JP6510381B2 - Ranging device - Google Patents

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 the light transmission to the object to the detection of the return light. Development of a (Time of Flight) distance measuring apparatus is in progress. It is assumed that such a distance measuring device is mounted, for example, in a vehicle such as a car as an automatic driving support system. In an automatic driving support system, a distance measuring device measures the distance between a traveling vehicle and an object (including a human body), and controls the vehicle speed and the like based on the measurement result, thereby avoiding collision between the vehicle and the object. Is expected.

  As a conventional distance measuring device, for example, there is a beam light emitting and receiving device described in Patent Document 1. This apparatus includes a scan mirror for reflecting and scanning a light projection beam emitted from a light source, and a light receiving element for receiving return light reflected by an object and then reflected by the scan mirror. A light emitting and receiving separation member formed of a single prism is disposed in the light path of the projection beam and the return light. The outer surface of the light emitting / receiving separation member is provided with an area for reflecting the light projection beam, an area for transmitting the return light, and an area for reflecting the return light.

  Further, the radar device described in Patent Document 2 includes a light source, a pixel, and a light detection control unit. In this device, 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 later than the timing when the scattered light inside the device due to the light emitted from the light source enters the SPAD.

Patent No. 5663251 gazette JP, 2015-117970, A

  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 return light. When these light receiving elements are used, it is necessary to have an optical system for detecting the return light of a sufficient light amount in order to expand the distance measurement possible distance. Therefore, in the device of Patent Document 1, an optical system is adopted in which the optical path width of the return light is made wider than the optical path width of the light transmission beam, and the condensing lens condenses the return light toward the light receiving element See, for example, 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, the light receiving sensitivity of SPAD is higher than that of a general PD or APD, so the principle is the same even if the light amount of return light is small. Distance measurement possible distance can be realized. However, when the light receiving element of the device of Patent Document 1 is simply replaced with SPAD, the optical path width of the return light is wide, the disturbance light is increased, and the S / N ratio of the signal is decreased. There is a possibility that the measurable distance and the ranging accuracy may not be sufficiently improved. Further, the fact that the optical path width of the return light is wide means that the field of view on the light receiving side is wide. Therefore, there is also a problem that the range detected by one pixel of the light receiving element is expanded and the resolution is lowered.

  The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a distance measuring apparatus which can ensure sufficient resolution and can improve the distance capable of distance measurement and the distance measuring accuracy.

  A distance measuring apparatus according to one aspect of the present invention is a distance measuring apparatus for measuring a distance to an object, and a light source emitting a light transmitting beam to the object and a part of the light transmitting beam emitted from the light source And an optical surface having a transmission region for transmitting the remaining part of the light transmission beam, and the light transmission beam reflected by the reflection region is reflected toward the object, and light returned from the object is reflected toward the optical surface The light receiving element for detecting the return light transmitted through the transmission area of the optical surface, the detection light receiving element being an avalanche photodiode operating in Geiger mode, the transmission area on the optical surface The area of is larger than the area of the reflection area.

  In this distance measuring device, an optical surface having a reflection area for reflecting a part of the light transmission beam emitted from the light source and a transmission area for transmitting the remaining part of the light transmission beam is provided. In addition, in the optical surface, the area of the transmission area is smaller than the area of the reflection area. Therefore, the influence of disturbance light when detecting the return light from the object with the light receiving element for detection can be reduced. In this distance measuring apparatus, an avalanche photodiode operating in Geiger mode is used as a light receiving element for detection. As a result, since the area of the transmission area is smaller than the area of the reflection area, even if the light quantity of the return light from the object is weak, 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 measurementable distance and the distance measurement accuracy can be sufficiently improved. Furthermore, in the optical surface, since the area of the transmission area is smaller than the area of the reflection area, the range detected by one pixel of the light receiving element is narrowed, so that sufficient resolution can be secured.

  Further, in the optical surface, the reflective area may be provided to surround the transmissive area. This makes it possible to more reliably reduce the influence of disturbance light when the return light from the object is detected by the detection light receiving element.

  In the optical surface, the center of the transmission area may be decentered with respect to the center of the reflection area. For example, when the light transmission beam is a Gaussian beam, the light amount of the light transmission beam is higher near the center than at the periphery. Therefore, by decentering the center of the transmission area with respect to the center of the reflection area, it is possible to secure a sufficient amount of light of the light transmitting beam directed to the object and to further improve the S / N ratio of the signal.

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

  In addition, a monitor light receiving element may be further provided to detect the remaining part of the light transmission beam transmitted through the transmission area of the optical surface. By monitoring the output state of the light transmission beam, the presence or absence of abnormality of the light source can be grasped.

