CN111025321A - Variable-focus depth measuring device and measuring method - Google Patents
Variable-focus depth measuring device and measuring method Download PDFInfo
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- CN111025321A CN111025321A CN201911385290.5A CN201911385290A CN111025321A CN 111025321 A CN111025321 A CN 111025321A CN 201911385290 A CN201911385290 A CN 201911385290A CN 111025321 A CN111025321 A CN 111025321A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/08—Systems determining position data of a target for measuring distance only
- G01S17/32—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
- G01S17/36—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated with phase comparison between the received signal and the contemporaneously transmitted signal
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/88—Lidar systems specially adapted for specific applications
- G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/481—Constructional features, e.g. arrangements of optical elements
- G01S7/4816—Constructional features, e.g. arrangements of optical elements of receivers alone
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Abstract
The invention discloses a variable-focus depth measuring device and a variable-focus depth measuring method, wherein the variable-focus depth measuring device comprises a transmitting unit, a receiving unit and a control and processing circuit connected with the transmitting unit and the receiving unit; wherein, the emission unit comprises a light source and an optical element; the receiving unit comprises a TOF image sensor and a zoom lens; the TOF image sensor is configured to acquire at least a portion of the light beam reflected back from the target region and form an electrical signal; the zoom lens is configured to project the reflected light beam into pixels of the TOF image sensor, and the field angle of collection of the reflected light beam by the TOF image sensor is changed by changing the focal length of the zoom lens; the control and processing circuit calculates a depth image of the target area according to the electrical signal. By arranging the zoom lens, the field angle of a TOF image sensor for collecting a reflected light beam can be regulated and controlled in real time, the light intensity or photon quantity of the received reflected light beam is further changed, and the measurement precision of the measuring device is improved.
Description
Technical Field
The invention relates to the technical field of optical measurement, in particular to a variable-focus depth measuring device and a variable-focus depth measuring method.
Background
The depth measuring device can be used for obtaining a depth image of an object, further can be used for 3D modeling, skeleton extraction, face recognition and the like, and has very wide application in the fields of 3D measurement, human-computer interaction and the like. The current depth measurement technologies mainly include a TOF ranging technology, a structured light ranging technology, a binocular ranging technology and the like.
TOF is called Time-of-Flight, i.e., Time-of-Flight, and TOF ranging technology is a technology for realizing accurate ranging by measuring the round-trip Time of Flight of an optical pulse between a transmitting/receiving device and a target object, and is classified into direct ranging technology and indirect ranging technology.
The direct ranging technology is that a target object distance is obtained by continuously sending light pulses to the target object, then receiving light signals reflected from the object by using a sensor and detecting the flight (round trip) time of the sent and reflected light pulses; the indirect ranging technique is to emit a time-sequence amplitude-modulated light beam to a target object, measure the phase delay of the reflected light beam relative to the emitted light beam, and calculate the flight time according to the phase delay. According to the modulation and demodulation type, the modulation and demodulation method can be divided into a Continuous Wave (CW) modulation and demodulation method and a Pulse Modulated (PM) modulation and demodulation method.
In a device for depth measurement by using a TOF technology, the measurement accuracy of the device is greatly influenced by the intensity of ambient light in different environments due to wide application scenes. Furthermore, there are target objects of significantly different light reflectivity, resulting in variations in the intensity of reflected light that affect the accuracy of the measurement. In addition, the different arrangement of the transmitting end and the receiving end in the depth measuring device also affects the measuring accuracy of the device.
The above background disclosure is only for the purpose of assisting understanding of the inventive concept and technical solutions of the present invention, and does not necessarily belong to the prior art of the present patent application, and should not be used for evaluating the novelty and inventive step of the present application in the case that there is no clear evidence that the above content is disclosed at the filing date of the present patent application.
Disclosure of Invention
The present invention is directed to a variable focus depth measurement apparatus and method for measuring a variable focus depth, so as to solve at least one of the above-mentioned problems of the related art.
In order to achieve the above purpose, the technical solution of the embodiment of the present invention is realized as follows:
a variable-focus depth measuring device comprises a transmitting unit, a receiving unit and a control and processing circuit connected with the transmitting unit and the receiving unit; wherein the content of the first and second substances,
the transmitting unit comprises a light source and an optical element; the light source is used for emitting a light beam, and the optical element is configured to receive the light beam and project the light beam to a target area;
the receiving unit comprises a TOF image sensor and a zoom lens; the TOF image sensor is configured to acquire at least a portion of the light beam reflected back from the target region and form an electrical signal; the zoom lens is configured to project the reflected light beam into pixels of the TOF image sensor, and the angle of field at which the TOF image sensor collects the reflected light beam is changed by changing the focal length of the zoom lens;
and the control and processing circuit calculates the depth image of the target area according to the electric signal.
In some embodiments, the zoom lens comprises at least two adjustable focal lengths; alternatively, the zoom lens is configured to be continuously variable-focus.
