Patent Publication Number: US-2013251495-A1

Title: Method for depositing sheet-like objects and an assembly for carrying out said method

Description:
The present invention relates to a method for depositing sheet-like objects, particularly for depositing electrodes and/or separators for constructing an electrochemical energy store or parts of such electrodes or separators as well as an assembly for carrying out such a method. 
     The handling of sheet-like objects plays an important roll in a number of very different fields of technology. Separating such sheet-like objects is thereby a problem that arises time and again. Numerous attempts have been made to solve the problems which thereby occur, particularly in the field of page printers, which are loaded with stacks of paper sheets, as well as in the field of bank note processing. 
     Thus, DE 193 03 70 A1 discloses an apparatus for withdrawing sheet-like recorded medium of a stack resting on a height-adjustable base plate, in which the uppermost recorded medium of the stack in each case is grasped by a circulating friction band and led through a neck of a transporting belt formed by the conveyor belt circulating at transport speed and a counter-rotating brake belt. Openings disposed slightly inclined to the transport direction are arranged in the base plate receiving the stack through which the friction of the lowermost recorded medium of the stack relative the friction belt grasping same is controllable by means of negative pressurization. 
     DE 20 05 270 A1 discloses a transport apparatus for sheet-like documents consisting of a hollow drum in which a vacuum chamber is provided which is connected to a vacuum source via a hollow shaft and has suction openings in its cylinder barrel. A pneumatically operated membrane valve is arranged behind a suction opening or a group of suction openings in the transport apparatus which selectively connects said openings to the vacuum chamber. A pneumatic logical control is connected to the membrane valve to connect the suction openings to the vacuum chamber when a document is to be held to the cylinder barrel of the drum and to interrupt the connection to the vacuum chamber when no document is to be held or when a previously held document is to be released. 
     DE 22 01 254 B2 discloses an apparatus for separating sheet material from the underside of a stack to a pair of feed rollers using a stationary stacking table having a slide plate capable of moving back and forth which grasps the respectively lowermost sheet of the stack at its rear edge, moves it over the stacking table and feeds it to the feed rollers, suctions bores associated with the stacking table through which the respective lowermost sheet is subjected to a vacuum, and support strips for the stack. Said stationary support strips form suction channels between themselves which open to the outer air on the ends opposite the feeder rolls. The slide plate comprises continuous notches on its upper side to below the lower edge of the contact surface for the sheets to be separated which each align with one of the suction channels formed between the support strips. In so doing, the rear edge of the next sheet to be advanced during the separating of the lowermost sheet is pulled downward. 
     Similar apparatus are described in the DE 26 50 438 C2, DE 30 23 157 A1, DE 32 20 237 C2 and DE 34 04 215 A1 published applications. 
     DE 34 41 479 A1 further discloses a vacuum-operated lifting apparatus for flat air-permeable objects of variable profile in which a housing containing a suction chamber having a plurality of evenly distributed suction openings is provided in the underside of the housing, and in which each suction opening is associated with a control valve comprising a valve member which seals the opening off from atmospheric pressure, a valve tappet projecting from the housing which penetrates the opening in a downward direction, and an operating piston connected to the valve member which is acted upon by atmospheric pressure over its entire diameter on the side facing away from the valve member when the opening is closed and over a reduced diameter when the opening is clear. 
     Similar apparatus having suction lifters are disclosed in the DE 37 10 994 A, DE 39 23 672 A1 and DE 40 33 870 A1 documents. 
     Each of these known proposed solutions is associated with advantages and limitations and have been developed for the needs and conditions of specific applications. Because of the particularly low inherent stability of sheet-like electrodes or separators for constructing an electrochemical energy store or of sheet-like parts of such electrodes or separators, technical teachings which offer advantages in the field of paper processing are not usually applicable to the handling of electrodes and/or separators for constructing an electrochemical energy store. 
     The present invention is based on the object of providing a technical teaching for handling sheet-like objects which in particular also offer advantages in the handling of sheet-like objects of lower inherent stability of electrode materials and/or separator materials in conjunction with the manufacture of electrochemical energy stores. 
