CN107515402A - TOF three-dimensional ranging system - Google Patents

Abstract

The invention belongs to the technical field of distance measuring systems, and particularly relates to a TOF three-dimensional distance measuring system which comprises an LED array light source, a signal processing circuit connected with the LED array light source and a CMOS photosensitive chip connected with the signal processing circuit, wherein a driving circuit is arranged between the signal processing circuit and the LED array light source, an emitting lens for collimating the light beam of the LED array light source is arranged in the emitting direction of the LED array light source, a signal conditioning circuit is arranged between the signal processing circuit and the CMOS photosensitive chip, and a receiving lens for focusing the reflected light beam is arranged in the receiving direction of the CMOS photosensitive chip. Compared with the prior art, the invention has the advantages that the measurement precision is high, the measurement distance is large, and the actual measurement distance can reach 15-25 m through the double control of the light source and the signal conditioning circuit. In addition, the measurement result of the invention is not influenced by the ambient light condition, thus meeting the requirements of the application scene of the automobile.

Description

A TOF three-dimensional ranging system

technical field

The invention belongs to the technical field of ranging systems, and in particular relates to a TOF three-dimensional ranging system.

Background technique

With the development of science and technology and the improvement of observation methods, people have deepened their research on optics. One of the signs is the accurate measurement of the speed of light propagation, and this data is used in various fields. Among them, using the propagation speed of light to measure the distance is an innovation in the distance measurement method, and this method is called Time of Flight (TOF) distance measurement method.

The goal of the time-of-flight (TOF) ranging method is to measure real-time information, which requires a modulated light source and a high-precision receiver. Light, the distance of the target can be calculated by calculating the time from the light emission to the receiver to receive the reflected light. 10 ^-8 m/s, so this method has high requirements on the speed and sensitivity of the receiver. In addition, the light source and the receiver must work at the same time to realize the function, so the TOF ranging method requires the cooperation of the light source and the receiver.

However, due to the limitation of the light receiving device, the traditional laser rangefinder can only measure the distance of a certain point, and can only obtain one-dimensional information. If you want to obtain three-dimensional information, the laser beam must scan the measured object from two directions. Adding a high-precision laser scanner to the rangefinder not only greatly increases the volume of the instrument, but also introduces vibration errors.

With the development and maturity of image sensor technology, new changes have appeared in time-of-flight ranging instruments. Compared with traditional ranging instruments, the image sensor of time-of-flight three-dimensional ranging instruments has been designed with unique functions, and each pixel is It is a complete demodulation receiver, so it is no longer necessary for the laser scanner to scan points one by one to form a three-dimensional image, but each pixel works in parallel to directly complete the real-time measurement of three-dimensional information.

The TOF three-dimensional ranging instrument has the advantages of miniaturization, high speed and low cost, and can perform image processing such as segmentation and tracking of the target image through distance information. In addition, multi-dimensional information acquisition enables the TOF three-dimensional ranging instrument to complete the analysis target Therefore, the TOF 3D ranging instrument has a very wide range of applications and can be combined with other media platforms for human-computer interaction, indoor ranging, machine vision, robotics, medical imaging, Fields such as video games and automotive electronics have very bright prospects for development.

The TOF three-dimensional ranging products of the prior art are mainly composed of a laser transmitter, a signal processor and a laser receiver, which can complete distance testing to a certain extent, but the TOF three-dimensional ranging products of the prior art are not suitable for long-distance laser ranging As far as the reflection conditions of the measured object are unknown and the reflected signal intensity changes greatly, the existing technology has no corresponding conditioning structure, which affects the accuracy and stability of the measurement to a certain extent, and the practicability is limited to a certain extent. limit.

In addition, because the existing TOF three-dimensional ranging products do not have supporting optical design, the working distance and the ability to resist ambient light need to be improved. The distance measurement range of the current TOF three-dimensional ranging products on the market is about 10 meters or even shorter. Moreover, when used under strong outdoor ambient light, there will be problems such as large data deviation and data loss, which prevents it from being widely promoted in the automotive field.

