Grid Framework Structure

Abstract

A grid framework structure for supporting a load handling device operative comprising a track system formed from horizontal members 52 which define a grid of cells, upright supports 54 to create stora

Description

Technical Field The present disclosure relates to the field of a storage and retrieval system for handling storage containers stacked in a grid framework structure, more particularly to a modular grid framework structure with a track system for supporting load handling devices, for use in a storage and retrieval system. Background Every storage and retrieval system is different, and can vary depending on the available space, the shape and size and footprint and height of the building in which the system is housed, the type and quantity of goods handled, the required storage capacity, any requirements for different temperatures, and other factors. Since the requirements are different for each system, grid framework structures tend to be bespoke designs with a different size, shape, and arrangement for each site. The process of designing, manufacturing, and assembling a bespoke grid framework structure can be time-consuming and expensive. Manufacturing the parts can be expensive as well as providing logistical challenges, if different components need to be manufactured at different sites, from different suppliers, and using specialist tooling. When a grid framework structure is assembled, the components must be aligned in order to ensure smooth motion of load handling devices on top of the track system; ideally the track system should be level, extending in a horizontal plane. Also the components underneath the track system must be aligned, for example upright supports supporting the track system should be vertical, in order to ensure smooth lifting / lowering of the storage containers. The process of assembling, aligning, and checking the many different components can be time-consuming and expensive. This disclosure provides a grid framework structure that is cheaper, more flexible, easier to manufacture, and easier and faster to assemble. Summary 03 03 25 A grid framework structure is provided for supporting a load handling device operative thereupon, the grid framework structure comprising: a track system comprising a plurality of horizontal members arranged in a grid pattern comprising a plurality 5 of grid cells and extending in a substantially horizontal plane, the horizontal members comprising tracks for guiding the load handling device on the track system; a plurality of upright supports each comprising one or more upright members, the upright supports supporting the track system above the ground to create a storage space comprising a plurality of storage columns, each storage column being arranged to store a stack of storage containers, such that, in use, the 10 load handling device operative on the track system is able to lift one or more storage containers through a grid cell from a stack in a storage column; a plurality of connectors configmed to connect the plurality of upright members and the plurality of horizontal members together to form the grid framework structure, wherein each of the plurality of connectors comprises two or more connector portions, each of the two or more connector portions having a 15 profile that enables the connector portion to connect to any one of the plurality of horizontal members and the plurality of upright members; and one or more vertically extending guides configured to guide a comer of a storage container in a vertical direction within a storage column when the storage container is lifted or lowered by the load handling device operative on the track system, each guide defining a comer of one of the plurality of storage columns, 20 wherein each guide is supported by one of the plurality of connectors. The advantage of each of the plurality of connectors being connectable to any of the plurality of horizontal members and the plurality of upright members is that the grid framework structure is much easier and faster to assemble. The connectors are essentially interchangeable, as are the horizontal members and the upright members. The interconnections between the connectors and the upright members, and between the 25 connectors and vertical members, are the same. The part count is much lower, and there is no need for a detailed assembly manual requiring identification and arrangement of a large number of different parts, since all parts are interchangeable. This has the advantage of fast and easy assembly. Each of the plurality of connectors may comprise two or more connector portions, each of the two or more connector portions having a profile that enables the connector portion to connect to any one of the plurality 30 of horizontal members and the plurality of upright members. This simple and interchangeable system allows any connector portion of any connector to connect with any upright member, and allows any connector portion to connect with any horizontal member. Interchangeable connections have the advantage of ease of assembly, and provide a grid framework structure with low cost, complexity, and part count. The system is easy to assemble because the connections between the connector portions and the horizontal members and the upright members are interchangeable: any connector portion can be used with any horizontal member, and any connector portion can be used with any upright member. There is no need for detailed assembly instructions to ensure that the correct connector in the correct orientation is assembled with the correct horizontal member(s) and / or the correct upright member(s), since all of the parts are interchangeable. Also, different kinds of connectors for connecting different numbers of horizontal members and / or upright members will have a similar design, with similar connector portions but in different arrangements / orientations. This commonality of design reduces costs during design, testing, and manufacture. The connector portions of the connectors fix the relative positions and orientations of connected horizontal members and upright members. Horizontal members and upright members are able to be assembled together with little or no adjustments to the alignment. The plurality of horizontal members and the plurality of upright members may be tubular, and the interior and / or exterior cross sectional profile of the plurality of horizontal members and the plurality of upright members may be substantially the same. An advantage of the horizontal members and the upright members being tubular, i.e. having a hollow cross section, is a high strength to weight ratio, giving good resistance to applied forces (for example, bending) without being too heavy. As well as the benefit of reduced material costs, lightness is advantageous because lighter parts are easier to transport, easier to handle, and easier to assemble. An advantage of the interior and / or exterior cross sectional profile of the upright members and the horizontal members being the same is that the design and manufacture of the parts is simplified; the same or similar tooling can be used to manufacture different parts. Different layouts and different shapes of grid framework structure can be constructed from the same set of parts, rather than needing a bespoke design for a grid framework structure to fit inside and suit the available space. Constraints imposed by the building can more easily be accommodated, for example it is possible to build a grid framework structure around pillars supporting the ceiling of the building. Another advantage is the ability to scale storage capacity incrementally, giving the opportunity to stagger capital investment over time and / or to respond to changing market demands. In some examples the plurality of upright members are interconnected at their top ends by a first set of horizontal members extending in a first direction, and a second set of horizontal members extending in a second direction, the second set of horizontal members running transversely to the first set of horizontal members in a substantially horizontal plane to form a grid comprising a plurality of grid cells or grid spaces. That is, the plurality of horizontal members comprises a first set of horizontal members and a second set of horizontal members, the first set extending in a direction perpendicular to the direction of the second set. The interior and / or exterior cross sectional profile of each of the plurality of horizontal members and each of the plurality of upright members may be a square cross-section. In particular a square and hollow cross section has the advantage of high strength and low weight, giving better resistance to bending than other cross section shapes, for example I-beams and C-beams and L-beams. A square exterior cross section provides a flat surface on the top, which is advantageous when the horizontal members are used as tracks or have separate track sections fitted on top. The plurality of horizontal members and the plurality of upright members may be manufactured by extrusion. Extrusion is particularly suitable for parts that have a constant cross section, and in cases where both the interior and the exterior cross sectional profile is the same for both upright members and horizontal members, it is easy to manufacture different lengths using the same tooling. Extrusion is a simple and widely available industrial process, which in most cases will allow the horizontal members and upright members to be manufactured either onsite or very close to the site where the grid framework structure will be located, hence reducing the cost, logistical burden, and carbon emissions required to transport parts from the place of manufacture to the place of assembly. The plurality of horizontal members and the plurality of upright members may comprise steel or be made of steel. Steel is a strong material, relatively inexpensive, and widely available. In cases where the interior cross sectional profile of the plurality of horizontal members and the plurality of upright members are substantially the same, each of the two or more connector portions of each of the plurality of connectors may be insertable into any one of the plurality of horizontal members and the plurality of upright members. The interior cross section of the horizontal members and upright members complements the exterior cross section of the connector portions of the connectors, thus permitting a connector portion to be inserted into a horizontal member or upright member. An advantage of this arrangement is that the interior cross sectional profile serves two different purposes: to provide a high strength-to-weight ratio for the horizontal members and upright members, and to provide a means of connecting the horizontal members and upright members to the connector portions of the connectors. Each of the two or more connector portions of each of the plurality of connectors may be tapered in order to facilitate insertion of the connector portion into any one of the plurality of horizontal members and the plurality of upright members. This has the advantage of making assembly easier and faster, since the connector portion does not have to be perfectly aligned with the horizontal member or upright member in order to assemble the two parts together. In cases where the exterior cross sectional profile of the plurality of horizontal members and the plurality of upright members are substantially the same, and each of the plurality of horizontal members and the plurality of upright members may be insertable into any one of the two or more connector portions of each of the plurality of connectors. The exterior cross section of the horizontal members and upright members complements the interior cross section of the connector portions of the connectors, thus permitting a horizontal member or upright member to be inserted into a connector portion. An advantage of this arrangement is that the connector portions are hollow, therefore saving on material costs. Each of the plurality of horizontal members and the plurality of upright members may comprise an I-beam having two flanges connected by a web. I-beams have the advantage of being strong, lightweight, and inexpensive. An I-beam has less material than a square tube of the same outer dimensions, so helps to reduce material costs and weight even further. Each of the connector portions may comprise protrusions spaced apart forming a slot for receiving the web of the I-beam such that the two flanges partially overlap the protrusions. This arrangement supports the ends of the I-beams and secures the I-beams in place. The protrusions may be connected to the two flanges and / or the web of I-beam by means of one or more fasteners. The one or more fasteners (for example, bolts, screws, or pins) help to secure the horizontal members and / or the upright members to the connectors. At least one of the plurality of upright supports may comprise at least two of the plurality of upright members connected together by at least one of the plurality of connectors. For example, two upright