     This object is accomplished by a method for depositing sheet-like objects, respectively by an assembly for carrying out said method in accordance with any one of the independent claims. 
     In accordance with the invention, a method for depositing sheet-like objects is provided in which a plurality of such objects are successively placed atop one another and in which individual or multiple objects are intermittently removed again from above. It is thereby additionally provided for the objects to be placed atop each other offset and/or rotated relative one another. 
     In conjunction hereto, a sheet-like object is to be understood as a flat object, preferably a thin flat object, thus preferably a flat object exhibiting dimensions in a direction perpendicular to its surface which are substantially smaller than the dimensions of its smallest segment completely within its surface. Examples of sheet-like objects are in particular electrochemical materials such as, for example, electrode materials or separator materials as used in the manufacture of electro-chemical energy stores. 
     In this context, a plurality of such objects refers to a number of objects greater than one. 
     To be understood in this context by the concept of laying such objects atop one another is the creating or maintaining of an assembly of such objects in which the surfaces of the objects are in contact. The surfaces of said objects are thereby preferably substantially perpendicular to the direction of gravity. In the sense of the present description of the invention, the objects are placed atop each other in offset manner from one another when they are deposited in displaced or offset manner in a direction tangential to their surfaces. They are placed atop each other in rotated manner when they are deposited atop one another and rotated relative each other about an axis perpendicular to their surfaces. The offsetting, displacing or rotating processes can also be combined in any desired manner when overlaying the sheet-like objects atop one another. 
     The invention preferably provides for at least one object to be removed by being lifted. The lifting of objects can thereby preferably occur in different ways, preferably by a mechanical gripping of the object to be lifted or by means of an electrostatic lifting device or, particularly preferably, by means of a vacuum lifter. Such lifting devices can preferably also be used to deposit an object on top of other objects, particularly offset and/or rotated relative each other. 
     In this context, a vacuum lifter s to be understood as a lifting device which is suited to lifting sheet-like objects by at least locally suctioning said sheet-like objects using a vacuum in that the outer atmospheric pressure acts on the opposite side of the sheet and presses the sheet against the vacuum chamber or against the vacuum chambers of the vacuum lifter. By switching the vacuum on and off and/or engaging an excess pressure, a lifted sheet can also be readily deposited. 
     In accordance with a preferred embodiment, the invention preferably provides for at least one first object to be held while at least one second object lying atop the at least one first object is removed. In terms of the present description of the invention, a second object lies over a first object in correspondence with the usual linguistic usage when the second object exerts the force of its weight on the first object. 
     One preferential embodiment of the invention provides for holding at least one first object while at least one second object lying atop the at least one first object is removed by a pressure being exerted from above onto at least one point or one part of said object. The at least one point or at least one part of said object thereby preferably lies at the edge of the object&#39;s surface. Particularly this embodiment of the invention has proven particularly advantageous when the sheet-like objects have a lower inherent stability, particularly a lower inherent stability than sheet-like objects made of paper, which is frequently the case with electrode or separator materials for constructing electrochemical energy stores. 
     It is particularly preferential when the objects employed are at least partially air-permeable objects. The inventive offset and/or rotated depositing of the sheet-like objects allows a particularly effective, reliable and simple separating of these sheet-like objects, particularly when they have a tendency to adhere to another one somewhat due to their material properties and associated adhesion or coherence or when a vacuum lifter suctions a plurality of them, particularly in the case of at least partially air-permeable objects. 
     It is likewise preferably provided for at least one object to be an electrode or a separator for constructing an electrochemical energy store or a part of such an electrode or separator. 
     It is preferably provided to use a lifting device rotatable about a vertical axis and/or displaceable in a horizontal plane to remove and/or deposit objects, said lifting device being aligned and/or positioned by means of a device which recognizes the position of an object to be removed using information technology. Preferred lifting devices are thereby mechanical gripping devices, electrostatic lifting devices or vacuum lifters. Feasible as devices for recognizing the position of an object to be removed are thereby all devices which are suited to recognizing the position of an object to be removed using information technology, preferably by means of signal processing and particularly preferably by means of pattern recognition. 
