Method and system for determining depth or obstacles of a gripping assembly

Abstract

A method and system for determining the depth or obstacle of a container gripping assembly are disclosed. The method and system determine the depth or obstacle of a container gripping assembly using a sensor.

Description

Technology Field

[0001] The present invention relates to a method and system for determining the depth of a gripping assembly used in a load handling device, etc. Background Technology

[0002] Some commercial and industrial activities require systems capable of storing and retrieving multiple different products. WO2015 / 185628A describes a storage and order processing system in which stacks of storage containers are placed within a grid storage structure. The containers are accessed from above by a load handling device operating on rails or tracks placed on the top of the grid storage structure. A load handling device is also described in WO2015 / 019055A1.

[0003] A load handling device includes a container lifting assembly that uses a lifting assembly to raise and / or lower a container gripping assembly. The lifting assembly controls the raising and lowering of the container gripping assembly according to the vertical position of the container gripping assembly. For example, when the container gripping assembly lowers to approach a container, the container gripping assembly is decelerated. To control deceleration, it is important to accurately determine the vertical position of the container gripping assembly. This is also true when the container gripping assembly rises to approach the load handling device. Additionally, it is important to determine whether the container gripping assembly is obstructed by an obstacle while being raised. The present invention was devised against this background.

[0004] In a first embodiment, a lifting assembly is provided for raising and / or lowering a container from and / or to a container stack within a grid storage structure, and the lifting assembly comprises:

[0005] A gripping assembly configured to grip a load; and

[0006] A lifting assembly configured to raise and lower a gripping assembly - the lifting assembly comprises: at least one tether connected to the gripping assembly; and a motor that winds and / or unwinds the one or each tether to raise and / or lower the gripping assembly -

[0007] Includes, and the lifting assembly is:

[0008] A sensor configured to detect movement of a gripping assembly - the sensor includes an input unit coupled by movement of the gripping assembly -; and

[0009] It further includes a controller configured to determine the vertical position of the gripping assembly using the output of the sensor.

[0010] This means that the degree to which the gripping assembly is raised and / or lowered can be monitored.

[0011] The lifting assembly may further include an electric cable connected to a gripping assembly, the electric cable is configured to be wound and / or unwound as the gripping assembly rises and / or lowers, and a sensor is configured to detect the degree to which the electric cable is wound and / or unwound. This means that the vertical position can be accurately determined using the direct elongation of the electric cable. In one embodiment, the lifting assembly further includes an electric cable spool on which the electric cable is wound and / or unwound, and a sensor includes a rotary encoder configured to work with the electric cable spool to detect the degree to which the electric cable spool rotates as the electric cable is wound and / or unwound.

[0012] The electric cable may have a higher elastic modulus than the above or each tether. This means that the effect of elongation is reduced, thereby maximizing accuracy.

[0013] The lifting assembly may further comprise the or each tether tether spool on which the or each tether is wound and / or unwound, and the electric cable spool and the or each tether spool are mounted on a shaft so that the electric cable spool can rotate relative to the or each tether spool. In one embodiment, the lifting assembly of the claim further comprises a biasing assembly configured to resist the unwinding of the electric cable spool or the winding of the electric cable spool so that the electric cable is kept taut between the lifting assembly and the gripping assembly. This means that the electric cable is kept taut so that accuracy is maximized.

[0014] The electric cable can transmit electrical signals to the gripping assembly. The electric cable may include a flat flexible cable (FFC) or a ribbon cable.

[0015] The sensor may include a motor encoder of the motor, and the motor encoder is configured to detect the degree to which the or each tether is wound and / or unwound. This means that the vertical position can be accurately determined using the direct elongation of the or each tether. In one embodiment, the lifting assembly may further include a tether spool for the or each tether to which the or each tether is wound and / or unwound, and the motor encoder detects the degree to which the or each tether spool is rotated as the or each tether is wound and / or unwound. The sensor may include a rotary encoder configured to detect the degree to which the or each tether is wound and / or unwound; or a rotary encoder for the tether spool for the or each tether, wherein each rotary encoder is configured to be coupled with each spool to detect the degree to which each spool is rotated as the or each tether is wound and / or unwound.

[0016] The sensor may include a rotary encoder for the above or each tether, and the rotary encoder is configured to contact the individual tether so that the winding and / or unwinding of the above or each tether rotates the input of the rotary encoder. This means that the vertical position can be accurately determined using the direct extension of the tether.

[0017] The lifting assembly may include an electric cable connected to a gripping assembly, and the electric cable is configured to be wound and / or unwound as the gripping mechanism rises and / or lowers; the sensor may include a rotary encoder, and the rotary encoder is configured to be coupled with the electric cable so that the winding and / or unwinding of the said or each tether causes the shaft of the rotary encoder to rotate. This means that the vertical position can be accurately determined using the direct elongation of the electric cable.

[0018] The lifting assembly may further include a biasing assembly configured such that each rotary encoder is biased to make contact with the said or each tether or electrical cable. This ensures that the rotary encoder maintains contact with the said or each tether or electrical cable.

[0019] The lifting assembly may include a wire connected to a gripping device, the wire is configured to be wound and / or unwound as the gripping assembly rises and / or descends, and includes a wire spool on which the wire is wound and / or unwound, the wire on the wire spool is configured to short-circuit as the wire is wound onto the wire spool, and a sensor may be configured to measure the electrical resistance of the wire as the wire is wound and / or unwound. This means that the vertical position can be accurately determined using the direct elongation of the wire.

[0020] The lifting assembly may further include a biasing assembly configured to resist the unwinding or winding of the wire spool so that the wire is kept taut between the lifting assembly and the gripping assembly. This means that the wire is kept taut so that accuracy is maximized.

[0021] The sensor may include a Time-of-Flight (ToF) sensor. This means that the vertical position can be accurately determined using the direct movement of the gripping assembly.

[0022] The sensor may include a light source and a photodetector, wherein the light source is configured to transmit a light signal to a moving surface as the gripping assembly rises and / or descends, and the photodetector is configured to detect the movement of the surface by detecting the reflection of the light signal from the surface. This means that the vertical position can be accurately determined using the direct movement of the gripping assembly. In one embodiment, the lifting assembly may include an electric cable connected to the gripping assembly, and the electric cable is configured to be wound and / or unwound as the gripping mechanism rises and / or descends. The lifting assembly may include a wheel that contacts a tether spool on which the or each tether is wound and / or unwound, or an electric cable spool on which the electric cable is wound and / or unwound, and the wheel includes a surface. The or each tether spool or electric cable spool may include a surface.

[0023] The controller can be configured to control / adjust the raising and / or lowering of the gripping assembly using a determined vertical position. This means that the gripping assembly can be accurately controlled using feedback.

[0024] In another embodiment, a load handling device for lifting and moving storage containers stacked within a grid framework structure is provided, and the load handling device is:

[0025] A load handling device comprises: a first set of parallel rails or tracks, and a second set of parallel rails or tracks extending substantially perpendicularly to the first set of rails or tracks 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 supports to form a plurality of vertical storage positions below the grid for containers to be stacked between the supports in a vertical direction through the plurality of grid spaces and guided by the supports, and the load handling device:

[0026] A body or skeleton mounted on a first set of wheels arranged to engage with a first set of parallel tracks, and a second set of wheels arranged to engage with a second set of parallel tracks; and

[0027] A container lifting assembly comprising a lifting assembly of any one of the prior embodiments, and a gripping assembly comprising a container gripping assembly configured to grip a container.

[0028] In another embodiment, a method for determining the vertical position of a gripping assembly of a lifting assembly of any one of the prior embodiments is provided, and the method is:

[0029] Raising and / or lowering the gripping assembly using a motor; and

[0030] It includes determining the vertical position of the gripping assembly using the sensor output with a controller.

[0031] In another embodiment, a computer program is provided that includes instructions that cause the computer to perform the method of the preceding embodiment when the program is executed by the computer.

[0032] A lifting assembly is provided for raising and / or lowering a container from and / or to a container stack within a grid storage structure, and the lifting assembly is:

[0033] A gripping assembly configured to grip a load; and

[0034] A lifting assembly configured to raise and lower a gripping assembly - the lifting assembly comprises: at least one tether connected to the gripping assembly; and a motor configured to raise and / or lower the gripping assembly by winding and / or unwinding the said or each tether around at least one shaft -,

[0035] Includes, and this lifting assembly is:

[0036] A sensor configured to detect movement of the gripping assembly; and

[0037] It further includes a controller configured to determine an obstacle of the gripping assembly when the current output of the sensor is not correlated with the winding and / or unwinding of the said or each tether centered on the said or each shaft so as to raise and / or lower the gripping assembly. This means that it is possible to detect a malfunction or incorrect operation during the raising and / or lowering of the gripping assembly.

[0038] The lifting assembly of claim 1 may further include a second sensor that directly detects the rotation of at least one shaft. This means that it can detect the winding and / or unwinding of the said or each tether.

[0039] In one embodiment, the second sensor may include a motor encoder of the motor, and the controller may be configured to determine an obstacle in the gripping assembly when the current output of the sensor is not correlated with the current output of the motor encoder. The controller may be configured to determine an obstacle in the grid assembly when the current output of the sensor is not correlated with the current output of the motor encoder by a threshold. This means that a tolerance is allowed to account for the elongation of the above or each tether.

