Patent Publication Number: US-2023134120-A1

Title: Delivery robot

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Pursuant to 35 U.S.C. § 119, this application claims the benefit of an earlier filing date and right of priority to International Application No. PCT/KR2021/015370, filed on Oct. 29, 2021, the contents of which are hereby incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a delivery robot capable of transporting a tray or the like. 
     BACKGROUND ART 
     Competition for transporting products in online and offline markets is heating up day by day, and product transportation on the day of purchase is sometimes provided for better convenience of the user. 
     In recent years, unmanned mobile robots for transporting products have been used on the ground or in the air, and relevant laws and regulations are being gradually being prepared. 
     A robot may be a machine that automatically deals with or performs a task given by its own capabilities. In particular, a robot having a function of recognizing an environment and performing an operation based on self-determination may be referred to as an intelligent robot, and various services may be provided using the intelligent robot. 
     Meanwhile, a delivery system using a robot requires information such as a map, a route, and the like of a traveling or driving region to provide a delivery service on the traveling region. Such information should be accumulated to establish a service, which allows a robot to deliver a product to a destination. 
     In addition, in recent years, daily life logistics such as delivery of goods at supermarkets, delivery logistics, and movement of logistic goods within a building are entering the scope of the existing logistics industry. Such daily life logistics require a structure that can transport logistic goods in various forms that are not restricted or affected by an appropriate amount of logistics in line with various living environments. 
     In particular, a delivery robot used in transporting daily logistic goods should recognize the surrounding environment to operate according to the mapped map. Further, there is a growing need for a delivery robot that can cover both small and large amounts of various types of logistics. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     The present disclosure is directed to providing implementations that can address the aforementioned necessity. 
     In detail, the present disclosure describes a delivery robot that can actively recognize the surrounding environment. The present disclosure also describes a delivery robot that can transport logistic goods whether it is a small or large amount. 
     Solution to Problem 
     According to one aspect of the subject matter described in this application, a delivery robot includes a main body configured to be movable with respect to a ground, a coupling module coupled to one surface of the main body, and a locking unit coupled to a tray that is configured to be movable. The coupling module includes an actuator configured to be driven to be coupled with the locking unit when the coupling module and the tray are located adjacent to each other. 
     Implementations according to this aspect may include one or more of the following features. For example, the main body may include a moving unit including a wheel configured to be movable with respect to the ground, an extension unit extending in one direction from one end of the moving unit, and a display unit extending from an end portion of the extension unit at a predetermined angle with respect to the extension unit. 
     In some implementations, the moving unit may include a coupling part disposed on an upper surface thereof and through which the coupling module is coupled, and a TOF camera disposed at a lateral surface thereof and provided in plurality spaced apart from one another along a periphery of the lateral surface. 
     In some implementations, the moving unit may further include a first wheel configured to move the main body in a direction in which the extension unit is defined and a direction opposite to the direction in which the extension unit is defined, and a second wheel configured to be steerable to allow the main body to rotate. 
     In some implementations, the moving unit may further include a main body lidar disposed toward the front and disposed above the TOF camera. 
     In some implementations, the extension unit may extend perpendicular to the upper surface of the moving unit, and the extension unit may include a camera part that is provided at a front surface thereof and includes a camera capable of shooting terrain ahead, a speaker that transmits sound to the outside, and an engaging part disposed at a rear surface thereof and configured to fix at least one of the coupling module and the tray. 
     In some implementations, the display unit may include a display configured to display a state of the main body and output a screen for controlling the main body, an inclined part configured to support the display, and an angle adjustment part configured to adjust an angle of the display. 
     In some implementations, the coupling module may include a module body coupled to one surface of the main body, and a docking part provided at an upper surface of the module body in a protruding manner and configured to determine whether or not docking is completed according to proximity of the tray. The actuator may include an actuator bar configured to move up when the tray and the coupling module are docked at the docking part, and a drive part configured to operate the actuator bar. 
     In some implementations, the docking part may be disposed adjacent to the extension unit. The actuator bar may be disposed in a direction opposite to the extension unit with respect to the docking part and be inserted into the module body before the coupling module and the tray are docked. 
     In some implementations, the module body may be provided with a front groove that is concavely recessed to allow the extension unit to be inserted therein, and a plurality of module TOF cameras may be provided at a lateral surface of the module body to be spaced apart from one another along a periphery of the module body. 
     In some implementations, the module body may include a module lidar formed toward the rear thereof and configured to scan a rear side of the main body. 
     In some implementations, the upper surface of the module body may be equal to or smaller than the upper surface of the moving unit, and the module body may include rolling pins disposed on the upper surface of the module body in a direction opposite to a direction in which the actuator bar is disposed and configured to be rotatable. 
     In some implementations, the locking unit may include a locking part mounted to one end of the tray and in which the actuator bar is inserted and a guide part extending from the locking part and having a width greater than a width of the locking part. At least a portion of the guide part may be guided by the rolling pins. 
     In some implementations, the guide part may include first portions extending from the locking part in an inclined manner, second portions having a width that corresponds to a separation distance between the rolling pins disposed at both sides of the module body and extending in a lengthwise direction of the guide part, and a third portion connecting the second portions disposed at both sides the locking part. 
     In some implementations, the first portions may be guided by the rolling pins when the coupling module approaches the locking part. 
     In some implementations, a gap may be defined between the coupling module and the second portions. 
     In some implementations, the coupling module may include a damper disposed at an upper surface of the coupling module, configured to surround the docking part, and extending along an extension direction of the extension unit. 
     In some implementations, the damper may include a damper groove through which the docking part is exposed to the outside and into which the docking part is inserted, and a front surface of the damper in which the damper groove is defined may protrude more to the actuator than a front surface of the docking part that is exposed to the outside. 
     In some implementations, the locking part may be provided with a locking groove into which the actuator bar is inserted, and the actuator bar may be disposed to be spaced apart from at least one of front and rear surfaces of the locking groove that define the locking groove. 
     In some implementations, a front surface of the locking part may be brought into contact with the damper when the tray moves forward relative to the main body as the main body is switched to a stationary state from a moving state. 
     Advantageous Effects of Invention 
     A delivery robot according to an implementation of the present disclosure can provide large power along front and rear directions through a first wheel of a moving unit. Also, steering and rotation are enabled through the moving unit including a second wheel. 
     In addition, the delivery robot of the present disclosure may provide recognition of the front and rear of the delivery robot through an extension unit disposed at one side of the moving unit. Also, information regarding a distance or height of nearby objects can be identified through a Lidar of the moving unit, a TOF camera, and a camera part of the extension unit. 
     Further, the delivery robot of the present disclosure can be easily manipulated by a user through a display unit. 
     The delivery robot according to an implementation of the present disclosure may include a coupling module that is integrally coupled to a main body. As the coupling module is detachably connected to the main body, different types of coupling modules can be coupled to the main body according to a type of tray and the like, thereby increasing the use of the main body. 
     In the delivery robot according to an implementation of the present disclosure, as a damper is disposed to surround or cover a docking part, and a front surface of the damper protrudes more than a front surface of the docking part, the docking part can be prevented from being damaged by a locking part when the locking part is excessively moved toward the docking part. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a block diagram of a delivery system. 
