JP4837413B2 - Ranging method and ranging device - Google Patents

Description

  The present invention relates to a distance measuring method and a distance measuring apparatus that measure a distance to a measurement object based on light projection and reception.

  As is well known, as a distance measuring device using light, the impulse light is emitted from the light projecting unit to the measurement object, the impulse light reflected by the measurement object is received by the light receiving unit, and the impulse light is received. A device that is configured to measure the distance to a measurement object based on a time difference from light projection to light reception is widely used.

In this type of distance measuring device, the time difference between the light projecting and receiving of the impulse light is determined by the generation timing of the trigger signal that determines the emission timing of the impulse light from the light projecting unit and the impulse light reflected by the measurement object received by the light receiving unit. The time difference from the generation timing of the received light signal output from the light receiving unit may be obtained. In this case, since the trigger signal and the light reception signal are separate signals, the time difference between the generation timings of both is generally measured by a counter circuit as disclosed in, for example, Patent Document 1 below. is there. Specifically, first, a trigger signal is generated and simultaneously the trigger signal is input to the counter circuit, and the counter circuit starts counting clock pulses supplied from the frequency generator. Thereafter, a light reception signal is generated and simultaneously the light reception signal is input to the counter circuit, and the counter circuit finishes counting the clock pulses. Then, the counter circuit measures the time difference between the generation timing of the trigger signal and the light reception signal from the count value of the clock pulse count from the start to the stop of the count.
US Pat. No. 5,455,669

  However, as described above, in the distance measuring device that measures the time difference between the generation timing of the trigger signal and the received light signal by the counter circuit, the distance measurement accuracy to the measurement object greatly depends on the frequency of the clock pulse. Therefore, in order to realize highly accurate distance measurement, it is essential to increase the frequency of the clock pulse, but if this is done, elements that can respond quickly to peripheral circuits such as counter circuits and frequency generators are used. In addition to causing an increase in cost, complicated processing is required, which is not practical in terms of cost and technology.

  Therefore, it is also conceivable to configure the distance measuring device so as to directly obtain the time difference between the generation timing of the trigger signal and the received light signal by the arithmetic processing without using the counter circuit. In this case, the trigger signal and the light reception signal are digitized before the arithmetic processing, but since each is a separate signal, an AD converter corresponding to both signals, a signal processing circuit, etc. are required separately. The signal processing in the signal processing system becomes complicated. In particular, the AD converter is expensive and has a variation in temperature and conversion accuracy for each device. Therefore, when individual AD converters are used, it becomes a major factor that causes an error in distance measurement. Therefore, even with a distance measuring device having such a configuration, it is difficult to realize highly accurate distance measurement.

  The subject of this invention is measuring the distance to a measuring object with high precision based on a trigger signal and a light reception signal.

  The distance measuring method according to the present invention, which was created to solve the above-described problems, generates a trigger signal, emits impulse light from the light projecting unit using the trigger signal as a starting point, and the light projecting unit. A light receiving step of generating a light reception signal by receiving the impulse light emitted and reflected by the measurement object by a light receiving unit, and combining the trigger signal and the light reception signal into one signal continuous along a single time axis And a calculation step of calculating a distance to the measurement object based on a rising position on the time axis of the trigger signal and the light reception signal in the combination signal. Characterized by

  According to such a method, since the trigger signal and the light receiving signal are combined into one combined signal that is continuous along a single time axis, the distance is directly obtained by calculation processing from the combined signal. However, the A / D converter that digitizes the signal, the signal processing circuit for the digitized signal, and the like can be combined into a single signal processing system. Therefore, unlike the case where the trigger signal and the light reception signal are separately calculated, there is no error in the calculation distance due to variations in the performance of the signal processing system, and highly accurate distance measurement can be realized.

  In the above method, based on a noise signal output from the light receiving unit before generating the trigger signal, a signal detection threshold for detecting the trigger signal and the rising position of the light receiving signal in the composite signal is set. It is preferable to further include a threshold setting step.

