RU2605628C1 - Method and optical device for determining distance to object - Google Patents

Abstract

FIELD: electronics.

SUBSTANCE: method of determining distances to objects includes a clock signal generation, modulation of the specified clock signal, the object is emitted with a modulated binary optical signal, a signal reflected from the object is received, calculated is correlation of the emitted and the reflected signals, calculated is the distance to the determined object as per a time delay of the reflected signal. Herewith created is at least one modulation as a pseudo-noise sequence matched with a cascade correlator. Performed is an integral accumulation of the reflected signal coming from the output of a photosensitive element. Performed is multiplexing of signals coming either from different photosensitive elements or from different pseudo-noise sequences.

EFFECT: technical result is increased dynamic range by reflected signals from objects and reduced power consumption of the device due to reduced load on computer modules.

16 cl, 6 tbl, 14 dwg

Description

FIELD OF THE INVENTION

This group of inventions relates to the field of measuring distances to an object using electromagnetic waves, and more particularly to optical devices, methods for determining distances to an object when a clock signal is generated, modulation of the specified clock signal is generated, a modulated binary optical signal is emitted to the object, and received by a photosensitive element the reflected optical signal from the object, the received reflected signal is converted from analog to digital, the correlation is calculated radiated on and reflected signals, calculate the distance to the object is determined from the time delay of the reflected signal. The invention can be used, for example, in a laser location.

The following terms are used in this description:

ADC - analog-to-digital converter.

CMOS (complementary metal-oxide-semiconductor structure; English CMOS, complementary metal-oxide-semiconductor) - electronic circuit design technology. A distinctive feature of CMOS circuits in comparison with bipolar technologies is the very low power consumption in static mode (in most cases, it can be assumed that energy is consumed only during state switching). CMOS circuits have high speed and low power consumption.

LADAR (LADAR) - a laser locator, an abbreviation for the Russian or English version of the "laser radar", where the radar from the English. radar (radio detection and ranging) - radio detection and ranging.

LIDAR (LIDAR transliteration. Light Identification Detection and Ranging - light detection and ranging) is a technology for obtaining and processing information about distant objects using active optical systems using the phenomena of light reflection and scattering in transparent and translucent media. Lidar as a device is, at a minimum, an active optical range finder. Usually in Russia, such devices are called laser rangefinders.

Pseudo-random (pseudo-noise) sequences are completely deterministic digital sequences that seem random to the outside observer.

Signal multiplexing - channel multiplexing, i.e. transmission of several streams of data signals on one channel.

Signal demultiplexing is the reverse operation.

VKF is a cross-correlation function. VKF Example:

, где [0, Т] интервал интегрирования, причем длительность опорного сигнала y(t), как правило, существенно меньше Т.

, where [0, T] is the integration interval, and the duration of the reference signal y (t), as a rule, is significantly less than T.

This is a mathematical operation, a measure of the similarity of 2 signals (reference and received), the maximum point of the correlation function corresponds to the point of minimum quadratic deviation between the signals.

A binary M-sequence or a maximum length sequence (MLS) is a pseudo-random binary sequence generated by a linear feedback shift register and having a maximum period N = p ⁿ -1, where n is an integer greater than 2 , and p is a prime number for the case of a binary sequence, equal to 2. For binary M - sequences written in the alphabet "0; 1 ”, the number of units is always greater by one than the number of zeros. When going to the alphabet "-1; 1 ”replace zero by one, and one by minus one.

The prior art method

According to a first of its aspects, the present invention relates to a method for determining distances to an object.

The distance to objects is measured by sending an optical signal, such as laser radiation, receiving a reflected signal, determining the delay time and calculating the distance from it.

So, in patent US 8537218, published in 2013, a method for determining distances to an object from a time delay is described, that is, determining a distance from an incoherent radiation source to a receiving matrix cell based on measuring the propagation time of an emitted pulse of incoherent radiation of a fixed duration T ₀ , while the pulse is emitted periodically. The receiving matrix and the emitter are located nearby. The measurement method is based on the fact that the exact distance to the object’s surface is defined as the transit time of the emitted pulse to the surface and the pulse reflected from it to the cells of the receiving matrix (in foreign patent literature it is designated as TOF - time of flight) multiplied by C / 2 (C - propagation velocity of electromagnetic radiation).

The method for determining TOF is that a priori the range of TOF = T ₁ + dt is known, where dt can vary from T ₁ to T ₁ + T ₀ . According to the patent US 8537218, the cell (pixel) of the receiving matrix contains one element generating a photocurrent (photo gate), and two structures (CMOS / MOS) that can accumulate, hold and remove charge Q. To determine dt in a period of time [T ₁ , T ₁ + T ₀ ], under the influence of control signals, the photo enters through the transfer gate 1 to the charge storage device Q ₁ , and in the period of time [T ₁ + T ₀ , T ₁ + 2 * T ₀ ] enters through the transfer gate 2 to the charge storage device Q ₂ . The charge stores act as integrators of the photocurrent on segments T ₀ . Draining gates are used to quickly remove accumulated charges Q ₁ and Q ₂ . The values of the accumulated charges Q ₁ and Q ₂ are used to determine dt by the following calculation:

dt = T ₀ (Q ₂ / (Q ₁ + Q ₂ )).

This method, as a rule, is used to determine the distance to the surface of objects in cases where T _{1 is} less than, or at least is, a multiple of the order of magnitude comparable with T ₀ . In the classification given in the Handbook of 3D Machine Vision - Optical Metrology and Imaging, edited by Song Zhang, published in 2013, this method is called “Time-Dependent Charge Detection”, which can be translated as determining charge dependent from time of flight (TOF). The frequency of the periodic charge accumulation Q in the cells of such a receiving matrix can reach 10-20 MHz.

To understand the essence of the method, we present an equivalent circuit (a signal integration unit at time intervals T ₀ ) that implements the pixel / cell functions of the receiving matrix and timing charts explaining the method implemented by this circuit.

A probe optical signal (impulse) of duration T _{0 is} radiated to the object (see figure 1, graph A).

The signal reflected from the object is delayed by the time T ₁ + dt (see figure 1, graph D).

The following method is used to determine dt.

