Container handling vehicle

Abstract

The present invention provides a container handling vehicle (501) for travel on a rail system (108), the rail system comprising a first set of parallel rails (110) and a second set of parallel rails (111) arranged at right angles to the first set of rails (110), the container handling vehicle comprising a first set of wheels and a second set of wheels for travel on the rail system in two perpendicular directions. In one embodiment, the first set of wheels are arranged to be movable in a direction perpendicular to the rest of the vehicle frame (Z) between an upper position in which the second set of wheels allows travel of the vehicle (501) along a second direction (X) and a lower position in which the first set of wheels allows travel of the vehicle (501) along a first direction (Y).

Description

[Technical field]

[0001] The present invention relates to a container handling vehicle for travel in two perpendicular directions on a horizontal grid-based rail system. [Background technology]

[0002] FIG. 1 discloses a prior art automated storage and retrieval system 1 having a framework structure 100, and FIGS. 2, 3 and 4 disclose three different prior art container handling vehicles 201, 301, 401 suitable for operating on such a system 1.

[0003] The framework structure 100 comprises upright members 102 and a storage volume comprising storage columns 105 arranged in rows between the upright members 102. In these storage columns 105, storage containers 106, also known as bins, are stacked on top of each other to form stacks 107. The upright members 102 may typically be made of metal, for example extruded aluminum profiles.

[0004] The framework structure 100 of the automated storage and retrieval system 1 includes a horizontal grid-based rail system 108 (i.e., rail grid) disposed across the top of the framework structure 100. A plurality of container handling vehicles 201, 301, 401 may be operated on the rail system 108 to raise the storage containers 106 from the storage columns 105, lower the storage containers 106 into the storage columns, and also transport the storage containers 106 up the storage columns 105. The rail system 108 includes a first set of parallel rails 110 disposed to guide the movement of the container handling vehicles 201, 301, 401 in a second direction X across the top of the framework structure 100, and a second set of parallel rails 111 disposed at right angles to the first set of rails 110 to guide the movement of the container handling vehicles 201, 301, 401 in a first direction Y perpendicular to the first direction Y. The containers 106 stored in the columns 105 are accessed by the container handling vehicles 201, 301, 401 through access openings 112 in the rail system 108. The container handling vehicles 201, 301, 401 can move laterally above the storage columns 105, i.e. in a plane parallel to the horizontal XY plane.

[0005] The uprights 102 of the framework structure 100 may be used to guide the storage containers during ascent from and descent into the column 105 of containers 106. The stack 107 of containers 106 is typically freestanding.

[0006] Each prior art container handling vehicle 201, 301, 401 comprises a body 201a, 301a, 401a and first and second sets of wheels 201b, 201c, 301b, 301c, 401b, 401c that allow lateral movement of the container handling vehicle 201, 301, 401 in the X and Y directions. In Figures 2, 3 and 4 two wheels of each set are fully visible. The first set of wheels 201c, 301b, 401c are arranged to engage two adjacent rails of the first set 110 of rails and the second set of wheels 201b, 301c, 401c are arranged to engage two adjacent rails of the second set 111 of rails. At least one of the sets of wheels 201b, 301b, 201c, 301c, 401b, 401c can be raised or lowered so that the first set of wheels 201c, 301b, 401b and / or the second set of wheels 201b, 301c, 401c can be engaged or disengaged with the respective sets of rails 110, 111.

[0007] Each prior art container handling vehicle 201, 301, 401 also comprises a lifting device 404 (i.e., a container lifting device) (see FIG. 4) for vertical transportation of the storage containers 106 (e.g., for raising the storage containers 106 from the storage columns 105 and lowering the storage containers 106 into the storage columns). The lifting device 404 features a lifting frame 2 comprising a container connector 3 and a guide pin 4 adapted to engage the storage containers 106. The lifting frame 2 can be lowered from the vehicle 201, 301, 401 so that the position of the lifting frame 2 relative to the vehicle 201, 301, 401 can be adjusted in a third direction Z perpendicular to the first direction Y and the second direction X. The lifting device of the container handling vehicle 201 is located in the vehicle body 201a in FIG. 2.

[0008] To raise and lower the lifting frame 2 (and optionally the connected storage containers 106), the lifting frame 2 is suspended from a band drive assembly by lifting bands 5. In the band drive assembly, the lifting bands are typically wound / unwound on at least one rotating lifting shaft or reel arranged on the container handling vehicle. Various designs of band drive assemblies are described, for example, in WO 2015 / 193278, WO 2017 / 129384 and WO 2019 / 206438.

[0009] Conventionally, and for purposes of this application, Z=1 identifies the top layer for storing storage containers below the rail system 108, i.e., the layer immediately below the rail system 108, Z=2 identifies the second layer below the rail system 108, Z=3 identifies the third layer, and so on. In the exemplary prior art disclosed in FIG. 1, Z=8 identifies the bottom layer, the lowest layer of storage containers. Similarly, X=1···n and Y=1···n identify the location of each storage column 105 in the horizontal plane. Thus, by way of example, using the Cartesian coordinate system X, Y, Z shown in FIG. 1, the storage container identified as 106′ in FIG. 1 can be said to occupy storage position X=17, Y=1, Z=6. The container handling vehicles 201, 301, 401 can be said to travel in layer Z=0, and each storage column 105 can be identified by its X and Y coordinates. Thus, the storage containers shown in FIG. 1 extending above the rail system 108 are also said to be located at layer Z=0.

[0010] The storage volume of the framework structure 100 is often referred to as a grid 104, and the possible storage locations within this grid are referred to as storage cells. Each storage column may be identified by a location in the X and Y directions, while each storage cell may be identified by a container number in the X, Y and Z directions.

[0011] Each prior art container handling vehicle 201, 301, 401 includes a storage compartment or space for receiving and housing the storage containers 106 as they are transported across the rail system 108. The storage space may include a cavity disposed internally within the vehicle body 201a, as shown in Figures 2 and 4 and described, for example, in WO 2015 / 193278 and WO 2019 / 206487, the contents of which are incorporated herein by reference.

[0012] Figure 3 shows an alternative form of container handling vehicle 301 with a cantilever configuration. Such a vehicle is described in detail, for example, in Norwegian Patent No. 317366, the contents of which are also incorporated herein by reference.

[0013] 2 may have a footprint covering an area having dimensions in the X and Y directions approximately equal to the lateral extent of the storage column 105, for example as described in WO 2015 / 193278, the contents of which are incorporated herein by reference. As used herein, the term "lateral" may mean "horizontal."

