CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority based on European patent application EP 11 170 544.8, filed Jun. 20, 2011. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to a fleece layer for producing a fleece from a card web. 
       BACKGROUND OF THE INVENTION 
       [0003]    Fleece layers are used to lay multiple layers of a card web, produced by a carding machine, as uniformly as possible on an output conveyor belt. The card web is usually guided first through an upper carriage and proceeds from there to a laying carriage, through the laying gap of which the card web is deposited onto the output conveyor belt. At least two card web conveyor belts are used to guide the card web through the fleece layer. The movements of the card web conveyor belts, of the upper carriage, and possibly of the laying carriage are controlled so as to coordinate with each other. 
         [0004]    Fleece layers are often preceded by mechanisms for changing the web line speed. Such mechanisms are used primarily to regulate the density of the card web as a way of profiling the laid fleece or to compensate for a thickness variation at the edges of the laid fleece. Mechanisms of this type for changing the line speed include, for example, take-off rolls, driven at different speeds, on the carding machine located upstream of the fleece layer, as known from U.S. Pat. No. 6,195,844, for example, or a separate web drafter, which can be installed between the carding machine and the fleece layer (see, for example, EP 1 532 302 B1). 
         [0005]    In both of the patent documents cited above, fluctuations in the line speeds of the incoming web are compensated for in the fleece layer by an integrated buffer, which is obtained by increasing the distance traveled by the upper carriage. This results in turn in an increase in the length of the loop in the first web conveyor belt. Because of the greater distance traveled by the upper carriage, the rear part of the fleece layer becomes longer, which is often undesirable and can exceed the amount of setup space available. 
       SUMMARY OF THE INVENTION 
       [0006]    It is an object of the present invention to provide a fleece layer which makes it easy to compensate for fluctuating card web infeed speeds and which simultaneously minimizes the amount of space which the fleece layer requires at the rear. 
         [0007]    According to an aspect of the invention, the method for operating a fleece layer for producing a fleece from a card web includes the steps of providing a fleece layer comprising an upper carriage, which moves in the transverse direction and through which a card web produced by a fiber web-forming device is conducted, and further including a laying carriage, which moves in the transverse direction, through which the card web coming from the upper carriage is conducted. The laying carriage serves to deposit the card web onto an output conveyor belt. The fleece layer also includes at least two card web conveyor belts to guide the card web to the laying carriage. 
         [0008]    According to a further aspect of the invention, the method includes providing a speed changing device installed upstream of the fleece layer or integrated into its infeed area for temporarily changing the speed of the card web, as a result of which the card web is supplied to the fleece layer at a variable card web infeed speed. 
         [0009]    The upper carriage and the laying carriage may be moved back and forth substantially in the same direction during a laying cycle by means of forward and return movements, wherein the laying carriage, during each laying cycle, moves back and forth between two permanently defined reversal points. 
         [0010]    The average of the absolute values of the laying-carriage speed during the forward movement of the laying carriage in each laying cycle or at least in some laying cycles differs from the average of the absolute values of the laying-carriage speed during the return movement of the laying carriage. The average of the absolute values of the laying-carriage speed during the forward movement of the laying carriage in each laying cycle or at least in some laying cycles differs from twice the average of the absolute values of the upper-carriage speed during the forward movement of the laying carriage. 
         [0011]    It is thus possible to compensate for variable card web infeed speeds in a simple manner and at the same time, thanks to the limited distance which the upper carriage must travel, to limit the amount of space required at the rear of the fleece layer. 
         [0012]    The average of the absolute values of the laying-carriage speed during the forward movement of the laying carriage in each laying cycle or at least in some laying cycles is preferably greater than twice the average of the absolute values of the upper-carriage speed during the forward movement of the laying carriage. The average value of the laying-carriage speed during the forward movement of the laying carriage in each laying cycle or at least during some laying cycles is greater than the average value of the laying-carriage speed during the return movement of the laying carriage. Thus the laying carriage catches up with the upper carriage more quickly during the forward movement, which has the effect of taking-up the loop which the belt forms around the upper carriage. Nevertheless, even though the card web infeed speed can be higher at times during the forward movement, the distance traveled by the upper carriage can still be limited to a certain value. Simultaneously, the higher card web infeed speed is compensated for by the higher asynchronous speed of the laying carriage during its forward movement. 
         [0013]    To maintain a constant mass flow, it is advantageous for the average of the absolute values of the laying-carriage speed after several laying cycles to be the same as the average of the absolute values of the variable card web infeed speed. 