In some embodiments, the zoom lens further comprises a driver, wherein the driver adjusts the focal length of the zoom lens to realize a zoom function.
In some embodiments, the TOF image sensor collects reflected light beams within a first field angle when the zoom lens is configured to have a first focal length; the TOF image sensor collects a reflected light beam within a second field of view angle when the zoom lens is configured to have a second focal length; wherein the first focal length is smaller than the second focal length, and the first field angle is larger than the second field angle.
In some embodiments, the emission unit is configured to emit a flood light beam and a spot pattern light beam toward a target area, and includes a light source array including a plurality of light sources and a liquid crystal element.
In some embodiments, the transmit unit transmits the speckle pattern beam toward the target area with increasing a focal length of the zoom lens to cause the TOF image sensor to collect the reflected beam within a small field angle, and transmits the flood beam toward the target area with decreasing the focal length of the zoom lens to cause the TOF image sensor to collect the reflected beam within a large field angle.
The other technical scheme of the invention is as follows:
a variable focus depth measurement method comprising the steps of:
controlling the emission unit to emit a light beam toward the target area; the emission unit comprises a light source and an optical element, and light beams emitted by the light source are projected to the target area after passing through the optical element;
controlling a receiving unit to collect at least part of the light beams reflected back by the target area and form an electric signal, wherein the receiving unit comprises a TOF image sensor and a zoom lens, and changing the angle of view of the TOF image sensor for collecting the reflected light beams by changing the focal length of the zoom lens;
and calculating the depth image of the target area according to the electric signal.
In some embodiments, the zoom lens comprises at least two adjustable focal lengths; alternatively, the zoom lens is configured to be continuously variable-focus.
In some embodiments, the TOF image sensor collects reflected light beams within a first field angle when the zoom lens is configured to have a first focal length; the TOF image sensor collects a reflected light beam within a second field of view angle when the zoom lens is configured to have a second focal length; wherein the first focal length is smaller than the second focal length, and the first field angle is larger than the second field angle.
In some embodiments, the depth image of the target area is further calculated by processing the electrical signals by control and processing circuitry and calculating a phase difference of the light beam received from emission to reflection, calculating a time of flight of the light beam based on the phase difference;
or processing the electric signal through a control and processing circuit, calculating the flight time of the light beam from emission to reception of reflection, and calculating the depth image of the target area according to the flight time.
The technical scheme of the invention has the beneficial effects that:
by arranging the zoom lens, the invention can regulate and control the angle of view of the TOF image sensor for collecting the reflected light beam in real time, further change the light intensity or photon quantity of the received reflected light beam and improve the measurement precision of the measuring device.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is a schematic diagram of the structure of a variable focus depth measurement device according to one embodiment of the present invention.
Fig. 2 is a schematic structural diagram of a receiving unit of a variable focus depth measurement device according to one embodiment of the present invention.
FIG. 3 is a flowchart illustration of a variable focus depth measurement method according to one embodiment of the invention.
FIG. 4 is a flowchart illustration of a depth measurement method according to yet another embodiment of the invention.
FIG. 5 is a flowchart illustration of a depth measurement method according to another embodiment of the present invention.
Fig. 6a-6c are schematic diagrams of received light signals forming a histogram in accordance with embodiments of the invention.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the embodiments of the present invention more clearly apparent, the present invention is further described in detail below with reference to the accompanying drawings and the embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
It will be understood that when an element is referred to as being "secured to" or "disposed on" another element, it can be directly on the other element or be indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or be indirectly connected to the other element. The connection may be for fixation or for circuit connection.
It is to be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like are used in an orientation or positional relationship indicated in the drawings for convenience in describing the embodiments of the present invention and to simplify the description, and are not intended to indicate or imply that the referenced device or element must have a particular orientation, be constructed in a particular orientation, and be in any way limiting of the present invention.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the embodiments of the present invention, "a plurality" means two or more unless specifically limited otherwise.
Referring to fig. 1, fig. 1 is a schematic diagram of a variable focus depth measuring device according to an embodiment of the invention, in which the depth measuring device 10 includes a transmitting unit 11, a receiving unit 12, and a control and processing circuit 13; wherein, the emitting unit 11 is used for emitting a light beam 30 to the target area 20, the light beam is emitted to the target area space to illuminate the target object in the space, at least part of the emitted light beam 30 forms a reflected light beam 40 after being reflected by the target area 20, at least part of the reflected light beam 40 is received by the receiving unit 12, the control and processing circuit 13 is respectively connected with the emitting unit 11 and the receiving unit 12 to control the emission and the reception of the light beam, and simultaneously receives the information generated by receiving the reflected light beam from the receiving unit 12, and calculates the information to obtain the depth information of the target object.
