CN118765252A - Guide rail sensor structure - Google Patents

Abstract

The present invention provides an improved guide rail sensor structure for an automated vehicle operating on an automated storage and retrieval system, whereby a sensor is arranged to directly detect the position of the vehicle relative to an access opening. In the context of the present invention, the term "direct detection" should be understood to mean that the gripping mechanism of the vehicle is correctly positioned relative to the access opening just when the sensor detects a specific structural feature of the guide rail. In one aspect, the specific structural feature of the guide rail is an intersection adjacent to the access opening.

Description

Guide rail sensor structure

Technical Field

The present invention relates to a remotely operated vehicle operating in conjunction with an automated storage and retrieval system, and more particularly to a structure including a track sensor mounted to the automated vehicle for determining the position of the vehicle on a grid-based track system of the automated storage and retrieval system.

Background Art

FIG. 1 discloses a prior art automated storage and retrieval system 1 having a frame 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 .

The frame structure 100 comprises upright members 102 arranged in rows to define a storage volume comprising storage columns 105 arranged in rows between the upright members 102. In these storage columns 105, storage containers 106 (also referred to as bins) are stacked one on top of another to form stacks 107. The members 102 may typically be made of metal, such as extruded aluminum profiles.

The frame structure 100 of the automated storage and retrieval system 1 comprises a rail system 108 arranged on the top of the frame structure 100, on which a plurality of container handling vehicles 201, 301, 401 can be operated to lift and lower storage containers 106 from and into the storage array 105, and also to transport storage containers 106 over the storage array 105. The rail system 108 comprises: a first set of parallel rails 110 arranged to guide the container handling vehicles 201, 301, 401 to move in a first direction X on the top of the frame structure 100; and a second set of parallel rails 111 arranged perpendicular to the first set of rails 110 to guide the movement of the container handling vehicles 201, 301, 401 in a second direction Y perpendicular to the first direction X. The containers 106 stored in the array 105 can be accessed by the container handling vehicles 201, 301, 401 through access openings 112 located in the rail system 108. The container handling vehicles 201, 301, 401 can move laterally on the storage row 105, i.e. in a plane parallel to the horizontal X-Y plane.

The upright members 102 of the frame structure 100 may be used to guide the storage containers during lifting and lowering of the containers from and into the row 105. The stack 107 of containers 106 is generally self-supporting.

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, which enable the container handling vehicle 201, 301, 401 to move laterally in the X direction and the Y direction, respectively. In Figures 2, 3 and 4, both wheels in each set are fully visible. The first set of wheels 201b, 301b, 401b is arranged to engage with two adjacent tracks in the first set of tracks 110, and the second set of wheels 201c, 301c, 401c is arranged to engage with two adjacent tracks in the second set of tracks 111. At least one of these sets of wheels 201b, 201c, 301b, 301c, 401b, 401c can be raised and lowered so that the first set of wheels 201b, 301b, 401b and/or the second set of wheels 201c, 301c, 401c can engage with a corresponding set of rails 110, 111 at any one time.

Each prior art container handling vehicle 201, 301, 401 further comprises a lifting device for vertically transporting storage containers 106, for example lifting storage containers 106 out of storage row 105 and lowering storage containers 106 into storage row. The lifting device comprises one or more gripping/engaging devices adapted to engage with storage containers 106, and these gripping/engaging devices can be lowered from the vehicle 201, 301, 401 so that the position of the gripping/engaging devices relative to the vehicle 201, 301, 401 can be adjusted in a third direction Z orthogonal to the first direction X and the second direction Y. Parts of the gripping devices of the container handling vehicle 301, 401 are indicated in FIGS. 3 and 4 using reference numerals 304, 404. The gripping devices of the container handling vehicle 201 are located within the vehicle body 201a in FIG. 2 and are therefore not shown.

Conventionally, and also for the purposes of this application, Z=1 identifies the uppermost layer available for storage containers below the tracks 110, 111, i.e., the layer immediately below the track system 108, Z=2 identifies the second layer below the track system 108, Z=3 identifies the third layer, and so on. In the exemplary prior art disclosed in FIG. 1, Z=8 identifies the lowest bottom layer of storage containers. Similarly, X=l...n and Y=1...n identify the position of each storage column 105 in the horizontal plane. Therefore, as an example, and using the Cartesian coordinate system X, Y, Z indicated in FIG. 1, the storage container identified as 106' in FIG. 1 can be said to occupy the storage position X=17, Y=1, Z=6. The container handling vehicle 201, 301, 401 can be said to be traveling in the Z=0 layer, and each storage column 105 can be identified by its X coordinate and Y coordinate. Therefore, the storage container extending above the track system 108 shown in FIG. 1 is also said to be arranged in the layer Z=0.

The storage volume of the frame structure 100 is generally referred to as a grid 104, wherein the possible storage positions within the grid are referred to as storage units. Each storage column can be identified by a position in the X and Y directions, and each storage unit can be identified by a container number in the X, Y and Z directions.

Each prior art container handling vehicle 201, 301, 401 includes a storage compartment or space for receiving and loading the storage container 106 when transporting the storage container 106 on the rail system 108. The storage space may include a cavity arranged in the vehicle body 201a, 401a, as shown in Figures 2 and 4, and as described in, for example, WO2015/193278A1 and WO2019/206487A1, the contents of which are incorporated herein by reference.

Figure 3 shows an alternative configuration of a container handling vehicle 301 having a cantilever configuration. Such a vehicle is described in detail in, for example, NO 317366, the contents of which are also incorporated herein by reference.

The chamber container handling vehicle 201 shown in Figure 2 can have a footprint covering an area with dimensions generally equal to the lateral extent of the storage row 105 in the X and Y directions, such as described in WO2015/193278A1, the contents of which are incorporated herein by reference. The term "lateral" as used herein can refer to "horizontal".

Alternatively, the cavity container handling vehicle 401 may have a larger footprint than the lateral area defined by the storage row 105 shown in Figures 1 and 4, such as disclosed in WO2014/090684A1 or WO2019/206487A1.