         [0014]    It is especially preferable for the average of the absolute values of the laying-carriage speed to be the same after each laying cycle as the average of the absolute values of the variable card web infeed speed. This makes it possible to establish a constant mass flow during every laying cycle, and the compensation during following laying cycles can be carried out with greater flexibility. 
         [0015]    To limit the amount of space which the fleece layer requires in the rear area more effectively (i.e., to reduce it to a minimum), it is advantageous to define physically two predetermined reversal points for the upper carriage and to set up the speed profile of the laying carriage in such a way that the upper carriage does not travel beyond these predetermined reversal points no matter what the variable card web infeed speed of the incoming card web might be. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    In order that the features and advantages of the invention will be readily understood, a more detailed description of the invention briefly described above will be rendered by reference to specific embodiments and examples that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity, features, advantages and detail through the use of the accompanying drawings, in which: 
           [0017]      FIG. 1  is a schematic cross-sectional diagram of one embodiment of a fleece layer in which the invention can be applied; 
           [0018]      FIG. 2  shows a graph of one example of speed profiles of the card web conveyor belt, of the upper carriage, and of the laying carriage of the fleece layer of  FIG. 1  at a constant card web infeed speed; 
           [0019]      FIG. 3   a  shows a graph of one possibility for the speed profiles of the card web conveyor belt, of the upper carriage, and of the laying carriage of the fleece layer of  FIG. 1  at a variable card web infeed speed and with a buffer formation according to the invention; 
           [0020]      FIG. 3   b  shows a graph of the distance traveled by the upper carriage in the case of the speed distribution according to  FIG. 3   a;    
           [0021]      FIG. 4   a  shows a graph of an additional possibility for the speed profiles of the card web conveyor belt, of the upper carriage, and of the laying carriage of the fleece layer of  FIG. 1  at variable card web infeed speed and with inventive buffer formation according to the invention; 
           [0022]      FIG. 4   b  shows a graph of the distance traveled by the upper carriage in the case of the speed distribution according to  FIG. 4   a;    
           [0023]      FIG. 5   a  shows a graph of an additional possibility for the speed profiles of the card web conveyor belt, of the upper carriage, and of the laying carriage of the fleece layer of  FIG. 1  at a variable card web infeed speed and with a buffer formation according to the invention; 
           [0024]      FIG. 5   b  shows a graph of the distance traveled by the upper carriage in the case of the speed distribution according to  FIG. 5   a ; and 
           [0025]      FIG. 6  is a schematic cross-sectional diagram of an additional embodiment of a fleece layer in which the invention can be applied. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]      FIG. 1  is a schematic cross-sectional diagram of a fleece layer  2  in which the present invention can be applied. Fleece layer  2  has an endless output conveyor belt  4 , which is intended to carry away the fleece produced from a card web  6  in a transport direction perpendicular to the plane of the drawing. An upper deflecting roll  8 , which represents one of the guide devices of output conveyor belt  4 , is shown. 
         [0027]    A laying carriage  10  can be moved back and forth on rails or pipes (not shown) above output conveyor belt  4 . Two freely rotatable deflecting rolls  12  and  14  are supported in laying carriage  10 . A web conveyor belt  16 , also called the “second web conveyor belt  16 ” below, wraps part of the way around first deflecting roll  12 . At its first end  18 , the second web conveyor belt  16  is permanently connected to the machine stand (not shown) of fleece layer  2  and extends from there above and only a short distance away from output conveyor belt  4  until it reaches laying carriage  10 , where it reverses direction by 180° and is then guided back over four stationary deflecting rolls  20 ,  22 ,  24 ,  26  before arriving back at second deflecting roll  14  in the laying carriage. The second web conveyor belt  16  wraps part of the way around deflecting roll  14 , which is also supported in freely rotatable fashion in laying carriage  10 . Web conveyor belt  16  thus reverses its direction here by 180° and then proceeds from the lower outlet area of laying carriage  10 , passing only a short distance above output conveyor belt  4 , to the machine stand of fleece layer  2 , to which its second end  28  is also permanently attached. 
         [0028]    On laying carriage  10 , a chain or a toothed belt is mounted, which passes, for example, over a drive gear wheel connected to a motor and a deflecting roll (none of these elements is shown). By means of these drive devices, laying carriage  10  can be moved back and forth above output conveyor belt  4  crosswise to the transport direction of the belt. 
         [0029]    At about the same height as laying carriage  10 , an upper carriage  30  is supported on rails or pipes (not shown) in the machine stand of fleece layer  2  so that it can move crosswise to the transport direction of output conveyor belt  4 . The rails or pipes can be the same rails or pipes as those on which laying carriage  10  is also movably supported. Upper carriage  30  has an upper deflecting roll  32  and a lower deflecting roll  34 , which are offset laterally from each other. Another web conveyor belt  36 , called the “first web conveyor belt  36 ”, passes over these two deflecting rolls  32 ,  34 . In the area bounded by two deflecting rolls  32 ,  34  in upper carriage  30 , the first web conveyor belt  36  passes downwards at a slant. 
