US3848327A

US3848327A - Apparatus for working on sheet material

Info

Publication number: US3848327A
Authority: US
Inventors: H Gerber; D Pearl
Original assignee: Gerber Garment Technology Inc
Current assignee: Gerber Technology LLC
Priority date: 1970-12-09
Filing date: 1973-06-21
Publication date: 1974-11-19
Anticipated expiration: 1991-11-19

Abstract

An apparatus is disclosed for working on sheet material, such as woven and non-woven fabrics, plastic or paper with a tool which translates over the sheet material to perform a cutting, plotting or other material processing operation. The apparatus holds the sheet material down during the operation and includes a table, such as a vacuum table, which supports the material, either a single sheet or a layup of the material, and a fluid compartment which is positioned over and exposes the material to pressurized air to force the material onto the supporting surface of the table. While maintaining a region of increased air pressure in the immediate vicinity of the tool, the compartment may be translated along one or two orthogonal directions in conjunction with the movements of the tool. The compartment is open or perforated at the side confronting the material to expose the material to the air under pressure within the compartment. When appropriate, a sheet of impervious material may be overlaid on a layup of the material to increase the effective pressure on each ply of the layup.

Description

United States Patent [191 Gerber et al.

[451 Nov. 19, 1974 APPARATUS FOR WORKING ON SHEET MATERIAL [73] Assignee: Gerber Garment Technology, Inc.,

East Hartford, Conn.

22 Filed: June 21,1973

21 Appl. No.2 372,429

Related US. Application Data [63] Continuation-in-part of Ser. No. 96,384, Dec. 9,

1970, Pat. No. 3,750,507.

[52] US. Cl 29/559, 83/22, 83/169,

83/374, 83/925 CC, 269/21 [51] Int. Cl D06h 7/00 [58] Field of Search 269/21, 20; 83/14, 22,

Primary ExaminerJ. M. Meister Attorney, Agent, or FirmMcCormick, Paulding & Huber [5 7] ABSTRACT An apparatus is disclosed for working on sheet material, such as woven and non-woven fabrics, plastic or paper with a tool which translates over the sheet material to perform a cutting, plotting or other material processing operation. The apparatus holds the sheet material down during the operation and includes a table, such as a vacuum table, which supports the material, either a single sheet or a layup of the material, and a fluid compartment which is positioned over and exposes the material to pressurized air to force the material onto the supporting surface of the table. While maintaining a region of increased air pressure in the immediate vicinity of the tool, the compartment I may be translated along one or two orthogonal directions in conjunction with the movements of the tool. The compartment is open or perforated at the side confronting the material to expose the material to the air under pressure within the compartment. When appropriate, a sheet of impervious material may be overlaid on a layup of the material to increase the effective pressure on each ply of the layup.

10 Claims, 13 Drawing Figures PATENIELRGVISISY'! 3,848.32?

sum 1 or 4 PATENTEL, HEY I 91974 SHEET 2 BF 4 PAIENIELHUYIQW 3.848.327

SHEET nor 4 H? H""" .n w W W i I60 ll I l Hi I62 Q76 i llllll \y \I I 52 w :5; 54 wt. 5% w ,p:

v l7] l/ l l APPARATUS FOR WORKING ON SHEET MATERIAL CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of applicants copending application Ser. No. 96,384, filed Dec. 9, 1970 now US. Pat. No. 3,750,507 entitled METHOD AND APPARATUS FOR HOLDING SHEET MATERIAL.

BACKGROUND OF THE INVENTION This invention relates to apparatus for working on sheet material with a tool while the material is held down on a work table.

In the past, it was cutomary to cut pattern pieces from a layup of sheet material formed by multiple plies of woven or non-woven fabric piled one upon the other by guiding a motor-driven, reciprocating knife by hand through the layup. To hold the layup in position during the cutting operation, the operator of the knife would use his free hand to press down on the layup at a point adjacent to the cutting path traversed by the knife.

More recent advances in the fabric cutting technology-have brought into use mechanically guided cutting devices which are numerically controlled by a digital computer to cut pattern pieces from a layup according to a program on a punched tape or other memory device. Obviously, it is dangerous and not feasible for an individual to attempt to press a layup of sheet material against a table while the layup is cut by a computer controlled knife. Other means for pressing the different plies of the layup together must be employed so that a clean and accurate cut can be made without lifting or shifting of the fabric during the cutting process and so that a reciprocating knife penetrates a layup of nominal thickness along a substantially vertical path to cut pattern pieces of substantially identical shapes from the upper and lower plies of the layup. One such apparatus which performs this function by means of a vacuum holddown device is disclosed in US. Pat. No.

3,495,492, issued Feb. 17, 1970, and entitIed APPA- RATUS FOR WORKING ON SHEET MATERIAL and having the same assignee as the present invention.

The general aim of the present invention is to provide an improved apparatus of the aforedescribed type for working on sheet material with a tool while the material is held down on a table.

