Stacking control device

Abstract

To provide a stacking control device capable of stacking pallets even when a pallet held by a fork is dislocated in a lateral direction with respect to the fork.SOLUTION: A stacking control device 20 includes an on-fork pallet position calculation unit 32 for detecting a position of a pallet 10A on a fork with respect to a forklift 1, a floor surface pallet position calculation unit 31 for detecting a position of a pallet 10B on a floor surface with respect to the forklift 1, a guide position calculation unit 33 for calculating a guide position G making the pallet 10A on the fork position immediately above the pallet 10B on the floor surface based on the position of the pallet 10A on the fork and the position of the pallet 10B on the floor surface, a guide control unit 36 for guiding the forklift 1 to the guide position G, and a stacking control unit 38 for lowering the fork 11 until the pallet 10A on the fork is stacked on a top surface 10d of the pallet 10B on the floor surface after the forklift 1 is guided to the guide position G.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a stacking control device.

Background Art

[0002] For example, Patent Document 1 describes generating curve trajectory data of a forklift from a start position to a goal position, and calculating a control command value for moving the forklift to the goal position based on the curve trajectory data and the self-position of the forklift calculated by odometry, and moving the forklift toward the goal position according to the control command value.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When applying the above-described conventional technique to pallet stacking control, after holding a pallet with the forks of a forklift, the forklift is guided to a position in front of, for example, a pallet placed on the floor surface (referred to as a floor pallet), and in this state, the pallet held by the forks (referred to as a pallet on the forks) is loaded onto the floor pallet. However, when the pallet on the forks is displaced in the left-right direction with respect to the forks, when the forklift is guided to a position in front of the floor pallet, the position of the pallet on the forks is displaced in the left-right direction with respect to the position of the floor pallet. For this reason, it may not be possible to stack the pallet on the forks onto the floor pallet.

[0005] An object of the present invention is to provide a stacking control device capable of stacking pallets even when the pallet held by the forks is displaced in the left-right direction with respect to the forks.

Means for Solving the Problem

[0006] One aspect of the present invention is a stacking control device that controls the stacking of a first pallet held by the forks of a forklift on top of an existing second pallet, comprising a first drive unit for driving the forklift, a second drive unit for raising and lowering the forks, a first pallet position detection unit for detecting the position of the first pallet with respect to the forklift, a second pallet position detection unit for detecting the position of the second pallet with respect to the forklift, and an induction position calculation unit for calculating an induction position of the forklift such that the first pallet is positioned directly above the second pallet based on the position of the first pallet detected by the first pallet position detection unit and the position of the second pallet detected by the second pallet position detection unit, an induction control unit for controlling the first drive unit to guide the forklift to the induction position calculated by the induction position calculation unit, and a loading control unit for controlling the second drive unit to lower the forks until the first pallet is loaded on the upper surface of the second pallet after the forklift is guided to the induction position by the induction control unit.

[0007] In such a stacking control device, the position of the first pallet with respect to the forklift is detected, and the position of the second pallet with respect to the forklift is detected. Then, based on the position of the first pallet and the position of the second pallet, an induction position of the forklift such that the first pallet is positioned directly above the second pallet is calculated, and the first drive unit is controlled to guide the forklift to the induction position. Then, after the forklift is guided to the induction position, the second drive unit is controlled to lower the forks until the first pallet is loaded on the upper surface of the second pallet, so that the first pallet is stacked on the second pallet. Therefore, even when the first pallet is displaced in the left-right direction with respect to the forks, when the forklift is guided to the induction position, the first pallet is guided directly above the second pallet. As a result, even if the first pallet is displaced in the left-right direction with respect to the forks, the first pallet can be stacked on the second pallet.

[0008] The stacking control device further includes a third drive unit that moves the fork in the left - right direction of the forklift, and an alignment control unit that controls the third drive unit to align the left - right position of the first pallet with respect to the second pallet after the forklift is guided to the induction position by the induction control unit. The stacking control unit may control the second drive unit to lower the fork until the first pallet is loaded on the upper surface of the second pallet after the left - right alignment of the first pallet with respect to the second pallet is performed by the alignment control unit.

