TOF Sensing Device and Its Distance Detection Method

Abstract

The present application discloses a TOF sensing device and a distance detection method thereof. The distance detection method includes: emitting pulsed detection light to irradiate a measured field of view; a pixel unit receiving the reflected light of the pulsed detection light and generating induced charges corresponding to the energy of the reflected light; using three consecutive charge accumulation windows to accumulate the induced charges generated by each pixel unit, the start edge of the first charge accumulation window being aligned with the pulse generation edge of the pulsed detection light, respectively obtaining three corresponding induced charge amounts Q1, Q2, and Q3, and a first measurement coefficient R1 and a second measurement coefficient R2, wherein, according to the first measurement coefficient R1, the measured distance of the corresponding pixel unit is obtained; when the second measurement coefficient R2 is greater than a first threshold, the measured distance corresponding to the pixel unit is invalid. The above method can improve the accuracy of distance detection.

Description

Technical Field

[0001] This application relates to the field of sensing technology, and particularly to a TOF sensing device and a distance detection method thereof. Background Art

[0002] A Time of Flight (ToF) sensor measures the distance, three-dimensional structure, or three-dimensional contour of an object to be measured by detecting the time interval between the emission and reception of a pulsed signal or the phase generated by a laser round-trip to the object to be measured once. The TOF sensor can obtain a grayscale image and a distance image simultaneously, and is widely used in many fields such as somatosensory control, behavior analysis, monitoring, autonomous driving, artificial intelligence, machine vision, and automatic 3D modeling.

[0003] In the actual distance detection process, due to the complex environment in the field of view to be measured, there are usually multiple reflection surfaces, resulting in the multi-path reflection problem, including: the detection light may reach the surface of the object to be measured after multiple reflections after emission, and the reflected light reflected by the object to be measured may also be received by the time-of-flight sensor after multiple reflections. The multi-path reflection problem will cause the distance traveled by the detection light from emission to reception after reflection to be greater than twice the actual distance of the object to be measured, thereby affecting the accuracy of distance detection. However, in the existing distance detection methods, it is impossible to determine whether the detection result is affected by the multi-path reflected light, and therefore, the detection result cannot be corrected.

[0004] How to accurately identify whether the detection result is affected by the multi-path reflected light is an urgent problem to be solved at present. Summary of the Invention

[0005] In view of this, this application provides a TOF sensing device and a distance detection method thereof to solve the problem that it is impossible to determine whether the detection result is affected by multi-path interference in the prior art, so as to improve the accuracy of distance detection.

[0006] A distance detection method for a TOF sensing device provided by this application includes: emitting pulsed detection light to irradiate the field of view to be measured; a pixel unit receiving the reflected light of the pulsed detection light and generating induced charges corresponding to the energy of the reflected light; using three consecutive charge accumulation windows to accumulate the induced charges generated by each pixel unit, with the opening edge of the first charge accumulation window aligned with the pulse generation edge of the pulsed detection light, respectively obtaining corresponding three induced charge amounts Q1, Q2, and Q3, and a first measurement coefficient R1 and a second measurement coefficient R2, where obtaining the measured distance of the corresponding pixel unit according to the first measurement coefficient R1; when the second measurement coefficient R2 is greater than a first threshold, the measured distance corresponding to this pixel unit is invalid.

[0007] Optionally, the range of the first threshold is 0 to 1.

[0008] Optionally, it further includes: using an ambient light charge accumulation window to accumulate the induced charge of the ambient light generated by each pixel unit to obtain the induced charge quantity Q0 of the ambient light. At this time,

[0009] Optionally, it further includes: comparing the second measurement coefficient with the calibrated measurement coefficient R0. When it is greater than the second threshold, the measured distance corresponding to this pixel unit is invalid.

[0010] Optionally, the range of the second threshold is 1 to 5.

[0011] Optionally, the calibrated measurement coefficient R0 corresponds to the second measurement coefficient obtained in a calibration environment without being interfered by multipath reflected light.

