JP6021324B2 - Laser radar equipment - Google Patents

Description

  The present invention relates to a laser radar device that derives a distance to a measurement object from a difference between a transmission time of laser light and a reception time of reflected light.

For example, in the laser radar device disclosed in Patent Document 1 below, an environmental condition detection unit that detects a change in the surrounding environment due to snow or rain is provided, and when the environmental condition detection unit detects a change in the surrounding environment, The scanning speed of the scanning unit is slowed down, and the period for opening the gate circuit is lengthened so as to correspond to the scanning speed.
As described above, since the amount of the received light signal of the reflected light is increased by increasing the period of opening the gate circuit, the threshold determination unit compares the signal intensity with the threshold value, and determines the received signal of the reflected light from the measurement object. When extracting, it is possible to reduce the probability of erroneously extracting the received signal of the reflected light from the noise factor.

However, for example, in an environment where the propagation loss of laser light energy is large, such as in the sea, in general, as the distance from the laser light transmission point increases, the signal is attenuated due to light intensity attenuation caused by the medium on the propagation path. The intensity decreases exponentially.
For this reason, on the path to the object to be measured, there is a marine snow in the sea, an environment where there are relatively large noise factors such as rain, snow, hail in the atmosphere, or on the propagation path of the laser beam. In an environment where backscattered light is generated in the medium, as shown in FIG. 10, the signal intensity of reflected light from noise factors and the signal intensity level of backscattered light are higher than the signal intensity of reflected light from the measurement object. growing.

JP-A-10-197635 (paragraph number [0008], FIG. 3)

  Since the conventional laser radar apparatus is configured as described above, in an environment where there is a noise factor having a relatively large particle diameter or an environment where backscattered light is generated, the laser scanning speed is reduced to reduce the gate. Even if the period for opening the circuit is lengthened, the loss of the signal amount depending on the distance is not improved. For this reason, even if a large threshold value is set, erroneous detection of unnecessary signals from noise factors, etc. existing in front of the measurement object is caused, and the distance to the measurement object cannot be accurately derived. There was a problem.

  The present invention has been made to solve the above-described problems, and the distance to the measurement object can be accurately determined even in an environment where there is a noise factor having a relatively large particle diameter or an environment where backscattered light is generated. An object is to obtain a laser radar device that can be derived.

The laser radar device according to the present invention is a transmission optical system that irradiates a measurement target with pulsed laser light, and is reflected by the measurement target every time one pulse of laser light is emitted from the transmission optical system. The received optical signal received by the receiving optical system is sampled at the current sampling timing in synchronization with the receiving optical system that receives the reflected light of the laser beam and the pulse signal output from the clock circuit. If the signal strength of the received signal of this sampling that is the received signal is lower than the signal strength of the received signal of the previous sampling that is the received signal sampled at the previous sampling timing, the signal strength of the received signal of the previous sampling is Divide by the signal strength of the received signal and divide the logarithm of the division result by the speed of light. An attenuation coefficient calculating means for calculating the attenuation coefficient of the energy of the laser beam caused by the medium on the propagation path by dividing by the time difference between the reception time of the reception signal of the pulling and the reception time of the reception signal of the current sampling; The bias is calculated by multiplying the difference between the transmission time of the laser beam corresponding to the reception signal of the sampling this time and the reception time of the reception signal, the attenuation coefficient calculated by the attenuation coefficient calculation means, and the speed of light, By applying the bias to the received signal of this sampling, the signal strength compensation means for compensating the signal strength of the received signal, and the received signal whose signal strength is compensated by the signal strength compensation means are applied to the measurement object. The received signal is extracted, and the distance to the measurement object is derived from the difference between the transmission time of the laser beam corresponding to the received signal and the received time of the received signal. Attenuation coefficient calculating means comprising: a separation deriving means; and an image generating means for imaging the measurement object from the distance derived by the distance deriving means and the signal strength of the received signal whose signal strength is compensated by the signal strength compensating means. However, the average value of the attenuation coefficient per pulse is calculated, the moving average process is performed on the average value of the attenuation coefficient, and the signal strength compensating means uses the attenuation coefficient after the moving average process by the attenuation coefficient calculating means. Thus, the bias is calculated.

According to the present invention, the received signal of the reflected light received by the receiving optical system is sampled in synchronization with the pulse signal output from the clock circuit , and the reception of the current sampling that is the received signal sampled at the current sampling timing is received. If the signal strength of the signal is lower than the signal strength of the reception signal of the previous sampling that is the reception signal sampled at the previous sampling timing, the signal strength of the reception signal of the previous sampling is divided by the signal strength of the reception signal of the current sampling, The logarithm of the division result is divided by the speed of light, and the laser light caused by the medium on the propagation path is divided by the time difference between the reception time of the reception signal of the previous sampling and the reception time of the reception signal of the current sampling. Attenuation coefficient calculation means for calculating the attenuation coefficient of the energy of The bias is calculated by multiplying the difference between the transmission time of the laser beam corresponding to the received signal of the optical signal and the reception time of the received signal, the attenuation coefficient calculated by the attenuation coefficient calculating means, and the speed of light. Is applied to the received signal of the current sampling to provide a signal strength compensating means for compensating the signal strength of the received signal, and the distance deriving means is selected from the received signals whose signal strength is compensated by the signal strength compensating means. Since the reception signal related to the measurement object is extracted and the difference between the transmission time of the laser beam corresponding to the reception signal and the reception time of the reception signal is configured to derive the distance to the measurement object, There is an effect that the distance to the measurement object can be accurately derived even in an environment where a noise factor having a relatively large particle size exists or in an environment where backscattered light is generated.

