Distance measuring device

Abstract

To reduce noise generated in a rangefinder while adding no member for bending an optical path.SOLUTION: A rangefinder 1 has a calculation unit for acquiring a result of receiving reflected light from a light receiving unit 13 to calculate the distance to an object based on the light reception result on a control board 11B. The calculation unit has a resonance circuit for filtering an output signal of the light receiving unit 13 according to a predetermined resonance frequency. With the rangefinder 1, a window 100, an emission unit 12, and the light receiving unit 13 are designed in advance such that the sum of the distance L1 from a light emitting element 122 of the emission unit 12 to the window 100 through reflection on a first mirror 161 and a second mirror 162 and the distance L2 from reflection on the window 100 to a light receiving element 131 through reflection on the second mirror 162 and a third mirror 163 becomes a distance at which measurement light propagates at a time corresponding to the resonance frequency of the resonance circuit.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] LIDAR (Laser Imaging Detection and Ranging) is a type of distance measuring device and is used in various fields such as autonomous driving. LIDAR emits light toward an object, detects the light reflected by the object, and measures the distance from the self-device to the object based on the propagation time of the light going and returning. When emitting this light, LIDAR may generate electrical noise (referred to as electrical noise).

[0003] If the light emitting unit that emits light and the light receiving unit that receives the reflected light in LIDAR are arranged close to each other, the electrical noise generated in the light emitting unit may affect the light receiving unit, and accurate distance measurement may be hindered. This is a common problem not only for LIDAR but also for distance measuring devices that use light.

[0004] Patent Document 1 discloses a configuration in which a light receiving return mirror is used to bend the path of the incident light in a direction different from the emission direction, so that the light emitting substrate and the light receiving substrate are arranged such that their electrical noises do not affect each other.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The technology described in Patent Document 1 requires a light-receiving folding mirror. Therefore, this technology causes, first, the problem of increased production costs, second, the problem of complicated angle adjustment of the light-receiving folding mirror, and third, the problem of attenuation of the received signal by the light-receiving folding mirror.

[0007] In addition, in general LIDAR, in order to prevent intrusion of rain, dust, etc., a window made of resin or glass is provided in the optical path. This window is formed of a material with a relatively high transmittance so as to receive as much reflected light as possible. However, since it is impossible to make the transmittance of the window 100%, a part of the light reaching the window is reflected without being transmitted, generating optical noise (referred to as optical noise).

[0008] One of the objects of the present invention is to reduce noise generated in the distance measuring device without adding a member for bending the optical path such as a light-receiving folding mirror.

Means for Solving the Problems

[0009] The present invention is a distance measuring device that measures the distance to an object based on the propagation time of measurement light emitted from an emitting unit, reflected by the object, and received by a light-receiving unit, comprising a light-transmitting member disposed on the optical path of the measurement light, and a resonance circuit to which the output signal of the light-receiving unit is input, wherein the light-transmitting member is disposed at a position where the output signal of the resonance circuit corresponding to each of the electrical noise generated at the time of emission of the measurement light and the reflected light of the measurement light in the light-transmitting member is canceled out, and provides this as a first aspect.

[0010] According to the distance measuring device of the first aspect, it is possible to reduce noise generated in the distance measuring device without adding a member for bending the optical path.

[0011] In the distance measuring device of the first aspect, a configuration may be adopted as a second aspect in which the light-transmitting member is disposed at a position where the total distance of the optical path of the measurement light from the emitting unit to the light-transmitting member and from the light-transmitting member to the light-receiving member is the distance that light propagates in a time corresponding to the resonance frequency of the resonance circuit.

[0012] According to the distance measuring device of the second aspect, noise is reduced by arranging the light transmitting member according to the resonance frequency of the resonance circuit.

[0013] In the distance measuring device of the second aspect, a configuration may be adopted as a third aspect in which the time corresponding to the resonance frequency is obtained by subtracting the time required for conversion from a current signal to a voltage signal in the light receiving portion from the half cycle of the resonance circuit.

