Patent Description:
This application claims priority from UK Patent Application No. <CIT>.

Methods of handling containers stacked in rows have been well known for decades. Some such systems, for example as described in <CIT>, comprise free-standing stacks of containers arranged in rows in order to reduce the storage volume associated with storing such containers but yet still provide access to a specific container if required. Access to a given container is made possible by providing relatively complicated hoisting mechanisms which can be used to stack and remove given containers from stacks. The costs of such systems are, however, impractical in many situations and they have mainly been commercialised for the storage and handling of large shipping containers.

The concept of using free-standing stacks of containers and providing a mechanism to retrieve and store specific containers has been developed further, for example as described in <CIT>. EP'<NUM> discloses a mechanism for removing a plurality of stacked containers, using a robotic load handler in the form of a rectangular tube which is lowered around the stack of containers, and which is configured to be able to grip a container at any level in the stack. In this way, several containers can be lifted at once from a stack. The movable tube can be used to move several containers from the top of one stack to the top of another stack, or to move containers from a stack to an external location and vice versa. Such systems can be particularly useful where all of the containers in a single stack contain the same product (known as a single-product stack).

In the system described in EP'<NUM>, the height of the tube has to be at least as high as the height of the largest stack of containers, so that that the highest stack of containers can be extracted in a single operation. Accordingly, when used in an enclosed space such as a warehouse, the maximum height of the stacks is restricted by the need to accommodate the tube of the load handler.

<CIT>) describes a system in which stacks of containers are arranged within a frame structure. A system of this type is illustrated schematically in <FIG> of the accompanying drawings. Robotic load handling devices can be controllably moved around the stack on a system of tracks on the uppermost surface of the stack.

A load handling device is described in UK Patent Application No. <CIT> - where each robotic load handler only covers one grid space, thus allowing high density of load handlers and thus high throughput of a given size system.

In the known robotic picking systems described above, robotic load handling devices are controllably moved around the top of the stacks on a track system forming a grid. A given load handling device lifts a bin from the stack, the container being lifted containing inventory items needed to fulfil a customer order. The container is carried to a pick station where the required inventory item may be manually removed from the bin and placed in a delivery container, the delivery container forming part of the customer order, and being manually filled for dispatch at the appropriate time. At the pick station, the items may also be picked by industrial robots, suitable for such work, for example as described in UK Patent Application No <CIT>.

As shown in <FIG> and <FIG>, stackable storage containers, known as bins <NUM>, are stacked on top of one another to form stacks <NUM>. The stacks <NUM> are arranged in a framework <NUM> in a warehousing or manufacturing environment. <FIG> is a schematic perspective view of the framework <NUM>, and <FIG> is a top-down view showing a single stack <NUM> of bins <NUM> arranged within the framework <NUM>. Each bin <NUM> typically holds a plurality of product or inventory items, and the inventory items within a bin <NUM> may be identical, or may be of different product types depending on the application. Furthermore, the bins <NUM> may be physically subdivided to accommodate a plurality of different inventory items.

The framework <NUM> comprises a plurality of upright members <NUM> that support horizontal members <NUM>, <NUM>. A first set of parallel horizontal members <NUM> is arranged perpendicularly to a second set of parallel horizontal members <NUM> to form a plurality of horizontal grid structures supported by the upright members <NUM>. The members <NUM>, <NUM>, <NUM> are typically manufactured from metal. The bins <NUM> are stacked between the members <NUM>, <NUM>, <NUM> of the framework <NUM>, so that the framework <NUM> guards against horizontal movement of the stacks <NUM> of bins <NUM>, and guides vertical movement of the bins <NUM>.

The top level of the framework <NUM> includes rails <NUM> arranged in a grid pattern across the top of the stacks <NUM>. Referring additionally to <FIG> and <FIG>, the rails <NUM> support a plurality of robotic load handling devices <NUM>. A first set 22a of parallel rails <NUM> guide movement of the load handling devices <NUM> in a first direction (X) across the top of the framework <NUM>, and a second set 22b of parallel rails <NUM>, arranged perpendicular to the first set 22a, guide movement of the load handling devices <NUM> in a second direction (Y), perpendicular to the first direction. In this way, the rails <NUM> allow movement of the load handling devices <NUM> in two dimensions in the X-Y plane, so that a load handling device <NUM> can be moved into position above any of the stacks <NUM>.

Each load handling device <NUM> comprises a vehicle <NUM> which is arranged to travel in the X and Y directions on the rails <NUM> of the framework <NUM>, above the stacks <NUM>. A first set of wheels <NUM>, consisting of a pair of wheels <NUM> on the front of the vehicle <NUM> and a pair of wheels <NUM> on the back of the vehicle <NUM>, are arranged to engage with two adjacent rails of the first set 22a of rails <NUM>. Similarly, a second set of wheels <NUM>, consisting of a pair of wheels <NUM> on each side of the vehicle <NUM>, are arranged to engage with two adjacent rails of the second set 22b of rails <NUM>. Each set of wheels <NUM>, <NUM> can be lifted and lowered, so that either the first set of wheels <NUM> or the second set of wheels <NUM> is engaged with the respective set of rails 22a, 22b at any one time.

When the first set of wheels <NUM> is engaged with the first set 22a of rails <NUM> and the second set of wheels <NUM> are lifted clear from the second set 22b of rails <NUM>, the first set of wheels <NUM> can be driven, by way of a drive mechanism (not shown) housed in the vehicle <NUM>, to move the load handling device <NUM> in the X direction. To move the load handling device <NUM> in the Y direction, the first set of wheels <NUM> are lifted clear of the first set 22a of rails <NUM>, and the second set of wheels <NUM> are lowered into engagement with the second set 22b of rails <NUM>. The drive mechanism can then be used to drive the second set of wheels <NUM> to achieve movement in the Y direction.

In this way, one or more robotic load handling devices <NUM> can move around the top surface of the stacks <NUM> on the framework <NUM>, as shown in <FIG> under the control of a centralised control utility (not shown). Each robotic load handling device <NUM> is provided with lifting means <NUM> for lifting one or more bins <NUM> from the stack <NUM> to access the required products.

