Error correction method of a scanning LiDAR

Abstract

Method for correcting an error of a scanning LiDAR, at least part of which is rotated and driven by a motor, the method comprising: an error detection operation in which a measurement time error is calculated between a time interval expectation value, which is a target measurement time interval of the sampling LiDAR, and a time interval measurement value, which is an actual measurement time interval of the sampling LiDAR, an error correction operation in which a measurement location of the sampling LiDAR is corrected according to the measurement time error, an initial value determination operation in which an initial emission time is determined from several laser light emission times of the sampling LiDAR, which is used to calculate the time interval measurement value, and a determination value enhancement operation in which at least one laser light emission time after the initial emission time is determined from the multiple laser light emission times, wherein In the fault detection operation, a difference is calculated between the determined laser light emission time and a laser light emission time according to the time interval expectation value, a difference between the difference result and a laser light emission time according to the time interval expectation value is calculated again, and then an absolute value of the result is calculated.

Description

Technical field

[0001] The present invention relates to a LiDAR system and, for example, a method for correcting an error of a scanning LiDAR. Technical background

[0002] A scanning LiDAR uses a motor to rotate at a constant speed, emits laser light while rotating at a constant speed, receives reflected light from an object, and measures positional information about the object within the rotational angle. The obtained positional information about the object is composed of angular information (degrees) and distance information (distance) from a reference point.

[0003] The sampling LiDAR must emit laser light at very short time intervals to accurately determine the location of an object, and for this purpose the sampling LiDAR uses a timer interrupt from a LiDAR control device or semiconductor.

[0004] In JP H08-248131A, a laser radar is disclosed which includes a nonlinear timer. The difference between adjacent count setpoints is set based on the distance of the laser diode to a scan start point and a scan end point.

[0005] However, if the interrupt task of the timer interrupt is too large, or if laser light is not emitted at regular time intervals due to a decrease in the operating speed of the semiconductor, a problem arises in that distortion is created in the position information about the object and distortion is generated in a sampling measurement result. Summary of the invention

[0006] The present invention was made in an effort to create a method for correcting an error in a scanning LiDAR, in which a measurement time interval of a scanning LiDAR, which emits laser light at regular time intervals during a rotation at constant speed via a motor using a time-to-digital converter (TDC), is measured, it is determined whether the measurement time interval has an error, and an object measurement location is corrected when the error is generated, thereby preventing a distortion in the measurement result.

[0007] According to the present invention, a method for correcting an error of a scanning LiDAR is provided, at least a part of which is rotated and driven by a motor, wherein the method comprises: an error detection operation in which a measurement time error is calculated between a time interval expectation value, which is a target measurement time interval of the scanning LiDAR, and a time interval measurement value, which is an actual measurement time interval of the scanning LiDAR, and an error correction operation in which a measurement location of the scanning LiDAR is corrected according to the measurement time error.

[0008] Furthermore, the procedure includes an initial value determination operation in which an initial emission time is determined from several laser light emission times of the sampling LiDAR, which is used to calculate the time interval measurement value, and a value enhancement operation in which at least one laser light emission time after the initial emission time is determined among the several laser light emission times.

[0009] In the error detection operation, a difference between the determined laser light emission time and a laser light emission time according to the time interval expectation value is calculated, a difference between the difference result and a laser light emission time according to the time interval expectation value is calculated again, and then an absolute value of the result is calculated.

[0010] During the error detection operation, it can be determined that an error is generated in the time interval measurement if the absolute value exceeds a permissible error.

[0011] The error detection operation can determine whether the time interval measurement has an error according to an error algorithm based on the following equation: |(ti−te)−te|>tc (in the equation t i the laser light emission time according to the time interval measurement, t e the laser light emission time according to the time interval expectation value and t c the permissible error).

[0012] In the error correction operation, a relative error can be calculated based on the determined laser light emission time and the laser light emission time according to the time interval expectation value, and a measurement location of the sampling LiDAR can be corrected by applying the relative error to a pre-created correction algorithm.

[0013] In the error correction operation, a difference between the determined laser light emission time and the laser light emission time according to the time interval expectation value can be calculated, and to calculate the relative error, the difference result is divided by the laser light emission time according to the time interval expectation value.

[0014] During the error correction operation, the relative error can be calculated according to the following equation: r=(ti−te) / te (in the equation, r is the relative error, t ithe specific laser light emission time and t e the laser light emission time according to the time interval expectation value).

