Distance measuring device

Abstract

A distance measuring device (10) emits light through a transmissive member (20) and detects reflected light from a target object. The distance measuring device (10) is provided with a light receiving unit (180) and a switching control unit (121). The light receiving unit (180) receives internally reflected light including reflected light reflected by the transmissive member (20), and reflected light from the target object. The switching control unit (121) uses a result of the reception of internally reflected light by the light receiving unit (180) to switch detection processing of reflected light from the target object.

Description

[Technical field]

[0001] The present invention relates to a distance measuring device. [Background technology]

[0002] In recent years, there has been development of distance measuring devices that can be used for automatic driving of automobiles, etc. One example of a distance measuring device is one that measures the distance to surrounding objects by measuring the time it takes for emitted light to be reflected by the object and return.

[0003] In such a distance measuring device, if any deposits form on the exit window through which light exits, the distance measurement is affected.

[0004] Patent Document 1 describes monitoring the received light power and operating a window cleaning device when it is necessary to remove dirt or the like from the window portion. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2009-503486 Summary of the Invention [Problem to be solved by the invention]

[0006] However, there are cases where the dirt cannot be removed immediately, such as when the range finder is not equipped with a window cleaning device.

[0007] In such a situation where there is a deposit on the exit window, the light receiving section may become saturated with light reflected from the window, and the effect of saturation may remain on the light receiving signal for a relatively long period of time. During the period in which the effect of saturation remains, it may not be possible to detect the reflected light from the object to be measured.

[0008] One example of a problem to be solved by the present invention is how to increase the possibility of distance measurement under conditions where there is the influence of attached matter. [Means for solving the problem]

[0009] The invention described in claim 1 is A distance measuring device that emits light through a transparent member and detects reflected light from an object, a light receiving unit that receives internally reflected light including light reflected by the transparent member and light reflected from the object; and a switching control unit that switches detection processes for the reflected light from the object using the result of receiving the internal reflected light by the light receiving unit. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating a configuration of a distance measuring device according to a first embodiment. [Diagram 2] 1 is a diagram illustrating a distance measuring device according to a first embodiment. [Diagram 3] 1 is a diagram illustrating in detail an example of the configuration of a distance measuring device according to a first embodiment. [Figure 4] 2 is a diagram illustrating a hardware configuration of a control unit according to the first embodiment. FIG. [Diagram 5] 4 is a diagram illustrating an example of a waveform of a light receiving signal of a light receiving unit. FIG. [Figure 6] 5 is a flowchart showing a flow of a first example of a switching process performed by a switching control unit according to the first embodiment. [Figure 7] 13 is a diagram showing another example of the waveform of the light receiving signal of the light receiving unit. FIG. [Figure 8] 10 is a flowchart showing a flow of a second example of a switching process performed by a switching control unit according to the first embodiment. [Figure 9] 11A and 11B are diagrams illustrating a map showing the distribution of the received light intensity of internally reflected light in a frame and a map showing the distribution of saturation time; [Figure 10] 10 is a flowchart illustrating a flow of a process performed by a switching control unit according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same components are given the same reference numerals and the description will be omitted as appropriate.

[0012] (First embodiment) FIG. 1 is a diagram illustrating a configuration of a distance measuring device 10 according to the first embodiment. FIG. 2 is a diagram illustrating a distance measuring device 10 according to this embodiment. In FIG. 1 and FIG. 2, the dashed arrows show the path of light. The distance measuring device 10 according to this embodiment is a device that emits light through a transparent member 20 and detects reflected light from an object 30. The distance measuring device 10 includes a light receiving unit 180 and a switching control unit 121. The light receiving unit 180 receives internal reflected light including reflected light reflected by the transparent member 20 and reflected light from the object 30. The switching control unit 121 switches the detection process of the reflected light from the object 30 using the result of receiving the internal reflected light by the light receiving unit 180. This will be described in detail below.

[0013] In the distance measuring device 10, the light output from the light source 14 is emitted to the outside of the distance measuring device 10 mainly via the transparent member 20 as shown in Fig. 2. However, at least a part of the light output from the light source 14 is reflected inside the distance measuring device 10 as shown in Fig. 1, becoming internally reflected light. The internally reflected light is received by the light receiving unit 180. This internally reflected light also includes light reflected by the transparent member 20. Furthermore, if there is an attachment to the transparent member 20, the internally reflected light includes reflected light caused by the attachment.

