Patent Publication Number: US-2023142253-A1

Title: Container handling vehicle comprising a container carrying position, associated system and methods

Description:
FIELD OF THE INVENTION 
     The invention relates to the field of automated storage and retrieval systems. In particular, the invention relates to a container handling vehicle with a cantilever section and an automated storage and retrieval system comprising a plurality of the container handling vehicles, where the container handling vehicles have at least one additional storage position thereon compared to prior art container handling vehicles of the cantilever type. It is further described methods of transferring a storage container between a first and second container handling vehicle as well as transferring a storage container between a container handling vehicle and an external container carrying position. 
     BACKGROUND AND PRIOR ART 
       FIG.  1 A  discloses a typical prior art automated storage and retrieval system  1  with a framework structure  100  and  FIGS.  2  and  3 A  discloses 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/grid openings  112  in the grid cells  122  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 A  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 set 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  is shown in in  FIG.  3 A  and is 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 A , 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 A , the storage container identified as  106 ′ in  FIG.  1 A  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 is referred to as a storage cell. 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. WO2015/193278A1, the contents of which are incorporated herein by reference. 
       FIG.  3 A  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 WO2015/193278A1, 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 WO2014/090684A1. 
     The rail system  108  typically comprises rails with grooves into which the wheels of the vehicles are inserted. 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 (so-called “double tracks” which is described in relation to  FIGS.  1 B- 1 D  below). 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 A , 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 A , 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 WO2014/075937A1, 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 A  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. 
     It is a drawback with the prior art container handling vehicles of the cantilever type that they can only transport one storage container at the time. 
     One objective of the invention is to provide a container handling vehicle of the cantilever type that can transport more than one storage container at the time. 
     SUMMARY OF THE INVENTION 
     The invention is set forth in the independent claims while the dependent claims describe alternatives of the invention. 
     The invention relates to a container handling vehicle for operation on a two-dimensional rail system comprising a first set of parallel rails arranged to guide movement of container handling vehicles in a first direction X across the top of the frame structure, and a second set of parallel rails arranged perpendicular to the first set of rails to guide movement of the container handling vehicles in a second direction which is perpendicular to the first direction, the first and second sets of parallel rails dividing the rail system into a plurality of grid cells, wherein the container handling vehicle comprises:
         a wheel base unit comprising first and second sets of wheels for guiding the container handling vehicle along the rail system in the first and second directions respectively, wherein the first and second sets of wheels form outer peripheries of the wheel base unit;   a body unit comprising:
           a lower section which is provided on the wheel base unit, the lower section having a footprint with a horizontal extent which is equal to or less than the wheel base unit, the lower section having an upper surface, wherein the upper surface provides a first container carrying position for carrying a storage container;   a support section extending vertically from the lower section, the support section having a footprint with a horizontal extent which is smaller than the footprint of the lower section; and   a cantilever section extending horizontally from the support section beyond the footprint of the lower section; and   
           a lifting device comprising a lifting frame that is suspended from the cantilever section.       

     In an aspect, when a storage container is positioned on the upper surface, an uppermost part of the storage container represents a first height; and the lifting device comprises a lifting frame that is suspended from the cantilever section, the lifting frame having a lowermost part at a second height when the lifting frame is docked in an upper position adjacent the cantilever section; wherein the second height, when the lifting frame is docked in its upper position, is above the first height, such that the lowermost part of a docked lifting frame of a first container handling vehicle can pass over the uppermost part of a storage container positioned on the upper surface of a lower section of the body unit of a second container handling vehicle when the first and second container vehicles pass one another on adjacent grid cells. 
     Other robots or human operator(s) can handle/pick items stored in the storage container positioned on the first container carrying position. I.e. the storage container positioned on the first container carrying position could thus make for a useful place to hold items that need regular access. At the same time it also provides a useful counterbalance for the vehicle when it needs to pick up heavy storage containers. 
     The first container carrying position may be recessed to provide sideways support for a storage container positioned on the first container carrying position. 
     The lifting device may comprise a lifting device motor and at least two lifting shafts, and wherein the at least two lifting shafts may be arranged in the cantilever section and the lifting device motor may be arranged in the lower section, and wherein the lifting device motor and at least two lifting shafts may be connected to each other via a drive coupling. The drive coupling may comprise any necessary components to transfer rotational movement from the lifting device motor and the lifting shafts. 
     The lifting device may comprise a lifting device motor and at least two lifting shafts arranged in the cantilever section. 
     The body unit may comprise an S-shaped housing linking the lower section, the support section and the cantilever section together. The S-shape is the shape that is seen when the housing is viewed from the side. 
     The first container carrying position may comprise a conveyor for transferring a storage container between the first container carrying position and an external support. The external support may be an external conveyor. In order to ease transfer of storage containers, an upper surface of the external support is preferably at the same height as an upper surface of the conveyor on the first container carrying position. 
     A footprint of the lower section of the body unit may be displaced with respect to the footprint of the wheel base unit by substantially or equally a width of a wheel. 
     Footprint shall in this instance be understood as that the vertical projection of the lower section does not step into an adjacent grid cell when the lower section is arranged directly above a grid cell. 
     The lifting frame may be suspended on lifting bands, and the lifting frame may extend horizontally and comprise gripping devices and corner guides, where a lowermost point of the corner guides may provide the lowermost part of the lifting frame. The lifting bands are preferably electrically and/or signally conductive such that power and instructions can be provided to the gripping devices on the lifting frame. 
     It is further described an automated storage and retrieval system comprising a two-dimensional rail system comprising a first set of parallel rails arranged to guide movement of container handling vehicles in a first direction X across the top of the frame structure, and a second set of parallel rails arranged perpendicular to the first set of rails to guide movement of the container handling vehicles in a second direction Y which is perpendicular to the first direction, the first and second sets of parallel rails dividing the rail system into a plurality of grid cells, wherein the automated storage and retrieval system comprises a plurality of container handling vehicles as defined above. 
     The wheel base unit with the first and second sets of wheels may be equal to a grid cell. 
     Two container handling vehicles, which have the same orientation, may occupy only three grid cell spaces along one row when passing each other along that row. 
     The first set of rails and or the second set of rails may comprise either a single track or a double track comprising two single tracks, and a grid cell may be defined as the horizontal area occupied by a grid opening delimited by the first and second set of rails in addition to the area occupied by single tracks in the first and second directions enclosing a single grid opening. 
     The wheel base unit may have a footprint equal to a horizontal extent in the first and second directions of a grid cell. 
     The container handling vehicle may comprise a support surface, wherein the support surface may provide a second container carrying position. 
     The second container carrying position may be arranged above the first container carrying position. Preferably, the second container carrying position has the same vertical projection as the first container carrying position. If arranged on a rail system, the size of the support section is preferably equal to or less than a grid cell. As an alternative to a second container carrying position, two or more storage containers may be stacked on top of each other where all of the stacked storage containers are supported by the first container carrying position. 
     The second container carrying position may be movable between:
         a retracted position where the second container carrying position is beyond a vertical projection of the first container carrying position, and   an extended position where the second container carrying position is at or within the vertical projection of the first container carrying position.       