The body of the vehicle <NUM> comprises a cavity <NUM>, the cavity <NUM> being of a size capable of holding a bin <NUM>. The lifting means <NUM> comprises winch means and a bin gripper assembly <NUM>. The lifting means lifts a bin <NUM> from the stack <NUM> to within the cavity <NUM> within the body of the vehicle <NUM>. When in the cavity <NUM>, the bin <NUM> is lifted clear of the rails beneath, so that the load handling device can move laterally to a different location on the grid. On reaching the target location, for example another stack, an access point in the storage system or a conveyor belt, the bin <NUM> can be lowered from the cavity and released from the gripper assembly <NUM>.

In this way, multiple products can be accessed from multiple locations in the grid and stacks at any one time.

The above description describes a storage system in connection with, for example, groceries. <FIG> shows a typical such storage system, the system having a plurality of load handling devices <NUM> active on the grid above the stacks <NUM>.

<FIG> and <FIG> show the bins <NUM> in stacks <NUM> within the storage system. It will be appreciated that there may be a large number of bins <NUM> in any given storage system and that many different items may be stored in the bins <NUM> in the stacks <NUM>. Each bin <NUM> may contain different categories of inventory items within a single stack <NUM>.

In one system described above and further in UK Patent Application Number <CIT>, - the storage system comprises a series of bins <NUM> that may further comprise delivery containers DT with customer orders contained therein or may further comprise bins <NUM> with inventory items awaiting picking contained therein. These different bins <NUM> and combinations thereof may be contained in the storage system and be accessed by the robotic load handling devices <NUM> as described above.

It will be appreciated that automated or semi-automated storage and retrieval systems are not limited to systems directed to groceries. For example, the technology can be applied to shipping, baggage handling, vehicle parking, indoor or hydroponic greenhouses and farming, modular buildings, self-storage facilities, cargo handling, transport switchyards, manufacturing facilities, pallet handling, parcel sortation, airport logistics (ULD) and general logistics to name but a few possible applications. It will be appreciated that storage and retrieval systems of different types will have different technical requirements.

A further example of a grid-based storage and retrieval system disclosing the preamble of claim <NUM> is shown in <CIT>.

It is against this background that the present invention has been devised.

Accordingly, there is provided a grid-based storage and retrieval system according to claim <NUM>.

The sling may be lifting tapes or wires. In normal use, typically both ends of the sling would be spooled or wound and unspooled or unwound in order to lift and lower the load. Advantageously, just one end of the sling may be spooled or unspooled allowing the lifting assembly to continue to be operational with only one hoist drum operational.

The first end of the sling may be attached to a first hoist drum and the second end of the sling is attached to a second hoist drum, and the first hoist drum is driven by a first motor and the second hoist drum is driven by a second motor.

The hoist drums may be independently operable to advantageously provide redundancy to the lifting assembly. Advantageously this may allow the load handling device to continue operating even with a fault or reduced power. It will be appreciated that this may mean that the lifting and lowering operation.

Both the first end of the sling and the second end of the sling may be attached to the same hoist drum, and the hoist drum is driven by one or more motors. The first motor and second motors me be independently powered by respective power supplies. The lifting assembly may comprise at least two sling assemblies.

In some arrangements, both ends of the sling may be attached to the same hoist drum. This arrangement has the advantage of taking less space. In addition, less control and communication facilities/volume may be required. This may additionally make inserting and removing the lifting assembly, and/or removing other components of the load handling device through or around the lifting assembly, easier. In some arrangements the drum may be operated by more than one motor to provide redundancy. In normal operation this would mean that a greater load could be lifted and lowered. In other circumstances, for example when a motor or power supply has a fault, then the lifting assembly may continue to be operational.

In some arrangements, the drum may be mounted so that it appears as a disc from above i.e. with the drum axis in the z- or vertical direction. In this arrangement, the drum may have a much larger diameter than would be possible to accommodate if it were arranged with the axis in the x,y plane. Having a large diameter drum means that the drum may be directly driven by a small high RPM motor without the need for step-down gearing.

The disc drum may be driven by a single motor. The single motor may be a direct drive worm gear transfer to the disc drum, or wherein the single motor is a direct drive pulley gear transfer to the disc drum.

Advantageously, using a single motor may reduce the cost (space and capital). Using a worm gear advantageously means that the drum may be directly driven, and that the motor may be arranged in the same plane as the drum. Further, using a worm gear arrangement enables more than one motor to be arranged around the drum, and advantageously provides redundancy.

The sling or one or more tapes may be arranged in a pulley system.

A pulley system may be used to reduce the force required to lift and lower the load. Advantageously, thinner tapes or wires may be used to lift a load that would otherwise require a much stronger tape.

The lifting assembly may further comprise at least one guide or guide-roller mounted on the gripper plate. One or more of guide-rollers may be powered assistant guide-rollers. The gripper plate has at least one sensor for detecting the balance of the gripper plate and or load attached to the gripper plate.

Guides and guide rollers may assist in ensuring durable operation of the lifting assembly and load handling device by ensuring that lifting tapes or wires remain in the correct position and that spooling is neat and remains compact.

Power assistant guide-rollers may reduce the load requirement on the drum motors. Further, power assistant guide-rollers may be used to keep the load level, for example, when the load is unevenly distributed, or for example, when there is more than one drum motor and they are unevenly matched.

One or more of the guide-rollers may be movable tensioning guide-rollers.

A tensioning roller may be used to keep the lifting tape taut, especially when the rate or direction of lifting is changed.

The lifting assembly may be under control of the load handling device. The gripper plate may have at least one sensor for detecting the balance of the gripper plate and or load attached to the gripper plate. The gripper plate may comprise at least one gripper assembly, or wherein the gripper plate comprises two or more gripper assemblies, preferably wherein the gripper plate comprises four gripper assemblies. The gripper assembly(ies) may be arranged to correspond positionally to latch recesses on a storage container. The gripper assembly may further comprise guides and or guide rollers mounted on the load handling device for guiding the sling or tapes.

A method of using a load handling device is provided for lifting and moving storage containers (<NUM>) stacked in a grid framework (<NUM>) according to any preceding claim, the method comprising the steps of: receiving a signal from a centralised control facility to perform a lifting operation, manoeuvring the load handling device to the lift location, lowering the gripper plate to insert grippers into cooperating recesses of a container; causing the grippers to latch to the container; and lifting the gripper plate and container into the cavity of the load handling device OR lowering the gripper plate and container until the container is supported beneath; causing the grippers to release to the container; and lifting the gripper plate into the cavity of the load handling device.

The gripper assembly may be self-locking.

