The invention generally relates to the handling and transportation of stacked sheets, in particular stacked sheets of fiber reinforced material that are to form a laminate.

Sheets or‘plies’ can be used for manufacturing fiber reinforced composite products. The fiber reinforced material can be supplied on relatively long and narrow tapes that are rolled up on a roll. Such tapes may e.g. be produced by impregnating a planar layer of parallel, longitudinally extending continuous fibers with a matrix material. The fibers may include carbon fibers, aramid fibers or other types of reinforcement fibers, and the matrix material may include thermosetting resin, or thermoplastic plastics material. The fiber reinforced material may be dry, but may also be impregnated. In addition, the plies may comprise a backing material.

Rolls of fiber reinforced tape material, in particular UD tape, are uncoiled and sections of tape or plies are typically cut from a sheet of uncoiled tape. Sheets of a predetermined length can be cut off, e.g.

transversely along the width of the relatively narrow tape, preferably such that the sheets have a substantially rectangular shape. The sheets may be subsequently stacked on top of each other. The stacked sheets may be temporarily welded together and transported for further processing, in particular a process in which heat and/or pressure is applied to the stack so as to obtain a fiber reinforced laminated product.

When subjecting the stacked sheets to transport, such as by conveyor belt, the stack may suffer loss of integrity. In particular, sheets in the stack may become contaminated, and sheets may wrinkle or shift relative to each other. This can give rise to visual defects and compromise the physical integrity of the stack in the further processing of the stacked plies. The invention aims to mitigate at least some of the above

mentioned drawbacks. In particular, the invention aims to provide an end effector, a system of an end effector and a robot arm, and a method for handling a set of press plates and stacked sheets.

According to a first aspect of the invention there is provided an end effector for handling a set of press plates and stacked sheets to be

sandwiched there between, comprising a carrier with a central portion and a peripheral portion. The central portion is provided with a number of suction grippers arranged to operate in a suction plane. The peripheral portion includes a number of hooks, each hook having a stem that is arranged to reach through the suction plane, and a catch carried thereon having a carrying face arranged to operate in a carrying plane parallel to the suction plane. The hooks are movably disposed, so that the catch can move along the carrying plane between a first position in which the catch can pass through a set of aligned handling apertures in the set of press plates, and a second position in which the catch hooks behind a periphery of a handling aperture in a bottom press plate of the set of press plates. By providing hooks that operate in a carrying plane, and that reach through the periphery of a suction plane, the end effector may efficiently handle a set of press plates and stacked sheets to be sandwiched there between so that the stack retains it integrity. In particular, the press plates and the sheets may be efficiently held together as a tight package in which the sheets are protected and held in place, so that contamination, wrinkling and shifting of the sheets is counteracted.

The sheets can be of various shapes. They can be cut or sectioned off perpendicularly to the length of the tape, so that the cut or sectioned sheets have a substantially rectangular shape. Such sheets are preferred. However, the sheets can also be cut or sectioned off obliquely to the length of the tape, so as to form a sheet that is shaped as a triangle, trapezoid or parallelepiped, and the sheets can also be cut or sectioned off with a curved cutting line. Also, the sheets may be cut out in any shape from a web of material, e.g. using a numerically controlled cutter. It is of course also possible, by using rolls of tape having off-axis fiber orientations or cross-ply tape, to cut or section off sheets with correspondingly different fiber orientations.

Optionally, the hooks are arranged such that when they are in the second position they abut with their stems to a peripheral edge of the bottom press plate, so as to tension at least the bottom plate in the carrying plane. The tensioning of the bottom plate may form a pre-tensioning that prevents or at least reduces the curvature of the bottom press plate under its own weight and that of the stacked sheets and the top press plate during transport thereof. In addition, also the top plate may be tensioned, and the top and bottom plates may also be held tightly together to sandwich the stack due to catch action of the hooks transverse to the carrying plane. This is increasingly important for press plates which are relatively thin. Curving or bending of the bottom plate may induce defects in the connection between sheets in the stack of sheets that can e.g. cause delamination, voids and wrinkles to develop and/or occur in laminated products. The top and bottom press plates may be between 1— 5 mm in thickness to allow for a desirable thermal conductivity to the stacked sheets sandwiched between these press plates.

