Laser ranging device, laser ranging method, and program

Abstract

Provided are a compact laser ranging device, a laser ranging method and a program with which it is possible to perform ranging that is robust with respect to a change in the distance to a measurement target object. The laser ranging device comprises: a laser light source that causes FMCW-type first laser light to oscillate; an intensity modulator for periodically modulating the intensity of the first laser light to generate pulsed second laser light; a first distance measuring instrument (F4) for detecting a beat frequency included in interference light, and acquiring first distance information to a measurement target object on the basis of the beat frequency; and a second distance measuring instrument (F5) for measuring a round-trip time of a pulse component to the measurement target object, and acquiring second distance information to the measurement target object on the basis of the round-trip time.

Description

Laser distance measuring device, laser distance measuring method, and program

[0001] The present invention relates to a laser distance measuring device, a laser distance measuring method, and a program.

[0002] In recent years, inspections of structural damage and deterioration over time are often performed by measuring the structure's shape using LiDAR (Light Detection and Raging). There are various LiDAR methods that differ in the distance measurement they use. For example, there are Time of Flight (ToF) LiDAR and Frequency Modulated Continuous Wave (FMCW) LiDAR.

[0003] Patent Document 1 mentions a ToF lidar and an FMCW lidar.

[0004] Special table 2017-524918 publication

[0005] Attempts are being made to detect defects known as "floating" by measuring the shape of structures such as bridges and tunnels with lidar. "Floating" here refers to a condition in which cracks form within the concrete, or defects that occurred at the time of construction become interconnected due to vibrations and deformation during use, causing the concrete near the surface of the structure to lose its integrity with the concrete inside. Concrete with floating will peel off if it continues to deteriorate or is subjected to impacts. Therefore, it is important to detect this floating as a damaged area during inspection.

[0006] To detect this lift using a lidar, it is necessary to measure the unevenness of the surface of the structure on the order of 0.1 mm, and a lidar with high measurement accuracy must be used.

[0007] However, the shapes of structures to be measured vary widely, and the distance from the laser ranging device to the structure is not always constant. Depending on the shape of the structure, the distance from the laser ranging device to the structure may change suddenly. Furthermore, for high-precision lidar, the light from the light source must be focused on the surface of the object to be measured from the standpoint of signal-to-noise ratio, which limits the measurable distance range.

[0008] Therefore, if the shape of the structure changes and it goes outside the measurable range of the lidar, it may not be possible to perform measurements.

[0009] It is also possible to provide a separate distance measuring device for high-precision lidar focus adjustment and perform high-precision lidar focus adjustment based on the distance information obtained by that separate distance measuring device. However, providing a separate distance measuring device for focus adjustment in this way would result in the device itself becoming larger, making it difficult to measure small-diameter tunnels and reducing maneuverability.

[0010] The present invention has been made in consideration of the above circumstances, and its purpose is to provide a miniaturized laser distance measuring device, a laser distance measuring method, and a program that can perform robust and accurate measurements despite changes in the distance to the object to be measured.

[0011] In order to achieve the above-mentioned object, a laser distance measuring device of a first aspect of the present invention comprises a laser light source that oscillates a first laser light of the FMCW (Frequency Modulated Continuous Wave) type, an intensity modulator that periodically modulates the intensity of the first laser light to generate a pulsed second laser light, a first distance measuring device that receives a first measurement light obtained from the second laser light and a first reference light obtained from the first laser light to generate interference light, detects a beat frequency contained in the interference light, and acquires first distance information to a measurement object based on the beat frequency, and a second distance measuring device that measures a round-trip time of the pulse component to the measurement object based on information regarding the emission timing of the second laser light from the intensity modulator and a pulse component contained in the first measurement light, and acquires second distance information to the measurement object based on the round-trip time.

[0012] The second aspect of the laser ranging device preferably has a processor in the first aspect, and when first distance information and second distance information are acquired, the processor determines that the first distance information is third distance information to be output.

[0013] In the third aspect of the laser ranging device, preferably, in the second aspect, when first distance information and second distance information are acquired, the processor stores the first distance information in memory as third distance information.

[0014] The laser distance measuring device of the fourth aspect is preferably the first aspect, further comprising a beam splitter that splits the first reference light from the first laser light.

[0015] The laser distance measuring device of the fifth aspect is preferably the same as that of the first aspect, but further comprising a beam splitter that splits the first measurement light reflected by the object to be measured into a second measurement light and a third measurement light, and the second measurement light is incident on the first distance measuring device and the third measurement light is incident on the second distance measuring device.

[0016] The laser distance measuring device of the sixth aspect preferably includes, in the first aspect, a focus adjustment mechanism that adjusts the focus position of the first measurement light and focuses the first measurement light on the surface of the object to be measured, and a processor, and the processor controls the focus adjustment mechanism based on the second distance information.

[0017] The laser distance measuring device of the seventh aspect is preferably the first aspect, wherein the intensity modulator is composed of an acousto-optical element, an LN modulator, or an optical switch.

[0018] The laser distance measuring device of the eighth aspect is preferably the first aspect, wherein the information relating to emission timing is information relating to emission timing of a pulse component of the second laser light.

