GB2530570A

GB2530570A - Materials handling system and equipment for use in a warehousing installation

Info

Publication number: GB2530570A
Application number: GB1417135.9A
Authority: GB
Inventors: Edward Wainwright
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-09-29
Filing date: 2014-09-29
Publication date: 2016-03-30
Also published as: GB201417135D0

Abstract

A materials handling unit 1, such as a forklift truck, for use in a very narrow aisle (VNA) storage environment comprises a body 2 with a first set of wheels 8a, 8b, 8c for running on a surface such as a floor and a second set of wheels 16a, 16b, 17a, 17b are raised clear of the floor for engaging with mounting surfaces 25, 26 of rails 23, 24. The central wheel (8a fig. 2) is driven by a motor. The rails 23, 24 may be laid so that rail mounting surfaces 25, 26 are substantially coplanar and provide a substantially horizontal reference surface upon which the raised wheels 16a, 16b, 17a, 17b can run when engaged with the mounting surfaces 25, 26. In this way the materials handling unit 1 can be oriented in a stable manner and is guided along the aisles within a VNA system, as it runs along the pair of guide rails 23, 24. This removes the need to provide a substantially flat floor surface as is required with known systems. The system can be retrofitted into existing installations if required. The second set of wheels 16a, 16b, 17a, 17b may have a circumferential lip (27c, 27d fig. 2). Each of the rails 23, 24 may have an inclined surface (30 fig. 5B) at its end.

Description

MATERIALS HANDLING SYSTEM AND EQUIPMENT FOR USE IN A

WAREHOUSING INSTALLATION

The present invention relates to a materials handling system and equipment for use in a warehousing installation, particularly, although not exclusively, for high density storage.

High density storage installations in warehouses typically store goods on pallets or boxes on high racking. The racking is typically greater than 12 metres in height and is separated by very narrow aisles. These are often referred to as Very Narrow Aisle (VNA) warehousing installations. VNA installations use materials handling equipment, such as forklift trucks, to remove and place the goods onto the racking and move the materials in and out of storage. Materials handling equipment may be operated by an operator, or may be automated and guided by additional means up along the narrow aisles. Typically, the very narrow aisles are only wide enough to accommodate the width of the materials handling equipment.

Forklift trucks used in VNA installations are well known and comprise a main body with a cabin for an operator and a mast at the front end which has an L-shaped fork lift supported on the mast and which can move up and down the mast to the required height in order to lift goods to and from the racking in a known way.

When the materials handling equipment is in the aisles it must be guided to avoid collision with the racking: current VNA installations use either inductive guidance using a wire buried in the floor, or physical guidance using rails situated along the side of the aisle. In both systems, the wheels of the materials handling equipment run on the floor. In installations in which the materials handling equipment runs on the floor, the materials handling equipment is able to transfer from very narrow aisle to very narrow aisle. In both systems the wheels of the materials handling equipment run on the floor. This relies on a very high standatd of concrete floor flatness (typically the DM1 specification according to Appendix C of the 2003 edition of the Concrete Society's Technical Report Number 34, or the DIN1 5185 German Specification) which can be difficult, costly and time consuming to achieve and maintain.

Materials handling equipment can also be guided using a combination of the system described above with a stabilising guide rail or channel mounted at the top of the mast portion of the forklift truck, above the racking (this is a top-guided system).

Known VNA installations as described above suffer from a number of drawbacks, It is time-consuming and costly to construct and maintain a concrete floor to a standard of flatness that is sufficient for a VNA system to work efficiently and safely. This is particularly true where the mast is 12 or more metres in height. If the concrete floor is not of a sufficient standard of flatness there is a risk of the materials handling equipment colliding with the racking (by swaying movements caused by the weight of the load at height and the unevenness of the floor), a greater amount of wastage caused by shed pallet loads, and premature failure of materials handling equipment components caused by the exaggerated stresses imposed on the structure (failed welds in materials handling equipment masts are a major cost, efficiency, and a health and safety problem). The maximum lift height of systems, and therefore the capacity of the warehouse installation, is limited by the quality of the concrete floor and the corresponding stability of the materials handling equipment.