[0015] The value enhancement operation, the error detection operation, and the error correction operation can be repeated until an error is detected and corrected for the last laser light emission time among the multiple laser light emission times.

[0016] According to the method for correcting the error of the scanning LiDAR according to the exemplary embodiments of the present invention, it is possible to correct an object measurement location when an error is generated in a measurement time interval, thereby preventing a distortion of a measurement result of the scanning LiDAR that arises due to the error in the measurement time interval.

[0017] The method for correcting the error of the scanning LiDAR according to the exemplary embodiments of the present invention can be applied extensively to 2D scanning, 3D scanning, radar and the like.

[0018] When the method for correcting the error of the scanning LiDAR according to the exemplary embodiments of the present invention is applied to an autonomous vehicle, it is possible to prevent an accident that is due to a distortion of a measurement result (road situation) of the scanning LiDAR.

[0019] The foregoing summary serves only for illustration and is in no way intended to be limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. Brief description of the drawings Fig. Figure 1 is a diagram illustrating a situation in which distortion occurs in a measurement result of a sampling LiDAR. Fig. Figure 2 is a block diagram illustrating a sampling LiDAR according to an exemplary embodiment of the present invention. Fig. Figure 3 is a diagram showing a comparison between a time interval expected value and a time interval measured value. Fig. Figure 4 is a diagram illustrating an error correction for a measurement time interval of the sampling LiDAR. Fig. Figure 5 is a flowchart illustrating a method for correcting an error of a scanning LiDAR according to an exemplary embodiment of the present invention.

[0020] It should be clear that the accompanying drawings are not necessarily to scale and show a somewhat simplified representation of various features that illustrate the basic principles of the invention. The specific design features of the present invention, as disclosed herein, which include, for example, certain dimensions, orientations, positions, and shapes, are partly determined by the respective application and operating environment.

[0021] In the several figures of the drawing, reference numerals consistently refer to the same or corresponding parts of the present invention. Detailed description

[0022] Exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings. It should first be noted that when specifying reference numerals for elements in each drawing, the same reference numerals refer to the same elements, even if the same elements are shown in different drawings. It should be clear that although exemplary embodiments of the present invention are described below, the nature of the present invention is not limited to these, and modifications and adaptations can be made by a person skilled in the art in various ways.

[0023] Fig. Figure 1 is a diagram illustrating a situation in which distortion occurs in a measurement result of a sampling LiDAR. Fig. Figure 1A is a diagram showing an object measurement situation of a typical scanning LiDAR. Fig. Figure 1B is a diagram showing an object measurement situation corresponding to an error in a measurement time interval of a sampling LiDAR. Fig. 1C is a diagram showing a measurement result distorted according to the error in the measurement time interval of the sampling LiDAR.

[0024] Fig. 1A: The scanning LiDAR 100 rotates at a constant speed via a motor drive. While rotating at this constant speed, the scanning LiDAR 100 emits laser light L at regular intervals, receives reflected light that strikes a surface point P of an object OB and is reflected back, thus obtaining precise positional information about the object OB. This positional information includes angular information θ and distance information D from a reference location.

[0025] Meanwhile, see: Fig. In 1B, the scanning LiDAR 100 emits laser light L during a measurement time interval in which an error is generated due to an excessive interruption of a timer interrupt, a decrease in the operating speed of a semiconductor, or similar factors. The scanning LiDAR 100 emits laser light L during the measurement time interval in which the error is generated while rotating at a constant speed, receiving reflected light that strikes the surface point P of object OB, is reflected back, and obtains positional information about object OB. This process introduces distortion into the received positional information about object OB.

[0026] In Fig. The 1C receives distorted location information about an object ER, not actual location information about the object (OB). This distorted location information about object ER can cause a serious problem in a technical field where the 100 is used, so appropriate correction is necessary.

[0027] The following describes a version of the sampling LiDAR that is able to detect the occurrence of an error in a measurement time interval and correct the error, thereby preventing distorted location information of an object from being obtained.

[0028] Fig. Figure 2 is a block diagram illustrating the scanning LiDAR according to the exemplary embodiment of the present invention.

[0029] With reference to Fig. 2. In an exemplary embodiment of the present invention, the scanning LiDAR 100 can comprise a light-emitting unit 110, a distance-measuring unit 120, and an error correction unit 130. In addition to the aforementioned configurations, the scanning LiDAR 100 can further comprise a light-receiving unit (not shown) that receives reflected light, a preprocessing unit (not shown) that preprocesses the reflected light received by the light-receiving unit, a motor (not shown) that rotates and drives the scanning LiDAR 100, and the like. A detailed description of the general design of the scanning LiDAR 100 is omitted below.

