Suction cup assembly

Abstract

A suction cup assembly (100 figure 8(a)) for an end effector (56 figure 6) of a robotic manipulator (52 figure 6) comprises an innermost suction cup 102, an outermost suction cup 104 surrounding the i

Description

TECHNICAL FIELD The present disclosure relates generally to suction cup assemblies for use on robotic manipulators used in warehouses or fulfilment centres, for example. Aspects relate to a suction cup assembly, a robotic manipulator, a picking station, and a grid-based storage and retrieval system comprising the picking station. BACKGROUND Online retail businesses selling multiple product lines, such as online grocers and supermarkets, require systems that are able to store tens or even tens of thousands of different product lines. The use of single-product stacks therefore can be impractical, since a very large floor area would be required to accommodate all of the stacks required. Furthermore, it can be desirable only to store small quantities of some items, such as perishables or infrequently-ordered goods, making single-product stacks an inefficient solution. PCT Publication No. WO2015 / 185628A (Ocado) describes a known storage and fulfilment system in which stacks of bins or containers are arranged within a framework structure. The bins or containers are accessed by load-handling devices operating on tracks located on the top of the frame structure. The load-handling devices are configured to lift bins or containers out from the stacks. Multiple load-handling devices can co-operating to access bins or containers located in the lowest positions of the stack. A system of this type is illustrated schematically in Figures 1 to 5 of the accompanying drawings. Figure 1 illustrates a framework structure 1 of a grid-based automated storage and retrieval system. The structure 1 comprises a number of upright members 3 supporting two sets of transversely arranged horizontal members 5, 7. The upright members 3 extend parallel to one another in the illustrated z-axis and stand orthogonally with respect to the horizontal members 5, 7. The first set of horizontal members 7 extend in the direction of the illustrated x-axis, while the second set of horizontal members 5 extend in the direction of the illustrated y-axis. The two sets of horizontal members 5, 7 form a grid pattern defining a plurality of grid cells. In the illustrated example, storage containers 9 are arranged in stacks 11, with each stack 11 being located beneath a respective grid cell. Figure 2 shows a large-scale plan view of a section of transverse track structure 13 forming part of the storage structure 1 illustrated in Figure 1. The track structure 13 is located on top of the sets of horizontal members 5, 7. The track structure 13 may be provided by the horizontal members 5, 7 themselves (e.g. formed in or on the surfaces of the horizontal members 5, 7) or by one or more additional components mounted on top of the horizontal members 5, 7. The illustrated track structure 13 comprises x-direction tracks 17 and y-direction tracks 19, i.e. a first set of tracks 17 which extend in the direction of the illustrated x-axis and a second set of tracks 19 which extend in the direction of the illustrated y-axis. The tracks 17, 19 define apertures 15 at the centres of the grid cells. The apertures 15 are sized to allow storage containers 9 located beneath the grid cells to be lifted and lowered through the apertures 15. The x-direction tracks 17 are provided in pairs separated by channels 21, and the y-direction tracks 19 are provided in pairs separated by channels 23. Other arrangements of track structure 13 are also envisaged. Figure 3 shows a plurality of load-handling devices 31 moving on top of the storage structure 1 illustrated in Figure 1. The load-handling devices 31, which may also be referred to as robots or bots, are provided with sets of wheels to engage with corresponding x- or y-direction tracks 17, 19 to enable the bots 31 to travel across the track structure 13 and reach specific grid cells. The illustrated pairs of tracks 17, 19, are separated by channels 21, 23, allowing the bots 31 to occupy or pass one another on neighbouring grid cells without colliding. As illustrated in Figure 4, a bot 31 comprises a body 33 on which are mounted one or more components which enable the bot 31 to perform its intended functions. These functions may include moving across the storage structure 1 on the track structure 13 and raising or lowering storage containers 9 (e.g. from or to stacks 11) so that the bot 31 can retrieve or deposit storage containers 9 in specific locations defined by the grid pattern. The bot 31 further comprises first and second sets of wheels 35, 37 which are mounted on the body 33 and enable the bot 31 to move in the x- and y-directions along the tracks 17 and 19, respectively. In particular, two wheels 35 are provided on the shorter side of the bot 31 visible in Figure 4, and a further two wheels 35 are provided on the opposite shorter side of the bot 31 (the side and further two wheels 35 not visible in Figure 4). The wheels 35 engage with tracks 17 and are rotatably mounted on the body 33 of the bot 31 to allow the bot 31 to move along the tracks 17. Analogously, two wheels 37 are provided on the longer side of the bot 31 visible in Figure 4, and a further two wheels 37 are provided on the opposite longer side of the bot 31 (the side and further two wheels 37 not visible in Figure 4). The wheels 37 engage with tracks 19 and are rotatably mounted on the body 33 of the bot 31 to allow the bot 31 to move along the tracks 19. The bot 31 also comprises container-lifting means, generally designated by 39, configured to raise and lower containers 9. The container-lifting means 39 comprises four tapes or reels 41 which are connected at their lower ends to a container-engaging assembly 43. The containerengaging assembly 43 comprises engaging means (which may, for example, be provided at the corners of the assembly 43, in the vicinity of the tapes 41) configured to engage with corresponding features of the containers 9. For instance, the containers 9 may be provided with one or more apertures in their upper sides with which the