According to the TX1 strobe pulse (see figure 1, graph B) of duration T ₀ delayed relative to the emitted signal (see figure 1, graph A) for a time T ₁ , the photocurrent is fed to integrator A (see figure 2). On the trailing edge of the TX1 strobe (see figure 1, graph B), a discrete readout Q _{1 is} read. Then, using the key S ₁ , the value is reset to the integrator A (see figure 2). The change in the signal at the output of the integrator A (see figure 2) is shown in graph D of figure 1.

According to the TX2 strobe pulse (see figure 1, graph B) of duration T ₀ delayed relative to the emitted signal (see figure 1, graph A) for a time T ₀ + T ₁ , the photocurrent is fed to integrator B (see figure 2). On the trailing edge of the TX2 strobe, a discrete sample Q _{2 is} read, then using the S ₂ key, the value is reset to the integrator B (see figure 2). The change in the signal at the output of the integrator B is shown in graph E of figure 1.

The delay of the reflected received signal relative to the probe is defined as

T _ass = T ₁ + dt,

where dt = T ₀ * Q ₂ / (Q ₁ + Q ₂ ) or dt = T ₀ * (1-Q ₁ / (Q ₁ + Q ₂ )).

On the graph W of figure 1 shows a graphical explanation of the method for determining dt.

Based on this method, there are methods and devices that have the following disadvantages:

- a small dynamic range of permitted targets, limited by the ability of the memory cell to accumulate a charge, which accordingly limits both the duration of the emitted signal and the maximum determined range to the object;

- inability to work in conditions of exposure from third-party radiation sources;

- a very small range (interval) of permitted ranges, equal to T ₀ * C / 2;

- a small value of the beginning of the range (interval) of permitted ranges, equal to T ₁ * C / 2, limited by the fact that the power of the received signal decreases back to the 4th degree from the distance to the object or TOF;

- the effect of induced interference associated with switching keys switching the photocurrent on the measurement results of Q ₁ and Q ₂ .

These shortcomings are solved in complex LIDAR and LADAR systems. They use high-frequency modulation of the emitted signals, but this significantly complicates the processing of the signals. In fact, each receiving cell needs its own radio frequency path.

To increase the measured range, the accumulation method is also used - multiple sounding of the target. Incoherent accumulation allows, subject to the statistical independence of the noise component in the received signal, to increase the signal-to-noise ratio by √N times. N is the number of soundings in the series (accumulation volume).

To increase the measurement of distances to the object, a periodic signal is applied, an example of a similar method for determining the range can be, for example, the method described in RF patent No. 2359228, published in 2009, or in international patent application WO / 2005/006016, published in 2005 .

However, this method has the disadvantage associated with a long time for determining the range, and due to the fact that the signal accumulation time is a multiple of the time of the recurrence period for sending probe pulses, the duration of which is equal to the maximum resolved range R _max times 2 / C. So, for R _max = 10 km, when the signal is accumulated over 200 recurrence periods, 13.4 ms will be required.

This disadvantage is eliminated by using the optical range modulated by the M-sequence as probing signals. This allows for the same power of the optical transmitter and the duration of the recurrence period to increase the energy of the probe signal in (N + 1) / 2, where N is the period of the M-sequence.

So, in patent US 6753950, published in 2004, describes a method for determining the distance to the object, which includes the following steps, in which:

- generate a clock signal,

- create a modulation of the specified clock signal,

- emit a modulated binary optical signal to the object,

- receive by means of the photosensitive element the reflected optical signal from the object,

- convert the received reflected signal from analog to digital,

- calculate the correlation of the emitted and reflected signals,

- calculate the distance to the determined object by the time delay of the reflected signal.

This method is the closest in technical essence and the achieved technical result and is selected for the prototype of the invention as a method.

The disadvantage of this prototype is that to increase the accuracy of determining the distance to the object, by finding the temporary position of the maximum cross-correlation, an increased frequency of quantization of time into discrete is used, equal to M / T ₀ , where T ₀ is the time interval of one position in the sequence of maximum length. This leads to a significant increase in energy consumption.

This is due to the fact that:

- to increase the accuracy of determining the distance, it is necessary to increase the clock frequency in M times. At the same time, the use of frequencies above 125 MHz, which is published, for example, in US Pat. No. 7,068,062, published in 2007, necessitates the use of expensive processors and ADCs with high power dissipation. In the patent, it is proposed to use an intermediate device of high-speed discrete-analog memory with subsequent multiplexing of data from a discrete analog memory device to an ADC converter to reduce the power dissipation for each ADC. In the patent US 7206062 it is indicated that for digitizing a signal with a frequency of 1 GHz using an ADC for 8-10 bits, an ADC will be required, scattering 0.5-6 W per one high-speed ADC. This technical solution leads to an increase in the processing time of the received signal.

The disadvantages of the prototype are the redundancy of calculations, so to calculate a single correlation reference for the initial rough determination of the range it is necessary to perform N addition operations. In addition, additional calculations are required to accurately determine the position of the correlation peak.

Another disadvantage is that the method described in the prototype has a limited range of the ratio of the amplitudes of the received signals, since if two or more reflected signals are received, then they can be distinguished after correlation processing only if the ratio of the amplitudes of the received signals is more than ~ 2 * √N, since limited by the level of the side lobes of the VKF between the pseudo-noise binary signal (for example, the M-sequence) in the alphabet {0, 1} and the same signal in the alphabet {-1, 1}.

Disclosure of the invention as a method

Based on this original observation, the present invention mainly aims to propose a method for determining distances to an object, which allows at least smoothing at least one of the above disadvantages, namely: increasing the dynamic range of the reflected signals from objects and reducing power consumption of the device by reducing the load on the computing modules, which is the technical task.

To achieve this goal, the method further comprises the following steps, in which:

- create at least one modulation in the form of a pseudo-noise sequence, consistent with the cascade calculator, configured to calculate the cross-correlation function of the emitted and received signals,

- produce integrated accumulation of the reflected signal coming from the output of the photosensitive element,

- multiplexing the signals coming from different M receiving elements, for which they feed the signals to the cascade computer through the multiplexer, providing the ability to calculate (process) one cascade computer many different discrete signals simultaneously.