[0019] A ninth aspect of the laser ranging method includes the steps of: oscillating a first laser light of the FMCW (Frequency Modulated Continuous Wave) type using a laser light source; periodically modulating the intensity of the first laser light to generate a pulsed second laser light using an intensity modulator; generating interference light by applying a first measurement light obtained from the second laser light and a first reference light obtained from the first laser light, detecting a beat frequency contained in the interference light, and acquiring first distance information to the measurement object based on the beat frequency using a first distance measuring device; and measuring a round-trip time of the pulse component to the measurement object based on information related to the emission timing of the second laser light from the intensity modulator and a pulse component contained in the first measurement light, and acquiring second distance information to the measurement object based on the round-trip time using a second distance measuring device.

[0020] A tenth aspect of the program executes the following steps: oscillating a first laser light of the FMCW (Frequency Modulated Continuous Wave) type using a laser light source; periodically modulating the intensity of the first laser light to generate a pulsed second laser light using an intensity modulator; generating interference light by irradiating a first measurement light obtained from the second laser light and a first reference light obtained from the first laser light, detecting a beat frequency contained in the interference light, and acquiring first distance information to the measurement object based on the beat frequency using a first distance measuring device; and measuring a round-trip time of the pulse component to the measurement object based on information related to the emission timing of the second laser light from the intensity modulator and a pulse component contained in the first measurement light, and acquiring second distance information to the measurement object based on the round-trip time using a second distance measuring device.

[0021] According to the present invention, distance is measured using a relatively accurate first distance measuring device and a relatively sensitive second distance measuring device using measurement light emitted from the same laser light source, so that measurements with high measurement accuracy and robustness against changes in distance to the object to be measured can be performed using a compact device.

[0022] FIG. 1 is a conceptual diagram illustrating an inspection device equipped with a laser distance measuring device. FIG. 2 is a conceptual diagram showing functional blocks and laser light in a measurement head. FIG. 3 is a diagram showing a specific configuration example of the measurement head. FIG. 4 is a block diagram showing an example of the hardware configuration of a control device. FIG. 5 is a block diagram showing main functions realized by a processor. FIG. 6 is a flowchart explaining a laser distance measuring method. FIG. 7 is a diagram showing a beat signal. FIG. 8 is a diagram showing a beat signal. FIG. 9 is a diagram showing an example of the storage configuration of table data.

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a laser distance measuring device, a laser distance measuring method, and a program according to the present invention will now be described with reference to the accompanying drawings.

[0024] <Inspection Device> FIG. 1 is a conceptual diagram illustrating an inspection device equipped with a laser distance measuring device according to one embodiment of the present invention.

[0025] The inspection device 11 measures the three-dimensional shape of the structure, which is the object to be measured, using the laser distance measuring device 1. Then, based on the obtained three-dimensional shape, damage such as lifting is detected. The following explanation will mainly focus on distance measurement for obtaining the three-dimensional shape, and will omit explanations of damage detection, etc.

[0026] The laser ranging device 1 includes a measurement head 5 and a control device 9. The laser ranging device 1 is mounted on a bogie 3. The bogie 3 travels on a track 13 in the positive direction of the Z axis. The laser ranging device 1 mounted on the bogie 3 acquires the distance to the inner wall T (hereinafter simply referred to as wall T) of the structure (tunnel) that is the measurement target. In this manner, by acquiring the distance to wall T and the three-dimensional shape of wall T using the laser ranging device 1, the three-dimensional shape of wall T can be acquired and damage (e.g., lifting) of wall T can be detected. Note that in the following example, a concrete tunnel will be described as a specific example of a structure to be measured, but the measurement target to which the present invention is applicable is not limited to this. For example, metal members or plastic members can also be measurement targets of the present invention.

[0027] Position information of the measuring head 5 is acquired by a position measurement device 112 (not shown in FIG. 1, see FIG. 4).

[0028] 1 also shows the scanning line 15 of the measuring head 5 at a certain position of the carriage 3. In this way, the measuring head 5 uses the scanning unit (scanner) 33 (see FIG. 3) to sequentially change the scan angle (irradiation angle) θ and scan the wall surface T to measure the distances at a large number of measurement points.

[0029] Here, the laser distance measuring device 1 can perform measurements using the FMCW method and measurements using the ToF method using a single measurement head 5, as will be described later. Therefore, when the focus position is aligned with the wall surface T, which is the object to be measured, highly accurate measurements can be performed using the FMCW method, and even when the focus position is not aligned with the object to be measured, highly sensitive measurements can be performed using the ToF method. Furthermore, such FMCW method measurements and ToF method measurements can be performed using a single head 5. Below, a case will be described in which the three-dimensional shape of the wall surface T is obtained using the distances obtained by the laser distance measuring device 1.

[0030] The control device 9 of the laser distance measuring device 1 calculates the distance to a measurement point on each scanning line of the laser light emitted from the measurement head 5. The control device 9 then measures the distance to a large number of measurement points on each scanning line of the laser light emitted from the scanning unit 33 (i.e., on the wall surface T), thereby obtaining three-dimensional measurement data in a polar coordinate system consisting of the irradiation direction of the laser light and the measurement distance (three-dimensional measurement data in the polar coordinate system that indicates the surface shape of the wall surface T). The control device 9 obtains three-dimensional measurement data (three-dimensional shape) that indicates the shape of the wall surface T by converting the three-dimensional measurement data in the polar coordinate system into three-dimensional data in a Cartesian coordinate system.

