Control method, control device, and control system

Abstract

To provide a control method capable of detecting abnormality that causes load collapse at low cost when a transport palette is carried to a loading destination using a forklift.SOLUTION: A control method of the present disclosure acquires load information of a transport palette loaded on a fork 28 and lifting height range information indicating a lifting height range that is a range of a height that allows insertion of the fork 28 formed when the load can be unloaded normally at a loading destination, executes lowering operation for lowering the fork 28 loaded with the transport palette from an upper part of the loading destination on the basis of the acquired information, and executes operation for pulling out the fork 28 when a load value detected by a load sensor 23 is a predetermined value or less and a lifting height value detected by a lifting height sensor 24 is within the lifting height range. During the lowering operation, abnormality is determined when the lifting height value is a lower limit value of the lifting height range or less, or the load value is a predetermined value or less and the lifting height value is an upper limit value of the lifting height value or more.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a control method, a control device, and a control system. [Background technology]

[0002] The operation of a forklift that loads and unloads cargo is controlled by a predetermined control program. When stacking pallets on which cargo is to be loaded using a forklift, the legs of the pallet being unloaded must be fitted into supports formed on the top of the pallet where the cargo will be unloaded. This type of work requires extremely high operational precision.

[0003] Patent Document 1 describes a method for stacking post pallets with a forklift, which aims to easily and reliably stack post pallets vertically when stacking post pallets using a forklift. In this stacking method, marks are provided at multiple locations on the top surface of the post pallet facing a pair of left and right forks, and mark detection sensors are provided on the undersides of the forks facing the marks, so that when the forks are lowered from above onto the post pallet, and each mark detection sensor detects the mark of the corresponding post pallet located below, the post pallet loaded on the forks is placed on top of the post pallet below. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 06-115897 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the method described in Patent Document 1 requires that the position of the lower pallet be recognized before stacking the pallets, which requires the installation of a sensor, resulting in increased costs. Furthermore, the method described in Patent Document 1 raises the risk of the load falling over when stacking pallets, such as when the lower pallet cannot be properly placed on the upper tier or when the pallet gets caught on an adjacent object. This is primarily due to the forklift being unable to accurately recognize its own position and therefore unable to move the forks to the correct position.

[0006] Therefore, there is a need for a low-cost technology that can detect abnormalities that could cause cargo to collapse in advance.

[0007] An object of the present disclosure is to provide a control method, a control device, and a control system that can detect abnormalities that may cause cargo to collapse at low cost when a transport pallet is placed at a destination by a forklift. [Means for solving the problem]

[0008] To achieve the above object, the present disclosure provides a control method for controlling a forklift equipped with a load sensor for detecting the load of a load on the forks and a height sensor for detecting the height of the forks, so as to place a transport pallet at a destination. The control method acquires load information for the transport pallet to be loaded on the forks and height range information indicating a height range within which the forks can be inserted when the pallet is successfully unloaded at the destination, executes a lowering operation to lower the forks carrying the transport pallet from above the destination based on the acquired load information and height range information, executes an operation to withdraw the forks when a load value detected by the load sensor is equal to or less than a predetermined value and a height value detected by the height sensor is within the height range, and determines an abnormality when the height value is equal to or less than a lower limit of the height range or when the load value is equal to or less than a predetermined value and the height value is equal to or greater than an upper limit of the height range during the lowering operation.

[0009] In the control method according to this aspect, an abnormality that may cause cargo to collapse is determined based on the load information and the lifting height range information. Therefore, according to the control method according to this aspect, when a transport pallet is placed at a destination by a forklift, an abnormality that may cause cargo to collapse can be detected at low cost.

[0010] The lifting height range may be a range of heights into which the forks can be inserted when the transport pallet is normally placed on an object or the ground that cannot be transported by the forklift, if the unloading destination is an object or the ground that cannot be transported by the forklift, or a range of heights into which the forks can be inserted when the transport pallet is normally placed on the unloading destination pallet, if the unloading destination is a transport pallet that can be stacked. This makes it possible to detect abnormalities that may cause cargo to collapse at low cost, even if the unloading destination is flat ground or a transport pallet that can be stacked.

[0011] The control method may be configured such that, if the abnormality is determined during the lowering operation, the robot returns to an initial position where the lowering operation started, and resumes the lowering operation in the initial position. This allows another attempt to place the cargo even if it is likely to collapse, thereby increasing the possibility of placing the cargo without causing it to collapse.

[0012] If the number of times that the abnormality is determined during the lowering operation reaches a predetermined number, the control of the loading of the cargo at the unloading destination may be stopped, thereby preventing repeated attempts to load the cargo when there is a high possibility of the cargo falling.

[0013] If the abnormality is detected during the lowering operation, the forklift may be returned to a predetermined position, and when it has returned to the predetermined position, it may resume moving to the position where the lowering operation will be performed. This allows another attempt to place the load even if the load is likely to collapse, increasing the possibility of successfully placing the load without collapse.

[0014] The lifting height range indicated by the acquired lifting height range information or used to determine whether an abnormality has occurred may be set by expanding the range of heights into which the forks can be inserted, which is formed when unloading is normally performed at the unloading destination, calculated based on the type of the transport pallet, by a machine difference value of the transport pallet. This makes it possible to detect abnormalities that may cause cargo to collapse, taking into account machine differences of the transport pallet.

[0015] The forklift may be an unmanned forklift, which can prevent cargo from shifting even when the forklift is an unmanned forklift that cannot be directly checked by a human.

[0016] The control method may also include acquiring first information that is information indicating the pallet at a position where the pallet is to be placed on the forks, executing a comparison process that compares the acquired first information with second information that is information indicating the pallet that corresponds to the acquired load information and lifting height range information, and executing the lowering operation if the comparison process is successful. This makes it possible to prevent the pallet from being transported to a wrong unloading destination, thereby preventing the pallet from being placed at a unloading destination that may cause the load to collapse.

[0017] The present disclosure provides a control device that controls a forklift equipped with a load sensor for detecting the load of a load on the forks and a height sensor for detecting the height of the forks to place a transport pallet at a destination. The control device includes a movement control unit for controlling at least one of the movement of the forklift and the horizontal movement of the forks, a lift control unit for controlling the elevation and lowering of the forks, an acquisition unit for acquiring load information on the transport pallet to be loaded on the forks and height range information indicating a height range within which the forks can be inserted when the pallet is successfully unloaded at the destination, and a determination unit for detecting abnormalities. The lift control unit executes a lowering operation to lower the forks carrying the transport pallet from above the destination based on the load information and height range information acquired by the acquisition unit. The movement control unit executes an operation to withdraw the forks when the load value detected by the load sensor is equal to or less than a predetermined value and the height value detected by the height sensor is within the height range. The judgment unit judges that an abnormality has occurred when, during the lowering operation, the lift height value is equal to or less than the lower limit of the lift height range, or when the load value is equal to or less than a predetermined value and the lift height value is equal to or greater than the upper limit of the lift height range.

