Patent Description:
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.

<CIT> discloses an autonomously navigating lawn mower having a motor-driven cutting blade, wheels and magnetic sensors for boundary detection. A charging station includes two signal generators for generating area signals in the form of pulse trains which are supplied to a boundary wire, a docking wire and a station wire.

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:.

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.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:.

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>, there is provided an illustration of an autonomous lawn mower <NUM> comprising: a mower body <NUM> having at least one motor <NUM> arranged to drive a cutting blade 212b and to propel the mower body <NUM> on an operating surface via a wheel arrangement, wherein the mower body <NUM> includes a navigation system <NUM> arranged to assist a controller <NUM> to control the operation of the mower body <NUM> within a predefined operating area <NUM>, wherein the mower body <NUM> further includes a signal detecting module <NUM> arranged to detect a signal representative of a navigational marker.

In this example, the autonomous lawn mower <NUM> 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 <NUM> 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 <NUM> or to calibrate the mower <NUM> with specific commands, but once these procedures have been undertaken, the mower <NUM> 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 <NUM> 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>, the autonomous lawn mower <NUM>, or referred to as the lawn mower or mower, includes a frame or housing <NUM> which supports the operating components of the mower <NUM>. 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 <NUM> so as to cut the grass of a lawn to which the mower <NUM> is mowing. The at least one motor may also be used to drive the mower <NUM> itself via the means of transmission systems, such as gearing mechanisms or gearboxes which transmit a driving force to its wheel arrangements <NUM>, although preferably, as is the case of this embodiment, separate motors are used to drive the mower <NUM> along its operating surface with each rear wheel 104R having its own individual motor and gearbox. This is advantageous in that manoeuvring the mower <NUM> 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>, the mower <NUM> includes a navigation system <NUM> which operates to locate and navigate the mower <NUM> around a working area <NUM> so that the mower <NUM> can cut the grass of a working area <NUM>. The navigation system <NUM> may include a number of specific navigation modules each arranged to provide individual navigation information obtained for the mower <NUM>. In turn, the navigation information obtained or determined by each of these navigation modules are then returned to the navigation system <NUM> for transmission to a controller <NUM>. Upon processing of the navigation information by the controller <NUM>, the controller <NUM> may then generate commands which are used to control the movement and operation of the mower <NUM> within a work or operation area.

These navigation modules may include at least the follow:.

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 <NUM> to devise suitable commands to operate the mower <NUM>. As it will be explained below with reference to <FIG> and <FIG>, in one example, the autonomous lawn mower <NUM> will operate by moving away from a docking station <NUM> as shown in <FIG> which will form a start and return point for the mower <NUM>. The mower <NUM>, when departing the docking station <NUM> may then use the navigation system <NUM> to assist with navigating the mower <NUM> around a work or operation area <NUM> by cutting the lawn in the operating area <NUM>, and then proceeding to navigate its way back to the docking station <NUM>.

With reference to <FIG>, there is provided a block diagram of the autonomous lawn mower <NUM> which illustrates the components of the autonomous lawn mower <NUM>. In this embodiment, the mower <NUM> includes a controller/processor <NUM> 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 <NUM> in order to operate the mower <NUM>. Preferably, the controller/processor <NUM> 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 <NUM> is arranged to receive navigation information from the navigation system <NUM> of the mower <NUM> and in turn, upon the receipt of this navigation information, will process the navigation information with existing information already accessible by the controller <NUM> such as the control algorithm <NUM> or predefined map of the operating area <NUM> to generate various commands to each of the mower <NUM> operating components, including the drive motors arranged to drive the mower <NUM> and/or the blade motors <NUM> which operates the blades 212b.

As shown in <FIG>, the navigation system <NUM> includes a signal detecting module <NUM> which detects a signal representative of a navigational marker generated by a signal generating module <NUM> and includes an odometry module <NUM>, which further includes wheel sensors <NUM> to detect the rotational displacement of the wheels <NUM> of the mower <NUM>. Each of these modules <NUM> and <NUM> are arranged to provide a specific function which are described below with reference to <FIG> and return individual navigation information either detected, calculated, gathered or surveyed.

As illustrated in this embodiment, the controller <NUM> is also arranged to control the mower drive motors <NUM> to drive the mower <NUM> along a work surface within a work area <NUM>. Preferably, as is the case in this embodiment, the mower <NUM> is driven by having a motor <NUM> placed adjacent to each of the rear wheels 104R with each motor <NUM> being arranged to drive each rear wheel 104R.

In turn, the controller <NUM> can direct electric current from a power source, such as a battery <NUM>, to the motors <NUM> so as to perform a controlled operation of one or both motors <NUM>. This can allow for forward, reverse and turning actions of the mower <NUM> by turning one or more wheels at different speeds or directions.

