Patent Publication Number: US-2023136087-A1

Title: Section based speed reduction

Description:
FIELD OF THE INVENTION 
     The present invention relates to an automated storage and retrieval system for storage and retrieval of containers, in particular to a system and a method for controlling movement of a plurality of container handling vehicles on a rail system to reduce speed and/or acceleration such that the movement of the container handling vehicle within a subsection of the rail system is below the container handling vehicle movement threshold of the subsection. 
     BACKGROUND AND PRIOR ART 
       FIG.  1    discloses a typical prior art automated storage and retrieval system  1  with a framework structure  100  and  FIGS.  2  and  3    disclose two different prior art container handling vehicles  201 , 301  suitable for operating on such a system  1 . 
     The framework structure  100  comprises upright members  102 , horizontal members  103  and a storage volume comprising storage columns  105  arranged in rows between the upright members  102  and the horizontal members  103 . In these storage columns  105  storage containers  106 , also known as bins, are stacked one on top of one another to form stacks  107 . The members  102 ,  103  may typically be made of metal, e.g. extruded aluminum profiles. 
     The framework structure  100  of the automated storage and retrieval system  1  comprises a rail system  108  arranged across the top of framework structure  100 , on which rail system  108  a plurality of container handling vehicles  201 , 301  are operated to raise storage containers  106  from, and lower storage containers  106  into, the storage columns  105 , and also to transport the storage containers  106  above the storage columns  105 . The rail system  108  comprises a first set of parallel rails  110  arranged to guide movement of the container handling vehicles  201 , 301  in a first direction X across the top of the frame structure  100 , and a second set of parallel rails  111  arranged perpendicular to the first set of rails  110  to guide movement of the container handling vehicles  201 , 301  in a second direction Y which is perpendicular to the first direction X. Containers  106  stored in the columns  105  are accessed by the container handling vehicles through access openings  112  in the rail system  108 . The container handling vehicles  201 , 301  can move laterally above the storage columns  105 , i.e. in a plane which is parallel to the horizontal X-Y plane. 
     The upright members  102  of the framework structure  100  may be used to guide the storage containers during raising of the containers out from and lowering of the containers into the columns  105 . The stacks  107  of containers  106  are typically self-supportive. 
     Each prior art container handling vehicle  201 , 301  comprises a vehicle body  201   a , 301   a , and first and second sets of wheels  201   b , 301   b , 201   c , 301   c  which enable the lateral movement of the container handling vehicles  201 , 301  in the X direction and in the Y direction, respectively. In  FIGS.  2  and  3    two wheels in each set are fully visible. The first set of wheels  201   b , 301   b  is arranged to engage with two adjacent rails of the first set  110  of rails, and the second set of wheels  201   c , 301   c  is arranged to engage with two adjacent rails of the second set  111  of rails. At least one of the sets of wheels  201   b , 301   b , 201   c , 301   c  can be lifted and lowered, so that the first set of wheels  201   b , 301   b  and/or the second set of wheels  201   c , 301   c  can be engaged with the respective set of rails  110 ,  111  at any one time. 
     Each prior art container handling vehicle  201 , 301  also comprises a lifting device (not shown) for vertical transportation of storage containers  106 , e.g. raising a storage container  106  from, and lowering a storage container  106  into, a storage column  105 . The lifting device comprises one or more gripping/engaging devices which are adapted to engage a storage container  106 , and which gripping/engaging devices can be lowered from the vehicle  201 , 301  so that the position of the gripping/engaging devices with respect to the vehicle  201 , 301  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  301  are shown in  FIG.  3    indicated with reference number  304 . The gripping device of the container handling device  201  is located within the vehicle body  301   a  in  FIG.  2   . 
     Conventionally, and also for the purpose of this application, Z=1 identifies the uppermost layer of storage containers, i.e. the layer immediately below the rail system  108 , Z=2 the second layer below the rail system  108 , Z=3 the third layer etc. In the exemplary prior art disclosed in  FIG.  1   , Z=8 identifies the lowermost, bottom layer of storage containers. Similarly, X=1 . . . n and Y=1 . . . n identifies the position of each storage column  105  in the horizontal plane. Consequently, as an example, and using the Cartesian coordinate system X, Y, Z indicated in  FIG.  1   , the storage container identified as  106 ′ in  FIG.  1    can be said to occupy storage position X=10, Y=2, Z=3. The container handling vehicles  201 , 301  can be said to travel in layer Z=0, and each storage column  105  can be identified by its X and Y coordinates. 
     The storage volume of the framework structure  100  has often been referred to as a grid  104 , 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. 
     Each prior art container handling vehicle  201 , 301  comprises a storage compartment or space for receiving and stowing a storage container  106  when transporting the storage container  106  across the rail system  108 . The storage space may comprise a cavity arranged centrally within the vehicle body  201   a  as shown in  FIG.  2    and as described in e.g. WO2015193278A1, the contents of which are incorporated herein by reference. 
       FIG.  3    shows an alternative configuration of a container handling vehicle  301  with a cantilever construction. Such a vehicle is described in detail in e.g. NO317366, the contents of which are also incorporated herein by reference. 
