JP2021169957A - Distance measuring device - Google Patents

Abstract

[Problem] To improve the reliability of distance calculation compared to the case where light of a single frequency is used. [Solution] A light source 11 is a light source that emits a CW laser. A half mirror 14 is a mirror that is provided in the optical path of the CW laser and reflects a part of the incident light and transmits the remaining part. A half mirror 15 is a mirror that is provided in an optical path A1 of the light reflected by the half mirror 14 and reflects the light incident on a first surface 151 and transmits the light incident on a second surface 152. An optical switch 12 is a switch that is provided in the optical path of the light that has transmitted through the half mirror 14 and switches between passing and blocking the light. A control unit 16 calculates the distance to an object based on the change over time in the characteristics of the incident light when a part of the light in a predetermined frequency band emitted from the light source 11 is incident on a light receiving element 13 and the remaining part of the light is reflected by the object and incident on the light receiving element 13. [Selected Figure] FIG.

Description

The present invention relates to a technique for measuring a distance to an object.

As a technique for measuring the distance to an object, Patent Document 1 describes that a pulse is radiated to perform frequency conversion on a reflected wave reflected by an object existing in space to generate a received signal, and the generated received signal is used. A technique for calculating the Doppler speed based on this is disclosed.

Japanese Unexamined Patent Publication No. 2013-190349

In a distance measuring device that irradiates light and receives the light reflected by an object to measure the distance, for example, the longer the distance to the object, the more the irradiated light is attenuated, and the distance is not received by a sufficient amount of light. May be difficult to measure.
In view of the above background, an object of the present invention is to improve the certainty of distance calculation.

In order to solve the above-mentioned problems, in the present invention, a part of the light of a predetermined frequency band emitted from the light source is incident on the light receiving element, and the remaining part of the light is reflected by the object to be reflected on the light receiving element. As the first aspect, a distance measuring device for calculating the distance to the object based on the change with time of the characteristics of the light incident on the light receiving element when the light is incident on the light source is provided.

According to the distance measuring device of the first aspect, the certainty of the calculation of the distance can be improved as compared with the case of using the light of a single frequency.

In the distance measuring device of the first aspect described above, the configuration that the characteristic is a frequency, an intensity or a combination of a frequency and an intensity may be adopted as the second aspect.

According to the distance measuring device of the second aspect, the distance can be measured based on the characteristics that can be easily measured by the light receiving element.

In the distance measuring device of the first or second aspect described above, the characteristics are frequency difference and intensity, the distance to the object is calculated based on the time-dependent change of the intensity, and the distance to the object is calculated based on the time-dependent change of the frequency. A configuration in which the velocity of the object is calculated may be adopted as the third aspect.

According to the distance measuring device of the third aspect, it is not necessary to separate the distance component and the speed component from the same characteristic, so that the calculation accuracy of the distance and the speed can be improved.

In the distance measuring device according to any one of the first to third aspects, the light source emits a CW (Continuous Wave) laser, and the light reflected by the half mirror provided in the optical path of the CW laser is the light. As a fourth aspect, a configuration in which the light incident on the light receiving element as a part of the light receiving element and the light transmitted through the half mirror is reflected by the object and incident on the light receiving element may be adopted.

According to the distance measuring device of the fourth aspect, the number of parts can be reduced as compared with the case of using light of a single frequency.

In the distance measuring device of the fourth aspect described above, the time when the switch for switching between passing and blocking the light provided in the optical path of the light transmitted through the half mirror is switched to passing and the light reflected by the object receives the light. A configuration in which the distance to the object is calculated based on the time of incidence on the element may be adopted as the fifth aspect.

According to the distance measuring device of the fifth aspect, the accuracy of the calculated distance and speed can be improved as compared with the case where the distance component and the speed component included in the light characteristics are separated.

The figure which shows the structure of the distance measuring apparatus which concerns on Example Diagram showing the characteristics of light emitted by a light source The figure which shows an example of the time-dependent change of the intensity of light emitted and received. The figure which shows an example of the operation procedure in the calculation process The figure which shows an example of the time-dependent change of the frequency of synthetic light

[1] Example FIG. 1 shows the configuration of the distance measuring device 10 according to the embodiment. The distance measuring device 10 is a device that irradiates light and measures the distance to the object based on the light reflected by the object and returned. The distance measuring device 10 includes a light source 11, an optical switch 12, a light receiving element 13, a half mirror 14, a half mirror 15, and a control unit 16.

