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'.

Within the art, such a location is normally referred to as a 'port' and the column in which the port is located may be referred to as a `port column' <NUM>,<NUM>.

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.

<CIT> describes a storage system, where the container handling vehicles are arranged with sensors that can detect the location of the vehicle, and proximity sensor to detect the location of nearby vehicles, and communicate that information to the control system <NUM>. The control system communicates with a plurality of container handling vehicles and commands the container handling vehicles to form a "train" of vehicles, i.e. a plurality of container handling vehicles proximately arranged in series and arranged to move with one another in tandem. The assembly of the train is accomplished with help of the sensors in the container handling vehicles, by the control system's knowledge about the container handling vehicles' relative positions, or a combination of both. However, the position of a container handling vehicle on the rail system is not known with certainty until it has passed a track crossing, after which the position of the container handling vehicle may be transmitted to the control system which processes this information. This results in a delay due to the command being relayed through, and processed in, the control system, and in insufficient positioning information for effective train driving for the container handling vehicles. Various methodologies to mitigate this problem is described, such as adding proximity sensors on each container handling vehicle or physical coupling such as latches, magnetic coupling etc..

In view of the above, it is desirable to provide an automated storage and retrieval system, and a method for operating such a system, that improves the control of the container handling vehicles.

In one aspect, the invention is related to an automated storage and retrieval system comprising:.

An advantage of this system is that it allows a plurality of container handling vehicles to form a "train" of vehicles, i.e. a plurality of container handling vehicles proximately arranged in series and arranged to move with one another in tandem, one after the other separated by the predetermined separation.

The target position may be any position on the rail system. The target position may be a final position on the rail system, such as port position, or the target position may be any intermediate positions on its way to a final position. The vehicle may for example be instructed to move to a first position on the rail system where the vehicle waits for another vehicle to pass, before getting instructions to move to a second position in step-by-step instructions.

Instructing the second container handling vehicle to move with and follow the first container handling vehicle may comprise instructing the second container handling vehicle to accelerate or decelerate until the second container handling vehicle is at the predetermined separation from the first container handling vehicle based on the received position data of the positions of the first and second container handling vehicles.

Instructing the second container handling vehicle to move with and follow the first container handling vehicle may comprise instructing the second container handling vehicle to move at a set speed based on the received position data of the positions of the first and second container handling vehicles.

Instructing the second container handling vehicle to move with and follow the first container handling vehicle may comprise instructing the second container handling vehicle to change speed at an acceleration or deceleration based on the received position data of the positions of the first and second container handling vehicles to stay within the predetermined separation.

Instructing the second container handling vehicle to move with and follow the first container handling vehicle may comprise instructing the second container handling vehicle to move to a position that is at the predetermined separation from the position of the first container handling vehicle based on the received position data of the positions of the first and second container handling vehicles.

The position at the predetermined separation from the position of the first container handling vehicle that the second container handling vehicle is instructed to move to may be a position at a predetermined separation from a future position of the first container handling vehicle determined based on a current speed and heading of the first container handling vehicle.

The signal measurements may be time of flight (TOF) measurements. More specifically, the TOF-measurements may be time difference of arrival (TDOA) measurements. TDOA, as discussed below requires less messaging than Two Way Ranging (TWR) and may be advantageously used when the number of container handling vehicles to be positioned increases.

The positioning node of each container handling vehicle and the at least three reference positioning nodes may be Ultra-Wideband (UWB) nodes. UWB is defined by the UWB PHY layer defined in the IEEE <NUM>. <NUM>-<NUM> revision standard and provides position resolution in the centimetre range.

In a second aspect, the invention relates to a method for controlling movement of a plurality of container handling vehicles in the system described above. The method comprises.

The step of instructing the second container handling vehicle to move with and follow the first container handling vehicle may comprise instructing the second container handling vehicle to accelerate or decelerate until the second container handling vehicle is at the predetermined separation from the first container handling vehicle based on the received position data of the positions of the first and second container handling vehicle.

