WO2011003462A1

WO2011003462A1 - Accelerometer system and method

Info

Publication number: WO2011003462A1
Application number: PCT/EP2009/058826
Authority: WO
Inventors: Stefan Kreim; Alexander Schmidt; Tom Winkler
Original assignee: Tomtom International B.V.
Priority date: 2009-07-10
Filing date: 2009-07-10
Publication date: 2011-01-13

Abstract

A vehicle accelerometer system comprises an accelerometer device (290); and a location determining device (250, 255, 492), wherein the location determining device (250, 255, 492) provides location data and the accelerometer device (290) provides accelerometer data, and the system further comprises processing means (210) to determine a time window for which at least one of the accelerometer data and the location data satisfy at least one predetermined condition; determine at least one property of motion of the vehicle (500) from the accelerometer data for the time window,- determine at least one property of motion of the vehicle (500) from the location data for the time window; and determine an orientation output representative of an orientation of the accelerometer device (290), for which the property of motion of the vehicle (500) determined from the accelerometer data matches the property of motion of the vehicle (500) determined from the location data.

Description

Accelerometer system and method

Field of the Invention

The present invention relates to an accelerometer system and method, and in particular to an accelerometer and method for installation or use in a vehicle. The invention may be of particular relevance to an accelerometer that is included in or configured to communicate with a navigation device.

Background to the Invention

Navigation devices that include GPS (Global Positioning System) signal reception and processing functionality are well known and are widely employed as in-car or other vehicle navigation systems.

In general terms, a modern navigation device may comprise a processor, memory (at least one of volatile and non-volatile, and commonly both), and map data stored within said memory. The processor and memory usually cooperate to provide an execution environment in which a software operating system may be established, and additionally it is commonplace for one or more additional software programs to be provided to enable the functionality of the navigation device to be controlled, and to provide various other functions.

Typically these devices further comprise one or more input interfaces that allow a user to interact with and control the device, and one or more output interfaces by means of which information may be relayed to the user. Illustrative examples of output interfaces include a visual display and a speaker for audible output. Illustrative examples of input interfaces include one or more physical buttons to control on/off operation or other features of the device (which buttons need not necessarily be on the device itself but could be on a steering wheel if the device is built into a vehicle), and a microphone for detecting user speech. In one arrangement the output interface display may be configured as a touch sensitive display (by means of a touch sensitive overlay or otherwise) to additionally provide an input interface by means of which a user can operate the device by touch.

Devices of this type will also often include one or more physical connector interfaces by means of which power and optionally data signals can be transmitted to and received from the device, and optionally one or more wireless transmitters/receivers to allow communication over cellular telecommunications and other signal and data networks, for example Wi-Fi, Wi-Max GSM and the like.

Navigation devices of this type also usually include a GPS antenna by means of which satellite-broadcast signals, including location data, can be received and subsequently processed to determine a current location of the device.

The navigation device may also include or be configured to communicate with angular or linear accelerometers which produce signals that can be processed to determine the current angular and linear acceleration, and in turn, and in conjunction with location information derived from the GPS signal, velocity and relative displacement of the device and thus the vehicle in which it is mounted. Typically such features are most commonly provided in in-vehicle navigation systems, but may also be provided in navigation devices if it is expedient to do so. Accelerometer data may be stored and used to determine whether any exceptional driving events (for example, harsh braking or acceleration, swerving or other emergency manoeuvres) have occurred during a period of time.

Accelerometers may also be included in black box devices for vehicles, which do not provide navigation functions but log location, speed, acceleration and other vehicle data for transmission to a central server. Such devices are often included in commercial vehicles such as lorries, buses and taxis for monitoring purposes.

The position of installation of a navigation device, or other telematic device inside a vehicle is important, as internal antennas of the device are directly influenced by the position. For example a GPS antenna should have a clear view to the sky, and if it is located on one side of the device, that side should be the "upper side" when it is installed.

Furthermore, it is necessary to know the orientation of an accelerometer accurately in order to correctly process acceleration data from the accelerometer, and to correctly detect driving events such as curve driving or harsh braking or acceleration. Another problem is that accelerometers are often susceptible to temperature fluctuations, resulting in changes of measured acceleration data.

The installation position of a telematic and/or accelerometer device may be determined by manual calibration, for example by manually pressing a button when the device is being installed and fixed to the car by the installer. At the time of calibration all relevant environmental conditions are known and can be used to calibrate the device correctly. Such calibrations are also usually performed on level ground, and the output of the accelerometer device can thus be calibrated.

However, such manual calibrations are time consuming. Furthermore, known calibrations are generally more effective at determining the pitch and roll of the accelerometer with respect to the vehicle than they are at determining the yaw of the accelerometer with respect to the vehicle (the angle between the longitudinal axis of the vehicle and the corresponding axis of the accelerometer). For example, if it is known than the vehicle is on level ground then the output of the accelerometer when stationary can be used to determine pitch and roll values, or at least to determine offset values that can be used to correct for pitch and roll. In contrast, yaw values can be relatively difficult to determine, and it is necessary to rely on accurate manual alignment of the accelerometer with the longitudinal axis of the vehicle during installation rather than calibration based on output signals from the accelerometer.

If the initial installation is carried out inaccurately or if the orientation of a device changes after installation, there may be persistent, systematic inaccuracies in operation of the accelerometer.

Summary of the Invention

I n a first independent aspect of the invention there is provided a vehicle accelerometer system comprising:- an accelerometer device; and a location determining device, wherein the location determining device is operable to provide location data representative of location and the accelerometer device is operable to provide accelerometer data representative of acceleration, and the system further comprises processing means that is configured to determine a time window for which at least one of the accelerometer data and the location data satisfy at least one predetermined condition ; to determine at least one property of motion of the vehicle from the accelerometer data for the time window; to determine at least one property of motion of the vehicle from the location data for the time window; and to determine an orientation output representative of an orientation of the accelerometer device, for which the at least one property of motion of the vehicle determined from the accelerometer data matches the at least one property of motion of the vehicle determined from the location data. The orientation of the accelerometer device may be the orientation of the accelerometer device with respect to the vehicle.

