Cargo handling device

Abstract

To provide a cargo handling device capable of miniaturizing a stopper for preventing a lift bracket from coming off.SOLUTION: A cargo handling device 2 comprises a lift cylinder 7 that raises and lowers the inner mast 4 relative to the outer mast 3, a lift chain 9 that raises and lowers the lift bracket 5 relative to the inner mast 4 in accordance with the extension and contraction of the lift cylinder 7, an inner mast stopper 23 attached to the inner mast 4, a lift bracket stopper 24 attached to the lift bracket 5, a contact detection unit that detects whether the lift bracket stopper 24 has come into contact with the inner mast stopper 23, an unload valve 29 that adjusts the pressure of the hydraulic oil supplied to the lift cylinder 7, and a pressure limiting control unit 32 that controls the unload valve 29 to limit the pressure of the hydraulic oil supplied to the lift cylinder 7 when it is detected that the lift bracket stopper 24 has come into contact with the inner mast stopper 23.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a cargo handling apparatus. [Background technology]

[0002] A known technology for a loading device for a forklift is described in Patent Document 1, for example. The loading device described in Patent Document 1 includes an outer mast, an inner mast that can be raised and lowered relative to the outer mast, a carriage that can be raised and lowered relative to the inner mast and supports forks, a lift cylinder that raises and lowers the inner mast relative to the outer mast, a chain wheel bracket attached to the upper part of the inner mast, a chain wheel attached to the chain wheel bracket, a lift chain that is looped around the chain wheel and has one end connected to a lift bracket attached to the carriage and the other end connected to a fixed part of the outer mast, and a chain anchor bracket fixed to the carriage. When the carriage is raised near the raised end due to the rise of the inner mast, the chain anchor bracket abuts against the chain wheel bracket from below. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-165991 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned conventional technology, when the lift cylinder is raised to its maximum height, the chain anchor bracket abuts against the chain wheel bracket, preventing the lift bracket from slipping off the inner mast. However, when the chain anchor bracket abuts against the chain wheel bracket, the thrust of the lift cylinder is applied to the chain anchor bracket and chain wheel bracket, which act as stoppers. This requires a stopper with high strength that can withstand the thrust of the lift cylinder. This inevitably results in a larger size of the stopper, which reduces productivity and increases costs.

[0005] SUMMARY OF THE INVENTION An object of the present invention is to provide a cargo handling device that can reduce the size of a stopper for preventing a lift bracket from coming off. [Means for solving the problem]

[0006] (1) One aspect of the present invention is a cargo handling device mounted on a forklift, comprising: outer masts; inner masts that can be raised and lowered relative to the outer masts; lift brackets that can be raised and lowered relative to the inner masts; forks attached to the lift brackets; lift cylinders that are driven by hydraulic oil from a hydraulic source and raise and lower the inner masts relative to the outer masts; chain wheels attached to the inner masts; and chain wheels that are connected to the outer masts and the lift brackets and are hung on the chain wheels and raise and lower the lift brackets relative to the inner masts in response to the extension and contraction of the lift cylinders. a first stopper attached to the inner mast; a second stopper attached to the lift bracket and abutting against the first stopper to prevent the lift bracket from slipping off the inner mast when the lift bracket is raised; a contact detection unit that detects whether the second stopper has abutted against the first stopper; a pressure regulation valve that adjusts the pressure of hydraulic oil supplied to the lift cylinder; and a pressure limit control unit that controls the pressure regulation valve to limit the pressure of hydraulic oil supplied to the lift cylinder when the abutment detection unit detects that the second stopper has abutted against the first stopper.

[0007] In this type of cargo handling device, when the lift cylinders extend to raise the inner masts relative to the outer masts, the lift chains raise the lift brackets relative to the inner masts in response to the extension of the lift cylinders. Even if the second stoppers attached to the lift brackets contact the first stoppers attached to the inner masts during the lift brackets' ascent, the pressure of the hydraulic oil supplied to the lift cylinders increases as the lift cylinders continue to extend. Therefore, a system detects whether the second stoppers have contacted the first stoppers. When this is detected, the pressure regulating valve is controlled to limit the pressure of the hydraulic oil supplied to the lift cylinders. This reduces the thrust of the lift cylinders acting on the first and second stoppers, eliminating the need for high-strength first and second stoppers that can withstand the thrust of the lift cylinders. This allows for the miniaturization of the first and second stoppers, which are used to prevent the lift brackets from slipping out.

[0008] (2) In (1) above, the contact detection unit may have a pressure sensor that detects the pressure of the hydraulic oil supplied to the lift cylinder, and may detect that the second stopper has contacted the first stopper when the detection value of the pressure sensor is equal to or greater than a predetermined judgment threshold.

