Heteregenous palletisation method and system

Abstract

The invention relates to a palletisation method, wherein: - articles (i) are transported towards a loading point, - the articles (i) are loaded by a loading device onto a container (5) arranged in the loading station, - the loading device being controlled by a computer control means, the method further comprising a step for generating a stable arrangement of the articles (i) on the container upstream of their loading, - the stable arrangement comprises placing articles having substantially similar heights to form layers, wherein a partial layer (Ci) having a first height occupies part of the container and at least one complementary partial layer (Ci') having a second height occupies a second unoccupied part such that the entire surface area of the container is occupied. The invention also relates to a system for carrying out the method.

Description

[0001] DESCRIPTION

[0002] TITLE: HETEROGENEOUS PALLETIZING PROCESS AND SYSTEM

[0003] Technical field of the invention

[0004] The invention relates to the field of logistics platforms for large and medium-sized distribution companies and relates to a method and system for palletizing items before delivery to a customer.

[0005] State of the art

[0006] Logistics platforms act as an intermediary between suppliers and various points of sale. Suppliers transport their products to these platforms, where they are received and processed for storage. The points of sale then send their replenishment requests to these platforms. For each request, the requested products are removed from inventory and sent to an order preparation area. In the preparation area, robots are used to place the products on shipping pallets, which are then transported to their destination.

[0007] In addition to managing the removal of products from stock and the delivery of orders to the customer, several decisions must be made, including determining the number of pallets to use, on which pallets to place the items, and how the items will be placed on each pallet. Regarding the placement of items on a pallet, there are two main representations of layered solutions:

[0008] - the first consists of a stack of interchangeable layers of the same Width / Length dimensions;

[0009] - the second, consists of placing layers of any size placed without any precise rules to follow. Due to the diversity of the items to be placed, the first representation is too restrictive, because many objects cannot be found in a complete layer, for example of size 1200x800 mm, due to their small quantity. The quasi-optimal solutions obtained by the methods dedicated to this representation therefore place too few objects.

[0010] Furthermore, with the second representation, the diversity of possible layer dimensions makes the construction of layered solutions too complex. Known methods fail to obtain good quality solutions, which results in layouts with a low number of placed objects and a lack of stability.

[0011] The objective of the invention is therefore to propose a palletizing system and method making it possible to solve the problems of the methods described above, and making it possible to obtain arrangements of articles in layers on a container which are efficient in terms of articles placed as well as stability.

[0012] Summary of the invention

[0013] To this end, the invention relates, according to a first aspect, to a palletizing method in which:

[0014] - articles of heterogeneous shapes (in particular those with variable dimensions) are transported to a loading station by conveyor means,

[0015] - the articles are then loaded in several layers by a loading device onto a container arranged in the loading station, in which, the loading device being controlled by a computer control means, the method further comprises a step of generating a stable arrangement of said articles on the container upstream of their loading.

[0016] According to the invention, said stable arrangement comprises a placement of articles having substantially similar heights to form either complete layers occupying substantially the entire surface area of ​​the container, or partial layers each occupying a part of the surface area of ​​the container, and in which a first partial layer having a first layer height occupies a part of the container and at least one complementary partial layer having a second layer height occupies a second part not occupied by said first layer so as to occupy the entire surface area of ​​the container.

[0017] Given the diversity of the dimensions of the articles to be placed (in particular their height), the method according to the invention defines layers of articles to be placed which can be complete (able to occupy the entire surface area of ​​the container), or partial (able to occupy part of the surface area). A layer being formed by articles having substantially similar heights (having a small difference).

[0018] By combining full layers and partial layers in the solution, the process allows a large number of items to be placed on the container and therefore limits the volume that can be lost.

[0019] In addition, by placing the items in layers and ensuring that their location according to height is well chosen, the stability of the container is reinforced.

[0020] Consequently, unlike known methods, the method according to the invention makes it possible to obtain efficient palletization in terms of the number of items placed and in terms of stability.

[0021] A container can be any container used to palletize items for shipment, for example, to a customer. For example, this could be a pallet.

[0022] According to exemplary embodiments, a partial layer can occupy half the surface area of ​​a container (for example half the length and the entire width or vice versa), it can also occupy other proportions such as 1 / 3 or 1 / 4.

[0023] By fixing the number of possible layer sizes, we limit the number of layers to consider, which can make it easier to obtain solutions quickly.

[0024] For example, add two quarter-layer stacks to the half-layer stacks. Depending on the dimensions of the objects to be placed, this variant can be much more efficient. This variant can be particularly interesting if there are many small objects of very different heights.

