WO2013141710A1

WO2013141710A1 - A theft detection unit and a theft detection method using the unit

Info

Publication number: WO2013141710A1
Application number: PCT/NL2013/050214
Authority: WO
Inventors: Sebastiaan Willem STRAMPEL
Original assignee: Strampel Sebastiaan Willem
Priority date: 2012-03-23
Filing date: 2013-03-22
Publication date: 2013-09-26
Also published as: NL2008526C2; EP2828837A1; EP2828837B1

Abstract

The invention relates to a method in a theft detection unit wherein the unit is secured to a movable object. The method repeatedly receives acceleration data from a three axes acceleration sensor (4), determines a reference orientation of the three axes acceleration sensor from the acceleration data, determines a difference signal representing a change in angle of the received acceleration data with respect to the reference orientation; and generates a control signal for activating an alarm when the difference signal exceeds a first threshold value for a predefined period of time. The method is very suitable for an object that rolls repeatedly from one side to the other without generating a false alarm due to said regular movement.

Description

A THEFT DETECTION UNIT AND A THEFT DETECTION METHOD USING THE UNIT

TECHNICAL FIELD

The invention relates to a method in a theft detection unit and a theft detection unit. Particularly, the invention relates to a theft detection unit and method for use in movable objects, more particular for use in an outboard motor for boats.

BACKGROUND

Theft alarm systems based on compass direction detection have been known for quite some time. When activated, the system will react on direction movements of the system relative to the Earth's magnetic field and set off an alarm if the direction changes. Theft alarm systems have primarily developed for vehicle use.

EP1213196A1 discloses a theft alarm system that may be used in connection with sailing ships, motor boats, motor vehicles, outboard motor or a trailer. The system detects the direction of the system relative to the orientation of the Earth's magnetic field and generates an alarm signal when the direction of the system is outside a non-alarm area.

US2010/032332A1 discloses a portable security container with tilt and movement detection. A MEMS three-axis low gravity acceleration sensor is used which provides its own instantaneous acceleration relative to the acceleration of the earth gravity. As soon as a change in the angle of tilt is such that the resolution of the accelerometer is exceeded, the accelerometer readings will change on at least two axes, which can be determined as a hostile event. In a timed mode, after a 3 second interval from the time motion/tilt was first determined, the system's acceleration is again tested with its previous criteria to determine motion/tilt and if it is being moved the alarm condition is activated. If the system is not being moved, normal monitoring is resumed. However, the tilt and movement detection is not suitable to protect objects which orientation with respect to the earth gravity vector is continuously changing.

US2006/0244576A1 discloses a vehicle theft detection device. The device includes an inclination detection unit and an operation control unit. The inclination detection unit detects an inclination of a vehicle. The operation control unit detects theft using an output of the inclination detection unit. If it is determined that the vehicle is in a situation where the vehicle will sway during parking, the operation control unit changes a threshold value of theft detection based on an output of the inclination detection unit to a higher value. The system uses only one threshold to determine theft.

Although the prior art systems provide a measure of protection against vehicle theft, their dependency on the absolute motion of the vehicle results in the non- detection of vehicle motion in some circumstances.

The known systems are not suitable to protect outboard motor attached to boat against theft. Due to the constant movement of the boat, the known systems generate too often a false-alarm when the non-alarm area is too small and generate no alarm when the non-alarm area is too wide. Furthermore, a subject containing iron passing in the proximity of a system comprising a magnetic-field sensor could trigger a false alarm. The many false alarms result in very low credibility of the known systems.

Another disadvantage of known theft detection systems is that they are integrated with the electronics of the device to be protected. Sometimes, the theft detection system interferes with the electronics, causing malfunctioning of the device to be protected.

SUMMARY

It is an object of the invention to provide an improved method for sensing unauthorized movement of a movable object and generating a control signal for activating an alarm, which overcomes at least one of the disadvantages mentioned above.

According to the invention, this object is achieved by a method in a theft detection unit having the features of Claim 1. Advantageous embodiments and further ways of carrying out the invention may be attained by the measures mentioned in the dependent claims.

According to a first aspect of the invention, there is provided a method in a theft detection unit for attachment to a movable object. Repeatedly, a control unit receives acceleration data from a three axes acceleration sensor. The control unit determines a reference orientation of the three axes acceleration sensor from the acceleration data. Subsequently, the control unit determines a difference signal representing a change in angle of received acceleration data with respect to the reference orientation. When the difference signal exceeds a first threshold value for a predefined period of time, the control unit generates a control signal for activating an alarm.

The method of the invention is based on the recognition that a boat sways, i.e. moves back and forth or sideways on the waves and regularly passes a "horizontal" state. The "horizontal" state corresponds to the orientation of the boat with respect to the gravity vector when there are no waves. When the boat does not return to the "horizontal" state within a predetermined time, this indicates that there is an abnormal situation which gives rise to generate an alarm. When applying this knowledge in a theft detection system which is built in an outboard motor, the normal movement of the boat will not cause false alarms. However, as soon as the outboard motor is not returning to its "horizontal" state within said predetermined time period, this is an indication that an unauthorized person has taken the motor from the boat. Subsequently, the theft detection system will generate an alarm. Thus a combination of both an angle deviation from a "horizontal" state and time is used to determine an abnormal situation and generating an alarm signal. Thus a method is provided which is not sensitive for normal movements of the object as long as the object returns within a region which is defined by its "horizontal" state within a predetermined time. The force of gravity defines a gravity vector, which direction can be measured with a three acceleration sensor. When the orientation of the object, i.e. detection unit, in "horizontal" position is known with respect to the gravity vector, any angular rotation of the object, i.e. roll and pitch of the boat, could be measured. A rotation of the object will result in a change in orientation of the gravity vector measured by the acceleration sensor. In this way a change in angle of the object with respect to its "horizontal" state could accurately be sensed.

