Patent Grant
12174305
This application is a National Stage application under 35 U.S.C. § 371 of International Application No. PCT/JP2019/036795, having an International Filing Date of Sep. 19, 2019, the disclosure of which is considered part of the disclosure of this application, and is incorporated in its entirety into this application.
The present invention relates to a technique for measuring an absolute position of a mobile object such as a traveling vehicle with high accuracy in autonomous vehicles, advanced driver assistance systems (ADAS), and the like.
In recent years, positioning using a Global Navigation Satellite System (GNSS) has been used in a wide range of applications.
One application that employs positioning using a GNSS is positioning for an autonomous vehicle. A submeter positioning accuracy for absolute positions (an order of several centimeters to several tens of centimeters) is required in an autonomous vehicle in order to allow lane determination.
However, in a case where GNSS positioning is used as absolute position measurement means, a delay (several tens of milliseconds or more) occurring in positioning computation processing makes it difficult to measure an absolute position with high accuracy in a moving direction in real time (current time). For example, in a case where a vehicle travels at a speed of 60 km per hour, the vehicle moves 16 cm per 10 ms.
Furthermore, in a case where GNSS positioning is used as absolute position measurement means, positioning may be temporarily unavailable in an environment in which a GNSS signal cannot be received, such as in a tunnel or under an elevated structure.
For example, as disclosed in NPL 1, in order to estimate the position of a mobile object, and the like with high accuracy and enable positioning even when positioning using a GNSS signal temporarily is unavailable, a GNSS/IMU (composite inertial measurement unit) that uses both of relative positioning means (an IMU, a vehicle speed pulse, or the like) and absolute positioning means in combination and performs positioning computation such as self-position estimation computation using a Kalman filter is widely used.
In general, relative positioning means such as an IMU or a vehicle speed pulse periodically outputs data of positioning results. However, when positioning computation processing based on Kalman filter computation or the like is performed using measurement results of absolute positioning means and measurement results of one or more relative positioning means in combination, the real-time performance of data may be impaired due to a difference in the cycle of data output between positioning means and standby for data output, which may affect the accuracy of positioning.
Additionally, in recent years, absolute positioning means and relative positioning means have increasingly diversified, and a delay in processing and/or a delay in propagation of data may affect the positioning accuracy in composite positioning in which positioning is performed by combining a plurality of positioning means.
The present invention is contrived in view of the above-described circumstances, and an object of the present invention is to provide a technique making it possible to measure an absolute position at any time with high accuracy in composite positioning in which positioning is performed by combining absolute positioning means and relative positioning means.
According to the disclosed technique, a position measurement system includes: an absolute positioning measuring unit configured to measure an absolute position of a mobile object, attach a first time stamp to an absolute position measurement result, and output the absolute position measurement result with the first time stamp;
According to the disclosed technology, a technique making it possible to measure an absolute position at any time with high accuracy in composite positioning in which positioning is performed by combining absolute positioning means and relative positioning means is provided.
Hereinafter, an embodiment of the present invention (the present embodiment) will be described with reference to the drawings. The embodiment to be described below is merely exemplary, and an embodiment to which the present invention is applied is not limited to the following embodiment.
In the following embodiment, a vehicle that travels on a road is exemplified as a mobile object subject to position measurement, but this is an example. The present invention is applicable to any mobile object that is not limited to vehicles that travel on roads.
Further, in
In the example illustrated in
The position measurement system 100 may be one apparatus which is physically integrated, or may be an apparatus in which some functional units are physically separated and the plurality of separate functional units are connected by a network. For example, the positioning computation unit 110 may be a computer operating in accordance with a program, and the other functional units may be configured to be connected to the computer.
Furthermore, the position measurement system 100 may be used such that the entire position measurement system is mounted on a mobile object, or may be used such that part of the entire position measurement system is mounted on a mobile object. For example, the absolute positioning measuring unit 120, the relative positioning measuring units 130A and 130B, and the clock 140 may be mounted on a mobile object, and the positioning computation unit 110 may be provided at a remote location (for example, a data center that implements the cloud, or the like). The control target apparatus 210 may be a mobile object itself.
