Locomotive for material handling train

An automated material handling system including one or more train assemblies moving along a rail with each train assembly including a locomotive pulling a plurality of trolley cars. The locomotive includes a front truck adapted for movement along the rail; a rear truck adapted for movement along the rail in spaced trailing relation to the front truck; a body structure mounted on and extending between the front and rear trucks; a tractor positioned between the front and rear trucks, disassociated from the body structure, and including a motor and a traction drive wheel driven by the motor and adapted to drivingly engage the rail; and a link pivotally interconnecting the tractor and the rear truck. The body structure defines a central downwardly opening compartment between the front and rear trucks and the tractor is positioned in the compartment. The tractor is thus free to essentially independently perform the pulling function for the train without concern for the carrying function of the locomotive. The tractor also includes a guide wheel coacting with the drive wheel of the locomotive to exert a clamping force on the rail and a traction control mechanism operative in response to variations in the draft load applied to the tractor by the associated train to vary the clamping force and thereby the locomotive traction.

FIELD OF THE INVENTION 
The invention is generally related to automated material handling systems 
utilizing one or more train-type guided vehicles transporting goods 
between induction and discharge stations in a sortation system. 
BACKGROUND OF THE INVENTION 
Automated material handling and sortation systems are known for receiving, 
transporting and discharging goods among various stations in large scale 
sortation operations such, for example, as warehousing, distribution, 
postal sortation and handling of mail and packages, and airport baggage 
handling. Whatever the operation, goods typically originate from one 
location within the facility and must be sorted and transported to several 
different locations for further handling, or originate from several 
locations within a facility and must be transported to a single location 
such as a shipping dock. The manner in which the various goods are stored 
and selectively distributed among various stations in a facility of course 
depends on the nature of the operation. 
One known sortation and delivery method involves using powered belt or 
roller conveyers to transport individual items or sorted loads of items to 
various destinations within a facility. When goods from multiple sources 
must be delivered to a single station, associated take away conveyors must 
be merged onto a main conveyor or discharge point. This requires careful 
coordination of each item as it arrives to prevent jams or damage. Each 
merge point on such a conveyor system accordingly requires a complex 
system of sensors, start/stop controls, actuators, power supply lines, 
etc. Similarly, when items must be delivered to multiple destinations or 
stations in a facility, a main conveyor must be provided with diverter 
apparatus to direct individual items or batches of items to either 
continue or be diverted at various points. Each diverter apparatus 
requires an additional closed system including sensors, actuators, control 
mechanisms, wiring power supply to accomplish the diverting operation and 
track and identify the items being diverted. 
The disadvantages of conveyor-type systems have led to the development of 
tracked systems in which a closed loop track carries cars propelled by a 
continuous chain drive. The cars are equipped with open trays which can be 
loaded from belts or chutes, and subsequently tilted to unload their 
carloads into bins which are located around the track. Such systems are 
designed for long term installations which sort and transport large 
volumes of goods. Although these closed loop track systems are an 
improvement over conveyor-type systems, the complexity of their track, 
drive and tilting mechanisms makes it a major undertaking to set them up 
or rearrange their sortation layout. Further, they must be totally shut 
down for nearly all maintenance tasks. 
An improvement over continuous belt or chain drive closed loop track 
systems is disclosed in U.S. Pat. No. 5,018,928 issued to Hartlepp and 
assigned to the assignee of the present invention. Hartlepp discloses a 
train-type automated track sortation system, including a number of trolley 
cars and a locomotive or tug for pulling the cars around the track between 
various discharge and induction stations. The cars on the train are loaded 
with goods to be sorted or delivered and given destination addresses for 
the goods at an induction or loading station. Once a train has left the 
loading station, functions such as keeping track of position, regulating 
speed and dumping cars are controlled by a microprocessor placed aboard 
each locomotive. 
Although train-type automated track sortation systems of the type disclosed 
by Hartlepp represent an improvement over conveyor-type and belt or 
chain-driven track systems, there is need for an improved tug or 
locomotive to pull the train. Prior art tugs or locomotives typically 
include front and rear trucks supporting the locomotive and a traction or 
drive unit incorporated in one of the trucks. Whereas this arrangement is 
generally satisfactory, it in effect integrates two distinct functions-the 
provision of a pulling force for the train and the provision of a support 
for the main body of the locomotive-in a single unit with the result that 
neither function can be optimized. 
