Track assembly for storage system

Abstract

A track system for a grid framework structure (14) configured to guide a load handling device (30) operated to move one or more containers (10), wherein the grid framework structure comprises a support framework structure including a plurality of storage columns, each of the plurality of storage columns is arranged to accommodate a stack of storage containers; the track system comprises a plurality of tracks arranged to form a grid pattern including a plurality of grid cells, each of the plurality of tracks comprises a plastic material, and the track system is configured to be mounted on the support framework structure such that each stack of storage containers is placed under each of the plurality of grid cells; and each of the plurality of tracks is characterized by having a surface resistance of 1 x 10¹⁰ ohms (Ω) or less, a surface resistivity of 1 x 10¹⁰ (Ω·m) or less, and a light reflectance value (LRV) greater than 30%.

Description

Technology Field

[0001] The present invention relates to the field of a storage or order processing system in which a stack of bins or containers is arranged within a grid framework structure, and more specifically, to a track or track assembly configured to guide one or more load handling devices operated to move one or more containers stored in the storage or order processing system. Background Technology

[0002] Storage systems comprising a three-dimensional storage grid structure in which storage containers / bins are stacked on top of each other are well known. PCT Publication WO2015 / 185628A (Ocado) describes a known storage and retrieval system in which stacks of bins or containers are placed within a grid framework structure. The bins or containers are accessed by a load handling device operating on a track located at the top of the grid framework structure. This type of system is schematically illustrated in FIGS. 1 to 3 of the attached drawings.

[0003] As illustrated in FIGS. 1 and 2, stackable containers known as bins (10) are stacked on top of each other to form a stack (12). The stack (12) is placed in a grid framework structure (14) in a warehouse or manufacturing environment. The grid framework structure consists of a plurality of storage columns or grid columns. Each grid of the grid framework structure has at least one grid column for storing the container stack. FIG. 1 is a schematic perspective view of the grid framework structure (14), and FIG. 2 is a plan view showing the stack (12) of bins (10) placed within the framework structure (14). Each bin (10) typically contains a plurality of product items (not shown), and the product items within the bin (10) may be the same or different product types depending on the application.

[0004] The grid framework structure (14) includes a plurality of upright members (16) that support horizontal members (18, 20). A detailed description of the grid framework structure is discussed in WO 2021175873 (Ocado Innovation Ltd), the contents of which are incorporated herein by reference. A first set of parallel horizontal grid members (18) are arranged vertically to a second set of parallel horizontal members (20) in a grid pattern to form a plurality of horizontal grid structures (15) supported by upright members (16). The members (16, 18, 20) are typically made of metal. A bin (10) is loaded between the members (16, 18, 20) of the grid framework structure (14) so ​​that the grid framework structure (14) prevents horizontal movement of the bin (10) stack (12) and guides vertical movement of the bin (10).

[0005] The top level of the grid framework structure (14) includes a track system (15) comprising a plurality of rails or tracks (22) arranged in a grid pattern across the top of the stack (12). Referring further to FIG. 3, the rails or tracks (22) guide a plurality of load handling devices (30). Parallel rails (22) of a first set (22a) guide the movement of the robotic load handling device (30) in a first direction (e.g., X-direction) across the top of the grid framework structure (14), and parallel rails (22) of a second set (22b) arranged perpendicular to the first set (22a) guide the movement of the load handling device (30) in a second direction (e.g., Y-direction) perpendicular to the first direction. In this way, the rails (22) allow the robotic load handling device (30) to move laterally in two dimensions in the horizontal XY plane, thereby allowing the load handling device (30) to be moved to a position on any stack (12).

[0006] The upright columns of a grid framework structure are connected to one another at their tops by rails or tracks that intersect in the grid. The intersection points of rails or tracks in a grid structure are generally referred to as 'nodes' of the grid structure. For the purposes of the present invention, a node is an area of ​​a track system where multiple rails or tracks intersect in a grid pattern. Typically, the first and second sets of rails comprise individual elongated rail or track sections that are interconnected together in the first and second directions at the interconnection where the track or rail sections meet at the tops of the upright columns. The rails or tracks typically comprise elongated elements profiled to guide a load handling device on the grid structure, and are typically profiled to provide a single track surface that allows a single load handling device to travel on the track, or a double track that allows two load handling devices to pass each other on the same track. When the slender element is profiled to provide a single track, the track includes opposing lips along the length of the track (one lip on one side of the track and another lip on the other side of the track) to guide or constrain the lateral movement of the wheels on the track. When the profile of the slender element is a double track, the track includes two pairs of lips along the length of the track so that the wheels of adjacent load-handling devices can pass each other in both directions on the same track. To provide two pairs of lips, the track typically includes a central ridge or a lip and lips on both sides of the central ridge. In all cases, when traversing the grid structure, the wheels of the load-handling devices are constrained on both sides or surfaces of the wheels of the load-handling devices.

[0007] WO2018 / 146304 (Autostore Technology AS) teaches a rail arrangement for wheeled vehicles in a storage system, wherein the rail arrangement comprises a first set of parallel rails and a second set of parallel rails. The first and second sets of parallel rails form a grid in which the second set is positioned perpendicular to the first set and intersects the first set at an intersection to form a parallel rail grid. The intersections of the intersecting rails correspond to the interconnections of the upright columns. Each rail of the two sets of rails comprises two parallel tracks suitable for guiding the wheels of a vehicle or load handling device. The rail or track comprises a plurality of longitudinal segments or sections having two edge ridges running along each longitudinal edge of the longitudinal segment and a central ridge running parallel to the edge ridges. The area between the ridges forms a track for receiving and guiding the wheels of the vehicle. The width of the central ridge is adjusted so that two vehicles can pass each other when traveling on the track in different directions on the same segment. The edge ridges of each intersecting rail come into contact with each other to form corner ridges. The corner ridges are positioned to be tightly connected to prevent the vehicle from getting stuck at the joints. The inner sides of the corner ridges are rounded so that the vehicle can travel smoothly across the intersections.

[0008] The known load handling device (30) illustrated in FIG. 4 and 5, comprising a vehicle body (32), is described in PCT Patent Publication No. WO2015 / 019055 (Ocado), which is incorporated herein by reference, wherein each load handling device (30) covers only one grid space of the grid framework structure (14). Here, the load handling device (30) comprises an upper part comprising a rechargeable power source and a controller for controlling one or more motors of the load handling device, and a lower part comprising a wheel assembly comprising a first set of wheels (34) consisting of a pair of wheels at the front of the vehicle body (32) and a pair of wheels (34) at the rear of the vehicle (32) for engaging with a first set of rails or tracks to guide the device in a first direction, and a second set of wheels (36) consisting of a pair of wheels (36) on both sides of the vehicle (32) for engaging with a second set of rails or tracks to guide the device in a second direction. Each set of wheels is driven to enable the vehicle to move along the rails in the X and Y directions, respectively. One or both sets of wheels can be moved vertically to lift each set of wheels off each rail, thereby enabling the vehicle to move in the desired direction on the grid.

