Abstract:
A sensing device for detecting a vehicle&#39;s skid, an attitude and a speed with lane markers. This sensing device allows sensors mounted on the vehicle to detect lane markers arranged on the lane center along a road. The lane markers are detected in a magnetic, electric, or optical manner. Based on outputs of the sensors, a movement of the vehicle is measured. Two sensors each are provided on front and rear of the vehicle. Four outputs from the respective sensors are calculated based on given equations (additions and subtractions) so that a skid amount of the vehicle from the lane center, the attitude and the speed of the vehicle can be found. This simple construction formed by the sensors detecting the lane markers and the circuits performing addition and subtraction can measure the skid, attitude and speed of the vehicle.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a sensing device detecting a movement of a vehicle by lane markers. More particularly, it relates to a sensing device detecting the vehicle&#39;s movement based on information from the lane markers, which are embedded in roads as main indicators of the Intelligent Transport Systems (ITS) including an automatic steering device, a veer-off-the-lane alarming device and the like. 
     BACKGROUND OF THE INVENTION 
     In the automatic steering device and veer-off-the-lane alarming device of the ITS, a deviated amount from the lane is frequently required for detecting a vehicle running on the lane because the deviated amount tells the driver whether the vehicle keeps running on the lane or drifts outside the lane. The lane markers are embedded in respective lanes of roads with given intervals as indicators from which veer-off from the lane and a skid amount from the lane can be found. The relative relation between the lane marker and vehicle is detected, thereby telling the movement of the vehicle. 
     FIG. 1 illustrates a conventional sensing device for detecting an attitude of a vehicle utilizing lane markers. Lane markers  52  are set on each lane in a road with given intervals. Vehicle  51  has two lane-marker detectors  53  and  54  on its front for detecting lane markers  52 , i.e. detector  53  on the front left of the vehicle for detecting lane markers on the left-hand side, and detector  54  on the front right of the vehicle for detecting lane markers on the right-hand side. When detecting lane marker  52 , detector  53  outputs FL, and when detecting lane marker  52 , detector  54  outputs FR. If vehicle  51  deviates to the right with regard to the lane, FL becomes greater than FR. If vehicle  51  deviates to the left with regard to the lane FR becomes greater than FL. 
     Skid-detector  55  finds skid amount TE from the following equation. 
     
       
           TE=K   1 ×( FL−FR ) 
       