In an embodiment, the method further comprises generating a control signal for activating an alarm when the difference signal exceeds a second threshold value, wherein the first threshold value is smaller than the second threshold value. This feature improves the method to generate immediately an alarm signal when the deviation from the "horizontal" state is larger than maximal expected swaying angle of the boat.

In an embodiment, the theft detection unit comprises at least one active mode and an alarm mode. The unit switches from an active mode to the alarm mode when a control signal for activating an alarm is generated. When after a predefined delay time the difference signal representing a change in angle of the received acceleration data with respect to the reference orientation is smaller than a third threshold value, the unit switches from alarm mode to the active mode. The third threshold value is smaller than or equal to the first threshold value. Regulations of theft detection systems require that the system will not continuously and/or repeatedly generates an alarm signal. The system has to be activated again by a user to enter an active mode which enables the system to detect theft. These features provide a method to set the system back from alarm mode to active mode without user intervention. This is done by detecting that the object is in its original "horizontal" position range. For example, if an outboard motor is unauthorized taken from a boat and has been deposited along the side of the road by a thief, the harbourmaster could take the motor and attach the motor to the boat again. After this, the motor will approximately be in the same position as before theft. The theft detection unit will autonomously detect this situation without any further instruction and set the system again in active mode. When an unauthorized person again takes the motor from the boat, the system will generate again an alarm.

In an embodiment, the theft detection unit comprises a first active mode and a second active mode. The first threshold value in the first active mode is smaller than the first threshold value in the second active mode. When the boat is in the harbour, the waves will be smaller than when the boat is in open water. Consequently, the movements of the boat will be smaller in the harbour than when the bout is in open water. These features provide a theft detection system for an outboard motor which can be used in harbour mode and in open water. The amount of false-alarms will be comparable in both modes whereas the sensitivity for theft in harbour mode will be higher than in open water mode. This is in line with the risk of theft in the harbour and open water.

In an embodiment, the determining a reference orientation action comprises retrieving over a predefined time interval data samples representing acceleration of the sensor along three axes; and, calculating the reference orientation from the data samples retrieved over said predefined time interval. In this way an accurate "horizontal" position of the object to be protected is obtained. Each time the unit is activated, the "horizontal" position is accurately determined.

In an alternative embodiment, the determining a reference orientation action further comprises retrieving over a predefined time interval data samples representing acceleration of the sensor along three axes, calculating a reference orientation from the data samples retrieved over said predefined time interval and, deriving a deviation value indicative for the deviation of the retrieved data samples. The retrieving and deriving actions are repeated as long as the deviation value is larger than a predefined deviation parameter. The reference orientation is finally updated with the value calculated from the data samples for which hold that the deviation value is smaller than the predefined deviation parameter. When a person is still walking on the boat after activation of the theft detection unit, the unit could not accurately determine the "horizontal" position. In a further embodiment, the theft detection unit comprises more than one active mode which is selectable by a user, and the predefined deviation parameter depends on the selected active mode. These features make the acceptance of the reference orientation dependent on the expected normal movement of the object. When lying in a harbour, the roll of the boat will normally be less than the roll of the boat in open water. Consequently, for an accurate calculation of the reference orientation of the boat, the deviation of the samples should be less in harbour-mode than in "open water" mode.

In a further embodiment, the theft detection unit comprises a first active mode and a second active mode, wherein the first threshold value in the first active mode is smaller than the first threshold value in the second active mode, when the user selects the first active mode the unit is further configured operate with the first threshold value of the second active mode when the deviation value for the deviation of the retrieved data samples is larger than the predefined deviation parameter associated with the first active mode. These features enable the unit to operate with less strict threshold values when a deviation of the retrieved samples is not within the range of the selected mode. For example, if one arrived in the harbour with windy weather, he would like to set the theft detection unit in harbour-mode. However, the boat will sway too much to determine accurately the reference orientation. When using an inaccurate reference orientation in harbour-mode, this could result in false-alarms. By using initially the inaccurate reference orientation and the thresholds corresponding to the "open water" mode, the amount of false alarms could be reduced significantly.

In a further embodiment, the unit is configured to operate with the first threshold value of the first active mode as soon as the deviation value for the deviation of the retrieved data samples is smaller than the predefined deviation parameter associated with the first active mode. These features enable the unit to operate with less strict threshold values and to switch over to the requested threshold values when a deviation of the retrieved samples is within the range of the selected mode. For example, if one arrived in the harbour with windy weather, he would like to set the theft detection unit in harbour- mode. However, the boat will sway too much to determine accurately the reference orientation. When using an inaccurate reference orientation in harbour-mode, this could result in false-alarms. By using initially the inaccurate reference orientation and the thresholds corresponding to the "open water" mode, the amount of false alarms could be reduced significantly. When the unit detects that the deviation is smaller than the predefined deviation parameter for harbour-mode, this in an indication that the wind has dropped. The reference orientation could now be determined accurately and the unit could use the thresholds corresponding to the harbour-mode without generating unnecessary false-alarms and uses the requested parameters to detect theft.

