Patent Publication Number: US-2012027555-A1

Title: Palletizer with box layer preparation

Description:
The present invention relates to palletization installations and, more particularly, a palletizer which comprises a device for preparing and prestacking layers of boxes or other items (packs, partitions, trays etc.) before they are deposited on a pallet. 
     In this palletization field, the palletizer is part of what is called the end of line, i.e. it receives boxes of products which are leaving a packaging installation at a certain rate, which rate is itself very often set by the rates of the preceding installations where the preparation and production of these products to be palletized are carried out. 
     In this context, the palletizer must respond to all sorts of constraints: firstly,—constraints linked to the nature of the products which are more or less fragile, more or less stable and more or less regular,—constraints linked to the rates as it is not conceivable to stop a complete production line outside of the stops which have been expressly programmed, and—constraints linked to the immediate surroundings of the palletizer such as the surface area available for its installation, for example. 
     It is known, as described in document DE 25 11 207, to prepare a pair of layers of boxes in order to improve palletization rates. The first layer is prepared at a station which is situated upstream of the palletization station and is lifted up by an appropriate device while a second layer is prepared. As soon as this second layer is ready, the first layer is deposited on the second and the two layers are conveyed to a station where they are picked up by a carriage which transfers them to the actual palletization station. The two layers are retained by a barrier while the carriage returns to its position for picking up another group of layers and they are automatically deposited, by gravity alone, onto the pallet or onto the layers already in place on said pallet. 
     It is also known, as described in document FR 2 861 714, to prepare several layers of products and to delay their palletization during the pallet-changing operation which constitutes dead time in the palletization cycle. 
     The different layers of products are prepared directly at the palletization station on pre-grouping tables which are superimposed vertically above the pallet to be loaded and these layers are left standing by during the pallet-changing time, i.e. during the operations of removing the pallet which is full and the setting up of a new pallet. 
     These different layers which are standing by are then deposited, in turn, on the new empty pallet, at the palletization station. 
     Document FR 2 897 341 describes a palletizer which itself also responds to some of the constraints described in detail above and, in particular, to the constraints linked to the nature of the products; it is arranged so as to allow the preparation of pallets with boxes containing relatively fragile products such as, for example, bottles. 
     This palletizer is arranged so as to gently carry out the operations of grouping together the boxes of products which involve boxes coming in contact with each other such as, in particular, operations which consist of grouping together the boxes which are in the form of rows so as to reassemble them in the form of layers, which layers are then transferred onto a palletization table which is responsible for depositing each layer onto the pallet provided for this purpose. 
     However, with the increase in the rates of production of the products and of the rates of packaging of these products, it is noted that, at a palletization station, the time which is required to complete the operation of removing a full pallet, added to the time required for the operation of setting up a new empty pallet, is much greater than the time needed to prepare a layer of boxes, and this is holding up the improvement in rates. 
     This time constraint, at the palletization station, determines the organization of the entire palletization installation; in terms of rates, it is therefore the palletization station which determines the rates upstream, i.e. the rate of preparation of the layers of boxes and also the rate at which these boxes arrive on the palletizer. 
     For certain palletization installations, where the constraints linked to the installation of the palletizer are severe, the time required for the operations of moving the pallets, full or empty, can be relatively significant, for example, because of the need to carry out changes in the orientation of the pallets. 
     Moreover, the table of the palletization station itself has its own rates and these are linked to the different operations which are carried out by this depositing or palletization table. Nowadays this depositing, or palletization, table, is in fact multifunctional and it carries out operations which will to a certain extent disturb its cycle and slow down its rate. 
     This table can in fact be used to create and align the adjacent layers which are superimposed on the pallet, which operation is, for example, carried out by means of longitudinal and transverse cleats, or pressers, arranged directly on said table. For this operation, which takes a certain time, the table starts by depositing the layer of boxes on the pallet, then it shifts vertically downwards so as to place the different pressers at an intermediate level, between two layers, so as to align the sides of these two superimposed layers. 
     This table can also be put on standby when the layers of boxes etc. have to be separated by an interlayer. This interlayer-insertion operation, which is carried out by appropriate equipment associated with the palletization station, has the effect of reducing the rate of the palletization table. 
     The document GB 1 129 944 describes a compact palletizer which comprises a combined station for the preparation of the layers of boxes and for palletization of these layers, as they are prepared. The first layer is prepared on a retractable table with means for calibration and means for adjustment of the position of the boxes relative to each other. 
     When the layer is ready, the preparation table is retracted and the prepared layer retained by a transverse abutment and, depending on the case, by the calibration structure, is placed directly on the pallet which is standing by under said preparation table, or is deposited on the layer previously deposited on said pallet, which pallet is borne by a lifting table which picks up the pallet for the time taken to load it. 
     The table for the preparation of the layers is constituted by slats and is mounted on chains which surround the lifting table of the palletization station, and which surround the pallet with its load. The chains in fact comprise two tables constituted by slats, which tables are relayed in order to pick up each layer of boxes and they form a kind of noria around the lifting table which bears the pallet to be loaded. 
     The present invention proposes, for a palletization installation of the type described in the abovementioned document FR 2 897 341, the use of means of the type of those which are described in the abovementioned document GB 1 129 944 so as to delay sending the boxes to the palletization station for the time which is necessary to complete all the operations linked to this palletization station. 
     The present invention makes it possible to improve the operation and the capacities of the palletization table without modifying its rate which is generally of the order of six operations, on average, per minute. It also makes it possible to reduce the stresses on this palletization table while improving its flow rate thanks to suitable preparation of the boxes to be palletized. 
