JP2020051846A - Distance measurement device - Google Patents

Abstract

To provide a distance measurement device in which measured distance can be corrected without limiting an observation azimuth.SOLUTION: The distance measurement device comprises: a half celestial sphere mirror 30; a light source unit 20 irradiating pulse-shaped light toward the half celestial sphere mirror 30; an image sensor 42 which is arranged on an axis leading from the spherical center of the half celestial sphere mirror 30 to an apex of the half celestial sphere mirror 30, and receives reflected light of the light having been emitted by the light source unit 20 and reflected on an object; a distance calculation unit calculating the distance to the object on the basis of a time difference from a time when the light source 20 has irradiated light to a time when the image sensor 42 receives reflected light; and a correction unit correcting the distance calculated by the distance calculation unit on the basis of the reception time of reflected light received in an apex corresponding area of the image sensor 42 that includes a point on the axis passing through the spherical center of the half celestial sphere mirror 30 and the apex of the half celestial sphere mirror 30.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a distance measuring device using light projecting and receiving light.

  Patent Literature 1 discloses a device in which a laser beam is projected outside the device and reflected light is received by one photodiode. Further, the device disclosed in Patent Document 1 includes a rotating mirror, and the angle of the horizontal direction for guiding the reflected light to the photodiode is sequentially changed by rotating the rotating mirror.

  In addition, taking advantage of the fact that there is a non-detection angle region where no object is detected in a part of the horizontal direction, an internal object whose optical path length is known is placed in the non-detection angle region, and the internal object is irradiated with laser light. Correction data for correcting the distance is calculated based on the light receiving time at the time of the correction. The reason for calculating the correction data is that a delay in signal transmission in the circuit occurs due to the effect of temperature.

JP 2010-203820 A

  A distance measuring device using a light source that emits light in a pulsed manner and an image sensor is also known. When an image sensor is used, reflected light can be received from a wide range at a time. Therefore, it is conceivable to provide a hemispherical mirror and irradiate the light emitted from the light source with the hemispherical mirror in all directions of 360 degrees in the horizontal direction.

  However, when light is irradiated in all directions of 360 degrees in the horizontal direction by the hemispherical mirror, the above-described non-detection angle region does not exist. Therefore, how to obtain the light receiving time for correcting the distance is a problem.

  The present disclosure has been made based on this situation, and an object of the present disclosure is to provide a distance measurement device that can perform distance correction without restricting an observation direction.

  The above object is achieved by a combination of features described in the independent claims, and the subclaims define further advantageous embodiments. Reference numerals in parentheses described in the claims indicate a correspondence relationship with specific means described in the embodiment described below as one aspect, and do not limit the disclosed technical scope.

The disclosure according to claim 1 for achieving the above object is as follows.
A semi-spherical mirror (30),
A light source unit (20) for irradiating pulsed light toward the hemispherical mirror;
An image sensor (42) disposed on an axis passing from the spherical center of the hemispherical mirror to the vertex of the hemispherical mirror and receiving reflected light generated by light emitted from the light source unit being reflected by an object;
A distance calculation unit (53) that calculates a distance to the object based on a time difference from when the light source unit emits light to when the image sensor receives the reflected light;
In the image sensor, the distance calculated by the distance calculation unit based on the light receiving time of the reflected light received in the vertex corresponding region including the point on the axis passing through the spherical center of the hemispheric mirror and the vertex of the hemisphere mirror And a correcting unit (54) for correcting the distance.

  When the image sensor is on an axis that passes through the spherical center of the hemispherical mirror and the vertex of the hemispherical mirror (hereinafter, hemispherical axis), the hemispherical mirror reflects reflected light (hereinafter, external Reflected light perpendicular to the semi-celestial sphere axis is deflected toward the image sensor. However, the vertex portion of the hemispherical mirror has almost no function of deflecting the external reflected light incident on the device perpendicular to the hemispherical axis in the direction of the image sensor.

