Abstract:
An embodiment of the invention provides a control method of a cleaning robot. The method includes the steps of: forming a cleaning area according to at least three points which are selected from a light generating device, a charging station or an obstacle; moving the cleaning robot along an outer of the cleaning area from a first position; recording a first cleaning route when the cleaning robot returns back to the first position; moving the cleaning robot to a second position and planning a second cleaning route according to the first cleaning route; and moving the cleaning robot along the second cleaning route.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/599,690 filed Feb. 16, 2012, the entirety of which is incorporated by reference herein. 
         [0002]    This application claims priority of Taiwan Patent Application No. 101126911, filed on Jul. 26, 2012, the entirety of which is incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The invention relates to a cleaning robot, and more particularly, to a cleaning robot with a non-omnidirectional light detector. 
         [0005]    2. Description of the Related Art 
         [0006]    A variety of movable robots, which generally include a driving means, a sensor and a travel controller, and perform many useful functions while autonomously operating, have been developed. For example, a cleaning robot for the home, is a cleaning device that sucks dust and dirt from the floor of a room while autonomously moving around the room without user manipulation. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    An embodiment of the invention provides a control method of a cleaning robot. The method comprises the steps of: forming a cleaning area according to at least three means which are selected from a light generating device, a charging station or an obstacle; circling along an outline of the cleaning area from a first position by the cleaning robot; recording a first cleaning route when the cleaning robot returns back to the first position; moving the cleaning robot to a second position and planning a second cleaning route according to the first cleaning route; and circling along the second cleaning route by the cleaning robot. 
         [0008]    Another embodiment of the invention provides a control method for a cleaning robot. The method comprises the steps of: forming a cleaning area according to at least three means which are selected from a light generating device, a charging station or an obstacle; estimating a center of the cleaning area; moving the cleaning robot to the center of the cleaning area; and moving the cleaning robot in a spiral route and cleaning the cleaning area. 
         [0009]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0011]      FIG. 1  is a schematic diagram of a light generating device and a cleaning robot according to an embodiment of the invention. 
           [0012]      FIGS. 2   a - 2   d  are schematic diagrams of cleaning route planning methods for a cleaning robot according to embodiments of the invention. 
           [0013]      FIG. 3  is a schematic diagram of an embodiment of a cleaning robot according to the invention. 
           [0014]      FIG. 4  is a schematic diagram of a control method for a cleaning robot according to another embodiment of the invention. 
           [0015]      FIG. 5  is a schematic diagram of a control method for a cleaning robot according to another embodiment of the invention. 
           [0016]      FIG. 6  is a flowchart of a cleaning route planning method for a cleaning robot according to an embodiment of the invention. 
           [0017]      FIG. 7  is a flowchart of a cleaning route planning method for a cleaning robot according to another embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0019]      FIG. 1  is a schematic diagram of a light generating device and a cleaning robot according to an embodiment of the invention. The light generating device  12  outputs a light beam  15  to label a restricted area that the cleaning robot  11  cannot enter. The cleaning robot  11  comprises a non-omnidirectional light detector  13  having a rib (or called mask)  14 , where the rib  14  produces a shadowed area on the non-omnidirectional light detector  13  by a predetermined angle and the range of the predetermined angle is from 30 degrees to 90 degrees. 
         [0020]    The rib  14  may be fixed on the surface of the non-omnidirectional light detector  13  or movable along the non-omnidirectional light detector  13 . The rib  14  can be spun in 360 degrees along the surface of the non-omnidirectional light detector  13 . In this embodiment, the term, non-omni, is a functional description to describe that the rib  14  causes an area on the surface of the non-omnidirectional light detector  13  and the non-omnidirectional light detector  13  cannot not detect light therein or light to not directly reach that area. 
         [0021]    Thus, the non-omnidirectional light detector  13  can be implemented in two ways. The first implementation is to combine an omni-light detector with a rib  14  and the rib  14  is fixed on a specific position of the surface of the omni-light detector. The non-omnidirectional light detector  13  is disposed on a plate that can be spun by a motor. Thus, the purpose of spinning of the non-omnidirectional light detector  13  can be achieved. When the non-omnidirectional light detector  13  detects the light beam, an incident angle of the light beam  15  can be determined by spinning the non-omnidirectional light detector  13 . 
         [0022]    Another implementation of the non-omnidirectional light detector  13  is implemented by telescoping a mask kit on an omni-light detector, wherein the omni light detector cannot be spun and the masking kit is movable along a predetermined track around the omni light detector. The mask kit is spun by a motor. When the non-omnidirectional light detector  13  detects the light beam  15 , the mask kit is spun to determine the incident angle of the light beam  15 . 
