Process and apparatus for the cutting to shape of sheets of plastic material

Abstract: In a process and apparatus for cutting to shape sheets of plastic material, the cutting to shape of the plastic material and the handling of the cut shaped sheet takes place by means of a mobile support, such as a pallet (18) on which the centering operations requested for the cutting of the material and the taking-up thereof in an area of assembly of laminate glass are carried out, the pallet (18) passing along a closed circuit, preferably in the presence of a plurality of additional similar pallets (18) (figure 1).

Description: The present invention relates to a process of cutting a continuous plastic material into cut-to-shape sheets. A further object of the present invention is an apparatus suitable for carrying out said process. More in particular, object of the invention is a process and an apparatus suitable for the automatic cutting to shape of sheets of plastic material as they arrive from lines of supply, and for presenting the material thus cut to shape in the area where it is to be finally used. The present invention finds particular application in plants for the production of laminated glass for vehicles or other means of transport, as well as for the production of safety glass in general. From the state of the art are known problems regarding the cutting to shape of plastic materials, for instance of the kind known as PVB (polyvinylbutiral), used in the manufacture of laminated glass, to which specific reference will be made in the course of the description. This glass, as it is known, is made up of two or more sheets of glass glued to each other, said glueing being performed by interposing between the sheets a film of plastic material, which will be indicated in the following as PVB. PVB is a transparent material resistant to tensile stress and it renders the glass shatter-proof as, in the case of breakage, the splinters of glass remain attached to the adhesive film. Multi-layer glass is substantially elastic and is used as a protection against implosion, for example in vehicles. From the state of the art are known systems suitable for the automatic manufacture of laminated glass. These known systems cooperate with suitable supply magazines from which the "male" and "female" sheets of glass are taken one at a time, as well as the shaped PVB film to be placed between the sheets of glass. A system of this kind is described for example in IT-A-83555. The sheets of PVB film are ready-cut to measure at special work stations separate from the glass assembly line, and are then transferred into the supply magazines. Furthermore, from EP-A-0319251 a process and an apparatus are known for automatically manufacturing laminated glass. According to EP-A-0319251 sheet blanks are peeled off and lifted from a stack of PVB sheet blanks, the individual sheet blanks so obtained being placed and positioned on the table of a positioning station, from which they are transferred to a cutting station. The cutting station is suitable for automatically cutting a sheet blank to shape while keeping it fixed on a cutting table, a cutting head being movable along X-, Y-, and Z-axes and being rotatable about the Z-axis. After cutting, the cut-to-shape sheet is lifted from the cutting table and transferred to a film placing station to be inserted between a pair of sheets of glass to be joined together. The invention has the aim of providing a process and an apparatus of the type indicated above, suitable to be perfectly integrated with in-line apparatuses for the assembly of glass laminates. This object is achieved by providing for a process according to claim 1 respectively an apparatus according to claim 9. According to the invention, the cutting to shape of the material, as well as the handling of the material thus cut, takes place by means of a moving support on which said material is positioned. The moving support is a pallet-type element, and this term will be used to indicate it in the following description. The pallet travels in cycle along the working line, passing from a first phase for loading and cutting of the PVB to a final phase in which the cut PVB is delivered to the apparatus for assembly of the glass laminates. Accurate centering of the pallet in the areas in which the PVB is cut and picked up for coupling with the sheets of glass, gives the whole process the desired and necessary precision. The film of cut PVB also retains the desired centering conditions on the pallet during the movements of the pallet itself, so that it is in a predetermined and certain position in the area of cooperation with the apparatus for assembly of the glass laminates. The invention provides for transit of the pallet in a cutting area formed by two cutting stations, operating alternately one to the other. A first station is equipped to perform the cutting of curved or, as it is known, "stretched" material