Patent Publication Number: US-2023139127-A1

Title: Storage system with modular container handling vehicles

Description:
TECHNICAL FIELD 
     The present invention relates to the field automated storage systems. 
     BACKGROUND 
       FIGS.  1 A and  2 B  disclose a typical prior art automated storage and retrieval system  1  with a framework structure  100 .  FIGS.  1 B and  2 B  disclose prior art container handling vehicles  200 , 300  operating in the system  1  disclosed in  FIGS.  1 A and  2 A , respectively. 
     The framework structure  100  defines a storage grid  104  comprising a plurality of upright members  102  and optionally a plurality of horizontal members  103  supporting the upright members  102 . The members  102 ,  103  may typically be made of metal, e.g., extruded aluminum profiles. 
     The storage grid  104  comprises multiple grid columns  112 . A large majority of the grid columns are also termed storage columns  105 , in which storage containers  106 , also known as bins, are stacked one on top of another to form stacks  107 . 
     Each storage container  106  may typically hold a plurality of product items (not shown), and the product items within a storage container  106  may be identical or may be of different product types depending on the application. 
     The grid columns  112  of the storage grid  104  guard against horizontal movement of the of storage containers  106  in the stacks  107 , and guides vertical movement of the containers  106 , but does normally not otherwise support the storage containers  106  when stacked. 
     The automated storage and retrieval system  1  comprises a rail system  108  (or a top rail grid) arranged in a grid pattern across the top of the storage grid  104 , on which rail system  108  a plurality of container handling vehicles  200 , 300  (as exemplified in  FIGS.  1 B and  2 B ) 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 horizontal extent of one of the grid cells  122  constituting the grid pattern is in  FIGS.  1 A and  2 A  marked by thick lines. 
     Each grid cell  122  has a width which is typically within the interval of 30 to 150 cm, and a length which is typically within the interval of 50 to 200 cm. Each grid opening  115  has a width and a length which is typically 2 to 10 cm less than the width and the length of the grid cell  122  due to the horizontal extent of the rails  110 , 111 . 
     The rail system  108  comprises a first set of parallel rails  110  arranged to guide movement of the container handling vehicles  200 , 300  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  200 , 300  in a second direction Y which is perpendicular to the first direction X. In this way, the rail system  108  defines the upper ends of the grid columns  112  above which the container handling vehicles  200 , 300  can move laterally, i.e., in a plane which is parallel to the horizontal X-Y plane. Commonly, at least one of the sets of rails  110 , 111  is made up of dual-track rails allowing two container handling vehicles to pass each other on neighboring grid cells  122 . Dual-track rails are well-known and disclosed in for instance WO 2015/193278 A1 and WO 2015/140216 A1, the contents of which are incorporated herein by reference. Each prior art container handling vehicle  200 , 300  comprises a vehicle body and a wheel arrangement of eight wheels  201 , 301 , wherein a first set of four wheels  32   a  enable the lateral movement of the container handling vehicles  200 , 300  in the X direction and a second set of four wheels  32   b  enable the lateral movement in the Y direction. One or both sets of wheels in the wheel arrangement can be lifted and lowered, so that the first set of wheels and/or the second set of wheels can be engaged with the respective set of rails  110 ,  111  at any one time. 
     Each prior art container handling vehicle  200 , 300  also comprises a lifting device  18  (only shown in  FIG.  2 B ) for vertical transportation of storage containers  106 , e.g., raising a storage container  106  from, and lowering a storage container  106  into, a grid column  112 . The lifting device  18  comprises four metal lifting bands  16  extending in a vertical direction and connected close to the corners of a lifting frame  17  (may also be termed a gripping device) such that the lifting frame is kept horizontal. The lifting frame  17  features container connecting elements  24  for releasable connection to a storage container, and guiding pins  30 . 