  On the other hand, the reflected light generated by reflecting the light emitted from the light source at the apex portion of the hemispherical mirror, and a portion of the reflected light (hereinafter, internally reflected light) that is not projected to the outside of the device, is the apex portion. The light is received by the image sensor due to the scattering of the light. Part of the external reflected light is also received by the vertex-corresponding region of the image sensor due to scattering by the semi-celepheral mirror. However, the intensity of the external reflected light is lower than that of the reflected light generated by the reflection at the apex of the hemispherical mirror, and is at a level that cannot be observed.

  That is, the reflected light received in the vertex corresponding region can be considered to be internally reflected light. For internally reflected light, the optical path length is known. Therefore, in this distance measuring device, the distance calculated by the distance calculating unit is corrected based on the light receiving time of the reflected light received in the vertex corresponding region. Further, since the vertex corresponding region is not a region that receives external reflected light, there is no limitation on the observation direction.

  In the distance measuring device according to the second aspect, the concave portion (31, 131, 231, 331) is formed at the vertex of the semi-celestial sphere mirror.

  The internally reflected light has a high intensity because the flight distance is short. Moreover, the internally reflected light generated by the scattering at the vertex of the semi-celestial sphere mirror is also received in a light receiving area other than the vertex corresponding area of the image sensor. Therefore, the internally reflected light may obstruct the observation of the external reflected light. However, in this distance measuring device, since the concave portion is formed at the vertex of the hemispherical mirror, a part of the internally reflected light traveling toward the light receiving region other than the region corresponding to the vertex of the image sensor is hindered by the wall surface of the concave portion. Therefore, it is difficult for the internally reflected light to travel to a light receiving area other than the vertex corresponding area of the image sensor. Therefore, in this distance measuring device, it is possible to suppress the detection accuracy of an object outside the device from being deteriorated due to the internally reflected light.

  On the other hand, since the depression is formed at the vertex of the hemispherical mirror, the internally reflected light traveling toward the vertex corresponding area of the image sensor is not hindered by the depression. Therefore, it is possible to suppress the intensity of the internally reflected light received by the vertex corresponding region from being too low.

  In the distance measuring device according to the third aspect, unevenness is formed on the surface of the recess. The number of light reflections inside the dent increases due to the formation of the irregularities on the surface of the dent. Therefore, the internally reflected light that goes out of the dent and goes to the light receiving area other than the vertex corresponding area is further weakened. Therefore, it is possible to further prevent the detection accuracy of an object outside the device from being reduced due to the internally reflected light.

  In addition, if the intensity of the internal reflected light received in the vertex corresponding region is too strong, the register provided in the pixel arranged in the vertex corresponding region of the image sensor may be saturated. Measurement accuracy decreases.

  However, if unevenness is formed on the surface of the dent, the internally reflected light is weakened. Therefore, the possibility that the register provided in the pixel arranged in the vertex corresponding region is saturated is reduced. Therefore, it is possible to suppress a decrease in the measurement accuracy of the light receiving time of the internally reflected light.

  In the distance measuring device according to claim 4, the portion that primarily reflects the light emitted by the light source unit in the recess, while deflecting the primary internal reflected light generated by the primary reflection in the direction toward the vertex corresponding region of the image sensor, It has a concave shape for collecting the light flux of the primary internal reflected light.

  When the portion that reflects light is concave, the light beam of the reflected light can be collected due to the concave shape, as compared with the case where the portion is flat. Further, the direction of the reflected light can be adjusted by adjusting the direction of the concave surface.

  In the case of claim 4, the internal reflection light received in the light receiving area other than the area corresponding to the vertex of the image sensor is further reduced. Therefore, it is possible to further prevent the detection accuracy of an object outside the device from being reduced due to the internally reflected light.

  In the distance measuring device according to claim 5, a portion of the dent that primarily reflects light emitted by the light source unit is made of a reflection suppressing material.

  By doing so, the internal reflection light received in the light receiving area other than the area corresponding to the vertex of the image sensor is further reduced. In addition, there are the following effects.

