Patent Description:
Each prior art container handling vehicle <NUM>,<NUM> also comprises a lifting device (not shown) for vertical transportation of storage containers <NUM>, e.g. raising a storage container <NUM> from, and lowering a storage container <NUM> into, a storage column <NUM>. The lifting device comprises one or more gripping / engaging devices which are adapted to engage a storage container <NUM>, and which gripping / engaging devices can be lowered from the vehicle <NUM>,<NUM> so that the position of the gripping / engaging devices with respect to the vehicle <NUM>,<NUM> can be adjusted in a third direction Z which is orthogonal the first direction X and the second direction Y. Parts of the gripping device of the container handling vehicle <NUM> are shown in <FIG> indicated with reference number <NUM>. The gripping device of the container handling device <NUM> is located within the vehicle body 301a in <FIG>.

The storage volume of the framework structure <NUM> has often been referred to as a grid <NUM>, where the possible storage positions within this grid are referred to as storage cells. Each storage column may be identified by a position in an X- and Y-direction, while each storage cell may be identified by a container number in the X-, Y and Z-direction.

The central cavity container handling vehicles <NUM> shown in <FIG> may have a footprint that covers an area with dimensions in the X and Y directions which is generally equal to the lateral extent of a storage column <NUM>, e.g. as is described in <CIT>. The term 'lateral' used herein may mean 'horizontal'.

<CIT>, illustrates a typical configuration of rail system <NUM> comprising rails and parallel tracks in both X and Y directions.

The access station may typically be a picking or a stocking station where product items are removed from or positioned into the storage containers <NUM>. In a picking or a stocking station, the storage containers <NUM> are normally not removed from the automated storage and retrieval system <NUM> but are returned into the framework structure <NUM> again once accessed. A port can also be used for transferring storage containers to another storage facility (e.g. to another framework structure or to another automated storage and retrieval system), to a transport vehicle (e.g. a train or a lorry), or to a production facility.

When a storage container <NUM> is to be stored in one of the columns <NUM>, one of the container handling vehicles <NUM>,<NUM> is instructed to pick up the storage container <NUM> from the pick-up port column <NUM> and transport it to a location above the storage column <NUM> where it is to be stored. After any storage containers positioned at or above the target position within the storage column stack <NUM> have been removed, the container handling vehicle <NUM>,<NUM> positions the storage container <NUM> at the desired position. The removed storage containers may then be lowered back into the storage column <NUM> or relocated to other storage columns.

When a vehicle is moving on the tracks, it is controlled to accelerate from a start position and decelerate to a stop position. The start and stop positions will depend on the route set up for a vehicle prior to picking up a bin from one storage column in the storage grid and placing it in another storage column. A set route of a vehicle will typically comprise several starts and stop positions. A route for a specific vehicle will be set up by a supervisory system having control of all storage bins and their content as well as the positions of the vehicles handling the bins.

When operating and controlling a vehicle following a set route relative to tracks laid out on a frame structure forming a grid, it is vital to keep track of all operating vehicles and their positions at all times. The positions of a vehicle can be acquired in different ways. One way is to track the position of the vehicle relative to the tracks on top of the frame structure. The position can be acquired by means of tracking devices located externally to the vehicle or by devices integrated in the vehicle.

Another method of tracking the position of the vehicle is by the integrated tracking devices to track the number of crossings passed in x- and y-directions relative to the tracks laid out as a grid structure.

By using integrated tracking devices, the vehicle itself will be able to keep track of its position. Integrated tracking devices are however quite complex systems and not necessarily very precise.

Publication <CIT> describes a method and a remotely operated vehicle for tracking the position of the vehicle following a set route relative to tracks laid out on a frame structure forming a grid.

The method comprising receiving information of the number of track crossings to pass between start and stop position in x- and y- directions according to the set route; directing sensors attached to the vehicle at the tracks along the route of the vehicle; detecting and monitoring track crossings passed when moving the vehicle in the x- and y-directions according to the set route, and transmitting a signal to the controller, controlling the drives of the wheels of the vehicle, when the number of track crossings passed is close to the total number of track crossings to pass between the start and stop positions in respective x-and y- directions along the set route. This system uses the sensors for detecting and monitoring track crossing along the tracks in the x-and y-direction.

