Patent Publication Number: US-2007100640-A1

Title: Method for operating a detector for identifying the overlapping of flat mail in a sorting machine

Description:
The invention relates to a method for operating a detector for identifying the overlapping of flat mail items in a transport path of a sorting machine following on from a separation unit.  
      In conventional mail processing systems batches of mail items are separated in sorting machines. It can occur here that a number of mail items are withdrawn from the stack simultaneously, i.e. a number of overlapping items of mail leave the feeder and lead, if this problem is not detected, to mis-sorting. For these reasons it is necessary to detect the overlaps in good time after they have left the separation unit in order to guide them into a rejected items terminal/reject compartment (cf. U.S. Pat. No. 6,023,034 A).  
      Corresponding detectors have previously been known which determine overlaps caused by multiple withdrawals from the separation unit on the basis of a number of different measurement principles. The multiple withdrawals detected are guided into the rejected items terminals of the sorting machines to avoid incorrect distribution of the mail items. Thus DE 43 37 004 A1 describes a device and a method for detecting overlaps of bendable flat mail items in which in the transport path at least one section of each item can be moved at right angles to the direction of conveyance. At least one deflection element is arranged on the transport path, through which the movable mail item sections are deflected at right angles to the direction of conveyance by a predetermined amount during conveyance in the transport path. In one direction of detection, because of the springback behavior of the mail items the presence of overlapping mail item sections is detected.  
      Also known are corresponding detectors in which the narrow sides of the separated mail items are recorded by image recording devices and then evaluated in an image processing device by evaluating the image signals to establish whether a number of mail items are being transported overlapped, e.g. by counting the dark-to-light transitions (FR 2 546 083 A, 2 057 309 A).  
      All these detectors have a fixed point of operation with a specific error and detection rate in which they are operated independently of the process in which they are included.  
      The object of the invention is to create a method for automatic operation of a detector for detecting overlaps of flat mail items in a transport path following on from a separation unit of a sorting machine, in which the detector is operated as a function of the sorting and distribution process conditions.  
      In accordance with the invention the object is achieved by the features of claim  1 .  
      In this case the average costs C NDD  of each undetected overlap in the distribution and sorting process and the average costs C RF  for the resorting and re-distribution of each detected overlapped mail item are determined off-line. Prior to sorting, the detection rate DR(P i ) and the error rate ER(P i ) of the detector is determined for different operating points, depending on a corresponding adjustment parameter P i . During sorting operation, for defined time intervals or intervals in which a defined number of mail items are processed in the sorting machine, the current overlap rate DFR′(P i ) of the sorting machine in each case is estimated from the detection result, the detection rate DR(P i ) and the error rate ER(P i ) depending on the adjustment parameters P i .  
      From the equation for the benefit CB′(P i ) of the operator of the sorting and distribution process 
 
 CB′ ( P   i )= N {( DFR ′( P   i )* DR ( P   i )*( C   NDD   −C   RF ))−( ER ( P   i )* C   RF *(1 −DFR ′( P   i )))}
 
 the current adjustment parameter in optimizing calculations P opt. is subsequently determined  with the greatest utility CB′(P opt. ) with which the detector can be operated up to the next Interval. This means that the detector can automatically be operated to optimize costs even where costs and process conditions differ. 
 
      It is advantageous to determine the current overlap rate DFR′(P i ) for the different setting parameters P i  from the relationship  
             DFR   ′     ⁡     (     P   i     )       =           N   AD     N     -       ER   ′     ⁡     (     P   i     )               DR   ′     ⁡     (     P   i     )       -       ER   ′     ⁡     (     P   i     )             ,       
 
 with N AD  being the number of overlaps determined by the detector for the number N of detected mail items in an interval.
 
    
    
      The invention will be explained in greater detail below with reference to the drawing in an exemplary embodiment.  
      The figures show  
       FIG. 1 a  diagram of the detection rate and the error rate of a detector as a function of adjustment parameter P i ;  
       FIG. 2 a  block diagram of the operating process. 
    
    
      The overlaps detected by the overlap detector, that its a number of mail items leaving the separation unit of the sorting machine overlapped, are directed into what is referred to as a reject compartment and then fed back again to the separation unit. The mail items filtered out in this way consist in this case of both true overlaps and mail items incorrectly detected as overlaps. If the overlapped mail items are not detected and filtered out the mail items associated with the item with the read address would at least be sent into the incorrect next distribution center and would then have to be forwarded to the correct address from there.  
      This naturally causes additional costs which, minus the costs of feeding the overlaps back through the unit, can be avoided by early detection of the overlaps. Since the detection process can also detect normal mail items incorrectly as overlaps as a result of incorrect detection, the costs for the additional sorting of these mail items in the relevant sorting machine must be subtracted from the additional costs saved.  
      The utility CB for the operator of the sorting and distribution process is thus produced by the following equation 
 
