JP3635154B2 - Distance measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a distance measuring apparatus that detects an electromagnetic wave reflected when an electromagnetic wave such as a light wave or a millimeter wave is emitted in a measurement target direction and measures a distance to an object.
[0002]
[Prior art]
Conventionally, a laser diode that emits light intermittently, detects the reflected light from a front object with a photo sensor, and measures the distance to the front object based on the time difference between the light emission time and the light reception time (laser radar) It has been known.
[0003]
Such a laser radar compares the received light signal with a threshold value VTH in order to remove noise existing as a background due to the influence of sunlight, etc., and determines the time when the received light signal exceeding the threshold value VTH is obtained. It is comprised so that it may be the light reception time of reflected light (refer Fig.5 (a)).
[0004]
[Problems to be solved by the invention]
By the way, the intensity of sunlight changes day and night, and the magnitude of noise is not constant. In addition, the thermal noise of the circuit in the laser radar, which is another noise factor, changes every moment.
[0005]
For this reason, if the threshold value is low, as shown in FIG. 5B, the noise B exceeds the threshold value before the actual received light signal A is detected, and the distance is measured incorrectly. There is a fear.
On the other hand, the intensity of the reflected light from the object to be measured becomes weaker as the distance becomes longer. Therefore, if the threshold value is increased, the measurable distance becomes shorter and sufficient performance cannot be exhibited.
[0006]
Accordingly, an object of the present invention is to provide a distance measuring device that is not affected by such a change in noise level without sacrificing the measurable distance.
[0007]
[Means for Solving the Problems]
According to the distance measuring device of the present invention, the time when the electromagnetic wave is emitted from the electromagnetic wave emitting means such as the laser diode and the determination signal obtained through the electromagnetic wave detecting means such as the photosensor are predetermined as described in claim 1. The distance to the object existing in the measurement target direction is calculated based on the time difference from the time when the threshold value is exceeded, and the electromagnetic wave emitting means is paused for a predetermined period, and the threshold is set. Adjustment means is provided for adjusting the relationship between the determination signal and the threshold value so that the value is substantially equal to the maximum value of the determination signal generated during the pause period .
[0008]
Here, the determination signal generated during the pause period of the electromagnetic wave emitting means corresponds to noise itself. Therefore, if (threshold value) = (maximum value of the noise amplification signal), the noise amplification signal does not exceed the threshold value, and an erroneous arrival signal due to the influence of noise is not generated. The problem of measuring the distance shorter than the actual distance is eliminated. If a detection signal slightly larger than the maximum noise value is obtained, the distance can be measured, and the measurable distance can be maximized. Even if the threshold value is slightly smaller than the maximum value, there is almost no problem of erroneous measurement in view of the probability that the maximum value will occur. Therefore, if (threshold value) ≈ (maximum value), the present invention is sufficient. The objective can be achieved.
[0009]
By the way, in performing such adjustment, as a specific method, a method of increasing or decreasing the threshold value of the comparison circuit that compares the determination signal and the threshold value can be considered. There is a problem that it takes a long time to determine whether or not the threshold is exceeded.
[0010]
Therefore, in the distance measuring device according to claim 1, the adjusting means is configured as means for adjusting the gain of the signal amplifying means . According to this configuration, the threshold value can be fixed, so that a comparison circuit with a short determination time can be employed. The gain can be easily adjusted by using a variable gain amplifier or the like as the signal amplifying means.
[0011]
More specifically, as described in claim 1 , the distance is calculated when the adjusting means gives a pseudo start pulse to the distance calculating means during the pause period. If the gain of the signal amplifying means is reduced, and if the distance is not calculated when a pseudo start pulse is given to the distance calculating means during the pause period, the gain of the signal amplifying means It is comprised as a means to raise. This is because a pseudo start pulse is given to the distance calculation means during the pause period, and when the determination signal during the pause period exceeds the threshold, an arrival signal is generated and the distance is increased. On the contrary, when the threshold value is not exceeded, the phenomenon that the distance is not calculated is used.
