Patent Description:
Conventionally, marker detection systems for vehicles using magnetic markers laid in a road for vehicle control have been known (for example, refer to Patent Literature <NUM>). By using this marker detection system to detect, for example, magnetic markers laid along a lane by a vehicle's magnetic sensor or the like, various driving assists can be achieved, such as automatic steering control, lane departure warning, and automatic driving.

<CIT> discloses a motor vehicle which is automatically steered to run along a running path on a road while detecting magnetic nails that are arranged on the road at spaced intervals along the running path. The motor vehicle has a pair of magnetic nail sensors on respective front and rear portions thereof for detecting lateral deviations of magnetic nails with respect to the motor vehicle at the respective front and rear portions thereof. The magnetic nail sensors are spaced from each other by a distance which is substantially an integral multiple of the interval between adjacent two of the magnetic nails. An azimuth deviation or a lateral deviation of the motor vehicle with respect to the running path is calculated based on lateral deviations of the magnetic nails which are detected substantially simultaneously by the magnetic nail sensors, respectively.

<CIT> discloses a road for guiding an automatically driven vehicle comprising a train of N-polarity magnetic nails arranged along a main path, and a train of S-polarity magnetic nails arranged on a branching path. An automatically driven motor vehicle, including magnetic sensors, runs and is automatically steered by detecting the magnetic nails.

However, the above-described conventional marker detection system has the following problem. That is, there is a problem in which reliability of magnetic marker detection may be impaired due to various external disturbances of magnetism acting on the magnetic sensors or the like. For example, a vehicle traveling alongside and an oncoming vehicle passing by can become a generation source of external disturbance of magnetism.

The present invention was made in view of the above-described conventional problem, and is to provide a marker detection system and marker detection method capable of reducing erroneous detection.

The present invention provides a marker detection system according to claim <NUM>, and a marker detection method according to claim <NUM>. Further embodiments of the present invention are disclosed in the dependent claims.

The marker detection system according to the present invention is a system including at least two magnetic markers arranged at spacings equal to spacings of said at least two magnetic detection units on a vehicle side. And, the marker detection method according to the present invention detects magnetism generation sources simultaneously detected by said at least two magnetic detection units as the magnetic markers.

For example, when a magnetism generation source resulting from a magnetized fallen object, a magnetism generation source such as a manhole, or the like is present on a road surface, there is a high possibility that only a part of said at least two magnetic detection unit detects the magnetism generation source. Thus, as a condition for detection as the magnetic markers, if a condition is set that they are magnetism generation sources simultaneously detected by said at least two magnetic detection units, the possibility of erroneously detecting a magnetism generation source such as, for example, a fallen object or manhole, as the magnetic marker can be reduced.

As described above, the marker detection system and the marker detection method according to the present invention are a system or method with an excellent characteristic capable of reducing erroneous detection.

Suitable aspects in the present invention are described.

In the present invention, said at least two magnetic markers are preferably arranged so that magnetic polarities form a predetermined pattern.

When this arrangement is adopted and when a combination of magnetic polarities of magnetism generation sources simultaneously detected by said at least two magnetic detection units matches the predetermined pattern, the magnetism generation sources simultaneously detected by said at least two magnetic detection units are preferably detected as the magnetic markers.

In this case, based on whether magnetic polarities acting on said at least two magnetic detection units have the predetermined pattern, erroneous detection of a magnetism generation source other than the magnetic markers can be effectively reduced. In particular, as for a magnetism generation source exceeding the full length of the vehicle, such as a large iron plate laid on a road surface during road construction or a steel frame of a bridge, there is a possibility that said at least two magnetic detection units simultaneously detect magnetism. If the magnetic polarity pattern is added to conditions, erroneous detection due to a large magnetism generation source as described above can be avoided.

A marker detection system of one suitable aspect in the present invention includes another magnetic detection unit which can detect the magnetic markers but is different from the said at least two magnetic detection units, and
the other magnetic detection unit is attached to the vehicle so as not to detect the magnetic markers when said at least two magnetic detection units simultaneously detect said at least two magnetic markers.

