Patent Publication Number: US-2023144509-A1

Title: A plurality of robot cleaners and method for controlling the same

Description:
TECHNICAL FIELD 
     The present disclosure relates to a plurality of robot cleaners and method for controlling the same, and more particularly, to a plurality of robot cleaners and method for controlling the same that are suitable for two robot cleaners to perform cleaning without interference therebetween. 
     BACKGROUND ART 
     In general, a cleaner includes a main body having a suction device and a dust container and a cleaning nozzle connected to the main body to perform cleaning in a state of being proximate to a face to be cleaned. Cleaners are categorized into a manual cleaner for a user to clean a face to be cleaned directly and manually and a robot cleaner to clean a face to be cleaned while a main body travels by itself. 
     In addition, regarding the robot cleaner, an ultrasonic sensor, a camera sensor and/or the like are further installed in the main body equipped with the suction device and the dust container. As the main body automatically travels around a face to be cleaned, the cleaning nozzle sucks foreign substance on the face to be cleaned by a suction force generated by the suction device and the sucked foreign substance is collected in the dust container. Thus, the cleaning of the face to be cleaned is performed. 
     As a prior art, there is Korean Patent Application 10-2017-0174493. However, since the prior art just discloses a general technology of operating two robot cleaners, it is necessary to suggest a technology of efficiently performing cleaning while two robot cleaners are operating. 
     In addition, as the prior art assumes that the two robot cleaners communicate with each other, it is necessary to suggest a technology of performing cleaning with two robot cleaners despite absence of communication between the two robot cleaners. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     One technical task of the present disclosure is to provide a plurality of robot cleaners and method for controlling the same, by which a plurality of robots can do the cleaning without user&#39;s intervention. 
     Another technical task of the present disclosure is to provide a plurality of robot cleaners and method for controlling the same, by which two robots can do the cleaning cooperatively in a situation that robot cleaners are unable to communicate with each other. 
     Further technical task of the present disclosure is to provide a plurality of robot cleaners and method for controlling the same, by which interference is prevented from occurring among the robot cleaners when a plurality of the robot cleaners are simul-taneously cleaning a traveling zone despite the possibility of collision or cleaning interference between the robot cleaners during the cleaning in a predetermined area. 
     Solution to Problem 
     In order to achieve the above technical tasks, the present disclosure provides a technology that traveling interference does not occur between a second robot cleaner and a first robot cleaner. Since the second robot cleaner is docked with a second cocking device while the first robot cleaner is cleaning, interference does not occur between the traveling of the first robot cleaner and the travelling of the second robot cleaner. On the other hand, since the first robot cleaner is docked with a first cocking device while the second robot cleaner is cleaning, interference does not occur between the traveling of the first robot cleaner and the travelling of the second robot cleaner. 
     In addition, the present disclosure suggests a technology that two robot cleaners can do the cleaning cooperatively despite not communicating with each other through communication units. One of the robot cleaners may determine whether the other is currently cleaning or whether the other is currently docked with a docking device depending on a presence or non-presence of reception of a signal transmitted from the docking device with which the corresponding robot cleaner is not docked. Namely, the present disclosure suggests a method of using cooperative travelling even in an offline environment. 
     To achieve these objects and other advantages and in accordance with the purpose of the present disclosure, as embodied and broadly described herein, a method of controlling a plurality of robot cleaners according to one embodiment of the present disclosure may include a first step of docking a first robot cleaner and a second robot cleaner with a first docking device and a second docking device, respectively, a second step of checking whether the first robot cleaner is undocked from the first docking device, and a third step of if the first robot cleaner docked with the first docking device again, undocking the second robot cleaner from the second docking device. 
     In another aspect of the disclosure, as embodied and broadly described herein, a plurality of robot cleaners according to one embodiment of the present disclosure may include a first docking device including a guide signal generating unit transmitting a docking guide signal, a second docking device including a guide signal generating unit transmitting a docking guide signal, a first robot cleaner docked with the first docking device, and a second robot cleaner docked with the second docking device, wherein a sensing unit is provided to each of the first robot cleaner and the second robot cleaner and wherein the sensing unit is capable of receiving a signal of the guide signal generating unit of the first docking device and a signal of the guide signal generating unit of the second docking device. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the disclosure as claimed. 