It is a block diagram which shows the laser radar apparatus by Embodiment 1 of this invention. It is a block diagram which shows the sampling circuit 9 of the laser radar apparatus by Embodiment 1 of this invention. It is a block diagram which shows the distance attenuation | damping estimation circuit 10 of the laser radar apparatus by Embodiment 1 of this invention. It is a block diagram which shows the gain circuit 11 of the laser radar apparatus by Embodiment 1 of this invention. It is a block diagram which shows the distance and intensity | strength detection circuit 13 of the laser radar apparatus by Embodiment 1 of this invention. It is a flowchart which shows the processing content of the distance attenuation | damping estimation circuit 10 of the laser radar apparatus by Embodiment 1 of this invention. It is explanatory drawing which shows the received signal before and after intensity compensation for a propagation loss. It is a block diagram which shows the sampling circuit 9 of the laser radar apparatus by Embodiment 2 of this invention. It is a block diagram which shows the distance attenuation | damping estimation circuit 10 of the laser radar apparatus by Embodiment 3 of this invention. It is explanatory drawing which shows a received signal when a laser beam is radiated | emitted in space in the environment where the noise factor with a comparatively large particle size exists, or the environment where backscattered light generate | occur | produces.

Embodiment 1 FIG.
1 is a block diagram showing a laser radar apparatus according to Embodiment 1 of the present invention.
In FIG. 1, a laser beam output unit 1 is composed of a laser driver 2 and a laser oscillator 3, which outputs a pulse oscillation trigger signal c and outputs a pulsed laser beam in synchronization with the pulse oscillation trigger signal c. Perform the process of oscillation.
When the laser driver 2 irradiates one pulse of laser light from the transmission optical system 4, the laser driver 2 performs a process of outputting a pulse oscillation trigger signal c to the laser oscillator 3, the signal intensity compensation unit 8, and the image processing unit 12.
The laser oscillator 3 is an oscillator that outputs one pulse of laser light to the transmission optical system 4 every time the pulse oscillation trigger signal c is received from the laser driver 2.

The transmission optical system 4 shapes the beam shape of the pulsed laser beam output from the laser oscillator 3, and irradiates the shaped laser beam toward the measurement object while scanning the measurement range with an internal beam scanner. At the same time, a process of outputting the scan angle of the beam scanner to the image processing unit 12 is performed.
The laser beam receiver 5 includes a receiving optical system 6 and a light receiver 7. The receiving optical system 6 receives the reflected light of the laser beam reflected by the measurement object after being irradiated from the transmitting optical system 4. Perform the process.
The light receiver 7 converts the reflected light received by the receiving optical system 6 into an electrical signal, and performs a process of outputting the received signal d, which is the electrical signal, to the signal intensity compensator 8.

The signal intensity compensator 8 includes a sampling circuit 9, a distance attenuation estimation circuit 10, and a gain circuit 11. The signal intensity compensation unit 8 calculates the attenuation coefficient of the energy of the laser beam due to the medium on the propagation path, and calculates the attenuation coefficient. The processing for compensating the signal intensity of the reception signal d output from the light receiver 7 is performed.
The sampling circuit 9 performs a process of A / D converting the reception signal d output from the light receiver 7 and outputting the sampling data f that is the digital reception signal d to the distance attenuation estimation circuit 10.

The distance attenuation estimation circuit 10 is output this time when the signal strength of the reception signal d indicated by the sampling data f output this time from the sampling circuit 9 is lower than the signal strength of the reception signal d indicated by the sampling data f output last time. Along with the reception time of the reception signal d indicated by the sampling data f, processing for storing the sampling data f in the internal memory is performed.
Further, the distance attenuation estimation circuit 10 uses the signal intensity of the reception signal d indicated by the sampling data f stored in the internal memory and the reception time, and the attenuation coefficient g of the energy of the laser beam caused by the medium on the propagation path. The process of calculating is performed.
The sampling circuit 9 and the distance attenuation estimation circuit 10 constitute attenuation coefficient calculation means.

  The gain circuit 11 uses the attenuation coefficient g calculated by the distance attenuation estimation circuit 10 to compensate the signal strength of the reception signal d output from the light receiver 7 and outputs the received signal e after the intensity compensation. To do. The gain circuit 11 constitutes signal strength compensation means.

The image processing unit 12 includes a distance / intensity detection circuit 13 and an image processing circuit 14, and performs a process of generating a two-dimensional image and a three-dimensional image showing a measurement object.
The distance / intensity detection circuit 13 extracts a reception signal related to the measurement object from the reception signal e whose signal intensity has been compensated by the gain circuit 11, and transmits a transmission time T _tx of the laser beam corresponding to the reception signal; From the time difference ΔT with the reception time T _rx of the received signal, a process for deriving the distance L to the measurement object is performed. The distance / intensity detection circuit 13 constitutes a distance deriving unit.