         [0030]    Proceeding from lower deflecting roll  34  in upper carriage  30 , first web conveyor belt  36  extends parallel to the right upper run of second web conveyor belt  16 . First web conveyor belt  36  extends in a straight line through laying carriage  10 , and, after leaving laying carriage  10 , it passes over a stationary, motor-driven deflecting roll  38 . From there, it is guided around a deflecting roll  42  supported in a tension carriage  40  and then proceeds over several stationary deflecting rolls  44 ,  46 ,  48 ,  50  supported in the machine stand of fleece layer  2  before reaching upper carriage  30  again. Upper carriage  30  and tension carriage  40  can be connected to each other by a chain or a toothed belt (not shown), which passes over a drive gear wheel connected to a motor and a deflecting pulley, which are mounted in the machine stand (not shown). Tension carriage  40  is also supported on rails or pipes (not shown), so that it can move back and forth. It can also be advantageous for the movements of upper carriage  30  and those of tension carriage  40  to be isolated from each other. 
         [0031]    In the area between lower deflecting roll  34  of upper carriage  30  and second deflecting roll  14  of laying carriage  10 , sections of first web conveyor belt  36  and of second web conveyor belt  16  are guided parallel to, and only a short distance away from, each other, so that card web  6  supplied by first web conveyor belt  36  is sandwiched between first web conveyor belt  36  and second web conveyor belt  16  in the just-mentioned area between upper carriage  30  and laying carriage  10 . Card web  6  is supported on second web conveyor belt  16 . In addition, the two sections of second web conveyor belt  16  extending between laying carriage  10  and the machine stand of fleece layer  2  simultaneously serve as a cover belt for the deposited fleece. 
         [0032]    It can be seen in  FIG. 1  that upper carriage  30  and its associated tension carriage  40  move in opposite directions during operation. Tension carriage  40  serves to keep the length of the loop of first web conveyor belt  36  constant. 
         [0033]    The movements of laying carriage  10  and of upper carriage  30  are usually coordinated with each other in such a way that, as card web  6  is being supplied at uniform speed to fleece layer  2 , card web  6  can be deposited in a controlled manner on output conveyor belt  4  without any stretching or squeezing within fleece layer  2 . Upper carriage  30  travels substantially in the same direction as laying carriage  10  but on average only half as fast. Account is also taken of the fact that laying carriage  10  is braked to a stop in the area where it reverses direction and then must be accelerated again. In the area of the reversal points, upper carriage  30  is usually moved for a brief period of time in such a way that it is not traveling in the same direction as laying carriage  10 . This, however, is to be considered covered by the phrase “substantially in the same direction”. Fleece layers  2  in which upper carriage  30  and laying carriage  10  move substantially in the same direction are also called “co-directional” machines. 
         [0034]    A gap, called the laying gap, is formed between two deflecting rolls  12  and  14  in laying carriage  10 . During the operation of fleece layer  2 , two web conveyor belts  16 ,  36  are driven in such a way that they travel at the same relative speed in the sandwich area so that they can transport card web  6  without distorting it. 
         [0035]    According to the invention, card web  6  is supplied to fleece layer  2  at fluctuating card web infeed speed in web travel direction A, because a speed changing device  52  for changing the card web speed is installed upstream of fleece layer  2  or in the infeed area of fleece layer  2  (see  FIG. 6 ). This speed changing device  52  can be a web drafter working in cycles, as shown in  FIG. 6 , which operates with pairs of clamping rolls to produce areas of alternating thickness in card web  6  for the purpose of achieving a transverse profiling of the laid fleece. A web drafter of this type is described in, for example, EP 1 381 721 B1, the entire content of which is incorporated herein by reference. Other known devices  52  for changing the card web infeed speed can also be used; for example, the card can be equipped with take-off rolls driven at variable speed as described in U.S. Pat. No. 6,195,844. 
         [0036]      FIGS. 2 ,  3   a ,  4   a , and  5   a  show graphs of speed profiles in the fleece layer, where V is the card web infeed speed as the card web enters fleece layer  2 , W is the speed of the laying carriage, and U is the speed of the upper carriage. In all of the graphs mentioned, the speed (in meters per minute) is plotted versus the time (in seconds). The zero point on the time axis establishes the front reversal point U 0  of laying carriage  10 , i.e., the reversal point of laying carriage  10  on the left in  FIGS. 1 and 6 . All of the figures show the exact course of a laying cycle, during which laying carriage  10  travels above the output conveyor belt  4  first from the front reversal point U 0  toward the rear reversal point U 1  (the reversal point located on the right in  FIGS. 1 and 6 ), where it reverses its direction and then proceeds back toward the front reversal point U 0 , which it reaches at the end of the laying cycle. The forward movement of laying carriage  10  between the reversal points U 0  and U 1  takes place during the time interval t 1 -t 0 , whereas the return movement of the laying carriage between the reversal points U 1  and U 0  takes place during the time interval t 2 -t 1 . The reversal points U 0  and U 1  of laying carriage  10  are defined in physical space and determine the laying width of fleece layer  2 . The laying width of fleece layer  2  may not be changed during operation. Many successive laying cycles are required to form a fleece. 
         [0037]    Under the assumption that no additional distortion of card web  6  occurs inside fleece layer  2  between upper carriage  30  and laying carriage  10 , the following equations apply to the speed U of the upper carriage at any point in time: forward movement: 
         [0000]    
       
