WO1998042917A1

WO1998042917A1 - A system for detecting reference point positions in a road or runway surface

Info

Publication number: WO1998042917A1
Application number: PCT/NO1998/000096
Authority: WO
Inventors: Klaus-Martin Berget
Original assignee: Berget Klaus Martin
Priority date: 1997-03-24
Filing date: 1998-03-24
Publication date: 1998-10-01
Also published as: NO971366D0; NO305134B1; NO971366L; AU6752698A

Abstract

Use of a reference marker for distance-based detection of position of the reference in multilayer field or roadways having at least one underlying support layer (BI) and a top wear layer (SI), where a reference point (Rp) has been placed down inside the support layer (BI) for protection against external influences. The reference point may be active, in that it itself transmits a signal, e.g. a magnetic or electromagnetic force field for detection of the position of the reference. In addition to be able to indicate the position for marking, the points may individually or in groups contain information of importance for the traffic, through the direction of the field polarity. The reference points may also be of a passive type, to influence a signal, or a reflection thereof, emitted by the detection equipment. The reference marker in accordance with the invention will, because it is arranged in the support layer of the road surface, not be subject to removal or damage by wear or road building.

Description

A SYSTEM FOR DETECTING REFERENCE POINT POSITIONS IN A ROAD OR RUNWAY SURFACE

The invention relates to use of position reference markers in the support layer of multilayer field or road surfaces. In addition to roadways, the invention can be used regarding marking all surface types where the structure consists of a permanent support layer having a top wear layer, like in airfields, parking squares etc.

The present method for new marking of road lines, takes place by manually measuring and marking the location by spraying spots on the surface, socalled pre- marking. Thereafter, through-going lines are marked up, for the following marking vehicle to be guided by when drawing up road lines. In addition to representing much work and much time, e.g. asphalted roads will represent a certain traffic hazard since it may take several weeks until the markings are brought in their right place.

Several methods are previously known regarding providing the roadway manually and mechanically with reference spots along the center line of the roadway, and it is referred to the publications SE-B-461 ,797, SE-C2-502.896, EP-0- 461.917-A1 , EP-0-736.630-A1 , as well as US 5,169,262 and US 5,540,518. In the first mentioned publication a method is disclosed for use of the roadway edge areas as reference points for determining the roadway center line. EP-0-461 ,917-A1 discloses a technique for arranging reference points on the road surface, and US 5,169,262 deals with a detection equipment in the form of a scanner or optical reader. SE-C2-502,896 describes a mechanical spot- and code-setting of the center line of the roadway.

Today's roadways are constructed in the form of an underlying support layer and a top wear layer. It is this wear layer that must be renewed from time to time, most often after first having been planed down somewhat. Also snow clearing and maintenance provides rough handling of particularly the highest ridges of the wear layer. Thus, it is not very practical to provide reference markers on the roadway such as disclosed by the above mentioned publications. On the whole, one must consider any implementation in the wear layer as a temporary implementation, since the layer itself has only a given lifetime.

The most recent prior art aims at using a camera picture of the roadway, transferred for algorithmic determination of the center line of the roadway. This technique avoids the problems mentioned above regarding exposed markers, and so far it is suitable for characteristic road stretches, but will then only provide information regarding the center line, and nothing else like e.g. type of marking and possible "offset" of the center line, or other specific information resulting from local conditions and human evaluation. Even more futuristic are ideas regarding satellite navigation, i.e plotting of the center line of the road surface into electronic maps. Despite rapid progress in that field, there is little indication to the effect that one in the forseeable future will be able to achieve accuracies as great as required here, since deviations are related to inter alia atmospherical conditions and fundamental limits related to wavelength.

The purpose of the invention is to achieve a position indication for marking and information, that is permanent and safeguarded against external influence like wear, maintenance work and similar.

The fundamental principle in accordance with the invention is to place permanent information transmitters down in the support layer of the roadway. These transmitters will then not be exposed to damage or removal by wear and maintenance. This makes special demands on the ability to place the transmitters in the support layer through the wear layer without removing or harming this top wear layer. Also, it must be possible to remove them if the information is to be changed, e.g. if the road is to be altered. Another challenge regarding this transmitter location is that the information must be able to pass through a relatively thick layer of asphalt.