The load handling device may grip onto storage containers and lift storage containers. The gripper assembly is stable in at least two configurations, and is self-locking in at least the locked configuration. The gripper operates below the fatigue limit of the material and is repeatedly movable between positions. In this way, the load handling device is able to securely and reliably grip a storage container for lifting and moving the storage container.

The bi-stable flexure may comprise: an actuator; two or more gripper-arms having hook-ends; and a number of hinge arrangements, the number of hinge arrangements corresponding to the number of gripper arms, wherein each hinge arrangement is deformable and connects the respective gripper-arms to the actuator. The hinge arrangements comprise a fulcrum, and first and second deformable sections connect to respective ends of the fulcrum. The fulcrum is substantially triangular. In the locked configuration the fulcrum engages with the gripper-arm and the compliant mechanism is open or wide; and in the release configuration the first and second sections of the hinge are flexed and the compliant mechanism is closed or narrow.

The hook-ends of the gripper arms allow the gripper to latch on to a cooperating part of a storage container, and the fulcrum means that the flexure is not able to move past the stable locked position without failure of the gripper. Thus, the configuration of the gripper assembly itself ensures that the gripper is reliably securable to the storage container for the purpose of lifting and moving the storage container.

The hinge arrangements may be connected to the gripper-arms spaced apart from the hook-ends and the fulcrum may extend above the line between the first and second hinge arrangements, or the fulcrum extends below the line between the first and second hinge arrangements. The gripper assembly may comprise two or more flexure mechanisms. The gripper assembly may comprise four flexure mechanisms.

It will be appreciated that the specific arrangement will depend on the intended use of the gripper assembly, and the intended scope is not limited to the specific examples disclosed herein.

The load handling device may further comprise a means for lifting storage containers, wherein the means for lifting storage containers comprises a gripper plate and the gripper assembly is mounted on the gripper plate. The means for lifting storage containers may be releasably mountable on the body of the load-handling device. Lifting tapes may be attached to the gripper-arms.

The flexure mechanism may be made using additive manufacturing.

If a malfunction and or failure of the load handling device is detected, the load handling device may be instructed to move to a maintenance area or the edge of the grid using non-malfunctioning and non-failed means.

The centralised control utility may communicate with the at least one load handling device operating on the grid to instruct the load handling device to move to a specific location on the grid.

Further the load handling device may be instructed to lift a container from a stack and move the container to another location on the grid, AND OR further instructing the load handling device to lower a container into a stack position beneath the grid.

Other aspects and advantages will become apparent from the following description.

The invention will now be described with reference to the accompanying diagrammatic drawings in which:.

In this document, the word "comprise" and its derivatives are intended to have an inclusive rather than an exclusive meaning. For example, "x comprises y" is intended to include the possibilities that x includes one and only one y, multiple y's, or one or more y's and one or more other elements. Where an exclusive meaning is intended, the language "x is composed of y" will be used, meaning that x includes only y and nothing else.

In this document, the language "movement in the n-direction" (and related wording), where n is one of x, y and z, is intended to mean movement substantially along or parallel to the n-axis, in either direction (i.e. towards the positive end of the n-axis or towards the negative end of the n-axis).

In this document, the word "connect" and its derivatives are intended to include the possibilities of direct and indirection connection. For example, "x is connected to y" is intended to include the possibility that x is directly connected to y, with no intervening components, and the possibility that x is indirectly connected to y, with one or more intervening components. Where a direct connection is intended, the words "directly connected", "direct connection" or similar will be used. Similarly, words such as "support", "mount" and their derivatives are intended to include the possibilities of direct and indirect contact.

In this document, some words such as "load handling device", "vehicle" and "bot" are used interchangeably. Similarly, words "body" ,"frame" and "skeleton " of the load handing device; "rails" and "tracks" of the storage frame; "bin", "container", or "tote" of the storage system. "DT" or "delivery tote" is a tote which contains completed or partially completed orders. "ST" or "storage tote" is a tote which contains items being stored in the storage and retrieval system. Similarly, "tapes", "ropes" and "wires" are used interchangeably.

The load handling devices operating on the grid of the storage and retrieval system are intended to be operated with or at the same time as other devices operating on the grid. The devices operating on the grid may be all of the same type, or more than one type of device may be operated on the grid at the same time.

The load handling devices described herein are intended to have at least some fault tolerant characteristics.

A load handling device comprises a skeleton <NUM> or frame which houses the other components of the load handling device, for example, the battery and associated electronics, controllers and communications devices, motors for driving wheels, motors for driving the lift assembly, and other sensors and systems. The skeleton <NUM> comprises a recess, sized to accommodate a container or bin when it is lifted by the lift assembly.

As noted above, with reference to other load handling devices, each load handling device is arranged to travel in the x- and y- directions on the rails <NUM> of the framework <NUM>, above the stacks <NUM> of containers or bins.

Each load handling device is fitted with two sets of wheels <NUM>, <NUM>, which run on rails provided at the top of the frame of a storage system of the type described above. At least one wheel of each set of wheels <NUM>, <NUM> is driven to enable movement of the load handling device in x- and y-directions respectively along the rails. The two sets of wheels <NUM>, <NUM> are arranged around the periphery of a skeleton <NUM> of the load handling device. As will be explained below, one of the first or second set of wheels <NUM>, <NUM> can be moved vertically to lift them clear of the rails leaving the other of the first or second set of wheels <NUM>, <NUM> in contact with the rails, thereby allowing the load handing device to change direction. In some instances, both sets of wheels <NUM>, <NUM> may be in contact with the rails at the same time.

As noted above, the load handling devices for operating on a storage and retrieval system typically comprise a space or cavity for receiving a container. The cavity is sized such that enough of a container can fit inside the cavity to enable the load handling device to move across the grid on top of storage framework without the underside of the container catching on the grid or another part of the storage framework. When the load handling device has reached its intended destination, the container-lifting mechanism controls lift tapes to lower the gripper assembly and the corresponding container out of the load handling device and into the intended position.

The intended position may be a stack of containers or an egress point of the storage framework, or an ingress point of the storage framework if the load handling device has moved to collect a container for storage in the storage framework. A lifting assembly may sometimes be referred to as a TGA (Tote Gripper Assembly).

<FIG> show a representation of a lifting assembly <NUM> of a load handling device for raising a container into or lowering the container from a cavity of the load handling device. The lifting assembly comprises two hoist drums A, B. Each hoist drum A, B is driven by respective motors, and the motors are independently powered by respective power supplies.