[0012] Optionally, it further includes correcting the invalid measured distance.

[0013] Optionally, the correction method includes: pre - establishing a correction table, where the correction table records the corresponding R2 / R0 values and correction values; finding the corresponding correction value from the correction table according to the actual value of R2 / R0 obtained during the detection process; and correcting the current measured distance according to the correction value to obtain a corrected measured distance to eliminate the influence of multipath reflected light.

[0014] The technical solution of the present invention also provides a TOF sensing device, including: a light source module for emitting pulsed detection light; a sensing module for receiving the reflected light of the pulsed detection light reflected by the object to be measured and generating corresponding induced charges; a processor connected to the light source module and the sensing module for controlling the light source module and the sensing module; a memory storing a computer application program that can run on the processor; wherein, when the computer program is executed by the processor, it implements the distance detection method as described in any one of the above.

[0015] In the above - mentioned TOF sensing device and its ranging method of the present application, by adding a charge accumulation window after the charge accumulation window used in distance detection to accumulate the induced charges generated by multipath reflected light, through the measurement coefficient related to the accumulated charge quantity, it can timely judge the degree to which the measured distances obtained by each pixel unit are affected by multipath reflected light, judge whether the measured distance is valid, and timely correct it, thereby improving the accuracy of distance detection. Description of the Drawings

[0016] To more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0017] Figure 1 is a schematic structural diagram of a TOF sensing device according to an embodiment of the present application;

[0018] Figure 2 is a schematic flowchart of a distance detection method for a TOF sensing device according to an embodiment of the present application;

[0019] Figure 3 is a schematic timing diagram of each charge accumulation window, pulsed detection light, and reflected light during the distance detection process according to an embodiment of the present application;

[0020] Figure 4 is a schematic diagram of the relationship curve between the first measurement coefficient, the calibrated distance, and the calibrated measurement coefficient according to an embodiment of the present application. Detailed implementation manners

[0021] In the prior art, it is usually impossible to determine whether the current detection result is affected by multi-path reflected light based on each detection result during the actual detection process. Usually, only during the calculation of the measured distance, through algorithm operations, the influence of possible multi-path reflections in the measurement result can be reduced, but the influence degree of multi-path reflected light actually received by each pixel unit cannot be determined.

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application. Without conflict, the following various embodiments and their technical features can be combined with each other.

[0023] Please refer to Figure 1 , which is a schematic structural diagram of a TOF sensing device according to an embodiment of the present invention.

[0024] The TOF sensing device includes: a light source module 101, a sensing module 102, a processor 103, and a memory 104.

[0025] The light source module 101 is used to emit pulsed detection light. The light source module 101 can be an infrared light source, and the processor 103 can send a control signal to the light source module 101 to adjust parameters such as the light emission intensity, pulse width, and period of the light source module 101.

[0026] The sensing module 102 is configured to receive the reflected light of the pulsed detection light reflected by the object to be measured. The sensing module 102 includes a pixel unit array, which can receive optical signals and convert the optical signals into electrical signals, generating induced charges corresponding to the received light. The processor 103 is connected to the sensing module 102 and is configured to obtain the sensing signal of the sensing module 102.

[0027] The memory 104 can be a non-volatile memory and stores a computer application program that can run on the processor 103. When the computer program is executed by the processor 703, the distance detection method described in the subsequent embodiments is implemented.

[0028] In some embodiments, during the distance detection process, the processor 103 can control the light source module 101 to emit pulsed detection light to irradiate the field of view to be measured. The pulsed detection light includes at least two types of pulses with different pulse widths. The reflected pulsed detection light is received by the sensing module 102. The processor 103 can call the computer application program in the memory 103, and based on the time interval from the emission to the reception of the pulses of the pulsed detection light, obtain the initial distance information at each position in the field of view to be measured, and merge the initial distance information obtained based on the pulses with different pulse widths to obtain the measured distance information at each position in the field of view to be measured.