[0014] According to the distance measuring device of the third aspect, the light reflected by the light transmitting member reaches the light receiving portion when a time obtained by subtracting the time required for conversion of the signal in the light receiving portion from the half cycle of the resonance circuit has elapsed since the light was emitted.

[0015] In the distance measuring device according to any one of the first to third aspects, a configuration may be adopted as a fourth aspect in which the device has a mechanism for adjusting the position of the light emitting portion so that the distance between the light emitting portion and the light transmitting member on the optical path of the measurement light changes.

[0016] According to the distance measuring device of the fourth aspect, an error with respect to the designed value of the actual resonance frequency can be adjusted by the position of the light emitting portion.

[0017] In the distance measuring device according to any one of the first to fourth aspects, a configuration may be adopted as a fifth aspect in which the device has a mechanism for adjusting the position of the light receiving portion so that the distance between the light receiving portion and the light transmitting member on the optical path of the measurement light changes.

[0018] According to the distance measuring device of the fifth aspect, an error with respect to the designed value of the actual resonance frequency can be adjusted by the position of the light receiving portion.

[0019] In the distance measuring device according to any one of the first to fifth aspects, a configuration may be adopted as a sixth aspect in which the device has a mechanism for adjusting the position of the light transmitting member so that the distances between the light emitting portion and the light receiving portion and the light transmitting member on the optical path of the measurement light change.

[0020] According to the distance measuring device of the sixth aspect, the error with respect to the design value of the actual resonance frequency can be adjusted by the position of the light transmission member.

[0021] In the distance measuring device according to any one of the first to sixth aspects, the configuration in which the resonance frequency of the resonance circuit is variable may be adopted as the seventh aspect.

[0022] According to the distance measuring device of the seventh aspect, the resonance frequency of the resonance circuit can be adjusted according to the position of the light transmission member.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0024] <Embodiment> <Overall Configuration of Distance Measuring Device> FIG. 1 is a diagram showing an example of the overall configuration of a distance measuring device 1 according to an embodiment of the present invention. FIG. 1 shows the physical arrangement of the components of the distance measuring device 1. The distance measuring device 1 shown in FIG. 1 includes a housing 10, a control board 11B, a light emitting unit 12, a light receiving unit 13, and an optical system 16.

[0025] The light emitting unit 12 includes a light emitting substrate 12B, a light emitting element 122, and a collimator lens 120. The light receiving unit 13 includes a light receiving substrate 13B, a light receiving element 131, and a condenser lens 130. The optical system 16 includes a first mirror 161, a second mirror 162, and a third mirror 163.

[0026] The control substrate 11B is connected to the light emitting substrate 12B of the light emitting unit 12 and the light receiving substrate 13B of the light receiving unit 13 by signal lines and controls them.

[0027] The housing 10 has a window 100 on the optical path of the measurement light emitted by the light emitting unit 12. The window 100 is formed of a material that transmits light, such as glass (referred to as a light transmitting member), and prevents rain, dust, etc. from entering the inside of the housing 10 while allowing the measurement light to proceed outside the housing 10. That is, this window 100 is an example of a light transmitting member disposed on the optical path of the measurement light.

[0028] The window 100, the light emitting unit 12, the light receiving unit 13, and the optical system 16 are all fixed by the housing 10. Therefore, the arrangements of the light emitting unit 12, the light receiving unit 13, and the optical system 16 with respect to the window 100 are all determined.

[0029] The control substrate 11B shown in FIG. 1 instructs the light emitting substrate 12B to emit measurement light from the light emitting element 122. The measurement light emitted from the light emitting element 122 proceeds along the arrow Pa shown by the solid line in FIG. 1. This measurement light becomes parallel light through the collimator lens 120, is reflected by the first mirror 161 and the second mirror 162 in sequence, and reaches the window 100. Most of the reached measurement light passes through this window 100, proceeds outside the housing 10, and reaches the object.