If the other magnetic detection unit is adopted, when said at least two magnetic detection units simultaneously detect magnetism generation sources while the other magnetic detection unit does not detect a magnetism generation source, the magnetism generation sources simultaneously detected by said at least two magnetic detection units are preferably detected as the magnetic markers.

In this manner, if a condition is set that said at least two magnetic detection units simultaneously detect magnetism generation sources while the other magnetic detection unit does not detect a magnetism generation source, reliability of detection of the magnetic markers can be improved. This condition is effective particularly for avoiding erroneous detection caused by a magnetism generation source exceeding the full length of the vehicle, such as a large iron plate laid on a road surface during road construction or a steel frame of a bridge.

In the present invention, the respective magnetic markers including said at least two magnetic markers are preferably arranged at substantially constant spacings in a road direction.

In this case, a situation does not occur in which while part of said at least two magnetic detection units at spacings equal to the spacings of said at least two magnetic markers can detect any of the magnetic markers, part of the rest cannot detect any of the magnetic markers. When detecting the magnetic markers, it is imperative that said at least two magnetic detection units simultaneously detect magnetism generation sources.

Embodiments of the present invention are specifically described by using the following examples.

The present embodiment is an example regarding a marker detection system <NUM> for detecting magnetic markers <NUM> laid in a road and a marker detection method. Details of this are described by using <FIG>.

The marker detection system <NUM> of the present embodiment is a system as in <FIG> for detecting the magnetic markers <NUM> laid in the road by sensor units <NUM>, which are one example of magnetic detection units, attached to a vehicle <NUM>.

This marker detection system <NUM> is configured to include two sensor units <NUM> arranged so as to be separated in a longitudinal direction of the vehicle <NUM> and two magnetic markers <NUM> as many as these two sensor units <NUM> and arranged at spacing equal thereto so as to be simultaneously detectable by these two sensor units <NUM>. In the following, the magnetic marker <NUM> is described, and then description is made on the sensor unit <NUM> including magnetic censors Cn (<FIG>) and a detection unit <NUM> which determines whether a magnetism generation source is the magnetic marker <NUM>.

The magnetic marker <NUM> is a marker laid in a road surface <NUM> of a road where the vehicle <NUM> travels, as in <FIG> and <FIG>. The magnetic markers <NUM> are arranged at spacings of <NUM> along the center of a lane, which indicates a traveling segment of the road. In the following, the spacings of <NUM> of the magnetic markers <NUM> are referred to as a marker span M.

The magnetic marker <NUM> forms a columnar shape having a diameter of <NUM> and a height of <NUM>, and is laid as being accommodated in a hole provided in the road surface <NUM>. A magnet forming the magnetic marker <NUM> is a ferrite plastic magnet formed by dispersing a magnetic powder of iron oxide as a magnetic material in a polymer material as a base material, and has a characteristic of a maximum energy product (BHmax)=<NUM> kJ/m<NUM>. Note that the magnetic marker <NUM> is laid in the road surface <NUM> so that the N pole is on a front surface side.

Part of specifications of the magnetic marker <NUM> of the present embodiment is provided in Table <NUM>.

This magnetic marker <NUM> can act magnetism of a magnetic flux density of <NUM>µT (microtesla) at a height of <NUM>, which is an upper limit of a range from <NUM> to <NUM> assumed as an attachment height of the sensor units <NUM>. Note that a magnetic flux density Gs of the surface of the magnet forming the magnetic marker <NUM> is <NUM> mT.

Next, the sensor units <NUM> and the detection unit <NUM> configuring the marker detection system <NUM> are described.

The sensor units <NUM> are magnetic detection units to be attached to the bottom surface of the vehicle <NUM>, as in <FIG> and <FIG>. The sensor units <NUM> are arranged at two locations at a spacing of <NUM> (sensor span S) in the longitudinal direction of the vehicle <NUM>. The front-side sensor unit <NUM> is attached to the rear side of a front axle, and the rear-side sensor unit <NUM> is attached to the front side of a rear axle. In the case of the vehicle <NUM> of the present embodiment, each attachment height with reference to the road surface <NUM> is <NUM>.

