Patent Publication Number: US-9851720-B2

Title: Method of controlling a cleaner

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Korean Patent Application No. 10-2014-0058563, filed on May 15, 2014 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     The present invention relates to a cleaner and a method of controlling the same. 
     2. Background 
     A cleaner is an apparatus that suctions dust from floor. In general, the cleaner includes a suction device having a suction port for air suction and a main body connected to the suction device via a hose defining an air suction channel. The main body is provided with an air suction fan for generating negative pressure to suction air through the suction port, and the suction device or the main body is provided with a dust collector for collecting dust introduced through the hose. 
     The suction device is moved by a user, and the main body follows the suction device. Generally, the main body is moved by tension applied from the hose. In recent years, there has been developed a cleaner including a motor mounted in the main body for rotating wheels of the main body such that the main body can move for itself. 
     In addition, there is known a cleaner including an ultrasonic transmitter provided at the suction device and an ultrasonic receiver provided at the main body such that the main body actively follows the suction device based on ultrasonic waves received through the ultrasonic receiver. However, if obstacles are present between the main body and the suction device, the conventional cleaners are inconvenient in that a user removes the obstacles his/herself such that the main body does not collide with the obstacles during travel. 
     Moreover, since the ultrasonic receiver also receives ultrasonic waves reflected from obstacles or walls in a cleaning region, the main body may not properly follow the suction device and thus interference may occur between a movement line of the user and movement route of the main body, thereby causing customer dissatisfaction. 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a cleaner including a movable body (or suction device) and a following body (or main body) capable of avoiding obstacles in a cleaning region when it follows the movable body, and a method of controlling the cleaner. 
     In addition, it is another object of the present invention to provide a cleaner and a method of controlling the same, in which a following body has improved following capability compared to a conventional method of using ultrasonic waves. 
     In addition, it is a further object of the present invention to provide a cleaner traveling along an optimal path in which a following body is capable of following a movable body while avoiding obstacles, and a method of controlling the same. 
     In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a method of controlling a cleaner a movable body for suctioning and a following body for collecting the dust suctioned by the movable body, the method including (a) acquiring an image for a view around the following body, (b) acquiring position information of the movable body in an real space, based on the image, (c) acquiring position information of an obstacle in the real space, based on the image, (d) setting a travel direction such that the following body avoids the obstacle to follow the movable body, based on the position information of the movable body and the position information of the obstacle, and (e) controlling the following body to travel in the set travel direction. 
     In accordance with another aspect of the present invention, there is provided a cleaner including a movable body for suctioning, a following body configured to follow the movable body, the following body collecting the dust suctioned by the movable body, a travel unit for allowing the following body to travel, an image acquisition unit acquiring an image for a view around the following body, and a controller acquiring position information of the movable body in an real space, based on the image, acquiring position information of an obstacle in the real space, setting a travel direction such that the following body avoids the obstacle to follow the movable body, based on the position information of the movable body and the position information of the obstacle, and controlling the travel unit such that the following body travels in the set travel direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein: 
         FIG. 1  is a view illustrating a cleaner according to an embodiment of the present invention; 
         FIG. 2  is a view illustrating that a main body follows a suction device; 
         FIG. 3  is a view illustrating one image captured by the cleaner according to the embodiment of the present invention; 
         FIG. 4  is a view for schematically explaining a change in position of a marker on an image, according to a change in distance of the marker from the main body; 
         FIG. 5  is a view schematically illustrating an irradiation range of a pattern light irradiation unit; 
         FIG. 6  is a view illustrating a change in shape of a marker on an image, according to a change in posture of the marker in an real space; 
         FIG. 7  is a block diagram illustrating a configuration of main components of the cleaner according to the embodiment of the present invention; 
         FIG. 8  is a view illustrating an example of positions of markers; 
         FIG. 9  is a view illustrating changes in positions of the markers illustrated in  FIG. 8  on images, according to movement of the suction device; 
         FIG. 10  is a view illustrating another example of a position of a marker; 
         FIG. 11  is a view illustrating configuration examples of a marker; 
         FIGS. 12 and 13  are views illustrating a change in shape of the marker in the acquired image based on the change in posture of the marker of  FIG. 11( c ) ; 
         FIG. 14  is a view for explaining positions at which markers are disposed; 
         FIGS. 15 and 16  are views illustrating another configuration example of a marker; 
         FIG. 17  is a flowchart illustrating a method of controlling a cleaner according to an embodiment of the present invention; 
         FIG. 18  is a view for explaining elements considered when a travel direction of a main body is set in step S 30  of  FIG. 17 ; 
         FIG. 19  is a view illustrating an example of a method of setting the travel direction of the main body in consideration of the elements explained with reference to  FIG. 18 ; 
         FIG. 20  is a view illustrating another example of the method of setting the travel direction of the main body in consideration of the elements explained with reference to  FIG. 18 ; and 
         FIG. 21  is a flowchart illustrating a method of controlling a cleaner according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Advantages, features and methods for achieving those of embodiments may become apparent upon referring to embodiments described later in detail together with attached drawings. However, embodiments are not limited to the embodiments disclosed hereinafter, but may be embodied in different modes. The embodiments are provided for perfection of disclosure and informing a scope to persons skilled in this field of art. The same reference numbers may refer to the same elements throughout the specification. 
       FIG. 1  is a view illustrating a cleaner according to an embodiment of the present invention.  FIG. 2  is a view illustrating that a main body follows a suction device.  FIG. 3  is a view illustrating one image captured by the cleaner according to the embodiment of the present invention.  FIG. 4  is a view for schematically explaining a change in position of a marker on an image, according to a change in distance of the marker from the main body.  FIG. 5  is a view schematically illustrating an irradiation range of a pattern light irradiation unit.  FIG. 6  is a view illustrating a change in shape of a marker on an image, according to a change in posture of the marker in an real space.  FIG. 7  is a block diagram illustrating a configuration of main components of the cleaner according to the embodiment of the present invention. 
     A cleaner according to an embodiment of the present invention includes a movable body configured to be movable for suctioning dust and a following body for collecting the dust suctioned by the movable body, the following body being mobile. The following body includes an image acquisition unit  220  for acquiring an image for a view around the following body and a controller  230  for controlling the following body to travel while following the movable body based on the acquired image. Referring to  FIG. 1 , the movable body may be a suction device  100 , and the following body may be a main body  200 . Hereinafter, by way of example, the movable body will be described as the suction device  100 , and the following body will be described as the main body  200 . 
     Referring to  FIG. 1 , a cleaner according to an embodiment of the present invention may include a suction device  100  and a main body  200 . The suction device  100  is connected to the main body  200  via a hose  300 . Air suctioned by the suction device  100  is introduced into the main body  200  via the hose  300 . The main body  200  may be provided with a dust collector (not shown) for collecting dust from the air introduced into the main body  200  via the hose  300 . The suction device  100  may be provided with a suction port (not shown), through external air is suctioned into the suction device  100 . The main body  200  may provide suction force via the hose  300  such that the external air can be suctioned into the suction device  100  through the suction port. The suction device  100  is moved along a floor according to manipulation of a user. 
     The suction device  100  may include a suction unit  120  configured such that the suction port, through which dust is suctioned into the suction device  100 , faces a floor of a cleaning zone, an intake pipe  130  extending from the suction unit  120  for defining a channel along which the dust suctioned through the suction port moves, and a handle  140  provided at the upper part of the intake pipe  130 . A user may push or pull the suction device  100  while holding the handle  140  to move the suction device  100 . 