members can be connected together end-to-end by one connector to form an upright support of approximately double the height of a single upright member. For example, three upright members can be connected together end-to-end by two connectors to form an upright support of approximately three times the height of a single upright member. Any number of upright members can be connected together to form an upright support. An advantage of this arrangement is that a grid framework structure can be built that is taller than the length of one upright member. Shorter upright members are easier to manufacture, easier to handle (less heavy and less cumbersome), easier to store, and easier to transport. At least one of the plurality of connectors may comprise two connector portions extending in opposite directions configured to connect two of the plurality of upright members end-to-end to form an upright support. The connector enables the length of the upright supports to be divided into two or more parts, which has the advantage of ease of assembly / storage / transport, as discussed above. These connectors will be positioned at different heights in the grid framework structure. Two or more neighbouring upright supports may be braced together via a bracing member connected to their respective connectors. The connectors of the two or more neighbouring upright supports may further comprise at least one further connector portion extending in a direction perpendicular to the two connector portions, each of the at least one further connector portion being configured to connect the bracing member. The further connector portion(s) allows bracing member(s) to connect in order to further strengthen the grid framework structure. Bracing provides additional strength and support to the grid framework structure. Bracing between neighbouring or adjacent uprights will not encroach on the storage columns, and thus will not be an obstruction for the stacks of storage containers within the grid framework structure. Bracing therefore enables the grid framework structure to be strengthened without losing any available storage space. The connector portions of the connectors may extend in perpendicular directions. To ensure that the upright members and horizontal members can be assembled together, it is essential that the shape of the grid framework structure in an assembly is substantially regular. Typically, the shape of the grid framework structure is a cuboid, such that multiple cuboidal shaped substructures can be assembled together in any form to create different arrangements of the grid framework structure. The cuboidal shape of the grid framework structure is largely controlled by the orientation of the horizontal members and upright members extending in horizontal and vertical directions. If any one of the horizontal members and upright members is not regular in size or in orientation, this is reflected in the connection between adjacent horizontal members and upright members in the assembly. For a regular cuboidal shape, it is essential that the angle between the horizontal members and upright members is substantially 90°, i.e. the support elements extend along the Cartesian coordinates in three dimensions. The connector portions of the connectors extending in perpendicular directions helps to control the orientation of the horizontal members and upright members, and keep the grid framework structure substantially regular. At least one of the plurality of connectors may be a four-way planar connector comprising four connector portions arranged perpendicularly to one another in a cross shape in the same plane, configured to connect four of the plurality of horizontal members at a node of the track system. The four-way connectors connect the horizontal members together to form the grid pattern of the track system, at the top of the grid framework structure. For example, a rectangular grid cell in the middle area of the track system can be formed from four horizontal members arranged in a rectangle, with one four-way planar connector at each of the four corners of the rectangular grid cell. The perpendicular arrangement of the connector portions ensures that the horizontal members are perpendicular, and keeps the horizontal members aligned so that the track system is planar and the grid cells are rectangular, in order to support load handling devices on the track system. At least one of the plurality of connectors may be a five-way connector comprising four connector portions arranged perpendicularly to one another in a cross shape in the same plane, and a fifth connector portion extending in a direction perpendicular to the plane of the four connector portions, configured to connect four of the plurality of horizontal members and one of the plurality of upright members at a node of the track system. The five-way connectors are similar to the four-way planar connectors, with the addition of the fifth connector portion extending downwards to connect to an upright member. The middle area of the track system can use a combination of five-way connectors at nodes that are supported by an upright member, and four-way planar connectors at nodes that are not supported by an upright member. This arrangement permits the track system to be supported by upright members at a subset of the nodes of the track system rather than at every node, therefore reducing the number of upright members needed. A reduced number of upright members results in lower costs, fewer parts, less weight, and faster and easier assembly. At least one of the plurality of connectors may be a three-way connector comprising three connector portions extending in three perpendicular directions, configured to connect two of the plurality of horizontal members and one of the plurality of upright members at a node at the corner of the track system. For example, a square or rectangular track system may have four three-way connectors, one at each of the four corners of the track system, to connect the comer of the track system to an upright member supporting the comer of the track system. At least one of the plurality of connectors may be a four-way connector comprising three connector portions arranged perpendicularly to one another in the same plane, and a fourth connector portion extending in a direction perpendicular to the plane of the three connector portions, configured to connect three of the plurality of horizontal members and one of the plurality of upright members at a node along an edge of the track system. A rectangular grid framework structure with a rectangular track system may therefore have four three-way connectors at each of the four corners, four-way connectors along the edges of the track system, and a combination of four-way planar connectors and five-way connectors in the middle of the track system. This is an example only, and other configurations and combinations of connectors can also be applied. Each of the plurality of horizontal members may be fastened to a respective connector portion by a fastener passing through an opening in the horizontal member and a corresponding opening in the connector portion, and the opening of at least one horizontal member and / or the opening of the respective connector portion may be elongated such that when the connector portion is fastened to the horizontal member, relative horizontal movement is permitted between the horizontal member and the connector portion. An advantage of this arrangement is allowing for thermal expansion in the track system, i.e. if changes in temperature cause the horizontal members to expand or contract, instead of the horizontal members buckling or breaking, the horizontal members can move relative to one another to allow for the expansion or contraction. Relative movement can be permitted in both horizontal directions (e.g. in the first direction and in the second direction). The upper surface of each of the plurality of horizontal members may be a track configured to support one or more load handling devices running on the track. In this example the track is the top surface of the horizontal members, and the load handling devices run on the track, i.e. directly on the upper surface of the horizontal members. This has the advantage of reducing the cost, complexity, and part count of the grid framework structure, since there is no need for separate track elements. The grid framework structure may further comprise a plurality of track dividers, each configured to divide the upper surface into two parallel tracks. The track divider enables two load handling devices to pass each other on the two parallel tracks. The track dividers enable load handling devices to occupy adjacent grid cells on the track system, so that the wheels of two load handling devices occupy the two parallel tracks on the upper surface of the same horizontal member, divided by the track divider. The plurality of track dividers may be removably attached to the plurality of horizontal members. For example, each track divider may comprise a plurality of tabs, each horizontal member may comprise a plurality of slots on the upper surface, and the tabs of the track divider may be configured to be inserted into the slots of the horizontal member in order to releasably attach the track divider to the horizontal member. Removable attachment via slots and tabs has the advantage that the track divider is easy to assemble, and no special tooling is required. The track divider may be made of silicone rubber, or another deformable material. The tabs may deform just enough to enable the tabs to be inserted into the slots, and then return to their original shape in order to lock the tabs in position. The track system may further comprise a plurality of track elements removably attached to the plurality of horizontal members, the plurality of track elements being configured to support one or more load handling devices running on the track system. For example, the plurality of track elements may be configured to be attached to the plurality of horizontal members by means of a plurality of U-shaped brackets underneath the plurality of horizontal members, and the plurality of track elements may be configured to be attached to the plurality of brackets by means of fasteners. Alternatively, the track elements can snap-fit onto the horizontal members. In cases where the horizontal members and vertical members comprise I-beams, the plurality of track elements may be configured to clip onto one of the two flanges of the plurality of horizontal members. This arrangement is simple and easy to assemble, and eliminates the need for further fasteners. The track elements are easy to assemble to the horizontal members, and can just as easily be removed. The upper flange of the I-beam fulfils multiple purposes: allowing the track elements to be attached to the horizontal members as well as supporting and providing a smooth level surface for the track elements, as well as contributing to the strength of the I-beam. The underside of the track element may comprise an inverted U-shaped cross-sectional profile that is shaped to cradle or overlap the top of the horizontal member. In cases where the edges of the horizontal member are chamfered, the profile of the underside of the track element may be complementary in shape to provide a closer fit between the track element and the horizontal 03 03 25 member. One or more lugs extending from each branch of the inverted U-shaped profile can engage with the edges of the horizontal member in a snap fit arrangement. A snap-fit arrangement is particularly suitable when the horizontal member is an I-beam, because the edges of the upper flange are conveniently shaped for lugs to snap onto. 5 The grid framework structure further comprises one or more vertically extending guides, each guide defining a corner of one of the plurality of storage columns, wherein each guide is supported by one of the plurality of connectors. For example, the guides may comprise two perpendicular elongated plates connected along the long edge of the plates. The purpose of the guides is to guide a corner of a storage container in a vertical direction within a storage column 10 when the storage container is lifted or lowered by the load handling device operative on the track system. Guides help to constrain the storage container to move in a vertical direction, reducing the likelihood of the storage container swinging or bumping into upright members while being lifted or lowered. An advantage of using the connectors to secure the guides is that one part is being used for two purposes: the connectors connect the horizontal members and 15 upright members, and also support the guides. Each guide may be supported by one of the plurality of connectors via a guide support removably secured to the connector. In cases where the connector portions are insertable into the horizontal members and upright members, the guide support may comprise an opening configured to receive one of the connector portions of the connector such that the guide support 20 is secured between the connector and one of the plurality of horizontal members and upright members. An advantage of this arrangement is that the connection between the connector portion and the horizontal member or upright member also helps to secure and constrain the guide connector, without the need for another part to fulfil this function. In cases where the upright supports comprise multiple upright members connected end-to-end 25 by connectors, multiple discrete guides can be provided rather than one longer continuous guide that spans substantially the whole of the distance from the track system to the ground. As with using multiple upright members to make up the upright supports, this arrangement has the advantage that the individual guides are shorter in length, and therefore have the advantage of ease of manufacture, storage, transportation, handling, and assembly. 