Method and system for detecting dirt on a photomask for laser radar

Abstract

A photomask contamination detection method (10) for a laser radar includes the steps of: transmitting a multi-pulse sequence having pulse encoding (S101), receiving a radar echo and obtaining an echo pulse sequence corresponding to the multi-pulse sequence in the radar echo (S102), and judging whether photomask contamination exists in the laser radar based on the flight time of the echo pulse sequence (S103). It detects photomask contamination using a beam generated by a transmitting unit of the laser radar, does not require additional light source and / or detection device, has a simple structure, saves the internal space of the laser radar, detects by the encoding time, flight time and echo point number of the laser radar, has high detection accuracy and avoids the occurrence of erroneous judgment.

Description

[Technical field]

[0001] The present invention relates to the field of laser detection, and in particular to a photomask contamination detection method and system for laser radar. [Background technology]

[0002] Laser radar is an important sensor for unmanned driving. Conventional laser radars generally do not have a photomask dirt detection device for detecting photomasks. During the driving of an unmanned vehicle, the laser radar may encounter weather conditions such as rain, snow, wind, sand, etc., which will form dust, scratches, sewage, mud, corrosion and other conditions on the photomask, preventing the laser radar from normally acquiring environmental information around the unmanned vehicle. Therefore, acquiring photomask dirt information for the laser radar is beneficial for the normal detection of the laser radar.

[0003] In the conventional photomask contamination detection method, it is necessary to add an additional light emitting device to detect photomask contamination, and the structure is relatively complicated, the detection accuracy is low, and erroneous judgments are likely to occur.

[0004] The contents of the Background Art section are merely technologies known to the discloser and do not necessarily represent the prior art in this field. Summary of the Invention

[0005] The present invention is used to improve the detection accuracy of photomask contamination and to avoid the occurrence of erroneous determination, A step S101 of transmitting a multi-pulse sequence having a pulse encoding; a step S102 of receiving a radar echo and acquiring an echo pulse sequence corresponding to the multi-pulse sequence in the radar echo; and determining whether photomask dirt exists in the laser radar based on the time of flight of the echo pulse sequence (S103).

[0006] According to one aspect of the present invention, step S103 includes: The method further includes determining that photomask contamination is present in the laser radar if the time of flight of the echo pulse sequence is less than a time of flight threshold.

[0007] According to one aspect of the present invention, step S103 includes: The method further includes a step of counting the number of echo points corresponding to the photomask dirt in the point cloud data of a single frame, and determining whether or not the photomask dirt is present in the laser radar based on the number of echo points.

[0008] According to one aspect of the present invention, the detection method comprises: The method further includes a step of determining that photomask dirt is present in the laser radar when the echo score is greater than a score threshold.

[0009] According to one aspect of the present invention, the detection method comprises: The method further includes a step of counting the number of echo points corresponding to the photomask dirt within a predetermined angle range of detection by the laser radar, and determining that the photomask dirt is present within the predetermined angle range if the number of echo points is greater than the point threshold value.

[0010] According to one aspect of the present invention, step S101 further includes transmitting a multi-pulse sequence encoded in time intervals, and step S102 includes: The method further includes the step of making the time interval of the echo pulse sequence coincide with the time interval of the multi-pulse sequence.

[0011] According to one aspect of the present invention, the detection method comprises: The method further includes setting a corresponding score threshold based on the time-of-flight threshold.

[0012] According to one aspect of the present invention, the detection method comprises: The method further includes a step of determining that photomask dirt is present in the laser radar when the number of echo points in each of the consecutive multi-frame point cloud data is greater than the point number threshold.

[0013] According to one aspect of the present invention, the detection method comprises: The method further includes determining a type of the photomask contamination based on the echo score.

[0014] According to one aspect of the present invention, the detection method comprises: determining that the photomask contamination is a reflective contamination when the number of echo points is greater than a first discrimination threshold; determining that the photomask contamination is a scattering type contamination when the number of echo points is equal to or less than a first discrimination threshold and is greater than a second discrimination threshold; The method further includes a step of determining that the photomask dirt is an absorption type dirt when the number of echo points is equal to or less than a second discrimination threshold.

[0015] According to one aspect of the present invention, the detection method comprises: The method further includes the step of rescanning the predetermined angle range in which the photomask contamination exists at a second predetermined angle, and determining a distribution state of the photomask contamination within the predetermined angle range.

[0016] The present invention relates to a transmitting unit configured to transmit a multi-pulse sequence having a pulse encoding; a receiving unit configured to receive radar echoes; a waveform detection unit coupled to the transmitting unit and the receiving unit, respectively, a waveform detection unit configured to obtain an echo pulse sequence corresponding to the multi-pulse sequence in the radar echo; and a photomask contamination determination unit configured to determine whether photomask contamination exists in the laser radar based on the flight time of the echo pulse sequence.

[0017] According to one aspect of the present invention, the photomask contamination determination unit further includes: The laser radar is configured to determine that photomask contamination is present when the time of flight of the echo pulse sequence is less than a time of flight threshold.

[0018] According to one aspect of the present invention, the photomask contamination detection system comprises: Further comprising a point counting unit configured to count echo points corresponding to the photomask stains in a single frame of point cloud data; The photomask contamination determination unit is further configured to determine whether photomask contamination exists in the laser radar based on the echo point number.

[0019] According to one aspect of the present invention, the photomask contamination determination unit further includes: The laser radar is configured to determine that photomask dirt is present when the echo score is greater than a score threshold.

[0020] According to one aspect of the present invention, the point counting unit further comprises: The method is configured to count the number of echo points corresponding to the photomask dirt within a predetermined angle range of detection by the laser radar, The photomask contamination determination unit is further configured to determine that photomask contamination exists within the predetermined angle range when the echo score is greater than the score threshold.

