Laser radar device

Abstract

To provide a laser radar device capable of suppressing omission in detecting interference light.SOLUTION: A laser radar device (10) includes: a distance measurement unit (71) that executes distance measurement control to measure a distance to an object on the basis of a time from projection of laser light by a light projecting unit (20) to reception of the laser light by a light receiving unit (30); and an interference light detection unit (72) that detects interference light, which is laser light received by the light receiving unit but not reflection light of the laser light projected by the light projecting unit, and is installed at a predetermined location. The interference light detection unit rotates a rotary mirror at a second rotational speed lower than a first rotational speed, which is the rotational speed of the rotary mirror during execution of the distance measurement control by the distance measurement unit, while the light projecting unit does not project laser light, thereby detecting the laser light received by the light receiving unit as the interference light.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laser radar device. [Background technology]

[0002] For example, there is a laser radar device that determines that interference is occurring if the light receiving signal received by the light receiving unit during a light receiving period in which the reflected laser light emitted by the light projecting unit is received for each object detection direction contains multiple received light waves that are laser light received by the light receiving unit and the received light waves are periodic (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-84978 Summary of the Invention [Problem to be solved by the invention]

[0004] The laser radar device described in Patent Document 1 checks whether interference occurs between multiple laser radar devices during a measurement period in which the distance to an object is measured. Therefore, the light-receiving period for each object detection direction is very short, and there is a risk that interference laser light (interference light) will not be projected during the light-receiving period. In that case, there is a risk that the interference laser light will not be detected even though it is present.

[0005] The present invention has been made to solve these problems, and a main object of the present invention is to provide a laser radar device that can suppress failure to detect interference light. [Means for solving the problem]

[0006] The first means for solving the above problem is: a light projection unit that projects laser light; a light receiving unit that receives laser light; a rotating mirror that is rotatable about a predetermined rotation axis, that reflects the incident laser light projected by the light projecting unit toward an external space, and that reflects the incident laser light so that it can be received by the light receiving unit; a distance measurement unit that performs distance measurement control to measure a distance to an object based on the time from when the laser light is projected by the light projecting unit to when the laser light is received by the light receiving unit; an interference light detection unit that detects interference light that is not a reflected light of the laser light projected by the light projecting unit but is a laser light received by the light receiving unit; A laser radar device installed at a predetermined location, The interference light detection unit does not cause the light projecting unit to project the laser light, and rotates the rotating mirror at a second rotation speed that is lower than a first rotation speed, which is the rotation speed of the rotating mirror when the distance measurement control is performed by the distance measurement unit, and detects the laser light received by the light receiving unit as the interference light.

[0007] According to the above configuration, the light-projecting unit projects a laser beam. The rotating mirror is rotatable about a predetermined rotation axis and reflects the laser beam projected by the light-projecting unit and incident on the rotating mirror toward external space. This allows the laser radar device to scan external space with the laser beam. The rotating mirror also reflects the laser beam incident on the rotating mirror so that it can be received by the light-receiving unit. The light-receiving unit receives the laser beam. The distance measuring unit then performs distance measurement control to measure the distance to an object based on the time from when the laser beam is projected by the light-projecting unit to when the laser beam is received by the light-receiving unit. This allows the laser radar device to detect surrounding objects at a predetermined location where it is installed, based on the distance to the object measured by the distance measuring unit.

[0008] For example, if other laser radar devices are installed around a predetermined location, the light receiving unit may receive laser light projected by the other laser radar devices or its diffuse reflection, which may result in so-called interference. Therefore, the interference light detection unit detects interference light, which is laser light received by the light receiving unit, rather than reflected light of the laser light projected by the light projecting unit. Specifically, the interference light detection unit does not cause the light projecting unit to project the laser light, but detects the laser light received by the light receiving unit as interference light. In other words, because the light projecting unit does not project the laser light, the laser light received by the light receiving unit can be considered interference light, rather than reflected light of the laser light projected by the light projecting unit.

[0009] Furthermore, the interference light detection unit detects the interference light while the rotating mirror is rotated at a second rotation speed that is lower than the first rotation speed of the rotating mirror when the ranging control is executed. Therefore, the period during which the laser light is received in each object detection direction when the rotating mirror is rotated at the second rotation speed during interference light detection can be made longer than the period during which the laser light is received in each object detection direction when the rotating mirror is rotated at the first rotation speed during ranging control. Therefore, it is possible to prevent the interference light from being unable to be detected despite its presence, i.e., to prevent the interference light from being missed.

[0010] In the second means, the interference light detection unit stores an interference rotation position, which is the rotation position of the rotating mirror when the interference light is detected, and an interference light waveform, which is the waveform of the light-receiving signal when the interference light is received by the light-receiving unit, and is equipped with an interference light determination unit that determines that the laser light received by the light-receiving unit is interference light if it can be considered that the rotation position of the rotating mirror when the laser light is received by the light-receiving unit matches the interference rotation position stored by the interference light detection unit and if it can be considered that the waveform of the light-receiving signal when the laser light is received by the light-receiving unit matches the interference light waveform stored by the interference light detection unit.

[0011] According to the above configuration, the interference light detection unit can store the interference rotation position, which is the rotation position of the rotating mirror when the interference light is detected, i.e., the direction in which the interference light is incident on the laser radar device. The interference light detection unit can also store the interference light waveform, which is the waveform of the light reception signal received by the light receiving unit when the interference light is received, i.e., the pulse width and intensity of the interference light. If the laser radar device and the other laser radar device are installed in fixed locations and do not move, it is highly likely that the interference rotation position and interference light waveform detected by the laser radar device will be constant and will not change.

[0012] Therefore, the interference light determination unit determines that the laser light received by the light receiving unit is interference light when it can consider that the rotational position of the rotating mirror when the laser light is received by the light receiving unit matches the interference rotational position and when it can consider that the waveform of the light receiving signal of the laser light received by the light receiving unit matches the interference light waveform. Therefore, the interference light determination unit can accurately determine interference light.