As shown in FIG. 5 , the track system 108 generally includes a track 110 having a groove 501 in which the wheels of the vehicle travel. The groove 501 is defined by an upwardly protruding element 502. These grooves 501 and the upwardly protruding element 502 are collectively referred to as guide rails 503, and the upwardly protruding element 502 may alternatively be referred to as a "guide rail wall" 502. Each track may include a guide rail, or each track 110, 111 may include two parallel guide rails. In other track systems 108, each track in one direction (e.g., the X direction) may include a guide rail, and each track in another vertical direction (e.g., the Y direction) may include two guide rails. Each track 110, 111 may also include two guide rail members fastened together, each guide rail member providing a guide rail for a pair of guide rails provided by each track. As also shown in FIG. 5 , the vertical guide rails 503 intersect to form a cross section 504, in which there is no upwardly protruding element 502 to allow the wheels of the vehicle to cross the cross section in the X direction or the Y direction.

WO 2018/146304 A1 (the contents of which are incorporated herein by reference) shows a common configuration of a track system 108, which includes tracks and parallel guides in the X-direction and the Y-direction.

In the frame structure 100, most of the columns 105 are storage columns 105, i.e., columns 105 in which storage containers 106 are stored in the form of stacks 107. However, some columns 105 may have other purposes. In FIG. 1 , columns 119 and 120 are special purpose columns of the type that container handling vehicles 201, 301, 401 use to unload and/or pick up storage containers 106 so that they can be transported to access stations (not shown), where storage containers 106 can be accessed from the outside of the frame structure 100 or transferred out of or into the frame structure 100. In the art, such locations are generally referred to as "ports", and the columns in which the ports are located may be referred to as "port columns" 119, 120. Transport to the access stations may be in any direction, i.e., horizontal, inclined, and/or vertical. For example, storage containers 106 may be placed in random or dedicated rows 105 within the frame structure 100 and then picked up by any container handling vehicle and transported to port rows 119, 120 for further transport to a storage and retrieval station. Transportation from the port to the storage and retrieval station may require movement along a variety of different locations with the aid of, for example, a delivery vehicle, a dolly or other transport line. Note that the term "inclined" refers to the transportation of storage containers 106 with a general transport orientation somewhere between horizontal and vertical.

In Figure 1, the first end port column 119 can be, for example, a dedicated unloading port column, where container handling vehicles 201, 301, 401 can unload storage containers 106 to be transported to an access station or a transfer station, and the second end port column 120 can be a dedicated picking port column, where container handling vehicles 201, 301, 401 can pick up storage containers 106 that have been transported from the access station or the transfer station.

The access station can generally be a picking station or storage station that removes products from or places products into the storage container 106. In the picking station or storage station, the storage container 106 is generally not removed from the automatic storage and retrieval system 1, but is returned to the frame structure 100 again after access. The port can also be used to transfer the storage container to another storage location (e.g., to another frame structure or another automatic storage and retrieval system), to a transport vehicle (e.g., a train or truck), or to a production location.

A conveying system including a conveyor is typically used to transport storage containers between the port rows 119, 120 and the access station.

If the port rows 119, 120 and the access station are located at different heights, the conveying system may include a lifting device with a vertical component for vertically transporting the storage containers 106 between the port rows 119, 120 and the access station.

The conveying system may be arranged to transfer storage containers 106 between different frame structures, for example as described in WO 2014/075937 A1, the contents of which are incorporated herein by reference.

When a storage container 106 stored in one of the columns 105 disclosed in FIG. 1 is to be accessed, one of the container handling vehicles 201, 301, 401 is instructed to take out the target storage container from the position where the target storage container 106 is located, and transport it to the unloading port column 119. This operation includes moving the container handling vehicle 201, 301, 401 to a position above the storage column 105 where the target storage container 106 is located, taking out the storage container 106 from the storage column 105 using a lifting device (not shown) of the container handling vehicle 201, 301, 401, and transporting the storage container 106 to the unloading port column 119. If the target storage container 106 is located deep in the stack 107, that is, one or more other storage containers 106 are located above the target storage container 106, the operation also includes temporarily moving the storage container located above before lifting the target storage container 106 from the storage column 105. This step, sometimes referred to in the art as "digging," may be performed with the same container handling vehicle that is subsequently used to transport the target storage container to the unloading port row 119, or with one or more other cooperating container handling vehicles. Alternatively or additionally, the automated storage and retrieval system 1 may have container handling vehicles 201, 301, 401 that are dedicated to the task of temporarily removing storage containers 106 from the storage row 105. After the target storage container 106 has been removed from the storage row 105, the temporarily removed storage container 106 may be relocated to the initial storage row 105. However, the removed storage container 106 may alternatively be relocated to other storage rows 105.

When a storage container 106 is to be stored in one of the rows 105, one of the container handling vehicles 201, 301, 401 is instructed to pick up a storage container 106 from the pick-up port row 120 and transport it to a position above the storage row 105 where the storage container is to be stored. After any storage container 106 located at or above the target position within the stack 107 is removed, the container handling vehicle 201, 301, 401 positions the storage container 106 at the desired position. The removed storage container 106 can then be lowered back into the storage row 105, or relocated to another storage row 105.

In order to monitor and control the automatic storage and retrieval system 1, for example, to monitor and control the position of each storage container 106 within the frame structure 100, the contents of each storage container 106, and the movement of the container handling vehicles 201, 301, 401, so that the desired storage container 106 can be delivered to the desired location at the desired time without the container handling vehicles 201, 301, 401 colliding with each other, the automatic storage and retrieval system 1 includes a control system 500, which is typically computerized and typically includes a database for tracking the storage containers 106.

Against this background, it would be desirable in the art to provide a container handling vehicle that combines the most valuable features of a cantilever type vehicle and a vehicle having an internally arranged cavity.

Guide rail sensor

It is desirable for the control system 500 to know the precise positioning of the container handling vehicles described above as they travel along and/or stop on the rail system 108. In particular, it is desirable for the container handling vehicles to be accurately positioned so that when a lifting or lowering operation is contemplated, the vehicle's lifting device is precisely aligned relative to the access openings 112. These access openings are defined by two sets of parallel rails that intersect, thereby forming four adjacent intersections 504 around the access openings.

It is known to arrange one or more sensors on a container handling vehicle that detect the position of the vehicle as it travels along or stops on the rails of a rail system. In particular, a known sensor arranged on a vehicle of the type shown as vehicle 301 is capable of detecting when vehicle 301 encounters an intersection 504 of vertical rails 503. Such a sensor has a single emitter and detector.

