NZ599688B - Method and apparatus for detecting wheels - Google Patents

Abstract

Patent 599688 Disclosed is an apparatus (9) for detecting wheels (4) of a vehicle (1) that is travelling on a roadway (2) in a travel direction (3). The apparatus (9) is comprised of at least one Doppler lidar or radar unit (6) and a downstream evaluation unit (8). The lidar or radar device (6) emits an electromagnetic measurement beam lobe (7) with a known temporal progression of frequency onto a target. This beam lobe (7) is directed from the side of the roadway (2) onto an area above the roadway (2) and is on a slant with respect to the direction of travel (3) along the roadway (2). The signal reflected from the target is then recorded as a reception frequency mixture. The downstream evaluation unit (8) detects a frequency spread in the reception frequency mixture which exceeds a predetermined threshold as a wheel (4). 6) emits an electromagnetic measurement beam lobe (7) with a known temporal progression of frequency onto a target. This beam lobe (7) is directed from the side of the roadway (2) onto an area above the roadway (2) and is on a slant with respect to the direction of travel (3) along the roadway (2). The signal reflected from the target is then recorded as a reception frequency mixture. The downstream evaluation unit (8) detects a frequency spread in the reception frequency mixture which exceeds a predetermined threshold as a wheel (4).

Description

Patents Form 5 NZ. No.

NEW ZEALAND Patents Act 1953 TE SPECIFICATION METHOD AND APPARATUS FOR DETECTING WHEELS We, Kapsch TrafficCom AG, an Austrian company of Am Europlatz 2, A—1120 Wien, Austria, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly bed in and by the following statement:— ~ 1 _ (Followed by 1A) Method and tus for Detecting Wheels The present invention relates to a method and an apparatus for detecting wheels of a vehicle that is traveling on a roadway in a travel direction and the wheels of which are at least partially exposed laterally.

Detecting vehicle wheels is of interest for numerous applications. Thus it is possible to infer with certainty from the recognition of wheels that a given traffic area is being driven on in order, for example, to r borders or to initiate certain actions such as triggering an alarm, switching on lighting, opening a barrier, taking a picture for monitoring es, etc. Modern traffic fee systems also ntly base the calculation of fees on the number of axles of'vehicles, so that the ion of wheels (wheel axles) can also be an important basis for road toll or parking fee s.

Detecting wheels of a moving vehicle based on the horiZOntal component of their tangential velocity, which s from that-of the rest of the vehicle and brings about a corresponding Doppler frequency shift of a radar measuring beam, is known from DE 10 2008 037 233 Al. For this purpose, a radar speed measuring unit is used that irradiates the lower area of passing vehicles with a radar beam lobe and, from the returning frequency e, ines a single speed measurement signal that has signal maxima at the locations of the wheels. Automatic detection of such maxima in a signal curve requires a signal—analytical search for extreme values and is correspondingly elaborate. In addition, gaps between a traction vehicle and its trailer can falsely indicate signal maxima and intermediate "false" maxima, which lead to an erroneous wheel detection.

The invention has the objective of creating methods and apparatuses for wheel detection that enable a more secure ion than that of knowu solutions.

This objective is achieved in a first aspect of the invention with a method that is characterized by the steps: emitting an electromagnetic measurement beam lobe with a known temporal progression (progression over time) of frequency from the side of the roadway onto an area above the roadway and at a slant with respect to the travel direction, receiving the measurement beam lobe reflected by a passing e and recording the temporal progression, relative to the known progression, of all of its frequencies appearing at the same time as a reception frequency mixture, and during the e of the vehicle, detecting a frequency spread appearing in the recorded progression of the reception frequency mixture and ing a predetermined threshold value as a wheel.

The invention is based on the novel approach of detecting wheels of a moving vehicle based on the horizontal component of their tangential velocity, which differs from that of the rest ofthe vehicle, and brings about a corresponding Doppler frequency shift of a lidar or radar measuring beam. If a measurement beam is used that is expanded over a larger beam cross- section ("measurement beam lobe"), which is spread out or distributed in a conical shape over a solid angle, it strikes at least a part of the passing wheel over an extended area of incidence, e.g., an ellipse with a height or width in the range of 10 cm to 50 cm. At every different height of a rotating wheel, it has a different horizontal component of its tangential velocity—constant across its width-and thus generates a different Doppler frequency shift, which leads to a "fragmentation" or ding" of the transmission ncy of the measuring beam lobe into a plurality of reception frequencies returned by the rotating wheel. When a rotating wheel is struck by a measurement beam lobe over an extended height area, it produces a frequency spread in the reception spectrum across its height, which can be used for detecting the wheel.

