JPS63109318A - Method for detecting azimuth of vehicle - Google Patents

Abstract

PURPOSE:To more accurately detect the azimuth of a vehicle, by a method wherein the azimuth due to map data is used but the azimuth from the output data of an earth magnetism sensor is not used during the confirmation processing of the present position of a vehicle on the basis of the map data. CONSTITUTION:At first, a CPU 7 judges whether one-revolutional correction is completed and, when said correction is not completed, a vehicle loaded with an earth magnetism sensor 1 is allowed to make one revolution and the calculated value is stored in a RAM 9. Next, after an initial azimuth is set, the output data of the sensor 1 is taken-in and further stored in the ring buffer within the RAM 9. When the output data is received in a window, at first, it is judged whether the azimuth (map azimuth) calculated from the map data presently stored in a recording medium 10 is utilizable. When the utilization of the map azimuth is not permitted, the azimuth calculated up to now is set to the azimuth of own vehicle and, when the map azimuth is utilizable, the map azimuth is utilized as it is when there is a window error and the azimuth calculated from the output data of the sensor 1 is used when there is no window error and the difference between the azimuth calculated from the sensor 1 and the map azimuth is a predetermined value or more.

Description

TECHNICAL FIELD The present invention relates to a method for detecting the direction of a vehicle, and more particularly to a method for detecting the direction of a vehicle using a geomagnetic sensor in a vehicle navigation system.

Background Art In recent years, in-vehicle navigation devices have been researched and developed that guide a vehicle to a predetermined destination by storing map information in a memory, reading the map information from the memory, and displaying the map information along with the vehicle's current location on a display device. has been done.

Such a navigation device requires a direction sensor that detects the direction of the vehicle, and as this direction sensor, for example, a geomagnetic sensor that detects the direction of the vehicle based on geomagnetism (earth's magnetic field) is used. However, this geomagnetic sensor is easily affected by disturbance time, and its output data may be affected when a vehicle passes a railroad crossing, a railway bridge, or when a large vehicle (such as a truck or bus) passes by the vehicle. will contain a large error.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a method for detecting the direction of a vehicle, which enables more accurate detection of the direction of the vehicle.

In the vehicle direction detection method according to the present invention, when the vehicle is running at a speed higher than a predetermined speed and the current location recognition process of the vehicle is being performed based on map data, It is characterized in that it uses the azimuth determined by the geomagnetic sensor, and does not use the azimuth determined from the output data of the geomagnetic sensor.

Example Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing the configuration of an in-vehicle navigation device to which a vehicle orientation detection method according to the present invention is applied. In the figure, 1 is a geomagnetic sensor for outputting vehicle orientation data based on geomagnetism (earth's magnetic field), 2 is an angular velocity sensor for detecting the angular velocity of the vehicle, and 3 is a geomagnetic sensor for detecting the distance traveled by the vehicle. Mileage sensor, 4 is a GP for detecting the current location of the vehicle from latitude and longitude information, etc.
S (Global Positlonlng Sy
The output of each of these sensors (devices) is supplied to the system controller 5.

The system controller 5 has an interface 6 which inputs the outputs of the sensors (devices) 1 to 4 and performs A/D (analog/digital) conversion, etc., and processes various image data which are sequentially sent from the interface 6. A CPU (central processing circuit) 7 that calculates the amount of movement of the vehicle, etc. based on the output data of each sensor (device) 1 to 4.
and a ROM (read-only) in which various processing programs and other necessary information for the CPU 7 are written in advance.
Memory) 8, RAM (Random Access Memory) 9 where information necessary for executing programs is written and read, and so-called CD-ROM% IC cards, etc., and are digitized (numerical). A recording medium 10 on which map information has been recorded, and a V-RAM (Vi
Graphic data such as a map sent from the CPU 7 is drawn in the graphic memory 11 and is stored as an image in the graphics memory 11.
It is composed of a graphic controller 13 that controls display on a display 12 such as an RT. The input device 14 consists of a keyboard or the like, and various commands and the like are issued to the system controller 5 by the user's keystrokes.

Next, the basic procedure executed by the CPU 7 will be explained according to the flowchart shown in FIG.

The CPU 7 first initializes the program to execute it (step S1), and then determines whether the current location of the vehicle has been set (step S2). If the current location has not been set, a current location setting routine is executed (step S3), for example, the current location is manually set using the keys on the input device 14. Next, the mileage is set to zero (step S4), and it is then determined whether there is any key input from the input device 14 (step S5).