There are frequently problems with joints in the concrete floors used in such warehouse installations. The high point loads imposed by materials handling equipment mean that effective load transfer across joints is vital to avoid the deterioration of thc joints spalling and cracking ofjoints is a major problem as damaged joints have a severely detrimental effect on the stability of the materials handling equipment when operating at height. The repair of these joints is a costly, inconvenient and repetitive maintenance problem.

If the concrete floor is not of a sufficiently high standard of flatness, or if there arc problems with the deterioration of the joints in the concrete floor, then the materials handling equipment cannot be operated at maximum speed, nor can it achieve its maximum lift height, and therefore the whole VNA installation cannot operate at its maximum capacity -in some cases it becomes impossible to usc the higher parts of the warehouse installation without an unacceptable risk to operatives, stored goods and the equipment.

A VNA system cannot be installed in an existing building without remedial works to the S concrete floor, a replacement concrete floor slab or a concrete overslab, all of which are costly, inconvenient and time-consuming operations.

Inductive guidance systems are susceptible to problems including interference from concrete floor reinforcement, wire damage in the course ofjoint repairs to the concrete floor and electrical component failure, Top-guided systems suffer the same drawbacks as other floor-running systems with the additional problem that they are more costly to procure and maintain because of the structures necessary to support the guidance system for the top of the MHE mast. This system can also cause broader maintenance problems for the warehouse operator as the structures supporting the top of the MHE system frequently obstruct maintenance operations to lighting and fire protection installations mounted above the VNA area.

In a crane VNA system, there is at least one piece of materials handling equipment permanently in each aisle, each mounted on a single rail on the floor of the aisle and a stabilising guide rail or channel mounted at the top of the mast of the materials handling equipment. This system requires one unit of materials handling equipment per aisle, as the materials handling equipment cannot transfer from aisle to aisle.

Crane VNA systems have the additional problem that they are more costly to procure and maintain than floor-running systems, not least because it is necessary to procure one crane for each VNA. Should a unit of materials handling equipment fail, it is impossible to reach any of the racking in the YNA system because the materials handling equipment cannot be transferred from aisle to aisle. This system can also cause broader maintenance problems for the warehouse operator as the structures supporting the top of the MilE system frequently obstruct maintenance operations to lighting and fire protection installations mounted above the VNA area.

According to thc present invention, there is provided a materials handling unit comprising a body having a first end, a second end, side faces, an underside and a first set of a plurality of wheels configured to support the materials handling unit on a surface for movement thereon, the materials handling unit further comprising a materials handling mechanism mounted on the vehicle body for supporting and moving materials, the body being arranged to house a drive means coupled to at least one of the first set of a plurality of wheels for driving the at least one of the first set of a plurality of wheels, wherein the body further includes a second set of a plurality of wheels comprising a first pair of wheels and a second pair of wheels, the first pair of wheels being located towards the first end of the vehicle body, one wheel of each first pair being on opposing side faces of the vehicle body and having a first common axis of rotation, and the second pair wheels being located towards the second end of the vehicle body, one wheel of each second pair being on opposing side faces of the vehicle body and having a second common axis of rotation, the first common axis of rotation and the second common axis of rotation being substantially parallel to each other, and displaced a predetermined distance from the underside of the vehicle body such that, when the first set of a plurality of wheels of the materials handling unit is in contact with the surface, the second set of a plurality of wheels are clear of the surface.

The drive means may be coupled to at least one of the second set of a plurality of wheels.

The drive means may be configured to drive at least one wheel of either the first pair of wheels or the second pair of wheels. Alternatively, the body may be arranged to house a second drive means coupled to at least one pair of the second set of a plurality of wheels to drive the one pair of wheels connected to the second drive means.