     Conventionally, and also for the purpose of this application, Z=1 identifies the uppermost layer of the storage grid  104 , 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 prior art storage grid disclosed in  FIGS.  1 A and  2 A , Z=8 identifies the lowermost, bottom layer of the storage grid  104 . Consequently, as an example, and using the Cartesian coordinate system X, Y, Z indicated in  FIGS.  1 A and  2 B , the storage container identified as  106 ′ in  FIG.  1    can be said to occupy grid location or cell X=10, Y=2, Z=3. The container handling vehicles  200 , 300  can be said to travel in layer Z=0 and each grid column can be identified by its X and Y coordinates. Each container handling vehicle  200  comprises a storage compartment or space (not shown) for receiving and stowing a storage container  106  when transporting the storage container  106  across the top of the storage grid  104 . The storage space may comprise a cavity arranged centrally within the vehicle body, e.g., as is described in W02014/090684A1, the contents of which are incorporated herein by reference. Alternatively, the container handling vehicles  300  may have a cantilever construction as described in N0317366, the contents of which are also incorporated herein by reference. 
     The container handling vehicles  200  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  122 , i.e., the extent of a grid cell  122  in the X and Y directions, e.g., as is described in WO2015/193278A1, the contents of which are incorporated herein by reference. Alternatively, the container handling vehicles  200  may have a footprint which is larger than the horizontal area of a grid cell  122 , e.g., as is disclosed in W02014/090684A1. 
     In a storage grid  104 , most of the grid columns  112  are storage columns  105 , i.e., grid columns wherein storage containers  106  are stored in stacks  107 . However, a storage grid  104  normally has at least one grid column  112  which is not used for storing storage containers  106 , but is arranged at a location wherein the container handling vehicles  200 , 300  can drop off and/or pick up storage containers  106  so that they can be transported to a second location (not shown) where the storage containers  106  can be accessed from outside of the storage grid  104  or transferred out of or into the grid  104 . Within the art, such a location is normally referred to as a “port” and the grid column  112  at which the port is located may be referred to as a transfer column  119 , 120 . The drop-off and pick-up ports are the upper ends/openings of a respective transfer column  119 , 120 . 
     The prior art storage grids  104  in  FIGS.  1 A and  2 A  comprise two transfer columns  119  and  120 . The first transfer column  119  may for example comprise a dedicated drop-off port where the container handling vehicles  200 , 300  can drop off storage containers  106  to be transported through the transfer column  119  and further to e.g., a picking/stocking station, and the second transfer column  120  may comprise a dedicated pick-up port where the container handling vehicles  200 , 300  can pick up storage containers  106  that have been transported through the transfer column  120  from e.g., a picking/stocking station. A storage container may be transported through a transfer column by use of the lifting device of a container handling vehicle  200 , 300  or by use of a storage container lift arranged in the transfer column. Each of the ports of the first and second transfer column may be suitable for both pick-up and drop-off of storage containers. 
     The second location may typically be a picking/stocking station, wherein product items are removed from and/or positioned into the storage containers  106 . In a picking/stocking station, the storage containers  106  are normally never removed from the automated storage and retrieval system  1  but are returned into the storage grid  104  once accessed. 
     For monitoring and controlling the automated storage and retrieval system  1 , e.g., monitoring and controlling the location of respective storage containers  106  within the storage grid  104 ; the content of each storage container  106 ; and the movement of the container handling vehicles  200 , 300  so that a desired storage container  106  can be delivered to the desired location at the desired time without the container handling vehicles  200 , 300  colliding with each other, the automated storage and retrieval system  1  comprises a computerized control system (not shown) which typically comprises a database for keeping track of the storage containers  106 . 
     A conveyor system including conveyor belts or rollers is commonly employed to transport the storage containers from a lower end of the transfer columns  119 , 120  to e.g., a picking/stocking station. 
     A conveyor system may also be arranged to transfer storage containers between different storage grids, e.g., as is described in WO2014/075937A1, the contents of which are incorporated herein by reference. 
     Further, WO2016/198467A1, the contents of which are incorporated herein by reference, discloses an example of a prior art access system having conveyor belts (FIGS. 5a and 5b in WO2016/198467A1) and a frame mounted rail (FIGS. 6a and 6b in WO2016/198467A1) for transporting storage containers between transfer columns and stations where operators can access the storage containers. 
