Device, system and method for locating a vehicle based on tire wear compensated odometry data and a wireless locating unit

Abstract

The invention relates to a vehicle locating device (10) comprising: a wireless locating unit (11) having at least one wireless locating device (12), an interface (15) configured for receiving odometry data, and a control unit (14) connected to the wireless locating unit (11) and the interface (15), wherein the control unit (14) is configured to determine a temporal sequence of at least two positions of the vehicle (1); determine a movement speed of the vehicle (1), determine a degree of tire wear of the tire (3) based on the determined movement speed and the odometry data, and approximate status data based on at least one previous position of the sequence of positions, the odometry data and the degree of tire wear, wherein the status data includes at least an approximated position of the vehicle (1). The invention further relates to a system and a method for locating a vehicle (1).

Description

[0001] DEVICE, SYSTEM AND METHOD FOR LOCATING A VEHICLE BASED ON TIRE WEAR COMPENSATED ODOMETRY DATA AND A WIRELESS LOCATING UNIT

[0002] The invention relates to a device, system and method for locating a vehicle. The vehicle comprises at least one wheel having a tire and one or more sensors configured to obtain odometry data. The device comprises an interface configured to be connected to the vehicle for receiving the odometry data and a control unit. The invention further relates to a system for locating a vehicle comprising such a device and to a method for locating a vehicle.

[0003] In industrial environments like factories, warehouses or logistic facilities industrial vehicles are commonly used for various purposes like transport of products, components, personnel or machinery. In this setting, an accurate positioning of the vehicle is desired for the purpose of navigation, management of transport capabilities, traffic guidance and safety of personnel and vehicles. It is therefore desirable to accurately localize a vehicle in industrial environments.

[0004] Inside industrial buildings, common vehicle locating systems like the Global Positioning System (GPS) are typically not available or unreliable due to signal obstruction. Instead, systems based on wireless range finding and triangulation between anchors mounted to stationary objects like the factory ceiling or walls can be used inside the building. However, these systems require a unit mounted on the vehicle being in range of typically at least three stationary locating modules or anchors at all times. In factory environments, large obstacles like machinery, shelves or the like can often block the wireless connection between anchors and the vehicle. Moreover, the obstacles may be moved frequently during regular operation of the industrial facility. Common wireless locating systems therefore require a large number of anchors to be installed in order to cover all possible positions of the vehicle and avoiding all obstacles. This makes these systems costly and cumbersome to install. They are also difficult to adapt to changing industrial environments.

[0005] An alternative approach for locating vehicles is odometry. Using data from motion sensors like velocity, steering angle and the like, the position of a vehicle relative to a starting position can be estimated. While this method is largely independent from other infrastructure, it is prone to large uncertainties. This is because the sensor data typically does not accurately reflect the actual movement of the vehicle. Many industrial vehicles, such as industrial trucks or forklifts, measure a rotational speed of a tire and calculate a speed and distance travelled by the vehicle based on this measurement. This is often relatively inaccurate as it does not take into account wheel slip, changes in wheel diameter and other factors compromising the accuracy of the measurement. A relation between the number of wheel rotations recorded by an odometry sensor and the true covered distance may therefore vary significantly over time and spoil the accuracy of odometry based positioning. Moreover, errors of odometry positioning accumulate over time. In addition, locating a vehicle using odometry data is only possible if the vehicle’s starting position is known, and the accuracy that can be achieved is highly dependent on the accuracy with which the starting position is determined.

[0006] US patent application US 2020 / 0011674 A1 describes systems and methods for material handling vehicle odometry calibration. One embodiment of a method includes determining a current location of the material handling vehicle, determining an odometry distance from the current location to a destination based on a calculation of a determined number of rotations of a wheel and a circumference of the wheel, and determining a positioning system distance from the current location to the destination. Some embodiments include comparing the odometry distance with data from the positioning system distance to calculate a scaling factor, applying the scaling factor to a fast alpha filter to achieve a fast filter result, and applying the scaling factor to a slow alpha filter to achieve a slow filter result. Similarly, some embodiments include applying the fast alpha filter to the scaling factor to smooth noise, calculating an updated odometry distance utilizing the scaling factor, and utilizing the updated odometry distance. US patent US 10,365,363 B2 relates to mobile localization of an object using sparse time- of-flight ranges and dead reckoning. As the object moves along its path, a determination is made using the dead-reckoning local frame of reference. When the object is within a predetermine range of one or more of the Ultra Wide Band transceivers, a "conversation" is initiated, and range data between the object and the UWB transceiver(s) is collected. Using multiple conversations to establish accurate range and bearing information, the system updates the object's position based on the collected data. However, the localization using dead reckoning still leaves room for improvement, in particular when relatively inaccurate odometry data is used.

[0007] US patent US 10,936,978 B2 describes methods and systems which can let an autonomous vehicle localize itself precisely and in near real-time in a digital map using visual place recognition. Commercial GPS solutions used in the production of autonomous vehicles generally have very low accuracy. For autonomous driving, the vehicle may need to be able to localize in the map very precisely, for example, within a few centimetres. The method and systems described in US 10,936,978 B2 incorporate visual place recognition into the digital map and localization process. The roadways or routes within the map can be characterized as a set of nodes, which can be augmented with feature vectors that represent the visual scenes captured using camera sensors. These feature vectors can be constantly updated on the map server and then provided to the vehicles driving the roadways. This process can help create and maintain a diverse set of features for visual place recognition.

[0008] Whilst many of the known methods and systems already allow a vehicle to be located, there is still room for improvement, particularly in terms of improving locating accuracy and / or reducing the cost associated with the systems used to locate one or more vehicles.

[0009] In this context, it is the object of the invention to provide a vehicle locating device and related method and system which localizes a vehicle in industrial environments while being cost efficient, easy to install and accurate over extended periods of time.

[0010] In a first aspect of the invention, the problem is solved by means of a vehicle locating device for locating a vehicle. The vehicle comprises at least one wheel having a tire and one or more sensors configured to obtain odometry data representing at least a rotational speed of the wheel. The vehicle locating device comprises at least one wireless locating unit having at least one wireless locating device configured to be mounted on the vehicle. The vehicle locating device further comprises an interface configured to be connected to the vehicle for receiving the odometry data, and a control unit connected to the wireless locating unit and the interface. The control unit is configured to determine a temporal sequence of at least two positions of the vehicle based on a locating signal provided by the wireless locating unit. The control unit is further configured to determine a movement speed of the vehicle based on the sequence of positions and to determine a degree of tire wear of the wheel based on the determined movement speed and / or the odometry data. The control unit is also configured to approximate status data based on at least one previous position of the sequence of positions, the odometry data and the degree of tire wear at least when no current locating signal is provided by the locating unit. The status data includes at least an approximated position of the vehicle.

[0011] The invention is based on the idea of combining accurate wireless positioning with odometry based positioning or odometry based position tracking. The wireless locating unit is usable for locating the vehicle either alone or in collaboration with one or more anchors, in particular stationary anchors. The wireless locating unit may be usable for initialization of the odometry position and for calibration of the odometry measurements. The wireless locating unit can provide the vehicle’s position or a good estimate thereof. This position is the usable for odometry based position tracking. Moreover, a comparison between the movement speed determined from odometry data and the movement speed detected using the wireless locating unit is used to determine a degree of tire wear and / or a static odometry error.

[0012] The vehicle may be any vehicle comprising at least one wheel with a tire and one or more sensors configured to obtain odometry data representing at least a rotational speed of the wheel. Preferably, the vehicle can be an industrial vehicle, in particular an indoor industrial vehicle like an industrial truck or a forklift or other material handling vehicle. Alternatively, the vehicle may be a robot either for production purposes or for material handling for instance in a warehouse. The vehicle may be operated by a driver or can be autonomous. In the case of an autonomous vehicle, the locating device may be integrated into the autonomous driving logic. The vehicle may be able to move freely, i.e. move to any position and point in any direction, or the vehicle may be restricted in its movement for instance by obstacles like machinery or shelves. The vehicle may also be mounted on rails and only be able to move along a predetermined paths along the rails.

