Autonomous mobile robot collision prevention method using v2v communication, and device and system therefor

Abstract

The present invention may provide an autonomous mobile robot collision prevention method using V2V communication performed by a mobile robot, the method comprising the steps of: collecting, from a plurality of surrounding guest mobile robots, movement information related to the position and speed of each guest mobile robot by using vehicle-to-vehicle (V2V) communication; determining a collision situation on the basis of the movement information of each guest mobile robot and movement information of a mobile robot itself; determining a deceleration ratio of the mobile robot or a guest mobile robot for preparing for the collision situation; and controlling driving, decelerating, or stopping of the mobile robot by applying the determined deceleration ratio, wherein the V2V communication employs a broadcast communication scheme.

Description

Collision avoidance method for autonomous mobile robots using V2V communication and device and system therefor

[0001] The present invention relates to a method for preventing collisions between autonomous mobile robots using vehicle-to-vehicle (V2V) communication, and to a device and system therefor. More specifically, the present invention relates to a method, device, and system for preventing collisions between and controlling the movements of multiple autonomous mobile robots using V2V communication in an environment where multiple autonomous mobile robots are moving.

[0002] V2V communication refers to wireless communication between vehicles. Recently, with the introduction of autonomous driving functions in automobiles, active research and development is being conducted to prevent collisions between vehicles by continuously transmitting and receiving data wirelessly with surrounding vehicles using terminals equipped with V2V wireless communication technology. This allows the vehicle to identify the speed and location of other vehicles. Furthermore, with the expansion of logistics automation, demand for autonomous guided vehicles (AGVs) is increasing, and research and development are being conducted on the movement control of mobile robots in such work environments.

[0003] Conventionally, research and development has focused on collision avoidance using V2V terminals to receive data such as a vehicle's speed and location and predict its path relative to other vehicles. Furthermore, research and development are underway to detect objects using sensors like depth cameras and LiDAR on mobile robots and prevent collisions by slowing or stopping them. Furthermore, control systems and methods, such as a central control center, are being developed to prevent traffic collisions among multiple mobile robots.

[0004] However, conventional collision avoidance technologies utilizing sensors focus on detecting objects, making it impossible to address shadow areas. Furthermore, collision avoidance is difficult in the event of sensor errors or malfunctions. Furthermore, if traffic control collision avoidance commands are not properly delivered from the control system or if an error occurs in the control system, collision avoidance of the mobile robot becomes impossible.

[0005] Therefore, in order to solve the above problems, a new method and device are required that can receive data of a mobile robot, such as the robot's location and path, in real time through V2V wireless communication and utilize the information in real time to implement collision prevention.

[0006] The purpose of the present invention is to provide a method and device for preventing collisions that may occur when a plurality of unmanned transport devices (Autonomous Guided Vehicles (AGVs)) or autonomous mobile robots (Autonomous Mobile Robots (AMRs)) are moved in an industrial site.

[0007] In addition, the present invention aims to provide a method for preventing collisions and controlling the speed of an autonomous mobile robot using V2V communication and a device therefor to solve the problem of collisions occurring due to malfunctions and shaded areas when recognizing objects through sensors such as cameras and lidars when there is an error in the control of a central control system that performs traffic control or when the system does not operate normally.

[0008] In addition, the present invention aims to provide a method and device that can prevent collisions by independently and independently controlling movement, such as deceleration and stopping, of each mobile robot by using data analysis through V2V communication between multiple mobile robots.

[0009] In addition, the present invention aims to provide a method, device, and system for more effectively preventing collisions of autonomous mobile robots by classifying intersection situations, following situations, and facing situations in an environment where multiple mobile robots are driving and deriving a deceleration ratio value for each situation.

[0010] The problems to be solved by the present invention are not limited to those mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0011] According to one embodiment of the present invention, a method for preventing collisions of an autonomous mobile robot using V2V (Vehicle-to-Vehicle Communication) communication performed in the mobile robot comprises: a step of collecting movement information related to the position and speed of a plurality of guest mobile robots located in the vicinity using V2V (Vehicle-to-Vehicle Communication); a step of determining a collision situation based on the movement information of the guest mobile robot and the movement information of the mobile robot itself; a step of determining a speed deceleration rate of the mobile robot or the guest mobile robot to prepare for the collision situation; and a step of performing driving, deceleration, or stop control of the mobile robot by applying the determined speed deceleration rate, wherein the V2V communication uses a broadcast communication method.

[0012] In addition, the step of determining the collision situation may include a step of determining whether the movement directions of the mobile robot and each guest mobile robot intersect each other in a crossing situation, and the step of determining whether the crossing situation is a crossing situation may include a step of determining whether predetermined paths of the mobile robot itself and the guest mobile robot intersect and are parallel, determining an error between the position of the guest mobile robot and the predetermined path of the guest mobile robot, and generating an intersection point of the paths of the mobile robot itself and the guest mobile robot.

[0013] In addition, if the step of determining the collision situation determines that the situation is an intersection situation, the step of processing the intersection situation may further include the step of listing the plurality of guest mobile robots determined to be intersection situations based on the distance between the current positions of the mobile robots and intersection points generated for each of the plurality of guest mobile robots determined to be intersection situations; and, in order to prevent a collision with the guest mobile robot corresponding to the intersection point closest to the current position of the mobile robot among the plurality of guest mobile robots determined to be intersection situations, the step of determining a speed deceleration rate of the mobile robot or the guest mobile robot using the guest mobile robot corresponding to the closest intersection point and the estimated time of arrival (ETA) from the current position of the mobile robot to the intersection point may include the step of determining the speed deceleration rate of the mobile robot or the guest mobile robot.

[0014] In addition, in order to prevent a collision with a guest mobile robot corresponding to the second closest intersection among the intersections generated for each of a plurality of guest mobile robots determined to be the intersection situation when the mobile robot arrives at the closest intersection, a step of determining a speed deceleration rate of the mobile robot or the guest mobile robot using the guest mobile robot corresponding to the second closest intersection and the expected arrival time from the current location of the mobile robot to the intersection may be further included.

[0015] Additionally, the step of determining a speed reduction ratio of the mobile robot or the guest mobile robot may include a step of determining a speed reduction target based on a task priority, a task distance, or a type of robot of the mobile robot and the guest mobile robot.