[0009] The load handling device (30) is equipped with a lifting device or crane mechanism for lifting a storage container from above. The crane mechanism includes a winch tether or cable (38) wound on a spool or reel (not shown) and a grabber device (39). The lifting device includes a set of lifting tethers (38) that extend vertically and are connected to the four corners of a lifting frame (39), also known as a grabber device, or to the four corners (one tether near each of the four corners of the grabber device) for a releaseable connection to the storage container (10). The grabber device (39) is configured to releaseably grasp the top of the storage container (10) to lift the storage container (10) from a container stack in a storage system of the type shown in FIGS. 1 and 2.

[0010] Wheels (34, 36) are positioned around the periphery of a cavity or recess known as a container receiving recess or container receiving space (41) in the lower part. The recess is sized to accommodate a container (10) when it is lifted by a crane mechanism, as shown in FIG. 5 (a and b). When inside the recess, the container is lifted from the rail below so that the vehicle can move laterally to another location. When a target location is reached, for example, another stack, an access point of a storage system, or a conveyor belt, the bin or container can be lowered from the container receiving part and released from the grabber device.

[0011] Typically, one or more load handling devices operated remotely on a grid structure are configured to receive commands from a master controller to retrieve storage containers from specific storage locations within the grid framework structure. Wireless communication and networks may be used to provide communication infrastructure from the master controller to the one or more load handling devices operating on the grid structure via one or more base stations. The controller of the load handling device is configured to control various drive mechanisms to control the movement of the load handling device in response to the reception of the command. For example, the load handling device may receive a command to retrieve a container from a storage column located at a specific location on the grid structure. The command may involve various movements in the XY direction on the grid structure. Upon arrival at the storage column, a lifting mechanism is activated to grasp the storage container and lift it into a container receiving space within the body of the load handling device, from where the storage container is subsequently transported to another location on the grid structure, commonly known as a drop-off port. The storage container is lowered to an appropriate pick station to retrieve items from the container. Movement of the load handling device on the grid structure or track system also includes the load handling device being commanded to move to a charging station, which is typically located around the grid structure. When the load handling device moves on the track, it is controlled to accelerate from the starting position and decelerate to the stopping position. The starting and stopping positions depend on the trajectory or path set for the load handling device before picking up a storage container from one storage column of the grid framework structure and placing it in another storage column.A detailed description of controlling the movement of a load handling device on a grid structure or track system is taught in international patent applications WO 2022136454 (Ocado Innovation Ltd); WO 2022136475 (Ocado Innovation Ltd); WO 2022136480 (Ocado Innovation Ltd); and WO 2022136482 (Ocado Innovation Ltd).

[0012] Each load handling device may be provided with a position sensor so that a controller can determine the position of the load handling device relative to the track system. Typically, a position sensor placed on the body of the load handling device detects and operates based on the principle of detecting light reflected from the track when the load handling device encounters a plurality of track intersections. WO2018082972 (Autostore Tech AS) teaches a method and a vehicle for tracking the position of a remotely operated vehicle following a set path on a track placed on a frame structure forming a grid, wherein the vehicle has first and second sets of wheels connected to a drive for moving the vehicle in the corresponding x and y directions on the grid, and the method comprises: receiving information regarding the number of track intersections to be passed between a starting position and a stopping position in the x and y directions according to the set path; and orienting a sensor attached to the vehicle to the track along the vehicle's path. The method includes the steps of detecting and monitoring track intersections passed when moving a vehicle in the x and y directions according to a set path, and transmitting a signal to a controller that controls the drive of the vehicle's wheels when the number of track intersections passed approaches the total number of track intersections to be passed between a starting position and a stopping position along the set path in each x and y direction. The sensor is an optical sensor for detecting the reflection of light from the track. Light is reflected from the track when the robot moves along the track in the x or y direction. When the robot passes a track intersection, the intensity of the detected reflected light will change. Detection of track intersections is based on the measured intensity of the reflected light. For example, when the robot passes a track intersection, light is not reflected, so the intensity of the reflected light will decrease.

[0013] Multiple rails or tracks are required to construct a track system. The greater the number of rails or tracks required to construct a track system, the more complex the assembly of the track system becomes. In most cases, there is a 2-to-1 relationship between the number of rails or tracks at each node or intersection of the tracks or rails in the track system, in the sense that multiple rails or tracks are connected together at each node of the track system. For example, in WO2018 / 146304 (Autostore Technology AS), when creating an intersection between a first set and a second set of rails or tracks, the rails or tracks of the second set all include a recess into which the rails or tracks of the first set can be placed. Additionally, multiple track or rail sections of different sizes are connected together in a grid structure to provide multiple rectangular or square grid cells. For example, for each grid cell, there is a rail or track section extending in one direction for one length and another track or rail section extending in a second direction for a different length. Rail or track sections of different lengths meet at the nodes where they intersect in the grid structure. The need to have rail or track sections of different lengths complicates assembling the track or rail sections in a grid pattern.

[0014] Since tracks are primarily manufactured from metals such as aluminum via an extrusion process, the issue of light reflected from the tracks being detected by optical sensors is not a major concern. Extrusion consists of forcibly pushing a metal workpiece through a forming die to reduce its cross-section and transform it into a desired shape. However, the dimensional tolerances of extrusion are lower compared to other forming processes, such as injection molding and additive manufacturing like 3D printing. Because track sections are manufactured with strict dimensional tolerances to provide a continuous and uninterrupted track surface when individual track sections are assembled together into a grid structure, the extruded track sections undergo a subsequent machining process. Furthermore, extrusion cannot create various cutouts and islands in the track profile without a subsequent machining process.

