Abstract:
A method for navigation of a movable platform is provided. The method includes the steps. First, a plurality of reflection devices is placed to mark a range. A coordinate location and a direction of the movable platform are received by a positioning system, At least one laser to measure relative positions and distances between the reflection devices and the movable platform are emitted by a laser range finder, respectively. Absolute locations of the reflection devices and the range are calculated by a processor according to the coordinate location and the direction of the movable platform, the relative positions and the distances between the reflection devices and the movable platform. The reflection devices are scanned and tracked by the processor, and the coordinate location and the direction of the movable platform and the absolute locations are calibrated by the processor to control the movable platform to move in the range.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is based on, and claims priority from, Taiwan (International) Application Serial Number 100149457, filed on Dec. 29, 2011, the disclosure of which is hereby incorporated by reference herein in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to a system and method for navigation, and in particular relates to a system and method for navigation of a movable platform. 
       BACKGROUND 
       [0003]    With the development of science and technology, service robots have gradually replaced many of the traditional human labor workforces. A variety of robots used in an indoor or outdoor environment have been widely available, such as in Europe and the United States. For current outdoor mobile platforms with a high-precision navigation system, one of the most important applications is an outdoor service robot. According to market research data and statistical data (Robot Home Cleaning, Cooking, Pool Cleaning, and Lawn Mowing Market Strategy, Market Shares, and Market Forecasts, 2008-2014), such as that analyzed by Wolfram Research, Inc, the technology of current outdoor service robots is still immature, but has a large potential market, such as that for a robot that mows, wherein the market size is expected to grow and reach US $305 billion in 2014. 
         [0004]    The outdoor mobile platform is mainly used for working in large outdoor areas. For many occasions and in many environments, for example, golf courses, parks, and yards in front of or behind a house and so on, the outdoor mobile platform is a useful product. A navigation system is the most important and critical component of the outdoor mobile platform. The navigation system can also determine whether the work efficiency of the mobile platform is good or bad. However, the navigation technology of current outdoor mobile platforms has limitations. 
       SUMMARY 
       [0005]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
         [0006]    Methods and systems for navigation of a movable platform are provided. 
         [0007]    In one exemplary embodiment, the disclosure is directed to a method for navigation of a movable platform. The method is used in a system. The system includes a plurality of reflection devices and a movable platform, wherein the movable platform further includes a positioning system, a laser range finder and a processor. The method comprises: placing the plurality of reflection devices to mark a range; receiving, by the positioning system, a coordinate location and a direction of the movable platform; emitting, by the laser range finder, at least one laser to measure relative positions and distances between the plurality of reflection devices and the movable platform, respectively; calculating, by the processor, absolute locations of the plurality of reflection devices and the range according to the coordinate location and the direction of the movable platform, and the relative position and the distances between the plurality of reflection devices and the movable platform; and scanning and tracking, by the laser range finder, the plurality of reflection devices, and calibrating, by the processor, the coordinate location and the direction of the movable platform and the absolute locations of the plurality of reflection devices to control the movable platform to move in the range. 
         [0008]    In one exemplary embodiment, the disclosure is directed to a system for navigation of a movable platform. The system comprises a plurality of reflection devices, a movable platform. The plurality of reflection devices is configured to mark a range. The movable platform is configured to move in the range, wherein the movable platform further includes a positioning system, a laser range finder and a processor. The positioning system is configured to position a coordinate location and a direction of the movable platform. The laser range finder is configured to emit at least one laser to measure relative positions and distances between the plurality of reflection devices and the movable platform, respectively. The processor coupled to the positioning system and the laser range finder is configured to calculate absolute locations of the plurality of reflection devices and the range according to the coordinate location and the direction of the movable platform, and the relative position and the distances between the plurality of reflection devices and the movable platform, wherein the movable platform scans and tracks the plurality of reflection devices by using the laser range finder, and calibrates the coordinate location and the direction of the movable platform and the absolute locations of the plurality of reflection devices to control the movable platform to move in the range. 