[0016] In addition, the step of determining whether there is a crossing situation with each of the guest mobile robots may determine that there is a crossing situation with respect to the guest mobile robot if the distance between the path of the mobile robot and the path of the guest mobile robot is less than a predetermined standard even if there is no direct crossing point between the path of the mobile robot and the guest mobile robot.

[0017] In addition, the step of determining whether or not there is a crossing situation with each guest mobile robot may generate an arbitrary intersection point formed by converting the curved path into a straight path by extending the straight path before or after the curved path, if the path of the mobile robot or the guest mobile robot includes a curved path that changes the direction of movement.

[0018] In addition, the step of determining the collision situation may further include a step of determining whether the direction of the paths of the mobile robot and the guest mobile robot are the same, which is a following situation, and a step of determining whether the direction of the paths of the mobile robot and the guest mobile robot are opposite to each other and the two paths are on the same line, which is a facing situation.

[0019] In addition, the method further includes a step of receiving object attribute information related to length and width information of a plurality of guest mobile robots located in the vicinity using the V2V communication, and the step of determining a collision situation can determine whether or not a collision has occurred based on the movement information and the object attribute information.

[0020] According to another embodiment of the present invention, a mobile robot for collision prevention of an autonomous mobile robot using V2V (Vehicle-to-Vehicle Communication) communication may be provided, comprising: a data collection processing unit configured to collect movement information related to the position and speed of a plurality of guest mobile robots located in the vicinity using a V2V (Vehicle-to-Vehicle Communication) communication unit; a situation determination processing unit configured to determine a collision situation based on the movement information of the guest mobile robot and the movement information of the mobile robot itself; and a speed control unit configured to determine a speed deceleration rate of the mobile robot or the guest mobile robot to prepare for the collision situation, and to perform driving, deceleration, or stop control of the mobile robot by applying the determined speed deceleration rate, wherein the V2V communication uses a broadcast communication method.

[0021] According to the present invention, a method and device for preventing collisions that may occur when a plurality of unmanned guided vehicles (AGVs) or autonomous mobile robots (AMRs) move in an industrial site can be provided.

[0022] In addition, according to the present invention, in order to solve the problem of collisions occurring due to malfunctions and shaded areas when recognizing objects through sensors such as cameras and lidars when there is an error in the control of a central control system performing traffic control or when the system is not operating normally, a method for preventing collisions and controlling the speed of an autonomous mobile robot using V2V communication and a device therefor can be provided.

[0023] In addition, according to the present invention, a method and device can be provided that can prevent collisions by independently and independently controlling movement, such as deceleration and stopping, of each mobile robot by using data analysis through V2V communication between multiple mobile robots.

[0024] In addition, according to the present invention, a method, device, and system for more effectively preventing collisions of autonomous mobile robots can be provided by classifying intersection situations, following situations, and facing situations in an environment where multiple mobile robots are driving and deriving a deceleration ratio value for each situation.

[0025] In addition, according to the present invention, by preventing collisions of mobile robots in a work environment, it is possible to reduce losses due to production stoppages, hardware replacement costs, and time that occur when collisions occur.

[0026] The effects of the present invention are not limited to those mentioned above, and other technical effects not mentioned will be clearly understood by those skilled in the art from the description below.

[0027] FIG. 1 is an exemplary diagram illustrating the configuration of a collision avoidance system for an autonomous mobile robot according to one embodiment of the present invention.

[0028] FIG. 2a and FIG. 2b are flowcharts for explaining a collision avoidance method of an autonomous mobile robot according to one embodiment of the present invention.

[0029] FIG. 3 is a block diagram illustrating the configuration of an autonomous mobile robot according to one embodiment of the present invention.

[0030] FIGS. 4A to 4D are exemplary diagrams for explaining a method for avoiding collision in a crossing situation according to one embodiment of the present invention.

[0031] FIG. 5 is an exemplary diagram illustrating a method for avoiding collision in a following situation according to one embodiment of the present invention.

[0032] FIG. 6 is an exemplary diagram illustrating a method for avoiding collision in a facing situation according to one embodiment of the present invention.

[0033] FIG. 7a and FIG. 7b are exemplary diagrams for explaining a method for avoiding a collision in an avoidance situation according to one embodiment of the present invention.

[0034] Below, embodiments of the present invention are described in detail with reference to the attached drawings so that those skilled in the art can easily implement the invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein. Furthermore, in order to clearly illustrate the embodiments of the present invention in the drawings, portions irrelevant to the description have been omitted.

[0035] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the present invention. Singular expressions may include plural expressions unless the context clearly dictates otherwise.

[0036] In this specification, terms such as “include,” “have,” or “comprising” are intended to indicate the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, and should be understood as not excluding in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0037] Furthermore, the components shown in the embodiments of the present invention are depicted independently to represent different characteristic functions, and this does not mean that each component is composed of separate hardware or a single software component. That is, each component is described by listing each component for convenience of explanation, and at least two of the components may be combined to form a single component, or a single component may be divided into multiple components to perform a function. Such integrated and separate embodiments of each component are also included in the scope of the present invention, as long as they do not deviate from the essence of the present invention.

[0038] In addition, the following examples are provided to provide a clearer explanation to a person having average knowledge in the art, and the shapes and sizes of elements in the drawings may be exaggerated for a clearer explanation.

[0039] Hereinafter, with reference to the attached drawings, a preferred embodiment according to the present invention will be described.

[0040]

[0041] FIG. 1 is an exemplary diagram illustrating the configuration of a collision avoidance system for an autonomous mobile robot according to one embodiment of the present invention.

[0042] Referring to FIG. 1, a mobile robot (100) is a robot device capable of autonomous driving, and may be an Autonomous Guided Vehicle (AGV) or an Autonomous Mobile Robot (AMR). The mobile robot (100) may include a V2V communication unit (110) for communication with other mobile robots.

[0043] The guest mobile robot (200) is an autonomous mobile robot that is positioned and moves around the mobile robot (100), and may include the same components as the mobile robot (100), including a V2V communication unit (210). There may be a plurality of guest mobile robots (200), and the mobile robot (100) and the plurality of guest mobile robots (200) may wirelessly transmit and receive data through the V2V communication unit, and may be configured to transmit and receive data to all mobile robots positioned around, i.e., within the communication range, using a broadcast communication method.