A first end of a lifting tape is attached to hoist drum A, and the second end of the lifting tape is attached to hoist drum B such that the lifting tape makes a sling between the hoist drums A, B. In normal use, when the hoist drums A, B are made to rotate by their respective motors, the lifting tape wraps around the hoist drums A, B thereby lifting a weight or payload supported by the sling arrangement.

At the lower end of the sling arrangement, the lifting tape is guided by guide-rollers C, D, E mounted on a gripper plate. The gripper plate is for gripping a container or bin with gripper assemblies as described in more detail below. The guide-rollers C, D may be independently powered to assist the hoist drums A, B. In normal use, guide-rollers C, D may be un-powered and as the lifting tape is raised or lowered, the lifting tape slides over the guide-rollers C, D. To compensate for uneven loading of the gripper plate, one or both of the guide-rollers C, D may be activated to assist hoist drums A or B respectively to keep the gripper plate level as determined from a sensor mounted on the gripper plate. For example, if heavy objects are placed in one side of a container then one of the assistant guide-rollers may be powered to compensate for the additional load on that side to keep the container relatively level.

Guide-roller E is a tensioning wheel or roller, positioned between rollers C and D and is movable to tighten or slacken the lifting tape. For example, guide-roller E may be mounted on a spring.

Typically, the lifting assembly comprises two sling arrangements A, B, C, D, E and A',B', C', D', E', as illustrated in <FIG>. Hoist drum A and hoist drum A' are driven by the same motor. Similarly, hoist drum B and hoist drum B' are driven by the same motor, and similarly rollers C and C' and rollers D and D' may be rotationally linked.

It will be appreciated that the pairs of drums and rollers A-A', B-B', C-C', and D-D' may be mounted on the same shaft, or the drums and roller pairs may be mounted on separate shafts.

It will be appreciated that the lifting assembly may comprise one or more additional sling assemblies, thereby proportionally reducing the load on each sling assembly.

In normal use each of the sling assemblies (lifting tape and roller set) are operated together to lift and lower the gripper plate. In normal use, the lifting tape is wrapped around both hoist drum A and hoist drum B by a substantially equal amount, and the hoist drums operate at a similar speed. As a result, the gripper plate is lifted at the speed of the hoist drums A, B.

If only one of the hoist drums A or B is used to coil the lifting tape to lift the gripper plate then the gripper plate is lifted at half the speed at which the hoist drum A or B is rotated at. Thus, the gripper plate would be lifted at half the speed compared with the lifting rate under normal use. In this case, the maximum amount of load that it is possible to lift will also be reduced because only one motor is producing torque.

With this arrangement, if for any reason it is not possible to operate one of the hoist drums A, B, then, as a result of the sling arrangement, it is still possible to lift or lower the gripper plate using the other of the hoist drums A, B to pull or feed the lifting tape through the guide-rollers C, D, E as the lifting tape is wrapped around or unwound from the operational hoist drum A, B respectively. Accordingly, a fault in a hoist drum A, B assembly does not result in total failure of the lifting assembly.

The illustrated lifting arrangement has various advantages, including that: cost and space within the body of the load handling device may be saved relative to arrangements incorporating more motors; the rates of winding and unwinding of the spools or hoist drums A-B, A'-B' do not need synchronising allowing them to be wound and unwound at the same rate without additional gearing, control or other intervention; only a single control unit is required to control the raising and lowering of the hoist drums.

As will be discussed in more detail below, the gripper plate has one or more griper assemblies mounted thereon for latching to a storage container.

<FIG> show representations of lifting assemblies <NUM>, <NUM> of a load handling device <NUM> for raising and lowering a container <NUM>. The lifting assembly <NUM>, <NUM> comprises a gear <NUM>, <NUM> and motor <NUM>, <NUM>.

Extending through the gear <NUM>, <NUM> a common axle <NUM>, <NUM> extends to first and second hoist drums <NUM>, <NUM>, around which lifting tape <NUM> is wound. A first end of the lifting tape <NUM> is attached to the hoist drums <NUM>, <NUM>, and the second end is attached to the same hoist drums <NUM>, <NUM> in a sling arrangement supporting a gripper plate as described above in connection with <FIG>. In an alternative arrangement a first end of the lifting tape <NUM> is attached to the hoist drums <NUM>, <NUM>, and the second end of the lifting tape is attached to a gripper plate. Slave wheels <NUM> are used to guide the lifting tape <NUM> to the gripper plate attached to the ends of the lifting tape <NUM> and/or to adjust the tension in the lifting tape <NUM>. The gripper plate is used to latch to a load, which may then be lifted and lowered by the lifting assembly <NUM>, <NUM>.

In the case of the assembly <NUM> shown in <FIG>, first and second lifting tapes <NUM> are wound alternately around the drums <NUM>. Thus, when the first and second drums <NUM> are rotated by the motor <NUM> to lower the gripper plate, both tapes <NUM> unwind at the same time and at the same speed. In reverse, the lifting tapes <NUM> wrap around the hoist drums <NUM> at the same time and speed, thereby lifting a weight or payload supported by the gripper plate.

In the case of the assembly <NUM> shown in <FIG>, first and second ends of lifting tapes <NUM> are wound around twin drums <NUM> at each end of the axle <NUM>.

For both assemblies <NUM>, <NUM>, at each end of the axle <NUM>, <NUM>, the tapes <NUM> unwind from the top and bottom of the drum <NUM>, <NUM> respectively to balance the forces applied to the assembly. For both assemblies <NUM>, <NUM> the drums <NUM>, <NUM> are in the z,x-plane. Alternatively, the drums <NUM>, <NUM> may be arranged in the z,y-plane.

It will be appreciated that the diameter of the drum <NUM> is necessarily larger than the respective drums <NUM> for a given length of lifting tape <NUM>. Correspondingly, the gear <NUM> is larger than the gear <NUM>, and the required torque produced by motor <NUM> is larger than the required torque produced by motor <NUM>.

The lifting assembly <NUM> has the advantage that fewer parts are required. The lifting assembly <NUM> has the advantage that the drums <NUM>, gear <NUM> and motor <NUM> are smaller. In both cases, the space required within the body of the load handling device <NUM> by the lifting assembly may be minimised.