         [0023]      FIG. 2   a  is a schematic diagram of a cleaning route planning method for a cleaning robot according to an embodiment of the invention. In  FIG. 2   a , a first light generating device  21 , a second light generating device  22 , a third light generating device  23  and a fourth light generating device  24  form a closed first region, and the cleaning robot  25  can move only within the first region. The embodiment is illustrated with four light generating devices, but the invention is not limited thereto. In another embodiment, only three or more than three means can form a cleaning area, wherein the means are selected from the light generating device, wall, charging station for the cleaning robot  25  or other device at a fixed position. 
         [0024]    In  FIG. 2   a , the cleaning robot  25  circles along the outline of the first region from the first light generating device  21  and records a cleaning route R 1 . When the cleaning robot  25  goes back to the starting point, the first light generating device  21 , the cleaning robot  25  records positions or coordinates of the first light generating device  21 , the second light generating device  22 , the third light generating device  23 , the fourth light generating device  24 , other obstacles or objects at fixed positions on the cleaning route R 1 . Thus, the cleaning robot  25  can estimate a position of a center of the cleaning area, i.e. the first region, according to the described coordinates. 
         [0025]    Refer to  FIG. 2   b . When the cleaning robot  25  goes back to the starting point, the cleaning robot  25  moves for a distance d to the center of the cleaning area. Then, the cleaning robot  25  circles along the outline of the cleaning area according to the cleaning route R 1  and records a cleaning route R 2 . In this embodiment, the distance d is half of a width of the cleaning robot  25 . Assuming the distance between the first light generating device  21  and the second light generating device  22  is D. In  FIG. 2   b , the cleaning robot  25  only moves for the distance (D- 2   d ) between the first light generating device  21  and the second light generating device  22  along the cleaning route R 2 . Thus, when the cleaning robot  25  moves from the new starting point to the second light generating device  22 , the cleaning robot  25  only moves for the distance (D- 2   d ) and then moves to the third light generating device  23 . 
         [0026]    Furthermore, the processor of the cleaning robot  25  estimates a second duration that the cleaning robot  25  circles along the cleaning route R 2  according to a first duration that the cleaning robot  25  circles along the cleaning route R 1 . This can prevent the cleaning robot  25  from cleaning the area around the cleaning route R 1  repeatedly. 
         [0027]    The cleaning robot  25  moves in the way shown in  FIG. 2  until the cleaning robot  25  moves to the center of the cleaning area. In another embodiment, the moving manner of the cleaning robot  25  shown in  FIG. 2   b  can be replaced by other moving manners. Please refer to  FIGS. 2   c  and  2   d . In  FIG. 2   c , the cleaning robot  25  first moves to the center C of the cleaning area. Then, the cleaning robot  25  moves along a spiral route from the center C to the outline of the cleaning area. The cleaning robot  25  stops when cleaning all the cleaning areas. 
         [0028]    In  FIGS. 2   a - 2   d , two moving manners are included.  FIG. 2   a  and  FIG. 2   b  show one moving manner and  FIGS. 2   a ,  2   c  and  2   d  show another moving manner. Moreover, when the cleaning robot  25  cleans all the cleaning areas, the cleaning robot  25  moves reversely to clean the cleaning area again. When the cleaning robot moves to the center of the cleaning area according to the moving manner of  FIG. 2   b , the cleaning robot  25  can choose one moving manner to clean the cleaning area again. The cleaning robot  25  can move reversely to clean the cleaning area until the cleaning robot  25  moves to the starting point as described in  FIG. 2   a . In another embodiment, the cleaning robot  25  moves in a spiral route, such as shown in  FIG. 2   d , to clean the cleaning area until the cleaning robot  25  has cleaned all of the cleaning areas. 
         [0029]    In  FIG. 2   a , when the cleaning robot  25  detects the light beam output by the light generating device, the cleaning robot  25  is guided by the light beam to move to or move away from the light generating device. Reference can be made to  FIGS. 3-5  for the operation where the cleaning robot  25  detects the light beam from the light generating device. 
         [0030]      FIG. 3  is a schematic diagram of an embodiment of a cleaning robot according to the invention. The cleaning robot  31  comprises a non-omnidirectional light detector  32 , a directional light detector  33  and a mask  34 . In  FIG. 3 , only the elements related to the invention are discussed, but the invention is not limited thereto. The cleaning robot  31  still may comprise other hardware devices, firmware or software for controlling the hardware, which are not discussed for brevity. 