     The intake pipe  130  forms a channel along which air suctioned through the suction unit  120  moves. The intake pipe  130  may include a lower pipe  131  connected to the suction unit  120  and an upper pipe  132  slidably connected to the lower pipe  131 . As the upper pipe  132  slides along the lower pipe  131 , the overall length of the intake pipe  130  may be varied. The handle  140  is configured to be located higher than the waist of the user during cleaning. In this embodiment, the handle  140  is provided at the upper pipe  132 . 
     Air is introduced through one end of the hose  300  connected to the intake pipe  130  and is discharged through the other end of the hose  300  connected to the main body  200 . The hose  300  may include a flexible portion  310 . The flexible portion  310  may be bent according to movement of the suction device  100 . The position of the suction device  100  relative to the main body  200  may be varied according to manipulation of the user. Since the suction device  100  is moved within a length of the hose  300 , however, the suction device  100  cannot be distant more than a predetermined distance from the main body  200 . 
     The hose  300  includes a main body connection unit  320  connected to the main body  200 . The main body connection unit  320  may be rigid body. The main body connection unit  320  is moved along with the main body  200 . The main body connection unit  320  may be separably coupled to the main body  200 . 
     The main body  200  may include a case  211  forming the external appearance of the main body  200  and at least one wheel rotatably mounted at the case  211 . The main body  200  may move straight and turn using the wheel. In this embodiment, a left wheel  212  and a right wheel  213  are provided at left and right sides of the case  211 , respectively. The main body  200  may turn based on a difference in rotational speed between the left wheel  212  and the right wheel  213 . 
     Referring to  FIG. 7 , the cleaner may include a travel unit  250  for allowing the main body  200  to travel. The travel unit  250  may be provided in the main body  200 . The travel unit  250  may include at least one motor for rotating the left and right wheels  212  and  213 . In the embodiment, the cleaner may also include a pair of motors for respectively driving the left and right wheels  212  and  213 , and alternatively may include one motor and a power transfer means for transferring driving force from the motor to the left and right wheels  212  and  213 . In the former case, the main body  200  may turn based on a difference in rotational speed between the motors. In the latter case, the main body  200  may turn based on a difference in rotational speed between the left wheel  212  and the right wheel  213  based on the power transmission means. 
     The main body  200  may further include a suction force provision unit  240 . The suction force provision unit  240  forms negative pressure for the suction device  100  to suction external air. The suction force provision unit  240  may include a fan motor (not shown) and a fan (not shown) rotated by the fan motor. The fan motor may be driven under control of a suction control module  234  of a controller  230 . The suction force provision unit  240  may be provided in the case  211 . In addition, the dust collector (not shown) for collecting dust suctioned through the hose  300  may be disposed in the case  211 . 
     The suction device  100  may further include a manipulation unit  110 . The manipulation unit  110  allows the user to input various control commands. In particular, it is possible to control the operation of the suction force provision unit  240  through the manipulation unit  110 . The position of the manipulation unit  110  is set such that the manipulation unit  110  can be manipulated by the thumb of the user holding the handle  140 . In this embodiment, the manipulation unit  110  is provided at the handle  140 . However, the present invention is not limited thereto. The suction control module  234  may control the operation of the suction force provision unit  240  according to a control command input through the manipulation unit  110 . 
     The image acquisition unit  220  acquires an image for a view around the main body  200 . For example, the image acquisition unit  220  may acquire an image for a view ahead of the main body  200  (or in a travel direction of the main body  200 ). The image acquisition unit  220  may include a camera. For example, the image acquisition unit  220  may include a digital camera that is capable of acquiring a digital image. The digital camera may be configured such that an optical axis O (see  FIG. 4 ) of a lens of the digital camera faces ahead of the main body  200 . (see  FIGS. 4 and 5 ). 
     The controller  230  controls the main body  200  to travel while following the suction device  100  based on the image acquired by the image acquisition unit  220 . The controller  230  may include a marker information acquisition module  231 , a travel operation setting module  232 , a travel control module  233 , and/or a suction control module  234 . These modules will hereinafter be described in more detail. 
     Meanwhile, the movement of the main body  200  may be classified as a passive movement of the main body  200  in which the main body  200  is moved by tension from the user or an active movement of the main body  200  in which the wheels  212  and  213  of the main body  200  are rotated by the motor. The term “following” or “active following” used in the following description is based on the active movement of the main body  200 . 
     The travel unit  250  may include a clutch for transmitting drive force from the motor to the wheels  212  and  213 . Drive force from the motor may be transmitted to the wheels  212  and  213  according to the operation of the clutch with the result that the active movement of the main body  200  may be achieved. On the other hand, the passive movement of the main body  200  may be achieved in a state in which the transmission of the drive force from the motor to the wheels  212  and  213  is released. 
     Referring to  FIGS. 3 to 6 , the cleaner according to the embodiment of the present invention may include a marker M displaced according to the movement of the suction device  100 . The controller  230  may control the travel operation of the main body  200  based on the position (or posture) of the marker M indicated in the image acquired by the image acquisition unit  220 . The image acquisition unit  220  may repeatedly acquire images during travel of the main body  200 . In this case, controller  230  may control the travel operation of the main body  200  based on the acquired images even during travel of the main body  200 . Even when the position or the posture of the marker M is changed during travel of the main body  200 , therefore, the controller  230  may sense the change in position or posture of the marker M based on the images and reset the travel operation of the main body  200  based on the sensed change in position or posture of the marker M. As a result, the main body  200  is moved based on the reset travel operation of the main body  200 . Consequently, it is possible for the main body  200  to follow the marker M. 
     Referring to  FIGS. 3 to 6 , when the user cleans the floor while moving the suction device  100 , the marker M is also moved according to the movement of the suction device  100 . As a result, the position (see  FIG. 4 ) or the posture (see  FIG. 6 ) of the marker M in the image acquired by the image acquisition unit  220  (hereinafter, referred to as the acquired image) is also varied. 
     More specifically, the position of the marker M indicated in the acquired image reflects position information of the marker M in a real space. The position information may include information regarding a distance from the main body  200  to the marker M or information regarding a direction in which the marker M is positioned relative to the main body  200 . The marker information acquisition module  231  may acquire the position information of the marker M in the real space based on the position of the marker M indicated in the image acquired by the image acquisition unit  220 . 
     Since the image acquisition unit  220  has a fixed visual field, and the height from the floor to the marker M in the real space is not substantially too much changed, the position in the vertical direction of the marker M indicated in the acquired image reflects a distance between the main body  200  and the marker M in the real space. For example, as the position of the marker M in the image at a region above the optical axis O is moved more downward, the marker M is more distant from the main body  200  in the real space. Distances from the main body  200  to points in the real space corresponding to coordinates in the image may be prestored as a database, and the marker information acquisition module  231  may acquire information regarding the distance to the marker M based on the database. 
     In addition, the position in the horizontal direction of the marker M in the image reflects a direction in which the marker M is positioned relative to the main body  200  in the real space. For example, in a case in which the marker M is positioned in the image at the left side on the basis of a vertical line passing through the optical axis O, the marker M is positioned at the left side of the main body  200  in the real space. On the other hand, in a case in which the marker M is positioned in the image at the right side, the marker M is positioned at the right side of the main body  200  in the real space. Direction from the main body  200  to points in the real space corresponding to coordinates in the image may be prestored as a database, and the marker information acquisition module  231  may acquire information regarding the direction in which the marker M is positioned relative to the main body  200  based on the database. 