  In this way, the signal detection threshold value can be appropriately adjusted to an optimal value according to the noise signal, so that the rate of erroneous detection of the noise signal as a trigger signal or a light reception signal can be reliably reduced. it can. Furthermore, since the pulse light is not emitted before the generation of the trigger signal, it is possible to prevent the received light signal from being erroneously processed as a part of the noise signal. From the viewpoint of simplifying the signal processing system, it is preferable to set the signal detection threshold based on the signal strength before the trigger signal in the combined signal.

  In the above method, in the calculation step, a differential signal obtained by differentiating the combined signal with respect to the time axis may be generated.

  In this way, the low frequency noise included in the synthesized signal is attenuated and the change of the signal becomes steep, so that the positions of the trigger signal and the light receiving signal included in the differential signal can be detected with high accuracy. .

  In this case, the rising position of the trigger signal and the light receiving signal on the time axis may be obtained from the barycentric position on the time axis of both signals included in the differential signal.

  In this way, the arithmetic processing becomes simple and a measurement resolution equal to or higher than the sampling period when the synthesized signal is digitized can be obtained. Even when the signal level (amplitude) of the trigger signal and the light reception signal in the composite signal varies, the variation in the barycentric position of the differential signal corresponding to the rising position of each signal on the time axis is extremely small. Therefore, it is possible to realize distance calculation with higher accuracy.

  Also, in this type of distance measurement method, it is known that even if the distance to the measurement object is constant, an error occurs in the calculation distance when the amount of received pulsed light received by the light receiving unit varies. It has been. When considering the effect of this error, it is considered that the distance correction value corresponding to the peak value of the received light signal is measured in advance and the calculation distance is corrected according to the peak value of the received light signal obtained during distance measurement. It is done. However, since the light reception signal is usually a signal amplified by an amplifier, when the amplifier is in a saturated state, the peak value of the light reception signal shows a substantially constant value even if the amount of received light varies. Therefore, when the amplifier is in a saturated state, a constant correlation is not established between the amount of received light and the peak value of the received light signal, and it is difficult to accurately correct the calculation distance.

  Therefore, when considering the above items, in the above method, in the calculation step, the received light signal in the composite signal is integrated with respect to the time axis, and the calculated distance is based on the obtained integrated value. It is preferable to further include a correction step for correcting.

  When the amplifier is in a saturated state, the signal level of the received light signal is substantially constant even if the received light amount received by the light receiving unit fluctuates, but the waveform shape of the received light signal varies with the received light amount. A predetermined change is shown according to For this reason, the integrated value has a certain correlation with the peak value of the amount of received light. Therefore, if the waveform shape of the received light signal changes, the integrated value also changes accordingly. Therefore, if the correction value of the calculation distance corresponding to the integrated value of the received light signal is obtained in advance, it can be obtained based on the integrated value of the received light signal even when the amplifier is saturated during actual distance measurement. It is possible to accurately correct the calculated distance. Of course, even when the amplifier is in a non-saturated state, the calculation distance can be accurately corrected by the integrated value, which is particularly advantageous when the dynamic range of the amount of impulse light received by the light receiving unit is large. Correction method.

  In the above method, in the emission step, the impulse light emitted from the light projecting unit may be scanned in the surrounding space.

  In this way, it is possible to measure the distance to an arbitrary measurement object existing in the surrounding space. In addition, the presence or absence of the measurement object in the light scanning area and the distance to the measurement object can be detected if the measurement object exists. For example, it can be applied to a method for confirming safety in a specific area. You can also

  The distance measuring device according to the present invention, which was created to solve the above problems, includes a control unit that generates a trigger signal, a light projecting unit that emits pulsed light from the trigger signal, and a light projecting unit. A light receiving unit that receives reflected light of the emitted pulsed light from the measurement object and generates a light reception signal, and combines the trigger signal and the light reception signal into a signal that is continuous along a single time axis. And a combining unit that generates a combined signal, and configured to calculate a distance to the measurement object based on a rising position on the time axis of the trigger signal and the light reception signal in the combined signal Characterized by

  According to such a configuration, it is possible to embody a distance measuring device for obtaining the same effect as the distance measuring method described above. In addition, since signal processing systems such as AD converters and signal processing circuits can be unified, the circuit configuration can be minimized, and it is possible to simultaneously reduce the size and cost of the device. Become.