[0013] For example, when a laser beam is reflected by an intruder approaching the laser radar device, the rotational position of the rotating mirror when the laser beam is received by the light receiving unit and the waveform of the light receiving signal of the laser beam received by the light receiving unit are likely to change each time. For this reason, it is rare that the rotational position of the rotating mirror when the laser beam is received by the light receiving unit matches the interference rotational position, and that the waveform of the light receiving signal of the laser beam received by the light receiving unit matches the interference light waveform.

[0014] Therefore, in the third means, the interference light determination unit determines that the laser light received by the light receiving unit is laser light reflected by an object when it cannot be determined that the rotational position of the rotating mirror when the laser light is received by the light receiving unit matches the interference rotational position stored by the interference light detection unit, or when it cannot be determined that the waveform of the light reception signal of the laser light received by the light receiving unit matches the interference light waveform stored by the interference light detection unit. Therefore, the interference light determination unit can prevent erroneous determination of laser light reflected by an object such as an intruder as interference light.

[0015] The fourth means includes a distance determination unit that ignores the distance measured by the distance measuring unit when the interference light determination unit determines that the laser light received by the light receiving unit is interference light, and that determines the distance measured by the distance measuring unit when the interference light determination unit determines that the laser light received by the light receiving unit is laser light reflected by an object. With this configuration, the laser radar device can prevent erroneous detection of an object due to interference light when detecting an object based on the distance to the object measured by the distance measuring unit.

[0016] The fifth means includes a distance determination unit that, when the interference light determination unit determines that the laser light received by the light receiving unit is interference light, omits the distance measurement control by the distance measurement unit for the laser light determined to be interference light, and when the interference light determination unit determines that the laser light received by the light receiving unit is laser light reflected by an object, determines the distance measured by the distance measurement unit. With this configuration, the laser radar device can also prevent erroneous detection of an object due to interference light, and can reduce the processing load by omitting unnecessary distance measurement control.

[0017] In the sixth means, the interference light detection unit stores an interference rotation position, which is the rotation position of the rotating mirror when the interference light is detected, and an interference interval, which is the interval at which multiple interference light beams are received by the light receiving unit during a light receiving period in which laser light is received for each object detection orientation, and includes an interference light determination unit that determines that the laser light received by the light receiving unit is interference light if it can be considered that the rotation position of the rotating mirror when the laser light is received by the light receiving unit matches the interference rotation position stored by the interference light detection unit and that the interval at which multiple laser light beams are received by the light receiving unit during the light receiving period matches the interference interval stored by the interference light detection unit.

[0018] According to the above configuration, the interference light detection unit can store an interference rotation position, which is the rotation position of the rotating mirror when the interference light is detected, i.e., the direction in which the interference light is incident on the laser radar device. The interference light detection unit can also store an interference interval, which is the interval at which multiple interference lights are received by the light receiving unit during a light receiving period in which laser light is received for each object detection orientation, i.e., the period in which the interference light is projected by the other laser radar device. If the laser radar device and the other laser radar device are installed in fixed locations and do not move, the interference rotation position and interference interval detected by the laser radar device are likely to be constant and unchanging.

[0019] Therefore, the interference light determination unit determines that the laser light received by the light receiving unit is interference light when it can consider that the rotational position of the rotating mirror when the laser light is received by the light receiving unit matches the interference rotational position stored by the interference light detection unit, and when it can consider that the interval at which the laser light is received by the light receiving unit during the light receiving period matches the interference interval stored by the interference light detection unit. Therefore, the interference light determination unit can accurately determine interference light.

[0020] For example, when a laser beam is reflected by an intruder approaching the laser radar device, the rotational position of the rotating mirror when the laser beam is received by the light receiving unit and the interval at which the multiple laser beams are received by the light receiving unit during the light receiving period in which the laser beam is received for each object detection direction are likely to change each time. For this reason, it is rare that the rotational position of the rotating mirror when the laser beam is received by the light receiving unit matches the interference rotation position, and that the interval at which the multiple laser beams are received by the light receiving unit during the light receiving period matches the interference interval.

[0021] Therefore, in the seventh means, the interference light determination unit determines that the laser light received by the light receiving unit is laser light reflected by an object when it cannot be determined that the rotational position of the rotating mirror when the laser light is received by the light receiving unit matches the interference rotational position stored by the interference light detection unit, or when it cannot be determined that the interval at which the laser light is received by the light receiving unit during the light receiving period matches the interference interval stored by the interference light detection unit. Therefore, the interference light determination unit can prevent erroneous determination of laser light reflected by an object such as an intruder as interference light.

[0022] The eighth means includes a distance determination unit that ignores the distance measured by the distance measuring unit when the interference light determination unit determines that the laser light received by the light receiving unit is interference light, and that determines the distance measured by the distance measuring unit when the interference light determination unit determines that the laser light received by the light receiving unit is laser light reflected by an object. With this configuration, the laser radar device can prevent erroneous detection of an object due to interference light when detecting an object based on the distance to the object measured by the distance measuring unit.

[0023] The ninth means includes a distance determination unit that, when the interference light determination unit determines that the laser light received by the light receiving unit is interference light, omits the distance measurement control by the distance measurement unit for the laser light determined to be interference light, and when the interference light determination unit determines that the laser light received by the light receiving unit is laser light reflected by an object, determines the distance measured by the distance measurement unit. With this configuration, the laser radar device can also prevent erroneous detection of an object due to interference light, and can reduce the processing load by omitting unnecessary distance measurement control.

[0024] In a tenth aspect, the second rotation speed is lower than 1 / 2 and higher than 1 / 15 of the first rotation speed.

