Patent Publication Number: US-10758103-B2

Title: Robot cleaner and controlling method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority under 35 U.S.C. § 119 to Korean Application No. 10-2017-0099753 filed on Aug. 7, 2017, whose entire disclosure is hereby incorporated by reference. 
     BACKGROUND 
     1. Field 
     The present application relates to controlling a robot cleaner and, more particularly, to controlling a robot cleaner having a rotation mop. 
     2. Background 
     The use of robots in the home has gradually expanded. One example of such a household robot is a cleaning robot (also referred to herein as an autonomous cleaner). The cleaning robot is a mobile robot that travels autonomously along a floor within a certain region and may automatically perform cleaning while moving within the region. For example, a robot vacuum cleaner may automatically suction foreign substances, such as dust accumulated on the floor, or may clean the floor using a mopping device. A cleaning robot that includes a rotating mop (also referred to herein as a rotation mop) may move based on the rotation of the mop. In addition, the mop may include a cloth or other cleaning surface, and the robot cleaner may supply water to the rotation mop to dampen the cleaning surface such that the wet cleaning surface contacts and cleans the floor. 
     Korean Patent Registration No. 10-1578879 describes a cleaning mobile robot that moves and cleans a floor surface using a rotation mop. However, this reference does not discuss controlling a water supply rate to the rotation mop of the mobile cleaning robot. If the water supplied to the rotation mop is not appropriately adjusted and the rotation mop receives excess water, the rotation mop may deposit the excess water on the floor to be cleaned, preventing the floor from being properly cleaned and leading to potentially unsafe wet floors. If the rotation mop receives insufficient amounts of water, the rotation mop may contact the floor with a relatively dry cloth such that the floor is not properly cleaned. Furthermore improper adjustment of the water supplied to the rotation mop is may prevent the robot cleaner from moving correctly and efficiently. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will be described in detail with reference to the following drawings in which like reference numerals refer to like elements, and wherein: 
         FIG. 1  is a perspective view of a robot cleaner according to an embodiment of the present application; 
         FIG. 2  is a bottom perspective view of a robot cleaner according to an embodiment of the present application; 
         FIG. 3  is a front view of a robot cleaner according to an embodiment of the present application; 
         FIG. 4  is a view for explaining an internal configuration of a robot cleaner according to an embodiment of the present application; 
         FIG. 5  is a block diagram illustrating a controller of a robot cleaner and a configuration relating to the controller according to an embodiment of the present application; 
         FIG. 6A  is a view for explaining rotation of a spin mop when a robot cleaner travels in a forward direction according to an embodiment of the present application; 
         FIG. 6B  is a view for explaining rotation of a spin mop when a robot cleaner turns round with a large radius according to another embodiment of the present application; 
         FIG. 6C  is a view for explaining rotation of a spin mop when a robot cleaner turns round with a small radius according to another embodiment of the present application; 
         FIG. 7  is a flowchart illustrating a method of measuring and controlling a water content rate of a robot cleaner according to an embodiment of the present application; 
         FIG. 8  is a view for explaining a portion of a spin mop of a robot cleaner in contact with a bottom surface according to an embodiment of the present application; 
         FIG. 9  is a view for explaining a range in which a spin mop is involved in movement of a robot cleaner according to an embodiment of the present application; and 
         FIG. 10  is a flowchart illustrating a method of controlling a water content rate of a robot cleaner according to an embodiment of the present application. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present application are described with reference to the accompanying drawings in detail. The same reference numbers are used throughout the drawings to refer to the same or like parts. Detailed descriptions of well-known functions and structures incorporated herein may be omitted to avoid obscuring the subject matter of the present application. Hereinafter, the present application will be described with reference to the drawings for explaining a control method of a robot cleaner according to embodiments of the present application. 
     Referring to  FIG. 1  to  FIG. 4 , a configuration of a robot cleaner  10  that performs motion by rotation of a mop according to certain embodiments will be briefly described. The robot cleaner  10  according to certain embodiments may include a main body  20  that forms an outer shape of the robot cleaner  10 , a rotation mop that moves the main body  20  along a floor surface, and a drive motor  38  that may drive the rotation of the rotation mop. 
     The rotation mop used in the robot cleaner  10  may be equipped with a mop pad or other surface that contacts a floor and that includes a microfiber or a fabric material. Therefore, during the rotation of the rotation mop  40 , a slip may occur in which the robot cleaner  10  cannot move in comparison with the actual rotation of the rotation mop since the microfiber or a fabric material of the mop pad may generate a relatively small friction force. 
