Abstract:
A printer for printing on a receiving medium of a predetermined type, including a plurality of feeders for holding receiving media and a control unit, wherein the control unit contains determining means for determining that at least two feeders of the said plurality of feeders hold receiving medium of the predetermined type, means for determining the amount of receiving medium which can be added to each of the two feeders up to a predetermined maximum amount for these feeders, and means for selecting the feeder to which the largest amount receiving medium can be added for feeding a receiving medium to the printing unit.

Description:
This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No(s). 03079005.9 filed in Europe on Dec. 19, 2003, the entire contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a printer comprising a printing unit for printing on a receiving medium of a predetermined type, a plurality of feeders for holding receiving media, and means for establishing the type of receiving medium held by each of the feeders. 
   The present invention furthermore relates to a method for printing a receiving medium of a predetermined type using a printer having a printing unit and a plurality of feeders for holding the receiving media, the method including the establishment of the type of receiving medium to be held by each of the said feeders. 
   The printer, which is known from U.S. Pat. No. 4,885,613 includes a plurality of feeders with the same receiving medium in the form of a roll or sheets wherein the feeder is selected from the largest amount of recording medium remaining therein. In such a printer, a nearly empty feeder will only be fully emptied if the other feeders holding the same type of receiving medium have been also emptied. Thus, a printer will almost never contain an empty feeder in which another type of receiving medium, for example receiving sheets having another format, another color or another thickness can be inserted. The feeders will be used successively since after using one feeder, the amount of receiving sheets remaining therein will be less than the amount of receiving sheets in another feeder so that said other feeder with the larger amount of receiving sheets will be selected by the control unit. For example, in the case where there are four feeders containing the same type of receiving sheets, all four feeders will be used successively and become empty at almost the same moment. At that moment the operator needs to replenish all feeders at the same time. By using the feeders successively, many feeder changes, involving relatively elaborate operator handling, will occur. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a printer whereby the feeders will be used in a more optimised manner. 
   This object is achieved by utilizing a printer containing a means for determining for at least two feeders holding a predetermined type of receiving material, the amount of receiving medium which can be added to each of these feeders up to a predetermined maximum amount, and means for selecting the feeder to which the largest amount of receiving medium can be added for feeding the receiving medium to the printing unit. 
   By utilizing receiving sheets from the feeder to which the largest amount of receiving medium can be added, this feeder will be fully emptied before another feeder will be selected. In this manner, only a relatively small number of feeder changes will occur. Since the feeder which is being selected will be fully emptied before another feeder will be selected, the feeder will become available for using another type of receiving medium, if necessary. Furthermore, if an operator wants to replenish the feeders, he can add a relatively large amount of receiving sheets to the feeder which is at that moment being selected by the control unit as the feeder for feeding receiving sheets to the printing unit. 
   The printer, according to the present invention, gives the operator substantial freedom to decide when he wants to replenish the feeders and which feeders he wants to replenish. 
   In one embodiment of the printer according to the present invention, the feeder closest to the printing unit is selected, for example by a control unit, in the case where there are more feeders to which the same largest amount of receiving medium can be added. By selecting the feeder closest to the printing unit, the printer will be able to print relatively fast on the receiving medium. In the case where there are more feeders at the same distance from the printing unit, the lowest feeder is preferably selected. 
   In another embodiment of the printer according to the present invention, the feeder which has the smallest amount of receiving medium therein is selected, for example by the control unit, in the case where there are more feeders having the same largest amount of receiving medium which can be added. By utilizing feeders having different predetermined maximum amounts, the feeder which has the smallest amount of receiving medium left therein will be selected. This feeder will thus be emptied relatively quickly so that it becomes available for other types of receiving medium. 
   In yet another embodiment of the printer according to the present invention, the printer includes a level detector means for determining the amount of receiving medium available in the feeders, and also includes subtraction means for subtracting the available amount from a predetermined maximum amount to obtain the amount of receiving medium which can be added to each feeder. In this manner the amount of receiving medium that can be added to each feeder can be determined in a relatively easy manner. 
   In a further embodiment of the printer according to the present invention, the printer contains means for measuring the distance between a first level at which the feeder is filled with receiving medium up to the predetermined maximum amount and a second level up to which said feeder is actually filled with receiving medium. By measuring this distance, the amount of receiving medium which can be added can be determined relatively easily. 
   The amount of receiving medium which can be added to each feeder can be determined relatively accurately or relatively rough in which latter case, there will be established a kind of threshold. For example, the amount of sheets can be determined by using increments equal to 100. In the latter case for example, the amount of sheets that can be added is determined as zero sheets, 100–200 sheets, 200–300 sheets etc. 