[0013] The wheel of the vehicle is understood as being any wheel, which rotates when the vehicle is moving along the ground. The vehicle may comprise multiple wheels at least one of which has a tire. The tire surrounds the wheel’s rim and therefore forms the outer surface of the wheel that is in contact with the ground. The tire typically comprises a material optimized for providing traction and optionally suspension to the vehicle. The tire may comprise synthetic or natural rubber. The tire may be an inflatable tire, made from solid material or may contain with other fillings like foams or liquids. The outer surface of the tire defines the diameter and thereby the circumference of the wheel. In operation, the material of the tire is worn down over time. This is due to friction between the tire’s surface and the ground. Tire wear may reduce the diameter of the tire, due to loss of tire material, and may also influence the traction of the tire on the ground due to wear of the tire tread.

[0014] The term “odometry data” relates to any kind of data that provides information on the vehicle's movement. Preferably, odometry data is related to the movement of the vehicle in relation to its previous position. The odometry data, may comprise data representing one or more of a movement speed, a movement direction, a wheel rotation speed or a number of wheel rotations, an acceleration of the vehicle or a component thereof, a vehicle alignment relative to an external unit, in particular one or more anchors, a vehicle spatial orientation a steering angle or vehicle inclination. The term odometry data may relate to real-time data representing the current movement or status of the vehicle as well as to data representing the movement or status of the vehicle in a past time interval. This can for instance be a sequence of previous measurements or a continuous representation of the vehicle’s movement.

[0015] The one or more sensors may include any kinds of sensors configured to obtain odometry data. The sensors may be or include a motion sensor, speed sensor and / or an inertial measurement unit like accelerometers, gyroscopes, magnetometers etc. The sensor include at least one sensor configured to obtain data presenting at least a rotational speed of the wheel. This sensor may for instance be a speedometer detecting for instance the frequency of full or partial rotations of the wheel. Thus, it is understood that it is not required that the sensor directly obtains the rotational speed of the wheel but it is sufficient that it obtains data indicative of or representing the rotational speed. It is possible that calculations and / or data processing is required to derive the rotational speed of the wheel from the data obtained from the sensor. For example, the sensor can be configured to provide an analogue signal which can be converted to a digital signal before a rotational speed of a tire is calculated.

[0016] The interface of the locating device is configured to be connected to the vehicle for receiving the odometry data. The interface can be an interface like a controller area network (CAN) bus, Automotive Ethernet or (quadrature)-encoder interface that is typically used in vehicles to transmit sensor data. In general, the interface can be any kind of interface via which the odometry data can be transmitted. The interface may also be a wireless interface configured to receive wireless odometry data.

[0017] The wireless locating unit may comprise several components one of which is a wireless locating device that is configured to be mounted on the vehicle. The wireless locating unit can also comprise multiple locating devices that may be connectable to the vehicle in a predetermined spatial relationship to each other. Optionally, the wireless locating unit may comprise a computing unit (i.e. a processor) for example for computing a position of the wireless locating device from a signal received by the wireless locating device. Additionally, or alternatively, the control unit can be configured to calculate a position of the wireless locating device from a signal provided by the wireless locating device. The wireless locating unit may also comprise an interface for transmitting a locating signal. The term “locating signal” may refer to any signal containing information on the position of the vehicle or information from which the position of the vehicle can be determined. If triangulation is applied to determine the position of the vehicle, the locating signal may for instance comprise a set of ranges between the wireless locating device and a set of anchors and / or a position derived from a set of ranges, wherein the position may have been determined directly by the wireless locating unit. The locating signal may additionally or alternatively comprise data indicative of directions between the wireless locating device and one or more anchors. The number of directions and or ranges required to localize the vehicle may depend on the type of vehicle and its freedom of movement. For instance, when the vehicle is mounted on rails, a single range or direction may suffice for locating the vehicle. When the vehicle is free to move on a factory floor, one direction in form of a 3D unit vector may also be sufficient for locating the vehicle. In the same situation, at least two ranges to two separate anchors may be required as an alternative. The locating signal may also comprise a combination of ranges and directions.

[0018] The wireless locating device preferably is or comprises a radio transceiver. In particular, the wireless locating device may be an ultra-wideband (UWB) transceiver that preferably is adapted to perform time of flight ranging between one or more UWB anchors in range. Alternatively, the wireless locating device may comprise or can be one of a laser ranging sensor, an ultrasound receiver, transmitter or transceiver, a WLAN / Bluetooth ranging device, a camera etc. The term “control unit” refers to a computing unit of the vehicle locating device. It can comprise a processor and preferably a memory. The control unit may be designed as a central computing unit of the vehicle locating device. Alternatively, the control unit may comprise several computing nodes or processors combined in a distributed computing system. The control unit is preferably configured to receive at least the odometry data via the interface of the locating device and the locating signal from the wireless locating unit of the vehicle locating device. In addition, the control unit may receive external input like information about the environment, map data, a type of floor or data indicative of a characteristic of a floor, tire information, positions of anchors, etc. The control unit can also be integrated into the wireless locating unit or vice versa. For example, the control unit, the wireless locating unit and / or the interface can be integrally formed. The vehicle locating device may only comprise a single control unit. This control unit is then preferably configured to control the wireless locating device and to approximate the status data. In some embodiments, the wireless locating function and the position approximation function of the vehicle locating device may for example be implemented by different software codes running on a single control unit.

[0019] The control unit is configured to determine a temporal sequence of at least two positions of the vehicle based on the locating signal provided by the wireless locating unit. This may be done by repeatedly evaluating the locating signal. In a preferred embodiment, the wireless locating unit provides the locating signal at regular time intervals. With each updated locating signal, the control unit may use the locating signal to determine the current position of the vehicle. Subsequently, the current position is preferably written into a memory of the control unit together with the time at which the locating signal was received to generate a temporal sequence of previous positions and the current position of the vehicle. The sequence of positions may further have a maximum capacity. When the maximum capacity is reached, the oldest position may be removed from the sequence when a new current position is added. When no locating signal is received, the temporal sequence of positions may not contain the current position but only consist of previous positions of the vehicle. The wireless locating unit may also provide a continuous locating signal.

[0020] The control unit is configured to determine a movement speed of the vehicle based on the sequence of positions. This is preferably done for each time interval between each of the positions in the sequence by using the respective time stamps and positions. For example, the movement speed may be calculated form a distance between two subsequent locations of the vehicle and a time it took the vehicle to travel from the first location to the second location. In alternative embodiments, the control unit may determine an average speed over a time interval in which more than two locating signals were received and more than two positions for this time interval are included in the temporal sequence of positions. The control unit may also employ typical methods of filtering or smoothing for instance by a discrete convolution with a smooth function. The determined movement speed of the vehicle represents the speed at a given time interval or moment in time.

[0021] In preferred further developments, the control unit is further configured to determine the spatial orientation of the vehicle based on the sequence of positions. This may be done by evaluating the spatial position of two subsequent positions in the sequence of positions and by determining that the vehicle is travelling in a direction of travel. Optionally, the control unit may be configured to additionally base the determination of the movement speed and or the orientation of the vehicle on some or all of the odometry data, like a direction of the rotation of the wheel or a steering angle.

[0022] The control unit is further configured to determine a degree of tire wear of the wheel based on the determined movement speed and the odometry data. Preferably, the degree of tire wear is only determined when odometry data and a locating signal are simultaneously provided to the control unit. In some embodiments, the degree of tire wear may by indicative of an outer diameter (and thereby the circumference of the tire) and / or the traction of the tire. The outer diameter and / or circumference of the tire may be deduced from the ratio of the movement speed of the vehicle and the rotational speed of the tire. The degree of tire wear may also be related to the amount of wheel slip due to loss of traction with advancing tire wear. Wheel slip refers to rotational movement of the wheel without corresponding movement of the vehicle. The determination of the degree of tire wear may also take wheel slip into account by using information or data included in the obtained odometry data or in additional odometry data obtained by sensors of the vehicle locating device. For instance, the derivation may take the acceleration of the vehicle at any given moment into account and assume that the effect of wheel slip is stronger at moments of larger acceleration. An accurate determination of the circumference of the tire may therefore be based on measurements which relate to time intervals at which an acceleration below a first predetermined threshold is measured by acceleration sensor. Additionally, the amount of wheel slip induced by tire wear may be determined by using measurements which relate to time intervals at which an acceleration above a second predetermined threshold is measured by an acceleration sensor. The first and second predetermined thresholds may be the same or different. It may also be considered that other information in the odometry data, like e.g. a steering angle, may influence the relation between the actual movement speed of the vehicle and the rotational speed of the wheel. The control unit may also take this into account when determining the degree of tire wear. This can be done by excluding measurements of the movement speed, which relate to the same time at which a steering angle above a predetermined threshold was detected, when determining the degree of tire wear. The control unit may be configured to determine whether the vehicle is travelling straight ahead and to determine a degree of tire wear only when the vehicle is travelling straight ahead.