SUMMARY OF THE INVENTION 
This invention is directed to the provision of an improved locomotive or 
tug for a material handling train. 
More specifically, this invention is directed to the provision of a 
locomotive or tug for a material handling train in which the pulling and 
carrying functions of the locomotive are separated so as to allow 
optimization of each function. 
The invention relates generally to a material handling system including a 
rail and a train moveable along the rail and including a locomotive 
pulling one or more cars. 
According to an important feature of the invention, the locomotive includes 
a locomotive subassembly comprising a truck adapted for movement along the 
rail and a body structure defining a hollow and mounted on the truck; a 
tractor positioned within the hollow of the body structure, free to move 
laterally relative to the body structure, and including a motor and a 
traction drive wheel driven by the motor and adapted to drivingly engage 
the rail; and drive means drivingly interconnecting the tractor and the 
locomotive subassembly. This basic arrangement allows separation of the 
pulling and carrying functions of the locomotive so that each function may 
be optimized. 
According to a further feature of the invention, the drive means drivingly 
interconnects the tractor and the truck. This specific interconnection 
further facilitates the separation of the pulling and carrying functions. 
According to a further feature of the invention, the drive means comprises 
a link pivotally connected at one end thereof to the tractor and pivotally 
connected at another end thereof to the truck. This specific linkage 
allows the tractor to function substantially independently of the 
remainder of the locomotive so as to allow the tractor to perform its 
pulling function without concern for the carrying function of the 
locomotive. 
According to a further feature of the invention, the locomotive truck 
comprises a front truck; the locomotive further includes a rear truck 
adapted for movement along the rail and spaced in trailing relation to the 
front truck; the body structure is mounted on and extends between the 
front and rear trucks; and the tractor is positioned between the front and 
rear trucks. This specific arrangement allows the spaced front and rear 
trucks to smoothly support the body structure and thereby optimize the 
carrying function of the locomotive while allowing the tractor to function 
independently, in the space between the front and rear trucks, to perform 
the pulling function. 
In the disclosed embodiment of the invention, the body structure defines a 
downwardly opening compartment between the front and rear trucks and the 
tractor is positioned on the rail between the front and rear trucks and 
extends upwardly into the compartment. This specific arrangement provides 
a compact and efficient locomotive package in which the tractor is 
effectively disassociated from the body so that the pulling and carrying 
functions are totally separated. 
According to a further feature of the invention, the traction drive wheel 
of the tractor is adapted to drivingly engage a first surface of the rail; 
the tractor further includes an opposing guide wheel adapted to drivingly 
engage a second surface of the rail opposed to the first surface; the 
drive wheel and the guide wheel coact to exert a clamping force on the 
rail and propel the tractor and an associated material handling train 
along the rail; and the locomotive further includes traction control means 
operative in response to variations in the draft load applied to the 
tractor by the associated train to vary the clamping force. This 
arrangement allows the clamping force, and thereby the traction, developed 
at the driving wheels to be selectively varied in response to, for 
example, acceleration, hill climbing, and braking. 
According to a further feature of the invention, the traction control means 
includes a draw bar mounted on the tractor, receiving the draft load, and 
movable relative to the tractor in response to variations in the draft 
load; and the traction control means is operative to vary the clamping 
force in response to movement of the draw bar relative to the tractor. 
