JP7684148B2 - distance measuring device - Google Patents

Description

The present invention relates to distance measuring device technology.

LIDAR (Laser Imaging Detection and Ranging) is a type of distance measuring device that is used in various fields such as autonomous driving. LIDAR emits light toward an object, detects the light reflected from the object, and measures the distance from the device to the object based on the propagation time of the light back and forth. When emitting this light, LIDAR can generate electrical noise.

In a LIDAR, if the light emitting section that emits light and the light receiving section that receives reflected light are placed close to each other, electrical noise generated in the light emitting section can affect the light receiving section, hindering accurate distance measurement. This is an issue that is common not only to LIDAR but to all distance measurement devices that use light.

Patent document 1 discloses a configuration in which the path of incoming light is bent in a direction different from the direction of emission using a light-receiving folding mirror, and the light-emitting board and the light-receiving board are arranged so that their electrical noises do not affect each other.

JP 2019-128231 A

The technology described in Patent Document 1 requires a light-receiving return mirror. Therefore, this technology causes the following problems: first, increased production costs; second, complicated adjustment of the angle of the light-receiving return mirror; and third, attenuation of the received signal due to the light-receiving return mirror.

In addition, typical LIDAR has a resin or glass window in the light path to prevent the intrusion of rain, dust, etc. This window is made 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 window 100% transmittance, some of the light that reaches the window is reflected rather than transmitted, generating optical noise.

One of the objectives of the present invention is to reduce noise generated in a distance measuring device without adding components that bend the optical path, such as a light-receiving folding mirror.

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

The distance measuring device of the first aspect can reduce noise generated in the distance measuring device without adding a component that bends the optical path.

In the distance measuring device of the first aspect, the light-transmitting member may be disposed at a position in the optical path of the measurement light such that the sum of the distance from the emission unit to the light-transmitting member and the distance from the light-transmitting member to the light-receiving unit is the distance that the light propagates in a time period according to the resonant frequency of the resonant circuit.

According to the distance measuring device of the second aspect, noise is reduced by arranging the light-transmitting member according to the resonant frequency of the resonant circuit.

In the distance measuring device of the second aspect, a configuration in which the time corresponding to the resonant frequency is the half period of the resonant circuit minus the time required for the light receiving unit to convert a current signal into a voltage signal may be adopted as a third aspect.

According to the distance measuring device of the third aspect, the light reflected by the light-transmitting member reaches the light receiving unit when the time from emission has elapsed that is the half period of the resonant circuit minus the time required for signal conversion in the light receiving unit.

A distance measuring device according to any one of the first to third aspects may be adopted as a fourth aspect, which has a mechanism for adjusting the position of the emission part so that the distance between the emission part and the light-transmitting member on the optical path of the measurement light changes.

According to the distance measuring device of the fourth aspect, the error of the actual resonant frequency relative to the design value can be adjusted by adjusting the position of the emission part.

A fifth aspect of the distance measuring device may be one 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.

According to the fifth aspect of the distance measuring device, the error of the actual resonant frequency from the design value can be adjusted by adjusting the position of the light receiving unit.

A sixth aspect of the distance measuring device may be one having a mechanism for adjusting the position of the light-transmitting member so that the distance between the light-emitting unit and the light-receiving unit on the optical path of the measurement light changes from the light-transmitting member to the light-transmitting member.

According to the sixth aspect of the distance measuring device, the error of the actual resonant frequency from the design value can be adjusted by adjusting the position of the light-transmitting member.

In the distance measuring device of any one of the first to sixth aspects, a seventh aspect may be adopted in which the resonant circuit has a variable resonant frequency.

According to the seventh aspect of the distance measuring device, the resonant frequency of the resonant circuit can be adjusted according to the position of the light-transmitting member.