         FIG.  2 A  is an exemplary view  1 - a  showing an example of a traveling region. 
         FIG.  2 B  is an exemplary view  1 - b  showing an example of a traveling region. 
         FIG.  3 A  is an exemplary view  2 - a  showing an example of a traveling region. 
         FIG.  3 B  is an exemplary view  2 - b  showing an example of a traveling region. 
         FIG.  4    is an exemplary view  3  showing an example of a traveling region. 
         FIGS.  5  and  6    are perspective views illustrating a delivery robot according to one implementation of the present disclosure. 
         FIG.  7    is a perspective view illustrating a delivery robot according to another implementation of the present disclosure. 
         FIG.  8    is a perspective view illustrating a tray and a locking unit according to one implementation of the present disclosure. 
         FIGS.  9  to  13    are views illustrating a process in which a coupling module and a locking unit are coupled by an actuator as the delivery robot in  FIG.  5    moves to be adjacent to a tray. 
         FIG.  14    is a cross-sectional view illustrating a state of coupling the coupling module and the locking unit. 
         FIG.  15    is a cross-sectional view illustrating a coupled state of the delivery robot and the tray. 
         FIG.  16    is a cross-sectional view illustrating a positional relationship between the coupling module and the locking unit when the delivery robot that is coupled to the tray travels on an incline. 
         FIG.  17    is a cross-sectional view illustrating a positional relationship between the coupling module and the locking unit when the delivery robot that is coupled to the tray stops while traveling. 
         FIG.  18    is a front view illustrating a coupled state of the delivery robot and the tray. 
     
    
    
     MODE FOR THE INVENTION 
     Description will now be given in detail according to exemplary implementations disclosed herein, with reference to the accompanying drawings. For the sake of brief description with reference to the drawings, the same or equivalent components may be provided with the same or similar reference numbers, and description thereof will not be repeated. In describing the present disclosure, if a detailed explanation for a related known function or construction is considered to unnecessarily divert the main point of the present disclosure, such explanation has been omitted but would be understood by those skilled in the art. 
     As illustrated in  FIG.  1   , a delivery system  1000  includes a delivery robot (DR,  10 ) that autonomously travels or self-drives in a traveling (or driving) region, and a control server  20  connected to communicate with the delivery robot DR through a communication network  40  so as to control an operation of the delivery robot DR. 
     In addition, the delivery system  1000  may further include one or more communication devices  30  connected to communicate with at least one of the delivery robot DR and the control server  20  to transmit and receive information to and from at least one of the delivery robot DR and the control server  20 . 
     The delivery robot DR may be an intelligent robot that automatically processes or operates a task given by its own capabilities. For example, the intelligent robot may be an automated guided vehicle (AGV), which is a transportation device that moves on the floor by a sensor, a magnetic field, a vision device, and the like, or a guide robot that provides guide information to a user in an airport, a shopping mall, a hotel, or the like. 
     The delivery robot DR may be provided with a drive unit including an actuator or a motor to perform various physical operations such as moving a robot joint. For instance, the delivery robot DR may autonomously travel in the traveling region. Autonomous driving (or traveling) refers to a self-driving technology, and the delivery robot DR may be an autonomous driving vehicle (robot) that travels without a user&#39;s manipulation or with a user&#39;s minimal manipulation. A technology for maintaining a driving lane, a technology for automatically adjusting speed such as adaptive cruise control, a technology for automatically driving along a predetermined path or route, a technology for automatically setting a path when a destination is set, and the like may be all included in the autonomous driving. 
     In order to perform such autonomous driving, the delivery robot DR may be a robot to which artificial intelligence (Al) and/or machine learning is applied. The delivery robot DR may autonomously travel in the traveling region to perform various operations through the artificial intelligence and/or machine learning. For example, an operation according to a command designated by the control server  20  may be performed, or a self-search/monitoring operation may be performed. 
     Hereinafter, artificial intelligence and/or machine learning technology applied to the delivery robot DR will be described in detail. 
     Artificial intelligence (AI) refers to a field of studying artificial intelligence or a methodology capable of creating artificial intelligence, and machine learning refers to a field of studying a methodology for defining various problems dealt with in the field of artificial intelligence and solves them. The machine learning technology is a technology that collects and learns a large amount of information based on at least one algorithm to determine and predict information based on the learned information. The learning of information refers to an operation of recognizing the features of information, rules and determination criteria, quantifying a relation between information and information, and predicting new data using the quantified patterns. Machine learning is also defined as an algorithm that improves the performance of a certain task through continuous experience in the task. 
     Algorithms used by the machine learning technology may be algorithms based on statistics, for example, a decision tree that uses a tree structure as a prediction model, an artificial neural network that mimics neural network structures and functions of living creatures, genetic programming based on biological evolutionary algorithms, clustering of distributing observed examples to a subset of clusters, a Monte Carlo method of computing function values as probability using randomly-extracted random numbers, and the like. As one field of the machine learning technology, there is a deep learning technology of performing at least one of learning, determining, and processing information using the artificial neural network algorithm. 
     An artificial neural network (ANN) as a model used in machine learning may refer to all of models having a problem-solving ability, which are composed of artificial neurons (nodes) that form a network by synaptic connections. The artificial neural network may have a structure of connecting between layers and transferring data between the layers. The deep learning technology may be employed to learn a vast amount of information through the artificial neural network using a graphic processing unit (GPU) optimized for parallel computing. 
     The artificial neural network may be defined by a connection pattern between neurons in different layers, a learning process of updating model parameters, and an activation function of generating an output value. The artificial neural network may include an input layer, an output layer, and optionally one or more hidden layers. Each layer may include one or more neurons, and the artificial neural network may include a synapse that connects neurons to neurons. In the artificial neural network, each neuron may output a function value of an activation function for input signals being input through the synapse, a weight, a bias, and the like. The model parameters refer to parameters determined through learning, and include a weight of a synaptic connection, a bias of a neuron, and the like. In addition, a hyperparameter refers to a parameter that must be set prior to learning in a machine learning algorithm, and includes a learning rate, a repetition number, a mini-batch size, an initialization function, and the like. 
     The purpose of learning in an artificial neural network can be seen as determining the model parameters that minimize a loss function. The loss function may be used as an index for determining an optimal model parameter in the learning process of the artificial neural network. 
     Machine learning can be classified into supervised learning, unsupervised learning, and reinforcement learning according to a learning method. 
     The supervised learning may refer to a method of training an artificial neural network in a state where a label for learning data is given, and the label may refer to a correct answer (or result value) that the artificial neural network must infer when learning data is input to the artificial neural network. The unsupervised learning may refer to a method of training an artificial neural network in a state where no label is given for learning data. The reinforcement learning may refer to a learning method of training an agent defined in a certain environment to select a behavior or a behavior sequence that maximizes cumulative compensation in each state. 
     Machine learning, which is implemented as a deep neural network (DNN) including a plurality of hidden layers among artificial neural networks, is also referred to as deep learning, and the deep learning is part of machine learning. Hereinafter, machine learning is used in a sense including deep learning. 
     The delivery robot DR may be implemented without employing such artificial intelligence and/or machine learning technology, but a delivery robot to which the artificial intelligence and/or machine learning technology is applied will be mainly described as the delivery robot DR. 
