Stacking system and stacking method

Abstract

The present invention provides a stacking system S and stacking method that can prevent transportation problems caused by uneven distribution of goods A when the number of goods A stacked on a pallet P is small. [Solution] The stacking system S comprises a plurality of stations 1A, etc., each having a transfer robot 4, and a controller 10 that controls the transfer robot 4. The storage unit 20 of the controller 10 stores arrangement patterns 21 in which a plurality of items A are stacked in layers on a pallet P, and in each layer a plurality of items A are arranged in a line to form the layers. When the controller 10 detects that the number of items A to be stacked on the pallet P is less than or equal to a first reference number, it determines whether or not to arrange the items A on the pallet P according to a transfer pattern 23 different from the arrangement pattern 21.

Description

Technical Field

[0001] The present invention relates to a stacking system and a stacking method for stacking a plurality of articles on a pallet.

Background Art

[0002] As a device for stacking a plurality of articles on a pallet, for example, a loading device described in Patent Document 1 is known. In this device, when the control device detects the occurrence of fractional workpieces, it selects a fractional-stage pattern corresponding to the number thereof and instructs the robot to stack the fractional stages in that pattern.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described conventional device, when the occurrence of fractional workpieces is detected, stacking is performed in a fractional-stage pattern. However, in this case, there is a drawback that the number of transfer times when the goods are loaded and unloaded at the next station increases. In the above-described conventional device, stacking is performed in a fractional-stage pattern, but the bias (uneven load) when the number of articles stacked on the pallet is small is not considered.

[0005] "When the number of articles stacked on the pallet is small" means, for example, a case where the number of articles is one or more. The "plurality of articles" in that case means a quantity that can be stacked in one or two or fewer stages on the pallet.

[0006] [[ID=,43]]An object of the present invention is to provide a stacking system and a stacking method that can prevent problems in conveyance caused by the articles being unevenly arranged when the number of articles stacked on the pallet is small. [Means for solving the problem]

[0007] [1] A stacking system according to one aspect of the present invention comprises one or more stations having a transfer robot for loading and unloading articles onto a pallet, and a controller for controlling the transfer robot, the controller having a storage unit for storing arrangement patterns which form multiple articles stacked on a pallet and which form layers with multiple articles lined up in each layer, the controller controls the transfer robot to place articles on the pallet according to the arrangement pattern, and when the controller detects that the number of articles to be stacked on the pallet is less than or equal to a first reference number, it determines whether or not to place articles on the pallet according to a transshipment pattern different from the arrangement pattern, taking into account the uneven load on the pallet.

[0008] According to this stacking system, when the number of items to be stacked on a pallet is detected to be less than or equal to a first standard number, the controller determines whether or not to arrange the items on the pallet according to a transshipment pattern that takes into account uneven load distribution on the pallet. This prevents transportation problems caused by uneven distribution of items when the number of items stacked on a pallet is small.

[0009] [2] In the stacking system described in [1] above, the transshipment pattern may be a pattern in which the goods are rearranged with respect to the center of the pallet. In this case, when the number of goods stacked on the pallet is small, a load configuration that suppresses uneven loading can be formed.

[0010] [3] If the stacking system described in [1] or [2] above includes multiple stations, and the controller detects that the number of items to be stacked on a pallet is greater than a first reference number and less than or equal to a second reference number greater than the first reference number, and determines that no new items will be stacked on the pallet at any other station, the controller may arrange the items on the pallet according to a transshipment pattern, taking into account the uneven load on the pallet. In this case, it becomes unnecessary to rearrange the items already stacked in order to stack new items at any other station.

[0011] [4] In any of the stacking systems described in [1] to [3] above, the arrangement pattern may be a pattern in which the goods are transferred to a position opposite the center of the pallet. For example, when stacking one or more items that do not amount to a full layer, it is possible to create a load that suppresses uneven loading.

[0012] [5] In any of the stacking systems described in [1] to [4] above, the station may have a temporary storage space for rearranging the goods stacked in the above arrangement patterns. In this case, the temporary storage space can be used to easily rearrange the goods on the pallets.

[0013] [6] In any of the stacking systems described in [1] to [5] above, the pallets are transported by a transport vehicle, and the controller may change the transport mode by the transport vehicle based on whether the goods are stacked according to an arrangement pattern or according to a transshipment pattern. In this case, improvements such as increasing transport capacity can be made while preventing the load from collapsing during transport.