The location determining device (for example, a GPS device) may thus be used in calibration of an accelerometer, and by determining a time window for which accelerometer data and location data both satisfy a predetermined condition it can be ensured that only data that is useful for the calibration is used. For example, it may be that only data that obtaining during clearly defined acceleration phases of the vehicle, which may be either positive acceleration or negative acceleration (braking) phases, may be used. It has been found that data representing significant variations in the magnitude or direction of acceleration, or that does not represent significantly sharp acceleration or braking may produce an inaccurate calibration, and such data may be excluded from the calibration by use of the determined of suitable time windows.

The location data and/or the accelerometer data may comprise a series of data items. Each data item may comprise location data or acceleration data and time data representative of a measurement time. The processing means may be, include, or form part of a processor.

Each of the accelerometer device and the location determining device may be installed in the vehicle. The processor may installed in the vehicle.

The at least one property of motion of the vehicle may comprise at least one of:- acceleration; velocity; direction of acceleration or velocity; distance and location.

The processor may be configured to process the accelerometer data for the time window to obtain a first direction value representative of a vehicle direction, to process the location data for the time window to obtain a second direction value representative of a vehicle direction, and to compare the first and second direction values to obtain the angle of orientation of the accelerometer device with respect to the vehicle.

The vehicle direction may comprise a direction of acceleration of the vehicle or a direction of velocity of the vehicle.

The processing means may be configured to determine a magnitude and/or direction of vehicle acceleration as a function of time from the accelerometer data. The processing means may be configured to determine a magnitude and/or direction of vehicle velocity or vehicle acceleration as a function of time, from the variation of location data with time (or the rate of variation of that variation of location data with time).

The system may further comprise a data store for storing data representative of at least one predetermined driving pattern, and the at least one predetermined condition may comprise a condition that a driving pattern represented by the location data or the accelerometer data matches the or at least one of the predetermined driving patterns.

By ensuring that a driving pattern determined from the location data or the accelerometer data matches a predetermined driving pattern, it can be ensured that only data useful for calibration of the accelerometer device may be used to determine the orientation output.

A driving pattern may be represented by a set of thresholds and/or ranges for at least one property of the vehicle's motion. The at least one property of the vehicle's motion may comprise at least one of location, distance of travel, magnitude and/or direction of acceleration, magnitude and/or direction of velocity, and variability of one or more of those properties. The at least one predetermined condition may comprise a condition that a vehicle trajectory property determined from at least one of the accelerometer data and the location data matches at least one predetermined trajectory property that is represented by the location data.

The at least one predetermined condition may comprise a condition that vehicle acceleration determined from at least one of the accelerometer data and the location data has a magnitude greater than a predetermined threshold magnitude of acceleration for substantially the whole of the time window. The predetermined threshold magnitude of acceleration may be greater than 0.5ms^"2, greater than 0.9ms^"2, and/or greater than 1.2 ms^"2.

The at least one predetermined condition may comprise a condition that the vehicle acceleration magnitude determined from the accelerometer data or the location data varies by less than a predetermined amount or proportion during the time window.

The at least one predetermined condition may comprise a condition that the vehicle acceleration magnitude determined from the accelerometer data or the location data is substantially constant for substantially the whole of the time window.

The at least one predetermined condition may comprise a condition that a direction of acceleration determined from at least one of the accelerometer data and the location data has an angular variation during substantially the whole of the time window less than a predetermined threshold angle. The predetermined threshold angle may be less than or equal to 2°, 5° and/or 10°.

The at least one predetermined condition may comprise a condition that the direction of acceleration determined from at least one of the accelerometer data and the location data is substantially constant for substantially the whole of the time window.

The at least one predetermined condition may comprise a condition that a direction of velocity determined from at least one of the accelerometer data and the location data has an angular variation during substantially the whole of the time window less than a predetermined threshold angle.

The at least one predetermined condition may comprise a condition that the direction of velocity determined from at least one of the accelerometer data and the location data is substantially constant for substantially the whole of the time window.

The processing means may be configured to determine the duration of the time window in dependence on at least one property of the accelerometer data and/or at least one property of the location data The duration of the time window may be variable. The time window may have a predetermined minimum length. The predetermined minimum length may be greater than or equal to at least one of 1 second, 5 seconds and 10 seconds.

The processing means may be configured to maximise the duration of the time window subject to the constraint that the accelerometer data and the location data for the time window satisfy the at least one predetermined condition.

The orientation may comprise a yaw angle between the accelerometer device and the vehicle.

The processing means may be configured to determine, for each of a plurality of time windows a respective orientation output, and to process the plurality of orientation outputs to obtain a combined orientation output representative of the orientation of the accelerometer device. The processing of the plurality of orientation outputs may comprise averaging at least some of the orientation outputs.

The processing means may be configured to rate the, or each of the, orientation outputs. The processing means may be configured to rate each of the orientation outputs and to weight each of the orientation outputs in dependence on its rating in the processing of the plurality of orientation outputs. Thus, the accuracy of determination of the angle of orientation may be improved, by rating

The processing means may be configured to rate each of the plurality of orientation outputs in dependence on at least one property of the time window, the accelerometer data or the location data. For example, the processing means may be configured to rate each orientation output in dependence on the magnitude or variation of acceleration or direction of the vehicle during the time window for which the orientation output was obtained.

The accelerometer device, the location determining device and the processor may be included in a navigation device. The accelerometer device, the location determining device and the processor may be positioned within a housing of the navigation device.

