A method for improving the ranging accuracy of time-of-flight measurement

Abstract

The present invention discloses a method for improving the ranging accuracy of time-of-flight ranging, which is characterized by including a light source module for emitting detection light to an object to be measured; a receiving module for receiving the returned light signal reflected by the object to be measured and converting it into an electrical signal; and a processing module for obtaining the distance of the object to be detected based on the electrical signal converted from the returned light signal obtained by the receiving module. There is a first time delay difference between the detection light emitted by the light source module and the demodulation signal used in the receiving module to receive the returned light signal. Through the solution of the present invention, the influence of time noise on the ranging accuracy at short distances can be reduced, the ranging accuracy at short distances can be improved, and the requirement for the ranging accuracy at short distances can be met.

Description

Technical Field

[0001] This application relates to the field of detection technology, and particularly to a method for improving the ranging accuracy of time-of-flight. Background Art

[0002] As a method for measuring the distance to an object in a scene, time-of-flight (TOF) technology has been developed. This TOF technology can be applied to various fields, such as the automotive industry, human-machine interfaces, gaming, robotics, and security, etc. Generally speaking, the working principle of TOF technology is to irradiate the scene with modulated light emitted by a light source and observe the reflected light reflected by the object in the scene. In existing detection systems, in order to ensure higher detection efficiency during the detection process and also ensure that the detection system has a wider field of view, an array-type receiving module is currently more commonly used. There can be thousands of pixel units in the array-type receiving module, and each pixel unit can be a diode of types such as charge-coupled semiconductor CCD or complementary metal-oxide semiconductor CMOS, etc. It is not limited here that only these two types of diodes are used to form the array-type receiving module.

[0003] In order to obtain distance information, the time delay information of the emitted light and the returned light is obtained indirectly in the TOF detection, and then the time delay phase or phase shift is obtained, and then the phase shift is converted into the final result information. This method converts the distance information of the detected object into the phase shift of the returned light and the emitted light instead of directly giving the distance result. This scheme is called indirect time of flight ranging (ITOF). In actual use, the complementary phase can be used to receive the returned light signal, and then the distance information is obtained. This method is called a two-phase scheme. There is also a scheme that uses four phases of 0°, 90°, 180° and 270° to obtain the target distance. Of course, there are also literatures that try to obtain the distance of the detected object with a 3-phase or even 5-phase scheme. The phase-shifted electrical signal is obtained, and the electrical signal needs to be processed by the processing unit to obtain the final distance information. However, the actual electrical signal corresponding to the returned light signal is due to environmental factors, including but not limited to temperature and ambient lighting conditions. For example, temperature changes in the sensor array can increase the so-called dark current of the pixel, and the dark current can change the measured phase shift, so that the measurement result will show a large distance fluctuation. At the same time, various components of the detection system can generate some noise that is unintentionally added to the collected signal. When this noise changes over time (for example, time noise caused by temperature fluctuations or other factors), it may lead to a reduction in ranging accuracy. In TOF detection technology, the accuracy requirements for short distances and long distances are different. According to the distance of the object to be measured, the ranging accuracy requirement is 1%-5% of the distance of the object to be measured. For example, the accuracy required for the object to be measured at 10cm is 1mm, and the ranging accuracy required for the object to be measured at 1m is 1cm. Therefore, reducing the impact of time noise on ranging accuracy at close distances is a technical problem that needs to be solved urgently. Summary of the invention

[0004] The purpose of this application is to provide a method for improving the accuracy of time-of-flight ranging in order to address the deficiencies in the above-mentioned prior art, reduce the impact of temporal noise on the accuracy of short-range ranging, improve the ranging accuracy at short distances, and meet the requirements of ranging accuracy at short distances.

[0005] To achieve the above purpose, the technical solution adopted in the embodiment of the present application is as follows:

[0006] An embodiment of the present application provides a method for improving the accuracy of time-of-flight ranging, characterized in that it includes a light source module for emitting detection light to an object to be measured; a receiving module for receiving a return light signal reflected by the object to be measured and converting it into an electrical signal; a processing module for obtaining the distance of the object to be detected based on the electrical signal converted from the return light signal obtained by the receiving module; and there is a first time delay difference between the detection light emitted by the light source module and the demodulation signal used to receive the return light signal in the receiving module.

[0007] Optionally, the first time delay difference is preset.

[0008] Optionally, the light source module introduces the detection light into the first time delay difference and then emits it towards the object to be measured.

[0009] Optionally, the phase differences between the demodulation signal and the detection light emitted by the light source module towards the object to be measured are 0°, 180°, 90°, and 270° respectively.

[0010] Optionally, there is also a first time delay difference between the demodulation signal and the detection light emitted by the light source module towards the object to be measured.