     In certain examples, the rotation mop  40  may include a rolling mop driven along a rotational axis that is substantially parallel to the floor or a spin mop  40  driven along a rotational axis that is substantially perpendicular to the floor. Hereinafter, a slip rate may be calculated for the spin mop  40  (e.g., the rotation mop having the rotational axis that is substantially perpendicular to the floor), and a water content rate (e.g., moisture level) of the spin mop  40  may be measured. 
     As used herein, the slip rate may refer to the degree of a slip that occurs as the spin mop rotates on the floor surface. A slip of rate of zero (‘0’) indicates that the robot cleaner  10  is moving at an ideal rotation speed in which the actual rotation speed corresponds to a desired rotation speed. In addition, the water content rate may refer to a degree to which the spin mop  40  contains water, and a water content rate value of zero (‘0’) corresponds to when relatively no water is contained in the spin mop  40 . The water content rate according to the present embodiment may be set as a ratio of water contained in the spin mop  40  (e.g., a difference between a weight of the wet spin mop  40  and the dry spin mop  40 ) to the weight of the spin mop  40 . The spin mop  40  may, for example, contain water of a same weight as the spin mop or may even contain water of a weight in excess of the weight of the mop pad. 
     The slip rate may vary depending on a water content rate corresponding to a degree that the rotation mop contains water. As the rotation mop holds more water, a friction force for the floor surface may increase due to the influence of water, thereby reducing the slip rate. The relationship between the slip rate and the water content rate may be experimentally determined, and may be stored as data in a storage unit (or memory)  130  described below. In addition, the relationship between the slip rate and the water content rate may vary depending on one or more attributes of the floor, such as a material, smoothness, hardness, etc. of the floor, which may also be experimentally determined and stored in the storage unit  130  as data. 
     The robot cleaner  10  according to the one embodiment may include a water tank  32  that is provided inside the main body  20  to store water, a pump  34  that supplies water stored in the water tank  32  to the spin mop  40 , and a connection hose  36  that forms a connection path connecting the pump  34  and the water tank  32  or connecting the pump  34  and the spin mop  40 . The robot cleaner  10  according to one embodiment may supply the water stored in the water tank  32  to the spin mop  40  using a water supply valve (not shown) and without a separate pump. For example, the water within the water tank  32  may flow downward toward the spin mop  40  due to gravity, and the water supply valve may control this downward flow. In certain examples, the connection hose  36  may be formed as a connection pipe or may be directly connected to the spin mop  40  from the water tank  32  without a separate connection path. 
     The robot cleaner  10  according to one embodiment may include a pair of spin mops  40 . The robot cleaner  10  may travel due to the respective rotations of the pair of spin mops  40 , as described in greater below with respect to  FIGS. 6A-6C . For example, the robot cleaner  10  may control travel by varying the rotational direction and/or rotation speed of each of the pair of spin mops  40 . The robot cleaner  10  according to one embodiment may further include a cleaning module (or cleaning head)  30  which is positioned in front of the spin mop  40  and removes foreign substances from a floor surface before the spin mop  40  wipes the floor surface with a damp cloth. 
     Referring to  FIG. 3 , the robot cleaner  10  according to one embodiment may be arranged in such a manner that the spin mop  40  is inclined by a certain angle θ relative the floor surface. In order to facilitate the movement of the robot cleaner  10 , the spin mops  40  may be arranged in such a manner that the entire surface of each of the spin mop  40  do not evenly contact the floor surface but, instead, is tilted by a certain angle θ so that a certain portion of the spin mop is mainly in contact with the floor surface. In addition, the spin mop  40  may be positioned in such a manner that the most friction force is generated at a certain portion of the spin mop  40  even if the entire surface of the spin mop  40  is in contact with the floor surface. For example, the spin mop  40  may be positioned such that the portion of the spin mop  40  supports a relatively larger portion of a weight of the robot cleaner  10 . 