     Advantageous Effects of Invention 
     According to the present disclosure, a plurality of robot cleaners can do the cleaning while cooperating with each other. For example, when two robot cleaners include robot cleaners of different types, cleaning may be performed in two ways without user&#39;s intervention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description serve to explain the principles of the disclosure. 
         FIG.  1    is a perspective diagram showing a robot cleaner and a docking device with which the robot cleaner is docked according to an embodiment of the present disclosure. 
         FIG.  2    is a diagram showing the robot cleaner of  FIG.  1   , viewed from a topside. 
         FIG.  3    is a diagram showing the robot cleaner of  FIG.  1   , viewed from a front side. 
         FIG.  4    is a diagram showing the robot cleaner of  FIG.  1   , viewed from a bottom side. 
         FIG.  5    is a block diagram showing the control configuration among main components of the robot cleaner of  FIG.  1   . 
         FIG.  6    is a conceptual diagram showing the network including a plurality of the robot cleaners of  FIG.  1    and a terminal. 
         FIG.  7    is a control flowchart according to an embodiment of the present disclosure. 
         FIG.  8    is a flowchart to describe an essential portion of  FIG.  7   . 
         FIG.  9    is a flowchart to describe another essential portion of  FIG.  7   . 
         FIG.  10    is a diagram to describe implementation of an embodiment according to  FIG.  7   . 
     
    
    
     MODE FOR THE INVENTION 
     Hereinafter, a preferred embodiment of the present disclosure that may specifically realize the above objects will be described with reference to the accompanying drawings. 
     In this process, a size, a shape, or the like of a component shown in the drawings may be exaggerated for clarity and convenience of the description. In addition, terms specifically defined in consideration of a configuration and an operation of the present disclosure may vary depending on a user or an operator&#39;s intention or practice. Def-initions of such terms should be made based on the contents throughout this specification. 
     Referring to  FIGS.  1  to  6   , a robot cleaner  100  includes a main body  110 . Hereinafter, in defining each portion of the main body  110 , a portion facing a ceiling in a travel zone is defined as a top face (see  FIG.  2   ), a portion facing a floor in the travel zone is defined as a bottom face (see  FIG.  4   ), and a portion directed in a travel direction among portions forming a perimeter of the main body  110  between the top face and the bottom face is defined as a front face (see  FIG.  3   ). In addition, a portion directed in an opposite direction to the front face of the main body  110  may be defined as a rear face. The main body  110  may include a casing  111  for defining therein a space in which various components constituting the robot cleaner  100  are accommodated. 
     The robot cleaner  100  includes a sensing unit  130  that performs sensing to obtain current state information. The sensing unit  130  may perform the sensing during travel. The sensing unit  130  may sense a situation around the robot cleaner  100 . The sensing unit  130  may sense a state of the robot cleaner  100 . 
     The sensing unit  130  may sense information on the travel zone. The sensing unit  130  may sense obstacles such as a wall body, furniture, a cliff, and the like on a travel face. The sensing unit  130  may sense a docking device  200 . The sensing unit  130  may sense information about the ceiling. Through the information sensed by the sensing unit  130 , the robot cleaner  100  may map the travel zone. 
     The sensing unit  130  may include at least one of a distance sensor  131 , a cliff sensor  132 , an external signal sensor (not shown), an impact sensor (not shown), an image sensor  138 ,  3 D sensors  138   a ,  139   a , and  139   b , and a docking sensor for sensing whether docking is successful. 
     The sensing unit  130  may include the distance sensor  131  that senses a distance to a surrounding object. The distance sensor  131  may be disposed on the front face or a side face of the main body  110 . The distance sensor  131  may sense a surrounding obstacle. 
     A plurality of distance sensors  131  may be arranged. 
     For example, the distance sensor  131  may be an infrared sensor equipped with a light emitter and a light receiver, an ultrasonic sensor, an RF sensor, a geomagnetic sensor, and the like. The distance sensor  131  may be implemented using an ultrasonic wave, an infrared ray, or the like. The distance sensor  131  may be implemented using a camera. The distance sensor  131  may be implemented with two or more types of sensors. 
     The sensing unit  130  may include the cliff sensor  132  that senses an obstacle on the floor in the travel zone. The cliff sensor  132  may sense whether a cliff exists on the floor. 
     The cliff sensor  132  may be disposed on the bottom face of the robot cleaner  100 . A plurality of cliff sensors  132  may be arranged. The cliff sensor  132  disposed on a front portion of the bottom face of the robot cleaner  100  may be disposed. The cliff sensor  132  disposed on a rear portion of the bottom face of the robot cleaner  100  may be disposed. 
