U.S. patent application number 13/718277 was filed with the patent office on 2014-06-19 for method of material handling with automatic guided vehicles.
The applicant listed for this patent is Christopher John Murphy. Invention is credited to Christopher John Murphy.
Application Number | 20140172223 13/718277 |
Document ID | / |
Family ID | 50931854 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140172223 |
Kind Code |
A1 |
Murphy; Christopher John |
June 19, 2014 |
METHOD OF MATERIAL HANDLING WITH AUTOMATIC GUIDED VEHICLES
Abstract
A system and method of automatic guided vehicles that are
capable of providing synchronized travel along a line or path such
that regular manufacturing operations may be performed to material
or workpieces on the vehicle without the need for a traditional
conveyor systems.
Inventors: |
Murphy; Christopher John;
(Ann Arbor, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Murphy; Christopher John |
Ann Arbor |
MI |
US |
|
|
Family ID: |
50931854 |
Appl. No.: |
13/718277 |
Filed: |
December 18, 2012 |
Current U.S.
Class: |
701/25 |
Current CPC
Class: |
G05D 1/0289 20130101;
G05D 1/00 20130101; G05D 2201/0216 20130101 |
Class at
Publication: |
701/25 |
International
Class: |
G05D 1/00 20060101
G05D001/00 |
Claims
1. A method of operating a conveyor system for material handling in
a facility, said conveyor system including a plurality of AGVs,
each having a controller including a communication system and a
guidance system, said method comprising the steps of: determining a
travel path having at least one line portion defined by an initial
line and an end line; inputting a guided route for the AGV to
follow, wherein the guided route includes instructions regarding
the AGVs travel along the at least one line portion; assigning a
unique ID to each AGV; guiding the plurality of AGVs along the
travel path; automatically determining a lead AGV in the line
portion; automatically determining a last AGV in the line portion;
automatically updating the last AGV in the line portion each time
an AGV from the plurality of AGVs crosses the initial line of the
line portion; automatically updating the lead AGV to the immediate
trailing AGV in the line portion each time the lead AGV from the
plurality of AGVs crosses the end line; and maintaining a
designated spacing between each AGV from the plurality of AGVs
within the line portion.
2. The method of claim 1 further including a step of inputting the
travel path, including the line portion, into each guidance system
of the plurality of AGVs.
3. The method of claim 1 wherein said step of inputting a guided
route for the AGV to follow also includes inputting a desired line
speed for the AGV to travel along the line portion.
4. The method of claim 3 wherein said step of inputting a guided
route for the AGV to follow also includes inputting a desired
travel speed for the AGV when the AGV is not in the line portion
and wherein the desired line speed and the desired travel speed are
not identical.
5. The method of claim 1 wherein said lead AGV has a lead AGV speed
and wherein each of said plurality of AGVs following said lead AGV
in the line portion match the lead AGV speed.
6. The method of claim 1 wherein said step of automatically
determining a lead AGV includes the step of assigning a lead token
to the lead AGV.
7. The method of claim 6 wherein said step of automatically
updating the lead AGV further includes the step of passing the lead
token from the lead AGV as it crosses the end line to the immediate
trailing AGV.
8. The method of claim 1 wherein said step of automatically
determining a last AGV includes the step of assigning an end token
to the last AGV.
9. The method of claim 8 wherein said step of automatically
updating the last AGV in the line portion each time an AGV from the
plurality of AGVs crosses the initial line of the line portion
further includes the step of passing the end token from the
preceding last AGV to the updated last AGV.
10. The method of claim 1 wherein said step of automatically
updating the last AGV in the line portion includes the step of
providing the unique ID of the AGV updated as the last AGV to at
least one of another AGV and a central controller.
11. The method of claim 1 wherein said step of guiding the
plurality of AGVs along the continuous travel path includes the
step of guiding the AGVs through the line portion.
12. The method of claim 11 wherein said step of guiding the
plurality of AGVs through the line portion further includes the
step of guiding the plurality of AGVs with consistent spacing and
speed in the line portion.
13. The method of claim 11 wherein said step of guiding the AGVs
through the line portion includes the steps of tracking the
distance traveled by the AGV since crossing the initial line to
enter the line portion.
14. The method of claim 13 wherein after the AGV crosses the end
line of the line portion the distance traveled is cleared from
memory.
15. The method of claim 1 wherein said step of maintaining a
designated spacing between each AGV from the plurality of AGVs
further includes the step of determining the distance traveled from
the initial line on the line portion for each AGV.
16. The method of claim 15 wherein said step of maintaining a
designated spacing between each AGV further includes the step of
ensuring that the distance between each AGV is determined by
subtracting the distance traveled of a trailing AGV from a prior
AGV and comparing the determined distance between matches the
designated spacing.
17. The method of claim 16 wherein said step of ensuring that the
distance between matches the designated spacing further includes
the step of adjusting the speed of the trailing AGV to approach the
designated spacing and repeating said step of subtracting the
distance traveled of the trailing AGV on which speed was adjusted
from the prior AGV and adjusting the speed, and repeating the steps
of subtracting and adjusting until the trailing AGV and prior AGV
are spaced apart with the designated spacing.
18. The method of claim 17 wherein said step of adjusting the speed
further includes the step of limiting any speed adjustment within a
specified range.
19. The method of claim 17 wherein as said step of adjusting the
speed for AGV is performed, each subsequent AGV automatically in
response to a speed adjustment by a prior AGV performs the steps of
ensuring that the distance between each AGV is the designated
spacing and adjusting speed as needed to maintain the designated
spacing with the prior AGV.
20. The method of claim 1 wherein said step of maintaining the
designated spacing further includes the step of continuously
calculating the distance traveled by each AGV from the initial line
along the line portion and communicating said distance traveled to
one of a prior and a trailing AGV.
