STORAGE AND REMOVAL SYSTEM FOR CONTAINERS

Description

[0001] The invention relates to a storage and retrieval system for containers, comprising: a grid structure with a plurality of grid cells, each grid cell defining a storage column of a container storage structure arranged below the grid structure, the storage columns each being configured to receive a vertical stack of containers, and the grid structure defining longitudinal transport paths in a longitudinal direction (x) and transverse transport paths in a transverse direction (z), as well as at least one transport vehicle comprising a vehicle body, means for picking up, transporting, and setting down containers stored in the container storage structure, a chassis connected to the vehicle body, the chassis comprising two x-wheel sets configured for movement of the transport vehicle along the longitudinal transport paths of the grid structure, and the chassis comprising two z-wheel sets,which are arranged for movement of the transport vehicle along the transverse transport paths of the lattice structure, and a wheel positioning mechanism arranged to selectively bring either the wheels of the x-wheel sets into contact with the longitudinal transport paths or the z-wheel sets into contact with the transverse transport paths, so as to enable movement of the transport vehicle either in the longitudinal direction or in the transverse direction.

[0002] Storage and retrieval systems for containers of the type in question have been known in practice for several years, particularly in the form of special automated block storage systems. These special warehouses were developed to improve conventional warehouses, particularly with regard to achievable storage density. In conventional warehouses, the goods are usually located in storage containers, which are stored on shelves arranged in rows of shelves. Each storage container contains a large number of products of one product type. Such a warehouse is served via open spaces between the rows of shelves, the so-called storage aisles, in which the individual shelf compartments can be accessed by means of a transport system, e.g., a storage and retrieval machine or a shuttle system. Since the storage aisles are not available for actual storage, the storage density of such warehouses is relatively low.In other words, the size of the space actually available for storing products is relatively small compared to the size of the space required for the warehouse as a whole.

[0003] In contrast, the automated block storage systems (so-called grid stores) mentioned above pursue an alternative approach. Instead of storing the storage containers in conventional racks, they are stacked on top of each other in a self-supporting modular aluminum grid that forms vertical shafts of defined sizes. The stacks are arranged in rows in a longitudinal and transverse direction. The individual storage containers are accessed from above using suitable transport vehicles, which typically move on corresponding rails arranged in a 2D matrix on the rack structure. Accordingly, no storage aisles are required between the rows, which is why this storage structure offers a significant improvement in storage density.Such automated block storage systems, which form one of the main fields of application for transport vehicles according to embodiments of the present invention, are also sometimes known under the designation AutoStore ®<.

[0004] WO 2017 / 153583 A1 shows such a storage system together with a corresponding transport vehicle. The transport vehicle, which comprises a central, downwardly opening cavity for accommodating transported goods in the form of standardized storage containers, has two wheelsets, each with four wheels. One of the wheelsets is designed for movement of the transport vehicle on a grid-like rail structure in a longitudinal direction (x), and the other wheelset is designed for movement in a transverse direction (y) orthogonal thereto.

[0005] To change direction, the wheel sets can be moved vertically to be lifted off the rail structure or lowered onto it. Specifically, a wheel positioning mechanism with at least two motors is provided for this purpose. One motor moves the two wheels of a first wheelset arranged on one side wall of the vehicle body, while the other motor moves the two wheels of the same wheelset arranged on the opposite side wall of the vehicle body. The wheels of the second wheelset are either permanently mounted to the vehicle body or also have a wheel positioning mechanism with two motors, which functions in a similar way to the wheel positioning mechanism for the first wheelset and is suitably synchronized with it.

[0006] The transport vehicle known from WO 2017 / 153583 A1 proves to be disadvantageous in that the mechanics of the wheel positioning mechanism must always be adapted to the respective size of the transport vehicle body in order to achieve optimal driving characteristics. If the wheel positioning mechanism, as shown in WO 2017 / 153583 A1 for a specific vehicle size, were to be installed 1:1 on a (significantly) larger transport vehicle, for example, this would result in unfavorably small wheelbases for this larger transport vehicle, which could, for example, lead to critical tipping of the transport vehicle during dynamic acceleration. Mounting the wheel positioning mechanism shown in WO 2017 / 153583 A1 on a (significantly) smaller transport vehicle is even impossible. Accordingly, each vehicle size requires a specially adapted and appropriately dimensioned wheel positioning mechanism.

