Distance measuring device and distance measuring method

Abstract

Provided is a distance measurement device with which it is possible to suppress erroneous measurement of distance. A generation unit (2) generates a plurality of transmission pulses having different frequency offsets for each transmission pulse. A transmission unit (4) repeatedly transmits the transmission pulses generated by the generation unit (2). A reception unit (6) receives reflected pulses resulting from the reflection of each of the transmission pulses by an object of distance measurement. A detection unit (8) detects the frequency offsets of the reflected pulses received by the reception unit (6). A distance calculation unit (10) calculates the distance to the object of distance measurement on the basis of the reception times of the reflected pulses received by the reception unit (6) and the transmission pulse transmission times corresponding to the detected frequency offsets of the reflected pulses. A deactivation processing unit (12) carries out a process such that the distance calculation process is deactivated for a fixed period on the basis of the transmission pulse transmission times.

Description

Technical Field

[0001] The present invention relates to a distance measuring device and a distance measuring method, and particularly to a distance measuring device and a distance measuring method that perform distance measurement by transmitting a pulse and receiving its reflection.

Background Art

[0002] As a method for measuring the distance to a distance measurement target, there is a Time of Flight (ToF) method. In the ToF method, a light pulse modulated toward a distance measurement target is emitted, and the distance to the distance measurement target is calculated by receiving the reflection of the modulated light pulse from the distance measurement target. Here, the light pulse can be transmitted periodically and repeatedly.

[0003] Related to this technology, Patent Document 1 discloses a distance measuring device. The distance measuring device according to Patent Document 1 includes a generation unit, a transmission unit, a reception unit, a detection unit, and a distance calculation unit. The generation unit generates a plurality of transmission pulses in which the intensity of the optical signal changes in a pulse shape. At this time, the generation unit generates a plurality of transmission pulses having different frequency offsets for each transmission pulse. The transmission unit repeatedly transmits the transmission pulses generated by the generation unit. The reception unit receives the reflected pulses obtained by reflecting each transmission pulse from the distance measurement target. The detection unit detects the frequency offset of the reflected pulse received by the reception unit. The distance calculation unit calculates the distance to the distance measurement target based on the reception timing of the reflected pulse received by the reception unit and the transmission timing of the transmission pulse corresponding to the frequency offset detected from the reflected pulse. The distance measuring device according to Patent Document 1 can appropriately perform distance measurement by the above configuration regardless of the distance to the distance measurement target or the transmission cycle of the transmission pulse.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When attempting to miniaturize a distance measuring device, there is a risk that light may leak from the transmission side to the reception side within the device. In this case, there is a risk that incorrect distance measurement may be performed due to the light that has leaked to the reception side. Therefore, there is a risk that accurate distance measurement cannot be performed.

[0006] The object of the present disclosure is to solve such problems, and to provide a distance measuring device and a distance measuring method capable of suppressing incorrect distance measurement.

Means for Solving the Problems

[0007] The distance measuring device according to the present disclosure includes: generating means for generating a plurality of transmission pulses in which the intensity of an optical signal changes in a pulse shape, and having a frequency offset with respect to a reference frequency, which is different for each of the transmission pulses; transmission means for repeatedly transmitting the generated transmission pulses; reception means for receiving a reflection pulse obtained by reflecting the transmission pulse from a distance measurement target; detection means for detecting the frequency offset of the received reflection pulse; and distance calculation means for calculating the distance to the distance measurement target based on the reception timing of the received reflection pulse and the transmission timing of the transmission pulse corresponding to the frequency offset detected from the reflection pulse. The distance measuring device further includes invalidation processing means for performing processing so that distance calculation processing is invalidated for a certain period based on the transmission timing of the transmission pulse.

[0008] In addition, the distance measurement method according to the present disclosure generates a plurality of transmission pulses in which the intensity of an optical signal changes in a pulse shape and which have different frequency offsets with respect to a reference frequency for each of the transmission pulses, repeatedly transmits the generated transmission pulses, receives a reflected pulse obtained by reflecting the transmission pulse from a distance measurement target, detects the frequency offset of the received reflected pulse, and calculates the distance to the distance measurement target based on the reception timing of the received reflected pulse and the transmission timing of the transmission pulse corresponding to the frequency offset detected from the reflected pulse, and performs processing so that distance calculation processing is invalidated for a certain period based on the transmission timing of the transmission pulse.

Effects of the Invention

[0009] According to the present disclosure, it is possible to provide a distance measurement device and a distance measurement method capable of suppressing incorrect distance measurement.

Brief Description of the Drawings

[0010]

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Embodiments for Carrying Out the Invention

[0011] (Outline of Embodiments According to the Present Disclosure) Prior to the description of the embodiments of the present disclosure, an outline of the embodiments according to the present disclosure will be described. FIG. 1 is a diagram showing an outline of the ranging device 1 according to the embodiment of the present disclosure. Further, FIG. 2 is a diagram showing an outline of the ranging method executed by the ranging device 1 according to the embodiment of the present disclosure.

[0012] The ranging device 1 includes a generation unit 2, a transmission unit 4, a reception unit 6, a detection unit 8, a distance calculation unit 10, and an inactivation processing unit 12. The generation unit 2 has a function as generation means. The transmission unit 4 has a function as transmission means. The reception unit 6 has a function as reception means. The detection unit 8 has a function as detection means. The distance calculation unit 10 has a function as distance calculation means. The inactivation processing unit 12 has a function as inactivation processing means. Note that the transmission unit 4 and the reception unit 6 may be physically integrated. Thereby, the ranging device 1 can be miniaturized.

[0013] The generation unit 2 generates a plurality of transmission pulses in which the intensity of the optical signal changes in a pulsed manner. At this time, the generation unit 2 generates a plurality of transmission pulses having different frequency offsets for each transmission pulse (step S12). Here, the frequency offset is a deviation (offset) from a certain reference frequency.

[0014] The transmission unit 4 repeatedly transmits the transmission pulses generated by the generation unit 2 (step S14). The reception unit 6 receives the reflected pulses obtained by reflecting the transmission pulses from the ranging object 90 (step S16). The detection unit 8 detects the frequency offset of the reflected pulses received by the reception unit 6 (step S18).

[0015] Further, the distance calculation unit 10 calculates the distance R to the object to be measured 90 based on the reception timing of the reflected pulse received by the reception unit 6 and the transmission timing of the transmission pulse corresponding to the frequency offset detected from the reflected pulse. On the other hand, the invalidation processing unit 12 performs processing so that the distance calculation processing by the distance calculation unit 10 is invalidated for a certain period based on the transmission timing of the transmission pulse. For example, the invalidation processing unit 12 may perform processing so that the distance calculation processing is invalidated by invalidating the reception-side signal input to the reception side for a certain period from the transmission timing.

[0016] Therefore, when the current time is within a certain period based on the transmission timing (YES in step S20), the invalidation processing unit 12 performs processing for invalidating the distance calculation processing (step S22). On the other hand, when the current time is not within a certain period based on the transmission timing (NO in S20), the distance calculation unit 10 calculates the distance R to the object to be measured 90 (step S24).

[0017] (First Comparative Example) Here, a first comparative example using a general ToF method will be described. FIG. 3 is a diagram for explaining the outline of a method for calculating the distance to the object to be measured 90 using pulses according to the first comparative example. FIG. 3 shows the operating principle of the ToF method. The transmission unit 4 transmits the transmission pulses Plst1 and Plst2 at a transmission period (transmission interval, pulse period) Tp. Here, let the pulse width, which is the width of each transmission pulse, be Tw. When the transmission pulse Plst1 is reflected by the object to be measured 90, the reception unit 6 receives the reflected pulse Plsr1, which is the reflected light. When the transmission pulse Plst2 is reflected by the object to be measured 90, the reception unit 6 receives the reflected pulse Plsr2, which is the reflected light.

[0018] Also, let the time difference between the time when the transmission pulse Plst1 is transmitted and the time when the reflected pulse Plsr1 is received, that is, the flight time of light (pulse), be Td. Also, let the speed of light be c. In this case, the distance R to the distance measurement target 90 is expressed by the following formula 1. (Formula 1) R = c × Td / 2 Thereby, the distance R is calculated by the distance calculation unit 10.

[0019] In the first comparative example shown in FIG. 3, two transmission pulses Plst1 and transmission pulse Plst2 are transmitted at the pulse period Tp, and the reflected pulses Plsr1 and reflected pulse Plsr2, which are the respective reflected lights, are received. Here, if the distance to the distance measurement target 90 is long, the time difference Td may become longer than the pulse period Tp. Also, even when the pulse period Tp is short, the time difference Td may become longer than the pulse period Tp. That is, depending on the distance to the distance measurement target 90 or the pulse period, Td > Tp may occur. In such a case, before the reflected pulse Plsr1 is received, the next transmission pulse Plst2 is transmitted. At this time, if it cannot be specified whether the received reflected pulse Plsr1 is the reflected light of the transmission pulse Plst1 or the reflected light of the transmission pulse Plst2, there is a risk that accurate distance measurement cannot be performed. That is, when distance measurement is performed from the time difference between the transmission time of the transmission pulse Plst2 and the reception time of the reflected pulse Plsr1, a distance shorter than the actual distance to the distance measurement target 90 is calculated. Hereinafter, such problems will be described in detail.

[0020] FIGS. 4 and 5 are diagrams for explaining the problems related to the first comparative example. FIGS. 4 and 5 are timing charts showing the relationship between the transmission pulse and the reflected pulse related to the first comparative example. In the examples shown in FIGS. 4 and 5, it is assumed that the transmission pulses Plst1, Plst2, Plst3 are transmitted at the pulse period Tp. Also, it is assumed that the frequencies of the transmission pulses Plst1, Plst2, Plst3 are the same. Further, in the example shown in FIG. 4, it is assumed that the flight time until the transmission pulse is reflected by the distance measurement target 90 and returns is longer than the pulse period Tp.

[0021] First, a transmission pulse Plst1 is transmitted. After that, after a transmission pulse Plst2 is transmitted, a reflected pulse Plsr1 generated by the transmission pulse Plst1 reflecting off the distance measurement target 90 is received. At this time, in the first comparative example shown in FIG. 4, there is a risk of performing distance measurement using the time difference Tdiff1’ between the transmission timing of the transmission pulse Plst2 and the reception timing of the reflected pulse Plsr1. In this way, if distance measurement is performed using the time difference Tdiff1’, the distance may be calculated incorrectly.

[0022] On the other hand, in the example shown in FIG. 5, assume that the flight time until the transmission pulse reflects off the distance measurement target 90 and returns is shorter than the pulse period Tp. Further, assume that since the transmission pulse Plst1 did not reflect, the reflected pulse Plsr1 of the transmission pulse Plst1 was not received. Also, assume that the transmission pulse Plst2 reflected off the distance measurement target and the reflected pulse Plsr2 was received. In this case, distance measurement is performed using the time difference Tdiff2 between the transmission timing of the transmission pulse Plst2 and the reception timing of the reflected pulse Plsr2. Although this distance measurement process is a correct process, it is indistinguishable from the process shown in FIG. 4.

[0023] To address the problems shown in FIGS. 4 and 5, when it is assumed that the distance to the distance measurement target is long, it is conceivable to increase the pulse period. This can suppress the distance measurement error as shown in FIG. 4. However, if the pulse period is increased, the time from when distance measurement is performed until the next distance measurement is performed becomes long, so there is a risk that the distance measurement speed will decrease. Therefore, since distance measurement cannot be performed at the desired speed, appropriate distance measurement cannot be performed. In contrast, as will be described later, the distance measurement device 50 according to the second comparative example can perform distance measurement without increasing the pulse period.

[0024] (Second Comparative Example) Next, the second comparative example will be described. FIG. 6 is a diagram showing the configuration of the distance measuring device 50 according to the second comparative example. The second comparative example corresponds to the disclosure described in Patent Document 1. The distance measuring device 50 according to the second comparative example includes, as a transmission system module, a frequency offset generator 102, a modulation signal generation unit 104, an optical modulator 106, a light source 108, and an optical transmission unit 122. The frequency offset generator 102, the modulation signal generation unit 104, the optical modulator 106, and the light source 108 constitute a transmission side unit 110. The transmission side unit 110 functions as a pulse generation unit that generates a plurality of transmission pulses having different frequency offsets from each other.

[0025] Further, the distance measuring device 50 according to the second comparative example includes, as a reception system module, an optical reception unit 124, an optical interference system unit 130, a photoelectric conversion unit 132, and an AD converter 134. Further, the distance measuring device 50 according to the second comparative example includes, as a reception system module, band pass filters 140-1 to 140-n, timing extraction units 150-1 to 150-n, and distance calculation units 160-1 to 160-n. Here, n is an integer of 2 or more. Further, hereinafter, when explaining without distinguishing the plurality of band pass filters 140-1 to 140-n and the like, they may be collectively referred to as band pass filters 140 and the like. Note that n indicates the number of frequency offsets. Further, the optical interference system unit 130, the photoelectric conversion unit 132, the AD converter 134, the band pass filter 140, the timing extraction unit 150, and the distance calculation unit 160 constitute a reception side unit 170.

[0026] Also, in the second comparative example, the frequency offsets are f1, f2, ···, fn. Therefore, the band pass filters 140-1 to 140-n respectively correspond to the frequency offsets f1 to fn. Similarly, the timing extraction units 150-1 to 150-n respectively correspond to the frequency offsets f1 to fn. Also, the distance calculation units 160-1 to 160-n respectively correspond to the frequency offsets f1 to fn. Note that each of the above-described components can be realized by some circuit such as a device or an arithmetic circuit. The arithmetic circuit is, for example, an FPGA (field-programmable gate array) or the like.

[0027] The frequency offset generator 102 outputs frequency offset information, which is information indicating a plurality of frequency offsets that are offsets from the reference frequency f0, to the modulation signal generation unit 104. Here, the frequency offset information indicates frequency offsets f1, f2, ···, fn. Note that the frequency offset generator 102 may output frequency offset information indicating the frequency offsets f1, f2, ···, fn to the modulation signal generation unit 104 for each pulse period Tp. That is, the frequency offset generator 102 may output frequency offset information indicating the frequency offset f1, and then, after a time Tp has elapsed, output frequency offset information indicating the frequency offset f2.

