Automotive attitude estimation system and method for calculating offset error of 3-axis accelerometer

Abstract

This invention provides a "vehicle attitude estimation system and a method for calculating offset errors of a 3-axis acceleration sensor" that corrects errors caused by the mounting orientation of the acceleration sensor on the vehicle. [Solution] The vehicle is parked facing forward in the parking space, and the Roll angle Roll_A and Pitch angle Pitch_A are measured using a 3-axis acceleration sensor 1 (b1). The vehicle is parked facing backward in the parking space, and the Roll angle Roll_B and Pitch angle Pitch_B are measured (b2). The average of Roll_A and Roll_B is set as the offset error in the Roll direction, and the average of Pitch_A and Pitch_B is set as the offset error in the Pitch direction.

Description

Technical Field

[0001] The present invention relates to an automobile attitude estimation system.

Background Art

[0002] As a technology related to an attitude estimation system for estimating the attitude of an automobile, in a system that calculates the pitch angle of an automobile using an acceleration sensor, the amount of azimuth change measured using a GPS receiver and the amount of azimuth change measured using a gyro sensor fixed to the same base as the acceleration sensor are made to match. Thus, the mounting attitude (relative attitude with respect to the automobile) of the acceleration sensor with respect to the automobile is obtained, and according to the obtained mounting attitude, the pitch angle calculated using the acceleration sensor is corrected (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to the technique of calculating the mounting attitude of the acceleration sensor with respect to the automobile and correcting the pitch angle calculated using the acceleration sensor, a gyro sensor and a GPS receiver are required for correction, and relatively a lot of time and processing amount are required for calculating the mounting attitude. Therefore, an object of the present invention is to correct an error caused by the mounting attitude of an acceleration sensor with respect to an automobile in a simple configuration in the calculation of the attitude of the automobile using the acceleration sensor.

Means for Solving the Problems

[0005] To achieve the above objectives, the present invention provides an automobile attitude estimation system comprising: a three-axis acceleration sensor fixed to the automobile; an attitude calculation means for calculating the roll angle of the automobile using the three-axis acceleration sensor; an offset error setting means for setting an offset error in the measurement of the automobile's roll angle using the three-axis acceleration sensor; and an attitude correction means for correcting the roll angle of the automobile calculated by the attitude calculation means so as to cancel the offset error. Here, the offset error setting means sets the offset error as the average of a first roll angle measured using the three-axis acceleration sensor when the automobile is parked in a first location in a first orientation and a second roll angle measured using the three-axis acceleration sensor when the automobile is parked in the first location in a second orientation opposite to the first orientation.

[0006] Furthermore, in order to achieve the above objectives, the present invention provides an automobile attitude estimation system comprising: a three-axis acceleration sensor fixed to the automobile; an attitude calculation means for calculating the pitch angle of the automobile using the three-axis acceleration sensor; an offset error setting means for setting an offset error in the measurement of the pitch angle of the automobile using the three-axis acceleration sensor; and an attitude correction means for correcting the pitch angle of the automobile calculated by the attitude calculation means so as to cancel the offset error. Here, the offset error setting means sets the offset error as the average of a first pitch angle measured using the three-axis acceleration sensor when the automobile is parked in a first location in a first orientation and a second pitch angle measured using the three-axis acceleration sensor when the automobile is parked in the first location in a second orientation opposite to the first orientation.

[0007] Furthermore, in order to achieve the above objectives, the present invention provides a 3-axis acceleration sensor fixed to an automobile, The present invention provides an automobile attitude estimation system comprising: attitude calculation means for calculating the roll angle and pitch angle of the automobile using the three-axis acceleration sensor; offset error setting means for setting the offset error of the roll angle measurement and the offset error of the pitch angle of the automobile using the three-axis acceleration sensor; and attitude correction means for correcting the roll angle of the automobile calculated by the attitude calculation means so as to cancel the offset error of the roll angle measurement, and correcting the pitch angle of the automobile calculated by the attitude calculation means so as to cancel the offset error of the pitch angle measurement. Here, the offset error setting means sets the average of a first roll angle measured using the 3-axis acceleration sensor when the vehicle is parked in the first location in a first orientation and a second roll angle measured using the 3-axis acceleration sensor when the vehicle is parked in the first location in a second orientation opposite to the first orientation as the offset error for the roll angle measurement, and sets the average of a first pitch angle measured using the 3-axis acceleration sensor when the vehicle is parked in the first location in a first orientation and a second pitch angle measured using the 3-axis acceleration sensor when the vehicle is parked in the first location in a second orientation as the offset error for the pitch angle measurement.