[0025] According to the above configuration, because the second rotation speed is lower than half the first rotation speed, the laser light reception period for each object detection orientation when the rotating mirror is rotating at the second rotation speed can be longer than twice the laser light reception period for each object detection orientation when the rotating mirror is rotating at the first rotation speed. This can prevent interference light from being missed and improve the accuracy of detecting the interference rotation position. Furthermore, because the second rotation speed is higher than 1 / 15 of the first rotation speed, it can prevent the time required for the interference light detection unit to detect the interference light from becoming excessively long. [Brief explanation of the drawings]

[0026] [Figure 1] FIG. 1 is a cross-sectional view showing an outline of a laser radar device. [Figure 2] FIG. 10 is a schematic diagram showing interference caused by a plurality of laser radar devices. [Figure 3] 3 is a time chart showing a laser light projection signal and a laser light reception signal in the case of FIG. 2; [Figure 4] 5A and 5B are schematic diagrams showing a mode of storing an interference rotation position and an interference light waveform. [Figure 5] 5 is a time chart showing a laser light reception signal in the case of FIG. 4; [Figure 6] 10 is a flowchart showing a procedure from installation to operation of a laser radar device. [Figure 7] 4 is a flowchart showing the procedure of a distance measurement mode of the laser radar device. [Figure 8] 4 is a time chart showing an example of reflected light and interference light received in response to projected light; DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, an embodiment of the present invention will be described with reference to the drawings, in which the present invention is embodied in a laser radar device that detects an object that has entered a monitored area, such as the vicinity of an industrial machine such as a robot, a train platform, or a restricted area.

[0028] As shown in FIG. 1, the laser radar device 10 includes a housing 11, a light projecting unit 20, a light receiving unit 30, a rotary reflecting mechanism 40, a transparent cover 60, a lid 12, etc. Note that in FIG. 1, the direction of the optical axis AX and the direction of the central axis CL are defined as the up and down directions, and a case where horizontal scanning is performed using laser light will be described as an example. The laser radar device 10 is installed, for example, on the ground or on a low platform installed on the ground. That is, the laser radar device 10 is installed in a predetermined location and horizontally scans a position close to the ground (a position at a predetermined height) using laser light. Note that the laser radar device 10 may be installed on the floor (predetermined location) of a factory or the like instead of on the ground.

[0029] The housing 11 is formed in a hollow rectangular parallelepiped (box-shaped) shape with an open top (top surface). A light-projecting unit 20, a light-receiving unit 30, and a partition member 29 are housed inside the housing 11. The light-projecting unit 20 and the light-receiving unit 30 are arranged side by side in the horizontal direction.

[0030] The light-projecting unit 20 includes a laser diode 21 and a projection lens 22. The laser diode 21 (light-emitting element) receives a pulse current from a drive circuit (not shown) under the control of a control circuit (not shown) and intermittently emits pulsed laser light upward in response to the pulse current. The laser light may be, for example, an infrared laser, a visible laser, or an ultraviolet laser. A projection lens 22 is provided on the optical axis AX of the laser light emitted from the laser diode 21. The projection lens 22 is configured as a collimating lens and converts the laser light from the laser diode 21 into a substantially parallel beam. For example, the beam of the laser light passing through the projection lens 22 gradually becomes thicker (the cross-sectional area of ​​the beam gradually increases). The optical axis AX (projection axis) extends vertically (up and down). That is, the light-projecting unit 20 faces upward, toward the rotating mirror 50 of the rotary reflecting mechanism 40. The light-projecting unit 20 projects the laser light upward, i.e., toward the rotating mirror 50.

[0031] A cylindrical transmission cover 60 is attached to the top of the housing 11. The transmission cover 60 is made of resin, glass, or the like that transmits laser light. The refractive index of resin and glass is greater than the refractive index of air, and the transmission cover 60 has a refractive index greater than the refractive index of air. The rotational reflection mechanism 40 is housed inside the transmission cover 60. The opening at the top of the transmission cover 60 is closed by the lid 12.

[0032] The rotary reflection mechanism 40 includes a support base 41, a motor 42, a shaft 43, a rotating mirror 50, etc. The support base 41 (support member) is formed in a columnar or cylindrical shape centered on a central axis CL and is fixed to, for example, the housing 11. The motor 42 (drive unit) rotates the shaft 43, thereby rotating the rotating mirror 50 connected to the shaft 43. The shaft 43 and the rotating mirror 50 rotate about the central axis CL (a predetermined rotation axis). Specific configurations of the motor 42 may include, for example, a servo motor, or a motor that rotates steadily, which outputs pulsed laser light in synchronization with the timing at which the rotating mirror 50 faces the object detection direction. The motor 42 and the rotating mirror 50 are supported by the support base 41. The support base 41 may also be fixed to the top of the lid 12 or the transparent cover 60.

[0033] The rotating mirror 50 is disposed so as to intersect with the optical axis AX, and deflects (reflects) the laser light from the laser diode 21 (light-projecting unit 20) toward the space outside the transparent cover 60. The rotating mirror 50 also deflects (reflects) the light reflected from an object present in the space outside the transparent cover 60 toward the photodiode 31 (light-receiving unit 30). That is, the rotating mirror 50 reflects the laser light projected by the light-projecting unit 20 and incident on the rotating mirror 50 toward the space outside, and also reflects the laser light incident on the rotating mirror 50 so that it can be received by the light-receiving unit 30. The rotating mirror 50 is inclined at an angle of, for example, 45° with respect to the vertical direction (optical axis AX), and is configured so that the laser light reflected by the rotating mirror 50 is irradiated horizontally.

[0034] The transparent cover 60 transmits the laser light directed from the rotating mirror 50 to the outside and the reflected light directed from an object (outside) to the rotating mirror 50.

[0035] The light-receiving unit 30 includes a photodiode 31 and a light-receiving lens 32. The light-receiving unit 30 faces upward, toward the rotating mirror 50 of the rotary reflection mechanism 40. That is, the light-projecting unit 20 and the light-receiving unit 30 face in the same direction. The light-receiving lens 32 collects the laser light reflected downward by the rotating mirror 50 and guides it to the photodiode 31. The optical axis (light-receiving axis) of the reflected light from the rotating mirror 50 toward the photodiode 31 (light-receiving unit 30) coincides with (is coaxial with) the central axis CL. Meanwhile, the central axis CL (light-receiving axis) and the optical axis AX (light-projecting axis) are parallel and offset (are non-coaxial). The photodiode 31 (light-receiving element) is composed of, for example, an avalanche photodiode. The photodiode 31 receives the laser light projected from the light-projecting unit 20 and reflected by an object, and converts the reflected light into an electrical signal (light-receiving signal).

