JPH05312950A - Ranging apparatus and method - Google Patents

Abstract

PURPOSE:To obtain the range of an object with high resolution through a rela tively simple constitution. CONSTITUTION:A laser diode 15 projects a laser beam, modulated by m-train signals generated from an m-train generator 13, toward an object. Single bit width (minimum pulse width) of the m-train is set equal to a time required by the laser beam for reciprocating a maximum detecting distance. A phase shifter 31 produces multiple shifted signals by shifting the m-train within the single bit width. A light signal received by a photodiode 21 and representing a light reflected on the object is correlated with each shifted signal. An arithmetic unit 30 determines two lines by minimum square method based on the correlated values and then calculates the distance upto the object from the cross point of two lines. Gain is regulated in the measurement depending on the strength of received signal and the like thus realizing an accurate measurement depending on the situation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring technique, and more particularly to improving the measurement accuracy.

[0002]

2. Description of the Related Art A method is widely used in which an electromagnetic wave is transmitted toward an object, the time until the reflected wave is received is measured, and the distance to the object is measured. For example, a vehicle random modulation radar device for measuring a distance to a vehicle traveling ahead is known.

A vehicle random modulation radar device amplitude-modulates a transmission electromagnetic wave by an m-sequence code and transmits it, and demodulates a reflection electromagnetic wave from a preceding vehicle to obtain a reception signal. At this time, a phase shift occurs between the m-sequence code represented by the transmission signal and the m-sequence code represented by the reception signal. This phase shift is proportional to the distance to the preceding vehicle. Therefore, the distance can be measured by detecting the amount of phase shift.

[0004]

The distance measuring technique as described above has the following problems. The amount of phase shift between the transmitted signal and the received signal is detected by determining "how much the received signal should be phase-shifted to correlate with the transmitted signal". Here, the correlation calculation between the transmission signal and the reception signal is performed in bit units of the m-sequence code. Therefore, the 1-bit width of the m-series code (minimum pulse width of the m-series coded pulse signal) is the distance measurement resolution, which causes a problem of low resolution.

In order to improve the resolution, the length of the m series must be lengthened. Then a very high speed clock signal is required. In addition, since many shift signals shifted in multiple stages are required to obtain the correlation, the configuration for the correlation processing becomes complicated and the processing takes a long time.

Further, depending on the situation (rain, fog, smoke, etc.), the received signal may not be received well, and the detection capability may be reduced.

The present invention solves the above-mentioned problems and provides a distance measuring device and method having a simple structure, high resolution, and capable of maintaining high detection capability regardless of the situation. With the goal.

[0008]

According to a first aspect of the present invention, there is provided a distance measuring device which directs an electromagnetic wave modulated by a code sequence generating means for generating a signal representing a code sequence and an output signal of the code sequence generating means to an object. Transmitting means, transmitting means for transmitting, receiving means for receiving and demodulating a reflected wave from an object, and outputting as a reception signal, the phase difference between the code sequence represented by the transmission signal and the phase of the code sequence represented by the reception signal. Based on this, processing means for calculating the distance to the object, and gain adjusting means for adjusting at least one of the transmission gain of the transmission means or the reception gain of the reception means based on the magnitude of the received signal are provided.

A distance measuring device according to a second aspect of the present invention is a code sequence generating means for generating a signal representing a code sequence, a transmitting means for transmitting an electromagnetic wave modulated by an output signal of the code sequence generating means toward an object. Receiving means for receiving the reflected wave from the object, demodulating it, and outputting it as a received signal, up to the object based on the phase shift of the code sequence represented by the received signal and the phase of the code sequence represented by the transmitted signal And a gain adjusting means for adjusting at least one of the transmission gain of the transmitting means and the receiving gain of the receiving means based on the calculation time of the calculating means.

In the distance measuring device according to the third aspect, the processing means sets the phase of the code sequence represented by the transmission signal to 1 by setting the 1-bit time width of the code sequence as the shift amount 1.
The phase shift means for shifting at least three types of shift amounts to generate at least three types of shift signals within the shift amount range, and the correlation value between the received signal and each shift signal obtained from the phase shift means are set to 1 Alternatively, two straight lines are obtained on the basis of a correlating unit that obtains a correlating output by integrating over a plurality of code sequence lengths, and at least three correlating outputs obtained from the correlating unit, and based on the coordinates of the intersections of these straight lines When the correlation value is greater than a predetermined value when the correlation value is integrated over one or a plurality of code sequence lengths by the correlation means, The feature is that the integration is stopped at this point and the time until this point is set as the calculation time.