     The main body  200  may further include a pattern light irradiation unit  260 . The pattern light irradiation unit  260  may include a light source and an optical pattern projection element (OPPE). Light emitted from the light source is transmitted through the optical pattern projection element with the result that a uniform pattern light (hereinafter, referred to as “pattern light”) is generated. The light source may be a laser diode (LD) or a light emitting diode (LED). Laser light exhibits monochromaticity, straightness, and connection characteristics superior to other light sources, and therefore accurate distance measurement is possible. However, infrared light or visible light has a problem in that distance measurement accuracy has a great deviation depending upon a factor, such as color or material, of an object. For these reasons, the laser diode (LD) may be used as the light source. The optical pattern projection element may include a mask or a diffractive optical element (DOE). A pattern generated by the optical pattern projection element may include at least one pattern component, such as a point, a line, or a plane. 
     A pattern light irradiation unit control module  235  controls the pattern light irradiation unit  260 . The pattern light irradiation unit control module  235  may control the pattern light irradiation unit  260  to irradiate pattern light not only before the travel of the main body  200  is commenced but also during travel of the main body  200 . 
     Referring to  FIG. 5 , the pattern light irradiation unit  260  may irradiate a predetermined pattern light ahead of the main body  200 . In particular, the pattern light is irradiated slightly downward such that the pattern light is irradiated to the floor of the cleaning zone. In order to form a view angle necessary to detect the distance to an obstacle, an irradiation direction of the pattern light and the optical axis O of the image acquisition unit  220  may not be parallel to each other but form a predetermined angle θ. An obstacle detection region of  FIG. 18  is a region at which it is possible to detect an obstacle based on the irradiated pattern light. The possible maximum distance for obstacle detection may be shorter than the length of the hose  300 . In addition, the maximum distance for obstacle detection may not reach a position at which the user normally stands. 
     Referring to  FIG. 3 , the obstacle information acquisition module  236  may sequentially compare brightness of points in the acquired image in a horizontal direction to extract a pattern P constituted by points a predetermined level brighter than the surroundings. A lower area LA of the acquired image is an area to which the pattern light is irradiated. The obstacle information acquisition module  236  extracts the pattern P from the lower area LA and acquires information regarding an obstacle in the cleaning zone based on the extracted pattern P. The obstacle information may include information regarding the position of the obstacle, the distance from the main body  200  to the obstacle, the width or height of the obstacle, etc. The lower area LA may be below the optical axis O of the image acquisition unit  220 . On the other hand, an upper area UA of the acquired image is an area from which the marker M is extracted. The upper area UA may be above the optical axis O of the image acquisition unit  220 . 
     The controller  230 , specifically the obstacle information acquisition module  236 , acquires the obstacle information in the real space based on the change in geometry of the pattern (for example, the change in shape of the pattern or the change in position between the pattern components) in the acquired image. In this embodiment, the pattern light irradiation unit  260  irradiates pattern light having a horizontal segment P. The shape of the horizontal segment P may be deformed depending upon a situation of the cleaning zone to which the pattern light is irradiated or a situation of the obstacle. As can be seen from the acquired image shown in  FIG. 17 , the deformed segment P has a point F 1  at which the segment is bent, the point F 1  corresponding to an interface between a wall and the floor, a slant line F 3  extending along the wall, and a portion F 4  of the segment deformed depending upon the shape of the surface of the obstacle. The obstacle information acquisition module  236  may acquire obstacle information based on the various characteristics of the pattern extracted from the acquired image. 
     A direction in which the pattern light is irradiated by the pattern light irradiation unit  260  is fixed. When the pattern light is irradiated to a region having no obstacle, therefore, the position of a pattern in an acquired image is always uniform. Hereinafter, the acquired image at this time will be referred to as a reference acquired image. Position information of the pattern in the reference acquired image may be pre-calculated using triangulation. On the assumption that coordinates of any pattern component Q constituting the pattern in the reference acquired image are Q(Yi, Zi), a distance value Li(Q) from the main body  200  to the pattern component Q may be pre-calculated using triangulation. Coordinates Q′(Yi′, Zi′) of the pattern component Q in the acquired image obtained by irradiating a pattern light into a region having an obstacle result from the movement of Q(Yi, Zi) of the pattern component Q in the reference acquired image. The obstacle information acquisition module  236  may compare the coordinates Q′(Yi′, Zi′) of the pattern component Q with the coordinates Q(Yi, Zi) of the pattern component Q to acquire obstacle information regarding the width and the height of the obstacle and the distance to the obstacle. In particular, it is possible to recognize the width or the shape of the obstacle or the distance to the obstacle based on a view angle or a degree in which the horizontal line constituting the pattern is bent. In addition, it is possible to recognize the height of the obstacle based on the vertical displacement of the horizontal line or the length of the vertical line. 
     The travel operation setting module  232  may set a travel operation or a travel route of the main body  200  in which the main body  200  can follow the marker M while avoiding the obstacle based on the marker information, such as the position, the movement, and the change in posture, of the marker acquired by the marker information acquisition module  231  and the obstacle information acquired by the obstacle information acquisition module  236 . 
     The travel control module  233  controls travel unit  250  such that the main body  200  travels in the travel direction set by the travel operation setting module  232 . Thus, the main body  200  may follow the suction device  100  while not striking the obstacle. 
     The travel control module  233  may control the travel of the main body  200  according to the travel direction set by the travel operation setting module  232 . As the travel unit  250  is controlled by the travel control module  233 , the main body  200  follows the suction device  100  while moving according to the set travel direction. The movement of the main body  200  is not necessarily achieved until the main body  200  reaches the suction device  100 . Since the user is generally located between the main body  200  and the suction device  100 , it is sufficient for the main body  200  to move to a position spaced apart from the suction device  100  by a predetermined distance. For example, in a case in which the length of the hose  300  is 1 m, the main body  200  may move to a position spaced apart from the suction device  100  by about 40 to 60 cm and then be stopped. The distance between the main body  200  and the suction device  100  may be measured on the floor. The distance between the main body  200  and the suction device  100  may be calculated based on the position of the marker M indicated in the image. 
     Referring to  FIG. 4 , the change in position of the marker M indicated in the acquired image reflects the movement of the marker M in the real space. For example, as shown in  FIG. 4 , as the marker M is more distant from the main body  200  in the real space, the position of the marker M in the image at the region above the optical axis O is moved more downward. Information regarding the movement of the marker M in the real space may be acquired based on the change in position of the marker M indicated in the image. Of course, the movement information may include the change in direction in which the marker M is moved as well as the change in distance from the main body  200  to the marker M. 
     As the marker M is more distant from the main body  200  within a visual field S of the image acquisition unit  220 , the position of the marker M in the acquired image is moved more downward. In this case, however, the marker M is positioned above the optical axis O of the image acquisition unit  220 . On the other hand, in a case in which the marker M is positioned below the optical axis O of the image acquisition unit  220  (for example, the marker M is moved along the floor), as the marker M is more distant from the main body  200 , the position of the marker M in the acquired image is moved more upward. 
     The marker information acquisition module  231  may extract the marker M from the acquired image to acquire movement information of the marker M. The travel operation setting module  232  may set a travelling direction and/or travel route along which the main body  200  approaches the marker M based on the movement information of the marker M. 
     In the same manner as in the case in which the travel of the main body  200  is controlled based on the position of the marker M indicated in the image as described above, the travel operation setting module  232  may set the travel operation of the main body  200  based on the movement information of the marker M, and the travel control module  233  controls the travel unit  250  according to the set travel direction or along the set travel route, so that the main body  200  may follow the suction device  100 . 
     Referring to  FIG. 6 , the shape of the marker M in the acquired image is changed based on the posture of the marker M in the real space. At this time, the posture of the marker M is changed based on movement patterns of the marker M or a portion at which the marker M is disposed. The movement patterns may include a pitching pattern, a yawing pattern, and a rolling pattern. In a case in which the marker M is properly configured, it is possible to estimate a movement pattern of the marker M or the portion at which the marker M is disposed based on the change in shape of the marker M indicated in the acquired image. 
