Patent Publication Number: US-2021176915-A1

Title: An autonomous lawn mower and a system for navigating thereof

Description:
TECHNICAL FIELD 
     The present invention relates to an autonomous lawn mower and a system for navigating thereof, and particularly, although not exclusively, to an autonomous lawn mower which uses a navigating system to control the navigation of the autonomous lawn mower during its operation. 
     BACKGROUND 
     The maintenance of lawns requires a significant amount of manual labour including constant watering, fertilizing and mowing of the lawn to maintain a strong grass coverage. Although watering and fertilizing can sometimes be handled with minimal effort by use of a sprinkler or irrigation system, the mowing process is one process that demands a significant amount of physical effort from gardeners. 
     Designers and manufacturers of lawn mowers have attempted to manufacture autonomous lawn mowers for some time to replace the traditional push pull mowers. However, the unpredictability of a landscape together with the cost of creating an accurate and usable product has meant many autonomous lawn mowers simply do not perform at an adequate level of performance. 
     This is in part due to the fact that gardens come in many different varieties and shapes, with different elevations and profiles. Thus the autonomous mowers have had significant trouble in navigating these different types of terrain. In turn, many push mowers are still preferred by users as their performance and control can still be manually controlled to overcome problems associated with different landscape profiles. 
     SUMMARY OF THE INVENTION 
     In the light of the foregoing background, it is an object of the present invention to provide an alternate lawn mower which eliminates or at least alleviates the above technical problems. 
     The above object is met by the combination of features of the main claim; the sub-claims disclose further advantageous embodiments of the invention. 
     One skilled in the art will derive from the following description other objects of the invention. Therefore, the foregoing statements of object are not exhaustive and serve merely to illustrate some of the many objects of the present invention. 
     In accordance with a first aspect of the present invention, there is provided an autonomous lawn mower comprising:
         a mower body having at least one motor arranged to drive a cutting blade and to propel the mower body on an operating surface via a wheel arrangement, wherein the mower body includes a navigation system arranged to assist a controller to control the operation of the mower body within a predefined operating area;   wherein the mower body further includes a signal detecting module arranged to detect a signal representative of a navigational marker.       

     In an embodiment of the first aspect, the navigational marker includes the location of an obstacle or boundary. 
     In an embodiment of the first aspect, the navigation system determines a position of the mower body within the predefined operating area based on the location of the obstacle or boundary. 
     In an embodiment of the first aspect, the autonomous lawn mower further includes a signal generating module arranged to generate the signal in the form of a loop. 
     In an embodiment of the first aspect, the signal detecting module includes a sensor arranged to detect the magnitude of the signal loop. 
     In an embodiment of the first aspect, the signal generating module generates a first aforesaid signal loop within the predefined operating area whereby the position of the mower body relative to the predefined operation area is determined by the controller based on the magnitude of the first signal loop detected by the sensor. 
     In an embodiment of the first aspect, the first aforesaid signal loop is emitted about the boundary of the predefined operation area. 
     In an embodiment of the first aspect, the signal generating module is positioned on a detachable docking module for detachably receiving the mower body. 
     In an embodiment of the first aspect, the detachable docking module generates a second aforesaid signal loop within a predefined docking area about the detachable docking module whereby the position of the mower body relative to the detachable docking module within the predefined docking area is determined by the controller based on the magnitude of the second signal loop detected by the sensor. 
     In an embodiment of the first aspect, the first and second signal loops are time shifted pulses with the same frequency. 
     In an embodiment of the first aspect, the sensor receives the pulse of the first and second signal loops when the mower body is at a position inside the predefined operating area and the predefined docking area. 
     In an embodiment of the first aspect, the controller identifies the first and second signal loops individually based on the time shift between the pulses of the first and second signal loops. 
     In an embodiment of the first aspect, the first signal loop includes a bidirectional current pulse. 
     In an embodiment of the first aspect, the sensor receives only the pulse of the first signal loop when the mower body is at a position inside the predefined operating area and outside the predefined docking area. 
     In an embodiment of the first aspect, the sensor detects two opposite polarity of the first signal loop when the mower body is positioned at a position inside the predefined operating area and a position outside the predefined operating area respectively. 
     In an embodiment of the first aspect, the sensor detects a first polarity of the first signal loop when the mower body is at a position inside the predefined operating area. 
     In an embodiment of the first aspect, the sensor detects a second, opposite polarity of the first signal loop when the mower body is at a position outside the predefined operating area. 
     In an embodiment of the first aspect, the mower body includes a plurality of aforesaid sensors, whereby the controller terminates the movement of the mower body upon all sensors are sandwiched between the first and second signal loops. 
     In an embodiment of the first aspect, the detachable docking module further includes a magnetic detection module for detecting the orientation of the mower body with respect to the detachable docking module. 
     In an embodiment of the first aspect, the magnetic detection module is a magnetomer. 
     In an embodiment of the first aspect, the second signal loop includes a unidirectional current pulse. 
     In an embodiment of the first aspect, the mower body, in a docking operation, is arranged to move towards a predefined docking area at the detachable docking module along the boundary of the predefined operation area. 
     In an embodiment of the first aspect, the mower body includes a plurality of aforesaid sensors, with at least two sensors each positioned on two opposite sides of the boundary of the predefined operation area respectively for detecting the magnitude of the first signal loop individually during the docking operation. 
     In an embodiment of the first aspect, the individual position of the two sensors relative to the boundary of the predefined operation area is determined by the controller based on the detected magnitude. 
     In an embodiment of the first aspect, the position of the mower body relative to the boundary of the predefined operation area is determined by the controller based on the individual position of the sensors relative to the boundary of the predefined operation area. 
     In an embodiment of the first aspect, the first signal loop detected by the sensors includes equal magnitude yet opposite polarity when the mower body is bisected by the boundary of the predefined operation area. 
     In an embodiment of the first aspect, the detachable docking module overlaps a portion of the boundary of the predefined operation area. 
     In an embodiment of the first aspect, the boundary of the predefined operation area bisects the detachable docking module in a longitudinal direction along which the mower body moves towards the predefined docking area. 
     In an embodiment of the first aspect, the mower body further includes an actuator for terminating the operation of the mower and, in response to the termination of the mower operation, releasing a portion of the mower body from a closed position at which a user control interface is covered to an opened position at which the user control interface is exposed. 
     In an embodiment of the first aspect, the actuator is arranged to actuate a micro switch for releasing a portion of the mower body from the closed position. 
     In an embodiment of the first aspect, the actuator is in communication with a magnetic sensor arranged to sense the movement of the cover between the closed position and the opened position. 
     In an embodiment of the first aspect, the mower body further includes a cutter module arranged to trim the edges of the predefined operating area. 
     In an embodiment of the first aspect, the cutting module includes at least two cutting bars movable in a reciprocating manner. 
     In an embodiment of the first aspect, the cutting bars are each driven by a driving motor respectively. 
     In an embodiment of the first aspect, the cutting module is placed at a position underneath the mower body and transverse to the longitudinal axis of the mower body. 
