crane

Abstract

To provide a crane that is able to more surely restrict an increase in an electrical current value output from a power supply device, caused by generation of an inrush electrical current.SOLUTION: In a crane 10 including a converter 21, an inverter 22, and an electric motor 23, an electrical current value of DC power output from the converter 21 is equal to or larger than a rated electrical current value Ir of the converter 21, and is limited to a limited electrical current value Ib smaller than a peak electric current value Ip caused by an inrush electrical current generated during power running drive of the electric motor 23; and a power storage device 24 is provided, which is connected in parallel with an inverter 22 with respect to the converter 21 during a time period including a time during which an electrical current value of the AC power supplied from at least the inverter 22 to the electric motor 23 is larger than the limited electrical current value Ib.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a crane, and more particularly to a crane that suppresses an increase in the current value output from a power supply device due to the occurrence of an inrush current. [Background technology]

[0002] The numerous cranes that handle goods at logistics facilities such as container terminals are powered by electric motors that use power supplied from a common power supply device (e.g., a substation) to perform operations such as container handling and their own travel. The allowable current value of the power supply device is set on the assumption that all of the equipment and devices in the logistics facility (including the electric motors of each of the numerous cranes) are driven by their rated current. In other words, as long as each of the electric motors of each of the numerous cranes is driven by its rated current, the current value output from the power supply device will not exceed the allowable current value.

[0003] However, each of the multiple cranes operates independently, and there are cases where the timing of inrush currents (starting currents) overlaps immediately after the start of power drive of each of the multiple cranes' electric motors. The peak current value of the inrush current is greater than the rated current value, and if the number of overlapping timings of inrush currents becomes excessive, the current value output from the power supply device temporarily exceeds the allowable current value, causing the power supply device to shut down. As a result, cargo handling operations throughout the logistics facility come to a halt.

[0004] A yard crane has been proposed in which the allowable power that the power receiving unit can pass is limited to be less than the power supplied to the cargo handling motor when the cargo handling motor is under maximum load, and even when the power receiving unit is connected to a power supply unit, if the power supplied to the cargo handling motor and the traveling motor is insufficient, power is supplied from a charging / discharging unit (see Patent Document 1).In the crane proposed in Patent Document 1, when the weight of the container is greater than a predetermined weight, two types of power, power output from the power receiving unit and power output from the charging / discharging unit, are supplied to the hoisting motor and trolley drive motor, and when the weight of the container is less than the predetermined weight, only the power output from the power receiving unit is supplied to those motors.

[0005] The above-mentioned inrush current occurs immediately after the electric motor starts powering, regardless of the weight of the container or the load on the electric motor. Therefore, in the proposed crane, even if an inrush current occurs in the electric motor when the weight of the container is less than a predetermined weight, power is not supplied to the charging / discharging unit. As such, since the proposed crane does not specifically target inrush current, measures to prevent the power supply device from stopping due to overlapping inrush currents in multiple cranes require consideration specific to inrush currents. Therefore, there is room for improvement in more reliably suppressing the increase in the current value of AC power output from the power supply device due to the occurrence of inrush current. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-137749 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a crane that can more reliably suppress an increase in the current value of AC power output from a power supply device due to the occurrence of an inrush current. [Means for solving the problem]

[0008] The crane of the present invention that achieves the above-mentioned object comprises a converter that converts AC power from a power supply device into DC power, an inverter that converts the DC power output from the converter into AC power, and an electric motor that is driven by the AC power output from the inverter, wherein the current value of the DC power output from the converter is limited to a limited current value that is equal to or greater than the rated current value of the converter and is smaller than the peak current value due to an inrush current that occurs when the electric motor is driven in power running, and the crane further comprises a power storage device that is connected in parallel with the inverter for the converter during at least a time that includes a time when the current value of the AC power supplied from the inverter to the electric motor is greater than the limited current value. [Effects of the Invention]

