NZ617610B2 - Method and device for detecting a rotating wheel - Google Patents

Abstract

The invention relates to a method for detecting a rotating wheel (4) of a vehicle (1), which is driving on a roadway (2) in a driving direction (3) and the wheels (4) of which are exposed laterally at least partially, comprising the following steps: emitting an electromagnetic measurement beam (9) having a known time curve of the frequency thereof to a first region above the roadway (2) in a direction obliquely relative to the vertical and normally or obliquely relative to the driving direction (3); receiving a reflected measurement beam (9) and recording the time curve of the frequencies thereof relative to the known curve as a received frequency mixed curve; and detecting a continually ascending or descending band of frequencies over a time period in the received frequency mixed curve as the wheel (4). The invention furthermore relates to a device (7) for carrying out the method. aving a known time curve of the frequency thereof to a first region above the roadway (2) in a direction obliquely relative to the vertical and normally or obliquely relative to the driving direction (3); receiving a reflected measurement beam (9) and recording the time curve of the frequencies thereof relative to the known curve as a received frequency mixed curve; and detecting a continually ascending or descending band of frequencies over a time period in the received frequency mixed curve as the wheel (4). The invention furthermore relates to a device (7) for carrying out the method.

Description

Method and Device for Detecting a Rotating Wheel The present invention relates to a method and an apparatus for detecting a rotating wheel of a vehicle that is ling on a roadway in a travel ion, 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 ition of wheels that a given traffic area is being driven on in order to, for example, monitor borders or to initiate certain actions such as triggering an alarm, switching on lighting, opening a barrier, taking a picture for ring purposes, etc. Modern traffic fee systems also frequently base the calculation of fees on the number of axles of a vehicles, such that the ion of wheels (wheel axles) can also be an important basis for charging or controlling road tolls, especially by means of mobile control vehicles, which are to control the number of axles of vehicles subject to road tolls while overtaking or in oncoming traffic.

From. DE 10 2008 037 233 A1 it is known to detect the wheels of a moving vehicle based on the horizontal ent of the tangential ty, which differs from the remainder of the vehicle and brings about a corresponding Doppler frequency shift of' a radar’ measuring" beanu For this purpose, a radar speed measuring unit is used which irradiates the lower area of passing vehicles with a radar beam lobe and, from the returning frequency mixture, determines a single speed ement signal that has signal maxima at the locations of the wheels. Gaps between a traction vehicle and its trailer can y indicate signal minima and intermediate "false" maxima, which lead to an erroneous wheel detection.

The invention aims to create a method and an apparatus for detecting wheels which enable a safer detection than the known solutions.

This aim is achieved in a first aspect of the invention with a method, which is characterised by the steps of emitting an electromagnetic measurement beam having a known temporal progression of its frequency onto a first section above the roadway in a direction which is in a slant with respect to the vertical and which is normal or at a slant with respect to the travel direction; receiving a reflected ement beam and recording the al progression of its frequencies relative to the known progression as a reception frequency mixture progression; and detecting a band of frequencies which is uously inclining or declining within a period of time in the reception frequency mixture progression as a wheel.

The ion is based on a novel approach of detecting a wheel passing substantially horizontally past a Doppler—sensor by the axle an inclining (e.g. if the Doppler—sensor lies above of the wheel, is pointed downwards and is moving towards the wheel) or declining (e.g. if the Doppler—sensor lies below the axle of the wheel, is pointed upwards and is moving towards the wheel) reception frequency mixture progression during the passage. Unlike the known state of the art (DE 10 2008 037 233 Al), not just a signal maximum per wheel is evaluated, but the signal progression during the passage of the wheel.

In the ideal case of a line—like :measuring' beanl which strikes the wheel from above or at a slant from the side and normal to the travel direction, the ssion of the frequency shift of the reflected measuring beam caused by the Doppler effect is line—like inclining or declining. If the measuring beam is not normal to, but at a slant with respect to 3O the driving ion, a horizontal ent of the tangential velocity of the wheel caused by the Doppler shift is added to this progression, which leads to an additional offset of the progression; however, this does not change the criterion of the ion of an inclining or declining reception frequency ssion during the passage of the wheel. _ 3 _ Furthermore, in reality the cross section of a ing beam is never y point—like but always expanded, e.g. to an. area of incidence on. the vehicle is the range of a few centimetres or some tens of centimetres. Thereby the reception frequencies are broadened or spread from the described line— like progression to a “mixture" or rather “band” of reception frequencies: On varying height or width positions in the area of incidence of the measuring' beam the ng wheel has varying vertical and horizontal components of the tangential velocity and thereby creates different Doppler frequency shifts which lead to a “splitting” or “spreading”, respectively, of the sending frequency of the measuring beam to a plurality of simultaneously reflected reception. ncies, a “reception frequency mixture”; viewed over time, the reception frequency mixture progresses as a band in the frequency/time plane with the bed inclining or declining progression.