[0011] Optionally, there is also a second time delay difference caused by the detection device between the detection light emitted by the light source module and the returned light signal reflected by the object to be measured.

[0012] Optionally, the influence of the second time delay difference on the detection distance is corrected by an algorithm.

[0013] Optionally, there is also a third time delay difference for obtaining the distance of the object to be measured between the detection light emitted by the light source module and the returned light signal reflected by the object to be measured.

[0014] Optionally, the processing module removes the influence of the first time delay difference on the detection distance according to the obtained distance of the detected object to obtain the actual distance of the object to be measured.

[0015] The beneficial effects of this application are as follows:

[0016] A method for improving the ranging accuracy of time-of-flight, characterized by comprising a light source module for emitting detection light towards an object to be measured; a receiving module for receiving the returned light signal reflected by the object to be measured and converting it into an electrical signal; a processing module for obtaining the distance of the detected object based on the electrical signal converted from the returned light signal obtained by the receiving module; there is a first time delay difference between the detection light emitted by the light source module and the demodulation signal for receiving the returned light signal in the receiving module. Through the solution of the present invention, the influence of time noise on the ranging accuracy at close range can be reduced, the ranging accuracy at close range can be improved, and the requirement for the ranging accuracy at close range can be met. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions of the embodiments of this application, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of this application, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0018] Figure 1Schematic diagram of the working principle of a detection system provided by the prior art;

[0019] Figure 2A Schematic diagram of the relationship between theoretical distance and time noise provided by an embodiment of the present application;

[0020] Figure 2B Schematic diagram of the relationship between measured distance and time noise provided by an embodiment of the present application;

[0021] Figure 3 Schematic diagram of a TOF ranging principle provided by an embodiment of the present application;

[0022] Figure 4 Another schematic diagram of a TOF ranging principle provided by an embodiment of the present application;

[0023] Figure 5 Another schematic diagram of a TOF ranging principle provided by an embodiment of the present application;

[0024] Figure 6 Workflow for reducing time noise at close range provided by an embodiment of the present application;

[0025] Figure 7 Another workflow for reducing time noise at close range provided by an embodiment of the present application. Detailed implementation manners

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. The components of the embodiments of the present application usually described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations.

[0027] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed present application, but merely represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts fall within the scope of protection of the present application.

[0028] It should be noted that: similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0029] Figure 1A schematic diagram of the working principle of a detection system provided for the prior art. The currently adopted detection system basically includes: an optical emission module, a processing module, and an optical reception module. Here, the ITOF ranging is taken as an example for illustration. The optical emission module includes but is not limited to semiconductor lasers, solid-state lasers, and may also include other types of lasers. When a semiconductor laser is used as the light source, a vertical-cavity surface-emitting laser (VCSEL) or an edge-emitting laser (EEL) can be adopted. Here, it is only for exemplary illustration and is not specifically limited. The optical emission module emits a sine wave, a square wave, a triangular wave, etc., and in ranging applications, it is mostly a laser with a certain wavelength, such as an infrared laser of 950 nm, etc. (optimally a near-infrared laser). The emitted light is projected into the field of view. The detected object existing in the field of view can reflect the projected laser to form a return light. The return light enters the detection system and is captured by the optical reception module. The optical reception module may include a photoelectric conversion part, such as an array-type sensor composed of CMOS, CCD, etc., and may also include multiple lenses to form more than one image plane, that is, the reception module includes more than one image plane. The photoelectric conversion part of the reception module is located at one of the image planes, and it can receive with the most commonly used four-phase scheme to obtain delay reception signals of 0°, 90°, 180°, and 270°. The distance calculation scheme using four phases is illustrated here by taking the sine wave method as an example.

[0030] Let c be the speed of light, T be the period, Q0, Q90, Q180, Q270 be the energies collected under the four phases respectively. Then the calculation formula for the distance obtained according to these values is:

[0031] If Q0 > Q180 and Q90 > Q270, then:

[0032]

[0033] If Q0 < Q180 and Q90 > Q270, then:

[0034]

[0035] If Q0 < Q180 and Q90 < Q270, then:

[0036]

[0037] If Q0 > Q180 and Q90 < Q270, then:

[0038]

[0039] In the field of radar detection technology, noise is a recurring problem. In this regard, various components of the detection system can generate some noise that is inadvertently added to the acquired signal. For example, certain circuit components (e.g., row or column amplifiers) can be used during the acquisition and reading of all pixel data associated with a given column or row. Therefore, manufacturing variations or calibration errors associated with such components may affect all pixel data acquired and read. This can cause the rows or columns of the acquired image to exhibit offsets that appear as horizontal or vertical lines. When this noise varies over time (e.g., time noise caused by temperature fluctuations or other factors), it may lead to a reduction in ranging accuracy. The calculation formula for the time noise variance of the distance formula shown in Formulas (1)-(4) is:

