Ceiling transport vehicle

Abstract

Provided is a ceiling transport vehicle capable of preventing an article from falling from a container being transported, using a simple mechanism without an increase in device size. The present invention is a ceiling transport vehicle (1) that transports a container (18) having a lateral opening (24) for taking in and out an article (22), with the opening kept open, the ceiling transport vehicle (1) being characterized by comprising: a body part (2); a gripping part (10) that grips the container in which the article is accommodated; a lifting part (8) that raises and lowers the gripping part with respect to the body part; a fall prevention member (52) that is provided so as to face the opening of the container to be transported by the ceiling transport vehicle, and prevents the article accommodated in the container from falling out of the opening; and a detection sensor (54) that detects whether the article is positioned below the fall prevention member.

Description

Ceiling transport vehicle

[0001] The present invention relates to an overhead transport vehicle, and more particularly to an overhead transport vehicle that transports a container containing articles while keeping an opening for putting the articles in and taking them out open.

[0002] Japanese Patent No. 5574177 (Patent Document 1) describes a transport device. This transport device is an overhead transport vehicle configured to transport a storage container containing wafers. The overhead transport vehicle has a holding unit that holds the storage container to be transported, and this holding unit is configured to be able to move up and down using a wire. That is, the overhead transport vehicle is configured to lower the holding unit from above the storage container to be transported and then lift the storage container while holding it with the holding unit. Then, while holding the storage container containing wafers with the holding unit, the storage container is transported by traveling along a traveling rail laid on the ceiling.

[0003] Furthermore, because the storage container is transported in an open state, the ceiling transport vehicle is equipped with a jump-out prevention mechanism to prevent the wafers from jumping out of the storage container during transport. This jump-out prevention mechanism is provided so as to be able to move up and down together with the holding unit, and when the holding unit is lowered from above the storage container to hold the storage container, it is retracted to a separate position where it does not interfere with the wafers stored in the storage container. After the lowered holding unit holds the storage container, the jump-out prevention mechanism is moved to a contact position facing the opening of the storage container to prevent the wafers from jumping out of the storage container during transport. Furthermore, if a wafer is stored in a state where it has jumped out of the storage container, the movement of the jump-out prevention mechanism pushes the wafer into the appropriate position in the storage container.

[0004] Patent No. 5574177

[0005] However, the transport device described in Patent Document 1 requires a mechanism for moving the pop-out prevention mechanism between the separated position and the contact position, which results in a complex configuration of the transport device. Furthermore, the transport device described in Patent Document 1 requires the pop-out prevention mechanism to be significantly retracted from the separated position so that it does not come into contact with the wafer even when the wafer is in a state where it has popped out of the container. Therefore, the pop-out prevention mechanism requires a large stroke to move from the separated position to the contact position, which results in an increase in the overall size of the transport device.

[0006] SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an overhead transport vehicle that can prevent articles from falling out of containers during transport using a simple mechanism without increasing the size of the device.

[0007] In order to solve the above-mentioned problems, the present invention provides a ceiling transport vehicle that transports a container having an opening on the side for putting items in and taking items out, with the opening kept open, and is characterized by having a main body, a gripping unit that grips the container containing the items, a lifting unit that raises and lowers the gripping unit relative to the main body, a fall prevention member that is arranged opposite the opening of the container to be transported by the ceiling transport vehicle and prevents the items contained in the container from falling out of the opening, and a detection sensor that detects whether an item is located below the fall prevention member.

[0008] According to the present invention configured as described above, a fall prevention member is provided that faces the opening of the container to be transported, thereby preventing items from falling out of the container during transport. Furthermore, according to the present invention configured as described above, a detection sensor detects whether an item is positioned below the fall prevention member. Therefore, when the container is received by the ceiling transport vehicle, it is possible to detect any misalignment of the items contained in the container. As a result, even without a mechanism for retracting the fall prevention member, it is possible to respond to misalignment of the items, prevent items from falling out with a simple mechanism, and reduce the size of the device.

[0009] In the present invention, the fall prevention member is preferably made up of a plurality of members extending in the vertical direction so as to face the opening of the container to be transported.

[0010] According to the present invention configured in this manner, the fall prevention member is composed of multiple members extending in the vertical direction so as to face the opening of the container to be transported, thereby reliably preventing items from falling out of the container.