SUMMARY OF THE INVENTION The present invention resides in an apparatus for working on sheet material with a tool, for example, a cutting tool which traverses the sheet material to cut out pattern pieces for garments and other articles. The apparatus comprises means such as a table which defines a material supporting surface for suppoing the sheet material in a spread condition and means for producing a region of increased fluid pressure above the supporting surface so that the fluid pressure may hold supported sheet material against the surface. The table defining the supporting surface may be a vacuum table having several vacuum zones energized when the tool is working over the respective zones. The means for producing the region of increased pressure includes a fluid compartment which defines a fluid discharge opening in a portion of the compartment confronting the material supporting surface for exposing the sheet material to a fluid under pressure. The fluid compartment generates a region of locally increased pressure above the sheet material supported on the surface and is provided with a positioning means to translate with a tool relative to the sheet material so that the region of increased pressure is maintained in the immediate vicinity of the tool.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of a numerically controlled cutting apparatus utilizing one cmbodiment of the present invention.

FIG. 2 is a sectional view of a portion of the cutting apparatus as seen along line 22 in' FIG. 1.

FIG. 3 is a fragmentary perspective view showing the detailed construction of a fluid compartment utilized in one embodiment of the present invention.

FIG. 4 is a fragmentary sectional view of the fluid compartment as seen along the line 44 in FIG. 3.

FIG. 5 is a fragmentary sectional view of the fluid compartment as seen along the line 5-5 in FIG. 3.

FIG. 6 is a perspective view of a cutting apparatus utilizing another embodiment of the present invention.

FIG. 7 is a sectional view of a portion of the cutting apparatus as seen along the line 77 in FIG. 6.

FIG. 8 is a perspective view of a cutting apparatus incorporating another embodiment of the present invention.

FIG. 9 is an elevated frontal view in section showing the details of the toroidal fluid compartment of FIG. 8.

FIG. 10 is an elevated frontal view in section showing another toroidal fluid compartment of a type which may be utilized in the cutting apparatus of FIG. 8.

FIG. 11 is a perspective view of a cutting apparatus incorporating still another embodiment of the present invention.

FIG. 12 is a perpsective view of a cutting device cmploying a still further embodiment of the present apparatus with the cutting device partially cut away.

FIG. 13 is a fragmentary sectional view of the cutting device as seen along the lines l3-l3 of FIG. I2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 disclose a cutting apparatus which is used to cut pattern pieces from a layup composed of sheets of fabric material laid flatwise one upon the other. The cutting apparatus employs a numerically controlled cutting tool which is translated over the layup in accordance with commands derived through a computer from punched tape or other memory device. The apparatus holds the sheet material in a fixed posi tion during the cutting operation and includes a table which defines a work surface for supporting the material and a pressure producing mechanism for forcing the material against the work surface of the table.

The cutting apparatus or device, generally designated 10, utilizes a cutting tool in the form of a reciprocating knife 12 which is translated over the layup 14 of sheet material by two numerically controlled carriages I6 and 18. The carriage I6 straddles the layup and in cludes a longitudinal drive motor (not shown) and two motor driven pinion gears (not shown) which respectively engage two parallel racks and 22 at opposite lateral sides of the layup 14. To translate the knife 12 back and forth over the layup 14 in the longitudinal direction, identified as the X direction on the layup, commands from a remotely located computer are transmitted through the control cable 24 to the longitudinal drive motor and the motor drives the pinions engaging the

racks

20 and 22 in accordance with the computer commands.

The carriage 18 supports the knife 12 and is mounted on the carriage 16 for translation with respect to the carriage 16 in the lateral direction identified as the Y direction on the layup 14. The carriage 18 is supported on the carriage 16 of rollers (not shown) which ride on a transverse guide 26 and a transverse frame member 28. A transverse lead screw 30 mounted to the carriage 16 threadably engages the carriage 18 so that rotation of the screw 30 causes the carriage 18 and knife 12 suspended from the carriage 18 to be translated back and forth on the carriage 16 in the Y direction. The combined motions of the carriages l6 and 18 along the orthogonal X and Y directions permit the knife 12 to be translated along irregularly shaped paths through the layup 14 in response to the computer commands while cutting the pattern pieces from the layup.

A knife orienting motor 32 is mounted at the projecting end of the carriage 18 opposite the frame member 28 of the carriage 16 and rotates a platform 34 from which the knife 12 is suspended about a vertical axis normal to the upper surface of the layup so that the knife remains tangent to the cutting line at the cutting or leading edge of the knife. Another motor (not shown) on the rotating platform 34 causes the knife to reciprocate along the vertical axis to produce the cutting strokes of the knife as it moves through the layup 14. A guide foot 36 is also suspended from the rotating platform and rotates with the knife 12. The foot 36 is positioned against the upper face of the layup 14 during the cutting operation and prevents the upper plies of the layup from being lifted during the upward stroke of the knife. The motor 32, platform 34, knife 12 and foot 36 may be suspended from the carriage 18 by means of an adjustable mount to permit the knife and foot to be adjusted in the vertical direction for layups of different thickness.