   The present invention also relates to a method for printing a receiving medium of a predetermined type using a printer having a printing unit and a plurality of feeders for holding receiving media, the method including the steps of establishing the type of receiving medium held by each of the feeders, and, if the predetermined type of receiving material is held by at least two feeders, determining the amount of receiving medium which can be added to each of the said at least two feeders up to a predetermined maximum amount, and selecting the feeder to which the largest amount of receiving medium can be added for feeding the receiving sheet to the printing unit. By following this method, a once chosen feeder will be fully emptied before another feeder will be selected unless another empty feeder will be refilled with a very small amount of paper, in the case of which this feeder will be selected. In this manner feeders will be emptied relatively quickly and become available for other types of receiving media. Furthermore an operator will have a relatively large freedom by replenishing the feeders. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will further be explained with reference to the drawings wherein, 
       FIG. 1  schematically shows a set of feeders of a printer according to the present invention; 
       FIG. 2  shows a printer according to the present invention; and 
       FIG. 3  schematically shows a feeder comprising sensing means according to the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a part of a known printer containing a printing unit (not shown), a plurality of feeders  1 ,  2 ,  3  for feeding receiving sheets  4  to the printing unit and a control unit (not shown) for controlling the printing process. The printer may include a large number of feeders of which only three feeders are being shown. In the three feeders, the same type of receiving sheets, for example sheets with an A4-format, 80 grams, and white color are available. In the present embodiment, this is established automatically by the printer by using art known sensing means for sensing the type of receiving material. In another embodiment, the type of receiving material is programmed by the operator and stored in a memory, for example the memory of a control unit of the printer. In feeder  1  a predetermined maximum amount of receiving sheets  4  is MAX 1 , the predetermined maximum amount of feeder  2  is MAX 2  and the predetermined maximum amount of feeder  3  is MAX  3 . The maximum amount for feeders  1 ,  2  is the same so that MAX 1 =MAX 2 , whereby MAX 1  is for example 1000 sheets. The predetermined maximum amount MAX 3  of feeder  3  is larger than the maximum amounts MAX 1 , MAX 2  and is for example 3000 sheets. 
     FIG. 2  shows a printer  5  utilizing the three feeders as shown in  FIG. 1 , a printing unit  6 , a control unit  7  for controlling the printer  5  as well as a tray  8  in which sheets on which information is printed by printing unit  6  can be stored. Although depicted as one single unit  7 , it is clear that the control unit may also consist of several subunits distributed over the printer. Other parts of the printing unit  6  are the imaging belt  20 , charging station  21 , printhead  22  with control unit  23 , developing station  24 , intermediate transfer belt  25  and transfer nip  26 . Such a printer is described in greater detail in European patent application EP 0 599 374 the subject matter of which is hereby incorporated by reference. 
   The printer  5  includes sensing means (not shown) for each feeder  1 ,  2 ,  3  provided with level detector means for determining the amount of receiving sheets Δ 1 , Δ 2 , Δ 3  available in each feeder  1 ,  2 ,  3 . The sensing means furthermore comprise subtracting means for subtracting the available amount Δ 1 , Δ 2 , Δ 3  from the predetermined maximum amount MAX 1 , MAX 2 , MAX 3  to obtain the amount ADD 1 , ADD 2 , ADD 3  of receiving sheets which can be added to each feeder  1 ,  2 ,  3 . 
   The feeder  1  comprises, for example, an amount Δ 1  of 300 receiving sheets  4  so that ADD 1  is 1000−300=700. In feeder  2  the available amount Δ 2  is 600 so that ADD 2  is 1000−600=400. In feeder  3  the available amount Δ 3  is 1600 so that ADD 3  is 3000−1600=1400. It is not absolutely necessary to determine the exact amount of receiving sheets  4  but a rough estimation rounded up to hundreds might work as well. 
   By using the control unit it can now be determined to which feeder the largest amount of receiving sheets can be added. By the example given above, the feeder  3  will be selected since ADD 3  (1400) is larger than ADD 2  (400) and ADD 1  (700). By selecting feeder  3 , several printing processes can be done until feeder  3  is fully emptied. By the control unit it will then be decided to use feeder  1  since ADD 1  with 700 sheets is larger than ADD 2  with 400 sheets. An operator can be informed of the available amount Δ 1 , Δ 2 , Δ 3  and/or the amount ADD 1 , ADD 2 , ADD 3  of receiving sheets which can be added to each feeder, by means of a display (not shown) or by an indicator means (not shown) on each feeder  1 ,  2 ,  3  or by opening each feeder  1 ,  2 ,  3 . The operator can then replenish the feeder  3  with a relatively large amount of receiving sheets. After replenishing the empty feeder  3 , the control unit will continue by emptying feeder  1 . After feeder  1  is emptied, the control unit will select feeder  2  since after emptying feeder  1  and replenishing feeder  3  up to the maximum amount MAX 3 , feeder  2  has the largest amount ADD 2  of receiving sheets which can be added. The operator can replenish feeder  1  before feeder  2  is fully emptied or can replenish both feeders  1  and  2  after the feeder  2  is also emptied. Preferably a feeder  1 ,  2 ,  3  is not replenished while a feeder  1 ,  2 ,  3  is being used as a feeder for feeding a receiving sheet to the printing unit, to prevent disruption of the printing process. If a feeder is opened, another feeder will be selected temporarily. 
   Instead of determining the amount Δ 1 , Δ 2 , Δ 3 , it is also possible to provide the printer with sensing means for measuring between a first level LM 1 , LM 2 , LM 3  at which the feeder  1 ,  2 ,  3  is filled with receiving sheets  4  up to the predetermined maximum amount MAX 1 , MAX 2 , MAX 3  and a second level L 1 , L 2 , L 3  up to which said feeder  1 ,  2 ,  3  is actually filled with receiving sheet  4 . The distance D 1 , D 2 , D 3  is a measure of the amount of receiving sheets which can be added, whereby the largest distance, in this example D 3 , corresponds with the largest amount of receiving sheets which can be added. 
     FIG. 3  shows another kind of feeder  9  in which the stack of receiving sheets  4  is located on a platform  10  which is movable under a spring force in an upward direction until the upper sheet  4  is located against a transport roller  11 . The level L 4  of the platform  10  is determined by means of the control unit  7  in which also the maximum level LM 4  of the platform  10  is also being stored. The difference between the maximum level LM 4  and L 4  provides the control unit  7  with information about the actual amount of receiving sheets in the feeder  9  while the level L 4  is a direct measure of the amount of receiving sheets which can be added to the feeder  9 . 
   The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.