[0028] The modulation signal generation unit 104 may generate a modulation signal for generating a transmission pulse according to the frequency offset information received from the frequency offset generator 102. Here, as shown in FIG. 7 described later, the modulation signal is an electrical signal having waveforms corresponding to the frequency offsets f1, f2, ···, fn. The modulation signal generation unit 104 outputs the generated modulation signal to the optical modulator 106.

[0029] Note that the frequency offset generator 102 may output frequency offset information indicating all the frequency offsets f1, f2, ···, fn to the modulation signal generation unit 104. In this case, the modulation signal generation unit 104 may generate modulation signals corresponding to the frequency offsets f1, f2, ···, fn for each pulse period Tp. That is, the modulation signal generation unit 104 may generate a modulation signal indicating the frequency offset f1, and then, after a time Tp has elapsed, generate a modulation signal indicating the frequency offset f2.

[0030] Furthermore, the modulation signal generation unit 104 outputs a measurement start trigger Trgt to the distance calculation unit 160 at the timing when each of the transmission pulses corresponding to the frequency offsets f1, f2, ···, fn is transmitted. Here, the measurement start trigger Trgt indicates the transmission timing of each transmission pulse having each frequency offset. Specifically, the modulation signal generation unit 104 outputs a measurement start trigger Trgt1 to the distance calculation unit 160-1 at the timing when it outputs a modulation signal corresponding to the frequency offset f1. Also, the modulation signal generation unit 104 outputs a measurement start trigger Trgt2 to the distance calculation unit 160-2 at the timing when it outputs a modulation signal corresponding to the frequency offset f2. Similarly hereinafter, the modulation signal generation unit 104 outputs a measurement start trigger Trgtn to the distance calculation unit 160-n at the timing when it outputs a modulation signal corresponding to the frequency offset fn.

[0031] The light source 108 generates an optical signal of a reference frequency f0 as shown in FIG. 7 described later. The optical signal is input to the optical modulator 106 and the optical interference system unit 130. The optical modulator 106 generates a plurality of transmission pulses having different frequency offsets f1, f2, ···, fn using the modulation signal input from the modulation signal generation unit 104 and the optical signal (modulator input signal) input from the light source 108. The optical modulator 106 outputs an optical signal including the generated transmission pulses to the optical transmission unit 122.

[0032] For example, the optical modulator 106 is an AO modulator (acousto-optic modulator). The optical modulator 106 modulates the optical signal (modulator input signal) using the modulation signal. Thereby, the optical modulator 106 generates a plurality of transmission pulses having different frequency offsets.

[0033] FIG. 7 is a diagram for explaining the operation of the optical modulator 106 according to the second comparative example. FIG. 7 shows an example where n = 3, that is, the number of frequency offsets is three. As shown in FIG. 7, the optical signal (modulator input signal) input to the optical modulator 106 is an optical signal having a constant frequency f0. The modulation signal has a pulsed waveform of frequency f1, a pulsed waveform of frequency f2, and a pulsed waveform of frequency f3. Note that the amplitude of the modulation signal is 0 V except for the pulsed waveforms. Each waveform is a sine wave with a width Tw.

[0034] At this time, the optical modulator 106 modulates the optical signal according to the pulsed waveform of the modulation signal and outputs a modulated optical signal (modulator output signal). This modulator output signal corresponds to the transmission pulse. When the optical modulator 106 receives a modulation signal having a pulsed waveform of frequency f1, it modulates the optical signal of frequency f0 so as to shift it by f1 and outputs a pulse of frequency (f0 + f1). This pulse corresponds to the transmission pulse Plst1. When the optical modulator 106 receives a modulation signal having a pulsed waveform of frequency f2, it modulates the optical signal of frequency f0 so as to shift it by f2 and outputs a pulse of frequency (f0 + f2). This pulse corresponds to the transmission pulse Plst2. When the optical modulator 106 receives a modulation signal having a pulsed waveform of frequency f3, it modulates the optical signal of frequency f0 so as to shift it by f3 and outputs a pulse of frequency (f0 + f3). This pulse corresponds to the transmission pulse Plst3. Therefore, the transmission pulse indicates a signal in which the light intensity changes in a pulsed manner. Thus, the transmission pulses Plst1, Plst2, and Plst3 each have different frequency offsets f1, f2, and f3. Here, the broken line in the modulator output signal indicates the light intensity (envelope).

[0035] Note that the modulation signal generation unit 104 may output the measurement start trigger Trgt1 to the distance calculation unit 160-1 at the timing of outputting a modulation signal having a pulsed waveform with a frequency f1. The modulation signal generation unit 104 may output the measurement start trigger Trgt2 to the distance calculation unit 160-2 at the timing of outputting a modulation signal having a pulsed waveform with a frequency f2. The modulation signal generation unit 104 may output the measurement start trigger Trgt3 to the distance calculation unit 160-3 at the timing of outputting a modulation signal having a pulsed waveform with a frequency f3.

[0036] The optical transmission unit 122 transmits (irradiates) an optical signal including a plurality of transmission pulses to the object to be distance-measured 90. The transmission pulses are reflected by the object to be distance-measured 90 and travel toward the distance measuring device 50. The optical reception unit 124 receives an optical signal including a plurality of reflected pulses generated by reflection at the object to be distance-measured 90. Here, the frequencies of the plurality of received reflected pulses are f0 + f1, f0 + f2, ···, f0 + fn. Note that the plurality of transmission pulses do not necessarily need to be irradiated to the same object to be distance-measured 90. Therefore, the round-trip flight time of the transmission pulse Plst1 and the round-trip flight time of the transmission pulse Plst2 may be different from each other.

[0037] The optical interference system unit 130 detects the frequency offset of the reflected pulse (received light) using the optical signal with the frequency f0 from the light source 108 as the reference light. Specifically, the optical interference system unit 130 causes the reference light from the light source 108 and the received light to interfere with each other to detect the beat frequency. Thereby, the optical interference system unit 130 detects the frequency offset of the reflected pulse. For example, the optical interference system unit 130 may be a mixer using an optical coupler. Further, for example, the optical interference system unit 130 may be a 90-degree hybrid circuit that causes interference with reference light having two phases of 0 degrees and 90 degrees as the reference light. The optical interference system unit 130 outputs optical signals with frequencies f1, f2, ···, fn corresponding to the frequency offset to the photoelectric conversion unit 132.

[0038] The photoelectric conversion unit 132 converts the optical signal from the optical interference system unit 130 into an electrical signal. The photoelectric conversion unit 132 may be, for example, a photoelectric converter using a photodetector, or a balanced optical receiver using two photodetectors. The AD converter 134 converts the electrical signal, which is an analog signal converted by the photoelectric conversion unit 132, into a digital signal. The electrical signals indicating the frequencies f1, f2, ···, fn converted into digital signals by the AD converter 134 are output to the band-pass filters 140-1 to 140-n.

[0039] The band-pass filter 140 (Band Pass Filter; BPF) has the frequency corresponding to the frequency offset as the center frequency. The center frequencies of the band-pass filters 140-1 to 140-n are the frequencies f1 to fn, respectively. Therefore, the band-pass filters 140-1 to 140-n respectively pass the electrical signals indicating the frequencies f1 to fn. Therefore, the band-pass filter 140 has a function as separation means for separating optical signals for each frequency offset of the reflected pulse detected by the optical interference system unit 130 (detection unit 8).

[0040] The timing extraction unit 150 functions as timing extraction means for extracting the reception timing of the received reflected pulse. The timing extraction units 150-1 to 150-n respectively extract the reception timing of the reflected pulse having the frequency offsets f1 to fn. Then, the timing extraction units 150-1 to 150-n output the measurement stop triggers Trgr1 to Trgrn to the distance calculation units 160-1 to 160-n at the reception timing of the reflected pulse having the frequency offsets f1 to fn, respectively. That is, the measurement stop trigger Trgr indicates the reception timing of the reflected pulse having the frequency offsets f1 to fn, respectively.

[0041] The distance calculation unit 160 calculates the distance R to the distance measurement target 90 using Equation 1 from the time difference between the output timing of the measurement start trigger Trgt (the first trigger signal) and the output timing of the measurement stop trigger Trgr (the second trigger signal). Here, the distance calculation unit 160-1 calculates the distance R related to the transmission pulse having the frequency offset f1 from the time difference between the output timing of the measurement start trigger Trgt1 and the output timing of the measurement stop trigger Trgr1. The distance calculation unit 160-2 calculates the distance R related to the transmission pulse having the frequency offset f2 from the time difference between the output timing of the measurement start trigger Trgt2 and the output timing of the measurement stop trigger Trgr2. Similarly hereinafter, the distance calculation unit 160-n calculates the distance R related to the transmission pulse having the frequency offset fn from the time difference between the output timing of the measurement start trigger Trgtn and the output timing of the measurement stop trigger Trgrn.

[0042] Note that the plurality of frequency offsets may be predetermined frequencies at equal intervals, such as f1 = +100 MHz, f2 = +200 MHz, f3 = +300 MHz. On the other hand, in order to avoid characteristic deterioration of a specific frequency due to the characteristics of the distance measurement device or the like, for example, the frequency offset of +200 MHz may not be available. In such a case, they may be predetermined frequencies that are not at equal intervals, such as f1 = +100 MHz, f2 = +350 MHz, f3 = +270 MHz.

[0043] FIG. 8 is a timing chart showing the relationship between the transmission pulse and the reflected pulse according to the second comparative example. In the example shown in FIG. 8, it is assumed that the transmission pulses Plst1 and Plst2 are transmitted at the pulse period Tp. Further, in the example shown in FIG. 8, it is assumed that the flight time until the transmission pulse is reflected by the distance measurement target 90 and returns is shorter than the pulse period Tp.

[0044] First, a transmission pulse Plst1 having a frequency offset f1 is transmitted. At this transmission timing, a measurement start trigger Trgt1 is output to the distance calculation unit 160-1. Then, before the transmission pulse Plst2 is transmitted, a reflected pulse Plsr1 having a frequency offset f1 is received. At this reception timing, the frequency offset f1 is detected, and the reflected pulse Plsr1 is separated by the band-pass filter 140-1, and a measurement stop trigger Trgr1 is output to the distance calculation unit 160-1 by the timing extraction unit 150-1. Note that the transmitted optical signal is attenuated in the reflection at the distance measurement target 90 and in the flight process of the optical signal. As a result, the envelope waveform of the reflected pulse Plsr1 is dulled compared to the envelope waveform of the transmission pulse Plst1. Therefore, the timing extraction unit 150-1 outputs the measurement stop trigger Trgr1 at the timing when the optical intensity of the reflected pulse Plsr1 exceeds a predetermined threshold value. This is the same for other reflected pulses Plsr2 and the like.

[0045] At this time, in the distance calculation unit 160-1, the transmission pulse Plst1 having the frequency offset f1 and the reflected pulse Plsr1 having the frequency offset f1 are associated with each other. Therefore, in the distance calculation unit 160-1, as indicated by the dashed arrow A1, the measurement start trigger Trgt1 indicating the transmission timing of the transmission pulse Plst1 and the measurement stop trigger Trgr1 indicating the reception timing of the reflected pulse Plsr1 are associated with each other. Thereby, the distance calculation unit 160-1 calculates the distance to the distance measurement target 90 from the time difference Tdiff1 between the measurement start trigger Trgt1 and the measurement stop trigger Trgr1. Therefore, the distance calculation unit 160-1 can appropriately calculate the distance to the distance measurement target 90 from which the transmission pulse Plst1 is reflected.

[0046] Similarly, a transmission pulse Plst2 having a frequency offset f2 is transmitted. At this transmission timing, a measurement start trigger Trgt2 is output to the distance calculation unit 160-2. Then, before a transmission pulse Plst3 (not shown) is transmitted, a reflected pulse Plsr2 having a frequency offset f2 is received. At this reception timing, the frequency offset f2 is detected, the reflected pulse Plsr2 is separated by the band-pass filter 140-2, and a measurement stop trigger Trgr2 is output to the distance calculation unit 160-2 by the timing extraction unit 150-2.

[0047] At this time, in the distance calculation unit 160-2, the transmission pulse Plst2 having the frequency offset f2 and the reflected pulse Plsr2 having the frequency offset f2 are associated with each other. Therefore, in the distance calculation unit 160-2, as indicated by the dashed arrow A2, the measurement start trigger Trgt2 indicating the transmission timing of the transmission pulse Plst2 and the measurement stop trigger Trgr2 indicating the reception timing of the reflected pulse Plsr2 are associated with each other. Thereby, the distance calculation unit 160-2 calculates the distance to the distance measurement target 90 from the time difference Tdiff2 between the measurement start trigger Trgt2 and the measurement stop trigger Trgr2. Therefore, the distance calculation unit 160-2 can appropriately calculate the distance to the distance measurement target 90 from which the transmission pulse Plst2 is reflected.

[0048] FIG. 9 is a timing chart showing the relationship between the transmission pulse and the reflected pulse according to the second comparative example. In the example shown in FIG. 9, it is assumed that the transmission pulses Plst1 and Plst2 are transmitted at a pulse period Tp. Further, in the example shown in FIG. 9, it is assumed that the flight time until the transmission pulse is reflected by the distance measurement target 90 and returns is longer than the pulse period Tp.

[0049] First, a transmission pulse Plst1 having a frequency offset f1 is transmitted. At this transmission timing, a measurement start trigger Trgt1 is output to the distance calculation unit 160-1. Then, after the transmission pulse Plst2 is transmitted, a reflected pulse Plsr1 having a frequency offset f1 is received. At this reception timing, the frequency offset f1 is detected, the reflected pulse Plsr1 is separated by the band-pass filter 140-1, and a measurement stop trigger Trgr1 is output to the distance calculation unit 160-1 by the timing extraction unit 150-1.