         [0031]    When the non-omnidirectional light detector  32  detects a light beam, a controller of the non-omnidirectional light detector  32  or a processor of the cleaning robot  31  first determines the strength of the detected light beam. If the strength of the received signal is less than a predetermined value, the controller or the processor does not respond thereto or take any action. When the strength of the received signal is larger than or equal to the predetermined value, the controller or the processor determines whether the light beam was output by a light generating device. 
         [0032]    When the light beam is output by the light generating device, the non-omnidirectional light detector  32  is spun to determine the direction of the light beam or an included angle between the light beam and the current moving direction of the cleaning robot  31 . When the direction of the light beam or the included angle is determined, the processor of the cleaning robot  31  determines a spin direction, such as a clockwise direction or counter clockwise direction. The cleaning robot  31  is spun in a circle at the same position. When the directional light detector  33  detects the light beam, the cleaning robot  31  stops spinning. 
         [0033]    In another embodiment, when the non-omnidirectional light detector  32  detects the light beam and the light beam is output from the light generating device, the non-omnidirectional light detector  32  and the cleaning robot  31  are spun in the clockwise direction or the counter clockwise direction simultaneously. When the directional light detector  33  detects the light beam, the cleaning robot  31  stops spinning. 
         [0034]    In other words, the processor of the cleaning robot  31  controls the cleaning robot  31  to spin in the clockwise direction or the counter clockwise direction according to the detection result of the non-omnidirectional light detector  32 . When the directional light detector  33  detects the light beam output by the light generating device, the cleaning robot  31  stops spinning, and the processor of the cleaning robot  31  controls the cleaning robot  31  to move to the light generating device straightforwardly. 
         [0035]    Before approaching to the light generating device, the cleaning robot  31  moves along the light beam output by the light generating device and from cleaning the area near the light beam. The processor of the cleaning robot  31  continuously monitors the directional light detector  33  to determine whether the directional light detector  33  receives the light beam output by the light generating device. Once the directional light detector  33  fails to detect the light beam, the cleaning robot  31  is spun to calibrate the moving direction of the cleaning robot  31 . 
         [0036]    In one embodiment, the directional light detector  33  comprises a plurality of light detection units and the processor slightly calibrates the moving direction of the cleaning robot  31  according to the detection results of the light detection units. 
         [0037]      FIG. 4  is a schematic diagram of a control method for a cleaning robot according to another embodiment of the invention. The light generating device  45  outputs a light beam to label a restricted area that the cleaning robot  41  should not enter. In other embodiments, the light generating device  41  is named as light house or light tower and outputs the light beam or other wireless signals. The light beam comprises a first boundary b 1  and a second boundary b 2 . At time T 1 , the cleaning robot  41  moves along a predetermined route. At time T 2 , the non-omnidirectional light detector  42  detects a first boundary b 2  of a light beam emitted by the light generating device  45 . The cleaning robot  41  stops moving, and the non-omnidirectional light detector  42  is spun in a counter clockwise direction or a clockwise direction. 
         [0038]    When the mask  44  blocks the light beam emitted from the light generating device  45 , the non-omnidirectional light detector  42  cannot detect the light beam. A controller of the cleaning robot  41  records a current position of the mask  44  and estimates a first spin angle of the non-omnidirectional light detector  42  according to an initial position of the mask  44  and the current position of the mask  44  to determine a spin direction of the cleaning robot  41 . 
         [0039]    For example, assuming the first spin angle is less than 180 degrees, the cleaning robot  41  is spun in the clockwise direction. The cleaning robot  41  is spun in the counter clockwise direction when the first spin angle is larger than 180 degrees. 
         [0040]    At time T 3 , the cleaning robot  41  is spun according to the determined direction until the directional light detector  43  detects the light beam output by the light generating device  45 . When the directional light detector  43  detects the light beam output by the light generating device  45 , the cleaning robot  41  stops spinning. Generally speaking, when the directional light detector detects the light beam output by the light generating device  45 , the light detection units detecting the light beam are located at the margin of the directional light detector  43 . Thus, when the cleaning robot  41  moves again, the directional light detector  43  may fail to detect the light beam quickly and the cleaning robot  41  has to stop again to calibrate the moving direction. 