  The optical block may further include an integrated optical block including an optical surface and an optical path of return light transmitted through the transmission region of the optical surface. By configuring the optical surface and the optical path by using the optical block, the device can be miniaturized. In addition, assembly of the optical component is facilitated.

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

  According to this distance measuring device, it is possible to secure sufficient resolution and to improve the distance capable of distance measurement and the distance measuring accuracy.

It is a perspective view showing one embodiment of a ranging 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 ranging apparatus. (A)-(c) is a figure which shows the modification of an optical surface.

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

  FIG. 1 is a perspective view showing an embodiment of a distance measuring apparatus. The distance measuring device 1 is, for example, a device mounted as an automatic driving support system in a vehicle such as a car. In the automatic driving support system, the distance between the traveling vehicle and the object K is measured in real time by the distance measuring apparatus 1, and the collision between the vehicle and the object K is avoided by controlling the vehicle speed and the like based on the measurement result. Control is performed. 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 to measure the distance between an object K located at a position separated by about 0.1 m to 100 m.

  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 These components are all assembled on a substantially plate-like stage 9.

  The light source 2 is a portion that emits the light transmission beam L1 to the object K. As the light source 2, for example, a laser diode that emits an infrared or ultraviolet pulse laser is used. The wavelength in the case of infrared light is, for example, about 800 nm to about 1000 nm, and the wavelength in the case of ultraviolet light is, for example, about 350 nm to about 400 nm. The light transmission beam L1 emitted from the light source 2 is collimated by the collimator 3 and is guided to the optical block 5 side in a state of being narrowed to a beam diameter of, for example, 10 mm or less by the aperture 4.

  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 monitor light receiving element 7, and an optical path from the optical surface 11 to the detection light receiving element 8. It is an integrated optical element. The optical block 5 has a function of separating the light transmission 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 in a block shape having a pentagonal 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 the first surface 5a at an obtuse angle on one side of the first surface 5a, and a reflecting surface 12 And a third surface 5c that forms an obtuse angle with the second surface 5b on one side of the second surface 5b, and a fourth surface 5d that forms an obtuse angle with the third surface 5c on one side of the third surface 5c. And a fifth surface 5e which is continuous with the fourth surface 5d and the first surface 5a at an obtuse angle on one side of the fourth surface 5d.

  The optical surface 11 has, as shown in FIG. 3, a reflection area 21 for reflecting a part of the transmission beam L1 and a transmission area 22 for transmitting the remaining part of the transmission beam L1. The reflective area 21 is formed by depositing a metal film of, for example, aluminum, silver or the like on the first surface 5 a in an annular manner. 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 the region inside the reflective region 21. That is, the reflective area 21 is formed to surround the entire periphery of the transmissive area 22. The center of the transmissive region 22 and the center of the reflective region 21 coincide with each other. In addition, 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 L2 to the light receiving element 8 for detection. In the present embodiment, the reflection area 21 has, for example, approximately the same diameter (φ 10 mm) as that of the light transmission beam L 1 that has passed through the aperture 4. On the other hand, the transmissive region 22 is, for example, about φ 0.5 mm.

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

  On the other hand, the peripheral portion of the light transmission beam L1 incident on the optical surface 11 is reflected by the reflection area 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 light-transmitting beam L1 directed to the object K. The diameter of the mirror portion of the scanning mirror 6 is, for example, about the same as the diameter (φ 10 mm) of the reflection area 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.

  In addition, the scanning mirror 6 reflects the return light L 2, which is the light K reflected by the object K, toward the optical surface 11. The return light L2 reflected by the scanning mirror 6 is guided through the transmission region 22 into the optical block 5, 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 inside the optical block 5 and disposed outside the fifth surface 5e. The reflective surface 12 is formed, for example, by depositing a metal film of aluminum, silver or the like on the entire third surface 5c. The reflecting surface 12 may be formed of a dielectric multilayer film or the like.

The light receiving element for detection 8 is a portion that detects the return light L2 transmitted through the transmission area 22 of the optical surface 11. As the light receiving element 8 for detection, 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 equal to or higher than the breakdown voltage. In the high electric field of Geiger mode, a discharge phenomenon (Geiger discharge) occurs even to the incidence of weak light, and the multiplication factor of electrons is about 10 ⁵ to 10 ⁶ .

  As an avalanche photodiode which operates in Geiger mode, for example, SPAD (Single-Photon Avalanche Diode), MPPC (Multi-Pixel Photon Counter / Silicon Photomultiplier), etc. may be mentioned. 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 of the pulse (number of events) or the amount of charge of the pulse on which the signal from each pixel is superimposed.