[0011] In the present invention, the detection sensor is preferably configured to detect whether or not an article has come into contact with the lower end of the fall prevention member.

[0012] According to the present invention configured in this manner, the detection sensor detects whether or not an article has come into contact with the lower end of the fall prevention member, so that interference between the fall prevention member and the article can be reliably detected.

[0013] In the present invention, the detection sensor is preferably a contact sensor provided at the lower end of the fall prevention member.

[0014] According to the present invention configured in this manner, the detection sensor is formed by a contact sensor provided at the lower end of the fall prevention member, so that interference between the fall prevention member and an item can be reliably detected using a simple mechanism and sensor.

[0015] In the present invention, the detection sensor is preferably a proximity sensor, a photoelectric sensor, or a laser sensor that detects an article.

[0016] According to the present invention configured in this manner, the detection sensor is composed of a proximity sensor, photoelectric sensor, or laser sensor that detects items, so it is possible to detect that an item has jumped out of the container before the item interferes with the fall prevention member, thereby avoiding damage to the item.

[0017] In the present invention, the lifting section is preferably stopped when an article is detected by the detection sensor.

[0018] According to the present invention configured in this manner, when an item is detected by the detection sensor, the lifting section is stopped, thereby reducing the risk of damage to the item even if the item comes into contact with the fall prevention member.

[0019] According to the ceiling transport vehicle of the present invention, it is possible to prevent articles from falling out of containers during transport using a simple mechanism without increasing the size of the device.

[0020] FIG. 1 is a side view showing a schematic configuration of the entire ceiling transport vehicle according to an embodiment of the present invention. FIG. 2 is a perspective view showing a schematic configuration of a holding device provided in the ceiling transport vehicle according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of the ceiling transport vehicle according to an embodiment of the present invention, taken along line III-III in FIG. 1. FIG. 4 is a diagram showing the operation of the ceiling transport vehicle according to an embodiment of the present invention, illustrating a case where each wafer is properly accommodated in an open cassette. FIG. 5 is a diagram showing the operation of the ceiling transport vehicle according to an embodiment of the present invention, illustrating a case where a wafer has protruded from an open cassette. FIG. 6 is a diagram showing modified fall prevention members and contact sensors in the ceiling transport vehicle according to an embodiment of the present invention. FIG. 7 is a diagram showing the operation of the ceiling transport vehicle according to a modified embodiment of the present invention.

[0021] Next, an overhead transport vehicle according to an embodiment of the present invention will be described with reference to the accompanying drawings. First, the overall configuration of an overhead transport vehicle according to an embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a side view showing a schematic overall configuration of an overhead transport vehicle according to an embodiment of the present invention. Note that the embodiment described below is an application of the present invention to a transport device that stores and transports semiconductor wafers in a clean room of a semiconductor manufacturing factory.

[0022] First, as shown in FIG. 1, the ceiling transport vehicle 1 of this embodiment comprises a carriage body 2, which is the main body, and this carriage body 2 is suspended from a track rail 4 attached to the ceiling inside a building such as a clean room, and is configured to travel by a traveling mechanism 6 that operates relative to the track rail 4, and move to a target position.

[0023] Next, the ceiling transport vehicle 1 includes a lifting device 8, which is a lifting section, and a holding device 10, which is a gripping section. The lifting device 8 is a device that raises and lowers the holding device 10 relative to the cart body 2 by lifting belts 12, 14 that function as a so-called hoist, and is attached to the cart body 2 at a position below the traveling mechanism 6 described above.

[0024] The holding device 10 is designed to grasp (hold) an open cassette 18, which is a container placed on a load port 16 of a semiconductor manufacturing device installed in a building, using a chuck 20, so that the wafer 22, which is an item inside the open cassette 18, can be transported.

[0025] The open cassette 18 has an opening 24 formed on one side thereof, and the wafers 22 on the load port 16 are transferred horizontally into the open cassette 18 through this opening 24 (the wafers 22 are taken in and out through the opening 24).