[0014] The transparent member 20 is a light-transmitting member that separates the inside and outside of the distance measuring device 10. The transparent member 20 is made of glass or resin, for example. At least one surface of the transparent member 20 is exposed to the space outside the distance measuring device 10, and dirt, raindrops, and the like may adhere to it. The reflected light caused by the adhesion includes, for example, light reflected at the interface between the transparent member 20 and the adhesion, light reflected inside the adhesion, and light reflected at the interface between the adhesion and air. The light receiving unit 180 receives the internally reflected light and the reflected light from the object 30. The switching control unit 121 switches the detection process of the reflected light from the object 30 using the result of receiving the internally reflected light by the light receiving unit 180. The result of receiving the internally reflected light includes the result of receiving the light during the period when the influence of receiving the internally reflected light occurs. The detection process will be described in detail later. Note that the object 30 is not an adhesion to the transparent member 20, that is, it is not in contact with the transparent member 20.

[0015] 3 is a diagram illustrating in detail the configuration of the distance measuring device 10 according to this embodiment. In this diagram, dashed arrows indicate the path of light. The configuration of the distance measuring device 10 will be described in detail with reference to this diagram.

[0016] The distance measuring device 10 is a device that measures the distance from the distance measuring device 10 to an object (target object 30) within a scanning range 160 based on, for example, the difference between the emission timing of pulsed light and the reception timing of reflected light (reflected pulsed light). The pulsed light is, for example, infrared light or other light. The pulsed light is, for example, a laser pulse. The pulsed light is output from the light source 14 provided in the distance measuring device 10 and emitted to the outside of the distance measuring device 10 through the transparent member 20, and is reflected by the object and at least a part of it returns toward the distance measuring device 10. Then, the reflected light passes through the transparent member 20 again and enters the distance measuring device 10. The reflected light that enters the distance measuring device 10 is received by the light receiving unit 180, and the intensity is detected. Here, in the distance measuring device 10, the time from when the pulsed light is emitted from the light source 14 to when the reflected light is detected by the light receiving unit 180 is measured. A control unit 120 provided in the distance measuring device 10 calculates the distance between the distance measuring device 10 and the object using the measured time and the propagation speed of the pulsed light. The distance measuring device 10 is, for example, a LIDAR (Laser Imaging Detection and Ranging, Laser Illuminated Detection and Ranging, or LiDAR (Light Detection and Ranging) device.

[0017] The light source 14 emits pulsed light. The light source 14 is, for example, a laser diode. The light receiving unit 180 includes a light receiving element 18 and a detection circuit 181. The light receiving element 18 receives the pulsed light incident on the distance measuring device 10 and the above-mentioned internally reflected light. The light receiving element 18 is, for example, a photodiode such as an avalanche photodiode (APD).

[0018] In the example of Fig. 3, the distance measuring device 10 further includes a movable mirror 16. The movable mirror 16 is, for example, a MEMS mirror movable along one axis or two axes. By changing the orientation of the reflecting surface of the movable mirror 16, the emission direction of the pulsed light emitted from the distance measuring device 10 can be changed. When the movable mirror 16 is a MEMS mirror movable along two axes, a predetermined range can be raster scanned with the pulsed light by driving the movable mirror 16 along two axes.

[0019] The control unit 120 generates point cloud data including the measurement results obtained by a plurality of pulsed lights. For example, when raster scanning within a scanning range 160, a line-shaped scan is performed by changing the light emission direction in a first direction 161. Then, by performing a plurality of line-shaped scans while changing the light emission direction in a second direction 162, it is possible to generate point cloud data including a plurality of measurement results within the scanning range 160. In the example shown in this figure, the first direction 161 and the second direction 162 are orthogonal to each other.

[0020] A unit of point cloud data generated by one raster scan is called a frame. When the measurement for one frame is completed, the light emission direction returns to the initial position, and the measurement for the next frame is performed. In this manner, frames are repeatedly generated. In the point cloud data, the distance measured by the pulsed light is associated with information indicating the emission direction of the pulsed light. Alternatively, the point cloud data may include three-dimensional coordinates indicating the reflection point of the pulsed light. The control unit 120 generates the point cloud data using the calculated distance and information indicating the angle of the movable mirror 16 when each pulsed light is emitted. The generated point cloud data may be output to the outside of the distance measuring device 10, or may be stored in a storage device accessible from the control unit 120.

[0021] In the example shown in the figure, the distance measuring device 10 further includes a holed mirror 15 and a condenser lens 13. The pulsed light output from the light source 14 passes through a hole in the holed mirror 15, is reflected by the movable mirror 16, and is then emitted from the distance measuring device 10. The reflected light incident on the distance measuring device 10 is reflected by the movable mirror 16 and the holed mirror 15, and then enters the light receiving unit 180 via the condenser lens 13. The distance measuring device 10 may further include a collimating lens, a mirror, etc.