[0009] According to the present invention, the current value of the DC power output from the converter is limited. If an inrush current occurs during power running of the electric motor, the DC power supplied from the converter to the inverter will be insufficient. However, this shortage is compensated for by the power storage device. In other words, a power shortage does not occur when an inrush current occurs, and an increase in the current value output from the power supply device due to the inrush current can be more reliably suppressed. This prevents the current value of the AC power output from the power supply device from exceeding a predetermined value, and maintains the current value below the predetermined value. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an explanatory diagram illustrating an embodiment of a crane. [Figure 2] 10 is an explanatory diagram illustrating an example of fluctuations in current value over time in an electric motor driven in power running mode. FIG. [Figure 3] FIG. 2 is an explanatory diagram illustrating the power system of FIG. 1. [Figure 4] FIG. 4 is an explanatory diagram illustrating an example of fluctuations in current value over time in a converter. [Figure 5]FIG. 3 is an explanatory diagram illustrating an example of the correlation between the charge capacity and the voltage value in the power storage device. [Figure 6] FIG. 2 is an explanatory diagram illustrating an example of the flow of electric power in the power system when the electric motor is regeneratively driven. [Figure 7] FIG. 2 is an explanatory diagram illustrating an example of the flow of power in a power system when an inrush current occurs during power running of an electric motor. [Figure 8] 10 is an explanatory diagram illustrating an example of the flow of power in the power system when an inrush current does not occur during power running of the electric motor; FIG. [Figure 9] FIG. 10 is an explanatory diagram illustrating a modified example of the crane embodiment. [Figure 10] FIG. 10 is an explanatory diagram illustrating the power system of FIG. 9. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, a crane according to the present invention will be described based on an embodiment shown in the drawings.

[0012] The embodiment of crane 10 (10a, 10b) illustrated in Figure 1 is a crane used for cargo handling in a logistics facility 1. This crane 10 is equipped with a power system 20 that takes measures against the occurrence of inrush current, as will be described later, in order to maintain the current value of AC power output from a power supply device 7 that is shared by various devices and equipment (including crane 10) in the logistics facility 1 below a predetermined value.

[0013] The logistics facility 1 represents a container terminal. The logistics facility 1 may be any of various known logistics facilities, such as a container terminal or warehouse facility that serves as a logistics hub. The logistics facility 1 also includes a manufacturing facility that produces and ships various types of steel plates. In the logistics facility 1, cargo 3 transported by multiple transportation devices 2 is temporarily stored in a storage area 4, and the stored cargo 3 is transported to the outside by the multiple transportation devices 2. The transportation devices 2 are various known vehicles that transport cargo 3, and examples of such vehicles in a container terminal include ships and vehicles that transport containers as cargo 3. The storage area 4 is an area where cargo 3 is temporarily stored. The storage area 4 in a container terminal corresponds to a storage lane where multiple containers are stored as cargo 3. The multiple cranes 10 may be any of various known cranes that handle cargo 3 at the logistics facility 1. The multiple cranes 10 in a container terminal include transfer cranes (yard cranes) 10a and gantry cranes 10b. In addition to the numerous cranes 10 as cargo handling equipment, the container terminal also has an on-site chassis 5 for transporting containers.

[0014] The crane 10 comprises a girder 11, a trolley 12, a hoisting device 13, a leg structure 14, a traveling device 15, a control device 16, and a power system 20 shown in Figure 3, which will be described later. The girder 11 supports the hoisting device 13 by suspending it via the trolley 12. The trolley 12 is configured to be able to move laterally along the girder 11 in the direction in which the girder 11 extends. The hoisting device 13 is configured to be able to move up and down in the vertical direction by a wire suspended from the trolley 12. The leg structure 14 supports the girder 11 from above. At least two traveling devices 15 are arranged spaced apart in the direction in which the girder 11 extends in a plan view, and are attached to the lower end of the leg structure 14. The traveling devices 15 enable the crane 10 to travel in a direction perpendicular to the direction in which the girder 11 extends.

[0015] The control device 16 controls each operation of the crane 10 (the traverse operation of the trolley 12, the lifting operation of the hoisting device 13, and the traveling operation of the crane 10 by the traveling device 15). Various known computers can be used for the control device 16. The control device 16 is not limited to one computer, but can also be configured with multiple computers (for example, a combination of a personal computer and a programmable logic controller (PLC)).

[0016] The power system 20 supplies power to operate each device (trolley 12, hoisting device 13, traveling device 15) based on commands from the control device 16. Details of this power system 20 will be described later.

