JP3558476B2 - Radar equipment - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a radar device used as a berthing speedometer and the like, and more particularly to a radar device having improved performance by reducing noise.
[0002]
[Prior art]
A sampling type berthing speed meter using a pulse laser radar is disclosed in Japanese Patent Publication No. 7-69423, Japanese Patent Publication No. 7-69427, Japanese Patent Publication No. 7-78537, etc., which the applicant of the present invention has previously applied for. I have. This sampling type berthing speedometer repeatedly transmits a pulsed laser beam at a fixed transmission cycle, and accumulates reflected pulses from the berthing ship, which is a reflector, by a smaller amount than the above transmission cycle. It is configured to receive the reflected pulse while elongating the time axis by receiving a large number of times in the reception cycle that is gradually increased. This sampling type laser radar can perform high-precision measurement by using a sharp laser pulse with a half width of a few nsec, but it requires several thousand times of transmission and reception of laser pulse for one point measurement. There is a problem that it takes time.
[0003]
When a conventional pulse laser radar that does not depend on the sampling method is configured to reduce the measurement time, how to reduce noise in securing the maximum measurable distance becomes a problem. In general, in the field of signal processing, a method is known in which a logical product of signals generated a plurality of times is taken to eliminate noise contained therein. That is, by creating a logical product of an apparent signal composed of a signal component and a noise component, only a noise component which is different from the signal component and has no regularity at the present time is removed.
[0004]
[Problems to be solved by the invention]
When applying the removal of noise components by creating the logical product to a pulse laser radar, there are various problems to be solved. First, since the time from transmitting the pulse signal to receiving the reflected pulse changes according to the position of the reflector, how should the reflected pulses received several times in the past be stored? There is a problem.
[0005]
If a configuration in which the reflected pulse received a plurality of times is converted into a digital signal or a frequency spectrum and stored in a memory each time can be adopted, there is no problem in the above-described data storage method. However, in the case of a berthing speedometer or the like, it is necessary to transmit and receive a sharp pulse having a half width of several nsec (frequency band: several tens MHz) in order to realize a high detection accuracy of about several tens of cm with respect to distance. There are circumstances. Such a sharp pulse can be directly converted to a digital signal by A / D conversion or converted to a frequency spectrum by fast Fourier transform without expanding the time axis by the sampling method in terms of processing speed. Have difficulty.
[0006]
For this reason, it is necessary to store past received signals using some delay circuit instead of a memory. In this case, what kind of circuit configuration should be adopted is a problem to be solved.
[0007]
Next, when a delay circuit is used, there are special circumstances peculiar to a berthing speedometer and the like in which the pulse to be delayed is a sharp pulse having a half-value width of several nsec, but the delay time becomes extremely long. In other words, in a normal signal processing circuit, the delay time is shortened to match this high speed as the speed increases, but a typical berthing speedometer assumes that the maximum measurable distance is 200 meters. The round trip propagation distance to the reflector is 400 meters, twice this maximum distance, and the required delay time is 1.33 μs.
[0008]
If a high-speed and large-delay delay circuit as described above is to be realized by a conventional delay circuit based on LC lumped constants, the number of cascade connection stages is required to be as large as one thousand, resulting in a problem of large size and high cost. . When a delay circuit having a distributed constant such as a coaxial cable is used, there is a problem that a length of about 160 meters is required even if the wavelength shortening effect due to the relative dielectric constant is taken into consideration. If an ultrasonic delay line can be used, it is small and inexpensive, but it is difficult to realize high-frequency characteristics of about several tens of MHz with this ultrasonic delay line.
[0009]
Under the circumstances described above, conventionally, in a radar device such as a berthing speedometer that transmits and receives a sharp pulse having a half-value width of several nsec, a method of removing a noise component by creating a logical product at a front end stage. Has not been adopted to the inventor's knowledge. Instead of performing the noise removal processing at the front end, the distance scattered by the noise is measured many times, and these measurement results are statistically processed to indirectly reduce the noise generated at the front end. Back-end processing of removal has been employed.
[0010]
However, the conventional noise removal by the statistical processing in the back end has a problem that it takes a long time to process because a large number of data to be processed is required. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a radar which removes a noise component at a front end in a short time by storing received pulses received a minimum number of times by using a delay circuit and creating a logical product of the received pulses. It is to implement the device.