If there is no key personnel available, a map of the area around the current location is displayed on the display 12, and the current location of the vehicle and its direction are displayed on this map using, for example, a vehicle mark, and when the vehicle moves, the map scrolls as the vehicle moves. Furthermore, when the vehicle position is likely to exceed the range of the map data currently on the graphic memory 11, the necessary map data is read out from the recording medium 10 and displayed on the display 12 (step S6).

If there is key human power, the current location is reset (step S7) and sensor correction (step S8) according to the input data.
, destination setting (step S9), and map enlargement/reduction (step 510).

Further, the CPU 7 constantly calculates the direction of the vehicle based on the output data of the geomagnetic sensor 1 and the angular velocity sensor 2 at regular time intervals, as shown in FIG. 3, by interrupt processing using a timer (step S11.312).

By the way, the geomagnetic sensor 1 generally consists of a pair of magnetic detection elements arranged on the same plane with a phase angle of 90° to each other, and one of the pair of elements is, for example, U
The geomagnetic component in the direction (north direction) is detected, and the other is in the V direction (
It is designed to detect the geomagnetic component in the east direction. When the geomagnetic sensor 1 having such a configuration is rotated once on a horizontal plane, the output data from both the U and V detection elements generates a circular shape centered on the origin O of the UV orthogonal coordinate system, as shown in FIG. The trajectory is drawn. Therefore, for example, point P
The clockwise azimuth θ from the north (U axis) at (U+, V+) is calculated by the following equation (1).

θ−t an″I (U/V) (1) Therefore, such a geomagnetic sensor 1 is attached to a vehicle at a predetermined angle with respect to the longitudinal or lateral direction of the vehicle, U
, V based on the output data from both detection elements (1)
By calculating the equation, the direction of the vehicle can be detected.

Ideally, only magnetic flux due to the earth's magnetic field exists around the geomagnetic sensor 1, but in a vehicle,
Generally, there is extra magnetic flux due to magnetization of the body steel plate. Therefore, in order to remove the influence of magnetization of the vehicle body and perform accurate direction detection,
For example, a method disclosed in Japanese Unexamined Patent Publication No. 57-28208 is proposed. In this method, when the U and V magnetic detection elements are fixed to the vehicle and there is no relative displacement between them, the center of a circle drawn by plotting the output obtained by rotating the magnetic detection elements once, Considering that the distance from the coordinate origin is due to the influence of body magnetization, the output data obtained from the rain detection element is corrected so that the center of the drawn circle moves to the origin, and body magnetization is adjusted. We are trying to remove the influence of magnetism. To be more specific, the center Q of the circle drawn by the output of the rain detection element is located at a position moved from the origin, as shown by ■ in FIG. Therefore, the output U of the rain detection element.

■The maximum value Uma, V and the minimum value U vil, V
B is determined, and from these, the coordinates of the center Q are calculated using the following equation (2).

Uo = (U+Uin)/2)...(2) VO-(V+Vvin)/2 Using the calculated values UO and vo, calculate the output of each magnetic detection element using the following equation (3). The values U and V are corrected, and the direction is calculated from the corrected U- and V-.

U"-U-UO) ......(3) V"-v-vO In addition, in order to increase the reliability of the output data of the geomagnetic sensor 1, the output data of the geomagnetic sensor 1 is A tolerance range (hereinafter referred to as a window) that allows variation is set. In other words, as shown by diagonal lines in Figure 5,
A window is set in the angular direction using the previously determined azimuth data (Unq+vn-1) as a reference, and the difference between the previously determined azimuth data and the currently determined azimuth data is constantly monitored. If the direction data is significantly different from the direction data set, that is, if it is outside the window, the data is treated as an error and replaced with predetermined data, such as the previous data or the average value of data from several times in the past (the number of times is arbitrary). , the reliability of the output data of the geomagnetic sensor 1 is increased. Furthermore, since the data output from the geomagnetic sensor 1 mathematically applies to the equation of a circle, data that does not fit into this equation can also be determined as an error. However, since the data varies due to A/D conversion errors, etc.
The window is set with a certain width in the radial direction as well. In FIG. 5, α represents an angle tolerance, and β represents a radius tolerance.

