Automated Guided Vehicle (AGV) Driving System and Automated Guided Vehicle Driving Control Method

Abstract

This system allows multiple automated guided vehicles (AGVs) to pass smoothly through intersections on the travel line, improving the operational efficiency of each AGV. [Solution] In the automated guided vehicle (AGV) travel system Sy, the first and second AGVs 31 and 32 request the management device 50 to transmit a semaphore indicating permission to pass through the intersection point G before reaching the intersection point G. The management device 50 transmits a semaphore to the first AGV 31, allowing the first AGV 31 to pass through the intersection point G, while simultaneously stopping the other AGV at the first position P1 before the intersection point G. The control unit 55 transmits a semaphore to the second AGV 32 when it receives return information from the first AGV 31 indicating the return of the semaphore, or when the timeout period T1 has elapsed since the return information was not received, allowing the second AGV 32 to pass through the intersection point G.

Description

Technical Field

[0001] The present invention relates to an unmanned transport vehicle driving system and an unmanned transport vehicle driving control method that detect a driving line laid on a road surface and cause an unmanned transport vehicle to drive along the driving line.

Background Art

[0002] As an unmanned transport vehicle, it is equipped with a sensor that detects a driving line laid on a road surface, controls the driving direction of the unmanned transport vehicle according to the position of the driving line detected by the sensor, causes the unmanned transport vehicle to drive along the driving line, and controls the driving, stopping, turning, etc. of the unmanned transport vehicle.

[0003] For example, in the unmanned transport vehicle described in Patent Document 1, a track line (driving line) is provided on the floor, a plurality of magnetic marks are sequentially arranged along the track line, and while detecting the track line by the track line detection sensor of the unmanned transport vehicle, the unmanned transport vehicle is caused to drive along the track line. Also, each time approaching a magnetic mark sequentially, the approaching magnetic mark is detected by either one of two mark detection sensors provided on both sides of the unmanned transport vehicle, the number of marks is counted up, and the driving of the unmanned transport vehicle is controlled based on a command corresponding to the counted-up number.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In this scenario, where multiple travel lines intersect at a point, and each automated guided vehicle (AGV) travels along its respective line, it is necessary to prevent contact or collision between the AGVs at the intersection. Therefore, each AGV was temporarily stopped before the intersection, and only after detecting that no other AGV had passed the intersection was it allowed to resume travel and pass through the intersection. However, because all AGVs were temporarily stopped before the intersection, the operational efficiency of each AGV was hindered.

[0006] This invention has been made in view of the above circumstances, and aims to improve the operational efficiency of each automated guided vehicle by enabling multiple automated guided vehicles to pass smoothly through intersections of travel lines. [Means for solving the problem]

[0007] An automated guided vehicle (AGV) travel system according to one aspect of the present invention comprises: a plurality of travel lines laid on a road surface that intersect each other at intersection points; a mark provided at a position spaced apart from the intersection point along the travel line for each of the travel lines; each AGV that travels along the plurality of travel lines; and a management device that transmits a semaphore indicating permission to pass through the intersection point to each AGV, wherein each AGV comprises: a first communication unit that wirelessly transmits information to the management device; a mark detection unit that detects the mark; and a first control unit that causes the first communication unit to transmit a request for the semaphore to the management device, and the management device wirelessly transmits information to each AGV The system includes a second communication unit that transmits messages, and a second control unit that, when the second communication unit receives a semaphore request from each of the automated guided vehicles, causes the second communication unit to transmit the semaphore to the automated guided vehicle that transmitted the semaphore request that was received first, in accordance with the semaphore request that was received first, and transmits the semaphore to another automated guided vehicle that transmitted the semaphore request when the second communication unit receives return information indicating the return of the semaphore transmitted from the automated guided vehicle that transmitted the semaphore, or when the time since the second communication unit has not received the return information reaches a predetermined time.

[0008] Furthermore, an automated guided vehicle (AGV) travel control method according to one aspect of the present invention includes the steps of: driving each AGV along a plurality of travel lines laid on the road surface that intersect each other at intersection points; requesting a semaphore indicating permission to pass the intersection point when the AGV reaches a predetermined position separated from the intersection point along the travel line; continuing the AGV's travel when the semaphore is received, and transmitting return information to the management device indicating that the semaphore is valid when the AGV has passed the intersection point; stopping the AGV if the AGV has not received the semaphore, and resuming the AGV's travel when the semaphore is received; and transmitting the semaphore to another AGV that has requested the semaphore when the management device receives return information indicating the return of the semaphore transmitted from the AGV that transmitted the semaphore, or when a predetermined period of time has passed during which the return information has not been received. [Effects of the Invention]

[0009] According to the present invention, multiple automated guided vehicles (AGVs) can be smoothly passed through intersections of travel lines, thereby improving the operational efficiency of each AGV. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing an automated guided vehicle (AGV) travel system according to one embodiment of the present invention. [Figure 2] This is a close-up diagram of an automated guided vehicle (AGV). [Figure 3] This is a plan view showing an enlarged view of the travel line and magnetic mark in the automated guided vehicle travel system of this embodiment. [Figure 4](A) is a diagram showing the rotation of each drive wheel when the automated guided vehicle (AGV) is moving forward, (B) is a diagram showing the rotation of each drive wheel when the AGV is moving backward, (C) is a diagram showing the rotation of each drive wheel when the AGV is changing direction to the right, and (D) is a diagram showing the rotation of each drive wheel when the AGV is changing direction to the left. [Figure 5] (A) is a diagram showing the rotation of each drive wheel when the automated guided vehicle (AGV) is turned to the right, and (B) is a diagram showing the rotation of each drive wheel when the AGV is turned to the left. [Figure 6] This is a block diagram showing the configuration of an automated guided vehicle and its management system. [Figure 7] This is a map showing the coordinates of the first and second running lines and each magnetic mark. [Figure 8] This figure shows the data table used by the automated guided vehicle (AGV) for its control. [Figure 9] This diagram shows a data table used by a control device for controlling automated guided vehicles (AGVs). [Figure 10] This flowchart shows the control system for smoothly navigating the first and second automated guided vehicles at the intersection. [Figure 11] This diagram shows three or more travel lines intersecting at each intersection point, and each automated guided vehicle traveling along each travel line. [Figure 12] This flowchart shows another embodiment of control for smoothly navigating the first and second automated guided vehicles at an intersection. [Modes for carrying out the invention]

[0011] Hereinafter, an automated guided vehicle (AGV) travel system and an AGV travel control method according to one embodiment of the present invention will be described with reference to the drawings. In the following, rotational directions or left / right and up / down directions may be indicated, but unless otherwise specified, these refer to directions as examples in each drawing.

[0012] Figure 1 is a schematic diagram showing an automated guided vehicle (AGV) travel system according to one embodiment of the present invention. The AGV travel system Sy shown in Figure 1 comprises a first travel line 11 and a second travel line 12 laid on the road surface and intersecting each other at intersection point G, a plurality of marks 20 arranged on one side of the first travel line 11 and the second travel line 12, a first AGV 31 that travels back and forth along the first travel line 11, a second AGV 32 that travels back and forth along the second travel line 12, and a management device 50. The type of marks 20 is not particularly limited, but in this embodiment, the case in which the marks 20 are magnetic marks will be described as an example. When the marks 20 are not magnetic marks, a sensor capable of detecting the applicable marks will be appropriately used instead of the magnetic sensor 15 described later.

[0013] Figure 2 is a magnified view of the automated guided vehicle (AGV). The AGV is either the first AGV 31 or the second AGV 32 (also simply referred to as the AGV), and both vehicles have the same configuration. The first and second AGVs 31 and 32 are equipped with line sensors 14 that are positioned facing the road surface and detect the first travel line 11 and the second travel line 12 (also simply referred to as the travel line), and magnetic sensors 15 that detect magnetic mark 20. The line sensor 14 includes, for example, an optical sensor such as a CCD (Charge Coupled Device). In this embodiment, an example in which the line sensor 14 includes a CCD will be described.

[0014] In addition, as a method of reading the first travel line 11 and the second travel line 12 by the line sensor 14 and making the automated guided vehicle travel, there are a magnetic induction method and an optical induction method. The magnetic induction method creates a travel line by pasting a magnetic tape or burying a magnetic rod on the floor surface, and makes the automated guided vehicle travel along the course indicated by the travel line detected by the magnetic sensor along the magnetic field of the travel line. Also, the optical induction method creates a course by pasting a guiding tape (for example, a vinyl tape) on the floor surface in the same manner as the magnetic induction method, and makes the automated guided vehicle travel from the semaphore request along the course indicated by the travel line detected by the reflection of light by the optical sensor. In the present embodiment, an example of adopting the optical induction method is shown. The first travel line 11 and the second travel line 12 are constituted by a guiding tape such as a vinyl tape.

[0015] In the main bodies 30A of the first and second automated guided vehicles 31 and 32, the line sensor 14 and the magnetic sensor 15 are arranged side by side at the center in the width direction of the main body 30A of the automated guided vehicle and along the travel direction A of the automated guided vehicle. The first and second automated guided vehicles 31 and 32 are controlled to travel, for example, with the first travel line 11 or the second travel line 12 positioned at the center in their width direction. At this time, the position where the magnetic sensor 15 is disposed in the first and second automated guided vehicles 31 and 32 is such that, regardless of whether traveling in either the one direction along the first travel line 11 or the second travel line 12 or the reverse direction, it is possible to read any one of the marks 20 arranged on both sides of the line at each position of the first travel line 11 and the second travel line 12. Here, the line sensor 14 is arranged on the traveling direction side of the automated guided vehicle with respect to the magnetic sensor 15, but the arrangement order of the line sensor 14 and the magnetic sensor 15 may be reversed. [[ID=⑤]] [[ID=⑥]]

[0016] [[ID=⑦]] [[ID=⑧]]In the first and second automated guided vehicles 31 and 32, steering control is performed according to the position of the travel line detected by the line sensor 14, and control such as making the automated guided vehicle travel, stop, and turn is performed according to the number of magnetic marks 20 sequentially detected by the magnetic sensor 15. [[ID=⑨]] [[ID=⑩]]

[0017] FIG. 3 is a diagram showing an enlarged view of the first and second travel lines 11 and 12 and the magnetic mark 20. As shown in FIG. 3, the first and second travel lines 11 and 12 are strip-shaped and sheet-shaped non-magnetic bodies having a uniform width, and are black or gray. The color or density of the first and second travel lines 11 and 12 has a sufficient difference from the color or density of the road surface.