     In the positioning and/or aligning of the lifting device rotatable about a vertical axis and/or displaceable in a horizontal plane using a device which recognizes the position of an object to be removed using information technology, the operative elements of the lifting device, preferably the suction cups of a vacuum lifter, are preferably aligned and/or positioned such that said operative elements of the lifting device cover as much as possible of the surface of the object to be removed, particularly lifted, and that said operative elements of the lifting device preferably do not come into contact or interact with other objects, particularly those underneath the object to be lifted or removed. 
     Further or the already cited embodiments of the invention preferably provide for at least one lifting device, particularly preferably a vacuum lifter, which is arranged on a lifting apparatus so as to be rotatable about a vertical axis and/or displaceable in a horizontal plane. The vertical axis is thereby preferably arranged substantially parallel to the direction of gravity and thus substantially orthogonal to the surfaces of the object to be deposited or lifted. The horizontal plane is preferably aligned perpendicular to the vertical axis. 
     The present or further embodiments of the invention preferably exhibit at least one hold-down element which holds at least one first object while at least one second object lying above the at least one first object is removed. In this context, a hold-down element refers to any device which is suited to holding a first object lying underneath a second object; i.e. preventing it from being lifted together with the object to be lifted due to adhesive or cohesive force. Preferably conceivable as hold-down elements are mechanical gripping devices, electrostatic retaining devices or hold-down elements operated by means of negative pressure or vacuum. 
     The present or further embodiments of the invention preferably exhibit a hold-down element which is structurally connected to the vacuum pickup or to another lifting device such that said hold-down element does not move, or at best only moves vertically, in the kinematic reference systems of the vacuum lifter when the vacuum lifter moves horizontally relative to a deposited or positioned object. The hold-down element is thereby preferably rigidly connected to the vacuum lifter or to the other lifting device or at least connected such that a relative motion between the hold-down element and the vacuum lifter is then not possible when the vacuum lifter or other lifting device moves horizontally in relation to a deposited or positioned object. 
     At least one vacuum lifter thereby preferably comprises a plurality of pressure chambers. Said pressure chambers can preferably be subjected to a vacuum independently of one another. It is particularly preferable for the pressure chambers to be arranged horizontally displaceable to one another. This is associated with the advantage of being able to adapt the position of the pressure chambers to the form of the sheet-like object. 
     The inventive assembly preferably comprises an IT device for recognizing the position of an object to be removed. The inventive assembly preferably likewise comprises an IT device for aligning and/or positioning a lifting device based on the position of an object to be removed as recognized by the same or by a further IT device. The IT device for recognizing the position of an object to be removed thereby preferably comprises a camera. 
    
    
     
       The following will draw on preferred embodiments in association with the accompanying figures in describing the invention in greater detail. Shown are: 
         FIG. 1  a schematic view of a first arrangement of sheet-like objects; 
         FIG. 2  a second arrangement of sheet-like objects; 
         FIG. 3  a third arrangement of sheet-like objects; 
         FIG. 4  a first embodiment of an assembly according to the invention; 
         FIG. 5  a second embodiment of an inventive assembly; 
         FIG. 6  a third embodiment of an inventive assembly; 
         FIG. 7  a fourth arrangement of sheet-like objects; 
         FIG. 8  a vacuum lifter in accordance with a preferred embodiment of the invention. 
     
    
    
     As shown schematically in  FIG. 1 , the sheet-like objects in this embodiment lie atop one another in offset manner, albeit not rotated with respect to one another, such that the edges or specific partial sections of a second sheet-like object lying underneath a first sheet-like object are freely accessible. When the uppermost sheet-like object  5  in  FIG. 1  is to be lifted, the sheet-like object  4  lying underneath can then be prevented from being lifted together with the sheet-like object  5  lying above it by said sheet-like object  4  being held down. At the same time, the further sheet-like objects underneath it are likewise prevented from being lifted. 
     Points  15   a ,  15   b ,  15   c  and  15   d , onto which pressure can be exerted, for example by means of a mechanical hold-down element, lend themselves to holding down the sheet-like objects, particularly sheet-like object  4 . 
       FIG. 2  depicts a similar situation using the example of sheet-like objects which are deposited one atop the other in rotated manner. Here, points  16   a ,  16   b,    16   c  and  16   d,  for example, lend themselves to holding down the sheet-like objects lying underneath. 