30 The guide support may be configured to support more than one guide. An advantage of this arrangement is that fewer parts are needed, not only reducing costs but also simplifying the design, manufacture, and assembly of the grid framework structure. In another aspect, an automated storage and retrieval system is provided, comprising: i) a grid framework structure as defined herein; ii) a plurality of stacks of storage containers arranged in the storage columns of the grid framework structure; and 5 iii) one or more load handling devices remotely operable to move the one or more storage containers stored in the grid framework structure, each of the one or more load handling devices comprising: a) a wheel assembly for guiding the load handling device on the track system; b) a container-receiving space; and 10 c) a lifting device arranged to lift a single storage container from a stack into the container-receiving space. Description of the Drawings Further features and aspects of the present disclosure will be apparent from the following detailed description of an illustrative embodiment made with reference to the drawings, in which: Figure lisa schematic diagram of a grid framework structure according to a known system. Figure 2 is a schematic diagram of a top down view showing a stack of bins arranged within the framework structure of Figure 1. Figure 3 is a schematic diagram of a system of a known load handling device operating on the grid framework structure. Figure 4 is a schematic perspective view of the load handling device showing the lifting device gripping a container from above. Figure 5(a) and 5(b) are schematic perspective cut away views of the load handling device of Figure 4 showing the load handling device with a container in the raised position within the container receiving space, and the load handling device with a container in the lowered position. Figure 6 is a schematic perspective view of a grid framework structure comprising horizontal members, upright members, and connectors. Figure 7 is a schematic perspective view of horizontal members and an upright member from the grid framework structure of Figure 6. Figure 8 is a schematic perspective view of a member showing constant cross-section. Figure 9 (a and b) schematically illustrates a connector in a grid framework structure. Figure 10 (a to g) schematically illustrates several different connectors, with different numbers and arrangements of connector portions: (a) a five-way connector, (b) a four-way planar connector, (c) a three-way connector, (d) a four-way connector, (e) a two-way connector, (f) a three-way planar connector, and (g) a six-way connector. Figure 11 schematically illustrates a connector and horizontal member. Figure 12 illustrates a horizontal member and a track divider. Figure 13 (a and b) schematically illustrates (a) a cross sectional view of the horizontal member and track divider, (b) how load handling devices run on the track system. Figure 14 (a and b) schematically illustrates a horizontal member supporting a track element in (a) side view and (b) end view. Figure 15 (a to c) schematically illustrates an arrangement of guides: (a) a top view of a grid cell, (b) a side view of the guide attached to an upright member, (c) a side view of a grid cell in a grid framework structure. Figure 16 (a and b) illustrates a guide support for connecting two guides to a connector, in (a) exploded view, and (b) assembled view. Figure 17 (a and b) illustrates a guide support for connecting four guides to a connector, in (a) exploded view, and (b) assembled view. Figure 18 (a and b) schematically illustrates (a) a connector with two guide supports for connecting guides both above and below the connector, (b) a section of a grid framework structure with connectors. Figure 19 schematically illustrates a grid framework structure with guides positioned at all four comers of each storage column. Figure 20 (a and b) schematically illustrates (a) a connector with connector portions insertable into horizontal members and upright members, and (b) a connector with horizontal and upright members insertable into the connector portions. Figure 21 (a and b) schematically illustrates (a) a horizontal I-beam, and (b) an upright I-beam. Figure 22 (a and b) schematically illustrates a connector for connecting with I-beam members. Figure 23 schematically illustrates horizontal and upright I-beams assembled with a connector. Figure 24 (a and b) schematically illustrates two guides and an upright I-beam in (a) exploded view, and (b) assembled view. Figure 25 schematically illustrates a bracing plate to further support the grid framework structure. Detailed Description Storage and retrieval systems Storage systems comprising a three-dimensional storage grid structure, within which storage containers / bins are stacked on top of each other, are well known. PCT Publication No. WO2021 / 175872A (Ocado) describes a known storage and fulfilment system in which stacks of bins or containers are arranged within a grid framework structure. The bins or containers are accessed by load handling devices remotely operative on tracks located on the top of the grid framework structure. A system of this type is illustrated schematically in Figures 1 to 3 of the accompanying drawings. As shown in Figures 1 and 2, stackable containers, known as bins or containers or storage containers 10, are stacked on top of one another to form stacks 12. The stacks 12 are arranged in a grid framework structure 14 in a warehousing or manufacturing environment. The grid framework is made up of a plurality of storage columns or grid columns 15. Each grid in the grid framework structure has at least one grid column for storage of a stack of containers. Figure 1 is a schematic perspective view of the grid framework structure 14, and Figure 2 is a top-down view showing a stack 12 of bins 10 arranged within the framework structure 14. Each storage container 10 typically holds a plurality of product items (not shown), and the product items within a storage container 10 may be identical, or may be of different product types depending on the application. The grid framework structure 14 comprises a plurality of upright membersl6 that support horizontal members 18, 20. A first set of parallel horizontal grid members 18 is arranged perpendicularly to a second set of parallel horizontal grid members 20 to form a plurality of horizontal grid structures supported by the upright members 16. The members 16, 18, 20 are typically manufactured from metal and typically welded or bolted together or a combination of both. The bins 10 are stacked between the members 16, 18, 20 of the grid framework structure 14, so that the grid framework structure 14 guards against horizontal movement of the stacks 12 of storage containers 10, and guides vertical movement of the storage containers 10. The top level of the grid framework structure 14 includes rails 22 arranged in a grid pattern across the top of the stacks 12. Referring additionally to Figure 3, the rails 22 support a plurality of load handling devices 30. A first set 22a of parallel rails 22 guides movement of the robotic load handling devices 30 in a first direction (for example, an X-direction) across the top of the grid framework structure 14, and a second set 22b of parallel rails 22, arranged perpendicular to the first set 22a, guides movement of the load handling devices 30 in a second direction (for example, a Y-direction), perpendicular to the first direction. In this way, the rails 22 allow movement of the robotic load handling devices 30 laterally in two dimensions in the horizontal X-Y plane, so that a load handling device 30 can be moved into position above any of the stacks 12. A known load handling device 30 shown in Figure 4 and 5 comprises a vehicle body 32 is described in PCT Patent Publication No. WO2015 / 019055 (Ocado), hereby incorporated by reference, where each load handling device 30 only covers one grid space of the grid framework structure 14. Here, the load handling device 30 comprises a wheel assembly comprising a first set of wheels 34 consisting a pair of wheels on the front of the vehicle body 32 and a pair of wheels 34 on the back of the vehicle body 32 for engaging with the first set of rails or tracks to guide movement of the device in a first direction and a second set of wheels 36 consisting of a pair of wheels 36 on each side of the vehicle 32 for engaging with the second set of rails or tracks to guide movement of the device in a second direction. Each set of wheels is driven to enable movement of the vehicle in X and Y directions respectively along the rails. One or both sets of wheels can be moved vertically to lift each set of wheels clear of the respective rails, thereby allowing the vehicle to move in the desired direction. The load handling device 30 is equipped with a lifting device or crane mechanism to lift a storage container from above. The crane mechanism comprises a winch, a tether or cable 38 wound on a spool or reel (not shown) and a grabber device 39. The lifting device or crane mechanism comprises a set of lifting tethers 38 extending in a vertical direction and connected nearby or at the four corners of a lifting frame 39, otherwise known as a grabber device (one tether near each of the four corners of the grabber device) for releasable connection to a storage container 10. The grabber device 39 is configured to releasably grip the top of a storage container 10 to lift it from a stack of containers in a storage system of the type shown in Figures 1 and 2. The wheels 34, 36 are arranged around the periphery of a cavity or recess, known as a container-receiving recess or container receiving space 40, in the lower part of the load handling device. The recess is sized to accommodate the storage container 10 when it is lifted by the crane mechanism, as shown in Figure 5 (a and b). When in the recess, the container is lifted clear of the rails beneath, so that the vehicle or load handling device can move laterally to a different location. On reaching the target location, for example another stack, an access point in the storage system or a conveyor belt, the storage container 10 can be lowered from the container receiving space 40 and released from the grabber device. Thus, upon receipt of a customer order, a load handling device operative to move on the tracks is instructed to pick up a storage bin containing the item of the order from a stack in the grid framework structure and transport the storage bin to an inventory handling station whereupon the item can be retrieved from the storage bin. Where the inventory handling station is used to pick one or more items such an inventory handling station is known as a pick station. Typically, the load handling device transports the storage bin or container to a bin lift device that is integrated into the grid framework structure. A mechanism of the bin lift device lowers the storage bin or container to the pick station. At the pick station, the item is retrieved from the storage bin. Picking can done manually by hand or by a robot as taught in GB2524383 (Ocado Innovation Limited). After retrieval from the storage bin, the storage bin is transported to a second bin lift device whereupon it is lifted to grid level to be retrieved by a load handling device and transported back into its location within the grid framework structure. A control system and a communication system keeps track of the location of the storage bins and their contents within the grid framework structure. As individual containers are stacked in vertical layers, their locations in the grid framework structure or “hive” may be indicated using coordinates in three dimensions to represent the load handling device or a container’s position and a container depth (e.g. container at (X, Y, Z), depth W). Equally, locations in the grid framework structure may be indicated in two dimensions to represent the load handling device or a container’s position and a container depth (e.g. container depth (e.g. container at (X, Y), depth Z). For example, Z=1 identifies the uppermost layer of the grid, i.e. the layer immediately below the rail system, Z=2 is the second layer below the rail system and so on to the lowermost, bottom layer of the grid. Equally