     The traveling region in which the delivery robot DR operates may be indoors or outdoors. The delivery robot DR may operate in a zone partitioned by walls or pillars. In this case, the operation zone of the delivery robot DR may be set in various ways according to a design purpose, a task attribute of the robot, mobility of the robot, and other various other factors. In addition, the delivery robot DR may operate in an open zone that is not predefined. Further, the delivery robot DR may sense a surrounding environment to determine an operation zone by itself. The operation may be made through artificial intelligence and/or machine learning technology applied to the delivery robot DR. 
     The delivery robot DR and the control server  20  may be connected to communicate through the communication network  40  to transmit and receive data to and from each other. In addition, each of the delivery robot DR and the control server  20  may transmit and receive data to and from the communication device  30  through the communication network  40 . Here, the communication network  40  may refer to a communication network that provides a communication environment for communication devices in a wired or wireless manner. For instance, the communication network  40  may be an LTE/5G network. In other words, the delivery robot DR may transmit and receive data to and from the control server  20  and/or the communication device  30  through an LTE/5G network. In this case, the delivery robot DR and the control server  20  may communicate through a base station that is connected to the communication network  40  or directly communicate without passing through the base station. Further, in addition to the LTE/5G network, other mobile communication technology standards or communication methods may be applied to the communication network  40 . For example, the other mobile communication technology standards or communication methods may include at least one of Global System for Mobile communication (GSM), Code Division Multi Access (CDMA), Code Division Multi Access 2000 (CDMA2000), Enhanced Voice-Data Optimized or Enhanced Voice-Data Only (EV-DO), Wideband CDMA (WCDMA), High Speed Downlink Packet Access (HSDPA), High Speed Uplink Packet Access (HSUPA), Long Term Evolution (LTE), Long Term Evolution-Advanced (LTE-A), and the like. 
     The communication network  40  may include a connection of network elements such as hubs, bridges, routers, switches and gateways. The communication network  40  may include one or more connected networks, for instance, a multi-network environment, including a public network such as the Internet and a private network such as a secure enterprise private network. Access to the communication network  40  may be provided through one or more wired or wireless access networks. Furthermore, the communication network  40  may support various types of M2M communications (Internet of Things (IoT), Internet of Everything (IoE), and Internet of Small Things (IoST) that exchange and process information between distributed components such as things. 
     The delivery robot DR may perform an operation in the traveling region, and may provide information or data related to the operation to the control server  20  through the communication network  40 . For instance, the delivery robot DR may provide a location of the delivery robot DR and information regarding a currently performing operation to the control server  20 . In addition, the delivery robot DR may receive information or data related to the operation from the control server  20  through the communication network  40 . For instance, the control server  20  may provide information regarding driving motion control of the delivery robot DR to the delivery robot DR. 
     The delivery robot DR may provide its own status (or state) information or data to the control server  20  through the communication network  40 . Here, the status information may include information regarding a location, battery level, durability of parts, replacement cycle of consumables, and the like of the delivery robot DR. Accordingly, the control server  20  may control the delivery robot DR based on the information provided from the delivery robot DR. 
     Meanwhile, the delivery robot DR may provide one or more communication services through the communication network  40 , and may also provide one or more communication platforms through the communication services. For instance, the delivery robot DR may communicate with a communication target using at least one service of enhanced mobile broadband (eMBB), ultra-reliable and low latency communications (URLLC), and massive machine-type communications (mMTC). 
     The enhanced mobile broadband (eMBB) is a mobile broadband service, through which multimedia content, wireless data access, and the like may be provided. In addition, more advanced mobile services such as a hot spot and wideband coverage for receiving explosively increasing mobile traffic may be provided through the eMBB. Large traffic may be received in an area with low mobility and high density of users through a hot spot. A wide and stable wireless environment and user mobility may be secured through wideband coverage. 
     The ultra-reliable and low latency communications (URLLC) service defines much more stringent requirements than the existing LTE in terms of data transmission/reception reliability and transmission delay, and includes 5G services for production process automation at industrial sites, telemedicine, telesurgery, transportation, safety, and the like. 
     The massive machine-type communications (mMTC) is a service that is not sensitive to transmission delay requiring a relatively small amount of data transmission. A much larger number of terminals general mobile phones, such as sensors may simultaneously access a wireless access network by the mMTC. In this case, the communication module of the terminal should be inexpensive, and improved power efficiency and power saving technology are required to allow operation for several years without battery replacement or recharging. 
     The communication service may further include all services that can be provided to the communication network  40  in addition to the eMBB, the URLLC, and the mMTC described above. 
     The control server  20  may be a server device that centrally controls the delivery system  1000 . The control server  20  may control traveling and operation of the delivery robot DR in the delivery system  1000 . The control server  20  may be provided in the traveling region to communicate with the delivery robot DR through the communication network  40 . For instance, the control server  20  may be provided in any one of buildings corresponding to the traveling region. The control server  20  may also be provided in a place different from the traveling region to control the operation of the delivery system  1000 . The control server  20  may be implemented as a single server, but may alternatively be implemented as a plurality of server sets, cloud servers, or a combination thereof. 
     The control server  20  may perform various analyses based on information or data provided from the delivery robot DR, and may control an overall operation of the delivery robot DR based on the analysis result. The control server  20  may directly control the driving of the delivery robot DR based on the analysis result. In addition, the control server  20  may derive useful information or data from the analysis result and output the derived information or data. Further, the control server  20  may adjust parameters related to the operation of the delivery system  1000  using the derived information or data. 
     At least one of the delivery robot DR and the control server  20  communicatively connected through the communication network  40  may be connected to communicate with the communication device  30  through the communication network  40 . In other words, the delivery robot DR and the control server  20  may communicate with a device that can be communicably connected to the communication network  40  among the communication devices  30  through the communication network  40 . At least one of the delivery robot DR and the control server  20  may also be connected to communicate with the communication device  30  through a communication method other than the communication network  40 . In other words, at least one of the delivery robot DR and the control server  20  may be in communication with a device that can be communicably connected in a manner different from that of the communication network  40  among the communication devices  30 . For example, at least one of the delivery robot DR and the control server  20  may be connected to communicate with the communication device  30  using at least one method of Wireless LAN (WLAN), Wireless Personal Area Network (WPAN), Wireless-Fidelity (Wi-Fi), Wireless Fidelity (Wi-Fi) Direct, Digital Living Network Alliance (DLNA), Wireless Broadband (WiBro), World Interoperability for Microwave Access (WiMAX), Zigbee, Z-wave, Blue-Tooth, Radio Frequency Identification (RFID), Infrared Data Association (IrDA), Ultrawide-Band (UWB), Wireless Universal Serial Bus (USB), Near Field Communication (NFC), Visible Light Communication, Light Fidelity (Li-Fi), and satellite communication. Other communication methods in addition to the above communication methods may also be used for the communication connection. 
     The communication device  30  may refer to any device and/or server capable of communicating with at least one of the delivery robot DR and the control server  20  through various communication methods including the communication network  40 . For instance, the communication device  30  may include at least one of a mobile terminal  31 , an information providing system  32 , and an electronic device  33 . 