According to a fourth aspect of the distance measuring method, a signal representing a code sequence is generated, an electromagnetic wave modulated by an output signal of the code sequence generating means is transmitted to an object, and a reflected wave from the object is transmitted. A distance measuring method for calculating a distance to an object based on the phase shift of the code sequence represented by the transmission signal and the phase of the code sequence represented by the transmission signal. It is characterized in that at least one of the transmission gain of the transmission means and the reception gain of the reception means is adjusted based on the magnitude of the reception signal.

[0012]

The distance measuring device and method according to the present invention comprises the gain adjusting means for adjusting at least one of the transmitting gain of the transmitting means and the receiving gain of the receiving means based on the magnitude of the received signal. Therefore, the next gain can be adjusted according to the state of the reception signal of the previous measurement, and the gain adjustment according to the measurement situation can be performed.

A distance measuring apparatus according to a second aspect of the present invention comprises a gain adjusting means for adjusting at least one of the transmitting gain of the transmitting means and the receiving gain of the receiving means based on the calculation time of the distance measurement. Therefore, the next gain can be adjusted according to the calculation time at the previous measurement, and the gain adjustment according to the measurement situation can be performed.

In the distance measuring device according to the third aspect, the correlation value is 1
Or, when integrating over multiple code sequence lengths, if the integrated value becomes larger than the specified value, the integration is stopped at this point and the time until this point is set as the calculation time. Is characterized by. Therefore,
The gain of the next measurement can be adjusted by this calculation time.

[0015]

1 is a block diagram of a distance measuring device according to an embodiment of the present invention. The clock signal generation circuit 11 outputs the first clock signal CK1 as shown in FIG. This clock signal CK1 is frequency-divided by the frequency dividing circuit 12 to become a clock signal CK2. The second clock signal CK2 is given to the m-sequence generator 13. The m-sequence generator 13 is composed of a shift register and a feedback ethics circuit, and outputs an m-sequence signal as shown in FIG. m
The m-sequence signal output from the sequence generator 13 is given to the drive circuit 14 as a transmission signal TS. The laser diode 15 is driven by the drive circuit 14 and generates a laser beam representing the m-series signal by the output light intensity. This laser light is projected toward an object.

The 1-bit width (minimum pulse width) of the m-series signal is set to be equal to or longer than the time required for the electromagnetic wave to make a round trip at the maximum detection distance. Preferably, the minimum pulse width is set equal to the time.

The reflected light of the projection laser light from the object is received by the photodiode 21. The output signal of the photodiode 21 represents the intensity of the reflected light,
It is amplified by the preamplifier 22 and given to a number of correlators as the received signal RS. The reception signal RS is subjected to waveform shaping by being binarized as necessary.

The first of the many correlators is the forward amplifier 23A, the inverting amplifier 24A, the analog switches 25A and 26A, the inverter 27A, and the integrator 28.
It is composed of A and. Similarly, the second to Jth correlators (J is a number equal to or greater than 3) similarly include the normal amplifiers 23B to 23J.
And inverting amplifiers 24B-24J, analog switches 25B-25J, and analog switches 26B-26J.
, Inverters 27B-27J, and integrators 28B-28
J and J respectively.

A phase shifter 31 is provided to provide a shift signal to these correlators. The phase shifter 31 is composed of, for example, a shift register. The phase sequencer 31 is provided with the transmission signal TS from the m-sequence generator 13 and the first clock signal CK1 for phase shift (for driving the shift register). The phaser 31 outputs various kinds of shift signals FSA, FSB to FSJ as shown in FIG. The first shift signal FSA is a signal in phase with the transmission signal TS, and
Given to the correlator of. The second shift signal FSB has a more appropriate shift amount than the transmission signal TS (for example, 1 / (J-
1): a signal having a delay of 1 bit width of the m sequence (where the shift amount is 1), and given to the second correlator. Similarly, other shift signals are also shifted from the transmission signal TS by an appropriate shift amount and given to other correlators. The Jth shift signal FSJ is a signal delayed by a shift amount from the transmission signal TS by 1 and is given to the Jth correlator. The shift amount of these shift signals FSA to FSJ is in the range of 0 to 1.

