Locus estimation device and locus estimating method

A processor of a locus estimation device accepts a measured value of a wheel speed of right and left front wheels of a moving object, and a measured value of a steering angle at which the traveling direction is changed. Based on a measured value of a wheel speed of the right and left front wheels, a measured value of a steering angle, a distance in the direction of the body of the moving object, a distance in the direction of the axle of the moving object, and a constant, the processor estimates an amount of rotation of the middle point of a rotation center of the right and left rear wheels on a circle having a center which is a point on a straight line passing through the rotation center of the right and left rear wheels, and an amount of translation of the middle point.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2014-044410, filed on Mar. 6, 2014, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a locus estimation device, a locus estimating method, and a program.

BACKGROUND

Recently, a technology of estimating a movement or a movement locus of a vehicle according to wheel speed information for a moving object such as a vehicle having right and left front wheels and right and left rear wheels, with the front wheels designed as steered wheels, has been proposed. For example, a technology of preventing a shift of a movement locus for automatic parking, and a technology of making an amendment for matching between an estimated drive locus and an actual drive locus although a driving condition of a vehicle changes, are well known (refer to patent documents 1 and 2, for example). A technology of geometrically estimating a movement locus of a moving object according to wheel speed information has also been proposed (refer to patent documents 3 through 5, for example).

SUMMARY

According to an aspect of the embodiments, a locus estimation device includes a storage device and a processor. The storage device stores the distance between right and left front wheels and right and left rear wheels provided behind the right and left front wheels in the moving object in the traveling direction of the moving object. The storage device also stores the distance between the right and left front wheels and a constant depending on the steering angle and the rotation radius of the moving object determined by the steering angle. The processor is configured to accept a measured value of a wheel speed of the right and left front wheels and a measured value of a steering angle which changes the traveling direction of the moving object and estimate as follows on the basis of the measured value of the speed of the right and left front wheels, the measured value of the steering angle, the distance from the front and the end of the moving object, the distance from the sides of the moving object, and the constant. That is, the processor estimates an amount of rotation of the middle point of the rotation center of right and left rear wheels on a circle having a center which is a point on a straight line passing through the rotation center of the right and left rear wheels, and the amount of translation of the middle point.

DESCRIPTION OF EMBODIMENTS

Many recent vehicles are front-wheel driven. Therefore, the front wheel speed is measured in many cases. In this case, when the movement of a moving object is estimated by considering its steering angle, it is preferable that movement of the middle point of two rear wheels is estimated.

However, in the above-mentioned conventional technology, there may be a case where movement of a front-wheel driven vehicle is not estimated with high accuracy because, for example, the direction of the vehicle is not appropriately considered on the basis of circular movement of the vehicle, an estimation is made by means of an equation using the wheel speeds of the front and rear wheels, thereby invalidating a measured value of front wheel speed to be adopted, etc.

The above-mentioned problems occur not only with a vehicle, but also with other moving objects having wheels.

(First embodiment) A locus estimation device1according to a first embodiment is described below with reference to the attached drawings.FIG. 1is an example of a functional configuration of the locus estimation device1according to the first embodiment of the present invention.FIG. 2is an example of a hardware configuration of the locus estimation device1according to the first embodiment of the present invention. The locus estimation device1is an apparatus that estimates a locus of a moving object with right and left front wheels and right and left rear wheels. The locus estimation device1estimates a locus of a moving object on the basis of a measured value of the wheel speed of each of the right and left front wheels and a measured value of the steering angle of the front wheels. Front wheels refer to wheels provided at the front of the moving object. Rear wheels refer to wheels provided at the rear of the moving object. Left and right refer to the direction viewed from the end to the front of the moving object. The steering angle refers to the turning angle of a steering wheel which changes the direction of the front wheels with respect to the direction of the body of the moving object.

The locus estimation device1estimates the locus on the basis of the wheel speed of the right and left front wheels, the steering angle, the distance between the front wheels and the rear wheels in the direction of the body of the moving object, the distance between the right and left front wheels, and the constant depending on the steering angle and the rotation radius of the moving object at the steering angle. In this case, the locus estimation device1estimates the amount of rotation of the middle point of the rotation center of the right and left rear wheels on a circle having a center which is a point on a straight line passing through the rotation center of the right and left rear wheels, and the amount of translation of the middle point. Thus, the locus of the moving object is estimated.

Described below is a case where a vehicle having two front wheels and two rear wheels is used as a moving object. With regard to the vehicle, it is assumed that the wheel speed of each of the right and left front wheels (hereafter also referred to respectively as left wheel speed and right wheel speed) and a steering angle are measured. The locus estimation device1may be a small information processing device such as a microcomputer etc., and may be installed in the vehicle.

As illustrated inFIG. 2, the locus estimation device1includes a central processing unit (CPU)21, memory23, a wheel speed acquisition interface (I/F)25, a steering angle acquisition I/F27, and an output I/F29, and these components are interconnected through a bus31.

The CPU21is a processor which controls the operation of the locus estimation device1. The CPU21performs a controlling process as the locus estimation device1by reading and executing a control program stored in advance in, for example, the memory23. The memory23is, for example, a read-only storage device, a storage device allowing writing and reading of data at any time, etc. The wheel speed acquisition I/F25is an interface device which performs management when accepting the wheel speed of each of the right and left front wheels from a wheel speed sensor33. The steering angle acquisition I/F27is an interface device which performs management when accepting from a steering angle sensor35a turning angle of a steering wheel which changes the direction of the front wheels of the vehicle. The output I/F29is an interface device which performs management when outputting a locus estimation result.

The wheel speed sensor33is provided for a vehicle, and outputs a measured value of the wheel speed of each of the right and left front wheels. The wheel speed refers to, for example, a rotation movement distance per unit time of a wheel. The steering angle sensor35is provided for a vehicle, and outputs a measured value of the steering angle of a steering wheel which changes the direction of the front wheels of the vehicle.

As illustrated inFIG. 1, the locus estimation device1includes a processing unit3and a storage unit5. The processing unit3has the functions of a wheel speed acceptance unit11, a steering angle acceptance unit13, and a locus estimation unit15. The storage unit5stores a parameter database (DB)19.

Each of the above-mentioned functions of the processing unit3is realized by, for example, the CPU21reading and executing a control program. The wheel speed acceptance unit11accepts the measured values of the left wheel speed and the right wheel speed from the wheel speed sensor33. The steering angle acceptance unit13accepts the measured value of the steering angle from the steering angle sensor35.

The locus estimation unit15estimates the locus of the vehicle on the basis of the measured values of the left wheel speed, the right wheel speed, and the steering angle. In this case, the locus estimation unit15makes an estimation using a parameter stored in the parameter DB19.

A geometric model of estimating a locus which is used in the locus estimation device1is described below with reference toFIGS. 4 through 8.FIG. 4is an explanatory illustration of a circular movement of a geometric model. As illustrated inFIG. 4, the locus estimation device1estimates the locus of movement of a vehicle50as a circular movement with respect to a rotation center M. The vehicle50includes a left front wheel52, a right front wheel54, a left rear wheel56, and a right rear wheel58. InFIG. 4, the x axis and the y axis are orthogonal to each other. The x axis may pass through the rotation center of the left rear wheel56and the rotation center of the right rear wheel58. The y axis may pass through a middle point O1between the rotation center of the left rear wheel56and the rotation center of the right rear wheel58, and may be parallel to the direction of the body of the vehicle50. The intersection of the x axis and the y axis is referred to as an origin P0.