[0036] In a configuration in which the light-projecting unit 20 and the light-receiving unit 30 are arranged side by side facing the rotating mirror 50, there is a risk that the laser light projected by the light-projecting unit 20 may leak into the light-receiving unit 30. Therefore, the laser radar device 10 is provided with a light-blocking partition member 29 that separates the light-projecting unit 20 and the light-receiving unit 30. The partition member 29 is formed in a plate shape and is arranged between the light-projecting unit 20 and the light-receiving unit 30.

[0037] If the length of the light-shielding partition member 29 separating the light-projecting unit 20 and the light-receiving unit 30 is too short in the direction of the optical axis AX and the central axis CL (the direction in which the laser light is projected from the light-projecting unit 20), the effect of the partition member 29 in blocking the laser light leaking from the light-projecting unit 20 toward the light-receiving unit 30 will be reduced. On the other hand, if the length by which the partition member 29 protrudes toward the rotating mirror 50 in the direction of the optical axis AX and the central axis CL is too long, there is a risk that the reflected light reflected by the rotating mirror 50 and traveling toward the light-receiving unit 30 will be blocked by the partition member 29. Therefore, the partition member 29 protrudes by 0 to 2 mm (for example, 1 mm) beyond the end 22 a of the light-projecting lens 22 (light-projecting unit 20) on the rotating mirror 50 side in the direction of the optical axis AX and the central axis CL.

[0038] The distance measurement unit 71 measures (calculates) the distance from the light projection unit 20 (laser radar device 10) to the object for each light projection direction (distance measurement control) based on the elapsed time from when the laser light is projected by the light projection unit 20 to when the reflected light is received by the light receiving unit 30. In detail, the distance measurement unit 71 calculates the distance from the laser radar device 10 to the object based on the principle of TOF (Time Of Flight) in proportion to the elapsed time from when the laser light is projected to when the reflected light is received (distance measurement mode).

[0039] The laser light projected from the light-projecting unit 20 is reflected by the rotating mirror 50 and irradiated to the outside (monitoring area) of the laser radar device 10 through the transparent cover 60. If an object is present on the optical path of the laser light irradiated to the monitoring area, the laser light is reflected by the object. The laser light reflected by the object enters the laser radar device 10 through the transparent cover 60, is reflected by the rotating mirror 50, and is received by the light-receiving unit 30.

[0040] 2 is a schematic diagram showing interference caused by multiple laser radar devices 10A and 10B. For example, a laser radar device 10B is installed around a laser radar device 10A that is installed in a predetermined location. In this case, the laser radar device 10A receives the laser light emitted by the laser radar device 10B and the diffuse reflected light thereof, which may cause interference between the laser radar devices 10A and 10B.

[0041] Figure 3 is a time chart showing the laser light projection signal and light reception signal in the case of Figure 2. The horizontal axis represents time [msec], and the vertical axis represents signal strength [V]. The light projection signal is shown by a solid line, and the light reception signal is shown by a dashed line. The figure shows the light projection signal and light reception signal in one object detection direction for each of the laser radar devices 10A and 10B.

[0042] When the laser radar devices 10A and 10B receive laser light within a predetermined light-reception period after outputting a light-projection signal, they measure the distance to the object (i.e., detect the object) based on the time from outputting the light-projection signal to inputting the light-reception signal. The light-reception period is, for example, the time it takes for the laser radar devices 10A and 10B (10) to receive laser light reflected by an object at the maximum distance that the laser radar devices 10A and 10B (10) can detect. If the distance to the detected object is shorter than a predetermined distance, the laser radar devices 10A and 10B determine that there is danger and issue an alarm or stop industrial machinery such as a robot. Therefore, there is a risk that the laser radar device 10B may receive the laser light projected by the laser radar device 10A and erroneously detect an object. There is also a risk that the laser radar device 10A may receive the laser light projected by the laser radar device 10B and erroneously detect an object.

[0043] To address this issue, interference can be suppressed by fine-tuning the position (coordinates, height), angle relative to the horizontal, and orientation (azimuth) of the laser radar device 10A. Interference can also be suppressed by using a PC to set the rotation speed of the rotating mirror 50 in the laser radar device 10A and the number of object detections required to confirm object detection. However, these operations are not only time-consuming but also require the user's knowledge and experience. Even if these operations are performed, the possibility of interference still remains.

[0044] 1, the laser radar device 10 includes an interference light detector 72 that detects interference light, which is not the reflected light of the laser light projected by the light projector 20 but the laser light received by the light receiver 30. Specifically, the interference light detector 72 does not project laser light from the light projector 20 and rotates the rotating mirror 50 at a second rotation speed N2 [rps] (rounds per second) lower than the first rotation speed N1 [rps], thereby detecting the laser light received by the light receiver 30 as interference light (light-receiving-only mode). The first rotation speed N1 is the rotation speed of the rotating mirror 50 in the distance measurement mode, and is, for example, 12.5 [rps] (equivalent to 80 [msec / revolution]). The second rotation speed N2 is the rotation speed of the rotating mirror 50 in the light-receiving-only mode, and is, for example, 1 to 5 [rps] (equivalent to 200 to 1000 [msec / revolution]). That is, the second rotation speed N2 is lower than 1 / 2 and higher than 1 / 15 of the first rotation speed N1.

[0045] The light-reception-only mode is a mode in which the light-projecting unit 20 stops projecting laser light and only the light-receiving unit 30 receives laser light. When the light-projecting unit 20 stops projecting laser light, the laser light received by the light-receiving unit 30 can be considered interference light. The interference light detection unit 72 rotates the rotating mirror 50 at the second rotation speed N2 and causes the light-receiving unit 30 to receive laser light in each object detection direction until the light-receiving period has elapsed. The interference light detection unit 72 then detects the laser light received by the light-receiving unit 30 as interference light and stores the interference rotation position, which is the rotation position of the rotating mirror 50 when the interference light is detected, and the interference light waveform, which is the waveform of the light-receiving signal received by the light-receiving unit 30. When multiple laser beams are received during one light-receiving period, the interference light detection unit 72 stores the interference rotation position and interference light waveform for each laser beam. Furthermore, when the interference light detector 72 receives a plurality of laser beams during one rotation of the rotating mirror 50, it stores the interference rotation position and interference light waveform for each laser beam.