The apparatus which holds the layup of sheet material in a fixed position during the cutting process includes a table 40 on which the layup 14 is spread and a fluid compartment 42 which is mounted on the carriage 16 and receives pressurized fluid from a source such as a blower 44 on the carriage 16. Another fluid compartment 46 is included in the embodiment of the apparatus shown in FIGS. 1 and 2 and cooperates with compartment 42 in holding the layup 14 on the table 40.

The table 40 is a vacuum table supported in a horizontal position on a plurality of table legs 48 and in cludes an outside casing or frame 50 and a bed of material 52 defining the work surface 54 on which the sheet material is positioned flatwise, one sheet on top of the other to form the multi-ply layup 14. The frame may be utilized as the supporting structure for the

racks

20 and 22 which in turn support the

carriages

16 and 18 and the knife 12. Various materials may be used to form the bed 52, but preferably it comprises an open or closed cell, low-density, foamed, polyethylene plastic material which may be readily penetrated by the knife 12 during the cutting operation. The reciprocating knife 12 is adjusted to partially penetrate the bed to assure accurate .and efficient cutting of the lower plies in the layup l4.

Ethafoam, a product of Dow Chemical Company. has proven particularly suitable as a bed material, and such material may be supplied in blocks, as shown, to permit selected portions of the bed which receive particularly heavy usage to be replaced from time to time as required. It will be understood that other materials such as bristled mats may be used as the bed material so long as the knife can readily penetrate the material and the material provides a sufficiently rigid work surface for supporting the layup 14 in a fixed position. Of course, in operations on sheet material which do not require that a tool pass through the material. for example, a plotting operation, the necessity fora penetrable bed is not present and non-penetrable materials can be em ployed to define the work surface.

The table 40 is a vacuum table which aids in holding the sheet material in place by producing a region of reduced ambient pressure or sub-atmospheric pressure at the supporting surface defined by the bed 52. A table of this type is illustrated and described in greater detail in US. Pat. No. 3,495,492 issued to the inventors of the present application and having the same assignee. ln one form, the vacuum table 40 is constructed to provide a region of reduced pressure at the supporting surface by drilling passageways 200 vertical through the penetrable bed material and by constructing a series of plenum or vacuum chambers 202 below the bed 52 in the frame 50 of the table. A vacuum pump 204 is connected through a manifold assembly 206 and valves 208 to each of the chambers 202. The valves 208 for each of the respective chambers 202 permit the chambers to be individually evacuated so that separate vacuum zones corresponding respectively to the chambers 202 are established in the bed 52 of the vacuum table. Each of the valves 208 is controlled in synchronism with the movement of carriage 16 supporting the knife 12 so that the vacuum zone energized will be the zone supporting sheet material through which the knife is cutting. Two or more zones may be energized at one time as the knife passes from one zone to another. A more detailed description and explanation of the zoned vacuum table is found in the above-referenced patent.

It will be understood that the bed 52 constructed from bristled mats is ideally suited to a vacuum system. For instance, bristled mats are inherently porous or fluid permeable and ambient air can be drawn through the bristles to produce a low pressure region at the supporting surface defined by the free ends of the bristles.

The fluid compartments 42 and 46 as seen in FIGS.

1 and 2 are inverted pans or shells located on opposite sides of the knife 12 and have a shape which is elongated in the Y-direction. A mounting plate connected to one side of the carriage 16 and a similar mounting plate (notvisible) at the other side of carriage 16 have guides or keys 6], 61 and 63, 63 which mate with corresponding keyways in the confronting end walls of the compartments. The

compartments

42 and 46 are adjustably suspended on the guides by means of springs or counterweights (not shown) connected to carriage 16 so that the compartments can be shifted in the vertical direction with respect to the horizontal work surface 54 to accommodate layups of different plies or thicknesses. Two flexible

fluid conduits

62 and 64 are connected respectively to the fluid compartments 42 and 46 to deliver the air under pressure from blower 44 to the interior of the compartments. Each of the compartments at the side adjacent the layup l4 defines a fluid discharge opening which exposes the upper face of the layup to the pressure of the air within the compartments. Air seals in the form of flexible

elastomeric skirts

66 and 68 are connected, respectively, to the peripheries of the openings of the compartments and extend downwardly toward the layup 14 and the table surface 54 to impede the leakage of the air out of the compartments and to generate a cushion of air at increased pressure above atmospheric pressure under the compartments, which cushion operates downwardly on the layup.

Adjustment of the biasing force of the springs or counterweights holding the

compartments

42 and 46 allows the pressure of the air within the compartment to be varied so that the compartments can be lifted off of the layup on the cushion of air. The total force on the affected region of the layup under the compartment equals the combination of the weight of the compartment plus the biasing and frictional forces. As the air escapes past the

skirts

66 and 68, the stream of air assists in spreading the sheet material smoothly on the table 40 and forms a fluid bearing which permits the compartments to translate over the layup 14 on the cushion of air which supports the compartment and holds the sheet material down on the table 40.