     For example, it is assumed that a three-dimensional X′Y′Z′ moving Cartesian coordinate system (based on a right hand) is defined on the basis of the marker M, and the marker M is viewed in an −X′ direction as shown in  FIG. 6 . In this case, pitching is a Y′-axis rotation. As shown, the length of the marker M in a Z′ direction seems to be changed according to the pitching. Yawing is a Z′-axis rotation. As shown, the length of the marker M in a Y′ direction seems to be changed. Rolling is an X′-axis rotation. As shown, the marker M seems to be rotated. 
     The marker information acquisition module  231  may further acquire information regarding the change in posture of the marker M in the real space based on the change in shape of the marker M indicated in the acquired image. In this case, the travel operation setting module  232  may set the travel operation of the main body  200  based on the posture change information of the marker M, and the travel control module  233  may control the travel unit  250  to travel the main body  200  according to the set travel operation of the main body  200 . The posture change information will be described in more detail later with reference to  FIGS. 12 and 13 . 
       FIG. 8  is a view illustrating an example of positions of markers.  FIG. 9  is a view illustrating changes in positions of the markers illustrated in  FIG. 8  on images, according to movement of the suction device. Referring to  FIGS. 8 and 9 , the cleaner may include a movement marker Ma disposed in the suction device  100  and a stationary marker Mb disposed in the main body  200  or at a fixed position relative to the main body  200 . It is preferably that the stationary marker Mb is always arranged at a position within the visual field of the image acquisition unit  220  regardless of movement of the suction device  100  or deformation of the hose  300 . Although the movement marker Ma is disposed in the upper pipe  132  of the intake pipe  130  and the stationary marker Mb is disposed in the main body connection section  320  of the hose  300  in the embodiment, the present invention is not necessarily limited thereto. 
     When the suction device  100  is away from the main body  200  in a state in which the stationary marker Mb and the movement marker Ma are located on the acquired image as illustrated in  FIG. 9( a ) , a position H 0  of the stationary marker Mb remains as it is on the acquired image and the movement marker Ma is moved downward (h2&lt;h1) as illustrated in  FIG. 9( b ) . Consequently, a distance between the movement marker Ma and the stationary marker Mb is decreased. 
       FIG. 9( c )  illustrated a state in which the suction device  100  is moved to the right from a position shown in  FIG. 9( a )  in the real space. The marker information acquisition module  231  may acquire information on a distance change between the suction device  100  and the main body  200  and/or a movement direction of the suction device  100  relative to the main body  200  in the real space, based on the displacement of the movement marker Ma or the position relation change between the movement marker Ma and the stationary marker Mb on the above acquired image. 
     In particular, since the position of the movement marker Ma on the acquired image reflects a distance of the movement marker Ma relative to the main body  200  in the real space, the marker information acquisition module  231  may acquire position information of the movement marker Ma on the acquired image and estimate a distance from the main body  200  to the suction device  100  based on the position information. 
     Meanwhile, the suction device  100  is always placed on the floor during cleaning. At this time, however, the intake pipe  130  may be pivoted on the floor. As a result, the movement marker Ma may be moved upward and downward in the acquired image even when the suction device  100  is not actually moved. In this case, therefore, the distance from the main body  200  to the suction device  100  calculated by the marker information acquisition module  231  may be different from a real distance between the main body  200  and the suction device  100 . In a normal situation, however, the user holds the handle  140  at the rear of the suction unit  120  in a state in which the suction port faces the floor of the cleaning zone. For this reason, the height from the floor to the movement marker Ma is almost uniform. Even if the height of the movement marker Ma is varied according to the pivot operation of the intake pipe  130 , a displacement range of the movement t marker Ma is limited. Consequently, it is possible to control the active following operation of the main body  200  with sufficient accuracy. 
     The marker information acquisition module  231  may acquire information regarding the change in distance from the suction device  100  to the main body  200  in the real space based on the change in distance between the movement marker Ma and the stationary marker Mb in the acquired image. In a case in which the distance change information reflects that the suction device  100  becomes distant from the main body  200  (see  FIG. 9( b ) ), the travel operation setting module  232  may set the travel operation of the main body  200  such that the main body  200  is moved forward to the suction device  100 , and the travel control module  233  may control the travel unit  250  according to the set travel operation (forward movement) of the main body  200 . 
     The marker information acquisition module  231  may acquire information regarding the change in direction of the suction device  100  in the real space based on the horizontal displacement of the movement marker Ma relative to the stationary marker Mb in the acquired image. In this case, the travel operation setting module  232  sets the travel direction of the main body  200  such that the main body  200  turns in the changed direction of the suction device  100 , and the travel control module  233  controls the travel unit  250  according to the set travel operation (change in direction) of the main body  200 . 
     Although the information on the position, movement, direction of the suction device  100  in the real space is acquired based on the changes in relative position or positions of the two markers Ma and Mb in the above embodiment described with reference to  FIG. 9 , the present invention is not necessarily limited thereto. The coordinate of each point on the acquired image reflects geometric characteristics at the point in the real space. Therefore, a variety of information on the movement marker Ma in the real space may be acquired based on the relative position or displacement of the movement marker Ma relative to the predetermined fixed point on the acquired image even though only one marker (for instance, the movement marker Ma) is present. 
       FIG. 10  is a view illustrating another example of a position of a marker. Referring to  FIG. 10 , the marker M may be disposed at the suction device  100 . Specifically, the marker M may be disposed at the upper end of the suction device  100 . In this embodiment, the marker M is disposed at the handle  140 . However, the present invention is not limited thereto. For example, the marker M may be disposed at a place exposed to the visual field of the image acquisition unit  220  as frequently as possible (i.e. a region rarely hidden by the user) in consideration of a general movement line of the user during cleaning. In this aspect, the handle  140  is suitable for a position at which the marker M is disposed since the hand of the user holding the handle  140  is exposed to the visual field of the image acquisition unit  220  as the hand of the user is naturally located beside the body of the user. 
       FIG. 11  is a view illustrating configuration examples of a marker. Referring to  FIG. 11 , the marker M may have various identification patterns. Hereinafter, a factor, such as a point, a line, or a plane, constituting the patterns will be defined as a marker component. The marker may have an identity, by which the marker is obviously distinguished from a background. In addition, such an identity may not be affected by lighting around the marker. The marker may have a point, a line, a contour, an area, or a combination thereof as a marker component. 
     The marker M may be brighter than the background in consideration of an identity of the marker M distinguished from the background. In this aspect, the marker M may be classified as a reflective type marker which reflects light around the marker to have an identity of higher luminance than the background or a self emissive type marker which self-emits light. 
     The reflective type marker M may be formed by applying a highly reflective paint to a surface of an object. Alternatively, the reflective type marker M may be formed by attaching a highly reflective material to the surface of the object. The reflective type marker has an advantage in that a position to which the reflective type marker is attached is not limited. In a low illuminance environment, however, the reflective type marker M has a low identity. For this reason, a lighting device for illuminating the marker M may be further provided. The lighting device may be provided at the main body  200  for illuminating ahead of the main body  200 . 
     The self emissive type marker M has a light source configured to electrically emit light. A light emitting diode (LED) or an infrared light source may be used as the light source. The self emissive type marker M has an advantage in that the self emissive type marker M can be identified even in a low illuminance environment. 
       FIG. 11  shows marker components, each of which is constituted by a point having a contour.  FIG. 11( a )  shows a case in which one marker component constitutes one marker,  FIG. 11( b )  shows a case in which two marker components constitute one marker, and  FIG. 11( c )  shows a case in which three marker components, which are arranged in the shape of a triangle, constitute one marker. In the following description, it is assumed that the marker components are points for convenience of description. 
     The change in position or shape of the marker indicated in the acquired image is complicated as a degree of freedom (dof) of the portion at which the marker is disposed is increased. Consequently, it is necessary to consider the degree of freedom of the portion at which the marker is disposed when designing patterns of the marker. 
