Patent Publication Number: US-2023144676-A1

Title: Container handling vehicle with cantilever construction and automated storage and retrieval system comprising a plurality of the container handling vehicles

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 a configuration allowing two container handling vehicles to pass each other by occupying fewer grid cells on an underlying rail system compared to prior art container handling vehicles of the cantilever-type. 
     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. 
     Each of the prior art container handling vehicles with cantilever construction (as disclosed in  FIG.  3 A ) occupies at least two grid cells on the rail system which result in that, when two of the prior art container handling vehicles pass each other on neighboring grid cells, at least four grid cells are occupied. 
     It is thus an objective of the invention to provide a container handling vehicle, and an associated storage and retrieval system, where the number of grid cells occupied by two container handling vehicles passing each other is less than in the prior art solutions. 
     In particular, it is an objective of the invention to provide a container handling vehicle with a cantilever construction that occupies fewer grid cells on the rail system when passing other container handling vehicles with a cantilever construction oriented in the same direction. 
     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 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 sets of wheels for guiding the container handling vehicle along the rail system in the first and second directions;   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 horizontal extent of one of the grid cells and a top surface which is at a first height;   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;   
           a lifting device comprising a lifting frame that is suspended from the cantilever section of the body unit, 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 of the lowermost part of the lifting frame, when the lifting frame is docked in its upper position, is above the first height of the top surface of the lower section of the body unit.       