     The second container carrying position may be movable between the retracted position and the extended position via a pivot connection. The pivot connection may be such that:
         in the retracted position the second surface extends substantially vertically, and,   in the extended position the second surface extends substantially horizontally.       

     The pivot connection could alternatively be arranged such that the second surface could be made to flip over onto the roof of the cantilever section. For example, it could be a hinge connection along the corner edge of the back of the cantilever at the top that connects to that section, the ends of the arms then resting against the vertical surfaces of the support section. 
     The second container carrying position may be linearly movable between the retracted position and the extended position via a linear movement arrangement. If using a linear movement arrangement, the linear movement arrangement can be arranged such that:
         in the retracted position the second container carrying position is moved to a position beyond the first container carrying position and above the cantilever section, and   in the extended position the second container carrying position is above the first container carrying position.       

     The second container carrying position may be provided with a conveyor, i.e., it can self-offload the storage container at the second container carrying position independently of the storage container at the first container carrying position through use of the conveyor and some receiving infrastructure that can catch a high level container coming off the conveyor. If the first container carrying position is provided with a conveyor, any storage container at the first container carrying position may be offloaded without first having to offload the storage container positioned at the second container carrying position. If both the first and second container carrying position are provided with conveyors, any storage container positioned on the first and/or second container carrying positions can be dispatched independently of the other storage container by using the conveyor. 
     It is further described a method of transferring a storage container between a first and second container handling vehicle as defined above, the first and second container handling vehicles operating on an automated storage and retrieval system comprising a two-dimensional rail system comprising a first set of parallel rails arranged to guide movement of container handling vehicles in a first direction X across the top of the frame structure, and a second set of parallel rails arranged perpendicular to the first set of rails to guide movement of the container handling vehicles in a second direction Y which is perpendicular to the first direction, the first and second sets of parallel rails dividing the rail system into a plurality of grid cells, wherein the method comprises the steps of:
         utilizing a main control system to instruct the first and second container handling vehicles to position themselves in neighboring grid cells such that the lifting device of the first container handling vehicle is directly above the upper surface of the lower section of the second container handling vehicle;   transferring a storage container between the first container carrying position of the lower section of the second container handling vehicle and the lifting device of the first container handling vehicle. The transfer of storage container can be from the first container handling vehicle and to the second container handling vehicle, and vice versa.       

     The step of transferring a storage container between the upper surface of the lower section of the second container handling vehicle and the lifting device of the first container handling vehicle may comprise the steps of:
         setting the container handling vehicle carrying or supporting the storage container as a master vehicle;   setting the other container handling vehicle as a slave vehicle;   sending a get_bin command to the slave vehicle;   the slave vehicle performs the get_bin command and updates its internal status when the storage container is confirmed positioned on vehicle;   the slave vehicle sends a confirmation to the control system when the storage container is in the confirmed positioned on vehicle such that the storage container is sufficiently clear from the first container carrying position of the master vehicle, preferably with margin;   the master vehicle detects that the storage container is gone and it will send a bin_update status to the control system;   the control system updates the logic state to match with the physical state of the master vehicle and the slave vehicle.       

     The get_bin command may include a parameter defining a height of the storage container to be transferred such that the lifting device of the master vehicle is lowered to a position equal to an uppermost part of the storage container positioned on the first container carrying position. The height of the storage container is the distance between the lifting device in the docked upper position and to the top of the storage container. This distance may vary dependent on the height of the storage container and whether the storage container is positioned on the first container carrying position or a container carrying position at another elevation. 
     The step of setting the other container handling vehicle as a slave vehicle may include a step of sending a synchronize_to_master command to the slave vehicle such that the slave vehicle moves with and follows the master vehicle. 
     After the step of sending a synchronize_to_master command to the slave vehicle the method may further comprise a step of sending a message from the slave vehicle to the main control system when the slave vehicle moves with and follows the master vehicle. 
     It is further described a method of transferring a storage container between a container handling vehicle as defined above and an external container carrying position, the container handling vehicle operating on an automated storage and retrieval system comprising a two-dimensional rail system comprising a first set of parallel rails arranged to guide movement of container handling vehicles in a first direction X across the top of the frame structure, and a second set of parallel rails arranged perpendicular to the first set of rails to guide movement of the container handling vehicles in a second direction Y which is perpendicular to the first direction, the first and second sets of parallel rails dividing the rail system into a plurality of grid cells, wherein the method comprises the steps of:
         utilizing a conveyor on the first container carrying position of the lower section to transfer a storage container between the container handling vehicle and an external position outside the container handling vehicle.       