  The image processing circuit 14 uses the distance L derived by the distance / intensity detection circuit 13 and the signal intensity S of the received signal related to the measurement object extracted by the distance / intensity detection circuit 13 to determine the beam scanner of the transmission optical system 4. The measurement object is imaged based on the scan angle, and processing for generating a two-dimensional image and a three-dimensional image showing the measurement object is performed. The image processing circuit 14 constitutes image generation means.

In the example of FIG. 1, each of the laser beam output unit 1, the transmission optical system 4, the laser beam reception unit 5, the signal intensity compensation unit 8, and the image processing unit 12, which are components of the laser radar apparatus, has dedicated hardware (for example, In this example, a semiconductor integrated circuit on which a CPU is mounted or a one-chip microcomputer) is assumed, but the laser radar device may be configured by a computer.
When the laser radar device is constituted by a computer, a program in which the processing contents of the laser light output unit 1, the transmission optical system 4, the laser light reception unit 5, the signal intensity compensation unit 8 and the image processing unit 12 are described is stored in the computer. The CPU of the computer may execute the program stored in the memory.

FIG. 2 is a block diagram showing a sampling circuit 9 of the laser radar apparatus according to Embodiment 1 of the present invention.
In FIG. 2, the clock circuit 21 performs a process of outputting a pulse signal a having a predetermined time period.
The A / D conversion circuit 22 performs A / D conversion on the analog reception signal d output from the light receiver 7 in synchronization with the pulse signal a output from the clock circuit 21 to obtain sampling data which is a digital reception signal d. A process of outputting f to the distance attenuation estimation circuit 10 is performed.

FIG. 3 is a block diagram showing the distance attenuation estimation circuit 10 of the laser radar apparatus according to Embodiment 1 of the present invention.
In FIG. 3, when receiving a pulse oscillation trigger signal c from the laser driver 2, the clock circuit 31 performs a process of outputting a pulse signal having a predetermined time period.
The time measuring circuit 32 counts the number of pulses output from the clock circuit 31, so that the pulse oscillation trigger signal c is output from the laser driver 2 (≈when the laser light is emitted from the transmission optical system 4). The process of measuring the elapsed time from is implemented.

  When the signal strength of the reception signal d indicated by the sampling data f output this time from the sampling circuit 9 is higher than the signal strength of the reception signal d indicated by the sampling data f output last time, the filter circuit 33 outputs the sampling data output this time. When the signal strength of the received signal d indicated by the sampling data f output this time is lower than the signal strength of the received signal d indicated by the previously output sampling data f, the f is discarded. In addition, time information indicating the elapsed time measured by the time measuring circuit 32 is added, a signal input order number is assigned, and the sampling data f is stored in the internal memory 34.

The internal memory 34 is a recording medium that stores sampling data f with time information in ascending order of assigned numbers.
The logarithmic arithmetic circuit 35 takes out two pieces of sampling data f from the sampling data f stored in the internal memory 34 in ascending order of the assigned numbers, and the smaller of the two sampling data f has the smaller number. The signal strength of the received signal d indicated by the sampling data f indicated by the sampling data f is divided by the signal strength of the received signal d indicated by the sampling data f having the larger number, and the logarithm of the division result is calculated.

The division circuit 36 obtains the difference in elapsed time indicated by the time information added to the two sampling data f taken out by the logarithmic operation circuit 35, divides the operation result of the logarithmic operation circuit 35 by the difference in elapsed time, A process of calculating an attenuation coefficient α between two sampling data f is performed by dividing by a constant speed of light.
Whenever the division circuit 36 calculates the attenuation coefficient α between the two sampling data f, the average arithmetic circuit 37 performs a process of calculating an average value of the attenuation coefficients α. The average value of the attenuation coefficient α calculated by the average calculation circuit 37 is a value indicating the average of the attenuation coefficient α during the time when one pulse of laser light is output from the laser oscillator 3.

The internal memory 38 is a recording medium that stores the average value of the attenuation coefficient α calculated by the average calculation circuit 37.
The moving average calculation circuit 39 performs a moving average process on the average value of the attenuation coefficient α stored in the internal memory 38, and executes a process of outputting the attenuation coefficient α after the moving average process to the gain circuit 11 as the attenuation coefficient g. To do.
FIG. 6 is a flowchart showing the processing contents of the distance attenuation estimation circuit 10 of the laser radar apparatus according to Embodiment 1 of the present invention.

FIG. 4 is a block diagram showing the gain circuit 11 of the laser radar apparatus according to Embodiment 1 of the present invention.
In FIG. 4, when receiving a pulse oscillation trigger signal c from the laser driver 2, the clock circuit 41 performs a process of outputting a pulse signal having a predetermined time period.
The bias calculation circuit 42 counts the number of pulses output from the clock circuit 41, so that the time point when the pulse oscillation trigger signal c is output from the laser driver 2 (≈ time point when the laser light is emitted from the transmission optical system 4). The process of measuring the elapsed time from the time and calculating the bias V applied to the variable gain circuit 43 using the elapsed time and the attenuation coefficient g calculated by the distance attenuation estimation circuit 10 is performed.
The variable gain circuit 43 applies the bias V calculated by the bias calculation circuit 42 to the reception signal d output from the light receiver 7, thereby compensating the signal intensity of the reception signal d and receiving signal e after the intensity compensation. Is output to the distance / intensity detection circuit 13.