[0015] WO 2022034190 (Ocado Innovation Limited) teaches a track system for a grid framework structure configured to guide a load handling device operated to move one or more containers, wherein the grid framework structure comprises a plurality of grid members that converge or intersect at nodes of a grid pattern to form a grid structure comprising a plurality of grid cells. The track system comprises a plurality of track sections mountable to the grid structure to form a track surface on which a load handling device can move, wherein each of the plurality of track sections is formed as a single unit to provide a track surface extending laterally. In other words, each of the plurality of track sections may be cross-shaped having a first track section element extending in a first direction and a second track section element intersecting the first track section element and extending in a second direction. Each of the plurality of plastic tracks is formed from a plastic material. Compared to using metal for track fabrication, using plastic material to form the track allows the track to be manufactured by a low-cost manufacturing method, e.g., injection molding, and is much lighter than metal. However, the problem with using plastic is that the track is prone to generating static electricity when interacting with robot wheels operating within the track system. To mitigate the accumulation of static electricity on the track, conductive materials such as carbon are incorporated into the plastic to make the track conductive, thereby safely discharging the accumulated charge to ground. However, the issue with imparting conductivity by incorporating carbon into the plastic lies in the position sensor's ability to determine the position of the load handling device relative to the track system, as the track does not reflect light with sufficient intensity to be detected by the position sensor.

[0016] Therefore, a track system is required that allows the load handling device to determine its position relative to the track system while having the advantage of using plastic materials.

[0017] The present invention alleviates the above problem by providing a track system comprising a plurality of tracks arranged in a grid pattern, wherein each of the plurality of tracks is formed of a plastic material having material properties such that it can dissipate static electricity and is sufficiently reflective to reflect light from the track with a strength sufficient to be detected by an optical sensor. To dissipate static electricity, each of the plurality of tracks is formed of a plastic material comprising an antistatic additive. More specifically, the present invention is a track system for a grid framework structure configured to guide a load handling device operated to move one or more storage containers, wherein the grid framework structure comprises a support framework structure comprising a plurality of storage columns, each of the plurality of storage columns is arranged to accommodate a stack of storage containers; and the track system comprises:

[0018] The track system comprises a plurality of tracks arranged to form a grid pattern including a plurality of grid cells, and is configured to be mounted on the support framework structure such that each storage container stack is positioned below a grid cell among the plurality of grid cells;

[0019] Each of the above plurality of tracks is 1 x 10 10 Surface resistance of ohms (Ω) or less, or 1 x 10⁻⁶ 10 It is characterized by having a surface resistivity of ohm meter (Ω·m) or less and a light reflectance value (LRV) greater than 30%.

[0020] Light Reflectance Value (LRV) is a property of a material and is a measure of the light reflected from a surface when illuminated by a light source. It is expressed as a number (or percentage value) between 1 and 100, where a higher number indicates more reflection from the surface. Typically, dark colors such as dark gray and black have an LRV of less than 30%, while light colors such as white have an LRV of more than 30%. For example, light white has an LRV of 85%, while black has an LRV of approximately 7%. Dark colors are poor at reflecting white light, and considering that position sensors operate based on the principle of light reflection from the track, using these dark colors would significantly reduce the intensity of light reflected from the track. In the worst-case scenario, a decrease in the amount of light reflected from the track would prevent the position sensor mounted on the load handling device from determining the position of the load handling device relative to the track system.

[0021] Typically, carbon black is added to plastic materials to make them conductive and prevent static electricity from building up on the track. However, adding carbon black to plastic materials during track manufacturing darkens the color of the track and consequently results in an inherently low LRV. In one aspect of the present disclosure, a non-carbon-based antistatic additive is added to the plastic material. Using a non-carbon-based antistatic additive increases the possibility of using plastic materials that have a relatively high LRV compared to darker materials. Optionally, each of the multiple tracks comprises acrylonitrile butadiene styrene (ABS plastic). An example of an antistatic ABS material used for manufacturing plastic tracks is traded under the name Premix's Pre-Elec® ESD22226.

[0022] Optionally, each of the multiple tracks has 1 x 10 to dissipate static electricity 5 Ω·m (ohm meter) to 1 x 10⁻⁶ 10It has a surface resistivity in the range of Ω·m (ohmmeter). Preferably, the surface resistivity is 1 x 10⁻⁶ 8 Up to 1 x 10 10 It is in the range of Ω·m. According to the present invention, surface resistivity is measured by measuring resistance from two separate points of a track section using a surface resistivity meter, such as the Bondline resistivity meter in Swindon, Wiltshire, UK. Typically, 1x10 10 The upper limit of Ω·m can dissipate static electricity buildup on the tracks. Optionally, to increase the reflection of light from the tracks, each of the multiple tracks is substantially white.

[0023] Using plastic materials to manufacture the track allows for the production of tracks with tighter tolerances than can be achieved by extrusion alone. When using plastic materials to manufacture the track of the present invention, the track can be injection molded. Unlike extrusion, injection molding allows for the formation of parts with very tight tolerances, thereby eliminating or mitigating the need for excessive machining on the finished product. Furthermore, injection molding enables the integration of one or more profiles into the track with precise or complex details, which is essential for guiding the wheels of a load handling device on the track without the possibility of derailment. For example, depending on the number of profiles, the track may be a single track profile containing opposing ribs—that is, ribs on both sides of the track—to guide or restrain each wheel on the track, or it may be a double track. In the case of a double track profile, the track includes two pairs of opposing ribs along the track to allow the load handling device to pass each other in both directions, that is, it has at least one central ridge separating the two tracks on both sides of the central ridge. The track of the present invention is not limited to a single track or a double track and may include one or more profiles to provide one or more track surfaces.

[0024] Optionally, the track system further comprises a plurality of track supports arranged in a grid pattern of the track system to define a track support structure, said plurality of tracks can be mounted on the track support structure. Optionally, each of the plurality of tracks includes means for snap-connection to one or more of the plurality of track supports. The applicant has realized that by mounting the track to the track supports so that the track supports support at least some or all of the weight of the load-carrying device operating on the track system, the track mounted thereon can be made of a less structurally supportive material that can be formed to very tight dimensional tolerances. This is because the track does not need to be composed of a material (e.g., metal) that provides sufficient load-carrying capacity.

[0025] Optionally, multiple tracks are arranged such that the raw materials of adjacent tracks are positioned between or in the middle of the intersections of multiple track supports. In the present invention, the raw materials of adjacent tracks meet between their respective intersections. Optionally, the raw materials of adjacent tracks meet at the midpoint between their respective intersections or in the middle. For the purposes of the present invention, the term “meet” includes contact, connection, or interlocking between adjacent track sections. This has the advantage that only a single-size track is required to cover a significant portion of the track supports instead of having multiple individual parts, thereby improving the manufacturability of the track, i.e., a single-tool design or one-size-fits-all design.

[0026] Optionally, multiple tracks include multiple track sections, and each of the multiple track sections is:

[0027] a) a first track section element extending in a first direction; and

[0028] b) Includes a second track section element that intersects the first track section element and extends in a second direction, wherein the second direction is transverse to the first direction.