[0031] Furthermore, by calculating the distance (height from the reference plane) in the normal direction of the three-dimensional measurement data relative to the defined reference plane of the wall surface T, it is possible to detect the amount of protrusion (amount of lift) of the wall surface T. In this way, the lift can be detected with high accuracy from the distance acquired by the laser distance measuring device 1.

[0032] The three-dimensional measurement data measured by the laser ranging device 1 in this example is three-dimensional measurement data (point cloud data) of a large number of measurement points on the wall surface T as described above, but in order to measure the minute uneven shape of the wall surface T, it is considered that this can be done under the following conditions.

[0033] Measurement accuracy: 50 μm Measurement distance: 2 to 7 m Measurement speed: 10 m per area 2 / sec (the speed of the laser light is equivalent to 4000 rpm). The scanning unit 33 of the measurement head 5 continuously emits laser light whose frequency has been modulated over a certain period of time.

[0034] <Laser Distance Meter> Next, the measurement head 5 of the laser distance meter 1 will be described.

[0035] FIG. 2 is a conceptual diagram showing the functional blocks and laser light in the measurement head 5.

[0036] The measurement head 5 mainly has the functions of an FMCW laser oscillation unit F1, an intensity modulation unit F2, a beam splitting unit F3, an FMCW lidar F4, a ToF lidar F5, and a distance information acquisition unit F6.

[0037] The first measurement laser beam PS (first laser beam) emitted from the FMCW laser oscillator F1 enters the intensity modulator F2. The intensity modulator F2 periodically applies intensity modulation to the first measurement laser beam PS to pulse the first measurement laser beam PS, thereby emitting a pulsed second measurement laser beam PP (second laser beam, first measurement beam) toward the wall surface T. The second measurement laser beam (PP) reflected by the wall surface T is split by the beam splitter F3. One of the split second measurement laser beams (PP) (second measurement beam) enters the FMCW lidar F4 (first distance measuring device), and distance information is acquired by the distance information acquirer F6. The other split second measurement laser beam (PP) (third measurement beam) enters the ToF lidar F5 (second distance measuring device), and distance information is acquired by the distance information acquirer F6. Furthermore, based on the distance information acquired by the distance information acquisition unit F6, the focus adjustment unit F7 adjusts the focus of the second measurement laser beam PP so that it is on the measurement surface.

[0038] In this way, in the measurement head 5, distance information is acquired by the FMCW lidar F4, which can measure distance with high accuracy when the focus is on the wall surface T, and the ToF lidar F5, which can measure distance with high sensitivity over a wide range of measurement distances, so that measurements can be made with high accuracy and robust against changes in the measurement distance. Also, in the measurement head 5, the measurement light from one FMCW laser oscillator F1 is split by the beam splitter F3, and distance measurement is performed by the FMCW lidar F4 and the ToF lidar F5, so distance measurement can be performed using a compact device.

[0039] 3 is a diagram showing a specific example of the configuration of the measuring head 5. The measuring head 5 is controlled in an integrated manner by a control device 9 (FIG. 4).

[0040] The measurement head 5 is composed of an FMCW laser light source 21, a first beam splitter 23, an intensity modulator 25, a second beam splitter 27, a third beam splitter 29, a focus adjustment mechanism 31, a scanning unit 33, a photodetector 35, a photodetector 37, and reference mirrors 41 and 43. With this configuration, the measurement head 5 combines the functions of an FMCW distance measuring device (first distance measuring device) and a ToF distance measuring device (second distance measuring device). The FMCW distance measuring device and the ToF distance measuring device will be described below.

[0041] <FMCW LIDAR> The FMCW LIDAR F4 will be described. The FMCW LIDAR F4 can measure the distance to a measurement object with high accuracy. However, in order to perform measurements with the FMCW LIDAR F4, it is necessary to focus on the measurement object with high accuracy. Note that a LIDAR that uses an FSF laser (Frequency-Shifted Feedback Laser), which is a type of FMCW LIDAR F4, is preferably used as the FMCW LIDAR F4.

[0042] The FMCW lidar F4 is composed of a laser light source 21, a first beam splitter 23, an intensity modulator 25, a second beam splitter 27, a third beam splitter 29, a focus adjustment mechanism 31, a scanning unit 33, reference mirrors 41 and 43, and a photodetector 37.

[0043] The laser light source 21 constitutes the FMCW laser oscillation unit F1. The laser light source 21 can be, for example, an FSF laser that has an acousto-optic modulator (AOM) as a frequency shift element inserted inside a resonator and that oscillates by feeding back first-order diffracted light that has been frequency-shifted by the AOM.

[0044] The first laser beam PO emitted from the laser source 21 is split by the first beam splitter 23 into a first measurement laser beam PS and a reference laser beam PR. The reference laser beam PR is reflected by reference mirrors 41 and 43 and enters the second beam splitter 27. On the other hand, the first measurement laser beam PS enters the intensity modulator 25. The reference laser beam PR is not input to the intensity modulator 25. This is because, if the reference laser beam PR is intensity-modulated, there is no guarantee that it will overlap in time with the light reflected by the wall surface T, and there may be cases where the beat frequency cannot be detected by the photodetector 37.

