JP2017075806A - Distance measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance measurement device with which it is possible to sufficiently secure a resolution, and also to improve a measurable distance and measurement accuracy.SOLUTION: A distance measurement device 1 comprises: a light source 2 for radiating a light-transmitting beam L1 to an object K; an optical surface 11 having a reflection region 21 for reflecting a portion of the light-transmitting beam L1 radiated from the light source 2 and a transmission region 22 for making the rest of the light-transmitting beam L1 pass through; a scanning mirror 6 for making the light-transmitting beam L1 reflected at the reflection region 21 reflected toward the object, and also making return light L2 from the object K reflected toward the optical surface 11; and a light-receiving element 8 for detection for detecting the return light L2 that passed through the transmission region 22 of the optical surface 11. The light-receiving element 8 for detection is an avalanche photodiode that operates in a Geiger mode, the area of the transmission region 22 on the optical surface 11 being smaller than the area of the reflection region 21.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a distance measuring device.

  Currently, after projecting light such as laser light toward an object, the return light from the object is detected, and the distance to the object is measured based on the time from light transmission to detection of the return light Development of a (Time of Flight) type distance measuring device is underway. Such a distance measuring device is assumed to be mounted as an automatic driving support system in a vehicle such as an automobile. In an automatic driving support system, the distance between a running vehicle and an object (including a human body) is measured by a distance measuring device, and the vehicle speed is controlled based on the measurement result, thereby avoiding a collision between the vehicle and the object. Is expected.

  As a conventional distance measuring device, for example, there is a beam light projecting / receiving device described in Patent Document 1. This apparatus includes a scan mirror that reflects and scans a light projection beam emitted from a light source, and a light receiving element that receives return light reflected by the scan mirror after being reflected by an object. A light projecting / receiving separation member formed of a single prism is disposed in the optical path of the light projecting beam and the return light. An outer surface of the light projecting / receiving separation member is provided with a region for reflecting the light projection beam, a region for transmitting the return light, and a region for reflecting the return light.

  Moreover, the radar apparatus described in Patent Document 2 includes a light source, pixels, and a light detection control unit. In this apparatus, SPAD (Single Photon Avalanche Diode) is used as a pixel for detecting return light from an object. The light detection unit is configured to eliminate the influence of the scattered light by operating the SPAD after the timing at which the scattered light inside the apparatus by the light emitted from the light source enters the SPAD.

Japanese Patent No. 5663251 Japanese Patent Laying-Open No. 2015-117970

  In Patent Document 1 described above, it is considered that a general PD (Photo Diode) or APD (Avalanche Photo Diode) can be used as a light receiving element for returning light. When these light receiving elements are used, an optical system that detects a sufficient amount of return light is required to increase the distance measurement possible distance. For this reason, the apparatus of Patent Document 1 employs an optical system in which the optical path width of the return light is made wider than the optical path width of the translucent beam and the return light is condensed toward the light receiving element by a condenser lens ( (See FIG. 6 of Patent Document 1).

  On the other hand, when SPAD is used as a light receiving element as in the device of Patent Document 2, since the light receiving sensitivity of SPAD is higher than that of general PD or APD, in principle, it is the same even if the amount of return light is small. A distance can be measured. However, when the light receiving element of the apparatus of Patent Document 1 is simply replaced with SPAD, the optical path width of the return light is widened, so the disturbance light increases and the S / N ratio of the signal decreases, resulting in measurement. There is a possibility that the distance and distance measurement accuracy may not be sufficiently improved. Also, the wide optical path width of the return light means that the field of view on the light receiving side is wide. Therefore, there is a problem that the detection range per pixel of the light receiving element is enlarged and the resolution is lowered.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a distance measuring device that can secure a sufficient resolution and can improve the distance measurement possible distance and the distance measurement accuracy.

  A distance measuring device according to an aspect of the present invention is a distance measuring device that measures a distance to an object, and reflects a light source that emits a light beam transmitted to the object and a part of the light beam emitted from the light source. An optical surface having a reflection region to be transmitted and a transmission region that transmits the remainder of the light transmission beam, and the light beam reflected by the reflection region is reflected toward the object, and return light from the object is reflected toward the optical surface. And a detection light receiving element that detects return light that has passed through the transmission region of the optical surface, the detection light receiving element is an avalanche photodiode that operates in Geiger mode. Is larger than the area of the reflective region.