[0008] Herein, the attitude estimation system may be provided with guidance means that guides the driver of the vehicle to park in the first location in the first orientation and to park in the first location in the second orientation, with the first location being a parking space demarcated by lane lines.

[0009] Furthermore, in order to achieve the above objectives, the present invention provides a method for calculating the offset error of a three-axis acceleration sensor, characterized by comprising the steps of: measuring the inclination angle with respect to the horizontal as a first inclination angle using a three-axis acceleration sensor fixed to the vehicle while the vehicle is parked in a first location in a first orientation; measuring the inclination angle as a second inclination angle using the three-axis acceleration sensor while the vehicle is parked in the first location in a second orientation opposite to the first orientation; and calculating the average of the first inclination angle and the second inclination angle as the offset error of the inclination angle of the vehicle with respect to the horizontal measured by the three-axis acceleration sensor.

[0010] According to the attitude estimation system and offset error calculation method described above, by simply performing measurements using a 3-axis accelerometer in a state where the car is parked in a first orientation at a first location, and in a state where the car is parked in a second orientation opposite to the first orientation at the first location, it becomes possible to correct errors that occur depending on the mounting orientation of the 3-axis accelerometer to the car when calculating the attitude of the car using the 3-axis accelerometer, regardless of whether the first location is horizontal or not. [Effects of the Invention]

[0011] As described above, according to the present invention, in calculating the attitude of an automobile using an acceleration sensor, errors that occur depending on the mounting position of the acceleration sensor on the automobile can be corrected with a simple configuration. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows the configuration of a posture estimation system according to an embodiment of the present invention. [Figure 2] This figure shows the coordinate system used in an embodiment of the present invention. [Figure 3] A flowchart of the calibration process according to an embodiment of the present invention is shown. [Figure 4] This figure shows an example of a calibration process according to an embodiment of the present invention. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described below. Figure 1 shows the configuration of the attitude estimation system according to this embodiment. The attitude estimation system is a system mounted on an automobile and, as shown in the figure, comprises a 3-axis acceleration sensor 1, other sensors 2 such as an angular velocity sensor and a speed sensor, an attitude calculation unit 3, an attitude correction unit 4, an attitude usage processing unit 5, a control unit 6, vehicle condition sensors 7 such as a vehicle speed sensor that detect various states of the automobile, and a UI device 8 that receives user input and outputs displays to the user.

[0014] Here, as shown in Figures 2a1 and 2b1, the attitude estimation system estimates the Roll angle, which is the tilt angle of the vehicle around the X axis, and the Pitch angle, which is the tilt angle of the vehicle around the Y axis, with Z being the vertical axis of the vehicle, X being the longitudinal axis of the vehicle, and Y being the lateral axis of the vehicle. Furthermore, the 3-axis accelerometer 1 is an orthogonal 3-axis accelerometer with axes LX-LY-LZ. As shown in Figures 2b1 and b2, the LX-LY-LZ system, which is the local coordinate system fixed to the 3-axis accelerometer 1, is tilted relative to the XYZ system, which is the fixed coordinate system of the vehicle, depending on the mounting angle of the 3-axis accelerometer 1 to the vehicle (its orientation relative to the vehicle).

