JP2009098127A - Navigator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a navigator which can detect positions with sufficient accuracy, even if it is the case where an offset error of an acceleration sensor exists. <P>SOLUTION: The navigator includes: an acceleration determination means which compares the acceleration obtained by the acceleration sensor with a predetermined threshold value; and a location calculation means which calculates the present location based on the acceleration and past location and moving velocity which are memorized by a memory means when it is determined that an absolute value of the acceleration is larger than the threshold value by the acceleration determination means and which calculates the present location based on an azimuth through the measurement by an azimuth sensor assuming as a constant velocity motion and based on the past location and moving velocity which are memorized in the memory means when it is determined that the absolute value of acceleration is smaller than the threshold value by the acceleration determination means. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a navigation apparatus for guiding a current position.

  There are two types of navigation devices that measure the position of a vehicle and provide travel guidance: a stationary type that is installed by wiring in the vehicle, and a portable type that is called a PND (Personal Navigation Device). In recent years, in a stationary navigation apparatus (see, for example, Patent Document 1), in addition to position information acquired based on GPS signals, a vehicle speed obtained from a built-in gyro sensor or a geomagnetic sensor and a vehicle speedometer provided in the vehicle. By using this information in combination, a device equipped with a function for obtaining the current position of the vehicle with high accuracy has been put into practical use. Such a function is particularly useful when the GPS signal cannot be acquired or the accuracy of the GPS signal is not good.

On the other hand, in a portable navigation device, it is not easy to obtain vehicle speed information from a vehicle speedometer installed inside a vehicle instrument panel, etc., so as an auxiliary means for cases where GPS signals cannot be obtained, etc. Conventionally, a method has been adopted in which vehicle speed is obtained by integrating acceleration measured using a built-in acceleration sensor, thereby obtaining a position.
JP-A-9-42979

  However, since an acceleration sensor generally has an offset error, there is a serious problem that a sufficiently good accuracy cannot be obtained in position measurement. Here, the offset error is an error in which a certain finite acceleration value is output from the acceleration sensor even though the acceleration due to the acceleration motion is originally zero. For example, when the acceleration sensor is not mounted horizontally with respect to the vehicle, or when the vehicle travels on a slope or other location inclined from a horizontal plane, the gravitational acceleration is mistaken as the acceleration applied to the vehicle. It can be caused by doing so. In particular, in the latter case, even if the acceleration sensor is mounted horizontally with respect to the vehicle, the occurrence of an offset error is inevitable, which is a serious problem.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a navigation device that can accurately obtain a position even when an offset error of an acceleration sensor exists.

  The present invention has been made to solve the above-described problem. In a navigation device that obtains a current position and performs position guidance, acceleration determination means that compares acceleration obtained from an acceleration sensor with a predetermined threshold value, and the acceleration When the determination means determines that the absolute value of the acceleration is greater than the threshold, the current position is calculated based on the acceleration and the past position and moving speed stored in the storage means, and the acceleration determination means If the absolute value of acceleration is determined to be smaller than the threshold value, it is assumed that the motion is constant velocity and based on the azimuth based on the measurement by the azimuth sensor and the past position and moving speed stored in the storage means. And a position calculation means for calculating the current position.

  According to the present invention, when the absolute value of the measured acceleration is smaller than the predetermined threshold, it is assumed that the acceleration is caused by the vehicle leaning (for example, traveling on a slope). The acceleration is assumed to be zero, and the current position is obtained by assuming that the vehicle moves at a constant speed. Therefore, even if an offset error occurs in the acceleration sensor due to the vehicle tilting, the position can be obtained with high accuracy.

  Further, the present invention provides a navigation device that obtains a position by GPS and obtains a moving speed from a plurality of positions at the obtained different times, a position and a moving speed obtained by the measuring means, A best value estimating means for inputting a position obtained by the position calculating means and a moving speed calculated based on the position to a Kalman filter to estimate a best value relating to the current most probable position; and the best value estimating means Based on the estimated best value, an acceleration offset value for correcting the acceleration by the amount of the offset error is calculated on the assumption that the position error obtained by the position calculation means is caused by the offset error of the acceleration sensor. An acceleration offset calculating means for performing the acceleration determination, Acceleration obtained from the velocity sensor is corrected using the acceleration offset calculated by the acceleration offset calculation means, characterized by comparing the with the corrected acceleration threshold.

