Forklift

Abstract

To increase the accuracy of detection of stacking positions.SOLUTION: A forklift comprises a fork, a one-dimensional distance meter, and a control unit. The control unit raises the fork while a target for placing a load is positioned forward. The control unit acquires the distance to the target for placing the load, which is measured by a distance meter while the fork is ascending. The control unit obtains a first straight line from the distance less than a threshold value among the distances acquired while the fork is ascending. The control unit obtains a second straight line representing a height at which the distance measured by the distance meter exceeds the threshold value. The control unit obtains a stacking position on a load placement surface on which a load is placed in the target for placing the load from an intersection point of the first straight line and the second straight line.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present disclosure relates to a forklift.

Background Art

[0002] The forklift disclosed in Patent Document 1 includes an external sensor that detects the position of an object in the coordinates of a three-dimensional coordinate system and a control device. The control device acquires the coordinates of the three-dimensional coordinate system from the external sensor. The control device detects a stacking position for loading the load from the acquired coordinates.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When the external sensor detects the coordinates of the three-dimensional coordinate system, the detection accuracy of the coordinates decreases. For example, in the case of an external sensor that detects the coordinates of a three-dimensional coordinate system by irradiating a laser, the laser element emits a laser while rotating a mirror by a rotation mechanism. Due to this, the detection accuracy of the coordinates decreases. As a result, the detection accuracy of the stacking position may decrease.

Means for Solving the Problems

[0005] The forklift for solving the above problems includes two forks on which a load is placed, a one-dimensional distance meter provided to move up and down together with the forks and measure the distance to an object existing in the front, and a control unit. The control unit raises the forks in a state where a load placement target on which the load is to be placed is located in the front, acquires the distance to the load placement target measured by the distance meter during the raising of the forks, obtains a first straight line from the distances less than a threshold value among the distances acquired during the raising of the forks, obtains a second straight line representing the height at which the distance measured by the distance meter exceeds the threshold value, and obtains the stacking position on the load placement surface where the load is placed on the load placement target from the intersection point between the first straight line and the second straight line.

[0006] When the forks are raised in a state where the load placement target is located in the front, the distance meter measures the distance to the load placement target while rising. When the height of the distance meter becomes higher than the load placement surface, the distance measured by the distance meter becomes longer. Therefore, the first straight line obtained from the distances less than the threshold value becomes a straight line following the shape of the part of the load placement target located below the load placement surface. Also, the second straight line represents the height of the load placement surface. Therefore, the stacking position can be obtained from the intersection point between the first straight line and the second straight line. Since the stacking position can be obtained using a one-dimensional distance meter, the detection accuracy of the stacking position can be increased.

[0007] Regarding the above forklift, the load placement target may be a truck, and the control unit may use, as the stacking position, a position obtained by adding a predetermined distance to the intersection point. Regarding the above forklift, the distance meter may be provided at the tip of the forks.

[0008] Regarding the above forklift, the distance meter is provided on each of the two forks, and the control unit obtains the intersection point for each of the distances measured by each of the two distance meters, and may adopt, as the intersection point used to obtain the stacking position, the intersection point with the longer distance from each of the two distance meters to the corresponding intersection point.

Advantages of the Invention

[0009] According to the present invention, the detection accuracy of the stacking position can be improved.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0011] An embodiment of a forklift will be described. In the following description, front, rear, left, right, up, and down are defined with reference to the forklift. <Forklift> As shown in FIG. 1, the forklift 10 is a reach-type forklift. The forklift 10 may be a counterbalanced forklift. The forklift 10 automatically performs cargo handling.

[0012] The forklift 10 includes a vehicle body 11, two reach legs 12, two front wheels 13, a rear wheel 14, a head guard 15, and a cargo handling device 21. The two reach legs 12 are provided in two, spaced apart from each other in the left-right direction. The reach legs 12 extend forward from the vehicle body 11. The front wheels 13 are provided one on each reach leg 12. The rear wheel 14 is provided on the vehicle body 11. The rear wheel 14 is a steering wheel. The rear wheel 14 is a drive wheel. The head guard 15 is provided above the vehicle body 11.

[0013] The cargo handling device 21 is provided in front of the vehicle body 11. The cargo handling device 21 includes a mast 22, a lift bracket 25, forks 26, a lift cylinder 31, and a reach cylinder 32.