[0017] The management system 6 receives and stores various data and processes the data. The management system 6 may use various known computers. The management system 6 manages the cargo 3 at the logistics facility 1 and instructs the control devices 16 of the numerous cranes 10 to handle the cargo 3. Specifically, the management system 6 creates cargo handling data indicating the cargo 3 to be handled by the cranes 10 based on the scheduled arrival and departure dates of the transportation equipment 2 and the number of cargo 3 entering and leaving the storage area 4. The management system 6 then transmits the respective cargo handling data to the control devices 16 of the numerous cranes 10, and the control devices 16 instruct the numerous cranes 10 to handle the cargo 3. In a container terminal, the management system 6 has multiple programs, including a program for managing the handling of cargo 3 onto ships by the transportation equipment 2, a program for managing the cargo 3 in the storage area 4, and a program for transmitting the cargo handling data as work instructions to the numerous cranes 10 and the on-site chassis 5. The management system 6 is not limited to a single computer, but may be configured with multiple computers, each dedicated for a different program.

[0018] The power supply device 7 supplies AC power to each of the multiple cranes 10 and is a common device for the multiple cranes 10. A known private power plant or extra-high voltage substation may be used as the power supply device 7. In one example of the logistics facility 1, an extra-high voltage substation is used as the power supply device 7. AC power is supplied from the power supply device 7 to each of the multiple cranes 10 using a power supply device 8 shown by the dashed dotted line in the figure. The power supply device 8 may be any of a variety of known power supply devices, such as a combination of a contact wire or bus bar and a current collector, or a combination of a cable reel and a power cable.

[0019] FIG. 2 shows an example of fluctuations in the current value of AC power supplied from the inverter 22 to the electric motor 23 over time during an operating period ΔT from the start to the end of a predetermined operation for powering a predetermined electric motor 23 of the power system 20. The current value of the AC power supplied from the inverter 22 to the electric motor 23 (the current value of the DC power output from the converter 21) increases to a peak current value Ip, which is greater than the rated current, immediately after the electric motor 23 starts powering. The period ΔTp during which the inrush current occurs occurs at the beginning of the operating period ΔT. The rated current value Ir, the peak current value Ip, and the period ΔTp are each determined in advance based on the specifications of the inverter 22 and the electric motor 23 of the power system 20. The peak current value Ip is, for example, approximately 1.7 to 2.2 times the rated current value Ir. The period ΔTp is, for example, approximately 1.5 to 2.5 seconds.

[0020] The allowable current value Ia of the power supply device 7 is set based on the overall power consumption of the logistics facility 1. For example, in a container terminal, in addition to the numerous cranes 10 and management system 6, a wide variety of devices and equipment consume power, such as lighting equipment, power sources for reefer containers in the storage area 4, and gate devices. The allowable current value Ia of the power supply device 7 is set assuming that all of these devices and equipment are driven at rated current. The allowable current value Ia is also set assuming that the electric motors 23 of the numerous cranes 10 are powered at rated current value Ir. Specifically, the allowable current value Ia is set to a value greater than the current value output from the power supply device 7 assuming that all of the devices and equipment in the logistics facility 1 are driven at rated current.

[0021] As mentioned above, the peak current value Ip due to inrush current is greater than the rated current value Ir. Therefore, as a countermeasure against inrush current, it is possible to set the allowable current value Ia of the power supply device 7 based on the peak current value Ip, but this would increase the cost required for the power supply device 7. Therefore, in order to operate the logistics facility 1 stably while reducing the cost required for the power supply device 7, a countermeasure against inrush current is necessary.

[0022] The power system 20 illustrated in FIG. 3 has been designed to counter the inrush current. Specifically, in the power system 20, the current value of the DC power output from the converter 21 is limited to a limited current value Ib. The power system 20 also includes a power storage device 24 connected in parallel with the inverter 22 for a period of time that includes a period when the current value of the AC power supplied from the inverter 22 to the electric motor 23 is greater than the limited current value Ib. Therefore, in the power system 20, when an inrush current occurs in the electric motor 23 and the AC power supplied from the inverter 22 to the electric motor 23 is insufficient due to the limitation imposed by the converter 21, the shortage is compensated for by the DC power stored in the power storage device 24. In this way, the power system 20 is designed to counter the inrush current by incorporating both a configuration that limits the current value of the DC power output from the converter 21 and a configuration that includes the power storage device 24 that compensates for the power shortage due to the limitation. The power system 20 will be described in detail below.