     In this aspect, since the marker of  FIG. 11( a )  is constituted by one point, the movement of the marker that can be recognized through the acquired image is limited to translation of the marker based on coordinates of the point. 
     Since the marker of  FIG. 11( b )  is constituted by two points, it is possible to further recognize rotation of the marker based on the change in distance between the two points. For example, it is possible to recognize pitching and yawing as previously described with reference to  FIG. 6 . 
     Since the marker of  FIG. 11( c )  is constituted by three points, it is possible to further recognize rolling. In addition, it is also possible to recognize similarity based on the change in area of a triangle constituted by the three points, and therefore it is possible to estimate the change in area of the triangle according to zooming, etc. 
     Since it is possible to recognize higher degree of freedom movement of the marker or the portion at which the marker is disposed as the number of the marker components constituting the marker is increased, the marker may include an appropriate number of marker components based on movement of the marker to be recognized. 
       FIGS. 12 and 13  are views illustrating a change in shape of the marker in the acquired image based on the change in posture of the marker of  FIG. 11( c ) .  FIG. 12( a )  shows that a marker including three marker components (for example, points) M 1 , M 2 , and M 3  as shown in  FIG. 11( c )  is indicated in the acquired image. X, Y, and Z shown in  FIG. 12( a )  constitute a three-dimensional Cartesian coordinate system (based on a right hand). The acquired image corresponds to a YZ plane. In the following description, the marker M is disposed at the handle  140 . 
     In case of which the marker M includes 2 marker components, the marker information acquisition module  231  may acquire rotation information of the marker for an axis orthogonal to an optical axis O of the image acquisition unit  220  in the real space based on a change in vertical distance between two marker components indicated in the acquired image. Especially, when the marker M includes tree marker component M 1 , M 2  and M 3 , the marker information acquisition module  231  may acquire rotation information of the marker for an axis orthogonal to an optical axis O of the image acquisition unit  220  in the real space based on a change in distance from one (M 3 ) of the three marker components indicated in the image to a segment formed by the other two (M 1 , M 2 ) of the tree marker components. 
       FIG. 12( b )  shows a phase of the marker M changed according to pitching (Y-axis rotation) of the handle  140  in the acquired image. It can be seen from  FIG. 12( b )  that the distance from a straight line interconnecting the marker components M 1  and M 2  to the marker component M 3  has been changed from L 2  to L 2 ′. The marker information acquisition module  231  may acquire information regarding a Y-axis rotation angle of the handle  140  based on the change in distance between the line interconnecting the marker components M 1  and M 2  and the marker component M 3 . 
       FIG. 12( c )  shows a phase of the marker M changed according to yawing (Z-axis rotation) of the handle  140  in the acquired image. It can be seen from  FIG. 12( c )  that the distance between the marker components M 1  and M 2  has been changed from L 1  to L 1 ′. The marker information acquisition module  231  may acquire information regarding a Z-axis rotation angle of the handle  140  based on the change in distance between the marker components M 1  and M 2 . 
       FIG. 12( d )  shows a phase of the marker M changed according to rolling (X-axis rotation) of the handle  140  in the acquired image. It can be seen from  FIG. 12( d )  that all of the marker components M 1 , M 2 , and M 3  have been rotated in a state in which relative positions among the marker components M 1 , M 2 , and M 3  are maintained. The marker information acquisition module  231  may acquire information regarding an X-axis rotation angle of the handle  140  based on the rotation angles of the marker components. 
       FIG. 13  shows similarity of a pattern recognized from the marker M including three marker components.  FIG. 13( a )  shows a triangle constituted by the three marker components in the acquired image, and  FIG. 13( b )  shows a state in which the marker M is rolled and thus changed as the marker M becomes distant from the main body  200 . It can be seen from  FIG. 13( b )  that the area of a region, i.e. a triangle, defined by the three marker components in the acquired image has been reduced from A to A′. 
     It is possible to recognize a distance from the main body  200  to the handle  14  based on the position of the marker M and to recognize a direction in which the handle  140  is moved relative to the main body  200  based on the displacement of the marker M in addition to the various movements of the marker M including the three marker components as described above with reference to  FIGS. 12 and 13 . 
     Referring to  FIG. 14 , the marker M may be disposed at the handle  140 , the intake pipe  130 , the suction unit  120 , or the hose  300 . (In the figure, the marker M is shown as a handle type marker, an intake pipe type marker, a suction unit type marker, or a hose type marker.) In addition, the marker M may be attached to a body of the user. For example, the marker M may be provided in the form of an armband (an armband type marker of  FIG. 14 ). 
       FIGS. 15 and 16  are views showing configurations of the marker according to other embodiments of the present invention. Referring to  FIG. 15 , the marker M may include marker components having different colors. In this case, it is possible for the marker information acquisition module  231  to more accurately acquire information regarding the change in phase of the marker M. The marker shown in  FIG. 15( a )  includes one grey marker component M 1  and two black marker components M 2  and M 3 . The marker is configured to have an isosceles triangular structure in which the distance between the grey marker component M 1  and one of the black marker components M 2  and M 3  (the distance between M 1  and M 2  or the distance between M 1  and M 3 ) is different from that between the black marker components M 2  and M 3 . A case in which the marker is rotated about a +X axis by 45 degrees (+X, 45 degree rolling) after the position of the grey marker component M 1  is changed according to pitching of the marker with the result that the marker components M 1 , M 2 , and M 3  are disposed at vertices of an equilateral triangle and a case in which the marker is rotated about a −X axis by 45 degrees (−X, 45 degree rolling) after the position of the grey marker component M 1  is changed according to pitching of the marker with the result that the marker components M 1 , M 2 , and M 3  are disposed at the vertices of the equilateral triangle are compared. As shown in the figure, in both a case in which the marker is rotated about the +X axis by 45 degrees and a case in which the marker is rotated about the −X axis by 45 degrees, the marker components are disposed to have an equilateral triangular structure. Since the marker component M 1  has a color different from that of the marker component M 2  or M 3 , however, it is possible to recognize a direction in which the marker is rotated in both the cases. On the other hand, in a case in which the marker components have the same color, as shown in  FIG. 15( b ) , the shape of the marker after pitching of the marker is identical to or very similar to that of the marker after rolling of the marker with the result that it is difficult for the marker information acquisition module  231  to accurately recognize a direction in which the marker is rolled in both the cases. For this reason, different colors are given to the marker components so as to recognize even the change in posture of the marker, which is difficult to recognize through only the arrangement structure of the marker components. 
     The marker may include marker components having different shapes. Even in this case, a shape characteristic of the marker components is provided in addition to the arrangement structure of the marker components in the same manner as in the case in which the marker components have different colors. Consequently, it is possible to increase information that can be acquired by the marker information acquisition module  231 . 
     A plurality of markers M may be provided. In this case, the markers M may have different features. These features may include a structural feature (for example, the arrangement structure of the marker components) as described above, a difference in shape between the markers or among the marker components, and a difference in color among the marker components. The marker information acquisition module  231  may estimate movement of the respective parts of the cleaner at which the markers are disposed based on information regarding the position of the markers, the movement of the markers, and the change in shape between the markers acquired through the acquired image.  FIG. 16  shows such an example. Specifically,  FIG. 16  shows images acquired in a case in which one of two markers, which are different from each other in terms of the shape and color of the marker components, is disposed at the handle  140 , and the other marker is disposed at the hose  300  (see  FIG. 16( a ) ). The handle  140  and the hose  300  are moved according to the movement of the suction device  100  during cleaning with the result that a positional relationship between the markers is changed from the positional relationship between the markers as shown in an acquired image (b) to the positional relationship between the markers as shown in another acquired image (c). In this case, the marker information acquisition module  231  may recognize the markers based on different features of the markers, and estimate movement aspects of the handle  140  and the hose  300  based on the position of the markers, the movement of the markers, and the change in shape between the markers in the acquired image. 