engaging means can engage. Alternatively or additionally, the container engaging means may be configured to hook under the rims or lips of the containers 9, and / or to clamp or grasp the containers 9. The tapes 41 may be wound up or down to raise or lower the container-engaging assembly, as required. One or more motors or other means may be provided to effect or control the winding up or down of the tapes 41. As can be seen in Figure 5, the body 33 of the bot 31 has an upper portion 45 and a lower portion 47. The upper portion 45 is configured to house the one or more operation components (not shown) that enable the bot 31 to perform its intended functions, and the lower portion 47 is arranged beneath the upper portion 45. The lower portion 47 comprises a container-receiving space or cavity for accommodating at least part of a container 9 that has been raised by the container-lifting means 39. The container-receiving space is sized such that enough of a container 9 can fit inside the cavity to enable the bot 31 to move across the track structure 13 on top of storage structure 1 without the underside of the container 9 catching on the track structure 13 or another part of the storage structure 1. When the bot 31 has reached its intended destination, the container-lifting means 39 controls the tapes 41 to lower the containergripping assembly 43 and the corresponding container 9 out of the cavity in the lower portion 47 and into the intended position. The intended position may be a stack 11 of containers 9 or an egress point of the storage structure 1 (or an ingress point of the storage structure 1 if the bot 31 has moved to collect a container 9 for storage in the storage structure 1). Although in the illustrated example the upper and lower portions 45, 47 are separated by a physical divider, in other embodiments, the upper and lower portions 45, 47 may not be physically divided by a specific component or part of the body 33 of the bot 31. In some embodiments, the container-receiving space may not be within the body 33 of the bot 31. For example, in some embodiments, the container-receiving space may be adjacent to the body 33 of the bot 31, e.g. in a cantilever arrangement with the weight of the body 33 of the bot 31 counterbalancing the weight of the container to be lifted. In such embodiments, a frame or arms of the container-lifting means 39 may protrude horizontally from the body 33, and the tapes / reels 41 may be arranged at respective locations on the protruding frame / arms and configured to be raised and lowered from those locations to raise and lower a container into the container-receiving space adjacent to the body 33. The height at which the frame / arms is / are mounted on and protrude(s) from the body 33 of the bot 31 may be chosen to provide a desired effect. For example, it may be preferable for the frame / arms to protrude at a high level on the body 33 of the bot 31 to allow a larger container (or a plurality of containers) to be raised into the container-receiving space beneath the frame / arms. Alternatively, the frame / arms may be arranged to protrude lower down the body 33 (but still high enough to accommodate at least one container between the frame / arms and the track structure 13) to keep the centre of mass of the bot 31 lower when the bot 31 is loaded with a container. To enable the bot 31 to move on the different wheels 35, 37 in the first and second directions, the bot 31 includes a wheel-positioning mechanism for selectively engaging either the first set of wheels 35 with the first set of tracks 17 or the second set of wheels 37 with the second set of tracks 19. The wheel-positioning mechanism is configured to raise and lower the first or second set of wheels 35, 37 relative to the body 33, thereby enabling the load-handling device 31 to selectively move in either the first direction or the second direction across the tracks 17, 19 of the storage structure 1. The wheel-positioning mechanism may include one or more linear actuators, rotary components or other means for raising and lowering at least one set of wheels 35, 37 relative to the body 33 to bring the at least one set of wheels 35, 37 out of and into contact with the tracks 17,19. In some examples, only one set of wheels 35, 37 is configured to be raised and lowered, and the act of lowering the one set of wheels 35, 37 may effectively lift the other set of wheels 35, 37 clear of the corresponding tracks 17, 19, while the act of raising the one set of wheels 35, 37 may effectively lower the other set of wheels 35, 37 into contact with the corresponding tracks 17, 19. In other examples, both sets of wheels 35, 37 may be capable of being raised and lowered, advantageously meaning that the body 33 of the bot 31 stays substantially at the same height and therefore the weight of the body 33 and the components mounted thereon does not need to be lifted and lowered by the wheel-positioning mechanism. As shown in Figure 3, a plurality of identical load-handling devices 31 are provided, so that each load-handling device 31 can operate simultaneously to increase the throughput of the system. The system illustrated in Figure 3 may include specific locations, known as ports, at which containers can be transferred into or out of the system. An additional conveyor system (not shown) is associated with each port, so that containers 9 transported to a port by a loadhandling device 31 can be transferred to another location by the conveyor system, for example to a picking station (not shown). Similarly, containers 9 can be moved by the conveyor system to a port from an external location, for example to a container-filling station (not shown), and transported to a stack 12 by the load-handling devices 30 to replenish the stock in the system. Each load-handling device 31 can lift and move one container 9 at a time. If it is necessary to retrieve a container 9 (“target container 9”) that is not located on the top of a stack, then the overlying containers 9 (“non-target containers 9”) must first be moved to allow access to the target container 9. This is achieved in an operation referred to hereafter as “digging”. During a digging operation, one of the load-handling devices 