The controller <NUM> can also command the blade motor <NUM> to operate so as to operate the blades 212b to cut the grass of a work surface. To perform these functions, the controller <NUM> will execute a control routine or process <NUM> which determines the conditions for and when the mower <NUM> is to be operated. These commands at least include instructions to command the direction of travel of the mower <NUM> and the operation of the blades 212b. Other commands are also possible, including the command of the mower <NUM> to travel to a particular location within a work area <NUM>, or to return to a specific location, such as a docking station <NUM> as well as specific commands such as the operating speed of the blade motor <NUM> or the height of the blade 212b so as to determine the level of grass that is cut.

As it will be explained below with reference to <FIG>, the controller <NUM> may also be pre-programmed with an initialization routine <NUM> wherein the mower's working area and work surfaces are initially identified. These process may assist in identify the boundaries of a working area <NUM> and the categorization that certain surfaces within the boundaries should be avoided (no travel zones) or should not have the blade motor <NUM> activated. Once these working areas <NUM> are identified, the mower <NUM> can then be controlled by the controller <NUM> to navigate to a starting point from the docking station <NUM>, wherein the mower <NUM> can proceed to cut the grass from the starting point as stipulated by the control algorithm <NUM>. The control algorithm <NUM> 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 <NUM> defined so as to cut the grass in the working area <NUM>. Other cutting programs are also possible and can be chosen base on the shape and profile of the working area <NUM> of the desired operation of a user.

Preferably, as the controller <NUM> will communicate with each of the navigation modules of the navigation system <NUM>, the controller <NUM> may, during initialisation and general operation, receive a large amount of different navigation information from each of these navigation modules <NUM>. In order to process this navigation information so as to determine operation commands for the mower <NUM>, the controller <NUM> may first apply a filter or an averaging function to all of navigation information received from the navigation system <NUM>.

Such a filtering function may allow the controller <NUM> 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 <NUM> may receive navigation information from the odometry module <NUM>. During processing, the odometry module <NUM> may have tracked that the mower <NUM> has travelled to a particular co-ordinate on a virtual map obtained during the initialization of the mower <NUM>. However, according to the navigation information obtained by the signal detecting module <NUM>, the location of the mower <NUM> may be at a distance substantially far away from the co-ordinates obtained from the odometry module <NUM>. In these instances, when the filtering function is applied to all navigation information of the odometry module <NUM> and other navigation information, the "best fit" or "average" may in turn indicate that the co-ordinates of the odometry module <NUM> is an anomaly, as it is completely inconsistent with the other navigation modules. Accordingly, the controller <NUM> may then proceed to ignore this anomaly in generating commands to the mower.

It is also expected that the controller <NUM> may also apply a similar filtering function to all data obtained from the navigation system <NUM> 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 <NUM>. 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 <NUM>, or signal interference by a random signal emitting source, in which case the navigation information obtained from the signal detecting module <NUM> 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 <NUM>. Thus this this would advantageous in that the navigation information sent to the controller <NUM> is likely to be more accurate, resulting in improved performance and less processing by the controller <NUM>.

With reference to <FIG>, there is provided a block diagram illustrating the process flow of the initialization process of the autonomous mower <NUM>. As illustrated, the user may start to issue commands to the mower <NUM> to drive the mower <NUM>. These commands are received (step <NUM>) and processed by the controller <NUM> so as to drive the mower <NUM> along a surface (step <NUM>).

Meanwhile, the navigation system <NUM> is operated (step <NUM>) so as continuously survey and records any navigation information for the mower <NUM> during its initialization process. The navigation system <NUM> may then active each of its navigation modules <NUM> (Odometry and other sensors) to record such navigation information (step <NUM>) which can be used for navigation purposes when the mower <NUM> is put into autonomous operation.

With reference to <FIG>, there is illustrated a signal generating module <NUM> 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 <NUM>, <NUM>. On the other hand, the mower body <NUM> includes a signal detecting module <NUM> e.g. a sensor arranged to detect the signal representative of such navigational marker. The navigation system <NUM> determines a position of the mower body <NUM> within a predefined operating area <NUM> based on the location of such obstacle or boundary.

The signal generating module <NUM> 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 <NUM> may include a boundary wire <NUM> for generating a first, boundary signal loop <NUM> within the predefined operating area <NUM>. The position of the mower body <NUM> relative to the predefined operating area <NUM> is determined by the controller <NUM> based on the magnitude of the first signal loop <NUM> detected by the sensor <NUM>. Preferably, the boundary signal loop <NUM> is emitted about the boundary of the predefined operating area <NUM>.

In one further embodiment, the signal generating module <NUM> is at least partially positioned on a detachable docking module <NUM> detachably receiving the mower body <NUM>. The detachable docking module <NUM> may include a docking wire <NUM> for generating a second, docking signal loop <NUM> within a predefined docking area <NUM> about the detachable docking module <NUM>. The position of the mower body <NUM> relative to the detachable docking module <NUM> within the predefined docking area <NUM> is determined by the controller <NUM> based on the magnitude of the second signal loop <NUM> detected by the sensor <NUM>.

