 10, such loading, which can be generated by the sheet
material through which the blade passes, bends the blade to the
phantom position and thus causes the lower portion of the cutting
blade to track a different cutting path and produce a different
pattern piece than the upper portion of the blade. Such loading
and its effect on the motion of the cutting blade can be corrected
by introducing a yaw angle that generally counteracts the effects
of the lateral forces and permits the cutting blade to continue
along the desired line of cut as suggested above with the scheduled
yaw program.
To this end, the transducer 160 measures the lateral
loading on the cutting blade and produces feedback signals pro-
portional to the loading. Within the computer 12, such feedback
forces may be operated upon by a program having a linear relation-
ship or transfer function such as shown in Fig. 11. Basically,when the feedback force F is detected, the amount of yaw bias is
calculated to be proportional to the force and opposite in sense.
O~ course, other feedback signals and other linear or non-linear
functions may be utilized to dynamically calculate or establish
the value of yaw in any given case.
If the interrogation gate 140 in Fig. 4b has not activa-
ted the derived program, then the interrogation gate 190 is
examined. The program associated with sate 190 adds a schedule of
yaw dither to the machine commands controlling blade orientation
and causes the blade to intermittently and rapidly rotate by
preselected amounts out of the position in alignment with the
cutting path and back again without traversing a substantial
segment of the cutting path during rotation. Such intermittent
rotations are desirable when, for example, the cutting blade 20
~ 18 -
6~J41
is receiving unbalanced lateral loading from limp sheet materialdue to the absence or lack of lateral support at one side of the
blade near the edges of the layup or at closely adjacent cuts, or
when the blade loading is unbalanced because an anisotropic material
characteristics as described in connection with Fig. 6. The blade
is preferably rotated toward the side of the path from which the
greatest lateral loading is applied and thus in the case of
traversing a curve, the blade is intermittently rotated toward the
inside of the curve or in the case of anisotropic materials, the
blade is rotated toward the stronger fibers. The abrupt rotation
as the blade advances cuts the material in a stepwise fashion and
relieves the loading and blade stress caused by the material.
Fig. 13 shows a fragmentary view of the layup L and the
cutting path P travexsed by the blade 20 when dither is imposed
upon the blade motion. It is assumed that the right side of the
blade experiences heavy, lateral loading under the conditions
illustrated and, therefore, the small steps d in the cutting path
are generated to the right. The illustrated steps d are greatly
exaggerated for clarity and would barely be noticeable in a cut
pattern piece as long as the amount of dither is limited to, for
example, no more than 10 and is executed within a short segment
of the path. Fig. 14 illustrates a time schedule of dither command
pulses that produce the cutting path shown in Fig. 13. The width
of each pulse should be relatively short, and the frequency of
the pulses may be selected in accordance with the speed of the
blade or curvatuxe of the path so that the advancing blade stays
generally on the desired cutting path.
The dither program associated with the "yes" branch of
the interrogation gate 190 is activated by the control switch 192
on the selector panel 72 in Fig. 3 and may take several different
forms depending upon how dither is to be applied. The program
illustra~ed in Fig. 4b applies dither to the calculated blade
rotation as a function of path curvature and thus curvature is
determined at 194. Since dither should rotate the blade inwardly
-- 19 --
41
o' the curve, the sense of the curvature is determined at 196.
If curvature is regarded to be positive in one sense, then d-ither
pulses are added to the calculated rotation at 198 and preferably
the pulses are added at a rate along the cutting path proportional
to curvature. In other words, if the curvature is severe, then
dither pulses are added more frequently whereas if the curvature
is mild, the dither pulses are less frequent. The program is then
exited at 200. If the curvature is negative in sense, then the
dither pulses are subtracted from the calculated rotation at 202,
again at a rate proportional to the curvature, and the program is
exited at 204. Of course, dither may be made a function or a
single variable or a combination of variables such as curvature
and the angular relationship of the cutting path and the fibers
in woven sheet material. Still other forms of dither may be
employed in accordance with the particular cutting problem bei~g
addressed. Although the flow diagram of Fig. 4 suggests that the
dither program is utilized alone, it is also feasible to employ
dither in combination with other optional prosrams.
In the event that the machine operator has not selected
any of the yaw programs in the optional program memory and corres-
pondingly, none of the programs have been activated by means of
the interrogation gates 86, 110, 130, 140 or 190 in Fig. 4, then
the subroutine outputs the calculated blade rotation at 170 with-
out yaw bias and exits at 172.
