Carrier

Abstract

To provide a carrier that can suppress, even when a power supply failure due to electric outage or the like occurs, the time and effort for recovery operation after the power supply failure is resolved.SOLUTION: A carrier for carrying an article includes: a holding device for holding the article; a lifting device for lifting and lowering the holding device; a controller 5; and a power supply unit 6 for receiving power supply from the outside and supplying the power to at least the lifting device. The lifting device includes: a lifting drive mechanism 40 for liftably driving the holding device; and a restriction mechanism 41 for mechanically restricting a lifting operation of the holding device by the lifting drive mechanism 40. The controller 5 includes a voltage monitoring section 51 for monitoring an objective voltage as a required lower-limit voltage that is a lower-limit voltage required for the lifting drive mechanism 40 to maintain a position of the holding device in a lifting direction, the objective voltage being a voltage supplied from the power supply unit 6 to the lifting drive mechanism 40. The controller 5 performs a preliminary restriction operation to activate the restriction mechanism 41 when the objective voltage becomes equal to or less than a determination threshold value set at a value lower than a voltage of the power supply unit 6 during a normal operation and higher than the required lower-limit voltage.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a transport vehicle for transporting articles. [Background technology]

[0002] An example of such a carrier vehicle is disclosed in the following Patent Document 1. In the following description of this background art, the reference symbols and names in Patent Document 1 will be cited in parentheses.

[0003] The ceiling transport vehicle (1) of Patent Document 1 includes a support mechanism (23) that suspends and supports the transported object (6), and a lifting operation mechanism (24) that raises and lowers the support mechanism (23). The lifting operation mechanism (24) includes a winding body (28) that winds a take-up belt (24a) whose tip end is connected to the support mechanism (23), and a lifting motor (29) that rotates the winding body (28). The lifting motor (29) rotates the winding body (28) forward and backward under the control of a motor driver to wind and unwind the take-up belt (24a), thereby lifting and lowering the support mechanism (23) relative to the traveling section (16).

[0004] In other words, the lifting operation mechanism (24) is configured to lift the transported object 6 supported by the support mechanism (23) to the support height by winding up the winding belt (24a) to raise the pair of transported object support parts 32 to the raised height, and to lower the transported object (6) supported by the support mechanism (23) to the transfer height by unwinding the winding belt (24a) to lower the pair of transported object support parts 32 to the lowered height. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-94263 A Summary of the Invention [Problem to be solved by the invention]

[0006] Here, while the overhead transport vehicle (1) is traveling, the torque of the lifting motor (29) may be used to control the support mechanism (23) and the transported object (6) to be maintained at the support height. In such a case, if a power outage or other power supply abnormality occurs, the torque of the lifting motor (29) cannot be maintained, and the take-up belt may be unwound, causing the support mechanism (23) to descend and the transported object (6) to fall. To prevent this, it may be possible to provide a brake to the lifting motor or the lifting operation mechanism (24).

[0007] However, because the brake is activated after a power supply abnormality due to a power outage or the like occurs, the support mechanism (23) and the transported object (6) are lowered to a certain extent. Therefore, when the power supply abnormality due to a power outage or the like is resolved, the support mechanism (23) needs to be returned to its original height, which increases the amount of work required for the restoration work.

[0008] It is therefore desirable to realize a transport vehicle that, even if a power supply abnormality occurs due to a power outage or the like, can minimize the effort required for recovery work after the current supply abnormality is resolved. [Means for solving the problem]

[0009] In view of the above, the characteristics and configuration of the transport vehicle are as follows: A transport vehicle for transporting an item, A holding device for holding the article; A lifting device that lifts and lowers the holding device; A control device; a power supply unit that receives power from an external source and supplies power to at least the lifting device; the lifting device includes a lifting drive mechanism that drives the holding device to lift and lower, and a restraining mechanism that mechanically restrains the lifting and lowering operation of the holding device by the lifting drive mechanism, a voltage supplied from the power supply unit to the lifting drive mechanism is defined as a target voltage, and a lower limit voltage required for the lifting drive mechanism to maintain the position of the holding device in the lifting direction is defined as a required lower limit voltage; The control device is equipped with a voltage monitoring unit that monitors the target voltage, and when the target voltage falls below a judgment threshold value that is set to a value lower than the voltage during normal operation of the power supply unit and higher than the required lower limit voltage, performs a preliminary restraint operation to activate the restraint mechanism.