In operation of the cutting apparatus 10, the layup of material is first positioned on the surface 54 of table 40 under carriage l6, and blower 44 and vacuum pump 204 are started to deliver air under pressure to the

compartments

42 and 46 and to withdraw air from between the layup and the supporting surface of the table in the zone or zones below the knife. The pressure of the air received within the compartments is applied to regions of the upper surface of the layup on opposite sides of and immediately adjacent to the knife 12. The air pressure forces the sheet material compactly against the work table and the vacuum below the sheet material also draws the material toward the table. The cutting operation is then begun.

As the knife 12 traverses a cutting path through the layup, the fluid compartments 42 and 46 move with the component of the knife displacement in the X direction and the knife translates relative to and between the compartments for components of its displacement in the Y direction. In this fashion, the two regions of increased pressure produced by the compartments move successively over adjacent portions of the layup and remain immediately adjacent the knife regardless of the position of the knife on the layup surface. The valves 208 between the vacuum pump and the bed 52 are opened and closed by the carriage 16 as the knife 12 traverses the vacuum zones controlled by the respective valves. Accordingly, a region of increased pressure above the layup and a region of decreased pressure below the layup holds the sheet material compactly in place on the supporting surface and the two regions move in synchronism along the table with the knife.

It will be understood that the pressure of the air received in

compartments

42 and 46 is applied to the upper ply of the layup l4 and the force holding the layup in a fixed position on the table 40 results from the pressure differential generatedacross the plies of the layup by the compartments and the vacuum table. In cases where the layup is formed of a fabric material which is air-pervious, the pressure differential across the individual plies at the upper portions of the layup 14 may be greatly reduced due to the filtering of the air through the pervious material. Such reduced pressure differentials may not be adequate to hold the upper plies of the fabric material fixedly in position during the cutting process and, accordingly. it may be desirable to provide an air-impervious covering over the layup. In such case, the upper ply of the layup, as seen for example in FIG. 2, would be an air-impervious covering. With an impervious covering, the force resulting from the pressure differential between the top and bottom plies of layup I4 is applied across all of the plies of the layup. Such an impervious covering may be easily provided by a sheet of thin, flexible plastic film. such as a polyethylene sheet. Although the knife 12 will cut through the polythylene in the same fashion that it cuts the fabric material, such polyethylene sheets are relatively inexpensive and may be considered expendable.

In some cutting operations. particularly those in which only one or just a few plies of sheet material are cut, the use of an air-impervious overlay may be unwarranted or undesired and the holddown forces may be generated simply by the air flow through the sheet ma terial between the compartments and vacuum table. Pressure differentials in the order of l to 10 inches of mercury may be produced across the sheet material by either the fluid compartments or the vacuum system. The combined operation of the compartments and vac uum table makes pressure differentials up to 20 inches of mercury possible. The vacuum table and pressurized compartments complement each other by increasing the volume of fluid flow through the permeable sheet material, and thereby, generating a greater pressure differential. Furthermore. the vacuum table receives some of the air discharged from the compartments and may reduce the stream of air escaping from the compartments and flowing horizontally across the upper surface of the sheet material. The lifting of the upper plies of the material that accompanies such horizontal flow is reduced.

The fragmentary views of FIGS. 3, 4 and 5 disclose an alternate construction of the sealing device which may be used on the fluid compartments 42 and 46 in FIGS. 1 and 2 in place of the flexible,

elastomeric skirts

66 and 68. In the alternate construction, the sealing device is formed by a porous or apertured member which is located at the periphery of the opening in the fluid compartment confronting the layup 14. In FIG. 3, a corner of a fluid compartment similar to the compartment 42 is shown with a lateral side wall 70 overhanging the edge of the layup 14 as would be the case where the layup had a Y dimension slightly less than the Y dimension of the compartment 42. A porous or apertured member 72 is connected to the inner surface of the lateral side wall 70 at the peripheral edge of the compartment opening confronting the layup 14. As seen in FIG. 5, the porous member 72 has an L-shaped cross-section and is provided with a series of apertures 74, 74 extending through the portion of the member positioned parallel to the upper surface of the layup 14. The member 72 serves as an inwardly extending seal to prevent air from escaping under the overhanging wall 70 of the compartment and the apertures 74, 74 act as pressurestaging orifices which create a staged pressure drop at the edge of the layup. If the wall 70 does not overhang the edge of the layup, the apertures 74, 74 allow air within the compartment to be admitted to the region within the member 72 and consequently the pressurized region under the compartment extends substantially to the wall 70 of the compartment without substantial differences in pressure. 7

Another apertured member 76 is connected to the exterior surface of the compartment wall 78 joined perpendicularly to the overhanging wall 70. The member 76 has an L-shaped configuration and contains pressure-staging orifices or apertures 80 in the portion of the member extending parallel to the upper surface of the layup. The member 76 terminates at a point adjacent the inwardly facing edge of member 72 and is closed at this point by end wall 82. The wall 78 to which the member 76'is attached is slightly foreshortened at the bottom edge 84 adjacent the layup 14 as best seen in FIG. 4. When the compartment is filled with air under pressure, the foreshortened edge 84 allows air to pass readily under wall 78, and member 76 with orifices 80 serves as a pressure-staging seal to drop the pressure within the chamber gradually at the periphery of the region of layup 14 experiencing the air,

pressure. The apertures 80 also direct the escaping air vertically away from the layup and thereby reduce the flow of air horizontally under the lower edge 86 of member 76, which flow lifts or shifts the upper plies of the layup, particularly where the layup has been cut by the knife 12. The member 76, therefore, helps keep the upper plies in a fixed position during cutting operatrons.