     Moreover, the equipment used, as described in the abovementioned document FR 2 897 341, allows manipulation of relatively fragile boxes and products. 
     The present invention therefore proposes a palletizer constituted by a preparation zone which comprises a conveyor for conveying the boxes, a station for the preparation of the groups or rows of boxes and a station for the preparation of each layer of boxes and by a zone for the actual palletization which comprises the palletization station and the deck, or deposit table, and this palletizer also comprises pushers for moving said boxes from one zone to the other, i.e. from said preparation zone towards said palletization zone and it comprises a conveyor for conveying pallets to said palletization station, which palletizer comprises a specific station for box layer preparation which is constituted by a buffer device equipped, on the one hand,—with means for preparing a first layer of boxes, for calibrating it and for moving it in order to leave room for—additional means which will, in the same way, prepare another layer of boxes and calibrate it and, on the other hand, with means for stacking said other layer of boxes on the previous layer and so on, so as to delay the transfer of these different layers towards the palletization station for a period of time which is at least equal to that which is necessary to carry out the different operations which take place at said palletization station, such as the pallet-changing operations, and/or the insertion of an interlayer between two layers, and/or of jogging in order to align the layers, for example, which box layer preparation device being associated with one of said pushers in order finally to move this stack of layers of boxes towards the palletization zone and in particular onto the deposit table of said palletization station. 
     According to a preferential arrangement of the invention the device of the station for the preparation and pre-stacking of each layer of boxes comprises:
         means for preparing a first layer of boxes, for calibrating it and for keeping it temporarily at the preparation station while moving it, which means are constituted by a main table which is vertically moveable between—a high position for receiving the rows of boxes in order to form a layer of boxes and—a low position which is situated at a distance corresponding substantially to the thickness of said layer of boxes, for receiving another layer of boxes, which calibration means are constituted by lateral cleats and a retractable transverse abutment for calibrating the layer of boxes at said preparation post, said main table being constituted by a motorized endless belt, which belt is used in particular for moving the boxes and for pressing them against the transverse abutment in order to calibrate said layer of boxes in the longitudinal direction.   means for preparing and calibrating another layer of boxes which are constituted by at least two interim tables capable of taking the place, in turn, of the main table when the latter is in the low position, which interim tables are horizontally moveable in the plane of circulation of the boxes, guided between an operative position of occupation of the window left free by said main table, in order to receive groups or rows of boxes and allow a new layer of boxes to be formed, and an inoperative position that they reach by being retracted and by being separated from said new layer, the latter being deposited on the layer which is standing by on said main table, said depositing taking place automatically, by gravity alone, as the interim table which is in operation is retracted,   a first pusher which moves the groups or rows of boxes between said station for preparing the groups or rows and the station for preparing the layers,   a second pusher which moves the layer or layers of boxes between said preparation station and said palletization station.       

     Still according to the invention, the device for preparing and for prestacking the layers of boxes comprises two identical interim tables which are each constituted by a flexible panel produced with rollers with a small diameter, mounted with a free wheel, which interim tables are arranged opposite each other, on endless chains, and the assembly forms a kind of noria around the main table, which endless chains are positioned laterally, on either side of the preparation station, each guided in a frame which extends around said main table, and the free space between the two interim tables corresponds at least to the length of the receiving surface area of said main table in order to allow the latter to pass through and be placed in the operative position for receiving a group of boxes, which endless chains are moved sequentially forwards in a direction which corresponds to the direction of advance of the layers of boxes towards the palletization station. 
     According to another arrangement of the invention, the rollers of each interim table are mounted on bearings comprising a free wheel so as to allow the boxes to be carried along during the movement of said table and for pushing or pressing said boxes against the transverse abutment in order to automatically calibrate the layer of boxes, in the longitudinal direction of circulation of said boxes on said interim table, according to the palletization scheme, as said rollers are retracted during the depositing of this layer of boxes on the lower layer of boxes which is situated on the main table. 
     Still according to the invention, the palletizer comprises means for calibrating each layer of boxes according to the palletization scheme, directly on said main table and, depending on the case, on the interim table, which means are constituted, on the one hand, by the retractable abutment which is arranged transversally with respect to the direction of travel of the boxes on the station for preparing the layers of boxes and at the downstream end of said preparation station and, on the other hand, by cleats arranged laterally on each side of said station for preparing the layers, which transverse abutment is arranged and positioned in such a way that in the inoperative position it acts as a slider bed joining the main table and the deposit table of the palletization station. 
     According to another arrangement of the invention, the main table comprises a support which is borne by a cradle, which cradle extends transversally beyond the frames of the noria, guided vertically on posts which form a general chassis on which said frames of the noria are fixed, and this cradle is maneuvered in the vertical direction by means of a mechanism integrated into said posts of said chassis and, in particular, a mechanism constituted by chains which are arranged in the side posts of the chassis, said endless chains being driven by a common servomotor. 