The light source 11 is a light source that emits light in a predetermined frequency band, and in this embodiment, is a light source that emits a CW (Continuous Wave) laser. A CW laser is a laser that is continuously output or a laser that is intermittently output at extremely short time intervals. The half mirror 14 is a mirror provided in the optical path of the CW laser, which reflects a part of the incident light and transmits the remaining part.

The half mirror 15 is a mirror provided in the optical path A1 of the light reflected by the half mirror 14, reflects the light incident on the first surface 151, and transmits the light incident on the second surface 152. The light reflected by the half mirror 14 is incident on the first surface 151 of the half mirror 15, and the light reflected by the first surface 151 is incident on the light receiving element 13. The light receiving element 13 is an element that converts the intensity of the received light into an electric signal, and is, for example, a PD (Photo Diode).

The optical switch 12 is a switch provided in the optical path of light transmitted through the half mirror 14 to switch between passing and blocking light. The light transmitted through the optical switch 12 travels in the optical path A2, and if an object exists in the optical path A2, it is reflected by the object. A part of the light reflected by the object travels along the optical path A3 toward the distance measuring device 10 and is incident on the second surface 152 of the half mirror 15. Since the half mirror 15 transmits the light incident on the second surface 152, the light traveling through the optical path A3 passes through the half mirror 15 and is incident on the light receiving element 13.

As described above, the light receiving element 13 is incident with two types of light: light emitted by the light source 11 and passing through the optical path A1, and light transmitted through the optical switch 12 and reflected by an object. As described above, in the distance measuring device 10, a part of the light of the predetermined frequency band emitted from the light source 11 is incident on the light receiving element 13, and the remaining part of the light is reflected on the object to be reflected on the light receiving element 13. Incident in. It can also be said that the light reflected by the half mirror 14 is incident on the light receiving element 13 as a part of the light from the light source 11, and the light transmitted through the half mirror 14 is reflected on the object and is incident on the light receiving element 13.

The control unit 16 controls the operations of the light source 11 and the optical switch 12. The control unit 16 includes a processor, a memory, and a storage. The processor includes, for example, an arithmetic unit such as a CPU (Central Processing Unit), registers, peripheral circuits, and the like. The memory is a recording medium that can be read by a processor, and includes a RAM (Random Access Memory), a ROM (Read Only Memory), and the like.

The storage is a recording medium that can be read by a processor, and includes, for example, a hard disk drive or a flash memory. The processor controls the operation of the light source 11 and the optical switch 12 by executing a program stored in the ROM or the storage using the RAM as a work area. Specifically, the control unit 16 controls the operation of the light source (light source 11 and optical switch 12) as follows.

FIG. 2 shows the characteristics of the light emitted by the light source. In FIG. 2, a graph showing a frequency on the horizontal axis and a light amount on the vertical axis is shown. The control unit 16 controls the optical switch 12 in a cut-off state, and as shown by the curve B1, has a frequency band from frequency f11 to frequency f12 (corresponding to the predetermined frequency band described above) and has a maximum light amount C1. The light source 11 is controlled so as to emit light. The control unit 16 controls the light emission of the light source 11 and then controls the optical switch 12 to be in a transmitted state.

The control unit 16 performs the above control, and a part of the light of a predetermined frequency band emitted from the light source 11 is incident on the light receiving element 13, and the remaining part of the light is reflected on the object and the light receiving element 13 The distance to the object is calculated based on the time course of the characteristics of the two lights incident on the light receiving element 13. In this embodiment, the control unit 16 calculates the distance to the object by using the intensity of light as a characteristic of light. The method of calculating the distance will be described with reference to FIGS. 3 and 4.

FIG. 3 shows an example of changes in the intensity of light emitted and received with time. In FIG. 3, the horizontal axis represents the time and the vertical axis represents the amount of light. First, the control unit 16 controls the light source 11 so as to continuously emit the light in the predetermined frequency band described above with the optical switch 12 shut off. Next, the control unit 16 controls to switch the optical switch 12 from the cutoff state to the transmission state. By this control, as shown in FIG. 3A, light having a light emission amount C11 is emitted from the distance measuring device 10 at time t1.

When the light emitted by the distance measuring device 10 reaches the object and is reflected, a part of the reflected light is directed to the distance measuring device 10 and the light and the light from the light source 11 passing through the optical path A1 shown in FIG. The combined light reaches the light receiving element 13. When the combined light reaches the light receiving element 13, the control unit 16 measures the amount of the combined light received by the light receiving element 13 (hereinafter referred to as “light receiving amount”). The control unit 16 calculates, for example, the average value of the intensities of light of two or more frequencies included in a predetermined frequency band as the amount of received light of the entire combined light.