FIGS. 6 and 7 disclose another embodiment of the apparatus for holding sheet material in a fixed position while the cutting operation is performed with the cutting device 10. ln this embodiment of the invention, the holding apparatus includes the table 40 which has the same construction as that shown in FIGS. 1 and 2 and a single shell-type fluid compartment 90 which is mounted to the carriage 16 by means of two

guide posts

92 and 94 which are fastened to carriage 16 at the respective ends of the carriage. The compartment 90 can shift vertically on the

posts

92 and 94 for vertical adjustment relative to the horizontal table similar to the keyway-mounted

compartments

42 and 46 of FIGS. 1 and 2. The compartment 90 envelopes the knife 12, carriage 18, the portion of the carriage 16 along which the carriage 18 translates and is large enough to envelope the knife and carriage at each point along the portion traversed by the carriage 18 so that the compartment can be held stationary on carriage 16 while the knife is translated in the Y direction. Movements of the knife in the X direction caused by movement of carriage 16 are accompanied by corresponding movement of the compartment 90 since the mounting of the comrack 22. The blower 96 has a discharging conduit 98' connected to the compartment 90 for discharging air at low pressure into the compartment. Since the blower 96 is mounted directly to the compartment. the conduit 98 can be a rigid rather than a, flexible conduit.

With the layup 14 positioned on the table under the cutting device 10, the blower 96 is started and air pressure within the compartment generates a cushion of air under the compartment which raises the compartment slightly off of the layup. Biasing springs on

posts

92 and 94 may be used to adjust the pressure which lifts the comparments off the layup. Leakage of the air along the interfaces of compartment 90 and the carriage l6 and

posts

92 and 94 can be minimized by providing sliding joints or bellows-type connections which maintain a sealed environment within the compartment in spite of relative movements in the vertical direction between the compartment and the carriage and posts. The cushion of air supporting the compartment 90 serves as a fluid bearing permitting the compartment to be translated over the layup in the X direc-- tion with the carriage 16 and knife 12. Since the compartment 90 envelopes all of the portion of carriage l6 along which the carriage 18 translates. displacements of the knife 12 in the Y direction are accommodated without moving the comparment.

Although the operation of the compartment 90 is basically the same as that of

compartments

42 and 48 of FIG. 1, it will be understood that the region of the layup 14 to which the air pressure is applied completely circumscribes the knife 12 and includes that portion of the layup which is in direct contact with the knife 12.

FIGS. 8 and 9 disclose another embodiment of the apparatus for holding sheet material which may be utilized by cutting device 10. The apparatus includes'a table defining a work surface on which the material is supported and a pressure generating mechanism which circumscribes the cutting tool and translates with the tool over the work surface in each of the two orthogonal X and Y directions. The table 40 has the same construction as that found in the embodiments of FIGS. 1 and 6, including a bed 52 of penetrable material. However, in addition, penetrable boundary blocks and 112 are positioned on the work surface 54 contiguously with the opposite lateral sides of the layup 14. The

blocks

110 and 112 have a height above the surface 54 which is substantially equal to the height or thickness of the layup 14 as seen in FIG. 9 and are formed from the same or similar material as the penetrablebed material 52 so that the cutting tool or knife 12 can be translated beyond the edge of the layup into the boundary blocks without damaging the knife. The mechanism which generates the fluid pressure against the layup is composed of a stationary source 114 of fluid pressure, a fluid compartment 116 having a generally toroidal shell configuration and a flexible fluid conduit 118 connecting the stationary source 114 to the compartment 116. The source 114 may be a large volume air tank or tanks but is preferably a continuous output blower which is mounted in a stationary fashion to an overhead beam or to an other permanent fixture adjacent the table 40. The source 114 delivers air or other fluid under pressure to the compartment 116 through the flexible conduit 118 which can follow movements of the knife 12 over the entire work surface 54 of table 40. The toroidal comparment 116 circumscribes the knife 12 and is suspended from the carriage 18 by means of two bracket plates 120 mounted to opposite lateral sides of carriage 18 so that the compartment moves with the knife 12 in both the X and Y directions. The compartment 116 may be mounted directly to the platform 34 which supports the knife 12 and foot 36 so that the compartment can be adjusted vertically above the work surface 54 in conjunction with the adjustment of the knife and foot for layups of different thicknesses. Relative movement between the stationary source 114 and movable compartment 116 may be readily accommodated by the flexible conduit 118 which may be, for example, a wire-reinforced plastic hose or similar flexible duct.

