JP2020160044A - Distance measuring device and distance measuring method - Google Patents

Abstract

To obtain a distance measuring device and a distance measuring method that can extend the range where distance is measurable.SOLUTION: A distance measuring device comprises: a light source that has light emitting areas arranged in a two-dimensional manner; and a light receiving unit that receives reflected light reflected by an object of distance measurement present in a distance measurement area. An area-classified light quantity control unit 41 performs preliminary light emission by simultaneously emitting light emission points of the light source with the same quantity of light, and controls the quantity of the light emission based on the quantity of received light of each of light receiving areas measured by an area light quantity measuring unit through the preliminary light emission. A distance measuring unit 42 measures the distance to the object of distance measurement for each of the light receiving areas through the light emission.SELECTED DRAWING: Figure 1

Description

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

A distance measuring method is known in which a laser beam is irradiated toward an imaging region, reflected light from an object existing in the imaging region is received, and the distance to the object is calculated from the time difference between emission and reception. Such a distance measuring method is already known as a TOF (Time of Flight) method. A distance measuring device that measures a distance by the TOF method is sometimes called a TOF camera or a distance measuring camera. Further, although Patent Document 1 describes the image pickup device, the image pickup device described in Patent Document 1 is an example of a TOF camera.

In a distance measuring device (TOF camera) that measures a distance by the TOF method, the light receiving level (light receiving amount) of the reflected light from the subject is important. If the light receiving level is low, the sensor output signal is buried in noise, and if the light receiving level is too high, the sensor output signal is saturated and an accurate ranging value cannot be obtained. The invention described in Patent Document 1 attempts to obtain an accurate distance measurement value by setting a photometric area by the photometric unit and controlling the photometric light amount by the photometric unit so that the photometric amount in the photometric area becomes a normal value. Is.

The imaging device (TOF camera) described in Patent Document 1 performs exposure control based on the photometric amount in the distance measurement target area. That is, the exposure amount is measured by the photometric unit, and if the photometric value is equal to or more than the normal value, the amount of illumination light by the illumination unit is decreased, and if the photometric value is equal to or less than the normal value, the amount of illumination light by the illumination unit is increased. However, in the image pickup device (TOF camera) described in Patent Document 1, the amount of reflected light that is reflected by the subject and reaches the image pickup device (TOF camera) after the irradiation light illuminated by the illumination unit on the subject is the amount of the reflected light. Is not considered to vary depending on the distance from the image pickup device (TOF camera) to the subject. Therefore, there is room for improvement from the viewpoint of expanding the range that can be measured.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a distance measuring device and a distance measuring method capable of expanding the range that can be measured.

The imaging device according to the present invention is
A light source in which multiple light emitting regions are arranged in two dimensions,
An optical element that guides the emitted light emitted from the light source to the ranging region,
A light receiving unit that receives the reflected light that the emitted light is reflected by the distance measuring object existing in the distance measuring region.
It is a distance measuring device equipped with
The light receiving portion is divided into a plurality of light receiving regions.
An area-specific light amount control unit that controls the amount of light emitted from each light source of the light source corresponding to the plurality of light receiving areas for each light source.
A region light amount measuring unit that measures the amount of received light for each light receiving area,
A distance measuring unit that measures the distance to the distance measuring target for each light receiving region by measuring the time from the light emission of the light source to the light reception by the light receiving unit for each light receiving region.
Have,
The region-specific light amount control unit simultaneously emits light at the same light amount at each light emitting point of the light source to perform preliminary light emission, and the main light emission is based on the light receiving amount for each light receiving region measured by the region light amount measuring unit by the preliminary light emission. Controls the amount of light emitted from
The most main feature of the distance measuring unit is to measure the distance to the distance measuring target for each light receiving region by the main light emission.