[0018] The control device according to this aspect determines whether an abnormality that may cause cargo to collapse is present based on the load information and the lifting height range information. Therefore, the control device according to this aspect can detect an abnormality that may cause cargo to collapse at low cost when a transport pallet is placed at a destination by a forklift.

[0019] The present disclosure provides a control system for controlling a forklift equipped with a load sensor for detecting the load of a load on the forks and a height sensor for detecting the height of the forks to place a transport pallet at a destination. The control system includes a movement control unit for controlling at least one of the movement of the forklift and the horizontal movement of the forks, a lift control unit for controlling the elevation and lowering of the forks, an acquisition unit for acquiring load information on the transport pallet to be loaded on the forks and height range information indicating a height range within which the forks can be inserted when the pallet is successfully unloaded at the destination, and a determination unit for detecting abnormalities. The lift control unit executes a lowering operation to lower the forks carrying the transport pallet from above the destination based on the load information and height range information acquired by the acquisition unit. The movement control unit executes an operation to withdraw the forks when the load value detected by the load sensor is equal to or less than a predetermined value and the height value detected by the height sensor is within the height range. The judgment unit judges that an abnormality has occurred when, during the lowering operation, the lift height value is equal to or less than the lower limit of the lift height range, or when the load value is equal to or less than a predetermined value and the lift height value is equal to or greater than the upper limit of the lift height range.

[0020] The control system according to this aspect determines whether an abnormality that could cause cargo to collapse is present based on the load information and the lifting height range information. Therefore, the control system according to this aspect can detect an abnormality that could cause cargo to collapse at low cost when a transport pallet is placed at a destination by a forklift. [Effects of the Invention]

[0021] According to the present disclosure, it is possible to provide a control method, a control device, and a control system that can detect abnormalities that may cause cargo to collapse at low cost when a transport pallet is placed at a destination by a forklift. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a block diagram showing an example of the configuration of a forklift according to an embodiment; [Figure 2] 1 is a side view showing an example of the appearance of a forklift according to an embodiment. [Figure 3] FIG. 1 is a perspective view showing an example of a transport pallet and an unloading destination pallet. [Figure 4] 10A and 10B are diagrams for explaining an example of a lifting height range and a case where it is determined to be normal. [Figure 5] FIG. 10 is a diagram for explaining a case where an abnormality is determined; [Figure 6] FIG. 10 is a diagram illustrating an example of data registered in a database. [Figure 7] FIG. 4 is a flow chart illustrating an example of a control method according to an embodiment. [Figure 8] This is a flow chart continuing from FIG. 7. [Figure 9] FIG. 10 is a diagram illustrating another example of data registered in the database. [Figure 10] FIG. 10 is a diagram for explaining the data in FIG. 9. [Figure 11] FIG. 10 is a diagram showing an example of a state in which cargo has been normally placed. [Figure 12] FIG. 10 is a diagram illustrating an example of a state that is determined to be abnormal. [Figure 13] FIG. 10 is a diagram illustrating another example of a state that is determined to be abnormal. [Figure 14] FIG. 10 is a diagram illustrating another example of a state that is determined to be abnormal. [Figure 15] FIG. 10 is a diagram illustrating another example of a state that is determined to be abnormal. [Figure 16] FIG. 10 is a diagram showing an example of a state in which a load is placed on a base. [Figure 17] FIG. 10 is a diagram showing an example of a state in which a load is placed on an inclined platform. [Figure 18] FIG. 10 is a perspective view showing another example of a transport pallet and an unloading destination pallet. [Figure 19] FIG. 2 illustrates an example of a hardware configuration of the apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be described below through embodiments of the invention, but the invention according to the claims is not limited to the following embodiments. Furthermore, not all of the configurations described in the embodiments are necessarily essential as means for solving the problems. The embodiments will be described below with reference to the drawings.

[0024] <Embodiment> Fig. 1 is a block diagram showing an example of the configuration of a forklift according to this embodiment, Fig. 2 is a side view showing an example of the appearance of the forklift according to this embodiment, and Fig. 3 is a perspective view showing an example of a transport pallet and an unloading destination pallet.

[0025] As shown in Fig. 1, the forklift 1 according to this embodiment includes the control device 10 according to this embodiment, and may also include a wheel drive unit 21, a fork drive unit 22, a load sensor 23, and a lifting height sensor 24. As shown in Fig. 2, the forklift 1 according to this embodiment may also include a forklift body 25, a mast 26, a fork lifting unit 27, and forks 28.

[0026] The wheel drive unit 21 drives the wheels of the forklift 1 to travel (move) the forklift 1. The wheel drive unit 21 drives the wheels to rotate. The wheel drive unit 21 can also drive the forklift 1 to turn in a desired direction, either left or right, by controlling the difference in rotation between the left and right wheels or by changing the direction of the wheel axles. The fork drive unit 22 drives the fork lifting unit 27 to move up and down relative to the mast 26 attached to the front of the main body 25, thereby raising and lowering the fork 28.

[0027] Furthermore, the forks 28 can be configured as a set of two, one on each side, but may be three or more. Each fork 28 can be configured, for example, with two sections 28a and 28b. The forks 28 can also be configured so that the section 28b extends and retracts horizontally relative to the section 28a connected to the fork lifting section 27. When such a configuration is adopted, the fork driving section 22 changes the length of the forks 28 by driving the section 28b to extend and retract horizontally relative to the section 28a. However, the forks 28 are not limited to being equipped with such a horizontal extension / retraction mechanism, and may not be equipped with an extension / retraction mechanism.

[0028] Fork 28 can also be configured so that the angle of portion 28b, as viewed from the horizontal direction, can be changed relative to portion 28a connected to fork lifting unit 27. When such a configuration is adopted, fork driving unit 22 changes the angle of portion 28b at the tip of fork 28 by driving portion 28b so that the vertical angle (elevation / depression angle) relative to portion 28a faces upward, horizontally, or downward. Changing the elevation / depression angle of portion 28b can also be achieved by providing a mechanism that can tilt mast 26 vertically relative to main body 25.

[0029] The load sensor 23 can be provided, for example, on the upper surface 28c of the fork 28, and detects the load of a load (baggage) placed on the fork 28 and passes the detected load to the control device 10. However, the load sensor 23 may also be provided somewhere other than on the fork 28, such as between the fork 28 and the fork lifting unit 27 or between the fork lifting unit 27 and the mast 26. By providing the load sensor 23 between these locations, damage to the load sensor 23 and erroneous detection can be prevented compared to when the load sensor 23 is provided on the upper surface 28c. Furthermore, any detection method may be used for the load sensor 23. Even if the forklift truck is not originally provided with a load sensor 23, the forklift truck 1 can be configured with a load sensor 23 provided later, and the function of this embodiment can be achieved.