An alternate method for cutting pattern pieces of slight-
ly different size from sheet material is illustrated in Fig. 12
and may also derive benefits from an optional cutting program in
the same manner as the more conventional cutting method which
attempts to guide the cutting blade along a cutting path coincident
with a pattern piece contour. Fig. 12 is a fragmentary plan view
of the layup L at a location occupied by pattern pieces A, B, C
and D. The cuttlng blade 20 is illustrated traversins a dotted
cutting path T which is not coincident with the given periphery
of pattern piece A, but is similar to the periphery and offset
- 20 -
6~4~
within the periphery by a predetermined amount b. While the
pieces cut along the path T will not be precisely the same size
as the defined pattern piece A, the difference in size is not
materially significant if the offset between the defined peri-
phery and the cutting path is not greater than l/32nd of an
inch tO.8 mm). Normally, pattern pieces are not cut to accuracies
greater than l/32nd of an inch, and consequently, a slightly
undersized piece may have little or no adverse effect upon the
final product.
From the point of view of cutting, the offset signifi-
cantly eases the problem of cutting pattern pieces which are
closely packed and define long, thin slivers of material in the
interstices of the pattern pieces. Pattern piece C does not con-
form precisely to pattern piece A and thus a very thin and
elongated section of cloth separates the pieces when they are
closely packed. Pattern piece B is tangent to pattern piece A
at one point and defines two slivers of intervening cloth at
each side of the point of tangency. A similar condition exists
between pattern piece A and pattern piece D. If conventional
cutting techniques are employed, that is, the cutting blade 20
is guided along a cutting path coincident with the pattern piece
peripheries, difficulties are encountered regardless of which
of the pattern pieces is cut first. With the offset as shown
and described, these difficulties are considerably eased provided
that the cutting blade moves along the offset cutting path accur-
ately. The optional programs described above aid this alternate
cutting method in this respect.
While the selection of the optional programs described
above is made by the cutting machine operator through the program
selector panel 72, such selection can also be made by the computer
12 itself based upon an analysis of the pattern data stored in the
pattern memory 54 and the conditions of a given cutting operation.
Such analysis would permit tangencies and closely adjacent cutting
paths to be identified so that yawing or slowdown could be ordered
- 21 -
i~6~41
by selection of the appropriate program. The selection is made,
if necessary, due to the depth of the layup being cut, the type
of material in the layup and other factors not comprehended by
the data stored in the memory 54 or the program in memory 64.
It is also feasible in automated systems having the
automatic marker generator 46 to identify the critical locations
in a marker, such as points of tangency or close approach and
closely adjacent parallel cutting paths, while the marker is being
generated. The marker generator then provides information or data
identifying the critical locations to the computer 12 so that the
computer can select the appropriate optional program based upon
analyses of the cutting conditions at the critical locations. ~ ;~
Figs. 15 and 16 illustrate another automatically
controlled cutting machine, generally designated 250, having a
cutting tool in the form of a reciprocated cutting blade 252
guided in cutting engagement with a layup L on a cutting table
254. In this embodiment of the invention, the cutting blade 252
cooperates with a foot ~not shown) that travels with the blade
under the layup of the sheet material and on top of the table 254.
Thus, the table does not have a penetrable bed, although a thin
layer of compressible material is desirable between the layup and
table to allow the foot to depress the material and pass undisturb-
ingly under the layup as the cutting blade traverses a cutting path.
For a more complete description and illustration of such a cutting
mechanism, reference may be had to U.S. Patent 3,245,295 issued
to Mueller.
The basic data for controlling movement of the cutting
blade during a cutting operation is contained in a marker drawing
D or other medium such as a template and is obtained by means of
a line follower 256. The line follower is a tracking device
which at a remote location follows a graphic representation of
the cutting path or contours to be cut and correspondingly
controls movement of the blade 252 in the layup L at the same
time. For example, the drawing D may bear a graphic representation
- 22 -
4~L
of the marker which is to be cut by the cutting blade 252 in the
layup L. During a cutting operation, the line follower advances
along the lines T and produces output signals which are operated
upon by the computer 262 and which continue movement of the line
follower in tracking relationship with the lines. The internal
structure and operations of a line follower are well known in the
art, and a more detailed description of one such follower may be
had by reference to U.S. Patent 3,529,084 issued to Rich.
In the illustrated embodiment of the cutting machine
250, the tables 254 and 260 are positioned in parallel relation-
ship, and a common X-carriage 262 straddles the tables and supports
both the cutting blade 252 and the line follower 256 in suspended
relationship. The carriage 262 traverses the tables in the
illustrated X-coordinate direction by means of an X-drive motor
264 and associated racks (not shown) in a manner similar to that
of the X-carriage 26 illustrated in Fig. 1. A Y-carriage 266
supports the cutting blade 252 for movement relative to the
X-carriage 262 and the table 254 in the illustrated Y-direction,
and another Y-carriage 268 supports the line follower 256 for
similar movement relative to the support table 260.
The carriages 266 and 268 are interconnected by means
of a lead screw 270 driven by a Y-drive motor 272. Thus, the
line follower 256 and the cutting blade 252 are mechanically
constrained by the carriages and interconnecting mechanism to
move in parallel relationship in both the X- and Y-coordinate
directions.