In an embodiment, the reference orientation of the three axes acceleration sensor is updated with a predefined update frequency. This feature allows reducing power consumption significantly with respect to continuous processing analogous signals.

A second aspect provides a theft detection unit for a movable object comprising a three axes acceleration sensor, an alarm unit, a processor and a memory to store instructions that, when executed by the processor, cause the unit to perform the in a theft detection unit according to the first aspect. An advantage of the theft detection unit according to the invention is that it does not need any interconnection with the electronics of the object. Therefore, the unit could be attached anywhere to the object where is sufficient space to place the unit.

A third aspect provides a use of a theft detection unit as set forth in the appended claims.

Other features and advantages will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, various features of embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, properties and advantages will be explained hereinafter based on the following description with reference to the drawings, wherein like reference numerals denote like or comparable parts, and in which:

Fig. 1 shows a block diagram of a theft detection unit;

Fig. 2 illustrates some parameters used to detect theft;

Fig. 3 illustrates a function graph of the parameters in Fig. 2;

Fig. 4 shows a flowchart illustrating basic actions for a method for detecting theft;

Fig. 5 shows a flowchart illustrating a first embodiment for a detecting theft routine;

Fig. 6 shows a flowchart illustrating a second embodiment for a detecting theft routine; Fig. 7 shows a flowchart illustrating another embodiment of basic actions for a method for detecting theft;

Fig. 8 shows a flowchart illustrating a first embodiment for a method for obtaining the reference orientation of the object;

Fig. 9 shows a flowchart illustrating an embodiment for a method for obtaining the reference orientation of an object and setting parameter for a detecting theft routine;

Fig. 10 shows a flowchart illustrating an embodiment for a routine to detect after an alarm that the object is in its original position,

Fig. 11 is a waveform chart to show the operation of the method when the boat sways on the water; and,

Fig. 12 is a waveform chart to show the operation of the method when a person enters a boat which sways slightly on the water.

DETAILED DESCRIPTION

Fig. 1 illustrates a block diagram of a theft detection unit 100. The theft detection unit 100 is a stand-alone unit that could be attached to a movable object to prevent the object for theft. In the description below the object is an outboard motor and the theft detection unit is fastened somewhere in the housing of the outboard motor. The unit should be attached to the object such that it cannot easily be removed from the object without moving the movable object. The term" active mode" in the present invention means a mode of the unit to detect theft of the object.

The theft detection unit 100 comprises a controller 110, a memory 115, an accelerometer 120, a power supply 130, a speaker 140, an interface 150, at least one port 160,170. The controller 110 is directly or indirectly connected to the other components of the theft detection unit. The controller 110 enables the communication between the different components and the interpretation of the signals in between the component. The communication and interpretation of the signals is defined through a method, or so-called algorithm, stored in the memory 115 as instructions which enable the controller to perform the method.

The controller 110 includes in particular a programmable microcontroller or processor which enables the communication between and the control of the different hardware components. The controller 110 makes transfer of all signals between the different hardware components and optional external applications/products/sensors connected to the theft detection unit 100 possible. Furthermore, the controller enables the programming of the behaviour of the components to instruct the components to respond to events (e.g. accelerometer values, sample frequency, interrupts, vibrations, shocks, and more).

The accelerometer 120 is an electronic three-axes accelerometer/3-axes MEMS accelerometer to measure the orientation of theft detection unit with respect to the gravity vector. The output of the MEMS accelerometer includes the acceleration of the accelerometer in X, Y and Z direction. It provides its own instantaneous acceleration relative to the acceleration of the earth gravity of lg. A MEMS accelerometer is preferred as it has a small size and sensitivity to small changes in acceleration. The accelerometer could also be used to measure acceleration along 3-axes. When the accelerometer is at rest, the value of vector determined from the acceleration along 3-axes corresponds to lg. The values of the accelerometer in X, Y and Z-direction form a vector. The measured acceleration along 3-axes could be used by the controller to calculate the actual speed and displacement of the theft detection unit. The speed and displacement of the theft detection unit could be calculated accurately if a moment in time is known in which the unit does not move, i.e. has a zero speed. Optionally the speed in one or more directions and/or displacement could be used to trigger an alarm signal.

The power supply unit 130 is connected to all components within the theft detection unit 100 which require electric power. The power supply unit 130 is integrated in the housing of the theft detection unit 100 and could include any type of battery, i.e. rechargeable or non-chargeable battery.

The speaker unit 140 is coupled to the controller 110 and configured to generate in response to a control signal generated by the controller 110 to generate an audible alarm signal.