[0044] For example, a guest mobile robot (200) can transmit data such as its movement information or object property information in a broadcast manner through a V2V communication unit (210), and at this time, a mobile robot (100) located within a communication range with the guest mobile robot (200) can receive the data transmitted by the guest mobile robot (200) through the V2V communication unit (110). Similarly, a mobile robot (100) can transmit data in a broadcast manner through a V2V communication unit (110), and at this time, a plurality of guest mobile robots (200) located within a communication range can receive the data transmitted by the mobile robot (100) through the V2V communication unit (210).

[0045] In addition, the mobile robot (100) and guest mobile robot (200) may be of the DD (Dual Drive) type that moves straight and turns with two motors and two drive axes, or of the QD (Quad Drive) type that moves straight, turns, moves vertically, moves sideways, and moves diagonally with two motors and four drive axes, and may have various other types of movement methods.

[0046] The present invention relates to a method and device for allowing a plurality of mobile robots, i.e., a mobile robot (100) and a plurality of guest mobile robots (200), to independently perform V2V terminal communication to recognize surrounding mobile robots and transmit and receive data necessary for collision prevention to prevent collisions between robots and control their movements. A specific collision prevention method will be described later with reference to FIG. 2, and a specific configuration of the mobile robot (100) will be described later with reference to FIG. 3.

[0047]

[0048] FIG. 2a and FIG. 2b are flowcharts for explaining a collision avoidance method of an autonomous mobile robot according to one embodiment of the present invention.

[0049] First, referring to FIG. 2A, a mobile robot (100) can receive data from a plurality of guest mobile robots (200) located in the vicinity and filter out necessary data. (S210) Here, the data transmitted and received by the mobile robots can include data related to movement information such as the location, timestamp, and speed of the mobile robot, and data related to object attribute information such as the length, width, and type of the mobile robot. The mobile robot (100) can filter out only the data of guest mobile robots necessary for collision prevention processing among the data received from the plurality of guest mobile robots (200).

[0050] The mobile robot (100) can perform data analysis to perform collision prevention logic using its own data and data received from multiple guest mobile robots (200). (S220) At this time, the mobile robot (100) can calculate and predict information about relative position and relative velocity at each time using its own position information and velocity information, and the position information and velocity information of the guest mobile robot (200).

[0051] Through such data analysis, the mobile robot (100) can classify and determine a collision situation among a crossing situation, a following situation, and a facing situation for each guest mobile robot (200). (S230) Here, a crossing situation means a situation in which the moving directions of two robots intersect each other, a following situation means a situation in which the moving directions of two robots are the same and one robot follows the preceding robot, and a facing situation means a situation in which the moving directions of two robots are opposite to each other and the two paths are on the same line. The mobile robot (100) can classify and determine which type of collision situation each guest mobile robot (200) in the vicinity is in.

[0052] Depending on the judgment of each situation, processing tasks (handling) such as intersecting situation processing, following situation processing, and facing situation processing can be performed to prepare for a collision situation. (S240) At this time, if it is judged to be an intersecting situation, logic for handling the intersecting situation is performed, if it is judged to be a following situation, logic for handling the following situation is performed, and if it is judged to be an facing situation, logic for handling the facing situation is performed. A more specific description of this will be described with reference to FIG. 2b.

[0053] Based on the deceleration ratio or speed ratio derived from each collision situation, the maximum speed of the mobile robot (100) or guest mobile robot (200) can be determined to limit the maximum speed and perform speed control accordingly. (S250) Here, the deceleration ratio is a rate for decelerating the maximum speed currently set for the mobile robot. If the set maximum speed is 20 m / s, when the deceleration ratio is applied at 60%, the maximum speed is determined to be 8 m / s. In addition, the maximum speed of the mobile robot can be determined by applying the minimum value among the maximum speeds determined for each collision situation by applying the maximum value among the deceleration ratios derived from each collision situation when there are multiple deceleration ratios. In addition, the target of the speed control can be either the mobile robot (100) or the guest mobile robot (200), or both as needed, and the target robot of the deceleration or stop control can be determined based on the priority considering the working distance of the mobile robot, the working priority, the type of robot, etc. In addition, the maximum driving speed of each mobile robot can be set to a designated speed determined by the control system.

[0054] Referring to Fig. 2b, in the collision situation determination step (S230), the intersection situation determination step (S231) may perform the following steps: determining whether the predetermined paths of each mobile robot intersect (a), determining whether they are parallel (b), determining the error between the predetermined paths of the mobile robots and their current positions (c), and extracting intersection points (d). At this time, in the following intersection situation processing step (S241), the intersection points of each guest mobile robot (200) classified as an intersection situation are extracted and sorted to find the closest intersection point (a), find the closest intersecting mobile robot corresponding to it (b), determine whether the mobile robot or itself is driving, decelerating, or stopping (c), and output the corresponding deceleration ratio (d).

[0055] Next, in the collision situation judgment step (S230), the following situation judgment step (S232) can perform the judgment of the identity and same directionality of the predetermined path of each mobile robot (a), the judgment of whether a curve is followed (b), and the extraction of the following point (c), wherein the following point may be the position value of the following mobile robot. At this time, in the following following situation processing step (S242), the following points of each guest mobile robot (200) classified as a following situation are extracted and sorted to find the closest following point (a), find the closest following mobile robot (b), determine whether the mobile robot or itself is driving, decelerating, or stopping (c), and output the deceleration ratio accordingly (d).

[0056] Next, in the collision situation judgment step (S230), the facing situation judgment step (S233) judges the sameness and opposite directionality of the predetermined paths of each mobile robot (a) and extracts a facing point, where the facing point may be the current position value of each mobile robot. At this time, in the following facing situation processing step (S243), the facing points of each guest mobile robot (200) classified as a facing situation are extracted and sorted to find the closest following point (a), find the closest facing mobile robot (b), determine whether the mobile robot or itself is driving, decelerating, or stopping (c), and output the deceleration ratio accordingly (d).

[0057] At this time, in the maximum speed determination and speed control step (S250), the highest value among the speed deceleration ratios for each judgment derived through each situation judgment step (S230) and situation processing step (S240) is selected, and the maximum speed of the mobile robot can be decelerated or stopped by applying the minimum value among the maximum speed values ​​derived in each situation.