  When deflecting the primary internal reflected light in the direction toward the vertex corresponding region of the image sensor, the intensity of the internal reflected light received in the vertex corresponding region is too strong, and the register of the pixel arranged in the vertex corresponding region is saturated. If there is a possibility that the register is saturated, the measurement accuracy of the light receiving time is reduced. However, according to the fifth aspect, the intensity of the primary internally reflected light can be reduced. Thereby, it is possible to suppress a decrease in measurement accuracy of the light receiving time of the internally reflected light.

  In the distance measuring device according to claim 6, the dent has a portion having a larger sectional area than the opening. This makes it possible to increase the number of times the internally reflected light is reflected in the recess, so that the intensity of the internally reflected light received by the image sensor can be reduced. Therefore, it is possible to further suppress a decrease in detection accuracy of an object outside the device due to the internally reflected light, and to suppress a decrease in measurement accuracy of the light receiving time of the internally reflected light.

1 is a block diagram illustrating a configuration of a distance measuring device 1 according to a first embodiment. FIG. 3 is a block diagram illustrating functions of a control unit 50. FIG. 3 is a diagram conceptually showing an image of a monitoring area 60. It is a figure showing distance measuring device 100 of a 2nd embodiment. It is a figure showing distance measuring device 200 of a 3rd embodiment. It is a figure showing distance measuring device 200 of a 4th embodiment.

<First embodiment>
Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of a distance measuring device 1 according to the first embodiment. The distance measuring device 1 includes a light source unit 20, a semi-spherical mirror 30, a light receiving unit 40, and a control unit 50 inside a housing 10. The distance measuring device 1 is arranged in a place where it is necessary to detect whether or not a moving object is present in the surroundings, so that a semi-celestial sphere axis C passing through a spherical center and a vertex of the semi-celular sphere mirror 30 is in a vertical direction. .

[Hardware configuration]
A part of the housing 10 has a light transmitting property so that the light projection F emitted from the light source unit 20 and the external reflection light Ro generated by reflecting the light projection F on the object S outside the apparatus can pass through. Has become.

  The light source unit 20 includes a light source 21 and a diffusion lens 22. The light source 21 is an LED or a pulse laser diode, and emits light in a pulsed manner. The diffusion lens 22 diffuses the light emitted by the light source 21 so that the projection light F is applied to the entire surface of the hemispherical mirror 30. In addition, the distance measuring device 1 includes two light source units 20, but if the projection light F irradiates the entire surface of the hemispherical mirror 30, one light source unit 20 may be used, or three or more light source units 20 may be used. May be.

  The hemispherical mirror 30 deflects the light projection F in a direction toward the outside of the apparatus. Further, the external reflected light Ro horizontally incident on the hemispherical mirror 30 from the outside of the apparatus is deflected toward the image sensor 42. The shape of the hemispherical mirror 30 does not need to be a shape obtained by halving a true sphere, but may be a hemispherical shape capable of deflecting the above-mentioned projection light F and deflecting the external reflected light Ro.

  A hole 31 is formed at the vertex of the semi-spherical spherical mirror 30. The hole 31 is a bottomed hole that is located at the vertex of the spherical mirror 30 and extends from the vertex toward the center of the spherical surface of the spherical mirror 30. The shape of the hole 31 is a cylinder or a prism. The size of the opening diameter of the hole 31 is appropriately set within a range that does not cause a problem in the function of deflecting the externally reflected light Ro of the semi-celular mirror 30. The specific opening diameter is determined based on experiments and the like. It should be noted that the semi-celestial sphere axis C is an axis passing through the vertex in the shape of the semi-celular sphere mirror 30 when there is no hole 31.

  The light receiving unit 40 includes a condenser lens 41 and an image sensor 42. The condenser lens 41 condenses the external reflected light Ro reflected by the hemispherical mirror 30 so as to enter the light receiving area of the image sensor 42.

  The image sensor 42 is arranged at a position that intersects the hemispherical axis C, and the light receiving surface is orthogonal to the hemispherical axis C. The image sensor 42 is an image sensor that measures a distance to an object by a TOF (Time-of-Flight) method. CMOS image sensors and CCD image sensors are widely known, and both the CMOS image sensor and the CCD image sensor can be used as the image sensor 42 of the present embodiment.