Due to the shape and configuration of the vehicle 301, in which the gripping device 304 is arranged on an extended cantilever, the gripping device is not aligned over the associated access opening at the moment the sensor detects the adjacent intersection 504. Instead, the sensor detects when the previous intersection is passed, and the control system 500 then "counts" a predetermined number of wheel rotations as the vehicle travels further to determine that the gripping mechanism 304 is correctly positioned over the associated access opening. Therefore, a sensor structure is needed that detects the structure of the guide rail system, in particular the intersection, at the moment the vehicle is correctly positioned (in which the gripping device of the vehicle is located over the associated access opening).

Summary of the invention

The invention is set forth and characterized in the independent claim, while the dependent claims describe further characteristics of the invention.

The present invention provides an improved guide rail sensor structure for an automated vehicle operating on an automated storage and retrieval system, whereby a sensor is arranged to directly detect the position of the vehicle relative to an access opening. In the context of the present invention, the term "direct detection" should be understood to mean that the gripping mechanism of the vehicle is correctly positioned relative to the access opening when the sensor simultaneously detects a specific structural feature of the guide rail. In one aspect, the specific structural feature of the guide rail is an intersection adjacent to the access opening, more specifically, the end of the guide rail wall located at the intersection.

The present invention relates to a track sensor arranged on a remotely operated container handling vehicle or other type of vehicle for operation on a two-dimensional grid-based track system of an automated storage and retrieval system. The vehicle may include a body, a first set of wheels that enable the remotely operated vehicle to move in a first direction of the track system, and a second set of wheels that enable the remotely operated vehicle to move in a second direction of the track system, the second direction being perpendicular to the first direction. The vehicle selectively raises or lowers each set of wheels to change direction on the grid-based track system through an operation called "track switching".

For the purposes of this application, the terms "container handling vehicle," "remotely operated vehicle," and "autonomous vehicle" all refer to a wheeled robotic vehicle that runs on a track system arranged on top of a frame structure that is part of an automated storage and retrieval system.

The term "storage container" as used herein defines a container for storing articles. Alternative descriptive terms for such containers may be "cargo container," "cargo holder," "article container," "storage box," etc. In this context, a storage container may be a box, a pallet box, a pallet, a tray, or the like. Different types of cargo holders may be used in the same automated storage and retrieval system. In some contexts, the term "storage container" may be considered to be similar to an actual article that can be gripped, lifted, and lowered by a vehicle of the system, even if the article is not stored in a separate container.

Relative terms "upper", "lower", "below", "above", "higher than" and the like are to be understood in their normal sense and as seen in a Cartesian coordinate system. When referred to in relation to a track system, "upper" or "above" are to be understood as a position closer to the surface of the track system (relative to another component), as opposed to the terms "lower" or "below", which are to be understood as a position further away from the track system (relative to another component).

According to one aspect, the present invention comprises:

a. An autonomous wheeled vehicle arranged to travel along a grid-based track system, the track system comprising a plurality of parallel tracks arranged in a first direction and a plurality of parallel tracks arranged in a second direction, the tracks in the first direction and the tracks in the second direction intersecting perpendicularly to form a plurality of intersections defining a plurality of grid access openings, each track being provided with a single guide rail or a pair of parallel guide rails for wheels of the vehicle, each guide rail being in the form of a groove defined by upwardly projecting guide rail walls terminating at ends at the intersections, the vehicle being capable of changing the direction of travel of the vehicle from a first direction to a second direction by alternately lifting each set of wheels out of the guide rails or lowering each set of wheels into the guide rails, the first set of wheels being arranged for travel in the first direction and the second set of wheels being arranged for travel in the second direction,

b. A sensor attached to the vehicle and arranged so that when the first set of wheels is lowered or raised, the sensor is lowered or raised, the sensor comprising:

i. A sensor body having a recess arranged to receive a rail wall of the rail when the first set of wheels is lowered into the rail.

ii. a plurality of emitters, each emitter being arranged to emit an energy beam; and one or more corresponding detectors arranged to detect the energy beam from the emitter,

iii. wherein the emitter and one or more corresponding detectors are arranged on opposite sides of the recess so that when the first set of wheels is lowered into the guide rail, the guide rail wall blocks the beam emitted from the emitter from reaching its corresponding detector,

iv. and additionally, wherein the sensor is attached to the vehicle at a position such that when a predetermined portion of the vehicle is located over an associated access opening, a beam from the emitter is able to reach its corresponding detector.

According to another aspect, the present invention comprises:

A method for determining the position of an automated vehicle operating on a grid-based track system, the track system comprising a plurality of parallel tracks arranged in a first direction, the tracks in the first direction and the tracks in the second direction intersecting perpendicularly to form a plurality of intersections defining a plurality of grid access openings, each track being provided with a single guide rail or a pair of parallel guide rails for wheels of the vehicle, each guide rail being in the form of a groove defined by an upwardly projecting guide rail wall, the guide rail wall terminating at a distal end at the intersection, the vehicle being able to change the direction of travel of the vehicle from the first direction to the second direction by alternately lifting each set of wheels out of the guide rail or lowering each set of wheels into the guide rail, the first set of wheels being arranged for travel in the first direction, and the second set of wheels being arranged for travel in the second direction, the method being characterized by comprising:

a. Set up the sensor, which includes:

i. a sensor body having a recess arranged to receive a rail wall of the rail when the first set of wheels is lowered into the rail,

ii. a plurality of emitters, each emitter arranged to emit an energy beam; and one or more corresponding detectors arranged to detect the energy beam from the emitter,

iii. wherein the emitter and one or more corresponding detectors are arranged on opposite sides of the recess so that when the first set of wheels is lowered into the guide rail, the guide rail wall blocks the beam emitted from the emitter from reaching its corresponding detector,

b. attaching the sensor to the vehicle at a position such that when a predetermined portion of the vehicle is located above the associated access opening, the beam from the emitter is able to reach its corresponding detector,

c. lowering a first set of wheels of the vehicle into the guide rail so that the vehicle travels in a first direction, whereby the sensor is also lowered such that the guide rail wall enters the recess and blocks the beam from the emitter from reaching its corresponding detector,

d. driving the vehicle in a first direction until the beam from the transmitter passes the end of the guideway wall at an intersection adjacent the associated access opening, and

e. When the sensor is positioned relative to the adjacent intersection such that a predetermined portion of the vehicle is aligned over the associated access opening, stopping the vehicle.

According to one aspect, the present invention provides a structure including at least one guide rail sensor mounted on an automated vehicle for detecting the position of the vehicle relative to a guide rail of a track system of an automated storage and retrieval system when the vehicle is traveling in a first direction. In one aspect, multiple sensor structures are on the vehicle, at least one sensor structure is configured to detect the position relative to traveling in the first direction, and at least one sensor structure is configured to detect the position relative to traveling in a second direction. Hereinafter, the structure will be described by reference to a single sensor (a sensor/the sensor), however, it should be understood that if the structure includes more than one sensor, the plural form of this description also applies.