[0040] In another embodiment, the lifting assembly may further include a tether spool for the or each tether on which the or each tether is wound and / or unwound, and a second sensor may include a tether rotary encoder for the or each tether spool, and the or each tether rotary encoder may be configured to be coupled with each spool to detect the degree to which each spool has rotated as the or each tether is wound and / or unwound, and a controller may be configured to determine an obstacle in the gripping assembly when the current output of the sensor is not correlated with the current output of the or each tether rotary encoder. The controller may be configured to determine an obstacle in the gripping assembly when the current output of the sensor is not correlated with the current output of the tether rotary encoder by a threshold. This means that a tolerance is allowed to account for the elongation of the or each tether.

[0041] In another embodiment, the lifting assembly may include an electric cable connected to the gripping assembly, the electric cable is configured to be wound and / or unwound as the gripping assembly rises and / or descends, and may include an electric cable spool on which the electric cable is wound and / or unwound, the electric cable spool may be fixedly mounted on the or each shaft, and the second sensor may include an electric cable rotary encoder for the electric cable spool, and the or each electric cable rotary encoder may be configured to be coupled with the electric cable spool to detect the degree to which the electric cable spool has rotated as the electric cable is wound and / or unwound, and the controller may be configured to determine an obstacle of the gripping assembly when the current output of the sensor is not correlated with the current output of the electric cable rotary encoder.

[0042] In another embodiment, the lifting assembly may further include a tether spool for said or each tether on which the said or each tether is wound and / or unwound, and the second sensor may include a sensor for the tether spool comprising a light source and a light detector, the light source may be configured to transmit a light signal to a moving surface as the gripping assembly rises and / or descends, the light detector may be configured to detect movement of the surface by detecting a reflection of the light signal from the surface, and the controller may be configured to determine an obstacle of the gripping assembly when the current output of the sensor is not correlated with the current output of the sensor for the tether spool. The lifting assembly may include a wheel in contact with the tether spool on which the said or each tether is wound and / or unwound, and the wheel includes a surface. said or each tether spool may include a surface.

[0043] In another embodiment, the lifting assembly may include an electric cable connected to a gripping assembly, the electric cable is configured to be wound and / or unwound as the gripping assembly rises and / or descends, and may include an electric cable spool on which the electric cable is wound and / or unwound, and the second sensor may include a sensor for the electric cable spool comprising a light source and a photodetector, the light source may be configured to transmit a light signal to a moving surface as the gripping assembly rises and / or descends, and the photodetector may be configured to detect movement of the surface by detecting a reflection of the light signal from the surface, and the controller may be configured to determine an obstacle of the gripping assembly if the current output of the sensor is not correlated with the current output of the sensor for the electric cable spool. The lifting assembly may include a wheel in contact with the electric cable spool on which the electric cable is wound and / or unwound, and the wheel includes a surface. The electric cable spool may include a surface.

[0044] The sensor may include an input unit linked by the movement of the gripping assembly, and the controller receives a motion profile controlling the raising and / or lowering of the gripping assembly, determines the vertical position of the gripping assembly using the output of the sensor, and may be configured to determine an obstacle of the gripping assembly if the vertical position of the gripping assembly at the current time is not correlated by a threshold with the corresponding vertical position derived from the motion profile. This means that an obstacle can be determined using only a single sensor.

[0045] The lifting assembly may include an electric cable connected to a gripping assembly, and the electric cable may be configured to be wound and / or unwound as the gripping assembly rises and / or descends, and a sensor may be configured to detect the degree to which the electric cable is wound and / or unwound, and may include a biasing assembly configured to resist the unwinding or winding of the electric cable spool so that the electric cable is kept taut between the lifting assembly and the gripping assembly. The lifting assembly may further include an electric cable spool on which the electric cable is wound and / or unwound, and a sensor may include a rotary encoder configured to be coupled with the electric cable spool to detect the degree to which the electric cable spool is rotated as the electric cable is wound and / or unwound, and the electric cable spool may be configured to rotate relative to the above or each shaft. This means that when the movement of the gripping assembly is obstructed, the electric cable returns to a biased state, which can be detected by the rotary encoder. In one embodiment, the electric cable may have a higher elastic modulus than the above or each tether. In another embodiment, the electric cable may transmit an electric signal to a gripping assembly. In another embodiment, the electric cable may include a flat flexible cable (FFC) or a ribbon cable.

[0046] The sensor may include a rotary encoder for the above or each tether, and the rotary encoder is configured to contact the individual tether so that the winding and / or unwinding of the above or each tether causes the input of the rotary encoder to rotate. The lifting assembly may include an electric cable connected to the gripping assembly, and the electric cable may be configured to be wound and / or unwound as the gripping mechanism rises and / or lowers, and the electric cable may optionally include a flat flexible cable (FFC) or a ribbon cable, and the sensor may include a rotary encoder, and the rotary encoder is configured to be coupled with the electric cable so that the winding and / or unwinding of the above or each tether causes the shaft of the rotary encoder to rotate. This means that a loss of contact (e.g., due to slack) between the rotary encoder and the above or each tether or electric cable is detected by the rotary encoder. The biasing assembly may be configured to be biased so that each rotary encoder contacts the above or each tether or electrical cable. This ensures contact between the rotary encoder and the above or each tether or electrical cable.

[0047] The lifting assembly may include an electric cable connected to a gripping assembly, and the electric cable may be configured to be wound and / or unwound as the gripping mechanism rises and / or descends, and the electric cable spool on which the electric cable is wound and / or unwound may be included, the electric cable spool may be configured to rotate relative to the or each shaft, and the biasing assembly may be configured to resist the unwinding or winding of the electric cable spool so that the electric cable is kept taut between the lifting assembly and the gripping assembly, and the sensor may include an electric cable spool sensor including a light source and a photodetector, the light source may be configured to transmit a light signal to a moving surface as the gripping assembly rises and / or descends, and the photodetector may be configured to detect movement of the surface by detecting the reflection of the light signal from the surface, and the lifting assembly may include a wheel on which the or each tether contacts the electric cable spool on which the electric cable spool is wound and / or unwound, the wheel may include a surface, or the electric cable spool may include a surface. This means that when the movement of the gripping assembly is obstructed, the electrical cable returns to a biased state, which is detected by the electrical cable spool sensor.

[0048] A lifting assembly may include a wire connected to a gripping device, the wire is configured to be wound and / or unwound as the gripping assembly rises and / or descends, and includes a wire spool on which the wire is wound and / or unwound, the wire is configured to be short-circuited on the wire spool by being wound onto the wire spool, the wire spool is configured to rotate relative to the above or each shaft, and includes a biasing assembly configured to resist the unwinding or winding of the wire spool so that the wire is kept taut between the lifting assembly and the gripping assembly, and a sensor is configured to measure the electrical resistance of the wire as the wire is wound and / or unwound. This means that when the movement of the gripping assembly is obstructed, the wire returns to a biased state, which is detected by the sensor.

[0049] The sensor may include a Time-of-Flight (ToF) sensor. This detects when the movement of the gripping assembly is obstructed.

[0050] The controller may be configured to stop the motor if it determines an obstacle in the gripping assembly. This means that the above or each tether is prevented from becoming loose and unwound.

[0051] In another embodiment, a load handling device for lifting and moving storage containers stacked within a grid framework structure is provided, and the load handling device is:

[0052] A load handling device comprises: a first set of parallel rails or tracks, and a second set of parallel rails or tracks extending substantially perpendicularly to the first set of rails or tracks 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 supports to form a plurality of vertical storage positions below the grid for containers to be stacked between the supports in a vertical direction through the plurality of grid spaces and guided by the supports, and the load handling device:

[0053] A body or skeleton mounted on a first set of wheels arranged to engage with a first set of parallel tracks, and a second set of wheels arranged to engage with a second set of parallel tracks; and

[0054] A container lifting assembly comprising a lifting assembly of any one of the prior embodiments, and a gripping assembly comprising a container gripping assembly configured to detachably grip a container.

[0055] In another embodiment, a method for determining an obstacle to a gripping assembly of a lifting assembly of any one of the prior embodiments is provided, the method being:

[0056] Raising and / or lowering the gripping assembly using a motor; and

[0057] It includes using a controller to determine an obstacle of the gripping assembly when the current output of the sensor is not correlated with the winding and / or unwinding of the said or each tether centered on the said or each shaft so that the winding and / or unwinding of the said or each tether causes the gripping assembly to rise and / or fall.

[0058] In another embodiment, a computer program is provided that includes instructions that cause the computer to perform the method of the preceding embodiment when the program is executed by the computer.

[0059] The present invention is described with reference to one or more embodiments illustrated in the attached drawings. Brief explanation of the drawing

[0060] FIG. 1 illustrates a storage structure and a container; FIG. 2 illustrates a track on top of the storage structure shown in FIG. 1; FIG. 3 illustrates a load handling device located on the upper part of the storage structure illustrated in FIG. 1; FIG. 4 illustrates a single load handling device having a container lifting means of a lowered configuration; FIGS. 5A and 5B illustrate cross-sectional views of a single load handling device having a container lifting means in a raised state and a lowered state; FIG. 7 illustrates a method according to the present invention; FIG. 8 illustrates a system according to the present invention; FIG. 9 illustrates a system according to the present invention; FIG. 10 illustrates a system according to the present invention; FIGS. 11a and FIGS. 11b illustrate a sensor according to the present invention; FIG. 12 illustrates another sensor according to the present invention; FIG. 13 illustrates another sensor according to the present invention; FIG. 14 illustrates another sensor according to the present invention; FIG. 15 illustrates another sensor according to the present invention; FIG. 16 illustrates a system according to the present invention; and FIG. 17 illustrates a method according to the present invention. Specific details for implementing the invention

[0061] Online retailers, such as online grocery stores or supermarkets selling multiple product lines, require systems capable of storing tens of thousands or hundreds of thousands of diverse product lines. In such cases, using single-product stacks may be impractical because accommodating all necessary stacks would require a vast amount of floor space. Furthermore, single-product stacks can be an inefficient solution, as it may be desirable to store only small quantities of certain items, such as fresh produce or low-order frequency goods.