     This device for preparing and stacking layers of boxes can also, preferentially, be presented in the form of a module which can be inserted between the station for preparing groups, or rows, of boxes and the palletization station, which module comprises:
         a main table which is vertically moveable from a high position for preparing the first layer of boxes to a low position, standing by for another layer of boxes, which main table is constituted by a motorized endless belt used in particular for setting the boxes in motion and, in particular, for pressing them in order to calibrate the layer of boxes in the longitudinal direction of circulation of said boxes,   means constituted by lateral cleats and a retractable transverse abutment for calibrating the layer of boxes,   at least two interim tables capable, in turn, of taking the place of the main table when the latter is in the low position with one or more layers of boxes, which interim tables are horizontally moveable, guided between an operative position of occupation of the window left free by said main table, in order to receive groups or rows of boxes and allow a new layer of boxes to be formed, and an inoperative position that they reach by being retracted and by being separated from said new layer, the latter being deposited on the layer which is present on said main table, said depositing taking place automatically, by gravity alone, as the interim table which is in operation is retracted.       

     Still according to the invention the module for preparing and stacking of layers of boxes comprises two identical interim tables which are each constituted by a flexible panel produced with rollers with a small diameter, mounted on a free wheel, which interim tables are mounted opposite each other, on endless chains, and the assembly forms a kind of noria, which endless chains are arranged laterally, guided in a frame which extends around the main table, and the free space between the two panels corresponds at least to the length of the receiving surface area of said main table in order to allow the latter to pass through and be placed in the operative position for receiving rows of boxes, which endless chains are moved sequentially forwards in a direction which corresponds to the direction of advance of the layers of boxes towards the palletization station. 
     According to another arrangement of the invention, the rollers of the interim table are mounted on bearings comprising a free wheel so as to set the boxes in motion and press them against the transverse abutment in order to automatically calibrate the layer of boxes according to the palletization scheme, as said rollers are retracted during the depositing of this layer of boxes on the layer of boxes which is situated on the main table. 
     Still according to the invention, the module for preparing and stacking layers of boxes also comprises means for calibrating each layer of boxes according to the palletization scheme, which means are constituted, on the one hand, by a retractable abutment which is arranged transversally, at the downstream end of said module, and on the other hand by cleats arranged laterally on each side; which transverse abutment, in the inoperative position, acts as a slider bed joining the main table and the table of the palletization station. 
     According to another arrangement of the invention, the main table comprises a support which is borne by a cradle, which cradle extends transversally beyond the frames of the noria, and it is guided vertically on posts which form part of the general chassis on which said frames of the noria are fixed, and this cradle is maneuvered in the vertical direction by means of a mechanism which is constituted by chains which are firmly fixed to said cradle, said chains are arranged in the side posts which form part of the chassis, they are driven by a common servomotor. 
     The invention also relates to the method for preparing and prestacking these layers of boxes which makes it possible to delay the operation of palletizing these different layers on a palletizer, which method consists of:
         preparing a layer of boxes on the main table of the preparation and stacking module, from a previously formed group of boxes;   calibrating this layer of boxes according to the palletization scheme and putting it into the format of a receiving pallet, on said main table;   vertically retracting said main table, by a height substantially greater than the thickness of the layer of boxes;   installing an interim table in the space left free by said main table;   conveying a new group of boxes onto said interim table and calibrating in the same way as the previous layer and vertical to this previous layer;   retracting said interim table keeping the corresponding layer of boxes framed in order to deposit it directly on the previous layer which is arranged on said main table, at a lower level;   once there is no longer any need for delay, bringing the main table back to the level of the palletization table, with its different superimposed layers of boxes; and,   transferring said superimposed layers of boxes to said palletization station in order to deposit them on said pallet.       

     According to another arrangement of the invention, the pre-stacking method consists of simultaneously carrying out,—the transfer of the superimposed layers of boxes towards the palletization station and,—the setting up of new rows of boxes on the main table for formation of the initial layer of boxes. 
     Still according to the invention, in order to carry out the calibration of each layer of boxes, the pre-stacking method consists of:
         stopping the boxes on the transverse abutment situated at the downstream end of the device or of the preparation and stacking module in order to longitudinally press said boxes by means of each layer-preparation table,   transversally pressing the boxes constituting each layer, by means of lateral cleats bordering said layer-preparation device, which cleats are moveable above the table which bears the corresponding layer and,   longitudinally pressing said boxes by means of the corresponding table, under the effect of the adherence between the different boxes and said corresponding table, by a longitudinal movement of the corresponding table in a direction from the table for preparing the rows of boxes towards the palletization station.       

    
    
     
       The invention is described in further detail by means of the following description and attached drawings, given by way of illustration and in which: 
         FIG. 1  is a diagrammatic plan view of the palletization installation which comprises a station equipped with the preparation and stacking device according to the invention; 
         FIG. 2  is a diagrammatic and simplified perspective view of a palletization installation which comprises the device for preparing and stacking layers of boxes with the system in the form of a noria which comprises the interim tables; 
         FIG. 3  shows, still diagrammatically, the main table for preparing and stacking layers, in the operative position, after the transfer of the layer or layers of boxes; 
         FIG. 4  is also a diagrammatic view showing the main table in the inoperative position and an interim table, which interim table is formed by a flexible panel constituted by rollers and it is in the operative position for receiving a group of boxes in order to form a layer; 
         FIG. 5  shows, in cross-section, one of the ends of a roller of the interim table; 
         FIG. 6  shows, also in cross-section, the other end of a roller of the interim table; 
         FIG. 7  is an elevation of the station for preparing and stacking layers of boxes, viewed from the side; 
         FIG. 8  is an elevation of the chassis of the preparation and stacking station, said chassis being represented without the noria, and without the main table; 
         FIG. 9  is a plan view showing the arrangement of the different control components of the noria and of the cradle of the main table; 
         FIG. 10  is an elevation of the chassis of the layer-preparation station, showing the cradle of the main table with a portion of this main table; 
         FIG. 11  is a partial diagrammatic elevation of the noria, viewed from the front; 
         FIG. 12  is a diagrammatic elevation, viewed from the front, of one side of the chassis on which the frame of the noria has also been mounted, as shown in  FIG. 11 ; 
         FIG. 13  is a plan view of one of the cleats which are arranged laterally with its means of implementation for pressing the boxes in the transverse direction; 
         FIG. 14  diagrammatically shows the transverse abutment which carries out the longitudinal confinement of the boxes, which transverse abutment is represented in bold lines in the inoperative abutment position, acting as a slider bed, and in fine dot-and-dash lines in the operative abutment position; 
         FIGS. 15A to 15I  show the different stages in the progress of an operation of preparing and stacking two layers of boxes and removing them towards the table of the palletization station. 