       FIG. 3  depicts a similar situation, wherein here the sheet-like objects are deposited in rotated and offset manner to one another. In this example, points  14   a ,  14   b,    14   c  land  14   d  lend themselves to holding down the sheet-like objects lying underneath. 
       FIG. 4  shows a preferred embodiment of an inventive assembly in which a lifting device  1 , preferably a suction lifter having suction cups  6  or vacuum chambers  6 , is mounted to a lifting apparatus  2 . Said lifting device  1  can be raised and/or lowered in the vertical direction  8  by means of the lifting apparatus  2 . This assembly of the lifting device  1  as shown exemplarily in  FIG. 4  can additionally also be offset or displaced horizontally or in any direction lying in horizontal plane  10  or rotated about vertical axis  9 . Doing so and/or by the displacing of the vacuum chambers  6 , the position of the vacuum chambers  6  can be adapted to the position and form of the sheet-like object  5  to be lifted such that said vacuum chambers preferably only suction the sheet-like object  5  to be lifted and preferably riot the object  4  lying underneath which is not to be lifted. 
       FIG. 4  schematically shows a preferred embodiment of an inventive assembly comprising a vacuum lifter  1 , thus a lifting device which is suited to lifting sheet-like objects by at least locally suctioning said sheet-like objects  4 ,  5  by means of a vacuum in that the outer atmospheric pressure acts on the opposite side of the sheet  5  and presses the sheet against the vacuum chamber or against the vacuum chambers  6  of the vacuum lifter  1 . By switching the vacuum on and off and/or engaging an excess pressure, a lifted sheet can also be readily deposited.  FIG. 4  shows this assembly according to a preferred embodiment in which at least one first object  4  is held while at least one second object  5  lying atop the at least one first object  4  is removed. 
     A pressure can thereby be exerted from above on at least one point of the points  14   a ,  14   b,    14   c,    14   d ,  15   a ,  15   b ,  15   c ,  15   d ,  16   a,    16   b,    16   c  and/or  16   d  shown in  FIGS. 1 ,  2  and/or  3 , or on one part of said object  4 . The at least one point or at least one part of said object thereby preferably lies at the edge of the object&#39;s surface. It is particularly preferential for the objects employed to be at least partially air-permeable objects. The offset and/or rotated depositing of the sheet-like objects shown in  FIGS. 1 ,  2  and/or  3  allows a particularly effective, reliable and easy separating of said sheet-like objects, particularly when they have a tendency to adhere to another one somewhat due to their material properties and associated adhesion or coherence, or when a vacuum lifter  1  suctions a plurality of them together, particularly in the case of at least partially air-permeable objects. 
       FIG. 5  depicts a further preferential embodiment of an inventive assembly in which the hold-down element  3  is affixed to the lifting device  1  such that the latter or the hold-down element  3  moves together with the lifting device  1  such that upon the lifting device  1  rotating about vertical axis  9  or upon a displacement of the lifting device  1  parallel to horizontal plane  10 , the hold-down element(s)  3  are preferably moved along therewith such that the object(s)  4  lying under the object  5  to be lifted are always held down, preferably by a pressure on the points  14   a ,  14   b ,  14   c ,  14   d ,  15   a ,  15   b ,  15   c ,  15   d ,  16   a ,  16   b,    16   c  and/or  16   d  shown in  FIG. 1 ,  2  or  3 . The pivot points or articulations  11  thereby allow the hold-down element  3  to move horizontally in direction  12 . Said pivot points or articulations  11  are preferably designed such that the hold-down element(s)  3  can also be moved in vertical direction  13 , preferably independently of the lifting device  1 . 
     For the removing and/or depositing of objects, it is preferably provided to make use of a lifting device  1  which is rotatable about a vertical axis  9  and/or displaceable in a horizontal plane  10  and is aligned and/or positioned by means of a device  7  which uses information technology to recognize the position of an object  5  to be removed. Preferential lifting devices are thereby mechanical griping devices, electrostatic lifting devices or vacuum lifters. Feasible as devices  7  for recognizing the position of an object  5  to be removed are thereby all devices which are suited to recognizing the position of an object to be removed using information technology, preferably by means of signal processing and particularly preferably by means of pattern recognition. 