The step of instructing the second container handling vehicle to move with and follow the first container handling vehicle may comprise instructing the second container handling vehicle to move at a set a speed based on the received position data of the positions of the first and second container handling vehicle.

The step of instructing the second container handling vehicle to move with and follow the first container handling vehicle, the method may comprise instructing the second container handling vehicle to move to a position at the predetermined separation from the position of the first container handling vehicle. In one embodiment, the position at the predetermined separation from the position of the first container handling vehicle that the second container handling vehicle is instructed to move to may be a position at a predetermined separation from a future position of the first container handling vehicle determined based on a current speed and heading of the first container handling vehicle.

The position of the first container handling vehicle and the position of the second container handling vehicle may be determined using time of flight (TOF) measurements. Specifically, the TOF-measurements may be time difference of arrival (TDOA).

In a third aspect, the invention provides a computer program product for a control system in the system described above, wherein the computer program product comprises instructions which when executed on the control system causes the system described above to perform the method described above.

One embodiment of the automated storage and retrieval system according to the invention will now be discussed in more detail with reference to <FIG>.

<FIG> illustrates two container handling vehicles <NUM> forming a "train" of vehicles, where the two container handling vehicles <NUM> move with one another at a predetermined separation S. Each container handling vehicle <NUM> comprises a positioning node <NUM>. The positioning node <NUM> may be positioned in any suitable position exterior or interior to the container handling vehicle <NUM>. The control system <NUM> may know the position of the positioning node <NUM> on the container handling vehicle <NUM> relative to the outer dimensions of the container handling vehicle. It may therefore be sufficient to know the separation between the two positioning nodes <NUM> to determine the separation S between the two container handling vehicles <NUM>. The predetermined separation S may be fixed in the control system <NUM> or vary depending on speed of the container handling vehicles etc. The predetermined separation should be as small as possible, preferably smaller than <NUM>. A small predetermined separation provides for shorter trains and more effective use of available rails system space.

<FIG> schematically illustrates the container handling vehicle <NUM> comprising a positioning node <NUM>, and a local controller <NUM> adapted to control movements of the container handling vehicle. The local controller <NUM> is in communication with the control system over a wireless communication link. The positioning node <NUM> may communicate with the control system directly or via the local controller <NUM>. In other embodiments, the positioning node <NUM> may only communicate with reference positioning nodes (reference positioning nodes <NUM>, <NUM>, <NUM> shown in <FIG>) spaced in fixed positions on and/or proximate the rail system <NUM>, <NUM>.

<FIG> illustrates another container handling vehicle according to an embodiment of the invention. <FIG> shows a container handling vehicle <NUM> for container delivery, and <FIG> shows the container handling vehicle <NUM> in relation to an automated storage and retrieval system <NUM>.

As <FIG> illustrates, the container handling vehicle <NUM>, which is in the form of a container delivery vehicle <NUM>, is arranged for receiving a storage container <NUM> in a top-down manner, and therefore comprises a container carrier <NUM> arranged above a vehicle body 601a to receive a storage container <NUM> from above. The container delivery vehicle <NUM> comprises drive means 601b in first direction X, and drive means 601c in the second direction Y, similar to that of the other aforementioned container handling vehicles <NUM>,<NUM>, <NUM>.

<FIG> illustrates a pair of container handling vehicles <NUM>, <NUM>, operating on upper and lower rail systems <NUM>, <NUM>.

The container delivery vehicle <NUM> operates on a rail system <NUM> below the rail system <NUM> of a storage grid <NUM> as shown. The delivery rail system <NUM> may be constructed in the same way or a similar way as the rail system <NUM> for the container handling vehicles <NUM>,<NUM>, <NUM> described in relation to <FIG>.