and, with this object, it cooperates with a group for feeding and adjustment of the stretched PVB wound on conical rolls. A second station is equipped for the cutting of so-called "flat" material and, with this object, it cooperates with apparatus for the feeding and adjustment of flat PVB wound on cylindrical rolls, and also with an apparatus known as a slacking apparatus, which has the object of unwinding the material, causing a slack in the latter. Cutting of the sheet of PVB takes place by means of a laser beam in a polar axes apparatus, that is to say with means that move according to polar coordinates with reference to the fixed material to be cut. The cutting stations are suitably equipped to cope with various sizes of shaped PVB, both straight and curved, and can be provided with means for the suction of any fumes that may be released during the cutting operations. Downstream of the cutting stations is provided a pallet rotation station, the function of which is to perform a 180° angular rotation of the pallet. This is required in the case of straight shape, for example those with a trapezoidal shape, which are cut in sequence and next to each other on the film of PVB, but each one placed specularly with respect to the next. The shaped sheets preferably face in the same direction when arriving in the area of cooperation with the glass assembly apparatus situated downstream. From said pallet rotation station, the pallet passes on to one or more waiting and transit stations situated upstream of the PVB take-up station, which is in its turn suitably situated in correspondence with the glass and PVB assembly area. In said PVB take-up station, the pallet with the material to be taken up undergoes a centering operation, and is then taken up. The empty pallet is re-cycled and returned once again to the PVB cutting area. These and other aspects particular to the invention will be better understood from the following description. With reference to the enclosed drawings, provided as a non-limiting example: figure 1 illustrates a plan view of a preferred embodiment of the invention; figure 2 illustrates in a side view and in enlarged scale, according to arrow A, part of the embodiment of figure 1; figure 3 illustrates in a side view and in enlarged scale, according to arrow B, another part of the embodiment of figure 1; figure 4 is an enlarged plan view of a part of the first cutting station of the embodiment of figure 1; figure 5 illustrates details of the station according to figure 4; and figures 6a to to 6e illustrate a preferred embodiment of a pallet used in the embodiment of figure 1. With reference to figure 1 and to figures 2 and 3, which are side views in vertical section according to arrows A and B of figure 1, respectively, the cutting apparatus 10 is made up in this embodiment of a plurality of stations arranged on two working groups which extend at right-angles one to the other. In the first working group are a pallet lifting station 11, a cutting station for stretched PVB 12, a cutting station for flat PVB 13 and a pallet rotation station 14. In the second working group, which, as stated above, is arranged at right-angles to the first, is a pallet transfer station 15, a station 16 for assembly of the sheets of glass with the PVB and a pallet lowering station 17. As a support for the cutting of the PVB and for its transfer into the glass assembly area, a pallet 18 is used, of the type illustrated in figures 6 and described in detail in the following description. The pallet 18 passes successively from the lifting station 11 to the lowering station 17, held in a horizontal position and travelling along said route at a high vertical level, as can be seen more clearly in figures 2 and 3. In the lowering station 17 the pallet 18 is returned to the cycle, being brought back to a lower level of travel (not shown in the drawings), corresponding to a route returning it towards the lifting station 11. Said return route is situated inside the basic structure 19 and is parallel to the outward route. Advantageosly, on the outward and return routes between stations 11 and 17, a plurality of pallets 18 is to be found. When the "re-cycled" pallet 18 arrives at the lifting station 11, it is picked up by the lifting means 20 and, by means of its motor member 21, is lifted onto the posts 22 of the station 11 until reaching the raised position for travelling through the cutting apparatus 10 (see figure 2). From said raised position in station 11 the pallet 18 is tranferred into the successive stretched PVB cutting station 12, for example by means of a blade pusher 23, moving on guides 24 through the action of a jack 25, similar to that which can be seen in the pallet lowering station 17 in figure 1. In the station 12 the pallet 18 is positioned on guide rollers 26, integral with the bearing structure 27 of the cutting station 12, and activated by their own