[0014] [7] In another aspect of the present invention, a stacking system is provided comprising one or more stations having a transfer robot for loading and unloading articles onto a pallet, wherein a controller controls the transfer robot to arrange the articles on the pallet according to an arrangement pattern in which multiple articles are stacked on the pallet and multiple articles are arranged in each layer. In this stacking method, when the controller detects that the number of articles to be stacked on the pallet is less than or equal to a first reference number, it determines whether or not to arrange the articles on the pallet according to a transshipment pattern different from the arrangement pattern, taking into account the uneven load on the pallet.

[0015] This stacking method also allows the controller to determine whether or not to arrange the items on the pallet according to a transshipment pattern that takes into account uneven load distribution on the pallet. This prevents transportation problems caused by uneven distribution of items when the number of items on the pallet is small. [Effects of the Invention]

[0016] According to some aspects of the present invention, when the number of items stacked on a pallet is small, it is possible to prevent transportation problems caused by uneven placement of items. [Brief explanation of the drawing]

[0017] [Figure 1] Figure 1 shows an example configuration of a stacking system according to one embodiment of the present invention. [Figure 2] Figure 2 is a functional block diagram of the controller shown in Figure 1. [Figure 3] Figures 3(a) and 3(b) show examples of stacking under normal conditions, while Figures 3(c) and 3(d) show examples of stacking three items (less than one layer). [Figure 4] Figures 4(a) and 4(b) show examples of stacking two items (less than one layer), and Figures 4(c) and 4(d) show examples of stacking one item (less than one layer). [Figure 5] FIG. 5(a) and FIG. 5(b) are diagrams showing an example of stacking one (less than one stack) article, and FIGS. 5(c) and FIG. 5(d) are diagrams showing an example of restacking it. [Figure 6] FIGS. 6(a) to FIG. 6(d) are diagrams showing examples of restacking articles of different weights. [Figure 7] FIGS. 7(a) to FIG. 7(h) are diagrams showing other examples of restacking articles of different weights. [Figure 8] FIGS. 8(a) to FIG. 8(h) are diagrams showing examples of determining whether restacking is necessary. [Figure 9] FIG. 9 is a diagram showing another example of restacking. BEST MODE FOR CARRYING OUT THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same reference numerals are given to the same elements, and redundant descriptions are omitted.

[0019] First, referring to FIGS. 1 and 2, the overall configuration of the stacking system S of the present embodiment will be described. As shown in FIG. 1, the stacking system S includes a plurality of carrier vehicles 2 and is a system for transporting a plurality of articles A by these carrier vehicles 2. The stacking system S is applied, for example, to a manufacturing factory of a product manufactured through a plurality of processes. In a factory to which the stacking system S is applied, an automation system for managing and automating the warehousing, storage, and shipping of articles A (including a plurality of types of articles, including other articles B (see FIG. 6)) may be applied. Note that the stacking system S may be incorporated into an automated warehouse system.

[0020] In the stacking system S, in particular, the carrier vehicle 2 transports a plurality of articles A via a pallet P. The pallet P is placed on the lifter of the carrier vehicle 2 and transported. The pallet P is, for example, a rectangular plate-like body having a square shape in plan view. A plurality of fork holes may be formed in the pallet P so that it can be transported by a forklift or the like (not shown).

[0021] The stacking system S includes, for example, a higher-level controller 5 (see Figure 2) that receives information from another system (such as a production management system) in a factory or warehouse, and a controller 10 that controls the transport of various items based on instructions from the higher-level controller 5. The controller 10 is a computer having a ROM (Read Only Memory) where programs are stored, a RAM (Random Access Memory) for temporarily storing data, a storage medium such as an HDD (Hard Disk Drive), a processor such as a CPU (Central Processing Unit), and a communication circuit such as a wireless LAN. The controller 10 can be configured as software, for example, where a program stored in ROM is loaded onto RAM and executed by the CPU. The controller 10 may also be configured as hardware using electronic circuits. The controller 10 may consist of one device or multiple devices. If it consists of multiple devices, they are connected via a communication network such as the Internet or an intranet to logically construct a single controller 10. The configuration of the higher-level controller 5 may be the same as that of the controller 10.