[0062] International patent application WO 98 / 049075A (Autostore) discloses a system in which multi-product stacks of containers are arranged within a frame structure, the contents of which are incorporated herein by reference.

[0063] PCT publication WO2015 / 185628A (Ocado) describes another known storage and order processing system in which stacks of containers are placed within a grid framework structure (or grid storage structure). The containers are accessed by one or more load handling devices (also referred to as “bots”) operating on tracks located on top of the grid framework structure. This type of system is schematically illustrated in FIGS. 1 through 3 of the attached drawings.

[0064] As illustrated in FIGS. 1 and 2, stackable containers (10) (also referred to as "bins") are stacked on top of each other to form a stack (12). The stack (12) is placed, for example, within a grid framework structure (14) in a warehouse or manufacturing environment. The grid framework structure (14) consists of a plurality of storage columns or grid columns. Each grid of the grid framework structure includes at least one grid column to store the container stack. FIG. 1 is a schematic perspective view of the grid framework structure (14), and FIG. 2 is a schematic plan view illustrating the stack (12) of bins (10) placed within the framework structure (14). Each bin (10) typically accommodates a plurality of product items (not shown). The product items within the bin (10) may be of the same or different product types depending on the application.

[0065] The grid framework structure (14) includes a plurality of support members (16) that support horizontal members (18, 20). A first set of parallel horizontal grid members (18) are arranged vertically with respect to a second set of parallel horizontal members (20) to form a horizontal grid structure (15) supported by the support members (16). The members (16, 18, 20) are generally made of metal. Bins (10) are stacked between the members (16, 18, 20) of the grid framework structure (14), so that the grid framework structure (14) prevents horizontal movement of the stack (12) of bins (10) and guides vertical movement of bins (10).

[0066] The uppermost part of the grid framework structure (14) includes a grid or grid structure (15) comprising rails (22) arranged in a grid pattern across the entire upper part of the stack (12). Referring to FIG. 3, the rails or tracks (22) guide a plurality of load handling devices (30). Parallel rails (22) of the first set (22a) guide the movement of the robot load handling device (30) across the upper part of the grid framework structure (14) in a first direction (e.g., X direction). Parallel rails (22) of the 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) enable the robot load handling device (30) to move in two dimensions in the horizontal XY plane. The load handling device (30) can be moved to any position on the upper part of the stack (12).

[0067] The known type of load handling device (30) illustrated in FIGS. 4, 5a and 5b is described in PCT Patent Publication WO2015 / 019055 (Ocado), incorporated herein by reference, wherein each load handling device (30) occupies a single grid space (17) of a grid framework structure (14). This arrangement enables a higher density load handling device and thus enables a higher throughput for a system of a given size.

[0068] The load handling device (30) includes a vehicle (32) positioned to travel on rails (22) of a frame structure (14). A first set of wheels (34) consists of a pair of wheels located at the front of the vehicle (32) and a pair of wheels located at the rear, and is positioned to engage with two adjacent rails (22) of the first set (22a). Similarly, a second set of wheels (36) consists of a pair of wheels located on each side of the vehicle (32) and is positioned to engage with two adjacent rails (22) of the second set (22b). Each set of wheels (34, 36) can be raised and lowered by a steering assembly so that at any given time, either the first set of wheels (34) or the second set of wheels (36) engage with their respective rail sets (22a, 22b). For example, when the first set of wheels (34) engages with the first set of rails (22a) and the second set of wheels (36) are raised from the rail (22), the first set of wheels (34) can be driven by a drive assembly housed in the vehicle (32) to move the load handling device (30) in the X direction. To move in the Y direction, the first set of wheels (34) are raised from the rail (22), and the second set of wheels (36) are lowered to engage with the rail (22) of the second set (22b). Then, the second set of wheels (36) can be driven using the drive assembly to move the load handling device (30) in the Y direction.

[0069] The load handling device (30) comprises a container lifting device or assembly, for example, a crane mechanism, for lifting a storage container from above. The container lifting assembly comprises a lifting assembly (an embodiment shown in FIG. 9) comprising a winch tether or cable (38) wound on a spool or reel, and a container gripping assembly (39). The lifting assembly also includes a motor for rotating the spool to wind and / or unwind the tether. The lifting assembly shown in FIG. 4 comprises a set of four lifting tethers (38) extending in a vertical direction. The tethers (38) are connected to each of the four corners of the container gripping assembly (39), such as a lifting frame, for example, so as to be detachably connected to the storage container (10). For example, each of the tethers (38) is positioned at each of the four corners of the container gripping assembly (39) or near them. The container gripping assembly (39) is configured to detachably grip the upper portion of the storage container (10) to lift the storage container (10) from the container stack of the type of storage system shown in FIGS. 1 and 2. For example, the container gripping assembly (39) may include a pin (not shown) that engages with a corresponding hole (not shown) formed in a rim forming the upper surface of the bin (10), and a sliding clip (not shown) that engages with the rim to grip the bin (10). The clip is driven to engage with the bin (10) by a suitable driving mechanism housed in the container gripping assembly (39), and the driving mechanism is driven and controlled by a signal transmitted through the cable (38) itself or a separate control cable (not shown).

[0070] To remove the bin (10) from the top of the stack (12), the load handling device (30) first moves in the X and Y directions to position the container gripping assembly (39) on the top of the stack (12). Then, the container gripping assembly is lowered vertically in the Z direction by the lifting assembly and engages with the bin (10) on the top of the stack (12) as shown in FIGS. 4 and FIGS. 5b. The container gripping assembly (39) grasps the bin (10) and is pulled upward by the cable (38) with the bin (10) attached. At the top position of the vertical movement, the bin (10) is held on the rail (22) housed inside the vehicle body (32). In this way, the load handling device (30) can move to another location in the XY plane while carrying the bin (10) together, thereby transporting the bin (10) to another location. When a target location (e.g., another stack (12), an access point of the storage system, or a conveyor belt) is reached, the bin or container (10) can be lowered from the container receiving section and released from the container gripping assembly (39). The cable (38) is long enough for the load handling device (30) to retrieve and place the bin from any level of the stack (12), including the bottom level.

[0071] As illustrated in FIG. 3, a plurality of identical load handling devices (30) are provided so that each load handling device (30) can operate simultaneously to increase the throughput of the system. The system illustrated in FIG. 3 may include a specific location known as a port, from which bins (10) can be brought into the system or taken out of the system. Each port is connected to an additional conveyor system (not shown), so that bins (10) transported to the port by the load handling device (30) can be transported by the conveyor system to another location, such as a picking station (not shown). Similarly, bins (10) can be moved by the conveyor system from an external location to the port, for example, to a bin filling station (not shown), and transported by the load handling device (30) to a stack (12) to replenish the inventory within the system.

[0072] Each load handling device (30) can lift and move one bin (10) at a time. The load handling device (30) has a container receiving cavity or recess (40) at the bottom. The recess (40) is sized to accommodate a container (10) when lifted by a lifting mechanism, as shown in FIGS. 5a and 5b. When the container (10) is in the recess, the container (10) is lifted onto the rail (22) at the bottom, allowing the vehicle (32) to move laterally to a different grid position. If it is necessary to retrieve a bin (10b) ("target bin") that is not located at the top of the stack (12), the bins (10a) ("non-target bins") placed on top of it must be moved first so that the target bin (10b) can be accessed. This is performed by an operation referred to as "digging". Referring to FIG. 3, during the digging operation, one of the load handling devices (30) sequentially lifts each non-target bin (10a) from a stack (12) containing a target bin (10b) and places it in an empty location on another stack (12). Then, the load handling device (30) can access the target bin (10b) and move it to a port to prepare for further transport.

[0073] Each provided load handling device (30) can be operated remotely under the control of a central computer. Each individual bin (10) within the system is also tracked so that the appropriate bin (10) can be retrieved, transported, and replaced as needed. For example, during a digging operation, the location of each non-target bin is recorded so that the non-target bin (10a) can be tracked.

[0074] Wireless communication and networks may be used to provide communication infrastructure from a central computer, for example, through one or more base stations, to one or more load handling devices operating on a grid structure. Upon receiving a command from the central computer, a controller within the load handling device is configured to control the movement of the load handling device by controlling various driving mechanisms. For example, the load handling device may be instructed to retrieve a container from a target storage column located at a specific location on the grid structure. Such commands may include various movements in the XY plane of the grid structure (15). As previously described, upon reaching the target storage column, the container lifting assembly may be operated to grasp and lift the storage container (10) using the lifting assembly and the container gripping assembly (39). Once the container (10) is received in the container receiving space (40) of the load handling device (30), the container (10) is then transported to another location on the grid structure (15), for example, a "drop-off port." At the drop-off port, the container (10) is lowered to a suitable picking station so that any item within the storage container can be retrieved. Movement of the load handling device (30) on the grid structure (15) may also include the load handling device (30) being instructed to move to a charging station located at the edge of the grid structure (15).