       FIG. 5  is a block diagram illustrating a controller of a robot cleaner and a configuration relating to the controller according to an embodiment of the present application. The robot cleaner  10  according to one embodiment may further include a motion detection unit (or motion sensor)  110  that senses a motion of the robot cleaner  10  according to a reference motion of the main body  20  when the spin mop  40  rotates. The motion detection unit  110  may further include a gyroscopic (or gyro) sensor  112  that detects the rotation speed of the robot  10  or an acceleration sensor  114  that senses an acceleration of the robot cleaner  10 . In addition, the motion detection unit  110  may include or may communicate with an encoder (not shown) that senses a moving distance of the robot cleaner  10 . 
     A reference motion in the present embodiment may be a motion when driving the spin mop  40  of the robot cleaner  10 . The slip rate of the robot cleaner  10  may be calculated by using at least one of the gyro sensor  112  or the acceleration sensor  114  when the spin mop  40  of the robot cleaner  10  is driven. The motion may be divided into a static motion in which the robot cleaner  10  rotates in place and a moving motion in which the robot cleaner  10  performs a straight movement or a turning movement. 
     The gyro sensor  112  may be a sensor that senses the rotation of the robot cleaner  10 . In one embodiment, the gyro sensor  112  may measure, as the reference motion, an actual rotation speed of the robot cleaner  10  when the robot cleaner  10  rotates in place or turns to move in a curved path. 
     The acceleration sensor  114  may be a sensor that senses a straight movement acceleration of the robot cleaner  10 . In one embodiment, in the acceleration sensor  114  may measure, as the reference motion, an actual speed of the robot cleaner  10  when the robot cleaner  10  moves straight. The encoder may include a sensor that senses a moving distance of the robot cleaner  10  and may measure the actual speed of the robot cleaner  10  when the robot cleaner  10  moves in the reference motion. 
     The robot cleaner  10  according to one embodiment may further include a floor detection unit (or floor sensor)  120  that detects information regarding a floor surface on which the robot cleaner moves. For example, the floor detection unit  120  may detect information related to classifying a type of material of the floor surface on which the robot cleaner  10  moves as marble or other hard floor, carpet, or the like. 
     The floor detection unit  120  may determine an attribute of the material of the floor based on sensing a current provided to the drive motor  38 . For example, the floor detection unit  120  may determine a relative smoothness and hardness of the floor based on an efficiency at which the drive motor  38  moves the robot cleaner  10 . In addition, the floor detection unit  120  may include a light source and an image sensor or camera, and the image sensor may obtain image information corresponding to a reflection of light from the light source. The obtained images may be compared or otherwise processed to determine the material of the floor. 
     The robot cleaner  10  may include a cliff sensor  120   a ,  120   b  (see  FIG. 2 ) that sense a presence or absence of a cliff on the floor in the cleaning area. The robot cleaner  10  according to the present embodiment may include a plurality of cliff sensors  120   a ,  120   b . The cliff sensors  120   a ,  120   b  according to the present embodiment may be disposed in a front portion of the robot cleaner  10 . 
     The cliff sensor  120   a ,  120   b  according to one embodiment may include at least one light emitting element (or light emitter) and at least one light receiving element (or light sensor). The cliff sensor  120   a ,  120   b  may be used as the floor detection unit  120 . For example, a controller  100  may determine the material of the floor based on the amount of reflected light which is outputted from the light emitting element, reflected from the floor, and subsequently received by the light receiving element. 
     For example, when an amount of the reflected light is equal to or greater than a certain value, the controller  100  may determine that the floor as a hard floor (e.g., includes wood, stone, or tile), and if the light amount of the reflected light is smaller than the certain value, the controller may determine the floor material includes carpeting. In detail, the floor may have a different degree of reflection of light depending on the material, such that a hard floor may reflect a relatively large amount of light, and the carpeted floor may reflect a relatively small amount of light. Therefore, the controller  100  may determine the material of the floor based on the amount of a light that is output from the light emitting element, reflected from the floor, and received by the light receiving element. 
     As previously described, if the amount of the detected reflected light is equal to or greater than a certain reference value, the controller  100  may determine that the floor is a hard floor surface, and if the light amount of the reflected light is smaller than the certain reference value, the controller  100  may determine that the floor includes a carpet. In one example, the reference value that is that is used to determine the material of the floor may be set based on a distance between the floor and the cliff sensor  120   a ,  120   b , such as setting different reference values for different distances between the floor and the cliff sensor  120   a ,  120   b . For example, a first reference value may be used when the distance from the floor detected by the cliff sensor  120   a  and  120   b  is 25 mm or less, and a second, different reference value may be used when the distance is 35 mm or more. 