Thanks to these advantageous characteristics, it becomes possible to organize a different scheme for determining the distance to the target, which is based on the possibility of using one cascade computer to simultaneously process many different, discrete signals coming from different receiving elements, which significantly reduces the number of operations and reduces power consumption. Indeed, TOF matrices usually do not allow working with frequencies above 10-20 MHz. At the same time, a cascade calculator can perform calculations using a clock frequency of 1 GHz or higher. This makes it possible to use the same cascade calculator for processing signals from multiple pixels (individual elements of the receiving matrix) or various pseudo-noise sequences.

So, if it is necessary to carry out calculations from M channels in parallel, then the number of delay clocks in all digital delay lines used in the cascade computer in each of the cascades should be increased M times. The signals in the cascade calculator are supplied through the multiplexer. This allows us to simplify processing and reduce the amount of memory used for computing, as well as increase the threshold threshold and dynamic range in terms of the amplitudes of the reflected signals from objects.

There is also an embodiment of the invention in which the signals from the first and second outputs of the cascade computer are sequentially accumulated, and additional pseudo noise additional sequences are used to modulate the probe signal.

Due to this advantageous characteristic, it becomes possible to suppress the component of background illumination in the signal and increase the dynamic range of the amplitudes of the received signals due to the mutual complete (in the absence of a noise component in the processed signal) or partial suppression of the side lobe of the VKF when summing the samples of the VKF from the first and second outputs of the cascade computer in accumulation unit.

There is, in addition, an embodiment of the invention in which an accumulation of a signal going to the input of a cascade computer is produced.

Due to this advantageous characteristic, it becomes possible to suppress the component of background illumination in the signal and increase the dynamic range of the amplitudes of the received signals by reducing the level of the side lobes of the accumulated signal and the matching sequence calculated by the cascade computer, and reduce the number of arithmetic operations performed by the cascade computer by several times.

There is another embodiment of the invention in which the demultiplexing of signals coming from the output of a cascade calculator or storage unit is performed.

Thanks to this advantageous characteristic, it becomes possible to group the processed samples according to their belonging to the corresponding receiving element or the corresponding processed sequence.

There is a variant of the invention in which two different modulations are created in the form of two additional pseudo-noise sequences, differing only in that in one of them the positions “0” are replaced by the positions “1”, and in the other position “0” is replaced by “-1” .

Due to this advantageous characteristic, it becomes possible to suppress the constant component in the signal (background light) calculated by the cascade computer and increase the dynamic range of the amplitudes of the received signals by reducing the level of the side lobes

There is also a variant of the invention in which various modulations are created in the form of additional pseudo-noise sequences, the number of which is a multiple of two.

Due to this advantageous characteristic, it becomes possible to completely suppress the component of the background illumination in the signal and increase the dynamic range of the amplitudes of the received signals due to the mutual complete (in the absence of a noise component in the processed signal) or partial suppression of the side lobes of the VKF when summing the samples of the VKF from the first and second outputs of the cascade computer in the accumulation unit. In addition, the use of various pseudo-noise sequences in each sensing cycle reduces the noise caused by the radiated probe signal from another source.

There is in addition a variant of the invention in which the elements for detecting the reflected signal on a gyrostabilized platform are sensitive to electromagnetic waves, including optical radiation.

Due to this advantageous characteristic, it becomes possible to expand the use of the proposed solution for vehicles moving in space, in particular for unmanned aerial vehicles, which can use the proposed solution as the basis for technical vision.

There is also an embodiment of the invention in which a polarizing filter is placed in front of the input of the optical signal to the photosensitive elements.

Thanks to this advantageous characteristic, it becomes possible to increase the ratio s / w and, therefore, increase the accuracy of measuring distances to reflective objects.

The set of essential features of the invention as a method is unknown from the prior art for methods of similar purpose, which allows us to conclude that the criterion of "novelty" for the invention. In addition, the set of essential features of the invention as a method is not obvious to a specialist, which allows us to conclude that the criterion of "inventive step" for the invention is met.

The prior art device

Another side of the present invention relates to an optical device for determining distances to an object.

In the patent US 6753950, published in 2004, describes an optical device for determining distances to an object, including:

- a radiation source to the object of a modulated binary optical signal, the input of which is connected to the first output

- modulation generator, the first input of which is connected to the output

- clock generator,

- a photosensitive element for detecting a reflected optical signal from an object whose output is connected to the first input

- a module for calculating the correlation of the emitted and reflected signals containing an analog-to-digital converter,

- the first output of the module for calculating the correlation of the emitted and reflected signals is connected to the input of the module for calculating the distance to the detected object by the time delay of the reflected signal, the first output of which is connected to the second input of the modulation generator, and the second output of which is connected to the second input of the module for calculating the correlation of reflected and reflected signals

- the second output of the modulation generator is connected to the third input of the module for calculating the correlation of the emitted and reflected signals.

This device is the closest in technical essence and the achieved technical result and is selected as a prototype of the invention as a device.

The disadvantage of this prototype is that to increase the accuracy of determining the distance to the object, by finding the temporary position of the maximum cross-correlation, an increased frequency of quantization of time into discrete is used, equal to M / T ₀ , where T ₀ is the time interval of one position in the sequence of maximum length. This leads to a significant increase in energy consumption.

This is due to the fact that:

- to increase the accuracy of determining the distance, it is necessary to increase the clock frequency in M times. At the same time, the use of frequencies above 125 MHz, which is published, for example, in US Pat. No. 7,068,062, published in 2007, necessitates the use of expensive processors and ADCs with high power dissipation. In the patent, it is proposed to use an intermediate device of high-speed discrete-analog memory with subsequent multiplexing of data from a discrete analog memory device to an ADC converter to reduce the power dissipation for each ADC. In the patent US 7206062 it is indicated that for digitizing a signal with a frequency of 1 GHz using an ADC for 8-10 bits, an ADC will be required, scattering 0.5-6 W per one high-speed ADC. This technical solution leads to an increase in the processing time of the received signal.

The disadvantage of the prototype is the redundancy of the calculations, so to calculate a single correlation reference for the initial rough determination of the range it is necessary to perform N addition operations. In addition, additional calculations are required to accurately determine the position of the correlation peak.

