Depth data measurement head, measurement device and measurement method

Abstract

Disclosed are a depth data measurement head, a measurement device and a measurement method. The measurement head comprises a projection device for projecting discrete light spots moving along a first direction to a measured region, wherein the projection device comprises a light source module for generating discrete light spots and a projection mechanism for projecting the generated discrete light spots to the measured region, wherein the projection mechanism makes the projected discrete light spots move along the first direction through its own movement; and a ToF sensor for receiving return light of the measured region and generating a sensing signal, the sensing signal characterizing a direct flight time of the light to calculate a distance of a photographed object in the measured region. The depth data measurement scheme of the present disclosure, when utilizing ToF technology, no longer projects a surface light source, but scans and projects discrete light spots. The discrete light spots are composed of a plurality of dispersed light points, which can greatly reduce various adverse effects caused by high-reflectivity objects and ensure the accuracy of measurement results.

Description

Technical Field

[0001] This invention relates to depth imaging, and more particularly to a depth data measurement head, measurement device, and measurement method. Background Technology

[0002] In recent years, 3D imaging technology has developed rapidly. This is inseparable from the significant progress in depth data measurement technology, in addition to conventional 2D image acquisition.

[0003] Currently, a depth measurement scheme based on a surface light source and Time-of-Flight (ToF) technology can perform real-time three-dimensional measurements of an object's surface. Simply put, this scheme projects a surface light array onto the surface of a natural object and uses ToF technology to determine the distance to the object's surface.

[0004] However, when highly reflective objects are present in the area being measured using area array light and ToF technology, highly reflective surfaces may cause problems such as signal oversaturation, distance measurement errors, and multipath interference, affecting the accuracy of the measurement results.

[0005] Therefore, an improved depth data measurement scheme is needed. Summary of the Invention

[0006] One technical problem this disclosure aims to solve is to provide a novel depth data measurement scheme, particularly suitable for scenarios with highly reflective objects. Specifically, when using Time-of-Flight (ToF) technology, the depth data measurement head of this disclosure no longer projects a surface light source, but instead scans and projects discrete light spots. These discrete light spots consist of multiple dispersed light points, which can significantly reduce the various adverse effects caused by highly reflective objects and ensure the accuracy of the measurement results.

[0007] According to a first aspect of this disclosure, a depth data measurement head is provided, comprising: a projection device for projecting a discrete light spot moving along a first direction onto a measured area, wherein the projection device includes a light source module for generating the discrete light spot and a projection mechanism for projecting the generated discrete light spot onto the measured area, wherein the projection mechanism moves the projected discrete light spot along the first direction by its own movement; and a ToF sensor for receiving reflected light from the measured area and generating a sensing signal, the sensing signal characterizing the direct time of flight of the light to calculate the distance to a photographed object within the measured area.

[0008] Optionally, the discrete light spot is composed of multiple dispersed light spots, each light spot having a size no larger than a first threshold range and a distance no less than a second threshold range from adjacent light spots.

[0009] Optionally, the discrete light spot is presented as an elongated discrete light spot pattern, the length direction of the elongated discrete light spot pattern is a second direction perpendicular to the first direction. In fact, the first direction corresponds to the pixel row direction of the ToF sensor, the second direction corresponds to the pixel column direction of the ToF sensor, and for each pixel row in the working area of ​​the ToF sensor, the discrete light spot contains at least one light spot.

[0010] Optionally, the discrete light spots are presented as a plurality of elongated discrete light spot patterns distributed in the first direction.

[0011] Optionally, the projection mechanism moves within a predetermined projection range such that the discrete light spot moving along the first direction covers the area under test, and the area under test corresponds to the operating range of the ToF sensor.

[0012] Optionally, the projection mechanism moves within a predetermined projection period, which matches the imaging period of the ToF sensor.

[0013] Optionally, the light source module projects discrete light spot pulses, and the movement speed of the projection mechanism is determined based on the pulse projection frequency, and the movement range of the projection mechanism is determined based on the shape of the discrete light spot, so that each pixel in the working area of ​​the ToF sensor is illuminated at least once within the predetermined period.

[0014] Optionally, the light source module includes at least one of the following: a lattice vertical cavity surface-emitting laser (SPOT VCSEL) array arranged to correspond to the discrete light spot; a laser generator for generating laser light and a diffractive optical element (DOE) for generating the discrete light spot based on the received laser light; a floodlight source and a mask element for generating the discrete light spot; and a laser generator for generating laser light and a metalenz for generating the discrete light spot.

[0015] According to a second aspect of this disclosure, a depth data measurement device is provided, comprising: a depth data measurement head as described in the first aspect; and a processor configured to perform distance calculation based on a sensing signal generated by the ToF sensor to obtain depth data output of the measured area.

[0016] According to a third aspect of this disclosure, a depth data measurement method is provided, comprising: projecting a discrete light spot moving along a first direction onto a region to be measured; and receiving reflected light from the region to be measured and generating a sensing signal, the sensing signal characterizing the direct time of flight of the light to calculate the distance of a photographed object within the region to be measured.

