Material handling system

Abstract

To provide a material handling system with a simple configuration that prevents the material handling cart from tilting significantly during lifting and lowering, suppresses wear on the lifting gears, and prevents the material from collapsing. [Solution] An article transport system 100 including a lifting track 130 and an article transport trolley 110, wherein the lifting track 130 has a lifting rack gear 131 and a lifting rail 132, and the article transport trolley 110 has a running wheel 111, a lifting gear 115, a running shaft Mc which is the rotation axis of the first contact wheel 113 and the second contact wheel 114, a lifting shaft Sc, a first contact rotation shaft and a second contact rotation shaft Rc, wherein the first contact rotation shaft and the second contact rotation shaft Rc are positioned at different heights and not aligned vertically.

Description

Technical Field

[0001] The present invention relates to an article conveying system capable of moving along 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 in Patent Document 1 an article conveying cart (climbing robot 10) having drive wheels 12 and support wheels 14 that travel 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 and 20 arranged vertically.

[0003] The article conveying cart (climbing robot 10) of the article conveying system known in 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, by lifting and lowering the article conveying cart (climbing robot 10) while the counter wheels 19 and 20 enter and abut on a lifting rail (counter wheel support surface) formed along the lifting rack (rack), the counter wheels 19 and 20 receive reverse forces 26 and 24 respectively, enabling the article conveying cart (climbing robot 10) to move up and down without significantly disturbing its posture.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the article conveying system known in Patent Document 1 still has room for improvement. In other words, 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 trolley is in contact with the floor surface. Therefore, when the article transport trolley 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 trolley. However, when the article transport trolley is raised and lowered, the vertically arranged counter wheels are not aligned vertically when viewed from the floor surface, causing the article transport trolley to tilt. This could cause a change in the distance between the lifting gear and the lifting rack, potentially leading to increased wear on the lifting gear. Furthermore, there was a risk that the items being transported on the transport cart might 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. [Means for solving the problem]

[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 be raised and lowered by engaging with the lifting rack gears, 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 axis and the second contact rotation axis 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 surface of the first contact wheel and the outer surface of the second contact wheel, the first contact wheel can come into contact with the first rail and the second contact wheel can come into contact with 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 transport trolley is stable, the distance between the axes of the lifting rack gear and the lifting gear does not change, which suppresses wear on the lifting gear.

[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 item transport trolley can reliably reach the lifting travel path by following the travel rails. According to the configuration described in claim 3, a pair of running rails have recesses formed in which a portion is cut out, and the recesses are formed near the lower part of the pair of lifting rails. For example, by moving the running wheels of the item transport trolley that has reached the lifting path into the recesses, the item 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, 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 transport trolley when it is in motion, and are extended outside the transport trolley only when lifting, they 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 transport trolley is in motion can be narrowed, and the space required when multiple 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 between the lifting path and the item transport trolley is slightly misaligned, the orientation of the lifting path and the item transport trolley can be corrected by the slopes of the first rail and the second rail and the tapered surfaces of the first contact surface and the second contact surface when the first contact wheel and the second contact wheel enter the lifting rail. This eliminates the need to precisely align the lifting path with the material transport cart, preventing increased work time and avoiding complexity in the material transport cart's control program. 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. [Brief explanation of the drawing]

[0012] [Figure 1] A schematic diagram showing an article transport system 100 according to one embodiment of the present invention. [Figure 2] A perspective view showing an article transport trolley 110 of an article transport system 100 according to one embodiment of the present invention. [Figure 3] A schematic side view of the item transport trolley 110 of the item transport system 100 according to one embodiment of the present invention. [Figure 4] A schematic top view of the item transport trolley 110 of the item transport system 100 according to one embodiment of the present invention. [Figure 5] A schematic front view of the article transport trolley 110 of the article transport system 100 according to one embodiment of the present invention. [Figure 6] A top view and a side view of the lifting and lowering path 120 of an article transport system 100 according to one embodiment of the present invention. [Figure 7] A top view showing the lifting and lowering procedure 1 of the item transport trolley 110 of the item transport system 100 according to one embodiment of the present invention. [Figure 8] An enlarged view showing the engagement procedure 1 between the article transport cart 110 and the lifting rail 132 of the article transport system 100 according to an embodiment of the present invention. [Figure 9] An enlarged view showing the engagement procedure 2 between the article transport cart 110 and the lifting rail 132 of the article transport system 100 according to an embodiment of the present invention. [Figure 10] A top view showing the lifting procedure 2 of the article transport cart 110 of the article transport system 100 according to an embodiment of the present invention. [Figure 11] A side view showing the lifting procedure 3 of the article transport cart 110 of the article transport system 100 according to an embodiment of the present invention.