     The central cavity container handling vehicles  201  shown in  FIG.  2    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  105 , e.g. as is described in WO2015193278A1, the contents of which are incorporated herein by reference. The term ‘lateral’ used herein may mean ‘horizontal’. 
     Alternatively, the central cavity container handling vehicles  101  may have a footprint which is larger than the lateral area defined by a storage column  105 , e.g. as is disclosed in WO2014090684A1. 
     The rail system  108  typically comprises rails with grooves in which the wheels of the vehicles run. Alternatively, the rails may comprise upwardly protruding elements, where the wheels of the vehicles comprise flanges to prevent derailing. These grooves and upwardly protruding elements are collectively known as tracks. Each rail may comprise one track, or each rail may comprise two parallel tracks. 
     WO2018146304, the contents of which are incorporated herein by reference, illustrates a typical configuration of rail system  108  comprising rails and parallel tracks in both X and Y directions. 
     In the framework structure  100 , a majority of the columns  105  are storage columns  105 , i.e. columns  105  where storage containers  106  are stored in stacks  107 . However, some columns  105  may have other purposes. In  FIG.  1   , columns  119  and  120  are such special-purpose columns used by the container handling vehicles  201 , 301  to drop off and/or pick up storage containers  106  so that they can be transported to an access station (not shown) where the storage containers  106  can be accessed from outside of the framework structure  100  or transferred out of or into the framework structure  100 . 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’  119 , 120 . The transportation to the access station may be in any direction, that is horizontal, tilted and/or vertical. For example, the storage containers  106  may be placed in a random or dedicated column  105  within the framework structure  100 , then picked up by any container handling vehicle and transported to a port column  119 , 120  for further transportation to an access station. Note that the term ‘tilted’ means transportation of storage containers  106  having a general transportation orientation somewhere between horizontal and vertical. 
     In  FIG.  1   , the first port column  119  may for example be a dedicated drop-off port column where the container handling vehicles  201 , 301  can drop off storage containers  106  to be transported to an access or a transfer station, and the second port column  120  may be a dedicated pick-up port column where the container handling vehicles  201 , 301  can pick up storage containers  106  that have been transported from an access or a transfer station. 
     The access station may typically be a picking or a stocking station where product items are removed from or positioned into the storage containers  106 . In a picking or a stocking station, the storage containers  106  are normally not removed from the automated storage and retrieval system  1 , but are returned into the framework structure  100  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. 
     A conveyor system comprising conveyors is normally employed to transport the storage containers between the port columns  119 , 120  and the access station. 
     If the port columns  119 , 120  and the access station are located at different levels, the conveyor system may comprise a lift device with a vertical component for transporting the storage containers  106  vertically between the port column  119 , 120  and the access station. 
     The conveyor system may be arranged to transfer storage containers  106  between different framework structures, e.g. as is described in WO2014075937A1, the contents of which are incorporated herein by reference. 
     When a storage container  106  stored in one of the columns  105  disclosed in  FIG.  1    is to be accessed, one of the container handling vehicles  201 , 301  is instructed to retrieve the target storage container  106  from its position and transport it to the drop-off port column  119 . This operation involves moving the container handling vehicle  201 , 301  to a location above the storage column  105  in which the target storage container  106  is positioned, retrieving the storage container  106  from the storage column  105  using the container handling vehicle&#39;s  201 , 301  lifting device (not shown), and transporting the storage container  106  to the drop-off port column  119 . If the target storage container  106  is located deep within a stack  107 , i.e. with one or a plurality of other storage containers  106  positioned above the target storage container  106 , the operation also involves temporarily moving the above-positioned storage containers prior to lifting the target storage container  106  from the storage column  105 . This step, which is sometimes referred to as “digging” within the art, may be performed with the same container handling vehicle that is subsequently used for transporting the target storage container to the drop-off port column  119 , or with one or a plurality of other cooperating container handling vehicles. Alternatively, or in addition, the automated storage and retrieval system  1  may have container handling vehicles specifically dedicated to the task of temporarily removing storage containers from a storage column  105 . Once the target storage container  106  has been removed from the storage column  105 , the temporarily removed storage containers can be repositioned into the original storage column  105 . However, the removed storage containers may alternatively be relocated to other storage columns. 
     When a storage container  106  is to be stored in one of the columns  105 , one of the container handling vehicles  201 , 301  is instructed to pick up the storage container  106  from the pick-up port column  120  and transport it to a location above the storage column  105  where it is to be stored. After any storage containers positioned at or above the target position within the storage column stack  107  have been removed, the container handling vehicle  201 , 301  positions the storage container  106  at the desired position. The removed storage containers may then be lowered back into the storage column  105 , or relocated to other storage columns. 
     For monitoring and controlling the automated storage and retrieval system  1 , e.g. monitoring and controlling the location of respective storage containers  106  within the framework structure  100 , the content of each storage container  106 ; and the movement of the container handling vehicles  201 , 301  so that a desired storage container  106  can be delivered to the desired location at the desired time without the container handling vehicles  201 , 301  colliding with each other, the automated storage and retrieval system  1  comprises a control system  500  which typically is computerized and which typically comprises a database for keeping track of the storage containers  106 . 
     WO2018146687 describes a system for controlling movement of plurality of container handling vehicles where the container handling vehicles transport storage containers, store and retrieve storage containers into/from storage columns. 