[0058]

[0059] FIG. 3 is a block diagram illustrating the configuration of an autonomous mobile robot according to one embodiment of the present invention.

[0060] The mobile robot (100) may include a V2V (Vehicle-to-Vehicle) communication unit (110) for communication with other mobile robots, and may be configured to support various wireless communications, such as short-range communication or wireless LAN-based communication such as WAVE (Wireless Access in Vehicular Environments), DSRC (Dedicated Short-Range Communications), WiFi, or cellular-based 4G, 5G communication in which a communication network is configured in a cellular manner. The mobile robot (100) may be configured to transmit and receive data with all mobile robots located in the vicinity, i.e., within the communication range, using a broadcast communication method through the V2V communication unit.

[0061] In addition, the mobile robot (100) may include a central processing unit (CPU), an application processor (AP), etc., and may include a memory internally capable of storing commands or data related to at least one other component, or may communicate with a memory unit within the device or an external memory, if necessary, to access necessary information.

[0062] In addition, the mobile robot (100) may include a data collection processing unit (120), a situation judgment processing unit (130), a speed control unit (140), and an avoidance path setting unit (150), and these components may include programs or program modules that can be executed by one or more processors. These programs or program modules may be configured in the form of an operating system, an application program, or a program, and may be physically stored on various types of widely used storage devices. Such programs or program modules may include one or more routines, subroutines, programs, objects, components, instructions, data structures, and various forms for performing specific tasks or executing specific data types, but are not limited to these forms.

[0063] The data collection processing unit (120) may be configured to collect movement information related to the position and speed of the guest mobile robot and object attribute information related to the length, width, type, etc. of the guest mobile robot from each of a plurality of guest mobile robots (200) located in the vicinity, and filter the necessary data.

[0064] The situation judgment processing unit (130) may be configured to determine a collision situation based on the movement information of the guest mobile robot and the movement information of the mobile robot itself, and to perform a processing process for each collision situation. At this time, object attribute information may be additionally considered in the movement information of the mobile robot to determine whether a collision has occurred. As illustrated in FIG. 2b, the situation judgment processing unit (130) may classify collision situations into intersection situations, following situations, and facing situations, and may derive a deceleration rate or speed rate value for each collision situation.

[0065] In addition, the situation judgment processing unit (130) is configured to determine whether there is an intersection situation, and when determining the intersection situation, it may be configured to determine whether the predetermined paths of the mobile robot itself and the guest mobile robot intersect and are parallel, determine the error between the position of the guest mobile robot and the predetermined path of the guest mobile robot, and generate an intersection point of the paths of the mobile robot itself and the guest mobile robot. At this time, the situation judgment processing unit (130) is also configured to process an intersection situation, and when processing an intersection situation, it may be configured to list a plurality of guest mobile robots determined to be in an intersection situation based on the distance between the current position of the mobile robot and the intersection point generated for each of the plurality of guest mobile robots determined to be in an intersection situation, and determine a speed deceleration rate of the mobile robot or the guest mobile robot using the guest mobile robot corresponding to the closest intersection point and the estimated time of arrival (ETA) from the current position of the mobile robot to the intersection point in order to prevent a collision with the guest mobile robot among the plurality of guest mobile robots determined to be in an intersection situation. In addition, in order to prevent a collision with a guest mobile robot corresponding to the second closest intersection among the intersections generated for each of a plurality of guest mobile robots determined to be intersection situations when the mobile robot arrives at the nearest intersection, a speed reduction rate of the mobile robot or the guest mobile robot can be determined using the expected arrival time from the current position of the mobile robot to the intersection and the guest mobile robot corresponding to the second closest intersection, and in this way, collision with the guest mobile robot corresponding to the intersection can be prevented sequentially.In addition, when determining whether or not there is an intersection with each guest mobile robot, the situation judgment processing unit (130) can make a situation judgment by considering information such as the width and length of the mobile robot (100) and the guest mobile robot (200) even when there is no direct intersection between the paths of the mobile robot (100) and the guest mobile robot (200), and can prevent a collision by configuring it to generate an arbitrary intersection.

[0066] In addition, the situation judgment processing unit (130) may be configured to generate an arbitrary intersection point formed by converting the curved path into a straight path by extending the straight path before or after the curved path when determining whether or not there is an intersection situation with each guest mobile robot, if the path of the mobile robot (100) or the guest mobile robot (200) includes a curved path that changes the direction of movement.

[0067] In addition, the situation judgment processing unit (130) may be configured to determine whether a following situation exists, and may be configured to determine the identity and the same directionality of predetermined paths of the mobile robot itself and the guest mobile robot when determining the following situation. At this time, the situation judgment processing unit (130) may also be configured to process the following situation, and may be configured to align a plurality of guest mobile robots determined to be in a following situation when processing the following situation based on the distance between the current position of the mobile robot and each position of the plurality of guest mobile robots determined to be in a following situation, and may be configured to determine a speed deceleration rate of the mobile robot itself to prevent a collision with the guest mobile robot determined to be in a following situation, that is, the guest mobile robot located closest to the current position of the mobile robot among the plurality of guest mobile robots ahead. At this time, when determining the speed deceleration rate of the mobile robot, the distance between the guest mobile robot located closest to the current position of the mobile robot and the mobile robot may be continuously calculated, and if the distance between the guest mobile robot located closest to the current position of the mobile robot and the mobile robot is less than or equal to a predetermined standard, the speed deceleration rate of the mobile robot may be determined. In addition, when determining the speed deceleration rate of the mobile robot, if the distance between the mobile robot and the guest mobile robot is greater than the stopping distance of the mobile robot following behind and less than the deceleration start distance, the speed of the mobile robot following behind may be decelerated, wherein the deceleration start distance may be a value obtained by adding a predetermined margin distance to the distance between the mobile robot and the guest mobile robot. In addition, when determining the speed deceleration rate of the mobile robot, if the speed of the mobile robot following behind among the mobile robot or the guest mobile robot is faster than the speed of the mobile robot leading behind, the speed of the mobile robot following behind may be decelerated to be the same as the speed of the mobile robot leading ahead.In addition, when processing a following situation, the situation judgment processing unit (130) may be configured to set a curved following area that extends a preset distance from the curved section when the path of the following mobile robot from behind among the mobile robot (100) or the guest mobile robot (200) includes a curved driving path that changes the direction of movement, and to set a deceleration rate or speed rate for deceleration or stop control of the following mobile robot when the preceding mobile robot is located within the curved following area.

