JP2008267920A - Laser range finding device and laser range finding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser range finding device shortening a range finding time by reducing a signal processing burden so as to be effective particularly in the case of high measuring density per unit time. <P>SOLUTION: The device includes a transmitting part 1 transmitting laser beams toward a measuring object; a receiving part 2 receiving a receive signal 21 reflected and returned from the measuring object; a time measuring part 3 and an intensity measuring part 4 branching and inputting the output of the receiving part 2; a constant fraction discriminator for suppressing a time measuring error included in a time measured value Δt<SB>1</SB>output by the time measuring part 3; a correcting part 5 correcting the time measuring error which exceeds the suppression limit at the constant fraction discriminator; and a correction table in which a correction quantity to an intensity measured value P<SB>1</SB>measured by the intensity measuring part 4 is predetermined and stored in a referable manner in the correcting part 5. The correcting part 5 is operated only when the intensity measured value P<SB>1</SB>exceeds a predetermined value. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a laser distance measuring device laser distance measuring method.

  Patent Document 1 below describes a radar apparatus that prevents deterioration in detection accuracy of an object due to the intensity of reflected waves being too high. In this radar apparatus, the laser radar sensor has a laser diode that emits laser light, and a polygon mirror that reflects the laser light emitted from the laser diode and scans a predetermined measurement area. This polygon mirror has reflecting surfaces with different laser beam reflectivities. Based on the traveling speed of the vehicle, the distance to the reflecting object, the received light intensity of the reflected wave from the reflecting object, etc. Switch the surface to change the intensity of the output laser beam. As a result, when detecting an object at a long distance or an object with a low reflectance of laser light, the intensity of the laser light is increased to detect an object at a short distance or an object with a high reflectance of laser light. Since the intensity can be changed so as to reduce the intensity of the laser beam, the object detection accuracy can be improved.

  Patent Document 2 below describes a laser distance measuring device that prevents fluctuations in measurement distance due to changes in the amount of received light in laser distance measurement. The laser distance measuring device includes a light receiving circuit that converts received laser light into an analog electric signal and outputs the signal, a digitizing circuit that converts the analog electric signal output from the light receiving circuit into a rectangular wave, and outputs the signal. A time measuring device that measures and records time by inputting a rectangular wave output from the digital circuit, and the digitizing circuit is a saturation countermeasure means that suppresses the output of the rectangular wave when an analog electric signal of a predetermined voltage or more is input. A saturation level detection circuit that outputs a control signal when an output of an amplification circuit that amplifies an analog electric signal exceeds an upper threshold, and a comparison circuit that suppresses conversion of the analog electric signal to a rectangular wave when the control signal is input. It is to have.

  Patent Document 3 listed below discloses a vehicle object recognition that can detect the adhesion of dirt on the surface of a laser radar sensor when laser light propagates inside or is scattered. An apparatus is described. In the vehicle object recognition device, when the laser light propagates inside the dirt or is scattered, a part of the laser light is received by the light receiving element of the laser radar sensor. Therefore, among the multiple irradiated laser beams, there is a laser beam whose intensity is so strong that the measurement time from irradiation until the reflected light is received is shorter than the predetermined measurement time and the received pulse of the reflected light exceeds the upper threshold. It is determined that dirt is attached on the condition that the number is not less than the first predetermined number. If the time from irradiation to light reception is shorter than the predetermined measurement time, it is reflected light due to the above-mentioned dirt, and if the intensity is so strong that the received light pulse exceeds the upper threshold, the amount of dirt attached is estimated to be large. it can. Therefore, when the number of such received light pulses exceeds the first predetermined number, it can be determined that the above-mentioned dirt has adhered.

  Further, Patent Document 3 also discloses the following technique. That is, the time width corresponding to the received light intensity and the correction time have a predetermined correspondence. Specifically, the correction time tends to monotonically increase as the time width corresponding to the received light intensity increases. Therefore, by obtaining the correspondence relationship by an experiment or the like in advance, the correction time can be obtained and corrected from the time width corresponding to the received light intensity. When the time when the received light signal reaches the maximum voltage is calculated, the distance to the reflecting object is measured based on the time difference from the light emission time of the laser diode to the time when it reaches the maximum voltage.