     
    
    
     The palletization installation shown in  FIG. 1  is similar to the palletizer which is described in the abovementioned document FR 2 897 341. This installation, called a palletizer in the remainder of the text can in particular be used for stacking layers of boxes  1  on a pallet  2  and, in particular, boxes  1  containing relatively fragile products, like bottles. 
     This palletizer comprises:
         a zone marked  3  which constitutes a preparatory zone at which the arrival of the boxes  1 , then their grouping together in the form of rows of boxes and then their grouping together in the form of layers of boxes  1 , take place,   a zone marked  4  which constitutes the actual palletization zone and which comprises a palletization station  5  at which the layer or layers of boxes  1  are placed on a pallet  2 ,   arrangements for the circulation of the empty pallets and of the loaded pallets.       

     The pallets  2  can be conveyed to the palletization station  5  in different ways. In the embodiment represented in  FIGS. 1 and 2 , the pallets  2  are conveyed to a level which is situated below the level of the arrival of the boxes  1  and the level of the preparation of the layers of boxes  1 , i.e. below the level of the preparation zone  3 . 
     The pallets  2  are introduced into the palletizer by means of a conveyor  6  which is situated at ground level. The preparatory zone  3  is situated above the conveyor  6  for conveying the pallets  2 , as well as the depositing and palletization table  7 , which table  7 , sometimes called a deck, is vertically moveable in order to deposit the layer or layers of boxes  1  on the pallet  2 , at the palletization station  5 . 
     The boxes  1  are introduced into the preparatory zone  3  of the palletizer by a supply conveyor  8  on which they are oriented before arriving at the preparation station  9  where they are grouped together on a table  10  in the form of (a) group(s) of boxes  1  or in the form of one or more rows, which rows are arranged transversally with respect to the subsequent direction of circulation of the boxes  1  towards the palletization station  5 . 
     The boxes  1  are grouped together on the preparation table  10  by means of an abutment  11  which is fixed to the downstream end of said table  10 . 
     The groups or rows of boxes  1  are then moved towards the station  12  for preparing the layers of boxes. At this preparation station  12 , the boxes  1  constituting each layer of boxes  1  are pressed, as described in detail below, so as to prepare a layer which is calibrated according to the format of the pallet  2  and according to the scheme of distribution of said boxes on the latter. 
     Under normal circumstances, i.e. outside the pallet-changing operations etc., each layer of boxes  1  can be transferred directly from the layer-preparation station  12  towards the palletization table  7  which, progressively, deposits these different layers on the pallet  2 , which table  7 , of the symmetrical opening type, comprises a first panel  13  which, with appropriate means, transfers half of the layer onto a second panel  14  and said layer is deposited on the pallet  2  as described in detail in the abovementioned document FR 2 897 341, by retracting said panels  13  and  14 . 
     The transfer of the groups or rows of boxes  1  then of the layers of boxes from one station to the other is also carried out by means of pushers  20 , as in the document referred to above. 
     These pushers  20  are represented diagrammatically in  FIG. 2 . A first pusher  20 , provided with a plate  21 , allows the transfer of the groups or rows of boxes  1  towards the layer-preparation station  12  and a second pusher  20 , provided with a plate  22 , is used to transfer the layer of boxes  1  towards the palletization table  7  and in particular to push it onto the large retractable panel  13  of this table  7 . 
     All these elements are described in the abovementioned document FR 2 897 341 for palletizing successive layers of boxes  1  by depositing these different layers on the pallet  2 . 
     As indicated previously, the time taken for the preparation of a layer of boxes  1  is clearly less than the time needed to remove the pallet  2  which is full and to convey a new pallet  2  to the palletization station  5 . 
     Thus, in order to account for the time which corresponds to the operations which take place at the palletization station  5 , such as changing pallets, inserting interlayers or also vertical alignment, or jogging of the layers, the station  12  for preparing the layers of boxes is arranged in order to prepare layers of boxes  1  that it retains so as to delay the movement of these layers of boxes  1  towards said palletization station  5 . 
     This station  12  for preparing the layers of boxes comprises a device  24  for preparing and stacking layers of boxes  1 , which device  24  is arranged so as to carry out a kind of temporary storage of said boxes  1  by stacking several layers of boxes  1  on top of each other, two or more according to requirements, and this operation of forming layers of boxes and stacking these layers of boxes is envisaged to last long enough to cover the time needed for the various operations which take place at the palletization station  5 . 
     In order to carry out this operation of preparing layers of boxes  1  and stacking at least two layers, the buffer device  24  comprises at least two tables which, in turn, receive the groups or rows of boxes  1  in order to form a layer of boxes  1 . 