     In an embodiment of the first aspect, the mower body further includes a height adjustment system arranged to assist the controller to restrict the operation of the cutting blade within a predefined operating height. 
     In an embodiment of the first aspect, the height adjustment system includes one or more sensors arranged to detect the presence of the cutting blade at the predetermined vertical position. 
     In an embodiment of the first aspect, the height adjustment system is arranged to communicate with the controller for terminating the operation of the cutting blade upon the cutting blade reached the predetermined vertical position. 
     In an embodiment of the first aspect, the navigation system further includes an odometry module arranged to track the movement of the mower body on the operating surface. 
     In an embodiment of the first aspect, the rate of rotation of each of the wheels is applied to a transmission ratio to determine the rotation distance of the wheel. 
     In an embodiment of the first aspect, the odometry module is arranged to transmit the rotation distance and the direction of rotation of each wheel to the navigation system. 
     In an embodiment of the first aspect, the detachable docking module is arranged to provide battery charging to the mower body. 
     In an embodiment of the first aspect, the detachable docking module includes a rotatable member arranged to contact the mower body with a predefined vertical offset relative to the detachable docking module for battery charging. 
     In an embodiment of the first aspect, the rotatable member extends laterally from the detachable docking module. 
     In an embodiment of the first aspect, the rotatable member is pivotable about a horizontal axis that is parallel to the operating surface. 
     In an embodiment of the first aspect, the mower body includes an opening for receiving the rotatable member. 
     In an embodiment of the first aspect, the detachable docking module is provided a pair of resilient means for acting against the opposite sides of the rotatable member to maintain the orientation of the rotatable member. 
     In an embodiment of the first aspect, the rotatable member is provided a protective gasket for sealing between the rotatable member and the mower body and for flexible rotation of the rotatable member. 
     In an embodiment of the first aspect, the mower body further includes a blade adjustment system arranged to adjust the vertical position of the cutting blade along its rotating axis. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which: 
         FIG. 1  is an illustration of an autonomous lawn mower in accordance with one embodiment of the present invention; 
         FIG. 2  is a block diagram illustrating an example of various control systems and modules of the autonomous lawn mower of  FIG. 1 ; 
         FIG. 3  is a block diagram illustrating process flow of an initialisation process for the autonomous lawn mower of  FIG. 1 ; 
         FIG. 4  is a diagram showing the boundary wire loop and the docking wire loop of the autonomous lawn mower of  FIG. 1 ; 
         FIG. 5A  is a diagram showing signals transmitted from the docking station to the boundary wire loop; 
         FIG. 5B  is a diagram showing signals transmitted from the docking station to the docking wire loop; 
         FIG. 6  is a diagram showing an example signal received by the sensor of the autonomous lawn mower; 
         FIG. 7  is a diagram showing time shift between the boundary signal and the docking signal; 
         FIG. 8  is a block diagram illustrating an example induction sensor data acquisition algorithm of the autonomous lawn mower of  FIG. 1 ; 
         FIG. 9  is a diagram showing a sampled ADC data of the autonomous lawn mower of  FIG. 1 ; 
         FIG. 10A  is a diagram showing signal with positive polarity detected by the sensor of the autonomous lawn mower of  FIG. 1 ; 
         FIG. 10B  is a diagram showing signal with negative polarity detected by the sensor of the autonomous lawn mower of  FIG. 1 ; 
         FIG. 11  is a partial view of  FIG. 4  illustrating the arrangement of the boundary wire loop and the docking wire loop about the docking station of the autonomous lawn mower of  FIG. 1 ; 
         FIG. 12  is a diagram showing the pairs of sensors sandwiched between the boundary wire loop and the docking wire loop of  FIG. 11 ; 
         FIG. 13  is a block diagram illustrating a method of operating the autonomous lawn mower of  FIG. 1 ; 
         FIG. 14  is a diagram showing the docking station of the autonomous lawn mower of  FIG. 1 ; 
         FIG. 15  is a diagram showing the docking station of  FIG. 14 , with the boundary wire loop and the docking wire loop; 
         FIG. 16  is a diagram showing part of the docking station of  FIG. 14 ; 
         FIG. 16A  is a schematic diagram illustrating a method of docking the autonomous lawn mower of  FIG. 1 ; 
         FIG. 16B  is a diagram showing another example implementation of a docking station with boundary wire loop and docking wire loop; 
         FIG. 17  is a diagram illustrating an example implementation of an odometry module on a pair of opposing wheels of the autonomous lawn mower of  FIG. 1 ; 
         FIG. 18  is a diagram illustrating an example implementation of a wheel of the autonomous lawn mower of  FIG. 1 ; 
         FIG. 19  are illustrations of an example implementation of a wheel of the autonomous lawn mower of  FIG. 1 ; 
         FIG. 20  are illustrations of another example implementation of a height adjustment system for the autonomous lawn mower of  FIG. 1 ; 
         FIG. 21  is a diagram illustrating another example implementation of the height adjustment system of  FIG. 20 ; 
         FIG. 22  is yet another illustration of an example implementation of the height adjustment system of  FIG. 20 ; 
         FIG. 23  are illustrations of an example implementation of a docking module of the autonomous lawn mower of  FIG. 1 ; 
         FIG. 24  are schematic diagrams illustrating an example implementation of a docking module of the autonomous lawn mower of  FIG. 1 ; 
         FIG. 25  are illustrations of an example implementation of an emergency shut-off switch of the autonomous lawn mower of  FIG. 1 ; 
         FIG. 26  is a diagram illustrating an example implementation of the emergency shut-off switch of  FIG. 25 ; 
         FIG. 27  is yet another illustration of an example implementation of the emergency shut-off switch of  FIG. 25 ; 
         FIG. 28  are illustrations of an example implementation of a cutter module of the autonomous lawn mower of  FIG. 1 ; 
         FIG. 29  is a diagram illustrating an example implementation of the cutter module of  FIG. 28 ; 
         FIG. 30  is yet another illustration of an example implementation of the cutter module of  FIG. 28 ; 
         FIG. 31  are illustrations of an example implementation of a blade adjustment system of the autonomous lawn mower of  FIG. 1 ; 
         FIG. 32  is a diagram illustrating an example implementation of the blade adjustment system of  FIG. 31 ; 
         FIG. 33  is yet another illustration of an example implementation of the blade adjustment system of  FIG. 31 ; and 
         FIG. 34  is a diagram illustrating an example implementation of the calibration method of the autonomous lawn mower of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. 
     Terms such as “horizontal”, “vertical”, “upwards”, “downwards”, “above”, “below” and similar terms as used herein are for the purpose of describing the invention in its normal in-use orientation and are not intended to limit the invention to any particular orientation. 
     With reference to  FIG. 1 , there is provided an illustration of an autonomous lawn mower  100  comprising: a mower body  102  having at least one motor  212  arranged to drive a cutting blade  212   b  and to propel the mower body  102  on an operating surface via a wheel arrangement, wherein the mower body  102  includes a navigation system  204  arranged to assist a controller  202  to control the operation of the mower body  102  within a predefined operating area  414 , wherein the mower body  102  further includes a signal detecting module  222  arranged to detect a signal representative of a navigational marker. 