     The framework structure  100  and the rail system  108  is specified and constructed to allow operation of the plurality of container handling vehicles  201 ,  301  at full speed and acceleration. However, after installation or during operation it may be determined that some areas of the framework structure  100  and/or the rail system  108  are outside specifications. This may lead to operational errors of the container handling vehicles  201 ,  301 . The operational errors may lead to system stop or crash of container handling vehicles  201 ,  301 . In order to be safe and avoid the operation errors, the speed and/or acceleration is reduced for all container handling vehicles  201 ,  301  on the rail system  108 . This leads to a considerably reduced capacity of the automated storage and retrieval system  1 . 
     In WO2019138392 an access control method is utilized in order to guarantee the structural integrity of a grid-like storage facility. The access control method limits the number of transporting devices in a constraint area by granting or withholding clearance to each transporting device to traverse the constraint area. It does not address operational errors of the transporting vehicles. 
     In view of the problems, the present invention aims to provide a system and method for the automated storage and retrieval system which avoids operational errors of the container handling vehicles in out of specification areas without significantly reducing the capacity of the automated storage and retrieval system. 
     SUMMARY OF THE INVENTION 
     The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention. 
     In one aspect, the invention is related to a method for controlling movement of a plurality of container handling vehicles on a rail system arranged at least partially across a top of framework structure of an automated storage and retrieval system, on which rail system the plurality of container handling vehicles are operable to raise storage containers from, and lower storage containers into, storage columns arranged in rows between upright members and horizontal members of the framework structure, and also to transport the storage containers above the storage columns. The following steps are performed by a central operational controller which is in communication with a local controller in each container handling vehicle. Receiving data relating to a subsection of the rail system, the data comprising a container handling vehicle movement threshold for the subsection. Instructing a container handling vehicle to follow a path which takes in at least a part of the subsection. Instructing the container handling vehicle to reduce speed and/or acceleration such that the movement of the container handling vehicle within the is below the container handling vehicle movement threshold of the subsection. Driving the container handling vehicle at slower speed/acceleration allows the control system to better handle operational errors. In this way, system stops or crashes can be avoided. 
     In an embodiment, the method may further comprise, prior to the step of instructing the container handling vehicle to reduce speed and/or acceleration, a step of determining that a current movement of the container handling vehicle exceeds the container handling vehicle movement threshold of the subsection. The central operation controller may then only instruct to reduce speed and/or acceleration when the current movement of the container handling vehicle exceeds the container handling vehicle movement threshold of the subsection. The number of instructions over the communication channel is therefore reduced and unwanted additional load on the communication channels is avoided. 
     In an embodiment, determining that the container handling vehicle exceeds the container handling vehicle movement threshold may further comprise classifying the container handling vehicle according to a container handling vehicle classification, and determining, based on the container handling vehicle classification, that the container handling vehicle exceeds the container handling vehicle movement threshold. The container handling vehicle classification comprises a default speed and/or acceleration of the container handling vehicle. 
     In an embodiment, determining that the container handling vehicle exceeds the container handling vehicle movement threshold may further comprise receiving data of the weight of a storage container transported by the container handling vehicle, and determining, based on the weight of the storage container and the container handling classification, that the container handling vehicle exceeds the container handling vehicle movement threshold. 
     In an embodiment, determining that the container handling vehicle exceeds the container handling vehicle movement threshold may further comprise receiving historical movement data of the container handling vehicle, and determining, based on the historical movement data of the container handling vehicle, that the container handling vehicle exceeds the container handling vehicle movement threshold. 
     In an embodiment, the method may further comprise instructing the container handling vehicle to revert to a default speed and/or acceleration when the container handling vehicle is leaving and/or about to leave the subsection. 
     In an embodiment, the container handling vehicle movement threshold sets a maximum speed of the container handling vehicle. 
     In an embodiment, the container handling vehicle movement threshold sets a maximum acceleration of the container handling vehicle. 
     In an embodiment, the container handling vehicle movement threshold sets a maximum linear momentum of the container handling vehicle. 
     In an embodiment, the method may further comprise determining, using a rail inspection vehicle traversing the rail system, the container handling vehicle movement threshold for the subsection of the rail system. The container handling vehicle movement threshold may be determined based on detected vertical and/or horizontal movement of the rail inspection vehicle due to movement in the rail system above a fault threshold. The container handling vehicle movement threshold may be determined based on detected changes in horizontal movement of the rail inspection vehicle due to a change in a condition of the rail system. The container handling vehicle movement threshold may also be determined based on visually detected faults in the rail system using the rail inspection vehicle or other method. 
     In an embodiment, the method may further comprise determining the container handling vehicle movement threshold for the subsection based on a reduced mechanical stability in the subsection of the of rail system compared to a mechanical stability of the rail system outside the subsection. 
     In an embodiment, the method may further comprise determining the container handling vehicle movement threshold for the subsection based on a displacement of the of rail system in the subsection in relation to the rail system outside the subsection. 
     In an embodiment, the method may further comprise determining the container handling vehicle movement threshold for the subsection based on a reduced friction in the subsection of the rail system compared to a friction of the rail system outside the subsection. 
     In an embodiment, the method may further comprise determining the container handling vehicle movement threshold for the subsection based on different environmental conditions in the subsection of the rail system than in the rail system outside the subsection. 