     In the embodiment shown diagrammatically in the different figures, the buffer device  24  comprises a main table  25  which is arranged in order to carry out a superimposition of two layers of boxes  1 ; this device  24  can however, without altering the nature of the invention, be arranged so as to allow the superimposition of more than two layers of boxes as a function of the rates and of the time needed to complete the various operations which take place at the palletization station  5 . 
       FIG. 2  shows the arrangement of the buffer device  24  which is shown with several tables: the main table  25  and another table  26 ; the main table  25  is in retracted position under the table  26 ; in fact this table  26  has taken the place of the main table  25 ; another table  26 ′, described in detail below, is positioned under the main table  25 . 
     For an operation which does not require stacking, i.e. during the setting up of the layers following each other on the pallet  2 , it is the table  25  which ensures the preparation of the layers and which ensures the continuity between the table  10  for preparing groups or rows of boxes  1  and the palletization station  5 . 
     Outside the periods of retention of the layers of boxes  1 , this table  25  is used as the main table for forming each layer of boxes  1  which, once prepared, is quite simply transferred towards the palletization station  5 , on the deposit table  7 , in order to fill the pallet  2  which is situated at said palletization station  5 , as described in detail in the abovementioned document. 
     The second layer-preparation tables  26 ,  26 ′ are used during the progress of the various operations to be carried out at the palletization station  5 . These second interim preparation tables  26 ,  26 ′ operate when it is necessary to delay sending the boxes  1  towards the palletization station  5 ; the different layers prepared by means of these interim tables  26 ,  26 ′ are kept at the layer-preparation station  12 , and they are stacked on top of each other and all calibrated according to the palletization scheme; they are substituted, in turn, for the main table  25 . 
     In  FIG. 2 , the main table  25  for preparation of the layers of boxes  1  is positioned below the level of the interim table  26 . This main table  25  also appears in  FIG. 3 , but in the high position, for the preparation of a layer of boxes and it appears in  FIG. 4 , as in  FIG. 2 , but in the low position, i.e. in a position where, normally, it bears a layer of boxes  1 , as represented by fine dot-and-dash lines. 
     The interim table  26  which appears in  FIG. 2  and  FIG. 4  is in operation; it is in the operative position in order to allow the preparation of an additional layer; it takes the place of the main table  25  when the latter is on standby, i.e. when it cannot deliver the layer of boxes  1  that it has prepared and when it is, in this case, retracted in the low position. 
     These tables  25 ,  26  and  26 ′ ensure a continuity between the table  10  for preparing the groups or rows of boxes and the panel  13  of the palletization table  7  which receives the layer of boxes  1  prepared for palletization. 
     The main table  25  is constituted, as in the abovementioned patent FR 2 897 341, by a deck in the form of an endless belt which is motorized by a geared motor and, as described in detail in this patent, the movement of this belt is coordinated with that of the plate  22  of the pusher  20 . 
     The belt of the table  25  is guided in a support  27  which is itself borne by a cradle  28  arranged transversally with respect to the direction of advance of said belt of the table  25 . This cradle  28  is vertically moveable, guided in a general chassis  29  and it is maneuvered by a mechanism which is described in detail below. 
     The table  26  and the table  26 ′, both interim, are presented in the form of flexible panels. These panels are constituted by rollers  30  with a small diameter, as shown in  FIGS. 5 and 6 . These rollers  30  are borne, at their ends, by endless chains  31 , which circulate in parallel and vertical planes arranged at the edge of the layer-preparation station  12 . 
     Each chain  31  is tensioned on pulleys marked from  32  to  35 ; which pulleys are positioned at the angles of a frame  36  which is firmly fixed to the general chassis  29  and, more particularly, with the posts  37  and  38  which form, on each side of the station  12 , the structure of this chassis  29 . Each frame  36  is arranged so as guide a chain  31  around the main table  25 , as also shown in  FIG. 7 . 
     The table  25  has a length L which is close to the distance which separates the row-preparation table  10  and the palletization table  7  and, more particularly, to the dimension F of the window which extends between the slider beds  39  and  40 , which slider beds  39  and  40  form, respectively, the junction between, on the one side, said table  10  and the main table  25  and, on the other side, downstream, said table  25  and the panel  13  of the palletization table  7 . 
     When, as shown in  FIG. 4 , it is the interim table  26 , or  26 ′, which forms the junction between the table  10  and the panel  13  of the palletization table  7 , the length of this interim table  26 , constituted by the rollers  30 , corresponds substantially to the length L of the surface of the main table  25 , also close to the distance F which separates the slider beds  39  and  40 . 
     These tables  25  and  26 ,  26 ′, are moveable, as described in detail below, in the direction of movement of the boxes  1 , i.e. in a direction from the table  10  for preparing the groups or rows of boxes towards the palletization table  7  in order to carry out a longitudinal confinement of said boxes  1  which constitute a layer, against an abutment which corresponds to the slider bed  40  as described in detail below. 
     The cradle  28  of the main table  25  is driven in a sequential upward and downward movement, by means of a servomotor  45  which makes it possible to control and manage this ascending movement between a high position for preparing the layer of boxes and one or more low standby positions for receiving one or more additional layers of boxes  1 . 
     The tables  26 ,  26 ′, are moveable, maneuvered by means of the chains  31  using a geared motor-type motor component  46 ; these tables  26  and  26 ′ rotate around the main table  25 . Furthermore, as described in detail hereafter, the movement of the tables  26 ,  26 ′ also makes it possible to press the boxes  1  in the longitudinal direction during the preparation of a layer; this layer is in fact calibrated, as also described in detail below, before being deposited on the layer which is standing by on the main table  25 . 