[0029] Please refer to Figure 2 , which is a schematic flowchart of the distance detection method according to an embodiment of the present invention.

[0030] In this embodiment, the distance detection includes the following steps:

[0031] Step S201: Emit pulsed detection light to irradiate the field of view to be measured. The pixel unit receives the reflected light of the pulsed detection light and generates induced charges corresponding to the energy of the reflected light.

[0032] The pulsed detection light is modulated pulsed light. The pulsed detection light can be LED light, laser, or other light that is easy to modulate. The pulsed detection light irradiates all objects within the range of the field of view to be measured. When the pulsed detection light reaches the surface of the object to be measured, it will be reflected on the surface of the object to be measured and form reflected light.

[0033] The pixel array of the sensing module 102 of the TOF sensing device includes a plurality of pixel units that can convert optical signals into electrical signals, so that the received reflected light can be converted into a certain number of induced charges corresponding to the energy of the reflected light through the sensing module.

[0034] Step S202: The induced charges generated by each pixel unit are accumulated using three consecutive charge accumulation windows, and a first measurement coefficient R1 and a second measurement coefficient R2 are obtained respectively.

[0035] Please refer to Figure 3 , which is a timing diagram of each charge accumulation window, pulsed detection light, and reflected light according to an embodiment of the present invention.

[0036] Since ambient light usually exists in the environment where the object to be measured is located, the light signal received by the sensing module includes both the reflected light of the pulsed detection light and the ambient light. Therefore, in this embodiment, an ambient light charge accumulation window G0 is also used to accumulate the induced charges of the ambient light generated by each pixel unit. The ambient light charge accumulation window G0, the first charge accumulation window G1, the second charge accumulation window G2, and the third charge accumulation window G3 are opened in sequence, and the window time of each charge accumulation window is the same as the pulse width of the pulsed detection light LO, both being T, and the opening edge of the first charge accumulation window G1 is aligned with the pulse generation edge of the pulsed detection light LO.

[0037] The ambient light charge accumulation window G0, the first charge accumulation window G1, the second charge accumulation window G2, and the third charge accumulation window G3 accumulate induced charges Q0, Q1, Q2, and Q3 respectively. The charge accumulation window includes a capacitive structure, and the generated induced charges are used to charge the capacitor plates. The amount of the induced charges accumulated can be obtained according to the voltage of the capacitor plates.

[0038] The ambient light charge accumulation window G0 can only accumulate the induced charges generated by the ambient light; the first charge accumulation window G1 and the second charge accumulation window G2 are used to accumulate the induced charges generated by the reflected light. Among them, in the presence of multi-path reflected light (MPI), the first charge accumulation window G1 and the second charge accumulation window G2 will also accumulate the induced charges generated by the multi-path reflected light. The third charge accumulation window G3 can only accumulate the induced charges generated by the multi-path reflected light (MPI). Since the multi-path reflected light undergoes multiple reflections, the optical path is longer than that of the direct reflected light, so it is received later than the direct reflected light, which will cause the distance detection result to be too large. The greater the lag of the MPI, the greater the impact on the detection result. Therefore, the larger the amount of induced charges accumulated by the third charge accumulation window G3, the higher the proportion of MPI in the reflected light, or the greater the lag of the MPI, that is, the greater the impact of the detection result by the MPI.

[0039] According to the amounts of charges accumulated by each charge accumulation window, the first measurement coefficient R1 and the second measurement coefficient R2 can be calculated. Specifically,

[0040]

[0041] Among them, the first measurement coefficient R1 is positively correlated with the detection distance, and the second measurement coefficient R2 is positively correlated with the energy of the multipath reflected light.

[0042] In other embodiments, in the detection structure where there is no ambient light, for example, in the dark state, charge accumulation can also be performed only using G1, G2, and G3. At this time,

[0043]

[0044] Step S203: Obtain the measurement distance corresponding to the pixel unit according to the first measurement coefficient R1.