     
     where K 1  is a proportionality constant. 
     When TE takes a positive value, the vehicle shifts to the right, and when TE takes a negative value, the vehicle shifts to the left. An absolute value of TE is proportional to the skid amount. 
     The construction discussed above allows the conventional sensing device to detect lane markers  52  set on the road by lane-marker detectors  53 ,  54  disposed on both sides on the front of the vehicle, thereby finding the skid amount including a skid-direction of right or left. 
     This construction of the conventional sensing device; however, only measures a skid amount, and other apparatus including cameras and speed sensors are essentially required for monitoring the movement including an attitude and speed of the vehicle. 
     In addition to this problem, detectors  53 ,  54  disposed only on the front of the vehicle results in detecting a different amount from an actual skid amount when the vehicle takes an attitude different from the road travelling direction. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the problems discussed above and aims to provide a sensing device for detecting a vehicle&#39;s movement including skid, an attitude, a running speed and the like. This sensing device can find skid, an attitude and a running speed of the vehicle with a simple construction—no camera or a speed sensor is required—by using the lane markers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a concept of a conventional sensing device of vehicle&#39;s movement by using the lane markers. 
     FIG. 2 illustrates a concept of a sensing device of the present invention by using the lane markers. 
     FIGS.  3 (A)- 3 (D) illustrate an operating theory of the sensing devices and changes of outputs of lane-marker detectors. 
     FIGS.  4 (A)- 4 (D) illustrate how the sensing device of the present invention detects a running speed of the vehicle. 
     FIG. 5 is a circuit diagram illustrating a construction of a skid detector of the sensing device of the present invention. 
     FIG. 6 is a block diagram illustrating how a predetermined length of the vehicle is corrected. 
     FIG. 7 is a block diagram illustrating a veer-off-the-lane alarming device of the sensing device of the present invention. 
     FIG. 8 is a block diagram illustrating an automatic steering device of the sensing device of the present invention. 
     FIG. 9 is a block diagram illustrating a space-between-vehicles controller. 
     FIG. 10 is a block diagram illustrating a car-navigation system of the sensing device of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An exemplary embodiment of the present invention is demonstrated hereinafter with reference to the accompanying drawings. 
     In FIG. 2, lane markers  2  are set or embedded on each lane in the road with given intervals. Lane-marker-sensors  3 ,  4 ,  5  and  6  (hereinafter referred to as sensors  3 ,  4 ,  5  and  6 ) are provided to vehicle  1  on its left and right side on front part as well as on its left and right side on rear part of vehicle  1  respectively in this order. These sensors  3 ,  4 ,  5  and  6  detect an intensity of some physical amount imparted from lane markers  2  by a certain method. For instance, when lane markers  2  are formed by light reflective panels, sensors  3 ,  4 ,  5  and  6  transmit light from vehicle  1  and detect intensities of reflected lights. Another instance is this: when lane markers  2  comprise a resonant circuit or a magnetostrictive element which resonates a frequency of a radio wave, the radio wave carrying the frequency is transmitted to the lane markers  2 , and detect an intensity of the echo from lane markers  2 . When lane markers  2  comprise permanent magnets, vehicle  1  employs a magnetic detecting device such as an MR element thereby detecting changes in the magnetic field. 
     Respective outputs from sensors  3 ,  4 ,  5  and  6  are supplied to skid detector  7 , attitude detector  8 , speed sensor  9 . These outputs undergo given addition and subtraction so that a skid amount, attitude and running speed can be detected. 
     Next, an operation of the sensing device is demonstrated. FIG.  3 (A) and FIG.  3 (C) show relations between vehicle  1  and lane markers  2  when vehicle  2  detects skid and an attitude drift (a yawing angle with respect to traveling direction) from lane markers  2 . FIG.  3 (B) and FIG.  3 (D) show changes of outputs from sensors  3 ,  4 ,  5  and  6 . 
     Respective sensors&#39; outputs are named FL for sensor  3  on front left, FR for sensor  4  on front right, RL for sensor  5  on rear left and RR for sensor  6  on rear right of the vehicle. 
     FIG.  3 (A) shows a case when vehicle  1  goes into a skid in the lane. When vehicle  1  runs upward in the drawing, vehicle  1  goes into a skid to the right by a skid amount TE from the center of the lane, i.e. from a row of lane markers  2 . At this time, sensors  3  and  5  nearer to lane markers  2  output greater values than the others. In other words, FL and RL are greater than FR and RR as shown in FIG.  3 (B). 
     Meanwhile, space “Ls” spans the distance between sensors  3  and  5  as well as sensors  4  and  6 , because of the difference between the mounting positions of front sensors and rear sensors. Due to this space “Ls”, a time difference corresponding to the time for travelling space “Ls” exists between FL and FR, or RL and RR, although FL and FR, or RL and RR output the intensity change from the identical lane marker  2 . 
     To the contrary, when vehicle  1  goes into a skid to the left from the lane center, FL and RL become smaller than FR and RR. 
     In FIG. 1, skid detector  7  performs addition and subtraction of respective outputs FL, FR, RL and RR when the four sensors detect the same lane marker  2 , thereby calculating skid amount TE with regard to the center of the lane by the following equation. 
     
       
           TE=K   1 ×{( FL+RL )−( FR+RR )} 
       
     
     where K 1  is a proportionality constant. 
     FIG.  3 (C) shows a case when vehicle  1  drifts from the lane markers  2 , so that the attitude of vehicle  1  changes. When the attitude drifts by yawing angle YE to the left from a row of lane markers  2 , FR and RL become greater than FL and RR as shown in FIG.  2 (D). In the case of drifting to the right, FR and RL become smaller than FL and RR. 
     Attitude detector  8  shown in FIG. 1 performs addition and subtraction of respective outputs FL, FR, RL and RR when the four sensors detect the same lane marker  2 , thereby calculating the attitude of vehicle  1  with regard to lane markers  2 , i.e. yawing-angle YE by the following equation. 
     