[0018] The magnetic mark 20 is a sheet-shaped magnetic body. When the unmanned transport vehicle travels in both directions, i.e., in one direction along the first and second travel lines 11 and 12 and in the reverse direction thereof, the magnetic mark 20 is disposed on both sides of the first and second travel lines 11 and 12. Also, when the unmanned transport vehicle travels only in one direction along the first and second travel lines 11 and 12, the magnetic mark 20 is disposed on one side of the first and second travel lines 11 and 12. In the present embodiment, a case where the unmanned transport vehicle travels in both directions, i.e., in one direction along the first and second travel lines 11 and 12 and in the reverse direction thereof, will be described. It is preferable that the color or density of the magnetic mark 20 is clearly different from the color or density of the first and second travel lines 11 and 12.

[0019] As shown in FIG. 2, casters (swivel casters) 33 are provided at the four corners of the bottom of the first and second unmanned transport vehicles 31 and 32, respectively. Inside the bottom of the first and second unmanned transport vehicles 31 and 32, four drive wheels 34 are provided so as to be spaced apart from each other in a direction orthogonal to the travel direction A of the unmanned transport vehicle, and the axes of the respective drive wheels 34 are arranged in a straight line. Under the control by a control unit 45 (FIG. 6) described later, each drive wheel 34 is rotationally driven by a respective travel drive motor, so that the unmanned transport vehicle travels and each caster 33 rotates in a driven manner.

[0020] Here, with each drive wheel 34 in contact with the floor, the control unit 45 controls the drive motor of each drive wheel 34, adjusting the rotation speed of the drive wheels 34 and switching the rotation direction of the drive wheels 34, causing the first and second automated guided vehicles 31 and 32 to travel. Steering control is also performed on the first and second automated guided vehicles 31 and 32, thereby changing the direction of travel of the first and second automated guided vehicles 31 and 32, and consequently causing each caster 33 to rotate in response and change its orientation.

[0021] The rotational control of each drive wheel 34 when the first and second automated guided vehicles 31 and 32 are driven will be explained. Figures 4(A) to (D) and 5(A) and (B) show the rotational direction and rotational speed of each drive wheel 34 for each direction of travel of the first and second automated guided vehicles 31 and 32. As mentioned above, the directions shown in the explanation referring to Figures 4 and 5 are for the examples shown in Figures 4 and 5. The rotational control of each drive wheel 34 shown below is performed by the control unit 45.

[0022] As shown in Figure 4(A), when the first and second automated guided vehicles 31 and 32 are moved forward, the four drive wheels 34 are rotated at the same rotational speed in the direction in which the automated guided vehicles move forward (hereinafter referred to as the forward direction).

[0023] As shown in Figure 4(B), when the first and second automated guided vehicles 31 and 32 are moved in reverse, the four drive wheels 34 are rotated at the same rotational speed in the direction in which the automated guided vehicles are moving in reverse (hereinafter referred to as the reverse direction).

[0024] As shown in Figure 4(C), when turning the first and second automated guided vehicles 31 and 32 to the right, the two left drive wheels 34 are rotated in the forward direction, while the two right drive wheels 34 are rotated in the forward direction at a slower rotational speed than each of the left drive wheels 34, or are stopped. At this time, the rotational speed of the left outer drive wheel 34 may be set to be the fastest, the rotational speed of the left inner drive wheel 34 to be the second fastest, the rotational speed of the right inner drive wheel 34 to be the third fastest, and the rotational speed of the right outer drive wheel 34 to be the slowest or stopped. By appropriately setting the rotational speeds of the four drive wheels 34, the turning radius of the automated guided vehicle can be changed.

[0025] As shown in Figure 4(D), when turning the first and second automated guided vehicles 31 and 32 to the left, the two right drive wheels 34 are rotated in the forward direction, while the two left drive wheels 34 are rotated in the forward direction at a slower rotational speed than each of the right drive wheels 34, or are stopped. At this time, the rotational speed of the right outer drive wheel 34 may be set to be the fastest, the rotational speed of the right inner drive wheel 34 to be the second fastest, the rotational speed of the left inner drive wheel 34 to be the third fastest, and the rotational speed of the left outer drive wheel 34 to be the slowest or stopped. By appropriately setting the rotational speeds of the four drive wheels 34, the turning radius of the automated guided vehicle can be changed.

[0026] Furthermore, as shown in Figure 5(A), when the first and second automated guided vehicles 31 and 32 are turned to the right (spin turn) around the pivot center Q of the automated guided vehicles, the two left drive wheels 34 are rotated in the forward direction, while the two right drive wheels 34 are rotated in the opposite direction at the same rotational speed as the two left drive wheels 34. Also, as shown in Figure 5(B), when the first and second automated guided vehicles 31 and 32 are turned to the left (spin turn) around the pivot center Q of the automated guided vehicles, the two right drive wheels 34 are rotated in the forward direction, while the two left drive wheels 34 are rotated in the opposite direction at the same rotational speed as the two right drive wheels 34.

[0027] In this way, the control unit 45 controls the rotational speed and rotational direction of the four drive wheels 34, respectively, thereby enabling the first and second automated guided vehicles 31 and 32 to move forward, backward, change direction to the right or left, and rotate to the right or left. In addition, the four casters 33 change their orientation according to the direction of travel of the first and second automated guided vehicles 31 and 32, stably supporting the first and second automated guided vehicles 31 and 32 so that they can move freely. As a result, despite the simple configuration, it is possible to stably change the orientation of the first and second automated guided vehicles 31 and 32 while they are in motion.

[0028] Although four drive wheels 34 are shown as an example here, it is also possible to configure the system by distributing two drive wheels 34 from the center of the width direction of the main body 30A of the automated guided vehicle (AGV) to the left and right, and controlling the rotation speed and rotation direction of the left and right drive wheels 34 respectively to drive the AGV as described above.

[0029] Figure 6 is a block diagram showing the configuration of the first and second automated guided vehicles 31 and 32 and the management device 50. As shown in Figure 6, the first and second automated guided vehicles 31 and 32 are equipped with a line sensor 14, a magnetic sensor 15, each drive motor 42 that rotates each drive wheel 34, a short-range communication unit 43, a storage unit 44, and a control unit 45.

[0030] As shown in Figure 2, the line sensor 14 is positioned approximately perpendicular to the travel line during the transport of the first and second automated guided vehicles 31 and 32, and optically detects the position of the travel line in the longitudinal direction of the line sensor 14 (the width direction of the main body 30A).

[0031] Furthermore, as shown in Figure 2, the magnetic sensor 15 is positioned in the center of the main body 30A of the first and second automated guided vehicles 31 and 32, and is aligned with the line sensor 14 along the travel direction A of the automated guided vehicle. The magnetic sensor 15 magnetically detects the magnetic mark 20 that is placed on top of the travel line.

[0032] The near-field communication unit 43 is a communication module that transmits and receives control information to and from the management device 50 using a near-field communication method, such as Bluetooth Low Energy (BLE), or Bluetooth®. Alternatively, the near-field communication method used by the near-field communication unit 43 may be WiFi® Direct, a method compliant with the IEEE 802.11 standard, or other methods.

[0033] The memory unit 44 is a volatile memory capable of temporary storage, such as RAM. The memory unit 44 stores control information for the first and second automated guided vehicles 31 and 32, associated with the number of magnetic marks 20 sequentially detected by the magnetic sensor 15. The memory unit 44 also stores valid information indicating the semaphore is "valid" or invalid information indicating it is "invalid". A valid semaphore indicates that the automated guided vehicle is permitted to pass through the intersection point G of the first and second travel lines 11 and 12. An invalid semaphore indicates that the automated guided vehicle is not permitted to pass through the intersection point G of the first and second travel lines 11 and 12. The memory unit 44 also stores a timeout period (the time specified in the claims) T1 instructed by the management device 50, as will be described later. The control unit 45 receives the control information, the valid information or invalid information, and the timeout period from the management device 50 via the short-range communication unit 43 at a predetermined timing before the automated guided vehicle starts moving, and stores them in the RAM. This control information stored in the storage unit 44 is erased after the power to the automated guided vehicle is turned off.

[0034] Alternatively, instead of this configuration, an HDD or SSD may be used as the storage unit 44, and the control information and the valid information or invalid information may be stored in the storage unit 44 at all times. In this case, the storage unit 44 stores the control information, the valid information or invalid information and the timeout period from the start of use of the automated guided vehicle, and this information continues to be stored even after the power to the automated guided vehicle is turned off.

[0035] The control unit 45 is comprised of a processor, RAM (Random Access Memory), ROM (Read Only Memory), and dedicated hardware circuitry. The processor is, for example, a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), or an MPU (Micro Processing Unit).

[0036] The control unit 45 executes the above-described controls and processes, including the control of the travel drive motor 42 (an example of a travel drive unit) for moving the first automated guided vehicle 31 or the second automated guided vehicle 32, by operation of the processor according to the control program stored in the memory unit 44. In other words, the control unit 45 comprehensively controls the first automated guided vehicle 31 or the second automated guided vehicle 32. However, the control unit 45 may be configured by hardware circuits such as ASICs instead of operation by a processor according to a control program.

[0037] For example, the control unit 45 controls the rotation speed and direction of each drive motor 42 to adjust the rotation speed and direction of each drive wheel 34. The control unit 45 also transmits and receives control information to and from the management device 50 via the short-range communication unit 43.

[0038] Furthermore, the management device 50 is, for example, a computer or workstation, and includes a short-range communication unit 53, a storage unit 54, and a control unit 55.

[0039] The short-range communication unit 53 is a communication module that transmits and receives control information between the first and second unmanned transport vehicles 31 and 32 using a short-range communication method.

[0040] The storage unit 54 includes an HDD or SSD, etc. The storage unit 54 stores the status of the first and second automated guided vehicles 31 and 32. In addition, the storage unit 54 stores either "enabled" information indicating the semaphore status or "inactive" information indicating the semaphore status separately for the first and second automated guided vehicles 31 and 32.