[0025] Advantageously, two partial layers of substantially the same surface area can be superimposed. This makes it possible to fill a container, such as a pallet, by creating columns that maximize the occupied volume and stability.

[0026] Advantageously, two partial layers are separated by a partial interlayer plate of substantially the same surface area as said partial layers. The use of interlayer between partial layers of the same stack provides a considerable advantage for the stability of the container after loading and therefore increases the robustness of the arrangement.

[0027] Optionally, the nature of the interlayer can make it possible to fill the height dispersions of the layer on which it is placed without remaining rigid, which further increases stability.

[0028] According to exemplary embodiments, a partial layer and at least one additional partial layer are placed on a complete layer. By choosing this strategy, the occupied volume and stability are increased.

[0029] Advantageously, a full interlayer plate can also separate the full layer from the partial layers, said full interlayer plate having substantially the same surface area as the container. This further increases stability.

[0030] According to embodiments, the method may comprise a step of generating a catalog of layers capable of being placed on the container, said catalog comprising at least one partial layer.

[0031] The advantage of a catalog is that it defines the possible layers upstream of any layer construction and the process is restricted to using them in the most efficient way. The fact that the layer catalog also includes partial layers makes it easy to obtain arrangements of items on a container (e.g. a pallet) that maximize the occupied volume as well as stability.

[0032] According to embodiments, the catalog can be progressively enriched by the addition of new possible layers having a strictly negative reduced cost, said reduced cost being deduced from the resolution of the following linear problem, the resolution being able to be done by methods known to those skilled in the art (for example the simplex method):

[0033] Or :

[0034] - z(C): is a value corresponding to the greatest profit of layers that it is possible to have by using a real number of layers from the catalog C.

[0035] - p c is the profit of layer c, evaluated as the volume of objects in layer c plus a penalty proportional to the volume occupied by layer c in the container.

[0036] - HAS c : the number of times layer c is used.

[0037] - q- the number of articles i in layer c. - I: is a set of references of articles i known to the system.

[0038] - ni: number of times that the reference i can be used.

[0039] This dynamic generation method uses the above calculation formula to assign a value of interest to each object for a given set of layers. This value, positive or negative, is used to evaluate a layer that does not yet belong to the catalog. If said layer has a strictly negative reduced cost, then it is added to the set of layers contained in the catalog to improve the arrangement of layered items obtained before palletization.

[0040] Another advantage is that if there are no more layers that satisfy the above condition, then the set of layers allows us to express an optimal solution. This property then allows us to know when to stop, but also, using other formulas, to determine a limit on the quality of an optimal solution.

[0041] The reduced cost can be expressed by the formula:

[0042] Where i / / is the dual value of the only constraint in the problem.

[0043] The profit of a layer can be described by the following formula:

[0044] Where v c is the volume of the layer and has a real sufficiently small so that the profit of two layers is first evaluated according to the volume of the objects placed. For this same volume, the profit is compared on the volume that the layer occupies (We can also speak of "density" of the layer).

[0045] By adding a variable £ i e N and by integrating it into the constraint we obtain:

[0046] It is also possible to reformulate the objective of maximizing volume as minimizing unplaced volume: According to exemplary embodiments, to generate a stable arrangement of articles, the layers that maximize the sum of profits are chosen from the catalog under the constraint that all the layers can be arranged on the container without exceeding a limit height of the container fixed upstream. For a catalog C of layers c, we can for example determine which ones to choose to constitute the solution by solving the following linear program (the resolution methods being known to specialists in operational research):

[0047] The constraint h(A) ensures that it is possible to place all the layers without any of them exceeding the fixed limit height, noted H.

[0048] Optionally, the method may include the use of a learning method to generate the layers given as parameters to the "integer linear program". This allows for improvement when the objects to be palletized change little from one resolution to another.

[0049] Optionally, the computer system can include internal memory, thus saving the recurrent layers which are transmitted as parameters to the “integer linear program”.

[0050] Optionally, the method may include applying the method to a set of objects to be placed on more than one pallet. The distribution of the objects must then be taken into consideration, their integration being facilitated by the concept of layers.

[0051] The invention according to a second aspect also relates to a palletizing system implementing the method according to one of the combinations of characteristics described above.

[0052] The palletizing system may include:

[0053] - a loading station which may include a container reception area and a loading device,

[0054] - conveying means for transporting articles of heterogeneous shapes to the loading station to be loaded in several layers (Ce, Ci) onto the container by the loading device (4), in which the loading device is controlled by a computer control means configured to generate a stable arrangement of said articles on the container by implementing the method according to the description above.

