Method and system for determining belt slippage

Abstract

A method and system for determining drive belt slippage is disclosed that uses two motors to determine drive belt slippage.

Description

[Technical Field]

[0001] The present invention relates to a method and system for determining slippage in a drive belt, such as those used in load handling devices. [Background technology]

[0002] Some commercial and industrial activities require a system that allows for the storage and retrieval of a large number of different products. WO 2015 / 185628 A describes a storage and fulfillment system in which stacks of storage containers are arranged in a grid storage structure. The containers are accessed from above by a load handling device operable on rails or tracks located on the top of the grid storage structure. Load handling devices are further described in WO 2015 / 019055 A1.

[0003] Within storage and fulfillment systems, it is important that load handling devices operate optimally. In particular, drive belts used in load handling devices should operate under optimal tension. It is against this background that the present invention has been devised. Summary of the Invention

[0004] In a first aspect, there is provided a system for determining drive belt slippage, the system comprising: A drive belt and first and second motors configured to drive the drive belt; Controller and The controller comprises: receiving first and second transient currents from the first and second motors, respectively, during simultaneous activation of the first and second motors to drive the drive belt; determining drive belt slippage when first and second current values ​​of the first and second current transients, respectively, substantially simultaneously differ by at least a threshold value; This means that the system can use only existing system components to determine drive belt slippage, and no external hardware is required to determine drive belt slippage.

[0005] The threshold may be defined by a minimum percentage difference between the first and second current values ​​and / or a minimum ampere difference between the first and second current values, which ensures that noise during transient currents is not interpreted as belt slippage.

[0006] 1. A load handling device for lifting and moving storage containers stacked in a grid framework structure, the grid framework structure comprising: a first set of parallel rails or tracks and a second set of parallel rails or tracks extending substantially perpendicular 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, the grid being supported by a set of uprights to form a plurality of vertical storage locations beneath the grid such that containers are stacked between and guided by the set of uprights vertically through the plurality of grid spaces; a body or skeleton mounted on a first set of wheels arranged to engage the first set of parallel tracks and a second set of wheels arranged to engage the second set of parallel tracks; a drive assembly comprising a first system according to the above aspect, wherein the drive belt and the first and second motors of the first system are configured to drive first or second sets of wheels, respectively, to move the load handling device along first or second sets of parallel rails, and wherein the controller of the first system is configured to receive first and second transient currents from the first and second motors of the first system, respectively, during driving of the first or second sets of wheels; and / or A diverting assembly comprising a second system according to the above aspect, wherein the drive belt and the first and second motors of the second system are configured to raise or lower the first set of wheels and / or lower or raise the second set of wheels relative to the body or skeleton to engage and disengage the wheels with the parallel tracks, and the controller of the second system is configured to receive first and second transient currents from the first and second motors of the second system, respectively, during the raising or lowering of the first set of wheels and / or the lowering or raising of the second set of wheels; and / or A container lifting assembly comprising a third system according to the above aspect, wherein the drive belt and the first and second motors of the third system are configured to raise or lower the gripping device in a vertical direction, and the controller of the third system is configured to receive first and second transient currents from the first and second motors of the third system, respectively, during the raising or lowering of the gripping device; This means that slippage in the drive belt of the load handling device can be detected.

[0007] The turning assembly may be arranged to raise or lower a first set of wheels and synchronously lower or raise, respectively, a second set of wheels relative to the body, meaning that slippage during turning may be detected.

[0008] The diverting assembly may include at least one diverting mechanism for either the first or second set of wheels, or for each of the first and second sets of wheels. The diverting assembly may include two diverting mechanisms for each of the first and second sets of wheels. The diverting mechanisms may be driven by a drive belt of the second system. This means that slippage may be correlated to a specific operation of the diverting mechanism.

[0009] The first and second motors may be mounted in opposite or adjacent locations of the load handling device. The opposite or adjacent locations may comprise corners of the load handling device. The opposite or adjacent locations or corners may be on the body or skeleton. The drive belt may substantially circumnavigate the skeleton or body of the load handling device. This means that the motors may be positioned to distribute the torque load between them.

[0010] The system may further include an automatic tensioning device, and the controller may be further configured to control the automatic tensioning device to increase the tension of the drive belt when it is determined that drive belt slippage has occurred, and / or to decrease the tension of the drive belt when it is determined that drive belt slippage is not occurring.

[0011] This means that the system can prevent drive belt slippage and / or optimize drive belt efficiency during subsequent operation.

[0012] In a second aspect, there is provided a method for determining drive belt slippage in a system, the system comprising the system of the previous aspect, the method comprising using a controller: receiving first and second transient currents from the first and second motors, respectively, during simultaneous activation of the first and second motors to drive the drive belt; determining that drive belt slippage has occurred when first and second current values ​​of the first and second transient currents, respectively, differ by at least a threshold value substantially simultaneously; There is a method comprising:

[0013] In a third aspect, there is a computer program comprising instructions that, when executed by a computer, cause the computer to perform a method according to the second aspect.

[0014] In a fourth aspect, there is a data processing system comprising a processor configured to perform the method of the second aspect.

[0015] The present invention will now be described with reference to one or more exemplary embodiments thereof, as illustrated in the accompanying drawings. [Brief explanation of the drawings]

[0016] [Figure 1] Storage structures and containers are shown. [Figure 2] 2 shows rails or tracks on the top of the storage structure illustrated in FIG. 1. [Figure 3] 2 shows a cargo handling device on top of the storage structure illustrated in FIG. 1. [Figure 4] 1 shows a single load handling device with the container lifting means in a lowered configuration; [Figure 5A] Figure 2 shows a cutaway view of a single load handling device with the container lifting means in a raised configuration. [Figure 5B] Figure 2 shows a cutaway view of a single load handling device with the container lifting means in a lowered configuration. [Figure 6] 1 is a schematic diagram of a cargo handling device having a turning mechanism. [Figure 7] FIG. 10 is a schematic diagram of a compliant mechanism for use in engaging first and second sets of wheels of a load handling device as part of a turning assembly. [Figure 8] FIG. 8 is a perspective view of a load handling device showing the compliant mechanism and wheel positions in a similar position to that shown in FIG. 7. [Figure 9] FIG. 10 shows a perspective view of a rigid linkage set for use in engaging first and second sets of wheels of a load handling device as part of a diverting assembly. [Figure 10a] FIG. 10 is a schematic diagram of a linkage set for use in engaging first and second sets of wheels of a load handling device as part of a diverting assembly. [Figure 10b] FIG. 10 is a schematic diagram of a linkage set for use in engaging first and second sets of wheels of a load handling device as part of a diverting assembly. [Figure 10c] FIG. 10 is a schematic diagram of a linkage set for use in engaging first and second sets of wheels of a load handling device as part of a diverting assembly. [Figure 11] 1 shows a cam mechanism for use in engaging first and second sets of wheels of a load handling device as part of a diverting assembly; [Figure 12] 1 shows a dual cam mechanism for use in engaging first and second sets of wheels of a load handling device as part of a diverting assembly. [Figure 13] 1 shows a dual cam mechanism for use in engaging first and second sets of wheels of a load handling device as part of a diverting assembly. [Figure 14] 1 illustrates an exemplary drive assembly for use in a load handling device. [Figure 15] 1 illustrates an exemplary container lifting assembly. [Figure 16] 1 illustrates a system according to an embodiment. [Figure 17] 1 illustrates a method for determining drive belt slippage in a system, according to an embodiment. [Figure 18] 1 illustrates first and second current transients according to an embodiment. [Figure 19] 1 illustrates first and second current transients according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] Online retailers that sell multiple product lines, such as online grocery stores and supermarkets, need systems that can store tens or hundreds of thousands of different product lines. Using a single product stack in such cases may be impractical because a large amount of floor space would be required to accommodate all of the required stacks. Furthermore, it may be desirable to store small quantities of some items, such as perishables or infrequently ordered goods, making a single product stack an inefficient solution.