21. The method of claim 20 wherein said step of maintaining further
includes the step of at least one of the prior and the trailing AGV
calculating the spacing between the two AGVs and wherein the
trailing AGV uses the calculated spacing to adjust the speed of the
trailing AGV to approach the desired designated spacing.
22. The method of claim 1 further including the step of stopping at
least one AGV in the line portion in response to a stop condition
and wherein the stopped AGV communicates a stop status to each
subsequent AGV within the line portion and wherein each subsequent
AGV stops upon receiving said stop status from any prior AGV.
23. The method of claim 22 wherein each stopped AGV determines the
distance to the immediate prior AGV.
24. The method of claim 23 wherein the leading AGV of the stopped
AGV automatically restarts upon removal of the stop condition and
communicates a restart signal to at least the trailing AGV upon
starting.
25. The method of claim 24 wherein the trailing AGV determines a
start delay.
26. The method of claim 25 wherein said step of determining a start
delay includes the step of determining a distance between the prior
AGV and the subject AGV and if the distance is greater than the
designated spacing a start delay of zero is determined and if the
determined distance is less than the designated distance a start
delay of sufficient time to ensure at least the designated spacing
is maintained to the prior AGV is determined.
27. The method of claim 25 wherein each subsequent AGV performs the
steps of determining a start delay upon receiving a restart signal
from the prior AGV.
28. The method of claim 1 wherein said step of maintaining a
designated distance further includes the step of automatically
determining the length of at least one of a carrier and a load on
the AGV and adjusting the spacing between the AGV to match the
designated distance while accounting for variations in length of
the load and carrier.
29. The method of claim 1 further including the step of maintaining
a communication link between each prior and each trailing AGV and
stopping a trailing AGV upon failure of the communication link.
30. The method of claim 1 wherein the travel path is a continuous
loop and further including the step of directing the AGV along the
travel path to the next initial line after the AGV crosses the end
line of the current line portion.
Description
TECHNICAL FIELD
[0001] The present invention is generally directed to material
handling vehicles and more particularly to a system and method of
automatic guided vehicles that are capable of providing
synchronized travel along a line or path such that regular
manufacturing operations may be performed to material or workpieces
on the vehicle without the need for a traditional conveyor
systems.
BACKGROUND OF THE INVENTION
[0002] For over a century now, manufacturers have used assembly
lines to provide reliable and consistent work flow of workpieces
and material through various manufacturing operations to create an
end product. These assembly lines widely vary depending on the
desired end product as well as the type of manufacturing process;
however, almost all have some common features. Most assembly lines
include a conveyor system such as a chain conveyor system, power
and free conveyor system or any other type of material conveyor
system that is designed and installed permanently into the
facility. To provide consistent work flow, most conveyor systems
are configured to couple to or support a workpiece at a
substantially uniform predetermined distance and configured to move
along a path at a set speed. Each conveyor system is configured to
keep the workpiece consistently spaced no matter the speed,
acceleration, deceleration, stop, or start conditions. As all
workpieces are securely coupled in some form together, consistent
travel of all workpieces automatically occurs. Most conveyor
systems also require a chain, belt, or track that forms the path,
couples all objects together and is installed permanently into the
manufacturing facility. As such, traditional assembly lines and
conveyor systems work extremely well at providing consistent
through put of work in manufacturing operations, especially where
the timing of workpieces entering and exiting a particular work
station is important, but they have been generally expensive to
initially install and also lack flexibility for easy
reconfiguration. The presence of the conveyor equipment often
prevents access to the part or workpiece from all sides and
prevents workers from easily and safely crossing the conveyor
path.
[0003] Automatic guided vehicles or AGVs are commonly used in many
industries to provide material handling and transport various loads
without a human operator. The term "AGV" is commonly used to refer
to robust vehicle designs having any number of available automated
guidance systems. The term "AGC" is also commonly used to refer to
less robust vehicles such as automatic guided carts which are
similar in nature to AGVs, however, are typically designed to carry
smaller loads. Throughout this application, including the claims,
the term "AGV" or automatic guided vehicle shall mean and include
both AGVs and AGCs as well as any other vehicle that is capable of
being autonomously guided. Autonomous guidance and AGVs do not
include vehicles being remotely controlled by human operators, but
instead must be capable of following a path or route without human
intervention.
[0004] Current AGV designs generally include a frame with at least
two wheels, one of which may be a drive wheel. The drive wheel
provides motion to the cart and may also be a steerable drive wheel
but in some instances, the non-driven wheels may instead or in
combination, act as the steerable wheel. An AGV requires a guidance
system to control its movement. A variety of guidance systems are
available for use in AGVs including wire guidance, laser guidance,
magnetic tape guidance, odometer guidance, inertial guidance,
dead-reckoning, optical guidance and a variety of other less used
guidance systems. Each type of guidance system generally has
associated positives and negatives. For example, an inertial
guidance system may be susceptible to tracking errors where the
travel distance and direction measured by the AGV differs from the
actual distance and direction of travel due to wheel slip on the
supporting surface. A variety of methods have been proposed to
minimize such tracking errors but the tracking errors may compound
over long travel distances. As such, many AGVs include backup or
secondary guidance systems which may provide a position or status
check, and as such be used to correct for any errors. For example,
way point reference markers may be added to the system such as
magnetic paint, radio frequency identifier tabs and optical tags to
allow an AGV to update its position to a correct position and
thereby minimize any guidance errors. Some AGV systems today that
use sensors that detect existing environmental features and do not
require the addition of reference markers.
[0005] Due to the variety of potential errors introduced by at
least one of the guidance and drive systems, AGVs have primarily
been used in facilities only for the moving of materials such as
delivery of raw materials to an assembly line, the removal of
finished materials to storage, and from storage to distribution and
shipping. In these instances, the AGV may be programmed with a
specific path that an individual AGV travels along, but none of the
issues associated with a conveyor system in a manufacturing
operation are of concern. In addition, while AGVs may be part of
material handling system and work in cooperation with the overall
system, they do not individually coordinate movement in the
facilities other than avoiding potential collisions between AGVs.