[0040] σ 2 =[d(distance)| Q0 2 +[d(distance)| Q180 2 +[d(distance)| Q90 2 +[d(distance)| Q270 2 (5)

[0041] Taking d(distance)| Q0 as an example, it can be calculated that

[0042]

[0043] Therefore, it can be obtained that

[0044]

[0045] Figure 2A is a schematic diagram of the relationship between the theoretical distance and time noise provided by the embodiments of the present application. Figure 2 shows the relationship between the time noise and distance of ranging at different distances obtained according to Formulas (1)-(7) under the condition that Q_total = Q0 + Q180 + Q90 + Q270 remains unchanged. Figure 2B is a schematic diagram of the relationship between the measured distance and time noise provided by the embodiments of the present application. In the TOF detection technology, different accuracy requirements are imposed for short distances and long distances. According to the distance of the object to be measured, the ranging accuracy requirement is 1%-5% of the distance of the object to be measured. For example, the accuracy requirement for the object to be measured at 10 cm is 1 mm, and the ranging accuracy requirement for the object to be measured at 1 m is 1 cm. From Figure 2A - Figure 2B it can be seen that whether it is the theoretical value or the measured data, it can be seen that the time noise has a relatively greater impact on the object to be measured at short distances, which is not conducive to meeting the ranging accuracy requirements at short distances. ​​​​

[0046] Figure 3 A schematic diagram of the TOF ranging principle provided by an embodiment of the present application is as follows Figure 3 As shown, the inherent delay td is caused by the ranging system itself. For example, some circuit components (such as row or column amplifiers), and the deviation of the inherent delay td is corrected by an algorithm. Δt is the time delay for the emitted light source to be reflected back by the object to be measured. Based on Δt, the distance of the object to be measured can be obtained. In Figure 3 301 is the detection light emitted by the light source, 302 is the reflected light of the object to be measured without considering the fixed delay td, and 303 is the signal reflected back by the object to be measured after considering the fixed delay td. The receiving end receives the signal of 303 with demodulation signals having a certain phase difference (i.e., a certain time delay), Figure 3 In, the phase difference between 304 and 301 is 0°, the phase difference between 305 and 301 is 180°, the phase difference between 306 and 301 is 90°, and the phase difference between 307 and 301 is 270°. According to the ranging principle of four phases, the distance of the object to be measured can be obtained. The specific process is as shown in the following formulas (8) - (15):

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053]

[0054] The actual distance obtained after considering the inherent time delay where the deviation of the inherent delay td can be corrected back by an algorithm.

[0055] Combined with Figure 2 and Figure 3 It can be seen that by adjusting the time delay (phase difference) between the demodulation signal at the receiving end and the light source emitted at the transmitting end, the time noise at close range can be made to be in a relatively small corresponding position in Figure 2, so that the ranging accuracy at close range can be satisfied.

[0056] Figure 4 Another schematic diagram of the TOF ranging principle provided by an embodiment of the present application. As Figure 4The emitted light source 401 is added with a time delay t1 to become 402. 403 is the reflected light of the object to be measured without considering the fixed delay td, and 404 is the signal reflected back by the object to be measured after considering the fixed delay td. The overall time delay at this time is Δt + td + t1. The receiving end receives the signal of 404 with demodulation signals having a certain phase difference (i.e., a certain time delay) from 401 respectively. Figure 4 In it, the phase difference between 405 and 401 is 0°, the phase difference between 406 and 401 is 180°, the phase difference between 407 and 401 is 90°, and the phase difference between 408 and 401 is 270°. According to the four-phase ranging principle, the distance of the object to be measured can be obtained:

[0057]

[0058] In Figure 4 the emitted light source 401 is delayed by t1. Of course, the emitted light source 401 can also be advanced by a time t1, and the principle is the same as above, so it will not be elaborated here.

[0059] Figure 5 This is another schematic diagram of the TOF ranging principle provided by the embodiment of the present application. As Figure 5 shown, the emitted light source is 501, 502 is the reflected light of the object to be measured without considering the fixed delay td, and 503 is the signal reflected back by the object to be measured after considering the fixed delay td. The overall time delay at this time is Δt + td. The receiving end receives the signal of 503 with demodulation signals having a certain phase difference (i.e., a certain time delay) from 501 respectively. Figure 5 In it, the phase difference between 504 and 501 is 0° and 504 also has an added time delay t1, the phase difference between 505 and 501 is 180° and 505 also has an added time delay t1, the phase difference between 506 and 501 is 90° and 506 also has an added time delay t1, and the phase difference between 507 and 501 is 270° and 507 also has an added time delay t1. According to the four-phase ranging principle, the distance of the object to be measured can be obtained:

[0060]

[0061] In Figure 5 the emitted demodulation signal is delayed by t1. Of course, the demodulation signal can also be advanced by a time t1, and the principle is the same as above, so it will not be elaborated here.