[0011]
[Means for Solving the Problems]
A radar apparatus according to the present invention for solving the above-mentioned problems of the prior art includes a transmission synchronization signal generating means for generating and outputting a transmission synchronization signal of a predetermined cycle, and a transmission synchronization signal output by the transmission synchronization signal generation means having a maximum measurement range. A transmission synchronization signal delay unit that outputs a signal after delaying by a predetermined time set based on the transmission synchronization signal output by the transmission synchronization signal generation unit and the delayed transmission synchronization unit output by the delay unit. Transmitting means for transmitting a pulsed beam, receiving means for receiving a reflected beam of the pulsed beam transmitted by the transmitting means by a reflector and outputting the received pulse as a received pulse, and delaying the received pulse by a predetermined time. Receiving pulse delay means for outputting the received pulse as a received pulse, and multiplying the delayed received pulse by the received pulse received and output by the receiving means next. And a multiplier circuit for removing the noise, and outputs the noise-removed received pulse by. The radar apparatus according to the present invention further includes a signal synthesizing unit and a signal separating unit respectively disposed before and after the shared delay unit in order to share the synchronization signal delay unit and the reception pulse delay unit. Means.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
According to a preferred embodiment of the present invention, the reception means includes a binarization circuit for binarizing the reception pulse, and the reception pulse delay means performs the transmission synchronization with the binarized reception pulse. It has a group of inverters connected in series to delay signals .
[0013]
According to a further preferred embodiment of the present invention, as the signal synthesizing means and the signal separating means , a logical sum signal of the transmission synchronization signal and the output of the binarization circuit is created and the reception pulse delay means An OR gate for sharing the reception pulse delay unit and the transmission synchronization signal delay unit by supplying the OR gate; and the OR signal output from the OR gate and the OR signal delayed by the reception pulse delay unit. by removing the output of the binarizing circuit, Bei Eteiru and means for supplying the transmission synchronization signal and the delayed transmission synchronization means to said transmitting means.
[0014]
【Example】
FIG. 1 is a block diagram showing a configuration of a radar head which is a front end portion of a berthing speedometer according to one embodiment of the present invention. This laser head includes a light transmitting unit 10, a light receiving unit 20, and a counter 30.
[0015]
The light transmitting unit 10 includes a laser diode 11, a laser diode driving circuit 12, a light transmitting lens 13, a transmission synchronization signal generating circuit 14, an OR gate 15, low-pass filtering circuits (LPFs) 16 and 18, and Schmitt trigger inverters 17 and 19. It has. The light receiving section 20 includes a photoelectric conversion circuit 21 mainly composed of an avalanche photodiode (APD), an amplifier circuit 22, a light receiving lens 23, a voltage comparison circuit 24, a delay circuit 25, and an AND gate 26.
[0016]
The transmission synchronization signal generating circuit 14 generates and outputs a rectangular wave having a frequency of 1 KHz as a transmission synchronization signal. This transmission synchronization signal is supplied to the laser diode driving circuit 12 via the OR gate 15, the low-pass filtering circuit 16, and the Schmitt trigger inverter 17. The laser diode drive circuit 12 generates a transmission trigger signal synchronized with the falling edge of the transmission synchronization signal, and drives the laser diode 11. The driven laser diode generates a sharp laser pulse having a half value width of several nsec. The laser pulse is transmitted to the ship in berthing operation while being focused by the light transmitting lens 13.
[0017]
On the other hand, a part of the transmission synchronization signal output from the transmission synchronization signal generation circuit 14 and passing through the OR gate 15 passes through the delay circuit 25, and then passes through the low-pass filtering circuit 18 and the Schmitt trigger inverter 19, whereupon the laser diode It is supplied to the drive circuit 12. The delay circuit 25 is composed of a large number of inverters connected in cascade, and generates a delay time of 1.33 μs in total for signals passing through the inverter. The delay time of 1.33 μs is a time required for the laser pulse emitted from the light transmitting unit 10 to reciprocate between the reflector located at the farthest point of 200 meters, that is, a space of 400 meters. Is set to a value equal to the required propagation delay time required to propagate
[0018]
The laser diode drive circuit 12 generates a transmission trigger signal in synchronization with the fall of the delayed transmission synchronization signal supplied through the low-pass filtering circuit 18 and the Schmitt trigger inverter 19, and thereby generates a laser diode. 11 is driven. As a result, as shown in the waveform diagram of FIG. 2, after being output from the OR gate 15, it is supplied to the laser diode drive circuit 12 through the low-pass filter circuit 16 and the Schmitt trigger inverter 17 without passing through the delay circuit 25. The first group of laser pulses P1 is generated at a period of 1 ms by the transmitted synchronization signal.