[0014] Alternatively, the cavity container handling vehicle 401 may have a footprint larger than the lateral area defined by the storage column 105 as shown in Figures 1 and 4, for example as disclosed in WO 2014 / 090684 (Patent Document 2) or WO 2019 / 206487.

[0015] The rail system 108 typically includes rails with grooves along which the vehicle wheels run. Alternatively, the rails may include upwardly projecting elements, and the vehicle wheels may include flanges to prevent derailment. These grooves and upwardly projecting elements are collectively known as tracks. Each rail may include one track, each rail may include two parallel tracks, or the rail system may include one track rail in one direction and two track rails in the other. Each rail may include a pair of track members, each track member provided with a single track, and the pair of track members fastened together to provide the rail in a given direction.

[0016] WO 2018 / 146304, the contents of which are incorporated herein by reference, shows an exemplary form of rail system 108, which comprises rails and parallel tracks in both the X and Y directions, which form a rail grid.

[0017] In the framework 100, most columns 105 are storage columns 105, i.e. columns 105 where storage containers 106 are stored in stacks 107. However, some columns 105 may have other purposes. In FIG. 1, columns 119 and 120 are such dedicated columns used by container handling vehicles 201, 301, 401 to drop off and / or pick up storage containers 106 so that they can be transported to access stations (not shown) where they can be accessed from outside the framework 100 or transferred to the outside or inside of the framework 100. In the art, such locations are usually called "ports" and the columns where the ports are located can be called "port columns" 119, 120. The transport to the access stations can be in any direction, i.e. horizontal, inclined and / or vertical. For example, storage containers 106 may be placed in random or dedicated columns 105 within the framework structure 100 and then picked up by any container handling vehicle and transported to port columns 119, 120 for further transport to an access station. Note that the term "inclined" refers to the transportation of storage containers 106 having a general transport direction somewhere between horizontal and vertical.

[0018] In FIG. 1 , the first port column 119 may, for example, be a dedicated drop-off port column where container handling vehicles 201, 301, 401 can drop off storage containers 106 to be transported to an access station or transfer station, and the second port column 120 may be a dedicated pick-up port column where container handling vehicles 201, 301, 401 can pick up storage containers 106 transported from an access station or transfer station.

[0019] An access station may typically be a picking or stocking station where product items are removed from or placed into the storage containers 106. At a picking or stocking station, the storage containers 106 are typically not removed from the automated storage and retrieval system 1 but are returned to the framework 100 again once accessed. A port may also be used to transfer storage containers to another storage facility (e.g., to another framework or to another automated storage and retrieval system), to a transport vehicle (e.g., a train or truck), or to a production facility.

[0020] A conveyor system comprising conveyors is typically used to transport the storage containers between the port columns 119, 120 and the access stations.

[0021] If the port columns 119, 120 and the access stations are located at different levels, the conveyor system may include a lifting device with a vertical component for vertically transporting the storage containers 106 between the port columns 119, 120 and the access stations.

[0022] A conveyor system may be arranged to transport the storage containers 106 between the different framework structures, for example as described in WO 2014 / 075937, the contents of which are incorporated herein by reference.

[0023] When a storage container 106 stored in one of the storage columns 105 disclosed in FIG. 1 is to be accessed, one of the container handling vehicles 201, 301, 401 is directed to retrieve the target storage container 106 from its location and transport it to the drop-off port column 119. This operation involves moving the container handling vehicle 201, 301, 401 to a position above the storage column 105 where the target storage container 106′ is located, using the lifting device 404 of the container handling vehicle 201, 301, 401 to retrieve the storage container 106 from the storage column 105, and transporting the storage container 106 to the drop-off port column 119. When the target storage container 106 is located deep within the stack 107, i.e., when one or more other storage containers 106 are positioned above the target storage container 106, the operation also involves temporarily moving the storage container positioned above before lifting the target storage container 106 out of the storage column 105. This step, sometimes referred to in the art as "digging," may be performed using the same container handling vehicle that is subsequently used to transport the target storage container to the drop-off port column 119, or using one or more other cooperating container handling vehicles. Alternatively, or in addition, the automated storage and retrieval system 1 may have container handling vehicles 201, 301, 401 dedicated to the task of temporarily removing the storage container 106 from the storage column 105. Once the target storage container 106 has been removed from the storage column 105, the temporarily removed storage container 106 may be repositioned back to the original storage column 105. However, the removed storage container 106 may alternatively be relocated to another storage column 105.

[0024] When a storage container 106 is to be stored in one of the columns 105, one of the container handling vehicles 201, 301, 401 is directed to pick up the storage container 106 from the pickup port column 120 and transport the storage container 106 to a position above the storage column 105 where the storage container is to be stored. After any storage container 106 positioned at or above the target position in the stack 107 is removed, the container handling vehicle 201, 301, 401 positions the storage container 106 in the desired position. The removed storage container 106 may then be lowered and placed back into the storage column 105 or transferred to another storage column 105.

[0025] To monitor and control the automated storage and retrieval system 1, e.g., to monitor and control the position of each storage container 106 within the framework structure 100, the contents of each storage container 106, and the movements of the container handling vehicles 201, 301, 401 so that the container handling vehicles 201, 301, 401 can deliver the desired storage containers 106 to the desired locations at the desired times without colliding with each other, the automated storage and retrieval system 1 includes a control system 500, which is typically computerized and typically includes a database for maintaining the trajectories of the storage containers 106.

[0026] The prior art container handling vehicles 201, 401 shown in Figures 2 and 4 have several advantageous properties in view of the cantilevered vehicle 301. The properties include the guide / support given to the storage containers housed within the cavity, and the possibility of lifting highly loaded storage containers without increasing the weight of the vehicle to counterbalance the weight of the storage containers. Both properties entail that the vehicle may have increased acceleration / deceleration relative to the cantilevered vehicle 301. However, due to the instability caused by both vehicles 201, 401 having substantially all drive and lifting components located above the cavity for housing the storage containers, the potential increase in acceleration / deceleration is not fully realized. [Prior art documents] [Patent documents]

[0027] [Patent Document 1] International Publication No. 2015 / 193278 [Patent Document 2] International Publication No. 2014 / 090684 Summary of the Invention [Means for solving the problem]

[0028] The invention is defined by the appended claims and the following.

