Article conveyance system

Abstract

Provided is an article conveyance system with a simple configuration in which an article conveyance carriage does not significantly tilt even during lifting or lowering, wear of a lifting gear can be suppressed, and load collapse of an article is prevented. An article conveyance system (100) includes a lifting movement path (130) and an article conveyance carriage (110). The lifting movement path (130) comprises a lifting rack gear (131) and a lifting rail (132). The article conveyance carriage (110) comprises a traveling shaft (Mc), a lifting shaft (Sc), a first contact rotation shaft, and a second contact rotation shaft (Rc), which serve as rotation shafts for a traveling wheel (111), a lifting gear (115), a first contact wheel (113), and a second contact wheel (114), respectively. The first contact rotation shaft and the second contact rotation shaft (Rc) are disposed at different heights and at positions that are not aligned in the vertical direction.

Description

Article conveying system

[0001] The present invention relates to an article conveying system capable of moving on a lifting and moving path provided on a shelf in an automated warehouse.

[0002] Conventionally, as an article conveying system for conveying articles in an automated warehouse, there is known an article conveying system in Patent Document 1, which is composed of an article conveying cart (climbing robot 10) having drive wheels 12 and support wheels 14 that run on a conveying path or the like, guide rollers 16, a pinion 18 that engages with a rack to enable lifting and lowering, and counter wheels 19, 20 arranged vertically.

[0003] The article conveying cart (climbing robot 10) of the article conveying system known from this Patent Document 1 can lift and lower a lifting rack (rack) by engaging a pair of left and right lifting gears (pinions) with the lifting rack (rack). Further, the article conveying cart (climbing robot 10) is lifted and lowered while the counter wheels 19, 20 enter and abut against a lifting rail (counter wheel support surface) formed along the lifting rack (rack), so that the article conveying cart (climbing robot 10) can receive reverse forces 26, 24 from the counter wheels 19, 20 respectively and perform lifting and lowering movement without significantly disturbing the posture.

[0004] Japanese Patent No. 7377836

[0005] However, the article transport system known from Patent Document 1 still had room for improvement. Specifically, in the article transport system known from Patent Document 1, the counter wheels are arranged vertically when viewed from the floor surface while the article transport cart is in contact with the floor surface. Therefore, when the article transport cart is raised and lowered using the lifting rack, the vertically arranged counter wheels contact one or the other of the opposing lifting rails to stabilize the posture of the article transport cart. However, when the article transport cart is raised and lowered, the vertically arranged counter wheels are not aligned vertically when viewed from the floor surface, causing the article transport cart to tilt. This can cause the distance between the axes of the lifting gear and the lifting rack to change, potentially leading to increased wear on the lifting gear. Furthermore, there was a risk that the articles to be transported on the article transport cart would tilt, shift position, or fall.

[0006] The present invention aims to solve these problems and provide an item transport system that has a simple configuration, prevents the item transport cart from tilting significantly when lifting or lowering, suppresses wear on the lifting gears, and prevents the items loaded on the item transport cart from collapsing.

[0007] The present invention relates to an article transport system comprising an article transport trolley and a lifting travel path having a lifting rack gear and lifting rails provided on shelves in an automated warehouse, wherein the lifting travel path has a pair of the lifting rack gears and a pair of lifting rails provided inside the pair of lifting rack gears, the lifting rails have a first rail that contacts the first contact surface and a second rail that contacts the second contact surface, the pair of lifting rails are arranged with a distance between them that allows the article transport trolley to enter, the article transport trolley has wheels that can move along the travel path, a lifting gear that can engage with the lifting rack gear to move up and down, and the lifting rails have a first contact surface and a second contact surface The invention solves the aforementioned problem by comprising a first contact wheel and a second contact wheel that are in contact with and rotatable, a drive unit that drives the running wheels and the lifting gear, a workpiece holding unit that holds the workpiece to be transported, a running shaft which is the rotation axis of the running wheels, a lifting shaft which is the rotation axis of the lifting gear, a first contact rotation shaft which is the rotation axis of the first contact wheel, and a second contact rotation shaft which is the rotation axis of the second contact wheel, wherein the running shaft, the lifting shaft, the first contact rotation shaft, and the second contact rotation shaft are arranged parallel to each other, the first contact rotation shaft and the second contact rotation shaft are arranged at different heights, and are positioned so as not to be aligned vertically when viewed from the floor surface when the article transport trolley is traveling on the floor surface.