The axis which connects the rotation center of the left rear wheel56to the rotation center of the right rear wheel58is referred to as a rear wheel axle. The distance between the front wheels and the rear wheels of the vehicle50in the direction of the body of the vehicle is the wheel base L. The right-left wheel distance value T is a half of the distance between the left front wheel52and the right front wheel54. With the geometric model, the estimation of the locus of the vehicle50is made as the locus of the middle point O1. Therefore, the middle point O1is hereafter referred to as an estimated point O1.

In the example illustrated inFIG. 4, the estimated point O1of the vehicle50indicates the state of the rotation movement from the intersection of the x and y axes (origin P0) to a position P1where a rotation angle ω is obtained with respect to the rotation center M. Rotation radius RRC is a radius of the circular movement of the estimated point O1. A state in which the estimated point O1is on the origin P0of the xy coordinate system inFIG. 4is referred to as pre-movement, and a state in which it is in the position P1is referred to as post-movement. Left front wheel speed VFL is expressed as, for example, a movement locus of the left front wheel52from the pre-movement to post-movement state in unit time. Right front wheel speed VFR is expressed as, for example, a movement locus of the right front wheel54from the pre-movement to post-movement state in unit time. Vehicle speed VRC is expressed as a movement locus of the estimated point O1from the pre-movement to post-movement state. Translation amount TRC is an amount of translation of the estimated point O1from the pre-movement to post-movement state. A traveling angle β is made by the direction of the translation amount TRC and the y axis. It is assumed that the angle made by the left front wheel52and the right front wheel54and the direction of the body of the vehicle is constant.

<Estimation of vehicle speed VRC at estimated point O1> InFIG. 4, the left front wheel speed VFL and the right front wheel speed VFR are expressed by equation 1 from the geometric relation.
VFL=RFL×ω=sqrt((RRC+T)^2+L^2)×ω
VFR=RFR×ω=sqrt((RRC−T)^2+L^2)×ω  (equation 1)

Here, sqrt (F) indicates the square root of F. In this case, when the root mean square value of each wheel speed of the left front wheel52and the right front wheel54is root mean square wheel speed VRMS, it is expressed by following equation 2.

When equation 2 is solved for the rotation angle ω, following equation 3 is obtained.
ω=VRMS/sqrt(RRC^2+L^2+T^2)  (equation 3)

Since the root mean square wheel speed VRMS is constantly represented by a positive value, the parameter k of following equation 4 is introduced as a parameter indicating a sign.
k=1:((VFL+VFR)/2≧0)
k=−1:((VFL+VFR)/2<0)  (equation 4)

The rotation angle ω is redefined by following equation 5 using equations 3 and 4 above.
ω=k×VRMS/sqrt(RRC^2+L^2+T^2)  (equation 5)

Therefore, the vehicle speed VRC at the estimated point O1located at the center of the rear wheel axle is represented by following equation 6.

Generally, since it is hard to perform a calculation for a description with the rotation radius RRC which refers to an infinite rotation radius in straight travel, a curvature c as a reciprocal of the rotation radius is introduced. The value c is defined by following equation 7.
c=1/RRC(RRC=1/c)  (equation 7)

Following equation 8 is obtained by means of equations 6 and 7.

By means of equation 8 above, a geometrically right vehicle speed VRC at the estimated point O1is estimated from the left front wheel speed VFL and the right front wheel speed VFR.

<Estimation of front wheel direction angle γ, rotation radius RRC, and curvature c> Next, the relationship between the front wheel direction angle γ and the curvature c is explained with reference toFIGS. 5 and 6.FIG. 5is an example of a steering mechanism model.FIG. 6illustrates the relationship between the front wheel direction angle γ and the curvature c.

As illustrated inFIG. 5, with the steering mechanism model according to the present embodiment, a model is generated as a parallel linkage as a first approximation. The front wheel direction angle γ refers to an angle made between the direction of the body of the vehicle50and the left front wheel52or the right front wheel54.

As illustrated inFIG. 5, a model of a steering mechanism of an actual vehicle is generated as a parallel linkage as a first approximation. With an actual vehicle, for example, a pinion gear is operated by a steering axis extended from the steering wheel, and received by a rack gear to displace a tie rod to the left or right. It is assumed that the tie rod is connected to a vehicle hub through a knuckle arm. In the steering mechanism model according to the present embodiment, knuckle arms66and68, and a rack (tie rod64) are approximated as a parallel link where they are located at 90 degrees.

InFIG. 5, with the present steering mechanism model, it is assumed that the left front wheel52and the right front wheel54are parallel to each other, and the wheels make the same angle with the direction of the body of the vehicle. A steering axis60is extended from the steering wheel, not illustrated in the attached drawings, and rotates by, for example, a steering angle φ depending on the operation of the steering wheel. A pinion gear62converts rotation of the steering axis60into a straight line displacement by means of a rack and pinion mechanism. One end of the knuckle arm66is connected to the left front wheel52, and the other end is connected to the tie rod64at a right angle. One end of the knuckle arm68is connected to the right front wheel54, and the other end is connected to the tie rod64at a right angle. The length of the knuckle arms66and68is equal to knuckle arm length A.

Displacement amount U indicates right and left displacement with respect to the tie rod64, and indicates the amount of displacement caused by conversion by the pinion gear62when the steering axis60rotates by the steering angle φ through operation of the steering wheel. The front wheel direction angle γ indicates the angle of the left front wheel52and the right front wheel54which changes through the knuckle arms66and68when the displacement of the tie rod64is the displacement amount U.

Following equation 9 holds true through the geometric relationship in the steering mechanism model illustrated inFIG. 5.
tan(γ)=U/sqrt(A^2−U^2)  (equation 9)

The displacement amount U is proportional to the steering angle φ, and is expressed by equation 10 with factor of proportionality p.
U=p×φ(equation 10)

Following equation 11 holds true through the geometric relationship between the front wheel direction angle γ and the rotation radius RRC.
RRC=L/tan(γ)  (equation 11)

Equation 12 holds true when the curvature c is introduced as described above.

The constant μ is expressed by following equation 13.
μ=A/p(equation 13)

FIG. 6illustrates the relationship between the steering angle φ and the curvature c in the steering mechanism model illustrated inFIG. 5. That is,FIG. 6illustrates the relationship of equation 12. As illustrated inFIG. 6, expression 12 indicates a relationship different from the case where there is a simple proportional relationship between the steering angle φ and the curvature c.

FIG. 7illustrates the relationship between the front wheel direction angle γ and the rotation radius RRC. For convenience of explanation below,FIG. 7illustrates front wheel80and rear wheel82. The front wheel80is located at the middle point between the left front wheel52and the right front wheel54. The rear wheel82is located at the estimated point O1. A direction89indicates the traveling direction of the vehicle50. The direction89makes an angle of the front wheel direction angle γ with an axis86indicating the direction of the body of the vehicle50.

In this case, a rear wheel locus90is a locus of the rotation movement of the rear wheel82when the vehicle50performs a circular movement with respect to the rotation center M. Likewise, a front wheel locus92is a locus of the front wheel80. Thus, the front wheel80and the rear wheel82make circular movements of different radii. Therefore, equation 12 is not to be applied to the case where the locus of the middle point of front wheels is indicated. That is, the curvature c expressed by equation 12 above indicates the locus of the estimated point O1which is expressed using the wheel speed of the left front wheel52and the right front wheel54. Thus, equation 12 above indicates a relationship between the steering angle φ and the curvature c which is less geometrically inconsistent and is higher in accuracy.