[0026] Here, the open cassette 18 is not provided with a structure for holding the wafers 22 in a horizontal position. Normally, large horizontal forces are not applied to the wafers 22, and therefore the open cassette 18 is transported by the ceiling transport vehicle 1 with the opening 24 remaining open. However, during travel, there is a possibility that the wafers 22 may move due to centrifugal force on curves or travel vibrations. Therefore, in this embodiment, as will be described later, a drop prevention member 52 ( FIG. 2 ) is provided opposite the opening 24 provided on the side of the open cassette 18, preventing the wafers 22 housed in the open cassette 18 from falling out of the opening 24.

[0027] 1, the lifting device 8 includes a pair of first lifting belts 12 (only one of which is shown in FIG. 1), a pair of lifting drums 26, and a pair of idler pulleys 28 (only one of each is shown in FIG. 1). The starting end of the first lifting belt 12 is attached to the lifting drum 26, and by driving the lifting drum 26 to rotate, the first lifting belt 12 is wound up or unwound via the idler pulley 28.

[0028] The lifting device 8 also includes a second lifting belt 14 consisting of a single belt, and a lifting drum 30 and two idler pulleys 32 for the second lifting belt, which are arranged between the pair of lifting drums 26. The starting end of the second lifting belt 14 is attached to the lifting drum 30, and by driving the lifting drum 30 to rotate, the second lifting belt 14 is wound up or unwound via the two idler pulleys 32.

[0029] The three lift drums 26, 30 are driven by a common drive shaft (not shown) connected to a motor (not shown), so that they are all driven at the same rotational speed and by the same amount of rotation. Furthermore, all three lift drums 26, 30 have the same diameter. Therefore, in this embodiment, with this configuration, the first lift belt 12 and the second lift belt 14 are wound up or unwound by the same length when the lift drums 26, 30 are rotated.

[0030] 1 , the lower ends of the first lifting belts 12 are attached to the holding device 10 on the opening 24 side of the open cassette 18, and the lower ends of the second lifting belts 14 are attached to the holding device 10 on the back side of the open cassette 18. In other words, the first lifting belts 12 suspend the holding device 10 on the opening 24 side of the open cassette 18, and the second lifting belts 14 suspend the holding device 10 on the back side of the holding device 10.

[0031] Next, the basic structure of the holding device 10 will be described with reference to Figures 2 and 3. Figure 2 is a perspective view showing the schematic configuration of the holding device 10 provided on the ceiling transport vehicle 1 according to an embodiment of the present invention. Figure 3 is a cross-sectional view taken along line III-III in Figure 1. Note that Figure 2 shows a state in which the holding device 10 has been lowered to a position where the chuck 20 grips the open cassette 18.

[0032] 2, the holding device 10 includes a base plate 50 to which various components are attached. A pair of first lifting belts 12 are attached to the upper surface of the base plate 50 via a pair of first connecting members 36. Furthermore, a second lifting belt 14 is attached to the upper surface of the base plate 50 via a second connecting member 40.

[0033] Meanwhile, a pair of chucks 20 (only one of which is shown in FIG. 2 ) for gripping the open cassette 18 are provided on the underside of the base plate 50. These chucks 20 are configured to be slidable laterally below the base plate 50. That is, each chuck 20 includes an engaging member 20 a that extends downward from the base plate 50 and engages with the open cassette 18, a sliding member 20 b that extends horizontally below the base plate 50, and a drive motor 20 c that moves each sliding member 20 b.

[0034] The engaging member 20a is a member attached so as to protrude downward from one end of the sliding member 20b, and its lower end is configured to be able to engage with the upper part of the open cassette 18. The sliding member 20b is a long, thin member attached to the underside of the base plate 50, and is configured to be slid along the base plate 50 by the drive motor 20c. With this configuration, as shown in FIG. 2 , after the holding device 10 is lowered to above the open cassette 18, when the sliding member 20b is slid by the drive motor 20c so that the engaging members 20a approach each other, the engaging members 20a engage with the upper part of the open cassette 18, and the open cassette 18 is gripped by the holding device 10.

[0035] Furthermore, two fall prevention members 52 are attached to the base plate 50 so as to extend vertically downward. These fall prevention members 52 are rod-shaped members that extend in the vertical direction so as to face the opening 24 of the open cassette 18 gripped by the holding device 10. That is, as shown in FIG. 3 , the two fall prevention members 52 are arranged so as to extend in the vertical direction so as to face the opening 24 of the open cassette 18, and prevent the wafers 22 from falling out of the open cassette 18 while the open cassette 18 is being transported.