     The relative terms “upper”, “lower”, “below”, “above”, “higher” etc. shall be understood in their normal sense and as seen in a cartesian coordinate system. 
     In the following, numerous specific details are introduced by way of example only to provide a thorough understanding of embodiments of the claimed system and vehicle. One skilled in the relevant art, however, will recognize that these embodiments can be practiced without one or more of the specific details, or with other components, systems, etc. In other instances, well-known structures or operations are not shown, or are not described in detail, to avoid obscuring aspects of the disclosed embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Following drawings are appended to facilitate the understanding of the invention. 
         FIG.  1 A  is a perspective view of a framework structure of a prior art automated storage and retrieval system; 
         FIGS.  1 B-D  are top views of a container handling vehicle rail system, where  FIG.  1 B  shows a single track rail system,  FIG.  1 C  shows a double track rail system and  FIG.  1 D  shows a double rail system with the width and length of a container handling vehicle grid cell indicated; 
         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 A  is a perspective view of a prior art container handling vehicle having a cantilever for carrying storage containers underneath; 
         FIGS.  3 B and  3 C  show an exemplary wheel base unit for the container handling vehicle; 
         FIG.  4 A  is a simplified side-view of a container handling vehicle according to an embodiment of the invention comprising a wheel base unit and a body unit, where the body unit comprises a lower section, a support section and a cantilever section; 
         FIG.  4 B  is a perspective view of a container handling vehicle according to an embodiment of the invention where protective covers have been removed to better illustrate the setup of the components in a lower section, support section and cantilever section of a body unit of the container handling vehicle; 
         FIG.  4 C  is a top view of  FIG.  4 B ; 
         FIGS.  4 D- 4 I  are exemplary side views of different setups providing opposite rotation of the lifting shafts; 
         FIG.  5    is an example of the cantilever section of the body unit, and indicates which parts that may form part of the cantilever section; 
         FIG.  6    is a simplified side-view of a container handling vehicle according to an embodiment of the invention supporting one storage container on a first container carrying position and one storage container by the lifting device, the container handling vehicle comprising a wheel base unit and a body unit, where the body unit comprises a lower section, a support section and a cantilever section; 
         FIGS.  7 A- 7 D  show step-by-step an example method of transferring a storage container between a first and a second container handling vehicle operating on an automated storage and retrieval system comprising a two-dimensional rail system; 
         FIGS.  8 A- 8 D  show examples of a container handling vehicle according to the invention with a conveyor on the first container carrying position, where  FIG.  8 A  shows a situation when not carrying a storage container on the first container carrying position,  FIG.  8 B  shows a situation with a storage container on the first container carrying position, and  FIG.  8 C  shows a possible transfer of the storage container from the conveyor on the first container carrying position and to an external conveyor, and  FIG.  8 D  show the conveyor oriented 90 degrees relative the conveyor on  FIG.  8 A ; 
         FIG.  9    shows an example of a container handling vehicle according to the invention comprising an upper surface providing a first container carrying position and a support surface providing a second container carrying position; 
         FIG.  10 A  shows the second container carrying position  426  of  FIG.  9    in a retracted position via a pivot connection such that in the retracted position the second container carrier position is directed upwards. 
         FIG.  10 B  shows another example of a possible extended position of the second container carrier position; 
         FIG.  10 C  shows the example of  FIG.  10 B  where the second container carrier position has been pivoted 180 degrees and rests upside down on the cantilever section when in the retraced position; 
         FIGS.  11 A and  11 B  show yet another example of the second container carrier position, where, in  FIG.  11 A  the second container carrier position is in the extended position directly above the first container carrying position, and in  FIG.  11 B , the second container carrying position is moved to a retracted position by means of a linear movement arrangement; 
     
    
    