A sensor according to one aspect of the present invention includes a sensor body having a recess arranged longitudinally in the direction of travel of the vehicle. A plurality of emitters are arranged along one side of the recess, each emitter having a corresponding detector arranged on the other side of the recess. The term "corresponding detector" for one emitter should be understood to include a structure in which each emitter is associated with its own unique detector, and a structure in which one detector can detect beams from more than one emitter. In the latter case, more than one emitter will have the same detector as its "corresponding" detector. In an alternative embodiment, the sensor body is an "L" shaped piece, wherein the emitters are arranged on the short legs of the "L" shaped piece, and the corresponding detectors are arranged at or near the ends of the long legs of the "L" shaped piece, wherein the beam is emitted upward and at an angle to its corresponding detector. In this embodiment, the direct space between the emitter and the detector can be considered to be similar to the "recess" described above.

The transmitter emits an energy beam in the form of an infrared signal, a light signal, or any other suitable signal known in the art.

The transmitters are arranged "in series" along the recess. In this context, the term "in series" means that when the vehicle is traveling in a given direction and the sensor passes a given point, the transmitters will encounter that point one after another in sequence. The first transmitter to encounter that point can be referred to as the "leading" transmitter, and the subsequent one or more transmitters in the series can be referred to as the "trailing" transmitters.

The sensor is attached to the vehicle so that when the associated set of wheels is lifted or lowered during the guideway switching operation, the sensor is lifted out of the groove of the guideway or lowered into the groove of the guideway. To achieve this coordinated lifting, the sensor can be attached to the wheel set, to a movable frame associated with the wheel set, to the vehicle body, or to any other structure of the vehicle that is lifted or lowered in connection with the guideway switching operation.

When the wheel set is lowered into contact with the track, the sensor associated with that wheel set is lowered so that the rail wall blocks the line of sight between the emitter and its corresponding detector. In one embodiment, the wall enters a recess in the sensor body, and in an embodiment with an L-shaped sensor body, the wall enters the recess between the emitter and its corresponding detector. Thus, the rail wall will block the beam from the emitter from reaching its corresponding detector. When the wheel set is lifted, the associated sensor is also lifted out of the recess so that the rail wall is not inside the recess and the beam is not blocked.

In one embodiment, the sensor structure of the present invention is on the bottom of the vehicle, within the perimeter of the vehicle defined by the outer wall or end of the body, and connected to the vehicle so that when the track switching operation of the vehicle is actuated to configure the vehicle to travel in a first direction, a first sensor associated with a first set of wheels is lowered to a position in the groove of the guide rail. A second sensor associated with a second set of wheels is raised to a position above the groove of the guide rail in the same operation. Conversely, when the track switching mechanism of the vehicle is actuated to configure the vehicle to travel in a second direction, the second sensor is lowered to a position in the groove of the guide rail and the first sensor is raised above the groove of the guide rail.

The sensor is in electronic communication with the control system of the automatic storage and retrieval system, or directly with the on-board control system of the vehicle itself. When the vehicle travels along a section of the guide rail with a guide rail wall, the beams from all the emitters of the sensors in the groove will be blocked. As described above, since the guide rails of the track system have guide rail walls between the intersections defining the access openings, when all the beams are blocked, the control system will recognize that the vehicle is currently located between the access openings of the grid. When the vehicle travels to a position where the guide rails do not have guide rail walls (such as the intersection of the vertical guide rails), the beams are not blocked and can thus reach their corresponding detectors. By means of the serial arrangement of the emitters, at the moment when the leading beam passes the end of the guide rail wall, the beam from the leading emitter will be able to reach its corresponding detector, while the beam from the trailing emitter will continue to be blocked. Thus, the leading sensor can immediately detect the end of the guide rail wall. Thus, the sensor directly detects the position of the vehicle relative to the end of the guide rail wall, in particular the intersection. According to one aspect, the distance between the leading sensor and the trailing sensor corresponds to the tolerance deviation of the positioning of the vehicle relative to the access opening.

According to one embodiment, the sensor comprises a leading transmitter, a first trailing transmitter and a second trailing transmitter. The sensor structure is on the vehicle so that when the beam of the leading transmitter is blocked by the structure adjacent to the intersection and cannot reach its corresponding detector, and the beams of the first trailing transmitter and the second trailing transmitter reach their corresponding detectors, the clamping device of the vehicle is aligned above the access opening. In addition, according to this embodiment, the transmitter is arranged on the sensor so that the position of the vehicle relative to the relevant access opening is incorrect if one of the following conditions is met:

a. The beam from the leading emitter and the beam from the first trailing emitter are detected by their corresponding detectors, while the beam from the second trailing emitter is blocked from reaching its detector, or,

b. the beams from the leading emitter and the second trailing emitter are detected by their corresponding detectors, while the beam from the first trailing emitter is blocked, or,

c. The beams from all three emitters are detected by their corresponding detectors.

When used with this embodiment, the vehicle will be driven to the intersection adjacent to the associated access opening. When the sensor passes the end of the guide rail wall, the beam from the leading transmitter is detected first, while the beams from the first and second trailing transmitters remain blocked. As the vehicle travels, the leading beam and the first trailing beam will be detected, while the second trailing beam remains blocked. When the vehicle travels to its correct position, the leading beam will be blocked by the end of the next guide rail wall at the intersection, while the beams from the two trailing transmitters are located at the intersection so that their beams are detected. The arrangement of the transmitters in the sensor body is such that any combination of detected/blocked beams, except "blocked-detected-detected", indicates incorrect alignment relative to the intersection.

The sensor of the present invention is preferably mounted to the vehicle at a position so that when the sensor is correctly positioned relative to the structure of the intersection, the vehicle's clamping device is accurately aligned over the access opening. Thus, the exact mounting position of the sensor on the vehicle depends on the shape and size of the vehicle and the position of the clamping device on the vehicle.

In one embodiment, the vehicle of the present invention is configured as follows, but it should be understood that the sensor of the present invention can be installed in other types of vehicles if space and configuration permit.