The first pair of wheels and/or the second pair of wheels may be connected by an axle which defines the common axis of rotation. Alternatively, the wheels could be mounted on a wheel carrier such as a spigot.

The one pair of wheels may be geared such that the speed of rotation of the one pair of wheels maybe configured to match the speed of rotation of the first set of plurality of wheels.

The wheels of the second set of plurality of wheels may have a circumferential lip.

According to another aspect of the present invention, there is provided a materials handling system comprising a materials handling unit and a pair of rails configured for laying on a ground surface in a substantially parallel arrangement, each rail of the pair of rails having a mounting surface, the materials handling unit comprising a body having a first end, a second end, side faces, an underside and a first set of a plurality of wheels configured to support the materials handling unit on the ground surface for movement thereon, the materials handling unit further comprising a materials handling mechanism mounted on the body for supporting and moving materials, the body being arranged to house a drive means coupled to at least one of the first set of a plurality of wheels for driving the at least one of the first set of a plurality of wheels, wherein the body further includes a second set of a plurality of wheels comprising a first pair of wheels and a second pair of wheels for engaging with the mounting surface of each of the pair of rails, the first pair of wheels being located towards the first end of the vehicle body, one wheel of each first pair being on opposing side faces of the vehicle body and having a first common axis of rotation, and the second pair wheels being located towards the second end of the vehicle body, one wheel of each second pair being on opposing side faces of the vehicle body and having a second common axis of rotation, the first common axis of rotation and the second common axis of rotation being substantially parallel to each other, and displaced a predetermined distance from the underside of the vehicle body such that, when the second set of a plurality of wheels are in in engagement with the mounting surface, the first set of a plurality of wheels of the materials handling unit are clear of the surface.

Each of the rails of the pair of rails may have an inclined surface at the ends.

The clearance between the ground surface and the first set of a plurality of wheels, when the materials handling unit is mounted on the rails, is up to 30mm and preferably between 5mm and 25mm and even more preferably between 10mm and 15mm, The rails may be laid so that the mounting surfaces are substantially coplanar and provide a substantially horizontal reference surface upon which the second set of a plurality of wheels can run when engaged with the mounting surface. In this way the materials handling unit can be oriented in a stable maimer and is guided along the aisles within a VNA system, as it runs along the pair of guide rails. With guide surfaces of each rail of the pair of guide rails providing a substantially horizontal reference surface, the materials handling unit may operate in a VNA system with improved stability.

This removes the need to provide a substantially flat floor surface as is required with known systems. The system can be retrofitted into existing installations if required.

The use of inclined ends on the rails enables the materials handling unit to mount the guide rails.

The present system allows the materials handling unit to run on rails when inside the aisles of a VNA system, but freely otherwise. As the vehicles can transfer from aisle to aisle within the VNA system, smaller numbers of vehicles may be required. This will incur a reduced procurement and operational cost with increased efficiency and safety because the materials handling units will be more stable al height and will be able to achieve greater lift heights in safety, thereby increasing capacity.

The rails inside the aisles of the V'NA system allow for infinite adjustment with regard to flatness and levelness at the installation stage. It will be possible to adjust the rails so that there is no practical difference in elevation between one rail and the other (certainly much flatter than that demanded by Properties A and B of the DM1 flatness specification according to table C.t of Appendix C to the 2003 edition of the Concrete Society's Technical Report Number 34 or Gennan Standard DINI 5185) and the rails will provide a greater degree of flatness than any concrete floor can (certainly much flatter than that demanded by Properties C and D of the DM1 flatness specification according to table C. 1 of Appendix C to the 2003 edition of the Concrete Society's Technical Report Number 34 or German Specification DIN! 5185). This means that the racking can be significantly higher than with a traditional non top-guided VNA system and so the installation may be accommodated in a smaller floor area than would otherwise be the case.

