Automated material handling system for a cargo trailer

The invention relates to the provision of an automated material handling system for a cargo trailer which is integrated with an automated material handling system provided for a manufacturing assembly plant. The system for the cargo trailer includes a protective guard rail for bar-coded targets provided within the cargo trailer, modification of an automated lift truck which permits shifting of parts racks as they are loaded or unloaded from a cargo trailer and also exact positionment of parts racks with respect to an automated lift truck.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The automated material handling system for a cargo trailer includes means 
to facilitate loading and unloading a cargo trailer which are integrated 
with automated material handling means provided on a loading dock. 
2. Description of Related Art 
Modern material handling systems increasingly utilize automated material 
handling equipment. This is particularly true in connection with 
automotive assembly operations. Increasingly, automotive assembly 
operations are utilizing what is referred to as "just-in-time" inventory 
control. As the term implies, this system has as an objective to delivery 
components to an automotive assembly plant as they are needed for assembly 
of vehicles. In the past, assembly plants have included large storage 
areas for storing large inventories of vehicle components which had been 
fabricated and shipped from remote manufacturing facilities. Not only does 
such an inventory system require that the assembly plant be provided with 
the storage area (which involves expensive initial construction, 
maintenance and utilities), such a system also requires the maintenance of 
a large parts and components inventory which is undesirable from a finance 
point of view. 
However, "just-in-time" delivery of parts and components requires highly 
efficient assembly plant material handling techniques in order that cargo 
can be quickly and effectively removed from trucks and delivered to the 
point of use and also that empty shipping racks be removed from assembly 
areas and loaded onto cargo trailers in an efficient manner in view of the 
fact that storage space is severely limited under such a system. 
One material handling system which has been in the process of 
implementation to achieve the desired ends above referred to involves the 
use of robotic lift trucks capable of moving cargo without human 
intervention. One useful technique involves a guidance system which 
operates with a combination of dead reckoning and laser guidance. This 
system does away with dependence on a fixed path (such as a buried wire) 
for robotic lift trucks. On-board computers are provided on the trucks. 
The trucks include sensors which work by triangulation from identifiable 
landmarks which are fixed in known positions within the area of operation. 
The landmarks are created by installing bar coded targets at convenient 
intervals throughout the operating area. Positions of these targets are 
accurately surveyed and the coordinates recorded in the system software. 
From information on the angle of the targets scanned, the on-board 
computer calculates the exact position of the vehicle by a process of 
triangulation. 
The vehicle follows an assigned loading track. In accordance with the 
present invention, a similar loading track is assigned to the floor of a 
cargo trailer for integration into the main system. However, the 
restricted space available in cargo trailers, as opposed to the more roomy 
area available in an assembly plant, presents special problems. The 
present invention provides means for overcoming these problems. 
SUMMARY OF THE INVENTION 
The invention is related to an automated material handling system for a 
manufacturing assembly plant. A loading dock having a loading dock surface 
forms part of the assembly plant. A loading track is assigned to the 
loading dock surface. An automated lift truck is provided for following 
the loading track while it moves cargo. Means, including bar-coded 
targets, are provided for causing the lift truck to follow the loading 
The present invention is concerned with expanding the automated material 
handling system to include cargo trailers. The cargo trailers include a 
rear loading opening from which extends forwardly thereof a cargo support 
surface upon which is also assigned a loading track. The automated lift 
truck functions to load and unload parts racks out of and into the cargo 
trailer for use in the assembly plant. 
The two loading tracks are aligned when the cargo trailer is in position 
for loading or unloading to facilitate such loading and unloading. Each 
cargo trailer has a pair of spaced apart upstanding sidewalls. A plurality 
of horizontally spaced apart bar-coded targets are mounted on each 
sidewall within the cargo trailer intermediate the upper and lower edges 
thereof. 
The lift truck includes scanning means for reading the bar-coded targets 
and controlling its path of movement to constrain it to follow the 
assigned loading track on the cargo support surface. Each bar-coded target 
within the cargo trailer is substantially flat and thin. A guard rail is 
provided on each sidewall within the cargo trailer extending horizontally 
along the length of the cargo trailer. The guard rails are positioned 
above the bar-coded targets. The guard rails are thicker than the 
bar-coded targets to thereby prevent contact therewith by parts racks. The 
lift truck has a mast including carriage means for engaging a parts rack. 
The lift truck mast includes means for mounting the carriage which permit 
lateral shifting of the carriage to facilitate lateral shifting of a parts 
rack carried by the lift truck upon contact of the parts rack with a guard 
rail. 
The mast carriage preferably includes a pair of spaced apart locating 
elements extending forwardly thereof. The parts racks have a wall 
including an upright member positioned centrally thereof. The locating 
elements are spaced apart a distance slightly greater than the width of 
the upright member. The lift truck is positioned with respect to the parts 
racks by advancing the lift truck toward a wall with the space between the 
locating elements in substantial alignment with the upright member until 
the upright member passes between the locating elements. A pair of parts 
rack grasping hooks are provided on the lift truck carriage extending 
forwardly thereof. A hook is positioned laterally outwardly of each 
locating element. The parts rack wall has a crossmember extending past the 
upright member. The hooks are adapted to engage the crossmember after the 
locating elements have positioned the lift truck with respect to the parts 
rack. 