<CIT> describes, in accordance with its abstract, a control unit to improve positioning of transporting devices to thereby allow transporting devices to be driven at faster speeds and/or accelerations with minimal positional errors allowing for a reduction in the spacing between transporting devices. In particular, there is described a control unit arranged to control movement of at least one transporting device, the at least one transporting device arranged to transport containers, the containers being stored in a facility, the facility arranged to store the containers in a plurality of stacks, the facility comprising a plurality of pathways arranged in cells so as to form a grid-like structure above the stacks, wherein the grid-like structure extends in a first direction and in a second direction, the at least one transporting device arranged to operate on the grid-like structure. The control unit comprises a receiving unit arranged to receive information from a first sensor mounted on the at least one transporting device. The control unit further comprises a calculating unit arranged to calculate a position of the at least one transporting device based on the received information.

<CIT> describes, in accordance with its abstract, a pallet transport apparatus within a rack installation oriented orthogonally with a longitudinal x direction, a transverse z direction and a vertical y direction having a travel route in the x direction and in the z direction. In the apparatus, an x traveling mechanism/x wheel units and a z traveling mechanism/z wheel units are designed so as to be vertically moveable in the y direction mechanically independently of one another.

The apparatus has an x lifting device for lifting the x traveling mechanism or of the x wheel units in the y direction, a z lifting device for lifting the z traveling mechanism or of the z wheel units, and a y lifting device for moving the pallet pickup unit. The x/z lifting devices can be activated in the y direction independently of one another and independently of the y lifting device.

<CIT> describes, in accordance with its abstract, a remotely operated vehicle or robot for picking up storage bins from a storage system. The vehicle or robot comprises a vehicle body, which vehicle body further comprises a first section for storing vehicle driving means and a second section for receiving any storage bin stored in a storage column within the storage system, a vehicle lifting device which is at least indirectly connected to the vehicle body in order to lift the storage bin into the second section, a first set of vehicle rolling means connected to the vehicle body in order to allow movement of the vehicle along a first direction within the storage system during use and a second set of vehicle rolling means connected to the vehicle body in order to allow movement of the vehicle along a second direction in the storage system during use. The second direction is oriented perpendicular to the first direction. The second section comprises a cavity arranged centrally within the vehicle body. This cavity has at least one bin receiving opening facing towards the underlying storage columns during use. In addition, at least one of the two sets of vehicle rolling means is arranged fully within the vehicle body.

An object of the present invention is to provide a precise tracking and confirmation of the position of the vehicle while situated on a grid cell.

Another object of the present invention is to provide a vehicle with a pre-alert arrangement informing of the remaining distance until it reaches a set position, during which the vehicle may react.

The invention is directed to a remotely operated vehicle with an apparatus to provide a pre-alert and tracking of a position of the vehicle following a travelling route relative to tracks laid out on a rail structure in x, y directions on a rail system. The vehicle having first and seconds sets of wheels connected to drives for moving the vehicle in corresponding x, y directions on the rail system.

The remotely operated vehicle, also referred to as the vehicle, may be a container handling vehicle or a delivery vehicle configured for operating on the rail system.

The arrangement comprises a controller and at least one sensor module provided with at least four sensors:.

The sensor module may be mounted into the structure of the vehicle in a corner position at least partly behind the wheels of the vehicle.

Before arrival at the set position, the first sensor or the second sensor may detect a rail structure in the corresponding travelling direction, and pre-alert a remaining distance to the set position.

At a set position, the first and second sensors may detect their respective rails and conforms the vehicle being in the set position. If for instance, any of the first or second sensors does not detect their respective rails, the controller will notice that the vehicle is not precisely in the set position.

Furthermore, in the set position, the third sensor will not detect any obstacle since it is located in the corner at the intersection between the rails in the x-direction and y-direction. If however, the third sensor, in the set position, detects a rail structure, then the controller would know that the vehicle is not precisely in the set position.

The arrangement may comprise two sensor modules; a first sensor module arranged in the corner position of the vehicle, and a second sensor module arranged at a diametrically opposite a corner position of the vehicle such that the corresponding sensors of the first and second sensor module are equally spaced from their corner position.

The first sensor module may be defined as the front sensor in relation to the travelling direction of the vehicle, and the second sensor module may be defined as the back sensor module.

Each of the first and second sensor module may comprise the at least three sensors; the first, the second and the third sensors, each directed/pointed vertically down towards the rails for determining the position of the vehicle. The sensors are arranged to register any obstacle breaking the beam such that a controller may notice every time the vehicle is passing a rail in the x-or y-direction.