In one aspect, a sensor is connected to a remotely operated vehicle for carrying storage containers while operating on a two-dimensional track system of an automated storage and retrieval system, wherein the vehicle includes a body, a first set of wheels, and a second set of wheels, the first set of wheels enabling the remotely operated vehicle to move in a first horizontal direction of the track system, the second set of wheels enabling the remotely operated vehicle to move in a second horizontal direction of the track system, the second direction being perpendicular to the first direction, wherein the body includes a motor section and a cavity section, the motor section accommodating at least one drive motor, the cavity section providing a cavity for storing storage containers, the center of gravity of the remotely operated vehicle being located in the cavity section, wherein the first set of wheels includes a pair of driving wheels and a pair of passive wheels, the pair of passive wheels being arranged in the cavity section to transfer part of the load from the remotely operated vehicle to the track system when the remotely operated vehicle moves in the first horizontal direction, and the pair of passive wheels being arranged on the other side of the center of gravity relative to the pair of driving wheels in the first set of wheels.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are attached to facilitate understanding of the present invention. The accompanying drawings illustrate embodiments of the present invention, which will now be described by way of example only, in which:

FIG. 1 is a perspective view of a frame structure of an automatic storage and retrieval system of the prior art.

2 is a perspective view of a prior art container handling vehicle having a centrally located cavity for carrying a storage container therein.

3 is a perspective view of a prior art container handling vehicle having a cantilevered arm section for carrying a storage container underneath.

4 is a perspective view from below of a prior art container handling vehicle having a centrally disposed cavity for carrying a storage container therein.

5 is a perspective view of a section of a prior art track system showing intersections between vertical rails.

6 is a side view of a remotely operated vehicle according to one embodiment of the present invention.

7 is a side view of a remotely operated vehicle according to another embodiment of the present invention.

FIG. 8 embodies the invention by showing two different scenarios in which a remotely operated vehicle according to an embodiment of the invention is located on tracks of a frame structure.

FIG. 9 is a diagram of a remotely operated vehicle viewed from below with sensors attached to the vehicle.

10A and 10B illustrate an alternative embodiment of a sensor body.

11 and 12 show sensors mounted to the bottom of a remotely operated vehicle.

Figures 13 and 14 show the sensor lowered into a groove in the rail.

FIG. 15 shows an embodiment of the invention in which the sensor is correctly positioned relative to the intersection, without the vehicle being shown for ease of viewing.

FIG. 16 is a detailed side perspective view of the sensor of FIG. 15 .

17 and 18 show the sensor entering the intersection but not yet advancing to the properly aligned position.

FIG. 19 shows the sensor having traveled past the correctly aligned position.

Figure 20 shows the sensor aligned relative to the associated access opening.

DETAILED DESCRIPTION

In the following, embodiments of the present invention will be discussed in more detail with reference to the accompanying drawings. It should be understood, however, that the drawings are not intended to limit the present invention to the subject matter depicted in the drawings.

The frame structure 100 of the automatic storage and retrieval system 1 is constructed according to the prior art frame structure 100 described above in conjunction with Figures 1 to 5, that is, it includes a plurality of upright members 102, wherein the frame structure 100 also includes a first upper rail system 108 in the X direction and the Y direction.

The frame structure 100 further comprises storage compartments in the form of storage rows 105 arranged between the components 102 , wherein storage containers 106 can be stacked in the form of stacks 107 in the storage rows 105 .

The frame structure 100 can be of any size. In particular, it should be understood that the frame structure can be wider and/or longer and/or deeper than the frame structure disclosed in Figure 1. For example, the frame structure 100 can have a horizontal extent of greater than 700×700 columns and a storage depth of greater than twelve containers.

As shown in FIG. 5 , the track system 108 generally includes a track 110 having a groove 501 in which the wheels of the vehicle travel. The groove 501 is defined by an upwardly protruding element 502. These grooves 501 and the upwardly protruding element 502 are collectively referred to as guide rails 503, and the upwardly protruding element 502 may alternatively be referred to as a "guide rail wall" 502. Each track may include one guide rail, or each track 110 may include two parallel guide rails. In other track systems 108, each track in one direction (e.g., the X direction) may include one guide rail, and each track in another vertical direction (e.g., the Y direction) may include two guide rails. Each track 110 may also include two guide rail members fastened together, each guide rail member providing a guide rail for a pair of guide rails provided by each track. As also shown in FIG. 5 , the vertical guide rails 503 intersect to form a cross section 504, in which there is no upwardly protruding element 502 to allow the wheels of the vehicle to cross the cross section in the X direction or the Y direction. At intersection 504 , rail wall 502 terminates at tip 506 .

Sensor structures associated with various vehicle implementations

In one aspect, the sensor structure of the present invention includes a sensor 600 that can be connected to a known remotely operated vehicle operating on a grid-based track system of an automated storage and retrieval system, as described in the background section above. In another aspect, the sensor structure includes a sensor 600 connected to a novel embodiment of an automated vehicle, as described below:

The remotely operated vehicle 50 in FIG. 6 is used to carry containers/cargo holders when running on the two-dimensional track system of the automated storage and retrieval system shown in FIG. 1 . The vehicle 50 includes a body 10, a first set of wheels 12, and a second set of wheels 14, wherein the first set of wheels enables the remotely operated vehicle 50 to move in a first horizontal direction (e.g., X direction) of the track system, and the second set of wheels enables the remotely operated vehicle 50 to move in a second horizontal direction (e.g., Y direction) of the track system. Referring to FIG. 1 , the second (Y) direction is perpendicular to the first (X) direction. The body 10 includes a motor section 16 and a cavity section 20, wherein the motor section accommodates at least one drive motor (shown in FIG. 6 ), and the cavity section provides a cavity 22 for storing cargo holders. As shown in FIG. 7 , the center of gravity COG (not visible in FIG. 6 ) of the remotely operated vehicle 50 is located in the cavity section 20.

Returning to FIG6 , the first set of wheels 12 includes a pair of driving wheels 12D and a pair of passive wheels 12P. In the illustrated embodiment, the pair of passive wheels 12P are disposed in the cavity section 20. When the remotely operated vehicle 50 moves in the first horizontal direction, the passive wheels 12P transfer part of the load from the remotely operated vehicle 50 to the track system. Referring to FIGS. 6 and 7 , the pair of passive wheels 12D are disposed on the other side of the center of gravity COG relative to the pair of driving wheels 12P.

By providing a remotely operated vehicle 50 with a pair of passive (non-driven) wheels 12P, a simplified and more robust vehicle design is achieved. This also means that maintenance procedures are less complicated.