     In this example, the autonomous lawn mower  100  is arranged to operate on a lawn or grass grown surface so as to cut the grass. This action is commonly known as “mow the lawn” and is often undertaken by gardeners and landscape workers to maintain a lawn surface. The term autonomous lawn mower  100  may also include any type of grass cutting device or lawn mower which can operate autonomously, that is, with minimum user intervention. It is expected that user intervention at some point is required to set up or initialize the mower  100  or to calibrate the mower  100  with specific commands, but once these procedures have been undertaken, the mower  100  is largely adapted to operate on its own until further commands are required or if servicing, calibration or error correction is required. Accordingly, autonomous lawn mowers  100  may also be known as automatic lawn mowers, self-driven lawn mowers, robotic lawn mowers or the like. 
     In this embodiment as shown in  FIG. 1 , the autonomous lawn mower  100 , or referred to as the lawn mower or mower, includes a frame or housing  102  which supports the operating components of the mower  100 . These operating components may include, without limitation at least one motor, such as an electric motor, which is arranged to drive the blades of the mower  100  so as to cut the grass of a lawn to which the mower  100  is mowing. The at least one motor may also be used to drive the mower  100  itself via the means of transmission systems, such as gearing mechanisms or gearboxes which transmit a driving force to its wheel arrangements  104 , although preferably, as is the case of this embodiment, separate motors are used to drive the mower  100  along its operating surface with each rear wheel  104 R having its own individual motor and gearbox. This is advantageous in that manoeuvring the mower  100  may be implemented by simple control of each of these motors. It is important to note that the term wheel arrangements may also include driving arrangements that are formed from various different types and combination of wheels, including tracks (such as in tank tracks), chains, belts (such as in snow belts) or other forms of driving arrangements. 
     Preferably, as shown in the embodiment of  FIG. 1 , the mower  100  includes a navigation system  204  which operates to locate and navigate the mower  100  around a working area  414  so that the mower  100  can cut the grass of a working area  414 . The navigation system  204  may include a number of specific navigation modules each arranged to provide individual navigation information obtained for the mower  100 . In turn, the navigation information obtained or determined by each of these navigation modules are then returned to the navigation system  204  for transmission to a controller  202 . Upon processing of the navigation information by the controller  202 , the controller  202  may then generate commands which are used to control the movement and operation of the mower  100  within a work or operation area. 
     These navigation modules may include at least the follow:
         A signal detecting module  222  arranged to detect a signal representative of a navigational marker;   An odometry module  220  arranged to determine the distance travelled by the wheels  104  so as to assist in the determination of the location of the mower  100  from a starting point;   Other additional navigation modules (not shown) may also be implemented to communicate with the navigation system  204  so as to provide further input to the navigation system  204  to adjust and control the mower  100 , including:
           GPS sensors which can be used to obtain a GPS coordinate of the mower  100 . In some examples, the mower  100  may be implemented to use “RTK GPS” or Real Time Kinematic GPS which includes two GPS modules, one fixed and one in the mower  100  in addition to advanced GPS information to determine the precise position of the mower  100  within the mowing area  414  and world;   Compass sensors to obtain a compass bearing of the mower  100 ;   Rain sensors or water sensors to detect if the immediate environment is subject to rain, high levels of moisture or entry of the mower  100  into a puddle of water and if so, adjust or terminate operation of the mower  100 ;   Edge sensors or cliff sensors to detect if the mower  100  has reached an edge or a cliff whereby any further movement may cause the mower  100  to experience a fall;   Light sensors to detect light or time of day and adjust operation accordingly, including the switching on of warning lights; and,   Other additional sensors and function modules, such as clock, WiFi, Bluetooth, GSM, RF, DECT, or any other communication protocol modules arranged to receive COMMUNICATION PROTOCOLS external information received via communications connections such as weather reports or remote commands to enhance and control the operation of the mower  100 .   
               

     These navigation modules are each arranged to obtain, detect and determine a set of navigation related information, which are in turn arranged to be processed by a processor on the controller  202  to devise suitable commands to operate the mower  100 . As it will be explained below with reference to  FIGS. 8 and 9 , in one example, the autonomous lawn mower  100  will operate by moving away from a docking station  900  as shown in  FIGS. 11 to 16  which will form a start and return point for the mower  100 . The mower  100 , when departing the docking station  900  may then use the navigation system  204  to assist with navigating the mower  100  around a work or operation area  414  by cutting the lawn in the operating area  414 , and then proceeding to navigate its way back to the docking station  900 . 
     With reference to  FIG. 2 , there is provided a block diagram of the autonomous lawn mower  100  which illustrates the components of the autonomous lawn mower  100 . In this embodiment, the mower  100  includes a controller/processor  202  which may be implemented as a computing device, or as one or more control boards, with each having one or more processors arranged to receive and analyse the information received and to provide instructions to the mower  100  in order to operate the mower  100 . Preferably, the controller/processor  202  is implemented with a main printed circuit board assembly (PCBA) arranged to have two processors on the PCBA and to operate together with an additional computing module. Several of the sensor PCBAs may also have their own individual Microcontroller units (MCUs). 
     The controller/processors  202  is arranged to receive navigation information from the navigation system  204  of the mower  100  and in turn, upon the receipt of this navigation information, will process the navigation information with existing information already accessible by the controller  202  such as the control algorithm  206  or predefined map of the operating area  414  to generate various commands to each of the mower  100  operating components, including the drive motors arranged to drive the mower  100  and/or the blade motors  212  which operates the blades  212   b.    
     As shown in  FIG. 2 , the navigation system  204  includes a signal detecting module  222  which detects a signal representative of a navigational marker generated by a signal generating module  221  and includes an odometry module  220 , which further includes wheel sensors  232  to detect the rotational displacement of the wheels  104  of the mower  100 . Each of these modules  222  and  220  are arranged to provide a specific function which are described below with reference to  FIGS. 4 to 19  and return individual navigation information either detected, calculated, gathered or surveyed. 
     As illustrated in this embodiment, the controller  202  is also arranged to control the mower drive motors  210  to drive the mower  100  along a work surface within a work area  414 . Preferably, as is the case in this embodiment, the mower  100  is driven by having a motor  210  placed adjacent to each of the rear wheels  104 R with each motor  210  being arranged to drive each rear wheel  104 R. 
     In turn, the controller  202  can direct electric current from a power source, such as a battery  214 , to the motors  210  so as to perform a controlled operation of one or both motors  210 . This can allow for forward, reverse and turning actions of the mower  100  by turning one or more wheels at different speeds or directions. 
     The controller  202  can also command the blade motor  212  to operate so as to operate the blades  212   b  to cut the grass of a work surface. To perform these functions, the controller  202  will execute a control routine or process  206  which determines the conditions for and when the mower  100  is to be operated. These commands at least include instructions to command the direction of travel of the mower  100  and the operation of the blades  212   b . Other commands are also possible, including the command of the mower  100  to travel to a particular location within a work area  414 , or to return to a specific location, such as a docking station  900  as well as specific commands such as the operating speed of the blade motor  212  or the height of the blade  212   b  so as to determine the level of grass that is cut. 