[0008] According to the article transport system of claim 1, the first contact rotation shaft and the second contact rotation shaft are positioned at different heights and are not aligned vertically when viewed from the roadway when the article transport trolley is traveling on the roadway. Therefore, if the distance between the first rail and the second rail is approximately the same as the distance between the furthest horizontal positions of the outer circumferential surfaces of the first contact wheel and the second contact wheel, the first contact wheel can contact the first rail and the second contact wheel can contact the second rail with only a slight tilt of the article transport trolley when it is raised or lowered. This allows the article transport trolley to remain stable without its posture being significantly disrupted, and prevents the articles being transported from collapsing. Furthermore, because the posture of the article transport trolley is stable, the distance between the axes of the lifting rack gear and the lifting gear does not change, and wear of the lifting gear can be suppressed.

[0009] According to the configuration described in claim 2, the travel path is composed of a pair of travel rails laid near the lower part of a pair of lifting rails, and the travel wheels are configured to be movable on the pair of travel rails, so that the goods transport trolley can reliably reach the lifting path by following the travel rails. According to the configuration described in claim 3, a recess is formed in the pair of travel rails, and the recess is formed near the lower part of the pair of lifting rails, so, for example, by moving the travel wheels of the goods transport trolley that has reached the lifting path into the recess, the goods transport trolley can be fixed in an appropriate position and then moved to the lifting path.

[0010] According to the configuration described in claim 4, since either the first contact wheel or the second contact wheel is a coaxial contact wheel in which the first contact rotation shaft and the second contact rotation shaft are arranged on the same axis as the lifting shaft, the coaxial contact wheel and the lifting gear can be configured without spacing them apart in the vertical direction, and the article transport trolley can be configured to be compact in the vertical direction. According to the configuration described in claim 5, since the lifting gear, the first contact wheel and the second contact wheel are configured to move forward and backward in the axial directions of the lifting shaft, the first contact shaft and the second contact shaft, respectively, for example, if the lifting gear, the first contact wheel and the second contact wheel are stored inside the article transport trolley when the article transport trolley is running, and are extended outside the article transport trolley only when lifting and lowering to engage with and contact the lifting rack gear, the first contact rail and the second contact rail, respectively, the width of the travel path required when the article transport trolley is running can be narrowed, and the space required when multiple article transport trolleys pass each other can be reduced.

[0011] According to the configuration described in claim 6, the first rail and the second rail are formed in a sloping shape that approaches each other as they move toward the lifting rack gear side, the first contact surface is composed of a tapered surface along the slope of the first rail, and the second contact surface is composed of a tapered surface along the slope of the second rail. Therefore, even if the alignment of the lifting path and the item transport trolley is slightly misaligned, when the first contact wheel and the second contact wheel enter the lifting rail, the slopes of the first rail and the second rail and the tapered surfaces of the first contact surface and the second contact surface can correct the orientation of the lifting path and the item transport trolley. This eliminates the need to precisely align the lifting path and the item transport trolley, preventing an increase in working time and preventing the control program of the item transport trolley from becoming complicated. According to the configuration described in claim 7, since the lifting rack gear and the lifting rail are constructed as separate components, the lifting rack gear and the lifting rail can be easily processed independently and can be individually removed for repair or replacement.