     When the distance from the floor is relatively small (e.g., less than a threshold distance), a significant difference in the amount of reflected light from different floor types (e.g., a hard floor or a carpeted floor) may not be detectable. Therefore, in an example in which the distance from the floor detected by the cliff sensor  120   a ,  120   b  is a certain distance or more, the controller may use the detected distance to determine the reference value used to identify the floor material. For example, the controller  100  may determine the material of the floor based on comparing the amount of reflected light which is detected to a certain threshold value when the distance from the floor to the cliff sensors  120   a ,  120   b  is 20 mm or more. 
     According to an embodiment of the present application, the controller  100  may determine that the floor surface includes carpeting based on the amount of reflected light detected by the cliff sensor  120   a ,  120   b , and the floor state may be further determined and/or verified using the amount of reflected light detected by the cliff sensor  120   a ,  120   b  and the current value of a load to the driving motor  38 . The drive motor  38  may use more power to rotate the spinning mop  40  when the robot cleaner  10  is positioned on a carpeted floor. Thus, the controller  100  may determine that the robot cleaner  10  is positioned on a carpeted floor when the motor load is greater than or equal to a threshold voltage value, and may determine that the robot cleaner  10  is positioned on a hard floor when the motor load is less than the threshold voltage value. In this way, the floor state may be more accurately identified. 
     The robot cleaner  10  according to an embodiment may include a controller  100  which measures the slip rate of the spin mop  40  based on the information sensed by the motion detection unit  110 , measures the water content rate based on the floor information by the floor detection unit  120  and the slip rate, and controls the rotation speed of the drive motor  38  and the water supply amount outputted by the pump  34  (or released through a water control valve). The robot cleaner  10  according to an embodiment may further include a storage unit (or memory  130 ) that stores data of a correlation between a slip rate measured with respect to a reference motion and a water content rate identifying the degree to which the rotation mop contains water. Optionally, the storage unit  130  of the robot cleaner  10  may further store data related to a specific correlation between the measured slip rate, information of the floor material, and water content rate. For example, the storage unit  130  may store data identifying floor materials and water content rates associated with different measured slip rates. 
     The storage unit  130  may also store experimental data experimentally identifying the correlation between the ideal rotation speed of the robot cleaner  10  according to the rotation amount of the spin mop  40  and the actual rotation speed of the robot cleaner  10  measured by the gyro sensor  112 . The storage unit  130  may also store experimentally determined data identifying the correlation between the actual straight moving speed (e.g., as measured by the acceleration sensor  114 ) and the ideal straight moving speed of the robot cleaner  10  even when the robot cleaner  10  performs a straight moving acceleration movement. 
     The controller  100  may measure the slip rate of the spin mop based on the information sensed by the motion detection unit  110 . The controller  100  may measure the slip rate of the spin mop based on the actual speed of the main body  20  measured by the motion detection unit  110  and the ideal speed of the main body  20  estimated according to the driving of the drive motor  38 , such as estimating the ideal speed based on the driving power supplied to the drive motor  38 . The controller  100  may measure the slip rate of the robot cleaner  10  based on the information sensed by the motion detection unit  110  when the robot cleaner  10  performs a reference motion. Specifically, when the robot cleaner  10  turns, the controller  100  may compare an ideal rotation speed of the robot cleaner  10  according to the rotation amount of the spin mop  40  with an actual rotation speed of the robot cleaner  10  measured by the gyro sensor  112  to calculate a slip rate. 
     When the robot cleaner  10  moves straight, the controller  100  may compare the ideal straight moving acceleration of the robot cleaner  10  according to the rotation amount of the spin mop  40  with the actual acceleration of the robot cleaner  10  measured by the acceleration sensor  114 , and calculate the slip rate. In addition, it is also possible that when the robot cleaner  10  moves, the controller  100  compares the ideal speed of the robot cleaner  10  according to the rotation of the spin mop  40  with the speed of the robot cleaner  10  measured by the encoder (not shown) to calculate the slip rate. 