[0030] The light transmitter 110 generates a laser pulse signal. The light transmitter 110 can control a laser diode (not shown) so that it emits laser light according to the laser pulse signal. The light transmitter 110 can then transmit the laser pulse signal to the distance measuring unit 120. This allows the light transmitter 110 to provide the distance measuring unit 120 with a laser light emission time corresponding to the laser pulse signal.

[0031] The distance measuring unit 120 can measure positional information about an object using a time interval between the laser light emission time and the laser light reception time. In the exemplary embodiment, the distance measuring unit 120 can be configured to measure a distance from the object using a time-to-digital converter (TDC).

[0032] The distance measuring unit 120 can receive multiple laser pulse signals from the light transmitter unit 110. Based on these multiple laser pulse signals received from the light transmitter unit 110, the distance measuring unit 120 can calculate multiple laser light emission times. The distance measuring unit 120 can then calculate a measurement time interval based on these multiple laser light emission times. The measurement time interval calculated by the distance measuring unit 120 is defined below as a time interval measurement value.

[0033] The error correction unit 130 can determine the suitability of the time interval measurement calculated by the distance measuring unit 120. Based on the operating speed (rotational speed) of the motor that rotates the scanning LiDAR 100 and the resolution, the error correction unit 130 can generate an expected time interval value for the measurement interval. Using this expected time interval value, the error correction unit 130 can determine whether the time interval measurement calculated by the distance measuring unit 120 contains an error. If an error is present in the time interval measurement, the error correction unit 130 can correct it using a predefined correction algorithm. The error correction unit 130 can then transfer the corrected time interval measurement to the distance measuring unit 120.The distance measuring unit 120 can measure the location information about the object based on the time interval measurement value, the error of which is corrected.

[0034] Fig. Figure 3 is a diagram showing a comparison between the time interval expected value and the time interval measured value.

[0035] With reference to Fig. 3. The error correction unit 130 can estimate a time interval expectation value for a measurement time interval according to the operating speed of the motor and the resolution as described above, and the time interval expectation value of the error correction unit 130 is a time from t0 to t1. In the exemplary embodiment, it is assumed that the time interval measurement value calculated by the distance measuring unit 120 by receiving the multiple laser pulse signals from the light transmitting unit 110 is a time from t0 to t2. In this case, the error ratio r is equal to t2 / t1.

[0036] If an error is generated in the time interval measurement value calculated by the distance measuring unit 120, the measurement result of the sampling LiDAR 100 for the location information about the object can be output on a screen at a constant time interval, or an error can be generated in a separate calculation program based on the measurement result.

[0037] The following describes a procedure for correcting an error in a time interval measurement to avoid the aforementioned problem.

[0038] Fig. Figure 4 is a diagram illustrating an error correction for the measurement time interval value calculated by the distance measuring unit 120. With reference to the Fig. 3 and Fig. Figure 4 shows a measurement angle d0 at time t0, a measurement angle d1 at time t1 (measurement angle before correction) and a measurement angle d2 at time t2 (actual angle or measurement angle after correction).

[0039] The error correction unit 130 can calculate the measurement angle d2 in the time interval measurement t2.

[0040] The distance measuring unit 120 can measure accurate location information about the object using the calculated measuring angle d2 and the time interval measurement value t2.

[0041] Fig. Figure 5 is a flowchart illustrating a method for correcting an error of a scanning LiDAR according to an exemplary embodiment of the present invention.

[0042] With reference to Fig. Figure 5 comprises a method for correcting an error of a sampling LiDAR according to an exemplary embodiment of the present invention, comprising a variable setting operation S510, an initial value setting operation S520, a variable increase operation S530, a determination value increase operation S540, an error detection operation S550 and an error correction operation S560.

[0043] In the variable-setting operation S510, when the error correction unit 130 receives a calculated time interval measurement from the distance measurement unit 120, the error correction unit 130 can first set a variable i to determine any one of several laser light emission times used to calculate a time interval measurement. The error correction unit 130 can set the variable i to 1 to determine a laser light initial emission time.

[0044] Next, during the initial value setting operation S520, the error correction unit 130 can determine an initial emission time from the multiple laser light emission times. In the exemplary embodiment, the error correction unit 130 can set an initial emission time t1 that corresponds to the variable value "1" obtained for the variable i from the multiple laser light emission times t iwas determined. Next, the error correction unit 130 can determine an initial emission angle d1 from the laser light emission angles, which corresponds to the initial emission time t1.