The emitting unit 11 includes a light source 111, an optical element 112, a light source driver (not shown in the figure), and the like. The light source 111 may be a Light Emitting Diode (LED), an Edge Emitting Laser (EEL), a Vertical Cavity Surface Emitting Laser (VCSEL), or the like, or may be a light source array composed of a plurality of light sources for emitting a spot-shaped light beam toward a target area. The arrangement of the light sources 111 may be regular or irregular, and the light beams emitted by the light sources 111 may be visible light, infrared light, ultraviolet light, and the like. The light source 111 emits light beams outward under control of a light source driver (which may be further controlled by the control and processing circuit 13), such as in one embodiment, the light source 111 emits light beams amplitude modulated in time sequence under control, which may be pulse modulated light beams, square wave modulated light beams, or sine wave modulated light beams. In another embodiment, the light source 111 emits a pulsed light beam under control. It will be appreciated that the light source 111 may be controlled to emit the associated light beam by means of a part of the control and processing circuitry 13 or independently of the sub-circuitry present in the control and processing circuitry 13, such as a pulse signal generator.
The optical element 112 receives the light beam from the light source 111 and projects the light beam to a target region after shaping. For example, in one embodiment, the optical element 112 receives the pulsed light beam from the light source 111 and optically modulates, such as diffracting, refracting, reflecting, etc., the pulsed light beam, and then emits the modulated light beam, such as a focused light beam, a flood light beam, a structured light beam, etc., into space. The optical element 112 may be one or more combinations of lens, liquid crystal element, diffractive optical element, microlens array, super surface (metassurface) optical element, mask, mirror, MEMS galvanometer, etc., preferably the optical element is a liquid crystal element.
The receiving unit 12 includes a TOF image sensor 121, a filter 122, and a zoom lens 123, the zoom lens 123 receives and images at least part of the light beam reflected by the target object on at least part of the TOF image sensor 121, and the filter 122 is provided as a narrow band filter matched with the wavelength of the light source for suppressing background light noise of the remaining wavelength bands. The TOF image sensor 121 may be a Charge Coupled Device (CCD), Complementary Metal Oxide Semiconductor (CMOS), Avalanche Diode (AD), Single Photon Avalanche Diode (SPAD), etc. image sensor with an array size representing the resolution of the depth camera, e.g., 320 × 240, etc. Generally, a readout circuit (not shown in the figure) composed of one or more of a signal amplifier, a time-to-digital converter (TDC), an analog-to-digital converter (ADC), and the like is also included in connection with the TOF image sensor 121. The zoom lens 123 may vary the focal distance, be continuously variable-focal, or have multiple adjustable focal lengths, e.g., in some embodiments, a zoom lens having at least two adjustable focal lengths. In some embodiments, the zoom lens may be a zoom function achieved by a driver changing the focus of the lens. In other embodiments, the variable focus lens may also be a liquid lens, the variable focus being achieved by changing the shape of the liquid.
In some embodiments, the TOF image sensor 121 includes at least one pixel, and in contrast to a conventional image sensor used only for taking pictures, each pixel of the TOF image sensor 121 includes two or more taps (taps for storing and reading or outputting charge signals generated by incident photons under control of respective electrodes), such as 2 taps, which are sequentially switched in a certain order within a single frame period (or single exposure time) to collect respective photons, receive light signals and convert them into electrical signals.
The control and processing circuit 13 supplies a modulation signal (emission signal) required when the light source 111 emits laser light, the light source emits a light beam whose amplitude is modulated in time series to a target object under the control of the modulation signal, and also supplies a demodulation signal (acquisition signal) of each tap in each pixel of the TOF image sensor 121. The zoom lens projects the reflected light beam reflected from the target area to pixels of the TOF image sensor, each tap collects the reflected light beam under the control of the demodulation signal and generates an electric signal, the control and processing circuit 13 calculates the intensity information of the reflected light beam in a weighted average mode after receiving the electric signal, the focal length of the zoom lens is adjusted according to the intensity information and a predefined threshold range, and the field angle of the TOF image collected reflected light beam is further adjusted. The electric signals are processed, phase differences reflecting the light beams from emitting to receiving are calculated, the flight time of the light beams is calculated based on the phase differences, and the depth image of the target area is further obtained.
In some embodiments, the TOF image sensor 121 is composed of a single photon avalanche photodiode (SPAD), and may also be an array pixel unit composed of a plurality of SPAD pixels, and the array size of the array pixel unit represents the resolution of the depth camera, such as 320 × 240. The SPAD can respond to incident single photons so as to realize the detection of the single photons, and can also realize the collection of the photons and the calculation of the flight time based on a time correlation single photon counting method (TCSPC).
The control and processing circuit 13 is connected with the transmitting unit 11 and the receiving unit 12 and synchronizes trigger signals of the transmitting unit 11 and the receiving unit 12, controls the light source 111 to transmit a pulse light beam, controls each SPAD pixel in the TOF image sensor 121 to receive photons in a reflected light beam projected into the TOF image sensor pixel through the zoom lens at the same time and form a photon signal, receives the photon signal and counts the number of the received photons to form a measurement histogram, performs matching calculation on the measurement waveform and a plurality of pre-stored reference waveforms according to a measurement waveform determined by the measurement histogram, adjusts the focal length of the zoom lens according to a matching result, and further adjusts the field angle of the TOF image sensor to collect light beams. Furthermore, the control and processing circuit 13 is also configured to determine a time corresponding to the measurement waveform in the measurement histogram, and calculate a depth image of the target region from the time corresponding to the measurement waveform.