The illustrated lifting arrangements have various advantages, including that: cost and space within the body of the load handling device may be saved relative to arrangements incorporating more motors; the rates of winding and unwinding of the spools or hoist drums <NUM>, <NUM> do not need synchronising, as they are all driven by the same motor <NUM>, <NUM>, allowing them to be wound and unwound at the same rate without additional gearing, control or other intervention; only a single control unit is required to control the raising and lowering of the hoist drums <NUM>, <NUM>.

It will be appreciated that where four tapes are used a gripper plate may be attached to the distal ends of the lifting tapes <NUM>. It will be appreciated with a sling arrangement as discussed above, a gripper plate is supported by the sling. The gripper plate will have one or more gripper assemblies (discussed in more detail below in connection with <FIG>) mounted thereon for latching to a storage container <NUM>.

<FIG> illustrate alternative drum arrangements for lifting assemblies <NUM>, <NUM>. For both assemblies <NUM>, <NUM> the drum <NUM>, <NUM> is in x,y-plane. This arrangement has the advantage that the drum can be much larger without occupying space within the body of a load handling device. Instead, the drum <NUM>, <NUM> is substantially in plane with the upper face or surface of the load handling device. The diameter of the drum <NUM>, <NUM> may be substantially up to the length of the shorter x or y side of the load handling device.

Advantageously the drum <NUM>, <NUM> is wound with a much smaller motor <NUM>, <NUM>. The drive shaft of the motor <NUM> has a worm gear <NUM> which directly drives the drum <NUM>. This allows the motor <NUM> to be arranged in the same plane as the drum <NUM>, and enables a large step down ratio without the need for additional gear wheels. The drive shaft of the motor <NUM> is coupled to the drum <NUM> with a simple direct drive pulley arrangement <NUM>. The motor <NUM> is arranged vertically or z direction, perpendicular to the plane of the drum <NUM>.

In the arrangements of <FIG>, four lifting tapes <NUM> are spooled around the same drum <NUM>, <NUM>. The four lifting tapes <NUM> are directed to the four corners of a gripper plate <NUM>. As a result, each corner of the gripper plate <NUM> is lifted and lowered in unison when the drum <NUM>, <NUM> is operated and the tapes are spooled or unspooled.

<FIG> and <FIG> illustrate two more alternative lifting assemblies <NUM>, <NUM>. In these examples, "lifting tapes <NUM>" are instead referred to as "ropes <NUM>" or "wires <NUM>". It will be appreciated that the terms are intended to be used interchangeably, and whether tapes, ropes or wires are used will depend on the intended purpose and tensile strength required.

In a rope and pulley system, sometimes known as "block and tackle", a single continuous rope transmits a tension force around one or more pulleys to lift a load. If there are p of these parts of the rope supporting the load W, then a force balance on the moving block shows that the tension in each of the parts of the rope must be W/p. This means the input force on the rope is T=W/p. Thus, the block and tackle reduces the required input force for lifting the load by the factor p. It will be appreciated that the mechanical gain requires a proportional increase in the required distance of travel of the rope.

In <FIG>, the lifting assembly <NUM> comprises four pulley systems. The four pulley systems are driven by a motor <NUM> which drives a spool wheel <NUM> arranged at the upper face of the lifting assembly <NUM>. Substantially adjacent to the spool wheel <NUM> is arranged an upper pulley <NUM>. A gripper plate <NUM> is at the lower end of the lifting assembly <NUM>, and mounted thereon at each corner there is a double pulley <NUM>. It will appreciated that the upper face is a fixed block of the pulley system and the lower face a movable block of the pulley system. The combination of the fixed block and the movable block form a "block and tackle". The upper and lower blocks or the pulley system may be mounted on the same axle.

A first end of a lifting rope <NUM> is fixed to the spool wheel <NUM>, and the lifting rope <NUM> may be spooled around the spool wheel <NUM>. The rope <NUM> extends from the spool wheel <NUM> around the double pulley <NUM>, over the upper pulley <NUM>, around the double pulley <NUM> for a second time and back up to the upper pulley <NUM> where the second end of the lifting rope <NUM> is fixed.

The operation of the four motors <NUM> is coordinated so that the gripper plate <NUM> is kept level. <FIG> illustrates a single z,x- or z,y-plane of a lifting assembly <NUM>, and <FIG> is a perspective view illustrating two z,x- or z,y-planes of the lifting assembly <NUM>. The arrangement of the lifting mechanism is similar to the arrangement of the lifting assembly described above in connection with <FIG>, where hoist drums <NUM> share a common axle <NUM>. A first pair of tapes <NUM> are spooled on a first drum <NUM>, and a second pair of tapes <NUM> are spooled on a second hoist drum. The two pairs of tapes <NUM> are directed to support each corner of a gripper plate <NUM>. Further, the tapes <NUM> of lifting assembly <NUM> comprise a pulley system sling arrangement.

Considering the pair of tapes <NUM> of a single hoist drum <NUM>, a first end of the tapes <NUM> is fixed to the respective drum <NUM>. The tapes <NUM> extend to opposed corners of the upper portion of the lifting assembly <NUM> where they are directed by a guide towards the gripper plate <NUM>. A first pulley <NUM> mounted on the gripper plate directs the tapes <NUM> along the gripper plate <NUM> to a second pulley <NUM> mounted on the gripper plate <NUM>. From the second pulley <NUM> the tapes <NUM> return to the upper portion of the lifting assembly <NUM> where the second end of the tapes <NUM> is fixed. Thus, the pair of tapes <NUM> form a nested pair of sling arrangements.

It will be appreciated that the lifting assembly <NUM> has the advantages of the shared motor arrangement of <FIG>, the advantages of the sling arrangement of <FIG>, and the advantages of the pulley arrangement of <FIG>.

The components of the lifting assembly may be mounted directly on or indirectly on a frame that is releasably mountable on a load handling device. Thus, the lifting assembly is used to lift containers into the cavity of the load handling device. It will be appreciated that the lifting assembly used in reverse is used to lower containers from the load handling device to a position in a stack below the grid.

Configuring the lifting assembly for releasable mountability on the load handling device may advantageously mean that lifting assembly can be easily removed and replaced with another lifting assembly (e.g. if the first assembly needs to be serviced or repaired), allowing the corresponding load handling device to return to service relatively quickly.

A communications cable reel may also mounted on the lifting assembly for transmitting control instructions from a control unit to the gripper assemblies. The communications cable may transmit sensor data to the control unit, for example, to ensure that the gripper plate is latched to the container. The communications cable is also raised and lowered with the gripper plate. Alternatively, other forms of communication may be employed between the lifting assembly and a control unit.