[0029] In other words, each of the plurality of track sections may be cross-shaped, having a first track section element extending in a first direction and a second track section element intersecting the first track section element and extending in a second direction. The first and second track section elements may also be referred to as transverse parts or branches of the track section. When formed as a monolithic or integral body, the track section can be mounted at each node of the track support structure where the track support intersects, and thus the track section can extend in both the first and second directions of the track support structure. This eliminates the need to have separate tracks extending separately in the first and second directions, as seen in solutions of the prior art. However, the present invention is not limited to having a one-to-one relationship between the number of track sections and the number of nodes of the track support structure. For example, a single track section formed as a monolithic body may be configured to provide a track surface that extends transversely while extending across multiple nodes of the track support structure. When the grid cell is square, preferably, each track section of the plurality of track sections may have rotational symmetry in a horizontal plane having a fourth-order rotational symmetry. By having a rotational symmetry angle of 90°, the track section of the present invention can still align with itself even after being rotated four times. This provides the flexibility to mount the track section of the present invention to a track support structure in a number of different orientations, thereby eliminating the "jigsaw" effect of track assembly that is limited to a single orientation.

[0030] The present disclosure provides a grid framework structure for supporting one or more robotic load handling devices operating on a grid framework structure, said grid framework structure comprising:

[0031] A support framework structure comprising a plurality of storage columns, wherein each of the plurality of storage columns is arranged to accommodate a stack of storage containers;

[0032] A track system comprising a track system according to the present disclosure, wherein the track system is mounted on a support framework structure such that each storage container stack is positioned below each grid cell of a plurality of grid cells of the track system.

[0033] The present invention further provides a storage and retrieval system comprising the following:

[0034] i) Grid framework structure according to the present disclosure;

[0035] ii) A plurality of storage container stacks arranged in storage columns located below a track system, wherein each storage column is located vertically below each grid cell among a plurality of grid cells;

[0036] iii) at least one load handling device for lifting and moving storage containers loaded on a stack, wherein the at least one load handling device is remotely operated to move laterally on a track system above a storage column to access the container through a grid cell, the at least one load handling device comprises:

[0037] a) A wheel assembly for guiding a load handling device on a track system;

[0038] b) Container receiving space located on the track system;

[0039] c) A container lifting mechanism comprising a grabber device for a releaseable connection to a storage container, wherein the container lifting mechanism is positioned to lift a single container from a stack into a container receiving space;

[0040] d) at least one position sensor for determining the position of at least one load handling device for a track system, wherein the at least one position sensor has a predetermined detection range of 5 mm to 100 mm.

[0041] Optionally, the position sensor has a predetermined detection range of 10 mm to 50 mm. Optionally, the position sensor is a photoelectric sensor operating in the visible red light and / or infrared frequency range. Optionally, the visible red light has a wavelength of 624 nm and the infrared light has a wavelength of 850 nm. An example of such a position sensor is a limited reflective photoelectric sensor with a detection range of 10 mm to 50 mm, traded under the name E3FA-VP21 by Omron Corporation of Kyoto, Japan. Brief explanation of the drawing

[0042] Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments made with reference to the drawings: Figure 1 is a schematic diagram of a grid framework structure according to a known system. FIG. 2 is a schematic plan view showing an empty stack placed within the support framework structure of FIG. 1. FIG. 3 is a schematic diagram of a known storage system including a load handling device operating on a grid framework structure. FIG. 4 is a schematic perspective view of a load handling device showing a container lifting mechanism holding a container from above. FIGS. 5(a) and 5(b) are schematic perspective cutaway views of the load handling device of FIG. 4, showing (a) a storage container accommodated within the container receiving space of the load handling device and (b) the container receiving space of the load handling device. FIG. 6 is a perspective view of a second example of a grid framework structure. Figure 7 is a perspective view of a track support element of a track system. FIG. 8 is a perspective view of a track or rail element. FIG. 9(a and b) is a perspective view of a track or rail system configured to be mounted on a track support structure, wherein (a) shows a track section mounted on a track support structure; and (b) shows a track section mounted on a track support structure. FIG. 10 is a perspective view showing a section of the lower track support structure at the node of the intersecting track support. FIG. 11 is a perspective view of the upper plan view of a track section according to one embodiment of the present disclosure. FIG. 12 is a perspective view of the lower surface of the track section shown in FIG. 9, showing a plurality of tabs for connecting to the track support structure shown in FIG. 10. FIG. 13 is a perspective view of a load handling device parked in a grid cell of a track system. FIG. 14 is a perspective view showing the wheels of a wheel assembly of a load handling device parked on a track. FIG. 15(a and b) is a schematic diagram showing (a) a wheel on the side of the load handling device in a raised position on the track; and (b) a wheel on the side of the load handling device in a lowered position to engage with the track. FIG. 16 (a and b) is a perspective view of the lower part of a load handling device showing (a) a set of wheels engaged with a track section; and (b) a load handling device with the set of wheels in a raised position moving away from the track section. Figure 17 is a plot showing the frequency of interruption in the intensity of light reflected from the track as the load handling device moves along the track in the X or Y direction. Specific details for implementing the invention

[0043] The present invention was devised in response to known features of storage systems, such as grid framework structures and load handling devices, as described above with reference to FIGS. 1 to 5.

[0044] The grid framework structure can be divided into a support framework structure (42, 142) in the lower part of the grid framework structure and a track system (15, 115) in the upper part of the grid framework structure (see FIG. 1 and 6). The support framework structure (42) includes a plurality of vertical members or vertical supports (16) arranged to provide a plurality of storage columns (44) for storing storage containers (10) in one or more stacks (12). Each of the vertical supports (16) is generally tubular. In the cross-section of the storage column (44) in the horizontal plane shown in FIG. 2, each of the vertical supports (16) includes a hollow center section (46) (typically a box section) extending along the longitudinal length of the vertical support (16) to guide the movement of the container along the storage column (44), and one or more tot guides (48) mounted or formed at the corners of the hollow center section (46). The storage column (44) corresponds to a single grid cell. The method of constructing the grid framework structure illustrated in FIG. 1 includes erecting a plurality of vertical supports (16) one by one in a "stick by stick" manner and then mounting a track system (15) on the support framework structure (42). An example of the "stick by stick" construction of the grid framework structure is taught in WO2021175873 (Ocado Innovation Ltd), the details of which are incorporated herein by reference.