  According to the present invention, since the acceleration offset value is obtained and the acceleration obtained from the acceleration sensor is corrected, the offset error is corrected and the position can be obtained with higher accuracy.

  According to the present invention, in the above navigation device, when the change in the acceleration obtained from the acceleration sensor at a predetermined time is equal to or less than a predetermined value, the acceleration is obtained according to the acceleration value obtained from the acceleration sensor. The apparatus further comprises acceleration offset calculating means for calculating an offset value, wherein the acceleration determining means corrects the acceleration obtained from the acceleration sensor using the acceleration offset value calculated by the acceleration offset calculating means, and the corrected acceleration And the threshold value are compared.

  According to the present invention, since the acceleration offset value is obtained from the change in acceleration obtained from the acceleration sensor and the acceleration obtained from the acceleration sensor is corrected, the GPS signal cannot be acquired or the reliability of the GPS signal is sufficient. Even in the case where it is not, the offset error is corrected, and the position can be obtained with higher accuracy.

  According to the present invention, it is possible to obtain the position with high accuracy even when there is an offset error of the acceleration sensor.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a configuration diagram of a navigation apparatus 1 according to the first embodiment of the present invention. The navigation device 1 includes a CPU 10, a GPS unit 11, an acceleration sensor 12, a magnetic sensor 13, a memory 14, an external storage device 15, a communication unit 16, a display device 17, and an audio output device 18. Each part is connected by a bus line 19. These parts of the navigation device 1 are accommodated in a single casing, and the navigation device 1 can be carried and attached to any position in the vehicle. Henceforth, the navigation apparatus 1 shall be attached in the vehicle.

  The CPU (central processing unit) 10 reads a program stored in the memory 14, controls and controls each part of the navigation device 1 according to the read program, and obtains it from the GPS unit 11, the acceleration sensor 12, and the magnetic sensor 13. The calculation processing described later (FIGS. 2 to 4) for calculating the current position from the data to be processed and the information processing for realizing the navigation function for guiding the current position to the user are executed.

  The GPS unit 11 measures the position (latitude and longitude) of the vehicle by a GPS (Global Positioning System) method, and calculates the speed and traveling direction of the vehicle based on the latest position and the position immediately before the position. Each information indicating the obtained position, speed, and traveling direction is output to the CPU 10. In the GPS system, a GPS signal from a GPS satellite is received, and the position is measured by arithmetic processing using data of a reception time (timed by a time measuring unit (not shown)) when the GPS signal is received.

  The acceleration sensor 12 measures the acceleration of the vehicle (that is, the navigation device 1) and outputs acceleration information representing the measurement result to the CPU 10. The measured acceleration includes gravitational acceleration due to the vehicle leaning on a slope or the like in addition to acceleration due to the vehicle performing acceleration motion. As the acceleration sensor 12, a two-axis acceleration sensor that detects acceleration components in two different directions perpendicular to each other is used. In the present embodiment, the acceleration sensor 12 has one axis (this is the y-axis and the other is the other). (X is the x-axis) is aligned with the orientation of the reference axis of the magnetic sensor 13 described below. The acceleration information output to the CPU 10 is an acceleration component in each axis direction (that is, in the xy coordinate system with reference to the reference axis of the magnetic sensor 13). Each component includes an offset error resulting from the gravitational acceleration being measured.

  The magnetic sensor 13 measures the geomagnetism in the vehicle (that is, the navigation device 1), calculates the direction in which the predetermined reference axis defined by the magnetic sensor 13 is directed, and outputs the direction information indicating the direction to the CPU 10. . In the present embodiment, the magnetic sensor 13 has a direction in which the reference axis is deviated by a certain angle with respect to the vehicle front direction (this is arbitrary when the portable navigation device 1 is placed in the vehicle). Arranged based on the As the magnetic sensor 13, either a two-axis magnetic sensor that detects magnetic components in two different directions perpendicular to each other or a three-axis magnetic sensor that detects magnetic components in three different directions perpendicular to each other is used. For example, in the case of a biaxial magnetic sensor, two elements (magnetoresistive elements) for detecting the magnitude of magnetism are arranged in two different directions, and based on the magnitude of geomagnetism detected by each element. The direction of the reference axis is calculated.