[0012]
According to this distance measuring device, when the maximum value of the determination signal during the pause period exceeds the threshold value, the gain is decreased, and conversely, when the threshold value is not exceeded, the gain is increased. The gain will converge to the optimum value. Therefore, it is possible to realize a state in which the threshold value is substantially equal to the maximum noise value.
[0018]
Since the rising angle of the noise signal is steep or gentle, it is practically difficult to always detect it systematically with a peak hold circuit or the like. In this regard, the distance measuring device according to claim 1 is based on whether or not an erroneous arrival signal is generated, and therefore has an advantage that an optimum gain can be realized with high accuracy.
[0019]
Here, as described in claim 2 , in the distance measuring device according to claim 1 , the adjustment unit is configured to have a remaining range excluding a range where it has been found that there is no optimum gain in the gain adjustment process. When configured as means for lowering and raising the gain so as to be the median value, the gain adjustment speed can be maximized. This device is excellent in that both high speed and high accuracy can be achieved.
[0020]
According to a third aspect of the present invention, the adjusting unit detects a maximum value of the determination signal generated during the pause period, and compares the detected maximum value with the threshold value. By roughly adjusting the gain of the signal amplification means and then using the rough adjustment result as a starting condition, it is possible to achieve both high speed and high accuracy.
[0021]
More specifically, it is possible to implement a gain adjustment method in which the gain is adjusted more accurately after first adjusting the gain roughly .
In order to increase the speed of the distance measuring device, it is preferable that a logic IC is provided as the determination means as described in claim 4 . The reason why such a logic IC can be provided is that a means for apparently increasing or decreasing the threshold value by adjusting the gain is employed.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a laser radar 1 as an embodiment. The laser radar 1 is mounted on an automobile and detects an obstacle (reflecting object) ahead.
[0023]
The laser radar 1 is configured as follows with a transmission / reception unit 31 and a calculation unit 33 as main parts. As shown in FIG. 1, the transmission / reception unit 31 includes a semiconductor laser diode (hereinafter simply referred to as a laser diode) 39 that emits a pulsed laser beam H forward via a scan mirror 35 and a light-emitting lens 37, A light receiving element 43 that receives the laser beam H reflected by the obstacle through the light receiving lens 41 and outputs a voltage corresponding to the intensity thereof.
[0024]
The laser diode 39 is connected to the calculation unit 33 via the drive circuit 45 and emits a laser beam H in response to a drive signal from the calculation unit 33. In addition, a mirror 47 is provided on the scan mirror 35 so as to be rotatable about a vertical axis. When a drive signal from the calculation unit 33 is input via the motor drive unit 49, the mirror 47 is connected to a motor (not shown). It is rotated by the driving force. Then, the laser beam H is irradiated while being scanned over a predetermined angle in the horizontal plane in front of the vehicle.
[0025]
On the other hand, the output voltage of the light receiving element 43 is amplified to a predetermined level via an STC (Sensitivity Time Control) circuit 51 and then input to the variable gain amplifier 53. The STC circuit 51 will be supplementarily described. Since the received signal intensity is inversely proportional to the fourth power of the distance to the target, this STC circuit 51 is provided to compensate for the case where there is a reflector having a high reflectivity at a short distance and the received light intensity becomes extremely strong. ing.
[0026]
The variable gain amplifier 53 is connected to the arithmetic unit 33 via the D / A converter 55, amplifies the input voltage according to the gain (gain) instructed by the arithmetic unit 33, and outputs the amplified input voltage to the comparator 57. The comparator 57 employs a logic IC configured to be capable of high-speed processing with an inverter and a transistor. The comparator 57 compares the output voltage V of the variable gain amplifier 53 with the threshold voltage VTH, and when V> VTH, a predetermined value is obtained. The reflected light arrival signal is input to the time measuring circuit 61.