     In an embodiment, the method may further comprise transmitting the container handling vehicle movement threshold for the subsection to the local controller in the container handling vehicle, and performing, using the local controller in the container handling vehicle, the step of instructing the container handling vehicle to reduce speed and/or acceleration such that the movement of the container handling vehicle within the subsection is below the container handling vehicle movement threshold of the subsection. 
     In a second aspect, the invention concerns a system comprising a rail system arranged at least partially across a top of framework structure of an automated storage and retrieval system, a plurality of container handling vehicles operating on the rail system to raise storage containers from, and lower storage containers into, storage columns arranged in rows between upright members and horizontal members of the framework structure, and also to transport the storage containers above the storage columns, each container handling vehicle comprising a local controller adapted to control movements of the container handling vehicle, and a central operational controller in communication with the local controller in each container handling vehicle. The central operational controller is adapted to perform receiving data relating to a subsection of the rail system, the data comprising a container handling vehicle movement threshold for the subsection, instructing a container handling vehicle to follow a path which takes in at least a part of the subsection, and instructing the container handling vehicle to reduce speed and/or acceleration such that the movement of the container handling vehicle within the subsection is below the container handling vehicle movement threshold of the subsection. Driving the container handling vehicle at slower speed/acceleration allows the control system to better handle operational errors. In this way, system stops or crashes can be avoided. 
     In an embodiment of the system, the central operational controller may be further adapted to, prior to instructing the container handling vehicle to reduce speed and/or acceleration, determining that a current movement of the container handling vehicle exceeds the container handling vehicle movement threshold of the subsection. The central operation controller may then only instruct to reduce speed and/or acceleration when the current movement of the container handling vehicle exceeds the container handling vehicle movement threshold of the subsection. The number of instructions over the communication channel is therefore reduced and unwanted additional load on the communication channels is avoided. 
     In an embodiment of the system, determining that the container handling vehicle exceeds the container handling vehicle movement threshold may further comprise classifying the container handling vehicle according to a container handling vehicle classification, and determining, based on the container handling vehicle classification, that the container handling vehicle exceeds the container handling vehicle movement threshold. The container handling vehicle classification comprises a default speed and/or acceleration of the container handling vehicle. 
     In an embodiment of the system, determining that the container handling vehicle exceeds the container handling vehicle movement threshold may further comprise receiving data of the weight of a storage container transported by the container handling vehicle, and determining, based on the weight of the storage container and the container handling classification, that the container handling vehicle exceeds the container handling vehicle movement threshold. 
     In an embodiment of the system, determining that the container handling vehicle exceeds the container handling vehicle movement threshold may further comprise receiving historical movement data of the container handling vehicle, and determining, based on the historical movement data of the container handling vehicle, that the container handling vehicle exceeds the container handling vehicle movement threshold. 
     In an embodiment of the system, the central operational controller may be further adapted to instructing the container handling vehicle to revert to a default speed and/or acceleration when the container handling vehicle is leaving and/or about to leave the subsection. 
     In an embodiment of the system, the container handling vehicle movement threshold sets a maximum speed of the container handling vehicle. 
     In an embodiment of the system, the container handling vehicle movement threshold sets a maximum acceleration of the container handling vehicle. 
     In an embodiment of the system, the container handling vehicle movement threshold sets a maximum linear momentum of the container handling vehicle. 
     In an embodiment of the system, the system may further comprise a rail inspection vehicle adapted to traverse the rail system, and is adapted to determining, using the rail inspection vehicle, the container handling vehicle movement threshold for the subsection of the rail system. The container handling vehicle movement threshold may be determined based on detected vertical and/or horizontal movement of the rail inspection vehicle due to movement in the rail system above a fault threshold. The container handling vehicle movement threshold may be determined based on detected changes in horizontal movement of the rail inspection vehicle due to a change in a condition of the rail system. The container handling vehicle movement threshold may also be determined based on visually detected faults in the rail system using the rail inspection vehicle or other method. 
     In an embodiment of the system, the container handling vehicle movement threshold for the subsection may be determined based on a reduced mechanical stability in the subsection of the of rail system compared to a mechanical stability of the rail system outside the subsection. 
     In an embodiment of the system, the container handling vehicle movement threshold for the subsection may be determined based on a displacement of the of rail system in the subsection in relation to the rail system outside the subsection. 
     In an embodiment of the system, the container handling vehicle movement threshold for the subsection may be determined based on a reduced friction in the subsection of the rail system compared to a friction of the rail system outside the subsection. 
     In an embodiment of the system, the container handling vehicle movement threshold for the subsection may be determined based on different environmental conditions in the subsection of the rail system than in the rail system outside the subsection. 
     In an embodiment of the system, the central operational controller may be further adapted to transmitting the container handling vehicle movement threshold for the subsection to the local controller in the container handling vehicle, and the local controller in the container handling vehicle may be further adapted to instructing the container handling vehicle to reduce speed and/or acceleration such that the movement of the container handling vehicle within the subsection is below the container handling vehicle movement threshold of the subsection. 