The memory 14 includes a ROM (read only memory) and a RAM (anytime read / write memory). In the ROM, a program executed by the CPU 10 is stored. The RAM is used as a storage area for storing temporary data during program execution.
The external storage device 15 is a large-capacity storage device such as a hard disk drive, and stores map information and the like necessary for navigation.
The communication unit 16 is connected to the Internet, for example, by wireless communication, and acquires the latest map information and the like via the Internet. The acquired map information and the like are stored in the external storage device 15.

The display device 17 graphically displays the travel guidance by the navigation function realized by the CPU 10 in a form that shows the current position and direction of the vehicle on a map, for example.
The voice output device 18 generates voice guidance voice such as turning an intersection at a necessary timing and performs voice guidance from a speaker.

  Next, processing in which the navigation apparatus 1 calculates the current position from data acquired from the GPS unit 11, the acceleration sensor 12, and the magnetic sensor 13 will be described. FIG. 2 is a diagram showing functional blocks related to the process of the navigation device 1, and this process is an INS system position calculation unit 101 (the acceleration sensor 12 and the magnetic sensor 13 are referred to as an INS (Internal Navigation System) system). The best value estimation unit 102, the position correction unit 103, the acceleration offset calculation unit 104, and the acceleration determination unit 105 are realized. Note that the functions of these units are realized by the CPU 10 reading and executing the program stored in the memory 14 as described above.

An acceleration a = (ax, ay) including an offset error is input from the acceleration sensor 12 to the INS system position calculation unit 101 (ax is an x-axis component, ay is a y-axis component), and the reference axis Is input, and the traveling direction φ of the vehicle is input from the GPS unit 11. Further, the acceleration offset value b = (bx, by) for correcting the offset error included in the acceleration a from the acceleration sensor 12 is input from the acceleration offset calculation unit 104 to the INS system positioning unit 101 (bx Is the x-axis component, and by is the y-axis component).
In response to an instruction from the acceleration determination unit 105, the INS system position calculation unit 101 calculates a vehicle position P _INS and a speed V _INS based on each of the input data. The calculation result is output to the best value estimation unit 102 and the position correction unit 103.

Specifically, if the acceleration determination unit 105 determines that the absolute value of the acceleration a + b is equal to or greater than a predetermined threshold, the INS system position calculation unit 101 calculates the position P _INS and the velocity V _INS according to the following equations.
aN = − (ax + bx) · sin θ + (ay + by) · cos θ (1A)
aE = (ax + bx) · cos θ + (ay + by) · sin θ (1B)
VN _INS = VN0 _INS + aN · Δt (1C)
VE _INS = VE0 _INS + aE · Δt (1D)
PN _INS = PN0 _INS + sin ⁻¹ [(VN _INS × Δt) / R] (1E)
PE _INS = PE0 _INS + sin ⁻¹ [(VE _INS × Δt) / {R × cos (PN0 _INS )}] (1F)
Where aN and aE are the latitude and longitude components of acceleration a + b, VN _INS and VE _INS are the latitude and longitude components of velocity V _INS , and PN _INS and PE _INS are the latitude and longitude components of position P _INS , respectively. . Also, VN0 _INS , VE0 _INS , PN0 _INS , PE0 _INS are the previously calculated values of VN _INS , VE _INS , PN _INS , PE _INS , Δt is the elapsed time from the previous calculation to this calculation, and R is the earth Is the radius.

On the other hand, when the acceleration determination unit 105 determines that the absolute value of the acceleration a + b is smaller than the predetermined threshold, the INS system position calculation unit 101 calculates the position P _INS and the velocity V _INS according to the following equations (PN _INS And PE _INS are the same as above).
V = √ (VN0 _INS ² + VE0 _INS ² ) (2A)
VN _INS = V × cos θ ′ (2B)
VE _INS = V × sin θ ′ (2C)
PN _INS = PN0 _INS + sin ⁻¹ [(VN _INS × Δt) / R (2D)
PE _INS = PE0 _INS + sin ⁻¹ [(VE _INS × Δt) / {R × cos (PN0 _INS )}] (2E)
However, θ ′ is a value obtained by correcting the azimuth θ as described later (see step S52 in the flowchart of FIG. 4) in consideration of the fact that the magnetic sensor 13 is deviated from the vehicle front direction.