     In the embodiment described above, the movement of the suction device  100  is recognized based on the position, displacement, and/or posture change of the marker indicated in the acquired image. On the other hand, the marker information acquisition module  231  may be configured to detect the user from the acquired image. A predetermined template may be configured based on characteristics (for example, two feet extending from one trunk) of a human body, and the marker information acquisition module  231  may extract a shape corresponding to the predetermined template (for example, a shape constituted by the characteristics of the human body) from the acquired image to acquire position information of the user. In this case, the travel operation setting module  232  may set the travel operation of the main body  200  such that the main body  200  follows the user based on the position information of the user, and the travel control module  233  may control the travel unit  250  according to the set travel operation of the main body  200 . 
       FIG. 17  is a flowchart illustrating a method of controlling a cleaner according to an embodiment of the present invention.  FIG. 18  is a view for explaining elements considered when a travel direction of a main body is set in step S 30  of  FIG. 17 .  FIG. 19  is a view illustrating an example of a method of setting the travel direction of the main body in consideration of the elements explained with reference to  FIG. 18 . 
     The method of controlling a cleaner according to the embodiment of the present invention includes a step of acquiring an image for a view (for instance, a front image or an image in a travel direction) around a main body  200 , a step of acquiring position information of a suction device  100  in an real space, based on the image, a step of acquiring position information of an obstacle in the real space, based on the image, a step of setting a travel direction such that the main body  200  avoids the obstacle to follow the suction device  100 , based on the position information of the suction device  10  and the position information of the obstacle, and a step in which the main body  200  travels in the set travel direction. Although an example in which the position information of the suction device  100  is determined based on a marker M disposed at the suction device  100  is described below in the embodiment, the present invention is not necessarily limited thereto. For example, the position information of the suction device  100  may also be determined based on characteristics (a silhouette, a color, and the like) of the suction device  100  identified through the acquired image. 
     In more detail, referring to  FIG. 17 , the method of controlling a cleaner according to the embodiment of the present invention may include an image acquisition step S 10 , a marker information and obstacle information acquisition step S 20 , a travel direction setting step S 30 , and a traveling step S 40 . 
     The image acquisition step S 10  is a step of acquiring the image (for instance, the front image or the image in the travel direction) for a view around the main body  200  by an image acquisition unit  220 . As illustrated in  FIG. 3 , a marker M and a pattern P deformed by an obstacle may be identified on the acquired image obtained by the image acquisition unit  220 . As described above, the upper region UA on the acquired image may be used as a region in which the marker M is extracted and the lower region LA may be used as a region in which the pattern P deformed or displaced by the obstacle is extracted. 
     In more detail, a marker information acquisition module  231  may detect a marker M in the upper region UA and acquire marker information from the detected marker M. The marker information may include position information of the marker M (a distance from the main body  200  to the marker M, see  FIG. 4 ), information on a direction in which the marker M is located relative to the main body  200  (see  FIG. 9( c ) ), movement information of the marker M (see  FIG. 4 ), posture change information of the marker M (see  FIGS. 12 and 13 ), and the like. 
     In addition, an obstacle information acquisition module  236  may detect an acquired image, preferably a pattern P in the lower region LA, and acquire obstacle information based on the detected pattern P in step S 20 . The obstacle information may include information such as a position of the obstacle or a distance from the main body  200  to the obstacle in the real space, a direction in which the obstacle is located relative to the main body  200 , a shape of the obstacle, and the number of obstacles. Particularly, the information on the distance from the main body  200  to the obstacle in the real space and/or on the direction in which the obstacle is located relative to the main body  200  is a important factor capable of being considered in setting of the travel direction such that the main body  200  avoids the obstacle to travel in step S 20  described later. 
     The travel direction setting step S 30  is a step of setting the travel direction such that the main body  200  avoids the obstacle while following the suction device  100  based on the marker information and the obstacle information obtained in step S 20 . A travel operation setting module  232  may set a travel direction (or a travel route) in which the main body  200  avoids the obstacle to follow the suction device  100  based on the marker information acquired by the marker information acquisition module  231  and the obstacle information acquired by the information acquisition module  236 . 
     The traveling step S 40  is a step in which the main body  200  travels in the travel direction set in step S 30 . A travel control module  233  may control a travel unit  250  such that the main body  200  is operated (for instance, changes its direction or travels) in the set travel direction. 
     Hereinafter, an example of the method of setting the travel direction (hereinafter, referred to as “avoidance following direction) in which the main body  200  avoids the obstacle to follow the suction device  100  in step S 30  will be described with reference to  FIGS. 18 and 19 . 
     The avoidance following direction may be set based on a position vector V 1  (hereinafter, referred to as “first vector) of a first marker M 1  disposed in the suction device  100  relative to the main body  200  and a position vector V 2  (hereinafter, referred to as “second vector) of the main body  200  relative to the obstacle. Although the first marker M 1  is illustrated to be disposed at the handle  140  in the embodiment, the present invention is not limited thereto. For example, the first marker M 1  may also be disposed at other portions constituting the suction device  100  (for instance, at an intake pipe  130 ). In addition, the first marker M 1  may be realized in various marker forms described with reference to  FIGS. 11 to 13 . The position vector V 1  of the first marker M 1  relative to the main body  200  has a large influence on setting of the avoidance following direction as the distance from the main body  200  to the first marker M 1  is increased. That is, the main body  200  travels toward the first marker M 1  as the magnitude of the first vector V 1  is further increased. 
     The first vector V 1  may be calculated based on the position of the first marker M 1  on the acquired image. As described above, the marker information acquisition module  231  may detect the first marker M 1  in the upper region UA on the acquired image and calculate the position vector V 1  of the first marker M 1  relative to the main body  200  in the real space, based on the position at which the detected first marker M 1  is located on the acquired image. In this case, the direction of the first vector V 1  is directed toward the first marker M 1  from the main body  200 , and the magnitude thereof is proportional to a distance Rt from the main body  200  to the first marker M 1 . 
     The position vector V 2  of the main body  200  relative to the obstacle may be calculated based on the position of the obstacle displayed on the acquired image. As described above, the obstacle information acquisition module  236  may detect the obstacle in the lower region LA on the acquired image and calculate the position vector V 2  of the main body  200  relative to the obstacle in the real space, based on the position at which the detected obstacle is located on the acquired image. In this case, the direction of the second vector V 2  is directed toward the main body  200  from the obstacle, and the magnitude thereof is proportional to a distance Ro from the main body  200  to the obstacle. 
     The travel operation setting module  232  may set an avoidance following direction based on the first and second vectors V 1  and V 2 . When no obstacle is present on a path of a straight line connecting the main body  200  to the first marker M 1 , the main body  200  most preferably travels straight toward the first marker M 1 . However, when an obstacle is present on a travel route of the main body  200 , the main body  200  should avoid the obstacle. Therefore, the travel direction of the main body  200  should be changed according to obstacle circumstances in the cleaning region. Here, whether the main body  200  changes its direction to an extent in order to avoid the obstacle is preferably set in consideration of the distance from the main body  200  to the obstacle. For example, when an obstacle is close to the main body  200 , the main body  200  strikes the obstacle even though slightly traveling so that the direction change of the main body  200  has to be rapidly performed. Accordingly, in this case, the travel direction of the main body  200  has to be changed at a larger angle. On the other hand, even though the direction change of the main body  200  is slightly performed when an obstacle is away from the main body  200  by a significant distance, a possibility of the main body  200  striking the obstacle is gradually decreased when the main body  200  continues to travel in the changed direction. In this case, since the direction change of the main body  200  is relatively slightly performed, the main body  200  may not strike the obstacle. That is, the direction change of the main body  200  should be set in consideration of influence by obstacles (influence increases as obstacles are close to the main body  200 ), and the main body  200  should change its direction by a larger angle as the influence by obstacles increases. 
     The avoidance following direction Vf set according to the above description may be expressed by the following equation: 
     