[0046] 4 is a schematic diagram showing how interference rotation positions and interference light waveforms are stored. For example, laser radar devices 10B and 10C are installed around a laser radar device 10A installed at a predetermined location. In this example, the rotation position (interference rotation position) of the rotating mirror 50 when the laser radar device 10A detects interference light from the laser radar device 10C is 45°, and the rotation position (interference rotation position) of the rotating mirror 50 when the laser radar device 10A detects interference light from the laser radar device 10B is 225°. Here, if the laser radar device 10A and the laser radar devices 10B and 10C are installed at predetermined locations and do not move, it is highly likely that the interference rotation positions and interference light waveforms detected by the laser radar device 10A will be constant and will not change.

[0047] On the other hand, when the laser light is reflected by an intruder approaching the laser radar device 10A, there is a high possibility that the rotational position of the rotating mirror 50 when the laser light is received by the light receiving unit 30 and the waveform of the light receiving signal of the laser light received by the light receiving unit 30 will change each time. In this case, it is rare that the rotational position of the rotating mirror 50 when the laser light is received by the light receiving unit 30 matches the interference rotational position, and that the waveform of the light receiving signal of the laser light received by the light receiving unit 30 matches the interference light waveform.

[0048] Figure 5 is a time chart showing the laser light reception signal in the case of Figure 4. The horizontal axis represents time [msec], and the vertical axis represents signal strength [V]. The figure shows the light reception signal in the 45° direction and the light reception signal in the 225° direction for the laser radar device 10A. Note that the light reception signal in the 225° direction is shown with the vertical axis reduced in size.

[0049] In the 45° direction, the time when the intensity of the received light signal exceeds the detection threshold Ir is the pulse width PWC. The pulse width PWC (pulse width PW) is an example of the waveform (interference light waveform) of the received light signal in the 45° direction and indicates the width of the received light signal. Here, the interference interval, which is the interval at which multiple interference lights are received by the light receiving unit 30 during the light receiving period, is 80 [msec]. In other words, it is considered that the laser radar device 10C scans the surroundings with laser light while rotating the rotating mirror 50 at a rotation speed of 12.5 [rps], which corresponds to 80 [msec / rotation]. The interference light detection unit 72 stores 45° as the interference rotation position, the pulse width PWC as the width of the received light signal indicating the interference light waveform, and 80 [msec] as the interference interval, in association with each other.

[0050] In the 225° direction, the time during which the intensity of the received light signal exceeds the detection threshold Ir is the pulse width PWB. The pulse width PWB (pulse width PW) is an example of the waveform (interference light waveform) of the received light signal in the 225° direction and indicates the width of the received light signal. Here, the interference interval, which is the interval at which multiple interference lights are received by the light receiving unit 30 during the light receiving period, is 40 [msec]. In other words, it is considered that the laser radar device 10C scans the surroundings with laser light while rotating the rotating mirror 50 at a rotation speed of 25 [rps], which corresponds to 40 [msec / rotation]. The interference light detection unit 72 stores 225° as the interference rotation position, the pulse width PWB as the width of the received light signal indicating the interference light waveform, and 40 [msec] as the interference interval, in association with each other.

[0051] FIG. 6 is a flowchart showing the procedure from installation to operation of the laser radar device 10.

[0052] First, the user installs the laser radar device 10 at a predetermined location and performs fine adjustments (S10). The predetermined location is a location suitable for monitoring a monitoring area using the laser radar device 10. After installing the laser radar device 10, the user fine-tunes the position (coordinates, height), angle relative to the horizontal, and direction (azimuth) of the laser radar device 10.

[0053] Next, the user sets the laser radar device 10 (S11). Specifically, the user operates the PC to set the rotation speed of the rotating mirror 50, the number of object detections required until object detection is confirmed, etc. In the following explanation, the number of object detections required until object detection is confirmed is assumed to be one.

[0054] Next, the laser radar device 10 detects and stores the interference light (S12). Specifically, the laser radar device 10 executes the light-receiving-only mode, and detects and stores the interference rotation position and the pulse width PW.

[0055] Next, the user fine-tunes and resets the laser radar device 10 based on the detection result of the interference light (S13). Specifically, the user causes the laser radar device 10 to project and receive light, and fine-tunes the position (coordinates, height), angle relative to the horizontal, and orientation (azimuth) of the laser radar device 10 so as to suppress reception of the detected interference light. The user also operates the PC to reset the rotation speed of the rotating mirror 50, the number of object detections required until object detection is confirmed, and so on so as to suppress reception of the detected interference light. Note that in this embodiment, the interference light is detected and stored, and is used to eliminate the interference light and execute the following ranging mode, so the processing of S13 can be omitted.

[0056] Next, the user switches the laser radar device 10 to the distance measurement mode and operates it (S14).

[0057] The process of S12 corresponds to the process performed by the interference light detector.

[0058] 7 is a flowchart showing the procedure for the distance measurement mode of the laser radar device 10. This series of processes is executed by the laser radar device 10. Note that the figure shows the processes executed at one rotation position (one object detection orientation) of the rotating mirror 50, and when this process is completed, the rotating mirror 50 is rotated to the next rotation position and the same processes are executed.

[0059] First, the rotating mirror 50 is rotated by the motor 42 at a first rotation speed N1 to the current rotation position and a laser beam is projected (S20). Next, the laser beam is received until a predetermined light-reception period has elapsed, and the distance to the object is measured based on the time from when the laser beam is projected to when the laser beam is received (S21).

[0060] Next, it is determined whether or not there is a received light pulse whose intensity exceeds the detection threshold Ir (S22). If it is determined that there is no received light pulse whose intensity exceeds the detection threshold Ir (S22: NO), the process is repeated from S20 for the next rotation position of the rotating mirror 50.