Because this invention allows for adjustment of levelness and flatness when the rails are installed it will not be necessary for the concrete floor slab to achieve very stringent levels of flatness and thus, because long-strip construction would be unnecessary, the construction of the slab could be accelerated and joint design could be optimised for longevity rather than flatness. It would be unnecessary to achieve the DM1 flatness specification according to table C.1 of Appendix C to the 2003 edition of the Concrete Society's Teclmical Report Number 34 -the FM2 flatness specification according to table 4.2 of the Concrete Society's Technical Report Number 34 could be more than sufficient for the use of the present invention.

Because the materials handling unit is used on a totally flat surface in the aisles it will be always possible to operate the materials handling unit and therefore the whole installation at maximum capacity.

In addition, the system of the present invention allows racking to be constructed to a higher level, meaning that the floor area of the warehouse could be reduced while providing the same volume, or volume could be increased for the same floor area. This would lead cost savings.

The system of the present invention will be less costly to procure than a traditional top-guided or crane system because there will be no need for any support to the top of the mast, which will allow for a more lightweight building structure, or the adoption of a clad racking structure.

The system of the present invention reduces the cycle of damage and repair to joints in floors. This is because, whilst in the aisles of a VNA system, the guide rails transfer the load of the materials handling unit across the joint without the damaging sudden impact that occurs when materials handling equipment with solid rubber or similar tyres cross a joint.

As this invention allows the materials handling unit to travel on a different set of wheels whilst in transfer areas (and therefore not at height), these wheels could be of a material which is less damaging to joints in the floor to extend the life of the joints in transfer areas and so reduce maintenance costs.

According to another aspect of the invention, there is provided a method of accessing materials stored in racking separated by aisles in a VNA system, the method using a materials handling system comprising a materials handling unit and a pair of substantially parallel guide rails located within the aisles, the method including the step of: aligning the materials handling unit with the ends of the guide rails and propelling the materials handling unit up onto the guide rails and driving the materials handling units along the guide rails alongside the racking to the required location within the aisle to access the materials.

The invention will now be described, with reference to the accompanying drawings, of which: Figure lA is a perspective view of a materials handling unit for use in a materials handling system of the present invention; Figure lB is a perspective view of the materials handling unit of Figure IA and a pair of guide rails, forming a materials handling system; Figure 2 is a schematic representation of a cross-section through the materials handling system of Figure lA along line A-A' in Figure 4; Figure 3 is a schematic representation of a cross section through the materials handling system of Figure IA along the line A-A' in Figure 4; "-9-Figure 4 is a schematic representation of the materials handling unit of Figure 1A as viewed from underneath the materials handling unit and illustrating the internal components of the materials handling unit; Figures 5A to 5C illustrate schematically the mounting on the materials handling unit onto the guide rails; and Figures 6A and 6B schematically illustrate the clearance of the respective wheels of the materials handling unit off and on the guide rails respectively.

A materials handling unit 1 of the present invention comprises a forklift truck. The materials handling unit I comprises a body 2 having a first end 3, a second end 4, side faces 5, 6, an underside 7 and a plurality of wheels 8a, Sb, Sc configured to support the materials handling unit 1 on a floor surface 20 of a warehouse.

The body 2 includes a cab 12 for enclosing an operator 100, and which houses the various unit control mechanisms (not shown) such a steering wheel, stop and start switches and controls for operation of a materials handling mechanism. The materials handling mechanism includes a forklift arrangement 13 which can translate up and down a mast 14 and a staged mast 9.

The forklift arrangement 13 is also rotatable about an axis so that it can move from side to side to access racking 29 in which materials are stored as well as move materials vertically using the staged mast 9 as in known materials handling equipment. The materials handling equipment is of a known type.

In the embodiment described herein, the body 2 includes three main wheels 8a, Sb, 8c, in a triangular configuration with two fixed main wheels Sb, Sc towards opposing side faces 5, 6 of the body 2 and a third, driven wheel 8a configured as steerable for free movement and coupled to a motor 11 which drives the third wheel 8a. The third wheel Sa is also coupled to a steering wheel, or other suitable steering mechanism (not shown) in the cab 12 for steering and driving to steer the materials handling unit I as required. Such steering and driving mechanisms are well known to persons skilled in the art, and variations and adaptations of this can be used as appropriate and required.