[0022] The control unit 120 can control the light emitting unit 140, the light receiving unit 180, and the movable reflecting unit 164 (see FIG. 4). The light emitting unit 140, the light receiving unit 180, and the movable reflecting unit 164 are included in the distance measuring device 10. The light emitting unit 140 includes a light source 14 and a driving circuit 141. The light receiving unit 180 includes a light receiving element 18 and a detection circuit 181. The movable reflecting unit 164 includes a movable mirror 16 and a driving circuit 163. The driving circuit 141 is a circuit for causing the light source 14 to emit light based on a control signal from the integrated circuit 80, and is configured to include, for example, a switching circuit and a capacitive element. The detection circuit 181 includes an IV converter and an amplifier, and outputs a signal indicating the detection intensity of light by the light receiving element 18. The control unit 120 obtains a light receiving signal from the light receiving unit 180, and detects a peak due to reflected light from the target 30 by performing a detection process described later on the light receiving signal. Then, using the detected peak light receiving timing and light emission timing, the distance from the distance measuring device 10 to the object 30 within the scanning range 160 is calculated as described above. The control unit 120 also includes a switching control unit 121, which switches detection processes for distance measurement.

[0023] 4 is a diagram illustrating a hardware configuration of the control unit 120 according to this embodiment. The control unit 120 is implemented using an integrated circuit 80. The integrated circuit 80 is, for example, a SoC (System On Chip).

[0024] The integrated circuit 80 has a bus 802, a processor 804, a memory 806, a storage device 808, an input / output interface 810, and a network interface 812. The bus 802 is a data transmission path for the processor 804, the memory 806, the storage device 808, the input / output interface 810, and the network interface 812 to transmit and receive data to and from each other. However, the method of connecting the processor 804 and the like to each other is not limited to bus connection. The processor 804 is an arithmetic processing device realized by using a microprocessor or the like. The memory 806 is a memory realized by using a RAM (Random Access Memory) or the like. The storage device 808 is a storage device realized by using a ROM (Read Only Memory), a flash memory, or the like.

[0025] The input / output interface 810 is an interface for connecting the integrated circuit 80 to peripheral devices. In this figure, the input / output interface 810 is connected to the drive circuit 141 of the light source 14, the detection circuit 181 of the light receiving element 18, and the drive circuit 163 of the movable mirror 16.

[0026] The network interface 812 is an interface for connecting the integrated circuit 80 to a communication network. This communication network is, for example, a controller area network (CAN), Ethernet, low voltage differential signaling (LVDS), etc. The method for connecting the network interface 812 to the communication network may be a wireless connection or a wired connection.

[0027] The storage device 808 stores a program module for implementing the functions of the control unit 120 including the switching control unit 121. The processor 804 implements the functions of the control unit 120 including the switching control unit 121 by reading the program module into the memory 806 and executing it.

[0028] The hardware configuration of the integrated circuit 80 is not limited to the configuration shown in the figure. For example, the program module may be stored in the memory 806. In this case, the integrated circuit 80 does not need to include the storage device 808.

[0029] FIG. 5 is a diagram illustrating an example of a waveform of a light receiving signal of the light receiving unit 180. The above-mentioned internally reflected light is received by the light receiving unit 180 immediately after light is emitted from the light source 14. On the other hand, the light reflected from the object 30 is received by the light receiving unit 180 at a timing according to the distance from the distance measuring device 10 to the object 30. When the object 30 is sufficiently far from the distance measuring device 10, a peak due to the reception of the internally reflected light (hereinafter also referred to as an "internal reflection peak") and a peak due to the reception of the reflected light from the object 30 (hereinafter also referred to as an "object peak") appear in a state separated from each other in the light receiving signal output from the light receiving unit 180. That is, in this case, it can be said that the first peak in the light receiving signal after the emission of light is the internal reflection peak, and the second and subsequent peaks are object peaks. However, the closer the object 30 is to the distance measuring device 10, the closer these peaks are to each other.

[0030] Here, if there is an attachment on the transparent member 20, the peak intensity due to the reception of the internally reflected light may exceed the detection range of the light receiving unit 180, and the light receiving signal of the light receiving unit 180 may become saturated as shown in Fig. 5. Once the light receiving unit 180 becomes saturated, it takes time to return to the original signal level (reference level) due to charge accumulation in the light receiving element 18, etc. Then, if reflected light from the target object 30 enters the light receiving unit 180 during the time it takes to return to this original signal level, it becomes necessary to detect the object peak while being influenced by the reception of the internally reflected light.