[0030] Note that the second mirror 162 may be provided so as to be rotatable about an axis fixed to the housing 10. Here, being rotatable means being rotatable in both forward and reverse directions. In this case, the control board 11B may control a drive unit such as a motor (not shown) to rotate the second mirror 162 and change the emission direction of the measurement light. Thereby, the measurement light scans the space where the object exists.

[0031] The measurement light reflected by the object enters the inside of the housing 10 through the window 100 along the arrow Pb shown by the broken line in FIG. 1. This reflected measurement light is reflected by the second mirror 162 and the third mirror 163 in sequence, collected by the condenser lens 130, and received (detected) by the light receiving element 131. The light receiving board 13B sends a signal indicating the timing when the light receiving element 131 receives the measurement light to the control board 11B. The control board 11B measures the distance to the object that reflected the measurement light based on the propagation time of the measurement light.

[0032] That is, this distance measuring device 1 is an example of a distance measuring device that measures the distance to an object based on the propagation time of measurement light emitted from an emission unit, reflected by the object, and received by a light receiving unit.

[0033] The emission board 12B may generate electrical noise when emitting measurement light from the light emitting element 122. If the distance between the light receiving board 13B and the emission board 12B is short, this electrical noise is detected by the light receiving board 13B.

[0034] FIG. 2 is a diagram for explaining reflection at the window 100 of the distance measuring device 1. As shown in FIG. 2, the window 100 does not transmit all of the measurement light emitted from the light emitting element 122, and reflects a part of it. The measurement light reflected at the window 100 travels along the arrow Pr shown by the two-dot chain line in FIG. 2, is reflected by the second mirror 162 and the third mirror 163 in sequence, collected by the condenser lens 130, and received by the light receiving element 131.

[0035] At this time, the light received by the light-receiving element 131 is not the light reflected by an object existing outside the housing 10, but the light reflected by the window 100. This light travels a distance that is the sum of the distance L1 from the light-emitting element 122, reflected by the first mirror 161 and the second mirror 162 respectively to reach the window 100, and the distance L2 from when it is reflected by the window 100 until it is reflected by the second mirror 162 and the third mirror 163 respectively and reaches the light-receiving element 131.

[0036] Note that the arrow Pr shown in FIG. 2 indicates an optical path different from the part inside the housing 10 of the arrow Pb shown in FIG. 1, but the difference is relatively small. Therefore, in the following description, these may sometimes be regarded as the same optical path.

[0037] <Circuit Configuration of the Distance Measuring Device> FIG. 3 is a diagram showing an example of the circuit configuration of the distance measuring device 1. The distance measuring device 1 shown in FIG. 3 includes a control unit 11, a light-emitting unit 12, a light-receiving unit 13, a light quantity measuring unit 14, and a calculation unit 15.

[0038] The control unit 11 is provided on the control board 11B shown in FIG. 1 described above. The control unit 11 has memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory) not shown, and controls each part of the distance measuring device 1 by reading and executing a computer program (hereinafter simply referred to as a program) stored in the memory.

[0039] The control unit 11 may be, for example, an FPGA (Field Programmable Gate Array), or may include an FPGA. The control unit 11 has an ASIC (Application Specific Integrated Circuit) or other programmable logic devices, and may perform control by these. Also, the control unit 11 may be a general-purpose processor such as a CPU (Central Processing Unit), for example.

[0040] The control unit 11 generates an emission trigger signal at the timing instructed by the user or determined in advance, and transmits this emission trigger signal to the emission unit 12. The emission trigger signal is a signal that instructs the emission unit 12 to emit measurement light.

[0041] The emission unit 12 emits light under the control of the control unit 11. The emission unit 12 shown in FIG. 3 includes a collimator lens 120, a driver 121, a light emitting element 122, and a detector 123. The driver 121, the light emitting element 122, and the detector 123 are provided, for example, on the emission substrate 12B shown in FIG. 1 described above.

[0042] When the driver 121 receives the emission trigger signal from the control unit 11, it drives the light emitting element 122.

[0043] The light emitting element 122 is a device that emits light toward the space where the object may exist, and is, for example, a laser diode (LD).