     The mobile terminal  31  may be a communication terminal capable of communicating with the delivery robot DR and the control server  20  through the communication network  40 . The mobile terminal  31  may include a mobile device such as a mobile phone, a smart phone, a wearable device, for example, a watch type terminal (smartwatch), a glass type terminal (smart glass), a head mounted display (HMD), a laptop computer, a digital broadcasting terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), a navigation device, a slate PC, a tablet PC, an ultrabook, and the like. 
     The information providing system  32  may refer to a system that stores and provides at least one of information reflected in the traveling region or related to the traveling region, and information related to the operation of the delivery system  1000 . The information providing system  32  may be a system (server) that is operable in connection with the delivery robot DR and the control server  20  to provide data and services to the delivery robot DR and the control server  20 . The information providing system  32  may include at least one of all systems (servers) capable of being communicably connected to and exchanging information with the delivery robot DR and the control server  20 . For instance, at least one of a database system, a service system, and a central control system may be included in the information providing system  32 . A specific example of the information providing system  32  may include at least one of a service system of a manufacturer of the delivery robot DR, a service system of a manufacturer of the control server  20 , a central (management) control system of a building corresponding to the traveling region, a service system of a provider that supplies energy to a building corresponding to the traveling region, an information system of a construction company of a building corresponding to the traveling region, a service system of a manufacturer of the mobile terminal  31 , a service system of a communication provider that provides a communication service through the communication network  40 , and a service system of a developer of an application applied to the delivery system  1000 . In addition, the information providing system  32  may further include all systems operable in connection with the delivery system  1000  in addition to the above systems. 
     The information providing system  32  provides various services/information to electronic devices including the delivery robot DR, the control server  20 , the mobile terminal  31 , and the electronic device  33 . The information providing system  32  may be implemented as a cloud to include a plurality of servers, perform calculations related to artificial intelligence that are difficult or time-consuming for the delivery robot DR, the mobile terminal  31 , and the like to generate a model related to artificial intelligence, and provide relevant information to the delivery robot DR, the mobile terminal  31 , and the like. 
     The electronic device  33  may be a communication device capable of communicating with at least one of the delivery robot DR and the control server  20  through various communication methods including the communication network  40  in the traveling region. For instance, the electronic device  33  may be at least one of a personal computer, a home appliance, a wall pad, a control device that controls facilities/equipment such as an air conditioner, an elevator, an escalator, and lighting, a watt-hour meter, an energy control device, an autonomous vehicle, and a home robot. The electronic device  33  may be connected to at least one of the delivery robot DR, the control server  20 , the mobile terminal  31 , and the information providing system  32  in a wired or wireless manner. 
     The communication device  30  may share the role of the control server  20 . For instance, the communication device  30  may acquire information or data from the delivery robot DR to provide the acquired information or data to the control server  20 , or acquire information or data from the control server  20  to provide the acquired information or data to the delivery robot DR. In addition, the communication device  30  may be in charge of at least part of an analysis to be performed by the control server  20 , and provide an analysis result to the control server  20 . Further, the communication device  30  may receive the analysis result, information or data from the control server  20  to simply output it. In addition, the communication device  30  may replace the role of the control server  20 . 
     In the delivery system  1000  as described above, the delivery robot DR may travel in the traveling region as shown in  FIGS.  2 A to  4   . 
     The traveling region may include at least a portion of an indoor zone IZ in a building BD with one or more floors, as shown in  FIGS.  2 A and  2 B . In other words, the delivery robot DR may travel in at least a portion of an indoor zone IZ in a building with one or more floors. For example, first and second floors in a building with a basement and first to third floors may be included in the traveling region, thereby allowing the delivery robot DR to travel on each of the first and second floors of the building. 
     In addition, the traveling region may further include at least a portion of an indoor zone IZ in each of a plurality of buildings BD 1  and BD 2 , as shown in  FIGS.  3 A and  3 B . That is, the delivery robot DR may travel in at least a portion of the indoor zone IZ in each of the plurality of buildings BD 1  and BD 2  with one or more floors. For instance, floors of a first building with a basement and one to three floors, and a floor of a second building with a single floor (story) may be included in the traveling region, thereby allowing the delivery robot DR to travel on each of the basement, first to third floors in the first building, and the first floor of the second building. 
     In addition, the traveling region may further include an outdoor zone OZ in one or more buildings BD 1  and BD 2 , as shown in  FIG.  4   . That is, the delivery robot DR may travel in the outdoor zone OZ in the one or more buildings BD 1  and BD 2 . For instance, a traveling route (or movement path) to a periphery in one or more buildings and the one or more buildings may be further included in the traveling region, thereby allowing the delivery robot DR to travel on the traveling route to the periphery of the one or more buildings and the one or more buildings. 
     The delivery system  1000  may be a system in which a delivery service is provided through the delivery robot DR in the traveling region. In the delivery system  1000 , the delivery robot DR may perform a specific operation while autonomously traveling in the traveling region including indoor and outdoor zones, and, for instance, the delivery robot DR may transport products while moving from one point to a specific point in the traveling region. In other words, the delivery robot DR may perform a delivery operation of delivering the products from the one point to the specific point. Accordingly, a delivery service through the delivery robot DR may be performed in the traveling region. 
     Hereinafter, a detailed configuration of the delivery robot DR will be described with reference to the drawings. 
       FIGS.  5  and  6    are perspective views illustrating a delivery robot according to one implementation of the present disclosure,  FIG.  7    is a perspective view illustrating a delivery robot according to another implementation of the present disclosure, and  FIG.  8    is a perspective view illustrating a tray and a locking unit according to one implementation of the present disclosure. 
     A delivery robot DR according to one implementation of the present disclosure includes a main body MB, a coupling module  400 , and a locking unit  500 . 
     The main body MB is configured to be movable with respect to the ground. In detail, the main body MB includes a moving unit  100  having wheels  102  and  104  at a lower portion thereof so as to be movable with respect to the ground. The moving unit  100  may include a first wheel  102  that provides main power and a second wheel  104  that enables steering and rotation. 
     The first wheel  102  may allow the main body MB to move forward or backward. In other words, the first wheel  102  may move the main body MB in a direction in which an extension unit  200  is defined and a direction opposite to the direction in which the extension unit  200  is formed. 
     In detail, referring to  FIGS.  5 ,  6 , and  14   , the first wheel  102  may be relatively larger in size than the second wheel  104 . The first wheel  102  is configured to be non-rotatable. As the first wheel  102  moves or operates, the main body MB may move forward or backward. Accordingly, the first wheel  102  can provide the main power in a direction in which the main body MB travels. 
     The second wheel  104  may be configured to be steerable so as to allow the main body MB to rotate. 
     In detail, referring to the drawings, the second wheel  104  may be relatively smaller in size than the first wheel  102 . The second wheel  104  is configured to be rotatable. Accordingly, in case rotation is required when the main body MB travels, an angle of the second wheel  104  is changed to rotate the main body MB. The second wheel  104  may change a traveling (or driving) direction of the main body MB while the main body MB is traveling, or may make the main body MB rotate in place. 