As such, AGVs have generally not worked in coordination but instead
each perform their own unique task and only coordinate to prevent
collisions, or move material along desired paths such that parts A
are coordinated to arrive with a parts B at a particular work
station.
[0006] Some manufacturers have tried to use automatic guided
vehicles in manufacturing operations or in various facilities as a
replacement for typical conveyor systems although until the present
invention, no manufacturer has successfully implemented such a
system. Coordinated movement of AGVs in a cost-effective and
reliable manner, similar to conveyor systems was not yet possible.
For example, if an AGV system was to coordinate all AGVs using a
central broadcast time signal, the time signal to each AGV has
complications with respect to starting and stopping, which is
frequently required in a manufacturing facility. More specifically,
there are many timing problems associated with identifying the
exact time a vehicle stops or starts due to inherent latencies in
communication systems. Without an exact time the vehicle stops or
starts, it is unknown where a particular vehicle is in relation to
other vehicles and in relation to the external manufacturing
operation. As such, problems may occur in restarting the system,
such with spacing between the AGVs.
SUMMARY OF THE INVENTION
[0007] The present invention is directed to a system and method of
automatic guided vehicles that are capable of providing
synchronized travel along a line or path such that regular
manufacturing operations may be performed to material or workpieces
on the vehicle without the need for a traditional conveyor
systems.
[0008] The method of operating a conveyor system for material
handling in a facility generally uses a plurality of AGVs, each
having a controller. The controller includes a communication system
and a guidance system. The AGVs may be in communication with a
central controller, at least one AGV, such as the lead AGV may be
in communication with the central controller, or the system may use
a distributed control system without the central controller, with
the control residing collectively in the AGV controllers.
[0009] The method generally includes the steps of determining a
travel path having at least one line portion defined by an initial
line and an end line; inputting a guided route for the AGV to
follow, wherein the guided route includes instructions regarding
the AGVs travel along the at least one line portion; assigning a
unique ID to each AGV; guiding the plurality of AGVs along the
travel path; automatically determining a lead AGV in the line
portion; automatically determining a last AGV in the line portion;
automatically updating the last AGV in the line portion each time
an AGV from the plurality of AGVs crosses the initial line of the
line portion; automatically updating the lead AGV to the immediate
trailing AGV in the line portion each time the lead AGV from the
plurality of AGVs crosses the end line; and maintaining a
designated spacing between each AGV from the plurality of AGVs
within the line portion.
[0010] The method may further include a step of inputting the
travel path, including the line portion, into each guidance system
of the plurality of AGVs. Of course, the input travel path may be
only input in the lead AGV and then distributed as needed to the
other AGVs. The method may also include inputting a desired line
speed for the AGV to travel along the line portion. The method may
also include a step of inputting a desired travel speed for the AGV
when the AGV is not in the line portion. The desired line speed and
the desired travel speed may be different, such that an AGV may
progress through a certain line segment at a reduced pace while
manufacturing operations are being performed and then travel
between line segments, or back to the entrance of the same line
segment as quickly as possible to reduce the number of AGVs used in
a particular facility or manufacturing operation.
[0011] The method may use a lead AGV and be configured such that
each of the following plurality of AGVs in the line portion match
the lead AGV speed. The method may automatically determine the lead
AGV and assign a lead token to the lead AGV. Of course, the method
may automatically update the lead AGV by passing a lead token from
the lead AGV as it crosses the end line to the next trailing AGV.
Similar to the lead token described above, the method may
automatically determine a last AGV and assign an end token to the
last AGV. Of course, the method may automatically update the last
AGV in the line portion each time an AGV from the plurality of AGVs
crosses the initial line of the line portion further includes the
step of passing the end token from the preceding last AGV to the
updated last AGV. The method may include automatically updating the
last AGV in the line portion by providing the unique ID of the AGV
updated as the new last AGV to at least one of another AGV and a
central controller.
[0012] The method step of guiding the plurality of AGVs along the
continuous travel path may include the step of guiding the AGVs
through the line portion, and further the step of guiding the
plurality of AGVs with consistent spacing and speed in the line
portion. More specifically, the step of guiding the AGVs through
the line portion may include the step of tracking the distance
traveled by the AGV since crossing the initial line to enter the
line portion. The AGV when it crosses the end line of the line
portion may clear the distance traveled from memory.
[0013] The method maintains a designated spacing between each AGV
and may further include the step of determining the distance
traveled from the initial line on the line portion for each AGV. As
such, the system may ensure that the distance between each AGV is
determined by subtracting the distance traveled of a trailing AGV
from a prior AGV and comparing the determined distance between
matches the designated spacing. More specifically, the step of
ensuring that the distance between matches the designated spacing
may further include the step of adjusting the speed of the trailing
AGV to approach the designated spacing and repeating the step of
subtracting the distance traveled of the trailing AGV on which
speed was adjusted from the prior AGV and adjusting the speed, and
repeating the steps of subtracting and adjusting until the trailing
AGV and prior AGV are spaced apart with the designated spacing. The
step of adjusting the speed may further include the step of
limiting any speed adjustment within a specified range. As the step
of adjusting the speed for AGV is performed, each subsequent AGV
may automatically, in response to a speed adjustment by a prior AGV
or any AGV in a line segment performs the steps of ensuring that
the distance between each AGV is the designated spacing and
adjusting speed as needed to maintain the designated spacing with
the prior AGV.
[0014] The step of maintaining the designated spacing may further
include the step of continuously calculating the distance traveled
by each AGV from the initial line along the line portion and
communicating the distance traveled to one of a prior and a
trailing AGV. The step of maintaining may further include the step
of at least one of the prior and the trailing AGV calculating the
spacing between the two AGVs and wherein the trailing AGV uses the
calculated spacing to adjust the speed of the trailing AGV to
approach the desired designated spacing.