In a further independent aspect of the invention there is provided a method of determining an orientation of an accelerometer device with respect to a vehicle, comprising:- receiving accelerometer data representative of acceleration of the accelerometer device; receiving location data representative of the location of the vehicle; determining a time window for which at least one of the accelerometer data and the location data satisfy at least one predetermined condition; determining at least one property of motion of the vehicle from the accelerometer data for the time window; determining at least one property of motion of the vehicle from the location data for the time window; and determining an orientation output representative of an angle of orientation of the accelerometer device, for which the at least one property of motion of the vehicle determined from the accelerometer data matches the at least one property of motion of the vehicle determined from the location data.

In another independent aspect of the invention there is provided a computer program product comprising computer readable instructions executable to put into effect a method as claimed or described herein.

Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, apparatus features may be applied to method features and vice versa.

Brief Description of the Drawings

At least one embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic illustration of a Global Positioning System (GPS) usable by a navigation device;

Figure 2 is a schematic illustration of electronic components of a navigation device;

Figure 3 is a schematic diagram of a communications system including a wireless communication channel for communication with the navigation device;

Figure 4 is a schematic representation of an architectural stack of the navigation device of Figure 2;

Figure 5 is an illustrative screenshot from the navigation device of Figure 2;

Figures 6, 7a and 7b are schematic diagrams showing the orientation of an accelerometer device installed in a vehicle;

Figure 8 is a flowchart illustrating in overview the processing of accelerometer data and location data to determine an orientation of an accelerometer device;

Figure 9 is a flow chart illustrating the selection of an acceleration phase;

Figure 10 is a flow chart illustrating the determination of whether location data matches a predetermined driving pattern for the selected acceleration phase;

Figure 1 1 is a plot of acceleration ranges;

Figure 12 is a set of graphs showing acceleration, speed and direction data as a function of time;

Figure 13 is a set of graphs showing acceleration, speed and direction data as a function of time, after correction of the acceleration data; and

Figure 14 is a schematic illustration of an alternative embodiment in which an accelerometer is included in a data logger device.

Detailed Description of Embodiments

Embodiments of the present invention will now be described with particular reference to a system that comprises a navigation device that includes an accelerometer or is configured to communicate with an accelerometer. The teachings of the present invention are not limited to such systems but are instead universally applicable to any type of accelerometer system. Furthermore, in the embodiments described below the navigation device is installed permanently in a vehicle, for example by an original equipment manufacturer. In alternative embodiments, the navigation device may be (without limitation) any type of route planning and/or navigation device, irrespective of whether that device is embodied as a portable navigation device (PND), a navigation device built into a vehicle, or indeed a computing resource (such as a personal computer (PC), mobile telephone or portable digital assistant (PDA)) executing route planning and/or navigation software.

Features of a navigation device will be described first, with reference to Figures 1 to 5. Features of an accelerometer that is included in or associated with the navigation device will then be described with reference to Figures 6 to 11.

Fig. 1 illustrates an example view of Global Positioning System (GPS), usable by navigation devices. Such systems are known and are used for a variety of purposes. In general, GPS is a satellite-radio based navigation system capable of determining continuous position, velocity, time, and in some instances direction information for an unlimited number of users. Formerly known as NAVSTAR, the GPS incorporates a plurality of satellites which orbit the earth in extremely precise orbits. Based on these precise orbits, GPS satellites can relay their location to any number of receiving units.

The GPS system is implemented when a device, specially equipped to receive GPS data, begins scanning radio frequencies for GPS satellite signals. Upon receiving a radio signal from a GPS satellite, the device determines the precise location of that satellite via one of a plurality of different conventional methods. The device will continue scanning, in most instances, for signals until it has acquired at least three different satellite signals (noting that position is not normally, but can be determined, with only two signals using other triangulation techniques). Implementing geometric triangulation, the receiver utilizes the three known positions to determine its own two-dimensional position relative to the satellites. This can be done in a known manner. Additionally, acquiring a fourth satellite signal will allow the receiving device to calculate its three dimensional position by the same geometrical calculation in a known manner. The position and velocity data can be updated in real time on a continuous basis by an unlimited number of users.

As shown in Figure 1 , the GPS system is denoted generally by reference numeral 100. A plurality of satellites 120 are in orbit about the earth 124. The orbit of each satellite 120 is not necessarily synchronous with the orbits of other satellites 120 and, in fact, is likely asynchronous. A GPS receiver 140 is shown receiving spread spectrum GPS satellite signals 160 from the various satellites 120.

The spread spectrum signals 160, continuously transmitted from each satellite 120, utilize a highly accurate frequency standard accomplished with an extremely accurate atomic clock. Each satellite 120, as part of its data signal transmission 160, transmits a data stream indicative of that particular satellite 120. It is appreciated by those skilled in the relevant art that the GPS receiver device 140 generally acquires spread spectrum GPS satellite signals 160 from at least three satellites 120 for the GPS receiver device 140 to calculate its two-dimensional position by triangulation. Acquisition of an additional signal, resulting in signals 160 from a total of four satellites 120, permits the GPS receiver device 140 to calculate its three-dimensional position in a known manner.

Figure 2 is an illustrative representation of electronic components of a navigation device 200 according to an embodiment of the present invention, in block component format. It should be noted that the block diagram of the navigation device 200 is not inclusive of all components of the navigation device, but is only representative of many example components.

The navigation device 200 is located within a housing (not shown). The housing includes a processor 210 connected to an input device 220 and a display screen 240. The input device 220 can include a keyboard device, voice input device, touch panel and/or any other known input device utilised to input information; and the display screen 240 can include any type of display screen such as an LCD display, for example. In one arrangement the input device 220 and display screen 240 are integrated into an integrated input and display device, including a touchpad or touchscreen input so that a user need only touch a portion of the display screen 240 to select one of a plurality of display choices or to activate one of a plurality of virtual buttons.