[0041] The control unit 55 is comprised of a processor, RAM (Random Access Memory), ROM (Read Only Memory), and dedicated hardware circuitry. The processor is, for example, a CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), or an MPU (Micro Processing Unit).

[0042] The control unit 55 comprehensively controls the management device 50 through the operation of the processor in accordance with the control program stored in the memory unit 54. However, the control unit 55 may be configured by hardware circuits such as ASICs instead of relying on the operation of a processor in accordance with the control program.

[0043] For example, the control unit 55 transmits and receives control information between the first and second unmanned transport vehicles 31 and 32 via the short-range communication unit 53.

[0044] Furthermore, the magnetic mark 20 corresponds to the mark in the claims, and the magnetic sensor 15 corresponds to the mark detection unit in the claims. In addition, the short-range communication unit 43 corresponds to the first communication unit in the claims, and the control unit 45 corresponds to the first control unit in the claims. Also, the short-range communication unit 53 corresponds to the second communication unit in the claims, and the control unit 55 corresponds to the second control unit in the claims.

[0045] In the first and second automated guided vehicles 31 and 32 configured as described above, the control unit 45 determines the amount of deviation between the position of the travel line in the longitudinal direction of the line sensor 14 (the width direction of the main body 30A of the automated guided vehicle) detected by the line sensor 14 and the center position of the line sensor 14 (the center position of the main body 30A). The control unit 45 controls the drive motors 42 of each drive wheel 34 to drive so that this amount of deviation becomes "0", thereby changing the orientation of the automated guided vehicle and controlling the automated guided vehicle to travel along the travel line.

[0046] As a result, the center of the main body 30A of the automated guided vehicle (AGV) aligns with the position of the travel line and the magnetic mark 20, and the AGV travels along the travel line and the magnetic mark 20.

[0047] Furthermore, when the automated guided vehicle (AGV) is traveling along the travel line, a magnetic sensor 15 positioned in the center of the width direction of the AGV's main body 30A magnetically detects each magnetic mark 20 superimposed on the travel line in sequence. After the control unit 45 starts the AGV 30 from a preset starting position, each time the magnetic sensor 15 sequentially detects each magnetic mark 20, it counts the number of detected magnetic marks 20, reads the AGV processing corresponding to this counted number of magnetic marks 20 from the storage unit 44, and controls the operation of the AGV based on this read processing. For example, based on the read processing, the control unit 45 controls the rotation speed and rotation direction of the drive motor 42 of each drive wheel 34 to adjust the rotation speed and rotation direction of the drive wheels 34, causing the AGV to move forward, backward, stop, and increase or decrease the AGV's travel speed.

[0048] Here, each magnetic mark 20 is placed on top of the travel line, but it is also possible to place each magnetic mark 20 along the travel line at a certain distance away from the travel line, and place the magnetic sensor 15 at the same certain distance from the center of the main body 30A of the automated guided vehicle, so that when the automated guided vehicle travels along the travel line, the magnetic sensor 15 sequentially detects each magnetic mark 20 arranged along the travel line.

[0049] Figure 7 illustrates a map MP of the road surface on which the first and second automated guided vehicles 31 and 32 travel. In Figure 7 and Figure 11 described later, for the sake of simplicity, the position of the mark 20 is shown as being on the travel line, and the position of the magnetic sensor 15 on the automated guided vehicle is shown as the position corresponding to the mark 20 at that position. As shown in Figure 7, the map MP is in a Cartesian coordinate system, and the coordinates of one end (X1, Y5) and the other end (XA, Y5) of the first travel line 11, the coordinates of one end (X5, Y1) and the other end (X5, YA) of the second travel line 12, and the coordinates of the intersection position G of the first travel line 11 and the second travel line 12 (X5, Y5) are determined by the combination of each position X1 to XA in the X direction and each position Y1 to YA in the Y direction.

[0050] Six coordinates (X1,Y5), (X3,Y5), (X4,Y5), (X6,Y5), (X7,Y5), and (XA,Y5) that overlap with the first travel line 11 have magnetic mark 20s placed there. Similarly, six coordinates (X5,Y1), (X5,Y3), (X5,Y4), (X5,Y6), (X5,Y7), and (X5,YA1) that overlap with the second travel line 12 have magnetic mark 20s placed there.

[0051] As shown in map MP, two coordinates (X4, Y5) and (X6, Y5) located on either side of the intersection point G along the first travel line 11 are designated as first positions P1, and two coordinates (X3, Y5) and (X7, Y5) located further apart from the first positions P1 on either side of the intersection point G are designated as second positions P2. Each first position P1 and each second position P2 is assigned a magnetic mark 20.

[0052] Similarly, two coordinates (X5, Y4) and (X5, Y6) located on either side of the intersection point G along the second travel line 12 are designated as first positions P1, and two coordinates (X5, Y3) and (X5, Y7) located further apart from the first positions P1 on either side of the intersection point G are designated as second positions P2. Each first position P1 and each second position P2 is positioned with its respective magnetic mark 20.

[0053] For example, the first automated guided vehicle 31 starts traveling from coordinates (X1, Y5) at one end of the first travel line 11 under the control of the control unit 45. The control unit 45 of the first automated guided vehicle 31 controls the drive motors 42 of each drive wheel 34 to drive along the first travel line 11 so that the amount of deviation between the position of the first travel line 11 detected by the line sensor 14 and the center position of the line sensor 14 becomes "0". At this time, the control unit 45 of the first automated guided vehicle 31 counts up the number of magnetic marks 20 each time the magnetic sensor 15 detects five coordinates (X3,Y5), (X4,Y5), (X6,Y5), (X7,Y5), and (XA,Y5) that overlap the first travel line 11. When this number reaches "5", that is, when the first automated guided vehicle 31 reaches the other end of the first travel line 11, it reads the control information associated with the number "5" from the storage unit 44. According to this control information, it drives the travel drive motors 42 of each drive wheel 34 to stop the first automated guided vehicle 31, rotate it 180°, make the first automated guided vehicle 31 move forward, and initializes the counted number of magnetic marks 20 "5" to "0".

[0054] After the 180° rotation described above, the control unit 45 of the first automated guided vehicle 31 causes the first automated guided vehicle 31 to travel along the first travel line 11 in the opposite direction to the above, based on the position of the first travel line 11 detected by the line sensor 14. At this time, the control unit 45 of the first automated guided vehicle 31 counts up the number of magnetic marks 20 each time the magnetic sensor 15 detects five coordinates (X7,Y5), (X6,Y5), (X4,Y5), (X3,Y5), and (X1,Y5) that overlap the first travel line 11. When this number reaches "5", that is, when the first automated guided vehicle 31 reaches one end of the first travel line 11, it reads the control information associated with the number "5" from the storage unit 44. According to this control information, it drives the travel drive motors 42 of each drive wheel 34 to stop the first automated guided vehicle 31, rotate it 180°, make the first automated guided vehicle 31 move forward, and initializes the counted number of magnetic marks 20 "5" to "0".

[0055] In this manner, the first automated guided vehicle 31 repeatedly travels back and forth between coordinates (X1, Y5) and coordinates (XA, Y5) along the first travel line 11 under the control of the control unit 45.

[0056] Similarly, the second automated guided vehicle 32 starts traveling from coordinates (X5, Y1) at one end of the second travel line 12 under the control of the control unit 45. The control unit 45 of the second automated guided vehicle 32 makes the second automated guided vehicle 32 travel along the second travel line 12 based on the position of the second travel line 12 detected by the line sensor 14. At this time, the control unit 45 of the second automated guided vehicle 32 counts up the number of magnetic marks 20 each time the magnetic sensor 15 detects five coordinates (X5,Y3), (X5,Y4), (X5,Y6), (X5,Y7), and (X5,YA) that overlap the second travel line 12. When this number reaches "5", and the second automated guided vehicle 32 reaches the other end of the second travel line 12, it reads the control information associated with the number "5" from the storage unit 44. According to this control information, it drives the travel drive motors 42 of each drive wheel 34 to stop the second automated guided vehicle 32, rotate it 180°, make the second automated guided vehicle 32 move forward, and initializes the counted number of magnetic marks 20 "5" to "0".

[0057] After the 180° turn described above, the control unit 45 of the second automated guided vehicle 32 moves the second automated guided vehicle 32 along the second travel line 12 in the opposite direction from before the turn, and each time the magnetic sensor 15 detects one of the five magnetic marks 20 at coordinates (X5,Y7), (X5,Y6), (X5,Y4), (X5,Y3), and (X5,Y1) that overlap the second travel line 12, it counts up the number of magnetic marks 20, and when this number reaches "5" Therefore, when the second automated guided vehicle 32 reaches one end of the second travel line 12, the control information associated with the number "5" is read from the storage unit 44, and according to this control information, the travel drive motors 42 of each drive wheel 34 are driven to stop the second automated guided vehicle 32, rotate it 180°, move the second automated guided vehicle 32 forward, and initialize the counted number of magnetic marks 20 from "5" to "0".

[0058] In this manner, the second automated guided vehicle 32 repeatedly travels back and forth between coordinates (X5, Y1) and coordinates (X5, YA) along the second travel line 12 under the control of the control unit 45.

[0059] As described above, when the first and second automated guided vehicles 31 and 32 are made to travel back and forth along the first and second travel lines 11 and 12, it is necessary to ensure that the first and second automated guided vehicles 31 and 32 do not come into contact or collide at the intersection point G. If the control system is such that the first and second automated guided vehicles 31 and 32 are made to temporarily stop before the intersection point G, and only resume travel after confirming that no other automated guided vehicles have passed the intersection point G, the operational efficiency of each automated guided vehicle will be reduced by temporarily stopping the first and second automated guided vehicles 31 and 32 before the intersection point G.

[0060] Therefore, in this embodiment, when the control units 45 of the first and second automated guided vehicles 31 and 32 reach the second position P2 before the intersection point G, they cause the short-range communication unit 43 to send a semaphore request indicating permission to pass through the intersection point G to the management device 50. When the control unit 55 of the management device 50 receives the semaphore request in the short-range communication unit 53, it causes the short-range communication unit 53 to send a semaphore to one of the first and second automated guided vehicles 31 or 32, in this case the automated guided vehicle that received the request first. The control unit 45 of the automated guided vehicle that sent the request first, on the condition that the semaphore is received by the short-range communication unit 43 from the management device 50, drives the travel drive motor 42 to maintain travel without stopping the automated guided vehicle and pass through the intersection point G, and after passing through the intersection point G, it causes the short-range communication unit 43 to send return information indicating the return of the semaphore to the management device 50.