31 sequentially lifts each non-target container 9 from the stack 11 containing the target container 9 and places it in a vacant position within another stack 11. The target container 9 can then be accessed by the load-handling device 31 and moved to a port for further transportation. Each of the load-handling devices 31 is under the control of a central computer. Each individual container 9 in the system is tracked so that it can be retrieved, transported and replaced as necessary. For example, during a digging operation, the locations of each of the non-target containers 9 is logged, so that the non-target containers 9 can be tracked. The system described with reference to Figures 1 to 5 has many advantages and is suitable for a wide range of storage and retrieval operations. In particular, it allows very dense storage of product, and it provides a very economical way of storing a wide range of different items in the containers, while allowing reasonably economical access to all of the containers 9 when required for picking. With reference to Figure 6, the system may further comprise a robotic picking station, generally designated by 50, mounted on top of the storage structure 1, alongside the load-handling devices 31 (not shown). The robotic picking station 50 comprises a robotic manipulator 52 comprising a robotic arm 54 and an end effector 56 for releasably engaging a product to be manipulated, together with several designated grid cells 60, 62. The robotic manipulator 52 is mounted on a plinth 58 above a single grid cell 60 and, depending on its location on the structure 1, can be surrounded by up to eight other grid cells 62. In general, the robotic manipulator 52 is configured to pick an item or product from any one of the containers 9 located in one of the designated grid cells 62 and place it in a containers located in another one of the cells 62. The load-handling devices 31 collect containers 9 from, and deliver them to, the designated grid cells 62 as necessary. In this way, the robotic picking station 50 and the loadhandling devices 31 work in conjunction to fulfil a customer order or redistribute products throughout the structure 1. The end effector 56 comprises a suction cup 64 connected to a vacuum source (not shown) via a stem 65, enabling the suction cup 64 to engage products or items using vacuum pressure. It is against this background that the invention was devised. SUMMARY Accordingly, there is provided, in one aspect, a suction cup assembly for an end effector of a robotic manipulator, the suction cup assembly comprising an innermost suction cup; an outermost suction cup surrounding the innermost suction cup; a duct configured to connect the innermost suction cup to a vacuum source; and, means for controlling the airflow between the inner- and outermost suction cups, the means for controlling the airflow between the inner- and outermost suction cups being operable to enable a vacuum to form within one of the innermost suction cup or the inner- and outermost suction cups when the suction cup assembly is connected to the vacuum source. In another aspect, there is provided an end effector for a robotic manipulator comprising a suction cup assembly according to the preceding aspect. In another aspect, there is provided a robotic manipulator comprising an end effector according to the preceding aspect. In another aspect, there is provided a storage and retrieval system comprising a robotic manipulator according to the preceding aspect. BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects will now be described, by way of example only, with reference to the accompanying drawing, in which: Figure 1 shows a schematic depiction of an automated storage and retrieval system; Figure 2 shows a schematic depiction of a plan view of a section of track structure forming part of the storage system of Figure 1; Figure 3 shows a schematic depiction of a plurality of load-handling devices moving on top of the storage system of Figure 1; Figures 4 and 5 showa schematic depiction of a load-handling device interacting with a container; Figure 6 shows a schematic depiction of a known robotic picking station; Figure 7 is a lower isometric view of a suction cup assembly in accordance with an embodiment for use in the robotic picking station of Figure 6; Figure 8a is a side view of the suction cup assembly of Figure 7 and Figure 8b is a cross-sectional view of the suction cup assembly of Figure 8a along section A-A; Figures 9a and 9b are two cross-sectional views of the suction cup assembly of Figure 8a in different modes of operation; Figure 10 is a cross-sectional view of a suction cup assembly in accordance with another embodiment; Figures 11a and 11b are two cross-sectional views of the suction cup assembly of Figure 10 in different modes of operation; Figures 12a and 12b are cross-sectional views of a suction cup assembly in accordance with another embodiment; and, Figures 13a and 13b are cross-sectional views of the suction cup assembly of Figures 12a and 12b in different modes of operation. In the drawings, like features are denoted by like reference signs where appropriate. DETAILED DESCRIPTION In the following description, some specific details are included to provide a thorough understanding of the disclosed examples. One skilled in the relevant art, however, will recognise that other examples may be practised without one or more of these specific details, or with other components, materials, etc., and structural changes may be made without departing from the scope defined in the appended claims. Moreover, references in the following description to any terms having an implied orientation are not intended to be limiting and refer only to the orientation of the features as shown in the accompanying drawings. In some instances, well-known features or systems, such as processors, sensors, storage devices, network interfaces, fasteners, electrical connectors, and the like are not shown or described in detail to avoid unnecessarily obscuring descriptions of the disclosed embodiment. Unless the context requires otherwise, throughout the specification and the appended claims, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.” Reference