[0018] International Patent Application No. WO98 / 049075A (Autostore), the contents of which are incorporated herein by reference, describes a system in which a multi-product stack of containers is arranged within a frame structure.

[0019] PCT Publication No. WO2015 / 185628A (Ocado) describes a further known storage and fulfilment system in which stacks of containers are arranged within a grid framework structure. The containers are accessed by one or more load handling devices, otherwise known as "bots", operable on trucks located on top of the grid framework structure. A system of this type is illustrated schematically in Figures 1 to 3 of the accompanying drawings.

[0020] As shown in FIGS. 1 and 2, stackable containers 10, also known as "bins" or "totes," are stacked on top of one another to form a stack 12. The stack 12 is arranged in a grid framework structure 14, for example, in a warehouse or manufacturing environment. The grid framework structure 14 is made up of a plurality of storage columns, or grid columns. Each grid in the grid framework structure has at least one grid column for storing a stack of containers. FIG. 1 is a schematic perspective view of the grid framework structure 14, and FIG. 2 is a schematic top view showing the stack 12 of containers 10 arranged within the framework structure 14. Each container 10 typically holds multiple product items (not shown). The product items in the containers 10 can be the same or different product types, depending on the application.

[0021] The grid framework structure 14 comprises a plurality of upright members 16 supporting horizontal members 18, 20. A first set of parallel horizontal grid members 18 are arranged perpendicular to a second set of parallel horizontal members 20 in a grid pattern to form a horizontal grid structure 15 supported by the upright members 16. The members 16, 18, 20 are typically fabricated from metal. The containers 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 containers 10 and guides vertical movement of the containers 10.

[0022] The top level of the grid framework structure 14 comprises a grid or grid structure 15 including rails 22 arranged in a grid pattern across the top of the stacks 12. Referring to FIG. 3 , the rails or tracks 22 guide a plurality of load handling devices 30. A first set 22a of parallel rails 22 guides movement of the robotic load handling devices 30 in a first direction (e.g., X direction) across the top of the grid framework structure 14. A second set 22b of parallel rails 22, positioned perpendicular to the first set 22a, guides movement of the load handling devices 30 in a second direction (e.g., Y direction) perpendicular to the first direction. In this manner, the rails 22 allow the robotic load handling devices 30 to move laterally in two dimensions within the horizontal XY plane. The load handling devices 30 can be moved to a position above any of the stacks 12.

[0023] 4, 5A, and 5B is described in PCT Patent Publication No. WO2015 / 019055 (Ocado), which is incorporated herein by reference, where each load handling device 30 covers a single grid space 17 of the grid framework structure 14. This configuration allows for a higher density of load handlers and hence a higher throughput for a system of a given size.

[0024] The load handling device 30 includes a vehicle 32 arranged to travel on the rails 22 of the frame structure 14. A first set of wheels 34, consisting of a pair of wheels 34 on the front of the vehicle 32 and a pair of wheels 34 on the rear of the vehicle 32, are arranged to engage two adjacent rails of the first set 22a of rails 22. Similarly, a second set of wheels 36, consisting of a pair of wheels 36 on each side of the vehicle 32, are arranged to engage two adjacent rails of the second set 22b of rails 22. Each set of wheels 34, 36 can be raised and lowered by a diverting assembly (examples of which are shown in FIGS. 6-13 ) so that either the first set of wheels 34 or the second set of wheels 36 is engaged with the respective set of rails 22a, 22b at any one time. For example, once the first set of wheels 34 is engaged with the first set of rails 22a and the second set of wheels 36 is lifted off the rails 22, the first set of wheels 34 may be driven by a drive mechanism housed in the vehicle 32 to move the load handling device 30 in the Y direction (an example of which is shown in FIG. 10b). To achieve movement in the X direction, the first set of wheels 34 is lifted off the rails 22 and the second set of wheels 36 is lowered into engagement with the second set 22b of the rails 22. The drive assembly may then be used to drive the second set of wheels 36 to move the load handling device 30 in the X direction.

[0025] The load handling device 30 is equipped with a container lifting device or assembly, such as a crane mechanism, for lifting a storage container from above. The lifting device includes a winch tether or cable 38 wound on a spool or reel and a gripper device 39. The lifting device shown in FIG. 4 (a further example is shown in FIG. 15) includes a set of four vertically extending lifting tethers 38. The tethers 38 are connected to or near each of the four corners of the gripper device 39, e.g., a lifting frame, for releasable connection to the storage container 10. For example, each tether 38 is positioned at or near each of the four corners of the lifting frame. The gripper device 39 is configured to releasably grasp the top of the storage container 10 to lift the storage container 10 from a stack of containers in a storage system of the type shown in FIGS. 1 and 2. For example, lifting frame 39 may include pins (not shown) that mate with corresponding holes (not shown) in a rim forming the top surface of container 10, and sliding clips (not shown) that are engageable with the rim to grip container 10. The clips are driven into engagement with container 10 by a suitable drive mechanism housed within lifting frame 39, which drive mechanism is powered and controlled by signals transmitted through cable 38 itself or a separate control cable (not shown).

[0026] To remove a container 10 from the top of a stack 12, the load handling device 30 is first moved in the X and Y directions to position the gripper device 39 above the stack 12. The gripper device 39 is then lowered vertically in the Z direction to engage the container 10 on top of the stack 12, as shown in FIGS. 4 and 5B . The gripper device 39 grasps the container 10 and is then pulled upward by the cable 38 with the container 10 attached. At the top of its vertical movement, the container 10 is held above the rails 22 housed within the car body 32. In this manner, the load handling device 30 can be moved to different positions in the XY plane, carrying the container 10 with it, to transport the container 10 to another location. Upon reaching the target location (e.g., another stack 12, an access point in a storage system, or a conveyor belt), the container or container 10 can be lowered from the container receiving portion and released from the grabber device 39. The cable 38 is of sufficient length to allow the load handling device 30 to retrieve and place containers from any level of the stack 12, including, for example, floor level.

[0027] As shown in FIG. 3 , multiple identical load handling devices 30 may be provided so that each load handling device 30 can operate simultaneously, increasing the throughput of the system. The system illustrated in FIG. 3 may include specific locations known as ports, where containers 10 may be transferred into or out of the system. Additional conveyor systems (not shown) are associated with each port, so that containers 10 transported to a port by a load handling device 30 may be transported by the conveyor system to another location, such as a picking station (not shown). Similarly, containers 10 may be moved by the conveyor system from an external location to a port, for example, a container filling station (not shown), and transported by a load handling device 30 to stack 12 to replenish stock in the system.

