GB2101920A

GB2101920A - Cutting apparatus with a blunt edge cutting wheel

Info

Publication number: GB2101920A
Application number: GB08220540A
Authority: GB
Inventors: David Raymond Pearl; Heinz Joseph Gerber
Original assignee: Gerber Garment Technology Inc
Current assignee: Gerber Technology LLC
Priority date: 1981-07-20
Filing date: 1982-07-15
Publication date: 1983-01-26
Also published as: JPS5877493A; GB2101920B; FR2509655A1; DE3227311A1

Abstract

An automatically controlled cutting machine for cutting sheet 5 material employs a cutting wheel 70 having a blunt peripheral cutting edge and a hard, smooth and continuous support surface 34, 35 on which the sheet material is spread for cutting. The cutting machine includes means 100, eg: a pneumatic or hydraulic cylinder 102 for pressing the peripheral edge of the wheel against the sheet material and means 18 for simultaneously moving the wheel relative to the support surface so that the sheet material is severed in a cutting and crushing action between the peripheral edge of the wheel and the support surface. <IMAGE>

Description

SPECIFICATION Cutting apparatus with a blunt edge cutting wheel Background of the invention This invention relates generally to an apparatus for cutting sheet material and deals more particularlywith an apparatus utilising a rotary cutting wheel to cut a low-ply lay-up of sheet material while the wheel is guided over the material.

It is known that sheet material spread in single or low-ply arrangement over a hard, smooth support surface can be cut by a rotary cutting wheel, or blade, as the wheel is pressed against and rolled across the surface. The cutting operation of the material is effected by the partial slicing and partial crushing action between the periphery of the wheel and the support surface. A rotary wheel and hard support surface combination is utilised in the cutting apparatus described in U.S. Patent No. 3,776,072, issued to Pavone and Landers.

A belief concomitant with the design of the prior art cutting wheel used with a hard support surface has been that the cutting wheel should be as sharp as possible along its peripheral edge for complete severance of the sheet material. Awell-sharpened cutting wheel would, logically, maximise the slicing action of the wheel as it rolls along a cutting path on the material and would minimise the amount of pressure required to be applied between the wheel and the support surface in order to sever the material. There are, however, disadvantages associated with the use of a sharp rotary wheel in combination with a hard support surface.

Afirst disadvantage and one which relates to the cutting wheel itself is that the wheel is very thin in the vicinity of the cutting edge and, therefore, is susceptible to damage as a consequence of the pressure exerted between the wheel and the support surface. As the cutting edge is pressed against the support surface, stresses internal to the wheel encourage chipping or spalling at the cutting edge.

A second disadvantage and one which relates to the support surface is that the support surface is likely to be scored or grooved by a sharp-edged wheel.

The damage resulting from the aforementioned disadvantages not only tends to reduce the useful life of the cutting wheel and support surface but, in addition, adversely affects the cutting operation. If the wheel is nicked or the support surface scratched, sheet material in the cutting path retracts or is depressed into the nick of the wheel or groove of the support surface as the wheel is rolled along the cutting path, and complete severance of the material along the cutting path is thereby hampered.

It is, therefore, an object of this invention to provide an apparatus with a rotary cutting wheel which circumvents the aforementioned disadvantages.

Summary of the invention The present invention resides in an apparatus for cutting sheet material spread in a single or low-ply arrangement over a support surface. The apparatus comprises a support surface for the sheet material, a rotary cutting wheel in the form of a thin circular disc, translating means for moving the cutting wheel along a cutting path, and means for pressing the edge of the cutting wheel against the support surface as the wheel is moved along the cutting path. Characteristics of the cutting wheel and regarded as the novel aspect of the present invention is a blunt peripheral cutting edge which rolls on the support surface in cutting engagement with the sheet material spread on the surface.A cutting operation is thereby effected by crushing apart the sheet material between the blunt edge of the cutting wheel and the support surface as the wheel is moved relative to the support surface.