[0023] The power system 20 includes one converter 21, multiple inverters 22 (22a-22d), multiple electric motors 23 (23a-23d), and one power storage device 24. The number of converters 21 is not limited to one, and may be multiple depending on the amount of power supplied to the multiple inverters 22. The multiple inverters 22 and multiple electric motors 23 include a traverse inverter 22a and a traverse motor 23a that move the trolley 12 traversely, a lift inverter 22b and a lift motor 23b that raise and lower the hoist 13, a travel inverter 22c and a travel motor 23c that move the traveling device 15, and a vibration suppression inverter 22d and a vibration suppression motor 23d that suppress vibration of the hoist 13. The number and types of inverters 22 and electric motors 23 vary depending on the specifications of the crane 10. For example, in gantry crane 10b, lift inverter 22b and lift motor 23b serve to raise and lower the boom (part of girder 11) extending from leg structure 14. Note that power system 20 may also have a separate inverter and electric motor for raising and lowering the boom. Also, depending on the mechanism for preventing the swing of hoisting device 13, anti-sway inverter 22d and anti-sway motor 23d may not be provided. The number of power storage devices 24 is not limited to one, and may be multiple depending on the charging capacity.

[0024] Converter 21 converts AC power output from power supply device 7 into DC power and supplies the DC power to each device of crane 10, such as each inverter 22 and control device 16, via common line 25. Converter 21 receives AC power from power supply device 7 via power feeder 8, high-voltage panel 27, and high-voltage transformer 28. Converter 21 generates DC power according to various voltages used by crane 10. Examples of various voltages include 385V and 400V.

[0025] Various known AC-DC converters can be used as the converter 21. A bidirectional (charge-discharge) converter is preferably used as the converter 21. By using a bidirectional converter as the converter 21, it becomes possible to supply surplus power generated by regenerative driving of the electric motor 23 to other cranes 10 via the power supply device 8. If a bidirectional converter is not used as the converter 21, the power system 20 is preferably provided with a resistor that converts surplus power generated by regenerative driving of the electric motor 23 into heat and dissipates the heat.

[0026] Converter 21 is electrically connected to control device 16 via signal line 26. The current value of the DC power output from converter 21 is limited to a limited current value Ib by control device 16. Note that if a converter control device capable of controlling the current value of the DC power output from converter 21 is provided separately from control device 16, and the current value can be limited to the limited current value Ib by this converter control device, then converter 21 and control device 16 do not need to be connected via signal line 26. The converter control device may be included in converter 21, or may be provided in crane 10 as a separate unit from converter 21.

[0027] FIG. 4 shows an example of fluctuations in the current value of the converter 21 over time during an operating period ΔT from the start to the end of a predetermined operation for powering a predetermined electric motor 23. The current value of the DC power output from the converter 21 (the current value of the DC power supplied to the inverter 22) is limited to a limit current value Ib. The limit current value Ib is equal to or greater than the rated current value Ir and smaller than the peak current value Ip of the inrush current generated when the electric motor 23 is powered. The limit current value Ib can be set to any value as long as it is equal to or greater than the rated current value Ir and smaller than the peak current value Ip. However, a value between 1.0 and 1.5 times (including 1.0 and 1.5 times) the rated current value Ir is desirable. If the limit current value Ib is smaller than the rated current value Ir, the output current value of the converter 21 will always be smaller than the rated current value Ir, which will interfere with the operation of each device. Furthermore, if the limit current value Ib is 1.5 times or more the rated current value Ic, the effectiveness of the inrush current countermeasure will be reduced. The limit current value Ib can also be set based on the peak current value Ip instead of the rated current value Ic. For example, the limit current value Ib can be set to a value that is 0.5 times or more and 0.8 times or less (including 0.5 times and 0.8 times) the peak current value Ip. However, when setting the peak current value Ip as the reference, it is necessary to ensure that the output current value does not fall below the rated current value Ir.

[0028] The inverter 22 converts the DC power output from the converter 21 into AC power and supplies the converted AC power to the electric motor 23. The electric motor 23 is driven by the AC power supplied from the inverter 22. The rotational power obtained by driving the electric motor 23 is used to power the operation of each device (the traverse movement of the trolley 12, the lifting and lowering movement of the hoisting device 13, and the traveling movement of the crane 10 by the traveling device 15).