throughout this specification to “one”, “an”, or “another” applied to “embodiment”, “example”, means that a particular referent feature, structure, or characteristic described in connection with the embodiment, example, or implementation is included in at least one embodiment, example, or implementation. Thus, the appearances of the phrase “in one embodiment” or the like in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments, examples, or implementations. It should be noted that, as used in this specification and the appended claims, the users forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and / or” unless the content clearly dictates otherwise. It is also to be understood that any feature described in relation to any one example may be used alone, or in combination with other features described, such as in combination with one or more features of any other of the examples, or any combination of examples. Figure 7 provides an isometric view of a suction cup assembly 100 in accordance with an embodiment for use with the end effector 56 of the robotic manipulator 52 shown in Figure 6. The suction cup assembly 100 is fixed to the bottom end of a stem 65 that is used in connecting the suction cup assembly 100 to a vacuum source (not shown). The suction cup assembly 100 comprises a plurality of multisized suction cups, with the smaller suction cups being arranged within the larger suction cups. The embodiment shown comprises two suction cups 102, 104: an innermost suction cup 102 and an outermost suction cup 104 surrounding the innermost suction cup 102. The inner- and outermost suction cups 102, 104 are concentrically arranged, but the skilled reader will understand that such an arrangement is not essential. With reference to Figures 8a and 8b, the suction cup assembly 100 further comprises a shaft 106 having, at one end 107, a screw thread 108 corresponding to a complementary screw thread located at the bottom end of the stem 65 to fasten the suction cup assembly 100 and stem 65. The innermost suction cup 102 comprises a collar section 111 that secures the innermost suction cup 102 to the other end 109 of the shaft 106. The collar section 111 abuts the underside of a stepped formation 113 in the shaft 106, preventing the collar section 111 from moving towards the threaded end 107 of the shaft 106. The shaft 106 defines a duct 110 that is arranged to connect the interior of the innermost suction cup 102 to the vacuum source. The suction cup assembly 100 further comprises a means for controlling airflow 112 between the inner- and outermost suction cups 102, 104 that is operable to enable at least a partial vacuum to form within one of the innermost suction cup 102 or both the inner- and outermost suction cups 102, 104 when the suction cup assembly 100 is connected to the vacuum source. In this embodiment, the means for controlling airflow 112 comprises a pair of vacuum check valves 112a, 112b that are arranged to open and substantially close respective openings 114a, 114b formed in the innermost suction cup 102. The openings 114a, 114b are arranged to provide a fluidic connection between the interior of the outermost suction cup 104 and vacuum source, via the innermost suction cup 102 and duct 110. The inner- and outermost suction cups 102, 104 further comprise bellowed sections that allow the suction cup assembly 100 to change volume upon the development of a partial vacuum within the innermost suction cup 102 or the inner- and outermost suction cups 102, 104. Specifically, the innermost suction cup 102 comprises upper and lower bellowed sections 116a, 116b located either side of the openings 114a, 114b or vacuum check valves 112a, 112b. The lower bellowed section 116b forms an open end 117 of the innermost suction cup 102. The bottom end of the upper bellowed section 116a is connected to the collar 111, holding it in a fixed location, while its upper end is connected to the outermost suction cup 104 and is slidably mounted to the shaft 106. This arrangement facilitates reciprocating movement of the outermost suction cup 104 along the shaft 106 as its volume changes. The outermost suction cup 104 comprises a single bellowed section 124 forming an open end 119 of the cup 104. The open ends 117, 119 are offset from each other such that the open end 117 of the innermost suction cup 102 extends from the outermost suction cup 104. The vacuum check valves 112a, 112b are biased in an open configuration, permitting air to flow unimpeded through the openings 114a, 114b from the interior of the outermost suction cup 104 to the duct 110, and are passively actuated to a closed configuration by the presence of a sufficient pressure differential. When in the open configuration, therefore, the pressure across the valves 112a, 112b is substantially equal, meaning that air is able to flow simultaneously through open ends 117, 119 of the inner- and outermost suction cups 102, 104 to the duct 110 under the force provided by the vacuum source as indicated by the arrow in Figure 8b. With reference to Figures 9a and 9b, when holding an item, the novel arrangement of the suction cup assembly 100 enables either the innermost suction cup 102 or both the inner- and outermost suction cups 102, 104 to be passively activated depending on the size of the item and / or the where on the item the suction cup assembly 100 is engaged. In one mode of operation, as shown in Figure 9a, an item 118 is positioned with respect to the suction cup assembly 100 and / or sized such that the surface 120 being engaged by the suction cup assembly 100 only extends fully across the open end 117 of the innermost suction cup 102, while the open end 119 of outermost suction cup 104 remains open to the atmosphere. In this situation, when the suction cup assembly 100 is connected to the vacuum source, a partial vacuum is formed within the innermost suction cup 102, thereby holding the item 118, and the volume of the innermost suction cup 102 is reduced through the compression of the lower bellowed section 116b. Simultaneously, air is drawn into the interior of the outermost suction cup 104, as indicated by arrow 122. The pressure difference across the vacuum check valves 