The likelihood of cutting wheel or support surface damage resulting from the use of the cutting wheel is substantially lessened by the use of a blunt-edged wheel for two reasons. Firstly, a wheel having a blunt edge is generally stronger in the vicinity of the peripheral edge than a wheel of similar diameter having a sharpened edge and is therefore less susceptible to nicking or spalling than a sharp-edged wheel. Secondly, a blunt-edged wheel is less apt to score the support surface as would a sharp-edged wheel. Because this invention discourages wheel and support surface damage in the form of wheel nicks or support surface scoring, the useful life of the wheel and support surface is prolonged and complete severance of the sheet material along the cutting path is achieved.

Brief description of the drawings Figure 1 is a perspective view of a cutting apparatus in which the present invention is embodied.

Figure 2 is a side elevation view of the cutting tool and cutting table of Figure 1 and shows the loading mechanism connected to the tool.

Figure 3 is a front elevation view of the apparatus of Figure 2.

Figure 4 is a front elevation view of the cutting wheel and holder of Figure 2 drawn to a slightly larger scale.

Figure 5 is a side elevation view of the cutting wheel and holder shown in Figure 4.

Figure 6 is an elevation view of a cutting wheel in another embodiment of this invention.

Figure 7 is an elevation view of a cutting wheel in still another embodiment of this invention.

Description of the preferred embodiments Figure 1 illustrates an automated cutting system for cutting sheet material in which the present invention is embodied. The system, generally designated 10, is comprised of a cutting table 12, a cutting tool 14 and a tool translating means comprised of an X-carriage 16 which moves over the cutting table 12 in the indicated X-direction, a Y-carriage 18 which is mounted to the X-carriage and moves relative to the table 12 and the X-carriage 16 in the indicated Y-direction and a control computer 20 connected to the carriages and the tool for controliing the motions of the tool during the cutting operation. The control computer 20 derives program information from a memory tape 22 and develops cutting control sig nals in accordance with the information.The control signals are transmitted through a command cable 24 to the carriages 16 and 18to cause the tool 14to be translated over the table 12 in cutting engagement with the sheet material S. From the program information defined by the memory tape 22, the computer guides the tool along cutting paths such as the peripheries of pattern pieces shown by dotted lines on the sheet materials.

The cutting table 12 has a frame 30 which rests on a plurality of table legs 32 and a bed 34 defining the work surface on which the sheet material S is spread. The work surface 35 defined by the bed 34 is hard enough to resist damage by the cutting tool as the tool is pressed against the surface during cutting.

The X-carriage 16 is supported above the cutting table 12 on a pair of racks 48 and 50 which extend longitudinally along the edge of the table in the X-direction and are held by brackets 52 projecting upwardly from the frame 30. Drive motors and pinions (not shown) within the carriage 16 engage the teeth of the racks 48 and 50 to drive the carriage 16 and the tool 14 back and forth over the table in the X direction in accordance with the movement commands transmitted from the computer 20.

The Y-carriage 18 is suspended from the Xcarriage 16 by means of a guide raii 58 and a lead screw 60 that extend in the Y direction between the lateral ends of the X-carriage 16. The lead screw 60 is rotated by another drive motor (not shown) controlled from the computer 20 and threadably engages the Y-carriage 18 to position the carriage and tool 14 in the Y-direction over the table. Composite motions of the X- and Y-carriages 16 and 18 permit the tool 14 to be translated in any given direction over the work surface of the table 12 in cutting engagement with the sheet material to cut along the periphery of a pattern piece.

As seen most clearly in Figures 2 and 3, the cutting tool 14 is suspended from the Y-carriage 18 by means of a support platform 62 which extends in cantilever fashion from an adjustable mount 64 on the projecting end of the Y-carriage 18. The adjustable mount 64 is elevated and lowered with respect to the work surface of the table 12 by a motor (not shown) controlled by the computer so that the cutting tool 14 can be brought into cutting engagement with the sheet material S at the beginning of a cutting operation or raised out of contact with the sheet material at the end of a cutting operation. The cutting tool 14 includes a cutting wheel 70 having a peripheral cutting edge which severs the sheet material S by a crushing action when the tool is uged downwardly into engagement with the material by a detrusive force from the support platform 62.The cutting wheel 70 is supported by a tool holder 72 so that the wheel rotates freely about an axis parallel with the work surface of the table 12 as the wheel is rolled over the work surfaces by the carriages 16 and 18 in cutting engagement with the sheet material.