     As it will be explained below with reference to  FIG. 2 , the controller  202  may also be pre-programmed with an initialization routine  228  wherein the mower&#39;s working area and work surfaces are initially identified. These process may assist in identify the boundaries of a working area  414  and the categorization that certain surfaces within the boundaries should be avoided (no travel zones) or should not have the blade motor  212  activated. Once these working areas  414  are identified, the mower  100  can then be controlled by the controller  202  to navigate to a starting point from the docking station  900 , wherein the mower  100  can proceed to cut the grass from the starting point as stipulated by the control algorithm  206 . The control algorithm  206  may include a specific cutting program, which mows the lawn along a longitudinal axis and then work each longitudinal axis in a latitudinal form within the working area  414  defined so as to cut the grass in the working area  414 . Other cutting programs are also possible and can be chosen base on the shape and profile of the working area  414  of the desired operation of a user. 
     Preferably, as the controller  202  will communicate with each of the navigation modules of the navigation system  204 , the controller  202  may, during initialisation and general operation, receive a large amount of different navigation information from each of these navigation modules  202 . In order to process this navigation information so as to determine operation commands for the mower  100 , the controller  202  may first apply a filter or an averaging function to all of navigation information received from the navigation system  204 . 
     Such a filtering function may allow the controller  202  to ignore or minimize any weighting placed on navigation information obtained from a first navigation module that appears to be incorrect when compared with navigation information obtained from other navigation modules. Example filters which can be used includes the Kalman Filter which can be applied to assist with identifying a “best fit” trend for all navigation information received by the controller and in turn, allowing anomalies, deviations or inconsistencies, which may be far away from the average or best fit trend, to be ignored or further investigated. 
     As an example, the controller  202  may receive navigation information from the odometry module  220 . During processing, the odometry module  220  may have tracked that the mower  100  has travelled to a particular co-ordinate on a virtual map obtained during the initialization of the mower  100 . However, according to the navigation information obtained by the signal detecting module  222 , the location of the mower  100  may be at a distance substantially far away from the co-ordinates obtained from the odometry module  220 . In these instances, when the filtering function is applied to all navigation information of the odometry module  220  and other navigation information, the “best fit” or “average” may in turn indicate that the co-ordinates of the odometry module  220  is an anomaly, as it is completely inconsistent with the other navigation modules. Accordingly, the controller  202  may then proceed to ignore this anomaly in generating commands to the mower. 
     It is also expected that the controller  202  may also apply a similar filtering function to all data obtained from the navigation system  204  and other sensors such as GPS sensors, compass, cliff sensors, water sensors etc. The Extended Kalman Filter, for example, may be advantageous in they are able to reduce/eliminate bad data points from each source and to assist in determining which sources of navigation/localization data are most reliable and use select these sources instead. 
     In some example embodiments, the filtering function or averaging function such as the Kalman Filter can also be applied by each navigation module to any navigation information obtained before the navigation information is communicated to the controller  202 . In these examples, as sensors and other electronic navigation modules are arranged to obtain data from environmental readings, it is possible that due to uncontrolled incidents or other environmental factors may cause certain readings to be incorrect within a short timeframe. Examples of these may include the mower experiencing wheel spin, and thus causing erroneous readings by the odometry module  220 , or signal interference by a random signal emitting source, in which case the navigation information obtained from the signal detecting module  222  may also be erroneous. 
     In these instances, by including a filtering function with each navigation module, such anomalies in the data collected by each navigation module may be filtered or “cleaned up” before it is sent to the controller  202 . Thus this this would advantageous in that the navigation information sent to the controller  202  is likely to be more accurate, resulting in improved performance and less processing by the controller  202 . 
     With reference to  FIG. 3 , there is provided a block diagram illustrating the process flow of the initialization process of the autonomous mower  100 . As illustrated, the user may start to issue commands to the mower  100  to drive the mower  100 . These commands are received (step  902 ) and processed by the controller  202  so as to drive the mower  100  along a surface (step  904 ). 
     Meanwhile, the navigation system  204  is operated (step  906 ) so as continuously survey and records any navigation information for the mower  100  during its initialization process. The navigation system  204  may then active each of its navigation modules  910  (Odometry and other sensors) to record such navigation information (step  908 ) which can be used for navigation purposes when the mower  100  is put into autonomous operation. 
     With reference to  FIG. 4 , there is illustrated a signal generating module  221  arranged to generate a signal, preferably in the form of a loop, representative of a navigational marker including the location of an obstacle or boundary  410 ,  420 . On the other hand, the mower body  102  includes a signal detecting module  222  e.g. a sensor arranged to detect the signal representative of such navigational marker. The navigation system  204  determines a position of the mower body  102  within a predefined operating area  414  based on the location of such obstacle or boundary. 
     The signal generating module  221  may generate a plurality of signal loops with different magnitude such that the signal may only be detected within a particular range or area. For instance, the signal generating module  221  may include a boundary wire  410  for generating a first, boundary signal loop  412  within the predefined operating area  414 . The position of the mower body  102  relative to the predefined operating area  414  is determined by the controller  202  based on the magnitude of the first signal loop  412  detected by the sensor  222 . Preferably, the boundary signal loop  412  is emitted about the boundary of the predefined operating area  414 . 
     In one further embodiment, the signal generating module  221  is at least partially positioned on a detachable docking module  900  detachably receiving the mower body  102 . The detachable docking module  900  may include a docking wire  420  for generating a second, docking signal loop  422  within a predefined docking area  424  about the detachable docking module  900 . The position of the mower body  102  relative to the detachable docking module  900  within the predefined docking area  424  is determined by the controller  202  based on the magnitude of the second signal loop  422  detected by the sensor  222 . 
     The first and second signal loops  412 ,  422  may be emitted by the same signal generating module  221  to the boundary wire  410  and the docking wire  420  as pulses with the same frequency e.g. 15 Hz at the same frequency e.g. 53 Hz respectively. Preferably, the first signal loop  412  may include a bidirectional current pulse with an example pattern of 1, 1, −1, 1 as depicted in  FIG. 5A . The second signal loop  422  may include a unidirectional current pulse with an example pattern of 0, 0, 1, 0, 1, 0 as depicted in  FIG. 5B . The combination of the two current pulses, as depicted in  FIG. 6 , are transmitted from the signal generating module  221  to the boundary wire  410  and the docking wire  420  respectively. 
     Advantageously, the docking station  900  may determine the length of the boundary wire  410  and calibrate at start-up to adjust the signal strength based on the wire length. This ensures that the signal is emitted by the signal generating module  221  at constant signal strength, regardless the dimension of the boundary wire  410 . 