     In the positioning and/or aligning of the lifting device  1  rotatable about a vertical axis  9  as depicted in  FIGS. 5 and 6  and/or displaceable in a horizontal plane  10  as likewise depicted in  FIGS. 5 and 6  using a device  7  which recognizes the position of an object  5  to be removed using information technology, the operative elements  6  of the lifting device, preferably the suction cups  6  of a vacuum lifter  1 , are preferably aligned and/or positioned such that said operative elements  6  of the lifting device cover as much as possible of the surface of the sheet-like object  5  to be removed, particularly lifted, and that said operative elements of the lifting device preferably do not come into contact or interact with other sheet-like objects  4 , particularly those lying underneath the sheet-like object  5  to be lifted or removed. 
       FIG. 6  shows a further preferential embodiment of an inventive assembly in which IT devices  7  are preferably mounted to the lifting device  1 , by means of which the position of a sheet-like object  5  can be recognized such that the lifting device  1  can be aligned to the recognized position. Said IT device  7  preferably comprises one or more cameras which preferably take images of the edges of the sheet-like objects from which the position of the sheet-like object(s) can be determined by means of information technology. Pattern recognition procedures are thereby preferably used, particularly preferably edge detection methods. 
     Edge detection is part of image processing segmentation which attempts to distinguish between flat regions within a digital image. There are many known methods of automatic segmentation. Basically, they are often divided into pixel-oriented, edge-oriented and region-oriented methods. There is also a differentiation made between model-based methods, which start with specific object forms, and texture-based methods, which also take a homogeneous internal structure of the objects into consideration. 
     The boundaries between the methods are often blurred. One can also combine various methods in order to obtain better results. 
     In edge detection, so-called edge operators are to recognize the transitions between said regions. These transitions are marked as edges. In contrast thereto, however, an individual region is also to be recognized as such and a good edge detector is not to divide it into two parts by an edge. An edge detector calculates its corresponding edge image from an image in which all the edges are accordingly seen. In order to achieve this, each pixel is re-localized by matrix calculation. 
     Edge-oriented methods of segmenting digital images search an image for edges or object transitions. Many algorithms therefore still do not furnish closed edge contours; they must first be combined with further methods so they will include objects. However, for determining the position of sheet-like objects of known form, this is often not necessary. Edges frequently lie between the pixel regions of an image. The results of an algorithm can be polygons (or lines), but some operations also return the edges as differently colored pixels. Methods such as the Sobel operator and the Laplace operator, as well as gradient search, allow finding the pixels associated with an edge. However, they are still loose and need to be completed by edge-tracing algorithms. One popular method of generating a coherent object outline or at least edge contours from the edge pixels is the live-wire method of authors E. Mortensen, W. A. Barrett and J. K. Udupa. The idea can be descriptively compared to a navigation system which determines the optimum route from a starting location to a destination. In the context of segmentation, optimum means that the route between start and destination always follows the strongest edge pixel. Optimum route selection is then a standard problem in information technology and can for example be solved by a breadth-first search. 
     Watershed transformation is also a very well-known method which works with grayscale images and always furnishes closed contours. Further methods include parallel and sequential edge extraction, optimal edge detection, the Felzenszwalb-Huttenlocher algorithm, active shape models and snakes. 
     At least one lifting device  1 , particularly preferably a vacuum lifter  1 , is preferably provided in the embodiments of the invention shown in  FIGS. 4 ,  5  and  6 , same being arranged on a lifting apparatus  2  rotatable about a vertical axis  9  and/or displaceable in a horizontal plane  10 . The vertical axis  9  is thereby preferably arranged substantially parallel to the direction of gravity and thus substantially orthogonal to the surfaces of the deposited or lifted objects. The horizontal plane  10  is preferably aligned perpendicular to the vertical axis  9 . 