[0009] In this configuration, the existing pressure sensor installed in the forklift is used to detect whether the second stopper has come into contact with the first stopper, eliminating the need for a new sensor, thereby reducing the cost of the sensor.

[0010] (3) In the above (1) or (2), the loading and unloading device may further include a height detection unit that detects the height position of the inner mast, and a judgment unit that determines whether the height position of the inner mast detected by the height detection unit is equal to or greater than a predetermined lower threshold, and the abutment detection unit may detect whether the second stopper has abutted against the first stopper when the judgment unit determines that the height position of the inner mast is equal to or greater than the lower threshold.

[0011] With this configuration, when it is determined that the height position of the inner mast is equal to or higher than the lower limit threshold, it is detected whether the second stopper has come into contact with the first stopper. Therefore, even if, for example, when lifting a load placed on the ground with the forks and the load gets caught on another load at a low position, causing the pressure of the hydraulic oil supplied to the lift cylinder to rise and exceed the determination threshold, the process of detecting whether the second stopper has come into contact with the first stopper is not executed. This prevents the second stopper from being erroneously detected as coming into contact with the first stopper when the load gets caught.

[0012] (4) In the above (1) or (2), the loading and unloading device may further include a height detection unit that detects the height position of the inner mast, and a judgment unit that determines whether the height position of the inner mast detected by the height detection unit is equal to or lower than a predetermined upper threshold value, and the abutment detection unit may detect whether the second stopper has abutted against the first stopper when the judgment unit determines that the height position of the inner mast is equal to or lower than the upper threshold value.

[0013] With this configuration, when it is determined that the height position of the inner mast is equal to or lower than the upper threshold, it is detected whether the second stopper has come into contact with the first stopper. Therefore, if the length of the lift chain from the outer mast connector to the lift bracket connector causes the lift cylinder to reach its extension limit before the second stopper comes into contact with the first stopper, the process of detecting whether the second stopper has come into contact with the first stopper is not executed. This prevents the second stopper from being erroneously detected as having come into contact with the first stopper when the lift cylinder reaches its extension limit.

[0014] (5) In (1) above, the contact detection unit may have a strain sensor that detects strain occurring in the first stopper or the second stopper, and may detect that the second stopper has contacted the first stopper when the strain sensor detects that strain of a specified amount or more has occurred in the first stopper or the second stopper.

[0015] When the second stopper abuts against the first stopper, strain is generated in the first stopper and the second stopper, and therefore, by detecting the strain generated in the first stopper or the second stopper, it is possible to directly and accurately detect whether the second stopper has abutted against the first stopper.

[0016] (6) In the above (5), the strain sensor may be attached to the first stopper.

[0017] In this configuration, the strain sensor is attached to the first stopper fixed to the inner mast. The range of motion of the inner mast is narrower than the range of motion of the lift bracket. Therefore, the strain sensor is less likely to break. [Effects of the Invention]

[0018] According to the present invention, it is possible to reduce the size of the stopper for preventing the lift bracket from coming off. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic side view showing a cargo handling device of a forklift according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of the cargo handling apparatus shown in FIG. [Figure 3] FIG. 2 is a top perspective view of the loading device shown in FIG. [Figure 4] 10 is a schematic side view showing the lifting operation of the lift bracket. FIG. [Figure 5] FIG. 10 is a schematic side view showing how the lift bracket comes off due to the lifting operation of the lift bracket. [Figure 6] FIG. 2 is a diagram showing a hydraulic circuit for driving a lift cylinder. [Figure 7] 1 is a block diagram showing a control system of a cargo handling apparatus according to a first embodiment of the present invention. FIG. [Figure 8] 8 is a flowchart showing a procedure of a control process executed by a controller shown in FIG. 7. [Figure 9] FIG. 10 is a schematic side view showing a state in which the lift bracket stopper comes into contact with the inner mast stopper due to the extension operation of the lift cylinder. [Figure 10] 10 is a graph showing how the operating pressure of the lift cylinder changes over time due to the extension operation of the lift cylinder in comparison with a conventional example. [Figure 11] FIG. 6 is a block diagram showing a control system of a cargo handling apparatus according to a second embodiment of the present invention. [Figure 12] FIG. 10 is a schematic side view showing a contact determination range for determining whether the lift bracket stopper contacts the inner mast stopper. [Figure 13] 12 is a flowchart showing the procedure of a control process executed by a controller shown in FIG. 11. [Figure 14] 10 is a graph showing how the operating pressure of the lift cylinder changes over time due to the extension operation of the lift cylinder when it is erroneously determined that the lift bracket stopper has come into contact with the inner mast stopper. [Figure 15] FIG. 10 is a block diagram showing a control system of a cargo handling apparatus according to a third embodiment of the present invention. [Figure 16] FIG. 10 is a perspective view showing a state in which a strain gauge is attached to an inner mast stopper. [Figure 17] 16 is a flowchart showing the procedure of a control process executed by a controller shown in FIG. 15. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements are designated by the same reference numerals, and redundant description will be omitted.