The imaging method according to the present invention is
A light source in which multiple light emitting regions are arranged in two dimensions,
An optical element that guides the emitted light emitted from the light source to the ranging region,
A light receiving unit that receives the reflected light that the emitted light is reflected by the distance measuring object existing in the distance measuring region.
It is a distance measuring method using a distance measuring device equipped with.
The light receiving portion is divided into a plurality of light receiving regions.
A region-specific light amount control step for controlling the light emission amount of each light emission region of the light source corresponding to the plurality of light receiving regions for each light emission region.
A region light amount measuring step for measuring the amount of received light for each light receiving area, and
A distance measuring step of measuring the distance to the measurement target in each light receiving area by measuring the time from the light emission of the light source to the light receiving by the light receiving unit in each light receiving area.
Have,
In the region-specific light amount control step, each light emitting point of the light source is simultaneously emitted with the same amount of light to perform preliminary light emission, and the light emission of the main light emission is based on the received light amount for each region measured in the region light amount measuring step by the preliminary light emission. Control the amount,
The most main feature of the distance measuring step is to measure the distance to the distance measuring target for each light receiving region by the main light emission.

According to the present invention, it is possible to extend the range that can be measured for both a long-distance subject and a short-distance subject.

It is a schematic diagram which shows schematic the optical system and the control system of the Example of the distance measuring device and distance measuring method which concerns on this invention. It is a front view and the illuminance distribution map in the vertical and horizontal directions which show an example of the laser light source which arranges a plurality of light emitting regions in a two-dimensional array. It is a graph which shows the range which can measure the distance and the range which cannot measure the distance when the amount of light emission of a laser light source is made constant. It is a graph which shows the example of the output control of a laser light source with respect to the TOF sensor output. It is a figure which shows the distribution of the TOF sensor output in each image pickup region when a laser light source is preliminarily emitted. It is a figure which shows the light emission amount distribution at the time of the main light emission of the laser light source corresponding to the distribution of the TOF sensor output in each image pickup region when the laser light source is pre-emitted. It is a flowchart which shows the operation at the time of a normal shooting by this invention. It is a flowchart which shows the operation at the time of a plurality of times shooting by this invention. It is a timing chart explaining the reason why distance measurement accuracy deteriorates and distance measurement is impossible when the subject distance is too close and too far.

Hereinafter, examples of the distance measuring device and the distance measuring method according to the present invention will be described with reference to the drawings.

[Example 1]
FIG. 1 shows a TOF camera 10 which is an example of the distance measuring device according to the present invention. In FIG. 1, the TOF camera 10 receives a light projecting system 20 that emits a rectangular wave or sine wave-shaped laser beam frequency-modulated to about megahertz [MHz] and light that is reflected by the projected light hitting an object, that is, a subject. The light receiving system 30 is provided.

The floodlight system 20 has a vertical resonator surface emitting laser (hereinafter referred to as “VCSEL”) 21 as a light source. In the VCSEL 21 in this embodiment, a plurality of light emitting regions are arranged two-dimensionally. The light emitting operation of each light emitting region of the VCSEL 21 is controlled by the light emitting control unit 50. The light projecting system 20 also has a lens 22 that spreads the light emitted from each light emitting point of the VCSEL 21 to a required angle of view and projects the light.

The TOF camera 10 has a determination unit 40. By controlling the light emission control unit 50, the determination unit 40 controls the light emission timing, the light emission amount, and the like in each light emission region of the VCSEL 21.

The light receiving system 30 includes a light receiving lens 31 that collects the light reflected by the subject and a light receiving sensor 32 that receives the light collected by the light receiving lens 31 and performs photoelectric conversion. In this embodiment, a TOF sensor is used as the light receiving sensor 32. In the light receiving sensor 32, the light receiving region by the sensor element is arranged in the same two dimensions as the arrangement of each light emitting region of the VCSEL 21, and the detection signal is divided and output for each region determined by each sensor element.

As described above, the TOF camera 10 uses a laser light source in which a plurality of light emitting regions are arranged two-dimensionally, and meshes the image pickup surface of the image pickup device into a plurality of regions having the same number and the same arrangement as the plurality of light emitting regions. The imaging area is divided into a plurality of areas by dividing the image into a shape, and the distance is measured for each area.