[0055] Brief description of the figures

[0056] Other features and advantages of the invention will appear in the description below in relation to the appended drawings, given as non-limiting examples, in which:

[0057] [Fig.1] Figure 1 represents an example of a palletizing system according to the invention;

[0058] [Fig.2] Figure 2 is an illustration of a loaded pallet comprising full layers of items and half layers.

[0059] Detailed description

[0060] Figure 1 shows an example of a palletizing system according to the invention. The system 1 comprises a conveying means 2 for transporting articles i to a loading station to load them onto an empty container 5 (pallet) arranged in the loading station. In the example, the conveying means 2 is a conveyor, but other conveying means can be used, in particular automatically guided robots (AMR / AGV).

[0061] The palletizing system 1 also comprises a loading means 4 for loading the articles i onto the pallet 5. The loading means 4 is for example a multiaxial robot provided with a gripper 4a for gripping the articles i one by one and placing them on the pallet 5. The gripper 4a may be a grid as shown in the figure or have other known shapes, for example provided with suction cups. In a variant not shown, the palletizing system 1 may also comprise an article detection means, for example a camera, arranged above the conveyor 2 in the vicinity of the loading station.

[0062] The system 1 also comprises a control means, not shown, arranged to manage the loading of the articles by the loading means 4. It can also control the conveying means.

[0063] The control means may comprise a calculation means, such as software that can determine a stacking order and spatial positions for the items i to be stacked on the pallet 5.

[0064] Advantageously, the control means may also comprise a memory configured to host a database containing the characteristics of the packages to be stacked, for example, following an order from a customer. The database may comprise the dimensions, weights or other characteristics of the items.

[0065] Figure 2 shows an example of an arrangement of articles on a pallet 5 being loaded using the method according to the invention. In the illustrated arrangement of articles, the method has made it possible to place two complete layers Ce superimposed, each comprising a set of articles having a similar height. Then, the articles i-1 to i-4 having similar heights are arranged in a partial layer Ci occupying half the surface area of ​​the pallet 5. The articles i-5 to i-8 which have similar heights are arranged in a complementary partial layer Ci' occupying the other half of the surface area of ​​the pallet.

[0066] Further partial layers can be added on top of layers Ci and Ci', for example one or more layers of the same dimensions can be superimposed on Ci'. These two layers can further be separated by an interlayer plate to reinforce the stability of the pallet. Interlayer plates can also be added between the complete layers and between the upper complete layer Ce and the partial layers Ci, Ci' to increase stability.

[0067] Dynamic generation of a layer catalog:

[0068] To generate the catalog, and gradually enrich it by considering the articles that are not yet included, a software included in the computer control means calculates a reduced cost for each complete layer Ce or partial Ci possible, which can correspond to:

[0069] If the value of the reduced cost is strictly negative, then the layer is added to the catalog.

[0070] The operation is repeated until no new partial or total layer satisfies the above condition.

[0071] In the above expression, is the dual value of the layer c considered (the only constraint of the problem).

[0072] The values ​​of Ui and the reduced cost are deduced from solving the following linear problem: with :

[0073] - z(C): is a value corresponding to the greatest profit of layers that it is possible to have by using a real number of layers from the catalog C.

[0074] - HAS c : the number of times layer c is used.

[0075] - q- the number of items i in layer c.

[0076] - 1: is a set of reference items i known to the system. - ni: number of times that reference i can be used.

[0077] - p cis the profit of layer c, evaluated as the volume of objects in layer c plus a penalty proportional to the volume occupied by layer c in the container. It can be expressed by the following formula:

[0078] Where Vc is the volume of the layer and has a real number small enough that the profit of two layers is first evaluated based on the volume of the objects placed. For this same volume, the profit is compared on the volume that the layer occupies.

[0079] The methods for solving such a problem are known to operational research specialists and are therefore not detailed here. Well-known balancers, such as GLPK, can be used to solve the problem.

[0080] Selection of layers to place:

[0081] In this step, the process is implemented by the software to choose from the catalog complete or partial layers to be placed on the container (pallet) by the robot 4. The layers from the catalog C chosen are those which maximize the sum of profits (p c ) under the constraint that all of the chosen layers can be placed on the container and without exceeding a limit height of the container, fixed upstream.

[0082] The layers are selected by solving the following linear program (the resolution methods being known to specialists in operational research):

[0083] The constraint h(A) ensures that it is possible to place all the layers without any of them exceeding the fixed limit height, noted H.

[0084] For example, for complete layers, the constraint h(A) can be expressed as: where h c is the height of layer c.