The first and second signal loops <NUM>, <NUM> may be emitted by the same signal generating module <NUM> to the boundary wire <NUM> and the docking wire <NUM> as pulses with the same frequency e.g. <NUM> at the same frequency e.g. <NUM> respectively. Preferably, the first signal loop <NUM> may include a bidirectional current pulse with an example pattern of <NUM>, <NUM>, -<NUM>, <NUM> as depicted in <FIG>. The second signal loop <NUM> may include a unidirectional current pulse with an example pattern of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> as depicted in <FIG>. The combination of the two current pulses, as depicted in <FIG>, are transmitted from the signal generating module <NUM> to the boundary wire <NUM> and the docking wire <NUM> respectively.

Advantageously, the docking station <NUM> may determine the length of the boundary wire <NUM> 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 <NUM> at constant signal strength, regardless the dimension of the boundary wire <NUM>.

In one example application, the sensor <NUM> receives the first and second signal loops <NUM> and <NUM> when the mower body <NUM> is at a position inside the predefined operating area <NUM> as well as the predefined docking area <NUM>. To allow the sensor <NUM> to distinguish between the signals <NUM>, <NUM> emitted by the boundary wire <NUM> and the docking wire <NUM> at the same frequency thereby identify each of the two signal loops individually and in turn determine the magnitude thereof respectively, the signals <NUM>, <NUM> are emitted as two time shifted pulses spaced by e.g.(<NUM>/<NUM>)*T therebetween. The time difference between the two signals <NUM>, <NUM> may be manipulated to identify each of the boundary and docking signals <NUM>, <NUM> on the sensor <NUM> side.

With reference to <FIG>, there is also provided an induction sensor data acquisition algorithm <NUM> for processing the data associated with the signals <NUM>, <NUM> received by the sensor <NUM>. The process begins at step <NUM> 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 <NUM> and docking loop signal <NUM> as shown partially in <FIG>. At step <NUM> of Data Filtering, a biquad band bass filter is used to filter noisy data.

At step <NUM> 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 <NUM>, 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 <NUM> of the mower body <NUM> is positioned within the operating area <NUM> as well as the docking area <NUM>. The process is then proceeded to step <NUM> for position based signal identification. The time difference between the start points of signals <NUM>, <NUM> would be used to identify each of the boundary loop signal <NUM> and the docking loop signal <NUM>.

Upon the completion of data processing, signal characterization and identification of steps <NUM> to <NUM>, the only remaining signal would be the signal <NUM> of the boundary loop <NUM>, as depicted in <FIG>.

The pulse count for boundary signal <NUM> is validated at step <NUM>. A pre-sampled data for boundary loop <NUM> 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 <NUM>. 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 <NUM> of the mower body <NUM> is positioned inside or outside the boundary loop <NUM>.

Meanwhile, the pulse count for docking signal <NUM> is also validated at step <NUM>, and the docking signal power is computed at step <NUM>.

Preferably, the sensor <NUM> may only receive the pulse <NUM> of the boundary loop <NUM> when the mower body <NUM> is at a position inside the predefined operating area <NUM> whilst outside the predefined docking area <NUM>. Upon detecting the pulse <NUM> of the boundary loop <NUM> with a magnitude exceeding a predetermined threshold by the sensor <NUM>, the movement of the lawn mower <NUM> would be significantly reduced, thereby preventing the lawn mower <NUM> from winding the boundary wire <NUM>.

In one example embodiment, the sensor <NUM> may detect whether the mower body <NUM> is positioned within the boundary wire <NUM> or outside the boundary wire <NUM> based on the polarity of the boundary loop signal <NUM>. For instance, the sensor <NUM> may detect a first polarity of the boundary signal loop <NUM>' e.g. a positive polarity, as depicted in <FIG>, when the mower body <NUM> is at a position inside the predefined operating area <NUM>. In contrast, the sensor <NUM> may detect a second opposite polarity of the boundary signal loop <NUM>" e.g. a negative polarity, as depicted in <FIG>, when the mower body <NUM> is at a position outside the predefined operating area <NUM>.

If only one signal is received in the sampled array, this implies the sensor <NUM> of the mower body <NUM> is not proximate to the docking loop <NUM> and thus only signal <NUM> from the boundary loop <NUM> is received. Before further processing, certain conditions are checked for verification. If the only signal received by the sensor <NUM> is verified to be the boundary loop <NUM>, the process will bypass step <NUM> and directly proceed to step <NUM> for validating the pulse count for boundary signal <NUM> and step <NUM> for cross correlating with the pre-sampled data.

With reference to <FIG>, the mower body <NUM> may include a plurality of aforesaid sensors <NUM> e.g. two pairs of front and rear sensors 222F, 222R, whereby the controller <NUM> terminates the movement of the mower body <NUM> upon all the front and rear sensors 222F, 222R are sandwiched between the boundary signal loop <NUM> and the docking signal loop <NUM>. For instance, the sensors 222F, 222R are placed inside the docking station <NUM> for accurate docking. The sensors 222F, 222R and the two loops i.e. boundary loop <NUM> and docking loop <NUM> within the docking station <NUM> are placed in such a fashion that when the lawn mower <NUM> is parked in the docking station <NUM>, each of the sensors 222F, 222R is outside the docking loop <NUM> whilst inside the boundary loop <NUM>.