     When the delivery robot DR is located in a narrow space, such as an elevator, in a state that the main body MB and a tray  50  are coupled to each other, the second wheel  104  may rotate the main body MB and the tray  50  in the narrow space. 
     The moving unit  100  may include a coupling part (not shown) and a TOF camera  120 . In detail, the coupling part may be disposed on an upper surface of the moving unit  100  and be configured such that the coupling module  400  is coupled thereto. The coupling part may have a detachable structure corresponding to the coupling module  400 , or be configured such that the coupling module  400  is fixed to the moving unit  100  using a spring or the like. Alternatively, the coupling part may be configured such that the coupling module  400  is fixed to the upper surface of the moving unit  100  by a screw or the like. As the coupling module  400  is coupled to the upper surface of the moving unit  100 , it may have a flat upper surface with respect to the ground. 
     The TOF camera  120  may be disposed at a lateral surface of the moving unit  100  and be provided in plurality spaced apart from one another along a periphery of the lateral surface. Referring to  FIGS.  5  and  6   , the TOF camera  120  may be disposed at each of a front surface, front side surface, and rear surface of the moving unit  100 . In detail, the TOF camera  120  of the moving unit  100  may include front TOF cameras  122  and rear TOF cameras  124 . 
     The TOF camera  120  may be disposed at a lateral surface of the main body MB such that a distance between the main body MB and the ground is not far. In detail, the TOF camera  120  is disposed at a height of  5  cm to  15  cm from the ground. The main body MB may identify a distance from a nearby object through the TOF camera  120 . 
     Meanwhile, the moving unit  100  may include a main body lidar (or Lidar, also LiDAR)  110  disposed toward the front and located above the TOF camera  120 . 
     In detail, referring to  FIGS.  5  and  6   , a main body lidar groove  112  is formed toward the front of the moving unit  100 . The main body lidar  110  capable of detecting a front side (or a forward direction) of the main body MB is disposed in the main body lidar groove  112 . 
     The main body lidar  110  may have a sensing or detection zone (or range) of approximately  180  degrees forward. The main body lidar  110  may sense all around the main body MB, together with a module lidar (or Lidar)  430  of the coupling module  400  to be described hereinafter. 
     In addition, the main body lidar  110  may collect data of measuring distances of objects around the main body MB, together with the TOF camera  120 . 
     The main body MB may include the extension unit  200  that extends from one end of the moving unit  100  in one direction, and a display unit  300  that extends from an end portion of the extension unit  200  at a predetermined angle with respect to the extension unit  200 . 
     Referring to  FIGS.  5  and  6   , the extension unit  200  extends perpendicular to the upper surface of the moving unit  100 . The extension unit  200  may be disposed at a center of one side of the moving unit  100 . Here, the extension unit  200  may be disposed at the front surface of the moving unit  100 . 
     The extension unit  200  may include a camera part  200  and a speaker  210 . In addition, the extension unit  200  may include an engaging part  202  disposed at a rear surface thereof. 
     First, the camera part  220  is provided on a front surface of the extension unit  200 . The camera part  220  may include a camera capable of capturing or shooting terrain ahead. Unlike the TOF camera  120  and the main body lidar  110 , the camera part  220  may detect a difference in terrain height, a height of an object, and the like. 
     The camera part  220  may identify terrains of different heights and nearby objects. Accordingly, the delivery robot DR may use information obtained from the camera part  220  when setting a traveling route or path. 
     The speaker  210  may transmit sound to the outside. The delivery robot DR may output a current state (or status) of the delivery robot DR, a user notification message, a message for notifying pedestrians, and the like through the speaker  210 . 
     The engaging part  202  may be formed by cutting a portion of a case at the rear surface of the extension unit  200 . In detail, the engaging part  202  may be formed by cutting three straight lines perpendicular to each other of the case of the extension unit  200 . Accordingly, the engaging part  202  is formed such that an upper portion or region of the case of the extension unit  200  is open by a predetermined distance, allowing at least one of the coupling module  400  and the tray  50  to be fixed into the open region. 
     For example, referring to  FIG.  7   , a damper  490  extends upward along a direction of the extension unit  200 . In this case, in order to fix the damper  490  to the extension unit  200 , a portion of the damper  490  and the engaging part  202  may be caught or engaged with each other to be fixed. The engaging part  202  serves to securely support an object with a different height on the extension unit  200 . 
     The display unit  300  may include a display  330 , an inclined part  310 , and an angle adjustment part  320 . 
     Referring to  FIGS.  5  and  6   , the display  330  may be configured to display a state (or status) of the main body MB and output a screen for controlling the main body MB. 
     The inclined part  310  extends from the extension unit  200  at a predetermined angle with respect to the extension unit  200  and supports the display  330 . The display  330  is inclinedly disposed toward the front by the inclined part  310 , allowing the display  330  to be easily seen from the above. 
     The angle adjustment part  320  is configured to finely adjust an angle of the display  330 . The angle of the display  330  may be adjusted within a predetermined range by the angle adjustment part  320  so as to allow a user to comfortably view the display  330 . 
     The delivery robot DR according to the present disclosure may provide a large amount of power along the front and rear sides through the first wheel  102  of the moving unit  100 . In addition, steering and rotation may be enabled through the moving unit  100  including the second wheel  104 . 
     In addition, the delivery robot DR of the present disclosure may provide recognition for the front and rear sides (or forward and rearward directions) of the delivery robot DR through the extension unit  200  disposed at one side of the moving unit  100 . In addition, information regarding a distance or height of a nearby object may be identified through the main body lidar  110  of the moving unit  100 , the TOF camera  120 , and the camera part  220  of the extension unit  200 . 
     Further, the delivery robot DR of the present disclosure may be easily manipulated by the user through the display unit  300 . 
     &lt;Coupling Module  400 &gt; 
     The coupling module  400  may be coupled to one surface of the main body MB. In detail, the coupling module  400  is coupled to the upper surface of the moving unit  100  of the main body MB. 
     The coupling module  400  includes a module body  410  and a docking part  450 . 
     The module body  410  is coupled to one surface of the main body MB. As described above, the module body  410  is coupled to the upper surface of the moving unit  100  of the main body MB. A terminal that is in contact with the module body  410  to transmit and receive power and/or electrical signals may be provided on a coupling surface of the main body MB. Through this terminal, the coupling module  400  may receive power from the main body MB and information obtained from the coupling module  400  may be transmitted to the main body MB. 
     Here, an upper surface of the module body  410  may be equal to or smaller than the upper surface of the moving unit  100 . In detail, as illustrated in  FIGS.  5  and  6   , the module body  410  may have the same area as a surface where the module body  410  is coupled to the moving unit  100 . Alternatively, the module body  410  may have a smaller area than a surface where the module body  410  is coupled to the moving unit  100 . 
     Accordingly, the coupling module  400  may be integrally coupled to the moving unit  100  of the main body MB. This may also prevent separation of the coupling module  400  from the main body MB by an external force caused when the coupling module  400  is caught or stuck externally due to its larger size. 
     The docking part  450  may be provided at the upper surface of the module body  410  in a protruding manner. The docking part  450  is disposed adjacent to the extension unit  200 . The docking part  450  may be configured to determine whether or not docking is completed according to the proximity of the tray  50 . 