[0014] The mast 22 is a multi-stage mast. The mast 22 includes an outer mast 23 and an inner mast 24. The inner mast 24 is provided so as to be able to move up and down with respect to the outer mast 23.

[0015] The lift bracket 25 is provided so as to be able to move up and down with respect to the inner mast 24. The forks 26 are fixed to the lift bracket 25. The forks 26 are provided in two, spaced apart from each other in the left-right direction.

[0016] The lift cylinder 31 is a hydraulic cylinder. The lift bracket 25 moves up and down by supplying and discharging hydraulic oil to the lift cylinder 31. The forks 26 move up and down together with the lift bracket 25.

[0017] The reach cylinder 32 is a hydraulic cylinder. The mast 22 moves in the front-rear direction by supplying and discharging hydraulic oil to the reach cylinder 32. The forks 26 move in the front-rear direction together with the mast 22.

[0018] As shown in FIG. 2, the forklift 10 includes a drive mechanism 41, a hydraulic mechanism 42, a lift height sensor 51, and an external sensor 52. The drive mechanism 41 is a member for causing the forklift 10 to perform a traveling operation. The drive mechanism 41 includes a drive source for driving the rear wheels 14 and a steering mechanism for steering the rear wheels 14. In the case of the forklift 10 having a motor as the drive source, the drive mechanism 41 includes a motor driver. In the case of the forklift 10 having an engine as the drive source, the drive mechanism 41 includes a fuel injection device.

[0019] The hydraulic mechanism 42 is a member for controlling the supply and discharge of hydraulic oil to hydraulic devices. The hydraulic devices include a lift cylinder 31 and a reach cylinder 32. The hydraulic mechanism 42 includes a pump for discharging hydraulic oil and a control valve for controlling the supply and discharge of hydraulic oil to the hydraulic devices.

[0020] The lift height sensor 51 detects the lift height, which is the height from the road surface to the fork 26. The lift height sensor 51 is, for example, a reel sensor. The forklift 10 may be provided with the lift height sensor 51. In this case, the existing lift height sensor 51 can be used without newly providing a lift height sensor.

[0021] The external sensor 52 detects the position of an object in the coordinates of a three-dimensional coordinate system. The external sensor 52 is, for example, a millimeter-wave radar, a stereo camera, a ToF (Time of Flight) camera, or a LIDAR (Laser Imaging Detection and Ranging). In the present embodiment, a LIDAR is used as the external sensor 52. The external sensor 52 includes a laser element that emits a laser, a mirror that reflects the laser emitted by the laser element, a rotation mechanism that rotates the mirror, and a light-receiving element that receives the reflected light. By rotating the mirror by the rotation mechanism while the laser element emits a laser, the external sensor 52 irradiates the laser in a plurality of directions. The external sensor 52 derives the distance to a point by receiving, with the light-receiving element, the reflected light reflected from the point where the laser hits. The point where the laser hits represents a part of the surface of the object. The position of the point can be represented in the coordinates of a polar coordinate system. The coordinates of the point in the polar coordinate system are converted into the coordinates of a rectangular coordinate system. The external sensor 52 derives the coordinates of the point in the sensor coordinate system. The sensor coordinate system is a three-axis orthogonal coordinate system with the external sensor 52 as the origin. The external sensor 52 is often arranged at a high place so that the laser is not blocked. For example, the external sensor 52 is arranged on the head guard 15.

[0022] The forklift 10 includes at least one distance meter 53. The distance meter 53 is a laser distance meter. The distance meter 53 measures the distance to the location where the laser hits by receiving the reflected light from the location where the laser hits. When the distance meter 53 cannot receive the reflected light despite irradiating the laser, the measured value is set to infinity. The measured value being infinity means that there is no location where the laser hits within the measurable distance of the distance meter 53. The distance meter 53 is a one-dimensional distance meter that can measure only the distance in one direction.

[0023] As shown in FIG. 3, the distance meter 53 is attached so as to move up and down together with the fork 26. The distance meter 53 is provided on the fork 26. Specifically, the distance meter 53 is built into the tip of the fork 26. The distance meter 53 is provided so as to irradiate a laser forward. Therefore, the distance measured by the distance meter 53 is the distance to an object existing in front of the forklift 10. The forklift 10 may be equipped with a distance meter 53 at the tip of the fork 26. In this case, the existing distance meter 53 can be used without newly providing a distance meter.