[0029] In a first aspect, the present invention provides a container handling vehicle for travel on a rail system comprising a first set of parallel rails and a second set of parallel rails arranged at right angles to the first set of rails, the container handling vehicle comprising: a vehicle frame defining a first section and a second section of a container handling vehicle, the first section and the second section being arranged side-by-side, the first section comprising a lifting device for lifting a storage container and providing a cavity in which the storage container being lifted may be accommodated; a first set of wheels comprising a first pair of wheels and a second pair of wheels, the first and second pairs of wheels being located on opposite portions of a first section, the first set of wheels enabling movement of the vehicle along a first direction on the rail system in use; a second set of wheels comprising a third pair of wheels and a fourth pair of wheels, the third pair of wheels and the fourth pair of wheels being disposed on opposite sides of the vehicle, each of the sides extending from one edge of the first section to one edge of the second section, and enabling, in use, movement of the vehicle along a second direction on the rail system, the second direction being perpendicular to the first direction; Equipped with the first set of wheels are positioned so as to be vertically movable relative to the vehicle frame between an upper position in which the second set of wheels permits movement of the vehicle along a second direction and a lower position in which the first set of wheels permits movement of the vehicle along a first direction; a first pair of wheels mounted to a first wheel support, the first wheel support being part of the second section; a second pair of wheels mounted to a second wheel support, the second wheel support being part of the first section; the first wheel support and the second wheel support are disposed on opposite sides of the cavity and are vertically movable relative to the vehicle frame; The first wheel support and the second wheel support are interconnected by two coupler links extending in a first direction on opposite sides of the cavity, each of the coupler links being part of a corresponding linkage assembly configured to replicate vertical movement of the first wheel support as vertical movement of the second wheel support.

[0030] Alternatively, the linkage assembly may be defined as configured to transfer vertical movement of the first wheel support to vertical movement of the second wheel support.

[0031] The first pair of wheels may be mounted at a predetermined level relative to the first wheel support. The first pair of wheels may be located on a side of the second section facing or adjacent to the first section.

[0032] The second pair of wheels may be mounted at a predetermined level relative to the second wheel support.

[0033] The first and second wheel supports may extend in a first direction. The first and second wheel supports may be disposed on opposite sides of the cavity.

[0034] The lifting device may include a lifting frame for releasable connection to the storage container.

[0035] The rail system on which the container handling vehicles may travel may be a horizontal grid-based rail system, which may also be referred to as a rail grid system.

[0036] Two coupler links are positioned on opposite sides of the cavity that allow the lifting frame of the lifting device and any storage containers connected to the lifting frame to pass between the two coupler links as they move in and out of the cavity.

[0037] The two coupler links may be parallel and positioned at a distance greater than the distance between the two parallel sides of the lift frame.

[0038] In one embodiment, the container handling vehicle may include an actuator assembly configured to move a first wheel support in a vertical direction between a first position and a second position, the movement of the first wheel support being transmitted to the second wheel support via a coupler link of the linkage assembly, whereby when the first wheel support is in the first position, both pairs of wheels of the first set of wheels are in an upper position, and when the first wheel support is in the second position, both pairs of wheels of the first set of wheels are in a lower position.

[0039] The vertical movement of the first wheel support and the second wheel support may be relative to the vehicle frame.

[0040] In one embodiment of the container handling vehicle, the actuator assembly is located in the second section.

[0041] In one embodiment of the container handling vehicle, the actuator assembly may comprise a wheel lift motor and crank assembly. Alternatively, the actuator assembly may comprise a linear actuator.

[0042] In one embodiment of the container handling vehicle, the crank assembly and the first wheel support may be located on opposite sides of the second section.

[0043] In one embodiment of the container handling vehicle, the crank assembly and the first wheel support may be connected by a first shaft and a second shaft extending in a first direction, and the first and second shafts may transmit vertical movement of the crank assembly to the first wheel support.

[0044] In one embodiment of the container handling vehicle, the crank assembly may include a coupler link connecting a first pivot element (or first link) and a second pivot element (or second link) disposed at opposite ends of the coupler link, and a crank arm.

[0045] In one embodiment of the container handling vehicle, the first and second pivot elements of the crank assembly may be connected to the first wheel support by first and second shafts, the first and second shafts may be attached to the vehicle frame via the first and second pivot elements, respectively, and may be attached to the first wheel support by third and fourth pivot elements.

[0046] In one embodiment of the container handling vehicle, the coupler link may be connected to the wheel lift motor via a crank arm such that when the motor is operated, the crank arm moves the coupler link laterally, i.e., in a first direction. Movement of the coupler link simultaneously moves the first and second pivot elements, which in turn raise or lower the first and second shafts and the first wheel support in a vertical direction, e.g., moving the first wheel support between a first position and a second position.

[0047] In one embodiment of the container handling vehicle, each linkage assembly may include two intermediate links pivotally connected to opposite ends of the coupler links of the linkage assembly, each intermediate link featuring a first pivot coupling to the coupler links, a second pivot coupling to the vehicle frame, and a third pivot coupling to one of the first and second wheel supports. The intermediate links may be configured such that when the first set of wheels is moved vertically from a lower position to an upper position, the coupler links of the linkage assembly move toward the second section.

[0048] In one embodiment of the container handling vehicle, the third swivel coupling is connected to one of the first and second wheel supports via a wheel support link, which has a fifth swivel coupling connected to the corresponding first or second wheel support.

[0049] The wheel support link may allow vertical movement of the wheel support to be transmitted to the intermediate link while avoiding lateral forces acting on the wheel support.

[0050] In one embodiment of the container handling vehicle, the intermediate link may be a tilt link. The tilt link may be configured to transfer horizontal movement of the coupler link in the second direction to a substantially vertical movement of the third pivot coupling. In other words, by having the tilt link, movement of the third pivot coupling in the second direction is minimized when the tilt link is moved about its second pivot coupling.

[0051] In one embodiment of the container handling vehicle, the first pair of wheels may be driven by a first wheel drive motor, one wheel of the third pair of wheels and one wheel of the fourth pair of wheels may be driven by a second wheel drive motor, and the first and second wheel drive motors may be located in the second section. The wheels driven by the first and second wheel drive motors may be referred to as drive wheels or motorized wheels.

[0052] In one embodiment of the container handling vehicle, a first wheel drive motor may be rigidly mounted to the first wheel support and operably connected to the first pair of wheels by at least one drive band.