         [0041]    To solve the aforementioned issue, in one embodiment, the processor of the cleaning robot  41  estimates a delay time according to the angular velocity of the cleaning robot  41  and the size of the directional light detector  43 . When the directional light detector  43  detects the light beam, the cleaning robot  41  stops spinning after the delay time. By the delay time, the light beam output by the light generating device  45  can be detected by the center of the directional light detector  43 . 
         [0042]    It is noted that the cleaning robot  41  stays at the same position at times T 2  and T 3 . At time T 2 , the cleaning robot  41  is not moved or spun and only the non-omnidirectional light detector  42  is spun. At time T 3 , the cleaning robot  41  is spun in a circle at the original position. Although the position of the cleaning robot  41  at time T 2  is different from the position of the cleaning robot  41  at time T 3  in  FIG. 4 , it represents only two operations at the same position but at different times. In fact, the position of the cleaning robot  41  does not change at time T 2  and T 3 . 
         [0043]    In another embodiment, the operations of the cleaning robot  41  at time T 2  and T 3  can be integrated in one step. At time T 2 , the non-omnidirectional light detector  42  is spun in a predetermined direction, and the cleaning robot is also spun in the predetermined direction. When the directional light detector  43  detects the light beam output by the light generating device  45 , the cleaning robot  41  stops spinning. When the cleaning robot  41  stops spinning, the non-omnidirectional light detector  42  may be stopped or continues to spin. If the non-omnidirectional light detector  42  is still spinning the processor of the cleaning robot  41  determines the direction of the light beam to calibrate the moving direction of the cleaning robot  41  according to the spin angle of the non-omnidirectional light detector  42 . 
         [0044]    When the cleaning robot  41  moves to the light generating device  45 , the processor of the cleaning robot  41  records the moving paths of the cleaning robot  41  and labels the moving path and a restricted area on a map. In another embodiment, when the processor of the cleaning robot  41  determines the direction of the light beam output by the light generating device, the processor labels the light beam and the restricted area on the map. The map is stored in a memory or a map database of the cleaning robot  41 . The processor modifies the map according to the movement of the cleaning robot  41  and labels the positions of obstacles on the map. 
         [0045]    When the cleaning robot  41  approaches to the light generating device  45  and the distance between the cleaning robot  41  and the light generating device  45  is less than a predetermined distance, a touch sensor or an acoustic sensor outputs a stop signal to the controller of the cleaning robot  41 . The touch sensor or the acoustic sensor is disposed in the front end of the cleaning robot  41  to detect whether there is any obstacle in front of the cleaning robot  41 . When the touch sensor or the acoustic sensor detects an obstacle, the cleaning robot  41  first determines whether the obstacle is the light generating device  45 . If the obstacle is the light generating device  45 , the cleaning robot  41  stops moving and moves in another direction. If the obstacle is not the light generating device  45 , the cleaning robot  41  first leaves the original route to prevent the obstacle and returns to the original route after avoiding the obstacle. 
         [0046]    When the cleaning robot  41  approaches to the light generating device  45 , the light generating device  45  outputs a radio frequency (RF) signal or an infrared signal to let the cleaning robot  41  know that the cleaning robot  41  is close to the light generating device  45 . In another embodiment, Near Field Communication (NFC) devices are embedded in both the cleaning robot  41  and the light generating device  45 . When the NFC device of the cleaning robot  41  receives signals or data from the NFC device of the light generating device  45 , it means that the cleaning robot  41  is close to the light generating device  45  and the cleaning robot  41  should stop accordingly. Generally speaking, the sensing distance of the NFC device is 20 cm. 
         [0047]    According to the above description, the cleaning robot  41  can clean the areas near the light beam output by the light generating device  45  and the cleaning robot  41  will not enter a restricted area. Furthermore, the controller of the cleaning robot  41  can draw a map of the cleaning area. When the cleaning robot  1  from cleaning the same area again, the cleaning robot  41  can move according to the map of the cleaning area to complete the cleaning job efficiently and quickly. 
         [0048]    Although the embodiment of  FIG. 4  is illustrated with the light generating device  45 , the invention is not limited thereto. The method of  FIG. 4  can be applied to the charging station. The charging station outputs a guiding signal, such as a light beam, to direct the cleaning robot  41  to enter the charging station for charging. 
         [0049]    Furthermore, the embodiment of  FIG. 4  is illustrated with the non-omnidirectional light detector  42  but the invention is not limited thereto. The non-omnidirectional light detector  42  can be replaced by an acoustic signal detector or other kinds of signal detector. 