[0010] With this configuration, even if the voltage supplied to the lifting drive mechanism drops due to a power outage or a malfunction of the power supply unit, the restraint mechanism can mechanically restrain the lifting and lowering movement of the holding device before the voltage drop renders the lifting drive mechanism unable to maintain the position of the holding device in the lifting and lowering direction. Therefore, even if a power outage or a malfunction of the power supply unit occurs, the holding device is prevented from descending unintentionally. Furthermore, in cases where the recovery process for the transport vehicle requires restoring the position of the holding device in the lifting direction, the effort required for the recovery process can be reduced. [Brief description of the drawings]

[0011] [Figure 1] Plan view of the goods transport facility [Diagram 2] Diagram showing transfer operation [Diagram 3] Front view of the transport vehicle [Figure 4] Block diagram showing the control configuration of the transport vehicle [Diagram 5] FIG. 11 is a block diagram showing a control configuration of a transport vehicle according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] 1. First embodiment A first embodiment of a transportation vehicle 1 will be described with reference to the drawings. The transport vehicle 1 is configured to travel along a travel path 10 and transport a container 8 having a predetermined shape. Below, an embodiment of the transport vehicle 1 will be described with reference to the drawings, taking as an example a case where the transport vehicle 1, which receives a contactless supply of power from a power supply line 12 arranged along the travel path 10, is applied to an article transport facility 100.

[0013] As shown in FIG. 1, the item transport equipment 100 includes a specified travel path 10, a transport vehicle 1 that travels along the travel path 10 to transport a container 8, and a plurality of transfer target locations 13 provided along the travel path 10.

[0014] The article transport facility 100 also includes a power supply system having a power supply line 12 and a power supply device (not shown) connected to the power supply line 12 to supply AC current to the power supply line 12, and supplies driving power to the transport vehicle 1 using wireless power supply technology. The power supply line 12 is disposed along the travel path 10, and is disposed on both sides of the power receiving device 60 in the path width direction perpendicular to the path direction that is the direction along the travel path 10. Note that it is preferable to provide a power supply system with multiple systems rather than just one system in order to prevent a decrease in power transmission efficiency and to prevent the entire facility from stopping in the event of a malfunction.

[0015] The travel path 10 is set at a position spaced above the floor surface. In this example, the travel path 10 is configured using rails 11 provided near the ceiling. The transport vehicle 1 is configured as a so-called ceiling transport vehicle 1, and travels along the rails 11. The transfer target location 13 is located below the travel path 10. The transport vehicle 1 is configured to transfer the container 8 between the transfer target location 13 by raising and lowering the container 8.

[0016] In this embodiment, the article transport facility 100 includes a plurality of transport vehicles 1. Each of the plurality of transport vehicles 1 is configured to receive a transport command from a higher-level control device (not shown) that manages the facility, and to execute a task according to the transport command. For example, the transport command includes information on the origin and destination of the container 8. The transport vehicle 1 that receives the transport command transports the container 8 from the origin to the destination. The origin and destination include the transfer target location 13.

[0017] There are various types of containers 8 that can be handled by the article transport equipment 100. In this example, the article transport equipment 100 is used in a semiconductor manufacturing factory. Therefore, the containers 8 may be substrate storage containers 8 (so-called FOUP: Front Opening Unified Pod) that store substrates (wafers, panels, etc.), reticle storage containers 8 (so-called reticle pods) that store reticles, etc. In this case, the transport vehicle 1 transports containers 8 such as the substrate storage container 8 or the reticle storage container 8 between each process along the travel path 10.