Another disadvantage is that the device described in the prototype has a limited range of the ratio of the amplitudes of the received signals, since if the device receives two or more reflected signals, then they can be distinguished after correlation processing only if the ratio of the amplitudes of the received signals is more than ~ 2 * √N, since it is limited by the level of the side lobes of the VKF between the pseudo-noise binary signal (for example, the M-sequence) in the alphabet {0, 1} and the same signal in the alphabet {-1, 1}.

Disclosure of the invention as a device

Based on this original observation, the present invention mainly aims to provide an optical device for determining distances to an object, which allows at least smoothing out at least one of the above disadvantages, namely, to increase the dynamic range by reflected signals from objects and reducing the power consumption of the device by reducing the load on the computing modules, which is the technical task.

To achieve this goal, the modulation generating generator is made in the form of a generator of at least one pseudo-noise sequence, matched with a cascade computer configured to calculate the cross-correlation function of the emitted and received signals. The output of the photosensitive element for detecting the reflected optical signal from the object is connected to the input of the integration module, the output of which is connected to the first input of the module for calculating the correlation of the emitted and reflected signals. The module for calculating the correlation of the emitted and reflected signals further comprises a series-connected multiplexer and a cascade computer.

Thanks to these advantageous characteristics, it becomes possible to organize a different scheme for determining the distance to the target, which is based on the possibility of using one cascade computer for simultaneous processing of many different, discrete signals coming either from various photosensitive elements or from various pseudo-noise sequences, which significantly reduces the number of operations, reduces Energy consumption. Indeed, TOF matrices usually do not allow working with frequencies above 10-20 MHz. At the same time, a cascade calculator can perform calculations using a clock frequency of 1 GHz or higher. This makes it possible to use the same cascade computer for processing signals from multiple pixels (individual elements of the receiving matrix) or various pseudo-noise sequences.

So if it is necessary to carry out calculations from M channels in parallel, the number of delay clocks in all digital delay lines used in the cascade computer in each of the cascades should be increased M times. The signals in the cascade calculator are supplied through the multiplexer. This simplifies processing and reduces the amount of memory used for computing.

There is also an embodiment of the invention, in which the module for calculating the correlation of the emitted and reflected signals further comprises a first storage unit, the input of which is connected to the output of the cascade computer.

Due to this advantageous characteristic, it becomes possible to suppress the component of the background illumination in the signal and increase the dynamic range of the amplitudes of the received signals by reducing the level of the side lobes of the accumulated signal and the matching sequence calculated by the cascade calculator.

There is also a variant of the invention, in which the module for calculating the correlation of the emitted and reflected signals further comprises a second storage unit, the output of which is connected to the input of the cascade computer, and the input of which is connected to the output of the multiplexer.

Due to this advantageous characteristic, it becomes possible to suppress the component of background illumination in the signal and increase the dynamic range of amplitudes of the received signals due to the complete suppression of the side lobes in the resulting sequence obtained by accumulating sequences from the VCF calculator.

There is also a variant of the invention, in which the module for calculating the correlation of the emitted and reflected signals further comprises a demultiplexer, the input of which is connected to the output of the first storage unit.

Thanks to this advantageous characteristic, it becomes possible to separate the signals after the cascade calculator according to their belonging to various sources.

There is also a variant of the invention, in which the modulation generator is made in the form of a generator of two additional pseudo-noise sequences, matched with a cascade computer.

Due to this advantageous characteristic, it becomes possible to suppress the constant component in the signal calculated by the cascade computer and increase the dynamic range of amplitudes of the received signals by reducing the side lobe level of the resulting VKF at the output of the VKF calculator.

There is also a variant of the invention, in which the modulation generator is made in the form of a generator of additional pseudo-noise sequences, the number of which is a multiple of two, matched with a cascade computer.

Due to this advantageous characteristic, it becomes possible to suppress the constant component in the signal calculated by the cascade computer and increase the dynamic range of the amplitudes of the received signals by completely suppressing the level of the side lobes in the resulting sequence obtained by accumulating sequences from the VCF computer.

There is also a variant of the invention in which the photosensitive element for detecting the reflected optical signal is located on a gyro-stabilized platform.

Due to this advantageous characteristic, it becomes possible to expand the use of the proposed solution for vehicles moving in space, in particular for unmanned aerial vehicles, which can use the proposed solution as the basis for technical vision.

There is also a variant of the invention in which the photosensitive element for detecting the reflected optical signal has a polarizing filter located in front of the input of the optical signal to the photosensitive element.

Due to this advantageous characteristic, it becomes possible to increase the signal-to-noise ratio and, therefore, increase the accuracy of measuring distances to reflecting objects.

The set of essential features of the present invention as a device is unknown from the prior art for devices of similar purpose, which allows us to conclude that the criterion of "novelty" for the invention. In addition, the set of essential features of the invention as a device is not obvious to a specialist, which allows us to conclude that the criterion of "inventive step" for the invention is met.

Brief Description of the Drawings

Other distinguishing features and advantages of this invention clearly follow from the description below for illustration and not being restrictive, with reference to the accompanying drawings, in which:

- figure 1 depicts time charts explaining the method of determining the distance implemented by the prior art,

- figure 2 depicts the unit of integration of the signal at time intervals T ₀ and the formation of discrete samples Q, according to the prior art,

- figure 3 depicts a functional diagram of an optical device for determining distances to an object according to the invention,

- figure 4 depicts a device for generating codes d ₁₀ , d ₁₁ ,

- figure 5 depicts a device for generating codes d ₂₀ , d ₂₁ , d ₂₂ , d ₂₃ ,

- figure 6 depicts a diagram of the cascade 2 of the cascade transmitter displayed in figure 7,

- figure 7 depicts a device that generates two additional D-sequences,

- figure 8 depicts a circuit cascade calculator VKF, allowing using a cascade calculator to calculate the four specified in table 3 VKF for their subsequent summation,

- figure 9 depicts a diagram of a cascade computer, consisting of nine cascades,

- figure 10 depicts a cross-correlation function,

- figure 11 depicts a cascade diagram obtained by permutation and connections between cascades,

- figure 12 depicts a minimax cross-correlation function,

- figure 13 depicts graphs B, E, K, O, which reflect the emitted signals modulated by sequences K1, K2, K3, K4, and the same signals reflected from the object (graphs B, G, L, P), the integration process received signals at time intervals of duration T ₀ (graphs G, Z, M, P), discrete samples obtained as a result of integration at intervals are shown respectively in graphs D, I, H, C. On graph A, clock pulses and their numbers are displayed, supplied to the modulation generator shown in FIG. 3,

- figure 14 shows the steps of the device according to the invention.