FIG. 5 is a block diagram showing the distance / intensity detection circuit 13 of the laser radar apparatus according to Embodiment 1 of the present invention.
In FIG. 5, when receiving a pulse oscillation trigger signal c from the laser driver 2, the clock circuit 51 performs a process of outputting a pulse signal having a predetermined time period.
The peak detection circuit 52 is a peak hold circuit that starts operation at the input timing of the pulse signal output from the clock circuit 51 and discharges after a predetermined time. Among the received signals e whose signal strength is compensated by the gain circuit 11, The process which detects the peak value of is implemented.

The comparator 53 is set with a threshold value for sorting the received signal and the unnecessary signal related to the measurement object. The comparator 53 compares the peak value detected by the peak detection circuit 52 with the threshold value, and if the peak value is larger than the threshold value, Processing for storing the peak value in the internal memory 55 together with time information indicating the elapsed time measured by the time measuring circuit 54 is performed.
The time measuring circuit 54 counts the number of pulses output from the clock circuit 51, so that the time when the pulse oscillation trigger signal c is output from the laser driver 2 (≈the time when the laser light is emitted from the transmission optical system 4). The process of measuring the elapsed time from is implemented.
The internal memory 55 is a recording medium that stores the peak value detected by the peak detection circuit 52 together with time information.

The intensity detection circuit 56 reads the peak value stored together with the time information from the internal memory 55, outputs the time information corresponding to the peak value to the distance calculation circuit 57, and the signal intensity S indicated by the peak value. Is output to the image processing circuit 14.
The distance calculation circuit 57 grasps the time difference ΔT between the transmission time T _{tx of the} laser beam and the reception time T _rx of the peak value from the elapsed time indicated by the time information output from the intensity detection circuit 56, and the time difference ΔT From this, the process of deriving the distance L to the measurement object is performed.

Next, the operation will be described.
First, the laser driver 2 of the laser light output unit 1 outputs a pulse oscillation trigger signal c to the laser oscillator 3, the signal intensity compensation unit 8, and the image processing unit 12 when irradiating one pulse of laser light from the transmission optical system 4. To do.
The laser oscillator 3 of the laser beam output unit 1 outputs one pulse of laser beam to the transmission optical system 4 every time the pulse oscillation trigger signal c is received from the laser driver 2.

Upon receiving pulsed laser light from the laser oscillator 3, the transmission optical system 4 shapes the beam shape of the laser light and scans the measurement range with an internal beam scanner, while shaping the laser light (substantially parallel light). Irradiate the object to be measured.
Further, the transmission optical system 4 outputs the scan angle of the beam scanner to the image processing unit 12.
At this time, if there is an object to be measured in the transmission direction of the laser light by the transmission optical system 4, the reflected light of the laser light by the measurement object every time the transmission optical system 4 transmits one pulse of laser light. Will come back.

The receiving optical system 6 of the laser beam receiving unit 5 receives the reflected light of the laser beam when the laser beam transmitted from the transmitting optical system 4 is reflected by the measurement object and returns.
When the receiving optical system 6 receives the reflected light, the light receiver 7 converts the reflected light into an electrical signal, and outputs the received signal d, which is the electrical signal, to the sampling circuit 9 and the gain circuit 11.

When the sampling circuit 9 receives the reception signal d from the light receiver 7, the sampling circuit 9 A / D converts the reception signal d and outputs the sampling data f that is the digital reception signal d to the distance attenuation estimation circuit 10.
That is, the clock circuit 21 of the sampling circuit 9 outputs a pulse signal a having a predetermined time period to the A / D conversion circuit 22.
When the A / D conversion circuit 22 of the sampling circuit 9 receives the reception signal d from the light receiver 7, the A / D conversion circuit 22 converts the reception signal d (analog reception signal) to A in synchronization with the pulse signal a output from the clock circuit 21. The D / D conversion is performed, and the sampling data f which is the digital reception signal d is output to the distance attenuation estimation circuit 10.

When the distance attenuation estimation circuit 10 receives the sampling data f from the sampling circuit 9, the distance attenuation estimation circuit 10 calculates the attenuation coefficient g of the energy of the laser beam caused by the medium on the propagation path based on the sampling data f.
Hereinafter, the processing content of the distance attenuation estimation circuit 10 will be described in detail with reference to FIG.

First, when receiving the pulse oscillation trigger signal c from the laser driver 2, the clock circuit 31 of the distance attenuation estimation circuit 10 outputs a pulse signal having a predetermined time period to the time measurement circuit 32 from the reception timing.
The time measuring circuit 32 counts the number of pulses output from the clock circuit 31, so that the time when the pulse oscillation trigger signal c is output from the laser driver 2 (≈the time when the laser light is emitted from the transmission optical system 4). ) Is measured.