[0018] In this embodiment, the transfer target location 13 includes a processing device 14 that processes the container 8, and a mounting table 15 that is arranged adjacent to the processing device 14. In this specification, "processing of the container 8" means processing of the objects (substrates or reticles) contained in the container 8. The transport vehicle 1 receives the container 8 that has been processed by the processing device 14 from the mounting table 15, or delivers the container 8 that has not been processed by the processing device 14 to the mounting table 15. The processing device 14 performs various processes, such as thin film formation, photolithography, and etching.

[0019] 2 and 3, the transport vehicle 1 includes a traveling device 2 that travels on rails 11, and a storage section 7 that stores a container 8 (item). The transport vehicle 1 also includes a holding device 3 that holds the container 8, a lifting device 4 that raises and lowers the holding device 3, a control device 5 (see FIG. 4), and a power supply unit 6 that receives power from an external source and supplies power to at least the lifting device 4. The storage section 7 includes the holding device 3 that holds the item, and the lifting device 4 that raises and lowers the holding device 3.

[0020] The traveling device 2 is configured to move the entire transport vehicle 1 along the travel path 10 by traveling on the rails 11. In this embodiment, the traveling device 2 includes a plurality of traveling wheels 20 that roll on the rails 11, and a traveling drive mechanism 21 that drives at least a portion of the plurality of traveling wheels 20. The traveling drive mechanism 21 includes a traveling drive motor 210 (e.g., a servo motor) and a drive driver 211 (drive circuit) that controls the traveling drive motor 210.

[0021] As shown in FIG. 4, the power supply unit 6 in this embodiment includes a power receiving device 60 that receives power from the power supply system, a rectifier circuit 61 for direct current conversion (e.g., a PSB board, etc.), and a DC-DC converter 62 for voltage adjustment, thereby supplying power to each part of the transport vehicle 1.

[0022] The power receiving device 60 includes a pickup coil 601 (see FIG. 3) arranged on the transportation vehicle 1 so as to face the power supply line 12, a power receiving unit (not shown) formed on a wiring board inside the transportation vehicle 1, and the like.

[0023] When the power supply system passes a high-frequency current through the power supply line 12, which is an induction line, and generates a magnetic field around the power supply line 12, the pickup coil 601 of the power receiving device 60 generates an induced electromotive force due to the AC current flowing through the power supply line 12. That is, power for driving the traveling device 2, the lifting device 4, the holding device 3, and the control device 5 is supplied to the power receiving device 60 of the power supply unit 6 in a non-contact manner from the power supply line 12. Note that, in this embodiment, a configuration in which power is supplied from the power supply unit 6 to the traveling device 2, the lifting device 4, the holding device 3, and the control device 5 is shown, but this is not limited thereto, and it is sufficient that the power supply from the power supply unit 6 is performed at least to the lifting device 4, and the traveling device 2, the holding device 3, and the control device 5 may be configured to receive power from a different power source.

[0024] As shown in FIG. 2, the holding device 3 is a device that is provided so as to be capable of being raised and lowered and that supports an article in a suspended state, and is provided inside the storage section .

[0025] The holding device 3 is configured to be able to hold a container 8. The holding device 3 includes a holding main body 30 suspended from the lifting device 4, a pair of holding bodies 31 supported by the holding main body 30, and a holding drive mechanism 32 that drives the pair of holding bodies 31. The holding drive mechanism 32 includes a holding drive motor 320 (e.g., a servo motor) and a drive driver 321 (drive circuit) that controls the motor.

[0026] The holding device 3 in this embodiment employs a chuck unit that holds the container 8 by engaging a pair of holders 31 with a gripped portion (not shown) of the container 8, but is not limited to this configuration. As another configuration, for example, the holding device 3 may be configured to include a fork-type transfer unit equipped with forks that support the container 8 and move in and out. Note that here, the member that supports the supported object and that moves in and out by the moving in and out device is referred to as a "fork," and the "fork" is not limited to a specific shape.