According to figure 3, the optical device for determining distances to the object includes a radiation source 1 to the object of a modulated binary optical signal, the input of which is connected to the first output of the modulation generator 2, the first input of which is connected to the output of the clock signal generator 3. The optical device for determining the distance to the object also includes a photosensitive element 4 for detecting the reflected optical signal from the object 5, the output of which is connected to the first input of the correlation calculation module 6 of the emitted and reflected signals containing the analog-to-digital converter 7. The first output of the correlation calculation module 6 the emitted and reflected signals is connected to the input of the module 8 for calculating the distance to the detected object by the time delay of the reflected signal.

The first output of module 8 is connected to the second input of the modulation generator 2, and the second output of generator 2 is connected to the second input of the module 6 for calculating the correlation of the emitted and reflected signals. The second output of module 8 is connected to the third input of the module for calculating the correlation of the emitted and reflected signals.

The generator 2 for creating modulation is made in the form of a generator of at least one pseudo-noise sequence, matched with a cascade computer 9. The output of the photosensitive element for detecting the reflected optical signal from the object is connected to the input of the integration module 10, the output of which is connected to the first input of the correlation calculation module 6 of the emitted and reflected signals. The module 6 for calculating the correlation of the emitted and reflected signals additionally contains a series-connected multiplexer 11 and a cascade calculator 9. (Modules 7 and 11 can be interchanged if the analog signal is multiplexed and a high-speed ADC is used).

The module 6 for calculating the correlation of the emitted and reflected signals may additionally contain a first storage unit 12, the output of which is connected to the input of the cascade computer VKF 9 (an example of the circuit of the cascade computer VKF is shown in Fig. 8), and the input of which is connected to the output of the multiplexer 11.

The module for calculating the correlation of the emitted and reflected signals may further comprise a second storage unit 13, the input of which is connected to the output of the cascade computer.

Module 6 for calculating the correlation of the emitted and reflected signals may additionally contain a demultiplexer 14, the input of which is connected to the output of the first storage unit 12.

The modulation generating generator can be made in the form of a generator of two additional pseudo-noise sequences, matched with the cascade computer 9.

The modulation generating generator can be made in the form of a generator of four additional pseudo-noise sequences, matched with a cascade computer 9.

The photosensitive detection element of the reflected optical signal can be located on a gyro-stabilized platform. Not shown in the figures.

The photosensitive element for detecting the reflected optical signal may have a polarizing filter placed in front of the input of the optical signal to the photosensitive element. Not shown in the figures.

The figure 8 shows the control unit of the cascade computer, the functions of which are performed by the module 8 for calculating the distance to the determined object from the time delay of the reflected signal, see Fig. 3.

The implementation of the invention

An optical device for determining distances to an object operates as follows. Here is the most comprehensive example of the invention, bearing in mind that this example does not limit the application of the invention. According to figure 14.

Stage E1. The generator 2 creates the modulation in the form of a binary pseudo-noise sequence, consistent with the cascade computer 9, and radiate it into space.

Stage E2. The signal reflected from the objects is received by the photosensitive detection element of the received signal 4.

Stage E3. Integration is carried out by block 10 at time intervals of duration T _{0 of the} reflected signal by the accumulation of capacitive charge.

Stage E4. Multiplex the integration results obtained in stage 3 on a high-speed ADC 7.

Stage E5. Convert the results of integration into a digital code (ADC block).

Stage E6. A digital code is supplied to the first accumulation unit 12, in which the discrete signal is accumulated by summing or subtracting the samples obtained from the output of the ADC 7 with the contents of the memory cells. Before starting the device, all memory cells of the first storage unit are reset.

Stage E7. Read the signal (sequence) accumulated in the memory cells of the accumulation unit 12, and feed it to the cascade calculator 9.

Stage E8. The sequence is supplied from the cascade calculator 9 to the second discrete signal accumulation unit 13 by adding or subtracting the samples received from the ADC output with the contents of the memory cells. Before starting the device, all memory cells of the first storage unit are reset.

Stage E9. The contents of the memory cells from the second storage unit 13 are demultiplexed (read in a specific order) to a threshold detector corresponding to a specific pixel (photosensitive detection element of the received signal 4).

Stage E10. If the threshold value is exceeded by one or two consecutive samples of the sample, the amplitudes and numbers of these samples are transmitted to the module 8 for calculating the distance to the determined object from the time delay of the reflected signal.

Stage E11. The distance to the reflecting object is calculated.

Stage E12. Repeat steps E1-E11.

Industrial applicability

The proposed optical device for determining the distances to the object can be implemented by a specialist in practice, and when implemented, it ensures the implementation of the declared purpose, which allows us to conclude that the criterion of "industrial applicability" for the invention is met.

In accordance with the proposed invention, calculations were made of the operation of the optical device to determine the distances to the object.

Calculations of the device showed that it provides the ability to:

- reducing the number of operations required to calculate the distance to the object,

- determination of distances exceeding the threshold range of the prototype.

We show this by example.

Device operation example

Additional sequences are known (see L. Varakin, “Communication Systems with Noise-Like Signals.” M.: Radio and Communications, 1985).

и

называются дополнительными, еслиThe sequence

and

are called optional if

при µ=0 или

при µ=+/-1, …, +/- (N-1), где

at µ = 0 or

for µ = + / - 1, ..., +/- (N-1), where

;

;

For example, sequences:

{1, 1, 1, -1, 1, 1, -1, 1}

{1, 1, 1, -1, -1, -1, 1, -1}

are optional.

The values of their autocorrelation functions, the sum of their ACF are given in table. one.

An example of such sequences are D codes.

Based on the rule of forming D-codes, it is possible to build an algorithm for their generation and calculation, based on the formation of them according to the rule of accession.