  This distance measuring device is provided with an optical surface having a reflection region for reflecting a part of a light transmission beam emitted from a light source and a transmission region for transmitting the remaining part of the light transmission beam. Further, on the optical surface, the area of the transmission region is smaller than the area of the reflection region. Therefore, it is possible to reduce the influence of disturbance light when the return light from the object is detected by the detection light receiving element. In this distance measuring device, an avalanche photodiode operating in a Geiger mode is used as a light receiving element for detection. Thereby, even if the amount of the return light from the object is weak because the area of the transmission region is smaller than the area of the reflection region, the return light can be detected with high sensitivity. Therefore, the S / N ratio of the signal can be secured at a high level, and the distance measurement possible distance and the distance measurement accuracy can be sufficiently improved. Furthermore, since the area of the transmissive region is smaller than the area of the reflective region on the optical surface, the detection range per pixel of the light receiving element is narrowed, so that sufficient resolution can be secured.

  Further, on the optical surface, the reflection region may be provided so as to surround the transmission region. Thereby, the influence of the disturbance light at the time of detecting the return light from an object with the light receiving element for a detection can be reduced more reliably.

  Further, on the optical surface, the center of the transmission region may be decentered with respect to the center of the reflection region. For example, when the translucent beam is a Gaussian beam, the light amount of the translucent beam is higher near the center than at the periphery. Therefore, by decentering the center of the transmissive region with respect to the center of the reflective region, a sufficient amount of light of the translucent beam directed to the object can be secured, and the signal S / N ratio can be further improved.

  Further, a reflection surface for reflecting the return light transmitted through the transmission region of the optical surface toward the detection light receiving element may be further provided between the optical surface and the detection light receiving element. As a result, the optical path length of the return light from the optical surface to the detection light receiving element can be increased, and the resolution can be further increased.

  Moreover, you may further provide the light receiving element for a monitor which detects the remainder of the light transmission beam which permeate | transmitted the transmission area | region of the optical surface. By monitoring the output state of the translucent beam, it is possible to determine whether the light source is abnormal.

  Moreover, you may further provide the optical block integrated including the optical path and the optical path of the return light which permeate | transmitted the permeation | transmission area | region of the optical surface. By configuring the optical surface and the optical path using the optical block, the apparatus can be miniaturized. In addition, the assembly of optical components is facilitated.

  Further, the scanning mirror may be constituted by a MEMS mirror. As a result, the light beam can be scanned with high accuracy. In this distance measuring apparatus, since the avalanche photodiode operating in the Geiger mode is used as the light receiving element for detection, the amount of return light from the object may be weak. Therefore, the area of the MEMS mirror may be set based on the diameter of the translucent beam, and it is not necessary to arrange a large mirror.

  According to this distance measuring device, the resolution can be sufficiently secured, and the distance measurement possible distance and the distance measuring accuracy can be improved.

It is a perspective view which shows one Embodiment of a distance measuring device. It is a top view of an optical block. It is a front view of the optical surface provided in the optical block. It is a perspective view which shows the modification of a distance measuring device. (A)-(c) is a figure which shows the modification of an optical surface.

  Hereinafter, a preferred embodiment of a distance measuring device according to one aspect of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a perspective view showing an embodiment of a distance measuring device. The distance measuring device 1 is a device mounted as an automatic driving support system in a vehicle such as an automobile. In the automatic driving support system, the distance between the running vehicle and the object K is measured in real time by the distance measuring device 1, and the vehicle speed and the like are controlled based on the measurement result, thereby avoiding the collision between the vehicle and the object K. Control is executed. The object K is, for example, another vehicle, an obstacle such as a wall, or a pedestrian. In the present embodiment, for example, it is assumed that the distance from the object K located at a position about 0.1 m to 100 m away is measured.

  As shown in FIG. 1, the distance measuring device 1 includes a light source 2, a collimator 3, an aperture 4, an optical block 5, a scanning mirror 6, a monitor light receiving element 7, and a detection light receiving element 8. It consists of All of these components are assembled on a substantially plate-like stage 9.