Embodiments for Carrying out the Invention

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

[0014] As shown in FIGS. 1 to 6, the article transport system 100 according to an embodiment of the present invention includes a lifting movement path 130 having a lifting rack gear 131 and a lifting rail 132 provided on a storage shelf T in an automated warehouse, a traveling rail 137 which is a traveling path laid in the traveling direction from the vicinity of the lower part of the lifting rail 132, and an article transport cart 110 which can be engaged with the lifting rack gear 131 and can be lifted and lowered. The article transfer cart 110 includes a main body 109, traveling wheels 111 (left traveling wheel 111a and right traveling wheel 111b) and traveling auxiliary wheels 112 that can travel on the traveling surface 138 of the traveling rail 137, a lifting gear 115 (left lifting gear 115a and right lifting gear 115b) that can engage with the rack gear teeth 131a of the lifting rack gear 131 to move up and down along the lifting movement path 130, a first contact wheel 113 (left first contact wheel 113a and right first contact wheel 113b) that abuts against the first rail 136a of the lifting rail 132, a second contact wheel 114 (left second contact wheel 114a and right second contact wheel 114b) that abuts against the second rail 136b of the lifting rail 132, an article holding part 116 that holds the container C which is the article to be transferred, and a control part (not shown).

[0015] The traveling wheels 111 are rotatably connected to the main body 109 by traveling connection shafts 117 (left traveling connection shaft 117a and right traveling connection shaft 117b) with the traveling shaft Mc as the rotation axis. The traveling drive parts 120 (left traveling drive part 120a and right traveling drive part 120b) are connected to the traveling connection shafts 117 (left traveling connection shaft 117a and right traveling connection shaft 117b) so as to be able to transmit driving force. The lifting gear 115 is rotatably connected to the main body 109 by a lifting connection shaft 118 with the lifting shaft Sc as the rotation axis. The lifting drive part 121 is connected to the lifting connection shaft 118 so as to be able to transmit driving force.

[0016] The first contact wheel 113 is configured to be rotatable with the first contact rotation axis coaxial with the lifting shaft Sc as the rotation axis, and has left and right first contact surfaces 122a and 122b formed in a tapered shape that can abut against the first rail 136a described later, and left and right first flanges 123a and 123b that can enter the first flange receiving part 135a described later. The second contact wheel 114 is configured to rotate around the 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] Furthermore, the lifting gear 115 (first contact wheel 113), the second contact wheel 114, and the running wheel 111 are configured to move forward and backward from the main body 109 side in the direction of the lifting axis Sc (first contact rotation axis), the second contact rotation axis Rc, and the running axis Mc, respectively. Furthermore, the auxiliary wheels 112 are configured to move forward and backward from the main body 109 in conjunction with the running wheels 111. Furthermore, 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 floor surface G when the goods transport trolley 110 is traveling on the running surface 138 of the running rail 137.

[0018] The item holding section 116 is configured to allow the container C to be transferred to and from the left and right sides 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 also configures the item transport trolley 110 to be movable and controls the loading and unloading of containers C into and out of the item holding unit 116.

[0019] The lifting and lowering passage 130 has a lifting rack gear 131 and a lifting rail 132, and is arranged in a pair facing each other with a distance between them that allows the item transport trolley 110 to enter, with the opening 134 (described later) facing it. The lifting 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) such 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 the engagement space 133 is formed further back than the opening 134. Furthermore, a first rail 136a and a second rail 136b are positioned opposite each other on the opening 134 side, 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 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. Furthermore, the outer sides of the pair of running rails 137, facing each other, are raised in a wall-like manner.

[0022] Next, the lifting and lowering movement of the article transport trolley 110 by the article transport system 100 of one embodiment of the present invention will be explained with reference to Figures 7 to 11. The transport trolley 110 is configured with its main wheels 111 and auxiliary wheels 112 already placed on the running surface 138 of the rail 137.

[0023] First, the travel drive unit 120 is driven to move the item transport trolley 110 along the travel rails, between a pair of opposing lifting and lowering movement paths 130. At this time, since the outer sides of the pair of running rails 137, which face opposite each other, are raised like walls, the goods transport trolley with running wheels 111 and auxiliary running wheels 112 on the running surface 138 can move towards the lifting and lowering path 130 without significantly changing direction. Furthermore, since a recess 139 is provided near the lower part of the lifting rail 132, which is a cutout of a portion of the running surface 138, the running wheels 111 can enter and easily fix the position when the goods transport trolley 110 reaches the lifting movement path 130, and the transition to lifting movement can be carried out stably.