when stocking the storage system with items or replenishing the inventory of the storage system, items delivered from a supplier are transported to the inventory handling station. Since items are supplied or decanted to replenish stock in the storage system, the inventory handling station is known as a decant station or a supply station. Here, the items are removed from their packaging and depending on the type of item, registered with a unique stock keeping unit or SKU, and placed in storage bins at the decant station. At the decant station, the storage bins are transported to a bin lift device whereupon it is lifted to grid level to be retrieved by a load handling device and transported to a location within the grid framework structure. In a storage grid, a majority of the grid columns are storage columns, i.e. grid columns where storage containers are stored in stacks. However, a grid normally has at least one grid column which is used not for storing storage containers, but which comprises a location where the container handling vehicles can drop off and / or pick up storage containers so that they can be transported to a second location (not shown in the prior art figures) where the storage containers can be accessed from outside of the grid or transferred out of or into the grid. Within the art, such a location is normally referred to as a “port” and the grid column in which the port is located may be referred to as a “delivery column”. The storage grids comprise two delivery columns. A first delivery column may for example comprise a dedicated drop-off port where the container handling vehicles or load handling vehicles can drop off storage containers to be transported through the delivery column and further to an access or a transfer station, and a second delivery column may comprise a dedicated pick-up port where the container handling vehicles can pick up storage containers that have been transported through the second delivery column from an access or a transfer station. Storage containers are fed into the access station via the first delivery column and exit the access station via the second delivery column. It is against the known features of the storage system such as the grid framework structure and the load handling device described above with reference to Figures 1 to 5, that the present disclosure has been devised. In a typical fulfilment centre, a large variety of items, such as grocery items are stored in storage bins or containers and the storage bins or containers are stored in one or more stacks in the grid framework structure, more specifically within grid columns. The grid columns are formed by a plurality of upright members or vertical uprights arranged as vertical storage locations. Individual containers may be stacked in vertical layers, and their locations in the grid framework structure or “hive” may be indicated using coordinates in three dimensions to represent the load handling device or a container’s position and a container depth (e.g. container at (X, Y, Z), depth W). Equally, locations in the grid framework structure may be indicated in two dimensions to represent the load handling device or a container’s position and a container depth (e.g. container depth (e.g. container at (X, Y), depth Z). For example, Z=1 identifies the uppermost layer of the grid framework structure, i.e. the layer immediately below the rail system, Z=2 is the second layer below the rail system and so on to the lowermost, bottom layer of the grid framework structure. A majority of the grid columns in the grid framework structure are storage columns. Modular grid framework structure Figure 6 is a schematic perspective view of a grid framework structure 50 comprising horizontal members 52, upright members 54, and connectors 56. The illustrated example is a 2x2 grid framework structure with four grid cells. A connector 56 is placed at each node of the grid pattern, where the horizontal members 52 intersect. Each node is supported by an upright member 54. At the node at the centre of the grid framework structure 50, a connector 56 connects four horizontal members 52 with one upright member 54. At the four nodes at the four corners of the grid framework structure 50, a connector 56 connects two horizontal members 52 with one upright member 54. At the four nodes along the four edges of the grid framework structure 50, a connector 56 connects three horizontal members 52 with one upright member 54. In the illustrated example, the grid cells are rectangular in shape, with two long sides and two short sides. The horizontal members 52 therefore can be divided into two sets of horizontal members, a first set of horizontal members 52a that extend in a first direction (for example an X-direction), and a second set of horizontal members 52b that extend in a second direction (for example a Y-direction). The first direction and the second direction are perpendicular to each other. The rectangular grid cells are oriented so that the long sides of the grid cells are the first set of horizontal members 52a, and the short sides of the grid cells are the second set of horizontal members 52b. A connector is placed at each of the four corners of the grid cells, in order to connect the first set of horizontal members 52a (long sides) and the second set of horizontal members 52b (short sides). Each connector connects four horizontal members 52 to each other and to an upright member. In the illustrated example, the connectors are all identical five-way connectors, though in other examples different kinds of connector could be used. Although only a small grid framework structure is shown with four grid cells, the grid framework structure could easily be expanded by adding further horizontal members 52, upright members 54, and connectors 56. Figure 7 is a schematic perspective view of horizontal members 52 and an upright member 54 from the grid framework structure of Figure 6. One of the first set of horizontal members 52a (the long side of a grid cell) and one of the second set of horizontal members 52b are illustrated, alongside an upright member 54. Since the cross section of the horizontal members 52 is the same as that of the upright members 54, the only difference between the horizontal members 52 and the upright members 54 is the length of the member. This is a great advantage in simplifying the manufacturing and assembly process. The horizontal member 52 and the upright members 54 can be manufactured by extrusion, and then cut to the desired length. In the example illustrated in Figures 6 and 7 the track system is a rectangular grid, i.e. each grid cell is a rectangular shape with a long side and a short side. Thus, the horizontal members 52 come in two different lengths, the first set of horizontal members 52a in a longer length to make the long sides of the grid cells, and the second set of horizontal members 52b in a shorter length to make the shorter sides of the grid cells. In some examples the track system may be a square grid, i.e. each grid cell is a square, and every horizontal member 52 is the same length. This arrangement has the further advantage of reducing the part count and complexity of the grid framework structure 50. The upright members 54 can be the same length as the horizontal members 52, or a different length. The horizontal members 52 and the upright members 54 in the illustrated example have a substantially constant cross section. Figure 8 illustrates a member (which could be either a horizontal member 52 or an upright member 54) with cross sections illustrated at different positions along the length of the member. It can be seen that the cross section is the same all the way along the length of the member. In this particular example the cross section is a hollow square cross section. A hollow cross section has the advantage of a good strength to weight ratio; members with a hollow cross section will be able to resist applied forces (e.g. bending, tension, compression, torsion), while still being light and having reduced material costs compared to a solid cross section. A square cross section has the advantage of having flat sides, so the top side of the horizontal members is substantially horizontal and can be used as a track, or to support a track, for load handling devices to run on top of the grid framework structure. It can be seen in Figure 8 that the edges of the horizontal members 52 and the upright members 54 are chamfered. The purpose of chamfering is to remove stress raisers, i.e. sharp edges where stress concentrates, so that the horizontal members 52 and upright members 54 are more resistant to applied forces and have greater durability. Chamfering applies both to the internal cross section and the external cross section of the horizontal members 52 and upright members 54. The edges of the connector portions of the connectors 56 are chamfered too, as will be described later. Although the horizontal members 52 and upright members 54 illustrated in Figure 6 to 8 have a square tubular cross section, other cross sectional profiles can also apply. For example, the horizontal members 52 and upright members 54 can have a cylindrical tubular cross section, or an I-beam cross section, or a C-beam cross section, or a back-to-back double C-beam cross section, or any other suitable cross sectional profile. Figure 21 schematically illustrates a horizontal member 52 that is an I-beam, and an upright member 54 that is an I-beam, for use in a grid framework structure 50. Again, the cross sectional profile of the horizontal and vertical members is the same along the length of the member, and the cross section of the horizontal members 52 is identical to the cross section of the upright members 54. The I-beam has a web 90 which connects two flanges 92. When assembled in a grid framework structure 50, the horizontal members may be oriented such that the span 90 is vertical and the flanges 92 are horizontal. This orientation has the advantage of providing a flat surface on top of the grid framework structure 50 to form the track system. As will be discussed later, the upper surface of the horizontal members 52 of the track system can form the tracks for load handling devices to travel upon, or separate track elements can be attached to the horizontal members 52. In either case, a flat upper surface is an advantage. Figure 9 (a and b) schematically illustrates a connector 56 in a grid framework structure 50. In Figure 9(a), the connector is shown connecting a vertical member 54 to two horizontal members 52. The two horizontal members comprise one of the first set of horizontal members 52a and one of the second set of horizontal members 52b, and are perpendicular to each other, and both lie in a substantially horizontal plane. The upright member 54 is substantially vertical, and is perpendicular to both horizontal members 52a, 52b. The three members 52a, 52b, 54 are all mutually perpendicular. Figure 9(b) shows the same connector 56 as Figure 9(b), but in exploded view, so that the parts can more easily be seen. The horizontal members 52a, 52b and the upright member 54 can assembled to the connector 56 by moving the parts in the direction of the arrows. The connector 56 comprises connector portions 58, extending outwards from the centre of the connector 56. The connector portions 58 are configured to fit inside the hollow cross section of the horizontal members 52a, 52b and the upright members 54, so the parts can easily be assembled with a push fit. As can be seen from Figure 9(b), the connector comprises several connector portions 58: a downwardly extending connector portion 58c for connecting with the upright member 54, and two laterally extending connector portions 58a and 58b for connecting with the horizontal members 52a, 52b of the first and second sets of horizontal members respectively. The connections between the connector portions 58 of the connector 56 and the upright and horizontal members 52, 54 are interchangeable, i.e. any connector portion 58 of any connector 56 can be inserted into either end of any horizontal member 52 or any upright member 54. The connector illustrated in Figure 9 (a and b) is a five-way connector, with five connector portions. Although only three of the connector portions 58 of the connector 56 are illustrated as being connected in Figure 9, the other two connector portions 58 could also be connected to horizontal members 52. In that case, the connector 56 would connect four horizontal members 52 (two of the first set of horizontal members 52a and two of the second set of horizontal members 52b) with the upright member 54 at a node of the grid framework structure. Other configurations of connectors 56 with different numbers of connector portions 58 are also possible. Connectors Figure 10 (a to g) schematically illustrates several different connectors 56, with different numbers and arrangements of connector portions 58: (a) a five-way connector 56a, (b) a fourway planar connector 56b, (c) a three-way connector 56c, (d) a four-way connector 56d, (e) a two-way connector 56e, (f) a three-way planar connector 56f, and (g) a