     In a third aspect the invention is directed to a computer program product for a central operational controller in a system comprising a plurality of container handling vehicles on a rail system arranged at least partially across a top of framework structure of an automated storage and retrieval system, on which rail system the plurality of container handling vehicles are operable to raise storage containers from, and lower storage containers into, storage columns arranged in rows between upright members and horizontal members of the framework structure, and also to transport the storage containers above the storage columns, each container handling vehicle comprising a local controller adapted to control movements of the container handling vehicle, and the central operational controller is in communication with the local controller in each container handling vehicle, the computer program product comprises instructions that when executed on the central operational controller performs the method according to the first aspect of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Following drawings are appended to facilitate the understanding of the invention. The drawings show embodiments of the invention, which will now be described by way of example only, where: 
         FIG.  1    is a perspective view of a framework structure of a prior art automated storage and retrieval system. 
         FIG.  2    is a perspective view of a prior art container handling vehicle having a centrally arranged cavity for carrying storage containers therein. 
         FIG.  3    is a perspective view of a prior art container handling vehicle having a cantilever for carrying storage containers underneath. 
         FIG.  4    is a schematic overview of exemplary subsections according to the present invention. 
         FIG.  5    is an exemplary flowchart of a method according to the present invention  FIG.  6    is another exemplary flowchart of a method according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following, embodiments of the invention will be discussed in more detail with reference to the appended drawings. It should be understood, however, that the drawings are not intended to limit the invention to the subject-matter depicted in the drawings. 
     The framework structure  100  of the automated storage and retrieval system  1  is constructed in accordance with the prior art framework structure  100  described above in connection with  FIGS.  1 - 3   , i.e. a number of upright members  102  and a number of horizontal members  103 , which are supported by the upright members  102 , and further that the framework structure  100  comprises a first, upper rail system  108  in the X direction and Y direction. 
     The framework structure  100  further comprises storage compartments in the form of storage columns  105  provided between the members  102 ,  103 , where storage containers  106  are stackable in stacks  107  within the storage columns  105 . 
     The framework structure  100  can be of any size. In particular it is understood that the framework structure can be considerably wider and/or longer and/or deeper than disclosed in  FIG.  1   . For example, the framework structure  100  may have a horizontal extent of more than 700×700 columns and a storage depth of more than twelve containers. 
     One embodiment of the automated storage and retrieval system according to the invention will now be discussed in more detail with reference to  FIGS.  4 ,  5  and  6   . 
       FIG.  4    is a schematic overview of a part of the rail system  108 , where it is shown container handling vehicles  201 ,  301  instructed to follow paths  402 ,  403 , respectively, taking in at least a part of two subsections  401   a ,  401   b . The two subsections  401   a ,  401   b  are for simplicity defined in terms of integer units of storage columns but may also be defined by fractional units of storage columns, or by other suitable coordinates. An exemplary third subsection  401   c  is defined by one and a half storage column in the Y-direction two storage columns in the X-direction. The subsections  401   a ,  401   b ,  401   c  are areas of the rail system  108  where there is a higher likelihood for operational errors of the container handling vehicles  201 ,  301  compared to the remaining areas of the rail system  108 . Operational errors may include that the container handling vehicles  201 ,  301  are incapable of stopping in the correct position, or the container handling vehicles  201 ,  301  detects that sensor data does not correlate with expected data. The operation errors may lead to a system stop, or worse, a crash between container handling vehicles. 
     Driving the container handling vehicle  201 ,  301  at slower speed/acceleration allows the control system  500  to better handle operational errors, in this way, system stops or crashes can be avoided. 
     Each container handling vehicle  201 ,  301  comprises a local controller adapted to control movements of the container handling vehicle  201 ,  301 . Controlling the movements of the container handling vehicle  201 ,  301  includes controlling electric motors driving the driving means, such as wheels, of the container handling vehicle. The container handling vehicle  201 ,  301  usually run at full speed and acceleration. The full speed and acceleration of the container handling vehicle  201 ,  301  is defined by the construction of the electric motors driving the driving means of the container handling vehicle. Depending on the type of the electric motor, the speed and acceleration of the electric motor may be controlled by adjusting frequency and or voltage of the power supplied to the electric motor. In real life electric motors, while being manufactured to a certain specification, there will be deviations from the specification in manufacture, thus different electric motors supplied with identical power may move at different speeds. The actual speed of the container handling vehicle  201 ,  301  may vary within the deviations from the specifications. Hence, the speed and acceleration of the container handling vehicle  201 ,  301  referred herein is not the true speed and acceleration of the container handling vehicle  201 ,  301 , rather it is the speed and acceleration obtained by each the container handling vehicle  201 ,  301  at a given power supplied to the electric motors. Furthermore, a reduced speed and acceleration is obtained by supplying the electric motors of the container handling vehicles  201 ,  301  with a fraction of the power supplied to the motors at full speed and acceleration. The term acceleration should be seen to also include negative acceleration, e.g. deceleration. 
     The system is provided with a central operational controller  501  in communication with the local controller in each container handling vehicle  201 ,  301 . The communication between the local controller and the central operational controller may be any suitable wired or wireless communication technology. The central operational controller  501  is also in communication with the control system  500  using any suitable wired or wireless communication technology. 