The navigation device may include an output device 260, for example an audible output device (e.g. a loudspeaker). As output device 260 can produce audible information for a user of the navigation device 200, it is should equally be understood that input device 240 can include a microphone and software for receiving input voice commands as well. The navigation device includes an accelerometer 290, and the processor 210 is configured to communicate with the accelerometer as described in more detail below.

In the navigation device 200, processor 210 is operatively connected to and set to receive input information from input device 220 via a connection 225, and operatively connected to at least one of display screen 240 and output device 260, via output connections 245, to output information thereto. Further, the processor 210 is operably coupled to a memory resource 230 via connection 235 and is further adapted to receive/send information from/to input/output (I/O) ports 270 via connection 275, wherein the I/O port 270 is connectible to an I/O device 280 external to the navigation device 200. The memory resource 230 comprises, for example, a volatile memory, such as a Random Access Memory (RAM) and a non-volatile memory, for example a digital memory, such as a flash memory. The external I/O device 280 may include, but is not limited to an external listening device such as an earpiece for example. The connection to I/O device 280 can further be a wired or wireless connection to any other external device such as a car stereo unit for hands-free operation and/or for voice activated operation for example, for connection to an ear piece or head phones, and/or for connection to a mobile phone for example, wherein the mobile phone connection may be used to establish a data connection between the navigation device 200 and the internet or any other network for example, and/or to establish a connection to a server via the internet or some other network for example.

Fig. 2 further illustrates an operative connection between the processor 210 and an antenna/receiver 250 via connection 255, wherein the antenna/receiver 250 can be a GPS antenna/receiver for example. It will be understood that the antenna and receiver designated by reference numeral 250 are combined schematically for illustration, but that the antenna and receiver may be separately located components, and that the antenna may be a GPS patch antenna or helical antenna for example.

Further, it will be understood by one of ordinary skill in the art that the electronic components shown in Fig. 2 are powered by power sources (not shown) in a conventional manner. As will be understood by one of ordinary skill in the art, different configurations of the components shown in Fig. 2 are considered to be within the scope of the present application. For example, the components shown in Fig. 2 may be in communication with one another via wired and/or wireless connections and the like.

Referring now to Fig. 3, the navigation device 200 may establish a "mobile" or telecommunications network connection with a server 302 via a mobile device (not shown) (such as a mobile phone, PDA, and/or any device with mobile phone technology) establishing a digital connection (such as a digital connection via known Bluetooth technology for example). Thereafter, through its network service provider, the mobile device can establish a network connection (through the internet for example) with a server 302. As such , a "mobile" network connection is established between the navigation device 200 (which can be, and often times is mobile as it travels alone and/or in a vehicle) and the server 302 to provide a "real-time" or at least very "up to date" gateway for information.

The establishing of the network connection between the mobile device (via a service provider) and another device such as the server 302, using an internet (such as the World Wide Web) for example, can be done in a known manner. This can include use of TCP/IP layered protocol for example. The mobile device can utilize any number of communication standards such as CDMA, GSM, WAN, etc.

As such, an internet connection may be utilised which is achieved via data connection, via a mobile phone or mobile phone technology within the navigation device 200 for example. For this connection, an internet connection between the server 302 and the navigation device 200 is established. This can be done, for example, through a mobile phone or other mobile device and a GPRS (General Packet Radio Service)- connection (GPRS connection is a high-speed data connection for mobile devices provided by telecom operators; GPRS is a method to connect to the internet).

The navigation device 200 can further complete a data connection with the mobile device, and eventually with the internet and server 302, via existing Bluetooth technology for example, in a known manner, wherein the data protocol can utilize any number of standards, such as the GSRM, the Data Protocol Standard for the GSM standard, for example.

The navigation device 200 may include its own mobile phone technology within the navigation device 200 itself (including an antenna for example, or optionally using the internal antenna of the navigation device 200). The mobile phone technology within the navigation device 200 can include internal components as specified above, and/or can include an insertable card (e.g. Subscriber Identity Module or SIM card), complete with necessary mobile phone technology and/or an antenna for example. As such, mobile phone technology within the navigation device 200 can similarly establish a network connection between the navigation device 200 and the server 302, via the internet for example, in a manner similar to that of any mobile device.

For GPRS phone settings, a Bluetooth enabled navigation device may be used to correctly work with the ever changing spectrum of mobile phone models, manufacturers, etc., model/manufacturer specific settings may be stored on the navigation device 200 for example. The data stored for this information can be updated. In Fig. 3 the navigation device 200 is depicted as being in communication with the server 302 via a generic communications channel 318 that can be implemented by any of a number of different arrangements. The server 302 and a navigation device 200 can communicate when a connection via communications channel 318 is established between the server 302 and the navigation device 200 (noting that such a connection can be a data connection via mobile device, a direct connection via personal computer via the internet, etc.).

The server 302 includes, in addition to other components which may not be illustrated, a processor 304 operatively connected to a memory 306 and further operatively connected, via a wired or wireless connection 314, to a mass data storage device 312. The processor 304 is further operatively connected to transmitter 308 and receiver 310, to transmit and send information to and from navigation device 200 via communications channel 318. The signals sent and received may include data, communication, and/or other propagated signals. The transmitter 308 and receiver 310 may be selected or designed according to the communications requirement and communication technology used in the communication design for the navigation system 200. Further, it should be noted that the functions of transmitter 308 and receiver 310 may be combined into a signal transceiver.

Server 302 is further connected to (or includes) a mass storage device 312, noting that the mass storage device 312 may be coupled to the server 302 via communication link 314. The mass storage device 312 contains a store of navigation data and map information, and can again be a separate device from the server 302 or can be incorporated into the server 302.

The navigation device 200 is adapted to communicate with the server 302 through communications channel 318, and includes processor, memory, etc. as previously described with regard to Fig. 2, as well as transmitter 320 and receiver 322 to send and receive signals and/or data through the communications channel 318, noting that these devices can further be used to communicate with devices other than server 302. Further, the transmitter 320 and receiver 322 are selected or designed according to communication requirements and communication technology used in the communication design for the navigation device 200 and the functions of the transmitter 320 and receiver 322 may be combined into a single transceiver.