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. 4A and 4B are diagrams for explaining reflection at a window 100 of the distance measuring device 1. FIG. 2 is a diagram showing an example of a circuit configuration of the distance measuring device 1. FIG. 4 is a diagram for explaining timing in the distance measuring device 1. 11 is a diagram showing an example of a sine wave outputted by the resonant circuit 150 after converting electrical noise and optical noise. FIG. FIG. 13 is a diagram showing an example of noise that has been canceled so as not to exceed a threshold. 4A and 4B are diagrams showing examples of light receiving sections 13 configured so that their placement can be adjusted. 1 is a diagram showing an example of a light receiving section 13 whose position on the optical path is fixed by a fixing section 102. FIG.

<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 layout of components of the distance measuring device 1. The distance measuring device 1 shown in Fig. 1 has a housing 10, a control board 11B, an emission unit 12, a light receiving unit 13, and an optical system 16.

The emission section 12 has an emission substrate 12B, a light-emitting element 122, and a collimator lens 120. The light-receiving section 13 has a light-receiving substrate 13B, a light-receiving element 131, and a condenser lens 130. The optical system 16 has a first mirror 161, a second mirror 162, and a third mirror 163.

The control board 11B is connected to the emission board 12B of the emission unit 12 and the light receiving board 13B of the light receiving unit 13 via signal lines, and controls them.

The housing 10 has a window 100 on the optical path of the measurement light emitted by the emission unit 12. The window 100 is made of a material that transmits light (called a light-transmitting member), such as glass, and allows the measurement light to travel to the outside of the housing 10 while preventing rain, dust, and the like from entering the inside of the housing 10. In other words, the window 100 is an example of a light-transmitting member arranged on the optical path of the measurement light.

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 positions of the light emitting unit 12, the light receiving unit 13, and the optical system 16 relative to the window 100 are all fixed.

The control board 11B shown in FIG. 1 instructs the emission board 12B to emit measurement light from the light emitting element 122. The measurement light emitted from the light emitting element 122 travels along the arrow Pa shown by a solid line in FIG. 1. This measurement light passes through the collimator lens 120 to become parallel light, and is reflected by the first mirror 161 and the second mirror 162 in this order to reach the window 100. Most of the arriving measurement light passes through the window 100, travels outside the housing 10, and reaches the target object.

The second mirror 162 may be provided so as to be rotatable around an axis fixed to the housing 10. Rotatable here means that it can rotate in both 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. This causes the measurement light to scan the space in which the object is present.

The measurement light reflected by the object passes through window 100 and enters the inside of housing 10 along arrow Pb, which is indicated by a dashed line in FIG. 1. This reflected measurement light is reflected in turn by second mirror 162 and third mirror 163, collected by condenser lens 130, and received (detected) by light-receiving element 131. Light-receiving board 13B sends a signal indicating the timing at which light-receiving element 131 receives the measurement light to control board 11B. Control board 11B measures the distance to the object that reflected the measurement light based on the propagation time of the measurement light.

In other words, 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 that is emitted from an emitting unit, reflected by the object, and received by a light receiving unit.

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

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

At this time, the light received by the light receiving element 131 is not reflected by an object outside the housing 10, but is reflected by the window 100. This light travels a distance equal to the sum of the distance L1 from the light emitting element 122 to the window 100 after being reflected by the first mirror 161 and the second mirror 162, and the distance L2 from the window 100 to the light receiving element 131 after being reflected by the second mirror 162 and the third mirror 163.

Note that the arrow Pr in FIG. 2 indicates a different optical path from the arrow Pb in FIG. 1 within the housing 10, but the difference is relatively small. Therefore, in the following description, these may be considered to be the same optical path.

<Circuit configuration of distance measuring device>
3 is a diagram showing an example of a circuit configuration of the distance measuring device 1. The distance measuring device 1 shown in FIG.

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 called a program) stored in the memory.

The control unit 11 may be, for example, a field programmable gate array (FPGA) or may include an FPGA. The control unit 11 may have an application specific integrated circuit (ASIC) or other programmable logic device and perform control using these. The control unit 11 may also be, for example, a general-purpose processor such as a central processing unit (CPU).

