Patent Publication Number: US-8543241-B2

Title: Method, medium, and system estimating pose of mobile robots

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Korean Patent Application No. 10-2006-0088726 filed on Sep. 13, 2006 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field of the Invention 
     One or more embodiments of the present invention relate to a mobile robot, and more particularly, to a method, medium, and system reducing the computational complexity of a Simultaneous Localization And Mapping (SLAM) algorithm applied to mobile robots. 
     2. Description of the Related Art 
     Robots or robotic devices were originally developed for industrial purposes and have been widely used for factory automation and for performing various functions in hazardous or extreme environments. Nowadays, robotics has evolved from the field of state-of-the-art space robots to the field of human-friendly home robots. In addition, robots have been proposed for replacing conventional medical equipment by being injected into the human body and repairing tissue that might not have been otherwise repaired. Thus, with recent achievements in the robotics field, robotics has moved into the limelight of the world in anticipation that robotics, as one of the most advanced fields of science, will increasingly replace other fields of science, such as Internet-based information technology and biotechnology. 
     In recent years, home mobile robots such as cleaning robots have been widely commercialized, so mobile robots are becoming more and more commonplace in people&#39;s daily lives. 
     In this regard, in robotics, localization techniques refer to processes by which a robot determines its position with respect to its surroundings. For example, in a “pure” localization system, the robot is provided with a map of its surroundings. Such “pure” localization systems are disadvantageous because generating a map via manual techniques is a relatively difficult, labor-intensive, and specialized task. Moreover, many environments are not static. For example, the rearranging of furniture in a room can render a preexisting map unusable. As a result, maps in pure localization systems are subject to relatively frequent and costly updates so that the map accurately represents its surroundings. 
     Therefore, it is desirable to develop localization techniques that are capable of planning the path of movement of a mobile robot and dynamically creating a map by determining the absolute position of the mobile robot based on a variation in the relative position of the mobile robot with respect to the surroundings of the mobile robot and one or more feature points of the surroundings of the mobile robot, even when no spatial information regarding the surroundings of the mobile robot is provided. 
     In the meantime, one of the most widely used techniques for determining the absolute position of a mobile robot based on the surroundings of the mobile robot and the relative position of the mobile robot with respect to the surroundings of the mobile robot is Simultaneous Localization And Mapping (SLAM). According to SLAM, even when a mobile robot does not have any spatial information (i.e., map information) regarding its surroundings, it still can extract one or more feature points with reference to distance data obtained using ultrasound waves, laser beams, or image data obtained using a camera, for example, and configure map information based on the extracted feature point. Then, the mobile robot can determine its position based on the configured map information. 
     Kalman filters are generally used to determine the pose of a mobile robot based on one or more feature points. However, pose estimation methods that involve the use of Kalman filters can be effective only when the distribution of estimated pose errors follow a Gaussian distribution. As part of the effort to address this problem, it has been suggested to use a pose estimation technique that extracts a number of samples regarding position estimates and determines an optimum pose of an object using the probability of each of the extracted samples even when the distribution of estimated pose errors does not follow a Gaussian distribution, i.e., a particle filter technique. 
     An example of such a particle filter technique is set forth in U.S. Pat. No. 7,015,831, which discusses incrementally updating the pose of a mobile device using visual SLAM techniques, and particularly, to a SLAM technique using a particle filter. To implement this technique, U.S. Pat. No. 7,015,831 sets forth using a plurality of sensors (i.e., odometer and a camera) using two particle sets. 
     However, such a SLAM technique using a particle filter generally requires a considerable number of samples, thereby increasing the amount of computation and making it difficult for a mobile robot to determine the pose of the mobile robot when the mobile robot moves from one place to another. Therefore, a particle filter-based SLAM technique capable of reducing the amount of computation and thus enabling real-time determination of the pose of a mobile robot is desired. 
     SUMMARY 
     One or more embodiments of the present invention provide a method, medium, and system performing real-time localization and mapping operations by reducing computational complexity for mobile robots that use a particle filter-based Simultaneous Localization And Mapping (SLAM) technique. 
     Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention. 