[0027]
The time measurement circuit 61 also receives a start pulse PA that means that a drive signal has been output from the calculation unit 33 to the drive circuit 45. Then, the time measuring circuit 61 uses the reflected light arrival signal as the stop pulse PB, encodes the phase difference (that is, input time difference) between the two pulses PA and PB into a binary digital signal, and calculates the value to the arithmetic unit 33. Is configured to input.
[0028]
As this time measuring circuit 61, for example, an odd-numbered ring oscillator in which an odd number of inverter gate delay circuits that invert and output an input signal are connected in a ring shape and a pulse edge circulates on the ring can be considered. . The phase difference (that is, input time difference) between the two pulses PA and PB is measured as follows. That is, when the start pulse PA is input, the pulse edge circulates on the ring oscillator, and when the stop pulse PB is input, the pulse edge activated by the start pulse PA becomes any inverter gate on the ring oscillator. By detecting whether the delay circuit has been reached, the phase difference between the two pulses PA and PB is measured.
[0029]
The time measuring circuit 61 also has a time resolution correction function in order to perform accurate time measurement. Here, digital calculation correction by a complete digital circuit is performed by using a reference signal (for example, a crystal oscillation clock).
The computing unit 33 calculates the distance and direction to the obstacle based on the input time difference from the time measuring circuit 61 and the rotation angle of the mirror 47 at that time. The output voltage V of the variable gain amplifier 53 is also input to the peak hold circuit 63, and the peak hold circuit 63 inputs the maximum peak value of the output voltage V to the calculation unit 33.
[0030]
In addition, a vehicle speed signal from a vehicle speed sensor is also input to the calculation unit 33.
Next, the operation of the laser radar 1 configured as described above will be described.
As shown in the flowchart of FIG. 2, the calculation unit 33 outputs a drive signal to the drive circuit 45 to cause the laser diode 39 to emit light (S100). Here, the drive signal is output so as to emit intermittent pulsed light over a certain period T1. Further, over this period T1, a drive signal is output to the motor drive circuit 49 to rotate the mirror 47 at a predetermined speed (S110). As a result, laser pulse light is emitted from the laser radar 1 toward a region within a predetermined angle range in the front. If an obstacle exists within this range, the pulse light is reflected and returned.
[0031]
The reflected light is input to the light receiving element 43 through the light receiving lens 41 and converted into a voltage signal corresponding to the intensity of the reflected light, and then passes through the STC circuit 51 and the variable gain amplifier 53 to become a determination signal V. To the comparator 57. The comparator 57 compares the determination signal V with the threshold value VTH, and inputs the reflected light arrival signal to the time measuring circuit 61 when V> VTH. The time measurement circuit 61 measures a time difference (distance data) between the light emission time and the light reception time and inputs the time difference to the calculation unit 33. The distance data input from the time difference measuring circuit 61 is stored in a RAM (not shown) of the calculation unit 33.
[0032]
When the scanning of the measurement range is completed (S120), it is determined whether or not distance data exists (S130). If there is no distance data, only the information that there is no problem obstacle is stored, and the distance data is not output (S140).
On the other hand, if distance data exists, the distance data is grouped according to the distance (S150). This “grouping according to distance” will be described. In the laser radar 1, since the laser diode 39 emits light every time the mirror 47 rotates by a predetermined angle, the emitting direction of the laser light H is also set discontinuously for every predetermined angle (for example, 0.5 degrees). Therefore, it is distinguished as distance data corresponding to the laser light H having a different emission direction, and as it is, distance data based on reflected light from the same object is processed as different data. Therefore, the subsequent processing is simplified by grouping adjacent distance data.
[0033]
Note that “proximity” may be defined according to various conditions. However, when there is distance data that is very close corresponding to the adjacent emission directions in consideration of the emission direction of the laser light H, the group Is preferable. This is because when the laser beam H is reflected back to the rear of the preceding vehicle, it is highly conceivable that a plurality of laser beams H emitted at predetermined angles are reflected on the same vehicle. .