     When a storage container  106  stored in the storage grid  104  disclosed in  FIG.  1 A  is to be accessed, one of the container handling vehicles  200 , 300  is instructed to retrieve the target storage container  106  from its position in the storage grid  104  and transport it to or through the transfer column  119 . This operation involves moving the container handling vehicle  200 , 300  to a grid 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 lifting device (not shown), and transporting the storage container  106  to the transfer 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 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  200 , 300  that is subsequently used for transporting the target storage container  106  to the transfer column, or with one or a plurality of other cooperating container handling vehicles  200 , 300 . Alternatively, or in addition, the automated storage and retrieval system  1  may have container handling vehicles  200 , 300  specifically dedicated to the task of temporarily removing storage containers  106  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  105 . 
     When a storage container  106  is to be stored in the grid  104 , one of the container handling vehicles  200 , 300  is instructed to pick up the storage container  106  from the transfer column  120  and to transport it to a grid 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  200 , 300  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  105 . 
     The applicant is developing highly advantageous solutions for obtaining storage systems that are both more efficient and flexible than the prior art systems. A common feature of these solutions is the requirement of multiple types of storage system vehicles for moving upon a rail grid, wherein each type of vehicle is specifically designed to be effective when performing a dedicated operation, such as transport of storage container, lifting of storage containers, digging etc. An optimum performance of the different storage system vehicles may be obtained when the vehicles are designed independent of each other. However, having different types of storage system vehicles designed independently of each other may have some disadvantages related to costs in that they may require different spare parts, require different solutions for charging of the vehicle batteries, different constructions of the wheel arrangement allowing them to move upon a rail grid etc. 
     The aim of the present invention is to alleviate or mitigate at least some of the possible disadvantages related to the construction of multiple types of vehicles for moving upon a rail grid of a storage system. 
     SUMMARY 
     The present invention is defined by the appended claims and in the following. In a first aspect, the present invention provides a storage system including: a storage grid including vertical column profiles defining a plurality of grid columns, the grid columns comprise storage columns, in which storage containers can be stored one on top of another in vertical stacks, the storage grid including at least one rail grid at the upper ends of the column profiles; a first container handling vehicle and a second container handling vehicle, the first and the second container handling vehicles each including at least one wheel base unit and a first container handling module or a second container handling module, respectively, connected to the wheel base unit; each wheel base unit having a wheel arrangement for movement of the wheel base unit in two perpendicular directions upon a rail grid of the storage system and a horizontal periphery fitting within the horizontal area defined by a grid cell of the rail grid such that two wheel base units may pass each other on any adjacent grid cells of the rail grid, each of the wheel base units comprises an upper surface configured as a connecting interface for connection to any of the first and second container handling modules, and the first container handling module is a different type of container handling module to the second container handling module. 
     In other words, the first type of container handling vehicle features a container handling module different to the container handling module of the second type of container handling vehicle. 
     In other words, the second type of container handling vehicle may feature any of the container handling modules not comprised by the first type of container handling vehicle. 
     In an embodiment of the storage system, the grid columns comprise storage columns, in which storage containers can be stored one on top of another in vertical stacks, and at least one transfer column, each of the grid columns being defined by four vertically extending column profiles, and the column profiles are 
     interconnected at their upper ends by top rails forming a horizontal top rail grid of the storage grid. 
     In an embodiment of the storage system, the first and/or the second container handling vehicles can lift and lower a storage container within a grid column and/or transfer a storage container upon a rail grid. 
     Each of the first and the second container handling module may comprise a connecting interface for connection to at least one wheel base unit, the connecting interface may be arranged to connect to the upper surface of a wheel base unit. 
     In an embodiment of the storage system, the connecting interface of the wheel base unit comprises a horizontal top panel featuring multiple connecting elements. The top panel may comprise a center opening, i.e., such that the top panel forms a flange extending inwards from the periphery of the wheel base unit. 
