Abstract:
A mail processing apparatus feeds mail articles one by one, along a transport path. A stamp detecting device is disposed along the path to detect a stamp on the mail article. The stamp detecting device includes a light source for radiating ultraviolet light towards both sides of the mail article in the transport path, and converters for converting the luminescences excited by the ultraviolet light on both sides of the mail article. Two signal levels are detected and compared for determining where the stamp is located. This way, a stamp does not appear to be on both sides of a very thin article.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an apparatus for processing mail articles such as postcards and letters, and more particularly to a stamp detector used in a mail processing apparatus such as a mail cancelling and/or facing apparatus. 
     Luminescent stamps that emit fluorescence or phosphorescence have been widely used as postage stamps in, for example, Europe and U.S.A. In mail cancelling and/or facing apparatus, therefore, the fluorescence or phosphorescence emitted from the postage stamps is utilized to detect the postage stamps. In the conventional mail cancelling and facing apparatus, as disclosed in the U.S. Pat. No. 3,938,435 entitled AUTOMATIC MAIL PROCESSING APPARATUS issued to Suda et al., the mail articles are taken one by one from a mail feeding portion and are transferred through a transport path. The stamp on the mail article is then detected by stamp detectors disposed along, and on both sides of, the transport path. Then, the stamp is cancelled by cancellers which are disposed on both sides of the transport path and are selectively actuated on the basis of the results of the stamp detection. The mail articles are positioned to face with the stamps in the same relative position, in response to the positions of the detected postage stamps. 
     In order to improve the mail processing efficiency in the mail cancelling and facing apparatuses of this kind, the sensitivity of the stamp detector has been increased to detect the stamps which emit a weak luminescence. However, when the stamp having large intensity of emitting fluorescence or phosphorescence is put on a thin mail article, such as a thin postcard, the emitted luminescence would penetrate to the reverse side of that article. Hence, both of the pair of stamp detectors disposed on opposite sides of the transport path would produce stamp detection outputs. In this case, the mail article is not processed and is rejected as an abnormal mail article. For this reason, the processing efficiency, or detection ratio, of the conventional mail cancelling and facing apparatus would drop if a large number of thin mail articles are contained in a batch of mail articles. If the sensitivity of the stamp detector is reduced to prevent such an erroneous operation, the stamp having a low luminescent intensity can not be detected and consequently, the subsequent cancelling and/or facing operation can not be effected. This also results in the deterioration of the processing efficiency of the apparatus. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a mail processing apparatus which can reliably detect a luminescent stamp on a mail article, even if the mail article is so thin that the luminescence emitted from the stamp penetrates from its upper surface to its reverse surface. 
     It is another object of the present invention to provide a mail processing apparatus which can reliably detect a stamp on a mail article, even if the stamp has low luminescent intensity. 
     In accordance with the present invention, a mail processing apparatus comprises a feeding device for feeding mail articles one by one to a transport path. A stamp detecting device is disposed along the transport path for detecting a stamp on the mail article. The stamp detecting device includes a light source for radiating ultraviolet light on to both sides of the mail article as it moves in the transport path. Converters on both sides of the mail article respond to the luminescences excited by the ultraviolet light to produce two signal levels. A comparator compares the two signal levels and selectively gates them in response to the output of the comparator. A stamp determining circuit compares the gated signal level with a predetermined thereshold level. 
     In accordance with a first embodiment of the present invention, a mail cancelling and facing apparatus comprises a feeding device for feeding mail articles one by one, in a standing state. A first transport path transfers the mail articles from the feeding device. A first stamp detecting device is disposed along the first transport path for detecting a stamp at the lower part of the mail article and on both sides of the mail article. A second transport path advances the mail article in a straight line if the stamp is detected by the first stamp detecting device and over a twisting path if the stamp is not detected. A third transport path transfers the mail article transported from the second transport path. A second stamp detecting device is disposed along the third transport path for detecting the stamp at the lower part of the mail article and at both sides of the mail article. 