[0061] When the control unit 55 of the management device 50 receives the return information from one of the automated guided vehicles (AGVs) via the short-range communication unit 53, it then instructs the other AGV to transmit a semaphore from the short-range communication unit 53. The control unit 45 of the other AGV temporarily stops it at the first position P1 before the intersection point G until the semaphore is received by the short-range communication unit 43. When the semaphore is received by the short-range communication unit 43 (the above condition is met), the control unit 45 of the other AGV drives the drive motor 42 to move the other AGV and pass through the intersection point G. This allows the AGV that previously requested the semaphore to pass through the intersection point G without being stopped, thus improving the operating efficiency of each AGV.

[0062] Here, as described above, the first and second automated guided vehicles 31 and 32 receive semaphores from the management device 50 and, in order to enable them to travel according to the semaphores, the storage units 44 of the first and second automated guided vehicles 31 and 32 have data tables used for controlling the automated guided vehicles pre-stored. In addition, the storage unit 54 of the management device 50 has another data table used for controlling the automated guided vehicles pre-stored.

[0063] Here, if, for example, short-range communication between the management device 50 and the automated guided vehicle is interrupted while one automated guided vehicle is passing through intersection point G, the control unit 55 of the management device 50 will not receive the return information indicating the return of the semaphore from the short-range communication unit 53, and therefore will not be able to transmit the semaphore to the next automated guided vehicle. As a result, the next automated guided vehicle will remain stopped before reaching intersection point G, causing a delay.

[0064] Therefore, in this embodiment, the control unit 55 of the management device 50 controls the transmission of the semaphore from the short-range communication unit 53 to the next unmanned transport vehicle when the short-range communication unit 53 receives semaphore return information transmitted from one unmanned transport vehicle. It also controls the transmission of the semaphore from the short-range communication unit 53 to the next unmanned transport vehicle when the time during which the semaphore return information is not received by the short-range communication unit 53 reaches the timeout period (the time specified in the claims) T1. This prevents the next unmanned transport vehicle from stopping and becoming stuck before the intersection point G.

[0065] Figure 8 shows a data table pre-stored in the memory unit 44 of the first and second automated guided vehicles 31 and 32 and used for controlling the automated guided vehicles. The data table DT1 shown in Figure 8 stores control information corresponding to the number of magnetic marks 20 detected by the magnetic sensor 15, from "1" to "5". The data table DT1 also stores "enabled" or "disabled" information indicating the semaphore state assigned to its own automated guided vehicle. Furthermore, the data table DT1 stores an intersection position ID indicating the intersection point where the automated guided vehicle crosses another automated guided vehicle on the travel line it is traveling on. In this embodiment, the data table DT1 stores information indicating the intersection position G(X5,Y5) as the intersection position ID. Furthermore, the data table DT1 also stores the timeout period (the time specified in the claims) T1 transmitted from the management device 50. In this embodiment, when the control units 45 of the first and second automated guided vehicles 31 and 32 start driving control of the first and second automated guided vehicles 31 and 32, they receive the data table DT1 from the management device 50 via the short-range communication unit 43 and store it in the storage unit 44.

[0066] For example, the first automated guided vehicle 31 starts traveling from one end (X1, Y5) of the first travel line 11 towards the intersection point G. At this point, the count of magnetic marks 20 by the control unit 45 is reset to "0". When the first automated guided vehicle 31 reaches the coordinates (X3, Y5) of the second position P2, the magnetic marks 20 located at that position are detected by the magnetic sensor 15, and the control unit 45 counts the number of magnetic marks 20 as "1". Similarly, when the second automated guided vehicle 32 starts traveling from one end (X5, Y1) of the second travel line 12 towards the intersection point G and reaches the coordinates (X5, Y3) of the second position P2, the control unit 45 counts the number of magnetic marks 20 detected by the magnetic sensor 15 as "1".

[0067] The data table DT1 stores control information associated with the number of magnetic mark 20, namely "1," including a semaphore request and the transmission of an intersection position ID. The intersection position ID is information indicating the intersection position corresponding to the second position P2 at the location of the automated guided vehicle when the number of marks is counted as "1." In this embodiment, the intersection position information is (X5, Y5).

[0068] When the first automated guided vehicle 31 continues traveling along the first travel line 11 and reaches the coordinates of the first position P1 (X4, Y5) from (X3, Y5), the control unit 45 counts up the number of magnetic marks 20 to "2" due to further detection of magnetic marks 20 by the magnetic sensor 15. Similarly, when the second automated guided vehicle 32 continues traveling along the second travel line 12 and reaches the coordinates of the first position P1 (X5, Y4), the number of magnetic marks 20 detected by the magnetic sensor 15 and counted up by the control unit 45 becomes "2".

[0069] Data table DT1 stores two pieces of control information associated with the number of magnetic mark 20s, which is "2". The two pieces of control information are: (1) "Continue driving" when a semaphore is received, and (2) "Stop driving temporarily and resume driving when a semaphore is received" when a semaphore is not received.

[0070] When the first automated guided vehicle 31 travels along the first travel line 11, passes the intersection point G from (X4, Y5) to (X5, Y5), and reaches the coordinates (X6, Y5) of the next first position P1, the magnetic sensor 15 detects magnetic marks 20, and the control unit 45 counts up the number of detected magnetic marks 20 to "3". Similarly, when the second automated guided vehicle 32 travels along the second travel line 12, passes the intersection point G, and reaches the coordinates (X5, Y6) of the next first position P1, the magnetic sensor 15 detects magnetic marks 20, and the control unit 45 counts up the number of detected magnetic marks 20 to "3".

[0071] The data table DT1 stores the transmission of the semaphore return as control information associated with the number "3" of magnetic mark 20 detected by the magnetic sensor 15.

[0072] When the first automated guided vehicle 31 travels along the first travel line 11 and reaches (X7, Y5), the magnetic sensor 15 detects magnetic marks 20, and the control unit 45 counts up the number of detected magnetic marks 20 to "4". When the second automated guided vehicle 32 travels along the first travel line 12 and reaches (X5, Y7), the magnetic sensor 15 detects magnetic marks 20, and the control unit 45 counts up the number of detected magnetic marks 20 to "4". The data table DT1 does not store control information associated with the number of magnetic marks 20 "4".

[0073] As described above, when the first automated guided vehicle 31 reaches the coordinates (XA, Y5) at the other end of the first travel line 11, the magnetic sensor 15 detects the magnetic marks 20, and the control unit 45 counts up the number of detected magnetic marks 20 to "5". Similarly, when the second automated guided vehicle 32 reaches the coordinates (X5, YA) at the other end of the second travel line 12, the magnetic sensor 15 detects the magnetic marks 20, and the control unit 45 counts up the number of detected magnetic marks 20 to "5". The data table DT1 stores control information associated with the number of magnetic marks 20 "5", including "stopping the automated guided vehicle, turning 180°, traveling (forward), and initializing the number of magnetic marks 20".

[0074] In this manner, magnetic marks 20 are successively detected by the magnetic sensors 15 of each automated guided vehicle (AGV), and control information corresponding to the number of detected magnetic marks 20 is read from the data table DT1. The control units 45 of each AGV then control the movement of the AGV according to the contents indicated by the control information.

[0075] Furthermore, when the first automated guided vehicle 31 starts traveling from the other end (XA, Y5) of the first travel line 11 toward the intersection point G, and the second automated guided vehicle 32 starts traveling from the other end (X5, YA) of the second travel line 12 toward the intersection point G, the magnetic marks 20 are detected sequentially by the magnetic sensors 15 of both automated guided vehicles in the same manner as described above. Control information corresponding to the number of detected magnetic marks 20 is read from the data table DT1, and the control unit 45 controls the movement of the automated guided vehicles according to the contents indicated by the control information.

[0076] Figure 9 shows a data table pre-stored in the storage unit 54 of the management device 50 and used for controlling automated guided vehicles (AGVs). The data table DT2 shown in Figure 9 stores, separately for the first and second AGVs 31 and 32, an intersection position ID indicating the intersection position, the semaphore status ("enabled" or "disabled"), and the operating status of the AGV. The control unit 55 stores the semaphore status in the storage unit 54 in two patterns: (1) all semaphores of the AGVs are "disabled", and (2) the semaphore of one AGV is "enabled" and the semaphores of all other AGVs are "disabled". In other words, the control unit 55 controls the transmission of semaphores to each AGV so that the semaphore status is either (1) or (2) above.

[0077] In the data table DT2 shown in Figure 9, the first and second automated guided vehicles 31 and 32 are shown as examples. However, as will be described later, when three or more automated guided vehicles are operated along their respective travel lines, the intersection position ID indicating the intersection point, the semaphore status ("enabled" or "disabled"), and the operating status of the automated guided vehicle are stored separately for each vehicle.

[0078] Next, the control for smoothly moving the first and second automated guided vehicles 31 and 32 at the intersection point G will be explained with reference to the flowchart shown in Figure 10. In the flowchart, the processing of the first and second automated guided vehicles 31 and 32 is shown in S101 to S111, and the processing of the second automated guided vehicle 32 is shown in S201 to S211.

[0079] Assume that the first automated guided vehicle 31 travels back and forth along the first travel line 11, and the second automated guided vehicle 32 travels back and forth along the second travel line 12.

[0080] Here, the first automated guided vehicle 31 is assumed to start traveling from either end of the first travel line 11. At this point, the number of magnetic marks 20 detected by the magnetic sensor 15 stored in the memory unit 44 is assumed to be "0" after being initialized by the control unit 45 (S101).

[0081] As described above with reference to Figures 7 and 8, the configuration of the automated guided vehicle (AGV) travel system Sy is as described above. When the first AGV 31 reaches either end of the first travel line 11, the control unit 45 of the first AGV 31 counts up the number of magnetic marks 20 to "5" based on the detection of magnetic marks 20 by the magnetic sensor 15. The control unit 45 reads the control information associated with the number "5" from the data table DT1, and according to this control information, drives the travel drive motors 42 of each drive wheel 34 to stop the first AGV 31, rotate it 180°, make the first AGV 31 travel forward, and initializes the number of magnetic marks 20 stored in the memory unit 44 to "0". At this time, the semaphore state in the data table DT1 is "inactive".