The control unit 11 generates an emission trigger signal at a timing instructed by the user or a predetermined timing, 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.

The emission unit 12 emits light under the control of the control unit 11. The emission unit 12 shown in FIG. 3 has 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 board 12B shown in FIG. 1 described above.

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

The light-emitting element 122 is a device that emits light toward a space in which an object may exist, such as a laser diode (LD).

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

When the light emitted by the emission unit 12 is reflected by an object, the light receiving unit 13 receives and detects the reflected light. The light receiving unit 13 shown in FIG. 1 has 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 board 13B shown in FIG. 1 described above.

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

The current-voltage converter 132 is a converter that converts the current when the light receiving element 131 detects reflected light into a voltage, and is, for example, a TIA (transimpedance amplifier).

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

The integrator 141 integrates the voltage value output from the current-voltage converter 132 of the light receiving unit 13 according to the amount of reflected light detected by the light receiving element 131.

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

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.

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 target object based on this light reception result. The calculation unit 15 shown in FIG. 1 has a resonant 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. The calculation unit 15 may also be provided on the light receiving board 13B shown in FIG. 1.

The resonant circuit 150 is a circuit that receives an output signal from the light receiving unit 13 and filters this output signal according to a predetermined resonant frequency. In other words, the resonant circuit 150 is an example of a resonant circuit to which the output signal of the light receiving unit is input. The resonant circuit 150 is, for example, an RLC parallel resonant circuit.

The resonant circuit 150 converts the voltage signal output from the current-voltage converter 132 of the light receiving unit 13 into a sine wave corresponding to a predetermined resonant frequency.

The comparator 151 is an element that compares the sine wave signal converted in the resonant circuit 150 with a threshold value, and notifies the time information generator 152 of the timing when this voltage value exceeds the threshold value.

The time information generator 152 is a device that generates time information indicating the time from when the light emitter 12 emits light to when the light receiver 13 receives the reflected light, and is equipped with, for example, a TDC (Time to Digital Converter) to achieve a time resolution according to the required spatial resolution.

The time information generator 152 acquires the signal transmitted from the detector 123 of the emission unit 12 to the control unit 11 by branching, and obtains information on the timing at which the light was emitted from this acquired signal. The time information generator 152 also receives a notification from the above-mentioned comparator 151, and regards the timing indicated by this notification as the timing at which the light receiving unit 13 received the reflected light.

Then, the time information generator 152 calculates the time difference between the timing when the emission unit 12 emits the measurement light and the timing when the light receiving unit 13 receives the reflected light as time information, and transmits it to the control unit 11. The control unit 11 calculates the distance from the distance measuring device 1 (its own device) to the target object based on the time information calculated by the time information generator 152.

<Operation of distance measuring device>
Fig. 4 is a diagram for explaining timing in the distance measuring device 1. The horizontal axis in Fig. 4 represents time, and the vertical axis represents signal magnitude. Fig. 4(a) shows the timing of the emission trigger signal, and Fig. 4(b) shows the timing of the emission light.

The emission trigger signal causes the driver 121 of the emission unit 12 to cause the light emitting element 122 to emit light and emit measurement light (also called emission light). There is almost no time difference between when the emission trigger signal is issued and when the measurement light is emitted, and the two are almost the same.

Figure 4(c) shows the timing of the reflected light. The reflected light here is 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 to when the reflected light is received.

Figure 4(d) shows the timing when electrical noise occurs, and Figure 4(e) shows the timing when optical noise occurs.

The electrical noise shown in FIG. 4(d) occurs when the driver 121 of the emission unit 12 receives an emission trigger signal from the control unit 11 and drives the light emitting element 122. The timing of receiving the emission trigger signal and the timing of generating the electrical noise are almost simultaneous.

The optical noise shown in FIG. 4(e) occurs when the light receiving unit 13 receives the measurement light reflected by the window 100. As shown in FIG. 4, there is a time difference Δt1 between the timing of occurrence of the electrical noise and the timing of occurrence of the optical noise.