[0075] To control the load handling device (30) on the grid structure (15), each load handling device (30) is equipped with a motor for driving the wheels (34, 36). The wheels (34, 36) may be driven via one or more belts connected to the wheels, or may be driven individually by a motor integrated into the wheels. In the case of a single-cell load handling device (where the footprint of the load handling device (30) occupies a single grid cell (17), since the available space within the vehicle body is limited, the motors driving the wheels may be integrated into the wheels. For example, the wheels of a single-cell load handling device are driven by individual hub motors. Each hub motor includes an outer rotor having a plurality of permanent magnets arranged to rotate around a wheel hub comprising a coil forming an inner stator.

[0076] The system described with reference to FIGS. 1 through 5 has many advantages and is suitable for various storage and retrieval operations. In particular, it enables very dense storage of products, provides a very economical way of storing various items in bins (10), and also enables reasonably economical access to all bins (10) when needed for picking.

[0077] During storage and retrieval operations, the container lifting assembly uses a lifting assembly (examples shown in FIG. 4, FIG. 5a, FIG. 5b, FIG. 8, and FIG. 9) to lift the container gripping assembly in the Z direction. The degree of lifting of the container gripping assembly varies throughout the grid storage structure (14). Each container stack of the grid storage structure (14) has a current dimension / height in the Z direction determined by the number of containers currently contained in that stack. The current dimension / height in the Z direction can be determined by tracking, for example, via a central computer, the containers lifted from and / or lowered into each container stack. For example, if a particular stack currently has 10 containers and the containers have a fixed dimension / height in the Z direction, the current dimension / height in the Z direction of that stack can be determined as 10 times the fixed dimension / height in the Z direction of the containers. It will be understood that the current dimension / height in the Z direction of the stack may be expressed in an absolute sense, for example, n meters from the ground, or in a relative position, n meters from the bottom of the grid storage structure (14) or n meters from the top of the grid storage structure.

[0078] The current dimension / height in the Z direction of the container stack where the load handling device is located can be transmitted to the load handling device. The lifting assembly of the load handling device may use the current dimension / height in the Z direction of the container stack to control the lifting motion of the container gripping assembly throughout the entire operation of retrieving or returning containers from the grid storage structure. In order to control the lifting of the container gripping assembly in this way, the Z position of the container gripping assembly (or, vertical position, or position in a direction perpendicular to the plane in which the bot moves across the grid storage structure (i.e., the plane defined by the X and Y directions)) must be known. It will be understood that the Z position may be an absolute position, for example, n meters from the ground, or a relative position, such as n meters from the container receiving cavity or recess (40), n meters from the top of the grid storage structure, or n meters from the top of the container stack where the load handling device is located. The Z position allows the container gripping assembly to determine how close it is to the load handling device and / or the top of the container stack. In this way, the container gripping assembly can be appropriately controlled, for example, accelerated after being lowered from the load handling device and decelerated when approaching the top of the top container of the container stack. Similarly, the container gripping assembly can accelerate after being raised from the top of the top container of the container stack and decelerated when approaching the load handling device.

[0079] During the lifting of the container gripping assembly, the container gripping assembly may encounter obstacles. For example, the container gripping assembly may encounter a defect in the grid storage structure (14) and fail to lift smoothly. An example of such a defect is when a protrusion of the vertical member (16) comes into contact with the container gripping assembly. Another example is when the container lifting assembly fails to recognize that it has come into contact with the top container in the stack and continues to unwind the tether. Excessive tether unwinds into an adjacent stack, which can cause an obstacle in that stack. Another defect is when the container gripping assembly is no longer horizontal with the XY plane while lifting, causing one side of the container gripping assembly to come into contact with the vertical member (16) and pivot around it, potentially tilting in a vertical orientation. In any of these cases, the container gripping assembly experiences an obstacle to operating correctly.

[0080] Therefore, it is advantageous to accurately determine the Z position throughout the lifting of the container gripping assembly. It is also advantageous to determine whether the container gripping assembly has received an obstacle, for example, when the tether (38) becomes loose while the container gripping assembly is being lifted. Although the Z position and obstacle have been described in the context of a load handling device, it will be understood that it is useful to determine the Z position and obstacle of the gripping assembly in any lifting device, such as a crane (i.e., lifting device) having a motor and a tether (i.e., lifting assembly) and a hook (i.e., gripping assembly) that grips and raises and / or lowers the load.

[0081] FIG. 6 illustrates a schematic diagram (600) of a load handling device (30) according to the present invention. A dashed line indicates the vehicle body (32) of the load handling device moving on wheels (34 / 36) on a grid (22). A lifting assembly (610) driven by a motor (not shown) (e.g., illustrated in FIG. 4, FIG. 5a, FIG. 5b, FIG. 8, and FIG. 9) lifts and unwinds a tether (38) to lift a container gripping assembly (39). One or more sensors (640) are configured to detect the movement of the container gripping assembly. The load handling device (600) may use a processor or controller (650) to receive and transmit data from and to each of the lifting assembly (610) and one or more sensors (640). This data may be stored in a storage unit (660). The data in the storage unit (660) can be periodically transmitted through one or more networks, such as a base station, and used for further processing.

[0082] FIG. 7 illustrates the steps of a method (700) used in a lifting assembly (e.g., used in a load handling device or a crane) comprising a gripping assembly configured to grip a load and a lifting assembly configured to raise the gripping assembly, wherein the lifting assembly comprises at least one tether connected to the gripping assembly and a motor that winds and / or unwinds said or each tether to raise and / or lower the gripping assembly. It will be understood that the method of FIG. 7 may be performed using a controller (e.g., the controller (650) of the load handling device of FIG. 6). In step 710, as illustrated in FIG. 8 or FIG. 9, the motor of the lifting assembly is used to raise the gripping assembly. In step 720, a sensor is used to detect movement of the gripping assembly. An embodiment of a sensor configured to detect movement of the gripping assembly is described below in relation to FIG. 9 through 15. Generally, the sensor includes an input that is coupled by the movement of the gripping assembly. In step 730, the controller is used to determine the vertical position of the gripping assembly using the output of the sensor. It will be understood that the detected movement of the gripping assembly may be correlated with the vertical position. For example, if it is detected that the tether (or FFC) has been unwound 1 meter from the lifting assembly, the vertical position of the gripping assembly has changed 1 meter relatively. If the starting position for the 1-meter unwound of the gripping assembly is known in absolute terms (for example, determined from when the gripper device is fully withdrawn from the container receiving space (40) of the load handling device (30) located in the grid storage framework (14), the current absolute vertical position of the gripping assembly can be determined. In the optional step 740, the controller is used to control / adjust the motion profile of the gripping assembly based on the determined vertical position. Typically, the motor is controlled using the motion profile.In an embodiment of a load handling device, a motor controls the lifting of a container gripping assembly according to a motion profile. One such embodiment is a trapezoidal speed versus time motion profile, which causes the container gripping assembly to be in a specific vertical position at a specific time. Therefore, monitoring this vertical position can provide feedback used to control / adjust the motion profile.

[0083] FIG. 8 illustrates an embodiment of a container lifting assembly (additionally described in PCT application number PCT / EP2022 / 081364 (Ocado)). In FIG. 8, the container lifting assembly (800) has a lifting assembly (802) comprising four spools (810) for winding and unwinding each tether (38). A drive belt (820) is driven by a motor (not shown) to rotate the spools of a drive shaft (805) in the opposite direction to the drive shaft (806). By rotating the drive shafts (805, 806) in the opposite direction, each tether (38) can be positioned at or near the corner of the lifting assembly. In particular, as illustrated in FIG. 8, the point where each tether is wound onto or unwound from the spool is at or near each corner of the lifting assembly. This allows tethers to be connected to each corner of the container gripping assembly (39), thereby increasing stability when lifting the container gripping assembly (39).

[0084] The tether may be a cable, rope, tape, or other form of tether having the necessary physical properties for lifting a container. In one embodiment, four tethers are used. In one embodiment, the tether may include a steel tape. In one embodiment, the tether may be formed of or include a polyester material (e.g., woven polyester material). In particular, the tether may include a woven polyester tape or belt, for example, a seat belt (i.e., a seat belt can be used as a tether). In another embodiment, the tether is Dyneema RTM It can be manufactured from ultra-high molecular weight polyethylene (UHMVPE or UHMW) (also known as high modulus polyethylene (HMPE)) such as tape. In another embodiment, the tether is Dyneema RTM It may include a polyester material (e.g., woven polyester) combined with a tape. In another embodiment, the tether may include a cotton material. In another embodiment, the tether may include a webbing material, e.g., woven polyester, nylon, or cotton. In another embodiment, the tether may include a conductive material, for example, the tether may include a woven material or woven polyester material in which a conductive element or wiring (e.g., copper) is woven into the tether's fabric or material. In another embodiment, the tether may include a woven belt (e.g., a seat belt) in which a conductive element or wiring is woven within the belt. In another embodiment, the tether may be configured to provide power and / or communication (i.e., electrical communication) to a gripping device by including a conductive element or wiring (e.g., copper) woven into the tether's fabric or material.

[0085] Additionally, optionally a fixed flexible cable (or ribbon cable), an FFC (830), and an FFC spool (840) are shown, which are used to drive and control the gripping of the container by transmitting electrical signals to the container gripping assembly (39) as described above with respect to FIG. 4. That is, the FFC is used to drive and control a pin or clip that engages with the bin (10) by a suitable driving mechanism housed in the container gripping assembly (39). One suitable FFC is the Axon' Cable RTM It is manufactured by FFC. Although FFC is illustrated, it can be understood that at least one wire may be used instead for the same purpose, or, as described above, a conductive element may be integrated into the tether.