So, for the formation of codes d ₁₀ = {1, 1} and d ₁₁ = {- 1, 1}, you can use a circuit of one adder, one subtractor and a delay device for a sequence of one clock cycle (in Fig. 4, a delay of one clock cycle is indicated as Z ^-1 ). Having fed a single impulse to this device, we get output 1, the sequence {1, 1}, and output 2 {-1, 1}.

And to generate codes d ₂₀ , d ₂₁ , d ₂₂ , d _23, respectively, the device shown in figure 5.

At the output (1) we get the sequence {-1, 1, 1, 1}

At the output (2) we get the sequence {1, -1, 1, 1}

At the output (3) we get the sequence {1, 1, -1, 1}

At the output (4) we get the sequence {-1, -1, -1, 1}

It can be seen from the structure of the compounds that any D-sequence can be obtained by connecting typical elements consisting of two adders (one adder and one subtractor) and a delay line for 2 ^(i-1) clock cycles (where i = 1, 2, 3 is the number corresponding cascade). A diagram of such a device (cascade) is shown in FIG. 6.

Suppose you want to get two additional D-sequences of length 8: {-1, -1, -1, 1, 1, 1, -1, 1} and {1, 1, 1, -1, 1, 1, -1 , one}. A pair of such discrete additional sequences has the feature that, when summing their ACFs, we obtain the total ACF with a zero level of side lobes. This is used in radar to suppress side lobes by adding two mutual correlation functions obtained from processing 2 additional signals.

In FIG. Figure 7 shows a device generating these sequences.

The sequence {1, 0, 0, 0, 0, 0, 0, 0, 0} is fed to the input of the device.

In the first block (Cascade No. 1), the delay is 1 cycle, in the second (Cascade No. 2) by 2, in the 3rd (Cascade No. 3) by 4. From the first output we get the sequence

D1 = {- 1, -1, -1, 1, 1, 1, -1, 1}, and from the second

D2 = {1, 1, 1, -1, -1, -1, 1, -1}.

These sequences are optional.

Table 2 shows only part of the ACF.

The same device (in Fig. 7) is a matched filter for additional sequences obtained from the generated sequences D1 and D2 by rearranging them in the reverse order.

These sequences, let's call them DM1 and DM2, are also optional. DM1 = {1, -1, 1, 1, 1, -1, -1, -1, -1}; DM2 = {1, -1, 1, 1, -1, 1, 1, 1}.

If you apply the sequence DM1 and then DM2 to the input of such a device (see Fig. 7) and add the results from output 1 and output 2, we obtain a sequence consisting of zeros and one member of the sequence with an amplitude of 16.

Cascading allows you to reduce the calculation, so if N sequence length = 2 ⁱ , where i is the number of cascades connected in series.

Then, to calculate one sample, you need 2 * i addition operations, not 2 ⁱ .

It is possible to use a similar method for processing the received binary signals taking the values 0, 1. For this, four sequences consisting of zeros and ones are formed from two additional sequences.

The sequence K1 is obtained by replacing minus ones with zeros in the additional sequence DM1.

The sequence K2 is obtained by replacing units with zeros and replacing minus units with units in the additional sequence DM1.

The sequence K3 is obtained by replacing minus ones with zeros in the additional sequence DM2.

The sequence K4 is obtained by replacing units with zeros and replacing minus units with units in the additional sequence DM2.

Next, the sequences K1, K2, K3, K4 of zeros and ones are used to modulate optical signals that are sent to the object and received from the object using a TOF matrix pixel or other photodetector and sent to a cascade calculator.

Table 3 shows the VKF (cross-correlation functions) of the DM1 sequences with K1, -DM1 and K2, DM2 and K3 and VKF -DM2 and K4.

The sequence -DM1 is the inverted sequence of DM1, and -DM2 is the inverted sequence of DM2

To summarize four VKFs or more (if necessary, additional signal accumulation), an accumulation block is used in which the signal is accumulated in the memory register, in which each calculation clock corresponds to its own memory cell, to the contents of which a corresponding count from the output of the calculator is added. In FIG. Figure 8 shows the VKF calculator circuitry, which allows the calculation of the four VKF indicated in Table 3 for their subsequent summation. First, the K1 sequence and the sequence from the output 1 of the cascade 3 of the cascade calculator are fed to the accumulation block through the output switch to the accumulation unit, for summing 4 VKF. Then the sequence K2 and the sequence from the output 1 of the cascade 3 of the cascade calculator are fed through the output switch and inverted and fed to the accumulation block (in Fig. 9, inversion by multiplying all its terms by “-1”). Then the sequence K3 and the sequence from the output 2 of the cascade 3 of the cascade calculator are fed through the output switch to the accumulation unit. Then the sequence K4 and the sequence from the output 2 of the cascade 3 of the cascade calculator are fed through the switch of outputs and inverted and fed to the accumulation unit.

From DM codes, one can select DM codes in which the number of units is equal to the number “-1”. Such codes provide complete suppression of the filtering illumination of the DC component in the received optical signal, without the use of accumulation. This allows, if necessary, to abandon the accumulation of signals (sequences) from the outputs of the cascade computer, provided that the level of the side lobes of the VKF allows the resolution of signals from several reflecting objects.

When rearranging typical cascades in a cascade computer, by applying a single pulse to the input, codes with similar properties are also obtained. In addition, from these codes, by enumerating (interchanging delays in cascades and connecting cascades to each other), you can always select codes with a lowered level of side lobes of ACF and VKF (for the case of VKF, sequences of -1 and 1 obtained by applying a cascade calculator to the input a single pulse and a sequence of zeros and units obtained from the indicated sequence), which is at least 2 times lower than the level of side lobes for ACF and VKF codes obtained by applying to the input of a cascade computer in which The signal delay term is 2 ^(i-1) , where i is the number of the cascade, unit count (pulse).

If integer adders are used in cascades of a cascade calculator, then in order to avoid overflow of the adder registers after addition or subtraction operations, the register is shifted by one position, which is equivalent to division by 2.

There are 4 options for cascades in a cascade computer:

The delay block is located after input 1,

The delay block is located after input 2,

The delay unit is located in front of input 1,

The delay block is located in front of input 2.