The operation of the first correlator will be described with reference to FIG. The normal amplifier 23A receives the received signal R
S is output as it is or after being amplified as necessary. The inverting amplifier 24A receives the input received signal RS
The 0 level of 1 is held as it is, and the 1 level is converted to the -1 level and output. The output signal of inverting amplifier 24A is shown as ISA.

The analog switch 25A inverts the first shift signal FSA (same as the transmission signal TS) and the analog switch 26A inverts the first shift signal FSA by the inverter 27A (the level of 1 and the level of 0 are exchanged). Are controlled by the signals obtained by the above. The analog switch 25A passes the received signal RS input when the shift signal FSA is at the 1 level. Output signal RSS of analog switch 25A
A is provided to the integrator 28A. Analog switch 2
6A passes the signal ISA input when the shift signal FSA is at the 0 level. The output signal ISSA of analog switch 26A is provided to integrator 28A. The input signal ASA of the integrator 28A is a signal obtained by combining both signals RSSA and ISSA.

Here, the phase-shifted transmission signals (FSA to FS)
The relationship between J), the received signal (RS) and the correlation value (ASA) is summarized in a table as shown in FIG. The reason why the received signal values are a and 0 instead of 1 and 0 is that the received intensity changes depending on the situation (distance, weather, etc.).

The counter 16 has a second clock signal CK2.
And a reset signal RR is given to the integrator 28A (and other integrators 28B to 28J) every time one cycle of the m-sequence (15-bit length) elapses. The reset signal RR has a width of 1 bit. The length from one trailing edge of a reset signal RR to the trailing edge of the next reset signal RR is one code sequence length (one cycle) of the m sequence, and this period is the integrator 28A (and This is the integration period of the other integrators 28B to 28J).

Integrator 28A (and other integrators 28B ...
28J) performs the reset operation while the reset signal RR is at the level of 1 (for example, discharging the electric charge of the capacitor),
The input signal ASA is integrated (for example, the capacitor is charged) in the integration period of 0 level, and the signal SSA representing the integration result is output. The value of the integrated signal SSA immediately before the reset of the integrator 28A represents the correlation value SA.

The arithmetic unit 30 is composed of, for example, a CPU, a memory and its peripheral circuits, and takes in the integration signal SSA immediately before the integrator 28A is reset (the integration signal SSA is taken in based on the reset signal RR and immediately thereafter). It is easy to reset the integrator 28A at.

Similarly, in the second to Jth correlators, the second to Jth shift signals FSB to FSJ are used to control the analog switches 25B and 26B to 25J, respectively.

Integrators 28B to 28J of these correlators output integrated signals SSB to SSJ, respectively. The arithmetic unit 30 takes in the correlation values respectively represented by the integration signals SSB to SSJ (these correlation values are respectively represented by SB to SJ) immediately before being reset by the integrators 28B to 28J counter 16.

FIG. 6 shows a graph in which the horizontal axis represents the shift amount and the vertical axis represents the correlation value. This means that the phase of the transmission signal and the phase of the reception signal are shifted by the amount of phase shift at the point α at which the correlation value becomes maximum. Therefore, by obtaining this shift amount D, the distance to the object can be obtained.

That is, the arithmetic unit 30 obtains two straight lines by using the acquired correlation values SA to SJ, and obtains the intersection of these straight lines to calculate the distance to the object. In order to obtain two straight lines, in principle, at least a shift signal FSA having a shift amount of 0, a shift signal FSJ having a shift amount of 1, and a shift signal having a shift amount of 0 to 1 are used. You can use the type. At least 3 between these at least 3 types of shift signals and received signals
Two correlation values are obtained. Then, one straight line is obtained using at least two correlation values. The other straight line has the same absolute value of the gradient and the opposite sign to the one straight line. Therefore, the other straight line can be obtained using the remaining one correlation value and the slope of the one straight line. If two straight lines are obtained, the distance is calculated from the intersection.