Thus, when the absolute value of the acceleration is equal to or higher than the predetermined threshold value, the acceleration aN, thereby calculates the position P _INS seeking speed V _INS as acceleration motion the motion of the vehicle using aE, the absolute value of the acceleration Is smaller than the predetermined threshold value, the previous speeds VN0 _INS and VE0 _INS are used to regard the motion of the vehicle as a constant speed motion, and the speed V _INS is obtained, thereby calculating the position P _INS . Therefore, even when the vehicle is actually moving at a constant speed but the traveling place is on a slope or the like, an offset error is included in the acceleration a output from the acceleration sensor 12. Since the unit 101 calculates the position by the latter method, that is, assuming that it is a constant velocity motion, the position can be accurately obtained without being affected by the offset error.

It should be noted that the process of calculating the position P _INS on the assumption that the motion is constant speed may be performed only when the GPS signal cannot be acquired by the GPS unit 11 or when the reliability of the GPS signal is not sufficient. While the GPS signal can be acquired, the best value estimation unit 102 and the acceleration offset calculation unit 104 described later function effectively to calculate the acceleration offset value b, thereby correcting the offset error of the acceleration sensor 12. Even if the values of the accelerations aN and aE are small, the position P _INS can be correctly obtained by the above equations (1A) to (1F) with confidence. On the other hand, if the GPS signal cannot be acquired as in a tunnel, for example, the best value estimation unit 102 and the acceleration offset calculation unit 104 do not function effectively, so that the offset error of the acceleration sensor 12 cannot be corrected, and the accelerations aN, aE The reliability of the value is lost. In such a case, if the absolute value of the acceleration is small, the influence of the offset error is large. Therefore, the processing is switched to the processing according to the above formulas (2A) to (2E) for calculating the position P _INS assuming that the motion is constant velocity. It has a big meaning.

The calculated value P _INS and velocity V _INS are input from the INS system position calculation unit 101 to the best value estimation unit 102, and the position P _GPS and velocity V _GPS are input from the GPS unit 11. The position P _INS and velocity V _INS calculated by the INS system position calculation unit 101 and the position P _GPS and velocity V _GPS obtained from the GPS unit 11 are different from each other because their measurement principles are different. In addition, each value has an inherent error. The best value estimation unit 102 is used to estimate the most probable value from such input values.

The best value estimation unit 102 calculates the input position difference δP ′ = P _GPS −P _INS and the input speed difference δV ′ = V _GPS −V _INS every time there is an input from the GPS unit 11. Based on the differences δP ′ and δV ′, δP and δV which are the most probable values (best values) are estimated. It is assumed that δP and δV are estimated by calculation using a Kalman filter. Details of the calculation will be described later. Best value estimation section 102 outputs best values δP and δV obtained by the estimation to position correction section 103 and acceleration offset calculation section 104.

Based on the vehicle position P _INS input from the INS system position calculation unit 101 and the best value δP of the position difference input from the best value estimation unit 102, the position correction unit 103
P = P _INS + δP
The current most probable position P is calculated by correcting the position P _INS according to, and the obtained position P is used as an output to the navigation software (CPU 10).

  The acceleration offset calculation unit 104 is a correction value for correcting an offset error included in the acceleration a output from the acceleration sensor 12 based on the best value δP of the position difference input from the best value estimation unit 102. The acceleration offset value b is calculated, and the calculated acceleration offset value b is output to the INS system position calculation unit 101. Here, a calculation formula for obtaining the acceleration offset value b from the best position difference δP is determined based on the following assumptions.

That is, if the INS system position calculation unit 101 previously corrected the acceleration a from the acceleration sensor 12 completely (that is, so as to eliminate the offset error), the best position difference obtained by the best value estimation unit 102 is obtained. The value δP should be zero. On the other hand, if the correction of the acceleration a is incomplete (that is, an offset error remains), the position calculated by the INS system position calculation unit 101 by the incomplete amount of acceleration (referred to as b ′). An error occurs in P _INS, and the best value δP of the position difference having a value corresponding to this error should be obtained from the best value estimation unit 102. Therefore, the output δP of the best value estimation unit 102 is a position error caused by the uniform acceleration motion at the acceleration b ′.
δP = (1/2) · b ′ · ΔT ²
Holds.