     In one example application, the sensor  222  receives the first and second signal loops  412  and  422  when the mower body  102  is at a position inside the predefined operating area  414  as well as the predefined docking area  424 . To allow the sensor  222  to distinguish between the signals  412 ,  422  emitted by the boundary wire  410  and the docking wire  420  at the same frequency thereby identify each of the two signal loops individually and in turn determine the magnitude thereof respectively, the signals  412 ,  422  are emitted as two time shifted pulses spaced by e.g. (⅓)*T therebetween. The time difference between the two signals  412 ,  422  may be manipulated to identify each of the boundary and docking signals  412 ,  422  on the sensor  222  side. 
     With reference to  FIG. 8 , there is also provided an induction sensor data acquisition algorithm  3000  for processing the data associated with the signals  412 ,  422  received by the sensor  222 . The process begins at step  3001  with ADC Data Sampling. ADC channel is sampled for a time span enough to capture sampled ADC data including at least two complete boundary loop signal  412  and docking loop signal  422  as shown partially in  FIG. 9 . At step  3002  of Data Filtering, a biquad band bass filter is used to filter noisy data. 
     At step  3003  of Data Processing and Signal Characterization, received data is processed to retrieve information associated with number of signals in acquired data, each signal position (start point) in sampled array, pulse count in each signal, and maximum and minimum value of each signal. 
     At step  3004 , the data acquisition may proceed to different steps depending on the amount of signal received. For instance, if more than one signal is received in the sampled array, this implies the sensor  222  of the mower body  102  is positioned within the operating area  414  as well as the docking area  424 . The process is then proceeded to step  3005  for position based signal identification. The time difference between the start points of signals  412 ,  422  would be used to identify each of the boundary loop signal  412  and the docking loop signal  422 . 
     Upon the completion of data processing, signal characterization and identification of steps  3003  to  3004 , the only remaining signal would be the signal  412  of the boundary loop  410 , as depicted in  FIG. 10A or 10B . 
     The pulse count for boundary signal  412  is validated at step  3006 . A pre-sampled data for boundary loop  412  is stored in memory. The received signal is cross-correlated with pre-sampled data e.g. a known signal at a specific distance to arrive final output data at step  3007 . Preferably, the cross-correlation may include the use of matched filter. 
     For instance, the cross-correlation may result in a negative value output when the matched filter is applied to the received signal which is opposite in polarity with presampled data. The sign of the matched filter output may indicate whether the sensor  222  of the mower body  102  is positioned inside or outside the boundary loop  410 . 
     Meanwhile, the pulse count for docking signal  424  is also validated at step  3008 , and the docking signal power is computed at step  3009 . 
     Preferably, the sensor  222  may only receive the pulse  412  of the boundary loop  410  when the mower body  102  is at a position inside the predefined operating area  414  whilst outside the predefined docking area  424 . Upon detecting the pulse  412  of the boundary loop  410  with a magnitude exceeding a predetermined threshold by the sensor  222 , the movement of the lawn mower  100  would be significantly reduced, thereby preventing the lawn mower  100  from winding the boundary wire  410 . 
     In one example embodiment, the sensor  222  may detect whether the mower body  102  is positioned within the boundary wire  410  or outside the boundary wire  410  based on the polarity of the boundary loop signal  412 . For instance, the sensor  222  may detect a first polarity of the boundary signal loop  412 ′ e.g. a positive polarity, as depicted in  FIG. 10A , when the mower body  102  is at a position inside the predefined operating area  414 . In contrast, the sensor  222  may detect a second opposite polarity of the boundary signal loop  412 ″ e.g. a negative polarity, as depicted in  FIG. 10B , when the mower body  102  is at a position outside the predefined operating area  414 . 
     If only one signal is received in the sampled array, this implies the sensor  222  of the mower body  102  is not proximate to the docking loop  422  and thus only signal  412  from the boundary loop  410  is received. Before further processing, certain conditions are checked for verification. If the only signal received by the sensor  222  is verified to be the boundary loop  410 , the process will bypass step  3005  and directly proceed to step  3006  for validating the pulse count for boundary signal  412  and step  3007  for cross correlating with the pre-sampled data. 
     With reference to  FIGS. 11 to 12 , the mower body  102  may include a plurality of aforesaid sensors  222  e.g. two pairs of front and rear sensors  222 F,  222 R, whereby the controller  202  terminates the movement of the mower body  102  upon all the front and rear sensors  222 F,  222 R are sandwiched between the boundary signal loop  412  and the docking signal loop  422 . For instance, the sensors  222 F,  222 R are placed inside the docking station  900  for accurate docking. The sensors  222 F,  222 R and the two loops i.e. boundary loop  412  and docking loop  444  within the docking station  900  are placed in such a fashion that when the lawn mower  100  is parked in the docking station  900 , each of the sensors  222 F,  222 R is outside the docking loop  420  whilst inside the boundary loop  410 . 
     The detachable docking module  900  also includes a magnetic detection module e.g. magnetomer for detecting the orientation of the mower body  102  with respect to the detachable docking module  900 . 
     During initial step up of the lawn mower  100 , the docking station  900  is secured in ground and a calibration process is performed prior to normal operation of the lawn mower  100  by the user. This calibration records the heading of the docking station  900  i.e. yaw position. Such information would be used in subsequent docking cycles for docking operation. The yaw position of the docking station  900  may be recalibrated by going through the same calibration process when necessary. 
     With reference to  FIG. 13 , there is also provided a method  4000  of operating the autonomous lawn mower  100 . The autonomous lawn mower  100  may be operated normally for automated lawn mowing, for example in a random cutting mode, until the battery charge is low. Upon the battery drops below a predefined threshold or receives a docking signal/instruction from the detachable docking module  900  at step  4001 , the autonomous lawn mower returns to the detachable docking module for battery charging. 
     For instance, during the cutting operation, the lawn mower  100  moves around the operating area  414  in a random manner and the sensors  222  attempt to detect the docking station signal at step  4002 . 
     In a first scenario, the lawn mower  100  is positioned remote from the docking station  900  and the sensor  222  yet to detect the docking station signal  422 . At step  4003 , the mower body  102  follows the boundary wire  410  until it is proximate to the docking station  900 . The presence of docking station  900  at any point is determined based on the power level of received docking wire signal  412  by the sensors  222 . For instance, this may be achieved by receiving docking wire signal  412  with a power higher than a predefined threshold. 
     At step  4004 , the lawn mower  100  is proximate to the docking station  900  and the controller  202  uses area sensors data along with yaw data to align itself with the docking station  900 , for example, by taking one or more turns e.g. turning at 90° twice to come in front of docking station  900 . Upon orienting the lawn mower  100  to the docking station  900 , the mower body  102  then moves towards docking station  900  until the boundary wire  410  is crossed by the pair of front sensors  222 F at step  4005 . Finally, the mower body  102  moves in a channel  430  formed between the boundary and docking wires  410 ,  420  as depicted in  FIG. 11 , and continue until a charging signal is detected by the docking station  900  at step  4006 . 
     In a second scenario, the lawn mower  100  is already proximate to the docking station  900  and the sensors  222 F,  222 R has already detected the docking station signal  422  at step  4002 . Without taking steps  4003  to  4004 , the mower body  102  will move towards the docking station  900  in a forward direction in a straight line based on yaw orientation of docking station  900  with respect to the lawn mower  100  and continues until the boundary wire  410  is first crossed by the pair of front sensors  222 F and the two pairs of front and rear sensors  222 F,  222 R move in the channel  430  between the boundary and docking wires  410 ,  420  from steps  4005  to  4006 . 