[0024] As shown in FIG. 2, the forklift 10 includes a control unit 61. The control unit 61 includes a processor 62 and a storage unit 63. The processor 62 is, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or a DSP (Digital Signal Processor). The storage unit 63 includes a RAM (Random Access Memory) and a ROM (Read Only Memory). The storage unit 63 stores program codes or instructions configured to cause the processor 62 to execute processing. The storage unit 63, that is, the computer-readable medium, includes any available medium accessible by a general-purpose or dedicated computer. The control unit 61 may be configured by a hardware circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The control unit 61, which is a processing circuit, may include one or more processors operating according to a computer program, one or more hardware circuits such as an ASIC or an FPGA, or a combination thereof.

[0025] The forklift 10 includes an auxiliary storage device 64. The auxiliary storage device 64 is a rewritable non-volatile storage device. The auxiliary storage device 64 is, for example, a hard disk drive or a solid state drive.

[0026] The auxiliary storage device 64 stores map data M1 indicating the environment in which the forklift 10 is used. The map data M1 is information regarding the physical structure such as the shape of the objects existing in the environment in which the forklift 10 is used and the size of the environment. In the present embodiment, the map data M1 is data representing the structure of the environment in which the forklift 10 is used in coordinates of a map coordinate system. The map coordinate system is, for example, a two-axis orthogonal coordinate system. The map coordinate system is a coordinate system with an arbitrary point as the origin.

[0027] The control unit 61 estimates the self-position of the forklift 10. The self-position is the coordinates indicating a point of the forklift 10 in the map coordinate system. Although a point of the forklift 10 is arbitrary, for example, it is the central position in the horizontal direction of the forklift 10.

[0028] The estimation of the self-position is performed by collating the detection result of the external sensor 52 with the map data M1. The control unit 61 acquires the point cloud data output by the external sensor 52. The control unit 61 extracts a landmark having the same shape as the landmark obtained from the point cloud data from the map data M1. The control unit 61 recognizes the position of the landmark from the map data M1. The positional relationship between the position of the landmark and the forklift 10 can be grasped from the detection result of the external sensor 52. Therefore, the control unit 61 can estimate the self-position by recognizing the position of the landmark. A landmark is an object having a feature distinguishable by the external sensor 52. A landmark is a physical structure whose position hardly changes. The estimation of the self-position may be performed by combining dead reckoning using an internal sensor with the estimation of the self-position using the external sensor 52. The estimation of the self-position may be performed by combining the estimation of the self-position using the external sensor 52 with the estimation of the self-position using a satellite signal transmitted from a GNSS (Global Navigation Satellite System) satellite.

[0029] <Stacking control> The stacking control performed by the control unit 61 will be described. The stacking control is control for stacking loads on a load placement surface where the loads are placed in the load placement target. The control unit 61 moves toward the load placement target while estimating its own position. The position of the load placement target may be a predetermined position or a position instructed by a higher-level control device. When the control unit 61 moves close to the load placement target and the load placement target is positioned in front of the forklift 10, the stacking control is started.

[0030] As shown in FIG. 4, the load W of the present embodiment includes a pallet P and a load L stacked on the pallet P. The load placement target of the present embodiment is the truck 100. The truck 100 is, for example, a wing truck or a flat-bed truck. The truck 100 includes a loading platform 101 and flaps 103 provided on both sides of the loading platform 101. The upper surface of the loading platform 101 is a load placement surface 102 on which the load W is placed. When the stacking control is performed, at least one flap 103 is open. That is, at least one flap 103 is rotated downward from the load placement surface 102. The control unit 61 starts the stacking control in a state where the open flap 103 is positioned in front of the forklift 10. In the example shown in FIG. 4, the stacking control is started in a state where the flap 103A is positioned in the front. In the following description, the height of the fork 26 is the lift height detected by the lift sensor 51.