[0031] The light receiving signal is a signal output from the detection circuit 181 and input to the control unit 120. The reference level is, for example, a light receiving signal level in a situation where no light is incident on the light receiving element 18, and is a light receiving signal level in a situation where no pulsed light is incident on the light receiving element 18. In the example of this figure, the greater the light receiving intensity at the light receiving element 18, the greater the light receiving signal is output in the positive direction. However, the light receiving signal is a signal that reflects the circuit characteristics of the light receiving element 18 and the detection circuit 181, and a negative light receiving signal may be output as shown in this figure due to the circuit characteristics. Note that the polarity of the light receiving signal relative to the light receiving intensity is not limited to the example of this figure. For example, the light receiving unit 180 may have a configuration in which the greater the light receiving intensity at the light receiving element 18, the greater the light receiving signal is output in the negative direction. In the following explanation, the polarity in the processing, etc. is set appropriately.

[0032] In the example shown in the figure, when internally reflected light is received, the received light signal rises and saturates. Once it leaves the saturated state, it returns to zero level (reference level), and the detection circuit 181 outputs a signal value with a negative polarity. After the received light signal reaches a minimum value, it gradually returns to the reference level. An object peak exists between the time when the signal reaches this minimum value and when it returns to the reference level.

[0033] <Detection process> The detection process for detecting a peak from the received light signal will be described below. In the distance measuring device 10 according to this embodiment, the switching control unit 121 switches between a first detection process and a second detection process as the detection process.

[0034] The first detection process is a detection process based on the level of the light receiving signal output from the light receiving unit 180 relative to a reference level. Specifically, in the first detection process, a value L is calculated by subtracting the reference level from the light receiving signal level. Then, a period during which the value L exceeds a predetermined threshold is identified, and the point during that period at which the value L is maximum is detected as the peak position. However, the peak position may be identified by further processing to improve the distance accuracy using this point and several points around this point. The predetermined threshold is set to a value greater than the noise level. In the first detection process, peaks whose peak intensity is below the reference level are not detected.

[0035] The second detection process is a detection process based on the gradient of the level of the received light signal output from the light receiving unit 180. Specifically, in the second detection process, a differential value is calculated at each point (time point) of the received light signal, and the point where the polarity of the calculated differential value switches from positive to negative is detected as the peak position. However, the peak position may be identified by further performing a process to improve the distance accuracy using this point and several points around this point.

[0036] Usually, the first detection process can detect peaks more accurately than the second detection process, so it is preferable to give priority to the first detection process as much as possible. However, in the example of FIG. 5, the peak intensity of the object peak is below the reference level, and is not detected by the first detection process. On the other hand, such an object peak can be detected by the second detection process. According to the distance measuring device 10 of this embodiment, the first detection process is given priority, and switching is performed to perform the second detection process in a situation where detection by the first detection process is difficult. Therefore, it is possible to increase the possibility of distance measurement under a situation where there is an influence of an attached object while maintaining high detection accuracy.

[0037] The switching control unit 121 according to the present embodiment performs switching so that the second detection process is performed until the light reception signal steadily returns to the reference level after the internal reflection light is received, and the first detection process is performed otherwise. This makes it possible to detect an object peak even under conditions where there is an influence of saturation of the internal reflection peak.

[0038] <Saturation period> The period during which the internal reflection peak is affected by saturation is referred to as the saturation period. The waveform of the internal reflection peak differs depending on the type of deposit, but when the deposit is water, for example, the waveform is affected by saturation for a long period of time.

[0039] In FIG. 5 and FIG. 7 described later, a period P indicates a saturation period. The start point of the saturation period is the start point of saturation at the internal reflection peak. A state in which the light receiving signal output by the light receiving unit 180 exceeds a predetermined saturation reference level is considered to be a state in which the light receiving unit 180 is saturated. That is, the switching control unit 121 specifies the point at which the light receiving signal first becomes equal to or higher than the predetermined saturation reference level after the light is emitted as the start point of the saturation period. The saturation reference level is, for example, slightly smaller than the saturation level of the light receiving unit 180. Here, the saturation level means the maximum light receiving intensity that the light receiving unit 180 can detect without being saturated.