motor means 28. In the station 12 is also present a bell-shaped element 29, which is substantially a box, supported at 30, vertically mobile with the object of bringing the pallet 18 into cooperation with the PVB sheet to be cut, while at the same time performing a centering of the pallet 18 itself. With this object, the bell-shaped element 29 has on its top suitable reference means, for example balls, which are brought into abutment with coordinated reference means situated on the pallet 18 itself, as will be more clearlyy described below. The bell-shaped element 29 is also advantageously under low pressure with the aim of sucking up the fumes given off during the cutting operations. The flat PVB cutting station 12 cooperates with a feeding group 31 for flat PVB, whose function, along with the continuous feeding of the film of PVB, is also that of regulating in real time the position of the film on a horizontal plane when entering cutting station 12. With this object the feeding group 31 has a platform 32 which moves on slide guides 33 by means of a motor means 34, said motor means 34 being servoed to means for the continuous control of the unrolling of the roll of PVB, for intance photocells. The PVB is wound onto a conical roll 35 placed on a vertical axis, said roll 35 cooperating with a tumbling device 36 powered by 37. The tumbling device 36 allows the operations of loading and unloading the roll 35, as well as any angular inclination of the axix of the same with the object of vertically orientating the generatrix of the cone at its unrolling point. With the same object, the conical roll 35 cooperates with tipping means 38, likewise powered by 39, so as to allow a double inclination of the axis of the roll 35 in the orthogonal planes X-Z and Y-Z, Z being the vertical axis of the conical roll 35. The film of PVB unwound from the roll 35 and supported by feeding guide rollers 40, is taken up in the cutting station 12 by pinching means carried by a pair of chain groups, indicated with a dotted line in 41 in figure 1. The chain groups 41, in a closed ring, are suitably powered at 42 and are carried by a pair of carriages 43 which move transversally to the direction of feeding of the film of PVB into the cutting station 12. Said carriages 43 can run in synchronism one towards the other along the bearing structure 27 due to screw means 44 activated by a motor means 45. The relative movement of the carriages 43 is necessary in order to adapt the apparatus to the various heights of the PVB film being worked. At the cutting station 12 are provided means for the adjustment of the curvature of the stretched PVB. With this object, on the carriages 43, curvature adjustment groups 46 are provided, as can be more clearly seen in figure 4. Said groups 46 are formed by a plurality of adjustment blocks 47 having windows 48, by means of which their position on the horizontal plane can be modified to form the desired curved cutting profile. Said adjustment blocks 47 form the guide means for the cain groups 41 in their action of feeding the film of PVB into the cutting station 12. In figure 5 can be more clearly seen the constructive details of the adjustment group 46, in which each block 47 has at the end thereof a C-shaped bar 49 to which are fixed the guide blocks 50 on which the chain 41 runs. To said chain 41 are fixed the pincers 51 driving the film of PVB, said pincers being kept during driving in a closed position, as illustrated in the example of figure 5, in abutment against a plate 52 integral with the block 47. When the plate 52 and pincer 51 are out of abutment, the latter opens, for example through an elastic means, abbandoning its hold on the film of PVB and therefore also ceasing to pull it. The guide plugs 50 are fixed to the C-shaped bar in a position opposite, with regard to chain 41, to that illustrated in figure 5, when it is required to make on the second carriage 43 a curvature complementary to that on the first carriage 43, as can be seen in figure 1. In the case of feeding of flat PVB which can take place at the successive station 13, on the C-shaped bar 49 the guide plugs 50 are fixed on both sides with respect to the chain 41. In figure 4 is shown, also in an enlarged vertical section, an eccentric group 53 for aligning the end of chain 41 with the first adjustment block 47 according to the various possible cutting curves. This alignment is made by moving a lever 54 which causes the rotation of an eccentric pin 55 which is integral with the pinion 56 of the chain 41. On reaching the desired position, it is fixed by means of suitable blocking wedges 57. Cutting of the PVB takes place by means of a laser beam cutting unit, preferably of the polar type or the like accomplishing the cutting by variation of its polar coordinates and x. With this object the laser beam generator is mounted on a rotating platform 59, on the arm 60 of which can be moved in a