[0061] On the other hand, if it is determined in step S22 that there is a received light pulse whose intensity exceeds the detection threshold Ir (S22: YES), the nth received light pulse is determined (S23). In other words, if there are multiple received light pulses within the light receiving period, each received light pulse is determined sequentially. The initial value of n is 1.

[0062] Next, it is determined whether the current rotational position of the rotating mirror 50 and the width of the light reception signal of the n-th light reception pulse match the stored interference rotational position and pulse width PW of the interference light (S24). For example, if the absolute value of the difference between the current rotational position and the interference rotational position of the interference light is smaller than a threshold, the current rotational position and the interference rotational position of the interference light are deemed to match. Also, if the absolute value of the difference between the pulse width of the light reception signal of the n-th light reception pulse and the pulse width PW of the interference light is smaller than a threshold, the pulse width of the light reception signal of the n-th light reception pulse and the pulse width PW of the interference light are deemed to match. As a result, if the current rotational position of the rotating mirror 50 and the interference rotational position can be deemed to match, and the width (waveform) of the light reception signal of the n-th light reception pulse can be deemed to match the stored pulse width PW of the interference light (interference light waveform) at the current rotational position, the n-th light reception pulse is determined to be interference light. On the other hand, if it is not possible to determine that the current rotational position of the rotating mirror 50 matches the interference rotational position, or if it is not possible to determine that the width (waveform) of the light receiving signal of the nth light receiving pulse matches the stored pulse width PW (interference light waveform) of the interference light at the current rotational position, it is determined that the nth light receiving pulse is laser light reflected by an object.

[0063] In the judgment of S24, if it is judged that the n-th received light pulse does not match the interference light (S24: NO), the measured distance is confirmed as the distance to the object (S25). In other words, if it is judged that the n-th received light pulse is laser light reflected by the object, the distance measured by the distance measuring unit 71 is confirmed. Then, the process of S26 is executed.

[0064] On the other hand, if it is determined that the n-th received light pulse matches the interference light (S24: YES), the distance measured by the distance measuring unit 71 is not confirmed, and n = n + 1 is set (S26). In other words, the distance measured by the distance measuring unit 71 is ignored.

[0065] Next, it is determined whether n is greater than the number of received light pulses (S27). If it is determined that n is not greater than the number of received light pulses (S27: NO), the process is executed again from S22. In other words, since there are still received light pulses to be determined, the next received light pulse is used as the determination target and the distance is determined.

[0066] On the other hand, if it is determined that n is greater than the number of received light pulses (S27: YES), the process is repeated from S20 for the next rotational position of the rotating mirror 50.

[0067] The processes of S20 and S21 correspond to the processes performed by the distance measurement section, the process of S24 corresponds to the processes performed by the interference light determination section 73, and the processes of S24 to S26 correspond to the processes performed by the distance determination section 74.

[0068] 8 is a time chart showing an example of reflected light and interference light received in response to projected light, where the horizontal axis represents time [msec] and the vertical axis represents signal strength [V].

[0069] At timing t1, the laser radar device 10A projects laser light, for example, at rotational position θ1 (object detection orientation θ1) of the rotating mirror 50. The pulse width of a projection signal P0 of the laser light projected by the laser radar device 10A is, for example, pulse width PWA.

[0070] At timing t2, the laser radar device 10A receives laser light when the rotating mirror 50 is at rotational position θ1. The time when the intensity of the light reception signal P1 of the received laser light exceeds the detection threshold Ir, i.e., the pulse width of the light reception signal P1, is pulse width PW1. Here, the interference light determination unit 73 determines that the rotational position θ1 and pulse width PW1 do not match the interference rotational position and pulse width W of the interference light, and determines that the laser light of the light reception signal P1 is laser light reflected by an object. The distance measurement unit 71 measures the distance to the object based on the time Te1 from the light projection signal P0 to the light reception signal P1. The distance determination unit 74 determines the distance measured by the distance measurement unit 71 as the distance to the object.

[0071] At timing t3, the laser radar device 10A projects laser light, for example, at the rotational position θ2 (object detection orientation θ2) of the rotating mirror 50. The pulse width of the projection signal P0 of the laser light projected by the laser radar device 10A is pulse width PWA.

[0072] At timing t4, the laser radar device 10A receives laser light when the rotating mirror 50 is at rotational position θ2. The time when the intensity of the light reception signal P2 of the received laser light exceeds the detection threshold Ir, i.e., the pulse width of the light reception signal P2, is pulse width PW2. Here, the interference light determination unit 73 determines that the rotational position θ2 and the pulse width PW2 match the interference rotational position and pulse width W of the interference light, and determines that the laser light of the light reception signal P2 is interference light. The distance determination unit 74 ignores the distance measured based on the time Te2 from when the laser light is projected to when the light reception signal P2 is detected.

[0073] At timing t5, the laser radar device 10A receives laser light when the rotating mirror 50 is at rotational position θ2. The time when the intensity of the light reception signal P3 of the received laser light exceeds the detection threshold Ir, i.e., the pulse width of the light reception signal P3, is pulse width PW3. Here, the interference light determination unit 73 determines that the rotational position θ2 and pulse width PW3 do not match the interference rotational position and pulse width W of the interference light, and determines that the laser light of the light reception signal P3 is laser light reflected by an object. The distance measurement unit 71 measures the distance to the object based on the time Te3 from the light projection signal P0 to the light reception signal P3. The distance determination unit 74 determines the distance measured by the distance measurement unit 71 as the distance to the object.

[0074] The present embodiment described above in detail has the following advantages.

[0075] The interference light detection unit 72 detects interference light that is not a reflected light of the laser light projected by the light projector 20 but is a laser light received by the light receiver 30. Specifically, in the light-receive-only mode, the interference light detection unit 72 does not cause the light projector 20 to project laser light, and detects the laser light received by the light receiver 30 as interference light. In other words, since the light projector 20 does not project laser light, the laser light received by the light receiver 30 can be considered as interference light, not as a reflected light of the laser light projected by the light projector 20.