Each time the sampling data f is output from the sampling circuit 9, the filter circuit 33 captures the sampling data f (step ST1 in FIG. 6), and the signal strength of the received signal d indicated by the sampling data f captured this time and the previous time The signal strength of the received signal d indicated by the acquired sampling data f is compared (step ST2).
When the signal strength of the reception signal d indicated by the sampling data f acquired this time is higher than the signal strength of the reception signal d indicated by the sampling data f acquired last time, the filter circuit 33 discards the sampling data f acquired this time (step). ST3).
By discarding the sampling data f in this way, it is possible to eliminate a received signal having an abnormal signal strength that affects the estimation of the attenuation coefficient.

When the signal strength of the reception signal d indicated by the sampling data f acquired this time is lower than the signal strength of the reception signal d indicated by the sampling data f acquired last time, the filter circuit 33 performs time processing on the sampling data f acquired this time. Time information indicating the elapsed time measured by the measurement circuit 32 is added (step ST4).
Then, the filter circuit 33 assigns a signal input order number to the sampling data f with time information and stores it in the internal memory 34 (step ST5).

Here, when the signal strength of the received signal d at time t second after the pulse oscillation trigger signal c from the laser driver 2 is output is assumed to be I _t, the attenuation coefficient alpha, if speed of light is a c The relationship between the signal intensity I _t1 after t ₁ second and the signal intensity I _t2 after t ₂ seconds is expressed by the following equation (1) from Lambert-Beer's law.
I _t2 / I _t1 = exp (−α × c × (t ₂ −t ₁ )) (1)
The distance attenuation estimation circuit 10 calculates the attenuation coefficient α using the equation (1) as shown below.

The logarithmic arithmetic circuit 35 is the second smallest sampling data f to which the assigned number is the smallest among the sampling data f stored in the internal memory 34 (excluding the sampling data f already taken out). The sampling data f is taken out, and division processing and logarithmic processing as shown below are performed.
Here, for convenience of explanation, the signal strength of the received signal d the signal strength of the received signal d indicated I _{t1, 2} th small sampling data f indicating that flies small sampling data f and I _t2.

Logarithmic operation circuit 35 is a No. 1 small sampling data f is the signal strength of the received signal d shown I _t1, implementing the division process of dividing the signal intensity I _t2 of the received signal d shown is smaller sampling data f second.
D = I _t2 / I _t1
The logarithmic operation circuit 35 calculates the logarithm of the division result D.
E = log (D)
Here, the calculation result E of the logarithmic calculation circuit 35 is expressed as follows from the equation (1).
E = log (I _t2 / I _t1 ) = − α × c × (t ₂ −t ₁ )

Dividing circuit 36, No. 1 small as the elapsed time t ₁ indicated by the time information added to the sampling data f, the time difference between the elapsed time t ₂ indicated by the time information added to the second smallest sampling data f Δt (= t ₂ −t ₁ ) is obtained, and the calculation result E of the logarithmic operation circuit 35 is divided by the time difference Δt and by the light speed c, which is a constant, to thereby reduce the attenuation coefficient α between the two sampling data f. Is calculated.
α = −E / (c × (t ₂ −t ₁ ))

Each time the division circuit 36 calculates the attenuation coefficient α between the two sampling data f, the average calculation circuit 37 calculates the average value of the attenuation coefficient α calculated by the division circuit 36 so far (step ST6).
The processing of the filter circuit 33, the logarithmic operation circuit 35, the division circuit 36, and the average operation circuit 37 is repeatedly performed while one pulse of laser light is being output.
Thus, the average value of the attenuation coefficient α calculated by the average arithmetic circuit 37 is a value indicating the average of the attenuation coefficient α during the time when one pulse of laser light is output from the laser oscillator 3.
The logarithmic arithmetic circuit 35 stores the average value of the attenuation coefficient α in the internal memory 38 (step ST7).

When the average calculation circuit 37 stores the average value of the attenuation coefficient α per pulse in the internal memory 38, the moving average calculation circuit 39 performs a moving average process on the average value of the attenuation coefficient α (step ST8). The attenuation coefficient α after the averaging process is output to the gain circuit 11 as the attenuation coefficient g (step ST9).
As a result, the latest attenuation coefficient can always be taken in even if the environment changes with time, so that it is possible to follow changes in the environment.
In addition, since the moving average calculation circuit 39 outputs the attenuation coefficient g after the moving average processing to the gain circuit 11, even if the attenuation coefficient α changes greatly, the change of the attenuation coefficient g given to the gain circuit 11 is alleviated. Thus, sudden control fluctuations can be prevented.

When the gain circuit 11 receives the attenuation coefficient g from the distance attenuation estimation circuit 10, the gain circuit 11 uses the attenuation coefficient g to compensate the signal intensity of the reception signal d output from the light receiver 7, and receives the received signal e after the intensity compensation. Is output to the distance / intensity detection circuit 13.
That is, when the clock circuit 41 of the gain circuit 11 receives the pulse oscillation trigger signal c from the laser driver 2, the clock circuit 41 outputs a pulse signal having a predetermined time period to the bias calculation circuit 42 from the reception timing.