     To achieve the above and/or other aspects and advantages, embodiments of the present invention include a movement system, the system including a particle filter unit to determine poses and weights of current particles by applying a detected pose variation to previously identified particles, with the detected pose variation being detected by a sensor to detect a pose variation in a pose of a mobile element, and an evolution unit to update the determined poses and weights of the current particles by applying an evolution algorithm to the determined poses and weights of the current particles to estimate a current pose of the mobile element. 
     To achieve the above and/or other aspects and advantages, embodiments of the present invention include a mobile movement controlling method, the method including determining poses and weights of current particles by applying a detected pose variation to previously identified particles, with the detected pose variation being a pose variation in a pose of a mobile element, and updating and outputting the determined poses and weights of the current particles by applying an evolution algorithm to the determined poses and weights of the current particles to estimate a current pose of the mobile robot. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  illustrates a mobile robot system, according to an embodiment of the present invention; 
         FIG. 2  illustrates a pose estimation unit, such as that illustrated in  FIG. 1 , according to an embodiment of the present invention; 
         FIG. 3  illustrates a calculation of gray gradient vectors of feature points, according to an embodiment of the present invention; 
         FIG. 4  illustrates a probability distribution regarding a pose of a mobile robot, such as mobile robot  100  of  FIG. 1 , that moves from a start point S to an end point E; 
         FIG. 5  illustrates differences between an observed pose and a plurality of estimated particle poses; 
         FIG. 6  is a diagram for explaining a crossover algorithm; 
         FIG. 7  is a diagram for explaining a mutation algorithm; 
         FIG. 8A  illustrates localization and mapping results obtained using a conventional particle filter method; and 
         FIG. 8B  illustrates localization and mapping results obtained using a particle filter method, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. In this regard, embodiments of the present invention may, be embodied in many different forms and should not be construed as being limited to embodiments set forth herein. Accordingly, below, embodiments are described below to explain the present invention by referring to the figures. 
     In order to address problems with conventional Kalman filter-based Simultaneous Localization And Mapping (SLAM) techniques, including the aforementioned problem of failing to properly handle non-Gaussian distributions and a problem caused by multiple hypotheses, one or more embodiments of the present invention adopt a particle filter-based SLAM algorithm. Here, such a problem caused by multiple hypotheses is a problem in that, once a wrongful assumption is adopted when more than one feature point matching assumption is available, the consequences of the wrongful assumption cannot be addressed. 
     According to one or more embodiments of the present invention, an optimum pose of a mobile robot may be estimated by matching an estimated feature point location, obtained by a particle filter using a small number of particles, to an observed feature point location. For optimal estimation of the pose of a mobile robot, evolutionary algorithms such as genetic algorithms may be used. Once the optimum feature point location is determined, a most recent optimum feature point location can be determined based on the optimum feature point location through feature point matching. 
     One or more embodiments of the present invention aim to provide a method, medium, and system capable of reducing computational complexity, with the use of fewer particles, and achieving better performance in terms of pose errors, than in a conventional particle filter-based SLAM techniques. According to one or more embodiments of the present invention, a genetic algorithm may be used in addition to a particle filter, thereby only slightly increasing computational complexity. Here, the degree to which the computational complexity is reduced by reducing the number of particles used outweighs the degree to which the computational complexity is increased by adopting a genetic algorithm. Thus, according to one or more embodiments of the present invention, it is possible to reduce computational complexity compared to the conventional techniques. 
       FIG. 1  illustrates a mobile robot system  100 , according to an embodiment of the present invention. Referring to  FIG. 1 , the mobile robot  100  may include a robot control module  110 , a travelling module  120 , an encoder  130 , a camera  140 , and a pose estimation module  200 , for example. 
     In an embodiment, the travelling module  120  may supply the mobile robot  100  with power so that the mobile robot  100  can move. Still further, the travelling module  120  may include a plurality of travelling wheels and/or an orientation control unit, for example, noting that alternative mechanisms for travelling are equally available. 