112a, 112b, established by the partial vacuum in the interior of the innermost suction cup 102 and the atmospheric pressure in the interior of the outermost suction cup 104, causes the valves 112a, 112b to close thereby limiting the airflow from the interior of the outermost suction cup 104 to the duct 110. Importantly, the valves 112a, 112b are configured to allow air to pass from the interior of the outermost suction cup 104 the interior of the innermost suction cup 102 when closed, but at a comparatively much reduced rate than when open as indicated by dashed arrows 126. This provides a continuous flow of air from the atmosphere, through the interior of the outermost suction cup 104, to the partial vacuum established in the interior of the innermost suction cup 102, maintaining the pressure differential across the valves 112a, 112b. The lower bellowed section 116b is configured such that when a partial vacuum is created in the innermost suction cup 102 causing it to compress, the open end 117 of the innermost suction cup 102 is substantially coplanar with the open end 119 of the outermost suction cup 104. This arrangement ensures that both the inner- and outermost suction cups 102, 104 contact the surface 120 even though the item 118 is held by only the innermost suction cup 102. In this situation, the bellowed section 124 of the outermost suction cup 104 provides a function of stabilising the item 118 during its manipulation by damping any oscillations experienced by the item 118 while it is moved, thus lessening the chances of the innermost suction cup 102 losing its vacuum seal on the surface 120. In another mode of operation, as shown in Figure 9b, the suction cup assembly 100 is positioned such that both open ends 117, 119 of the inner- and outermost suction cups 102, 104 fully engage the surface 120 of the item 118, enabling them to form a vacuum seal on the surface 120 to hold the item 118. That is, neither of the open ends 117, 119 are exposed to the atmosphere, and so a partial vacuum is established in both suction cups 102, 104 under the force of the vacuum source and, since the pressure difference across the valves 112a, 112b is negligible, the values 112a, 112b are open. In this situation, both the lower bellowed section 116b of the innermost suction cup 102 and the bellowed section 124 of the outermost suction cup 104 compress such that their respective open ends 117, 119 are substantially coplanar. In order to ensure this coplanar arrangement, the upper bellowed section 116a of the innermost suction cup 102 is configured also to compress as the pressure in the outermost suction cup 104 starts to fall below atmospheric pressure, pulling its upper end, and so the outermost suction cup 104, along the shaft 106, changing the position of the outermost suction cup 104 relative to the innermost suction cup 102. This embodiment of the suction cup assembly 100 provides the benefit of passively switching between either mode of operation depending on the size and / or position of an item, to either hold the item with only the innermost suction cup 102, if the outermost suction cup 104 is unable to form a seal, or the inner- and outermost suction cups 102, 104, thus increasing the range of items that the suction cup assembly 100 can pick and decreasing its positional sensitivity. Other embodiments also provide similar benefits. Figure 10 provides a cross-sectional view of a suction cup assembly 200 according to another embodiment. This embodiment is much like the previous one insofar that it comprises an innermost suction cup 202 and an outermost suction cup 204 surrounding the innermost suction cup 202 in a concentric arrangement. The suction cup assembly 200 further comprises a shaft 206 having, at one end 207, a screw thread 208 corresponding to a complementary screw thread located at the bottom end of the stem 65 of Figure 7 to fasten the suction cup assembly 200 to the stem 65. The innermost suction cup 202 comprises a collar section 211 that secures the innermost suction cup 202 to the other end 209 of the shaft 206. The collar section 211 abuts the underside of a stepped formation 213 in the shaft 206, preventing the collar section 211 from moving towards the threaded end 207 of the shaft 206. The shaft 206 defines a duct 210 that is arranged to connect the interior of the innermost suction cup 202 to the vacuum source. As with the previous embodiment, this suction cup assembly 200 also comprises a means for controlling airflow 212 between the inner-and outermost suction cups 202, 204 that is operable to enable at least a partial vacuum to form within one of the innermost suction cup 202 or both the inner- and outermost suction cups 202, 204 when the suction cup assembly 200 is connected to the vacuum source. However, in this embodiment, the means for controlling airflow 212 comprises a pair of compliant valves 212a, 212b that are arranged to open and substantially close respective openings 214a, 214b formed in the innermost suction cup 202. The openings 214a, 214b are arranged to provide a fluidic connection between the interior of the outermost suction cup 204 and vacuum source, via the innermost suction cup 202 and duct 210. The compliant valves 212a, 212b sit across their respective openings 214a, 214b and, at one end 235a, 235b, are secured in fixed positions to the top of the lower bellowed section 116b of the innermost suction cup 202. The other ends 237a, 237b of the compliant valves 212a, 212b are secured to an inner side wall 240 of the outermost suction cup 204. As with the vacuum check valves 112a, 112b of the previous embodiment, the compliant valves 212a, 212b of this embodiment are similarly configured to allow air to pass from the interior of the outermost suction cup 204 to the interior of the innermost suction cup 202 when closed but at a comparatively much reduced rate than when open. In the configuration shown in Figure 10, therefore, when the suction cup assembly 200 is connected to the vacuum source, the flow rate through the innermost suction cup 202 is greater than that of the outermost suction cup 204, as illustrated by the dashed arrows 226. The inner- and outermost suction cups 202, 204 comprise