         
           
             U 
             = 
             
               
                 1 
                 2 
               
                
               V 
             
           
         
       
     
         [0000]    return movement: 
         [0000]    
       
         
           
             U 
             = 
             
               
                 
                   1 
                   2 
                 
                  
                 V 
               
               + 
               W 
             
           
         
       
     
         [0038]      FIG. 2  shows by way of example the speed profiles in a fleece layer at a constant card web infeed speed V. Because upper carriage  30  is always moving toward the rear at half the card web infeed speed V during the forward movement of laying carriage  10 , the speed U of upper carriage  30  is also constant during the forward movement of laying carriage  10 . The speed W of laying carriage  10 , however, first undergoes a linear increase during its forward movement until it reaches a speed plateau, after which laying carriage  10  is braked and finally changes its direction at the rear reversal point U 1  (in the example here at t 1 =2.10 s). During the normal operation of a conventional fleece layer  2 , the two parts of the speed profile of the laying-carriage speed W are identical, except for their sign, during the forward and return movements. In other words, the average of the absolute values of the speed of laying carriage  10  during its forward movement (interval t 1 -t 0 ) is the same as the average of the absolute values of the speed of laying carriage  10  during its return movement (interval t 2 -t 1 ). The movement of laying carriage  10  on its forward and return journeys is synchronous. Expressed as a formula, this relationship looks as follows: 
         [0000]    
       