Further, in a case where the absolute positioning measuring unit 120 is a GNSS receiver, a positioning computation function using a GNSS signal may be provided at a remote location (for example, a data center that implements a cloud, or the like) together with the positioning computation unit 110. In this case, the absolute positioning measuring unit 120 transmits observation data (also referred to as raw data) to the positioning computation function, and the positioning computation function performs positioning computation. The positioning computation unit 110 performs positioning computation using an extended Kalman filter or the like, based on positioning computation results and relative positioning results received from the relative positioning measuring unit 130.
Each unit will be described below.
The absolute positioning measuring unit 120 is a functional unit that measures an absolute position, and is a remote sensing device such as a GNSS receiver, a simultaneous localization and mapping (SLAM), or a LiDAR.
The absolute positioning measuring unit 120 includes a time stamper 121 that stamps a time stamp to a positioning result at a timing when an absolute position measuring result (absolute positioning result) is output (a timing immediately after positioning result data is generated without performing buffering and standby). For example, in a case where the absolute positioning measuring unit 120 is a GNSS receiver, a time obtained by correcting a time included in a navigation message of a navigation satellite signal of a certain time by a propagation delay time elapsed until the navigation satellite signal reaches a receiver, is stamped on a positioning result calculated from the navigation satellite signal. The time stamper 121 has a function of performing time correction or time stamping.
In addition, the absolute positioning measuring unit 120 has a function of synchronizing the clock 140 with absolute time by acquiring highly accurate absolute time information (time information synchronized with coordinated universal time (UTC)) from a GNSS signal received from a positioning satellite and supplying the absolute time information to the clock 140 included in the position measurement system 100.
The clock 140 acquires the above-described absolute time information to operate in synchronization with absolute time. Further, in a case where the absolute positioning measuring unit 120 cannot successfully receive a GNSS signal, that is, even when the absolute positioning measuring unit 120 cannot acquire the absolute time information, the clock 140 has a function of continually outputting highly accurate time for a certain period of time by an operation of calculating time information of the clock based on a clock signal of an oscillator (holdover).
That is, in a case where a mobile object having the absolute positioning measuring unit 120 mounted thereon enters an urban canyon, and a reception environment for a GNSS signal deteriorates, the clock 140 can provide absolute time information with the accuracy of an order of 10 microseconds with respect to the UTC even when a GNSS signal cannot temporarily be received at the time of passing through a tunnel or under an elevated structure, or the like. In addition, a holdover operation can be performed for several tens of minutes under the frequency stability of a crystal oscillator such as TCXO or OCXO included in the clock 140.
The relative positioning measuring unit 130 is a functional unit that measures a relative displacement or the like from a certain position, and is, for example, a vehicle speed pulse measuring device, an acceleration sensor, a gyro, an IMU, an in-vehicle camera, or the like.
In addition, the relative positioning measuring unit 130 includes a time stamper 131 that can stamp a highly accurate time on relative positioning results.
More specifically, the clock 140 and the relative positioning measuring unit 130 (and the time stamper 131) mentioned above are connected to each other by a time synchronization network such as a PTP or a TSN (IEEE802.1 time sensitive network (TSN)), and the clock 140 and the time stamper 131 are time-synchronized. As described above, the clock 140 can supply an accurate absolute time (with an extremely small error), and thus the time stamper 131 time-synchronized with the clock 140 can stamp the accurate absolute time on a positioning result as a time stamp.
In addition, the time stamper 131 stamps a time stamp on a positioning result at a timing when the relative positioning measuring unit 130 outputs a positioning result (a timing immediately after positioning result data is generated without performing buffering and standby).
Note that, in a case where a physical distance between the clock 140 and the relative positioning measuring unit 130 is short such as a case where the clock 140 and the relative positioning measuring unit 130 are present in the same housing, the clock 140 and the relative positioning measuring unit 130 may be connected by means other than a time synchronization network such as a PTP or a TSN (IEEE802.1 time sensitive network (TSN)).
A detailed example of operations related to the clock 140 will be described with reference to
A GNSS may cause system failures from which recovery takes about a week, and thus it can be expected that such system failures will occur in the future.