[0021] According to one aspect of the present invention, the photomask contamination detection system comprises: The radar apparatus further includes a data acquisition unit coupled between the receiving unit and the waveform detection unit, the data acquisition unit being used for performing data acquisition on the radar echo and transmitting a data signal of the radar echo to the waveform detection unit.

[0022] According to one aspect of the present invention, the transmitting unit is further configured to transmit a multi-pulse sequence encoded in a time interval, and the waveform detection unit further comprises: The time interval of the echo pulse sequence is configured to match the time interval of the multi-pulse sequence.

[0023] According to one aspect of the present invention, the photomask contamination determination unit includes: In each column, the photomask dirt determination results detected within the same predetermined angle range when the laser radar scans in continuous multi-frames are stored in correspondence with each other, Each row includes a multi-bit storage table that is set so that the photomask contamination determination results within each predetermined angle range when the laser radar scans in a single frame are stored in association with each other.

[0024] According to one aspect of the present invention, the photomask contamination detection system further comprises: When all of the storage results of the same column in the multi-bit storage table indicate the presence of photomask dirt in the laser radar, the photomask dirt judgment unit is configured to determine that photomask dirt exists within the specified angle range corresponding to the same column.

[0025] The present invention provides a photomask dirt detection method and photomask dirt detection system for laser radar, which detects photomask dirt using a beam generated by a transmitting unit of a laser radar, does not require additional light sources and / or detection devices, and detects photomask dirt using the encoding time, flight time, and echo points of the laser radar, and has higher detection accuracy and avoids the occurrence of erroneous judgment compared to the case where photomask dirt is detected only by setting a threshold value for the signal waveform, and the echo points can be used to determine the type of photomask dirt, providing a basis for subsequent dirt removal. The present invention completes photomask dirt detection by a transmitting unit and a receiving unit in the laser radar to detect the target, which has a simple structure and saves the internal space of the laser radar. [Brief description of the drawings]

[0026] The drawings are intended to provide a further understanding of the embodiments of the present invention, to constitute a part of the specification, and to be used to interpret the present invention together with the embodiments of the present invention, but are not intended to limit the present invention. [Figure 1A] This shows the light path when there is no dirt on the laser radar photomask. [Figure 1B] This shows the light path when dirt is present on the laser radar photomask. [Diagram 2] 2 illustrates a schematic diagram of a photomask contamination detection optical path according to one embodiment of the present invention. [Diagram 3] 1 illustrates a method for detecting contamination on a photomask for a laser radar according to one preferred embodiment of the present invention. [Figure 4] 13 shows a schematic diagram of the relative positional relationship between an echo pulse sequence corresponding to a stain on a photomask and an echo pulse sequence corresponding to a target. [Figure 5A] When the flight time threshold is 1 ns, the number of echo points corresponding to photomask dirt in the point cloud data of a single frame is shown. [Figure 5B] When the flight time threshold is 2 ns, the number of echo points corresponding to photomask dirt in the point cloud data of a single frame is shown. [Figure 6] 1 illustrates a schematic diagram of a photomask contamination detection system according to one preferred embodiment of the present invention. [Figure 7] 3 is a schematic diagram showing a two-dimensional storage table of a photomask contamination judgment unit according to one preferred embodiment of the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] In the following, only some exemplary embodiments are briefly described. As can be understood by those skilled in the art, the described embodiments can be modified in various ways without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be understood as illustrative in nature and not restrictive.

[0028] In describing the present invention, it is to be understood that the orientations or positional relationships indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc. are based on the drawings and are merely for the purpose of easily explaining and simplifying the description of the present invention, and do not indicate or imply that the devices or elements described necessarily have a particular orientation or are constructed or operated in a particular orientation, and should not be understood as limiting the present invention. In addition, the terms "first" and "second" are merely for descriptive purposes and should not be understood as indicating or implying a relative importance or quantity of the technical features indicated. Thus, a feature limited as "first" or "second" may explicitly or implicitly include one or more of the said features. In describing the present invention, unless expressly and specifically limited, "plurality" means two or more than two.

[0029] In the description of the present invention, unless otherwise clearly specified or limited, the terms "attach", "couple" and "connect" should be understood in a broad sense, for example, fixedly connected, detachably connected, integrally connected, mechanically connected, electrically connected, or in communication with each other, directly connected, or indirectly connected through an intermediate medium, or the insides of two elements may communicate with each other, or the relationship of interaction between two elements. Those skilled in the art may understand the specific meaning of the above terms in the present invention according to the specific situation.

[0030] In the present invention, unless otherwise clearly specified or limited, a first feature being "above" or "below" a second feature may include a case where the first and second features are in direct contact with each other, or may include a case where the first and second features are not in direct contact with each other but are in contact with each other through another feature between them. Furthermore, a first feature being "above," "above," and "on the upper surface" of a second feature may include a case where the first feature is directly above and diagonally above the second feature, or may simply mean that the horizontal height of the first feature is higher than that of the second feature. A first feature being "below," "below," and "on the lower surface" of a second feature may include a case where the first feature is directly below and diagonally below the second feature, or may simply mean that the horizontal height of the first feature is smaller than that of the second feature.

[0031] In the following disclosure, many different embodiments or examples are provided to realize different structures of the present invention. In order to simplify the disclosure of the present invention, the following describes specific example components and configurations. Of course, they are merely examples and are not intended to limit the present invention. In addition, the present invention may duplicate reference numerals and / or alphabets in different examples, and such duplication is for the sake of brevity and clarity, and does not in itself indicate a relationship between the various embodiments and / or configurations described. In addition, the present invention provides examples of various specific processes and materials, but those skilled in the art may envision the application of other processes and / or the use of other materials.

[0032] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. It should be understood that the embodiment described herein is merely for the purpose of explaining and interpreting the present invention and is not intended to limit the present invention.