       
         
           
             
               
                 
                   
                     
                       
                         V 
                         ⁢ 
                         
                             
                         
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                     = 
                     
                       
                         
                           
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                             ⁢ 
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                       k 
                       ⁢ 
                       
                           
                       
                       ⁢ 
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                       ⁢ 
                       
                           
                       
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                     ⁢ 
                     
                         
                     
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     where each of {right arrow over (v1)}, {right arrow over (v2)} is a unit vector having a magnitude of 1. 
     As seen by Equation 1, the avoidance following direction Vf may be determined by a linear combination of the first vector V 1  and the second vector V 2 . Here, each of k1 and k2 is influence when the suction device  100  and the obstacle set the avoidance following direction Vf, k1 is proportional to the distance Rt from the main body  200  to the first marker M 1 , k2 is inversely proportional to the distance Ro from the main body  200  to the obstacle. 
     The travel operation setting module  232  may reset the avoidance following direction Vf while the main body  200  travels. Since the first and second vectors V 1  and V 2  are also changed when the main body  200  is displaced during traveling, the travel operation setting module  232  may accurately control the traveling of the main body  200  by repeatedly resetting the avoidance following direction Vf even when the main body  200  travels. A travel route PT illustrated in  FIG. 19  refers to a movement trajectory of the main body  200  obtained by repeated resetting of the avoidance following direction Vf when the main body  200  travels. 
     Meanwhile, an instant travel direction ingredient V 3  is a travel direction ingredient of the main body  200  which is varied according to the direction of tension acting on the main body  200  from the hose  300 . According to the above-mentioned definition in which the movement of the main body  200  is classified into the active movement and the passive movement, the instant travel direction ingredient V 3  is a direction ingredient generated due to the effect of the passive movement, from among direction ingredients for determining the travel direction of the main body  200 . 
     The cleaner may further include a sensing means (not shown) for sensing the instant travel direction ingredient V 3 . The sensing means may be a sensor for sensing an extension direction of the hose  300  in the real space. The sensor, for example, may include a strain gauge for sensing the magnitude and direction of tension acting from the hose  300 , a gyroscope for sensing a posture change according to deformation of the hose  200 , and the like. 
     In addition, the instant travel direction ingredient V 3  may be sensed through the posture change of the hose  300  displayed on the acquired image. When the hose  300  is assumed to be connected to the front portion of the main body  200 , the image acquisition unit  220  acquires an image capturing a portion of the hose  300  adjacent to the main body  200 . When it is assumed that the suction device  100  moves straight and the main body  200  move straight toward the suction device  100  so that the hose  300  naturally hangs down between the suction device  100  and the main body  200 , geometry characteristics such as a position, a posture, and a shape of the hose  300  displayed on the acquired image in this case substantially exhibit a constant aspect. However, deformation of the hose  300  is observed in the real space and on the acquired image as the travel direction of the suction device  100  is changed. Accordingly, the controller  230  may sense the instant travel direction ingredient V 3 , based on the deformation of the hose  300  observed through the acquired image. 
     A second marker M 2  may be disposed at the hose  300 . In addition, the second marker M 2  may be realized in various marker forms described with reference to  FIGS. 11 to 13 . The marker information acquisition module  231  may determine an instant travel direction ingredient V 3 , based on the position of the second marker M 2  displayed on the acquired image (hereinafter, a vector V 3  being referred to as “third vector”). The second marker M 2  is preferably disposed at a portion adjacent to the main body  200  such that a direction of tension acting on the main body  200  from the hose  300  may be significantly accurately estimated. The direction of the third vector V 3  is a direction of tension acting on the main body  200  from the hose  300 , and the magnitude thereof is proportional to influence of the hose  300  on movement of the main body  200 . Here, the influence of the hose  300  may be determined in consideration of flexibility, length, and the like of the hose  300 . For example, when the suction device  100  is moved, the hose may have a large value of influence as the tension acting on the main body  200  from the hose  300  increases. Unlike this, the influence of the hose  300  may be inversely proportional to flexibility of the hose  300 . 
       FIG. 20  is a view illustrating another example of the method of setting the travel direction of the main body in consideration of the elements explained with reference to  FIG. 18 . Referring to  FIG. 20 , an avoidance following direction Vf′ may be set based on the first vector V 1 , the second vector V 2 , and the third vector V 3 . The avoidance following direction Vf according to the embodiment may be expressed by the following equation: 
     
       
         
           
             
               
                 
                   
                     
                       
                         Vf 
                         ′ 
                       
                       ⇀ 
                     
                     = 
                     
                       
                         