This spreading effect caused by the velocity of the wheel is superposed by a second parasitic frequency spreading effect which can be attributed to the ent tion angles of the al and horizontal components of the tangential ty onto the direction to the receiver: This projection angle varies according to the respective place of reflection in the area of incidence. The second spreading effect is independent of whether the vehicle body or the rotating wheel is passing the receiver at that moment and is solely determined by the geometrical constraints of the measurement setup. Both effects superpose to the mentioned. band—like ion frequency mixture ssion over time.

In a first embodiment of the invention said detecting can 3O be carried out by evaluating the progression of the frequency average of the band, which frequency' average shows the de— scribed incline or decline during the passage of the wheel.

In a second embodiment of the invention said detecting can be carried out by checking if the band falls into a given con— tour in the frequency/time plane. The contour constitutes the maximal boundaries in which the reception frequency progression for different ng progressions can occur, and if all of the measurement data of the Doppler ion frequencies over time fall into said contour, there is a continuously inclining or ing' band. of frequencies in the reception. frequency mixture ssion, which indicates a wheel.

According to a preferred embodiment, the measurement beam is emitted normally with respect to the travel direction at a slant downwards. y a shadowing of the wheels can be mini— mised and the gap between a r and a traction vehicle can safely be detected on the one hand, and — with exception of the spreading effects mentioned above - the horizontal components of the velocity of the rotating wheel as well as the velocity component of the vehicle are ignored on the other hand, which eases the detection of said inclining and declining bands in the reception frequency mixture progression.

For further improvement of the band detection, in an op— tional embodiment the method according to the ion can se following steps: measuring the velocity of the body of the vehicle relative to the location of on of the measurement beam and recep— tion of the reflected measurement beam; and compensating the reception frequency mixture progression by those frequency parts which are caused by the velocity of the vehicle body, before said detecting of the band is con— ducted.

For the same reasons the method of the invention can also comprise the ing steps: detecting the presence of a part of the body of the vehi— 3O cle in a second section which lies above the first section, in the temporal progression as a passage time window; wherein. detecting the wheel in the reception. frequency mixture progression is only conducted during said passage time window.

In knowledge of the passage time window of the vehicle the reception. frequency' mixture progression. can. be further processed to ease the detection of the band therein, namely by the steps determining an interfering signal fraction in a section of the reception frequency mixture progression immediately preced— ing the passage time ; and compensating the reception frequency mixture progression in the passage time window by the interfering signal fraction, before said step of detecting the band is conducted.

In another further embodiment of the method according to the invention , which are detected during the same pas— sage time window, are assigned to the very same vehicle. The number of wheels of a vehicle can be used as a basis for e.g. a road—toll charging dependent on the number of axles.

To further keep said parasitic spreading effects low and to obtain a distinct inclining or declining progression of the reception frequency mixture, the area of incidence of the meas— uring beam on the vehicle is preferably minimised. ably the measuring beam has an area of incidence whose diameter is less than a wheel which is to be detected, preferably less than cm, especially preferred less than 5 cm.

In a ion of the ion, a concentrated laser beam can be used for this purpose, or, in an alternative preferred t, the measuring beam is a radar beam emitted by a direc— tional antenna, preferably in a frequency range above 70 GHz.

With such high frequencies the wavelength is very small and the antennas can thereby be mechanically realised very small with a high a gain, e.g. in form of horn antennas or antenna ar— 3O rays.

In a second aspect the ion creates an apparatus for detecting a ng wheel of a vehicle that is travelling on a roadway in a travel direction, the wheels of which are at least partially exposed laterally, the apparatus being characterised by _.6_ a Doppler—lidar device or a Doppler—radar device which emits an electromagnetic measurement beam having a known temporal progression of its frequency onto a target above the roadway in a direction which is in a slant with respect to the vertical and which is normal or in a slant with respect to the travel direction; and which records the temporal progression of the ncies of the measurement beam reflected by the target, ve to the known ssion, as a reception frequency mixture progression; and a subsequent evaluation device configured to detect a band of frequencies which is continuously inclining‘ or declining over a period of time in the reception frequency mixture progression, as a wheel.

With regard to the advantages of the apparatus according to the invention it is ed to the teachings stated above for the method according to the invention.

Preferably the measuring beam of the Doppler-lidar device or the Doppler—radar device is oriented normally with respect to the travel direction and at a slant downwards.