Thereby, the measurement error due to the difference in the received light intensity of the reflected wave is corrected by the correction time, and the distance to the object is measured as the time difference up to the same time. The relationship between the time width corresponding to the received light intensity and the correction time is stored in a ROM or the like as a map (hereinafter also referred to as “correction table”).
JP 2005-77379 A JP 2003-294840 A Japanese Patent Laying-Open No. 2005-10094

  However, in the technique described in Patent Document 3, there is a problem that the distance measurement time becomes long because the calculation processing load of the CPU increases by referring to the “correction table” stored in the ROM or the like.

  The present invention has been made in view of the above-described circumstances, and provides a laser distance measuring device that shortens a distance measuring time by reducing a signal processing burden for correction so as to eliminate a measurement error. Objective. In particular, it is effective when the measurement density per unit time is large.

In order to achieve the object, the laser distance measuring apparatus according to the first invention employs the following first means.
A transmission unit that transmits laser light toward the measurement target, a reception unit that receives a reception signal reflected and returned from the measurement target, and a time measurement unit and an intensity measurement unit connected to the output of the reception unit; The time measurement unit includes a constant fraction discriminator that can extract timing information that does not depend on the wave height of the received signal, and a correction unit that corrects a time measurement error that exceeds a suppression limit in the constant fraction discriminator, The correction unit is operated only when the intensity measurement value exceeds a predetermined value.

According to the laser range finder according to the first aspect of the invention, the laser beam is transmitted from the transmission unit to the measurement target, and the reception signal reflected and returned from the measurement target is received by the reception unit. The output of the receiving unit is branched and input to the time measuring unit and the intensity measuring unit.
When the received signal in the laser distance measuring device is detected by a single fixed simple threshold value, a time measurement error (jitter) accompanying fluctuation in the wave height of the received signal occurs. For example, when detecting at the timing of the rising slope of the sine wave, it is detected earlier as the signal strength is stronger even at the same measurement distance, so it is mistaken as if it is closer to the true measurement distance, and conversely Since it is detected later as the signal strength is weaker, it is mistaken as if it is farther than the true measurement distance.

  Thus, in order to suppress the time measurement error included in the time measurement value output from the time measurement unit, the constant fraction discriminator is always operating. However, when a time measurement error exceeding the suppression limit of the constant fraction discriminator occurs, it is corrected by the correction unit. In this way, the distance measurement time can be shortened by reducing the signal processing burden for correcting the measurement error. In particular, it is effective when the measurement density per unit time is large.

The laser distance measuring apparatus according to the second invention employs the following second means in addition to the first means.
A correction table that preliminarily stores a correction amount for the intensity measurement value measured by the intensity measurement unit in the correction unit, and a calculation processing unit that corrects the time measurement error with reference to the correction table; Equipped with.

  According to the laser range finder according to claim 2, when the correction is made with reference to the correction table, the calculation processing load of the calculation processing means (CPU) increases and the distance measurement time becomes long. The correction unit is activated only when the value exceeds Then, the signal processing burden for correcting the measurement error is reduced, and the distance measurement time can be shortened. In particular, it is effective when the measurement density per unit time is large.

The laser ranging method according to the third invention employs the following third means.
A laser beam is transmitted toward the measurement object, a reception signal reflected and returned from the measurement object is received, and a measurement is performed according to a relational expression of the speed of light from a time difference between the transmission signal that transmits the laser beam and the reception signal. In the laser distance measuring device that converts the distance to the target,
Time measurement end step for measuring the time difference, saturation determination step for determining whether or not the received signal is saturated, and measurement error caused by saturation if determined to be saturated in this saturation determination step From the time difference measured without correction to the measurement object if it is determined that it is not saturated in the saturation conversion step and the distance conversion step after the correction is correctly performed in the saturation correction step. And a distance conversion step for calculating the distance.