[0015] The method may include a step of stopping at least one AGV
in the line portion in response to a stop condition and wherein the
stopped AGV communicates a stop status to each subsequent AGV
within the line portion and wherein each subsequent AGV stops upon
receiving said stop status from any prior AGV. Upon stopping, each
stopped AGV determines the distance to at least the immediate prior
AGV. The leading AGV of the stopped AGV may automatically restart
upon removal of the stop condition and communicate a restart signal
to other stopped AGVs, including at least the trailing AGV upon
starting. Upon receiving a restart signal, the trailing AGV would
determine a start delay. The step of determining a start delay may
include the step of determining a distance between the prior AGV
and the subject AGV and if the distance is greater than the
designated spacing a start delay of zero is determined and if the
determined distance is less than the designated distance a start
delay of sufficient time to ensure at least the designated spacing
is maintained to the prior AGV is determined. At least each
subsequent AGV would perform the steps of determining a start delay
upon receiving a restart signal from the prior AGV.
[0016] In the method, the step of maintaining a designated distance
may further include the step of automatically determining the
length of at least one of a carrier and a load on the AGV and
adjusting the spacing between the AGVs to match the designated
distance while accounting for variations in length of the load and
carrier.
[0017] The method may include the step of maintaining a
communication link between each prior and each trailing AGV and
stopping a trailing AGV upon failure of the communication link.
[0018] The travel path may be a continuous loop and the method may
include a step of directing the AGV along the travel path to the
next initial line after the AGV crosses the end line of the current
line portion.
[0019] Further scope and applicability of the present invention
will become apparent from the following detailed description,
claims, and drawings. However, it should be understood that the
detailed description and specific examples, while indicating
preferred embodiments of the invention, are given by way of
illustration only, since various changes and modifications within
the spirit and scope of the invention will become apparent to those
skilled in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The present invention will become more fully understood from
the detailed description given here below, the appended claims, and
the accompanying drawings in which:
[0021] FIG. 1 is a schematic view of an exemplary conveyor system
using automatic guided vehicles;
[0022] FIG. 2 is a side view of automatic guided vehicles within a
portion of an exemplary conveyor system; and
[0023] FIG. 3 is a schematic drawing of an exemplary AGV
controller.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] The present invention is generally directed to material
handling vehicles and more particularly to a system and method of
automatic guided vehicles that are capable of providing
synchronized travel along a path such that regular manufacturing
operations may be performed to material or workpieces on such
automatic guided vehicles without the need for traditional conveyor
systems.
[0025] The system 10, as illustrated in FIGS. 1 and 2, generally
includes a travel path 20 having individual line segments or
portions 22 bound by an initial line 30 and an end line 40. As an
automatic guided vehicle (AGV) 50 travels along the path 20 within
the line segment 22, each AGV 50 maintains a separation distance 60
from adjacent AGVs. With any given line segment 22 with at least
two AGVs, there is a lead AGV 52, a subsequent AGV 54 and a last
AGV 58. Of course, in some instances the subsequent AGV 54 and last
AGV 58 may be the same. The system 10 may include a central
controller 70 having a communication system 72 communicating with
each AGV 50. However, in some systems 10, no central controller 70
or communication system 72 is used and instead each AGV 50 may
communicate with each other independently in a distributed
communication system or in addition to the central controller 70.
Each AGV 50 may include an AGV controller 90 generally having a
control module 74, a guidance module 76, and a sensor module 82
coupled to at least one sensor 84. The guidance module 76 may
include a travel distance encoder module 80. The controller 90 may
be in communication with an antennae 78 communicating with at least
one of the central controllers 70 and an adjacent AGV 50, or any
other AGV 50 in the travel path 20. It is expected that each AGV
have wheels 56 of which one may be a drive wheel and one a
steerable wheel.
[0026] The method generally includes providing a system 10 having
AGVs 50 configured to travel along a determined travel path 20. The
system 10 is generally configured to work in and around the
facility such as a manufacturing, distribution, or warehouse
facility. It is particularly suited to a manufacturing facility in
that the system is configured to allow for consistent spacing and
speed as it moves along the line portion 22 or in some instances
between individual work stations at which manufacturing operations
may be performed.
[0027] The travel path 20 and included line segments 22, as well as
the initial line 30 and end line 40 of such line segments 22, are
provided and input into the AGV controller, specifically the
guidance controller 76. Once each AGV 50 has learned the desired
travel path 20 including line segments 22, a unique ID is assigned.
During operation, a central controller or a distributed control
between the AGVs 50 may guide the plurality of AGVs 50 along the
travel path 20. The system 10 automatically determines a lead AGV
52 in the line portion 22 as well as a last AGV 58 in the line
portion 22. As each AGV 50 continues to move along the line segment
22, at some time the lead AGV 52 will cross the end line 40 of the
line segment 22 and the system 10 will automatically update which
AGV 50 is the lead AGV 52 in the line segment 22. In addition, as
AGVs continuously enter the line segment 22, the system
automatically updates which is the last AGV 58 in a particular line
segment 22. As the AGVs 50 progress along the line segment 22, each
AGV 50 maintains a designated spacing between each AGV 50 forming
the plurality of AGVs 50 in the line segment 22. Of course, the
line segment 22 may be broken into multiple sub-segments in 24
which the spacing may vary between manufacturing operations.
However, in each instance within a particular line segment 22 or
sub-segment 24, which could be considered just smaller line
segments 22, the spacing is maintained as a designated spacing 60
between each AGV 50.