Optionally, hooks are disposed in a pair to move away from each other between the first position and the second position and preferably the hooks are arranged in diametrically opposed pairs. Optionally, a line of tension between hooks of a first pair, and a line of tension between a second pair cross, such that the crossing of those lines corresponds to the center of the plate.

Optionally, the effector comprises abutting surfaces surrounding the stems of the hooks and extending parallel to the carrying plane, arranged for cooperating with a top face of a top press plate of the set of press plates. The abutting surfaces are here the carrying surface of the hooks on which in the second position, the bottom plate is rested for carrying.

Optionally, the end effector comprises four suction grippers. A benefit is that this allows gripping at several interspaced locations, so that the end effector can handle a stack of sheets in such a manner that the downward bending or sagging of the stack of sheets is prevented. Thus preventing defects in the connection between sheets of the stack.

According to a second aspect of the invention there is provided a system of a robotic arm and an end effector according to the first aspect of this invention. The end effector is connected to a distal end of the robotic arm. The robotic arm may be provided with a computer system arranged for operating the movement of the arm and end effector components such as the hooks and suction grippers.

According to a third aspect of the invention there is provided a method for handling a set of press plates and stacked sheets, in particular according to claim 1. The method comprises gripping and placing of a bottom press plate, gripping and placing of the stacked sheets onto the bottom press plate, and gripping and placing of a top press plate onto the stacked sheets such that the sheets are sandwiched between the bottom and top press plates. This allows the stacked sheets to be prepared for transport, such as by a conveyor.

Optionally the method further comprises gripping of the set of press plates with a stack of sheets sandwiched there between, and

tensioning of the bottom press plate, in outward direction along its plane, for transport, and transporting of the set of press plates with the stack of sheets there between to a station or between treatment stations. A benefit is that this allows construction and transport means to be integrated into the same system. Accordingly, the system requires fewer components to work. Note that a treatment station can e.g. be a pressing station or a heating or cooling station.

Optionally, the method comprises gripping and removing of the top press plate, and gripping and separating of the treated stack of sheets from the bottom press plate. The separation of the treated stack of sheets from the bottom press plate preferably occurs by gripping and removing the treated stack of sheets, and by subsequently gripping and removing the bottom press plate. The top plate can be removed from the package by lowering the end effector, the hooks being in the first position, wherein the end effector is lowered to a level in which when the hooks are moved into the second position, the hooks only hook the top plate. Subsequently, the hooks are moved into the second position and the end effector is then raised to remove the top plate. The top plate can be returned to a source of the press plates. The end effector can subsequently be used to separate the treated stack of sheets from the bottom plate via the suction grippers. The end effector is lowered with the hooks in the first position. The end effector is lowered such that the hooks are moved through the aligned handling apertures of the bottom plate. The end effector is raised after gripping the treated stack of sheets using the suction grippers. The hooks remain in the first position such as to prevent gripping of the bottom plate. The treated stack of sheets is delivered to an end station. The end effector may further also proceed to grip and move the bottom plate to the source of the press plates for later reuse.

Optionally, the method further comprises the machining of the removed stack of treated sheets, preferably along a single side thereof, to include a straight reference edge, in particular a reference edge having a face that extends perpendicularly to a plane of the stack of sheets. The machining may e.g. occur by a cutter, mill or trimmer. A benefit is that the treated stack of sheets can be distinguished from the pre -treated stack of sheets by having a single straight edge. Additionally or alternatively, the reference edge may be provided for positioning and/or alignment of the machined stack of treated sheets during further steps towards a final product.

According to a further aspect of the invention there is provided compressed stack of fiber reinforced laminate, comprising a stack of superimposed substantially planar sheets, the stack including fiber reinforced sheets, preferably sheets of fiber reinforced material having a bundle of parallel longitudinally oriented fibers embedded in a matrix material, in particular a thermosetting or thermoplastic matrix material, which sheets have been mutually consolidated together by heat and/or pressure, and wherein the stack has been machined along a side thereof, preferably a single side thereof, to include a straight reference edge, in particular a reference edge having a face that extends perpendicular to the plane of the stack of fiber reinforced laminate. The stack of sheets with the machined reference edge may form an intermediate product, in which the reference edge is provided for positioning and/or alignment of the

intermediate product during further steps towards a final product.