[0045] Next, during the variable increment operation S530, the error correction unit 130 can increment the variable i by adding 1 to it to account for an error in the measurement time interval corresponding to the initial emission time and the next laser emission time. In the exemplary embodiment, a variable value to which the variable i is set can be "2". Here, the variable i can continuously increment by the number of multiple laser emission times through repeated execution of operation S530.

[0046] Next, in the value enhancement operation S540, the error correction unit 130 can determine a laser light emission time t. iThe variable i is redefined according to which its value is increased by "1" during the variable increment operation S530. In the exemplary embodiment, the error correction unit 130 can set the laser light emission time t1, at which the laser light is emitted at the i-th time. The error correction unit 130 can set a second laser light emission time t2 corresponding to the laser light emission time t1. i Determine the variable value "2". Then the error correction unit 130 can detect an error in the measurement time interval corresponding to the initial emission time t1 and the second laser light emission time t2 and correct the error.

[0047] Next, in the error detection operation S550, the error correction unit 130 calculates a measurement time error between a time interval expectation value, which is a target measurement time interval of the scanning LiDAR 100, and the time interval measurement value, which is the actual measurement time interval of the scanning LiDAR 100. Before the calculation, the error correction unit 130 determines whether the time interval measurement value (measurement time interval) received from the distance measuring unit 120 has an error by comparing it to the laser light emission time t determined in operation S540. i applies to a pre-defined error algorithm.

[0048] The error algorithm can be formed according to equation 2 below. |(ti−te)−te|>tc

[0049] In equation 2, t1 is a laser light emission time corresponding to the time interval measurement value, t ea laser light emission time corresponding to the time interval expectation value and t c an acceptable error. The acceptable error can be t c be determined in a suitable manner according to the needs of the user.

[0050] The error correction unit 130 can correct a difference between the time interval measurement t i and the time interval expected value t c calculates a difference between the difference and the expected value of the time interval t c a second time, and then calculates an absolute value (measurement time error) of the obtained result. If the calculated absolute value exceeds the permissible error t c If the value exceeds 130, the error correction unit can determine that the error originates in the time interval measurement.

[0051] Next, during error correction operation S560, the error correction unit 130 corrects a measurement location (laser emission angle) of the scanning LiDAR 100 according to the measurement time error. If it is determined that the error is generated in the time interval measurement, the error correction unit 130 can calculate a relative error corresponding to the generation of the error and, based on the calculated relative error, recalculate a laser emission angle according to the determined laser emission time.

[0052] The laser light emission angle can be calculated using a correction algorithm.

[0053] The error correction unit 130 calculates a difference between the laser light emission time t i according to the time interval measurement value and the laser light emission time t e according to the expected time interval value and divides the difference result by the laser light emission time t. eaccording to the time interval expected value, in order to calculate the relative error.

[0054] After calculating a laser light emission angle d (i) at a laser light emission time t i Errors in a further laser light emission time point, derived from the multiple laser light emission times and a laser light emission angle corresponding to a further laser light emission time point, can be detected and corrected by repeatedly performing operations S530 to S560. These repeated operations can continue until the error for the last laser light emission time point, derived from the multiple laser light emission times, has been detected and corrected.

[0055] The error correction unit 130 can transmit the calculated laser emission angle to the distance measuring unit 120. Based on the time interval measurement and the laser emission angle recalculated in the error correction unit 130, the distance measuring unit 120 can precisely obtain positional information about an object.

[0056] Although the exemplary embodiment of the present invention has been described for illustrative purposes, it is clear to those skilled in the art that various modifications, additions, and substitutions are possible without altering the scope and essence of the invention. Therefore, the exemplary embodiments and the accompanying drawings disclosed in the present invention are not limited to the technical essence of the present invention but are intended to illustrate the scope of the technical concept of the present invention, and the scope of the present invention is not limited by the embodiment and the accompanying drawings.

[0057] The steps and / or processes according to the present invention can be carried out in different sequences, in parallel or simultaneously in different exemplary embodiments for different periods of time and the like, as is apparent to the person skilled in the art.

[0058] Depending on the embodiment, some or all of the steps and / or processes can be carried out or executed using commands stored in one or more non-temporary computer-readable media, a program, an interactive data structure, or one or more processors that control a client and / or a server.