     In the drawings, like reference numerals have been used to indicate like parts, elements or features unless otherwise explicitly stated or implicitly understood from the context. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following, embodiments of the invention will be discussed in more detail by way of example only and 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 A- 1 D , 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 A . 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. 
     The rail system  108  may be a single rail (also denoted single track) system, as is shown in  FIG.  1 B . Alternatively, the rail system  108  may be a double rail (also denoted double track) system, as is shown in  FIG.  1 C , thus allowing a container handling vehicle  201  having a footprint generally corresponding to the lateral area defined by an access opening/grid column  112  to travel along a row of grid columns even if another container handling vehicle  201  is positioned above a grid column neighboring that row. Both the single and double track system, or a combination comprising a single and double track arrangement in a single rail system  108 , forms a grid pattern in the horizontal plane P comprising a plurality of rectangular and uniform grid locations or grid cells  122 , where each grid cell  122  comprises a grid opening  115  being delimited by a pair of tracks  110   a , 110   b  of the first set of rails  110  and a pair of tracks  111   a , 111   b  of the second set of rails  111 . In  FIG.  1 C  the grid cell  122  is indicated by a dashed box. For example, the sections of the rail-based system being made of aluminium are the rails, and on the upper surface of the rails, there are a pair of tracks that the wheels of the vehicle run in. However, the sections could be separate rails each with a track. 
     Consequently, tracks  110   a  and  110   b  form pairs of rails defining parallel rows of grid cells running in the X direction, and tracks  111   a  and  111   b  form pairs of rails defining parallel rows of grid cells running in the Y direction. 
     As shown in  FIG.  1 D , each grid cell  122  has a width W c  which is typically within the interval of 30 to 150 cm, and a length L c  which is typically within the interval of 50 to 200 cm. Each grid opening  115  has a width W o  and a length L o  which is typically 2 to 10 cm less than the width W c  and the length L c  of the grid cell  122 . 
     In the X and Y directions, neighboring grid cells are arranged in contact with each other such that there is no space therebetween. 
       FIG.  3 A  is a perspective view of a prior art container handling vehicle  301  having a cantilever for carrying storage containers underneath. 
     An exemplary wheel base unit for a container handling vehicle  401  according to the invention is shown in  FIGS.  3 B and  3 C . The wheel base unit  2  features a wheel arrangement  32   a , 32   b  having a first set of wheels  32   a  for movement in a first direction upon a rail system  108  and a second set of wheels  32   b  for movement in a second direction perpendicular to the first direction. Each set of wheels comprises two pairs of wheels arranged on opposite sides of the wheel base unit  2 . To change the direction in which the wheel base unit may travel upon the rail system, one of the sets of wheels  32   b  is connected to a wheel displacement assembly  7 . The wheel displacement assembly is able to lift and lower the connected set of wheels  32   b  relative to the other set of wheels  32   a  such that only the set of wheels travelling in a desired direction is in contact with the rail system. The wheel displacement assembly  7  is driven by an electric motor  8 . Further, two electric motors  4 , 4 ′, powered by a rechargeable battery  6 , are connected to the set of wheels  32   a , 32   b  to move the wheel base unit in the desired direction. 
     Further referring to  FIGS.  3 B and  3 C , the horizontal periphery of the wheel base unit  2  is dimensioned to fit within the horizontal area defined by a grid cell, such that two wheel base units  2  may pass each other on any adjacent grid cells of the rail system  108 . In other words, the wheel base unit  2  may have a footprint, i.e. an extent in the X and Y directions, which is generally equal to the horizontal area of a grid cell, i.e. the extent of a grid cell in the X and Y directions, e.g. as is described in WO2015/193278A1, the contents of which are incorporated herein by reference. 
       FIG.  4 A  is a simplified side-view of a container handling vehicle  401  according to an embodiment of the invention comprising a wheel base unit  2  and a body unit  410 , where the body unit  410  comprises a lower section  411 , a support section  412  and a cantilever section  413 . The lower section  411  having an upper surface, wherein the upper surface  425  provides a first container carrying position  425  for carrying a storage container  106 . 
     Referring to  FIGS.  3 B and  4 A , the wheel base unit  2  has a top panel/flange  9  (i.e. an upper surface) configured as a connecting interface for connection to a body unit  410  of a container handling vehicle  401 . The top panel  9  have a centre opening  20  and features multiple through-holes  10  (i.e. connecting elements) suitable for a bolt connection via corresponding through-holes in a lower section  411  of the body unit  401 . In other embodiments, the connecting elements of the top panel  9  may for instance be threaded pins for interaction with the through-holes of the lower section  411 . In yet another embodiment, the container handling vehicle  401  is not in this modular design, but rather made in one or a few pieces. The presence of a centre opening  20  is advantageous as it provides access to internal components of the wheel base unit  2 , such as the rechargeable battery  6  and an electronic control system  21 . 
     Further referring to  FIG.  4 A , the body unit  410  is disclosed as comprising an S-shaped housing linking the lower section  411 , the support section  412  and the cantilever section  413  together. The container handling vehicle  401  of  FIG.  4 A  is operable on a rail system  108  as described in connection with  FIGS.  1 A- 1 D , and comprises a wheel base unit  2  and a body unit  410 . The wheel base unit  2  comprising sets of wheels  32   a ,  32   b  for guiding the container handling vehicle  401  along the rail system  108  in the first and second directions X, Y. The body unit  410  comprising a lower section  411 , a support section  412  and a cantilever section  413 . The lower section  411  is mounted on an upper surface of the wheel base unit  2 . The lower section  411  may have a footprint with a horizontal extent which is equal to or less than the horizontal extent of one of the grid cells  122 . The top of the storage container  106  is at a first height h1. I.e. the first height h1 is the distance from the top of the rail system  108  to the top of the storage container  106  positioned on the first container carrying position on the upper surface the lower section  411  when the lower section  411  is mounted on the wheel base unit  2 . The support section  412  extends vertically from the lower section  411  and has a footprint with a horizontal extent which is smaller than the footprint of the lower section  411 . The width of the support section  412  (i.e. the extension in the X direction) may be equal to the width of the lower section  411  (in the X direction). The extension of the support section  412  in the Y direction is smaller than the extension of the lower section  411  in the Y direction. 