[0031] As shown in FIGS. 5 and 6, in step S1, the control unit 61 raises the fork 26. The starting position of the upward movement of the fork 26 is, for example, a predetermined height. The starting position is a position below the loading surface 102. If the height of the fork 26 at the time of step S1 is higher than the starting position of the upward movement, the control unit 61 may lower the fork 26 to position the fork 26 at the starting position of the upward movement. The control unit 61 controls the hydraulic mechanism 42 so that the fork 26 rises at a constant speed while recognizing the height of the fork 26 by the lift sensor 51. The upward movement of the fork 26 by the control unit 61 continues until the height of the fork 26 reaches the end position of the upward movement. The end position of the upward movement is, for example, a predetermined height. The end position of the upward movement is a height higher than the loading surface 102. If there are multiple types of trucks 100 used in the environment where the forklift 10 is operated, the end position of the upward movement may be determined based on the truck 100 with the highest loading surface 102 among the multiple types of trucks 100.

[0032] In step S2, the control unit 61 acquires the distance measured by the distance meter 53 during the upward movement of the fork 26. The control unit 61 acquires the distance from the distance meter 53 at a predetermined time interval while the fork 26 rises from the starting position of the upward movement to the end position of the upward movement. The distance measured by the distance meter 53 is the distance from the distance meter 53 to the object to be loaded.

[0033] As shown in FIGS. 5 and 7, next, in step S3, the control unit 61 obtains the first straight line L1. The first straight line L1 is a straight line obtained from the distances less than the threshold value among the distances acquired from the distance meter 53 during the upward movement of the fork 26. The threshold value is set to determine whether the distance obtained from the distance meter 53 measures the distance to a position lower than the loading surface 102.

[0034] When the fork 26 is raised from a position below the loading surface 102 to a position above the loading surface 102, the distance measured by the distance meter 53 changes significantly with the height of the loading surface 102 as the boundary. At a position below the loading surface 102, the distance meter 53 measures the distance to a member constituting the truck 100 such as the tilt 103A. In contrast, above the loading surface 102, the distance to the member constituting the truck 100 is not measured. Even if the distance to the load W stacked on the loading surface 102 or the opposite tilt 103B is measured, a distance longer than the distance measured by the distance meter 53 below the loading surface 102 is measured. Therefore, the distance measured by the distance meter 53 changes significantly with the height of the loading surface 102 as the boundary. As the threshold value, a value slightly longer than the distance from the distance meter 53 to the opened tilt 103A in the state where the forklift 10 is positioned at the position where the stacking control is started may be set. In addition, when the distance measured by the distance meter 53 is infinite, that is, when there is no place where the laser hits within the measurable distance of the distance meter 53, the distance measured by the distance meter 53 is treated as being equal to or greater than the threshold value.

[0035] The first straight line L1 is, for example, an approximate straight line obtained by regression analysis. The regression analysis is, for example, the least squares method or RANSAC (Random Sample Consensus). Assuming that the position where the distance is measured by the distance meter 53 is P1, the control unit 61 obtains the first straight line L1 from the change in the position P1 in the coordinate system with the distance from the distance meter 53 to P1 as the X-axis and the lift amount or elapsed time of the fork 26 as the Y-axis. When the distance meter 53 is a laser distance meter, the position P1 is the place where the laser hits. It is assumed that the first straight line L1 is calculated using the distance from the distance meter 53 to the tilt 103A. Therefore, when the first straight line L1 is obtained, the first straight line L1 has a shape following the tilt 103A.

[0036] The position P1 where the distance is measured by the distance meter 53 may include a position P11 different from the sway 103A. For example, when the ascending start position is set below the sway 103A, or when there are irregularities or undulations on the loading platform 101, the distance to the position P11 different from the sway 103A may be measured by the distance meter 53. In the example shown in FIG. 7, the distance to the position P11 is measured due to the irregularities existing on the loading platform 101. Thus, among the distances obtained in step S2, the distances less than the threshold value may include outliers that are different from the distance to the sway 103A. When obtaining the first straight line L1, the control unit 61 may obtain the first straight line L1 excluding the outliers. For example, the control unit 61 may obtain the first straight line L1 excluding at least either the distance to the lowest position or the distance to the highest position among the distances less than the threshold value.