     The longitudinal confinement of the boxes  1  of each layer is carried out in cooperation and by means of an abutment which extends transversally with respect to the direction of advance of said boxes  1  towards the palletization station  5 . This transverse abutment  40  in fact corresponds to the slider bed  40  and it fulfils a double function: it in fact constitutes the slider bed  40 , as described in detail above, in order to form the junction between the main table  25  and the panel  13  of the palletization table  7  and it plays this role of transverse abutment, also marked  40 , in order to carry out the longitudinal confinement of the layer of boxes  1 . This slider bed or abutment  40  is described in detail below in connection with  FIG. 14 . 
     This slider bed or abutment  40  therefore allows the longitudinal calibration of the layer of boxes  1  by means of the advancing movement of the groups or rows of boxes  1 , when this layer is borne by the main table  25  or, depending on the case, by the interim table  26  or  26 ′; all these tables  25 ,  26  and  26 ′ are moveable at a speed chosen for gently carrying out a longitudinal calibration. 
     The transversal calibration of each layer of boxes  1  is carried out by means of cleats  47  situated on each side of the layer-preparation station  12 , above the level of the table  25  and of the table  26 ,  26 ′ depending on the case. These lateral cleats  47  are borne by a system of sliders  48  which cooperate with runners arranged on a casing  49  details of which are given below in connection with  FIG. 13 . 
     Given the movement of the interim table  26  and its installation on chains  31  which rotate around the main table  25 , said chains  31  bear, as indicated previously, two tables  26  and  26 ′ which are opposed, separated from each other by a distance which corresponds at least to the length F of the window which extends between the slider beds  39  and  40 . 
     In  FIG. 2 , the two tables  26  and  26 ′ are shown in opposition; the table  26  is in the operative position for receiving groups or rows of boxes  1  and the table  26 ′ is in the inoperative position below the main table  25 , but above the conveyor  6  on which the pallets  2  circulate. These two tables  26  and  26 ′ form, with the chains  31 , a kind of noria which turns in a very precise direction, which direction corresponds, when they are in the operative position for receiving a group of boxes  1 , to the direction of advance of this group of boxes and to the subsequent direction of advance of the layer or layers of boxes  1  towards the palletization station  5 . 
     In order to carry along the boxes  1  and exert a pressure on them, when they are supported on the abutment  40 , as shown in  FIG. 4 , the rollers  30  of the tables  26 ,  26 ′ are mounted on the chains  31  with at least one free wheel, as shown in  FIG. 5 . 
     Each roller  30  is constituted by a tube with a small diameter, of the order of 30 mm, and this tube comprises at each of its ends a welded end piece  50 , for example, each end piece  50  comprises a journal  51  in a bearing  52  and, on one side, the journal  51  is extended in order to cooperate with a free wheel  53 . 
     The bearings  52  are each housed in a socket  54  which acts as a support, which socket  54  is firmly fixed, by means of a right-angle bracket  55 , to a link of the chain  31 , on each side of the station  12  for the preparation of the layers of boxes  1 . One of the sockets  54  contains, in addition to the bearing  52 , the free wheel  53  and the other socket  54  is arranged in order to immobilize the roller in translation by means of the corresponding bearing  52  which is firmly fixed to the end piece  50 . 
     The sockets  54  which bear the ends of the rollers  30  are guided, on each side, over a longitudinal block  56  which extends between the upper pulleys  34  and  35 , which block  56  is borne by a right-angle bracket  57  which is firmly fixed to the corresponding frame  36 . These blocks  56 , made of resistant material with a low coefficient of friction, support the weight of the layer of boxes  1  when it is in preparation on one of the interim tables  26 ,  26 ′. 
     The cradle  28  of the main table  25  is guided over each pair of posts  37 ,  38 , and it is vertically moveable by means of a maneuvering mechanism which comprises a chain-lifting system, arranged in each of said posts  37 ,  38  the section of which is U-shaped with flanges. 
       FIG. 8  shows a pair of posts  37 ,  38  and the maneuvering means which make it possible to move the cradle  28 , vertically, between several positions, depending on the number of layers of boxes  1  which are capable of being deposited on the main table  25 . 
     The cradle  28  is guided, for example, over the post  38  by means of guide rollers  58  arranged laterally and it is also guided over the bottom of each post  37 ,  38 , by means of the guide rollers  59 , respectively. 
     The vertical movement of the cradle  28  is carried out by means of chains  60  which are respectively fixed on said cradle  28  and which are tensioned between pulleys: pulleys  61  and  62  arranged respectively at the top and towards the bottom of the posts  37  and  38 . 
     These two chains  60  are moveable under the effect of the servomotor  45  mentioned previously, which servomotor  45  drives, by means of belts or chains  66  and  67 , said chains  60  in order to raise or lower the cradle  28  which bears the main table  25 . 
       FIG. 9  shows the installation of the motorization systems for the cradle  28  and in particular for the chains  60  which are firmly fixed to this cradle  28 . It again shows the servomotor  45  which drives, by means of the belts or chains  66  and  67 , shafts  68  and  69  on the ends of which the pulleys  62  driving the chains  60  are installed. 
     This  FIG. 9  also shows the geared motor  46  which drives the chains  31  of the noria on which are positioned the rollers  30  which form the interim tables  26  and  26 ′. A shaft  71  extends between the chains  31  which are situated on each side of the station  12  for preparing the layers of boxes  1 , which shaft  71  bears the pulleys  32  driving said chains  31  and it is guided in bearings arranged at the lower part of the frames  36  which form, with the chassis  29 , the structure of the noria. 
