EP2605867B1 - Postal sorting machine with clamping conveyor and method for operating the same - Google Patents

Description

Technical area

The invention relates to a postal sorting machine comprising pinch conveying means and its method of implementation. It relates more particularly to such a machine that is able to sort both "large format" objects also called "flats", as well as letters. The invention also relates to a method of implementing this sorting machine.

Prior art

In the postal field, the different types of postal items are distinguished according to their dimensions: height, length, thickness and weight. These different categories of shipments are defined according to ISO-269. For example, an envelope that can contain a sheet in A4 or A5 format is a letter having respectively a C4 or C5 format. A C4-size envelope has dimensions in width and height of 229 millimeters and 324 millimeters. A C5-size envelope has dimensions in height and width respectively of 162 millimeters and 229 millimeters.

Currently, the spectrum of mail items that can be sorted automatically by machines mainly includes: letters up to C5 format and having a thickness of less than 8mm for a weight not exceeding 100g, flat objects called "large format" which can be even bigger than C4 and up, with a thickness of up to 32mm and weight up to 2kg.

In general, there are today postal sorting machines that are dedicated to different types of mail, letters or large format objects, and postal sorting machines capable of processing both letters and large format objects.

These machines conventionally comprise a feed inlet with an unstacker for the serialization on edge of postal items, means for recognizing the address of postal items, and a conveyor which directs postal items to sorting outlets according to the recognized address. Usually the address means any registration, in the form of letters and / or numbers and / or other signs, on the surface of a shipment for identification.

The present invention more particularly relates to a conveying system, wherein the items are set in motion by pinching between two conveying members, which are usually belts. For the record, it will be recalled that this conveyance can be operated by means of buckets, which do not apply in contrast to the present invention.

In a postal sorting machine with video-coding, the postal objects pass in front of optical acquisition means, generally constituted by a camera that forms a digital image of each object having address information. This digital image is processed in an automatic OCR (Optical Character Recognition) and / or VCS (Video Coding System) address evaluation system.

These acquisition means, associated with these evaluation means, form the address recognition means, within the meaning of the invention. When the address carried by the shipment can be satisfactorily recognized, the latter is directed to a corresponding sorting outlet of the machine.

Two solutions can usually be used, which may be combined, in order to support items whose address can not be fully recognized.

It is firstly possible to perform an online video coding, by means of a delay line, also called LAR. In this case, the sorting machine integrates a preliminary conveying zone, between the acquisition camera and the beginning of the sorting area itself. The additional journey time of the shipments along this line makes it possible to process unacknowledged shipments upstream.

This first solution, however, has certain disadvantages, related first of all to the large ground area occupied by the delay line. This is all the more sensitive, it is necessary to be able to access this line, in order to settle there possible jams and to carry out periodic maintenance operations.

In addition, this delay line tends to induce slips of the items that run through it, which requires catching leading to rejections or jams. This phenomenon is due in particular to the difference between the respective coefficients of friction, which are of various types of mail, such as for example postcards and paper folds. This is prohibitive for an extended spectrum of mail, for which variations in thickness, size and nature of material are very significant.

In addition, in order to reduce their grip, the delay lines often tend to describe very tight curves. This can damage the mail, or even make it impossible to pass some types of folds, especially when they are large and / or high rigidity.

Finally, the totality of the consignments borrows this line with delay whereas, in general, only a small fraction requires an additional time for a correct recognition. In other words, most shipments have their travel time increase unnecessarily.

An alternative solution to online video-coding presented above, is called "off-line" video-coding. According to the latter, consignments that have not been recognized are marked, either physically by an identification code or chronograph (IdTag), or virtually according to the method (V-Id) ^™ , developed by the Applicant.

These shipments are then extracted by a sorting outlet which is specifically dedicated to them, for temporary storage. They are then reintroduced, in the same sorting machine or in another, for subsequent treatment.

This second solution is, however, accompanied by disadvantages of its own. Thus, it requires grouping and storing shipments, which involves reserving at least one specific sorting outlet, as well as occupying the ground surface.

In addition, since these items are subjected to a second sorting pass, they undergo in particular additional unstacking, which is necessarily a traumatic operation. This can therefore lead to the formation of double sockets, or induce a degradation of the shipments. In addition, this second pass involves additional handling.

The publication US 2006/0 037 888 discloses a postal sorting machine comprising a destacker postal items, means for recognizing the address of these shipments, and a conveying area of the shipments comprising a main loop and shortened loops allowing each mailing to be oriented to the sorting exit for which it is intended without having to go around the entire main loop. This postal sorting machine, however, does not optimize sorting of postal items whose address can not be fully recognized during a first pass.

exposed of the invention

That being said, the invention aims to remedy these various disadvantages. It aims in particular to provide a sorting machine which, while having a reduced footprint, ensures a fast and effective processing of unrecognized shipments. It also aims to provide such a sorting machine, which is likely to handle shipments whose spectrum is extensive, while ensuring their mechanical integrity.

For this purpose, the subject of the invention is a postal sorting machine comprising a destacker, suitable for putting on singing postal items, means for recognizing the address of these items, and a zone for conveying items by pinching, this conveying zone comprising an unstacking zone extending from the unstacker, and a sorting zone having a plurality of sorting outlets, distributed between an upstream sorting outlet adjacent to the unstacker, and a downstream sorting outlet, characterized in what this machine further comprises a recycling zone, connecting the downstream sorting outlet and the upstream sorting outlet, this recycling zone defining, with the unstacking zone, a confluence point situated between the unstacker and the upstream sorting outlet, postal sorting machine further comprising synchronization means, adapted to synchronize movements, on the one hand so-called depilated shipments circulating between the unstacker and the confluence point and, on the other hand, so-called recycled shipments circulating in the area recycling, the synchronization means comprising means for detecting the presence of at least one recycled shipment, and control means adapted to act on the unstacker, in response to information transmitted by the detection means.

The idea underlying the invention is to use the sorting zone, equipped with its outputs, as a delay line. Under these conditions, it avoids the use of a specific section for this delay line, as in the "online" solution. In addition, the invention eliminates any sorting output specific to unrecognized items, as in the "offline" solution.

It is to the Claimant's merit to have identified that, given the very nature of the mail, most items are correctly recognized at the beginning of their first visit to the sorting area. Under these conditions, only a small fraction of these shipments is allowed in the recycling zone, which is not detrimental to the operational sorting capacity of the machine.

The conveying zone thus forms a loop, due to the presence of the recycling zone mentioned above. This makes it possible to direct the unrecognized shipments directly upstream of the sorting area, which avoids any operation likely to damage them.