Therefore, the calculation formula for the acceleration offset calculation unit 104 to calculate the acceleration offset value b is
b = b0 + 2 · δPxy / ΔT ²
And Here, b0 is an acceleration offset value used for the previous acceleration correction in the INS system position calculation unit 101, and ΔT is an elapsed time from the previous acceleration correction to the current time. Further, δPxy is obtained by converting the best value δP expressed by the latitude and longitude obtained from the best value estimation unit 102 into the xy coordinate system fixed to the vehicle (rotation of the azimuth θ).

The acceleration offset value b calculated in this way is input to the INS system position calculation unit 101 and is added to the acceleration a as shown in the above formulas (1A) and (1B), whereby the acceleration obtained from the acceleration sensor 12 is obtained. Correction of a is performed.
The navigation device 1 may calculate the acceleration offset value b by the acceleration offset calculation unit 104 and correct the acceleration a by the INS system position calculation unit 101 using the acceleration offset value b as necessary. (The acceleration determined by the acceleration determination unit 105 described below is a instead of a + b). However, when this processing is performed, the position including the offset error from the acceleration sensor 12 is corrected, and the position is calculated as a constant velocity motion when the corrected acceleration is smaller than the threshold value described above. Therefore, it is possible to obtain the position with higher accuracy.

  Next, a specific example of the operation of the navigation device 1 will be described. FIG. 3 is a flowchart showing an operation example of the navigation device 1.

First, the CPU 10 acquires the position P _GPS , the speed V _GPS, and the traveling direction φ of the vehicle from the GPS unit 11 and stores them in the memory 14 (step S1). Further, the acceleration a including an offset error from the acceleration sensor 12 is obtained. Are acquired from the magnetic sensor 13 and stored in the memory 14 (step S2). Next, the CPU 10 calculates the sum a + b of the acquired acceleration a and the acceleration offset value b held in the memory 14, and determines whether or not the absolute value is equal to or greater than a predetermined threshold (step S3). The acceleration offset value b is an initial value b = (0, 0) when the step S3 is executed for the first time, and is a value calculated at the step S14 after executing the step S14 described below. These are memorized.

When the absolute value of the sum a + b is equal to or greater than a predetermined threshold, the INS system position calculation unit 101 calculates the vehicle position P _INS and the speed V _INS according to the above-described equations (1A) to (1F) (step S4). When the absolute value of the sum a + b is smaller than the predetermined threshold, the INS system position calculation unit 101 calculates the vehicle position P _INS and the speed V _INS in accordance with the above-described equations (2A) to (2E) (step S5).
Before step S3, a step for determining the accuracy of measurement by the GPS unit 11 is provided. For example, step S3 is executed only when the GPS signal cannot be acquired or when the GPS signal is acquired but the accuracy is not good. If the accuracy is sufficiently good, the position P _INS and the speed V _INS may be calculated in step S4. If the accuracy of the measurement result from the GPS unit 11 is good, the acceleration offset value b is calculated in the following step S14, and the above equation (1A) is used using the acceleration corrected by the acceleration offset value b. This is because the position P _INS calculated from (1F) can be expected to be relatively reliable.

Next, the CPU 10 determines whether or not the position P _GPS and the speed V _GPS have been updated (step S6). As will be described later, step S1 is repeated at time Δt _GPS intervals, and step S2 is repeated at time Δt _INS (<Δt _GPS ) intervals. When time Δt _GPS has not yet elapsed, position P _GPS and speed are repeated. Since V _GPS is not updated, the determination in step S6 is NO.

In this case, the position correcting unit 103 corrects the position P _INS calculated in step S4 or step S5 using the latest best value δP held in the memory 14, thereby correcting the current most probable vehicle position P. Is calculated (step S7). The best value δP is calculated and stored in the memory 14 at the previous execution of step S13 described below. In this way, the position correction unit 103 outputs the position P obtained by correcting the position P _INS calculated by the INS system position calculation unit 101 to the navigation software (step S8).

Subsequently, CPU 10 determines whether the elapsed time Delta] t _GPS (step S9), and the process is repeated from step S1 once again the time Delta] t _GPS has elapsed. If not elapsed time Delta] t _GPS is still, CPU 10 determines whether or not next time Delta] t _INS has elapsed (step S10), and repeats the process from step S2 again when the time Delta] t _INS has elapsed. In this way, the data from the GPS unit 11 is updated at the time Δt _GPS interval, and the INS data is updated at the time Δt _INS interval. As an example, Δt _GPS = 1 second and Δt _INS = 0.2 seconds.