[0007] WO 2013 / 167907 A1 and WO 2016 / 172793 A1 each disclose a storage and retrieval system for containers comprising a number of transport vehicles. The transport vehicles each comprise a vehicle body and a chassis connected to the vehicle body, wherein the chassis comprises two first wheel sets for movement of the transport vehicle in a first direction and two second wheel sets for movement in a second direction orthogonal to the first direction. A wheel positioning mechanism acts on corresponding wheel sets, i.e., jointly on direction-specific wheels. WO 2013 / 167907 A1 discloses the features of the preamble of claim 1.

[0008] CN 202 988 038 U discloses a vehicle designed for traveling on tracks, comprising a vehicle body and a running gear connected to the vehicle body, the running gear comprising two first wheel sets for moving the transport vehicle in a first direction and two second wheel sets for moving it in a second direction orthogonal to the first direction. The vehicle also comprises a wheel positioning mechanism driven by a lifting motor, the drive acting exclusively on adjacent or opposite wheels (i.e., the wheels of the wheel sets designed for a specific direction of travel).

[0009] CN 206 088 191 U also shows a vehicle with a vehicle body and a chassis connected to the vehicle body, the chassis comprising two first wheel sets for moving the transport vehicle in a first direction and two second wheel sets for moving the vehicle in a second direction orthogonal to the first direction. The vehicle also comprises a motor-driven wheel positioning mechanism, the drive acting jointly on two wheels arranged diagonally adjacent to each other in the manner of a rocker.

[0010] US 2017 / 334643 A1 discloses a vehicle with a vehicle body and a chassis connected to the vehicle body. The chassis comprises two first wheel sets for moving the transport vehicle in an x-direction and two second wheel sets for moving the vehicle in a y-direction orthogonal to the x-direction. A wheel positioning mechanism acts on corresponding wheel sets, i.e., jointly on direction-specific wheels.

[0011] The present invention is therefore based on the object of designing and developing a storage and removal system of the type mentioned at the outset in such a way that the above-mentioned disadvantages are avoided as far as possible and a largely problem-free adaptation of the wheel positioning mechanism to different vehicle sizes is possible.

[0012] According to the invention, the above object is achieved by the features of claim 1.

[0013] Advantageous embodiments of the teaching according to the invention are specified in the dependent claims.

[0014] According to the invention, it has been recognized that various advantages can be achieved by coupling adjacent wheels of a transport vehicle that are diagonally adjacent to one another in such a way that a drive means of a wheel positioning mechanism acts jointly on these two wheels. In particular, this results in simplified scalability of the transport vehicle for different vehicle sizes. The entire mechanics of the wheel positioning mechanism for raising or lowering the wheels of the transport vehicle in the transport vehicle proposed according to the invention are completely independent of the respective dimensions of the vehicle body of the transport vehicle. Accordingly, predominantly identical parts can be used - regardless of size - which results in problem-free mechanical adjustment of the wheelbase of the transport vehicle.For transport vehicles according to the invention, a maximum possible wheelbase can almost always be realized, which effectively counteracts tipping of the transport vehicle during dynamic acceleration.

[0015] In a preferred embodiment, each wheel set of the transport vehicle comprises two wheels arranged at a distance from one another on a respective side wall of the vehicle body. In this case, all wheels of the transport vehicle form corresponding wheel pairs, each with a wheel of an x-wheel set and a wheel of a z-wheel set adjacent to it at an angle, and can accordingly be moved by a wheel positioning mechanism with a total of four drive means. Alternatively, it is also conceivable for one or more of the wheel sets to comprise an additional, substantially centrally positioned third wheel, which can prove particularly useful in larger transport vehicles, for example, from a stability perspective. A separate wheel positioning mechanism could be provided for this additional wheel.

[0016] Advantageously, the drive means of the wheel positioning mechanism are configured to raise one wheel of the respective wheel pair and simultaneously lower the other wheel of the respective wheel pair. This allows for a particularly rapid wheel change to change the direction of movement of the transport vehicle.

[0017] In a further advantageous manner, the drive means of the wheel positioning mechanism are synchronized with each other, so that a position change (i.e., raising or lowering) for all wheels of the transport vehicle occurs simultaneously. According to an alternative embodiment, only the two wheels of a respective wheel pair can be permanently synchronized, while the individual drive means of the wheel positioning mechanism are not synchronized with each other but operate independently of one another.