[0019]
Further, after being output from the OR gate 15, the first group is transmitted by the transmission synchronization signal supplied to the laser diode driving circuit 12 through the delay circuit 25, the low-pass filtering circuit 18, and the Schmitt trigger inverter 19. The laser pulse P2 of the second group is generated at a delay of 1.33 μs from the laser pulse P1 of the second group and at the same period of 1 ms as that of the first group.
[0020]
The laser radar has a JIS safety standard with respect to the energy density so that a failure does not occur even if the user inadvertently receives the laser pulse in the eyes. If a laser pulse is radiated in a short period of 1 μs, the level of a pulse laser beam that can be radiated every time becomes extremely low due to the limitation of energy density based on safety standards, and a distance as far as 200 m cannot be monitored. In addition to the safety standards, it is difficult to generate a large-level pulsed laser beam at a short period of about 1 μs due to the circuit configuration.
[0021]
In this embodiment, in order to generate a sharp laser pulse having a half width of several nsec, the DC power charged in the charging capacitor is instantaneously discharged by a high-speed switching transistor inside the laser diode drive circuit 12. Two systems of charging / discharging circuits for driving the laser diode are provided corresponding to the first group and the second group of laser pulses, respectively. Each charging / discharging circuit executes a charging / discharging operation of discharging the DC power charged in about 1 ms in a period of 1 to 3 nsec at a timing shifted by 1.33 μs.
[0022]
The laser pulse emitted from the light transmitting unit 10 at the timing described above, reflected by a ship located within a distance of 200 m from the farthest point, and propagated in the direction opposite to the outward path is received by the avalanche while being focused by the light receiving lens 23. The light is incident on a photoelectric conversion circuit 21 mainly composed of a photodiode, where it is converted into a received pulse composed of a sharp electric pulse having a half width of several nsec. The received pulse is amplified by the high-frequency and low-noise amplifier circuit 22 and supplied to one input terminal of the voltage comparison circuit 24.
[0023]
A constant reference voltage Vref is supplied to the other input terminal of the voltage comparison circuit 24 from a reference voltage generation circuit (not shown). The voltage comparison circuit 24 compares the output of the amplifier circuit 22 supplied to each input terminal with the reference voltage Vref, and raises the output to high if the former is larger than the latter, and outputs if the former is less than the latter. Fall to low, the analog signal output from the amplifier circuit 22 is binarized. The binarized output of the voltage comparison circuit 24 is superimposed on the transmission synchronization signal in the OR gate 15, and a part thereof is supplied to the delay circuit 25.
[0024]
Referring to the waveform diagram of FIG. 3, the waveform (A) is a transmission synchronization signal output from the transmission synchronization signal generation circuit 14 and formed of a rectangular wave having a frequency of 1 KHz. A waveform (B) is a binarized signal output from the voltage comparison circuit 24, and illustrates a state in which noise is irregularly transitioning between an on state and an off state. When the OR of the signals of the waveforms (A) and (B) is created in the OR gate 15, a combined signal is obtained by combining the noise and the transmission synchronization signal as shown in the waveform (C).
[0025]
When the synthesized signal shown in the waveform (C) passes through the low-pass filtering circuit 16, as shown in the waveform (D), the high-frequency noise component is removed, and the transmission synchronizing signal whose rising and falling edges are dull is obtained. Become. The synchronous signal having a dull edge is supplied to the laser diode drive circuit 12 through the Schmitt trigger inverter 17 to generate a transmission trigger signal shown in a waveform (E). The laser diode receiving this transmission trigger signal generates a sharp laser pulse having a half width of several nsec as shown in the waveform (F). This laser pulse is radiated through the light transmitting lens 13 to the ship on the shore.