[0022] The stacking system S comprises, for example, a path 3 provided on the floor of a factory, and a plurality of stations 1A, 1B, and 1C connected by the path 3. Each of the stations 1A, 1B, and 1C corresponds to either a palletizer area, a depalletizer area, or both. "Palletizing" means the work of stacking goods on a pallet P, and "depalletizing" means the work of unloading goods from the pallet P. The stacking system S further comprises a plurality of transfer robots 4 installed at each of the stations 1A, 1B, and 1C to perform palletizing or depalletizing, and a plurality of conveyors 6 that transport (or sometimes store) goods between the transfer robots 4 and the transport vehicles 2. One transfer robot 4 may be provided at one station, or multiple transfer robots 4 may be provided at one station. One conveyor 6 may be provided at one station, or multiple conveyors 6 may be provided at one station.

[0023] In the example shown in Figure 1, for instance, stations 1A and 1B are located on the first floor of a building such as a factory, and station 1C is located on the second floor (or higher) of the building. The layout of each station 1A, etc., and route 3, as well as the number and arrangement of the multiple transport vehicles 2, are not particularly limited.

[0024] The transfer robot 4, for example, has a multi-jointed arm and is a robot that holds and transfers goods (packages). Known configurations and mechanisms can be used for the transfer robot 4. The transfer robot 4 loads and unloads goods A onto pallets P on the conveyor 6 or onto pallets P on the transport vehicle 2. Each transfer robot 4 is controlled by the controller 10 to perform palletizing or depalletizing.

[0025] The transport vehicle 2 autonomously travels along a pre-set route 3. The transport vehicle 2 is, for example, an AGV (Automated Guided Vehicle). Each transport vehicle 2 is controlled by the controller 10 to transport item A.

[0026] The controller 10 controls the work performed by the transfer robots 4 and the operation of the conveyor 6 at multiple stations 1A, 1B, and 1C, as well as the transport and travel of multiple transport vehicles 2. In particular, the controller 10 controls palletizing and depalletizing of pallets P at each station 1A, 1B, and 1C. The controller 10 can communicate with each transfer robot 4 and each transport vehicle 2 via wired or wireless means.

[0027] The following explanation describes the case where rectangular parallelepiped items A (or item B) are stacked in layers on a pallet P that is square in shape when viewed from above. For example, as shown in Figure 3(a), a total of eight items A (or item B) are stacked on the pallet P: four on the bottom layer (2x2 rows) and four on the top layer (2x2 rows).

[0028] The controller 10 includes a stacking control unit 10A and a storage unit 20. The stacking control unit 10A includes a transport vehicle control unit 11, a transfer robot control unit 12, a palletizing planning unit 13, and an information acquisition unit 15. The palletizing planning unit 13 includes a transshipment determination unit 14. The transport vehicle control unit 11 controls transport and travel in each transport vehicle 2. The transfer robot control unit 12 controls each transfer robot 4. The palletizing planning unit 13 plans palletizing and depalletizing according to commands from the higher-level controller 5. The information acquisition unit 15 acquires various commands in the stacking system S and information regarding the status of each piece of equipment by communicating with the higher-level controller 5, each transfer robot 4, and each transport vehicle 2.

[0029] In the stacking system S, the controller 10 is capable of handling both pre-planned palletizing and depalletizing acquired by the palletizing planning unit 13, and palletizing and depalletizing that differ from the pre-planned ones, based on commands from the higher-level controller 5 or another system. The controller 10 basically controls the transfer robot 4 to sequentially load items A (or items B) onto pallets P as they become transportable. The number of items A to be loaded onto one pallet P (i.e., the final number loaded) is determined when there are no more items A to be loaded, or when there are no more commands. The controller 10 recognizes the end of stacking (also called lot end in the production process) by receiving information from the higher-level controller 5 or another system.

[0030] The controller 10 stores various arrangement patterns 21 in which multiple items A (or items B) are stacked on the pallet P, and multiple items are arranged in each layer to form the layers. The transfer robot control unit 12 and the palletizing planning unit 13 of the controller 10 basically select one of the appropriate arrangement patterns 21 and control the transfer robot 4 to place items A (or items B) on the pallet P according to the arrangement pattern 21.

[0031] However, the controller 10 has limitations in knowing the scheduled completion date of loading. Palletizing or depalletizing may be suddenly terminated by the higher-level controller 5 or another system for various reasons. Therefore, the controller 10 is designed to respond to such unexpected palletizing or depalletizing, enabling the stable transport of one or more items on the pallet P in each transport vehicle 2.