[0085] If we use full layers and half layers of dimensions 600x800 or half layers 1200x400, the constraints to be added are:

[0086] Or c ! ç C is the set of complete layers in the catalog, and Ci / 2 cc | es half-layers from the catalog.

[0087] The variables respectively indicate the number of half-layers on the right and left that will be stacked on the pile of full layers. with a random method:

[0088] To evaluate the effectiveness of the dynamic generation method described above, it is compared to a random generation method known from the state of the art.

[0089] The results obtained for Z(C) in both cases, as well as the results obtained for a Lagrangian bound (known to those skilled in the art) used as a reference, are shown below.

[0090] Simple instances: Z(C) (Dynamic): 172; 0(u): 170; Z(C) (Random): 179

[0091] Average instances: Z(C) (Dynamic): 171; 0(u): 155; Z(c) (Random): 230

[0092] Difficult Instances: Z(C) (Dynamic): 145; 0(u): 128; Z(C) (Random): 190

[0093] To illustrate the gap between the two methods, we calculate the GAP (as a percentage) between the value z(C), with C being the catalog generated by one method or the other, and a Lagrangian bound on z(C). The lower the GAP, the more efficient the method.

[0094] The difference between the value z(C) and a Lagrangian bound on z(C) obtained are as follows:

[0095] Easy Instance: Dynamic: 1.18%; Random: 5.70%

[0096] Average Instance: Dynamic: 10.30%; Random: 47.85%

[0097] Hard Instance: Dynamic: 13.54%; Random: 48.44%

[0098] These results clearly show the effectiveness of the dynamic method described above compared to the random method known from the state of the art.

Claims

CLAIMS Palletizing process in which: - articles (i) of heterogeneous shapes are transported to a loading station by conveying means (2), - the articles (i) are then loaded in several layers (Ce, Ci) by a loading device (4) onto a container (5) arranged in the loading station, wherein, the loading device (4) being controlled by a computer control means, the process further comprises a step of generating a stable arrangement of said articles (i) on the container upstream of their loading, characterized in that said stable arrangement comprises a placement of articles having substantially similar heights to form either complete layers (Ce) occupying substantially the entire surface of the container, or partial layers (Ci, Ci') each occupying a part of the surface of the container,and in that a first partial layer (Ci) having a first layer height occupies a portion of the container and at least one complementary partial layer (Ci') having a second layer height occupies a second portion not occupied by said first layer so as to occupy the entire surface area of ​​the container. A palletizing method according to the preceding claim, wherein two partial layers of substantially the same surface area are superimposed. A palletizing method according to the preceding claim, wherein said two partial layers are separated by a partial interlayer plate having substantially the same surface area as said partial layers. A palletizing method according to any one of the preceding claims, wherein a partial layer (Ci) and at least one additional partial layer (Ci') are placed on a complete layer (Ce). A palletizing method according to the preceding claim, wherein a complete interlayer plate separates the complete layer (Ce) from the partial layers (Ci, Ci'), said complete interlayer plate having substantially the same surface area as the container (5). A palletizing method according to any one of the preceding claims, further comprising a step of generating a catalog C of layers that can be placed on the container, said catalog comprising at least one partial layer.

7. A palletizing method according to the preceding claim, wherein the catalog is progressively enriched by the addition of new possible layers c having a strictly negative cost, said cost being deduced from the solution of the following linear problem: Or : - z(C): is a value corresponding to the greatest possible layer profit that can be obtained using a real number of layers from the C catalog. - p c is the profit of layer c, evaluated as the volume of objects in layer c, plus a penalty proportional to the volume occupied by layer c in the container. - HAS c : the number of times the c layer is used. - q- the number of articles i in layer c. - I: is a set of references to articles i known to the system. - ni: number of times that reference i can be used. This cost CR(c) is expressed by the formula: Where i / / is the dual value of the constraint: The profit p c of a layer being expressed by the following formula: Where v c is the volume of the layer, v t the volume of an item i and a is a real number. Palletizing method according to the preceding claim, wherein complete or partial layers are selected from the catalog, which maximize the sum of profits (p c ) under the constraint that the set of chosen layers can be arranged on the container and without exceeding a maximum height of the container, fixed beforehand.

9. Palletizing system comprising: - a loading station including a container receiving area (5) and a loading device (4), - conveying means (2) for transporting articles (i) of heterogeneous shapes to the loading station to be loaded in several layers (Ce, Ci) onto the container (5) by the loading device (4), wherein the loading device (4) is controlled by a computer control means configured to generate a stable arrangement of said articles on the container by implementing the method according to one of the preceding claims.

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