  The image sensor 42 has a configuration in which pixels are arranged in a grid pattern on a plane. Each pixel has a configuration including one photoelectric conversion element, a plurality of registers, and a shutter corresponding to each register. The photoelectric conversion element is, for example, a photodiode, and the register is, for example, a capacitor.

  The control unit 50 is a computer including a CPU, a ROM, a RAM, and the like, and also includes a drive circuit for driving the light source 21. The CPU executes a program stored in a recording medium such as a ROM while using the temporary storage function of the RAM. By executing this program, emission control of the light source 21, control of the image sensor 42, calculation of the distance to the object, and the like are performed. Executing a program also means that a method corresponding to the program is executed.

[Distance measurement processing]
Next, a distance measurement process executed by the control unit 50 will be described. As shown in FIG. 2, the control unit 50 includes a light emission control unit 51, a time measurement unit 52, a distance calculation unit 53, and a correction unit 54.

  The light emission control unit 51 outputs a light emission command to the drive circuit, and generates light from the light source 21 in a pulse shape. The light emission command includes information indicating a drive voltage value, and the drive circuit causes the light source 21 to emit light at a drive voltage value determined by the light emission command. By making the change in the drive voltage value into a pulse shape, a pulsed laser beam is generated from the light source 21. The light emission control unit 51 generates light in a pulsed manner at a constant cycle.

  The light projection F output from the light source 21 is deflected by the hemispherical mirror 30 and is projected outside the device. The light projection F output to the outside of the apparatus is in a direction orthogonal to the semicelular axis C and in all directions around the semispherical axis C by 360 degrees.

  When the external reflection light Ro generated by the reflection of the light F from an object outside the device enters the inside of the distance measuring device 1, the light is deflected by the hemispherical mirror 30 and the external reflection light Ro travels to the light receiving unit 40. The external reflected light Ro is condensed by the condenser lens 41 of the light receiving unit 40 and received by the image sensor 42. The image sensor 42 outputs the intensity of the received signal. This signal is a signal indicating an image detected by the image sensor 42.

  FIG. 3 conceptually shows an image of the monitoring area 60 in which the distance to the object can be monitored by the image sensor 42. The semi-spherical mirror 30 allows the image sensor 42 to receive light incident from all directions of 360 degrees outside the device. Therefore, as shown in FIG. 3, the monitoring area 60 is circular.

  The monitoring area 60 shown in FIG. 3 has a blind spot area 61 at the center. The blind spot area 61 is an area in which an object outside the device has not been detected. The blind spot area 61 is an area corresponding to the vertex of the semi-celestial sphere mirror 30, and corresponds to the vertex corresponding area. The vertex portion of the hemispherical mirror 30 has almost no function of deflecting external light horizontally incident from the outside of the apparatus, that is, external light incident in a direction orthogonal to the hemispherical axis C, in the direction of the image sensor 42. Therefore, the blind spot area 61 exists in the monitoring area 60.

  The time measuring unit 52 measures the reflected light detection time, which is the time from when the light source 21 emits light to when the image sensor 42 detects the external reflected light Ro. The time when the light source 21 emits light is the time when the light emission control unit 51 outputs a light emission command to the drive circuit. The time point at which the image sensor 42 detects the external reflected light Ro is a time point at which an electric signal output by the image sensor 42 is acquired and the electric signal exceeds a predetermined reflected light detection threshold value.

  The distance calculation unit 53 calculates the distance to the object using the reflected light detection time and a distance calculation formula stored in advance.

  The correction unit 54 corrects a correction coefficient of the distance calculation formula. The reason for performing the correction is that the delay time generated in the arithmetic processing, such as the transmission time of the signal to the light source 21 and the transmission time of the signal from the image sensor 42, dynamically changes under the influence of the temperature characteristics. is there. The correction is performed at a constant cycle. The correction unit 54 corrects the correction coefficient of the distance calculation formula, so that the distance calculated by the distance calculation unit 53 is corrected.

  For the correction, the reflected light detection time calculated by the time measuring unit 52 for the internally reflected light Ri (hereinafter, the internally reflected light detection time) is used. The image sensor 42 receives not only the external reflected light Ro but also the internal reflected light Ri. As the internal reflected light Ri used for the correction, an image signal of the blind spot area 61, that is, the internal reflected light Ri detected in the blind spot area 61 of the image sensor 42 is used.