     Here, in this example, the encoder  130  may sense the rotation speed of such travelling wheels of the travelling module  120 , for example, thereby determining variations in the location and orientation of the mobile robot  100 . The encoder  130  may be provided in order to control the movement of the mobile robot  100  when the mobile robot  100  moves in response to a command to change the location or orientation of the mobile robot  100 , for example, and by using the encoder  130 , it may be possible to determine a current location of the mobile robot  100  by integrating the distance and the direction traveled by the mobile robot  100 . If no such integration error exists, then precise localization of the mobile robot  100  may be possible simply using the encoder  130 . However, while the encoder  130  may be accurate, over a relatively short period of time, the encoder  130  may accumulate errors over time as sampling is further performed. In another embodiment, an inertial sensor such as a gyroscope may be used, instead of the encoder  130 , to sense the movement of the mobile robot  100 , again noting that alternatives are equally available. 
     The camera  140  may capture a digital image of the outside of the mobile robot  100 , for example. Here, the camera  140  may include a charge coupled device (CCD) module or a complementary metal oxide semiconductor (CMOS) module, also as an example. 
     The robot control module  110  may control the travelling module  120  and the camera  140  of the mobile robot  100 . In other words, in such an embodiment, the robot control module  110  may control the mobile robot  100  to move to a location desired by a user in response to an example user command, or controls an image capturing operation of the camera  140 , etc. 
     The pose estimation module  200  may, thus, estimate a pose of the mobile robot by applying an evolutionary algorithm to a particle filter. In addition to such pose estimation operations, the pose estimation module  200  may also perform a mapping operation, depending on embodiment. 
     Here, the pose estimation module  200  may include a particle filter unit  210 , a feature point processing unit  220 , an evolution unit  230 , and a memory  240 , for example. 
     The feature point processing unit  220  may extract a feature point by processing the example image captured by the camera  140 . Then, the feature point processing unit  220  may update a plurality of previously stored feature points based on the extracted feature point. In other words, in this example, the feature point processing unit  220  may change the previously stored feature points based on the extracted feature point or may add the extracted feature point to the previously stored feature points. 
     The particle filter unit  210  applies a particle filter. In detail, the particle filter unit  210  may select a plurality of particles, vary the weights of the selected particles according to a phase of movement of the mobile robot  100 , and perform resampling on the selected particles according to the varied weights. 
     The evolution unit  230  may further apply an evolution algorithm to each of the selected particles, for example, thereby obtaining a plurality of evolved particles and a plurality of evolved weights respectively corresponding to the evolved particles. 
     The memory  240  may further be used to store a plurality of feature points. The memory  240  may also be used to create a map based on the feature points stored therein. 
     Accordingly,  FIG. 2  illustrates a block diagram of a pose estimation module  200 , such as that illustrated in  FIG. 1 , according to an embodiment of the present invention. Referring to  FIG. 2 , the feature point processing unit  220  may include a feature point extractor  221 , a feature point converter  222 , and a feature point matcher  223 , for example. 
     Here, the feature point extractor  221  may extract one or more feature points that are scale-invariant and rotation-invariant from an image that is captured by the camera  140 , for example. Feature points can be used to create a map during SLAM, and can also be referred to as landmarks. As a mobile robot moves, feature points should become larger or smaller or may rotate about other feature points. Thus, in order to properly extract feature points regardless of the aforementioned feature point variations, feature points that are scale-invariant and rotation-invariant should be sorted out and then used as landmarks. According to an embodiment of the present invention, the extraction of feature points may involve the below exemplary operations (a) through (e), noting that alternatives are also available. 
     Operation (a) Obtaining Original Image 
     An original image, e.g., an image obtained by digitalizing an image captured by a CCD camera through sampling, may be obtained. 
     Operation (b) Obtaining Gaussian-Blurred Images 
     Further, N Gaussian-blurred images may be obtained by performing Gaussian blurring on the original image N times. Thus, a number of images having different scales can be obtained by a number of iterations of Gaussian blurring. The more the original image is Gaussian-blurred, the longer the observation distance becomes or is represented. Such a representation is based on the characteristic of human visual perceptions, that long observation distances result in a blurry image. 
     Operation (c) Calculating Difference Between Gaussian-Blurred Images 
     A difference of Gaussian (DoG) may be calculated based on the difference between a pair of adjacent Gaussian-blurred images. In an embodiment, a distance D 1  between two Gaussian-blurred images I 1  and I 2  may be determined by the below Equation 1, for example.
 