[0023] The control unit is further configured to approximate status data based on at least one previous position of the sequence of positions, the odometry data and the degree of tire wear at least when no current locating signal is provided by the locating unit. The status data includes at least an approximated position of the vehicle. The previous position or the previous positions serve as a starting point to the approximation of the status data. From this point the current position included in the status data can be derived by tracking the odometry data and propagating the current position of the vehicle. For instance, the rotational speed of the tire and the steering angle may be used to determine the movement of the vehicle since the last detected position. Preferably, the control unit is configured to track or approximate a trajectory of the vehicle starting from the previous position. When determining the movement of the vehicle from the odometry data, the degree of tire wear may be used to improve the approximation of the current position. For instance, in embodiments in which the degree of tire wear is related to the circumference of the wheel, the degree of tire wear is used to determine the distance travelled by the vehicle from the number of rotations of the wheel. Without the degree of tire wear, a calculation of the travelled distance could be extremely inaccurate, as an actual tire diameter may differ significantly from an assumed tire wear used to calculate the distance travelled.

[0024] The control unit may further take other effects into account. For instance, a circumference of the tire may increase with increasing rotation speed. This effect may also depend on the degree of tire wear. Thus, the control unit may be configured to adapt the relation between rotation speed of the wheel and the movement speed in accordance with the expected circumference which may depend on the degree of tire wear and the rotation speed. The vehicle locating device according to the invention may allow to significantly reduce the cost of implementing a locating system and / or to improve the accuracy of a locating system. The wireless locating unit is usable to accurately determine a position of the vehicle. For example, the wireless locating unit may cooperate with one or more anchors to accurately determine the current position of the vehicle, while the vehicle is within range of the anchors. If the vehicle is out of range of the anchors, for example if an anchor is obstructed by a warehouse shelf, the control unit can approximate the position of the vehicle based on odometry data and the determined degree of tire wear. Including the degree of tire wear may significantly increase the accuracy of the approximation. The improved accuracy can make it possible to operate the vehicle in areas not covered by anchors while still providing accurate positional data and thus enabling safe operation.

[0025] In a preferred embodiment, the status data further includes a current spatial orientation of the vehicle. This has the advantage that the direction of travel can be deduced from the rotational speed of the wheel. In addition, when the control unit also approximates the spatial orientation of the vehicle it may track the position of the vehicle over extended distances and arbitrary trajectories even when no locating signal is available.

[0026] In a preferred embodiment, the wireless locating unit is configured to use one or more of electromagnetic waves and / or sound waves, preferably one or more of radio waves, ultra- wideband radio, microwaves, laser light and / or ultrasound to determine at least one relative distance and / or at least one direction between the wireless locating device and one or more anchors. In this embodiment the control unit is configured to determine a current position of the vehicle based on the determined relative distance and / or direction. In other embodiments, the wireless locating device may be configured to determine a position of the vehicle using GPS.

[0027] The term “anchor” refers to any device whose range or direction can be determined wirelessly using the wireless locating unit and which can preferably be mounted on static objects. The position of an anchor may be static and / or predetermined. In general, an anchor may be active or passive. For instance, a passive anchor may comprise a reflector, e.g. a laser or radar reflector for ranging. When image recognition is used by the wireless locating unit, a passive anchor may comprise a recognizable pattern or a specifically coloured object that can be located more easily using image recognition. Active anchors transmit signals such as radio, laser or ultrasound signals. An anchor is typically configured to be mounted on prominent positions within the operating area of the vehicle, in order to be in range of the vehicle for as much of the operating time of the vehicle as possible. In this way a precise positioning can be ensured in designated areas, typically in area where fewer obstacles are expected. For example, an anchor may be mounted on a pillar of a warehouse or the like.

[0028] In a related embodiment, the wireless locating unit is configured to use radio waves, in particular ultra-wideband (UWB) radio, to determine the least one relative distance and / or at least one direction between the wireless locating device and one or more anchors and wherein the anchors are UWB anchors. The UWB anchors may be communicating with an UWB transceiver of the wireless locating device. The inventors have found that UWB provides a reliable and accurate signal for locating a vehicle in harsh industrial conditions. UWB also enables data transfer and thereby allows to identify individual UWB transceivers from their respective signal. In a related embodiment, the wireless locating unit is further configured to identify the UWB anchor from an UWB signal received from the UWB anchor, preferably when determining the at least one relative distance and / or at least one direction between the wireless locating device and one or more UWB anchors. This has the advantage that the vehicle locating device can identify the specific anchor to which a distance and / or direction is measured thus allowing to locate the vehicle with fewer assumptions or previous knowledge about the vehicle’s position.

[0029] In a further embodiment, the control unit is additionally configured to determine the approximated position of the vehicle based on at least one previous position of the sequence of positions, the odometry data and the degree of tire wear also when a current locating signal is provided by the locating unit. The control unit is also configured to determine a positional drift using the approximated position and the current position determined from the locating signal, and determine and store a correction factor for the approximated position based on the determined positional drift. The term “positional” drift refers to the difference between the approximated position and the position determined from the locating signal provided by the locating unit. Optionally, the positional drift may refer to this difference as a function of time and / or the recorded odometry data. For instance, the positional drift may increase with the time span between the time of the approximated position and the last position in the sequence of positions used for the approximation. This may be due to accumulation of an uncertainty or error included in the odometry data (odometry error). The positional drift may alternatively or additionally depend on odometry data. For instance, a given steering angle may result in a larger positional drift. The positional drift may also be a vector like quantity and may include both the absolute difference between the determined and the approximated positions as well as the direction of the difference. The correction factor may refer to any correction factor that can be used to optimize the approximation of the tracking in subsequent approximations when a locating signal is not available. The correction factor may also involve an update of the degree of tire wear. The correction factor is, however, not limited to this example and may also refer to other factors that enter the approximation of the vehicle position from the odometry data. Examples are the amount of tire expansion with increasing rotation speed, a correction factor for odometry data like steering angles, accelerations or spatial orientations, etc.

[0030] In a related embodiment, the control unit is further configured to apply the correction factor to the approximated position to determine a corrected approximated position, preferably when no current locating signal is provided by the locating unit. This has the advantage of effectively calibrating the odometry system when a locating signal is available. In this way, the calibration may be performed during regular operation and possibly without the user noticing or having to intervene. Applying the correction factor to the approximated position may allow a more accurate determination of the approximated position when no location signal is provided.

[0031] It may be advantageous to obtain as many accurate positions of the vehicle from the locating unit as possible. Therefore, in a preferred embodiment, the wireless locating unit is configured to repeatedly provide a locating signal to the control unit when one or more of the anchors are within range of the wireless locating device. The wireless locating unit may particularly be configured to provide a locating signal to the control unit at least every 2 s, preferably every 0.25 s to 1 s.

[0032] For an accurate approximation of the position of the vehicle based on the odometry data, it is advantageous when the odometry data is updated with high frequency. This allows a tracking of the vehicle in closely spaced time steps and may reduce the error which is accumulated over time. Accordingly, the control unit may further be configured to receive updated odometry data at least every 0.5 s, preferably at least every 0.1 s.

[0033] In another embodiment, the control unit is further configured to build a statistical distribution of potential positions of the vehicle, update the statistical distribution based on the odometry data and / or map information and select the most probable position as the approximated position of the vehicle during approximation of the status data. A statistical distribution may for instance be represented by a particle cloud in parameter space / phase space. Each particle may represent one possible state, for example position and / or spatial orientation and / or movement speed of the vehicle. Alternatively, the probability distribution may be represented by a continuous probability distribution or any discretized form of such a distribution. The probability distribution may for instance be initialized using a Gaussian distribution centred around the determined position and with a standard deviation set to the expected measurement uncertainty. Other appropriate distributions may also be used. When the position of the vehicle is approximated, the control unit may update the statistical distribution based on the odometry data. For instance, when the odometry data indicates that the vehicle has travelled in a certain direction, the probability distribution may be shifted in this direction. Additionally, the distribution may be widened in order to account for the measurement uncertainty of the travelled distance, in particular to account for an accumulation of measurement errors. As indicated above, the control unit may also take map data into account when updating the probability distribution. A map of the environment may be available to the control unit and can for instance contain areas into which the vehicle cannot travel. The probability distribution may then be updated by setting the distribution to zero for all positions into which the vehicle cannot travel. For example, certain possible position to the left or right of the vehicle may be cut from the probability distribution, if the vehicle travels through a gap between two shelfs. Updating the distribution may also involve other steps like renormalizing the distribution, applying smoothing filters etc. After updating the probability distribution, the most likely position may be selected as the approximated position. Alternatively, the expectation value may be used as the approximated position.