     Furthermore, referring to  FIG.  4 C , when seen in a plan view from above, the footprint of the support section  412  falls within the footprint of the lower section  411 . In other words, as disclosed in  FIGS.  4 A- 4 C , the support section  412  does not extend beyond the lower section  411 . The cantilever section  413  extends horizontally from the support section  412  beyond the footprint of the lower section  411  and comprises a lifting device  414  suspended from the cantilever section  413 . 
     The lifting device  414  comprising a lifting frame  415  having a lowermost part at a second height h2 when the lifting frame  415  is docked in an upper position adjacent the cantilever section  413  ( FIGS.  4 A and  4 B  show docked position of lifting frame  415 ). I.e. the second height h2 is the distance from the top of the rail system  108  to the lowermost part of the lifting frame  415 . The lifting frame  415  is suspended from the cantilever section  413  via lifting bands  419 . The lifting frame  415  may comprise gripping devices  420  extending from a lower surface thereof for connecting the lifting frame to complementary lifting holes of the storage containers  106  thereby rendering possible lifting and lowering of the storage containers  106 . In addition, the lifting frame  415  may comprise guides  421  arranged in the corners of the lower surface of the lifting frame  415  to align the gripping devices  420  of the lifting frame  415  relative the complementary lifting holes on the storage containers  106 . In many situations the guides  421  or the gripping devices  420  may constitute the lowermost part of the lifting frame  415  such that the second height h2 is the lowermost part of any of these components. However, according to an embodiment of the invention, the second height h2 of the lowermost part of the lifting frame  415 , when the lifting frame  415  is docked in its upper position, is always above the first height h1 of the storage container  106  positioned on the first container carrying position. 
     By ensuring that the lowermost part of a docked lifting frame  415  of a first container handling vehicle  401  can pass over a storage container  106  supported on the first container carrying position of a second container handling vehicle  401  when the first and second container vehicles  401  pass one another on adjacent grid cells  122 , the first and second container handling vehicles  401  can pass each other while collectively occupying fewer grid cells than required in prior art solutions. 
       FIG.  4 B  is a perspective view of a container handling vehicle  401  according to the embodiment of the invention where protective covers have been removed to better illustrate the setup of the components in the lower section  411 , the support section  412  and the cantilever section  413  constituting the body unit  410  of the container handling vehicle  401 . In the embodiment of  FIG.  4 B , the lifting device  414  is disclosed as comprising a lifting device motor  416 ′ and at least two lifting shafts  417 ′, 417 ″. The two lifting shafts  417 ′, 417 ″ are arranged in parallel in the cantilever section  413 . The lifting bands  419  connected to the lifting frame  415 , are spooled onto and off the lifting shafts  417 ′, 417 ″, thereby moving the lifting frame  416  and any storage container  106  carried by the lifting frame  415  up and down. Lifting shaft wheels  423 ′, 423 ″ are arranged on each end of the lifting shafts  417  and operate together with the lifting shafts  417 , respectively. As shown in  FIG.  4 B , the lifting device motor  416 ′ is arranged in the lower section  411 . The lifting device motor  416 ′ and the two lifting shafts  417  are connected to each other via the lifting shaft wheels  423 ′,  423 ″ and an endless flexible force transferring element  418 , such as e.g. belt, running via sheaves  422  to ensure that the first and second lifting shafts  417  rotate simultaneously in the same direction. Any necessary power source (not shown) for supplying power to the lifting device motor  416 ′ may be arranged in the lower section  413  in order to obtain a favorable center of gravity with reduced risk of tilting of the container handling vehicle in the event lifting a heavy storage container  106  and/or as a result of too high acceleration/deceleration of the container handling vehicle  401 . 
     The lifting frame  415  is shown with guides  421  arranged in the corners of the lower surface of the lifting frame  415  to align the gripping devices  420  of the lifting frame  41  relative the complementary lifting holes on the storage containers  106 . 
     Any necessary power source (not shown) for supplying power to the lifting device motor  416 ″ may be arranged in the lower section  413  in order to obtain a favorable center of gravity with reduced risk of tilting of the container handling vehicle in the event lifting a heavy storage container  106  and/or as a result of too high acceleration/deceleration of the container handling vehicle  401 . 
       FIG.  4 C  is a top view of  FIG.  4 B , showing the lower section  411 , the support section  412  and the cantilever section  413 . 
       FIGS.  4 D- 41    are examples of different setups providing opposite rotation of the lifting shafts  417 ′, 417 ″. As disclosed in all of the examples of  FIGS.  4 D- 4 I , common to all of the force transferring setups, is the presence of a rotatable lifting device motor  416 ′, a first and second lifting shaft wheel  423 ′,  423 ″ whereof each is connected for rotation with the respective lifting shafts  417 ′, 417 ″, at least one sheave  422 ′,  422 ″, a force transferring element  418  in the form of an endless belt forming a closed loop and where at least one of sheaves  422 ′, 422 ″ is arranged inside the closed loop. In addition, the first or second lifting shaft wheel  423 ′,  423 ″ is in contact with an inner surface of the endless belt  418  and the other of the first or second lifting shaft wheel  423 ′,  423 ″ is in contact with the outer surface of the endless belt  418 . This is achieved by arranging one of the first or second lifting shaft wheels  423 ′,  423 ″ inside the closed loop formed by the force transferring element  418  and the other of the first or second lifting shaft wheel  423 ′,  423 ″ outside the closed loop formed by the force transferring element  418 . The mutual setup of the first and second lifting shaft wheels  423 ′,  423 ″ (e.g., acting on opposite sides of the endless belt), the guide sheaves  422 ′,  422 ″ and the force transferring element  418 , are such that the first and second lifting shafts  417 ′,  417 ″ (via first and second lifting shaft wheels  423 ′,  423 ″, respectively) rotate in opposite directions (counter rotates). The first and second lifting shaft wheels  423 ′,  423 ″ are preferably arranged in the same horizontal plane in order to ensure horizontal stability during lifting. The sheave(s)  422 ′,  422 ″ are arranged along the travel of the force transferring element  418  at fixed positions such that they provide for a “change” in the travel direction of the force transferring element  418 . Each of the sheaves  422 ′,  422 ″ are arranged to lead the force transferring element  418  correctly onto the first and second lifting shaft wheel  423 ′,  423 ″ thereby allowing the first and second lifting shaft wheels  423 ′,  423 ″ (and thus the lifting shafts  417 ′,  417 ″) to rotate in opposite directions. 