[0017] Therefore, the depth data measurement scheme of the present invention utilizes discrete light spots, especially discrete light spot patterns with carefully designed specific shapes, to achieve high-precision depth data measurement based on direct time of flight, which can significantly suppress or even completely eliminate pixel expansion and multipath reflection problems caused by highly reflective surfaces. Attached Figure Description

[0018] The above and other objects, features and advantages of this disclosure will become more apparent from the more detailed description of exemplary embodiments thereof taken in conjunction with the accompanying drawings, in which the same reference numerals generally represent the same components.

[0019] Figure 1 A schematic diagram of the composition of a depth data measurement head according to an embodiment of the present disclosure is shown.

[0020] Figure 2 Two examples of discrete spot patterns projected by the depth data measuring head of this disclosure are shown.

[0021] Figure 3 An example of a discrete spot pattern projected by the depth data measuring head of this disclosure is shown.

[0022] Figure 4 An example of a discrete spot pattern projected by the depth data measuring head of this disclosure is shown.

[0023] Figure 5 A schematic diagram of the composition of a depth data measurement device according to an embodiment of the present disclosure is shown.

[0024] Figure 6 An exemplary flowchart of a depth data measurement method according to an embodiment of the present invention is shown. Detailed Implementation

[0025] Preferred embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While preferred embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0026] Currently, a depth measurement scheme based on a surface light source and Time-of-Flight (ToF) technology can perform real-time three-dimensional measurements of an object's surface. Simply put, this scheme projects a surface light array onto the surface of a natural object and uses ToF technology to determine the distance to the object's surface by measuring the time of flight and combining this with the speed of light.

[0027] However, when highly reflective objects are present in the area being measured using area array light and ToF technology, highly reflective surfaces may cause problems such as pixel expansion and multipath interference, affecting the accuracy of the measurement results.

[0028] Highly reflective objects (surfaces) refer to objects that can effectively reflect most light and whose surfaces have a high reflectivity, such as white surfaces (white walls, white paper), metal surfaces, and brightly colored surfaces (e.g., reflective strips, reflective coatings).

[0029] Time-of-flight (TOF) technology calculates distance based on measuring the time of flight of a light pulse. When the light pulse is reflected back to the sensor, the intensity of the reflected signal is directly related to the reflectivity of the object's surface. If the object's surface is highly reflective (such as a specularly reflective metal surface or a smooth glass surface), the reflected signal intensity may be too strong, causing signal oversaturation of the receiving sensor. This can affect the signals of that pixel and its neighboring pixels, resulting in pixel dilation.

[0030] Specifically, when the sensor receives excessively strong light signals reflected from the surface of a highly reflective object, a single pixel unit may exceed its maximum stored charge, leading to pixel saturation. When the charge stored in a pixel unit exceeds its capacity, the excess charge overflows into adjacent pixel units, affecting the signals of surrounding pixels and resulting in erroneous pixel responses. Pixel dilation manifests in the image as an enlarged spot area or blurred boundaries, causing the ToF sensor to generate incorrect time-of-flight data and affecting the accuracy of depth measurement data.

[0031] Furthermore, for highly reflective surfaces, light pulses may not only be reflected back from the target object's surface but also from other surfaces (such as walls or floors) before reflecting back to the sensor. This longer reflected light path causes a multipath effect, leading to inaccurate sensor measurement timing and thus affecting the accuracy of depth measurement.

[0032] Various strategies for addressing high reflectivity issues have been proposed in existing technologies. One approach involves adjusting the light source and sensor themselves. For example, adjusting the emission power of the area array light source can reduce light intensity oversaturation on highly reflective surfaces, or optimizing the sensor's exposure time can reduce the impact of excessively strong reflection signals from highly reflective surfaces. Improving the sensor's dynamic range allows it to adapt to different signal intensities from low-reflectivity to high-reflectivity objects, thus avoiding signal saturation. Alternatively, optical filters at the receiver can be used to limit unwanted reflected light, especially reducing interference from highly reflective objects. Furthermore, multi-point measurement techniques can be employed, combining information from different viewing angles and distances, and algorithms can be used to compensate for interference signals from highly reflective surfaces.

[0033] However, the methods mentioned above cannot fundamentally solve the high reflectivity problem. For example, reducing the emission power of the area array light source and decreasing the sensor exposure time will affect the sensitivity of depth measurement; while increasing the dynamic range of the sensor and using multi-point measurement and algorithm compensation will greatly increase the overhead of measurement.

[0034] To address this, this disclosure proposes a novel depth data measurement scheme, particularly suitable for scenarios involving highly reflective objects. The depth data measurement head of this disclosure, when utilizing Time-of-Flight (ToF) technology, no longer projects a surface array of light, but instead scans and projects discrete light spots. These discrete light spots consist of multiple dispersed light points; this dispersion significantly reduces the adverse effects of highly reflective surfaces in the measured area on depth data detection, ensuring the accuracy of the measurement results.