  An output signal from the light receiving element for detection 8 is output to an operation unit (not shown). In the computing unit, the distance to the object K is computed based on the TOF (Time of Flight) method. That is, in the calculation unit, the distance to the object K is calculated based on the difference between the time when the pulse of the light transmission 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 reflecting surface 12 may have a function of attenuating the light amount of the return light L2 directed to the light receiving element 8 for detection. Thus, the light amount of the return light L2 can be adjusted so that the detection light receiving element 8 is not saturated. From the same viewpoint, the diameter of the transmission region 22 may be smaller than the diameter of the incident light beam L1, and a pinhole with a smaller diameter than the diameter of the return light L2 on the front side of the detection light receiving element 8. May be arranged.

  As described above, in the distance measuring device 1, the optical surface 11 has the reflection area 21 for reflecting a part of the light transmission beam L1 emitted from the light source 2 and the transmission area 22 for transmitting the remaining part of the light transmission beam L1. It is provided. In the optical surface 11, the area of the transmission area 22 is smaller than the area of the reflection area 21, and the light amount of the light traveling toward the light receiving element for detection 8 is limited. Therefore, the influence of disturbance light when detecting the return light L2 from the object K by the detection light receiving element 8 can be reduced.

  Here, in the distance measuring device 1, an avalanche photodiode operating in Geiger mode such as MPPC is used as the light receiving element 8 for detection. Thereby, even if the light amount of the return light L2 from the object K is weak because the area of the transmission area 22 is smaller than the area of the reflection area 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 measurement possible distance and the distance measurement accuracy by the ToF method can be sufficiently improved. Furthermore, in the optical surface 11, the area of the transmission area 22 is smaller than the area of the reflection area 21, so that the range to be detected per pixel of the detection light receiving element 8 is narrowed, so that sufficient resolution is ensured. it can. A lens or the like for condensing the return light L2 in a wide range on the detection light receiving element 8 is not necessary, and the apparatus can be miniaturized.

  Further, in the distance measuring device 1, in the optical surface 11, the reflection area 21 is provided in an annular shape so as to surround the circular transmission area 22. As a result, the area of the transmission region 22 becomes sufficiently smaller than the area of the reflection region 21, and the influence of disturbance light when detecting the return light L 2 from the object K with the light receiving element 8 for detection can be reduced more reliably. .

  Further, in the distance measuring device 1, the reflection surface 12 is provided in the light path between the optical surface and the light receiving element for detection to reflect the return light L2 transmitted through the transmission region 22 of the optical surface 11 toward the light receiving element for detection. ing. Since the return light L2 having 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, the size of the device is not increased and the distance from the optical surface 11 to the light receiving element 8 for detection is 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 aperture diameter of the transmission region 22 on the optical surface 11 and the light receiving surface size of the light receiving element 8 for detection. Therefore, by lengthening the optical path length of the return light L2 from the optical surface 11 to the light receiving element for detection 8, it is possible to further increase the resolution.

  Further, in the distance measuring device 1, a monitor light receiving element 7 is provided which detects the remaining part of the light transmission beam L 1 transmitted through the transmission region 22 of the optical surface 11. By monitoring the output state of the light transmission beam L1 and the like by the monitor light receiving element 7, fluctuation of the light amount of the light transmission beam L1 due to the temperature characteristic of the light source 2 and presence / absence of abnormality of the light source 2 can be grasped.

  In the distance measuring device 1, the optical surface 11, the reflective surface 12, the optical path of the remaining portion of the transmitted beam L 1 transmitted through the transmission region of the optical surface 11, and the optical path of the return light L 2 transmitted through the transmission region 22 of the optical surface 11 An optical block 5 is provided. By configuring the optical surface 11, the reflective surface 12, the optical path of the light transmission beam L1, and the optical path of the return light L2 using the optical block 5, the device can be miniaturized. In addition, since the calibration is not necessary, the assembly of the optical component becomes easy.

  Further, in the distance measuring device 1, the scanning mirror 6 is configured by a MEMS mirror. Thereby, scanning of the light transmission beam L1 can be performed with high accuracy. In this distance measuring device 1, since the avalanche photodiode operating in Geiger mode is used as the light receiving element 8 for detection, the light 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 light transmission beam L1, and it is not necessary to arrange a large mirror.

  The present invention is not limited to the above embodiment. For example, although the optical surface 11, the reflective surface 12, and the optical path are integrated using the optical block 5 in the above embodiment, these optical elements may not necessarily 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 the position corresponding to the first surface 5 a of the optical block 5, and the reflection mirror 32 corresponding to the reflection surface 12 is the optical block 5. It may be disposed at a position corresponding to the third surface 5c of

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

  In the above embodiment, the scanning mirror 6 is swung in the in-plane direction of the stage 9, but the scanning mirror 6 may be swung in two dimensions in the in-plane direction of the stage 9 and the normal direction of the stage 9. . In this case, for example, two-dimensional position information of the object K having resolutions in the horizontal direction and the vertical direction can be obtained.