         [0050]      FIG. 5  is a schematic diagram of a control method for a cleaning robot according to another embodiment of the invention. The light generating device  55  outputs a light beam to label a restricted area that the cleaning robot  51  should not enter. In other embodiments, the light generating device  51  is named as light house or light tower and outputs the light beam or other wireless signals. The light beam comprises a first boundary b 1  and a second boundary b 2 . At time T 1 , the cleaning robot  51  moves along a predetermined route. At time T 2 , the non-omnidirectional light detector  52  detects a first boundary b 2  of a light beam emitted by the light generating device  55 . The cleaning robot  51  keeps moving along the predetermined route. At time T 3 , the non-omnidirectional light detector  52  detects the light beam and the cleaning robot  51  stops moving. The non-omnidirectional light detector  52  is then spun in a counter clockwise direction or a clockwise direction. 
         [0051]    When the mask  54  blocks the light beam emitted from the light generating device  54 , the non-omnidirectional light detector  52  cannot detect the light beam. A controller of the cleaning robot  51  records a current position of the mask  54  and estimates a first spin angle of the non-omnidirectional light detector  52  according to an initial position of the mask  54  and the current position of the mask  54  to determine a spin direction of the cleaning robot  51 . 
         [0052]    For example, assuming the first spin angle is less than 180 degrees, the cleaning robot  51  is spun in the clockwise direction. The cleaning robot  51  is spun in the counter clockwise direction when the first spin angle is larger than 180 degrees. 
         [0053]    At time T 4 , the cleaning robot  51  is spun according to the determined direction until the directional light detector  53  detects the light beam output by the light generating device  55 . When the directional light detector  53  detects the light beam output by the light generating device  55 , the cleaning robot  51  stops spinning. Generally speaking, when the directional light detector detects the light beam output by the light generating device  55 , the light detection units detecting the light beam are located at the margin of the directional light detector  53 . Thus, when the cleaning robot  51  moves again, the directional light detector  53  may fail to detect the light beam quickly and the cleaning robot  51  has to stop again to calibrate the moving direction. 
         [0054]    To solve the aforementioned issue, in one embodiment, the processor of the cleaning robot  51  estimates a delay time according to the angular velocity of the cleaning robot  51  and the size of the directional light detector  53 . When the directional light detector  53  detects the light beam, the cleaning robot  51  stops spinning after the delay time. By the delay time, the light beam output by the light generating device  55  can be detected by the center of the directional light detector  53 . 
         [0055]    It is noted that the cleaning robot  51  stays at the same position at times T 3  and T 4 . At time T 3 , the cleaning robot  51  is not moved or spun and only the non-omnidirectional light detector  52  is spun. At time T 4 , the cleaning robot  51  is spun in a circle at the original position. Although the position of the cleaning robot  51  at time T 3  is different from the position of the cleaning robot  51  at time T 4  in  FIG. 4 , it represents only two operations at the same position but at different times. In fact, the position of the cleaning robot  51  does not change at time T 3  and T 4 . 
         [0056]    In another embodiment, the operations of the cleaning robot  51  at time T 3  and T 4  can be integrated in one step. At time T 3 , the non-omnidirectional light detector  52  is spun in a predetermined direction, and the cleaning robot is also spun in the predetermined direction. When the directional light detector  53  detects the light beam output by the light generating device  55 , the cleaning robot  51  stops spinning. When the cleaning robot  51  stops spinning, the non-omnidirectional light detector  52  may be stopped or continues to spin. If the non-omnidirectional light detector  52  is still spinning the processor of the cleaning robot  51  determines the direction of the light beam to calibrate the moving direction of the cleaning robot  41  according to the spin angle of the non-omnidirectional light detector  52 . 
         [0057]    When the cleaning robot  51  moves to the light generating device  55 , the processor of the cleaning robot  51  records the moving paths of the cleaning robot  51  and labels the moving path and a restricted area on a map. In another embodiment, when the processor of the cleaning robot  51  determines the direction of the light beam output by the light generating device, the processor labels the light beam and the restricted area on the map. The map is stored in a memory or a map database of the cleaning robot  51 . The processor modifies the map according to the movement of the cleaning robot  51  and labels the positions of obstacles on the map. 
         [0058]    When the cleaning robot  51  approaches to the light generating device  55  and the distance between the cleaning robot  51  and the light generating device  55  is less than a predetermined distance, a touch sensor or an acoustic sensor outputs a stop signal to the controller of the cleaning robot  51 . The touch sensor or the acoustic sensor is disposed in the front end of the cleaning robot  51  to detect whether there is any obstacle in front of the cleaning robot  51 . When the touch sensor or the acoustic sensor detects an obstacle, the cleaning robot  51  first determines whether the obstacle is the light generating device  55 . If the obstacle is the light generating device  55 , the cleaning robot  51  stops moving and moves in another direction. If the obstacle is not the light generating device  55 , the cleaning robot  51  first leaves the original route to prevent the obstacle and returns to the original route after avoiding the obstacle. 