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 reflect off 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 to convert the current signal output from the light receiving element 131 in the light receiving unit 13 into a voltage signal.

In other words, the following equation (1) holds for the time difference Δt1, the round trip time Δt2, and the delay time Δt3.

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

When only detected as a pulse wave, electrical noise and optical noise are both positive signals and do not cancel each other out. However, if the phases of the noise and optical noise are adjusted so that, for example, the period when the instantaneous value of the sine wave converted from electrical noise is negative overlaps with the period when the instantaneous value of the sine wave converted from optical noise is positive, it is possible for the optical noise to cancel out part of the electrical noise waveform.

Figure 5 shows an example of a sine wave output by the resonant circuit 150 after converting electrical noise and optical noise. Each sine wave (also called the resonant circuit output) shown in Figure 5 shows only one cycle, and the waveform after that is omitted. In the resonant circuit output shown in Figure 5, part of the period during which the instantaneous value of the electrical noise is negative overlaps with the period during which the instantaneous value of the optical noise is positive.

For the periods to overlap in this way, the optical noise needs to occur later than the electrical noise, for example, by half a period of the resonant circuit output. One period of the resonant circuit output is the reciprocal of the resonant frequency f0 of the resonant circuit 150, so the half period of the resonant circuit output is half of that. If this half period is equal to the time difference Δt1 described above, then part of the waveform of the electrical noise is offset by the optical noise.

In other words, when the following equation (2) holds for the resonant frequency f0 and the time difference Δt1, part of the electrical noise waveform is offset by the optical noise.

The round trip time Δt2 included in the time difference Δt1 shown in the above formula (1) is the time required for the measurement light to travel the total distance of the above-mentioned distance L1 and distance L2. In other words, if the speed of light is c, this round trip time Δt2 is expressed by the following formula (3).

In this distance measuring device 1, the distance L1, the distance L2, and the resonant frequency f0 are determined in advance so that the above-mentioned formulas (1), (2), and (3) are all satisfied. In other words, the arrangement of the window 100, the emitter 12, and the light receiver 13 is designed in advance so that the sum of the distance L1 from the emitter 12 to the window 100 and the distance L2 from the window 100 to the light receiver 13 is the distance that the measurement light propagates in a time period corresponding to the resonant frequency f0 of the resonant circuit 150.

Here, "the time according to the resonant frequency f0" refers to the round trip time Δt2 that satisfies the above-mentioned formula (1) and formula (2). The time difference Δt1 that satisfies formula (2) is a half period of the resonant circuit 150 that determines the resonant frequency f0. The round trip time Δt2 that satisfies formula (1) is the time that becomes the time difference Δt1 when added to the delay time Δt3. In other words, this round trip time Δt2 is calculated by subtracting the delay time Δt3 from the time difference Δt1, which is the half period of the resonant circuit 150.

In other words, this "time according to the resonant frequency f0" is an example of the time obtained by subtracting the time required for the current signal in the light receiving unit to be converted into a voltage signal from the half period of the resonant circuit.

This distance measuring device 1 is an example of a distance measuring device in which the light-transmitting member is positioned at a position where the total distance in the optical path of the measurement light from the emission unit to the light-transmitting member and from the light-transmitting member to the light-receiving unit is the distance that the light propagates in a time period that depends on the resonant frequency of the resonant circuit.

Because of this design, in this distance measuring device 1, at least a portion of the signal in the sine wave converted from electrical noise during the period when the instantaneous value is negative is offset by the signal in the sine wave converted from optical noise during the period when the instantaneous value is positive.

In other words, the window 100 of this distance measuring device 1 is an example of a light-transmitting member that is positioned at a position where the output signal of the resonant circuit corresponding to each of the electrical noise generated when the measurement light is emitted and the reflected light of the measurement light at the light-transmitting member are cancelled out.