Each sensor unit <NUM> includes fifteen magnetic sensors Cn (n is an integer of <NUM> to <NUM>) arrayed on a straight line along a vehicle-width direction and a detection processing circuit <NUM> having a CPU and so forth not depicted incorporated therein (<FIG>).

The magnetic sensors Cn adopted in the present embodiment are MI sensors which detect magnetism by using the known MI effect (Magneto Impedance Effect) in which the impedance of a magneto-sensitive body such as an amorphous wire sensitively changes in response to the external magnetic field. The magnetic sensors Cn are incorporated in the sensor unit <NUM> so that the magneto-sensitive bodies are along the vertical direction so as to detect magnetism in the vertical direction.

The magnetic sensors Cn achieve high sensitivity with a measurement range of the magnetic flux density of ±<NUM> mT and a magnetic flux density resolution of <NUM>µT within the measurement range. As described above, the magnetic markers <NUM> act magnetism on the order of <NUM>µT at <NUM>, which is an upper limit in the range assumed as the attachment height of the sensor units <NUM>. According to the magnetic sensors Cn having a magnetic flux density resolution of <NUM>µT, the magnetism of the magnetic markers <NUM> can be sensed with high reliability. With the sensor units <NUM> at the attachment height of <NUM> of the present embodiment, the magnetism of the magnetic markers <NUM> can be further readily detected.

Part of specifications of the magnetic sensors Cn is provided in Table <NUM>.

The detection processing circuit <NUM> (<FIG>) is an arithmetic circuit which performs various arithmetic processes such as a magnetic detection process (detection process) for detecting any magnetic marker <NUM>. This detection processing circuit <NUM> is configured by using a CPU (central processing unit) which performs various computations as well as memory elements such as a ROM (read only memory) and RAM (random access memory), and so forth. The detection processing circuit <NUM> acquires sensor signals outputted from each of the magnetic sensors Cn to perform a magnetic detection process and so forth. The magnetic detection result generated by the detection processing circuit <NUM> is inputted to the detection unit <NUM>.

The detection unit <NUM> is a unit which controls the front-side and rear-side sensor units <NUM> and outputs the result of detection of any magnetic marker <NUM>, as in <FIG> and <FIG>. The detection unit <NUM> includes an electronic substrate (not depicted) having a CPU which performs various computations as well as memory elements such as a ROM and RAM and so forth implemented thereon. To this detection unit <NUM>, in addition to the front-side and rear-side sensor units <NUM>, a vehicle ECU, a vehicle speed sensor for measuring a speed of the vehicle, and so forth are electrically connected.

This detection unit <NUM> takes in the magnetic detection result of each sensor unit <NUM>, and generates and outputs a marker detection result which is a determination result as to whether the magnetic marker <NUM> has been detected or the like. The marker detection result is inputted to the vehicle ECU not depicted to be used in various controls on the vehicle side, such as automatic steering control, lane departure warning, and automatic driving for keeping the lane.

The detection unit <NUM> uses the magnetic detection results of the front-side sensor unit <NUM> and the rear-side sensor unit <NUM> to perform a marker detection process for magnetic marker detection and so forth. Then, the marker detection result is generated, which is a determination result or the like as to whether the magnetic marker <NUM> has been detected, and is inputted to the vehicle ECU.

Next, (<NUM>) a magnetic detection process for each sensor unit <NUM> to detect a magnetism generation source is described, and then (<NUM>) a marker detection process by the detection unit <NUM> is described.

The front-side and rear-side sensor units <NUM> perform a magnetic detection process at a frequency of <NUM> by control of the detection unit <NUM>. For every execution period (p1 to p7) of the magnetic detection process, each sensor unit <NUM> samples a magnetic measurement value indicated by a sensor signal of each of fifteen magnetic sensors Cn to acquire a magnetic distribution in the vehicle-width direction (refer to <FIG>). A peak value in this magnetic distribution in the vehicle-width direction becomes maximum at the time of passage over a magnetism generation source such as the magnetic marker <NUM> (period p4 in <FIG>).