[0033] The photomask of the laser radar is placed on the outside of the laser radar to protect the devices inside the laser radar, and the photomask allows the detection beam and the echo beam to pass through. The photomask of the laser radar often has surface defects and dirt such as oil sweat, scratches, stone pits, dirty water, dust, stains, soil, etc. These surface defects and dirt have a negative effect on the normal detection of the laser radar.

[0034] The inventors classify the dirt on the photomask of the laser radar into three types: absorption type, reflection type and scattering type, and the characteristics of the three dirt types will be described in detail below with reference to the drawings. As shown in Figure 1A, when there is no dirt on the photomask of the laser radar, the detection beam transmitted from the transmitting unit passes through the photomask of the laser radar and is emitted linearly, the detection beam is emitted into the target space and reflected by the target to form an echo, the detection echo is also incident on the receiving unit of the laser radar and received by the receiving unit, the optical signal is converted into an electrical signal, and the information such as the distance, speed, reflectivity, etc. of the target is analyzed by the processor. As shown in Figure 1B, when there are different types of dirt such as oil sweat, scratches, stone pits, dirty water, dust, stains, and soil on the photomask of the laser radar, the detection beam transmitted from the transmitting unit cannot be emitted linearly when it encounters the photomask dirt, and the emission path of the detection beam is often changed due to the influence of different types of dirt. Regarding the absorption type photomask dirt, as shown in the point (1) of FIG. 1B, the photomask at the point has absorption type dirt such as asphalt or paint, and a part of the detection beam is absorbed by the absorption type dirt, and the outgoing beam cannot be formed. Regarding the reflection type photomask dirt, as shown in the point (2) of FIG. 1B, the photomask at the point has reflection type dirt such as dust or mud, and a part of the detection beam is reflected by the reflection type dirt, and the outgoing beam cannot be formed. Regarding the scattering type photomask dirt, as shown in the point (3) of FIG. 1B, the photomask at the point has scattering type dirt such as scratches, stone pits, insect corpses, bird droppings, oily sweat, fingerprints, dirty water, fresh water, photomask corrosion, and the like, and a part of the detection beam is scattered by the scattering type dirt, and the outgoing beam can pass through the scattering type dirt, but the propagation direction changes.

[0035] If dirt is present on the photomask of a laser radar, the detection beam cannot be emitted or the propagation direction of the detection beam changes, which may have the following effects on normal detection by the laser radar: 1), 2) and 3).

[0036] 1) The power of the detection beam incident on the target is weakened, resulting in reduced ranging capability and increased point loss. 2) Since the reflectance of a target is calculated depending on the optical power, a decrease in optical power also leads to a decrease in the accuracy of the reflectance measurement. 3) Reflected echoes from dirt on the photomask cause increased noise.

[0037] Therefore, the present invention provides a photomask dirt detection method for laser radar, in which the photomask dirt is detected by using the beam generated by the transmitting unit (e.g., semiconductor laser device) of the laser radar for detecting the target, as shown in FIG. 2, and no additional light source is required to detect the photomask dirt. The above-mentioned three types of dirt all generate reflections to the detection beam, where the reflectance of the reflective dirt is the highest, the reflectance of the absorbing dirt is the lowest, and the scattering dirt is partially reflected, with the reflectance being between the two. Therefore, the receiving unit (e.g., an avalanche photodiode represented by APD, which is only an example, and the receiving unit used in the present invention is not limited to APD) of the laser radar for detecting the target can be used to receive the echo of the detection beam reflected by the photomask dirt, convert the optical signal into an electrical signal, and further analyze the position, distribution and / or type of the photomask dirt based on the waveform information.

[0038] As shown in FIG. 3, according to one preferred embodiment of the present invention, the present invention provides a photomask contamination detection method 10 for laser radar, including steps S101 to S103.

[0039] In step S101, a multi-pulse sequence having a pulse encoding is transmitted.

[0040] Laser radars are used for distance measurement based on the direct time-of-flight (TOF) method, i.e., by transmitting a laser pulse of high peak power with a narrow pulse width and measuring the flight time of the laser pulse between the laser radar and the target and back.

[0041] In situations where multiple laser radars are operating simultaneously within the same measurement range, for example when multiple laser radars are installed on one vehicle, or when multiple vehicles equipped with laser radars are located at relatively close distances, the measurement principle of laser radar is based on measuring the flight time of the transmitted laser pulse, so each laser radar cannot determine whether the received echo pulse was sent by itself or not, and even when it receives an echo pulse transmitted from another radar with a certain probability, it is determined to be an echo signal, which causes errors in the distance measurement results, i.e., crosstalk.

[0042] At present, using multi-pulse encoding to identify echo signals is an effective anti-interference method for laser radar. The basic idea of ​​the pulse encoding method is that the laser radar transmits a laser pulse containing preset encoding information to detect a target, and when receiving the echo, it identifies it according to the preset encoding information to determine the reflected echo of the detection beam transmitted by the radar.

[0043] The pulse encoding may use one or more of the following encoding methods: time interval encoding, peak intensity encoding, pulse width encoding, and the like.

[0044] In the laser radar photomask contamination detection method 10, the laser radar uses a pulse-encoded multi-pulse sequence during detection. There is no need to provide a separate detection light source or use an encoding mechanism different from the actual detection. Specifically, the preferred embodiment of the present invention does not need to transmit encoding pulses different from the detection encoding in a time sequence to detect contamination, but can directly use the echo pulse to determine photomask contamination.

[0045] In step S102, a radar echo is received, and an echo pulse sequence corresponding to the multi-pulse sequence is obtained in the radar echo.

[0046] When photomask dirt of the laser radar exists on the photomask surface, the laser reflected by the photomask dirt is received by the receiving unit. Therefore, the presence or absence of photomask dirt can be detected by detecting whether or not there is an echo caused by the photomask dirt in the echo waveform of the receiving unit. The preferred embodiment of the present invention uses the encoding information of the transmitted laser pulse to identify the echo caused by the photomask dirt, so that there is no need to add a light source and / or a receiving device to detect the photomask dirt, thus saving the structure and layout of the laser radar.