[0028] The step of determining a travel path 20 having at least one
line portion 22 defined by initial line and an end line is
generally performed in the manufacturing facility, warehouse or
distribution center. The terms manufacturing facility, warehouse,
distribution center or other building in which the AGV operates in
the present invention hereinafter shall be generally referred to as
a facility. It is expected that an AGV will operate in and about a
particular facility. As such, the operator of a system 10 will
generally set up the facility similar to when a conveyor system is
used between individual work stations. However, instead of
installing a traditional conveyor system, the operator of the
facility determines a travel path 20 for AGVs 50 to travel between
particular work stations or destinations. It is expected that the
travel path 20 determined is a substantially continuous travel path
such that each AGV 50 after exiting a particular line portion 22
within the travel path 20 eventually circles back to enter the
initial line portion 30 within particular line segment 22. As the
travel path 20 is virtually determined in many instances, the only
changes to a facility needed in moving a travel path may be as
simple as providing new initial or end lines 30, 40 by painting on
the floor of the facility. As such, the present invention provides
all the positives of a traditional conveyor system, but is much
more flexible and has very low cost in making any changes in the
travel paths 20.
[0029] Although not illustrated in the Figures, each travel path 20
may have a variety of different segments 22, 24 and be much more
complex than the simple loop route illustrated in FIG. 1. Once the
travel path 20 is determined, each line portion 22 is defined by an
initial line 30 and an end line 40. As illustrated in FIG. 1, the
travel path 20 includes multiple line portions 22 and in some
instances, the initial line 30 and end line 40 are the same line
such that an AGV 50 crossing the end line 40 of one line segment 22
is also crossing the initial line 30 of a subsequent line segment
22. In such instances, the adjacent line portions or segments 22
may be considered all one large line segment or portion 22 with
sub-segments 24. It should be recognized that the illustrated
travel path 20 and line segments 22 are only exemplary and such
travel path and line segments 20, 22 will vary widely depending
upon the type of facility, layout of the facility, type of
manufacturing operations, travel paths selected to avoid people and
any other desired considerations. It should also be recognized that
a particular facility may have multiple travel paths 20 such that a
particular group of AGVs may stay on a first travel path while a
second group may stay on a second travel path, although the system
is so flexible such that AGVs could be easily added or taken away
depending upon the need in any one given travel path.
[0030] Once the travel path 20 and line portions 22 are determined,
they are input into at least one of a central controller 70 or AGV
controller 90. The input may be simply a program upload or in some
instances may be a learning system wherein the AGV 50 is manually
directed along the path 20. While the initial line 30 and end line
40 forming a particular line portion 22 may be completely virtual
and programmed into an AGV controller 90, it is expected that in
most instances such an initial line 30 and end line 40 will be
physically delineated within the facility. More specifically, it is
expected that the sensor module 82 and sensors 84 may determine and
sense the initial line 30 and end line 40. By providing actual,
physical markers within the facility such as optical markers or
magnetic tape on the supporting surface, the potential for errors
is minimized and it ensures that each AGV 50 is capable of tracking
the distance or time since the AGV 50 crossed the initial line 30
within a particular line segment 22 in a consistent and reliable
manner. Any number of known techniques may be used to input the
guided route for the AGV to follow into one of the controllers 70,
90. It should be recognized in some systems 10 the system 10 will
not include a central controller 70 but may be distributed and
controlled amongst the individual AGVs 50.
[0031] Each AGV 50 will be assigned a unique ID. The unique ID may
be hard-built into the AGV 50 by the manufacturer or may be
virtually assigned when each AGV 50 is added to a particular travel
path 20. The unique ID allows each system 10 to easily determine
which AGV 50 is in a particular line segment 22 as well as
communicate spacing and distance traveled over an initial line
segment 30. In addition, the unique ID may be used in determining
the lead AGV 52, subsequent AGVs 54 and last AGV 58 in a particular
line segment 22. The unique ID assigned to each AGV 50 may also be
used in associating a lead token with the lead AGV 52 as well as a
last token with the last AGV 58. These tokens then may be
automatically updated as described below as AGVs cross in and out
of a particular line segment 22.
[0032] During operation, the system 10 may guide the plurality of
AGVs along the travel path and in and out of particular line
segments 22. The guiding of individual AGVs 50 along the travel
path 20 may be done by any known method including methods such as
inertial guidance, dead-reckoning, magnetic systems including
magnetic tape, markers, paint or guide wires, optical guidance
systems, or any other type of guidance system. It is expected that
markers or other instructions needed for any particular guidance
system will be added by the facility as needed for that particular
guidance system. The additional markers added are markers
specifically delineating the start and end of line segments
particularly the initial line 30 and end line 40 of particular line
segments unless the particular guidance system supports virtual
markers, however, a virtual initial line 30 and a virtual end line
40 must then be. As such, it is expected that if an AGV uses an
inertial guidance which is free from external sensor inputs other
than accelerometers and wheel encoders, an optical or magnetic
sensor will form one of the sensors 84 and be used to determine the
added initial and end lines 30, 40.
[0033] When the system 10 is operational, the system 10
automatically determines the lead AGV 52 in a particular line
portion 22 as well as the last AGV 58 in a line portion 22. With
the lead AGV 52 and last AGV 58 determined, the order of each
subsequent AGV 54 following the lead AGV 52 is also known. The
unique IDs assigned above allow the system 10, even if it is a
distributed control system, to easily and readily determine the
order of AGVs along a travel path 20 and in particular the order of
the AGVs within a particular line segment 22.
[0034] With the system 10 knowing the location of each AGV 50
within a particular line segment 22, as the AGVs 50 progress along
the travel path 20 and a lead AGV 52 crosses the end line 40, the
system 10 will automatically update the lead AGV 52 to correspond
to the immediate subsequent or trailing AGV 54. As such, the
immediate subsequent or trailing AGV 54 becomes the lead AGV 52.
Similarly, the system 10 automatically updates the last AGV in the
line portion 22 each time an AGV 50 from the plurality of AGVs 50
in a particular travel path 20 crosses the initial line 30 of the
line portion 22. The system 10 may use a lead token which is
transferred from AGV 50 to AGV 50 such as being associated with
each unique ID as well as a last token which is also transferred
between each AGV 50 as a new AGV 50 becomes the last AGV 58. It is
important to note that the system 10 automatically updates the last
58 and lead 52 AGVs which is always changing in a particular line
segment 22.