     A pair of cancellers are disposed downstream of the second stamp detecting device, one canceller on each side of the third transport path for cancelling the stamp. A fourth transport path is disposed in succession to the third transport path downstream of the pair of cancellers for reversing the direction of the mail article whose stamp is cancelled by one of the cancellers and for transferring the mail article whose stamp is cancelled by the other canceller. 
     A stacker is disposed downstream of the fourth transport path for stacking the mail articles. Each of the first and second stamp detecting devices include two luminescence receiving elements for receiving the luminescence derived from the same position on both surfaces of the mail article. A comparing circuit compares the output level delivered from the two luminescence receiving elements and a selecting circuit selects one of the outputs from the two luminescence receiving elements, in accordance with the output of the comparing circuit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an embodiment of the present invention, especially its mechanical portions, taken as a whole; 
     FIGS. 2(a), 2(b), 2(c) and 2(d) indicate the four possible positions of a stamp on a mail article which is supplied to the embodiment shown in FIG. 1; 
     FIG. 2 illustrates the construction of the stamp detecting device according to the present invention; 
     FIG. 4 shows waveforms which are useful for explaining the operation of the stamp detecting device shown in FIG. 3; and 
     FIG. 5 illustrates the second embodiment of the present invention, especially its stamp detecting device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In a first embodiment of the present invention shown in FIG. 1, mail articles are fed, one by one, from a feedding device 1 and are transferred through a first transport path 2 while being kept in a standing state. A stamp on the mail article is detected at both sides of the transport path by a first stamp detecting device 3 that is disposed along the transport path 2. In this embodiment, the numeral 1&#39; indicates a sub-transport path which receives a mail article supplied from another mail handling apparatus. The first stamp detecting device 3 comprises two stamp detectors 3a and 3b disposed on both sides of the transport path and positioned to scan the lower part of the mail articles. 
     The mail articles fed from the feeding device 1 can be classified into four groups, as shown in FIGS. 2(a) through 2(d), depending upon the position of the stamp. The first stamp detecting device 3 can detect the stamp positions shown in FIGS. 2(b) and 2(c). Among the mail particles that leave the first stamp detecting device 3, the mail article whose stamp is detected by the detecting device 3 passes through a straight path 4a. The mail article whose stamp is not detected passes through a twisting path 4b, including twist belts which turn it upside down, and then it is sent to a third path 5. Thus, all of the mail articles that pass through the third transport path 5 are sent under the positions shown in FIGS. 2(b) and 2(c), except for those which have no stamp. 
     A second stamp detecting device 6 is disposed along the third transport path 5 and it also scans the lower parts of the mail articles. The second stamp detecting device 6 also comprises a pair of stamp detectors 6a and 6b which are disposed at opposite sides of the transport path 5. The stamp detector 6a detects the stamp on the mail article whose stamp is put on the left side with respect to the travelling direction, and this stamp is cancelled by a canceller 7. On the other hand, the stamp detector 6b detects the stamp on the mail article whose stamp is put on the right side, with respect to the travelling direction, and a canceller 8 imprints the cancelling mark (postmark) upon it. 
     A fourth transport path 9 is formed downstream of these cancellers 7 and 8 and consists of a straight path 9a and a direction reversing path (switch-back path) 9b. The mail article whose stamp is cancelled by the canceller 8 passes through the straight path 9a and is stacked in a stacker 10. On the other hand, the mail article whose stamp is cancelled by the canceller 7 passes through the switchback path 9b and is stacked in the stacker 10. The mail article whose stamp is not detected is transferred to the straight path 9a and then stacked in a rejection stacker 11. 
     Diverters 12 and 13 are disposed at the inlets of the second and fourth transport paths 4 and 9, to selectively feed the mail article into the transport path 4a and 4b, and 9a and 9b, respectively, in accordance with the detection results of the stamp detecting devices 3 and 6. Accordingly, all the mail articles packed in the stacker 10 are facing in the same stamp position. 