  The light source 2 is a portion that emits a light transmission beam L1 to the object K. For example, a laser diode that emits an infrared or ultraviolet pulse laser is used as the light source 2. The wavelength in the case of infrared light is, for example, about 800 nm to 1000 nm, and the wavelength in the case of ultraviolet light is, for example, about 350 nm to 400 nm. The translucent beam L1 emitted from the light source 2 is collimated by the collimator 3 and guided to the optical block 5 side by the aperture 4 while being reduced to a beam diameter of, for example, φ10 mm or less.

  As shown in FIG. 2, the optical block 5 includes an optical surface 11, a reflecting surface 12, an optical path from the optical surface 11 to the monitoring light receiving element 7, and an optical path from the optical surface 11 to the detecting light receiving element 8. An integrated optical element. The optical block 5 has a function of separating the translucent beam L1 from the light source 2 toward the object K and the return light L2 reflected from the object K. The optical block 5 is formed into a pentagonal block shape in plan view by cutting and polishing glass or the like.

  The side surface of the optical block 5 is provided with a first surface 5a provided with the optical surface 11, a second surface 5b continuous with an obtuse angle with the first surface 5a on one side of the first surface 5a, and a reflecting surface 12. And a fourth surface 5d continuous with an obtuse angle with the second surface 5b on one side of the second surface 5b and an obtuse angle with the third surface 5c on one side of the third surface 5c. And a fifth surface 5e that forms an obtuse angle with the fourth surface 5d and the first surface 5a on one side of the fourth surface 5d.

  As shown in FIG. 3, the optical surface 11 includes a reflection region 21 that reflects a part of the light transmission beam L1, and a transmission region 22 that transmits the remaining part of the light transmission beam L1. The reflection region 21 is formed by vapor-depositing a metal film such as aluminum or silver on the first surface 5a in an annular shape. The reflective region 21 may be formed of a dielectric multilayer film or the like.

  The transmissive region 22 is formed in a circular shape by exposing the first surface 5 a in a region inside the reflective region 21. That is, the reflective region 21 is formed so as to surround the entire periphery of the transmissive region 22. The center of the transmissive region 22 and the center of the reflective region 21 coincide. Further, the area of the transmission region 22 is smaller than the area of the reflection region 21. With this configuration, the optical surface 11 functions as an aperture that limits the incident range of the return light L <b> 2 with respect to the detection light-receiving element 8. In the present embodiment, the reflection region 21 has, for example, approximately the same diameter (φ10 mm) as the light transmission beam L1 that has passed through the aperture 4. On the other hand, the transmission region 22 is about φ0.5 mm, for example.

  As shown in FIG. 1, the optical surface 11 is disposed at an acute angle with respect to the optical axis of the light-transmitting beam L <b> 1 that has passed through the aperture 4. The central portion of the transmitted light beam L1 incident on the optical surface 11 is guided from the transmission region 22 into the optical block 5 and detected by the monitoring light receiving element 7 disposed outside the fourth surface 5d. The light-receiving element for monitoring 7 is a part that detects the remaining part of the light-transmitting beam L1 that has passed through the transmission region 22 of the optical surface 11. As the monitor light receiving element 7, a general photodiode is used. The output state of the translucent beam L1 from the light source 2 (for example, fluctuation of the amount of light due to the temperature characteristics of the light source 2) is monitored at any time by a monitoring unit (not shown) based on the detection signal from the monitor light receiving element 7.

  On the other hand, the peripheral portion of the translucent beam L 1 incident on the optical surface 11 is reflected by the reflection region 21 and guided to the scanning mirror 6. The scanning mirror 6 is, for example, a MEMS (Micro Electro Mechanical Systems) mirror. The scanning mirror 6 swings in the in-plane direction of the stage 9 based on control by a control unit (not shown), and scans the direction of the translucent beam L1 toward the object K. The diameter of the mirror portion of the scanning mirror 6 is, for example, about the same as the diameter (φ10 mm) of the reflection region 21. The swing angle of the scanning mirror 6 is, for example, about ± 30 °. The scanning speed of the scanning mirror 6 is, for example, about 1 kHz to 10 kHz.