[0035] To provide consistent through-put, the system 10
automatically maintains a designated space 60 between each AGV 50
from the plurality of AGVs 50 within the line portion 22. In
addition, it is expected that the system 10 will maintain a
consistent speed between each of the AGVs 50 in a line portion 22.
A central controller 70 may control the AGVs 50 to maintain the
designated spacing 60, however, each AGV 50 may individually
control the spacing 60 between it and the prior AGV. More
specifically, a prior AGV 50 may communicate with a subsequent AGV
54 its distance traveled from the initial line 30, which the
subsequent AGV 54 compares at that time to its distance traveled
from the initial line 30 to determine the designated space 60
between the AGVs. If the spacing does not match the preset
designated spacing, the AGV 50 may adjust its speed and continue
the process of cycling communication, determination, and adjusting
the speed until the designated spacing 60 is maintained.
[0036] It is expected that while inputting the travel path and line
segments into the guidance system of an AGV 50, the desired line
speed for the AGV to travel along any particular line portion 22 is
also input. As such, both the designated spacing and line speed may
be predetermined for a particular line portion 22 such that the
AGVs 50 act similar to a traditional conveyor system and are
capable of replacing a traditional conveyor system. In addition, a
variety of travel speeds may exist such as the AGV 50 in one line
segment 22 traveling faster than the AGV 50 in a subsequent line
segment 22. Furthermore, in areas of the travel path 20 which are
not line segments 22, it may be desirable to quickly move the AGV
from the end line 40 of one line segment 22 to the start or initial
line 30 of another line segment 22. By increasing the speed of the
AGVs 50 in areas that do not form part of the line portion 22, the
number of AGVs needed are minimized as an AGV may quickly exit a
particular line portion 22 and travel with increased speed travel
to the start of the next line portion 22. Of course, consistent
speed may be kept through the whole travel path.
[0037] Even though the speed of a particular AGV in a line segment
22 is typically predetermined, or should match a set speed or speed
range, the lead AGV 52 in any particular line segment 22 indirectly
sets the actual speed of subsequent AGVs 54. By the lead AGV 52
indirectly setting the actual speed of the subsequent AGVs 54, each
AGV following matches the lead AGV's speed. More specifically, the
AGVs maintain the desired spacing 60 between each AGV 50 in a line
portion 22 and as such, the speed of the individual AGVs is
substantially matched. Only the lead AGV 52 attempts to follow the
set or predetermined speed while all subsequent AGVs 54 try to
indirectly match the speed of the lead AGV 52 by maintaining the
designated spacing 60. More specifically, while the lead AGV 52
generally attempts to match its preprogrammed speed for its
particular position along a travel path and particularly along a
line portion 22, some variations occur and to ensure designated
spacing 60 between subsequent AGVs 54, the subsequent AGVs only
match the lead AGVs speed by maintaining designated spacing 60.
More specifically, the subsequent AGVs 54 do not specifically match
the lead AGVs' 52 speed and the lead AGV does not communicate its
speed to other AGVs, but by maintaining the designated spacing 60,
the speed of the lead AGV 52 is indirectly matched with minor
variations. The designated spacing 60 is easier to match than speed
as an encoder on a wheel may easily track the distance traveled
from the point where the AGV entered the line segment 22 for each
AGV. As the initial line 30 is physically delineated, the lead AGV
52 and subsequent AGVs 54 use the distance traveled in calculating
the spacing, which is more consistent than speed for any given AGV.
Therefore, while the lead AGV 52 generally sets the speed for
subsequent AGVs, the system in reality is using the distance
traveled as a comparison of spacing 60 and any adjustments of speed
in subsequent AGVs 54 are to adjust the spacing 60 not generally to
match the speed of the previous AGV. However, to maintain spacing,
the subsequent AGVs 54 will need to match the speed of the prior
AGV as well as lead AGV 52 and will do so indirectly through
calculating the distance between the AGVs. As such, the system 10
uses very little computational power as it only tracks the distance
traveled by the AGVs since crossing the initial line 30 to enter
the line portion 22. Therefore, after an AGV 50 crosses the end
line 40 of a particular line portion 22, the distance traveled is
cleared from the memory of the AGV because it is either in a new
line segment 22 or it is in a travel path 20 between line segments
or portions. Therefore, as each AGV 50 travels along a particular
line portion 22, an AGV determines its distance traveled and
communicates it to at least the subsequent AGV 54. The subsequent
AGV 54 then takes its own distance traveled and compares it to the
distance traveled to the prior AGV to determine the current
distance between such AGVs and if the determined distance matches
the designated spacing 60 desired at that position along the line
portion 22. If the designated spacing 60 does not match the actual
spacing, the subsequent AGV 54 will adjust its speed slightly to
either increase or decrease the speed and as such, decrease or
increase the distance between such AGVs. The system 10 continuously
cycles by communicating from one AGV 50 to at least the subsequent
AGV 54 the distance traveled, receiving a communication of the
distance traveled by the prior AGV, determining its own distance
traveled, comparing it to the distance traveled of the prior AGV
and adjusting speed as necessary. Adjustments in speed may be
limited such that an AGV does not go faster or slower than a
desired range within a particular line portion 22. In addition, the
adjustments in speed may be limited as the designated spacing is
approached such that the AGV is not constantly overcorrecting.
Therefore, a range of error is allowed on each side of the
designated spacing. This range may be determined and vary widely
between systems. In each event, the system, in particular each AGV
50, attempts to match the designated spacing 60 by continuously
calculating the designated spacing using distance traveled for each
adjacent AGV adjusting as needed and then performing the
calculations again. The type of operations being performed, type of
facility, and spacing 60 designated between each AGV 50 may all
affect how often the system 10 needs to cycle its calculations.