[0047] For example, when a laser radar uses time interval encoding to transmit multiple laser pulses containing time encoding information, the receiving side determines whether the received pulse signal is an echo resulting from the reflection of multiple laser pulses based on the time interval of the received pulse signal.

[0048] Also, for example, when a laser radar uses peak intensity encoding to transmit multiple laser pulses containing peak intensity encoding information, the receiving side determines whether or not the received pulse signal is an echo resulting from the reflection of multiple laser pulses based on the ratio of peak intensities of the received pulse signals (the peak intensity of the received pulse signal is attenuated compared to the transmitted pulse, but the ratio basically remains the same, and a certain tolerance can be set).

[0049] Also, for example, when a laser radar uses pulse width encoding to transmit multiple laser pulses containing pulse width encoding information, the receiving side determines whether the received pulse signal is an echo resulting from the reflection of multiple laser pulses based on the pulse width ratio of the received pulse signal (the pulse width of the received pulse signal will be wider than that of the transmitted pulse, but the ratio will basically remain the same, and a certain tolerance can be set).

[0050] Preferably, the transmitting unit of the laser radar uses time interval encoding, as shown in Fig. 4. For example, when the transmitting unit transmits a double pulse sequence with time interval encoding t, the echo caused by the photomask dirt and the echo waveform of the detection beam scanned into the target space and reflected by the target are shown in Fig. 4, and there is a time interval t between the two photomask echoes, and there is also a time interval t between the two detection echoes.

[0051] First, an echo pulse sequence corresponding to the search beam is determined based on the time interval encoding, and then the echo pulse sequence caused by the photomask dirt is screened from the echo pulse sequence. The photomask echo is characterized in that a small pulse is formed before each of a plurality of normal echo pulses, and the time interval between two adjacent small pulses is equal to the time interval between two adjacent normal echoes, i.e., the encoding time.

[0052] In step S103, it is determined whether photomask dirt is present on the laser radar based on the flight time of the echo pulse sequence.

[0053] Because the distance between the photomask and the transmitting unit is very close and the flight time of the echo pulse sequence corresponding to the photomask dirt is short, it is possible to determine whether the echo pulse sequence corresponds to the photomask dirt by setting the flight time of the corresponding echo pulse sequence.Preferably, the flight time of the echo pulse sequence is determined according to the leading edge time of the first pulse in the echo pulse sequence.As shown in FIG. 4, preferably, the transmitting unit transmits a double pulse sequence with time interval encoding t, in which case, there are two conditions 1) and 2) below for determining the echo pulse sequence corresponding to the photomask dirt detected once.

[0054] 1) The two preceding and succeeding echo signals satisfy the encoding condition, i.e., when the encoding time of the transmit pulse sequence is t, the leading edge time interval between the echo signals corresponding to two adjacent photomask stains is also t. 2) The leading edge time of the first pulse in the echo pulse sequence corresponding to the photomask dirt is less than t1, for example, t1 is 1 ns. The leading edge time t1 may have a certain value range, and the value of t1 can be determined according to the requirements of detection accuracy and the type of laser radar (the distance between the photomask and the transmitting unit).

[0055] The function of condition 1) is to screen the echo pulse sequence that satisfies the encoding condition, and the function of condition 2) is that the echo of a close-range target is similar to the echo corresponding to the photomask dirt and may cause a false alarm, and in order to reduce the probability of a false alarm as much as possible, the false alarm caused by the echo of a close-range target can be eliminated by using the characteristic that the leading edge time of the echo is different at different distances, for example, by setting a flight time threshold (for example, the leading edge time of the echo pulse sequence is less than 1 ns).

[0056] The photomask contamination detection method provided in the preferred embodiment of the present invention does not require any additional device or structure to be added to the laser radar, and performs detection using the encoding method used in the actual detection of the laser radar, resulting in high detection accuracy.

[0057] According to one preferred embodiment of the present invention, in the detection method 10, step S103 (determining whether photomask contamination exists in the laser radar based on the flight time of the echo pulse sequence) includes: The method further includes counting the number of echo points corresponding to the photomask dirt in the single frame point cloud data, and determining whether the photomask dirt is present in the laser radar based on the number of echo points, where the number of echo points means the number of echo-corresponding points in the radar point cloud.

[0058] Taking mechanical laser radar as an example, its opto-mechanical rotor usually includes multiple laser devices, the light emission direction of each laser device corresponds to one vertical field of view or one angle, and the opto-mechanical rotor rotates around the vertical axis, thereby realizing 360-degree scanning and detection in the horizontal direction, and forming one frame of point cloud data of the laser radar. During the rotation process, one of the laser devices transmits a detection beam at every certain rotation angle (i.e., the angular resolution of the laser radar, for example, 0.1 degree), and the receiving unit of the laser radar receives the echo after the detection beam is diffusely reflected by the obstacle to generate point cloud data. After one round of scanning, the laser radar generates one frame of point cloud data including obstacle information in the surrounding environment of the current position of the radar.

[0059] For example, for a 128-line laser radar, if all laser devices are emitting light and the angular resolution is assumed to be 0.1°, one frame of point cloud data having 460,800 points is generated within one detection cycle.

[0060] According to one preferred embodiment of the present invention, the detection method 10 further includes determining that photomask contamination is present in the laser radar if the echo score is greater than a score threshold.

[0061] In a preferred embodiment of the present invention, in addition to the condition of determining photomask contamination by flight time, a limiting condition is added to count the number of echo points corresponding to photomask contamination in a single frame of point cloud data. For example, for a 128-line laser radar, when all laser devices emit light, assuming that the angular resolution is 0.1°, one frame of point cloud data having 460800 points is generated within one detection period, and if the number of points that meet the flight time threshold condition is 100 or more, it is deemed that photomask contamination exists.