     The present or further embodiments of the invention preferably exhibit at least one hold-down element  3  which holds at least one first object  4  while at least one second object  5  lying above the at least one first object  4  is removed. Preferably conceivable as hold-down elements  3  are mechanical gripping devices, electrostatic retaining devices or hold-down elements operated by means of negative pressure or vacuum. 
     The embodiment of the invention shown in  FIG. 5  comprises a hold-down element  3  which is structurally connected to the vacuum pickup  1  or to another lifting device such that said hold-down element does not move, or at best only moves vertically, in the kinematic reference systems of the vacuum lifter when the vacuum lifter moves horizontally relative to a deposited or positioned object. As  FIG. 5  shows, the hold-down element  3  is thereby preferably rigidly connected to the vacuum lifter  1  or to the other lifting device or at least connected such that a relative motion between the hold-down element and the vacuum lifter is then not possible when the vacuum lifter or other lifting devices move horizontally in relation to a deposited or positioned object. 
     At least one vacuum lifter  1  thereby preferably comprises—as shown in  FIGS. 4 ,  5  and  6 —a plurality of pressure chambers  6 . Said pressure chambers  6  can preferably be subjected to a vacuum independently of one another. It is particularly preferable for the pressure chambers to be arranged displaceable to one another in the horizontal direction  10 . This is associated with the advantage of being able to adapt the position of the pressure chambers to the form of the sheet-like object. 
     As  FIG. 6  shows, one preferential embodiment of the inventive assembly exhibits an IT device  7  for recognizing the position of an object  5  to be removed. The inventive assembly preferably likewise comprises an IT device for aligning and/or positioning a lifting device based on the position of an object to be removed recognized by the same or a further IT device. The IT device for recognizing the position of an object to be removed thereby preferably comprises a camera  7 . 
     As  FIG. 7  shows, the sheet-like objects  4 ,  5  can preferably be rotated relative each other, particularly preferably rotated relative each other by an angle of approx. 26 degrees or alternatingly deposited individually or in groups in two interpenetrating stacks rotated relative one another. The sheet-like objects can thereby be secured against unintentional rotating or displacing at their ends or edges by limiting elements  17 ,  18 . Such limiting elements  17 ,  18  can preferably support the intended stacks of sheet-like objects so as to keep deviations from the desired position as minimal as possible. 
     As shown in  FIG. 8  by means of a preferential embodiment of a vacuum lifter or vacuum gripper for use in conjunction with an assembly according to the invention, such a vacuum lifter  1  preferably comprises a number of pressure chambers  6  with respective vacuum connections  20 . The vacuum connections of the vacuum chambers are preferably independent of one another so that improper gripping by the vacuum lifter can be prevented wherever possible upon a drop in pressure. The vacuum lifter preferably exhibits a groove  19  in the proximity of the edge into which a caulking strip is or can be fit. The vacuum lifter preferably exhibits a plurality of hold-down elements  3  which, in the embodiment shown in  FIG. 8 , are preferentially designed as spring hold-down elements  3 . The points of contact of said hold-down elements preferably lie as close as possible to the edge of the vacuum gripper  1  so as to prevent unwanted kinking of the sheet-like objects when the vacuum gripper lifts them. Should the sheet-like objects be separator films or electrodes for manufacturing galvanic cells, the vacuum lifter is preferably operated at a negative pressure of 0.7 bar. In such cases, the hold-down element preferably exerts a force totaling 18 N on the sheet-like object to be held down. 
     The invention is expressly not limited to applications in which only individual sheet-like objects are to be lifted or deposited. Embodiments of the invention are preferred in the manufacturing of electrochemical energy stores, particularly galvanic cells, in which sheet-like objects of different types and/or compositions, preferably electrode and/or separator films, are lifted and/or deposited together or such that an electrode is first lifted and thereafter a separator film is lifted by the same vacuum lifter without the electrode being deposited beforehand, or the reverse case; i.e. first the separator film and thereafter the electrode. The separator film is thereby frequently gas-permeable, particularly air-permeable. An annular gap which is preferably approx. 2 mm wide is preferably provided around the anode. Cut separator films are often somewhat larger than electrodes. The invention is therefore also expressly applicable to sheet-like objects of different size or form. 
     The features of all the described embodiments or the embodiments depicted in the figures can also be combined with one another.