[0034]
When the distance data can be grouped in this way, the result is output (S160). Then, after executing the gain adjustment process (S170) and the mirror return process (S180), the routine exits. This gain adjustment processing is executed within a period T2 in which laser light emission is not performed.
[0035]
The gain adjustment process is configured as shown in FIG.
In this process, first, light emission is stopped (S210), and the gain of the variable gain amplifier 53 is set to the maximum (S220). Here, the D / A converter 55 has a function of setting the gain of the variable gain amplifier 53 in 256 stages of 0 to 255. Accordingly, in S220, “255” is output to the D / A converter 55.
[0036]
Subsequently, a pseudo start pulse is output to the time measurement circuit 61 to give an opportunity for time measurement (S230). Then, it is determined whether or not the distance data is calculated in the time measuring circuit 61 (S240). If the distance data is calculated, the amplifier gain is decreased (S250), and conversely, the distance data is calculated. If not, the amplifier gain is increased (S260).
[0037]
Here, the amplifier gain is lowered and raised to a median value in a range where an optimum gain may exist. As a specific example, if distance data exists when a gain of “255” level is initially set, it is found that the optimum gain is less than “255”, so “0” to “254”. The gain is reduced to “127”, which is the median value of “”. If the distance data is still calculated even in this state, it is reduced to “63” which is the median value of “0” to “126”. If the distance data is not calculated at this time, the optimum value is found to be within the range of “64” to “127” from the adjustment process so far, and then the gain is set to “96”. To do. If the distance data is not yet calculated, the gain is increased to the median value “112” in the range of “97” to “127”. In this way, the gain is adjusted while gradually narrowing the range. In this example, the optimum gain can be obtained by changing the gain eight times.
[0038]
After the amplifier gain is lowered or raised in this way, this routine is exited when the end condition is reached (S270). The end condition is satisfied when the amplifier gain is adjusted eight times.
When the termination condition is satisfied in this way, the value subjected to the smoothing process according to the following equation is stored as the current adjustment result Gn from the previous amplifier gain adjustment result Gn-1 and the current adjustment result Gn, and for the next distance measurement timing. Is set (S280, S290).
[0039]
[Expression 1]
Gn = 0.1Gn + 0.9Gn-1
As a result of narrowing the amplifier gain as described above, the amplifier gain set at the distance measurement timing is such that the peak value of the signal due to the influence of sunlight or thermal noise that appears as noise does not exceed the threshold value VTH. There is no mistake in measurement. Moreover, if reflected light slightly exceeding noise is obtained, this exceeds the threshold value VTH, and distance data can be calculated. Therefore, it is possible to eliminate the erroneous measurement of the distance and maximize the measurable distance.
[0040]
Next, a second embodiment will be described.
The hardware configuration of the laser radar in the second embodiment is the same as that of the above-described embodiment. The configuration of the distance measurement main routine is also the same. What is different from the above-described embodiment is the content of the gain adjustment processing.
[0041]
In the gain adjustment process, as shown in FIG. 4, after the light emitting circuit is stopped (S310), the amplifier gain is set to the maximum value Gmax (S320), and the peak hold circuit 63 is reset (S330). The reason why the maximum value Gmax is set is to improve the sensitivity of subsequent processing.
[0042]
Then, the maximum noise level VNmax held in the peak hold circuit after the predetermined gate time has elapsed is input (S340), and the ratio P = VTH / VNmax with the threshold value VTH is calculated (S350).
Then, a value Gn = PGmax obtained by multiplying the current set value Gmax by this ratio P is calculated (S360), and the value Gn = 0.1Gn + 0.9Gn−, which is smoothed with the previous set value Gn−1 according to the equation (1). 1 is stored as the current adjustment result Gn, and the amplifier gain is set for the next distance measurement timing (S370, S380).