[0030] The height sensor 24 detects the height of the forks 28. That is, the height sensor 24 detects the height Hf from the ground to the top surfaces 28c of the forks 28 when the forklift 1 is standing on level ground. The detection method used by the height sensor 24 is not critical. The height sensor 24 may be provided, for example, on the mast 26, and may be, for example, an RGB camera or an infrared camera. However, the height sensor 24 is not limited to this example. For example, the height sensor 24 may be a distance measuring sensor provided on the underside of the forks 28, or an acquisition unit that acquires a control value for the fork lifting unit 27. As in the example in which the height sensor 24 is a distance measuring sensor provided on the underside of the forks 28, the height Hf may be defined as the height from the ground to the bottom surfaces of the forks 28. The height Hf may also be defined as the height from the ground to a predetermined vertical position of the forks 28, such as the height from the ground to the center between the top surface 28c and the bottom surface. However, the definitions of the upper and lower limits of the lifting height range shall be in accordance with the definition of the height Hf. Even if the forklift is not originally equipped with a lifting height sensor 24, the forklift 1 can be configured to have a lifting height sensor 24 installed later and perform the function of this embodiment.

[0031] The control device 10 controls the wheel drive unit 21, the fork drive unit 22, the load sensor 23, and the height sensor 24. As shown in Fig. 1, the control device 10 can include an information acquisition unit 11, a movement control unit 12, a lift control unit 13, and a determination unit 14, thereby controlling the forklift 1 to deposit the transport pallet at the destination. Therefore, the control method according to this embodiment can also be called a method for depositing cargo in the forklift 1.

[0032] The control device 10 may also include a main control unit (not shown) that controls the entire device. This main control unit may be realized by, for example, a processor such as a CPU (Central Processing Unit) or an MPU (Micro Processor Unit), a working memory, and a non-volatile storage device. A control program to be executed by the processor is stored in this storage device, and the processor reads the program into the working memory and executes it, thereby achieving the functions of each of the units 11 to 14 described below. This main control unit may also be realized by a configuration including an integrated circuit.

[0033] The information acquisition unit 11 acquires information from a database (DB) 2a. The DB 2a can be stored in a management system 2 that includes a computer wirelessly connected to the forklift 1. In this case, the information acquisition unit 11 includes a wireless communication unit that wirelessly communicates with the management system 2, and the management system 2 can also include a wireless communication unit that wirelessly communicates with the forklift 1. However, the DB 2a can also be stored in a storage device internal to the control device 10 of the forklift 1. The following description will be given on the assumption that the information acquisition unit 11 acquires information from the DB 2a. However, some or all of the acquired information can also be information stored as setting information, for example, in the storage device of the control device 10 or in the internal memory of the determination unit 14.

[0034] The DB2a stores load information for the transport pallet 31 to be loaded onto the forks 28 and lifting height range information indicating the range of heights within which the forks 28 can be inserted when unloading is performed normally at the unloading destination. This information can be stored for each type of transport pallet 31. The lifting height range refers to the range of heights within which the forks 28 can move up and down (raise and lower) when unloading is performed normally at the unloading destination. The unloading destination pallet 41 has the same shape as the transport pallet 31, and therefore, it can be said that the load information and lifting height range information can be stored for each type of transport pallet 31 and unloading destination pallet 41. However, the unloading destination pallet 41 is not limited to a pallet with the same shape as the transport pallet 31. It can also be a pallet with a different shape as long as it can accommodate the transport pallet 31. The information acquisition unit 11 acquires information including the load information and lifting height range information from the DB2a.

[0035] As shown in Figure 3, the transport pallet 31 may have, for example, four legs 32 on the bottom and a support portion on the top. These support portions correspond to the support portions 42 indicated by the reference numeral 42 on the destination pallet 41 in Figure 3. The legs 32 of the transport pallet 31 and the support portions 42 of the destination pallet 41 are configured in shapes that allow them to fit together or otherwise engage with each other.

[0036] With this configuration, as shown by the dotted arrows in Figure 3, each leg 32 of the transport pallet 31 can be lowered toward each support part 42 formed on the top of the destination pallet 41 to be unloaded, and each leg 32 can be engaged with each support part 42, allowing the transport pallet 31 to be stacked on top of the destination pallet 41.

[0037] The movement control unit 12 controls at least one of the movement of the forklift 1 and the horizontal movement of the forks 28. The former movement can be achieved by the movement control unit 12 controlling the wheel drive unit 21. However, for this control, the forklift 1 is equipped with a function for measuring its own position or a function for estimating its own position (not shown), and controls movement to a destination based on the measured or estimated self-position. The latter movement is achieved by the movement control unit 12 controlling the fork drive unit 22, which controls the horizontal extension and contraction of part 28b relative to part 28a.

[0038] The lifting control unit 13 controls the fork driving unit 22 to control the lifting and lowering of the forks 28. In particular, the lifting control unit 13 executes a lowering operation to lower the forks 28 loaded with the transport pallet 31 from above the unloading destination based on the load information and lifting height range information acquired by the information acquisition unit 11. Furthermore, the lifting control unit 13 can stop the lowering operation when (at the time when) either the load value (load sensor value) detected by the load sensor 23 becomes equal to or less than a predetermined value, or the lifting height value (lifting height sensor value) detected by the lifting height sensor 24 becomes smaller than the lower limit value of the lifting height range indicated by the lifting height range information is satisfied. When the load value is equal to or greater than the predetermined value, it means that the transport pallet 31 is placed on the forks 28. In other words, when the load value is less than the predetermined value, it means that the transport pallet 31 is not placed on the forks 28.

[0039] Furthermore, when the load value (load sensor value) detected by the load sensor 23 is equal to or less than a predetermined value and the lifting height value (lifting height sensor value) detected by the lifting height sensor 24 is within the lifting height range indicated by the lifting height range information, the movement control unit 12 executes an operation to pull out the forks 28 as part of the operation to place the transport pallet 31. Note that the operation to place the transport pallet 31 can mean the operation to deposit the transport pallet 31.

[0040] The determination unit 14 determines an abnormality. In particular, the determination unit 14 determines an abnormality when, during the above-described lowering operation, the lifting height value is equal to or less than the lower limit of the lifting height range, or when the load value is equal to or less than a predetermined value and the lifting height value is equal to or greater than the upper limit of the lifting height range. Therefore, the control method according to this embodiment can also be called a method for detecting an abnormality in unloading of the forklift 1. Specific examples of such determinations will be described later.