The vehicle design according to FIG. 6 also contributes to a significant reduction in the weight of the vehicle 50, since the additional drive motor and the motion transmission mechanism become redundant in this configuration. In addition, the overall weight reduction of the vehicle 50 allows the vehicle to have better acceleration characteristics. In a related context, the total kinetic energy of moving the vehicle 50 is significantly reduced. Therefore, the consequences of an accidental collision involving another vehicle and/or an operator occurring on the track system shown in FIG. 1 will not be too severe.

Still referring to Figure 6, the cavity section 20 includes an outer wall 28 that forms a portion of the perimeter of the remotely operated vehicle 50. The outer wall 28 is flat and perpendicular to the horizontal (XY) plane of Figure 1 .

Regarding the second set of wheels 14, the second set of wheels 14 includes a pair of wheels mounted to a structural cross member 30 in the vehicle body 10. In FIG. 6, the pair of wheels is a pair of driving wheels 14D. FIG. 6 also shows a motor 15 for driving the driving wheels 14D in the second set of wheels 14. Arranged opposite to the pair of driving wheels 14D is a pair of passive wheels 14P in the second set of wheels 14. As shown in FIG. 6, the pair of passive wheels 14P are arranged in the outer wall 28 of the remotely operated vehicle 50. A motor (not shown) for lifting/lowering the second set of wheels 14 is provided in the motor section 16 of the vehicle 50. In the art, the lifting and lowering of the wheel set in order to change the moving direction of the container handling vehicle from the X direction in FIG. 1 to the Y direction or vice versa is referred to as "guideway conversion". Multiple parts of the guideway conversion mechanism 17 are also shown.

FIG7 is a side view of a remotely operated vehicle 50 according to another embodiment of the present invention. More specifically, the embodiment in FIG7 employs a different track conversion mechanism. FIG7 shows portions of a track conversion mechanism 19.

As can be readily inferred, the footprint of the illustrated remotely operated vehicle 50 is rectangular, whereas the vehicle body 10 has an asymmetrical shape in a plane extending along the YZ directions.

Returning to the first set of wheels 12 (discussed in conjunction with FIG. 6 ), a pair of drive wheels 12D in the first set of wheels 12 are disposed in the motor section 16 of the remotely operated vehicle 50. In addition, a wheel axle (not visible in FIGS. 6 and 7 ) associated with a pair of drive wheels 12D in the first set of wheels 12 is disposed in the motor section 16 of the remotely operated vehicle 50. A drive motor 18 for powering the drive wheels 12D is disposed in the motor section 16, which also holds the battery 26 of the remotely operated vehicle 50. The motor section 16 and the cavity section 20 are arranged side by side. A pair of passive wheels 12P are arranged on the other side of the center of gravity COG relative to the pair of drive wheels 12D. The passive wheels 12P in the first set of wheels 12 are not connected by axles and rotate independently of each other. In this way, the individual wheels are isolated, and possible wheel slip (spin) occurs in a single wheel of the wheel pair. A second set of wheels 14 (discussed fully in conjunction with FIG. 6 ) is also shown.

At a general level, the presence of non-driven wheels reduces the risk that these wheels will start to slip due to a loss of traction between the wheels and the supporting rail.

Still referring to FIG. 7 , a distance D1 between the center of a driving wheel 12D in the first set of wheels 12 and a corner 13D of the vehicle 50 associated with the driving wheel is greater than a distance D2 between the center of a driven wheel 12P in the first set of wheels 12 and a corner 13P of the vehicle 50 associated with the driven wheel. In a relevant context, the two driving wheels 12D in the first set of wheels are equal in size, and the two driven wheels 12P in the first set of wheels are equal in size. The diameters of the two driving wheels 12P are greater than the diameters of the two driven wheels 12P.

Providing a smaller passive wheel 12P and a larger driving wheel 12D means that the passive wheel 12P can be moved closer to the corner 13P of the vehicle, that is, closer to the peripheral edge of the vehicle. Therefore, a more stable vehicle with a passive wheel that is less likely to slip is achieved.

FIG. 8 embodies the present invention by showing two different scenarios in which a remotely operated vehicle is located on the track 108 of the frame structure.

As shown in FIG. 8 , the vehicle 50 is positioned above a storage column that is immediately adjacent to the top support column 32. By virtue of its design, the vehicle 50 is able to access cargo holders stored in the storage column. More specifically, the cavity section of the vehicle 50 (shown and discussed in conjunction with FIGS. 5 and 6 ) includes a peripheral outer wall 28 that faces the top support column 32. The outer wall 28 is flat and perpendicular to the horizontal (XY) plane. When the flat outer wall 28 of the vehicle 50 is very close to or even close to the top support column 32, the cavity section is aligned with the storage column below so that the cargo holder can be vertically removed by remotely operating the vehicle 50.

Another remotely operated vehicle 50 shown in Figure 8 is shown positioned at the perimeter of the grid structure and adjacent to the protective fence 34 that defines the grid structure. Similar to the discussion in conjunction with the first remotely operated vehicle 50 in Figure 8, the outer wall 28 of the vehicle 50 is flat and perpendicular to the horizontal (XY) plane, which means the benefits discussed above, such as improving the ability to retrieve difficult to access cargo holders.

The common feature of both scenarios in FIG. 8 is that when lifting cargo holders from or lowering cargo holders into a storage column, the remotely operated vehicle 50 covers a single storage column in one horizontal direction of the rail system 108 and covers one to two storage columns in another horizontal direction of the rail system 108. For a given grid size, the relatively small footprint of the vehicles allows a greater number of remotely operated vehicles to be used than previously available. More specifically, two remotely operated vehicles 50 can occupy adjacent grid positions in one horizontal direction such that the flat outer wall 28 of one vehicle 50 faces the flat outer wall 28 of the other vehicle 50.

Sensor structure

The sensor structure will be described in conjunction with being installed on the vehicle 50 as described above, however, it should be understood that the sensor 600 can be installed on vehicles having different configurations if the size and shape allow the sensor 600 to be in the correct position relative to the operation of the guideway conversion mechanism, and allow the relative distance between the position of the sensor on the vehicle and the clamping device 404 of the vehicle to be such that when the sensor detects the end 506 of the guideway wall 502 at the intersection 504, the clamping device 404 of the vehicle is located above the access opening 112.

