Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Automatic route guidance vehicle
Reexamination Certificate
2002-05-07
2004-04-13
Louis-Jacques, Jacques H. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Automatic route guidance vehicle
C701S041000, C180S408000, C180S409000, C180S410000, C180S411000, C180S445000, C180S446000
Reexamination Certificate
active
06721638
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to automatic guided vehicles, and more particularly to the steering and control of automatic guided vehicles. Automatic guided vehicles, often referred to as AGVs, are driverless vehicles that are often used for material handling purposes. AGVs are capable of carrying or towing material from one point to another without the need for a driver. AGVs generally come in two types, depending upon how they guide themselves. In a first type, the AGVs guide themselves by following current-carrying wires buried in the floor. Such AGVs typically have sensors positioned on their underside which are able to detect the magnetic field created by the current flowing through the wires. By laying these wires along desired pathways, the AGV is able to follow the wires to its intended destination, thereby avoiding the need for a human to steer the vehicle.
A second type of AGV guides without the use of wires, and is generally referred to as a wireless AGV. These AGVs are capable of driving themselves from a first location to a second location without the need of wires imbedded in the floor. Instead of following the wires, the wireless AGVs use navigation sensors to determine their position and heading. This position and heading information is then used by the vehicle in order for it to automatically steer itself along a desired path. The navigation sensors may include gyroscopes, sensors for detecting magnets embedded in the floor, laser reflectors, wheel encoders, transponder sensors, and a variety of other types of sensors.
Whether of a wire or wireless type, prior art AGVs have typically steered themselves to desired locations by first determining their position, comparing this position to a desired position, and implementing an appropriate steer correction based upon the difference between the desired and measured position. The AGV repeats this process as it moves. For tricycle style AGVs that include a front steered wheel and two rear, unsteered wheels, the steering correction is applied to the front, steered wheel. For AGVs that use differential steering (steering by running side-by-side wheels at different velocities), the steering correction is translated into appropriate velocity commands for each of the side-by-side wheels and applied to them. In the past, AGVs which have guided themselves by this method have suffered from the potential to increase their heading errors while making corrections to their position. This is due to the fact the AGV can only attempt to correct its position error by making changes in its heading. Oftentimes this change in the heading creates an even larger heading error.
An example of this heading error magnification is depicted in FIG.
5
. An AGV
100
is depicted in an initial position
102
a
in FIG.
5
. In position
102
a
, vehicle
100
is oriented parallel to a guidepath
104
, and thus has no heading error. Vehicle
100
includes a center guidepoint
106
which denotes the point on the vehicle which the vehicle considers to be its position. Stated alternatively, guidepoint
106
is the point on the vehicle which the vehicle attempts to maintain over guidepath
104
. Therefore, in initial position
102
a
, vehicle
100
is laterally offset to the left of guidepath
104
. In response to this position error, vehicle
100
would turn its wheels to the right to thereby steer back toward guidepath
104
. As illustrated in positions
102
b, c, d, e
, and
f
, the steering of vehicle
100
back toward guidepath
104
will cause vehicle
100
to change its orientation. In position
102
b
, vehicle
100
has rotated several degrees in a clockwise direction and is no longer oriented parallel to guidepath
104
. Vehicle
100
therefore has gone from position
102
a
, in which it had no heading error (i.e., it was parallel to guidepath
104
), to position
102
b
, in which its heading is different from the orientation of guidepath
104
. In position
102
c
, vehicle
100
has rotated even further in a clockwise direction, thus increasing its heading error with respect to guidepath
104
even further. Thus, the correction of the position error of vehicle
100
in initial position
102
a
is only corrected by increasing the heading error of vehicle
100
.
There are several disadvantages resulting from the AGV control scheme illustrated in FIG.
5
. First, as can be seen in
FIG. 5
, the rotation of vehicle
100
increases the necessary width of the corridor down which vehicle
100
travels. Therefore using AGVs which steer as illustrated in
FIG. 5
require corridors of sufficient width to accommodate the rotation of the AGV as it steers itself along the guidepath. Additionally, AGVs that guide in the manner illustrated in
FIG. 5
often have severe heading errors after they have guided around a curved or arced portion of a guidepath. As the vehicle completes the turn, it often has a significant heading error that only decreases after a significant amount of straight guidepath has been traversed. This is illustrated in
FIG. 7
wherein an AGV
100
includes a front steered wheel
108
and an unsteered rear wheel
110
(as well as a suitable number of support casters which are not illustrated). The point above front wheel
108
is assumed to be the guidepoint
106
, and vehicle
100
is illustrated in four different positions in which guidepoint
106
is perfectly aligned with a guidepath
104
(i.e. no position error). As can be seen, when vehicle
100
reaches position
102
d
, it is substantially misaligned with guidepath
104
. Thus, it is virtually impossible to have vehicle
100
stop immediately after this turn and be oriented in the same direction as guidepath
104
. These and other disadvantages arise from prior art methods of steering and controlling the movement of AGVs. The desire for an AGV control method that overcomes these disadvantages can therefore be seen.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a method for controlling an automatic guided vehicle which overcomes these and other disadvantages of prior art guidance methods. The present invention not only allows for AGV corridors to be narrower, but it more accurately controls the heading of AGVs as they traverse turns. The present invention provides the AGVs with a method of independently simultaneously being able to control both their heading and position.
According to one aspect of the present invention, a method for controlling an automatic guided vehicle includes measuring the AGV's heading and location. Any error between the AGV's measured heading and desired heading is determined. Also, any error between the AGV's measured location and a desired location is determined. The vehicle is then steered to simultaneously attempt to reduce both the error between the AGV's measured heading and desired heading and also the error between the AGV's measured position and the desired position.
According to another aspect of the present invention, a method for controlling an automatic guided vehicle includes measuring the AGV's heading and location, along with providing a first control loop that generates a steering command based upon any difference between the measured AGV heading and a desired AGV heading. A second control loop is also provided that generates a steering command based upon any difference between the measured AGV position and a desired AGV position.
According to yet another aspect of the present invention, a method for controlling an automatic guided vehicle is provided. The method includes measuring the AGV's position and determining a desired position for the AGV. The AGV's measured position and desired position are compared and a steering command is generated for the AGV based upon any difference between the measured position of the AGV and the desired position of the AGV. The steering command alters the AGV's position without altering the AGV's orientation as the AGV moves.
According to still another aspect of the present invention, an apparatus is
Gibson Eric
Louis-Jacques Jacques H.
Rapistan Systems Advertising Corp.
Van Dyke Gardner, Linn & Burkhart, LLP
LandOfFree
AGV position and heading controller does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with AGV position and heading controller, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and AGV position and heading controller will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3274473