[0021] Fig. 1 is a schematic side view showing a load handling device of a forklift according to an embodiment of the present invention. In Fig. 1, the forklift 1 is equipped with a load handling device 2 arranged in front of a traveling device (not shown). The load handling device 2 is a device that handles loads.

[0022] The cargo handling device 2 includes an outer mast 3, an inner mast 4, a lift bracket 5, a pair of left and right forks 6, a pair of left and right lift cylinders 7, a pair of left and right chain wheels 8, and a pair of left and right lift chains 9. Note that only one each of the fork 6, lift cylinder 7, chain wheel 8, and lift chain 9 is shown in FIG.

[0023] As shown in FIG. 2, the outer mast 3 has a pair of left and right outer rails 11 extending in the vertical direction, and an outer upper beam 12 connecting the upper ends of these outer rails 11 together.

[0024] As shown in Fig. 2, the inner masts 4 are arranged inside the outer masts 3 in the left-right direction (width direction). The inner masts 4 can be raised and lowered relative to the outer masts 3. The inner masts 4 have a pair of left and right inner rails 13 extending in the vertical direction, a plurality of left and right rollers 14 arranged on the left and right outer sides of the inner rails 13 and rolling along the outer rails 11, and an inner upper beam 15 connecting the upper ends of the pair of left and right inner rails 13.

[0025] As shown in Figures 2 and 3, the lift bracket 5 is disposed on the front side of the inner mast 4. The lift bracket 5 is movable up and down relative to the inner mast 4. The lift bracket 5 has a bracket main body 16, a pair of left and right side plates 17 disposed on the rear side of the bracket main body 16, and a plurality of left and right rollers 18 disposed outside the side plates 17 in the left-right direction and rolling along the inner rail 13. The side plates 17 are fixed to both the left and right sides of the bracket main body 16 and extend in the vertical direction.

[0026] As shown in Figures 2 and 3, a pair of left and right forks 6 are attached to the lift bracket 5. Specifically, the forks 6 are detachably attached to both the left and right sides of the bracket body 16. The forks 6 hold luggage.

[0027] A pair of left and right lift cylinders 7 are arranged between the outer masts 3 and inner masts 4. The tips (upper ends) of the piston rods 7a of the lift cylinders 7 are connected to supports 19 attached to the tops of the inner masts 4. The lift cylinders 7 are hydraulic cylinders that are driven by hydraulic oil from a hydraulic pump 25 (see Figure 6) and raise and lower the inner masts 4 relative to the outer masts 3.

[0028] A pair of left and right chain wheels 8 are attached to the upper parts of the inner masts 4. Specifically, the chain wheels 8 are attached to the upper parts of the inner rails 13 in the left-right direction.

[0029] A pair of left and right lift chains 9 are connected to the outer masts 3 and lift brackets 5, and are also looped around the chain wheels 8. One end of the lift chains 9 is connected to a connecting portion 21 of the outer masts 3. The other end of the lift chains 9 is connected to a connecting portion 22 of the lift brackets 5. The connecting portion 21 is provided, for example, on each outer rail 11. The connecting portion 22 is provided, for example, on each side plate 17. The lift chains 9 raise and lower the lift brackets 5 relative to the inner masts 4 in response to the extension and retraction of the lift cylinders 7.

[0030] At the connecting portion 21, the fixing position of one end portion of the lift chain 9 can be adjusted by an anchor bolt (not shown). This makes it possible to adjust the length of the lift chain 9 from the connecting portion 21 to the connecting portion 22.

[0031] As shown in FIG. 4, when the lift cylinder 7 is extended, the inner mast 4 rises relative to the outer mast 3, and the lift bracket 5 rises relative to the inner mast 4 via the lift chain 9 hung on the chain wheel 8.

[0032] However, if the fixing position of the lift chain 9 is adjusted so that the length of the lift chain 9 from the connecting part 21 of the outer mast 3 to the connecting part 22 of the lift bracket 5 is shortened, the following problem occurs: That is, as shown in Figure 5, when the lift cylinder 7 is extended to the extension end (highest lift end), the roller 18 of the lift bracket 5 comes off the inner rail 13 of the inner mast 4, and the lift bracket 5 comes off the inner mast 4.

[0033] Therefore, the cargo handling device 2 further includes an inner mast stopper 23 and a lift bracket stopper 24, as shown in FIGS.

[0034] The inner mast stopper 23 is a first stopper attached to the inner mast 4. The inner mast stopper 23 has, for example, a rectangular parallelepiped shape. The inner mast stopper 23 is made of, for example, metal. The inner mast stopper 23 is fixed to the inner upper beam 15 by welding. In other words, a weld 23a is provided between the inner upper beam 15 and the inner mast stopper 23.