[0044] The detector 123 has, for example, a photodiode and a signal processing circuit, detects the light emission by the light emitting element 122, and notifies the control unit 11 of the timing.

[0045] When the light emitted by the emission unit 12 is reflected by the object, the light receiving unit 13 receives and detects the reflected light. The light receiving unit 13 shown in FIG. 1 includes a condenser lens 130, a light receiving element 131, and a current-voltage converter 132. The light receiving element 131 and the current-voltage converter 132 are provided, for example, on the light receiving substrate 13B shown in FIG. 1 described above.

[0046] The light receiving element 131 is an element that detects the reflected light from the object described above and generates a signal by current, and is, for example, an APD (avalanche photodiode).

[0047] The current-voltage converter 132 is a converter that converts the current when the light receiving element 131 detects the reflected light into a voltage, and is, for example, a TIA (Transimpedance Amplifier).

[0048] The light quantity measurement unit 14 measures the light quantity of the reflected light detected by the light receiving element 131. The light quantity measurement unit 14 shown in FIG. 1 includes an integrator 141, a peak hold circuit 142, and an A / D converter 143. This light quantity measurement unit 14 is provided, for example, on the control board 11B shown in FIG. 1. Note that the light quantity measurement unit 14 may be provided on the light receiving board 13B shown in FIG. 1.

[0049] The integrator 141 integrates the voltage value corresponding to the light quantity of the reflected light detected by the light receiving element 131, which is output from the current-voltage converter 132 of the light receiving unit 13.

[0050] The peak hold circuit 142 holds the peak value of the value integrated by the integrator 141.

[0051] The A / D converter 143 converts the analog signal of the light quantity indicated by the peak value held by the peak hold circuit 142 into a digital signal and transmits this to the control unit 11.

[0052] The calculation unit 15 is a device that acquires the light reception result of the reflected light by the light receiving unit 13 and calculates the distance to the object based on this light reception result. The calculation unit 15 shown in FIG. 1 includes a resonance circuit 150, a comparator 151, and a time information generator 152. The calculation unit 15 is provided, for example, on the control board 11B shown in FIG. 1. Note that the calculation unit 15 may be provided on the light receiving board 13B shown in FIG. 1.

[0053] The resonance circuit 150 is a circuit that receives the input of the output signal from the light receiving unit 13 and filters this output signal according to a predetermined resonance frequency. That is, the resonance circuit 150 is an example of a resonance circuit to which the output signal of the light receiving unit is input. The resonance circuit 150 is, for example, an RLC parallel resonance circuit.

[0054] The resonance circuit 150 converts the signal of the voltage value output from the current-voltage converter 132 of the light receiving unit 13 into a sine wave according to a predetermined resonance frequency.

[0055] Comparator 151 compares the sine wave signal converted in resonance circuit 150 with a threshold value, and notifies time information generator 152 of the timing when this voltage value exceeds the threshold value.

[0056] Time information generator 152 is a device that generates time information indicating the time from when emitting unit 12 emits light until receiving unit 13 receives the reflected light. In order to achieve a time resolution corresponding to the required spatial resolution, for example, it is equipped with a TDC (Time to Digital Converter).

[0057] Time information generator 152 obtains, by branching, the signal transmitted from detector 123 of emitting unit 12 to control unit 11, and obtains information on the timing of emitting light from this obtained signal. Further, time information generator 152 receives the notification from comparator 151 described above, and regards the timing indicated by this notification as the timing when receiving unit 13 receives the reflected light.

[0058] Then, time information generator 152 calculates the time difference between the timing when emitting unit 12 emits the measurement light and the timing when receiving unit 13 receives the reflected light as time information, and transmits it to control unit 11. Control unit 11 calculates the distance from ranging device 1 (itself) to the object based on the time information calculated by time information generator 152.