When the vehicle <NUM> travels along the lane where the magnetic markers <NUM> are laid, the peak value of the magnetic distribution in the vehicle-width direction appears at every passage over the magnetic marker <NUM> as in <FIG>. The sensor unit <NUM> makes a threshold determination regarding this peak value and, when it is equal to or larger than a predetermined threshold, determines that a magnetism generation source that is likely to be the magnetic marker <NUM> has been detected.

Note that when the sensor unit <NUM> detects a magnetism generation source, it is identified which magnetic measurement value of any of the magnetic sensors Cn is a peak value. Then, a positional shift amount of the peak value in the vehicle-width direction of the magnetic sensor Cn from the center position of the sensor unit <NUM> is identified, and is measured as a lateral shift amount of the vehicle <NUM> with respect to the magnetic marker <NUM>.

The detection unit <NUM> controls the front-side sensor unit <NUM> and the rear-side sensor unit <NUM> to acquire each magnetic detection result. Then, based on a combination of the acquired two magnetic detection results, the detection unit <NUM> performs a marker detection process for detecting the magnetic marker <NUM>.

When the rear-side sensor unit <NUM> detects a magnetism generation source at the same time when the front-side sensor unit <NUM> detects a magnetism generation source, the detection unit <NUM> determines that each magnetism generation source is the magnetic marker <NUM>. As exemplarily depicted in <FIG>, when the front-side and rear-side sensor units <NUM> each reach straight above the magnetic marker <NUM>, as exemplarily depicted in graphs in the drawing each illustrating temporal changes of the magnetic measurement value, the magnetic measurement values of the respective sensor units <NUM> simultaneously become peak values. When the magnetic measurement values of the respective sensor units <NUM> simultaneously become peak values, the detection unit <NUM> determines that each magnetism generation source is the magnetic marker <NUM>.

Note that simultaneity of detection time of magnetism generation sources by the front-side and rear-side sensor units <NUM> does not mean strictly physical simultaneity. For example, in a temporal range in which the vehicle <NUM> travels with a spacing on the order of <NUM>, which is <NUM>/<NUM> of the marker span M of <NUM>, the front-side and rear-side sensor units <NUM> do not detect the same magnetism generation source. Thus, in the marker detection process, simultaneity is determined when the front-side and rear-side sensor units <NUM> each detect a magnetism generation source in this temporal range.

Specifically, of the front-side and rear-side sensor units <NUM>, with reference to a detection time (first time) of one sensor unit <NUM> which momentarily in advance detects a magnetism generation source, the detection unit <NUM> sets a temporal range required for the vehicle to travel <NUM> as a detection period. If a detection time (second time) of the other sensor unit <NUM> which detects a magnetism generation source is included in this detection period, it can be regarded that the front-side and rear-side sensor units <NUM> simultaneously detected magnetism generation sources. In this case, the detection unit <NUM> determines each of the magnetism generation sources simultaneously detected by the front-side and rear-side sensor units <NUM> as the magnetic marker <NUM>. Note that the time of momentarily in advance detecting a magnetism generation source means a detection time strictly earlier in time between detection times treated by the detection unit <NUM> as simultaneous as described above.

On determining that the magnetism generation sources detected by each sensor unit <NUM> are the magnetic markers <NUM>, the detection unit <NUM> inputs the marker detection result that the magnetic marker <NUM> has been detected to the vehicle ECU. Note that, at this time, the detection unit <NUM> simultaneously inputs the lateral shift amount measured by each sensor unit <NUM> as described above. The vehicle ECU acquiring the lateral shift amounts as well as the indication that the magnetic markers <NUM> have been detected can perform driving assist control such as lane following control by using the lateral shift amounts as control inputs.