[0012] A schematic diagram showing an article transport system 100 according to one embodiment of the present invention. A perspective view showing an article transport trolley 110 of the article transport system 100 according to one embodiment of the present invention. A schematic side view of the article transport trolley 110 of the article transport system 100 according to one embodiment of the present invention. A schematic top view of the article transport trolley 110 of the article transport system 100 according to one embodiment of the present invention. A schematic front view of the article transport trolley 110 of the article transport system 100 according to one embodiment of the present invention. A top view and a side view of the lifting and lowering path 120 of the article transport system 100 according to one embodiment of the present invention. A top view showing the lifting and lowering procedure 1 of the article transport trolley 110 of the article transport system 100 according to one embodiment of the present invention. An enlarged view showing the engagement procedure 1 between the article transport trolley 110 and the lifting rail 132 of the article transport system 100 according to one embodiment of the present invention. An enlarged view showing the engagement procedure 2 between the article transport trolley 110 and the lifting rail 132 of the article transport system 100 according to one embodiment of the present invention. A top view showing the lifting and lowering procedure 2 of the article transport trolley 110 of the article transport system 100 according to one embodiment of the present invention. A side view showing the lifting and lowering procedure 3 of the article transport trolley 110 of the article transport system 100 according to one embodiment of the present invention.

[0013] Below, an article transport system 100 according to one embodiment of the present invention will be described with reference to Figures 1 to 11.

[0014] An article transport system 100 according to one embodiment of the present invention, as shown in Figures 1 to 6, includes a lifting travel path 130 having a lifting rack gear 131 and a lifting rail 132 provided on a storage shelf T in an automated warehouse, a travel rail 137 which is a travel path laid in the direction of travel from near the lower part of the lifting rail 132, and an article transport trolley 110 that can be lifted up and down by engaging with the lifting rack gear 131. The article transport trolley 110 includes a main body 109, travel wheels 111 (left wheel 111a, right wheel 111b) and travel auxiliary wheels 112 that can travel on the travel surface 138 of the travel rail 137, a lifting gear 115 (left lifting gear 115a, right lifting gear 115b) that can be lifted up and down on the lifting travel path 130 by engaging with the rack gear teeth 131a of the lifting rack gear 131, and the lifting rail 132 It includes first contact wheels 113 (left first contact wheel 113a, right first contact wheel 113b) that contact the first rail 136a of the lifting rail 132, second contact wheels 114 (left second contact wheel 114a, right second contact wheel 114b) that contact the second rail 136b of the lifting rail 132, an article holding section 116 that holds the container C which is the item being transported, and a control unit (not shown).

[0015] The running wheels 111 are connected to the main body 109 by running connecting shafts 117 (left running connecting shaft 117a, right running connecting shaft 117b) so as to be rotatable around the running shaft Mc as the axis of rotation, and the running drive units 120 (left running drive unit 120a, right running drive unit 120b) are connected to the running connecting shafts 117 (left running connecting shaft 117a, right running connecting shaft 117b) so as to be able to transmit driving force. The lifting gear 115 is connected to the main body 109 by a lifting connecting shaft 118 so as to be rotatable around the lifting shaft Sc as the axis of rotation, and the lifting drive unit 121 is connected to the lifting connecting shaft 118 so as to be able to transmit driving force.

[0016] The first contact wheel 113 is configured to rotate around a first contact rotation axis coaxial with the lifting axis Sc, and has a tapered left first contact surface 122a and a right first contact surface 122b that can contact the first rail 136a (described later), and a left first flange 123a and a right first flange 123b that can enter the first flange receiving portion 135a (described later). The second contact wheel 114 is configured to rotate around a second contact rotation axis Rc, and has a tapered left second contact surface 124a and a right second contact surface 124b that can contact the second rail 136b (described later), and a left second flange 125a and a right second flange 125b that can enter the second flange receiving portion 135b (described later).