In some embodiments, the depth measuring device 10 may further include a driving circuit, a power supply, a color camera, an infrared camera, an IMU, and so on, which are not shown in the drawings, and the combination with these devices may realize more abundant functions, such as 3D texture modeling, infrared face recognition, SLAM, and so on. In addition, the depth measurement device 10 may be embedded in an electronic product such as a mobile phone, a tablet computer, a computer, or the like.
Fig. 2 is a schematic structural diagram of a receiving unit of the depth measuring device according to an embodiment of the present invention. The receiving unit includes a TOF image sensor 121 and a zoom lens 122. The TOF image sensor 121 is configured to collect at least part of the light beam reflected back by the target area and form an electrical signal, the zoom lens 122 is configured to project the reflected light beam into pixels of the TOF image sensor 121, and the angle of field at which the TOF image sensor 121 collects the reflected light beam is changed by changing the focal length of the zoom lens 122. The zoom lens 122 may be continuously or discontinuously variable-zooming, for example, in some embodiments, it may be a zoom lens with at least two adjustable focal lengths, and when the focal point of the zoom lens is located at the first position (marked as a in fig. 2), it has a first focal length f1, and when the TOF image sensor collects the partial light beam reflected by the target area 20 within the first field angle 201; when the focal point of the zoom lens is at the second position (labeled B in fig. 2), having a second focal length f2, the TOF image sensor now captures a portion of the light beam reflected by the target region 20 within the second field angle 202. As the focal length of the zoom lens is increased, the field angle of the TOF image sensor for collecting the reflected light beam in the target area is reduced, so that the collected reflected light beam is also reduced; on the contrary, as the focal length decreases, the field angle increases and thus the collected light beam also increases, based on which the collection design of different scenes can be realized through reasonable configuration.
In general, a TOF image sensor needs to acquire a proper light beam, receive a proper light intensity or photon quantity on a pixel of the sensor, and then generate an effective electrical signal to be transmitted to a control and processing circuit, and then perform processing calculation to obtain an accurate depth image of a target region. TOF ranging techniques require a high signal-to-noise ratio of the returning light to achieve high accuracy measurements, which would result in an insufficient signal-to-noise ratio of the reflected light or pulse if the reflected light or pulse is too weak to make accurate measurements, but which would result in saturation of the sensor if the reflected light beam or pulse is too strong, and also make it difficult to obtain accurate depth images. For example, when the target object is located at a different distance from the measuring device, the light reflected by the target object at a far distance is less than the light reflected by the target object at a near distance; or, when a plurality of target objects with different reflectivities are in the detection area, the target object with high reflectivity reflects light higher than the target object with low reflectivity; or, when the measuring device is applied in different application scenarios, strong ambient light may also cause a saturation phenomenon of the TOF image sensor, which may affect the measurement accuracy of the device alone or in combination.
Therefore, the zoom lens arranged on the receiving unit can regulate and control the field angle of the TOF image sensor for collecting the reflected light beam in real time, further changes the light intensity or photon quantity of the received reflected light beam, and improves the measurement accuracy of the system.
In some embodiments, the emission unit may be configured to emit a plurality of light beams of different intensities towards the target area for a measurement application of multiple functions. For example, in one embodiment, the emission unit includes a light source array of a plurality of light sources and a liquid crystal element configured to emit a flood beam and a speckle pattern beam toward a target area.
Each light source emits a point-shaped light beam, the point-shaped light beam is projected through transparent liquid crystal, the light beam directly penetrates through the liquid crystal element to irradiate a target area, the size of each light spot is small and is distributed in a projection area at a certain interval, light energy at each light spot is relatively concentrated and high, the intensity of a reflected light beam projected into the target area is also high, in order to reduce the occurrence of the situation that the sensor is saturated due to overhigh reflected light energy, the focal length of the zoom lens is increased to enable the TOF image sensor to collect the reflected light beam in a small field angle, and the fact that the proper reflected light beam is collected to measure the depth image of the target area is guaranteed.
In contrast, the spot light beams emitted by each light source pass through the liquid crystal element in a diffusion state and then project the floodlight beams to the target area, at the moment, each spot light beam is diffracted after passing through the liquid crystal, the light spot size is increased and is uniformly distributed in the whole projection area, and compared with the spot pattern light beams, the light energy is smaller but is uniformly distributed. If the light beams are collected at the same field angle, the reflected light intensity may be lower, so that the focal length of the zoom lens is reduced to enable the TOF image sensor to collect the reflected light beams within a larger field angle, and it is ensured that a proper reflected light beam is collected to measure the depth image of the target area.