This journey of shipments, along a loop, also has other advantages, regardless of those related to the recognition of shipments. Thus, assuming that a sorting output is unavailable, for example if it is completely filled, the shipments which are theoretically intended for it circulate along the loop, until this output is available again.

In addition, it sometimes happens that one wants to evacuate folds in a particular sequence, at a sorting outlet, but that this sequence is not properly ordered upstream of the unstacker. In this case, only a portion of these folds are extracted during the first pass, and the other part of these folds is circulated along the loop at least once, in order to respect the planned order.

Finally, during the sorting operation, it happens that the trace of some shipments is lost, or that they have undergone a problem of acquisition. Under these conditions these shipments are then recycled, so as to pass again before the camera.

• les moyens de détection de la présence d'au moins un envoi recyclé comprennent deux capteurs de présence, disposés sur la zone de recyclage.
• le dépileur est pourvu d'un système de rattrapage, propre à modifier l'écart entre deux envois dépilés consécutifs.
• les moyens de synchronisation comprennent en outre des moyens de variation de la vitesse d'au moins un envoi circulant dans la zone de recyclage et, éventuellement, dans la zone de tri.
• les moyens de variation de la vitesse comprennent au moins un premier organe de variation de la vitesse placé sur la zone de recyclage, ainsi qu'éventuellement un second organe de variation de la vitesse placé sur la zone de tri, entre deux séries de sortie de tri.
• le premier organe de variation de la vitesse est placé entre le capteur de présence aval et le point de confluence.
• la zone de tri présente deux branches droites reliées par un demi-tour.
• la zone de tri présente une longueur supérieure à 40 mètres, ainsi qu'un nombre de sorties supérieur à 100.
• la zone de convoyage forme, au voisinage de la zone de recyclage, globalement un demi-tour dont la longueur est inférieure à 2.5 mètres.
• le rapport entre la longueur de la zone de tri et la longueur de la zone de recyclage est très supérieur à 1, notamment supérieur à 10, en particulier supérieur à 20.

The sorting machine according to the invention may advantageously have the following particularities:

• the means for detecting the presence of at least one recycled shipment comprise two presence sensors, arranged on the recycling zone.
• the unstacker is provided with a retrofit system, able to change the gap between two consecutive depilated shipments.
• the synchronization means furthermore comprise means for varying the speed of at least one item of mail circulating in the recycling zone and, possibly, in the sorting zone.
• the means for varying the speed comprise at least a first speed variation member placed on the recycling zone, as well as possibly a second speed variation member placed on the sorting zone, between two series of output of sorting.
• the first velocity variation member is placed between the downstream presence sensor and the confluence point.
• the sorting area has two straight branches connected by a half turn.
• the sorting zone has a length greater than 40 meters and a number of outlets greater than 100.
• the conveying zone forms, in the vicinity of the recycling zone, generally a half-turn whose length is less than 2.5 meters.
• the ratio between the length of the sorting zone and the length of the recycling zone is much greater than 1, in particular greater than 10, in particular greater than 20.

The subject of the invention is also a method of implementing the above sorting machine, in which the mailpieces are unstacked by means of the unstacker, the recognition means are used so as to recognize the address of these items, at least some of the items whose address has been correctly identified are sent to corresponding sorting outlets and at least the items whose address has not been correctly recognized are circulated in the recycling zone in order to admit them back into the sorting area.

• on détecte la présence d'au moins un envoi recyclé grâce aux moyens de détection et on agit sur le dépileur grâce aux moyens de commande, de manière à synchroniser les mouvements respectifs des envois dépilés et des envois recyclés.
• on dépile les envois à écart constant et on arrête ce dépilage tant qu'au moins un envoi recyclé occulte au moins un des deux capteurs de présence
• on utilise un dépileur pourvu d'un système de rattrapage, et on espace les deux capteurs de présence d'une distance D'(1-2) = (2*Gn + Lmax - Δd), où Gn correspond à l'écart nominal entre deux envois, Lmax correspond à la longueur maximale d'un envoi, et Δd est la différence entre, d'une part, la distance parcourue, pendant la durée de redémarrage d'un envoi stoppé au niveau du dépileur, par un envoi recyclé circulant à la vitesse de convoyage et, d'autre part, la distance de redémarrage d'un envoi stoppé au niveau du dépileur.
• on identifie l'écart séparant le front arrière d'un envoi dépilé aval avec le front avant d'un envoi recyclé amont, et on intercale un envoi dépilé intermédiaire entre cet envoi dépilé aval et cet envoi recyclé amont si l'écart identifié est supérieur à un écart minimal théorique.
• on intercale un envoi recyclé entre deux envois dépilés amont et aval, et on utilise les moyens de variation de vitesse pour accélérer l'envoi recyclé afin qu'il soit distant d'un écart aussi proche que possible de l'écart théorique minimal avec l'envoi aval, et on utilise le système de rattrapage afin que l'envoi amont soit distant d'un écart aussi proche que possible de l'écart théorique minimal avec l'envoi recyclé.
• on utilise un dépileur pourvu d'un système de rattrapage, on identifie l'écart réel séparant le front arrière d'un envoi dépilé aval avec le front avant d'un envoi recyclé amont, on détermine l'écart minimal théorique permettant d'intercaler un envoi dépilé intermédiaire, on identifie l'avance du front avant, entre cet écart réel et cet écart minimal et, si cette avance est inférieure à une valeur de retard maximale permise par les moyens de variation de vitesse, on intercale l'envoi dépilé intermédiaire entre cet envoi dépilé aval et cet envoi recyclé amont, puis on utilise les moyens de variation de vitesse pour retarder cet envoi recyclé d'une valeur correspondant à l'avance de son front avant.
• l'écart minimal théorique correspond à $$\mathrm{ds}\left(\mathrm{1}-\mathrm{3}\right)=\mathrm{L}\mathrm{2}+\mathrm{Gmin}\left(\mathrm{1}-\mathrm{2}\right)+\mathrm{Gmin}\left(\mathrm{2}-\mathrm{3}\right),$$
  
  
  où L2 est la longueur de l'envoi intermédiaire, et
  Gmin(1-2) et Gmin(2-3) sont les écarts minimaux à respecter entre, d'une part, le front arrière de l'envoi aval et le front avant de l'envoi intermédiaire et, d'autre part, le front arrière de l'envoi intermédiaire et le front avant de l'envoi amont,
• on utilise les moyens de variation de vitesse uniquement pour ralentir les envois recyclés et on espace les deux capteurs de présence d'une distance D'(1-2) = (2*Gn + Lmax - Δd - Dret), où Gn correspond à l'écart nominal entre deux envois, Lmax correspond à la longueur maximale d'un envoi, Δd est la différence entre, d'une part, la distance parcourue, pendant la durée de redémarrage d'un envoi stoppé au niveau du dépileur, par un envoi recyclé circulant à la vitesse de convoyage et, d'autre part, la distance de redémarrage d'un envoi stoppé au niveau du dépileur, et Dret est la distance maximale de retard permise par les moyens de variation de vitesse.
• on identifie, en amont du second organe de variation de vitesse, deux envois successifs destinés à emprunter la zone de recyclage et, dans le cas où au moins un envoi adjacent à ces deux envois successifs a déjà été déchargé, on utilise le second organe de variation de vitesse pour écarter mutuellement ces deux envois successifs.