[0037] Next, the control unit 61 obtains the second straight line L2 in step S4. The second straight line L2 represents the height at which the distance measured by the distance meter 53 exceeds the threshold value. The control unit 61 sets the height at which the distance measured by the distance meter 53 exceeds the threshold value at the time when the distance obtained in step S2 exceeds the threshold value as the height at which the distance measured by the distance meter 53 exceeds the threshold value. In the example shown in FIG. 7, the height at which the distance meter 53 measures the distance after measuring the distance to the position P11 is the height at which the distance measured by the distance meter 53 exceeds the threshold value. The second straight line L2 is a straight line extending along the X-axis, with the height at which the distance measured by the distance meter 53 exceeds the threshold value as the value of the Y-axis in the coordinate system of the X-axis and Y-axis described above.

[0038] Next, in step S5, the control unit 61 obtains the stacking position SP on the loading surface 102 from the intersection point C of the first straight line L1 and the second straight line L2. The intersection point C of the first straight line L1 and the second straight line L2 is at the end on the forklift 10 side of the loading surface 102, or at a position within a predetermined range from this end when the forklift 10 performs stacking. When the object to be loaded is the truck 100, since the sway 103A is located closer to the forklift 10 side than the loading surface 102, the position of the intersection point C will be closer to the forklift 10 side than the loading surface 102.

[0039] The stacking position SP is, for example, the position in the front-rear direction that becomes the target point of the rear end E1 of the load W. The control unit 61 sets the stacking position SP to the position obtained by adding a predetermined distance d1 to the intersection point C of the first straight line L1 and the second straight line L2. When the object to be placed is the truck 100, it is necessary to avoid contact between the tilting part 103A and the load W placed at the stacking position SP when the tilting part 103A is closed. For this reason, the position obtained by adding the predetermined distance d1 to the intersection point C is set as the stacking position SP. The predetermined distance d1 is a predetermined distance. The predetermined distance d1 is set so that the tilting part 103A and the load W do not come into contact when the tilting part 103A is closed with the rear end E1 of the load W positioned at the stacking position SP. The predetermined distance d1 is added so that the stacking position SP is displaced from the intersection point C in the direction from the forklift 10 toward the truck 100.

[0040] Next, in step S6, the control unit 61 stacks the load W. The control unit 61 adds the distance from the distance meter 53 to the stacking position SP and the distance d3 from the rear end E1 of the load W to the distance meter 53. The distance from the distance meter 53 to the stacking position SP is the distance obtained by adding the distance d2 from the distance meter 53 to the intersection point C and the predetermined distance d1. The control unit 61 sets the distance obtained by summing the predetermined distance d1, the distance d2, and the distance d3 as the forward distance. The distance d3 from the rear end E1 of the load W to the distance meter 53 is predetermined. The distance from the assumed position where the rear end E1 of the load W is located when the load W is loaded on the fork 26 to the distance meter 53 may be predetermined as the distance d3. The forward distance is the distance from the rear end E1 of the load W to the stacking position SP.

[0041] The control unit 61 moves the fork 26 forward by the forward distance. The movement of the fork 26 may be performed using at least one of the forward movement of the forklift 10 and the forward movement of the mast 22 using the reach cylinder 32. When the fork 26 is moved forward by the forward distance, the front-rear direction positions of the rear end E1 of the load W and the loading position SP coincide. In this state, the fork 26 is lowered to place the load W on the load placement surface 102, thereby loading the load W. When moving the forklift 10 forward, the forklift 10 may be moved forward by the forward distance by self-position estimation without using an external sensor 52 such as dead reckoning. When moving the mast 22 forward using the reach cylinder 32, the mast 22 may be moved forward by the forward distance using a reach sensor that detects the reach amount.

[0042] [Operation of this Embodiment] The forklift 10 is provided with an external sensor 52. Since the external sensor 52 detects the position of an object in the coordinates of a three-dimensional coordinate system, when the external sensor 52 is used to detect the loading position SP, the detection accuracy of the loading position SP may decrease. In addition, the external sensor 52 is often arranged at a high place. Since the detection range of the external sensor 52 in the vertical direction is limited, when the external sensor 52 is arranged at a high place, a region near the forklift 10 and relatively below becomes a blind spot. For this reason, when trying to detect the loading position SP using the external sensor 52, it is necessary to detect the loading position SP using the detection result at a position away from the load placement target. As a result, the distance that the forklift 10 travels from the detection of the loading position SP to the loading becomes longer. For this reason, due to the influence of the traveling accuracy, there is a possibility that the difference between the detected loading position SP and the position where the load W is actually loaded becomes large.