[0036] 3, when the chuck 20 of the holding device 10 grips the open cassette 18, the wafers 22 properly accommodated in the open cassette 18 are spaced apart from the respective fall prevention members 52 in a top view, and the wafers 22 do not come into contact with the fall prevention members 52. However, as shown by the imaginary lines in FIG. 3, if the wafers 22 are not accommodated in the proper position and protrude from the open cassette 18, the lower ends of the fall prevention members 52 may come into contact with the wafers 22 when the holding device 10 is lowered to grip the open cassette 18.

[0037] Here, a contact sensor 54 serving as a detection sensor is attached to the lower end of each fall prevention member 52, and a tip 54a at the lower end of each contact sensor 54 is bent obliquely toward the wafers 22 contained in the open cassette 18. Each contact sensor 54 is configured to detect when an object comes into contact with the tip 54a. Note that the tip 54a of the contact sensor 54 extends closer to the opening 24 of the open cassette 18 than the outer circumferential surface of the fall prevention member 52. Therefore, when the holding device 10 is lowered, the fall prevention member 52 will not come into contact with the wafer 22 unless the tip 54a of the contact sensor 54 comes into contact with the wafer 22. In other words, the contact sensor 54 is configured to detect whether an object (wafer 22) has come into contact with the lower end of the fall prevention member 52, thereby detecting whether an object is located below the fall prevention member 52.

[0038] Furthermore, a detection signal from the contact sensor 54 is transmitted to a control unit (not shown) provided in the cart body 2. When the contact sensor 54 detects an article (wafer 22), the control unit sends a control signal to the lifting device 8 to stop the lifting device 8 from raising or lowering the holding device 10. When the contact sensor 54 detects an article, the control unit is configured to generate a warning sound from a sound generator (not shown) provided in the cart body 2 to notify the user that the wafer 22 has come into contact with the contact sensor 54. The present invention can also be configured so that a warning light is turned on to notify the user of contact, along with or instead of the warning sound.

[0039] Next, the operation of the ceiling transport vehicle 1 according to the embodiment of the present invention will be described with reference to Figures 4 and 5. Figure 4 is a diagram showing the operation of the ceiling transport vehicle 1 when each wafer 22 is properly accommodated in the open cassette 18. Figure 5 is a diagram showing the operation of the ceiling transport vehicle 1 when a wafer 22 protrudes from the open cassette 18.

[0040] First, as shown in (a) of Figure 4, when an open cassette 18 placed on a load port 16 is to be transported by the overhead transport vehicle 1, the overhead transport vehicle 1 is caused to travel along the track rail 4 until it is directly above the open cassette 18 to be transported and is then stopped. In this state, the lifting device 8 (Figure 1) is operated to lower the holding device 10.

[0041] Next, as shown in FIG. 4B, when the holding device 10 is lowered to a predetermined position above the open cassette 18, the lifting device 8 stops the lowering of the holding device 10. At this time, because each wafer 22 is accommodated in the appropriate position in the open cassette 18, the lower tip 54a of the fall prevention member 52 does not come into contact with the wafer 22. Next, the drive motor 20c (FIG. 2) provided on the holding device 10 is operated, and the engaging members 20a of the chuck 20 are moved in directions toward each other. As a result, the open cassette 18 is gripped by the chuck 20 of the holding device 10.

[0042] When the open cassette 18 is gripped by the holding device 10, as shown in FIG. 4C, the lifting device 8 is operated, and the open cassette 18 is lifted upward from the load port 16. When the open cassette 18 is lifted to a predetermined position, the lifting device 8 is stopped. Next, with the open cassette 18 suspended, the traveling mechanism 6 of the overhead transport vehicle 1 is operated, and the overhead transport vehicle 1 travels along the track rail 4 to the intended destination. At this time, a fall prevention member 52 positioned opposite the opening 24 of the open cassette 18 prevents the wafers 22 from falling out of the open cassette 18.

[0043] Next, referring to Figure 5, we will explain the operation of the ceiling transport vehicle 1 when wafers 22 are protruding from the open cassette 18. First, as shown in Figure 5(a), in order to transport the open cassette 18 placed on the load port 16, the lifting device 8 (Figure 1) is operated to lower the holding device 10.