[0068] In addition, the situation judgment processing unit (130) may be configured to determine whether a facing situation exists, and may be configured to determine whether the predetermined paths of the mobile robot itself and the guest mobile robot are identical or opposite in direction when determining the facing situation. At this time, the situation judgment processing unit (130) may also be configured to process a facing situation, and may be configured to align a plurality of guest mobile robots determined to be facing situations when processing the facing situation based on the distance between the current position of the mobile robot and each position of the plurality of guest mobile robots determined to be facing situations, and may be configured to determine a speed deceleration rate of the mobile robot or the guest mobile robot in order to prevent a collision with the guest mobile robot that is located closest to the position of the current mobile robot among the plurality of guest mobile robots determined to be facing situations. When determining the speed deceleration rate of the mobile robot, the situation judgment processing unit (130) is configured to decelerate the speed of at least one of the mobile robot and the guest mobile robot when the distance between the mobile robot and the guest mobile robot located closest to the mobile robot is greater than the stopping distance of the mobile robot or the guest mobile robot and less than the deceleration start distance, and the deceleration start distance may be a value obtained by adding a predetermined margin distance to the stopping distance of the mobile robot or the guest mobile robot. In addition, when determining the speed deceleration rate of the mobile robot, the situation judgment processing unit (130) may set the speeds of the mobile robot and the guest mobile robot to 0 when the distance between the mobile robot and the guest mobile robot located closest to the mobile robot is less than the stopping distance of the mobile robot or the guest mobile robot.In addition, when processing a facing situation, the situation judgment processing unit (130) may be configured to determine a final destination within the same path among the paths of the mobile robot (100) or guest mobile robot (200) if the path includes a driving path that changes the direction of movement, and to process it as not being a facing situation if the final destinations within the same path of the mobile robot and guest mobile robot do not meet each other.

[0069] The speed control unit (140) may be configured to determine a speed deceleration ratio of the mobile robot (100) or the guest mobile robot (200) to prepare for a collision situation, and to perform driving, deceleration, or stop control of the mobile robot by applying the determined speed deceleration ratio. Here, the highest value among the deceleration ratios derived according to each situation judgment may be selected, or the lowest value among the speed ratios may be selected to control the speed of the corresponding mobile robot to be decelerated or stopped. That is, the situation judgment processing unit (130) may select the highest value among the multiple speed deceleration ratios derived for each situation judgment, and may decelerate or stop the maximum speed of the corresponding mobile robot by applying the minimum value among the maximum speed values ​​derived in each situation.

[0070]

[0071] The avoidance path setting unit (150) may be configured to determine whether an error has occurred in the guest mobile robot when the preceding guest mobile robot or the facing guest mobile robot is stopped due to a motion error or the like, and to generate an avoidance path for the mobile robot if it is determined that there is an error in the guest mobile robot. At this time, the situation judgment processing unit (130) may be configured to determine a collision situation between the avoidance path of the mobile robot generated by the avoidance path setting unit (150) and another guest mobile robot, and to determine the collision situation between the avoidance path of the mobile robot and another guest mobile robot. At this time, it is determined whether the directions of the paths of the mobile robot and the other guest mobile robot are opposite to each other and are facing each other on the same line, and if it is determined to be a facing situation, the movement of the mobile robot is set so that after a temporary stop of either the mobile robot or the other guest mobile robot, the mobile robot re-enters the normal path through the avoidance path, thereby controlling the timing for avoiding a collision with the other mobile robot when changing to the avoidance path.

[0072]

[0073] FIGS. 4A and 4B are exemplary diagrams for explaining a method for avoiding collision in a crossing situation according to one embodiment of the present invention.

[0074] First, as shown in Fig. 2b, in order to determine whether the moving directions of the mobile robot (R1) and the guest mobile robots (C1, C2, C3) intersect each other, the presence or absence of path intersection of the two robots, intersection point extraction, parallel judgment, and error of the mobile robots from the path are performed, and the mobile robots in the intersection situation can be determined and classified. At this time, when determining whether or not the paths of each mobile robot intersect, the final target point can be taken into consideration to determine whether or not the intersection and the intersection point can be extracted.

[0075] Referring to FIG. 4a, first, among multiple guest mobile robots (C1, C2, C3) classified as intersection situations, the extracted intersection points can be listed and sorted in order of distance between the mobile mobile robot and the extracted intersection points, and the speed can be controlled to decelerate or stop by making a collision avoidance judgment from the first guest mobile robot (C2) that is closest among the sorted guest mobile robots.

[0076] Collision prevention judgment basically determines whether to slow down, stop, or drive by prioritizing each mobile robot based on the estimated time of arrival (ETA) from the current location to the intersection, and can also be set to make judgments by considering the work distance, work priority, and type of mobile robot depending on other circumstances.

[0077] In addition, assuming that no collision occurs with the first guest mobile robot (C2), when passing the first intersection, the robot can decelerate or stop in advance to prevent collision with a number of aligned guest mobile robots in order to prevent collisions that may occur at the next intersection, and in this way, collisions that may occur with the next guest mobile robot at the intersection can be prevented sequentially.

[0078] Referring to Fig. 4b, even if the movement paths of the two robots are not orthogonal as in Fig. 4a, the intersection point of the paths of the mobile robot (R1) and the guest mobile robot (C1) can be extracted and collision can be prevented.

[0079] Referring to Fig. 4c, situations (c-3), (c-4), and (c-5) are examples of situations in which two mobile robots do not form a direct intersecting path, but are determined to be an intersection situation. As in (c-3) and (c-4), if the width between the paths of the two mobile robots is sufficiently wide, the two robots can proceed without collision because there is no overlapping part when driving. At this time, the presence or absence of a collision can be determined by using the width of the paths of the mobile robots together with object attribute information such as length information or width information of each mobile robot or footprint information. Meanwhile, in case of (c-5), if the width between the paths of the two mobile robots is narrow and the width between the paths is smaller than the width length of the mobile robots, the two paths are determined to overlap, and at this time, the vertical path of the mobile robot (R1) is extended by a certain distance calculated based on the width or length information of the mobile robots to generate an intersection with the path of the guest mobile robot (C1), and a collision prevention determination is made at the intersection to decelerate and stop.