It is especially favourable if the apparatus has a sensor ted to the evaluation device for measuring the velocity of the body of the vehicle, wherein the evaluation device com— pensates the reception frequency mixture progression by those frequency parts which are caused by the velocity of the vehicle body. ing to another preferred feature the apparatus com— prises a sensor connected to the evaluation device which de— tects the presence of a part of the body of the vehicle above that section onto which the measurement beam is directed in the temporal ssion as a passage time window, wherein the evaluation device detects a wheel in the reception frequency mixture progression only during said e time . In this case, the evaluation device can optionally be configured to determine an interfering signal fraction in a section of the reception frequency mixture progression immediately preceding said passage time window and to compensate the reception fre— quency mixture progression in the passage time window by said interfering signal fraction.

In case of a Doppler-radar device, its measuring beam is preferably a radar beam d by a directional antenna, espe— cially preferred in a frequency range above 70 GHz; in case of a Doppler—lidar device the measuring beam is preferably a con— centrated laser beam.

The apparatus of the invention is suited for both a sta— tionary as well as a transportable, especially a mobile use. In the first case the apparatus can — if it works with a Doppler— radar device — be designed especially as to be assembled with the radio beacons of an already existing radio—road infrastruc— ture, like WLAN (wireless local area network), WAVE (wireless access in a vehicle environment) or DSRC (dedicated short range ication). In a practicable ment the Doppler—radar device is designed as a roadside WLAN, WAVE or DSRC radio bea— con. In the second case the Doppler—lidar device or the Dop— pler—radar device is mounted on a mobile platform, preferably a control e, to permit the control of vehicles on different road lane or in the oncoming traffic.

Further features and advantages of the method and of the apparatus of the invention will become apparent from the subse- quent description of a red embodiment with regard to the enclosed drawings, in which: Figs. 1 and 2 show the apparatus of the invention mounted on a l vehicle in combination with a vehicle controlled by it in a top view (Fig. l) and viewed in the travel ion (Fig. 2); Fig. 3 shows the velocity relations in a ng wheel in detail; Fig. 4 shows an exemplary reception frequency mixture pro— gression in the frequency/time plane during measurement of the wheel of Fig. 3 laterally from above and normally to the direc— tion of travel in ng traffic; Fig. 5 shows the tion of a detection contour for de— tecting an inclining and declining band in the reception fre— quency mixture progression in the frequency/time plane; Fig. 6 shows the geometrical relations in a real expanded measurement beam for exemplification of the frequency spreading effects caused by velocity and by geometry; Figs. 7a to 7g ShOW’ exemplary" idealised. reception. fre— quency progression and the frequency averages, respectively, of ion frequency mixture progressions at different angular positions of the Doppler ement beam with respect to the wheel; Fig. 8 shows the effect of the frequency spreading caused by geometry during the passage of a vehicle in the temporal progression; and Fig. 9 shows the implications of the effects of the fre— quency spreading of the reception frequency mixture progression caused by velocity and geometry during the passage of a vehicle with two exemplary wheels, wherein in the left and in the right half of Fig. 9 two ent cross sections of the measuring beam are used.

In Figs. 1 and 2 a vehicle 1 is moving on a y 2, more precisely on a lane 2' of the roadway 2, in a travel direction 3’. The e 1 has wheels 4 which protrude downwards above the body 5 of the vehicle 2 and are thereby exposed — — at least partially on the sides of the vehicle body in recesses thereof, i.e. they can be seen from the side.

On a second lane 2” of the roadway 2 a control vehicle 6 3O is moving in an opposite travel direction 3”. The travel ions 3’, 3” are preferably anti—parallel, but could also be parallel, i.e. the control vehicle 6 could overtake the vehicle 1 or vice versa. The control vehicle 6 could also be stationary* and the travel directions 3’, 3” could be non— el; in the following the ve movement direction of the vehicle 1 with. respect to to the control vehicle 6 is denoted as the travel ion 3 of the vehicle 1. For simplicity it is also assumed that the travel direction 3 is approximately normal to the axles 4' of the wheels 4 and is approximately horizontal, although this is not sory and deviations thereof are merely reflected in correspondingly changed projection angles of the velocity components considered in the following.

The control vehicle 6 carries a measuring apparatus 7 with a Doppler—lidar or Doppler-radar device 8 which emits an electromagnetic ing beam 9, in this case a lidar or radar measuring beam, onto the vehicle 1 or its wheels 4, tively, during the passage to detect the wheels 4 of the e 1. The measuring beam 9 is oriented in an angle B to the vertical V and in an angle v to the travel direction 3. The angle 6 is O S B < 90° or 90° < B S 180°, in any case ¢ 90°, i.e. the measuring beam 9 runs at a slant to the vertical V, preferably at a slant rds as shown, e.g. in an angle of B = 100° to 170°, preferably B = 120° to 150°. In an alternative (not shown) embodiment the measuring' beanl 9 could also be directed at a slant upwards, e.g. B = 10° to 80°, preferably 6 = 30° to 60°, if the Doppler lidar/radar device 8 is mounted close to the ground, e.g. stationary on the side of the road 2, and aims at the vehicle 1 and its wheels 4 at a slant from below.