[0027] 4, the lifting device 4 includes a lifting drive mechanism 40 that drives the holding device 3 to lift and lower, and a restraining mechanism 41 that mechanically restrains the lifting and lowering operation of the holding device 3 by the lifting drive mechanism 40. The lifting drive mechanism 40 includes a rotating body, a lifting belt 400 (an example of a wound member) wound around the rotating body so as to be freely wound up and unwound, a lifting drive motor 401 (e.g., a servo motor) that drives the rotating body to rotate, and a driving driver 402 (drive circuit) that controls the lifting drive motor 401.

[0028] The rotating body in this embodiment means a member that winds up the wound member, and examples thereof include a known rotating drum, etc. Although the lifting belt is given as an example of the wound member, the member is not particularly limited as long as it is a member that can be wound up on the rotating body of the lifting device 4, and other members such as a wire may also be used.

[0029] The lift drive motor 401 is provided with a constraint mechanism 41 that mechanically restricts the lifting and lowering operation of the holding device 3. The constraint mechanism 41 is configured to be capable of performing both a constraint operation and a constraint release operation, and an example of such a constraint mechanism 41 is a lift motor holding brake.

[0030] 2, the lifting device 4 is configured to lift and lower the holding device 3 between the storage section 7 and a transfer target location 13 arranged below the travel path 10. The lifting belt 400 is connected to the holding device 3. With the holding device 3 suspended by the lifting belt 400, the holding device 3 is lowered by unwinding the lifting belt 400 from the rotating body, and the holding device 3 is raised by winding the lifting belt 400 around the rotating body.

[0031] The storage unit 7 is configured to be able to store the container 8 to be transported. In this embodiment, the storage unit 7 is suspended from the traveling device 2 and is disposed below the rail 11. The storage unit 7 is configured to be able to store the container 8 held by the holding device 3. When the transport vehicle 1 transports the container 8 along the travel path 10, the container 8 is stored in the storage unit 7.

[0032] 4, the control device 5 includes a controller 50 that controls the overall operation of the transport vehicle 1, and a voltage monitoring unit 51 that monitors a target voltage. For example, an OPC board can be used as the controller 50. The controller 50 is not limited to controlling the overall operation of the transport vehicle 1, and may be configured to control only the lifting device 4. The target voltage in this embodiment refers to the voltage supplied from the power supply unit 6 to the lifting drive mechanism 40.

[0033] The transport vehicle 1 receives a continuous supply of power by switching between multiple power supply systems and travels freely within the article transport facility 100. The article transport facility 100 is equipped with a host control device (not shown), which issues transport commands to the control devices 5 of each transport vehicle 1 to transport articles.

[0034] The transport vehicle 1 travels autonomously based on a transport command, and at a predetermined transfer target location 13 (such as a storage facility) that stores semiconductor substrates or the like, the lifting device 4 lowers the holding device 3 to hold the container 8 to be transferred, and then the holding device 3 is raised to store the container 8 in the storage section 7. Next, the transport vehicle 1 moves along the travel path 10 to another predetermined transfer target location 13, where the lifting device 4 lowers the holding device 3 to unload the previously stored container 8. In this way, the transport vehicle 1 transports goods between the predetermined transfer target locations 13. The upper control device selects the transport vehicle 1 according to the transport source and destination so that the number of transport vehicles 1 supplied with power from each power supply system is within a predetermined number of power recipients, and issues a transport command to the selected transport vehicle 1.