[0045] The intensity modulator 25 constitutes the intensity modulation unit F2. The intensity modulator 25 periodically modulates the intensity of the first measurement laser beam PS to emit a pulsed second measurement laser beam PP. Specifically, the intensity modulator 25 is an acousto-optic modulator (AOM), an LN modulator, or an optical switch.

[0046] The second measurement laser beam PP passes through the second beam splitter 27 and the third beam splitter 29 and enters the focus adjustment mechanism 31. The focus adjustment mechanism 31 has a function of adjusting the focus position of the second measurement laser beam PP and focusing the measurement laser beam on the surface of the measurement object. For example, the focus adjustment mechanism 31 adjusts the focus position of the second measurement laser beam PP by moving a focus lens along the optical axis direction. The amount of movement of the focus adjustment mechanism 31 is input from the control device 9 as a focus operation amount. Furthermore, the specific aspect of the focus adjustment mechanism 31 is not limited to adjusting the focus position by moving the focus lens along the optical axis direction. For example, the focus position may be changed by changing the curvature of the spherical surface of a liquid lens.

[0047] The second measurement laser beam PP passes through the focus adjustment mechanism 31 and then enters the scanning unit 33. The scanning unit 33 changes the emission direction of the second measurement laser beam PP and performs scanning to measure the distance. For example, the scanning unit 33 sequentially irradiates the second measurement laser beam PP along a scanning line 15 ( FIG. 1 ) on the wall surface T. The scanning unit 33 is configured, for example, with a polygon mirror and a motor for rotating the polygon mirror, and the measurement laser beam is incident on the polygon mirror. The scanning unit 33 rotates the polygon mirror around the first axis using the motor, thereby rotating (orbiting) the measurement laser beam reflected by the polygon mirror. This allows the surface of the wall surface T to be scanned with the second measurement laser beam PP. The rotational speed of the polygon mirror around the first axis can be, for example, 4000 rpm.

[0048] The second measurement laser beam (signal beam) (PP) reflected by the surface of the wall T enters the scanning unit 33 as reflected light. Thereafter, the second measurement laser beam (PP) passes through the focus adjustment mechanism 31 and enters the third beam splitter 29. Here, the third beam splitter 29 constitutes the beam splitting unit F3.

[0049] The second measurement laser light (PP) incident on the third beam splitter 29 is split into light that is incident on the second beam splitter 27 and light that is incident on a photodetector 35 for calculating the time of flight.

[0050] The second measurement laser beam (PP) incident on the second beam splitter 27 is combined with the reference laser beam PR by the second beam splitter 27 and output as interference light PA.

[0051] The photodetector 37 photoelectrically converts the interference light PA output from the second beam splitter 27 and detects a beat signal PB (interference signal) indicative of the interference light PA. The beat signal PB detected by the photodetector 37 is input to the FMCW LIDAR processing unit 110B of the control device 9. The FMCW LIDAR processing unit 110B then obtains the distance to the wall surface T based on the beat signal PB. In this way, the measurement head 5 can measure the distance to the wall surface T using the FMCW LIDAR F4.

[0052] <ToF LIDAR> Next, the ToF LIDAR F5 provided in the measurement head 5 will be described.

[0053] The measurement distance range of the ToF LIDAR F5 is longer than that of the FMCW LIDAR F4, but its measurement accuracy is lower than that of the FMCW LIDAR F4. For example, the distance measurement range of the ToF LIDAR F5 is 1 m to 100 m, while the distance measurement range of the FMCW LIDAR F4 is 1 m to 1.5 m or 2 m to 3 m. Therefore, the ToF LIDAR F5 is capable of high-sensitivity distance measurement and can perform alternative measurements when the FMCW LIDAR F4 is unable to achieve a good distance measurement due to poor focus. The ToF LIDAR F5 is composed of a laser light source 21, an intensity modulator 25, a third beam splitter 29, a focus adjustment mechanism 31, a scanning unit 33, and a photodetector 35.

[0054] As described above, the laser light source 21 is an FSF laser. The first laser beam PO emitted from the laser light source 21 is split by the first beam splitter 23 into the first measurement laser beam PS and the reference laser beam PR. The first measurement laser beam PS is then incident on the intensity modulator 25. The intensity modulator 25 periodically modulates the intensity of the first measurement laser beam PS to emit a pulsed second measurement laser beam PP. The second measurement laser beam PP passes through the second beam splitter 27, the third beam splitter 29, and the focus adjustment mechanism 31 and is input to the scanning unit 33. The scanning unit 33 changes the emission direction of the second measurement laser beam PP in accordance with the control of the control device 9. The scanning unit 33 sequentially irradiates the laser beam P along the scanning line 15 ( FIG. 1 ) on the wall surface T. The scanning unit 33 also receives a second measurement laser beam (PP) that is the emitted laser beam reflected by the wall surface T. The second measurement laser beam (PP) is then split by the third beam splitter 29 and detected by the photodetector 35.

[0055] The photodetector 35 detects the second measurement laser beam (PP) and outputs a detection signal. The photodetector 35 also receives an RF (Radio Frequency) signal PQ from the intensity modulator 25 to obtain information about the emission timing of the pulse component of the second measurement laser beam PP.

