Method and apparatus for controlling a buffer stock of flat objects

For temporarily storing sheets, envelopes and the like, the objects are received one by one in a buffer apparatus and delivered one by one from that apparatus. For each object, a code associated with that object is determined, which code is stored in accordance with the order of receipt of the objects. Each object that is discharged is scanned and the scanning result is compared with a code that on the basis of order information is supposed to be associated with that object. If a particular minimum extent of agreement between the compared data is found, a normal operating status is adhered to. If less than the particular extent of agreement between the compared data is found, an error message status is selected. There is also described a buffer apparatus for temporarily storing the objects. Different objects can indiscriminately be processed in an irregular order and checked for separation.

FIELD AND BACKGROUND OF THE INVENTION 
This invention relates to a method for temporarily storing flat objects in 
the form of sheets, envelopes or compositions therefrom. 
For producing a mail item different operations can be carried out in line. 
It is for instance known to collect documents and appendices such as 
preprinted sheets and return envelopes, to fold them before or after 
collecting and finally to pack the thus obtained compositions in 
envelopes, in a mechanized and in-line manner. The stations for performing 
these operations in a mechanized manner have been especially designed for 
this purpose and for mutual cooperation, allowing the flow of mail items 
in the making to be controlled by a central control unit or by 
intercommunication between the stations, and accumulations of successive 
components intended for different mail items to be prevented. 
However, if it is desired to print the documents in line, a printer should 
be disposed upstream of the stations that have been attuned to each other. 
Printers are apparatuses having a specific technology. For this reason, it 
is generally more attractive to utilize commercially available printers 
for this than to develop or adapt a printer especially for that purpose. 
Moreover, for many users, the possibility of using a standard printer 
offers the advantage that a printer which is already present can be used 
in combination with the apparatus for composing mail items for in-line 
printing and finishing printed documents to become mail items. Normally, 
however, printers for general use are not designed for cooperation with 
apparatuses disposed downstream thereof, as a consequence of which 
provisions are required for causing the output of the printer to connect 
with the input of the downstream apparatus (for instance an apparatus for 
composing mail items). 
SUMMARY OF THE INVENTION 
The object of the invention is to provide a method with which the output of 
a station delivering flat objects, such as a printer, and the input of an 
apparatus, disposed downstream and in line therewith, for processing those 
delivered objects, can be adjusted to each other in a reliable and 
user-friendly manner. 
In accordance with the present invention, this object is realized with a 
method for temporarily storing flat objects such as sheets, envelopes or 
compositions therefrom. 
The objects are received one by one, for each received object a code is 
determined that is associated with that object, and reference data 
corresponding to that code (optionally identical to that code) are stored 
in accordance with the order of receipt of the objects. 
After a short or longer time, received objects are discharged one by one in 
an order dependent on the order of receipt of those objects. 
Each object that is discharged is scanned. Registered measuring values are 
processed into a scanning result obtained upon the scanning of the object. 
On the basis of the order of receipt of the objects, the reference data 
associated with the discharged object are read and the scanning result 
obtained upon the scanning of the object is compared with that one of the 
codes that is associated with or is represented by the reference data 
read. 
Finally, if at least a predetermined extent of agreement between the code 
and the scanning result is found, a first operating status is selected or, 
if less than the predetermined extent of agreement between the code and 
the scanning result is found, a different operating status is selected. 
Because the received objects are temporarily stored, the output of objects 
can temporarily be greater and subsequently smaller than the input of 
objects in the apparatus disposed downstream of the object-delivering 
apparatus. 
In the case of for instance printers, the problem that a double or multiple 
object is delivered does not infrequently occur, because objects are not 
separated from one another when delivered from a storage holder of the 
printer. This double object consists of a printed first object and an 
unprinted second object, the objects lying completely or partly on top of 
each other. 
It may also occur that double objects are delivered upon the delivery of 
objects after the temporary storage. These objects may have the same 
composition as the supplied double objects or may consist of two printed, 
separately supplied and received objects. 
If a double object is delivered by the printer and this object, after 
having been temporarily stored, is delivered in the form of two separate 
single objects, or if two separately supplied objects are delivered as a 
double object, errors in the processing of those and subsequently objects 
may be caused in various ways. 