[0032] The palletizing planning unit 13 of the controller 10 includes a transshipment decision unit 14 that determines whether or not to arrange the items on the pallet P according to a transshipment pattern different from the various arrangement patterns described above, that is, whether or not to perform transshipment work, taking into account the uneven load on the pallet P. Based on the information acquired by the information acquisition unit 15, the transshipment decision unit 14 detects that the number of items to be stacked on the pallet P is less than or equal to a first standard number, and determines whether or not to arrange the items on the pallet P according to one of the transshipment patterns, taking into account the uneven load on the pallet P.

[0033] The transshipment determination unit 14 stores, for example, several reference numbers (predetermined numbers) related to the number of items to be loaded onto the pallet P (final loading quantity) as thresholds used in determining whether transshipment is necessary. These reference numbers may be determined for each type of pallet P, or they may be determined in addition to the type of items. The transshipment determination unit 14 stores at least the first reference number described above and a second reference number used for further determinations. The first and second reference numbers are smaller than the maximum quantity that can be loaded onto the pallet P. The second reference number is larger than the first reference number.

[0034] The storage unit 20 of the controller 10 stores, for example, multiple arrangement patterns 21, multiple modification patterns 22, and multiple transshipment patterns 23. The arrangement patterns 21 may be set for each type of pallet P, or they may be set taking into account the type of goods. A "pattern" refers to the arrangement of one or more goods on the pallet P. Patterns may be set after distinguishing between the types of goods (size, shape, and weight).

[0035] Arrangement pattern 21 is a pattern in which multiple items are formed in a stacked manner. "Stacked manner" includes 1 layer, 2 layers, and 3 layers. In arrangement pattern 21, each layer is formed with multiple items arranged side by side. Referring to Figure 3 and onward, a concrete example of arrangement pattern 21 is when, on pallet P, a total of 8 items A (or items B) are stacked, with 4 items (2x2 rows) on the bottom layer and 4 items (2x2 rows) on the top layer.

[0036] Arrangement pattern 21 is, for example, a pattern in which item A is moved to a position opposite the center of pallet P. As shown in Figure 4(a), one example is a pattern in which item A is moved to one diagonal of pallet P.

[0037] Pattern requiring correction 22 is a pattern that is highly likely to require correction, i.e., transshipment. Pattern requiring correction 22 is a pattern in which the uneven load on pallet P is relatively large. The presence of pattern requiring correction 22 does not necessarily mean that transshipment is immediately determined to be necessary by the transshipment determination unit 14. However, pattern requiring correction 22 includes several typical patterns in which transshipment is more preferable.

[0038] The transshipment pattern 23 is a pattern that can reduce the uneven load on pallet P when transshipment is deemed necessary. In other words, for each of the modification patterns 22, a modification pattern is set in which the uneven load on pallet P becomes smaller (improved) than that of modification pattern 22.

[0039] Transshipment pattern 23 is, for example, a pattern in which the items are rearranged with respect to the center of pallet P. As shown in Figures 5(a) and 5(b), one type of modification pattern 22 is a pattern in which one item A is stacked in one corner of pallet P. In that case, as shown in Figures 5(c) and 5(d), a transshipment pattern 23 is provided in which that one item A is stacked at the center position of pallet P.

[0040] The arrangement pattern 21, the modification pattern 22, and the transshipment pattern 23 are not limited to the examples given above, and can be set based on various types of pallets P, various maximum loading capacities (the maximum quantity that can be loaded onto a pallet P), and various types of goods.

[0041] The controller 10 causes the transfer robot 4 to perform the transfer operation when the following two conditions are met. More specifically, the transfer determination unit 14 determines that both of the following conditions are met: the number of items to be loaded onto the pallet P is greater than the first standard number and less than or equal to the second standard number (quantity condition), and no new items will be loaded onto the pallet P at any other station (subsequent process loading condition). In such cases, the transfer determination unit 14 arranges the items on the pallet P according to one of the transfer patterns 23, taking into account the uneven load on the pallet P (rearrangement, i.e., transfer). In addition to these conditions, the transfer determination unit 14 may also add an uneven load condition.