FIG. 9 shows a detailed construction of the toroidal compartment 116 in which the side of the compartment confronting the layup 14 defines an annular opening that produces an annular region of increased pressure circumscribing the knife 12. A flexible skirt 122 is mounted to the lower edge of compartment 116 along the inner periphery of the annular opening and another flexible skirt 124 is mounted to the lower portion of compartment along the outer periphery of the annular opening. Both of the

flexible skirts

122 and 124 extend downwardly toward the layup 14 and the work surface 54 and may be constructed of an elastomeric material similar to the

skirts

66 and 68 in FIG. 2 so that leakage of the pressurized air delivered to the compartment is minimized and a cushion of air is generated on which the compartment can ride during translation over the layup with the knife. The toroidal compartment 116 is shown in FIG. 9 at a position overlying portions of both the block 110 and the layup 14 at a lateral edge of the layup. The construction of the chamber 116 with the

flexible skirt

122 and 124 requires that the

blocks

110 and 112 be provided at the edges of the layup with substantially the same height as the layup and in contiguous relationship with the layup so that the knife can work in regions adjacent the edges of the layup without losing the cushion of air on which the compartment translates and without catching the compartment 116 or seal 124. on the blocks as the compartment moves over the blocks. Of course a set of blocks having graduated heights might be provided for layups of different thicknesses.

FIG. discloses another fluid compartment 130 having a toroidal shell configuration which may be utilized by the cutting apparatus 10 by connecting the compartment 130 directly to the carriage 18 in the same manner that the compartment 116 is connected in FIG. 8. A flexible conduit 132 is connected to the compartment 130 for supplying air under pressure to the compartment from either a stationary source, such as source 114 in FIG. 8, or a translating source, such as the blower 44 in FIG. 1 or the blower 96 in FIG. 6. The side of the compartment 130 confronting the layup 14 is a porous or perforated annulus 134 having a plurality of fine, closely spaced fluid discharge openings or

channels

136, 136 forming orifices through which the air passes to generate a pressure on an annular region circumscribing the cutting tool. The annulus may be formed as an apertured plate or may be formed from a sintered material which allows air to seep through the annulus at a limited rate. The porous annulus eliminates the need for the blocks of penetrable material along the edges of the layup 14 since the inherent orificing effect of the channels 136 136 limits the leakage of air out of the compartment 130 when the compartment overhangs the edge of the layup 14 as shown in FIG. 10.. The operation of the annulus is similar to that of the porous member 72 in FIGS. 3 and 5 except that the compartment can overhang the edge of the layup by any amount without losing the cushion of air under the portion of the compartment over the layup since the annulus extends completely over the bottom side of the toroidal compartment. Even though a small quantity of air may leak through the overhanging portion of the compartment. the orificing effect maintains a pressure within the compartment sufficient to force the region of layup 14 adjacent the annulus against the work surface 54. Of course. there is no danger of damaging the cutting tool if it should exit from the layup during the cutting process since there are no obstacles which could be hit by the tool at the edge of the layup.

FIG. 11 discloses still another embodiment of the apparatus for holding sheet material under the cutting device 10 which apparatus includes a table defining a work surface and a pressure generating mechanism which moves with the cutting tool along the X and Y directions. The table 40 which defines the work surface 54 includes the penetrable bed 52 in the same fashion as that shown in FIG.1. The pressure generating mechanism includes a stationary source 140 of fluid under pressure, a fluid compartment 142 in the shape of a cylindrical shell mounted to the carriage 18 and enveloping the cutting knife 12 and a flexible hose 144 serving as the fluid conduit for delivering air under pressure from the source 140 to the compartment 142. The fluid compartment 142 is mounted to the carriage 18 for adjustment in a vertical direction normal to the surface 54 and is provided with seals (not shown) at the interfaces with the carriage 18 to maintain a pressurized envirow ment within the compartment in spite of the vertical adjustment relative to carriage 18. At the lower portion of the compartment 142 confronting the layup 14, a porous annulus 146 is secured to the internal surface of the compartment and circumscribes the cutting knife 12 and foot 36. Since the compartment '142 is mounted to the carriage 18, the compartment moves with the knife 12 in both the X and Y directions and generates a circular region of increased pressure centered on the knife at the upper face of layup 14. The annulus 146 may have a construction identical to the annulus 134 in FIG. 10 and operates in essentially the same manner as annulus 134 when the cutting tool 12 overruns the edge of layup 14. To prevent the undue loss of air if the knife 12 translates beyond the edge of the layup, it is advantageous to provide a seal between the foot 36 and the inner circular edge of annulus 146. It is also possible that the compartment 142 could have an open face confronting the layup and a flexible elastomeric skirt such as skirt 124 in FIG. 10 at the lower periphery of compartment 142 in place of annulus 146. Of course, with the skirt, it is desirable to employ boundary blocks similar to

blocks

110 and 112 in FIGS. 8 and 9 to allow the knife and compartment to operate in regions near the edges of the layup.