A container handling vehicle <NUM>, according to the embodiment of <FIG> is shown operating on the rail system <NUM> of the storage grid <NUM>. However, as will be apparent to the person skilled in the art, any kind of container handling vehicle <NUM>,<NUM>, <NUM> may be operated on the rail system <NUM> of the grid. The container handling vehicles <NUM> operating on an upper rail system <NUM> may thus lower storage containers down to container delivery vehicles <NUM> operated on the lower rail system <NUM>. The container delivery vehicles <NUM> are typically arranged for delivery of storage containers <NUM> to an access point (not shown) at the periphery of the rail system <NUM>, where the storage containers <NUM> may be picked. Though not illustrated herein, the lower rail system <NUM> typically comprises a multitude of container delivery vehicles <NUM>, and as they move between cells below port columns and access points on the periphery of the lower rail system <NUM>, problems of congestion and queuing may arise. Thus, the invention is advantageously applied to rail systems <NUM> with container delivery vehicles <NUM> in a similar manner as for container handling vehicles <NUM>,<NUM>, <NUM> of a rail system <NUM> of a grid <NUM>.

<FIG> is a top view of the rail system <NUM> of the system <NUM>. The system <NUM> comprises a positioning system comprising at least three reference positioning nodes <NUM>, <NUM>, <NUM>, spaced in fixed positions on and proximate the rail system <NUM>. The positioning system is adapted to determine the position of the container handling vehicles <NUM> on the rail system <NUM> based on signal measurements between the positioning node <NUM> of each container handling vehicle <NUM> and the at least three reference positioning nodes <NUM>, <NUM>, <NUM>. The reference positioning nodes <NUM>, <NUM>, <NUM> and the positioning node <NUM> on the container handling vehicle <NUM> are off-the-shelf products and various methods of signal measurements may be used to determine the position of the positioning node <NUM> on the grid.

One such method used for traditional radio technologies such as Bluetooth or Wi-Fi is Received Signal Strength Indicator, RSSI, where the positioning node <NUM> measures signal strength to each of the at least three reference positioning nodes <NUM>, <NUM>, <NUM> and combines this with a propagation model to determine the distance to each point. The positioning system may, based on the measured distances and a knowledge of the position of the reference positioning nodes <NUM>, <NUM>, <NUM> on the grid <NUM>, use multilateration techniques to determine the position of the positioning node <NUM> on the grid as illustrated by the three intersecting spheres S701, S702, S703 in <FIG>.

Another method used for the traditional radio technologies are time of flight, TOF, measurements. For these systems the TOF is measured by sending a message between the positioning node <NUM> and each of the at least three reference positioning nodes <NUM>, <NUM>, <NUM>, and measure the time from sending the message to receiving an acknowledgement message, ACK. Again, multilateration techniques may be used to determine the position of the positioning node <NUM> on the grid.

A problem with the traditional radio technologies, relying on modulated sine waves to transmit information, is dealing with multipath signal propagation causing localization errors. Wi-Fi positioning systems have resolution of <NUM> - <NUM> meters.

For efficient train driving of the container handling vehicles it would be advantageous to have a position resolution of decimeters instead of meters. In one advantageous embodiment of the present invention, the positioning node <NUM> of each container handling vehicle and the at least three reference positioning nodes <NUM>, <NUM>, <NUM> are Ultra-Wideband (UWB) nodes. UWB is defined by the UWB PHY layer defined in the IEEE <NUM>. <NUM>-<NUM> revision standard.

UWB utilizes a train of impulses rather than a modulated sine wave to transmit information. This characteristic makes it perfect for precise ranging applications. Since the pulse occupies such a wide frequency band, its rising edge is very steep and this allows the receiver to very accurately measure the arrival time of the signal. The pulses themselves are very narrow, typically no more than two nanoseconds. Due to the nature of the signals, UWB pulses can be distinguished even in noisy environments, and the signals are resistant to multipath effects. All of these traits give UWB a big advantage over traditional narrowband signals in case of ranging capabilities. Also due to a strict spectral mask, the transmission power lies at the noise floor, which means that UWB does not interfere with other radio communication systems operating in the same frequency bands, since it just increases the overall noise floor. The framework structure <NUM> of the system <NUM> is susceptible for multipath effects and UWB positioning is suitable to overcome those problems. UWB positioning systems has a resolution in the decimeter range, and so offers much finer resolution than for the known WiFi positioning systems.