     
    
     
       DRAWINGS 
         [0009]    The present disclosure can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0010]      FIG. 1  is an architecture diagram of a system for navigation of a movable platform according to an embodiment of the present disclosure; 
           [0011]      FIG. 2  is a schematic diagram illustrating the mobile platform according to an embodiment of the present disclosure; 
           [0012]      FIG. 3A  is a side diagram of the laser range finder according to an embodiment of the present disclosure; 
           [0013]      FIG. 3B  is a cross-sectional diagram of the laser range finder according to an embodiment of the present disclosure; 
           [0014]      FIG. 4  is a schematic diagram illustrating how the mobile platform according to an embodiment of the present disclosure; and 
           [0015]      FIGS. 5A˜5B  are a flow diagram illustrating the method for navigation of the movable platform according to an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Several exemplary embodiments of the application are described with reference to  FIGS. 1 through 5 , which generally relate to navigation of a movable platform. It is to be understood that the following disclosure provides various different embodiments as examples for implementing different features of the application. Specific examples of components and arrangements are described in the following to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various described embodiments and/or configurations. 
         [0017]    Embodiments described below illustrate methods and systems for navigation of a movable platform of the present disclosure. 
         [0018]      FIG. 1  is an architecture diagram of a system  100  for navigation of a movable platform according to an embodiment of the present disclosure. 
         [0019]    Referring to  FIG. 1 , the system  100  for navigation of a movable platform comprises a plurality of reflection devices  101 ˜ 104  and a mobile platform  110 . The reflection devices  101 ˜ 104  can be placed on the outside to mark a work range. In one embodiment, reflection devices  101 ˜ 104  are reflection columns or reflection marks. The mobile platform  110  moves within the work range. 
         [0020]      FIG. 2  is a schematic diagram illustrating the mobile platform  110  according to an embodiment of the present disclosure. The movable platform  110  comprises a positioning system  112 , a laser range finder  114  and a processor  116 . The positioning system  112  and the laser range finder  114  are coupled to the processor  116 . The positioning system is a global positioning system (GPS), a GLObal NAvigation Satellite System (GLONASS), a Galileo and a satellite based augmentation system (SBAS) and so on. In one embodiment, the distance between any two of the plurality of reflection devices  101 ˜ 104  is greater than a positioning error of the positioning system. 
         [0021]    In another embodiment, the laser range finder  114  is installed above the mobile platform  110  via a rotating platform, and the laser range finder  114  can rotate 360 degrees. 
         [0022]    In another embodiment, the laser range finder  114  can be used to measure the laser in an outdoor open environment, and a laser emitted by the laser range finder  114  can be only reflected by specific reflecting materials. 
         [0023]    Referring to  FIG. 3A  and  FIG. 3B ,  FIG. 3A  is a side diagram of the laser range finder  114  according to an embodiment of the present disclosure.  FIG. 3B  is a cross-sectional diagram of the laser range finder  114  according to an embodiment of the present disclosure, wherein  FIG. 3B  is the cross-sectional diagram taken along line A-A of the laser range finder  114  in  FIG. 3A . In  FIG. 3A , the laser range finder  114  comprises a laser-emitting source  301 , a receiver  302  and a shield plate  303 . A receiving hole  304  is formed through the shield plate  303 . Because the noise of the outdoor light is too large, it is difficult for the laser range finder in the prior art to measure the distance. Therefore, the shield plate with the receiving hole is added to the original receiver in the embodiment, so that the laser range finder  114  can receive the laser reflected by a specific reflecting material to reduce influence of the outdoor light. As shown in  FIG. 3A , the diameter of the receiving hole  304  is between 0.5˜15 mm. In  FIG. 3B , similar or corresponding elements are assigned the same labels, and the characteristics described above will be omitted in the following instructions. 