This arrangement defines a convenient and compact structure for providing 
the desired variations in the clamping and thereby the traction force. In 
the disclosed embodiment of the invention, the traction control means 
includes a cam bar secured to the draw bar and defining a cam surface and 
a cam follower connected to the guide wheel and coacting with the cam bar 
in response to movement of the draw bar relative to the tractor to raise 
and lower the guide wheel and thereby vary the clamping force.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The material handling system seen in the drawings includes a rail 10 
arranged in a desired predetermined configuration such for example as the 
closed loop seen in FIG. 1; one or more trains 12 arranged to run on the 
rail and each including a locomotive 14 pulling a plurality of trolley 
cars 16; at least one load station 17 and one unload station 18; a central 
dispatch CPU 19 located proximate but removed from the rail and 
communicating with a radio frequency transmitter 20; an information CPU 21 
communicating with dispatch CPU 19 and including a printer 21a; and an 
input terminal 22. It will be understood that trains 12 move along rail 10 
under the control of dispatch CPU 19 and selectively receive discrete 
products 22 at a load station 17, transport the products to an unload 
station 18, and discharge the products at the unload station. Rail 10 may 
take various forms and may, as best seen in FIGS. 6 and 7, have an I 
configuration including a central upstanding web 10a; an upper triangular 
portion 10b defining a flat upper traction surface 10c and opposite, 
angled downwardly converging clamping surfaces 10d; and a lower base 
portion 10e of triangular configuration including a lower support surface 
10f and opposite, angled upwardly converging guide surfaces 10g. This 
invention relates to improvements in the locomotive 14 utilized to pull 
each train along the rail 10. 
Locomotive 14 (FIGS. 2 and 3) includes a body structure 24, a front truck 
26, a rear truck 28, a tractor 30, a connecting means 32, and a traction 
control mechanism 34. 
Body structure 24 includes a perimeter frame 36 supporting a hollow 
downwardly opening body shell 38 positioned in surrounding relation to the 
perimeter frame and supported by the perimeter frame. Shell 38 includes 
gull wing doors 40 which pivot upwardly to provide access to the interior 
of the shell 38 for maintenance and repair purposes. Front and rear 
partitions 42,44 divide the interior volume of the shell 38 into a front 
compartment 46, a central compartment 48 and a rear compartment 50. Front 
and rear compartments 46 and 50 have floor structures so that the 
compartments, with doors 40 closed, are totally enclosed but central 
compartment. 48 is open at the bottom of the body structure and may 
therefore be readily accessed from beneath the body structure. 
Compartments 46 and 50 house suitable electric control equipment for the 
locomotive and the associated train. For example, front compartment 46 may 
house a computer 51 and interface boards and rear compartment 50 may house 
a power supply for the trolley cars of the associated train, relays, and a 
variable frequency drive for the drive motor of tractor 30. Computer 51 
maintains RF communication with transmitter/receiver 20, and thereby 
dispatch CPU 19, via an antenna 51a. 
Front truck 26 includes a frame structure 52 of inverted U configuration 
positioned in straddling configuration over rail 10 with four lower guide 
rollers 54 (two on each side of the rail) rollably engaging rail guide 
surfaces 10g and four upper guide rollers 56 (two on each side of the 
rail) rollably engaging rail guide surfaces 10d. Front truck 26 is 
positioned beneath body structure 24 within perimeter frame 26 in 
underlying relation to front compartment 46 and is suitably connected to 
the floor structure of compartment 46, or to a cross member of frame 36, 
by a universal joint 57 so as to allow relative movement between the body 
structure and the truck about both a vertical axis 58 and a horizontal 
axis 59. 
Rear truck 28 is identical to front truck 26 and includes a frame structure 
52 straddling rail 10, lower guide rollers 54 rollably engaging rail guide 
surfaces 10g, and upper guide rollers 56 rollably engaging guide surfaces 
10d. Rear truck 28 is positioned beneath body structure 24 within 
perimeter frame 36 in underlying relation to rear compartment 50 and is 
joined to the floor structure of compartment 50, or to a cross member of 
frame 36, by universal joint 57 so as to allow relative movement between 
the body structure and the truck about both a vertical axis 58 and a 
horizontal axis 59. It will be understood that the permitted relative 
movement between the body structure and the truck about a vertical axis 
allows the locomotive to negotiate rail curves and the permitted relative 
movement between the body structure and the truck about a horizontal axis 
allows the locomotive to negotiate rail inclines. 
Tractor 30 includes a support structure 60, an electric motor 62, and 
traction drive wheels 64. 