The detection signal of the light receiving sensor 32 is input to the metering / control unit 60. The photometric / control unit 60 functions as a region light amount measuring unit that statistically processes sensor output values from each detection area of the light receiving sensor 32 composed of a TOF sensor and measures the light receiving level (light receiving amount) for each imaging region. The metering / control unit 60 also controls the light receiving time, light receiving sensitivity, timing, etc. of the light receiving sensor 32 in synchronization with the light projection control from each light emitting region of the VCSEL 21. The function as the region light amount measuring unit measures the light receiving level (light receiving amount) for each imaging region even during the preliminary emission of the laser light by the VCSEL21, and the light emitting amount at the time of the main light emission is based on the received light amount for each imaging region. It is controlled by the area-specific light amount control unit 41, which will be described later.

The determination unit 40 has a region-specific light amount control unit 41 that determines the light emission amount for each light emission region of the VCSEL 21 and the light reception sensitivity of the light reception sensor 32 at the time of photographing from the sensor output statistical value for each light reception region of the light reception sensor 32. Further, the determination unit 40 measures the distance to the distance measurement target for each imaging region by measuring the time from the emission of the laser light by the VCSEL 21 to the reception by the light receiving sensor 32 for each imaging region. Have.

The distance measurement operation by the TOF camera 10 is equivalent to the TOF camera operation of a general phase detection method, and is a well-known technique. For example, the same technique as the TOF camera described in JP-A-2018-077143 can be used. Therefore, a detailed description of the distance measurement operation by the TOF camera 10 will be omitted.

Next, the element arrangement of the two-dimensional array of VCSEL21 used as the light source shown in FIG. 2 will be described. FIG. 2 is a diagram schematically showing the light emitting surface of the VCSEL 21, in which black circles indicate light emitting regions, and eight light emitting regions are arranged in each of the vertical and horizontal directions, for a total of 64 light emitting regions. Further, a plurality of VCSEL elements are arranged at equal intervals in each light emitting region.

In FIG. 2, a horizontal illuminance distribution curve and a vertical illuminance distribution curve are shown along the upper edge portion and the left side edge portion of the VCSEL element, respectively. Of these illuminance distribution curves, the dotted line shows the illuminance distribution curve of each element, and the solid line shows the illuminance distribution curve when all the elements emit light at the same time. As can be seen from these illuminance distribution curves, when all elements emit light at the same time, surface emission is almost uniform. In other words, the arrangement interval of the elements is determined so that the surface emission is uniform. Although it depends on the specifications of the VCSEL element, the scale is about 50 μm on one side.

FIG. 3 shows a detection signal in which the entire region of the VCSEL 21 is emitted with the same amount of light, the reflected light from the subject is received by the light receiving sensor 32, and the light receiving sensor 32 outputs the detection signal. The output relationship is shown. The horizontal axis of FIG. 3 represents the subject distance, and the vertical axis represents the output of the light receiving sensor 32 at a level from 0 to 255. As a matter of course, the subject is a subject within the field of view of the light receiving sensor 32.

Here, if the horizontal direction of the light receiving surface in the light receiving sensor 32 is defined as the X direction, the vertical direction is defined as the Y direction, and the direction orthogonal to the light receiving surface and away from the light receiving surface is defined as the Z direction, the light receiving surface becomes an XY plane. When looking at the distance measuring area (distance measuring area) from the light receiving sensor 32, the distance to the object existing in each divided area on the XY plane, that is, unless the object existing in the distance measuring area is a plane parallel to the XY plane. The distance to the subject differs for each divided area.

Then, when the amount of the distance measurement light by the TOF method is made uniform and emitted toward the imaging region, the level of the reflected light becomes high in the region where a subject at a short distance exists, and the output level of the light receiving sensor 32 is saturated. Further, in a region where a long-distance subject exists, the level of reflected light becomes low, and the output signal of the light receiving sensor 32 is buried in noise. That is, whether the subject position is too close or too far, distance measurement becomes impossible or the distance measurement accuracy deteriorates, and as a result, the distance range of the subject that can be measured is limited.

This will be described in detail. When the VCSEL 21 emits light with the same amount of light for all the pixels arranged in an array, the reflected light from a distant subject is attenuated and the output of the light receiving sensor 32 becomes small, as shown in FIG. In the example shown in FIG. 3, when the subject distance exceeds 7 m, the relationship between the sensor output and the subject distance becomes non-linear and the distance measurement accuracy deteriorates, so that the output of the light receiving sensor 32 is invalid. Since the reflected light is less attenuated for a short-distance subject, the output of the light receiving sensor 32 is large.