  The internally reflected light Ri is generated by reflecting the light projection F at various places inside the apparatus, in addition to the light projection F being reflected at the vertex of the semi-celestial sphere mirror 30. However, the internal reflected light Ri received by the image sensor 42 is mainly light generated by being reflected at the vertex of the hemispherical mirror 30. This is because the light projection F applied to the portion other than the apex is almost deflected to the outside of the apparatus due to the inclination of the surface of the semi-celepherical mirror 30. Hereinafter, when it is simply described as the internally reflected light Ri, it means light generated by being reflected at the apex of the semi-celestial sphere mirror 30.

  When the incident angle and the reflection angle are the same, the internally reflected light Ri generated by the reflection of the projection light F applied to the apex of the hemispherical mirror 30 is not received by the image sensor 42. However, the projection light F is scattered by the hemispherical mirror 30, and the internally reflected light Ri generated by scattering of the projection light F near the vertex is partially directed to the image sensor 42 and received by the image sensor 42.

  Note that the external reflected light Ro is also partially received by the blind spot area 61 of the image sensor 42 due to the scattering at the semi-spherical mirror 30. However, the intensity of the external reflected light Ro is lower than that of the internal reflected light Ri, and it can be considered that the external reflected light Ro is not substantially received by the blind spot area 61. That is, the reflected light received in the blind spot area 61 can be considered to be the internal reflected light Ri.

  The optical path length of the internally reflected light Ri has no disturbance factor during the measurement and is known. Therefore, a change in the internal reflected light detection time measured by the time measuring unit 52 corresponds to a change in the delay time of the arithmetic processing. Therefore, the correction coefficient can be corrected based on the internal reflected light detection time measured by the time measuring unit 52.

[Operation of Hole 31]
In the present embodiment, a hole 31 is formed at the vertex of the semi-celestial sphere mirror 30. Next, the operation of the hole 31 will be described. First, the hole 31 has an effect of reducing the intensity of the internally reflected light Ri received in the blind spot area 61 of the image sensor 42. Second, the hole 31 has an effect of reducing the intensity of the internal reflection light Ri received in the monitoring area 60 other than the blind spot area 61 in the image sensor 42. Hereinafter, in the image sensor 42, the monitoring area 60 other than the blind spot area 61 is referred to as an external reflected light receiving area 62.

  The first operation will be described. The internal reflected light Ri has a high intensity because the optical path length is short. For this reason, the intensity of the internal reflected light Ri is too strong, and the register provided in the pixel arranged in the blind spot area 61 of the image sensor 42 may be saturated. Therefore, the intensity of the internally reflected light Ri received in the blind spot area 61 is reduced by the hole 31. When the light F emitted by the light source 21 enters the hole 31, the light F is reflected by the hole 31 a plurality of times, then exits the hole 31 and is received by the blind spot area 61 of the image sensor 42. . The internal reflection light Ri is weakened by being reflected a plurality of times in the hole 31.

  The second operation will be described. Even if the direction of the internal reflected light Ri is directed toward the external reflected light receiving area 62 of the image sensor 42 inside the hole 31, it may be blocked by the wall portion of the hole 31. Therefore, the hole 31 can reduce the intensity of the internal reflected light Ri received by the external reflected light receiving area 62.

[Effects of First Embodiment]
As described above, in the distance measuring device 1 of the first embodiment described above, the distance calculation unit 53 corrects the distance calculation formula for calculating the distance based on the light receiving time of the reflected light received in the blind spot area 61. The reflected light received in the blind spot area 61 can be considered to be the internal reflected light Ri, and since the optical path length of the internal reflected light Ri is known, the distance calculation formula can be corrected. Further, since the blind spot area 61 is not an area for receiving the external reflected light Ro, the observation direction is not limited.