For instance, if the objects are in each case collected in pairs for 
collective dispatch as first and second sheets of the same mail item, an 
unprinted sheet delivered by the printer as part of a double sheet will be 
processed as first or second sheet of a mail item, as a result of which 
the second sheet of that mail item will be processed as first sheet of a 
next mail item. Hence, if no further irregularities occur, all following 
mail items will further consist of the second sheet of the preceding mail 
item and the first sheet. As a consequence, a large number of addressees 
will receive a sheet intended for another addressee. A comparable effect 
may also occur if after the temporary storage separately supplied sheets 
are delivered as a double sheet. If different, predetermined appendices 
are to be selectively added to successive single objects or objects 
collected to form sets, the above-outlined failures may cause a large 
number of appendices to be added to the wrong printed objects. 
It will be understood that these effects are particularly undesirable, 
especially if the printed objects and/or the appendices contain more or 
less confidential information specifically intended for the addressee. 
It is per se known to guard whether double sheets are supplied by scanning 
whether the thickness of a particular object exceeds a particular limiting 
value. However, this limiting value should be set in accordance with the 
thickness of the objects to be processed. This setting is in the first 
place laborious and hence not user-friendly. In the second place, a fixed 
setting is not suitable for guarding objects of different thicknesses 
passing in a random order. This is for instance necessary if a printer has 
several storage holders, each storage holder containing sheets of a 
different thickness, and sheets supplied from different storage holders 
are printed without a fixed order. 
However, because, in accordance with the invention, for each received 
object a code is determined that is associated with that object and 
reference data associated with this code are stored according to the order 
of receipt of the objects, upon delivery of each object it is known on the 
basis of the reference data which code is associated therewith. Hence, for 
each object that is discharged, the scanning results found when the 
received objects are discharged and scanned one by one--which is generally 
carried out simultaneously with the receiving, one by one, of further 
objects--can be compared with a reference value associated with or 
represented by reference data which are read from the memory and which, on 
the basis of the sequence information, should be associated with that 
object. 
By selecting, in each case after the scanning of each object discharged, a 
first operating status if at least a predetermined extent of agreement has 
been found between the compared scanning results and the reference data 
read from the memory, or selecting a different operating status if less 
than that predetermined extent of agreement has been found, the downstream 
apparatus for composing mail items can for instance be brought into a 
stand-by position (the other operating status) as soon as scanning results 
of an object deviate too much from the reference data read from the memory 
that would have to be associated with that object. The other operating 
status could also involve further measures in connection with the message 
of a deviation in respect of the discharged object, such as the discharge 
of the object that was last detected to a discharge position and/or 
issuing an alarm signal. The first operating status will generally consist 
of the further operation, in a normal manner, of the upstream discharge 
station, the downstream apparatus and the buffer apparatus. 
Instead of or in addition to the printing of objects, other operations can 
also be carried out upstream of the buffer apparatus, such as special 
folding treatments, attaching sheets to one another or writing data in a 
strip of magnetizable material or in a chip integrated in the flat object. 
The invention can also be embodied in a buffer apparatus according to claim 
9, which is essentially adapted to carry out the method according to the 
invention. 
Hereinafter, the invention will be further explained with reference to some 
practical elaborations and exemplary embodiments.

MODES FOR CARRYING OUT THE INVENTION 
FIG. 1 shows an embodiment of a buffer apparatus according to the invention 
that is presently most preferred. The flow diagrams in FIGS. 2 and 3 
represent subroutines for carrying out the method according to the 
invention that are presently most preferred. 
FIG. 1 shows a buffer apparatus 1 according to the invention, arranged 
upstream of an apparatus for composing mail items and downstream of a 
printer 2. The main direction in which components of the mail items to be 
composed are conveyed in operation is designated by an arrow 7. The 
apparatus for composing mail items shown consists of an inserter station 
3, a folding station 4 and a feeder station 5. The folding station 4 and 
the feeder station 5 are disposed on a conveyor 6. The portion of the 
conveyor 6 upstream of the feeder station 5 is adapted to stackwise 
collect the objects, such as sheets and envelopes, that are delivered by 
the buffer apparatus 1. As stations 3, 4, 5 and conveyor 6, commercially 
available components of the Neopost "System 7" product line can be 
employed. 
The buffer apparatus 1 is intended for receiving, one by one, the printed 
objects delivered by the printer 2, temporarily storing the received 
objects if they cannot be fed to the apparatus for composing mail items 
right away, and feeding flat objects one by one to the apparatus for 
composing mail items as soon as this apparatus is ready to receive now 
objects. 