         [0024]    In addition, the specific reflective material is for attachment to the surface of the reflection devices  101 ˜ 104 . Because a known reflection rate of the specific reflective material is adopted, a sensing range that the laser range finder receives the laser can be set in advance, so that the laser range finder can recognize the laser reflected by the specific reflecting material. In one embodiment, the reflection rate of the specific reflective material is greater than 60%, for the specific reflective material to scatter the incident light. It should be noted that the receiving hole diameter of the laser range finder is related to the reflection rate of the specific reflecting material. When the reflection rate of the specific reflective material is higher, the receiving hole diameter of the laser range finder can be smaller. In addition, the reflection devices are the reflecting objects with the specific reflecting material. In a preferred embodiment, the wavelength of the laser emitted by the laser range finder is 650 nm, and the reflective material is a 3M™ series 6500 High Gloss Sparkle Film. The diameter R of the receiving hole is almost 2 millimeters (mm) according to the design of the wavelength of the laser and the reflective material. It should be understood for a person of ordinary skill in the art that the disclosure is not limited, and the reflection devices can be any shape. 
         [0025]    As shown in  FIG. 1  and  FIG. 2 , the user places the plurality of reflection devices  101 ˜ 104  to mark a range, and puts the movable platform  110  in the range. First, the mobile platform  110  moves around the small area within the positioning error, and the positioning system  112  receives a current coordinate location and a current direction of the movable platform  110 , wherein the coordinate location can be, for example, a location in degrees of latitude and longitude. In one embodiment, the positioning system is the global positioning system (GPS), and the positioning error of the positioning system is 3 meters. 
         [0026]    The laser range finder emits at least one laser to search all the reflection devices  101 ˜ 104 , and measures the distances L 1 ˜L 4  between the reflection devices  101 ˜ 104  and the movable platform  110 , respectively. The processor  116  calculates and records absolute locations of the reflection devices  101 ˜ 104  and the range according to the coordinate location of the movable platform  110  and the distances L 1 ˜L 4  between the reflection devices  101 ˜ 104  and the movable platform  110 . The processor  116  further determines whether the distance between any two of the reflection devices  101 ˜ 104  is greater than the positioning error. When the distance between any two of the reflection devices  101 ˜ 104  is smaller than or equal to the positioning error, the processor  116  sends a signal to inform the user to replace the reflection devices. 
         [0027]    After calculating the absolute locations of the reflection devices  101 ˜ 104  and the range, the mobile platform  110  can start operation in the range, and emit the laser and change the emitting degree of the laser through the laser range finder  114  to lock a first reflection device  101  which is closest to the movable platform  110 . It is worth noting that when the mobile platform  110  moves or rotates, the laser range finder  114  can rotate in any direction. For example, the laser range finder  114  maintains locking a reflection device which is closest to the movable platform  110  via the rotation of the mobile platform  110 . 
         [0028]    When the laser range finder  114  locks the first reflection device  101 , the processor  116  continues to calibrate the current coordinate location of the mobile platform  110 , and determines whether the mobile platform  110  is close to a boundary of the range. As shown in  FIG. 4 , when the mobile platform  110  is close to a boundary  201  of the range, the laser range finder  114  finds a second reflection device  102  which is closest to the movable platform  110  except the first reflection device  101 , and the processor  116  obtains an angle θ between a line from the mobile platform  110  to the first reflection device  101  and a line from the mobile platform  110  to the second reflection device  102 . The laser range finder  114  continues to emit the laser between the first reflection device  101  and the second reflection device  102 . When the angle θ reaches 180 degrees, the processor  116  controls the mobile platform  110  to rotate in another direction to avoid exceeding the boundary  201  of the range. 
         [0029]    In some embodiments, when the distance between the mobile platform  110  and the reflection device which is closest to the movable platform  110  is too far or the mobile platform  110  can not keep tracking of the reflection device which is closest to the movable platform  110  due to topography factors, the processor  116  controls the laser range finder  114  to find another one reflection device which is closest to the movable platform  110 . In another embodiment, when the mobile platform  110  finds another reflection device which is closer to the current location of the mobile platform  110  according to the absolute location of each reflection device recorded by the processor  116  previously, the processor  116  controls the laser range finder  114  to find the reflection device which is closest to the mobile platform  110  currently. 