 D   1 ( x,y )= I   2 ( x,y )− I   1 ( x,y )  Equation 1
 
     Here, x and y respectively indicate x and y coordinates of an image. 
     In this example, a total of (N−1) DoG images can be obtained from N Gaussian-blurred images. 
     Operation (d) Detecting Extremas from DoG Image 
     Extremas may further be detected from the DoG image. Extremas are pixels having a higher or lower greyscale value than the surrounding pixels, and are pixels that clearly change after being Gaussian-blurred. Extremas are highly stable against scale variation or rotation variation. 
     Operation (e) Selecting Feature Points in Order to Obtain Feature Points 
     The above extrema in a DoG image can be referred to as a candidate key point. Thus, in order to improve the stability of feature points, points that are mistakenly chosen from along edges as feature points are removed. In this regard, in an embodiment, operation (e) becomes a necessary operation. 
     The feature point converter  222  may determine the exact locations and orientations of feature points that are extracted from an estimated current location of the mobile robot  100  and the gradient of the grayscale of the feature points, for example. For this, the feature point converter  222  may sample a local image in the vicinity of a key point, calculate the locations and orientations of all feature points, and calculate a plurality of gray gradient vectors that respectively describe the feature points from a gray gradient viewpoint. 
     In detail, for example, the feature point converter  222  may perform the below operations (f) and (g). 
     Operation (f) Calculating Locations and Orientations of Feature Points 
     The feature point converter  222  may, thus, represent a current location of a key point using pixel coordinates. In order to improve precision or accuracy, pixel coordinates may be interpolated. The feature point converter  222  may further allocate a fixed orientation to each key point according to the gray gradient of a 64×64 pixel image, for example, including a corresponding key point, thereby obtaining the effect of rotation-invariance. 
     Operation (g) Calculating Gray Gradient Vectors of Feature Points 
     Referring to  FIG. 3 , the feature point converter  222 , for example, may thus allocate four sub-regions for each feature point. Each of the example four sub-regions can correspond to eight gray gradient vectors. Accordingly, a total of 32 example gray gradient vectors may be provided for each feature point. Referring to  FIG. 3 , the magnitude of a gray gradient vector is represented by the length of an arrow. In other words, a long arrow indicates a large gray gradient. 
     The feature point matcher  223 , for example, may further compare the gray gradient vector of a current feature point with the gray gradient vectors of stored feature points, such as those stored in the memory  240 , and may search the stored feature points for a match for the current feature point. When the difference between the gray gradient vectors of a pair of feature points meets or is less than a predefined threshold, it may be determined that the feature points match. If more than one feature point stored in the memory  240  matches the current feature point, a feature point that is most similar to the current feature point may be chosen as a match for the current feature point, for example. If none of the feature points stored in the memory  240  match the current feature point, then the current feature point may be stored in the memory  240 , for example, as a new feature point. 
     Referring to  FIG. 2  again, the particle filter unit  210  may include a sampler  211 , a pose estimator  212 , and a weight calculator  213 , for example. The particle filter unit  210  may calculate the location and orientation of the example mobile robot  100 , which can be estimated based on the properties of the feature points provided by the feature point processing unit  220 , e.g., the weights of a plurality of pose sample values, and estimate an optimum pose of the example mobile robot  100  based on the weights of the pose sample values. Here, the weights of the pose sample values indicates the probabilities of the pose sample values being true. Herein, though embodiments of the present invention have been set forth with an emphasis on the pose of a mobile robot, embodiments of the present invention are not limited thereto. 
     Thus, in detail, the pose estimator  212  may represent, as a probability distribution, the pose of the mobile robot  100  when the mobile robot  100  moves, for example. The probability distribution may be defined by a conditional probability p(xt|xt−1, ut−1) where xt−1 indicates a pose at a time (t−1), ut−1 indicates data measured by an encoder, and xt indicates a pose at a time t (current time). The pose of the mobile robot  100  may be based on three components including a pair of coordinates of the mobile robot  100  on a two-dimensional (2D) orthogonal coordinate system and the azimuth of the mobile robot  100 , for example. Thus, in an embodiment, the probability distribution is a probability distribution regarding the pose of the mobile robot  100  at a time t when the mobile robot  100  moves from xt−1 to xt with dynamic noise or other uncertain factors present in a system. 
     In this regard,  FIG. 4  illustrates a probability distribution regarding a pose of the mobile robot  100  that moves from a start point S to an end point E. Referring to  FIG. 4 , the more distant the mobile robot  100  is from the start point S, the more the particles are illustrated as being dispersed. This is because error of an example encoder increases according to the distance from the start point S. 
     Accordingly, assuming that the number of particles in a particle filter is N, an i-th particle (where i is an integer between 1 and N) can be represented by (xt(i), wt(i)) where xt(i) indicates a feasible pose of an i-th particle at a time t and wt(i) is a weight of the i-th particle and indicates the probability of an actual pose of the mobile robot  100  coinciding with the feasible pose xt(i). The pose estimator  212  may, thus, calculate the feasible pose xt(i) according to a probability model p(xt|xt−1, ut−1). 
     The sampler  211  performs random sampling, thereby obtaining a set of N initial particles. Then, when a time count t increases by 1, a number of initial particles with low weight values are excluded, and a number of initial particles with high weight values are repeatedly sampled, thereby obtaining another set of N particles. This operation is referred to as resampling. In other words, the sampler  211  performs an initial sampling operation and then a number of resampling operations. 
     The initial random sampling operation is an operation of selecting N arbitrary points, i.e., N particles, near an initial location of the mobile robot  100 . The initial random sampling operation may be represented by the below Equation 2, for example.
 