FIG. 8 explains the reason why the distance measurement accuracy by the light receiving sensor 32 deteriorates or the distance measurement becomes impossible in a short-distance or long-distance subject. FIG. 8A shows the amount of light emitted from VCSEL21 and the time. The emission waveform is a rectangular waveform.

FIG. 8B shows the output waveform of the light receiving sensor 32 when the subject distance is an intermediate distance (1 to 7 m). The light-receiving waveform is not a rectangle, but a sinusoidal waveform with a slight delay. In order to determine the point at which the phase difference Δt between light emission and light reception is measured, an output determination threshold is set in the light-receiving sensor 32, and the time required to reach this level is set. Measure and convert the phase difference into distance. Accurate distance measurement is possible for subjects at intermediate distances.

FIG. 8C shows the output waveform of the light receiving sensor 32 when the subject distance is short (within 1 m). When the subject is at a short distance, the output of the light receiving sensor 32 is greatly saturated, so that the rising edge of the waveform becomes steep. Therefore, an error occurs in the time when the output of the light receiving sensor 32 reaches the determination threshold value (50% in this example) with respect to the originally assumed sine waveform. This error component is indicated by E in FIG. 2 (b). The effect of this error E becomes larger as the phase difference Δt is smaller at a short distance, so that the distance measurement error becomes large when the output of the light receiving sensor 32 is saturated at a short distance. Therefore, when the output of the light receiving sensor 32 is saturated, the distance measurement calculation is not performed.

FIG. 8D shows the output of the light receiving sensor 32 when the subject is at a long distance (7 m or more). The farther the subject is, the lower the amount of light received by the light receiving sensor 32. Therefore, the output of the light receiving sensor 32 does not exceed the determination threshold value required for the phase difference measurement, and the phase difference Δt cannot be measured. In this case as well, the distance measurement calculation is not performed.

As is clear from FIG. 8, the subject distance that can be measured by the same amount of light and simultaneous light emission by all the elements of the VCSEL 21 is limited to a certain range.

FIG. 4 shows the light emission amount control of the VCSEL 21 according to the output of the light receiving sensor 32. The horizontal axis of FIG. 4 is the output of the light receiving sensor 32, and the maximum level is 255 and the minimum level is 0. The vertical axis is the amount of light emitted from VCSEL21, which is a maximum of 3 W.

As shown in FIG. 4, when all the elements of the VCSEL 21 emit light at the same time (first light emission, preliminary light emission), the light emission amount of the VCSEL 21 in the second light emission, that is, the main light emission is determined according to the output of the light receiving sensor 32. Control. When the distance to the subject is long and the output of the light receiving sensor 32 is too small to measure the distance in the preliminary light emission, the amount of light emitted by the VCSEL 21 in the main light emission is increased. When the distance to the subject is short and the output of the light receiving sensor 32 is saturated in the preliminary light emission and the distance cannot be measured, the light emission amount of the VCSEL 21 in the main light emission is reduced. The control of the light emission amount in the main light emission is performed by the area-specific light amount control unit 41 controlling the light emission control unit 50.

5A and 5B describe the light emission amount control of the VCSEL 21 according to the photometric value for each light receiving region of the light receiving sensor 32. FIG. 5A shows an example of the output distribution of the light receiving sensor 32 in each region in the preliminary light emission when the light receiving region of the light receiving sensor 32 is divided into 8 × 8 by changing the fill pattern. Specifically, according to the output of the light receiving sensor 32, a region having a large output is represented by a fill pattern having a low density, and a region having a low output is represented by a fill pattern having a high density. In other words, the area represented by the light-dense fill pattern indicates that the distance to the subject in this area is short, and the area represented by the dark-dense fill pattern is to the subject in this area. It indicates that the distance is long. The area where the subject is substantially infinite is represented by the darkest fill pattern, and the area where the subject is closest to the subject, in other words, the area where the output of the light receiving sensor 32 is maximum (light receiving). The region where the output of the sensor 32 is saturated) is shown in white without using a fill pattern. In FIG. 5A, for simplification of the explanation, five types of fill patterns including white are used, but the actual output of the light receiving sensor 32 is shown in five stages. It's not a thing.