     The connecting elements of the top panel/flange may be through-holes or bolts arranged to interact with corresponding bolts or through-holes of the connecting interface of the container handling modules. In an embodiment, the connecting interface of both the wheel base unit and the container handling modules comprises corresponding through-holes and the wheel base unit is connected to a container handling module by bolts. 
     In an embodiment of the storage system, each of the first and the second container handling module comprises a connecting interface for connection to the connecting interface of the wheel base unit. 
     In an embodiment of the storage system, the connecting interface of the first and the second container handling module comprises connecting elements arranged at positions corresponding to the multiple connecting elements of the top panel/flange. 
     In an embodiment of the storage system, the top panel/flange features a center opening allowing access to internal components of the wheel base unit. The internal components may include electric motors for driving the wheel arrangement, a rechargeable battery and electronic control systems. Access to the rechargeable battery and the electronic control system allows them to be easily connected to a container handling module connected to the wheel base unit. 
     In an embodiment of the storage system, one of the first and the second container handling modules includes a cantilever section having a lifting device, wherein the container handling module is connected to a single wheel base unit and the lifting device is arranged to raise and lower a storage container within a grid column positioned below the cantilever section. 
     In an embodiment of the storage system, one of the first and the second container handling modules includes a bridge section to which at least one lifting device is connected, wherein the container handling module is connected to two separate wheel base units, such that the bridge section is supported by a wheel base unit at each of two opposite ends and the lifting device is arranged to raise and lower a storage container within a grid column positioned below the bridge section. 
     In an embodiment of the storage system, one of the first and the second container handling modules includes a storage container carrier, wherein the container handling module is connected to a single wheel base unit, such that a storage container may be supported on top of the wheel base unit. 
     In an embodiment of the storage system, one of the first and the second container handling modules includes a storage container carrier, wherein the container handling module is connected to a single wheel base unit, the storage container carrier including a conveyor unit, such that a storage container may be supported on top of the wheel base unit and moved in a lateral direction when the conveyor unit is activated. 
     In an embodiment of the storage system, the first or the second container handling vehicle includes two wheel base units and only one of the wheel base units includes electric motors for driving the wheel arrangement. 
     In an embodiment of the storage system, the first container handling vehicle includes a lifting device arranged to raise and lower a storage container within a grid column. 
     In an embodiment of the storage system, the first container handling vehicle includes a cantilever section and a lifting device, the lifting device is arranged to raise and lower a storage container within a grid column positioned below the cantilever section and comprises a lifting shaft, a motor for rotating the lifting shaft, a lifting frame for releasably connecting a storage container, and lifting bands connecting the lifting shaft to the lifting frame. 
     The cantilever section may extend beyond a horizontal periphery of the wheel base unit. The cantilever section may extend over a grid cell being adjacent to the grid cell occupied by the wheel base unit. The lifting frame may be suspended from the cantilever section. 
     In an embodiment of the storage system, the second container handling vehicle includes a container carrier connected to a single wheel base unit, such that a storage container may be supported on top of the wheel base unit. 
     In an embodiment, the storage system includes a transfer rail grid being separate from the rail grid at the upper ends of the column profiles, where the transfer rail grid includes rails upon which the wheel base unit may move in two perpendicular horizontal directions. 
     In an embodiment of the storage system, the transfer rail grid is arranged at a level below the level of the rail grid at the upper ends of the column profiles. 
     In an embodiment of the storage system, the transfer rail grid includes a section arranged below a transfer column of the storage grid structure, such that the first and/or the second container handling vehicle may raise or lower a storage container between the rail grid at the upper ends of the column profiles and a first and/or second container handling vehicle arranged on the transfer rail grid below the transfer column. 
     The horizontal periphery of the wheel base unit may fit within the horizontal area defined by a grid cell of any of the rail grid at the upper ends of the column profiles and the transfer rail grid. 
     In a second aspect, the present invention provides a wheel base unit for a storage system according to the first aspect, including a connecting interface for connection to the first or second container handling module, the connecting interface arranged at a topside of the wheel base unit and including a top plate having multiple through-holes and a center opening. 