  According to the laser distance measuring method according to the third invention, the same effects as the laser distance measuring apparatus according to the first invention are obtained.

The laser ranging method according to the fourth invention employs the following fourth means.
In the saturation correction step, a correction table in which a correction amount for the intensity measurement value obtained by measuring the intensity of the received signal is determined and stored is referred to.

  According to the laser distance measuring method according to the fourth aspect of the invention, the same effects as those of the laser distance measuring apparatus according to the second aspect of the invention can be achieved.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the laser ranging apparatus which reduced the signal processing burden and shortened the ranging time. In particular, the effect of shortening the distance measurement time is high when the measurement density (number of times) per unit time is large.

  Hereinafter, with reference to the drawings, an embodiment of the present invention (hereinafter referred to as “the present embodiment”) will be described by appropriately interweaving the configuration and operation. In addition, in each figure, the same function attaches | subjects the same code | symbol and abbreviate | omits description.

FIG. 1 is a block diagram showing a schematic configuration of a laser distance measuring device E according to the present embodiment. As shown in FIG. 1, the laser range finder E receives a transmission unit 1 that transmits laser light toward a measurement target 12 (FIG. 2) and a reception signal 21 that is reflected by the measurement target 12 and returned. Unit 2, time measuring unit 3 and intensity measuring unit 4 that branch and input the output of receiving unit 2, and correction unit that corrects an error included in time measurement value Δt ₁ output by time measuring unit 3 5. The correction unit 5 includes arithmetic processing means (hereinafter abbreviated as “CPU”) and a pulse width-correction amount map (hereinafter also referred to as “correction table (FIG. 6B))”. Yes.

Intensity measurement unit 4 outputs an intensity measurement value P ₁ by measuring the intensity of the received signal 21. The time measurement value Δt ₁ input to the correction unit 5 is corrected using the intensity measurement value P ₁ and then output as the time measurement value Δt ₃ . The correction unit 5 is provided with a predetermined correction table correction amount for the pulse width of the intensity measured values P _1, that - along the "pulse width correction amount map", time measuring the time measurement value △ t ₁ Corrected to a value Δt ₃ and output. That is, the principle that the signal intensity can be estimated in proportion to the pulse width is applied.

  FIG. 2 is a block diagram showing a schematic configuration around the scanner 22 in the laser distance measuring device E according to the present embodiment. As shown in FIG. 2, when the laser distance measuring device E transmits a transmission signal 11 by laser light from the transmission unit 1 to the measurement object 12 and receives the reception signal 2, a polygon mirror for scanning a predetermined measurement area. Is interposed. That is, the transmission signal 11 transmitted from the transmission unit 1 is first projected onto the scanner 22, reflected so as to scan in an appropriate direction, and projected onto the measurement object 12.

The reception signal 21 reflected and returned from the measurement object 12 is also projected onto the scanner 22 and appropriately reflected toward the reception unit 2. The reception signal 21 received by the reception unit 2 is sent to the signal processing unit 23, the time measurement unit 3, and the control unit 25. Control unit 25 controls the scanner 22 by using the time measurement value △ t ₁ or the corrected time measurements △ t ₃ obtained from the time measuring unit 3.

  FIG. 3 is an explanatory diagram of an error due to a simple threshold in the laser distance measuring device E according to the present embodiment. As shown in FIG. 3, when the received signal 21 (FIGS. 1 and 4) in the laser distance measuring device E is detected by the single fixed simple threshold 32, for example, when detecting at the timing of the rising slope of the sine wave, the same. Even if it is a measurement distance, it is detected earlier as the signal strength is stronger, so it is mistaken as if it is closer to the true measurement distance, and conversely, it is detected later as the signal strength is weaker. Are misunderstood as if they were far away.

  Further, when the received signal 21 in the laser distance measuring device E is detected by a single fixed simple threshold 32, a time measurement error (jitter) accompanying a fluctuation in the wave height of the received signal 21 occurs. That is, when the received signal 21 is an excessive input, for example, if it exceeds the dynamic range of the amplifier, an amplified output larger than the power supply voltage of the amplifier cannot be obtained, and the subsequent signal processing with distortion shown in the saturated signal 31 occurs. It will be sent to the unit 23, which naturally causes measurement errors.