As such, these aspects of the configuration and operation of such a materials handling unit is well known to persons skilled in the art and need not be described in any ftirther detail herein except as is relevant to the present invention.

In addition to the steering and driving mechanism described above, the materials handling unit 1 has a second set of a plurality of wheels.

This second set of wheels comprise four wheels arranged in two pairs 16a, lob; 17a, 17b.

The first pair of wheels lOa, l6b are located towards the first end 3 of the vehicle body 2, one wheel of each first pair being on opposing side faces 5, 6 of the vehicle body 2 and having a first common axis of rotation 18. The second pair wheels 1 7a, I 7b are located towards the second end 4 of the vehicle body 1, one wheel of each second pair 17a, 17b being on opposing side faces 5, 6 of the body 2 and having a second common axis of rotation 19.

The first common axis of rotation 18 and the second common axis of rotation 19 are substantially parallel to each other, and displaced a predetermined distance from the underside 7 of the unit body 2 such that, when the plurality of wheels 8a, Sb, Sc of materials handling unit 1 are in contact with the floor surface 20, the second set of wheels lOa, 16b; 17a, l7b are raised from the ground surface such that they are clear the floor surface 20 and in non-contact with the floor surface 20. The second set of wheels 16a, 1 6h; I 7a, 1 7h are never in contact with the floor surface 20.

This is illustrated in Figure 2 which shows the second pair of wheels 17a, 17b raised from the floor surface 20 and arranged in the plane Y which is displaced clear of the floor surface 20. In the embodiment described herein, this clearance, x, between the bottom of the second pair of wheels 17a, 17b would be 55mm from the ground surface 20, should rails 23, 24 of the type A45 defined by D1N536 part I be used see Figure 6A.

The clearance will depend upon the elevation of the uppermost surface mounting surface 25, 26 of rails 23, 24 used with the material handling unit 1 -and which are described in further detail below. Generally, the second set of wheels 1 6a, I 6b; I 7a, 1 7b may be clear of the ground surface by 10-15mm less than the elevation of the corresponding paired rails which the materials handling unit will be mounted upon.

In the first pair of wheels l6a, l6b, each wheel 16a, 16b is connected to the respective side face 5, 6 by means of a spigot 22a, 22b for free rotation around it. In an alternative, the first pair of wheels 16a, 16b could also be connected to each other via an axle (not shown).

The second pair of wheels 1 7a, I 7b are connected to the motor 11 via a drive shaft 10, or other suitable drive-link so that the second pair of wheels 17a, 17b can be driven by the motor 11. In an alternative, the drive shaft 10 could be connected to a separate drive mechanism (not shown). These are the drive wheels of the second set of wheels 16a, l6b; 17a, l7b.

Each of the wheels of the second set of wheels l6a, 16b, 17a, 17b have a circumferential lip 27a, 27b, 27c, 27d to assist in retaining the wheels on rails 23, 24, as described in further detail below.

The materials handling unit I is part of a materials handling system which comprises the materials handling unit 1 and at least one pair of rails 23, 24-one pair of rails 23, 24 for each aisle in a YNA warehouse installation.

The rails 23, 24 can be any suitable known rail as used in known crane systems -but using two parallel rails which can be fixed to the floor surface 20 at the outer edges of the rather than a single rails as utilised in known crane systems. A suitable rail could be the A45 type as defined by D1N536 part 1 as its 55mm height would minimise its interference with storage space, although any suitable established type of rail and fastening system could be used.

In the present invention, the rails 23, 24 have an I-shaped cross-sectional profile and define upper mounting surfaces 25, 26 upon which the wheels of the second set of plurality of wheels 1 6a, 1 6b; I 7a, 1 7b can be mounted so that the wheels of the second set of plurality of wheels 16a, 16b; 17a, 17b engage with the mounting surfaces 25,26 and can move backwards and forwards along the rails 23, 24.