[0040] The end point of the saturation period is the point at which the light reception signal steadily returns to the reference level. For example, the end point of the saturation period can be the earlier of the second zero crossing after saturation or the first convergence after saturation. The switching control unit 121 determines that the signal value is in a convergence state when the state in which the signal value is within a predetermined convergence level range continues for a predetermined length of time. If it is determined that the convergence state has occurred, the time when the state started, that is, the time when the signal value went from outside the convergence level range to within the convergence level range, is specified as the first convergence after saturation. Note that the convergence level range is a range that includes zero, and the upper limit of the convergence level range is slightly greater than zero, and the lower limit of the convergence level range is slightly less than zero. However, the difference between the upper limit of the convergence level range and zero can be greater than the difference between the lower limit of the convergence level range and zero. For example, when disturbance light is incident on the distance measuring device 10, the light reception signal may converge to a level greater than zero by the amount of the disturbance light.

[0041] The switching control unit 121 selects the earlier of the second zero crossing point after saturation or the first convergence point after saturation, and specifies it as the end point of the saturation period. Note that either the second zero crossing point after saturation or the first convergence point after saturation may not exist. In that case, the switching control unit 121 specifies the earlier of the second zero crossing point after saturation or the first convergence point after saturation as the end point of the saturation period.

[0042] In addition, the end point of the saturation period may be the first point after the end of the saturation state where the received light signal is within the convergence level range and the slope of the received light signal is within a predetermined range including zero, or the point at which such a state continues for a predetermined number of points.

[0043] FIG. 6 is a flowchart showing the flow of a first example of the switching process performed by the switching control unit 121 according to this embodiment.

[0044] First, when a pulsed light is emitted (S10), the switching control unit 121 monitors the received light signal and judges whether or not the intensity of the first received light pulse is equal to or greater than the saturation reference level (S11). If the intensity of the first received light pulse is not equal to or greater than the saturation reference level (No in S11), the switching control unit 121 sets a first detection process as the detection process to be performed after the first received light pulse (S15). Thereafter, the first detection process is set as the detection process to be performed on all detection values ​​until the next pulsed light is emitted.

[0045] If the first light receiving pulse has an intensity equal to or greater than the saturation reference level (Yes in S11), the switching control unit 121 then judges whether the saturation state of the light receiving signal has been resolved (S12). If the saturation state has not been resolved (No in S12), the switching control unit 121 continues to monitor the detection value from the light receiving unit 180 and repeats this judgment until the saturation state is resolved (S12). If the saturation state is resolved (Yes in S12), the switching control unit 121 judges whether the detection value (point of the light receiving signal) after the saturation state is resolved is within the range of the period P by the above-mentioned method (S13). If the detection value is within the period P (saturation period) (Yes in S13), the switching control unit 121 sets the second detection process as the detection process to be performed on the detection value (S14). Next, the switching control unit 121 judges whether the next detection value is within the range of the period P (S13). In this manner, the judgment in S13 and the setting of the second detection process are repeated for each detection value until the range of the period P is passed. When the detection value is no longer within the range of the period P (No in S13), the switching control unit 121 sets the first detection process as the detection process to be performed on that detection value (S15). After that, the first detection process is set as the detection process to be performed on all detection values ​​until the next pulsed light emission.

[0046] According to the above flow, the first detection process or the second detection process is set for all detection values ​​for which peak detection should be performed. When the detection process to be performed is set by the switching control unit 121, the set detection process is executed by the control unit 120. According to the example of this figure, switching and detection can be performed almost in real time for the reception of light. However, since peak detection, that is, specifying whether a certain detection value is a peak or not, may require multiple detection values ​​before and after the detection value, the execution of the detection process by the control unit 120 may be delayed from the setting of the detection process by the switching control unit 121. Furthermore, the setting contents of the detection process for each detection value by the switching control unit 121 may be held at least temporarily in a storage unit (for example, the storage device 808). Furthermore, the determination of the detection process by the switching control unit 121 and the peak detection by the control unit 120 may be performed collectively for each emission of light, or may be performed collectively for each frame.

[0047] According to the processing example of Fig. 6, the detection process is set as shown in Fig. 5. In Fig. 5, "S2" indicates a period in which peak detection is performed by the second detection process, and "S1" indicates a period in which peak detection is performed by the first detection process.

[0048] 7 is a diagram showing another example of the waveform of the light receiving signal of the light receiving unit 180. In this example, the object peak is located within the saturation period. This is because it cannot be said that the light receiving signal has converged to the reference level at the position of the object peak. However, the peak intensity of the object peak exceeds the reference level, and it is possible to detect the object peak in the first detection process.