bellowed sections that allow the suction cup assembly 200 to change volume upon the development of a partial vacuum within the innermost suction cup 202 or the inner- and outermost suction cups 202, 204. Specifically, the innermost suction cup 202 comprises upper and lower bellowed sections 216a, 216b located either side of the openings 214a, 214b or compliant valves 212a, 212b. The lower bellowed section 216b forms an open end 217 of the innermost suction cup 202 that is used to form a vacuum seal on an item. The bottom end of the upper bellowed section 216a is connected to the collar 211, holding it in a fixed location, while its upper end is connected to the outermost suction cup 204 and is slidably mounted to the shaft 206. This arrangement facilitates reciprocating movement of the outermost suction cup 204 along the shaft 206 as its volume changes. The outermost suction cup 204 comprises a single bellowed section 224 forming an open end 219 of the cup 204. With reference to Figures 11a and 11b, this embodiment of the suction cup assembly 200 works substantially similar as the previous embodiment insofar that its novel arrangement provides passive actuation of either the innermost suction cup 202 or both the inner- and outermost suction cups 202, 204 according to the size of an item and / or the where on the item the suction cup assembly 200 is engaged. In one mode of operation, as shown in Figure 11a, an item 218 is positioned with respect to the suction cup assembly 200 and / or sized such that the surface 220 being engaged by the suction cup assembly 200 only extends fully across the open end 217 of the innermost suction cup 202, while the open end 219 of outermost suction cup 204 remains open to the atmosphere. In this situation, when the suction cup assembly 200 is connected to the vacuum source, a partial vacuum is formed within the innermost suction cup 202 to hold the item 218 and the volume of the innermost suction cup 202 is reduced through the compression of the lower bellowed section 216b. Simultaneously, air is drawn into the interior of the outermost suction cup 204, as indicated by arrow 222. The pressure difference across the compliant valves 212a, 212b, established by the partial vacuum in the interior of the innermost suction cup 202 and the atmospheric pressure in the interior of the outermost suction cup 204, causes the air within the outermost suction cup 204 to leak across the valves 212a, 212b to the interior of the innermost suction cup 202, but at a comparatively much reduced rate than when open as indicated by dashed arrows 227. The lower bellowed section 216b is configured such that when a partial vacuum is created in the innermost suction cup 202, causing it to compress, the open end 217 of the innermost suction cup 202 is substantially coplanar with the open end 219 of the outermost suction cup 204. This arrangement ensures that both the inner- and outermost suction cups 202, 204 contact the surface 220 even though the item 218 is held by only the innermost suction cup 202. In this situation, the bellowed section 224 of the outermost suction cup 204 provides a function of stabilising the item 218 during its manipulation by damping any movements experienced by the item 218 while it is moved, thus lessening the chances of the innermost suction cup 202 losing its vacuum seal on the surface 220. In another mode of operation, as shown in Figure 11b, the suction cup assembly 200 is positioned such that both open ends 217, 219 of the inner- and outermost suction cups 202, 204 fully engage the surface 220 of the item 218, enabling them both to form a vacuum seal on the surface 220 to hold the item 218. That is, neither of the open ends 217, 219 are exposed to the atmosphere, and so a partial vacuum is established in both suction cups 202, 204 under the force of the vacuum source. In this situation, both the lower bellowed section 216b of the innermost suction cup 202 and the bellowed section 224 of the outermost suction cup 204 compress such that their respective open ends 217, 219 are substantially coplanar. In order to ensure this coplanar arrangement and assure a vacuum pressure in both cups 202, 204, the upper bellowed section 216a of the innermost suction cup 202 is configured also to compress progressively as the pressure in the outermost suction cup 204 begins to fall below atmospheric pressure, pulling its upper end, and so the outermost suction cup 204, along the shaft 206, changing the position of the outermost suction cup 204 relative to the innermost suction cup 202. This relative movement pulls the ends 237a, 237b of the compliant valves 212a, 212b that are secured to the inner side wall 240 downwards, towards the bellowed section 224 of the outermost suction cup 204, to open the compliant valve 212a, 212b and ensure a uniform partial vacuum pressure throughout the interiors of the inner- and outermost suction cups 202, 204. This embodiment of the suction cup assembly 200, therefore, also provides the benefit of passively switching between either mode of operation depending on the size and / or position of an item, to either hold the item with only the innermost suction cup 202, if the outermost suction cup 204 is unable to form a seal, or the inner- and outermost suction cups 202, 204, thus increasing the range of items that the suction cup assembly 200 can pick and decreasing its positional sensitivity. Further embodiments also provide similar benefits. Figures 12a and 12b provide cross-sectional views of a suction cup assembly 300 according to yet another embodiment. This embodiment is much like the previous ones insofar that it comprises an innermost suction cup 302 and an outermost suction cup 304 surrounding the innermost suction cup 302 in a concentric arrangement. As before, the suction cup assembly 300 further comprises a shaft 306 having, at one end 307, a screw thread 308 corresponding to a complementary screw thread located at the bottom end of the stem 65 of Figure 7 to fasten the suction cup assembly 300 to the stem 65. An upper end 311 of the innermost suction cup 302 is secured to the other end 309 of the shaft 306 and abuts the underside of a stepped formation 313 in the shaft 306, preventing