[0029] Various known inverters and electric motors can be used for the inverter 22 and the electric motor 23, respectively. The inverter 22 is electrically connected to the control device 16 via a signal line 26. The inverter 22 adjusts the amount of power supplied to the electric motor 23 in response to commands from the control device 16, thereby adjusting the rotational speed of the electric motor 23. The electric motor 23 operates various devices by being powered and regeneratively driven by the inverter 22. For example, during the traverse movement of the trolley 12 and the travel movement of the crane 10 by the traveling device 15, the electric motor 23 is powered to perform acceleration and constant-speed movement, and is regeneratively driven to perform deceleration. Furthermore, during the lifting and lowering movement of the hoisting device 13, the electric motor 23 is powered to perform the lifting movement (hoisting up movement) and is regeneratively driven to perform the lowering movement (hoisting down movement). When the electric motor 23 is powered, power supplied from the inverter 22 is consumed, and when it is regeneratively driven, power is generated by the regenerative drive of the electric motor 23.

[0030] The power storage device 24 can be any of various known power storage devices, such as a secondary battery (storage battery) or a power storage device (capacitor). Examples of secondary batteries include lithium ion batteries and nickel-metal hydride batteries. Examples of power storage devices include electric double layer capacitors. The power storage device 24 is not particularly limited, and can be selected appropriately taking into consideration the advantages and disadvantages of each.

[0031] The power storage devices 24 are connected in parallel with the respective inverters 22 to the converter 21 at least during a time period including a time period during which the current value of the AC power supplied from the inverters 22 to the electric motors 23 is greater than the limit current value Ib. The power storage devices 24 only need to be connected to the common line 25 during that time period, and may be connected to the common line 25 via a switch or a branch, such as a switch, controlled by the control device 16.

[0032] It is more desirable that the power storage devices 24 be always connected in parallel with the respective inverters 22 to the converter 21. Always connected means that the power storage devices 24 are connected to the common line 25 without using a switch or other open / close device or a branch. A connection method in which the power storage devices 24 are always connected in parallel with the inverters 22 to the converter 21 is the so-called float charging method. Connecting the power storage devices 24 using this connection method makes it possible to automate the charging and discharging of the power storage devices 24. This eliminates the need for complex data processing and control processing, which are required in trickle charging methods to counter inrush currents, and allows for simpler countermeasures against inrush currents. Furthermore, when the state of charge (SOC) of the power storage devices 24 becomes low, they can be automatically charged.

[0033] The power storage device 24 has a power storage control device 24a. A known battery management system (BMS) can be used as the power storage control device 24a. The power storage control device 24a monitors the voltage, current, temperature, and state of charge (SOC) of each cell as the state of the power storage device 24. The power storage control device 24a also adjusts the charging and discharging of each cell inside the power storage device 24. Depending on the power storage device 24, there may be cases where the charging and discharging does not need to be adjusted by the power storage control device 24a.

[0034] FIG. 5 shows an example of the correlation between the state of charge (SOC) and voltage value (natural potential, open circuit voltage: OCV) of the power storage device 24. The voltage value of the power storage device 24 increases as the charge capacity increases, and decreases as the charge capacity decreases. A lower limit voltage value Va is set for the voltage value, at which the electric motor 23 no longer operates as instructed by the control device 16. The lower limit voltage value Va is lower than the rated voltage value Vc of the converter 21. The lower limit voltage value Va is, for example, 85% or more of the rated voltage value Vc. This lower limit voltage value Va differs depending on the specifications of the inverter 22 and the electric motor 23. The charge capacity at which the voltage value becomes the lower limit voltage value Va is set as a lower limit charge capacity Sa of the power storage device 24. If full discharge (complete discharge) is set to 0% and full charge (complete charge) is set to 100%, the lower limit charge capacity Sa is, for example, approximately 20%.