[0045] The measurement distance can be calculated through the first measurement coefficient R1:

[0046] Due to the system error in the detection system, the calculation result obtained by the above theoretical calculation usually has a large error. In the actual detection process, calibration is required. By calibrating the first measurement coefficient R1 and the corresponding actual distance in a standard environment, a corresponding measurement curve between the first measurement coefficient R1 and the calibration distance depth can be obtained. There is a positive correlation between the first measurement coefficient R1 and the calibration distance depth (please refer to Figure 4 ). In the actual distance detection process, according to the value of the first measurement coefficient R1 obtained, the corresponding measurement distance can be obtained through the pre-calibrated measurement curve.

[0047] Since the calculation result of R1 is affected by MPI, the accuracy of judging the measurement distance depends on the influence degree of MPI, that is, the degree to which MPI lags behind the direct reflected light.

[0048] Step S204: Determine whether the second measurement coefficient R2 is greater than the first threshold; if yes, execute Step S205: Determine that the measurement distance corresponding to the pixel unit is invalid; if not, execute Step S206: Determine that the measurement distance corresponding to the pixel unit is valid.

[0049] In the actual measurement process, various different reflectivity situations will be faced. Under different reflectivities, the induced charge amounts generated by the direct reflected light and the multipath reflected light generated by the same intensity of pulsed detection light are different. Therefore, it is impossible to directly judge the proportion of the received multipath reflected light by using the accumulated charge amount Q3.

[0050] In this embodiment, the second measurement coefficient R2 is used for judgment. The second measurement coefficient R2 is the ratio of Q3 to Q2 + Q1 (without considering ambient light), which can eliminate the influence of reflectivity.

[0051] If the second measurement coefficient R2 is small, or R2 = 0, it indicates that the amount of electric charge generated by the multipath reflected light that has not been accumulated in the third charge accumulation window G3 (R2 = 0), or compared with the amount of electric charge accumulated in the second charge accumulation window G2 and the first charge accumulation window G1, the proportion of Q3 is very small. Thus, it can be judged that in the reflected light received by the corresponding pixel unit, the proportion of multipath reflected light is small, or the delay of the multipath reflected light is small, and the influence on the detection result is small, so the measured distance is valid. According to the actual measurement accuracy requirements, a first threshold can be set. When the second measurement coefficient R2 is less than or equal to the first threshold, the measured distance is valid.

[0052] If the second measurement coefficient R2 is greater than the first threshold, it indicates that the proportion of multipath reflected light received by the corresponding pixel unit is large, the delay is relatively serious, and the influence on the measured distance is large. Therefore, it can be considered that the measured distance of the corresponding pixel unit is invalid, and this measured distance is discarded.

[0053] The first threshold can be set according to the measurement accuracy requirements, and the range of the first threshold can be 0 to 1.

[0054] In another embodiment of the present invention, the second measurement coefficient R2 can also be compared with the calibrated measurement coefficient R0. When is greater than the second threshold, the measured distance of this pixel unit is invalid.

[0055] The calibrated measurement coefficient R0 corresponds to the second measurement coefficient obtained in a calibrated measurement environment where there is no interference or less influence from multipath reflected light. During the calibration process, in addition to being able to obtain the actual distance depth corresponding to the first measurement coefficient R1, the calibrated measurement coefficient R0 corresponding to the first measurement coefficient R1 can also be obtained, forming Figure 4 the shown curve. There is a positive correlation between the calibrated measurement coefficient R0 corresponding to the first measurement coefficient R1. In step S203, in addition to being able to obtain the corresponding measured distance through the first measurement coefficient R1 obtained in step S202, the calibrated measurement coefficient R0 corresponding to the first measurement coefficient R1 can also be obtained, so as to compare the second measurement coefficient R2 with the calibrated measurement coefficient R0.

[0056] By it can more accurately reflect the influence degree of multipath reflected light on distance detection. The second threshold can be set according to the measurement accuracy requirements, and the range of the second threshold can be 1 to 5.