The results of their use are similar.

Example 1. VKF without optimization by rearranging cascades and connection options

We feed to the input of the cascade computer (see Fig. 9), consisting of nine cascades in which the delays are set to 1, 2, 4, 8, 16, 32, 64, 128, 256, respectively, a single count. The sequence of 512 samples obtained from output 2 is read in the reverse order. In this case, minus units are replaced by zeros. We feed this sequence back to the input of the circuit shown in FIG. 9. As a result, we obtain a correlation response with an amplitude of 256 at the 512th step, while the amplitude of the side peaks of the calculated VKF will not exceed 37. This VKF is shown in figure 10. The abscissa axis shows the clock cycles of the calculator from Fig. 9, starting from the first. On the ordinate axis is the amplitude of the signal from the output of the calculator of Fig. 9.

Example 2. Minimax VKF

Example two differs from example one only in that it optimizes the resulting code by rearranging cascades and connections between cascades (the device in Fig. 11). In FIG. 12 shows the minimax FCF, which is obtained at the output of a cascade computer (see FIG. 11), in which the delays are as follows. In the first cascade, 128 cycles, in the second - 1, and so on, 64, 2, 32, 4, 16, 8, 256, and between the last and penultimate cascade of connections are made so that the first output of the penultimate cascade is connected to the second input of the last cascade and the second output of the penultimate stage is connected to the first input of the last stage.

We feed a single sample to the input of the optimized cascade calculator. The resulting sequence of 512 samples obtained at the output 2 is read in the reverse order, while minus one is replaced by zeros. We feed this sequence back to the input of the circuit shown in FIG. 11. As a result, I received a correlation response with an amplitude of 256 at the 512th cycle, while the amplitude of the side peaks of the calculated VKF will not exceed 17.

This VKF is shown in FIG. 12. On the abscissa, the clock cycles of the calculator of FIG. 11, starting from the first. On the ordinate axis, the signal amplitude from the output of the calculator of FIG. eleven.

Example 3. Using the first drive signal

The cascade calculator specified in Example 2 is used.

We feed a single sample to the input of the optimized cascade calculator. The resulting sequence of 512 samples obtained at the output 2 is read in the reverse order. From the obtained sequence we form 2 sequences, in the first of which “minus one” in the obtained sequence is replaced by “zeros”, and in the second “unit” we are replaced by “zeros”, and “minus one” by “ones”. To the obtained sequence members we add a constant value C, an analogue of the illumination signal. Next, we feed the members of sequence 1 into the first accumulation block, where the members of the sequence are written sequentially to memory cells. Next, we feed the 2nd sequence to the accumulation unit, while from each memory cell in the same order we read the members of sequence 1 and subtract the corresponding members of sequence 2 from them. (The result of the subtraction, if necessary, further accumulation, is written sequentially to the same memory cells). We feed the sequence representing the result of the subtraction to the cascade calculator from Example 2 (see Fig. 11). As a result, I received a correlation response with an amplitude of 512 at the 512th cycle, and the amplitude of the side peaks of the calculated VKF will not exceed 17. Thus, after the UBL of the resulting VKF, it decreased by 2 times (when using one sequence 17/256, and when using 2 with accumulation block 17/512).

Example 4. Using the second accumulation block

We use additional codes of length N = 4.

From them we get 4 additional sequences used to modulate the optical signal emitted to the object.

Further, the sequences K1, K2, K3, K4 are used to modulate the four optical signals emitted into space with an interval of more than T ₀ * N.

The emitted signal is received by the photosensitive element for detecting the received signal, integrated on the segments T ₀ .

Figure 13 depicts graphs B, E, K, O, which reflect the emitted signals modulated by the sequences K1, K2, K3, K4, and the same signals reflected from the object (graphs B, F, L, P), the integration process received signals (graphs G, Z, M, P), at time intervals of duration, discrete samples obtained as a result of integration at intervals are shown respectively in graphs D, I, H, C. On graph A, clock pulses and their numbers are shown a modulation generating generator 2 shown in FIG. 3.

As a result, discrete sequences are obtained. In FIG. 13 graphs are presented, which reflect the emitted sequences K1, K2, K3, K4 (graphs B, E, K, O in figure 13). And the same sequences received by the photosensitive element of the detection of the reflected optical signal with some delay that needs to be determined (graphs B, G, L, P in figure 13). The process of integration of the detected optical signal is also displayed (graphs G, Z, M, P in figure 13) and the discrete samples obtained as a result of integration on the segments T ₀ (graphs D, I, H, C in figure 13), which are then transmitted through the multiplexer and high-speed ADCs are fed to the computer VKF. The first discrete sequence obtained by detecting the reflected signal K1 is fed to a transverse filter, in which N (T = 4) discrete samples are added, namely, the sample supplied to the input of the filter with a weight coefficient {1}, the sample applied to the input earlier by 1 a clock cycle with a weight factor {1}, a count of the signal fed to the input earlier by 2 clock cycles of a clock with a weight factor {-1}, and a count of a clock fed earlier by 3 clock cycles with a weight coefficient {1}. Or in other words, we can say that the sequence is fed to a discrete transverse filter with a response to a single pulse {1, 0, 0, 0} equal to {1, 1, -1, 1}, i.e. corresponding to the code D1 indicated in the example, read in the reverse order.

The second discrete sequence obtained by detecting the reflected signal K2 is fed to a transverse filter with an impulse response {-1, -1, 1, -1}, i.e. corresponding to the code D1 indicated in the example, read in the reverse order and inverted.

The third discrete sequence obtained by detecting the reflected signal K3 is fed to a transverse filter with a pulse response {1, 1, 1, -1}, i.e. corresponding to the code D2 indicated in the example, read in the reverse order.

The fourth discrete sequence obtained by detecting the reflected signal K4 is fed to a transverse filter with an impulse response {-1, -1, -1, 1}, i.e. corresponding to the code D2 indicated in the example, read in the reverse order and inverted.

The four sequences from the outputs of the transverse filters are sequentially summed in the accumulation unit.

Table 6 shows the results of feeding the sequences obtained as a result of synchronous detection to transverse filters with corresponding weighting factors, and the resulting signal from the accumulation block used to determine the delay.