     In the example in  FIG.  4 D , one sheave  422 ′ is shown. 
     In the examples of  FIGS.  4 E- 41   , a number of examples of force transferring setups comprising two sheaves  422 ′,  422 ″, are shown. The sheaves  422 ′,  422 ″ are arranged alternating along the path of the force transferring element  418  such that the first lifting shaft wheel  423 ′ is followed by a sheave  422 ′,  422 ″ and the second lifting shaft wheel  423 ″ is followed by a sheave  422 ′,  422 ″ in both directions of travel of the force transferring element  418 . 
     In the examples of  FIGS.  4 G,  4 H,  4 I , there are disclosed examples comprising a tightening wheel  424  for tensioning of the force transferring element  418 . The tightening wheel  424  may for example be an eccentric tensioning mechanism comprising a rotatable sheave with an axle that can be adjusted within an opening in a fixed bracket. The location of the tightening wheel  424  along the path of the force transferring element  418  is preferably at a location where the path length of the force transferring element  418  can be affected (i.e. the path of the force transferring element can be shortened or prolonged in order to further tension or reduce tension in the force transferring element). The tightening wheel  424  can be arranged inside ( FIGS.  4 G and  41   ) or outside ( FIG.  4 H ) the closed loop formed by the force transferring element  418 . 
     In the examples in  FIGS.  4 D- 4 F , a dedicated tensioning mechanism such as a tightening wheel is not shown; however, if a tensioning mechanism is required, one of the sheaves  422 ′ or  422 ″ may be a tensioning mechanism and can be replaced by a tightening wheel  424 . 
       FIG.  5    is an example of another setup of the lifting device  414 , where, in addition to the lifting shafts  417  and the lifting bands spoolable onto and off the lifting shafts  417 ′,  417 ″, also the lifting device motor  416 ″ is arranged in the cantilever section  413  of the body unit  410 . The lifting device motor(s)  416 ″ in  FIG.  5    is a brushless DC motor encircling one of the lifting shafts  417 ′,  417 ″. Synchronous operation of the lifting shafts  417 ′,  417 ″ can be obtained by a synchronization element such as a force transferring element as disclosed in  FIGS.  5 A- 5 E and  6 A- 6 H  in WO 2019/137870 A1 (Applicant: Autostore Technology AS), the contents of which are incorporated herein by reference. 
       FIG.  6    is a simplified side-view of a container handling vehicle  401  according to an embodiment of the invention supporting one storage container  106  on a first container carrying position  425  and one storage container  106  by the lifting device  415 , the container handling vehicle  401  comprising a wheel base unit  2  and a body unit, where the body unit comprises a lower section  411 , a support section  412  and a cantilever section  413 . The components of the container handling vehicle in  FIG.  6    are similar to the container handling vehicle in  FIG.  4 A . The first container carrying position  425  is preferably recessed to provide sideways support for a storage container  425  positioned on the first container carrying position  425 . 
       FIGS.  7 A- 7 D  show step-by-step an exemplary method of transferring a storage container  106  between a first and a second container handling vehicle  401  operating on an automated storage and retrieval system  1  comprising a two-dimensional rail system  108 . Referring to  FIG.  7 A , a first container handling vehicle  401  (i.e. the vehicle to the right in the figure not carrying a storage container  106 ) is positioned in a distance from the second container handling vehicle  401  (i.e. the vehicle to the left in the figure carrying a storage container  106  in the lifting device and carrying a storage container  106  on the first container carrying position  425 ). The first container handling vehicle  401  and the second container handling vehicle  4011  operate in neighboring rows on the rail system  108 . 
     In  FIG.  7 B  the first and second container handling vehicles  401  have moved closer to each other compared to the situation in  FIG.  7 A  and the lifting device  414  of the first container handling vehicle  401  is almost above the upper surface/first container carrying position  425  of the lower section  411  of the second container handling vehicle  401 . 
     In  FIG.  7 C  the first and second container handling vehicles  401  have positioned themselves in neighboring grid cells  122  such that the lifting device  414  of the first container handling vehicle  401  is directly above the upper surface/first container carrying position  425  of the lower section  411  of the second container handling vehicle  401 . 
     In  FIG.  7 D  the lifting device  414  of the first container handling vehicle  401  has been lowered down to lift the storage container  106  positioned on the first container carrying position  425  on the second container handling vehicle  401  and lifted the storage container  106  off the first container carrying position  425 . The transfer of the storage container  106  is now complete. 
     Referring to  FIGS.  7 A- 7 D , the method of transferring the storage container may comprise the steps of:
         utilizing a main control system to instruct the first and second container handling vehicles  401  to position themselves in neighboring grid cells  122  such that the lifting device  414  of the first container handling vehicle  401  is directly above the upper surface of the lower section  411  of the second container handling vehicle  401 ;   transferring a storage container  106  between the first container carrying position  425  of the lower section  411  of the second container handling vehicle  401  and the lifting device  414  of the first container handling vehicle  401 . The step of transferring a storage container  106  between the upper surface of the lower section  411  of the second container handling vehicle  401  and the lifting device  414  of the first container handling vehicle  401  may comprise the steps of:   setting the container handling vehicle  401  carrying or supporting the storage container  106  as a master vehicle;   setting the other container handling vehicle  401  as a slave vehicle;   sending a get_bin command to the slave vehicle;   the slave vehicle performs the get_bin command and updates its internal status when the storage container  106  is confirmed positioned on vehicle  401 ;   the slave vehicle sends a confirmation to the control system when the storage container is in the confirmed positioned on vehicle such that the storage container  106  is sufficiently clear from the first container carrying position  425  of the master vehicle;   the master vehicle detects that the storage container  106  is gone and it will send a bin_update status to the control system  500 ;   the control system  500  updates the logic state to match with the physical state of the master vehicle and the slave vehicle.       