[0018] Within the scope of a preferred embodiment, the wheels on the vehicle body of the transport vehicle can be arranged in such a way that, during a wheel change effected by the wheel positioning mechanism, uninterrupted contact of the wheels with the respective transport paths is ensured. In other words, for example, when the wheels of the x-wheel sets are lifted from the longitudinal transport paths, the wheels of the z-wheel sets touch down on the transverse transport paths before the actual vehicle body of the transport vehicle comes into contact with the ground. An alternative embodiment, in which the vehicle body briefly touches down during a wheel change, can in principle also be realized, for example by means of a higher wheel suspension on the vehicle body.

[0019] To ensure the simplest possible design of the wheel positioning mechanism, the drive means can act in opposite directions on the two wheels of the respective wheel pair. In specific embodiments, the drive means can comprise, for example, linear motors, electromagnetic actuators, worm gears, threaded spindles, cam discs, linkages, and / or the like.

[0020] According to a specific embodiment, the wheel positioning mechanism can have a screw drive for each wheel coupled to the respective drive means, wherein the screw drive could be part of a linear guide. Advantageously, the screw drive can be coupled to the respective drive means by means of a belt drive, a rack and pinion, a toothed chain, or the like. According to a preferred embodiment, the screw drives assigned to the wheels of a wheel pair operate in opposite directions, so as to raise one wheel of the wheel pair while lowering the other wheel of the wheel pair. Alternatively, the counter-rotation of the wheels could also be achieved by coupling the respective screw drives to the drive means in opposite directions, while the screw drives themselves operate in the same direction.

[0021] In a preferred embodiment, the drive means are coupled to the respective wheel via a toggle lever mechanism, which preferably engages directly on the respective side wall of the vehicle body. A toggle lever mechanism offers the advantage of a non-linear force curve with very low load when raised. Furthermore, the mechanism can be implemented with a very narrow design. With regard to the coordinated lifting and lowering movement of the individual wheels that predominates when changing wheel sets, the toggle lever mechanism, thanks to its non-linear transmission ratio, offers the possibility of translating a constant drive force into the required lifting force on the chassis, which depends on the current chassis position.Furthermore, the non-linear force curve reduces the required power of the drive means, which enables the use of space-saving drives and consequently supports the realization of a narrow structure.

[0022] The storage and retrieval system for containers according to the invention, which has at least one transport vehicle, comprises a grid structure with a plurality of grid cells, each grid cell defining a storage column of a container storage structure arranged below the grid structure, the storage columns each being configured to accommodate a vertical stack of containers. The grid structure defines the longitudinal transport paths for movement of the transport vehicle in a longitudinal direction (x) and the transverse transport paths for movement of the transport vehicle in a transverse direction (z).

[0023] The transport vehicle comprises means for picking up, transporting, and setting down containers stored in the container storage structure. According to a specific embodiment, the transport vehicle can have a suitable load-handling device inside the vehicle body, with which a container can be transported into a cavity formed, for example, inside the vehicle body.

[0024] In a further advantageous manner, the wheel sets and the wheel positioning mechanism, including the drive means, are designed such that the overall construction has a structural depth in a direction orthogonal to the respective side wall of 100 mm or less, particularly preferably 40 mm or less. This would result in a transport vehicle that could be used in particular in standardized variants of KLT (small load carrier) systems, and which, with the transport vehicle positioned centrally above a storage column, could be passed by other transport vehicles on all sides.

[0025] There are now various possibilities for advantageously embodying and developing the teaching of the present invention. Reference is made, on the one hand, to the dependent claims and, on the other hand, to the following explanation of preferred embodiments of the invention with reference to the drawings. In conjunction with the explanation of the preferred embodiments of the invention with reference to the drawings, preferred embodiments and developments of the teaching are also explained in general. The drawings show: Fig. 1 in a schematic perspective view a transport vehicle of a storage and retrieval system according to an embodiment of the invention, Fig. 2 in a schematic perspective view a wheel positioning mechanism of the transport vehicle according to Fig. 1 in an enlarged view, Fig. 3 in a schematic side view the transport vehicle according to Fig. 1with a positioning of the wheel sets for a movement of the transport vehicle in a longitudinal direction (x), Fig. 4 in a schematic side view the transport vehicle according to Fig. 1 with a positioning of the wheel sets in a wheel changing position, Fig. 5 in a schematic side view the transport vehicle according to Fig. 1 with a positioning of the wheel sets for a movement of the transport vehicle in a transverse direction (z), Fig. 6 in a schematic plan view a lattice structure of a storage and removal system for containers suitable for use with a transport vehicle according to an embodiment of the invention, and Fig. 7 in a schematic sectional view a transport vehicle of a storage and removal system according to an embodiment of the invention.