[0059] <Operation of the Ranging Device> FIG. 4 is a diagram for explaining the timing in ranging device 1. The horizontal axis in FIG. 4 represents time, and the vertical axis represents the magnitude of the signal. The timing of the emission trigger signal is shown in FIG. 4(a), and the timing of the emitted light is shown in FIG. 4(b).

[0060] Driver 121 of emitting unit 12 causes light emitting element 122 to emit light by the emission trigger signal, and emits measurement light (also referred to as emitted light). There is almost no time difference between the timing when the emission trigger signal is issued and the timing when the measurement light is emitted, and the two are almost the same.

[0061] Figure 4(c) shows the timing of the reflected light. The reflected light here refers to the measurement light reflected by an object located outside the housing 10 of the distance measuring device 1. The time Δt shown in Figure 4 is the time from when the measurement light is emitted until the reflected light is received.

[0062] Figure 4(d) shows the timing of the generation of electrical noise, and Figure 4(e) shows the timing of the generation of optical noise.

[0063] The electrical noise shown in Figure 4(d) is generated when the driver 121 of the emitting unit 12 drives the light emitting element 122 upon receiving an emission trigger signal from the control unit 11. The timing of the reception of the emission trigger signal and the timing of the generation of the electrical noise are almost simultaneous.

[0064] The optical noise shown in Figure 4(e) is generated when the light receiving unit 13 receives the measurement light reflected by the window 100. There is a time difference Δt1 as shown in Figure 4 from the timing of the generation of the electrical noise to the timing of the generation of the optical noise.

[0065] This time difference Δt1 is the sum of the round-trip time Δt2 and the delay time Δt3. The round-trip time Δt2 is the time required for the measurement light to be reflected by the window 100 and travel back and forth inside the housing 10. The delay time Δt3 is the time required for the current-voltage converter 132 in the light receiving unit 13 to convert the current signal output from the light receiving element 131 into a voltage signal.

[0066] That is, the following equation (1) holds for the time difference Δt1, the round-trip time Δt2, and the delay time Δt3.

[0067]

Equation

[0068] Here, the current-voltage converter 132 of the light receiving unit 13 detects the electrical noise and the optical noise as pulse waves. Then, in the distance measuring device 1, the resonance circuit 150 of the calculation unit 15 converts this pulse wave into a sine wave.

[0069] As long as they are only detected as pulse waves, since both electrical noise and optical noise are positive signals, they do not cancel each other out. However, for example, if the phases are adjusted such that the period during which the instantaneous value of the sine wave converted from electrical noise becomes negative overlaps with the period during which the instantaneous value of the sine wave converted from optical noise becomes positive, it is possible to cancel out a part of the waveform of the electrical noise by the optical noise.

[0070] FIG. 5 is a diagram showing an example of sine waves output after being converted by the resonance circuit 150 for electrical noise and optical noise. The sine waves shown in FIG. 5 (also referred to as resonance circuit outputs) each represent only one period, and the subsequent waveforms are omitted. In the resonance circuit outputs shown in FIG. 5, a part of the period during which the instantaneous value of the electrical noise becomes negative overlaps with the period during which the instantaneous value of the optical noise becomes positive.

[0071] In order for these periods to overlap in this way, the optical noise may be generated, for example, with a delay of half a period of the resonance circuit output compared to the electrical noise. Since one period of the resonance circuit output is the reciprocal of the resonance frequency f0 of the resonance circuit 150, half a period of the resonance circuit output is half of that. And if this half period is equal to the time difference Δt1 described above, a part of the waveform of the electrical noise is canceled out by the optical noise.

[0072] That is, when the following equation (2) holds for the resonance frequency f0 and the time difference Δt1, a part of the waveform of the electrical noise is canceled out by the optical noise.

[0073]

Equation

[0074] By the way, the round-trip time Δt2 included in the time difference Δt1 shown in the above equation (1) is the time required for the measurement light to travel the total distance of the above-mentioned distance L1 and distance L2. That is, assuming the speed of light is c, this round-trip time Δt2 is represented by the following equation (3).