[0082] Under similar control, the second automated guided vehicle 32 will begin traveling from either end of the second travel line 12. At this point, the number of magnetic marks 20 detected by the magnetic sensor 15 stored in the memory unit 44 will be initialized to "0" by the control unit 45 (S201). The semaphore state in the data table DT1 is "invalid".

[0083] Then, for example, when the first automated guided vehicle 31 starts traveling from one end (X1, Y5) of the first travel line 11 and reaches the coordinates (X3, Y5) of the second position P2, the control unit 45 of the first automated guided vehicle 31 counts up the number of magnetic marks 20 detected by the magnetic sensor 15, reads the control information associated with the number "1" from the data table DT1, and, according to this control information, has the short-range communication unit 43 transmit a semaphore request and an intersection position ID (information indicating (X5, Y5) in this example) along with identification information indicating the first automated guided vehicle 31 to the management device 50 (S102 "Yes"). After this, the control unit 45 determines whether the semaphore has been received by the short-range communication unit 43 (S103).

[0084] Similarly, when the second automated guided vehicle 32 starts traveling from one end (X5, Y1) of the second travel line 12 and reaches the coordinates (X5, Y3) of the second position P2, the control unit 45 of the second automated guided vehicle 32 counts up the number of magnetic marks 20 detected by the magnetic sensor 15 to "1", reads the control information associated with the number "1" from the data table DT1, and, according to this control information, has the short-range communication unit 43 transmit a semaphore request and an intersection position ID (information indicating (X5, Y5) in this example) along with the identification information of the second automated guided vehicle 32 to the management device 50 (S202 "Yes"). After this, the control unit 45 determines whether the semaphore has been received by the short-range communication unit 43 (S203).

[0085] Meanwhile, when the first automated guided vehicle 31 and the second automated guided vehicle 32 start traveling, the control unit 55 of the management device 50 initializes the state of the semaphores of the first and second automated guided vehicles 31 and 32 stored in the data table DT2 to "disabled" (S301). The control unit 55 then determines whether the semaphore request, the crossing position ID, and the identification information of the automated guided vehicles have been received by the short-range communication unit 53 (S302).

[0086] Here, the control unit 55 of the management device 50, if it receives the semaphore request, the intersection position ID, and the identification information of the first automated guided vehicle 31 first (S302 "Yes"), stores the intersection position ID in the data table DT2 in association with the first automated guided vehicle 31, and determines whether there is an automated guided vehicle that has transmitted an intersection position ID that indicates the same intersection position G(X5,Y5) as the intersection position G(X5,Y5) indicated by the said intersection position ID, along with the semaphore request and the identification information of the automated guided vehicle (S303).

[0087] Here, it is assumed that in the management device 50, after the semaphore request, the intersection position ID, and the identification information of the first automated guided vehicle 31 are received by the short-range communication unit 53 from the first automated guided vehicle 31, the semaphore request, the intersection position ID, and the identification information of the second automated guided vehicle 32 are received from the second automated guided vehicle 32.

[0088] In this case, when the control unit 55 receives the semaphore request from the first automated guided vehicle 31, it has not received a semaphore request from the second automated guided vehicle 31, and therefore determines that there is no automated guided vehicle that has sent the semaphore request and identification information along with the intersection position ID indicating the same intersection position G(X5,Y5) (NO in S303). The control unit 55 rewrites the semaphore status of the first automated guided vehicle 31, which sent the semaphore request first, to "enabled" in the data table DT2, and has the short-range communication unit 53 send the semaphore, the intersection position ID indicating the intersection position G(X5,Y5), and the timeout period T1 to the first automated guided vehicle 31 (S305). After this, the process returns to S302.

[0089] The timeout period T1 is set to a predetermined time that is longer than or equal to a predetermined time required for the automated guided vehicle (AGV) to travel the distance from the second position P2 where it receives the semaphore to the intersection position G. The control unit 55 stores the timeout period T1 in its built-in non-volatile memory or the like. The handling of the timeout period T1 will be described later.

[0090] On the other hand, when the control unit 55 receives a semaphore request from the second automated guided vehicle 31 after receiving a semaphore request from the first automated guided vehicle 31 (YES in S302), it determines that there is an automated guided vehicle, i.e., the first automated guided vehicle 31, that has transmitted the semaphore request and the identification information of the automated guided vehicle, along with an intersection position ID indicating the same intersection position G(X5,Y5) as the intersection position ID indicated by the intersection position ID (YES in S303).

[0091] At this point, the control unit 55, noting that the semaphore state of the first automated guided vehicle 31, which sent the semaphore request first, is "active" in the data table DT2, and the semaphore state of the second automated guided vehicle 32 is "inactive," rewrites the semaphore state of the second automated guided vehicle 32 to "waiting state" and stores it in the data table DT2 (S306). After this, the process returns to S302.

[0092] Furthermore, in S302, if the control unit 55 determines that it has not received any requests for the semaphore from any automated guided vehicle (S302 "No"), it determines whether or not there are any automated guided vehicles whose semaphore status in data table DT2 is "enabled" (S320).

[0093] Here, if the semaphore state remains at the initial setting "disabled" and the control unit 55 determines that there are no automated guided vehicles with the semaphore state set to "enabled" (S320 "No"), it then determines whether the return information indicating the return of the semaphore and the identification information of the automated guided vehicle have been received by the short-range communication unit 53 (S307). That is, at this point, the control unit 55 has not transmitted a semaphore to each automated guided vehicle, so in S307 it determines that the return information indicating the return of the semaphore and the identification information of the automated guided vehicle have not been received by the short-range communication unit 53 (S307 "No"). After this, the process returns to S302.

[0094] On the other hand, if the control unit 55 of the management device 50 has not received a semaphore request from any automated guided vehicle (S302 "No"), and determines that there is an automated guided vehicle with a semaphore state of "enabled" in the data table DT2 (S320 "Yes"), it determines whether short-range communication with the automated guided vehicle with the semaphore state of "enabled" is being performed normally (S321). For example, the control unit 55 of the management device 50 periodically communicates with the automated guided vehicle with the semaphore state of "enabled" at predetermined short intervals (e.g., 100 msec) via the short-range communication unit 53, and determines that short-range communication is not being performed normally when this communication is interrupted. Alternatively, the control unit 55 may cause the short-range communication unit 53 to transmit a signal indicating the identification information of the automated guided vehicle (AGV) whose semaphore state is "enabled". If the short-range communication unit 53 receives a response signal from the AGV, the control unit 55 determines that short-range communication with the AGV is functioning normally. If the short-range communication unit 53 does not receive the response signal from the AGV, the control unit 55 determines that short-range communication with the AGV has been disconnected.

[0095] If the control unit 55 of the management device 50 determines that short-range communication is established with the automated guided vehicle 31 whose semaphore status is "enabled" (S321 "Yes"), it determines whether the short-range communication unit 53 has received the return information indicating the return of the semaphore and the crossing position ID (S307). If it determines that the return information has not been received (S307 "No"), the process returns to S302.

[0096] When the first automated guided vehicle 31, which sent the semaphore request, receives the semaphore, the above-mentioned intersection position ID, and the timeout period T1 from the management device 50 via the short-range communication unit 43 (S103 "Yes"), its control unit 45 stores the semaphore status "enabled" and the timeout period T1 in the data table DT1 (S104). The control unit 45 then controls the drive motor to continue the movement of the first automated guided vehicle 31.

[0097] Then, when the first automated guided vehicle 31 continues its journey and reaches the coordinates (X4, Y5) of the first position P1 on the first travel line 11, the control unit 45 counts up the number of magnetic marks 20 to "2" because the magnetic sensor 15 has detected a second magnetic mark 20, and reads the control information associated with the number "2" from the data table DT1.

[0098] In this case, the control information associated with the number "2" when a semaphore is received is "Continue driving". In this situation, the semaphore state for the intersection position G(X5,Y5) in the data table DT1 of the first automated guided vehicle 31 is "active" and a semaphore has been received. Therefore, the control unit 45 continues driving the first automated guided vehicle 31 according to the control information for when a semaphore is received (S105).

[0099] In contrast, in the second automated guided vehicle 32, when the second automated guided vehicle 32 reaches the coordinates (X5, Y4) of the first position P1 of the second travel line 12, the control unit 45 counts up the number of magnetic marks 20 to "2" because the magnetic sensor 15 detects the second magnetic mark 20, and reads the control information associated with the number "2" from the data table DT1. The control information associated with the number "2" when a semaphore has not been received is "Stop until a semaphore is received, and travel when a semaphore is received". In this situation, since the second automated guided vehicle 32 has not received a semaphore, the control unit 45 controls the travel drive motor 42 according to the control information to temporarily stop the second automated guided vehicle 32 at the coordinates (X5, Y4) of the first position P1 of the second travel line 12 before the intersection position G (S207). In other words, when the second automated guided vehicle 32 reaches the coordinates (X5, Y4) of the first position P1 on the second travel line 12 just before the intersection point G, the management device 50 transmits the semaphore and the intersection point ID (indicating the intersection point G (X5, Y5)) only to the first automated guided vehicle 31, and does not transmit the semaphore and the intersection point ID to the second automated guided vehicle 32.

[0100] Furthermore, when the first automated guided vehicle 31 passes the intersection point G before the second automated guided vehicle 32, which is stopped as described above, and reaches the coordinates (X6, Y5) of the next first position P1 on the first travel line 11, and the magnetic sensor 15 detects the third magnetic mark 20, the control unit 45 counts up the number of magnetic marks 20 to "3" and reads the control information (semaphore return) associated with the number "3" from the data table DT1. In accordance with the read control information, the control unit 45 has the short-range communication unit 43 transmit the return information indicating the semaphore return for the intersection point G (X5, Y5), which is currently "enabled", to the management device 50, along with the identification information of the first automated guided vehicle 31. Then, the control unit 45 rewrites the semaphore state for the intersection point G (X5, Y5) stored in the data table DT1 from "enabled" to "invalid" (S106). After this, the process returns to S102.