<Formulation of moving direction with a rotation model in low speed movement> Next, the relationship between the moving direction and the amount of rotation of the vehicle50is explained with reference toFIG. 8.FIG. 8is an explanatory illustration of the relationship between the moving direction and the amount of rotation of the vehicle50. InFIG. 8, the estimated point O1moves from the origin P0(movement start point t1) of the coordinate system expressed by the x and y axes to the position P1(time t2after movement). In this case, the rotation center M is located on the x axis. The rotation angle of the vehicle50before and after a movement is expressed by the rotation angle ω. Axes105and107indicate an orthogonal coordinate system having the position P1after movement as an origin. Assume that the driving speed of the vehicle50is sufficiently low. Therefore, there is no slipping with the driven wheels and the steered wheels, the wheels are driven by rotation, and their movements approximate circular movements. In this case, circular movements of the vehicle50are expressed as movement of the position of the estimated point O1.

When the estimated point O1is located at the origin P0as the start point of a circular movement of the vehicle50, the following equation holds true through the geometric relationship illustrated inFIG. 8.
distance(P0 throughM)=distance(P1 throughM)  (equation 14)

That is, the triangle P0-P1-M is an equilateral triangle having the rotation amount ω of a moving object as a vertex. Therefore, the expression of angle P0-P1-M=angle P1-P0-M=ξ is obtained, and the following equation holds true.
ξ=(180°−ω)/2=90°−ω/2  (equation 15)

According to equation 15, the traveling angle β as an angle made by the traveling direction of the vehicle50and the y axis is expressed by following equation 16.

That is, when the rotation amount ω of a moving object is known, the traveling direction β of the moving object at time t1is determined by the physical restriction of the moving object. The arc which connects the origin P0and the origin P1is a movement locus at time t1through t2, and the traveling distance may be the vehicle speed VRC of the estimated point O1. If the chord from the origin P0to the origin P1is the translation amount TRC, the translation amount TRC is a translation component of the estimated point O1. From the geometric relationship inFIG. 8, following equation 17 holds true.
TRC=(2×VRC×sin(ω/2))/ω  (equation 17)

Therefore, a geometrically right amount of translation may be estimated as follows. Assuming that the x component of the amount of translation is a movement amount tx, and the y component is a movement amount ty, following equation 18 is obtained.
tx=TRC×sin(β)=TRC×sin(ω/2)
ty=TRC×cos(β)=TRC×cos(ω/2)   (equation 18)

The locus estimating process of the locus estimation device1is described below with reference toFIG. 9.FIG. 9is a flowchart of an example of operation of the locus estimation device1. In the locus estimation device1, the wheel speed acceptance unit11accepts a measured value of the wheel speed of each of the right and left front wheels. The steering angle acceptance unit13accepts a measured value of the steering angle of the front wheels (S121). The locus estimation unit15estimates the locus of a moving object by means of equations 1 through 18 above using the measured value of the wheel speed of each of the right and left front wheels and the measured value of the steering angle of the front wheels. In this case, the locus estimation device1estimates the locus on the basis of the wheel speed of the right and left front wheels, the steering angle, the distance between the front and rear wheels in the direction of the body of the vehicle, and a constant depending on the steering angle and the rotation radius of the moving object at the steering angle (S122).

Thus, the locus estimation device1estimates the movement of the middle point of the rotation center of the right and left rear wheels as a circular movement. The circular movement has a point on the straight line which passes through the rotation center of the two rear wheels as the center. The locus is estimated as the amount of rotation and the amount of translation of the moving object. The locus estimation device1repeats the processes in S121and S122until a pause of the system is detected (NO in S123), and terminates the processes when a pause is detected (YES in S123).

As described above, according to the locus estimation device1of the present embodiment, with regard to movement for a short time which may be described by a circular movement, the locus of the vehicle50may be estimated with high accuracy using the rotation amount ω and the amount of translation (tx, ty).

In this case, the locus estimation device1uses measured values of the wheel speed of the front wheels and the steering angle. The locus estimation device1also uses predetermined right-left wheel distance value T, wheel base L, and constant μ. Thus, when the vehicle50is assumed to perform a circular movement, the locus may be estimated with high accuracy as the movement of the estimated point O1which is the middle point of the rear wheel axle. In this case, the direction of translation of the vehicle50is estimated as a direction different from the direction of the vehicle50. For example, the rotation amount ω, the translation amount TRC, and the amount of translation (tx, ty) are calculated by means of equations 5, 8, 12, 17, and 18.

The proportion between the steering angle and the measured value of the rotation radius of a vehicle is not always determined, but a value close to the measured value may be used with the relationship between the steering angle and the rotation radius of a vehicle, and the accuracy of locus estimation may be further improved.

For a moving object having front wheels as steered wheels and a total of four front and rear wheels, the above-mentioned locus estimation device1may estimate a movement locus at a low speed according to the amount of rotation and the amount of translation using as input the wheel speed of the right and left front wheels and the steering angle. The locus estimation device may be used in, for example, automatic drive when parking or starting a vehicle, generation of a contact alarm regarding surrounding objects by measuring their positions on the basis of movement stereo using an onboard camera image, etc.

(Second embodiment) A locus estimation device150according to a second embodiment is described below. In the second embodiment, configuration elements and operations identical to those in the locus estimation device1are assigned the same reference numerals to avoid duplicate explanation. An example of the hardware configuration of the locus estimation device150is the same as the example of the locus estimation device1.

FIG. 10is a block diagram of an example of a functional configuration of the locus estimation device150according to the second embodiment of the present invention. The locus estimation device150accepts measured values of the wheel speed and the steering angle which have been measured at each specified measuring time. The locus estimation device150sets a reference time from among the measuring times, estimates the locus of the vehicle50from the set reference time to the latest measuring time, and estimates the locus from the measuring time immediately before to the latest measuring time on the basis of the estimated locus. Furthermore, the locus estimation device150updates the reference time on the basis of the locus of the vehicle50from the reference time to the latest measuring time. The reference time refers to the starting time when the starting time and the average steering angle are calculated to accumulate the wheel speed, and corresponds to the position before movement when a locus is estimated. The latest measuring time refers to the time when the measured value last input from the wheel speed acceptance unit11or the steering angle acceptance unit13is measured, and may be, for convenience, the time when input is last accepted. The time may be not only an absolute time but also a relative time which is appropriately defined.

As illustrated inFIG. 10, the locus estimation device150according to the second embodiment includes an processing unit151and a storage unit160. The processing unit151includes the wheel speed acceptance unit11, a wheel speed accumulation unit12, the steering angle acceptance unit13, a steering angle estimation unit14, the locus estimation unit15, a reference time update unit153, and a locus calculation unit155. The storage unit160includes the parameter DB19, a threshold DB162, a cumulative measured value DB164, and a prior time locus DB166.

The wheel speed accumulation unit12accumulates from the reference time for each specified time each wheel speed of the left front wheel52and the right front wheel54accepted by the wheel speed acceptance unit11, and stores a result in the cumulative measured value DB164. The steering angle estimation unit14accumulates from the reference time the steering angle accepted by the steering angle acceptance unit13, and stores the calculated cumulative steering angle and the accumulation frequency in the cumulative measured value DB164.

In this case, the wheel speed acceptance unit11accepts the wheel speed of each of the right and left wheels measured at each specified time. The wheel speed accumulation unit12reads the wheel speed cumulative values of the right and left wheels up to the prior measuring time stored in the cumulative measured value DB164, adds the wheel speed last input from the wheel speed acceptance unit11, and writes back the totaled value to the cumulative measured value DB164. Furthermore, the wheel speed accumulation unit12outputs the cumulative value of the wheel speed to the locus estimation unit15. In addition, the wheel speed accumulation unit12judges whether or not the vehicle50has stopped from the level of the wheel speed at the latest measuring time, and outputs the existence of a movement to the steering angle estimation unit14.