The rails 23, 24 are located within the aisles 28 of a VNA warehouse installation and adjacent the racking 29. This is illustrated in Figure 4.

The rails 23, 24 are inclined at each end (typically at the end of each aisle 28) to provide a ramped portion 30 for the materials handling vehicle I to ascend onto the guide rails 23, 24 -see Figures SA to SC. The length and degree of ramp is exaggerated in these figures for clarity and, may, in practice be between 100mm and 3000mm in length.

When the second set of a plurality of wheels 16a, 16b, 17a, l7b is in contact with the respective mounting surface 25, 26 of the paired set of rails 23, 24 then the first set of a plurality of wheels 8a, 8b, 8c are clear of the floor 20 enabling the materials handling unit ito run on the flat mounting surface 25, 26 of the rails 23, 24.

The clearance,y, between the first set of a plurality of wheels 8a, 8b, 8c and the floor surface 20 when running on the paired rails 23, 24 need only be small: between 10mm and 15mm -see Figure 6B. This obviates the need for a steep or long inclined surface at the end of each set of paired rails 23, 24. The height, z, of the rails 23, 24 can therefore be selected as appropriate, given that z = x + y.

When the materials handling unit 1 is needed to access materials stored on the racking 29, the materials handling unit I is driven, under control of the operator 100 in the usual way, using the three main wheels 8a, 8b, 8c, so that the materials handling unit 1 is aligned with the rails 23, 24 so that the whcels of the second set of a plurality ofwheelslóa, I 6b; 1 7a, 17b are aligned with the guide rails 23, 24-two wheels on each side of the body 2 with the respective guide rails 23, 24. This is illustrated in Figure 5A.

The second pair of wheel 17a, 17b, which are the driven wheels, are used to propel the materials handling unit 1 forward so that the materials handling unit 1 is propelled onto the guide rails 23,24 via the ramped portion 30-see Figure SB. Further propulsion of the materials handling vehicle I drives the materials handling unit 1 fully onto the guide rails 23, 24 for moving along the guide rails 23, 24 and down the aisle 28 to the required location.

The materials handling unit I is dismounted from the guide rails 23, 24 in a reverse operation.

The second pair of wheels l7a, 17b and wheel 8a are geared such that the speed of rotation of all the driven wheels Sa, 17a, 17b of the materials handling unit 1 are at the same speed at the point that the materials handling unit 1 mounts and dismounts the guide rails 23, 24 in order to avoid a sudden jolt caused by a change of gearing caused by any difference in wheel diameter. This is because the contact of wheels 1 7a, 1 7b with the inclined surface at the ends of the guide rails 23, 24 will result in wheel 8a being lifted clear of the floor as the materials handling unit I enters the VNA. At this point wheels 1 7a, I 7b would propel the materials handling unit 1 along the guide rails into the VNA. This transition must be smooth and so the drive wheels must be geared identically.

Alternatively, the first pair of wheels l6a, 16b can be the driven wheels.

One pair of the second set of a plurality of wheels I 6a, 1 6b; I 7a, I 7b could be mounted on an axle (not shown) which is configured to pivot on a horizontal axis to avoid structural stress or instability being caused by any slight difference in elevation between the wheels of the second set of a plurality of wheels I 6a, lob; 1 7a, 1 7b.

When operating outside the aisles 28 the materials handling unit 1 would move as a conventional inductive wire-guided or rail-guided materials handling unit.

As an alternative, the main wheels 8a, 8b, 8c could be made of a material that is less damaging to joints in concrete floors.