Based on the variable-focus depth measuring device in each embodiment, the application also provides a variable-focus depth measuring method. Referring to fig. 3, fig. 3 is a flowchart illustration of a variable focus depth measurement method according to another embodiment of the present invention, the variable focus depth measurement method including:
s31, controlling an emission unit to emit light beams towards the target area, wherein the emission unit comprises a light source and an optical element, and the light beams emitted by the light source are projected to the target area after passing through the optical element;
s32, controlling a receiving unit to collect at least part of the light beams reflected back by the target area and form an electric signal, wherein the receiving unit comprises a TOF image sensor and a zoom lens, and the TOF image sensor is used for collecting the field angle of the reflected light beams by changing the focal length of the zoom lens;
and S33, calculating the depth image of the target area according to the electric signals.
Specifically, the control and processing circuit is connected with the transmitting unit and the receiving unit, controls the transmitting unit to emit light beams towards the target area and controls the receiving unit to collect partial light beams reflected by the target area, and calculates the depth image according to the electric signals formed by the receiving unit. In some embodiments, the control and processing circuitry processes the electrical signals and calculates a phase difference of the light beam from emission to reflection back to reception, calculates a time of flight of the light beam based on the phase difference, and further calculates a depth image of the target area. In some embodiments, the control and processing circuitry processes the electrical signals and calculates the time of flight of the beam from emission to reflection back to reception, from which time of flight a depth image of the target area is calculated.
In particular, the zoom lens may be a continuous zoom lens or a lens having a plurality of adjustable focal lengths. As the focal length of the zoom lens is increased, the field angle of the TOF image sensor for collecting the reflected light beam in the target area is reduced, so that the collected reflected light beam is also reduced; conversely, as the focal length decreases, the field angle increases and the collected beam also increases. Therefore, the zoom lens arranged on the receiving unit can regulate and control the angle of view of the TOF image sensor for collecting the reflected light beam in real time, further change the light intensity of the received reflected light beam and improve the measurement accuracy of the measuring device.
In some embodiments, the transmitting unit may be configured to transmit the flood light beam and the speckle pattern beam, when the flood light beam is transmitted, to reduce a focal length of the zoom lens, causing the TOF image sensor to collect the reflected light beam within a small field angle; when the speckle pattern beam is emitted, the focal length of the zoom lens is increased, causing the TOF image sensor to collect the reflected beam over a large field angle.
Referring to fig. 4, another embodiment of the present invention provides a depth measuring method including the steps of:
s41, controlling the emission unit to emit the light beam with amplitude modulated in time sequence towards the target area;
s42, controlling a receiving unit to collect at least part of the light beam reflected back through the target area, wherein the receiving unit comprises a TOF image sensor and a zoom lens, the TOF image sensor is configured to collect at least part of the light beam reflected back through the target area and form an electric signal, and the zoom lens is configured to project the reflected light beam into pixels of the TOF image sensor;
and S43, calculating the light intensity of the reflected light beam, adjusting the focal length of the zoom lens according to the light intensity and a predefined threshold range, and further changing the field angle of the TOF image sensor for collecting the reflected light beam.
Specifically, the emission unit comprises a light source and an optical element, wherein the light source is configured to emit a light beam with amplitude modulated in time sequence, and the light beam passes through the optical element and then is projected to a target area; the control and processing circuit provides a modulation signal required by the light source to emit light beams, the light source is controlled to emit light beams with amplitude modulated by sine waves, square waves or pulses in time sequence towards a target area, the optical element receives the light beams from the light source, shapes the light beams and then projects the light beams to the target area, and the shaped light beams are kept to be modulated by the sine waves, the square waves or the pulses in amplitude.
Specifically, the TOF image sensor includes a plurality of pixels, each pixel in the TOF image sensor includes at least 2 taps, and the taps are sequentially switched in a certain order within a single frame period (or a single exposure time) to acquire corresponding photons, receive optical signals, and convert the optical signals into electrical signals. The zoom lens may be a continuous zoom lens or a lens having a plurality of adjustable focal lengths.
Specifically, the transmitting unit and the receiving unit are respectively connected to the control and processing circuit, the transmitting unit is controlled to transmit light beams through the control and processing circuit, the receiving unit is controlled to receive electric signals formed by the light beams reflected back through the target area, intensity information of the reflected light beams is calculated, the focal length of the zoom lens is adjusted according to the intensity information and a predefined threshold range, and the field angle of the TOF image collecting reflected light beams is further adjusted. The control and processing circuit has stored therein a predefined threshold range of light intensities within which a minimum light intensity L1 and a maximum light intensity L2 are set. The minimum light intensity is defined as that if the light intensity of the reflected light beam collected by the TOF image sensor is less than or equal to the minimum light intensity, the TOF image sensor is difficult to generate an effective electric signal and transmit the effective electric signal to the control and processing circuit to obtain an accurate depth image. The maximum light intensity is defined as that if the light intensity of the reflected light beam collected by the TOF image sensor is greater than or equal to the maximum light intensity, the TOF image sensor is saturated and is difficult to generate an effective electric signal, and the effective electric signal is transmitted to the control and processing circuit to obtain an accurate depth image.