six-way connector 56g. In all of these examples the connector portions extend outwardly from the centre of the connector 56, in a horizontal or vertical direction. When assembled in a grid framework structure 50, the connector 56 are positioned at nodes of the grid framework structure. The illustrated connectors 56 are examples only, and are not exhaustive. Other types and configurations of connector 56 may also be applicable. The connector illustrated in Figure 10(a) is a five-way connector 56a, similar to the connector illustrated in Figure 9(a and b) and described above. The five-way connector 56a is configured to connect four horizontal members 52 with one upright member 54. The five-way connector 56a has four-fold rotational symmetry about the vertical axis, and can be used in any of the four orientations. The connector illustrated in Figure 10(b) is a four-way planar connector 56b. The four-way planar connector 56b is cross-shaped, with four connector portions extending outwards from the centre of the connector 56b, configured to connect four horizontal members 52 in a substantially horizontal plane. The four-way planar connector 56b has rotational symmetry about three axes of rotation, and can be used in any orientation. In some examples of grid framework structures, only a subset of nodes are supported by upright members 54, for example alternate nodes can be supported by upright members 54 such that storage columns have upright members at diagonally opposing comers. In such cases, nodes that are supported by upright members 54 can use five-way connectors 56a and nodes that are not supported by upright members 54 can use four-way planar connectors 56b. Four horizontal members 52 meet at each node in the centre portion of the grid framework structure. In some examples, different connectors 56 may be used at the comers and edges of the grid framework structure. For example, the connector 56c illustrated in Figure 10(c) is a three-way connector 56c. The three-way connector 56c can be used at the four corners of a rectangular grid framework structure 50, to connect one upright member 54 with two horizontal members 52. The three connector portions 58 of the three-way connector 56c are mutually perpendicular. The three-way connector 56c has threefold rotational symmetry, and can be used in any orientation (i.e. any of the three connector portions 58 can be used to connect to the upright member 54, and the other two connector portions used for connecting to the two horizontal members 52). The connector 56d illustrated in Figure 10(d) is a four-way connector 56d. The four-way connector 56d can be used along the edges of a grid framework structure 50, to connect one upright member 54 with three horizontal members 52. The two connector portions 58 that extend in opposite directions are used to connect two horizontal members 52 extending in opposite directions (e.g. along the first direction or the second direction), either of the other two connector portions 58 can be used to connect to the upright member 54, and the other connector portion used for connecting to a third horizontal member 52. In some examples, three-way connectors 56c may be used at the corners of the grid framework structure 50 and four-way connectors 56d along the edges of the grid framework structure 50. However, in other examples, five-way connectors 56a can be used at the comers and edges of the grid framework structure. The latter arrangement has the advantage of needing fewer different kinds of connectors 56, thus resulting in a grid framework structure 50 with a simpler design and lower part count. In some examples, the track system of the grid framework structure is supported by upright supports comprising two or more upright members connected end-to-end by one or more connectors. A grid framework structure with upright supports comprising multiple upright members is illustrated in Figure 19, and will be described in more detail later. The main advantage of this arrangement is that a taller grid framework structure can be built, without requiring the individual upright members 54 to be too long. Shorter members are easier to manufacture, handle, store, and assemble. The connector 56e illustrated in Figure 10(e) is a two-way connector 56e. The two-way connector 56e can be used to connect two upright members 54 to form an upright support, so that the grid framework structure can be taller than the length of a single upright member 54. The two connector portions 58 extend in opposite directions, and the two-way connector 56e can be used either way up. An upright support can comprise two upright members connected by a two-way connector 56e, or three upright members connected by two two-way connectors 56e, or any number of upright members 54 connected by two-way connectors 56e. Other kinds of connectors 56 can also be used. In some examples, a grid framework structure 50 with upright supports comprising multiple upright members may have bracing members between the upright supports, in order to further support and strengthen the grid framework structure 50. In some examples the bracing members can be horizontal members 52 of the same kind as used to support the track system. Connectors 56 that are used to join upright members 54 to form the upright supports can also be used to connect the bracing members. One, two, three, or four bracing members can connect to a node in an upright support. A connector 56 used to connect two upright members 54 together to form an upright support has two opposing connector portions 58 extending in opposite directions to connect the two upright members 54, and one or more additional connector portions 58 extending in a perpendicular direction for connecting to one or more bracing members 52. When assembled in a grid framework structure 50, the two opposing connector portions 58 extend vertically (one upwards and one downwards), and the additional connector portions 58 extend horizontally. The connector 56f illustrated in Figure 10(f) is a three-way planar connector 56f. The three-way planar connector 56f can be used to connect two upright members 54 to form an upright support, and one horizontal member 52 used as a bracing member. Two opposing connector portions 58 extend in opposite directions, and a third connector portion 58 extends in a perpendicular direction. The three connector portions lie in the same plane (a vertical plane when assembled). When assembled in a grid framework structure 50, the two opposing connector portions 58 extend vertically (one upwards and one downwards) and connect to the two upright members 54, and the third connector portion 58 extends horizontally and connects to the horizontal member 52. The other end of the horizontal member 52 is connected to another connector 56 at a node in an adjacent upright support. To connect two bracing members at the same node in an upright support, a four-way connector 56 can be used. This could be a four-way planar connector 56b as illustrated in Figure 10(b), in which case the two horizontal members 52 acting as bracing members extend horizontally in opposite directions. Alternatively a four-way connector 56d as illustrated in Figure 10(d) could be used, in which case the two horizontal members 52 extend horizontally in perpendicular directions. To connect three bracing members at the same node in an upright support, a five-way connector 56a, as illustrated in Figure 10(a), can be used. The orientation would be different to that illustrated in Figure 10(a), i.e. the five-way connector 56a would be oriented such that an opposing pair of connector portions 58 extend vertically (one upwards, one downwards). The opposing pair of connector portions extending vertically connect to the two upright members 54, and the three connector portions extending horizontally connect to three horizontal members 52 that act as bracing members. To connect four bracing members at the same node in an upright support, a six-way connector 56g, as illustrated in Figure 10(g), can be used. Two opposing connector portions, which extend upwards and downwards in use, are used to connect the two upright members 52. The remaining four connector portions 58 extend horizontally in use and connect to four horizontal members 52 acting as bracing members. In other examples, rather than using different kinds of connector 56 at different nodes in the grid framework structure 50, the same kind of connector can be used. Any connector portions that are not used to connect to horizontal members or upright members will not obstruct the movement of storage containers being raised or lowered by load handling devices, since the connector portions do not extend into the storage columns. The only exception is that the connectors 56 on top of the grid framework structure cannot have a connector portion extending upwards, because this would obstruct the movement of load handling devices on the track system. A grid framework structure 50 could be constructed with all of the connectors 50 being five-way connectors 56a, for example. An advantage of this arrangement is simplicity of design, a reduced part count, and simpler / easier / faster assembly, since there is no need to select the correct type of connector 56 for each node. In some examples, the connector portions 58 of the connectors 56 can be tapered in shape, to facilitate insertion into the bore of the horizontal members and / or upright members. In the examples described above, the grid framework structure is assembled by inserting the connector portions 58 into the horizontal members 52 and upright members 54. An alternative is for the connector portions 58 to be hollow, and the horizontal members 52 and upright members 54 to be inserted into the connector portions 58. Figure 20 (a and b) schematically illustrates (a) a connector 56 with connector portions 58 insertable into horizontal members 52 and upright members 54, and (b) a connector 56 with horizontal members 52 and upright members 54 insertable into the connector portions 58. Figure 20(a) is similar to the arrangement discussed above with reference to Figures 6, 9, and 10, where the connector portions 58 are solid and fit inside the interior cross section of the horizontal members 52 and the upright members 54. In other examples the connector portions 58 do not have to be solid, and can take any suitable shape so long as the exterior cross section of the connector portions is suitable for connecting with the horizontal members 52 and upright members 54. The interior cross section of the horizontal members 52 and the upright members 54 corresponds to the exterior cross section of the connector portions. An advantage of this arrangement is that the connectors can be simple in shape, e.g. with solid connector portions, so will be easier to manufacture. By contrast, in the arrangement of Figure 20(b), the connector portions 58 are hollow, and have an interior cross section that corresponds to the exterior cross section of the horizontal members 52 and the upright members 54. The horizontal members 52 and the upright members 54 fit inside the connector portions, rather than the other way round. An advantage of this arrangement is that the connectors 58 require less material since the connector portions 58 are hollow, thus saving on weight and material costs. Figure 22 (a and b) illustrates a connector 56 for use with I-beam horizontal members 52 and upright members 54. The connector portions 58 of the connector 56 each comprise a pair of protrusions 94 separated by a slot 96 between the two portions. The slot 94 is sized to receive the web 90 of the I-beam. The connector 56 is oriented such that the slots 94 for connecting to horizontal members 52 are substantially vertical. Figure 22(b) shows the same connector 56 as Figure 22(a) from a different angle, so the connector portion 58 underneath the connector 56 can be seen. The slot 96 between the two protrusions 94 is shaped and sized to receive the web 90 of the I-beam upright member 94. Figure 23 illustrates the connector 56 of Figure 22, along with horizontal members 52 and a vertical member 54, where the horizontal members 52 and upright member 54 are all I-beams. The arrows in Figure 23 indicate the direction of assembly, i.e. the horizontal members 52 can be moved horizontally relative to the connector 56 in order to assemble or disassemble the horizontal members 52 to the connector 56. Similarly the upright member 54 can be moved vertically relative to the connector 56 in order to assemble or disassemble the upright member 54 to the connector 56. It can be seen from Figure 23 that the web 90 of the horizontal members is configured to fit inside the slot 96 between the two protrusions 94 of the connector portions. The upper of the two flanges 92 rests on top of the two protrusions 94, and the lower of the two flanges 92 fits underneath the two protrusions 94. Similarly the web 90 of the upright member fits into the slot 96 of the connector portion underneath the connector 56. In the illustrated example the protrusions 94 do not extend all the way to the edges of the face of the