When the data from the GPS unit 11 is updated, the determination in step S6 is YES. In this case, the CPU 10 determines whether or not the accuracy of measurement by the GPS unit 11 is sufficiently good (step S11). For example, if the vehicle speed V _GPS obtained from the GPS unit 11 is greater than or equal to a predetermined value, it is determined that the accuracy is sufficiently good. When it is determined that the accuracy is sufficiently good, the CPU 10 calculates a difference δ = θ−φ between the traveling direction φ acquired in step S1 and the orientation θ of the reference axis of the magnetic sensor 13 acquired in step S2, The obtained value of difference δ is added to array A (step S12). This difference δ represents how much the azimuth θ obtained from the magnetic sensor 13 deviates from the traveling direction φ of the vehicle.

Next, the best value estimator 102 calculates the difference δP ′ = P _GPS −P _INS and δV ′ = V _GPS −V _INS calculated from the positions and velocities obtained in steps S1, S4 and S5. The best values δP and δV are estimated (step S13). This estimation result is stored in the memory 14. The acceleration offset calculation unit 104 calculates the acceleration offset value b from the obtained best value δP (step S14). The calculated acceleration offset value b is stored in the memory 14 and used for threshold value determination of the acceleration a + b in step S3. After step S14, the position correcting unit 103 calculates the current most probable vehicle position P using the best value δP estimated in step S13 (step S7).

  On the other hand, if it is determined in step S11 that the accuracy of measurement by the GPS unit 11 is not sufficiently good, the best values δP and δV in step S13 and the acceleration offset value b in step S14 are not calculated. The process moves to step S7. This is because the inaccurate best value δP is estimated based on inaccurate data from the GPS unit 11, and as a result, the position P output from the position correcting unit 103 and the acceleration offset value b output from the acceleration offset calculating unit 104. This is to prevent the accuracy of the process from deteriorating.

Next, the specific process of step S5 mentioned above is demonstrated. FIG. 4 is a flowchart illustrating an example of processing in which the INS system position calculation unit 101 calculates the position and speed when the absolute value of the acceleration a + b is smaller than a predetermined threshold.
The INS system position calculation unit 101 calculates an average δave of each difference δ (a plurality of differences δ corresponding to different times) in the array A in which the value of the difference δ is stored in step S12 (step S51). Using the value δave, the azimuth θ from the magnetic sensor 13 obtained in step S2 is
θ ′ = θ−δave
(Step S52). As a result, the bearing θ is corrected to θ ′ representing the traveling direction of the vehicle, and the traveling direction of the vehicle is obtained from the output θ of the magnetic sensor 13. Using this corrected azimuth θ ′, INS system position calculation unit 101 calculates speed V _INS according to the above-described equations (2B) and (2C) (step S53), and further according to equations (2D) and (2E). The position P _INS is calculated (step S54).

Next, details of the calculation process in which the best value estimation unit 102 estimates the best values δP and δV will be described.
A Kalman filter is applied to the arithmetic processing of the best value estimation unit 102. In the present embodiment, a measurement vector z that is an input to the Kalman filter, a state vector x that is an output thereof, and a state equation that represents a time change of the state vector x are Define as follows.

Here, PN _GPS and PE _GPS are the latitude and longitude components of the position P _GPS obtained from the GPS unit 11, and VN _GPS and VE _GPS are the latitude and longitude components of the velocity V _GPS obtained from the GPS unit 11, respectively. Further, δPN and δPE are the latitude and longitude components of the best value δP, respectively, and δVN and δVE are the latitude and longitude components of the best value δV, respectively. Note that the variable of the subscript INS is of the INS system (described above).

  Under such a definition, the state vector x, which is the output of the Kalman filter, is expressed as follows. However, k (= 1, 2,...) Is a subscript indicating that the best value is estimated for the kth time, and corresponds to time.

Here, K _k is a Kalman gain and is calculated by the following equation.

  However, Δt is an elapsed time from the correction of the acceleration by the acceleration offset value b calculated based on the best value δP estimated at the previous time (k−1th time) to the current time (k time), and each matrix R, P The initial values of Q are as follows.

  The best value estimation unit 102 calculates the state vector x from the measurement vector z according to these equations. The state vector x obtained by this calculation is the best value δP (its latitude and longitude components) and δV (its latitude and longitude components).