[0035] The lift bracket stopper 24 is a second stopper attached to the lift bracket 5. The lift bracket stopper 24 has, for example, a rectangular parallelepiped shape that extends in the vertical direction. The lift bracket stopper 24 is made of the same material as the inner mast stopper 23. The lift bracket stopper 24 is fixed to the side plate 17 of the lift bracket 5 by welding. In other words, a weld 24a is provided between the side plate 17 and the lift bracket stopper 24.

[0036] The lift bracket stopper 24 abuts against the inner mast stopper 23 to prevent the lift bracket 5 from slipping out of the inner mast 4 when the lift bracket 5 is raised. The lift bracket stopper 24 cooperates with the inner mast stopper 23 to prevent the lift bracket 5 from slipping out.

[0037] As shown in FIG. 6, the cargo handling device 2 also includes a hydraulic pump 25 and a control valve 26.

[0038] The hydraulic pump 25 is a hydraulic pressure source that supplies hydraulic oil to the lift cylinder 7. The hydraulic pump 25 draws hydraulic oil stored in a tank 27 and supplies it to the bottom chamber 7b of the lift cylinder 7.

[0039] The control valve 26 has a lift directional control valve 28 and an unloading valve 29 .

[0040] The lift direction switching valve 28 is disposed between the hydraulic pump 25 and tank 27 and the lift cylinder 7. The lift direction switching valve 28 is a valve that switches the direction in which hydraulic oil flows between the hydraulic pump 25 and tank 27 and the bottom chamber 7b of the lift cylinder 7.

[0041] The unloading valve 29 is disposed between the hydraulic pump 25 and the tank 27. The unloading valve 29 is a valve that opens when the pressure of the hydraulic oil supplied from the hydraulic pump 25 to the lift cylinder 7 (hereinafter referred to as the working pressure of the lift cylinder 7) reaches or exceeds a set pressure. The unloading valve 29 is a pressure regulating valve that adjusts the working pressure of the lift cylinder 7.

[0042] For example, a solenoid-operated relief valve is used as the unloading valve 29. The unloading valve 29 opens when the operating pressure of the lift cylinder 7 reaches a preset relief pressure, and also opens when a valve-opening control signal is input from a controller 30, which will be described later.

[0043] 7 is a block diagram showing a control system of the cargo handling apparatus according to the first embodiment of the present invention. In FIG. 7, the forklift 1 further includes a pressure sensor 35 and a controller 30.

[0044] 6, the pressure sensor 35 is a sensor that detects the working pressure of the lift cylinder 7. The pressure sensor 35 detects the pressure in the bottom chamber 7b of the lift cylinder 7 as the working pressure of the lift cylinder 7.

[0045] The controller 30 is configured with a CPU, RAM, ROM, an input / output interface, etc. The controller 30 has a contact determination unit 31 and a pressure restriction control unit 32.

[0046] The abutment determination unit 31 determines whether the lift bracket stopper 24 has abutted against the inner mast stopper 23 based on the detection value of the pressure sensor 35. The abutment determination unit 31 works in cooperation with the pressure sensor 35 to form a contact detection unit that detects whether the lift bracket stopper 24 has abutted against the inner mast stopper 23. The abutment determination unit 31 determines that the lift bracket stopper 24 has abutted against the inner mast stopper 23 when the detection value of the pressure sensor 35 is equal to or greater than a predetermined determination threshold value.

[0047] The pressure limiting control section 32 controls the unloading valve 29 to limit the operating pressure of the lift cylinder 7 when the abutment determining section 31 determines that the lift bracket stopper 24 has abutted against the inner mast stopper 23 .

[0048] Figure 8 is a flowchart showing the procedure of the control process executed by the controller 30. This process is executed when the lift cylinder 7 is raised using the lift operation lever (not shown). When the lift cylinder 7 is raised, hydraulic oil from the hydraulic pump 25 is supplied to the bottom chamber 7b of the lift cylinder 7 through the lift directional control valve 28, thereby extending the lift cylinder 7 (see Figure 9).

[0049] In Figure 8, the controller 30 first acquires the detection value of the pressure sensor 35 (step S101). Then, based on the detection value of the pressure sensor 35, the controller 30 determines whether the operating pressure of the lift cylinder 7 is equal to or greater than the determination threshold value S (step S102). The determination threshold value S is a pressure lower than the relief pressure of the unloading valve 29 (see Figure 10(b)). The determination threshold value S is determined in advance through experiments or the like. If the controller 30 determines that the operating pressure of the lift cylinder 7 is not equal to or greater than the determination threshold value S, the controller 30 executes the above-described step S101 again.