     With reference to  FIG. 16A , there is provided an alternative docking method for in-line docking the autonomous lawn mower  100  to the aforementioned predefined docking area  424  along the aforementioned boundary wire  410 . For instance, the predefined docking area  424  may be located about the boundary of the predefined operating area  414  and overlap at least a portion of the boundary wire  410 . 
     In one example embodiment, the boundary wire  410  may bisect the predefined docking area  424  in a longitudinal direction, such that the boundary wire  410  may overlap the centre line of the predefined docking area  424 . The mower body  102  may enter the docking area  424  from one end  426  of the predefined docking area  424  along the centre line and until the front mower body  102  reaches the further end  428  of the predefined docking area  424 . Accordingly, the mower body  102  may dock accurately within the predefined docking area  424  once the centre of the mower body  102  is in line with the boundary wire  410  in the early stage of the docking operation. 
     Preferably, the mower body  102  may move towards and dock within the docking area  424  with the aiding of only single boundary wire  410 . Throughout the in-line docking operation, two, left and right front sensors  222 FL and  222 FR on the mower body  102  are each positioned on two opposite sides of the boundary wire  410  and each receives the boundary signal  412  emitted from the boundary wire  410  respectively. The left and right front sensors  222 FL should receive boundary signal  412  in opposite polarity. For instance, the left front sensor  222 FL may receive the boundary signal  412  with a first, negative polarity and the right front sensor  222 FR may receive the boundary signal  412  with a second, positive polarity. 
     To maintain the spacing between each of the two front sensors  222 FL and  222 FR and the boundary wire  410  individually, the autonomous lawn mower  100  may further include a controller e.g. a closed loop controller for detecting the individual spacing of the front sensors  222 FL and  222 FR from the boundary wire  410 . For instance, the magnitude of the boundary signal  412  may be detected by the front sensors  222 FL and  222 FR respectively and the individual spacing between the sensors  222 FL and  222 FR and the boundary wire  410  may be determined based on the detected magnitude. Subsequently, the position of the mower body  102  relative to the boundary wire  410  may be determined by the controller based on the relative positions of the sensors  222 FL and  222 FR. In general, the left and right front sensors  222 FL and  222 FR should receive equal magnitude of signal loop  412  with opposite polarity from the boundary wire  410  respectively when the mower body  102  is bisected by the boundary wire  410  i.e. the centre of the mower body  102  is in line with the boundary wire  410 . 
     During the continuous docking operation, the controller may manipulate the movement and orientation of the mower body  102  based on the real-time positioning feedback from the two front sensors  222 FL and  222 FR. This ensures that the mower body  102 , on its way to the docking area  424 , may be positioned in a desirable orientation and travel in a path overlapping the boundary wire  410  to reach the predefined docking area  424 . 
     Optionally, there may also be provided an additional pair of rear sensors  222 R on the rear end of the mower body  102  for determining the magnitude of the boundary signal  412  in a similar manner. The accuracy of the position and orientation of the mower body  102  determined by the controller may be improved. 
     In one alternative example embodiment as shown in  FIG. 16B , there is shown a docking module  900  having part of the boundary wire  410  and an auxiliary docking wire  420  provided within a predefined docking area  424  in the detachable docking module  900 . The auxiliary docking wire  420  emits a boundary signal  422  for assisting the docking operation of the mower  100 , especially when the mower  100  proximate to the docking module  900 . Preferably, the auxiliary docking wire  420  is bisected by at least a portion of the boundary wire  410 . 
     Upon the mower  100  enters the docking area  424  from one end  426  of the predefined docking area  424  along the centre line, the front sensors  222 FL and  222 FR may detect two, a boundary signal  412  and a docking signal  422 . The magnitudes of these signals, especially the docking signal  422  may be detected by the front sensors  222 FL and  222 FR respectively. The individual spacing between the sensors  222 FL and  222 FR and the adjacent portions of the docking wire  420  may be determined based on the detected magnitude. Subsequently, the position of the mower body  102  relative to the docking wire  420  may be determined by the controller based on the relative positions of the sensors  222 FL and  222 FR. 
     If the mower  100  reaches the final docking position, the left and right front sensors  222 FL and  222 FR should receive equal magnitude of signal loop  412  with opposite polarity as well as equal magnitude of signal loop  422 . This indicates that the left and right front sensors  222 FL and  222 FR are positioned outside and about the docking wire  420  whilst one of the front sensors  222 FL and  222 FR remains inside the boundary loop  410 . 
     With reference to  FIG. 17 , there is illustrated an example of an odometry module  220  arranged to be implemented with an autonomous mower  100 . In this example embodiment, the odometry module  220  is arranged to be implemented into each of two motors arranged to drive the rear wheels  104 R of the mower  100 , although as a person skilled in the art would appreciate, if additional motors are used to drive other wheels of the mower  100 , than this odometry module  220  can also be implemented into each of the motor windings  302 . 
     In this example, the odometry module  202  is arranged to measure the number of rotations of the wheels  104 R to which the odometry module  202  is implemented to operate with. In turn, the number of rotations, when coupled with the circumference of the wheel  104 R will provide an estimation as to the distance travelled by the mower  100  on a work surface (taking into account any gear ratios, if applicable). As the mower  100  may also turn along its work surface by allowing its opposing wheels to spin in opposite directions, such movements and rotation can also be detected and measured so as to determine the direction and rate of turn of the mower  100  along a work surface. 
     As illustrated in  FIG. 17 , the odometry module  202  is implemented onto a motor  302  and gearbox arrangement  304  which drives one of the rear wheels  104 R, with each rear wheel  104 R having its own motor  302  and gearbox  304 . When the motor  302  is energised by its power source, in most instances by command of the controller  202 , the motor will rotate  302  and thus also driving a gearbox  304  which is rotatably attached to the motor  302 . 
     The gearbox  304  will then also transmit this rotational force to the wheels  104 R and thus turning the wheels  104 R in a desired direction. As the gearbox ratio is known, either by presetting at the factory, or user adjustment, the odometry module  202  can thus operate by detecting the number of rotation of the motor  302  which can in turn be used to calculate the number of rotations of the wheel  104 R. 
     In this implementation, the motor has a Print Circuit Board (PCB)  306  connected to the motor windings  302  and rotor which is implemented with a number of hall sensors  308 . These hall sensors  308  allow a magnetic signal to be detected upon each sensor  308  being rotated passed a magnet (or have a magnet rotated pass the sensor  308 ) and thus when the motor is rotated, the PCB  306 , which is static, will detect the magnets held in the rotor of the motor  302 . The hall sensors  308  located on the PCB  306  can thus detect a magnet as it is passed during the rotation of the motor windings  302 . In turn, this data from the hall sensors  308  can then be used to calculate the number of or portions of rotations of the motor  302 , which can then be used to calculate the number of rotations of the wheel  104 R via the gearbox  304 . 