The method of implementation according to the invention can advantageously have the following particularities:

• the presence of at least one recycled shipment is detected by the detection means and the unstacker is operated by the control means so as to synchronize the respective movements of the unstacked items and the recycled items.
• we unstack the shipments at constant distance and stop unstacking as long as at least one recycled shipment occult at least one of the two presence sensors
• a destacker equipped with a retrofit system is used, and the two presence sensors are separated by a distance D '(1-2) = (2 * Gn + Lmax - Δd), where Gn corresponds to the nominal difference between two shipments, Lmax is the maximum length of a shipment, and Δd is the difference between, on the one hand, the distance traveled, during the period of restart of a stopped shipment at the unstacker, by a recycled shipment circulating at the conveying speed and, secondly, the restart distance of a stopped shipment at the unstacker.
• the gap separating the trailing edge of a downstream depilated consignment is identified with the front edge of an upstream recycled consignment, and an intermediate depolled consignment is inserted between this downstream depolled consignment and this upstream recycled consignment if the identified deviation is greater than at a theoretical minimum distance.
• a recycled consignment is inserted between two upstream and downstream depilated shipments, and the speed variation means are used to accelerate the recycled consignment so that it is distant from a distance as close as possible to the minimum theoretical distance with respect to downstream shipment, and the catch-up system is used so that the upstream shipment is distant as close as possible to the minimum theoretical distance with the recycled shipment.
• a destacker equipped with a catch-up system is used, the real difference separating the trailing edge of a downstream depilated consignment is identified with the front edge of an upstream recycled consignment, the theoretical minimum deviation allowing to be inserted is determined an intermediate depilated dispatch, the advance of the front edge is identified between this real difference and this minimum deviation and, if this advance is less than a maximum delay value allowed by the speed variation means, the forwarded item is intercalated intermediate between this downstream depolled shipment and this upstream recycled shipment, then the speed variation means is used to delay this recycled shipment by a value corresponding to the advance of its front edge.
• the theoretical minimum difference corresponds to $$\mathrm{ds}\left(\mathrm{1}-\mathrm{3}\right)=\mathrm{The}\mathrm{2}+\mathrm{G\; min}\left(\mathrm{1}-\mathrm{2}\right)+\mathrm{G\; min}\left(\mathrm{2}-\mathrm{3}\right),$$
  
  
  where L2 is the length of the intermediate shipment, and
  Gmin (1-2) and Gmin (2-3) are the minimum differences to be observed between, on the one hand, the trailing edge of the downstream consignment and the front edge of the intermediate consignment and, on the other hand, the trailing edge of the intermediate consignment and the front edge of the upstream consignment,
• the velocity variation means are used solely to slow down the recycled items and the two presence sensors are separated by a distance D '(1-2) = (2 * Gn + Lmax - Δd - Dret), where Gn corresponds to the nominal difference between two consignments, Lmax corresponds to the maximum length of a shipment, Δd is the difference between, on the one hand, the distance traveled, during the period of restart of a stopped consignment at the unstacker, by a recycled consignment circulating at the conveying speed and, secondly, the restart distance of a stopped shipment at the unstacker, and Dret is the maximum delay distance allowed by the speed variation means.
• upstream of the second speed variation member, two successive shipments intended to take the recycling zone are identified, and in the case where at least one consignment adjacent to these two successive shipments has already been unloaded, the second gear member is used. speed variation to mutually separate these two successive shipments.

Brief description of the drawings

• La figure 1 est une représentation schématique, en vue de dessus, d'une machine de tri postal conforme à l'invention ;
• La figure 2 est une représentation schématique, à plus grande échelle, d'une partie de la machine de tri postal illustrée à la figure 1;
• La figure 3 est une représentation schématique, analogue à la figure 2, d'une machine de tri postal conforme à une première variante de réalisation de l'invention ;
• La figure 4 est une vue de côté, illustrant à plus grande échelle un dépileur appartenant à la machine de tri de la figure 3 ;
• Les figures 5 et 6 sont des représentations schématiques, illustrant différentes mises en oeuvre de la machine de tri des figures 3 et 4 ;
• La figure 7 est une représentation schématique, analogue à la figure 2, d'une machine de tri postal conforme à une seconde variante de réalisation de l'invention ;
• Les figures 8 à 11 sont des représentations schématiques, illustrant différentes mises en oeuvre de la machine de tri de la figure 7.

The invention will be described in more detail with reference to the accompanying drawings given solely by way of non-limiting examples, in which:

• The figure 1 is a schematic representation, in top view, of a postal sorting machine according to the invention;
• The figure 2 is a schematic representation, on a larger scale, of a part of the postal sorting machine illustrated in figure 1 ;
• The figure 3 is a schematic representation, analogous to figure 2 , a postal sorting machine according to a first embodiment of the invention;
• The figure 4 is a side view, illustrating on a larger scale a destacker belonging to the sorting machine of the figure 3 ;
• The Figures 5 and 6 are schematic representations, illustrating different implementations of the sorting machine of Figures 3 and 4 ;
• The figure 7 is a schematic representation, analogous to figure 2 , a postal sorting machine according to a second embodiment of the invention;
• The Figures 8 to 11 are schematic representations, illustrating different implementations of the sorting machine of the figure 7 .

Description of the embodiments

The figure 1 represents a sorting machine for postal items or folds, which is represented schematically. It is equipped with different bodies ensuring the conveying of these items by pinching, in particular by means of usual belts. As recalled above, the invention does not apply to conveying means, bucket type or the like.

The sorting machine comprises an unstacking zone 1, a confluence point C, an upstream intermediate zone 2, a sorting zone 3 and a recycling zone 4. The routing of the shipments is indicated by the arrows F, on this figure 1 .

