Patent Application
20220082675
The present invention relates to a range finding apparatus and a range finding method, and particularly relates to a time-of-flight range finding technique
A known technique for measuring a distance to an object is a time-of-flight (TOF) method. In a TOF range finding process, a time of flight from when laser light is emitted until the laser light is reflected and returned by and from an object is measured, and the time of flight is multiplied by a speed of light to derive a distance to the object (see Non Patent Literature 1).
In a specific example of the TOF range finding technique, Non Patent Literature 2 discloses a range finding apparatus for measuring, by a TOF method, a position of an underground excavator used in a construction work for building a tube channel such as a sewerage tube without excavating a ground.
In addition, in the techniques described in Non Patent Literatures 1 and 2, there is a need of measuring a time period difference between two signals, that is, a reference signal serving as a reference for measuring a time period and a detection signal obtained by photoelectrically converting light reflected by and returned from a surface of an object to be measured in distance. For example, these two signals are captured by using an analog-to-digital converter (ADC) having two channels. At this time, if the time period difference between the two signals is Δt, a measurement value L of a distance to the object is expressed as cΔt/2. Here, c indicates a speed of light.
Such a known range finding apparatus has a problem that accurate range finding is not possible if a timing difference (skew) between the channels of the ADC fluctuates over time. That is, if there is a deviation (skew) in signal acquisition time period between the channels of the ADC, the measurement value L of a distance will fluctuate accordingly. For example, if the detection signal is delayed by δt with respect to the reference signal due to a skew between the channels of the ADC, a measurement value L′ of a distance to the object is c(Δt+δt)/2, and this results in a difference by cδt/2.
In this case, if the skew δt is a fixed value and the skew δt is measured in advance, when the distance is measured, the skew δt measured in advance is subtracted from a time period difference between the reference signal and the detection signal, and as a result, a correct distance is obtained. However, there is a problem that if the skew δt is different in each signal acquisition, a measurement value of a distance is different in each signal acquisition and the accuracy of the obtained distance is decreased.
NPL1: Koushi Oishi, Mitsuhiko Ota, and Hiroyuki Matsubara, “Measurement of Time of Flight for Plurality of Reflected Light Beams Using FPGA in Laser Radar”, The Institute of Electronics, Information and Communication Engineers, The 2018 IEICE General Conference, Proceedings of Electronics Lecture 2, p. 38, C-12-3, published on Mar. 6, 2018
NPL2: Tooru Kodaira, Shogo Yagi, Kazuo Fujiura, Jiro Mori, and Takeshi Watanabe, “Light Swept Position Measurement System Applying Wavelength Swept Technology”, Optical and Electro-Optical Engineering Contact, Volume 55, No. 8, pp. 18 to 27, published on Aug. 20, 2017
Embodiments of the present invention have been made to resolve the above problems, and an object thereof is to provide a range finding apparatus and a range finding method capable of highly accurately measuring a distance to an object even if a timing difference (skew) between channels of an ADC fluctuates in each signal acquisition.
In order to solve the problems described above, a range finding apparatus according to embodiments of the present invention includes an optical system including a light source that outputs light cyclically modulated in intensity, an optical splitter that splits the light from the light source into two light beams, an optical deflector that deflects one light beam of the two light beams output from the optical splitter to emit the one light beam toward an object to be measured, a mirror arranged near the object to be measured as viewed from the optical deflector, and a photodetector that detects first reflected light and second reflected light resultant from the one light bean emitted from the optical deflector being reflected respectively by the object to be measured and the mirror, and a signal processing device including a first range finding unit that outputs a first distance signal indicating a distance to the object to be measured, where the first distance signal includes a plurality of the first distance signals, based on a time period from when the one light beam is output from the optical splitter until the first reflected light is detected by the photodetector, a second range finding unit that outputs a second distance signal indicating a distance to the mirror, based on a time period from when the one light beam is output from the optical splitter until the second reflected light is detected by the photodetector, and a distance correction unit that corrects the first distance signal, based on the second distance signal, to output a third distance signal indicating a distance to the object to be measured.