As described above, the embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the scope of the present invention. It is possible to
For example, the present invention is suitable for use in a portable navigation device, but is also applicable to a stationary navigation device. In the above embodiment, the vehicle includes an automobile, a motorcycle, a bicycle, and the like.

The calculation formula for the acceleration offset calculation unit 104 to calculate the acceleration offset value b is as follows:
b = b0 + 2 · δPxy / ΔT ² · r
It may be as follows. Here, r is a coefficient for adjusting the degree of change when the acceleration offset value is updated from the previous value b0, and is set as appropriate, for example, r = 0.03.
The calculation formula for the acceleration offset calculation unit 104 to calculate the acceleration offset value b is expressed by the following equation using the best speed value δV obtained from the best value estimation unit 102:
b = b0 + δVxy / ΔT
It may be as follows. However, δVxy is obtained by converting the best value δV represented by latitude and longitude into the xy coordinate system fixed to the vehicle (rotation of the azimuth θ).

The best value estimation unit 102 calculates the position P _GPS and P _INS and the speed V _GPS without calculating the position and speed differences δP ′ = P _GPS −P _INS and δV ′ = V _GPS −V _INS. The best position value P and the best speed value V may be estimated directly from V _INS . In this case, in the calculation of the Kalman filter for estimation, the measurement vector z to be input and the state vector x to be output are appropriately corrected, and the best value P given by the calculated state vector x is directly used as navigation software (CPU 10 ).
Further, instead of the magnetic sensor 13, another direction sensor such as a gyro sensor may be used.

If the GPS unit 11 cannot acquire a GPS signal or if the reliability of the GPS signal is not sufficient, the acceleration offset value can be calculated by the method shown in FIGS.
That is, the acceleration and deceleration of the vehicle is usually completed in a short period (for example, a few seconds), and the acceleration caused by the acceleration changes abruptly in a short period, while the slope of the road does not change abruptly. Focusing on the fact that acceleration shows a constant value over a long period of time, it is possible to determine whether the acceleration output from the acceleration sensor is due to acceleration or deceleration of the vehicle, or due to road inclination, etc. An acceleration offset value can be calculated based on the result.

  Hereinafter, a method for distinguishing between vehicle acceleration and deceleration and road inclination will be described in detail. FIG. 5 is a graph showing an output example of the acceleration sensor obtained by running the vehicle. In FIG. 5, an acceleration waveform a1 represents a change in the output of the acceleration sensor 12 due to acceleration or deceleration of the vehicle. In the acceleration waveform a1, the acceleration changes greatly from a to b in the period t1. Further, the acceleration waveform a2 represents a change in the output of the acceleration sensor 12 due to the road inclination. In the acceleration waveform a2, the acceleration hardly changes from c to d in the period t2. Thus, the amount of change in acceleration within a certain period differs between the case of acceleration or deceleration of the vehicle and the case of slope of the road. Therefore, if the difference (change amount) between the maximum value and the minimum value of acceleration is larger than a predetermined value, it is determined that the vehicle is accelerating or decelerating. If it is smaller than the predetermined value, it is determined that the road is inclined. Thus, the two can be distinguished.

  Next, a specific example of calculating an acceleration offset value using the above method according to the acceleration output from the acceleration sensor will be described. FIG. 6 is a graph showing an example of a method for calculating the acceleration offset value from the output of the acceleration sensor. First, when acceleration such as the acceleration waveform A1 shown in FIG. 6A is output from the acceleration sensor 12, a short-cycle noise indicating a vehicle vibration component is suppressed by using a low-pass filter, and FIG. A filter output waveform B1 shown in (B) is obtained.

  Next, the acceleration offset calculation unit 104 calculates an average value in a predetermined period, and a maximum value and a minimum value in the period, from the filter output waveform B1 in FIG. The acceleration offset calculation unit 104 determines that the vehicle is accelerated or decelerated when the difference between the calculated maximum value and the minimum value is equal to or greater than a predetermined value, and the difference between the calculated maximum value and the minimum value is determined. Is less than or equal to a predetermined value, it is determined that the vehicle is not accelerating or decelerating, that is, acceleration due to road inclination or the like. In the filter output waveform B1 of FIG. 6B, it is determined that the period a and the period c are accelerating or decelerating, and the period b is determined as a road slope.