  As described above, according to the present invention, the distance to the measurement object is calculated based on the combined signal obtained by combining the trigger signal and the light receiving signal into one signal on a single time axis. It is possible to unify the processing system and realize highly accurate distance measurement.

  A distance measuring apparatus according to an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a block diagram illustrating a schematic configuration of a distance measuring apparatus according to the present embodiment. As shown in the figure, the distance measuring device 1 includes a light projecting unit 2, a light receiving unit 3, a synthesis circuit 4, an AD converter 5, a control unit 6, and a distance calculation unit 7. I have.

  The light projecting unit 2 includes a light emitting element 21 and a light emitting element driving circuit 22. The light emitting element driving circuit 22 converts the trigger signal S1 that is a pulse signal input from the control unit 6 into a current signal necessary for driving the light emitting element 21, and outputs the current signal to the light emitting element 21. . The light emitting element 21 converts the input trigger signal S1 into impulse light S2 and emits it to a measurement object (not shown). For example, a semiconductor laser (LD) or a light emitting diode (LED) is used as the light emitting element 21.

  The light receiving unit 3 includes a light receiving element 31 and a light receiving circuit 32. The light receiving element 31 receives the impulse light S3 reflected from the measurement object, converts it into an electrical signal, and outputs it to the light receiving circuit 32. The light receiving circuit 32 amplifies the electric signal input from the light receiving element 31 and outputs a light receiving signal S4 to the combining circuit 4. For example, an avalanche photodiode (APD) is used as the light receiving element 31.

  The synthesizing circuit 4 generates a synthesized signal S5 that is a signal that is continuous from the trigger signal S1 input from the control unit 6 and the light receiving signal S4 input from the light receiving unit 3 along a single time axis. The combined signal S5 is output to the AD converter 5. In this embodiment, an adding circuit composed of an analog circuit is employed as the combining circuit 4, and the combined signal S5 is generated by sequentially adding the trigger signal S1 and the light receiving signal S4 along a single time axis. It is supposed to be.

The AD converter 5 samples the input composite signal S5 based on the sampling frequency f _s supplied from the oscillator 8 and converts it into a digital signal S6, and the digital signal is converted into a control unit 6 (first unit described later). The data is output to the memory 62). In this embodiment, the synthesized signal S5 is input to the AD converter 5 without waveform shaping and is directly digitized.

  As shown in FIG. 2, the control unit 6 includes a signal generation circuit 61, a first memory 62, a low-pass filter (LPF) 63, a differentiation circuit 64, a threshold setting circuit 65, and a received light amount detection circuit. 66, a time detection circuit 67, and a second memory 68.

  In the control unit 6, the signal generation circuit 61 generates a trigger signal S 1 and outputs the trigger signal S 1 to the light emitting element driving circuit 22 and the synthesis circuit 4. Further, the signal generation circuit 61 outputs a conversion start signal S7 to the AD converter 5 before generating the trigger signal S1, and the AD converter 5 starts to digitize the signal. As a result, the digital signal digitized by the AD converter 5 includes a noise signal NS due to disturbance light or the like output from the light receiving unit 3 before the trigger signal S1 is generated (see FIG. 4).

The first memory 62 is composed of, for example, a RAM, and sequentially stores the digital signal input from the AD converter 5 at each address, and outputs the stored digital signal to the low-pass filter 63. Yes. At this time, the address of the first memory 62 corresponds to the time of 1 / f _s per address corresponding to the sampling frequency f _s of the AD converter 5, so that the synthesized signal synthesized by the synthesis circuit 4 The time axis is reproduced on the address of the first memory 62.