[0044] 5(b), if the wafer 22 protrudes from the open cassette 18, the tip 54a at the lower end of the fall prevention member 52 comes into contact with the protruding wafer 22 before the holding device 10 is lowered to a predetermined position above the open cassette 18. This contact is detected by a contact sensor 54 provided at the lower end of the fall prevention member 52. A detection signal from the contact sensor 54 is transmitted to a control unit (not shown) provided in the carriage body 2 of the ceiling transport vehicle 1. When the contact is detected by the contact sensor 54, the control unit stops the lifting device 8 and halts the descent of the holding device 10.

[0045] The control unit also issues a warning sound from a sound generator (not shown) and flashes a warning light (not shown) to notify the operator that an abnormality has occurred. When the alarm is issued, the operator checks the status of the ceiling transport vehicle 1 where the abnormality has occurred and takes necessary measures. For example, the operator moves the protruding wafer 22 to an appropriate position in the open cassette 18 and resumes operation of the ceiling transport vehicle 1. Alternatively, if the wafer 22 has been damaged by contact, the operator removes the damaged wafer 22 and resumes operation of the ceiling transport vehicle 1 after confirming that no fragments of the damaged wafer 22 remain.

[0046] Preferably, the lowering of the holding device 10 is stopped immediately after detecting contact so as not to damage the wafer 22 even if the tip 54a comes into contact with the wafer 22. Alternatively, the tip 54a can be made of a flexible material so as not to damage the wafer 22 even if it comes into contact with the wafer 22.

[0047] The ceiling transport vehicle 1 according to the embodiment of the present invention is provided with a fall prevention member 52 that is provided to face the opening 24 of the open cassette 18 to be transported, thereby preventing the wafers 22 from falling out of the open cassette 18 during transport. Furthermore, the ceiling transport vehicle 1 according to the present embodiment uses a contact sensor 54 to detect whether the wafers 22 are positioned below the fall prevention member 52. Therefore, even without a mechanism for retracting the fall prevention member 52, it is possible to deal with misalignment of the wafers 22 contained in the open cassette 18, preventing the wafers 22 from falling out with a simple mechanism, and enabling the device to be made more compact.

[0048] Furthermore, according to the ceiling transport vehicle 1 of this embodiment, the fall prevention member 52 is composed of multiple members extending in the vertical direction so as to face the opening 24 of the open cassette 18 to be transported, thereby reliably preventing the wafers 22 from flying out of the open cassette 18.

[0049] Furthermore, according to the ceiling transport vehicle 1 of this embodiment, the contact sensor 54 detects whether the wafer 22 has come into contact with the lower end of the fall prevention member 52, so that interference between the fall prevention member 52 and the wafer 22 can be reliably detected.

[0050] Furthermore, according to the ceiling transport vehicle 1 of this embodiment, the wafer 22 is detected by a contact sensor 54 provided at the lower end of the fall prevention member 52, so that interference between the fall prevention member 52 and the wafer 22 can be reliably detected using a simple mechanism and sensor.

[0051] Furthermore, according to the ceiling transport vehicle 1 of this embodiment, when the wafer 22 is detected by the contact sensor 54, the lifting device 8 is stopped, so that even if the fall prevention member 52 comes into contact with the wafer 22, the risk of damage to the wafer 22 can be reduced.

[0052] Although the embodiment of the present invention has been described above, various modifications can be made to the above-described embodiment. In particular, in the above-described embodiment, the present invention is applied to the overhead transport vehicle 1 that transports the open cassette 18 containing the wafers 22, but the present invention can be applied to an overhead transport vehicle that transports any container that contains any item.

[0053] In the above-described embodiment, the lower tip 54a of the contact sensor 54, which is a detection sensor, is configured to come into contact with the wafer 22 protruding from the open cassette 18. However, as a modified example, the contact sensor can be configured as shown in FIG. 6. In the modified example shown in FIG. 6, a circular contact plate 58a is attached to the lower end of the contact sensor 58 provided at the lower end of the fall prevention member 56. Each contact sensor 58 is configured to detect when an object comes into contact with the contact plate 58a attached to the lower end. Note that the diameter of the contact plate 58a of the contact sensor 58 is configured larger than the outer diameter of the fall prevention member 56. Therefore, when the holding device 10 is lowered, the fall prevention member 56 will not come into contact with the wafer 22 unless the contact plate 58a comes into contact with the wafer 22. With this configuration, if the wafer 22 protrudes from the open cassette 18 to a position where it interferes with the fall prevention member 56, the protruding wafer 22 first comes into contact with the contact plate 58a of the contact sensor 58. Therefore, the contact sensor 58 can detect whether or not an article is positioned below the fall prevention member.