connector 56, so there is a narrow ledge 98 around the base of the protrusions 94. The connector 56 is therefore supported on top of the web 90 and both flanges 92 of the upright member 54 underneath. The narrow ledge 98 also helps to ensure that the upper surface of the horizontal members (i.e. the upper surface of the upper flange 92 of the I-beam) is flush with the upper surface of the connector 56. The upper flange 92 rests on top of the protrusions 94 of the connector portion, and the depth of the upper flange is substantially the same as the depth of the narrow ledge 98, so the upper surfaces of the upper flange 92 and the connector 56 are at the same vertical level, therefore ensuring that a load handling device running on the track system has a smooth ride. An alternative way of describing the connection between the I-beams and the connector portions is that each of the two protrusions fits into the cavity formed between the two flanges 92 and web 90 of the I-beam. The connectors 56 can be manufactured by compression moulding, which is an inexpensive manufacturing method that produces sufficiently accurate parts. The connectors can be made from plastic, metal, or any other suitable material. The connectors 56 can be manufactured by 3D printing or additive manufacturing. Thermal expansion Figure 11 illustrates a connector 56 and horizontal member 52. In this particular example, the connector 56 is a five-way connector 56a with five connector portions 58, four of which extend horizontally for connecting to horizontal members, and the fifth connector portion 58 extends vertically downwards for connecting to an upright member. Each connector portion 58 has a through hole or opening 60, 62. The horizontal member 52 has a pair of openings 64 (only one of which is visible in Figure 11). When assembled, the connector portion 58 is connected to an end of a horizontal member or upright member by means of a fastener, for example a bolt. The fastener (not shown) passes into the horizontal member 52 through one of the openings 64 in the side of the horizontal member 52, through the opening 60, 62 in the connector portion 58 of the connector 56, and out through the other opening 64 in the other side of the horizontal member 52. The fastener acts to secure the connector portion 58 of the connector 56 to the horizontal member 52. Upright members 54 can be secured to the connectors 56 in the same way. In the illustrated example, two of the connector portions 58 have substantially circular openings 60, and two of the connector portions 58 have elongated openings 62. The purpose of the elongated openings is to allow for relative movement of the horizontal members due to thermal expansion. The fastener connecting the horizontal member 52 to the connector portion 58 is constrained to move horizontally within the elongated opening 62. The connection between the connector 56 and the horizontal members 52 can be described as an expansion joint or slip joint. The illustrated example shows elongated openings 62 in the connector portions 58 and circular openings 60 in the corresponding horizontal members 52. In other examples the horizontal members 52 can be provided with elongated openings 62, and the corresponding openings in the connector portions 58 can be circular openings 60. The two elongated openings 62 are in two connector portions 58 extending in perpendicular directions, so when assembled in a grid framework structure 50, the connector permits movement in both the first direction and the second direction (e.g. in the X and Y directions). In some examples, all of the connectors 56 in a grid framework structure 50 have elongated openings 62 in two connector portions 58, one extending in the first direction and one extending in the second direction, so that relative movement in both directions is permitted at every node of the track system. An advantage of this arrangement is that the connectors 56 remain interchangeable, i.e. there are no “special” thermal expansion connectors that have to be assembled in certain positions, and perform the function of permitting thermal expansion in both directions irrespective of their orientation, i.e. a connector can be rotated by 90° and still allow for thermal expansion. It can be seen in Figure 11 that the edges of the connector portions 58 are chamfered. The purpose of chamfering is to remove stress raisers, i.e. sharp edges where stress concentrates. This applies both to the connector portions 58 of the connectors 56 and to the cross section of the horizontal members 52 and upright members 54. The chamfered profile of the connector portions 58 corresponds to and co-operates with the chamfered inner cross section of the horizontal members 52 and upright members 54, so that the connector portions 58 can fit inside the inner cross section of the horizontal members 52 and upright members 54. A similar arrangement can be used to permit relative movement of the horizontal member 52 and the connector 56 when the horizontal member 52 is insertable into the connector portion 58, as illustrated in Figure 20(b). In this case the hollow connector portion 58 can be provided with a pair of openings on opposite sides of the connector portion, and either the openings in the connector portion or the openings in the horizontal member 52 can be elongated openings. Track system In some examples, the horizontal members 52 that make up the track system 13 support separate track elements, and in other examples the upper surfaces of the horizontal members 52 are the tracks, i.e. the load handling devices run directly on the upper surface of the horizontal members 52. Figure 12 illustrates a horizontal member 52 and a track divider 66. The track divider 66 divides the upper surface of the horizontal member 52 into two parallel sections. Each of the two parallel sections can be used as a track to support the wheels of a load handling device 30. In the illustrated example the track divider 66 is an elongated element with a trapezoidal cross section, i.e. tapered so that the top of the divider 66 is narrower than the bottom of the track divider 66. The track divider 66 comprises a plurality of tabs 68 extending downwards below the main part of the track divider. The horizontal member 52 comprises a corresponding number of slots 70 on the upper surface of the horizontal member 52. The shape of the slots 70 corresponds to the shape of the tabs 68. In order to assemble the track divider 66 onto the horizontal member 52, the tabs 68 of the track divider 66 are inserted into respective slots 70 on the upper surface of the horizontal member 52. The track divider can be made of any suitable material. For example, the track divider 66 can be made of silicone rubber or another resilient material, so that the tabs 68 of the track divider 66 deform enough to be inserted into the slots 70 of the horizontal members, and then return to their original shape to retain the tabs 68 in the slots 70. Thus the track divider 66 can be removably mounted on the horizontal member 52, and it is very easy to assemble the track divider 66 to the horizontal member 52 by hand, with no specialist tooling required. Figure 13 (a) illustrates a cross sectional view of the horizontal member 52 and track divider 66. It can be seen that the tabs 68 of the track divider 66 extend downwards inside the cross section of the horizontal member 52. The tabs 68 are flared at the base to help retain the track divider 66 on the horizontal member 52, so the tabs 68 cannot accidentally be pulled out of the slots 70 in the horizontal member. Because the track divider 66 is made of a resilient material, the tabs 68 can simply be pushed into the slots 70. The tabs 68 deform enough to allow the tabs 68 to be inserted into the slots 70. The track divider 66 extends along the full length of the horizontal member 52, and divides the upper surface of the horizontal member 52 into two parallel sections (for example, a left section and a right section). The two parallel sections each act as a track so support and guide the wheels 34, 36 of a load handling device 30. Figure 13(b) schematically illustrates how load handling devices 30 run on the track system. Three horizontal members 52 are illustrated, in cross section view. The three horizontal members 52 extend in a direction parallel to one another. For reference the horizontal member 52 on the left of Figure 13(b) is labelled 52a, the horizontal member in the centre is labelled 52b, and the horizontal member on the right is labelled 52c. Each horizontal member 52 is divided into a double track by a track divider 66 as discussed above. Two load handling devices are supported on the tracks; the load handling device 30 on the left of the figure is referred to as the left load handling device 30a, and the load handling device 30 on the right of the figure is referred to as the right load handling device 30b. Similarly the wheels of the load handling device are referred to as the left wheel 34a and the right wheel 34b according to their position on the left or right of the load handling devices 30 as viewed in the figure. Each load handling device is supported and guided by the track of two adjacent horizontal members 52. The left horizontal member 52a supports the left wheel 34a of the left load handling device 30a, and the centre horizontal member 52b supports the right wheel 34 of the left load handling device 30a. Similarly, the centre horizontal member 52b supports the left wheel 34 of the right load handling device 30b, and the right horizontal member 52c supports the right wheel 34 of the right load handling device 30b. The centre horizontal member 52b is supporting two load handling devices 30 at the same time; the right wheel 34 of the left load handling device 30a runs on the left section of the track, and the left wheel 34 of the right load handling device 30b runs on the right section of the track. The track divider 66 divides the top surface of the horizontal member into a left track section and a right track section to allow two load handling devices 30 to pass each other on adjacent grid cells. The track divider 66 constrains the movement of the wheels 34 of the load handling devices, so the right wheel 34b of the left load handling device 30a remains on the left section of the track, and does not stray into or encroach upon the right section of the track. Similarly, the track divider 66 ensures that the left wheel 34a of the right load handling device 30b remains on the right section of the track, and does not stray into or encroach upon the left section of the track. Each load handling device is constrained by two track dividers 66 on two parallel horizontal members 52 on the outside of the wheels. In order to ensure that the wheels 34 of the load handling device 30 stay on the correct side of the track when passing over the connectors 56 between grid cells, the connector 56 comprises an island 72 in the centre of the upper surface (as can be seen in Figure 11). The island has the same cross sectional profile as the track divider 66, i.e. a trapezoidal profile. Because the island has the same cross sectional profile in two directions (i.e. in the first direction and the second direction), the shape of the island is a truncated square-based pyramid. The island helps to constrain the wheels of the load handling devices 30 to run on the correct section of the double track by minimising the gap in the profile of the track divider 66. In other examples, the track may be provided by separate track elements supported by the horizontal members. The track elements can be attached to the horizontal members by any suitable means, for example by brackets or by a snap-fit arrangement. Figure 14(a and b) schematically illustrates a horizontal member 52 supporting a track element 74. The track element 74 is attached to the horizontal member 52 by means of U-shaped brackets 76 underneath the horizontal member 52, and the track element 74 is attached to the bracket 76 by means of fasteners 78 (for example, bolts or screws). Figure 14(a) schematically illustrates a side view of two horizontal members 52 connected to an upright member 54 with a connector 56. The track element 74 extends partially over both horizontal members 52 and over the connector 56. A U-shaped bracket 76 is used to secure the track element 74 to the horizontal member 52 underneath. Although only one bracket 75 is pictured for ease of illustration, in practice a plurality of brackets can be used. The bracket 76 is attached to the track element by means of fasteners 78. Figure 14(b) schematically illustrates an end view of the horizontal member 52, the track element 74, and the bracket 76. Two fasteners 78 are provided for attaching the track element 74 to the two ends of the U-shaped bracket 76, with one fastener 78 at each end of the U. Although not illustrated in this example, the track may be a double track with a track divider in the centre, in order to allow two load handling devices to pass each other on the same track element. In some examples, cross-shaped track elements can be used, with