Support structure 60 includes front and rear inverted U-shaped yokes 66,68 
and a frame structure Yokes 66,68 are positioned in straddling relation to 
the rail 10 and are mounted for rolling movement along the rail by guide 
rollers 69 rollably engaging guide surfaces 10g. Frame structure 70 has a 
generally box configuration and extends between front and rear yokes 66,68 
to form the rigid body structure 60. 
Motor 62 may comprise for example a three horsepower three-phase AC motor 
and is fixedly mounted on top of frame structure 70. Drive wheels 64 
include front and rear wheels 64a, 64b positioned generally within frame 
structure 70 in driving, traction engagement with the upper surface 10c of 
rail 10. Traction wheels 64a, 64b include central drive shafts 64c, 64d 
journaled in side walls 70a of frame structure 70 and are driven from 
motor 62 by a drive train comprising a motor output pulley 72, an endless 
member 74 driven by pulley 72 and driving a pulley 76 mounted on shaft 
64c, and an endless member 78 driven from shaft 64cand driving a pulley 79 
mounted on shaft 64d. It will be seen that drive train 72-79 operates in 
response to energization of motor 62 to rotate traction wheels 64a, 64b in 
the same direction, either forwardly or backwardly, depending upon the 
direction of energization of the motor. 
Tractor 30 will be seen to be positioned on rail 10 between front truck 26 
and rear truck 28 and to extend upwardly from the rail 10 into downwardly 
opening compartment 48. 
Connecting means 32 includes a link 80 pivotably or swively connected at 
its forward end 80a to a clevis 82 carried by the tractor and pivotably or 
swively connected at its rear end 80b to a clevis 84 carried by a bracket 
86 upstanding from and secured to the frame structure 52 of rear truck 28. 
Link 80 enables the connecting means to operate (with the locomotive 
negotiating a straight rail section) to transmit forces to the locomotive 
subassembly only in directions substantially parallel to the direction of 
movement of the locomotive along the rail. 
Traction control mechanism 34 includes a draw bar 88 mounting clevis 82 and 
positioned immediately rearwardly of tractor 30; a pair of cam bars 90 
extending forwardly from opposite ends of draw bar 88 along opposite sides 
of tractor frame structure 70; a transverse cam follower bar 92 of 
circular cross section passing through vertical slots 70b in frame 
structure side walls 70a; vertical bars 94 secured to opposite ends of cam 
follower bar 92 and extending downwardly therefrom; a cross bar 96 
positioned at the lower end of each vertical bar 94; and a pair of clamp 
wheels or rollers 98 journaled on front and rear ends of each bar 96 and 
rollably and clampingly engaging rail surfaces 10d. Cam bars 90 are guided 
in brackets 99 secured to frame side walls 70a and each bar defines a 
generally U-shaped cam surface 90a proximate the front end of the cam bar 
receiving a respective end of cam follower bar 92. 
It will be seen that wheels 98 coact with traction wheels 64a, 64b to clamp 
the upper portion 10b of the rail therebetween and pull wheels 64a, 64b 
downwardly into frictional engagement with the upper traction surface 10c 
of the rail. It will further be seen that the magnitude of the clamping 
force and therefore the magnitude of the traction force generated between 
wheels 64a, 64b and rail surface 10c is varied in response to movement of 
cam follower rod 92 relative to cam surfaces 90a. Specifically, it will be 
seen that the traction force generated by the traction control means will 
be at a relatively lower value when cam follower bar 92 is positioned in 
the bottom or dwell portion 90b of the cam surfaces 90a (as seen in FIG. 
6) and will increase as the cam follower moves upwardly (as seen in FIGS. 
5A and 5B) along the rise portions 90c, 90d of the cam surfaces 90a in 
response to relative movement between the cam bars 90 and the cam follower 
92. 