[0034] In a related preferred embodiment, the statistical distribution is represented by a set of possible states and associated probabilities and the control unit is configured to update the statistical distribution using a sequential Monte Carlo filter. The possible states may be well represented by a Markov process. The odometry data may influence the probabilities to change states from one to another. In such a discrete representation of the probability distribution, a sequential Monte Carlo filter may be a computationally efficient method for updating the probability distribution in accordance with dynamical variables, like the odometry data.

[0035] In a further embodiment, the control unit is also configured to include tire data representing the type of tire and / or floor data representing the type of floor on which the vehicle is moving into the determination of the degree of tire wear. For instance, the tire data may comprise information on how quickly tire wear can be expected. The control unit may therefore anticipate an increasing amount of tire wear and include it into the approximation of the position even before the tire wear has been determined again as described above. Additionally, the control unit may include floor data, which may also influence the amount of tire wear. Certain types of floors result in the tire wearing down more quickly than others. The type of floor may also have an influence on the amount of wheel slip. Including floor data into the approximation of the vehicle position may therefore also be advantageous independently from the degree of tire wear.

[0036] The vehicle locating device as described above, relies on odometry data received from the vehicle via an interface. This is advantageous as sensors which are typically preinstalled as standard into industrial trucks, like speedometers may be used by the locating device. However, depending in the number and types of pre-installed sensors, it may also be advantageous to provide additional sensors for obtaining additional odometry data independently from the sensor of the vehicle. In a preferred embodiment, the locating device therefore further comprises one or more sensors configured to obtain additional odometry data, and wherein the control unit is configured to receive the additional odometry data and to include the additional odometry data in the approximation of the status data. Which kind of odometry data is obtained by the sensors of the vehicle and which obtained by the sensors of the locating device may vary. The odometry data obtained from the vehicle and the additional odometry data from the locating device sensors may be used equally. The additional odometry data may serve the purpose of providing different kinds of information or to provide measurements with improved accuracy in comparison to pre-installed sensors in the vehicle.

[0037] In a related preferred embodiment, the one or more sensors of the vehicle locating device comprise a gyroscope. The gyroscope is configured to obtain additional odometry data representing the spatial orientation of the vehicle. Gyroscopes are particularly well-suited for determining the orientation of the vehicle in relation to a starting position. They are usually not included as standard in typical industrial trucks. Alternatively, or additionally, the one or more sensors of the vehicle locating device may comprise an inertial measurement unit (IMU), and wherein the IMU is configured to obtain additional odometry data representing the spatial orientation of the vehicle and the acceleration of the vehicle. An IMU may consist of three acceleration sensors, preferably arranged on three pairwise orthogonal axes, and one or more gyroscopes for determining the orientation of the vehicle.

[0038] Inertial measurements may suffer from drift of a zero-point measurement, i.e. a value detected by an accelerometer at no acceleration and / or a value detected by a gyroscope at standstill. It may therefore, be necessary to update offsets applied to the measurements of the gyroscope and / or IMU. Thus, in another embodiment, the control unit is further configured to, upon determining from the sequence of positions of the vehicle that the vehicle has not changed for a predetermined amount of time, recalibrate one or more offsets which are applied to the received additional odometry data from the gyroscope and / or IMU. The recalibration of offsets is performed when the vehicle is stationary as is the moment when only the offset is present and usually no motion induced additional values are measured by the gyroscope and / or IMU. For setting the offsets of the gyroscope, it may also be beneficial to include the current speed and other information available on the vehicle interface as described above. Preferably, an accelerometer of the vehicle locating device is used or usable to (re)calibrate a gyroscope or to correct measurements provided by a gyroscope of the vehicle locating device. Gyroscopes typically measure turn-rates in at least two perpendicular spatial orientations. However, if an orientation of the gyroscope on a vehicle is unknown, the measurements signals or data provided by the gyroscope cannot be used to derive a corresponding spatial orientation and / or change of spatial orientation of the vehicle therefrom. An accelerometer may be used to determine the direction of the earth’s gravitational force (the direction of gravity). Knowledge of the direction of gravity with respect to the IMU can then be used to “translate” turn-rate measurements of the gyroscope to movements of the vehicle. Preferably, the control unit is configured to determine a direction of gravity, preferably based on an acceleration signal provided by an accelerometer of the vehicle locating device, and to recalibrate additional odometry data, in particular turn-rates, provided from a gyroscope of the vehicle locating device taking into account the determined direction of gravity.

[0039] In another embodiment of the invention described above, the obtained odometry data further represents one or more of a steering angle, a rotation speed of multiple wheels of the vehicle, a degree of slip of the one or more wheels, a load of the vehicle and / or an acceleration of the vehicle. If the locating device contains sensors for obtaining additional odometry data, each of these types of odometry data may additionally or alternatively be included in the additional odometry data obtained by the sensors of the locating device.

[0040] In a preferred embodiment, the degree of tire wear is indicative of at least an outer diameter of the tire. The outer diameter of the tire may be particularly relevant for improving the accuracy of the vehicle position approximation. Also, other kinds of information that may be included in derivable from the degree of tire wear have been described above. Depending on the application of the vehicle locating device, it may be desirable to distribute the information on the vehicles position to other systems. In an according embodiment, the control unit is further configured to transmit the position or approximated position of the vehicle to other vehicles in the vicinity and / or an external control unit and / or a cloud server. This may enable tracking of the vehicle for security purposes, navigation, remote control, autonomous driving, etc.

[0041] As previously mentioned, industrial trucks may be prone to substantial tire wear and the tire may have to be replaced regularly during normal operation. In order to avoid unnecessary inspections of the tires and to use each tire for as long as possible, it may be beneficial to use the determined information on the degree of tire wear for maintenance. Therefore, the vehicle locating device is further configured to transmit an indication to an operator, when the tire wear exceeds a predetermined threshold. The operator may react by replacing the tire or by scheduling a replacement.

[0042] In a second aspect of the invention, a system for locating a vehicle is provided. The system comprises a vehicle locating device as described in any of the embodiments above and one or more anchors, configured to be attached to stationary reference points. The wireless locating unit of the vehicle locating device is configured to use one or more of electro-magnetic waves and / or sound waves, preferably one or more of radio waves, ultra-wideband radio, microwaves, laser light and / or ultrasound to determine at least one relative distance and / or direction between the wireless locating device and the one or more anchors. The control unit of the vehicle locating device is configured to determine the position of the vehicle based on the determined relative distance and / or direction.

[0043] In a third aspect of the invention, a method is provided for locating a vehicle, in particular an indoor industrial vehicle The method comprises providing a wireless locating unit having at least one wireless locating device configured be mounted on a vehicle; receiving odometry data representing at least a rotational speed of the wheel from the vehicle; and determining a temporal sequence of at least two positions of the vehicle based on a locating signal received from the wireless locating unit. The method further comprises determining a movement speed of the vehicle based on the sequence of positions and determining a degree of tire wear of the wheel based on the determined movement speed and the odometry data. In another step, the method comprises approximating the position of the vehicle based on at least one previous position of the sequence of positions, the odometry data and the degree of tire wear at least when no current locating signal is provided by the locating unit. According to a first preferred embodiment, the method further comprises attaching one or more anchors to stationary reference points and thereby defining a locating area in which the wireless locating unit is within range of the one or more anchors. The locating area preferably is part of usual operating area of the vehicle or a subarea of an operation area of the vehicle. The usual operating area is larger than the locating area. For example, the locating area may be part of a larger industrial hall, wherein the locating area is covered by anchors and the rest of the industrial hall is not. The wireless locating unit preferably only provides a current locating signal when the wireless locating device is in the locating area. By providing a locating area being a subarea of an operational are, installation cost and or operation cost may be significantly reduced. In particular, it may be advantageous to define a locating area in an area of a commercial building where no or few obstacles are expected that may obstruct locating communication between the anchors and the vehicle. It may also be beneficial to select a locating area through which the vehicles travel regularly during normal operation, thus enabling frequent determination of tire wear, restarting of the odometry approximation and recalibration of the odometry data.