Software stored in server memory 306 provides instructions for the processor 304 and allows the server 302 to provide services to the navigation device 200. One service provided by the server 302 involves processing requests from the navigation device 200 and transmitting navigation data from the mass data storage 312 to the navigation device 200. Another service provided by the server 302 includes processing the navigation data using various algorithms for a desired application and sending the results of these calculations to the navigation device 200.

The communication channel 318 generically represents the propagating medium or path that connects the navigation device 200 and the server 302. Both the server 302 and navigation device 200 include a transmitter for transmitting data through the communication channel and a receiver for receiving data that has been transmitted through the communication channel.

The communication channel 318 is not limited to a particular communication technology. Additionally, the communication channel 318 is not limited to a single communication technology; that is, the channel 318 may include several communication links that use a variety of technology. For example, the communication channel 318 can be ad a pted to p rovi d e a path fo r e l ectrical, optical, and/or electromagnetic communications, etc. As such, the communication channel 318 includes, but is not limited to, one or a combination of the following: electric circuits, electrical conductors such as wires and coaxial cables, fibre optic cables, converters, radio-frequency (RF) waves, the atmosphere, empty space, etc. Furthermore, the communication channel 318 can include intermediate devices such as routers, repeaters, buffers, transmitters, and receivers, for example.

In one illustrative arrangement, the communication channel 318 includes telephone and computer networks. Furthermore, the communication channel 318 may be capable of accommodating wireless communication such as radio frequency, microwave frequency, infrared communication, etc. Additionally, the communication channel 318 can accommodate satellite communication.

The communication signals transmitted through the communication channel 318 include, but are not limited to, signals as may be required or desired for given communication technology. For example, the signals may be adapted to be used in cellular communication technology such as Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Code Division Multiple Access (CDMA), Global System for Mobile Communications (GSM), etc. Both digital and analogue signals can be transmitted through the communication channel 318. These signals may be modulated, encrypted and/or compressed signals as may be desirable for the communication technology.

The server 302 includes a remote server accessible by the navigation device 200 via a wireless channel. The server 302 may include a network server located on a local area network (LAN), wide area network (WAN), virtual private network (VPN), etc. The server 302 may include a personal computer such as a desktop or laptop computer, and the communication channel 318 may be a cable connected between the personal computer and the navigation device 200. Alternatively, a personal computer may be connected between the navigation device 200 and the server 302 to establish an internet connection between the server 302 and the navigation device 200. Alternatively, a mobile telephone or other handheld device may establish a wireless connection to the internet, for connecting the navigation device 200 to the server 302 via the internet.

The navigation device 200 may be provided with information from the server 302 via information downloads which may be periodically updated automatically or upon a user connecting navigation device 200 to the server 302 and/or may be more dynamic upon a more constant or frequent connection being made between the server 302 and navigation device 200 via a wireless mobile connection device and TCP/IP connection for example. For many dynamic calculations, the processor 304 in the server 302 may be used to handle the bulk of the processing needs, however, processor 210 of navigation device 200 can also handle much processing and calculation, oftentimes independent of a connection to a server 302.

As indicated above in Fig. 2, a navigation device 200 includes a processor 210, an input device 220, and a display screen 240. The input device 220 and display screen 240 are integrated into an integrated input and display device to enable both input of information (via direct input, menu selection, etc.) and display of information through a touch panel screen, for example. Such a screen may be a touch input LCD screen, for example, as is well known to those of ordinary skill in the art. Further, the navigation device 200 can also include any additional input device 220 and/or any additional output device 241 , such as audio input/output devices for example.

Referring now to Fig. 4 of the accompanying drawings, the memory resource 230 stores a boot loader program (not shown) that is executed by the processor 210 in order to load an operating system 470 from the memory resource 230 for execution by functional hardware components 460, which provides an environment in which application software 480 can run. The operating system 470 serves to control the functional hardware components 460 and resides between the application software 480 and the functional hardware components 460. The application software 480 provides an operational environment including the GUI that supports core functions of the navigation device 200, for example map viewing, route planning, navigation functions and any other functions associated therewith.

The application software 480 also includes an accelerometer module 490 that is configured to receive and process accelerometer data from the accelerometer 290, a location determining module 492 and a GPS pattern recognition module 494. The function and operation of the accelerometer module 490 is described in more detail below.

When the user switches on the device 200, the device 200 acquires a GPS fix and calculates (in a known manner) the current location of the navigation device 200. The location is calculated using a location determin ing un it comprisi ng the antenna/receiver 250, the connection 255 and the location determining module 492 included in the processor 210. The user is then presented, as shown in Figure 5, with a view in pseudo three dimensions on a touch screen display 240 of the local environment 494 in which the navigation device 200 is determined to be located, and in a region 496 of the display 240 below the local environment a series of control and status messages. The device 200 provides route planning, mapping and navigation functions to the user, in dependence on user input provided by a series of interlinked soft or virtual buttons and menu screens that can be displayed on the display 240. The device 200 continues to determine its location using the location determination unit on an ongoing basis whilst it is operational.

The accelerometer in certain embodiments is a three-axis accelerometer and measures acceleration along each of three orthogonal axes (x, y, z). In alternative embodiments the accelerometer is a two axis accelerometer. The accelerometer may be an analogue or digital acceleration sensor and can be of any type. I n one embodiment, the accelerometer is a Bosch Sensortec SMB380 triaxial acceleration sensor.