The unstacking zone, located upstream of the confluence point C, as well as the intermediate zone, located between the confluence point C and the first output S1 of the sorting zone, are of conventional type. The unstacking zone is in particular equipped with a unstacker 10 of any suitable type.

In addition, one or other of these zones comprises various equipment, among which an image acquisition device 20, of the camera type, which is indispensable in the context of the present invention. Some other equipment not shown is optional, namely inter alia a multiple tap detector, a thickness measuring device, a rigidity detector, a device for rejecting too rigid items, barcode readers, or even printing devices.

Note that, by construction, the unstacker 10 is located in the unstacking zone 1. In contrast, the other equipment mentioned above, including the camera 20, can be placed upstream or downstream of the confluence point C.

Thus, placing the camera 20 in the unstacking zone 1, before the confluence point C, is advantageous in terms of overall compactness. On the other hand, the fact of placing the camera 20 in the intermediate zone 2, after the confluence point C, allows the recycled items to pass in front of this camera, which ensures the possibility of additional acquisition of information.

In the usual way, the acquisition camera 20 is associated with evaluation means 25, shown schematically. The combination of 20 and 25 forms address recognition means, in the usual sense.

Without limitation, the length L1 of the unstacking zone 1, between the outlet of the unstacker 10 and the point C, is advantageously less than the length of the recycling zone 4. Moreover, the length L2 of the zone intermediate 2, between the point C and the first sorting output S1, advantageously allows to give an OCR-type response, even when the image acquisition is located after the confluent C. If this was not the case, the first exits may be unusable. Under these conditions, this length has a minimum value advantageously greater than 4 meters, ie a path of at least 1 second at maximum conveying speed.

The sorting zone 3, which has approximately a U-shape, consists of two straight branches 31 and 33, as well as a half-turn 32. The branch 31 is equipped with a first series of sorting outlets. S1 to SM, while the branch 32 is equipped with a second series of sorting outlets SM + 1 to SN, all these outputs being of conventional type.

The outputs, provided in a total number N advantageously greater than 40, are distributed in a substantially identical manner between the two series. L31 and L33 denote the length of each branch, respectively between the outputs S1 and SM, and between the outputs SM + 1 and SN, and L32 the length of the half-turn 32. The total length L3 of the sorting zone, which corresponds to the sum of the lengths L31, L32 and L33, is advantageously greater than 40 meters.

The recycling zone 4 extends between the last outlet SN and the confluence point C. It has a length L4 very much smaller than the total length L3 of the sorting zone. Thus, the ratio between L3 and L4 is advantageously greater than 10, especially 20. This ensures that only a small fraction of the machine is not used for sorting shipments.

The recycling zone 4 defines a half-turn whose length L4 is advantageously less than 2.50 meters. In the illustrated example, this half-turn is entirely formed by the recycling zone. However, for example if the orientation of the unstacker is different from that illustrated, it is possible that the confluence point C is located in the u-turn proper, usually in the downstream part thereof. In the latter case, this half-turn of the conveying zone is then formed, both by the recycling zone 4, as well as by the intermediate zone 2.

In the foregoing, there has been described a conveying loop formed by two rectilinear sections 31 and 32, as well as by two half-turns 32 and 4. However, it can be provided that each of these constituent elements has a shape different from that described. Note that it is in any case advantageous, the first and last sorting outlets S1 and SN are close to each other, to give the recycling zone 4 a small length.

The implementation of the postal sorting machine described above firstly involves, in a conventional manner, an unstacking of items and the passage of the latter in front of the camera 20. This then forms, in a known manner in itself, a digital image of each shipment that is processed by the evaluation means 25, again in the usual way. These operations allow, in most cases, the recognition of the address carried by the items.

When this address is correctly recognized, the item in question is directed to a corresponding sorting output S1 to SN. On the other hand, in the case where this address can not be completely recognized, the item under consideration takes the conveying loop beyond the last SN exit, namely along the recycling zone towards the confluence point C .

Under these conditions, it is conceivable that it is advantageous to provide means for synchronizing the movements of the items circulating respectively in the unstacking zone 1 and 4 dedicated to recycling. These synchronization means firstly comprise means for detecting the presence of a shipment, in the recycling zone 4. In the example illustrated, there are two sensors B1 and B2, of any appropriate type.

The detection means are associated with control means 15, illustrated only on the figure 2 but which are present in all embodiments. These control means are capable of acting on the operation of the unstacker 10, in response to information provided by the sensors B1 and B2 above. Finally, as will be seen in more detail in the following, it is advantageous to provide means for changing the speed of shipments in the recycling zone, or even in the sorting area.

In general, the invention provides for slowing down, or even stopping unstacking, when a shipment is detected on the recycling zone. This operation can be completed by modifying the speed of this sending, usually by braking it. This then allows to insert, judiciously, the recycled shipment between two shipments from the unstacker.

First, it is assumed that a first type of conventional unstacker, such as that fitted to the Applicant's STAR sorting machine, is used. This unstacker is suitable for unstacking the items with a constant distance, namely the distance between the rear edge of the downstream fold and the front edge of the upstream fold. However, this unstacker is not able to change the speed profile of a popped parcel.

où

• Gn correspond à l'écart nominal entre deux plis pendant leur convoyage. Cette valeur, fixée a priori, est typiquement de 95mm dans le cas d'une lettre et de 155mm dans le cas d'un « flat ». Lorsque la machine est destinée à traiter différents types d'envois, on choisit la valeur la plus élevée.
• Lmax correspond à la longueur maximale d'un pli. Cette valeur prédéterminée est par exemple de 328mm, dans le cas d'un flat.
• Vc est la vitesse nominale de convoyage.
• t0 correspond au temps total pour suspendre le dépilage.

In this case, the two detection sensors B1 and B2 are spaced apart by a distance D, $$\mathrm{D}\left(\mathrm{1}-\mathrm{2}\right)=\mathrm{2}*\mathrm{Gen.}+\mathrm{Lmax}+\mathrm{Vc}*\mathrm{t}\mathrm{0},$$

or

• Gn corresponds to the nominal difference between two folds during their conveying. This value, fixed a priori, is typically 95mm in the case of a letter and 155mm in the case of a "flat". When the machine is intended to handle different types of shipments, the highest value is chosen.
• Lmax is the maximum length of a fold. This predetermined value is for example 328mm, in the case of a flat.
• Vc is the nominal conveying speed.
• t0 is the total time to suspend unstacking.

In addition, the upstream sensor B1 of the confluence point C is spaced apart by a distance D1 = D10 + Vc * t0, where D is the distance separating C from the unstacker outlet.