[0017] The lifting gear 115 (first contact wheel 113), the second contact wheel 114, and the running wheels 111 are configured to move forward and backward from the main body 109 in the direction of the lifting axis Sc (first contact rotation axis), the second contact rotation axis Rc, and the running axis Mc, respectively. The running auxiliary wheels 112 are configured to move forward and backward from the main body 109 in conjunction with the running wheels 111. The second contact rotation axis Rc is positioned above the lifting axis Sc (first contact rotation axis) and is located on the auxiliary wheel 112 side of the vertical when viewed from the floor surface G when the item transport trolley 110 is running on the running surface 138 of the running rail 137.

[0018] The item holding section 116 is configured to be able to receive and transfer containers C from the left and right directions of the main body section 109. The control unit (not shown) controls the travel drive unit 120 and the lifting drive unit 121 to enable the operation of a direction changing mechanism (not shown) that changes the direction of the item transport trolley 110 on the floor surface G at a position away from the travel rail 137, and is configured to be movable, as well as controlling the loading and unloading of containers C into and out of the item holding section 116.

[0019] The lifting and lowering passage 130 has a lifting rack gear 131 and a lifting rail 132, and is arranged opposite each other in a pair, facing the opening 134 (described later) with a distance sufficient for the item transport trolley 110 to enter. The lifting and lowering rack gear 131 has rack gear teeth 131a that can engage with the lifting gear 115, and is mounted in the engagement space 113 (described later) so that the rack gear teeth 131a are aligned vertically.

[0020] The lifting rail 132 is formed in a U-shape when viewed from above, and an engagement space 133 is formed behind the opening 134. On the opening 134 side, a first rail 136a and a second rail 136b are arranged opposite each other, and the first rail 136a and the second rail 136b are formed with inclined surfaces that gradually approach each other from the opening side of the opening 134 toward the engagement space 133 side. A first flange receiving portion 135a and a second flange receiving portion 135b are formed at the opening-side ends of the first rail 136a and the second rail 136b, respectively.

[0021] Each pair of running rails 137 has a running surface 138 on which a pair of running wheels 111 and a pair of auxiliary running wheels 112 can run, and a recess 139 is provided near the lower part of the lifting rail 132, which is a cutout of part of the running surface 138. In addition, the outer sides of each pair of running rails 137, facing each other, are raised in a wall-like manner.

[0022] Next, the lifting and lowering of the item transport trolley 110 by the item transport system 100 of one embodiment of the present invention will be explained with reference to Figures 7 to 11. The item transport trolley 110 is in a state in which the running wheels 111 and running auxiliary wheels 112 are placed in advance on the running surface 138 of the running rail 137.

[0023] First, the drive unit 120 is driven to move the item transport trolley 110 along the running rails, between a pair of opposing lifting and lowering tracks 130. At this time, since the outer sides of the pair of running rails 137 facing each other are raised like walls, the item transport trolley with running wheels 111 and auxiliary running wheels 112 on the running surface 138 can move reliably toward the lifting and lowering track 130 without significant deviation in orientation. In addition, a recess 139 is provided near the lower part of the lifting and lowering rail 132, which is a cutout of part of the running surface 138. Therefore, when the item transport trolley 110 reaches the lifting and lowering track 130, the running wheels 111 can enter and easily fix its position, allowing for a stable transition to lifting and lowering movement.

[0024] Furthermore, since the travel axis Mc and the lifting axis Sc are arranged parallel to each other, if the lifting gear 115 and the lifting rack gear 131 are facing each other, the item transport trolley 110 can be controlled by the control unit (not shown) so that the left travel drive unit 120a and the right travel drive unit 120b rotate synchronously, thereby allowing it to approach the lifting path 130 side with even less deviation in orientation. In addition, since the lifting axis Sc and the travel axis Mc can be given different driving forces by the lifting drive unit 121 and the travel drive unit 120 (left travel drive unit 120a, right travel drive unit 120b), the phase of the rack gear teeth 131a and the lifting gear 115 can be pre-aligned while the item transport trolley 110 is moving toward the lifting path 130, and the lifting gear 115 can be quickly engaged with the rack gear teeth 131a to switch to the lifting movement of the item transport trolley 110.