[0009] In such a configuration, after the forklift is guided to the induction position, the third drive unit is controlled to align the left - right position of the first pallet with respect to the second pallet. Then, by controlling the second drive unit to lower the fork until the first pallet is loaded on the upper surface of the second pallet, the first pallet is stacked on the second pallet. Therefore, even when an induction error occurs when the forklift is guided to the induction position, the induction error is absorbed by aligning the left - right position of the first pallet with respect to the second pallet. Thus, the first pallet can be appropriately stacked on the second pallet.

[0010] The stacking control device further includes a self - position estimation unit that estimates the self - position of the forklift. The alignment control unit may calculate the left - right deviation amount between the self - position of the forklift estimated by the self - position estimation unit and the induction position when the forklift reaches the induction position, and control the third drive unit so that the left - right deviation amount approaches zero.

[0011] In such a configuration, when the forklift reaches the induction position, by controlling the third drive unit so that the left - right deviation amount between the self - position of the forklift and the induction position approaches zero, the left - right alignment of the first pallet with respect to the second pallet can be accurately performed.

[0012] The positions of the first pallet and the second pallet with respect to the forklift are represented as two-dimensional coordinate values and inclination angles of the first pallet and the second pallet with respect to the forklift, and the guidance position calculation unit may calculate the guidance position of the forklift using a calculation formula related to the subtraction of the position of the second pallet from the position of the first pallet.

[0013] In such a configuration, since a calculation formula related to the subtraction of the position of the second pallet from the position of the first pallet is used, the guidance position of the forklift can be calculated by simple arithmetic processing.

Advantages of the Invention

[0014] According to the present invention, even if the pallet held by the fork is displaced in the left-right direction with respect to the fork, the pallets can be stacked.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying out the Invention

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0017] FIG. 1 is a side view showing a forklift to which a stacking control device according to an embodiment of the present invention is applied. In FIG. 1, the forklift 1 includes a traveling device 2 and a cargo handling device 3 disposed on the front side of the traveling device 2.

[0018] The traveling device 2 has a vehicle body 4, a pair of left - and - right drive wheels (front wheels 5) disposed at the front of the vehicle body 4, and a pair of left - and - right steering wheels (rear wheels 6) disposed at the rear of the vehicle body 4.

[0019] The cargo handling device 3 includes a mast 7 attached to the front end of the vehicle body 4, a pair of left - and - right forks 11 that are attached to the mast 7 via a lift bracket 8 and a load bracket 9 so as to be liftable and hold a pallet 10, a lift cylinder 12 for raising and lowering the lift bracket 8, a tilt cylinder 13 for tilting the mast 7, and a side - shift cylinder 14 (see FIG. 2) for moving the load bracket 9 in the left - right direction (lateral direction) with respect to the lift bracket 8.

[0020] The pallet 10 is, for example, a flat pallet made of plastic or wood. The pallet 10 has a rectangular shape in plan view. Goods (not shown) are placed on the pallet 10. The pallet 10 has a front surface 10a, a rear surface 10b, two side surfaces 10c, an upper surface 10d, and a lower surface 10e. The front surface 10a is the surface facing the forklift 1 when the pallet 10 is held by the forks 11.

[0021] The pallet 10 is provided with a pair of left and right fork holes 15 (see FIG. 3) into which each fork 11 is inserted. The fork holes 15 extend from the front surface 10a to the rear surface 10b of the pallet 10.

[0022] FIG. 2 is a block diagram showing the configuration of a stacking control device according to an embodiment of the present invention. In FIG. 2, as shown in FIG. 3, the stacking control device 20 of the present embodiment is a device that automatically controls the pallet 10 held by the fork 11 to be stacked on the existing pallet 10 in a state where the forklift 1 is located on the front surface 10a side of the existing pallet 10.

[0023] Here, the pallet 10 held by the fork 11 is referred to as an on-fork pallet 10A (first pallet). The existing pallet 10 is referred to as a floor pallet 10B (second pallet) placed on, for example, the floor surface F (see FIG. 7).

[0024] After the fork 11 is inserted into the fork hole 15 of the on-fork pallet 10A, the fork 11 is lifted by the lift cylinder 12, and the on-fork pallet 10A is lifted and held by the fork 11. In FIG. 3, the fork hole 15 of the on-fork pallet 10A is omitted for convenience.

