JPH09318736A - Distance measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a distance measuring apparatus which prevents effect on various controls using distance data by detecting the condition that hinders accurate measurement of a distance because of the intensity of background light such as sunlight. SOLUTION: When the value of a monitor voltage of a photodetector 43 indicates that background light is too intense (monitor voltage < threshold voltage Vx), the obtaining of measuring data of a long distance is found to be impossible. In this case, a driver or the like is told that accurate measurement of distance is impossible by lighting a fail lamp 64a in stead of obtaining a distance data. This can prevent abnormal control possibly based on abnormal distance data. Thus, abnormality is made clear to the driver or the like by reporting the abnormal condition to the drivers or the like, thereby preventing the drivers or the like from occurring possible confusion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device, and more particularly to irradiating light to detect light reflected by a reflecting object,
The present invention relates to a distance measuring device that calculates a distance to a reflecting object based on a time difference between the timing of irradiating light and the timing of detecting reflected light.

[0002]

2. Description of the Related Art Conventionally, it is attached to an automobile,
Detects the reflected light reflected by the reflecting object by intermittently irradiating pulsed light, and the timing of irradiating that light,
There is known a distance measuring device that measures a time difference from the timing at which reflected light is detected and calculates the distance to a reflecting object based on the time difference. For example, JP-A-59-142
488, JP-A 60-201276, JP-A 62-
No. 15480 is known.

[0003]

However, as in the case where the vehicle is traveling westward in the evening, the sunlight is reflected in the reflected light detecting portion of the distance measuring device mounted toward the front of the vehicle. When a strong light hits, the reflected light from the reflecting object is particularly weak when the distance to the reflecting object is long, so it becomes equivalent to the noise level of the detection signal, and it may not be possible to accurately detect. . Therefore, there is a problem that various controls based on the measured distance may be hindered depending on the intensity of background light such as sunlight.

An object of the present invention is to realize a distance measuring device capable of preventing the influence on various controls using distance data in advance by detecting such a state in which the distance cannot be accurately measured. It is a thing.

[0005]

Means for Solving the Problems and Effects of the Invention A distance measuring device of the present invention comprises a background light intensity detecting means for detecting the intensity of background light, and a degree of background light detected by the background light intensity detecting means. The distance measuring capability deterioration detecting means for detecting the distance measuring capability deterioration.

In this way, the intensity of the background light with which the reflected light detecting means is irradiated, that is, the other light (sunlight) except for the reflected light that is the light irradiated by the irradiation means is reflected from the reflector. Intensity of external light), or the intensity of both the other light and the reflected light, is provided by providing background light intensity detection means, and from this detection result, a decrease in distance measurement capability is detected. Since the means has detected a decrease in the distance measuring ability, it is determined whether or not the distance data measured by the distance measuring device may be used by utilizing the detection result of the distance measuring ability decrease detecting means. Therefore, it is possible to prevent abnormalities in various controls caused by using incorrect distance data.

If the reflected light detecting means also inputs the background light at the same time, the reflected light detecting means can also serve as the background light intensity detecting means. Therefore, it is not necessary to separately provide the background light intensity detection means in terms of hardware configuration, which is advantageous in manufacturing cost.

As the reflected light detecting means which also serves as the background light intensity detecting means, a load resistance, a light receiving element for flowing a current of a current amount corresponding to the intensity of light, and a load resistance are arranged in series in this order. A configuration for detecting the reflected light based on a voltage change at one end side of the light receiving element of the circuit to which the constant voltage is applied and detecting the intensity of the background light based on a voltage at the other end side of the light receiving element. Is mentioned. For example, the reflected light detection means detects reflected light based on the voltage change on the low potential side of the light receiving element, and detects that the lower the voltage is, the stronger the background light based on the voltage on the high potential side of the light receiving element. It can be configured.

Therefore, the timing at which the reflected light returns can be detected by the voltage change, while the intensity of the background light can be detected by the high voltage. Further, as described above, since the detection position of the voltage change for detecting the reflected light and the detection position of the voltage value for detecting the background light are different across the light receiving element, it is possible to detect the reflected light that is easily affected by noise. This is preferable for accurate measurement of the reflected light detection timing, because the influence of noise inclusion on the mechanism for detecting the voltage is prevented in detecting the voltage change.

