Method and apparatus for gripping and separating sheets
BACKGROUND OF THE INVENTION 
     The invention is particularly used for the gripping of textile sheets, but can also be used for other sheet materials which allow the penetration or pointed tips into the surface structure, the tips serving for the removal of the respective top sheet or layer from the stack, as well as for the secure holding of the sheet during transport within the production process. 
     Methods and apparatus for the separating of textile sheets from a stack are known, in which needle-like gripping devices penetrate the material, grip the top material layer and remove it. Various constructions of needle gripping devices have been developed. There are, for example, apparatus, which grip the top layer with needle-like elements, pointing in an obliquely outward direction, penetrating the material, and with the material being subsequently stretched because of the expansion of these elements. The danger of damage to the material is considerable, since in order to securely grip the material layer, sufficient force has to be present to spread the needles. 
     Another method introduces needles, directed opposite to one another, into the material in such a way that they cross over inside the material, thus allowing a punctiform gripping of the top material layer. These types of apparatus require high production and monitoring costs, since their functioning depends on the accuracy of the depth of penetration of the needles, as compared to the strength or thickness of the material. 
     In an additional group of methods, the top layer of a stack of textile sheets is lifted, with gripping devices pushing the material into a fold by their gripping movements, and in this manner gripping the material. Apparatus configurations are known, which differ from each other in the way by which they push the material together to a fold. The folding, which is typical for this method, has the disadvantage that the displacement of the top layer of material which is, necessary for the fold formation, requires the overcoming of frictional forces along the mating surfaces of the material layer to be gripped, and the material layer underneath it. An improvement of the attachment between the contoured bottom sides of the gripping device and the upper side of the top material layer, by increasing the attachment power of the gripping apparatus, is successful only in the case of smooth materials, however, this increases the probability that several layers will be gripped at the same time. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to develop a method and a gripping apparatus, with which, at low cost, stacks of sheets particularly textile sheets, can be securely separated, eliminating permanent monitoring. The use of the invention is coordinated into the particular technological process, and is controlled by remote control. 
     It is another object and the technical task of the invention to develop a method and a gripping apparatus with which in particular textile sheets, but also other sheet materials as well, having a surface structure which allows the penetration of pointed tips, can be securely gripped and held, while reducing the adhesive effect between two layers of textile sheets or other materials, and with gradual positioning of the gripping devices used for the method, with the objective of reducing monitoring expenditures for the precise attachment of the gripping devices. The gripping of several layers at the same time is avoided, with the gripping device piercing the surface structure of the top layer or a stack of sheets, without completely penetrating it. 
     These and other objects and advantages of the present invention will become evident from the description which follows. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The objects are accomplished in the present invention by clamping jaws, arranged on the gripping device, and divided and spaced apart, and having rows of pointed tips, located parallel to one another at the edges of an aperture jaws which jaws, when open, attach via their planar bottom side to the upper surface of the textile sheet to be gripped, with the pointed tips, which are located perpendicular to the planar bottom side, piercing the upper surface structure. The depth of penetration depends on the length of the pointed tips and is additionally limited by the large support area of the planar bottom side of the clamping jaw, as compared to the points themselves. Having been attached, the clamping jaws are closed. The minimal aperture prior to the closing, assures that only a small portion of the upper surface of material structure is gripped between the points subsequent to the closure and held. The gripping devices are preferably fastened to a holder in a row, or a plurality of parallel rows in such a way that the bottom sides, prior to the attachment of the clamping jaws, are spaced at different distances from the upper side of the top layer of textile sheets. The holder with the gripping device is lowered so that all clamping jaws, elastically or spring mounted in the gripping device, lie against the upper side of the textile sheet. With the lifting of the holder, the seized textile sheet is lifted, according to the set distance, so that preferably every other gripping device still holds the textile sheet down, while the intermediary gripping device lifts the textile sheet. Thus, the adhesive effect between adjacent sheets is reduced. This is an advantage of the invention. The elastically mounted clamping jaws enable position monitoring of the holder, in relationship to the respective top layer of textile sheets in the stack, in discretely staggered steps. Following the lifting, in support of the transport of the textile sheet, and when required, and if the gripping devices attach at an edge of the textile sheet, additional finger grippers position