[0059] One or more non-temporary, computer-readable media include, for example, software, firmware, hardware, and / or any combination thereof. Furthermore, the "module" function described in this document can be implemented using software, firmware, hardware, and / or any combination thereof.

[0060] The embodiments according to the present invention can be implemented in the form of program instructions that can be executed by computers and can be recorded on computer-readable media. The computer-readable media can contain program instructions, a data file, a data structure, or a combination thereof. By way of example, and without limitation, computer-readable media can include computer storage media and communication media. Computer storage media include both volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information, such as computer-readable instructions, data structures, program modules, or other data.Computer storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other storage technologies, CD-ROM, Digital Versatile Discs (DVDs) or other optical disk storage, magnetic cartridges, magnetic tapes, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to store the desired information and that can be accessed by a computer. Communication media typically represent computer-readable instructions, data structures, program modules, or other data in a modulated data signal, such as a carrier wave or other transport mechanism, and include any information transmission media. The term "modulated data signal" refers to a signal in which one or more of its properties are set or modified in such a way that information is encoded in the signal.As an example, and not a limitation, communication media include wired media, such as a wired network or a directly wired connection, as well as wireless media, such as acoustic, RF, infrared, and other wireless media. Combinations of any of the above should also be included in the scope of computer-readable media.

[0061] As described above, the exemplary embodiments are described and illustrated in the drawings and the description. These exemplary embodiments were selected and described to explain certain principles of the invention and their practical application, thereby enabling other skilled persons to create and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. As can be seen from the foregoing description, certain aspects of the present invention are not limited by the specific details of the examples illustrated herein, and it is therefore considered that skilled persons will conceive of further modifications and applications or equivalents thereof.Many modifications, alterations, variations, and other uses and applications of the present embodiment will become apparent to the person skilled in the art upon examination of the description and the accompanying drawings. All such modifications, alterations, variations, and other uses and applications that do not deviate from the essence and scope of the invention shall be deemed to be covered by the invention, which is limited only by the claims below.

Claims

[1] Method for correcting an error of a scanning LiDAR, at least part of which is rotated and driven by a motor, the method comprising: an error detection operation in which a measurement time error is calculated between a time interval expectation value, which is a target measurement time interval of the sampling LiDAR, and a time interval measurement value, which is an actual measurement time interval of the sampling LiDAR, an error correction operation in which a measurement location of the sampling LiDAR is corrected according to the measurement time error, an initial value determination operation in which an initial emission time is determined from several laser light emission times of the sampling LiDAR, which is used to calculate the time interval measurement value, and a determination value enhancement operation in which at least one laser light emission time after the initial emission time is determined from the multiple laser light emission times, wherein In the fault detection operation, a difference between the determined laser light emission time and a laser light emission time according to the time interval expectation value is calculated, a difference between the difference result and a laser light emission time according to the time interval expectation value is calculated again, and then an absolute value of the result is calculated. [2] Method according to claim 1, wherein the error detection operation determines that an error is generated in the time interval measurement if the absolute value exceeds a permissible error. [3] Method according to claim 1 or 2, wherein the fault detection operation determines whether the time interval measurement has a fault according to a fault algorithm based on an equation below, |(ti−te)−te|>tc, (in the equation t i the laser light emission time according to the time interval measurement, t e the laser light emission time according to the time interval expectation value and t c the permissible error). [4] Method according to one of claims 1 to 3, wherein in the error correction operation a relative error is calculated based on the determined laser light emission time and the laser light emission time according to the time interval expectation value and a measurement location of the scanning LiDAR is corrected by applying the relative error to a pre-created correction algorithm. [5] Method according to claim 4, wherein in the error correction operation a difference between the determined laser light emission time and the laser light emission time according to the time interval expectation value is calculated and the difference result is divided by the laser light emission time according to the time interval expectation value to calculate the relative error. [6] Method according to claim 4 or 5, wherein in the error correction operation the relative error is calculated according to an equation below, r=(ti−te) / te, (in the equation, r is the relative error, t i the specific laser light emission time and t e the laser light emission time according to the time interval expectation value). [7] Method according to any one of claims 1 to 6, wherein in the determination value increase operation at least one laser light emission time is re-determined after the determined laser light emission time after the error detection operation or the error correction operation. [8] Method according to claim 7, wherein the determination value enhancement operation, the error detection operation and the error correction operation are repeatedly performed until an error for the last laser light emission time among the multiple laser light emission times is detected and corrected.

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