[0026] Fig. 1shows a schematic perspective view of a transport vehicle of a storage and retrieval system according to an embodiment of the invention. Fig. 2 shows the Fig. 1 marked section 'A' in an enlarged view.

[0027] The transport vehicle comprises a vehicle body 1 and a chassis connected to the vehicle body 1. The chassis comprises two x-wheel sets 2, 2', which are configured for movement of the transport vehicle along longitudinal transport paths in a longitudinal direction x, and two z-wheel sets 3, 3', which are configured for movement of the transport vehicle along transverse transport paths in a transverse direction z. In the perspective view of Fig. 1 only the front wheel sets 2, 3 are visible, while the corresponding wheel sets 2', 3' arranged on the opposite sides of the vehicle body 1 are hidden by the vehicle body 1.

[0028] Furthermore, the transport vehicle comprises a wheel positioning mechanism which is configured to effect suitable height movements of the wheels of the x-wheel sets 2, 2' and the z-wheel sets 3, 3' in the y-direction such that for a movement of the transport vehicle in the longitudinal direction x only the wheels of the x-wheel sets 2, 2' are lowered and in contact with the respective track, while the wheels of the z-wheel sets 2, 2' are raised and not in contact with the respective track, and vice versa.

[0029] According to the invention, the wheel positioning mechanism comprises drive means 4, which each act jointly on the wheels of a wheel pair. A wheel pair comprises a wheel of an x-wheel set 2, 2' and a wheel of a z-wheel set 3, 3' adjacent thereto at an angle. In the illustrated embodiment, each wheel set comprises two wheels 2a, 2b, 3a, 3b, which are assigned in pairs at an angle to a drive means 4. For example, the Fig. 2 The drive means 4, shown enlarged, acts on the wheel 2a of the x-wheel set 2 and simultaneously on the wheel 3b of the z-wheel set 3, which is adjacent at a corner. In other words, two wheels which are adjacent at a corner are each moved together by one drive means 4.

[0030] In the illustrated embodiment, the drive means 4 each comprise a motor 5, which is preferably arranged symmetrically and is accordingly positioned on or at the edge of the adjacent side walls 6 of the rectangular or substantially rectangular vehicle body 1. The motor 5 is coupled via a belt drive 7 to linear guides 8 mounted on the respective side walls 6. In a specific embodiment, the drive means 4 each comprise a lifting carriage 9, which can be moved by means of a spindle device 10 along the vertically aligned linear guide 8 between an upper and a lower stop block 11, 11'.

[0031] A pressure lever 12 is pivotally connected to each lifting carriage 9. The pressure lever 12 is part of a toggle lever mechanism, with an upper toggle lever 13 and a lower toggle lever 14 being pivotally connected to the end of the pressure lever 12 facing away from the lifting carriage 9. The end of the lower toggle lever 14 facing away from the pressure lever 12 is pivotally connected to a suspension of the respective wheel 2a, 2b, 3a, 3b, while the end of the upper toggle lever 13 facing away from the pressure lever 12 is pivotally fixed to the respective side wall 6 of the vehicle body 1. Both the pressure levers 12 and the toggle levers 13, 14 are preferably made of plastic or as flat aluminum profiles.

[0032] In the illustrated embodiment, the spindle devices 10 assigned to the respective wheels of a wheel pair are designed to rotate in opposite directions. When the motor 5 is activated to implement a wheel change, the lifting carriage 9 assigned to one wheel of the wheel pair moves upwards on the associated spindle device 10, while the lifting carriage 9 assigned to the other wheel of the wheel pair moves downwards on the associated spindle device 10.

[0033] As the lifting carriage 9 moves upward on the spindle device 10, the pressure lever 12 becomes increasingly inclined, causing the common pivot point of the lower toggle lever 14 and the upper toggle lever 13 on the pressure lever 12 to move toward the spindle device 10, i.e., the knee formed by the lower and upper toggle levers 14, 13 is bent. Consequently, the distance in the vertical direction between the lower pivot point of the lower toggle lever 14 on the wheel suspension and the upper pivot point of the upper toggle lever 13, which is fixed relative to the vehicle body 1, decreases, and the corresponding wheel is raised. The lowering of the other wheel of the wheel pair occurs in a correspondingly reverse manner.