Contents of the invention

The purpose of the present invention is to provide a TOF three-dimensional distance measuring system to solve the problem that the measuring distance is not far, in view of the defects that the existing TOF three-dimensional distance measuring instrument has short measurement distance, is easily disturbed by ambient light, and has low measurement accuracy. Low measurement accuracy and poor stability.

In order to achieve the above object, the present invention adopts the following technical solutions:

A TOF three-dimensional ranging system, comprising an LED array light source, a signal processing circuit connected to the LED array light source, and a CMOS photosensitive chip connected to the signal processing circuit, the signal processing circuit and the LED array A driving circuit is provided between the light sources, a transmitting lens for collimating the light beam of the LED array light source is provided in the emission direction of the LED array light source, and a signal conditioning circuit is provided between the signal processing circuit and the CMOS photosensitive chip , a receiving lens for focusing the reflected light beam is provided in the receiving direction of the CMOS photosensitive chip;

The signal conditioning circuit includes a current-voltage conversion circuit, an impedance matching pre-amplification circuit electrically connected to the current-voltage conversion circuit, an adjustable gain amplification circuit electrically connected to the impedance matching pre-amplification circuit, and the adjustable An impedance matching circuit electrically connected to the adjustable gain amplifier circuit, the adjustable gain amplifier circuit is electrically connected to the gain amplifier control signal terminal of the signal processing circuit;

The modulation frequency of the modulated light emitted by the LED array light source is greater than 100MHz;

The power P _{source of the LED array light source} satisfies the relational expression:

in:

N _e is the number of electrons generated on the photosensitive chip pixel;

A _image is the area of the photosensitive chip; A _pix is the area of the photosensitive part of the photosensitive chip;

h is Planck's constant, c is the speed of light, and λ is the wavelength of the modulated light source;

ρ is the reflectivity of the object, and K _len is the passing efficiency of the receiving lens;

D is the diameter of the receiving lens, R is the distance from the measured object to the receiving lens;

T _int is the integration time;

QE(λ) is the quantum efficiency;

The divergence angle of the LED array light source is greater than θ, where θ satisfies the relational expression:

Among them: R is the object distance, f is the focal length of the receiving lens, p is the object height, and q is the image height.

As an improvement of the TOF three-dimensional ranging system of the present invention, it further includes a wireless signal receiving circuit electrically connected to the signal processing circuit.

As an improvement of the TOF three-dimensional ranging system of the present invention, it further includes an indicator circuit electrically connected to the signal processing circuit.

As an improvement of the TOF three-dimensional ranging system of the present invention, it further includes a communication interface circuit connected to the signal processing circuit.

As an improvement of the TOF three-dimensional distance measuring system of the present invention, the plane refraction surfaces of the front surfaces of the transmitting lens and the receiving lens and the free-form refraction surfaces of the rear surfaces of the lenses are in the shape of central axis symmetry.

As an improvement of the TOF three-dimensional distance measuring system in the present invention, the materials of the transmitting lens and the receiving lens are both PMMA, and the refractive index is n=1.4935.

As an improvement of the TOF three-dimensional ranging system of the present invention, the ranging range of the ranging system is 15-25m.

As an improvement of the TOF three-dimensional ranging system described in the present invention, the wavelength of light emitted by the LED array light source is in the infrared band.

As an improvement of the TOF three-dimensional ranging system of the present invention, the power P _source of the LED array light source is 100-150W.

As an improvement of the TOF three-dimensional ranging system of the present invention, the divergence angle of the LED array light source is greater than 8 degrees.

The beneficial effects of the present invention are: on the one hand, the present invention has a simple structure and is equipped with a signal conditioning circuit. For long-distance laser ranging, the received signal can be adjusted in time according to the intensity of the reflected signal of the measured object. To a certain extent, it can reduce the measurement error caused by signal distortion, effectively improve the accuracy and stability of ranging, and has strong applicability and practicality; on the other hand, this product effectively controls the frequency, power and The divergence angle makes the present invention have high measurement accuracy and large measurement distance, and the actual measurement distance can reach 15-25m. Therefore, through the dual control of the light source and the signal conditioning circuit, the present invention makes the measurement results of the present invention completely free from the interference of vibration, sound and other signals, greatly improving the stability of the product and the accuracy of measurement. In addition, the measurement results of the present invention are not affected by ambient light conditions, and can work stably regardless of day and night, summer, snow, desert and other scenarios, thus meeting the requirements of most automotive application scenarios.