The detachable docking module <NUM> also includes a magnetic detection module e.g. magnetomer for detecting the orientation of the mower body <NUM> with respect to the detachable docking module <NUM>.

During initial step up of the lawn mower <NUM>, the docking station <NUM> is secured in ground and a calibration process is performed prior to normal operation of the lawn mower <NUM> by the user. This calibration records the heading of the docking station <NUM> i.e. yaw position. Such information would be used in subsequent docking cycles for docking operation. The yaw position of the docking station <NUM> may be recalibrated by going through the same calibration process when necessary.

With reference to <FIG>, there is also provided a method <NUM> of operating the autonomous lawn mower <NUM>. The autonomous lawn mower <NUM> 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 <NUM> at step <NUM>, the autonomous lawn mower returns to the detachable docking module for battery charging.

For instance, during the cutting operation, the lawn mower <NUM> moves around the operating area <NUM> in a random manner and the sensors <NUM> attempt to detect the docking station signal at step <NUM>.

In a first scenario, the lawn mower <NUM> is positioned remote from the docking station <NUM> and the sensor <NUM> yet to detect the docking station signal <NUM>. At step <NUM>, the mower body <NUM> follows the boundary wire <NUM> until it is proximate to the docking station <NUM>. The presence of docking station <NUM> at any point is determined based on the power level of received docking wire signal <NUM> by the sensors <NUM>. For instance, this may be achieved by receiving docking wire signal <NUM> with a power higher than a predefined threshold.

At step <NUM>, the lawn mower <NUM> is proximate to the docking station <NUM> and the controller <NUM> uses area sensors data along with yaw data to align itself with the docking station <NUM>, for example, by taking one or more turns e.g. turning at <NUM>° twice to come in front of docking station <NUM>. Upon orienting the lawn mower <NUM> to the docking station <NUM>, the mower body <NUM> then moves towards docking station <NUM> until the boundary wire <NUM> is crossed by the pair of front sensors 222F at step <NUM>. Finally, the mower body <NUM> moves in a channel <NUM> formed between the boundary and docking wires <NUM>, <NUM> as depicted in <FIG>, and continue until a charging signal is detected by the docking station <NUM> at step <NUM>.

In a second scenario, the lawn mower <NUM> is already proximate to the docking station <NUM> and the sensors 222F, 222R has already detected the docking station signal <NUM> at step <NUM>. Without taking steps <NUM> to <NUM>, the mower body <NUM> will move towards the docking station <NUM> in a forward direction in a straight line based on yaw orientation of docking station <NUM> with respect to the lawn mower <NUM> and continues until the boundary wire <NUM> is first crossed by the pair of front sensors 222F and the two pairs of front and rear sensors 222F, 222R move in the channel <NUM> between the boundary and docking wires <NUM>, <NUM> from steps <NUM> to <NUM>.

With reference to <FIG>, there is provided an alternative docking method for in-line docking the autonomous lawn mower <NUM> to the aforementioned predefined docking area <NUM> along the aforementioned boundary wire <NUM>. For instance, the predefined docking area <NUM> may be located about the boundary of the predefined operating area <NUM> and overlap at least a portion of the boundary wire <NUM>.

In one example embodiment, the boundary wire <NUM> may bisect the predefined docking area <NUM> in a longitudinal direction, such that the boundary wire <NUM> may overlap the centre line of the predefined docking area <NUM>. The mower body <NUM> may enter the docking area <NUM> from one end <NUM> of the predefined docking area <NUM> along the centre line and until the front mower body <NUM> reaches the further end <NUM> of the predefined docking area <NUM>. Accordingly, the mower body <NUM> may dock accurately within the predefined docking area <NUM> once the centre of the mower body <NUM> is in line with the boundary wire <NUM> in the early stage of the docking operation.

Preferably, the mower body <NUM> may move towards and dock within the docking area <NUM> with the aiding of only single boundary wire <NUM>. Throughout the in-line docking operation, two, left and right front sensors 222FL and 222FR on the mower body <NUM> are each positioned on two opposite sides of the boundary wire <NUM> and each receives the boundary signal <NUM> emitted from the boundary wire <NUM> respectively. The left and right front sensors 222FL should receive boundary signal <NUM> in opposite polarity. For instance, the left front sensor 222FL may receive the boundary signal <NUM> with a first, negative polarity and the right front sensor 222FR may receive the boundary signal <NUM> with a second, positive polarity.

To maintain the spacing between each of the two front sensors 222FL and 222FR and the boundary wire <NUM> individually, the autonomous lawn mower <NUM> may further include a controller e.g. a closed loop controller for detecting the individual spacing of the front sensors 222FL and 222FR from the boundary wire <NUM>. For instance, the magnitude of the boundary signal <NUM> may be detected by the front sensors 222FL and 222FR respectively and the individual spacing between the sensors 222FL and 222FR and the boundary wire <NUM> may be determined based on the detected magnitude. Subsequently, the position of the mower body <NUM> relative to the boundary wire <NUM> may be determined by the controller based on the relative positions of the sensors 222FL and 222FR. In general, the left and right front sensors 222FL and 222FR should receive equal magnitude of signal loop <NUM> with opposite polarity from the boundary wire <NUM> respectively when the mower body <NUM> is bisected by the boundary wire <NUM> i.e. the centre of the mower body <NUM> is in line with the boundary wire <NUM>.