In the example of FIG. 3, the control unit 16 measures the light of the received light amount C21 at the time t2 and the light of the received light amount C22 at the time t3 as shown in FIG. 3 (b). Further, the control unit 16 measures the received amount C0 of the light passing through the optical path A1 even before the time t2. The received light amounts C21 and C22 represent the light amount of the combined light of the light passing through the optical path A1 and the reflected light of the light from the optical switch 12 reflected by the object. The amount of light received is gradually increasing because the object has undulations and the like, and the light reflected from the distance measuring device 10 reaches the light receiving element 13 at time t2 and is transmitted from the distance measuring device 10. This is because the light reflected at the portion where the distance is long reaches the light receiving element 13 at time t3.

The control unit 16 calculates the distance to the object based on the time difference d2 and d3 between the time t1 when the optical switch 12 is switched to transmission and the times t2 and t3 when the combined light including the reflected light of the object is received. .. Specifically, the control unit 16 calculates a half of the distance that light travels in the air with time differences d2 and d3 as the distance to the object. As described above, the control unit 16 calculates the distance to the object based on the time when the optical switch 12 is switched to pass and the time when the light reflected by the object is incident on the light receiving element 13. The control unit 16 calculates the distances to the objects in each direction corresponding to the pixels arranged in two dimensions, and generates an image of the three-dimensional object.

The control unit 16 performs a calculation process for calculating the distance to the object based on the above configuration.
FIG. 4 shows an example of an operation procedure in the calculation process. First, the control unit 16 starts light emission by the light source 11 (step S11). Next, the control unit 16 records an IF signal (Intermediate Frequency signal) based on the light from the light source 11 (step S12). Subsequently, the control unit 16 switches the optical switch 12 from shut-off to passing (step S13).

Next, the control unit 16 acquires the time when the measurement of the received amount of the synthetic light including a part of the reflected light by the object is started (step S14). Subsequently, the control unit 16 reaches the object based on the time difference between the time when the optical switch 12 is switched in step S12 (time t1 in the example of FIG. 3) and the measurement start time of the received light amount acquired in step S13. Calculate the distance (step S15). Then, the control unit 16 determines whether or not the calculation of the distance to the object corresponding to all the pixels described above is completed (step S16), and if not completed (NO), returns to step S12 and operates. If it is completed (YES), the calculation process is terminated.

For example, when light of a single frequency is emitted and the distance to an object is measured, the intensity of the light is increased by using an optical amplifier or the like so that the characteristics of the reflected light are likely to appear. In this embodiment, the distance is calculated based on the intensity of light of two or more frequencies in a predetermined frequency band. As a result, the intensity of the received light can be increased as compared with the case where the light of a single frequency is emitted, and the certainty of the calculation of the distance can be improved.

Further, in this embodiment, the distance can be measured based on the characteristics that can be easily measured by the light receiving element 13, such as the intensity of the reflected light. Further, since the light source 11 outputs a CW laser, it is possible to emit light of sufficient intensity for measurement without using an optical amplifier or the like, and the number of parts can be reduced as compared with the case of using light of a single frequency. Can be done.

Depending on the characteristics of the surface of the object, the amount of reflected light on the surface may differ depending on the frequency of the light. In that case, when light of a single frequency is emitted, the amount of received light may be insufficient for an object having a small amount of reflected light of that frequency, and the accuracy of the distance may be lowered. In this embodiment, since the distance to the object is calculated based on the change over time of the average value of the light intensity of two or more frequencies in a predetermined frequency band, the light is received as compared with the case of emitting light of a single frequency. It becomes difficult for the intensity of the light to be insufficient to be insufficient, and the accuracy of calculating the distance can be improved.

[2] Modifications The above-mentioned examples are merely examples of the implementation of the present invention, and may be modified as follows. Further, the examples and the modified examples may be combined as necessary.

[2-1] Light Characteristics In the embodiment, the control unit 16 calculates the distance to an object by using the light intensity as the characteristics of light having two or more frequencies in a predetermined frequency band, but the present invention is not limited to this. .. For example, the control unit 16 may calculate the distance to the object based on the time course of the frequencies of the two lights (light from the light source 11 and light from the optical switch 12) incident on the light receiving element 13.

Similar to the embodiment, the control unit 16 controls the light source 11 so as to continuously emit light in a predetermined frequency band, and then controls the optical switch 12 so as to switch from blocking to passing. When the combined light of the light from the light source 11 that has passed through the optical path A1 and a part of the light reflected by the object reaches the light receiving element 13, the control unit 16 measures the frequency of the combined light received by the light receiving element 13. ..