[0075]

Number

[0076] In this distance measuring device 1, the distance L1, the distance L2, and the resonance frequency f0 are predetermined so that all of the above-described equations (1), (2), and (3) are satisfied. That is, in this distance measuring device 1, the arrangement of the window 100, the light emitting unit 12, and the light receiving unit 13 is designed in advance so that the sum of the distance L1 from the light emitting unit 12 to the window 100 and the distance L2 from the window 100 to the light receiving unit 13 is equal to the distance that the measurement light propagates in a time corresponding to the resonance frequency f0 of the resonance circuit 150.

[0077] Here, the "time corresponding to the resonance frequency f0" is the round-trip time Δt2 that satisfies the above-described equations (1) and (2). The time difference Δt1 that satisfies equation (2) is the half period of the resonance circuit 150 that determines the resonance frequency f0. And the round-trip time Δt2 that satisfies equation (1) is the time that becomes the time difference Δt1 by adding the delay time Δt3. That is, this round-trip time Δt2 is calculated by subtracting the delay time Δt3 from the time difference Δt1 that is the half period of the resonance circuit 150.

[0078] That is, this "time corresponding to the resonance frequency f0" is an example of the time obtained by subtracting the time required for converting the current signal to the voltage signal in the light receiving unit from the half period of the resonance circuit.

[0079] And this distance measuring device 1 is an example of a distance measuring device in which the light transmissive member is arranged at a position where the sum of the distances from the light emitting unit to the light transmissive member and from the light transmissive member to the light receiving unit in the optical path of the measurement light is equal to the distance that the light propagates in a time corresponding to the resonance frequency of the resonance circuit.

[0080] Because it is designed in this way, in this distance measuring device 1, at least a part of the signal in the period when the instantaneous value becomes negative among the sine waves converted from the electrical noise is canceled by the signal in the period when the instantaneous value becomes positive among the sine waves converted from the optical noise.

[0081] That is, the window 100 of the distance measuring device 1 is an example of a light transmissive member disposed at a position where output signals of resonance circuits corresponding to each of the electrical noise generated at the time of emission of the measurement light and the reflected light in the light transmissive member of the measurement light are canceled out.

[0082] FIG. 6 is a diagram showing an example of noise canceled out so as not to exceed the threshold value. If the outputs of the current-voltage converter 132 of the electrical noise shown in FIG. 4(d) and the optical noise shown in FIG. 4(e) are simply combined, the combined signal has the waveform of the received signal shown in FIG. 6(a). In this case, since the optical noise does not cancel out the electrical noise, the noise may interfere with distance measurement.

[0083] On the other hand, the outputs of the above-described resonance circuit 150 of the electrical noise and the optical noise have the shapes indicated by broken lines in FIG. 6(b). When these are superimposed, as shown by the solid line in FIG. 6(b), the output signal of the resonance circuit 150 derived from the electrical noise is canceled out by the optical noise during the period when the instantaneous value becomes negative.

[0084] The calculation unit 15 of the distance measuring device 1 sets a negative threshold value in the comparator 151. The time information generator 152 of the calculation unit 15 calculates the distance to the object when a signal less than this threshold value is detected by the comparator 151. As described above, the output signal derived from the electrical noise is canceled out by the superposition with the output signal derived from the optical noise during the period when the instantaneous value becomes negative, so that it is not detected below the set negative threshold value as shown in FIG. 6(b). Thereby, the distance measuring device 1 is less likely to be affected by electrical noise and optical noise when measuring the distance to the object.

[0085] Assuming that the distance from the window 100 of the distance measuring device 1 to the object is L, this distance L is the distance that the measurement light and its reflected light travel at the time obtained by subtracting the time difference Δt1 from the above-described time Δt. That is, the following equation (4) holds for the time Δt, the time difference Δt1, the speed of light c, and the distance L.

[0086]

Equation

[0087] <Design Example> The ranging device 1 described above is designed as follows, for example. When the resonance frequency f0 of the resonance circuit 150 is 100 MHz, one period of the resonance circuit output is 10 ns, and a half period is 5 ns. The ranging device 1 is designed such that this half period becomes the time difference Δt1 described above.