[0086] Systems for determining the vertical position of a container gripping assembly using the method of FIG. 7 are described below. Although the lifting assembly illustrated in FIG. 8 (and FIG. 9 below) is illustrated as having four spools (810) and respective tethers for raising and lowering the container gripping assembly using the illustrated configuration, it will be recognized that the systems described below are not limited to a specific number of spools, tethers, and the illustrated configuration for raising and / or lowering the container gripping device.

[0087] Referring to FIGS. 9, FIGS. 10, FIGS. 11a and FIGS. 11b, a container lifting assembly (900) equipped with a sensor capable of determining the vertical position of a container gripping assembly is described. Similar to FIG. 8, the lifting assembly includes four spools (910) for winding and unwinding each tether (38). A drive belt (920) is driven by a motor (901) (via the drive belt (925) and spool (911)) to rotate the spools of a drive shaft (905) in the opposite direction of the drive shaft (906). The drive belt (920) drives a pulley connected to the spool (910). By rotating the drive shafts (905, 906) in the opposite direction, each tether (38) can be positioned at or near the corner of the lifting assembly. In particular, as illustrated in FIG. 9, the point where the tether is wound onto or unwound from the spool is at or near each corner of the lifting assembly. This allows the tethers to be connected to each corner of the container gripping assembly (39) (not shown), thereby increasing stability when lifting the container gripping device (39). The container lifting assembly also includes an FFC spool (940). The FFC (not shown) is wound onto the spool and extends to the container gripping assembly (39) to transmit electrical signals to the container gripping assembly (39). Thus, as the motor rotates the drive shaft (906), the FFC is wound and unwound. A stator (960) is used to transmit and receive signals from and to the FFC on the FFC spool (945).

[0088] In one embodiment, the FFC spool (940) has a rotary encoder (950) (i.e., a sensor) for detecting the movement of the FFC spool (940). For example, the rotary encoder (950) may be fixed between a stator and a horizontal bar (925) (although other means of linking the rotary encoder (950) to the FFC spool are obvious). The rotary encoder (950) includes a rotary electromechanical device that generates a pulse when the FFC spool rotates. For example, one pulse is generated when the FFC spool rotates by a predetermined rotation angle. As illustrated in FIGS. 11a and 11b, the encoder configuration (1000) has an encoder disk (945) attached to the FFC spool (840 / 940). The encoder disk (945) has a slot (946) along its circumference (or outer edge). This slot allows the transmitter and receiver elements (951) of the encoder (950) to transmit and receive optical signals. The solid space between these slots will prevent the reception of optical signals. Thus, as the FFC spool rotates, optical signals are received and blocked, which can be correlated to the rotation angle of the FFC spool (940). Although an optical rotary encoder has been described, a mechanical encoder may be used alternatively, in which case the FFC spool (940) engages directly with the input of the mechanical encoder to rotate the input. Alternatively, the motor (920) may have an encoder that can be used to determine the number of rotations of the FFC spool (940). Regardless of the type of rotary encoder implementation, the rotation angle and direction of the FFC spool (940) can be determined as the container gripping assembly (39) rises and falls.

[0089] Using the dimensions of the FFC spool (940) and the FFC, the rotation angle and direction of the FFC spool (940) can be correlated with the length of the FFC extended from the current FFC spool. The length of the FFC extended from the current FFC spool (940) can be correlated with the vertical position of the container gripping assembly as described above with respect to FIG. 7.

[0090] Although the use of a rotary encoder (950) has been described as being used for an FFC spool (840 / 940), it will be understood that any tether spool (810 / 910) can be monitored using the encoder configuration (1100) shown in FIG. 11a and FIG. 11Bb. That is, an encoder disk is attached to the tether spool (810 / 910). Thus, the rotation of the tether spool (910) can be monitored instead. Using the dimensions of the tether spool (910) and the tether (38), the rotation angle of the tether spool (910) can be correlated with the length of the tether extended from the current tether spool (910), which can be correlated with the vertical position of the container gripping assembly as described above with respect to FIG. 7. Alternatively, the motor (901) may have a motor encoder that can be used to determine the number of rotations of the tether spool (910). Regardless of the type of rotary encoder implementation, the rotation angle and direction of the tether spool (910) can be determined as the container gripping assembly (39) rises and falls.

[0091] Additionally, it will be understood that the encoder configuration (1100) illustrated in FIGS. 11a and 11b can be used to monitor each tether spool (810 / 910) and FFC spool (840 / 940). Using two encoder configurations (1100) enables redundancy in case one of the encoder configurations fails. Using two encoder configurations (1100) for each tether spool (910) allows determining whether the container gripping assembly (39) is horizontal during a lifting or rising motion. If the two encoder configurations (1100) detect the same rotation angle of each tether spool (910), it can be inferred that the container gripping assembly (39) is horizontal. This can occur when one tether spool slips on the shaft on which it is rotating. If the output of one encoder configuration (1100) is different from the output of another encoder configuration (1100), it may indicate that the container gripping assembly (39) is not horizontal. By using four encoder configurations (1100), the orientation of the container gripping assembly can be detected.

[0092] Determining the vertical position of the container lifting assembly using an FFC spool (940) may be advantageous when the FFC has a relatively higher elastic modulus than the tether (39), for example, when a woven polyester belt is used as the tether (39). The woven polyester belt tends to stretch during unwinding and winding depending on the load carried by the container gripping assembly (39). Similarly, the woven polyester belt tends to be unwound from the tether spool (910) and wound onto the tether spool (910) in an unpredictable manner. In contrast, the FFC tends to stretch less and is unwound from and wound onto the FFC spool in a predictable manner, so the detected movement of the FFC spool allows for a more accurate determination of the vertical position of the container lifting assembly (39).

[0093] Additionally or alternatively, the FFC spool (940) may be rotatably mounted to the shaft (906), for example, via a bearing, so that the FFC spool (940) can rotate independently or relative to the shaft (906). Thus, the FFC spool (940) can be unwound to extend the FFC cable when the tether is unwound to lower the container gripping assembly (39). Additionally, the FFC does not support the load of the container gripping assembly (39). A biasing assembly may be used to ensure that the FFC is wound back onto the FFC spool (940) when the container gripping assembly (39) is raised. The biasing assembly resists the unwinding of the FFC to keep the FFC taut, which allows for a more accurate determination of the vertical position of the container gripping assembly (39). For example, if the FFC is extended 1 meter from the FFC spool (940) and it is determined that the FFC is in a taut state, it may be determined that the position of the container gripping assembly has changed by 1 meter. As illustrated in FIG. 10, the biasing assembly includes a biasing plate (960) and a torsion spring (930) acting on the FFC spool (940) which is rotatably mounted on the shaft (906). The biasing plate (960) is fixedly mounted on the shaft (906). The torsion spring (930) is connected to the biasing plate (960) and the FFC spool (945) so as to resist the unwinding of the FFC spool (945). In other words, the FFC spool (945) is spring-tensioned to resist rotational force when a rotational force (within the elastic limit of the torsion spring) is applied in the unwinding direction against the stationary shaft (925). Therefore, when this rotational force (within the elastic limit of the torsion spring) is removed, the FFC spool is wound again. Generally, any biasing assembly can be used as long as it acts on a rotatably mounted FFC spool (940) to keep the FFC taut.For example, a tension spring may be used to connect the biasing plate (960) and the FFC spool (945). Alternatively, the FFC spool (945) may be fixedly mounted on the shaft (906), and the biasing configuration may be located within the container gripping assembly (39). In this embodiment, the biasing configuration resists the winding of the FFC spool (940). This ensures that the FFC remains taut during the lifting of the container gripping assembly (39).

[0094] Referring to FIG. 12, another sensor (1200) capable of determining the vertical position of the container gripping assembly is described. A spool (any of 810 / 910 / 840 / 940) is used to wind and / or unwind each tether (38) or FFC (830). A rotary encoder wheel (1210) is biased against the tether (38) or FFC (830) using an arm (1220), and the wheel (1210) rotates around this arm (1220) via a pivot (1215). As illustrated in FIG. 12, the rotary encoder wheel (1210) rotates as the tether (38) or FFC (830) moves while being wound and / or unwound from the spool (810 / 910 / 840 / 940). That is, the shaft / input portion of the rotary encoder wheel is rotated by the tether (38) or FFC (830). The rotation of the rotary encoder wheel (1210) may be correlated with the length of the tether (38) or FFC (830) that caused the rotation, which may be correlated with the vertical position of the container gripping assembly in the context of the above embodiments. The encoder wheel may be part of an optical or mechanical encoder.