[0050] At this time, in the distance calculation unit 160-1, the transmission pulse Plst1 having the frequency offset f1 and the reflected pulse Plsr1 having the frequency offset f1 are associated with each other. Therefore, in the distance calculation unit 160-1, as indicated by the dashed arrow B1, the measurement start trigger Trgt1 indicating the transmission timing of the transmission pulse Plst1 and the measurement stop trigger Trgr1 indicating the reception timing of the reflected pulse Plsr1 are associated with each other. Thereby, the distance calculation unit 160-1 calculates the distance to the distance measurement object 90 from the time difference Tdiff1 between the measurement start trigger Trgt1 and the measurement stop trigger Trgr1. Therefore, even when the flight time of the optical signal is longer than the pulse period, the distance calculation unit 160-1 can appropriately calculate the distance to the distance measurement object 90 from which the transmission pulse Plst1 is reflected.

[0051] Similarly, a transmission pulse Plst2 having a frequency offset f2 is transmitted. At this transmission timing, a measurement start trigger Trgt2 is output to the distance calculation unit 160-2. Then, after the transmission pulse Plst3 (not shown) is transmitted, a reflected pulse Plsr2 having a frequency offset f2 is received. At this reception timing, the frequency offset f2 is detected, the reflected pulse Plsr2 is separated by the band-pass filter 140-2, and a measurement stop trigger Trgr2 is output to the distance calculation unit 160-2 by the timing extraction unit 150-2.

[0052] At this time, in the distance calculation unit 160-2, a transmission pulse Plst2 having a frequency offset f2 and a reflected pulse Plsr2 having a frequency offset f2 are associated with each other. Therefore, in the distance calculation unit 160-2, as indicated by the dashed arrow B2, a measurement start trigger Trgt2 indicating the transmission timing of the transmission pulse Plst2 and a measurement stop trigger Trgr2 indicating the reception timing of the reflected pulse Plsr2 are associated with each other. Thereby, the distance calculation unit 160-2 calculates the distance to the distance measurement object 90 from the time difference Tdiff2 between the measurement start trigger Trgt2 and the measurement stop trigger Trgr2. Therefore, even when the flight time of the optical signal is longer than the pulse period, the distance calculation unit 160-2 can appropriately calculate the distance to the distance measurement object 90 from which the transmission pulse Plst2 is reflected.

[0053] As described above, the distance calculation unit 160 according to the second comparative example associates a measurement start trigger signal related to a transmission pulse having a certain frequency offset with a measurement stop trigger signal related to a reflected pulse having this frequency offset, and calculates the distance R. In other words, in the distance calculation unit 160, a transmission pulse and a reflected pulse having corresponding frequency offsets are associated with each other. Thereby, the distance measurement device 50 according to the second comparative example can appropriately associate a transmission pulse with a reflected pulse that is the reflected light of the transmission pulse reflected by the distance measurement object 90. Therefore, it becomes possible to appropriately perform distance measurement regardless of the distance to the distance measurement object or the transmission period of the transmission pulse.

[0054] In addition, the distance measuring device 50 according to the second comparative example is configured to separate the received optical signal for each frequency offset of the reflection pulse using a band-pass filter 140 (separation means). Since the separation of the optical signal using the band-pass filter 140 can be performed by hardware, it can be performed at a higher speed compared to the processing performed by software. And by the separation by the band-pass filter 140, parallel processing can be performed for each frequency offset. That is, the distance calculation unit 160 can calculate the distance R for each separated signal. Therefore, the distance measuring device 50 according to the second comparative example can perform the distance measurement process at high speed. Also, by separating the received signal for each frequency offset of the reflection pulse, it becomes possible to easily extract the reception timing of each reflection pulse.

[0055] Here, the case of miniaturizing the distance measuring device will be described. FIG. 10 and FIG. 11 are diagrams illustrating configurations in the case of miniaturizing the distance measuring device. FIG. 10 shows an example when the optical transmission unit 122 and the optical reception unit 124 are integrally configured. FIG. 11 shows an example when the optical transmission unit 122 and the optical reception unit 124 are integrated.

[0056] The distance measuring device 50 shown in FIG. 10 includes a transmission-side unit 110, a reception-side unit 170, and an optical transceiver device 120A. The optical transceiver device 120A includes an optical transceiver 121 and a circulator 125. Here, the optical transceiver 121 and the circulator 125 can constitute a transmit-receive coaxial optical system.

[0057] The optical transceiver 121 transmits a transmission pulse (transmission light Op1) and receives (photoreceives) a reflected pulse (received light Op2). It can be said that the optical transceiver 121 is configured by integrating an optical transmission unit 122 and an optical reception unit 124. In this way, by integrating the optical transmission unit 122 and the optical reception unit 124, the miniaturization of the distance measuring device 50 can be achieved. Also, in the optical transceiver 121, the transmission direction and the reception direction of light can be made coaxial with each other. Therefore, by using the optical transceiver 121, it becomes unnecessary to adjust the optical axis between the optical transmission unit and the optical reception unit.

[0058] The circulator 125 is connected to the transmission-side unit 110 (optical modulator 106), the optical transceiver 121, and the reception-side unit 170 (optical interference system unit 130). Specifically, the transmission-side unit 110 is connected to port #1 of the circulator 125, the optical transceiver 121 is connected to port #2, and the reception-side unit 170 is connected to port #3. Here, the circulator 125 is configured to transmit signals only in a determined direction between ports. Specifically, the circulator 125 is configured to transmit a signal (light) input to port #1 to port #2, a signal (light) input to port #2 to port #3, and a signal (light) input to port #3 to port #1. Therefore, the circulator 125 is configured to output the transmission pulse (transmission light Op1) output from the transmission-side unit 110 (optical modulator 106) to the optical transceiver 121. Also, the circulator 125 is configured to output the reflected pulse (received light Op2) photoreceived by the optical transceiver 121 to the reception-side unit 170.

[0059] Here, depending on the circulator 125, its performance may be vulnerable. In that case, signals may be transmitted in a direction different from the transmission of signals in a predetermined direction between the ports described above. Due to such an imperfection (vulnerability of performance) of the circulator 125, for example, a signal (light) input to port #1 may be erroneously transmitted to port #3. In this case, the transmission pulse output from the transmission-side unit 110 (optical modulator 106) may be directly transmitted to the reception-side unit 170 as leakage light Opx1.

[0060] In addition, the transmitted light output from port #2 of the circulator 125 may be reflected at the transmission end (such as a lens) of the optical transceiver 121 instead of the distance measurement target 90. In this case, the transmission-end reflected light Opx2 generated by the reflection of the transmitted light at the transmission end of the optical transceiver 121 may be transmitted to the reception-side unit 170. Thus, in the example shown in FIG. 10, there is a possibility that light may leak from the transmission side to the reception side, such as leakage light Opx1 and transmission-end reflected light Opx2.

[0061] The distance measurement device 50 shown in FIG. 11 includes an optical system integrated circuit 101. The optical system integrated circuit 101 can be realized, for example, by silicon photonics technology. The optical system integrated circuit 101 is a single chip that integrates at least an optical transmission unit 122 and an optical reception unit 124. The optical system integrated circuit 101 may integrate not only the optical transmission unit 122 and the optical reception unit 124 but also the optical modulator 106, the optical interference system unit 130, and the optoelectronic conversion unit 132. By means of the optical system integrated circuit 101, the distance measurement device 50 can be miniaturized. Here, by integrating the optical transmission unit 122 and the optical reception unit 124 into the optical system integrated circuit 101, which is a single miniaturized chip, the light output from the optical reception unit 124 may be directly transmitted to the optical reception unit 124 as leakage light Opx3. Thus, in the example shown in FIG. 11, there is a possibility that light may leak from the transmission side to the reception side, such as leakage light Opx3.

[0062] The above-mentioned leakage light Opx1, transmission-end reflected light Opx2, and leakage light Opx3 are collectively referred to as crosstalk signals. The crosstalk signal is a signal that bypasses the distance measurement target 90 and loops from the transmission side (transmission-side unit 110 or optical transmission unit 122) to the reception side (reception-side unit 170 or optical reception unit 124). That is, the crosstalk signal is a signal that directly loops from the transmission side (transmission-side unit 110 or optical transmission unit 122) to the reception side (reception-side unit 170 or optical reception unit 124).

[0063] Here, since the transmitted optical signal is reflected by the distance measurement target 90 and attenuated in the process of the flight of the optical signal, the power (electric power level) of the reflected pulse can become smaller as the distance to the distance measurement target 90 increases. On the other hand, since the crosstalk signal is a signal transmitted only within the distance measurement device, it may not be attenuated much. Therefore, the power of the crosstalk signal can be much larger (for example, about 1000 times) than the power of the reflected pulse.

[0064] In addition, when a crosstalk signal occurs, the optical interference system unit 130, the photoelectric conversion unit 132, and the AD converter 134 can also process the crosstalk signal in the same way as the reflected pulse. Therefore, the optical interference system unit 130 can detect the frequency offset of the crosstalk signal by using the optical signal of frequency f0 from the light source 108 as the reference light. The optical interference system unit 130 can output optical signals of frequencies f1, f2, ···, fn corresponding to the frequency offset of the crosstalk signal to the photoelectric conversion unit 132.

[0065] Also, the photoelectric conversion unit 132 can convert the optical signal corresponding to the crosstalk signal into an electrical signal that is an analog signal. The AD converter 134 can convert the electrical signal corresponding to the crosstalk signal into a digital signal. The electrical signal corresponding to the crosstalk signal converted into a digital signal by the AD converter 134 can be output to the band-pass filters 140-1 to 140-n. Hereinafter, the problems when the reception-side unit 170 processes the crosstalk signal will be further described.

[0066] FIG. 12 is a timing chart when miniaturizing the distance measuring device in the second comparative example. FIG. 12 is a timing chart showing the relationship between the transmission pulse, the reception-side signal (reflection pulse and crosstalk signal), and the output signal of the band-pass filter 140. Note that FIG. 12 is a diagram for explaining the problem when the reception-side unit 170 processes the crosstalk signal. In the example shown in FIG. 12, it is assumed that transmission pulses Plst1, Plst2, and Plst3 are transmitted at a pulse period Tp. Also, the signal transmitted on the reception side (reception-side unit 170) of the distance measuring device 50 is referred to as the reception-side signal. As will be described later, the reception-side signal may include a reflection pulse (reflected light) and a crosstalk signal.

[0067] First, a transmission pulse Plst1 having a frequency offset f1 is transmitted. At this time, as indicated by arrow C1, a reflection pulse Plsr1 having a frequency offset f1 is received and transmitted by the reception-side unit 170. Further, immediately after the transmission timing of the transmission pulse Plst1, as indicated by arrow C1x, a crosstalk signal Plst1x corresponding to the transmission pulse Plst1 is generated from the transmission side to the reception side. Therefore, the crosstalk signal Plst1x is transmitted by the reception-side unit 170 at the timing immediately after the transmission timing of the transmission pulse Plst1.

[0068] Next, a transmission pulse Plst2 having a frequency offset f2 is transmitted. At this time, as indicated by arrow C2, a reflection pulse Plsr2 having a frequency offset f2 is received and transmitted by the reception-side unit 170. Further, immediately after the transmission timing of the transmission pulse Plst2, as indicated by arrow C2x, a crosstalk signal Plst2x corresponding to the transmission pulse Plst2 is generated from the transmission side to the reception side. Therefore, the crosstalk signal Plst2x is transmitted by the reception-side unit 170 at the timing immediately after the transmission timing of the transmission pulse Plst2.

[0069] Next, a transmission pulse Plst3 having a frequency offset f3 is transmitted. At this time, a reflected pulse Plsr3 (not shown) having a frequency offset f3 is received by the receiving unit 170 and transmitted. Further, immediately after the transmission timing of the transmission pulse Plst3, as indicated by the arrow C3x, a crosstalk signal Plst3x corresponding to the transmission pulse Plst3 is generated from the transmitting side to the receiving side. Therefore, the crosstalk signal Plst3x is transmitted by the receiving unit 170 at the timing immediately after the transmission timing of the transmission pulse Plst3.

[0070] The bandpass filter 140-1 corresponding to the frequency f1 outputs a post-filter signal Plst1x_f1 corresponding to the crosstalk signal Plst1x at the timing when the crosstalk signal Plst1x is generated. The post-filter signal Plst1x_f1 has the frequency f1. Also, the bandpass filter 140-1 outputs a post-filter signal Plsr1_f1 corresponding to the reflected pulse Plsr1 at the timing when the reflected pulse Plsr1 is received. The post-filter signal Plsr1_f1 has the frequency f1.

[0071] Also, the bandpass filter 140-2 corresponding to the frequency f2 outputs a post-filter signal Plst2x_f2 corresponding to the crosstalk signal Plst2x at the timing when the crosstalk signal Plst2x is generated. The post-filter signal Plst2x_f2 has the frequency f2. Also, the bandpass filter 140-2 outputs a post-filter signal Plsr2_f2 corresponding to the reflected pulse Plsr2 at the timing when the reflected pulse Plsr2 is received. The post-filter signal Plsr2_f2 has the frequency f2.

[0072] Note that the harmonic components of the original transmission signal Plst1 may include, although slightly, frequency components other than the frequency offset f1 (such as frequency offsets f2, f3, etc.). Therefore, the harmonics of the crosstalk signal Plst1x may include, although slightly, frequency components other than the frequency offset f1 (such as frequency offsets f2, f3, etc.). Similarly, the harmonic components of the transmission signal Plst2 may include, although slightly, frequency components other than the frequency offset f2 (such as frequency offsets f1, f3, etc.). Therefore, the harmonic components of the crosstalk signal Plst2x may include, although slightly, frequency components other than the frequency offset f2 (such as frequency offsets f1, f3, etc.). The same applies to the crosstalk signal Plst3x. Furthermore, the same applies to the reflection pulses (Plsr1, Plsr2). Therefore, the bandpass filter 140 may not be able to completely separate the crosstalk signal (and the reflection pulse) according to the frequency offset.