     In detail, the docking part  450  includes a docking TOF camera  452  disposed toward the rear of the main body MB. Referring further to  FIG.  14   , the docking TOF camera  452  of the docking part  450  may determine whether or not docking is completed according to the proximity of a locking part  510  of the locking unit  500  to be described hereinafter. 
     The coupling module  400  includes an actuator (or actuator unit)  440  configured to be driven to be coupled with the locking unit  500  when the coupling module  400  and the tray  50  are located adjacent to each other. 
     In detail, referring to  FIGS.  5  and  6   , the actuator  440  is disposed adjacent to the extension unit  200 . The actuator  440  that is defined at the coupling module  400  includes an actuator bar  442  and a drive (or driving) part  444 . 
     The actuator bar  442  moves up as the tray  50  and the coupling module  400  are docked at the docking part  450 . That is, the locking unit  500  and the coupling module  400  are coupled to each other by the actuator bar  442 . When the main body MB travels in a state that the locking unit  500  and the coupling module  400  are coupled to each other, the main body MB, the coupling module  400 , the locking unit  500 , and the tray  50  are all movable. 
     The drive part  444  is configured to operate the actuator bar  442 . In detail, referring to  FIG.  14   , when the locking unit  500  and the coupling module  400  are located at positions available for docking with each other, the docking part  450  transmits a signal to a controller (or control unit) upon sensing this. When the signal is received, the controller may transmit a signal to the actuator  440  such that the actuator bar  442  can be driven by the drive part  444 . 
     The actuator bar  442  may be disposed in a direction opposite to the extension unit  200  based on the docking part  450 . The actuator bar  442  may be inserted into the module body  410  before the coupling module  400  and the tray  50  are docked. 
     In detail, referring to  FIG.  14   , the actuator bar  442  may be disposed at the same height as an upper surface of the coupling module  400  in an undocked state. Alternatively, the actuator bar  442  may be located more inward than the upper surface of the coupling module  400  in the undocked state. 
     In another implementation, the actuator may be provided with an actuator bar that protrudes in a horizontal direction and is configured to grip the locking unit  500 , instead of the actuator bar  442  that protrudes in a vertical direction. 
     Referring to  FIG.  6   , the module body  410  may be provided with a front groove  412  that is concavely recessed to allow the extension unit  200  to be inserted therein. The front groove  412  may be formed toward a front side (or direction)  410   a  of the module body  410 . The module body  410  may be integrally coupled to the upper surface of the moving unit  100  through the front groove  412 . 
     A module TOF camera  420  that is disposed at a lateral surface of the module body  410  may be provided in plurality spaced apart from one another along a periphery of the module body  410 . 
     In detail, the module TOF camera  420  may include module side TOF cameras  422  and  426  disposed at both sides of the module body  410 , and module rear TOF cameras  424  disposed at a rear surface of the module body  410 . The module TOF camera  420  may measure a distance between the main body MB and nearby objects, together with the TOF camera  120  of the main body MB. Unlike the TOF camera  120  of the main body MB, the module TOF camera  420  may be disposed at a distance of  20  cm to  40  cm from the ground. 
     The module body  410  may include a module lidar  430  that is formed toward the rear of the module body  410  and is configured to scan the rear side of the main body MB. 
     In detail, a module lidar groove  432  is formed toward a rear side (or direction)  410   b  of the module body  410 . In addition, the module lidar  430  may be defined in the module lidar groove  432 . The module lidar  430  may measure a distance of objects around the main body MB, together with the main body lidar  110  that is disposed at the moving unit  100 . 
     The module lidar  430  and the module rear TOF camera  120  of the module body  410  may also be used to measure a distance when the main body MB and the tray  50  described hereinafter are located adjacent to each other. 
     The module body  410  may include a rolling pin  460  that is disposed on the upper surface of the module body  410  in a direction opposite to a direction in which the actuator bar  442  is disposed and is rotatably provided. 
     The rolling pin  460  may be disposed adjacent to the rear surface of the module body  410 . Two rolling pins  460  may be provided. The rolling pins  460  may be disposed adjacent to both side surfaces of the module body  410 , respectively, in a spaced manner. The rolling pins  460  may be in contact with the locking unit  500  described hereinafter to guide the locking unit  500  and the tray  50 . The rolling pins  460  may be configured to rotate when being in contact with the locking unit  500 . 
     Meanwhile, the module body  410  may further include a module camera part  470 . The module camera part  470  may be disposed between the module rear TOF cameras  424 . The module camera part  470  may acquire information regarding objects ahead of and behind the main body MB, together with the camera part  220  of the main body MB. 
     The delivery robot DR according to the present disclosure may include the coupling module  400  that is integrally coupled to the main body MB. In addition, since the coupling module  400  is detachably coupled to the main body MB, different types of coupling modules  410  can be coupled to the main body MB according to a type of tray  50  and the like, thereby increasing the use of the main body MB. &lt;Locking Unit  500 &gt; 
     The locking unit  500  is coupled to the tray  50  that is configured to be movable. In detail, referring to  FIG.  8   , the locking unit  500  may be coupled to a lower surface and side surface of the tray  50 . 
     The locking unit  500  may include a locking part  510  and a guide part  520 . 
     The locking part  510  may be mounted to a side surface adjacent to the lower surface of the tray  50 . A locking groove  512  into which the actuator bar  442  is inserted may be defined in the locking part  510 . The locking groove  512  corresponds to a shape of the actuator bar  442  so as to allow the actuator bar  442  to be inserted therein. 
     As the locking part  510  is mounted to the side surface of the tray  50 , the locking part  510  can get close to the docking part  450  before the side surface of the tray  50  comes near to the docking part  450  when approaching close to the coupling module  400 . 
     However, unlike the above description of disposing the locking part  510  at the side surface of the tray  50 , the locking part  510  may be disposed at the lower surface of the tray  50 . This may prevent the side surface of the tray  50  from protruding to one side. 
     The guide part  520  may extend from the locking part  510  and be greater in width than the locking part  510 . Here, at least a portion of the guide part  520  may be guided by the rolling pin  460 . 
     The guide part  520  may include first portions  521 , second portions  522 , and a third portion  523 . 
     The first portions  521  may extend from the locking part  510  and be inclined with respect to the locking part  510 . 
     The first portions  521  extend obliquely from both sides of the locking part  510 , and thus, the guide part  520  is greater in width than the locking part  510 . 
     The second portions  522  may have a width that corresponds to a separation distance between the rolling pins  460  that are disposed at both sides of the module body  410 . The second portions  522  may extend in a lengthwise (or longitudinal) direction of the guide part  520 . 
     In detail, referring to  FIG.  12   , when the locking unit  500  is disposed in a position to be coupled to an upper end of the coupling module  400 , the second portions  522  are disposed between the rolling pins  460  disposed at the both sides of the module body  410 . 
     If a width between the second portions  522  is equal to or greater than a width between the rolling pins  460 , the locking unit  500  is not inserted between the rolling pins  460 , and the width between the second portions  522  is considerably narrower (or smaller) than the width between the rolling pins  460 , the rolling pins  460  may not properly guide the locking unit  500  when inserting the locking unit  500  between the rolling pins  460 . Accordingly, the width between the second portions  522  that are spaced apart from each other corresponds to the width between the rolling pins  460 . 