[0080] Referring to Fig. 4d, first, in (c-6), when the mobile robot (R1) drives in a straight line, an intersection point between the paths of the mobile robot (R1) and the guest mobile robot (C1) is created, and in (c-7), when the mobile robot (R1) drives in a curve, the straight path before or after the curved driving is extended to convert the curved path into a straight path, thereby creating an arbitrary intersection point, and thus, a collision avoidance judgment can be performed in the same manner as in (c-6) to decelerate and stop.

[0081] Next, referring to (c-8), the mobile robot (R1) has a path that performs two C-turns, and since the mobile robot (R1) is driven in a curve, there is no intersection with the paths of the actual guest mobile robots (C1, C2). Therefore, at this time, by extending the straight driving path before or after the curved driving, the curved path is converted into a straight path, thereby generating an arbitrary virtual target point, and based on the intersection point generated based on this virtual target point, a collision avoidance decision can be made for the guest mobile robots (C1, C2) to decelerate or stop. In addition, the guest mobile robots (C1, C2) can also receive information about the mobile robot (R1) and make the same collision avoidance decision based on the same intersection point information.

[0082] In common situations like these, when a guest mobile robot is stopped near an intersection, it is possible to determine whether it can pass without collision by considering object attribute information such as length information or width information of the guest mobile robot.

[0083]

[0084] FIG. 5 is an exemplary diagram illustrating a method for avoiding collision in a following situation according to one embodiment of the present invention.

[0085] First, in order to determine whether the mobile robot (R1) is following the guest mobile robot (F1), the paths of the two mobile robots are identical, the directions are identical, a curve following area is created when the preceding robot drives along a curve, etc., and the following point is extracted, thereby enabling the robot being followed to be determined and classified.

[0086] In a tracking situation, collision avoidance judgment is made by first listing and sorting the guest mobile robots classified as tracking situations in descending order of distance between the extracted tracking points and the mobile robot (R1), and then performing a collision avoidance judgment on the first guest mobile robot (F1) that is closest among the sorted guest mobile robots. The tracking point used in this judgment method is the position value of the guest mobile robot that the mobile mobile robot is following. Based on this position value, the distance between the mobile robot (R1) and the guest mobile robot (F1) can be continuously calculated to determine whether to decelerate or stop. For example, if the distance between the guest mobile robot located closest to the position of the mobile robot and the mobile robot is less than a predetermined standard, for example, less than the stopping distance, the mobile robot (R1) can be stopped. In this case, the stopping distance can be set to a preset default value or a distance value transmitted from the control system.

[0087] In addition, the method of determining deceleration here can be such that deceleration is performed when the position of the mobile robot is greater than the stopping distance and less than the deceleration start distance. At this time, the deceleration start distance can be a value obtained by adding a predetermined margin to the distance between the two mobile robots. (a) In addition, for example, the speed deceleration ratio can be set to reflect the highest deceleration ratio among the values ​​obtained by dividing the difference between the stopping distance and the actual distance from the tracking point in real time by the deceleration section distance and the ratio of the speed of the current guest mobile robot divided by the speed of the current mobile robot, and the maximum speed specified for the paths traveled by the current mobile robot and the guest mobile robot can be calculated in the same way, and the highest value selected by comparing it with a previously calculated smaller value. Here, the deceleration section distance is the value obtained by subtracting the stopping distance from the deceleration start distance, and for example, the method of determining the final applicable speed deceleration ratio is as follows.

[0088] (Example of determining speed reduction ratio)

[0089] Speed ​​reduction ratio 1: (actual distance - stopping distance) / deceleration section distance

[0090] Speed ​​Deceleration Ratio 2: Real-time guest robot speed / Real-time moving robot speed

[0091] Speed ​​reduction ratio 3: Guest robot's set path speed / Robot's set path speed

[0092] Speed ​​reduction ratio 4: Maximum reduction ratio = 1.0

[0093] Among the speed reduction ratios 1, 2, and 3 derived above, the maximum value of the speed reduction ratio is determined, and the maximum value is set not to exceed the preset speed reduction ratio 4 (maximum reduction ratio). If the maximum value of the speed reduction ratio is greater than the maximum reduction ratio, the maximum reduction ratio can be set to be adopted as the speed reduction ratio.

[0094] Now, referring to (d-1) of Fig. 5, as a basic following situation, when the speed of the guest mobile robot (F1) is slower than that of the mobile robot (R1), the mobile robot (R1) can be controlled to move at a constant speed by decelerating to the same speed as the guest mobile robot (F1) in the deceleration section, and also, when the mobile robot (F1) is stopped, the following mobile robot (R1) can be controlled to stop when it gets closer than the stopping distance.

[0095] Also, referring to (d-2) of FIG. 5, although the paths of the mobile robot (R1) and the guest mobile robot (F1) are different, their footprints overlap. At this time, the width information of the mobile robot (R1) and the guest mobile robot (F1) is checked to determine whether their footprints overlap, and if so, a collision avoidance judgment is performed to control deceleration, constant-speed driving, and stopping operations.

[0096] In addition, referring to (d-3) of FIG. 5, the moving directions of the mobile robot (R1) and the guest mobile robot (F1) are the same, but the two paths do not overlap and are disconnected. At this time, if the distance between the target point of the mobile robot (R1) and the position of the guest mobile robot (F1) is a distance that does not cause a collision when the mobile robot (R1) moves, the mobile robot (R1) is controlled to proceed as is, and if not, the mobile robot (R1) can perform a collision avoidance judgment to control deceleration, constant-speed driving, and stopping operations.

[0097] In addition, referring to (d-4) of FIG. 5, the mobile robot (R1) is driving along a curved path, and the guest mobile robot (F1) is located at the back after the curved driving is finished. At this time, a curve following area (510) is set from the curved section to a preset distance for the path of the mobile robot (R1), and if there is a guest mobile robot (F1) ahead within the curve following area (510), deceleration, constant speed driving, and stopping operations can be controlled. In addition, if the guest mobile robot (F1) intersects the point where the curved section ends and enters the curve following area (510), the mobile robot (R1) can make a collision avoidance judgment and decelerate and stop even in other situations.