In operation, the accelerometer continuously provides data representing the results of accelerometer measurements to the accelerometer module 490 operating at the processor 210. The data provided by the accelerometer comprises acceleration data (ax, ay, az) for each axis (x, y, z) of the accelerometer. The accelerometer module 490 treats data representative of each measurement as an accelerometer output data item. The measurement may be perfomed at a single instant, or may be averaged over a period of time. The averaging can be performed by the accelerometer 290 itself or by the accelerometer module 490. Each accelerometer output data item may be, or may be representative of, an acceleration vector (ax, ay, az).

The accelerometer data items are stored in the memory 230 for subsequent transmission to the server 302 and/or processing.

Similarly, GPS location data is continuously output by the location determining unit and stored in the memory 230. Time data representative of the time of each GPS location or accelerometer measurement is stored with each data item. Each piece of time data may also be referred to as a time stamp.

In one mode of operation the accelerometer data items are processed either by the accelerometer module 490 or the server 302 in order to identify whether exceptional driving events (for example, harsh braking or acceleration, swerving or other emergency manoeuvres) have occurred during a period of time.

The correct processing of accelerometer data requires that the output from the accelerometer when stationary is known. Each accelerometer data item comprises, or can be processed to provide, a measured acceleration vector a = (ax, ay, az).

If the accelerometer 290 is stationary (not moving), the magnitude of the acceleration vector a = (ax, ay, az) is substantially equal to the Earth's gravity (g) (static acceleration). If the device is being moved, additional forces acting on the accelerometer can be determined from the measured acceleration vector, compensated for the acceleration vector when the device is stationary.

The magnitude of g determined by the accelerometer 290 differs under changing temperatures or other environmental conditions due to the effect of such changing temperatures or other environmental conditions on operation of the accelerometer 290.

Furthermore, the vector components ax, ay and az of the acceleration vector when the device is stationary depend on the orientation of the accelerometer with respect to the ground at that time.

It is an important feature of the embodiment that the accelerometer module 490 is able to determine an orientation output representative of the accelerometer with respect to the vehicle from stored accelerometer output data items, and to use that orientation output in subsequent processing and analysis of accelerometer measurements. An example of the determination of the orientation output is described in relation to Figures 6, 7a and 7b.

Figures 6, 7a and 7b show the device 200 installed in a vehicle 500, in a top view, a side view and a head-on view with respect to the vehicle respectively. A vehicle frame of reference when the vehicle is on level ground is illustrated in Figures 6, 7a and 7b in which an x-axis is aligned with the forward direction of motion of the vehicle, a y- axis is aligned at 90° to the x-axis in a horizontal plane, and a z-axis is the vertical axis. It can be seen that in this example the device 200 is oriented at an angle of α° rotated around the y-axis of the vehicle in the x-z plane (also referred to as the pitch angle), at angle of β° rotated around the x-axis in the z-y plane (also referred to as the roll angle) and at angle Φ° rotated around the z-axis in the x-y plane (also referred to as the yaw angle). In one mode of operation, the pitch and roll angles are known from a previous calibration procedure or measurement and the accelerometer output data items are pre- processed to correct for those pitch and roll angles. For example, a rotation matrix is constructed from the calibrated pitch and roll angles, and the acceleration vector for each accelerometer data item is rotated to the horizontal (x-y) plane of the vehicle's coordinate system in the pre-processing procedure. In an alternative mode of operation, it is presumed that the accelerometer has been installed correctly in alignment with the horizontal (x-y) plane and that all acceleration vectors already point to somewhere in the horizontal (x-y) plane during normal vehicle movements on a planar (non-inclined) driving surface.

The processing of accelerometer data and location data is illustrated in overview in the flowchart of Figure 8.

In operation the accelerometer module 490 monitors the accelerometer data items as a function of measurement time for phases of acceleration that may be suitable for use in calibration of the accelerometer. The monitoring can be performed in real time as accelerometer data items are received from the accelerometer 290, or can be performed subsequently on stored accelerometer data items.

Acceleration phases that may be suitable for use in calibration of the accelerometer include phases in which the acceleration has a magnitude above a pre- determined level and/or in which the acceleration has a substantially constant direction. The accelerometer module 490 identifies the start time and end time of each suitable acceleration phase.

A flow chart illustrating in overview the selection of a constant direction acceleration phase is provided in Figure 9, in which a series of accelerometer data items are processed in succession. In the figure, each acceleration data item is referred to as

Data and has a magnitude referred to as Magnitude and a direction referred to as

Direcrtion. The predetermined level is referred to as Threshold, and the determination of whether the acceleration has a substantially constant direction is based upon whether the direction for each successive acceleration data item is within a threshold amount of the direction for the last acceleration data item (whether the direction is nearby or far away from the direction for the last acceleration data item). A list of accelerometer data items is built up until the next acceleration data item has an acceleration less than the threshold, or a direction difference greater than the direction threshold. If a list of 10 or more acceleration data items is built up, the acceleration data items are taken to represent an acceptable acceleration phase, and the time window is defined by the time data for the first and last items in the list. In one example, a suitable acceleration phase is a variable length tuple of acceleration data items which all point to or nearly to the same direction (for example, having a deviation in acceleration direction of less than 10 degrees) in the x-y-plane and which all have a magnitude greater than a specified recognition threshold (for example, 0.92 m/s²).

For each acceleration phase identified as being suitable, the GPS pattern recognition module 494 obtains GPS time and location data from the memory 230 for the time window (bounded by the start and end time identified by the accelerometer module 490) of the acceleration phase. The GPS pattern recognition module 494 processes the GPS time and location data to obtain GPS speed and direction data as a function of time for the time window (speed and direction can be obtained from the rate of change of location as a function of time, using standard techniques).

The GPS pattern recognition module 494 then processes the GPS speed and direction data for the identified acceleration phase and determines whether it corresponds to a predetermined driving pattern. Usually, the GPS pattern recognition module 494 compares the data to a plurality of predetermined patterns and determines whether the data matches any of the patterns. Examples of driving patterns include ACCELERATE (and BRAKE), which are patterns in which each successive speed measurement has a value greater than (or less than) the preceding measurement, and in which the variation in direction determined from GPS data is less than a predetermined threshold (for example 5°).