[0073] Therefore, the bandpass filter 140-1 can output a post-filter signal Plst2x_f1 corresponding to the crosstalk signal Plst2x at the timing when the crosstalk signal Plst2x occurs. Similarly, the bandpass filter 140-1 can output a post-filter signal Plst3x_f1 corresponding to the crosstalk signal Plst3x at the timing when the crosstalk signal Plst3x occurs. Also, the bandpass filter 140-1 can output a post-filter signal Plsr2_f1 corresponding to the reflection pulse Plsr2 at the timing when the reflection pulse Plsr2 is received. The post-filter signals Plst2x_f1, Plst3x_f1, Plsr2_f1 have the frequency f1.

[0074] Also, the band-pass filter 140-2 can output a post-filter signal Plst1x_f2 corresponding to the crosstalk signal Plst1x at the timing when the crosstalk signal Plst1x occurs. Similarly, the band-pass filter 140-2 can output a post-filter signal Plst3x_f2 corresponding to the crosstalk signal Plst3x at the timing when the crosstalk signal Plst3x occurs. Also, the band-pass filter 140-2 can output a post-filter signal Plsr1_f2 corresponding to the reflection pulse Plsr1 at the timing when the reflection pulse Plsr1 is received. The post-filter signals Plst1x_f2, Plst3x_f2, and Plsr1_f2 have the frequency f2.

[0075] Thus, the band-pass filter 140-1 may output not only the post-filter signal Plsr1_f1 corresponding to the reflection pulse Plsr1 but also post-filter signals corresponding to other signals (such as crosstalk signals and the reflection pulse Plsr2). Therefore, the timing extraction unit 150-1 may also extract the reception timing of signals (received-side signals) other than the reception timing of the reflection pulse Plsr1 that should originally be extracted. That is, the timing extraction unit 150-1 may output a measurement stop trigger corresponding to the crosstalk signal Plst1x or the crosstalk signal Plst2x before outputting the measurement stop trigger Trgr1 corresponding to the reflection pulse Plsr1. That is, the timing extraction unit 150-1 may output a measurement stop trigger corresponding to the post-filter signal Plst1x_f1 or the post-filter signal Plst2x_f1. Therefore, the distance calculation unit 160-1 may perform incorrect distance measurement.

[0076] Similarly, the band-pass filter 140-2 may output not only the post-filter signal Plsr2_f2 corresponding to the reflection pulse Plsr2 but also post-filter signals corresponding to other signals (such as crosstalk signals and the reflection pulse Plsr1). Therefore, the timing extraction unit 150-2 may extract the reception timing of signals (reception-side signals) other than the reception timing of the reflection pulse Plsr2 that should originally be extracted. That is, the timing extraction unit 150-2 may output a measurement stop trigger corresponding to the crosstalk signal Plst1x or the crosstalk signal Plst2x before outputting the measurement stop trigger Trgr2 corresponding to the reflection pulse Plsr2. That is, the timing extraction unit 150-2 may output a measurement stop trigger corresponding to the post-filter signal Plst1x_f2 or the post-filter signal Plst2x_f2. Therefore, the distance calculation unit 160-2 may perform incorrect distance measurement.

[0077] As described above, the band-pass filter 140-1 can output Plsr2_f1 corresponding to the reflection pulse Plsr2. Similarly, the band-pass filter 140-2 can output Plsr1_f2 corresponding to the reflection pulse Plsr1. However, as described above, originally, the power of the reflection pulse is small. Therefore, the post-filter signal due to the reflection pulse corresponding to a frequency offset different from the frequency corresponding to the band-pass filter 140 can be ignored. On the other hand, since the power of the crosstalk signal is large, there is a possibility that it cannot be ignored. Therefore, when miniaturizing the device, there is a possibility that incorrect distance measurement as described above may be performed.

[0078] In contrast, the distance measurement device 1 according to the present embodiment is configured to perform processing so as to invalidate the distance calculation processing by the distance calculation unit 10 for a certain period based on the transmission timing of the transmission pulse. Thereby, the distance measurement device 1 according to the present embodiment can prevent incorrect distance measurement due to the above-described crosstalk signal. Therefore, the distance measurement device 1 according to the present embodiment can suppress incorrect distance measurement even when the size of the device is reduced. Also, the distance measurement method executed by the distance measurement device 1 can suppress incorrect distance measurement.

[0079] (Embodiment 1) Next, Embodiment 1 will be described. FIG. 13 is a diagram showing the configuration of the distance measurement device 100 according to Embodiment 1. The distance measurement device 100 according to Embodiment 1 includes, as a transmission system module, a frequency offset generator 102, a modulation signal generation unit 104, an optical modulator 106, a light source 108, a transmission timing control unit 112, and an optical transmission unit 122. The frequency offset generator 102, the modulation signal generation unit 104, the optical modulator 106, the light source 108, and the transmission timing control unit 112 constitute a transmission side unit 110. The transmission side unit 110 functions as a pulse generation unit that generates a plurality of transmission pulses having different frequency offsets. This transmission side unit 110 (pulse generation unit) corresponds to the generation unit 2 shown in FIG. 1. Also, the optical transmission unit 122 corresponds to the transmission unit 4 shown in FIG. 1. Note that the functions of the frequency offset generator 102, the modulation signal generation unit 104, the optical modulator 106, the light source 108, and the optical transmission unit 122 in the transmission system module are substantially the same as those shown in FIG. 6, and thus the description will be omitted as appropriate.

[0080] In addition, the distance measurement device 100 according to Embodiment 1 includes, as a reception system module, a light reception unit 124, an optical interference system unit 130, a photoelectric conversion unit 132, an AD converter 134, and a disabling processing unit 136. The light reception unit 124 corresponds to the reception unit 6 shown in FIG. 1. Further, the optical interference system unit 130 corresponds to the detection unit 8 shown in FIG. 1. The disabling processing unit 136 corresponds to the disabling processing unit 12 shown in FIG. 1.

[0081] In addition, the light transmission and reception unit 120 is configured by the light transmission unit 122 and the light reception unit 124. The light transmission and reception unit 120 may have the configuration of the light transmission and reception device 120A illustrated in FIG. 10. Alternatively, the light transmission and reception unit 120 (the light transmission unit 122 and the light reception unit 124) may be formed in the optical system integrated circuit 101 as illustrated in FIG. 11. As will be described later in Embodiment 4, the light transmission and reception unit 120 may measure the three-dimensional shape of the distance measurement target 90 while sweeping (scanning) the emission direction of the transmitted light. Thereby, point cloud data indicating the positions of the respective points of the distance measurement target 90 (that is, the three-dimensional shape of the distance measurement target 90) can be acquired.

[0082] In addition, the distance measurement device 100 according to Embodiment 1 includes, as a reception system module, band pass filters 140-1 to 140-n, timing extraction units 150-1 to 150-n, and distance calculation units 160-1 to 160-n. The distance calculation units 160-1 to 160-n correspond to the distance calculation units 10 shown in FIG. 1. Further, the optical interference system unit 130, the photoelectric conversion unit 132, the AD converter 134, the disabling processing unit 136, the band pass filter 140, the timing extraction unit 150, and the distance calculation unit 160 constitute a reception side unit 170. Note that, regarding the functions of the light reception unit 124, the optical interference system unit 130, the photoelectric conversion unit 132, the AD converter 134, the band pass filter 140, the timing extraction unit 150, and the distance calculation unit 160 among the reception system modules, since they are substantially the same as those shown in FIG. 6, the description will be omitted as appropriate.

[0083] The transmission timing control unit 112 has a function as transmission timing control means. The transmission timing control unit 112 can be realized by an arithmetic circuit such as an FPGA or a microcomputer, for example. The transmission timing control unit 112 controls the transmission timing of a transmission pulse (transmission light). Specifically, the transmission timing control unit 112 controls the transmission timing of the transmission pulse according to the transmission interval ΔT from when a transmission pulse is transmitted until the next transmission pulse is transmitted.

[0084] More specifically, the transmission timing control unit 112 generates a transmission trigger that serves as a trigger for transmitting a transmission pulse every time the transmission interval ΔT elapses. Here, in Embodiment 1, the transmission timing control unit 112 generates a transmission trigger that serves as a trigger for transmitting a transmission pulse every time a constant transmission interval ΔT0 elapses. Since there is a transmission timing for each transmission interval ΔT, it can be said that the transmission timing control unit 112 generates a transmission trigger that serves as a trigger for transmitting a transmission pulse at the transmission timing. When the transmission interval ΔT is constant, the transmission interval ΔT (ΔT0) may correspond to the above-described pulse period Tp.

[0085] Then, the transmission timing control unit 112 outputs the transmission trigger to the modulation signal generation unit 104 at the transmission timing of the transmission pulse (that is, every time the transmission interval ΔT elapses). In this case, the modulation signal generation unit 104 may generate a modulation signal at the timing when it receives the transmission trigger. The transmission timing control unit 112 may output the transmission trigger to the frequency offset generator 102 at the transmission timing of the transmission pulse. In this case, the frequency offset generator 102 may output frequency offset information to the modulation signal generation unit 104 at the timing when it receives the transmission trigger. Then, the modulation signal generation unit 104 may generate a modulation signal according to the frequency offset information received from the frequency offset generator 102. In this way, the transmission timing control unit 112 controls the transmission timing of the transmission pulse. Also, the transmission timing control unit 112 outputs the transmission trigger to the invalidation processing unit 136 at the transmission timing of the transmission pulse.

[0086] The inactivation processing unit 136 has a function as inactivation processing means. The inactivation processing unit 136 can be realized by an arithmetic circuit such as an FPGA or a microcomputer, for example. The inactivation processing unit 136 inactivates the digital signal (received-side signal) output from the AD converter 134 for a certain period from the timing when the transmission trigger is received.

[0087] Specifically, the inactivation processing unit 136 performs a masking process on the digital signal output from the AD converter 134 for a certain period from the timing when the transmission trigger is received. For example, the inactivation processing unit 136 may perform processing to set the level (power) of the digital signal output from the AD converter 134 to zero for a certain period from the timing when the transmission trigger is received. Alternatively, the inactivation processing unit 136 may perform processing so as not to output the digital signal output from the AD converter 134 to the subsequent stage (band-pass filter 140) for a certain period from the timing when the transmission trigger is received. Alternatively, the inactivation processing unit 136 may perform processing to stop the subsequent-stage processing for a certain period from the timing when the transmission trigger is received. In other words, the inactivation processing unit 136 may perform processing so that the subsequent-stage processing is executed during a period excluding a certain period from the timing when the transmission trigger is received.

[0088] Note that the "fixed period" is a period determined in advance according to the structure of the distance measuring device 100. The "fixed period" is determined according to the optical path length of the crosstalk signal and the speed of light in the distance measuring device 100. That is, the "fixed period" may correspond to a value obtained by dividing the optical path length of the crosstalk signal by the speed of light. For example, when the optical transceiver unit 120 is configured as in the example of FIG. 10, the "fixed period" may be determined according to the distance from the optical modulator 106 to the circulator 125, the distance from the circulator 125 to the optical interference system unit 130, and the distance from the circulator 125 to the optical transceiver 121. The "fixed period" may be determined according to the longer optical path length among the optical path length of the leakage light Opx1 and the optical path length of the transmission end reflected light Opx2. Further, for example, when the optical transceiver unit 120 is configured as in the example of FIG. 11, the "fixed period" may be determined according to the distance from the optical transmission unit 122 to the optical reception unit 124 in the optical system integrated circuit 101. That is, the "fixed period" may be determined according to the optical path length of the leakage light Opx3.

[0089] FIG. 14 is a timing chart showing the relationship between the transmission pulse, the reception side signal, and the output signal of the band-pass filter 140 according to the first embodiment. In the first embodiment, the transmission pulses are transmitted at a fixed transmission interval ΔT0. That is, in the first embodiment, the transmission interval ΔT0 corresponds to the above-described pulse period Tp. Therefore, at the timing when ΔT0 has elapsed after the transmission pulse Plst1 having the frequency offset f1 is transmitted, the transmission pulse Plst2 having the frequency offset f2 is transmitted. Further, at the timing when ΔT0 has elapsed after the transmission pulse Plst2 having the frequency offset f2 is transmitted, the transmission pulse Plst3 having the frequency offset f3 is transmitted.

[0090] When a transmission pulse Plst1 having a frequency offset f1 is transmitted, a crosstalk signal Plst1x is transmitted by the receiving unit 170 at a timing immediately after the transmission timing of the transmission pulse Plst1. Also, when a transmission pulse Plst1 having a frequency offset f1 is transmitted, a reflection pulse Plsr1 having a frequency offset f1 is transmitted by the receiving unit 170. Note that, also when a transmission pulse Plst2 having a frequency offset f2 is transmitted, a crosstalk signal and a reflection pulse (receiving-side signal) are transmitted by the receiving unit 170 in the same manner as in the case shown in FIG. 12. Also, when a transmission pulse Plst3 having a frequency offset f3 is transmitted, a crosstalk signal and a reflection pulse (receiving-side signal) are transmitted by the receiving unit 170 in the same manner as in the case shown in FIG. 12.

[0091] Here, in the first embodiment, the invalidation processing unit 136 invalidates the receiving-side signal for a certain period Tm from the transmission timing. Here, the crosstalk signal can be transmitted during the certain period Tm. Therefore, as shown in FIG. 14, the invalidation processing unit 136 invalidates the crosstalk signal. As a result, since the band-pass filter 140 does not receive a signal corresponding to the crosstalk signal, it does not output a signal corresponding to the crosstalk signal. Therefore, the output of the band-pass filter 140 can be only that corresponding to the reflection pulse.