During the continuous docking operation, the controller may manipulate the movement and orientation of the mower body <NUM> based on the real-time positioning feedback from the two front sensors 222FL and 222FR. This ensures that the mower body <NUM>, on its way to the docking area <NUM>, may be positioned in a desirable orientation and travel in a path overlapping the boundary wire <NUM> to reach the predefined docking area <NUM>.

Optionally, there may also be provided an additional pair of rear sensors 222R on the rear end of the mower body <NUM> for determining the magnitude of the boundary signal <NUM> in a similar manner. The accuracy of the position and orientation of the mower body <NUM> determined by the controller may be improved.

In one alternative example embodiment as shown in <FIG>, there is shown a docking module <NUM> having part of the boundary wire <NUM> and an auxiliary docking wire <NUM> provided within a predefined docking area <NUM> in the detachable docking module <NUM>. The auxiliary docking wire <NUM> emits a boundary signal <NUM> for assisting the docking operation of the mower <NUM>, especially when the mower <NUM> proximate to the docking module <NUM>. Preferably, the auxiliary docking wire <NUM> is bisected by at least a portion of the boundary wire <NUM>.

Upon the mower <NUM> enters the docking area <NUM> from one end <NUM> of the predefined docking area <NUM> along the centre line, the front sensors 222FL and 222FR may detect two, a boundary signal <NUM> and a docking signal <NUM>. The magnitudes of these signals, especially the docking signal <NUM> may be detected by the front sensors 222FL and 222FR respectively. The individual spacing between the sensors 222FL and 222FR and the adjacent portions of the docking wire <NUM> may be determined based on the detected magnitude. Subsequently, the position of the mower body <NUM> relative to the docking wire <NUM> may be determined by the controller based on the relative positions of the sensors 222FL and 222FR.

If the mower <NUM> reaches the final docking position, the left and right front sensors 222FL and 222FR should receive equal magnitude of signal loop <NUM> with opposite polarity as well as equal magnitude of signal loop <NUM>. This indicates that the left and right front sensors 222FL and 222FR are positioned outside and about the docking wire <NUM> whilst one of the front sensors 222FL and 222FR remains inside the boundary loop <NUM>.

With reference to <FIG>, there is illustrated an example of an odometry module <NUM> arranged to be implemented with an autonomous mower <NUM>. In this example embodiment, the odometry module <NUM> is arranged to be implemented into each of two motors arranged to drive the rear wheels 104R of the mower <NUM>, although as a person skilled in the art would appreciate, if additional motors are used to drive other wheels of the mower <NUM>, than this odometry module <NUM> can also be implemented into each of the motor windings <NUM>.

In this example, the odometry module <NUM> is arranged to measure the number of rotations of the wheels 104R to which the odometry module <NUM> is implemented to operate with. In turn, the number of rotations, when coupled with the circumference of the wheel 104R will provide an estimation as to the distance travelled by the mower <NUM> on a work surface (taking into account any gear ratios, if applicable). As the mower <NUM> 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 <NUM> along a work surface.

As illustrated in <FIG>, the odometry module <NUM> is implemented onto a motor <NUM> and gearbox arrangement <NUM> which drives one of the rear wheels 104R, with each rear wheel 104R having its own motor <NUM> and gearbox <NUM>. When the motor <NUM> is energised by its power source, in most instances by command of the controller <NUM>, the motor will rotate <NUM> and thus also driving a gearbox <NUM> which is rotatably attached to the motor <NUM>.

The gearbox <NUM> will then also transmit this rotational force to the wheels 104R and thus turning the wheels 104R in a desired direction. As the gearbox ratio is known, either by presetting at the factory, or user adjustment, the odometry module <NUM> can thus operate by detecting the number of rotation of the motor <NUM> which can in turn be used to calculate the number of rotations of the wheel 104R.

In this implementation, the motor has a Print Circuit Board (PCB) <NUM> connected to the motor windings <NUM> and rotor which is implemented with a number of hall sensors <NUM>. These hall sensors <NUM> allow a magnetic signal to be detected upon each sensor <NUM> being rotated passed a magnet (or have a magnet rotated pass the sensor <NUM>) and thus when the motor is rotated, the PCB <NUM>, which is static, will detect the magnets held in the rotor of the motor <NUM>. The hall sensors <NUM> located on the PCB <NUM> can thus detect a magnet as it is passed during the rotation of the motor windings <NUM>. In turn, this data from the hall sensors <NUM> can then be used to calculate the number of or portions of rotations of the motor <NUM>, which can then be used to calculate the number of rotations of the wheel 104R via the gearbox <NUM>.