The third sensor may be located on respective first and second sensor module, such that the third sensor of the second sensor module, may pre-alert the remaining distance to the set position when moving in x-or y-direction. Thus, when the third sensor of the second sensor module detects the rail structure of the grid cell of the set position, the controller would know that the remaining distance for the vehicle to travel to the set position, corresponds to the width of the rail structure. The output of the sensor may be used in a feedback loop in a controller for providing signals causing additional or less deceleration of the vehicle.

The arrangement may further comprise a fourth sensor configured to pre-alert a remaining distance to the arrival of the vehicle at the position, by detecting any of the rails in the x-or y-direction.

The fourth sensor position may be located such that it detects a rail when the vehicle is moving towards the set position. According to the location of the fourth sensor relative to the vehicle, the sensor may detect and pre-alert a predefined remaining distance to the set position. For instance, if the preferable pre-alert distance is <NUM> prior to arrival of the vehicle in the set position, the fourth sensor is located accordingly relative to the vehicle. The output of the fourth sensor may be used in a feedback loop in a controller for providing signals causing additional or less deceleration of the vehicle.

The fourth sensor may be arranged in the sensor module together with the first, second and third sensors. All sensors may be provided in the sensor module which may be adapted to plug into the structure of the vehicle behind the wheels.

Each of the first and second sensor module may comprise the first, second, third and fourth sensor. The first and second sensor module may be the same module but arranged to be mounted at diametrically opposite corners of the vehicle.

The first and second module may be mounted into the structure of the vehicle and at least partly behind the wheels of the vehicle at diametrically opposite corners of the vehicle, such that the corresponding sensors of the first and second module are equally spaced from the corner position.

The first and sensor module needs to be of a sufficient surface area to support all four sensors, the sensors being spaced as necessary with respect to underside of the vehicle. Any variations in how the modules attach to the vehicles could have knock-on effects for the accuracy of the sensors and the ability of the signals to provide reliable positional data. The module may be mounted onto the underside of the vehicle nested into a right-angled corner of the vehicle base, which will help to ensure that the module is accurately mounted with respect to the vehicle. Moreover, all the sensors being mounted and fixed within the body of the module will mean that the relative position of the sensors can be accurately adhered to, once the mounted position of the module can be ensured.

The sensors may also be able to share some of the signal processing electronics.

Each of the four sensors of the first and second sensor module may be configured to pre-alert a remaining distance to the arrival of the vehicle at the position, by detecting any of the rail structure in the x-or y-direction.

The output of any of the first, second, third or fourth sensors are used in a feedback loop in a controller for providing signals causing additional or less deceleration of the vehicle. The additional or less deceleration may be provided as necessary based on a predetermined or model of the change of speed profile stored in the controller's memory.

For example, the vehicle may have different mass (weight) between loaded and unloaded storage containers, the change in the momentum required may be hard to predict accurately. Therefore, the signals the sensors give during the acceleration phase may provide information whether the vehicle has picked up a heavy or a light storage container. This information may be used in the deceleration phase to guide the vehicle to a more accurate stop.

The sensors may be optical sensors detecting reflection of lights from the rails. Other or additional sensors for detecting the rails and/or tracks for determining the position and pre-alert may also be used, e.g. acoustic sensors. A sensor having a narrow beam may be advantageous for the signal it will need to output in order to provide a stronger peak/trough signal.

The vehicle may further comprise means for receiving instructions with information of the number of rails crossings to pass between start and stop positions in x- and y-directions according to the set route.

Light is reflected from rails when a vehicle is moving along the tracks in x- or y-directions. When the vehicle is passing a rail in any of the x-or y-direction the light will be reflected such that the controller receives information of the rail passing. The vehicle may further comprise a controller for controlling the drives of the vehicle according to the number of rails in x-and y-direction passed. When this is close to the total number of rails to pass between the start and stop positions in respective x- and y-directions along the set route, the controller may initiate deceleration of the vehicle.

The signal transmitted to the controller can be used for performing precise control of deceleration and acceleration of the vehicle for following a set route along x- and y-directions. The controller may for example control precise deceleration of the vehicle prior to the next rail crossing where it is to change direction.

The following describes an example of how a remotely operated vehicle may be operated.