[0038] It should be noted that as the AGV 50 uses distance traveled
in calculating and maintaining the designated spacing 60, wheel
slip may occur thereby providing false readings on the distance
traveled. In addition, while the present invention refers to the
distance traveled with an encoder on the wheels, other systems may
be used to calculate the distance traveled, such as optical markers
or any other known system. As most AGVs include an obstacle
avoidance system such as detecting unexpected objects in the path,
which many times are people crossing the path of the AGV, such
systems may also be used to ensure that the AGVs do not collide in
the event that any particular AGV in the line portion 22 has an
incorrect distance traveled, which leads the subsequent AGVs 54 to
believe that the prior AGV 50 is located a greater distance away
than its current actual distance. Therefore, the obstacle avoidance
system may be used to ensure adjacent AGVs do not collide if a
mistake occurs in the travel distance, as the travel distance is
used to adjust the designated spacing 60 between individual
AGVs.
[0039] The use of a travel distance is particularly beneficial in
maintaining designated spacing in the event of a stopped condition.
A stopped condition may occur from a variety of events such as an
error on a machine in the facility such that all of the AGVs
subsequent to a particular work station must stop, a breakdown of
an AGV, or even a person crossing the path of the AGV. As AGVs are
already communicating distance traveled, a particular AGV may
detect that the AGV ahead of it is stopped by the fact that the
distance between it and the AGV ahead is shrinking. The trailing
AGV will slow to maintain spacing. A minimum allowed spacing is set
for the particular AGV/load/segment combination. When the distance
between the AGV and the AGV ahead fall to or below that minimum
distance the AGV stops. Each subsequent AGV in the segment
similarly slows and stops. In some systems, it is desirable that
all AGVs in the segment remain within proper spacing or a very
small range in spacing. In some systems, it is desirable to stop
the entire line when any AGV stops. As AGVs are already
communicating distance traveled, a particular AGV may communicate
to all AGVs or all subsequent AGVs in the segment the stop status
upon stopping in response to a stopped condition.
[0040] All AGVs 54 in the particular segment or all subsequent
AGVs, as soon as a stopped status is received from any prior AGV,
would stop until it receives a restart signal from the originally
stopped AGV. Upon the removal of a stopped condition of the any
stopped AGV particularly a first stopped AGV, it would communicate
a restart signal to all of the AGVs in the same segment. This
restart signal may be communicated down the complete line of AGVs
in a particular line segment or communicated from AGV to AGV such
that a prior AGV only communicates with the subsequent AGV 54 such
that once the subsequent AGV restarts, it then sends a restart
signal to the next subsequent AGV. In any stopped condition, it is
likely that many of the AGVs need to stop quickly and as such, the
designated spacing between particular AGVs may vary in a stopped
condition due to timing in receiving the stopped signal or even
differences in the braking capabilities of AGVs, loads carried or
other conditions. Once each AGV is stopped or in response to a
restart signal, the subsequent AGV calculates the designated
spacing between adjacent AGVs and determines if any adjustment is
needed during the starting or restart procedure to maintain the
designated spacing. For example, if a prior AGV entered a stopped
condition due to a person stepping the path of the AGV, it would
stop quickly and at the same time send a stop signal to the
subsequent AGV. Upon receiving the stopped signal, the subsequent
AGV would stop, however, minor communication delays may cause the
subsequent AGV to reduce the designated spacing to an amount less
than desired. Therefore, when a restart signal is sent, the AGV
receiving the restart signal would calculate the distance to the
prior AGV during the stopped condition and determine if a start
delay is needed.
[0041] If the determined distance between the adjacent AGVs is
greater than or approximately equal to the desired maintained
spacing 60, the AGV would start as soon as receiving restart signal
as the start delay would be zero. However, if the spacing 60 is
less than what is desired, the AGV would calculate a start delay
which upon starting would place it in the designated spacing 60 to
minimize further adjustments needed. Therefore, upon exiting a
stopped condition and receiving a restart signal, the start delay
is automatically calculated and adjusts so that upon restart the
AGV is immediately within the designated spacing. Therefore, a
starting procedure for a plurality of AGVs has little effect on the
system and only minor adjustments are needed once each AGV is
operational and traveling down the travel path 20. However, it is
expected that due to variances in AGVs and loads, some AGVs may
accelerate faster than other AGVs, even if the acceleration is
limited in a restart condition. Therefore, the AGV, upon restart,
would as described above, determine the distance between the two
adjacent AGVs and adjusting its speed as necessary to approach the
desired spacing 60. It should also be noted that if an AGV 50 in
the center of a line portion experiences a stopped condition, the
prior AGVs may continue on without stopping and as each AGV exits
the line portion, such as passing through the end line 40, the lead
token is passed from one AGV to another and as such, the first
stopped AGV may receive the lead token as the last AGV exits from
the moving group of AGVs. If an AGV experiences a stopped
condition, once the designated spacing grows beyond a certain
distance with a prior AGV, the stopped AGV, upon restarting may
also be assigned a lead token such that two AGVs within the line
portion are acting as lead AGVs so that the second lead AGV does
not try to catch up to the last AGV in the group with the original
lead AGV.
[0042] The system may also be configured to automatically receive
and adjust spacing depending upon the particular loads carried by
an AGV. In some instances, a load carried by an AGV such as a
tugger or forklift may vary in length and such length may be
provided to the AGV automatically and the AGV may adjust
automatically the desired designated spacing 60 such that it
accounts for variations in the length of the load and the carrier.
Therefore, the AGVs may maintain the designated spacing between
adjacent AGVs irrespective of the type of load or length of a
particular load or even variations between the AGVs used on a
particular line segment.
[0043] As the AGVs communicate distance traveled and use such
communicated distance to determine and maintain the designated
spacing 60 between particular AGVs 50, upon a failure of
communication by a particular AGV, a variety of steps may be taken.