In use, when the upstream sensor B1 detects the arrival of a shipment, it directs a signal via line 16 to the control means 15 which in turn act on the unstacker 10. The latter finishes unstacking the shipment being unstacked and then suspended.

Then, as long as a shipment is present between the two cells, or a sending occult one of these cells, the unstacker is kept in the suspended state. Finally, when the trailing edge of the last sending passes to the right of the downstream sensor B2, the latter sends a corresponding signal, via line 17, to the control means 15 which initiate the resumption of unstacking.

In the second embodiment, shown with reference to Figures 3 to 6 Another type of unstacker 110 of conventional type is used, which however has additional functionalities compared to that described above. This second destacker, which is for example consistent with the teaching of the French patent 2,797,437 , is provided with a catch-up system 112, schematically illustrated on the figure 4 , able to change the gap between two successive depilated shipments.

For this purpose, such an unstacker is equipped with at least one set of rollers 113, whose rotation speed is variable. The point of nip 114 is the zone of passage of the items, delimited by the set of rollers furthest upstream.

This unstacker is able to instantly suspend unstacking, on solicitation of control-command, then resume after an additional request. The advantage of this device is that it makes it possible to reduce the unstacking interruption time, compared with the first type of unstacker presented above.

An additional sensor, denoted B11, is placed at the right of the pinch point 114. It will be noted that the length and the thickness of the mailpiece being unstacked are known when it arrives at B11. Moreover, as soon as this sending occult B11, it can not be stopped anymore.

Furthermore, in nominal mode, the duration of the blocking phase of B11 by sending, namely the time taken by the latter to pass entirely before B11, is predictable and controlled. Indeed, it depends solely on the conveying speed and the length of the consignment considered. It will be noted that when its front edge reaches the right of B11, the sending is driven by this conveying speed.

Finally, the decision to stop or not a shipment is taken, when his front reaches the right of B11. The stop is implemented according to a predetermined speed profile, to give all shipments an identical stopping distance. In addition, the restart is performed according to a speed profile also predetermined, to bring all shipments at the conveying speed, after a distance and a time fixed beforehand. Note that if the stop and restart parameters are invariant for a given sequence of the sorting machine, they can be modified from one sequence to another.

• Da la distance d'arrêt, nécessaire pour arrêter un envoi, à partir du moment où son front avant passe au droit de B11.
• A le point d'arrêt de cet envoi.
• Dr la distance de redémarrage, nécessaire pour amener l'envoi à sa vitesse de convoyage, à partir du moment où il est stoppé au point A.
• Le temps de redémarrage Tr, nécessaire pour amener l'envoi à sa vitesse de convoyage, à partir du moment où il est stoppé au point A.
• R le point où l'envoi retrouve cette vitesse nominale.
• Δd la différence entre, d'une part, la distance parcourue pendant la durée Tr par un pli recyclé circulant à la vitesse de convoyage et, d'autre part, la distance de redémarrage Dr. En d'autres termes,

$$\mathrm{\Delta d}=\mathrm{Dr}-\left(\mathrm{Vc}*\mathrm{Tr}\right)\mathrm{.}$$

That being said, we will now list various operating parameters, with reference to the figure 4 which illustrates the unstacker 110 on a larger scale. We notice :

• Da the stopping distance, necessary to stop a shipment, from the moment when its front edge passes to the right of B11.
• At the stop point of this shipment.
• Dr the restart distance, necessary to bring the shipment to its conveying speed, from the moment it is stopped at point A.
• The restart time Tr, necessary to bring the shipment to its conveying speed, from the moment it is stopped at point A.
• R the point where the sending returns to this nominal speed.
• Δd the difference between, on the one hand, the distance traveled during the duration Tr by a recycled fold circulating at the conveying speed and, on the other hand, the restart distance Dr. In other words,

$$\mathrm{Dd}=\mathrm{Dr.}-\left(\mathrm{Vc}*\mathrm{Tr}\right)\mathrm{.}$$

• D'1 = D11 + Lmax + Gn et D'2 = D11 - Gn - Δd, où D11 correspond à la distance entre B11 et C. On note ainsi que la distance entre les deux cellules est de D'(1-2) = (2*Gn + Lmax - Δd), ce qui est sensiblement plus faible que dans le premier mode de réalisation.

With reference to figures 3 and 5 the two cells B1 and B2 are positioned at respective distances D'1 and D'2, with respect to the point C:

• From 1 = D11 + Lmax + Gn and D'2 = D11 - Gn - Δd, where D11 corresponds to the distance between B11 and C. It is thus noted that the distance between the two cells is D '(1-2) = (2 * Gn + Lmax - Δd), which is substantially lower than in the first embodiment.

It is then assumed that two items E1 and E2 have been unstacked, while an E3 recycled item is in area 4. A first situation is illustrated in figure 5 on which, for the sake of clarity, the recycling zone 4 is rectilinearly represented above the unstacking zone 1.

In this case, the sending E2 has already obscured the cell B11 while the front edge of the recycled mail E3 arrives at the right of the cell B1. The unstacking kinematics of E2 are then not modified, so that the latter is directed in a normal manner towards the confluence point C, so as to be interposed between E1 and E3.

In a second situation, illustrated in figure 6 it is now assumed that the sending E2 is still upstream of the cell B11, while the front edge of the recycled mail E3 arrives at the right of the cell B1. Even if one could then suppose that it is not possible to insert E2 between E1 and E3, this is possible under certain conditions.

soit la condition (I0, où

• d(1-3) est l'écart réel entre E1 et E3, à savoir la distance entre le front arrière AR1 de E1 et le front avant AV3 de E3,
• ds(1-3) désigne la valeur seuil de cet écart. Sur la figure 6, on a représenté d(1-3) égale à ds(1-3).
• L2 est la longueur de l'envoi E2, et
• Gmin(1-2) et Gmin(2-3) sont les écarts minimaux à respecter entre, d'une part, le front arrière de E1 et le front avant de E2 et, d'autre part, le front arrière de E2 et le front avant de E3. Ces écarts s'entendent en référence aux envois, une fois placés les uns derrière les autres dans la zone de tri.