         [0030]      FIGS. 5A˜5B  are a flow diagram illustrating the method for navigation of the movable platform  110  according to an embodiment of the present disclosure. 
         [0031]    Referring  FIG. 1  to  FIG. 4 , first, the user places the plurality of reflection devices to mark a range, and puts the movable platform in the range. In step S 401 , the positioning system positions a current coordinate location and a current direction of the movable platform. In step S 402 , the laser range finder emits at least one laser and the movable platform rotates and stays at the same place to measure the relative positions and the distances between the reflection devices and the mobile platform. Then, in step S 403 , the processor calculates the absolute locations of the reflection devices according to the coordinate location and the direction of the movable platform positioned by the positioning system and the relative positions and the distances between the reflection devices and the mobile platform. In step S 404 , the processor determines whether the distance between any two of the reflection devices is greater than the positioning error. When the processor determines that the distance between any two of the reflection devices is smaller than or equal to the positioning error (“No” in step S 404 ), in step S 405 , the processor sends a signal to inform the user to replace the reflection devices. When the processor determines that the distance between any two of the reflection devices is greater than the positioning error (“Yes” in step S 404 ), in step S 406 , the processor calculates the range, such as an area surrounded by all the reflection devices. In step S 407 , the mobile platform starts operation in the range. 
         [0032]    During the operation of the mobile platform, in step S 408 , the laser range finder uses the laser to lock a reflection device which is closest to the movable platform, and calibrates the coordinate location of the mobile platform and the absolute locations of the reflection devices. In step S 409 , the processor determines whether the mobile platform is close to a boundary of the range. When the mobile platform is close to the boundary of the range (“Yes” in the step S 409 ), in step S 410 , the processor finds another reflection device which is closest to the movable platform except the reflection device to obtain an angle between a line from the mobile platform to the reflection device and a line from the mobile platform to another reflection device, and determines whether the angle is greater than 180 degrees. When the angle is greater than 180 degrees (“Yes” in step S 410 ), in S 411 , the processor controls the mobile platform to rotate in another direction, and keeps detecting whether the angle is greater than 180 degrees. In another embodiment, when the angle is close to or reaches 180 degrees (“Yes” in step S 410 ), in step S 411 , the processor controls the mobile platform to stop moving. 
         [0033]    When the mobile platform is not close to the boundary of the range (“Yes” in the step S 409 ) and the processor determines that the angle is smaller than or equal than 180 degrees (“Yes” in step S 410 ), step S 407  is performed and the mobile platform keeps working. 
         [0034]    When the positioning system is the global positioning system (GPS), the positioning error of the receiver is about three to five meters, and the error of the laser range finder is smaller than 1 centimeter. This means that the error of the laser range finder is smaller than the positioning error of the positioning system. Therefore, the system for navigation of the mobile platform in the present disclosure can use the laser range finder installed on the top of the mobile platform and the positioning system to determine absolute locations, the latitudes and the longitudes of the reflection devices and the mobile platform, and further use the laser range finder to calibrate the relative positions of the mobile platform so that the positioning error can be reduced to achieve positioning accuracy within centimeters. 
         [0035]    In addition, the number of reflection devices can be increased or decreased according to the range and the shape required. When there are obstacles in the range of operation, for example, houses, trees and other obstacles, the reflection devices can be arranged to mark the obstacles or the reflective films with specific reflective materials attached to the obstacles. When encountering an obstacle, the mobile platform moves along the edge of the obstacle until the mobile platform travels around the obstacle and goes back to the original path, and then the mobile platform continues operation. The absolute location of the obstacle can be stored and recorded by the mobile platform. 
         [0036]    The technology of the present disclosure can be applied to a variety of outdoor mobile platforms, for example, outdoor service robots. The mobile platform in the disclosure can calculate the work location and the traveling direction exactly, and store and record the traveling path and the location of obstacles. 
         [0037]    While the disclosure has been described by way of example and in terms of the preferred embodiments, it is to be understood that the disclosure is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.