First, a particular AGV that is subsequent to the AGV with the
communication failure may stop. Second, the AGV with the
communication failure may stop as it is unable to receive distance
traveled from a prior AGV. Third, the AGV may use external markers
to update the position. Fourth, the AGV with the communication
failure may be configured to automatically leave the line segment
and travel path and travel to a repair area. Similarly, the AGV may
be manually removed from the segment. For example, the system may
automatically determine that the AGV with the communication failure
is no longer responsive and the unique ID is removed from the
system and as such, system controller, or the distributed
controller determines then new order for the AGVs in the segment.
With the new order, each AGV performs its function of lead AGV,
subsequent AGV, and last AGV to maintain proper spacing. In view of
the above, the system 10 may automatically remove an AGV 50 and
adjust the spacing 60 as needed between the remaining AGVs such
that the operations being performed in any particular line portion
22 do not need to stop due to a simple communication failure. When
an AGV breaks down, operators remove the AGV from the path. The
system automatically performs the steps above to re-sequence the
vehicles to allow a restart.
[0044] Therefore, during operation in the present invention, the
first AGV 52 which is the lead AGV generally acts as a pace car to
the subsequent AGVs. The first AGV 52 travels through the line
segment or portion 22 at the desired speed and the second AGV in
line or subsequent AGV 54 follows the lead AGV 52 at the desired
spacing distance. Therefore, the second or subsequent AGV 54 to the
lead AGV 52 and each one thereafter is allowed to travel at the
nominal speed but with enough speed modulation and range in the
allowed speed to allow it to track and maintain a desired distance
60 behind the lead AGV 52 or any prior AGVs.
[0045] Therefore, the system 10 is aware of a particular AGV's 50
position on the line segment 22, which is accomplished as described
above using a sensor that detects the initial line 30 and then
detects the distance traveled along the line segment 22 since
crossing the initial line 30. The sensor 84 used to detect the
initial line 30 may be any type sensor, such as proximity switch,
limit switch, photo cell, magnetic sensor, bar code reader, RFID
sensor, or any other sensor capable of detecting an appropriate
target that senses or provides data that the AGV is crossing the
initial line 30. The sensors 84 may also be used to update the
guidance system to targets along the line segment. However, a
simple way to determine distance from the line segment would be a
second sensor such as an encoder attached to the wheel of the AGV,
preferably a trailing wheel and not a drive wheel, such that the
encoder provides the distance traveled as the wheel turns.
[0046] As the system 10 needs to communicate distance traveled
between each AGV 50, the system generally 10 includes the
communication system 72 as described above. The communication may
be centrally controlled such that each AGV communicates only with a
central controller 70 or may be distributed such that each AGV
communicates directly with other AGVs in the system 10. However,
the communication works, the AGVs communicate their position on the
line segment 22 by communicating the distance traveled from the
initial line 30. By communicating the distance traveled and any
unique ID of a particular AGV, the relationship of each AGV on a
line segment 22 may be determined such that a central controller
may determine the order of the AGVs on the line segment and the
distance between each AGV or each AGV may determine such
information. If the communication is distributed, such as only at
each AGV level, each AGV may determine the position of the AGV
ahead of it by scanning the distances reported by each of the other
AGVs in the segment. As described above, the unique vehicle ID or
token may be assigned to each AGV allowing it to communicate its
position on the line and in particular, the tokens may be useful in
determining the lead and last AGVs 52, 58. Therefore, when a
particular AGV enters a line segment 22 by crossing an initial line
30, the communication system may query the ID of the last vehicle
to cross and provide it with a last vehicle token while the former
last AGV either clears or transfers such token. Similarly, the lead
AGV token may be transferred between AGVs.
[0047] As each AGV broadcasts its position on the line segment,
particularly its distance traveled, each AGV may determine the
spacing between it and the prior AGV. The AGV controller 90 may use
known control methods such as PID to modulate its speed and
maintain a constant distance between itself and the prior AGV. In
the event a particular AGV stops due to failure, operator
intervention or other stopped conditions, the controller of the
stopped AGV may send a signal to the other AGV controllers to stop
and every AGV currently on the line segment 22 or just subsequent
AGVs may stop. When the AGV restarts, a similar communicated signal
from the restarted vehicle to the other AGVs provides a
restart.
[0048] As described above when AGVs stop, communication delays,
equipment failures, or just differences between particular AGVs may
cause each AGV to lose its proper designated spacing 60. To control
spacing and prevent collision, the system uses the computed and
communicated distance above such as by determining the difference
in the position of the AGVs as well as the length of any particular
carrier and any system specific factors for minimal allowable
spacing. Therefore, each AGV may travel up to the designated
spacing without interfering with the AGV ahead during a stopped
condition as each AGV controller 90 includes the distance to the
AGV ahead or prior AGV. In addition, as each AGV is able to detect
any errors in spacing such that when the prior AGV restarts from a
stopped condition, a start delay may be calculated such that any
restart is delayed until proper spacing exists. Similarly, if the
spacing is larger than the desired minimal spacing, the subsequent
AGVs may increase speed in a limited manner to approach the desired
designated spacing. Even in the event of a severe failure such as
failure of the communication system or communication between each
AGV, based upon the last communicated position of a prior AGV, the
subsequent AGV knows the safe distance it may travel before
requiring a stop. Therefore, if a failed vehicle is removed from a
particular line segment, the data may be immediately sorted such
that the distances between the vehicles are reestablished without
including the removed AGV and the signals to start may be initiated
from one vehicle and sent through other AGVs within the line
segment 22.
[0049] The foregoing discussion discloses and describes an
exemplary embodiment of the present invention. One skilled in the
art will readily recognize from such discussion, and from the
accompanying drawings and claims that various changes,
modifications and variations can be made therein without departing
from the true spirit and fair scope of the invention as defined by
the following claims.
* * * * *