The steering angle acceptance unit13accepts the measured value of the steering angle measured at each specified time. When it is judged that the vehicle50has not stopped, the steering angle estimation unit14reads the steering angle cumulative value up to the prior measuring time stored in the cumulative measured value DB164, and adds the steering angle last input from the steering angle acceptance unit13. When it is judged that the vehicle50has not stopped, the steering angle estimation unit14reads the accumulation frequency from the cumulative measured value DB164and adds 1 to the read value, and writes back the steering angle cumulative value and the accumulation frequency to the cumulative measured value DB164.

The locus estimation unit15estimates the locus of the vehicle50on the basis of the cumulative value of the wheel speed stored in the cumulative measured value DB164and the average steering angle depending on the cumulative steering angle and the accumulation frequency. The process of the locus estimation unit15is performed using the cumulative value of wheel speed and the average value of the steering angle instead of the wheel speed and the steering angle with the locus estimation device1according to the first embodiment of the present invention.

On the basis of the estimation result of the locus estimation unit15, the reference time update unit153updates the reference time when it is judged that the reference time is to be updated. Details of the judgment on the update of the reference time are described later.

The locus calculation unit155calculates the locus of the vehicle50on the basis of the locus estimated by the locus estimation unit15and the locus stored in the prior time locus DB166. The calculated rotation amount ω and the amount of translation are stored in the prior time locus DB166.

The threshold DB162is a database which stores thresholds for use in the process of the locus estimation unit15, the process of the reference time update unit153, and the process of the locus calculation unit155.FIG. 11is an example of a threshold table182. The threshold table182is an example of the data structure of the threshold DB162. As illustrated inFIG. 11, the threshold table182includes a movement judgment threshold TH1, a movement frequency threshold TH2, a rotation judgment threshold THω, and a reference time update threshold THK.

The movement judgment threshold TH1is a threshold for the wheel speed for judgment of existence of movement, and is, for example, a real number representing kilometers per hour. The movement frequency threshold TH2is a threshold for hysteresis to prevent chattering of a stop flag STOP_F described later, and is an integer value corresponding to a frequency judged as a stop. The rotation judgment threshold THω is a threshold for judgment of an existence of a rotation, and is, for example, a real number representing degrees. The reference time update threshold THK is a threshold for judgment as to whether or not a reference time is to be updated, and is, for example, a real number representing centimeters.

FIG. 12is an example of a cumulative measured value table184. The cumulative measured value table184is an example of a data structure of the cumulative measured value DB164. As illustrated inFIG. 12, the cumulative measured value table184includes a cumulative left wheel speed CUMVL, a cumulative right wheel speed CUMVR, a stop counter SCOUNT, a stop flag STOP_F, a cumulative steering angle amount CUMφ, and an accumulation frequency Nφ. The cumulative left wheel speed CUMVL is obtained by accumulating the left wheel speed measured at each specified time from the reference time, and is, for example, a real number representing meters per second. The cumulative right wheel speed CUMVR is obtained by accumulating the right wheel speed measured at each specified time from the reference time, and is, for example, a real number representing meters per second. The stop counter SCOUNT is a count value used in judging movement, and is an integer value. The stop flag STOP_F is a discriminant value used in judging a stop, and is, for example, set to “1” when a stop is confirmed, and to “0” when no stopping is confirmed. The cumulative steering angle amount CUMφ is obtained by accumulating the steering angle φ measured at each specified time, and is, for example, a real number representing degrees. The accumulation frequency Nφ is an accumulation frequency of the steering angle φ, and is an integer value.

FIG. 13is an example of the prior time locus table186. The prior time locus table186is an example of a data structure of the prior time locus DB166. As illustrated inFIG. 13, the prior time locus table186includes a prior time rotation amount αp from the reference time to the measuring time immediately before the latest measuring time, a prior time x translation amount qxp, and a prior time y translation amount qyp. The prior time rotation amount αp is, for example, a real number representing degrees. The prior time x translation amount qxp and the prior time y translation amount qyp are, for example, real numbers representing meters.

FIG. 14is an explanatory illustration of the influence of accumulated error.FIG. 14illustrates the vehicle50moving on a road surface170. Locus172indicates actual movement of the vehicle50. An estimated locus174continuously indicates the locus at each specified time estimated by the locus estimation device150as a result of updating the reference time at each measuring time. In the example illustrated inFIG. 14, the error between the locus172and the estimated locus174increases each time a measurement is performed, and reaches, for example, an error176. It is considered that the error is caused by measuring the wheel speed, the steering angle, etc. as digital values at each specified time, and approximating the locus of the vehicle50. Thus, to eliminate error caused by accumulation, a reference time is set in the present embodiment to estimate the locus to some distance from the reference time.

FIGS. 15 and 16are explanatory illustrations of a locus estimating method according to the present embodiment. As illustrated inFIG. 15, measuring time estimated positions200-1,200-2, . . . (which may be collectively referred to as measuring time estimated positions200) indicate the estimated positions of the vehicle50at each specified wheel speed measuring time. A locus204is a curve which connects the measuring time estimated positions200, and is an estimated movement locus of the vehicle50. In this case, the reference time estimated positions202-k1,202-k2, . . . indicate the estimated positions of the vehicle50at the reference time. A reference time update threshold THK1indicates a distance as a threshold for an update of the reference time. In the present embodiment, when the estimated translation distance from the reference time is more than the reference time update threshold THK1, the latest measuring time is defined as a new reference time. Furthermore, the estimated position at each measuring time is estimated on the basis of the cumulative wheel speed from the latest reference time to the latest measuring time, and the average steering angle. The method of calculating an estimated position output corresponding to each measuring time is described later.

As illustrated inFIG. 16, a measuring time estimated position208-1is a reference time estimated position209-k1. That is, the reference time is a measuring time corresponding to the measuring time estimated position208-1. Next, the locus estimation unit15estimates the locus between the measuring time estimated position208-1and the measuring time estimated position208-2of the vehicle50on the basis of the cumulative wheel speed from the reference time up to the measuring time corresponding to the measuring time estimated position208-2and the average steering angle. A translation amount210-1is an estimated amount of translation between the measuring time estimated position208-1and the measuring time estimated position208-2. When the translation amount210-1is not more than the reference time update threshold THK1, the locus of the vehicle50is estimated at the next measuring time on the basis of the cumulative wheel speed and the average steering angle from the reference time, thereby obtaining a measuring time estimated position208-3. In the example inFIG. 16, a translation amount210-4estimated at a measuring time estimated position208-5is more than reference time update threshold THK1. In this case, the measuring time corresponding to a reference time estimated position209-k2is an updated reference time.

FIG. 17is an explanatory illustration of reducing cumulative error by reference time selection according to the second embodiment of the present invention. As illustrated inFIG. 17, for example, input of the wheel speed and the steering angle is performed at times corresponding to the measuring time estimated positions200-1,200-2, . . . . The reference time is updated when the estimated amount of translation from the reference time immediately before is more than the reference time update threshold THK1. The estimation of a locus is performed on the basis of the measurement result of the wheel speed and the steering angle from the reference time to the measuring time. The output estimation result is calculated as a difference between the estimation result from the reference time to the prior measuring time and the estimation result from the reference time to the latest measuring time.

