Improvements to a vacuum-grip cutting table

Abstract: Improvements to a cutting table with vacuum grip, consist­ ing of the provision of the means required to connect the vacuum to a conveyor (14) on which the strip material (12) to be cut with a numerically controlled machine is fixed. In particular, the conveyor (14) is of the type made up by a succession of tiles (48) connected to the links of two chains (50) (or group thereof) which are closed and which slip or run along guides and mesh with at least two toothed wheels (54) which provide the movement. On the upper face of the loop formed by the succession of tiles, a bridge (20) runs with supports and movement dev­ ices (30) of its own which provide it with the movement in - the same direction as the conveyor (14). - On this bridge (20), a carriage (22) moves with the tools for working the material (12). - In order to hold the strip material (12), a vacuum is applied in accordance with the subject of this invention, under the working surface, formed by the upper face of the con­ veyor (14).- The said vacuum is applied to each of the tiles (48) which are hermetic enclosures with outlets only on the outside faces of the loop created by the conveyor (14).

Description: The invention relates to a conveyor table for a numerically controlled cutting machine for cutting vacuum gripped strip material, comprising a conveyor consisting of a succession of tiles, linked to chains which are driven by a conveyor drive motor, and of a plurality of bristle mats forming a penetrable air-permeable cutting table, and a vacuum system with a vacuum source, whereby the tiles are parts of the vacuum system. Background of the invention In connection with automatically controlled cutting machines for cutting textiles or similar limp sheet materials held in place or gripped by vacuum conveyer table replaced fixed tables because of the large length of the sheet material to be cut, so that section cutting operations are possible in order to prevent dimensions of the cutting table as large or larger as the length of the sheet material to be cut. With conveyor table there are problems with vacuum gripping as all moving parts has to be sealed against atmosphere whereas vacuum has to be supplied to the limb sheet material while it being fed and/or worked upon. Such a conveyor table is known from US-A-4 528 878. In machines like DE-A1-3 630 363 including a device for generating vacuum below a conveyorised bristle bed conveying the material to be cut the vacuum is conducted by a main conduit tube to a succession of tiles interconnected by wheel driven chains forming a roller supported conveyor belt and bearing the bristle mats whereas the vacuum is applied to the surface of the cutting table through corresponding holes in the conduit tube and the tiles. For sealing against atmosphere the conduit tube is provided with a plurality of lip type sealing means and parallel to the holes with flat sealing means and being held in tight contact with said tiles which are supported on both ends by said roles. Further, in order to prevent vaccum leaks between adjacent tiles Mylar strips are provided between each of said tiles, said strips have to be replaced after each cutting operation as they are cut also during the cutting process for cutting the limb sheet material. Accordingly, the problem underlying the present invention is to improve conveyorized vacuum table of a numerical controlled cutting machine by simplifying the parts and reducing their quantity to form a new conveyorized vacuum table in order to minimize lost of vacuum and wear during the cutting operations. Summary of the Invention The general object of the invention is a conveyor table for a numerically controlled cutting machine for cutting vacuum gripped strip material, comprising a conveyor consisting of a succession of tiles, linked to chains which are driven by a conveyor drive motor, and of a plurality of bristle mats forming a penetrable air-permeable cutting table, and a vacuum system with a stationary vacuum source, whereby the tiles are parts of the vacuum system and having holes on the upper surface for communication with the bristle mats and openings at the underside aligned and communicating with holes at the topside of a central tube being moored to the frame of the machine and arranged transverse to the tiles and linked to the vacuum source, the tiles, on which the bristle mats are fixed, are hermetically sealed at the ends by end sections, and in which the tube has on its upper face a plastic support strip of low friction and with wide openings corresponding with the openings of the tube and rubber strips in contact with the plastic support strip and which rub on the bottom surface of the tile, and that the tiles are provided with gaskets for preventing leaks between the tiles to complete the hermetic vacuum seal of the inside face of the conveyor working surface. According to the invention the load due to the pressure difference between the top- and bottom-side of the conveyor is supported at the same point where it is created as said wide antifriction plastic strip is situated between the rubber seals thus avoiding unnecessary stresses and deformations of elements and tiles forming the conveyor. A further object of the invention is improvement of the configuration of the tiles with respect to the connection between tiles and bristle mats in such a way that the tiles are formed to receive the bristle