Further, in the range finding apparatus according to embodiments of the present invention, the mirror may be disposed at a position different from a position on a line linking the optical deflector and the object to be measured.
Further, in the range finding apparatus according to embodiments of the present invention, the distance correction unit may output information including a value obtained by subtracting the second distance signal from the first distance signal as the third distance signal indicating the distance to the object to be measured.
Further, in the range finding apparatus according to embodiments of the present invention, the first range finding unit may acquire time information corresponding to each of the plurality of first distance signals evaluated, and the signal processing device may include a time period-angle degree conversion unit that converts the time information acquired by the first range finding unit into information about a degree of a deflection angle by the optical deflector and outputs an angle degree-distance signal in which a degree of a deflection angle and a distance are associated.
Further, in the range finding apparatus according to embodiments of the present invention, the first range finding unit may discretely acquire the first distance signal indicating the distance to the object to be measured at a peak time of a light intensity of the light source.
Further, the range finding apparatus according to embodiments of the present invention may include an interpolation unit that interpolates the third distance signal, based on the first distance signal indicating the distance to the object to be measured and being discretely acquired by the first range finding unit.
Further, in the range finding apparatus according to embodiments of the present invention, the light source may be wavelength swept light source in which a wavelength changes with time, and the optical deflector may include a diffraction grating or a prism.
In order to solve the problems described above, a range finding method according to embodiments of the present invention includes outputting, from a light source, light cyclically modulated in intensity, splitting, by an optical splitter, the light from the light source into two light beams, deflecting, by an optical deflector, one light beam of the two light beams output from the optical splitter to emit the one light beam toward an object to be measured, detecting, by a photodetector, first reflected light and second reflected light resultant from the one light beam emitted from the optical deflector being reflected respectively by the object to be measured and a mirror disposed near the object to be measured as viewed from the optical deflector, outputting a first distance signal indicating a distance to the object to be measured, based on a time period from when the one light beam is output from the optical splitter until the first reflected light is detected by the photodetector, outputting a second distance signal indicating a distance to the mirror, based on a time period from when the one light beam is output from the optical splitter until the second reflected light is detected by the photodetector, and correcting the first distance signal, based on the second distance signal to output a third distance signal indicating a distance to the object to be measured.
According to embodiments of the present invention, a first distance signal indicating a distance to an object is corrected by using a second distance signal indicating a distance to a mirror disposed near the object, as viewed from the light source, and thus, even if a time period difference (skew) between channels of an ADC fluctuates in each signal acquisition, it is possible to highly accurately measure the distance to the object.
Embodiments of the present invention will be described in detail below with reference to
As illustrated in
The light source 100, the coupler 101, the circulator 102, the optical deflector 103, the correction mirror 105, the PDr 106, and the PDs 107 configure an optical system provided in the range finding apparatus 1.
The light source 100 emits light cyclically modulated in intensity toward the object 104. Specifically, the light source 100 generates light cyclically modulated in intensity, such as a sinusoidal wave or a pulse signal. Light emitted from the light source 100 is incident on the optical deflector 103 described below.
The coupler 101 divides light emitted from the light source 100 into a reference optical path and an object optical path. One of the light beams divided by the coupler 101 is input to the PDr 106 on the reference optical path, and the other of the light beams enters, with irradiation, the object 104 and the correction mirror 105 via the circulator 102 and the optical deflector 103 on the object optical path.
The PDr 106 detects light output from the light source 100 and converts the light into a first reference signal r1 that is an analog signal. The resultant first reference signal r1 is input to a channel 1 (CH1) of the ADC 108.
The circulator 102 separates light beams traveling in a direction opposite to each other on an optical path. More specifically, the circulator 102 separates light beams being emitted from the coupler 101 and entering, with irradiation, the object 104 and the correction mirror 105, and light reflected by and returned from the object 104 and the correction mirror 105.
The optical deflector 103 emits light with deflecting an optical axis of light incident from the light source 100. More specifically, the optical deflector 103 deflects and emits light emitted from the light source 100 and incident on the optical deflector 103 via the coupler 101 and the circulator 102. Hereinafter, emitting incident light while changing an optical axis of the incident light by the optical deflector 103 refers to “light being deflected”.