[0025] The stacking control device 20 is mounted on the forklift 1. The stacking control device 20 includes laser sensors 21 and 22, a map storage unit 23, a traveling drive unit 24, a lift drive unit 25, a side shift drive unit 26, and a controller 30.

[0026] The laser sensor 21 irradiates laser light toward an area including the front of the forklift 1, receives the reflected light of the laser light, and detects the distance to an object existing around the forklift 1 to acquire point cloud data. The point cloud is a collection of reflection points of the laser light. As the laser sensor 21, for example, LIDAR (light detection and ranging) or a laser rangefinder is used.

[0027] The laser sensor 22 irradiates a laser beam toward an area including the lower surface 10e of the on-fork pallet 10A which is the pallet 10 held by the fork 11, and receives the reflected light of the laser beam, thereby detecting the distance to the lower surface 10e of the on-fork pallet 10A and acquiring point cloud data. As the laser sensor 22, similar to the laser sensor 21, LIDAR, a laser rangefinder, or the like is used.

[0028] The map storage unit 23 stores map data of the area where the stacking operation is performed. The map data includes pillars, shelves, walls, and the like.

[0029] The traveling drive unit 24 is a first drive unit that causes the forklift 1 to travel. The traveling drive unit 24 has, for example (not shown in the figure), a traveling motor that rotates the front wheels 5 which are drive wheels, and a steering motor that steers the rear wheels 6 which are steering wheels.

[0030] The lift drive unit 25 expands and contracts the lift cylinder 12. The lift drive unit 25, in cooperation with the lift cylinder 12, constitutes a second drive unit that raises and lowers the fork 11. The lift drive unit 25 is, for example (not shown in the figure), an electromagnetic control valve arranged between the hydraulic pump and the lift cylinder 12.

[0031] The side shift drive unit 26 expands and contracts the side shift cylinder 14. The side shift drive unit 26, in cooperation with the side shift cylinder 14, constitutes a third drive unit that moves the fork 11 in the left-right direction. The side shift drive unit 26 is, for example (not shown in the figure), an electromagnetic control valve arranged between the hydraulic pump and the side shift cylinder 14.

[0032] The controller 30 is composed of a CPU, a RAM, a ROM, an input / output interface, etc. The controller 30 includes a floor pallet position calculation unit 31, a pallet position calculation unit 32 on the fork, a guidance position calculation unit 33, a self-position estimation unit 34, a travel route generation unit 35, a guidance control unit 36, an alignment control unit 37, and a loading control unit 38. These functions are executed after the pallet 10 is lifted by the fork 11.

[0033] Based on the point cloud data of the laser sensor 21, the floor pallet position calculation unit 31 calculates the position of the floor pallet 10B relative to the forklift 1. The floor pallet position calculation unit 31, in cooperation with the laser sensor 21, constitutes a second pallet position detection unit that detects the position of the floor pallet 10B relative to the forklift 1.

[0034] FIG. 4 is a flowchart showing an example of the procedure of the position calculation process executed by the floor pallet position calculation unit 31. This process is executed when the start of the stacking control is instructed by, for example, a manual switch (not shown).

[0035] In FIG. 4, the floor pallet position calculation unit 31 first acquires the point cloud data of the laser sensor 21 (step S101). Subsequently, the floor pallet position calculation unit 31 extracts the point cloud data corresponding to the front surface 10a of the floor pallet 10B from the point cloud data of the laser sensor 21 (step S102).

[0036] Subsequently, the floor pallet position calculation unit 31 performs a filtering process on the point cloud data extracted in step S102 (step S103). As a result, point cloud data from which the reflection points corresponding to noise other than the floor pallet 10B are removed is obtained.

[0037] Subsequently, based on the point cloud data obtained in step S103, the floor pallet position calculation unit 31 calculates the plane equation of the front surface 10a of the floor pallet 10B (step S104). At this time, for example, a robust estimation method such as RANSAC (Random Sample Consensus) or the least squares method is used to calculate the plane equation of the front surface 10a of the floor pallet 10B.