mats such that after extracting the end section the bristle mats can be removed from said tiles. Brief description of the figures Figure 1 is a perspective view of a cutting machine with a conveyorized cutting table according the invention. Figure 2 is a detail view of the X-Y-carriages for transmission of cutting tool of the cutting machine according figure 1. Figure 3 is a diagrammatic profile view of the cutting machine according figure 1. Figure 4 is a detail view of the conveyorized cutting table with mobile tiles. Figure 5 is a perspective view of detail of a section of the cutting table showing the vacuum delivery to the cutting zone. Figure 6 is a sectional view of the mobile tiles. Figure 7 is a perspective view of the tiles, with another design for the end seal. Figure 8 is a diagram of the general pressure distribution. DESCRIPTION OF THE INVENTION. Figure 1 shows the cutting machine which incorporates this invention -1-, of the type generally used in this process, and which is briefly described hereinbelow. From a spreading table -5-, the stacking of strip-material -12- is fed by the conveyor -14.- The cut panels -18- are withdrawn at zone -16- and, as well, at the adjacent section of the conveyor. The geometry of the cut is obtained by movement of the bridge - 20 - or X carriage, and the Y carriage -22-. A controller -24- handles these movements, driving the motors of the X and Y carriages. The carriage -22- has a suitable cutting tool for the material to be worked which, as can be seen from figure 2, is directed on guides -26-. This figure also shows the drive motor -28- and the belt which transmits the movement -30-. Three motors are to be found in this carriage; the blade drive motor, that for aligning the blade in the tangential direction on the cutting line, and the sharpening motor. The X axis carriage is directed on the guides -32- and its motor -34-, moored on the frame, moves the bridge by means of belt -36-. The interaction between the cut and the table movement described in Spanish patent no. 541,826 held by the applicant is briefly described by way of continuation. The conveyor is divided into three sections, as can be seen in figure 3; a feed zone -38-, a cutting zone -40- and a collection zone -42-. The material is spread in advance on a table -5- in which holes for the admission of pressurised air facilitate the slippage of the material in the direction of the cutting machine. After cutting the panels which are whole in the cutting zone, beginning at the point of the X=0 abscissus, the conveyor, driven by a motor -44- can move along the minimum abscissus, corresponding to the next panel to be cut, and which was not wholly within the cutting window -40-. The previously cut section of material will be in zone -42- which continues to a collection table -16. The panels furthest from the cutting zone will be collected, and, when the bridge is close to the maximum abscissus, those which are closest, for reasons which will be explained below. The connection between tables -16- and -5- with the conveyor is by means of combs, -46-, which provide a smooth transition in feed and collection. Figure 4 shows the conveyor table; for clarity, the loading and unloading tables are not shown, nor are the X carriage drives and guides. The chain of tiles -48- is shown, fixed to the chain -50- which is guided on a suitable section, preferably of plastic material for elimination of friction and noise. The wheels -54- driven by motor -44- move the chains in accordance with the orders and data from the controller, which follows the working sequence previously described. An optical encoder -56- secured to the shaft gives ongoing information on the exact position of the chain so that, by comparison against the signal from the codifier which is incorporated into the X carriage drive motor -34-. the relative positions of the bridge and conveyor will be available. Figure 5 shows detail of the construction of the tiles -48-, along with the vacuum communication system which maintains the material to be worked in place under atmospheric pressure, which is the basic purpose of this patent. The said tiles are made up of a hollow tube -58- which is hermetically sealed at the ends by sections -60-; on the underside there is a large opening -62- and, on the upper surface, a variety of holes which connect with blocks of bristles or mats which are permeable to air -64-. Figure 6 shows the detail of a preferred connection between the said tube and mats; with this system, by extracting the end section -60-, the mats can be removed. The drill holes -59- and the base - 61-, permeable to air, are shown. The succession of the said blocks forms the working surface which, in this case, is a surface which can be penetrated by a cutting blade. The tube -66- is secured in the conveyor; with the appropriate connections, it links with the vacuum generated by pump -68-. On the upper face of tube -66-, a strip of plastic material -70- is fixed, with low friction and wear rates. Tube - 66- and strip -70- have wide openings -72- delivering the vacuum through holes -62- to the tiles -48- which slip over the said strip. When the chains -50- linked to the tubes -58-, drive the tiles, drill-holes 62 and 72 are always wholly or partially aligned, so that the vacuum can be delivered; this is because the distance between holes -72- is less than their length while, at the same time, they are the same size as the holes -62- in