[0054] In the above-described embodiment, the contact sensor is provided at the lower end of the fall prevention member, but the contact sensor can be provided at another position. For example, the fall prevention member can be attached so as to be slidable in the vertical direction, and configured so that the fall prevention member moves upward when it comes into contact with the wafer. The present invention can also be configured so that the upward sliding of the fall prevention member is detected by a contact sensor provided at the upper end of the fall prevention member.

[0055] Furthermore, in the above-described embodiment, a protruding wafer is detected by a contact sensor. However, as a modification, a proximity sensor, photoelectric sensor, laser sensor, or the like that detects objects without contact can be used as the detection sensor. In this case, as shown in FIG. 7 , a proximity sensor 62 is attached to the lower end of the fall prevention member 60. When the wafer 22 approaches within a predetermined distance L below the proximity sensor 62, the proximity sensor 62 detects the wafer 22. When the wafer 22 is detected below the proximity sensor 62, a control unit (not shown) sends a control signal to the lifting device 8 to stop the descent of the holding device 10. According to this modification, the protruding wafer 22 can be detected before the detection sensor contacts the wafer 22. Therefore, the descent of the holding device 10 can be stopped before the proximity sensor 62 contacts the wafer 22, reliably preventing damage to the wafer 22.

[0056] In the above-described embodiment, the fall prevention member is attached to the holding device 10, and when the holding device 10 is lowered to grip the open cassette 18, the contact or approach of the protruding wafers 22 with the detection sensor is detected. However, as a modified example, the fall prevention member can also be provided on the side of the carriage body 2. In this case, when the open cassette 18 is raised up to the carriage body 2, the fall prevention member faces the opening 24 of the open cassette 18. Therefore, in this modified example, the open cassette 18 is gripped by the holding device 10, and the protruding wafers 22 are detected by the detection sensor while the open cassette 18 is being raised up by the lifting device 8.

[0057] DESCRIPTION OF SYMBOLS 1 Ceiling transport vehicle 2 Carriage body (body portion) 4 Track rail 6 Traveling mechanism 8 Lifting device (lifting portion) 10 Holding device (gripping portion) 12, 14 Lifting belt 16 Load port 18 Open cassette (container) 20 Chuck 20a Engagement member 20b Sliding member 20c Drive motor 22 Wafer (article) 24 Opening 26 Lifting drum 28 Idler pulley 30 Lifting drum 32 Idler pulley 36 First connecting member 40 Second connecting member 50 Base plate 52 Fall prevention member 54 Contact sensor (detection sensor) 54a Tip portion 56 Fall prevention member 58 Contact sensor (detection sensor) 58a Contact plate 60 Fall prevention member 62 Proximity sensor (detection sensor)

Claims

1. A ceiling transport vehicle that transports a container with an opening on the side for putting in and taking out items, with the opening kept open, comprising: a main body; a gripping unit that grips the container containing an item; a lifting unit that raises and lowers the gripping unit relative to the main body; a fall prevention member that is arranged opposite the opening of the container to be transported by the ceiling transport vehicle and prevents the items contained in the container from falling out of the opening; and a detection sensor that detects whether or not an item is located below the fall prevention member.

2. The ceiling transport vehicle according to claim 1, wherein the fall prevention member is composed of a plurality of members extending in the vertical direction so as to face the opening of the container to be transported.

3. A ceiling transport vehicle as described in claim 1 or 2, wherein the detection sensor is configured to detect whether or not an article has come into contact with the lower end of the fall prevention member.

4. The ceiling transport vehicle according to claim 3, wherein the detection sensor is a contact sensor provided at the lower end of the fall prevention member.

5. The overhead transport vehicle according to claim 1 or 2, wherein the detection sensor is a proximity sensor, a photoelectric sensor, or a laser sensor for detecting an object.

6. The ceiling transport vehicle according to claim 1 or 2, wherein the lifting section is stopped when an article is detected by the detection sensor.

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