Once the number of rotations is determined, the number of rotations of each wheel 104R, including its direction and whether the wheels 10R are undergoing a turning direction, will then be transmitted to the controller <NUM> for processing. In turn, the controller <NUM> can then process this result with other information from the navigation system <NUM> to ascertain the location of the mower <NUM>.

It is expected that the wheels of the mower <NUM> may undergo some wheel spin when the mower <NUM> is in operation, as the surface type may cause the wheels 104R to spin without moving the mower <NUM>. Such wheel spins will result in error when determining the position of the mower <NUM>. However, such errors are factored into the calculation by the controller <NUM> as other navigation information obtained by other modules of the navigation system <NUM> 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 <NUM> may also be measured and compared against the rotation rate detected by the odometry module <NUM>. In such examples, if the current drawn by the motor <NUM> is very low relative to the number of rotations detected of the wheel 104R, then the wheels 104R of the mower <NUM> may indeed be spinning along its working surface. Accordingly, such information may also be considered by the controller <NUM> in determining the distance of the mower <NUM> based on its odometry measurement.

With reference to <FIG>, there is provided an illustration of an autonomous lawn mower <NUM> comprising: a mower body <NUM> having at least one motor arranged to drive a cutting blade 212b and to propel the mower body <NUM> on an operating surface via a wheel arrangement, wherein the mower body <NUM> includes a navigation system <NUM> arranged to assist a controller <NUM> to control the operation of the mower body <NUM> within a predefined operating area <NUM>; wherein the mower body <NUM> further includes a signal detecting module <NUM> arranged to detect a signal representative of a navigational marker and the navigation system <NUM> further includes an odometry module <NUM> arranged to track the movement of the mower body <NUM> on the operating surface.

With reference to <FIG>, there is provided an illustration of an autonomous lawn mower <NUM> comprising: a mower body <NUM> having at least one motor arranged to drive a cutting blade 212b and to propel the mower body <NUM> on an operating surface via a wheel arrangement, wherein the mower body <NUM> includes a navigation system <NUM> arranged to assist a controller <NUM> to control the operation of the mower body <NUM> within a predefined operating area <NUM>; wherein the mower body <NUM> further includes a signal detecting module <NUM> arranged to detect a signal representative of a navigational marker and the mower body <NUM> further includes a height adjustment system <NUM> arranged to assist the controller <NUM> to control the operation of the cutting blade 212b within a predefined operating height.

In this embodiment as shown in <FIG>, the autonomous lawn mower <NUM> includes a height adjustment system <NUM> comprising a height adjustment motor <NUM>, a worm shaft <NUM> driven by the height adjustment motor <NUM>, a limit switch <NUM>, and a hall sensor <NUM>. Advantageously, the motor <NUM> may manipulate the rotating direction of the worm shaft <NUM> in clockwise or anticlockwise directions, such that the height of the cutting blade 212b with respect to the operating surface may be manipulated by the motor <NUM> indirectly.

The motor <NUM> may be secured to the mower body <NUM> and remains stationary throughout the height adjusting operations. For instance, the cutting blade 212b may be moved towards the operating surface when the worm shaft <NUM> rotates in a clockwise direction, and on the other hand, moved further away from the operating surface when the worm shaft <NUM> rotates in an anti-clockwise direction.

Optionally, the mechanical transmission between the motor <NUM> and the cutting blade 212b through the worm shaft <NUM> may be enhanced by the use of a ring shaped structure <NUM>. In this embodiment, the ring shaped structure <NUM> preferably comprises a plurality of bushings <NUM>, e.g. made of Polyoxymethylene (POM), a plurality of linear bearings <NUM>, or alternatively a combination thereof for supporting the height adjustment system <NUM>. Advantageously, the linear bearing <NUM> may counter the torsional force induced by the distance between the worm shaft <NUM> and the opposite support.

In one embodiment, the plurality of bushings <NUM> may be disposed about the blade motor <NUM>. A plurality of through holes <NUM> may be disposed preferably equidistantly for receiving these bushings <NUM>, and at least one linear bearing <NUM> may be disposed about the lower end of the bushing <NUM> opposed to the worm shaft <NUM>. During the height adjusting operation, the ring shaped structure <NUM> may reinforce the worm shaft <NUM>, such that the rotational force of the motor <NUM> is converted into lateral forces steadily without out any vibrations or at least with minimal vibrations.

Although the worm shaft <NUM> is located eccentrically to the central axis of the height adjustment system <NUM> and it may inevitably exert a side loading against the height adjustment system <NUM>, the linear bearing <NUM> may advantageously reduce the friction between the shaft <NUM> and the ring shaped structure <NUM> due to the bending moment. Accordingly, the rotational force of the motor <NUM> is converted into lateral forces steadily without transmitting the bending moment to the height adjustment system <NUM>.