FIGS. 12 and 13 disclose still another embodiment of the apparatus specially adapted for holding sheets of air-pervious material against a work surface while the cutting device 10 is operated. The cutting device 10 has the same construction as that shown in FIG. 1; however, the portion of the carriage l6 suspended over the table 40 and the carriage 18 which supports the knife 12 have been cut away for the sake of clarity. The construction of the apparatus for producing the region of increased pressure in the vicinity of the knife 12 is similar to the apparatus shown in FIGS. 1 and 2 in that two fluid compartments 150 and 152 in the form of inverted shells or pans are mounted for vertical adjustment with respect to surface 54 on their respective

vertical guides

174 and 176 fixed to support plates 154 and 156 which are connected in turn directly to the carriage 16 at the opposite lateral sides of the table 40. A blower 158 is carried by the carriage l6 and delivers air to the compartment 150 and 152 through the flexible conduits 1M) and 162. In addition to this structure, however, an endless belt 164 of an air-impervious material is mounted on two

rollers

166 and 168 at opposite end faces of the chamber 150. The belt 164 circumscribes the chamber 150 and has one portion of the belt interposed between the compartment 150 and the layup 14. The

rollers

166 and 168 are mounted in vertical slots 170 at each end and, therefore, are allowed to float in the vertical direction in the same manner as the compartment 150 which slides on the vertical guides 174. In the same fashion, the compartment 152 is circumscribed by an endless belt 180 of air-impervious material which is carried by two

rollers

182 and 184 at opposite end faces of the compartment 152. The

rollers

182 and 184 are also mounted in slots 186 in the mounting plates 154 and 156 to permit the rollers to float vertically with the compartment 152 on guides 176. Since the

rollers

166, 168, 182 and 184 and the compartments 150 and 152 are all mounted to the support plates 154 and 156, the

endless belts

164 and 180 are translated with the compartments and the knife 12 in the X direction by the carriage 16.

The fluid compartments 150 and 152 have open sides adjacent the layup 14 so that air delivered to the compartments 150 and 152 from blower 158 generates a pressure which is applied to the layup 14 through the portions of the impervious belts interposed between the lower, open sides of the compartments and the upper face of the layup. Friction between the

belts

164 and 180 and the layup 14 causes the belts to rotate as carriage 16 translates the knife 12 in the X direction. Of course, a separate drive arrangement connected to the rollers and belts and operated synchronously with the drive motors for the carriage 16 can be provided to insure that the belts do not slide over the upper plies of the layup 14 and shift the upper plies out of position during the cutting operation. The compartments 150 and 152 remain positionedwithin the

belts

164 and 180 during the translation in the X direction and ride on the cushion of air between the compartments and the belts. The force of the air pressure on each belt is equal to the weight of the compartment plus any biasing and frictional forces and is transmitted through the belt to a region of the layup adjacent of the knife 12 as the knife performs its cutting operation. With two regions being compressed on opposite sides of the knife, the material under the knife is also held in place.

Although the apparatus in FIG. 12 which holds the material during the cutting operation operates in basically the same fashion as the apparatus in FIG. 1, that is, the fluid compartments translate with the knife 12 only in the X direction while the knife translates between the compartments and belts in the Y direction, it is apparent that a layup composed of an air-pervious pressure produced by the compartments immediately above the layup is transmitted to every ply within the layup with full force and effect. Additionally. in the apparatus of FIGS. 12 and 13, air escaping from the peripheral edges of the compartments 150 and 152 is prevented from streaming over the sheet material and. therefore, cannot lift or blow the sheet material out of position. The redirection of the fluid flowing from the compartments allows the apparatus in FIG. 12 to be utilized in cases where the fluid generating the pressure on the material should not contact the material.

While the present invention has been described in a number of different embodiments, it should be understood that still further modifications and substitutions to the method and apparatus disclosed can be had without departing from the spirit of the invention. The specific shapes, sizes and mounting means for the fluid compartments can be varied according to the needs of any given operation. The fluids employed to'force the sheet material against the work surface may be varied to be compatible with the particular sheet materials and processes under consideration. Each of the disclosed fluid compartments can be utilized in combination with a support table that may or may not have vacuum holddown features. The utility of the invention is not limited to a cutting device or process since the invention may be applied with equally satisfactory results to numerically controlled plotters, sewing machines. drafting equipment, and other devices. Accordingly. the present invention while disclosed in a number of specific embodiments-has been described by way of illustration rather than limitation.

We claim:

1. Apparatus for holding sheet material comprising: a support table having a bed defining a supporting surface on which the sheet material can be spread; vacuum means for producing sub-atmospheric pressure in at least one region of the supporting surface; and pressurizing means cooperating with the vacuum means and positioned above the supporting surface of the table for producing a region of increased pressure above atmospheric pressure over sheet material on the supporting surface, the pressurizing means including a fluid compartment positioned over the region of subatmospheric pressure at the supporting surface and defining a chamber receiving pressurized fluid and having at least one opening confronting the supporting surface of the table and overlying said one region in which the sub-atmospheric pressure is produced whereby the sheet material between the region of sub-atmospheric material can be cut by the apparatus in FIG. 12 without 65 expending a cover sheet of impervious material during the cutting process. In both apparatuses, however,

pressure and the fluid compartment is forced tightly against the supporting surface.