[0092] Therefore, the band-pass filter 140-1 outputs a post-filter signal Plsr1_f1 corresponding to the reflection pulse Plsr1 and a post-filter signal Plsr2_f1 corresponding to the reflection pulse Plsr2. Similarly, the band-pass filter 140-2 outputs a post-filter signal Plsr1_f2 corresponding to the reflection pulse Plsr1 and a post-filter signal Plsr2_f2 corresponding to the reflection pulse Plsr2. Therefore, the distance calculation unit 160 is less likely to perform incorrect distance measurement due to the crosstalk signal as described above. Note that, as described above, the powers of the post-filter signal Plsr2_f1 and the post-filter signal Plsr1_f2 are very small. Therefore, the timing extraction unit 150 can ignore the post-filter signal Plsr2_f1 and the post-filter signal Plsr1_f2.

[0093] Through such processing, the distance calculation unit 160-1 can perform distance measurement corresponding to the frequency offset f1 according to the post-filter signal Plsr1_f1 corresponding to the reflection pulse Plsr1. Similarly, the distance calculation unit 160-2 can perform distance measurement corresponding to the frequency offset f2 according to the post-filter signal Plsr2_f2 corresponding to the reflection pulse Plsr2. Therefore, the distance measurement device 100 according to the first embodiment can suppress incorrect distance measurement from being performed even when a crosstalk signal occurs.

[0094] FIG. 15 is a flowchart showing a distance measurement method executed by the distance measurement device 100 according to the first embodiment. The processes of S100 to S106 are executed by the transmission system module, and the processes of S112 to S124 are executed by the reception system module. As described above, the transmission timing control unit 112 generates a transmission trigger and transmits the generated transmission trigger to the modulation signal generation unit 104 and the invalidation processing unit 136 (step S100). The transmission side unit 110 generates transmission pulses having different frequency offsets for each transmission pulse as described above (step S102). The optical transmission unit 122 transmits (irradiates) an optical signal including the transmission pulse generated in the process of S102 to the distance measurement object 90 (step S104).

[0095] Specifically, the optical modulator 106 of the transmission-side unit 110 modulates an optical signal (modulator input signal) using the modulation signal generated by the modulation signal generation unit 104 at the timing when the transmission trigger is transmitted. As a result, the optical modulator 106 generates each of a plurality of transmission pulses having different frequency offsets at the timing when the transmission trigger is transmitted. Further, the optical transmission unit 122 transmits, to the ranging object 90, an optical signal including the transmission pulses generated in the process of S102 at the timing when the transmission trigger is transmitted. Also, by this process, different frequency offsets are applied to each transmission pulse for each timing when the transmission trigger is transmitted. Note that, at the timing of S104, a measurement start trigger Trgt corresponding to each transmission pulse can be output to the distance calculation unit 160.

[0096] The transmission timing control unit 112 determines whether or not a transmission interval ΔT0 has elapsed since the immediately preceding transmission pulse was transmitted (step S106). If the transmission interval ΔT0 has not elapsed (NO in S106), the transmission timing control unit 112 repeats the process of S106 and waits until the transmission interval ΔT0 elapses. Then, when the transmission interval ΔT0 elapses (YES in S106), the processing flow returns to S100. That is, the transmission timing control unit 112 generates a transmission trigger (S100).

[0097] The reception-side unit 170 receives a reception-side signal (step S112). As described above, the reception-side signal may include not only reflected pulses but also crosstalk signals. When the reception-side signal is a reflected pulse, the optical reception unit 124 receives the reflected pulse, and the received reflected pulse is transmitted by the reception-side unit 170. On the other hand, when the reception-side signal is a crosstalk signal, the crosstalk signal loops from the transmission-side unit 110 to the reception-side unit 170 and is transmitted by the reception-side unit 170.

[0098] As described above, the optical interference system unit 130 detects the frequency offset of the received signal (reflection pulse or crosstalk signal) using the reference light (step S114). Here, when it is within a certain period Tm from the transmission timing (YES in step S116), the inactivation processing unit 136 inactivates the received signal as described above (step S118). Thereby, when the received signal is a crosstalk signal, the crosstalk signal can be inactivated.

[0099] On the other hand, when it is not within the certain period Tm from the transmission timing (NO in S116), the inactivation processing unit 136 does not inactivate the received signal. Therefore, in this case, the bandpass filter 140 (separation means) separates the optical signal for each frequency offset as described above (step S120). Thereby, the optical signal is separated for each reflection pulse (received signal).

[0100] As described above, the timing extraction unit 150 extracts the reception timing for each separated reflection pulse and outputs the measurement stop trigger Trgr at the extracted reception timing (step S122). The distance calculation unit 160 calculates the distance R to the distance measurement target 90 using the measurement start trigger Trgt and the measurement stop trigger Trgr as described above (step S124).

[0101] (Embodiment 2) Next, Embodiment 2 will be described. Embodiment 2 is different from Embodiment 1 in that the transmission interval ΔT changes. Note that the configuration of the distance measurement device 100 according to Embodiment 2 is substantially the same as that according to Embodiment 1. Note that the operation of the transmission timing control unit 112 according to Embodiment 2 is different from the operation of the transmission timing control unit 112 according to Embodiment 1. Since the operations of the other components according to Embodiment 2 are substantially the same as those of Embodiment 1, the description thereof is omitted.

[0102] In Embodiment 2, the transmission timing control unit 112 performs control so as to change the transmission interval ΔT. As a result, the transmission timing control unit 112 controls the transmission timing of the transmission pulse. As a result, the transmission interval ΔT can be different for each transmission pulse. That is, the transmission interval ΔT becomes variable. In other words, the transmission timing of the next transmission pulse after a certain transmission pulse is transmitted becomes variable. Further, similar to Embodiment 1, the transmission timing control unit 112 generates a transmission trigger that serves as a trigger for transmitting a transmission pulse every time the transmission interval ΔT elapses. Then, the transmission timing control unit 112 outputs the transmission trigger to the modulation signal generation unit 104 (or the frequency offset generator 102) and the inactivation processing unit 136 every time the transmission interval ΔT elapses.

[0103] The transmission timing control unit 112 may perform control so as to change the transmission interval ΔT at a predetermined cycle as in the first example described later. That is, the transmission interval ΔT does not necessarily have to be always different for each transmission pulse. Further, the transmission timing control unit 112 may perform control so as to change the transmission interval ΔT for each transmission pulse according to a predetermined rule as in the second example described later. Further, the transmission timing control unit 112 may perform control so as to randomly change the transmission interval ΔT for each transmission pulse as in the third example described later. Note that the first example, the second example, and the third example are merely examples, and the transmission timing control unit 112 may change the transmission cycle ΔT by other methods.

[0104] FIG. 16 is a diagram for explaining a first example of a method for changing the transmission interval ΔT according to Embodiment 2. FIG. 16 shows the relationship between the transmission interval ΔT and the number of transmission pulses (elapsed time). As illustrated in FIG. 16, in the first example, the transmission interval ΔT changes every N transmission pulses. Note that N is an integer of 1 or more.

[0105] Specifically, first, the first consecutive N transmission pulses are transmitted at transmission intervals of ΔT = ΔT0 + dT. Then, the next consecutive N transmission pulses are transmitted at transmission intervals of ΔT = ΔT0 - dT. Then, the next consecutive N transmission pulses are transmitted at transmission intervals of ΔT = ΔT0 + dT. Then, the next consecutive N transmission pulses are transmitted at transmission intervals of ΔT = ΔT0 - dT. Similarly hereinafter, the transmission interval ΔT changes.

[0106] That is, the transmission interval ΔT when N consecutive transmission pulses are transmitted is constant (for example, ΔT0 + dT), and the transmission interval ΔT when the next consecutive N transmission pulses are transmitted is constant (for example, ΔT0 - dT). Thus, in the example shown in FIG. 16, the transmission timing control unit 112 changes the transmission interval ΔT every predetermined period, that is, every period corresponding to the period during which N transmission pulses are transmitted. Therefore, in the example shown in FIG. 16, the transmission interval ΔT (transmission timing) is alternately shifted every N transmission pulses.

[0107] Note that the transmission timing control unit 112 may determine the transmission period ΔT according to a function corresponding to the waveform illustrated in FIG. 16 (a function showing the relationship between the number of pulses and the transmission period ΔT). Alternatively, a look-up table showing the correspondence between the order of transmission pulses and the transmission period ΔT as illustrated in FIG. 16 may be prepared in advance. In this case, the transmission timing control unit 112 may determine the transmission period ΔT by referring to the look-up table.

[0108] FIG. 17 is a diagram for explaining a second example of a method for changing the transmission interval ΔT according to Embodiment 2. FIG. 17 shows the relationship between the transmission interval ΔT and the number of transmission pulses (elapsed time). As illustrated in FIG. 17, in the second example, the transmission interval ΔT changes regularly for each transmission pulse. And for every N transmission pulses, the tendency of the change in the transmission interval ΔT changes.

[0109] Specifically, for the first N transmission pulses, the transmission timing control unit 112 gradually increases the transmission period ΔT from ΔT0 - dT to ΔT + dT. For example, the transmission timing control unit 112 increases the transmission period ΔT in proportion to the number of transmission pulses to be transmitted. Then, for the next N transmission pulses, the transmission timing control unit 112 gradually decreases the transmission period ΔT from ΔT0 + dT to ΔT - dT. For example, the transmission timing control unit 112 decreases the transmission period ΔT in proportion to the number of transmission pulses to be transmitted. Then, for the next N transmission pulses, the transmission timing control unit 112 gradually increases the transmission period ΔT from ΔT0 - dT to ΔT + dT. Then, for the next N transmission pulses, the transmission timing control unit 112 gradually decreases the transmission period ΔT from ΔT0 + dT to ΔT - dT. In the same way hereinafter, the transmission interval ΔT changes.

[0110] In this way, in the example shown in FIG. 17, the transmission timing control unit 112 increases or decreases the transmission period ΔT every N transmission pulses. That is, the transmission timing control unit 112 controls so as to change the transmission interval for each transmission pulse according to a predetermined rule. Therefore, in the example shown in FIG. 17, for every N transmission pulses, the transmission interval ΔT (transmission timing) is shifted in a triangular wave shape.

[0111] Note that the transmission timing control unit 112 may determine the transmission period ΔT according to a function corresponding to the waveform illustrated in FIG. 17 (a function showing the relationship between the number of pulses and the transmission period ΔT). Alternatively, a look-up table showing the correspondence between the order of transmission pulses and the transmission period ΔT as illustrated in FIG. 17 may be prepared in advance. In this case, the transmission timing control unit 112 may determine the transmission period ΔT by referring to the look-up table.

[0112] FIG. 18 is a diagram for explaining a third example of a method for changing the transmission interval ΔT according to Embodiment 2. FIG. 18 shows the relationship between the transmission interval ΔT and the number of transmission pulses (elapsed time). As illustrated in FIG. 18, in the third example, the transmission interval ΔT changes randomly for each transmission pulse.

[0113] The transmission timing control unit 112 may determine the transmission period ΔT using a random number generator. That is, the transmission timing control unit 112 may determine the transmission period ΔT using a random number (pseudo-random number) output by inputting the number of transmission pulses transmitted so far to the random number generator. Alternatively, a look-up table showing the correspondence between the order of a predetermined number (for example, 100) of transmission pulses and the randomly set transmission period ΔT may be prepared in advance. In this case, the transmission timing control unit 112 may determine the transmission period ΔT by referring to the look-up table.

[0114] FIGS. 19 and 20 are diagrams for explaining the effects of the features according to Embodiment 2. FIG. 19 is a timing chart showing the relationship between the transmission pulse, the received signal, and the output signal of the band-pass filter 140 according to Embodiment 1. In the example of FIG. 19, the transmission pulses are transmitted at a constant transmission interval ΔT0. Also, in the example of FIG. 19, it is assumed that the flight time Td from when the transmission pulse is transmitted until it is reflected by the distance measurement target 90 and returns to the distance measurement device 100 is substantially constant.

[0115] Here, depending on the distance from the distance measurement device 100 to the distance measurement target 90, the flight time Td of the transmission pulse may approximately coincide with the transmission interval ΔT between that transmission pulse and the next transmission pulse. In this case, as in the example of FIG. 19, the reflected pulse and the crosstalk signal caused by the next transmission pulse may overlap with each other, and both may be transmitted by the receiving unit 170 at the same timing. Hereinafter, such a phenomenon in which the timing at which the reflected pulse is received overlaps with the timing at which crosstalk occurs is referred to as "signal overlap".

[0116] Specifically, in the example of FIG. 19, the timing at which the reflected pulse Plsr1 is received overlaps with the timing at which the crosstalk signal Plst2x generated immediately after the transmission of the transmission pulse Plst2 wraps around to the receiving unit 170. Similarly, the timing at which the reflected pulse Plsr2 is received overlaps with the timing at which the crosstalk signal Plst3x generated immediately after the transmission of the transmission pulse Plst3 wraps around to the receiving unit 170. In this case, if the disabling processing unit 136 disables the received signal for a certain period Tm, there is a possibility that not only the crosstalk signal but also the reflected pulse will be disabled. Therefore, there is a possibility that the distance measurement result cannot be obtained.

[0117] And, for example, in applications where the three-dimensional shape of the distance measurement object is measured by sweeping the emission direction of the transmitted light, when the distance measurement object 90 is relatively large and has a generally flat shape, the distance from the distance measurement device 100 to the distance measurement object 90 may be generally constant. In this case, the flight time Td of the transmission pulse may be generally constant. In this case, if the transmission interval ΔT is constant as in the first embodiment, the above-described signal overlap may occur repeatedly (continuously). In this case, it may happen repeatedly that the distance measurement result cannot be obtained. And when generating point cloud data by performing multiple distance measurements while sweeping the emission direction of the transmitted light, there is a possibility that the data in the point cloud data will decrease.

[0118] FIG. 20 is a timing chart showing the relationship between the transmission pulse, the received signal, and the output signal of the band-pass filter 140 according to the second embodiment. In the example of FIG. 20, the transmission pulse Plst2 is transmitted at a timing when a transmission interval ΔT1 has elapsed from the timing at which the transmission pulse Plst1 is transmitted. On the other hand, the transmission pulse Plst3 is transmitted at a timing when a transmission interval ΔT2 has elapsed from the timing at which the transmission pulse Plst2 is transmitted. Here, ΔT1≠ΔT2.