[0056] The ToF LIDAR processing unit 110C (FIG. 4) implemented by the processor 110 in the control device 9 processes the detection signal output from the photodetector 35 by executing a program stored in the memory 120. Specifically, the ToF LIDAR processing unit 110C outputs the distance to the wall surface T based on emission timing information obtained from the RF signal PQ and a detection signal indicating the intensity of the light received by the photodetector 35. In this way, the measurement head 5 can measure the distance to the wall surface T using the ToF LIDAR F5.

[0057] <Controller> Next, the controller 9 will be described. The controller 9 is configured by, for example, a computer or a microcomputer. The controller 9 controls the measuring head 5 and realizes measurement of the distance to the wall surface T.

[0058] Fig. 4 is a block diagram showing an example of the hardware configuration of the control device 9. Fig. 5 is a block diagram showing main functions realized by the processor 110. The processor 110 achieves the functions shown in Fig. 5 by executing a dedicated program stored in the memory 120.

[0059] The control device 9 includes a processor 110 , a memory 120 , a display 130 , an input / output interface 140 , and an operation unit 150 .

[0060] The processor 110 is composed of a CPU (Central Processing Unit) and the like, and controls the overall operations of each unit of the control device 9, as well as controlling the distance measurement of the laser ranging device 1. As shown in Fig. 5, the processor 110 is composed of a laser irradiation control unit 110A, an FMCW LIDAR processing unit 110B, a ToF LIDAR processing unit 110C, a table data updating unit 110D, a table data reference unit 110E, a focus control unit 110F, and a distance information determination unit 110G.

[0061] The memory 120 includes a flash memory, a read-only memory (ROM), a random access memory (RAM), a hard disk drive, etc. The flash memory, ROM, or hard disk drive is a non-volatile memory that stores various programs, including an operating system. The RAM functions as a work area for processing by the processor 110 and temporarily stores programs, etc., stored in the flash memory, etc. The processor 110 may have a portion of the memory 120 (RAM) built in. The memory 120 stores table data D ( FIG. 8 ) that includes position information acquired by the position measurement device 112 and distance information (third distance information) acquired by the FMCW LIDAR F4 or the ToF LIDAR F5.

[0062] The display 130 displays images under the control of the processor 110. The display 130 is also used as part of a GUI (Graphical User Interface) when various types of information are received from the operation unit 150.

[0063] The input / output interface 140 includes a connection unit that can be connected to an external device and a communication unit that can be connected to a network. The input / output interface 140 can connect to the external device and the network via a wired or wireless connection. For example, the input / output interface 140 is connected to the position measurement device 112.

[0064] Here, the position measurement device 112 measures the position information of the bogie 3. Specifically, the position measurement device 112 measures the travel distance of the bogie 3, and the travel speed and elapsed time of the bogie 3, thereby measuring the position information of the bogie 3. For example, the bogie 3 has a rotation speed measurement sensor on its wheel, and measures the travel distance or travel speed of the bogie 3 based on the number of rotations of the wheel obtained from the rotation speed measurement sensor. Note that the acquisition of the position information by the position measurement device 112 is not limited to the above example, and the position information may be acquired by other methods. For example, the position measurement device 112 may acquire the position information using a global positioning system (GPS).

[0065] The operation unit 150 includes a pointing device such as a mouse, a keyboard, and the like, and functions as part of a GUI that accepts input of various information and instructions by user operation.

[0066] <Laser Distance Measuring Method> Next, a laser distance measuring method using the laser distance measuring device 1 will be described.

[0067] 6 is a flowchart illustrating a laser distance measuring method using the laser distance measuring device 1. The laser distance measuring method is performed by the processor 110 of the laser distance measuring device 1 executing a dedicated program.

[0068] Fig. 6A is a flow diagram showing a laser irradiation step, Fig. 6B is a flow diagram showing a distance information acquisition step, and Fig. 6C is a flow diagram showing a focus adjustment step.

[0069] The laser irradiation step shown in FIG. 6A will be described.

[0070] First, laser irradiation control unit 110A causes laser light source 21 to emit first laser beam PO (FMCW laser beam) (step S_A01). Then, first beam splitter 23 splits first measurement laser beam PS and reference laser beam PR. Then, intensity modulator 25 intensity-modulates first measurement laser beam PS, and pulsed second measurement laser beam PP is emitted from intensity modulator 25 (step S_A02). Then, second measurement laser beam PP passes through second beam splitter 27, third beam splitter 29, focus adjustment mechanism 31, and scanning unit 33 and is emitted toward the measurement object (wall surface T) (step S_A03).

[0071] Next, the flow diagram showing the distance information acquisition process shown in FIG. 6B will be described.