         
           
             
               
                 
                   ∫ 
                   
                     t 
                     0 
                   
                   
                     t 
                     1 
                   
                 
                  
                 
                   
                      
                     
                       W 
                        
                       
                         ( 
                         t 
                         ) 
                       
                     
                      
                   
                    
                   
                       
                   
                    
                   
                      
                     t 
                   
                 
               
               
                 
                   t 
                   1 
                 
                 - 
                 
                   t 
                   0 
                 
               
             
             = 
             
               
                 
                   ∫ 
                   
                     t 
                     1 
                   
                   
                     t 
                     2 
                   
                 
                  
                 
                   
                      
                     
                       W 
                        
                       
                         ( 
                         t 
                         ) 
                       
                     
                      
                   
                    
                   
                       
                   
                    
                   
                      
                     t 
                   
                 
               
               
                 
                   t 
                   2 
                 
                 - 
                 
                   t 
                   1 
                 
               
             
           
         
       
     
         [0039]    Upper carriage  30  continues to travel a short distance after laying carriage  10  has reached its reversal point U 1 , but then it, too, is braked, and arrives at its own rear reversal point U 3  shortly after laying carriage  10  reaches its own reversal point, whereupon the upper carriage is accelerated in linear fashion in the opposite direction until it reaches a speed with an absolute value greater than the constant speed during the forward movement. This speed plateau continues until a braking phase begins, which concludes at the front reversal point U 2 . Upper carriage  30  then proceeds to accelerate in the opposite direction. In terms of elapsed time, upper carriage  30  thus reaches its front reversal point U 2  before laying carriage  10  reaches its front reversal point U 0 . Then a new laying cycle begins. 
         [0040]    There are many different ways in which the speed profiles can be varied, especially with respect to the degree of acceleration, the length of the plateau phases, etc. Nevertheless, it is common to all conventional speed profiles that the average of the absolute values of the upper-carriage speed U during the forward movement of the laying carriage  10  (i.e., while laying carriage  10  is moving from the front reversal point U 0  to the rear reversal point U 1 ) is always half of the average of the absolute values of the card web infeed speed V. Expressed as a formula, this means: 
         [0000]    
       
         
           
             
               
                 
                   ∫ 
                   
                     t 
                     0 
                   
                   
                     t 
                     1 
                   
                 
                  
                 
                   
                      
                     
                       U 
                        
                       
                         ( 
                         t 
                         ) 
                       
                     
                      
                   
                    
                   
                       
                   
                    
                   
                      
                     t 
                   
                 
               
               
                 
                   t 
                   1 
                 
                 - 
                 
                   t 
                   0 
                 
               
             
             = 
             
               
                 1 
                 2 
               
                
               
                 
                   
                     ∫ 
                     
                       t 
                       0 
                     
                     
                       t 
                       1 
                     
                   
                    
                   
                     
                        
                       
                         V 
                          
                         
                           ( 
                           t 
                           ) 
                         
                       
                        
                     
                      
                     
                         
                     
                      
                     
                        
                       t 
                     
                   
                 
                 
                   
                     t 
                     1 
                   
                   - 
                   
                     t 
                     0 
                   
                 
               
             
           
         
       
     
         [0041]    During the forward movement of laying carriage  10 , furthermore, the average of the absolute values of the speed of laying carriage  10  is twice as high as the average of the absolute values of the speed of upper carriage  30  during the same time period. Expressed as a formula, this means: 
         [0000]    
       
         
           
             
               
                 
                   ∫ 
                   
                     t 
                     0 
                   
                   
                     t 
                     1 
                   
                 
                  
                 
                   
                      
                     
                       W 
                        
                       
                         ( 
                         t 
                         ) 
                       
                     
                      
                   
                    
                   
                       
                   
                    
                   
                      
                     t 
                   
                 
               
               
                 
                   t 
                   1 
                 
                 - 
                 
                   t 
                   0 
                 
               
             
             = 
             
               2 
                
               
                 
                   
                     ∫ 
                     
                       t 
                       0 
                     
                     
                       t 
                       1 
                     
                   
                    