Preferably, the bar-coded targets on the cargo trailer walls are spaced 
apart a distance of from about nine to ten feet. The bar-coded target on 
each sidewall of the cargo trailer closest to the rear loading opening is 
far enough distant from the opening to not effect the path of movement of 
the lift truck as the lift truck enters or leaves the cargo trailer.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
The environment in which the cargo trailer material handling means of the 
present invention is used is illustrated in FIGS. 1 and 2. As will therein 
be noted, a vehicle assembly plant 10 has an interior space 12 within 
which is located an assembly work station 14. The work station 14 includes 
a rack storage structure 16. The structure 16 includes a pair of spaced 
apart rack receiving structures 18, 20 which function to receive loaded 
racks 22a and convey these racks towards a platform 24 as needed. Assembly 
operators are stationed on the platform 24 for unloading vehicle 
components from a loaded rack 22a positioned by the structure for such 
unloading. The racks illustrated are, for example, adapted to carry 
vehicle seats. The assembly operators remove seats from the rack and place 
them on a seat delivery conveyor 25 which takes them to a point of use for 
mounting in a vehicle. A rack transfer structure 26 is provided for 
receiving racks and moving the racks after they have been unloaded. A 
central rack receiving structure 28 is provided between the structures 18, 
20 for receiving empty racks 22b which are conveyed rearwardly of the 
structure 28. 
Racks are loaded and unloaded from the work station racks storage structure 
16 from a loading dock 30 which is separated from the space 12 by a wall 
32. The loading dock 30 illustratively has two bays 34, 36 from which 
racks can be loaded or unloaded from cargo trailers 38, 40 which are 
backed up to the bays. The means for transporting loaded and unloaded 
racks comprise a lift truck 42. The lift truck 42 is controlled by means 
of a computer programmed dead reckoning system and by means of a series of 
bar-coded targets 44 mounted on the wall 46 of the loading dock. The lift 
truck 42 includes on-board computer means and scanning means 43 for 
relating to the targets 44 which result in the guidance system. As will be 
noted in FIG. 3, the targets 44 are V-shaped and present two surfaces 45, 
47 which extend outwardly from the wall 46 to permit easy reading by the 
scanners regardless of which direction the lift truck 42 is traveling. The 
guidance system defines an assigned loading track complex 48 on the floor 
surface 50 of the loading dock and assembly area. The self-guided vehicle 
system and automated lift trucks of the type contemplated for use in the 
present invention may be models ARC or ARL available from Caterpillar 
Tractor Co. Elements 52, 54 of the loading track complex extend to the 
outer edge 56 of the loading dock. The elements 52, 54 are so positioned 
as to cause the lift truck 42 to enter the rear loading openings 58, 60 of 
the cargo trailers 38, 40. The lift truck can unload loaded racks 22a and 
load unloaded racks 22b into the cargo trailers. 
The cargo trailers are also provided with assigned loading tracks 62, 64 on 
the cargo support surfaces 66, 69 which extend forwardly of the cargo 
trailers from the rear thereof. Bar-coded targets 68, 70 are provided on 
the upstanding sidewalls 72, 74 of the cargo trailers to define the 
loading tracks. These targets work in the manner of the targets 44. 
However, it will be noted in FIGS. 4 and 5 that the targets 68, 70 are 
substantially flat and thin. Outwardly extending V-shaped targets, such as 
the targets 44, are not used because of the space limitations of a cargo 
trailer. Therefore, about twice as many targets are used per lineal foot 
of the trailer to facilitate scanning of the targets. Preferably, the 
targets 68, 70 are spaced apart about nine to ten feet. Also, it will be 
noted that no targets are provided at the trailer opening 60 of trailer 
40. The bar-coded target 68, 70 on each sidewall 72, 74 of the cargo 
trailer closest to the rear loading opening 60 is far enough distant from 
the opening to not affect the path of movement of the lift truck as the 
lift truck enters or leaves the cargo trailer. The reason for this is that 
there may be a crack or bump at the juncture of the loading dock and 
trailer which could cause oversteering if the lift truck direction were 
changed at that point. 
In order for this system to function properly, it is necessary to align the 
cargo trailers 38, 40 with the bays 34, 36 in such a manner to result in 
alignment of the loading dock tracks 52, 54 with the tracks 62, 64 of the 
cargo trailers as shown. The racks are frequently almost as large as the 
distance between the sidewalls of the trailers, thus not permitting very 
much deviation and requiring that the lift truck follow a exact path for 
proper loading and unloading. 