The tracks laid out on a rail structure in x-and y-direction forming a grid can be addressed similar as the cells in a spreadsheet. If for instance a storage grid comprises <NUM> columns or cells for storing bins, each cell can be given a unique identity. A grid with <NUM> cells in the x-direction and <NUM>-cells in the y-direction will make a <NUM>-dimensional track configuration running on top of <NUM> cells.

When the movements of the vehicle are controlled, a controller will keep track of which cell the robot is to pick up a bin from, and which cell to place a bin in. Based on this, the controller will set up a route the vehicle is to follow.

If for instance, the vehicle is to pick up a bin from cell C2, and place it in cell H8, and cells C8 and H2 are blocked by other vehicles, the following route may be set up by the controller. First leg of the route is from C2 to C5, the next leg is from C5 to H5, and the last leg is from H5 to H8. According to said route, the vehicle must start and stop three times. It will first drive in the y-direction, then the x-direction, and finally in the y-direction. The vehicle will receive the number of rails (and track) crossings to pass between each start and stop position according to said route.

The sensors attached to the vehicle and detecting means comprised in the vehicle may detect the number of rails and track crossings passed in each direction. When the number of passed crossings is close to the total number of rail crossings to pass on each leg, a signal is transmitted to the controller controlling the movements of the vehicle. In this way, the controller will know exactly when deceleration should start, as well as the rate and duration of acceleration.

The invention is also directed to a method for pre-alerting and tracking of a position of a remotely operated vehicle following a travelling route relative to tracks laid out on rails in x, y directions on a rail system (<NUM>). The vehicle having first and seconds sets of wheels connected to drives for moving the vehicle in corresponding x-, y-directions on the rail system.

The vehicle comprises an arrangement of a controller and comprising at least three sensors:.

The first, second, third and fourth sensors may be arranged in a sensor module.

The arrangement comprises two sensor modules; a first sensor module arranged in the corner position of the vehicle, and a second sensor module arranged at a diametrically opposite a corner position of the vehicle such that the corresponding sensors of the first and second sensor module are equally spaced from their corner position.

Following drawings are appended by way of example only to facilitate the understanding of the invention.

Furthermore, even if some of the features of the present invention are described in relation to a rails system of a storage and retrieval system <NUM> with a framework structure <NUM> in combination with container handling vehicles <NUM>,<NUM> suitable for operating on such system, it is apparent that the features of the present invention are valid for other rail systems (such as delivery rail system) and vehicles (such as delivery vehicles) and vice versa.

With reference to <FIG> the storage grid <NUM> of each storage structure <NUM> constitutes a framework <NUM> of in total <NUM> grid columns <NUM>, where the width and length of the framework corresponds to the width and length of <NUM> and <NUM> grid columns <NUM>, respectively. The top layer of the framework <NUM> is a rail system <NUM> onto which a plurality of container handling vehicles <NUM>,<NUM> are operated.

The framework <NUM> of the storage system <NUM> is constructed in accordance with the above mentioned prior art framework <NUM> described above, i.e. a plurality of upright members <NUM> and a plurality of horizontal members <NUM> which are supported by the upright members <NUM>, and further that the horizontal members <NUM> includes the rail system <NUM> of parallel rails <NUM>,<NUM> in the X direction and the Y direction, respectively, arranged across the top of storage columns <NUM>. The horizontal area of a single grid cell <NUM>, i.e. along the X and Y directions, may be defined by the distance between adjacent rails <NUM> and <NUM>, respectively.

The rail system <NUM> allows the container handling vehicles <NUM>, <NUM> to move horizontally between different grid locations, where each grid location is associated with a grid cell <NUM>.

In <FIG>, the storage grid <NUM> is shown with a height of eight cells. It is understood, however, that the storage grid <NUM> can in principle be of any size. In particular it is understood that storage grid <NUM> can be considerably wider and/or longer than disclosed in <FIG>.

The storage container vehicles <NUM>,<NUM> may be of any type known in the art, e.g. any one of the automated container handling vehicles disclosed in <CIT>, in <CIT> or in <CIT>.

The rail system <NUM> may comprise a single track system. Alternatively, the rail system <NUM> may be a double track system. The rail system <NUM> may also be a combination of single and double tracks.

<FIG> shows an arrangement of sensors for pre-alert and tracking of a position of ta remotely operated vehicle (not shown) following a travelling route relative to tracks laid out on rails in x-, y-directions on a rail system (not shown).