                   
                     
                        
                       
                         U 
                          
                         
                           ( 
                           t 
                           ) 
                         
                       
                        
                     
                      
                     
                         
                     
                      
                     
                        
                       t 
                     
                   
                 
                 
                   
                     t 
                     1 
                   
                   - 
                   
                     t 
                     0 
                   
                 
               
             
           
         
       
     
         [0042]    Expressed in concrete numbers, the speed U of upper carriage  30  in the example of  FIG. 2  is constant at 50 m/min during the forward movement of the laying carriage, whereas the average of the absolute values of the speed W of laying carriage  10  during its forward movement is 100 m/min, thus corresponding to the average card web infeed speed V. During the return movement of laying carriage  10 , the average of the absolute values of the laying-carriage speed W is also 100 m/min. It can be seen that the laying width, which is 3.5 m in the present case, is traversed once in each direction by the laying carriage in a time of 4.20 s. 
         [0043]    All of the relationships expressed above as formulas also apply to the conventional operation of fleece layer  2  under conditions of fluctuating card web infeed speeds V. 
         [0044]      FIG. 3   a  now shows an example of the operation of fleece layer  2  according to the invention. The first essential point here is that, because of the upstream installation of speed changing device  52  for changing the card web speed, the card web infeed speed V is variable, thus showing a peak-and-valley type of profile. The speed U of the upper carriage  30  during the forward movement of laying carriage  10 , i.e., during the time that the laying carriage  10  is moving from the front reversal point U 0  to the rear reversal point U 1 , is again half as great as the card web infeed speed V and thus, in terms of its absolute value, the speed of the upper carriage is equal to half the card web infeed speed V but has the identical speed profile as V. Laying carriage  10  is initially accelerated more quickly during its forward movement and then reaches a speed plateau, which is higher than the continuous card web infeed speed V. The braking process extending up as far as the rear reversal point U 1  also proceeds more quickly, whereupon laying carriage  10  is then accelerated in the opposite direction, leading again to a speed plateau. Laying carriage  10  is then braked as it approaches the front reversal point U 0 . What is conspicuous and especially relevant here is that the increase in the average of the absolute values of the laying-carriage speed W during the forward movement of laying carriage  10  is greater than that during its return movement. This asynchronous increase in the laying-carriage speed W is an essential feature and ensures that the distance traveled by upper carriage  30  is limited. Expressed as a formula, we have: 
         [0000]    
       
         
           
             
               
                 
                   ∫ 
                   
                     t 
                     0 
                   
                   
                     t 
                     1 
                   
                 
                  
                 
                   
                      
                     
                       W 
                        
                       
                         ( 
                         t 
                         ) 
                       
                     
                      
                   
                    
                   
                       
                   
                    
                   
                      
                     t 
                   
                 
               
               
                 
                   t 
                   1 
                 
                 - 
                 
                   t 
                   0 
                 
               
             
             &gt; 
             
               
                 
                   ∫ 
                   
                     t 
                     1 
                   
                   
                     t 
                     2 
                   
                 
                  
                 
                   
                      
                     
                       W 
                        
                       
                         ( 
                         t 
                         ) 
                       
                     
                      
                   
                    
                   
                       
                   
                    
                   
                      
                     t 
                   
                 
               
               
                 
                   t 
                   2 
                 
                 - 
                 
                   t 
                   1 
                 
               
             
           
         
       
     
         [0045]    This also means that the average of the absolute values of the laying-carriage speed W during the forward movement of laying carriage  10  is greater than twice the average of the absolute values of the upper-carriage speed U during the forward movement of laying carriage  10 . Laying carriage  10  therefore travels, on average, more than twice as fast during its forward movement than upper carriage  30  does and catches up with it earlier than is the case with synchronous operation. Expressed as a formula, this means: 
         [0000]    
       
         
           
             
               
                 
                   ∫ 
                   
                     t 
                     0 
                   
                   
                     t 
                     1 
                   
                 
                  
                 
                   
                      
                     
                       W 
                        
                       
                         ( 
                         t 
                         ) 
                       