The operation of the locus estimation device150according to the second embodiment is explained with reference toFIGS. 18 through 21.FIG. 18is a flowchart of the main process of the locus estimation device150. As illustrated inFIG. 18, in the locus estimation device150, the wheel speed accumulation unit12accumulates the measured value of the wheel speed accepted by the wheel speed acceptance unit11, and stores the value in the cumulative measured value DB164. When the wheel speed accumulation unit12judges that the vehicle50is moving, the steering angle estimation unit14accumulates the measured value of the steering angle accepted by the steering angle acceptance unit13and calculates the average steering angle, and stores the cumulative value in the cumulative measured value DB164(S221). Details of the process in S221are described later.

The locus estimation unit15estimates the amount of rotation and the amount of translation as in the first embodiment on the basis of the cumulative wheel speed calculated by the wheel speed accumulation unit12and the average steering angle calculated by the steering angle estimation unit14(S222). Details of the process in S222are described later.

The reference time update unit153updates the reference time (S224) when the estimated amount of translation is more than the reference time update threshold THK1(YES in S223). When the estimated amount of translation is not more than the reference time update threshold THK1(NO in S223), the reference time update unit153performs the process in S225.

The locus calculation unit155calculates the amount of rotation and the amount of translation from the prior time on the basis of the information stored in the prior time locus table186, the estimated rotation angle ω, and the amount of translation dx and dy (S225). The processing unit151judges whether or not there has been an operation etc. for termination of the system. If there has not been such an operation (NO in S226), the processing unit151repeats the processes from S221. If there has been such an operation (YES in S226), the processing unit151terminates the locus estimating process.

FIG. 19is a flowchart of the wheel speed accumulating process of the locus estimation device150. The process inFIG. 19indicates the details of the process in S221. As illustrated inFIG. 19, the wheel speed accumulation unit12performs the following operation on the left front wheel speed VFL (t), the right front wheel speed VFR (t), the cumulative left wheel speed CUMVL, and the cumulative right wheel speed CUMVR at measuring time t accepted by the wheel speed acceptance unit11(S231).
CUMVL=CUMVL+VFL(t)
CUMVR=CUMVR+VFR(t)   (equation 19)

The wheel speed accumulation unit12updates the cumulative measured value table184by writing back to the cumulative measured value table184the calculated cumulative left wheel speed CUMVL and the cumulative right wheel speed CUMVR, and outputs it to the locus estimation unit15. The wheel speed accumulation unit12passes control to the judgment of movement inFIG. 20.

FIG. 20is a flowchart of the movement judging process. The wheel speed accumulation unit12sets the initial values of the stop counter SCOUNT and the stop flag STOP_F to “0”. When the maximum value in the right and left wheel speeds VFL (t) and VFR (t) at the latest measuring time is smaller than the movement judgment threshold TH1(YES in S241), the wheel speed accumulation unit12adds “1” to the stop counter SCOUNT, and updates the cumulative measured value table184(S242). When the stop counter SCOUNT is larger than the movement frequency threshold TH2(YES in S243), the wheel speed accumulation unit12sets stop flag STOP_F=1 (S244), and passes control to the steering angle accumulating process. The wheel speed accumulation unit12passes control to the steering angle accumulating process when the stop counter SCOUNT is not more than the movement frequency threshold TH2(NO in S243).

The wheel speed accumulation unit12passes control to the process in S245when the maximum value in the right and left wheel speeds VFL (t) and the VFR (t) at the latest measuring time is not less than the movement judgment threshold TH1(NO in S241). In S245, the wheel speed accumulation unit12sets stop counter SCOUNT=0 and stop flag STOP_F=0, updates the cumulative measured value table184(S245), and passes control to the steering angle accumulating process. Thus, in the movement judgment, the stop flag STOP_F is output as a judgment result to the cumulative measured value table184.

FIG. 21is a flowchart of the steering angle calculating process. The initial value of the cumulative steering angle amount CUMφ and the initial value of the accumulation frequency Nφ are “0”. The steering angle estimation unit14estimates a steering angle on the basis of a steering angle accepted by the steering angle acceptance unit13at, for example, each specified time from the steering angle sensor35of the steering attached to the vehicle50. The steering angle estimation unit14reads the stop flag STOP_F from the cumulative measured value table184, and returns control to the process inFIG. 18when the read value is “1” (YES in S251).

When the stop flag is “0” (NO in S251), the steering angle estimation unit14adds the steering angle φ(t) at the measuring time t to the cumulative steering angle amount CUMφ, adds “1” to the accumulation frequency Nφ, and updates the cumulative measured value table184(S252). That is, the steering angle estimation unit14reads the cumulative steering angle amount CUMφ stored in the cumulative measured value table184, and adds the input steering angle φ(t), thereby obtaining the average steering angle in the period when the vehicle50is moving.

The steering angle estimation unit14sets average steering angle φa=CUMφ/Nφ (S253). When Nφ=0, φa may be set to φ(t) (φa=φ(t)). Thus, the steering angle estimation unit14accumulates and averages the steering angle only when the vehicle50is moving, calculates the average steering angle φa, and outputs the result to the locus estimation unit15.

The process in S222performed by the locus estimation unit15is described below in detail. Assume that the cumulative wheel speed and the average steering angle from the current reference time to the latest measuring time are the cumulative left wheel speed CUMVL, the cumulative right wheel speed CUMVR, and the average steering angle φa. In this case, the curvature c of rotation of the vehicle50is obtained by means of following equation 20 by replacing the steering angle φ in equation 12 with the average steering angle φa.
c=φa/(L×sqrt(μ^2−φa^2))  (equation 20)

Also assume that the root mean square value of the cumulative wheel speed is VRMS, it is obtained by means of following equation 21 using the cumulative left wheel speed CUMVL and the cumulative right wheel speed CUMVR.
VRMS=sqrt((CUMVL^2+CUMVR^2)/2)  (equation 21)

Thus, the vehicle speed VRC at the estimated point O1of the vehicle50from the current reference time to the latest measuring time is obtained by means of following equation 22.
VRC=k×VRMS/sqrt(c^2×(L^2+T^2)+1)   (equation 22)

In the equation, k is a parameter indicating the sign of the moving speed, and is defined by following equation 23.

The rotation angle ω of the vehicle50is calculated by means of following equation 24.
ω=c×VRC(equation 24)

The locus estimation unit15calculates the rotation amount α and the translation movement amount (qx, qy) of the vehicle50from the current reference time to the measuring time immediately before by means of equations 22 and 24. Practically, the relationship indicated by following equation 25 holds true.
α=ω  (equation 25)

Furthermore, the vehicle speed VRC indicates the length of the arc when the action of the vehicle50from the current reference time to the latest measuring time is a circular movement. When the length of the chord corresponding to the arc is the translation amount TRC, equation 26 holds true.

In the equation, the rotation judgment threshold THω is a threshold for judgment as to whether or not the rotation angle ω is very close to 0. Using the translation amount TRC, the translation movement amount (qx, qy) of the vehicle50is obtained by means of following equation 27.
qx=TRC×sin(ω/2)
qy=TRC×cos(ω/2)   (equation 27)

The locus estimation unit15outputs the above-mentioned rotation amount α and translation movement amount (qx, qy) to the locus calculation unit155, and outputs the translation amount TRC to the reference time update unit153.

The process of the locus calculation unit155is further explained below. The locus calculation unit155calculates the rotation amount α and the translation movement amount (qx, qy) on the basis of the cumulative left wheel speed CUMVL, the cumulative right wheel speed CUMVR, and the average steering angle φa, and outputs them outside the locus estimation device150.