Thus, the free space between E1 and E3 is potentially sufficient if $$\mathrm{d}\left(\mathrm{1}-\mathrm{3}\right)\ge \mathrm{ds}\left(\mathrm{1}-\mathrm{3}\right)=\mathrm{The}\mathrm{2}+\mathrm{G\; min}\left(\mathrm{1}-\mathrm{2}\right)+\mathrm{G\; min}\left(\mathrm{2}-\mathrm{3}\right),\mathrm{either\; the\; condition}\left(\mathrm{I}\right),$$

the condition (I0, where

• d (1-3) is the real difference between E1 and E3, namely the distance between the rear edge AR1 of E1 and the front edge AV3 of E3,
• ds (1-3) denotes the threshold value of this difference. On the figure 6 d (1-3) is equal to ds (1-3).
• L2 is the length of the sending E2, and
• Gmin (1-2) and Gmin (2-3) are the minimum differences to be observed between, on the one hand, the trailing edge of E1 and the front edge of E2 and, on the other hand, the trailing edge of E2 and the front edge of E3. These differences are understood in reference to shipments, once placed one behind the other in the sorting area.

• Longueur et épaisseur du couple d'envois adjacents, E1 et E2, ou bien E2 et E3 ;
• Glissement de l'envoi recyclé E3, observé lors de son parcours le long de la zone de tri ;
• Distance restant à parcourir par E3 pour atteindre sa sortie de tri ; et
• Coefficient éventuel permettant d'introduire une marge de sécurité.

The values of Gmin can, by default, be taken equal to Gn. However, in order to increase the productivity of the sorting sequence, it is possible to choose a value of Gmin less than Gn. The person skilled in the art may assign an appropriate value to Gmin depending in particular on the following parameters:

• Length and thickness of the pair of adjacent shipments, E1 and E2, or E2 and E3;
• Slip of the recycled E3 consignment observed during its journey along the sorting area;
• Remaining distance to be traveled by E3 to reach its sorting exit; and
• Possible coefficient allowing to introduce a margin of safety.

If the condition (I) above is verified, the sending E2 is then injected in the usual way by the pinch point, namely without stopping. In the opposite case, this sending E2 is stopped, until the rear edge of the recycled sending E3 passes to the right of the cell B2, as in the first embodiment.

In the third embodiment, at least one gap management device, or GMD (Gap Management Device), is used, capable of modifying the speed of a shipment in the recycling zone, or even upstream in the zone. sorting. This device equips for example the STAR sorting machine of the Applicant. Preferably, it is associated with a destacker provided with a retrofit system, such as the one 110 used in the second embodiment presented immediately above.

A first management device, referenced GMD1 and so named in what follows for convenience, is placed on the recycling zone 4 between the downstream detection cell B2 and the confluence point C. This GMD1 is controlled, among others, thanks to two additional cells B3 and B4. One of them B3 is disposed on the recycling zone, between the B2 cell and GMD1 itself, while the other B4 is provided on the unstacking zone. These two cells B3 and B4 are equidistant from the confluence point C, namely that the distances D3 and D4 on the figure 7 are the same.

With reference to Figures 8 and 9 , we will now present a first type of implementation of GMD1, in which the latter is able both to slow down and speed up a recycled shipment. In this case, the distance between the cells B1 and B2 is identical to that of the second mode above, namely (2 * Gn + Lmax - Δd). It will be seen later that, in another embodiment, this distance can be reduced.

The Figures 8 and 9 illustrate the progress of two E1 and E2 depilated shipments, as well as an E3 recycled consignment. Depending on the phase difference between E2 and E3, it is first necessary to choose which of these shipments will be directed before the other, towards the confluence point C.

On the figure 8 , the recycled mail E3 is substantially late on E2, so it seems judicious to be able to interpose E2 between E1 and E3. As in the second embodiment, it is known that this is possible if condition (I) is fulfilled, namely: d (1-3) ≥ ds (1-3).

The use of the GMD makes it possible, if necessary, to insert E2, even if this condition (I) is not satisfied. Indeed, the GMD has a characteristic distance Dret, which corresponds to the maximum delay that can confer this GMD to a shipment, by decelerating it. Thus, we now take into account condition (I bis), which is written $$\mathrm{d}\left(\mathrm{1}-\mathrm{3}\right)\ge \mathrm{d\text{'}s}\left(\mathrm{1}-\mathrm{3}\right)=\mathrm{The}\mathrm{2}+\mathrm{G\; min}\left(\mathrm{1}-\mathrm{2}\right)+\mathrm{G\; min}\left(\mathrm{2}-\mathrm{3}\right)-\mathrm{Dret}\mathrm{.}$$

To the figure 8 AR1 has been noted the position of the trailing edge of E1, AV3 the actual position of the front edge of E3, AV'3 the theoretical position of this front edge to fulfill condition (Ia), as well as δ the advance of the front. before E3 with respect to this theoretical position. If δ is lower than Dret, we know that the GMD can then delay the sending E3 of a value, such that E3 can be replaced at AV'3. There will then be enough space between E1 and E3 to let E2 intercalate, so that the normal injection of this fold E2 is allowed.

Then, during its progression along the recycling zone, E3 is delayed by the distance δ, so that its front edge is spaced from the rear edge of E2 according to the gap Gmin (2-3). In practice, we make tender Gmin (2-3) to Gn, as far as possible. This delay is implemented in a conventional manner, using the B3 and B4 cells.

On the other hand, in the case where δ is greater than Dret, the sending E2 is stopped, until E3 no longer blocks the cell B2.

où
d(1-2) est l'écart entre E1 et E2, à savoir la distance entre le front arrière de E1 et le front avant de E2,
L3 est la longueur de l'envoi E3, et
Gmin(1-3) et Gmin(3-2) sont les écarts minimaux à respecter entre, d'une part, le front arrière de E1 et le front avant de E3 et, d'autre part, le front arrière de E3 et le front avant de E2. Comme ci-dessus, on fait tendre Gmin(1-3) et Gmin(3-2) vers Gn, dans la mesure du possible.We now see, at the figure 9 , that the recycled mail E3 is late compared to E1, a relatively small distance, so it seems advisable to interpose E3 between E1 and E2. It is also known that the condition (I), applied to this case, must be fulfilled, namely: $$\mathrm{d}\left(\mathrm{1}-2\right)\ge \mathrm{ds}\left(\mathrm{1}-\mathrm{2}\right)=\mathrm{The}\mathrm{3}+\mathrm{G\; min}\left(\mathrm{1}-\mathrm{3}\right)+\mathrm{G\; min}\left(3-\mathrm{2}\right),$$

or
d (1-2) is the difference between E1 and E2, ie the distance between the rear edge of E1 and the front edge of E2,
L3 is the length of the sending E3, and
Gmin (1-3) and Gmin (3-2) are the minimum deviations to be observed between, on the one hand, the trailing edge of E1 and the front edge of E3 and, on the other hand, the trailing edge of E3 and the front edge of E2. As above, Gmin (1-3) and Gmin (3-2) are made to Gn as far as possible.