A flowchart illustrating in overview an example of the determination of whether GPS data corresponds to a predetermined driving pattern (in this case, ACCELERATE or BRAKE) is provided in Figure 10. Each new GPS position data item is referred to as newData, the speed determined from that new data item is referred to as Speed or currentSpeed, and the speed determined from the previous data item is referred to as lastSpeed. A list of GPS data items for which acceleration and direction conditions is built up. If more than three data items satisfy the predetermined conditions the GPS data can be used in the calibration procedure. In one mode of operation, the time window determined from the acceleration data may be shortened if the GPS data does not satisfy the predetermined conditions for the whole of the time window.

If the GPS speed and direction data satisfy the predetermined conditions, for example corresponding to a predetermined driving pattern, the GPS pattern recognition module 494 then calculates the average direction of travel obtained from that GPS data for the acceleration phase time window. The accelerometer module 490 then correlates the direction obtained from the GPS data with the mean direction angle obtained from acceleration data during the acceleration phase.

In one example, the accelerometer module 490 maps the average direction of travel (for example ACCELERATION: 0°, BRAKE: 180°) obtained from the GPS data to the measured mean direction obtained from the accelerometer data for the corresponding acceleration phase. The difference between the average direction of travel from the GPS data and the measured mean direction, is the yaw angle of the accelerometer with respect to the vehicle, calculated for that acceleration phase.

A rating is determined by the accelerometer module 490 for each calculated yaw angle. The rating is determined in dependence on, for example, the magnitude of acceleration, signal quality, the duration of the acceleration phase, and the GPS direction deviation. Each calculated yaw angle and rating is stored in the memory 230.

In one example, illustrated graphically in Figure 11 , each calculated yaw angle is rated in dependence on whether the magnitude of acceleration of the vehicle from which the yaw angle was determined was within a high 550 or normal 552 range. The high 550 and normal 552 ranges are shown in Figure 11 , which is a plot of acceleration magnitudes in the x-y plane. Yaw angles determined from acceleration phases having a magnitude in the high range are rated more highly and weighted more heavily than yaw angles determined from acceleration phases having a magnitude in the normal range.

In the example shown, accelerometer data for acceleration phases having a magnitude in the low range 554 is not used to determine yaw angle as the magnitude of acceleration is below the predetermined threshold. Accelerometer data for acceleration phases having a magnitude above that of the high range 550 is also excluded, as it is taken to be too high to be correct. In general, any outlying data, having values outside reasonable acceleration, time, velocity and location ranges, is excluded.

The accelerometer module 490 comprises a statistical sub-system that processes stored yaw angles in dependence on their rating to obtain a mean yaw angle. In one example, the statistical subsystem calculates a weighted average of all stored yaw angles, weighted by their ratings and excluding yaw angles having outlying values or ratings below a threshold rating value, to obtain the mean yaw angle.

The accelerometer module 490 comprises a transformation sub-system that processes each accelerometer data item received from the accelerometer by rotating the measured acceleration vector represented by the accelerometer data item around the gravity axis by the mean yaw angle. The accelerometer data can thus be transformed in real time to compensate for the yaw angle.

The accelerometer module 490 includes an event recognition subsystem that identifies acceleration events from the accelerometer data compensated for the calculated mean yaw angle. Figure 12 shows a graphs of accelerometer data, representing measured acceleration in x, y and z directions, and speed and direction determined from GPS data, all as a function of time for a 15 second data stream. The accelerometer data of Figure 12 is not corrected for the yaw angle. Figure 13 shows the same data as Figure 12, following yaw angle compensation. The data represents a longitudinal acceleration followed by a deceleration.

The accelerometer module 490 may be configured to continually monitor accelerometer and GPS data to identify suitable acceleration phases, and to obtain new angle measurements and update the mean yaw angle in real time.

It will be understood that the selection of time windows for which accelerometer and location data is used to determine the orientation of the accelerometer device is not limited to being performed in dependence on the conditions described above in relation to Figures 6 to 12. The selection of suitable time windows and/or data may be carried out in dependence on any suitable condition relating to vehicle motion, for example a suitable range or threshold, or combination or ranges or thresholds, relating to one or more of location , distance of travel, magnitude and/or direction of acceleration, magnitude and/or direction of velocity, and variability of one or more of those properties.

In the embodiment of Figure 2, the accelerometer 290 is integrated in, or in communication with, a navigation device that provides navigation functions to a user under control of the user. In alternative embodiments, the accelerometer is included in a data logger device that logs location data and/or accelerometer data and/or other vehicle data and communicates such data to the server 302. An example of such an alternative embodiment is illustrated in Figure 14, which shows a black-box type device 600 for installation in a vehicle.

The device 600 includes some of the components of the device 200, including the accelerometer 290, the processor 210, the memory 230, and the antenna/receiver 250. The temperature or other environmental sensor 602 is also shown in Figure 1 1. The device 600 is optionally also able to interface with vehicle systems to obtain and log other vehicle data. The location-determining and accelerometer functions of device 600 are as described in relation to the device 200 of Figure 2, but the device 600 does not provide navigation or display functions to the driver of a vehicle but instead logs and transmits data to the server 302 for subsequent analysis. The device 600 is particularly suitable for installation in a commercial vehicle. Both the device 600 and the device 200 may be used in commercial vehicle and fleet management systems, for example the TomTom Work and TomTom Webfleet systems.

It will be appreciated that whilst various aspects and embodiments of the present invention have heretofore been described, the scope of the present invention is not limited to the particular arrangements set out herein and instead extends to encompass all arrangements, and modifications and alterations thereto, which fall within the scope of the appended claims.