     The fact that the second height of the lowermost part of the lifting frame, when the lifting frame is docked in its upper position, is above the first height of the top surface of the lower section of the body unit. As such, the lowermost part of a docked lifting frame of a first container handling vehicle can pass over the top 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. 
     In this way, it is possible for two container handling vehicles of the automated storage and retrieval system having the same orientation to occupy fewer grid cells when passing each other because a cantilever section of one container handling vehicle is able to pass over the lower section and wheel base unit of another container handling vehicle (with a clearance). In other words, the cantilever section of one container handling vehicle will overlap vertically with the lower section and wheel base unit of the other container handling vehicle that it is passing. 
     The vertical extension of the support section determines the difference between the first height and the second height. If the support section has a relatively large extension, the difference between the first height and the second height is relatively large. Similarly, if the support section has a relatively small extension, the difference between the first height and the second height is relatively small. In any case, the support section should be of such an extension that the two container handling vehicles can pass each other with a clearance between the lowermost part of the lifting frame and the top surface of the lower section. Such a clearance may be at least identical to an expected vertical movement of the lifting frame when docked in its upper position resulting from acceleration and deceleration of the container handling vehicle. In one example, the clearance between the two container handling vehicles may range from a few millimeters up to several centimeters. 
     A horizontal extent (in the X and Y directions) of the top surface may be the equal to, or substantially equal to, a horizontal extent of a part of the cantilever section extending horizontally beyond the support section. 
     The wheel base unit and body unit may be modules that can be attached one to the other. The body unit may be mounted on an upper surface of the wheel base unit or attached to it in some other way. Alternatively, the wheel base unit and the body unit can be formed in one piece, i.e. they may form one common unit. 
     The wheel base unit may feature a wheel arrangement having a first set of wheels for movement in a first direction upon a rail system and a second set of wheels 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. To change the direction in which the wheel base unit may travel upon the rail system, one of the sets of wheels is connected to a wheel displacement assembly. The wheel displacement assembly is able to lift and lower the connected set of wheels relative to the other set of wheels such that only the set of wheels travelling in a desired direction is in contact with the rail system. The wheel displacement assembly is driven by an electric motor. Further, two electric motors, powered by a rechargeable battery, may be connected to the set of wheels to move the wheel base unit in the desired direction. 
     The first height may be defined as the distance from the top of the rail system to the top of the top surface of the lower section when the lower section is mounted on the wheel base unit. 
     The second height may be defined as the distance from the top of the rail system to the lowermost part of the lifting frame. 
     The support section may extend for a height greater than a storage container and the difference between the second height and the first height may at least correspond to a height of a storage container in addition to a minor clearance. One advantage of this construction is that robots, i.e., container handling vehicles, can pass each other with an overlap independent of whether none, one or both is carrying a storage container. 
     The lifting device may comprise a lifting device motor and at least two lifting shafts. The at least two lifting shafts may be arranged in the cantilever section and the lifting device motor can be arranged in the lower section. The lifting device motor and at least two lifting shafts may be connected to each other via a flexible force transferring element. The force transferring element can be a belt, chain, band or another relatively flexible component able to transfer rotational movement between the lifting device motor and the lifting shafts. 
     The lifting device may further comprise a gripping device being configured to releasably grip a storage container and a power source, such as an independent rechargeable battery or the same battery used for displacement of the wheels, for driving the lifting device motor. To increase stability of the container handling vehicle, the battery may be arranged in the lower section or the wheel base unit (or both, for example, where there is some overlap between the lower section and the wheel base unit). 
     The lifting device may comprise a lifting device motor and at least two lifting shafts for raising and lowering the lifting device, wherein the lifting device motor and the at least two lifting shafts may be arranged in the cantilever section. The lifting device motor can comprise a brushless DC motor. Various types of brushless DC motors are known, including permanent magnet synchronous motor (using permanent magnets) and switched reluctance motors (does not use any permanent magnets), as described in WO 2019/137870 A1 (Applicant: Autostore Technology AS), the contents of which are incorporated herein by reference. However, the lifting device motor could comprise other forms of electric motor(s) as well. 
     The body unit may comprise an S-shaped housing linking the lower section, the support section and the cantilever section together (e.g., S-shaped when viewed from a side of the body unit). 
     In an aspect, 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. The width dimension is in an axial direction of the wheel. The lower section may be positioned to extend vertically from the outer edge of a second track of the rail system under the cantilever section and from the inner edge of a first track of the rail system on an opposite side of the lower section, when the wheel base unit has its wheels positioned over the first tracks (or tracks closest to a grid opening), for example, when the container handling vehicle is positioned for lowering/raising the lifting frame into/out of a storage column of the frame structure. A footprint is defined as an outer dimension when looking in plan view of that section. 
     The lifting frame may be suspended on lifting bands, and the lifting frame may extend horizontally and comprise gripping devices and corner guides. A lowermost point of the corner guides may provide the lowermost part of the lifting frame such that it is this point that needs to be accounted for in terms of minimum second height for passing over or above the first height of the upper surface of the lower section. 
     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 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 automated storage and retrieval system comprises a plurality of container handling vehicles as defined above. 
     Two container handling vehicles of the automated storage and retrieval system, which two container handling vehicles have the same orientation, may occupy a total of three grid cells when passing each other. 
     The two container handling vehicles, i.e. a first container handling vehicle and a second container handling vehicle, of the automated storage and retrieval system may be configured such that the lowermost part of a docked lifting frame of the first container handling vehicle can pass over the top surface of a lower section of the body unit of the second container handling vehicle when the first and second container vehicles pass one another on adjacent grid cells. This may be made possible for example by configuring a horizontal extent (in the X and Y directions) of the top surface equal to, or substantially equal to, a horizontal extent (in the X and Y directions) of a part of the cantilever section extending horizontally beyond the support section. 
     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 set of rails and second set of rails together with an area occupied by single tracks of the first and second sets of rails in the first and second directions enclosing and closest to the 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 as an underlying grid cell. In other words, the wheel base unit may have a footprint of a single grid cell. 
     At least one of the container handling vehicles may carry a storage container when passing another container handling vehicle. In an aspect, both container handling vehicles can carry a storage container (of a regular size) when passing each other. Clearance between the two container handling vehicles may range from a few millimeters up to several centimeters. 
     A lowermost point of the storage container when carried may be higher than the first height of the lower section. 
     A width of the support section in one direction may correspond to the width of a rail and/or two tracks. 
     The automated storage and retrieval system may further comprise at least one dual container handling vehicle comprising a first cantilever section arranged opposite a second cantilever section. At least a first container handling vehicle may have a first orientation and at least a second container handling vehicle may have a second orientation opposite the first orientation, and the dual container handling vehicle and the first and second container handling vehicles may occupy a total of five grid cells when simultaneously passing each other. 
     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 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 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; 
         FIGS.  6 A- 6 C  show different views of a first embodiment of two container handling vehicles passing each other, where only one of the container handling vehicles can carry a storage container during passing; 
         FIGS.  7 A- 7 C  show different views of a second embodiment of two container handling vehicles passing each other, where both of the container handling vehicles can carry a storage container during passing; 
         FIG.  7 D  shows a container handling vehicle according to the second embodiment of  FIGS.  7 A- 7 C  when not carrying a storage container; 
         FIG.  8    shows an embodiment with a dual container handling vehicle having two cantilever sections on opposite ends thereof as well as two container handling vehicles with opposite orientation relative each other such that the three container handling vehicles only occupy five cells when passing each other; 
     
    
    