The bias calculation circuit 42 counts the number of pulses output from the clock circuit 41, so that the pulse oscillation trigger signal c is output from the laser driver 2 (≈the time when the laser light is emitted from the transmission optical system 4). The elapsed time t from) is measured.
Then, the bias calculation circuit 42 calculates the bias V applied to the variable gain circuit 43 using the elapsed time t and the attenuation coefficient g calculated by the distance attenuation estimation circuit 10 as shown in the following equation (2). To do.
V = g × c × t / β (2)
Here, c is the speed of light, and β is the amount of gain change per bias of the variable gain circuit 43.

When the variable gain circuit 43 receives the bias V from the bias calculation circuit 42, the variable gain circuit 43 applies the bias V to the reception signal d output from the light receiver 7, thereby compensating the signal intensity of the reception signal d, thereby compensating the intensity. The subsequent reception signal e is output to the distance / intensity detection circuit 13.
The gain circuit 11 uses the attenuation coefficient g newly calculated by the distance attenuation estimation circuit 10 for each timing at which one pulse of laser light is transmitted from the laser oscillator 3 and receives the signal output from the light receiver 7. The signal strength of the signal d is compensated.
Here, FIG. 7 is an explanatory diagram showing received signals before and after intensity compensation for propagation loss.
As apparent from FIG. 7, since the intensity loss that depends on the propagation distance of the laser is compensated, the signal intensity of the reflected light depends only on the reflectance of the substance that reflects the transmitted laser light. It becomes possible to convert to signal strength.

When the distance / intensity detection circuit 13 receives the received signal e after the intensity compensation from the gain circuit 11, the distance / intensity detection circuit 13 extracts the received signal related to the measurement object from the received signal e after the intensity compensation, and corresponds to the received signal. The distance L to the measurement object is derived from the time difference ΔT between the transmission time T _tx of the laser light to be received and the reception time T _rx of the received signal.
The processing contents of the distance / intensity detection circuit 13 will be specifically described below.

When receiving the pulse oscillation trigger signal c from the laser driver 2, the clock circuit 51 of the distance / intensity detection circuit 13 sends a pulse signal having a predetermined time period to the peak detection circuit 52 and the time measurement circuit 54 from the reception timing. Output.
The time measuring circuit 54 counts the number of pulses output from the clock circuit 51, so that the time when the pulse oscillation trigger signal c is output from the laser driver 2 (≈the time when the laser light is emitted from the transmission optical system 4). The elapsed time t from) is measured.

The peak detection circuit 52 is a peak hold circuit that starts operation at the input timing of the pulse signal output from the clock circuit 51 and discharges after a predetermined time. The peak detection circuit 52 receives the received signal e whose signal strength is compensated by the gain circuit 11. The peak value in the middle is detected.
As shown in FIG. 7B, the comparator 53 is set with a threshold value for sorting the received signal and the unnecessary signal related to the measurement object, and compares the peak value detected by the peak detection circuit 52 with the threshold value. .
If the peak value detected by the peak detection circuit 52 is greater than the threshold value, the comparator 53 determines that the peak value is a received signal related to the measurement object, and the time measured by the time measurement circuit 54 is measured. It is stored in the internal memory 55 together with time information indicating the time t.

The intensity detection circuit 56 reads the peak value stored together with the time information from the internal memory 55, outputs the time information corresponding to the peak value to the distance calculation circuit 57, and the signal intensity indicated by the peak value. S is output to the image processing circuit 14.
When the distance calculation circuit 57 receives the time information corresponding to the peak value from the intensity detection circuit 56, the distance calculation circuit 57 calculates the transmission time T _{tx of the} laser light from the elapsed time t indicated by the time information and the reception time T _rx of the peak value. The time difference ΔT is grasped.
That is, the distance calculation circuit 57 recognizes the time when the elapsed time measured by the time measurement circuit 54 is 0 (the time when the pulse oscillation trigger signal c is output from the laser driver 2) as the laser light transmission time T _tx , the transmission time _{T tx} time obtained by adding the elapsed time t since the _(T tx + t) recognizes the reception time _{T rx} peak value, the time difference between the receiving time _{T rx} transmission time _{T tx} and peak value of the laser beam Know ΔT.
The distance calculation circuit 57 derives the distance L to the measurement object from the time difference ΔT and the speed of light c, and outputs the distance L to the image processing circuit 14.
L = c × ΔT

When the image processing circuit 14 receives the signal intensity S of the received signal related to the measurement object and the distance L to the measurement object from the distance / intensity detection circuit 13, the image processing circuit 14 receives the signal intensity S and the distance L from the transmission optical system 7. The measurement object is imaged based on the output scan angle of the beam scanner, and a two-dimensional image and a three-dimensional image showing the measurement object are generated.
Since the technique itself for imaging the measurement object from the signal intensity S and the distance L is a known technique, detailed description thereof is omitted.