[0098]

[0099] FIG. 6 is an exemplary diagram illustrating a method for avoiding collision in a facing situation according to one embodiment of the present invention.

[0100] First, in order to determine whether a mobile robot (R1) and a guest mobile robot (F1) are in a following situation where they face each other and drive while facing each other, the robots in the facing situation can be determined and classified by extracting the sameness of the paths, sameness of the directions, and facing points of the two mobile robots.

[0101] In a face-to-face situation, collision avoidance is determined by sorting the guest mobile robots listed for the face-to-face situation in order of proximity to the mobile robot (R1). The distance to avoid collision is based on the distance transmitted by the control system, and can be set as a parameter in case the distance is incorrect. Additionally, the deceleration start distance can be set to a value equal to the stopping distance plus a predetermined margin of error.

[0102] Among the collision avoidance judgment conditions, deceleration control can be set to operate between the deceleration start distance and the stop distance from the extracted facing point, and can be set to stop if the distance from the mobile robot (R1) to the facing point becomes closer than the set stop distance.

[0103] Referring to (e-1) of Fig. 6, a general facing situation can be seen, in which the mobile robot (R1) is moving toward the guest mobile robot (A1), and the guest mobile robot (A1) is moving toward the mobile robot (R1), facing each other. In this facing situation, a collision avoidance judgment can be made to decelerate and stop.

[0104] Also, referring to (e-2) of Fig. 6, the paths of the two mobile robots are facing each other on different lines, not the same line. Furthermore, the footprints of the two mobile robots can be seen to overlap. At this time, the width information of the mobile robot (R1) and the guest mobile robot (A1) can be checked to determine whether their footprints overlap. If so, a collision avoidance judgment can be performed to control the deceleration and stopping actions.

[0105] In addition, referring to (e-3) and (e-4) of FIG. 6, there is an exception in which two mobile robots face each other, and the mobile robot (R1) or the guest mobile robot (A1) changes its direction of movement to dock out. In this case, since the target points of the mobile robot (R1) and the guest mobile robot (A1) do not overlap, there is no need to stop each other under the condition that they do not interfere with each other and their footprints do not overlap, this case is not considered a facing situation, so it can be controlled to continue driving without unnecessary actions by handling it as an exception.

[0106]

[0107] FIG. 7a and FIG. 7b are exemplary diagrams for explaining a method for avoiding a collision in an avoidance situation according to one embodiment of the present invention.

[0108] If an error occurs in some mobile robots during a task and they stop, there may be cases where other mobile robots need to move while avoiding the stopped mobile robots to ensure smooth operation. At this time, if the guest mobile robot (A1) ahead in the following situation stops, it is determined whether an error has occurred in the guest mobile robot (A1), and if it is determined that there is an error in the guest mobile robot (A1), an avoidance path for the mobile robot (R1) can be generated so that it can move while avoiding the guest mobile robot (A1). At this time, it may be configured to determine a collision situation between the avoidance path (720) of the mobile robot (A1) and another guest mobile robot (A2). The collision situation judgment according to the avoidance path is determined by judging whether the directions of the paths of the mobile robot (R1) and another guest mobile robot (A2) are opposite to each other and whether the two paths are facing each other on the same line, and if it is determined to be a facing situation, after one of the mobile robots (R1) and the other guest mobile robot (A2) stops temporarily, the movement of the mobile robot (R1) is set so that the mobile robot (R1) passes through the avoidance path (720) and then re-enters the normal path (720), thereby allowing the two mobile robots to pass through the avoidance path without collision.

[0109] Referring to (f-1) of Fig. 7a, in a following situation, a leading guest mobile robot (A1) has stopped due to an error while moving, and a mobile robot (R1) is following the guest mobile robot (A1). In addition, another guest mobile robot (A2) is moving in an opposite direction.

[0110] Referring to (f-2) of Fig. 7a, the mobile robot (R1) can use the collision avoidance judgment method of the following situation to stop at a certain distance behind the guest mobile robot (A1), and then determine whether the guest mobile robot (A1) has stopped due to an error and whether it can evade. At this time, the mobile robot (R1) determines a collision situation based on the evasion path (720) to determine whether it can return to the original normal path (710) by passing the evasion path (720), and at this time, the distance to another guest mobile robot (A2) coming from the opposite direction is calculated and the footprint is checked, and if the distance between the two paths is a distance that secures a space for evasion, as in (f-3), it can proceed with evasion by determining that the mobile robot (R1) and another guest mobile robot (A2) are not facing each other.

[0111] Referring to Fig. 7b, if it is determined that the footprints of two mobile robots overlap based on the width of the mobile robots and the length between the two paths, then it is determined that they are facing each other based on the avoidance path (720) and compared with the path of another guest mobile robot (A2), and it is possible to determine whether the two mobile robots collide. If the mobile robot (R1) performs an avoidance maneuver, the path of the mobile robot (R1) at this time is not the original normal path (710), but rather the newly set avoidance path (720). For example, as in (f-4), the mobile robot (R1) can be set to stop until the guest mobile robot (A2) passes, and then proceed through the avoidance path (720) after the guest mobile robot (A2) passes the side of the mobile robot (R1). In addition, if it is determined that there is a risk of collision between the two mobile robots, as in (f-5), the guest mobile robot (A2) can be stopped first, and after the mobile robot (R1) completes evasion driving through the evasion path (720) and then enters the normal path (710), the guest mobile robot (A2) can be set to drive again.

[0112] In addition, when the guest mobile robot (A2) facing the guest mobile robot (A1) in a situation such as (f-5) receives an error state of the guest mobile robot (A1) and that the mobile robot (R1) is in an evasive state, the guest mobile robot (A2) can gradually decelerate and stop first to leave a sufficient distance for the mobile robot (R1) to evade. When the mobile robot (R1) completes evasive driving through the evasive path (720) and then enters the normal path (710), the guest mobile robot (A2) can be set to drive again.

[0113]

[0114] The various embodiments described herein may be implemented in hardware, middleware, microcode, software, and / or a combination thereof. For example, the various embodiments may be implemented in one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof.