At the point in time corresponding to the 8th and 9th sync pulses, the threshold detector detected an excess of the threshold at the output of the accumulation block (the allowable threshold level of signal detection is 1, 0). We determine the distance to the object roughly by the number of the sync pulse at which the threshold detection occurred. The number of this clock in the example is 8.

Rgr. = ((m-1-N) T ₀ ) C / 2, where N is the number of positions 0 and 1 in the probe signal N = 4, and m is the number of the clock at which the threshold detection m = 8.

Rgr. = 3T ₀ C / 2

We determine the correction to the distance to the object using information about the amplitude of the second sample from the output of the accumulation block following the first sample that exceeds the threshold.

dR = Q2 / (Q1 + Q2) T ₀ = 5.3333 / (5.3333 + 2.6667) T ₀ = 0.6667 * T ₀ * C / 2, where Q1 is the amplitude of the first reference at the output of the accumulation side exceeding the threshold value (in table 6 is the count with number 8), and Q2 is the second following it.

The distance to the object Rtoch. = Rgr. + DR = 3,6667 * Т ₀ * С / 2.

Thus, in this invention, the goal is achieved - an increase in the dynamic range of reflected signals from objects and a reduction in the power consumption of the device by reducing the load on the computing modules.

In addition, it turned out that technical results such as:

- complete suppression of the side lobes in the sequence supplied to the threshold detector, which allows to increase the dynamic range in terms of the amplitude of the reflected signals from objects, the distance to which is determined.

- full (100%) suppression of the backlight signal.

It is recommended to use this invention for:

- laser ranging

- three-dimensional laser mapping,

- systems of technical vision, including and for aircraft, robotic systems, security systems and monitoring the movement of remote objects,

- reflectometry of optical fibers, finding defects in fiber optic cables,

- devices for fiber-optic monitoring of remote extended objects,

- in millimeter and submillimeter range radars with direct detection of signals from receiving elements (antennas) located in the form of a receiving matrix.

Claims (16)

1. The method of determining the distances to the object, which includes the following steps, in which:
- generate a clock signal,
- create a modulation of the specified clock signal,
- emit a modulated binary optical signal to the object,
- receive by means of the photosensitive element the reflected optical signal from the object,
- convert the received reflected signal from analog to digital,
- calculate the correlation of the emitted and reflected signals,
- calculate the distance to the determined object by the time delay of the reflected signal,
characterized in that
- create at least one modulation in the form of a pseudo-noise sequence, consistent with the cascade calculator, configured to calculate the cross-correlation function of the emitted and received signals,
- produce integrated accumulation of the reflected signal coming from the output of the photosensitive element,
- multiplexing the signals coming from different M receiving elements, for which they feed the signals to the cascade computer through the multiplexer, providing the ability to calculate (process) one cascade computer many different discrete signals simultaneously. 2. The method according to p. 1, characterized in that they produce sequential accumulation of signals coming from the first and second outputs of the cascade computer, while pseudo-noise additional sequences are used to modulate the probe signal. 3. The method according to p. 1, characterized in that the accumulation of the signal going to the input of the cascade computer. 4. The method according to p. 1, characterized in that they demultiplex the signals coming from the output of the cascade computer or accumulation unit. 5. The method according to p. 1, characterized in that they create two different modulations in the form of two additional pseudo-noise sequences, differing only in that in one of them the positions “0” are replaced by the positions “1”, and in the other position “0” replaced by "-1". 6. The method according to p. 1, characterized in that they create various modulations in additional pseudo-noise sequences, the number of which is a multiple of two. 7. The method according to p. 1, characterized in that they are sensitive to electromagnetic waves, including optical radiation, elements for detecting the reflected signal on a gyro-stabilized platform. 8. The method according to p. 1, characterized in that they have a polarizing filter in front of the input of the optical signal to the photosensitive elements. 9. An optical device for determining distances to an object, including:
- a radiation source to the object of a modulated binary optical signal, the input of which is connected to the first output
- modulation generator, the first input of which is connected to the output
- clock generator,
- a photosensitive element for detecting a reflected optical signal from an object whose output is connected to the first input
- a module for calculating the correlation of the emitted and reflected signals containing an analog-to-digital converter,
- the first output of the module for calculating the correlation of the emitted and reflected signals is connected to the input of the module for calculating the distance to the detected object by the time delay of the reflected signal, the first output of which is connected to the second input of the modulation generator, and the second output of which is connected to the second input of the module for calculating the correlation of reflected and reflected signals
- the second output of the modulation generator is connected to the third input of the module for calculating the correlation of the emitted and reflected signals,
characterized in that
- the generator for creating modulation is made in the form of a generator of at least one pseudo-noise sequence, consistent with the cascade computer,
- the output of the photosensitive element for detecting the reflected optical signal from the object is connected to the input of the integration module, the output of which is connected to the first input of the module for calculating the correlation of the emitted and reflected signals,
- the module for calculating the correlation of the emitted and reflected signals further comprises a series-connected multiplexer and a cascade calculator. 10. The optical device according to claim 9, characterized in that the module for calculating the correlation of the emitted and reflected signals further comprises a first storage unit, the output of which is connected to the input of the cascade computer, and the input of which is connected to the output of the multiplexer. 11. The optical device according to claim 10, characterized in that the module for calculating the correlation of the emitted and reflected signals further comprises a second storage unit, the input of which is connected to the output of the cascade computer. 12. The optical device according to claim 10, characterized in that the module for calculating the correlation of the emitted and reflected signals further comprises a demultiplexer, the input of which is connected to the output of the first storage unit. 13. The optical device according to p. 9, characterized in that the modulation generator is made in the form of a generator of two additional pseudo-noise sequences, matched with a cascade computer. 14. The optical device according to p. 9, characterized in that the modulation generator is made in the form of a generator of additional pseudo-noise sequences, the number of which is a multiple of two, matched with a cascade computer. 15. The optical device according to claim 9, characterized in that the photosensitive element for detecting the reflected optical signal is located on a gyro-stabilized platform. 16. The optical device according to claim 9, characterized in that the photosensitive element for detecting the reflected optical signal has a polarizing filter located in front of the input of the optical signal to the photosensitive element.

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