four perpendicular track portions extending outwards, each of the four track portions configured to attach to one of the four horizontal members that meet at a node on the track system. An advantage of this arrangement is that the joins between adjacent track elements are positioned at or near the centre of a horizontal member, so the join is supported by a single flat member rather than at a node of the grid framework structure. This ensures a more even join between track sections and a smoother ride for the load handling devices on the track system. In other examples, track elements 74 may be a single length of track corresponding to the length of the underlying horizontal members 52. Other arrangements of track elements are also possible. Guides In some examples of grid framework structures, guides may be provided at the comers of the storage columns, to help guide the movement of storage containers while being lifted or lowered by a load handling device on top of the track system. Figure 15 (a to c) illustrates one possible arrangement of guides. Figure 15(a) is a top view of a grid cell. The space inside the grid cell is a storage column, for storing a stack of storage containers. Four horizontal members 52 are connected in a rectangular configuration by four connectors 56 to form the grid cell. Two guides 80 are positioned in the grid cell, at diagonally opposite corners of the grid cell. In some examples, guides 80 may be provided at one, two, three, or all four comers of the grid cell. Guides 80 at diagonally opposite corners of the grid cell have the advantage of providing enough stability and support to guide the storage container, while still using less material and fewer parts than guides at every corner of the grid cell. The guides 80 comprise two perpendicular elongated plates, extending in the vertical direction. Figure 15(b) schematically illustrates a side view of the guide 80 attached to an upright member 54. The guide 80 is connected to the upright member 54 by means of a guide support 82 (also shown from the top view in Figure 15(b)). In the illustrated example the guide support 82 takes the form of a flat plate, but the guide support can take any suitable shape. The guide support 82 has an opening or eyelet 84 with a square shape, sized to co-operate with the connector portions of the connectors 56. The connector portion of the connector 56 fits through the opening 84 in the guide support 82. The connector portion of the connector is then inserted into the bore of the upright member 54, so the guide support 82 is secured between the connector 56 and the top end of the upright member 54. Similarly, the bottom end of the guide is connected to the bottom end of the same upright member 54 by means of a second guide support 84. Figure 15(c) schematically illustrates a side view of a grid cell in a grid framework structure 50. In this example, the upright members 54 of the grid framework structure are arranged end-to-end to form upright supports, the upright supports being taller than an individual upright member. Two upright members 54 are connected together with a connector 56 to form an upright support that is approximately double the height of the upright members. This arrangement permits a taller grid framework structure to be built, without the need for longer upright members. In other examples, more than two upright members 54 can be connected together to form upright supports of different heights. As well as being connected by horizontal members at the top, the upright supports are braced together by a horizontal member 52. The horizontal member acts as a bracing member, and will be referred to as a horizontal bracing member. The horizontal bracing member connects to the two upright members 52 that form the upright support by a connector 56. The two upright members 54 forming the upright support each have a guide 80. As described above, the guides 80 are attached by means of guide supports 82. Figure 25 illustrates an additional option for bracing the grid framework structure 50. A bracing plate 102 is provided to further support the grid framework structure and to help to ensure that the horizontal members 52 remain perpendicular to the upright members 54. The bracing plate 102 is triangular in shape, and connects a horizontal member 52 to an upright member 54, ensuring that the horizontal member 52 and the upright member 54 remain perpendicular. The bracing plate 102 can be attached to the horizontal member 52 and the upright member 54 by any suitable attachment means, for example by rivets or bolts or screws or adhesive. In the illustrated example, the bracing plate 102 braces a horizontal member 52 and an upright member 54. Alternatively or additionally, a bracing plate 102 can be used to connect an upright member 54 to a bracing member linking neighbouring upright supports. Bracing plates 102 can be fitted on the periphery of the grid framework structure 50, and / or within the grid framework structure 50. In either case the bracing plate(s) 102 are positioned below the horizontal members 52 so do not encroach on the storage columns. An advantage of this arrangement is that the bracing plates 102 strengthen the grid framework structure and maintain alignment of the horizontal members 52 and / or bracing members, and upright members 54, without any reduction in available storage space. In the example illustrated in Figure 15, one guide support 82 is used to connect one guide 80 to a connector 56. In other examples, a guide support can be used to connect more than one guide 80 to the same connector 56. Figure 16 (a and b) illustrates a guide support 82 for connecting two guides 80 to a connector 56, in (a) exploded view, and (b) assembled view. The guide support 82 comprises a square opening 84. In this example the opening 84 is square in order to co-operate with the square exterior cross section of the horizontal member 52; in other examples where the horizontal members have a different exterior cross section, a different shaped opening 84 can be used. When assembled in a grid framework structure 50, a connector portion 58 of the connector 56 passes through the opening 84 and inside the horizontal member 52, securing the guide support 82 between the connector 56 and the horizontal member 52. In this example the guide support 82 takes the form of a rectangular plate with two smaller plates protruding in a perpendicular direction. The rectangular plate and the smaller plates provide a right angled bracket at each side of the guide support, where a guide can be connected. Any suitable attachment means can be used to attach the guide to the right angled brackets, for example bolts or screws. The bottom ends of the guides 80 are connected to another connector 56 by means of another guide support 82 in a similar manner. Figure 17 (a and b) illustrates a guide support 82 for connecting four guides 80 to a connector 56, in (a) exploded view, and (b) assembled view. The guide support 82 can be either integral with the connector 56 (as shown), or can be a separate part. In the case where the guide support 82 is a separate part, the guide support comprises an opening 84 which co-operates with a connector portion 58 of the connector 56, so the connector portion 58 of the connector 56 can be inserted into the opening 84 of the guide support 82 in order to assemble the two parts together. The guide support 84 comprises eight slots 86, for connecting the guides 80. As in the previous examples, the guides 80 comprise two perpendicular elongated plates, extending in the vertical direction. In this example the perpendicular plates of the guides 80 are bent round at the edges to form a pair of lips 88, which also extend along the length of the guides 80. To assemble the guides 80 to the connector 56, the lips 88 of the guides 80 are inserted into the slots 86. The horizontal members 52 and the upright member 54 are assembled to the connector 56 by inserting the connector portions 58 of the connector 56 into the bores of the horizontal members52 and upright member 54. In the case where the guide support 82 is a separate part rather than integral with the connector, the connector portion 58 of the connector 56 is inserted into the opening 84 of the guide support 82 in order to assemble the two parts together. The bottom ends of the guides 80 are connected to another connector 56 by means of another guide support 82 in a similar manner. In examples where the grid framework structure 50 is taller than a single upright member 54, i.e. where several upright members 54 are connected together to form an upright support, several guides 80 can be used end-to-end along the upright support, rather than one long guide extending all the way from the ground to the track system at the top of the grid framework structure 50. Again, this arrangement has the advantage that the individual guides can be shorter, so are easier to manufacture, store, transport, handle, and assemble. Figure 18 (a) schematically illustrates a connector 56 with two guide supports 82, for connecting guides 80 both above and below the connector 56. Figure 18(b) schematically illustrates a section of a grid framework structure with connectors 56 as illustrated in Figure 18(a). The guides 80 are not pictured in these figures, for ease of illustrating the connectors 56 and guide supports 82. This arrangement is suitable for use at nodes of the grid framework structure where two upright members 54 are connected to form an upright support. Again, the guide supports 82 can be either integral with the connector 56, or separate parts that are connected by inserting the connector portions 58 of the connector 56 into corresponding openings or eyelets (not shown) in the guide supports 82. A first guide support 82a is located on top of the connector 56, and a second guide support 82b is located underneath the connector 56. The first guide support 82a connects the bottom end of the guides 80 above the connector 56, and the second guide support 82b connects the top end of the guides 80 below the connector 56. Figure 19 schematically illustrates a grid framework structure 50 with guides 80 positioned at all four corners of each storage column. The connectors 56 at the top of the grid framework structure 50 comprise a guide support 82 to secure the top end of the guides 80 in the top half of the grid framework structure 50. The connectors 56 in the centre of the upright supports, about halfway up the grid structure 50, comprise two guide supports 82a, 82b as described above and as illustrated in Figure 18. The guide supports 82a on top of the connectors 56 secure the bottom half of the guides 80 in the top half of the grid framework structure 50, and the guide supports 82b underneath the connectors 56 secure the top half of the guides 80 in the bottom half of the grid framework structure 50. The bottom half of the guides 80 in the bottom half of the grid framework structure 50 can be secured with another guide support 82, or with anchor feet (not shown). Figure 24 schematically illustrates another arrangement of guides in (a) exploded view (b) assembled view, suitable for cases where the horizontal members 52 and upright members 54 are I-beams. In this example the guide connector is a pair of attachment plates 100 integrated with the guides 80. The pair of attachment plates 100 fit on either side of the edges of the flange 92 of the I-beam upright member 54. The upright member 54 can support four guides 80, one on either edge of each of the two flanges 92. Other suitable attachment means can be used in place of the two attachment plates 100. The above examples described with reference to Figures 15 to 19 and Figure 24 are nonlimiting examples of guides 80 and guide supports 82. Other arrangements are also applicable. Grid levelling In some examples, the upright members 56 and guides 80 can be supported by anchor feet on the ground or floor at the base of the upright supports. The feet can be adjustable, in order to control the height of the upright supports and ensure that the track system is level. The anchor feet can also support the bottom end of the guides 80, either with a guide support 80 or otherwise. In other examples, levelling mechanisms can be installed at the top of the upright supports. WO2022 / 034189 discloses an adjustable grid levelling mechanism for adjusting the level of a track system of a grid framework structure by adjusting a vertical distance between the at least one upright support and the track system. In one embodiment the adjustable grid levelling mechanism comprises an extendible section comprising a pair of mating washers having opposing or mating faces, the opposing or mating faces of each of the pair of mating washers having a profile or contour with a variable height extending in the circumferential direction such that rotation of the at least one of the pair of mating washers relative to the other causes 5 the height of the pair of the mating washers to be adjusted. This adjustable grid levelling mechanism, or other mechanisms, can be applied to the grid framework structure.