However, it is needless to say that two straight lines can be obtained more accurately by using various kinds of shift signals. In particular, when the obtained correlation values vary due to noise, circuit error, etc., the more the number of correlation values is, the more accurately the two straight lines can be obtained.

Next, the automatic gain control according to this embodiment will be described. As described above, the arithmetic unit 3
0 calculates the distance based on the correlation value obtained by integration. At this time, the arithmetic unit 30 gives the maximum value (A in FIG. 6) of the integrated value (correlation value) to the gain adjustment circuit 42. The maximum value A of this integrated value is proportional to the strength of the received signal. Therefore, when the measurement condition is bad due to rain or fog, it becomes small. Further, it becomes large when measuring a short distance.

The gain adjusting circuit 42 receives the maximum integrated value and decreases the measurement gain when the maximum integrated value is large, and increases the measured gain when the maximum integrated value is small. As a result, when the measurement situation is bad, the gain can be automatically increased and accurate measurement can be performed.

The measurement gain is adjusted by the drive circuit 14
Is controlled to control the light emission amount of the LD 15 and the amplification factor of the preamplifier 22. For example, if the value that can be integrated is up to 4095, and the maximum integrated value is 2000 or less, according to FIG.
I try to double the gain.

By the way, when the object is too close, the intensity of the received signal becomes excessively large. In this case, the integrator may be saturated by the end of the integration period, and accurate measurement may not be possible. Therefore, in this embodiment, as shown in FIG. 1, an integrator saturation detection circuit 40 is provided.

The details of the integrator saturation detection circuit 40 are shown in FIG. Any one of the integrating circuits 28A to 28J,
When the integrated value exceeds the reference voltage, a saturated output is output via the OR circuit 70. This saturated output is given to the counter 16 to forcibly reset the counter 16 and output the reset signal RR. As a result, each of the integrators 28A to 28J is reset. In other words, even if the integration operation is performed any more, accurate measurement cannot be performed.
Stop integration operation.

At the same time, the counter 16 supplies a count value (proportional to the calculation time) immediately before resetting to the gain adjusting circuit 42. If the count value is lower than usual, the gain adjusting circuit 42 knows that the integrator is saturated and lowers the measured gain. As a result, from the next measurement, it is possible to prevent saturation of the integrator and perform accurate measurement. For example, if the calculation time in the state where the integrator is not saturated is 30 mS, the calculation time is 20
When it is less than mS, the gain is controlled to be 1/2.

If the received signal is too large or the noise is large, the preamplifier 22 may be saturated and accurate measurement may not be possible. Therefore, in this embodiment, as shown in FIG. 9, the saturation determination output is output from the comparator 80 when the output of the preamplifier 22 exceeds a predetermined value (reference voltage). This saturation determination output is given to the gain adjusting circuit 42. Gain adjustment circuit 42
In case of the saturation judgment output, the gain is reduced to 1/2. This prevents erroneous measurement due to saturation of the preamplifier 22.

It should be noted that the above-described gain adjustment is performed by using FIG.
This is performed based on the reflection signal from the object located at the shortest distance among the objects within the range shown by 0.
Therefore, if the object is farther than the range of FIG. 10, or if there are multiple objects within the range, the object farther away is not the object for gain adjustment.

[0039]

According to the distance measuring apparatus and method of the present invention, there is provided a gain adjusting means for adjusting at least one of the transmitting gain of the transmitting means and the receiving gain of the receiving means based on the magnitude of the received signal. There is. Therefore, the next gain can be adjusted according to the state of the reception signal of the previous measurement, and the gain adjustment according to the measurement situation can be performed.

A distance measuring device according to a second aspect of the invention is provided with a gain adjusting means for adjusting at least one of the transmitting gain of the transmitting means and the receiving gain of the receiving means based on the calculation time of the distance measurement. Therefore, the next gain can be adjusted according to the calculation time at the previous measurement, and the gain adjustment according to the measurement situation can be performed.

According to the distance measuring device of claim 3, the correlation value is 1
Or, when integrating over multiple code sequence lengths, if the integrated value becomes larger than the specified value, the integration is stopped at this point and the time until this point is set as the calculation time. Is characterized by. Therefore,
The gain of the next measurement can be adjusted by this calculation time.