This effect is superimposed by a second parasitic frequency spreading , which can be traced back to the different tion angle of the horizontal component of the tangential velocity relative to the direction from the receiver: this projection direction varies as a function of the observed reflection point in the area of incidence. This second spreading effect is independent of whether the vehicle body or the rotating wheel passes by the receiver, and is determined solely by the l geometric conditions of the measurement arrangement. The amount of spreading from the entioned ncy fragmentation induced by the Doppler effect that must be exceeded for detection of a wheel is therefore defined in such a manner that it is r than the ncy spread produced by the second-mentioned geometrically induced frequency fragmentation. As a , a wheel detection method with a high detection certainty is achieved based on the "Doppler signature" produced by a wheel.

The predetermined threshold value is ably ined in advance from a frequency spreading that s during the passage of a wheel-less part of a vehicle. Thereby the method can be calibrated on-site by means of nce measurements.

In a second aspect, the invention creates an apparatus for detecting wheels of a vehicle that is traveling on a roadway in a travel direction and the wheels of which are at least partially exposed laterally, characterized by at least one r lidar or radar device that emits an electromagnetic measurement beam lobe with a known temporal progression of frequency onto a target and records the al progressiori, relative to the known progression, of all frequencies occurring at the same time from the target-reflected measurement beam lobe as a reception frequency mixture, wherein the measurement beam lobe is oriented from the side of the roadway onto an area, above the roadway and at a slant with respect to the direction of travel, and a ream evaluation unit that detects a frequency spread appearing in the recorded temporal progression of the reception frequency mixture during the passage of the vehicle and exceeding a predetermined threshold value as a wheel.

With respect to the advantages of the apparatus according to the invention, the reader is referred to the above discussions of the method according to the invention.

The invention—if it operates with a Doppler radar device—is particularly suitable in tion with the radio beacon of an y existing wireless roadway infrastructure such as a WLAN (wireless local area k), WAVE (wireless access in a vehicle environment), or DSRC (dedicated short range communication). An especially advantageous embodiment ofthe invention is characterized in that the Doppler radar device is constituted by a roadside WLAN, WAVE, or DSRC radio beacon.

Further characteristics and advantages of the method and the apparatus foilow from the ption below of a red exemplary embodiment with reference to the accompanying drawings, in which: Figure 1 shows a first embodiment of an apparatus for wheel detection in a schematic perspective view in order to explain the fundamentals of the invention; Figure 2 shows several exemplary scanning progressions of the measurement beam in an tus according to Figure l on a passing vehicle; Figure 3 shows timing diagrams of the ined ssions of reception frequency or speed for the scanning progressions of Figure 2; Figure 4 shows the speed relationships on a rotating wheel in detail; Figure 5 shows an embodiment of the apparatus of the invention in a schematic perspective view; Figure 6 shows the osition of several ssions of reception frequency or speed from Figure 3 in order to illustrate the Doppler—induced frequency spreading during the passage of a wheel; Figure 7 shows the geometric relationships in the measurement beam lobe of the apparatus from Figure 5 in order to illustrate the geometry-induced frequency spreading during the e of a vehicle; Figure 8 shows the effect of the ssion over time of the geometry-induced frequency spreading during the passage; Figure 9 shows the combined effect of the geometry-induced frequency spreading of Figure 8 and the Doppler-induced frequency spreading of Figure 6 in their progression over time during the passage of a vehicle; and Figure 10 shows a variant of Figure 9.

In Figure 1, a vehicle 1 is moving on a roadway 2 in a travel direction 3. The vehicle 1 has wheels 4 that project downward from the body 5 of the vehicle 2 and that at the same time are—at least lly—exposed on the sides of the body in openings thereof, i.e., are visible from the side.

A Doppler lidar or radar device 6 emits a concentrated lidar or radar measurement beam 7 from the side of the roadway l at a slant to the travel direction 3 and slightly above the surface of the roadway, so that the measurement beam 7 strikes a passing vehicle 1 roughly in the area of its wheels 4.

The Doppler lidar/radar device 6 evaluates, in a manner known in the art, the reception frequency of the measurement beam 7 ed by the vehicle 1 or its wheels 4, wherein the cted) component vp of the vehicle velocity v of the vehicle 1 in the direction of the measurement beam 7, or the tangential velocity vt (Figure 2) of the wheels 4 at the point of incidence of the measurement beam 7, can be determined from the Doppler effect—induced frequency shift between emitted and reflected measurement beam 7. The wheels 4 of the vehicle 1 can then be detected from this information, as will be described in greater detail below. For this purpose, an evaluation unit 8 that undertakes the ponding evaluations of the reception frequency of measurement beam 7 is arranged downstream of the device 6. The lidar/radar device 6 and the evaluation unit 8 thus er form an apparatus 9 for detecting wheels 4 of the vehicle 1.