  As is apparent from the above, according to the first embodiment, the sampling circuit 9 that samples the reception signal d, which is an electrical signal converted by the light receiver 7, and the signal strength of the reception signal d of the current sampling are the previous sampling. If the received signal d is lower than the signal strength of the received signal d, distance attenuation estimation for calculating the attenuation coefficient g of the energy of the laser beam caused by the medium on the propagation path using the signal strength of the received signal d sampled this time and the reception time A circuit 10 and a gain circuit 11 that compensates for the signal strength of the received signal d, which is an electrical signal converted by the light receiver 7, using the attenuation coefficient g calculated by the distance attenuation estimation circuit 10, are provided. The detection circuit 13 extracts the reception signal related to the measurement object from the reception signal e whose signal intensity is compensated by the gain circuit 11, and corresponds to the reception signal. Since the distance L to the measurement object is derived from the difference between the transmission time of the laser beam and the reception time of the received signal, the environment where there is a noise factor having a relatively large particle size, backscattering Even in an environment where light is generated, the distance L to the measurement object can be accurately derived.

That is, according to the first embodiment, at the timing when the laser oscillator 3 outputs the pulsed laser beam to the transmission optical system 4, the distance attenuation estimation circuit 10 causes the attenuation coefficient g caused by the medium on the propagation path. Since the gain circuit 11 performs intensity compensation for the propagation loss using the attenuation coefficient g, the influence of the propagation loss is removed from the received signal d which is an electrical signal converted by the light receiver 7. And is replaced by a signal intensity that depends on the reflectivity of the measurement object.
As a result, it becomes possible to eliminate the reflected signal from the noise factor that could not be removed even if the threshold value was made variable, and it is possible to perform stable signal detection and distance measurement from the measurement object. .

  Further, according to the first embodiment, every time one pulse of laser light is transmitted, the attenuation coefficient g caused by the medium on the propagation path is estimated and moved together with the previously estimated attenuation coefficient g. Since the average is taken, even if the surrounding environment changes and the attenuation coefficient g on the propagation path gradually changes, the latest distance is taken in and the distance measurement is stable. Is possible.

In the first embodiment, the comparator 53 of the distance / intensity detection circuit 13 compares the peak value detected by the peak detection circuit 52 with a threshold value, and if the peak value is larger than the threshold value, the peak value is measured. Although the signal that is judged to be a received signal related to the object is shown, the signal strength from the object to be measured even if the intensity compensation for the propagation loss is performed when the reflectance from the noise factor on the propagation path is high Compared with, the signal intensity from the noise factor may be equal or high.
In this case, even if the threshold value used by the comparator 53 is adjusted, a plurality of peak values may be larger than the threshold value.
However, since the measurement object always exists behind the noise factor, the peak value obtained last by transmission of the pulse laser beam once becomes a reception signal related to the measurement object.

Therefore, when the plurality of peak values are larger than the threshold, the comparator 53 refers to the reception times of those peak values and determines that the peak value with the latest reception time is the received signal related to the measurement object. The peak value is stored in the internal memory 55.
Thereby, since the reflectance from the noise factor on the propagation path is high, there is an effect that the distance L to the measurement object can be accurately derived even when the plurality of peak values are larger than the threshold value.

Embodiment 2. FIG.
In the first embodiment, the sampling circuit 9 includes the clock circuit 21 and the A / D conversion circuit 22, but the sampling circuit 9 may have other configurations.
8 is a block diagram showing a sampling circuit 9 of a laser radar device according to Embodiment 2 of the present invention. In the figure, the same reference numerals as those in FIG.
Each time the gate circuit 61 receives a pulse signal from the clock circuit 21, the gate circuit 61 performs a process of sequentially switching the cells of the multi-channel A / D circuit 62 that provides the reception signal d that is an electric signal converted by the light receiver 7.
The multi-channel A / D conversion circuit 62 has a plurality of cells (each cell has an A / D conversion function), and the cell to which the reception signal d is given from the gate circuit 61 is A / D converted. Processing is performed to output sampling data f that is a digital received signal.

In the first embodiment, since the A / D conversion circuit 22 of the sampling circuit 9 does not have a multi-channel configuration, it is necessary to mount a high-speed A / D conversion circuit that can follow the pulse period of the clock circuit 21. .
In the second embodiment, the multi-channel A / D conversion circuit 62 has a plurality of cells, and the gate circuit 61 distributes the pulse signal output from the clock circuit 21 to the plurality of cells. Even if the A / D conversion processing is performed at a low speed, the same processing as that of the sampling circuit 9 of the first embodiment can be realized.
For example, when the multi-channel A / D conversion circuit 62 has N cells, the processing cycle of each cell can be reduced to 1 / N times the pulse cycle of the clock circuit 21. .

Embodiment 3 FIG.
In the first embodiment, the distance attenuation estimation circuit 10 has a configuration in which the division circuit 36 and the average arithmetic circuit 37 are mounted. However, the distance attenuation estimation circuit 10 may have other configurations.
FIG. 9 is a block diagram showing a distance attenuation estimation circuit 10 of a laser radar apparatus according to Embodiment 3 of the present invention. In the figure, the same reference numerals as those in FIG.
The least square method arithmetic circuit 70 performs a process of calculating an average value of the attenuation coefficient α by performing a linear least square method process on the calculation result of the logarithmic arithmetic circuit 35.