[0028] Each cargo handling device 30 is capable of lifting and moving one container 10 at a time. The cargo handling device 30 has a container-receiving cavity or recess 40 in its lower portion. The recess 40 is sized to accommodate the container 10 when it is lifted by a lifting mechanism, as shown in Figures 5A and 5B. When in the recess, the container 10 is lifted off the rails 22 underneath, allowing the vehicle 32 to move laterally to a different location.

[0029] When a container 10b that is not located at the top of a stack 12 (the "target container") needs to be removed, the containers 10a above (the "non-target containers") must first be moved to allow access to the target container 10b. This is accomplished by an operation hereafter referred to as "digging." Referring to FIG. 3, during a digging operation, one of the cargo handling devices 30 sequentially lifts each non-target container 10a from the stack 12 containing the target container 10b and places it in a vacant position in another stack 12. The target container 10b can then be accessed by the cargo handling device 30 and moved to a port for further transport.

[0030] Each of the provided load handling devices 30 is remotely operated under the control of a central computer. Each individual container 10 in the system is also tracked so that the appropriate container 10 can be retrieved, transported, and replaced as needed. For example, during an excavation operation, each non-target container location is logged so that non-target containers 10a can be tracked.

[0031] Wireless communications and networks may be used to provide a communications infrastructure from a master controller, e.g., via one or more base stations, to one or more load handling devices operable on the grid structure. In response to receiving commands from the master controller, a controller in the load handling device is configured to control various drive mechanisms to control movement of the load handling device. For example, the load handling device may be instructed to retrieve a container from a target storage column at a specific location on the grid structure. This command may include various movements within the XY plane of the grid structure 15. As previously described, upon reaching the target storage column, the lifting mechanism may be operated to grasp and lift the storage container 10. 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, e.g., a "drop-off port." At the drop-off port, the container 10 is lowered to a suitable picking station to allow retrieval of any items in the storage container. Movement of the load handling device 30 on the grid structure 15 may also involve the load handling device 30 being commanded to move to a charging station, typically located on the periphery of the grid structure 15 .

[0032] To move the load handling devices 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 individually driven by motors 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), the motors for driving the wheels may be integrated into the wheels due to the limited availability of space within the vehicle body. For example, the wheels of a single-cell load handling device are driven by respective hub motors. Each hub motor includes an external rotor having multiple permanent magnets arranged to rotate around a wheel hub with coils forming an internal stator.

[0033] 1-5 has many advantages and is suitable for a wide range of storage and retrieval operations. In particular, it allows for very high density storage of products and provides a very economical way of storing a wide range of different items in containers 10 while also allowing reasonably economical access to all of the containers 10 when required for picking.

[0034] An illustrative diverter assembly is shown in Figure 6, where the first and second sets of wheels 34, 36 can be raised off the rails or lowered onto the rails. The diverter assembly includes compliant mechanism(s) 110 (or linkage set 300 shown in Figures 9 and 10, or cam mechanisms 120, 130 as shown in Figures 11-13) located on opposite sides of the body or skeleton 102 of the load handling device.

[0035] Each of the turning compliant mechanisms 110 (further described in PCT Publication No. WO2021175922A1 (Ocado)) is deformable in a first and second direction. Figure 7 illustrates the compliant mechanism 110 in three positions, underneath which is illustrated the position of the wheels 34, 36 relative to the carbody or skeleton 102 and rails in each of those positions. Figure 8 is a perspective view of the load handling device showing the position of the compliant mechanism 110 (or linkage set 300, or cam mechanisms 120, 130) and wheels in a position similar to that shown in Figure 7.

[0036] When there is no input force, the compliant mechanism 110 is at rest or in a neutral position, i.e., the compliant mechanism 110 is not elastically deformed and both sets of wheels 34, 36 are horizontal and resting on the surface. In this configuration, the load handling device cannot move in either the x or y direction and the load handling device is parked (FIGS. 7a and 8a). The elastic deformation of the compliant mechanism 110 holds each of the wheels and is linked to an arm that can move in the vertical (i.e., z) direction to raise and lower the wheels.

[0037] When a first input force F1 is provided, the body of the compliant mechanism 110 deforms in a first direction. The displacement of the mechanism body is translated vertically, raising the first set of wheels 34 and lowering the second set of wheels 36. As shown in Figures 7c and 8c, the wheels of the first set of wheels 34 move upward to move away from the rails, and the wheels of the second set of wheels 36 move downward to engage the rails and support the vehicle. From this, the vehicle 30 can be driven in the x-direction.

[0038] When a second input force F2 is provided in a direction opposite to the first input force, the body of the compliant mechanism 110 deforms in a second direction. The displacement of the mechanism body translates to vertical movement, lowering the first set of wheels 34 and raising the second set of wheels 36, so that the load handling device can be supported by the first set of wheels 34 and driven in the y direction (FIGS. 7b and 8b).

[0039] The compliant mechanism 110 is connected to the wheel sets 34, 36 via a transmission linkage. Thus, in this manner, the compliant mechanism 110 (or linkage set 300 or cams 120, 130) provides a means for diverting the direction of motion of the movement of the load handling device 30.

[0040] It will be appreciated that the compliant mechanism 110 illustrated in Figures 7a-c comprises a series of columns or trunk sections attached to rails or braces. The columns or trunk sections 111 are attached to the rails or braces 112a,b via relatively narrow sections that preferentially flex when a horizontal force is applied to the rails or braces. The narrow sections may therefore be considered to be hinges 113.

[0041] Figures 9 and 10 show an example of a rigid linkage set 300 (further described in PCT Publication No. WO2021175922A1 (Ocado)) for use in engaging first and second sets of wheels of a load handling device as part of a diverting assembly having similar functional behavior as the compliant mechanism 110 described above.

[0042] The linkage set mechanism 300 comprises a series of pivotally connected two-part linkages. Considering a single two-part linkage, at one end, a primary linkage member (track portion) 311 is pivotally attached to a traveler or upper brace 312a at the knee joint 316, and at the opposite end, a secondary linkage member (branch portion) 313 is hingedly attached to a fixed brace or lower brace 312b at the ankle joint 315. The opposite end of the secondary linkage 313 is pivotally attached to a fixed brace or lower brace 312b at a toe hinge 314. Thus, each single two-part linkage extends between the traveler 312a and the fixed brace 312b. To create the linkage set 300, a series of similar two-part linkages are positioned in parallel between the traveler brace 312a and the fixed brace 312b, as shown in FIG. 9 .

[0043] The rotational or angular motion of the knee joint 316, ankle joint 315, and toe joint 314 is limited as described below. At the ankle joint 315, the primary linkage 311 has a single knuckle that intersects with two knuckles of the secondary linkage 313.

[0044] 10a shows the linkage set in a neutral or parked position, where the first set of wheels 34 and the second set of wheels 36 are engaged with the track (shown in the thumbnail) and the load handling device 30 is not allowed to move in either the x or y direction. In this position, no force F is applied to the traveler 312a and the lower surface 319 of the primary linkage 311 abuts the upper surface 320 of the secondary linkage 313.