[0044] For reducing the costs of installation of a system and subsequently applying the method for locating the vehicle, it may be beneficial to define the locating area as a small part of the total operating area of the vehicle. Therefore, in a preferred embodiment, the locating area is part of a usual operating area of the vehicle and the usual operating area is larger than the locating area.

[0045] Preferably the method further comprises providing an inertial measurement unit (IMU) and / or a gyroscope that is are configured to obtain IMU additional odometry data indicative of an acceleration of the vehicle and / or a spatial orientation of the vehicle. Upon determining from the sequence of positions of the vehicle that the vehicle has not changed for a predetermined amount of time, the method may include recalibrating one or more offsets which are applied to the received additional odometry data from the IMU and / or gyroscope.

[0046] The step of determining the degree of tire wear preferably further comprises determining a sequence of positions of the vehicle in the locating area, determining at least one approximated position of the vehicle based on at least one position of the sequence of positions in the locating area and the odometry data; evaluating if one or more predetermined criteria are met by the sequence of positions and / or the odometry data; and determining the degree of tire wear based on a comparison between the approximated position and the sequence of positions, preferably only when the sequence of positions and / or the odometry data meet the predetermined criteria.

[0047] The one or more predetermined criteria may be one or more of a minimal distance covered by the vehicle, a maximal steering angle, a sufficiently straight trajectory, a maximal acceleration and / or a speed range. For example, accuracy of the determined degree of tire wear may be enhanced, when a straight trajectory of the vehicle is used. Moreover, determination of the degree of tire wear may be facilitated, since lateral accelerations of the vehicle need not be taken into account when the trajectory is sufficiently straight. A sufficiently straight trajectory may include a lateral movement of the vehicle of less than 0.5 m per 10m of straight travel. For an accurate determination of tire wear, the distance travelled by the vehicle through the locating area may have to be sufficiently long. For instance 10 m, preferably 5 m to 15 m, may be sufficient. In addition, a straight trajectory may be beneficial for determining the degree of tire wear since uncertainties related to the distance covered as a function of the steering and the rotation of the wheel may be reduced. Strong acceleration may induce slip and therefore spoil the determination of the degree of tire wear. Furthermore, the speed plays a role. While the vehicle must at least travel with some nonzero speed in order to cover a sufficient distance, the speed should also not exceed a predetermined threshold because the position of the vehicle may not be determined as accurately when it is travelling at high speeds.

[0048] It shall be understood that the device according to the first aspect of the invention, the system according to the second aspect of the invention and the method according to the third aspect of the invention comprise similar and identical sub-aspects as in particular defined in the dependent claims to the device, the system and the method. Insofar, reference is made to the above description.

[0049] For a more complete understanding of the invention, the invention will now be described in detail with reference to the accompanying drawings. The detailed description will illustrate and describe what is considered as a preferred embodiment of the invention. It should of course be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention may not be limited to the exact form and detail shown and described herein, nor to anything less than the whole of the invention disclosed herein and as claimed herein after. Further, the features described in the description, the drawings and the claims disclosing the invention may be essential for the invention considered alone or in combination. In particular, any reference signs in the claims shall not be construed as limiting the scope of the invention. The wording “comprising” does not exclude other elements or steps. The word “a” or “an” does not exclude the plurality. The wording “a number of’ items comprising also the number 1 , i.e. a single item, and further numbers like 2, 3, 4 and so forth.

[0050] In the accompanying drawings:

[0051] Fig. 1 is a schematic view of the locating device and system according to the invention.

[0052] Fig. 2 is a schematic view of the comparison of the determination of the degree of tire wear and calibration of the odometry data according.

[0053] Fig. 3 is a schematic view of the locating device and system in a warehouse.

[0054] Fig. 4 is a schematic view illustrating the locating method according to the invention.

[0055] Fig. 5 is a schematic view of a tire that may be used on a vehicle using the locating device.

[0056] Fig. 6 is a schematic view of the process of using map information for updating the probability distribution of the current position.

[0057] Fig. 7 shows an example of a method to derive a correction factor for calibrating odometry data.

[0058] Fig. 1 shows a schematic view of the locating device 10, the vehicle 1 and an anchor 16. The vehicle 1 is depicted as an industrial truck, specifically a forklift. The vehicle 1 in this embodiment comprises four wheels 2, two of which are visible in the side view of Fig. 1. However, the vehicle 1 may also have only three or more than four wheels 2. Each of the wheels 2 comprises a tire 3 indicated by dashed lines in Fig. 1. The dashed lines show the maximal circumference 52 and minimal circumference 51 of the wheels 2 (Fig. 5) which may be reduced with increasing tire wear. Details on the wheels 2 in this embodiment are described with relation to Fig. 5 below. The vehicle locating device 10 and its components are also depicted in Fig. 1. The control unit 14 may be located at any part of the vehicle 1. In the depicted embodiment, it is built into the lower body of the vehicle 1. The locating device comprises an interface 15 that is connected to the vehicle 1 such that odometry data can be received. Since the received odometry data comprises at least a rotational speed of the wheel 2, the interface 15 is connected in Fig. 1 to the wheel 2, where for instance an incremental encoder (not shown) may be located for generating the odometry data. In other embodiments, the interface 15 of the vehicle locating device 10 could be connected to a controller of the vehicle 1 (not shown). The interface 15 is configured to receive the odometry data. In the present embodiment, the odometry data received at the interface 15 is then provided to the control unit 14 via a wire connection. The interface 15 could also be a wireless interface configured to receive wireless odometry data.

[0059] The locating device 10 further comprises a wireless locating unit 11 . The wireless locating unit 11 , in this embodiment comprises a wireless locating device 12 and a wireless locating processing unit 13. The wireless locating unit 11 is mounted on the roof of the vehicle 1 . This may be advantageous for ensuring a good connection to the anchor 16. In other embodiments, the wireless locating device 12 and the wireless locating processing unit 13 can be integrated into the control unit 14 or the wireless locating device 12, the wireless locating processing unit 13 and / or the control unit 14 can be integrally formed. For example, the wireless locating processing unit 13 and the control unit 14 can be formed by a single control unit. The wireless locating processing unit 13 and the control unit 14 may then, for example, be distinguished in a software layer only.

[0060] The wireless locating device 12 is configured to receive and / or transmit signals from / to an anchor 16, which are indicative of a distance and / or direction 4 between the wireless locating device 12 and the anchor 16. This distance and direction 4 changes when the vehicle 1 is moving. The determined range and direction 4 between the wireless locating device 12 and the anchor 16 is illustrated by a double-sided dashed arrow in Fig. 1. It shall be understood that the signals may represent a distance 4 or a direction 4 only. The dashed line also illustrates the wireless interface via which the wireless locating device 12 and the anchor 16 may exchange signals.

[0061] In Fig. 1 , the wireless locating device 12 is connected to the wireless locating processing unit 13. This connection may be any interface configured to provide the obtained information by the wireless locating device 12 to the wireless locating processing unit 13. The wireless locating processing unit 13 is configured to receive the information from the wireless locating device 12 and generate a locating signal. This locating signal may comprise distances and / or directions 4 to an anchor 16 and / or a determined position of the vehicle 1 .

[0062] In other embodiments, the wireless locating unit 11 of the locating device 10 can comprise multiple wireless locating devices 12. When multiple wireless locating devices 12 are provided, a position of the vehicle 1 may be determined using triangulation methods. However, triangulation is also possible if multiple anchors 16 are used. The wireless locating device 12 preferably is or includes an antenna.

[0063] The locating device 10, in particular its control unit 14 is configured to determine the position of the vehicle 1 based on the locating signals provided by the wireless locating unit 11. In the present embodiment, the wireless locating unit 11 and the anchors communicate via UWB signals. UWB signals are highly accurate such that in the present embodiment, the position of the vehicle 1 determined based on the locating signals is considered to represent an actual or current position 20 of the vehicle. However, it shall be understood that the current position 20 or the position of the vehicle 1 determined based on the locating signals provided by the wireless locating unit 11 may differ from the exact position of the vehicle. The locating device 10 is further configured to approximate a position of the vehicle 1 using odometry data received via the interface 15. This position is an approximated position 22, since odometry data is usually less accurate than the current position 20 determined based on the locating signal of the wireless locating unit 11.