[0041] In this embodiment, an abnormality that may cause cargo to collapse is determined based on the load information and lifting height range information stored in DB2a. Therefore, according to this embodiment, when the transport pallet 31 is placed at the unloading destination by the forklift 1, an abnormality that may cause cargo to collapse can be detected at low cost. Therefore, according to this embodiment, cargo collapse can be prevented. Note that although the unloading destination pallet 41 has been described as the unloading destination here, a similar response can be achieved even on flat ground by registering the lifting height range information in DB2a as information for flat ground. A specific example of flat ground will be described later.

[0042] The forklift 1 may also be an unmanned forklift. An unmanned forklift may have either an autonomous movement function or a function for autonomously raising and lowering or extending the forks 28. An unmanned forklift may also be unmanned, even if it does not have the function for autonomous movement or raising and lowering, etc., and may be configured to be remotely controlled from a remote control device wirelessly connected to the forklift 1 by attaching a camera (not shown) to at least one of the work location and the forklift 1. This makes it possible to prevent cargo from shifting even with an unmanned forklift that cannot be directly checked by a person. Of course, the forklift 1 may also be a forklift operated by a person on board.

[0043] The control device 10 has been described above, but the control device 10 according to this embodiment can also be constructed as a control system. This control system is a system in which the functions of the control device 10 are distributed among multiple devices, and can also be configured to include a DB 2a like the management system 2.

[0044] Next, an example of the lifting height range information stored in DB2a will be described with reference to Fig. 4 to Fig. 6. Fig. 4 is a diagram for explaining an example of the lifting height range and a case where it is determined to be normal. Fig. 5 is a diagram for explaining a case where it is determined to be abnormal. Fig. 6 is a diagram showing an example of data registered in DB2a.

[0045] In the following, when there is no need to distinguish between the transport pallet and the unloading destination pallets 41, 51, they will be referred to simply as "pallet PA." The pallet PA can be made of any material, such as an iron pallet, wooden pallet, or resin pallet, and can have any shape or size, as long as it has a space formed therein into which the fork 28 can be inserted.

[0046] For pallets PA (pallets 31, 41, 51) that are intended to be stacked in three layers as shown in Fig. 4, lifting height range information such as that shown in Fig. 6 can be registered in DB2a. As shown in Fig. 5, for example, when placing transport pallet 31 on unloading destination pallet 41, the lifting height range is set so that if legs 32 climb onto support parts 42, it is determined to be an abnormality.

[0047] Therefore, in the example shown in Figure 4, if the range for inserting the forks 28 between the first pallet 51 and the second pallet 41 is 900 to 1000 mm, the lower limit of the lifting height range can be set to 900 mm and the upper limit of the lifting height range can be set to 1010 mm, as shown in Figure 6. Of course, the upper limit can also be set to 1000 mm, but in this example, the upper limit is set to 1010 mm to accommodate the situation illustrated in Figure 5. Here, the difference of 10 mm can be set to a value corresponding to the height at which the support portion 42 overlaps with the leg portion 32 when the support portion 42 is engaged with the leg portion 32, and details of this will be described with reference to Figures 9 and 10.

[0048] Figure 6 shows an example in which a lower limit value and an upper limit value of the lifting height of the forks 28 are set for one type of pallet PA for each of the second to fifth tiers. Figure 4 shows only an example in which pallets are stacked three tiers, and Figure 6 shows an example that can accommodate stacks up to five tiers, but it goes without saying that lifting height range information can be stored to accommodate stacks of six tiers or more. Furthermore, by similarly registering lifting height range information in DB2a for pallets of shapes and sizes other than pallet PA, it is possible to accommodate those pallets as well.

[0049] Next, an example of a control method according to this embodiment will be specifically described with reference to Fig. 7 to Fig. 15. Fig. 7 is a flow diagram for explaining an example of a control method according to this embodiment, and Fig. 8 is a flow diagram following Fig. 7. Fig. 9 is a diagram showing another example of data registered in DB2a, and Fig. 10 is a diagram for explaining the data in Fig. 9. Fig. 11 is a diagram showing an example of a state in which cargo has been normally placed, and Figs. 12 to 15 are diagrams showing examples of states that are determined to be abnormal.

[0050] First, the control device 10 of the forklift 1 acquires information about the transport pallet 31 and information about the unloading destination pallet 41 from the management system 2 (step S1). This acquisition can also be achieved, for example, by receiving a stacking instruction from the management system 2. The information about the transport pallet 31 includes load information indicating the load including the cargo loaded on the transport pallet 31, and information indicating the position of the transport pallet 31. The information about the unloading destination pallet 41 also includes information indicating the position of the unloading destination pallet 41, i.e., the position of the destination where the transport pallet 31 will be unloaded. The information indicating the positions of the transport pallet 31 and the unloading destination pallet 41 can be managed by a transport management system (not shown) different from DB2a, but can also be included in DB2a.

[0051] If the destination pallet for unloading pallet PA is stacked in two layers, in step S1, the control device 10 only needs to acquire information on the destination pallets 41, 51, or information on the destination pallet 41 taking into account that it is stacked on the destination pallet 51 (information on the third layer in FIG. 6). Although the case where pallet PA is stacked in two layers has been described, the same concept can also be applied to cases where there is one layer or three or more layers.

[0052] Next, the control device 10 extracts an appropriate lifting height range for the forks 28 based on the acquired information (step S2). For example, if the unloading destination is a location where the destination pallet 41 is stacked one level, the lower and upper limits for the second level in Figure 6 can be extracted from the acquired information as this appropriate lifting height range. In this way, in step S2, the current vertical position of the destination pallet 41, i.e., the number of levels loaded, is referenced, and the lower and upper limits for the appropriate lifting height of the forks 28 are extracted from the information acquired from DB2a.

[0053] Next, the control device 10 controls the wheel drive unit 21 to travel to the storage location of the transport pallet 31 based on the measurement or estimation result of its own position and the acquired information indicating the position of the transport pallet 31 (step S3).

[0054] Next, the control device 10 acquires information about the transport pallet 31 at the storage location of the transport pallet 31 using the information acquisition unit 11 or an information acquisition unit such as a camera (not shown) separately provided on the forklift 1 (step S4). The information about the transport pallet 31 at the storage location may be, for example, information indicating the weight of the cargo or the unloading destination, written on a QR code (registered trademark) or barcode attached to the transport pallet 31, the cargo loaded on it, or the storage location, but is not limited to this. This information may also include information such as the pallet number.

[0055] Next, the control device 10 compares the information on the transport pallet 31 acquired in step S1 with the information on the transport pallet 31 acquired in step S4 (step S5). The judgment unit 14 can perform the judgment described below, including this comparison.

[0056] The control device 10 determines whether the matching in step S5 is successful or not (step S6). If the matching is unsuccessful (NO in step S6), the control device 10 executes abnormality processing A (step S7) and terminates abnormally. The abnormality processing A can be, for example, a process of sending a notification to the management system 2 or the like indicating that the transport pallet 31 to be loaded is incorrect. However, the control device 10 may also send a notification of success when the matching, which will be described next, is successful.