The optical deflector 103 deflects light from the light source 100 within a previously set range of a degree of a deflection angle. An example of the optical deflector 103 includes a deflector using a galvanomirror, a polygon mirror, and a potassium tantalate niobate (KTN) crystal. A degree of a deflection angle of the optical deflector 103 can be set to be in a desired range of a degree of a deflection angle through design of a mirror and a control by a drive device (not illustrated) provided in the optical deflector 103.
The optical deflector 103 deflects and emits light from the light source 100 to scan (sweep spatially, that is, deflect) the object 104, the correction mirror 105, and a space around the object 104 and the correction mirror 105, and reflects the light by a surface of the object 104 to be measured in distance and the correction mirror 105. Each time the optical deflector 103 performs scanning with light obtained by emitting, within a set range of a degree of a deflection angle, light from the light source 100, reflected light (first reflected light) from the object 104 and reflected light (second reflected light) from the correction mirror 105 are each detected by the PDs 107 described below.
As illustrated in
The PDs 107 detects reflected light from the object 104 or the correction mirror 105 via the circulator 102 and converts the reflected light into a first detection signal s1 that is an analog signal. The resultant first detection signal s1 is input to a channel 2 (CH2) of the ADC 108.
The ADC 108 includes three channels and converts an analog input signal into a digital signal and outputs the digital signal. A digital signal output and converted by the ADC 108 in each channel is input to the signal processing device 109. The analog first reference signal r1 input to the channel CH1 is converted into a digital, second reference signal r2, and is input to a range finding unit 110 described below. The first detection signal s1 input to the channel CH2 is also converted into a digital, second detection signal s2 and is input to the range finding unit 110. Further, a first angle degree signal θ1, which is an analog signal indicating a degree of a deflection angle of the optical deflector 103, is input to a channel CH3, and is converted into a digital, second angle degree signal θ2 and is input to a time period-angle degree conversion unit 113 described below.
Each of
In
As illustrated in
The signal processing device 109 includes the range finding unit (first range finding unit) 110, a correction mirror range finding unit (second range finding unit) 111, a distance correction unit 112, the time period-angle degree conversion unit 113, and an interpolation unit 114.
Based on the second reference signal r2 and the second detection signal s2 output from the ADC 108, the range finding unit 110 acquires a time of a peak of the second reference signal r2 and measures a distance to the object 104 from the range finding apparatus 1 at that time. In a case where the optical deflector 103 measures the distance within a range of a degree of an angle where light is deflected in a one-dimensional manner, the distance would be measured for each more detailed degree of an angle. In the present embodiment, it is assumed that the distance is measured for each peak of the second reference signal r2. In a case where a distance between peaks is necessary, the interpolation unit 114 described below interpolates the distance between the peaks by using a distance between peak positions to evaluate a more detailed distance to the object 104 from the range finding apparatus 1.
If Tm denotes a cycle of an optical modulation of the light source 100 and Tsw denotes a cycle of scans of the optical deflector 103 as described above, the number of peaks of the second reference signal r2, is expressed as about Np=Tsw/Tm. A time at which the optical deflector 103 starts to deflect light is o, and tn denotes a time of an nth peak counting from time o. A position corresponding to a broken line commonly shown in a waveform of
Hereinafter, data of a distance corresponding to the time tn is particularly referred to as an uncorrected distance signal (first distance signal) Ln. Thus, the range finding unit 110 measures a distance on the basis of both reflected light from the object 104 and reflected light from the correction mirror 105, in each cycle in which the optical deflector 103 performs scanning with light.
Here, in
In the present embodiment, at least Tme−Tms>Tm is required. This is because it is not possible to measure a distance to the correction mirror 105 unless there are at least one peak of the second detection signal s2 and at least one peak of the second reference signal r2 between the times Tms and Tme.