The control and processing circuit receives the electrical signal generated by the sensor and calculates the light intensity L of the reflected beam, which is preferably calculated as a weighted average. In some embodiments, the zoom lens may be configured for continuous zoom, increasing the focal length of the zoom lens when the calculated light intensity is less than or equal to the minimum light intensity, i.e., L ≦ L1, causing the TOF image sensor to collect the reflected light beam over a large field angle; when the calculated light intensity is greater than or equal to the maximum light intensity, namely L is greater than or equal to L2, reducing the focal length of the zoom lens, and enabling the TOF image sensor to collect the reflected light beam in a small field angle; when the calculated light intensity satisfies the threshold range, i.e., L1< L2, the TOF image sensor receives the reflected light beam and forms a valid electrical signal. The control and processing circuit calculates a depth image of the target area from the formed effective electrical signal.
In some embodiments, the zoom lens may be configured to have a plurality of adjustable focal lengths. For example, the zoom lens is set to have at least three adjustable focal lengths, the initial focal length of the zoom lens is configured to be a first focal length, the TOF image sensor is enabled to receive the light intensity meeting a threshold range, the TOF image sensor collects the reflected light beam within a first field angle and generates an electrical signal, and the control and processor calculates the light intensity and performs analysis according to a predefined threshold range of light intensity. If the light intensity received by the sensor pixel is smaller than or equal to the minimum light intensity, adjusting the focal length of the zoom lens to be a second focal length, and collecting a reflected light beam by the TOF image sensor in a second field angle to generate an electric signal; and if the light intensity received by the sensor pixel is greater than or equal to the maximum light intensity, adjusting the focal length of the zoom lens to be a third focal length, and collecting the reflected light beam by the TOF image sensor in a third field angle to generate an electric signal. And after the TOF image sensor receives the reflected light beam and forms an effective electric signal, namely when the light intensity collected on the pixel meets a threshold range, the control and processing circuit calculates the depth image of the target area according to the formed effective electric signal.
Referring to fig. 5, fig. 5 is a flowchart illustrating a depth measurement method according to another embodiment of the present invention, the depth measurement method including:
s51, controlling the emission unit to emit the pulse light beam towards the target area;
s52, controlling a receiving unit to collect at least part of the light beam reflected back by the target area, wherein the receiving unit comprises a TOF image sensor and a zoom lens, the TOF image sensor is configured to collect photons in the at least part of the light beam reflected back by the target area and form photon signals, and the zoom lens is configured to project the reflected light beam into pixels of the TOF image sensor;
and S53, receiving the photon signals, counting the number of received photons to form a measurement histogram, determining a measurement waveform according to the measurement histogram, performing matching calculation on the measurement waveform and a plurality of pre-stored reference waveforms, adjusting the focal length of the zoom lens according to a matching result, and further adjusting the field angle of the TOF image collecting light beam.
Specifically, the emission unit comprises a light source and an optical element, wherein the light source is configured to emit a pulse light beam, and the light beam is projected to a target area after passing through the optical element; the TOF image sensor comprises a plurality of single photon avalanche photodiodes (SPADs), and the zoom lens can be continuously zoomed or have a plurality of adjustable focal lengths.
The emitting unit and the receiving unit are respectively connected with the control and processing circuit, and the control and processing circuit controls the emitting unit to emit light beams and controls the receiving unit to receive the light beams reflected by the target area. Specifically, the control and processing circuit synchronizes trigger signals of the emitting unit and the receiving unit, the emitting unit is controlled to emit pulse beams towards a target area, the pulse beams are reflected by the target area and then enter the SPAD, a single photon enters a SPAD pixel to cause avalanche, a response signal is generated and input into the control and processing circuit, and the control and processing circuit detects and records a time interval from the emitting of the photon to the causing of the avalanche according to the input response signal. After multiple measurements, a statistical histogram is formed by using a Time Correlation Single Photon Counting (TCSPC) technology for a time interval to recover the waveform of the whole pulse signal, the minimum time unit (minimum storage unit bin) of the histogram represents the resolution of the system, the time interval corresponding to the waveform peak value in the histogram is determined to be the flight time, and the depth image of the target area is calculated according to the flight time.