On the other hand, if either of the sensor units <NUM> detects a magnetism generation source but the other sensor unit <NUM> cannot simultaneously detect a magnetism generation source, the detection unit <NUM> determines that the magnetism generation source detected by said either of the sensor units <NUM> is not the magnetic marker <NUM> and there is a possibility of erroneous detection.

This situation can occur when, for example, as in <FIG>, either of the sensor units <NUM> detects magnetism of a magnetism generation source 10F other than the magnetic marker <NUM>. In this case, while the magnetic measurement value of the rear-side sensor unit <NUM> becomes a peak value, the magnetic measurement value of the front-side sensor unit <NUM> remains low. Here, the detection unit <NUM> determines that magnetism detected by the rear-side sensor unit <NUM> derives from the magnetism generation source 10F other than the magnetic marker <NUM>.

As described above, in the marker detection system <NUM> of the present embodiment, the marker span M on a road side and a sensor span S on a vehicle side match each other. If this configuration is adopted, when the front-side and rear-side sensor units <NUM> simultaneously detect magnetism generation sources, these magnetism generation sources can be determined as the magnetic markers <NUM>.

When either one of the sensor units <NUM> detects a magnetism generation source while the other sensor unit <NUM> does not detect a magnetism generation source, it can be determined that the possibility is high that the detected magnetism generation source is not the magnetic marker <NUM>. According to this determination, it can be determined that the possibility is high that the magnetism generation source such as a fallen object or manhole is not a magnetic marker, and erroneous detection can be avoided.

Note that the present embodiment is an example in which the magnetic markers <NUM> are arranged in the road at constant spacings (marker span M). In place of this, as in <FIG>, two magnetic markers <NUM> separated with the marker span M may be laid in one laying location <NUM>, and laying locations <NUM> may be arranged at spacings of <NUM>, <NUM>, or the like longer than the marker span M. As for the present embodiment in which the magnetic markers <NUM> are laid at constant spacings (marker span M=<NUM>), this can be restated as a configuration example in which the laying locations <NUM> each having two magnetic markers <NUM> arranged are successively provided at spacings of <NUM>.

Furthermore, the number of magnetic markers <NUM> per laying location may be three or more. In this case, the spacings of the magnetic marker <NUM> may be equal or inequal. On the vehicle <NUM> side, the sensor units <NUM> as many as the number of the magnetic markers <NUM> per laying location may be attached at the same spacings.

As in <FIG> in which an N-pole magnetic marker 10N is indicated by a black circle and an S-pole magnetic marker <NUM> is indicated by a white circle, a configuration may be made so that magnetic polarities of the magnetic markers <NUM> on a front surface side form a predetermined pattern. In this case, two magnetic markers <NUM> forming a predetermined magnetic polarity pattern can be simultaneously detected by the front-side sensor unit <NUM> and the rear-side sensor unit <NUM>. In addition to the condition of simultaneous detection, if a condition is additionally set that magnetic polarities of two magnetic markers <NUM> simultaneously detected form a predetermined pattern, erroneous detection of a magnetism generation source other than the magnetic marker <NUM> can further be reduced.

As a magnetic polarity pattern, for example, a pattern of a combination of (N pole-S pole), a pattern of a combination of (S pole-N-pole), and so forth can be thought. Furthermore, the pattern of a combination of magnetic polarities may be changed for each laying location of the magnetic markers. In particular, if a pattern including both of the N pole and the S pole is set, for example, erroneous detection due to a large magnetism generation source which acts uniform magnetism such as a steel frame buried in a bridge, a reinforced-concrete tunnel, or a large iron plate laid on a road surface for road construction can be avoided.

Furthermore, for example, when a pattern of a combination at one laying location is represented with parentheses such as (N pole-N pole), a pattern of (N pole-S pole), (S pole-N pole), (N pole-S pole), (S pole-N pole),. may be set for a plurality of successive locations. In this case, among four magnetic markers belonging to adjacent two laying locations, the combination is such that magnetic polarities of inner two magnetic markers are the same, and a pattern of magnetic polarities between different laying locations can be formed. Also, for example, when the N pole is treated as a binary bit <NUM> and the S pole is treated as a binary bit <NUM>, a pattern at each laying location may be set so as to form a specific data sequence.