[0064] Fig. 2 shows an example how the approximated position 22 of the vehicle 1 may differ from the current position 20. The vehicle 1 is initially located using the wireless locating system at a starting position 24. The starting position 24 may be determined as illustrated in Fig. 2 by determining the distances 4 between the locating device 10 or its wireless locating unit 11 respectively and three anchors 16.

[0065] The vehicle 1 then travels a travelled distance 21 or trajectory 21 to arrive at the current position 20. The current position 20 can also be determined from three distances 4 to the same three anchors 16 or different anchors 16. Additionally, the position of the vehicle 1 may be approximated. That is the approximated position 22 may be determined. This approximation is based on the starting position 24 and odometry data received via the interface 15 in the time interval between the vehicle 1 being located at the starting position 24 and being located at the current position 20. The odometry data is used to determine an approximated distance 23 or approximated trajectory 23 of the vehicle 1 and includes at least a rotational speed of one of the wheels 2 within this time interval.

[0066] While it is in range of the anchors 16, the vehicle locating device 10 can therefore determine the position of the vehicle 1 based on the locating signal provided by the wireless locating device 12 (i.e. the current position 20) and based on the odometry data received via the interface 15 (i.e. the approximated position 22). When no anchor 16 or an insufficient amount of anchors 16 is in range of the wireless locating device 12 of the vehicle locating device 10, determining the current position 20 is no longer possible. However, the vehicle locating device 10 can still determine the approximated position 22.

[0067] The control unit 14 may be configured to minimize the difference between the approximated position 22 and the current position 20. For this purpose, a degree of tire wear is determined from the comparison of the approximated position 22 and the current position 20 while the vehicle locating device 10 is in range of the anchors 16. The degree of tire wear can then be used for the next approximation of the vehicle’s position regardless of whether a locating signal is provided or not. The comparison of the approximated position 22 and the current position 20 may also be used for determining other correction factors entering the approximation of the vehicle’s position. For example, the degree of tire wear may reflect the current diameter of the wheels 2 of the vehicle. If the odometry data include a rotational speed of the wheels 2, a distance travelled by the vehicle 1 from the starting position 24 may be calculated with a higher accuracy compared to a calculation based on the maximum circumference 2.1 or minimum circumference 2.2. An error between the approximated position 20 and the actual position of the vehicle 1 may then be reduced.

[0068] As illustrated in Fig. 2 by the coordinate systems in each of the vehicle’s position, the wireless locating unit 11 also is in the present embodiment further configured to determine the spatial orientation of the vehicle 1 , both at the starting position 24 and at the current position 20. This can be done by determining the movement direction of the vehicle 1 from two positions determined in short sequence. The approximated position 22 may be included in status data and the status data may also comprise an approximated orientation of the vehicle 1 . This is also approximated based on the starting position 24 and the odometry data. In some embodiments, the vehicle locating device 10 comprises one or more of an acceleration sensor or a gyroscope. In the present embodiment, the vehicle locating device 10 includes an inertial measurement unit IMU that includes three acceleration sensors and a gyroscope configured to determine an angular moment in three perpendicular spatial directions. The IMU (not shown) provides IMU data to the control unit 12 which is configured to determine the orientation of the vehicle 1 based on said data. In other embodiments, data representative of the vehicles 1 orientation may be received via the interface 15.

[0069] While Fig. 2 does not illustrate uncertainties of the starting position 24, the current position 20 and the approximated position 22 it is clear that each of these positions may be afflicted with a related uncertainty. Typically the wireless locating unit 11 can determine the position of the vehicle 1 with a relatively small uncertainty. For instance, an UWB locating system may have an accuracy of 30 cm or less. Other methods can achieve similar or the same degree of accuracy.

[0070] Fig. 3 is an illustration of an embodiment of the invention in an industrial environment. In particular, Fig. 3 illustrates a system for locating a vehicle 1 comprising a vehicle locating device 10 arranged on the vehicle 1 (only wireless locating device 12 of vehicle locating device 10 shown in Fig. 3) and a total of four anchors 16. The vehicle 1 is moving through within an operating area 31. The operating area 31 may be inside an industrial building, a factory hall or a warehouse. For wirelessly locating the vehicle 1 , the anchors 16 are mounted on stationary infrastructure like pillars, walls or the ceiling. The anchors 16 define a locating area 30, in which the vehicle 1 can be wirelessly located. As long as the vehicle 1 is within the locating area 30, the position of the wireless locating device 12 mounted on the vehicle 1 is detected with high frequency using the wireless locating unit 11. This allows to generate a sequence of positions 32 of the vehicle 1 , which is illustrated by the dotted line in Fig. 3. The sequence of positions 32 may be used both for locating the vehicle 1 as well as determining the degree of tire wear and optionally one or more correction factors. The locating area 30 is a sub-area of the operating area 31 and can be much smaller than the operating area 31 . Since only the locating area 30 needs to be covered by the anchors 16, a required number of anchors 16 is significantly less than a number of anchors 16 that would be required for to cover the entire operating area 31 . In the present embodiment and preferably, the control unit 14 is configured to determine a temporal sequence of positions from the sequence of positions 32. For example, the control unit 14 can be configured to associate a respective time stamp to each position of the sequence of positions 32.

[0071] The locating area 30 may preferably be defined in an area with few obstacles 33 which could otherwise block the transmission between the anchors 16 and the locating device 12. As shown in Fig. 3, the locating area 30 may be in an open space in front of a series of shelves or other obstacles 33. Preferably, the locating area 30 is in an open area with few obstacles 33 through which the vehicle 1 passes frequently during normal operation. The vehicle 1 then frequently travels through the locating area 30. Each time the vehicle 1 travels through the locating area 30, the approximation of the position can then be recalibrated. For example, the degree of tire wear may be determined each time the vehicle 1 travels through or within the locating area 30. Alternatively or additionally, a new previous position may be set to be used as a starting point for approximating a position of the vehicle 1 when the vehicle is in the locating area 30. Thus an approximation of the vehicle’s 1 location outside of the locating area 30 can be provided with a higher accuracy.

[0072] Fig. 4 shows a bird’s eye view of how the vehicle’s position is determined when the vehicle 1 is inside or outside the locating area 30. When the vehicle 1 is in the locating area 30, a sequence of determined positions 32 is generated from the detected distances and / or directions 4 to one or more anchors 16. When the vehicle 1 leaves the locating area 30, the position and / or orientation of the vehicle 1 is approximated based on the last determined position in the locating area 30 and the odometry data. This results in a sequence of approximated positions 40. The sequence of approximated positions 40 may be continued until the vehicle 1 returns back to the locating area 30. The operating area 31 may also comprise narrow points like a gate 41 . The control unit 14 may take this kind of map information into account when approximating the position of the vehicle 1. This is further described in relation to figure 6 below.

[0073] Fig. 5 is a schematic view of a wheel 2 which may be part of the vehicle 1 for which the vehicle locating device 10 is used. The wheel 2 may comprise a rim 50, which is the outer edge of the wheel 2 holding the tire 3. The tire 3 may be comprised of a material which is worn down with increasing degree of tire wear. The wheel 2 shown in Fig. 5, has a maximal circumference 52 which is the circumference of the new wheel 2 when it is first installed on a vehicle 1. During regular operation of the vehicle 1 , the tire material is gradually worn down. The double sided arrow in Fig. 5 indicates an acceptable degree of tire wear 53. This is essentially between the maximal circumference 52 and a safety line 51 . A safety line 51 is a mark which may be built into the tire 3, often at the side of the tire 3, in order to indicate the minimal circumference, i.e. maximal degree of tire wear. In some embodiments, the radius of the tire 3 may be reduced by up to 7 cm due to tire wear. Typically, the tire 3 should be replaced before the outer surface of the tire 3 reaches the safety line 51. The safety line 51 therefore indicates a minimum circumference 51 of the tire 3. Below the safety line 51 , the tire 3 may also comprise an inflatable volume filled with a gas, foam or liquid for providing suspension to the vehicle 1 . As can be seen from Fig. 5, the circumference of the tire 3 or wheel 2 respectively significantly varies between the maximal circumference 52 and the minimum circumference 51. The circumference of the wheel 2 directly corresponds to a distance travelled by the vehicle with one revolution of the wheel 2. When the rotational speed of the wheel 2 is used to determine a distance travelled by the vehicle 1 , the accuracy of such a determination is significantly dependent on the tire wear. Incorporating a degree of tire wear into when determining the approximated position 22 may therefore greatly improve the accuracy of such an approximation.