A standard automated lift truck 42 has been modified in order to enhance 
its ability to load and unload parts racks from a trailer 40. The 
modification is illustrated in FIGS. 6-11. As will be noted in FIG. 6, the 
lift truck 42 has the usual mast 76. The mast 76 is operated to move up 
and down by conventional mechanism. In practice, the mast 76 is lowered in 
order to engage a parts rack and is raised once the parts rack has been 
engaged to lift the parts rack off the ground for transportation. The 
modification involves providing a carriage 78 on the mast 76. As will be 
noted in FIGS. 8 and 9, the carriage 78 is attached to the mast 76 by 
means of a pair of arms 80, 82. The upper ends of the arms are pivotally 
attached to the mast 76 at 84, 86 while the lower ends of the arms are 
pivotally attached to the carriage 78 at 88, 90. This arrangement permits 
lateral swinging of the carriage 78 with respect to the mast 76 in a 
pendulum-type action. The carriage 78 may be shifted laterally in either 
direction a distance of about four inches. Guide cross members 92, 94 are 
provided on the mast 76. Bracket structures 96, 98 and 100, 102 are 
provided on the carriage 78 to cooperate with the guides 92, 94 to limit 
fore and aft movement of the carriage 78 with respect to the mast 76. 
The swinging motion thus provided for the carriage 78 comes into play in 
the event that a parts rack carried by the carriage bumps into a fixed 
object. This small movement provided by the carriage permits continued 
travel of the lift truck even if it contacts a fixed structure. Such 
contact is most likely to occur within the cargo trailer 40. 
Referring to FIGS. 4 and 5, it will be noted that a guard rail 104, 106 is 
provided on each sidewall 72, 74 within the cargo trailer 40 extending 
horizontally along the length of the cargo trailer. The guard rails 104, 
106 are positioned above the plurality of horizontally spaced apart 
bar-coded targets 68, 70 which are mounted on each sidewall within the 
cargo trailer intermediate the upper and lower edges thereof. The guard 
rails 104, 106 are thicker than the bar-coded targets 68, 70 to thereby 
prevent contact therewith by parts racks. When the lift truck 42 enters 
the cargo trailer 40, it is possible for the parts rack to impinge upon 
one of the guard rails 104, 106. As will be noted in dotted lines in FIGS. 
4 and 5, there is very little space between the sidewall 72, 74 and the 
outer edges of the parts racks 22 which are illustrated in dotted lines. A 
slight deviation in the path of the lift truck 42 could cause such 
impingement. However, more commonly, such impingement occurs as the result 
of the cargo trailer sidewalls 72, 74 being slanted one way or the other 
to result in the interior space of the cargo trailer not being exactly 
rectangular. Trailer sidewalls are sometimes canted after the trailer has 
been subjected to the rigors of ordinary use. If contact is made with the 
guard rails, the lateral shifting permitted by the carriage 78 is 
sufficient to permit loading and unloading of racks. 
The lift truck 42 has also been modified in another respect. As will be 
noted in FIGS. 6 and 7, 10 and 11, instead of the mast 76 being provided 
with the usual fork for lifting a rack, it is provided with a pair of 
parts rack grasping hooks 108, 110 on the lift truck carriage 78. The 
hooks 108, 110 extend forwardly of the carriage 78. Additionally, a pair 
of spaced apart locating elements 112, 114 extend forwardly of the 
carriage 78. One hook 108, 110 is positioned laterally outwardly of each 
locating element 112, 114, the hook 108 being positioned outwardly of the 
locating element 112 and the hook 110 being positioned outwardly of the 
locating element 114. 
The parts racks 22 have a wall 116 including an upright member 118 
positioned centrally thereof. The racks 22 are longer than they are wide 
and are loaded longways as will be noted in FIG. 4. The locating elements 
112, 114 are spaced apart a distance slightly greater and the width of the 
upright member 118. When it is desired to engage a rack 22, the lift truck 
42 is positioned with respect to the parts rack by advancing the lift 
truck towards the wall 116 with the space between the locating elements 
112, 114 in substantial alignment with the upright member 118 until the 
upright member passes between the locating elements as, illustrated in 
FIGS. 7 and 11. At this time, the lift truck 22 is properly positioned 
with respect to the parts rack. This arrangement facilitates conveying the 
racks in the desired pattern and depositing them at an exact desired 
location. This feature is of particular importance with respect to loading 
and unloading racks from the confined space of a cargo trailer 40. 
The parts rack also has a crossmember 120 which extends past the upright 
member 118 as will be noted in FIGS. 7 and 11. The hooks 108, 110 are 
adapted to engage the crossmember 120 after the locating elements 112, 114 
have positioned the lift truck 42 with respect to the parts rack. The mast 
76 is moved upwardly whereupon the hooks 108, 110 firmly engage the cross 
member 120. The wall 116 of the parts rack is flush against the carriage 
78. This arrangement prevents tilting of the parts rack when it is lifted. 
The use of hooks 108, 110 is advantageous in that it ensures the position 
of the parts rack 22 with respect to the lift truck.