[0045] Alternatively, the support framework structure (142) may be erected from a three-dimensional array of prefabricated modular structural components (46), namely prefabricated frames (46), each prefabricated frame comprising a plurality of vertical supports (48) reinforced by one or more bracing members (50) (see FIG. 6). The prefabricated modular structural components are load-bearing in that they provide a three-dimensional load-bearing structure to support one or more load-handling devices moving on a track system (115) when assembled together to form a grid framework structure. Using prefabricated modular structural components to erect the grid framework structure allows the grid framework structure to be assembled at a much faster speed than the traditional 'stick-built' method, in which individual vertical supports are initially erected one by one on the floor and then track supports are mounted on the tops of the vertical supports. A detailed description of erecting the support framework structure from prefabricated modular structural components is discussed in WO 2022034195 (Ocado Innovation Limited), the contents of which are incorporated herein by reference. However, the present disclosure is not limited to the support framework structures discussed above, and may be any type of support framework structure comprising a plurality of storage columns capable of storing storage containers in one or more storage container stacks.

[0046] Supported by a support framework structure (42, 142) is a track system (15, 115) comprising a plurality of tracks (22), including a first set of tracks (22a) extending in a first direction and a second set of tracks (22b) extending in a second direction, wherein the second direction is substantially perpendicular to the first direction so that the plurality of tracks (22) are arranged in a grid pattern comprising a plurality of grid cells. A load handling device (30) operates on the grid framework structure by being guided by the plurality of tracks (22). The track system (15, 115) may further comprise a track support structure comprising a plurality of track supports extending in the first direction and the second direction. The plurality of tracks (22) may be integrated into the plurality of track supports as a single unit, for example, by extrusion. In the present disclosure, the plurality of tracks (22) are mounted on the track support structure, for example, by snap-fit ​​joints. The track supports may also be subdivided into individual track support elements (56) that are connected to each other or fixedly connected to form the track supports. Individual track support elements (56) used to form the track support are shown in FIG. 7. In cross-section, the track support may be a rigid support with a C-shaped, U-shaped, or I-shaped cross section, or even a double C-shaped or double U-shaped support.

[0047] Tracks (22a, 22b) are mounted on the track support elements (56) to complete the track system (15, 115) when the track support elements (56) are interlocked together in a grid pattern including track support members extending in a first direction and track support members extending in a second direction. The tracks (22a, 22b) are snap-fitted or fitted onto the track support members in a slide-fit arrangement. Like the track support members, the tracks include a first set of tracks (22a) extending in a first direction (e.g., X direction) and a second set of tracks (22b) extending in a second direction (e.g., Y direction), where the first direction is perpendicular to the second direction. The first set of tracks (22a) is subdivided into a plurality of track elements (58) in the first direction so that when assembled, adjacent parallel track elements (58) in the first direction are offset by at least one grid cell. Similarly, the second set of tracks (22b) is subdivided into a plurality of track elements (58) in the second direction so that when assembled, adjacent track elements in the second direction are offset by at least one grid cell. Further details regarding the arrangement of track elements on the track support structure are described in detail in WO2021175873 (Ocado Innovation Ltd), the contents of which are incorporated herein by reference. An example of a single track element (68) is shown in FIG. 8. As with the track support element, a plurality of track elements in the first and second directions are placed together to form a track in both directions. The fitting of the track element (58) to the track support includes an inverted U-shaped cross-sectional profile formed to wrap around or overlap the top of the track support. One or more lugs extending from each branch of the U-shaped profile engage with the ends of the track support in a snap-joint arrangement. It is equally reasonable that the tracks (22a, 22b) can be integrated into the track support rather than as separate parts.

[0048] Instead of individual track elements constituting a track system, a plurality of tracks (122) may be subdivided into a plurality of track sections (158), each track section (158) being formed as a single integral body and including a track element or part (122a, 122b) extending in the direction of a lower track support (18, 20) to provide a track surface extending in a first direction and a second direction, that is, each track section (158) has a connecting part or element (122a, 122b) extending in a transverse direction (see FIG. 9(a and b)). For the purpose of describing the invention, the connecting part or track section element (122a, 122b) may be referred to as a 'branch' extending transversely from a node (50).

[0049] Similar to the individual track elements (58) discussed above, a plurality of tracks (122a, 122b) are configured to be mounted on a track support structure comprising a first set of track supports (18) extending in a first direction and a second set of track supports (20) extending in a second direction (see FIG. 9(a and b)). To secure the plurality of tracks (22) to the track support structure, each track section (158) may be snap-coupled to the track support structure. The plurality of track supports (18, 20) extending in the first and second directions may include one or more openings or slots (60) so that the plurality of tracks can be snap-coupled to the track support structure (see FIG. 10). In a specific embodiment of the present disclosure, the lower surface of the track section (158) shown in FIG. 12 includes one or more lugs or tabs (62) configured to be snap-coupled to the track supports (18, 20). One or more lugs (62) may include a bead or protruding edge (64) positioned to be deflected and received in one or more openings (60) in the opposing sidewalls (or vertical elements) of the track support (18, 20) in a snap-fit ​​arrangement as illustrated in FIG. 8(a) and 8(b). The specific snap-fit ​​feature illustrated in FIG. 12 is a cantilever snap-fit. However, other forms of snap-fit ​​connections generally known in the art for securing a track section to a track support are applicable to the present invention. Likewise, other forms other than snap-fit ​​joints for securing a track section to a track support, such as the use of fasteners or adhesives, are applicable to the present invention.

[0050] There are two types of tracks for guiding one or more load-handling devices on a grid framework structure, which are generally referred to as double tracks or single tracks. A double track allows two adjacent load-handling devices to pass each other on the same track. To allow two load-handling devices to pass each other on the same track, a double track typically includes two paths or track surfaces (66, 68) separated by a central ridge or rib (70), as clearly illustrated in FIGS. 8 and 11. To guide two load-handling devices separately on the same track, each set of wheels of adjacent load-handling devices is guided by a pair of ribs (70, 72, 74) on both sides of the track (the central ridge (70) is shared by the two paths). In other words, each rib of the pair of ribs (70, 72, 74) of the track defines a guide surface extending from the track surface to guide both sides of the wheel (inner and outer surfaces of the wheel). That is, there are two pairs of guide surfaces on each track, one pair for each wheel. Guide surfaces provided by a pair of ribs to guide a load handling device along the track are illustrated in FIGS. 8 and 11. The track of the present disclosure is not limited to a double track, and the track may be one or more tracks comprising one or more track surfaces provided by one or more grooves or ridges. For example, the track may be a single track comprising a single track surface formed by a pair of ribs on both sides of the track surface to guide a single wheel along the track.