[0035] In the transport vehicle 1 according to the present invention, the voltage supplied from the power supply unit 6 to the lift drive mechanism 40 is set as the target voltage, and the lower limit voltage required for the lift drive mechanism 40 to maintain the position of the holding device 3 in the lift direction is set as the "required lower limit voltage." More specifically, the "required lower limit voltage" is a concept that includes not only the voltage value when the lift drive mechanism 40 becomes unable to maintain the position of the holding device 3 in the lift direction due to an error in the drive driver 402 that controls the lift drive motor 401, but also the voltage value when the lift drive motor 401 becomes insufficient in torque due to a power shortage.

[0036] As shown in FIG. 4, the control device 5 includes a voltage monitoring unit 51 that monitors the target voltage as described above. When the voltage monitoring unit 51 detects that the target voltage is equal to or lower than a "determination threshold" that is set to a value lower than the voltage during normal operation of the power supply unit 6 (this voltage is referred to as the normal voltage) and higher than the necessary lower limit voltage, the controller 50 is configured to execute a preliminary restraining operation (operation to mechanically restrain the lifting operation) that activates the restraining mechanism 41 of the lifting drive motor 401. For example, if the normal voltage is 320V, the necessary lower limit voltage is 200V, and the determination threshold is set to 250V, when the target voltage is equal to or lower than 250V, the controller 50 activates the restraining mechanism 41 to stop the lifting drive motor 401, thereby preventing the holding device 3 from descending unintentionally. Note that when there is a range for the normal voltage, the lower limit voltage is interpreted as the normal voltage.

[0037] The power supply unit 6 may also be provided with a power storage device that temporarily stores power, and the voltage of the power storage device may be configured to be supplied to the lift drive mechanism 40. In this embodiment, the power storage device is provided to compensate for a power shortage when there is a momentary power shortage in the DC conversion rectifier circuit 61 (PSB board, etc.) during the travel or lift operation of the transport vehicle 1. Examples of such a power storage device include a capacitor (e.g., a regenerative charging capacitor) and a small storage battery.

[0038] In addition, when the controller 50 holds the position of the holding device 3 in the lifting / lowering direction and performs a position holding operation to hold the position of the holding device 3 in the lifting / lowering direction by controlling the driving force of the lifting / lowering drive motor 401 when the target voltage is greater than the judgment threshold value, the required lower limit voltage is the lower limit voltage at which the position holding operation can be performed by the lifting / lowering drive motor 401, or the voltage required for normal operation of the drive driver 402 of the lifting / lowering drive motor 401.

[0039] The transport vehicle 1 may be provided with an "article height detection sensor" in, for example, the storage unit 7, which detects that the position of the holding device 3 or the container 8 held by the holding device 3 in the lifting direction is lower than a predetermined reference height. In this case, while the article height detection sensor is detecting an article height, the transport vehicle 1 cannot be restored to a normal operation mode unless the container 8 is returned to its normal position. Therefore, in the case of a conventional transport vehicle, it is necessary to perform an operation to return the height of the container 8 to its normal position.

[0040] On the other hand, according to this configuration, before the lifting drive mechanism 40 is unable to maintain the position of the holding device 3 in the lifting direction due to a drop in the voltage supplied to the lifting drive mechanism 40, i.e., before the holding device 3 descends and the position of the container 8 in the lifting direction becomes lower than a predetermined reference height, the lifting operation of the holding device 3 can be mechanically restrained by the restraining mechanism 41. Therefore, even if a power outage or a malfunction of the power supply unit 6 occurs, the holding device 3 is prevented from descending unintentionally and the position of the container 8 in the lifting direction is maintained at the predetermined reference height, so that the article height detection sensor will not detect it, and therefore there is no need to return the height of the container 8 to its original position.

[0041] 2. Second embodiment Next, a second embodiment of the transport vehicle 1 will be described with reference to FIG. 5. This embodiment differs from the first embodiment in that a controller 50 that controls the overall operation of the transport vehicle 1 and a voltage monitoring unit 51 that monitors the target voltage are integrated together. The following describes the transport vehicle 1 according to this embodiment, focusing on the differences from the first embodiment. Note that points that are not specifically described are the same as those in the first embodiment.