[0025] As shown in Figure 7, the item transport trolley 110 may not be able to be perfectly aligned with the lifting path 130, but as shown in Figure 8, when the first contact wheel 113 and the second contact wheel 114 are moved axially away from the main body 109, the left first contact surface 122a and the left second contact surface 124a make contact with the first rail 136a, and the right first contact surface 122b and the right second contact surface 124b make contact with the first rail 136a. If the misalignment is within a range that allows contact with each of the two rails 136b, as shown in Figures 9 and 10, the orientation of the item transport trolley 110 can be corrected to an appropriate orientation with respect to the lifting path 130 by aligning the tapered surfaces of the left first contact surface 122a and the right first contact surface 124a with the slope of the first rail 136a, and the tapered surfaces of the left second contact surface 122b and the right second contact surface 124b with the slope of the second rail 136b. Furthermore, by having the left first flange 123a and the right first flange 123b contact the first flange receiving portion 135a, and the left second flange 125a and the right second flange 125b contact the second flange receiving portion 135b, the axial movement of the lifting gear 115 can be stopped at an appropriate position for engagement with the rack gear teeth 131a. This eliminates the need to precisely align the lifting path 130 with the item transport trolley 110, preventing an increase in working time and preventing the control program of the item transport trolley 110 from becoming overly complex.

[0026] After engaging the lifting gear 115 with the rack gear teeth 131a, applying driving force from the lifting drive unit 121 to the lifting connecting shaft 118 causes the lifting gear 115 to rotate and mesh with the rack gear teeth 131a one after another, allowing the goods transport trolley 110 to be raised upward. At this time, by raising and lowering the trolley with the first contact wheel 113 and the second contact wheel 114 in contact with the first rail 136a and the second rail 136b respectively, they act as guide rollers when the goods transport trolley 110 is raised and lowered, allowing the goods transport trolley 110 to be raised and lowered more stably and preventing the cargo in the container C mounted on the goods holding unit 116 from collapsing.

[0027] In particular, the second contact rotation axis Rc is positioned above the lifting axis Sc (first contact rotation axis) and is located on the auxiliary wheel 112 side rather than the vertical side when viewed from the running surface 138 of the running rail 137 when the item transport trolley 110 is traveling on the running surface 138. Therefore, even if a force acts to cause the item holding part 116 side to fall with the engagement position between the lifting gear 115 and the rack gear teeth 131a as the pivot point, the second contact wheel 114 and the second rail 136b come into contact quickly, thereby suppressing the tilt of the entire item transport trolley 110. Furthermore, since the first contact wheel 113 and the second contact wheel 114 are positioned to contact and brace against the first rail 136a and the second rail 136b, respectively, the distance between the axes of the lifting gear 115 and the rack gear teeth 131a does not change, thus suppressing wear of the lifting gear 115.

[0028] After the lifting gear 115 engages with the rack gear teeth 131a and reaches the desired storage position on the storage shelf T, the container C is loaded and unloaded from the item transport trolley 110. Once the loading and unloading operation is complete, the item transport trolley 110 descends along the lifting movement path 130 and makes contact with the running surface 138 of the running rail 137. Then, the lifting gear 115, the first contact wheel 113, and the second contact wheel 114 are moved axially toward the main body 109 to disengage from the lifting movement path 130, and the trolley travels along the running rail 137 to move to the next process.

[0029] As described above, the first contact rotation axis, which is the lifting axis Sc, and the second contact rotation axis Rc are positioned at different heights and are positioned so that they are not aligned vertically when viewed from the running surface 138 when the item transport trolley 110 is traveling on the running rail 137. This makes it possible to suppress the tilt of the item transport trolley 110 when it is raised or lowered, and to reliably prevent wear of the lifting gear 115.