     In an embodiment of the wheel base unit, the center opening allows access to at least one of a rechargeable battery and an electronic control system of the wheel base unit. 
     In an embodiment of the wheel base unit, the wheel arrangement includes a first set of wheels for movement in a first direction upon a rail grid and a second set of wheels for movement in a second direction perpendicular to the first direction, and each set of wheels includes two pairs of wheels arranged on opposite sides of the wheel base unit. 
     In a third aspect, the present invention provides a container handling vehicle for a storage system according to the first aspect, including at least one wheel base unit and a container handling module having a cantilever section including a lifting device, where the container handling module is connected to a single wheel base unit. 
     The lifting device of the container handling vehicle is arranged to raise/lower a storage container and includes a lifting frame for releasably connecting to a storage container, and optionally lifting bands/wires connecting the lifting frame to a lifting shaft on which the lifting bands/wires may be spooled. 
     In an embodiment, the container handling vehicle includes a bridge section to which at least one lifting device is connected and two wheel base units, the bridge section is connected to one of the wheel base units at each of two opposite ends of the bridge section and the lifting device is arranged between the wheel base units. 
     In a fourth aspect, the present invention provides a modular container handling vehicle system for a storage system according to the first aspect, including at least one wheel base unit and at least a first and a second type of container handling module, where the wheel base unit comprises a wheel arrangement for movement of the wheel base unit in two perpendicular directions upon a rail grid and an upper surface configured as a connecting interface for connection to any of the first and second container handling modules. 
     In an embodiment of the modular container handling vehicle system, the first and the second type of container handling module are selected from a container handling module including: a cantilever section having a lifting device, wherein the container handling module is connectable to a single wheel base unit and the lifting device is for raising and lowering a storage container positioned below the cantilever section; a bridge section to which at least one lifting device is connected, wherein the bridge section is connectable to two wheel base units, such that the bridge section is supported by a wheel base unit at each of two opposite ends and the lifting device is for raising and lowering a storage container positioned below the bridge section; a storage container carrier connectable to a single wheel base unit, such that a storage container may be supported on top of the wheel base unit; or a storage container carrier connectable to a single wheel base unit, the storage container carrier including a conveyor unit, such that a storage container may be supported on top of the wheel base unit and moved in a lateral direction when the conveyor unit is activated. 
     In an embodiment of the modular container handling vehicle system, one of the first and the second type of container handling modules is selected from a container handling module including a cantilever section having a lifting device, and the lifting device is arranged to raise and lower a storage container positioned below the cantilever section and includes a lifting shaft, a motor for rotating the lifting shaft, a lifting frame for releasably connecting the storage container and lifting bands connecting the lifting shaft to the lifting frame. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Certain embodiments of the present invention will now be described in detail by way of example only and with reference to the following drawings: 
         FIGS.  1 A and  1 B  show a perspective side view of a prior art storage system and a prior art container handling vehicle. 
         FIGS.  2 A and  2 B  show a perspective side view of a prior art storage system and a prior art container handling vehicle. 
         FIG.  3    is a perspective side view of a novel storage system. 
         FIG.  4    is a perspective view of a novel container handling vehicle. 
         FIG.  5    is a perspective side view of an exemplary embodiment of a storage system according to the invention. 
         FIGS.  6 - 11    are perspective views of an exemplary embodiment of a wheel base unit according to the invention. 
         FIG.  12    is a perspective view of a modular vehicle system according to the invention. 
         FIGS.  13 - 21    are perspective views of exemplary container handling vehicles according to the invention. embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The applicant is developing highly advantageous solutions for obtaining storage systems that are both more efficient and flexible than the prior art systems. A common feature of these solutions is the requirement of multiple types of storage system vehicles for moving upon a rail grid, wherein each type of vehicle is specifically designed to be effective when performing a dedicated operation, such as transport of storage container, lifting of storage containers, digging etc. An optimum performance of the different storage system vehicles may be obtained when the vehicles are designed independent of each other. However, having different types of storage system vehicles designed independently of each other may have some disadvantages related to costs in that they may require different spare parts, require different solutions for charging of the vehicle batteries, different constructions of the wheel arrangement allowing them to move upon a rail grid. 