[0042] In the first embodiment, a controller 50 that controls the overall operation of the transport vehicle 1 and a voltage monitoring unit 51 that monitors the target voltage were provided separately, but in this embodiment, the controller 50 is configured to control the overall operation of the transport vehicle 1 and monitor the target voltage.

[0043] In this embodiment, the controller 50 is connected to the driver 211 for driving the travel drive motor 210, the driver 402 for driving the lift drive motor 401, and the driver 321 for driving the holding drive motor 320 via a LAN 9, and is configured to monitor the voltages of the drivers 211, 321, 402 via the LAN 9. When the controller 50 detects that the target voltage has fallen below the determination threshold value, the controller 50 executes a preliminary restraint operation to activate the restraint mechanism 41 of the lift drive motor 401.

[0044] In addition, the configurations disclosed in each of the above-mentioned embodiments can be applied in combination with configurations disclosed in other embodiments as long as no contradiction occurs. Regarding other configurations, the embodiments disclosed in this specification are merely examples in all respects. Therefore, various modifications can be made as appropriate within the scope of the present disclosure.

[0045] 3. Summary of this embodiment The following provides a summary of the embodiments of the transport vehicle described above.

[0046] The transport vehicle is a transport vehicle that transports items, A holding device for holding the article; A lifting device that lifts and lowers the holding device; A control device; a power supply unit that receives power from an external source and supplies power to at least the lifting device; the lifting device includes a lifting drive mechanism that drives the holding device to lift and lower, and a restraining mechanism that mechanically restrains the lifting and lowering operation of the holding device by the lifting drive mechanism, a voltage supplied from the power supply unit to the lifting drive mechanism is defined as a target voltage, and a lower limit voltage required for the lifting drive mechanism to maintain the position of the holding device in the lifting direction is defined as a required lower limit voltage; The control device is equipped with a voltage monitoring unit that monitors the target voltage, and when the target voltage falls below a judgment threshold value that is set to a value lower than the voltage during normal operation of the power supply unit and higher than the required lower limit voltage, performs a preliminary restraint operation to activate the restraint mechanism.

[0047] With this configuration, even if the voltage supplied to the lifting drive mechanism drops due to a power outage or a malfunction of the power supply unit, the restraint mechanism can mechanically restrain the lifting and lowering movement of the holding device before the voltage drop renders the lifting drive mechanism unable to maintain the position of the holding device in the lifting and lowering direction. Therefore, even if a power outage or a malfunction of the power supply unit occurs, the holding device is prevented from descending unintentionally. Furthermore, in cases where the recovery process for the transport vehicle requires restoring the position of the holding device in the lifting direction, the effort required for the recovery process can be reduced.

[0048] Here, the power supply unit includes a power storage device that temporarily stores power, It is preferable that a voltage of the power storage device is supplied to the lift drive mechanism.

[0049] According to this configuration, even if a power outage or a malfunction of the power supply unit occurs, the power storage device can compensate for the momentary power shortage, and a sudden drop in the voltage supplied to the lift drive mechanism can be avoided. Therefore, the reliability of the execution of the preliminary restraint operation by the control device can be increased.

[0050] The lifting drive mechanism includes a rotating body, a wound member wound around the rotating body so as to be freely wound and unwound, and a lifting drive motor that drives the rotating body to rotate, and is configured to lower the holding device by unwinding the wound member from the rotating body while the holding device is suspended by the wound member, and to lift the holding device by winding the wound member onto the rotating body, the lifting drive motor is a servo motor, when the control device is to hold a position of the holding device in a lifting / lowering direction and the target voltage is greater than the determination threshold value, the control device executes a position holding operation to hold the position of the holding device in the lifting / lowering direction by controlling the driving force of the lifting / lowering drive motor; The necessary lower limit voltage is preferably a lower limit voltage at which the lift drive motor can perform the position holding operation, or a voltage required for normal operation of a driver for driving the lift drive motor.