[0038] Subsequently, based on the plane equation of the front surface 10a of the floor pallet 10B calculated in step S104, the floor pallet position calculation unit 31 detects the positions of the two fork holes 15 provided in the floor pallet 10B (step S105).

[0039] Subsequently, based on the plane equation of the front surface 10a of the floor pallet 10B and the positions of the two fork holes 15, the floor pallet position calculation unit 31 calculates the position of the floor pallet 10B with respect to the forklift 1 (step S106).

[0040] The position of the floor pallet 10B with respect to the forklift 1 is represented as the two-dimensional coordinate values (XY coordinate values) and the inclination angle of the floor pallet 10B with respect to the forklift 1. Specifically, when an arbitrary position of the forklift 1 (for example, the center position of the vehicle body 4) is set as the origin (0, 0, 0), the position of the floor pallet 10B with respect to the forklift 1 is represented by (X_p, Y_p, θ_p).

[0041] Returning to FIG. 2, based on the point cloud data of the laser sensor 22, the on-fork pallet position calculation unit 32 calculates the position of the on-fork pallet 10A with respect to the forklift 1. The on-fork pallet position calculation unit 32 constitutes a first pallet position detection unit that cooperates with the laser sensor 22 to detect the position of the on-fork pallet 10A with respect to the forklift 1.

[0042] FIG. 5 is a flowchart showing an example of the procedure of the position calculation process executed by the on-fork pallet position calculation unit 32. Note that this process is executed at the same timing as the floor pallet position calculation unit 31.

[0043] In FIG. 5, the on-fork pallet position calculation unit 32 first acquires the point cloud data of the laser sensor 22 (step S111). Subsequently, the on-fork pallet position calculation unit 32 extracts the point cloud data corresponding to the lower surface 10e of the on-fork pallet 10A from the point cloud data of the laser sensor 22 (step S112).

[0044] Subsequently, the on-fork pallet position calculation unit 32 performs filtering processing on the point cloud data extracted in step S112 (step S113). As a result, point cloud data with reflection points corresponding to noise other than the on-fork pallet 10A removed is obtained.

[0045] Subsequently, the on-fork pallet position calculation unit 32 extracts a straight line corresponding to the edge of the lower surface 10e of the on-fork pallet 10A based on the point cloud data obtained in step S113 (step S114). At this time, for example, the RANSAC or least squares method is used to extract a straight line corresponding to the edge of the lower surface 10e of the on-fork pallet 10A.

[0046] Subsequently, the on-fork pallet position calculation unit 32 calculates the center position of the on-fork pallet 10A based on the straight line corresponding to the edge of the lower surface 10e of the on-fork pallet 10A (step S115). The center position of the on-fork pallet 10A is the center position in the vehicle width direction (left-right direction) of the front edge portion with respect to the vehicle body 4 on the lower surface 10e of the on-fork pallet 10A.

[0047] Subsequently, the on-fork pallet position calculation unit 32 calculates the position of the on-fork pallet 10A with respect to the forklift 1 based on the straight line corresponding to the edge of the lower surface 10e of the on-fork pallet 10A and the center position of the on-fork pallet 10A (step S116).

[0048] The position of the on-fork pallet 10A with respect to the forklift 1 is represented as the two-dimensional coordinate values and the inclination angle of the on-fork pallet 10A with respect to the forklift 1, similar to the position of the floor pallet 10B with respect to the forklift 1. Specifically, the position of the on-fork pallet 10A with respect to the forklift 1 is represented by (X_fp, Y_fp, θ_fp).

[0049] Returning to FIG. 2, the guidance position calculation unit 33 calculates a guidance position G (see FIG. 3(b)) of the forklift 1 such that the on-fork pallet 10A is positioned directly above the floor pallet 10B, based on the position of the floor pallet 10B calculated by the floor pallet position calculation unit 31 and the position of the on-fork pallet 10A calculated by the on-fork pallet position calculation unit 32.

[0050] Here, even if the center of the upper surface 10d of the on-fork pallet 10A does not coincide with the center of the upper surface 10d of the floor pallet 10B and the on-fork pallet 10A is displaced front, rear, left, or right with respect to the floor pallet 10B, if most of the on-fork pallet 10A overlaps with the floor pallet 10B, the on-fork pallet 10A is included in the state of being positioned directly above the floor pallet 10B.