[0049] FIG. 8 is a flowchart showing the flow of a second example of the switching process performed by the switching control unit 121 according to this embodiment.

[0050] First, when a pulsed light is emitted (S10), the switching control unit 121 monitors the received light signal and judges whether or not the intensity of the first received light pulse is equal to or greater than the saturation reference level (S11). If the intensity of the first received light pulse is not equal to or greater than the saturation reference level (No in S11), the switching control unit 121 sets a first detection process as the detection process to be performed after the first received light pulse (S15). Thereafter, the first detection process is set as the detection process to be performed on all detection values ​​until the next pulsed light is emitted.

[0051] If the first light receiving pulse has an intensity equal to or greater than the saturation reference level (Yes in S11), the switching control unit 121 then judges whether or not the light receiving signal is below the reference level (S121). If the light receiving signal is not below the reference level (No in S121), the switching control unit 121 continues to monitor the detection value from the light receiving unit 180 until it falls below the reference level, and repeats this judgment (S121). If the light receiving signal falls below the reference level (Yes in S121), the switching control unit 121 judges whether or not the detection value after falling below the reference level is within the range of the period P by the above-mentioned method (S13). If the detection value is within the range of the period P (Yes in S13), the switching control unit 121 then judges whether or not the detection value is above the reference level (S132). If the detection value is not above the reference level (No in S132), the switching control unit 121 sets the second detection processing as the detection processing to be performed on the detection value (S14). Next, the switching control unit 121 judges whether the next detection value is within the period P (S13). If the detection value is equal to or greater than the reference level in S132 (Yes in S132), the switching control unit 121 sets the first detection process as the detection process to be performed on that detection value (S152). Next, the switching control unit 121 returns to S13 for the next detection value and judges whether it is within the period P. If the detection value is not within the period P in S13 (No in S13), the switching control unit 121 sets the first detection process as the detection process to be performed on that detection value (S15). Thereafter, the first detection process is set as the detection process to be performed on all detection values ​​until the next pulsed light emission.

[0052] The above flow also sets the first detection process or the second detection process for all detection values ​​for which peak detection should be performed. When the detection process to be performed is set by the switching control unit 121, the set detection process is executed by the control unit 120. According to the example in this figure, switching and detection can be performed almost in real time for the reception of light. However, since peak detection, that is, specifying whether a certain detection value is a peak or not, may require multiple detection values ​​before and after the detection value, the execution of the detection process by the control unit 120 may be delayed from the setting of the detection process by the switching control unit 121. Furthermore, the setting contents of the detection process for each detection value by the switching control unit 121 may be held in the storage unit at least temporarily. Furthermore, the determination of the detection process by the switching control unit 121 and the peak detection by the control unit 120 may be performed collectively for each emission of light, or may be performed collectively for each frame.

[0053] According to the processing example of Fig. 8, the detection process is set as shown in Fig. 7. In Fig. 7, "S2" indicates a period in which peak detection is performed by the second detection process, and "S1" indicates a period in which peak detection is performed by the first detection process. According to this processing example, the first detection process can be applied to peaks that are detectable by the first detection process even within the saturation period.

[0054] As described above, according to this embodiment, the switching control unit 121 switches the detection process of the reflected light from the target object 30, using the result of receiving the internally reflected light by the light receiving unit 180. Therefore, it is possible to increase the possibility of distance measurement even in a situation where there is an influence of an attached object.

[0055] Second embodiment The distance measuring device 10 according to the second embodiment is the same as the distance measuring device 10 according to the first embodiment, except that a switching control unit 121 switches the detection process using the distribution of the reception results of the internally reflected light in a frame.

[0056] FIG. 9 illustrates a map showing the distribution of the received intensity of internally reflected light in a frame (hereinafter referred to as the "internal reflected light intensity map") and a map showing the distribution of saturation time (hereinafter referred to as the "saturation time map"). The two maps in this figure are the results of simultaneous measurements. In each map, the emission direction of the pulsed light is associated with the received result of the internally reflected light. The map in this figure was obtained when there was an attachment on the transparent member 20, and the influence of the attachment is apparent in the area inside the dashed ellipse.

[0057] The internal reflected light intensity map shows the peak intensity (maximum intensity) at the internal reflection peak for each output light as the internal reflected light intensity. The saturation time map shows the length of the above-mentioned saturation period for each output light. However, the internal reflected light intensity map in this figure shows the difference between the internal reflected light intensity at the time of measurement and the internal reflected light intensity measured in the initial state when there is no adhesion. Also, the saturation time map in this figure shows the difference between the saturation time at the time of measurement and the saturation time measured in the initial state when there is no adhesion. Since a certain amount of internal reflected light occurs even when there is no adhesion, the effect of adhesion can be made clearer by taking the difference from the initial state.