[0053] Rigidly mounting the first wheel drive motor to the first wheel support ensures that the length of the drive band remains constant and avoids wear on the drive band due to stretching as the first wheel support moves between the first and second positions.

[0054] In one embodiment, the container handling vehicle may include a drive shaft operably connecting one wheel of the third pair of wheels and one wheel of the fourth pair of wheels to a second wheel drive motor, and the wheels operably connected to the drive shaft and the second wheel drive motor may be disposed in the second section.

[0055] In one embodiment of the container handling vehicle, the second pair of wheels, one wheel of the third pair of wheels, and one wheel of the fourth pair of wheels may be non-driven wheels and may be located in the first section. Alternatively, the non-driven wheels may be referred to as non-motorized wheels.

[0056] In one embodiment of the container handling vehicle, the lifting device may include a lifting frame and at least one rotatable lifting shaft configured to raise and lower the lifting frame via a set of lifting bands. The at least one lifting shaft may be disposed in a first section above the cavity.

[0057] In one embodiment, the container handling vehicle may include a lift drive motor for rotating the at least one lift shaft, and the lift drive motor may be disposed in the second section.

[0058] In one embodiment, the container handling vehicle may include a set of replaceable or adjustable distance pins that are configured to interact with a switch or sensor on the lift frame when the lift frame is in the upper position. The switch or sensor may be used to detect when the lift frame is in the upper position and to help prevent movement and / or tilting of the lift frame when it and any storage containers connected thereto are in the upper position.

[0059] In one embodiment, the container handling vehicle may include a rechargeable battery disposed in the second section.

[0060] In one embodiment, the container handling vehicle may include a set of electrodes for receiving power from a charging station, the electrodes being disposed in the second section and connected to a rechargeable battery. When the set of electrodes includes two separate electrodes, the two electrodes may be disposed on opposite sides of a vertical center plane of the container handling vehicle, the vertical center plane extending in a second direction (if the second section has a footprint larger than half a grid cell, the second direction may be referred to as the longitudinal direction of the vehicle). The electrodes may be disposed on a side or area of ​​the second section facing away from the first section. Each electrode may have an outer periphery, and the outer peripheries may be horizontally spaced apart from each other by a distance equal to or greater than the diameter of the periphery. The two electrodes may be disposed symmetrically with respect to the vertical center plane.

[0061] In one embodiment, the container handling vehicle may include a control unit located in the second section.

[0062] In a second aspect, the present invention provides a storage system comprising a container handling vehicle according to any embodiment of the first aspect, the storage system comprising a framework structure having a plurality of storage columns for accommodating vertical stacks of storage containers, and a rail system along which the vehicle can move in two perpendicular directions above the storage columns.

[0063] In one embodiment, the storage system comprises a plurality of upright members, with each storage column defined by four upright members.

[0064] In one embodiment of the storage system, a rail system is disposed on the upright members, the rail system including a first set of parallel rails and a second set of parallel rails disposed perpendicular to the first set of rails, the first and second sets of rails providing a horizontal grid-based rail system that defines a plurality of grid cells.

[0065] In one embodiment of the storage system, the footprint of the first section of the container handling vehicle may have a footprint approximately equal to the area of ​​a grid cell of the rail system. The second section of the container handling vehicle may have a footprint equal to or less than the area of ​​a grid cell. The footprint of the container handling vehicle is the horizontal area occupied or defined by the horizontal perimeter of the container handling vehicle. The footprint of the container handling vehicle is equal to or less than the area of ​​two adjacent grid cells. When the first section has a footprint approximately equal to the area of ​​a grid cell of the rail system and the second section has a footprint greater than half the area of ​​a grid cell, the first direction may be referred to as the horizontal direction and the second direction may be referred to as the vertical direction.

[0066] In one embodiment of the storage system, the container handling vehicle may have a first pair of wheels and a second pair of wheels disposed on rails on opposite sides of a grid opening in which the first section is located, the rails defining two sides of a grid cell.

[0067] A grid cell may be defined as the cross-sectional area between the vertical center plane of opposing rails extending in the X direction and the vertical center plane of opposing rails extending in the Y direction.

[0068] A grid cell opening may be defined as the open cross-sectional area between two opposing rails extending in the X direction and two opposing rails extending in the Y direction.

[0069] In a third aspect, the present invention provides a method of changing the direction of travel of a container handling vehicle for travel on a rail system, the rail system comprising a first set of parallel rails and a second set of parallel rails arranged at a right angle to the first set of rails, the container handling vehicle comprising: a vehicle frame defining a first section and a second section of a container handling vehicle, the first section and the second section being disposed side-by-side, the first section comprising a lifting device for lifting a storage container and providing a cavity in which the storage container being lifted may be accommodated; a first set of wheels comprising a first pair of wheels and a second pair of wheels, the first and second pairs of wheels being located on opposite portions of the first section, the first set of wheels enabling movement of the vehicle along a first direction on the rail system in use; a second set of wheels comprising a third pair of wheels and a fourth pair of wheels, the third pair of wheels and the fourth pair of wheels being disposed on opposite sides of the vehicle, each of the sides extending from one edge of the first section to one edge of the second section, and enabling, in use, movement of the vehicle along a second direction on the rail system, the second direction being perpendicular to the first direction; Equipped with the first set of wheels are positioned to be vertically movable relative to a remainder of the vehicle frame between an upper position in which the second set of wheels permits movement of the vehicle along a second direction and a lower position in which the first set of wheels permits movement of the vehicle along a first direction; a first pair of wheels mounted to a first wheel support, the first wheel support being part of the second section; a second pair of wheels mounted to a second wheel support, the second wheel support being part of the first section; the first wheel support and the second wheel support are disposed on opposite sides of the cavity and are vertically movable relative to the vehicle frame; The first wheel support and the second wheel support are interconnected by two coupler links extending in a first direction on opposite sides of the cavity, each of the coupler links being part of a linkage assembly, the linkage assembly being configured to replicate vertical movement of the first wheel support as vertical movement of the second wheel support, and the method further comprising: - vertically moving a first wheel support; - simultaneously replicating the vertical movement of the first wheel support as the vertical movement of the second wheel support via a linkage assembly such that the first set of wheels move between an upper position and a lower position; Includes.

[0070] In one embodiment of the method according to the third aspect, the container handling vehicle comprises an actuator assembly disposed in the second section, the actuator assembly comprising a motor and a crank assembly, and the method further comprises: - driving the motor to operate the crank assembly such that the first wheel support is moved vertically by a first shaft and a second shaft connected to the first wheel support and the crank assembly.