Figure 6 is a diagram showing an example of noise that has been offset so as not to exceed a threshold. If the outputs of the current-to-voltage converter 132 for the electrical noise shown in Figure 4(d) and the optical noise shown in Figure 4(e) are simply combined, the combined signal will have the waveform of the received signal shown in Figure 6(a). In this case, the optical noise does not offset the electrical noise, and the noise may interfere with distance measurement.

On the other hand, the outputs of the above-mentioned resonant circuit 150 for electrical noise and optical noise are respectively shown by the dashed lines in FIG. 6(b). When these are superimposed, as shown by the solid lines in FIG. 6(b), the output signal of the resonant circuit 150 originating from electrical noise is offset by the optical noise during the period when the instantaneous value is negative.

The calculation unit 15 of the distance measuring device 1 sets a negative threshold in the comparator 151. The time information generator 152 of the calculation unit 15 calculates the distance to the target when the comparator 151 detects a signal below this threshold. As described above, the output signal derived from electrical noise is offset during the period when the instantaneous value is negative due to superposition with the output signal derived from optical noise, and is not detected below the set negative threshold, as shown in FIG. 6(b). This makes the distance measuring device 1 less susceptible to the effects of electrical noise and optical noise when measuring the distance to the target.

If the distance from the window 100 of the distance measuring device 1 to the object is L, this distance L is the distance traveled by the measurement light and its reflected light in the time obtained by subtracting the time difference Δt1 from the time Δt described above. In other words, the following equation (4) holds for the time Δt, the time difference Δt1, the speed of light c, and the distance L.

<Design example>
The above-mentioned distance measuring device 1 is designed, for example, as follows. When the resonant frequency f0 of the resonant circuit 150 is 100 MHz, one period of the resonant circuit output is 10 ns, and a half period is 5 ns. The distance measuring device 1 is designed so that this half period becomes the above-mentioned time difference Δt1.

The delay time Δt3 can be predicted to some extent from the configuration of the circuit and board, but actual measurement is necessary due to large individual differences in the components that make up the circuit and board. If this delay time Δt3 is found to be, for example, 4 ns through actual measurement, the round trip time Δt2 described above is 1 ns because it satisfies formula (1).

Since the measurement light and its reflected light travel the total distance of distance L1 and distance L2 in this round trip time Δt2, if the speed of light c is about 3× ¹⁰ m/s, this total distance is about 0.3 m. In other words, in distance measuring device 1, window 100 is provided so that the total distance of distance L1 to light emitting unit 12 and distance L2 to light receiving unit 13 is about 30 centimeters.

By designing it in this way, the distance measuring device 1 cancels out electrical noise generated in the emission section 12 with optical noise generated by reflected light at the window 100, making it less likely that noise will impede distance measurement.

The configuration, shape, size, and layout relationship described in the above embodiments are merely shown in a schematic manner to enable the present invention to be understood and implemented. Therefore, the present invention is not limited to the described embodiments, and can be modified in various forms without departing from the scope of the technical ideas set forth in the claims.

<Modification>
The above is a description of the embodiment, but the contents of this embodiment may be modified as follows. In addition, the following modifications may be combined.

＜1＞
In the above-described embodiment, the arrangement of the window 100, the emitter 12, and the light-receiving unit 13 of the distance measuring device 1 is designed in advance so that the sum of the distance L1 from the emitter 12 to the window 100 and the distance L2 from the window 100 to the light-receiving unit 13 is the distance that the measurement light propagates in a time corresponding to the resonant frequency f0 of the resonant circuit 150. However, the delay time Δt3 needs to be actually measured because there is a large individual difference between the components that constitute the current-voltage converter 132, for example, and the ideal distance as the sum of the distances L1 and L2 may change from the design stage depending on the actual delay time Δt3. Therefore, any of the window 100, the emitter 12, and the light-receiving unit 13 may be configured so that the position can be adjusted along the optical path so that at least one of the distances L1 and L2 can be changed.