That is, according to the present invention, it is possible to provide a distance measuring device and method having a simple structure, high resolution, and capable of maintaining high detection capability regardless of the situation.

[Brief description of drawings]

FIG. 1 is a block diagram of a distance measuring device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing a clock signal and an m-sequence code generated by using the clock signal.

FIG. 3 is a diagram showing a waveform of each block in FIG.

FIG. 4 is a diagram showing a waveform of each block in FIG.

FIG. 5 is a diagram showing an example of calculation of a correlation value.

FIG. 6 is a diagram showing a relationship between a shift amount (distance) and a correlation value.

FIG. 7 is a diagram showing a stage of gain adjustment performed by a gain adjustment circuit.

8 is a diagram showing details of an integrator saturation detection circuit 40. FIG.

FIG. 9 is a diagram showing a circuit for performing saturation determination of the preamplifier 22.

FIG. 10 is a diagram showing an area of an object for which gain adjustment is performed.

[Explanation of symbols]

11 ... Clock signal generator 12 ... Frequency divider 13 ... m sequence generator 14 ... Drive circuit 15 ... Laser diode 16 ... Counter 21 ... Photodiode 23A-23J・ ・ ・ Normal amplifier 24A to 24J ・ ・ ・ Inverting amplifier 25A to 25J, 26A to 26J ・ ・ ・ Analog switch 28A to 28J ・ ・ ・ Integrator 30 ・ ・ ・ Computing device 31 ・ ・ ・ Phase shifter 40 ・ ・ ・・ Integrator saturation detection circuit 42 ・ ・ ・ Gain adjustment circuit

Claims (4)

[Claims] 1. A code sequence generating means for generating a signal representing a code sequence, a transmitting means for transmitting an electromagnetic wave modulated by an output signal of the code sequence generating means toward an object, and a reflected wave from the object. Receiving means for receiving and demodulating and outputting as a received signal, processing means for calculating the distance to the object based on the phase shift of the code sequence represented by the transmitted signal and the phase of the code sequence represented by the received signal A distance measuring device comprising: a gain adjusting unit that adjusts at least one of the transmitting gain of the transmitting unit and the receiving gain of the receiving unit based on the magnitude of the received signal. 2. Code sequence generating means for generating a signal representing a code sequence, transmitting means for transmitting an electromagnetic wave modulated by an output signal of the code sequence generating means toward an object, and a reflected wave from the object. Receiving means for receiving and demodulating and outputting as a received signal, processing means for calculating the distance to the object based on the phase shift of the code sequence represented by the transmitted signal and the phase of the code sequence represented by the received signal A distance measuring device comprising: a gain adjusting unit that adjusts at least one of a transmitting gain of the transmitting unit and a receiving gain of the receiving unit based on a calculation time of the calculating unit. 3. The distance measuring device according to claim 2, wherein the processing means has at least a phase of the code sequence represented by the transmission signal within a range of 1 shift amount, where 1 bit time width of the code sequence is a shift amount 1. A phase shift means for shifting at least three kinds of shift signals by shifting three kinds of shift amounts, and a correlation value between the received signal and each shift signal obtained from the phase shift means are integrated over one or a plurality of code sequence lengths. Then, a correlating means for obtaining a correlating output, and a calculating means for calculating two straight lines based on at least three correlating outputs obtained from the correlating means, and calculating a distance to the object based on the coordinates of the intersection of the straight lines, When the correlation value is integrated over one or a plurality of code sequence lengths in the correlation means, the integrated value becomes larger than a predetermined value. Case, as well as stop the integration at this time, the distance measuring device being characterized in that the time for this until such a calculation time. 4. A signal representing a code sequence is generated, an electromagnetic wave modulated by an output signal of a code sequence generating means is transmitted toward an object, a reflected wave from the object is received and demodulated, A method for measuring the distance to an object, which is output as a received signal and calculates the distance to an object based on the phase shift between the code sequence represented by the transmitted signal and the phase of the code sequence represented by the received signal. A distance measuring method, characterized in that at least one of the transmission gain of the transmission means and the reception gain of the reception means is adjusted based on the magnitude.