       
           YE=K   2 ×{( FL+RR )−( FR+RL )} 
       
     
     where K 2  is a proportionality constant. 
     Space Ls between sensors  3 ,  4  and sensors  5 ,  6  produce a time difference between FL, FR (outputs from sensors  3 ,  4 ) and RL, RR (outputs from sensors  5 ,  6 ) although the lane marker  2  imparts a single intensity change. This time-difference “dt” is expressed in the following equation. 
     
       
         
           dt=Ls/V 
         
       
     
     Therefore, a predetermined space Ls can find speed V by measuring “dt”. 
     FIGS.  4 (A) through  4 (D) illustrate the theory of measuring time-difference “dt”. FIG.  4 (A) illustrates a status where vehicle  1  runs just above lane markers  2 . FIG.  4 (B) shows the four outputs of sensors  3 ,  4 ,  5  and  6 . As shown in FIG.  4 (B), when the sensors are compared at the same timing, the front sensors have different outputs from the rear sensors due to space Ls, i.e. difference of the mounting positions. 
     The outputs sum SF of sensors  3 ,  4  and the outputs sum SR of sensors  5 ,  6  are calculated by the following equations: 
     
       
         
           SF=FL+FR 
         
       
     
     
       
         
           SR=RL+RR 
         
       
     
     FIG.  4 (C) shows SF and SR thus calculated on a time axis. The same output change observed in SF can be seen in SR after time difference “dt” from SF. This time difference “dt” equals to the time difference between the peaks of output signals of SF and SR, and the output peaks are measured when the front sensors and the rear sensors pass the same lane marker  2 . This relation is expressed in the following equation. 
     
       
           dt=SF−SR= ( FL+FR )−( RL+RR ) 
       
     
     Therefore, speed sensor  9  shown in FIG. 1 can find speed V by the following equation. 
     
       
           V={ ( FL+FR )−( RL+RR )}/Ls 
       
     
     The detected outputs from sensors  3 ,  4 ,  5  and  6  sometimes include disturbances—which change in rather greater cycles—such as changes of road-reflection-factor, clatter noises proper to the road. These disturbances cause an error in measuring time difference “dt”. This error can be corrected by the following method: Find an output difference DFR between the front sensors and rear sensors by the equation as follows: 
     
       
           DFR=K   3 ×{( FL+FR )−( RL+RR )} 
       
     
     where K 3  is a proportionality constant. 
     As such, the disturbances changing in rather greater cycles can be thus eliminated. 
     FIG.  4 (D) shows the changes of DFR on the time axis. Time difference “dt” between a positive peak and negative peak gained from the same lane marker  2  is found from difference DFR. Speed V can be found by calculating Ls/dt, where Ls has been measured and is handled as a known quantity. 
     FIG. 5 shows how the skid detector of the sensing device of the present invention is normalized. In FIG. 5, the outputs FL, FR, RL and RR of sensors  3 ,  4 ,  5  and  6  have some dispersions due to the road condition and mounting dispersions of the sensors in height and the like. These dispersions also produce dispersion in a relation between inputs to skid detector  7  and outputs from detector  7 , where the inputs are referred to as the output changes of sensors  3 ,  4 ,  5  and  6 , and the outputs are referred to as the skid amount. In other words, the dispersions of FL, FR, RL and RR affect the sensitivity of skid detector  7 . In order to suppress this sensitivity dispersion of the skid-detector, the total output of sensors  3 ,  4 ,  5  and  6  is calculated by total-sum-calculator  11 . 
     