[0095] Referring to FIG. 13, another sensor (1300) capable of determining the vertical position of the container gripping assembly is described. The spool (1310) may be mounted on a shaft (805 / 806 / 905 / 906). Thus, as the lifting assembly lifts the container gripping assembly, the spool (1310) rotates. The spool (1310) may be conductive. Additionally or alternatively, the spool (1310) has a channel or groove in which a conductive wire (1320) can be wound so that the conductive wire (1320) within the adjacent channel / groove is physically in contact. This means that in a fully wound spool (1310), the conductive wire (1320) is short-circuited so that the voltage applied between the first end connected to the spool (1310) and the second end connected to the container gripping assembly produces a specific current value. As the spool (1310) is unwound, a portion of the length of the conductive wire (1320) is no longer short-circuited (see FIG. 13). Accordingly, the voltage applied to the first and second ends of the conductive wire (1320) yields a reduced current value due to the increase in electrical resistance of the configuration of the conductive wire (1320). In one embodiment, the second end may be connected to the FFC connection of the container gripping assembly (39) to form a closed circuit in which the current value can be determined. The change in electrical resistance that occurs as the conductive wire (1320) is wound and unwound may be correlated with the length of the conductive wire (and tether (38 and FFC (830)) that caused the change in electrical resistance, which may again be correlated with the vertical position of the container gripping assembly in accordance with the context of the above embodiments. As long as the biasing assembly keeps the spool taut, the biasing assembly (e.g., those described above in relation to the FFC spool) may be used with the spool (1310). That is, the biasing assembly resists the winding or unwinding of the spool (1310) as described above in relation to the FFC spool.

[0096] Referring to FIG. 14, another sensor (1400) capable of determining the vertical position of the container gripping assembly is described. FIG. 14 illustrates the same configuration described above in relation to FIG. 8. The description of FIG. 8 also applies to that illustrated in FIG. 14. Additionally, a Time of Flight (ToF) sensor (1410) is mounted on the container lifting assembly (39). The ToF sensor (1410) is configured to transmit an optical signal (1420) to a reflective surface (not shown) and to receive a reflection (1430) of the transmitted optical signal (1420). The time between the transmission and reception of the optical signal (e.g., laser or LED) can be used to calculate the distance between the container lifting assembly (39) and the reflective surface. The reflective surface does not move as the container lifting assembly (39) rises and / or descends. For example, the reflective surface may be located within the lifting mechanism (802) or in a load handling device or other suitable part of the system. Therefore, the distance between the container lifting assembly (39) and the reflective surface can be used to determine the vertical position of the container gripping assembly (39). It will be understood that the ToF sensor (1410) may instead be located at a fixed position within the lifting mechanism (802) or at another suitable part of the load handling device or system to transmit and receive an optical signal to the reflective surface of the container lifting assembly (39). Suitable ToF sensors are Texas Instruments RTM The OPT3101 is a ToF-based long-range proximity and distance sensor AFE evaluation module. Generally, any laser sensor for measuring distance can be used. In principle, in this implementation, any rangefinder type sensor, such as Light Detection and Ranging (LiDAR) or ultrasound, can be used to implement the ToF sensor.

[0097] Referring to FIG. 15, another sensor (1500) capable of determining the vertical position of the container gripping assembly is described. A spool (any of 810 / 910 / 840 / 940) is used to wind and / or unwind each tether (38) or FFC (830). A wheel (1510) is biased against the spool (810 / 910 / 840 / 940) using an arm (1520), and the wheel (1510) rotates around this arm (1220) via a pivot (1515). As illustrated in FIG. 15, the wheel (1510) rotates as the spool (810 / 910 / 840 / 940) rotates. The wheel (1510) has an outer textured surface that allows the sensor (1530) to track its movement. One such suitable surface is aluminum or nylon. The sensor (1530) tracks the movement of the outer texture surface of the spool (1510) by irradiating a light signal (e.g., laser or LED) onto the outer texture surface of the spool (1510) so that reflected light (1550) is detected (e.g., via a photodiode). The operation is similar to the operation of an optical computer mouse. The detected movement of the outer texture surface of the spool (1510) may be correlated with the rotation of the spool (810 / 910 / 840 / 940) and thus with the extension of the tether (39) or FFC (820), which may be correlated with the vertical position of the container gripping assembly in accordance with the above implementations. It will be understood that the wheel (1510) may be omitted if there is a surface on the spool (810 / 910 / 840 / 940) on which the sensor (1530) can track the movement.

[0098] Referring to FIG. 16, a system using the sensors described above to determine an obstacle of the container gripping assembly (39) is described. The motor (901) performs the winding and unwinding of the tether (38 / 830). Thus, any of the sensors directly monitoring the motor will detect whether the motor is currently operating and, consequently, whether the tethers are being wound and unwound. In other words, if the motor is operating, any of the sensors directly monitoring the motor will detect the operation of the motor. When the container gripping assembly (39) encounters an obstacle, the motor continues to wind and / or unwind the tether, but the tether (38 / 830) and / or FFC (830) will experience a change in configuration. For example, if the container gripping assembly (39) hits an obstacle while descending, the tether (38 / 830) and / or FFC (830) will become loose. Accordingly, by using the sensors described above, which can detect changes in the state of the tether (38 / 830) and / or FFC (830), together with the sensors that detect the state of the motor (901), an obstacle in the container gripping assembly (39) can be determined. In particular, if it is detected by specific sensors that the motor is operating and by specific sensors that the tether (38 / 830) and / or FFC (830) is loose, it can be inferred that an obstacle has occurred in the container gripping assembly (39). That is, if the container gripping assembly encounters an obstacle while descending, the motor no longer performs the descent of the container gripping assembly (39).

[0099] A processor / controller (1610) (which may be identical to the processor / controller (650)) can receive input from a motor operation sensor (1620). The sensor (1620) includes sensors as described above, such as:

[0100] - Motor encoder of the motor (910)

[0101] - FFC or tether spool (810 / 910 / 840 / 940) monitored using the encoder array (1100) shown in FIGS. 11a and 11b

[0102] - As illustrated in Fig. 15

[0103] All sensors (1620) detect the motor operation itself directly or through the movement of a spool (FFC or tether spool (810 / 910 / 840 / 940)) fixed to a shaft rotated by the motor. Generally, the motor drive sensor (1620) indicates whether the motor is driven to wind and / or unwind the tether (38 / 830). If the motor is rotating the shaft that winds and / or unwinds the tether / FFC, it is assumed that the container lifting assembly (39) is rising and / or lowering.

[0104] The processor / controller (1610) may receive different inputs to verify whether the container lifting assembly (39) is actually being raised and / or lowered. One input that may be used for this purpose is provided by a sensor (1630) that detects the movement of the gripping assembly. The sensor (1630) includes sensors as described above, such as:

[0105] - FFC spool (940), encoder (950), and biasing configuration shown in FIG. 10

[0106] - As illustrated in Fig. 12

[0107] - As shown in Fig. 13 and biasing configuration

[0108] - As illustrated in Fig. 14

[0109] - As illustrated in Fig. 15 (when used with FFC spool 940 / 940 and biasing configuration)

[0110] The output of the sensor (1630) depends on the movement of the container gripping assembly (39). That is, the sensor (1630) can indicate whether the container gripping assembly (39) is rising and / or falling and the degree of rising and / or falling. Accordingly, the processor / controller (1610) can determine whether the motor operation (indicated by the sensor 1620) actually causes the lifting of the container lifting assembly (indicated by the sensor 1630).

[0111] Alternatively, since the sensor (1630) can indicate whether and to what extent the container gripping assembly (39) is being raised, the processor / controller (1610) can correlate the output of the sensor (1630) with the motor motion profile used to control the raising of the container gripping assembly (39). That is, the processor / controller (1610) can determine whether the current raising and / or lowering of the container gripping assembly (39) (indicated by the sensor 1630) is correlated with being controlled by the motor. For example, the trapezoidal motion profile of the motor mapping time to the speed of the container gripping assembly (39) can be converted by the controller into a corresponding time-distance profile. Any deviation of the determined vertical position of the container gripping assembly (39) from the converted time-distance profile can be detected.

[0112] Generally, the system of FIG. 16 can be used to determine a discrepancy between the drive of the motor and the resulting raising and / or lowering of the container gripping assembly. The presence of such a discrepancy can be detected using the method of FIG. 17.

[0113] FIG. 17 illustrates the steps of a method (1700) used in a lifting assembly (e.g., used in a load handling device or a crane) comprising a gripping assembly configured to grip a load and a lifting assembly configured to raise the gripping assembly, wherein the lifting assembly comprises at least one tether connected to the gripping assembly and a motor that winds and / or unwinds said or each tether around at least one shaft to raise and / or lower the gripping assembly. It will be understood that the method of FIG. 17 can be performed using a controller (e.g., the controller (650) of the load handling device of FIG. 6). In step 1710, a motor (e.g., motor (901)) rotates at least one shaft (e.g., 805, 906, 905, 906) to wind and / or unwind at least one tether (e.g., tether (38)) to raise and / or lower a gripping assembly (e.g., container gripping assembly (39)). In step 1720, a sensor (e.g., sensor (1630)) is used to detect the movement of the gripping assembly. An embodiment of the sensor (1630) configured to detect the movement of the gripping assembly is described in relation to FIGS. 9 through 15. In step 1730, a controller is used to determine an obstacle in the gripping assembly if the current output of the sensor does not correspond to the winding and / or unwinding of the tether around at least one shaft for raising and / or lowering the gripping assembly. That is, the controller determines a discrepancy between the drive of the motor and the resulting raising and / or lowering of the gripping assembly. An embodiment for implementing step 1730 using a sensor (1620) and / or an input (1640) is described below.

[0114] In the optional step 1740, the motor is stopped using the controller if an obstacle is detected in the gripping assembly. This prevents the tether from being wound and / or unwound, thereby preventing damage to the gripping device (e.g., container gripping assembly (39)), and / or the lifting device (e.g., container lifting assembly (39)), and / or the surrounding environment (e.g., grid storage structure (14)).