[0057] On the other hand, if the matching is successful (YES in step S6), the transport pallet 31 is stacked (step S8). This stacking operation first includes loading the transport pallet 31 onto the forks 28. The stacking operation after the loading operation can include moving to the unloading destination and lowering the forks 28. At least this lowering operation is performed while monitoring the height sensor value, which is the sensor value detected by the height sensor 24, and the load sensor value, which is the sensor value detected by the load sensor 23.

[0058] As explained in step S4, the control device 10 can acquire first information, which is information indicating the transport pallet 31, at the position where the transport pallet 31 is placed on the forks 28. Then, as explained in steps S5 to S8, a comparison process is performed to compare the acquired first information with second information, which is information indicating the transport pallet 31 corresponding to the load information and lifting height range information acquired from DB2a, and if the comparison process is successful, a lowering operation can be performed. This makes it possible to prevent the transport pallet 31 from being transported to the wrong unloading destination, in other words, to prevent the wrong transport pallet 31 from being transported to the unloading destination, thereby making it possible to prevent the transport pallet 31 from being placed at the unloading destination in a way that could cause the load to collapse.

[0059] Here, positioning that can be applied to the stacking operation after the loading operation will be described, but this positioning technique can also be applied to the loading operation of the transport pallet 31 onto the forks 28. Regarding the left-right position of the forks 28, the management system 2 can read the position of the destination pallet 41 placed thereon using a sensor or the like installed at the work site of the forklift 1 and transmit the value to the forklift 1. The control device 10 can turn the forklift 1 left and right to move it in accordance with the position of the forks 28 based on the sensor value. Alternatively, if the forklift 1 is equipped with a fork shift mechanism that moves the forks 28 left and right, the control device 10 can control the mechanism to align the position of the forks 28 with the sensor value. If the forklift 1 does not have a fork shift mechanism, left-right positioning can be performed by adjusting the position of the forklift 1 before approaching the destination pallet 41. If the fork shift mechanism is installed, left-right positioning can be performed before stacking (before the forks 28 are lowered).

[0060] The control device 10 determines the self-position of the forklift 1 using a self-position estimation function such as SLAM (Simultaneous Localization and Mapping) or laser guidance for the fork 28 in the forward and backward directions. The forklift 1 also confirms the position of the destination pallet 41 where the load is to be placed using a sensor installed on the forklift 1 or an external sensor, and proceeds toward the destination pallet 41. When the forklift reaches the desired loading location, it brakes and stops there. At this time, it may back up if necessary. Since SLAM alone may not be sufficiently accurate, providing a sensor to detect the position of the destination pallet 41 can improve accuracy.

[0061] However, even if a sensor for detecting the position of the destination pallet 41 is provided, if the accuracy of the sensor for measuring or estimating the self-position is poor, the correct stacking position cannot be reached with high accuracy. However, as will be described later, this embodiment can detect situations where cargo is likely to collapse, thereby compensating for such poor accuracy of the self-position. For the same reason, this embodiment can be said to be advantageous because it can detect situations where cargo is likely to collapse even without providing a sensor for detecting the position of the destination pallet 41.

[0062] Next, the stacking operation after the loading operation will be described. After step S8, the control device 10 determines whether only one of the following conditions is met: that the lifting height sensor value is smaller than the lower limit of the lifting height range acquired from DB2a, or that the load sensor value is equal to or less than a threshold value (step S9). Note that, as described above, the description here is based on the assumption that the forks 28 are in the middle of being lowered from above, and that both conditions do not occur simultaneously. Also, this threshold value is the predetermined value described above, and if the value is equal to or greater than the threshold value, it means that the transport pallet 31 is placed on the forks 28. The stacking operation continues until either condition is met in this determination. If either condition is met, i.e., if step S9 returns YES, the control device 10 stops the stacking operation (step S10). Note that this stop control is performed even when the work is completed, but is also performed for safety reasons when there is a possibility of an abnormality. The determination of which of the following conditions exists can be performed as described below.

[0063] Here, other examples of the setting values ​​in DB2a will be described with reference to Figures 9 and 10. Figure 9 shows pallets 31, 41, and 51 stacked in three layers, similar to the example shown in Figure 4. The lifting height range indicates the range in which the forks can be inserted, and can be expressed by its lower limit value (lower end value) and upper limit value (upper end value).

[0064] The lower limit of the lifting height range can be registered in DB2a as a value obtained by subtracting α [mm] from the actual design value shown in Figure 4, as exemplified by 900-α [mm] between the first and second steps from the ground, and 1850-α [mm] between the second and third steps from the ground, or the value obtained by subtracting α [mm] can be used for judgment on the control device 10 side.

[0065] In addition, the upper limit value of the lifting height range can be registered in DB2a as a value obtained by adding α [mm] to the actual design value shown in Figure 4, as exemplified by 1000 + α [mm] between the first and second steps from the ground, and 1950 + α [mm] between the second and third steps from the ground, or the value obtained by adding α [mm] can be used for judgment on the control device 10 side.

[0066] Here, as shown in FIG. 10, α can be set to a value corresponding to the height h at which the support portion 42 overlaps with the leg portion 32 when the support portion 42 is engaged with the leg portion 32, and can be set to a value that takes into account the machine difference between the pallets PA. In FIG. 6, the example shows that the upper limit value α is pre-registered as, for example, 10 [mm], and the lower limit value α is pre-registered as 0 [mm]. In this way, the values ​​that take into account the machine difference can be different for the upper limit value and the lower limit value. Furthermore, a different value can be adopted for this value α depending on the type of pallet PA, and it may be determined in advance as, for example, the machine difference β [%].

[0067] As described with reference to FIGS. 9 and 10, the lifting height range indicated by the lifting height range information stored and acquired in DB2a or the lifting height range used for the judgment can be set as follows. That is, the lifting height range ultimately used for the judgment can be set by expanding the range of heights into which the forks 28 can be inserted, which is calculated based on the type of pallet PA and is formed when the pallet is normally unloaded at the unloading destination, by the machine error value of the pallet PA (by an amount that takes machine error into account). The machine error of the pallet PA can refer to dimensional errors that may occur during manufacturing. By using such a setting, it becomes possible to judge an abnormality when there is an obvious abnormality, while avoiding erroneously judging an abnormality when the pallets are stacked normally. This makes it possible to detect abnormalities that may cause cargo collapse by taking into account the machine error of the transport pallet 31, i.e., the machine error of the pallet PA.

[0068] 7 and 8. Following step S10, the control device 10 determines whether the height sensor value is equal to or greater than the lower limit of the height range acquired from DB2a (step S11). If the determination in step S11 is NO, the control device 10 determines whether the number of retries n1 is greater than a predetermined set value N1 (step S12).