 S   0 ={( x   0   (j)   ,w   0   (j) )| j= 1 , . . . , N}   Equation 2
 
     Here, x0(j) and w0(j) indicate an initial pose and an initial weight, respectively, of a j-th particle. The initial weight w0(j) may be set to 1/N. 
     When the time count t increases, the sampler  211  may, thus, obtains N random samples from an existing set St−1 of particles through resampling, and obtain a new set of samples based on a weight wt−1(j). 
     Whenever the time count increases, the weight calculator  213  may further calculate a new weight of each particle and update the current weight wt(j) with the new weight. 
     Referring to (xt(j), wt(j)), which is particle obtained at the time t regarding the j-th particle, wt(j) indicates the probability of an actual pose of the mobile robot  100  at the time t coinciding with xt(j). 
     When the example mobile robot  100  obtains new information, the weight calculator  213  may calculate a new weight for each particle based on the new information. Here, the calculation of a weight for each particle indicates the localization of the mobile robot  100  by modifying a probability regarding the mobile robot  100 . Since the encoder  130  typically accumulates errors over time, it is desirable to calculate a new weight for each particle after a feature point matching operation performed by the feature point matcher  223 . 
     The new weight wt(j) may be calculated using the below Equation 3, for example. 
     
       
         
           
             
               
                 
                   
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     Here, yt indicates an observed pose of the mobile robot  100  at the time t. According to the above Equation 3, the weight wt(j) can be interpreted as being the probability of the pose xt(j) coinciding with an actually observed pose, i.e., yt. The observed pose yt can be determined based on a plurality of feature points that are matched by the feature point matcher  223 . 
     For example, referring to  FIG. 5 , and assuming that a total of N estimated particle poses are provided, the weight wt(j) can be calculated as being proportional to the inverse numbers of distances d 1 , d 2 , . . . , and dN between the N estimated particle poses and an observed pose. In other words, the less distant the estimated particle pose is from the observed pose, the higher the weight wt(j) becomes. 
     Referring to  FIG. 2 , the evolution unit  230  may include an initializer  231 , a crossover applicator  232 , and a mutation applicator  233 , for example. The evolution unit  230  may optimize a plurality of state parameters using an evolution algorithm. In an embodiment, the state parameters include xt(j) and wt(j) where xt(j) indicate the pose of the j-th particle at the time t and may be estimated by the pose estimator  212 , for example, and wt %) indicates the weight of the j-th particle and is calculated and updated by the weight calculator  213 , also as an example. 
     As a result of the aforementioned pose estimation and weight calculation, N feasible poses and respective corresponding probabilities can be obtained. However, none of the N feasible poses may match the actual pose of the mobile robot  100 . In order to precisely determine the pose of the mobile robot  100 , a considerable number of particles of a particle filter are typically needed. However, as the number of particles used increases, the computational requirements and memory resources considerably increase. Therefore, the evolution unit  230  may optimize a number of feasible poses so that the feasible poses can more approximate the actual pose of the mobile robot  100 . As a result of the optimization, the number of particles that are needed to localize the mobile robot  100  can be further reduced. 
     Examples of the evolution algorithm used by the evolution unit  230  include a crossover algorithm and/or a mutation algorithm, for example. One or more embodiments of the present invention will hereinafter be described in view of such crossover and/or mutation algorithms, which are expected to provide good performance, as examples of the evolution algorithm, e.g., as used by the evolution unit  230 . 
     The initializer  231  may determine an evolution level G and an evolution sample quantity M that may be applied to an evolution algorithm. The evolution level G and the evolution sample quantity M may be set according to user input or may be respectively set to default values that are predetermined, e.g., by the pose estimation module  200 . The higher the evolution level G, the higher the precision may become. However, the higher the evolution level G, the greater the number of computations. Therefore, the evolution level G is desirably set to an appropriate value. In an embodiment, the evolution level G may be set to a value of 3 to 5. The evolution level G may also vary or be based on the computing capability of the example pose estimation module  200 . 
     Likewise, the greater the evolution sample quantity M, the higher the precision may become. However, the greater the evolution sample quantity M, the greater the number of computations. Therefore, in an embodiment, the evolution sample quantity M may desirably be set to an appropriate value, such as a value of 10, for example. The evolution sample quantity M may thus vary from one particle to another or may be the same for all or groups of particles. 
     The crossover applicator  232  may extract a pair of samples xt(A) and xt(B) that may be randomly selected from among M evolution samples that are chosen for a predetermined particle, and apply a crossover algorithm to the extracted samples xt(A) and xt(B), for example Such a crossover algorithm may be represented by the below Equation 4, for example. 
     