[0051] The guidance position calculation unit 33 calculates the guidance position G of the forklift 1 using a calculation formula related to the subtraction of the position of the floor pallet 10B and the position of the on-fork pallet 10A. The calculation formula related to the subtraction is as follows. θ = θ_p - θ_fp X_temp = (-X_fp * cosθ) + (Y_fp * sinθ) Y_temp = (-X_fp * sinθ) + (-Y_fp * cosθ) X = X_p + X_temp Y = Y_p + Y_temp

[0052] Note that X_temp is an equation for correcting by θ degrees when calculating the difference between the X coordinate value of the floor pallet 10B with respect to the forklift 1 and the X coordinate value of the on-fork pallet 10A with respect to the forklift 1. Y_temp is an equation for correcting by θ degrees when calculating the difference between the Y coordinate value of the floor pallet 10B with respect to the forklift 1 and the Y coordinate value of the on-fork pallet 10A with respect to the forklift 1.

[0053] When the inclination angle θ_p of the floor pallet 10B with respect to the forklift 1 is equal to the inclination angle θ_fp of the on-fork pallet 10A with respect to the forklift 1, θ becomes 0, so X and Y are represented by the following equations. X = X_p - X_fp Y = Y_p - Y_fp

[0054] The self-position estimation unit 34 estimates the self-position of the forklift 1 based on the point cloud data of the laser sensor 21 and the map data stored in the map storage unit 23. Specifically, the self-position estimation unit 34 estimates the self-position of the forklift 1 by matching the point cloud data of the laser sensor 21 and the map data using, for example, the SLAM (simultaneous localization and mapping) method. SLAM is a self-position estimation technology that performs self-position estimation using sensor data and map data.

[0055] The travel route generation unit 35 acquires the guidance position G of the forklift 1 calculated by the guidance position calculation unit 33 and the self-position of the forklift 1 estimated by the self-position estimation unit 34, and generates a travel route R (see Fig. 3(a)) of the forklift 1 from the current position to the guidance position G.

[0056] The guidance control unit 36 controls the travel drive unit 24 to guide the forklift 1 from the current position to the guidance position G according to the travel route R generated by the travel route generation unit 35.

[0057] FIG. 6 is a flowchart showing an example of the procedure of the guidance control process executed by the guidance control unit 36. This process is executed when the guidance position calculation unit 33 calculates the guidance position G of the forklift 1.

[0058] In FIG. 6, the guidance control unit 36 first controls the traveling drive unit 24 so that the forklift 1 travels along the traveling route R toward the guidance position G (step S121). At this time, the guidance control unit 36 controls the traveling drive unit 24 so that the deviation amount between the self-position of the forklift 1 estimated by the self-position estimation unit 34 and the traveling route R approaches zero.

[0059] Subsequently, the guidance control unit 36 determines whether the forklift 1 has reached the guidance position G based on the self-position of the forklift 1 (step S122). When the guidance control unit 36 determines that the forklift 1 has not reached the guidance position G, it executes the above step S121 again. When the guidance control unit 36 determines that the forklift 1 has reached the guidance position G, it controls the traveling drive unit 24 to stop the forklift 1 (step S123).

[0060] Returning to FIG. 2, after the forklift 1 is guided to the guidance position G by the guidance control unit 36, the alignment control unit 37 controls the side shift drive unit 26 to perform alignment in the left-right direction (X direction in FIG. 3) of the upper-fork pallet 10A with respect to the floor pallet 10B.

[0061] When the forklift 1 reaches the guidance position G, the alignment control unit 37 calculates the lateral deviation amount (left-right direction deviation amount) between the self-position of the forklift 1 estimated by the self-position estimation unit 34 and the guidance position G, and controls the side shift drive unit 26 so that the lateral deviation amount approaches zero. Thereby, alignment in the left-right direction of the upper-fork pallet 10A with respect to the floor pallet 10B is performed.