[0045] In FIG. 10b, a positive force F (i.e., from left to right as illustrated) is applied to traveler 312a. Applying positive force F causes primary linkage 311 to rotate clockwise about knee joint 316 and counterclockwise about ankle joint 315. Rotation about ankle joint 315 is limited by face 317 contacting surface 318. By moving traveler 312a further to the right, secondary linkage 313 lifts away from fixed brace 312b by rotating clockwise about toe hinge 314. This causes traveler 312a to be horizontally displaced in a positive direction relative to fixed brace 312b. A positive displacement of the traveler 312a will cause the first set of wheels 34 to be lowered into engagement with the track and the second set of wheels 36 to be raised (shown in the thumbnail), allowing the load handling device 100 to move in the y direction.

[0046] In FIG. 10c, a negative force F (i.e., from right to left as illustrated) is applied to traveler 312a. Applying the negative force F causes the primary linkage 311 to rotate counterclockwise about the knee joint 316 and clockwise about the ankle joint 315. Rotation about the ankle joint 315 is limited by face 317 contacting surface 321, and the heel of the two-part linkage is forced into fixed brace 312b. This causes traveler 312a to be horizontally displaced in a negative direction relative to fixed brace 312b. The negative displacement of traveler 312b will cause first set of wheels 34 to be raised and second set of wheels 36 to be lowered into engagement with the track (shown in the thumbnail), allowing load handling device 30 to move in the x-direction.

[0047] It will be appreciated that between the x-travel position and the y-travel position, the linkage set moves through a neutral or park position.

[0048] Figure 11 illustrates yet another example redirection mechanism incorporating a cam mechanism redirection assembly component (further described in PCT Application No. PCT / EP2022 / 073670 (Ocado)). Figure 11 illustrates a cam mechanism 120 for use in a redirection assembly of the type described in connection with Figure 6, for example. Cam mechanism 120 includes a traveler 121 (similar to 112a, 312a), a fixed brace 122 (similar to 112b or 312b), a cam profile 123 arranged as a slot in a face surface of traveler 121, and a follower 124 engaged with cam 123 and extending between the opposing face or cover of fixed brace 122. It will be appreciated that the fixed brace 122 may be made from a single piece or block having sufficient depth to have a slot to accommodate the depth of the traveler 121 and positioned to hold the follower 124 in place, or the fixed brace 122 may be made from two planes of material sandwiched together with the follower 124 fixed therebetween.

[0049] The cam or slot profile 123 extends between a first limit 125 and a second limit 126. Between these limits, as illustrated, the slot extends substantially horizontally from the first limit 125, slopes upward, and then continues substantially horizontally to the second limit 126 with sufficient space to accommodate the follower 124.

[0050] In a first of the configurations of the cam mechanism 120 shown, the traveler 121 is capable of moving horizontally and is fixed vertically, while the fixed brace 122 is fixed horizontally and capable of moving vertically. Therefore, as the cam 123 moves horizontally across the follower from the first limit 125 to the second limit 126, the fixed brace 122 will be raised by an amount equal to the vertical change in the cam profile 123. It will be appreciated that, alternatively, in a second configuration, the fixed brace 122 can be fixed vertically and capable of moving horizontally, and the traveler 121 can be fixed horizontally and capable of moving vertically. The relative positions between the traveler 121 and fixed brace 122 according to the first configuration are illustrated in FIG. 11 , which shows the cam 120 in various positions.

[0051] 11a-c illustrate the cam mechanism where the front face of the fixed brace 122 has been removed to make it easier to see and understand the position of the follower 124. A vertical dotted line is positioned through the follower 124 to aid in understanding the relative position of the cam mechanism 120 between the figures.

[0052] In FIG. 11a, the traveler 121 is positioned horizontally to the right. The follower 124, connected to the fixed brace 122, is positioned at the first limit 125 of the cam 123. In FIG. 11b, the traveler 121 is positioned centered to the left of the position in FIG. 11a. From the position shown in FIG. 11a, the cam 123 has moved relative to the follower 124 so that the follower 124 is at the first inflection point of the cam slot. The fixed brace 122 has not moved its position relative to its position in FIG. 11a. In FIG. 11c, the traveler 122 is positioned horizontally to the left. The cam 123 has moved relative to the follower 124 so that the follower 124 had to move vertically to move up the slope to be at the second limit 126. Since the follower 124 is fixed to the fixed brace 122 and the fixed brace 122 is fixed horizontally, it follows that the fixed brace 122 is moved vertically. In Figures 11a and 11b, the fixed brace 122 is in a lowered position relative to the traveler 121, while in Figure 11c, the fixed brace 122 is in an raised position relative to the traveler 121.

[0053] It will be appreciated that if a pair of wheels is fixedly attached to a fixed brace 122, a cam mechanism 120 can be used to raise and lower the wheels as needed by applying a horizontal force to the traveler 121. The position of cam 120 shown in Figure 11b can be used as a "park" position, where the wheels are ready to be moved to an engaged position (Figure 11a) or a disengaged position (Figure 11c). It will be appreciated that the cam profile can be designed to provide any desired horizontal to vertical movement profile.

[0054] FIG. 12 illustrates another cam mechanism 130 employing a dual cam configuration. The first cam 133a and the second cam 133b are horizontally adjacent to each other. The first cam profile 133a and the second cam profile 133b are substantially identical. Similarly, a pair of followers 124a and 124b are positioned to engage with the respective cams 133a and 133b. This configuration further differs from the configuration shown in FIGS. 11a-c in that the first cam 133a and the second cam 133b are positioned on fixed braces 132a and 132b, while the first follower 124a and the second follower 124b are attached to the traveler 131, i.e., it is inverted. The fixed brace portions 132a and 132b are joined by a pair of bars.

[0055] Operation of cam mechanism 130 is similar to that of cam mechanism 120. When a horizontal force is applied to traveler 131, followers 124a and 124b move in unison along first cam path 133a and second cam path 133b between first limits 135a, 135b and second limits 136a, 136b, respectively. Assuming fixed braces 132a, 132b are constrained to move only vertically, horizontal movement of traveler 131 results in the raising and lowering of fixed braces 132a, 132b, similar to the function of cam mechanism 120. FIGS. 13a-c illustrate an inverted dual cam mechanism 130 in positions corresponding to the illustrated positions of single cam mechanism 120 in FIGS. 11a-c, respectively. It will be appreciated that any number of cams may be used.

[0056] As can be seen in Figures 6 and 8, a first pair of compliant mechanisms 110 (or linkage set 300 as shown in Figures 9 and 10, or cam mechanisms 120, 130 as shown in Figures 11-13) are positioned on opposing faces within the body or skeleton 102 of the load handling device to control the position of the first set of wheels 34, and a second pair of compliant mechanisms 110 (or linkage set 300, or cam mechanisms 120, 130) are positioned on orthogonally opposing faces within the body or skeleton of the load handling device to control the position of the second set of wheels 36. Thus, each face of the load handling device is provided with a compliant mechanism 110, or linkage set 300, or cam mechanism 120, 130. The compliant mechanism 110, or linkage set 300, or pair of cam mechanisms 120, 130, are coupled via a transfer or drive belt 108 that substantially circumnavigates the skeleton 102 of the load handling device and is mechanically coupled to the upper brace or traveller 112a, 312a of the compliant mechanism 110, 300, or 120, 130 of the cam mechanism redirection assembly component.