If Tme−Tms≥3Tm, the second detection signal s2 obtained from the reflected light from the correction mirror 105 has three peaks, but the peaks located at the ends, of the three peaks, have a decreased intensity due to an influence that part of the beam does not return from the correction mirror 105 (part of the beam deviates from the correction mirror 105). On the other hand, the peak in the middle of the three peaks is less susceptible to an influence that part of the beam deviates from the correction mirror 105, and is in a signal shape possibly obtained by multiplying a signal having a peak in a cycle Tm by an unimodal window function. In such a case, a position of a peak in an area where an inclination is close to o, such as an area near the peak of the window function is mostly the same as a position of the peak obtained when the window function is not yet applied, but a peak in an area with a larger inclination of the window function is more likely to change in position from the original position.
Thus, if there are three peaks, when the peak in the middle less likely to receive an influence by a peak position misalignment is used, it is possible to more accurately measure the position of the correction mirror 105 than in the case of Tme−Tms<3Tm. As Tme−Tms is larger than Tm, the influence of the peak position misalignment is likely to be smaller, and thus, the position of the correction mirror 105 is more accurately measured.
The correction mirror range finding unit 111 outputs, as a correction value, a distance signal (second distance signal) indicating a distance to the correction mirror 105, evaluated based on a time period from when light is emitted from the coupler 101 until the reflected light reflected by the correction mirror 105 is received by the PDs 107. More specifically, of uncorrected distance signals Ln evaluated by the range finding unit 110, the correction mirror range finding unit 111 evaluates a correction value Lcor used by the distance correction unit 112, based on the second detection signal s2 measured in a time period zone from Tms to Tme during which light is reflected from the correction mirror 105 in
For example, the correction mirror range finding unit 111 may use an average value of uncorrected distance signals Ln in the time period zone from Tms to Tme, as the correction value Lcor. Alternatively, the correction mirror range finding unit 111 may use a value of the uncorrected distance signal Ln at a center time (Tms to Tme)/2 in the time period zone from Tms to Tme, as the correction value Lcor.
Alternatively, the correction mirror range finding unit 111 may acquire a time period zone in which the intensity is not decreased for the uncorrected distance signal Ln, and use an average value of uncorrected distance signals Ln in the time period zone, as the correction value Lcor . A method of acquiring a time period zone in which the intensity is not modulated may include previously selecting a time period zone, and obtaining a peak value in the time period zone from Tms to Tme, and thereafter, selecting a time period zone in which there is a peak in a range of a certain ratio (for example, 90%) or more of the peak value.
The distance correction unit 112 corrects an uncorrected distance signal Ln evaluated by the range finding unit 110, based on the correction value Lcor, and outputs a corrected distance signal (third distance signal) Ln, cor. Specifically, the distance correction unit 112 outputs a result obtained by subtracting the correction value Lcor from the uncorrected distance signal Ln, as the corrected distance signal Ln, cor. For example, the corrected distance signal Ln,cor at time tn is calculated according to Ln−Lcor . A distance obtained according to such a calculation is a distance in which the correction mirror 105 is a reference of the distance (o m).
In another example, the distance correction unit 112 may calculate the corrected distance signal Ln, cor according to Ln−Lcor+Lmirror. Lmirror is mirror is a distance precisely evaluated in advance as a distance to the correction mirror 105. When the distance Lmirror of the correction mirror 105 is evaluated, for example, a large number of correction values Lcor are evaluated in advance and an average value thereof may be used as the distance Lmirror of the correction mirror 105.
A distance to the object 104 evaluated according to such a calculation is a distance relative to a difference in optical path length between the coupler 101 to the PDr 106 and the coupler 101 to the PDs 107 starting from the coupler 101, as illustrated in
Further, if a distance Ldeflector, mirror between the optical deflector 103 and the correction mirror 105 is known in advance, for example by measuring the distance Ldeflector, mirror, a distance to the object 104 from the optical deflector 103 can be evaluated according to Ln−Lcor+Ldeflector, mirror.