  Further, in the above embodiment, collimated light beam L1 is collimated by collimator 3. However, instead of this, for example, using a lens (cylindrical lens etc.) having a curved surface formed in only one direction, The cross-sectional shape of the light transmission 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 multichanneled in the normal direction of the stage 9 as the light receiving element 8 for detection, it becomes possible to obtain position information of the object K having a resolution in the vertical direction. As the scanning mirror 6 swings in the in-plane direction of the stage 9, it is possible to obtain position information of the object K having a resolution in the horizontal direction, and as a result, resolutions are respectively provided in the horizontal and vertical directions. It becomes possible to obtain two-dimensional position information of the object K.

  Further, in the above embodiment, as shown in FIG. 3, in the optical surface 11, the circular transmission region 22 is provided at the center of the annular reflection region 21, but in the reflection region 21 and the transmission region 22 The configuration can take various modifications. For example, as shown to Fig.5 (a), it is good also as a rectangular permeable area | region 22. FIG. The transmissive area 22 may be an ellipse, a triangle, or another polygon besides a rectangle.

  The center of the reflective area 21 and the center of the transmissive area 22 may not necessarily coincide with each other. For example, as shown in FIG. 5 (b), the center of the transmission region 22 may be decentered with respect to the center of the reflection region 21. In FIG. 5B, the center of the reflection area 21 is located in the transmission area 22, but the center of the transmission area 22 is in the center of the reflection area 21 to the extent that the center of the reflection area 21 is outside the transmission area 22. It may be eccentric. For example, when a laser diode is used as the light source 2, the light transmission beam L1 is a Gaussian beam. Since the intensity profile of the Gaussian beam has a Gaussian distribution centered on the optical axis, the light quantity of the light transmitting 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, the portion of the light transmission beam L 1 having a high light amount can be reflected by the reflection region 21. Therefore, the light quantity of the light transmitting beam L1 directed to the object K can be sufficiently secured, and the signal S / N ratio can be further improved.

  Further, for example, as shown in FIG. 5C, a plurality of transmission regions 22 decentered with respect to the reflection region 21 may be provided. In FIG. 5C, circular transmission areas 22 are arranged at four positions around the center of the reflection area 21 at the edge of the reflection area 21 with a phase angle of 90 °. In this case, the transmission regions 22 arranged at a plurality of places can be selectively used as a region for transmitting the light transmission beam L1 and the return light L2.

  DESCRIPTION OF SYMBOLS 1 ... ranging apparatus, 2 ... light source, 5 ... optical block, 6 ... scanning mirror, 7 ... monitor light receiving element, 8 ... detection light receiving element, 11 ... optical surface, 12 ... reflective surface, 21 ... reflection area, 22 ... Transmission area, 31 ... Aperture mirror (optical surface), 32 ... Reflection mirror (reflection surface), L1 ... Transmissive beam, L2 ... Return light, K ... Object.

Claims (7)

A distance measuring device that measures the distance to an object, and
A light source for emitting a light transmission beam to the object;
An optical surface having a reflection area for reflecting a part of the light transmission beam emitted from the light source, and a transmission area for transmitting the remaining part of the light transmission beam;
A scanning mirror that reflects the light transmitting beam reflected by the reflection area toward the object and reflects return light from the object toward the optical surface;
A detection light receiving element for detecting the return light transmitted through the transmission area of the optical surface;
The light receiving element for detection is an avalanche photodiode operating in Geiger mode,
A range finder in which an area of the transmission area is smaller than an area of the reflection area on the optical surface.   The distance measuring apparatus according to claim 1, wherein the reflection area is provided to surround the transmission area on the optical surface.   The distance measuring apparatus according to claim 2, wherein a center of the transmission area is decentered with respect to a center of the reflection area 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 light receiving element for a detection. A range finder according to any one of the preceding claims.   The distance measuring apparatus according to any one of claims 1 to 4, further comprising a monitor light receiving element for detecting the remaining part of the light transmitting beam transmitted through the transmission area of the optical surface.   The distance measuring apparatus according to any one of claims 1 to 5, further comprising: an optical block integrated with the optical surface and an optical path of the return light transmitted through the transmission region of the optical surface.   The distance measuring apparatus according to any one of claims 1 to 6, wherein the scanning mirror is constituted by a MEMS mirror.

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