 CB=N {( DFR*DR* ( C   NDD   −C   RF ))−( ER*C   RF *(1 −DFR )}
 
Where 
 
N*DFR*DR 
 
 is the number of overlaps detected in the observation period and 
 
 N*ER* (1 −DFR ) 
 
 is the number of incorrectly detected individual mail items, with 
 
      N=the number of mail items processed  
      DFR=the overlap rate of the sorting machine  
      DR=the detection rate of the detector  
      ER=the error rate of the detector  
      C NDD =the costs of each overlap not detected  
      C RF =the costs of each feed back to the relevant sorting machine of detected overlaps  
      These costs are dependent on the relevant type of mail item processing, i.e. whether for example input sorting or output sorting of the item is involved.  
      Detectors for determining overlapping previously operated with a fixed operation point with a specific detection rate DR and a specific error rate ER, which can be determined for example in accordance with DE file ref. 103 10 546.8-27.  
      In order to influence the utility for operation it is necessary to parameterize the detection and error rate, i.e. they are able to be changed as a function of an adjustment parameter P i . Examples of this dependency are shown in Tab. 1 and  FIG. 1 .  
                                                   TABLE 1                                   P 1     P 2     P 3     P 4     P 5     P 6     P 7     P 8                                                                          ER   0.1   0.4   0.7   1   1.3   1.7   2   2.3       DR   80.0   84.3   87.5   90.3   92.5   95.0   96.3   97.5                  
 
      It can be seen from this table that as the detection rate increases the error rate also increases.  
      Thus the utility for the operator is produced by the following parameterized equation 
 
 CB ′( P   i )= N {( DFR ′( P   i )* DR ( P   i )*( C   NDD   −C   RF ))−(ER(P i )* CRF *(1−DFR′(P i )))}
 
      The following estimated value for the current overlap rate of the relevant sorting machine is produced  
           DFR   ′     ⁡     (     P   i     )       ⁢           N   AD     N     -       ER   ′     ⁡     (     P   i     )               DR   ′     ⁡     (     P   i     )       -       ER   ′     ⁡     (     P   i     )               
 
      The overall detection and optimization process is shown in  FIG. 2 .  
      The block diagram in  FIG. 2  provides an overview of the execution sequence of the method. The overlap detector detects the overlaps during the sorting and distribution process  1 , said overlaps then been fed into the reject compartment and thus being excluded from the regular process. This reduces the number of incorrect sortings and also the costs C NDD  of each overlap not correctly detected. The mail items from the reject compartments are fed back into the sorting machine and thus generate additional costs C RF  per mail item. These costs C NDD , C RF  serve as input data for the utility optimization  2  for the process operator. They are derived off-line from the process model. It is evident in this case that these costs are dependent on the type of process involved, i.e. the incorrect sorting costs for what is known as input sorting and distribution process in accordance with a street and house number are different from the incorrect sorting costs and for what is known as the output sorting and distribution process in accordance with zip code and geographical location. In Table 2 for example the corresponding costs for a specific machine type (FVM) are specified.  
                                   TABLE 2                                       Machine   C NDD     C RF             Type of sorting   type   [US $]   [US $]                          Input sorting   FVM   0.058   0.0035           Output sorting   FVM   0.040   0.0035                      
 
      The sorting process  3  with the overlapping detection includes the major components separation 3.1, followed by overlapping detection 3.2 and thereafter the sorting 3.3 in accordance with the destination addresses read. The detected overlaps are fed again via the reject compartments to the separation process 3.1. The mail items detected as individual mail items (including the undetected overlaps) are distributed into the sort compartments provided in accordance with the sorting plan.  
      From the number of overlaps detected with in the observation period and the parameterized performance figures ER′(P i ) and DR′(P i ) 2.2 the current estimated overlap rate DFR′ 2.4 is detected in the utility optimization  2 .  
      From the utility equation/utility model 2.3 
 
 CB ′( P   i )= N {( DFR ′( P   i )* DR ( P   i )*( C   NDD   −C   RF ))−( ER ( P   i )* C   RF *(1 −DFR ′))}
 
 the parameter P opt  with the maximum utility CB′ is then determined in an optimization process 2.1 
 
      For the detector with the performance parameters shown in Tab. 1 and  FIG. 1 , error costs C NDD =0,058, C RF =0.0035 and N=1,000.000 processed mail items, Tab. 3 shows the utility depending on the overlap rate DFR′ and on the parameter P i . The maximum utility for each overlap rate is shown underscored and in bold type. The associated adjustment parameter P i  is then the selected and automatic set parameter P opt .  
                                               TABLE 3                       DFR   P1   P2   P3   P4   P5   P6   P7   P8                  0.10%                                                       0.40%                                                       0.70%                                                       1.00%                                                       1.30%                                                       1.60%                                                       1.90%                                                       2.20%                                                       2.50%