[0051] Typically, when moving on a track system, the load handling device receives a command from a control system or controller to pick up or place a storage container from or to a target storage column of a grid framework structure. Such a command includes instructing the load handling device to move to a target storage column along a specific trajectory or path on the track system. Depending on the location of the target storage column within the grid framework structure, this may include the load handling device moving across multiple grid cells in the X and Y Cartesian directions on the track system. This also includes the load handling device accelerating from a starting position at the current position and decelerating to a stopping position. To determine the position of the load handling device relative to the track system, the load handling device includes at least one position sensor (76, 78), typically an optical sensor, mounted on the body (32) of the load handling device (30), more specifically on a wheel mount (80) located on the lower part of the load handling device. Since the first set of wheels (34) and the second set of wheels (36) are configured to move in a vertical direction when changing direction on the track system, at least one position sensor is mounted on at least two sides of the body (32) of the load handling device (30) as shown in FIG. 13. A first position sensor (76) is mounted on one side of the load handling device to detect movement of the load handling device in the X-direction on the track system, and a second position sensor (78) is mounted on the other side of the load handling device to detect movement of the load handling device in the Y-direction on the track system. The first or second position sensor is operated or activated when the load handling device moves in the X-direction or Y-direction to count the number of grid cells crossed.

[0052] To actuate the first or second position sensors (76, 78) when the load handling device moves in the X-direction or Y-direction, respectively, the first and second position sensors (76, 78) are mounted on each wheel mount (80) of the first and second sets of wheels (34, 36). Considering that the wheel assembly of the load handling device includes a pair of wheels at the front of the vehicle body (32) and a pair of wheels (34) at the rear of the vehicle (32) to guide the device in the first or X-direction, and a pair of wheels (36) on each side of the vehicle (32) to guide the device in the second or Y-direction, each wheel mount (80) typically supports two wheels as shown in FIG. 13. The first and second position sensors (76, 78) are actuated or activated during the direction change of the load handling device on the track system. A pair of wheel mounts (80) on the opposite side of the load handling device body are simultaneously operated or activated when lowered from the body (32) during a turning operation on the track system and engaged with the track. It is important that the load handling device be correctly positioned on the target grid cell before lowering the first or second set of wheels to engage with the track. The target grid cell is defined as the grid cell of the track system located directly above the target storage column discussed above. When lowering the first or second set of wheels to engage with the track, the wheels (82), specifically the tires (84), should ideally be seated upright on the track surface (66, 68) between the opposing lips (70, 72) of the track surface, as illustrated in the track cross-section of FIG. 14. The operation of lowering the first or second set of wheels so that the wheels are seated upright on the track surface is referred to as "parking" the wheels on the track. Typically, there is a strict dimensional tolerance between the width of the wheels (82) and the width of the track surface. Nominally, when the wheel is lowered onto the track surface, the distance X between the edge of the wheel and the lip of the track is about 4 mm or less (see Fig. 14).If it deviates from this distance, there is a risk that the wheel will be parked on one of the track lips (70, 72, 74), and in the worst case, the load handling device may derail while moving on the track system. Consequently, it is of utmost importance that the load handling device be correctly positioned on the target grid cell when parking the wheel on the track.

[0053] In a specific example of the present disclosure, the position sensor operates based on the principle of detecting light reflected from the track as the load handling device moves along the track in the X-direction or Y-direction on the track system. In an example of the present disclosure, the position sensor (76, 78) is an optical photoelectric sensor comprising an LED (light-emitting diode) light source that emits light in the visible red light wavelength range. Examples of such sensors include, but are not limited to, the photoelectric sensor traded under the name E3FA-VP21 by Omron Corporation of Kyoto, Japan, and other optical sensors configured to function as position sensors mounted on the load handling device are also permitted in the present disclosure. The E3FA-VP21 has a detection range of 10 mm to 50 mm, and beyond this, the optical sensor has a limited detection range for reflected light and operates at a red LED wavelength (624 nm). The detection range d of the position sensor includes the vertical movement range of the first or second set of wheels in the rising and falling positions as illustrated in FIG. 15 (a and b). This enables the position sensor to receive a reflected signal when the first or second set of wheels is in an up or down position relative to the track. The detection range d is selected to prevent light reflected from below the track, for example, light reflected from a storage container in a storage column, from being inverted by the position sensor and registering a false reading by the control system. As the position sensor is mounted on each wheel mount (80) supporting the first or second set of wheels, the position sensor moves vertically when the first or second set of wheels rises or falls to engage with the track below during a change of direction.

[0054] Referring to FIG. 15(a and b), when the first or second set of wheels is in the raised position, the distance between the position sensor and the track (or the surface of the track) is referred to as "y" (see FIG. 15a), and when the first or second set of wheels is in the lowered position to engage with the track, the distance between the position sensor and the track (or the surface of the track) is referred to as "x" (see FIG. 15b). Since the position sensor is mounted on the wheel mount (80), the distance "y" is greater than the distance "x". The detection range d of the position sensor is selected to be greater than the distance y to cover the limit error when the first or second set of wheels is in the raised position, but not so large as to receive reflections from below the track, for example, from a storage container below the track. The detection range of the position sensor depends largely on the vertical movement range of the first or second set of wheels and / or the position of the position sensor mounted on the wheel mount. Mathematically, the detection range d can be expressed as x ≤ d ≤ (y + ε); Here, ε is the limit error that the detection range must cover when the first or second set of wheels is in a raised position. In a specific example of the present disclosure, the detection range d is selected to be from 10 mm to 50 mm.

[0055] Changes in the intensity of light reflected from the track are used to provide an indication of the number of grid cells crossed as the load handling device moves in the X-direction or Y-direction on the track system. As the load handling device crosses the track, the light reflected from the track decreases as the depth within the grid cell exceeds the detection range d of the position sensor, which consequently causes a change in the intensity of the light returning to the position sensor.

[0056] There are various techniques for measuring the number of grid cells traversed by a position sensor as a load handling device moves along a track system. In one example, the position sensor is configured to measure the number of track intersections passed when moving in the X and / or Y directions on the track system, as taught in WO 2018 / 082972 (Autostore Technology AS). A track intersection is an area of ​​the track system where multiple tracks intersect, namely the intersection of the X and Y tracks. This area is defined as a "node" of the track system and is indicated by reference number 50 in FIGS. 9 (a and b). As the load handling device moves along the track in the X or Y direction, light is reflected from the ribs of the track. When the load handling device passes a track intersection, light is not reflected, so the intensity of the reflected light will drop. The drop in the intensity of the reflected light provides an indication that a single grid cell has been traveled, and thus the frequency of the interruption in the intensity of the reflected light provides an indication of the number of grid cells traveled by the load handling device.