[0119] In this case, even if the reflected pulse corresponding to a certain transmission pulse overlaps with the crosstalk signal, the possibility that the reflected pulse corresponding to another transmission pulse does not overlap with the crosstalk signal increases. Specifically, the timing at which the reflected pulse Plsr1 is received overlaps with the timing of the intrusion of the crosstalk signal Plst2x generated immediately after the transmission of the transmission pulse Plst2 into the receiving unit 170. On the other hand, the timing at which the reflected pulse Plsr2 is received does not overlap with the timing of the intrusion of the crosstalk signal Plst3x generated immediately after the transmission of the transmission pulse Plst3 into the receiving unit 170. In this case, when the invalidation processing unit 136 invalidates the received signal for a certain period Tm, for the reflected pulse Plsr1, as indicated by arrow A, it is invalidated together with the crosstalk signal Plst2x. On the other hand, for the reflected pulse Plsr2, as indicated by arrow B, even if the crosstalk signal Plst3x is invalidated, it is not invalidated. Therefore, distance measurement can be performed using the post-filter signal Plsr2_f2 corresponding to the reflected pulse Plsr2.

[0120] As described above, in the second embodiment, the transmission timing control unit 112 is configured to change the transmission interval ΔT. Thereby, as described above, it is possible to suppress the occurrence of signal overlap. Therefore, it is possible to suppress the situation where the reflected pulse is invalidated together with the crosstalk signal, and thus it is possible to suppress the situation where the distance measurement result cannot be obtained frequently. Therefore, it is possible to suppress the reduction of the point cloud data.

[0121] Also, as in the first example described above, the transmission timing control unit 112 may be configured to perform control so as to change the transmission interval ΔT at a predetermined cycle. With such a configuration, it is possible to realize the transmission timing control unit 112 according to the second embodiment with a simple circuit.

[0122] Also, as in the second example described above, the transmission timing control unit 112 may be configured to control the transmission interval ΔT to change for each transmission pulse in accordance with a predetermined rule. With such a configuration, it becomes possible to realize the transmission timing control unit 112 according to Embodiment 2 with a simple circuit. Here, in the first example described above, since N consecutive pulses can be transmitted at a constant transmission interval ΔT (=ΔT0±dT), signal superposition as described above may continuously occur while N consecutive pulses are being transmitted. In particular, this may occur when the scanning speed of the distance measuring device 100 (the amount of change per unit time in the transmission direction of the transmission pulse) is slow. In this case, it may continuously happen that no distance measurement result can be obtained.

[0123] On the other hand, since the transmission timing control unit 112 according to the second example changes the transmission interval ΔT for each transmission pulse, it is possible to further suppress the continuous occurrence of signal superposition as compared with the first example. Therefore, it is possible to further suppress the continuous occurrence of the situation where no distance measurement result can be obtained. Therefore, it is possible to further suppress the reduction of the point cloud data.

[0124] Also, as in the third example described above, the transmission timing control unit 112 may be configured to control the transmission interval ΔT to change randomly for each transmission pulse. With such a configuration, it is possible to further suppress the continuous occurrence of signal superposition as compared with the first example and the second example. Therefore, it is possible to further suppress the continuous occurrence of the situation where no distance measurement result can be obtained. That is, when the shape of the distance measurement object 90 corresponds to the triangular wave shape illustrated in FIG. 17, depending on the scanning speed and the distance to the distance measurement object 90, even if the transmission interval ΔT is changed, the flight time Td may change in the same way as the change in the transmission interval ΔT. In this case, there is a possibility that the situation where no distance measurement result can be obtained may continuously occur. That is, also in the second example, the situation where no distance measurement result can be obtained may occur many times, and the point cloud data may be reduced.

[0125] On the other hand, the probability that the random waveform shape illustrated in FIG. 18 corresponds to the shape of the distance measurement target 90 is extremely low. Therefore, by randomly changing the transmission interval ΔT for each transmission pulse, it is possible to further suppress the possibility that the distance measurement result cannot be obtained continuously as compared with the second example. Therefore, it is possible to further suppress the reduction of the point cloud data as compared with the second example.

[0126] FIG. 21 is a flowchart showing a distance measurement method executed by the distance measurement device 100 according to Embodiment 2. The processes of S200 to S208 are executed by the transmission system module, and the processes of S212 to S224 are executed by the reception system module. The transmission timing control unit 112 generates a transmission trigger in the same manner as the process of S100 in FIG. 15, and transmits the generated transmission trigger to the modulation signal generation unit 104 and the invalidation processing unit 136 (step S200). The transmission side unit 110 generates transmission pulses having different frequency offsets for each transmission pulse in the same manner as the process of S102 in FIG. 15 (step S202). The optical transmission unit 122 transmits (irradiates) an optical signal including the transmission pulse generated in the process of S202 to the distance measurement target 90 in the same manner as the process of S104 in FIG. 15 (step S204).

[0127] The transmission timing control unit 112 changes the transmission interval ΔT as described above (step S206). The transmission timing control unit 112 determines whether or not the transmission interval ΔT has elapsed since the immediately preceding transmission pulse was transmitted (step S208). If the transmission interval ΔT has not elapsed (NO in S208), the transmission timing control unit 112 repeats the process of S208 and waits until the transmission interval ΔT elapses. Then, when the transmission interval ΔT elapses (YES in S208), the processing flow returns to S200. That is, the transmission timing control unit 112 generates a transmission trigger (S200). Note that, as in the first example, it is not necessary to change the transmission interval ΔT for each transmission pulse. Therefore, the process of S206 does not always need to be executed. Further, the process of S206 may be executed after the YES determination in the process of S208.

[0128] The receiving unit 170 receives the received signal in the same manner as the process of S112 in FIG. 15 (step S212). The optical interference system unit 130 detects the frequency offset of the received signal (reflection pulse or crosstalk signal) using the reference light in the same manner as the process of S114 in FIG. 15 (step S214). Here, when it is within a certain period Tm from the transmission timing (YES in step S216), the invalidation processing unit 136 invalidates the received signal in the same manner as the process of S118 in FIG. 15 (step S218). Thereby, when the received signal is a crosstalk signal, the crosstalk signal can be invalidated.

[0129] On the other hand, when it is not within a certain period Tm from the transmission timing (NO in S216), the invalidation processing unit 136 does not invalidate the received signal. Therefore, in this case, the bandpass filter 140 (separation means) separates the optical signals for each frequency offset in the same manner as the process of S120 in FIG. 15 (step S220). The timing extraction unit 150 extracts the reception timing for each separated reflection pulse in the same manner as the process of S122 in FIG. 15, and outputs the measurement stop trigger Trgr at the extracted reception timing (step S222). The distance calculation unit 160 calculates the distance R to the distance measurement object 90 using the measurement start trigger Trgt and the measurement stop trigger Trgr in the same manner as the process of S124 in FIG. 15 (step S224).

[0130] (Embodiment 3) Next, Embodiment 3 will be described. Embodiment 3 is different from Embodiment 2 in that the transmission interval ΔT (transmission timing) is changed according to the distance measurement result. Note that, among the components according to Embodiment 3, the components that are substantially the same as the components in Embodiment 1 are given the same reference numerals. Also, in the following description, the description of the components that are substantially the same as the components in Embodiment 1 will be omitted as appropriate.

[0131] FIG. 22 is a diagram showing the configuration of the distance measuring device 100 according to Embodiment 3. The distance measuring device 100 according to Embodiment 3 includes, as a transmission system module, a frequency offset generator 102, a modulation signal generation unit 104, an optical modulator 106, a light source 108, a transmission timing control unit 112, and an optical transmission unit 122. The transmission side unit 110 is configured by the frequency offset generator 102, the modulation signal generation unit 104, the optical modulator 106, the light source 108, and the transmission timing control unit 112. Note that, among the transmission system modules, the functions of the frequency offset generator 102, the modulation signal generation unit 104, the optical modulator 106, the light source 108, and the optical transmission unit 122 are substantially the same as those shown in FIG. 6, and thus the description thereof will be omitted as appropriate.

[0132] Further, the distance measuring device 100 according to Embodiment 3 includes, as a reception system module, an optical reception unit 124, an optical interference system unit 130, a photoelectric conversion unit 132, an AD converter 134, and an invalidation processing unit 136. Also, in the same manner as in Embodiment 1, the optical transmission and reception unit 120 is configured by the optical transmission unit 122 and the optical reception unit 124.

[0133] Further, the distance measuring device 100 according to Embodiment 3 includes, as a reception system module, band-pass filters 140-1 to 140-n, timing extraction units 150-1 to 150-n, and distance calculation units 160-1 to 160-n. Also, the reception side unit 170 is configured by the optical interference system unit 130, the photoelectric conversion unit 132, the AD converter 134, the invalidation processing unit 136, the band-pass filter 140, the timing extraction unit 150, and the distance calculation unit 160. Note that the functions of the reception system modules are substantially the same as those shown in FIG. 6, and thus the description thereof will be omitted as appropriate. Also, the function of the invalidation processing unit 136 is substantially the same as that in Embodiment 1, and thus the description thereof will be omitted as appropriate. Further, the distance measuring device 100 according to Embodiment 3 includes an estimation unit 370.

[0134] The transmission timing control unit 112 according to Embodiment 3 controls the transmission timing based on the previously obtained ranging results. Specifically, the transmission timing control unit 112 controls the transmission timing according to the next ranging result estimated by an estimation unit 370 described later. More specifically, the transmission timing control unit 112 controls the transmission timing based on two or more ranging results obtained immediately before. Details will be described later.

[0135] The estimation unit 370 has a function as an estimation means. The estimation unit 370 can be realized by an arithmetic circuit such as an FPGA or a microcomputer, for example. The estimation unit 370 estimates the next ranging result (the distance to the ranging object 90) based on the previously obtained ranging results. Specifically, the estimation unit 370 estimates the next ranging result based on two or more ranging results obtained immediately before.

[0136] For example, the estimation unit 370 acquires the previous n (n is an integer of 2 or more) ranging results (distances). Then, the estimation unit 370 estimates the next ranging result by extrapolation from the n measurement results. Specifically, the estimation unit 370 applies the n measurement results (the distances obtained by ranging from the first to the nth time) to some function (a graph with the ranging order on the horizontal axis and the distance on the vertical axis). For example, the estimation unit 370 plots the distance data obtained by ranging from the first to the nth time on a graph with the ranging order on the horizontal axis and the distance on the vertical axis, and calculates the function corresponding to the plot. Then, the estimation unit 370 estimates the ranging result of the next ranging result (the (n + 1)th time) using the function. For example, assuming that the next ranging is the Mth ranging, the ranging result of the (M - 2)th ranging is 100 m, and the ranging result of the (M - 1)th ranging is 101 m. In this case, since the ranging result increases by 1 m for each ranging (receiving of the reflected pulse), the estimation unit 370 can estimate the ranging result of the Mth ranging to be 102 m.

[0137] As described above, when the reception timing of the reflected pulse generated by the reflection of a certain transmission pulse by the distance measurement target 90 coincides with the transmission timing of the next transmission pulse, there is a possibility that the crosstalk signal due to the next transmission pulse overlaps with the reflected pulse on the reception side. That is, the above-described signal overlap may occur.

[0138] Therefore, the transmission timing control unit 112 according to the third embodiment controls the transmission timing so as to suppress the occurrence of signal overlap. In other words, the transmission timing control unit 112 determines the transmission interval ΔT so as to suppress the occurrence of signal overlap. Therefore, the transmission timing control unit 112 determines the transmission timing so that the timing at which the reflected pulse corresponding to the estimated distance measurement result is estimated to be received is different from the transmission timing. In other words, the transmission timing control unit 112 performs control so that the transmission pulse is transmitted at a timing other than the timing at which the reflected pulse corresponding to the estimated distance measurement result is estimated to be received. That is, the transmission timing control unit 112 determines the transmission interval ΔT so that the time (flight time) from the transmission timing of the transmission pulse corresponding to the estimated distance measurement result to the reception timing of the reflected pulse corresponding to the transmission pulse does not match the transmission interval ΔT.

[0139] Specifically, the transmission timing control unit 112 acquires the estimation result from the estimation unit 370. The transmission timing control unit 112 performs control so that the transmission pulse is not transmitted at the timing corresponding to the estimated distance measurement result (distance to the distance measurement target 90). That is, the transmission timing control unit 112 determines the transmission interval ΔT so that the transmission interval ΔT does not match the flight time (estimated flight time Tdx) corresponding to the estimated distance measurement result. For example, the transmission timing control unit 112 may determine the transmission interval ΔT so as to satisfy ΔT = Tdx / 2. Alternatively, in consideration of a certain period Tm, the transmission timing control unit 112 may determine the transmission interval ΔT so that the sum of the transmission interval ΔT and the certain period Tm does not match the estimated flight time Tdx.

[0140] As described above, the distance measuring device 100 according to Embodiment 3 is configured to determine the transmission interval ΔT based on the estimated distance measurement result. As a result, the possibility that the transmission interval ΔT does not match the estimated flight time Tdx increases. Therefore, it is possible to suppress the occurrence of signal superimposition. Therefore, it is suppressed that the reflected pulse is invalidated at the timing when the reception-side signal is invalidated on the reception side. That is, it is suppressed that the invalidation processing unit 136 invalidates the reflected pulse. Therefore, it is possible to suppress the occurrence of the situation where the distance measurement result cannot be obtained.

[0141] Here, in Embodiment 2, the transmission interval ΔT is changed regardless of the distance to the distance measurement object 90. Therefore, depending on the distance to the distance measurement object 90, it is not the case that the flight time Td cannot match the changed transmission interval ΔT. In such a case, there is a possibility that the distance measurement result cannot be obtained. On the other hand, in Embodiment 3, since the transmission interval ΔT is determined based on the estimated distance measurement result, the possibility that the flight time Td matches the transmission interval ΔT is smaller than in the case of Embodiment 2. Therefore, with the configuration according to Embodiment 3, it is further suppressed that the reflected pulse is invalidated at the timing when the reception-side signal is invalidated on the reception side compared to the configuration according to Embodiment 2. Therefore, it is possible to further suppress the occurrence of the situation where the distance measurement result cannot be obtained.