     Similar to the above-described method of measuring the slip rate, a method of experimentally determining a correlation between the ideal rotation speed of the robot cleaner  10  according to the rotation amount of the spin mop  40  and the actual rotation speed of the robot cleaner  10  measured by the gyro sensor  112  and estimating a slip rate by using a correlation table, or a method of calculating a slip rate through a slip rate formula by using the ideal rotation speed of the robot cleaner  10  and the measured rotation speed of the robot cleaner  10  may be used. Similarly, even when the robot cleaner  10  performs a relatively straight direction acceleration movement, a method of experimentally defining a correlation between the actual straight moving speed and the ideal straight moving speed of the robot cleaner  10  and estimating a slip rate by using a correlation table, or a method of calculating a slip rate through a slip rate formula by using the ideal straight moving speed of the robot cleaner  10  and the measured straight moving speed of the robot cleaner  10  may be used. 
     In one example, the controller  100  may determine the water content rate of the robot cleaner  10  based on the material of the floor surface determined by the floor detection unit  120  and the slip rate of the robot cleaner  10  measured in the reference motion. The controller  100  may determine the water content rate based on stored data related to a correlation between the slip rate and the water content rate according to the material of the floor surface determined by the floor detection unit  120 . 
     Typically, as the water content rate becomes higher, a speed closer to the ideal moving speed of the robot cleaner  10  in which no slip occurs may be achieved because the spinning mop  40 , when wet, may apply a relatively larger friction force to the floor when rotating. A specific relationship between the water content rate and the slip rate may vary depending on the floor material, which can be determined experimentally. 
     The robot cleaner  10  according to the present embodiment may further include an input unit (or user interface)  140  that receives an input associated with a user&#39;s command. For example, a user may set the traveling method of the robot cleaner  10  or the water content rate of the spin mop  40 , through the input unit  140 . The input unit  140  may include, for example, a button, keypad, a touch screen, etc. 
       FIGS. 6A-6C  are views related to the motion of the robot cleaner  10  according to an embodiment of the present application. Hereinafter, with reference to  FIGS. 6A-6C , a method of determining a slip rate according to the traveling of the robot cleaner due to the rotation of the spin mop and the movement of the robot cleaner will be described. 
     The robot cleaner  10  according to an embodiment may include a pair of spin mops  40 , and may move by rotating the pair of spin mops  40 . The robot cleaner  10  may control the traveling of the robot cleaner  10 , for example, by varying the rotation direction or rotation speed of each of the pair of spin mops  40 . 
     Referring to  FIG. 6A , the straight movement of the robot cleaner  10  may be performed by rotating each of the pair of spin mops  40  in opposite directions. In this case, the rotation speed of each of the pair of spin mops  40  may be substantially the same, but the rotation direction may be different. The robot cleaner  10  may perform a forward movement or a backward movement by changing the rotation direction of both spin mops  40 . 
     Referring to  FIGS. 6B and 6C , the robot cleaner  10  may turn when each of the pair of spin mops  40  rotates in the same direction. The robot cleaner  10  may rotate in place or turn along a round path to move curvedly by varying the rotation speed of each of the pair of spin mop  40 . The radius of turning round may be adjusted by varying the rotation speed ratio of each of the pair of spin mops  40  of the robot cleaner  10 . 
       FIG. 7  is a flowchart illustrating a method of measuring and controlling a water content rate of a robot cleaner  10  according to an embodiment of the present application.  FIG. 8  is a view for explaining a portion of a spin mop  40  of a robot cleaner  10  in contact with a bottom surface according to an embodiment of the present application.  FIG. 9  is a view for explaining a range in which a spin mop  40  is involved in movement of a robot cleaner  10  according to an embodiment of the present application.  FIG. 10  is a flowchart illustrating a method of controlling a water content rate of a robot cleaner  10  according to an embodiment of the present application. 
     Hereinafter, a method of controlling the water content rate of the robot cleaner  10  according to the present embodiment will be described with reference to  FIG. 7  to  FIG. 10 . The robot cleaner  10  according to one embodiment may detect floor information (S 100 ). The robot cleaner  10  according to the present embodiment may detect the material of the floor surface on which the robot cleaner  10  moves by the floor detection unit  120 . 
     The robot cleaner  10  according to one embodiment may perform a reference motion (S 200 ). The reference motion refers to a motion related to driving the spin mop  40  of the robot cleaner  10  so as to calculate the slip rate of the robot cleaner  10  by using the gyro sensor  112  and/or the acceleration sensor  114 . The motion may include at least one of a static motion in which the robot cleaner  10  rotates in place or a moving motion in which the robot cleaner  10  performs a straight movement or a curved path movement. In the step S 200  of performing the reference motion, the robot cleaner  10  may travel in a curved path or may travel in a substantially straight path. 