     With additional reference to  FIG.  5    illustrating a method of controlling movement of the container handling vehicle  201 ,  301 . The central operational controller  501  receives data relating to a subsection  401   a ,  401   b  of the rail system  108 , the data comprises a container handling vehicle movement threshold for the subsection  401   a ,  401   b . The central operation controller  501  may receive the container handling vehicle movement threshold from the control system  500 . The container handling vehicle movement threshold may set at least one of a maximum speed of the container handling vehicle  201 ,  301 , a maximum acceleration of the container handling vehicle  201 ,  301 , and a maximum linear momentum of the container handling vehicle  201 ,  301 . 
     The central operational controller  501  instructs the container handling vehicle  201 ,  301  to follow a path  402 ,  403  on the rail system  108 . The central operation controller  501  may receive data from the control system  500  related to columns on the rail system  108  that requires a container handling vehicle  201 ,  301  to pick up a storage bin, and to columns where the storage bin should be dropped off. The central operational controller  501  may instruct the container handling vehicle to follow the path  402 ,  403  by step-by-step instructions. The central operational controller  501  may instruct the container handling vehicle  201 ,  301  to follow a path  402 ,  403  which takes in at least a part of the subsection  401   a ,  401   b . Furthermore, the central operational controller  501  instructs the container handling vehicle  201 ,  301  to reduce speed and/or acceleration such that the movement of the container handling vehicle within the subsection  401   a ,  401   b  is below the container handling vehicle movement threshold of the subsection  401   a ,  401   b . While instructing the container handling vehicle to follow a path and instructing the container handling vehicle to reduce speed and/or acceleration is described in separate steps, both instructions may be part of a joint step-by-step instruction from the central operational controller to the container handling vehicle. In one embodiment, some of the steps may be performed by the local controller in each container handling vehicle  201 ,  301  under the control of the central operational controller  501 . In one example, the container handling vehicle movement threshold of the subsection  401   a ,  401   b  may be transmitted to and stored in the local controller. The local controller of the container handling vehicle  201 ,  301  may then make the determination to reduce speed and/or acceleration on its own behalf. 
     The central operational controller  501  having knowledge of the path  402 ,  403  of the container handling vehicle may instruct the container handling vehicle  201 ,  301  prior to the container handling entering the subsection  401   a ,  401   b , such that the container vehicle  201 ,  301  has reduced the speed prior to entering the subsection. The central operational controller  501  having knowledge of the container handling vehicle  201 ,  301  may also predict the latest point in time when the instructions needs to be effectuated in order for the container handling vehicle to have reduced its speed below the vehicle movement threshold at the time a side of the container handling vehicle crosses a border of the subsection  401   a ,  401   b.    
     In another embodiment, the central operational controller  501  having knowledge of the path  402 ,  403  of the container handling vehicle  201 ,  301  may instruct the container handling vehicle  201 ,  301  to reduce the speed and/or acceleration below the vehicle movement threshold once a side of the container handling vehicle  201 ,  301  crosses a border of the subsection  401   a ,  401   b . Instructions to the container handling vehicle  201 ,  301  to reduce speed and/or acceleration may be part of the instructions to the container handling vehicle  201 ,  301  to follow the path  402 ,  403 . 
     When the container handling vehicle  201 ,  301  is leaving the subsection  401   a ,  401   b , the central operation controller instructs the container handling vehicle  201 ,  301  to revert to a default speed and/or acceleration. The default speed and/or acceleration would typically be the maximum speed and/or acceleration of the container handling device  201 ,  301 . The instructions to the container handling vehicle  201 ,  301  to revert to a default speed and/or acceleration may be part of the instructions to the container handling vehicle  201 ,  301  to follow the path  402 ,  403 . The point in time when the container handling vehicle  201 ,  301  is leaving the subsection  401   a ,  401   b  may depend on the specific requirements of the system. However, one suitable point in time may be when a first side of the container handling vehicle  201 ,  301  crosses a border of the subsection  401   a ,  401   b  on its way out of the subsection  401   a ,  401   b . Another suitable point in time may be when the container handling vehicle  201 ,  301  has completely left the subsection  401   a ,  401   b.    
     In some instances, for example when movement of the container handling vehicle  201 ,  301  outside the subsection  401   a ,  401   b  is below the container handling movement threshold of the subsection  401   a ,  401   b , the instruction to the container handling vehicle  201 ,  301  is redundant. In an automated storage and retrieval systems  1  having many container handling vehicles  201 ,  301  redundant messages may cause an unwanted additional load on the communication channels. With additional reference to  FIG.  6    illustrating one embodiment of the invention, the central operational controller  501  is further adapted to, prior to instructing the container handling vehicle  201 ,  301  to reduce speed and/or acceleration, determining that a current movement of the container handling vehicle exceeds the container handling vehicle movement threshold of the subsection  401   a ,  401   b . The central operation controller  501  may then only instruct to reduce speed and/or acceleration when the current movement of the container handling vehicle exceeds the container handling vehicle movement threshold of the subsection  401   a ,  401   b.    
     Determining that a current movement of the container handling vehicle exceeds the container handling vehicle movement threshold of the subsection  401   a ,  401   b , may also be directional for the vehicles themselves, for example, due to a non-symmetry in the container handling vehicle  201 ,  301  and its engagement with the rail system  108 . E.g., the container handling vehicle  201  might have different length to width thresholds due to asymmetry in the internal arrangement of the components and the resultant asymmetric weight distribution and wheelbase. The container handling vehicle  301  are usually arranged as left or right-handed cantilevers. The asymmetry in handling will depend on the load being carried in the container and the balance with respect to the motor weight. 