According to use, two main transmitter types are utilized in the support layer, "active" and "passive" type. The active type is characterized in that the transmitter itself transmits signals or surrounds itself with force fields to be detected by the search equipment. On the other hand, the passive transmitters influence signals or echoes from signals transmitted by the search equipment. Examples of principles regarding active transmitters, are magnetic, electromagnetic, radioactive and for that matter sounding transmitters. Correspondingly, regarding passive principles, one may mention metals, based on metal probing, and cavities or material differences, based on ultrasound or seismology. The choice of transmitters and detection principles may vary from one application to another, since this concerns quantity, new or old projects, type of wear layer, like e.g. asphalt or concrete, and what the transmitters shall be used for.

In e.g airfields one may also visualize that such transmitters underneath the runway, besides marking, may also be used for information carriers/guides regarding taxiways etc. for the airplanes. In such a case it will be of interest to use active transmitters that do not produce electromagnetic disturbances, but at the same time have a certain interaction range. Permanent magnets may then be of large interest, and for an airport this is a relatively cheap investment. Detectors for magnetic fields are simple, cheap and have low weight.

Permanent magnets have the advantage that they may provide binary information by replacing the ordinary, logical (Boolean) values "0" and "1" by the pole direction of the magnet "north" (N) and "south" (S) in the same manner as in early ferrite memory cells. However, in this case reading and direction finding must be made with sensors located a relatively long distance away from the transmitter. Fig. 1 shows this principle, in which permanent magnets are utilized by means of Hall effect sensors. A Hall effect sensor has the characteristic that a current flowing therethrough depends on the magnetic field strength. Whether the current increases or decreases with an increase of the field strength, depends on the direction of the magnetic field through the sensor.

The principle is shown in fig. 1a and fig. 1b. The permanent magnet (Mg) down inside the support layer (BI) maintains a force field (F) having a flux direction upward through the wear layer (SI). In fig. 1a the Hall sensors (Hv) and (Hh) are located in exactly the same manner on both sides of the magnet. Therefore the attached instruments (Mv) and (Mh) give the same deflection toward the "+" side. If the magnet had been arranged in the opposite direction, the deflections in the instruments would have been the same again, however toward the "-" side.

In fig. 1b it is shown how the deflection in the instruments changes when the sensors are shifted to the left relative to the magnet. Because sensor (Hv) enters a weaker part of the field, the deflection in instrument (Mv) decreases. At the same time the opposite takes place in instrument (Hh), because this sensor enters a stronger field. If sensor (Hv) goes past the magnet to the left side, the force field will be reversed, and the instrument (Mh) will deflect toward the "-" side.

Two sensors will be preferable above one single sensor (H) as shown in fig. 2. This single sensor must possibly oscillate back and forth over the magnet in order to measure maximum field strength as a starting point for detecting the magnet position. The deviation must be expected to be larger, and sudden changes in the sensor distance above the magnet, e.g. a springing movement or bumps, will influence the accuracy negatively. Again, the decisive factor is the purpose of the detector and which demands are made on accuracy. The interesting part is that the same transmitter can be used in connection with different detectors.

Thus, it seems obvious that the field strength variation when the location of the sensors deviate relative to the magnet, can be used for guiding e.g. a vehicle so that it will follow a road of such magnets located down inside the support layer. As previously mentioned, one single magnet may, due to its two polar positions, represent logical "0" or "1". A group of e.g. 4 magnets with close spacing will provide, theoretically, 16 possible combinations that are doubled further for each new magnet added to the group. For road works one will then , in addition to indicate the center stripe position e.g. when marking up roads, also be able to enter information regarding the type of marking, speed limit, further signposting and similar. Even if the strength of the fields decrease rapidly with distance, it will clearly be possible to pick up the logic signals from both of the laterally adjacent roadways. It means that in receivers in cars one may have instruments that all the time show e.g. speed limit, possibly provide a warning regarding exceeding the limit, and other traffic information. Instead of using Hall effect sensors, vehicles may instead use coils as a detector element, due to the relatively fast motion through the magnetic fields.