     The cliff sensor  132  may be an infrared ray sensor equipped with a light emitter and a light receiver, an ultrasonic sensor, an RF sensor, a location sensitive detector (PSD) sensor, and the like. For example, the cliff sensor may be the PSD sensor, but may be composed of a plurality of different types of sensors. The PSD sensor includes a light emitter that emits an infrared ray on the obstacle and a light receiver that receives the infrared ray that is reflected back from the obstacle. 
     The sensing unit  130  may include the impact sensor that senses an impact resulted from contact between the robot cleaner  100  and the external object. 
     The sensing unit  130  may include the external signal sensor that senses a signal transmitted from outside of the robot cleaner  100 . The external signal sensor may include at least one of an infrared ray sensor that senses an infrared signal from the outside, an ultrasonic sensor that senses an ultrasonic signal from the outside, and an RF sensor (radio frequency sensor) that senses an RF signal from the outside. 
     The sensing unit  130  may include the image sensor  138  that senses an image of an outside of the robot cleaner  100 . 
     The image sensor  138  may include a digital camera. The digital camera may include an image sensor (e.g., a CMOS image sensor) including at least one optical lens and a plurality of photodiodes (e.g., pixels) on which an image is focused by light passed through the optical lens, and a digital signal processor (DSP) that composes an image based on signals output from the photodiodes. The digital signal processor is capable of generating a moving image composed of frames composed of still images as well as a still image. 
     The image sensor  138  may include a front face image sensor  138   a  that senses an image in a forward direction of the robot cleaner  100 . The front face image sensor  138   a  may sense an image of the surrounding object such as the obstacle, the docking device  200 , or the like. 
     The image sensor  138  may include a top face image sensor  138   b  that senses an image in an upward direction of the robot cleaner  100 . The top face image sensor  138   b  may sense an image such as the ceiling, a bottom face of furniture disposed above the robot cleaner  100 , and the like. 
     The image sensor  138  may include a bottom face image sensor  138   c  that senses an image in a downward direction of the robot cleaner  100 . The bottom face image sensor  138   c  may sense an image of the floor. 
     In addition, the image sensor  138  may include a sensor that senses an image in a lateral or rearward direction. 
     The sensing unit  130  may include the  3 D sensors  138   a ,  139   a , and  139   b  that sense  3 D information of an external environment. 
     The  3 D sensors  138   a ,  139   a , and  139   b  may include a  3 D depth camera  138   a  that calculates a distance between the robot cleaner  100  and an object to be captured. 
     In the present embodiment, the  3 D sensors  138   a ,  139   a , and  139   b  include a pattern irradiator  139  for irradiating light of a predetermined pattern in the forward direction of the main body  110 , and a front face image sensor  138   a  that acquires an image of a front of the main body  110 . The pattern irradiator  139  may include a first pattern irradiator  139   a  for irradiating light of a first pattern in a forward and downward direction of the main body  110  and a second pattern irradiator  139   b  for irradiating light of a second pattern in a forward and upward direction of the main body  110 . The front face image sensor  138   a  may acquire an image of a region into which the light of the first pattern and the light of the second pattern are incident. 
     The pattern irradiator  139  may be disposed to irradiate an infrared pattern. 
     In this case, the front face image sensor  138   a  may measure a distance between the  3 D sensor and the object to be captured by capturing a shape of the infrared pattern projected on the object to be captured. 
     The light of the first pattern and the light of the second pattern may be irradiated in a form of straight lines crossing each other. The light of the first pattern and the light of the second pattern may be irradiated in a form of horizontal straight lines spaced from each other in a vertical direction. 
     A second laser may apply laser in form of a single straight line. According to this, a bottom laser is used to sense an obstacle of a bottom part, a top laser is used to sense an obstacle of a top part, and a middle laser between the bottom laser and the top laser is used to sense an obstacle of a middle part. 
     The sensing unit  130  may include a docking sensor (not shown) that senses whether the robot cleaner  100  is successfully docked with the docking device  200 . The docking sensor may be implemented to sense by contact between a corresponding terminal  190  and a charging terminal  210 , may be implemented as a sensor disposed separately from the corresponding terminal  190 , or may be implemented by sensing a state of a battery  177  during charging. A docking success status and a docking failure status may be sensed by the docking sensor. 