     The third portion  523  may connect the second portions  522  disposed at both sides of the locking part  510 . Accordingly, the second portions  522  may be prevented from being moved by an external force applied in an inward direction. 
     Referring to  FIGS.  11  and  12   , the rolling pins  460  are disposed on the upper surface of the coupling module  400 . The rolling pins  460  may guide a movement path of the guide part  520  by being brought into contact with the guide part  520 , namely, the first portions  521  and the second portions  522  while the main body MB is entering below the tray  50 . 
     In other words, as the rolling pins  460  guide the guide part  520 , the locking unit  500 , namely, the tray  50  may be located at a desired or intended position on the coupling module  400 . During the process of guiding the guide part  520 , the rolling pins  460  may be rotated by being in contact with the first portions  521  and the second portions  522 . 
     Referring to  FIG.  8   , the tray  50  may include a front surface  51 , a rear surface  52  that is open, side frames  54  in which a plurality of opening grooves  53  are formed, leg parts  55 , reflective sheets  57  provided at front surfaces of the leg parts  55 , respectively, a tray bottom surface  58 , and tray wheels  59 . 
     The front surface  51  of the tray  50  may be blocked or closed to prevent a cargo loaded on the tray  50  from falling out while traveling or stopping. The rear surface  52  of the tray  50  is open such that items can be easily loaded. However, an openable door may be provided on the rear surface  52  of the tray  50 . 
     The opening grooves  53  may be formed on side surfaces of the tray  50  to allow an inside of the tray  50  to be visually recognized from the outside. Alternatively, unlike the drawing, an additional frame connecting the side surfaces of the tray  50  may be provided. The side frames  54  are provided at the side surfaces of the tray  50 , respectively, so as to prevent a cargo loaded on the tray  50  from falling out while traveling. 
     The reflective sheets  57  may be provided on the front surfaces of the leg parts  55 , respectively. The leg parts  55  may each have a predetermined thickness or more to be easily recognized by the module TOF camera  420  and the module lidar  430 . For example, the leg parts  55  may each have a thickness of 5 cm or more, so as to be easily recognized by the module TOF camera  420  and the module lidar  430 . 
     The reflective sheets  57  attached to the respective leg parts  55  may better reflect signals transmitted from the module TOF camera  420  and the module lidar  430  of the coupling module  400 . This may allow the module TOF camera  420  and the module lidar  430  to recognize the leg parts  55  of the tray  50  more easily. Accordingly, a position of the main body MB may be more accurately aligned when the main body MB and the locking unit  500  are coupled to each other. 
     [ FIG.  7   : Implementation Including Damper  490 ] 
     A delivery robot DR according to another implementation of the present disclosure in  FIG.  7    may further include a damper (or damper part)  490 . In detail, the damper  490  may be configured to cover or surround the docking part  450 . The damper  490  may extend along a direction in which the extension unit  200  extends with respect to the moving unit  100 . 
     The damper  490  may include a damper groove  492   a  through which the docking part  450  is exposed to the outside and into which the docking part  450  is inserted. 
     A front surface  492  of the damper  490  in which the damper groove  492   a  is defined may protrude more to the actuator  440  than a front surface  451  of the docking part  450  that is exposed to the outside. 
     In detail, referring to  FIG.  7   , the front surface  451  of the docking part  450  disposed in the damper groove  492   a  is located more inward than the front surface  492  of the damper  490 . 
     In the delivery robot DR according to this implementation of the present disclosure, as the docking part  450  is disposed to be covered by the damper  490 , and the front surface of the damper  490  protrudes more than the front surface of the docking part  450 , the docking part  450  can be prevented from being damaged by the locking part  510  when the locking part  510  is excessively moved toward the docking part  450 . 
       FIGS.  9  to  13    illustrate a process in which the coupling module  400  and the locking unit  500  are coupled by the actuator  440  as the delivery robot DR in  FIG.  5    moves to be adjacent to the tray  50 ;  FIG.  14    is a cross-sectional view illustrating a state of coupling the coupling module  400  and the locking unit  500 ;  FIG.  15    is a cross-sectional view illustrating a coupled state of the delivery robot DR and the tray  50 ;  FIG.  16    is a cross-sectional view illustrating a positional relationship between the coupling module  400  and the locking unit  500  when the delivery robot DR that is coupled to the tray  50  travels on an incline;  FIG.  17    is a cross-sectional view illustrating a positional relationship between the coupling module  400  and the locking unit  500  when the delivery robot DR that is coupled to the tray  50  stops while traveling; and  FIG.  18    is a front view illustrating a coupled state of the delivery robot DR and the tray  50 . For the sake of better understanding, some portions of the tray  50  are not shown in  FIGS.  11  to  13   . 
     Referring to  FIGS.  9  to  12   , in order for docking, the main body MB that is coupled to the coupling module  400  travels or moves backward to the tray  50  to reach a docking position. As described above, the locking unit  500  may be guided by the rolling pins  460  when the coupling module  400  approaches the locking part  510 . 
     First, referring to  FIG.  9   , the delivery robot DR is aligned such that a rear surface of the main body MB is directed to the tray  50  in a state that the coupling module  400  is coupled to the main body MB, so as to travel backwards under a bottom surface of the tray  50 . 
     Of the locking unit  500  mounted to the tray  50 , the locking part  510  protrudes from the side surface of the tray  50 , which allows the delivery robot DR to identify a position of the locking unit  500  through the module lidar  430 . 
     Referring to  FIG.  10   , a portion of the main body MB enters below the tray  50 . Here, the locking unit  500  may be guided by the rolling pins  460 . In detail, when the locking unit  500  is brought into contact with the rolling pins  460 , the rolling pins  460  may rotate to guide the locking unit  500  to be inserted between the rolling pins  460  disposed at the both sides of the module body  410 . 
     In addition, the docking TOF camera  452  of the docking part  450  may identify a position of the locking part  510  and adjust a position of the main body MB so as to allow the locking part  510  to be located between the rolling pins  460 . 
     Referring to  FIG.  11   , a more portion of the main body MB enters below the tray  50 . Here, at least a portion of the guide part  520  may be guided by the rolling pins  460 . In detail, the first portions  521  of the guide part  520  may be guided by the rolling pins  460 . 
     As the first portions  521  have a shape that is wide open on both sides with respect to the locking part  510 , the first portions  521  can be brought into contact with the rolling pins  460  when the main body MB enters below the tray  50 , allowing a position of the tray  50  or the main body MB to be adjusted. Accordingly, the position of the locking part  510  can be properly matched with the actuator  440 . In other words, the main body MB can enter below the tray  50  in a manner that its center is aligned with a center C of the tray  50 . 
     Referring to  FIG.  12    and (a) of  FIG.  14   , the main body MB moves further toward the tray  50 . During this process, the second portions  522  of the guide part  520  are disposed between the rolling pins  460 . The rolling pins  460  and the second portions  522  may be in contact with each other. As the main body MB moves toward the tray  50 , the rolling pins  460  in contact with the second portions  522  rotate to thereby allow the main body MB to be inserted below the tray  50 . As the second portions  522  are disposed between the rolling pins  460 , the position of the locking part  510  may be more properly matched with the actuator  440 . 
