A time-of-flight detection method and a detection device

Abstract

The present invention discloses a time-of-flight detection method, which is characterized by comprising a light source module for emitting detection light to an object to be measured; a receiving module for receiving the returned optical 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 optical signal obtained by the receiving module; and an adjustment module for adjusting the light source module and the receiving module according to the first flight distance of the detected object obtained by the processing module. Through the solution of the present invention, the ranging accuracy in the scenario of only focusing on the distance between a specific target object and the lens can be improved.

Description

Technical Field

[0001] This application relates to the field of detection technologies, and particularly relates to a time-of-flight detection method and a detection device. 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 used more frequently. 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] To obtain distance information, in indirect Time-of-Flight (TOF) detection, the time delay information of the emitted light and the returned light is first obtained, and then the time delay phase or phase shift is obtained. Subsequently, the phase shift is converted into the final result information. This method converts the distance information of the object to be detected into the phase shift between 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 to obtain the distance information. This method is called the 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 attempting to use three-phase or even five-phase schemes to obtain the distance of the detected object. To obtain the electrical signal of the phase shift, the electrical signal needs to be processed by a processing unit to obtain the final distance information. However, the electrical signal corresponding to the actually obtained returned light signal is affected by 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 pixels, and the dark current can in turn change the measured phase shift. As a result, larger distance fluctuations will appear in the measurement results. At the same time, various components of the detection system can inadvertently add some noise 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 decrease in ranging accuracy. In addition, if the integration time is too short during the detection process, too few echo signals will be received at the receiving end, and the signal-to-noise ratio will be too low. If the integration time is too long, it will cause overflow of the detection device and the useful echo signals arriving later cannot be received, affecting the ranging accuracy. In some application scenarios of TOF detection technology, only the distance between a specific target object and the lens is concerned, such as the change in the distance of the carriage, face recognition, etc. For such application scenarios, even when the external conditions remain unchanged, such as optical power, background light, scene, etc.; the accuracy of the ranging result will change with the distance of the target object. Therefore, there is an urgent need for a detection method to improve the ranging accuracy in such scenarios. Summary of the Invention

[0004] The purpose of this application is to provide a time-of-flight detection method to improve the ranging accuracy in scenarios where only the distance between a specific target object and the lens is concerned, aiming at the deficiencies in the above-mentioned prior art.

[0005] To achieve the above purpose, the technical solutions adopted in the embodiments of this application are as follows:

[0006] An embodiment of the present application provides a time-of-flight detection method, 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; 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; and an adjustment module for adjusting the light source module and the receiving module according to the first flight distance of the object to be detected obtained by the processing module.

[0007] Optionally, the processing module determines a first flight distance according to the returned light signal within a first time period, and determines a second flight distance according to the returned light signal within a second time period.

[0008] Optionally, the first time period is earlier than the second time period.

[0009] Optionally, the adjustment module adjusts the time delay difference between the detection light source and the demodulated signal received according to the first flight distance.

[0010] Optionally, the adjustment module adjusts the non-linear correction function according to the first flight distance.

[0011] Optionally, the adjustment module adjusts the integration duration of the receiving module according to the first flight distance.

[0012] Optionally, the adjustment module is included in the processing module.

[0013] Optionally, the adjustment module is electrically connected to the light source module and the receiving module respectively.

[0014] In a second aspect, an embodiment of the present application provides a detection device, 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; 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; and an adjustment module for adjusting the light source module and the receiving module according to the first flight distance of the object to be detected obtained by the processing module.

[0015] Optionally, the processing module determines a first flight distance according to the returned light signal within a first time period, and determines a second flight distance according to the returned light signal within a second time period, and the first time period is earlier than the second time period.

[0016] The beneficial effects of the present application are:

[0017] A time-of-flight detection method, characterized by comprising 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; 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; and an adjustment module for adjusting the light source module and the receiving module according to the first flight distance of the detected object. Through the solution of the present invention, the ranging accuracy in the scenario of only focusing on the distance between a specific target object and the lens can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present 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 the present application, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0019] Figure 1 A schematic diagram of the working principle of a detection system provided by the prior art;

[0020] Figure 2A A schematic diagram of the relationship between theoretical distance and time noise provided by the embodiments of the present application;

[0021] Figure 2B A schematic diagram of the relationship between measured distance and time noise provided by the embodiments of the present application;

[0022] Figure 3 A schematic diagram of the TOF ranging principle provided by the embodiments of the present application;

[0023] Figure 4 A flowchart of a detection method provided by the embodiments of the present application;

[0024] Figure 5 Another flowchart of a detection method provided by the embodiments of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Usually, the components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0026] Accordingly, 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 in the present application without creative efforts fall within the scope of protection of the present application.

