Method of checking and combining separate documents or part documents of the letter and envelope type

A method for checking and combining separate documents having sections of text imprinted thereon for ensuring that documents taken from two or more groups possess the same identical sections of text includes the steps of conveying the documents taken from the groups of documents along a conveyor to a scanning position in front of an opto-electrical scanning device and scanning the documents with the opto-electrical scanning device in order to produce a series of digital signals. The digital signals associated with documents from two different groups of documents are then compared in a comparator to determine if the signals are identical.

FIELD OF THE INVENTION 
The present invention relates to a method of checking and combining 
documents and more particularly, a method of checking and combining 
separate documents or parts of documents of the letter and envelope type. 
BACKGROUND OF THE INVENTION 
It is known that separate documents of the letter and envelope type may be 
combined with the help of automatic machines which fold up the letter 
paper, open the envelope, insert the folded-up letter in the envelope and 
then seal the envelope with the letter inside. 
It is also known that machines of the abovementioned type may be combined 
with devices for imprinting the name and address of the envelope as well 
as the letter. However, the printing of the envelope can be avoided 
through use of window envelopes which permit the address imprinted on the 
letter to be visible through the transparent window of the envelope. 
In certain cases it is desirable to distribute more personally formulated 
letters in mass edition, which can be done with the help of modern 
techniques. Even though such letters contain a large amount of standard 
text, they will yet include parts directed just to the person to whom the 
letter is addressed. In the case of such personalized letters it is of 
great importance that the "right letter reach the right person". The use 
of so-called window envelopes is considered undesirable in the case of 
personalized letters and instead the use of envelopes with the address 
written thereon is perferred, since this underlines the personal character 
of the letter. The technical problem is to ensure that the right letter is 
combined with the right addressee. In principle, known devices exist by 
means of which such a combination can be arrived at with great safety. 
This can be achieved, for example, by providing the letter as well as the 
envelope with an electronically readable bar code that corresponds to the 
name and address of the addressee. However the presence of such a bar code 
takes away from the personal character of the letter and for this reason, 
bar code markings are oftentimes avoided. 
OBJECTS AND SUMMARY OF THE INVENTION 
To solve this problem a method is proposed in accordance with the present 
invention which in that document or part of the document, e.g. letter and 
envelope, is conducted by means of a conveyor device to a scanning 
position in front of an opto-electrical scanning device of the TV-camera 
type which is allocated to each type of document or document part. The 
imprinted text sections on the documents or parts of documents are 
scanned. The result of the scanning operation is defined by an analog 
video signal which is received in a computer. The computer converts the 
analog video signal to digital information which is the type of 
information which a computer can process. When the two pictures which are 
to be compared have been stored in the computer's memory a comparison of 
the stored picture information is begun. The comparison is made pixel by 
pixel and is controlled by a number of parameters in order to compensate 
for external factors such as e.g. differences in light intensity, dust, 
angular errors etc. 
Should the information deviate more than is permissible according to the 
parameters which have been set via the software, the machine can be made, 
via its interface with the machine, to stop the paper feed or indicate an 
error.

DETAILED DESCRIPTION OF THE PREFERRED 
As illustrated in the drawing, the apparatus includes two intermittently 
movable conveyor belts 1 and 2 and a letter inserting and envelop sealing 
machine 3. A stock of preprinted letter paper 4 and a stock or preprinted 
envelopes 5 are shown positioned on the conveyor belts 2, 1 respectively. 
Two TV cameras 6 and 7 and a comparator or comparing device 8. Moreover, a 
signal line 9 between the comparator 8 are also provided and the device 
for inserting letters 3 is shown, as is and the finished sealed envelope 
10. 