  4A and 4B are explanatory diagrams of a constant fraction discriminator (hereinafter abbreviated as “CFD”) in the laser distance measuring device E according to the present embodiment, and FIG. 4A is a block diagram and FIG. 4B is a signal waveform diagram. As shown in the block diagram of FIG. 4A, the received signal 21 is branched and input to the delay circuit 41 and the attenuation circuit 42. The output terminals of the delay circuit 41 and the attenuation circuit 42 are connected to the comparator 43, respectively.

  Actually, the output terminal of the comparator 43 is input to the D terminal of a D-type flip-flop (not shown), and timing information independent of the wave height of the received signal 21 is extracted from the Q terminal of the D-type flip-flop. The Q terminal of the D-type flip-flop is connected to a counter (not shown), and the time after the counter is reset at the projection timing of the transmission signal 11 output from the transmitter 1 of the laser distance measuring device E is measured. Thus, the time measuring unit 3 functions as a time measuring counter. However, this time measurement counter, which has already been made into one chip, has been put into practical use, and further illustration will be omitted.

  The delay signal 41a output from the delay circuit 41 and the attenuation signal 42a output from the attenuation circuit 42 are input to the comparator 43 and compared. Here, as shown in the signal waveform diagram of FIG. 4B, the time measuring unit 3 using the CFD can extract timing information independent of the wave height of the received signal 21, so that the delay signal 41a and the attenuation signal 42a can be extracted. The position of the intersection 45a is always constant without depending on the signal intensity.

In this way, the CFD is always operating in order to suppress the time measurement error included in the time measurement value Δt ₁ output from the time measurement unit 4. However, the correction unit 5 operates and corrects only when a time measurement error exceeding the suppression limit in the CFD occurs. When the correction unit 5 operates, the CPU performs correction with reference to the correction table (FIG. 6B) read from the ROM.

  At that time, since a considerable burden is imposed on the CPU and a predetermined time is required for the calculation, the correction unit 5 is not operated when the suppression limit in the CFD is not exceeded. In this way, the distance measurement time can be shortened by reducing the signal processing burden for correcting the measurement error. In particular, it is effective when the measurement density per unit time is large.

  FIG. 5 is a waveform diagram showing intersections of saturation signals in the laser distance measuring device E according to the present embodiment. As shown in FIG. 5, the intersection 45b of the saturated delayed signal 41b and the saturated attenuation signal 42b is a true intersection 45a (FIG. 4 (b) that would otherwise have been obtained if these signals were not saturated. )) Is detected before this, and in this case as well, it is misunderstood closer than the true measurement distance.

  6A and 6B are explanatory diagrams of a correction method in the laser distance measuring device E according to the present embodiment, in which FIG. 6A is a waveform diagram of a saturation signal, and FIG. 6B is a graph showing a relationship between a pulse width and a measurement error. As shown in FIG. 6A, it can be confirmed that the pulse widths 61d, 62d, and 63d of the saturated signals 61c, 62c, and 63c in order of increasing signal intensity are also wide. From this, it is known that the measurement error increases as the signal intensity increases and the pulse width increases.

As shown in FIG. 6B, by maintaining the relationship between the pulse width and the measurement error as back data, the correction unit 5 shown in FIG. 1 can perform accurate correction. That is, the time measurement value Δt ₁ is corrected to the time measurement value Δt ₃ along with the “pulse width-correction amount map” stored so that the relationship between the pulse width and the measurement error can be used as back data.

  FIG. 7 is a flowchart showing the procedure of saturation correction in the laser distance measuring device E according to this embodiment. As shown in FIG. 7, in the laser distance measuring device E, whether or not the received signal 21 is saturated in the intensity measuring unit 4 after the time measurement is finished (step S1)? Saturation determination (step S2) is continued, and if it is determined in this saturation determination (step S2) that it is saturated (Yes), the process proceeds to saturation correction (step S3), and after correct correction, distance conversion ( Step S4) is executed. On the other hand, if it is determined in the saturation determination (step S2) that it is not saturated (No), the distance conversion (step S4) is executed without correction.