[0027] It should be noted that like reference numerals and letters denote like 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.

[0028] Figure 1 A 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, 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 semiconductor laser (EEL) can be used. Here, it is only for illustrative purposes and not specifically limited. The optical emission module emits a sine wave, a square wave, a triangular wave, etc. 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. It may also include multiple lenses that can 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. 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.

[0029] Let c be the speed of light, T be the period, Q0, Q90, Q180, Q270 be the energies collected under the four-phase respectively. Then the calculation formula for the distance calculated according to these values is:

[0030] If Q0 > Q180 and Q90 > Q270, then:

[0031]

[0032] If Q0 < Q180 and Q90 > Q270, then:

[0033]

[0034] If Q0 < Q180 and Q90 < Q270, then:

[0035]

[0036] If Q0 > Q180 and Q90 < Q270, then:

[0037]

[0038] 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.

[0039] Figure 2A It is a schematic diagram of the relationship between theoretical distance and time noise provided by the embodiments of the present application. Figure 2 shows the relationship between the time noise of ranging and distance at different distances obtained according to formulas (1)-(4) under the condition that Q_total = Q0 + Q180 + Q90 + Q270 remains unchanged. Figure 2B It is a schematic diagram of the relationship between measured distance and time noise provided by the embodiments of the present application. From Figure 2A - Figure 2B It can be seen that whether it is the theoretical value or the measured data, the time noise shows a periodic characteristic and the influence of the time noise on objects to be measured at different distances is different. For the object to be measured of concern, it is expected to minimize the influence of the time noise on ranging by adjusting the time delay.

[0040] During the TOF ranging process, the light source emits modulated near-infrared light. After encountering an object, it is reflected to a light sensing unit. Further, the time difference or phase difference between the emitted light and the received light is calculated by a processor to calculate the depth information of the object, and the imaging of the object is obtained through the photosensitive effect of the received light, and the depth image information is obtained by combining the depth information. However, in the actual ranging of existing TOF ranging, there is a problem that the obtained depth information is inaccurate. Therefore, there is an urgent need for a detection method to solve this technical problem.

[0041] During the laboratory calibration process, it was found that even when the distances are the same, the reflectivities of different objects are different due to different materials. Therefore, in high-precision ranging scenarios, the calibration functions for different objects at the same distance are also different.

[0042] Figure 3 FIG. is a schematic diagram of the TOF ranging principle provided by an embodiment of the present application. As Figure 3 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 which 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):

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

[0049]

[0050] The actual distance obtained after considering the inherent time delay (15), where the deviation of the inherent delay td can be corrected back by an algorithm.

[0051] From Figure 3As can be seen from the ranging principle shown, the integration duration of the demodulated signal affects the ranging accuracy. If the integration duration is too short, there will be too little useful charge information for calculating the detection distance, and the signal-to-noise ratio will be too low. If the integration duration is too long, the detection device storing the useful charge will overflow, causing the subsequent arriving useful echo signals not to be integrally used. Therefore, an appropriate integration duration needs to be used in distance detection to improve the ranging accuracy. During the detection process, detection arrays are used. So, we will adjust the integration duration according to the signal-to-noise ratio within a region, rather than just focusing on the integration duration of a single pixel.

[0052] Figure 4 This is a flowchart of a detection method provided by an embodiment of the present application. As Figure 4 shown, it includes:

[0053] S401: Drive the light source to generate a detection optical signal and emit the detection light to the object to be measured;

[0054] S402: Calculate the distance of the object to be measured based on the echo signal within the first time; Here, the first time can be one frame, and the distance obtained in S402 can show the influence of the time noise shown in Figure 2 on this distance;

[0055] S403: Determine the time delay difference between the detection light and the received signal according to the distance of the object to be measured obtained within the first time; In step S402, the influence of time noise on this distance can be obtained, and by adjusting the time delay difference between the transmitted signal and the received signal, the influence of time noise on this distance detection can be minimized.

[0056] S404: According to the determined time delay difference, adjust the time delay difference and detect the distance of the object to be measured within the second time; In ITOF ranging, the receiving end receives the echo signal with a demodulated signal having a certain phase difference (i.e., a certain time delay) with respect to the transmitted detection light; In addition to the phase differences of 0°, 180°, 90°, and 270° in the original detection principle, an additional time delay t1 needs to be introduced to minimize the influence of time noise on distance detection. The introduction of this additional time delay t1 can be achieved by changing the time delay of the detection light or the time delay of the demodulated signal at the receiving end, ultimately achieving the purpose of changing the time delay difference between the detection light and the demodulated signal at the receiving end and minimizing the influence of time noise on distance detection. The adjustment process is completed by an adjustment module. The adjustment module can be one of the functional modules included in the processing module shown in Figure 1 shown, or it can be a separate module to complete the adjustment process. The adjustment module is electrically connected to the light source module and the receiving module.