[0101] When the control unit 53 of the management device 50 receives return information indicating the return of the semaphore and identification information of the first automated guided vehicle 31 (S307 "Yes"), the control unit 55 of the management device 50 rewrites the received semaphore status of the first automated guided vehicle 31 (for intersection position G(X5,Y5)) in the data table DT2 from "enabled" to "disabled" (S308).

[0102] Then, the control unit 55 of the management device 50 determines whether there is an automated guided vehicle (AGV) whose "operating status" in the data table DT2 is in a waiting state (S309). In this situation, the control unit 55 determines that the "operating status" of the second AGV 32 is in a waiting state (S309 "Yes"), so it deletes the waiting state, which is the "operating status" of the second AGV 32, from the data table DT2 and rewrites the state of the semaphore associated with the second AGV 32 in the data table DT2 to "enabled" (S310). Furthermore, the control unit 45 has the semaphore and the intersection position ID indicating the intersection position G(X5,Y5) transmitted from the short-range communication unit 43 to the second AGV 32 (S310). After this, the process returns to S302.

[0103] As the first automated guided vehicle 31 continues to move, the magnetic sensor 15 detects the fourth magnetic mark 20 at position (X7, Y5). Subsequently, when the first automated guided vehicle 31 reaches the other end (XA, Y5) of the first travel line 11, the control unit 45 counts up the number of magnetic marks 20 to "5" because the magnetic sensor 15 has detected the fifth magnetic mark 20, and reads the control information associated with the number "5" from the data table DT1. In accordance with the read control information, the control unit 45 stops the first automated guided vehicle 31, rotates it 180°, and makes the first automated guided vehicle 31 move forward. The control unit 45 rewrites (initializes) the stored number of magnetic marks 20 "5" to "0".

[0104] After the second automated guided vehicle 32 has come to a complete stop as described above, the control unit 45 of the second automated guided vehicle 32 continues the stopped state of the second automated guided vehicle 32 until it receives a semaphore and an intersection position ID indicating the intersection position G(X5,Y5) from the management device 50 (NO in S208, S207). When the semaphore and the above-mentioned intersection position information transmitted from the management device 50 are received by the short-range communication unit 43 in S310 (YES in S208), the semaphore state in the data table DT1 is rewritten to "enabled" and stored (S209). Upon receiving the semaphore in this manner, the control unit 45 resumes the movement of the second automated guided vehicle 32 based on the control information associated with the number "2" (different control information from the one used in S207) (S210).

[0105] When the second automated guided vehicle 32 passes the intersection point G and reaches the coordinates (X5, Y6) of the next first position P1 on the second travel line 12, the control unit 45 detects that the magnetic sensor 15 has detected the third magnetic mark 20, increments the number of magnetic marks 20 to "3", and reads the control information associated with the number "3" from the data table DT1. In accordance with the read control information, the control unit 45 has the short-range communication unit 43 transmit return information indicating the return of the semaphore, along with the identification information of the second automated guided vehicle 32, to the management device 50, and rewrites the semaphore state in the data table DT1 from "enabled" to "disabled" (S211). After this, the process returns to S202.

[0106] As the second automated guided vehicle 32 continues to move, the magnetic sensor 15 detects the fourth magnetic mark 20 at position (X5, Y7). Subsequently, when the vehicle reaches the other end (X5, YA) of the second travel line 12, the control unit 45 counts up the number of magnetic marks 20 to "5" because the magnetic sensor 15 has detected the fifth magnetic mark 20, and reads the control information associated with the number "5" from the data table DT1. The control unit 45 controls the travel drive motor 42 according to the read control information to stop the second automated guided vehicle 32, rotate it 180°, and make the second automated guided vehicle 32 move forward. The control unit 45 rewrites the stored number of magnetic marks 20 "5" to "0" and initializes it.

[0107] The control unit 55 of the management device 50 repeats the processes from S302 to S309, and when the short-range communication unit 53 receives return information indicating the return of the semaphore and identification information of the second automated guided vehicle 32 (S307 "Yes"), it rewrites the semaphore status of the second automated guided vehicle 32 in the data table DT2 from "enabled" to "disabled" (S308).

[0108] Then, the control unit 55 of the management device 50 determines whether there are any automated guided vehicles (AGVs) whose "operating status" is "waiting" in the data table DT2 (S309). At this point, there are no AGVs whose "operating status" is "waiting" in the data table DT2, so the control unit 55 determines that there are no AGVs whose "operating status" is "waiting" (S309 "No"). If this determination is made, the process returns to S302.

[0109] Furthermore, if the second automated guided vehicle 32 reaches the second position P2 of the second travel line 12 and sends a semaphore request (YES in S202), and then the first automated guided vehicle 31 reaches the second position P2 of the first travel line 11 and sends a semaphore request, the control device 50 sends a semaphore to the second automated guided vehicle 32 using the same control as described above (S305), and the second automated guided vehicle 32 continues traveling without stopping before the intersection position G based on the reception of the semaphore and passes through the intersection position G (S207~S211). On the other hand, in this case, the first automated guided vehicle 31 does not receive a semaphore from the management device 50 (NO in S103), so it stops temporarily at the first position P1 of the first travel line 11 before the intersection point G (S107). When the second automated guided vehicle 32 passes the intersection point G and transmits return information indicating the return of the semaphore to the management device 50 (S206), the management device 50 transmits a semaphore to the first automated guided vehicle 31 (S310). Based on the reception of the semaphore, the first automated guided vehicle 31 resumes travel (YES in S108, S109, S110) and passes the intersection point G. After passing the intersection point G, the control unit 45 has the short-range communication unit 43 transmit the return information indicating the return of the semaphore, along with the identification information of the first automated guided vehicle 31, to the management device 50, and rewrites the semaphore status in the data table DT1 from "enabled" to "disabled" (S111). After this, the process returns to S102.

[0110] In this embodiment, the control described above allows the management device 50 to transmit a semaphore to only one of the first and second automated guided vehicles 31 and 32 that will pass through the same intersection point, allowing only that one vehicle to proceed to the intersection point G, while the other vehicle is temporarily stopped at the first position P1 before the intersection point G. When the vehicle that has passed through the intersection point G transmits semaphore return information to the management device 50, the management device 50 transmits a semaphore to the other vehicle, which then resumes travel based on the receipt of the semaphore and passes through the intersection point G. This prevents the situation in which both the first and second automated guided vehicles 31 and 32 stop before the intersection point G, allowing them to pass through the intersection point G quickly without contact or collision, thereby improving the operational efficiency of the first and second automated guided vehicles 31 and 32.

[0111] Next, the control procedure for the case where, as described above, one automated guided vehicle (AGV) passes through intersection point G, but short-range communication between the management device 50 and the AGV is disconnected, and return information indicating the return of the semaphore is not transmitted from the AGV to the management device 50, will be explained with reference to Figure 10.

[0112] In this embodiment, if the management device 50 does not receive return information indicating the return of the semaphore from the automated guided vehicle (AGV) that first sent the semaphore request within the timeout period T1, the management device 50 will transmit the semaphore and the crossing position ID to the other AGV that later sent the semaphore request, even if the return information is not received by the management device 50 from the AGV.

[0113] A situation in which the return of a semaphore is not received is, for example, when the management device 50 is waiting to receive return information indicating the return of a semaphore transmitted from one wireless transport vehicle, and the short-range communication between the management device 50 and the one wireless transport vehicle is disconnected. After the control unit 55 of the management device 50 has the semaphore transmitted from the short-range communication unit 53 to the one wireless transport vehicle, if the time during which short-range communication is not being performed normally with the one wireless transport vehicle (disconnection time tt) reaches a predetermined timeout time T1 (for example, 30 seconds), the control unit 55 will transmit the semaphore from the short-range communication unit 53 to the other automated guided vehicle, even if the return information indicating the return of the semaphore has not been received. The time during which short-range communication is not being performed normally with the wireless transport vehicles is an example of the time during which the situation in which the return information of the semaphore is not received is described in the claims. The timeout time T1 is set according to the driving speed of the automated guided vehicles, etc., and is determined in advance through experiments or other means to be a suitable time for multiple automated guided vehicles to pass the same intersection point normally. As shown in Figure 11 later, when controlling multiple automated guided vehicles to pass through multiple intersection points, an optimal timeout period T1 may be set individually for each intersection point.

[0114] For example, the control unit 45 of the first automated guided vehicle 31 causes the short-range communication unit 43 to send a semaphore request (S102 "Yes"), and when the short-range communication unit 43 receives the semaphore, the identification information of the first automated guided vehicle 31, and the timeout period T1 (S103 "Yes", S104), it causes the first automated guided vehicle 31 to continue moving (S105).

[0115] Furthermore, if the control unit 45 of the second automated guided vehicle 32 causes the short-range communication unit 43 to send a semaphore request (S202 "Yes"), but the semaphore is not received by the short-range communication unit 43 (S203 "No"), it controls the travel drive motor 42 to stop the second automated guided vehicle 32 at the first position P1 of the second travel line 12 before the crossing position G (S207).

[0116] The control unit 55 of the management device 50, upon receiving the semaphore request transmitted from the first automated guided vehicle 31 first at the short-range communication unit 53 (S302 "Yes"), and determining that no other automated guided vehicle has transmitted the semaphore request and identification information along with the intersection position ID indicating the same intersection position G(X5,Y5) (S303 "NO"), rewrites the semaphore state associated with the identification information of the first automated guided vehicle 31 to "enabled", causes the short-range communication unit 53 to transmit the semaphore, the intersection position ID indicating the intersection position G(X5,Y5), and the timeout period T1 (S305), and repeats the process from S302 onwards until return information indicating the return of the semaphore is received (S304 "No").

[0117] Furthermore, when the control unit 55 of the management device 50 receives the semaphore request transmitted from the second automated guided vehicle 32 in the short-range communication unit 53 after the semaphore request from the first automated guided vehicle 31 (S302 "Yes"), it determines that there is an automated guided vehicle that transmitted the semaphore request and the identification information of the automated guided vehicle, i.e., the first automated guided vehicle 31, along with an intersection position ID indicating the same intersection position G(X5,Y5) as the intersection position ID indicated by the above intersection position ID (YES in S303). At this time, the control unit 55 finds that the semaphore state of the first automated guided vehicle 31, which transmitted the semaphore request first, is "active" in the data table DT2, and the semaphore state of the second automated guided vehicle 32 is "inactive". Therefore, it rewrites the semaphore state of the second automated guided vehicle 32 to "waiting state" and stores it in the data table DT2 (S306). After this, the process returns to S302.