Before the lifting assembly raises or lowers the gripper plate and any engaged container, the load handling device may be put into a parked configuration. This may provide additional stability as the lifting assembly is raised and lowered.

The gripper plate <NUM> comprises at least one gripper assembly arranged to be aligned with recesses or holes in the upper surface of a storage container <NUM> such that the gripper assembly may latch to the storage container <NUM>. More usually the gripper plate <NUM> will comprise two or more gripper assemblies. Typically the gripper plate <NUM> will comprise four gripper assemblies arranged in locations to correspond to cooperating recesses of a storage container <NUM>.

<FIG> illustrates a self-locking gripper assembly for use on the load handling devices described here. The gripper assembly comprises a flexure mechanism <NUM> movable between bi-stable locked and release configurations. The flexure mechanism <NUM> comprises an actuator <NUM>, two gripper-arms <NUM> having hook-ends <NUM> and two flexural hinge arrangements connecting the gripper-arms <NUM> to the actuator <NUM>. The flexural hinge arrangements each comprise a triangular fulcrum or keystone-form <NUM>, a first deformable section <NUM> between the actuator and the keystone-form and a second deformable section <NUM> between the keystone-form and the gripper-arms <NUM>. The deformable sections <NUM>, <NUM> are relatively thin sections compared with the other sections of the flexure mechanism <NUM>. In this way, the deformable sections preferentially bend or flex when an appropriate force is applied to the flexure mechanism <NUM>.

Referring to <FIG>, in the locked configuration (<FIG>) the keystone-forms <NUM> engages or abuts the respective gripper-arms <NUM>. In the locked configuration the flexure mechanism <NUM> is open or wide and the gripper-arms spread. The flexure mechanism <NUM> may be moved into the locked configuration by applying a downward force on the actuator <NUM>. When in this configuration, the actuator <NUM> is in a downward position relative to the gripper-arms <NUM>.

The flexure mechanism <NUM> may be moved from the locked configuration into the unlocked or release configuration by applying an upward force or pulling force on the actuator <NUM> as indicated in <FIG>. Referring to <FIG>, when such a force is applied, the first and second hinges <NUM>, <NUM> bend or flex, releasing the keystone-form <NUM> from engagement with the gripper-arms <NUM>. The first hinges <NUM> bend so that the keystone-forms <NUM> pivot downward relative to the actuator <NUM>. The second hinges <NUM> bend so that the keystone-forms <NUM> pivot upwards relative to the gripper-arms <NUM>. Thus, the actuator <NUM> moves to an upward position relative to the gripper-arms <NUM> which draws the hooked end <NUM> of the gripper-arms together, as indicated by the solid arrows in figure 15c, into a narrow or closed arrangement.

In an alternative arrangement, a flexure mechanism <NUM> may be moved into the unlocked or release configuration by applying a downward force or pushing force on the actuator <NUM>.

As mentioned above, the gripper assembly is for latching to a storage container <NUM> so that the storage container <NUM> may be lifted. The gripper assembly is arranged to be compatible with the storage container <NUM>. Typically storage containers <NUM> have recesses around the edge of the container on the upper faces.

In use, in the narrow or flexed configuration shown in <FIG>, the flexure mechanism <NUM> is inserted into the recess. Once inserted, a downward force may be applied to the actuator <NUM>. This puts the flexure mechanism <NUM> into the locked configuration, and the flexure mechanism <NUM> is wide as shown in <FIG>. It is then not possible to remove the flexure mechanism <NUM> from the recess of the container. The hooked end <NUM> of the gripper-arms engages with the underside of the upper surface of the container <NUM>. Therefore, a lifting force may be applied to the gripper-arms <NUM> to lift the container <NUM>.

In use, as part of a load handling device <NUM>, gripper assemblies <NUM> are mounted on a gripper plate <NUM> and the actuators <NUM> may be operated by a solenoid motor, or electromagnet for example.

In use with a load handling device, grippers <NUM> are used at each corner of a container <NUM>, to latch the lifting assembly <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> to the container <NUM>. The lifting assembly <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is then operated to lift the container <NUM> into the cavity of a load handling device so that the container <NUM> may be transported by the load handling device. <FIG> illustrates a load handling device <NUM> without a container, and <FIG> illustrates a load handling device <NUM> having a container <NUM> lifted into the cavity.

It will be appreciated that the gripper assembly <NUM> may have more than two gripper-arms and a corresponding number of flexural hinge arrangements arranged around the actuator. In some arrangements, additional gripper-arms may provide more secure attachment to the storage container.

A communications cable reel may also be mounted on the lifting assembly. The communication cable transmits control instructions from a control unit to the assistant guide-rollers, and the gripper assemblies. The communications cable may transmit sensor data to the control unit, for example, to ensure that the gripper plate and a lifted container are kept level. The communications cable is also raised and lowered with the gripper plate. In an alternative arrangement, communication between the upper portion of the lifting assembly and the gripper plate may be by optical communications.

<FIG> illustrate means for manoeuvring the load handling device on a grid based storage and retrieval system. <FIG> illustrate a four wheel drive arrangement, and <FIG> illustrate an eight wheel drive arrangement. As noted above, the load handling device has a first set of wheels <NUM> and a second set of wheels <NUM> for moving the load handling device in a first direction and a second direction respectively. The first set of wheels <NUM> comprises four wheels arranged in pairs on opposed sides, and the second set of wheels <NUM> comprises four wheels arranged in pairs on opposite sides, perpendicular to the first set of wheels <NUM>.