The theft detection unit 100 comprises a user interface 150 to activate/deactivate the theft detection unit. In an embodiment, the user interface uses an electronic key, for example in the form of an iButton, to activate/deactivate the unit 100. In that case, the interface comprises a probe (not shown) to read out the code of the electronic key. The duration a user holds the electronic key in the vicinity of the probe, could be used to identify the mode a user would like to select. For example, if the unit is deactivated, active mode 1 is selected when a user holds the key for less than two seconds in the vicinity of the probe. Active mode 2 is selected when the user holds the key for more than two seconds and less than four seconds in the vicinity of the probe and active mode 3 is selected if the user holds the key for more than four seconds in the vicinity of the probe. However, the skilled person could easily adapt this method to more than three modes. In another embodiment, the number of times the user brings the key in the vicinity of the probe in a predefined period defines the mode to select.

The theft detection unit 100 further comprises one or more ports 160, 170 configured to couple external sensors systems or devices to the theft detection unit. An example in the outboard motor application is a switch to detect opening of the engine cover. When someone opens the engine cover, the switch is closed/opened, the controller checks regularly the port to which the engine cover switch is coupled to detect a change in state of the switch. When the theft detection unit 100 is in an active mode, the controller will generate in response to the detection of the change in state of the switch a control signal to generate an alarm by means of the speaker 140. Other examples of external sensors that could be coupled to the unit are: a motion sensor, earth magnetic field sensor, GPS, acceleration sensor, distance sensor, ultrasound sensor, gyroscope, shock sensor, height sensor, temperature sensor, rotation sensor, infra-red sensor, strain gauges, force sensor, image sensor, sonar, radar, etc. Depending on the application of the theft detection unit, one or more external sensors could be coupled to the unit. The signals generated by the external sensors could be used as additional signals to detect theft. An example of a system that could be coupled to the theft detection unit is a telecommunication system. In the event the unit detects theft, the controller could instruct the telecommunication system to send a message, for example sms, mms, or email, to a person to inform him about the event. A port 160, 170 could also be used to couple a flashing light or any other light source to the detection unit. The controller is then configured to control the light source in response to the detection of theft. In principle any suitable device configured to generate a signal indicating theft could be coupled to the theft detection unit 100 via one of the interface or ports 160, 170.

Fig. 2 illustrates some parameters used to in a method to detect theft. Fig. 2 shows from the rear a boat 200 with an outboard motor 210 in a stable position. The stable position corresponds to the position wherein the boat is stationary on the water, i.e. does have any roll. The stable position will be referred to as horizontal position or reference orientation in the present description. When the boat is in the reference orientation, the accelerometer will generate acceleration values in X-, Y- and Z-direction. In the reference position, the values of the accelerometer in X, Y and Z-direction form a reference vector. Vertical line indicated with ref is the direction of the reference orientation of the boat when the boat is in stationary position. Assumed is that the reference orientation of the boat in stationary position, i.e. the reference vector, coincides with the gravity vector. A three axes acceleration sensor in stationary positions measures continuously the gravity force of the earth. In this way, the unit could measure the orientation of the three axes acceleration sensor with respect to the gravity vector and determine the reference orientation of the boat. If the boat rolls from one side to another, the orientation of the three axes acceleration sensor with respect to the gravity vector will change. The change in orientation is used to determine the angle of the boat with respect to the reference orientation. The actual orientation of the boat is defined by the actual acceleration values in X-, Y- and Z-direction, which form again a vector. The change in angle between actual orientation and reference orientation could be calculated by the following well known equation:

A B = A II B cos Θ

wherein A is the reference vector, B is the actual vector, A-B is the dot product of two Euclidean vectors A and B, || A || is the magnitude of the reference vector, || B || is the magnitude of the actual vector and Θ is the angle between the reference vector and the actual vector, wherein 0 < Θ < 180. If Θ = 0, the object is in its reference orientation. If Θ = 180, the object is upside down relative to its horizontal orientation.

Fig. 2 shows with dotted lines the boat and motor with a roll with an angle of thrl and thr2 degrees with respect to the stationary position or reference orientation ref of the boat, thus an angle of thrl and thr2 with respect to the gravity vector. The roll can be to the left and to the right. Next to the roll of a boat, the boat has two other rotation motions: pitch and yaw. Roll is the rotation of a boat about the longitudinal (front/back) axis of the boat, pitch is the rotation of the boat about the transverse (side-to-side) axis and yaw is the rotation of the boat about the vertical (up-down) axis. Fig. 3 illustrates a function graph of the parameters in Fig. 2. Circle with radius thrl corresponds to all positions of the boat wherein the boat makes an angle of thrl degrees with respect to the gravity vector. Fig. 3 makes clear that the angle a boat can make with respect to the gravity vector can be a combination of roll and pitch. The use of the parameters ref, thrl, thr2 and dev in a method will be explained hereafter. It should further be noted that if the accelerometer moves up- and downwards and/or rotates around an axis parallel to the gravity vector, the angle between reference orientation and actual orientation will not change. Furthermore, the change in angle is one value. The angle is always positive and provides information on the combination of "roll" angle and "pitch" angle and not information on the individual amount of "roll" and "pitch" with respect to the reference orientation of the object.