         [0059]    When the cleaning robot  51  approaches to the light generating device  55 , the light generating device  55  outputs a radio frequency (RF) signal or an infrared signal to inform the cleaning robot  51  know that the cleaning robot  51  is close to the light generating device  55 . In another embodiment, Near Field Communication (NFC) devices are embedded in both the cleaning robot  51  and the light generating device  55 . When the NFC device of the cleaning robot  51  receives signals or data from the NFC device of the light generating device  55 , it means that the cleaning robot  51  is close to the light generating device  55  and the cleaning robot  51  should stop accordingly. Generally speaking, the sensing distance of the NFC device is 20 cm. 
         [0060]      FIG. 6  is a flowchart of a cleaning route planning method for a cleaning robot according to an embodiment of the invention. In the step S 61 , the cleaning robot plans a cleaning area according to at least three means, which are selected from a light generating device, a wall, a charging station, an obstacle or an object at fixed positions. The light generating device, the wall, the charging station, the obstacle or the object may be an endpoint of the cleaning area or form a boundary of the cleaning area. The embodiment of  FIG. 6  is illustrated with the cleaning robot shown in  FIG. 3 . 
         [0061]    In the step S 62 , the cleaning robot estimates a center of the cleaning area. Then, the cleaning robot circles along the outline of the cleaning area from a first position. In another embodiment, the cleaning robot is placed near to one of the light generating device, the wall, the charging station, the obstacle or the object and circles along the outline of the cleaning area. 
         [0062]    When the cleaning robot moves within the cleaning area and detects the light beam output by the light generating device, the cleaning robot moves to or moves away from the light generating device along the light beam. Reference can be made to  FIG. 4  or  FIG. 5  for the detailed operation of the cleaning robot detecting the light beam. 
         [0063]    In step S 63 , the cleaning robot moves back to the first position and records a first cleaning route. In the step S 64 , the cleaning robot plans a second cleaning route according to the first cleaning route. Reference can be made to  FIG. 2   b  for the planning method of the second cleaning route. At first, the cleaning robot moves from the first position to a second position for a distance d. Then, the cleaning robot circles along the inter line of the first cleaning route. In this embodiment, the distance d is preset to be half of a width of the cleaning robot. 
         [0064]    In the step S 65 , the cleaning robot returns back to the second position. In the step S 66 , the cleaning robot first determines whether the second position is the center of the cleaning area or a distance between the second position and the center of the cleaning area is less than the distance d. If yes, the cleaning robot finishes its work. Then the cleaning robot can move to the charging station or move reversely to clean the cleaning area again. If not, step S 64  is executed and the cleaning robot moves the distance d to the center of the cleaning area and then moves according to the second cleaning route. 
         [0065]    In one embodiment, the step S 66  can be integrated in the step S 64 . When the cleaning robot moves to the second position, the cleaning robot first determines whether the second position is the center of the cleaning area or a distance between the second position and the center of the cleaning area is less than the distance d. If yes, the cleaning robot finishes its work and does not need to plan the second cleaning route. If not, the cleaning robot continues to execute its work. 
         [0066]      FIG. 7  is a flowchart of a cleaning route planning method for a cleaning robot according to another embodiment of the invention. In the step S 71 , the cleaning robot plans a cleaning area according to at least three means, which are selected from a light generating device, a wall, a charging station, an obstacle or an object at fixed positions. The light generating device, the wall, the charging station, the obstacle or the object may be an endpoint of the cleaning area or form a boundary of the cleaning area. The embodiment of  FIG. 7  is illustrated with the cleaning robot shown in  FIG. 3 . 
         [0067]    In the step S 72 , the cleaning robot estimates a center of the cleaning area. Then, the cleaning robot moves to the center, such as shown in  FIG. 2   c . Then, in the step S 74 , the cleaning robot moves and cleans the cleaning area in a spiral route. 
         [0068]    When the cleaning robot moves within the cleaning area and detects the light beam output by the light generating device, the cleaning robot moves to or moves away from the light generating device along the light beam. Reference can be made to  FIG. 4  or  FIG. 5  for the detailed operation of the cleaning robot detecting the light beam. 
         [0069]    While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To 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.