[0035] If the charge capacity of the power storage device 24 is equal to or greater than the lower limit charge capacity Sa, an inrush current occurs during power running of the electric motor 23. If the power output from the converter 21 is insufficient to supply power to the inverter 22, the power storage device 24 discharges DC power to make up for the shortfall. Furthermore, if the charge capacity is less than the lower limit charge capacity Sa, the power storage device 24 is charged with DC power output from the converter 21 in accordance with the difference between the rated voltage value Vc of the converter 21 and its own voltage value. At this time, the power storage device 24 is charged to an upper limit charge capacity Sb at which the voltage value becomes the rated current value Vc. Additionally, if the charge capacity is not fully charged, the power storage device 24 is charged with power generated during regenerative operation of the electric motor 23. At this time, the power storage device 24 can be charged to a full charge (100%) exceeding the upper limit charge capacity Sc. When the charge capacity is fully charged, charging is stopped to prevent overcharging. To prevent overcharging, charging may be stopped when the charge capacity reaches a value less than full charge. The charge capacity just before full charge at which charging is stopped is, for example, about 80%.

[0036] When the converter 21 and the control device 16 are connected via a signal line 26, the control device 16 not only transmits commands regarding the rotation speed of the electric motor 23 to the inverter 22, but also controls the limiting of the current value of the DC power output from the converter 21 and the lifting of the limit. Specifically, the control device 16 is connected to the power storage control device 24a via the signal line 26 and constantly monitors the charge capacity of the power storage device 24. The control device 16 compares the charge capacity with a lower limit charge capacity Sa and executes data processing to impose a limit on the current value of the DC power output from the converter 21 if the charge capacity is equal to or greater than the lower limit charge capacity Sa. On the other hand, the control device 16 executes data processing to lift the limit on the current value of the DC power output from the converter 21 if the charge capacity is less than the lower limit charge capacity Sa. By executing such data processing, it is possible to avoid a situation in which, when an inrush current occurs in the electric motor 23, the power storage device 24 is unable to make up for the shortfall and a drive delay of the electric motor 23 occurs. Therefore, by connecting the converter 21 and the control device 16 via the signal line 26, it becomes possible to control the limit on the output current value of the converter 21 and the release of that limit, which is advantageous in eliminating the effect of the limit on the loading and unloading operation of the crane 10.

[0037] The various cargo handling operations, namely the traveling operation of the crane 10 by the traveling device 15, the lateral movement of the trolley 12, and the lifting and lowering operation of the hoisting device 13, may be performed simultaneously. For example, the lifting and lowering operation of the hoisting device 13 may be started while the trolley 12 is moving laterally, or the lateral movement of the trolley 12 may be started while the hoisting device 13 is moving laterally. When multiple cargo handling operations are performed simultaneously on a single crane 10, it is advisable to adjust each cargo handling operation using the control device 16 so that the electric motor 23 is regeneratively driven during one cargo handling operation and the electric motor 23 is powered during the other cargo handling operation. In this case, a power shortage caused by an inrush current in the electric motor 23, which is powered by limiting the current value of the DC power output from the converter 21, can be covered by the power generated by the regeneratively driven electric motor 23.

[0038] In the logistics facility 1, each of the numerous cranes 10 performs loading and unloading operations at its own timing. Therefore, the control device 16 may release the restriction on the current value of the DC power output from the converter 21 based on the timing of each loading and unloading operation. Specifically, the timing of each loading and unloading operation is aggregated in the management system 6, and based on the aggregated timing, the management system 6 identifies a timing at which the inrush current generation periods ΔTp of the cranes 10 do not overlap. The identified timing is then transmitted from the management system 6 to each of the control devices 16. Next, at the timing received, the control device 16 releases the restriction on the current value of the DC power output from the converter 21 or varies the value of the limited current value Ib.

[0039] In this way, by connecting the control device 16 and the converter 21 via the signal line 26, the control device 16 can limit the output current value of the converter 21, lift the limit, or vary the value of the limit current Ib, depending on the charge capacity of the power storage device 24 and the power supply status of the power supply device 7. When the control device 16 determines whether to impose or lift the limit, it is advisable to give top priority to ensuring that the current value of the power supply device 7 does not exceed the allowable current value Ia. The impact of the limit on the loading and unloading operations of the crane 10 is limited to a reduction in the loading and unloading efficiency of a single crane 10, but a shutdown of the power supply device 7 will stop all loading and unloading operations at the logistics facility 1, significantly reducing loading and unloading efficiency. Therefore, giving top priority to ensuring that the current value of the power supply device 7 does not exceed the allowable current value Ia is advantageous in avoiding a situation in which the power supply device 7 shuts down.