In the present embodiment, for a long term GNSS system failure, the accuracy of time information is maintained by the clock 140 being network-synchronized with a highly accurate oscillator, such as a cesium or optical lattice clock, which is installed in a network to which the clock 140 is connected.
In other words, as illustrated in
In a case where it is assumed that the frequency accuracy of the cesium atomic oscillator is 0.01 ppb (10−11), and a necessary time accuracy (a deviation in time) is set to be within 5 microseconds, a holdover time is 5×10−6/10−11=5×105 (sec)≈139 hours.
Conceivable modes of network synchronization include synchronization based on a frequency synchronization network such as synchronous Ethernet (SyncE) with respect to an intra-network clock source using a highly accurate cesium atomic oscillator, and synchronization based on a time synchronization network such as a precision time protocol (PTP) with respect to a clock in a network operated by a highly accurate cesium atomic oscillator.
Next, the positioning computation unit 110 in the position measurement system 100 illustrated in
In addition, the positioning computation unit 110 includes a time stamper 111. The positioning computation unit 110 (and the time stamper 111) is time-synchronized with the clock 140 by a PTP, a TSN, or the like. For this reason, the time stamper 111 can stamp a time stamp of an accurate time on a positioning computation result at a timing immediately after the positioning computation result is generated (=a timing at which the positioning computation result is output).
The positioning computation unit 110 can be implemented, for example, by a computer operating in accordance with a program.
A program for implementing processing in the computer is provided by, for example, a recording medium 1001 such as a CD-ROM or a memory card. When the recording medium 1001 that stores a program is set in the drive device 1000, the program is installed in the auxiliary storage device 1002 from the recording medium 1001 via the drive device 1000. Here, the program may not necessarily be installed from the recording medium 1001 and may be downloaded from another computer via a network. The auxiliary storage device 1002 stores the installed program and also stores necessary files, data, and the like.
The memory device 1003 reads the program from the auxiliary storage device 1002 and stores the program in a case where an instruction to start the program is given. The CPU 1004 performs functions related to the positioning computation unit 110 and the like in accordance with the program stored in the memory device 1003. The interface device 1005 is used as an interface for connection to a network. The display device 1006 displays a graphical user interface (GUI) or the like according to a program. The input device 1007 is constituted by a keyboard, a mouse, buttons, a touch panel, or the like, and is used to input various operation instructions.
As described above, the positioning computation unit 110 can output a positioning computation result at any time including real time and a future time with a time stamp.
In addition, the positioning computation unit 110 may output a data output time (that is, the value of a time stamp attached to a positioning result) in the positioning measuring unit (the absolute positioning measuring unit 120 or the relative positioning measuring unit 130, or both the absolute positioning measuring unit 120 and the relative positioning measuring unit 130) as information regarding the freshness of a positioning computation result.
In addition, the positioning computation unit 110 may output a delay in processing (including a delay in propagation of a signal), which is a difference between a data output time in the positioning measuring unit (the value of a time stamp attached to a positioning result) and an output time of a positioning computation result (the value of a time stamp attached to a positioning computation result) as information regarding the freshness of a positioning computation result. The positioning measuring unit is the absolute positioning measuring unit 120 or the relative positioning measuring unit 130, or both the absolute positioning measuring unit 120 and the relative positioning measuring unit 130.
In the example illustrated in
For example, in consideration of a delay time (hereinafter referred to as Ta) between the time at which the positioning computation result is output in the positioning computation unit 110 and the time at which the positioning computation result is received in the remote driving control apparatus 200 and a signal propagation delay time (hereinafter, Tb) from the remote driving control apparatus 200 to the control target apparatus 210, the positioning computation unit 110 outputs a positioning estimation result at Ta+Tb minutes ahead as a positioning computation result. The remote driving control apparatus 200 that has received the positioning computation result can display a console screen of AR using a dynamic map based on the positioning computation result to perform driving control.
In addition, the remote driving control apparatus 200 can perform control, such as estimation of an error, using the above-described information regarding the freshness. Note that outputting the information regarding the freshness by the positioning computation unit 110 is optional, and the information may not be output.