The arrangement comprises a first sensor <NUM> directed to the rails in the x-direction <NUM>, a second sensor <NUM> directed to the rails in the y-direction <NUM>, and a third sensor <NUM> directed to a corner of an intersection between the rails in the x-direction and y-direction <NUM>,<NUM>.

The arrangement may also comprise a fourth sensor arranged to pre-alert a remaining distance to the arrival of the vehicle <NUM>,<NUM> at the position, by detecting any of the rails in the x-or y-direction <NUM>,<NUM>.

In <FIG>, <FIG>, <FIG>, <FIG> the beam of the sensors <NUM>,<NUM>,<NUM>,<NUM> are shown to illustrate the position of the sensors and the direction of their beams. In operation the beams of the vehicle may also be invisible for the human eye.

Each of the sensors <NUM>,<NUM>,<NUM> may be directed downwardly towards the rails in x-, y-directions for determining the position of the vehicle relative to the rails <NUM>,<NUM>.

The sensors may be arranged on a sensor module as shown in <FIG>.

The module may be mounted into the structure of the vehicle <NUM>,<NUM> and at least partly behind the wheels of the vehicle as shown in <FIG>.

The arrangement of the present invention may comprise a first or a second sensor module <NUM>,<NUM>. Each sensor module <NUM>,<NUM> comprises one or more sensors <NUM>,<NUM>,<NUM>,<NUM> directed vertically downwardly towards the rails for determining the position of the vehicle <NUM>,<NUM> relative to the rails (shown in <FIG>).

The first and second sensor module <NUM>,<NUM> may be one type of senor module with the same pre-arrangement of sensors provided in the sensor module. Each sensor module <NUM>,<NUM> may be adapted to be arranged at a diametrically opposite a corner position of the vehicle, for pre-alerting and tracking of a position of the vehicle following a travelling route relative to tracks laid out on a rail structure in x, y directions <NUM>,<NUM> on a rail system <NUM>. The travelling direction of the vehicle <NUM>,<NUM> may define which is the first and second sensor module <NUM>,<NUM>.

The sensor module <NUM>,<NUM> may comprise at least three sensors where a first sensor <NUM> is directed to the rails in the x-direction <NUM>, a second sensor <NUM> is directed to the rails in the y-direction <NUM>, the first and second sensors <NUM>,<NUM> are equally spaced from the corner position of the vehicle <NUM>,<NUM> so that they detect any of the rails in the x- and/or y-direction <NUM>,<NUM>. A third sensor <NUM> directed to a corner of an intersection between the rail structure in the x-direction <NUM> and y-direction <NUM>.

The sensor module <NUM>,<NUM> may further comprise a forth sensor <NUM> configured to pre-alert a remaining distance to the arrival of the vehicle at the position, by detecting the rail structure in the x-or y-direction <NUM>,<NUM>.

<FIG>,<FIG>,<FIG>, <FIG> shows the sensor module <NUM>,<NUM> comprising the four sensors <NUM>,<NUM>,<NUM>,<NUM> each located at a predetermined location on the sensor module <NUM>,<NUM> for detecting and reading a position of the vehicle <NUM>,<NUM>.

The first and second sensor module <NUM>,<NUM> are mounted into the structure and at least partly behind the wheels 201b,301b,201c,301c of the vehicle <NUM>,<NUM> such that the corresponding sensors <NUM>,<NUM>,<NUM>,<NUM> of the first and second sensor module <NUM>,<NUM> are equally spaced from the corner position.

<FIG> shows a rail system <NUM> from above and the sensors <NUM>,<NUM>,<NUM>,<NUM> of a vehicle <NUM>,<NUM> moving in the y-direction on the rail system <NUM>. The vehicle (not shown) comprises a first sensor system <NUM> located in a front corner in the moving direction of the vehicle <NUM>,<NUM>, and a second sensor module <NUM> located in a diametrically opposite corner position at the back of the moving direction of the vehicle <NUM>,<NUM>.