[0040] Next, a description will be given of the operation of the embodiment of the crane 10. Specifically, the operation of the crane 10 will be described in terms of a series of operations in which the hoisting tool 13 moves downward to grab the load 3, and then the hoisting tool 13 moves upward to lift the load 3.

[0041] 6 shows the flow of power during the lowering operation of the hoisting tool 13. When the hoisting tool 13 is lowered, the lifting motor 23b is driven in a regenerative manner. The power generated by this regenerative driving is supplied from the hoisting tool inverter 22b to the converter 21 and the power storage device 24 via the common line 25. The power supplied to the converter 21 is consumed via the power supply device 8 for power running operations of other crane 10 (the traverse operation of the trolley 12, the lifting operation of the hoisting tool 13, and the traveling operation of the crane 10 by the traveling device 15). The power supplied to the power storage device 24 is stored in the power storage device 24 except when the charge capacity of the power storage device 24 is not fully charged.

[0042] 7 shows the flow of power while an inrush current is occurring in the lift motor 23b immediately after the lifting operation of the hoist 13 begins. During the lifting operation of the hoist 13, the lift motor 23b is powered. The power consumed by the lift motor 23b due to this powering operation (power supplied to the hoist inverter 22b) is mainly covered by the power supplied from the converter 21. However, because the current value of the DC power output from the converter 21 is limited to the limited current value Ib, when an inrush current occurs immediately after the lift motor 23b begins to drive, the DC power supplied from the converter 21 alone is insufficient. At this time, the DC power stored in the power storage device 24 is supplied to the lift inverter 22b via the common line 25 to make up for the shortage.

[0043] 8 shows the flow of power after the inrush current generated in the lifting motor 23b subsides during the lifting operation of the hoisting tool 13. When the charge capacity of the power storage device 24 falls below the lower limit charge capacity Sa by compensating for the shortage caused by the inrush current generated in the lifting motor 23b, the power supplied from the converter 21 is stored in the power storage device 24. In this way, by charging the power storage device 24 using the float charging method, it is possible to avoid a situation in which the charge capacity is insufficient and the shortage caused by the inrush current during the next powering operation cannot be compensated for.

[0044] As described above, according to this embodiment, the current value of the DC power output from the converter 21 is limited. If an inrush current occurs when the electric motor 23 is powered, the power supplied from the converter 21 to the inverter 22 will be insufficient. However, this insufficiency is compensated for by the power storage device 24. In other words, a power shortage will not occur when an inrush current occurs, and an increase in the current value output from the power supply device 7 due to the occurrence of an inrush current can be more reliably suppressed. This prevents the current value output by the power supply device 7 from exceeding the allowable current value Ia, and the current value can be maintained below the allowable current value Ia. As a result, this is advantageous in avoiding a situation in which the power supply device 7 is stopped, and contributes to improving loading and unloading efficiency by ensuring stable loading and unloading at the logistics facility 1.

[0045] Furthermore, according to this embodiment, inverter 22 and power storage device 24 are always connected in parallel to converter 21, so that power storage device 24 automatically compensates for any shortage of power supplied to inverter 22 that occurs due to restrictions on the output current value of converter 21. Furthermore, power storage device 24, whose charge capacity has become low, can automatically charge the output power of converter 21. As described above, this embodiment has a relatively simple configuration, but is able to maintain the output current value of power supply device 7 below allowable current value Ia by taking measures against inrush current.

[0046] Next, a first modified example of the embodiment of the crane 10A will be described.

[0047] Each of the cranes 10A illustrated in Figure 9 is equipped with an independent power supply device 30. It is not necessary for all of the cranes 10A in the logistics facility 1 to be equipped with a power supply device 30. For example, depending on the logistics facility 1, each of the transfer cranes 10a may be equipped with an independent power supply device 30, and each of the gantry cranes 10b may be supplied with power from a common power supply device 7.

[0048] The power system 20A illustrated in FIG. 10 differs from the power system 20 described above in that the power supply source is a power supply device 30. The power supply device 30 includes an internal combustion engine 31 that uses hydrogen fuel and a generator 32 that rotates using the power of the internal combustion engine 31. Various known engines that use hydrogen fuel can be used as the internal combustion engine 31. Various known generators can be used as the generator 32. Since the current value of the DC power output from the converter 21 is limited to the limited current value Ib, the current value of the AC power output from the generator 32 is also limited to the limited current value Ib. Accordingly, the internal combustion engine 31 can operate at a substantially constant rotational speed without needing to significantly increase its rotational speed. It is desirable to set the power supply device 30 so that the fuel efficiency of the internal combustion engine 31 is maximized when the current value of the AC power output from the generator 32 is at the rated current value Ir. For example, the fuel efficiency can be adjusted by adjusting the specifications of the internal combustion engine 31 and the generator 32, the speed ratio between the rotation speed of the internal combustion engine 31 and the rotation speed of the generator 32, and the like.