[0088] Although the delay time Δt3 can be predicted to some extent from the circuit and substrate configurations, actual measurement is necessary because of the large individual differences in the components that make up the circuit and substrate. If it is found by actual measurement that this delay time Δt3 is, for example, 4 ns, the round-trip time Δt2 described above is 1 ns because it satisfies Equation (1).

[0089] With this round-trip time Δt2, the measurement light and its reflected light travel the total distance of the distances L1 and L2. Therefore, if the speed of light c is about 3×10 8 m / s, this total distance is about 0.3 m. That is, in the ranging device 1, the window 100 is provided such that the total distance between the distance L1 to the emission unit 12 and the distance L2 to the light receiving unit 13 is about 30 centimeters.

[0090] By being designed in this way, in the ranging device 1, the electrical noise generated in the emission unit 12 is canceled out by the optical noise generated by the reflected light in the window 100, so it is difficult for noise to inhibit ranging.

[0091] The configurations, shapes, sizes, and arrangement relationships described in the above embodiments are only schematically shown to the extent that the present invention can be understood and implemented. Therefore, the present invention is not limited to the described embodiments, and can be changed into various forms without departing from the scope of the technical idea shown in the claims.

[0092] <Modification Example> The above is the description of the embodiment, but the content of this embodiment can be modified as follows. Also, the following modification examples may be combined.

[0093] <1> In the above-described embodiment, the distance measuring device 1 is designed in advance such that the sum of the distance L1 from the emitting unit 12 to the window 100 and the distance L2 from the window 100 to the light receiving unit 13 is equal to the distance that the measurement light propagates in a time corresponding to the resonance frequency f0 of the resonance circuit 150. However, since the individual differences of the components constituting the current-voltage converter 132 are large, for example, the actual measurement of the delay time Δt3 is necessary, and the ideal distance as the total distance between the distance L1 and the distance L2 may change from the design stage depending on the actual delay time Δt3. Therefore, any one of the window 100, the emitting unit 12, and the light receiving unit 13 may be configured to be able to adjust its position along the optical path so that at least one of the distance L1 and the distance L2 can be changed.

[0094] FIG. 7 is a diagram showing an example of the light receiving unit 13 configured to be adjustable in arrangement. The light receiving unit 13 shown in FIG. 7 is a cylindrical plug that fixes the condenser lens 130 and has a connecting portion 133. A screw is provided on this connecting portion 133.

[0095] On the other hand, the housing 10 shown in FIG. 7 has a socket 101 and a fixing portion 102. The socket 101 is a hole into which the light receiving unit 13 is inserted in the direction of the arrow shown by the broken line in FIG. 7, and a screw that fits into the screw provided on the connecting portion 133 is provided. The fixing portion 102 is a member that fixes the position of the light receiving unit 13 inserted in the arrow direction, and is, for example, a screw called a so-called wood screw. The fixing portion 102 is screwed in a direction intersecting the direction of the arrow shown by the broken line described above, for example, and fixes the light receiving unit 13 at the adjusted position in the housing 10 by pressing the connecting portion 133.

[0096] FIG. 8 is a diagram showing an example of the light receiving unit 13 whose position on the optical path is fixed by the fixing portion 102. The position of the light receiving unit 13 in the socket 101 is fixed by the connecting portion 133 being pressed by the fixing portion 102.

[0097] When the user of the distance measuring device 1 knows the actual delay time Δt3 through measurement, the user determines the depth at which the light receiving unit 13 is inserted into the socket 101 accordingly. Then, the user turns the fixing unit 102 and presses the light receiving unit 13 inserted into the socket 101 to the determined depth from the side, thereby fixing the position of the light receiving unit 13 in the socket 101. As a result, the distance L2 is adjusted according to the actually measured value of the delay time Δt3.

[0098] In this case, the connecting portion 133, the socket 101, and the fixing portion 102 are examples of a mechanism for adjusting the position of the light receiving unit so that the distance between the light receiving unit and the light transmitting member on the optical path of the measurement light changes.