[0030] Furthermore, since the first contact wheel 113 is a coaxial contact wheel in which the first contact rotation axis is located on the same axis as the lifting axis Sc, the first contact wheel 113 and the lifting gear 115 can be configured without spacing them apart in the vertical direction, and the item transport trolley 110 can be configured to be compact in the vertical direction. Furthermore, since the lifting gear 115, the first contact wheel 113, and the second contact wheel 114 are configured to move forward and backward in the axial direction of the lifting shaft Sc (first contact rotation shaft) and the second contact rotation shaft Rc, respectively, for example, if the lifting gear 115, the first contact wheel 113, and the second contact wheel 114 are stored inside the item transport trolley 110 when the item transport trolley 110 is traveling, and are extended outside the item transport trolley 110 only when lifting or lowering to engage with and contact the lifting rack gear 131, the first contact rail 136a, and the second contact rail 136b, respectively, the width of the travel path required when the item transport trolley 110 is traveling horizontally can be narrowed, and the space required when multiple item transport trolleys 110 pass each other can be reduced.

[0031] Furthermore, since the lifting rack gear 131 and the lifting rail 132 are constructed as separate components, the lifting rack gear 131 and the lifting rail 132 can be easily processed independently, and can be easily removed and repaired or replaced individually.

[0032] Alternatively, the item transport trolley 110 may travel directly on the floor surface G without the running rails 137. In this case, by adjusting the rotation of the left running drive unit 120a and the right running drive unit 120b using a direction changing mechanism (not shown), the item transport trolley 110 can be changed direction in place without moving significantly forward or backward. Therefore, even in narrow passages, the orientation of the item transport trolley 110 and the lifting / lowering path 130 can be adjusted in advance.

[0033] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and various design modifications can be made without departing from the present invention as described in the claims.

[0034] In the embodiments described above, the first contact wheel was described as a coaxial contact wheel in which the first contact rotation axis is located on the same axis as the lifting axis. However, the positional relationship between the first and second contact wheels is not limited to this. For example, the second contact wheel may be configured to be a coaxial contact wheel, and neither the first contact rotation axis nor the second contact rotation axis may be located on the same axis as the lifting axis. Furthermore, in the embodiments described above, the lifting gear (first contact wheel), the second contact wheel, and the running wheels were described as being able to move forward and backward from the main body in the direction of the lifting axis (first contact rotation axis), the direction of the second contact rotation axis, and the direction of the running axis, respectively, and the running auxiliary wheels were described as being able to move forward and backward from the main body in conjunction with the running wheels. However, the presence or absence of forward and backward movement of each component is not limited to this. For example, the running wheels may not have the function of moving forward and backward in the direction of the running axis.

[0035] Furthermore, in the above-described embodiment, the left first contact surface and the right first contact surface, and the left second contact surface and the right second contact surface are each formed in a tapered shape, and the first rail and the second rail are formed as inclined surfaces that gradually approach each other from the opening side of the opening toward the engagement space. However, the configurations are not limited to this, and for example, the left first contact surface and the right first contact surface, and the left second contact surface and the right second contact surface do not have to be formed in a tapered shape, and the first rail and the second rail do not have to be formed as inclined surfaces that gradually approach each other from the opening side of the opening toward the engagement space. Also, in the above-described embodiment, the lifting rail is described as being formed in a U-shape when viewed from the top side, but the configuration of the lifting rail is not limited to this, and for example, the first rail and the second rail may be configured as separate parts.

[0036] Furthermore, although the above-described embodiments were explained assuming that the first contact wheel and the second contact wheel each have a first flange and a second flange, respectively, the configuration of the first contact wheel and the second contact wheel is not limited to this, and for example, the first flange and the second flange may be omitted. Also, although the above-described embodiments were explained assuming that the running rail has recesses, the configuration of the running rail is not limited to this, and for example, the recesses may not be present, and the running rail may be configured to have intermittent protrusions on the upper part of the running surface, with the running wheels entering between adjacent protrusions to easily fix the position of the item transport trolley.