[0076] In the light-receive-only mode, the interference light detection unit 72 detects interference light while the rotating mirror 50 is rotating at a second rotation speed N2 that is lower than the first rotation speed N1 of the rotating mirror 50 when distance measurement control is performed. Therefore, the period during which laser light is received in each object detection direction when the rotating mirror 50 is rotating at the second rotation speed N2 during interference light detection (light-receive-only mode) can be made longer than the period during which laser light is received in each object detection direction when the rotating mirror 50 is rotating at the first rotation speed N1 during distance measurement control (distance measurement mode). Therefore, it is possible to prevent interference light from being detected even when it is present, i.e., to prevent interference light from being missed.

[0077] The interference light detection unit 72 can store the interference rotation position, which is the rotation position of the rotating mirror 50 when the interference light is detected, i.e., the direction in which the interference light is incident on the laser radar device 10. The interference light detection unit 72 can also store the interference light waveform, which is the waveform of the light-receiving signal in which the interference light is received by the light-receiving unit 30, i.e., the pulse width and intensity of the interference light. The interference light determination unit 73 determines that the laser light received by the light-receiving unit 30 is interference light if it can determine that the rotation position of the rotating mirror 50 when the laser light is received by the light-receiving unit 30 matches the interference rotation position and that the waveform (pulse width PW2) of the light-receiving signal in which the laser light is received by the light-receiving unit 30 matches the interference light waveform (pulse width W). Therefore, the interference light determination unit 73 can accurately determine whether the laser light is interference light.

[0078] The interference light determination unit 73 determines that the laser light received by the light receiving unit 30 is laser light reflected by an object when it cannot be determined that the rotational position of the rotating mirror 50 when the laser light is received by the light receiving unit 30 matches the interference rotational position stored by the interference light detection unit 72, or when it cannot be determined that the waveform (pulse widths W1, W3) of the light reception signal of the laser light received by the light receiving unit 30 matches the interference light waveform (pulse width W) stored by the interference light detection unit 72. Therefore, the interference light determination unit 73 can prevent erroneous determination that laser light reflected by an object such as an intruder is interference light.

[0079] The laser radar device 10 includes a distance determination unit 74 that ignores the distance measured by the distance measurement unit 71 when the interference light determination unit 73 determines that the laser light received by the light receiving unit 30 is interference light, and that determines the distance measured by the distance measurement unit 71 when the interference light determination unit 73 determines that the laser light received by the light receiving unit 30 is laser light reflected by an object. This configuration allows the laser radar device 10 to prevent erroneous detection of an object due to interference light when detecting an object based on the distance to the object measured by the distance measurement unit 71. Note that the laser radar device 10 may set (change) the distance measured by the distance measurement unit 71 to a value that is not normally possible when the laser light received by the light receiving unit 30 is determined to be interference light. In this case, the distance to the object can also be invalidated. In addition, the laser radar device 10 may first determine whether the laser light received by the light receiving unit 30 is interference light, and if it determines that the received laser light is interference light, may not measure the distance using that laser light.

[0080] Because the second rotation speed N2 is lower than half the first rotation speed N1, the laser light reception period for each object detection orientation when the rotating mirror 50 is rotating at the second rotation speed N2 can be longer than twice the laser light reception period for each object detection orientation when the rotating mirror 50 is rotating at the first rotation speed N1. This can prevent interference light from being missed and improve the accuracy of detecting the interference rotation position. Furthermore, because the second rotation speed N2 is higher than 1 / 15 of the first rotation speed N1, it can prevent the time required for the interference light detection unit 72 to detect the interference light from becoming excessively long.

[0081] The above embodiment can be modified as follows: The same parts as those in the above embodiment are denoted by the same reference numerals and the description thereof will be incorporated herein.

[0082] The second rotation speed N2 may be a rotation speed higher than 1 / 30 of the first rotation speed N1.

[0083] The half-value width of the received light signal can be used as the width of the received light signal (waveform of the received light signal, interference light waveform). Also, the peak value or half-value of the received light signal can be used as the waveform of the received light signal (interference light waveform).

[0084] If the laser radar device 10A and the other laser radar devices 10B and 10C are installed in fixed locations and do not move, the interference rotation position and the interference interval detected by the laser radar device 10A are likely to be constant and unchanging. Therefore, the interference light determination unit 73 may determine that the laser light received by the light receiving unit 30 is interference light if it can determine that the rotation position of the rotating mirror 50 when the laser light is received by the light receiving unit 30 matches the interference rotation position stored by the interference light detection unit 72 and that the interval at which multiple laser light beams are received by the light receiving unit 30 during the light reception period matches the interference interval stored by the interference light detection unit 72. This configuration also allows the interference light determination unit 73 to accurately determine interference light. It is also possible to determine that the laser light received by the light receiving unit 30 is interference light if the intensity of the laser light reception signal is higher than a predetermined intensity that cannot be achieved by reflected light. Then, by shifting the interval at which the light projecting unit 20 of the laser radar device 10 projects the laser light (the first rotation speed N1 during distance measurement) from the interference interval, it is possible to suppress interference.

[0085] For example, if the laser light is reflected by an intruder approaching the laser radar device 10A, there is a high possibility that the rotational position of the rotating mirror 50 when the laser light is received by the light receiving unit 30 and the interval at which multiple laser beams are received by the light receiving unit 30 during the light receiving period in which the laser light is received for each object detection direction will change each time. In this case, it is rare for the rotational position of the rotating mirror 50 when the laser light is received by the light receiving unit 30 to match the interference rotation position, and for the interval at which multiple laser beams are received by the light receiving unit 30 during the light receiving period to match the interference interval.

[0086] Therefore, the interference light determination unit 73 may determine that the laser light received by the light receiving unit 30 is laser light reflected by an object when it cannot be determined that the rotational position of the rotating mirror 50 when the laser light is received by the light receiving unit 30 matches the interference rotational position stored by the interference light detection unit 72, or when it cannot be determined that the interval at which multiple laser lights are received by the light receiving unit 30 during the light receiving period matches the interference interval stored by the interference light detection unit 72. With this configuration as well, the interference light determination unit 73 can prevent erroneous determination that laser light reflected by an object such as an intruder is interference light.