2. Apparatus for holding as defined in claim 1 wherein the support table is a vacuum table having a porous bed at the supporting surface and the vacuum means for producing the region of sub-atmospheric pressure includes the table and a vacuum pump connected to the porous bed.

3. Apparatus for holding as defined in claim 2 wherein the vacuum table has a porous bed.

4. Apparatus for holding sheet material according to claim 1 further including a carriage translatable over the support table parallel to the supporting surface and relative to sheet material on the bed; and wherein the fluid compartment is suspended from the carriage for moving the region of increased pressure over the sheet material on the bed.

5. Apparatus for holding as defined in claim 4 wherein the support table is a vacuum table having a bed divided into separate vacuum zones; and the vacuum means for producing a region of sub-atmospheric pressure includes the table. a vacuum pump and at least one valve between the pump and each zone in the bed to produce the sub-atmospheric pressure at the supporting surface in each individual zone of the bed.

6. A method of holding sheet material comprising:

providing a supporting surface on which the sheet material may rest in a spread condition; spreading the sheet material on the supporting surface; producing a region of increased ambient pressure over a portion of the spread sheet material on the supporting surface;

producing a region of decreased ambient pressure below said portion of the sheet material on the supporting surface during the step of producing the region of increased ambient pressure; and

jointly moving the regions of increased and decreased ambient pressures over and below the sheet material cooperatively relative to the sheet material to another portion of the material on the support surface whereby selected portions of the material are consecutively exposed to holding forces generated by the cooperative increased and decreased pressures.

7. A method of holding sheet material as defined in claim 6 wherein the step of producing a region of increased ambient pressure comprises placing a fluid compartment over said portion of the sheet material. pressurizing the interior of the compartment with a pressurized fluid and exposing said region of the sheet material to the pressurized fluid in the compartment.

8. A method of holding sheet material as defined in claim 6 wherein the step of producing a region of decreased ambient pressure comprises evacuating ambient air from between said portion of the sheet material and the supporting surface with a vacuum pump.

9. A method of holding as defined in claim 6 wherein the step of providing a supporting surface comprises providing a .porous support bed defining the supporting surface; and the step of producing a region of decreased ambient pressure comprises drawing air from between said portion of sheet material and the supporting surface through the porous bed.

10. Apparatus for holding sheet material as defined in claim 1 wherein:

sealing means circumscribing the opening of the fluid compartment are interposed between the sheet material on the supporting surface and the opening to impede the leakage of pressurized fluid from the

Claims

1. Apparatus for holding sheet material comprising: a support table having a bed defining a supporting surface on which the sheet material can be spread; vacuum means for producing subatmospheric pressure in at least one region of the supporting surface; and pressurizing means cooperating with the vacuum means and positioned above the supporting surface of the table for producing a region of increased pressure above atmospheric pressure over sheet material on the supporting surface, the pressurizing means including a fluid compartment positioned over the region of sub-atmospheric pressure at the supporting surface and defining a chamber receiving pressurized fluid and having at least one opening confronting the supporting surface of the table and overlying said one region in which the subatmospheric pressure is produced whereby the sheet material between the region of sub-atmospheric pressure and the fluid compartment is forced tightly against the supporting surface.

5. Apparatus for holding as defined in claim 4 wherein the support table is a vacuum table having a bed divided into separate vacuum zones; and the vacuum means for producing a region of sub-atmospheric pressure includes the table, a vacuum pump and at least one valve between the pump and each zone in the bed to produce the sub-atmospheric pressure at the supporting surface in each individual zone of the bed.

6. A method of holding sheet material comprising: providing a supporting surface on which the sheet material may rest in a spread condition; spreading the sheet material on the supporting surface; producing a region of increased ambient pressure over a portion of the spread sheet material on the supporting surface; producing a region of decreased ambient pressure below said portion of the sheet material on the supporting surface during the step of producing the region of increased ambient pressure; and jointly moving the regions of increased and decreased ambient pressures over and below the sheet material cooperatively relative to the sheet material to another portion of the material on the support surface whereby selected portions of the material are consecutively exposed to holding forces generated by the cooperative increased and decreased pressures.

7. A method of holding sheet material as defined in claim 6 wherein the step of producing a region of increased ambient pressure comprises placing a fluid compartment over said portion of the sheet material, pressurizing the interior of the compartment with a pressurized fluid and exposing said region of the sheet material to the pressurized fluid in the compartment.

9. A method of holding as defined in claim 6 wherein the step of providing a supporting surface comprises providing a porous support bed defining the supporting surface; and the step of producing a region of decreased ambient pressure comprises drawing air from between said portion of sheet material and the supporting surface through the porous bed.

10. Apparatus for holding sheet material as defined in claim 1 wherein: sealing means circumscribing the opening of the fluid compartment are interposed between the sheet material on the supporting surface and the opening to impede the leakage of pressurized fluid from the chamber.