Whilst embodiments described in the foregoing detailed description refer to GPS, it should be noted that the navigation device may utilise any kind of position sensing technology as an alternative to (or indeed in addition to) GPS. For example the navigation device may utilise using other global navigation satellite systems such as the European Galileo system. Equally, it is not limited to satellite based but could readily function using ground based beacons or any other kind of system that enables the device to determine its geographic location.

Alternative embodiments of the invention can be implemented as a computer program product for use with a computer system, the computer program product being, for example, a series of computer instructions stored on a tangible data recording medium, such as a diskette, CD-ROM, ROM, or fixed disk, or embodied in a computer data signal, the signal being transmitted over a tangible medium or a wireless medium, for example, microwave or infrared. The series of computer instructions can constitute all or part of the functionality described above, and can also be stored in any memory device, volatile or non-volatile, such as semiconductor, magnetic, optical or other memory device.

It will also be well understood by persons of ordinary skill in the art that whilst embodiments described herein implement certain functionality by means of software, that functionality could equally be implemented solely in hardware (for example by means of one or more ASICs (application specific integrated circuit)) or indeed by a mix of hardware and software. As such, the scope of the present invention should not be interpreted as being limited only to being implemented in software.

It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.

Lastly, it should also be noted that whilst the accompanying claims set out particular combinations of features described herein, the scope of the present invention is not limited to the particular combinations hereafter claimed, but instead extends to encompass any combination of features or embodiments herein disclosed irrespective of whether or not that particular combination has been specifically enumerated in the accompanying claims at this time.

Claims

1. A vehicle accelerometer system comprising:- an accelerometer device (290); and

a location determining device (250, 255, 492), wherein

the location determining device (250, 255, 492) is operable to provide location data representative of location and the accelerometer device (290) is operable to provide accelerometer data representative of acceleration, and the system further comprises processing means (210) that is configured to:- determine a time window for which at least one of the accelerometer data and the location data satisfy at least one predetermined condition;

determine at least one property of motion of the vehicle (500) from the accelerometer data for the time window;

determine at least one property of motion of the vehicle (500) from the location data for the time window; and

determine an orientation output representative of an orientation of the accelerometer device (290), for which the at least one property of motion of the vehicle (500) determined from the accelerometer data matches the at least one property of motion of the vehicle (500) determined from the location data.

2. A system according to Claim 1 , wherein the at least one property of motion of the vehicle comprises at least one of:- acceleration; velocity; direction of acceleration or velocity; distance and location.

3. A system according to Claim 1 or 2, wherein the processing means (210) is configured to process the accelerometer data for the time window to obtain a first direction value representative of a vehicle direction, to process the location data for the time window to obtain a second direction value representative of a vehicle direction, and to compare the first and second direction values to obtain the angle of orientation of the accelerometer device (290) with respect to the vehicle (500).

4. A system according to Claim 3, wherein the vehicle direction comprises a direction of acceleration of the vehicle (500) or a direction of velocity of the vehicle (500).

5. A system according to any preceding claim, wherein the system further comprises a data store (230) for storing data representative of at least one predetermined driving pattern, and the at least one predetermined condition comprises a condition that a driving pattern represented by the location data or the accelerometer data matches the or at least one of the predetermined driving patterns.

6. A system according to any preceding claim, wherein the at least one predetermined condition comprises a condition that vehicle acceleration determined from at least one of the accelerometer data and the location data has a magnitude greater than a predetermined threshold magnitude of acceleration for substantially the whole of the time window.

7. A system accord i ng to any preceding claim, wherein the at least one predetermined condition comprises a condition that a direction of acceleration determined from at least one of the accelerometer data and the location data has an angular variation during substantially the whole of the time window less than a predetermined threshold angle.

8. A system accordi ng to any preced ing claim , wherein the at least one predetermined condition comprises a condition that a direction of velocity determined from at least one of the accelerometer data and the location data has an angular variation during substantially the whole of the time window less than a predetermined threshold angle.

9. A system according to any preceding claim, wherein the processing means (210) is configured to determine the duration of the time window in dependence on at least one property of the accelerometer data and/or at least one property of the location data.

10. A system according to any preceding claim, wherein the processing means (210) is configured to maximise the duration of the time window subject to the constraint that the accelerometer data and the location data for the time window satisfy the at least one predetermined condition.

1 1. A system according to any preceding claim, wherein the orientation comprises a yaw angle between the accelerometer device (290) and the vehicle (500).

12. A system according to any preceding claim, wherein the processing means (210) is configured to determine, for each of a plurality of time windows a respective orientation output, and to process the plurality of orientation outputs to obtain a combined orientation output representative of the orientation of the accelerometer device (290).

13. A system according to Claim 12, wherein the processing means (210) is configured to rate each of the orientation outputs and to weight each of the orientation outputs in dependence on its rating in the processing of the plurality of orientation outputs.

14. A system according to Claim 13, wherein the processing means (210) is configured to rate each of the plurality of orientation outputs in dependence on at least one property of the time window, the accelerometer data or the location data.

15. A system according to any preceding claim, wherein the accelerometer device (290), the location determining device (250, 255, 492) and the processing means (210) are included in a navigation device (200).

16. A method of determining an orientation of an accelerometer device (290) with respect to a vehicle (500), comprising:- receiving accelerometer data representative of acceleration of the accelerometer device (290);

receiving location data representative of the location of the vehicle (500);

determining a time window for which at least one of the accelerometer data and the location data satisfy at least one predetermined condition;

determining at least one property of motion of the vehicle (500) from the accelerometer data for the time window;

determining at least one property of motion of the vehicle (500) from the location data for the time window; and

determining an orientation output representative of an angle of orientation of the accelerometer device (290) with respect to the vehicle (500), for which the at least one property of motion of the vehicle (500) determined from the accelerometer data matches the at least one property of motion of the vehicle (500) determined from the location data.

17. A computer program product comprising computer readable instructions that are executable by a computer to perform a method according to Claim 16.