FIG. 5 shows an example of the time course of the frequency of the synthesized light. In FIG. 5, a graph is shown in which the horizontal axis represents time and the vertical axis represents frequency. The control unit 16 measures the frequency f0 during the period in which only the light passing through the optical path A1 is received. When the light to be received has a frequency band, the control unit 16 calculates the average value of the frequencies calculated by weighting the received amount of the light of that frequency to each frequency included in the frequency band. Measure as frequency.

As shown in FIG. 5, the control unit 16 measures the light of frequency f21 at time t2 and the light of frequency f22 at time t3. The frequencies f21 and f22 represent the frequencies of the combined light of the light that has passed through the optical path A1 and the light that is reflected by the object. The control unit 16 calculates the distance to the object based on the time difference d2 and d3 between the time t1 when the optical switch 12 emits light and the times t2 and t3 when the combined light is received. Specifically, the control unit 16 calculates a half of the distance that light travels in the air with time differences d2 and d3 as the distance to the object.

The control unit 16 calculates the distance to the object based on the change over time in the combination of the amount and frequency of the two lights (the light that has passed through the optical path A1 and the light that is reflected by the object) incident on the light receiving element 13. You may. In that case, the control unit 16 measures the amount of synthetic light as in the embodiment, measures the frequency of the synthetic light as described above, substitutes the measured amount of light and frequency into, for example, a predetermined function, and sets the value of the combination. Is calculated.

Based on the time-dependent change of the calculated combination value, the control unit 16 obtains the time difference between the time when the optical switch 12 is switched to pass and the time when the combined light is received, as in the examples of FIGS. 3 and 5. Calculate the distance to the object. According to this modification, the distance can be measured based on the characteristics that can be easily measured by the light receiving element, such as the frequency or the combination of frequency and intensity, as in the embodiment.

[2-2] Measurement of Distance and Speed The control unit 16 may measure not only the distance to the object but also the moving speed of the object. At that time, the control unit 16 controls, for example, to emit light of a single frequency to the light source 11, calculates the distance to the object based on the time course of the intensity measured after the control, and also the same. The velocity of the object is calculated based on the time course of the frequency measured after the control. The control unit 16 may calculate the distance to the object in the same manner as in the embodiment.

When the object is moving away from or approaching the distance measuring device 10, the frequency of the reflected light changes due to the Doppler effect. When the object is approaching, the frequency changes to be high, and when the object is moving away, the frequency changes to be low. The control unit 16 calculates, as the speed of the object, a speed corresponding to the difference between the frequency of the synthetic light measured when the object does not move and the frequency of the measured synthetic light.

For example, when the time-dependent change of the measured light characteristics includes the distance component to the object and the velocity component of the object, the distance and the velocity are calculated by separating them. In that case, if the accuracy of separation is poor, the accuracy of the measured distance and velocity will also be poor. In this modification, it is not necessary to separate the distance component and the velocity component included in the light characteristics, so that the accuracy of the calculated distance and velocity can be improved as compared with the case where the separation is performed.

[2-3] Category of Invention The present invention can be regarded as an information processing method for realizing the processing performed by the control unit 16 of the distance measuring device 10 in addition to the distance measuring device 10, and the distance measuring device 10 can be used. It can also be regarded as a program for operating the controlling computer. This program may be provided in the form of a recording medium such as an optical disk that stores it, or may be provided in the form of being downloaded to a computer via a network such as the Internet and installed and made available. May be done.

10 ... ranging device, 11 ... light source, 12 ... optical switch, 13 ... light receiving element, 14 ... half mirror, 15 ... half mirror, 16 ... control unit.

Claims (5)

When a part of the light of a predetermined frequency band emitted from a light source is incident on a light receiving element and the remaining part of the light is reflected by an object and is incident on the light receiving element, the light incident on the light receiving element A distance measuring device that calculates the distance to the object based on the change over time in the characteristics of. The distance measuring device according to claim 1, wherein the characteristic is frequency, intensity, or a combination of frequency and intensity. The characteristic is a frequency difference and an intensity, and according to claim 1 or 2, the distance to the object is calculated based on the time course of the intensity, and the speed of the object is calculated based on the time course of the frequency. Distance measuring device. The light source emits a CW (Continuous Wave) laser, and the light reflected by the half mirror provided in the optical path of the CW laser is incident on the light receiving element as a part of the light, and the light transmitted through the half mirror is emitted. The distance measuring device according to any one of claims 1 to 3, which reflects on the object and is incident on the light receiving element. To the object based on the time when the switch for switching between passing and blocking the light provided in the optical path of the light transmitted through the half mirror is switched to passing and the time when the light reflected by the object is incident on the light receiving element. The distance measuring device according to claim 4, wherein the distance is calculated.

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