The arrangement operates in such a manner that the conveyor devices 1 and 2 
are intermittently advanced over a distance corresponding to one step of 
operation for the letter paper which is delivered from the stack 4 as well 
as for the envelopes which are delivered from the stack 5. Because the 
letter paper and envelope often do not have the same dimension, the 
conveyor device 2, for example, may have a longer feed distance than the 
conveyor device 1. In the device 3 for insertion of the letter and sealing 
of the envelope, which may be of a known commercial kind, the letter paper 
arriving from the conveyor belt 2 is folded, whereafter it is put into an 
envelope delivered similarly by means of the conveyor belt 1. Thereafter 
the envelope is sealed and the combined envelope and letter are delivered 
as a finished item 10. The TV-cameras 6 and 7 are arranged in 
vibration-absorbing stands and may be adjusted in their position in such a 
manner that the cameras are synchronized with the delivery of the 
documents, so that the text section which is to be scanned will be located 
in front of the cameras 6 and 7. 
As mentioned previously, the text section may consist of any kind of text 
part and may even consist of pictures and the like. The only requirement 
is that the pictures or text sections on the two documents scanned should 
be identical in form and preferably also in size. When a document has been 
delivered to one of the TV-cameras 6, 7 the image of the actual text 
section will be focussed by means of a system of optical lenses onto a 
device which converts optical signals to electrical ones, a so-called 
CCD-chip, which results in a large number of analog signals being 
generated. These analog signals correspond to the dark and lights portions 
respectively of the actual text section and may be used for recreating a 
picture on a TV-screen. In the present case a visual reproduction of the 
text section on a TV-screen in most cases is of no interest since it is 
only desired to compare the signals which are generated by the cameras 6 
and 7 from the same text section and then determine whether the text 
sections are identical or not. The scanning of the pictures by means of TV 
cameras can be done with a varying amount of accuracy depending on the 
design of the TV-cameras and it can be said that it is possible to divide 
the field into a certain number of "pixels". 
The signals from the TV-cameras 6 and 7 are fed to a comparing device, a 
so-called comparator 8, wherein the pulses are compared with one another, 
figuratively speaking, by being placed on top of one another. The 
comparison is done, of course, electronically with the help of known 
devices, and since it is a large number of dots or "pixels" which are to 
be compared with one another total conformity cannot be expected in the 
comparison because minor differences can exist in the print and the 
adjustment of the pictures which produce deviations in the scanning. It 
has been found by experience, however, that a certain percentage of 
conformity between the mutual positions of the pixels recorded, e.g. 80 to 
90%, represent adequate safety for the text sections agreeing with one 
another. Should the percentage of conforming "pixels" be less, the device 
would sound the alarm through acoustic or optical signals at the same time 
as the conveyor belts 1, 2 are stopped to permit a manual correction to be 
performed. The minium percentage of conforming "pixels" which is 
considered acceptable for approval of the identity of a text section, may 
be adjustable and must be set by taking into account the nature of the 
base material, the light conditions, the appearance of the text etc. In 
other words it is the sensitivity of the set-up which is adjusted and 
which, according to experience, must be done so as to ensure at all times 
that identity exists between the read and compared text section. At the 
same time the sensitivity of the set-up must not be so great that a large 
number of text sections, which in reality are identical, fail to be 
recognized as such, as a result of the inability of the device to achieve 
absolute conformity of the position of the pictures. 
It has been found advantageous not to feed the signals from the TV-cameras 
6 and 7 directly into the comparator 8 for comparison, but to store the 
signals in a memory large enough to accomodate a certain number, say 10 to 
15, complete text section readings. The reason why it is advantageous to 
operate with an intermediate memory between the TV-cameras 6 and 7 and the 
comparator 8 is that it will not be necessary to completely synchronize 
the readings by the TV-cameras 6 and 7. Since the readings by the 
TV-cameras 6 and 7 need not take place at the same time, greater freedom 
also exists for placing the TV-cameras at points along the conveyor belts 
1 and 2 where preconditions for reading are most favourable bearing in 
mind light conditions, freedom from vibrations, access for service etc. It 
is possible, therefore, to read one text section with one TV-camera while 
at the same time reading a wholly different text section on a different 
document by the other TV-camera 7. In such cases it is necessary, of 
course, to keep count of the number of documents by which the reading of 
one TV-camera is offset with respect to the other. That that is to say, 
how the displacement in the reading cycle between the two TV-cameras must 
be kept track of so that readings of identical text sections will always 
be compared at the same time in the comparator 8. This may be done by a 
simple switching or delay in the memory units which keep count of the 
extent of the displacement between the documents read. 