     An embodiment of a storage system being developed by the applicant is disclosed in  FIG.  3   . Similar to the prior art storage systems in  FIGS.  1  and  2   , the storage grid structure  104  is made up of multiple vertical column profiles  102  upon which a top rail grid  108  is arranged. The storage grid structure provides multiple storage columns  105  in which storage containers  106  may be stacked on top of each other. 
     A container handling vehicle  300  is arranged to move in two perpendicular directions upon the top rail grid  108  and features a lifting device to raise and/or lower storage container out of or into the storage columns, see description in the background section. In addition to the features known from the prior art, the storage system in  FIG.  3    comprises a transfer rail grid  5  upon which a container transfer vehicle may move in two perpendicular directions. The transfer rail grid  5  features a section arranged below a transfer column  119 , 120  such that the container handling vehicle may lower a storage container to, or retrieve a storage container from, a container transfer vehicle  400  positioned below the transfer column. Further details of the storage system in  FIG.  3    is described in the Norwegian patent applications N020181039 and N020181005, the contents of which is incorporated by reference. 
     Another container handling vehicle  500  being developed by the applicant is shown in  FIG.  4   . The vehicle is somewhat similar to the prior art container handling vehicle  200  in  FIG.  1 B  in that it features a cavity  25  in which a storage container  106  may be accommodated. However, in addition to a lifting device including a lifting frame  17 , the vehicle in  FIG.  4    comprises a guide shuttle  19  which allows the vehicle to lift a storage container a substantially increased height compared to the prior art vehicles. 
     Although providing several advantages in obtaining more efficient storage systems, the requirement of having container vehicles  300 , 400 , 500  of different designs may also increase the cost of such storage systems. 
     To alleviate some of the costs and potential disadvantages of a storage system requiring multiple types container vehicles, the applicant has developed a new storage system in which the various container vehicles comprises a common type of wheel base unit. By having a common type of wheel base unit, many service intensive parts are the same over the whole range of container vehicles and the production of different container vehicles are more standardized. 
     An exemplary embodiment of an inventive storage system is shown in  FIG.  5   . To better illustrate the present invention, the specific embodiment comprises five different container vehicles, each featuring the same type of wheel base unit  2 . Each of the different container vehicles features different container handling modules connected to the respective wheel base unit(s)  2  to obtain the required specialized function. 
     The storage grid structure  104  comprises the same features as the storage grid structure in  FIG.  3   . 
     An exemplary wheel base unit is shown in  FIGS.  6 - 11   . 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 grid (i.e., any of the top rail grid  108  and the transfer rail grid  5 ) 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 grid, 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 grid. 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. 
     The horizontal periphery of the wheel base unit  2  is dimensioned to fit within the horizontal area defined by a grid cell  122 , see  FIGS.  1 - 3   , of the rail grid such that two wheel base units may pass each other on any adjacent grid cells of the rail grid. 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  122 , i.e., the extent of a grid cell  122  in the X and Y directions, e.g., as is described in WO2015/193278A1, the contents of which are incorporated herein by reference. 
     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 connecting interface of a selected container handling module. The top panel  9  have a center opening  20  and features multiple through-holes  10  (i.e., connecting elements) suitable for a bolt  11  connection via corresponding through-holes  10 ′ in the connecting interface of a container handling module, see  FIG.  19    for connection between a wheel base unit  2  and a container handling module featuring a cantilever section. 
     In other embodiments, the connecting elements of the top panel  9  may for instance be threaded pins for interaction with the through-holes  10 ′ of the connecting interface of the container handling module, or vice versa. The presence of a center opening  20  is highly advantageous as it provides access to internal components of the wheel base unit, such as the rechargeable battery  6  and an electronic control system  21 . The access allows the rechargeable battery  6  and the electronic control system  21  to be easily connected to a container handling module connected to the wheel base unit, thus the container handling module is not required to have its own dedicated power source and/or control system. 