UWB positioning systems use one of two different methods for Time of Flight measurements for positioning. One method is two-way ranging, TWR. For TWR, three messages have to be sent, the positioning node <NUM> sends a poll message to one of the at least three reference positioning nodes <NUM>, <NUM>, <NUM>, the poll message comprising a time of sending Poll, TSP. The one of the at least three reference positioning nodes <NUM>, <NUM>, <NUM>, records the time of poll reception, TRP, and replies with a response message at a time TSR. The positioning node <NUM> records the response message time, TRR. The positioning node <NUM> sends a final message, comprising TSP, TRR and the time of sending final message, TSF, to the one of the at least three reference positioning nodes <NUM>, <NUM>, <NUM>, which records the time of reception of the final message, TRF. It is then possible to calculate the TOF and the distance. When the distances to at least three reference positioning nodes <NUM>, <NUM>, <NUM> has been determined, multilateration techniques may be used to determine the position of the positioning node <NUM> on the grid <NUM>. <MAT> <MAT>.

The one of the at least three reference positioning nodes <NUM>, <NUM>, <NUM>, may determine the TOF and distance by itself, or it may forward the information to a real time location server, RTLS, in communication with the at least three reference positioning nodes <NUM>, <NUM>, <NUM>, for the RTLS to perform the determination. The determined distance may also be sent in a message back to positioning node <NUM>. The RTLS of the positioning system repeatedly reports position data of the position of each of the positioning nodes <NUM> to the control system <NUM>.

A second method for Time of Flight measurements for UWB positioning systems is Time Difference of Arrival, TDoA, that is based on precise measurements of time difference between signals arrival to the at least three reference positioning nodes <NUM>, <NUM>, <NUM>. In this method the at least three reference positioning nodes <NUM>, <NUM>, <NUM> need to be accurately synchronized, and so they need to run the same clock. The positioning node <NUM> transmits in a regular interval (refresh rate) a short Blink message. The Blink message is received by all reference positioning nodes <NUM>, <NUM>, <NUM> within the communication range of the positioning node <NUM>. Each of the reference positioning nodes <NUM>, <NUM>, <NUM> records the time of Blink message reception, e.g. timestamps TR701, TR702, TR703, and transmits the timestamps to the RTLS server. The RTLS-server uses multilateration techniques to determine the position of the positioning node <NUM> based on the time difference of arrival TR701, TR702, TR703.

An advantage of TDoA over TWR is that the positioning node <NUM> doesn't communicate with the reference positioning nodes <NUM>, <NUM>, <NUM>. While TWR requires <NUM> messages to localize the positioning node <NUM>, TDoA requires only one. Furthermore, the positioning node <NUM> uses only a short time to send the Blink message, therefore a high number of positioning nodes <NUM> may transmit a Blink message within the regular interval (refresh rate). TDoA may therefore be advantageously used when the number of container handling vehicles <NUM>,<NUM>, <NUM>, <NUM> to be positioned increases.

The automated storage and retrieval system <NUM> comprises, as discussed above, a computerized control system <NUM> which comprises a database for keeping track of the storage containers <NUM>. The control system <NUM> is adapted to communicate with the local controller <NUM> in each container handling vehicle <NUM>, <NUM>, <NUM>, <NUM>, e.g. to send instructions to the container handling vehicle on where to move on the grid <NUM>, or where to pick up or drop a storage container <NUM>. The control system <NUM> is also adapted to communicate with the positioning system, e.g. the RTLS-server, to receive real time position data for each of the container handling vehicles <NUM>, <NUM>, <NUM>, <NUM>. The positioning system provides the control system <NUM> with knowledge about the container handling vehicles' relative positions such that the control system <NUM> may instruct the container handling vehicles to form a "train" of vehicles, i.e. a plurality of container handling vehicles proximately arranged in series and arranged to move with one another in tandem. The control system <NUM> is adapted to instruct a first container handling vehicle to move to a target position, repeatedly receive position data from the positioning system of a position of the first container handling vehicle and repeatedly receive position data from the positioning system of a position of a second container handling vehicle, and instruct the second container handling vehicle to move with and follow the first container handling vehicle within a predetermined separation S from the first container handling vehicle based on the received position data of the positions of the first and second container vehicles. The predetermined separation between the first container handling vehicle and the second container handling vehicle may be fixed in the control system <NUM> or vary depending on speed of the container handling vehicles etc. The predetermined separation may be viewed as a target separation between the first container handling vehicle and the second container handling vehicle. As the vehicles move independently of each other the instantaneous separation may vary within a given tolerance of the predetermined separation. The second container handling vehicle may be instructed to speed up if it falls behind, or slow down if it comes too close. The given tolerance may be plus/minus <NUM>%, plus/minus <NUM>%, plus/minus <NUM>%, plus/minus <NUM>%, and may vary depending on the configuration of the automated storage and retrieval system. Various factors as the type of container handling vehicles, the total number of container handling vehicles etc. may influence the given tolerance.

