JP6260418B2 - Distance measuring device, distance measuring method, and distance measuring program - Google Patents

Description

  This case relates to a distance measuring device, a distance measuring method, and a distance measuring program.

  In recent years, distance measuring devices (laser radars) have been used for various purposes, not only for measuring distances to objects, but also for detecting obstacles in automobiles and for detecting people between vehicles and doors in railway platforms. It is used in the scene.

  Patent Document 1 discloses a first optical means that combines the function of condensing the first reflected light of the laser light reflected by an obstacle in a predetermined direction of the vehicle while narrowing the laser light to an appropriate divergence angle. The monitor optical element that receives the second reflected light reflected by the optical means of the laser light and the output signal of the monitor light receiving element is subtracted from the output signal of the light receiving element, A technology for preventing false detection is disclosed.

  Patent Document 2 records an integrated signal obtained by integrating a predetermined number of received light signals output from the light receiving element 83 of the laser radar sensor 5 when there is no reflecting object to be detected in the detection area as a noise reference value. A technique for removing a noise component by subtracting a noise reference value from an integrated signal in a difference calculation block 92 when detecting a reflection object is disclosed.

Japanese Patent Publication No. 3-26793 JP 2005-257405 A

  However, the reflected light from the lens varies depending on the irradiation angle of the laser. Therefore, in the techniques of Patent Documents 1 and 2, there is a risk of erroneous measurement due to reflection at the lens.

  In one aspect, an object of the present invention is to provide a distance measurement device, a distance measurement method, and a distance measurement program that can reduce erroneous measurement caused by reflection at a lens.

  In one aspect, the distance measuring device includes an angle changing unit capable of changing an irradiation angle for irradiating the lens with laser light, and a return light of the laser light that passes through the lens and is reflected by the distance measuring object. A light receiving element that receives light through the lens, an acquisition unit that acquires an influence of reflection on a surface of the lens on which the laser light is incident, according to the irradiation angle, and an influence of the reflection that the acquisition unit acquires. And a correction unit that corrects a signal output from the light receiving element.

  Incorrect measurement due to reflection at the lens can be reduced.

It is the schematic of the distance measuring device which concerns on a comparative example. It is explanatory drawing of a TOF system. It is a figure which illustrates the relationship between reflected light and return light. It is a figure which illustrates the relationship between an irradiation angle and the amount of reflected light. 1 is a schematic diagram of a distance measuring apparatus according to Embodiment 1. FIG. It is a figure which illustrates the table which the table storage part has memorized. It is an example of a flowchart. 6 is a schematic diagram of a distance measuring apparatus according to Embodiment 2. FIG. It is an example of a flowchart. It is a block diagram for demonstrating the other hardware constitutions of a calculating part.

  Prior to the description of the embodiments, an outline of the distance measuring device will be described.

  FIG. 1 is a schematic diagram of a distance measuring device 200 according to a comparative example. As illustrated in FIG. 1, the distance measuring device 200 includes a light emitting element 11, a collimating lens 12, a mirror 13, a two-dimensional scanning mirror 14, a magnifying lens 15, a condenser lens 16, and a light receiving element 17.

  The light emitting element 11 is a device that emits laser light, and emits pulsed light as an example. The collimating lens 12 suppresses the spread of the laser light emitted from the light emitting element 11 to make parallel light. The mirror 13 is a perforated mirror having a hole formed in the center. The angle of the mirror 13 is fixed in the distance measuring device 200. Laser light emitted from the collimating lens 12 passes through a hole in the mirror 13.

  The two-dimensional scanning mirror 14 is a mirror whose angle changes in accordance with an instruction from the outside. For example, a MEMS (Micro Electro Mechanical System) mirror, a galvanometer mirror, or the like can be used as the two-dimensional scanning mirror 14. The laser light passing through the hole of the mirror 13 is deflected according to the rotation angle of the two-dimensional scanning mirror 14. The magnifying lens 15 further magnifies the angle of the light changed by the two-dimensional scanning mirror 14. The incident angle of the laser beam with respect to the magnifying lens 15 is changed by the scanning of the two-dimensional scanning mirror 14. The laser light emitted from the magnifying lens 15 is irradiated on the object to be measured, scattered (reflected), and returns to the magnifying lens 15 with a spread. The return light passes through the magnifying lens 15, is reflected by the two-dimensional scanning mirror 14, is reflected by the mirror 13, is collected by the condenser lens 16, and is received by the light receiving element 17. Thus, the distance measuring device 200 employs a coaxial optical system in which emitted laser light and return light pass through the same magnifying lens 15.