Note that since the difference in orientation varies depending on the time interval at which the orientation data is obtained, it is also possible to determine it based on the relationship between angular velocity and vehicle speed. For example, if the vehicle speed is 40 [km/h] and the maximum angular velocity is 30 [degrees/s], if the output data of the geomagnetic sensor 1 exceeds this range, it will be considered an error, and the previous data or past data will be displayed. Replace with the average value of the data. In addition, when setting a window using an angle, it is also possible to set the angle according to changes in vehicle speed.In addition to setting the angle as a linear function relative to vehicle speed, it is also possible to set a window according to vehicle speed by providing a certain hysteresis. This eliminates the need to frequently change the response angle in response to changes.

Next, the procedure of the vehicle orientation detection method according to the present invention executed by the CPU 7 will be explained according to the flowcharts shown in FIGS. 6(A) to 6(C).

The CPU 7 first determines whether so-called one-rotation correction has been completed (step 520). If not completed, execute one rotation correction routine (step 521)
. In this one-rotation correction routine, the vehicle equipped with the geomagnetic sensor 1 is rotated once, and the values of Uo, Vo (center value), and radius r are determined. The determined value is stored in RAM9.

Next, an initial orientation is set (step 522).

Since the vehicle is stationary when the engine is started and the orientation of the vehicle should be constant, it is preferable to set the initial value at this time. After setting the initial orientation, the output data of the geomagnetic sensor 1 is taken in, and this data is sequentially stored in the ring buffer in the RAMQ (step 523). The amount of data stored in this ring buffer may be for a certain predetermined period of time. Next, it is determined whether or not this output data falls within the aforementioned window (the shaded area in FIG. 5) (step 524). If it is within the window, the direction of the vehicle is calculated based on the above-mentioned equations (1) to (3) from the output data of the captured geomagnetic sensor 1 (
Step 525).

Next, the count value N of the window error counter that counts the number of times the output data of the geomagnetic sensor 1 is outside the window and the count value E of the center value deviation determination counter that counts the number of times that the center value deviation has occurred are both set to zero. (step 526), and further sets a flag indicating no window error (step 527). The flow described above is the flow during normal operation when the output data of the geomagnetic sensor 1 is within the window without being affected by the disturbance magnetic field.

Next, we begin the process of determining the direction of our troops. First, in step S40, a direction (hereinafter referred to as a map direction) determined from the map data currently stored in the recording medium 10 is determined.
It is determined whether or not the map orientation usage prohibition flag, which will be described later, is "0". Note that the determination as to whether or not the map orientation can be used is made by the method described later. If the use of the map orientation is not permitted, the orientation obtained so far is set as the own army orientation (step 541), and then the process returns to step 52B. If the use of map orientation is permitted, geomagnetic sensor 1
It is determined whether or not the output data of is included in the window, based on whether or not a window error-free flag is set (step 542). If there is a window error, use the map direction as is (step 843),
Thereafter, the process returns to step S23. If there is no window error, it is determined whether the difference between the azimuth determined from the output data 1 of the geomagnetic sensor 1 and the map azimuth is greater than a predetermined value (step 544), and if it is greater than the predetermined value, a pull-in operation is performed. Since it seems suspicious, the use of the map direction as the own military direction is prohibited for a predetermined period of time (step 546).
, the direction determined from the output data of the geomagnetic sensor 1 is used (step 547). If it is not equal to or greater than the predetermined value, the map direction is used as is (step 545), and then the process returns to step S23.

On the other hand, if it is determined in step S24 that the output data of the geomagnetic sensor 1 is not within the window,
The count value N of the window error counter is counted up by "1" (step 528), and then it is determined whether the count value N has reached the maximum window error value Nmx (step 529). Then, until the window error maximum value NIIX is reached, the output data of the geomagnetic sensor 1 that has been imported this time is regarded as an error, and the direction obtained based on the previous value or the average value of the past several times of the output data of the geomagnetic sensor 1 is (step 530),
Furthermore, a flag indicating that there is a window error is set (step 531), and then the process proceeds to step S40, where the above-described operations are performed.

Further, when the count value N of the window error counter reaches the window error maximum value N, the count value E of the center value deviation counter is counted up by "1" (step 532), and then the count value E is set to the center value. Value deviation determination It is determined whether the maximum value E view has been reached (step 833).