In this embodiment as shown in <FIG>, the limit switch <NUM> is disposed on the blade motor <NUM>, with a thin and elongated portion <NUM> further extended away from the blade motor <NUM> and towards the inner mower body <NUM>. Preferably, the hall sensor <NUM> is disposed on top of the motor <NUM> for detecting the presence of the elongated portion <NUM> of the limit switch <NUM>, thereby determining if the cutting blade 212b has reached the maximum height with respect to the operating surface. Advantageously, the hall sensor <NUM> may further derive the number of rotations required by the motor <NUM> to reach the predefined desirable operating height, and in turn assist the controller <NUM> to control the operation of the cutting blade 212b.

Optionally, the combination of limit switch <NUM> and hall sensor <NUM> may be substituted by sensors e.g. photoelectric sensors. For instance, the photoelectric sensor may provide a signal to the height adjustment system <NUM>, indicating the height position of the cutting blade 212b, upon detecting the presence of the elongated portion <NUM>, or alternatively in the absence of the elongated portion <NUM>. 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 212b is adjustable for carrying out a normal mowing operation at a desirable operating level. Initially, the blade assembly 212b is adjusted to an uppermost position through a first rotating direction of the blade motor <NUM> until the limit switch <NUM> is engaged by an engaging member (not shown). Subsequently, the blade motor <NUM> 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 212b and the desirable position of the blade assembly 212b is calculated by the hall sensor <NUM>.

With reference to <FIG>, there is provided an illustration of an autonomous lawn mower <NUM> comprising: a mower body <NUM> having at least one motor arranged to drive a cutting blade 212b and to propel the mower body <NUM> on an operating surface via a wheel arrangement, wherein the mower body <NUM> includes a navigation system <NUM> arranged to assist a controller <NUM> to control the operation of the mower body <NUM> within a predefined operating area; a detachable docking module <NUM> arranged to provide battery charging to the mower body <NUM>; wherein the mower body <NUM> further includes a signal detecting module <NUM> arranged to detect a signal representative of a navigational marker.

Preferably, the detachable docking module <NUM> further includes a rotatable member <NUM> arranged to contact the mower body <NUM> with a predefined vertical offset relative to the detachable docking module <NUM> for battery charging.

Upon the lawn mower <NUM> has been used over certain time period, there may be an offset between the opening <NUM> of the motor body <NUM> and the charging terminal. For instance, if there is mud and grass stuck on the mower's wheels <NUM>, the height of the mower <NUM> may be shifted upwards relative to the docking station <NUM>. Furthermore, if the wheels <NUM> wear down over time, the height of the charging area on the mower <NUM> may be lowered relative to the docking station <NUM>. A rotatable charging member <NUM> may compensate such vertical offset between the docking station <NUM> and the mower body <NUM>.

In one example, there may be provided a rotatable, spring loaded charging terminals <NUM>. The rotatable member <NUM> may extend laterally from the detachable docking module <NUM> and pivotable about a horizontal axis that is parallel to the operating surface. On the other hand, the mower body <NUM> may include an opening <NUM> for receiving the rotatable member <NUM>. Advantageously, the charging terminals <NUM> may be pivotable about an axis perpendicular to the charging terminals <NUM> such that the terminal <NUM> 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 <NUM> upon the rotatable member <NUM> is inserted into the opening <NUM> of a mower body <NUM> with a vertical offset therebetween, the docking module <NUM> may provide a pair of resilient means <NUM> for acting against the opposite sides of the rotatable member <NUM>. For instance, a pair of springs <NUM> may be used to ensure that the terminals <NUM> rest at the nominal designed position and do not sag due to gravity.

Optionally, to facilitate the matching between the rotatable member <NUM> and the opening <NUM> with a substantial vertical offset therebetween, the rotatable member <NUM> may further provide a flexible, protective gasket <NUM> e.g. made of rubber for reducing the impact between the rotatable member <NUM> and the mower body <NUM> during the docking process. Advantageously, the protective gasket <NUM> provides a tight sealing between the rotatable member <NUM> and the mower body <NUM> and allows a flexible rotation of the rotatable member <NUM>.

With reference to <FIG>, there is provided an illustration of an autonomous lawn mower <NUM> comprising: a mower body <NUM> having at least one motor arranged to drive a cutting blade 212b and to propel the mower body <NUM> on an operating surface via a wheel arrangement, wherein the mower body <NUM> includes a navigation system <NUM> arranged to assist a controller <NUM> to control the operation of the mower body <NUM> within a predefined operating area, wherein the mower body <NUM> further includes a signal detecting module <NUM> arranged to detect a signal representative of a navigational marker and an actuator for terminating the operation of the mower <NUM> and, in response to the termination of the mower <NUM> operation, releasing a portion of the mower body <NUM> 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 <NUM> has a chassis <NUM> e.g. a base, a hood <NUM> e.g. cover of a control compartment/panel <NUM> movable relative to the chassis <NUM>, and one or more magnetic sensors <NUM> mounted for detecting displacement of the hood <NUM> relative to the chassis <NUM>. An actuator <NUM> e.g. an emergency shut-off switch, in the form of a push button or embedding a micro switch <NUM>, is provided in a recess of the hood <NUM> and communicated with the magnetic sensors <NUM>.