The angle y is preferably 90°, i.e. the measuring beam 8 is oriented normally to the travel direction 3. In alternative variants of the ion the angle Y can also be ¢ 90°, e.g. at a slant forwards or backwards, as viewed from the control 3O vehicle 6.

In. a manner known. in the art, the Doppler lidar/radar device 8 evaluates the reception frequency of the measurement beam 9 reflected by the vehicle 1 or its wheels 4, wherein the (projected) ent vp of the relative vehicle velocity v of the vehicle 1, or the tangential velocity v1 of the wheel 4 at the respective point P of the nce area of the measurement beam 9 (see Figs. 3 and 5), respectively, lying in the direction of the ement beam 9, can be determined e.g. from the Doppler effect induced frequency shift between emitted and reflected ement beams 9. The wheels 4 of the vehicle 1 can then. be detected from this information, as will be described in greater detail below.

The Doppler lidar/radar device 8 itself can be of any type known. in the art, whether‘ with. a continuous, modulated, or pulsed measurement beam 9. For a uous measurement beam 9 a r frequency shift between the natural frequencies (“carrier frequencies”) of the emitted and reflected measurement beanl 9 can be determined by interference measurement. For a pulsed or ted. measurement beam, a Doppler shift between the pulse rates or modulation frequencies of the emitted and the reflected ement beams 9 can be measured. The terms “sending frequency” of the measuring beam 9 and “reception frequency" of the reflected measurement beam 9 used herein are understood to mean all such natural, carrier, pulse, or modulation ncies of the measurement beam 7, i.e., the term reception frequency comprises any type of frequency of the measurement beam 9 which can be influenced by the Doppler .

As shown in Fig. 2, the measuring' apparatus 7 further comprises a velocity' sensor 10 to measure the (relative) nt v of the vehicle 1 with respect to the control vehicle 6, as well as a presence sensor 11 to detect the presence of a part of the vehicle body 5 during the passage of the vehicle 1 at the control vehicle 6. The presence sensor 11 “sees” and detects the vehicle body 5 in a section in which the measuring beam 9 is ed onto the vehicle 1 during. the vehicle passage, whereby a passage time window TF of the vehicle 1 can be determined with respect to the lidar/radar device 8, as will be described in greater detail below. The presence sensor 11 and its line of sight 12 are preferably' arranged above the _ 11 _ measuring beam 9 of the lidar/radar device 8 — or in a known rical relation thereto — to obtain a temporal relation between the passage time window TF and the measurement signals of the lidar/radar device 8. From the passage time window TF and in knowledge of the velocity v ed by the sensor 10 the length L of the vehicle 1 can also be calculated according to L 2 v - T.

The radar‘ device 8 and. the velocity' and. presence sensors 10, 11 are connected to an evaluation unit 14 of the device 7, which performs the evaluation calculations illustrated hereinafter.

Fig. 3 shows different embodiments of the measuring beam 9 with respect to its concentration or expansion, respectively, by means of several exemplary areas of incidence 16, 16’, 16” with varying size on a wheel 4. In a first variant the measurement beam 9 is strongly concentrated, so that its area of incidence 16 on the vehicle body 5 or the wheel 4 has a small diameter in the range of several centimetres, preferably < 2 cm. d requirements are placed on the concentration of the measurement beam 9, depending on the distance of the device 8 from the vehicle 1: In the ideal case, the measurement beam 9 is a bundle of nearly parallel light or radar rays that can preferably' be ed. with. a laser. But everL witll a radar measurement beam, a corresponding tration can be achieved by using radar waves with a very high frequency, preferably above 70 GHz, which have nearly the properties of light and can be concentrated e.g. by radar lenses. The use of directional antennas, e.g. horn antennas, antenna arrays and patch antennas, with the most parallel, small—diameter radiation 3O characteristic le, also generates an appropriate radar measurement beam. Especially suited are radar devices from the automotive field, such as those used in vehicles as collision and ce warning devices. Such concentrated measurement beams 9 have a concentration or a ion or expansion range _ 12 _ (aperture angle) of less than 10 (which corresponds to a solid angle of less than approximately 0.00024 sr).