     In one embodiment, determining that the container handling vehicle exceeds the container handling vehicle movement may be based on classifying the container handling vehicle  201 ,  301  according to a container handling vehicle classification. The container handling vehicle classification may be different types of container handling vehicles, such as cantilever type  301  or cavity type  201 , or versions of the same type of container handling vehicles having different specifications, such as different electric motors, different weights, different wheels etc. The container handling vehicle classification comprises a default speed and/or acceleration of the container handling vehicle, e.g. a measured average maximum speed and/or acceleration, or an expected maximum speed and/or acceleration based on the specifications of the container handling vehicles in the classification. The determination that the container handling vehicle exceeds the container vehicle movement threshold in the subsection  401   a ,  401   b , is then simply based on determining the container handling vehicle classification. 
     In one embodiment, the central operation controller  501  may additionally receive data of the weight of a storage container transported by the container handling vehicle. The central operation controller  501  may receive the weight from weight sensors in the container handling vehicle or get information about the weight from the control system  500  that has knowledge about the content of the storage container. Determining that that the container handling vehicle exceeds the container handling vehicle movement threshold may then be based on the combined knowledge of the weight of the storage container and the container handling classification. Weight in a storage container may for example affect the handling of a cantilever type container handling device in larger degree than a cavity type container handling device. 
     In one embodiment, the central operation controller  501  may receive historical movement data of the container handling vehicle  201 ,  301  and determining that the container handling vehicle  201 ,  301  exceeds the container handling vehicle movement threshold based on the historical movement data. The determination may for example based on that the historical movement data show instability in the vehicle. Other historical movement data may include a number of derailings, a number of navigational errors, such as missed detections of rail crossings, etc. 
       FIG.  4    shows two different container handling vehicles  201 ,  301  instructed to follow paths  402  and  403 , respectively. The central operational controller  501  have knowledge of footprints of the container handling vehicles on the rail system  108 . The exemplary container handling vehicles  201 ,  301  illustrates exemplary sizes and footprints of container handling vehicles that may be put on the rail system  108 . 
     The container handling vehicle  201  shown in  FIG.  4    may have a footprint which is generally equal to the lateral extent of one storage column  105 . The container handling vehicle  201  is instructed to follow a path  402  that crosses subsection  401   a . As discussed above, the central operational controller  501  has knowledge of the path  402  and that the path crosses subsection  401   a , and instructs the container handling vehicle  201  to reduce speed and/or acceleration such that the movement of the container handling vehicle  201  within the subsection  401   a  is below the container handling vehicle movement threshold of the subsection  401   a . The instructions may in one example be effectuated when the first long side of the footprint of the container handling vehicle  201  crosses the perimeter of the subsection  401   a . When the container handling vehicle  201  leaves the subsection  401   a , the central operation controller instructs  501  the container handling vehicle  201  to revert to the default speed and/or acceleration and continue to follow the path  402 . In some embodiments, if the central operation controller  501  determine that the container handling vehicle  201  does not exceeds the container handling vehicle movement threshold of the subsection  401   a  both instructions are redundant and none of them are sent to the container handling vehicle  201 . When the container handling vehicle is about to enter the next subsection  401   b , the instructions to reduce speed and/or acceleration may in one example be effectuated when the first short side of the footprint of the container handling vehicle  201  crosses the perimeter of the next subsection  401   b.    
     The container handling vehicle  301  shown in  FIG.  4    has a cantilever construction and may have a footprint approximately the lateral extent of two storage columns  105 . The container handling vehicle  301  is instructed to follow a path  403  that takes in subsection  401   b . As discussed above, the central operational controller  501  has knowledge of the path  403  and that the path takes in subsection  401   b , and instructs the container handling vehicle  301  to reduce speed and/or acceleration such that the movement of the container handling vehicle  301  within the subsection  401   b  is below the container handling vehicle movement threshold of the subsection  401   b . The instructions may in one example be effectuated when the first short side of the footprint of the container handling vehicle  301  crosses the perimeter of the subsection  401   b . In another example, when the container handling vehicle  301  enters the subsection  401   b  with the cantilever first, the instructions may be effectuated when the first wheels following the cantilever crosses the perimeter of the subsection  401   b . When the container handling vehicle  301  leaves the subsection  401   b , the central operation controller instructs  501  the container handling vehicle  301  to revert to the default speed and/or acceleration and continue to follow the path  403 . In this illustrated example, the instructions to revert to default speed and/or acceleration may be effectuated when the first or second long side of the footprint of the container handling vehicle  301  crosses the perimeter of the subsection  401   b . In some embodiments, if the central operation controller  501  determine that the container handling vehicle  301  does not exceeds the container handling vehicle movement threshold of the subsection  401   b  both instructions are redundant and none of them are sent to the container handling vehicle  301 . 