  The low-pass filter 63 attenuates the high frequency noise included in the digital signal input from the first memory 62 and also converts the digital signal attenuated the high frequency noise into a differentiation circuit 64, a threshold setting circuit 65, and a received light amount detection circuit. 66 to output each. In this embodiment, a moving average filter that is a digital filter is used as the low-pass filter 63 from the viewpoint of preventing distortion of the signal waveform of the digital signal that has passed through the low-pass filter 63.

  The differentiating circuit 64 differentiates the digital signal input from the low-pass filter 63 to generate a differentiated signal, and outputs the differentiated signal to the time detection circuit 67.

  The threshold setting circuit 65 subtracts the minimum value from the maximum value of the signal level of the noise signal NS before generation of the trigger signal S1 included in the digital signal input from the low-pass filter 63, The first threshold value L1 for detecting the trigger signal S1 and the light reception signal S4 is determined based on the above. At the same time, in this embodiment, the threshold value setting circuit 65 determines the second threshold value L2 corresponding to the offset value of the entire digital signal based on the average value of the signal level of the noise signal NS. Yes. The threshold setting circuit 65 outputs the first threshold L1 and the second threshold L2 to the received light amount detection circuit 66 and the first threshold L1 to the time detection circuit 67, respectively.

  The received light amount detection circuit 66 corresponds to the received light signal S4 among the digital signals input from the low-pass filter 63 based on the first threshold value L1 and the second threshold value L2 input from the threshold setting circuit 65. The digital signal is integrated and the integrated value is output to the second memory 68. In this way, a value corresponding to the amount of received light of the impulse light S3 received by the light receiving unit 3 is defined by the area of the light reception signal S4.

  The time detection circuit 67 obtains the rising positions of the trigger signal S1 and the light reception signal S4 from the differential signal input from the differentiation circuit 64 based on the first threshold value L1 input from the threshold setting circuit 65, and both The time difference Δt between the generation timings of the trigger signal S1 and the light receiving signal S4 is calculated from the difference between the rising positions of the two, and the time difference Δt is output to the second memory 68. Here, the rising edge of the signal means the whole rising portion from the starting point where the signal starts rising to the top of the signal, and the rising position of the signal is a characteristic position of the rising portion (for example, as described above). It is specified by the signal waveform starting point and vertex. In this embodiment, the time detection circuit 67 defines the rising positions of the trigger signal S1 and the light reception signal S4 by the center of gravity calculation by the center of gravity position of the rising of both signals.

  The second memory 68 is constituted by a RAM, for example, and stores the time difference input by the time detection circuit 67 and the integral value input by the received light amount detection circuit 66, respectively.

  As shown in FIGS. 1 and 2, the distance calculation unit 7 receives the calculation processing stored in the second memory 68 of the control unit 6 in response to the completion of the calculation processing of the control unit 6, and trigger signal S <b> 1 and light reception signal The distance to the measurement object is calculated based on the time difference Δt of the generation timing of S4. Further, the distance calculation unit 7 stores the correction value of the calculation distance corresponding to the integral value of the received light signal in advance, and selects and obtains the distance correction value corresponding to the integral value fetched from the second memory 68. The calculation distance is corrected and the final calculation distance result is output to the external interface.

  Next, an outline of the operation of the distance measuring apparatus 1 configured as described above will be described.

  First, the conversion start signal generated by the signal generation circuit 61 of the control unit 6 is output to the AD converter 5, and digitization of the signal by the AD converter 5 starts. Thereafter, after a predetermined time has elapsed since the generation of the conversion start signal, the signal generation circuit 61 generates a trigger signal S1, and the trigger signal S1 is output to the light emitting element drive circuit 22 and the synthesis circuit 4. The light emitting element driving circuit 22 converts the trigger signal S1 into a current and outputs the current to the light emitting element 21, and the impulse light S2 is emitted from the light emitting element 21 to the measurement object with the trigger signal S1 as a starting point. On the other hand, the impulse light S3 reflected by the measurement object is received by the light receiving element 31 and converted into a light reception signal S4. The light reception signal S4 is amplified by the light reception circuit 32 and output to the synthesis circuit 4.