     The robot cleaner  100  includes a travel unit  160  that moves the main body  110  with respect to the floor. The travel unit  160  may include at least one driving wheel  166  that moves the main body  110 . The travel unit  160  may include a driving motor. The driving wheel  166  may include a left wheel  166 (L) and a right wheel  166 (R) arranged on left and right sides of the main body  110 , respectively. 
     The left wheel  166 (L) and the right wheel  166 (R) may be driven by one driving motor, but a left wheel driving motor for driving the left wheel  166 (L) and a right wheel driving motor for driving the right wheel  166 (R) may be separately arranged as needed. The travel direction of the main body  110  may be switched in a left or right direction by making a difference in rotation speeds of the left wheel  166 (L) and the right wheel  166 (R). 
     The travel unit  160  may include an auxiliary wheel  168  that does not provide a separate driving force, but supports the main body against the floor. 
     The robot cleaner  100  may include a travel sensing module  150  that senses the behavior of the robot cleaner  100 . The travel sensing module  150  may sense the behavior of the robot cleaner  100  by the travel unit  160 . 
     The travel sensing module  150  may include an encoder (not shown) that senses a travel distance of the robot cleaner  100 . The travel sensing module  150  may include an acceleration sensor (not shown) that senses acceleration of the robot cleaner  100 . The travel sensing module  150  may include a gyro sensor (not shown) that senses turning of the robot cleaner  100 . 
     Through the sensing of the travel sensing module  150 , the controller  140  may obtain information about a travel path of the robot cleaner  100 . For example, based on the rotation speed of the driving wheel  166  sensed by the encoder, information about a current or past travel speed, the travel distance, and the like of the robot cleaner  100  may be obtained. For example, based on a turning direction of each of the driving wheels  166 (L) and  166 (R), information about a current or past direction switching process may be obtained. 
     The robot cleaner  100  includes a task unit  180  that performs a prescribed task. For example, the task unit  180  may be configured to perform household tasks such as cleaning (e.g., sweep, suction, mop, etc.), washing dishes, cooking, washing laundry, garbage disposal, etc. For another example, the task unit  180  may perform tasks such as finding objects, exterminating bugs, etc. In the present embodiment, it is described that the task unit  180  performs the cleaning task, but there are many examples of the types of the tasks done by the task unit  180 . 
     The robot cleaner  100  may clean the floor by the task unit  180  while moving in the travel zone. The task unit  180  may suck the foreign substance. The task unit  180  may perform mopping. 
     The task unit  180  may include a suction device for sucking the foreign substance, brushes  184  and  185  for performing sweeping, a dust container (not shown) for storing therein the foreign substance collected by the suction device or the brushes, and/or a mop for performing mopping (not shown), and the like. 
     A suction hole  180   h  into which air is sucked may be defined in the bottom face of the main body  110 . The suction device (not shown) for providing a suction force to suck the air through the suction hole  180   h  and the dust container (not shown) for collecting dust sucked together with the air through the suction hole  180   h  may be arranged in the main body  110 . 
     An opening for insertion and removal of the dust container may be defined in the casing  111 , and a dust container cover  112  for opening and closing the opening may be pivotably disposed with respect to the casing  111 . 
     The task unit  180  may include a roll-type main brush  184  exposed through the suction hole  180   h  and an auxiliary brush  185  located at a front portion of the bottom face of the main body  110  and including multiple wings extending radially. Rotation of such brushes  184  and  185  removes the dust from the floor in the travel zone, and the dust thus separated from the floor is sucked through the suction hole  180   h  and collected in the dust container. 
     The robot cleaner  100  includes the corresponding terminal  190  for charging the battery  177  when being docked with the docking device  200 . The corresponding terminal  190  is disposed at a location accessible to the charging terminal  210  of the docking device  200  in the docking success state of the robot cleaner  100 . In the present embodiment, a pair of the corresponding terminals  190  are arranged on the bottom face of the main body  110 . 
     The robot cleaner  100  may include an input unit  171  for inputting information. The input unit  171  may receive on/off or various commands. The input unit  171  may include a button, a key, a touch-type display, or the like. The input unit  171  may include a microphone for speech recognition. 
     The robot cleaner  100  may include an output unit  173  for outputting information. The output unit  173  may inform the user of various informations. The output unit  173  may include a speaker and/or a display. 