[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 control unit (not shown) can control the item transport trolley 110 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. Furthermore, since the lifting axis Sc and the travel axis Mc can be supplied with different driving forces by the lifting drive unit 121 and the travel drive unit 120 (left travel drive unit 120a and right travel drive unit 120b), respectively, 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 perfectly align 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, 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, as shown in Figures 9 and 10. Furthermore, the left first flange 123a and the right first flange 123b abut against the first flange receiving portion 135a, and the left second flange 125a and the right second flange 125b abut against the second flange receiving portion 135b, thereby stopping the axial movement of the lifting gear 115 at a position appropriate 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, when driving force is applied from the lifting drive unit 121 to the lifting connecting shaft 118, the lifting gear 115 rotates and engages with the rack gear teeth 131a one after another, allowing the item transport trolley 110 to be raised upward. At this time, by raising and lowering 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 section 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 tilting 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, and wear of the lifting gear 115 can be suppressed.

[0028] After the lifting gear 115 and the rack gear teeth 131a engage to reach the desired storage position on the storage shelf T, the container C is loaded and unloaded from the item transport trolley 110. After the loading and unloading operations are completed, the goods transport trolley 110 descends along the lifting 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 path 130, and it travels along the running rail 137 to move to the next process.

[0029] As described above, the first contact rotation axis, 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 provision of 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), second contact wheel, and running wheel are configured to move forward and backward from the main body in the direction of the lifting axis (first contact rotation axis), the second contact rotation axis, and the running axis, respectively, and the running auxiliary wheel is configured to move forward and backward from the main body in conjunction with the running wheel. However, the presence or absence of forward and backward movement of each component is not limited to this, and for example, the running wheel does not need to have a function to move forward and backward in the running axis direction.

[0035] Furthermore, in the embodiments described above, 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 these, 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. Furthermore, although the above-described embodiment explained that the lifting rail is formed in a U-shape when viewed from above, 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 components.

[0036] Furthermore, although the embodiments described above assumed 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. Furthermore, although the above-described embodiment was explained as having recesses formed in the running rail, the configuration of the running rail is not limited to this. For example, there may be no recesses, and the running surface may be configured with intermittent protrusions on the upper part, allowing the running wheels to enter between adjacent protrusions to easily fix the position of the goods transport trolley. [Explanation of symbols]

[0037] 100 ··· Goods handling system 109 ··· Main body 110 ··· Goods transport cart 111 ··· Running wheels 111a...Left wheel 111b...Right wheel 112 ··· Driving aid wheels 113 ··· First contact wheel 113a ··· Left side first contact wheel 113b ··· Right side first contact wheel 114 ··· Second contact wheel 114a ··· Left side second contact wheel 114b ··· Right side second contact wheel 115 ··· Lifting gear 115a ··· Left-side lifting gear 115b...Right side lifting gear 116... Article holding part 117 ··· Travel connection shaft 117a ··· Left travel connecting axle 117b ··· Right travel connecting shaft 118 ··· Lifting connection shaft 119... Auxiliary connecting shaft 120 ··· Drive unit 120a ··· Left-hand drive unit 120b ··· Right-hand drive unit 121 ··· Lifting drive unit 122a...Left side first contact surface 122b... Right side first contact surface 123a ··· Left side, first flange 123b ··· Right side, first flange 124a... Second left contact surface 124b... Second right contact surface 125a ··· Left side second flange 125b ··· Right side second flange 130 ··· Elevator access path 131 ··· Lifting rack gear 131a ··· Rack gear teeth 132 ··· Lifting rail 133 ··· Engagement space 134 ··· Opening 135a ··· First flange receiving section 135b ··· Second flange receiving section 136a ··· First rail 136b ··· Second rail 137 ··· Rails for running 138 ··· Running surface 139 ··· Recess Mc... Travel axis Sc ··· Lifting axis (first contact rotation axis) Rc ··· Second contact rotation axis G...Floor surface C ··· Container (goods) T... Storage shelf

Claims

1. An article transport system including an article transport cart and an elevator path having a lifting rack gear and lifting rails installed on shelves in an automated warehouse, The lifting path comprises a pair of lifting rack gears and a pair of lifting rails provided inside the pair of lifting rack gears. The lifting rail has 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 item transport trolley to enter. The aforementioned article transport trolley includes: a travel 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 travel wheel and the lifting gear; a workpiece holding unit that holds the workpiece to be transported; a travel shaft which is the rotation axis of the travel 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 aforementioned travel shaft, the aforementioned lifting shaft, the first contact rotation shaft, and the second contact rotation shaft are arranged parallel to each other. The article transport system is characterized in that the first contact rotation axis and the second contact rotation axis are arranged at different heights and are positioned so as not to be aligned perpendicularly when the article transport trolley travels along the travel path.

2. The aforementioned track consists of a pair of running rails laid near the lower part of the pair of lifting rails, The article transport system according to claim 1, characterized in that the aforementioned wheels are configured to be movable on a pair of aforementioned rails.

3. A recess is formed in a part of the pair of aforementioned running rails. The article transport system according to claim 2, characterized in that 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 first rail and the second rail are configured 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, The article conveying system according to claim 5, characterized in that the second contact surface is 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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