  The distance measuring apparatus 200 measures the distance to the distance measurement object by adopting a TOF (Time of Flight) method. FIG. 2 is an explanatory diagram of the TOF method. As illustrated in FIG. 2, the distance measuring device 200 measures a round-trip time (ΔT) from when the light emitting element 11 emits a pulse of laser light until the return light returns from the object to be measured, and multiplies the speed of light. Thus, the distance to the object to be measured is calculated.

In the distance measuring device 200, noise is reflected directly or after a part of light reflected on the rear surface (two-dimensional scanning mirror 14 side) of the magnifying lens 15 (hereinafter referred to as reflected light) is reflected by another member. There is a possibility of entering the light receiving element 17 as light. Such noise light becomes a factor of reducing the S / N in the light receiving element 17. As a countermeasure against reflected light, it is generally considered to apply an antireflection treatment. However, it is inevitable that back surface reflected light having an intensity of about 10 ⁻³ relative to the intensity of the laser light incident on the magnifying lens 15 is generated. On the other hand, the intensity of the return light that the light receiving element 17 must detect may be attenuated to about 10 ⁻⁸ of the intensity of the irradiated laser light. Therefore, if only the antireflection treatment is performed, there is a possibility that the distance measurement may have a great adverse effect.

  Furthermore, as illustrated in FIG. 3, in the TOF method, it is difficult to separate the waveform between the reflected light and the return light when the object to be measured is at a short distance. Therefore, it is conceivable to perform correction by taking a reflected waveform digitally by AD conversion in advance and storing it, and subtracting it from the measured waveform taken digitally. However, with this technique, there is a risk of erroneous measurement due to reflection at the lens.

  Here, as illustrated in FIG. 4, it was newly found that the reflected light from the lens varies depending on the irradiation angle of the laser. As a result, the size of the reflected light from the lens changes due to the change in the scanning angle, so it is understood that erroneous measurement due to reflection at the lens may be made by storing only one waveform. It was. In the following embodiments, a distance measurement device, a distance measurement method, and a distance measurement program that can reduce erroneous measurement caused by reflection at a lens will be described.

  FIG. 5 is a schematic diagram of the distance measuring apparatus 100 according to the first embodiment. As illustrated in FIG. 5, the distance measuring device 100 includes a light projecting / receiving unit 10 and a calculation unit 20. The light projecting / receiving integrated unit 10 includes a light emitting element 11, a collimating lens 12, a mirror 13, a two-dimensional scanning mirror 14, a magnifying lens 15, a condensing lens 16, a light receiving element 17, a light receiving element 18, and the like. The calculation unit 20 includes a conversion circuit 21, a conversion circuit 22, a mirror position detection circuit 23, a table storage unit 24, an amplification circuit 25, an amplification circuit 26, a difference circuit 27, a measurement circuit 28, and the like.

  About the same structure as the distance measuring device 200 of FIG. 1, description is abbreviate | omitted by attaching | subjecting the same code | symbol. The light receiving element 18 is a photodiode that performs photoelectric conversion, and receives light scattered by the hole when the laser light that has passed through the collimator lens 12 passes through the hole of the mirror 13. That is, the light receiving element 18 can detect laser light that is not affected by the reflection on the back surface of the magnifying lens 15.

  The photocurrent output from the light receiving element 17 is input to the conversion circuit 21. The conversion circuit 21 converts the input photocurrent into a voltage signal and inputs the voltage signal to the amplifier circuit 25. The photocurrent output from the light receiving element 18 is input to the conversion circuit 22. The conversion circuit 22 converts the input photocurrent into a voltage signal and inputs the voltage signal to the amplifier circuit 26. The mirror position detection circuit 23 detects the position of the two-dimensional scanning mirror 14 (laser beam irradiation angle with respect to the magnifying lens 15), and inputs the detection result to the table storage unit 24.

  The table storage unit 24 stores the position of the two-dimensional scanning mirror 14 and the amplification factor associated therewith as a table. The table storage unit 24 individually inputs the amplification factor corresponding to the position input from the mirror position detection circuit 23 to the amplification circuit 25 and the amplification circuit 26. These gains are the same as or different from each other in the photocurrents of the light receiving element 17 and the light receiving element 18 when there is no object around the distance measuring device 100 (the object to be measured does not exist more than a predetermined distance). The amplification factor is such that These amplification factors can be acquired in advance.