Claims

03 03 251. A grid framework structure for supporting a load handling device operative thereupon, the grid framework structure comprising:a track system comprising a plurality of horizontal members arranged in a grid pattern 5 comprising a plurality of grid cells and extending in a substantially horizontal plane, the horizontal members comprising tracks for guiding the load handling device on the track system;a plurality of upright supports each comprising one or more upright members, the upright supports supporting the track system above the ground to create a storage space comprising a plurality of storage columns, each storage column being arranged to store a stack of storage 10 containers, such that, in use, the load handling device operative on the track system is able tolift one or more storage containers through a grid cell from a stack in a storage column;a plurality of connectors configured to connect the plurality of upright members and the plurality of horizontal members together to form the grid framework structure, wherein each of the plurality of connectors comprises two or more connector portions, each of the two or 15 more connector portions having a profile that enables the connector portion to connect to anyone of the plurality of horizontal members and the plurality of upright members; andone or more vertically extending guides configured to guide a comer of a storage container in a vertical direction within a storage column when the storage container is lifted or lowered by the load handling device operative on the track system, each guide defining a corner of one of 20 the plurality of storage columns, wherein each guide is supported by one of the plurality ofconnectors.

2. The grid framework structure of claim 1, wherein the plurality of horizontal members and the plurality of upright members are tubular, and the interior and / or exterior cross sectional 25 profile of the plurality of horizontal members and the plurality of upright members are substantially the same.

3. The grid framework structure of claim 2, wherein the interior and / or exterior cross sectional profile of each of the plurality of horizontal members and each of the plurality of upright 30 members is a square cross section.03 03 254. The grid framework structure of claim 3, wherein the interior cross sectional profile of the plurality of horizontal members and the plurality of upright members are substantially the same and each of the two or more connector portions of each of the plurality of connectors is 5 insertable into any one of the plurality of horizontal members and the plurality of upright members.

5. The grid framework structure of claim 4, wherein each of the two or more connector portions of each of the plurality of connectors is tapered in order to facilitate insertion of the connector 10 portion into any one of the plurality of horizontal members and the plurality of upright members.

6. The grid framework structure of claim 3, wherein the exterior cross sectional profile of the plurality of horizontal members and the plurality of upright members are substantially the same 15 and each of the plurality of horizontal members and the plurality of upright members is insertable into any one of the two or more connector portions of each of the plurality of connectors.

7. The grid framework structure of claim 1, wherein each of the plurality of horizontal members 20 and the plurality of upright members comprises an I-beam having two flanges connected by a web.

8. The grid framework structure of claim 7, wherein each of the connector portions comprises protrusions spaced apart forming a slot for receiving the web of the I-beam such that the two 25 flanges partially overlap the protrusions.

9. The grid framework structure of claim 8, wherein the protrusions are connected to the two flanges and / or the web of I-beam by means of one or more fasteners.03 03 2510. The grid framework structure of any preceding claim, wherein at least one of the plurality of upright supports comprises at least two of the plurality of upright members connected together by at least one of the plurality of connectors.5 11. The grid framework structure of claim 10, wherein two or more neighbouring uprightsupports are braced together via a bracing member connected to their respective connectors.

12. The grid framework structure of any preceding claim, wherein each of the plurality of horizontal members is fastened to a respective connector portion by a fastener passing through 10 an opening in the horizontal member and a corresponding opening in the connector portion, and the opening of at least one horizontal member and / or the opening of the respective connector portion is elongated such that when the connector portion is fastened to the horizontal member, relative horizontal movement is permitted between the horizontal member and the connector portion.1513. The grid framework structure of any preceding claim, wherein the upper surface of each of the plurality of horizontal members is a track configured to support one or more load handling devices running on the track.20 14. The grid framework structure of claim 13, further comprising a plurality of track dividerseach configured to divide the upper surface into two parallel tracks.

15. The grid framework structure of claim 14, wherein the plurality of track dividers are removably attached to the plurality of horizontal members.2516. The grid framework structure of any of claims 1 to 12, wherein the track system further comprises a plurality of track elements removably attached to the plurality of horizontal members, the plurality of track elements being configured to support one or more load handling devices running on the track system.03 03 2517. The grid framework structure of claim 16 where dependent on claim 7, wherein the plurality of track elements are configured to clip onto one of the two flanges of the plurality of horizontal members.

518. The grid framework structure of any preceding claim, wherein each guide is supported by one of the plurality of connectors via a guide support removably secured to the connector.

19. The grid framework structure of claim 18 where dependent on claim 4 , wherein the guide 10 support comprises an opening configured to receive one of the connector portions of the connector such that the guide support is secured between the connector and one of the plurality of horizontal members and upright members.

20. The grid framework structure of claim 18 or 19, wherein the guide support is configured to 15 support more than one guide.

21. An automated storage and retrieval system comprising:i) a grid framework structure as defined in any preceding claim;ii) a plurality of stacks of storage containers arranged in the storage columns of the grid 20 framework structure; andiii) one or more load handling devices remotely operable to move the one or more storage containers stored in the grid framework structure, each of the one or more load handling devices comprising:a) a wheel assembly for guiding the load handling device on the track system;25 b) a container-receiving space; andc) a lifting device arranged to lift a single storage container from a stack into the container-receiving space.

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