       
         Sum= FL+FR+RL+RR   
       
     
     Then the output from skid detector  7  is divided by this “Sum”. This division is performed in normalizing device  12 . As a result, the sensitivity dispersion of the skid detector can be suppressed. 
     In the same way, the output from attitude detector  8  is divided by the “Sum”. This division is performed in normalizing device  13 . As a result, the sensitivity dispersion of attitude detector  8  is suppressed. 
     FIG. 6 illustrates how a space-correcting device corrects space Ls between front sensors  3 ,  4  and rear sensors  5 ,  6  of the sensing device of the present invention. 
     When speed sensor  9  measures a speed of the vehicle, the measured speed has some error if the known quantity Ls has included an error. In this embodiment, global positioning system (GPS)  15  can correct this speed error. 
     GPS  15  can find an absolute position and absolute speed of a receiver based on information from GPS satellite in the sky. However, the receiver is not always able to receive the information from the satellite and the satellite is available only when the sky is open. Therefore, when GPS  15  can receive the information from the GPS satellite and calculate a speed, space-correcting device  16  can correct an error of space Ls by comparing the speed obtained by GPS  15  with the speed obtained by speed sensor  9 . This results in finding a correct speed of the vehicle even if the known quantity Ls includes some error. GPS  15 , as a speed measuring device, is disclosed in U.S. Pat. No. 5,686,925, the description thereof is thus omitted here. 
     FIG. 7 illustrates a working mechanism of a veer-off-the-lane alarming device employing the sensing device of the present invention. Sensing device  17  shown in FIG. 1 of the present invention provides the information of skid, an attitude and speed of the vehicle. Based on this information, veer-off-the-lane detecting device  18  determines whether or not the present skid amount is over a given amount, or guesses danger that the present skid amount will exceed the given value before long considering the attitude and speed. This judge can be established by calculations in a microcomputer. Veer-off-the-lane alarming device  19  gives an alarm with a sound or a display when detecting device  18  determines that vehicle  1  is out of the lane or guesses the danger of veering off the lane. A driver of vehicle  1  can correct the attitude of vehicle  1  by this alarm. 
     This alarming device not only informs whether or not the vehicle is out of the lane, but also guesses the danger of vehicle&#39;s veering off the lane considering the attitude and speed. 
     FIG. 8 illustrates a working mechanism of an automatic steering device employing the sensing device of the present invention. Based on the data about skid-amount and attitude of vehicle  1  by sensing device  17 , steering device  20  controls the yawing angle of vehicle  1  so that vehicle  1  can keep the lane not requiring the driver&#39;s manipulation. Steering device  20  is a known element because U.S. Pat. No. 5,245,422 discloses the similar thing. The description of device  20  is thus omitted here. 
     FIG. 9 illustrates a working mechanism of a space-between-vehicles controller employing the sensing device of the present invention. Based on the data of skid-amount and attitude of vehicle  1  by sensing device  17 , another vehicle ahead of vehicle  1  on the same lane can be guessed its existing direction by monitoring the positional relation between vehicle  1  and the lane. Space-between-vehicles measuring device  21 , such as an extremely-high-frequency (EHF) radar, searches whether or not a vehicle ahead exists in a direction guessed. When it exists, the distance between vehicle  1  and the vehicle ahead is found. Trailing device  22  determines the amount of speed to be increased or decreased of vehicle  1  based on the distance and the speed obtained by sensing device  17 , thereby trailing the vehicle ahead on the same lane in a steady manner. Space-between-vehicles measuring device  21  is disclosed e.g. by U.S. Pat. No. 5,165,497. The description of device  21  is thus omitted here. 
     FIG. 10 illustrates a working mechanism of a car-navigation-system employing the sensing device of the present invention. Based on the skid and attitude measured by sensing device  17 , changing-lane detector  23  recognizes the vehicle has changed the lane when the measured values exceed given values, then informs vehicle-position detector  24  of this lane change. Detector  24  recognizes that vehicle  1  has changed the lane from the inside lane to a fast lane, or vehicle  1  has entered an exit lane from a free way and then gets off an interchange via an exit ramp, thereby identifying the present position of vehicle  1 . This information is displayed on the car-navigation system so that the driver can identify correctly the present location. 
     As such, this construction allows the car-navigation system to recognize vehicle  1  changing the lane or veering off the road when the measured values of skid and attitude exceed the given values. Thus this car-navigation system can guide the driver to a lane in the more delicate manner by recognizing a lane change.