[0051] According to this configuration, when the voltage supplied from the power supply unit to the lifting drive mechanism is normal, the driving force of the lifting drive motor is controlled to perform a position holding operation in the lifting and lowering direction of the holding device, thereby eliminating the need to frequently switch between restraint and release by the restraint mechanism, and making it easier to quickly perform the lifting and lowering operation of the holding device. On the other hand, when the voltage supplied to the lifting drive mechanism drops due to a power outage or a malfunction of the power supply unit, it becomes difficult to properly perform the position holding operation by controlling the driving force of the lifting drive motor, but with this configuration, as described above, the lifting operation of the holding device can be mechanically restrained by the restraining mechanism before the lifting drive mechanism is unable to maintain the position of the holding device in the lifting direction due to a drop in the voltage supplied to the lifting drive mechanism. Therefore, even if a power outage or a malfunction of the power supply unit occurs, the holding device is prevented from descending unintentionally. [Industrial Applicability]

[0052] The technology disclosed herein can be used in a transport vehicle that travels along a travel path to transport articles. [Explanation of symbols]

[0053] 1: Transport vehicle 2: Running gear 20: Running wheel 21: Travel drive mechanism 210: Travel drive motor 211: Driving driver 3: Holding device 30: Holding body part 31: Holding body 32: Holding drive mechanism 320: Holding drive motor 321: Driving driver 4: Lifting device 40: Lifting drive mechanism 400: Lifting belt (wound member) 401: Lift drive motor 402: Driving driver 41: Restraint mechanism 5: Control device 50: Controller 51: Voltage monitoring unit 6: Power supply unit 60: Power receiving device 601: Pickup coil 61: DC conversion rectifier circuit 62: DC-DC converter for voltage regulation 7: Storage unit 8: Container (article) 9: LAN 10:Route 11: Rail 12:Power line 13: Transfer target location 14: Processing device 15: Placement table 100: Goods handling equipment

Claims

1. A transport vehicle for transporting an item, A holding device for holding the article; A lifting device that lifts and lowers the holding device; A control device; a power supply unit that receives power from an external source and supplies power to at least the lifting device; the lifting device includes a lifting drive mechanism that drives the holding device to lift and lower, and a restraining mechanism that mechanically restrains the lifting and lowering operation of the holding device by the lifting drive mechanism, a voltage supplied from the power supply unit to the lifting drive mechanism is defined as a target voltage, and a lower limit voltage required for the lifting drive mechanism to maintain the position of the holding device in the lifting direction is defined as a required lower limit voltage; The control device is equipped with a voltage monitoring unit that monitors the target voltage, and when the target voltage falls below a judgment threshold value that is set to a value lower than the voltage during normal operation of the power supply unit and higher than the required lower limit voltage, the transport vehicle performs a preliminary restraint operation to activate the restraint mechanism.

2. The power supply unit includes a power storage device that temporarily stores power, The transport vehicle according to claim 1 , wherein a voltage of the power storage device is supplied to the lifting drive mechanism.

3. the lifting drive mechanism includes a rotating body, a wound member wound around the rotating body so as to be freely wound and unwound, and a lifting drive motor that drives the rotating body to rotate, and is configured such that, with the holding device suspended by the wound member, the holding device is lowered by unwinding the wound member from the rotating body, and the holding device is raised by winding the wound member onto the rotating body; the lifting drive motor is a servo motor, when the control device is to hold the position of the holding device in the lifting / lowering direction and the target voltage is greater than the determination threshold value, the control device executes a position holding operation to hold the position of the holding device in the lifting / lowering direction by controlling the driving force of the lifting / lowering drive motor; 3. The transport vehicle according to claim 1, wherein the necessary lower limit voltage is a lower limit voltage at which the lift drive motor can perform the position maintaining operation, or a voltage required for normal operation of a driver for the lift drive motor.

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