In a second embodiment the ing beam 9 is expanded wider, e.g. scattered or expanded in a plane or cone, in the manner of a “measuring beam lobe” with a substantially larger area of incidence 16’. Such an area of incidence 16’ can be achieved in a lidar device e.g. by a disperging lens placed in front thereof, appears devices whose ’or with radar concentration is not exact.

In. the case of radar, a widened. measurement beanl 9 is characterised by the aperture angle of the radar antenna being used. The aperture angle (or the half—value width) of a directional a refers to the points where the power has declined to half (—3 dB) relative to the maximum. As known to those skilled in the art, the gain of the antenna in its main radiation direction can be ted with the following formula from knowledge of the respective aperture angle: where g = gain [dBi] Aw = horizontal re angle (in degrees) A6 = vertical aperture angle (in degrees) The aperture angle of the radar antenna of the device 8 should allow for a good separation of the individual wheels 4 in the measurement signal of the vehicle 1. to be detected.

Thus, it is e.g. favorable if the nce area 16' of the measurement beam lobe 15 does not exceed half the diameter of 3O the wheel 4 of the vehicle 1. The optimal area of incidence 16’ results from. the ing' distance fronl the vehicle 1 and therefore the selection of the radar antenna depends on the ry of the overall arrangement. In general, antennas with _ 13 _ a gain g of more than 10 dB are especially suitable, depending on the arrangement and frequency of the radar device 8.

Directional antennas usually' have an antenna gain g; of more than 20 dB (which corresponds to an aperture angle Am = Afi = approx. 16°). Thus, an area 16' that is 28 cm in diameter can be illuminated 1 meter away from the vehicle 1 with an a gain of 20 dB. An antenna gain 9 of 30 dB can be necessary for more distant vehicles 1 in order to achieve an aperture angle Am 2 Ad 2 approx. 5°, which implies an illumination area 16’ of approx. 30 cm in size at a distance of 3 m.

In a third variant the size of the area of incidence 16” of the measuring beam 9 on a wheel 4 is between the size of the variants l6 and 16’, e.g. in a range of 2 - 10 cm, preferably 2 — 5 cm.

Fig. 3 shows the movement of the area of incidence 16, 16’, 16" during the mutual passage of the vehicle 1 and the control vehicle 6 along a sampling line 17 which crosses the wheel 4 about in the middle of its upper half in this example.

The tangential velocity vt or vt(P) occurring on a point P of the sampling line 17 on a radius r of the wheel 4 rotating in the rotation direction. U can be d into a horizontal component vnh(P) and a vertical component VLV(P). The ntal ent th(P) stays substantially constant on a given ntal ng line 17, whereas the vertical component VLV(P) changes from a negative maximum value VLV(A) on a point A on the circumference of the wheel to the value 0 at a point B on the axis 4’ of the wheel up to a positive maximum value VLV(C) at a point C on the other circumference of the wheel. 3O In detail, the tangential velocity vg(r) on a radius r is proportional to this radius r, namely v,(r>=7:~v, <1) _ 14 _ The vertical component vnv(r) of the tangential velocity vt(r) at an angle a is a cosine projection corresponding to v,,v(r) 2%v, cosa (2) With c0sa=§ (3) the horizontal component VLV(r) of the tangential velocity results to vt,v (r) : v! —- ( 4: ) where g is the horizontal distance to the center of the wheel and thereby — - when sampling with. a constant ty v proportional to the time t, which describes a linear incline or decline.

If the measuring beam 9 is directed normally to the travel direction (v = 90°) and e.g. at a slant from above (90° << 8 < 180°), the radar device 8 measures a frequency shift Af due to the Doppler effect, which corresponds y to this vertical component VLV(P). The frequency shift Af is depicted in Fig. 4 over the time t as a ion frequency progression 18. The Doppler shift Af of the reception frequency with respect to the sending frequency is proportional to the vertical velocity component VLV of the ponding sampled parts (points P) of the vehicle 1 or wheel 4, respectively; the reception frequency progression 18 depicted in Fig. 4 is ore equivalent to a vertical ty progression.

The reception frequency progression 18 of Fig. 4 is an idealised progression for an idealised measuring beam 9 with a 3O point—like cross section of the beam. The progression 18 shows a linear incline from vtN(A) to VLV(B) crossing the point of origin during a time segment TR which corresponds to the sampling' of the wheel along the sampling line 17 with. the ty v. Would the measuring beam 9 be directed at a slant front below onto the wheel 4 (B > 90°) or be moved. in the opposite direction. along' the sampling line 17 (e.g. control vehicle 6 overtakes vehicle 1), then the reception frequency progression 18 shows a decline, i.e. it is mirrored about the time axis t of Fig. 4. e of the expansion of the area of incidence 16, 16’ or 16", respectively, of a real, non—idealised measuring beam 9, for each sending frequency emitted at a specific point in time t not only one reception frequency, which is shifted by the Doppler effect, is received, but a slightly differing reception frequency from each different point in the area of incidence 16, 16’, 16”. On one hand this is due to the fact that on a height hl differing from the height h of the sampling ssion 17 the vertical component st (and also the horizontal component vmh) of the tangential velocity Vt each has a slightly differing value, such that the reception frequencies originating from different points of incidence P in the areas 16, 16', 16” — compare the exemplary sampling progression 17’ in Fig. 3 — superpose to a mixture of differing reception frequencies or velocities, respectively, see Fig. 4.