[0043] On the other hand, by enabling the attachment position SP to be detected using the one-dimensional distance meter 53, the detection accuracy of the attachment position SP is higher than when the attachment position SP is detected using the external sensor 52. Further, the distance meter 53 is provided so as to move up and down with the fork 26. Therefore, even when the forklift 10 and the object to be placed are close, the distance meter 53 can measure the distance to the object to be placed located in front of the forklift 10. As a result, the distance that the forklift 10 travels from the detection of the attachment position SP to the loading is shortened. It is possible to suppress an increase in the difference between the detected attachment position SP and the position where the load W is actually loaded.

[0044] [Effects of the present embodiment] (1) When the fork 26 is raised in a state where the object to be placed is located in front, the distance meter 53 rises while measuring the distance to the object to be placed. When the height of the distance meter 53 becomes higher than the placement surface 102, the distance measured by the distance meter 53 becomes longer. Therefore, the first straight line L1 obtained from the distance less than the threshold value becomes a straight line following the shape of the portion of the object to be placed that is located below the placement surface 102. Further, the second straight line L2 represents the height of the placement surface 102. Therefore, the attachment position SP can be obtained from the intersection point C of the first straight line L1 and the second straight line L2. Since the attachment position SP can be obtained using the one-dimensional distance meter 53, the detection accuracy of the attachment position SP can be increased.

[0045] (2) The control unit 61 sets the position obtained by adding the predetermined distance d1 to the intersection point C as the attachment position SP. Thereby, when the load W is placed at the attachment position SP, it is possible to suppress the load W from coming into contact with the sway 103A.

[0046] (3) The distance meter 53 is provided at the tip of the fork 26. For example, if the distance meter 53 is provided on the lift bracket 25, there is a risk that the distance to the load W loaded on the fork 26 will be measured. Therefore, when the distance meter 53 is provided on the lift bracket 25, it is necessary to provide the distance meter 53 so that the distance to the load W loaded on the fork 26 is not measured. On the other hand, by providing the distance meter 53 at the tip of the fork 26, the distance meter 53 can be provided so that the distance to the load W is not measured. Therefore, layout constraints are less likely to occur.

[0047] [Modified Example] The embodiment can be implemented with the following modifications. The embodiment and the following modified examples can be implemented in combination with each other as long as they do not technically conflict.

[0048] ○ As shown in FIG. 8, the distance meter 53 may be provided one by one on each of the two forks 26. Let one of the two forks 26 be the first fork 26A and the other be the second fork 26B. The distance meter 53 provided on the first fork 26A is the first distance meter 53A, and the distance meter 53 provided on the second fork 26B is the second distance meter 53B.

[0049] The control unit 61 performs the processes of steps S3 and S4 in the stacking control for each measurement result of the first distance meter 53A and the second distance meter 53B. That is, the control unit 61 obtains the first straight line L1 and the second straight line L2 using the distance obtained from the first distance meter 53A, and also obtains the first straight line L1 and the second straight line L2 using the distance obtained from the second distance meter 53B.

[0050] The control unit 61 obtains intersection points C1 and C2 for each distance measured by each of the two distance meters 53. In the example shown in FIG. 8, the intersection point C1 obtained using the distance acquired from the first distance meter 53A and the intersection point C2 obtained using the distance acquired from the second distance meter 53B can be obtained. The intersection point C1 obtained using the distance acquired from the first distance meter 53A is the intersection point corresponding to the first distance meter 53A. The intersection point C2 obtained using the distance acquired from the second distance meter 53B is the intersection point corresponding to the second distance meter 53B.

[0051] The control unit 61 adopts, as the intersection point C used to obtain the stacking position SP, the one with the longer distance from each of the distance meters 53 to the corresponding intersection points C1 and C2. In the example shown in FIG. 8, the distance from the first distance meter 53A to the intersection point C1 is longer than the distance from the second distance meter 53B to the intersection point C2. Therefore, the intersection point C1 is used to obtain the stacking position SP. Then, the control unit 61 calculates the forward distance using the obtained stacking position SP.