The buffer apparatus 1 comprises a feed track 8 for receiving the objects 
one by one, a structure for supporting the received objects, which 
structure bounds a buffer space 9 for storing the received objects, and a 
discharge track 10 having means for discharging, one by one, objects 
stored in the buffer space 9. The means for discharging, one by one, 
objects from the buffer space 9 are constructed in accordance with the 
bottom-feed principle for delivering sheets one by one from the bottom. 
For this purpose, these means comprise a feed roller 40, a conveying 
roller 16 and a separating roller 17. Various examples of such separating 
systems are known, inter alia in the field of mechanized mail composition. 
Provided along the discharge track is a detector 11 for detecting for each 
passing object a value of a quantity depending on the thickness thereof. 
For the detector 11 shown, the quantity referred to is the displacement of 
a suspension element connected with a scanning roller. Alternatively, 
however, other quantities can be measured as well, such as the capacity of 
a capacitor formed by two capacitor plates arranged on both sides of the 
discharge track and an object (whose thickness is to be scanned) between 
those plates, the intensity of the light penetrating an object, or the 
weight of an object. 
The buffer apparatus 1 further comprises a memory for receiving and storing 
signals which each represent a reference value associated with one of the 
objects. This memory is schematically shown as a memory block 12 located 
outside the apparatus. Comparing means for receiving and comparing signals 
coming from the memory 12 and from the detector 11, which comparing means 
are coupled to the memory 12 and the detector 11, are schematically shown 
as a comparator block 13. Control means coupled to the detector 11, to the 
memory 12 and to the comparing means 13 are schematically shown as a 
control system block 14. These control means 14 are adapted to supply, in 
accordance with the discharge of objects, reference values stored in the 
memory 12 and associated with those objects to the comparing means 13, to 
select a first operating status if more than a particular value of 
agreement between values added thereto has been found by the comparing 
means 13, and to select a different, second operating status if less than 
a particular value of agreement between values added thereto has been 
found by the comparing means 13. 
To the memory 12, the comparing means 13 and the control means 14, it 
applies that they are shown as blocks located outside the housing of the 
buffer apparatus only for clarity's sake, but in practice they are of 
course preferably accommodated within the housing of the buffer apparatus 
1. In particular the memory 12, the comparator 13 and the control system 
14 are preferably integrated into a single, suitably programmed processor 
assembly. 
Provided along the feed track 8 is a further detector 15 for detecting the 
value of a quantity depending on the thickness of a supplied object. 
According to the exemplary embodiment shown, this detector is identical to 
the detector 11 provided along the discharge track 10. The memory 12 is 
coupled to the detector 15 provided along the feed track 8, for storing 
values detected by that detector 15. For easy reference, the detector 11 
provided along the discharge track 10 will hereinafter be referred to as 
the discharge detector 11 and the detector 15 provided along the feed 
track 8 will hereinafter be referred to as the feed detector 15. 
To enable communication with the control means of the apparatus for 
composing mail items, inter alia for controlling the delivery of objects 
from the buffer apparatus, the control system is coupled to the control 
means of the apparatus for composing mail items. In the drawing, this 
connection is schematically designated by the arrow 32. For controlling 
the delivery of documents, the control system is connected with means for 
operating the drive of the conveying roller 16. This connection is 
represented by the connection line 33. 
In the following description of the operation of the buffer apparatus 
according to the embodiment shown, it is presumed that the processed flat 
objects are separate sheets, although they could be other objects as well, 
such as envelopes, plastic cards of the type that is for instance used as 
credit card or compositions from different flat parts, such as carriers 
having invitation cards, discount coupons, etc. attached thereto. The 
operation is described with reference to FIGS. 3 and 4. These Figures show 
the flow diagrams of routines of the method according to the example 
described hereinafter. FIG. 2 shows the steps relating to the receipt of 
sheets and FIG. 3 shows the steps relating to the delivery of sheets. 
After the buffer apparatus has been set in operation or reset, the counters 
n and e for counting incoming and outgoing sheets respectively are set at 
1 (steps 16 and 17 respectively) and it is checked whether a sheet is 
present in the area of the feed track 8, which is shown as step 18. This 
step can for instance be carried out by testing whether a thickness value 
in excess of a particular limiting value is observed by the feed detector 
15, or by testing whether the intensity of light received by a 
light-sensitive sensor drops below a particular limiting value. As long as 
no sheet is detected at the location of the inlet, step 18 is repeated as 
is shown by means of the connecting arrow 19. 