  In the distance measuring device 1 of the present embodiment, a hole 31 is formed at the apex of the semi-celestial sphere mirror 30. A part of the internal reflected light Ri of the image sensor 42 toward the external reflected light receiving area 62 is hindered by the wall surface of the hole 31. Therefore, the internal reflected light Ri is less likely to reach the external reflected light receiving area 62 of the image sensor 42. Therefore, in the distance measuring device 1, it is possible to prevent the detection accuracy of an object outside the device from being deteriorated due to the internal reflected light Ri.

  In addition, if the intensity of the internal reflected light Ri received in the blind spot area 61 is too strong, the register provided in the pixel disposed in the blind spot area 61 may be saturated. When the register is saturated, the light receiving time is measured. Accuracy decreases. However, the intensity of the internally reflected light Ri is reduced by being reflected a plurality of times inside the hole 31. Therefore, the possibility that the register provided in the pixel arranged in the blind spot area 61 is saturated is reduced. Therefore, it is possible to suppress a decrease in the measurement accuracy of the light receiving time of the internal reflected light Ri.

<Second embodiment>
Next, a second embodiment will be described. In the following description of the second embodiment, elements having the same reference numerals as those used so far are the same as the elements of the same reference numerals in the previous embodiments, unless otherwise specified. When only a part of the configuration is described, the above-described embodiment can be applied to the other part of the configuration.

  FIG. 4 shows a distance measuring device 100 according to the second embodiment. The distance measuring device 100 differs from the hole 31 of the first embodiment in the shape of the hole 131. The hole 131 has the same opening diameter and depth as the hole 31 of the first embodiment. However, the holes 131 have irregularities on the side surfaces.

  Due to the formation of the unevenness, the number of times of light reflection inside the hole 131 increases. Therefore, the internal reflected light Ri that exits from the hole 131 and travels toward the external reflected light receiving area 62 of the image sensor 42 is further weakened. Therefore, it is possible to further prevent the detection accuracy of an object outside the device from being reduced due to the internal reflected light Ri.

  Further, since the unevenness is formed on the surface of the hole 131, the internal reflected light Ri toward the blind spot area 61 of the image sensor 42 is further weakened. Therefore, the possibility that the register provided in the pixel arranged in the blind spot area 61 is saturated is further reduced. Therefore, it is possible to further suppress a decrease in measurement accuracy of the light receiving time of the internal reflected light Ri. Note that the specific number of irregularities on the surface of the hole 131 and the difference in the height of the irregularities are determined based on experiments and the like so that the internal reflected light Ri can be appropriately reduced.

<Third embodiment>
FIG. 5 shows a distance measuring device 200 according to the third embodiment. The distance measuring device 200 differs from the hole 31 of the first embodiment in the shape of the hole 231. The hole 231 has the same opening diameter as the hole 31 of the first embodiment. However, unlike the hole 31 of the first embodiment, the hole 231 does not have a flat upper surface. The hole 231 has a concave shape in which a side surface and an upper bottom surface are continuous.

  Therefore, the portion of the hole 231 that primarily reflects the light projection F emitted by the light source 21 is also concave. When the portion that primarily reflects the light projection F has a concave shape, the light flux of the primary internal reflected light, which is the internal reflected light Ri generated by the primary reflection, can be collected. The light condensing here is not limited to collecting the light beam at one point, but means making the light beam thinner than before the reflection.

  Where the primary internal reflected light is collected can be adjusted by the shape of the concave surface and the direction of the concave surface. Therefore, the concave shape of the portion where the projection F is primarily reflected is such that the hole 231 deflects the primary internal reflected light in the direction toward the blind spot area 61 of the image sensor 42 while condensing the primary reflected light. Has been adjusted. The concave surface can be any of a paraboloid, an ellipsoid, and a hyperboloid. Further, the concave shape may be another free-form surface.

  According to the third embodiment, since the primary internal reflected light is less likely to be received by the external reflected light receiving area 62 of the image sensor 42, the internal reflected light Ri received by the external reflected light receiving area 62 is reduced. Decrease. Therefore, it is possible to further prevent the detection accuracy of an object outside the device from being reduced due to the internal reflected light Ri.