Each sensor module <NUM>,<NUM> comprises four sensors; a first sensor <NUM> directed to the rail in the x-direction <NUM>, a second sensor <NUM> directed to the rail in the y-direction <NUM>, a third sensor <NUM> directed to a corner of an intersection between the rail structure in the x-direction and y-direction <NUM>,<NUM>, and a forth sensor <NUM> located at a predefined location and configured to pre-alert a remaining distance to the arrival of the vehicle <NUM>,<NUM> at the position, by detecting the rail structure in the x or y direction <NUM>,<NUM>. The "remaining distance" may vary according to the location of the fourth sensor <NUM> relative to the vehicle <NUM>,<NUM>. The first <NUM> and second <NUM> sensors are spaced from the corner position so that they may detect the rail in the x- and y-direction simultaneously while located at the set position, such that the set position can be confirmed with reference to the rails in x-and y-direction <NUM>,<NUM>.

While the vehicle <NUM>,<NUM> is moving in the y-direction of the rail system towards a set location on a grid cell <NUM>, the second sensor <NUM> detects the rails in the y-direction <NUM> continuously (the sensor is following the rails in y-direction). The fourth sensor <NUM> of the second sensor module <NUM> is located at a location relative to the vehicle, such that when the sensor <NUM> detects the rail structure in the x-direction <NUM> of the grid cell <NUM> of the set position, it sends a signal to a controller so as to pre-alert the remaining distance to the set position. Thus, the remaining distance to the set position is defined by the position of the fourth sensor <NUM> relative to the vehicle <NUM>,<NUM>. As shown in <FIG>, the remaining distance may be set to about <NUM>. If a longer "remaining distance" is preferred, the fourth sensor <NUM> may be moved closer towards the center of the vehicle, such that the remaining distance can be increased accordingly. The fourth sensor may be integrated into the sensor modules <NUM>,<NUM> or it may be located separate at the underside of the vehicle <NUM>,<NUM>.

Furthermore, when the vehicle <NUM>,<NUM> arrives at a set position located on a grid cell <NUM> of the rail system <NUM>, the first sensor <NUM> of the first and second sensor <NUM>,<NUM> detects the rail in the x-direction <NUM>, the second sensor <NUM> of the first and second sensor <NUM>,<NUM> detects the rail in the y-direction <NUM>, the third sensor <NUM> the first and second sensor <NUM>,<NUM> detects no obstacles since it is located in the corner at the intersection between the rail structure in the x-direction and y-direction <NUM>,<NUM>. If the third sensor <NUM> should detect an obstacle (i.e. a rail structure), then the controller would know that the vehicle <NUM>,<NUM> is located in an offset position (hence, not correctly at the set position on the grid cell). While at the set position on a grid cell <NUM>, the first, second and third sensors <NUM>,<NUM>,<NUM> confirms the vehicle being in the set position.

The first and second sensor system <NUM>,<NUM> will work the same way when the vehicle <NUM>,<NUM> is moving in the opposite y-direction on the rail system <NUM>. The first sensor module <NUM> may be defined as the front sensor module of the vehicle, in the moving direction of the vehicle <NUM>,<NUM>. Such that when the vehicle <NUM>,<NUM> moves in opposite direction, the previous second sensor module <NUM> becomes the first sensor module <NUM>.

The <FIG> shows the sensors <NUM>,<NUM>,<NUM>,<NUM> of the first and second sensor module <NUM>,<NUM> in a vehicle <NUM>,<NUM> moving in the x-direction of a rail system <NUM>. Accordingly, the first sensor module <NUM> is located in the front corner of the vehicle <NUM>,<NUM>, and the second sensor module <NUM> is located in a diametrically opposite corner position at the back of the vehicle <NUM>,<NUM> (seen in the moving direction of the vehicle).

Each sensor module <NUM>,<NUM> comprises four sensors; a first sensor <NUM> directed to the rail in the x-direction <NUM>, a second sensor <NUM> directed to the rail in the y-direction <NUM>, a third sensor <NUM> directed to a corner of an intersection between the rail structure in the x-direction and y-direction <NUM>,<NUM>, and a forth sensor <NUM> configured to pre-alert a remaining distance to the arrival of the vehicle at the position, by detecting the rail structure in the x or y direction <NUM>,<NUM>. The first <NUM> and second <NUM> sensor are spaced from the corner position so that they may detect the rails in respective the x- and y-direction <NUM>,<NUM>. Each of the first and second sensor module <NUM> may be equally spaced from the corner position on the vehicle <NUM>,<NUM>.