There is also provided an operation interface <NUM> with a stop button <NUM>, and a display (not shown) within the chassis <NUM> and concealed by the hood <NUM> during normal operation. The emergency shutoff switch <NUM>, when actuated by the user, stops the autonomous lawn mower <NUM> and releases the hood cover <NUM> to expose the control compartment/panel <NUM> to the user.

With reference to <FIG>, there is provided an illustration of an autonomous lawn mower <NUM> comprising: a mower body <NUM> having at least one motor arranged to drive a cutting blade 212b and to propel the mower body <NUM> on an operating surface via a wheel arrangement, wherein the mower body <NUM> includes a navigation system <NUM> arranged to assist a controller to control the operation of the mower body <NUM> within a predefined operating area, wherein the mower body <NUM> 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 <FIG>, the autonomous lawn mower <NUM> includes a cutter module <NUM> positioned underneath the mower body <NUM> and transverse to the longitudinal axis of the mower body <NUM>. The cutter module <NUM> includes a perimeter cutter <NUM> for trimming the edges of a predefined operating area <NUM>. Preferably, the cutting module <NUM> includes at least two cutting bars <NUM>, <NUM> movable in a reciprocating manner. The cutting bars <NUM>, <NUM> are each driven by a driving motor <NUM> respectively. Optionally, the cutting bars <NUM>, <NUM> may be driven by two individual motors (not shown) individually.

With reference to <FIG>, there is provided an illustration of an autonomous lawn mower <NUM> comprising: a mower body <NUM> having at least one motor arranged to drive a cutting blade 212b and to propel the mower body <NUM> on an operating surface via a wheel arrangement, wherein the mower body <NUM> includes a navigation system <NUM> arranged to assist a controller <NUM> to control the operation of the mower body <NUM> within a predefined operating area <NUM>, wherein the mower body <NUM> 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 212b along its rotating axis <NUM>.

In this embodiment as shown in <FIG>, the cutting blade 212b is rotatably mounted on a rotating shaft <NUM> driven by the motor <NUM>. The front end of the rotating shaft <NUM> is provided external thread 213a about which a nut <NUM> is rotatably mounted for sandwiching the centre portion of the cutting blade 212b therebetween. The advantages of the blade adjustment system in that, the position of the nut <NUM> may be adjusted along the external thread 213a. This ensures that the lawn mower <NUM> may be readily adapted for accommodating cutting blades 212b with different thickness.

With reference finally to <FIG>, there is provided a method of calibrating the autonomous lawn mower <NUM>. In one example embodiment, the autonomous lawn mower <NUM> is positioned in front of the docking station <NUM>. To trigger the calibration, the autonomous lawn mower <NUM> is positioned to face towards the docking station charging terminal and adjacent to the edge of the docking pad <NUM>. 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 <NUM> 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.

Claim 1:
An autonomous lawn mower (<NUM>) comprising a mower body (<NUM>) having at least one motor (<NUM>) arranged to drive a cutting blade (212b) and to propel the mower body (<NUM>) on an operating surface via a wheel arrangement (<NUM>),
wherein the mower body (<NUM>) includes a navigation system (<NUM>) arranged to assist a controller (<NUM>) to control the operation of the mower body (<NUM>) within a predefined operating area (<NUM>); and
wherein the mower body (<NUM>) further includes a signal detecting module (<NUM>) arranged to detect a signal representative of a navigational marker,
wherein the autonomous lawn mower (<NUM>) further includes a signal generating module (<NUM>) arranged to generate the signal in the form of a signal loop (<NUM>, <NUM>), wherein:
the signal detecting module (<NUM>) includes a sensor (<NUM>) arranged to detect the magnitude of the signal loop (<NUM>, <NUM>); and
the signal generating module (<NUM>) is configured to generate a first aforesaid signal loop (<NUM>) within the predefined operating area (<NUM>) whereby the position of the mower body (<NUM>) relative to the predefined operation area is determined by the controller (<NUM>) based on the magnitude of the first signal loop (<NUM>) detected by the sensor (<NUM>),
wherein the signal generating module (<NUM>) is positioned on a detachable docking module (<NUM>) for detachably receiving the mower body (<NUM>); and
the detachable docking module (<NUM>) is configured to generate a second aforesaid signal loop (<NUM>) within a predefined docking area (<NUM>) about the detachable docking module (<NUM>) whereby the position of the mower body (<NUM>) relative to the detachable docking module (<NUM>) within the predefined docking area (<NUM>) is determined by the controller (<NUM>) based on the magnitude of the second signal loop (<NUM>) detected by the sensor (<NUM>),
wherein the first and second signal loops (<NUM>, <NUM>) are time shifted pulses with the same frequency and the first and second signal loops (<NUM>, <NUM>) are received by the sensor (<NUM>) when the mower body (<NUM>) is at a position inside the predefined operating area (<NUM>) and the predefined docking area (<NUM>),
wherein the controller (<NUM>) is configured to identify the first and second signal loops (<NUM>, <NUM>) individually based on the time shift between the pulses of the first and second signal loops (<NUM>, <NUM>).