The Doppler lidar/radar device 6 itself can be of any type known in the art, whether with a continuous, modulated, or pulsed measurement beam 7. For a continuous measurement beam 7, a Doppler frequency shift between the natural frequencies ("carrier frequencies") of the emitted and reflected measurement beam 7 can be determined by interference measurement. For a pulsed or modulated measurement beam, a Doppler shift n the pulse rates or modulation frequencies of the emitted and the reflected measurement beam 7 can be measured. The term "reception frequency" used here is tood to mean all such natural, carrier, pulse, or modulation frequencies of the ement beam 7, i.e., the term reception frequency comprises any type of frequency of the ement beam 7 influenced by a Doppler effect.

In principle, the nature of the measurement beam 7 itself is also arbitrary, so long as it is an omagnetic wave, whether it be visible light or infrared light as in a lidar device, or radio waves, especially aves, as in a radar device.

The measurement beam 7 in the explanatory example of Figure l is strongly concentrated so that its point of incidence on the body 5 or the wheel 4 has an extremely small diameter.

Figure 2 shows the scanning progressions of such a concentrated measurement beam 7, which s the vehicle 1 or its wheels 4 ntially in point form during the passage of the vehicle 1 past the apparatus 9. For explanatory purposes, six different scanning progressions H1 through H6 are shown for the sake of e, but it is understood that only a single scanning progression Hl—H6 from a concentrated measurement beam 7 occurs during the passage of a Figure 3 shows the reception frequency f of the ed measurement beam 7 over time for the scanning progressions Hl—H6 continuously received by the lidar/radar device 6. The Doppler shift Af of the reception frequency f relative to the transmission ncy is tional to the velocity component vp of the respectively scanned parts of the vehicle 1 or the wheel 4. The reception frequency progressions El—E6 illustrated in Figure 3 are ore equivalent to the velocity progressions.

It is evident from the reception frequency progression El of Figure 3 that the scanning progression H1, which strikes the body 5 of the vehicle 1 outside the wheels 4, has a substantially constant reception frequency shift Af of the measurement beam 7 and thus the velocity ent vp during the on T1) of the body passage, which is expressed as a square wave pulse R in the reception frequency progression.

For the scanning progression H2, which strikes the wheels 4 at their uppermost point, where their tial velocity Vt is added to the vehicle ty v, the reception frequency progression E2 has a peak 10 of 2vp above the body square wave pulse R for each wheel 4.

If the measurement beam 7 strikes the wheels 4 at a level between the wheel axle and the upper side of the wheel, as in the scanning progressions at H3 and H4, an abruptly varying Doppler shift in the measurement direction relative to the body pulse R, and thus a shift in the reception frequency or speed, is measured during the passage of a wheel 4, corresponding to the projection vP of its tangential velocity v1, as illustrated by the square wave pulses l l of the progressions E3 and E4. Each pulse 1 1 ses a rising edge 12 and a subsequent falling edge 13, i.e., two successive alternating frequency discontinuities.

The reception frequency progression E5 shows the special case where the measurement beam 7 strikes the wheels 4 precisely at the level of their axies, where no tangential velocity of the wheel that could be projected in the ion of the measurement beam 7 exists, so that the wheels 4 are not detectable.

The reception frequency progression E6 scans the wheels 4 at a level between their underside and their axle, and resembles that of E4, but with reversed changes 1 1-13.

Figure 4 analytically shows the extent of the offset 1 l of a wheel 4 as a function of the height h of the respective scanning progression Hl—H6 relative to the wheel axle A, using the scanning ssion H4 as an example. If R is the radius of the wheel 4 and r an arbitrary radius inside of wheel 4, then the tangential velocity vt(r) at a radius r is proportional to this radius r, specifically v, (r) = —v, R (1) The horizontal component v[h(r) of the tangential velocity vt(r) in the travel direction 3 at an angle at is a sine projection corresponding to 7" . v”, (r) = —v[ sm a R (2) With . h sm 0: = — r (3) the horizontal component vth(r) of the tangential velocity thus results as vlh (r) = v, R (4) The horizontal component v,h(r) of the tangential velocity is thus directly proportional to the respectively considered height h of the scanning progression and is constant over this height h while the wheel 4 is being d.