     The servomotor  45  is borne by a support  74  arranged in the central part of the station  12  at the lower part of the frames  36 . This support  74  rests on cross members  75  which link the posts  37 , on the one hand, and the posts  38 , on the other hand. 
       FIG. 10  is a partial front view of the chassis  29 , which chassis  29  bears and guides the cradle  28  on which the support  27  of the main table  25  is placed. The cradle  28  is maneuvered on each side by the chains  60  which extend from the upper part of the posts  37 ,  38 , up to a level which is situated substantially above the level of the cross members  75  which extend between the pairs of posts  37 ,  38  and which also form the structure of the chassis  29 . 
       FIG. 10  again shows the cradle  28  which bears the support  27  of the main table  25 . This cradle  28  is guided over the chassis  29  and in particular over the bottom of the posts  37 ,  38 , by means of the guide rollers  59  and it is maneuvered on each side by means of the chains  60 , as described in detail above. 
     The lateral cleat  47  which is borne by the casing  49  and the sliders  48  is situated at the upper part of the post  38 ; the casing  49  is fixed to the upper part of the post  38  and the assembly is described in detail below in connection with  FIG. 13 . 
       FIG. 11  shows a partial front view of a frame  36  of the noria, arranged facing the chassis  29  and posts  37  and  38  in  FIG. 10 . 
     This  FIG. 11  again shows the servomotor  46  which drives the shaft  71  by means of a belt or chain  76 . There can also be seen, in this  FIG. 11 , the block  56  which is arranged at the upper part of the frame  36  in order to guide and support the sockets  54  of the rollers  30 . A block  77  is also arranged at the lower part of the frame  36 , in order to guide and support the rollers  30  which constitute the interim tables  26 ,  26 ′, when they are in the inoperative position, at the lower part of said frame  36 , below the main table  25  and above the conveyor  6  which delivers the pallets  2  to the palletization station  5 . 
       FIG. 12  shows a partial front view of the chassis  29  with the frame  36  of the noria in the normal position, installed on this chassis  29 . This frame  36  rests, at its lower part, on the cross members  75  which are fixed to the posts  37  and  38  constituting the support  29  and it comprises, at its upper part, lugs  78 , in the form of right-angle brackets, which make it possible to fix it to the upper part of said posts  37  and  38 . 
     This chassis  29  forms, viewed from the front, a kind of U open at the top, which top part comprises, on each of the posts  38 , the lateral cleats  47  which make it possible to press the boxes  1  and calibrate the layer in the transversal direction in order to make it correspond to the palletization scheme and in particular to the perimeter of the pallet  2 , for example. These cleats  47  are borne, as shown in  FIG. 13 , by a pair of sliders  48  which cooperate with runners  79  arranged laterally on the casing  49 , which casing  49  is fixed to the upper part of each of the posts  38 , i.e. posts which are situated on the side of the palletization station  5 . 
     A cylinder  80  is interposed between the casing  49  and the cleat  47  in order to move the latter transversally with respect to the direction of advance of the boxes  1  on the table  25  or the table  26 ,  26 ′ depending on the case, at the station  12  for preparing and stacking the layers of boxes  1 . 
     These cleats  47  are situated substantially set back from the abutment  40  which also acts as a slider bed. This abutment  40 , shown in  FIG. 14 , extends over the entire width of the station  12 , downstream of the cleats  47 ; it is articulated on the frame  36  of the noria and it is borne, on each side, by a kind of arm  85  in the form of a right-angle bracket. This arm  85  is mobile about a pin  86  which corresponds, for example, to the pin of the pulley  34  of the chain  31 , on each frame  36  of the noria, which arm  85  is maneuvered by means of a cylinder  87  in order to cause the abutment to pass from its operative abutment position  40  to its operative slider bed position  40 , depending on the case, and vice versa. 
     The abutment  40  also acts to provide security during the transfer of the boxes  1 , when they are pushed by the plate  22  of the pusher  20 ; in fact, when the boxes  1  are moved into place by the plate  22 , in particular on the interim table  26 ,  26 ′, these boxes  1  are borne by the rollers  30  which are free to rotate in the direction which corresponds to the advance of said boxes  1  towards the palletization table  7 . The abutment  40  can therefore stop the boxes  1  which would tend to continue on their path and go beyond the interim table  26 ,  26 ′. 
     The device  24  for preparing and prestacking layers of boxes  1  is also presented in the form of a module which can be inserted into a palletization installation once this installation requires temporary storage of the boxes  1  by stacking several layers of boxes on top of each other, two or more according to need, in order to cover the time needed for the various operations which take place at the palletization station  5 . 
       FIG. 15  diagrammatically illustrate from A to I, the different stages which make it possible to carry out a stacking of layers of boxes  1  at the layer-preparation station  12 , in order to take up the down time which results from the different operations carried out at the palletization station  5 . 
       FIG. 15A  shows a pair of rows of boxes  1 , pushed by the plate  21  of the pusher  20 , from the table  10  of the station  9  for preparing the rows of boxes  1  up to the main table  25  which is in the high position, i.e. in the operative position for preparing a layer of boxes  1 . 
     In this  FIG. 15A , the presence of the transverse abutment  40  which is in the operative abutment position can be seen. The interim table  26  and the table  26 ′ of the noria are both in the inoperative position, forming vertical walls on each side and below the level of the main table  25 . 