     Once the number of rotations is determined, the number of rotations of each wheel  104 R, including its direction and whether the wheels  10 R are undergoing a turning direction, will then be transmitted to the controller  202  for processing. In turn, the controller  202  can then process this result with other information from the navigation system  204  to ascertain the location of the mower  100 . 
     It is expected that the wheels of the mower  100  may undergo some wheel spin when the mower  100  is in operation, as the surface type may cause the wheels  104 R to spin without moving the mower  100 . Such wheel spins will result in error when determining the position of the mower  100 . However, such errors are factored into the calculation by the controller  202  as other navigation information obtained by other modules of the navigation system  204  will be used to compensate for any errors of one individual navigation module. 
     In another example implementation, the amount of electric current drawn by the motor  302  may also be measured and compared against the rotation rate detected by the odometry module  202 . In such examples, if the current drawn by the motor  302  is very low relative to the number of rotations detected of the wheel  104 R, then the wheels  104 R of the mower  100  may indeed be spinning along its working surface. Accordingly, such information may also be considered by the controller  202  in determining the distance of the mower  100  based on its odometry measurement. 
     With reference to  FIGS. 18 to 19 , there is provided an illustration of an autonomous lawn mower  100  comprising: a mower body  102  having at least one motor arranged to drive a cutting blade  212   b  and to propel the mower body  102  on an operating surface via a wheel arrangement, wherein the mower body  102  includes a navigation system  204  arranged to assist a controller  202  to control the operation of the mower body  102  within a predefined operating area  414 ; wherein the mower body  102  further includes a signal detecting module  222  arranged to detect a signal representative of a navigational marker and the navigation system  204  further includes an odometry module  202  arranged to track the movement of the mower body  102  on the operating surface. 
     With reference to  FIGS. 20 to 22 , there is provided an illustration of an autonomous lawn mower  100  comprising: a mower body  102  having at least one motor arranged to drive a cutting blade  212   b  and to propel the mower body  102  on an operating surface via a wheel arrangement, wherein the mower body  102  includes a navigation system  204  arranged to assist a controller  202  to control the operation of the mower body  102  within a predefined operating area  414 ; wherein the mower body  102  further includes a signal detecting module  222  arranged to detect a signal representative of a navigational marker and the mower body  102  further includes a height adjustment system  1100  arranged to assist the controller  202  to control the operation of the cutting blade  212   b  within a predefined operating height. 
     In this embodiment as shown in  FIGS. 20 to 22 , the autonomous lawn mower  100  includes a height adjustment system  1100  comprising a height adjustment motor  1110 , a worm shaft  1120  driven by the height adjustment motor  1110 , a limit switch  1130 , and a hall sensor  1140 . Advantageously, the motor  1110  may manipulate the rotating direction of the worm shaft  1120  in clockwise or anticlockwise directions, such that the height of the cutting blade  212   b  with respect to the operating surface may be manipulated by the motor  1110  indirectly. 
     The motor  1110  may be secured to the mower body  102  and remains stationary throughout the height adjusting operations. For instance, the cutting blade  212   b  may be moved towards the operating surface when the worm shaft  1120  rotates in a clockwise direction, and on the other hand, moved further away from the operating surface when the worm shaft  1120  rotates in an anti-clockwise direction. 
     Optionally, the mechanical transmission between the motor  1110  and the cutting blade  212   b  through the worm shaft  1120  may be enhanced by the use of a ring shaped structure  1150 . In this embodiment, the ring shaped structure  1150  preferably comprises a plurality of bushings  1152 , e.g. made of Polyoxymethylene (POM), a plurality of linear bearings  1156 , or alternatively a combination thereof for supporting the height adjustment system  1100 . Advantageously, the linear bearing  1156  may counter the torsional force induced by the distance between the worm shaft  1120  and the opposite support. 
     In one embodiment, the plurality of bushings  1152  may be disposed about the blade motor  212 . A plurality of through holes  1154  may be disposed preferably equidistantly for receiving these bushings  1152 , and at least one linear bearing  1156  may be disposed about the lower end of the bushing  1152  opposed to the worm shaft  1120 . During the height adjusting operation, the ring shaped structure  1150  may reinforce the worm shaft  1120 , such that the rotational force of the motor  1110  is converted into lateral forces steadily without out any vibrations or at least with minimal vibrations. 
     Although the worm shaft  1120  is located eccentrically to the central axis of the height adjustment system  1100  and it may inevitably exert a side loading against the height adjustment system  1100 , the linear bearing  1156  may advantageously reduce the friction between the shaft  1120  and the ring shaped structure  1150  due to the bending moment. Accordingly, the rotational force of the motor  1110  is converted into lateral forces steadily without transmitting the bending moment to the height adjustment system  1100 . 
     In this embodiment as shown in  FIGS. 20 to 21 , the limit switch  1130  is disposed on the blade motor  212 , with a thin and elongated portion  1132  further extended away from the blade motor  212  and towards the inner mower body  102 . Preferably, the hall sensor  1140  is disposed on top of the motor  1110  for detecting the presence of the elongated portion  1132  of the limit switch  1130 , thereby determining if the cutting blade  212   b  has reached the maximum height with respect to the operating surface. Advantageously, the hall sensor  1140  may further derive the number of rotations required by the motor  1110  to reach the predefined desirable operating height, and in turn assist the controller  202  to control the operation of the cutting blade  212   b.    
     Optionally, the combination of limit switch  1130  and hall sensor  1140  may be substituted by sensors e.g. photoelectric sensors. For instance, the photoelectric sensor may provide a signal to the height adjustment system  1100 , indicating the height position of the cutting blade  212   b , upon detecting the presence of the elongated portion  1132 , or alternatively in the absence of the elongated portion  1132 . It would also be appreciated by person skilled in the art that the sensing function may be achieved by other alternative sensing means. 
     In one example embodiment, the cut height of the blade assembly  212   b  is adjustable for carrying out a normal mowing operation at a desirable operating level. Initially, the blade assembly  212   b  is adjusted to an uppermost position through a first rotating direction of the blade motor  212  until the limit switch  130  is engaged by an engaging member (not shown). Subsequently, the blade motor  212  is driven in an opposite rotating direction until it reaches the desirable operating level. The vertical distance between the uppermost position of the blade assembly  212   b  and the desirable position of the blade assembly  212   b  is calculated by the hall sensor  1140 . 
     With reference to  FIGS. 23 to 24 , there is provided an illustration of an autonomous lawn mower  100  comprising: a mower body  102  having at least one motor arranged to drive a cutting blade  212   b  and to propel the mower body  102  on an operating surface via a wheel arrangement, wherein the mower body  102  includes a navigation system  204  arranged to assist a controller  202  to control the operation of the mower body  102  within a predefined operating area; a detachable docking module  900  arranged to provide battery charging to the mower body  102 ; wherein the mower body  102  further includes a signal detecting module  222  arranged to detect a signal representative of a navigational marker. 
     Preferably, the detachable docking module  900  further includes a rotatable member  940  arranged to contact the mower body  102  with a predefined vertical offset relative to the detachable docking module  900  for battery charging. 