linear direction the optical group for 90° reflection and focusing of the beam 58 in order to obtain the desired coordinate x. The cutting apparatus is mounted on a carriage 61 which is movable above the structure of the stations 11 and 12 so as to perform alternately cutting of the stretched PVB at 12 or the cutting of the flat PVB at 13. The moving carriage 61, activated by the motor means 62, positions itself in the desired cutting area by means of suitable stops 63. Said carriage 61 also carries the console for the laser generator 64, as well as a service console 65 for control and adjustment of the operating functions connected to the performance of cutting. By means of said console 65, for example, the working parameters relating to the optic group 58, to the axes of the four chains 41 in the working stations 12 and 13, and to the power of the laser beam are controlled and coordinated. To each cutting station 12 or 13 can be associated a bin for collection of the waste produced during cutting. The station for cutting of flat PVB 13 has a conformation substantially similar to the station for cutting of stretched PVB 12, with the adjustments required. It cooperates with a group for feeding the flat PVB 66, having the function of feeding the film of PVB and of regulating in real time the transversal position of the film on entering the cutting station 13, so as to keep it aligned with the chain groups 41 of the station 13. The transversal regulation can take place by means of an axis governed by optical means which read for istance the position of one of the two edges of the film. For said transversal regulation the group 66 is provided with two pairs of motor feeder rollers 67 mounted on a support structure 68 moving on a platform 69 by means of a suitable motor meand, the latter being for example governed by photocell means. The PVB forms a loop between the pairs of rollers 67 so as to form a slack in the material to avoid stretching. The flat PVB feeding group 66 cooperates upstream with a slacking apparatus 70 for slacking off the material. In the pallet rotation station 14 the pallet 18 can be rotated, according to requirements, by 180° before being sent on to the following stations by means of a pusher 23, as previously illustrated for station 17. Station 14 is formed by a structure for the housing and running of the pallet 18, similar to the previous ones, and cooperates with a shelf structure 71, bearing the activating means of an orientation chuck 72. Said chuck 72 is provided at its end with moving pincers 73 for picking up the pallet 18, in order to lift it and rotate it. The pallet transfer station 15 is built in a similar manner to the previous one, and is a waiting and transit station. In figures 1 and 3 are illustrated in said station 15 and in the following station 16 a means for stopping the pallet 18 in position, for example by means of a lever 74 activated by a jack 75. In the assembly station 16 the cut to shape PVB is picked up from its respective pallet 18 to be inserted between the sheets of glass 76 in the respective glass assembly station 77. In said station 16 the pallet 18 is temporarily lifted into a known and predetermined position for picking up of the PVB, centering of the pallet 18 itself being performed during said lifting. Said operation is performed in effect by means of four centering groups 78, substantially placed in correspondence with the corners of the pallet 18 and formed for example by piston groups with a contact sphere at their ends. The pallet 18 is illustrated in figures 6, in which 6a illustrated a plan view, 6b a side view and figures 6c, 6d and 6e the enlarged partial sections according to arrows C, D and E, respectively. Pallet 18 is formed by a frame 79, preferably metal, containing grill-shaped bearing planes 80 for the sheet of PVB. It has transversal grooves 81 suitable to house outer fork carrier means, indicated with a dotted line in 82 in figure 1, for removal of the shaped PVB from the pallet 18. For lifting and complete centering of the pallet 18 by means of the sphere means mentioned above, the frame 79 has in this case at its corners a cone reference 83 (figure 6c), two flat references 84 (figurs 6d) and a V-shaped reference 85 (figure 6e). The empty pallet 18 passes successively to the descent station 17, in which, by means of a suitable descender 86 activated by motor means 87, it is brought down to the lower transit level descending along the uprights 88. In said lowered position it is pushed, as stated, by the pusher 23 onto the means for returning it to station 11, said means being a roller, or belt, or chain conveyor or any other means suited to this purpose. While a description has been given of a preferred embodiment of the invention, it is evident that for those skilled in the art a number of variations are possible without departing from the scope of the invention as defined by the claims.