[0057] In another embodiment, after the measured distance of the pixel unit is considered invalid, it further includes correcting the invalid measured distance.

[0058] The correction method may include: establishing a correction table in advance, where the correction table records the corresponding R2 / R0 values and correction values one by one; finding the corresponding correction value from the correction table according to the actual ratio of R2 and R0 obtained during the detection process; and correcting the current measured distance according to the correction value to obtain a corrected measured distance so as to eliminate the influence of multipath reflected light. The correction table can be obtained in advance from the R2 / R0 values, measured distances, and actual distances obtained through multiple measurements.

[0059] The correction value may be a specific correction distance d, then the corrected measured distance D' = D + d.

[0060] The correction value may also be a correction ratio k, then the corrected measured distance D' = D(1 + k).

[0061] The above TOF sensing device and its ranging method can timely judge the degree to which the measured distances obtained by each pixel unit are affected by multipath reflected light, determine whether the measured distances are valid, and perform corrections in a timely manner, thereby improving the accuracy of distance detection.

[0062] That is, the above is only an embodiment of the present application, and does not limit the patent scope of the present application. Any equivalent structural or equivalent process transformation using the content of the specification and drawings of the present application, such as the mutual combination of technical features between various embodiments, or direct or indirect application in other related technical fields, is similarly included in the patent protection scope of the present application.

Claims

1. A distance detection method for a TOF sensing device, characterized in that, emitting pulsed detection light to irradiate the measured field of view; the pixel unit receives the reflected light of the pulsed detection light and generates induced charges corresponding to the energy of the reflected light; The induced charges generated by each pixel unit are accumulated using three consecutive charge accumulation windows. The opening edge of the first charge accumulation window is aligned with the pulse generation edge of the pulsed detection light, and three corresponding induced charge amounts Q1, Q2, and Q3, as well as a first measurement coefficient R1 and a second measurement coefficient R2, are obtained. Among them, The measurement distance of the corresponding pixel unit is obtained according to the first measurement coefficient R1; when the second measurement coefficient R2 is greater than the first threshold, the measured distance corresponding to this pixel unit is invalid.

2. The distance detection method according to claim 1, characterized in that, the range of the first threshold is 0 to 1.

3. The distance detection method according to claim 1, characterized in that, further comprising: The environmental light charge accumulation window is used to accumulate the induced charge of the environmental light generated by each pixel unit to obtain the induced charge quantity Q0 of the environmental light. At this time, 4. The distance detection method according to claim 1, characterized in that, further comprising: Compare the second measurement coefficient with the calibrated measurement coefficient R0. When is greater than the second threshold, the measured distance corresponding to the pixel unit is invalid.

5. The distance detection method according to claim 4, characterized in that, the range of the second threshold is 1 to 5.

6. The distance detection method according to claim 4, characterized in that, the calibrated measurement coefficient R0 corresponds to the second measurement coefficient obtained in a calibration environment without interference from multipath reflected light.

7. The distance detection method according to claim 3, characterized in that, further comprising correcting the invalid measured distance.

8. The distance detection method according to claim 7, characterized in that, the correction method includes: pre-establishing a correction table, the correction table records the corresponding R2 / R0 values and correction values; according to the actual value of R2 / R0 obtained during the detection process, finding the corresponding correction value from the correction table; correcting the current measured distance according to the correction value to obtain a corrected measured distance to eliminate the influence of multipath reflected light, where R0 is the calibrated measurement coefficient.

9. A TOF sensing device, characterized in that, comprising: a light source module for emitting pulsed detection light; a sensing module for receiving the reflected light of the pulsed detection light reflected by the object to be measured and generating corresponding induced charges; a processor connected to the light source module and the sensing module for controlling the light source module and the sensing module; a memory storing a computer application program capable of running on the processor; wherein, when the computer application program is executed by the processor, it implements the distance detection method according to any one of claims 1 to 8.

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