[0026]
The reflected pulse reflected from the berthing ship is converted into an electric pulse by the photoelectric conversion circuit 21 to be a received pulse, amplified, binarized, and then inputted to one input terminal of the OR gate 15 as described above. Supplied to As shown in the waveform (G), the binarized reception pulse is mixed with noise and is difficult to recognize, so the appearance position is indicated by an upward arrow added below. The binarized reception pulse mixed with this noise is combined with the transmission synchronization signal shown in the waveform (A) by the OR gate 15, becomes a combined signal shown in the waveform (H), and is supplied to the delay circuit 25.
[0027]
The time difference between the present time of the light transmission laser pulse shown in the waveform (F) and the present time of the binary reception pulse included in the composite signal of the waveform (H) is determined by the round trip of the laser pulse between the berthing ship and the ship. Is the propagation time τ required to perform The required propagation time τ is smaller than a fixed delay time td (1.33 μs in this example) by the delay circuit 25 set to determine the farthest measurable point. The composite signal shown in waveform (H) is delayed by delay time td (= 1.33 μs) in delay circuit 25, and becomes a delayed composite signal as shown in waveform (I).
[0028]
When the delayed synthesized signal passes through the low-pass filtering circuit 18, as shown in the waveform (J), the high-frequency noise component is removed, and the delayed transmission synchronizing signal whose rising and falling edges are dull. become. The delayed synchronization signal is supplied to the laser diode drive circuit 12 through the Schmitt trigger inverter 19, and generates a transmission trigger signal shown in a waveform (K). The laser diode receiving this transmission trigger signal generates a second sharp laser pulse as shown by a waveform (L), which is radiated through the light transmitting lens 13 to the ship approaching the shore.
[0029]
The reflected pulse generated by the second laser pulse being reflected by the ship approaching the shore is converted into an electric pulse by the light receiving circuit 21 similarly to the case of the reflected pulse generated by the first laser pulse described above. The signal is converted into a reception pulse, amplified, binarized and converted into a binarized reception pulse mixed with noise as shown in waveform (M), and combined with the transmission synchronization signal shown in waveform (A) in OR gate 15. , And is supplied to one input terminal of the AND gate 26 and the delay circuit 25.
[0030]
The other input terminal of the AND gate 26 is supplied with a composite signal output from the delay circuit 25 delayed by td from the waveform (H), as shown in the waveform (I). When the AND of the composite signals shown in the waveform (I) and the waveform (N) is calculated in the AND gate 26, the noises having no regularity at the present time are canceled out as shown in the waveform (O). At the same time, a waveform is obtained in which only the received pulses having the regularity at the present time remain.
[0031]
Referring to the waveform (O) in FIG. 3 and the circuit configuration in FIG. 1, the counter 30 starts the output pulse from the Schmitt trigger inverter 19 that generates a transmission trigger signal for driving the second laser pulse. The count operation is started in response to the terminal. The counter 30 that has started the counting operation as described above stops the counting operation when receiving the reception pulse appearing in the signal of the waveform (O) output from the AND gate 26 at the stop terminal.
[0032]
Referring to the waveform in FIG. 3 , the counting operation of the counter 30 is continued for a propagation time τ for the laser pulse to reciprocate with the ship on the shore. That is, the counter 30 measures the required reciprocating propagation time τ of the laser pulse, and notifies this to a data processor (not shown). The data processor calculates the required one-way propagation time τ / 2 by dividing the required propagation time τ of the round trip of the laser pulse into two equal parts, and further divides the required time τ / 2 by the speed of light to obtain the berth. Detect the distance to the operating ship. The data processor detects the berthing speed of the ship from the speed of change in the distance to the ship during the berthing operation.
[0033]
As the inverter constituting the delay circuit 25, for example, 74AC04 can be used. The 74AC04 is composed of six inverters connected in cascade, and its delay time is about 12 nsec at room temperature. Accordingly, a delay time of 1.33 μs can be realized by connecting approximately 110 such 74AC04s in cascade. Since the rise / fall time of each inverter is 1.5 nsec when the load capacitance is 5 pF at room temperature, a signal obtained by binarizing a reception pulse having a sharp waveform having a half-value width several nsec without deteriorating the waveform is obtained. Can be delayed.