  Further, the scanning mirror 6 reflects the return light L <b> 2 reflected by the light transmission beam L <b> 1 on the object K toward the optical surface 11. The return light L2 reflected by the scanning mirror 6 is guided into the optical block 5 through the transmission region 22, and is reflected by the reflection surface 12 provided on the third surface 5c. Then, the return light L2 is detected by the detection light receiving element 8 which is folded back in the optical block 5 and arranged outside the fifth surface 5e. The reflecting surface 12 is formed by evaporating a metal film such as aluminum or silver over the entire third surface 5c. The reflective surface 12 may be formed of a dielectric multilayer film or the like.

The detection light receiving element 8 is a part that detects the return light L2 that has passed through the transmission region 22 of the optical surface 11. As the detection light-receiving element 8, an avalanche photodiode operating in Geiger mode is used. The Geiger mode is a mode in which the reverse voltage of the avalanche photodiode is set to be higher than the breakdown voltage. In a high electric field of Geiger mode, a discharge phenomenon (Geiger discharge) occurs even when weak light is incident, and an electron multiplication factor is about 10 ⁵ to 10 ⁶ .

  Examples of the avalanche photodiode operating in the Geiger mode include a single-photon avalanche diode (SPAD) and a multi-pixel photon counter / silicon photomultiplier (MPPC). For example, in MPPC, each pixel of an avalanche photodiode operating in Geiger mode is connected in two dimensions in parallel. A quenching resistor is connected to each pixel, and each quenching resistor is connected to one readout channel. Therefore, the number of photons detected by the MPPC can be detected by measuring the height (number of events) or the amount of charge of the pulse on which the signals from each pixel are superimposed.

  An output signal from the detection light receiving element 8 is output to a calculation unit (not shown). In the calculation unit, the distance to the object K is calculated based on the TOF (Time of Flight) method. In other words, the calculation unit calculates the distance to the object K based on the difference between the time when the pulse of the translucent beam L1 is emitted from the light source 2 and the time when the return light L2 is detected by the detection light receiving element 8.

  The reflective surface 12 may have a function of attenuating the amount of return light L2 that travels toward the detection light receiving element 8. Thereby, the light quantity of the return light L2 can be adjusted so that the detection light receiving element 8 is not saturated. From the same point of view, the diameter of the transmission region 22 may be smaller than the diameter of the incident light transmission beam L1, and it returns to the front side of the detection light receiving element 8 and has a smaller diameter than the diameter of the light L2. May be arranged.

  As described above, in the distance measuring device 1, the optical surface 11 having the reflection region 21 that reflects a part of the light transmission beam L <b> 1 emitted from the light source 2 and the transmission region 22 that transmits the remaining part of the light transmission beam L <b> 1. Is provided. Further, in the optical surface 11, the area of the transmission region 22 is smaller than the area of the reflection region 21, and the amount of light traveling toward the detection light receiving element 8 is limited. Therefore, it is possible to reduce the influence of disturbance light when the detection light receiving element 8 detects the return light L2 from the object K.

  Here, in the distance measuring device 1, an avalanche photodiode operating in a Geiger mode such as MPPC is used as the detection light receiving element 8. Thereby, even if the light quantity of the return light L2 from the object K is weak because the area of the transmission region 22 is smaller than the area of the reflection region 21, the return light L2 can be detected with high sensitivity. Therefore, the S / N ratio of the signal can be secured at a high level, and the distance that can be measured by the ToF method and the distance measurement accuracy can be sufficiently improved. Furthermore, since the area of the transmissive region 22 is smaller than the area of the reflective region 21 on the optical surface 11, the detection range per pixel of the light receiving element 8 for detection is narrowed, so that sufficient resolution is ensured. it can. A lens for condensing the return light L2 in a wide range on the light receiving element 8 for detection is unnecessary, and the apparatus can be downsized.

  In the distance measuring device 1, the reflection area 21 is provided in an annular shape on the optical surface 11 so as to surround the circular transmission area 22. As a result, the area of the transmission region 22 is sufficiently smaller than the area of the reflection region 21, and the influence of disturbance light when the return light L2 from the object K is detected by the detection light receiving element 8 can be reduced more reliably. .