       FIG. 15B  shows the operation of the main table  25  and in particular its movement of advance which makes it possible, in collaboration with the abutment  40 , to group together the rows of boxes  14  and to calibrate, in the longitudinal direction, the layer of boxes  1  on said abutment  40 . During this longitudinal calibration, and transversal calibration operation using the cleats  47  which are not shown in this figure, the plate  21  returns to the starting position in order to pick up the new groups or rows of boxes  1  which are formed on the preparation table  10 . 
       FIG. 15C  shows the vertical movement of the main table  25  from its high position for preparing the layer to its low position standing by to receive another layer of boxes  1 . 
     Still in this  FIG. 15C , it can be seen that the plate  21  is in position for picking up the rows of boxes  1  in order to convey them to the station  12  for preparing a new layer of boxes  1 . 
       FIG. 15D  shows the moving into place of the interim table  26  which will fill the window left empty by the main table  25 . At the same time, the plate  21  picks up the new rows of boxes  1  and, as shown in  FIG. 15E , it positions them on the interim table  26  which is positioned in the space left free by the main table  25 . 
     The rows of boxes  1  placed on the interim table  26  advance towards the abutment  40  under the effect of the movement of this table  26  which is, it will be recalled, constituted by rollers  30  mounted with a free wheel  53 . In its movement, the interim table  26  carries the boxes  1  along and it confines these boxes  1  on the abutment  40  and, as it moves, as shown in  FIG. 15G , this interim table  26  drops the layer of boxes  1 , which layer is positioned, by gravity alone, on the previous layer which is borne by the main table  25 . 
       FIG. 15F  shows that, during the preparation of the second layer of boxes  1  and during its deposition on the previous layer, the plate  22  of the pusher  20  is moved in order to be put into the operative position for picking up the two layers of boxes  1  which have just been prepared and which are superimposed on the main table  25 . 
     In  FIG. 15H , this main table  25  is passed from its low position to its normal high position, i.e. to the level of the table  10  and palletization table  7 . In order to avoid too violent a docking between the plate  22  and the layer of boxes  1 , it can be seen in  FIG. 15I  that the main table  25  is also set in motion, as described in detail elsewhere in the abovementioned document FR 2 897 341, in order to start the boxes moving towards the palletization table  7  and set these layers of boxes  1  in motion in order to avoid too violent a docking between the plate  22  and all of these boxes  1  which represents a sometimes significant mass in motion. It is the plate  22  which conveys the layer into the optimum position on the panel  13  of the palletization table  7 . During this removal of the different layers of boxes  1 , it can be seen, still in  FIG. 15I , that the plate  21  has picked up the new rows of boxes  1  in order to convey them, with no loss of time, onto the main table  25  recommencing its cycle. 
     In order to be able to remove the layers of boxes  1  which have been prepared on the main table  25 , as shown in  FIG. 15H , the abutment  40  passes from its operative abutment position to the operative slider bed position  40  in order to form the junction between the main table  25  and the panel  13  of the palletization table  7 . This position of the slider bed  40  is maintained throughout the transfer time of the layers of boxes  1 , as shown in  FIG. 15I . The abutment  40  is repositioned immediately after the complete removal of the layers of boxes  1 , in order to allow the calibration of the rows of boxes conveyed by the plate  21  and form a new layer of boxes  1  on the main table  25 . According to need, the main table  25  can receive several layers of boxes which are stacked on top of each other standing by in order to be transferred to the palletization table  7 . 
     The method for prestacking several layers of boxes  1 , in order to delay the operation of palletization of these different layers, therefore consists of:
         preparing a layer of boxes on the main table  25  from a previously formed group of boxes  1 ;   calibrating this layer of boxes according to the palletization scheme and putting it into the format of the receiving pallet  2 , on said main table  25 ;   vertically retracting said main table  25 , by a height substantially greater than the thickness of the layer of boxes  1 ;   installing an interim table  26 ,  26 ′, in the space left free by said main table  25 .   conveying a new group of boxes  1 , onto said interim table  26 ,  26 ′ and calibrating it in the same way as the previous layer and vertical to this previous layer;   retracting said interim table  26 ,  26 ′ while keeping the corresponding layer of boxes  1  framed in order to deposit it directly on the previous layer which is arranged on said main table  25 ;   once there is no longer any need for delay, conveying the main table  25  to the level of the palletization table  7 , with its different superimposed layers of boxes  1 ; and,   transferring said superimposed layers of boxes  1  to said palletization station  7  to be deposited on the new pallet  2 .       

     The method also consists of simultaneously transferring the superimposed layers of boxes  1  towards the palletization station  7  and the moving into place of new rows of boxes  1  on the main table  25  for forming the initial layer of boxes. 
     In order to carry out the calibration of each layer of boxes  1  at the layer-preparation and prestacking station  12 , the method also consists of:
         stopping the boxes  1  on the transverse abutment  40  situated at the downstream end of said station  12  in order to longitudinally press said boxes  1  by means of each layer-preparation table  25  or  26 ,  26 ′,   transversally pressing the boxes  1  constituting each layer, by means of lateral cleats  47  which border said layer-preparation station  12  and which are moveable above the table ( 25 ,  26 ,  26 ′), which bears the corresponding layer and,   longitudinally pressing said boxes  1  by means of the corresponding table  25 ,  26 ,  26 ′, under the effect of the adherence between the different boxes  1  and said corresponding table, by a longitudinal movement of said corresponding table in a direction from the table  10  for preparing the rows of boxes towards the palletization station  7 .