[0042] Alternatively, the transshipment determination unit 14 may simply determine whether transshipment is necessary by matching it with the above-described modification pattern 22.

[0043] Controller 10 may determine whether or not new items will be loaded at another station based on the destination. For example, if the destination (another station) is a loading station, Controller 10 can determine that new items will be loaded. Controller 10 may also determine whether or not new items will be loaded based on information from the higher-level controller 5.

[0044] For example, in the examples shown in Figures 3(a) and 3(b), four items A are stacked evenly with respect to the center of pallet P, and in this case, it is determined that transshipment is not necessary. In the examples shown in Figures 3(c) and 3(d), the quantity condition or the uneven load condition is met, but for example, it is known that new items will be stacked at another station, and therefore, transshipment is not carried out, leaving the upper right area empty in the plan view.

[0045] In the examples shown in Figures 4(a) and 4(b), the quantity condition is met, but for example, it is known that new goods will be loaded at another station, and therefore the transshipment is not carried out, leaving the upper right and lower left areas empty in the plan view. In the examples shown in Figures 4(c) and 4(d), one item A is stacked evenly with respect to the center of pallet P, and in this case, it is determined that transshipment is not necessary.

[0046] Furthermore, to illustrate the case where the weight of the items is taken into consideration, as shown in Figures 6(a) and 6(b), suppose there is an item A weighing 60 kg each and an item B weighing 10 kg each, and these are stacked one by one in the upper left and lower right areas in a plan view. In this case, the uneven load condition is met, so it is determined that re-stacking is necessary. As shown in Figures 6(c) and 6(d), the controller 10 controls the re-stacking so that items A and B are stacked in the center.

[0047] To explain the above transshipment procedure in more detail, as shown in Figures 7(c) and 7(d), first, item B is unloaded from pallet P. Each station 1A, 1B, and 1C is provided with a temporary storage space 7 (see Figure 1) for transshipping item A and / or item B, which are stacked in one of the arrangement patterns. In this case, the unloaded item B is temporarily placed in the temporary storage space 7. Then, as shown in Figures 7(e) and 7(f), item A is moved to the central position. After that, as shown in Figures 7(g) and 7(h), item B is stacked on top of item A.

[0048] As illustrated in Figures 8(a) to 8(h), even if any of the conditions are met, it may still be determined that transshipment is unnecessary. In each example, a triangular mark (▲) is placed in the plan view where only one layer of goods is stacked. In all other cases, two layers of goods are stacked. The examples shown in Figures 8(a) and 8(b) are arrangement patterns, while the others are patterns that require modification due to the uneven load condition, but are still determined to be unnecessary for transshipment.

[0049] Furthermore, when only three items are stacked on the first layer and one corner is empty, a rearrangement pattern that moves the items towards the center, as shown in Figure 9, may be adopted.

[0050] Furthermore, the transport vehicle control unit 11 of the controller 10 changes the transport mode by the transport vehicle 2 based on whether the items are stacked according to an arrangement pattern or according to a transshipment pattern. For example, the transport vehicle control unit 11 may increase the transport speed when the items are stacked according to an arrangement pattern. The transport vehicle control unit 11 may also increase the transport speed when the items are stacked according to a transshipment pattern. The transport vehicle control unit 11 may decrease the transport speed when the items are stacked according to a pattern requiring correction (but are not transshipped).

[0051] According to the stacking system S of this embodiment, when the controller 10 detects that the number of items to be stacked on the pallet P is less than or equal to a first reference number, it determines whether or not to arrange the items on the pallet P according to a transshipment pattern that takes into account uneven loading on the pallet P. This prevents transportation problems caused by uneven distribution of items when the number of items stacked on the pallet P is small.

[0052] The transshipment pattern is a pattern in which the goods are rearranged based on the center of pallet P. This makes it possible to create a load configuration that suppresses uneven loading when the number of goods stacked on pallet P is small.

[0053] The stacking system S has multiple stations, and the controller 10 detects that the number of items to be stacked on pallet P is greater than a first reference number and less than or equal to a second reference number greater than the first reference number, and determines that no new items will be stacked on pallet P at other stations, then arranges the items on pallet P according to a transshipment pattern, taking into account the uneven load on pallet P. This eliminates the need to rearrange already stacked items in order to stack new items at other stations.