<Calculating amount of rotation and amount of translation in one time period> As illustrated inFIG. 13, the prior time locus table186stores the prior time rotation amount αp, the prior time x translation amount qxp, and the prior time y translation amount qyp. The prior time refers to a measuring time immediately before the latest measuring time. In this case, the rotation amount α1and the translation movement amount (qx1, qy1) from the prior time to the latest measuring time are obtained by means of following equation 28.
α1=α−αp
qx1=cos(αp)×(qx−qxp)−sin(αp)×(qy−qyp)
qy1=sin(αp)×(qx−qxp)+cos(αp)×(qy−qyp)   (equation 28)
The locus calculation unit155outputs the rotation amount α1and the translation movement amount (qx1, qy1) outside the locus estimation device150. The locus calculation unit155also stores the rotation amount α and the translation movement amount (qx, qy) as the rotation amount αp and the translation movement amount (qxp, qyp) in the prior time locus table186for preparation of the process at the next measuring time.

The process of the reference time update unit153is further described below. The reference time update unit153receives the translation amount TRC estimated by the locus estimation unit15, compares it with the reference time update threshold THK1, and updates the reference time depending on the result of the comparison.

The update of the reference time is performed as follows. That is, when following equation 29 is satisfied, the reference time is updated as the latest measuring time.
|TRC|>THK1  (equation 29)
When equation 29 is satisfied, the amount of movement of the vehicle50from the reference time exceeds a specified amount.

When the reference time update unit153updates the reference time, the following settings are performed in the cumulative measured value DB164.
CUMVL=0
CUMVR=0
CUMφ=0
Nφ=0   (equation 30)
With regard to the prior time locus DB166, the following settings equation 31 are performed in the prior time locus table186when the reference time is updated.
αp=0
qxp=0
gyp=0   (equation 31)

As described above, the locus estimation device150according to the second embodiment estimates the locus of a moving object by a circular movement performed only by a movement for a short time, accumulates the amount of rotation and the amount of translation estimated for a short time, thereby estimating the movement locus of any movement of the moving object. A reference time is set for the locus estimation device150as a reference of an estimation of a locus. The reference time is not updated at each measuring time, but is updated when a specified condition is satisfied. Until the specified condition is satisfied, the locus from the reference time to the latest measuring time is calculated on the basis of the wheel speed and the steering angle measured at each specified time from the reference time. In this case, a cumulative value from the reference time to the latest measuring time is used as the wheel speed. As the steering angle, an average value from the reference time to the latest measuring time is used. If the amount of translation of the vehicle50in the calculated locus exceeds the reference time update threshold THK1, the reference time is updated at the latest measuring time. Furthermore, the locus estimation device150outputs as a locus the amount of rotation and the amount of translation on the basis of the difference between the locus from the reference time to the latest measuring time and the locus from the reference time to the measuring time immediately before the latest measuring time.

As described above, the locus estimation device150does not update the reference time at each measuring time in time series, but fixes the time within a specified condition, and updates only measuring times in a time series. When the estimated amount of translation from the reference time to the latest measuring time exceeds a specified reference time update threshold THK1, the amount of rotation and the amount of translation are estimated, and the latest measuring time is updated as a new reference time. Thus, by configuring the translation distance in estimating a locus as longer than a specified distance, the occurrence of accumulated error by accumulating a rotation angle and an amount of translation may be prevented. Thus, if a locus is described as a single circular movement or a linear movement, the reference time is not updated, and the reference time may be updated when the type of movement is changed. Therefore, since the range of a single movement evaluates the cumulative value of a wheel speed over a long distance in a period, the error included in the accumulated wheel speed may be reduced, and the accuracy of the estimation value of the rotation and the translation may be improved. Thus, for example, a measured value is discretely acquired, and error caused by adding the locus calculated by approximating the locus by a circular movement may be reduced, thereby estimating the locus of a moving object with high accuracy.

The amount of rotation and the amount of translation are estimated at each measuring time, and are converted into an amount of rotation and an amount of translation from the measuring time immediately before, and output externally. By outputting the deviation between the locus up to the measuring time immediately before and the locus up to the latest measuring time, a locus is estimated on the basis of the estimation value from the reference time. Therefore, cumulative error is not included.

In addition, when the moving speed of the vehicle50is low, the amount of movement in a specified time is small. Therefore, it is considered that error of an amount of movement may develop. However, the locus estimation device150may reduce the error by performing estimation for a long distance. Accordingly, the locus estimating method of the locus estimation device150may be used for the vehicle50driven at a low speed. Furthermore, although there is movement of the vehicle50with a change in the time series, the amount of rotation and the amount of translation may be estimated with high accuracy.

(Third embodiment) Described below is a locus estimation device250according to a third embodiment of the present invention. In the third embodiment, configuration elements and operations similar to those of the locus estimation device1or the locus estimation device150are assigned the same reference numerals, and duplicate explanation is omitted. An example of a hardware configuration of the locus estimation device250is similar to the example of the locus estimation device1.

FIG. 22is a block diagram of an example of a functional configuration of the locus estimation device250according to the third embodiment. The locus estimation device250accepts measured values of the wheel speed and the steering angle which have been measured at each specified measuring time. The locus estimation device250sets a reference time from among the measuring times as with the locus estimation device150according to the second embodiment, estimates the locus from the latest reference time to the latest measuring time, and estimates the locus from the measuring time immediately before to the latest measuring time on the basis of the estimated locus. Furthermore, the locus estimation device250updates the reference time on the basis of the locus of the vehicle50from the reference time. The locus estimation device250differs from the locus estimation device150according to the second embodiment in its reference time updating method.

The locus estimation device250includes an processing unit251and a storage unit260. As compared with the processing unit151in the locus estimation device150according to the second embodiment, the processing unit251includes a reference time update unit253instead of the reference time update unit153, and further includes a cumulative movement amount estimation unit255.

The cumulative movement amount estimation unit255calculates backward the cumulative wheel speed from the locus estimated by the locus estimation unit15, and outputs the result to the reference time update unit253. The reference time update unit253updates the reference time when it is judged that the reference time is to be updated on the basis of the estimation result by the locus estimation unit15and the calculation result by the cumulative movement amount estimation unit255. Details of the judgment on the update of the reference time are described later.

The storage unit260includes a threshold DB262in addition to the parameter DB19, the cumulative measured value DB164, and the prior time locus DB166.FIG. 23is an example of a threshold table275. The threshold table275is an example of the data structure of data stored in the threshold DB262. The threshold table275includes a cumulative wheel speed difference threshold THK2in addition to each parameter of the threshold table182explained with regard to the second embodiment. The cumulative wheel speed difference threshold THK2indicates the amount of maximum wheel speed difference with the real number not updated, and is a real number representing, for example, centimeters.

FIGS. 24 and 25are explanatory illustrations of a locus estimating method according to the present embodiment. As illustrated inFIG. 24, the measuring time estimated positions200-1,200-2, . . . (also referred to collectively as measuring time estimated positions200) indicate the estimated positions of the vehicle50at each specified wheel speed measuring time. The locus204is a curve which connects the measuring time estimated positions200, and is an estimated movement locus of the vehicle50. In this case, the reference time estimated positions270-k1,270-k2, . . . indicate the estimated positions of the vehicle50. According to the present embodiment, when the wheel speed calculated backward from the estimated distance of translation from the reference time and the cumulative wheel speed exceed the cumulative wheel speed difference threshold THK2, the latest measuring time is defined as a new reference time. The estimated position at each measuring time is estimated on the basis of the cumulative wheel speed from the latest reference time to the latest measuring time, and the average steering angle. The method of calculating the estimated position output corresponding to each measuring time is similar to the method according to the second embodiment.