[0072] The scanning unit 33 acquires the second measurement laser beam (PP) reflected by the measurement object, and the acquired second measurement beam (PP) is split by the third beam splitter 29 (denoted as BS in the figure) (step S_B01). One of the split second measurement beams (PP) enters the second beam splitter 27 and is combined with the reference laser beam PR to generate interference beam PA, and a beat signal PB is detected by the photodetector 37. Based on the detected beat signal PB, the FMCW LIDAR processing unit 110B calculates the distance to the measurement object (FMCW distance calculation) (step S_B02). The other split second measurement beam (PP) enters and is detected by the photodetector 35, and the ToF LIDAR processing unit 110C calculates the round-trip time of flight of the second measurement laser beam PP (PP) to the measurement object (ToF distance calculation) (step S_B03). Next, the distance information determiner 110G determines whether the focus is sufficient and the distance can be calculated using the FMCW method (step S_B04). The distance information determiner 110G can determine whether the focus is sufficient and the distance can be calculated using the FMCW method using various methods. For example, the distance information determiner 110G can determine whether the focus is sufficient and the distance can be calculated using the FMCW method based on the peak height of the beat signal PB, the sharpness of the peak of the beat signal PB, or the width of the beat signal PB.

[0073] An example in which the distance information determiner 110G makes a determination based on the height of the peak of the beat signal PB and an example in which the distance information determiner 110G makes a determination based on the sharpness of the peak of the beat signal PB will be described below.

[0074] First, an example in which the distance information determining unit 110G makes a determination based on the height of the peak of the beat signal PB will be described.

[0075] Fig. 7 is a diagram showing the beat signal PB detected by the photodetector 37. In Fig. 7, the vertical axis represents the signal intensity of the beat signal PB, and the horizontal axis represents the frequency, showing the beat signal PB detected by the photodetector 37. Fig. 7 also shows the peak intensity, or peak signal intensity E, of the beat signal PB.

[0076] The distance information determination unit 110G can determine whether the focus is sufficient and distance calculation is possible using the FMCW method based on whether the peak signal strength E is equal to or greater than the threshold SH1. If the peak signal strength E is equal to or greater than the threshold SH1, the distance information determination unit 110G determines that the focus is sufficient and distance calculation is possible using the FMCW method. On the other hand, if the peak signal strength E is less than the threshold SH1, the distance information determination unit 110G determines that the focus is sufficient and distance calculation is not possible using the FMCW method. The threshold SH1 is determined based on the measurement environment, the intensity of the laser light source 21, and the like. The threshold SH1 is also determined by adding an offset to the noise floor NF.

[0077] Next, an example will be described in which the distance information determining unit 110G makes a determination based on the sharpness of the peak of the beat signal PB.

[0078] 8 is a diagram showing the beat signal PB, where the vertical axis represents the signal intensity of the beat signal PB and the horizontal axis represents the frequency, and the beat signal PB detected by the photodetector 37 is shown.

[0079] In Figure 8(A), a sharp peak appears in the beat signal PB. If such a peak is obtained in the beat signal PB, the distance information determiner 110G determines that the focus is sufficient and that the FMCW LIDAR F4 was able to calculate the distance. In Figure 8(B), a sharp peak is not obtained in the beat signal PB. If such a sharp peak is not obtained in the beat signal PB, the distance information determiner 110G determines that the FMCW LIDAR F4 was not able to calculate the distance. Note that a known technique is used to measure the sharpness of the beat signal PB.

[0080] Then, when the focus is sufficiently correct and the distance can be calculated by the FMCW LIDAR F4, the distance information determination unit 110G determines the distance R obtained by the FMCW LIDAR F4 as FMCWOn the other hand, when the focus is sufficiently correct and the distance cannot be calculated by the FMCW method, the distance information determining unit 110G determines the distance R acquired by the ToF LIDAR F5 as the distance information R (third distance information) to be stored in the table data D (step S_B05). TOF is determined as distance information R to be stored in table data D (step S_B06). Thereafter, table data update unit 110D stores distance information R in table data D (step S_B07).

[0081] FIG. 9 is a diagram showing an example of the storage configuration of the table data D.

[0082] 9, the table data D stores the distance information R in association with the scan angle of the scanning unit 33 and the position information of the carriage 3. The table data D also stores the distance information R obtained by the FMCW method. FMCW Is it the distance R obtained by the ToF method? TOF For example, when the scan angle is angle 1, the distance information R is stored in association with the distance R obtained by the FMCW method. FMCW are stored from position 0 to position N. On the other hand, when the scan angle is angle 2, the distance information R is the distance R obtained by the ToF method. TOF are stored from position 0 to position N. Based on the distances of the respective measurement points stored in the table data D, three-dimensional shape data of the wall surface T can be obtained.

[0083] Returning to FIG. 6, the flow chart showing the focus control process shown in FIG. 6(C) will be described.

[0084] The focus control unit 110F determines the current focus position R FOCUS For example, the focus control unit 110F calculates the focus position R from the current position of the focus lens in the focus adjustment mechanism 31 (step S_C01). FOCUS After that, the focus control unit 110F acquires the focus position R FOCUS Specifically, the focus control unit 110F determines whether R FOCUS -RTOF is equal to or greater than a threshold SH2, the focus position R FOCUS The focus control unit 110F determines whether R FOCUS -R TOF If the absolute value of is equal to or greater than the threshold SH2, R FOCUS , R TOF On the other hand, the focus control unit 110F adjusts the focus position based on R FOCUS -R TOF If the absolute value of is less than the threshold SH2, the current focus position R FOCUS While maintaining this, the FMCW laser is emitted and measurement is performed at the next measurement point. The threshold value SH2 is determined based on conditions such as the surface condition of the measurement object, the measurement distance, and the accuracy of the focus adjustment mechanism 31.