Optionally, the reference edge is substantially parallel or perpendicular to the direction of the longitudinally oriented fibers of at least one outer sheet of the stack. A benefit is that this prevents delamination of sheets or fibers in the stack during the cutting of the stack. A further benefit is that no close-up inspection is required to derive the orientation of certain fibers in the stack of sheets, as the orientation now can be

determined by means of the edge.

According to yet another aspect of the invention a method is provided for machining a compressed stack of fiber reinforced laminate sheets, in particular as an intermediate product, the stack comprising superimposed substantially planar sheets, and including fiber reinforced sheets, preferably sheets of fiber reinforced material having a bundle of parallel longitudinally oriented fibers embedded in a matrix material, in particular a thermosetting or thermoplastic matrix material, which sheets have been mutually consolidated together by heat and/or pressure. The stack is machined along a side thereof, preferably a single side thereof, to provide a straight reference edge, in particular a reference edge having a face that extends perpendicularly to the plane of the stack. The reference edge may be provided for positioning and/or alignment of the intermediate product during further steps towards a final product.

It will be clear to the skilled person that the technical features of the present invention can be advantageously used for handling stacked sheets not only each alone but also in any possible combination. The technical features described in the paragraphs can be isolated from the context, and the isolated technical features from the different paragraphs can be combined. Such combinations are herewith specifically disclosed in this description.

The invention will be further elucidated on the basis of a non limiting exemplary embodiment, which is represented in the drawings. In the drawings:

Fig. 1 shows a perspective view of an end effector for handling a package according to the invention;

Fig. 2 shows a top down view of cross section A- A of the end effector according carrying the package;

Fig. 3 shows an exploded view of the package;

Fig. 4 shows a schematic view of a system of a robotic arm and the end effector according to figure 1;

Fig. 5A-B show a schematic side view of part of the end effector according to figure 1 in which the hooks of the end effector are in a first position in figure 5A and in a second position in figure 5B; and

Fig. 6 shows a schematic top view of a treated stack of fiber reinforced laminate. It is noted that the drawings are only schematic representations of a preferred embodiment of the invention. In the drawings, identical or corresponding parts are represented with the same reference numerals.

Figure 1 shows a perspective view of an end effector 1 which is arranged for handling press plates 31, 33 and stacked sheet 35 and a package 10 of a set of press plates 31, 33 and stacked sheets 35 sandwiched there between. However, it will herein further also be explained that the effector 1 is arranged for handling each press plate and stack of sheets separately. The effector 1 comprises a support frame 3 having a first face 4, which first face 4 defines a connective structure 5 by which the effector 1 is, in use, connected to a robotic arm 2 (shown in figure 4) for moving the effector 1 in a vertical direction 7, such as defined by gravity, and in a horizontal direction 8. The support structure 3 further has a second face 9. The second face 9 has a central portion 11 and a peripheral portion 13. The central portion 11 comprises a set of four suction grippers 15. i (i = 1, 2, 3, 4} each having a carrying face that is arranged to operate in a suction plane A (shown in figures 5A and 5B). The peripheral portion 13 comprises a set of four hooks 17. i {i = 1, 2, 3, 4}. Each hook 17.i has a stem 19 that is arranged to reach through the suction plane A as can be seen in figures 5A and 5B. Each hook 17. i further has a catch 21 which has a carrying face 23 arranged to operate in a carrying plane B which is parallel to the suction plane A. Each hook is 17. i is hinged by its stem 19 and actuated by a reciprocating mechanical actuator 25. The hook 17.i is arranged to be moved by the actuator 25 from a first position (shown in figure 5 A) into second position (shown in figure 5B) and vice versa. In the first position the hook 17.i assumes a retracted position wherein it is tilted such that, from an imaginary top view X of the hook, the carrying face 23 of the hook 17.i would be hidden behind the stem 19. Top view X is here defined as a line of sight that is vertically downwards from above a hinge point 20 of the hook 17.i. In the first position each hook 17.i is able to pass through a corresponding aligned handling aperture 37.i, 39. i when the end effector is lowered or raised without the carrying face 23 of the hook 17.i becoming snagged behind a periphery of such an aperture. In this example the corresponding apertures 37. i, 39. i, are disposed on a press plate 31, 33, and the apertures 37. i, 39. i and hooks 17. i are vertically aligned. In the second position the hooks 17.i are oriented such that a carrying surface 29 of the carrying face 23 of each hook 17.i is parallel to the carrying plane B. This second position allows the hooks 17.i to catch behind the periphery of the handling apertures 37.i, 39.i in said press plate 31, 33, thereby allowing the press plate 31, 33 to be lifted when the end effector is raised. The hooks 17. i are disposed in two diametrically opposed pairs, namely 17.1 and 17.4, and 17.2 and 17.3 to move away from each other between the first and the second position. The stems the hooks 17. i have a length suitable for allowing a plurality of press plates 31, 33 and stacked sheets 35 to be lifted by means of the end effector 1. The press plate 31, 33 can be released from the end effector 1 by moving the hooks from the second position into the first position. The end effector 1 is further arranged to, in a separate operation, grip a horizontally disposed stacked sheets 35 by lowering the effector to meet the stacked sheets 35 in suction plane A and engaging the suction grippers 15.i such that the stacked sheets 35 are sucked onto the suction grippers 15. i. By cessation of suction through the suction grippers 15. i the stacked sheets 35 are released by the end effector 1.