[0058] As can be seen from this figure, the internal reflection light intensity is very high in the region corresponding to the attachment. It can also be seen that the saturation time is also long in the region corresponding to the attachment. It can also be seen that the saturation time is longer in the region where the attachment is located closer to the center. In such a region with a long saturation time, it is preferable to perform the second detection process because there is a possibility that an object peak will occur during the saturation period. The switching control unit 121 according to this embodiment performs the following process.

[0059] The switching control unit 121 switches the detection process using the intensity of the internally reflected light in the light reception result. In detail, the switching control unit 121 identifies an attachment region corresponding to an area where an attachment exists on the transparent member 20 using the distribution of the light reception results of the internally reflected light in a plurality of light emission directions, and switches the detection process for each emission direction based on the position within the attachment region. According to the distance measuring device 10 of this embodiment, it is not necessarily necessary to identify the saturation time.

[0060] FIG. 10 is a flow chart illustrating the flow of processing performed by the switching control unit 121 according to the present embodiment. When measurement for a certain frame is completed, the switching control unit 121 acquires the light receiving signals of all the measurement points of that frame (S21). The switching control unit 121 generates an internal reflection light intensity map using the internal reflection light intensities corresponding to a plurality of emission directions (S22). As described above, the internal reflection light intensity used here is preferably the amount of change from the value in the initial state. From the internal reflection light intensity map, it is possible to identify an area where an attachment occurs in the scanning range. Specifically, the switching control unit 121 identifies an area in the internal reflection light intensity map where the internal reflection light intensity is equal to or greater than a predetermined value A as an attachment area (S23).

[0061] Then, the switching control unit 121 calculates the shortest distance from the outer edge of the object region for each point (each emission direction) in the identified object region (S24). It can be said that the longer the shortest distance, the closer the point is to the center of the object region, and the longer the saturation time.

[0062] Next, the switching control unit 121 judges whether or not the internal reflection light intensity of a certain measurement point in the frame is equal to or greater than a predetermined value B and the shortest distance from the outer edge of the attachment area is equal to or greater than a predetermined value C (S25). If the internal reflection light intensity is equal to or greater than the predetermined value B and the shortest distance from the outer edge of the attachment area is equal to or greater than a predetermined value C (Yes in S25), the switching control unit 121 sets the second detection process as a detection process for performing peak detection for that measurement (S26). If the condition that the internal reflection light intensity is equal to or greater than the predetermined value B and the shortest distance from the outer edge of the attachment area is equal to or greater than a predetermined value C is not satisfied (No in S25), the switching control unit 121 sets the first detection process as a detection process for performing peak detection for that measurement (S27). After performing either S26 or S27, the switching control unit 121 judges whether or not the detection process has been set for all measurement points in the frame (S28). If detection processing has not been set for all measurement points (No in S28), the process of S25 is performed for the measurement points for which detection processing has not yet been set. If detection processing has been set for all measurement points (Yes in S28), the switching control unit 121 ends the processing for that frame.

[0063] In this way, the detection process to be applied is set for all measurement points in the frame. Then, the control unit 120 detects object peaks from the light receiving signals of each measurement point using the set detection process, and performs distance calculation. In this way, a distance map of the frame is obtained. The timing at which the detection process is set by the switching control unit 121 and the distance calculation is performed by the control unit 120 is arbitrary. For example, it may be performed for each frame, or may be performed for each predetermined number of frames. In addition, the timing (unit) at which the detection process is set by the switching control unit 121 and the distance calculation is performed by the control unit 120 may be different.

[0064] The control unit 120 may perform peak detection by the second detection process on the entire light receiving signal of the measurement point where the second detection process is set, or may perform peak detection by the second detection process on only a part of the light receiving signal. In the latter case, specifically, the control unit 120 performs the second detection process from the emission of the pulsed light until a predetermined time has elapsed, and performs peak detection by the first detection process on the remaining part of the light receiving signal. This is because if a sufficient amount of time has elapsed since the emission, the detection of the object peak is unlikely to be affected by the internal reflection peak.