[0142] FIG. 23 is a flowchart showing the distance measurement method executed by the distance measuring device 100 according to Embodiment 3. Note that the processing of the reception system module is substantially the same as the processing of S212 to S224 in FIG. 21, and thus the description thereof is omitted.

[0143] The transmission timing control unit 112 generates a transmission trigger in the same manner as the process of S200 in FIG. 21, and transmits the generated transmission trigger to the modulation signal generation unit 104 and the inactivation processing unit 136 (step S300). The transmission side unit 110 generates transmission pulses having different frequency offsets for each transmission pulse in the same manner as the process of S202 in FIG. 21 (step S302). The optical transmission unit 122 transmits (irradiates) an optical signal including the transmission pulses generated in the process of S302 to the ranging object 90 in the same manner as the process of S204 in FIG. 21 (step S304).

[0144] The transmission timing control unit 112 determines whether or not a transmission interval ΔT has elapsed since the immediately preceding transmission pulse was transmitted (step S308). If the transmission interval ΔT has not elapsed (NO in S308), the transmission timing control unit 112 repeats the process of S308 and waits until the transmission interval ΔT0 elapses. Then, when the transmission interval ΔT elapses (YES in S308), the estimation unit 370 estimates the next ranging result as described above (step S310). Then, the transmission timing control unit 112 determines the transmission interval ΔT according to the estimated ranging result as described above (step S312). Note that the process of S310 does not necessarily need to be executed after the process of S308. For example, the process of S310 may be executed after the process of S304.

[0145] (Embodiment 4) Next, Embodiment 4 will be described. Embodiment 4 is different from Embodiment 3 in that the transmission interval ΔT (transmission timing) is changed according to the pre-generated ranging information and the irradiation direction of the transmission pulse. Note that, among the components according to Embodiment 4, the components that are substantially the same as the components in Embodiment 1 are denoted by the same reference numerals. Also, in the following description, the description of the components that are substantially the same as the components in Embodiment 1 will be omitted as appropriate.

[0146] FIG. 24 is a diagram showing the configuration of the distance measuring device 100 according to Embodiment 4. The distance measuring device 100 according to Embodiment 4 includes, as a transmission system module, a frequency offset generator 102, a modulation signal generation unit 104, an optical modulator 106, a light source 108, a transmission timing control unit 112, and an optical transmission unit 122. The frequency offset generator 102, the modulation signal generation unit 104, the optical modulator 106, the light source 108, and the transmission timing control unit 112 constitute a transmission side unit 110. Note that, among the transmission system modules, the functions of the frequency offset generator 102, the modulation signal generation unit 104, the optical modulator 106, the light source 108, and the optical transmission unit 122 are substantially the same as those shown in FIG. 6, and thus the description thereof will be omitted as appropriate.

[0147] Further, the distance measuring device 100 according to Embodiment 4 includes, as a reception system module, an optical reception unit 124, an optical interference system unit 130, a photoelectric conversion unit 132, an AD converter 134, and an invalidation processing unit 136. The distance measuring device 100 according to Embodiment 4 also includes an optical scanning unit 426. The optical transmission unit 122, the optical reception unit 124, and the optical scanning unit 426 constitute an optical transmission / reception unit 120.

[0148] The optical scanning unit 426 has a function as an optical scanning means. The optical scanning unit 426 scans (scans) a transmission pulse (transmission light) toward the distance measurement target 90. The optical scanning unit 426 is configured to adjust the direction (azimuth angle and elevation angle) in which the distance measurement is performed. That is, the optical scanning unit 426 adjusts the direction in which the transmission pulse is irradiated. The optical scanning unit 426 can be realized by, for example, a MEMS (Micro Electro Mechanical Systems) mirror.

[0149] Further, the distance measurement device 100 according to Embodiment 4 includes, as a reception system module, band-pass filters 140-1 to 140-n, timing extraction units 150-1 to 150-n, and distance calculation units 160-1 to 160-n. Further, the optical interference system unit 130, the photoelectric conversion unit 132, the AD converter 134, the invalidation processing unit 136, the band-pass filter 140, the timing extraction unit 150, and the distance calculation unit 160 constitute the reception side unit 170. Note that the functions of the reception system module are substantially the same as those shown in FIG. 6, and thus the description thereof will be omitted as appropriate. Further, since the function of the invalidation processing unit 136 is substantially the same as that in Embodiment 1, the description thereof will be omitted as appropriate.

[0150] Further, the distance measurement device 100 according to Embodiment 4 includes an estimation unit 470 and a database 472. Further, the distance measurement device 100 according to Embodiment 4 performs distance measurement on a predetermined distance measurement object 90, for example. For example, Embodiment 4 is applicable when the distance measurement device 100 is used for monitoring a predetermined object (distance measurement object 90).

[0151] The transmission timing control unit 112 according to Embodiment 4 controls the transmission timing based on the previously acquired distance measurement results. Specifically, the transmission timing control unit 112 controls the transmission timing according to the next distance measurement result estimated by the estimation unit 470 described later. More specifically, the transmission timing control unit 112 controls the transmission timing based on information in which a scanning direction and the distance measurement results in the scanning direction are associated in advance. Details will be described later.

[0152] The estimation unit 470 has a function as an estimation means. The estimation unit 470 can be realized by an arithmetic circuit such as an FPGA or a microcomputer, for example. Further, the database 472 has a function as a distance measurement information storage means. The database 472 stores distance measurement information in which a scanning direction and the distance measurement results in the scanning direction are associated. This distance measurement information can be generated by performing distance measurement on the distance measurement object 90 in advance.

[0153] FIG. 25 is a diagram illustrating ranging information stored in the database 472 according to Embodiment 4. The ranging information associates a scanning direction with a ranging result (distance) obtained when a transmission pulse is irradiated in the scanning direction. The scanning direction indicates, for example, an azimuth angle and an elevation angle. In the example of FIG. 25, for example, the ranging result obtained when the scanning direction is Direction #1 is distance D1. Also, the ranging result obtained when the scanning direction is Direction #2 is distance D2. Note that the ranging information may be generated using ranging results obtained in advance by the ranging device 100.

[0154] The estimation unit 470 acquires, from the light scanning unit 426, the direction (scanning direction) in which the next transmission pulse is to be irradiated. The estimation unit 470 estimates the next ranging result using the acquired scanning direction and the ranging information stored in the database 472. Specifically, the estimation unit 470 estimates, as the next ranging result, the distance corresponding to the next scanning direction in the ranging information. For example, when the next scanning direction is Direction #1, the estimation unit 470 estimates that the next ranging result is distance D1. Also, when the next scanning direction is a direction between Direction #1 and Direction #2, the estimation unit 470 may estimate, as the next ranging result, a distance between distance D1 and distance D2. In this case, the estimation unit 470 may estimate the next ranging result by interpolation.

[0155] The transmission timing control unit 112 controls the transmission timing so as to suppress the occurrence of signal overlap, as in Embodiment 3. In other words, the transmission timing control unit 112 determines the transmission interval ΔT so as to suppress the occurrence of signal overlap. Therefore, as in Embodiment 3, the transmission timing control unit 112 determines the transmission interval ΔT so that the flight time corresponding to the estimated ranging result does not match the transmission interval ΔT. Specifically, as in Embodiment 3, the transmission timing control unit 112 acquires the estimation result from the estimation unit 470. The transmission timing control unit 112 performs control so as not to transmit a transmission pulse at the timing corresponding to the estimated ranging result (distance to the ranging object 90), as in Embodiment 3.

[0156] Thus, similar to the third embodiment, the distance measuring device 100 according to the fourth embodiment is configured to determine the transmission interval ΔT based on the estimated distance measurement result. As a result, the possibility that the transmission interval ΔT does not match the estimated flight time Tdx increases. Therefore, it is suppressed that the reflected pulse is invalidated at the timing when the reception-side signal is invalidated on the reception side. Therefore, it is possible to suppress the occurrence of the situation where the distance measurement result cannot be obtained.

[0157] Here, the distance measuring device 100 according to the third embodiment estimates the next distance measurement result using the distance measurement result obtained immediately before. However, in this method, when the next distance measurement result is different from the tendency of the change in the distance measurement result obtained immediately before, there is a possibility that the distance measurement cannot be performed appropriately. That is, when the direction in which the transmission pulse was irradiated immediately before corresponds to the edge of the distance measurement object 90, there is also a possibility that the distance measurement object 90 on which the transmission pulse was irradiated until immediately before does not exist in the direction in which the transmission pulse will be irradiated next. In such a case, there is a possibility that the next distance measurement result cannot be appropriately estimated from the distance measurement result obtained immediately before.

[0158] On the other hand, when the distance measurement object 90 is determined in advance, such as when the distance measuring device 100 is used for monitoring a predetermined object (distance measurement object 90), it is possible to acquire in advance the distance measurement results obtained previously for the distance measurement object 90. And the distance measuring device 100 according to the fourth embodiment is configured to estimate the next distance measurement result using the distance measurement information generated from the distance measurement results acquired in advance. Therefore, it is possible to estimate the distance measurement result more accurately. Therefore, the possibility that the flight time Td matches the transmission interval ΔT is smaller than in the case of the third embodiment. Therefore, with the configuration according to the fourth embodiment, compared with the configuration according to the third embodiment, it is further suppressed that the reflected pulse is invalidated at the timing when the reception-side signal is invalidated on the reception side. Therefore, it is possible to further suppress the occurrence of the situation where the distance measurement result cannot be obtained.

[0159] FIG. 26 is a flowchart showing a distance measurement method executed by the distance measurement device 100 according to Embodiment 4. Note that the processing of the reception system module is substantially the same as the processing of S212 to S224 in FIG. 21, and thus the description thereof is omitted.

[0160] The transmission timing control unit 112 generates a transmission trigger in the same manner as the processing of S200 and the like in FIG. 21, and transmits the generated transmission trigger to the modulation signal generation unit 104 and the invalidation processing unit 136 (step S400). The transmission side unit 110 generates transmission pulses having different frequency offsets for each transmission pulse in the same manner as the processing of S202 and the like in FIG. 21 (step S402). The optical transmission unit 122 transmits (irradiates) an optical signal including the transmission pulse generated in the process of S402 to the distance measurement object 90 in the same manner as the processing of S204 and the like in FIG. 21 (step S404).

[0161] The transmission timing control unit 112 determines whether or not a transmission interval ΔT has elapsed since the immediately preceding transmission pulse was transmitted (step S408). If the transmission interval ΔT has not elapsed (NO in S408), the transmission timing control unit 112 repeats the process of S408 and waits until the transmission interval ΔT0 elapses. When the transmission interval ΔT elapses (YES in S408), the estimation unit 370 acquires the next scanning direction as described above (step S409). Then, the estimation unit 370 estimates the next distance measurement result using the next scanning direction and the distance measurement information as described above (step S410). Then, the transmission timing control unit 112 determines the transmission interval ΔT according to the estimated distance measurement result as described above (step S412). Note that the processes of S409 and S410 do not necessarily need to be executed after the process of S408. For example, the processes of S409 and S410 may be executed after the process of S404.

[0162] (Modification example) Note that the present invention is not limited to the above-described embodiments and can be appropriately modified without departing from the gist. For example, the order of each step (process) of the above-described flowchart can be appropriately changed. Also, one or more of the steps (processes) of the flowchart can be appropriately omitted.

[0163] Further, the invalidation processing unit 136 may perform processing to invalidate a signal (received-side signal) transmitted between the optical transceiver 120 and the AD converter 134. Note that the signal transmitted between the optical transceiver 120 and the AD converter 134 is an analog signal, and invalidating an analog signal is more difficult than invalidating a digital signal. Therefore, by having the invalidation processing unit 136 perform processing to invalidate the digital signal (received-side signal) output from the AD converter 134, the processing and circuit configuration are simplified.

[0164] Alternatively, the invalidation processing unit 136 may perform processing to invalidate a signal transmitted between the band-pass filter 140 and the distance calculation unit 160. Note that the signal transmitted between the band-pass filter 140 and the distance calculation unit 160 is transmitted through different routes for each frequency (frequency offset). Therefore, the invalidation processing unit 136 needs to perform processing for invalidating the received-side signal for each of the different routes for each frequency. Therefore, by having the invalidation processing unit 136 perform processing to invalidate the received-side signal at a stage before the optical signal is separated and before it is input to the band-pass filter 140, the processing and circuit configuration are simplified.

[0165] In addition, in the above-described embodiment, it is assumed that there is one light source, but the configuration is not limited to this. As disclosed in Patent Document 1, a plurality of light sources may be used. Further, in the above-described embodiment, a predetermined frequency offset is applied to the transmission pulse, but the configuration is not limited to this. As disclosed in Patent Document 1, the frequency offset may be set randomly. Further, in the present embodiment, the measurement start trigger signal and the measurement stop trigger signal are output to measure the time of flight, but the present invention is not limited to this. For example, any means capable of measuring the time difference between the transmission pulse and the corresponding reflected pulse, such as calculating the time of flight from the position of the time-series data sample acquired by the AD converter, may be employed. Further, in the present embodiment, in order to extract the timing of the reflected pulse, the timing is extracted based on whether the signal exceeds a certain threshold value, but the present invention is not limited to this. For example, any means capable of measuring the temporal position of the reflected pulse, such as detecting the peak value of the signal and extracting the pulse timing, may be employed.

[0166] In addition, in the above-described embodiment, the optical signal is separated for each frequency offset of the reflected pulse using the band-pass filter, but the configuration is not limited to this. The signal may be separated by components other than the band-pass filter. Further, if the reception timing of the reflected pulse can be extracted for each frequency offset, it is not necessary to separate the received optical signal. On the other hand, by separating the optical signal for each frequency offset of the reflected pulse using the band-pass filter, as described above, it becomes possible to perform the distance measurement process at high speed. Further, by separating the optical signal for each frequency offset of the reflected pulse using the band-pass filter, it becomes easy to extract the reception timing of each reflected pulse.

