Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Automatic route guidance vehicle
Reexamination Certificate
1998-03-09
2001-08-07
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Automatic route guidance vehicle
C701S018000, C701S025000, C340S933000, C340S961000, C340S988000, C340S991000, 36, C342S457000
Reexamination Certificate
active
06272406
ABSTRACT:
The present invention is directed toward a guidance system for guiding an automated guided vehicle (AGV) along a pathway, and more specifically, toward a guidance system for an AGV that uses rails to guide the AGV through first portions of a pathway and a non-rail control system to guide the AGV through second portions of the pathway.
BACKGROUND OF THE INVENTION
There are two general types of AGV guidance systems, rail systems and non-rail systems. In the first type of system, a pathway is formed out of rails. These rails may support an AGV or merely guide the AGV's wheels as they roll along the ground. In a non-rail system, the AGV may include detectors for detecting and following a wire in the ground that marks out a pathway, or a controller for following a set of commands to navigate between various types of reference markers. Each of these systems has certain advantages and drawbacks, and the choice of which system to use is normally based on many factors such as the needs of the particular user and the environment in which the system will operate.
Rail guidance allows for precise control over the position of an AGV. Where only a limited number of pathways are needed, and where these pathways do not need to be changed frequently, rail guidance offers a relatively simple method of keeping an AGV on a selected path. One of the biggest drawbacks to rail guidance, however, is that switches are needed to direct AGV's from one pathway to another. These switches are relatively costly and include moving parts that can wear out. In addition, each switch must be connected to a power source, a sensor for determining the position of the switch, and a controller for moving the switch from one position to another at appropriate times. The switches are often connected to a controller and to one another by a series of wires that run along the pathways, and these wires are expensive to install and maintain. Furthermore, the wires must be reconfigured each time the system is modified. Another disadvantage to such systems is that the rails themselves are generally raised off the ground and can interfere with the free movement of people and other vehicles.
Non-rail guidance systems offer increased design flexibility since pathways can be changed by reprogramming the AGV's or their controllers and without removing and re-laying rails. Moreover, because each vehicle receives or is programmed with instructions concerning the pathway to follow, switches are not needed to shift a vehicle from one path to another. However, because AGV's in such a system can stray from their pathways, extra care is required to make sure that each AGV is in its intended location and often this entails virtually constant communication with each AGV in the system. The quality of the communication link and the speed at which information about the AGV's and their positions can be processed also limits the maximum rate of travel of these systems. Moreover, collision avoidance becomes more complicated when AGV's travel along pathways that are not defined by rails. The need to constantly monitor and control a large number of AGV's, and to keep them on course and to avoid collisions, requires a significant amount of processing power which can make non-rail guidance systems more complex and expensive to operate than rail systems.
For high speed transport, that is for speeds in the range of 2200 feet per minute, rail guidance has traditionally been the only practical method for guiding an AGV. This is in part due to a perception that it is unsafe to operate vehicles at high speeds without physical path constraints and partly due to control problems. For example, the servo-control mechanisms used to steer AGV's often cannot respond quickly enough to the changing location of a guide wire in order to control a fast-moving vehicle. In addition, the signal to noise ratio of the position sensors may be too low to allow them to accurately sense the presence of a wire in the ground or to communicate reliably with a central controller when moving rapidly. Therefore, in applications where high speeds are needed, it has heretofore been necessary to use rail based control with all of its attendant drawbacks.
SUMMARY OF THE INVENTION
The present invention addresses the above and other problems by providing an AGV control system that uses rails for controlling an AGV through high speed portions of a pathway and non-rail controls for guiding the AGV through turns and other low speed portions of the pathway. Beneficially, this system eliminates the need to use track or rail switches. The result is a control system for AGV's that allows vehicles to operate at the same high speeds as rail-based systems with a high degree of safety. In addition, this system does not require the monitoring of switches or constant communication with each vehicle because the vehicles are physically constrained to a guidepath over the majority of the pathway that they traverse.
In the preferred embodiment, a pathway is designed which connects various loading and unloading sites and which includes straight sections, branches, and curves. Guiding rails are laid out along the straight-aways and gaps are left at the curves and near branches. A non-rail guidance system, such as an in-the-ground wire, is used to continue the pathways between the ends of the rails. The AGV's are provided with steering arms for engaging and following the rail or track sections and sensors for following the in-the-ground wires. Machine-readable tags are positioned at various points along the rail sections to provide information concerning the identity and length of the rail, and the radii of the turns which might be made at the end of the section. The AGV's also include sensors for reading the in-the-ground wires.
In operation, a central controller provides an AGV with instructions for traveling from an origin to a destination which instructions tell the AGV which rails to follow and how to turn at the end of each segment. The AGV is inserted into the system at the entrance end of a straight rail section and moved along the rail until it passes an initial reference marker that tells the vehicle where it is. If this location is consistent with its instructions for reaching a destination, it will accelerate to a high speed and travel along the rail looking for additional reference markers. One of these reference markers will tell the AGV the distance to the end of the rail. If the AGV's instructions are to continue in a straight line to the next rail section, the AGV will lock its steering wheels, maintain its speed, and travel past the end of the first rail and onto the entrance to a second rail collinear with the first rail. It will then continue along that rail section until another reference marker is encountered. Alternately, if the AGV's instructions provide that the vehicle is to make a 90 degree turn to the right at the end of the first rail, the AGV will begin to decelerate when the reference marker indicates that the end of the rail is approaching. The AGV will decelerate to a safe turning speed by the time it reaches the end of the rail and then use its onboard sensors to follow the in-the-ground wire that leads from the end of one rail segment to the beginning of the next. The AGV travels onto the second rail and resumes its high speed. This process continues until the vehicle reaches its final destination.
It is therefore the principal object of the present invention to provide an improved guidance system for automated guided vehicles.
It is another object of the present invention to provide a switchless rail-based AGV guidance system.
It is a further object of the present invention to provide an AGV guidance system that uses a first guidance mechanism for guiding the AGV along high speed portions of the pathway and a second guidance mechanism for guiding the AGV along low speed portions of the pathway.
It is still another object of the present invention to provide an AGV guidance system to which additional branches
Alofs Cornell W.
Drenth Ronald R.
Cuchlinski Jr. William A.
Dickinson Wright PLLC
Jervis B. Webb Company
To Tuan
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