[0071] The container handling vehicle of the method according to the third aspect may comprise any of the features of the container handling vehicle of the first aspect.

[0072] In a fourth aspect, the present invention provides a method of changing a direction of travel for a container handling vehicle according to any embodiment of the first aspect, the method comprising: - vertically moving the first wheel support; - simultaneously transmitting vertical movement of the first wheel support to the second wheel support via a linkage assembly; Includes.

[0073] In one embodiment of the method, the simultaneous transmission of vertical movement of the first wheel support to the second wheel support is obtained by moving the wheel support links vertically, rotating the intermediate links about their second pivot couplings, and moving the coupler link in a second direction.

[0074] In one embodiment, the method comprises: - operating the actuator assembly to move the first wheel support vertically. [Brief description of the drawings]

[0075] Embodiments of the invention will now be described in detail, by way of example only, with reference to the following drawings, in which:

[0076] [Figure 1] FIG. 1 is a perspective view of a framework structure of a prior art automated storage and retrieval system.

[0077] [Diagram 2] FIG. 1 is a perspective view of a prior art container handling vehicle having a centrally located cavity for carrying a storage container therein.

[0078] [Diagram 3] FIG. 1 is a perspective view of a prior art container handling vehicle having a cantilevered section for carrying storage containers downward.

[0079] [Figure 4] FIG. 1 is a perspective view of a prior art container handling vehicle in which a container lifting assembly is shown;

[0080] [Diagram 5] FIG. 5 is a perspective view of the container handling vehicle of FIG. 4 without the side panels.

[0081] [Figure 6] FIG. 1 is a perspective view of a typical container handling vehicle with the second set of wheels in the lowest position. [Figure 7]FIG. 1 is a perspective view of a typical container handling vehicle with the second set of wheels in the lowest position.

[0082] [Figure 8] FIG. 7 is a side view of the container handling vehicle of FIG. 6.

[0083] [Figure 9] FIG. 7 is a perspective view of the container handling vehicle of FIG. 6 with the second set of wheels in an upper position. [Figure 10] FIG. 7 is a perspective view of the container handling vehicle of FIG. 6 with the second set of wheels in an upper position.

[0084] [Figure 11] FIG. 10 is a side view of the container handling vehicle of FIG.

[0085] [Figure 12] FIG. 1 is a perspective view of a typical container handling vehicle.

[0086] [Figure 13] FIG. 9 is a cross-sectional view of the container handling vehicle of FIG.

[0087] [Figure 14] FIG. 12 is a cross-sectional view of the container handling vehicle of FIG.

[0088] [Figure 15a] FIG. 1 is a perspective view of a typical container handling vehicle with side panels. [Figure 15b] FIG. 1 is a perspective view of a typical container handling vehicle with side panels. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0089] Embodiments of the invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:

[0090] As explained in the Background section, prior art container handling vehicles equipped with a cavity for accommodating storage containers have certain advantageous features (see Figures 2, 4 and 5). In particular, the guide / support provided to the storage container when accommodated in the cavity entails that the vehicle may have increased acceleration / delay relative to the cantilevered container handling vehicle 301 shown in Figure 3. However, the potential increase in acceleration / delay is not fully realized due to vehicle instability. The instability is caused by both vehicles 201, 401 having most of their drive, power, control and lifting components located above the cavity (which results in a high center of gravity).

[0091] The container handling vehicle body of FIG. 4 and FIG. 5 comprises a first section S1 and a second section S2 arranged side by side. An arrangement with a first section S1 and a second section S2 is disclosed in PCT / EP2018 / 077732. Due to the increased footprint compared to the footprint of the vehicle of FIG. 2, the stability is slightly improved. However, as shown in FIG. 5, the prior art container handling vehicle 401 features wheel lifting components including at least a control unit 19, a replaceable battery 18, and a wheel lifting shaft 20 arranged above the cavity 26. The wheel lifting shaft 20 extends above the cavity connecting two opposing wheel lifting plates 21a, 21b. It is noted that the wheel drive motor of the container handling vehicle 401 is not arranged above the cavity. The positioning of the wheel motor is made possible by using a wheel hub motor 41. The advantage of using a wheel hub motor is that all the wheels of the container handling vehicle can be drive wheels providing high wheel traction. The disadvantages of using multiple wheel hub motors are relatively high cost and potentially increased service / maintenance. In addition, the power and torque that can be provided by the wheel hub motors is limited because they must be sized to allow them to fit within the vehicle without extending into the cavity of the first section or interfering with each other in the second section.

[0092] The present invention provides a container handling vehicle with improved drive wheel stability and traction. Further advantages of the container handling vehicle described below include lower service costs.

[0093] An exemplary embodiment of a container handling vehicle 501 according to the present invention is shown in Figures 6 to 15.

[0094] The container handling vehicle is suitable for use in a prior art storage system, as described in the Background section and shown in FIG.

[0095] The container handling vehicle 501 features a vehicle frame 6 which defines a first section S1 and a second section S2 of the container handling vehicle 501 arranged side by side, similar to the vehicle frame of the prior art vehicle 401 described above.

[0096] The first section S1 comprises a lifting device for lifting the storage container 106 and provides a cavity 26 in which the storage container 106 can be accommodated. The lifting device has a lifting frame 2 and two rotatable lifting shafts 33 configured to raise and lower the lifting frame 2 via a pair of lifting bands 5. A lifting drive motor 32 for driving the lifting device (i.e. for rotating the lifting shafts) is disposed in the second section S2.

[0097] The container handling vehicle has a first set of wheels and a second set of wheels configured to move the vehicle on a rail system 108. The rail system includes a first set of parallel rails 110 and a second set of parallel rails 111 arranged at a right angle to the first set of rails 110. The rail system is arranged in a horizontal grid-based manner.

[0098] The first set of wheels comprises a first pair of wheels 7a, 7b and a second pair of wheels 7c, 7d. The first and second pairs of wheels are arranged on opposite portions of the first section S1 of the container handling vehicle and enable movement of the vehicle 501 along a first direction Y on the rail system 108.

[0099] The second set of wheels comprises a third pair of wheels 8a, 8b and a fourth pair of wheels 8c, 8d. The third and fourth pairs of wheels are arranged on either side of the vehicle, each of which extends from one edge of the first section S1 to one edge of the second section S2. The second set of wheels enables movement of the vehicle 501 on the rail system 108 along a second direction X, which is perpendicular to the first direction Y.