In other words, the reception frequency f splits or spreads to a mixture F of reception frequencies (or velocities) caused by the Doppler effect, respectively, during the passage Tf of a vehicle 1 when a wheel 4 , which leads to a reception frequency mixture 20 over time t.

The ncy spread effect caused by the velocity of the wheel is superposed parasitically by a second frequency spreading effect which is caused by the geometry of a measuring beam 9 flared in a cone shape. As can be seen from Fig. 6, the radar/lidar device 8 observes, from a position P1, different points P2', P5’ in the area of incidence 16’ of the ing beam 9 each under a ent spatial direction 21’, 21”, which each enclose a ent solid. angle with. the vertical and _ l6 _ horizontal components st and vnh of the tangential velocity Vt of the wheel 4 or the velocity' v of the vehicle body 5, respectively. The projection of the velocity' v5”, or th, tively, onto the measuring beam direction 21', 21” et cet. in the measuring beam 9 thereby leads to a splittering or Spreading, tively, caused by the geometry in the areas 16, 16’, 16”.

The spread caused by the velocities of the rotating wheel (Fig. 3) superposes with. the spread. caused. by" the geometry (Fig. 6) to the “real" ion frequency mixture progression with the frequency spread F g over time t.

As can be seen from Fig. 4, the reception frequency mix— ture progression 20 therefore shows for a measuring beam 9, which is directed at a slant from above or at a slant from be— low (0 < B < 180°) and approximately normally to the travel di— rection 3 (y 90°), a continuously inclining or - = depending on the viewing direction — declining band 22 during the passage time TF of the wheel 4, which can be used as a criterion for the occurrence of a wheel and therefore for the detection of the wheel 4. For example, the band 22 can be detected by signal analytical means by averaging the occurring reception frequency mixture F, i.e. by analysis of the frequency average (which again substantially ponds to the idealised ssion 18).

Fig. 5 shows an alternative way of the detection of the occurrence of an inclining or declining" band. 22, namely' by checking if the ion frequency' mixture progression 22 falls into a given contour 22’, which constitutes the maximum boundaries in which reception frequency progressions 180, 18h 3O 182, m, generally 181, for different sampling progressions 17m 171, 172, on different s ho, hl, h2, m, can occur. The superposition of all possible reception frequency progressions 18i for a certain area of incidence 16 provides the given con— tour 22’ in the ncy/time plane of Fig. 4 or 5, respec— tively, into which a band 22 falls in any case. _ 17 _ Although the size and form of the contour 22’ indeed de— pends on the size of the area of incidence 16, the global pro~ gression of the contour 22' over time t is always inclining or declining. By ng' if all (or at least the predominant part, i.e. except for a few statistical “outliers”) ion frequency measurements of the reception frequency mixture pro— gression 20 lie within the contour 22’, the occurrence of a band 22 continually inclining or declining over a period of time can again be detected.

If the measuring beam 9 is not directed normally to the travel direction 3 but at a slant (Y % 90°) o onto the vehicle 1 or the wheels 4, respectively, due to the projection of the horizontal components vnh of the tangential velocity Vt of the wheel 4 onto the direction of the measuring beam an ad— ditional horizontal velocity" component is measured. which is constant for a certain height h, hl of the sampling line 17 and weighs in as an offset on the idealised ion frequency progression 18 or real ion frequency mixture progression of Fig. 4. In Fig. 7 this is shown for the idealised recep— 2O tion frequency ssion 18 of Fig. 4, and the following Ta— ble 1 depicts the values of B and y for the examples of Figs. 7a to 7g: In knowledge of the velocity v, which e.g. is measured by the velocity sensor 10 or by the device 8 itself, the reception - 18 _ frequency progressions 18 or reception frequency mixture pro— ons 20 can be corrected or compensated, respectively, by the respective parts th caused by the velocity, which corre— spond to an offset compensation of Figs. 7a) to 79) and again leads back to the exemplary reception frequency mixture pro— gression shown in Fig. 4 or to a progression ed about the time axis t.