Fig. 6a-6c are schematic illustrations of several examples of received light signal histogram formation according to embodiments of the invention. When a single photon is incident into the SPAD pixel, an avalanche effect is caused, the SPAD pixel is in a cut-off state at the moment, the incident photon is not received any more, the pixel transmits a response signal of the received photon to the control and processing circuit for counting, after the counting is finished for one time, the reverse bias voltage on the SPAD pixel is increased to enable the SPAD pixel to be in a geiger mode to start the photon collection for a new time, a statistical histogram is formed after the counting is repeated for many times, as shown in fig. 6a, the time t corresponding to the pulse waveform in the histogram is determined to be the flight time, and the depth image of the target area is calculated according to the flight time. However, in some embodiments, the reflected beam intensity from the target region is low, which results in that the SPAD pixels cannot collect enough photons, and it is difficult to form an accurate statistical histogram in the control and processing circuit, as shown in fig. 6c, and at this time, no waveform peak appears in the histogram, which makes it impossible to determine the specific flight time, which makes it difficult to calculate an accurate depth image. In some embodiments, there are also situations of too strong ambient light, too high target reflectivity, etc., where the number of photons reflected after the emission light beam is projected onto the target is large, and at this time, a large number of photons enter a single SPAD pixel to cause cutoff, so that the photons cannot be collected any more, and in each pulse period, the incident photons are concentrated in one bin, so that the waveform in the finally formed test histogram is too narrow to exceed 1 bin, as shown in fig. 6c, in this case, the time corresponding to the pulse waveform in the histogram cannot be determined, and it is difficult to calculate the depth image of the target region.
In order to solve the problems, the control and processing circuit determines a measurement waveform according to a formed measurement histogram, compares the measurement waveform with a preset reference waveform, judges whether the obtained histogram is effective, and determines the flight time according to the waveform peak value of the histogram and calculates a depth image if the histogram is effective; and if the intensity information of the collected light beam of the TOF image sensor is invalid, adjusting the focal length of the zoom lens, changing the field angle of the collected light beam of the TOF image sensor, and adjusting the intensity information of the collected light beam of the TOF image sensor.
The control and processing circuit is internally pre-stored with a plurality of reference waveforms, the reference waveforms have a one-to-one correspondence with the photon number in the light beam received by the TOF image sensor, the matching degree of the measurement waveforms obtained by calculating the measurement histogram and the reference waveforms through a matching method is used for determining the photon number in the collected light beam, if the matching degree meets a preset condition, the two waveforms are similar, at the moment, the focal length of the zoom lens is adjusted according to the photon number information corresponding to the reference waveforms, and then the field angle of the light beam received by the TOF image sensor is adjusted. The reference waveforms comprise at least a first reference waveform, a second reference waveform and a third reference waveform; when the number of photons received by the TOF sensor corresponding to the first reference waveform is within a threshold range, the control and processing circuit carries out statistics on a histogram formed according to the number of enough received photons, the obtained histogram is an effective histogram, and the flight time can be determined and the depth image can be calculated according to the waveform of the histogram. Wherein the threshold range comprises a minimum number of photons and a maximum number of photons, the threshold range being configured to be defined by the minimum number of photons and the maximum number of photons; it is understood that the minimum photon number and the maximum photon number are used as two endpoints of the threshold range, and in a specific process, the threshold range may include the endpoints or not, and in any case, the minimum photon number and the maximum photon number should fall within the protection scope of the present application without departing from the inventive concept.
When the number of photons received by the second reference waveform is less than or equal to the minimum number of photons, the TOF image sensor cannot receive enough photons, and no peak appears in a histogram formed by the TOF image sensor; when the number of photons received by the third reference waveform is greater than or equal to the maximum number of photons, the TOF image sensor is saturated by receiving a large number of photons, and the formed histogram waveform is too narrow.
The control and processing circuit calculates the matching degree of the measured waveform and the reference waveform, determines a preset condition that the matching degree of the measured waveform and one of the reference waveforms meets, and regulates the focal length of the zoom lens or calculates the flight time according to the photon quantity condition corresponding to the reference waveform, wherein the focal length of the zoom lens can be continuously changed. For example, if the measured waveform is similar to the first reference waveform, determining the time of flight and calculating the depth image of the target region by using the measured waveform; if the measurement waveform is similar to the second reference waveform, reducing the focal length of the zoom lens, and enabling the TOF image sensor to gather the reflected light beam again within a large field angle to form a measurement histogram; and if the measurement waveform is similar to the third reference waveform, increasing the focal length of the zoom lens, and enabling the TOF image sensor to gather the reflected light beam again within a small field angle to form a measurement histogram.
In some embodiments, to improve the measurement time, the zoom lens may be configured to have a plurality of adjustable focal lengths, for example, at least three adjustable focal lengths may be designed, corresponding to the case of three reference waveforms. The initial focal length of the zoom lens is set to a first focal length, ensuring that the measurement waveform determined in the measurement histogram is similar to a first reference waveform in most cases, and determining the time-of-flight based on the acquired measurement waveform to calculate the depth image. And when the measurement waveform obtained by matching the calculation result is similar to the second reference waveform, adjusting the focal length of the zoom lens to be the second focal length, so that the TOF image sensor collects light beams in the second field angle to obtain a measurement histogram and calculate a depth image. Similarly, when the measurement waveform is similar to the third reference waveform, the focal length of the zoom lens is adjusted to the third focal length, so that the TOF image sensor collects the light beam in the third field angle to obtain a measurement histogram and calculate a depth image.