[0050] When the controller 30 determines that the operating pressure of the lift cylinder 7 is equal to or greater than the determination threshold value S, it determines that the lift bracket stopper 24 and the inner mast stopper 23 have come into contact with each other (step S103).Then, the controller 30 outputs a valve opening control signal to the unloading valve 29 to open the unloading valve 29 (step S104), and ends this process.

[0051] Here, the contact determination unit 31 executes steps S101 to S103, and the pressure limitation control unit 32 executes step S104.

[0052] In the cargo handling apparatus 2 as described above, when the lift cylinder 7 is extended, the inner mast 4 rises relative to the outer mast 3, and the lift bracket 5 rises relative to the inner mast 4 via the lift chain 9, thereby raising the fork 6, as described above.

[0053] If the length of the lift chain 9 from the connecting part 21 of the outer mast 3 to the connecting part 22 of the lift bracket 5 is adjusted to be shorter than the normal specified length, when the lift cylinder 7 is extended, the lift bracket stopper 24 will come into contact with the inner mast stopper 23 before the lift cylinder 7 reaches the extension end, as shown in Figure 9. Normally, when the lift cylinder 7 reaches the extension end, there is almost no space left in the rod chamber 7c of the lift cylinder 7, so the lift cylinder 7 will no longer extend.

[0054] However, as shown in Figure 10(a), if the lift bracket stopper 24 comes into contact with the inner mast stopper 23 (see point A in the figure) before the lift cylinder 7 reaches the extension end, the lift cylinder 7 will continue to try to extend. As a result, the operating pressure of the lift cylinder 7 will continue to rise until it reaches the relief pressure R of the unloading valve 29.

[0055] Therefore, because the thrust of the lift cylinder 7 is applied to the inner mast stopper 23 and the lift bracket stopper 24, the inner mast stopper 23 and the lift bracket stopper 24 must be sized to withstand the thrust of the lift cylinder 7. If the sizes of the inner mast stopper 23 and the lift bracket stopper 24 are increased, the welding length of the inner mast stopper 23 and the lift bracket stopper 24 will increase, reducing productivity. Furthermore, if the sizes of the inner mast stopper 23 and the lift bracket stopper 24 are increased, the material costs of the inner mast stopper 23 and the lift bracket stopper 24 will also increase, resulting in higher costs.

[0056] To address this issue, in this embodiment, as shown in Figure 10(b), when the operating pressure of the lift cylinder 7 reaches the judgment threshold value S, it is determined that the lift bracket stopper 24 has come into contact with the inner mast stopper 23, and the unloading valve 29 opens. Therefore, the operating pressure of the lift cylinder 7 is limited because the hydraulic oil from the hydraulic pump 25 is relieved to the tank 27 through the unloading valve 29.

[0057] As described above, in this embodiment, when the lift cylinder 7 performs an extension operation to raise the inner mast 4 relative to the outer mast 3, the lift chain 9 raises the lift bracket 5 relative to the inner mast 4 in response to the extension operation of the lift cylinder 7. Even if the lift bracket stopper 24 attached to the lift bracket 5 comes into contact with the inner mast stopper 23 attached to the inner mast 4 during the lift bracket 5's ascent, if the extension operation of the lift cylinder 7 continues, the operating pressure of the lift cylinder 7 will increase. Therefore, whether the lift bracket stopper 24 has come into contact with the inner mast stopper 23 is detected. Then, when it is detected that the lift bracket stopper 24 has come into contact with the inner mast stopper 23, the unload valve 29 is controlled to limit the operating pressure of the lift cylinder 7. Therefore, the thrust of the lift cylinder 7 applied to the inner mast stopper 23 and the lift bracket stopper 24 is reduced, eliminating the need to use high-strength inner mast stoppers 23 and lift bracket stoppers 24 that can withstand the thrust of the lift cylinder 7. This makes it possible to reduce the size of the inner mast stopper 23 and lift bracket stopper 24, which are stoppers that prevent the lift bracket 5 from slipping out.

[0058] As a result, productivity can be improved because the welding length of the inner mast stopper 23 and the lift bracket stopper 24 is shortened. Also, costs for the inner mast stopper 23 and the lift bracket stopper 24 can be reduced, leading to cost reductions.

[0059] Furthermore, this embodiment has a pressure sensor 35 that detects the operating pressure of the lift cylinder 7, and when the detected value of the pressure sensor 35 is equal to or greater than the judgment threshold value, it is detected that the lift bracket stopper 24 has come into contact with the inner mast stopper 23. In this way, the existing pressure sensor 35 mounted on the forklift 1 is used to detect whether the lift bracket stopper 24 has come into contact with the inner mast stopper 23, so there is no need to prepare a new sensor separately. This makes it possible to reduce the cost of the sensor.