     The robot cleaner  100  may include a communication unit  175  that transmits and receives information to and from other external devices. The communication unit  175  may be connected to a terminal device and/or another device located in a specific region in one of wired, wireless, and satellite communication schemes to transmit and receive data. 
     The communication unit  175  may be configured to communicate with a terminal  300 , a wireless router  400 , a server  500 , and/or the like. The communication unit  175  of the first robot cleaner  100   a  may be configured to communicate with the communication unit  175  of the second robot cleaner  100   b . The communication unit  175  may communicate with other devices such as the terminal  300 , another robot cleaner, and the like, located in the specific area. 
     The communication unit  175  may receive various command signals from the external device such as the terminal  300  and the like. The communication unit  175  may transmit information to be output to the external device such as the terminal  300  and the like. The terminal  300  may output the information received from the communication unit  175 . 
     The robot cleaner  100  includes the battery  177  for supplying a drive power to each component. The battery  177  supplies power for the robot cleaner  100  to perform a behavior based on selected behavior information. The battery  177  is mounted in the main body  110 . The battery  177  may be detachably provided to the main body  110 . 
     The battery  177  is configured rechargeable. The robot cleaner  100  is docked with the docking device  200 , so that the battery  177  may be charged through connection between the charging terminal  210  and the corresponding terminal  190 . When a charge amount of the battery  177  becomes equal to or smaller than a predetermined value, the robot cleaner  100  may start a docking mode for the charging. In the docking mode, the robot cleaner  100  travels to return to the docking device  200 . 
     The robot cleaner  100  includes a storage  179  that stores various informations. The storage  179  may include a volatile or a non-volatile recording medium. 
     A map for the travel zone may be stored in the storage  179 . The map may be input by a terminal and the like that may exchange information with the robot cleaner  100  through the communication unit  175  or may be generated by the robot cleaner  100  as the robot cleaner  100  learns by itself. In the former case, the terminal may be ex-emplified as a remote control, a PDA, a laptop, a smart phone, a tablet, and the like equipped with an application for setting the map. 
     For one example, a plurality of the robot cleaners  100   a  and  100   b  may share the map with each other. A plurality of the robot cleaners  100   a  and  100   b  may transceive information on the map with each other through the communication units  175 . For another example, a plurality of the robot cleaners  100   a  and  100   b  may store maps of their own, respectively but may not share the maps. 
     The robot cleaner  100  includes the controller  140  that processes and determines various informations such as mapping and/or recognizing a current location. The controller  140  may control overall operations of the robot cleaner  100  through control of various components of the robot cleaner  100 . The controller  140  may map the travel zone through the image and recognize the current location on the map. That is, the controller  140  may perform a simultaneous localization and mapping (SLAM) function. 
     The controller  140  may receive the information from the input unit  171  and process the received information. The controller  140  may receive the information from the communication unit  175  and process the received information. The controller  140  may receive the information from the sensing unit  130  and process the received information. 
     The controller  140  may control the communication unit  175  to transmit the information. 
     The controller  140  may control the output of the output unit  173 . The controller  140  may control the driving of the travel unit  160 . The controller  140  may control the operation of the task unit  180 . 
     In some implementations, the docking device includes the charging terminal  210  configured to be connected to the corresponding terminal  190  in the docking success state of the robot cleaner  100 . The docking device  200  may include a guide signal generating unit  220  that generates a docking guide signal for guiding the robot cleaner  100  to dock. The guide signal generating unit  220  generates an IR signal to guide the robot cleaner  100  to be docked with the docking device  200 . Meanwhile, once the robot cleaner  100  is docked, the guide signal generating unit  220  stops generating the guide signal. If the robot cleaner  100  is released from the docking, the guide signal generating unit  220  may generate the guide signal. Namely, if the robot cleaner  100  is undocked from the docking device  200 , the robot cleaner  100  is detached from the docking device  200  and needs to be guided so as to be docked with the docking device  200  after completing a task such as a cleaning or the like. The docking device  200  may be configured so as to be placed on the floor. 
     Referring to  FIG.  6   , one robot cleaner  100   a  may communicate with another robot cleaner  100   b  through a prescribed network. Each of the robot cleaners  100   a  and  100   b  may communicate with a terminal  300  via the prescribed network. 