Description of drawings

Fig. 1 is a structural block diagram of the present invention.

FIG. 2 is a structural block diagram of the signal conditioning circuit in FIG. 1 .

Fig. 3 is a schematic diagram of a Lambert reflection structure.

Fig. 4 is a diagram showing the relationship between the divergence angle of the light source and the imaging system.

In the figure: 1-LED array light source; 2-signal processing circuit; 3-CMOS photosensitive chip; 4-driving circuit; 5-transmitting lens; 6-signal conditioning circuit; 7-receiving lens; 8-wireless signal receiving circuit; 9 - indicator lamp circuit; 10 - communication interface circuit; 11 - measured object.

detailed description

In order to make the technical solutions and advantages of the present invention clearer, the present invention and its beneficial effects will be further described in detail below in conjunction with specific embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

As shown in Figures 1-2, a TOF three-dimensional ranging system of the present invention includes an LED array light source 1, a signal processing circuit 2 connected to the LED array light source 1, and a CMOS photosensitive chip 3 connected to the signal processing circuit 2, A driving circuit 4 is provided between the signal processing circuit 2 and the LED array light source 1, and an emitting lens 5 for collimating the light beam of the LED array light source 1 is provided in the emission direction of the LED array light source 1. Between the signal processing circuit 2 and the CMOS photosensitive A signal conditioning circuit 6 is provided between the chips 3, and a receiving lens 7 that focuses the reflected light beam is provided on the receiving direction of the CMOS photosensitive chip 3; The strength of the reflected signal of the measuring object 11 changes, and the received signal is adjusted in time, which can reduce the measurement error caused by the signal distortion to a certain extent.

The signal conditioning circuit 6 includes a current-voltage conversion circuit, an impedance matching pre-amplification circuit electrically connected to the current-voltage conversion circuit, an adjustable gain amplifying circuit electrically connected to the impedance matching pre-amplification circuit, and an adjustable gain amplifying circuit electrically connected to the adjustable gain amplifying circuit. The impedance matching circuit, the adjustable gain amplifier circuit is electrically connected to the gain amplifier control signal terminal of the signal processing circuit 2; when the signal amplitude is small, the signal gain needs to be increased; when the signal amplitude is too large, the signal gain needs to be reduced to achieve conditioning signal.

The system also includes a wireless signal receiving circuit 8 electrically connected to the signal processing circuit 2 , an indicator light circuit 9 electrically connected to the signal processing circuit 2 , and a communication interface circuit 10 connected to the signal processing circuit 2 .

Among them, the LED array light source 1 adds an aspheric emitting lens 5 to realize the convergence of emitted LED energy, reduces the divergence angle of the emitted energy, and increases the transmission distance of the optical signal; the CMOS photosensitive chip 3 adds an aspheric receiving lens 7 to realize the optical signal Collect and focus on the CMOS photosensitive chip 3, improve the utilization rate of light signals, and greatly enhance the detection distance.

Among them, the LED array light source 1 realizes the emission of 100-150 MHz pulse light signal required for TOF photoelectric distance measurement; the CMOS photosensitive chip 3 realizes the detection and reception of the transmitted light pulse signal required for TOF photoelectric distance measurement.

In addition, the power of the light source has a very important impact on the ranging system, and the power is high enough to make the CMOS photosensitive chip 3 generate enough photo-generated electrons, so as to realize the function of measuring distance information. The power of the light source is related to many factors, such as the quantum efficiency of the photosensitive chip, the size of the pixel array, the distance of the target and the parameters of the lens, etc., so the selection of the power of the light source should consider the relevant parameters of the entire system.