[0057] In another example, at least one position sensor (76, 78) is mounted on each side of the load handling device and configured to detect the number of tracks crossed by the leading edge and / or trailing edge of the load handling device as it moves in the X or Y direction on the track system. This is illustrated in the schematic diagram of the load handling device (30) on part of the track system in FIG. 16 (a and b). In FIG. 16a, the position sensor (76, 78) detects light reflected from the track (58) when the load handling device is in the center of the grid cell. In this example, the position sensor is positioned to detect light reflected from the surface of one of the ribs (72, 74) on the edge of the track. As the load handling device moves in the X or Y direction toward an adjacent grid cell, the position sensor moves away from the track toward the adjacent grid cell, as shown in FIG. 16b. As a result, the intensity of the reflected light will decrease because light is not reflected within the grid cell. When a load handling device is positioned over an adjacent grid cell and a position sensor is positioned over the track, the intensity of light detected by the position sensor increases as light is reflected from the track of the adjacent grid cell. As the load handling device moves across multiple grid cells in the X or Y direction, the number of interruptions in the intensity of light reflected from the track or the frequency change of the light intensity provides an indication of the number of grid cells the load handling device has crossed. FIG. 17 is a plot showing the intensity of reflected light detected by the position sensor over time. In the plot, the light intensity is measured by at least one position sensor located at the leading edge and / or trailing edge of the load handling device. The leading edge and / or trailing edge of the load handling device will vary depending on the direction of movement of the load handling device on the track system and corresponds to a measurement from a position sensor located on one of the sides of the load handling device crossing the track, particularly the lip of the track.The interval between each interruption of light intensity (indicated as Y in FIG. 17) corresponds to one grid signal traversed. In a specific example of the plot shown in FIG. 17, the frequency at which the intensity of the reflected light changes as the load handling device moves along the track in the X or Y direction is 14, and thus this is an indication of the number of grid cells traversed by the load handling device.

[0058] At least one position sensor mounted on each side of the load handling device can also be used to determine whether the load handling device is positioned upright or centered on the grid cell, that is, under the storage column. Upon reaching the grid cell, the first and second sets of wheels are temporarily parked on the track simultaneously or all at once before lifting the first or second set of wheels according to the direction of movement of the load handling device on the track (i.e., X direction or Y direction). That is, they are placed in a lowered or engaged position on the track. The moment when the position sensors on all four sides of the load handling device detect light reflected from each track section, in particular from each lip, provides an indication that the load handling device is positioned upright or centered on the grid cell. For example, if one or more position sensors fail to detect light reflected from each track section, even though the load handling device is stopped at the target position or before changing direction on the track system, this indicates that the load handling device is not seated upright or centered on the grid cell.

[0059] When using tracks composed primarily of plastic, there is a risk of static electricity accumulating on the track due to interaction with the wheels or tires of load handling devices. This is resolved by making the plastic track conductive using carbon, as taught in WO 2022034190 (Ocado Innovation Limited). Typically, to dissipate static electricity, the surface resistance of the track is 1011 It must not exceed Ω (ohm), and preferably 10 10 It must not exceed Ω (ohm). Typically, carbon reduces the surface resistance of plastic tracks to 10 2 Ω to 10 6 Reduce it to between Ω. Surface resistivity is measured using a surface resistivity meter (SRM100 - Half Decade Resistance Meter) manufactured by Bondline in Swindon, Wiltshire, UK.

[0060] Due to the inherent black color of carbon, the color of plastic tracks containing carbon tends to be dark. Consequently, the intensity of light reflected from the track is low or non-existent, making it impossible for position sensors based on illuminating the track with visible red light to detect the reflected light. If the position sensor fails to detect the light reflected from the track, the load handling device may fail to follow the predetermined trajectory or path set by the control system. In the worst case, the load handling device may overshoot or undershoot the target grid cell, or fail to determine its position relative to the track system as described above. Given that the position sensor operates on the principle of detecting light reflected from the track to determine whether the load handling device is sitting upright on the grid cell or moving away from it, it is necessary to provide a track system having a reflective surface so that the light reflected by the position sensor discussed above can be detected. In the present disclosure, each of the plurality of tracks is formed from a plastic material, but instead of using excessive carbon to make the track surface electrically conductive, the plastic track is made of a bright color to reflect light with sufficient intensity to be detected by a position sensor, while the track surface is electrically conductive enough to dissipate static electricity.

[0061] The surface of a plastic track is measured to reflect light in the visible red region with sufficient intensity to be detected by a position sensor, having physical parameters that are the reflectivity characteristics of the material. Given that multiple tracks are manufactured on a large scale at a relatively low cost, ideally, the composition of the plastic track has measurable physical parameters that are the reflectivity characteristics of the material. For the purposes of this disclosure, particularly in the visible red region, the light reflectivity value (LRV) was considered as a measurable physical parameter that is the reflectivity characteristic of the material used for the plastic track. The light reflectivity value (LRV) is a measure of the light reflected from a surface when illuminated by a light source in the visible region of wavelength and is a characteristic of the material's color. It is expressed as a number (or percentage value) from 1 to 100, where a higher number indicates more reflection from the surface and vice versa. It has been found that a position sensor can detect light reflected from a light-colored material better than from a dark-colored material, such as black. However, physical parameters related to the reflectance of a material are not limited to LRV and may be based on the emissivity values ​​of plastic materials and depend primarily on the wavelength of light emitted from the position sensor. For example, if the position sensor is based on the detection of reflectance of infrared or laser light, the measured parameter, which is a reflectance characteristic of the material, is emissivity. In the present disclosure, the position sensor operates in the visible red light and infrared regions, in which case LRV is considered a good measure of the reflectance of the material surface. A test method used to measure the LRV of a track surface comprises illuminating the track surface with visible red light and detecting the reflected light using a reflection spectrophotometer (e.g., Ocean SR or Ocean HDX) that uses light having a wavelength in the range of 380 nm to 780 nm.