[0069] If the answer is YES in step S12, the following cases may be considered: those illustrated in Figures 12, 13, and 14. Figure 12 shows a case where the position of the stacking operation is significantly shifted due to the influence of the self-position measurement result or the accuracy of the measurement result, and the destination pallet 41 does not exist nearby, or a case where the destination pallet 41 that should exist at the loading destination does not exist in the first place. Although an example of loading in two tiers is given, even if a pallet does not exist in the "stacking number - 1" tier included in the information acquired in step S1 and the pallet cannot be stacked to the specified number of tiers, the situation will be similar to that described in Figure 12, although pallet PA will exist in the tier further below.

[0070] Figure 13 shows a case where the position of the stacking operation is significantly shifted due to the influence of the self-position measurement result or the accuracy of the measurement result, and the position of the destination pallet 41 is not the position for the lowering operation. Figure 14 shows a case where the position of the stacking operation is shifted due to the influence of the self-position measurement result or the accuracy of the measurement result, and the upper end of the engagement part of the leg part 32 is positioned below the upper end of the support part 42, and the transport pallet 31 rides up on the destination pallet 41.

[0071] Therefore, if the result of step S12 is YES, the control device 10 executes abnormality processing B (step S13) and ends the process with an abnormality. The abnormality processing B can be, for example, a process of sending a notification indicating that the state is one of those shown in Figures 12 to 14 to the management system 2, etc. However, even if the result of step S12 is NO, the control device 10 may be configured to send a notification that a retry of the stacking operation is in progress, as will be described later.

[0072] If the answer is NO in step S12, the control device 10 returns to step S8 and retries the stacking operation. However, as described above, the loading operation of the transport pallet 31 onto the forks 28 is not required except for the first time. A retry means a reapproach to stacking. The number of retries n1 mentioned above is the number of times that the answer is YES in step S12, and this number can be stored in the memory of the control device 10 and read out when necessary.

[0073] When retrying, because it is determined that an abnormality occurred during the lowering operation, the control device 10 returns to the initial position where the lowering operation started and resumes the lowering operation from the initial position. By retrying in this way, it is possible to try placing the cargo again even if it is likely to collapse, which increases the possibility that the cargo can be placed without collapsing, and reduces the man-hours required for the manager or the like to respond to abnormalities.

[0074] During a retry, instead of or in addition to restarting from the initial position, the control device 10 can return the forklift 1 to a predetermined position and, once it has returned to the predetermined position, resume the operation of moving it to a position for the lowering operation. This allows another attempt to place the load even if it is likely to collapse, increasing the possibility that the load can be placed without collapse and reducing the amount of work required for the manager or other person to respond to abnormalities.

[0075] The predetermined position can be, for example, a position at a predetermined distance from the unloading destination, or a position where the position of the unloading destination pallet 41 can be confirmed by a camera installed on the forklift 1 or the work site. This allows the control device 10 to correct its own position while approaching again, and repeat this process as necessary to determine a good position.

[0076] Furthermore, as explained in the judgment of step S12 and step S13, the control device 10 can stop the control of the placement of the cargo at the unloading destination (stop the placement work) when the number of times that it is judged to be abnormal during the lowering operation reaches a predetermined number (N1 times). This makes it possible to prevent repeated attempts to place the cargo when there is a high possibility of the cargo collapsing.

[0077] On the other hand, if the result in step S11 is YES, the determination in step S9 is YES, which means that the load sensor value is below the threshold, that is, the transport pallet 31 is not loaded on the forks 28. Therefore, in this case, if the height sensor value is equal to or less than the upper limit of the height range acquired from DB2a, it means that the state is as shown in FIG. 11, that is, the state in which the load has been successfully placed.

[0078] Therefore, the control device 10 determines whether the height sensor value is equal to or less than the upper limit of the height range acquired from DB2a (step S14). If the answer is YES in step S14, this means that the height sensor value is within the height range acquired from DB2a and the load sensor value is equal to or less than the threshold value, meaning that the loading was successful. Therefore, if the answer is YES in step S14, the control device 10 executes an operation to withdraw the forks 28 by at least one of moving the forklift 1 and retracting the forks 28 (step S17). The loading operation is successfully completed by step S17. Thereafter, the forklift 1 may be moved, for example, to return to the designated original position.

[0079] If the answer is NO in step S14, the control device 10 determines whether the number of retries n2 is greater than a predetermined set value N2 (step S15), and if the answer is NO in step S15, the process returns to step S8 and the stacking operation continues. However, as described above, the loading operation of the transport pallet 31 onto the forks 28 is not required except for the first time. The number of retries n2 is different from the number of retries n1 and is the number of times that the answer is YES in step S15. This number can be stored in the memory of the control device 10 and read out when necessary.

[0080] If the result in step S15 is NO, the process returns to step S8 and the stacking operation is retried. However, as described above, the loading operation of the transport pallet 31 onto the forks 28 is not required except for the first time. Other retries are as described for the case where the result in step S12 is NO. However, the predetermined number of times in this case is N2 times.

[0081] If step S15 returns YES, it is possible that the lower ends of the legs 32 have climbed onto the upper ends of the supports 42 due to the influence of the self-position measurement results or the accuracy of the measurement results, as illustrated in FIG. 15. Therefore, if step S15 returns YES, the control device 10 executes abnormality processing C (step S16) and terminates abnormally. The abnormality processing C can be, for example, processing to send a notice indicating that the state shown in FIG. 15 is occurring to the management system 2, etc. However, the control device 10 may also be configured to send a notice that a retry of the stacking operation is in progress even if step S15 returns NO.

[0082] As described above, according to this embodiment, it is possible to detect at low cost any abnormality that may cause the load to collapse when the transport pallet 31 is placed at the unloading destination by the forklift 1. Therefore, according to this embodiment, it is possible to prevent the load from collapsing.

[0083] Here, as a comparative example, the effect of this embodiment will be explained using an example of an unmanned forklift that is capable of detecting the height at which the forks should be advanced (the height at which they should be inserted). The unmanned forklift according to the comparative example can detect the height at which the load is scooped or loaded, but cannot detect the accuracy of the horizontal position when loading, which means there is a risk of the pallet collapsing. In contrast, this embodiment can prevent the load from collapsing.

[0084] In addition, not only in this comparative example, but in any other case, if a pallet collapses, safety will be reduced due to contact with falling objects, costs and quality will be reduced due to defective products inside the pallet, and the labor required to respond to abnormalities will increase, resulting in a decrease in availability. In particular, when using multiple types of irregularly shaped pallets, that is, when building a system that can stack pallets of any size and shape and stack them correctly and repeatedly without being affected by external disturbances, high precision is required in the following multiple elements, which is technically difficult and requires a large investment. These multiple elements include the accuracy of recognizing the position of the pallet to be unloaded, the accuracy of the forklift stopping position, the accuracy of the fork lift position, and the accuracy of the pallet dimensions.