[0034] The Figs. 3, 4 and 5 show a sequence of a wheel change in a transport vehicle according to an embodiment of the invention. In the illustration according to Fig. 3the wheels of the x-wheel sets 2, 2' are fully raised (i.e., the corresponding lifting carriages 9 of the drives 4 shown in the front view are in the upper stop position) and the wheels of the z-wheel sets 3, 3' are fully lowered (i.e., the corresponding lifting carriages 9 of the drives 4 shown in the side view are in the lower stop position). Accordingly, the transport vehicle is configured for movement in the transverse direction z (i.e., orthogonal to the plane of the drawing).

[0035] Fig. 4shows the situation during a wheel change process in order to change from the movement of the transport vehicle in the transverse direction z to a movement in the longitudinal direction x. For this purpose, the motors 5 of all four drive means 4 are actuated in such a way that the wheels of the x-wheel sets 2, 2' are lowered, whereby the wheels of the z-wheel sets 3, 3' are lowered simultaneously due to the pairwise coupling of wheels at an angle and the counter-rotating spindle devices 10. In the Fig. 4 In the situation shown, all lifting carriages 9 are in a central position and the transport vehicle stands on both the wheels of the x-wheel sets 2, 2' and the wheels of the z-wheel sets 3, 3'.

[0036] Fig. 5shows the situation after completion of the wheel changing process. The wheels of the z-wheel sets 3, 3' are now fully raised (i.e., the corresponding lifting carriages 9 of the drives 4 shown in the side view are in the upper stop position) and the wheels of the x-wheel sets 2, 2' are fully lowered (i.e., the corresponding lifting carriages 9 of the drives 4 shown in the front view are in the lower stop position). Accordingly, the transport vehicle is configured for movement in the transverse direction x.

[0037] Fig. 6schematically shows the use of a transport vehicle according to the invention in a storage and retrieval system for containers 16 designed as a block storage 15. The block storage 15 comprises, as its upper end, a grid structure designed as a rail grid 17, which defines the longitudinal transport paths in the x-direction and the transverse transport paths in the y-direction for the transport vehicle(s). The rail grid 17 is accordingly coordinated in the sense of a checkerboard pattern with the respective block storage 15 to be served from above. In this variant of a warehouse, storage containers 16 are stacked on top of one another, and a very high degree of space utilization is achieved compared to other automated storage variants.In order to achieve the highest possible performance, the checkerboard pattern on the block storage 15 is designed in such a way that the use of the largest possible number of transport vehicles according to embodiments of the invention is possible and that these can operate directly next to one another in the block storage 15 at the same time.

[0038] The transport vehicle according to Fig. 6is dimensioned such that it occupies only a single grid space of the grid structure, i.e. in other words, when in a central position above a storage column, it can be passed on all sides by other transport vehicles. Such a dimensioning can be achieved by components of the wheel positioning mechanism and the wheels themselves that are correspondingly narrow in construction. It should be noted, however, that the present invention is not limited to such a dimensioning of the transport vehicles, rather the transport vehicle can be dimensioned almost arbitrarily. Although this can result in a restricted freedom of movement of the individual transport vehicles when using a large number of transport vehicles on the grid structure, a larger dimensioning of the transport vehicles (all or only some of the transport vehicles used) may be desirable in certain situations, for exampleto be able to accommodate and transport more than one storage container 16 per transport vehicle.

[0039] Fig. 7shows, by way of example, a transport vehicle of a storage and retrieval system according to an exemplary embodiment of the invention in a sectional view. The transport vehicle comprises a load-handling device 18 arranged inside the vehicle body 1 for removing a container 16 from the block storage area 15 which is to be served from above. For example, a mechanism can be provided which is tailored to the possibly selected KLT variant and which can reliably transport the containers 16 upwards from a depth of, for example, up to 9 m. Furthermore, a robust connection is provided between the load-handling device 18 and the container 16, which connection is space-saving on the one hand and can be quickly fixed and released on the other. In order to minimize costs, the interface design between the load-handling device 18 and the load carrier orFor the container 16, it is provided that the more cost-intensive components and assemblies are installed in the load-handling device 18, and the interface on the container 16 is kept as simple as possible, so that standardized small load carriers can be used. This takes into account that the number of containers 16 can significantly exceed the number of transport vehicles and thus also the number of load-handling devices 18. Furthermore, a cavity 19 is formed inside the vehicle body 1, in which a container 16 can be accommodated by the transport vehicle during transport.