As illustrated in <FIG> the pair of wheels on each side face of the load handling device comprise an idler wheel <NUM> and a driven wheel <NUM>, <NUM>. For each driven wheel <NUM>, <NUM> a respective drive motor <NUM> is positioned such that its drive shaft is parallel and non-coaxially arranged with respect to the rotational axis of its driven wheel <NUM>, <NUM>. In this example, the drive motors <NUM> are arranged on the perpendicular face sharing an edge with the face of the driven wheel <NUM>, <NUM>. Thus, each side face of the load handling device comprises one drive motor <NUM>. A gear arrangement, such as a pulley gear <NUM>, transfers the torque from the motors <NUM> around the corner through <NUM>° to the wheel <NUM>, <NUM>. This arrangement allows the motor to be arranged with the axis of the drive shaft extending along the perpendicular face of the load handling device. The motor <NUM> may conveniently be arranged within the side of the load handling device, such that the motor <NUM> is substantially encompassed by the side, or the motor <NUM> may be mounted on the outside of the load handling device. However, regardless of its location on the load handling device, as a consequence of the parallel and non-coaxial arrangement between its drive shaft and the rotational axis of its respective driven wheel <NUM>, <NUM>, the drive shaft of the motor <NUM> may be much longer than if the wheels where directly driven, for example, by a hub motor. The motor <NUM> may be a lightweight high RPM motor. The pulley gear arrangement <NUM> may comprise a planetary gear system to reduce the RPM of the wheels and provide the correct torque. As the motor <NUM> is positioned proximal to the wheel, the length of the drive belt or pulley may be minimal.

The idler wheels <NUM> are passive, and simply provide support to the load handling device. In this way, the number of motors <NUM> required for separately driven wheels <NUM>, <NUM> is reduced. Typically, in a four wheel driven arrangement, the wheels in diagonally opposite corners are driven for the x-direction and the wheels <NUM>, <NUM> in diagonally opposite corners are driven for y-directions, as shown in <FIG>.

As the pair of wheels on each side face of the load handling device comprise an idler wheel <NUM> and a driven wheel <NUM>, <NUM>, it will be appreciated that both first set of wheels <NUM> and the second set of wheels <NUM> comprise idler wheels <NUM> and drive wheels <NUM>, <NUM>.

The driven wheels <NUM>, <NUM> can be grouped according to power source provided to the motors <NUM>. A first sub-set of driven wheels <NUM> may be powered by a first power source and a second sub-set of driven wheels <NUM> may be powered by a second power source. One driven wheel <NUM> of the first set of wheels <NUM> may be powered by the first power source, and one driven wheel <NUM> of the second set of wheels <NUM> may be powered by the first power source. Similarly, one driven wheel <NUM> of the first set of wheels <NUM> may be powered by the second power source, and one driven wheel <NUM> of the second set of wheels <NUM> may be powered by the second power source. In this way, in the event that the first power source or the second power source has a fault or fails, at least one driven wheel <NUM>, <NUM> in the x-direction and at least one driven wheel in the y-direction will continue to be operational, allowing the load handling device to be manoeuvred at reduced speed to a maintenance or recovery area on the grid, or to the edge of the grid.

As illustrated in <FIG> the pair of wheels on each side face of the load handling device comprises a driven wheel <NUM> of a first sub-set and a driven wheel <NUM> of a second sub-set. For each driven wheel <NUM>, <NUM> a drive motor <NUM> is arranged on the perpendicular face sharing an edge with the face of the driven wheel <NUM>, <NUM>. Thus, each side face of the load handling device comprises two drive motors <NUM> positioned such that their drive shafts are parallel and non-coaxially arranged with respect to the rotational axis of its respective driven wheel <NUM>, <NUM>. In other examples, the drive motors <NUM> may be positioned inside the load handling device or within the side of the load handling device, such that the drive motors <NUM> are substantially encompassed by the side. Similarly to the arrangement described in connection with <FIG>, a gear arrangement, such as a pulley gear <NUM>, transfers the torque from the motors <NUM> around the corner through <NUM>° to the wheel <NUM>, <NUM>. It will be appreciated that, while the drive shaft of the motor <NUM> may be much longer than if the wheels were directly driven, compared with the arrangement illustrated in <FIG>, because there are two drive motors <NUM> on each side face, the amount of space for one of the drive motors <NUM> is more limited. Further, it should be noted that while the illustration of <FIG> shows more details of the motor <NUM> and pulley gear arrangement <NUM> compared with the motor and pulley gear arrangement <NUM> of <FIG>, the arrangements are intended to be similar.

As with the four driven wheel arrangement, and as shown in <FIG>, the driven wheels <NUM>, <NUM> can be grouped according to power source provided to the motors <NUM>. A first sub-set of driven wheels <NUM> may be powered by a first power source and a second sub-set of driven wheels <NUM> may be powered by a second power source. Two driven wheels <NUM> of the first set of wheels <NUM> may be powered by the first power source, and two driven wheels <NUM> of the second set of wheels <NUM> may be powered by the first power source. Similarly, two driven wheels <NUM> of the first set of wheels <NUM> may be powered by the second power source, and two driven wheels <NUM> of the second set of wheels <NUM> may be powered by the second power source. In this way, in the event that the first power source or the second power source has a fault or fails, at least two driven wheels <NUM>, <NUM> in the x-direction and at least one driven wheel in the y-direction will continue to be operational, allowing the load handling device to be manoeuvred at reduced speed to a maintenance or recovery area on the grid, or to the edge of the grid. It will be appreciated that in an eight driven wheel arrangement, first and second sub-set driven wheels <NUM>, <NUM> may be further divided according to the arrangements for the four driven wheels - providing two cooperating four drive wheel arrangements - to provide further redundancy and opportunity for reduced capability self-recovery of a load handling device experiencing drive faults or failures.

It will be appreciated that in the foregoing description it is intended that the first power source and the second power source, and any sub-divisions thereof are intended to be independent.

Further, it will appreciated that although the drive arrangement has been described with a particular motor arrangement, the pattern of driven wheels <NUM>, <NUM> is independent of the particular motor arrangement, and may be achieved with hub motors for example.

<FIG> illustrates the drive arrangement and a direction-change assembly of a load handling device in more detail. It will be appreciated that the illustrated corner edge is similar to one of the corners of <FIG>, and shows one wheel of the first set of wheels <NUM> and one wheel of the second set of wheels where both wheels are driven by respective motors <NUM> and pulley gear arrangements <NUM> as described above.

It will be appreciated, that the load handling device is able to move on the grid in the x-direction when the first set of wheels <NUM> are engaged with the tracks, or the load handling device is able to move on the grid in the y-direction when the second set of wheels <NUM> are engaged with the tracks. When both the first set of wheels <NUM> and the second set of wheels <NUM> are engaged with the tracks then the load handling device is unable to move in any direction. Accordingly, as well as being able to selectively drive the wheels in forward and reverse direction, it is necessary to have the ability to selectively engage the first set of wheels <NUM> and the second set of wheels <NUM> with the track.