Further, it is possible to provide an alarm means for issuing an alarm when it is determined that the degree of the distance measurement capability deterioration detected by the distance measurement capability deterioration detecting means is larger than a predetermined state. For example, as an alarm by the alarm means, lighting of a lamp for notifying an abnormality or ringing of a buzzer for notifying an abnormality can be mentioned. By doing so, it is possible to notify the driver or the like that the distance measurement is not accurately performed, so that appropriate measures can be performed.

Further, the distance measuring stopping means for stopping the processing of the distance calculating means when it is judged that the degree of the distance measuring ability deterioration detected by the distance measuring ability deterioration detecting means is larger than a predetermined state. May be provided. By doing so, it is possible to prevent abnormal distance data from being used in various controls.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic configuration diagram showing a distance measuring device 1 according to an embodiment. The distance measuring device 1 according to the present embodiment is mounted on an automobile to detect a reflecting object such as a vehicle in front or an obstacle.

The distance measuring device 1 is constructed as follows with the transmitting / receiving unit 31 and the computing unit 33 as main components. As shown in FIG. 1, the transmitting / receiving unit 31 emits a pulsed laser beam H through a scan mirror 35 and a light emitting lens 37 to a semiconductor laser diode (hereinafter, simply referred to as a laser diode) 39, and a laser diode. 39
A light receiving element 40, which is arranged in a position close to, and which directly detects laser light from the laser diode 39 and outputs it as a voltage change corresponding to the pulse-like intensity change, and an obstacle as a reflecting object not shown. Receiving the laser light H reflected and returned by the light receiving lens 41 through the light receiving lens 41, outputting a voltage change corresponding to the pulse-like intensity change thereof, and outputting the intensity of the background light as a voltage value. And the element 43.

The laser diode 39 is a light emission drive circuit 45.
Is connected to the calculation unit 33 via a drive signal as a trigger signal from the calculation unit 33, and emits a laser beam H.
Illuminates the front of the vehicle. Further, the scan mirror 35 is provided with a mirror 47 capable of swinging about a vertical axis, and when a drive signal from the arithmetic unit 33 is input via the motor drive unit 49, the mirror 47 is driven by a motor (not shown). It swings due to the driving force. Then, the laser light H is swept and irradiated in front of the vehicle over a predetermined angle in the horizontal plane.

The light receiving element 43 is a photodiode which allows a current of an amount corresponding to the intensity of light to flow, and the light receiving circuit 4 shown in FIG.
4 is incorporated. The light receiving circuit 44 includes a load resistor 44
a, the light receiving element 43, and the load resistor 44b are arranged in series in this order, and a predetermined constant voltage, here, 8V is supplied from the 8V power supply 44c
The constant voltage of is applied.

The reflected light is detected based on the voltage change of the light receiving element 43 on the low potential side (point J in FIG. 2). That is, the output voltage of the light receiving element 43 at the point J is STC.
After being amplified to a predetermined level via the (Sensitivity Time Control) circuit 51, it is input to the variable gain amplifier 53. This STC circuit 51 is provided because the received signal strength is inversely proportional to the fourth power of the distance to the target object, and therefore when there is a high reflectance such as a reflector at a short distance and the received light strength becomes extremely strong. This is to compensate for In addition, the variable gain amplifier 53 is connected to the arithmetic unit 33 via the D / A converter 55, amplifies the input voltage according to the gain (gain) instructed by the arithmetic unit 33, and the comparator 5
Output to 7. The comparator 57 is the variable gain amplifier 53.
The output voltage V is compared with a predetermined voltage V0, and when V> V0, a predetermined light receiving signal (stop pulse PB) is input to the time measuring circuit 61 as the light receiving timing.

On the other hand, the high potential side of the light receiving element 43 (I in FIG. 2).
The calculation unit 33 monitors the voltage of the point) to detect the intensity of the background light. The monitor voltage at point I is calculated by the calculation unit 33.
Is converted into a digital value by the A / D conversion unit 33a provided inside and is taken into the calculation unit 33. If the background light is strong, the amount of current flowing through the light receiving element 43 also increases, and the voltage drop at the point I also drops correspondingly. From this, the calculation unit 33 can determine the intensity of background light based on the degree of voltage drop.