  As shown in FIG. 3, the synthesizing circuit 4 generates a synthesized signal S5 obtained by synthesizing the trigger signal S1 and the light receiving signal S2 into one signal continuous along a single time axis. In FIG. 3, S <b> 2 indicates pulse light emitted from the light emitting element 21, and S <b> 3 indicates impulse light received by the light receiving element 31.

  The combined signal S5 generated by the combining circuit 4 is input to the AD converter 5, sampled according to the sampling frequency from the oscillator 8, and converted into a digital signal. Since the digitization of the synthesized signal S5 by the AD converter 5 is started from a conversion start signal generated before the trigger signal S1, the trigger signal S1 is generated in the digital signal obtained by digitizing the synthesized signal. Before, the noise signal NS by the disturbance light etc. which are output from the light-receiving part 3 is included.

  The control unit 6 stores all digital signals input from the AD converter 5 in the first memory 62. Thereafter, the high frequency noise contained in the digital signal is removed from the stored digital signal by the low-pass filter (average moving filter) 63, and for example, a digital signal as shown in FIG. 4 is obtained. In the figure, the horizontal axis indicates the sample order of the digital signal read from the first memory 62, and the vertical axis indicates the digital signal value calculated by the low-pass filter 63. This signal is input to the differentiation circuit 64, the threshold setting circuit 65, and the received light amount detection circuit 66, respectively.

  The differentiation circuit 64 differentiates the input digital signal to generate a differential signal. The digital signals input to and output from the differentiating circuit 64 are conceptually shown in FIGS. In the figure, the horizontal axis indicates the sample order calculated by the low-pass filter 63, and the vertical axis indicates the digital signal value. Specifically, for example, by calculating the difference value between the kth digital signal value and the (k−1) th digital signal value for the digital signal shown in FIG. The differential signal shown is generated. In this embodiment, when the kth digital signal value is smaller than the (k−1) th digital signal value for convenience of calculation, the difference value at that time is set to zero. If the digital signal is differentiated (differed) in this way, low-frequency noise included in the digital signal is attenuated and the change of the signal becomes steep. Therefore, the trigger signal S1 and the light receiving signal S4 included in the differentiated signal are differentiated. The detection accuracy can be improved.

  The threshold setting circuit 65 determines the first threshold L1 and the second threshold L2 based on the noise signal NS before the generation of the trigger signal S1 shown in FIG. 4 among the input digital signals. The second threshold L2 is determined based on the average value of the signal level of the noise signal NS. On the other hand, the first threshold L1 is determined based on the value obtained by subtracting the minimum value from the maximum value of the signal level of the noise signal NS. Then, the threshold setting circuit 65 inputs the first threshold L1 to the time detection circuit 67 and the first threshold L1 and the second threshold L2 to the received light amount detection circuit 66, respectively. In this way, it is possible to appropriately adjust each threshold L1 for detecting the trigger signal S1 and the light reception signal S4 to an optimal value according to the amount of noise caused by disturbance light, etc. The ratio of erroneous detection as the trigger signal S1 or the light reception signal S4 can be reliably reduced. Furthermore, since the pulse light S2 is not emitted before the generation of the trigger signal S1, it is possible to prevent the light reception signal S4 from being erroneously processed as a part of the noise signal NS.

  As shown in FIG. 4, the received light amount detection circuit 66 is one of the digital signals input from the low-pass filter 63 that has exceeded the value obtained by adding the second threshold value L2 to the first threshold value L1 for the first time. The digital signal is integrated with the integration range R1 from the previous digital signal value sample to the digital signal value sample that is below the second threshold L2 for the first time. At this time, an integral value corresponding to a region below the average value of the signal level of the noise signal NS is subtracted from the calculated integral value. Instead of subtracting the integral value corresponding to the area below the average value of the signal level of the noise signal NS from the integral value, the digital signal value inputted in advance from the low-pass filter 63 corresponds to the integral range R1. The average value of the signal level of the noise signal NS may be subtracted from the digital signal value in advance. In this way, the integration calculation can be simplified, which is practically preferable.