[0057] The output of the compliant mechanism 110, or linkage set 300, or cam mechanism 120, 130 is transmitted to the wheels 34, 36 via the chassis, which converts the horizontal movement of the compliant mechanism into vertical movement of the wheels. In some configurations, the upper brace or traveler 112a, 312a of the compliant mechanism 110, 300 or 120, 130 of the cam mechanism may be attached via glide bearings to a rod structure that extends along the face of the load handling device 30 between each of the horizontal edges of the load handling device 30. The rod structure may then be attached to corner pieces at first and second ends.

[0058] The wheel sets 34, 36 can be moved in unison via motors, for example, to engage the x- and / or y-direction wheel sets with the rails of the storage system grid. In this manner, the turning assembly can be operated by two motors located at opposite or adjacent corners. The use of two motors increases the torque transmitted to the drive belt. In some examples of the load handling device 30, both motors can be located in or near their respective opposite or adjacent corner pieces so as not to occupy space within the skeleton or body and for accessibility. Activating the motors in a clockwise direction can move the wheel mounts on the surface upward, raising the wheels on the surface and lowering the wheels on the surface perpendicular to the first surface, or vice versa.

[0059] In some examples of the diverter assembly, the transport or drive belt 108 may pass over one or more idler pulleys to monitor rotational speed as it moves between its x- and y-engaged positions to provide immediate detection of a fault in the belt 108. If the belt 108 or another part of the diverter assembly fails, this information may be fed back to and utilized by the central control facility to prevent bot collisions.

[0060] An illustrative drive assembly 1400 for a set of wheels 34, 36 is shown in FIG. 14 . A drive belt assembly is provided for each set of wheels 34, 36. The drive belt assembly comprises a drive belt pulley gear arrangement for engaging toothed edges of a pair of wheels 34, 36 on one side of the load handling device 30, as illustrated in FIG. 14 . A toothed drive belt 1410 engages both wheels 1420 (corresponding to the pair of wheels of the set of wheels 34 or 36). The drive belt 1410 is guided by first and second drive wheels 1430, 1450 mounted on the load handling device, and two tensioning wheel arrangements 1440. The tensioning wheel arrangements are movably mounted to the load handling device using springs (not shown) intended to keep the drive belt tensioned and maintain engagement between the drive belt and the wheels. The drive wheels 1450 are provided mounted on the load handling device. The first drive wheel 1430 and the second drive wheel 1450 are coupled to the axles of respective motors (not shown in FIG. 14). The use of two motors increases the torque transmitted to the drive belt.

[0061] The load handling device is provided with a drive assembly 1400 for each pair of wheels. Each pair of wheels comprises a set of wheels 34, 36. The drive wheels on each side of the load handling device may share a common motor axle so that the wheels of each pair of wheels of the set of wheels 34, 36 are driven simultaneously and at the same speed. The first set of wheels 34 and the second set of wheels 36 may be selectively driven under the control of the load handling device.

[0062] It will be appreciated that in the configuration of FIG. 14, when the set of wheels 34, 36 is moved from its position for engaging the grid tracks, the drive belt may slacken because the distance between the top of the drive belt assembly and the wheels changes as the wheels are lowered and raised. Therefore, depending on the selected diverting assembly, an additional tensioning mechanism may be required. For example, an idler pulley on a mechanical linkage connected to the diverting assembly may be employed to keep the notional drive belt length constant throughout the diverting assembly's full range of motion. Thus, drive belt tension is optimized. Furthermore, when the bot is moving in either the x or y direction, drive belt tension should be optimized to account for drive belt slippage and efficiency.

[0063] An illustrative container lifting assembly (further described in PCT Application No. PCT / EP2022 / 081364 (Ocado)) is shown in FIG. 15. In the embodiment of FIG. 15, lifting assembly 1500 has four spools 1501, 1502, 1503, and 1504 for winding and unwinding respective tethers 38. Spools 1501 and 1502 are on drive shaft 1505, whereas spools 1503 and 1504 are on drive shaft 1506. Drive shafts 1505 and 1506 are configured to rotate in opposite directions when driven by a motor. By rotating drive shafts 1505 and 1506 in opposite directions, each tether 38a-d can be positioned at or near a corner of the lifting assembly, similar to the above embodiment. In particular, as shown in FIG. 15 , the point at which each tether winds onto or unwinds from the spool is at or near a respective corner of the lifting assembly. This allows the tethers to connect to the container gripping device 39 at each corner of the gripping assembly, which increases stability when raising and lowering the container gripping device 39. FIG. 15 shows an example of how drive shafts 1505 and 1506 can be rotated in opposite directions. Drive shafts 1505 and 1506 are connected to pulleys 1510 and 1511, respectively. Pulleys 1507 and 1509 are coupled to the axles of respective motors (not shown in FIG. 15 ). The use of two motors increases the torque transmitted to drive belt 1508. Drive belt 1508 transmits torque to pulleys 1509, 1510, and 1511 to ensure that spools 1501 and 1502 and spools 1503 and 1504 rotate in opposite directions. In particular, pulleys 1507 and 1509 are disposed around pulley 1511 to provide an opposite rotation to pulley 1510.

[0064] It will be appreciated that the load handling device 30 has three systems, each of which may use a drive belt and two motors: a diverting assembly, a drive assembly, and a container lifting assembly. The drive belt tension for each system should be optimized taking into account drive belt slippage and efficiency. Setting a high drive belt tension ensures no drive belt slippage, but this reduces the power efficiency of the various systems of the load handling device. Reducing drive belt tension increases the likelihood of slippage, meaning the systems of the load handling device will not function in a timely and smooth manner. Any slippage in the drive belt should be determined so that the drive belt tension can be adjusted accordingly. It should be appreciated that these issues are common to all systems in which drive belt slippage must be determined so that the drive belt tension can be adjusted accordingly. The above is merely an illustration of how an exemplary drive belt may be used in a load handling device. The ability to determine drive belt slippage in any system is desirable.