[0034]
Further, in the laser radar of this embodiment, the transmission synchronization signal output from the transmission synchronization signal generation circuit 14 and the binarized reception pulse output from the voltage comparison circuit 24 are combined by the OR gate 15 so that both signals are combined. Is delayed through a common delay circuit 25, and only a transmission synchronization signal is extracted by a low-pass filtering circuit. Therefore, the number of delay circuits used, and thus the installation space and cost, are reduced by half, and the temperature dependence of the delay time in both delay circuits is reduced, as compared with the case where both signals are delayed using individual delay circuits. It is possible to effectively avoid disadvantages such as a difference in timing between the two signals due to a difference or the like and deterioration in performance.
[0035]
As described above, the present invention has been described by taking the case of application to a berthing speedometer as an example, but the present invention can be applied to a laser radar for a vehicle for collision prevention and the like.
[0036]
Although the present invention has been described by taking the case of a laser radar for transmitting a laser pulse as an example, the present invention can be applied to a radar for transmitting a pulse of an electromagnetic wave.
[0037]
【The invention's effect】
As described above in detail, the radar device of the present invention is configured to delay a sharp reception pulse by the delay circuit and multiply the result by a subsequent reception pulse, so that the radar device is generated in a light receiving element such as an avalanche photodiode. There is an effect that a light receiving pulse having a level equal to or lower than shot noise can be detected.
[0038]
Further, since the radar apparatus of the present invention is configured to perform noise removal at the front end stage in the radar head, compared with the conventional indirect noise removal by statistical processing at the back end, the number of objects to be removed is larger than that of the conventional radar apparatus. And the processing time is greatly reduced.
[0039]
Further, since the reception pulse and the transmission synchronization signal are combined and delayed through a common delay circuit, the two signals are separated from each other. Thus, the number of delay circuits used, and thus the installation space and cost, are halved. Further, there is an advantage that defects such as a timing shift between the two signals and a deterioration in performance due to a difference in temperature dependence of the delay time between the two delay circuits can be effectively avoided.
[0040]
Further, according to the embodiment in which the received pulse is binarized and the binarized received pulse is delayed by the inverter group connected in series, there is an advantage that a small and inexpensive delay circuit can be realized.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a laser radar head which is a front end portion of a berthing speedometer according to one embodiment of the present invention.
FIG. 2 is a waveform diagram illustrating the operation of the laser radar head of FIG.
FIG. 3 is a waveform diagram illustrating an operation of the laser radar head of FIG. 1;
[Explanation of symbols]
REFERENCE SIGNS LIST 10 light transmitting unit 11 laser diode 12 laser diode driving circuit 14 transmission synchronization signal 15 OR gate 16, 18 low-pass filtering circuit 17, 19 Schmitt trigger inverter 20 light receiving unit 21 photoelectric conversion circuit 22 mainly composed of APD 22 amplification circuit 24 voltage Comparison circuit 25 Delay circuit 26 AND gate 30 Counter

Claims (4)

Transmission synchronization signal generating means for generating and outputting a transmission synchronization signal of a predetermined period,
Transmission synchronization signal delay means for outputting the transmission synchronization signal output by the transmission synchronization signal generation means with a delay for a predetermined time set based on the maximum measurement range;
Transmission means for transmitting a pulse beam in synchronization with the transmission synchronization signal output by the transmission synchronization signal generation means and the delayed transmission synchronization signal output by the transmission synchronization signal delay means,
A receiving unit that receives a reflected beam of the pulsed beam transmitted by the transmitting unit and is output as a received pulse;
Reception pulse delay means for delaying the reception pulse by a predetermined time and outputting the received pulse as a delayed reception pulse;
A multiplication circuit that removes noise by multiplying the delayed reception pulse by the reception pulse received and output by the receiving means next time, and outputs the noise-removed reception pulse;
A signal synthesizing unit and a signal separating unit disposed at each of a preceding stage and a succeeding stage of the shared delay unit in order to share the synchronization signal delay unit and the reception pulse delay unit . A radar device characterized by the above-mentioned. In claim 1,
The receiving means includes a binarization circuit for binarizing the reception pulse, and the shared delay means includes a serially connected inverter for delaying the binarized reception pulse and the transmission synchronization signal. A radar device comprising a group. In claim 1 or 2 ,
The pulsed beam transmitted by the transmitting means is a laser beam. In claim 1 or 2 ,
The pulse beam transmitted by the transmitting means is a radio wave beam.

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