If the printer 2 functions in the intended manner, sheets are delivered one 
by one. These sheets are supplied to the buffer apparatus 1 via the feed 
track 8. The presence of a sheet at the location of the inlet causes the 
result of the test 18 to change, as a result of which the following step 
is proceeded to; determining a code that is dependent on the thickness of 
the received sheet. In the present example, this code depends on the value 
detected by the feed detector 15 upon the scanning of the object. This 
step is shown as function block 20. 
After the thickness value a has been determined, reference data are stored 
in accordance with this code and the order of receipt of the sheets. In 
the method according to the above-described example, this step, 
represented by block 21, consist in storing the thickness value a, 
associated with the sheet just scanned, in association with the actual 
value of the counter n, forming the serial number of entry of the sheet, 
as reference date r.sub.n. Subsequently, the actual value of the counter n 
is increased (step 22). The routine involved in receiving sheets has now 
been completed, and the status wherein it is regularly checked whether a 
sheet is present at the location of the inlet is returned to. This return 
is represented by connecting arrow 23. As soon as the thickness value of a 
sheet has been scanned, the scanned sheet can be conveyed to the buffer 
space 9. Optionally, a delay can be incorporated into the routine in order 
to avoid determination of the thickness value of the same sheet more than 
once. For this purpose, however, the routine can also be designed so that 
it should first at least once be established that no sheet is present at 
the location of the inlet, before the determination of a next thickness 
value a is proceeded to. 
When a next sheet can be received by the conveying track 6, the separation 
and discharge of one of the received sheets is proceeded to. For this 
purpose, the feed roller 40 is driven, whereby a subjacent sheet is fed 
via the conveying track 10 to the conveying roller 16 and separating 
roller 17 provided opposite one another on both sides of the conveying 
track. If a sheet is carried along with the subjacent sheet, it will, if 
the separating means function in the intended manner, be retained by the 
separating roller 17, so as to pass only the subjacent sheet along the 
discharge detector 11 and to the conveyor 6. 
It is regularly tested whether a sheet is present in the discharge track 10 
in the area of the detector 11. This is represented by the diamond 24 in 
FIG. 3. As long as no sheet is present, the test is repeated, as is 
represented by connecting arrow 25. 
When a sheet that is discharged is indeed present in the discharge track 
10, the test of the presence of a sheet at the location of the outlet will 
yield a positive result. For each sheet that is discharged, the thickness 
is scanned by the discharge detector, which results in a signal being 
provided representing a value of the scanned thickness. In response to the 
observed presence of a sheet in the discharge track 10, the value b 
observed by the discharge detector 11 is read, as is represented by block 
26. 
The reference data stored in association with the actual value of the 
counter e, representing the serial number of discharge of the discharged 
sheet, are also read (block 27). In the present case, these reference data 
r.sub.e represent the thickness value associated with the serial number e. 
Subsequently, the value scanned by the discharge detector 11 is compared 
with the reference value read, associated with the actual serial number. 
This is represented by diamond 28. According to the present example, it is 
tested whether the thickness value b detected by the discharge detector 11 
lies within a margin plus or minus t around the stored reference value 
R.sub.e associated with the actual serial number e. The value of t can be 
fixed, for instance corresponding to half the thickness of a thinnest 
sheet processable, or variable and for instance correspond to a quarter of 
the value of r.sub.e or b. 
If the thickness value b detected by the discharge detector 11 lies within 
a margin plus or minus t around the stored reference value r.sub.e 
associated with the actual serial number e, a first operating status is 
selected, essentially consisting in the apparatus further operating in a 
normal manner and the scanned sheet being further discharged to the 
conveyor 6. The counter e is increased (block 29) and the stage in which 
the presence of a sheet in the discharge track 10 is regularly tested is 
returned to (connecting arrow 30). 
If the thickness value b detected by the discharge detector 11 is not 
within a margin plus or minus t around the stored reference value r.sub.e 
associated with the actual serial number e, a second operating status is 
selected, wherein the transport of the sheet is ceased (block 31). If 
desired, an alarm signal can be provided as well, but in general, 
personnel operating the system will soon notice that no sheets are 
delivered by the buffer apparatus 1. Preferably, it is indicated in a 
display that for the sheet in the discharge track 10 insufficient 
agreement has been determined between the thickness values found upon the 
inlet detection and the outlet detection. 
Because for each received sheet a code is determined that depends on the 
thickness of that sheet, and reference data in agreement with this code 
are stored in accordance with the order of receipt of the sheets, the 
thickness area in which the thickness of a sheet should lie is known for 
each sheet upon delivery, on the basis of the reference data. Hence, when 
the received sheets are discharged one by one--which is generally 
performed simultaneously with the receipt, one by one, of further 
objects--the detected thickness value can for each sheet that is 
discharged be compared with a reference thickness value associated with 
that sheet. 