[0100] In order to enable the container handling vehicle 501 to change the direction in which it travels on the rail system 108, the first set of wheels are arranged to be movable in a direction Z perpendicular to the vehicle frame 6 between an upper position in which the second set of wheels enable movement of the vehicle 501 along a second direction X, and a lower position in which the first set of wheels enable movement of the vehicle 501 along a first direction Y.

[0101] Vertical movement of the first set of wheels 7a-7d is obtained by a wheel lifting mechanism characterized by a first wheel support 24, a second wheel support 25, actuator assemblies 17, 27 configured to move the first wheel support 24 vertically relative to the vehicle frame 6, and two linkage assemblies 15 configured to transmit the vertical movement of the first wheel support 24 to vertical movement of the second wheel support 25 relative to the vehicle frame 6.

[0102] The first pair of wheels 7a, 7b are mounted on a first wheel support 24, which can be considered as part of the second section S2, and the second pair of wheels 7c, 7d are mounted on a second wheel support 25, which is part of the first section S1. The first wheel support 24 and the second wheel support 25 are arranged on either side of a cavity 26. The first wheel support 24 and the second wheel support 25 extend in a first direction Y.

[0103] Each of the linkage assemblies 15 includes a coupler link 22, two tilt links 23 (e.g., bell cranks or intermediate links) pivotally connected to either end of the coupler link 22, and two wheel support links 28 connecting the corresponding tilt links 23 to one of the first and second wheel supports 24, 25.

[0104] Each of the tilt links 23 features a first pivot coupling 23a to the coupler link 22, a second pivot coupling 23b to the vehicle frame 6, and a third pivot coupling 23c connected to a corresponding first or second wheel support 24, 25 via a wheel support link 28. The wheel support link 28 has a fifth pivot coupling 28a connected to the corresponding first or second wheel support.

[0105] The angles of the inclined links 23 minimize lateral movement of the third pivot coupling 23c in the second direction X when the inclined links 23 are pivoted about their second pivot couplings 23b, causing the third pivot coupling 23 to move vertically.

[0106] The wheel support link 28 allows vertical movement of the wheel supports 24,25 to be transmitted through the tilt link 23 while avoiding any lateral forces acting on the wheel supports 24,25.

[0107] The coupler links 22 extend in a second direction X on either side of the cavity 26 allowing a storage container 106 to be received between the coupler links.

[0108] The first pair of wheels 7a, 7b can be driven in a first direction Y by a first wheel drive motor 29. The third pair of wheels 8a and the fourth pair of wheels 8d can be driven in a second direction X by a second wheel drive motor 30. The first and second wheel drive motors are arranged in the second section S2.

[0109] The first wheel drive motor 29 is rigidly mounted to the first wheel support 24 and operatively connected to the first pair of wheels 7a, 7b by a drive band 43 (see FIG. 13). Rigidly mounting the first wheel drive motor 29 to the first wheel support 24 ensures that the length of the drive band 43 remains constant, avoiding wear on the band due to stretching as the first wheel support 24 moves between the first and second positions.

[0110] The second wheel drive motor 30 is operatively connected to the drive wheels 8a of the third pair of wheels and the drive wheels 8d of the fourth pair of wheels by a drive shaft 31. The second wheel drive motor 30 and the drive shaft 31 are disposed in the second section S2.

[0111] In an alternative embodiment of the container handling vehicle, the remaining non-motorized wheels of the container handling vehicle of Figures 6-15, i.e., the second pair of wheels 7c, 7d, one wheel of the third pair of wheels 8b, and one wheel of the fourth pair of wheels 8c, may be driven by wheel hub motors. However, the addition of an additional wheel drive motor is expensive and is not considered to provide significant speed and / or acceleration related benefits to warrant the addition in all circumstances. As a result, using a combination of driven and non-driven wheels can provide a cost-effective solution with minimal performance differential. Weight is also reduced by avoiding the weight of the additional drive wheel motors.

[0112] The first wheel support 24 can be moved vertically between a first position and a second position by a crank assembly 27 driven by a wheel lift motor 17 (see Figures 7, 10 and 12). The crank assembly features a coupler link 38 connecting a first pivot element 39a and a second pivot element 39b disposed on opposite ends of the coupler link 38, and a crank arm 40.

[0113] The first and second pivot elements 39a and 39b are connected to the first wheel support 24 by first and second shafts 35a and 35b (see Figures 9 and 10). The first and second shafts 25a and 25b are attached to the vehicle frame 12 via the first and second pivot elements 39a and 39b, respectively, and to the first wheel support 24 by third and fourth pivot elements 39c and 39c (which, like the third pivot element, are not visible in the drawings).

[0114] The coupler link 38 is connected to the wheel lift motor 17 via a crank arm 40. When the wheel lift motor 17 is operated, the crank arm 40 moves the coupler link 38 laterally, i.e., in the first direction Y. The movement of the coupler link 38 simultaneously moves the first and second pivot elements 39a, 39b, which in turn raise and lower the first and second shafts 35a, 35b and the first wheel support 24 vertically, for example, between a first position and a second position. By having the crank assembly 27 and the first wheel support located on both sides of the second section S2, the available space in the second section is optimized. The optimized space allows the wheel drive motors 29, 30 and the drive shaft 31 to be located at a lower level in the second section S2 to improve the stability of the vehicle.

[0115] The power for driving the motor of the container handling vehicle 501 is provided by a rechargeable battery 44 arranged in the second section S2. The rechargeable battery 44 is connected to a pair of electrodes 37. The electrodes 37 are configured to receive power from a charging station. The two electrodes 37 are arranged on either side of a vertical centre plane of the container handling vehicle, the vertical centre plane extending in a second direction X. An advantageous effect of having the electrodes 37 thus separated, i.e. arranged symmetrically with respect to the vertical centre plane, is that a lateral skew of the container handling vehicle with respect to the second direction X during initial connection to the charging station is minimized. A suitable charging station is disclosed, for example, in PCT / EP2021 / 074340.

[0116] A control unit 19 for controlling at least the drive components, i.e. the first and second electric motors 29, 31, the wheel lift motor 17 and the lift drive motor 32, is located in the second section S2. By locating all drive components and the rechargeable battery 44 in the second section S2, the cabling from the control unit 19 to any of the controllable components is minimized.