[0062] The above Figure 4For example, if our minimum distance requirement is 0m, we can add a delay of t1 = T / 8 = 6.25ns (which can also be 1, 3, 5, 7... times of T / 8) between the emission light source 401 and the received modulated signal, so that the estimated result at 0 distance is 0.9375m, in order to achieve the purpose of reducing the time noise at 0m. From Figure 2B It can be seen that the time noise is the smallest at 0.9375m.

[0063] At this time, for the object to be measured with an actual distance of L, the ranging result is L + 0.9375m. Therefore, we only need to subtract 0.9375m from the final result to obtain the true distance of the object to be measured. Figure 5 The principle of introducing the time delay t1 in Figure 4 is the same as the process described above and will not be elaborated here. From the above process, it can be seen that by adding a time delay between the emission light source and the demodulated signal at the receiving end, the purpose of reducing the time noise at short distances can be achieved, and the ranging accuracy at short distances can be improved.

[0064] Figure 6 The following is a workflow for reducing time noise at short distances provided by an embodiment of the present application. As Figure 6 shown, it includes:

[0065] S601: Drive the light source to generate a detection optical signal;

[0066] S602: Introduce a certain time delay difference into the detection optical signal generated in step S601;

[0067] S603: Transmit the detection optical signal with the introduced time delay difference to the object to be measured;

[0068] S604: According to the four-phase detection principle, receive the echo signals reflected by the object to be measured with phase differences of 0°, 180°, 90°, and 270° from the phase of the detection optical signal generated in S601 respectively;

[0069] S605: Calculate the distance of the object to be measured according to the received echo signals of the object to be measured;

[0070] S606: Because a certain time delay difference is introduced into the transmitted detection signal and this time delay difference is known, it is necessary to remove the influence of the introduced time delay difference on the distance from the distance of the object to be measured calculated in S605 to obtain the actual distance of the object to be measured.

[0071] Figure 7 The following is another workflow for reducing time noise at short distances provided by an embodiment of the present application. As Figure 7 shown, it includes:

[0072] S701: Drive the light source to generate a detection optical signal;

[0073] S702: Transmit the generated detection optical signal to the object to be measured;

[0074] S703: According to the four-phase detection principle, use demodulation signals with phase differences of 0°, 180°, 90°, and 270° from the phase of the detection optical signal generated in S701 and introduce a certain time delay difference t1 to receive the echo signals reflected by the object to be measured respectively;

[0075] S704: Calculate the distance of the object to be measured based on the received echo signals of the object to be measured;

[0076] S705: Since a certain time delay difference is introduced in the demodulation signal and this time delay difference is known, it is necessary to remove the influence of the introduced time delay difference on the distance from the distance of the object to be measured calculated in S704 to obtain the actual distance of the object to be measured;

[0077] It should be noted that the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the phrase "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the said element.

[0078] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application. It should be noted that similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for improving the ranging accuracy of time-of-flight measurement, characterized in that, It includes a light source module for emitting detection light to the object to be measured; a receiving module for receiving the returned light signal reflected by the object to be measured and converting it into an electrical signal; a processing module for obtaining the distance of the object to be measured based on the electrical signal converted from the returned light signal obtained by the receiving module; there is a first time delay difference between the detection light emitted by the light source module and the demodulation signal used in the receiving module to receive the returned light signal, and the first time delay difference is the time delay difference introduced between the detection light and the receiving module to reduce time noise; there is also a second time delay difference caused by the detection device between the detection light emitted by the light source module and the returned light signal reflected by the object to be measured; there is also a third time delay difference for obtaining the distance of the object to be measured between the detection light emitted by the light source module and the returned light signal reflected by the object to be measured; the processing module removes the influence of the introduced first time delay difference on the distance according to the obtained distance of the object to be measured to obtain the actual distance of the object to be measured.

2. The method for improving the ranging accuracy of time-of-flight ranging according to claim 1, characterized in that, The light source module introduces a first time delay difference to the detection light and then emits it to the object to be measured.

3. The method for improving the ranging accuracy of time-of-flight ranging according to claim 1, characterized in that, The phase differences between the demodulation signal and the detection light emitted by the light source module to the object to be measured are 0°, 180°, 90°, and 270° respectively.

4. The method for improving the ranging accuracy of time-of-flight ranging according to claim 3, wherein There is also a first time delay difference between the demodulation signal and the detection light emitted by the light source module to the object to be measured.

5. The method for improving the ranging accuracy of time-of-flight ranging according to claim 1, wherein, The influence of the second time delay difference on the detection distance is corrected by an algorithm.

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