     The communication unit  175  communicates with another device (e.g., another robot cleaner, a terminal, etc.) via the prescribed network. The prescribed network means a communication network connected by wire and/or wireless directly or indirectly. Namely, ‘the communication unit  175  communicates with another device via the prescribed network’ inclusively means a case that the communication unit  175  indirectly communicates with another device via the wireless router  400  or the like as well as a case that the communication unit  175  directly communicates with another device. 
     The network may be established based on Wi-Fi, Ethernet, Zigbee, Z-wave, Bluetooth, etc. 
       FIG.  7    is a control flowchart according to an embodiment of the present disclosure.  FIG.  8    is a flowchart to describe an essential portion of  FIG.  7   .  FIG.  9    is a flowchart to describe another essential portion of  FIG.  7   .  FIG.  10    is a diagram to describe implementation of an embodiment according to  FIG.  7   . 
     Referring to  FIGS.  7  to  10   , a first robot cleaner  100   a  is docked with a first docking device  200   a  and a second robot cleaner  100   b  is docked with a second docking device  200   b  [S 100 ]. As shown in  FIG.  10  ( a ) , the robot cleaners contact with the docking devices, respectively. Each of the first and second docking devices  200   a  and  200   b  includes the docking device described in  FIG.  1   , and the docking devices are provided to the robot cleaners, respectively. Here, each of the first and second docking devices  200   a  and  200   b  has the same configuration of the docking device but is docked with a different robot cleaner. 
     While the robot cleaner is docked with the docking devices, a battery of the robot cleaner may be charged. Meanwhile, once the robot cleaner is docked with the docking device, a guide signal generating unit  220  does not generate a guide signal. Namely, since the robot cleaner is currently docked with the docking device, it is unnecessary to guide the robot cleaner to the docking device, whereby the guide signal generating unit  220  does not generate a signal for guiding the robot cleaner to the docking device. 
     The first robot cleaner  100   a  is undocked from the first docking device  200   a  according to a user&#39;s command or a pre-stored program [S 110 ]. In this case, a user may input a command through a user terminal  300  or command a task start through an input unit  171  provided to the first robot cleaner  100   a.    
     As shown in  FIG.  10  ( b ) , if the first robot cleaner  100   a  is undocked from the first docking device  200   a , the first robot cleaner  100   a  may perform the cleaning. The first robot cleaner  100   a  performs the cleaning in a manner of moving a cleaning-required section. In doing so, the first robot cleaner  100   a  may perform the cleaning according to a determined moving scheme. The first robot cleaner  100   a  may perform the cleaning in a manner of moving in a zigzag pattern not to miss a cleaning-required area. 
     After the first robot cleaner  100   a  has finished the cleaning, it is checked whether the first robot cleaner  100   a  is docked with the first docking device  200   a  [S 120 ]. If the first robot cleaner  100   a  is not docked with the first docking device  200   a , the first robot cleaner  100   a  may be determined as performing the cleaning or moving to the first docking device  100   a  currently [S 130 ]. 
     On the other hand, if the first robot cleaner  100   a  is docked with the first docking device  200   a , the second robot cleaner  100   b  is undocked from the second docking device  200   b  [S 140 ]. Once the second robot cleaner  100   b  is undocked from the second docking device  200   b , the second robot cleaner  100  may perform the cleaning. As shown in  FIG.  19  ( c ) , the second robot cleaner  100   b  may clean the area that has been cleaned by the first robot cleaner  100   a.    
     Since the second robot cleaner  100   b  performs the cleaning after the first robot cleaner  100   a  has been docked with the docking device, travel interference does not occur between the second robot cleaner and the first robot cleaner. Since the second robot cleaner is docked with the second docking device while the first robot cleaner is doing the cleaning, travel interference does not occur between the first robot cleaner and the second robot cleaner. In addition, since the first robot cleaner is docked with the first docking device while the second robot cleaner is doing the cleaning, travel interference does not occur between the first robot cleaner and the second robot cleaner. 
     For example, when the first robot cleaner is a dust-suction cleaner and the second Since the second robot cleaner is docked with the second docking device while the first robot cleaner is doing the cleaning, travel interference does not occur between the first robot cleaner and the second robot cleaner is a mopping cleaner, it is possible to perform the cleaning using two robot cleaners of different types. In addition, since the second robot cleaner cleans the area that has been cleaned by the first robot cleaner, the same area is cleaned twice to provide a user with a cleaner environment. 
     After the second robot cleaner  100   b  has performed the cleaning, as shown in  FIG.  10    ( d ), it is docked with the second docking device  200   b  [S 150 ]. If so, the cleaning of the same section can be completed by the first and second robot cleaners. 