[0085] It is also possible to use a method such as using a camera to check the legs of the pallet to be unloaded before stacking, but this is difficult to do with a camera that can be mounted on a forklift because the transported pallet blocks the camera's view.On the other hand, it is also possible to use a method such as using a ceiling camera, but this is difficult in terms of accuracy and requires a large investment if the area is wide.In addition, the pallet may slip and shift position due to rotation and vibration during pallet transport, and the position of the pallet stored on the forks when scooping the load may differ from the position of the pallet on the forks when stacking.

[0086] In contrast, in this embodiment, it is possible to prevent cargo from shifting at low cost. Note that although the unloading destination has been described above as an unloading destination pallet 41, a similar solution can be achieved even on flat ground by registering the lifting height range information in DB2a as information for flat ground. Such an example will be described with reference to Figures 16 and 17.

[0087] Fig. 16 is a diagram showing an example of how a load is placed when the unloading destination is a pedestal that is higher than the ground by a height H1. In this embodiment, a horizontal platform that is higher than the ground, such as pedestal 61 shown in Fig. 16, can also be used as the unloading destination. In this case, the insertable range of fork 28 has a lower limit of H1 and an upper limit of H1+H2, which can be registered as lifting range information. As for other examples, the various examples described above can be applied.

[0088] This makes it possible to detect, for example, the risk of the pallet climbing over an unexpected obstacle placed at the unloading destination and causing the load to collapse. In particular, compared to when determination is made based solely on the height sensor value, there is a possibility that the pallet may be unloaded in a floating state due to sensor error, but in this example, the height sensor value and the load sensor value are used to determine the abnormality, so it is possible to detect an abnormality even in such a situation. Furthermore, when determination is made based solely on the load sensor value, it is not possible to detect the pallet climbing over an obstacle, but in this example, the height sensor value and the load sensor value are used to determine the abnormality, so it is possible to detect an abnormality even in such a situation.

[0089] FIG. 17 shows an example of how a load is placed on an inclined platform. In this embodiment, the loading destination can also be an inclined platform higher than the ground, such as platform 61a shown in FIG. 17. Platform 61a can also be a chute on a work line for transporting transport pallets 31. In this example, transport pallet 71 is a pallet equipped with fork pockets. That is, instead of transport pallet 31, transport pallet 71 is employed, which has components provided below the space for inserting forks 28. The insertable range of the forks 28 in transport pallet 71 is the range indicated by height H5. The forklift 1 illustrated in FIG. 17 is equipped with a mechanism for adjusting the elevation and depression angles of the forks 28. When loading onto platform 61a, the angle of the forks 28 can be adjusted to match the angle of the surface of platform 61a. The elevation and depression angles of the forks 28 can also be changed by providing a mechanism for changing the elevation and depression angles of the mast 26 relative to the main body 25, as described above.

[0090] In this case, the insertable range of the fork 28 is H3+H4 as the lower limit and H3+H4+H5 as the upper limit, which can be registered as the lifting range information. For other examples, the various examples described above can be applied.

[0091] Here, height H3 is illustrated as the height of the base of the fork 28 on a surface along the slope of the base 61a, but is not limited to this. For example, when changing the inclination of the fork 28 in this manner, a DB that takes this into account for the lower and upper limit values ​​can be prepared in advance. However, by using the height of the base of the fork 28 as the reference, the information registered in DB2a does not need to be changed even if the fork 28 is tilted. Note that the load sensor does not change particularly whether it is on an inclined surface or a flat surface.

[0092] The DB to be used can also be switched depending on the unloading destination, i.e., depending on the use of the forklift 1, and this can be applied to switching between at least two of the various examples described above. The transport pallet 71 can also be applied to the examples described in Figures 1 to 16, and in that case, lifting height range information can be registered using the same concept.

[0093] When a pallet equipped with fork pockets as illustrated is unloaded onto an inclined base 61a such as a chute, the pallet must be lifted with high precision to prevent it from sliding even when it is floating above the base 61a (in a floating state) or when the forks 28 are pushing down on it. However, in this embodiment, even when such high precision control is required, it is possible to detect abnormalities that could cause cargo to collapse at low cost.

[0094] 16 and 17, when the unloading destination is an object or ground (floor, etc.) that cannot be transported by the forklift 1, the lifting height range can be the range of heights into which the forks 28 can be inserted, which is formed when the transport pallet 31 is normally placed (laid flat) on the object or ground. The object may also be the bed of a truck.

[0095] On the other hand, as explained using Figures 1 to 15, when the destination pallet 41 onto which the transport pallet 31 is to be unloaded is a pallet of the same shape as the transport pallet 31, and the transport pallet 31 can be stacked, the lifting height range can be the range of height into which the forks 28 can be inserted, which is formed when the transport pallet 31 is normally placed on the destination pallet 41.

[0096] By adopting such a lifting range, abnormalities that may cause cargo to collapse can be detected at low cost, even if the unloading destination is the above-mentioned object or the ground, or even if the transport pallet 31 is a pallet that can be stacked.

[0097] In the various examples above, the transport pallet has been described assuming that cargo is loaded inside, but the transport pallet may also be a flat pallet. This flat pallet may also be a sieve-shaped flat pallet. Such an example will be described with reference to Figure 18. Figure 18 is a perspective view showing another example of a transport pallet and a pallet to be unloaded.

[0098] 18 are both flat pallets, and have insertion holes 81a, 91a formed as fork pockets for the forks 28. If similar insertion holes are also formed on the side surfaces perpendicular to the surfaces shown by the insertion holes 81a, 91a, the forks 28 can be inserted from either side.

[0099] In the example of FIG. 18 , not only is a load 82 placed on the transport pallet 81, but a load 92 is also placed on the unloading pallet 91. Therefore, the insertion range of the fork 28 has a lower limit of H6 and an upper limit of H6 + H7, which can be registered as lifting height range information. Here, height H6 refers to the distance from the ground to the bottom of the insertion hole 81a of the transport pallet 81. Thus, in the example of FIG. 18 , the lifting height range indicated by the lifting height range information depends on the height of the loaded load 92, and information on the height of the load 92 is also required. Furthermore, if the load 92 is made up of multiple loads, i.e., if the loads are stacked in multiple layers, information on the stack height of the loads must be obtained or calculated. Furthermore, the various examples described above can be applied to the example of FIG. 18 and other examples.

[0100] (Alternative examples, etc.) The forklift according to the above-described embodiment is not limited to the configuration examples shown in Figures 1, 2, 17, etc., and is not limited to the shapes shown in Figures 2 and 17. Furthermore, the forklift according to the above-described embodiment is not limited to the configuration that executes the above-described control example, and various application examples can be applied. In addition, various examples other than those shown in the drawings can be applied to the type of pallet, the shape of the fork, etc.