     When the locking part  510  is located adjacent to the docking part  450 , the docking part  450  detects this through the TOF camera  452 . In addition, the main body MB may stop at a position suitable for docking. 
     Referring to  FIG.  13    and (b) of  FIG.  14   , as the actuator  440  of the coupling module  400  is operated, the actuator bar  442  is inserted into the locking part  510 . Accordingly, the coupling module  400  and the locking unit  500  can be docked. 
     Meanwhile, referring to  FIG.  15   , a gap g may be formed between the coupling module  400  and the locking unit  500 . More specifically, the gap g is defined between the coupling module  400  and a lower surface  522   a  of the second portion  522 . This gap serves to prevent weight of the tray  50  in the direction of gravity from being transmitted to the coupling module  400 . Further, due to the gap g between the coupling module  400  and the locking unit  500 , the weight of the tray  50  may not be transferred to the coupling module  400  even when the main body MB that is coupled to the tray  50  moves on an incline. 
     Referring to  FIG.  16   , when the main body MB is moved from a flat ground (or surface)  1  to an inclined ground s 1 , a height of the front surface of the main body MB may be increased relative to a height of the rear surface of the main body MB. However, since the gap g exists between the coupling module  400  and the locking unit  500 , a front gap g 1  between the coupling module  400  and the locking unit  500  is reduced. That is, the weight of the tray  50  is not transmitted to the coupling module  400 . Meanwhile, as the height of the front surface of the main body MB is increased relative to the height of the rear surface of the main body MB, a rear gap g 2  between the coupling module  400  and the locking unit  500  may increase. With this structure, the present disclosure can prevent the weight of the tray  50  from being transferred when the delivery robot DR travels on an incline. 
     When the locking unit  500  and the coupling module  400  are coupled by the actuator  440 , the actuator bar  442  may be disposed to be spaced apart from at least one of a front surface  512   a  and a rear surface  512   b  of the locking groove  512  that define the locking groove  512 . That is, when the actuator bar  442  is inserted into the locking groove  512 , a separation distance exists between the actuator bar  442  and the locking groove  512 . 
     In detail, referring to (a) of  FIG.  14   , the locking groove  512  have the front surface  512   a  in the front direction and the rear face  512   b  in the rear direction that are opposite to each other. Referring to (b) of  FIG.  14   , when the actuator bar  442  is inserted into the locking groove  512 , the actuator bar  442  may not come in contact with the front surface  512   a  and the rear surface  512   b  of the locking groove  512 . 
     Meanwhile, referring to  FIG.  15   , a separation distance d may be defined between a front surface  510   a  of the locking part  510  and the front surface  492  of the damper  490 . At this time, since the front surface  451  of the docking part  450  is located more inward than the front surface  492  of the damper  490 , a separation distance d may also be defined between the front surface  510   a  of the locking part  510  and the front surface  451  of the docking part  450 . 
     As the separation distance d exists between the front surface  510   a  of the locking part  510  and the front surface  492  of the damper  490 , the damper  490  and the locking part  510  may not be brought into contact with each other when the main body MB travels in an inclined section. 
     In detail, referring to  FIG.  16   , when the main body MB moves from the flat ground  1  to the inclined ground s 1 , the height of the front surface of the main body MB may be increased relative to the height of the rear surface of the main body MB. Here, a separation distance dl between the damper  490  and an upper portion of the locking part  510  may be relatively reduced, and a separation distance d 2  between the damper  490  and a lower portion of the locking part  510  may be greater than or equal to the original separation distance d. 
     As the separation distance d exists between the front surface  510   a  of the locking part  510  and the front surface  492  of the damper  490 , the damper  490 , and the docking part  450  may not come in contact with the locking part  510  when the main body MB travels in an inclined section. 
     In addition, as the separation distance d is defined between the front surface  510   a  of the locking part  510  and the front surface  492  of the damper  490 , transmission of weight of the tray  50  to the actuator bar  442  can be reduced when the main body MB stops while traveling. 
     In detail, (a) of  FIG.  17    illustrates a state immediately after the actuator bar  442  being inserted into the locking groove  512 . 
     Here, the actuator bar  442  may be spaced apart from the front surface  512   a  and the rear surface  512   b  of the locking groove  512 . In other words, a width of the actuator bar  442  is narrower (or smaller) than that of the locking groove  512 , and thus, the actuator bar  442  drawn into the locking groove  512  can be spaced apart from the front surface  512   a  and/or the rear surface  512   b  of the locking groove  512 . 
     Referring to (b) of  FIG.  17   , the main body MB is moved forward as it starts traveling. Accordingly, the actuator bar  442  moves and comes in contact with the front surface  512   a  of the locking groove  512 . The actuator bar  442  presses the front surface  510   a  of the locking part  510  so that force to move the tray  50  is applied. 
     (c) of  FIG.  17    illustrates a state in which the main body MB stops while traveling. When the main body MB stops, the tray  50  may be moved forward by inertia. As the tray  50  is moved forward, the locking part  510  is moved forward. The front surface  510   a  of the locking part  510  may be brought into contact with the front surface  492  of the damper  490 . Accordingly, an inertia force of the tray  50  can be absorbed by the damper  490  through contact with the damper  490 . 
     That is, since the inertia force of the tray  50  is absorbed by the damper  490 , transmission of weight of the tray  50  to the actuator bar  442  can be reduced when the main body MB stops while traveling. 
     In addition, as described above, the docking part  450  may include the damper groove  492   a  through which the damper  490  is exposed to the outside and into which the docking part  450  is inserted, and the front surface  492  of the damper  490  may protrude more to the actuator  440  than the front surface  451  of the docking part  450  that is exposed outside. 
     When the tray  50  moves relatively forward with respect to the main body MB as the main body MB is switched to a stationary state from a moving state, the front surface  510   a  of the locking part  510  is brought into with the damper  490 . Accordingly, transmission of inertial force of the tray  50  to the docking part  450  can be reduced. 
     Referring to  FIG.  18   , the main body MB that is docked with the tray  50  may be disposed at the middle of the tray  50 . An overall width  50   w  of the tray  50  should be within a range of the standard lift (or elevator) size. More specifically, the overall width  50   w  of the tray  50  should be within a range of the standard lift size for 10 persons. 
     A width  100   w  of the main body MB is narrower than a width  55   w  between the leg parts  55  of the tray  50 . Further, an angle between the tray  50  and the main body MB may be widened or increased during steering and rotation while the main body MB is traveling, and thus, the width  100   w  of the main body MB may, preferably, be defined in a spaced manner from the leg parts  55  of the tray  50  by a predetermined distance. 
     In other words, when the tray  50  is rotated as the main body MB rotates, a distance between the main body MB and the tray leg parts  55  may be reduced, and thus, the main body MB may, preferably, have a narrow width enough to absorb this clearance or gap. 
     Although the foregoing description has been given with reference to the preferred implementations, it will be understood by those skilled in the art that various modifications, changes, deletion, or addition of the components can be made without departing from the scope of the present disclosure disclosed in the following claims. Therefore, the scope of the present disclosure should not be limited to the implementations described above.