  FIG. 6 is a diagram illustrating a table stored in the table storage unit 24. As illustrated in FIG. 6, the amplification factor is stored in correspondence with the vertical scanning angle and the horizontal scanning angle of the two-dimensional scanning mirror 14. The vertical scanning angle and the horizontal scanning angle are factors that determine the irradiation angle of the laser light to the magnifying lens 15. In the example of FIG. 6, only the amplification factor of either the amplification circuit 25 or the amplification circuit 26 is stored, but in correspondence with the vertical side scanning angle and the horizontal side scanning angle of the two-dimensional scanning mirror 14, The amplification factors of both the amplifier circuit 25 and the amplifier circuit 26 may be stored separately. Further, the amplification factor of both the amplification circuits 25 and 26 or the amplification factor of either one of the amplification circuits 25 and 26 may be calculated according to a mathematical expression using the angle of the two-dimensional scanning mirror 14 as a variable instead of the table. .

  The voltage signal output from the amplifier circuit 25 and the voltage signal output from the amplifier circuit 26 are input to the difference circuit 27. The difference circuit 27 obtains a correction signal by subtracting the voltage signal output from the amplifier circuit 26 from the voltage signal output from the amplifier circuit 25 to obtain a difference. The acquired correction signal is input to the measurement circuit 28. The measurement circuit 28 measures the distance to the distance measurement object using the input correction signal.

  FIG. 7 shows an example of the above operation as a flowchart. The flowchart in FIG. 7 is executed in synchronization with the timing at which the position of the two-dimensional scanning mirror 14 is changed. First, the mirror position detection circuit 23 detects the position of the two-dimensional scanning mirror 14 (step S1). Next, the light emitting element 11 emits pulsed light (step S2). Next, the measurement circuit 28 starts time measurement (step S3).

  Next, the photocurrents output from the light receiving element 17 and the light receiving element 18 are converted into voltage signals by the conversion circuit 21 and the conversion circuit 22, respectively (step S4). On the other hand, in parallel with steps S2 to S4, the table storage unit 24 acquires the amplification factor corresponding to the position acquired by the mirror position detection circuit 23 and inputs it to the amplification circuit 25 and the amplification circuit 26 (step S5).

  After execution of step S4 and step S5, the amplifier circuit 25 and the amplifier circuit 26 amplify the voltage signal, respectively (step S6). Next, the difference circuit 27 acquires a correction signal from the voltage signal output from the amplifier circuit 25 and the voltage signal output from the amplifier circuit 26 (step S7), and inputs the correction signal to the measurement circuit 28 (step S8). The measurement circuit 28 measures the distance to the distance measurement object using the input correction signal (step S9). After the execution of step S9, the process is executed again from step S1 at the timing when the angle of the two-dimensional scanning mirror 2 is changed.

  According to the present embodiment, the influence of the reflection on the back surface of the magnifying lens 15 is obtained by obtaining the amplification factor of at least one of the amplification circuits 25 and 26 according to the irradiation angle of the laser beam to the magnifying lens 15. be able to. Since the output signal of the light receiving element 17 is corrected using the acquired influence of reflection, erroneous measurement caused by reflection at the magnifying lens 15 can be reduced.

  FIG. 8 is a schematic diagram of a distance measuring apparatus 100a according to the second embodiment. As illustrated in FIG. 8, the distance measuring device 100 a is different from the distance measuring device 100 of FIG. 5 in that the light projecting / receiving unit 10 a is provided instead of the light projecting / receiving unit 10, and the computing unit 20 a is used instead of the computing unit 20. It is a point provided with. The light emitting / receiving unit 10a is different from the light projecting / receiving unit 10 in that the light receiving element 18 is not provided. The difference between the calculation unit 20 a and the calculation unit 20 is that a drive current monitor circuit 29 and a waveform correction circuit 30 are provided instead of the conversion circuit 22. About the same structure as the distance measuring device 100 of FIG. 5, description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  The drive current monitor circuit 29 detects a drive current input to the light emitting element 11 from a drive circuit for driving the light emitting element 11. Thereby, even if the light receiving element 18 of Example 1 is not provided, it is possible to detect the emitted light that is not affected by the reflection on the back surface of the magnifying lens 15. The waveform correction circuit 30 outputs a voltage signal obtained by converting the photocurrent obtained by photoelectrically converting the output waveform of the light emitting element 11 based on the drive current detected by the drive current monitor circuit 29. The output voltage signal is input to the amplifier circuit 26. Other operations are the same as those in the first embodiment.

  FIG. 9 shows an example of the above operation as a flowchart. The flowchart of FIG. 9 differs from the flowchart of FIG. 7 in that step S4a is executed instead of step S4. In step S4a, the photocurrent output from the light receiving element 17 is converted into a voltage signal by the conversion circuit 21, and the voltage signal obtained by converting the photocurrent obtained by photoelectrically converting the output waveform of the light emitting element 11 is converted into a waveform correction circuit. 30 is output.