To the figure 9 the position of the trailing edge of E1, AV3 the actual position of the front edge of E3, AV'3 the theoretical position of this front edge to respect the minimum deviation Gmin (1-3), as well as δ ', has been noted AR1. the delay of the front edge of E3 with respect to this theoretical position.

The use of the GMD makes it possible to advance E3, in order to bring it closer to this theoretical position, which is advantageous in terms of productivity. It is known that the GMD has another characteristic distance Dav, which corresponds to the maximum advance that this GMD can give to a shipment by accelerating it.

Under these conditions, if δ 'is less than Dav, E3 is accelerated so that it is positioned as close as possible to E1, in order to respect the minimum difference Gmin (1-3). On the other hand, if δ 'is greater than Dav, E3 is accelerated so as to bring it closer to the aforementioned maximum value Dav, knowing that it will remain distant from E1 by a difference greater than Gmin (1-3).

Moreover, it is a question of respecting the minimum difference Gmin (3-2) between E3 and E2. To do this, the retrofit system 112 of the unstacker 110 is used. to delay the progression of E2 and to space it from E3 appropriately. The difference between E2 and E3 is calculated taking into account, not the actual position of E3, but the position it will occupy once it has been advanced, the value δ 'or Dav as seen here. -above.

The second type of implementation of the GMD1, said simplified, is based on the very nature of such a GMD. Indeed, it is known that it is much more efficient, in terms of accuracy and amplitude, to apply a deceleration to a shipment, rather than an acceleration.

Under these conditions, GMD1 is now used only in deceleration mode, which brings the cell B1 closer to the confluence point, a distance Dret. Consequently, the distance between these two cells is further reduced since it now has the value D "(1-2) = (2 * Gn + Lmax - Δd - Dret) This second type of implementation, not illustrated in FIG. the figures, is conducted in the same way as the first mode in its version "deceleration" of the figure 8 .

The advantages of the different embodiments, presented above, are clear from the foregoing.

Thus, the first embodiment can be implemented in a simple manner, using a conventional and robust unstacker. The distance D (1-2) separating the cells B1 and B2 is then typically 1393mm, in the case where Gn = 155mm, Lmax = 328mm, Vc = 3.5m / s and to = 0.215 seconds. This distance D is important because it determines the unstacking disruption time, which is suspended as a recycled shipment occults one of these cells.

The second embodiment makes it possible to reduce the value of this distance, by playing on the fact that the unstacker provided with means of catching up the gap, is able to suspend and resume unstacking immediately. Therefore, for the same values of Lmax and Gn, the distance D '(1-2) can be reduced to 650mm, a reduction of more than 50% compared to the first embodiment. The use of such a destacker also makes it possible not to stop this unstacking, in certain circumstances where the unstacker of the first mode would have required to suspend this unstacking, as in particular in the case of the figure 6 .

The third embodiment makes it possible to make up the position of the recycled items, which in certain cases avoids the unstacking. Thus, if the position of the recycled consignment is such that it will be too close to an adjacent depilated consignment at the level of the confluence point, the position catching then ensures it a sufficient distance with this adjacent consignment, in view of authorize their serialization downstream of the confluence point. In addition, it is possible, on the contrary, to reconcile a recycled item with an adjacent depilated item, if they are initially too far apart from one another, for the sake of productivity.

In addition, in the variant of this third mode where only the deceleration is implemented, it is possible to bring the two cells B1 and B2 closer together. Thus, for the same values of Lmax and Gn as previously, the distance D "(1-2) is brought back to 450mm, less than a third of the base value.

It will be noted that, optionally, another GMD, denoted GMD 2, can be placed between the two sets of sorting outlets, namely at the half-turn 32. More precisely, this GMD2 is typically placed in the downstream part of this half-turn while the sensor B5, which ensures the control, is disposed in the upstream part of this half-turn.

The implementation of this second GMD involves the identification, at the level of the half-turn, of items intended to be recycled. On the figure 10 these are the items E'2 and E'3, which are separated by a nominal space Gn measured by the cell B5.

In the case where at least one of the items E'1 and E'4, adjacent to these items intended for recycling, has already been unloaded in a sorting outlet, the speed of E'2 or E'3 can be modified. This makes it possible to increase the difference between these two shipments, while keeping an appropriate gap with the adjacent shipments.

In the illustrated example, it is assumed that E'4 has already been unloaded at the first set of sorting outlets, which explains that it is represented in dashed lines. GMD2 then slows E'3, so as to move it away from E'2, according to the double arrow F at the figure 11 , while keeping it at an appropriate distance from the next E'5 mailing. Moreover, the gap between E'1 and E'2 is unchanged.

Claims (20)