[0060] 11 is a block diagram showing a control system of a cargo handling apparatus according to a second embodiment of the present invention. In FIG. 11, cargo handling apparatus 2A of this embodiment includes unloading valve 29, pressure sensor 35, height sensor 36, and controller 30A.

[0061] The height sensor 36 is a height detection unit that detects the height position of the inner mast 4. As shown in Figure 12, the height sensor 36 detects the height position of the inner mast 4 relative to the ground G as the height. The height sensor 36 is attached to the top of the outer mast 3.

[0062] As shown in Figure 12, the height sensor 36 is, for example, a reel-type encoder having a reel 36a that winds up a height sensor wire 37. One end of the height sensor wire 37 is connected to a connection part 38 at the lower end of the outer mast 3. The other end of the height sensor wire 37 is connected to a connection part 39 at the upper end of the inner mast 4. The height sensor 36 detects the height position of the inner mast 4 based on the position of the height sensor wire 37 on the reel 36a.

[0063] The controller 30A includes a determination region determination unit 33, a contact determination unit 31A, and the pressure restriction control unit 32 described above.

[0064] The judgment area judgment unit 33 constitutes a judgment unit that judges whether the height position of the inner mast 4 detected by the height sensor 36 is equal to or higher than a predetermined lower threshold value, and also judges whether the height position of the inner mast 4 detected by the height sensor 36 is equal to or lower than a predetermined upper threshold value.

[0065] The abutment determination unit 31A detects whether the lift bracket stopper 24 has abutted against the inner mast stopper 23 when the determination area determination unit 33 determines that the height position of the inner mast 4 is equal to or higher than the lower threshold. The abutment determination unit 31A also detects whether the lift bracket stopper 24 has abutted against the inner mast stopper 23 when the determination area determination unit 33 determines that the height position of the inner mast 4 is equal to or lower than the upper threshold.

[0066] FIG. 13 is a flowchart showing the procedure of the control process executed by the controller 30A, and corresponds to FIG.

[0067] 13, the controller 30A first obtains the detection value of the height sensor 36 (step S111). Then, based on the detection value of the height sensor 36, the controller 30A determines whether the height position of the inner mast 4 is within the contact determination range P (step S112). The contact determination range P is equal to or greater than a lower threshold value S1 and equal to or less than an upper threshold value S2 (see FIG. 12). The lower threshold value S1 is lower than the upper threshold value S2. The lower threshold value S1 and the upper threshold value S2 are determined in advance through experiments or the like.

[0068] When the controller 30A determines that the height position of the inner mast 4 is within the abutment determination range P, it executes steps S101 to S104 as in the first embodiment. When the controller 30A determines that the height position of the inner mast 4 is not within the abutment determination range P, it does not execute steps S101 to S104.

[0069] Here, the determination region determination unit 33 executes steps S111 and S112. The contact determination unit 31A executes steps S101 to S103. The pressure limitation control unit 32 executes step S104.

[0070] For example, when a pallet (not shown) placed on the ground G is lifted by the forks 6, the lift cylinder 7 is extended. At this time, as shown in Figure 14, if an abnormality occurs such as the pallet held by the forks 6 getting caught on an adjacent load or pallet (see B in the figure), the operating pressure of the lift cylinder 7 temporarily rises and exceeds the judgment threshold value S, resulting in an erroneous judgment that the lift bracket stopper 24 has come into contact with the inner mast stopper 23.

[0071] Furthermore, if the length of the lift chain 9 from the connecting part 21 of the outer mast 3 to the connecting part 22 of the lift bracket 5 is adjusted to the normal specified length, the lift cylinder 7 will reach the extension end before the lift bracket stopper 24 comes into contact with the inner mast stopper 23. In this case, as shown in Figure 14, even if the lift cylinder 7 reaches the extension end (see C in the figure), if the extension operation of the lift cylinder 7 continues, the operating pressure of the lift cylinder 7 will increase and exceed the judgment threshold value S, and it will be erroneously determined that the lift bracket stopper 24 has come into contact with the inner mast stopper 23.

[0072] However, in this embodiment, when the height position of the inner mast 4 is lower than the lower threshold value S1, no judgment is made as to whether the inner mast stopper 23 and the lift bracket stopper 24 have come into contact with each other. Therefore, by setting the lower threshold value S1 to a height position where no abnormalities such as snagging of the pallet or cargo will occur, even if the operating pressure of the lift cylinder 7 temporarily rises and exceeds the judgment threshold value S due to an abnormality such as snagging, it will not be erroneously judged that the lift bracket stopper 24 has come into contact with the inner mast stopper 23.