[0062] In the preferred embodiment of the present invention, a score threshold is set in the single frame point cloud data, and when the score corresponding to the photomask stain is greater than the score threshold, it is determined that the photomask stain exists. In the previous embodiment, after performing the screening based on the time of flight threshold, the judgment condition of the score threshold is added, so as to avoid the misjudgment caused by various interference factors, and to make the judgment result more accurate.

[0063] According to one preferred embodiment of the present invention, the detection method 10 comprises: The method further includes a step of counting the number of echo points corresponding to the photomask dirt within a predetermined angle range of detection by the laser radar, and determining that the photomask dirt is present within the predetermined angle range if the number of echo points is greater than the point threshold value.

[0064] The dirt on the photomask of the laser radar is usually not distributed at each position of the photomask, but concentrated within one angle range. Therefore, a specific angle range can be set, for example, at 10° intervals, the total number of echo points corresponding to the photomask dirt within the range per 10° is calculated, a point threshold is set, and if the total number of echo points corresponding to the photomask dirt within the range of 10° is greater than the point threshold, it is determined that the photomask dirt exists within the range of 10°.

[0065] For example, assume that a 128-line laser radar has all laser devices turned on and has an angular resolution of 0.1°. The laser radar generates point cloud data with a total of 12800 points within a 10° scan range. The point number threshold is set so that photomask dirt is deemed to exist when 5 out of the 12800 points are echo points corresponding to photomask dirt. Also, a multi-line laser radar may have some laser devices turned on or use other angular resolutions.

[0066] In this embodiment, based on the addition of a score threshold in the previous embodiment, the range of photomask dirt is limited to within a specified angle range, which not only makes it possible to accurately determine whether photomask dirt exists or not, but also makes it possible to predict the range of dirt and facilitate subsequent dirt removal work.

[0067] According to one preferred embodiment of the present invention, step S101 in the detection method 10 further includes transmitting a multi-pulse sequence encoded in time intervals, and step S102 includes: The method further includes the step of making the time interval of the echo pulse sequence coincide with the time interval of the multi-pulse sequence.

[0068] According to one preferred embodiment of the present invention, preferably, the transmitting unit of the laser radar transmits a multi-pulse sequence using time interval encoding, an analog-to-digital converter (ADC) samples to obtain a full-wave waveform of the radar echo, and an intensity threshold is set to screen a plurality of echo pulse signals among the radar echoes whose peak intensities are higher than the intensity threshold. If the time intervals of the selected plurality of echo pulse signals are consistent with the time intervals of the transmission pulse sequence, the selected echo pulse signal is the echo pulse sequence corresponding to the transmission pulse sequence.

[0069] According to one preferred embodiment of the present invention, in the detection method 10, step S103 (determining whether photomask contamination exists in the laser radar based on the flight time of the echo pulse sequence) includes: The method further includes determining that photomask contamination is present in the laser radar if the time of flight of the echo pulse sequence is less than a time of flight threshold.

[0070] Returning to Fig. 4, because the distance between the photomask of the laser radar and the transmitting unit is very close, when there is photomask dirt, the flight time of the detection beam transmitted from the transmitting unit after being reflected by the photomask dirt and received by the receiving unit is also very short, which is much shorter than the flight time of the detection beam received by the receiving unit after being reflected by an obstacle. The flight time of the echo pulse sequence can be determined by the leading edge time of the first echo pulse in the echo pulse sequence, or the flight time of the echo pulse sequence can be further determined by the peak time of the first echo pulse in the echo pulse sequence or by converting to another time point in the echo pulse sequence, all of which are within the scope of protection of the present invention. If the flight time of the echo pulse sequence is smaller than the flight time threshold, it is determined that the echo pulse sequence is an echo pulse signal generated by the receiving unit after the detection beam is reflected by the photomask dirt, that is, it is determined that there is photomask dirt in the laser radar.

[0071] As the target moves from being in close contact with the photomask (0 cm) to gradually moving away from the photomask, the number of echo points corresponding to photomask dirt detected in a single frame first increases and then decreases; when the target is about 5 cm away from the photomask, the number of detected echo points becomes even greater than when dirt is present on the photomask surface. Therefore, the time-of-flight threshold alone cannot completely prevent false alarms caused by close-range targets.

[0072] A method for preventing false alarms due to close range targets is described in detail below.

[0073] According to one preferred embodiment of the present invention, the detection method 10 further includes a step of setting a corresponding point number threshold based on the time-of-flight threshold, in which different time-of-flight thresholds correspond to different point number thresholds, and the time-of-flight threshold and its corresponding point number threshold can be used to accurately determine photomask dirt and avoid false alarms caused by close-range targets. As shown in Figures 5A and 5B, Figure 5A shows the number of echo points corresponding to each angle in the point cloud data of a single frame when the time-of-flight threshold is set to 1 ns. Figure 5B shows the number of echo points corresponding to each angle in the point cloud data of a single frame when the time-of-flight threshold is set to 2 ns. As can be seen from Figures 5A and 5B, increasing the time-of-flight threshold increases the number of echo points corresponding to detected photomask dirt, and increasing the time-of-flight threshold can provide effective detection results for photomask dirt in a wider range (e.g., photomask dirt at an oblique angle), but the false alarm rate may increase.

[0074] As shown in Fig. 5A, when the flight time threshold is 1 ns, a corresponding point number threshold D1 can be set, and whether the echo point number corresponding to the photomask dirt in the single frame point cloud data exceeds the point number threshold can be calculated. As shown in Fig. 5B, when the flight time threshold is 2 ns, a corresponding point number threshold D2 can be set, and whether the echo point number corresponding to the photomask dirt in the single frame point cloud data exceeds the point number threshold can be calculated. Here, the point number threshold when the flight time is 2 ns is higher than the point number threshold when the flight time is 1 ns.