[0074] Fig. 6 illustrates how map information can be used for approximating the position of the vehicle 1. When the position of the vehicle 1 is approximated, the control unit 14 builds a statistical distribution 60 representing the probability for each position on the map to be the current position 20 of the vehicle 1. The distribution 60 is regularly updated by the control unit 14 when the position of the vehicle 1 is repeatedly approximated based on the odometry data. The left half of Fig. 6 shows the usual effect when no map information is included in the approximation. The initially quite narrow probability distribution 60 starts to drift apart with increasing travelled distance 21 of the vehicle 1. This is because each subsequent approximation is based on the previous one and therefore the approximation uncertainty coming from the uncertainties of the odometry data accumulates over time. This effect can be mitigated by including map information into the approximation. In Fig. 6, the vehicle 1 passes a narrow point or gate 41 which is formed by two obstacles 33 on either side of the narrow point. The control unit 14 may include its knowledge about the position of the gate 41 to update the probability distribution 60 and conclude that the vehicle 1 must have passed through the gate 41. Therefore, the distribution 60 becomes narrower again, since a large fraction of otherwise possible positions may be excluded. The control unit 14 may not only take narrow point or gates 41 but also other obstacles 33 into account. For instance, the probability distribution 60 may be truncated in one direction, when the vehicle 1 passes near an obstacle 33, such that all positions within the obstacle 33 are excluded.

[0075] Fig. 7 illustrates a method of how the vehicle locating device 10 may be used when the vehicle 1 is in the locating area 30. The method is carried out by the control unit 14. As described above, the locating device may comprise an IMU for obtaining additional odometry data. In the present disclosure, odometry data is external odometry data provide to the vehicle locating device 1 externally, in particular via the interface 15. Additional odometry data is odometry data determined by a unit or device of the vehicle locating device 1 itself, such as the IMU. When using IMUs it may be advantageous to frequently calibrate the offsets which are applied to measurements of the spatial orientation as well as measurements of acceleration. Accordingly, the method describes how the IMU data may be calibrated and how a correction factor may be determined when the vehicle 1 is in the locating area 30.

[0076] The first step S1 is performed directly after the start of the method. At this step the control unit 14 buffers IMU and / or speed data and / or other odometry data. The IMU data is received from the IMU of the vehicle locating device 10 in the form of additional odometry data. Speed data may also be received from the sensors of the vehicle locating device 10 or from the vehicle 1 via the interface 15. Buffering the data refers to storing at least one data point for each of these measurements. Typically, a larger number of measurements are stored at this step. The control unit 14 continues at step S2 to determine whether the IMU is calibrated. The IMU may be regarded as calibrated when the last calibration has been performed within a predetermined time interval, like for instance the last 10 minutes. Whether the IMU is calibrated may alternatively or additionally be indicated by a flag stored within the control unit 14. When the control unit 14 finds that the IMU is not calibrated, it proceeds to step S3 and determines if the vehicle 1 is stationary. This may be done by looking at the latest speed data or by comparing the latest positions in a sequence of determined positions 32. Data or signals of the IMU may alternatively or additionally be used to determine whether the vehicle 1 is stationary or not. If the control unit 14 finds that the vehicle 1 is not stationary, it returns to the start of the method. Otherwise, it continues with step S4 at which the IMU calibration offsets are taken. Specifically, for a gyroscope of the IMU, a signal, measurement or data provided by an acceleration sensor of the IMU may be used to determine the direction of gravity. In the present embodiment, the control unit 14 then uses the determined direction of gravity to calibrate signals provided by the gyroscope, in particular signals or data representing a turn-rate. Alternatively, or additionally, a reading of an acceleration sensor at standstill may be taken as an offset defining the zero-point measurement.

[0077] After either calibrating the IMU or determining that the IMU is calibrated the method continues with step S5 and receives UWB signals. As many UWB signals as possible are received using the wireless locating device 12. Subsequently, the control unit 14 attempts to determine the position of the vehicle 1 based on the UWB ranges 4 determined from the UWB signals. At step S7, the control unit 14 determines whether the vehicle 1 is in the locating area 30. If the vehicle 1 is not in the locating area 30, it returns to method step S5. Otherwise, it proceeds at step S8 to determine if the locating filter is initialized. Initialization of the locating filter refers to building an initial probability distribution 60 from which the approximation of subsequent positions as described above starts. If the control unit 14 finds that the locating filter is not initialized, the control unit 14 performs the initialization at step S9.

[0078] Either after initialization of the locating filter or after determining that the locating filter is initialized, the method continues at step S10. At this step, odometry data, additional odometry data and / or the locating signals are processed. In particular, the additional odometry data may comprise the IMU data. Speed data may be included in the additional odometry data or in the odometry data received from the vehicle 1. The locating signal may comprise UWB ranges 4 received from the wireless locating unit 11. At the subsequent step S11 , the control unit 14 determines if a set of process criteria are met. These criteria are predetermined to define when correction factors can be accurately determined. The criteria may also depend on the respective correction factors. For instance, a process criterion for determining the degree of tire 3 wear may be given by a speed range, a maximal acceleration and or a maximal degree of turning, i.e. a sufficiently straight trajectory. A criterion for determining the amount of expansion of the tire 3 with increasing speed may on the other hand be given by a minimal speed. A criterion for determining the degree of slip may be given by a minimal acceleration. It is understood that a number of other criteria may be formulated for determining different correction factors that may be used for approximating the position of the vehicle 1 when no locating signal is provided by the wireless locating unit 11 .

[0079] If the process criteria are met, the method continues to determine the respective correction factor which may include the degree of tire wear in method step S12. Subsequently, at step S13 the method includes a statistical processing of the determined correction factor. For instance, the correction factor may be compared with previous values of the correction factor and a smoothing filter may be applied. The statistical processing may also comprise calculating an uncertainty for the correction factor which may also be included for the approximation of the vehicle’s position. After this last step, the method terminates.

[0080] The control unit 14 may be configured to apply methods other than the one illustrated in Fig. 7. In particular, the approximation of the vehicle’s position when no locating signal is available is not included in the method of Fig. 7. Reference

[0081] 1 Vehicle

[0082] 2 Wheel

[0083] 3 Tire

[0084] 4 Determined distance / direction

[0085] 10 Vehicle locating device

[0086] 11 Wireless locating unit

[0087] 12 Wireless locating device

[0088] 13 Wireless locating processing unit

[0089] 14 Control unit

[0090] 15 Interface

[0091] 16 Anchor

[0092] 20 Current position

[0093] 21 Travelled distance

[0094] 22 Approximated position

[0095] 23 Approximated distance

[0096] 24 Starting position

[0097] 30 Locating area

[0098] 31 Operating area

[0099] 32 Sequence of positions

[0100] 33 Obstacle

[0101] 40 Sequence of approximated positions

[0102] 41 Gate

[0103] 50 Rim

[0104] 51 Safety line

[0105] 52 Maximal tire circumference

[0106] 53 Potential tire wear

[0107] 60 Probability distribution

[0108] 5 Method steps

Claims

Claims:

1. A vehicle locating device (10) for locating a vehicle (1), in particular an indoor industrial vehicle, the vehicle (1) comprising at least one wheel (2) having a tire (3) and one or more sensors configured to obtain odometry data representing at least a rotational speed of the wheel (3), the vehicle locating device (10) comprising: at least one wireless locating unit (11) having at least one wireless locating device (12) configured to be mounted on the vehicle (1), an interface (15) configured to be connected to the vehicle (1) for receiving the odometry data, and a control unit (14) connected to the wireless locating unit (11) and the interface(15), wherein the control unit (14) is configured to determine a temporal sequence of at least two positions of the vehicle (1) based on a locating signal provided by the wireless locating unit (11); determine a movement speed of the vehicle (1) based on the sequence of positions, determine a degree of tire wear of the tire (3) based on the determined movement speed and the odometry data, and approximate status data based on at least one previous position of the sequence of positions, the odometry data and the degree of tire wear at least when no current locating signal is provided by the wireless locating unit (11), wherein the status data includes at least an approximated position of the vehicle (1).