[0065] The switching control unit 121 may generate a saturation time map using saturation times corresponding to a plurality of emission directions or the amount of change in the saturation time from the initial value instead of the internal reflection light intensity map, and set the second detection process for points where the saturation time is equal to or greater than a predetermined value D. Even in this case, as described above, the control unit 120 may perform peak detection by the second detection process for the entire light receiving signal of the measurement point where the second detection process is set, or may perform peak detection by the second detection process only for a part of the signal. In the internal reflection light intensity map and the saturation time map, distortion of the image may occur due to the trajectory of the movable mirror 16 and the effect of the optical lens. Since such distortion is known, a process of correcting each map using a predetermined correction parameter may be performed. In that case, the outer shape of the map may not be rectangular. Alternatively, the outer shape of the map may remain rectangular, and a process of correcting distortion of the projected object, attached matter, etc. may be performed as necessary.

[0066] According to the distance measuring device 10 of this embodiment, the same actions and effects as those of the distance measuring device 10 of the first embodiment can be obtained.

[0067] Although the embodiments of the present invention have been described above with reference to the drawings, these are merely examples of the present invention, and various configurations other than those described above may also be adopted. For example, in the sequence diagrams and flow charts used in the above description, multiple steps (processing) are described in order, but the order of execution of the steps performed in each embodiment is not limited to the order described. In each embodiment, the order of the steps shown in the drawings may be changed to the extent that does not cause any problems in terms of content. In addition, the above-mentioned embodiments may be combined to the extent that the contents are not contradictory. Below, examples of reference forms are given. 1. A distance measuring device that emits light through a transparent member and detects reflected light from an object, a light receiving unit that receives internally reflected light including light reflected by the transparent member and light reflected from the object; A distance measuring device comprising: a switching control unit that switches the detection process of the reflected light from the object using the result of receiving the internal reflected light by the light receiving unit. 2. In the distance measuring device according to claim 1, the switching control unit switches, as the detection process, between a first detection process and a second detection process; the first detection process is a detection process based on a level of the light receiving signal output from the light receiving unit relative to a reference level, The second detection process is a detection process based on a gradient of a level of the light receiving signal output from the light receiving unit. Ranging device. 3. In the distance measuring device according to 2., The switching control unit performs switching so that the second detection process is performed until the light reception signal steadily returns to the reference level after the internal reflection light is received, and the first detection process is performed otherwise. Ranging device. 4. In the distance measuring device according to any one of 1. to 3., The switching control unit switches the detection process using the intensity of the internally reflected light in the light receiving result. Ranging device. 5. In the distance measuring device according to 4., The switching control unit is identifying a deposition region corresponding to a region where a deposition is present on the transparent member using a distribution of the results of receiving the internally reflected light in a plurality of light emission directions; The detection process is switched for each emission direction based on the position within the attachment region. Ranging device.

[0068] This application claims priority based on Japanese Patent Application No. 2021-187618, filed on November 18, 2021, the disclosure of which is incorporated herein in its entirety. [Explanation of symbols]

[0069] 10 Ranging device 14 Light source 16 Movable mirror 18 Photodetector 20 Transparent material 30 Objects 80 Integrated Circuits 120 Control section 121 Switching control section 140 Light emitting part 141 Drive circuit 160 Scanning Range 163 Drive circuit 164 Movable reflector 180 Light receiving section 181 Detection circuit

Claims

1. A distance measuring device that emits light through a transparent member and detects reflected light from an object, a light receiving unit that receives internally reflected light including light reflected by the transparent member and light reflected from the object; A distance measuring device comprising: a switching control unit that switches the detection process of reflected light from the object using the result of determining whether the internal reflected light receiving signal by the light receiving unit is saturated.

2. 2. The distance measuring device according to claim 1, the switching control unit switches, as the detection process, between a first detection process and a second detection process; the first detection process is a detection process based on a level of the light receiving signal output from the light receiving unit with respect to a reference level, The second detection process is a detection process based on a gradient of a level of the light receiving signal output from the light receiving unit. Ranging device.

3. 3. The distance measuring device according to claim 2, The switching control unit performs switching so that, after receiving the internally reflected light, the second detection process is performed during a saturation period of the received light signal, and the first detection process is performed otherwise. Ranging device.

4. In the distance measuring device according to claim 3, The saturation period is the period until the light receiving signal steadily returns to the reference level. Ranging device.

5. The distance measuring device according to any one of claims 1 to 4, The switching control unit switches the detection process using an intensity of the internally reflected light in a light receiving result by the light receiving unit. Ranging device.

6. 6. The distance measuring device according to claim 5, The switching control unit is identifying a deposition region corresponding to a region where a deposition is present on the transparent member using a distribution of the results of receiving the internally reflected light in a plurality of light emission directions; The detection process is switched for each emission direction based on the position within the attachment region. Ranging device.

Images