[0118] Thus, while the control unit 55 of the management device 50 is repeating the processing from S302 onwards, assume that the short-range communication between the management device 50 and the first automated guided vehicle 31 that received the semaphore has been disconnected. In this case, the control unit 55 of the management device 50 will determine in the data table DT2 that there is an automated guided vehicle with a semaphore state of "active" (NO in S302, YES in S320). At this time, the control unit 55 of the management device 50 will determine whether the short-range communication with the automated guided vehicle 31 with the semaphore state of "active" is being performed normally (S321).

[0119] Then, when the control unit 55 determines that short-range communication with the automated guided vehicle 31, which has the semaphore state "enabled", is not being performed normally (NO in S321), it determines whether or not it has started timing the disconnection time tt for short-range communication (S322). If it has not yet started timing the disconnection time tt (No in S322), it starts timing the disconnection time tt at this point (S323). Then, the control unit 55 compares the timing-determined disconnection time tt with the time-out time T1 and determines whether or not the disconnection time tt has reached the time-out time T1 (S324). When the control unit 55 determines that the disconnection time tt has not reached the time-out time T1 (No in S324), it determines whether short-range communication with the first automated guided vehicle 31, which is an automated guided vehicle whose communication was interrupted and whose semaphore state is "enabled", has been restored (S325). The control unit 55 makes the determination by performing the same process as in S321, or by determining whether the transmission and reception of signals or data with the first automated guided vehicle 31 has been established at this point. If the control unit 55 of the management device 50 determines that short-range communication with the first automated guided vehicle 31 has not been restored (S325 "No"), the process moves to S302, and the process from S302 onward is repeated.

[0120] After this, for example, if, after S302 "No" and S320 "Yes", in S321 it is determined that the short-range communication with the first automated guided vehicle 31 is still disconnected (S321 "No"), the timing of the short-range communication disconnection time tt has already started (S322 "Yes"), so S323 is skipped and it is determined whether the disconnection time tt has reached the timeout time T1 (S324). Here, if the control unit 55 determines that the short-range communication with the first automated guided vehicle 31 is still disconnected and the disconnection time tt has reached the timeout time T1 (S324 "Yes"), the disconnection time tt is initialized to "0" (S326), and the semaphore state associated with the identification information of the first automated guided vehicle 31 in the data table DT2 is rewritten from "enabled" to "disabled" (S308). In other words, even if the control unit 55 has not received semaphore return information from the first automated guided vehicle 31, it disables the semaphore state of the first automated guided vehicle 31.

[0121] As described above, the timeout period T1 is set to a predetermined time that is longer than the time calculated in advance for the automated guided vehicle (AGV) to travel the distance from the second position P2 where it receives the semaphore to the intersection position G. Therefore, when the disconnection time tt from the time the AGV loses communication (a time later than when the AGV receives the semaphore or when the AGV is at the second position P2) reaches the timeout period T1, the AGV has already passed the intersection position G. For this reason, the control unit 55 changes the status of the semaphore associated with the identification information of the first AGV 31 in the data table DT2 from "enabled" to "disabled".

[0122] At this point, the control unit 55 of the management device 50 determines that the operating state of the second automated guided vehicle 32 is stored in the data table DT2 as "waiting state" (S309 "Yes"). Therefore, it rewrites the semaphore state stored in the data table DT2 as "active" and deletes the operating state "waiting state" from the data table DT2. Furthermore, it transmits the semaphore, the intersection position ID (indicating the position (X5, Y5)), and the timeout period T1 from the short-range communication unit 53 to the second automated guided vehicle 32 (S310). After this, the process returns to S302.

[0123] When the control unit 45 of the second automated guided vehicle 32 receives the semaphore, crossing position ID, and timeout time T1 transmitted from the management device 50 in S310 via the short-range communication unit 43 (S208), it stores the semaphore state "enabled" and the timeout time T1 in the data table DT1 (S209), and controls the drive motor 42 to move the second automated guided vehicle 32 forward (S210). When the second automated guided vehicle 32 passes the intersection point G and reaches the coordinates (X5, Y6) of the next first position P1 on the second travel line 12, the control unit 45 counts up the number of magnetic marks 20 to "3" because the magnetic sensor 15 has detected the fourth magnetic mark 20, and reads the control information associated with the number "3" from the data table DT1. In accordance with the read control information, the control unit 45 has the short-range communication unit 43 transmit return information indicating the return of the semaphore, along with the identification information of the second automated guided vehicle 32, to the management device 50, and rewrites the semaphore state in the data table DT1 from "enabled" to "disabled" (S211). After this, the process returns to S202.

[0124] Furthermore, when the control unit 45 of the first automated guided vehicle 31 is running with the semaphore state in the data table DT1 set to "enabled" (S105), it determines whether short-range communication between the first automated guided vehicle 31 and the management device 50 is functioning correctly by the same process as in S308. If the control unit 45 determines that the short-range communication is not functioning correctly, it starts timing the disconnection time tt at this point. When the disconnection time tt reaches the timeout time T1, the control unit 45 changes the semaphore state in the data table DT1 from "enabled" to "disabled" (S106), even if it has not yet sent the semaphore return information to the management device 50. After this, the process returns to S102. For example, the control unit 45 of the first automated guided vehicle 31 communicates periodically with the management device 50 at predetermined short intervals via the short-range communication unit 43. When this communication is interrupted, it determines that the short-range communication is not functioning properly, and starts timing the disconnection time tt from the time of this determination.

[0125] By controlling the system in this way, even if the short-range communication between the management device 50 and the first automated guided vehicle 31 is disconnected while the first automated guided vehicle 31 receives the semaphore first and travels to the intersection point G, and the second automated guided vehicle 32 is stopped at the first position P1 before the intersection point G, and the management device 50 does not receive the semaphore return information from the first automated guided vehicle 31, the semaphore will be transmitted from the management device 50 to the second automated guided vehicle 32 after the short-range communication disconnection time tt reaches the timeout time T1 and the first automated guided vehicle 31 has passed the intersection point G, allowing the second automated guided vehicle 32 to resume travel and pass the intersection point G, thus preventing the second automated guided vehicle 32 from becoming stuck before the intersection point G.

[0126] Furthermore, even if short-range communication between the management device 50 and the second automated guided vehicle 32 is interrupted while the second automated guided vehicle 32 has received the semaphore first and is traveling to the intersection point G, and the first automated guided vehicle 31 is stopped at the first position P1 before the intersection point G, the management device 50 will similarly transmit a semaphore to the first automated guided vehicle 31 after the short-range communication interruption time tt reaches the timeout time T1 and the second automated guided vehicle 32 has passed the intersection point G, thereby restarting the movement of the first automated guided vehicle 31 and allowing it to pass the intersection point G. This prevents the first automated guided vehicle 31 from becoming stuck before the intersection point G.

[0127] In the above embodiment, the example is described in which two travel lines 11 and 12 intersect at an intersection point, and the first and second automated guided vehicles 31 and 32 travel along the travel lines 11 and 12. However, the travel control for each automated guided vehicle described above can also be applied when three or more travel lines intersect at a single intersection point, and three or more wireless transport vehicles travel along each travel line. In this case, when the control unit 55 of the management device 50 receives each semaphore request transmitted from each automated guided vehicle at the short-range communication unit 53, the short-range communication unit 53 transmits a semaphore to the automated guided vehicle that transmitted the semaphore request first. When the short-range communication unit 53 receives return information indicating the return of the semaphore from the automated guided vehicle that transmitted the semaphore in this way, the short-range communication unit 53 transmits the semaphore to the other two automated guided vehicles that transmitted the semaphore first.

[0128] For example, the control unit 55 of the management device 50 may store the order in which semaphore requests were received for each automated guided vehicle (AGV) and transmit semaphores to each AGV via the short-range communication unit 53 in the order in which the semaphore requests were sent. As described above, the control unit 45 of each AGV transmits the return information from the short-range communication unit 43 to the management device 50 after the AGV has passed the intersection point G.

[0129] Furthermore, although the above embodiment illustrates first and second automated guided vehicles 31 and 32, as shown in Figure 11, the above-described travel control for each automated guided vehicle can also be applied to a configuration in which three or more first travel lines 11 and three or more second travel lines 12 intersect at their respective intersection points G, with each first automated guided vehicle 31 traveling along each first travel line 11 and each second automated guided vehicle 32 traveling along each second travel line 11. In this case, the data table DT2 of the management device 50 shown in Figure 9 stores the intersection point ID, the semaphore status ("enabled" or "disabled"), and the operating status of each automated guided vehicle separately for each first automated guided vehicle 31 and each second automated guided vehicle 32. Then, at each intersection point G of the first travel line 11 and the second travel line 12, the first automated guided vehicle 31 traveling on the first travel line 11, the first automated guided vehicle 32 traveling on the second travel line 12, and the control device 50 perform travel control of each automated guided vehicle as described above. <Another embodiment>

[0130] Figure 12 is a flowchart showing the control for smoothly moving the first and second automated guided vehicles at the intersection point. The flowchart in Figure 12 is similar to the flowchart of the embodiment shown in Figure 10, but the processes such as S104A, S106A, S109A, S111A, S204A, S206A, S209A, S211A, S306A, S311A, S321, S322, and S323 are different. Therefore, these different processes will be explained.

[0131] Initial movement of the first and second automated guided vehicles 31 and 32 begins. For example, in the management device 50, the semaphore request and the identification information of the first automated guided vehicle 31 are received first by the short-range communication unit 53, and the semaphore request and the identification information of the second automated guided vehicle 32 are received later. In this case, when the control unit 55 of the management device 50 receives the semaphore request and the identification information of the first automated guided vehicle 31 first (S302 "Yes"), it goes through NO in S303, rewrites the semaphore state associated with the identification information of the first automated guided vehicle 31 to "enabled", and has the semaphore and crossing position ID transmitted from the short-range communication unit 53 (S305A), and starts timing the waiting time st from the time of the semaphore transmission (S328). After this, the process moves to S302.