From two roadways in opposite directions, the information must then be read in opposite succession, in other words the reading automatics must know in what direction the information has been laid out. This may e.g. be achieved by having reserved codes, e.g. SSNN=0011 , making reception of this code like e.g. NNSS=1100 mean that the reading direction shall be changed. Just for this purpose it may also be of interest to arrange code groups in the middle of the traffic lanes where the driving direction is always one and the same. In road surfaces where both wear layer and support layer consist of asphalt, it will be possible to hammer or shoot the magnet transmitters down into the support layer. For harder surfaces like e.g. concrete, one may possibly have to drill holes into which the transmitters are put down.

One example of such a magnetic transmitter is shown in fig. 3. In both ends thereof there is arranged a threaded section (Gj) as an attachment part, so that it will be possible to pull the transmitter up in a possible later removal operation.

In principle, passive transmitters do not provide the same encoding opportunities as active transmitters like e.g. magnets. This is because each respective transmitter can only be located, but it does not in itself produce logic "0" or "1" signals. But since such a transmitter may be so simple as to merely constitute a cavity which is detected preferably by means of ultrasound, the principle is interesting in road-marking, where there is a question of very large numbers of transmitters. Such a transmitter can be arranged very simply by drilling a hole down through the wear layer and into the support layer. This hole can then be filled by foam. In possible later planing down and re-asphalting, the top layer of the foam will be replaced by asphalt, but the transmitter will nevertheless be quite easily detectable because it is located right under the relatively thin wear layer.

The principle of locating such a passive sensor by ultrasound detection, is shown in fig. 4, and is similar to the previous principle with a magnetic transmitter that oscillates. (Ud) is an ordinary ultrasound transmitter and echo receiver. If the transmitter in the reference point (Rp) is made of an absorbing material, the echo will be weakened and amplified when the signal falls outside the reference point. Thus, during oscillation of transmitter/receiver one will perceive an accurate position.

It seems obvious that the transmitter may have an opposite function by being constituted by a material that reflects the ultrasound better than the pavement materials.

The general illustration for reference transmitters in accordance with the invention, arranged in the support layer of multilayer road surfaces, is shown in fig. 5. The patent claims relate to reference transmitters in the support layer and the use of these transmitters for achieving the purposes. The detection and tracking equipment must in principle be regarded as prior art, and is referred to in fig. 5 as (D). (Kg) illustrates a group of reference transmitters, put together in order to provide information codes.

Claims

PATENT CLAIMS

1. A system for detecting reference point positions in a field or road surface having at least one underlying support layer (BI) and a top wear layer (SI), by distance-based detection from a search equipment (D) e.g. on a vehicle, characterized in that active or passive transmitter units (Rp) are arranged in the support layer (BI) of the field or road surface in the reference point positions to be detected, whereby the transmitter units (Rp) are protected against damage of the wear layer (SI).

2. The system of claim 1 , characterized in that the transmitter units (Rp) are adapted to form magnetic fields to be used in the detection and for locating the transmitter units (Rp) and thereby the positions of the reference points.

3. The system of claim 2, characterized in that the transmitter units comprise permanent magnets (Mg).

4. The system of claim 2, characterized in that the transmitter units comprise electromagnets (Mg).

5. The system of claim 2, 3 or 4, characterized in that the transmitter units (Rp) are arranged with magnetic polarities having different directions individually or by group, to represent logic bit values, for providing detectable binary information codes.

6. The system of claim 5, characterized in that the transmitter units (Rp) are arranged in ordered succession regarding polarities, for supplying information regarding local speed limits, signposting, traffic lanes and similar in the following road stretch.

7. The system of claim 1 , characterized in that the transmitter units (Rp) are adapted for passive and detectable influence on a signal emitted from the search equipment (D) and which at least partly is reflected to the search equipment (D), so that the search equipment (D) may detect the position of a reference point from a change in reflected signal when passing the reference point.

8. The system of claim 7, characterized in that the transmitter units (Rp) have the characteristic of absorbing the search equipment (D) signal to a higher degree than the surrounding field or road surface material.

9. The system of claim 7, characterized in that the transmitter units (Rp) have the characteristic of reflecting the signal from the search unit (D) to a higher degree than the surrounding field or road surface material.

10. A method for field or road marking, where a marking vehicle that moves to deposit surface marks on the surface of the field or roadway, is guided for positioning by means of positioning reference points, characterized in that search equipment (D) on the marking vehicle interacts with active or passive transmitter units (Rp) that have been pre-arranged in the support layer (BI) of the field or roadway in those reference point positions to be detected.