  The time detection circuit 67 obtains a sample position corresponding to each rising position of the trigger signal S1 and the light reception signal S4 from the differential signal input from the differentiation circuit 64 based on the first threshold value L1. Then, a time difference Δt between the generation timings of the trigger signal S 1 and the light receiving signal S 4 is calculated based on the difference between the two sample positions calculated, and the time difference Δt is input to the second memory 68. More specifically, the time detection circuit 67 obtains the rising positions of the trigger signal S1 and the light reception signal S4 by the center of gravity calculation by the center of gravity of the rising edge of the signal.

Specifically, as shown in FIG. 5, a portion of the differential signal that exceeds the first threshold value L1 twice in succession is detected, and the differential signal value D of the address that exceeds the first threshold value for the second time. _The center of gravity calculation is performed with _n as the center, for example, the sample positions (n−10 to n + 10) at the front and rear 10 points as the center of gravity calculation range R2, and the rising center positions of the trigger signal S1 and the light reception signal S4 are expressed by the following equations 1, Ask.

Then, the difference ΔP between the respective gravity center positions P of the trigger signal S1 and the light reception signal S4 obtained from the equation (1) is obtained, and the time difference Δt between the generation timings of the trigger signal S1 and the light reception signal S4 is calculated from the following equation 2. Note that fs in the equation represents a sampling frequency.

Thus, by defining the rising position of the trigger signal S1 and the light-receiving signal S4 in the center of gravity position, the calculation of the rise position of the signal is simplified, the resolution of the calculation process, to raise more than the sampling frequency f _s Can do. Further, even when the signal levels (amplitudes) of the trigger signal S1 and the light reception signal S4 in the composite signal vary, the barycentric position of the differentiated signal corresponding to the rising position of each signal on the time axis Since the fluctuation of is extremely small, highly accurate distance calculation can be realized.

When all the calculations are completed, the control unit 6 notifies the distance calculation unit 7 of the completion of the calculation. Upon receiving the notification, the distance calculation unit 7 takes in the calculation result stored in the second memory 68 of the control unit 6 and calculates the distance to the measurement object based on the time difference Δt included in the calculation result. Specifically, assuming that the distance to the measurement object is L and the speed of light is C, the distance L to the measurement object is calculated by the following Equation 3.

  In addition, the distance calculation unit 7 stores in advance a correction value of the calculation distance corresponding to the integral value of the light reception signal S4, selects a distance correction value corresponding to the integration value fetched from the second memory 68, and obtains it. The calculated calculation distance is corrected. In this way, even when the amplifier (light receiving circuit 32) is saturated, there is a certain correlation between the received light amount of the pulsed light received by the light receiving unit 3 and the integrated value of the received light signal. The calculation distance obtained by Expression 3 can be corrected accurately. Therefore, this correction method is advantageous when the dynamic range of the received light amount of the pulsed light S3 received by the light receiving unit 3 is large.

  As described above, according to the distance measuring apparatus 1 of the present embodiment, the trigger signal S1 and the light reception signal S4 are combined into one combined signal S5 that is continuous along a single time axis. Even if the distance is obtained directly from S5 by arithmetic processing, the A / D converter that digitizes the signal, the signal processing circuit that processes the digital signal, etc. are combined into a single signal processing system. Can be planned. Therefore, unlike the case where the trigger signal S1 and the light reception signal S4 are separately calculated, there is no error in the calculation distance due to variations in the performance of the signal processing system, and highly accurate distance measurement can be realized. Become. At the same time, since the circuit configuration can be simplified, it is possible to reduce the size and cost of the apparatus, which is extremely advantageous in practical use.

  In addition, this invention is not limited to said embodiment, A various deformation | transformation is possible.

  In the above embodiment, the trigger signal and the light reception signal rise position are determined by the center of gravity position of the signal rise, but the trigger signal and the light reception signal rise position, for example, the signal rise is linearly approximated or Polynomial approximation may be performed and determined by the position of the intersection of the approximate line and the offset line of the composite signal.