9, the sensor structure of the present invention includes one or more sensors 600 connected to the remotely operated vehicle 50. As will be described below, the location where the sensors are mounted on the vehicle enables the sensors 600 to directly detect when the gripping device 404 is properly positioned over the access opening 112.

10A and 10B illustrate alternative embodiments of a sensor 600. The sensor 600 includes a sensor body 602 on which are mounted a plurality of emitters 604 and detectors 606, specifically a leading emitter 604, a first trailing emitter 604', and a second trailing emitter 604''. The emitters 604 emit energy beams 608 that are detected by the detectors 606. The beams 608 pass through a recess 610. In the embodiment shown in FIG. 10A, the sensor body 602 is an L-shaped piece, wherein the emitters 604 are mounted on the short legs of the L-shaped piece, and the detectors are mounted near the ends of the long legs of the L-shaped piece, with the space between the emitters and the detectors defining the recess 610. In the embodiment shown in FIG. 10B, the emitters and detectors are mounted on an extension leg 612, with the space between the emitters and the detectors defining the recess 610.

FIG. 11 shows a sensor 600 mounted to the bottom of the remotely operated vehicle 50. The sensor 600 is mounted to a body frame 614. A second set of wheels 14 (one wheel of the set is shown) is raiseable and lowerable as part of a track switching operation. When the wheels 14 are lowered, the sensor 600 will be raised. When the wheels 14 are raised, the sensor 600 will be lowered. FIG. 12 again shows the sensor 600 mounted on the body frame 614, but also allows for a second sensor 600' mounted on a movable wheel frame 616 to be shown. During the track switching operation, the wheel frame 616 moves up and down with the wheels 14. Compared to the sensor 600, the sensor 600' will be lowered when the wheels 14 are lowered, and will be raised when the wheels 14 are raised. Thus, when the vehicle is traveling in a first direction, the sensor 600 will be lowered into the track, and when the vehicle is traveling in a second direction, the sensor 600' will be lowered into the track.

Figure 13 shows the sensor 600 lowered into the groove 501 of the guide rail 503. As can be seen, the guide rail wall 502 blocks the beam 608 from reaching its corresponding detector.

Figure 14 shows the sensor 600 encountering the intersection 504. As described above, the rail 503 terminates at the end 506 at the intersection 504. As shown, the beam 608 is thus not blocked by the rail wall 502 at the intersection.

This is also shown in FIGS. 15 and 16 , which show an embodiment of the sensor of FIG. 10A having a leading emitter 604, a first trailing emitter 604′ and a second trailing emitter 604″ (with corresponding beams 608). For ease of viewing, the vehicle 50 is omitted. Also for ease of viewing, FIG. 15 shows only the short leg of the L-shaped sensor body (on which the emitters are mounted). FIGS. 15 and 16 show the sensor 600 correctly positioned relative to the intersection 504. As shown, the sensor 600 is positioned relative to the intersection 504 so that the leading beam 608 is blocked by the end 506 of the guideway wall 502, while the first trailing beam 608′ and the second trailing beam 608″ are located within the intersection so that the first trailing beam and the second trailing beam can reach their respective detectors. As can be understood from FIG. 16 , the distance between the emitters corresponds to the positional tolerance deviation of the sensor between the guideway walls of the guideway. According to one aspect, the distance between the leading emitter (604, generating beam 608) and the first trailing emitter (604') is less than the width of the guide rail wall (502), and the distance between the first trailing emitter (604', generating beam 608') and the second trailing emitter (604'', generating beam 608'') is 0 mm to 4 mm less than the width of the groove (501) of the guide rail (503), preferably 2 mm to 4 mm less. Thus, the sensor can deviate within the groove by less than 2 mm, preferably by 1 mm to 2 mm, and most preferably by 1.5 mm.

17 and 18 show the sensor as it travels toward the correct position. As the vehicle approaches the intersection adjacent to the associated access opening, the sensor will first pass the end 506' of the first guide rail wall 502'. As the sensor moves forward, the leading beam 608 will first be detected, and then the first rearward beam 608' will be detected. The second rearward beam 608'' will still be blocked by the guide rail wall 502. As the vehicle travels further, the beam 608 will eventually be blocked by the second end 506'' of the second guide rail wall 502'' and positioned as shown in FIGS. 15 and 16. Until then the sensor recognizes via communication with the control system 500 that the vehicle is not yet in the correct position.

FIG19 shows the sensor having traveled past the correct position. The sensor 600 has traveled so that the leading beam 608 and the second trailing beam 608'' are detected, while the first trailing beam 608' is blocked by the second track wall 502''. If desired, the vehicle can be backed up until the leading beam 608 is blocked, as shown in FIG15, to reposition the vehicle.

Figure 20 (viewed in conjunction with Figure 9) shows the sensors 600 and 600' mounted on the vehicle 50 so that, with the aid of the sensors positioned as shown in Figures 15 and 16, when the sensors detect an adjacent intersection 504, the gripping device 404 of the vehicle is positioned over the associated access opening 112. In Figure 20, the vehicle body has been omitted for ease of viewing, however, the placement of the wheels 14 and 12 when viewed in conjunction with Figure 9 demonstrates this.

In the foregoing description, various aspects of the rail sensor structure for the storage and retrieval system have been described with reference to illustrative embodiments. For illustrative purposes, specific numbers, systems, and configurations are set forth to provide a comprehensive understanding of the system and its operation. However, the description is not intended to be interpreted in a restrictive sense. It will be apparent to those skilled in the art to which the disclosed subject matter belongs that various modifications and variations of the illustrative embodiments and other embodiments of the system are considered to fall within the scope of the present invention.

Reference Numbers List

Prior art (Figures 1 to 5):

Vehicle Implementation Method

Claims (16)

1. A rail sensor structure comprising:

a. An automatic wheeled vehicle (50) arranged to travel along a grid-based track system (108) comprising a plurality of parallel tracks (110) arranged in a first direction (X) and a plurality of parallel tracks arranged in a second direction (Y), the tracks in the first direction and the tracks in the second direction intersecting perpendicularly to form a plurality of intersections (504) defining a plurality of grid access openings (112), each track being provided with a single rail (503) or a pair of parallel rails for wheels (14, 12) of the vehicle, each rail being in the form of a groove (501) defined by upwardly projecting rail walls (502) ending at a tip (506) at the intersections, the vehicle being capable of changing the travel direction of the vehicle from the first direction to the second direction by alternately lifting or lowering a plurality of sets of wheels into the rails, the first set of wheels being arranged for travel in the first direction and the second set of wheels being arranged for travel in the second direction,

B. A sensor (600) attached to the vehicle and arranged such that when the first set of wheels is lowered or raised, the sensor comprising:

i. A sensor body (602) having a recess (610) arranged to receive a rail wall of the rail when the first set of wheels is lowered into the rail,

A plurality of emitters (604), each emitter being arranged to emit an energy beam (608); and one or more corresponding detectors (606) arranged to detect the energy beam from the emitter,

Wherein the emitter and the one or more corresponding detectors are arranged on opposite sides of the recess such that when the first set of wheels is lowered into the rail, the rail wall blocks a beam emitted from the emitter from reaching its corresponding detector,

And further wherein the sensor is attached to the vehicle at a location such that the beam from the emitter can reach its corresponding detector when a predetermined portion of the vehicle is above the associated access opening.