2. The vehicle locating device (10) according to claim 1 , wherein the status data further includes a current spatial orientation of the vehicle (1).

3. The vehicle locating device (10) according to claim 1 or 2, wherein the wireless locating unit (11) is configured to use radio waves, in particular ultra-wideband (UWB) radio, to determine at least one relative distance and / or at least one direction between the wireless locating device (12) and one or more anchors(16), and wherein the control unit (14) is configured to determine a current position of the vehicle (1) based on the determined relative distance and / or direction.

4. The vehicle locating device (10) according to claim 3, wherein the wireless locating unit (11) is configured to use radio waves, in particular ultra-wideband (UWB) radio, to determine the least one relative distance and / or at least one direction between thewireless locating device (12) and one or more anchors (16) and wherein the anchors (16) are UWB anchors (16).

5. The vehicle locating device (10) according to claim 4, wherein the wireless locating unit (11) is further configured to identify the UWB anchor (16) from an UWB signal received from the UWB anchor (16), when determining the at least one relative distance and / or at least one direction between the wireless locating device (12) and one or more UWB anchors (16).

6. The vehicle locating device (10) according to one of claims 3 to 5, wherein the control unit (14) is further configured to determine the approximated position of the vehicle (1) based on at least one previous position of the sequence of positions, the odometry data and the degree of tire wear also when a current locating signal is provided by the wireless locating unit (11), determine a positional drift using the approximated position and the current position determined from the locating signal, and determine and store a correction factor for the approximated position based on the determined positional drift.

7. The vehicle locating device (10) according to claim 6, wherein the control unit (14) is further configured to apply the correction factor to the approximated position to determine a corrected approximated position, preferably when no current locating signal is provided by the wireless locating unit (11).

8. The vehicle locating device (10) according to any of claims 3 to 7, wherein the wireless locating unit (11) is configured to repeatedly provide a locating signal to the control unit (14) when one or more of the anchors (16) are within range of the wireless locating device (12).

9. The vehicle locating device (10) according to claim 8, wherein the wireless locating unit (11) is configured to provide a locating signal to the control unit (14) at least every 2 s, preferably every 0.25 s to 1 s, when one or more of the one or more anchors (16) are within range of the wireless locating device (12).

10. The vehicle locating device (10) according to any of the preceding claims, wherein the control unit (14) is further configured to receive updated odometry data at least every 0.5 s, preferably at least every 0.1 s.

11. The vehicle locating device (10) according to any of the preceding claims, wherein the control unit (14) is further configured to build a statistical distribution (60) of potential positions of the vehicle (1), update the statistical distribution (60) based on the odometry data and / or map information and select the most probable position as the approximated position of the vehicle (1) during approximation of the status data.

12. The vehicle locating device (10) according to claim 11 , wherein the statistical distribution (60) is represented by a set of possible states and associated probabilities and the control unit (14) is configured to update the statistical distribution (60) using a sequential Monte Carlo filter.

13. The vehicle locating device (10) according to any of the preceding claims, wherein the control unit (14) is further configured to include tire data representing the type of tire and / or floor data representing the type of floor on which the vehicle is moving into the determination of the degree of tire wear.

14. The vehicle locating device (10) according to any of the preceding claims, wherein the locating device (10 )further comprises one or more sensors configured to obtain additional odometry data, and wherein the control unit (14) is configured to receive the additional odometry data and to include the additional odometry data in the approximation of the status data.

15. The vehicle locating device (10) according to claim 14, wherein the one or more sensors of the vehicle locating device (10) comprise a gyroscope, and wherein the gyroscope is configured to obtain additional odometry data representing the spatial orientation of the vehicle (1).

16. The vehicle locating device (10) according to claim 14, wherein the one or more sensors of the vehicle locating device (10) comprise an inertial measurement unit (IMU), and wherein the IMU is configured to obtain additional odometry data representing the spatial orientation of the vehicle (1) and the acceleration of the vehicle (1).

17. The vehicle locating device (10) according to claim 15 or 16, wherein the control unit (14) is further configured to, upon determining from the sequence of positions of the vehicle (1) that the vehicle (1) has not changed for a predetermined amount of time,recalibrate one or more offsets which are applied to the received additional odometry data from the gyroscope and / or IMU.

18. The vehicle locating device (10) according to any of the preceding claims, wherein the obtained odometry data further represents one or more of a steering angle, a rotation speed of multiple wheels (2) of the vehicle (1), a degree of slip of the one or more wheels (2), a load of the vehicle (1) and / or an acceleration of the vehicle (1).

19. The vehicle locating device (10) according to any of the preceding claims, wherein the degree of tire wear is indicative of at least an outer diameter of the tire (3).

20. The vehicle locating device (10) according to any of the preceding claims, wherein the control unit (14) is further configured to transmit the position or approximated position of the vehicle (1) to other vehicles in the vicinity and / or an external control unit and / or a cloud server.

21. The vehicle locating device (10) according to any of the preceding claims, wherein the vehicle locating device (10) is further configured to transmit an indication to an operator, when the tire wear exceeds a predetermined threshold.

22. A system for locating a vehicle (1), comprising a vehicle locating device (10) according to any of the previous claims, and one or more anchors (16), configured to be attached to stationary reference points, wherein the wireless locating unit (11) of the vehicle locating device (10) is configured to use one or more of electro-magnetic waves and / or sound waves, preferably one or more of radio waves, ultra-wideband radio, microwaves, laser light and / or ultrasound to determine at least one relative distance and / or direction between the wireless locating device (12) and the one or more anchors (16), wherein the control unit (14) of the vehicle locating device is configured to determine the position of the vehicle (1) based on the determined relative distance and / or direction.

23. The system according to claim 22, further comprising a vehicle (1) comprising at least one wheel (2) with a tire (3) and one or more sensors to obtain odometry data representing at least a rotational speed of the wheel (2), wherein the wireless locating device (12) of the vehicle locating device (10) is mounted on the vehicle (1).

24. A method for locating a vehicle (1), in particular an indoor industrial vehicle, comprising providing a wireless locating unit (11) having at least one wireless locating device (12) configured to be mounted on a vehicle (1); receiving odometry data representing at least a rotational speed of the wheel (3) from the vehicle (1); determining a temporal sequence of at least two positions of the vehicle (1) based on a locating signal received from the wireless locating unit (11); determining a movement speed of the vehicle (1) based on the sequence of positions; determining a degree of tire wear of the wheel (2) based on the determined movement speed and the odometry data; approximating the position of the vehicle (1) based on at least one previous position of the sequence of positions, the odometry data and the degree of tire wear at least when no current locating signal is provided by the wireless locating unit (11).

25. The method according to claim 24, further comprising attaching one or more anchors (16) to stationary reference points and thereby defining a locating area (30) in which the wireless locating unit (11) is within range of the one or more anchors (16), wherein the wireless locating unit (11) only provides a current locating signal when the wireless locating device (12) is in the locating area (30).

26. The method according to claim 25, wherein the locating area (30) is part of a usual operating area (31) of the vehicle (1) and the usual operating area (31) is larger than the locating area (30).

27. The method according to claim 24, further comprising providing an inertial measurement unit (IMU) and / or a gyroscope that are configured to obtain additional odometry data indicative of an acceleration of the vehicle (1) and / or a spatial orientation of the vehicle (1), and upon determining from the sequence of positions of the vehicle (1) that the vehicle (1) has not changed for a predetermined amount of time, recalibrating one or more offsets which are applied to the received additional odometry data from the IMU and / or gyroscope.

28. The method according to claim 25, wherein the step of determining the degree of tire wear further comprises determining a sequence of positions of the vehicle (1) in the locating area (30), determining at least one approximated position of the vehicle (1) based on at least one position of the sequence of positions in the locating area (30) and the odometry data; evaluating if one or more predetermined criteria are met by the sequence of positions and / or the odometry data; and determining the degree of tire wear based on a comparison between the approximated position and the sequence of positions, preferably only when the sequence of positions and / or the odometry data meet the predetermined criteria.

29. The method according to claim 28, wherein the one or more predetermined criteria are one or more of a minimal distance covered by the vehicle (1), a maximal steering angle, a sufficiently straight trajectory, a maximal acceleration and / or a speed range.

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