       
         
           
             
               
                 
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                   4 
                 
               
             
           
         
       
     
     Here, xt(A) and xt(B) indicate parent samples, xt(Ac) and xt(Bc) indicate child samples, ξ indicates an arbitrary real number that is chosen from a random uniform distribution between 0 and 1, wt(Ac) indicates the weight of the child sample xt(Ac), and wt(Bc) indicates the weight of the child sample xt(Bc). The weights wt(Ac) and wt(Bc) are probabilities that the child samples xt(Ac) and xt(Bc) will match an observed value. Each of the child samples xt(Ac) and xt(Bc) can be represented by a weighted sum of the parent samples xt(A) and xt(B), as indicated by Equation 4. 
     In detail, referring to  FIG. 6 , the crossover applicator  232  may, thus, choose a pair of samples with the highest weight values from among the parent samples xt(A) and xt(B) and the child samples xt(Ac) and xt(Bc), and update the parent samples xt(A) and xt(B) with the chosen samples. This type of crossover can be applied to any arbitrary pair of samples that can be made up of the M evolution samples, for example. 
     The mutation applicator  233  may further extract one of the M evolution samples to which a crossover algorithm is applied by the crossover applicator  232 , e.g., xt(A). Then, if a weight wt(A) of the extracted sample xt(A) exceeds or meets a predefined threshold, the mutation applicator  233  may apply a mutation algorithm to the extracted sample xt(A) in consideration that mutation is likely to increase errors when being applied to samples with low weight values. 
     Such a mutation algorithm may be represented by the below Equation 5, for example. 
     
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           
                             x 
                             t 
                             
                               ( 
                               Am 
                               ) 
                             
                           
                           = 
                           
                             
                               x 
                               t 
                               
                                 ( 
                                 A 
                                 ) 
                               
                             
                             + 
                             τ 
                           
                         
                       
                     
                     
                       
                         
                           
                             w 
                             t 
                             
                               ( 
                               Am 
                               ) 
                             
                           
                           = 
                           
                             p 
                             ⁡ 
                             
                               ( 
                               
                                 
                                   y 
                                   t 
                                 
                                 | 
                                 
                                   x 
                                   t 
                                   
                                     ( 
                                     Am 
                                     ) 
                                   
                                 
                               
                               ) 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   5 
                 
               
             
           
         
       
     
     Here, τ indicates random noise and is a three-dimensional (3D) vector that follows a Gaussian distribution N(0, σ2) (where σ indicates standard deviation), xt(A) indicates a parent sample, and xt(Am) indicates a child sample obtained from the parent sample xt(A) through mutation. 
     In detail, referring to  FIG. 7 , the mutation applicator  233 , for example, may choose whichever of the parent sample xt(A) and the child sample xt(Am) has a higher weight value than the other, e.g., the parent sample xt(A), and update the child sample xt(Am) with the parent sample xt(A). 
     Whenever the example crossover and/or mutation performed on the M evolution samples are complete, an evolution level may be increased by 1. The aforementioned crossover and mutation operations may further be repeatedly performed on the M evolution samples until the evolution level reaches the evolution level G determined by the initializer  231 . 
     According to one embodiment, a crossover algorithm may be applied first to a number of evolution samples, and then a mutation algorithm applied. However, embodiments of the present invention are not limited thereto. For example, a mutation algorithm may be applied first to a number of evolution samples, and then a crossover algorithm applied. Alternatively, only one of the example crossover and mutation algorithms may be applied to a number of evolution samples. 
     A weight wt(j) of the j-th particle that may be optimized by the evolution unit  230  may be further normalized using the below Equation 6, for example. 
     