themselves to the planar bottom side of the clamping jaw, holding the intermediary textile sheet. When separating stacks, prior to the first lifting stage or process, needles are stuck through the stack from below, with the point of the needles piercing the top layer immediately behind the attached gripping devices, securing the stack in its position. Having lifted the respective top layer above the needle points, a lifting track is guided between the top layer and the subsequent layer, separating both layers from each other, and covering the end of the needle points when in its end position. The seized textile sheet can now be transported from above the lifting track. The gripping device with electric, hydraulic or pneumatic actuating means, necessary for the execution of the method, includes in the present invention a conical base, fastened to a piston rod, divided and forming two expandable clamping jaws. The slit lower edges of the jaws each have a row of points, i.e.; tips, of preferably semipyramid shape, the rows being located parallel to one another and with pointed tips perpendicular to the planar bottom side of the base. The conical base with the piston rod is slidingly arranged in a housing or sleeve, with an equally conical opening, the sleeve serving as a piston guide. The base with the piston guide is axially movable and elastically mounted in a gripper housing. A finger gripper, actuated by the same means as the piston rod and mounted onto the gripping device, is rotatably arranged, so that it lies against the bottom side of the clamping jaw, when it is in working position. The open clamping jaws attach with their planar bottom sides onto the upper side of the textile sheet to be seized. The points or tips pierce the thread structure perpendicularly, without penetrating the layer to be gripped. After the clamping jaws have been closed, the textile sheet can be lifted by the thus seized threads or fibers. When gripping the textile sheet at the edges of the stack, finger grippers can be held in the working position against the bottom side of the clamping device, in order to increase the holding effect, as well as holding the material edge. By the movable arrangement of the clamping jaws in the gripper housing, the requirements for monitoring of the positioning of the gripping device for the attachment onto the textile sheet can be reduced. 
     In summary, the present invention entails a method and gripping apparatus for gripping and separating sheets, expecially textile sheets. 
     The method and apparatus is used for the separation of sheets, especially of textile sheets, and serves particularly for the lifting of the top layer or sheet from a stack, as well as the secure holding of a textile sheet during transport. 
     The method and gripping apparatus allow the separation of sheets, especially of textile sheets, from a stack, as well as their secure gripping in an all-automatic process. Points or tips are arranged on the clamping jaws of the gripping device, which pointed tips pierce the top material layer of a stack, and grip the layer when the clamping jaws are closed. By a different arrangement or spacing of the gripping devices relative to the stack surface, there is an undulated lifting of the top layer from the stack. Preferably, at every other gripping device of a row or array of such devices, needles are stuck through the stack from below, securing an additional positioning of the stack. 
     By using additional finger grippers, the lifted textile sheet can be held during transport. The present method and gripping devices apparatus is particularly useful in the clothing industry, for the automation of production processes. 
     Following is a reference glossary of elements and structural members as employed in the present invention. 
     GLOSSARY 
     1. Textile sheet 
     2. Gripping device 
     3. Holder 
     4. Clamping jaws 
     5. Finger gripper 
     6. Needle 
     7. Needle point 
     8. Lifting track 
     9. Gripper housing 
     10. Connection piece 
     11. Piston guide 
     12. Piston rod 
     13. Working piston 
     14. Counter spring 
     15. Base 
     16. Expanding spring 
     17. Points 
     18. Clamp 
     19. Pistons 
     20. Toothed rack 
     21. Gear wheel 
     22. Bushing 
     The invention accordingly consists in the method and apparatus for gripping and separating sheets as described supra, and as will be described infra and shown in the drawings, and as recited in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be illustrated by means of the drawings, in which: 
     FIG. 1 shows gripping devices arranged in a row with a seized material layer; 
     FIG. 2 shows a functional arrangement of operating points disposed so as to carry out the method of the invention; 
     FIG. 3 shows a gripping device in cross-section. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, a number of gripping devices 2, corresponding to the size of a textile sheet 1, are fastened to one or several holders 3, so that the clamping jaws 4, of the gripping devices 2, which are planar and divided on the bottom side, have at least two different distances to the upper side of the textile sheet 1 to be seized. By lowering the holder 3, the clamping jaws 4 are attached to the top layer of the stacked textile sheet 1, with the elastic mounting of the clamping jaws 4 in the gripping devices 2 equalizing the different distances to the upper side of the top layer. Prior to attaching, the clamping jaws 4 open, with a small, adjustable slit being formed between them, corresponding to the strength or thickness, and the structure of the textile sheet 1. When attaching the clamping jaws 4, points or tips, located in rows parallel to one another at the edges of the aperture, and perpendicular to the planar bottom side of the clamping jaw 4, pierce the upper surface of the textile sheet 1. Because of their