FIG. 5B shows that when the output distribution of the light receiving sensor 32 becomes as shown in the example shown in FIG. 5A in the preliminary light emission, the light emission amount for each region set for the VCSEL 21 is filled and the pattern is changed. It is represented by. The thinner the density of the fill pattern, the larger the amount of light emitted. Corresponding to FIG. 5A, the light emission amount of the VCSEL 21 is small in the region where the subject is considered to be at a short distance, and the light emission amount of the VCSEL 21 is large in the region where the subject is considered to be at a long distance. To control. Similar to FIG. 5 (a), in FIG. 5 (b), in order to simplify the explanation, five types of fill patterns including white are used, but the actual emission amount of VCSEL 21 is five levels. It does not indicate that.

FIG. 6 shows a processing flow of normal photographing in which the light receiving sensor 32 is set to the standard sensitivity. In STEP 1, preliminary light emission is performed before shooting. At this time, the light emission amount of the VCSEL 21 is set to be common to all pixels, and the light emission amount is set to be uniform in all areas.

In STEP2, the reflected light of the preliminary emission is received and detected by the light receiving sensor 32. The light receiving region of the light receiving sensor 32 is divided as described above, and the statistical value of each region is calculated from the sensor output value in each region.

In STEP3, the amount of light emitted in each region of VCSEL21 at the time of main shooting is set from the statistical value of each light receiving region calculated in STEP2. The amount of light emitted from the VCSEL 21 is as described in FIGS. 5 (a) and 5 (b).

In STEP4, the light emission amount of VCSEL21 set in STEP3 is emitted to perform the main light emission. In STEP 5, the data of the light receiving sensor 32 is acquired according to the light emission timing.

In STEP 6, distance measurement processing is executed from the data of the light receiving sensor 32 acquired in STEP 5, and the distance information of the subject within the angle of view is calculated. As described above, by setting an appropriate amount of light emission for each light emission region of the VCSEL 21, it is possible to expand the range of the subject distance that can be measured.

[Example 2]
FIG. 7 shows a case where the sensitivity of the light receiving sensor 32 is reset, and shows an example of a processing flow of photographing with high sensitivity. STEPs 1 to 5 in FIG. 7 are the same as STEPs 1 to 5 in the processing flow of FIG. 6, and the acquisition of shooting data is executed. In STEP 6, the light receiving sensor 32 detects the reflected light at the time of the main light emission, calculates the statistical value of the sensor output for each light receiving area, and detects the area where the sensor output is small and the distance cannot be measured, that is, the area where sensitivity is required to be increased.

In STEP 7, the light receiving sensitivity of the light receiving sensor 32 is increased only in the sensitivity increasing region detected in STEP 6. In STEP 8, the amount of light emitted is set for each light emitting region of VCSEL 21, and each light emitting region of VCSEL 21 is made to emit light in STEP 9 according to this setting.

In STEP 10, the light receiving sensor 32 measures the light for each light receiving region. In STEP 11, it is confirmed whether or not there is a sensitivity increasing region as a result of the photometry in STEP 10, and if the sensitivity increasing region remains, the process returns to STEP 7 to increase the sensitivity of the region and perform rephotometry. If there is no sensitivity-requiring region, the process proceeds to STEP 12 to perform shooting processing, and the detection data by the light receiving sensor 32 is stored. In STEP 11, if the sensitivity-requiring region remains, the flow from STEP 7 is repeated, the number of times of photographing is limited to N times, and the photographing process of STEP 12 is performed.

In STEP 13, distance measurement processing is executed from the data of the light receiving sensor 32 acquired in STEP 12, and the distance information of the subject within the angle of view is calculated.

By processing as described above, the appropriate amount of light emitted for each light emitting region of the VCSEL 21 and the appropriate sensitivity for each light receiving region of the light receiving sensor 32 are obtained, and the range of the subject distance that can be measured is further increased than the range shown in FIG. It will be possible to expand.