[0035] Figure 1 A schematic diagram of a depth data measurement head according to an embodiment of the present disclosure is shown. This depth data measurement head may be a depth camera, or a depth data acquisition head, used to acquire sensing signals required to obtain depth data. As shown, the depth data measurement head 100 may include a projection device 110 and a ToF sensor 120.

[0036] The projection device 110 is used to project discrete light spots moving along a first direction onto the area to be measured. Here, a discrete light spot refers to a group of dispersed, independent light points with a defined spatial distribution generated by an optical projection system and projected onto the area to be measured (e.g., onto the surface of the object being measured). These light points typically exhibit a regular or random spatial distribution. In this disclosure, the discrete light spots projected by the projection device 110 are a two-dimensional specific optical projection pattern formed by multiple light points according to certain geometric rules or random distribution rules; that is, a discrete light spot pattern is projected. This discrete light spot pattern is distributed in two dimensions along the first and second directions. Here, the first direction is the direction of movement of the discrete light spot pattern, and the second direction is the direction perpendicular to the first direction. The first and second directions also correspond to the area to be measured. When the area to be measured corresponds to a rectangular region, the first direction can be the length direction of the rectangular region, and the second direction can be the width direction of the rectangular region; or vice versa, that is, the first direction is the width direction of the rectangular region, and the second direction is the length direction of the rectangular region.

[0037] The projection device 110 may include a light source module 111 and a projection mechanism 112. The light source module 111 is used to generate discrete light spots. The projection mechanism 112 is used to project the generated discrete light spots onto the area under test. The projection mechanism 112 can move the projected discrete light spots along the first direction by its own movement. The ToF sensor 120 is used to receive the reflected light from the area under test and generate a sensing signal, which characterizes the direct time of flight of the light to calculate the distance to the object being photographed within the area under test. That is, the ToF sensor 120 used in this disclosure is a dToF (direct time of flight) sensor, rather than an iToF (indirect time of flight) sensor that calculates distance based on phase.

[0038] The astigmatic spot is scanned and projected by the projection mechanism 112. This scanning projection corresponds to spatial sequence scanning, meaning the discrete spot pattern itself is fully projected, and then, through the movement of the projection mechanism, it covers other areas (the concept of "time sequence scanning" corresponds to spatial sequence scanning, where time sequence scanning only projects a portion of the complete pattern at any given moment). Figure 1 In the example shown, the projected discrete light spot is a strip pattern composed of 12 light points. At any projection moment, these 12 light points are completely projected and form the strip pattern. The strip pattern moves along the first direction as a whole with the movement of the projection mechanism.

[0039] Because the light spots are dispersed among each other, the pixel expansion problem caused by simultaneous illumination of large areas of highly reflective surfaces can be mitigated. Furthermore, since only a limited number of positions within the measured area are illuminated at the same time, the probability of multipath reflection can be reduced.

[0040] The discrete light spot consists of multiple dispersed light points. To further mitigate or even eliminate pixel dilation, the size and distribution of the light points can be restricted. Specifically, the size of each light point in the discrete light spot can be specified to be no larger than a first threshold range. For example, pixel dilation can be observed, and an upper limit on the size of the light points that cause pixel dilation (or cause significant pixel dilation) can be determined. This upper limit is used as the first threshold range. In one embodiment, the size of each light point can correspond to a pixel area illuminating only one ToF sensor.

[0041] Additionally, it can be specified that the distance between each light spot in the discrete light spot and its neighboring light spots is not less than a second threshold range. For example, pixel dilation can be observed, and the range of surrounding pixels affected by pixel dilation can be determined, with this range serving as the second threshold range. In one embodiment, the second threshold range can be the surrounding 8 pixel regions. That is, it is necessary to ensure that the 8 pixel regions surrounding each pixel region illuminated by a light spot are not illuminated.

[0042] For example, in Figure 1 In the example, assume the ToF sensor has a 12x16 resolution (i.e., 12 pixel rows and 16 pixel columns, totaling 192 pixels; it should be understood that real-world ToF sensors can include more rows and columns, such as 600 pixel rows and 800 pixel columns). The projected discrete light spots, as shown in the figure, follow the rule that each light spot illuminates only one pixel, and the area illuminated by adjacent light spots is outside the surrounding 8 pixels. Additionally, it should be understood that... Figure 1 In the accompanying figures, the light spots that make up the discrete light spot are shown in square form for ease of explanation. However, in actual projection, the light spots contained in the projected discrete light spot can have other forms, such as round dots.

[0043] Therefore, by limiting the size of each light spot that makes up the discrete light spot and the position of adjacent light spots, this disclosure can further reduce or even eliminate the effect of pixel dilation and alleviate the problem of multipath reflection.