Figure 2 shows a top down view of a horizontal cross section A-A of an end effector 1 carrying the package 10 of a set of press plates 31, 33 and stacked sheets 35 such as shown in figure 4. An exploded view of the package 10 is shown in figure 3. The set of press plates 31, 33 comprises a top press plate 31 and bottom press plate 33. The top and bottom press plates 31, 33 are substantially identical and are of a metal or alloy material. In this example the top and bottom press plates 31, 33 are of SEA 304 stainless steel. However, other steel types such as SEA 306 stainless steel are also possible as are other metals and alloys. The press plates 31 ,33 are each 1— 5 mm in thickness approximately 0.5— 1 m in width and 0.5— 1 m in length. It will be understood that press plates 31, 33 may also be sized differently. In order to allow the end effector 1 to handle each of the press plates 31, 33 the top press plate 31 comprises a set of four apertures 37. i {i = 1, 2, 3 , 4}. Each of the apertures 37. i is arranged for being vertically aligned with a corresponding hook 17.i. The bottom press plate 33 also has a set of four apertures 39.i {i = 1, 2, 3 , 4}. Each of these apertures 39.i are also arranged for being vertically aligned with a corresponding hook 17. i. The manner in which a package 10 is built and transported will be discussed below.

In practice a system 6 of the robotic arm 2 and the end effector 1 is used to assemble the package 10 and for handling the package 10 further. Figure 4 shows such a system 6. The end effector 1 is connected to a distal end of the robotic arm 2. The movement of the robotic arm 2, the actuation of the hooks 17.i by means of actuators, and actuation of suction grippers 15. i are controlled by a control unit (not shown, but customary), such as a computer.

The system 6 is arranged for assembling the package 10 by retrieving a bottom press plate 33 from a predefined location XI by gripping and lifting the bottom press plate 33 using the hooks 17.i of the end effector 1, wherein XI is the source location of press plates. The bottom press plate 33 is moved to and released at a package 10 building surface X2. The system 6 is further arranged for retrieving the stacked sheets 35 from location X3 using the suction grippers 15.i of the end effector 1, wherein X3 is the source location of stacked sheets. The stacked sheets 35 are then placed onto the bottom press plate 35. The top press plate 31 is also retrieved from location XI and placed onto the stacked sheets 35 and bottom press plate in such a manner that the sheets 35 are sandwiched between the top and bottom press plates on surface X2, and such that the apertures 37. i of the top plate 31 and the apertures 39. i of the bottom plate 33 both align with the hooks 17.i of the end effector 1.