While moving in the x-direction of the rail system <NUM> towards a set location on a grid cell <NUM>, the first sensor <NUM> detects the rails in the x-direction <NUM> continuously as the vehicle <NUM>,<NUM> moves along rails in the x-direction. The fourth sensor <NUM> of the second sensor module <NUM> is located such that when the sensor <NUM> detects the rail structure in the y-direction <NUM> of the grid cell <NUM> of the set position, it sends a signal to a controller so as to pre-alert the remaining distance to the set position. Thus, the remaining distance to the set position is defined by the position of the fourth sensor <NUM> relative to the vehicle <NUM>,<NUM>. As shown in <FIG>, the remaining distance may be set to about <NUM>. Any pre-preferable distance may be obtained by moving the location of the fourth sensor <NUM>, relative to the vehicle.

Furthermore, when the vehicle <NUM>,<NUM> arrives at a set position located on a grid cell <NUM> of the rails system <NUM>, the first sensor <NUM> of the first and second sensor module <NUM>,<NUM> detects the rails in the x-direction <NUM>, the second sensor <NUM> of the first and second sensor <NUM>,<NUM> detects the rails in the y-direction <NUM>, the third sensor <NUM> of the first and second sensor <NUM>,<NUM> detects no obstacles since it is located in the corner at the intersection between the rail structure in the x-direction and y-direction <NUM>,<NUM>. If the third sensor <NUM> should detect an obstacle (i.e. a rail structure), then the controller would know that the vehicle <NUM>,<NUM> is located in an offset position (hence, not correctly at the set position on the grid cell). The first, second and third sensors <NUM>,<NUM>,<NUM> detects and confirms the position of the vehicle <NUM>,<NUM>.

Accordingly, sensors <NUM>,<NUM>,<NUM>,<NUM> of the first and second sensor system <NUM>,<NUM> will work the same way when the vehicle <NUM>,<NUM> is moving in the opposite x-direction of the rail system <NUM>. The first sensor module <NUM> may be defined as the front sensor module in the moving direction of the vehicle <NUM>,<NUM>. Such that when the vehicle <NUM>,<NUM> moves in opposite direction, the previous second sensor module <NUM> becomes the first sensor module <NUM>.

<FIG> shows a cross section of the remotely operated vehicle <NUM>,<NUM> taken horizontally through the first or second sensor module <NUM>,<NUM>. The sensor module <NUM>,<NUM> comprises a first <NUM>, a second <NUM>, a third <NUM> and a fourth <NUM> sensor, each of the sensors are directed vertically downward to detect the rail structures. The vehicle <NUM>,<NUM> is located at the set position such that the first sensor <NUM> is detecting the rail in the x-direction <NUM>, and the second sensor <NUM> is detecting the rail in the y-direction <NUM>. The third sensor is situated at the corner of the intersection between the x-rail <NUM> and y-rail <NUM> and detects no obstacles.

Claim 1:
A remotely operated vehicle (<NUM>,<NUM>) comprising an arrangement to provide a pre-alert and tracking of a position of the vehicle following a travelling route relative to tracks laid out on rails in x-, y-directions (<NUM>,<NUM>) on a rail system (<NUM>), the vehicle (<NUM>,<NUM>) having first and seconds sets of wheels (201b,301b,201c,301c) connected to drives for moving the vehicle (<NUM>,<NUM>) in corresponding x-, y-directions on the rail system (<NUM>),
wherein the arrangement comprises a controller and at least one sensor module provided with at least four sensors:
- a first sensor (<NUM>) directed vertically downwards to detect the rails in the x-direction (<NUM>) on the sensor module,
- a second sensor (<NUM>) directed vertically downwards to detect the rails in the y-direction (<NUM>) on the sensor module,
- a third sensor (<NUM>) positioned on the sensor module to detect a corner of an intersection between the rails in the x-direction and y-direction (<NUM>,<NUM>),
- a fourth sensor (<NUM>) configured to detect a remaining distance to the arrival of the vehicle (<NUM>,<NUM>) at a set position, by detecting the rails in the x direction (<NUM>) when travelling in the y direction (<NUM>), and detecting the rail in the y direction (<NUM>) when travelling in the x direction (<NUM>), said sensor (<NUM>) being placed at a predefined position on the sensor module
- the controller provided on the vehicle to receive the output from at least one of the sensors (<NUM>, <NUM>, <NUM>, <NUM>) and said fourth sensor is configured to send a signal to the controller to so as to pre-alert the remaining distance of the arrival of the vehicle at the set position.