Then, set a timer for a certain period of time until the center value deviation judgment maximum value Emx is reached (step 534).
, the output data of the geomagnetic sensor 1 is taken in until it is determined that time is up in step S35 (step 536).
, and calculates the orientation based on the data (step 537). That is, if the output data of the geomagnetic sensor 1 does not fit into the window for a certain period of time, the window is temporarily canceled and error processing is not performed for a certain period of time. Through this processing, it is possible to cope with the case where non-standard data is captured due to, for example, a sudden steering wheel.

Next, it is determined whether the current map direction can be used or not in the same manner as in step S40 (step 548).
. If the use of the map direction is not permitted, step 549 sets the previously requested direction as the own direction.
), if the use of the map orientation is permitted, the map orientation is used as is (step 550), and the process returns to step S35.

When the count value E of the center value deviation counter reaches the maximum value E for determining center value deviation, it is determined in step 333 that there is a center value deviation, and the center value deviation is correctly corrected using other data (step 538); Both the count value N of the window error counter and the count value E of the center value deviation determination counter are set to zero (step 539), and then the process returns to step 823. For example, when a vehicle passes through a railroad crossing, the vehicle body is magnetized by the strong magnetic field at the railroad crossing, which causes the output data of the geomagnetic sensor 1 to have a DC component, resulting in a center value shift as shown in FIG. , so that it is no longer possible to correctly determine the direction.

If the vehicle body is magnetized in this way and the center value shifts, the output data of the geomagnetic sensor 1 will not enter the window no matter how long it takes, so by counting the number of times it does not enter the window for a certain period of time, ,
It can be determined that this state has occurred.

In such a situation, even if the output data of the geomagnetic sensor 1 has a DC component, only the center coordinates of the circle equation change and the radius r does not change (the strength of the geomagnetic field changes). (The radius r will not change unless
The center coordinates can be determined using other data, and the center value deviation can therefore be corrected.

In the correction of this center value deviation, for example, output data of the angular velocity sensor 2 is used as other data. Although the angular velocity sensor 2 cannot determine the absolute value, it can determine the angle by integrating on the time axis. The known value when the center value is shifted is geomagnetic sensor 1.
The output data (U, V) are the radius r determined by one-rotation correction and the output data of the angular velocity sensor 2, and these values have the relationship expressed by the following equation (4).

U-r conflict sin θ+U.

) ・・・・・・(4) V-r-cosθ+vO By transforming the equation (4), the following equation (5) is obtained.

Uo =U-r φsin θ) (5) V□-V-r·cos θ Therefore, the current center value (Uo, VO) can be obtained from equation (5).

Further, as another method for determining the angle θ, the angle of the road on which the vehicle is currently traveling may be calculated using map data, and the angle of this road may be set as the angle θ. That is, a road is represented by a line (line segment) connecting two points, each point is digitized and stored in the recording medium 10 as map data, and from this map data the line segment where the vehicle is located is determined. Since we know the values at both ends (two points) of , we can find the angle θ by calculating the slope of the linear function from these values.

Next, a method for determining whether or not the map orientation can be used will be explained.

When the CPU 7 receives a travel pulse from the travel distance sensor 3 for detecting the travel distance and speed of the vehicle, it performs an interrupt process using the travel pulse.

In this running pulse interrupt processing, distance errors caused by detection errors of the mileage sensor 3, digitizing errors of map data, etc. are corrected by calculating the above-mentioned distance from the previously detected position based on the map data every time the vehicle travels a certain distance. By detecting a position on the road that is far away from the vehicle and using this detected position as the current location, current location recognition processing is performed that always accurately recognizes the current location of the vehicle. Regarding the specific method of processing this current location recognition, the present applicant filed a patent application in 1986-15.
This has already been proposed in No. 6883.

In this current location recognition process, every time the vehicle travels a certain distance, the road closest to the current location is searched from the map data and the current location is drawn onto that road. Interrupt processing by running pulses is also performed in parallel. That is, the CPU 7 first determines whether or not current location recognition processing is being performed (step 551). An example of a case where current location recognition processing is not performed is when the road closest to the current location cannot be found from the map data. If the current location recognition process is not being performed, the flag for prohibiting the use of the map direction is set to "1°," that is, the use of the map direction is prohibited (step 552), and the process ends. If so, it is determined whether the vehicle speed is less than the predetermined vehicle speed Sfat (step 353), and if the vehicle speed is less than the predetermined vehicle speed 5Ifflt, it is determined in step S52.
If the vehicle speed is greater than or equal to the predetermined vehicle speed S1g+, the process ends.