In the above-described embodiment, as a laser light source in which a plurality of light emitting regions are arranged two-dimensionally, a VCSEL in which a plurality of light emitting regions are arranged two-dimensionally is used. However, the light source is not limited to the VCSEL as long as it is a light source in which a plurality of light emitting regions are arranged two-dimensionally.

20 Floodlight system 22 Optical element 30 Light receiving system 32 Light receiving sensor 41 Area-specific light amount control unit 42 Distance measuring unit 50 Light emission control unit

Japanese Patent Application No. 2012-198337

Claims (8)

A light source in which multiple light emitting regions are arranged in two dimensions,
An optical element that guides the emitted light emitted from the light source to the ranging region,
A light receiving unit that receives the reflected light that the emitted light is reflected by the distance measuring object existing in the distance measuring region.
It is a distance measuring device equipped with
The light receiving portion is divided into a plurality of light receiving regions.
An area-specific light amount control unit that controls the amount of light emitted from each light source of the light source corresponding to the plurality of light receiving areas for each light source.
A region light amount measuring unit that measures the amount of received light for each light receiving area,
A distance measuring unit that measures the distance to the distance measuring target for each light receiving region by measuring the time from the light emission of the light source to the light reception by the light receiving unit for each light receiving region.
Have,
The region-specific light amount control unit simultaneously emits light at the same light amount at each light emitting point of the light source to perform preliminary light emission, and the main light emission is based on the light receiving amount for each light receiving region measured by the region light amount measuring unit by the preliminary light emission. Controls the amount of light emitted from
The distance measuring unit is a distance measuring device characterized in that the distance to the distance measuring target is measured for each light receiving region by the main light emission. It has a control unit that controls the light receiving sensitivity of each light receiving region of the light receiving unit.
The imaging device according to claim 1, wherein the distance measuring unit raises the light receiving sensitivity of a light receiving region in which the light receiving amount measured by the region light quantity measuring unit is insufficient by the control unit to perform distance measurement. It has a control unit that controls the light receiving sensitivity of each light receiving region of the light receiving unit.
The distance measuring device according to claim 1, wherein the distance measuring unit reduces the light receiving sensitivity of the light receiving region where the light receiving amount measured by the region light quantity measuring unit is saturated by the control unit to perform distance measurement. The distance measuring device according to any one of claims 1 to 3, wherein the light source is a vertical resonator surface emitting laser. The distance measuring device according to any one of claims 1 to 4, wherein the optical element is a wide-angle lens. A light source in which multiple light emitting regions are arranged in two dimensions,
An optical element that guides the emitted light emitted from the light source to the ranging region,
A light receiving unit that receives the reflected light that the emitted light is reflected by the distance measuring object existing in the distance measuring region.
It is a distance measuring method using a distance measuring device equipped with.
The light receiving portion is divided into a plurality of light receiving regions.
A region-specific light amount control step for controlling the light emission amount of each light emission region of the light source corresponding to the plurality of light receiving regions for each light emission region.
A region light amount measuring step for measuring the amount of received light for each light receiving area, and
A distance measuring step of measuring the distance to the measurement target in each light receiving area by measuring the time from the light emission of the light source to the light receiving by the light receiving unit in each light receiving area.
Have,
In the region-specific light amount control step, each light emitting point of the light source is simultaneously emitted with the same amount of light to perform preliminary light emission, and the light emission of the main light emission is based on the received light amount for each region measured in the region light amount measuring step by the preliminary light emission. Control the amount,
The distance measuring step is a distance measuring method characterized in that the distance to the distance measuring target is measured for each light receiving region by the main light emission. It has a control unit that controls the light receiving sensitivity of each light receiving region of the light receiving unit.
The distance measuring method according to claim 6, wherein the distance measuring step is performed by increasing the light receiving sensitivity of the light receiving region where the light receiving amount measured in the region light quantity measuring step is insufficient by the control unit. It has a control unit that controls the light receiving sensitivity of each light receiving region of the light receiving unit.
The distance measuring device according to claim 6, wherein in the distance measuring step, the light receiving sensitivity of the light receiving region where the light receiving amount measured in the region light quantity measuring step is saturated is lowered by the control unit to perform distance measurement.

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