FIG. 25is an explanatory illustration of reducing cumulative error by reference time selection according to the present embodiment. As illustrated inFIG. 25, for example, input of the wheel speed and the steering angle is performed at times corresponding to the measuring time estimated positions200-1,200-2, . . . . The reference time is, for example, updated when the difference between the wheel speed calculated backward from the estimated amount of translation from the reference time estimated position270-k1to the measuring time estimated position200-n1and the cumulative wheel speed stored in the cumulative measured value table184exceeds the cumulative wheel speed difference threshold THK2. The estimation of a locus is performed on the basis of the measurement results of the wheel speed and the steering angle from the reference time to the measuring time and the steering angle. The estimation result to be output is calculated on the basis of the estimation result from the reference time to the prior measuring time and the estimation result from the reference time to the latest measuring time.

The operation of the locus estimation device250according to the third embodiment is described below with reference toFIG. 26.FIG. 26is a flowchart of the main process of the locus estimation device250. As illustrated inFIG. 26, in the locus estimation device250, the wheel speed accumulation unit12accumulates the measured values of the wheel speed accepted by the wheel speed acceptance unit11, and stores the accumulated value in the cumulative measured value DB164. When wheel speed accumulation unit12judges that the vehicle50is moving, the steering angle estimation unit14accumulates the measured values of the steering angle accepted by the steering angle acceptance unit13, calculates an average steering angle, and stores the cumulative value in the cumulative measured value DB164(S281). The process in S281is similar to the process in S221according to the second embodiment.

The locus estimation unit15estimates the amount of rotation and the amount of translation as in the first and second embodiments on the basis of the cumulative wheel speed stored in the cumulative measured value DB164as in the cumulative measured value table184and the calculated average steering angle (S282). The details of the process in S282are similar to the process in S222according to the second embodiment.

The cumulative movement amount estimation unit255calculates backward the wheel speed cumulative value of a left front wheel and a right front wheel from the amount of rotation and the amount of translation estimated in S282(S283). The details of the process are described later.

When the estimated amount of translation is more than the reference time update threshold THK1, or when the absolute value of the difference between the calculated wheel speed cumulative value and the measured wheel speed cumulative value is more than the cumulative wheel speed difference threshold THK2(YES in S284), the reference time update unit253updates the reference time (S285). When the estimated amount of translation is not more than the reference time update threshold THK1and the absolute value of the difference between the calculated wheel speed cumulative value and the measured wheel speed cumulative value is not more than the cumulative wheel speed difference threshold THK2(NO in S284), the reference time update unit253passes control to S286.

The locus calculation unit155calculates the amount of rotation and the amount of translation from the prior time on the basis of the prior time locus table186, the estimated rotation angle α, and the amount of translation (dx, dy) (S286). The processing unit251judges whether or not an operation etc. for termination of the system has been performed. If there has not been such an operation (NO in S287), then the processing unit251repeats the processes from S281. If there has been such an operation (YES in S286), then the processing unit251terminates the locus estimating process.

Details of the processes in S283and S284are described below. The locus estimation device250performs the cumulative operations on the wheel speed and the steering angle as with the locus estimation device150, and the locus estimation unit15calculates the rotation amount α of the vehicle50from the reference time immediately before to the latest measuring time, and the amount of translation (qx, qy). The locus estimation unit15outputs the rotation amount α and the translation movement amount (qx, qy) to the locus calculation unit155, and outputs the rotation amount α, the wheel speed VRC, and the translation amount TRC to the cumulative movement amount estimation unit255.

In the third embodiment, the cumulative movement amount estimation unit255receives the rotation amount α, the translation movement amount (qx, qy), and the translation amount TRC from the reference time to the latest measuring time, and calculates each cumulative wheel speed of the left front wheel52and the right front wheel54. The cumulative movement amount estimation unit255compares the calculated cumulative wheel speed with the cumulative left wheel speed CUMVL and the cumulative right wheel speed CUMVR, and outputs the difference and the translation movement amount (qx, qy) to the reference time update unit253.

<Calculation of cumulative wheel speeds of right and left front wheels> Following equation 32 holds true from the basic equation of rotation movement relating to the estimated rotation amount α, vehicle speed VRC, and curvature c of the vehicle50from the reference time to the latest measuring time.
α=c×VRC(equation 32)
Therefore, the rotation radius RRC at the estimated point O1is expressed by following equation 33.
RRC=1/c=VRC/α(equation 33)

Left radius RFL and right radius RFR as the respective rotation radii of the left front wheel52and the right front wheel54are expressed by following equation 34.
RFL=sqrt((RRC+T)^2+L^2)
RFR=sqrt((RRC−T)^2+L^2)   (equation 34)

Therefore, estimated left wheel speed EVL and estimated right wheel speed EVR of the respective wheel speeds of the left front wheel52and the right front wheel54are expressed by following equation 35.

EVL=RFL×α=sqrt⁡((RRC+T)^2+L^2)×α=sqrt⁡((VRC/α+T)^2+L^2)×α=k×sqrt⁡((VRC+α×T)^2+(α×L)^2)⁢⁢EVR=RFR×α=sqrt⁡((RRC-T)^2+L^2)×α=sqrt⁡((VRC/α-T)^2+L^2)×α=k×sqrt⁡((VRC-α×T)^2+(α×L)^2)(equation⁢⁢35)
where k indicates a parameter which expresses the sign of a moving speed, and is defined as shown below.

<Difference between wheel speed cumulative value and estimated wheel speed cumulative value> A difference value DIFF, which is stored in the cumulative measured value table184, between the cumulative left wheel speed CUMVL and cumulative right wheel speed CUMVR on the basis of the measured values, and the estimated left wheel speed EVL and estimated right wheel speed EVR, is defined by equation 37.
DIFF=MIN(|CUMVL−EVL|,|CUMVR−EVR|)   (equation 37)
The cumulative movement amount estimation unit255outputs the difference value DIFF to the reference time update unit253.

<Judging reference time update> The reference time update unit253receives the estimated translation amount TRC and the difference value DIFF, judges the necessity of a reference time update, and updates the reference time as necessary. The reference time update unit253updates the reference time when following equation 38 is satisfied.
TRC>THK1 or |DIFF|>THK2  (equation 38)

When the reference time update unit253updates the reference time, equations 30 and 31 are set in the cumulative measured value table184as in the second embodiment.

As explained above, the locus estimation device250according to the third embodiment has a similar effect to that of the locus estimation device150according to the second embodiment. Furthermore, since judgment as to a real number update is performed by introducing the difference value DIFF, a locus may be estimated with accuracy although the type of movement has been changed with a smaller translation amount TRC. That is, the cumulative wheel speed is calculated backward from the estimated amount of translation, and compared with the cumulative wheel speed on the basis of the measured value, thereby judging a case where movement of the vehicle50is not described by a circular movement. Therefore, when movement of the vehicle50is not described by a circular movement, the reference time is updated, and cumulative error may be reduced. The reference time update unit253may judge only on the basis of the difference value DIFF, without the reference time update threshold THK1.

(Variation example) A variation example based on each of the first through third embodiments is described below. The present variation example is an example of the process of the locus estimation unit15according to the first through third embodiments. In the present variation example, configuration elements and operations similar to those of the locus estimation device1, the locus estimation device150or the locus estimation device250according to the first through third embodiments are assigned the same reference numerals to avoid duplicate explanation. An example of the hardware configuration of the locus estimation device in the present variation example is similar to the example of the locus estimation device1.