The wheel 70 and holder 72 are translated with the platform 62 in part by means of a journaled supporting shaft 80 which provides angular rotation of the tool about the S axis 82 perpendicular to the work surface of the table 12. A rotational drive motor 84 is connected to the shaft 80 by means of a toothed belt 86 extending between motor pulley 88 and a large shaft pulley 89 secured to the upper end of the shaft 80. Rotation commands are derived from the memory tape 22 by the computer 20 and are applied to the drive motor 84 to control the angular position of the cutting wheel so that it translates tangentially along the edge of the pattern piece at each point on the edge.

A load control mechanism is interposed between the cutting tool 14 and the tool carriage 18 from which the tool is supported for supplying the detrusive force with which the cutting tool is urged along the S axis 82 into cutting engagement with the sheet material S on the work surface. The load control mechanism, generally designated 100, includes a pneumatic or hydraulic load cylinder assembly 102 which is fixedly mounted on a small bridge 104 connected to the support platform 62.

The load cylinder assembly 102 includes a piston rod 106 which extends coaxially through a central bore in the shaft 80 and connects through a thrust bearing 110 with the tool holder 72 secured rotatively to splines on the depending end of the shaft 80 by a collar 112 so that the chuck and the tool 14 rotate with the shaft and slide axially along the shaft relative to the support platform 62. The thrust bearing 110 permits the holder 72 to rotate the cutting wheel 70 about the S axis 82 while the detrusive force is applied by the piston rod 106 to the cutting wheel.

The load applied to the cutting wheel 70 and hence the detrusive force with which the cutting wheel is urged into the sheet material S is determined by the pressure applied to the load control cylinder assembly 102 through the pressure lines 114 and 116. The applied load must be large enough that the sheet material is severed by a crushing action as the wheel is rolled across the sheet material surface. After a cutting operaiton, the pressure in the lines 114 and 116 is reduced to zero and the tool 14 is lifted from the cutting table by the platform 62 and the adjustable mount 64 when the lifting ring 120 fixed to the lower end of the shaft 80 makes contact with the collar 112.

The diameter of the cutting wheel 70 is within a range limited by practical considerations associated with this type of cutting system. As a first consideration, the wheel diameter must be large enough that the height of the lay-up is not above the horizontal midplane or rotational axis of the wheel when the wheel periphery is pressed into the support surface in cutting engagement with the sheet material. With the height of the lay-up below the horizontal midplane of the wheel, the sheet material in the path of the rolling cutting wheel is pressed against the support surface by the wheel's cutting edge and no portion of the lay-up makes contact with or interferes with the tool holder 72.

Also, relating to the smallest value of the wheel diameter is the consideration that the wheel must rotate along a cutting path as a consequence of frictional driving forces between the wheel edge and the sheet material andlor support surface. In order for the wheel to rotate, the frictional driving forces must be large enough to overcome the opposing frictional forces which act between the wheel 70 and the wheel holder 72 in the vicinity of the wheel axle.

As a general rule, the larger the wheel diameter, the easier it is for the frictional driving forces to overcome the forces apposing rotation.

The largest value of the wheel diameter is limited to prevent excessive displacement of the sheet material as the wheel is turned to follow a curve or angle in the cutting path. The larger the wheel, the greater the likelihood that the sheet material adjacent the cutting path will be displaced or ruffled as the wheel twists about the S axis.

Because of the aforementioned practical considerations limiting the range of the wheel diameter, it is preferred that the diameter of the wheel be not greater than 3.0 inches (76.2 mm) and not less than .25 inches (6.35 mm).