<Fourth embodiment>
FIG. 6 shows a distance measuring device 300 according to the fourth embodiment. The distance measuring device 300 differs from the hole 31 of the first embodiment in the shape of the hole 331. The hole 331 has the same opening diameter as the hole 31 of the first embodiment. However, unlike the hole 31 of the first embodiment, the hole 331 has a shape in which the cross-sectional area perpendicular to the semicelestial sphere axis C increases toward the bottom of the hole.

  Accordingly, the number of times of reflection of the internally reflected light Ri inside the hole 331 can be increased, so that the light receiving intensity of the internally reflected light Ri received by the image sensor 42 can be reduced. For this reason, it is possible to further suppress a decrease in the detection accuracy of an object outside the apparatus due to the internal reflected light Ri, and to suppress a decrease in the measurement accuracy of the light receiving time of the internal reflected light Ri.

  As described above, the embodiments have been described, but the disclosed technology is not limited to the above-described embodiments, and the following modified examples are also included in the disclosed range. Various modifications can be made.

<Modification 1>
In the third embodiment, the portion that primarily reflects the light projection F may be made of a reflection suppressing material. A thin film having a low refractive index, such as MgF ₂ , SiO ₂ , or a fluororesin, is an example of the reflection suppressing material. In order to make the portion of the light projection F that is primarily reflected from a reflection suppressing material, a thin film having a low refractive index may be coated on the portion of the hole 231 that primarily reflects the light projection F. Further, in the hole 231, a portion other than the portion where the light projection F is primarily reflected may be made of a reflection suppressing material.

<Modification 2>
In the embodiment, the holes 31, 131, 231, and 331 have been described as the recesses. However, the recess may have a shape that is not as deep as the holes 31, 131, 231, 331.

<Modification 3>
In addition, the concave portion may not be provided at the vertex of the semi-celestial sphere mirror 30, and the vertex may be subjected to reflection suppression processing. As the anti-reflection processing, there is a means of providing the anti-reflection material at the top portion, such as coating the anti-reflection material. Further, the surface shape of the vertex itself of the semi-celestial sphere mirror 30 may be a small uneven shape.

1, 100, 200, 300: Distance measuring device 10: Housing 20: Light source 21: Light source 22: Diffusion lens 30: Semi-spherical mirror 31, 131, 231, 331: Hole (dent) 40: Light receiving unit 41: Collection Optical lens 42: Image sensor 50: Control unit 51: Emission control unit 52: Time measurement unit 53: Distance calculation unit 54: Correction unit 60: Monitoring area 61: Blind spot area 62: External reflected light receiving area C: Semispherical axis F : Flood light Ri: Internal reflected light Ro: External reflected light S: Object

Claims (6)

A semi-spherical mirror (30),
A light source unit (20) for irradiating pulsed light toward the hemispherical mirror;
An image sensor (42) disposed on an axis passing from the spherical center of the hemispherical mirror to the vertex of the hemispherical mirror and receiving reflected light generated by reflecting light emitted from the light source unit on an object;
A distance calculation unit (53) that calculates a distance to the object based on a time difference from when the light source unit emits light to when the image sensor receives the reflected light;
In the image sensor, the distance calculation is performed based on a light receiving time of the reflected light received in a vertex corresponding region including a point on an axis passing through the spherical center of the hemispherical mirror and the vertex of the hemispherical mirror. A correction unit (54) for correcting the distance calculated by the unit.   The distance measuring device according to claim 1, wherein a concave portion (31, 131, 231, 331) is formed at an apex of the semi-celestial sphere mirror.   The distance measuring device according to claim 2, wherein unevenness is formed on a surface of the recess.   The portion of the dent that primarily reflects the light emitted by the light source unit, while deflecting the primary internal reflected light generated by the primary reflection in a direction toward the vertex corresponding region of the image sensor, 3. The distance measuring device according to claim 2, wherein the distance measuring device has a concave shape for condensing a light beam.   The distance measuring device according to claim 4, wherein a portion of the dent that primarily reflects light emitted by the light source unit is made of a reflection suppressing material.   The distance measuring device according to claim 2, wherein the recess has a portion having a larger cross-sectional area than the opening.

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