[0015] Returning to Figure 1, the attitude calculation unit 3 uses the outputs of the 3-axis acceleration sensor 1 and other sensors 2 to calculate the attitude of the vehicle, including the roll angle and pitch angle. However, the attitude calculation unit 3 calculates the attitude of the vehicle using the output of the 3-axis acceleration sensor 1, assuming that the local system LX-LY-LZ of the 3-axis acceleration sensor 1 matches the vehicle's fixed system XYZ.

[0016] The posture correction unit 4 corrects the Roll angle and Pitch angle among the postures of the automobile calculated by the posture calculation unit 3 by using the correction parameters set from the control unit 6 so that the inclination of the local system LX-LY-LZ of the three-axis acceleration sensor 1 with respect to the fixed system X-Y-Z of the automobile is reflected. The posture use processing unit 5 performs processing using the Roll angle and Pitch angle corrected by the posture correction unit 4 and other postures calculated by the posture calculation unit 3. Here, as the posture use processing unit 5, for example, a processing unit that causes the posture estimation system to function as an inclination angle meter of the automobile by displaying the Roll angle and Pitch angle of the automobile can be used. When the control unit 6 is instructed to execute calibration of the mounting angle of the three-axis acceleration sensor 1 via the UI device 8 from a user, a maintenance worker, etc., the control unit 6 performs calibration processing and sets the correction parameters used by the posture correction unit 4 for correction. Fig. 3 shows the procedure of this calibration processing. As shown in the figure, in this processing, the control unit 6 first guides the driver to park in the forward direction in the parking section (step 302). Here, parking in the forward direction is defined as reverse parking, and parking in the reverse direction is defined as forward parking. However, conversely, parking in the forward direction may be defined as forward parking, and parking in the reverse direction may be defined as reverse parking.

[0017] This guidance is performed, for example, by displaying and outputting a message such as "Please park in the reverse direction in the parking section" from the UI device 8. In this embodiment, as the parking section, as shown in Fig. 4a, a parking section for automobiles at least bounded by white lines on the left and right is targeted. Returning to Fig. 3, it is determined whether the driver has completed parking in the forward direction in the parking section (step 304). This determination can be made, for example, by receiving an operation indicating parking completion from the driver via the UI device 8. However, the determination may also be made taking into account whether the vehicle state sensor 7 has detected a vehicle speed of 0, whether the three-axis acceleration sensor 1 has detected no acceleration variation above a predetermined level, etc.

[0018] Then, for example, once the vehicle has completed parking in the parking space facing forward as shown in Figure 4b1, the Roll angle and Pitch angle calculated by the attitude calculation unit 3 are measured as Roll_A and Pitch_A, respectively (step 306). However, the Roll angle, which is the tilt angle around the LX axis of the 3-axis accelerometer 1, may be measured directly from the 3-axis accelerometer 1, and the Pitch angle, which is the tilt angle around the LY axis of the 3-axis accelerometer 1, may be measured as Roll_A. Furthermore, let ax be the acceleration in the LX direction, ay be the acceleration in the LY direction, and az be the acceleration in the LZ direction detected by the 3-axis accelerometer 1. When the car is stationary, the Roll angle, which is the tilt angle around the LX axis of the 3-axis accelerometer 1, and the Pitch angle, which is the tilt angle around the LY axis, are as follows: Roll angle = arctan(ax / ay) Pitch angle = arctan(-az / {ax}) 2 +ay 2} 1 / 2 ) It is expressed as follows.

[0019] Next, the driver is instructed to park in the reverse direction into the parking space (step 308). This guidance is provided, for example, by displaying a message from the UI device 8 such as, "Now, please park facing forward in the same parking space." Next, it is determined whether the driver has completed parking in the reverse direction into the parking space (step 310). For example, if the driver has completed parking in the reverse direction into the parking space as shown in Figure 4b2, the Roll angle and Pitch angle calculated by the attitude calculation unit 3 are measured as Roll_B and Pitch_B (step 312).