Further, as shown in FIG. 9, the CPU 7 determines whether or not the flag for prohibiting the use of the map direction is "12", that is, the use of the map direction is prohibited, as shown in FIG. 9, by the interrupt processing by the timer. In this case, the time is monitored until a predetermined time has elapsed (Step 555), and when the predetermined time has elapsed, the flag for prohibiting the use of the map direction is set to 0'' to prohibit the use of the map direction (Step 5).
56). If the use of the map direction is initially permitted, the process ends without doing anything.

That is, in the above-mentioned method for detecting the vehicle direction, when the vehicle is traveling at a predetermined speed (for example, 40 [Km/hl) or higher, the direction of the vehicle does not change significantly, and the direction of the vehicle does not change significantly, and the direction of the vehicle does not change significantly. Since it is determined that a straight line approximation is possible for roads (roads are represented by connecting minutes), errors may occur in map digitization work in such a situation.
The reliability of the orientation obtained from map data is determined by the geomagnetic sensor 1.
If the current location of the vehicle is being recognized while the vehicle is running at a speed higher than the specified speed, the orientation obtained from the map data is used in this process, and the orientation obtained from the geomagnetic sensor is The direction determined by 1 is not used. This allows the direction of the vehicle to be detected more accurately.

Although the passage of time is monitored in step S55 of FIG. 9, it is also possible to monitor whether the vehicle has traveled a predetermined distance.

As described in detail, according to the present invention, only when the vehicle is traveling at a predetermined speed and the process of recognizing the vehicle's current location based on the map data is performed, information can be obtained from the map data. By using the calculated direction as the own military direction and not using the direction determined by the geomagnetic sensor,
Since direction detection can always be performed based on highly reliable direction data, the direction of the vehicle can be detected more accurately.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an in-vehicle navigation device to which the vehicle orientation detection method according to the present invention is applied;
3 and 3 are flowcharts showing the basic procedures executed by the CPU in FIG. 1, FIG. 4 is a line diagram showing the locus drawn by the output data of the geomagnetic sensor, and FIG. A line diagram showing a state in which a window is set on the trajectory to be drawn; FIGS. 6(A) to (C) are a flowchart showing the procedure of the vehicle orientation detection method according to the present invention executed by the CPU in FIG. 1; FIG. 8 is a flowchart showing the procedure for processing an interrupt by a running pulse, and FIG. 9 is a flowchart showing the procedure for processing a timer interrupt. be. Explanation of symbols of main parts

Claims (4)

[Claims] (1) A direction detection method comprising a geomagnetic sensor that outputs vehicle direction data based on geomagnetism, and detecting the vehicle direction based on the output data of the geomagnetic sensor,
When the vehicle is traveling at a predetermined speed or higher and the current location recognition process of the vehicle is being performed based on map data, the direction determined from the map data is used to detect the geomagnetic field. A vehicle orientation detection method characterized in that the orientation determined from sensor output data is not used. (2) When the current location recognition processing is not being performed, the use of the orientation determined from the map data is prohibited for a predetermined time or a predetermined travel distance, and during that time, the orientation determined from the output data of the geomagnetic sensor is prohibited. A method for detecting the direction of a vehicle according to claim 1, characterized in that the method uses: (3) When the vehicle is traveling at less than the predetermined speed, the use of the direction determined from the map data is prohibited for a predetermined time or a predetermined distance, and during that time, the direction determined from the output data of the geomagnetic sensor is prohibited. 2. A method for detecting a vehicle orientation according to claim 1, characterized in that the vehicle orientation is determined by using an orientation determined by the vehicle orientation. (4) A tolerance range is set to allow variations in the output data of the geomagnetic sensor, and when the output data of the geomagnetic sensor is within this tolerance range, the direction determined from the output data of the geomagnetic sensor and the map Claim 1, characterized in that the difference between the orientation and the orientation determined from the data is monitored, and when this orientation difference is equal to or greater than a predetermined value, the orientation determined from the output data of the geomagnetic sensor is used. The vehicle orientation detection method described.