Fig. 8 shows the measurement of a passage time slot TF for the the device 8 passage of a whole vehicle 1 with respect to or measurement beam 9, respectively, preferably by means of a separate presence sensor 11. For example, the presence sensor 11 can again be a radar or lidar device, which emits a radar or lidar measurement beam 12 onto the passing vehicle 1 to measure the duration TF of the e passage and to reference the re— corded reception ncy mixture progression 20 thereto.

In Fig. 8 the measurement beam 9 was exclusively ed onto the vehicle body 5 for means of comparison, namely under an angle of y ¢ 90°, i.e. at a slant to the travel direction 3, such that the relative velocity v of the vehicle 1 during the vehicle passage TF can be measured as a rectangular frequency shift, which is spread to a reception frequency mixture F in a band 23, which is caused exclusively by the spread caused by the geometry of an conically flared measuring beam 9 according to Fig. 6.

An interfering signal fraction in the reception signal of the lidar/radar device 8 which is occurring outside of the ve- hicle passage TF is d by 24. In knowledge of the passage time window TF, a section 25 immediately preceding the e time window TF, or a section 26 immediately succeeding the pas— 3O fre— sage window slot TF can be extracted from the reception frac— quency e progression 20 and the interfering signal tion. 24 can be determined therein; this interfering signal fraction 24 can be used to compensate the reception frequency mixture progression 20 for this interfering signal fraction 24.

For example, a frequency is of the reception frequencies occurring in the sections 25, 26 could be performed and these could be d or subtracted, respectively, from the recep— tion frequency mixtures F during the vehicle passage TF.

To this end preferably only the section 25 preceding the vehicle the vehicle 1 could, for passage TF is used, because example, have a r which could mistakenly be used as an interfering signal in the succeeding section 26.

Furthermore the determination of the passage time window TF can be used to assign all those wheels which are detected during the passage time window TF to this very same e 1, which can be ated accordingly from the evaluation unit 14 of the apparatus 7.

The window the vehicle passage could passage time TF of also be directly determined from the radar/lidar device 8 in— stead of the separate presence sensor 11, i.e. with the very same ing beam 9. If the measuring beam 9 is directed un— der an angle of ¢ 90° (as in Fig. 8) onto the e 1, the e time slot I} could be determined e.g. on the basis of the frequency shifts on leaps 27, 28 of the band 23, and/or 2O from the ence of the ncy spread caused by the ge— ometry in the reception frequency mixture progression 20.

The determination of the relative velocity v of the vehi— cle 1 could also be conducted by e.g. the lidar/radar-device 8 itself, by means of the size of the frequency leaps 27, 28 e.g. of the band 23, instead of the separate velocity sensor 10.

Fig. 9 shows two exemplary reception. frequency' mixture progressions 20, after these have been corrected by the compo— nents due to the velocity v of the vehicle 1 on the one hand and by the interfering signal fractures 24 that were determined 3O in the preceding section 25 on the other hand. In the left half of Fig. 9 the occurrence of a continuously inclining band 22 in the reception frequency mixture 20 is apparent, which indicates a wheel 4, in the case of a small area of incidence 16. In the right half of Fig. 9 the same situation is depicted when the area of incidence 16’ of the measuring beam 9 on the wheel 4 is -20.. larger than half the wheel diameter, such that the ing beam 9 simultaneously measures icant ve and nega— tive vertical components VLV of the wheel 4 at certain points in time. This leads to a closer “merging” of the beginning and ending spikes of the reception frequency mixture 20, i.e. to a steeper incline or e 18.

The device 7 can both be realised in mobile form, e.g. mounted on the vehicle 6, and in stationary form, e.g. using existing wireless tructure 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 ents of the WLAN, WAVE, or DSRC radio beacons can be used as transmission components of the Doppler radar device 8; receiver sections of the radio beacons can likewise be used as the receiver components of the Doppler radar device 8, or can at least be integrated into the er components of the radio beacons. The apparatus and the method of the invention can be implemented in this manner as a software application running a conventional mobile or stationary WLAN, WAVE, or DSRC radio control device or , for example.

It has been assumed that the transmission frequency of the radar/lidar device 8 or the measurement beam 9 is constant, i.e., its progression over time (temporal progression) is a constant ssion. However, it is also possible that the device 8 could emit a measurement beam 9 with a temporally non— constant transmission frequency progression, e.g., as in frequency hopping methods in which the frequency changes constantly according to a predetermined or known n. The recorded ion frequency (mixture) progressions 18, 20 are recorded relative to the known temporal progression of the transmission frequency" of the measurement beam 9 —— whether constant or varying, i.e., referenced or standardized thereto, so that the effect of known transmission frequency progressions can be compensated. -21_ The invention is thus not restricted to the described em— nts, but also encompasses all variations and modifica- tions which fall under the scope of the enclosed claims.