Operation 
It will be understood that energization of motor 62 operates to move the 
tractor 30 along the rail 10 and thereby move the locomotive and the 
trailing trolley car 16 along the rail by virtue of the connecting link 
80. It will be seen that the described arrangement effectively isolates 
the pulling and load carrying functions of the locomotive so that both 
functions may be optimized. Specifically, tractor 30 performs the pulling 
function and is connected to the remainder of the locomotive only by the 
link 80 so that the tractor is effectively disassociated from the body 
structure and need not be concerned with performing any kind of a load 
carrying function and so that static and dynamic load forces generated by 
the main body of the locomotive are not transmitted to the traction 
control or the drive wheels of the tractor with the result that the 
pull/push and locomotive weight force vectors are totally decoupled. This 
allows the tractor to have a very tight coupling geometry to the rail so 
that any normal horizontal or vertical track curve motion can be followed 
precisely by the tractor without the need to fight load and torque forces 
generated by the locomotive as it changes direction. Further, minor track 
size defects and roll orientations (undesired track rotation about its 
direction of travel axis) can be followed without transferring these back 
to the locomotive main body. Central locomotive compartment 48 has a width 
substantially exceeding the width of tractor 30 so that, as shown by the 
dash lines in FIG. 4, the tractor 30 is free to move laterally relative to 
the body structure of the locomotive to negotiate curves in the rail so 
that each of the trucks and the tractor may seek its own path of least 
resistance along the rails as the rails curve. This isolates the body 
structure and integrated controls from much of the vibration and impact 
loads generated by the operation of the tractor. This also has the effect 
of minimizing the amount of swing imparted to the body structure of the 
locomotive as the locomotive negotiates curves. This greatly simplifies 
installation of the material handling system since it minimizes concerns 
with respect to impacts between the locomotive and track side obstacles or 
personnel. 
As the locomotive accelerates, or moves up an incline in the track such as 
the incline seen at 10a in FIG. 1, traction control mechanism 34 functions 
to increase the frictional force between the drive rollers 64a, 64b and 
the track, and thereby increase the pulling power of the locomotive, as 
the result of movement of cam bars 90 rearwardly relatively to cam 
follower 92 by virtue of the draft load exerted on draw bar 88 via link 
80. This relative rearward movement of the cam bars 90 has the effect 
(FIG. 5A) of walking cam follower bar 92 up cam rise portions 90c to 
impart vertical movement to vertical bars 94 and thereby move rollers 98 
upwardly with respect to the rail to increase the clamping or squeezing 
action exerted on the rail by the coaction of the rollers 98 and drive 
rollers 64a, 64b. 
Conversely, when the locomotive is braking, or moving down hill, the draft 
load generated by the associated train and transmitted to the locomotive 
by link 80 and draw bar 88 has the effect of moving the draw bars 90 
forward relative to the cam follower bar 92 (FIG. 5B) with the result that 
the cam follower bar 92 walks up the cam rise portions 90d and again 
causes the rollers to move upwardly into tighter relationship with the 
track to increase the clamping and traction force. 
The invention locomotive and associated material handling system will be 
seen to provide many important advantages. Specifically, the invention 
locomotive construction isolates the static and dynamic load forces 
generated by the main body of the locomotive from the power unit of the 
locomotive; allows the power module to have a very tight coupling geometry 
to the rail so that any normal horizontal or vertical track curve motion 
can be followed precisely by the locomotive without the need to fight load 
and torque forces generated by the locomotive as it changes direction; 
allows minor track size defects and roll orientations to be followed 
without transferring these back to the locomotive main body; provides a 
single point of mechanical contact to the rear truck of the locomotive so 
as to provide one axis coupling and therefore no up/down, left/right, or 
rotational torque transmission between the tractor and the main body of 
the locomotive; enables the drive means to operate, with the locomotive 
negotiating a straight rail section, to transmit forces to the locomotive 
main body only in directions substantially parallel to the direction of 
movement of the locomotive along the rail, facilitates modular 
construction of the locomotive; allows a family of tractors with different 
power sizes and characteristics to be provided; facilitates the provision 
of a simple and effective traction control mechanism for the locomotive; 
allows the tractor to be covered and protected by the shell of the 
locomotive for safety and aesthetic advantages so that the tractor does 
not need its own case or shielding; and minimizes swing of the locomotive 
on curves so as to minimize concerns with respect to track side equipment 
or personnel. 
Whereas a preferred embodiment of the invention has been illustrated and 
described in detail, it will be apparent that various changes may be made 
in the disclosed embodiment without departing from the scope or spirit of 
the invention.