[0049] According to the first modification, the current value of the DC power output from the converter 21 is limited to the limited current value Ib, which is smaller than the peak current value Ip, and therefore the current value of the AC power output from the power supply device 30 can be prevented from exceeding the limited current value Ib. In other words, the current value of the AC power output from the generator 32 is maintained below the limited current value Ib, thereby suppressing a significant increase in the rotation speed of the internal combustion engine 31. This allows the internal combustion engine 31 to operate at a rotation speed that is advantageous for fuel efficiency, which is advantageous for improving fuel efficiency.

[0050] Immediately after the internal combustion engine 31 starts operating, the amount of power generated by the generator 32 may not reach the desired amount of power. Therefore, the power stored in the power storage device 24 can also be used during the time until the power generated by the generator 32 stabilizes. This is advantageous in shortening the time required to start the crane 10.

[0051] Although the embodiments of the present invention have been described above, the crane of the present invention is not limited to the specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention.

[0052] The control device 16 may adjust the charging and discharging of the power storage device 24 via the power storage control device 24a. The control device 16 controls the cargo handling operations of the crane 10 (the traverse operation of the trolley 12, the lifting and lowering operation of the hoisting device 13, and the traveling operation of the crane 10 using the traveling device 15). In other words, the control device 16 can roughly predict the power balance and the timing of the occurrence of inrush current during a cargo handling cycle. Therefore, the control device 16 may control the charging and discharging of the power storage device 24 based on the predicted power balance and the timing of the occurrence of inrush current. For example, when the charge capacity of the power storage device 24 falls below the lower limit charge capacity Sa and charging of the power storage device 24 is started, the control device 16 controls the end of the charging based on the power balance and the timing of the occurrence of inrush current. In this way, by charging and discharging the power storage device 24 based on the cargo handling cycle of the crane 10 and the timing of the occurrence of inrush current, it is possible to avoid a situation in which the power storage device 24 is unable to take measures against the inrush current or is unable to charge. [Explanation of symbols]

[0053] 7 Power supply device 8 Power Supply Device 10 Crane 16 Control device 20 Power System 21 Converter 22 Inverter 23 Electric motor 24 Energy storage device 25 Common Line 26 Signal line

Claims

1. A crane including a converter that converts AC power from a power supply device into DC power, an inverter that converts the DC power output from the converter into AC power, and an electric motor that is driven by the AC power output from the inverter, a current value of the DC power output from the converter is limited to a limited current value that is equal to or greater than a rated current value of the converter and is smaller than a peak current value due to an inrush current generated when the electric motor is driven in power running mode, a power storage device connected in parallel with the inverter to the converter at least during a time including a time during which a current value of AC power supplied from the inverter to the electric motor is greater than the limited current value.

2. The crane according to claim 1 , wherein the power storage device is always connected in parallel with the inverter with respect to the converter.

3. The crane according to claim 1, further comprising a control device connected to the converter via a signal line and executing data processing to limit the current value of the DC power output from the converter to the limited current value.

4. The crane according to claim 3, wherein the control device executes data processing to monitor a charge capacity of the power storage device, and when the charge capacity is equal to or greater than a preset lower limit charge capacity, limit a current value of the DC power output from the converter to the limited current value, and when the charge capacity is less than the lower limit charge capacity, release the limit on the current value.

5. The crane according to claim 1, wherein the limit current value is a value that is 1.0 times or more and 1.5 times or less the rated current value of the converter.

6. 2. The crane according to claim 1, wherein the power supply device is shared by a large number of cranes operated in a logistics facility, and AC power is supplied from the power supply device to the converter via a power feeding device.

7. 2. The crane according to claim 1, wherein the power supply device comprises an internal combustion engine that uses hydrogen fuel and a generator that is rotated by the power of the internal combustion engine.

Images