In the arrangement illustrated in <FIG> and <FIG>, the wheels <NUM>, <NUM> are individually lift-able in the vertical or z-direction by a linear actuator <NUM> arranged on the body of the load handling device above the wheel axle. In this arrangement, the wheel axle may be movable in a vertical direction. It will be appreciated, that the lifting actuators <NUM> for the first wheel set <NUM>, and the lifting actuators <NUM> for the second wheel set <NUM> are coordinated by a control utility to ensure that the load handling device is properly supported.

It will be appreciated, that having individual wheel actuators <NUM> means that a single wheel of the first set of wheels <NUM>, or the second set of wheels <NUM> may be lifted where there is a fault in the single wheel/drive arrangement and the wheel is unable to rotate (when driven or un-driven) so that the load handling device may return to a maintenance or recovery area on the grid, or to the edge of the grid.

In a variation, the wheel <NUM>, <NUM> may be lifted by locking the wheel <NUM>, <NUM> rotation while allowing the wheel axis to move upwards in the z-direction. The wheel <NUM>, <NUM> can then be powered by the drive motor <NUM>.

It will be understood that as a result of lifting or raising the wheels <NUM>, <NUM> the drive belt may become slack. Accordingly, additional slave pulleys <NUM> may be provided, to maintain tension in the drive belt when the wheel <NUM>, <NUM> is lifted. In a variation, the motor <NUM> maybe arranged to be lifted together with the wheels <NUM>, <NUM> thereby avoiding a slackening of the drive belt.

As illustrated in <FIG>, <FIG> and <FIG> the drive assembly and the direction-change assembly are positioned on the outside of the load handling device body, and this has the advantage of maximising the volume within the load handing device for receiving a container in a cavity receiving space. It will be appreciated that in an alternative arrangement, the drive assembly and the direction-change assembly could be positioned on the inside face of the load handling device body.

In order to operate autonomously, the load handling device has its own power supply means. The power supply means may be in the form of rechargeable or interchangeable batteries.

The batteries may be located within the skeleton or body of the load handling device. For example, where the skeleton comprises a hollow rod structure, batteries may be inserted into the rods.

Various control and sensor arrangements are described in <CIT>), which is incorporated herein by reference.

The load handling device is controlled by an on-board control facility.

The control facility may comprise communication means such as a transceiver unit, or transmitter and receiver units, for sending and receiving instructions from a centralised control facility of the system. The load handling device is able to act substantially autonomously based on instructions or tasks from the centralised control facility.

The on-board control facility is able to control and operate the direction-change mechanism, the drive assembly and the lifting assembly according to instructions received from the centralised control facility. The on-board control facility further comprises input from various sensors and cameras to provide feedback to the control facilities regarding the condition of the load handling device and the environment around the load handling device.

Based on the condition and environment around the load handling device, the on-board control facility operates the direction-change, drive and lifting assemblies to carry out tasks.

Accurate knowledge of the condition of the load handling devices is required to determine the speed at which the load handling device may operate, and when tasks are completed and when the load handling device is available to complete subsequent tasks.

Accurate positioning of each load handling device is required to allow load handling devices to be driven at faster speeds and/or accelerations with minimal positional errors allowing for a reduction in the spacing between load handling devices on the grid system to increase the efficiency of the system.

More than one type of sensor may be used to determine the condition and environment of the load handling device, in order to verify that the received information is correct. More than one sensor of the same type may be mounted on the load handling device at different locations.

In this way, each of the sensors detects different parts of the environment in which the load handling device is operating. Multiple sensors are advantageous because they provide redundancy on the device in that if one sensor fails to capture appropriate information from the environment then one of the other sensors may be more successful.

Moreover, in positions where one sensor is unable to capture the environment (such as over rail intersections) then another sensor may be able to capture the environment more successfully. In addition, with multiple sensors other measurements may be taken such as determining a rotational orientation of the transporting device by comparing positional measurements from one sensor to the same positional measurement on a sensor mounted on an opposing face of the transporting device to determine an angle between the sensors.

It will be appreciated that for operating in a larger system, even though some faults may be tolerated and that it is possible to operate larger systems efficiently with some components of the system operating beyond the point of failure, redundancy on individual load handling devices is desirable for other reasons.

A load handling device may comprise many different types of sensors, for example: cameras, ultrasonic detectors, x-ray cameras, trundle, or dead reckoning wheel arrangement, gyroscopic, barcode or QR scanner for reading markings provided on the grid; RFID reader for identifying items stored in the system.

Sensors may be provided for: assessing the communications functions within the load handling device, measuring traction between the wheels and the grid tracks, measuring the distance travelled, measuring the speed of travel, determining the grid position of the load handling device on the grid, accurate positioning of the load handling device in a single grid space.

It will be appreciated that the load handling device may comprise all, one or any combination of the features described above and that it is not essential to the invention for the service device to include all the sensors and features described.

It is envisaged that any one or more of the variations described in the foregoing paragraphs may be implemented in the same embodiment of a load-handling device. It will be appreciated that the storage system and devices described herein are not limited to the type of article stored and managed therein.

Further, it will be appreciated that some embodiments of the invention may be used in connection with manual handling equipment other than load handling devices.

Claim 1:
A grid-based storage and retrieval system comprising:
a grid framework (<NUM>) structure comprising:
a first set of parallel rails or tracks (22a) and a second set of parallel rails or tracks (22a) extending substantially perpendicularly to the first set of rails or tracks (22b) in a substantially horizontal plane to form a grid pattern comprising a plurality of grid spaces, wherein the grid is supported by a set of uprights (<NUM>) to form a plurality of vertical storage locations beneath the grid for containers (<NUM>) to be stacked between and be guided by the uprights in a vertical direction through the plurality of grid spaces,
a load handling device (<NUM>) comprising:
a body mounted on a first set of wheels (<NUM>) being arranged to engage with the first set of parallel tracks (22a) and a second set of wheels being arranged to engage with the second set of parallel tracks (22b); and,
a lifting assembly (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising:
at least one hoist drum (<NUM>, <NUM>, <NUM>);
a gripper plate (<NUM>); the grid-based storage and retrieval system further comprising a centralised control utility for controlling the at least one load handling device; characterized in that the load handling device further comprises
a sling assembly arranged to support, raise and lower a load, the sling assembly comprising a sling extending between a support mountable to the body of the load handling device and the gripper plate for supporting the load, wherein first and second ends of the sling are attached to the at least one hoist drum (<NUM>, <NUM>, <NUM>).