The system 6 is arranged for handling the package 10 by lowering the end effector 1, the hooks 17. i being in the first position, such that the hooks 17.i pass through the aligned handling apertures 37. i, 39.i of the top and bottom plates 31, 33. Subsequently extending the hooks 17. i to their second position and raising the end effector 1 such that the hooks 17. i catch behind the periphery of the apertures 39. i of the bottom press plate 33 only. The hooks 17. i are further arranged to abut with their stems 19 to a peripheral edge of the bottom press plate 35, this allows the hooks 17.i to exert a force that tenses the bottom plate 35 along its carrying plane, and when e.g. the circumferential edges of the apertures 39. i of the bottom press plate 35 are made to match up with the circumferential edges of the apertures 37. i of the top press plate 31, so that they both abut the stem 19 of the hook. The hooks 17.i are in this example each pre-biased into the second position by a spring element (not shown, but conventional). Accordingly, the spring element can provide a force to (pre-)tension the bottom plate 35 and also the top plate 31 . However, alternatively, in the absence of a spring element, the actuator 25 could provide a force to (pre-)tension the bottom plate 35, and the top plate 31. In addition, a catch action of carrying face 23 of the catch 21 of the hooks 17. i transverse to the carrying plane B when the hooks 17.i move towards the second position can be used to press the top press plate 31 and de bottom press plate 35 together between the carrying face 23 of the hooks 17.1 and an abutment face for the top press plate 31 provided at the stems 19, e.g. on the outgoing part of the actuator 25. This tightens the package, and further secures the integrity of the stacked sheets 35 that are sandwiched between the press plates 31, 33. The package 10 is subsequently transported to a first treatment station X4 and placed there.

In this example, treatment station X4 is a heating station for heating the package 10. The system 6 is further arranged to retrieve the package at treatment station X4 and transport the package 10 to a second treatment station X5. In this example, treatment station X5 is a compression station for pressing the top and bottom press plates 31, 33 towards each other.

The system 6 is further arranged for deconstructing the package at a deconstruction station, wherein the top press plate 31 is gripped and removed from the package, and the now treated stack of sheets 35 is separated using the suction grippers 15.i and placed on a cutting station X6 for cutting. The bottom plate 33 is subsequently also gripped and removed. The now treated stack of sheets 35 is in this example cut at the cutting station X6 along a single side thereof to include a straight reference edge 43, such as shown in figure 6. The face B-B of this reference edge 43 extends perpendicular to a plane P of the stacked sheets 35.

Figure 6 shows that the now treated stack of sheets 35 is a compressed stack of fiber reinforced laminates. The stack consists of superimposed substantially planar sheets. The stack 35 includes fiber reinforced sheets, preferably sheets of fiber reinforced material having a bundle of parallel longitudinally oriented fibers embedded in a matrix material, in particular a thermosetting or thermoplastic matrix material, which sheets have been mutually consolidated together by the previously applied heat and/or pressure. The temperature to which the heating station X4 heats the package 10 e.g. corresponds to the glass transition temperature of the thermoplastic material used. In this example the thermoplastic material is polyethylene, but other thermoplastics are also possible. The pressure exerted on the package by the compression station X5 corresponds to the pressure required to fuse and/or consolidate the sheets together. This depends entirely on the material. The pressure may vary between 0.1 - 10 MPa. The reference edge 43 is substantially parallel to the direction of the longitudinally oriented fibers of the top and bottom sheets of the stack 35.

Accordingly, there is described an end effector, system and methods for handling stacked sheets, such as fiber reinforced laminate, a compressed stack of fiber reinforced laminate and a method of machining the compressed stack of fiber reinforced laminate. The end effector is arranged for handling a set of press plates and stacked sheets to be sandwiched there between and comprises a carrier with a central portion and a peripheral portion. The central portion is provided with a number of suction grippers arranged to operate in a suction plane. The peripheral portion includes a number of hooks, each hook having a stem that is arranged to reach through the suction plane, and a catch carried thereon having a carrying face arranged to operate in a carrying plane parallel to the suction plane. The hooks are movably disposed, so that the catch can move along the carrying plane between a first position in which the catch can pass through a set of aligned handling apertures in the set of press plates, and a second position in which the catch hooks behind a periphery of a handling aperture in a bottom press plate of the set of press plates.

As for the scope of this disclosure, it is pointed out that technical features which have been specifically described may be susceptible of a functional generalization. Furthermore, it is pointed out that - as far as not explicitly indicated - such technical features can be seen separately from the context of the given exemplary embodiment, and furthermore can be seen separately from the technical features with which they cooperate in the context of the example.

As for the scope of protection, it is pointed out that the invention is not limited to the exemplary embodiment represented here, and that many variants are possible. Such variants will be clear to the skilled person and are understood to fall within the scope of the invention as set forth in the following claims.