the innermost suction cup 302 from moving towards the threaded end 307 of the shaft 306. The shaft 306 defines a duct 310 that is arranged to connect the interior of the innermost suction cup 302 to the vacuum source. As with the previous embodiments, this suction cup assembly 300 also comprises a means for controlling airflow 312 between the inner-and outermost suction cups 302, 304 that is operable to permit at least a partial vacuum to form within one of the innermost suction cup 302 or both the inner- and outermost suction cups 302, 304 when the suction cup assembly 300 is connected to the vacuum source. However, in this embodiment, the means for controlling airflow 312 comprises a passageway 315 configured to fluidically connect the interior of the outermost suction cup 304 and the duct 310, and a valve arrangement 317. The passageway 315 comprises a chamber 323, formed within a collar 319 that is connected to the outermost suction cup 304, and one or more radial channels 325 formed within the stem 306. The chamber 323 is fluidically connected to the interior of the outermost suction cup 304 by one or more longitudinal channels 327 also formed with collar 319. The longitudinal channels 327 also form part of the passageway 315 and are circumferentially offset from the radial channels 325 such that no direct connection exists therebetween when the valve arrangement 317 in is a closed position. In general, it is envisaged that the valve arrangement 317 is configured to open or close the passageway 315 based on a relative movement between the inner- and outermost suction cups 302, 304. That is, the valve arrangement 317 is configured to open the passageway 315, allowing airflow through both the inner- and outermost suction cups 302, 304, when one of the inner- or outermost suction cups 302, 304 moves relative to the other of the inner- or outermost suction cups 302, 304 in a first direction and close the passageway 315, allowing air flow through only the innermost suction cup 302, when the one of the inner- or outermost suction cups 302, 304 moves relative to the other of the inner- or outermost suction cups 302, 304 in a second direction, which may be opposite to the first direction but not necessarily so. This embodiment is arranged such that the outermost suction cup 304 moves relative to the innermost suction cup 302, causing the valve arrangement 317 to open and close the passageway 315. Specifically, the valve arrangement 317 comprises the shaft 306 and collar 319. The collar 319 is connected to the outermost suction cup 304 and movably mounted on the shaft 306 to effect movement of the outermost suction cup 304 in the first and second directions along the shaft 306 under the force of an actuator 321. In some embodiments, the actuator 321 is used to move the collar 319 in the first direction, in an opening stroke to open the passageway 315, and a biasing means is used to urge the collar 319 in the opposite direction (i.e. the second direction) in a closing stroke to close the passageway 315. As with the previous embodiments, the inner- and outermost suction cups 302, 304 comprise bellowed sections that allow the suction cup assembly 300 to change volume upon the development of a partial vacuum within the innermost suction cup 302 or the inner- and outermost suction cups 302, 304. Specifically, the inner- and outermost suction cups 302, 304 each comprise one bellowed section 316, 324 forming open ends 317, 319 of respective cups 302, 304. In one mode of operation, as shown in Figure 13a, an item 318 is positioned with respect to the suction cup assembly 300 and / or sized such that the surface 320 being engaged by the suction cup assembly 300 only extends fully across the open end 317 of the innermost suction cup 302, while the open end 345 of outermost suction cup 304 remains open to the atmosphere. In this situation, when the suction cup assembly 300 is connected to the vacuum source, a partial vacuum is formed within the innermost suction cup 302 to hold the item 318 and the volume of the innermost suction cup 302 is reduced through the compression of the bellowed section 316. The bellowed section 316 is configured such that when a partial vacuum is created in the innermost suction cup 302, causing it to compress, the open end 317 of the innermost suction cup 302 is substantially coplanar with the open end 345 of the outermost suction cup 304. This arrangement ensures that both the inner- and outermost suction cups 302, 304 contact the surface 320 even though the item 318 is held by only the innermost suction cup 302. In this situation, the bellowed section 324 of the outermost suction cup 304 provides a function of stabilising the item 318 during its manipulation by damping any movements experienced by the item 318 while it is moved, thus lessening the chances of the innermost suction cup 302 losing its vacuum seal on the surface 320. In another mode of operation, as shown in Figure 13b, the suction cup assembly 300 is positioned such that both open ends 317, 345 of the inner- and outermost suction cups 302, 304 fully engage the surface 320 of the item 318, enabling them both to form a vacuum seal on the surface 320 to hold the item 318. That is, neither of the open ends 317, 345 are exposed to the atmosphere, and so a partial vacuum is established in both suction cups 302, 304 under the force of the vacuum source. This is achieved by moving the collar 319 downwards, as indicated by arrow 340, with respect to the innermost suction cup 302 under the force of the actuator 321, thereby moving the valve arrangement 317 from a closed position to an open position and exposing the interior of the outermost suction cup 304 to the vacuum. In the open configuration, the chamber 323 is brought into longitudinal alignment with the radial channels 325, thereby allowing air to flow from the interior of the outermost suction cup 304 through passageway 315 to the vacuum source as indicated by dashed arrows 380. In this situation, both the bellowed section 316 of the innermost suction cup 302 and the bellowed section 324 of the outermost suction cup 304 compress such that their respective open ends 317, 345 are substantially coplanar.