[0115] Also, for example, various embodiments may be embodied or encoded in a computer-readable medium containing instructions. Instructions embodied or encoded in the computer-readable medium can cause a programmable processor or other processor to perform a method when the instructions are executed, for example. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. Storage media may be any available media that can be accessed by a computer. For example, such computer-readable media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage media, magnetic disk storage media or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of computer-accessible instructions or data structures.

[0116] Such hardware, software, firmware, etc. may be implemented within the same device or within separate devices to support the various operations and functions described herein. Additionally, components, units, modules, components, etc. described as “units” in the present invention may be implemented together or individually as separate but interoperable logic devices. The depiction of different features for modules, units, etc. is intended to highlight different functional embodiments and does not necessarily imply that they must be realized by separate hardware or software components. Rather, the functionality associated with one or more modules or units may be performed by separate hardware or software components, or integrated into common or separate hardware or software components.

[0117] Furthermore, while operations are depicted in the drawings in a specific order, this should not be construed as requiring that these operations be performed in the specific order depicted, or in any sequential order, or that all depicted operations be performed to achieve the desired results. In certain circumstances, multitasking and parallel processing may be advantageous. Furthermore, the distinction between the various components in the embodiments described above should not be construed as requiring such distinction in all embodiments, and it should be understood that the components depicted may generally be integrated together into a single software product or packaged into multiple software products.

[0118] While the present invention has been described with reference to the embodiments illustrated in the drawings, these are merely exemplary, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible. Therefore, the true scope of technical protection of the present invention should be determined by the technical spirit of the appended claims.

Claims

1. A method for preventing collisions in an autonomous mobile robot using V2V communication performed in the mobile robot, A step of collecting movement information related to the location and speed of a plurality of guest mobile robots located in the vicinity using V2V (Vehicle-to-Vehicle Communication) communication; A step of determining a collision situation based on the movement information of the guest mobile robot and the movement information of the mobile robot itself; A step of determining a speed reduction ratio of the mobile robot or the guest mobile robot to prepare for the collision situation; and A step of performing driving, deceleration, or stopping control of the mobile robot by applying the above-determined speed reduction ratio. Including, A method for preventing collisions in an autonomous mobile robot, wherein the above V2V communication uses a broadcast communication method.

2. In the first paragraph, the step of determining the collision situation includes a step of determining whether the movement directions of the mobile robot and each guest mobile robot intersect each other in a crossing situation, and the step of determining whether the crossing situation includes a step of determining whether a predetermined path of the mobile robot itself and the guest mobile robot intersects and is parallel, determining an error between the position of the guest mobile robot and the predetermined path of the guest mobile robot, and generating an intersection point of the paths of the mobile robot itself and the guest mobile robot. A method for preventing collisions of an autonomous mobile robot.

3. In the second paragraph, if the step of determining the collision situation determines that it is a crossover situation, a step for processing the crossover situation is further included. The steps to handle the above cross-reference situation are: A step of listing a plurality of guest mobile robots determined to be in an intersection situation based on the distance between the current location of the mobile robot and the intersection point generated for each of the plurality of guest mobile robots determined to be in an intersection situation; and In order to prevent collision with a guest mobile robot corresponding to the intersection point closest to the current location of the mobile robot among the plurality of guest mobile robots determined to be in the above intersection situation, a step of determining a speed reduction rate of the mobile robot or the guest mobile robot using the guest mobile robot corresponding to the closest intersection point and the estimated time of arrival (ETA) from the current location of the mobile robot to the intersection point A collision avoidance method for an autonomous mobile robot, comprising:

4. In the third paragraph, in order to prevent collision with the guest mobile robot corresponding to the second closest intersection among the intersections generated for each of the plurality of guest mobile robots determined to be the intersection situation when the mobile robot arrives at the closest intersection, a step of determining a speed deceleration rate of the mobile robot or the guest mobile robot using the expected arrival time from the current location of the mobile robot to the intersection and the guest mobile robot corresponding to the second closest intersection. A collision avoidance method for an autonomous mobile robot, comprising:

5. A method for preventing collisions of an autonomous mobile robot, wherein the step of determining a speed reduction ratio of the mobile robot or the guest mobile robot in the third paragraph includes a step of determining a speed reduction target based on the work priority, work distance, or type of robot of the mobile robot and the guest mobile robot.

6. In the second paragraph, the step of determining whether there is a crossing situation with each guest mobile robot is a method for preventing collisions of an autonomous mobile robot, wherein even if there is no direct crossing point between the paths of the mobile robot and the guest mobile robot, if the distance between the paths of the mobile robot and the guest mobile robot is less than a predetermined standard, the guest mobile robot is determined to be in a crossing situation.

7. In the second paragraph, the step of determining whether or not there is a crossing situation with each guest mobile robot is a method for preventing collisions of an autonomous mobile robot, wherein, if the path of the mobile robot or the guest mobile robot includes a curved driving path that changes the direction of movement, the method generates an arbitrary intersection point formed by converting the curved path into a straight path by extending the straight driving path before or after the curved driving.

8. A method for preventing collisions in an autonomous mobile robot, wherein in the second paragraph, the step of determining the collision situation further includes a step of determining whether the direction of the paths of the mobile robot and the guest mobile robot are the same, which is a following situation, and a step of determining whether the direction of the paths of the mobile robot and the guest mobile robot are opposite to each other and the two paths are on the same line, which is a facing situation.

9. In the first paragraph, the step of receiving object attribute information related to length and width information of the guest mobile robot from each of a plurality of guest mobile robots located in the vicinity using the V2V communication is further included. A method for preventing collisions in an autonomous mobile robot, wherein the step of determining the collision situation is to determine whether or not a collision has occurred based on the movement information and the object attribute information.

10. In a mobile robot for collision prevention of an autonomous mobile robot using V2V communication, A data collection processing unit configured to collect movement information related to the location and speed of a plurality of guest mobile robots located in the vicinity using a V2V (Vehicle-to-Vehicle Communication) communication unit; A situation judgment processing unit configured to judge a collision situation based on the movement information of the guest mobile robot and the movement information of the mobile robot itself; and A speed control unit configured to determine a speed deceleration ratio of the mobile robot or the guest mobile robot to prepare for the above collision situation, and to perform driving, deceleration, or stop control of the mobile robot by applying the determined speed deceleration ratio. A mobile robot including, and wherein the V2V communication uses a broadcast communication method.

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