By selecting a first operating status if at least a predetermined extent of 
agreement between the compared values is found, or selecting a second 
operating status if less than the predetermined extent of agreement 
between the compared values is found, a sheet can be retained in the 
buffer apparatus, if the detected thickness of that sheet deviates too 
much from the thickness which it should have according to the reference 
data. The fact the difference between the values detected by the feed 
detector 15 and the discharge detector 11 is greater than it should be 
according to the intended extent of agreement, shows that a double or 
multiple sheet has been delivered either by the printer 2 or by the 
separating means of the buffer apparatus 1, while the components of the 
multiple sheet have been separated or have at least been separated 
differently by the separating means of the buffer apparatus 1 or by the 
printer 2 respectively. If the system continued its operation normally, 
the serial numbers of discharged sheets would no longer correspond to the 
serial numbers allocated to those sheets when supplied, as a consequence 
of which each set would include sheets intended for a set that precedes it 
or follows it. However, because a sheet whose thickness value 
insufficiently corresponds to the reference value is not discharged to the 
conveyor 6, this is prevented. Personnel operating the system is then 
given an opportunity to remove the wrongly processed sheets from the 
system, in order to collect, after a restart, sheets again to form sets of 
the intended composition. 
Moreover, in order to resume the processing of sheets after an error 
message in the intended manner, all sheets following the wrongly processed 
sheets can be removed from the buffer apparatus 1 and the printer 2 and 
printed again after restart. In that case, it is preferred if in the 
second operating condition, i.e. after a message of insufficiently 
corresponding thickness, the printer be stopped as well, which minimizes 
the number of superfluously printed sheets. Instead, it is also possible 
to adjust the counter e in accordance with the number of removed documents 
and the location where a double of multiple sheet was delivered. 
Accordingly, the removed sheets can for instance be manually processed 
into mail items. 
The other operating status can also comprise an automatic recovery 
procedure, wherein, if it is detected that a multiple sheet has been 
received and discharged as single sheets, the counter e is retained in 
accordance with the difference between the numbers of separately received 
and discharged objects. This difference can be determined from the 
difference in thickness between the supplied and the discharged objects. 
In that case, it is accepted that a mail item may contain an empty sheet. 
If it is desired that a multiple sheet is discharged, while all sheets 
included therein are intended for the same set, the counter e can be 
increased in accordance with the number of additional sheets carried along 
in the multiple sheet according to the difference in thickness measured. 
Because the determination of the codes depending on the thickness of each 
sheet is performed by passing the sheets along a feed detector 15 and 
scanning, by means of that detector 15, values of a quantity depending on 
the thickness of the sheets, a new reference value is automatically 
determined for each new object, as a result of which no separate setting 
phase is required for inputting those values, the risk of drift of the 
reference value is very small and sheets of different thicknesses, not 
priorly known, at least within a specific range, can indiscriminately be 
processed in random order. A further advantage is that the response time 
between delivery of a multiple sheet by the printer 2 and the transition 
to the second operating condition is relatively short. For a multiple 
sheet, a reference value corresponding to the thickness thereof is stored. 
If the multiple sheet is separated differently when delivered, for 
instance only in separate, individual sheets, the value detected by the 
discharge detector and compared with the reference value associated with 
the serial number of the multiple sheet will indicate a thickness value 
that is substantially less than the reference value, as a result of which 
the second operating condition is directly changed to and the delivery of 
documents from the buffer apparatus 1 is interrupted until further order. 
If the components of the multiple sheet are fixedly attached to one another 
so that the multiple sheet is discharged in the same composition as the 
composition in which it was supplied, the thickness values detected by the 
feed detector 15 and the discharge detector 11 will essentially 
correspond, as a consequence of which no error message due to transition 
to the second operating condition follows. This behavior of the buffer 
apparatus 1 is advantageous, because in this case, the incorrect 
separation does not cause printed sheets to be incorporated into sets 
other than the sets for which they are intended. The result is merely that 
the set containing the multiple document contains one or more unprinted 
sheets. 
Instead of or in addition to the printing of objects, upstream of the 
apparatus for composing mail items other operations can be performed as 
well, such as special folding operations, attaching sheets to one another 
or writing data, for instance in a strip of magnetizable material or in a 
chip integrated into the flat object. 
FIG. 4 shows a control system 35 of the printer 2, connected, via 
connections 36, 37, with the operating elements 41, 42 of separating and 
conveying means associated with one of two storage trays 38, 39. 