[0132] When the control unit 55 of the management device 50 receives the semaphore request and the crossing position ID later (S302 "Yes"), it goes through YES in S303 and stores the "operating state" associated with the identification information of the second automated guided vehicle 32 as a "waiting state" in the data table DT2 (S306). After this, the process moves to S302.

[0133] If the control unit 55 of the management device 50 has not received a semaphore request and identification information of the automated guided vehicle (S302 "No"), it determines whether the waiting time st has reached a predetermined time T2 (S329). If the waiting time st has not reached the predetermined time T2 (S329 "No"), the control unit 55 determines whether the return information indicating the return of the semaphore and identification information of the automated guided vehicle have been received by the short-range communication unit 53 (S307). If the control unit 55 determines that the semaphore return information has not been received (S307 "No"), the process moves to S302.

[0134] The specified time T2 is set to a predetermined time that is greater than or equal to the time required for the automated guided vehicle to travel the distance from the second position P2, where it receives the "valid" signal from the semaphore, to the intersection position G.

[0135] The control unit 45 of the first automated guided vehicle 31 causes the short-range communication unit 43 to transmit a semaphore request and an intersection position ID (S102 "Yes"), and when it receives the semaphore and intersection position ID from the management device 50 (S103 "Yes", S104A), it controls the drive motor 42 to move the first automated guided vehicle 31 forward (S105).

[0136] When the first automated guided vehicle 31 passes the intersection point G and reaches the coordinates (X6, Y5) of the next first position P1 on the first travel line 11, the control unit 45 counts up the number of magnetic marks 20 to "3" because the magnetic sensor 15 has detected the fourth magnetic mark 20, and reads the control information associated with the number "3" from the data table DT1. In accordance with the read control information, the control unit 45 has the short-range communication unit 43 transmit return information indicating the return of the semaphore, along with the intersection point ID, to the management device 50. Then, the control unit 55 rewrites the state of the semaphore stored in the data table DT1 from "enabled" to "disabled" (S106A). After this, the process returns to S102.

[0137] If the control unit 55 of the management device 50 receives semaphore return information and identification information of the first automated guided vehicle 31 via the short-range communication unit 53 before the waiting time st reaches the specified time T2 (S329 "No") (S309 "Yes"), it refers to the data table DT2 and rewrites the semaphore information associated with the identification information of the first automated guided vehicle 31 from "enabled" to "inactive" (S308).

[0138] Then, the control unit 55, knowing that the semaphore's waiting state is associated with the second automated guided vehicle 32 and stored in the data table DT2 (S309 "Yes"), deletes the semaphore's waiting state from the data table DT2, rewrites the semaphore state associated with the identification information of the second automated guided vehicle 32 in the data table DT2 to "enabled", and transmits the identification information of the semaphore and the second automated guided vehicle from the short-range communication unit 53 to the automated guided vehicle (S311A). After this, the process returns to S302.

[0139] Furthermore, if the semaphore return information and intersection position ID are not received by the short-range communication unit 53 (S307 "No") and the waiting time st reaches the specified time T2 (S302 "No", S329 "Yes"), the control unit 55 of the management device 50 initializes the waiting time st to "0" (S330) and rewrites the semaphore status associated with the identification information of the first automated guided vehicle 31 in the data table DT2 from "enabled" to "disabled" (S308). At this time, the control unit 55 erases the operation status of "waiting state" stored in the data table DT2 associated with the second automated guided vehicle 32 (S309 "Yes") from the data table DT2, rewrites the semaphore status associated with the second automated guided vehicle 32 to "enabled", and transmits the semaphore and intersection position ID from the short-range communication unit 53 to the automated guided vehicle (S311A). After this, the process returns to S302.

[0140] As described above, the specified time T2 is a predetermined time that is greater than or equal to the time required for the automated guided vehicle (AGV) to travel the distance from the second position P2 where it receives the "enabled" status of the semaphore to the intersection position G. Therefore, when the waiting time st reaches the specified time T2, the AGV has passed the intersection position G. Based on this, the control unit 55 rewrites the semaphore status associated with the first AGV 31 in the data table DT2 from "enabled" to "inactive," even if it has not received the semaphore return information.

[0141] Furthermore, if the control unit 45 of the first automated guided vehicle 31 is unable to transmit the semaphore return information, along with the identification information of the first automated guided vehicle 31, from the short-range communication unit 43 to the management device 50, due to a disconnection of short-range communication with the management device 50, even while traveling towards the intersection position G, it rewrites the semaphore information stored in the data table DT1 from "enabled" to "invalid" (S106A). After this, the process returns to S102.

[0142] Furthermore, when the control unit 45 of the second automated guided vehicle 32 has the short-range communication unit 43 send a semaphore request (S202 "Yes"), but has not received a semaphore from the management device 50 (S203 "No"), and is stopped before the intersection point G (S207), if it has received a semaphore from the management device 50 (S208, S209A), it controls the drive motor 42 to move the second automated guided vehicle 32 forward (S210).

[0143] When the second automated guided vehicle 32 passes the intersection point G and reaches the coordinates (X5, Y6) of the next first position P1 on the second travel line 12, the control unit 45 counts up the number of magnetic marks 20 to "3" because the magnetic sensor 15 has detected the third magnetic mark 20, and reads the control information associated with the number "3" from the data table DT1. In accordance with the read control information, the control unit 45 has the short-range communication unit 43 transmit return information indicating the return of the semaphore, along with the identification information of the second automated guided vehicle 32, to the management device 50, and rewrites the semaphore state in the data table DT1 from "enabled" to "disabled" (S211A). After this, the process returns to S202.

[0144] This type of control also prevents the second automated guided vehicle 32 from getting stuck before the intersection point G, allowing the first and second automated guided vehicles to move smoothly through the intersection point.

[0145] Furthermore, even if the second automated guided vehicle 32 receives the semaphore before the first automated guided vehicle 31, the same control mechanism prevents the second automated guided vehicle 32 from stalling before the intersection point G, allowing the first and second automated guided vehicles to move smoothly through the intersection point.

[0146] Furthermore, the configuration and processing of the above embodiment described with reference to Figures 1 to 12 are merely one embodiment of the present invention, and the present invention is not intended to be limited to this configuration and processing. For example, the timeout period described above can be input by a user operating the operation unit 57 of the management device 50. [Explanation of symbols]

[0147] 11. First running line 12. Second running line 14 line sensors 15 Magnetic Sensor 20 Magnetic mark 31. First Automated Transport Vehicle 32. Second Automated Transport Vehicle 33 Casters 34 drive wheels 42. Drive motor 43 Near Field Communication Department 44 Memory section 45 Control Unit 50 Management device 53 Near Field Communication Department 54 Memory section 55 Control Unit Sy Automated Guided Vehicle Driving System

Claims

1. Multiple driving lines laid on the road surface that intersect each other at intersections, For each of the aforementioned travel lines, a mark is provided at a position spaced apart from the intersection point along the travel line, Each of the automated guided vehicles traveling along the aforementioned multiple travel lines, The system includes a management device that transmits a semaphore indicating permission to pass through the aforementioned intersection to each of the automated guided vehicles, Each of the aforementioned automated guided vehicles is: A first communication unit that wirelessly transmits information to the aforementioned management device, A mark detection unit for detecting the aforementioned mark, The system comprises a first control unit which causes the first communication unit to transmit a request for the semaphore to the management device, The aforementioned control device is A second communication unit that wirelessly transmits information to each of the aforementioned unmanned transport vehicles, When the second communication unit receives a semaphore request transmitted from each of the aforementioned automated guided vehicles, the second communication unit causes the semaphore to be transmitted from the automated guided vehicle that transmitted the previously received semaphore request to the vehicle that transmitted the previously received semaphore request, An automated guided vehicle system comprising: a second control unit that transmits the semaphore to another automated guided vehicle that has sent a request for the semaphore when the second communication unit receives return information indicating the return of the semaphore transmitted from the automated guided vehicle that transmitted the semaphore, or when the time during which the second communication unit has not received the return information reaches a predetermined time which is equal to or greater than the time required for the automated guided vehicle to travel the distance from the position where it receives the semaphore to the intersection position.

2. The situation in which the aforementioned return information is not received is a situation in which the wireless communication between the management device and the automated guided vehicle that transmitted the semaphore has been disconnected. The automated guided vehicle system according to claim 1, wherein the second control unit of the management device transmits the semaphore to another automated guided vehicle that has transmitted the request for the semaphore when the time of disconnection of the wireless communication from the time the semaphore was transmitted reaches the predetermined time.

3. The automated guided vehicle system according to claim 2, wherein the first control unit of the automated guided vehicle disables the semaphore received by the first communication unit when the wireless communication disconnection time reaches the specified time while the return information has not been transmitted from the first communication unit.

4. The situation in which the return of the semaphore is not received is a situation in which the system has been waiting to receive the return information since the semaphore was transmitted to the automated guided vehicle. The automated guided vehicle system according to claim 1, wherein the second control unit of the management device transmits the semaphore to another automated guided vehicle that has sent the request for the semaphore when the waiting time for receiving the return information reaches the specified time.

5. The management device includes an operating unit that receives instructions to specify the prescribed time, The automated guided vehicle system according to claim 2 or 4, wherein the second control unit controls the transmission of the semaphore using a specified time indicated by the instruction received by the operation unit.

6. A step of driving each automated guided vehicle along multiple driving lines laid on the road surface that intersect each other at intersection points, The steps include: requesting a semaphore indicating permission to pass the intersection when the automated guided vehicle reaches a predetermined position separated from the intersection along the travel line; The steps include: when the semaphore is received, the automated guided vehicle continues to travel, and when the automated guided vehicle passes the intersection, return information indicating that the semaphore is valid is transmitted to the management device; The steps include: stopping the automated guided vehicle if it does not receive the semaphore, and resuming the vehicle's movement when it receives the semaphore; An automated guided vehicle (AGV) travel control method comprising: a step of transmitting the semaphore to another AGV that has transmitted a request for the semaphore when the management device receives return information indicating the return of the semaphore transmitted from the AGV that transmitted the semaphore, or when the time during which the return information is not received reaches a predetermined time which is equal to or greater than the time required for the AGV to travel the distance from the position where it receives the semaphore to the intersection position.

Images