  In the above-described embodiment, the case where the measurement object is directly irradiated with the impulse light S2 emitted from the light projecting unit 2 has been described. However, the impulse light S2 emitted from the light projecting unit 2 is rotated by a mirror. The impulse light S3 reflected by the measurement object may be made incident on the light receiving unit 3 by scanning the surrounding space by using a common rotating mirror or another rotating mirror synchronized with the rotating mirror. In this case, when the influence of the time delay of the impulse light S2 on the trigger signal S1 in the light projecting unit 2 is taken into consideration, the light projecting unit 2 and the light receiving unit 3 are set at a certain optical path length in a part of the scanning region. A reference reflecting plate that is optically connected is arranged, a distance to the reference reflecting plate is calculated, and the calculated distance is subtracted from the above calculated distance, whereby the light projecting unit 2 and the light receiving unit 3 that are generated by temperature. The variation in the delay time of photoelectric conversion in the above may be corrected.

It is a block diagram which shows the structure of one Embodiment of this invention. It is a block diagram which shows the structure of the control part shown in FIG. It is a figure which shows notionally the signal state of each part until a synthetic | combination signal is produced | generated after a trigger signal is produced | generated. It is a figure which shows an example of the signal waveform of the digitized synthetic signal. (A) is a figure which shows notionally the signal waveform corresponding to a light reception signal among the synthetic | combination signals which passed the low-pass filter, (b) is the signal waveform of the differential signal which differentiated the signal. It is a figure shown notionally.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Distance measuring device 2 Light projection part 21 Light emitting element 22 Light emitting element drive circuit 3 Light receiving part 31 Light receiving element 32 Light receiving circuit 4 Synthesis circuit 5 AD converter 6 Control part 61 Signal generation circuit 62 First memory 63 Low-pass filter 64 Differentiation circuit 65 Threshold setting circuit 66 Light reception amount detection circuit 67 Time detection circuit 68 Second memory 7 Distance calculation unit 8 Oscillator S1 Trigger signal S2, S3 Impulse light S4 Light reception signal S5 Composite signal

Claims (7)

An emission step of generating a trigger signal and emitting impulse light from the light projecting unit starting from the trigger signal;
A light receiving step of generating a light reception signal by receiving the impulse light emitted from the light projecting unit and reflected by the measurement object by a light receiving unit;
A synthesis step of synthesizing the trigger signal and the light reception signal into a single signal continuous along a single time axis;
A ranging method comprising: calculating a distance to the measurement object based on a rising position of the trigger signal and the received light signal on the time axis in the combined signal.   A threshold setting step of setting a signal detection threshold for detecting the trigger signal and the rising position of the light reception signal in the composite signal based on a noise signal output from the light receiving unit before generating the trigger signal; The distance measuring method according to claim 1, further comprising:   3. The distance measuring method according to claim 1, wherein, in the calculation step, a differential signal obtained by differentiating the composite signal with respect to the time axis is generated.   4. The measurement according to claim 3, wherein rising positions of the trigger signal and the received light signal on the time axis are obtained from a center of gravity position on the time axis of both signals included in the differential signal. Distance method.   The calculation step further includes a correction step of integrating the received light signal in the combined signal with respect to the time axis and correcting a distance calculated based on the obtained integrated value. 5. The distance measuring method according to any one of 4 above.   6. The distance measuring method according to claim 1, wherein in the emitting step, the impulse light emitted from the light projecting unit is scanned in a surrounding space. A control unit for generating a trigger signal;
A light projecting unit that emits impulse light starting from the trigger signal;
A light receiving unit that receives reflected light from the measurement object of the impulse light emitted from the light projecting unit and generates a light reception signal;
A combining unit that generates a combined signal formed by combining the trigger signal and the light receiving signal into a signal continuous along a single time axis;
A distance measuring apparatus configured to calculate a distance to the measurement object based on a rising position on the time axis of the trigger signal and the light reception signal in the combined signal.

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