[0085] As described above, according to the laser ranging method using the laser ranging device 1, distance is measured using measurement light emitted from the same laser light source 21 by the relatively highly accurate FMCW type lidar F4 and the relatively robust ToF type lidar F5, which is relatively robust to changes in distance, so that measurements with high measurement accuracy and robust to changes in distance to the object to be measured can be performed using a compact device.

[0086] <Others> In the above embodiment, the hardware structure of the processing units (laser irradiation control unit 110A, FMCW LIDAR processing unit 110B, ToF LIDAR processing unit 110C, table data update unit 110D, table data reference unit 110E, focus control unit 110F, and distance information determination unit 110G) that perform various processes is the following various processors. The various processors include a CPU (Central Processing Unit), which is a general-purpose processor that executes software (programs) and functions as various processing units, a programmable logic device (PLD), such as an FPGA (Field Programmable Gate Array), whose circuit configuration can be changed after manufacture, and a dedicated electrical circuit, such as an ASIC (Application Specific Integrated Circuit), which is a processor having a circuit configuration designed specifically for performing specific processes.

[0087] A single processing unit may be configured with one of these various processors, or may be configured with two or more processors of the same or different types (e.g., multiple FPGAs, or a combination of a CPU and an FPGA). Multiple processing units may also be configured with a single processor. Examples of multiple processing units configured with a single processor include: a first configuration, as typified by client or server computers, in which a single processor is configured with a combination of one or more CPUs and software, and this processor functions as multiple processing units; and a second configuration, as typified by system-on-chip (SoC), in which a processor is used to realize the functions of an entire system including multiple processing units on a single IC (Integrated Circuit) chip. In this way, the various processing units are configured with one or more of the above-mentioned various processors as a hardware structure.

[0088] Furthermore, the hardware structure of these various processors is, more specifically, an electric circuit made up of a combination of circuit elements such as semiconductor elements.

[0089] The above-described configurations and functions can be realized by any hardware, software, or a combination of both. For example, the present invention can be applied to a program that causes a computer to execute the above-described processing steps (processing procedures), a computer-readable recording medium (non-transitory recording medium) on which such a program is recorded, or a computer on which such a program can be installed.

[0090] <Additional Notes> The above disclosure includes, for example, the following inventions.

[0091] (Aspect 1) A laser distance measuring device comprising: a laser light source that oscillates a first laser light of the FMCW (Frequency Modulated Continuous Wave) type; an intensity modulator that periodically modulates the intensity of the first laser light to generate a pulsed second laser light; a first distance measuring device that receives a first measurement light obtained from the second laser light and a first reference light obtained from the first laser light to generate interference light, detects a beat frequency contained in the interference light, and acquires first distance information to a measurement object based on the beat frequency; and a second distance measuring device that measures a round-trip time of the pulse component to the measurement object based on information related to the emission timing of the second laser light from the intensity modulator and a pulse component contained in the first measurement light, and acquires second distance information to the measurement object based on the round-trip time.

[0092] (Aspect 2) The laser ranging device according to Aspect 1, further comprising a processor, wherein when first distance information and second distance information are acquired, the processor determines the first distance information as third distance information to be output.

[0093] (Aspect 3) In the laser distance measuring device according to aspect 2, the processor stores the first distance information in the memory as third distance information when the first distance information and the second distance information are acquired.

[0094] (Aspect 4) The laser distance measuring device according to any one of aspects 1 to 3, further comprising a beam splitter that splits the first reference light from the first laser light.

[0095] (Aspect 5) A laser distance measuring device according to any one of aspects 1 to 4, comprising a beam splitter that splits the first measurement light reflected by the object to be measured into the second measurement light and the third measurement light, wherein the second measurement light is incident on the first distance measuring device and the third measurement light is incident on the second distance measuring device.

[0096] (Aspect 6) A laser distance measuring device according to any one of Aspects 1 to 5, comprising: a focus adjustment mechanism that adjusts the focus position of the first measurement light and focuses the first measurement light on a surface of the object to be measured; and a processor, wherein the processor controls the focus adjustment mechanism based on the second distance information.

[0097] (Aspect 7) The laser distance measuring device according to any one of Aspects 1 to 6, wherein the intensity modulator is an acousto-optical element, an LN modulator, or an optical switch.

[0098] (Aspect 8) The laser distance measuring device according to any one of aspects 1 to 7, wherein the information relating to the emission timing is information relating to the emission timing of a pulse component of the second laser light.

[0099] (Aspect 9) A laser ranging method including the steps of: oscillating a first laser light of an FMCW (Frequency Modulated Continuous Wave) system using a laser light source; periodically modulating the intensity of the first laser light to generate a pulsed second laser light using an intensity modulator; generating interference light by inputting a first measurement light obtained from the second laser light and a first reference light obtained from the first laser light, detecting a beat frequency contained in the interference light, and acquiring first distance information to the measurement object based on the beat frequency using a first distance measuring device; and measuring a round-trip time of the pulse component to the measurement object based on information related to the emission timing of the second laser light from the intensity modulator and a pulse component contained in the first measurement light, and acquiring second distance information to the measurement object based on the round-trip time using a second distance measuring device.