<FIG> is a flow diagram schematically representing the steps of a method for operating an automated storage and retrieval system <NUM>.

The method is typically initiated by a step <NUM> where the control system <NUM> instructs a first container handling vehicle 401A to move to a target position TA. A target position may typically be a storage column, on rail system <NUM>,<NUM>. The local controller of the first container handling vehicle <NUM> receives the instructions and initiates movement of the first container handling vehicle 401A towards the target position TA. The control system <NUM> knows that it intends to create a train of container handling vehicles moving together towards the target position TA. The train comprises at least a second container handling vehicle 401B. In steps <NUM> and <NUM>, the control system <NUM> receives the position data from the positioning system of a position of the first container handling vehicle 401A and receives the position data from the positioning system of a position of the second container handling vehicle 401B. The order of receiving the position information of the first container handling vehicle 401A prior to receiving the position information of the second container handling vehicle 401A is arbitrary chosen for the simplicity of illustration. The step <NUM> may instead precede the step <NUM>, or step <NUM> and <NUM> may occur substantially at the same time.

The positioning system determines the positions of the first container handling vehicle 401A and the second container handling vehicle 401B by performing signal measurements between the positioning node <NUM> of each container handling vehicle 401A, 401B and the at least three reference positioning nodes <NUM>, <NUM>, <NUM>. In step <NUM>, the control system <NUM> instructs the second container handling vehicle 401B to move with and follow the first container handling vehicle 401B at a predetermined separation S from the first container handling vehicle 401A. The local controller of the second container handling vehicle 401B receives the instructions and initiates movement of the second container handling vehicle 401B towards the first container handling vehicle 401A until it is at the predetermined separation S and continues to move with the first container handling vehicle at the predetermined separation S. In so doing, the second container handling vehicle 401B follows the first container handling vehicle 401A. The control system <NUM> repeatedly receives the position data from the positioning system of the position of the first container handling vehicle 401A and repeatedly receives the position data from the positioning system of the position of the second container handling vehicle 401B, as illustrated by the method returning to step <NUM>. After receiving updated position information, the control system may send instructions to the second container handling vehicle 401B to again instruct the second container handling vehicle 401B to move with the first container handling vehicle 401A at the predetermined separation S.

In the following, with reference to <FIG>, various steps of methods of operating an automated storage and retrieval system are exemplified in accordance with the invention.

<FIG> is a schematic top view of a rail system <NUM>, illustrating steps of a method where two container handling vehicles 401A, 401B controlled by the control system <NUM> are forming a train of vehicles. The two container handling vehicles 401A, 401B are initially in adjacent cells on the rail system <NUM> as shown in in <FIG>. In <FIG> the control system instructs a first container handling vehicle 401A to move towards a target position TA. The target position may be any position on the rail system. The target position may be a final position on the rail system, such as port position, or the target position may be any intermediate positions on its way to a final position. The vehicle may for example be instructed to move to a first position on the rail system where the vehicle waits for another vehicle to pass, before getting instructions to move to a second position in step-by-step instructions. The control system <NUM> receives position data from the positioning system of a position of the first container handling vehicle 401A and position data from the positioning system of a position of a second container handling vehicle 401B. Once the separation between the first and second container handling vehicle is within a predetermined separation S, as shown in <FIG>, the second container handling vehicle 401A is instructed to move with and follow the first container handling vehicle within the predetermined separation S.