[0044] Typically, the measured area is the region that the light source module needs to illuminate and that can be imaged by the ToF sensor. That is, it can be considered as the overlapping area of ​​the light source module's illumination area and the ToF sensor's field of view. When the light source module's illumination area is larger than the ToF sensor's field of view, the measured area corresponds to the ToF sensor's field of view. In this case, the ToF sensor may receive returned signals across its entire field of view; therefore, the ToF sensor's operating range corresponds to its field of view, encompassing every pixel row and column. Conversely, when the ToF sensor's field of view is larger than the light source module's illumination area, the measured area corresponds to the light source module's illumination area. In this case, only a portion of the ToF sensor's entire field of view will receive returned signals (typically the pixel area in the center of the field of view); therefore, the ToF sensor's operating range corresponds to the area illuminated by the light source module within its field of view. In either case, the ToF sensor's operating range corresponds to the area swept by the discrete light spot along a first direction. The accompanying figures describe the case where the light source module's illumination area covers the entire field of view of the ToF sensor. At this time, when the projection mechanism moves within the predetermined projection range, the discrete light spot moving along the first direction can cover the measured area, and the measured area corresponds to the working range of the ToF sensor.

[0045] Typically, the row direction of a ToF sensor corresponds to the first direction, and the column direction corresponds to the second direction; alternatively, it can be the opposite, with the first direction corresponding to the column direction and the second direction corresponding to the row direction. For ease of explanation, let's assume... Figure 1As shown, the first direction corresponds to the length direction of the measured area and the row direction of the ToF sensor, and the second direction corresponds to the width direction of the measured area and the column direction of the ToF sensor. However, those skilled in the art should understand that the inventive principle of this disclosure is exactly the same whether the first direction corresponds to the width direction of the measured area or the column direction of the ToF sensor.

[0046] In one embodiment, the projected discrete light spot can be presented as an elongated discrete light spot pattern. The length direction of this elongated discrete light spot pattern is a second direction corresponding to the direction of the pixel column of the ToF sensor, and corresponds to each pixel row within the working area of ​​the ToF sensor. The elongated discrete light spot contains at least one light spot. Thus, as the elongated discrete light spot moves along the first direction, the light spot it contains can pass through each pixel row within the working area of ​​the ToF sensor.

[0047] exist Figure 1 In the example, the projected discrete light spot is a long, strip-shaped discrete light spot pattern with 12 light points. The distribution position of each light point corresponds to a pixel row of the ToF sensor, and to avoid pixel dilation issues, the light points in adjacent rows are separated by a column. Figure 1 In the discrete light spot pattern, the discrete light spot pattern has three columns wide, and the light spots included in the discrete light spot pattern are concentrated in two columns.

[0048] In other embodiments, other discrete spot patterns may also be used. Figure 2 Two examples of discrete spot patterns projected by the depth data measurement head of this disclosure are shown. The left side of the figure shows a discrete spot pattern with 12 light spots regularly distributed in three columns, and the right side shows a discrete spot pattern with 12 light spots randomly distributed in five columns. Both discrete spot patterns are five columns wide, and the distribution of light spots within the five columns is different, but they both satisfy the rule that each light spot illuminates one pixel area, the eight pixel areas surrounding the illuminated pixel area are not illuminated, and each row corresponds to one light spot. Regardless of which of the three discrete spot patterns is projected, in the projection mechanism, for example, Figure 1 As shown, when the projection is moved along the first direction, it is possible to illuminate every pixel in the working area of ​​the ToF sensor during the projection process (but the projection...). Figure 1 Patterns and Figure 2 When projecting patterns, the predetermined projection range of the projection mechanism varies.

[0049] Since the projected discrete light spot has relative motion with respect to the ToF sensor, the ToF sensor is implemented using a dToF sensor. dToF sensors typically measure light pulses; therefore, in the implementation of this disclosure, the light source module preferably emits light pulses with a discrete light spot pattern at a predetermined frequency.

[0050] Meanwhile, in order to illuminate every pixel of the working area of ​​the ToF sensor during the projection process, the predetermined projection range of the projection mechanism needs to meet the following requirements: the movement of the projection pattern along the first direction needs to start from the first column of the pattern and be projected onto the first column of the working area of ​​the ToF sensor, and continue until the last column of the pattern is projected onto the last column of the working area of ​​the ToF sensor.

[0051] Therefore, when the light source module projects discrete light spot pulses, the movement speed of the projection mechanism can be determined based on the pulse projection frequency, and the movement range of the projection mechanism can be determined based on the shape of the discrete light spot, so that each pixel in the working area of ​​the ToF sensor is lit at least once within a predetermined period of one scanning projection by the projection mechanism (which is usually matched with the imaging period of the ToF sensor). (For example, each pixel is lit exactly once.)

[0052] The following will be based on Figure 1 and Figure 2 Three discrete light spot patterns are used as examples to illustrate scanning projection. Here, it can be assumed that the predetermined time interval of the light source projection pulses is t. p The predetermined projection cycle for the projection mechanism is t. c In different implementations, the predetermined projection period is t. c This can typically be a predetermined time interval t. p Different multiples of.