The buffer apparatus 1 shown in FIG. 4 comprises means for inputting, in 
association with each received object, a code associated with the object. 
These means are designed as a connection 34 with the control system 35 of 
the printer 2. 
The determination of the codes that are dependent on the thickness of each 
object is carried out by inputting, from the control system, a code 
associated with the objects, indicating from which of the storage trays 
38, 39 the object is supplied. In the memory 12 of the buffer apparatus it 
is stored which thickness value is associated with each of the storage 
tray codes, enabling determination of the reference value for each object 
supplied to the buffer apparatus 1 via the serial number and the 
associated storage tray code, with which reference value the thickness 
value detected by the discharge detector should be compared when the 
object having the same serial number is discharged. 
The discharge detector 11 is connected with the memory 12 for storing the 
values, detected by that detector 11, of a quantity depending on the 
thickness of the objects in association with codes which each represent a 
type of object. 
Consequently, the inputting of the thickness values associated with the 
storage tray codes can be effected by placing, during a setting phase, 
samples of the objects to be processed in the buffer space 9, passing them 
one by one along the detector 11, detecting for each sample a value of a 
quantity depending on the thickness of that object and storing it in the 
memory 12 in association with a code representing that type of object or 
the storage tray 38 or 39 wherein that type of object is placed. The 
setting phase is followed by the operating phase wherein the determination 
of the codes depending on the thickness of each received object is carried 
out by reading from the memory 12 the code associated with that object. 
Another possibility for inputting reference values or reference areas 
associated with objects that are supplied from a particular source is to 
store thickness values for particular types of objects in a memory, for 
instance the memory 12, in association with a type code. By indicating 
which type code is associated with the objects that are placed in a 
particular holder, it can be determined with which reference value or with 
which reference area the thickness value should be compared, which is 
obtained by scanning an object discharged from the buffer space 9 and 
originally coming from that holder. 
In spite of the fact that the use of the apparatus according to FIG. 4 does 
not involve scanning of the thickness of the supplied objects upon receipt 
of the objects, multiple objects delivered by the printer 2 can be 
detected all the same, even if they are discharged individually upon 
discharge from the buffer space 9. Because objects of different 
thicknesses from different storage trays have been supplied in a known 
order, the delivery of a multiple object by the printer 2 and the 
individual discharge of these objects from the buffer space 9 will have as 
a result that at least during the scanning of following objects at the 
moment when an object from a different storage tray should be discharged, 
another object is discharged from the preceding storage tray. 
Consequently, the thickness scanned will exhibit less than the required 
extent of agreement with the reference value. In response thereto, the 
buffer apparatus 1 will change into the second operating condition which, 
as described hereinabove, implics an error message. If the objects from 
the two storage trays have such an equal thickness, agreement will still 
be found, even though instead of an object from one storage tray, an 
object from the other storage tray is discharged. In that case, multiple 
objects delivered by the printer 2 cannot be detected without detection of 
objects when received by the buffer apparatus 1. 
As appears from above, the codes associated with an object supplied to the 
buffer apparatus 1 can each refer to a thickness value stored in the 
memory 12 and are read for determining an associated thickness value. This 
thickness value is used as reference value and is compared with the value, 
scanned upon the discharge of the object having the same serial number, of 
a quantity depending on the thickness of the discharged object. As 
appeared from the example, wherein the reference value associated with an 
object is determined by scanning the thickness of that object, the codes 
can, however, also represent thickness values directly. 
In the above-described examples, the stored objects are in each case 
delivered in accordance with the first-in-first-out principle. This offers 
the advantage that when the printer 2 and the buffer apparatus 1 operate 
properly, the order of entry of the objects is identical to the order of 
discharge of the objects, so that it can readily be controlled and an 
arrangement according to postal code, if any, is maintained. However, as 
desired, it is also possible to discharge the objects according to the 
first-in-last-out principle or in random order according to the two 
principles, if the numbers to be allocated to the objects to be discharged 
are selected accordingly, so as to maintain for each object correspondence 
with the serial number of receipt allocated thereto. 
Within the purview of the above-described invention, many other examples 
other than those described hereinabove have been brought within the reach 
of a skilled person. For instance, the codes associated with each object 
and the scanning results that are in each case compared with one of the 
codes may also represent, instead of the thickness, other properties of 
the objects, such as brightness patterns (optionally in the form of 
special optical characters), lengths, dielectric properties, magnetic 
properties, weights and transparency.