As illustrated in <FIG>, the first container handling vehicle 401A acts as the locomotive, and the position of the second container handling vehicle 401B is adjusted relative to the first container handling vehicle 401A by the control system when the position data received from the position system indicates that the separation is different from the predetermined separation S. When the first container handling vehicle 401A arrives and stops at the target position TA, the second container handling vehicle 401B is instructed to stop in a position at the predetermined separation S as illustrated in <FIG>. As mention above, the target position of TA may not be the final position of the first container handling vehicle 401A, so the second container handling vehicle 401B is kept at the predetermined separation in case the first container handling vehicle 401A begins to move again towards a new target position (not shown). If the target position TA was the final position for the first container handling vehicle 401A, the control system <NUM> could instruct the second container handling vehicle 401B to move to a position adjacent the first container handling vehicle 401A.

If on the other hand, the second container handling vehicle 401B arrives at its own target position TB (not shown) prior to the first container handling vehicle 401A arriving at the target position TA, then the second container handling vehicle 401B would stop at the target position TB. That is, the second container handling vehicle stops moving with the first container handling vehicle 401A when arriving at TB.

Instructing the second container handling vehicle to move with and to follow the first container handling vehicle may comprise repeatedly instructing the second container handling vehicle 401B to move to a position that is at the predetermined separation S from the position of the first container handling vehicle 401A. That is, every time the controls system <NUM> receives position data from the positioning system of the position of the first container handling vehicle 401A, the control system <NUM> determines a new position the second container handling vehicle 401B should be in to be within the predetermined separation S from the position of the first container handling vehicle 401A.

Alternatively, instead of sending a message every time the second container handling vehicle 401B should move to move with the first container handling vehicle, the control system <NUM> may instruct the second container handling vehicle 401B to move with and to follow the first container handling vehicle 401A at a set speed. When the position data received from the position system indicates that the separation between the first and second container handling vehicles 401A, 401B is different from the predetermined separation S, the control system may instruct the second container handling vehicle 401B to accelerate or decelerate until the second container handling vehicle 401B again is at the predetermined separation S from the first container handling vehicle 401A. Once at the predetermined separation S, the second container handling vehicle 401B may be instructed to move at a set speed to move with and to follow the first container handling vehicle 401A.

Instructing the second container handling vehicle to move with and to follow the first container handling vehicle may prior to instructing the second container handling vehicle 401B to move with and follow the first container handling vehicle 401A, comprise instructing the second container handling vehicle 401B to move to a position that is at the predetermined separation S from the position of the first container handling vehicle 401A. The position at the predetermined separation S from the position of the first container handling vehicle 401A that the second container handling vehicle 401B is instructed to move to is a position at a predetermined separation S from a future position of the first container handling vehicle 401A. The future position of the first container handling vehicle 401A may be determine based on a current speed and heading of the first container handling vehicle 401A. Alternatively, as will be discussed below with reference to <FIG>, the control system <NUM> knows where it will send the first container handling vehicle 401A and may determine to send the second container handling vehicle 401B to a position at predetermined separation S of that future position of the first container handling vehicle 401A. In some situations, this may save the time needed to form a train of vehicles.