the tiles. From tubes -58-, the vacuum flows to the mats -64-; to prevent leaks between the tiles gaskets -74- are provided. Similarly, to ensure the seal between strip -70- and the tubes -58-, rubber strips are provided -76- to complete the hermetic seal of the inside face of the conveyor's working surface. Another preferred design replaces the drill-holes -72- for a continuous opening of the length corresponding to the area of application of the vacuum, so that the air movement in the holes -62- in this area is never impeded. The upper face formed by the mats -64- is the support for the material to be cut; if it is not sufficiently impermeable, throw-away plastic can be used to close this surface, and the material, or the plastic and material is held in place under atmospheric pressure. In the sections -60-, there are drill holes -78- for securing the covering plastic by means of the vacuum, thus preventing these sections -60- from entering the connections. Another design for the tile ends shown in figure 7 would be to replace the sections -60- with blocks of flexible material -120- which is also impermeable, e.g. some type of plastic foam, which would be at the same height as the mats -64-, but slightly wider; the compression of this excess over the tile is what would prevent side leaks; in the previous version, this was the function of the gasket -74- on the side of section -60-. Depending on the length of zones 38, 40 and 42 in figure 3, the length is fixed of the drilled section of tube -66- or, in other words, the length over which the vacuum is applied to the tiles. Figure 8 shows a general layout of pressures, described qualitatively by way of continuation. The pump -68- generates a P0 vacuum, part of which is lost in the ducting to the input to tube -66-. If a pressure of P1 is obtained at the said input, there is a further loss of load in the transition to the tiles, in other words, at the mat, pressure P2 will be greater than P1. As the securing of the material -12- is based on the difference between pressures Pa - P2, P2 needs to be as low as possible, thus requiring the smallest possible loss between the pump output and the mat or, in other words, P2 should be similar to P0, which is the lowest pressure in the entire circuit. The said difference of pressure should be at a maximum in the cutting zone -40-, and, at zone -38-, it should be enough to carry the fabric from the spreading table. At sections A and B, where the loop begins to curve, there is an opening to the atmosphere, so that pressure P2 should increase progressively through the mat, until reaching atmospheric pressure Pa. The vacuum application must be introduced as far as possible into zone -38-; however, if in this zone the pressure is P3, the loss of load Pa-P3 needed at opening B will be obtained with high flows, so that the pump's level of impulsion will not be sufficient. Thus the section zone tends to be concentrated and to be kept away from the open end sections, so as to obtain a good Pa-P3 difference. This gentle drop, because of the length of mat reached, ensures that the material will be sufficiently secured over an area which will allow it to be moved. In the A section on the discharge end, the problem is not so great; all that is required is to take the precaution described above in the method for operation of collection from zone -42-, first, of panels which are nearest to section A and, when the cutting bridge is at the end of the cutting zone -40-, to collect the panels which are inside the collection zone.

Claims: Conveyor table (14) for a numerically controlled cutting machine (1) for cutting vacuum gripped strip material (12), comprising a conveyor consisting of a succession (48) of tiles (58), linked to chains (50) which are driven by a conveyor drive motor (44), and of a plurality of bristle mats (64) forming a penetrable air-permeable cutting table, said bristle mats are fixed on the tiles (58), and a vacuum system with a stationary vacuum source (68), whereby the tiles (58) are parts of the vacuum system and having holes (59) on the upper surface for communication with the bristle mats and openings (62) at the underside aligned and communicating with holes (72) at the topside of a central tube (66) being moored to the frame of the machine and arranged transverse to the tiles and linked to the vacuum source (68), the tiles (58), on which the bristle mats are fixed, are hermetically sealed at the ends by end sections (60), characterized in that the tube (66) has on its upper face a plastic support strip (70) of low friction and with wide openings (72) corresponding with the openings (72) of the tube (66) and rubber strips (76) in contact with the plastic support strip and which rub on the bottom surface of the tiles, and that the tiles (58) are provided with gaskets (74) for preventing leaks between the tiles (58) to complete the hermetic vacuum seal of the inside face of the conveyor working surface. Conveyor table (14) according claim 1, characterized in that the tiles (58) are formed to receive the bristle mats (64) such that after extracting the end section (60) the bristle mats can be removed from said tiles (58).

Inventors: GALAN MARIO ANDRADA, GONZALEZ NARCISO MURILLO, PEREZ BERNARDO ALCANTARA, GALAN, MARIO ANDRADA, GONZALEZ, NARCISO MURILLO, PEREZ, BERNARDO ALCANTARA
Applicants: INVESTRONICA SA, INVESTRONICA S.A.
Application year: 1987
Main classification: D06H7
IPC codes: B25B11, B26D7