[0053] In projection Figure 1 When projecting a pattern, during the predetermined projection period t c At the initial time t0, the first discrete light spot pulse is projected, at which point the first column of the pattern illuminates the odd-numbered rows of pixels in the first column of the ToF sensor. Subsequently, at an interval t from the initial time t0... p At time t1, the second discrete light spot pulse is projected. At this time, the position of the projected pattern shifts along the first direction by a width corresponding to one pixel, so the first column of the pattern illuminates the odd-numbered rows of pixels in the second column of the ToF sensor. Subsequently, at an interval t from time t1... p At time t2, the third discrete light spot pulse is projected. At this time, the position of the projected pattern shifts along the first direction by the width corresponding to one pixel. Therefore, the first column of the pattern illuminates the odd-numbered rows of pixels in the third column of the ToF sensor, and the second column illuminates the even-numbered rows of pixels in the first column of the ToF sensor. This process is repeated until time t...15 The 16th discrete light pulse is projected. The first column of this pattern illuminates the odd-numbered rows of pixels in the 16th column of the ToF sensor, and the second column illuminates the even-numbered rows of pixels in the 14th column. At this point, all odd-numbered rows of pixels in the ToF sensor have been illuminated once. At time t... 15 Interval t p The moment t 16 The 17th discrete light pulse is projected. At this point, the first column of the pattern has moved out of the measured area, and the second column of the pattern illuminates the even-numbered rows of pixels in the 15th column of the ToF sensor. At time t... 16 Interval t p The moment t 17 The 18th discrete light pulse is projected, illuminating the second column of the pattern to the even-numbered rows of pixels in the 16th column of the ToF sensor. At this point, all even-numbered rows of pixels in the ToF sensor have been illuminated once. Thus, all pixels are illuminated once after 18 projections from the light source module. During the projection... Figure 1 When a discrete light spot pulse with a width of 3 columns is used to illuminate a 16-column wide ToF sensor, the light source module needs to project 18 (16+3-1) pulses, with a predetermined projection period t. c It must be at least equal to 17t p (17 = 18 - 1). That is, the number of pulse projections (and the predetermined projection period t). c The length of the light source is related to the column width of the ToF sensor and the width of the discrete light spot pattern.

[0054] In projection, for example Figure 2 When the pattern on the left is shown, it occurs within a predetermined period t. c At the initial time t0, the first discrete light spot pulse is projected, at which time the first column of the pattern illuminates the pixels in rows 1, 4, 7, and 10 of the first column of the working area of ​​the ToF sensor. At time t2, the third discrete light spot pulse is projected, at which time the first column of the pattern illuminates the pixels in rows 1, 4, 7, and 10 of the third column of the working area of ​​the ToF sensor, and the second column of the pattern illuminates the pixels in rows 5, 5, 8, and 11 of the first column of the working area of ​​the ToF sensor. At time t4, the fifth discrete light spot pulse is projected, at which time the first column of the pattern illuminates the pixels in rows 1, 4, 7, and 10 of the fifth column of the working area of ​​the ToF sensor, the second column of the pattern illuminates the pixels in rows 2, 5, 8, and 11 of the third column of the working area of ​​the ToF sensor, and the third column of the pattern illuminates the pixels in rows 3, 6, 9, and 12 of the first column of the working area of ​​the ToF sensor. At time t... 15 After the event, all pixels in rows 1, 4, 7, and 10 of the ToF sensor were illuminated once by the light spot. At time t 17After the event, all pixels in rows 2, 5, 8, and 11 of the ToF sensor were illuminated once by the light spot. At time t 19 After completion, all pixels in rows 3, 6, 9, and 12 of the ToF sensor were illuminated once. Therefore, all pixels were illuminated once during projection. Figure 2 When a discrete light spot pulse with a width of 5 columns is used to illuminate a 16-column wide ToF sensor, the light source module needs to project 20 (16+5-1) pulses, with a predetermined projection period t. c It must be at least equal to 19t p (19 = 20 - 1).

[0055] When the pulse interval of the light source module corresponds to the displacement of one pixel in the projected pattern, the speed of the projection mechanism can be directly determined by the pulse projection frequency (i.e., 1 / t). p The range of motion of the projection mechanism (corresponding to a predetermined period during uniform motion) is determined by the column width of the ToF sensor and the shape of the discrete light spot (width in this case).

[0056] In one embodiment, the discrete spot pattern can also be presented as multiple elongated discrete spots distributed in the first direction. These elongated discrete spots preferably have the same pattern and are evenly spaced, so that the projection mechanism can achieve full pixel coverage of the ToF sensor in a shorter predetermined cycle.

[0057] Figure 3 An example of a discrete spot pattern projected by the depth data measuring head of this disclosure is shown. The left, middle, and right images correspond to a predetermined projection period t, respectively. c The start time t0, time t7, and end time t9 are specified. Here, the projected discrete light spot pattern consists of two elongated discrete light spot patterns spaced 8 pixels apart from each other on the ToF sensor. At this time, the light source module projects a pulse containing 24 light points each time. Because there are two elongated discrete light spots, the number of pixels each elongated discrete light spot needs to cover changes from 16 columns to 8 columns, thus compared to… Figure 1 The pattern, projection Figure 3 The pattern can make the number of pulse projections and the predetermined period t c Significantly reduced. The light source module needs to project 18 (16+3-1) pulses, with a predetermined period t. c It must be at least equal to 17t p (17 = 18 - 1), to become a light source module, it needs to project 10(8 + 3 - 1) pulses, with a predetermined period t. c It must be at least equal to 9t p (9 = 10 - 1).