The cutting wheel 70 is illustrated in detail in Figures 4 and 5, and is comprised by a thin disc having a substantially uniform thickness between axial sides of the wheel and a blunt cutting edge 71.

The blunt cutting edge 71, for example, may have a radius of curvature R which is not substantially less than half the thickness of the wheel. Typically, the radius of curvature falls within a range of .001 to .010 inches (.025 to .254 mm).

A blunt peripheral cutting edge 71 is preferred over a conventional sharpened edge for several reasons. With the load control mechanism 100 applying a detrusive force to the cutting wheel 70, there is substantial stress created between the cutting edge and the first support surface 35 of the bed 34. High levels of stress which accompany a sharp cutting edge have several adverse consequences that deleteriously effect the cutting operation.

One consequence of high stress levels is the deterioration of the cutting edge on the wheel. When the wheel is comprised of a hard material that is frangible, breakdown occurs along the cutting edge by spalling in which small pieces or fragments fracture and separate from the remaining portions of the cutting wheel. Small nicks and a general lack of continuity along the cutting edge results in intermittent cutting along a cutting path. Following such a cutting operation, uncut threads or other material extend between the pattern piece and the surrounding material, and if removal of the pattern piece is attempted, the material may be damaged due to snagging or tearing as the uncut material is pulled.

Furthermore, the high stresses associated with a sharp peripheral cutting edge adversely affect the support surface 35 of the cutting table. As a general rule, the support surface has a hardness which is less than the hardness of the cutting wheel. It is preferred that the support surface be no harder than 40 on the Rockwell "C" hardness scale. Ideally, the surface must be smooth, but the concentrated stresses along a cutting path result in scoring of the surface. Consequently, after repeated use, the support surface 35 may contain a series of grooves that replicate the pattern pieces cut in previous operations. Such grooves or scoring comprise discontinuities in the cutting surface and have substantially the same effect as discontinuities in the peripheral cutting edge.The sheet material recedes or retreats into the grooves and inhibits locai cutting at intersections of the grooves and the cutting paths.

With the cutting wheel of the present invention and the blunt peripheral cutting edge 71, the spalling and scoring problems are substantially eliminated.

With a blunt cutting edge, the wheel has substantially greater strength at the cutting edge and produces a correspondingly reduced level of stress in both the wheel and the support surface. With a stronger wheel and reduced stress, the likelihood of spalling is effectively eliminated.

Similarly, the larger area of contact between the cutting edge and the support surface produces lower stresses in the bed 34, and permanent deformation and scoring of the surface 35 is reduced, if not eliminated, to a level which does not interfere with the cutting operation.

It has been determined from experience, that the cutting action of a blunt cutting edge still allows limp sheet materials, such as woven and non-woven fabrics to be cut in spite of the rounded nature of the cutting edge. The cutting operation is shifted from one in which severance of the material occurs through both a slicing and a crushing operation, to one in which severance occurs primarily through crushing. In tests, it has been observed that small traces of pulverised sheet material may be found along the line of cut, but severance of the material is accomplished nevertheless. For some materials it may be necessary to increase the level of the detrusion force, but the increase in contact area between the blunt edge and the support surface does not result in higher levels of stress and the consequential scoring.

Figures 6 and 7 show further embodiments of the blunt cutting wheel of this invention, both wheels 90 and 92 having cutting edges 91 and 93, respectively defined by narrow and flat cylindrical surfaces extending circumferentially around the wheels. Preferably, the diameter of the wheels 90,92 is not greater than 3.0 inches and not less than .25 inches for the same reasons cited above in connection with the embodiment of Figures 3 and 4. The flat cylindrical cutting edges function in substantially the same manner as the blunt cutting edge 71 having a rounded curvature between opposite axial end faces of the cutting wheel. The flat cutting edges are effectively round edges in which the radius of curvature approaches infinity. In order to maintain cutting efficiency with a flat edge, the width of the edge should generally lie within the range of .002 to .005 inches (.050 to .127 mm).