     In some implementations, the guide signal generating unit provided to each of the docking devices  200   a  and  200   b  is receivable by all the robot cleaners  100   a  and  100   b . A docking guide signal transmitted from the guide signal generating unit  220  of the first docking device  200   a  can be received by the first robot cleaner  100   a  and the second robot cleaner  100   b . Moreover, a docking guide signal transmitted from the guide signal generating unit  220  of the second docking device  200   b  can be received by the first robot cleaner  100   a  and the second robot cleaner  100   b . Namely, the guide signal generating unit generates an IR signal and a sensing unit of each of the robot cleaners can receive the IR signal. 
     Although the guide signal generating unit of the first docking device  200   a  transmits a docking guide signal, if the first robot cleaner  100   a  is docked with the first docking device  200   a , the guide signal generating unit may not transmit the docking guide signal. If the first robot cleaner  100   a  is docked with the first docking device  200   a , a docking sensing unit linked to a charging terminal  210  may sense the docking of the first robot cleaner. Hence, the guide signal generating unit does not generate a guide signal. 
     Although the guide signal generating unit of the second docking device  200   b  transmits a docking guide signal, if the second robot cleaner  100   b  is docked with the second docking device  200   b , the guide signal generating unit may not transmit the docking guide signal. If the second robot cleaner  100   b  is docked with the second docking device  200   b , a docking sensing unit linked to a charging terminal  210  may sense the docking of the second robot cleaner. Hence, the guide signal generating unit does not generate a guide signal. 
     As shown in  FIG.  8   , it is determined whether the second robot cleaner  100   b  receives the docking guide signal of the first docking device  200   a  [S 210 ]. In doing so, the second robot cleaner  100   b  is currently docked with the second docking device  200   b.    
     If the second robot cleaner  100   b  senses the guide signal transmitted from the first docking device, the first robot cleaner may be determined as undocked from the first docking device  200   a  [S 220 ]. 
     On the contrary, if the second robot cleaner  100   b  does not sense the guide signal transmitted from the first docking device, the first robot cleaner may be determined as docked with the first docking device  200   a  [S 230 ]. 
     As shown in  FIG.  9   , it is determined whether the first robot cleaner  100   a  receives the docking guide signal of the second docking device  200   b  [S 310 ]. In doing so, the first robot cleaner  100   a  is currently docked with the first docking device  200   a.    
     If the first robot cleaner  100   a  senses the guide signal transmitted from the second docking device, the second robot cleaner may be determined as undocked from the second docking device  200   b  [S 320 ]. 
     On the contrary, if the first robot cleaner  100   a  does not sense the guide signal transmitted from the second docking device, the second robot cleaner may be determined as docked with the second docking device  200   b  [S 330 ]. 
     As described above, while the first robot cleaner is docked with the first docking device, it may sense and determine whether the second robot cleaner is docked with the second docking device. Likewise, while the second robot cleaner is docked with the second docking device, it may sense and determine whether the first robot cleaner is docked with the first docking device. Therefore, only if the second robot cleaner is docked with the second docking device, the first robot cleaner may perform the cleaning by being undocked from the first docking device. Only if the first robot cleaner is docked with the first docking device, the second robot cleaner may perform the cleaning by being undocked from the second docking device. 
     To implement such features, while the second robot cleaner  100   b  is docked with the second docking device  200   b , the first docking device  200   a  is disposed in a distance in which the second robot cleaner  100   b  can receive a docking guide signal transmitted by the first docking device  200   a.    
     In addition, while the first robot cleaner  100   a  is docked with the first docking device  200   a , the second docking device  200   b  is disposed in a distance in which the first robot cleaner  100   a  can receive a docking guide signal transmitted by the second docking device  200   b.    
     Namely, each of the first docking device  200   a  and the second docking device  200   b  is disposed in a distance in which a robot cleaner docked with one docking device can receive a signal transmitted from a guide signal generating unit provided to the other docking device. If the guide signal generating unit includes an IR transmitting device, two docking devices are preferably disposed in about 5 meters. Of course, the two docking devices may be disposed in a distance shorter than 5 meters, whereby each of the robot cleaners can stably receive a signal transmitted from the docking device for the other robot cleaner. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the spirit or scope of the inventions. Thus, it is intended that the present disclosure covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.