[0020] However, the Roll angle, which is the tilt angle around the LX axis of the 3-axis accelerometer 1, may be measured directly from the 3-axis accelerometer 1, and the Pitch angle, which is the tilt angle around the LY axis of the 3-axis accelerometer 1, may be measured as Roll_B. Then, the average of Roll_A and Roll_B (Roll_A + Roll_B) / 2 is set as the Roll offset (step 314), and the average of Pitch_A and Pitch_B (Pitch_A + Pitch_B) / 2 is set as the Pitch offset (step 316). Then, the Roll offset and Pitch offset are set as correction parameters in the attitude correction unit 4 (step 318), and the process is terminated. Here, Roll_A and Roll_B each represent the sum of the offset error, which is the difference between the Roll angle calculated by the attitude calculation unit 3 and the actual Roll angle of the vehicle, and the inclination angle of the road surface in the Roll direction. Furthermore, since the slope within a single parking space can be considered uniform, as shown in Figures 4c1 and c2, when parking in the same parking space in the opposite direction, the slope of the road surface in the Roll direction will have its sign reversed. Therefore, in the case of Figures 4c1 and 4c2, if we assume that the slope of the road surface in the Roll direction in Figure 4c1 is -θ and the offset error of the Roll angle of the attitude calculation unit 3 is dR, then Roll_A = -θ + dR and Roll_B = θ + dR, and their average is (-θ + dR + θ + dR) / 2 = 2dR / 2 = dR, so even if the road surface is not horizontal, the offset error dR of the Roll angle of the attitude calculation unit 3 can be obtained.

[0021] Similarly, Pitch_A and Pitch_B represent the sum of the offset error, which is the difference between the pitch angle calculated by the attitude calculation unit 3 and the actual pitch angle of the vehicle, and the inclination angle of the road surface in the pitch direction. Furthermore, since the slope within a single parking space can be considered uniform, as shown in Figures 4d1 and d2, when parking in the same parking space in opposite directions, the slope of the road surface in the pitch direction will have its sign reversed. In the case of Figures 4d1 and 4d2, if we let φ be the slope of the road surface in the pitch direction in Figure 4d1, and dP be the offset error of the pitch angle of the attitude calculation unit 3, then Pitch_A = φ + dP and φl_B = -φ + dP, and their average is {φ + dP + (-φ + dP)} / 2 = 2dP / 2 = dP, so even if the road surface is not horizontal, the offset error dP of the pitch angle of the attitude calculation unit 3 can be obtained.

[0022] Therefore, the offset error of the roll angle obtained in this way is set as the roll offset, and the offset error of the pitch angle is set as the pitch offset, and both are set as correction parameters in the attitude correction unit 4. Furthermore, the offset errors in the Roll angle and Pitch angle represent the errors in the Roll angle and Pitch angle calculations performed by the attitude calculation unit 3, which are caused by the deviation (tilt) of the local system LX-LY-LZ of the 3-axis acceleration sensor 1 relative to the vehicle's fixed system XYZ. Now, the attitude correction unit 4, with the correction parameters set in this manner, cancels the offset error of the Roll angle by subtracting the Roll offset set as a correction parameter from the Roll angle of the vehicle calculated by the attitude calculation unit 3, and cancels the offset error of the Pitch angle by subtracting the Pitch offset set as a correction parameter from the Pitch angle of the vehicle calculated by the attitude calculation unit 3, thereby correcting the Roll angle and Pitch angle of the vehicle calculated by the attitude calculation unit 3, and outputs them to the attitude usage processing unit 5.

[0023] For example, if the roll offset is 1 degree, the pitch offset is -20 degrees, and the attitude calculation unit 3 calculates the vehicle's attitude with a roll angle of 3 degrees and a pitch angle of -18 degrees, then the roll angle is corrected to 3-1=2 degrees and the pitch angle to -18-(-20)=2 degrees. Embodiments of the present invention have been described above. Thus, according to this embodiment, by simply performing measurements using the 3-axis acceleration sensor 1 in both the state where the car is parked facing forward and the state where the car is parked facing backward in the same parking space, errors caused by the mounting orientation of the 3-axis acceleration sensor 1 to the car can be corrected in the calculation of the car's attitude using the 3-axis acceleration sensor 1, regardless of whether the parking space is level or not.