Additionally, the cutting blade 252 is rotated about
a ~-axis perpendicular to the cutting table 254 by means of a
~-drive motor 286 (Fig. 17) on the carriage 266, and is elevated
in and out of cutting engagement with the layup L by means of
another carriage-mounted motor (not shown). The motor (not shown)
for reciprocating the cutting blade is also mounted on the
Y-carriage 266.
During a cutting operation while the line follower 256
- 23 -
6~
is tracking a line T, the output signals from the follower indicate
the tangential ~irection or orientation of the traced line at each
point, and the signals are transmitted through an electrical cable
to a control computer 280. Within the computer, the output signals
are used to develop machine command signals that are supplied to
the drive motors 264 and 272 and cause the line follower to advance
along the trac~ed line. Since the movements of the cutting blade
252 parallel the movements of the line follower, the cutting path
P produced by the blade 252 in engagement with the material
corresponds to the traced line. In other words, the cutting blade
52 is slaved to the line follower and generates cutting paths in
the layup corresponding to the lines tracked in the marker drawing D.
Fig. 17 illustrates schematically a control system by
which the cuttins blade and line follower cooperate in accordance
with the present invention. The components within the control
computer 280 are identified within the dotted line.
The line follower produces two analog voltage signals
~x and Ey, which are processed through a feed rate programmer 282
to energize the X-drive motor 264 and the Y-drive motor 272. The
drive motors in turn cause the line follower to move along the
traced line and the cutting blade to generate a corresponding
cutting path. The programmer 282 establishes the rate at which the
motors are driven and the line follower and cutting blade advance.
The output voltage signals Ex and Ey are also supplied
to a slope generator 284 which from the ratio of the voltages
determines the angular orientation of traced line segment relative
to the X- or Y-coordinate axis. The generator produces an orienta-
tion control signal that is applied to the ~-drive motor 286
through a summing junction 288, and the drive motor orients the
blade 252 accordingly. To this extent, the line follower controls
are conventional and produce fundamental commands which cause the
drive motors to translate the cutting blade tangentially along
the cutting path.
To introduce yaw control in accordance with the invention,
- 24 -
P41
a yaw programmer 290 is provided within the control computer 280and receives the voltage signals from which the angular orienta-
tion is determined for the traced line and cutting path. In
- addition, however, the programmer 290 may include one or more
optional programs such as those described more particularly in
connection with the embodiment of the invention and described in
Figs. 4a and 4b. For example, the programmer may include a pre-
scheduled yaw program such as illustrated in Fig. 7. Additionally,
or alternatively, a sensor 292 may be associated with the cutting
blade to measure cutting parameters such as forces as described
above in connection with Figs. 9 and 10, and the programmer may
include a yaw program such as illustrated in Fig. 11. From the
programs, the programmer produces supplemental commands that are
added to the fundamental commands at the summing junction 288.
The cutting blade is then translated along the cutting path with
fundamental commands as modified by the supplemental yaw commands.
When the line follower is an optical device that traces
representations of the cutting path on the drawing D, the line
follower can identify difficult cutting conditions within its
fiela of view such as sharp curves, tangencies, points of close
approach and closely spaced parallel lines. By producing an
appropriate signal, as indicated at 294, the line follower can
automatically call for selected yaw programs that accommodate the
identified cutting condition. The yaw programmer 290 then
generates supplemental commands which modify blade orientation.
In addition to the yaw programs, it is also possible
to incorporate within the programmer 282 special feed rate
programs which, for example, slow the cuttin~ blade down at
difficult or critica] cutting conditions such as tangencies and
points of close approach. Again, the line follower may provide
signals as indicated at 296 which call upon the special feed rate
programs within the programmer 282. Also, the feed rate programmer
may be connected as shown to receive signals from the blade
sensor 292 and to modify feed rate in accordance with cutting
- 25 -
11~6@~1
parameters detected by the sensor.
In summary, the method and apparatus for cutting sheet
material are provlded by an automatically controlled cutting
machine in which the computer includes an optional program memory
and selector means by which various optional cutting programs
may be selected and combined with a standard cutting program to
produce an improved cutting operation. With the optional programs,
the cutting machine is not limited by the standard cutting program
but based on prior experience, testing and knowledge of the cutting
technology that program or combination of programs which produces
the most favorable results may be selected. A number of the
optional programs define special methods of cutting sheet material
which methods are themselves novel, and these methods contribute
to improved cutting performance quite apart from the optional
programming apparatus.
While the present invention has been described in
preferred embodiments, it will be understood that numerous modi-
fications and substitutions can be made without departing from
the spirit of the invention. For example, although specific
optional yaw programs have been identified and described, it
should be readily apparent that numerous other optional programs
may be used in combination with or in place of the described
programs and the described programs can also be used in combination.
The programs may be utilized to control blade yaw or other blade
motions such as the feed rate of the blade along the cu~ting path
and the stroking rate of a reciprocating blade. The selection
of optional programs may be made once at the start of cutting an
entire marker, or more frequently. Accordingly, the present
invention has been described in a number of preferred embodiments
by way of illustration rather than limitation.