The system is based on the different documents being previously sorted in 
the correct order in the document stacks 4 and 5, so that the checking 
device does not have to be employed. That is the case where absolutely 
correct sorting exists. Unfortunately, however, it sometimes happens that 
during handling some documents disappear or are damaged, which means that 
the delivery of the different documents which are to be sorted will be out 
of step and that consequently all documents which follow the missing 
document would be incorrectly combined. However, the present invention 
solves this monitoring problem and will stop the combination of documents 
as soon as the system detects that the scanned text sections do not 
correspond to one another. As mentioned earlier, the text sections must be 
wholly identical and preferably must be printed by the same printing unit 
for the checking arrangement to function properly. It is inevitable, 
though, that in the course of their delivery by the conveyor belts 1 and 2 
the documents will be displaced from their nominal delivery positions. The 
documents may be displaced by as least fractions of millimeters in the 
longitudinal as well the transverse direction and may also be displaced 
slightly obliquely. A further source of error may be that the print is not 
placed accurately in the same place on the different documents even though 
it is the objective and is a precondition for the system to be able to 
function. In order to compensate for displacements of the documents 
delivered, the checking operation is initiated by determining the 
righthand and lefthand edge limits of the text section scanned. If the 
distance between these edge limits is not the same as determined through 
scanning with the different TV-cameras 6, 7, it is quite certain that 
identity does not exist, and thus, the scanning is stopped. Since the 
document should lie correctly assorted, the distances between the 
righthand and lefthand limit edges agree in most cases and adjustment of 
the pictures of the text sections scanned takes place electronically so 
that the readings of the text section from the lefthand limit edge 
commences simultaneously on both text sections. This guarantees that the 
pulse sequence or "pixel scanning" will be correct across the text section 
from left to right. In the same manner the lower lefthand limit edges of 
the text section are scanned, whereafter an electronic adjustment takes 
place so that the "electronic pictures" of the text section are 
positionally adjusted vertically as well as laterally. A further 
adjustment redresses the slop of the text section and this adjustment too 
can be electronically, so that the bottom righthand and lefthand limit 
edges are established in their position and compensation for any slope is 
made electronically. After these adjustments the electronic pictures will 
"overlap" one another so that scanning of the picture can take place to 
obtain the signals which, from the two TV-cameras 6 and 7 via an 
intermediate memory, can be fed to the comparator 8. Depending on the 
result of the comparison, the comparator 8 either approves the identity of 
the text section, whereupon the processing of the documents continues, or 
else fails to recognize the identity of the text section which results in 
the conveyor belts 1, 2 being stopped so that manual adjustment may be 
performed. In the present embodiment an arrangement is shown for combining 
documents consisting of letters and envelopes, both provided with 
identical text sections, in particular constituting the name and/ address 
of the addressee. As mentioned earlier, it is also possible to use the 
arrangement for comparing and conforming documents containing series of 
numbers, pictures etc., and it is also possible to combine more than two 
documents by introducing further TV-cameras into the system and by 
increasing in a corresponding manner the capacity of the intermediate 
memory and of the comparator 8. 
It has been found that the arrangement in accordance with the invention 
functions with great reliability and that through the use of the 
arrangement it is possible to avoid a great number of manual checks and to 
avoid the use of bar codes and other markings which are considered to 
spoil the appearance of the documents which are to be combined. 
While this invention has been illustrated and described in accordance with 
a preferred embodiment, it is recognized that variations and changes may 
be made and equivalents employed herein without departing from the 
invention as set forth in the claims.