[0040] The energy supply of the transport vehicle is preferably based on an on-board energy source.

[0041] With regard to further advantageous embodiments of the device according to the invention, reference is made to the general part of the description and to the appended claims in order to avoid repetition.

[0042] Finally, it should be expressly pointed out that the embodiments of the device according to the invention described above serve only to explain the claimed teaching, but do not limit it to the embodiments. List of reference symbols

[0043] 1Vehicle body 2, 2'x-wheel sets 2a, 2bx wheels 3, 3'z-wheel sets 3a, 3bz-wheels 4Drive mechanism 5Motor 6Side wall 7Belt drive 8Linear guide 9Lifting carriage 10Spindle device 11, 11'Upper / lower stop block 12Pressure lever 13Upper toggle lever 14Lower toggle lever 15Block bearing 16Container 17Rail grid 18Load handling device 19Cavity

Claims

1. Storage and retrieval system for containers comprising: a grid structure having a large number of grid cells, wherein each grid cell defines a storage column of a container storage structure which is arranged below the grid structure, wherein the storage columns are configured to each receive a vertical stack of containers (16), and wherein the grid structure defines longitudinal transport paths in a longitudinal direction (x) and transverse transport paths in a transverse direction (z), and at least one transport vehicle comprising a vehicle body (1), means for receiving, transporting and depositing containers (16) which are stored in the container storage structure, a chassis which is connected to the vehicle body (1), wherein the chassis comprises two x wheel sets (2, 2') which are configured for movement of the transport vehicle along longitudinal transport paths in a longitudinal direction (x), and wherein the chassis comprises two z wheel sets (3, 3') which are configured for movement of the transport vehicle along transverse transport paths in a transverse direction (z), and a wheel positioning mechanism which is configured to selectively bring either the wheels of the x wheel sets (2, 2') into contact with the longitudinal transport paths or the z wheel sets (3, 3') into contact with the transverse transport paths in order to thus enable a movement of the transport vehicle either in the longitudinal direction or in the transverse direction, characterised in that the wheel positioning mechanism has four drive means (4) each having a motor (5), wherein the drive means (4) together act in each case on the wheels of a wheel pair, wherein a wheel pair in each case comprises a wheel of an x wheel set (2, 2') and a wheel of a z wheel set (3, 3') which is diagonally adjacent thereto, wherein a wheel set (2, 2'; 3, 3') comprises two wheels (2a, 2b, 2'a, 2'b; 3a, 3b, 3'a, 3'b) which are arranged adjacent to each other on a respective side wall (6) of the vehicle body (1).

2. Storage and retrieval system according to claim 1, characterised in that the drive means (4) of the wheel positioning mechanism are configured to raise a wheel of the respective wheel pair and at the same time to lower the other wheel of the respective wheel pair.

3. Storage and retrieval system according to claim 1 or 2, characterised in that the drive means (4) of the wheel positioning mechanism are synchronised with each other.

4. Storage and retrieval system according to any one of claims 1 to 3, characterised in that the wheels (2a, 2b, 2'a, 2'b; 3a, 3b, 3'a, 3'b) are arranged on the vehicle body (1) in such a manner that during a wheel change which is brought about by the wheel positioning mechanism an uninterrupted contact of wheels with the respective transport paths is provided.

5. Storage and retrieval system according to any one of claims 1 to 4, characterised in that the drive means (4) of the wheel positioning mechanism in each case act in opposing directions on the two wheels of the respective wheel pair.

6. Storage and retrieval system according to any one of claims 1 to 5, characterised in that the wheel positioning mechanism has per wheel a screw drive which is coupled to the respective drive means (4).

7. Storage and retrieval system according to claim 6, characterised in that the screw drive is coupled to the respective drive means (4) by means of a belt drive (7), a toothed rack, a toothed chain or the like.

8. Storage and retrieval system according to claim 6 or 7, characterised in that the screw drives which are associated with the wheels of a wheel pair work in opposing directions.

9. Storage and retrieval system according to any one of claims 1 to 8, characterised in that the drive means (4) are coupled to the respective wheel by means of a knee lever mechanism.

10. Storage and retrieval system according to any one of claims 1 to 9, characterised in that the chassis together with the wheel positioning mechanism has a structural depth in a direction which is orthogonal with respect to a respective side wall (6) of the vehicle body (1) of less than 100 mm, preferably of 40 mm or less.