The parameters thrl and thr2 define three zones. A first zone 301, wherein the angle of the boat is smaller than thrl, a second zone 302, wherein the angle of the boat is greater than thrl and smaller than thr2 and a third zone 303, wherein the angle of the boat is larger than thr2. When the angle is in the first zone 301, this indicates that the object is safe. When the angle is in the second zone 302, this could indicate that someone tries to steal the object. According to the invention, when the angle is for more than a predefined period continuously in the second zone 302, this will be regarded as the signal that someone is stealing the object and an alarm signal will be generated. When the angle enters the third zone 303, this is also an indication that someone is stealing the object and an alarm is generated immediately.

In an outboard motor application of a theft detection unit, at least two active modes could be defined. In the following description three different active modes will be used. We distinguish the following active modes, each having their associated parameters: Trailer-mode, harbour-mode and open water-mode. Trailer-mode is used when the outboard motor is attached to a boat positioned on land, for example a trailer. In this mode, the unit has the highest sensitivity in change of orientation to activate the alarm. Harbour-mode has to be used when the boat with outboard motor is in a harbour and "Open water"-mode has to be used when the boat with outboard motor is in open water. A difference between harbour-mode and open water-mode is that the amount of roll and pitch needed to activate the alarm is higher in open water-mode. Thus in "open water"-mode the unit is less sensitive than in harbour-mode and in harbour-mode the unit is less sensitive than in trailer-mode.

Fig. 4 shows a flowchart illustrating basic actions for a method for detecting theft. The method is run at the controller, i.e. processor, as a program which is stored in the memory of the unit. The program comprises instructions when read from the memory when executed by the controller cause the unit to perform the method. After starting up the theft detection unit in step 400, a user has to activate the unit. This could be done by using an electronic key as described before, so that only authorized persons could activate/deactivate the unit. The controller will retrieve the selected active mode in step 401. In step 402, the controller retrieves from the memory the parameters thrl, thr2, dev associated with the selected active mode. Block 403 is the routine to determine the reference orientation of the theft detection unit. The reference orientation could be in the form of a reference vector defined by the acceleration values in X-, Y and Z-direction from the accelerometer. This routine will be described in more detail below with reference to Figs 8 and 9. Block 404 is activated as soon as a reference orientation has been determined. Block 404 is the routine to detect theft. This routine will be described in more detail below with reference to Figs. 5 and 6. In this embodiment, after theft has been detected and an alarms the method will end in 405.

Fig. 5 illustrates a flowchart of a first embodiment for a detecting theft routine. After a reference orientation of the unit has been determined in the routine 403, the program will be started in step 500. A counter T is reset in step 501. In step 502, a sample is retrieved from the three axis acceleration sensor. A sample comprises acceleration data in X-, Y- and Z-direction. From this sample, the actual orientation of the unit with respect to the gravity vector is determined. In step 503, a change in angle alpha of the unit is calculated from the actual orientation and the reference orientation. In other words, the angle between the reference vector and the vector obtained from the acceleration data in X-, Y- and Z-direction of the sample. The angle alpha can be regarded as a difference signal defining the angle difference between the actual orientation of the unit with respect to the gravity vector and the reference orientation of the unit with respect to the gravity vector.

At step 504 is determined whether the angle alpha is greater than a threshold value thrl . It should be noted that each active mode has his associated threshold value thrl . Furthermore, it's clear that thrl has a value which is larger than 0. For example, in trailer-mode thrl = 2°, in harbour-mode thrl = 8° and in "open water"-mode thrl = 30°. If the angle alpha is greater than thrl, in step 505, the counter T is increased with 1. Then in step 506, value of counter T is checked. If the value of counter T is smaller than or equal to a predefined value T_per, the process will return to step 502 to retrieve a subsequent sample from the three-axis acceleration sensor. However, if at step 504 is concluded that angle alpha is smaller than or equal to thrl, the value of counter T set to zero in step 507 and the program will return to step 502.

If at step 506 is determined that the value of counter T is larger than T_per, the controller will generate in step 508 a control signal to activate an alarm and the program will end at step 509. T_per is a representative for a predefined period of time. In this embodiment the predefined period of time is defined by the product of the value T per and the sampling frequency of the accelerometer. It should be noted, that the counter T could be replaced by a timer. In that case, in steps 501 and 507 the timer is reset and in step 505 the timer is activated. If the timer is activated a subsequent instruction to activate the timer will not change the content of the timer. Step 506 is than performed by the timer, causing the program to jump to step 508.

The program illustrated in Fig. 5 can be summarized in the following way: a control signal for activating an alarm is generated if a difference signal exceeds a first threshold value thrl for a predefined period of time T_per. In the outboard motor application this corresponds to the following behaviour. When the roll/pitch of the boat is greater than thrl and the duration of a swing with an angle larger than thrl back to an angle smaller than thrl is shorter than T_per, the alarm will not be triggered and no false alarm will be given. The time between exceeding an angle > thrl and triggering the alarm is T_per.

Fig. 6 shows a flowchart illustrating a second embodiment for a detecting theft routine. In this embodiment steps 600 - 609 corresponds to steps 500 - 509. This embodiment comprises an additional step 610. In step 610, the actual angle alpha is compared with a second threshold value thr2, wherein thr2 > thrl . Step 610 is performed when alpha is larger than thrl . When alpha is greater than thr2, step 608 will be performed. If alpha is not greater than thr2 the program will proceed with step 605.