     The get_bin command may include a parameter defining a height of the storage container  106  to be transferred such that the lifting device  414  of the master vehicle is lowered to a position equal to an uppermost part of the storage container positioned on the first container carrying position. 
     The step of setting the other container handling vehicle  401  as a slave vehicle may comprise the step of sending a synchronize_to_master command to the slave vehicle, such that the slave vehicle moves with and follows the master vehicle. This allows for transferring the storage container  106  between the upper surface of the lower section  411  of the second container handling vehicle  401  and the lifting device  414  of the first container handling vehicle  401  in motion. The slave vehicle may optionally send a message to the main control system when synchronization has been obtained. Alternatively, the main control system may determine that synchronization has been obtained based on positional information of the slave vehicle and the master vehicle. Synchronization has been obtained when the slave vehicle moves with and follows the master vehicle. 
     The master vehicle may send movement data, such as speed, acceleration, and position data to the slave vehicle. The slave vehicle may use the movement data to synchronize its own movements to the received movement data. The master vehicle may send the movement data via the main control system. The master vehicle may alternatively, or additionally send the movement data directly to the slave vehicle using local communication between the master vehicle and the slave vehicle. The local communication may be any suitable means of local wireless communication, such as near field communication (NFC) or infrared (IR). 
     Synchronized movement of the slave vehicle and the master vehicle may include a train-like synchronization where the slave vehicle follows behind the master vehicle, or the synchronized movement may include a parallel synchronization where the slave vehicle moves with the master vehicle side by side. 
     The automated storage and retrieval system may comprise a positioning system using multilateration techniques, such as a Time of Flight (TOF) measurement system, for determining the position of both the master vehicle and the slave vehicle. The main control system continuously receives position data from the positioning system of a position of the first container handling vehicle and position data of a position of the second container handling vehicle. The main control system may use the position data to instruct slave vehicle to move with and follow the master vehicle within a predetermined separation from the master vehicle. The movement of the master vehicle and the slave vehicle is thereby synchronized such that the step of transferring the storage container  106  between the upper surface of the lower section  411  of the second container handling vehicle  401  and the lifting device  414  of the first container handling vehicle  401  may be performed in motion. 
     The container handling vehicles may be arranged with sensors that can detect the position of the container handling vehicles on the rail system, and/or proximity sensors that detects the distance to nearby container handling vehicles. The main control system may instruct the slave vehicle to move with and follow the master vehicle within a predetermined separation from the master vehicle based on received distance data from the proximity sensor of the slave vehicle. The movement of the master vehicle and the slave vehicle is thereby synchronized such that the step of transferring the storage container  106  between the upper surface of the lower section  411  of the second container handling vehicle  401  and the lifting device  414  of the first container handling vehicle  401  may be performed in motion. 
     The container handling vehicles may be adapted to move together in physical contact with one another. The main control system may instruct the slave vehicle to move with and follow the master vehicle by first moving into physical contact of the master vehicle, and after contact continue to apply a push force on the master vehicle to maintain physical contact. The movement of the master vehicle and the slave vehicle is thereby synchronized such that the step of transferring the storage container  106  between the upper surface of the lower section  411  of the second container handling vehicle  401  and the lifting device  414  of the first container handling vehicle  401  may be performed in motion. 
       FIGS.  8 A- 8 D  show examples of a container handling vehicle  401  according to an embodiment of the invention with a conveyor  427  on the first container carrying position  425  adapted to transfer the storage container  106  backwards onto another container handling vehicle or to an external conveyor. through any of the short sides of the container handling vehicle  401 . The conveyor  427  could also have been oriented 90 degrees relative the embodiment of  FIG.  8 A  such that storage containers  106  could be transferred directly backwards onto another container handling vehicle or to an external conveyor (see  FIG.  8 D ).  FIG.  8 A  shows a situation when not carrying a storage container on the first container carrying position  425 , while  FIG.  8 B  shows a situation with a storage container  106  on the first container carrying position  425 , and  FIG.  8 C  shows a possible transfer of the storage container  106  from the conveyor  427  on the first container carrying position  425  and to an external conveyor  428 . An upper surface of the external conveyor  428  is preferably arranged at the substantially same height as an upper surface of the conveyor  427  on first container carrier position  425 . 
     Referring to  FIGS.  7 A,  7 B and  8 A  the lower section  411  has an upper surface  425  which is recessed with respect to a pair of support webs  429 , wherein the upper surface  425  provides the first container carrying position  425  for carrying a storage container  106 . The support section  412  extends vertically from the pair of support webs  429  of the lower section  411 , the support section  412  having a footprint with a horizontal extent which is smaller than the footprint of the lower section  411 . 
       FIG.  9    shows an example of a container handling vehicle  401  according to an embodiment of the invention comprising an upper surface  425  providing a first container carrying position  425  and a support surface  426  providing a second container carrying position  426 . The container handling vehicle  401  of  FIG.  9    comprises similar components as the container handling vehicle of  FIGS.  4 A and  6   , which will not be repeated herein. However, the container handling vehicle  401  in  FIG.  9    additionally comprises the second container carrying position  426 . The second container carrying position  426  is disclosed as being arranged above the first container carrying position  425 . Preferably, the first and second container carrying positions  425 ,  426  form the same vertical projection on the underlying rail system  108 . 
       FIG.  10 A  shows the second container carrying position of  FIG.  9    in a retracted position via a pivot connection  430  such that in the retracted position the second container carrier position  426  is directed upwards. The arrow A shows the direction of movement from a horizontal extended position (in  FIG.  9   ) and a vertical retracted position in  FIG.  10 A . The pivot connection  430  shows the axle of rotation of the second container carrier  426 . 
       FIG.  10 B  shows another example of a possible extended position of the second container carrier position  426 . In  FIG.  10 B  the second container carrier position  426  is in the extended horizontal position where it can receive a storage container (not shown). 
       FIG.  10 C  shows the example of  FIG.  10 B  where the second container carrier position  426  has been pivoted 180 degrees and rests upside down on the cantilever section  413  of the container handing vehicle  401  when in the retraced position. The second container carrying position  426  has been pivoted from the retracted position to the extended position around the pivot connection arrangement  430  as shown with the arrow A. 
       FIGS.  11 A and  11 B  show yet another example of the second container carrier position  426 , where, in  FIG.  11 A  the second container carrier position  426  is in the extended position directly above the first container carrying position  425 , and in  FIG.  11 B , the second container carrying position is moved linearly (as indicated with arrow A) to a retracted position by means of a linear movement arrangement (not shown). 
     Thus, referring to  FIGS.  10 A,  10 B,  10 C and  11 A and  11 B , in order to obtain access to a storage container  106  positioned on the first container carrying position  425 , the second container carrying position  426  is preferably movable between:
         a retracted position where the second container carrying position  426  is beyond a vertical projection of the first container carrying position  425 , providing access to the upper surface of the first container carrying position  425  and or the storage container  106  positioned on the first container carrying position  425 , and   an extended position where the second container carrying position  426  is at or within the vertical projection of the first container carrying position  425 . The second container carrying position  426  can be movable between the retracted position and the extended position via a pivot connection arrangement  430  ( FIGS.  10 A- 10 C )) or a linear movement arrangement ( FIGS.  11 A and  11 B ) where it is linearly movable between the retracted position and the extended position via a linear movement arrangement.       