[0117] Substantially all drive, power and control components of the container handling vehicle 501 are located in the second section S2. The weight of these components is primarily supported by the drive wheels 7a, 7b, 8a, 8d in or at the second section S2, whereby the drive wheels have excellent traction enabling high acceleration of the vehicle.

[0118] A set of replaceable distance pins 34 are positioned above the lift frame 2 (see FIG. 7). The distance pins 34 are configured to interact with a switch 36 or sensor on the top of the lift frame 2 when the lift frame 2 is in the upper position.

[0119] The distance pins 34 ensure that the operating efficiency of the container handling vehicle 501 is optimized with respect to the height of the storage container 106 being lifted. If the container handling vehicle 501 is to be used for lower storage containers, longer distance pins can be installed to ensure that the storage container 106 is not lifted higher than required to enter the cavity 26.

[0120] In an alternative embodiment, the distance pin 34 may be adjustable, i.e., the distance pin is not replaceable but may have an adjustable height. An adjustable distance pin may be obtained, for example, by having a telescoping or collapsible distance pin.

[0121] The container handling vehicle 501 includes four distance pins 34 positioned to interact with the lift frame 2 at its four corners. The distance pins 34 may also be configured to stabilize the lift frame 2, and any storage containers 106 connected thereto, when the lift frame 2 is in the upper position.

[0122] In Figures 15a and 15b the container handling vehicle is shown with a cover plate 42. The cover plate 42 and the vehicle frame 6 provide the body of the container handling vehicle. (List of reference numbers) 1. Prior Art Automatic Storage and Retrieval System 2 Lifting frame 3 Container Connector 4 Guide pins 5. Lifting Band 6 Vehicle Frame 7a~7d Wheels of the first pair of wheels 8a~8d Second pair of wheels 12 Vehicle frame 15 Linkage Assembly 17 Wheel lift motor 18 Replaceable Battery 19 Control Unit 20 Wheel lift shaft 21a, 21b Wheel lift plate 22 Coupler Link 23 Intermediate Links 24 First wheel support 25 Second wheel support 26 Cavity 27 Crank Assembly 28 Wheel support link 29 First wheel drive motor 30 Second wheel drive motor 31 Drive shaft 32 Lift drive motor 33 Lifting shaft 34 Distance Pin 35a, 35b First shaft, second shaft 36 Switches and sensors 37 electrode 38 Coupler Link 39a, 39b First pivoting element, second pivoting element 40 Crank arm 41 Wheel hub motor 42 Cover plate 43 Drive Bandwidth 44 Rechargeable Batteries 100 Frame structure 102 Upright members of frame structures 103 Horizontal members of frame structures 105 Storage Column 106 Storage Container 106' Storage container identification location 107 Stack 108 Rail System 110 Parallel rail in the second direction (X) 110a: first rail in second direction (X) 110b second rail in second direction (X) 111 Parallel rail in the first direction (Y) 111a First rail in first direction (Y) 111b Second rail in first direction (Y) 112 Access opening 119 First Port Column 120 Second Port Column 201 Prior Art Container Handling Vehicles 201a Body of container handling vehicle 201 201b Drive means / wheel arrangement, first direction (X) 201c Drive means / wheel arrangement, second direction (Y) 301 Prior art cantilever container handling vehicle 301a Body of container handling vehicle 301 301b Driving means in the second direction (X) 301c Driving means in the first direction (Y) 401 Prior art container handling vehicles 401a Body of container handling vehicle 401 401b Driving means in the first direction (X) 401c Driving means in the second direction (Y) X Second Direction Y Primary Direction Z third direction

Claims

1. A container handling vehicle (501) for travelling on a rail system (108), said rail system comprising a first set of parallel rails (110) and a second set of parallel rails (111) arranged at right angles to said first set of rails (110), said container handling vehicle comprising: a vehicle frame (6) defining a first section (S1) and a second section (S2) of the container handling vehicle, the first section and the second section being arranged side by side, the first section (S1) being provided with a lifting device (2) for lifting a storage container (106) and providing a cavity (26) in which the lifted storage container can be accommodated; a first set of wheels comprising a first pair of wheels (7a, 7b) and a second pair of wheels (7c, 7d), the first and second pairs of wheels being arranged on opposite parts of the first section (S1), the first set of wheels enabling movement of the vehicle (501) along a first direction (Y) on the rail system (108) in use; a second set of wheels comprising a third pair of wheels (8a, 8b) and a fourth pair of wheels (8c, 8d), the third pair of wheels and the fourth pair of wheels being arranged on opposite sides of the vehicle, each of the sides extending from one edge of the first section (S1) to one edge of the second section (S2), and allowing, in use, movement of the vehicle (501) on the rail system (108) along a second direction (X), the second direction (X) being perpendicular to the first direction (Y); Equipped with the first set of wheels are arranged to be movable in a direction (Z) perpendicular to the rest of the vehicle frame between an upper position in which the second set of wheels allows movement of the vehicle (501) along the second direction (X) and a lower position in which the first set of wheels allows movement of the vehicle (501) along the first direction (Y); the first pair of wheels (7a, 7b) are mounted on a first wheel support (24), the first wheel support being part of the second section (S2); the second pair of wheels (7c, 7d) are mounted on a second wheel support (25), the second wheel support being part of the first section (S1); the first wheel support and the second wheel support are disposed on opposite sides of the cavity (26) and are vertically movable relative to the remainder of the vehicle frame (6); The container handling vehicle (501), wherein the first wheel support (24) and the second wheel support (25) are interconnected by two coupler links (22) extending in the first direction (Y) on opposite sides of the cavity (6), each of the coupler links being part of a linkage assembly (15), the linkage assembly being configured to replicate vertical movement of the first wheel support (24) as vertical movement of the second wheel support (25).

2. an actuator assembly (17, 27) configured to vertically move the first wheel support (24) between a first position and a second position, the movement of the first wheel support (24) being transmitted to the second wheel support (25) via the coupler link (22) of the linkage assembly (15); 2. The container handling vehicle of claim 1, wherein when the first wheel support (24) is in the first position, both pairs of wheels of the first set of wheels are in the upper position, and when the first wheel support (24) is in the second position, both pairs of wheels of the first set of wheels are in the lower position.

3. 3. A container handling vehicle according to claim 2, wherein the actuator assembly (17, 27) is arranged in the second section (S2).