[0073] Furthermore, when the height position of the inner mast 4 is higher than the upper limit threshold S2, no determination is made as to whether the inner mast stopper 23 and the lift bracket stopper 24 have come into contact with each other. Therefore, by setting the upper limit threshold S2 at a height position lower than the extension end of the lift cylinder 7, even if the operating pressure of the lift cylinder 7 increases and exceeds the determination threshold S due to the lift cylinder 7 reaching the extension end, it will not be erroneously determined that the lift bracket stopper 24 has come into contact with the inner mast stopper 23.

[0074] As described above, according to this embodiment, when it is determined that the height position of the inner mast 4 is equal to or higher than the lower threshold value S1, it is detected whether the lift bracket stopper 24 has come into contact with the inner mast stopper 23. For this reason, even if, for example, an object placed on the ground G is lifted by the forks 6 and the object gets caught on another object at a low position, causing the operating pressure of the lift cylinder 7 to rise and exceed the determination threshold value S, the process of detecting whether the lift bracket stopper 24 has come into contact with the inner mast stopper 23 is not executed. This prevents the lift bracket stopper 24 from being erroneously detected as coming into contact with the inner mast stopper 23 when the object gets caught on another object, etc.

[0075] Furthermore, in this embodiment, when it is determined that the height position of the inner mast 4 is equal to or lower than the upper limit threshold value S2, it is detected whether the lift bracket stopper 24 has come into contact with the inner mast stopper 23. Therefore, if the length of the lift chain 9 from the connecting part 21 of the outer mast 3 to the connecting part 22 of the lift bracket 5 causes the lift cylinder 7 to reach the extension end before the lift bracket stopper 24 comes into contact with the inner mast stopper 23, the process of detecting whether the lift bracket stopper 24 has come into contact with the inner mast stopper 23 is not executed. This prevents the lift cylinder 7 from erroneously detecting that the lift bracket stopper 24 has come into contact with the inner mast stopper 23 when it reaches the extension end.

[0076] In this embodiment, whether the lift bracket stopper 24 has come into contact with the inner mast stopper 23 is detected when it is determined that the height position of the inner mast 4 is within the contact determination range P, which is equal to or greater than the lower threshold value S1 and equal to or less than the upper threshold value S2. However, the present invention is not limited to such a configuration.

[0077] For example, if the length of the lift chain 9 from the connecting part 21 of the outer mast 3 to the connecting part 22 of the lift bracket 5 is such that the lift cylinder 7 does not reach the end of extension before the lift bracket stopper 24 abuts against the inner mast stopper 23, it is possible to detect whether the lift bracket stopper 24 has abutted against the inner mast stopper 23 only when it is determined that the height position of the inner mast 4 is equal to or higher than the lower threshold value S1.

[0078] In addition, when cargo handling is carried out under conditions where there is no risk of the cargo getting caught, it is possible to detect whether the lift bracket stopper 24 has come into contact with the inner mast stopper 23 only when it is determined that the height position of the inner mast 4 is below the upper limit threshold value S2.

[0079] 15 is a block diagram showing a control system of a cargo handling apparatus according to a third embodiment of the present invention. In FIG. 15, a cargo handling apparatus 2B of this embodiment includes the unloading valve 29, a strain gauge 40, and a controller 30B.

[0080] As shown in Figure 16, the strain gauge 40 is attached to the inner mast stopper 23. The strain gauge 40 is attached to the upper surface 23b of the inner mast stopper 23. The strain gauge 40 is a strain sensor that detects strain generated in the inner mast stopper 23. Specifically, the strain gauge 40 detects the amount of strain generated in the inner mast stopper 23.

[0081] The controller 30B includes a contact determination unit 31B and the pressure restriction control unit 32 described above.

[0082] The contact determination unit 31B determines whether the lift bracket stopper 24 has contacted the inner mast stopper 23 based on the detection value of the strain gauge 40. The contact determination unit 31B cooperates with the strain gauge 40 to form a contact detection unit that detects whether the lift bracket stopper 24 has contacted the inner mast stopper 23.

[0083] FIG. 17 is a flowchart showing the procedure of the control process executed by the controller 30B, and corresponds to FIG.

[0084] 17, the controller 30B first acquires the detection value of the strain gauge 40 (step S121). Then, based on the detection value of the strain gauge 40, the controller 30B determines whether or not a strain equal to or greater than a specified amount has occurred in the inner mast stopper 23 (step S122). At this time, the controller 30B may determine whether or not a strain equal to or greater than a specified amount has continuously occurred in the inner mast stopper 23 for a certain period of time.

[0085] If the controller 30B determines that the distortion of the inner mast stopper 23 is not equal to or greater than the specified amount, it executes the above-mentioned step S121 again. If the controller 30B determines that the distortion of the inner mast stopper 23 is equal to or greater than the specified amount, it determines that the inner mast stopper 23 and the lift bracket stopper 24 have come into contact with each other (step S123). Then, the controller 30B controls the unload valve 29 to open (step S104).