[0101] Furthermore, all of the devices and multiple devices constituting the system, such as the control device, control system, and management system in the above-described embodiments, can have the following hardware configuration, for example. Fig. 19 is a diagram showing an example of the hardware configuration of such a device.

[0102] 19 may include a processor 101, a memory 102, and an interface 103. The interface 103 may include an interface with an operation device that accepts user operations, an interface with a display device that displays information, a communication interface for sending and receiving information, and the like.

[0103] The processor 101 may be, for example, a microprocessor, an MPU (Micro Processor Unit), or a CPU. The processor 101 may include multiple processors. The memory 102 is configured, for example, by a combination of a volatile memory and a non-volatile memory. The functions of each device are realized by the processor 101 reading a control program stored in the memory 102 and executing the program while exchanging necessary information via the interface 103.

[0104] The above program is a program for causing a computer to execute the control method described above. The various application examples described as the control method, control device, and control system can also be applied to this program.

[0105] The above-mentioned program includes a set of instructions (or software code) that, when loaded into a computer, causes the computer to perform one or more functions described in the embodiments. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable medium or tangible storage medium includes random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disc (DVD), Blu-ray (registered trademark) disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The program may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, transitory computer-readable medium or communication medium includes electrical, optical, acoustic, or other forms of propagated signals.

[0106] The present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the invention. [Explanation of symbols]

[0107] 1 forklift 2 Management System 2a DB 10 Control device 11 Information acquisition department 12 Movement control unit 13 Lift control section 14 Judgment section 21 Wheel drive unit 22 Fork drive unit 23 Load sensor 24 Height sensor 25 Main Unit 26 Mast 27 Fork lifting section 28 Fork 31, 71, 81 Transport pallets 32 Legs 41, 51, 91 Unloading pallets 42 Support part 61 Pedestal 61a Inclined Pedestal 82, 92 Luggage 100 devices 101 processors 102 memory 103 Interface

Claims

1. A control method for controlling a forklift equipped with a load sensor that detects the load of a load placed on a fork and a height sensor that detects the height of the fork, so as to place a transport pallet at a destination, comprising: Acquire load information of the transport pallet to be loaded onto the forks and lifting height range information indicating a lifting height range that is a range of heights into which the forks can be inserted when the pallet is normally unloaded at the unloading destination, Based on the acquired load information and lifting height range information, a lowering operation is performed to lower the forks loaded with the transport pallet from above the unloading destination; When the load value detected by the load sensor is equal to or less than a predetermined value and the height value detected by the height sensor is within the height range, an operation of pulling out the forks is executed, During the lowering operation, if the lift height value is equal to or less than the lower limit value of the lift height range, or if the load value is equal to or less than a predetermined value and the lift height value is equal to or greater than the upper limit value of the lift height range, it is determined that an abnormality has occurred. Control method.

2. The lifting height range is: When the unloading destination is an object that cannot be transported by the forklift or the ground, the range of height into which the forks can be inserted is formed when the transport pallet is normally placed on the object, When the unloading destination is a transport pallet that can be stacked, the range of height into which the forks can be inserted is formed when the transport pallet is normally placed on the unloading destination pallet, The control method according to claim 1 .

3. If it is determined that an abnormality has occurred during the lowering operation, the lowering operation returns to an initial position where the lowering operation was started, and the lowering operation is resumed in the state where the lowering operation has returned to the initial position. The control method according to claim 1 or 2.

4. When the number of times that the abnormality is determined during the lowering operation reaches a predetermined number, the control of the placement of the cargo at the unloading destination is stopped. The control method according to claim 3 .

5. If it is determined that an abnormality has occurred during the lowering operation, the forklift is returned to a predetermined position, and, in a state where the forklift has returned to the predetermined position, the forklift resumes moving to a position where the lowering operation will be performed. The control method according to claim 1 or 2.

6. The lifting height range indicated by the acquired lifting height range information or used to determine whether there is an abnormality is a range calculated based on the type of the transporting pallet, and set by expanding the range of heights into which the forks can be inserted when the unloading is normally performed at the unloading destination by a machine error value of the transporting pallet. The control method according to claim 1 or 2.

7. The forklift is an unmanned forklift. The control method according to claim 1 or 2.

8. At a position where the transport pallet is placed on the forks, first information is acquired, which is information indicating the transport pallet; execute a matching process to match the acquired first information with second information, which is information indicating the transport pallet corresponding to the acquired load information and lifting height range information; Executing the lowering operation when the matching process is successful. The control method according to claim 1 or 2.

9. A control device that controls a forklift equipped with a load sensor that detects the load of a load placed on a fork and a height sensor that detects the height of the fork, so as to place a transport pallet at a destination, a movement control unit that controls at least one of the movement of the forklift and the horizontal movement of the forks; a lifting / lowering control unit that controls the lifting / lowering of the forks; an acquisition unit that acquires load information of the transport pallet to be loaded onto the forks and lifting height range information that indicates a lifting height range that is a range of heights into which the forks can be inserted when the pallet is normally unloaded at the unloading destination; a determination unit that determines an abnormality; Equipped with the lifting control unit executes a lowering operation of lowering the forks loaded with the transport pallet from above the unloading destination based on the load information and the lifting height range information acquired by the acquisition unit, the movement control unit executes an operation of pulling out the forks when the load value detected by the load sensor is equal to or less than a predetermined value and the lift height value detected by the lift height sensor is within the lift height range, The determination unit determines that an abnormality has occurred when, during the lowering operation, the lift height value is equal to or less than the lower limit value of the lift height range, or when the load value is equal to or less than a predetermined value and the lift height value is equal to or greater than the upper limit value of the lift height range. Control device.

10. A control system for controlling a forklift equipped with a load sensor that detects the load of a load placed on a fork and a height sensor that detects the height of the fork, so as to place a transport pallet at a destination, comprising: a movement control unit that controls at least one of the movement of the forklift and the horizontal movement of the forks; a lifting / lowering control unit that controls the lifting / lowering of the forks; an acquisition unit that acquires load information of the transport pallet to be loaded onto the forks and lifting height range information that indicates a lifting height range that is a range of heights into which the forks can be inserted when the pallet is normally unloaded at the unloading destination; a determination unit that determines an abnormality; Equipped with the lifting control unit executes a lowering operation of lowering the forks loaded with the transport pallet from above the unloading destination based on the load information and the lifting height range information acquired by the acquisition unit, the movement control unit executes an operation of pulling out the forks when the load value detected by the load sensor is equal to or less than a predetermined value and the lift height value detected by the lift height sensor is within the lift height range, The determination unit determines that an abnormality has occurred when, during the lowering operation, the lift height value is equal to or less than the lower limit value of the lift height range, or when the load value is equal to or less than a predetermined value and the lift height value is equal to or greater than the upper limit value of the lift height range. Control system.

Images