  In the distance measuring apparatus 1, a reflection surface 12 is provided on the optical path between the optical surface and the detection light receiving element to reflect the return light L <b> 2 transmitted through the transmission region 22 of the optical surface 11 toward the detection light receiving element. ing. The return light L2 that has passed through the transmission region 22 of the optical surface 11 is folded back toward the light receiving element 8 for detection by the reflecting surface 12, and the size from the optical surface 11 to the light receiving element 8 for detection is not increased. The optical path length of the return light L2 can be increased. In the present embodiment, the resolution of the distance measuring device 1 depends on the opening diameter of the transmission region 22 in the optical surface 11 and the light receiving surface size of the light receiving element 8 for detection. For this reason, it is possible to further increase the resolution by increasing the optical path length of the return light L2 from the optical surface 11 to the detection light receiving element 8.

  In the distance measuring device 1, a monitor light-receiving element 7 is provided for detecting the remaining portion of the transmitted light beam L <b> 1 transmitted through the transmission region 22 of the optical surface 11. By monitoring the output state of the translucent beam L1 by the monitor light receiving element 7, it is possible to grasp the fluctuation of the light amount of the translucent beam L1 due to the temperature characteristics of the light source 2, the presence or absence of abnormality of the light source 2, and the like.

  Further, in the distance measuring device 1, the optical path 11, the reflection plane 12, the remaining optical path of the transmitted light beam L 1 that has passed through the transmission area of the optical plane 11, and the optical path of the return light L 2 that has passed through the transmission area 22 of the optical plane 11. Is integrated with the optical block 5. By using the optical block 5 to configure the optical surface 11, the reflective surface 12, the optical path of the transmitted light beam L1, and the optical path of the return light L2, the apparatus can be miniaturized. In addition, since calibration is not necessary, assembly of optical components is facilitated.

  Further, in the distance measuring device 1, the scanning mirror 6 is constituted by a MEMS mirror. Thereby, the scanning of the translucent beam L1 can be performed with high accuracy. In the distance measuring device 1, since the avalanche photodiode operating in the Geiger mode is used as the light receiving element 8 for detection, the amount of the return light L2 from the object K may be weak. Therefore, the area of the MEMS mirror may be set based on the diameter of the translucent beam L1, and it is not necessary to arrange a large mirror.

  The present invention is not limited to the above embodiment. For example, in the above embodiment, the optical surface 11, the reflecting surface 12, and the optical path are integrated using the optical block 5, but these optical elements do not necessarily have to be integrated in the optical block 5. In this case, for example, as shown in FIG. 4, the aperture mirror 31 corresponding to the optical surface 11 is disposed at a position corresponding to the first surface 5 a of the optical block 5, and the reflecting mirror 32 corresponding to the reflecting surface 12 is disposed in the optical block 5. What is necessary is just to arrange | position in the position corresponding to the 3rd surface 5c.

  The monitor light-receiving element 7 is not necessarily arranged, and the distance measuring device 1 may be further downsized by omitting the arrangement. Similarly, the arrangement of the reflecting surface 12 or the reflecting mirror 32 may be omitted. In this case, for example, the ranging device 1 can be downsized by arranging the detection light receiving element 8 at the position of the reflecting surface 12 or the reflecting mirror 32.

  In the above embodiment, the scanning mirror 6 swings in the in-plane direction of the stage 9. However, the scanning mirror 6 may swing two-dimensionally in the in-plane direction of the stage 9 and the normal direction of the stage 9. . In this case, for example, it is possible to acquire the two-dimensional position information of the object K having resolution in the horizontal direction and the vertical direction.

  In the above embodiment, the collimator 3 converts the translucent beam L1 into parallel light. Instead, for example, a lens (cylindrical lens or the like) having a curved surface formed in only one direction is used. The cross-sectional shape of the translucent beam L1 may be shaped into a substantially rectangular shape that is long in the normal direction of the stage 9. In this case, by using, for example, an MPPC array with multiple channels in the normal direction of the stage 9 as the light receiving element 8 for detection, it is possible to acquire position information of the object K having resolution in the vertical direction. Since the position information of the object K having resolution in the horizontal direction can be acquired by swinging the scanning mirror 6 in the in-plane direction of the stage 9, as a result, the resolution has been obtained in the horizontal direction and the vertical direction, respectively. The two-dimensional position information of the object K can be acquired.