                           
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                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
     where k3 is influence of the hose  300  and each of {right arrow over (v1)}, {right arrow over (v2)}, {right arrow over (v3)} is a unit vector having a magnitude of 1. 
     As seen by Equation 2, the avoidance following direction Vf′ may be determined by a linear combination of the first vector V 1 , the second vector V 2 , and the third vector V 3 . Particularly, in the embodiment, the third vector V 3  is further considered to set the avoidance following direction Vf′, compared to Equation 1. 
     A travel route PT′ illustrated in  FIG. 20  refers to a movement trajectory of the main body  200  obtained by repeated resetting of the avoidance following direction Vf′ when the main body  200  travels. 
       FIG. 21  is a flowchart illustrating a method of controlling a cleaner according to another embodiment of the present invention. Referring to  FIG. 21 , the cleaner may selectively set an active following mode and a passive following mode. A main body  200  actively follows a suction device  100  when the active following mode is set, and passively follows the suction device  100  when the passive following mode is set. The active following mode or the passive following mode may be set and/or released through the manipulation unit  110  by a user, but the present invention is not limited thereto. For example, the active following mode or the passive following mode may be automatically performed based on marker information or obstacle information obtained through an acquired image. 
     A clutch may be operated such that driving force is transferred from a motor to wheels  212  and  213  in a state in which the active following mode is set. A marker information extraction step S 120  is performed in the state in which the active following mode is set (S 110 ). A controller  230  acquires position information of a marker M 1  based on the acquired image. The marker M 1  is detected on the acquired image by a marker information acquisition module  231 , and the position information of the marker M 1  may be acquired in an real space, based on the same. The detected position information of the marker M 1  may be stored in a recording medium (not shown) such as RAM. 
     In particular, the above first vector V 1  described with reference to  FIG. 18  may be calculated in the marker information extraction step S 120 . Furthermore, position information of a marker M 2  disposed at a hose  300  may be further acquired in the marker information extraction step S 120 . 
     When the marker is detected in the marker information extraction step S 120  (“YES” in step S 130 ), an initial obstacle position information extraction step S 140  of extracting position information of an obstacle based on the acquired image may be performed by the controller  230 . The obstacle is detected on the acquired image by an obstacle information acquisition module  236 , and the position information of the obstacle may be acquired in the real space, based on the same. Particularly, the above second vector V 2  described with reference to  FIG. 18  may be calculated in the obstacle information extraction step S 140 . 
     When the detection of the marker M 1  fails in the marker information extraction step S 120  (“NO” in step S 130 ), the active following mode is released (S 230 ) and may be changed to the passive following mode (S 240 ). 
     In a travel direction setting step S 150 , an avoidance following direction in which the main body  200  avoids the obstacle to follow the suction device  100  may be set based on the position information of the marker extracted in the marker information extraction step S 120  and the position information of the obstacle extracted in the initial obstacle position information extraction step S 140 . In the embodiment, a travel operation setting module  232  may set the avoidance following direction Vf or Vf′ according to Equation 1 or 2. 
     A traveling step S 160  is a step of controlling the traveling of the main body  200 , based on the avoidance following direction Vf or Vf′ set in the travel direction setting step S 150 . A travel control module  233  controls a travel unit  250  such that the main body  200  is operated (changes its direction and/or travels) in the avoidance following direction Vf or Vf′. 
     The obstacle may be redetected through the acquired image when the main body  200  travels based on the set avoidance following direction Vf or Vf′ (an obstacle redetection step S 170 ). When the obstacle is detected in the obstacle redetection step S 170  (“YES” in step S 170 ), an obstacle information acquisition module  236  recalculates a position vector V 2 ′ of the main body  200  relative to the obstacle, and reset the avoidance following direction based on the same (S 220 ). In Equation 1 or 2, the second vector V 2  is converted into a newly calculated vector V 2 ′. Of course, the obstacle detected in step S 140  and a new obstacle may also be additionally detected in the obstacle redetection step S 170 . In addition, a position vector V 1 ′ of a first marker M 1  relative to the main body  200  and/or a position vector V 3 ′ of a second marker M 2  relative to the main body  200  may be recalculated in step S 170 . In this case, in Equation 1 or 2, the first and third vectors V 1  and V 3  are converted into newly calculated vectors V 1 ′ and V 3 ′. In the embodiment, the avoidance following direction may be reset based on the vectors V 1 ′ and V 2 ′ (see Equation 1) or the vectors V 1 ′, V 2 ′, and V 3 ′. 
     The main body  200  is operated based on the reset avoidance following direction (S 220 →S 160 ), and a step S 170  is repeated again when the main body  200  travels (S 160 →S 170 ). The position information of the markers M 1  and M 2  may be repeatedly detected and stored during the travel of the main body  200 . A series of steps S 170 , S 220 , and S 160  are preferably performed when the marker M 1  is detected on the acquired image while the main body  200  travels. When the marker M 1  is not detected on the acquired image (“YES” in step S 180 ), the marker M 1  may be redetected based on the position information of the marker M 1  finally stored in the recording medium (a marker redetection step S 190 ). 
     In the marker redetection step S 190 , the travel control module  233  may change the direction of the main body  200  such that a point in the real space corresponding to the recorded position information is displayed on the acquired image, based on the position information of the marker M 1  finally stored in the recording medium. The marker information acquisition module  231  attempts to redetect the marker M 1  on the acquired image in the state in which the direction of the main body  200  is changed. 
     When the marker M 1  is detected again through the acquired image in the marker redetection step S 190  (“YES” in step S 200 , the obstacle is detected and the position information of the obstacle (for instance, V 2 ) is acquired again by the obstacle information acquisition module  236  (S 210 ), the avoidance following direction is reset based on the position information of the marker M 1  (for instance, V 1 ) and the obstacle information (for instance, V 2 ) acquired in step S 200  (S 150 ), and thus the main body  200  travels (S 160 ). In the embodiment, the position information of the marker M 2  (for instance, V 3 ) disposed at the hose  300  may be further acquired in step S 200 . In this case, the resetting of the avoidance following direction (S 150 ) performed after step S 200  is performed according to Equation 2, and the vectors V 1 , V 2 , and V 3  in Equation 2 are converted into those calculated in step S 200  or step S 210 . 
     Meanwhile, when the detection of the marker M 1  fails through the acquired image in step S 190  (“NO” in step S 200 ), the active following mode is released (S 230 ) and the passive following mode may be set (S 240 ). The clutch may be operated such that the transfer of driving force from the motor to the wheels  212  and  213  is released in step S 240 . 
     Meanwhile, considering that the main body  200  travels on a two-dimensional plane, the first, second, and/or third vector(s) V 1 , V 2 , and/or V 3  is(are) enough to be a vector(s) on the two-dimensional plane. However, since the marker information acquisition module  231  and the obstacle information acquisition module  236  also acquire three-dimensional position information of the marker M 1  or M 2  or obstacle, the first, second, and/or third vector(s) V 1 , V 2 , and/or V 3  calculated based on the three-dimensional position information may also be a vector(s) in a three-dimension space. In this case, the avoidance following direction may be determined based on a coordinate of the marker M 1  or M 2  or obstacle on the plane (for instance, on the X-Y plane in  FIG. 13 ) on which the main body  200  travels, from among ingredients of the three-dimensional orthogonal coordinate (X-, Y-, and Z-axes in  FIGS. 12 and 13 ) constituting the respective vectors. 
     In accordance with the cleaner and the method of controlling the same, the following body (or main body) may follow the movable body (or suction device) while avoiding an obstacle even though the obstacle is present in the cleaning region. 
     In addition, since the position of the movable body and the obstacle circumstances are directly recognized based on the image capturing the front of the following body, accuracy of the following body may be significantly improved compared to an indirect following method of using ultrasonic waves. 
     In addition, the following body may follow the movable body while avoiding the obstacle and an optimal direction (or path) in which the following body moves may be set by considering the positions of the movable body and obstacle together. 
     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.