The program illustrated in Fig. 6 has the additional feature that when the difference signal exceeds a second threshold value, the controller will generate a control signal for activating an alarm. In the outboard motor application this corresponds to the following behaviour. As long as the roll/pitch of the boat is smaller than thr2 and the duration of a swing with an angle greater than thrl from horizontal position back to the horizontal position is shorter than T_per, the alarm will not be triggered and no false alarm will be given. However, as soon as the swing is larger the thr2, an alarm will be generated immediately. For example, in trailer- mode thr2 could be 3°, in harbour-mode thr2 = 30° and in "open water"-mode thr2 = 45°.

Fig. 7 shows a flowchart illustrating another embodiment of basic actions for a method for detecting theft. Actions 700 - 704 correspond to the actions 400 - 404 in Fig. 4. This embodiment comprises an additional feature performed by routine 706. Routine 706 detects after an alarm is generated by routine 704 when the theft detection unit is essentially positioned back to its reference orientation. When this is detected, the detect theft routine 704 will be activated again. An exemplar embodiment of routine 706 will be described below with reference to Fig. 10. This embodiment has the advantage over the embodiment in Fig. 4 in that the unit will become active again without user interaction after an alarm has been generated. This feature is advantageous in the outboard motor application. When an outboard motor is taken away the alarm will sound. The thief could decide to drop the outboard motor near the boat, to take it with him another time. When the harbourmaster finds the outboard motor and positions the motor on the boat again, the motor will be positioned with essentially the same orientation with respect to the gravity vector. The unit will detect this and will automatically activate the theft detection routine again in the originally selected active mode.

Fig. 8 shows a flowchart illustrating a first embodiment for a method for obtaining the reference orientation of the object. The method is a kind of calibration wherein the direction of the gravity vector with respect to the theft detection unit, read movable object, is determined. This method could be performed in step 403 in Fig. 4 and step 703 in Fig. 7. After starting the method in step 800, in step 801 the parameters corresponding to selected active mode are read from the memory. A parameter to determine the reference orientation from samples from the acceleration sensor is in this embodiment the number N of samples used to estimate the reference orientation of the unit. In step 802, N samples are retrieved from the acceleration sensor. In an embodiment N is 10 and the sample rate is 1 sample/second. Thus samples are retrieved over a period of 10 seconds. In step 803 the reference orientation of the theft detection unit is determined. The reference orientation is the orientation of the object in stable position. The x,y,z acceleration values measured by the acceleration sensor in this position only comprises the gravity force. As the gravity force is always significantly present in a sample, this component could be used to determine a change in angle of the theft detection unit with respect to the reference orientation. The reference orientation is in an embodiment determined by the average value of the samples. In another embodiment, a Least Square Error (LSE) method is used to determine the reference orientation. In yet another embodiment, the reference orientation is the midpoint between the samples having the largest distance in angle measured with respect to the gravity vector. As soon as the reference orientation of the object is determined, the theft detection routine 404and 704 in Figs. 4 and 7 respectively is started. After calculation of the reference orientation by means of a predefined function for the N samples, in step 804 a predetermine time is waited to perform a recalibration of the object. Recalibration is the repetition of the step 802 and 803. The predetermine time could be 30 minutes. Step 804 is optionally but very useful in application wherein the average orientation of the object changes very slowly. This is the case in the outboard motor application. Due to rain falling into the boat the orientation of the boat changes. If a correction or recalibration is not performed regularly, the change in angle of the boat with respect to the reference orientation could become continuously larger the thrl and the possibility that the angle becomes larger than thr2 increases. In both case, the alarm will be activated erroneously and generates a false alarm. This is undesirable.

Fig. 9 shows a flowchart illustrating a second embodiment of a method for obtaining the reference orientation of an object. This method differs from the method described with reference to Fig. 8 in that this method also defines initially the settings of the active mode. These settings are the values of thrl and thr2 parameters used in the theft detection routine. As described above, each active mode has its own values for thrl and thr2. These values have a relationship with the expected normal roll and pitch of the boat. However, it could be possible that during a storm one enters the harbour and activates the harbour-mode (mode 1). The waves can be so high that the reference orientation could not be determined accurately and consequently the alarm could give rise to false alarms. To avoid false alarms, the method determines in step 905 the variance var of the retrieved N samples. This variance is an indication of the amount of roll/pitch of the boat and thus the undulating movement of the surface. In step 906, the value var of the variance is compared with deviation parameter dev. If the var is not smaller than dev, than the theft detection routine will be started with the settings of active mode 2 in step 906. In Fig. 3 the range of dev is indicated. Active mode 2 corresponds to the "open water"-mode. As soon as var is smaller than dev step 907 will be performed. The parameters thrl and thr2 of the running theft detection routine will then be overwritten by the parameter values corresponding to active model and the detecting theft routine will from that moment operate with the parameters thrl and thr2 corresponding to the active mode selected by the user. After step 907 the routine ends in step 908. It might be clear that step 908 might be replaced by step 804 in Fig. 8 to enhance the method with the recalibration feature by repeating at predefined intervals the routine steps from step 903.

Fig. 10 shows a flowchart illustrating an embodiment for step 706 in Fig. 7.