[0099] And this distance measuring device 1 is an example of a distance measuring device having a mechanism for adjusting the position of the light receiving unit so that the distance between the light receiving unit and the light transmitting member on the optical path of the measurement light changes. <2> In the above-described modification, the light receiving unit 13 of the distance measuring device 1 has a mechanism capable of adjusting the position on the optical path, but this mechanism may be provided in the light emitting unit 12. In this case, this distance measuring device 1 is an example of a distance measuring device having a mechanism for adjusting the position of the light emitting unit so that the distance between the light emitting unit and the light transmitting member on the optical path of the measurement light changes.

[0100] Also, this mechanism may be provided in the window 100. In this case, this distance measuring device 1 is an example of a distance measuring device having a mechanism for adjusting the position of the light transmitting member so that the distances between the light emitting unit and the light receiving unit on the optical path of the measurement light and the light transmitting member change.

[0101] <3> In the above-described embodiment, the resonance circuit 150 filters the input signal according to a predetermined resonance frequency f0, but it may have a mechanism capable of changing the resonance frequency f0. For example, the resonance circuit 150 may change the resonance frequency f0 by using a variable resistor, a variable capacitor, or the like. In this case, the resonance circuit 150 is an example of a resonance circuit whose resonance frequency is variable. Thereby, the distance measuring device 1 can cancel out noise by changing the resonance frequency f0 without adjusting either the distance L1 or the distance L2 according to the actually measured delay time Δt3.

Explanation of Signs

[0102] 1... Distance measuring device, 10... Housing, 100... Window, 101... Socket, 102... Fixed part, 11... Control part, 11B... Control board, 12... Emission part, 120... Collimator lens, 121... Driver, 122... Light emitting element, 123... Detector, 12B... Emission board, 13... Light receiving part, 130... Condensing lens, 131... Light receiving element, 132... Current-voltage converter, 133... Connecting part, 13B... Light receiving board, 14... Light quantity measuring part, 141... Integrator, 142... Peak hold circuit, 143... A / D converter, 15... Calculation part, 150... Resonance circuit, 151... Comparator, 152... Time information generator, 16... Optical system, 161... First mirror, 162... Second mirror, 163... Third mirror.

Claims

1. A distance measuring device that measures the distance to an object based on the propagation time of measurement light emitted from an emission unit, reflected by the object, and received by a light receiving unit, comprising: a light transmission member disposed on the optical path of the measurement light; and a resonance circuit to which an output signal of the light receiving unit is input. The light transmission member is disposed at a position where output signals of the resonance circuit corresponding to each of electrical noise generated at the time of emission of the measurement light and reflected light of the measurement light in the light transmission member cancel each other out. Distance measuring device.

2. The light transmission member is disposed at a position where the sum of the distances from the emission unit to the light transmission member and from the light transmission member to the light receiving unit in the optical path of the measurement light is equal to the distance that light propagates in a time corresponding to the resonance frequency of the resonance circuit. The distance measuring device according to Claim 1.

3. The time corresponding to the resonance frequency is obtained by subtracting the time required for conversion from a current signal to a voltage signal in the light receiving unit from half of the period of the resonance circuit. The distance measuring device according to Claim 2.

4. It has a mechanism for adjusting the position of the emission unit so that the distance between the emission unit and the light transmission member on the optical path of the measurement light changes. The distance measuring device according to any one of Claims 1 to 3.

5. It has a mechanism for adjusting the position of the light receiving unit so that the distance between the light receiving unit and the light transmission member on the optical path of the measurement light changes. The distance measuring device according to any one of Claims 1 to 4.

6. It has a mechanism for adjusting the position of the light transmission member so that the distances between the emission unit and the light receiving unit and the light transmission member on the optical path of the measurement light change. The distance measuring device according to any one of Claims 1 to 5.

7. The resonance circuit has a variable resonance frequency. The distance measuring device according to any one of Claims 1 to 6.

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