                     
                      
                   
                    
                   
                       
                   
                    
                   
                      
                     t 
                   
                 
               
               
                 
                   t 
                   1 
                 
                 - 
                 
                   t 
                   0 
                 
               
             
             &gt; 
             
               2 
                
               
                 
                   
                     ∫ 
                     
                       t 
                       0 
                     
                     
                       t 
                       1 
                     
                   
                    
                   
                     
                        
                       
                         U 
                          
                         
                           ( 
                           t 
                           ) 
                         
                       
                        
                     
                      
                     
                         
                     
                      
                     
                        
                       t 
                     
                   
                 
                 
                   
                     t 
                     1 
                   
                   - 
                   
                     t 
                     0 
                   
                 
               
             
           
         
       
     
         [0046]    As can be clearly seen from the graph, a laying cycle now lasts only about 3.80s, which is logical when we consider that the mass flow must remain constant. Constancy of mass flow means in this context that, on average, the average card web infeed speed V of the incoming card web should be the same as the average laying-carriage speed W. Because of the permanently defined laying width of 3.5 m, the laying cycle must necessarily be shorter. It should be noted however, that the laying carriage reaches the rear reversal point U 1  after only about 1.80 s and thus considerably before half of the duration of a laying cycle has been completed. 
         [0047]    In the example of  FIG. 3   a , the following values may be obtained: average of the absolute values of the speed of laying carriage  10  during its forward movement: 116 m/min; average of the absolute values of the speed of laying carriage  10  during its return movement: 107 m/min; and average of the absolute values of the speed of the upper carriage  30  during the forward movement of laying carriage  10 : 55 m/min. 
         [0048]      FIG. 3   b  shows a graph of the resulting distance/traveled by upper carriage  30  (in meters). Between its front reversal point U 2  and the rear reversal point U 3 , this carriage travels a distance of exactly 1.90 m. 
         [0049]      FIG. 4   a  shows another example of an inventive speed distribution during the operation of fleece layer  2 . The example is similar to that shown in  FIG. 3   a  with the difference that the acceleration and braking phases of laying carriage  10  are even steeper, and the speed plateaus are accordingly longer, although on a slightly lower level than in the case of the example of  FIG. 3   a . In the example of  FIG. 4   a , the following values may be obtained: average of the absolute values of the speed of laying carriage  10  during its forward movement: 114/min; average of the absolute values of the speed of laying carriage  10  during its return movement: 108 m/min; and average of the absolute values of the speed of upper carriage  30  during the forward movement of laying carriage  10 : 55 m/min. 
         [0050]    The associated graph of the distance traveled by the upper carriage  30  in  FIG. 4   b  shows that the upper carriage  30  again travels a distance/of 1.90 m. 
         [0051]    Finally,  FIG. 5   a  shows yet another example of inventive speed profiles in fleece layer  2 . Here the average of the absolute values of the laying-carriage speed W during the return movement of laying carriage  10  is greater than that during its forward movement. The following formula therefore applies: 
         [0000]    
       
         
           
             
               