  Also in the present embodiment, the influence of the reflection on the back surface of the magnifying lens 15 is obtained by obtaining the amplification factor of at least one of the amplifier circuits 25 and 26 according to the irradiation angle of the laser beam to the magnifying lens 15. Can do. Since the output signal of the light receiving element 17 is corrected using the acquired influence of reflection, erroneous measurement caused by reflection at the magnifying lens 15 can be reduced.

  In each of the above-described embodiments, the two-dimensional scanning mirror 14 functions as an angle changing unit that can change the irradiation angle at which the lens is irradiated with laser light. The light receiving element 17 functions as a light receiving element that receives the return light of the laser beam that is transmitted through the lens and reflected and returned from the object to be measured via the lens. The mirror position detection circuit 23 and the table storage unit 24 function as an acquisition unit that acquires the influence of reflection on the surface of the lens on the side on which the laser light is incident, according to the irradiation angle. The amplifier circuits 25 and 26 and the difference circuit 27 function as a correction unit that corrects a signal output from the light receiving element using the influence of reflection acquired by the acquisition unit.

(Other examples)
FIG. 10 is a block diagram for explaining another hardware configuration of the arithmetic units 20 and 20a. Referring to FIG. 10, the arithmetic units 20 and 20a include a CPU 101, a RAM 102, a storage device 103, an interface 104, and the like. Each of these devices is connected by a bus or the like. A CPU (Central Processing Unit) 101 is a central processing unit. The CPU 101 includes one or more cores. A RAM (Random Access Memory) 102 is a volatile memory that temporarily stores programs executed by the CPU 101, data processed by the CPU 101, and the like. The storage device 103 is a nonvolatile storage device. As the storage device 103, for example, a ROM (Read Only Memory), a solid state drive (SSD) such as a flash memory, a hard disk driven by a hard disk drive, or the like can be used. When the CPU 101 executes the distance measurement program, the calculation unit 20 is realized in the distance measurement device 100, or the calculation unit 20a is realized in the distance measurement device 100a.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

DESCRIPTION OF SYMBOLS 10 Light emitting / receiving integrated unit 11 Light emitting element 12 Collimating lens 13 Mirror 14 Two-dimensional scanning mirror 15 Magnifying lens 16 Condensing lens 17, 18 Light receiving element 20 Arithmetic unit 21, 22 Conversion circuit 23 Mirror position detection circuit 24 Table storage unit 25, 26 Amplifier circuit 27 Difference circuit 28 Measuring circuit 100 Distance measuring device

Claims (8)

An angle changing unit capable of changing an irradiation angle at which the lens is irradiated with laser light;
A light-receiving element that receives the return light of the laser light that passes through the lens and is reflected and returned from the object to be measured, via the lens;
An acquisition unit that acquires an influence of reflection of a surface of the lens on which the laser beam is incident according to the irradiation angle;
A distance measurement apparatus comprising: a correction unit that corrects a signal output from the light receiving element using the influence of the reflection acquired by the acquisition unit.   The distance measuring apparatus according to claim 1, wherein the acquisition unit acquires the influence of reflection corresponding to the irradiation angle from a table that stores the influence of reflection and the irradiation angle in association with each other. The acquisition unit acquires a correction light amount obtained by correcting the light amount of the laser light according to the irradiation angle as an influence of the reflection,
The distance measuring device according to claim 1, wherein the correction unit corrects a signal output from the light receiving element by subtracting the correction light amount from a light amount of the return light.   The distance measuring device according to claim 3, wherein the acquisition unit acquires the correction light amount using a part of the light before the laser light enters the lens.   The distance measuring apparatus according to claim 3, wherein the acquisition unit acquires the correction light amount using a drive current of a light emitting element that emits the laser light.   The distance measuring device according to claim 1, wherein the angle changing unit is a MEMS mirror that changes a reflection angle of the laser light. The return light of the laser beam that passes through the lens and is reflected by the object to be measured is received by the light receiving element through the lens,
The influence of the reflection of the surface on which the laser beam is incident on the lens is acquired according to the irradiation angle at which the laser beam is applied to the lens,
A distance measuring method, wherein the signal output from the light receiving element is corrected by using the influence of the reflection. The influence of the reflection of the surface of the lens on which the laser beam is incident is acquired according to the irradiation angle at which the laser beam is applied to the lens,
A computer that corrects a signal output from a light receiving element that receives the return light of the laser light that passes through the lens and is reflected by a distance measurement target through the lens, using the influence of the reflection. A distance measurement program that is executed by a computer.

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