Described below is the process of the locus estimation unit15according to the present variation example. In the present variation example, the locus estimation unit15estimates a locus on the basis of the wheel speed and the steering angle, or the wheel speed cumulative value and the average steering angle. The process on the basis of the wheel speed cumulative value and the average steering angle is explained below as with the process according to the second or third embodiment, but a similar method may also be applied to the first embodiment.

In the present variation example, equations 20, 33, and 34 according to the second embodiment are used as described below for comprehensibility.
c=φa/(L×sqrt(μ^2−φa^2))  (equation 20)
RRC=1/c(equation 33)
RFL=sqrt((RRC+T)^2+L^2)
RFR=sqrt((RRC−T)^2+L^2)   (equation 34)

Assuming that the angular velocity is ω in the estimated circular movement, the left front wheel speed VFL of the left front wheel52, and the right front wheel speed VFR of the right front wheel54, are obtained by following equation 39.
VFL=RFL×ω
VFR=RFR×ω(equation 39)

When equation 39 is expressed by a matrix expression, it is expressed by following equation 40.

When equation 40 is solved by the least squares method using a pseudo-inverse matrix, equation 41 is solved.

Equation 41 is solved and equation 42 is obtained.

Therefore, the vehicle speed VRC of the vehicle50at the estimated point O1is expressed by following equation 43.

In the second or third embodiment, the left front wheel speed VFL and the right front wheel speed VFR are obtained by means of the cumulative left wheel speed CUMVL and the cumulative right wheel speed CUMVR. Therefore, equation 43 is transformed as following equation 44.
VRC=(sqrt((1+c×T)^2+c×L^2)×CUMVL+sqrt((1−c×T)^2+c×L^2)×CUMVR)/(2×((c^2×(L^2+T^2)+1))   (equation 44)

Next, the rotation amount α and the translation movement amount (qx, qy) of the vehicle50from the reference time and the latest measuring time are calculated from the vehicle speed VRC and the rotation amount ω above. Practically, they are obtained by equations 26 and 27 according to the second embodiment.

The rotation amount α and the translation movement amount (qx, qy) calculated as described above are output to the locus calculation unit155. When they are applied to the third embodiment, the rotation amount α, the vehicle speed VRC, and the translation amount TRC are output to the cumulative movement amount estimation unit255. When the present variation example is applied to the locus estimation device1according to the first embodiment, equations 1, 7, and 12 may replace equations 20, 33, and 34.

As explained above, the present variation example may be the variation example according to the first through third embodiments. According to the present variation example, for example, although there may be a variance in value due to error between the measured left front wheel speed VFL and right front wheel speed VFR, a locus may be estimated with high accuracy through use of the least squares method.

(Fourth embodiment)Described below is a locus estimation device450according to a fourth embodiment. In the fourth embodiment, configuration elements and operations similar to those of the locus estimation device1, the locus estimation device150, or the locus estimation device250are assigned the same reference numerals to avoid duplicate explanation.

The locus estimation device450according to the fourth embodiment is connected to a detection device410through a communication network430.FIG. 27illustrates a configuration of the locus estimation device450and the detection device410according to the fourth embodiment.

As illustrated inFIG. 27, the detection device410is installed in a vehicle400. The detection device410detects the left front wheel speed VFL, the right front wheel speed VFR, and the cumulative steering angle amount CUMφ using a wheel speed sensor402and a steering angle sensor404provided for the vehicle400, and transmits them to the locus estimation device450through the communication network430. The locus estimation device450receives a measured value from the detection device410, and estimates the locus of the vehicle400.

The detection device410includes a CPU412, memory414, a wheel speed acquisition I/F416, a steering angle acquisition I/F418, an output I/F420, and a transmission/reception device422. The CPU412is an processor which controls the operation of the detection device410. The CPU412performs a controlling process as the detection device410by, for example, reading a control program stored in advance in the memory414and executing the program. The memory414is, for example, a read-only storage device, a storage device allowing reading and writing of data at any time, etc. The wheel speed acquisition I/F416is an interface device which performs management when accepting the wheel speeds of the right and left front wheels from the wheel speed sensor402. The steering angle acquisition I/F418is an interface device which performs management when accepting from the steering angle sensor404a turning angle of a steering wheel which changes the direction of the front wheels of a vehicle. The output I/F420is an interface device which performs management when outputting a locus estimation result. The transmission/reception device422is a transmission/reception device which performs communications with the locus estimation device450through the communication network430.

The locus estimation device450includes a CPU452, memory454, an input device456, an output device458, and a transmission/reception device460. The CPU452is an processor which controls the operation of the locus estimation device450. The CPU452performs control as the locus estimation device450by, for example, reading a control program stored in advance in the memory454, and executing the program. The memory454is, for example, a read-only storage device, a storage device allowing reading and writing of data at any time, etc. The input device456accepts a wheel speed, a steering angle, etc. from the detection device410. The output device458outputs a result. The transmission/reception device460communicates with the detection device410through the communication network430. The locus estimation device450may be the locus estimation device1, the locus estimation device150, or the locus estimation device250according to the first through fourth embodiments or variation examples.

With the above-mentioned configuration, the locus estimation device450may estimate a locus of the vehicle400through the communication network430on the basis of a measured value measured by the vehicle400. The locus estimation device450may obtain a similar effect by using any of the first through third embodiments. According to one embodiment, the movement locus of a moving object may be estimated with high accuracy.

Described below is an example of a computer commonly applied to perform an operation of a locus estimating method according to the first through fourth embodiments and variation examples.FIG. 28is a block diagram of an example of a hardware configuration of a standard computer. As illustrated inFIG. 28, a computer500includes a central processing unit (CPU)502, memory504, an input device506, an output device508, an external storage device512, a medium drive device514, a network connecting device, etc., connected through a bus510.

The CPU502is a processor which controls the operation of the entire computer500. The memory504is a storage unit which stores in advance a program for control of the operation of the computer500, and which is used by the computer500as a work area as necessary when executing the program. The memory504is, for example, random access memory (RAM), read only memory (ROM), etc. The input device506is a device which acquires input of various types of information from a computer user corresponding to the operation contents when the computer user operates the input device506, and transmits the acquired input information to the CPU502, and a keyboard device, a mouse device, etc. The output device508outputs a process result from the computer500, and includes a display device etc. For example, a display device displays text and an image depending on display data transmitted by the CPU502.

The external storage device512is, for example, a storage device such as a hard disk etc., and stores various types of control programs executed by the CPU502, acquired data, etc. The medium drive device514is a device which writes and reads data to and from a portable recording medium516. The CPU502may perform various controlling processes by reading and executing a specified control program stored in the portable recording medium516through the medium drive device514. The portable recording medium516may be, for example, a compact disc (CD)-ROM, a digital versatile disc (DVD), universal serial bus (USB) memory, etc. A network connection device518is an interface device which performs management for communication of various data performed with an external unit by cable or wireless. The bus510is a communication path which connects each of the above-mentioned devices for communication of data.

A program for directing a computer to perform a locus estimating method according to the first through fourth embodiments described above is stored in, for example, the external storage device512. The CPU502reads a program from the external storage device512, and allows the computer500to perform an operation of estimating a locus. In this case, a control program for directing the CPU502to perform the process of estimating a locus is first generated and stored in the external storage device512. Then, a specified instruction is provided to the CPU502from the input device506, and the control program is read from the external storage device512and executed. Furthermore, the program may be stored in the portable recording medium516.

The present invention is not limited to the embodiments described above, but may have various configurations or embodiments within the scope of the gist of the present invention.