[0115] In one embodiment of the method of FIG. 17, the sensor (1620) is a motor encoder of a motor (e.g., motor (901)), and the controller is configured to determine an obstacle in the gripping assembly when the current output of the sensor is not correlated with the current output of the motor encoder. For example, both the motor encoder and the sensor (1630) may be configured to generate a corresponding output for every increment of rotation of at least one shaft. Thus, the output deviation between the motor encoder (i.e., sensor (1620)) and the sensor (1630) may be used to indicate that the shaft rotation no longer causes the lifting assembly to rise and / or fall. The controller may be configured to determine an obstacle in the gripper assembly when the current output of the sensor (1630) is not correlated with the current output of the motor encoder within a predetermined threshold. The threshold may, of course, be set to allow a small deviation before an obstacle is determined. For example, the threshold may require that two consecutive outputs be different.

[0116] In another embodiment of the method of FIG. 17, each tether spool (e.g., spool (810 / 910)) is used for winding and / or unwinding each tether. The or each tether spool is fixedly mounted on a shaft rotated by a motor. A sensor (1620) is a tether rotary encoder for the or each tether spool. The or each tether rotary encoder is configured to engage with each spool to detect the degree to which each spool has rotated as the or each tether is wound and / or unwound. Any rotary encoder described above, such as those shown in FIG. 11a and FIG. 11b, may be used as a tether rotary encoder. A controller is configured to determine an obstacle in the gripping assembly if the current output of the sensor does not correlate with the current output of the or each tether rotary encoder. For example, the tether rotary encoder and sensor (1630) may both be configured to generate a corresponding output for every increment of rotation of at least one shaft. Thus, the output deviation between the above or each tether rotary encoder (i.e., sensor (1620)) and sensor (1630) may be used to indicate that shaft rotation no longer causes the lifting assembly to rise and / or fall. The controller may be configured to determine an obstacle in the gripping assembly if the current output of the sensor (1630) is not correlated with the current output of the tether rotary encoder by a threshold. A threshold may, of course, be set to allow a small deviation before an obstacle is determined. For example, the threshold may require two consecutive outputs to be different.

[0117] In another embodiment of the method of FIG. 17, an electric cable spool (e.g., FFC spool (840 / 940)) on which an electric cable (e.g., FFC (830)) is unwound and wound is used. The electric cable spool is fixedly mounted on a shaft rotated by a motor. The electric cable spool is connected to a gripping assembly and communicates electrically with the gripping assembly. A sensor (1620) is an electric cable rotary encoder for the electric cable spool. The electric cable rotary encoder is configured to engage with each spool to detect the degree to which each spool is rotated as the above or each tether is wound and / or unwound. Any rotary encoder described above, such as that shown in FIG. 11a and FIG. 11b, may be used as the electric cable rotary encoder. A controller is configured to determine an obstacle in the gripping assembly if the current output of the sensor does not correlate with the current output of the tether rotary encoder. For example, the electric cable rotary encoder and the sensor (1630) may both be configured to generate a corresponding output for every increment of rotation of at least one shaft. Thus, the output deviation between the electric cable rotary encoder (i.e., the sensor (1620)) and the sensor (1630) may be used to indicate that the shaft rotation no longer causes the lifting assembly to rise and / or fall. The controller may be configured to determine an obstacle in the grid assembly if the current output of the sensor (1630) is not correlated with the current output of the electric cable rotary encoder by a threshold. A threshold may, of course, be set to allow a small deviation before an obstacle is determined. For example, the threshold may require that two consecutive outputs be different.

[0118] In another embodiment of the method of FIG. 17, each tether spool (e.g., spool (810 / 910)) on which each tether is wound and / or unwound is used. The or each tether spool is fixedly mounted on a shaft rotated by a motor. A sensor (1620) includes a tether spool sensor comprising a light source and a light detector as illustrated in FIG. 15 and described above. As described above, the light source is configured to transmit a light signal to a moving surface as the gripping assembly rises and / or descends. The light detector is configured to detect movement of the surface by detecting a reflection of the light signal from the surface. The lifting assembly includes a wheel that contacts the tether spool on which each tether is wound and / or unwound, the wheel having a surface, or alternatively, the or each tether spool having a surface. A controller is configured to determine an obstacle of the gripping assembly when the current output of the sensor is not correlated with the current output of the sensor for the tether spool. For example, the tether spool sensor and the sensor (1630) may both be configured to generate a corresponding output for every increment of rotation of at least one shaft. Thus, the output deviation between the or each tether spool sensor (i.e., sensor (1620)) and the sensor (1630) may be used to indicate that shaft rotation no longer causes the lifting assembly to rise and / or fall. The controller may be configured to determine an obstacle in the gripping assembly if the current output of the sensor (1630) is not correlated with the current output of the tether spool sensor by a threshold. A threshold may, of course, be set to allow a small deviation before an obstacle is determined. For example, the threshold may require two consecutive outputs to be different.

[0119] In another embodiment of the method of FIG. 17, an electric cable spool (e.g., FFC spool (840 / 940)) on which an electric cable (e.g., FFC (830)) is wound and unwound is used. The electric cable spool is fixedly mounted on a shaft rotated by a motor. The electric cable spool is connected to a gripping assembly and communicates electrically with the gripping assembly. The sensor (1620) includes an electric cable spool sensor comprising a light source and a photodetector as shown in FIG. 15 and described above. As described above, the light source is configured to transmit a light signal to a moving surface as the gripping assembly rises and / or descends. The photodetector is configured to detect the movement of the surface by detecting the reflection of the light signal from the surface. The lifting assembly includes a wheel that contacts the electric cable spool on which the electric cable is wound and / or unwound, and this wheel covers the surface, or alternatively, the electric cable spool covers the surface. The controller is configured to determine an obstacle in the gripping assembly when the current output of the sensor is not correlated with the current output of the electric cable spool sensor. For example, the electric cable spool sensor and the sensor (1630) may both be configured to generate a corresponding output for every increment of rotation of at least one shaft. Thus, the output deviation between the electric cable spool sensor (i.e., sensor (1620)) and the sensor (1630) may be used to indicate that shaft rotation no longer causes the lifting assembly to rise and / or fall. The controller may be configured to determine an obstacle in the gripping assembly when the current output of the sensor (1630) is not correlated with the current output of the electric cable spool sensor by a threshold. A threshold may, of course, be set to allow a small deviation before an obstacle is determined. For example, the threshold may require that two consecutive outputs be different.

[0120] The above five implementation forms use a sensor (1620) indicating direct driving of the motor in a processor / controller executing the method of FIG. 17.

[0121] Additionally or alternatively, the controller may receive a motion profile so that the expected state of the gripping assembly can be derived. That is, the controller is commanded how the gripping assembly should move. As described above, a motion profile of the motor mapped to the speed of the container gripping assembly (39) may be provided to the controller. A corresponding time-distance profile may be provided instead, or may be derived from the motion profile by the processor. Thus, as soon as the controller detects the movement of the gripping assembly through the sensor (1630), the controller can compare the movement of the gripping assembly with the expected movement derived from the motion profile. This can be used to further verify that an obstacle has occurred, if the input (1640) is used in addition to the input (1620).

[0122] The method of FIG. 17 also uses a sensor (1630), an embodiment of which is described below.

[0123] In one embodiment of the method of FIG. 17, an electric cable spool (e.g., FFC spool (840 / 940)) is used to unwind and wind an electric cable (e.g., FFC (830)). The electric cable spool is rotatably mounted on a shaft rotated by a motor, as described above and illustrated in FIG. 9 as the FFC spool (940) and biasing configuration. The electric cable spool is connected to a gripping assembly and communicates electrically with the gripping assembly. The sensor (1630) includes a rotary encoder (e.g., encoder 950). When the gripping assembly receives an obstacle, the FFC spool (940) of FIG. 9 returns to its biasing state. That is, the FFC spool and FFC are no longer subjected to tension caused by the movement of the container lifting assembly and return to their biasing state. Return to the bias state means that in this implementation, the rotary encoder output of the sensor (1630) is no longer correlated with the output provided by the sensor (1620), and an obstacle is detected as described above. Additionally or alternatively, in this implementation, the vertical position of the gripper assembly can be derived from the sensor (1630) and compared with the input (1640) to determine the obstacle.

[0124] In another embodiment of the method of FIG. 17, the sensor (1630) includes a rotary encoder such as the rotary encoder (1210) described above and illustrated in FIG. 12. When the gripping assembly receives an obstacle, the rotary encoder (1210) of FIG. 12 no longer rotates due to a decrease in traction with the tether (38) or FFC (830). The loss of traction means that in this embodiment, the rotary encoder output of the sensor (1630) is no longer correlated with the output provided by the sensor (1620), and the obstacle is detected as described above.

[0125] In another embodiment of the method of FIG. 17, a wire spool (e.g., wire spool (1310)) on which a wire (e.g., wire (1320)) is wound and unwound is used. The wire spool is rotatably mounted on a shaft rotated by a motor, as in the wire spool (1310) and biasing configuration described above and illustrated in FIG. 13. The wire spool is connected to a gripping assembly. The sensor (1630) includes the sensor (1300). When the gripping assembly receives an obstacle, the wire spool (1310) of FIG. 13 returns to its biased state. That is, the wire spool (1310) no longer receives tension caused by the movement of the container lifting assembly and returns to its biased state. Return to the biased state means that in this embodiment, the output of the sensor (1300) is no longer correlated with the output provided by the sensor (1620), and the obstacle is detected as described above. Additionally or alternatively, in this implementation, the vertical position of the gripper assembly is derived from the sensor (1630) and compared with the input (1640) to determine an obstacle.