[0054] The arrangement pattern involves transferring items to positions opposite the center of pallet P. For example, when stacking one or more items that do not constitute a full layer, it is possible to create a load arrangement that minimizes uneven loading.

[0055] The station has a temporary storage space 7 for rearranging items stacked in the above arrangement pattern. This allows for easy rearrangement of items on pallets P by utilizing the temporary storage space 7.

[0056] Pallet P is transported by transport vehicle 2, and controller 10 may change the transport mode by transport vehicle 2 based on whether the goods are stacked according to the arrangement pattern or according to the transshipment pattern. In this case, improvements such as increasing transport capacity can be made while preventing the load from collapsing during transport.

[0057] From another perspective, a stacking method is provided for a stacking system S equipped with one or more stations 1A, etc., having a transfer robot 4 for loading and unloading goods onto a pallet P, wherein a controller 10 controls the transfer robot 4 to arrange the goods on the pallet P according to an arrangement pattern in which multiple goods are stacked in layers on the pallet P, and multiple goods are arranged in each layer. In this stacking method, when the controller 10 detects that the number of goods to be stacked on the pallet P is less than or equal to a first reference number, it determines whether or not to arrange the goods on the pallet P according to a transshipment pattern different from the arrangement pattern, taking into account the uneven load on the pallet P.

[0058] This stacking method also allows the controller 10 to determine whether or not to place items on pallet P according to a transshipment pattern that takes into account uneven load distribution on pallet P. This prevents transport problems caused by uneven distribution of items when the number of items stacked on pallet P is small.

[0059] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, at least one of the arrangement pattern 21, the modification pattern 22, and the repacking pattern 23 may not be used. These patterns may not be used at all, and various patterns may be generated by the controller 10.

[0060] Information regarding the transfer of goods may be received in advance.

[0061] The stacking system S may have only one station. [Explanation of Symbols]

[0062] 2... Transport vehicle, 4... Transfer robot, 6... Conveyor, 7... Temporary storage space, 10... Controller, 10A... Stacking control unit, 14... Transshipment judgment unit, 20... Memory unit, 21... Arrangement pattern, 22... Pattern requiring correction, 23... Transshipment pattern, A, B... Items, S... Stacking system.

Claims

1. One or more stations having transfer robots for loading and unloading goods onto pallets, The system includes a controller for controlling the transfer robot, The aforementioned controller, The pallet has a storage unit that stores arrangement patterns in which multiple items are stacked on top of each other, and in which multiple items are arranged in each layer to form the layers. The transfer robot is controlled to arrange the items on the pallet according to the arrangement pattern. A stacking system in which, when the controller detects that the number of items to be stacked on the pallet is less than or equal to a first reference number, the controller determines whether or not to arrange the items on the pallet according to a transshipment pattern different from the arrangement pattern, taking into account the uneven load on the pallet.

2. The stacking system according to claim 1, wherein the transshipment pattern is a pattern in which the articles are rearranged with respect to the center of the pallet.

3. The station comprises multiple such stations, The aforementioned controller, A stacking system according to claim 1 or 2, which detects that the number of items to be stacked on the pallet is greater than the first reference number and less than or equal to a second reference number greater than the first reference number, and determines that no new items will be stacked on the pallet at any other station, and then arranges the items on the pallet according to the transshipment pattern, taking into account the uneven load on the pallet.

4. The stacking system according to claim 1 or 2, wherein the arrangement pattern is a pattern in which articles are transferred to a position opposite the center of the pallet.

5. The stacking system according to claim 1 or 2, wherein the station has a temporary storage space for rearranging the items stacked in the arrangement pattern.

6. The aforementioned pallet is transported by a transport vehicle. The stacking system according to claim 1 or 2, wherein the controller changes the transport mode by the transport vehicle based on whether the articles are stacked according to the arrangement pattern or whether the articles are stacked according to the transshipment pattern.

7. A stacking system comprising one or more stations having a transfer robot for loading and unloading goods onto a pallet, wherein a controller controls the transfer robot to arrange the goods on the pallet according to an arrangement pattern in which multiple goods are stacked in layers on the pallet, and multiple goods are arranged in each layer, thereby forming the layers, The aforementioned controller A stacking method that, when it is detected that the number of items to be stacked on the pallet is less than or equal to a first reference number, determines whether or not to arrange the items on the pallet according to a transshipment pattern different from the arrangement pattern, taking into account the uneven load on the pallet.

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