[0052] The control unit 61 may obtain intersection points C1 and C2 for each distance measured by each of the two distance meters 53 and calculate the stacking position SP using the respective intersection points C1 and C2. In this case, the control unit 61 calculates the forward distance using the respective intersection points C1 and C2 and performs the stacking of the load W using the longer one of the forward distances. Even in this case, the control unit 61 adopts, as the intersection point C used to obtain the stacking position SP, the one with the longer distance from each of the two distance meters 53 to the corresponding intersection points C1 and C2.

[0053] As shown in FIG. 8, the forklift 10 may be inclined in the left-right direction with respect to the truck 100. In this case, if the shorter distance from each of the two distance meters 53 to the corresponding intersections C1 and C2 is adopted as the intersection C used to obtain the loading position SP, a part of the load W may be located outside the intersection C. If the object to be loaded is the truck 100, when the tilt 103A is closed, the load W and the tilt 103A may come into contact with each other. On the other hand, by adopting the longer distance from each of the two distance meters 53 to the corresponding intersections C1 and C2 as the intersection C used to obtain the loading position SP, it is possible to suppress a part of the load W from being located outside the intersection C.

[0054] ○ The object to be loaded may be a shelf. In this case, the loading surface 102 is the upper surface of the shelf board. The first straight line L1 is a straight line obtained by the distance to the side surface of the shelf board. The intersection C is the position where the upper surface and the side surface of the shelf board intersect, that is, the edge on the upper surface of the shelf board. When the object to be loaded is a shelf, the intersection C may be used as the loading position SP.

[0055] ○ The forklift 10 may be manually operated. In this case, for example, a display unit may be provided on the forklift 10, and the forward distance may be displayed on the display unit. The control unit 61 may shorten the forward distance displayed on the display unit as the fork 26 approaches the object to be loaded. The operator of the forklift 10 can appropriately load the load W by operating the forklift 10 while recognizing the forward distance displayed on the display unit.

[0056] ○ The distance meter 53 only needs to be provided so as to move up and down together with the fork 26. For example, the distance meter 53 may be provided on the lift bracket 25. Further, a fixing member for fixing the distance meter 53 may be provided on the fork 26 or the lift bracket 25, and the distance meter 53 may be fixed to the fixing member.

[0057] ○ The ascending end position may be determined according to the measurement result of the distance meter 53. When the control unit 61 acquires the distance during the ascending of the fork 26 in step S2, it acquires the height at which the distance measured by the distance meter 53 switches from less than the threshold value to equal to or greater than the threshold value. Then, the height obtained by adding a predetermined height to the said height may be used as the ascending end position. The height when the distance measured by the distance meter 53 becomes equal to or greater than the threshold value is the height of the loading surface 102. The predetermined height may be set so that the load W is at a position higher than the loading surface 102 when stacking.

[0058] ○ The distance meter 53 may be an optical type or an ultrasonic type.

Explanation of Signs

[0059] C... intersection point, L1... first straight line, L2... second straight line, SP... stacking position, W... load, 10... forklift, 26... fork, 53... distance meter, 61... control unit, 100... a truck which is an example of the object to be loaded.

Claims

1. Two forks on which a load is placed, a one-dimensional distance meter provided so as to move up and down together with the forks and measure the distance to an object existing in front, and a control unit, wherein the control unit raises the forks in a state where a load placement target for placing the load is located in front, acquires the distance to the load placement target measured by the distance meter during the raising of the forks, obtains a first straight line from the distances less than a threshold among the distances acquired during the raising of the forks, obtains a second straight line representing a height at which the distance measured by the distance meter exceeds the threshold, and obtains a stacking position on a stacking surface of the load placement target where the load is placed from an intersection point between the first straight line and the second straight line, a forklift.

2. The load placement target is a truck, and the control unit sets a position obtained by adding a predetermined distance to the intersection point as the stacking position, the forklift according to Claim 1.

3. The distance meter is provided at the tip of the fork, the forklift according to Claim 1 or Claim 2.

4. The distance meter is provided on each of the two forks, and the control unit obtains the intersection point for each of the distances measured by each of the two distance meters, and adopts, as the intersection point used to obtain the stacking position, the intersection point for which the distance from each of the two distance meters to the corresponding intersection point is longer, the forklift according to Claim 1 or Claim 2.

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