     Upon the lawn mower  100  has been used over certain time period, there may be an offset between the opening  922  of the motor body  102  and the charging terminal. For instance, if there is mud and grass stuck on the mower&#39;s wheels  104 , the height of the mower  100  may be shifted upwards relative to the docking station  900 . Furthermore, if the wheels  104  wear down over time, the height of the charging area on the mower  100  may be lowered relative to the docking station  900 . A rotatable charging member  940  may compensate such vertical offset between the docking station  900  and the mower body  102 . 
     In one example, there may be provided a rotatable, spring loaded charging terminals  940 . The rotatable member  940  may extend laterally from the detachable docking module  900  and pivotable about a horizontal axis that is parallel to the operating surface. On the other hand, the mower body  102  may include an opening  922  for receiving the rotatable member  940 . Advantageously, the charging terminals  940  may be pivotable about an axis perpendicular to the charging terminals  940  such that the terminal  940  may rotate only in the vertical direction within a desirable range of rotation angles, rather than rotate in the horizontal direction. 
     To maintain the orientation of the rotatable member  940  upon the rotatable member  940  is inserted into the opening  922  of a mower body  102  with a vertical offset therebetween, the docking module  900  may provide a pair of resilient means  942  for acting against the opposite sides of the rotatable member  940 . For instance, a pair of springs  942  may be used to ensure that the terminals  940  rest at the nominal designed position and do not sag due to gravity. 
     Optionally, to facilitate the matching between the rotatable member  940  and the opening  922  with a substantial vertical offset therebetween, the rotatable member  940  may further provide a flexible, protective gasket  944  e.g. made of rubber for reducing the impact between the rotatable member  940  and the mower body  102  during the docking process. Advantageously, the protective gasket  944  provides a tight sealing between the rotatable member  940  and the mower body  102  and allows a flexible rotation of the rotatable member  940 . 
     With reference to  FIGS. 25 to 27 , there is provided an illustration of an autonomous lawn mower  100  comprising: a mower body  102  having at least one motor arranged to drive a cutting blade  212   b  and to propel the mower body  102  on an operating surface via a wheel arrangement, wherein the mower body  102  includes a navigation system  204  arranged to assist a controller  202  to control the operation of the mower body  102  within a predefined operating area, wherein the mower body  102  further includes a signal detecting module  222  arranged to detect a signal representative of a navigational marker and an actuator for terminating the operation of the mower  100  and, in response to the termination of the mower  100  operation, releasing a portion of the mower body  102  from a closed position at which a user control interface is covered to an opened position at which the user control interface is exposed. 
     In one example, the mower body  102  has a chassis  103  e.g. a base, a hood  105  e.g. cover of a control compartment/panel  106  movable relative to the chassis  103 , and one or more magnetic sensors  107  mounted for detecting displacement of the hood  105  relative to the chassis  103 . An actuator  110  e.g. an emergency shut-off switch, in the form of a push button or embedding a micro switch  112 , is provided in a recess of the hood  105  and communicated with the magnetic sensors  107 . 
     There is also provided an operation interface  114  with a stop button  115 , and a display (not shown) within the chassis  103  and concealed by the hood  105  during normal operation. The emergency shutoff switch  110 , when actuated by the user, stops the autonomous lawn mower  100  and releases the hood cover  105  to expose the control compartment/panel  106  to the user. 
     With reference to  FIGS. 28 to 30 , there is provided an illustration of an autonomous lawn mower  100  comprising: a mower body  102  having at least one motor arranged to drive a cutting blade  212   b  and to propel the mower body  102  on an operating surface via a wheel arrangement, wherein the mower body  102  includes a navigation system  204  arranged to assist a controller to control the operation of the mower body  102  within a predefined operating area, wherein the mower body  102  further includes a signal detecting module arranged to detect a signal representative of a navigational marker and a cutter module arranged to trim the edges of the predefined operating area. 
     In this embodiment as shown in  FIGS. 29 to 30 , the autonomous lawn mower  100  includes a cutter module  1500  positioned underneath the mower body  102  and transverse to the longitudinal axis of the mower body  102 . The cutter module  1500  includes a perimeter cutter  1502  for trimming the edges of a predefined operating area  414 . Preferably, the cutting module  1500  includes at least two cutting bars  1510 ,  1520  movable in a reciprocating manner. The cutting bars  1510 ,  1520  are each driven by a driving motor  1530  respectively. Optionally, the cutting bars  1510 ,  1520  may be driven by two individual motors (not shown) individually. 
     With reference to  FIGS. 31 to 33 , there is provided an illustration of an autonomous lawn mower  100  comprising: a mower body  102  having at least one motor arranged to drive a cutting blade  212   b  and to propel the mower body  102  on an operating surface via a wheel arrangement, wherein the mower body  102  includes a navigation system  204  arranged to assist a controller  202  to control the operation of the mower body  102  within a predefined operating area  414 , wherein the mower body  102  further includes a signal detecting module arranged to detect a signal representative of a navigational marker and a blade adjustment system arranged to adjust the vertical position of the cutting blade  212   b  along its rotating axis  213 . 
     In this embodiment as shown in  FIGS. 31 to 33 , the cutting blade  212   b  is rotatably mounted on a rotating shaft  213  driven by the motor  212 . The front end of the rotating shaft  213  is provided external thread  213   a  about which a nut  215  is rotatably mounted for sandwiching the centre portion of the cutting blade  212   b  therebetween. The advantages of the blade adjustment system in that, the position of the nut  215  may be adjusted along the external thread  213   a . This ensures that the lawn mower  100  may be readily adapted for accommodating cutting blades  212   b  with different thickness. 
     With reference finally to  FIG. 34 , there is provided a method of calibrating the autonomous lawn mower  100 . In one example embodiment, the autonomous lawn mower  100  is positioned in front of the docking station  900 . To trigger the calibration, the autonomous lawn mower  100  is positioned to face towards the docking station charging terminal and adjacent to the edge of the docking pad  901 . In response to this triggering act, the docking station yew angle is measured and such measurement may assist the docking the aforesaid docking process. Preferably, the power of the signal of the boundary wire  410  received by the induction sensor is magnified by a predetermined factor, thereby improving the calibration accuracy. 
     Although not required, the embodiments described with reference to the Figures can be implemented as an application programming interface (API) or as a series of libraries for use by a developer or can be included within another software application, such as a terminal or personal computer operating system or a portable computing device operating system. Generally, as program modules include routines, programs, objects, components and data files assisting in the performance of particular functions, the skilled person will understand that the functionality of the software application may be distributed across a number of routines, objects or components to achieve the same functionality desired herein. 
     It will also be appreciated that where the methods and systems of the present invention are either wholly implemented by computing system or partly implemented by computing systems then any appropriate computing system architecture may be utilised. This will include stand alone computers, network computers and dedicated hardware devices. Where the terms “computing system” and “computing device” are used, these terms are intended to cover any appropriate arrangement of computer hardware capable of implementing the function described. 
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. 
     Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge, unless otherwise indicated.