Claims: Process of cutting a continuous plastic material into cut-to-shape sheets, in particular of the PVB type used in the manufacture of laminated glass, said plastic material being either flat or stretched into a curved shape, said cut-to-shape sheets being picked up one at a time in correspondence with a production line for laminated glass in order to be inserted between a pair of sheets of glass to be joined together, in which said cutting to shape of the continuous plastic material as well as the movement of the cut-to-shape sheets takes place using a pallet (18), upon which are carried out the required operations of centering for the cutting of the plastic material into sheets and for the transfer thereof in the assembly area for laminated glass, said pallet (18) being made to move, preferably in the presence of a plurality of other pallets (18) of the same kind, along a closed circuit route, and in which the following working phases are carried out automatically and in succession: positioning of the pallet (18) in correspondence with the start of cutting cycle; transferring the pallet (18) into a cutting area formed by a cutting station for the plastic material stretched into a curved shape and a cutting station for the flat plastic material; spatial centering of the pallet (18) substantially contemporarily with the feeding of the plastic material into one of the cutting stations to set said material down on said pallet (18); cutting the continuous plastic material into cut-to-shape sheets using a laser beam cutting system operating along polar coordinates, and keeping the material to be cut fixed and moving the cutting system, said laser beam cutting system alternatively serving the cutting station for the plastic material stretched into a curved shape and the cutting station for the flat plastic material; transferring of the pallet (18) with the cut-to-shape sheet, its rotation by 180° if necessary, and its positioning in a transit area upstream of said assembly area for laminated glass; transferring the pallet (18) with the cut-to-shape sheet into the area of cooperation with the apparatus for the assembly of the laminated glass; spatial centering the pallet (18); picking-up the cut-to-shape sheet from the pallet (18); transferring the empty pallet (18) into an area for recirculation of empty pallets (18); transferring the empty pallet (18) to reposition it in correspondence with the start of a new cutting cycle. Process according to claim 1, characterized by the fact that the closed circuit route of the pallet (18) takes place on two parallel transit lines arranged on horizontal planes having different vertical levels. Process according to claim 1 or 2 , characterized by the fact that the cutting stations of the stretched into a curved shape and flat plastic material cooperate with a system for the feeding, control and automatic adjustment of the position of the plastic material being fed in. Process according to anyone of the preceding claims, characterized by the fact that the curvature of the curved plastic material to be cut can be adjusted. Process according to anyone of the preceding claims, characterized by the fact that the cutting station of the flat plastic material cooperates with a system (70) placed upstream for slacking off the material. Process according to anyone of the preceding claims, characterized by the fact that it provides for the cutting of plastic material of various widths, as desired. Process according to anyone of the preceding claims, characterized by the fact that the spatial centering of the pallet (18) is performed by the engagement of reference means (83, 84, 85) in the pallet (18) with respectives centering means placed in the cutting and assembling stations. Process according to anyone of the preceding claims, characterized by the fact that the area for pickup of the cut to shape sheets from the pallet (18) forms an integral part of the production line for laminated glass. Apparatus for the cutting of a continuous plastic material into cut-to-shape sheets, in particular of the PVB type used in the manufacture of laminated glass, said plastic material being either flat or stretched into a curved shape, said cut-to-shape sheets being picked up one at a time in correspondence with a production line for laminated glass in order to be inserted between a pair of sheets of glass to be joined together, said apparatus being suitable for carrying out the process as claimed in claim 1, the apparatus comprising a structure having an upper line (26) for outward transit of the pallets (18) and a lower line (19) for return transit of said pallets (18), said transit lines (26, 19) forming part of the following main working groups placed one after the other: pallet raising station (11); cutting station (12) for PVB plastic material stretched into a curved shape; flat PVB plastic material cutting station (13); pallet rotation