The time period-angle degree conversion unit 113 replaces a time at which a peak of the second reference signal r2 acquired by the range finding unit 110 appears, that is, a time corresponding to the corrected distance signal Ln, cor, with a deflection angle. For example, it is assumed that the intensity of the second angle degree signal θ2 at time tn is ξn. The time period-angle degree conversion unit 113 substitutes the intensity ξn of the second angle degree signal θ2 into a previously evaluated conversion curve θ(ξ) shown in
The time period-angle degree conversion unit 113 evaluates deflection angles at all peak times included in the second reference signal r2 to output data of a corrected distance corresponding to each of the deflection angles.
The interpolation unit 114 uses interpolation to evaluate the deflection angle-distance data in which the corrected distance signal Ln, cor and the deflection angle at a degree of a deflection angle (time) included between peaks of the second reference signal r2 are associated. The interpolation unit 114 outputs data of a distance relative to a more detailed deflection angle (time) included between peaks of the second reference signal r2, as interpolated deflection angle-distance data b. Thus, if the interpolation unit 114 is provided, it is possible to evaluate data more densely indicating a distance in terms of time period (degree of an angle).
Hardware Configuration of Signal Processing Device
Next, an example of a hardware configuration of the signal processing device 109 including the above functions will be described with reference to
As illustrated in
The main storage device 193 is realized by a semiconductor memory such as SRAM, DRAM, and ROM. A program used by the processor 192 to perform various types of controls and calculations is previously stored in the main storage device 193. With the processor 192 and the main storage device 193, each function of the signal processing device 109 including the range finding unit 110, the correction mirror range finding unit 111, the distance correction unit 112, the time period-angle degree conversion unit 113, and the interpolation unit 114 illustrated in
The communication interface 194 is an interface circuit for communicating with various external electronic devices via a communication network NW. The signal processing device 109 may deliver, for example, the interpolated deflection angle-distance data to outside via the communication interface 194.
Examples of the communication interface 194 include an interface and an antenna that comply with the radio data communication standards such as LTE, 3G, radio LAN, and Bluetooth (registered trademark). The communication network NW includes, for example, Wide Area Network (WAN), Local Area Network (LAN), the Internet, a dedicated line, a radio base station, and a provider.
The auxiliary storage device 195 includes a readable/writable storage medium, and a drive device for reading and writing various information such as a program and data to and from the storage medium. A semiconductor memory such as a hard disk or flash memory which serves as a storage medium can be used as the auxiliary storage device 195.
The auxiliary storage device 195 includes a program storage area for storing a program used by the signal processing device 109 to perform a range finding process, a correction process, a conversion process, and an interpolation process. Further, the auxiliary storage device 195 may include a backup area and the like for backing up the above-described data, programs, and the like.
The auxiliary storage device 195 stores information about a time period range Tms to Tme in which reflected light from the correction mirror 105 is received by the PDs 107, where the information is used by the correction mirror range finding unit 111. Further, the auxiliary storage device 195 stores a conversion curve used by the time period-angle degree conversion unit 113 for the conversion process.
The input/output device 196 includes an I/O terminal that receives a signal from an external device such as the display device 197 and outputs a signal to an external device.
Note that the signal processing device 109 may be realized by one single computer and also realized by being distributed over a plurality of computers connected to each other through the communication network NW. The processor 192 may be realized by using hardware such as a field-programmable gate array (FPGA), a large scale integration (LSI), or an application specific integrated circuit (ASIC).
Operation of Range Finding Apparatus
Next, an operation of the range finding apparatus 1 according to the present embodiment will be described with reference to a flowchart of
Firstly, the light source 100 outputs light cyclically modulated in intensity, for example, light modulated in intensity by a sinusoidal wave (step S1). The light emitted from the light source 100 is divided into a reference optical path side and an object optical path side by the coupler 101. The light on the reference optical path side is received by the PDr 106 and is photoelectrically converted, and the first reference signal r1 is output. On the other hand, the light on the object optical path side is deflected by the optical deflector 103 via the circulator 102, and a space around the object 104 is scanned with the light in a scanning cycle of Tsw (step S2).