[0024] Here, we have determined the roll offset and pitch offset by parking a car in the same parking space facing forward and backward. However, the place where the car is parked facing forward and backward does not have to be a parking space; it can be any same location with a roughly uniform slope. [Explanation of Symbols]

[0025] 1...3-axis acceleration sensor, 2...other sensors, 3...attitude calculation unit, 4...attitude correction unit, 5...attitude usage processing unit, 6...control unit, 7...vehicle status sensor, 8...UI device.

Claims

1. A three-axis accelerometer fixed to the car, A posture calculation means for calculating the roll angle of the automobile using the three-axis acceleration sensor, Offset error setting means for setting the offset error of measuring the roll angle of the automobile using the three-axis acceleration sensor, The vehicle has a posture correction means that corrects the roll angle of the vehicle calculated by the posture calculation means so that the offset error is canceled, The vehicle attitude estimation system is characterized in that the offset error setting means sets the average of a first roll angle measured using the three-axis acceleration sensor when the vehicle is parked in a first location in a first orientation and a second roll angle measured using the three-axis acceleration sensor when the vehicle is parked in a first location in a second orientation opposite to the first orientation as the offset error.

2. A three-axis accelerometer fixed to the car, A posture calculation means for calculating the pitch angle of the automobile using the three-axis acceleration sensor, An offset error setting means for setting the offset error of the pitch angle measurement of the automobile using the three-axis acceleration sensor, The vehicle has a posture correction means that corrects the pitch angle of the vehicle calculated by the posture calculation means so that the offset error is canceled, The vehicle attitude estimation system is characterized in that the offset error setting means sets the average of a first pitch angle measured using the three-axis acceleration sensor when the vehicle is parked in a first location in a first orientation and a second pitch angle measured using the three-axis acceleration sensor when the vehicle is parked in a first location in a second orientation opposite to the first orientation as the offset error.

3. A three-axis accelerometer fixed to the car, A posture calculation means for calculating the roll angle and pitch angle of the automobile using the three-axis acceleration sensor, An offset error setting means for setting the offset error of the roll angle measurement and the pitch angle offset error of the automobile using the three-axis acceleration sensor, The vehicle has a posture correction means that corrects the roll angle of the vehicle calculated by the posture calculation means so as to cancel the offset error of the roll angle measurement, and corrects the pitch angle of the vehicle calculated by the posture calculation means so as to cancel the offset error of the pitch angle measurement. The vehicle attitude estimation system is characterized in that the offset error setting means sets the average of a first roll angle measured using the three-axis acceleration sensor when the vehicle is parked in a first location in a first orientation and a second roll angle measured using the three-axis acceleration sensor when the vehicle is parked in a first location in a second orientation opposite to the first orientation as the offset error for roll angle measurement, and sets the average of a first pitch angle measured using the three-axis acceleration sensor when the vehicle is parked in a first location in a first orientation and a second pitch angle measured using the three-axis acceleration sensor when the vehicle is parked in a first location in a second orientation as the offset error for pitch angle measurement.

4. A posture estimation system according to claim 1, 2, or 3, An automobile attitude estimation system characterized in that the first location is a parking space demarcated by lane lines, and the system has guidance means for guiding the driver of the automobile to park in the first location in the first orientation and to park in the first location in the second orientation.

5. With the vehicle parked in a first location in a first orientation, the three-axis acceleration sensor fixed to the vehicle is used to measure the tilt angle relative to the horizontal as the first tilt angle. The steps include: measuring the tilt angle as the second tilt angle using the three-axis acceleration sensor while the vehicle is parked in the first location in a second orientation opposite to the first orientation; A method for calculating the offset error of a three-axis acceleration sensor, characterized by comprising the step of calculating the average of the first tilt angle and the second tilt angle as the offset error of the tilt angle of the vehicle with respect to the horizontal, as measured by the three-axis acceleration sensor.

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