<FIG> is a schematic top view of a rail system <NUM>, illustrating steps of a method where two container handling vehicles 401A, 401B controlled by the control system <NUM> are forming a "train" of vehicles. The two container handling vehicles 401A, 401B are initially in different rows and columns on the rail system <NUM> as shown in in <FIG>. In <FIG> the control system instructs a first container handling vehicle 401A to move to a second target position TA<NUM>. The control system <NUM> receives position data from the positioning system of a position of the first container handling vehicle 401A and position data from the positioning system of the position of the second container handling vehicle 401B. The control system <NUM> instructs the first container handling vehicle 401A to first move two rows in the Y- direction to a first target position TA<NUM> and knows that it from there will instruct the first container handling vehicle 401A to move two columns in the X+ direction to the second target position TA<NUM>. Knowing where the first container handling device 401A will be in the future, the control system also instructs the second container handling vehicle 401B to move to a position that is at the predetermined separation S from the future position TA<NUM> of the first container handling vehicle 401A, as illustrated in <FIG>. The future position of the first container handling vehicle 401A may be determined based on a current speed and heading of the first container handling vehicle 401A. The instructions to the second container handling vehicle 401B may be timed such that the second container handling vehicle 401B reaches its position just in time for the first container handling vehicle to arrive. Alternatively, the instructions to the second container handling vehicle 401B may be timed such that the second container handling vehicle 401b arrives prior to the first container handling vehicle 401A arrives at the first target position TA<NUM>.

Once the first container handing vehicle 401A and second container handling vehicle 401B are separated by the predetermined separation S as shown in <FIG>, the control system <NUM> instructs the first container handling vehicle 401A and the second container handling vehicle 401B to move as shown in <FIG> as described above with reference to <FIG>.

<FIG> is a schematic top view of a rail system <NUM>, illustrating steps of a method where three container handling vehicles 401A, 401B, 401C controlled by the control system <NUM> are forming a "train" of vehicles. The container handling vehicles 401B, 401C move with and follow the first container handling vehicle 401A with a predetermined separation S between each pair of container handling vehicles. The predetermined separation S may be the same for each pair of container handling vehicles or vary for each of the pairs. Any number of container handling vehicles may move together with the first container handling vehicle 401A.

<FIG> is a schematic top view of a rail system <NUM>, illustrating steps of a method where a plurality of container handling vehicles controlled by the control system <NUM> forming a single train are split into two separate trains heading for different target positions. The uppermost row may in one exemplary implementation function as a motorway for large trains moving many container handling vehicles. The large train may be split into smaller trains of container handling vehicles moving on side roads, where the train may move slower and/or yield for other moving container handling vehicles. Three container handling vehicles 401A, 401B, 401C are initially on the same row of the rails system <NUM> as shown in <FIG>, moving in the X+ direction toward a target position TA (outside the illustrated rail section) for the first container handling vehicle 401A. The fourth container handling vehicle 401D is on another row. Two container handling vehicles 401B, 401C initially move with the first container handling vehicle 401A as discussed with reference to <FIG>.

The control system <NUM> knows that the second container handling device 401B and the fourth container handling device 401D are heading towards a different target position TB<NUM> (outside the illustrated rail section) compared to the first container handling vehicle 401A. The controls system <NUM> may also know or determine that it would be advantageous to move the second container handling vehicle 401B and the fourth container handling vehicle 401D together as a train towards the target position TB<NUM>. The control system <NUM> instructs the second container handling vehicle to move to a target position TB<NUM>, that is, one row in the Y- direction. Knowing that the second container handling vehicle 401B will be at position TB<NUM> in the future, the control system <NUM> instructs the fourth container handling vehicle 401D to move to a position that is at the predetermined separation S from the future position TB<NUM>, as illustrated in <FIG>. The fourth container handling vehicle 401D may reach the position just in time, or prior to the second container handling vehicle 401B arrives at TB<NUM>. The fourth container handling vehicle 401D may in this example have to accelerate to arrive at the predetermined separation S from TB<NUM> in time.

The control system <NUM> also receives position data from the positioning system of the position of the first container handling vehicle 401A and position data from the positioning system of the position of the third container handling vehicle 401C and instructs the third container handing vehicle 401C to move with the first container handling vehicle 401A at the predetermined separation S. In this case, that would include first accelerating the third container handling vehicle 401C to catch up with the first container handling vehicle 401A, as illustrated in <FIG>. Furthermore, the fourth container handling vehicle 401D is instructed to move with the second container handling vehicle 401B at the predetermined separation S towards the target position TB<NUM>. The same methodology could be used to include a smaller train or a single container handling device into another train.