Claims

CLAIMS1. A materials handling unit comprising a body having a first end, a second end, side faces, an underside and a first set of a plurality of wheels configured to support the materials handling unit on a surface for movement thereon, the materials handling unit thither comprising a materials handling mechanism mounted on the vehicle body for supporting and moving materials, the body being arranged to house a drive means coupled to at least one of the first set of a plurality of wheels for driving the at least one of the first set of a plurality of wheels, wherein the body further includes a second set of a plurality of wheels comprising a first pair of wheels and a second pair of wheels, the first pair of wheels being located towards the first end of the vehicle body, one wheel of each first pair being on opposing side faces of the vehicle body and having a first common axis of rotation, and the sccond pair wheels being located towards the second end of the vehicle body, one wheel of each second pair being on opposing side faces of the vehicle body and having a second common axis of rotation, the first common axis of rotation and the second common axis of rotation being substantially parallel to each other, and displaced a predetermined distance from the underside of the vehicle body such that, when the first set of a plurality of wheels of the materials handling unit is in contact with the surface, the second set of a plurality of wheels are clear of the surface.
2. A materials handling unit according to claim 1, wherein the drive means is coupled to at least one pair of the second set of a plurality of wheels for driving the at least one of the second set of wheels.
3. A materials handling unit according to claim 2, wherein the drive means is configured to drive at least one wheel of either the first pair of wheels or the second pair of wheels.
4. A materials handling unit according to claim 1, wherein the body houses a second drive means, and at least one pair of second set of a plurality of wheels is coupled to the second drive means to drive the one pair of wheels connected to the second drive means.
5. A materials handling unit according to any preceding claim, wherein the first pair of wheels and/or the second pair of wheels are connected by an axle which defines the common axis of rotation.
6. A materials handling unit according to any of claims 1 to 4, wherein, the wheels of the second set of a plurality of wheels are mounted on a wheel carrier such as a spigot.
7. A materials handling unit according to any of claims 2, 3 or 4, wherein the one pair of wheels coupled to the first or second drive means is geared such that the speed of rotation of the one pair of wheels coupled to the first or second drivc means matches the speed of rotation of the first set of plurality of wheels.
8. A materials handling unit according to any preceding claim, wherein the wheels of the second set of plurality of wheels may have a circumferential lip.
9. A materials handling system comprising a materials handling unit and a pair of rails configured for laying on a ground surface in a substantially parallel arrangement, each rail of the pair of rails having a mounting surface, the materials handling unit comprising a body having a first end, a second end, side faces, an underside and a first set of a plurality of wheels configured to support the materials handling unit on the ground surface for movement thereon, the materials handling unit further comprising a materials handling mechanism mounted on the body for supporting and moving materials, the body being arranged to house a drive means coupled to at least one of the first set of a plurality of wheels for driving the at least one of the first set of a plurality of wheels, wherein the body further includes a second set of a plurality of wheels comprising a first pair of wheels and a second pair of wheels for engaging with the mounting surface of each of the pair of rails, the first pair of wheels being locatcd towards the first end of the vehicle body, one wheel of each first pair being on opposing side faces of the vehicle body and having a first common axis of rotation, and the second pair wheels being located towards the second end of the vehicle body, one wheel of each second pair being on opposing side faces of the vehicle body and having a second common axis of rotation, the first common axis of rotation and the second common axis of rotation being substantially parallel to each other, and displaced a predetermined distance from the underside of the vehicle body such that, when the second set of a plurality of wheels are in in engagement with the mounting surface, the first set of a plurality of wheels of the materials handling unit are clear of the surface.
10. A materials handling system according to claim 9, wherein, each of the rails of the pair of rails has an inclined surface at the ends.
11. A materials handling system according to claim 9 or claim 10, wherein the clearance between the ground surface and the first set of a plurality of wheels, when the materials handling unit is mounted on the rails, is betweón 10mm and 15mm.
12. A method of accessing materials stored in racking separated by aisles in a very narrow aisle system, the method using a materials handling system according to any of claims 9 to II, the method including the steps of: aligning the materials handling unit with the ends of the guide rails and propelling the materials handling unit up onto the rails and driving the materials handling units along the rails alongside the racking to the required location within the aisle to access the materials.