Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Automatic route guidance vehicle
Reexamination Certificate
2000-04-11
2001-10-23
Chin, Gary (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Automatic route guidance vehicle
C318S587000, C180S167000
Reexamination Certificate
active
06308118
ABSTRACT:
SCOPE OF THE INVENTION
The invention relates to a method for determining the position of an automated guided vehicle.
STATE OF THE ART
Automated guided vehicles are used in many industrial settings, for example in the form of trucks for transport of goods in factories and warehouses. According to a commonly used system, magnetic loops or similar are laid out along the transport paths of the trucks. As a result of high initial costs and difficulties in later modification of the route followed by the trucks, systems with locational light reflectors have been developed.
According to certain known systems, reflectors are used with identification, i.e., on the basis of the reflected signal instruments on the vehicles can directly determine which unique reflector the signal is coming from. Such systems can be fast and effective, but the unique reflectors are relatively expensive. There are also limitations as regards the distance at which the signal can be registered and similar problems.
A navigation system with completely anonymous reflectors in the form of reflector strips or similar is illustrated and described in U.S. Pat. No. 4,811,228. The reflectors lack identity, but they are exactly calibrated as to their position. The position of each reflector is stored on board the vehicle together with relevant coordinates for the transport area. A light source on board the vehicle sends out a concentrated laser beam that sweeps over the transport area. Reflections from the reflectors and other objects are registered and give bearings to a possible reflector.
The following measures are taken initially with stationary vehicles for association of the bearing or angle positions to physical reflectors when the vehicle is located in a known position. Thus, the prerequisite according to this known system is that information regarding the actual position of the vehicle has been transmitted to the vehicle. Three angle values are chosen with suitable distribution over the area to be searched across. The angle values are associated with reflectors and the position of the vehicle is determined on the basis of the known position of the detected reflectors. If the position of the vehicle determined in this way is in agreement with the known position, the remaining angle values are associated, and the vehicle position can be verified. This initial process can be time consuming when a great number of reflectors are used.
The following measures are continually taken for association of the angle positions to physical reflectors. A detected angle position is compared with possible angle positions of stored positions for reflectors, and this angle position is associated with a physical reflector, which yields good agreement with the stored position of a reflector.
After the angle positions or bearings to the reflectors have been associated to actual reflectors, the determination of position and navigation can occur in various ways. Initially triangulation is used. With certain knowledge of the expected position at a point of measurement other methods are used during further travel. The automated guided vehicle is also provided with equipment for continuous updating of the vehicle's motion, for example, through an odometer. In the first place, it is the route traveled by the vehicle between measurement points that is continuously determined, but also the movement of the vehicle while making turns and its direction of movement is determined. Measurement can occur, for example, with respect to the rotation of the drive wheels or other wheels, such rotation then being converted to distance. Also the angle of turn of the vehicle's steering wheel is preferably determined continuously. Data regarding the distance and direction are used as a basis for determination of position and navigation.
In order for the system described in U.S. Pat. No. 4,811,228 to achieve the best performance, a large number of reflectors is required. Since calculation of many combinations is required before a certain association can be made, the time needed for calculation is long. This disadvantage can be only worse if many detected signals originate from sources other than the anonymous reflectors known by their positions, for example from metal objects or windows.
It would therefore be desirable that improved possibilities to filter out undesirable reflections, to increase effectiveness of association, and to lessen the number of required reflectors be present in a system of the type described in U.S. Pat. No. 4,811,228.
THE INVENTION IN SUMMARY
A purpose of the invention is to produce a method for position finding of automated guided vehicles, whereby the disadvantages cited above are avoided at the same time as the desired improvements are achieved.
The vehicle's starting point is at an unknown position in a transport area with several anonymous reflectors. The vehicle, thus, entirely lacks information concerning its current actual position. Multiple angle values corresponding to angle positions towards reflections from reflective objects are determined and stored. An array of at least three angle values with suitable distribution, preferably in a circumferencial and symmetrical fashion, are selected across the search sector. The selected angle values are associated to an array of reflectors, and an assumed position for the vehicle is determined on the basis of the known position of the assumed reflectors.
If the assumed position of the vehicle is within a certain part of the transport area, the remaining angle values are associated to stored reflector positions. For each array of angle values any existing deviation between detected angle values and angle values expected between the vehicle position and known reflector positions is determined. The measures taken are repeated for each possible combination of three angle values, and there is chosen a combination of associations which provides for a good agreement for an assumed vehicle position. After an association has been made in this way, the current vehicle position is determined to be the assumed position.
According to one embodiment of the invention the current distance to the object from where the signal has been reflected is determined in connection with the receiving of a reflected signal on board the vehicle. The distance is compared with the corresponding distance between a reference point on the vehicle in an assumed position and the stored position of a possible reflector. Information concerning the distance is used to make possible more certain judgment of the identity of the reflector.
Further certainty can be achieved if more complete information about the reflectors is collected ahead of time and is available for judgment of the identity of the reflectors. For example, it can be determined ahead of time how the intensity of a signal reflected from reflectors varies with the angle of incidence and distance to the reference point on the vehicle. The sweep time across the reflector can also be determined. This can be true of different types of reflectors, both with respect to the form of the reflectors and the material from which they are manufactured. Another advantage that can be achieved according to the invention is that the determination of the position can occur faster and with greater certainty, even initially, with no knowledge of the current position.
Further advantages and special features of the invention can be seen from the following description drawings.
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Altera Law Group LLC
Chin Gary
NDC Netzler & Dahlgren Co. AB
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