     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 We 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 . 
     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  4111 . 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  and a top surface which is at a first height h 1 . I.e. the first height h 1  is the distance from the top of the rail system  108  to the top of the top surface of the lower section  411  when the lower section 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 in  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 h 2  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 h 2  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  41  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 h 2  is the lowermost part of any of these components. However, according to the invention, the second height h 2  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 h 1  of the top surface of the lower section  411  of the body unit  410 . 
     By ensuring that the lowermost part of a docked lifting frame  415  of a first container handling vehicle  401  can pass over the top surface of a lower section  411  of the body unit  410  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  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- 4 I  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- 4 I , 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  4 I ) 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. 
       FIGS.  6 A- 6 C  show different views of a first embodiment of two container handling vehicles  401  passing each other, where one of the container handling vehicles  401  is able to carry a storage container  106  when passing another container handling vehicle  401  in the same orientation. Thus, two container handling vehicles  401  can occupy fewer grid cells  122  when passing each other than with the prior art cantilever container handling vehicles because a cantilever section  413  of one is able to pass over the lower section  411  and wheel base unit  2  of the other (with a clearance). During the passing, the cantilever section  413  of one container handling vehicle will overlap vertically with the lower section  411  and wheel base unit  2  of the other container handling vehicle  401 . 
     As is seen  FIGS.  6 A- 6 C , the difference in the first height h 1  of the upper surface of the lower section  411  and the second height h 2  of the lowermost part of the lifting frame  415 , is less than the height of the storage container  106 , which results in that only the “front” container handling vehicle (i.e. the container handling vehicle to the left in the figure) can carry a storage container during passing. However, with this arrangement, during passing the container handling vehicles occupy fewer grid cells  122  than compared to the prior art cantilever vehicles, namely three grid cells  122  rather than four. A clearance c is shown between the lower section  411  of the container handling vehicle  401  to the left in  FIG.  6 C  and the lowermost part of the lifting frame  415  of the container handling vehicle  401  to the right in  FIG.  6 C . 
     The container handling vehicles  401  form part of an automated storage and retrieval system  1  comprising a rail system  108  on which the container handling vehicles  401  operate. 
     As seen in  FIG.  6 C , a footprint of the lower section  413  of the body unit  410  may be displaced with respect to the footprint of the wheel base unit  2  by substantially or equally a width of a wheel  32   a,    32   b.  The lower section  411  is positioned to extend vertically from the outer edge of the second track under the cantilever section  413  and from the inner edge of the first track on the opposite side, when the wheel base unit  2  has its wheels  32   a  positioned over the first tracks (or tracks closest to the grid opening). When two container handling vehicles  401 , which have the same orientation as shown in  FIGS.  6 A- 6 C , pass each other, they occupy a total of three grid cells  122 . 
       FIGS.  7 A- 7 C  show different views of a second embodiment of two container handling vehicles  401  passing each other, where both of the container handling vehicles  401  can carry a storage container during passing. The container handling vehicles  401  form part of an automated storage and retrieval system  1  comprising a rail system  108  on which the container handling vehicles  401  operate. 
       FIG.  7 D  shows a container handling vehicle according to the second embodiment of  FIGS.  7 A- 7 C  when not carrying a storage container. As indicated in  FIGS.  7 A- 7 D , the difference between the second height h 2  and the first height h 1  is at least corresponding to a height of a storage container  106  including a minor clearance c (see  FIG.  7 C ). 
       FIG.  8    shows an embodiment with a dual container handling vehicle  501  comprising a first cantilever section  513 ″ arranged opposite a second cantilever section  513 ′. The container handling vehicles  401  in  FIG.  8    are container handling vehicles according to the second embodiment (i.e. as disclosed in  FIGS.  7 A- 7 C  where both of the container handling vehicles  401  can carry a storage container during passing). The dual container handling vehicle  501  comprises two lifting devices as described above in relation to  FIGS.  4 A- 4 C,  5 ,  6 A- 6 C and  7 A- 7 C . As shown in  FIG.  8    a first container handling vehicle  401  has a first orientation and a second container handling vehicle  401  has a second orientation opposite the orientation of the first container handling vehicle  401 . In a prior art configuration, the dual container handling vehicle  501  and the first and second container handling vehicles  401  would occupy seven cells when passing each other, however, the container handling vehicles  401 , 501  as defined herein render possible that they occupy only five cells when passing each other. The dual container handling vehicle  501  in  FIG.  8    carries two storage containers  106 , and each of the container handling vehicles  401  carry one storage container  106  when passing. 
     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 
                 Prior art 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 
               
               
                  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 
               
               
                 500 
                 Control system 
               
               
                 501 
                 Dual container handling vehicle with two cantilever 
               
               
                   
                 sections 
               
               
                 X 
                 First direction 
               
               
                 Y 
                 Second direction 
               
               
                 Z 
                 Third direction 
               
               
                 C 
                 clearance 
               
               
                 h1 
                 First height 
               
               
                 h2 
                 Second height