[0126] In another embodiment of the method of FIG. 17, the sensor (1630) includes a ToF sensor (ToF sensor (1410)) as described above and illustrated in FIG. 14, or any laser sensor that generally measures distance may be used. When the gripping assembly receives an obstacle, the ToF sensor no longer detects a change in distance. Alternatively, the gripper assembly may be tilted so that the ToF sensor loses alignment with the reflective surface and no longer detects a return light signal. The lack of a change in distance measurement or the absence of a return light signal means, in this embodiment, that the output of the sensor (1630) is no longer correlated with the output provided by the sensor (1620), and the obstacle is detected as described above. Additionally, or alternatively, in this embodiment, the vertical position of the gripper assembly may be derived from the sensor (1630) and compared with the input (1640) to determine the obstacle.

[0127] In one embodiment of the method of FIG. 17, an electric cable spool (e.g., FFC spool (840 / 940)) on which an electric cable (e.g., FFC (830)) is wound and unwound is used. The electric cable spool is rotatably mounted on a shaft rotated by a motor, as described above and illustrated in FIG. 9, such as the FFC spool (940) and biasing configuration. The electric cable spool is connected to a gripping assembly and communicates electrically with the gripping assembly. The sensor (1630) includes an electric cable spool sensor comprising a light source and a photodetector as illustrated in FIG. 15 and described above. As described above, the light source is configured to transmit a light signal to a moving surface as the gripping assembly rises and / or descends. The photodetector is configured to detect movement of the surface by detecting a reflection of the light signal from the surface. The lifting assembly includes a wheel that contacts the electric cable spool on which the electric cable is wound and / or unwound, the wheel having a surface, or alternatively, the electric cable spool having a surface. When the gripping assembly receives an obstacle, the FFC spool (940) of FIG. 9 returns to its biased state. That is, the FFC spool and the FFC no longer receive tension caused by the movement of the container lifting assembly and return to its biased state. Return to the biased state means that, in this embodiment, the rotary encoder output of the sensor (1630) is no longer correlated with the output provided by the sensor (1620), and an obstacle is detected as described above. Additionally or alternatively, in this embodiment, the vertical position of the gripper assembly can be derived from the sensor (1630) and compared with the input (1640) to determine the obstacle.

[0128] In this document, the expression “movement in the n direction” (and related terms) is intended to mean movement in both directions (i.e., towards the positive and negative ends of the n-axis) substantially along the n-axis or parallel to the n-axis, where n is one of x, y, and z.

[0129] In this document, the word “connect” and its derivatives are intended to include the possibility of both direct and indirect connections. For example, “x is connected to y” includes both the possibility that x is directly connected to y without any intermediaries and the possibility that x is indirectly connected through one or more intermediaries. Where a direct connection is intended, “is directly connected,” “direct connection,” or similar terms are used. Similarly, the word “support” and its derivatives are intended to include the possibility of both direct and indirect contact. For example, “x supports y” includes both the possibility that x directly supports and directly contacts y without any intermediaries and the possibility that x indirectly supports y by one or more intermediaries in contact with x and / or y. The word “mount” and its derivatives are intended to include the possibility of both direct and indirect mounting. For example, “x is mounted on y” includes both the possibility that x is mounted directly on y without any intermediaries and the possibility that x is mounted indirectly on y through one or more intermediaries.

[0130] In this document, the word "include" and its derivatives are intended to have an inclusive rather than an exclusive meaning. For example, "x includes y" includes the possibility that x includes only y, the possibility that x includes multiple ys, or the possibility that x includes one or more ys and one or more other elements. Where an exclusive meaning is intended, the expression "x consists only of y" is used, which means that x includes only y and nothing else.

[0131] In this document, the term "controller" is intended to include all hardware suitable for controlling one or more other components (e.g., providing instructions). For example, it includes a processor equipped with one or more memories and appropriate software for processing data related to a component or components and transmitting appropriate instructions to the component(s) so that the component can perform its intended function.

[0132] As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise. Additionally, it will be understood that as used herein, the terms "comprising" and / or "comprising" specify the presence of the described features, integers, steps, actions, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, actions, elements, components, and / or groups thereof.

[0133] The present invention may take an entirely hardware implementation, an entirely software implementation, or an implementation that includes both hardware and software elements. In a preferred implementation, the present invention is implemented in software.

[0134] Additionally, the present invention may take the form of a computer program implemented on a computer-readable medium having computer-executable code for use with a computer or in connection with a computer. For the purposes of this description, the computer-readable medium may include any type of tangible device capable of containing, storing, transmitting, propagating, or carrying the program for use with a computer or in connection with a computer. Additionally, the computer-readable medium may be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or device or equipment) or a radio medium. Examples of computer-readable media include semiconductor or solid-state memory, magnetic tape, removable computer diskette, RAM (Random Access Memory), ROM (Read-Only Memory), fixed magnetic disk, and optical disk. Current examples of optical disks include CD-ROM, CD-R / W, and DVD.

[0135] The flowcharts illustrated in the drawings describe the structure, function, and operation of possible implementations of methods according to various embodiments of the present invention. In this regard, each block of the flowchart may represent a module, segment, or part of code containing one or more execution instructions for implementing a specified logical function. Additionally, it should be noted that in some alternative implementations, the functions indicated within the blocks may occur differently from the order described in the drawings. For example, two consecutive blocks may be executed substantially simultaneously, and depending on the related functions, the blocks may sometimes be executed in reverse order. Additionally, it should be noted that each block of the flowchart and combinations of blocks may be implemented by a special-purpose hardware-based system or a combination of special-purpose hardware and computer instructions that performs a specified function or operation.

[0136] The foregoing description is provided merely as an example, and those skilled in the art will understand that various modifications are possible without departing from the scope of the invention. Although various embodiments have been described above with respect to one or more individual embodiments to a certain degree of specificity, those skilled in the art may make numerous changes to the disclosed embodiments without departing from the scope of the invention.

Claims

Claim 1 A lifting assembly for raising a container from a stack of containers within a grid storage structure and also lowering a container to a stack of containers, wherein the lifting assembly comprises: a gripping assembly configured to grasp a load; and a lifting assembly configured to raise and lower the gripping assembly, wherein the lifting assembly comprises: at least one tether connected to the gripping assembly; and a motor configured to raise and lower the gripping assembly by winding and unwinding the tether, wherein the lifting assembly further comprises: a sensor configured to detect movement of the gripping assembly - the sensor comprises an input unit coupled by the movement of the gripping assembly -; a controller configured to determine the vertical position of the gripping assembly using the output of the sensor; and an electric cable connected to the gripping assembly - the electric cable is configured to be wound and unwound as the gripping assembly is raised and lowered, and the electric cable does not support the load of the gripping assembly - wherein the sensor is configured to detect the degree to which the electric cable is wound and unwound. Claim 2 A lifting assembly according to claim 1, wherein the lifting assembly further comprises an electric cable spool on which an electric cable is wound and unwound, and the sensor comprises a rotary encoder configured to be coupled with the electric cable spool to detect the degree to which the electric cable spool is rotated as the electric cable is wound and unwound. Claim 3 In claim 1, the lifting assembly, wherein the electric cable has a higher elastic modulus than the tether. Claim 4 In paragraph 2, the lifting assembly further comprises a tether spool on which a tether is wound and unwound, and the electric cable spool and the tether spool are mounted on a shaft so that the electric cable spool can rotate relative to the tether spool. Claim 5 In paragraph 2, the lifting assembly further comprises a biasing assembly, wherein the biasing assembly is configured to resist the unwinding or winding of an electric cable spool so that the electric cable is kept taut between the lifting assembly and the gripping assembly. Claim 6 In paragraph 1, the electric cable transmits an electric signal to a gripping assembly, a lifting assembly. Claim 7 In claim 1, the electric cable comprises a fixed flexible cable, an FFC, or a ribbon cable, in a lifting assembly. Claim 8 A lifting assembly according to claim 1, wherein the controller is configured to control and adjust the raising and lowering of the gripping assembly using a determined vertical position. Claim 9 A lifting assembly according to claim 1, wherein the number of tethers is four, and the tethers comprise steel tape or woven polyester tape. Claim 10 A load handling device for lifting and moving storage containers stacked within a grid framework structure, wherein the load handling device comprises: a first set of parallel rails or tracks and a second set of parallel rails or tracks extending substantially perpendicularly to the first set of parallel rails or tracks 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 supports to form a plurality of vertical storage positions below the grid, so that containers are stacked vertically between the supports through the plurality of grid spaces and are also guided by the supports, and wherein the load handling device comprises: a first set of wheels arranged to engage with the first set of parallel rails or tracks and a body or skeleton mounted on a second set of wheels arranged to engage with the second set of parallel rails or tracks; and a container lifting assembly comprising a lifting assembly of any one of claims 1 to 9, wherein the gripping assembly comprises a container gripping assembly configured to grip the container. Claim 11 A method for determining the vertical position of a gripping assembly of a lifting assembly according to any one of claims 1 to 9, wherein the method comprises: raising and lowering the gripping assembly using a motor; and determining the vertical position of the gripping assembly using the output of a sensor using a controller. Claim 12 A computer program stored on a medium, wherein the computer program includes instructions that cause the computer to perform the method of claim 11 when the program is executed by the computer. 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