Next, when the light deflected by the optical deflector 103 scans an area within the space once, each of the object 104 and the correction mirror 105 is irradiated with the light, and the reflected light is detected by the PDs 107 via the optical deflector 103 and the circulator 102 (step S3). Note that the correction mirror 105 may be disposed at a position at the maximum deflection angle, for example. Further, the first angle degree signal θ1 indicating a degree of a deflection angle at which the optical deflector 103 deflects light is input to the channel CH3 of the ADC 108.
Thereafter, the ADC 108 converts an analog signal input to the channels CH1, CH2, and CH3 into a digital signal (step S4). More specifically, the analog, first reference signal r1 is input to the channel CH1 of the ADC 108 where the input first reference signal r1 is converted into the digital, second reference signal r2. The analog, first detection signal s1 based on the reflected light from the object 104 and the correction mirror 105 is input to the channel CH2 of the ADC 108 where the input first detection signal s1 is converted into the digital, second detection signal s2. The first angle degree signal θ1 is input to the channel CH3 of the ADC 108 where the input first angle degree signal θ1 is converted into the digital, second angle degree signal θ2.
Next, in the signal processing device 109, the range finding unit 110 evaluates, based on the second reference signal r2 and the second detection signal s2, an uncorrected distance signal Ln and time tn corresponding to Ln (step S5). More specifically, the range finding unit 110 calculates an uncorrected distance signal Ln (
Next, the correction mirror range finding unit 111 evaluates a correction value Lcor for correcting the distance signal Ln evaluated by the range finding unit 110 (step S6). Specifically, as shown in
Next, the distance correction unit 112 uses the correction value Lcor evaluated in step S6 to correct the uncorrected distance signal Ln evaluated by the range finding unit 110 in step S5 (step S7). Specifically, the distance correction unit 112 calculates a corrected distance signal Ln, cor at the time tn according to Ln−Lcor.
After that, the time period-angle degree conversion unit 113 converts the corrected distance signals Ln, cor evaluated in step S7, and outputs deflection angle-distance data a obtained by replacing the peak time of the second reference signal r2 evaluated by the range finding unit 110, that is, time tn corresponding to the corrected distance signal Ln, cor with the deflection angle θn (step S8). More specifically, the time period-angle degree conversion unit 113 reads the conversion curve θ(ξ) shown in
Next, the interpolation unit 114 interpolates a value between peaks of the second reference signal r2, based on the data a in which the deflection angle and the distance are associated, which is evaluated in step S8 (step S9). Thereafter, the interpolation unit 114 outputs interpolated deflection angle-distance data b (step S10).
Next, uncorrected and corrected distances to the object 104 at one time, processed by the signal processing device 109 according to the present embodiment are shown in
In examples of the measurement shown in
If the correction process by the signal processing device 109 according to the present embodiment was performed, as shown in
Further, in
When the average value is set to Lmirror, and the corrected distance signal is calculated by using Ln−Lcor+Lmirror, it is possible to calculate a distance to the object 104 relative to a difference in optical path length between the coupler 101—the PDr 106 and the coupler 101—the PDs 107 starting from the coupler 101 described in
The standard deviation of the uncorrected distances shown in
The average value of the uncorrected distances to the object 104 shown in
As described above, according to the range finding apparatus 1 of the present embodiment, the correction value Lcor is evaluated based on reflected light from the correction mirror 105 to correct the distance signal Ln from the range finding apparatus 1 to the object 104. As a result, even if a timing difference (skew) between the channels of the ADC fluctuates in each signal acquisition, it is possible to highly accurately measure a distance to the object.
In addition, the range finding apparatus 1 according to the present embodiment interpolates distance data between peaks of the reference signal, and thus, it is possible to highly accurately measure a distance to the object.
Although the embodiment of the range finding apparatus and the range finding method of the present invention has been described above, the present disclosure is not limited to the described embodiment, and various types of modification that can be conceived by a person skilled in the art can be made within the scope of the disclosure described in the claims.