[0062] In one extreme case, 10 is sufficient to dissipate static electricity. 5The intensity of light reflected from a black track containing carbon with a measured resistivity of Ω·m and a measured LRV of less than 30%, for example, about 5%, was so poor that the position sensor could not determine the position of the load handling device relative to the track system. To be sufficiently conductive to dissipate static electricity 10 10 A gray track containing a smaller amount of carbon with a measured resistivity of Ω·m and a measured LRV greater than 30%, for example, about 40%, could detect light reflected from the track, and thus the load handling device could determine its position relative to the track. In the other extreme case, 10 sufficient to dissipate static electricity 8 In the case of a white track having a measured intensity of Ω·m and a measured LRV greater than 30%, for example, about 85%, the position sensor was able to detect light reflected from the track, and thus the load handling device could determine its position relative to the track. Therefore, a light-colored plastic track is more helpful than a dark-colored plastic in reflecting light from an optical position sensor with sufficient intensity to be detected by the optical position sensor. In the examples of the present disclosure, a light-colored track capable of reflecting light with sufficient intensity to be detected by a position sensor while being sufficiently conductive to dissipate static electricity comprises acrylonitrile butadiene styrene (ABS). To dissipate static electricity, the ABS material preferably comprises an antistatic additive. Commercially available plastic materials having antistatic properties and a color bright enough to reflect light with sufficient intensity to be detected by a position sensor include, but are not limited to, Pre-Elect® from Premix Group of Finland or Sicoflex® AG314L from Ravago of Europe.

[0063] Ideally, for a position sensor operating in the visible red region to detect light reflected from the track, the LRV should be greater than 30%, and preferably greater than 50%. Examples of colors of such materials having an LRV of 30% or more include, but are not limited to, blue, orange, gray, and white, and examples of dark-colored materials having an LRV of less than 30% include black and brown. However, the present disclosure is not limited to light-colored materials being suitable for use in manufacturing tracks, as this can increase the reflective properties on the surface of dark-colored materials, causing each LRV to exceed 30%.

[0064] Having plastic tracks of different colors offers advantages beyond the ability to reflect visible light. One of the risks associated with items or goods (e.g., food or medicine) ingested by animals is the risk of physical contamination by foreign substances. To address this risk, an increasing number of companies are investing in contamination detection equipment, such as metal detectors or X-ray machines. While this equipment is useful for detecting metal (metal detectors) or high-density contamination (X-rays), many other materials are used in production areas that cannot be detected by metal detectors or X-ray machines. To resolve this risk, detectable versions of objects used in production areas have been developed. Detectability is achieved by using special metal-sensing plastics or by incorporating aluminum or metal components into the objects. Another solution for detecting potential physical contamination is to use contrasting colors that do not typically occur in natural foods. Since blue does not occur naturally in food, it is very frequently used in the production of objects used in the food industry. These contrasting colors allow potential food contaminants to be detected visually. If items are stored in the grid framework structure discussed above, any contaminants from the grid framework structure may need to be easily detectable in the storage container. One of the components of the grid framework structure that can generate contaminants in the storage container is the load handling device, specifically the track system resulting from continuous interaction with the wheels of the load handling device. In the case of the plastic track discussed above, contaminants generated from the track system can be visually detected by having a contrasting color (e.g., blue) of the plastic track with an LRV of 30% or more.

Claims

Claim 1 A track system for a grid framework structure (14) configured to guide a load handling device (30) operated to move one or more storage containers (10), wherein the grid framework structure comprises a support framework structure comprising a plurality of storage columns, each of the plurality of storage columns is arranged to accommodate a stack of storage containers, and the track system comprises a plurality of tracks arranged to form a grid pattern comprising a plurality of grid cells, each of the plurality of tracks comprises a plastic material, and the track system is configured to be mounted on the support framework structure such that each stack of storage containers is placed under each grid cell among the plurality of grid cells, and each of the plurality of tracks is 1 x 10 10 Surface resistance of less than ohms (Ω) or 1 x 10⁻⁶ 10 A track system characterized by having a surface resistivity of ohm meter (Ω·m) or less and a light reflectance value (LRV) greater than 30%. Claim 2 A track system according to claim 1, wherein each of the plurality of tracks is substantially white. Claim 3 A track system according to claim 1 or 2, wherein each of the plurality of tracks comprises acrylonitrile butadiene styrene (ABS plastic). Claim 4 A track system according to any one of claims 1 to 3, wherein each of the plurality of tracks is injection molded. Claim 5 A track system according to any one of claims 1 to 4, wherein the track system further comprises a plurality of track support members arranged in a grid pattern of the track system to form a track support structure, and wherein the plurality of tracks are mountable to the track support structure. Claim 6 A track system according to claim 5, wherein each of the plurality of tracks includes means for snap-fitting to one or more of the plurality of track supports. Claim 7 A track system according to claim 5 or 6, wherein the plurality of tracks are arranged such that the original portions of adjacent tracks are positioned between or in the middle of the intersection points of the plurality of track supports. Claim 8 A track system according to any one of claims 1 to 7, wherein each of the plurality of tracks is formed as a single unit. Claim 9 A track system according to claim 8, wherein the plurality of tracks comprises a plurality of track sections, each of the plurality of track sections comprises: a) a first track section element extending in a first direction; and b) a second track section element intersecting the first track section element and extending in a second direction, wherein the second direction is transverse to the first direction. Claim 10 A grid framework structure for supporting one or more robotic load handling devices operating on a grid framework structure, wherein the grid framework structure comprises: a supporting framework structure including a plurality of storage columns, each of which is arranged to accommodate a stack of storage containers; and a track system including a track system defined in any one of claims 1 to 9, wherein the track system is mounted on the supporting framework structure such that each stack of storage containers is placed under each of the plurality of grid cells of the track system. Claim 11 A storage and retrieval system comprising: i) a grid framework structure as defined in claim 10; ii) a plurality of storage container stacks arranged in storage columns located below a track system, each storage column located vertically below a grid cell; iii) at least one load handling device for lifting and moving storage containers loaded in the stack, wherein the at least one load handling device is remotely operated to move laterally on a track system above the storage column to access the containers through the grid cell, and the at least one load handling device comprises: a) a wheel assembly for guiding the load handling device on the track system; b) a container receiving space located above the track system; c) a container lifting mechanism comprising a grabber device for a releaseable connection to a storage container, wherein the container lifting mechanism is positioned to lift a single container from the stack into the container receiving space; and d) at least one position sensor for determining the position of the at least one load handling device relative to the track system, wherein the at least one position sensor has a predetermined detection range of 5 mm to 100 mm. Claim 12 A storage and retrieval system according to claim 11, wherein the predetermined detection range is in the range of 10 mm to 50 mm. Claim 13 A storage and retrieval system according to claim 11 or 12, wherein the position sensor is a photoelectric sensor operating in the visible red light and / or infrared frequency range. Claim 14 A storage and retrieval system according to claim 13, wherein the visible red light has a wavelength of 624 nm and the infrared light has a wavelength of 850 nm.

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