4. 3. The container handling vehicle of claim 2, wherein the actuator assembly comprises a motor (17) and crank assembly (27), or a linear actuator.

5. 5. The container handling vehicle of claim 4, further comprising the motor (17) and the crank assembly (27), the crank assembly (27) and the first wheel support (24) being arranged in opposite regions of the second section (S2).

6. 2. The container handling vehicle of claim 1, wherein each linkage assembly (15) comprises two intermediate links (23) pivotally connected to opposite ends of the coupler links (22), each intermediate link (23) characterized by a first pivot coupling (23a) to the coupler link, a second pivot coupling (23b) to the vehicle frame (6), and a third pivot coupling (23c) to one of the first wheel support and the second wheel support.

7. 7. The container handling vehicle of claim 6, wherein each of the third swivel couplings (23c) is connected to one of the first wheel support and the second wheel support via a wheel support link (28), the wheel support link having a fifth swivel coupling (28a) connected to the corresponding first or second wheel support.

8. 7. A container handling vehicle according to claim 6, wherein the intermediate link is a tilt link (23).

9. 2. The container handling vehicle according to claim 1, wherein the first pair of wheels (7a, 7b) are driven by a first wheel drive motor (29), one wheel (8a) of the third pair of wheels and one wheel (8d) of the fourth pair of wheels are driven by a second wheel drive motor (30), and the first wheel drive motor and the second wheel drive motor are arranged in the second section (S2).

10. 10. A container handling vehicle as claimed in claim 9, wherein the first wheel drive motor (29) is rigidly mounted to the first wheel support (24) and operably connected to the first pair of wheels (7a, 7b) by at least one drive band (43).

11. 2. The container handling vehicle of claim 1, further comprising a drive shaft (31) operably connecting one wheel (8 a) of the third pair of wheels and one wheel (8 d) of the fourth pair of wheels to the second wheel drive motor (30), wherein the wheels (8 a, 8 d) operably connected to the drive shaft and the second wheel drive motor (31) are arranged in the second section (S2).

12. 2. The container handling vehicle according to claim 1, wherein the second pair of wheels (7c, 7d), one wheel of the third pair of wheels (8b), and one wheel of the fourth pair of wheels (8c) are non-driven wheels, and the non-driven wheels are arranged in the first section (S1).

13. 2. The container handling vehicle of claim 1, wherein the lifting device comprises a lifting frame (2) and at least one rotatable lifting shaft (33) configured to raise and lower the lifting frame (2) via a set of lifting bands (5), the lifting shaft being arranged in the first section (S1) above the cavity (26).

14. 14. The container handling vehicle of claim 13, further comprising a lift drive motor (32) for rotating the at least one lift shaft (33), the lift drive motor (32) being disposed in the second section (S2).

15. 2. The container handling vehicle of claim 1, further comprising a set of replaceable or adjustable distance pins (34), said distance pins configured to interact with a switch (36) or sensor on said lifting frame (2) when said lifting frame is in an upper position.

16. 2. The container handling vehicle of claim 1, further comprising a rechargeable battery (44) disposed in the second section (S2).

17. 17. The container handling vehicle of claim 16, further comprising a set of electrodes (37) for receiving power from a charging station, said electrodes being arranged in said second section (S2) and connected to said rechargeable battery (44).

18. 2. The container handling vehicle of claim 1, further comprising a control unit (19) located in the second section (S2).

19. A storage system comprising a container handling vehicle (501) as described in any one of claims 1 to 18, the storage system comprising a framework structure (100) having a plurality of storage columns (105) for accommodating vertical stacks of storage containers (106), and a rail system (108) above the storage columns along which the vehicle can move in two perpendicular directions.

20. 1. A method of changing the direction of travel of a container handling vehicle (501) for travel on a rail system (108), the rail system comprising a first set of parallel rails (110) and a second set of parallel rails (111) disposed perpendicular to the first set of rails (110), the container handling vehicle comprising: a vehicle frame (6) defining a first section (S1) and a second section (S2) of the container handling vehicle, the first section and the second section being arranged side by side, the first section (S1) being provided with a lifting device (2) for lifting a storage container (106) and providing a cavity (26) in which the lifted storage container can be accommodated; a first set of wheels comprising a first pair of wheels (7a, 7b) and a second pair of wheels (7c, 7d), the first and second pairs of wheels being arranged on opposite parts of the first section (S1), the first set of wheels enabling movement of the vehicle (501) along a first direction (Y) on the rail system (108) in use; a second set of wheels comprising a third pair of wheels (8a, 8b) and a fourth pair of wheels (8c, 8d), the third pair of wheels and the fourth pair of wheels being arranged on opposite sides of the vehicle, each of the sides extending from one edge of the first section (S1) to one edge of the second section (S2), and allowing, in use, movement of the vehicle (501) on the rail system (108) along a second direction (X), the second direction (X) being perpendicular to the first direction (Y); Equipped with the first set of wheels are arranged to be movable in a direction (Z) perpendicular to the rest of the vehicle frame between an upper position in which the second set of wheels allows movement of the vehicle (501) along the second direction (X) and a lower position in which the first set of wheels allows movement of the vehicle (501) along the first direction (Y); the first pair of wheels (7a, 7b) are mounted on a first wheel support (24), the first wheel support being part of the second section (S2); the second pair of wheels (7c, 7d) are mounted on a second wheel support (25), the second wheel support being part of the first section (S1); the first wheel support and the second wheel support are disposed on opposite sides of the cavity (26) and are vertically movable relative to the remainder of the vehicle frame (6); the first wheel support (24) and the second wheel support (25) are interconnected by two coupler links (22) extending in the first direction (Y) on opposite sides of the cavity (6), each of the coupler links being part of a linkage assembly (15), the linkage assembly being configured to replicate vertical movement of the first wheel support (24) as vertical movement of the second wheel support (25), the method comprising: - vertically moving said first wheel support (24); - simultaneously replicating the vertical movement of the first wheel support as a vertical movement of the second wheel support via the linkage assembly so that the first set of wheels moves between the upper position and the lower position; A method comprising:

21. The container handling vehicle includes an actuator assembly (17, 27) disposed in the second section (S2), the actuator assembly including a motor (17) and a crank assembly (27), and the method includes: - driving said motor (17) to operate said crank assembly, 21. The method of claim 20, whereby the first wheel support (24) is moved vertically by a first shaft (35a) and a second shaft (35b) connected to the first wheel support and the crank assembly.

Images