     When performing the reference motion in step S 200  that includes a turning motion, the robot cleaner  10  according to one embodiment may rotate the pair of spin mops  40  in the same direction, so that the robot cleaner  10  can turn. The robot cleaner  10  may rotate in place or may turn the robot cleaner  10  along a curved path by varying the rotation speed of each of the pair of spin mops  40 . 
     When performing the reference motion in step S 200  that includes a straight moving acceleration, the robot cleaner  10  according to one embodiment may accelerate the robot cleaner  10  by changing the actual rotation speed of one or more of the spin mops  40 . For example, the robot cleaner  10  may accelerate the robot cleaner  10  by differentiating the rotation direction of each of the pair of spin mops  40 , and by changing the driving speed of the spin mop  40 . 
     Thereafter, a slip rate of the robot cleaner  10  may be measured (S 300 ). The controller  100  may measure the slip rate based on the actual speed of the main body  20  measured by the motion detection unit  110  in the reference motion and the ideal speed of the main body  20  estimated according to the driving of the drive motor  38 . When measuring the slip rate in step S 300 , the motion of the main body  20  of the robot cleaner  10  and the motion of the rotation mop may be measured, and the slip rate of the robot cleaner  10  may be measured based on the motion measurement information. 
     When the robot cleaner  10  turns, the controller  100  may measure the slip rate by using the actual rotation speed measured by the gyro sensor  112  and an estimated rotation speed of the robot cleaner  10  corresponding to the rotation of the spin mop  40 . When the robot cleaner  10  performs a straight acceleration movement, the controller  100  may measure the slip rate by using the actual moving speed of the robot cleaner measured by the acceleration sensor  114  and an estimated moving speed of the robot cleaner corresponding to the rotation of the spin mop  40 . 
     The slip rate may be obtained by using a method of experimentally defining a correlation between the ideal moving speed of the robot cleaner  10  according to the rotation amount of the spin mop  40  and the actual moving speed of the robot cleaner  10  measured by the motion detection unit  110  and estimating a slip rate by using a correlation table, or a method of calculating a slip rate by applying the ideal moving speed of the robot cleaner  10  and the measured moving speed of the robot cleaner  10  to a slip rate formula. Hereinafter, a method of calculating the slip rate by using the slip rate formula will be described. First, the radius and speed of the spin mop  40  involved in the movement of the robot cleaner  10  will be described, and a method of measuring a corresponding slip rate will be described. 
     The rotation speed of the robot cleaner  10  may depend on the radius R of the spin mop  40  and the rotation speed of each spin mop  40 . As shown in  FIG. 8 , when a portion in which the spin mop  40  is inclined to the floor surface forms a set angle  81  with respect to a virtual line connecting the centers of the pair of spin mops  40 , the radius R′ of the spin mop  40  involved in the actual movement may be obtained as shown in the following equation 1 with reference to  FIG. 9 .
 
 R′=R *cos θ1  &lt;Equation 1&gt;
 
     Since a linear speed V 1  at a portion where the spin mop  40  is in contact with the floor surface is formed at a portion having a set angle θ 1  for the actual traveling of the spin mop  40 , a linear speed V 2  for the actual traveling direction may be expressed as shown in the following equation 2,
 
 V 2= V 1*cos θ1  &lt;Equation 2&gt;
 
Referring to  FIG. 9 , a portion perpendicular to the linear speed V 2  with respect to the actual traveling direction may be a radius R′ of the spin mop  40  involved in the actual movement.
 
     Hereinafter, an embodiment in which the slip rate of the robot cleaner  10  is determined depending on whether the robot cleaner  10  turns or moves straight will be described. The slip rate Sr 1  associated with the robot cleaner  10  turning may be calculated based on the following equation 3 by using the ideal rotation speed Rf of the robot cleaner  10  according to the rotation of each of the pair of spin mops  40  and the actual rotation speed Rr measured by the gyro sensor  112 .
 
 Sr 1=( Rf−Rr )/ Rf* 100  &lt;Equation 3&gt;
 
     The slip ratio Sr 2  associated with the robot cleaner  10  moving substantially straight may be obtained by using the acceleration sensor  114 . For example, the robot cleaner  10  may compare the ideal speed of the robot cleaner  10  according to the rotation of each of the pair of spin mops  40  with the actual speed of the robot cleaner  10  measured by the acceleration sensor  114 , and may calculate the slip rate. 