                 
                   ∫ 
                   
                     t 
                     0 
                   
                   
                     t 
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         [0052]    The average of the absolute values of the speed of laying carriage  10  during its forward movement is smaller than twice the average of the absolute values of the speed of the upper carriage  30  during the forward movement of laying carriage  10 . Expressed mathematically, it reads: 
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         [0053]    Specifically the following values for the example shown in  FIG. 5   a  may be obtained: average of the absolute values of the speed of the laying carriage  10  during its forward movement: 106 m/min; average of the absolute values of the speed of laying carriage  10  during its return movement: 117 m/min; and average of the absolute values of the speed of the upper carriage  30  during the forward movement of laying carriage  10 : 56 m/min. 
         [0054]    The associated graph of the distance traveled by upper carriage  30  is shown in  FIG. 5   b . It can be seen from this graph that the distance/traveled by upper carriage  30  has increased slightly to 1.96 m. Nevertheless, there is no shift in the rear reversal point U 3 ; instead, it is the front reversal point U 2  which is shifted (toward the left in FIGS.  1  and  6 ,), which has no effect on the physical dimensions of fleece layer  2 , because upper carriage  30  reaches a point only about in the middle of fleece layer  2  as it travels toward the front. Care must be taken, however, to ensure that upper carriage  30  does not collide with other components such as tension carriage  40 . 
         [0055]    Overall, however, embodiments are preferred in which, on average, laying carriage  10  travels faster during its forward movement than during its return movement. When this is realized, it is possible to eliminate completely any increase in the distance traveled by the upper carriage. 
         [0056]    It is especially preferable to define physically in space two predetermined reversal points U 2 , U 3  for upper carriage  30  and to adjust the profile of the speed W of laying carriage  10  in such a way that upper carriage  30  does not travel beyond the predetermined reversal points U 2 , U 3  no matter what the variable card web infeed speed V is at which the card web enters fleece layer  2 . 
         [0057]    Considered overall, there are many different ways in which the speed profiles can be configured. They can also include more stages than in the examples discussed herein. They can, for example, include brief elevations within the plateau area of the laying-carriage speed. In all of the examples discussed herein, furthermore, the speed profiles have been set up so that the starting state is already present again at the end of each laying cycle, which means that the process of compensating for the variable card web infeed speed V has already been completed after one laying cycle. It is also possible, however, to reach this goal only after several laying cycles. For example, the average speed of laying carriage  10  during its forward movement can be set very high during the first laying cycle, and this difference would then be compensated over the course of several return movements during subsequent laying cycles. It is also conceivable that several normal laying cycles with a synchronous laying-carriage speed profile could follow the asynchronous laying cycle as disclosed herein. 
         [0058]    According to the embodiments discussed above, a total of two card web conveyor belts  16 ,  36  are installed in fleece layer  2 . The invention can also be applied in other types of fleece layers with two card web conveyor belts and also to any other type of fleece layer designed as a co-directional machine, including those with three belts. An example of a fleece layer of this type with three card web conveyor belts is shown in  FIG. 6 . In the case of the fleece layer shown in  FIG. 6 , second card web conveyor belt  16  of the embodiment according to  FIG. 1  is replaced by a second card web conveyor belt  70  and third card web conveyor belt  72 , which are deflected in a common tensioning carriage  74 . 
         [0059]    Reference throughout this specification to “the embodiment,” “this embodiment,” “the previous embodiment,” “one embodiment,” “an embodiment,” “a preferred embodiment” “another preferred embodiment” “the example,” “this example,” “the previous example,” “one example,” “an example,” “a preferred example t” “another preferred example” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. Thus, appearances of the phrases “in the embodiment,” “in this embodiment,” “in the previous embodiment,” “in one embodiment,” “in an embodiment,” “in a preferred embodiment,” “in another preferred embodiment,” “in the example,” “in this example,” “in the previous example,” “in one example,” “in an example,” “in a preferred example,” “in another preferred example, and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. 
         [0060]    Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments or examples. One skilled in the relevant art will recognize that the invention may be practiced without one or more of the specific features or advantages of a particular embodiment or example. In other instances, additional features and advantages may be recognized in certain embodiments or examples that may not be present in all embodiments of the invention. 
         [0061]    While the present invention has been described in connection with certain exemplary or specific embodiments or examples, it is to be understood that the invention is not limited to the disclosed embodiments or examples, but, on the contrary, is intended to cover various modifications, alternatives, modifications and equivalent arrangements as will be apparent to those skilled in the art. Any such changes, modifications, alternatives, modifications, equivalents and the like may be made without departing from the spirit and scope of the invention.
The method for operating a fleece layer requires a fleece layer, to which the card web is supplied at variable card web infeed speed. To limit the amount of space required for the upper carriage at the rear of the machine, the average of the absolute values of the laying-carriage speed during the forward movement of the laying carriage in at least some laying cycles differs from the average of the absolute values of the laying-carriage speed during the return movement of the laying carriage, and the average of the absolute values of the laying-carriage speed in at least some laying cycles during the forward movement of the laying carriage differs from twice the average of the absolute values of the upper-carriage speed during the forward movement of the laying carriage.