The trains obviously do not have to move parallel to one another but may also move perpendicular to one another. <FIG> is a schematic top view of a rail system <NUM>, illustrating steps of a method where a plurality of container handling vehicles controlled by the control system <NUM> forming a single train are split into two separate trains heading for different target positions. Three container handling vehicles 401A, 401B, 401C are initially on the same row of the rails system <NUM> as shown in <FIG>, moving in the X+ direction toward a target position TA (outside the illustrated rail section) for the first container handling vehicle 401A. The fourth container handling vehicle 401D is on another row. Two container handling vehicles 401B, 401C initially move with the first container handling vehicle 401A as discussed with reference to <FIG>.

The control system <NUM> knows that the second container handling device 401B and the fourth container handling device 401D are heading towards a different target position TB<NUM> (outside the illustrated rail section) compared to the first container handling vehicle 401A. The controls system <NUM> may also know or determine that it would be advantageous to move the second container handling vehicle 401B and the fourth container handling vehicle 401D together as a train towards the target position TB<NUM>. The control system <NUM> instructs the second container handling vehicle to move to a target position TB<NUM>, that is, two rows in the Y- direction. Knowing that the second container handling vehicle 401B will be at position TB<NUM> in the future, the control system <NUM> instructs the fourth container handling vehicle 401D to move to a position that is at the predetermined separation S from the future position TB<NUM>, as illustrated in <FIG>. The control system <NUM> knows that the second container handling vehicle 401B will have to pass this position before the fourth container handing vehicle 401B reaches that position, and times the fourth container handling vehicle 401B to arrive at the position after the second container handling vehicle 401D arrived at the target position TB<NUM>. The fourth container handling vehicle 401D may in this example have to decelerate to arrive at the predetermined separation S from TB<NUM> after the second container handling vehicle 401B. As illustrated in <FIG>, in this case where the fourth container handling vehicle 401D move at a perpendicular angle to the second container handling vehicle 401B, the fourth container handling vehicle 401D may arrive in position closer than the predetermined separation S, before the second container handling vehicle 401B and the fourth container handling vehicle 401D is instructed to move together in the same direction Y- as illustrated in <FIG>.

Claim 1:
An automated storage and retrieval system (<NUM>) comprising:
a rail system (<NUM>, <NUM>) with a first set of parallel rails (<NUM>) extending in a first direction (X) and a second set of parallel rails (<NUM>) extending in second direction (Y), wherein the second direction (Y) is perpendicular to the first direction (X);
a plurality of container handling vehicles (<NUM>, <NUM>, <NUM>, <NUM>) on the rail system (<NUM>, <NUM>) operable to handle storage containers (<NUM>), each container handling vehicle (<NUM>, <NUM>, <NUM>, <NUM>) comprising:
a positioning node (<NUM>), and
a local controller adapted to control movements of the container handling vehicle (<NUM>, <NUM>, <NUM>, <NUM>);
a positioning system comprising at least three reference positioning nodes (<NUM>,<NUM>, <NUM>) spaced in fixed positions on and/or proximate the rail system (<NUM>, <NUM>), the positioning system being adapted to determine a position on the rail system for each of the container handling vehicles (<NUM>, <NUM>, <NUM>, <NUM>) based on signal measurements between the positioning node (<NUM>) of each container handling vehicle (<NUM>, <NUM>, <NUM>, <NUM>) and the at least three reference positioning nodes (<NUM>, <NUM>, <NUM>); and
a control system (<NUM>) adapted to communicate with each local controller in each container handling vehicle (<NUM>, <NUM>, <NUM>, <NUM>) and the positioning system, the control system (<NUM>) being adapted to:
- instruct a first container handling vehicle to move to a target position,
- repeatedly receive position data from the positioning system of a position of the first container handling vehicle and repeatedly receive position data from the positioning system of a position of a second container handling vehicle, and
- instruct the second container handling vehicle to move with and follow the first container handling vehicle within a predetermined separation (S) from the first container handling vehicle based on the received position data of the positions of the first and second container handling vehicles.