Figure 7 is a diagram showing an example of a light receiving unit 13 configured so that its position can be adjusted. The light receiving unit 13 shown in Figure 7 is a cylindrical plug that fixes the condenser lens 130 and has a connecting part 133. This connecting part 133 is provided with a screw.

On the other hand, the housing 10 shown in FIG. 7 has a socket 101 and a fixing part 102. The socket 101 is a hole into which the light receiving unit 13 is inserted in the direction of the dashed arrow in FIG. 7, and is provided with a screw that fits into a screw provided in the connecting part 133. The fixing part 102 is a member that fixes the position of the light receiving unit 13 inserted in the direction of the arrow, and is, for example, a screw called a set screw. The fixing part 102 is, for example, screwed in a direction that intersects with the above-mentioned dashed arrow direction, and presses against the connecting part 133 to fix the light receiving unit 13 to an adjusted position in the housing 10.

Figure 8 is a diagram showing an example of a light receiving unit 13 whose position on the optical path is fixed by a fixing unit 102. The position of the light receiving unit 13 in the socket 101 is fixed by pressing the connecting unit 133 against the fixing unit 102.

When the user of the distance measuring device 1 knows the actual delay time Δt3 through measurement, he or she determines the depth to which the light receiving unit 13 is to be inserted into the socket 101 accordingly. The user then turns the fixing part 102 to press the light receiving unit 13, which has been 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. This causes the distance L2 to be adjusted according to the actual measured value of the delay time Δt3.

In this case, the connecting portion 133, the socket 101, and the fixing portion 102 are examples of a mechanism that adjusts 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.

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 as to change the distance between the light receiving unit and a light transmitting member on the optical path of the measurement light.
＜2＞
In the above-described modified example, the light receiving unit 13 of the distance measuring device 1 has a mechanism capable of adjusting its position on the optical path, but this mechanism may be provided in the emission unit 12. In this case, the distance measuring device 1 is an example of a distance measuring device having a mechanism for adjusting the position of the emission unit so as to change the distance between the emission unit and the light-transmitting member on the optical path of the measurement light.

This mechanism may also be provided in the window 100. In this case, the 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 distance between the light-emitting part and the light-receiving part on the optical path of the measurement light changes from the light-transmitting member.

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

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... condenser lens, 131... light receiving element, 132... current-voltage converter, 133... connection 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 (7)

A distance measuring device that measures a distance to an object based on a propagation time of measurement light that is emitted from an emission unit, reflected by the object, and received by a light receiving unit, comprising:
a light transmitting member disposed on an optical path of the measurement light; and a resonant circuit to which an output signal of the light receiving unit is input,
the light transmitting member is disposed at a position where output signals of the resonant circuit corresponding to electrical noise generated when measurement light is emitted and reflected light of the measurement light at the light transmitting member are cancelled out. 2. The distance measuring device according to claim 1, wherein the light-transmitting member is positioned at a position on the optical path of the measurement light such that the sum of the distance from the emission portion to the light-transmitting member and the distance from the light-transmitting member to the light-receiving portion is a distance that the light propagates in a time period corresponding to the resonant frequency of the resonant circuit. 3. The distance measuring device according to claim 2, wherein the time according to the resonant frequency is a half period of the resonant circuit minus a time required for conversion from a current signal to a voltage signal in the light receiving section. The distance measuring device according to claim 1 , further comprising a mechanism for adjusting a position of the emission part so that a distance between the emission part and the light transmitting member on an optical path of the measurement light changes. The distance measuring device according to claim 1 , further comprising a mechanism for adjusting a position of the light receiving unit so that a distance between the light receiving unit and the light transmitting member on an optical path of the measurement light changes. The distance measuring device according to claim 1 , further comprising a mechanism for adjusting a position of the light transmitting member so that a distance between the light transmitting member and the light emitting unit and the light receiving unit on an optical path of the measurement light changes. The distance measuring device according to claim 1 , wherein the resonant circuit has a variable resonant frequency.

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