[0058] In other implementations, discrete spot patterns that include more spots can also be projected. Figure 4 An example of a discrete light spot projected by the depth data measuring head of this disclosure is shown. Figure 4 The discrete spot pattern shown can be considered an extreme case, that is, including the most spots while satisfying the spacing rule. Specifically, Figure 4 The pattern shown can be viewed as being composed of multiple Figure 1 The image shows a series of elongated discrete light spots, comprising 54 spots. The light source module projects pulses four times at times t0, t1, t2, and t3. Each time, the projection mechanism moves along the first direction by a distance corresponding to one pixel in the ToF sensor (for clarity, the discrete light spots projected at different times are shown in different colors in the figure; however, it should be understood that each projected discrete light spot should typically have a wavelength). After four projections, each pixel of the ToF sensor has been illuminated once. For ease of understanding, Figure 4 The right side shows the superimposed effect of pixels being lit during the time period t0 to t3. Thus, the projection mechanism, based on a predetermined time interval t of pulse projection, achieves this effect. p The movement, in 3t p The predetermined projection period t c The entire working area of ​​the ToF sensor is projected.

[0059] Under the rules that a single light spot must not exceed one pixel in size, adjacent light spots must be located within eight pixels of the illuminated pixel, and each row must contain a corresponding light spot, it can be considered that... Figure 4 The discrete spot pattern shown is the densest pattern conforming to the above rules, suitable for ToF sensors of various pixel sizes, and all require only 3t. p The predetermined projection period t c This allows projection of the entire working area of ​​the ToF sensor.

[0060] However, it should be understood that in other embodiments, the first threshold range may not correspond to a range of one pixel. In some embodiments, such as in applications where the reflectivity of highly reflective surfaces is typically low, the first threshold range for limiting the size of a single light spot may have a larger value, for example, corresponding to a range of four or even nine pixels. Similarly, the second threshold range may not correspond to the surrounding eight pixels, but may have a larger or smaller range. A larger light spot and a larger distance between adjacent light spots mean lower precision requirements for the light source module and projection mechanism. In practice, the values ​​of the first and second threshold ranges can be determined by comprehensively considering the various requirements of the current application scenario.

[0061] In addition, although Figure 4The denser discrete spot pattern shown can achieve full pixel coverage more quickly, but an excessively dense discrete spot pattern will still increase the overall pixel dilation and multipath reflection phenomena, which have an adverse effect on measurement accuracy. Therefore, in practical operation, the pattern of the discrete spot pattern can also be determined by comprehensively considering the various requirements of the current application scenario.

[0062] The light source module 111 can be implemented in different ways. In one embodiment, the light source module 111 can be implemented as an array of SPOT VCSELs (lattice vertical-cavity surface-emitting lasers) arranged to correspond to the discrete light spots. For example, in situations where projection is required... Figure 1 When the discrete light spot is shown, the light source module 111 can be implemented as a discrete light spot. Figure 1 The light-emitting array shown is composed of 12 spoTVCSEL units. In another embodiment, the light source module 111 can be implemented as a laser generator (e.g., a side-emitting laser) for generating laser light and a diffractive optical element (DOE) for generating discrete light spots based on the received laser light. In another embodiment, the light source module 111 can be implemented as a floodlight source and a mask element for generating the discrete light spots. In yet another embodiment, the light source module 111 can be implemented as a laser generator (e.g., a VCSEL unit or array) for generating laser light and a meta-lens for generating discrete light spots. Here, the meta-lens is an optical element (also called a metaoptic) fabricated on a silicon wafer using semiconductor processes and utilizing metasurface technology. Metasurface technology is a technique based on artificially designed two-dimensional nanostructure arrays used to precisely control the phase, amplitude, polarization, and other properties of electromagnetic waves (such as light waves). It achieves flexible manipulation of electromagnetic waves through subwavelength scale (smaller than wavelength) microstructure units on a single-layer metasurface, thereby replacing the complex functions of traditional optical devices. For example, it can realize diffraction control based on incident point laser to obtain the desired discrete light spot pattern.

[0063] The projection mechanism 112 can be as follows: Figure 1 As shown, an axially rotating mechanism capable of reciprocating or unidirectional movement within a certain range along the axial direction can be, for example, a rotating mirror or a galvanometer. The projection mechanism 112 receives and reflects light emitted from the light source module 111. Because the projection mechanism 112 can move axially within a certain range, the reflected light can move along the first direction, thereby covering the area to be measured. In other implementations, the projection mechanism 112 can also achieve the scanning projection of discrete light spots using principles other than axial movement and reflection. For example, the projection mechanism 112 can be a slide rail device that has its own light source module 111 mounted on it and is capable of reciprocating movement in the first direction.