1. A postal sorting machine comprising an unstacker (10; 110) suitable for putting mailpieces (E1-E3) on edge, address recognition means (20, 25) for recognizing the addresses of said mailpieces, and a conveying zone (2, 3, 4) for conveying the mailpieces by nipping them, which zone is made up of an unstacking zone (1) extending from the unstacker, and of a sorting zone (3) having a plurality of sorting outlets (S1 - SN), distributed from an upstream sorting outlet (S1) adjacent to the unstacker, to a downstream sorting outlet (SN), comprising a recirculation zone (4) interconnecting the downstream sorting outlet (SN) and the upstream sorting outlet (S1), said recirculation zone co-operating with the unstacking zone (1) to define a point of confluence (C) situated between the unstacker and the upstream sorting outlet, said postal sorting machine being characterized in that said machine comprises synchronization means (B1, B2, 15, GMD1, GMD2) suitable for synchronizing the movements firstly of the "unstacked" mailpieces traveling between the unstacker (10) and the point of confluence (C), and secondly of "recirculated" mailpieces traveling in the recirculation zone (4), these synchronization means (B1, B2, 15, GMD1, GMD2) comprising detection means (B1, B2) for detecting the presence of at least one recirculated mailpiece, and control means (15) suitable for acting on the unstacker (10) in response to information transmitted by the detection means.
2. A machine according to claim 1, wherein the detection means for detecting the presence of at least one recirculated mailpiece comprise two presence sensors (B1, B2) disposed in the recirculation zone (4).
3. A machine according to either preceding claim, wherein the unstacker (110) is provided with a catch-up system (112), suitable for modifying the gap between two consecutive mailpieces.
4. A machine according to claim 2 or claim 3, wherein the synchronization means (B1, B2, 15, GMD1, GMD2) further comprise speed variation means (GMD1, GDM2) for varying the speed of at least one mailpiece traveling in the recirculation zone (4) and optionally in the sorting zone (3).
5. A machine according to claim 4, wherein the speed variation means comprise at least a first speed variation member (GMD1) placed in the recirculation zone (4), and optionally a second speed variation member (GMD2) placed in the sorting zone (3) between two series of sorting outlets.
6. A machine according to claims 2 and 5, wherein the first speed variation member (GMD1) is placed between the downstream presence sensor (B2) and the point of confluence (C).
7. A machine according to any preceding claim, wherein the sorting zone (3) has two straight branches (31, 33) interconnected by a U-turn (32).
8. A machine according to the preceding claim, wherein the sorting zone (3) has a length (L31 + L32 + L33) greater than 40 m, and a number of sorting outlets (S1-SN) greater than 100.
9. A machine according to any preceding claim, wherein, in the vicinity of the recirculation zone (4), the conveying zone substantially forms a U-turn having a length (L4) less than 2.5 m.
10. A machine according to the preceding claim, wherein the ratio between the length (L31 + L32 + L33) of the sorting zone (3) and the length (L4) of the recirculation zone (4) is considerably greater than 1, in particular greater than 10, and more particularly greater than 20.
11. A method of using the sorting machine according to any preceding claim, wherein the mailpieces are unstacked by means of the unstacker (10; 110), the recognition means (20, 25) are used in such manner as to recognize the addresses of said mailpieces, at least some of the mailpieces that have had their addresses correctly recognized are directed towards corresponding sorting outlets, and at least the mailpieces that have not had their addresses correctly recognized are caused to travel through the recirculation zone (4) so that they are fed back into the sorting zone (3).
12. A method according to the preceding claim, for using the sorting machine according to any one of claims 2 to 10, wherein the presence of at least one recirculated mailpiece is detected by detection means (B1, B2) and action is taken on the stacker (10) by using the control means (15), in such manner as to synchronize the respective movements of the unstacked mailpieces and of the recirculated mailpieces.
13. A method according to claim 11 or claim 12, for using the sorting machine according to any one of claims 2 to 10, wherein the mailpieces are unstacked with a constant gap and the unstacking is stopped so long as at least one recirculated mailpiece masks at least one of the two presence sensors (B1, B2).
14. A method according to claim 11 or claim 12, for using the sorting machine according to any one of claims 3 to 10, wherein an unstacker (110) is used that is provided with a catch-up system, and the two presence sensors (B1, B2) are spaced apart at a distance D'(1-2)=(2×Gn+Lmax-Δd) where Gn corresponds to the nominal gap between two mailpieces, Lmax corresponds to the maximum length of a mailpiece, and Δd is the difference between firstly the distance travelled, during the time take to restart a mailpieces stopped at the unstacker, by a recirculated mailpiece traveling at the conveying speed, and secondly the distance for restarting a mailpiece stopped at the unstacker.
15. A method according to any preceding claim, wherein the gap (d(1-3)) between the trailing edge (AR1) of a downstream unstacked mailpiece (E1) and the leading edge (AV3) of an upstream recirculated mailpiece (E3) is identified, and an intermediate unstacked mailpiece (E2) is interposed between said downstream unstacked mailpiece, and said upstream recirculated mailpiece if the identified gap is greater than a theoretical minimum gap (ds(1-3)).
16. A method according to claim 11 or claim 12, for using the sorting machine according to claims 3 and 4, wherein a recirculated mailpiece (E3) is interposed between two upstream and downstream unstacked mailpieces (respectively E2 and E1), and the speed variation means (GMD1) are used for accelerating the recirculated mailpiece so that it is distant from the downstream mailpiece by a gap that is as close as possible to a theoretical minimum gap (Gmin(1-3), and the catch-up system (112) is used so that the upstream mailpiece (E2) is distant from the recirculated mailpiece (E3) by a gap that is as close as possible to a theoretical minimum gap (Gmin(3-2)).
17. A method according to claim 11 or claim 12, for using the sorting machine according to claims 3 and 4, wherein an unstacker (110) is used that is provided with a catch-up system (112), the real gap between the trailing edge (AR1) of a downstream unstacked mailpiece (E1) and the leading edge (AV3) of an upstream recirculated mailpiece (E3) is determined, the theoretical minimum gap (d's(1-3)) making it possible to interpose an intermediate unstacked mailpiece is identified, and the advance (δ) of the leading edge, between said real gap and said minimum gap, is identified, and if said advance is less than a maximum retard value (Dret) allowed by the speed variation means (GMD1), an intermediate unstacked mailpiece (E2) is interposed between said downstream unstacked mailpiece and said upstream recirculated mailpiece, and then the speed variation means are used to retard said recirculated mailpiece (E3) by a value corresponding to the advance of its leading edge.
18. A method according to claim 15 or claim 17, wherein the theoretical minimum gap corresponds to: $$\mathrm{d}\left(\mathrm{1}-3\right)=\mathrm{L}\mathrm{2}+\mathrm{Gmin}\left(\mathrm{1}-\mathrm{2}\right)+\mathrm{Gmin}\left(2-\mathrm{3}\right)$$

    

    
    where:

    L2 is the length of the intermediate mailpiece; and

    Gmin(1-2) and Gmin(2-3) are the minimum gaps to be complied with firstly between the trailing edge of the downstream mailpiece and the leading edge of the intermediate mailpiece, and secondly between the trailing edge of the intermediate mailpiece and the leading edge of the upstream mailpiece.
19. A method according to claim 11 or claim 12, for using the sorting machine according to claims 3 and 4, wherein the speed variation means are used solely for slowing down the recirculated mailpieces, and the two presence sensors are spaced apart at a distance $$\mathrm{Dʹ}\left(1-2\right)=\left(2\times \mathrm{Gn}+\mathrm{Lmax}-\mathrm{\Delta d}-\mathrm{Dret}\right)$$

    

    
    where:

    Gn corresponds to the nominal gap between two mailpieces;

    Lmax corresponds to the maximum length of a mailpiece; and

    Δd is the difference between firstly the distance travelled, during the time taken to restart a mailpiece stopped at the unstacker, by a recirculated mailpiece traveling at the conveying speed, and secondly the distance for restarting a mailpiece stopped at the unstacker, and Dret is the maximum retard distance allowed by the speed variation means.
20. A method according to any one of claims 11 to 19, for using the sorting machine according to any one of claims 5 to 10, wherein, upstream from the second speed variation member (GMD2), two successive mailpieces (E'2, E'3) that are to go through the recirculation zone (4) are identified and, when at least one adjacent mailpiece (E'4) that is adjacent to the two successive mailpieces has already been unloaded, the second speed variation member (GMD2) is used to space the two successive mailpieces apart.

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