     Three different types of container vehicles  300 ′,  500 ′,  600 ′ are arranged on the top rail grid  108 . Two different types of container handling vehicles  400 ′, 400 ″ are arranged on the transfer rail grid  5 . 
     The first type of container vehicle  600 ′ is adapted to lift/lower several storage containers at the same time and is particularly suited for digging operations upon the top rail grid. In this embodiment, the container vehicle  600 ′ comprises four lifting devices having a lifting frame  17 , each able to lift a separate storage container. Commonly, the first type of container vehicle  600 ′ will comprise two, three or four lifting devices. The first type of container vehicle comprises two wheel base units  2  positioned at opposite ends of the container vehicle  600 ′. The wheel base units  2  are interconnected by a container handling module including a bridge section  3  to which the four lifting devices are connected. When a container vehicle comprises two wheel base units  2 , one of the wheel base units  2  may be used without electric motors  4 , 4 ′ driving the set of wheels  32   a ,  32   b . A prior art container vehicle adapted for lifting multiple storage containers and being suitable for digging operations is disclosed in WO 2019/101366 A1. 
     The second type of container vehicle  300 ′ is adapted to perform the same functions as the prior art vehicle  300  described above. Details of the second type of container vehicle  300 ′ is shown in  FIGS.  16 - 19   . The container handling module of the second type of container vehicle  300 ′ comprises a cantilever section  12  featuring a lifting device arranged to raise and lower a storage container within a storage or transfer column positioned below the cantilever section (i.e., a container handling module). The lifting device comprises a lifting shaft  22  and a motor  23  for rotating the lifting shaft  22 , a lifting frame  17  for releasably connecting a storage container and lifting bands  16  connecting the lifting shaft to the lifting frame. 
     The third type of container vehicle  500 ′ is similar to the container handling vehicle  500  shown in  FIG.  4   . A detailed view of the third type of container vehicle  500 ′ is shown in  FIGS.  20  and  21   . The container vehicle  500 ′ comprises two wheel base units  2  arranged on opposite sides of a bridge section  3 ′ (i.e., a container handling module). The bridge section features a lifting device including a lifting frame  17 , a guide shuttle  19 , a lifting shaft  22 ′ upon which wires or lifting bands (not shown) connected to the lifting frame or guide shuttle may be spooled, and a lift motor  23 ′ for driving the lifting shaft. Further, the bridge section  3 ′ features a connecting interface (not shown but comprises through-holes as shown in  FIG.  19   ) on each of its opposite sides, each of the connecting interfaces connected to the connecting interface (i.e., top plate/flange  9 ) of a corresponding wheel base unit  2 . The guide shuttle is arranged to interact with the vertical column profiles  102  of a storage grid structure  104  and prevent detrimental tilting of the lifting frame  17 , and any storage container  106  connected thereto, when the lifting frame  17  is raised/lowered inside a transfer column  119 , 120 . 
     The fourth  400 ′ and fifth  400 ″ type of container vehicle are arranged to travel upon the transfer rail grid  5 . Detailed views of the container vehicles  400 ′,  400 ″ are shown in  FIGS.  13 - 15   . Both container vehicles comprise a single wheel base unit  2  and a storage container carrier  13 , 14  (i.e., a container handling module) suitable for supporting a storage container  106 . Each of the storage container carriers  13 , 14  comprises a connecting interface suitable for connecting to the top plate/flange  9  (i.e., connecting interface) of the wheel base unit  2 . The container handling module  13  of the fourth type of container handling vehicle  400 ′ comprises an open top box-shaped container receiver in which a storage container  106  may be accommodated. The container handling module  14  of the fifth type of container handling vehicle  400 ″ comprises a roller conveyor  15  upon which a storage container  106  may be accommodated. By use of the roller conveyor  15 , a storage container  106  may be transferred onto or off the container handling vehicle  400 ″ in a lateral direction.