Claims (19)

WHAT WE CLAIM IS:

1. A method for detecting a rotating wheel of a vehicle that is travelling’ on a roadway in a 'travel direction, the 5 wheels of which are at least partially exposed laterally, the method being terised by the steps emitting an electromagnetic measurement beam having a known temporal progression of its frequency onto a first section above the roadway in a direction which is in a slant 10 with respect to the al and which is normal or at a slant with respect to the travel direction; receiving a reflected measurement beam and recording the temporal progression of its frequencies relative to the known ssion as a reception frequency mixture progression; and 15 detecting a band of frequencies which is continuously inclining or declining over a period of time in the reception frequency mixture progression as a wheel.

2. The method of clainl 1, terised. in that said detecting is carried out by evaluating the ssion of the 20 frequency average of the band.

3. The method of clain1 1, characterised. in that said detecting is carried out by checking if the band falls into a given contour in the frequency/time plane.

4. The method of any one of the claims 1 to 3, 25 terised in that the measurement beam is emitted normally with respect to the travel direction at a slant rds.

5. The method of any one of the claims 1 to 4, characterised by the steps measuring the velocity of the body of the vehicle relative 30 to the location of emission of the measurement beam and reception of the reflected measurement beam; and compensating the reception frequency deture progression by those frequency parts which are caused by the velocity of the vehicle body, before said detecting of the band is 35 conducted. _23_

6. The method of any one of the claims 1 to 5, characterised by the step ing the presence of a part of the body of the vehicle in a second section which lies above the first section in the temporal progression as a passage time window; wherein. detecting the wheel in. the reception frequency mixture progression is only conducted during said passage time window.

7. The method of claim 6, characterised by the steps 10 determining an interfering signal fraction in a section of the reception frequency mixture progression immediately preceding the passage time window; and compensating the -reception frequency mixture in the passage time window by the ering signal fraction, before 15 said step of detecting the band is ted.

8. The method of claim 6 or 7, characterised that wheels, which are detected during the same passage time window, are ed to the very same vehicle.

9. The method of any one of the claims 1 to 8, 20 characterised in that the measuring beam has an area of incidence, whose diameter is less than a wheel which is to be detected.

10. The method of any one of the claims 1 to 9, characterised in that the measuring beam has an area of 25 nce, whose diameter is less than 10 cm.

ll. The method of any one of the claims 1 to 10, characterised in that the measuring beam has an area of incidence, whose diameter is less than 5 cm.

12. The method of any one of the claims 1 to 11, 30 characterised in that the measuring beam is a radar beam emitted by a ional antenna.

13. The method of any one of the claims 1 to 12, characterised in that the measuring beam is a radar beam emitted by a directional antenna in a frequency range above 70 35 GHz. -24—

14. An apparatus for detecting a rotating wheel of a vehicle, that is travelling on a roadway in a travel direction, the wheels of which are at least partially exposed laterally, the apparatus being characterised by a Doppler—lidar device or a Doppler—radar device which emits an electromagnetic measurement beam having a known temporal progression of its frequency onto a target above the roadway in a direction which is in a slant with respect to the vertical and which is normal or in a slant with respect to the 10 travel direction; and which records the temporal progression of the frequencies of the measurement beam reflected by the target, relative to the known progression, as a reception frequency mixture progression; and 15 a subsequent evaluation device configured to detect a band of frequencies which is continuously inclining or declining within a period of time, in the reception frequency deture progression as a wheel.

15. The apparatus of claim 14, characterised by a sensor 20 connected to the evaluation device for measuring the velocity of the body of the vehicle, n the evaluation device compensates the reception frequency mixture progression by those frequency parts which are caused by the velocity of the e body. 25

16. The apparatus according to clain1 14 or 15, characterised by a sensor connected to the evaluation device which detects the presence of a part of the body of the e above that section onto which the ement beam is directed in the temporal progression as a passage time window; 3O n the evaluation device detects a wheel in the reception frequency e progression only during said passage time window.

17. The tus of claim 16, characterised in that the evaluation device is further configured to determine an 35 interfering signal fraction in a n of the reception _25_ frequency mixture progression immediately preceding said passage time window and to compensate the reception frequency mixture ssion in the passage time window by said interfering signal fraction. 5

18. The apparatus of any one of the claims 14 to 17, characterised in that the Doppler—lidar device or Doppler—radar device is mounted on a mobile platform.

19. The apparatus of any one of the claims 14 to 18, characterised in that the Doppler—lidar device or Doppler—radar 10 device is d on a control vehicle.