[0075] Preferably, calculate the echo points corresponding to the photomask dirt within a predetermined angle range. As shown in FIG. 5A, when the flight time threshold is 1 ns, set the corresponding point number threshold (for example, set to 5 points) within a range of 10°, and calculate whether the echo points corresponding to the photomask dirt in the point cloud data generated within the range of 10° exceed the point number threshold 5. As shown in FIG. 5B, when the flight time threshold is 2 ns, set the corresponding point number threshold (for example, set to 40 points) within a range of 10°, and calculate whether the echo points corresponding to the photomask dirt in the point cloud data generated within the range of 10° exceed the point number threshold 40.

[0076] In this embodiment, the flight time threshold and the score threshold are combined to avoid false alarms caused by close-range targets. In actual operation, a query table can be set to dynamically select the corresponding flight time threshold and score threshold, or the threshold can be adjusted according to the actual detection situation to reduce false alarms.

[0077] Considering that photomask dirt always exists steadily and that nearby targets may exist for a short time (e.g., moving targets), a frame number limit can be further set to reduce false alarms due to nearby targets, for example, when the echo points corresponding to photomask dirt at the same time-of-flight threshold in 10 consecutive frames all reach the point number threshold, the photomask dirt is deemed to be detected. According to one preferred embodiment of the present invention, the detection method 10 includes: The method further includes a step of determining that photomask dirt is present in the laser radar when the number of echo points in each of the consecutive multi-frame point cloud data is greater than the point number threshold.

[0078] According to one preferred embodiment of the present invention, the detection method 10 further includes determining a type of the photomask contamination based on the echo point count.

[0079] Returning to FIG. 1B, for the absorbing type dirt at position (1), the corresponding reflected echo is very weak, and the number of echo points corresponding to the generated photomask dirt is also small. For the reflective type dirt at position (2), the corresponding reflected echo is strong, and the number of echo points corresponding to the generated photomask dirt is large. For the scattering type dirt at position (3), the corresponding reflected echo is relatively weak, and the number of echo points corresponding to the generated photomask dirt is smaller than that of the reflective dirt, but is larger than that of the absorbing dirt. The number of echo points corresponding to the photomask dirt is statistically significant, and a discrimination threshold for the number of echo points can be set to determine the dirt type.

[0080] According to one preferred embodiment of the present invention, the detection method 10 further includes:

[0081] If the number of echo points is greater than a first discrimination threshold, the photomask contamination is determined to be reflective contamination, where reflective contamination includes stains, dirt, dust, mud, and the like.

[0082] When the number of echo points is less than or equal to a first discrimination threshold and greater than a second discrimination threshold, the photomask stain is determined to be a scattering type stain, where scattering type stains include sewage, scratches, stone pits, insect corpses, bird droppings, oily sweat, fingerprints, fresh water, photomask corrosion, etc.

[0083] If the number of echo points is equal to or less than a second discrimination threshold, the photomask dirt is determined to be an absorption type dirt, where the absorption type dirt includes oily sweat, asphalt, paint, etc.

[0084] Based on the echo points, the type of photomask dirt is determined and the next dirt removal operation is prepared.

[0085] According to one preferred embodiment of the present invention, the detection method 10 comprises: The method further includes the step of rescanning the predetermined angle range in which the photomask contamination exists at a second predetermined angle, and determining a distribution state of the photomask contamination within the predetermined angle range.

[0086] According to one preferred embodiment of the present invention, for example, a laser radar with an angular resolution of 0.1° and 128 lines emitted by all laser devices is used. Within a given 10° range, there are a total of 12800 points, and the point threshold is set to 5. If the number of echo points corresponding to photomask dirt within a given 10° range exceeds 5, it is determined that photomask dirt exists within the given 10° range. Preferably, if the number of echo points corresponding to photomask dirt within the given 10° range in 10 consecutive frames is greater than 5, it is determined that photomask dirt exists within the given 10° range. After determining the specific angle range in which photomask dirt exists, the laser radar may rescan within the given angle range with the original angular resolution, and subdivide the given angle range into a number of predetermined angles. For example, the given 10° range is subdivided into 10 1° angle ranges. Within each given 1° angle range, the number of echo points corresponding to photomask dirt is counted, thereby determining the specific location and intensity distribution of the photomask dirt. The laser radar may rescan within the angle range with other angular resolutions, all of which are within the scope of protection of the present invention. Here, the echo points corresponding to the photomask dirt are determined based on encoding matching and a time-of-flight threshold, which will not be described here.

[0087] As shown in FIG. 6, according to one preferred embodiment of the present invention, the present invention further provides a laser radar photomask dirt detection system 100, including a transmitting unit 110, a receiving unit 120, a waveform detection unit 130 and a photomask dirt judgment unit 140.

[0088] The transmitting unit 110 is configured to transmit a multi-pulse sequence with pulse encoding, using the encoding laser pulses commonly used in laser radar detection, without the need to provide a separate detection light source or use a different encoding mechanism than the actual detection.

[0089] The receiving unit 120 is configured to receive radar echoes.

[0090] The waveform detection unit 130 is coupled to the transmitting unit 110 and the receiving unit 120, The radar echo is configured to obtain an echo pulse sequence corresponding to the multi-pulse sequence, and the waveform detection unit is used to generate waveform information including information such as pulse width, peak intensity, leading edge time, distance, angle, etc., and match the encoding of the transmission pulse sequence to obtain the corresponding echo pulse sequence.

[0091] The photomask dirt determination unit 140 is configured to determine whether photomask dirt exists in the laser radar according to the flight time of the echo pulse sequence. The echo pulse sequence corresponding to the photomask dirt is different from the echo pulse sequence of the search beam, because the distance between the photomask and the transmitting unit is very close and the flight time of the echo corresponding to the photomask dirt is very short, so by setting the flight time of the corresponding echo pulse sequence, it can be determined whether the echo pulse sequence corresponds to the photomask dirt.