For example, in the described embodiment, a specific example is described where in the signal processing device 109, after the time period-angle degree conversion unit 113 converts the corrected distance signal Ln, cor into the deflection angle-distance data a, the interpolation unit 114 performs the interpolation process. However, the interpolation process may be performed before the conversion process by the time period-angle degree conversion unit 113. In this case, the interpolation unit 114 interpolates a value between peaks of the second reference signal r2, based on the corrected distance signal Ln, cor, and thereafter, the time period-angle degree conversion unit 113 will convert a time into a deflection angle.
When the interpolation process is performed before the time-angle degree conversion process, the peak time of the second reference signal r2 acquired in the range finding unit 110 cannot be used directly for time information required in the time period-angle degree conversion unit 113. This is because the number of distances obtained in the range finding unit 110 (equal to the number of times obtained in the range finding unit 110) is different from the number of distances output from the interpolation unit 114. Thus, the interpolation unit 114 uses a peak time of the second reference signal r2 acquired in the range finding unit 110 to calculate a time corresponding to the distance information obtained through the interpolation. The time period-angle degree conversion unit 113 uses the time to convert the time into an angle.
In the embodiment described above, a case is described in which light output from the light source 100 is light cyclically modulated in intensity, such as a sinusoidal wave, and is not light swept in wavelength. However, the light source 100 may be a wavelength swept light source including a function of cyclically modulating the intensity. In this case, a passive optical element such as a transmission type or reflection type diffraction grating or a prism made of a material having a large refractive index dispersion, is employed for the optical deflector 103. In addition, even if the light source 100 is a wavelength swept light source including the function of cyclically modulating the intensity, a spatial light modulator well-known as the optical deflector 103 may be employed.
In this case, a grating constant and the like of the diffraction grating may be designed to deflect light within a desired range of a degree of an angle depending on a wavelength of light of the light source 100, a maximum distance required for measurement, a size of the range finding apparatus 1, and the like. Further, likewise, in selecting a wavelength dispersion and a refractive index of the prism, it is possible to select a material having the refractive index and the wavelength dispersion to deflect light at a desired degree of an angle. In addition, if the wavelength swept light source including a function of cyclically modulating the intensity is employed for the light source 100, a configuration is employed in which the first angle degree signal θ1 is linked with a wavelength of light output from the light source 100.
An advantage obtained when the light source 100 is a wavelength swept light source including a function of cyclically modulating the intensity and the optical deflector 103 is a passive optical element such as a diffraction grating and a prism is that it is possible to eliminate a component requiring a mechanical operation from the optical deflector 103. As a result, for example, if the optical system provided in the range finding apparatus 1 is separated into the optical deflector 103 and the others, a deflector is used as a probe and the others are used as a main body, and the probe and the main body are connected via an optical fiber, the size of the probe can be decreased. Thus, a probe unit may be installed in a narrow location and the like, or a person may easily carry the probe unit to measure a distance. Further, the probe does not include a component involving a mechanical operation, and thus, it is possible to increase resistance to vibration of the probe. As a result, the main body and the probe may be separated to place the main body at a location with a slow vibration, and thus, it is possible to provide an exact measurement even under an environment with a strong vibration.
1 . . . Range finding apparatus
100 . . . Light source
101 . . . Coupler
102 . . . Circulator
103 . . . Optical deflector
104 . . . Object
105 . . . Correction mirror
106 . . . Photodetector PDr
107 . . . Photodetector PDs
108 . . . ADC
109 . . . Signal processing device
110 . . . Range finding unit
111 . . . Correction mirror range finding unit
112 . . . Distance correction unit
113 . . . Time period-angle degree conversion unit
114 . . . Interpolation unit
191 . . . Bus
192 . . . Processor
193 . . . Main storage device
194 . . . Communication interface
195 . . . Auxiliary storage device
196 . . . Input/output device
197 . . . Display device.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-027168 | Feb 2019 | JP | national |
This application is a national phase entry of PCT Application No. PCT/JP2020/004041, filed on Feb. 4, 2020, which claims priority to Japanese Application No., 2019-027168 filed on Feb. 19, 2019, which applications are hereby incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/004041 | 2/4/2020 | WO | 00 |