  Moreover, in the said embodiment, as shown in FIG. 3, although the circular transmissive area | region 22 was provided in the center of the annular | circular shaped reflective area | region 21 in the optical surface 11, the reflective area | region 21 and the transmissive area | region 22 of FIG. The configuration can take various modifications. For example, as shown in FIG. 5A, a rectangular transmission region 22 may be used. The transmission region 22 may be an ellipse, a triangle, or another polygon in addition to a rectangle.

  The center of the reflective region 21 and the center of the transmissive region 22 do not necessarily coincide with each other. For example, as shown in FIG. 5B, the center of the transmission region 22 may be eccentric with respect to the center of the reflection region 21. In FIG. 5B, the center of the reflection region 21 is located in the transmission region 22, but the center of the transmission region 22 is centered on the reflection region 21 so that the center of the reflection region 21 is outside the transmission region 22. It may be eccentric. For example, when a laser diode is used as the light source 2, the translucent beam L1 is a Gaussian beam. Since the intensity profile of the Gaussian beam has a Gaussian distribution centered on the optical axis, the amount of light of the translucent beam L1 is higher near the center of the optical axis than at the periphery. Therefore, by decentering the center of the transmission region 22 with respect to the center of the reflection region 21, a portion having a high light amount in the light transmission beam L <b> 1 can be reflected by the reflection region 21. Therefore, a sufficient amount of light of the translucent beam L1 toward the object K can be secured, and the signal S / N ratio can be further improved.

  For example, as shown in FIG. 5C, a plurality of transmission regions 22 that are eccentric with respect to the reflection region 21 may be provided. In FIG. 5C, circular transmission regions 22 are arranged at four locations with a phase angle of 90 ° around the center of the reflection region 21 at the edge of the reflection region 21. In this case, the transmissive regions 22 arranged at a plurality of locations can be selectively used as a region through which the light transmissive beam L1 and the return light L2 are transmitted.

  DESCRIPTION OF SYMBOLS 1 ... Distance measuring device, 2 ... Light source, 5 ... Optical block, 6 ... Scanning mirror, 7 ... Monitor light receiving element, 8 ... Detection light receiving element, 11 ... Optical surface, 12 ... Reflecting surface, 21 ... Reflecting area, 22 ... transmission region, 31 ... aperture mirror (optical surface), 32 ... reflection mirror (reflection surface), L1 ... translucent beam, L2 ... return light, K ... object.

Claims (7)

A distance measuring device that measures the distance to an object,
A light source that emits a translucent beam to the object;
An optical surface having a reflection region that reflects a part of the light transmission beam emitted from the light source, and a transmission region that transmits the remainder of the light transmission beam;
A scanning mirror that reflects the translucent beam reflected by the reflection region toward the object and reflects return light from the object toward the optical surface;
A light receiving element for detection that detects the return light transmitted through the transmission region of the optical surface,
The detection light receiving element is an avalanche photodiode operating in a Geiger mode,
A distance measuring device in which the area of the transmission region is smaller than the area of the reflection region on the optical surface.   The distance measuring apparatus according to claim 1, wherein the reflection area is provided on the optical surface so as to surround the transmission area.   The distance measuring device according to claim 2, wherein a center of the transmission region is decentered with respect to a center of the reflection region on the optical surface.   The reflective surface which reflects the said return light which permeate | transmitted the said permeation | transmission area | region of the said optical surface toward the said light receiving element for a detection is further provided between the said optical surface and the said light receiving element for a detection. The distance measuring device according to one item.   The distance measuring device according to any one of claims 1 to 4, further comprising a monitor light receiving element that detects a remaining portion of the light transmitting beam that has passed through the transmission region of the optical surface.   The distance measuring device according to any one of claims 1 to 5, further comprising an integrated optical block including the optical surface and an optical path of the return light transmitted through the transmission region of the optical surface.   The distance measuring device according to any one of claims 1 to 6, wherein the scanning mirror is configured by a MEMS mirror.

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