It shows a routine to detect after an alarm that the object is in its original position. Regulations of theft alarm systems require that the system could not be continuously in a mode wherein the system generates an alarm. It is even not allowed to generate repeatedly an alarm signal of half a minute. After starting the routine with step 1000, in step 1001 N samples from the acceleration sensor are obtained. In step 1002 from these N samples a kind of reference orientation is calculated, however the reference orientation calculated in step 1002 is now expressed as angle alpha with respect to the reference orientation used by the . A similar algorithm to calculate the reference orientation in step 803 of Fig. 8 or step 904 of Fig. 9 could be used in step 1002 to calculate the value alpha. In step 1003, the value alpha is compared with the parameter dev. If alpha is not smaller than dev, this is an indication that the object is not back in its original position/orientation and the procedure will wait a predefined time in step 1004 to perform the steps 1001 to 1003 again. When alpha is smaller than dev, this indicates that the object is back in its original position/orientation and the theft detection routine could be activated again.

Fig. 11 is a waveform chart to show the operation of the method when the boat sways on the water. The waveform chart shows along the vertical axis the angle in degrees with respect to the horizontal orientation of the boat and along the horizontal axis the time in seconds. In this figure it is assumed that the boat is only rolling from the left to the right wherein the maximum roll is 29°. The roll angle is indicated by the solid line indicated with "Roll". It can be seen that the roll angle is repeatedly increasing to +29° and decreasing to -29°. If the boat is in horizontal position, the roll angle is 0°. The time period to make a full cycle 0° - +29° - 0° - -29° - 0° is about 5,4 seconds. The horizontal position has a corresponding reference vector with associated accelerometer values in X-, Y- and Z-direction. Each second, the accelerometer supplies to the processor the actual X- , Y-, and Z- value forming an actual vector indicating the actual orientation of the accelerometer with respect to the gravity vector. The processor subsequently calculates the angle between the reference vector and the actual vector. The sample values corresponding to the angle between the reference vector and the actual vector at time t are indicated in Fig. 11 with little circles. As the angle between two vectors is always positive, a sample when the boat has a negative roll angle has a value corresponding to the absolute value of said negative roll angle.

The dashed line indicated with thrl corresponds to the first threshold value thrl as described above. In Fig. 11, the value of thrl is 8, which corresponds to active mode 1 or harbour mode.

At the bottom side of the waveform chart, the value of the counter T in time is shown. When a sample value is above the threshold value thrl the value of counter T is increased by 1. When a sample value is below the threshold value thrl the value of counter T is reset to 0. An alarm will be given, when the value counter T is larger than T_per. In Fig. 11, T_per has the value 7. With a sample period of 1 second, an alarm will be given when after 7 seconds the subsequent sample value is above the threshold value thrl . However, despite the maximum roll angle of 29° and a threshold value thrl of 8, the counter T is never larger than 7. Therefore the alarm signal does not change from idle state to active state. The idle state corresponds to value 7 in the bottom part of Fig. 11 and the active state corresponds to value 12 in Fig. 11.

Fig. 12 is a waveform chart to show the operation of the method when a person enters a boat which has a slight roll on the water up to a maximum of 10°. The same threshold value thrl is used to increase/reset the counter value. Furthermore, the same value for T_per is used to determine when the alarm signal has to change in the active state.

It can be seen in Fig. 12 that due to the smaller roll angle fever samples have a value which are larger than the value of the first threshold thrl . Consequently, the counter T is more reset to zero than increased by one. At time t=10, the counter T obtains a value 2.

In Fig. 12 at time t = 20, a person enters the boat. As a consequence, the boat has an offset roll of 17, 1°. Due to this offset roll, most of the samples have a value larger than thrl . As a consequence, at time t = 39 the value of counter T is increased to a value larger than T _per and the alarm signal changes from idle state to active state. Once the alarm is in the active state, the reset of counter T at time t = 42 will not change the alarm signal from active state to idle state.

Despite that the maximum roll due to the person entering the boat is smaller than the maximum roll in Fig. 11 ; in Fig. 12 the alarm signal changes from the idle mode to the active mode. It might be clear that when the water surface is plane and the boat does not roll, a person entering the boat will likely cause an offset roll of more than 8° which will result in that case in activating the alarm after about 8 - 9 seconds.

It might be clear that the method described above is not limited to be used for outboard motor applications. The method could also be used to protect any other object that is movable such as cars, trucks, motorcycles, cycles, trailers, robots, boats. However also to protect computers, pianos, portable cabins and portable toilets the method could be applied. For all of these object is that they are tilted when they will be stolen. A MEMS three axis accelerometer allows measuring very small tilts and when the tilt is longer than the predefined period, the control signal to active an alarm will be generated. Furthermore, if the object is accelerated in a direction perpendicular to the gravity force, this will be recognized as a change in angle that could result in generating the control signal to activate an alarm. The acceleration could be an additional input for the theft detection. For example, when the acceleration is greater than a predefined acceleration value the controller will generate a control signal to activate an alarm. There are three axis accelerometers available on the market that could generate an interrupt signal by inertial wake-up/free-fall events as well as by the position of the device itself. Thresholds and timing of the internal interrupt generators are programmable by the controller. The interrupt can be used as events to trigger the controller to generate an alarm. It should further be noted that parameter dev in Fig. 9 could have another value as parameter dev in Fig. 10. The value depends on the parameter values of the mode that is active.