As in <FIG>, while two magnetic markers <NUM> are laid at each laying location <NUM>, on the vehicle <NUM> side, two sensor units <NUM> capable of simultaneously detecting these two magnetic markers <NUM> may be arranged in the longitudinal direction and another third sensor unit <NUM> may be arranged in the middle. In this case, as a condition for determining a magnetic marker, a condition may be set that the sensor units <NUM> on both outer sides simultaneously detect magnetism generation sources while the intermediate sensor unit <NUM> does not detect a magnetism generation source.

When the vehicle passes over a large magnetism generation source such as a large iron plate laid on a road surface during road construction, a reinforced-concrete tunnel, or a steel frame buried in a bridge; a large vehicle traveling alongside such as a trailer, which may become a magnetism generation source; or the like, there is a possibility that magnetism uniformly acts on all sensor units <NUM>. Thus, as in <FIG>, a condition may be set that the sensor units <NUM> on both outer sides simultaneously detect magnetism generation sources while the intermediate sensor unit <NUM> does not detect a magnetism generation source. If this condition is set, for example, erroneous detection due to a large magnetism generation source which uniformly acts magnetism on each sensor unit <NUM> can be avoided in advance.

In the present embodiment, the magnetic sensors Cn with sensitivity in the vertical direction are adopted. However, magnetic sensors with sensitivity in a forwarding direction may be used, or magnetic sensors with sensitivity in the vehicle-width direction may be used. Furthermore, for example, magnetic sensors with sensitivity in a biaxial direction of the vehicle-width direction and the forwarding direction, a biaxial direction of the vehicle-width direction and the vertical direction, or a biaxial direction of the forwarding direction and the vertical direction may be adopted. For example, magnetic sensors with sensitivity in a triaxial direction of the vehicle-width direction, the forwarding direction, and the vertical direction may be adopted. If magnetic sensors with sensitivity in a plurality of axial directions are used, the magnitude of magnetism as well as the magnetism acting direction can be measured, and magnetic vectors can be generated. By using a difference between magnetic vectors and a change ratio of the difference in the forwarding direction, magnetism of the magnetic markers <NUM> and external disturbance of magnetism may be distinguished.

In the present embodiment, the magnetic marker <NUM> in a columnar shape having a diameter of <NUM> and a height of <NUM> is exemplarily described. However, for example, a magnetic marker in a sheet shape having a thickness on the order of <NUM> to <NUM> and a diameter on the order of <NUM> to <NUM> can also be adopted. As a magnet of this magnetic marker, for example, a ferrite rubber magnet, which is a magnet similar to a magnet sheet for business use or to be used in the kitchen or the like, and so forth may be adopted.

Claim 1:
A marker detection system (<NUM>) for a vehicle (<NUM>) configured to travel on a road having a plurality of laying locations (<NUM>) where two magnetic markers (<NUM>) are laid with a marker span (M), the system (<NUM>) comprising:
two magnetic detection units (<NUM>) arranged so as to be separated in a longitudinal direction of the vehicle (<NUM>) with a spacing equal to the marker span (M) so as to be configured to detect the two magnetic markers (<NUM>) simultaneously; and
a unit (<NUM>) configured to set, when one of the two magnetic detection units (<NUM>) detects a magnetism generation source, a detection period which is a temporal range for determining whether the detected magnetism generation source is one of the two magnetic markers (<NUM>) or not, the temporal range being set such that the two magnetic detection units (<NUM>) do not detect the same magnetism generation source;
the system being characterized in that it further comprises:
a unit (<NUM>) configured to determine a possibility of erroneous detection that the magnetism generation source detected by the one of the two magnetic detection units (<NUM>) is not one of the two magnetic markers (<NUM>), when the other one of the two magnetic detection units (<NUM>) does not detect a magnetism generation source in the detection period.