2. Rail sensor structure according to claim 1, wherein the predetermined part of the vehicle is a clamping device (404) arranged to clamp storage containers (106) stored in a storage column (105) below the access opening.

3. Rail sensor according to one of the preceding claims, wherein the sensor comprises a leading emitter (604), a first trailing emitter (604 ') and a second trailing emitter (604 "), and whereby the sensor is mounted on the vehicle at a position such that the clamping means of the vehicle are aligned above the associated access opening when the beam (608) of the leading emitter is blocked by the structure of the adjacent intersection from reaching its corresponding detector (606), whereas the beams (608', 608") of the first and second trailing emitters reach their respective detectors.

4. A rail sensor according to claim 3, wherein the distance between the leading emitter (604) and the first trailing emitter (604 ') is smaller than the width of the rail wall (502) and the distance between the first trailing emitter (604') and the second trailing emitter (604 ") is smaller than the width of the groove (501) of the rail (503) by 0mm to 4 mm, preferably by 2 mm to 4 mm.

5. Rail sensor according to one of the preceding claims, wherein the distance between two transmitters corresponds to a predetermined tolerance range of the position of the vehicle relative to the intersection.

6. Rail sensor according to one of the preceding claims, further comprising a control system (500) in electronic communication with the sensor.

7. Rail sensor according to one of the preceding claims, wherein the sensor body is an L-shaped piece, wherein the emitter is arranged on a short leg of the L-shaped piece and the detector is arranged on a long leg of the L-shaped piece.

8. A method for determining the position of an automated vehicle running on a grid-based track system (108), the track system comprising a plurality of parallel tracks (110) arranged in a first direction (Y), the tracks in the first direction and the tracks in the second direction intersecting perpendicularly to form a plurality of intersections (504) defining a plurality of grid access openings (112), each track being provided with a single rail (503) or a pair of parallel rails for wheels (14, 12) of the vehicle, each rail being in the form of a groove (501) defined by upwardly protruding rail walls (502) ending at an extremity (506) at the intersections, the vehicle being capable of changing the direction of travel of the vehicle from the first direction to the second direction by alternately lifting or lowering a plurality of sets of wheels into the rails, the first set of wheels being arranged for travel in the first direction and the second set of wheels being arranged for travel in the second direction, characterized in that the method comprises:

a. -providing a sensor (600), the sensor comprising:

i. A sensor body (602) having a recess (610) arranged to receive a rail wall of the rail when the first set of wheels is lowered into the rail,

A plurality of emitters (604), each emitter being arranged to emit an energy beam (608); and one or more corresponding detectors (606) arranged to detect the energy beam from the emitter,

Wherein the emitter and the one or more corresponding detectors are arranged on opposite sides of the recess such that when the first set of wheels is lowered into the rail, the rail wall blocks a beam emitted from the emitter from reaching its corresponding detector,

B. Attaching the sensor to the vehicle at a location such that, when a predetermined portion of the vehicle is above an associated access opening, the beam from the emitter can reach its corresponding detector,

C. Lowering the first set of wheels of the vehicle into a guideway to cause the vehicle to travel in the first direction, whereby the sensor is also lowered such that the guideway wall enters the recess and blocks the beam from the emitter from reaching its corresponding detector,

D. causing the vehicle to travel in the first direction until the beam from the emitter passes the end of the guideway wall at an intersection adjacent the associated access opening, an

E. The vehicle is stopped when the sensor is positioned relative to an adjacent intersection such that the predetermined portion of the vehicle is aligned over an associated access opening.

9. The method of claim 8, wherein the predetermined portion of the vehicle is a gripping device (404) arranged to grip an item stored under the access opening.

10. The method of claim 8, wherein the items are containers (106) in a stack of containers arranged in a storage column (105) below the access opening.

11. The method of one of claims 8 to 10, wherein the sensor comprises a leading emitter (604), a first trailing emitter (604 ') and a second trailing emitter (604 "), and the emitters are located on the sensor body (602) such that when a beam (608) of the leading emitter is blocked from reaching its corresponding detector (606) by a rail wall (502"), and the first emitter and the second emitter are located in an intersection (504) such that their beams (608', 608 ") reach their corresponding detectors, the clamping device of the vehicle is aligned over the access opening.

12. The method of claim 11, wherein the structure that blocks the beam from the leading emitter is an end of a rail wall (506) when the clamping device is aligned over the access opening.

13. The method according to claim 12, wherein the distance between the leading emitter (604) and the first trailing emitter (604 ') is smaller than the width of the rail wall (502), and the distance between the first trailing emitter (604') and the second trailing emitter (604 ") is smaller than the width of the groove (501) of the rail (503) by 0mm to 4 mm, preferably by 2 mm to 4 mm.

14. The method according to one of claims 11 to 13, further comprising the step of: determining that the vehicle is not in position relative to the associated access opening if one of the following conditions is satisfied:

a. The beam from the leading emitter (604) and the beam from the first trailing emitter (604') are detected by their corresponding detectors, while the beam from the second trailing emitter (604 ") is blocked from reaching its detector, or

B. The beams from the leading emitter (604) and the second trailing emitter (604 ") are detected by their corresponding detectors, while the beam from the first trailing emitter (604') is blocked, or

C. Beams from all three of the emitters are detected by their corresponding detectors.

15. The method of claim 14, further comprising the step of: the vehicle is repositioned by moving the vehicle determined to be out of position until the beams from the leading emitter are blocked from reaching its detector, while the beams from the first and second trailing emitters are detected.

16. The method of one of claims 8 to 15, wherein the sensor is in electronic communication with a control system (500) that directs the positioning of the vehicle in response to input from the sensor.