[0064] It should be understood that "movement along the first direction" can refer to the first direction and its opposite direction. That is, "movement along the first direction" can include movement along the first direction itself within a predetermined projection period (e.g., corresponding to...). Figure 1 (Moving from left to right), and then moving in the opposite direction of the first direction in the next predetermined projection cycle (e.g., corresponding to...). Figure 1 (Moving from right to left). In some embodiments, the projection direction of the discrete light spot can also change within a predetermined projection period, as long as it corresponds to the activation of the corresponding pixel of the ToF sensor.

[0065] In addition, although the example of the light source module projecting pulses was given above, in some embodiments, the light source module can also continuously project discrete light spots, as long as the activation of the corresponding pixel of the ToF sensor is set.

[0066] As previously mentioned, the projection mechanism moves within a predetermined projection period, which can be matched with the imaging period of the ToF sensor. For example, during projection... Figure 1 When the discrete light spot is shown, the predetermined projection period t c It can be equal to 17t p (or slightly larger), the imaging period of a ToF sensor can also be equal to 17t. p (or slightly larger). And in the projection... Figure 4 When the discrete light spot is shown, the predetermined projection period t c It can be equal to 3t p (or slightly larger), the imaging period of a ToF sensor can also be equal to 33t. p (or slightly larger). And in, for example... Figure 1 or Figure 2 When the discrete light spot pattern shown only occupies a small portion of the measured area, the pixel columns of the ToF sensor can be turned on in turn, corresponding to the illuminated area, to further reduce the influence of ambient light and multipath reflection.

[0067] The ToF sensor in this application can be a device that obtains a high-resolution distance / depth distribution of the measured scene based on direct time of flight through a high-density ToF sensing pixel array. In a preferred embodiment, the ToF sensor can be a Geiger mode-based sensor array.

[0068] To facilitate understanding of the invention, the "Gegege mode" is explained here. The difference between a conventional avalanche photodiode (APD) and a typical pn junction photodiode is that the APD can withstand a higher bias voltage. When a photon is absorbed by the APD, an electron-hole pair is generated; this pair is called the master electron. The master electron is accelerated under the strong electric field generated by the high bias voltage, gaining sufficient energy, and then collides with the crystal lattice to generate another electron-hole pair. Some kinetic energy is lost in the collision; this process is the familiar collisional ionization. Then, electrons (or holes) and secondary electrons (or holes) are accelerated again by the strong electric field, generating even more electron-hole pairs, the so-called "avalanche" phenomenon, with the current increasing exponentially. After several hops, the generation and absorption rates of electron-hole pairs reach equilibrium. If the bias voltage of the APD is lower than its breakdown voltage, the absorption rate of electron-hole pairs will be greater than the generation rate, causing the number of electron-hole pairs to decrease. At this time, the average photocurrent generated by the APD is proportional to the incident light, with the proportionality coefficient being the gain factor M; therefore, this process is called the linear operating mode. By utilizing the linear proportional relationship, the intensity of the incident light signal can be measured.

[0069] However, if the bias voltage of the APD is higher than its breakdown voltage, the rate at which the APD generates electron-hole pairs due to collisional ionization will be greatly accelerated, exceeding the absorption rate of electron-hole pairs. This causes the current to increase exponentially over time, resulting in avalanche and generating current pulses. The increase in photocurrent weakens the strong electric field formed by the high bias voltage of the APD, which reduces the avalanche rate and the photocurrent, eventually reaching equilibrium. After equilibrium, the photocurrent will not change further. The formation of the equilibrium process is mainly due to the negative feedback provided by the equivalent resistance on the APD. The increase in photocurrent increases the voltage drop across the equivalent resistance, thereby offsetting part of the bias voltage and causing the bias voltage on the APD to decrease. This leads to a decrease in the avalanche rate and a decrease in photocurrent, which in turn decreases the voltage drop across the equivalent resistance, resulting in the reverse process and an increase in photocurrent. After a period of time, an equilibrium state is formed. If the photocurrent stabilizes and exceeds several hundred microamps, the photocurrent will remain constant, i.e., it will maintain this equilibrium state, and at this point, it will no longer respond to incident photons. This is the Geiger mode. The most significant characteristic of this mode is its ability to respond to single-photon events. Its biggest difference from the linear mode is that it only responds to the presence or absence of photons, but cannot distinguish the number of photons. This is also the most prominent feature of GAPD (Geiger mode avalanche photodiode). To respond to the next photon event, the APD must be connected to a quenching circuit for quenching, and then recharged for it to function properly. Ideally, during the quenching process, the APD does not respond to any photons until charging is complete; this period is called the "blind time."

[0070] SPAD is a photodiode operating in Geiger mode, functioning like a photon-triggered switch, with states of "on" or "off". The ToF sensor preferably used in this invention is a silicon photomultiplier tube (SiPM) composed of multiple independent SPAD sensors. Each SiPM has its own quenching resistor, overcoming the limitation of a single SPAD not being able to simultaneously measure multiple photons. Because this invention uses a SiPM that receives returned light column by column, it enables efficient and rapid computation of depth data despite limitations in computing power and blind time.