[0062] After the alignment control unit 37 aligns the pallet 10A on the fork with the floor pallet 10B, the loading control unit 38 controls the lift drive unit 25 to lower the fork 11 until the pallet 10A on the fork is loaded onto the upper surface 10d of the floor pallet 10B.

[0063] When stacking the pallet 10A held by the fork 11 of the forklift 1 located on the front surface 10a side of the floor pallet 10B onto the floor pallet 10B by the stacking control device 20 as described above, the laser sensor 21 irradiates the area including the front surface 10a of the floor pallet 10B with laser light, and the laser sensor 22 irradiates the area including the lower surface 10e of the pallet 10A on the fork with laser light.

[0064] Then, based on the point cloud data of the laser sensor 21, the position of the floor pallet 10B with respect to the forklift 1 is calculated, and based on the point cloud data of the laser sensor 22, the position of the pallet 10A on the fork with respect to the forklift 1 is calculated. Then, based on the position of the floor pallet 10B and the position of the pallet 10A on the fork, the guiding position G (see Fig. 3(b)) of the forklift 1 for positioning the pallet 10A on the fork directly above the floor pallet 10B is calculated.

[0065] Then, the travel route R of the forklift 1 from the current position of the forklift 1 to the guiding position G is generated, and the forklift 1 travels along the travel route R to the guiding position G. When the forklift 1 reaches the guiding position G, as shown in Fig. 7(a), the pallet 10A on the fork is guided directly above the floor pallet 10B.

[0066] Then, the lateral displacement amount between the self-position of the forklift 1 and the guiding position G is calculated, and the fork 11 is moved laterally by the side shift cylinder 14 so that the lateral displacement amount approaches zero, so that, as shown in Fig. 7(b), the pallet 10A on the fork is aligned with the floor pallet 10B in the left-right direction.

[0067] In that state, when the fork 11 is lowered by the lift cylinder 12, as shown in FIG. 7(c), the upper pallet 10A on the fork is placed on the upper surface 10d of the floor pallet 10B. Then, when the forklift 1 retreats, the fork 11 comes out of the fork hole 15 of the upper pallet 10A on the fork. Thus, the stacking operation of one pallet 10 is completed.

[0068] By the way, as shown in FIG. 8, when the upper pallet 10A on the fork is held in a state of being displaced in the left - right direction (X - direction) with respect to the fork 11, when the forklift 1 is guided to a position in front of the floor pallet 10B, the upper pallet 10A on the fork will be displaced in the left - right direction with respect to the floor pallet 10B. In this case, the position of the upper pallet 10A on the fork is adjusted to the position of the floor pallet 10B by moving the fork 11 in the left - right direction by the side - shift cylinder 14.

[0069] However, depending on the guiding error that occurs when guiding the forklift 1, it may not be possible to align the left - right positions of the upper pallet 10A on the fork and the floor pallet 10B. For example, as shown in FIG. 8(b), when the direction P of the occurrence of the guiding error is opposite to the displacement direction Q of the upper pallet 10A on the fork with respect to the fork 11, the side - shift cylinder 14 cannot absorb the total error amount obtained by combining the displacement amount of the upper pallet 10A on the fork with respect to the fork 11 and the guiding error amount, and there is a possibility that the upper pallet 10A cannot be stacked on the floor pallet 10B.

[0070] In response to such problems, in the present embodiment, instead of guiding the forklift 1 to a position in front of the floor pallet 10B, as shown in FIG. 3, the on-fork pallet 10A is guided to a position directly above the floor pallet 10B. In this case, since the amount of lateral displacement of the on-fork pallet 10A with respect to the forks 11 is absorbed, only the guiding error remains after the forklift 1 is guided. That is, since the total error amount is reduced by the amount of lateral displacement of the on-fork pallet 10A with respect to the forks 11, it can be absorbed by the side shift cylinder 14. Therefore, it becomes easier to align the on-fork pallet 10A and the floor pallet 10B in the lateral direction.