     If using a pivot connection (see  FIGS.  10 A- 10 C ), the pivot connection  430  can be arranged such that:
         in the retracted position the second container carrying position  426  is substantially vertical, and   in the extended position the second container carrier position  426  extends substantially horizontally.       

     If using a linear movement arrangement (see  FIGS.  11 A and  11 B ), the linear movement arrangement can be arranged such that:
         in the retracted position the second container carrying position  426  is moved to a position beyond the first container carrying position  425  and above the cantilever section  413 , and   in the extended position the second container carrying position  426  is above the first container carrying position  425 .       

     In the preceding description, various aspects of an automated storage and retrieval system according to the invention have been described with reference to the illustrative embodiment. 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, are deemed to lie within the scope of the present invention as defined by the following claims. 
     
       
         
           
               
             
               
                   
               
               
                 List of reference numbers 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                  1 
                 Automated storage and retrieval system 
               
               
                  2 
                 Wheel base unit 
               
               
                  4, 4′ 
                 Electric motor 
               
               
                  6 
                 Rechargeable battery 
               
               
                  7 
                 Wheel displacement assembly 
               
               
                  8 
                 Electric motor for wheel displacement assembly 
               
               
                  9 
                 Top panel/flange 
               
               
                  10 
                 Through-holes 
               
               
                  20 
                 Centre opening 
               
               
                  21 
                 Electronic control system 
               
               
                  30 
                 Remotely operated delivery vehicle 
               
               
                 32a, 32b 
                 Wheel arrangement, first and second set of wheels 
               
               
                 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 
                 First set of parallel rails in first direction (X) 
               
               
                 110a, 110b 
                 Tracks of first set of rails 
               
               
                 111 
                 Second set of parallel rail in second direction (Y) 
               
               
                 111a, 111b 
                 Tracks of second set of rails 
               
               
                 112 
                 Access opening/grid column 
               
               
                 115 
                 Grid opening 
               
               
                 119 
                 First port column 
               
               
                 120 
                 Second port column 
               
               
                 122 
                 Grid cell 
               
               
                 201 
                 Prior art storage container vehicle 
               
               
                  201a 
                 Vehicle body of the storage container vehicle 201 
               
               
                  201b 
                 Drive means/wheel arrangement, first direction (X) 
               
               
                  201c 
                 Drive means/wheel arrangement, second direction (Y) 
               
               
                 301 
                 Prior art cantilever storage container vehicle 
               
               
                  301a 
                 Vehicle body of the storage container vehicle 301 
               
               
                  301b 
                 Drive means in first direction (X) 
               
               
                  301c 
                 Drive means in second direction (Y) 
               
               
                 304 
                 Parts of the gripping device of the container handling 
               
               
                   
                 vehicle 301 
               
               
                 401 
                 Container handling vehicle 
               
               
                 410 
                 Body unit 
               
               
                 411 
                 Lower section of body unit 
               
               
                 412 
                 Support section of body unit 
               
               
                 413 
                 Cantilever section of body unit 
               
               
                 414 
                 Lifting device 
               
               
                 415 
                 Lifting frame 
               
               
                  416′, 416″ 
                 Lifting device motor 
               
               
                  417′, 417″ 
                 Lifting shaft 
               
               
                 418 
                 Force transferring element 
               
               
                 419 
                 Lifting band 
               
               
                 420 
                 Gripping device 
               
               
                 421 
                 Guide 
               
               
                  422′, 422″ 
                 sheaves 
               
               
                  423′, 423″ 
                 Lifting shaft wheels 
               
               
                 424 
                 Tightening wheel 
               
               
                 425 
                 Upper surface/first container carrying position 
               
               
                 426 
                 Support surface/second container carrying position 
               
               
                 427 
                 Conveyor 
               
               
                 428 
                 External conveyor 
               
               
                 429 
                 Support webs 
               
               
                 430 
                 Pivot connection arrangement 
               
               
                 500 
                 Control system 
               
               
                 A 
                 Arrow showing movement direction(s) 
               
               
                 X 
                 First direction 
               
               
                 Y 
                 Second direction 
               
               
                 Z 
                 Third direction 
               
               
                 C 
                 clearance 
               
               
                 h1 
                 First height 
               
               
                 h2 
                 Second height