     Next, the stamp detecting devices 3 and 6 shown in FIG. 1 will be explained, referring to FIG. 3. Since they have the same construction, only the stamp detecting device 3 will be described. In FIG. 3, the fluorescence- or phosphorescence-emitting stamp 15 is on the transported mail article 14. The stamp detecting device 3 includes the pair of stamp detectors 3a and 3b. The stamp detectors 3a and 3b includes ultraviolet light sources 16a and 16b, scanning optical elements 17a and 17b, and photoelectric conversion elements 18a and 18b, respectively. The ultraviolet lights from the ultraviolet light sources 16a and 16b excite both the luminescent emitting stamp 15 and the opposite side of the mail article. 
     The secondary luminescence, such as fluorescence and phosphorescence, is derived from the stamp 15. This luminescence is detected by the photoelectric conversion elements 18a and 18b. The detection levels A and A&#39; (FIG. 4) are delivered from the respective elements 18a and 18b and are applied to stamp determining circuits 20a and 20b via gates 19a and 19b, respectively. The stamp detectors 3a and 3b, in this case, are located to detect the same position on opposite sides of the mail article. When the detected level of the signal supplied to the determining circuit 20a or 20b is greater than a predetermined threshold level, the circuit determines that the stamp is detected. A control circuit 21 receives the outputs of both determining circuits 20a and 20b and controls the diverter 12 (FIG. 1) in accordance with the result. 
     In the prior art apparatus, the stamp detection outputs are sometimes derived simultaneously from both the determining circuits 20a and 20b so that the mail article is transferred to the rejecting stacker. In contrast, the present invention eliminates such a problem by the use of comparators 22a and 22b which compare the detection levels A and A&#39; with each other. Only if the detection level A from the photoelectric conversion element 18a is greater than a predetermined amount above a predetermined threshold value β, as compared to the detection level A&#39; from the element 18b (A&gt;A&#39;+β), the comparator 22a does not produce an inhibit signal for the gate 19a. In this case, the other comparator 22b produces an inhibit signal for the other gate 19b. When A&#39;&gt;A+β, on the other hand, the comparator 22b does not produce the inhibit signal for the gate 19b while the comparator 22a produces the inhibit signal for the other gate 19a. According to this arrangement, the two stamp determining circuits do not simultaneously produce two stamp detection outputs, which cause the mail article rejection. Thus, there is no article rejection even when a stamp having a high luminescent intensity is put on a very thin mail article. 
     According to the present invention, only the detection level corresponding to a more sufficient luminescent intensity is applied for detecting the stamp. Furthermore, according to the present invention, it is possible to shift to a lower threshold level α, in order to detect a stamp having a lower luminescent intensity. In this embodiment the scanning optical elements 17a and 17b scan the same position on both sides of mail article. Therefore, a signal timing adjustment is easily performed in the blocks 22a, 22b, etc. 
     In FIG. 4, the detection levels A and A&#39; are derived from the photoelectric conversion elements 18a and 18b both exceed the threshold value α. Hence, both stamp determining circuits 20a and 20b detect a stamp without comparators 22a and 22b. In the present invention, since the comparator 22b produces the inhibit signal E&#39;, only the output B of the stamp determining circuit 20a is applied to the control circuit 21. 
     The embodiment shown in FIG. 3 makes use of the two comparators 22a and 22b. However, the gates 19a and 19b can be easily and selectively controlled by use of one comparator. FIG. 5 shows such an embodiment. The outputs of the photoelectric conversion elements 18a and 18b are directly applied to the stamp determining circuits 20a and 20b. The outputs of these circuits 20a and 20b are applied to the control circuit 23. The comparator 22 compares the detection levels of the elements 18a and 18b with each other. The control circuit 23 selects one of two outputs delivered from the circuits 20a and 20b, and produces either a diverting signal for the diverter 12 or a cancelling signal for the canceller when the circuit 23 selects a predetermined one of the two outputs and the selected one is effective, i.e. when the level from the photoelectric conversion element supplied to the selected stamp determining circuit 20a, 20b is greater than the threshold level. 
     As mentioned above, when the apparatus embodying the present invention is operated for cancelling and facing the mail article having the luminescent stamp on it, it can detect exactly the stamp even if there are variations in emitting luminescence.