     The higher likelihood for operational errors of the container handling vehicle  201 ,  301  in the subsections  401   a ,  401   b  may be due to mechanical differences in the rail system  108  and/or the framework structure  100  that leads to reduced mechanical stability of the subsection  401   a ,  401   b , or a displacement of the rail system  108  in the subsection  401   a ,  401   b  in relation to the rail system  108  outside the subsection  401   a ,  401   b . The reduced mechanical stability and displacement of the rail system may stem from a floor not according to specifications, erroneous mounting of the framework structure, damages on framework structure, displacement of framework structure, a building that has moved etc. 
     Determining the container handling vehicle movement threshold for the subsection  401   a ,  401   b  may be based on reduced mechanical stability in the subsection  401   a ,  401   b  of the of rail system  108  compared to a mechanical stability of the rail system  108  outside the subsection  401   a ,  401   b.    
     The higher likelihood for operational errors of the container handling vehicle  201 ,  301  in the subsections  401   a ,  401   b  may also be due to reduced friction in the subsection  401   a ,  401   b  compared to a friction of the rail system  108  outside the subsection  401   a ,  401   b , for example based on detection of oil, water, grease etc. on the rail system  108 . 
     Determining the container handling vehicle movement threshold for the subsection  401   a ,  401   b  may be based on a displacement of the of rail system  108  in the subsection  401   a ,  401   b  in relation to the rail system  108  outside the subsection  401   a ,  401   b.    
     The higher likelihood for operational errors of the container handling vehicle  201 ,  301  in the subsections  401   a ,  401   b  may also be due to a difference in environmental conditions in the subsection  401   a ,  401   b , such as difference in temperature, air pressure, humidity, ambient gasses etc. Changes in environmental conditions may change the performance of the container handling vehicle  201 ,  301 . In one example, water may condense on the wheels of a container handling vehicle  201 ,  301  entering a cold zone from a warmer and more humid zone, which may cause reduced friction. In another example, the efficiency of the motor may change such that the speed of the container handling vehicle increases. 
     Determining the container handling vehicle movement threshold for the subsection  401   a ,  401   b  may be based on a reduced friction in the subsection  401   a ,  401   b  of the rail system  108  compared to a friction of the rail system  108  outside the subsection  401   a ,  401   b.    
     The container handling vehicle movement threshold for the subsection  401   a ,  401   b  may be different in the first direction X and the second direction Y. The rails are closer together in the first direction X, that may make the structure stronger or more rigid than for the wider spacing between the junction points in the second direction Y. 
     The higher likelihood for operational errors of the container handling vehicle  201 ,  301  in the subsections  401   a ,  401   b  may be determined by physical and/or visual inspection of the rail system  108  and the framework structure  100 . The physical and/or visual inspection may be performed manually. 
     In one embodiment, the system comprises a rail inspection vehicle adapted to traverse the rail system  108 . The system is adapted to determining, using the rail inspection vehicle, the container handling vehicle movement threshold for the subsection  401   a ,  401   b  of the rail system  108 . 
     The rail inspection vehicle may be provided with gyros, accelerometers, or other suitable movement sensor to determine vertical and/or horizontal movement of the rail inspection vehicle due to movement in the rail system while traversing the rail system  108 . The system may then determine the container handling vehicle movement threshold based on detected vertical and/or horizontal movement of the rail inspection vehicle due to movement in the rail system above a fault threshold. 
     In addition, or alternatively, the container handling vehicle movement threshold may be determined by the system based on detected changes in horizontal movement of the rail inspection vehicle due to a change in a condition of the rail system. 
     The rail inspection vehicle may be provided with an imaging device, such as a camera, in any suitable range of the electromagnetic spectrum, adapted to visually detect faults in the rail system while traversing the rail system  108 . The system may then determine the container handling vehicle movement threshold based on visually detected faults in the rail system  108 . 
     In the preceding description, various aspects of the container handling vehicle and the automated storage and retrieval system according to the invention have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the system and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the system, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention. 
     LIST OF REFERENCE NUMBERS 
     Prior art ( FIGS.  1 - 3   ):
       1  Prior art automated storage and retrieval system     100  Framework structure     102  Upright members of framework structure     103  Horizontal members of framework structure     104  Storage grid     105  Storage column     106  Storage container     106 ′ Particular position of storage container     107  Stack     108  Rail system     110  Parallel rails in first direction (X)     110   a  First rail in first direction (X)     110   b  Second rail in first direction (X)     111  Parallel rail in second direction (Y)     111   a  First rail of second direction (Y)     111   b  Second rail of second direction (Y)     112  Access opening     119  First port column     120  Second port column     201  Prior art storage container vehicle     201   a  Vehicle body of the storage container vehicle  201       201   b  Drive means/wheel arrangement, first direction (X)     201   c  Drive means/wheel arrangement, second direction (Y)     301  Prior art cantilever storage container vehicle     301   a  Vehicle body of the storage container vehicle  301       301   b  Drive means in first direction (X)     301   c  Drive means in second direction (Y)     304  Gripping device     500  Control system   X First direction   Y Second direction   Z Third direction   

       FIG.  4   :
       108  Rail system     201  Prior art storage container vehicle     301  Prior art cantilever storage container vehicle     401   a  Subsection of rail system     401   b  Subsection of rail system     402  Path for container vehicle  201       403  Path for container vehicle  301       500  Control system     501  Central operational controller   X First direction   Y Second direction   Z Third direction