small dimensions, as compared to the thickness of the textile sheet 1, and because of the limited depth of penetration, due to the planar bottom side of the clamping jaw 4, serving as a contact point, a total penetration of the top material layer is prevented. When attached onto the material layer, the clamping jaws 4 are now closed and the fiber components located between the row of points or tips is held. When lifting the holder 3, the clamping jaws 4 spring out of the gripping devices 2 with different height. Because of the different height of the adjacent individual clamping jaws 4 to the upper surface of the top layer, the top layer gripped by the clamping jaws 4 with the largest height are the first to be lifted, while the other clamping jaws 4 still serve as clamps and are lifted later. This lifting of the top material layer, being laterally different at various points, reduces the adhesion of the layers to one another in a favorable and advantageous fashion, as compared to a simultaneous lifting. If the gripping devices 2, which seize the textile sheets 1, are arranged at the edges of the sheets, additional digital grippers 5, arranged in a perpendicular fashion relative to the gripping devices 2 when not in operation, can additionally hold the edges of the textile sheets 1. Having lifted the textile sheet 1, the finger gripper 5 is rotated around a fulcrum and attaches itself onto the bottom side of the clamping jaws 4, with the seized material edge being clamped. When separating stacks, prior to the initial lifting process with attached clamping jaws 4, needles 6, serving as clamps, are stuck through the stack of textile sheets 1, preferably at every other gripping device 2, and immediately behind the clamping jaws 4, starting with the contact surface of the stack. The needle points 7 pierce the upper surface of the top stack layer. The needles 6 position the stack in its position. Following the described lifting of the top layer of the stack by gripping devices 2 above the height of the needle points 7, a lifting track 8 is moved immediately above the needle points 7 and parallel to the upper side of the stack, and between the already lifted layer and the subsequent layer, and from the edge towards the middle of the stack, covering the needle points 7 in its final or end position. Following the transport of the textile sheet 1, the lifting track 8 moves into a starting position outside the stack. 
     In the gripping device 2, and necessary for the execution of the method, a working piston 13, connected to a piston rod 12, is provided in a gripper housing 9, with two connection pieces 10 for compressed air, and a piston guide 11, the working piston being held in its uppermost position by a counter spring 14. A conical base 15, fastened to the other end of the piston rod 12, is divided and forms two clamping jaws 4, which can be expanded by an expanding spring 16, and the cone-shaped shell surface which lie against the surface of a hollow cone on the bottom side of the piston guide 11. At the aperture edges of the clamping jaws 4, a row of points or tips 17 with a semi-pyramid shape have been arranged parallel to one another and perpendicular to the bottom side of the base 15. The piston guide 11 is axially movable within the gripper housing 9, and is held in its lowest position by a clamping spring 18. 
     A second piston 19, located in the gripper housing 9, is connected with a toothed rack and engages with a gear wheel 21, which forms the unit with a finger gripper 5. Prior to attaching the gripping device 2 onto the textile sheet 1 to be seized, the working piston 13 is moved into the working position by compressed air. The base 15, connected with the working piston 13, slides along the conical surface, is pushed outwardly by the expanding spring 16, whereafter the two clamping jaws 4 open. The gripping device 2 is lowered onto the textile sheet 1, with base 15 attaching with constant force, due to the elastic spring mounting. During the attachment, the points or tips 17 pierce the surface of the textile structure, without completely penetrating the entire thickness the textile sheet 1. Having attached the gripping device 2, the pressure system is ventilated, and the working piston 13 is then moved by the counter spring 14 into a resting position. The clamping jaws 4 are closed, with fibers from the upper surface of the textile sheet 1 being clamped between the row of points or tips 17. By lifting the gripping device 2, the top sheet or layer is removed from the stack. 
     If the gripping device 2 for the seizure of the top layer is located at the edge of the stack, the finger gripper 5 is pushed by the rack and pinion drive against the bottom side of the clamping jaw 4, by actuating the second piston 19 by compressed air, thus holding the material. 
     By exchanging the bushing 22 for a bushing with a different length dimension, the distance between base 15 and the working piston 13 changes, and thus the distance of the clamping jaws 4 relative to one another is changed, allowing adjustment possibilities for the gripping of textile sheets of varying or different dimensions (thickness). 
     It thus will be seen that there is provided a method and apparatus for gripping and separating sheets, especially textile sheets, which attains the various objects of the invention, and which is well adapted for the conditions of practical use. As numerous alternatives within the scope of the present invention, besides those alternatives, variations, modifications and embodiments contemplated supra and as shown in the drawings, will occur to those skilled in the art, it will be understood that the present invention extends fully to all such, and other alternatives and equivalents within the scope of the present invention, and is to be limited only by the recitations in the appended claims, and functional and structural equivalents thereof.