The invention provides a plurality of schemes of a variable-focus depth measuring device, and provides an adjustable depth measuring method based on the schemes, wherein a zoom lens is arranged at a receiving end, the focal length of the zoom lens is adjusted to adjust the field angle of a TOF image sensor for receiving a reflected light beam, and further adjust the light intensity of the sensor for receiving the reflected light beam, so that the field angle of a received signal can be adjusted in real time when detecting objects with different reflectivities and different distances in different environments, and the detection precision of the device is improved because the sensor can receive effective response signals under different conditions.
It is to be understood that the foregoing is a more detailed description of the invention, and that specific embodiments are not to be considered as limiting the invention. It will be apparent to those skilled in the art that various substitutions and modifications can be made to the described embodiments without departing from the spirit of the invention, and these substitutions and modifications should be considered to fall within the scope of the invention. In the description herein, references to the description of the term "one embodiment," "some embodiments," "preferred embodiments," "an example," "a specific example," or "some examples" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention.
In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction. Although embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope of the invention as defined by the appended claims.
Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. One of ordinary skill in the art will readily appreciate that the above-disclosed, presently existing or later to be developed, processes, machines, manufacture, compositions of matter, means, methods, or steps, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
Claims (10)
1. A variable-focus depth measuring device is characterized by comprising a transmitting unit, a receiving unit and a control and processing circuit connected with the transmitting unit and the receiving unit; wherein the content of the first and second substances,
the transmitting unit comprises a light source and an optical element; the light source is used for emitting a light beam, and the optical element is configured to receive the light beam and project the light beam to a target area;
the receiving unit comprises a TOF image sensor and a zoom lens; the TOF image sensor is configured to acquire at least a portion of the light beam reflected back from the target region and form an electrical signal; the zoom lens is configured to project the reflected light beam into pixels of the TOF image sensor, and the angle of field at which the TOF image sensor collects the reflected light beam is changed by changing the focal length of the zoom lens;
and the control and processing circuit calculates the depth image of the target area according to the electric signal.
2. The variable focus depth measurement device of claim 1, wherein: the zoom lens comprises at least two adjustable focal lengths; alternatively, the zoom lens is configured to be continuously variable-focus.
3. The variable focus depth measurement device of claim 1, wherein: the zoom lens further comprises a driver, and the driver adjusts the focal length of the zoom lens to realize the zoom function.
4. The variable focus depth measurement device of claim 1, wherein: the TOF image sensor collects a reflected light beam within a first field angle when the zoom lens is configured to have a first focal length; the TOF image sensor collects a reflected light beam within a second field of view angle when the zoom lens is configured to have a second focal length; wherein the first focal length is smaller than the second focal length, and the first field angle is larger than the second field angle.
5. The variable focus depth measurement device of claim 1, wherein: the emission unit is configured to emit a floodlight beam and a speckle pattern beam toward a target area, and includes a light source array composed of a plurality of light sources and a liquid crystal element.
6. The depth measurement apparatus according to claim 5, wherein the TOF image sensor collects the reflected light beam within a small field angle by increasing a focal length of the zoom lens when the emission unit emits the spot pattern light beam toward the target area,
and when the transmitting unit transmits the floodlight beam towards the target area, the focal length of the zoom lens is reduced, so that the TOF image sensor collects the reflected light beam in a large field angle.
7. A variable focus depth measurement method, comprising the steps of:
controlling the emission unit to emit a light beam toward the target area; the emission unit comprises a light source and an optical element, and light beams emitted by the light source are projected to the target area after passing through the optical element;
controlling a receiving unit to collect at least part of the light beams reflected back by the target area and form an electric signal, wherein the receiving unit comprises a TOF image sensor and a zoom lens, and changing the angle of view of the TOF image sensor for collecting the reflected light beams by changing the focal length of the zoom lens;
and calculating the depth image of the target area according to the electric signal.
8. The variable focus depth measurement method of claim 7, wherein: the zoom lens comprises at least two adjustable focal lengths; alternatively, the zoom lens is configured to be continuously variable-focus.
9. The variable focus depth measurement method of claim 7, wherein: the TOF image sensor collects a reflected light beam within a first field angle when the zoom lens is configured to have a first focal length; the TOF image sensor collects a reflected light beam within a second field of view angle when the zoom lens is configured to have a second focal length; wherein the first focal length is smaller than the second focal length, and the first field angle is larger than the second field angle.
10. The variable focus depth measurement method of claim 9, wherein: further calculating a depth image of the target area by processing the electrical signal by a control and processing circuit and calculating a phase difference of the light beam received from emission to reflection, calculating a time of flight of the light beam based on the phase difference;
or processing the electric signal through a control and processing circuit, calculating the flight time of the light beam from emission to reception of reflection, and calculating the depth image of the target area according to the flight time.
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