[0065] FIG. 16 shows a schematic diagram 1600 of a load handling device 30 in accordance with the present invention. A diverting assembly 1610, as shown in FIG. 6, is driven by a drive belt, a first motor, and a second motor 1620. It will be appreciated that the system 1610 may alternatively be a drive assembly (such as that shown in FIG. 14) or a container lifting assembly (such as that shown in FIG. 15). In FIG. 16, only a pair of wheels 34 is shown for moving the load handling device 30 in the Y direction on the grid structure. However, a complete set of wheels for each of the X and Y directions may be included, such as the first set 34 and second set 36 of wheels described in the previous example. One or more current monitors 1640 allow the current drawn by the first and second motors to be monitored. That is, the current draw of the first and second motors when activated is monitored. The current monitors may be implemented, for example, by taking appropriate outputs from the motor drive circuitry. In one implementation, the current monitors may be implemented on output lines from the motor driver components. The current monitor can function in a variety of ways. One example is a current sensor resistor, where the motor current is passed through the resistor and a voltage can then be measured across the resistor. From this voltage, the current can be calculated. Another example is a magnetic current sensor that uses the Hall effect to determine the current flowing in the output lines from the motor driver. One or more automatic tensioning systems 1630 can be included. The load handling device 1600 can use a processor or controller 1650 to receive data from and transmit data to each of the diverting assembly 1610, one or more sets of first and second motors and drive belts, one or more automatic tensioning systems 1630, and one or more current monitors 1640. This data can be stored in a memory device 1660. The data in the memory device 1660 can be periodically transmitted via one or more networks, such as a base station, for further processing.

[0066] Figure 17 shows steps of a method 1700 for determining slippage of a drive belt used in a system including a drive belt and first and second motors, the first and second motors driving the drive belt. It will be appreciated that the method of Figure 17 may be implemented using a controller of the system (e.g., the controller of the load handling device of Figure 16). In step 1710, first and second transient currents are received from the first and second motors, respectively, during simultaneous activation of the first and second motors to drive the drive belt. In other words, the current draw of each motor during activation is received.

[0067] The simultaneous activation of the first and second motors may be for the purpose of activating a diverting assembly to raise or lower a first set of wheels and / or lower or raise a second set of wheels relative to a body or skeleton to engage and disengage the wheels with parallel tracks. Alternatively, the simultaneous activation of the first and second motors may be for the purpose of activating a drive assembly to drive a first or second set of wheels, respectively, to move a load handling device along a first or second set of parallel rails. Alternatively, the simultaneous activation of the first and second motors may be for the purpose of activating a container lifting assembly to vertically raise or lower a container gripping device. While these examples are in the context of a load handling device, the method of FIG. 17 applies to any system in which the simultaneous activation of first and second motors is used to drive a drive belt for any purpose, such as overcoming a load applied to the system.

[0068] In step 1720, drive belt slippage is determined to have occurred if the first and second current values ​​of the first and second current transients, respectively, differ by at least a threshold value at substantially the same time. The threshold value may be a predetermined ampere (A) difference between the first and second current values. The predetermined ampere value may be an absolute value or a modular value. Alternatively, the threshold may require that the first current value differ from the second current value by a predetermined percentage of the first current value, or vice versa. In other words, assuming the first current value is higher than the second current value, it is determined whether the second current value is at least a predetermined percentage of the first current value below the first current value. Alternatively, it is determined whether the first current value is at least a predetermined percentage of the second current value above the second current value. In practice, the threshold value allows for the detection of a pattern in the first and second current transients where the first and second current values ​​deviate significantly from each other at a given time. In particular, a sudden increase in one current transient and a simultaneous sudden decrease in the other current transient is a pattern indicative of drive belt slippage.

[0069] To improve accuracy, the threshold may require that both a predetermined amperage value and a predetermined percentage be met. While a percentage threshold may be easily detected, requiring a minimum amperage difference also ensures that transient current noise is not interpreted as belt slippage. It will be appreciated that the threshold used will vary depending on the configuration of the system, but may nevertheless be set to determine drive belt slippage.

[0070] FIG. 18 shows a plot / graph 1800 with a first current transient 1810 and a second current transient 1820 and regions 1830 where belt slippage is detected. The thresholds in this example require that (1) the first and second current values ​​differ by at least 0.8 A and (2) the second current value be at least 20% lower than the first current value. In practice, a pattern of first and second current transients indicative of drive belt slippage is detected. FIG. 19 shows a plot / graph 1900 with a first current transient 1910 and a second current transient 1920 and multiple regions 1930 where belt slippage is detected.

[0071] Advantageously, the method of Figure 17 can be used to determine drive belt slippage using the system's existing hardware. No downtime of the system for observation is required.

[0072] The method of Figure 17 has several uses. One such use is to execute the method as part of a system boot sequence. Once it is determined that drive belt slippage is not occurring, the system can proceed to normal operation.

[0073] Another application is to correlate detected drive belt slippage with system operation. For example, if slippage is detected simultaneously within a system's operating cycle, there may be some aspect of the system that is causing the slippage. While it may be possible to overcome this type of slippage by increasing the drive belt tension, doing so may mean that the system is not performing at optimum efficiency. This information can therefore be used to improve the system design. Similarly, if multiple slippages are detected within a system's operating cycle, it may be concluded that the drive belt tension is significantly lower than the optimum drive belt tension.

[0074] Another application is to increase the tension of the drive belt when it is determined that drive belt slippage has occurred. Additionally or alternatively, when it is determined that drive belt slippage is not occurring, the tension of the drive belt can be decreased. The purpose of decreasing the belt tension is to improve efficiency to the extent possible without introducing belt slippage. The system can include an automatic tensioning system 1630, such as by coupling one of the tensioning wheel arrangements 1440 to a stepper motor that can move the tensioning wheel arrangement to increase / decrease the drive belt tension to an optimal value. Another example of an automatic tensioning system is a linear actuator that moves a tensioning pulley on which the drive belt operates. Moving the tensioning pulley via the linear actuator can increase the tension of the drive belt. Typically, an automatic tensioning system moves a pulley or drive belt guide to increase the tension of the drive belt. As described above, the tension of the drive belt may be estimated to be significantly lower than the optimal tension. Once the automatic tensioning system adjusts the tension, the method of FIG. 17 can be re-executed to ensure that drive belt slippage is no longer occurring. Such information can be used by the processor / controller to control the degree to which the automatic tensioning system increases tension in the drive belt.

[0075] In this document, the phrase "movement in the n-direction," where n is one of x, y, and z (and related phrases) is intended to mean movement in either direction (i.e., toward the positive end of the n-axis or toward the negative end of the n-axis) substantially along or parallel to the n-axis.

[0076] In this document, the word "connect" and its derivatives are intended to encompass the possibilities of direct and indirect connections. For example, "x is connected to y" is intended to encompass the possibilities of x being directly connected to y with no intervening components, and the possibilities of x being indirectly connected to y with one or more intervening components. When a direct connection is intended, the words "directly connected," "directly connected," or similar words will be used. Similarly, the word "support" and its derivatives are intended to encompass the possibilities of direct and indirect contact. For example, "x supports y" is intended to encompass the possibilities of x directly supporting and directly contacting y with no intervening components, and the possibilities of x indirectly supporting y with one or more intervening components that contact x and / or y. The word "mount" and its derivatives are intended to encompass the possibilities of direct and indirect mounting. For example, "x is mounted on y" is intended to include the possibility that x is directly mounted on y with no intervening components, and the possibility that x is indirectly mounted on y with one or more intervening components.

[0077] In this document, the word "comprises" and its derivatives are intended to have an inclusive rather than exclusive meaning. For example, "x comprises y" is intended to include the possibility that x includes one and only one y, multiple y, or one or more y and one or more other elements. When an exclusive meaning is intended, the phrase "x consists of y" is used, which would mean that x includes only y and nothing else.