[0092] As shown in FIG. 6, according to one preferred embodiment of the present invention, the photomask dirt detection system 100 further includes a point counting unit 150 configured to count the number of echo points corresponding to the photomask dirt in the point cloud data of a single frame, and the photomask dirt judgment unit 140 is further configured to judge whether the photomask dirt exists in the laser radar based on the number of echo points.

[0093] The laser radar generates one frame of point cloud data for each scan period, where the point counting unit 150 counts the number of echo points corresponding to photomask dirt in the single frame of point cloud data, and the photomask dirt judgment unit 140 judges whether photomask dirt is present on the laser radar based on the number of echo points.

[0094] According to one preferred embodiment of the present invention, in the photomask contamination detection system 100, the photomask contamination determination unit 140 further comprises: The laser radar is configured to determine that photomask dirt is present when the echo score is greater than a score threshold.

[0095] In the process of forming a single-frame point cloud by the radar, specifically, for a 128-line laser radar, assuming that the angular resolution is 0.1° when all laser devices are emitting light, the single-frame point threshold means that when the number of echo points exceeding the point threshold among 460,800 points meets the flight time condition, it is deemed that photomask dirt exists.

[0096] In a preferred embodiment of the present invention, a point threshold is used to set in the single frame point cloud data, and when the point number corresponding to the photomask stain is greater than the point threshold, it is determined that the photomask stain exists, thus avoiding false alarms caused by close-range targets (e.g., a fly passing by the radar photomask).

[0097] According to one preferred embodiment of the present invention, in the photomask dirt detection system 100, the point counting unit 150 is further configured to count the number of echo points corresponding to the photomask dirt within a predetermined angle range of detection by the laser radar, and the photomask dirt judgment unit 140 is further configured to determine that photomask dirt exists within the predetermined angle range when the number of echo points is greater than the point threshold.

[0098] The dirt on the photomask of the laser radar is usually not distributed at each position of the photomask, but concentrated within one angle range. Therefore, a specific angle range can be set, for example, at 10° intervals, the total number of photomask echo points within the range per 10° is calculated, a point threshold is set, and if the total number of photomask echo points within the 10° range is greater than the point threshold, it is determined that photomask dirt exists within the 10° range.

[0099] As an example, for a 128-line laser radar, assuming an angular resolution of 0.1° when all laser devices are emitting light, the score threshold is set so that photomask dirt is deemed to be present when 5 out of 12,800 echo points correspond to photomask dirt.

[0100] This embodiment not only avoids false reports of photomask echoes due to close-range targets, but also limits the range of photomask contamination to within a specified angle range, facilitating the subsequent work of removing the contamination.

[0101] According to one preferred embodiment of the present invention, as shown in FIG. 6, a photomask contamination detection system 100 includes: The signal processing device further includes a data collection unit 160, coupled between the receiving unit 120 and the waveform detection unit 130, for performing data collection on the radar echo and transmitting a data signal of the radar echo to the waveform detection unit 140. Here, the data collection unit 160 may include an analog-to-digital converter (ADC) or a time-to-digital converter (TDC).

[0102] According to one preferred embodiment of the present invention, the transmitting unit 110 in the photomask contamination detection system 100 is further configured to transmit a multi-pulse sequence encoded with a time interval, and the waveform detection unit 130 is further configured to: The time interval of the echo pulse sequence is configured to match the time interval of the multi-pulse sequence.

[0103] According to one preferred embodiment of the present invention, the photomask contamination determination unit 140 in the photomask contamination detection system 100 further comprises: The echo pulse sequence is configured to determine that a photomask stain exists in the laser radar when the flight time of the echo pulse sequence is smaller than a flight time threshold value, and to determine that the echo pulse sequence is an echo signal generated by the receiving unit 110 after the detection beam is reflected by the photomask stain, i.e., to determine that a photomask stain exists in the laser radar when the flight time of the echo pulse sequence is smaller than a flight time threshold value.

[0104] Here, the flight time threshold and the score threshold can be used in combination, and a corresponding score threshold can be set according to the flight time threshold.

[0105] As shown in FIG. 7, according to one preferred embodiment of the present invention, in the photomask contamination detection system 100, the photomask contamination determination unit 140: In each column, the photomask dirt determination results detected within the same predetermined angle range when the laser radar scans in continuous multi-frames are stored in correspondence with each other, Each row includes a multi-bit storage table that is set so that the photomask contamination determination results within each predetermined angle range when the laser radar scans in a single frame are stored in association with each other.

[0106] Preferably, as shown in FIG. 7, a 36-bit binary memory is used, and in its length direction (X direction shown in the figure), each column represents an angle range such as 0 to 10°, 10° to 20°, ... 350° to 360°, etc., and in its width direction (Y direction shown in the figure), each row represents one frame. The first row in the width direction represents that when the laser radar scans the first rotation (360°), the point counting unit counts the echo points corresponding to the photomask dirt for each 10° range, and if the echo points are greater than the point threshold, this bit in the memory is stored as 1. If the values ​​stored in the same column of consecutive rows are all 1, it reflects that the echo points corresponding to the photomask dirt in the predetermined angle range of consecutive multi-frames are all greater than the point threshold.

[0107] According to one preferred embodiment of the present invention, when the storage results of the same column in the multi-bit storage table all indicate the presence of photomask dirt in the laser radar, the photomask dirt judgment unit 140 determines that photomask dirt exists within the specified angle range corresponding to the same column.

[0108] Preferably, when the storage results of the same columns in consecutive rows of the multi-bit binary memory all indicate the presence of photomask dirt, it is determined that photomask dirt is present at the average values ​​of the maximum and minimum specified angle ranges corresponding to the same columns.