[0071] As described above, according to the present embodiment, the position of the on-fork pallet 10A with respect to the forklift 1 is detected, and the position of the floor pallet 10B with respect to the forklift 1 is detected. Then, based on the position of the on-fork pallet 10A and the position of the floor pallet 10B, a guiding position G of the forklift 1 for positioning the on-fork pallet 10A directly above the floor pallet 10B is calculated, and the traveling drive unit 24 is controlled to guide the forklift 1 to the guiding position G. After the forklift 1 is guided to the guiding position G, the lift drive unit 25 is controlled to lower the forks 11 until the on-fork pallet 10A is loaded on the upper surface 10d of the floor pallet 10B, so that the on-fork pallet 10A is stacked on the floor pallet 10B. Therefore, even when the on-fork pallet 10A is displaced laterally with respect to the forks 11, when the forklift 1 is guided to the guiding position G, the on-fork pallet 10A is guided directly above the floor pallet 10B. Thereby, even if the on-fork pallet 10A is displaced laterally with respect to the forks 11, the on-fork pallet 10A can be stacked on the floor pallet 10B.

[0072] Also, in this embodiment, after the forklift 1 is guided to the guiding position G, the side shift driving unit 26 is controlled to align the forklift upper pallet 10A with respect to the floor pallet 10B in the left-right direction. Then, the lift driving unit 25 is controlled to lower the forks 11 until the forklift upper pallet 10A is loaded on the upper surface 10d of the floor pallet 10B, so that the forklift upper pallet 10A is stacked on the floor pallet 10B. Therefore, even if a guiding error occurs when the forklift 1 is guided to the guiding position G, the guiding error is absorbed by aligning the forklift upper pallet 10A with respect to the floor pallet 10B in the left-right direction. Accordingly, the forklift upper pallet 10A can be appropriately stacked on the floor pallet 10B.

[0073] Also, in this embodiment, when the forklift 1 reaches the guiding position G, the side shift driving unit 26 is controlled so that the amount of deviation in the left-right direction between the self-position of the forklift 1 and the guiding position G approaches zero, whereby the alignment of the forklift upper pallet 10A with respect to the floor pallet 10B in the left-right direction can be accurately performed.

[0074] Also, in this embodiment, the positions of the forklift upper pallet 10A and the floor pallet 10B with respect to the forklift 1 are represented as two-dimensional coordinate values and inclination angles of the forklift upper pallet 10A and the floor pallet 10B with respect to the forklift 1, and the guiding position G of the forklift 1 is calculated using a calculation formula related to the subtraction between the position of the floor pallet 10B and the position of the forklift upper pallet 10A. Since the calculation formula related to the subtraction between the position of the floor pallet 10B and the position of the forklift upper pallet 10A is used in this way, the guiding position G of the forklift 1 can be calculated by simple arithmetic processing.

[0075] Note that the present invention is not limited to the above embodiments. For example, in the above embodiments, the fork 11 is moved in the left - right direction by the side - shift cylinder 14 to align the pallet 10A on the fork in the left - right direction with respect to the floor pallet 10B. However, it is not particularly limited to such a form. For example, in the forklift 1 not equipped with the side - shift cylinder 14, the travel route R to the induction position G of the forklift 1 may be re - generated to align the pallet 10A on the fork in the left - right direction with respect to the floor pallet 10B.

[0076] Also, when there are few induction errors generated when guiding the forklift 1, after the forklift 1 is guided to the induction position G, the pallet 10A on the fork may be stacked on the floor pallet 10B without performing the left - right alignment of the pallet 10A on the fork with respect to the floor pallet 10B.

[0077] Also, in the above embodiments, based on the point - cloud data of the laser sensor 21, the position of the floor pallet 10B with respect to the forklift 1 is calculated, and based on the point - cloud data of the laser sensor 22, the position of the pallet 10A on the fork with respect to the forklift 1 is calculated. However, it is not particularly limited to such a form. For example, instead of the laser sensors 21 and 22, a stereo camera may be used. In this case, based on the image data of the stereo camera, the distances to the floor pallet 10B and the pallet 10A on the fork are respectively detected, and the positions of the floor pallet 10B and the pallet 10A on the fork with respect to the forklift 1 are respectively detected.