Figure 5 shows an extension of the method according of s 1—4 in which, instead of a concentrated measurement beam 7, a widened measurement beam, scattered or expanded two- dimensionally or in a funnel—shape for example, is used, referred to below as "measurement beam lobe" 15 for the sake of brevity. The measurement beam lobe 15 can be achieved in a lidar device by means of an output-side concave lens, or occurs with radar s that lack e focusing. As an example, Figure 5 shows a Doppler radar device 16, which together with the evaluation unit 8 forms an tus 9. 1n the case of radar, the measurement beam lobe 15 is characterized by the acceptance angle of the radar antenna being used. The acceptance angle (or the half-value width) of a directional antenna refers to the points where the power has declined to half (—3 dB) relative to the maximum. As is familiar to those d in the art, the gain of the antenna in its main radiation direction can be calculated with the following formula from knowledge of the respective acceptance angle: 27.000 g=lOlg ApAd where g = gain [dBi] Atp = horizontal ance angle (in degrees) A13 = vertical acceptance angle (in degrees) The acceptance angle of the radar antenna should allow a good tion of the individual wheels 4 in the measurement signal of the vehicle 1 to be detected. Thus it is particularly favorable if the incidence area 17 of the measurement beam lobe 15 is substantially the size of wheel 4 of the e 1, and does not cover only the wheel 4, but also lies somewhat above it, as shown in Figure 7. The optimal incidence area 17 results from the measuring distance from the vehicle I, and therefore the selection of the radar antenna s on the geometry of the overall arrangement. In general, antennas with a gain g of more than 10 dB are especially suitable, depending on the arrangement and frequency of the radar device 16.

Directional antennas usually have an antenna gain g of more than 20 dB (corresponds to an ance angle Acp = All = approx. 16°). Thus an area 17 that is 56 cm in diameter can be illuminated 2 m away from the vehicle 1 with an antenna gain of 20 dB. An antenna gain g of dB can be necessary for more distant vehicles 1 in order to achieve an acceptance angle M) = A19 = approx. 5°, which implies an illumination area 17 . 90 cm in size at a distance of 10 m.

When using such a measurement beam lobe 15, which strikes a relatively large area 17 of the vehicle 1 or the wheels 4, the respective reception frequencies—cf. El—E6—from the various points of incidence in area 17Mcf. the ary scanning progressions Hl—Hé in Figure 2-are superimposed onto a mixture l8 of various reception frequencies or velocities; see Figure 6. In other words, when the ion frequency f strikes a wheel 4, it fragments or spreads into a Doppler effect-induced mixture 18 of ion frequencies or velocities during the passage Tp of a vehicle 1, the extent of the spreading uency spread'") being labeled A] in Figure 6. The occurrence of such a frequency spread 18 can thus be used as a characteristic for a wheel 4.

The Doppler effect—induced frequency spread 18 with an extent ofA1 is parasitically mposed by a second frequency spread effect that is induced by the ry of the measurement beam lobe 15 itself. From its location P1, a radar/lidar device 16 observes, as is e from Figure 7, various points Pz', Pg" in the area of incidence 17 of the measuring beam lobe 15 from a different l direction 7', 7" in each case, which, together with the horizontal component vth of the tangential velocity VI of the wheel 4 or the velocity v of the vehicle body 5, encloses a reSpectively different solid angle [31, 62. The projection of the velocity v or v“, onto the respective measurement beam direction 7’, 7" in the measurement beam lobe 15 thereby leads—m across the area l7—to a geometry—induced fragmentation or spreading uency spread") 18’ of the reception frequencies, as shown in Figure 8 for the velocity v of the vehicle body 5 at the level H1 as a geometry-induced spread of the reception frequency progression El', and assumes the dimension S.

The Doppler effect-induced spread 18 in the extent A (Figure 6) is superimposed by the geometry-induced spread 18' in the extent S (Figure 8) into an "actual" reception frequency mixture F in the progression over time, as illustrated in Figure 9. A frequency spread to the extent A2, which is ed of the Doppler-induced spread A; and the geometry-induced spread S, is measured at the locations of the wheels 4.

The geometry~induced frequency spread 18' is substantially dependent only on the installation location and orientation of the radar/lidar device 16 relative to the roadway 2 or the g position of the vehicle 1, and can therefore be determined by reference measurements with vehicles 1 (with covered wheels or if the measurement beam lobe 18 strikes only the body ). The extent S of the ry—induced frequency spread 18' can then be utilized as a reference or predetermined value for the actual radar detection process, which tes the reception frequency ssion of Figure 9 and detects a wheel 4 if the recorded progression F of reception frequencies shows a Spread A2 that exceeds the spread amount S specified as the reference.