[0109] After determining the angle range in which the photomask dirt exists, the photomask dirt detection system 100 rescans at a second predetermined angle within the angle range corresponding to the photomask dirt, and determines the distribution status of the photomask dirt within the predetermined angle range.

[0110] The transmitting unit includes at least one semiconductor laser device selected from the group consisting of a Vertical-Cavity Surface-Emitting Laser (VCSEL) and an Edge-Emitting Laser (EEL).The receiving unit includes at least one detector selected from the group consisting of a Single Photon Avalanche Diode (SPAD) detector, an Avalanche Photo Diode (APD) detector, and a Silicon Photomultiplier (SiPM) detector.

[0111] A preferred embodiment of the present invention provides a photomask dirt detection method and a photomask dirt detection system for a laser radar, which detects photomask dirt using a beam generated by a transmitting unit of a laser radar, without the need for additional light sources and / or detection devices, and detects by the encoding time, flight time, and echo points of the laser radar, which has high detection accuracy and avoids the occurrence of erroneous judgment. A preferred embodiment of the present invention completes the photomask dirt detection by a transmitting unit and a receiving unit in a laser radar for detecting a target, which is simple in structure and saves the internal space of the laser radar. A preferred embodiment of the present invention can determine the type and distribution of photomask dirt by the echo points, providing a basis for subsequent dirt removal work.

[0112] Finally, it should be explained that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention, and the present invention has been described in detail with reference to the above embodiments, but those skilled in the art can still modify the technical solutions described in the above embodiments or make equivalent substitutions for some of the technical features therein. All modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A step S101 of transmitting a multi-pulse sequence having a pulse encoding; A step S102 of receiving radar echoes and acquiring an echo pulse sequence corresponding to the multi-pulse sequence in the radar echoes; and determining that photomask contamination is present on the laser radar if the time of flight of the echo pulse sequence is less than a time of flight threshold. Step S103 is Counting the number of echo points corresponding to the photomask dirt in the point cloud data of a single frame, and determining that the photomask dirt is present on the laser radar when the number of echo points is greater than a point threshold value; The photomask contamination detection method for laser radar further comprises a step of determining a type of the photomask contamination based on the number of echo points.

2. The detection method according to claim 1, further comprising a step of counting the number of echo points corresponding to the photomask dirt within a predetermined angle range of detection by the laser radar, and determining that the photomask dirt is present within the predetermined angle range if the number of echo points is greater than the point threshold.

3. Step S101 further includes transmitting a multi-pulse sequence encoded in time intervals, and step S102 includes: The method of detection according to claim 1 , further comprising the step of: matching a time interval of the echo pulse sequence with a time interval of the multi-pulse sequence.

4. The method of claim 2 , further comprising the step of setting a corresponding score threshold based on the time-of-flight threshold.

5. The detection method according to claim 2 , further comprising a step of determining that photomask dirt is present in the laser radar when the number of echo points in all of the point cloud data of consecutive multiframes is greater than the point number threshold.

6. determining that the photomask contamination is a reflective contamination when the number of echo points is greater than a first discrimination threshold; determining that the photomask contamination is a scattering type contamination when the number of echo points is equal to or less than a first discrimination threshold and is greater than a second discrimination threshold; The detection method according to claim 1 , further comprising the step of determining that the photomask contamination is an absorbing type contamination if the number of echo points is equal to or less than a second discrimination threshold.

7. 3. The detection method according to claim 2, further comprising the step of rescanning the predetermined angle range in which the photomask contamination exists at a second predetermined angle, and determining a distribution state of the photomask contamination within the predetermined angle range.

8. a transmitting unit configured to transmit a multi-pulse sequence having a pulse encoding; a receiving unit configured to receive radar echoes; a waveform detection unit coupled to the transmitting unit and the receiving unit, respectively, configured to obtain an echo pulse sequence in the radar echo corresponding to the multi-pulse sequence; A point counting unit configured to count the number of echo points corresponding to the photomask stains in the single frame point cloud data, and counting the number of echo points corresponding to the photomask stains within a predetermined angle range of detection by the laser radar; a judgment unit configured to judge whether photomask dirt is present on the laser radar based on the flight time of the echo pulse sequence, the judgment unit determining that photomask dirt is present on the laser radar when the number of echo points corresponding to the photomask dirt in the single frame point cloud data is greater than a first point threshold, or when the number of echo points corresponding to the photomask dirt within a predetermined angle range of detection by the laser radar is greater than a second point threshold; The judgment unit is In each column, the photomask dirt determination results detected within the same predetermined angle range when the laser radar scans in continuous multi-frames are stored in correspondence with each other, A laser radar photomask dirt detection system including a multi-bit storage table configured so that each row corresponds to and stores the photomask dirt determination results within each specified angle range when the laser radar scans in a single frame.

9. The judgment unit further comprises: The photomask contamination detection system of claim 8 , configured to determine that photomask contamination is present in a laser radar if the time of flight of the echo pulse sequence is less than a time of flight threshold.

10. 10. The photomask contamination detection system of claim 8, further comprising a data collection unit coupled between the receiving unit and the waveform detection unit, the data collection unit being used to perform data collection on the radar echo and to transmit a data signal of the radar echo to the waveform detection unit.

11. The transmitting unit is further configured to transmit a multi-pulse sequence encoded in a time interval, and the waveform detection unit is further configured to:

10. The photomask contamination detection system of claim 8 or 9, wherein a time interval of the echo pulse sequence is configured to match a time interval of the multi-pulse sequence.

12. The photomask contamination detection system of claim 8, wherein when all of the storage results of the same column in the multi-bit storage table indicate the presence of photomask contamination in the laser radar, the judgment unit is further configured to determine that photomask contamination exists within the specified angle range corresponding to the same column.

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