The wheel 90 in Figure 6 has an integral construction and differs in this respect from the wheel 92 in Figure 7. The wheel 92 is essentially a thin disc having a width no greater then the flat peripheral cutting edge 93 and reinforcing plates 94,96 are added at each side coaxially of the disc to provide additional bearing strength in the vicinity of the axle 98.

While the present invention has been described in several embodiments, it should be understood that numerous modifications and substitutions can be had without departing from the spirit of the inven tion. For example, the cutting wheels with blunt peripheral cutting edges may have both tapered, stepped hyperbolic or uniform widths between the centre and the peripheral cutting edge. Bearing inserts may be provided in the centres of the wheels or the wheels can be fixedly attached to axles that are subsequently journaled in the tool holder. It is important that the bearing structure permitting the wheel to rotate freely within the holder have little or preferably no freedom of motion since the alignment of the wheel in the machine is critical to accurate tracking of a cutting path. The precise contour of the blunt cutting edge may range from rounded to flat edges including curvatures which increase in radius between the apex of the edge and axial sides of the cutting wheel. Accordingly, the present invention has been described in several embodiments by way of illustration rather than limitation.

Claims

1. Apparatus for cutting sheet material comprising: support means defining a support surface on which the sheet material is spread for cutting; a cutting tool having a cutting wheel with a blunt peripheral cutting edge which rolls on the support surface of the support means in cutting engagement with sheet material spread on the surface; controlled translating means connected with the cutting tool and the support means for controllably moving the cutting wheel relative to the support surface along a desired line of cut in the sheet material spread on the surface; and means for pressing the blunt edge of the cutting wheel against the support surface so that a cutting operation is effected by crushing apart the sheet material between the blunt edge of the cutting wheel and the support surface as the wheel is moved relative to the support surface.

2. Apparatus for cutting sheet material as defined in Claim 1 wherein the cutting wheel is a thin disc having a substantially uniform thickness between the axial sides of the wheel, and the blunt peripheral cutting edge of the wheel has a radius of curvature between the axial sides not substantially less than half the thickness of the wheel.

3. Apparatus for cutting sheet material as defined in Claim 2 wherein the thickness of the cutting wheel is small relative to the diameter of the wheel, and the diameter of the wheel is within the range of .25 to 3 inches (6.35 to 76.2 mm).

4. Apparatus for cutting sheet material as defined in Claim 1 wherein the blunt edge of the cutting wheel has a radius of curvature in the range of .001 to .010 inches (.025 to .254 mm).

5. Apparatus for cutting sheet material as defined in Claim 1 wherein the blunt edge of the cutting wheel has a radius of curvature approaching infinity.

6. Apparatus for cutting sheet material as defined in Claim 1 wherein the blunt edge is flat.

7. Apparatus for cutting sheet material as defined in Claim 1 wherein the support surface has a hardness less than the hardness of the cutting wheel.

8. Apparatus for cutting single plies of limp sheet material comprising: support means defining a support surface on which the single ply of limp sheet material is spread for cutting; a cutting tool including a cutting wheel having a peripheral cutting edge which rolls on the support surface in cutting engagement with the sheet material spread on the surface, the peripheral cutting edge being formed by a narrow and flat cylindrical surface extending circumferentially around the wheel; translating means connected with the cutting tool and the support means for moving the cutting wheel relative to the support surface along a desired line of cut in the sheet material spread on the surface; and means for pressing the flat peripheral edge of the wheel against the support surface with sufficient force to crush the sheet material apart as the wheel is moved relative to the support surface.

9. Apparatus for cutting single plies of limp sheet material as defined in Claim 8 wherein the narrow flat cylindrical surface of the peripheral cutting edge has a width in the range of .002 to .005 inches (.050 to .127 mm).

10. Apparatus for cutting single plies of limp sheet material as defined in Claim 8 wherein the narrow flat cylindrical surface of the wheel has a width selected to cut the sheet material without scoring the support surface under the force of the means for pressing.

11. Apparatus for cutting sheet material substantially as herein described and shown in the accompanying drawings.