In the embodiments described above, three zones are used. It might be clear that the second zone 302 in Fig. 3 could be divided in two or more zones. Each zone is defined by a lower limit thr_L and an upper limit thr_H and the upper limit of one zone coincides with the lower limit of the neighbouring zone. Each zone will have an associated parameter defining the period of time wherein the measured angle of the object minimally should be before an alarm signal will be generated by the theft detection device. The value of the parameter defining the period of time decreases with the radius of the zone. Thus, the larger the radius of a zone the shorter the period of time the angle of the object may be in the corresponding zone to prevent that an alarm is generated.

The present invention and its exemplary embodiment can be realized in many ways. For example, one embodiment includes a computer-readable medium or a computer program product having computer readable code stored thereon that are executable by a processor of a theft detection unit/system to cause the unit/system to perform the method of the exemplary embodiments as previously described.

While the invention has been described in terms of several embodiments, it is contemplated that alternatives, modifications, permutations and equivalents thereof will become apparent to those skilled in the art upon reading the specification and upon study of the drawings. The invention is not limited to the illustrated embodiments. Changes can be made without departing from the idea of the invention. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of suitably programmable components. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. A method in a theft detection unit (2) for attachment to a movable object, the method comprising:

- repeatedly receiving acceleration data from a three axes acceleration sensor (4);

- determining a reference orientation of the three axes acceleration sensor from the acceleration data;

- determining a difference signal representing a change in angle of the received acceleration data with respect to the reference orientation; and,

- generating a control signal for activating an alarm when the difference signal exceeds a first threshold value for a predefined period of time.

2. A method according to claim 1, wherein the method further comprises generating a control signal for activating an alarm when the difference signal exceeds a second threshold value, wherein the first threshold value is smaller than the second threshold value.

3. A method according to claim 1 or 2, characterized in that the theft detection unit comprises at least one active mode and an alarm mode, wherein the unit switches from an active mode to the alarm mode when a control signal for activating an alarm is generated, the unit switches from alarm mode to the active mode when after a predefined delay time the difference signal representing a change in angle of the received acceleration data with respect to the reference orientation is smaller than a third threshold value, the third threshold value being smaller than or equal to the first threshold value.

4. A method according to claim 1, characterized in that the theft detection unit comprises a first active mode and a second active mode, wherein the first threshold value in the first active mode is smaller than the first threshold value in the second active mode.

5. A method according to any of the claims 1 - 4, wherein determining a reference orientation comprises:

- retrieving over a predefined time interval data samples representing acceleration of the sensor along three axes; and, - calculating the reference orientation from the data samples retrieved over said predefined time interval.

6. A method according to any of the claims 1 - 4, wherein determining a reference orientation further comprises:

- retrieving over a predefined time interval data samples representing acceleration of the sensor along three axes;

- calculating a reference orientation from the data samples retrieved over said predefined time interval and,

- deriving a deviation value indicative for the deviation of the retrieved data samples;

- repeating the retrieving and deriving actions as long as the deviation value is larger than a predefined deviation parameter;

- update the reference orientation with the value calculated from the data samples for which hold that the deviation value is smaller than the predefined deviation parameter.

7. A method according to claim 6, wherein the theft detection unit comprises more than one active mode which is selectable by a user and the predefined deviation parameter depends on the selected active mode.

8. A method according to claim 7, wherein the theft detection unit comprises a first active mode and a second active mode, wherein the first threshold value in the first active mode is smaller than the first threshold value in the second active mode, when the user selects the first active mode the unit is further configured operate with the first threshold value of the second active mode when the deviation value for the deviation of the retrieved data samples is larger than the predefined deviation parameter associated with the first active mode.

9. A method according to claim 8, wherein the unit is further configured to operate with the first threshold value of the first active mode as soon as the deviation value for the deviation of the retrieved data samples is smaller than the predefined deviation parameter associated with the first active mode.

10. A method according to any of the claims 1 - 9, wherein the reference orientation of the three axes acceleration sensor is updated with a predefined update frequency.

11. A theft detection unit for a movable object comprising a three axes acceleration sensor, an alarm unit, a processor and a memory to store instructions that, when executed by the processor (410), cause the unit to:

- repeatedly receive acceleration data from a three axes acceleration sensor (4);

- determine a reference orientation of the three axes acceleration sensor from the acceleration data;

- determine a difference signal representing a change in angle of the received acceleration data with respect to the reference orientation;

- generate a control signal for activating an alarm when the difference signal exceeds a first threshold value for a predefined period of time.

12. A theft detection unit according to claim 11, wherein the instructions when executed by the processor cause the unit to perform the method according any of the claims 2 - 10.

13. A theft detection unit according to any of the claims 11 - 12, wherein the unit further comprises at least one additional sensor input configured to couple at least one additional sensor to the theft detection unit, wherein the instructions further enable the processor to cause the unit to sense at least one sensor signal received at the at least one additional sensor input and to generate a control signal for activating an alarm in response to the at least one sensor signal.

14. Use of a theft detection unit comprising the technical features of any of the claims 11 - 13 attached to a movable object.

15. Use of a theft detection according to claim 14, wherein the movable object is an outboard motor.