station (14); pallet transfer station (15); assembly station (16); pallet descent station (17), said cutting stations (12, 13) being provided with a laser beam cutting group (58-65) operating along polar coordinates and alternatively serving the cutting station for the PVB plastic material stretched into a curved shape and the cutting station for the flat PVB plastic material ; and with a group for feeding in stretched PVB plastic material (31) and a group for feeding in flat PVB plastic material (66), respectively. Apparatus according to claim 9, characterized by the fact that said cutting group is formed by a moving carriage (61) bearing a rotating platform (59), an arm (60) and an optical group (58) running on said arm (60), along with a laser generator console (64) and a service console (65). Apparatus according to claim 9 or 10, characterized by the fact that the pallet raising station (11) has lifting means (20, 21, 22) for the pallet (18) to be recirculated. Apparatus according to anyone of claims 9 to 11, characterized by the fact that each cutting station (12, 13) is provided with pincer pulling means (41, 42, 51) for pulling the plastic material. Apparatus according to claim 12, characterized by the fact that said pincer pulling means (41, 42, 51) are mounted on moving carriages (43) arranged symmetrically. Apparatus according to anyone of claims 9 to 13, characterized by the fact that each cutting station (12, 13) is provided with a bell-shaped element (29) for raising the pallet (18). Apparatus according to claim 14, characterized by the fact that said bell-shaped element (29) is under vacuum. Apparatus according to claim 14 or 15, characterized by the fact that said bell-shaped element (29) has means for raising and centering the pallet, preferably of a spherical kind. Apparatus according to anyone of claims 9 to 16, characterized by the fact that the pallet (18) has reference and centering means (83, 84, 85). Apparatus according to anyone of claims 9 to 17, characterized by the fact that the cutting station for the stretched material (12) has means for the adjustment of the curve of the material (46). Apparatus according to anyone of claims 9 to 18, characterized by the fact that said stretched PVB feeding group (31) is made up of a moving platform (32) carrying loading and unloading means (36) for the package (35) of plastic material with a vertical axis. Apparatus according to claim 19, characterized by the fact that said package (35) of plastic material has means for the adjustment of its inclination. Apparatus according to anyone of claims 9 to 20, characterized by the fact that said stretched PVB feeding group (31) has means for the control of the posision of the material being unwound. Apparatus according to anyone of claims 9 to 21, characterized by the fact that said flat PVB feeding group (66) is formed by a structure (68), moving on a platform (69), carrying rollers (67) feeding in the plastic material. Apparatus according to anyone of claims 9 to 22, characterized by the fact that said flat PVB feeding group (66) has means for control of the position of the material being fed in. Apparatus according to anyone of claims 9 to 23, characterized by the fact that said pallet rotation station (14) has a structure (71) bearing pincer gripping means (73) and chuck rotation means (72) for the pallet (18). Apparatus according to anyone of claims 9 to 24, characterized by the fact that said assembly station (16) has centering groups (78) of the pallets (18). Apparatus according to anyone of claims 9 to 25, characterized by the fact that pallet descent station (17) has lowering means (86, 87, 88) for the pallet (18) to be recirculated. Apparatus according to anyone of claims 9 to 26, characterized by the fact that the upper transit line is formed by rollers (26) which are motorized (28). Apparatus according to anyone of claims 9 to 27, characterized by the fact that said pallet raising (11), pallet rotation (14) and pallet lowering (17) stations have means for the expulsion of the pallet (23, 24, 25). Apparatus according to anyone of claims 9 to 28, characterized by the fact that said working stations (11-17) are arranged in a right-angled route. Apparatus according to anyone of claims 9 to 29, characterized by the fact that the assembly station (16) is an integral part of the assembly line (77). Apparatus according to anyone of claims 9 to 30, characterized by the fact that said flat PVB feeding group (66) is arranged immediately downstream of a slacking apparatus (79). Apparatus according to anyone of claims 9 to 31, characterized by the fact that said cutting stations (12, 13) are provided with means for collecting waste.

Inventors: DE LEONIBUS VITTORE, GILLI LUIGI, DE LEONIBUS, VITTORE, GILLI, LUIGI
Applicants: SIV SOC ITALIANA VETRO, SOCIETA' ITALIANA VETRO- SIV-SPA
Application year: 1991
Main classification: B32B17
IPC codes: B29C37, B32B17