[0078] In this document, a "controller" is intended to include any hardware suitable for controlling (e.g., providing instructions to) one or more other components, such as a processor equipped with one or more memories and appropriate software for processing data relating to one or more components and sending appropriate instructions to the component(s) to enable the component(s) to perform its / their intended function(s).

[0079] As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0080] The invention can take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment containing both hardware and software elements. In a preferred embodiment, the invention is implemented in software.

[0081] Furthermore, the present invention may take the form of a computer program product embodied as a computer-readable medium having computer-executable code thereon for use by or in connection with a computer. For purposes of this description, a computer-readable medium may be any tangible apparatus that can contain, store, communicate, propagate, or carry a program for use by or in connection with a computer. Moreover, a computer-readable medium may be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device) or propagation medium. Examples of computer-readable media include semiconductor or solid-state memory, magnetic tape, removable computer diskettes, random access memory (RAM), read-only memory (ROM), rigid magnetic disks, and optical disks. Current examples of optical disks include compact disk-read-only memory (CD-ROM), compact disk-read / write (CD-R / W), and DVD.

[0082] The flow diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of methods according to various embodiments of the present invention. In this regard, each block in the flow diagrams may represent a module, segment, or portion of code, comprising one or more executable instructions for implementing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the blocks may not occur in the order noted in the figures. For example, depending on the functionality involved, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order. It should also be noted that each block of the flow diagrams, and combinations of blocks in the flow diagrams, may be implemented by a special-purpose hardware-based system that executes the specified functions or operations, or a combination of special-purpose hardware and computer instructions.

[0083] It will be understood that the above description is given by way of example only, and that various modifications may be made by those skilled in the art. Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous changes to the disclosed embodiments without departing from the scope of the invention.

[0084] The following is a non-exhaustive list of embodiments that may be or will be claimed:

[0085] [Embodiment 1] 1. A system for determining drive belt slippage, the system comprising: A drive belt and first and second motors configured to drive the drive belt; Controller and The controller comprises: receiving first and second transient currents from the first and second motors, respectively, during simultaneous activation of the first and second motors to drive the drive belt; determining drive belt slippage when first and second current values ​​of the first and second current transients, respectively, substantially simultaneously differ by at least a threshold value; A system configured to:

[0086] [Embodiment 2] The threshold is a minimum percentage difference between the first current value and the second current value; and / or Minimum ampere difference between the first current value and the second current value 2. The system of claim 1, wherein:

[0087] [Embodiment 3] A load handling device for lifting and moving storage containers (10) stacked in a grid framework structure, the grid framework structure comprising: a first set of parallel rails or tracks and a second set of parallel rails or tracks extending substantially perpendicular 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, the grid being supported by a set of uprights to form a plurality of vertical storage locations beneath the grid such that containers are stacked between and guided by the set of uprights vertically through the plurality of grid spaces; a body or skeleton mounted on a first set of wheels arranged to engage the first set of parallel tracks and a second set of wheels arranged to engage the second set of parallel tracks; A drive assembly comprising a first system according to embodiment 1 or 2, wherein the drive belt and the first and second motors of the first system are configured to drive the first or second sets of wheels, respectively, to move the load handling device along the first or second sets of parallel rails, and the controller of the first system is configured to receive first and second transient currents from the first and second motors of the first system, respectively, during driving of the first or second sets of wheels; and / or A diverting assembly comprising a second system according to embodiment 1 or 2, wherein the drive belt and the first and second motors of the second system are configured to raise or lower the first set of wheels and / or lower or raise the second set of wheels relative to the body or skeleton to engage and disengage the wheels with the parallel tracks, and a controller of the second system is configured to receive first and second transient currents from the first and second motors of the second system, respectively, during the raising or lowering of the first set of wheels and / or the lowering or raising of the second set of wheels; and / or A container lifting assembly comprising a third system according to embodiment 1 or 2, wherein the drive belt and the first and second motors of the third system are configured to raise or lower the gripping device in a vertical direction, and the controller of the third system is configured to receive first and second transient currents from the first and second motors of the third system, respectively, during the raising or lowering of the gripping device; A load handling device comprising:

[0088] [Embodiment 4] 4. A cargo handling device as described in embodiment 3, wherein the diverting assembly is arranged to raise or lower the first set of wheels and synchronously lower or raise, respectively, the second set of wheels relative to the body.

[0089] [Embodiment 5] The diverting assembly is either the first or second set of wheels; or each of the first and second sets of wheels 5. A cargo handling device according to embodiment 3 or 4, comprising at least one turning mechanism for

[0090] [Embodiment 6] 6. A load handling device according to any one of embodiments 3 to 5, wherein the turning assembly comprises two turning mechanisms for each of the first and second sets of wheels.

[0091] [Embodiment 7] 7. A load handling device according to embodiment 5 or 6, wherein the or each diverting mechanism is driven by a drive belt.

[0092] [Embodiment 8] 7. A load handling device according to any one of embodiments 3 to 6, wherein the two motors are mounted in opposite or adjacent locations of the load handling device.

[0093] [Embodiment 9] 9. A load handling device as described in embodiment 8, wherein the opposing or adjacent locations comprise corners of the load handling device.

[0094] [Embodiment 10] 9. A load handling device as described in embodiment 8, wherein the opposing or adjacent locations or corners are on the body or skeleton.

[0095] [Embodiment 11] 11. A load handling device according to any one of embodiments 3 to 10, wherein the drive belt substantially circumnavigates the skeleton or body of the load handling device.

[0096] [Embodiment 12] The system of any one of embodiments 1 to 11, further comprising an automatic tensioning device, wherein the controller is further configured to control the automatic tensioning device to increase the tension of the drive belt when it is determined that slippage of the drive belt has occurred, and / or to decrease the tension of the drive belt when it is determined that slippage of the drive belt has not occurred.

[0097] [Embodiment 13] 1. A method for determining slippage of a drive belt in a system comprising a drive belt, first and second motors configured to drive the drive belt, and a controller, the method comprising using the controller to: receiving first and second transient currents from the first and second motors, respectively, during simultaneous activation of the first and second motors to drive the drive belt; determining drive belt slippage when first and second current values ​​of the first and second current transients, respectively, substantially simultaneously differ by at least a threshold value; A method comprising:

[0098] [Embodiment 14] The threshold is a minimum percentage difference between the first current value and the second current value; and / or Minimum ampere difference between the first current value and the second current value 14. The method of embodiment 13, wherein the method is defined by:

[0099] [Embodiment 15] 1. A method of operating a load handling device for lifting and moving storage containers stacked in a grid framework structure, the grid framework structure comprising: a first set of parallel rails or tracks and a second set of parallel rails or tracks extending substantially perpendicular 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, the grid being supported by a set of uprights to form a plurality of vertical storage locations beneath the grid such that containers are stacked between and guided by the set of uprights vertically through the plurality of grid spaces; a body or skeleton mounted on a first set of wheels arranged to engage the first set of parallel tracks and a second set of wheels arranged to engage the second set of parallel tracks; a drive assembly comprising a first drive belt, a first motor, and a second motor configured to drive a first or second set of wheels, respectively, to move a load handling device along a first or second set of parallel rails, wherein the first method of embodiment 13 or 14 is used to receive first and second transient currents from the first and second motors, respectively, during driving of the first or second set of wheels; and / or a turning assembly comprising a second drive belt, a third motor, and a fourth motor configured to raise or lower a first set of wheels and / or lower or raise a second set of wheels relative to a body or skeleton to engage and disengage the wheels with parallel tracks, wherein the second method of embodiment 13 or 14 is used to receive first and second transient currents from the third and fourth motors, respectively, during the raising or lowering of the first set of wheels and / or the lowering or raising of the second set of wheels; and / or A container lifting assembly comprising a third drive belt, a fifth motor, and a sixth motor configured to raise or lower a gripping device in a vertical direction, wherein the third method of embodiment 13 or 14 is used to receive first and second transient currents from the fifth and sixth motors, respectively, during the raising or lowering of the gripping device; A method comprising:

[0100] [Embodiment 16] 16. The method of embodiment 15, wherein the steering assembly is arranged to raise or lower the first set of wheels and synchronously lower or raise, respectively, the second set of wheels relative to the body.

[0101] [Embodiment 17] The diverting assembly is either the first or second set of wheels; or each of the first and second sets of wheels 17. The method of claim 15 or 16, comprising at least one redirection mechanism for

[0102] [Embodiment 18] 18. The method according to any one of embodiments 15 to 17, wherein the turning assembly comprises two turning mechanisms for each of the first and second sets of wheels.

[0103] [Embodiment 19] 19. The method of embodiment 17 or 18, wherein the or each diverting mechanism is driven by a drive belt of the second system.

[0104] [Embodiment 20] 20. The method according to any one of embodiments 15 to 19, wherein the third and fourth motors are mounted in opposite or adjacent locations of the load handling device.

[0105] [Embodiment 21] 21. The method of embodiment 20, wherein the opposing or adjacent location comprises a corner of the load handling device.

[0106] [Embodiment 22] 21. The method of embodiment 20, wherein the opposing or adjacent locations or corners are on the body or skeleton.

[0107] [Embodiment 23] 23. The method according to any one of embodiments 15 to 22, wherein the second drive belt substantially circumnavigates the skeleton or body of the load handling device.

[0108] [Embodiment 24] 24. The method of any one of embodiments 15 to 23, wherein the system further comprises an automatic tensioning device, and the method further comprises using a controller to control the automatic tensioning device to increase the tension of the drive belt when it is determined that drive belt slippage has occurred, and / or to decrease the tension of the drive belt when it is determined that drive belt slippage is not occurring.

[0109] [Embodiment 25] A computer program comprising instructions, which when executed by a computer, cause the computer to perform the method according to any one of embodiments 15 to 24.

[0110] [Embodiment 26] A data processing system comprising a processor configured to perform the method according to any one of embodiments 15 to 24.

Claims

1. 1. A system for determining drive belt slippage, the system comprising: A drive belt and first and second motors configured to drive the drive belt; Controller and wherein the controller receiving first and second transient currents from the first and second motors, respectively, during simultaneous activation of the first and second motors to drive the drive belt; determining slippage of the drive belt when first and second current values ​​of the first and second current transients, respectively, differ by at least a threshold value substantially simultaneously; A system configured to:

2. The threshold value is a minimum percentage difference between the first current value and the second current value; and / or a minimum ampere difference between the first current value and the second current value; The system of claim 1 , wherein:

3. 1. A load handling device for lifting and moving storage containers stacked in a grid framework structure, said grid framework structure comprising: a first set of parallel rails or tracks and a second set of parallel rails or tracks extending substantially perpendicular to said first set of parallel rails or tracks in a substantially horizontal plane to form a grid pattern comprising a plurality of grid spaces, said grid being supported by a set of uprights to form a plurality of vertical storage locations beneath said grid such that containers are stacked between and guided by the set of uprights vertically through a plurality of said grid spaces; a body or skeleton mounted on a first set of wheels arranged to engage the first set of parallel tracks and a second set of wheels arranged to engage the second set of parallel tracks; a drive assembly comprising a first system as claimed in claim 1 or 2, wherein the drive belt and first and second motors of the first system are configured to drive the first or second sets of wheels, respectively, to move the load handling device along the first or second sets of parallel rails, and the controller of the first system is configured to receive the first and second transient currents from the first and second motors of the first system, respectively, during driving of the first or second sets of wheels; and / or A diverting assembly comprising a second system as claimed in claim 1 or 2, wherein the drive belt and first and second motors of the second system are configured to raise or lower the first set of wheels and / or lower or raise the second set of wheels relative to the body or skeleton to engage and disengage the wheels with the parallel tracks, and the controller of the second system is configured to receive the first and second transient currents from the first and second motors of the second system, respectively, during the raising or lowering of the first set of wheels and / or the lowering or raising of the second set of wheels; and / or 3. A container lifting assembly comprising a third system, the system of claim 1 or 2, wherein the drive belt and first and second motors of the third system are configured to raise or lower a gripping device in the vertical direction, and the controller of the third system is configured to receive the first and second transient currents from the first and second motors of the third system, respectively, during the raising or lowering of the gripping device; A load handling device comprising:

4. 4. The load handling device of claim 3, wherein the diverting assembly is arranged to raise or lower the first set of wheels and synchronously lower or raise, respectively, the second set of wheels relative to the body.

5. The diverter assembly includes: either the first or second set of wheels; or each of said first and second sets of wheels 5. A cargo handling device according to claim 3 or 4, comprising at least one turning mechanism for

6. A load handling device according to any one of claims 3 to 5, wherein the diverting assembly comprises two diverting mechanisms for each of the first and second sets of wheels.

7. 7. A load handling device according to claim 5 or 6, wherein the or each diverting mechanism is driven by the drive belt of the second system.

8. A load handling device according to any one of claims 3 to 6, wherein the first and second motors are mounted in opposite or adjacent locations on the load handling device.

9. The load handling device of claim 8 , wherein the opposing or adjacent locations comprise corners of the load handling device.

10. 9. A load handling device according to claim 8, wherein the opposing or adjacent locations or corners are on the body or skeleton.

11. A load handling device according to any one of claims 3 to 10, wherein the drive belt substantially circumnavigates the skeleton or body of the load handling device.

12. 12. The system of claim 1, further comprising an automatic tensioning device, and wherein the controller is further configured to control the automatic tensioning device to increase tension in the drive belt when it is determined that slippage of the drive belt has occurred, and / or to decrease tension in the drive belt when it is determined that slippage of the drive belt has not occurred.

13. 13. A method for determining slippage of a drive belt in a system, the system comprising a system according to any one of claims 1 to 12, the method comprising using the controller: receiving first and second transient currents from the first and second motors, respectively, during simultaneous activation of the first and second motors to drive the drive belt; determining that slippage of the drive belt has occurred when first and second current values ​​of the first and second transient currents, respectively, differ by at least a threshold value substantially simultaneously; A method comprising:

14. A computer program comprising instructions which, when executed by a computer, cause the computer to perform the method of claim 13.

15. 14. A data processing system comprising a processor configured to perform the method of claim 13.

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