An operation example of the position measurement system 100 in
The absolute positioning measuring unit 120 outputs an absolute positioning result X at time 1, and the positioning computation unit 110 receives the absolute positioning result X (+time stamp: 1) at time 2. This indicates that it took a time of time 1 for a signal to be propagated.
The relative positioning measuring unit 130A outputs a relative positioning result A at time 2, and the positioning computation unit 110 receives the relative positioning result A (+time stamp: 2) at time 3. The relative positioning measuring unit 130B outputs a relative positioning result B at time 4, and the positioning computation unit 110 receives the relative positioning result B (+time stamp: 4) at time 5.
The positioning computation unit 110 performs positioning computation based on received information, and outputs a positioning computation result of “the position at time 11 is Y” (time stamp: 8) at time 8.
For example, the output calculation result reaches the remote driving control apparatus 200 at time 10, is transmitted from the remote driving control apparatus 200 to the control target apparatus 210, and reaches the control target apparatus 210 at time 11. Thereby, the control target apparatus 210 can acquire a real-time estimation position.
As described above, according to the position measurement system 100 of the present embodiment, each of the positioning measuring units attaches a time stamp to a positioning result and outputs the positioning result without a delay. The positioning computation unit 110 performs positioning computation based on the time stamp and a positioning result obtained at the time of the time stamp, and thus it is possible to output a highly accurate positioning computation result even when a delay in processing of data and/or a delay in propagation of a signal occur.
In the example of
In the example illustrated in
Each vehicle includes V2V communication means, which is vehicle-to-vehicle communication means, and V2I (vehicle-to-infrastructure)/V2N (vehicle-to-network) communication means. By these means, each vehicle can communicate with the other vehicles by a sidelink, and can communicate with the positioning computation unit 110 of the cloud through a 5G network or the like.
As illustrated in
Further, in a case where the positioning computation processing is performed in the cloud, the vehicles transmit respective positioning results (with respective time stamps) to the positioning computation unit 110 of the cloud and receive the positioning computation results obtained by the positioning computation unit 110.
In the example illustrated in
The absolute positioning measuring unit mounted on each vehicle constituting the platoon may be different for each vehicle (for example, a GNSS receiver in a certain vehicle, LiDAR in another vehicle, or the like). In addition, the relative positioning measuring unit mounted on each vehicle constituting the platoon may be different from one another (for example, an IMU in a certain vehicle, an in-vehicle camera in another vehicle, or the like).
In the present embodiment, an absolute time (time stamp) is stamped with high accuracy at a timing when pieces of data output from the absolute positioning measuring unit and the relative positioning measuring unit are generated, and thus it is possible to improve the availability of positioning and improve the accuracy of absolute position measurement in real time.
Additionally, in composite positioning using a plurality of positioning measuring units, the influence of a delay in propagation of information can be reduced, and thus a positioning measuring unit and a positioning computation unit can be installed at any locations.
In the present embodiment, at least the following position measurement system, position measurement method, and program are provided.
A position measurement system including:
The position measurement system according to item 1,
The position measurement system according to item 1 or 2,
The position measurement system according to any one of items 1 to 3,
The position measurement system according to any one of items 1 to 4,
The position measurement system according to any one of items 1 to 4,
A positioning calculation apparatus that executes positioning computation for calculating an absolute position of a mobile object based on an absolute position measurement result with a first time stamp received from an absolute positioning measuring unit that measures the absolute position of the mobile object and a relative displacement measurement result with a second time stamp received from a relative positioning measuring unit that measures a relative displacement of the mobile object, attaches a third time stamp to a positioning computation result, and outputs the positioning computation result with the third time stamp.
A position measurement method executed by a position measurement system including an absolute positioning measuring unit, a relative positioning measuring unit, and a positioning computation unit, the method including:
A program causing a computer to function as the positioning computation unit in the position measurement system according to any one of items 1 to 6.
Although the present embodiment has been described above, the present invention is not limited to such a specific embodiment, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/036795 | 9/19/2019 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2021/053795 | 3/25/2021 | WO | A |
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| 20220342086 A1 | Oct 2022 | US |