  The acceleration offset calculation unit 104 sets the calculated average value as the offset value of the acceleration sensor 12 during the period (period b) in which it is determined that acceleration or deceleration is not performed. Further, the acceleration offset calculation unit 104 maintains the previous value and does not change the offset value of the period (period a and period c) determined as accelerating or decelerating. That is, since the offset value has not yet been obtained at time “0”, offset value = “0” is maintained in period a, and the last offset value in period b is maintained in period c. The acceleration offset calculation unit 104 outputs the acceleration offset value calculated in this way to the INS system position calculation unit 101. A graph representing the acceleration offset value calculated by the acceleration offset calculation unit 104 is an offset waveform C1 in FIG. As described above, when the GPS unit 11 cannot acquire the GPS signal or the reliability of the GPS signal is not sufficient, the acceleration offset value can be calculated without using the GPS signal.

  Further, when the vehicle is traveling, the acceleration output from the acceleration sensor 12 is also changed by the centrifugal force while traveling along the curve. In order to obtain the correct acceleration due to acceleration or deceleration of the vehicle in consideration of the acceleration due to this curve, the acceleration in the θ ′ direction of the acceleration output from the acceleration sensor 12 is based on the traveling direction θ ′ of the vehicle obtained in step S52 described above. A component and a component in a direction perpendicular to θ ′ are obtained, and the former is determined as acceleration or deceleration of the vehicle, and the latter is determined as a centrifugal force on the curve. It is also possible to use only the component in the traveling direction θ ′ as the acceleration value due to acceleration or deceleration of the vehicle. As a result, the acceleration of the vehicle can be obtained with higher accuracy.

It is a block diagram of the navigation apparatus by one Embodiment of this invention. It is a figure which shows the functional block of a navigation apparatus. It is a flowchart which shows the operation example of a navigation apparatus. It is a flowchart which shows the example of a process which calculates a position and speed when the absolute value of an acceleration is smaller than a predetermined threshold value. It is the graph which showed the output example of the acceleration sensor obtained by driving | running | working of a vehicle. It is the graph which showed the example of the method of calculating an acceleration offset value from the output of an acceleration sensor.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... CPU 11 ... GPS part 12 ... Acceleration sensor 13 ... Magnetic sensor 14 ... Memory 15 ... External storage device 16 ... Communication part 17 ... Display device 18 ... Audio output device 19 ... Bus line 101 ... INS system position calculation part 102 ... Best Value estimating unit 103 ... Position correcting unit 104 ... Acceleration offset calculating unit 105 ... Acceleration determining unit

Claims (3)

In a navigation device that obtains the current position and provides position guidance,
Acceleration determining means for comparing the acceleration obtained from the acceleration sensor with a predetermined threshold;
If the acceleration determining means determines that the absolute value of the acceleration is greater than the threshold, the current position is calculated based on the acceleration and the past position and moving speed stored in the storage means, and the acceleration When the determination means determines that the absolute value of the acceleration is smaller than the threshold value, it is regarded as a constant velocity motion, and the azimuth based on the measurement by the azimuth sensor and the past position and movement speed stored in the storage means A position calculating means for calculating a current position based on;
A navigation device comprising: Measuring means for obtaining a position by GPS and obtaining a moving speed from a plurality of positions at different times obtained;
The position and moving speed obtained by the measuring means and the position obtained by the position calculating means and the moving speed calculated based on the position are input to the Kalman filter to obtain the best value regarding the current most probable position. A best value estimating means for estimating;
Based on the best value estimated by the best value estimating means, the position error obtained by the position calculating means is assumed to be caused by the offset error of the acceleration sensor, and the acceleration is corrected by the offset error. Acceleration offset calculating means for calculating an acceleration offset value of
Further comprising
The acceleration determination means corrects the acceleration obtained from the acceleration sensor using the acceleration offset value calculated by the acceleration offset calculation means, and compares the corrected acceleration with the threshold value. Item 4. The navigation device according to Item 1. Acceleration offset calculating means for calculating an acceleration offset value according to the acceleration value obtained from the acceleration sensor when a change in the acceleration obtained from the acceleration sensor at a predetermined time is equal to or less than a predetermined value. ,
The acceleration determination means corrects the acceleration obtained from the acceleration sensor using the acceleration offset value calculated by the acceleration offset calculation means, and compares the corrected acceleration with the threshold value. Item 4. The navigation device according to Item 1.

Images