[0100] (Aspect 10) A program that executes the steps of: oscillating a first laser light of the FMCW (Frequency Modulated Continuous Wave) type using a laser light source; periodically modulating the intensity of the first laser light to generate a pulsed second laser light using an intensity modulator; generating interference light by inputting a first measurement light obtained from the second laser light and a first reference light obtained from the first laser light, detecting a beat frequency contained in the interference light, and acquiring, based on the beat frequency, first distance information to the measurement object using a first distance measuring device; and measuring a round-trip time of the pulse component to the measurement object based on information related to the emission timing of the second laser light from the intensity modulator and a pulse component contained in the first measurement light, and acquiring, based on the round-trip time, second distance information to the measurement object using a second distance measuring device.

[0101] Although examples of the present invention have been described above, it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the present invention.

[0102] 1: Laser distance measuring device 2: Angle 3: Cart 5: Measuring head 9: Control device 11: Inspection device 13: Track 15: Scanning line 21: Laser light source 23: First beam splitter 25: Intensity modulator 27: Second beam splitter 29: Third beam splitter 31: Focus adjustment mechanism 33: Scanning unit 35: Photodetector 37: Photodetector 41: Reference mirror 43: Reference mirror 110: Processor

Claims

1. a laser light source that emits a first laser beam of an FMCW (Frequency Modulated Continuous Wave) type; an intensity modulator that periodically modulates the intensity of the first laser beam to generate a pulsed second laser beam; a beam splitter that irradiates a measurement object with a first measurement light obtained from the second laser light and splits reflected light obtained from the measurement object into a second measurement light and a third measurement light; a first distance measuring device that receives the second measurement light and a first reference light obtained from the first laser light to generate interference light, detects a beat signal indicating the interference light, and acquires first distance information to a measurement object based on the beat signal; a second distance measuring device that measures a round-trip time of the pulse component to the measurement object based on information about the emission timing of the second laser beam from the intensity modulator and a pulse component included in a third measurement beam, and acquires second distance information to the measurement object based on the round-trip time; A laser distance measuring device comprising:

2. a processor; The processor: determining whether the first distance information was obtained by the first distance measuring device based on the beat signal; If it is determined that the first distance information has been acquired by the first distance measuring device, it determines the first distance information as third distance information to be output; 2. The laser distance measuring device according to claim 1, wherein when it is determined that the first distance information has not been acquired by the first distance measuring device, the second distance information is determined to be the third distance information to be output.

3. 3. The laser ranging device according to claim 2, wherein the processor determines whether the first distance information has been acquired by the first distance measuring device based on the height of the peak of the beat signal, the sharpness of the peak of the beat signal, or the width of the beat signal.

4. The processor: storing the third distance information in a memory; 4. The laser distance measuring device according to claim 2 or 3.

5. 2. The laser distance measuring device according to claim 1, further comprising a beam splitter that splits the first reference light from the first laser light.

6. a focus adjustment mechanism that adjusts a focus position of the first measurement light and focuses the first measurement light on a surface of the measurement object; a processor, The laser distance measuring device according to claim 1 , wherein the processor controls the focus adjustment mechanism based on the second distance information.

7. 2. The laser distance measuring device according to claim 1, wherein the intensity modulator is an acousto-optical element, an LN modulator, or an optical switch.

8. 2. The laser distance measuring device according to claim 1, wherein the information relating to the emission timing is information relating to the emission timing of the pulse component of the second laser light.

9. a step of oscillating a first laser beam of an FMCW (Frequency Modulated Continuous Wave) type by a laser light source; periodically modulating the intensity of the first laser beam to generate a pulsed second laser beam by an intensity modulator; irradiating a measurement object with a first measurement light obtained from the second laser light; splitting the reflected light from the measurement object into a second measurement light and a third measurement light by a beam splitter; generating interference light by the second measurement light and a first reference light obtained from the first laser light, detecting a beat signal indicating the interference light, and acquiring first distance information to a measurement object based on the beat signal by a first distance measuring device; measuring a round-trip time of the pulse component to the measurement object based on information on the emission timing of the second laser beam from the intensity modulator and a pulse component included in the third measurement beam, and acquiring second distance information to the measurement object based on the round-trip time by a second distance measuring device; A laser ranging method comprising:

10. a step of oscillating a first laser beam of an FMCW (Frequency Modulated Continuous Wave) type by a laser light source; periodically modulating the intensity of the first laser beam to generate a pulsed second laser beam by an intensity modulator; a step of irradiating a measurement object with a first measurement light obtained from the second laser light, detecting a beat signal indicating interference light when a second measurement light obtained by splitting reflected light from the measurement object using a beam splitting unit and a first reference light obtained from the first laser light are incident, and acquiring first distance information to the measurement object based on the beat signal using a first distance measuring device; measuring a round-trip time of the pulse component to the measurement object based on information on the emission timing of the second laser light from the intensity modulator and a pulse component included in a third measurement light obtained by splitting the reflected light by the beam splitting unit, and acquiring second distance information to the measurement object based on the round-trip time by a second distance measuring device; A program that executes the following.

11. A non-transitory computer-readable recording medium on which the program according to claim 10 is recorded.