[0167] Further, the distance calculation unit 160 may consider the processing time in the optical modulator 106 or the like at the output timing of the measurement start trigger. In other words, the distance calculation unit 160 may consider the processing time from when it receives the measurement start trigger until the transmission pulse corresponding to the measurement start trigger is actually transmitted. In this case, the distance calculation unit 160 may use, as the start timing of the distance measurement, the timing obtained by adding the processing time in the optical modulator 106 or the like to the output timing of the measurement start trigger. It is assumed that the processing time in the optical modulator 106 or the like is substantially constant.

[0168] Similarly, the distance calculation unit 160 may consider the processing time in the optical interference system unit 130 or the like before the measurement stop trigger is output for the measurement stop trigger. In other words, the distance calculation unit 160 may consider the processing time from when the reflected pulse is received by the optical reception unit 124 until the measurement stop trigger is output by the timing extraction unit 150. In this case, the distance calculation unit 160 may use, as the end timing of the distance measurement, the timing obtained by subtracting the processing time in the optical interference system unit 130 or the like from the output timing of the measurement stop trigger. It is assumed that the processing time in the optical interference system unit 130 or the like is substantially constant.

[0169] Alternatively, the modulation signal generation unit 104 may output a measurement start trigger indicating the time when the transmission pulse is transmitted, taking into account the processing time until the transmission pulse is transmitted by the subsequent optical transmission unit 122. That is, if the time when the modulation signal is generated is t1 and the processing time in the optical modulator 106 or the like is Δt1, the modulation signal generation unit 104 may output a measurement start trigger indicating the time (t1 + Δt1). Similarly, the timing extraction unit 150 may output a measurement stop trigger indicating the time when the reflected pulse is received, taking into account the processing time in the preceding optical interference unit 130 or the like. That is, if the time when the timing extraction unit 150 receives a signal from the band-pass filter 140 is t2 and the processing time in the optical interference unit 130 or the like is Δt2, the timing extraction unit 150 may output a measurement stop trigger indicating the time (t2 - Δt2). In this case, the distance calculation unit 160 may calculate the distance R using Equation 1 with Td = (t2 - Δt2) - (t1 + Δt1).

[0170] Further, the transmission timing control unit 112 may output a transmission trigger to the invalidation processing unit 136, taking into account the processing time in the modulation signal generation unit 104 and the optical modulator 106. That is, the transmission timing control unit 112 may output a transmission trigger to the invalidation processing unit 136 after the processing time in the modulation signal generation unit 104 and the optical modulator 106 has elapsed since the transmission trigger was output to the modulation signal generation unit 104. Alternatively, the invalidation processing unit 136 may invalidate the received-side signal, taking into account the processing time in the modulation signal generation unit 104 and the optical modulator 106. That is, the invalidation processing unit 136 may invalidate the received-side signal within a certain period Tm after the transmission trigger is received and the processing time in the modulation signal generation unit 104 and the optical modulator 106 has elapsed. Further, the invalidation processing unit 136 may invalidate the received-side signal, taking into account the processing time in the optical interference unit 130 or the like. That is, the invalidation processing unit 136 may invalidate the received-side signal within a certain period Tm after the transmission trigger is received and the processing time in the optical interference unit 130 or the like has elapsed.

[0171] In the above-described embodiment, the present embodiment has been described as a hardware configuration. However, the present embodiment is not limited thereto. The present embodiment can also be realized by causing a CPU (Central Processing Unit) to execute a computer program for at least one process of each circuit in the distance measuring device.

[0172] When the above-described program is loaded into a computer, it includes a group of instructions (or software code) for causing the computer to perform one or more functions described in the embodiment. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, the computer-readable medium or tangible storage medium includes random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD), or other memory technologies, CD-ROM, digital versatile disk (DVD), Blu-ray (registered trademark) disk, or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage, or other magnetic storage devices. The program may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, the transitory computer-readable medium or communication medium includes electrical, optical, acoustic, or other forms of propagated signals.

[0173] Some or all of the above-described embodiments may be described as follows in the appended claims, but are not limited thereto. (Appended Claim 1) Generating means for generating a plurality of transmission pulses in which the intensity of an optical signal changes in a pulsed manner, the plurality of transmission pulses having a frequency offset with respect to a reference frequency that is different for each of the transmission pulses; Transmitting means for repeatedly transmitting the generated transmission pulses; Receiving means for receiving a reflected pulse obtained by reflecting the transmission pulse from a distance measurement target; Detecting means for detecting the frequency offset of the received reflected pulse; Distance calculation means for calculating the distance to the object to be measured based on the reception timing of the received reflected pulse and the transmission timing of the transmission pulse corresponding to the frequency offset detected from the reflected pulse; Invalidation processing means for performing processing so that the distance calculation processing is invalidated for a certain period based on the transmission timing of the transmission pulse; A distance measuring device having the above. (Appendix 2) The invalidation processing means performs processing so that the distance calculation processing is invalidated by invalidating the reception side signal transmitted on the reception side of the distance measuring device for a certain period based on the transmission timing of the transmission pulse. The distance measuring device according to Appendix 1. (Appendix 3) Transmission timing control means for controlling the transmission timing by controlling to change the transmission interval from when a transmission pulse is transmitted until the next transmission pulse is transmitted; The distance measuring device according to Appendix 1 or 2, further comprising the above. (Appendix 4) The transmission timing control means performs control so as to change the transmission interval at a predetermined period. The distance measuring device according to Appendix 3. (Appendix 5) The transmission timing control means performs control so as to change the transmission interval for each transmission pulse according to a predetermined rule. The distance measuring device according to Appendix 3. (Appendix 6) The transmission timing control means performs control so as to randomly change the transmission interval for each transmission pulse. The distance measuring device according to Appendix 3. (Appendix 7) The transmission timing control means performs control of the transmission timing based on the previously obtained distance measurement result. The distance measuring device according to Appendix 3. (Appendix 8) Estimation means for estimating the next distance measurement result based on the previously obtained distance measurement result; Further comprising the above, The transmission timing control means determines the transmission interval such that the flight time from the transmission timing of the transmission pulse corresponding to the estimated ranging result to the reception timing of the reflected pulse corresponding to the transmission pulse does not match the transmission interval. The ranging device according to Supplementary Note 7. (Supplementary Note 9) The transmission timing control means controls the transmission timing based on two or more ranging results acquired immediately before. The ranging device according to Supplementary Note 7 or 8. (Supplementary Note 10) The transmission timing control means controls the transmission timing based on information in which a previously generated sweeping direction and the ranging result in the sweeping direction are associated with each other. The ranging device according to Supplementary Note 7 or 8. (Supplementary Note 11) The receiving means receives an optical signal including the reflected pulse. Separation means for separating the received optical signal for each frequency offset of the reflected pulse detected by the detection means. further includes The distance calculation means calculates the distance to the ranging object for each separated optical signal. The ranging device according to any one of Supplementary Notes 1 to 10. (Supplementary Note 12) The invalidation processing means performs processing so that the distance calculation processing is invalidated by invalidating the reception-side signal input to the reception side at a stage before the optical signal is separated. The ranging device according to Supplementary Note 11. (Supplementary Note 13) Generate a plurality of transmission pulses in which the intensity of the optical signal changes in a pulse shape and which have different frequency offsets with respect to a reference frequency for each of the transmission pulses. Repeatedly transmit the generated transmission pulses. Receive a reflected pulse obtained by reflecting the transmission pulse from a ranging object. Detect the frequency offset of the received reflected pulse. Based on the reception timing of the received reflected pulse and the transmission timing of the transmission pulse corresponding to the frequency offset detected from the reflected pulse, calculate the distance to the object to be measured, Based on the transmission timing of the transmission pulse, perform processing so that the distance calculation process is invalidated for a certain period. A distance measurement method having the above. (Appendix 14) Based on the transmission timing of the transmission pulse, perform processing so that the distance calculation process is invalidated by invalidating the reception-side signal transmitted on the reception side for a certain period. The distance measurement method according to Appendix 13. (Appendix 15) Control the transmission timing by controlling to change the transmission interval from when a transmission pulse is transmitted until the next transmission pulse is transmitted. The distance measurement method according to Appendix 13 or 14. (Appendix 16) Control to change the transmission interval at a predetermined period. The distance measurement method according to Appendix 15. (Appendix 17) Control to change the transmission interval for each transmission pulse according to a predetermined rule. The distance measurement method according to Appendix 15. (Appendix 18) Control to change the transmission interval randomly for each transmission pulse. The distance measurement method according to Appendix 15. (Appendix 19) Control the transmission timing based on the previously obtained distance measurement result. The distance measurement method according to Appendix 15. (Appendix 20) Estimate the next distance measurement result based on the previously obtained distance measurement result, Determine the transmission interval so that the flight time from the transmission timing of the transmission pulse corresponding to the estimated distance measurement result to the reception timing of the reflected pulse corresponding to the transmission pulse does not match the transmission interval. The distance measurement method described in Supplementary Note 19. (Supplementary Note 21) Based on two or more distance measurement results obtained immediately before, controlling the transmission timing. The distance measurement method described in Supplementary Note 19 or 20. (Supplementary Note 22) Based on information in which a pre-generated sweep direction and the distance measurement result in the sweep direction are associated, controlling the transmission timing. The distance measurement method described in Supplementary Note 19 or 20. (Supplementary Note 23) Receiving the optical signal including the reflected pulse. Separating the received optical signal for each frequency offset of the detected reflected pulse. Calculating the distance to the object to be measured for each separated optical signal. The distance measurement method according to any one of Supplementary Notes 13 to 22. (Supplementary Note 24) Before the stage where the optical signal is separated, performing processing so that the distance calculation process is invalidated by invalidating the received-side signal input to the receiving side. The distance measurement method described in Supplementary Note 23.

Explanation of Signs

[0174] 1 Distance measurement device 2 Generation unit 4 Transmission unit 6 Receiving unit 8 Detection unit 10 Distance calculation unit 12 Invalidation processing unit 50 Distance measurement device 90 Object to be measured 100 Distance measurement device 101 Optical system integrated circuit 102 Frequency offset generator 104 Modulation signal generation unit 106 Optical modulator 108 Light source 110 Transmission-side unit 112 Transmission timing control unit 120 Optical transceiver 120A Optical Transceiver 121 Optical Transceiver 122 Optical Transmitter 124 Optical Receiver 125 Circulator 130 Optical Interference Unit 132 Photoelectric Conversion Unit 134 AD Converter 136 Invalidation Processing Unit 140 Band - Pass Filter 150 Timing Extraction Unit 160 Distance Calculation Unit 170 Receiver - side Unit 370 Estimation Unit 426 Optical Scanning Unit 470 Estimation Unit 472 Database

Claims

1. Generating means for generating a plurality of transmission pulses in which the intensity of an optical signal changes in a pulsed manner, the plurality of transmission pulses having a frequency offset with respect to a reference frequency, the frequency offset being different for each of the transmission pulses; Transmission means for repeatedly transmitting the generated transmission pulses; Receiving means for receiving an optical signal including a reflected pulse obtained by reflecting the transmission pulse from a distance measurement target; Detection means for detecting the frequency offset of the received reflected pulse; Separation means for separating the received optical signal for each frequency offset of the reflected pulse detected by the detection means; Distance calculation means for calculating the distance to the distance measurement target for each of the separated optical signals based on the reception timing of the received reflected pulse and the transmission timing of the transmission pulse corresponding to the frequency offset detected from the reflected pulse; Invalidation processing means for performing processing such that distance calculation processing is invalidated by invalidating a reception-side signal input to the reception side at a stage before the optical signal is separated for a certain period based on the transmission timing of the transmission pulse; A distance measurement device having the above.

2. The invalidation processing means performs processing such that the distance calculation processing is invalidated by invalidating a reception-side signal transmitted on the reception side of the distance measurement device for a certain period based on the transmission timing of the transmission pulse. The distance measurement device according to claim 1.

3. Transmission timing control means for controlling the transmission timing by controlling so as to change the transmission interval from when a transmission pulse is transmitted until the next transmission pulse is transmitted; The distance measurement device according to claim 1 or 2, further comprising the above.

4. The transmission timing control means controls so as to change the transmission interval at a predetermined period. The distance measurement device according to claim 3.

5. The transmission timing control means controls so as to change the transmission interval for each of the transmission pulses along a predetermined rule. The distance measurement device according to claim 3.

6. The transmission timing control means controls so as to randomly change the transmission interval for each of the transmission pulses. The distance measurement device according to claim 3.

7. The transmission timing control means controls the transmission timing based on a previously obtained distance measurement result. The distance measurement device according to claim 3.

8. Estimation means for estimating a next acquired distance measurement result based on a previously acquired distance measurement result further comprising The transmission timing control means determines the transmission interval so that the flight time from the transmission timing of the transmission pulse to the reception timing of the reflected pulse corresponding to the transmission pulse, which corresponds to the estimated distance measurement result, does not match the transmission interval. The distance measurement device according to claim 7

9. The transmission timing control means controls the transmission timing based on two or more distance measurement results acquired immediately before. The distance measurement device according to claim 7 or 8

10. Generating a plurality of transmission pulses in which the intensity of the optical signal changes in a pulse shape, and having a frequency offset with respect to a reference frequency that is different for each of the transmission pulses Repeatedly transmitting the generated transmission pulses Receiving an optical signal including a reflected pulse reflected by the distance measurement object by the transmission pulse Detecting the frequency offset of the received reflected pulse Separating the received optical signal for each of the detected frequency offsets of the reflected pulse Calculating the distance to the distance measurement object for each of the separated optical signals based on the reception timing of the received reflected pulse and the transmission timing of the transmission pulse corresponding to the frequency offset detected from the reflected pulse Based on the transmission timing of the transmission pulse, at a stage before the optical signal is separated for a certain period, performing processing so that the distance calculation process is invalidated by invalidating a reception-side signal input to the reception side A distance measurement method having

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