The spread extent S could atively be determined all over again each time for the current detection process during the passage of a vehicle 1, by storing the frequency spread 18‘ appearing in the first milliseconds of a e passage when the vehicle body 5 enters into the measurement beam lobe l8, and using it as a threshold value for the subsequent wheel detection.

As can be seen based on Figure 4 and equation (4), the envelOping curve of the Doppler— induced frequency spread 18 corresponds roughly to the circumferential r of the wheel 4, viewed at the angles 6', B“, i.e., it is generally an ellipse, which may be truncated if the area 17 does not cover the entire wheel 4; see Figure 6. 1f the geometry—induced frequency spread 18' is additionally taken into cousideration; the enveloping curve becomes more "unsharp" to the extent of the spread S, but its rough shape can still be analyzed, e.g., by storing the ion frequency mixture F of the reference passage for a reference wheel as "reference signature" 2], e.g., in a memory 22 ofthe apparatus 9 in order to subsequently compare it to the reception frequency progression F of an actual vehicle passage.

Figure 10 shows a real case in which interruptions 23 appear in the reflected ement beam lobe 15 and thus in the reception frequency progression signai F during the passage Tp of a vehicle 1. In the comparison of the reference signatures 21 to such an actual reception frequency progression F, suitabie comparisons of r, surface area, and/or shape ("best fit matches") can be undertaken in order to achieve a high recognition nty in such cases.

In an advantageous practical realization of the embodiment from Figure 5, the Doppler radar device 16 of the apparatus 9 is ucted using existing wireless infrastructure of a roadway, e.g., using WAVE or DSRC radio beacons of a road toll system or WLAN radio beacons of a roadside Internet infrastructure. Thereby already existing transmitter components of the WLAN, WAVE, or DSRC radio beacons can be used as transmission components of the Doppler radar device 16; er sections of the radio beacons can likewise be used as the receiver components of the Doppler radar device 16, or can at least be integrated into the receiver components of the radio beacons. The apparatus and the method of the invention can be implemented in this manner as a software application running on a conventional WLAN, WAVE, or DSRC radio beacon, for example.

It has so far been assumed that the transmission frequency of the radar/lidar device 6 or the measurement beam lobe 15 is constant, i.e., its progression over time (temporal progression) is a constant progression. It is also possible, however, that the device 6 could emit a measurement beam lobe 15 with a temporally non—constant transmission ncy, e.g., as in frequency hopping methods in which the frequency changes constantly according to a predetermined or known pattern. The recorded reception frequency progressions F are recorded relative to the previously known al ssion of the transmission ncy for the ement beam lobe lS—whether constant or varying—Le, referenced or standardized thereto, so that the effect ofknOWn transmission frequency progressions can be compensated.

The invention is accordingly not d to the illustrated embodiments, but instead comprises all variants and modifications that fall within the scope of the appended claims.

Claims

Claims (4)

What we claim is:

1. A method for detecting wheels of a vehicle that is traveling on a roadway in a travel direction, the wheels of which are at least partially exposed laterally, with the step: emitting an electromagnetic measurement beam lobe having a known temporal progression of frequency from the side of the roadway onto an area above the roadway and at a slant with respect to the travel direction, characterized by the steps: receiving the measurement beam lobe reflected by a passing e and recording the al progressiOn, relative to the knowri progression, of all of its frequencies appearing at the same time as a reception frequency mixture, and during the passage of the e, detecting a frequency spread ing in the recorded temporal progression of the reception ncy mixture and exceeding a predetermined threshold value as a wheel.

2. The method according to Claim 1, characterized in that the predetermined threshold value is determined in a previous step from a frequency spread that occurs during the passage of a less part of the vehicle.

3. An apparatus for detecting wheels of a vehicle that is traveling on a roadway in a travel direction, the wheels of which are at least partially exposed laterally, characterized by at least one Doppler lidar or radar device that emits an electromagnetic measurement beam lobe with a knowu temporal progression of frequency onto a target and records the temporal progression, relative to the known progression, of all frequencies occurring at the same time from the ement beam lobe reflected by the target as a reception frequency e, wherein the measurement beam lobe is oriented from the side of the y onto an area above the roadway and at a slant with respect to the direction of travel, and the recorded a ream evaluation unit that s a frequency spread appearing in temporal progression of the reception frequency mixture during the passage of the vehicle and exceeding a predetermined threshold value as a wheel.

4. The apparatus ing to Claim 3 with a Doppler radar device, characterized in that it is constituted by a roadside WLAN, WAVE, or DSRC radio beacon.