Claims

1. A suction cup assembly for an end effector of a robotic manipulator, the suction cup assembly comprising:an innermost suction cup;an outermost suction cup surrounding the innermost suction cup;a duct configured to connect the innermost suction cup to a vacuum source; and, means for controlling airflow between the inner- and outermost suction cups, the means for controlling the airflow between the inner- and outermost suction cups being operable to enable a vacuum to form within one of the innermost suction cup or the inner- and outermost suction cups when the suction cup assembly is connected to the vacuum source.

2. A suction cup assembly according to claim 1, wherein the means for controlling the airflow between the inner- and outermost suction cups is passively actuated.

3. A suction cup assembly according to claim 2, wherein the means for controlling the passage of air between the inner- and outermost suction cups comprises a vacuum check valve that, when in a closed position, restricts the airflow from the outermost suction cup to the innermost suction cup.

4. A suction cup assembly according to claim 2, wherein the means for controlling the passage of air between the inner- and outermost suction cups comprises a compliant valve that, when in a closed position, restricts the airflow from the outermost suction cup to the innermost suction cup.

5. A suction cup assembly according to claim 4, wherein the compliant valve is connected to the outermost suction cup and is configured to be actuated from the closed position to an open position as the internal volume of the outermost suction cup reduces.

6. A suction cup assembly according to any one of claims 3 to 5, wherein the innermost suction cup comprises bellowed sections either side of the vacuum check valve or the compliant valve.

7. A suction cup assembly according to any one of claims 3 to 6, wherein the vacuum check valve or the compliant valve is mounted within an opening in the innermost suction cup.

8. A suction cup assembly according to claim 1, wherein the inner- and outermost suction cups are configured to move relative to each other and wherein the means for controlling the airflow between the inner- and outermost suction cups comprises:a passageway configured to fluidically connect the interior of the outermost suction cup and the duct; and,a valve arrangement configured to open the passageway when one of the inner- or outermost suction cups moves relative to the other of the inner- or outermost suction cups in a first direction and close the passageway when the one of the inner- or outermost suction cups moves relative to the other of the inner- or outermost suction cups in a second direction.

9. A suction cup assembly according to claim 8, wherein the valve arrangement comprises: a shaft in which the duct is formed; and,a collar connected to the outermost suction cup, the collar being movably mounted on the shaft to effect movement of the outermost cup in the first and second directions10. A suction cup assembly according to claim 9, wherein the passageway comprises a chamber formed within the collar and one or more radial channels formed within the stem.

11. A suction cup assembly according to any one of claims 8 to 10, further comprising a biasing means for urging the valve arrangement into closing the passageway.

12. A suction cup assembly according to any preceding claim, wherein the respective ends of the inner- and outermost suction cups are offset.

13. A suction cup assembly according to any preceding claim, wherein the innermost suction cup is concentrically arranged with respect to the outermost suction cup.

14. An end effector for a robotic manipulator comprising a suction cup assembly according to any preceding claim.

15. A robotic manipulator comprising an end effector according to claim 14.

16. An automated storage and retrieval system comprising a robotic manipulator according to claim 15.21

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