[0078] In the above embodiment, laser light is irradiated from the laser sensor 22 toward the area including the lower surface 10e of the on-fork pallet 10A, and the position of the on-fork pallet 10A with respect to the forklift 1 is calculated based on the point cloud data corresponding to the lower surface 10e of the on-fork pallet 10A among the point cloud data of the laser sensor 22. However, it is not particularly limited to such a form. For example, laser light may be irradiated from the laser sensor 22 toward the area including the side surface 10c or the upper surface 10d of the on-fork pallet 10A, and the position of the on-fork pallet 10A with respect to the forklift 1 may be calculated based on the point cloud data corresponding to the side surface 10c or the upper surface 10d of the on-fork pallet 10A among the point cloud data of the laser sensor 22.

[0079] In the above embodiment, the self-position of the forklift 1 is estimated based on the point cloud data of the laser sensor 21 and the map data stored in the map storage unit 23. However, it is not particularly limited to such a form. For example, a laser sensor for self-position may be provided separately from the laser sensors 21 and 22, and the self-position of the forklift 1 may be estimated based on the point cloud data of the laser sensor for self-position and the map data.

[0080] In the above embodiment, the self-position of the forklift 1 is estimated using the SLAM method based on the point cloud data of the laser sensor 21. However, it is not particularly limited to such a form. As a method for estimating the self-position of the forklift 1, for example, a SLAM method using image data of a camera, an odometry sensor that detects the amount and direction of movement of the forklift 1, or an inertial measurement unit (IMU) that measures the angular velocity and acceleration of the forklift 1 may be used.

[0081] In the above embodiment, the existing pallet 10 is the floor pallet 10B placed on the floor surface F. However, the form of the existing pallet 10 is not particularly limited thereto, and for example, it may be placed on the loading platform of a truck.

Explanation of Reference Numerals

[0082] 1... forklift, 10... pallet, 10d... upper surface, 10A... pallet on forks (first pallet), 10B... floor pallet (second pallet), 11... forks, 12... lift cylinder (second drive unit), 14... side shift cylinder (third drive unit), 20... stacking control device, 21... laser sensor (second pallet position detection unit), 22... laser sensor (first pallet position detection unit), 24... travel drive unit (first drive unit), 25... lift drive unit (second drive unit), 26... side shift drive unit (third drive unit), 31... floor pallet position calculation unit (second pallet position detection unit), 32... pallet on forks position calculation unit (first pallet position detection unit), 33... guidance position calculation unit, 34... self-position estimation unit, 36... guidance control unit, 37... alignment control unit, 38... loading control unit, G... guidance position.

Claims

1. A stacking control device that controls to stack a first pallet held by a fork of a forklift on top of an existing second pallet, a first drive unit that drives the forklift, a second drive unit that raises and lowers the fork, a third drive unit that moves the fork in the left - right direction of the forklift, a first pallet position detection unit that detects the position of the first pallet with respect to the forklift, a second pallet position detection unit that detects the position of the second pallet with respect to the forklift, a guiding position calculation unit that calculates a guiding position of the forklift such that the first pallet is positioned directly above the second pallet based on the position of the first pallet detected by the first pallet position detection unit and the position of the second pallet detected by the second pallet position detection unit, a guiding control unit that controls the first drive unit to guide the forklift to the guiding position calculated by the guiding position calculation unit, an alignment control unit that controls the third drive unit to align the first pallet with respect to the second pallet in the left - right direction after the forklift is guided to the guiding position by the guiding control unit, a loading control unit that controls the second drive unit to lower the fork until the first pallet is loaded on the upper surface of the second pallet after the alignment of the first pallet with respect to the second pallet in the left - right direction is performed by the alignment control unit, and a self - position estimation unit that estimates the self - position of the forklift, wherein the alignment control unit calculates a deviation amount in the left - right direction between the self - position of the forklift estimated by the self - position estimation unit and the guiding position when the forklift reaches the guiding position, and controls the third drive unit so that the deviation amount in the left - right direction approaches zero. A stacking control device according to claim 1.

2. The positions of the first pallet and the second pallet with respect to the forklift are represented as two - dimensional coordinate values and inclination angles of the first pallet and the second pallet with respect to the forklift, The stacking control device according to claim 1, wherein the guiding position calculation unit calculates the guiding position of the forklift using a calculation formula related to subtraction of the position of the second pallet and the position of the first pallet.

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