[0086] Here, the contact determination unit 31B executes steps S121 to S123. The pressure limitation control unit 32 executes step S104.

[0087] In this embodiment, a strain gauge 40 is provided to detect strain generated in the inner mast stopper 23, and when the strain gauge 40 detects that strain equal to or greater than a specified amount has occurred in the inner mast stopper 23, it is detected that the lift bracket stopper 24 has come into contact with the inner mast stopper 23. When the lift bracket stopper 24 comes into contact with the inner mast stopper 23, strain is generated in the inner mast stopper 23 and the lift bracket stopper 24. Therefore, by detecting the strain generated in the inner mast stopper 23, it is possible to directly and accurately detect whether the lift bracket stopper 24 has come into contact with the inner mast stopper 23.

[0088] In this embodiment, the strain gauges 40 are attached to the inner mast stoppers 23 fixed to the inner masts 4. The range of movement of the inner masts 4 is narrower than the range of movement of the lift brackets 5. Therefore, breakage of the strain gauges 40 is unlikely to occur.

[0089] The strain gauge 40 may be attached to the lift bracket stopper 24. When the lift bracket stopper 24 comes into contact with the inner mast stopper 23, strain is generated in the lift bracket stopper 24. Therefore, in this case as well, it is possible to directly and accurately detect whether the lift bracket stopper 24 has come into contact with the inner mast stopper 23. [Explanation of symbols]

[0090] 1...forklift, 2, 2A, 2B...load handling device, 3...outer mast, 4...inner mast, 5...lift bracket, 6...fork, 7...lift cylinder, 8...chain wheel, 9...lift chain, 23...inner mast stopper (first stopper), 24...lift bracket stopper (second stopper), 25...hydraulic pump (hydraulic source), 29...unload valve (pressure adjustment valve), 31, 31A, 31B...contact determination unit (contact detection unit), 32...pressure limit control unit, 33...determination range determination unit (determination unit), 35...pressure sensor (contact detection unit), 36...lift height sensor (lift height detection unit), 40...strain gauge (strain sensor, contact detection unit), S...determination threshold, S1...lower limit threshold, S2...upper limit threshold.

Claims

1. A loading device mounted on a forklift, Outer must and an inner mast that can be raised and lowered relative to the outer mast; a lift bracket that can be raised and lowered relative to the inner mast; a fork attached to the lift bracket; a lift cylinder driven by hydraulic oil from a hydraulic source to raise and lower the inner mast relative to the outer mast; a chain wheel attached to the inner mast; a lift chain connected to the outer mast and the lift bracket and looped around the chain wheel, for raising and lowering the lift bracket relative to the inner mast in response to the extension and contraction of the lift cylinder; a first stopper attached to the inner mast; a second stopper attached to the lift bracket and abutting against the first stopper to prevent the lift bracket from slipping out of the inner mast when the lift bracket is raised; a contact detection unit that detects whether the second stopper contacts the first stopper; a pressure regulating valve that adjusts the pressure of the hydraulic oil supplied to the lift cylinder; a pressure limiting control unit that controls the pressure regulating valve to limit the pressure of hydraulic oil supplied to the lift cylinder when the contact detection unit detects that the second stopper has contacted the first stopper.

2. 2. The loading and unloading device according to claim 1, wherein the contact detection unit has a pressure sensor that detects the pressure of hydraulic oil supplied to the lift cylinder, and detects that the second stopper has contacted the first stopper when the detected value of the pressure sensor is equal to or greater than a predetermined judgment threshold value.

3. a height detection unit for detecting the height position of the inner mast; a determination unit that determines whether the height position of the inner mast detected by the height detection unit is equal to or greater than a predetermined lower limit threshold, 2. The loading and unloading apparatus according to claim 1, wherein the contact detection unit detects whether the second stopper has contacted the first stopper when the determination unit determines that the height position of the inner mast is equal to or higher than the lower limit threshold.

4. a height detection unit for detecting the height position of the inner mast; a determination unit that determines whether the height position of the inner mast detected by the height detection unit is equal to or lower than a predetermined upper threshold value, 2. The loading and unloading apparatus according to claim 1, wherein the contact detection unit detects whether the second stopper has contacted the first stopper when the determination unit determines that the height position of the inner mast is equal to or lower than the upper threshold value.

5. 2. The loading and unloading device according to claim 1, wherein the contact detection unit has a strain sensor that detects strain generated in the first stopper or the second stopper, and detects that the second stopper has contacted the first stopper when the strain sensor detects that strain of a specified amount or more has occurred in the first stopper or the second stopper.

6. 6. The cargo handling apparatus according to claim 5, wherein the strain sensor is attached to the first stopper.

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