       
         
           
             
               
                 
                   
                     w 
                     t 
                     
                       ( 
                       j 
                       ) 
                     
                   
                   = 
                   
                     
                       w 
                       t 
                       
                         ( 
                         j 
                         ) 
                       
                     
                     / 
                     
                       
                         ∑ 
                         
                           k 
                           = 
                           1 
                         
                         N 
                       
                       ⁢ 
                       
                         w 
                         t 
                         
                           ( 
                           k 
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   6 
                 
               
             
           
         
       
     
     Here, in this case, the sum of the weights of all the N particles is 1. 
     As a result of the aforementioned operation, an optimized parameter set St may be obtained according to the below Equation 7, for example.
 
 S   t ={( x   t   (j)   ,w   t   (j) )| j= 1 , . . . , N}   Equation 7
 
     Here, the optimized parameter set St may be provided to the sampler  211 , for example. Then, when the tie count increases by 1, the sampler  211  may perform resampling on N particles having the optimized parameter set St. Thereafter, the pose estimator may  212  perform pose estimation on the N particles obtained by the resampling, and the weight calculator  213  may calculate a weight of each of the N particles obtained by the resampling. Still further, the evolution applicator  230  may apply an evolution algorithm to the N particles obtained by the resampling. Accordingly, these operations may be repeatedly performed until the time count ends, e.g., until the example mobile robot  100  arrives at the example end point E represented in  FIG. 4 . 
     The pose of whichever of the optimized particles provided by the evolution unit  230  has a highest weight value may, thus, be identified as a current pose of the example mobile robot  100 . The pose of the optimized particle with the highest weight value may further be provided to such a robot control module  110 . Then, the robot control module  110  may control the mobile robot  100  to move and perform an operation, such as cleaning, based on the pose of the optimized particle with the highest weight value. 
       FIGS. 8A and 8B  are diagrams comparing a result from an embodiment of the present invention with results of a conventional system. Specifically,  FIG. 8A  illustrates localization and mapping results obtained using a conventional particle filter technique, and  FIG. 8B  illustrates localization and mapping results obtained using a particle filter technique according to an embodiment of the present invention. The number of particles used to produce the localization and mapping results presented in  FIG. 8A  was 100, whereas the number of particles used to produce the localization and mapping results presented in  FIG. 8B  was 50 (evolution level: 5). Accordingly, it is possible to more precisely create a map even with fewer particles than conventional systems. 
     In addition, referring to  FIGS. 8A and 8B , the time taken to perform SLAM in the prior art was 474.7 ms, whereas the time taken to perform SLAM according to the embodiment of the present invention was 443.5 ms. In short, according to one or more embodiments of the present invention, it is possible to provide better results, while potentially spending essentially the same time as in conventional systems. 
     The term ‘module’, as used herein, means, but is not limited to, a software and/or hardware component, such as a Field Programmable Gate Array (FPGA) or Application Specific Integrated Circuit (ASIC), which performs certain tasks. A module may advantageously be configured to reside on the addressable storage medium and configured to execute on one or more processors. Thus, a module may include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. The operations provided for in the components and modules may be combined into fewer components and modules or further separated into additional components and modules. 
     In addition, embodiments of the present invention can also be implemented through computer readable code/instructions in/on a medium, e.g., a computer readable medium, to control at least one processing element to implement any above described embodiment. The medium can correspond to any medium/media permitting the storing and/or transmission of the computer readable code. 
     The computer readable code can be recorded/transferred on a medium in a variety of ways, with examples of the medium including recording media, such as magnetic storage media (e.g., ROM, floppy disks, hard disks, etc.) and optical recording media (e.g., CD-ROMs, or DVDs), and transmission media such as carrier waves, as well as through the Internet, for example. Thus, the medium may further be a signal, such as a resultant signal or bitstream, according to embodiments of the present invention. The media may also be a distributed network, so that the computer readable code is stored/transferred and executed in a distributed fashion. Still further, as only an example, the processing element could include a processor or a computer processor, and processing elements may be distributed and/or included in a single device. 
     As described above, according to one or more embodiments of the present invention, it is possible to reduce the number of particles used for moving a mobile robot by applying an evolution algorithm to a particle filter technique estimating the pose of the mobile robot. Accordingly, computation speed of SLAM for the mobile robot can be enhanced, and required memory sizes can be reduced. 
     Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.