First consider the relationship between the light reflected by the object and the light entering the lens. The reflection process can be regarded as Lambert reflection, that is, the reflected light is evenly distributed in space, and the light intensity entering the lens is proportional to the cosine of the angle _θc , as shown in Figure 3 , which can be expressed as a formula:

in:

P _len is the optical power entering the lens.

P _ob is the optical power reflected by the object.

D is the lens diameter, R is the distance from the measured object to the lens.

Considering the reflectivity of the object and the loss of light passing through the lens, the light power on the pixel is:

Among them: ρ is the reflectivity of the object, and K _len is the passing efficiency of the lens.

A _image is the area of the photosensitive chip; A _pix is the area of the photosensitive part of the photosensitive chip.

It can be seen from the formula that if you want to calculate the power of the required modulated light source, you need to know the light power P _pixel irradiated on the pixel array. If you know the number of electrons generated on each pixel, you can calculate P _pixel . You can use The following formula expresses:

Wherein: N _e is the number of electrons generated on the photosensitive chip pixel; N _p is the number of photons.

E _pix is the energy impinging on the pixel and E _pho is the energy of the photon.

T _int is the integration time.

h is Planck's constant, c is the speed of light, and λ is the wavelength of the modulated light source.

QE(λ) is the quantum efficiency.

In summary, the formula for modulating the light source power can be deduced:

Wherein, for Lambert reflection, the reflection coefficient of the object is between 0 and 1.

In addition, when measuring the distance information of an object, in addition to ensuring that the light source has a suitable optical power, it is also necessary to ensure that the target in the field of view of the pixel array is within the irradiation range of the light source, otherwise the target cannot reflect the modulated light, and the chip cannot receive the modulated information. , which affects the measurement results. As shown in Figure 4, the angle θ can be used to measure the coverage of the light source. As long as the divergence angle of the light source is greater than the angle θ, the irradiation range of the light source can cover the field of view of the chip. Among them, the angle θ can be expressed by the following formula:

Among them: R is the object distance, f is the focal length of the lens, p is the object height, and q is the image height.

As a preferred version of the present invention, the front surface plane refraction surface and the free-form surface refraction surface of the lens rear surface of the transmitting lens 5 and the receiving lens 7 are central axisymmetric shapes; the materials of the transmitting lens 5 and the receiving lens 7 are PMMA, and the refractive index is n=1.4935.

As a preferred solution of the present invention, the wavelength of light emitted by the LED array light source 1 is in the infrared band; the power P _source of the LED array light source 1 is 100-150 W; and the divergence angle of the LED array light source 1 is greater than 8 degrees.

According to the disclosure and teaching of the above specification, those skilled in the art to which the present invention pertains can also change and modify the above embodiment. Therefore, the present invention is not limited to the above-mentioned specific implementation manners, and any obvious improvement, substitution or modification made by those skilled in the art on the basis of the present invention shall fall within the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims (10)