  The various shapes and combinations of the constituent members shown in the above-described embodiments are merely examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention. For example, regardless of the designation of “correction table” or “pulse width-correction amount map” in the present invention, as shown in the correction unit 5 in FIG. 1 and FIG. 6B, the received light intensity (received signal 21). Any relationship may be used as long as the relationship between the time width corresponding to the above and the correction time is stored in a ROM or the like in advance by experiments or the like. Further, the storage medium is not limited to the ROM and is free.

In short, when the intensity measuring unit 4 measures the received signal 21 received by the receiving unit 2, the intensity measuring value P ₁ exceeds a predetermined value. All of the techniques related to the laser distance measuring device E that improve the performance and increase the distance measuring speed by activating the correction unit 5 only at the time and reducing the processing burden of unnecessary arithmetic processing means CPU. Included in the invention.

  In the above embodiment, a laser radar sensor using laser light is employed, but electromagnetic waves, light (millimeter waves, X-rays, etc.) and ultrasonic waves may be used.

It is a block diagram which shows schematic structure of the laser ranging apparatus which concerns on this embodiment. It is a block diagram which shows schematic structure of the scanner periphery in the laser distance measuring device which concerns on this embodiment. It is explanatory drawing of the error by the simple threshold value in the laser distance measuring device which concerns on this embodiment. It is explanatory drawing of the constant fraction discriminator CFD in the laser ranging apparatus which concerns on this embodiment, (a) A block diagram, (b) It is a signal waveform diagram. It is a wave form diagram which shows the intersection of the saturation signal in the laser distance measuring device which concerns on this embodiment. It is explanatory drawing of the correction method in the laser ranging apparatus which concerns on this embodiment, (a) Waveform figure of a saturation signal, (b) It is a graph which shows the relationship between a pulse width and a measurement error. It is a flowchart which shows the procedure of the saturation correction | amendment in the laser ranging apparatus which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmission part 3 Time measurement part 4 Intensity measurement part 5 Correction | amendment part 12 Measurement object 21 Received signal E Laser ranging device Δt ₁ hour measurement value P ₁ Intensity measurement CFD Constant fraction discriminator

Claims (4)

A transmitter for transmitting laser light toward the measurement target;
A receiving unit for receiving a reception signal reflected back from the measurement object;
A time measuring unit and an intensity measuring unit connected to the output end of the receiving unit;
The time measuring unit is a constant fraction discriminator capable of extracting timing information independent of the wave height of the received signal;
A correction unit that corrects a time measurement error that exceeds the suppression limit in the constant fraction discriminator,
The laser distance measuring device, wherein the correction unit is operated only when the intensity measurement value exceeds a predetermined value. In the correction unit, a correction table in which a correction amount for the intensity measurement value measured by the intensity measurement unit is determined in advance and stored for reference, and
2. The laser distance measuring device according to claim 1, further comprising arithmetic processing means for correcting the time measurement error with reference to the correction table. Send laser light to the measurement object,
Receive the received signal reflected back from the measurement object,
In the laser distance measuring device that converts the distance to the measurement object by the relational expression of the speed of light from the time difference between the transmission signal and the reception signal that transmitted the laser light,
A time measurement ending step for measuring the time difference; and
A saturation determination step of determining whether or not the received signal is saturated;
A saturation correction step for correcting a measurement error due to saturation if it is determined that it is saturated in this saturation determination step;
A distance conversion step after being correctly corrected by the saturation correction step;
A laser distance measuring method comprising: a distance conversion step of calculating a distance to a measurement object from a time difference measured without correction if it is determined in the saturation determination step that it is not saturated. In the saturation correction step,
4. The laser distance measuring method according to claim 3, wherein a correction table in which a correction amount for an intensity measurement value obtained by measuring the intensity of the received signal is determined and stored in advance is referred to.

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