[0043]
Also in this embodiment, it is possible to take the maximum measurable distance without erroneous distance measurement.
As mentioned above, although several embodiment of this invention was described, this invention is not restricted to these, Furthermore, it is possible to implement with a various form.
[0044]
For example, in the gain adjustment process, first, the gain is roughly adjusted from the peak value by the method of the second embodiment, and then the gain adjustment is performed by the method of the first embodiment using the rough adjustment result as a starting condition. As described above, it is possible to achieve both high speed, which is a feature of the second embodiment, and high precision, which is a feature of the first embodiment.
[0045]
Further, in the first embodiment, the quick constriction is aimed at by increasing / decreasing the gain to the median of the range where the optimum value can exist. However, in the case of combining with the second embodiment as described above. Since the gain can be adjusted at a reasonable speed even if a configuration in which the gain command is incremented or decremented by 1 is adopted, the method is not limited to the squeezing method employed in the first embodiment.
[0046]
Furthermore, although the embodiment was about a radar using a laser diode, even a radar using a millimeter wave or the like may be subject to problems such as thermal noise or the influence of electromagnetic waves in the environment. Therefore, it is needless to say that the present invention can be applied as it is.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a laser radar as a first embodiment.
FIG. 2 is a flowchart showing a main routine of distance measurement in the first embodiment.
FIG. 3 is a flowchart showing a gain adjustment routine in the first embodiment.
FIG. 4 is a flowchart showing a gain adjustment routine in the second embodiment.
FIG. 5 is an explanatory diagram showing a conventional problem.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Laser radar, 31 ... Transmission / reception part, 33 ... Operation part, 35 ... Scan mirror, 37 ... Light emitting lens, 39 ... Laser diode, 41 ... Light receiving lens, 43 ... Light receiving element, 45 ... Drive circuit, 47 ... Mirror, 49 ... Motor drive, 51 ... STC circuit, 53 ... Variable gain amplifier, 55 ... D / A conversion , 57 ... comparator, 61 ... time measuring circuit, 63 ... peak hold circuit, H ... laser light.

Claims (4)

Electromagnetic wave emitting means for emitting electromagnetic waves in the direction of the measurement object;
An electromagnetic wave detecting means arranged to output a detection signal corresponding to the intensity of the electromagnetic wave incident from the direction of the measurement object;
Signal amplifying means for generating a determination signal obtained by amplifying the detection signal according to a predetermined gain;
A determination means for outputting an arrival signal notifying the arrival of the reflected wave when the determination signal exceeds a predetermined threshold;
A distance measuring device comprising: a distance calculating unit that calculates a distance to an object existing in the measurement target direction based on a time delay from when the electromagnetic wave emitting unit emits the electromagnetic wave until the arrival signal is obtained. In
The electromagnetic wave emitting means is paused for a predetermined period, and the determination signal and the threshold value are set so that the threshold value is substantially equal to the maximum value of the determination signal generated during the pause period. With adjustment means to adjust the relationship,
When the distance is calculated when the adjusting means gives a pseudo start pulse to the distance calculating means during the pause period, the gain of the signal amplifying means is decreased, and conversely, the pause period A distance measuring apparatus comprising: a means for increasing a gain of the signal amplifying means when a distance is not calculated when a pseudo start pulse is given to the distance calculating means . 2. The distance measuring device according to claim 1 , wherein the adjusting means is configured to decrease and increase the gain so as to be a median value of the remaining range excluding a range in which an optimum gain does not exist in the gain adjusting process. A distance measuring device configured as means for performing The distance measuring device according to claim 1,
The adjusting means includes
Detecting the maximum value of the determination signal generated during the pause period, comparing the detected maximum value with the threshold value, and roughly adjusting the gain of the signal amplification means;
A distance measuring device characterized in that the rough adjustment result is used as a starting condition thereafter . In the distance measuring device according to any one of claims 1 to 3 ,
A distance measuring device comprising a logic IC as the determining means.

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