[0071] It should be understood that the laser pulses emitted by the light source module of the present invention are pulses outside the visible light band, such as near-infrared pulses, thereby enabling the use of a bandpass filter to filter out interference from irrelevant ambient light.

[0072] In addition, the depth data measurement head disclosed herein may also include a controller for controlling the coordination between the discrete spot projection of the projection device and the imaging of the ToF sensor.

[0073] The present invention can also be implemented as a depth data measurement device. Figure 5 A schematic diagram of a depth data measurement device according to an embodiment of the present disclosure is shown. As shown, the depth data measurement device 500 includes a depth data measurement head composed of a projection device 510 and a ToF sensor 520. Figure 5 The controller 530 is also shown. Furthermore, the depth data measurement device 500 includes a processor 540, which performs distance calculations based on the sensing signals generated by the ToF sensor 520 to obtain depth data output for the measured area.

[0074] In some embodiments, the measuring device may have a separate controller 530 and processor 540, while in other embodiments, the processor 540 may integrate all or part of the functions of the controller 530.

[0075] The present invention can also be implemented as a depth data measurement method. This method can be implemented by the controller and / or processor of the depth measuring head or measuring device disclosed above. Figure 6 An exemplary flowchart of a depth data measurement method according to an embodiment of the present invention is shown.

[0076] In step S610, a discrete light spot moving along a first direction is projected onto the area under test. In step S620, the reflected light from the area under test is received and a sensing signal is generated, the sensing signal representing the direct time of flight of the light to calculate the distance to the object being photographed within the area under test.

[0077] The depth data measurement method of the present invention can be combined with the depth data measurement head and measurement device disclosed above to execute the depth data measurement scheme of the present invention.

[0078] The depth data measurement scheme according to the present invention has been described in detail above with reference to the accompanying drawings. This scheme utilizes discrete light spots, especially discrete light spot patterns with carefully designed morphologies, to achieve high-precision depth data measurement based on direct time-of-flight, which can significantly suppress or even completely eliminate pixel dilation and multipath reflection problems caused by highly reflective surfaces.

[0079] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems and methods according to various embodiments of the present invention. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than those marked in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0080] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A depth data measurement head, comprising: A projection device is used to project a discrete light spot moving along a first direction onto a test area. The projection device includes a light source module for generating the discrete light spot and a projection mechanism for projecting the generated discrete light spot onto the test area. The projection mechanism moves the projected discrete light spot along the first direction by its own movement. A time-of-flight (ToF) sensor is used to receive the reflected light from the measured area and generate a sensing signal that characterizes the direct time of flight of the light to calculate the distance to the object being photographed within the measured area.

2. The depth data measurement head as described in claim 1, wherein, The discrete light spot is composed of multiple dispersed light spots, each light spot being no larger than a first threshold range, and the distance between adjacent light spots being no less than a second threshold range.

3. The depth data measurement head as described in claim 1, wherein, The discrete light spot appears as an elongated discrete light spot pattern. The length direction of the elongated discrete light spot pattern is a second direction perpendicular to the first direction. In fact, the first direction corresponds to the pixel row direction of the ToF sensor, and the second direction corresponds to the pixel column direction of the ToF sensor. Furthermore, for each pixel row within the working area of ​​the ToF sensor, the discrete light spot contains at least one light point.

4. The depth data measurement head as described in claim 3, wherein, The discrete light spots are presented as a plurality of elongated discrete light spot patterns distributed in the first direction.

5. The depth data measurement head as described in claim 1, wherein, The projection mechanism moves within a predetermined projection range such that the discrete light spot moving along a first direction covers the area under test, and the area under test corresponds to the operating range of the ToF sensor.

6. The depth data measurement head as described in claim 1, wherein, The projection mechanism moves within a predetermined projection period, which matches the imaging period of the ToF sensor.

7. The depth data measurement head as described in claim 6, wherein, The light source module projects discrete light spot pulses, and the movement speed of the projection mechanism is determined based on the pulse projection frequency. The movement range of the projection mechanism is determined based on the shape of the discrete light spot, so that each pixel in the working area of ​​the ToF sensor is illuminated at least once within the predetermined period.

8. The depth data measurement head as described in claim 1, wherein, The light source module includes at least one of the following: The array of vertical cavity surface-emitting lasers (SPOT VCSELs) is arranged to correspond to the discrete light spots. A laser generator for generating laser light and a diffractive optical element (DOE) for generating the discrete light spot based on the received laser light; A floodlight source and a mask element for generating the discrete light spot; as well as Laser generators for producing laser light and metalenz lenses for generating discrete light spots.

9. A depth data measurement device, comprising: Depth data measurement head as described in any one of claims 1-8; Processor, used for: Distance calculation is performed based on the sensing signal generated by the ToF sensor to obtain depth data output of the measured area.

10. A depth data measurement method, comprising: A discrete light spot moving along a first direction is projected onto the area to be measured; as well as The system receives the reflected light from the measured area and generates a sensing signal, which characterizes the direct flight time of the light to calculate the distance to the object being photographed within the measured area.

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