1. A TOF three-dimensional ranging system, characterized in that: comprise an LED array light source, a signal processing circuit connected with the LED array light source and a CMOS photosensitive chip connected with the signal processing circuit, in the signal processing A driving circuit is provided between the circuit and the LED array light source, and an emitting lens for collimating the light beam of the LED array light source is provided in the emitting direction of the LED array light source, and between the signal processing circuit and the CMOS photosensitive chip A signal conditioning circuit is provided between them, and a receiving lens for focusing the reflected light beam is provided in the receiving direction of the CMOS photosensitive chip; The signal conditioning circuit includes a current-voltage conversion circuit, an impedance matching pre-amplification circuit electrically connected to the current-voltage conversion circuit, an adjustable gain amplification circuit electrically connected to the impedance matching pre-amplification circuit, and the adjustable An impedance matching circuit electrically connected to the adjustable gain amplifier circuit, the adjustable gain amplifier circuit is electrically connected to the gain amplifier control signal terminal of the signal processing circuit; The modulation frequency of the modulated light emitted by the LED array light source is greater than 100MHz; The power P _{source of the LED array light source} satisfies the relational expression: <mrow><msub><mi>P</mi><mrow><mi>s</mi><mi>o</mi><mi>u</mi><mi>r</mi><mi>c</mi><mi>e</mi></mrow></msub><mo>=</mo><mfrac><mrow><msub><mi>N</mi><mi>e</mi></msub><mo>&amp;CenterDot;</mo><mfrac><msub><mi>A</mi><mrow><mi>i</mi><mi>m</mi><mi>a</mi><mi>g</mi><mi>e</mi></mrow></msub><msub><mi>A</mi><mrow><mi>p</mi><mi>i</mi><mi>x</mi></mrow></msub></mfrac><mo>&amp;CenterDot;</mo><mi>h</mi><mo>&amp;CenterDot;</mo><mi>c</mi></mrow><mrow><mi>&amp;rho;</mi><mo>&amp;CenterDot;</mo><msup><mrow><mo>(</mo><mfrac><mi>D</mi><mrow><mn>2</mn><mo>&amp;CenterDot;</mo><mi>R</mi></mrow></mfrac><mo>)</mo></mrow><mn>2</mn></msup><mo>&amp;CenterDot;</mo><msub><mi>K</mi><mrow><mi>l</mi><mi>e</mi><mi>n</mi></mrow></msub><mo>&amp;CenterDot;</mo><mi>Q</mi><mi>E</mi><mrow><mo>(</mo><mi>&amp;lambda;</mi><mo>)</mo></mrow><mo>&amp;CenterDot;</mo><mi>&amp;lambda;</mi><mo>&amp;CenterDot;</mo><msub><mi>T</mo>mi><mi>int</mi></msub></mrow></mfrac><mo>;</mo></mrow> in: N _e is the number of electrons generated on the photosensitive chip pixel; A _image is the area of the photosensitive chip; A _pix is the area of the photosensitive part of the photosensitive chip; h is Planck's constant, c is the speed of light, and λ is the wavelength of the modulated light source; ρ is the reflectivity of the object, and K _len is the passing efficiency of the receiving lens; D is the diameter of the receiving lens, R is the distance from the measured object to the receiving lens; T _int is the integration time; QE(λ) is the quantum efficiency; The divergence angle of the LED array light source is greater than θ, where θ satisfies the relational expression: <mrow><mi>&amp;theta;</mi><mo>=</mo><mi>arctan</mi><mrow><mo>(</mo><mfrac><mi>p</mo>mi><mn>2</mn></mfrac><mo>/</mo><mi>R</mi><mo>)</mo></mrow><mo>;</mo></mrow> <mrow><mfrac><mi>R</mi><mi>f</mi></mfrac><mo>=</mo><mfrac><mi>p</mi><mi>q</mi></mfrac><mo>;</mo></mrow> Among them: R is the object distance, f is the focal length of the receiving lens, p is the object height, and q is the image height. 2. The TOF three-dimensional ranging system according to claim 1, further comprising a wireless signal receiving circuit electrically connected to the signal processing circuit. 3. The TOF three-dimensional ranging system according to claim 1, further comprising an indicator light circuit electrically connected to the signal processing circuit. 4. The TOF three-dimensional ranging system according to claim 1, further comprising a communication interface circuit connected to the signal processing circuit. 5. The TOF three-dimensional distance measuring system according to claim 1, characterized in that: the plane refraction surface of the front surface of the transmitting lens and the receiving lens and the free-form refraction surface of the rear surface of the lens are central axis-symmetrical shapes. 6. The TOF three-dimensional ranging system according to claim 1, characterized in that: the materials of the transmitting lens and the receiving lens are both PMMA, and the refractive index is n=1.4935. 7. The TOF three-dimensional ranging system according to claim 1, characterized in that: the ranging range of the ranging system is 15-25m. 8. The TOF three-dimensional ranging system according to claim 1, characterized in that: the wavelength of light emitted by the LED array light source is in the infrared band. 9. The TOF three-dimensional ranging system according to claim 1, characterized in that: the power P _source of the LED array light source is 100-150W. 10. The TOF three-dimensional ranging system according to claim 1, characterized in that: the divergence angle of the LED array light source is greater than 8 degrees.