     The slip rate Sr 2  in the case where the robot cleaner  10  accelerates or decelerate to move may be calculated by the following equation 4 by using the ideal speed Vf of the robot cleaner  10  according to the rotation of each of the pair of spin mops  40  and the actual speed Vr of the robot cleaner  10  measured by the acceleration sensor  114 . In the straight movement of the robot cleaner  10 , the ideal speed Vf of the robot cleaner may be expressed as the linear speed V 2  of the spin mop calculated in the above equation 2. The speed Vr of the robot cleaner  10  measured by the acceleration sensor  114  may be obtained by integrating the acceleration value measured by the acceleration sensor  114 .
 
 Sr 2=( Vf−Vr )/ Vf* 100  &lt;Formula 4&gt;
 
     In addition, it is also possible to obtain the slip rate by calculating the ratio of the ideal rotation number of the spin mop  40  and the actual rotation number of the spin mop  40  operated by the drive motor  38 , in the range of the changed rotation angle determined by the gyro sensor  112 . 
     Continuing with  FIG. 7 , the water content rate of the robot cleaner  10  may be measured (S 400 ). The controller  100  may measure the water content rate according to the degree of slip rate, based on the data stored in the storage unit  130 . The controller  100  may measure the water content rate based on the information on the floor material and the measured slip rate. The controller  100  may measure the water content rate according to the measured slip rate, based on the data on the correlation between the slip rate and the water content rate according to the type of floor detected in the floor information sensing step S 100 . 
     Thereafter, the water content rate of the robot cleaner may be controlled based on the measured water content rate (S 500 ). The robot cleaner according to the present embodiment may control the amount of water supplied to the rotation mop of the robot cleaner  10  based on the slip rate measured by performing the reference motion. That is, the water content rate measurement according to one embodiment may be determined based on the slip rate measurement, and the data related to the correlation between the slip rate and the water content rate, and the water content rate of the robot cleaner may be controlled according to the slip rate measurement. 
     Referring to  FIG. 10 , the step S 500  of controlling the water content rate of the robot cleaner  10  may include a step S 510  of comparing a set water content rate with an actual water content rate measured in the above process. The set water content rate may be a water content rate which is previously set before measuring the slip rate. The set water content rate may be set by user&#39;s input (e.g., via the input unit  140 ), or may be set to an experimentally determined water content rate for mopping with a damp cloth. The set water content rate may be changed by the user&#39;s input. The actual water content may be an actual water content rate of the robot cleaner and may be calculated based the floor material and the slip rate. 
     When the actual water content is less than the set water content, the controller  100  may operate a pump (S 530 ) to supply the water stored in a water tank  32  to the spin mop  40 . When the robot cleaner omits the pump  34  and includes, instead, a water control valve to regulate a flow of water to the spin mop  40 , step S 530  may include the controller  100  operating the water control valve to supply the water stored in a water tank  32  to the spin mop  40 . Thereafter, the controller  100  may operate the drive motor to move the robot cleaner (S 535 ), and mop the floor with a damp cloth associated with the spin mop  40 . 
     When the actual water content rate is greater than the set water content rate, the controller  100  may stop the operation of the pump  34  (S 520 ), and operate the drive motor to move the robot cleaner  10  (S 525 ). Similarly, when the robot cleaner  10  includes a water control valve to regulate a flow of water to the spin mop  40 , step S 520  may include the controller  100  controlling the water control valve to reduce or stop a supply of the water stored in the water tank  34  to the spin mop  40 . Since the robot cleaner  10  mops the floor with a damp cloth through the rotation mop during the movement process, the water content rate of the rotation mop may be reduced during operation of the rotation mop. The controller  100  may stop the pump operation and move the robot cleaner until the desired set water content rate is measured to be less than the actual water content. Thereafter, when the actual water content rate is less than the set water content rate, the controller  100  may operate the pump to move the robot cleaner  10 . 
     According to the robot cleaner  10  of the present application, one or more of the following aspects may be obtained. First, the control method of the robot cleaner  10  according to the present application may control the amount of water supplied to the rotation mop by determining the moving motion of the robot cleaner, without a separate water content rate sensor. Second, the control method of the robot cleaner  10  according to the present application can measure and control the water content rate of the rotation mop, and supply an appropriate amount of water to the rotation mop to clean the floor. Third, the robot cleaner  10  according to the present application can determine the slip rate of the robot cleaner  10  according to the floor material, measure the water content rate, supply an appropriate amount of water to the rotation mop, and effectively mop the floor with a damp cloth according to the floor material. 