[0057] S405: Obtain the final detection distance of the object to be measured based on the echo signal within the second time; the second time here can be another frame different from the first time and later than the first time. For example, the first time can be the first frame, the second time can be the second frame, or other frames later than the first time, and no specific restrictions are made here.

[0058] Because a certain additional time delay difference is introduced in distance detection 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 S405 to obtain the actual distance of the object to be measured.

[0059] Figure 5 Another flowchart of the detection method provided for the embodiment of this application; as Figure 5 shown includes:

[0060] S501: Drive the light source to generate a detection optical signal and emit the detection light to the object to be measured;

[0061] S502: Calculate the distance of the object to be measured based on the echo signal within the first time; the first time here can be one frame;

[0062] S503: Select the first calibration function to calibrate the distance of the object to be measured obtained within the first time and estimate the reflectivity based on the first distance; in this step, the first distance of the target object is corrected based on a pre - rough non - linear calibration function, and the energy range of the return optical signal is estimated based on this distance.

[0063] S504: Select the second calibration function to correct the first distance according to the reflectivity estimated from the first distance to obtain the second distance. The first calibration function selected in step S503 is a rough calibration, and the second calibration function selected in step S504 is a second non - linear calibration function selected according to the reflectivity estimated from the energy of the actual echo signal in the first distance for re - calibration. This can improve the detection accuracy of the first distance.

[0064] S505: Adjust the integration time according to the reflectivity obtained from the echo signal. If the integration time is too short, there will be too little useful charge information for calculating the detection distance and the signal - to - noise ratio is low; if the integration time is too long, the detection device storing the useful charge will overflow, making the subsequent useful echo signals unable to be integrated for use. Therefore, it is necessary to determine the appropriate integration time according to the echo energy obtained from the first distance to improve the detection accuracy.

[0065] S506: Obtain the final detection distance of the object to be measured based on the echo signal within the second time; the second time here can be another frame different from the first time and later than the first time. For example, the first time can be the first frame, the second time can be the second frame, or any other frame later than the first time, and no specific limitation is made here. The integration duration adjusted according to the first distance is used in the detection at the second time, which can improve the detection accuracy. The adjustment process is completed by an adjustment module. The adjustment module can be one of the functional modules included in the processing module as shown in Figure 1 or can be a separate module to complete the adjustment process. The adjustment module is electrically connected to the light source module and the receiving module.

[0066] 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 statement "including one..." does not exclude the existence of another identical element in the process, method, article or device including the said element.

[0067] 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, the present application can have various changes and modifications. 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 indicate 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, the present application can have various changes and modifications. 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 time-of-flight detection method, the detection method comprising: S1: Driving a light source to generate a detection optical signal and emitting the detection light to an object to be measured; S2: Calculating a first flight distance of the object to be measured based on the echo signal within a first time; S3: Determining an additional time delay difference between the transmitted signal and the received signal according to the first flight distance obtained within the first time, specifically: determining the time delay difference between the transmitted signal and the received signal according to the influence of time noise on the first flight distance, so that the influence of time noise on the distance of the object to be measured is minimized; S4: Adjusting the time delay difference between the transmitted signal and the received signal according to the determined additional time delay difference, and detecting a second flight distance of the object to be measured within a second time, specifically: obtaining the final detection distance of the object to be measured according to the echo signal within the second time.

2. The time-of-flight detection method according to claim 1, characterized in that Estimating the reflectivity of the echo signal according to the first flight distance and adjusting the integration duration according to the reflectivity.

3. A distance detection device that performs detection using the detection method of claim 1, characterized in that, Including: A light source module for generating a detection optical signal and emitting the detection light to an object to be measured; A receiving module for receiving the returned optical signal reflected by the object to be measured within a first time and converting it into an electrical signal; A processing module for obtaining a first flight distance of the object to be measured according to the electrical signal and determining an additional time delay difference between the transmitted signal and the received signal based on the first flight distance, specifically: determining the time delay difference between the transmitted signal and the received signal according to the influence of time noise on the first flight distance, so that the influence of time noise on the distance of the object to be measured is minimized; An adjustment module for adjusting the time delay difference between the transmitted signal and the received signal according to the determined additional time delay difference, estimating the reflectivity of the echo signal according to the first flight distance, and adjusting the integration duration according to the reflectivity; The processing module detects a second flight distance of the object to be measured within a second time, specifically: obtaining the final detection distance of the object to be measured according to the echo signal within the second time.

4. The distance detection device according to claim 3, characterized in that, The adjustment module is included in the processing module.

5. The distance detection device according to claim 3, wherein The adjustment module is electrically connected to the light source module and the receiving module respectively.

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