Next, the operation will be described.
However, since the distance attenuation estimation circuit 10 is the same as that of the first embodiment except that the least square method calculation circuit 70 is mounted instead of the division circuit 36 and the average calculation circuit 37, the least square method is used. Only the processing contents of the arithmetic circuit 70 will be described.

When receiving the calculation result from the logarithmic calculation circuit 35, the least square method calculation circuit 70 performs a least square method process of a linear expression on the calculation result.
As can be seen from the equation (1), the estimated attenuation coefficient α is a slope of a linear equation with respect to time when the signal intensity is expressed in a logarithm.
From this, the slope of the approximate expression obtained by applying the least square method of the linear equation to the sampling data f stored in the internal memory 34 is calculated as the attenuation coefficient α.

Specifically, the number of sampling data f stored in the internal memory 34 is N, n-th logarithmic processing signal strength is A _n, when the reception time of the received signal according to sampling data f is a t _n Then, the attenuation coefficient α is expressed as the following formula (3).

The least square method arithmetic circuit 70 calculates the attenuation coefficient α by calculating Expression (3), and stores the attenuation coefficient α in the internal memory 38.
This calculation process is performed each time one pulse of laser light is transmitted.

In the first embodiment, when N pieces of sampling data f are stored in the internal memory 34 when calculating the attenuation coefficient α, the logarithmic arithmetic circuit 35 performs (N−1) times of division processing. Further, since the division circuit 36 performs (N−1) division processing, it is necessary to perform 2 (N−1) division processing by calculating the attenuation coefficient α once.
In the third embodiment, the least squares method arithmetic circuit 70 only needs to perform the division process of Expression (3) once, and the speed of the calculation process can be greatly improved.

  In the present invention, within the scope of the invention, any combination of the embodiments, or any modification of any component in each embodiment, or omission of any component in each embodiment is possible. .

  DESCRIPTION OF SYMBOLS 1 Laser light output part, 2 Laser driver, 3 Laser oscillator, 4 Transmission optical system, 5 Laser light receiving part, 6 Reception optical system, 7 Light receiver, 8 Signal intensity compensation part, 9 Sampling circuit (Attenuation coefficient calculation means), DESCRIPTION OF SYMBOLS 10 Distance attenuation | damping estimation circuit (attenuation coefficient calculation means), 11 Gain circuit (signal strength compensation means), 12 Image processing part, 13 Distance / intensity detection circuit (distance derivation means), 14 Image processing circuit (image generation means), 21 Clock circuit, 22 A / D conversion circuit, 31 clock circuit, 32 time measurement circuit, 33 filter circuit, 34 internal memory, 35 logarithmic operation circuit, 36 division circuit, 37 average operation circuit, 38 internal memory, 39 moving average operation circuit , 41 clock circuit, 42 bias calculation circuit, 43 variable gain circuit, 51 clock circuit, 52 peak detection circuit, Third comparator, 54 hours measuring circuit, 55 an internal memory, 56 intensity detection circuit, 57 a distance computation circuit, 61 a gate circuit, 62 a multi-channel A / D conversion circuit, 70 the least squares method calculation circuit.

Claims (2)

A transmission optical system that irradiates the measurement target with pulsed laser light, and reflected light of the laser light reflected by the measurement target every time one pulse of laser light is emitted from the transmission optical system This is a received signal sampled at the current sampling timing by sampling the received signal of the reflected light received by the receiving optical system in synchronization with the receiving optical system that receives the signal and the pulse signal output from the clock circuit If the signal strength of the received signal of sampling is lower than the signal strength of the received signal of the previous sampling that is the received signal sampled at the previous sampling timing, the signal strength of the received signal of the previous sampling is the signal strength of the received signal of the current sampling. Divide the result and divide the logarithm of the result by the speed of light. An attenuation coefficient calculating means for calculating the attenuation coefficient of the energy of the laser beam caused by the medium on the propagation path by dividing by the time difference between the transmission time and the reception time of the reception signal of the current sampling; The bias is calculated by multiplying the difference between the transmission time of the laser beam corresponding to the reception signal and the reception time of the reception signal, the attenuation coefficient calculated by the attenuation coefficient calculation means, and the speed of light, and the bias Is applied to the received signal sampled this time, the signal strength compensation means for compensating the signal strength of the received signal, and the received signal whose signal strength is compensated by the signal strength compensation means, to the measurement object. The received signal is extracted, and the distance to the measurement object is derived from the difference between the transmission time of the laser beam corresponding to the received signal and the received time of the received signal. Distance deriving means from the signal strength of the received signals the signal intensity is compensated for by the distance and the signal intensity compensation means derived by said distance deriving means, and an image generating means for imaging the measurement object,
The attenuation coefficient calculating means calculates an average value of the attenuation coefficient per pulse , and performs a moving average process on the average value of the attenuation coefficient,
The laser radar apparatus according to claim 1, wherein the signal intensity compensation means calculates the bias using an attenuation coefficient after the moving average processing by the attenuation coefficient calculation means.   The distance deriving means includes a plurality of received signal candidates when there are a plurality of received signal candidates related to the measurement object in the received signal whose signal strength is compensated by the signal strength compensating means. 2. The laser radar apparatus according to claim 1, wherein a received signal having the latest reception time is extracted from the received signal.

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