[0037] 100 ... Goods transport system 109 ... Main body 110 ... Goods transport trolley 111 ... Driving wheels 111a ... Left wheel 111b ... Right wheel 112 ... Driving auxiliary wheels 113 ... First contact wheel 113a ... Left first contact wheel 113b ... Right first contact wheel 114 ... Second contact wheel 114a ... Left second contact wheel 114b ... Right second contact wheel 115 ... Lifting gear 115a ... Left lifting gear 115b ... Right lifting gear 116 ... Goods holding section 117 ... Driving connection shaft 117a ... Left driving connection shaft 117b ... Right driving connection shaft 118 ... Lifting connection shaft 119 ... Auxiliary connection shaft 120 ... Driving drive section 120a ...Left travel drive unit 120b ...Right travel drive unit 121 ...Lifting drive unit 122a ...Left first contact surface 122b ...Right first contact surface 123a ...Left first flange 123b ...Right first flange 124a ...Left second contact surface 124b ...Right second contact surface 125a ...Left second flange 125b ...Right second flange 130 ...Lifting travel path 131 ...Lifting rack gear 131a ...Rack gear teeth 132 ...Lifting rail 133 ...Engagement space 134 ...Opening 135a ...First flange receiving part 135b ...Second flange receiving part 136a ...First rail 136b ...Second rail 137 ...Traveling rail 138 ...Traveling surface 139... Recess Mc... Travel axis Sc... Lifting axis (first contact rotation axis) Rc... Second contact rotation axis G... Floor C... Container (goods) T... Storage shelf

Claims

1. An article transport system including an article transport cart and an elevator track having a lifting rack gear and lifting rails installed on shelves in an automated warehouse, wherein the elevator track has a pair of the lifting rack gears and a pair of the lifting rails installed inside the pair of the lifting rack gears, the lifting rails have a first rail that contacts the first contact surface and a second rail that contacts the second contact surface, and the pair of lifting rails are arranged with a distance between them that allows the article transport cart to enter. The article transport trolley comprises: a traveling wheel that can move along a travel path; a lifting gear that can be raised and lowered by engaging with the lifting rack gear; a first contact wheel and a second contact wheel that can rotate by contacting the lifting rail with a first contact surface and a second contact surface; a drive unit that drives the traveling wheel and the lifting gear; a workpiece holding unit that holds the workpiece to be transported; a traveling shaft which is the rotation axis of the traveling wheel; a lifting shaft which is the rotation axis of the lifting gear; a first contact rotation shaft which is the rotation axis of the first contact wheel; and a second contact rotation shaft which is the rotation axis of the second contact wheel. The article transport system is characterized in that the traveling shaft, the lifting shaft, the first contact rotation shaft, and the second contact rotation shaft are arranged parallel to each other; the first contact rotation shaft and the second contact rotation shaft are arranged at different heights; and are positioned so as not to be aligned perpendicularly when viewed from the travel path when the article transport trolley is traveling along the travel path.

2. The article transport system according to claim 1, characterized in that the travel path is composed of a pair of travel rails laid near the lower part of a pair of lifting rails, and the travel wheels are configured to be movable on the pair of travel rails.

3. The article transport system according to claim 2, characterized in that a recess is formed in a part of the pair of running rails, and the recess is formed near the lower part of the pair of lifting rails.

4. The article conveying system according to claim 1, characterized in that either the first contact wheel or the second contact wheel is a coaxial contact wheel in which the first contact rotation axis and the second contact rotation axis are arranged on the same axis as the lifting axis.

5. The article conveying system according to claim 1, characterized in that the lifting gear, the first contact wheel, and the second contact wheel are configured to move forward and backward in the axial direction of the lifting shaft, the first contact shaft, and the second contact shaft, respectively.

6. The article conveying system according to claim 5, characterized in that the first rail and the second rail are configured as sloping surfaces that approach each other as they move toward the lifting rack gear, the first contact surface is configured as a tapered surface along the slope of the first rail, and the second contact surface is configured as a tapered surface along the slope of the second rail.

7. The article transport system according to claim 1, characterized in that the lifting rack gear and the lifting rail are configured as separate components.

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