     Similarly, an aspect of the present application provides a method of controlling a robot cleaner in which a water content rate of a rotation mop of the robot cleaner is measured without having a water content rate detection sensor. The present application further provides a method of controlling a robot cleaner  10  based on detecting a movement of the robot cleaner and measuring a water content rate of a rotation mop of the robot cleaner. 
     In accordance with an aspect of the present application, a robot cleaner may include: a main body which forms an external shape; a water tank which stores water; a rotation mop which is in contact with a floor while rotating and moves the main body; a drive motor which rotates the rotation mop; a motion detection unit which measures a reference motion of the main body when the rotation mop rotates; and a controller which measures a slip rate based on an actual speed of the main body measured by the motion detection unit in the reference motion and an ideal speed of the main body estimated according to driving of the drive motor, and controls an amount of water supplied to the rotation mop. 
     The robot cleaner may further include a floor detection unit which senses information of a floor on which the rotation mop moves. The controller adjusts an amount of water supplied to the rotation mop based on the information of the floor detected by the floor detection unit and the slip rate measured in the reference motion. A speed measured by the motion detection unit includes at least one of a rotation speed of the main body and a straight moving speed of the main body. The motion detection unit is a gyro sensor for measuring a rotation speed of the main body according to rotation of the rotation mop. The controller measures the slip ratio by using an ideal rotation speed of the main body according to the rotation of the rotation mop and an actual rotation speed of the main body measured by the gyro sensor. 
     The robot cleaner may further include a storage memory unit for storing data related to a correlation between a slip rate measured in the reference motion and a water content rate which is a degree to which the rotation mop contains water. The controller determines an actual water content rate for the measured slip rate from the storage unit, and compares the actual water content rate with a set water content rate to adjust an amount of water supplied to the rotation mop. 
     In accordance with another aspect of the present application, a method of controlling a robot cleaner may include: (a) performing a reference motion by a robot cleaner which moves a main body by using a rotation mop; (b) measuring a motion of the main body of the robot cleaner and a motion of the rotation mop; (c) measuring a slip rate of the robot cleaner based on information measured in the step (b); and (d) controlling an amount of water supplied to the rotation mop, based on the slip rate measured in the step (c). 
     The method of controlling a robot cleaner, before the step (d), may further include a step (e) of determining material information of a floor on which the robot cleaner moves. The step (d) may include controlling the amount of water supplied to the rotation mop in consideration of floor material information sensed in the step (e) and the slip rate sensed in the step (c). 
     The step (d) of controlling an amount of water supplied to the rotation mop may include steps of (d1) measuring a water content rate of the robot cleaner, based on the slip rate measured in the step (c); (d2) comparing a set water content rate with an actual water content rate measured in the step (d1); and (d3) supplying water to the spin mop and driving the spin mop, when the set water content rate is equal to or greater than the actual water content rate. 
     In another example, the step (d) of controlling an amount of water supplied to the rotation mop may include steps of (d1′) measuring a water content rate of the robot cleaner, based on the slip rate measured in the step (c); (d2′) comparing a set water content rate with an actual water content rate measured in the step (d1′); and (d3′) driving the rotation mop without supplying water to the rotation mop, when the set water content rate is smaller than the actual water content rate. 
     Hereinabove, although the present application has been described with reference to exemplary embodiments and the accompanying drawings, the present application is not limited thereto, but may be variously modified and altered by those skilled in the art to which the present application pertains without departing from the spirit and scope of the present application claimed in the following claims. 
     It will be understood that when an element or layer is referred to as being “on” another element or layer, the element or layer can be directly on another element or layer or intervening elements or layers. In contrast, when an element is referred to as being “directly on” another element or layer, there are no intervening elements or layers present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that, although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section could be termed a second element, component, region, layer or section without departing from the teachings of the present application. 
     Spatially relative terms, such as “lower”, “upper” and the like, may be used herein for ease of description to describe the relationship of one element or feature to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation, in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “lower” relative to other elements or features would then be oriented “upper” relative the other elements or features. Thus, the exemplary term “lower” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Embodiments of the disclosure are described herein with reference to cross-section illustrations that are schematic illustrations of idealized embodiments (and intermediate structures) of the disclosure. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the disclosure should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the application. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.