[0087] 7, the laser beam may be received until a predetermined light-reception period has elapsed. Then, in S25, the distance to the object may be measured based on the time between projecting the laser beam and receiving it. The measured distance may then be determined as the distance to the object. On the other hand, if, in S24, it is determined that the nth received light pulse corresponds to interference light (S24: YES), the distance to the object may not be measured, and n may be set to n + 1 (S26). That is, the distance measurement control by the distance measurement unit 71 for laser light determined to be interference light may be omitted. In the above case, the processes of S20 and S25 correspond to the processing of the distance measurement unit 71. The same applies when the interference light determination unit 73 determines whether the received laser beam is interference light based on the rotational position and interference rotational position of the rotating mirror 50, the interval at which multiple laser beams are received, and the interference interval. With these configurations, the laser radar device 10 can prevent erroneous object detection due to interference light and reduce the processing load by omitting unnecessary distance measurement control.

[0088] The rotary reflection mechanism 40 can also be configured such that a through passage is formed in the rotary mirror 50, and the laser light passes through the through passage and is projected into the external space, while the reflected light is reflected by the rotary mirror 50 toward the photodiode 31 (light receiving unit).

[0089] The above-described embodiments and their modifications can be combined within the scope of possible combinations. [Explanation of symbols]

[0090] 10...laser radar device, 10A...laser radar device, 20...light projecting unit, 30...light receiving unit, 50...rotating mirror, 71...distance measuring unit, 72...interference light detecting unit, 73...interference light determining unit, 74...distance determining unit.

Claims

1. a light projection unit that projects laser light; a light receiving unit that receives laser light; a rotating mirror that is rotatable about a predetermined rotation axis, that reflects the incident laser light projected by the light projecting unit toward an external space, and that reflects the incident laser light so that it can be received by the light receiving unit; a distance measurement unit that performs distance measurement control to measure a distance to an object based on the time from when the laser light is projected by the light projecting unit to when the laser light is received by the light receiving unit; an interference light detection unit that detects interference light that is not a reflected light of the laser light projected by the light projecting unit but is a laser light received by the light receiving unit; A laser radar device installed at a predetermined location, The interference light detection unit of the laser radar device does not cause the light projecting unit to project the laser light, and rotates the rotating mirror at a second rotation speed that is lower than a first rotation speed, which is the rotation speed of the rotating mirror when the ranging control is performed by the ranging unit, and detects the laser light received by the light receiving unit as the interference light.

2. the interference light detection unit stores an interference rotation position, which is a rotation position of the rotating mirror when the interference light is detected, and an interference light waveform, which is a waveform of a light receiving signal obtained by receiving the interference light by the light receiving unit; 2. The laser radar device according to claim 1, further comprising an interference light determination unit that determines that the laser light received by the light receiving unit is interference light when it can be considered that the rotational position of the rotating mirror when the laser light is received by the light receiving unit matches the interference rotation position stored by the interference light detection unit, and when it can be considered that the waveform of a light reception signal of the laser light received by the light receiving unit matches the interference light waveform stored by the interference light detection unit.

3. 3. The laser radar device according to claim 2, wherein the interference light determination unit determines that the laser light received by the light receiving unit is laser light reflected by an object when it cannot be determined that the rotational position of the rotating mirror when the laser light is received by the light receiving unit matches the interference rotational position stored by the interference light detection unit, or when it cannot be determined that the waveform of a light reception signal of the laser light received by the light receiving unit matches the interference light waveform stored by the interference light detection unit.

4. 4. The laser radar device of claim 3, further comprising a distance determination unit that ignores the distance measured by the distance measuring unit when the interference light determination unit determines that the laser light received by the light receiving unit is interference light, and that determines the distance measured by the distance measuring unit when the interference light determination unit determines that the laser light received by the light receiving unit is laser light reflected by an object.

5. The laser radar device of claim 3, further comprising a distance determination unit that, when the interference light determination unit determines that the laser light received by the light receiving unit is interference light, omits the distance measurement control by the distance measuring unit for the laser light determined to be interference light, and when the interference light determination unit determines that the laser light received by the light receiving unit is laser light reflected by an object, determines the distance measured by the distance measuring unit.

6. the interference light detection unit stores an interference rotation position, which is a rotation position of the rotating mirror when the interference light is detected, and an interference interval, which is an interval at which a plurality of the interference lights are received by the light receiving unit during a light receiving period in which the laser light is received for each object detection orientation; 2. The laser radar device according to claim 1, further comprising an interference light determination unit that determines that the laser light received by the light receiving unit is interference light when it can be considered that the rotational position of the rotating mirror when the laser light is received by the light receiving unit matches the interference rotation position stored by the interference light detection unit, and when it can be considered that the interval at which the plurality of laser lights are received by the light receiving unit during the light receiving period matches the interference interval stored by the interference light detection unit.

7. 7. The laser radar device according to claim 6, wherein the interference light determination unit determines that the laser light received by the light receiving unit is laser light reflected by an object when it cannot be determined that the rotational position of the rotating mirror when the laser light is received by the light receiving unit matches the interference rotational position stored by the interference light detection unit, or when it cannot be determined that the interval at which the laser light is received by the light receiving unit during the light receiving period matches the interference interval stored by the interference light detection unit.

8. 8. The laser radar device of claim 7, further comprising a distance determination unit that ignores the distance measured by the distance measuring unit when the interference light determination unit determines that the laser light received by the light receiving unit is interference light, and that determines the distance measured by the distance measuring unit when the interference light determination unit determines that the laser light received by the light receiving unit is laser light reflected by an object.

9. The laser radar device of claim 7, further comprising a distance determination unit that, when the interference light determination unit determines that the laser light received by the light receiving unit is interference light, omits the distance measurement control by the distance measuring unit for the laser light determined to be interference light, and when the interference light determination unit determines that the laser light received by the light receiving unit is laser light reflected by an object, determines the distance measured by the distance measuring unit.

10. 10. The laser radar device according to claim 1, wherein the second rotation speed is lower than 1 / 2 and higher than 1 / 15 of the first rotation speed.

Images