The light emission monitor circuit 54 amplifies an input voltage from the light receiving element 40 according to a predetermined gain and inputs the amplified voltage to an internal comparator. The comparator compares this input with a predetermined voltage and outputs a predetermined voltage. When the above is reached,
A light reception signal (start pulse PA) is output to the time measuring circuit 61 and the calculation unit 33 on the assumption that it is the light emission timing of the laser diode 39.

The detailed structure of the light emission monitor circuit 54 is shown in FIG. The light emission monitor circuit 54 includes an 8V power source 71,
A noise removing resistor 73 provided between the light receiving element 40 and the 8V power source 71, a charge supply capacitor block 75 connected to both ends of the noise removing resistor 73 to supply charges to the light receiving element 40, the light receiving element 40 and the ground. A load resistor 77 disposed between the light receiving element 40 and the load resistor 77, and an amplifier circuit block 79 that is connected between the light receiving element 40 and the load resistor 77 and amplifies a light receiving signal from the light receiving element 40. The amplifier circuit block 79 includes a capacitor 79 from the side of the light receiving element 40.
a, amplifier 79b, capacitor 79c, amplifier 79d,
The inverters 79e are arranged in this order to amplify the light receiving element output (point A in FIG. 3) shown in FIG. 4 and exceed a predetermined threshold value Vth determined based on the input threshold voltage and the input signal voltage of the inverter 79e. At the timing, the pulsed light emission monitor circuit output shown in FIG. 4, that is, the start pulse PA (point B in FIG. 3) is output to the arithmetic unit 33 and the time measuring circuit 61. Note that this predetermined threshold Vt
h is a fixed value, or the light receiving element 40 or the light receiving element 43
It may be variable according to the light receiving state of the.

The time measuring circuit 61 inputs the light receiving signal from the light emission monitor circuit 54 as a start pulse PA and the light receiving signal from the comparator 57 as a stop pulse PB. The time measuring circuit 61 uses two pulses PA,
The phase difference between PBs (that is, the input time difference) is encoded into a binary digital signal, and the value is output as multi-wrap data to the arithmetic unit 33 according to the data selector signal from the arithmetic unit 33. The time measuring circuit 61 can digitize a minute time, and can detect the time difference between the respective signals even if there are a plurality of received light signals for one shot of the emitted laser light H. Is.

The time measuring circuit 61 uses, for example, an odd number stage ring oscillator in which an odd number of inverter gate delay circuits for inverting and outputting an input signal are connected in a ring shape and a pulse edge is circulated on the ring. Can be considered. The phase difference between the two pulses PA and PB (that is, the input time difference) is measured as follows. That is, when the start pulse PA is input, the pulse edge is circulated on the ring oscillator,
When the stop pulse PB is input, by detecting which inverter gate delay circuit on the ring oscillator the pulse edge activated by the start pulse PA has reached, the two pulses PA and PB are detected.
The phase difference (time difference) between them is measured.

The time measuring circuit 61 also has a time resolution correction function for accurate time measurement.
Here, a digital signal is corrected by a completely digital circuit by using a reference signal (for example, a crystal oscillation clock). Conventionally, when a digital circuit is used for time measurement, the clock cycle is used as the resolution. However, the time measuring circuit 61 configured as described above has a much finer resolution than the clock circuit (the two pulse P
The phase difference between A and PB) can be digitized. Therefore, even if there are a plurality of received light signals for one shot of the emitted laser light H (that is, even if there are two or more stop pulses PB for one start pulse PA), the time difference for each signal Can be detected. This is expressed as "possible for multi-wrapping", and the data thus obtained is expressed as multi-wrapping data.

The calculation unit 33 calculates the distance and direction to the obstacle based on the time difference data obtained from the time measuring circuit 61 and the swing angle of the mirror 47 at that time. The output voltage V of the variable gain amplifier 53 is also input to the peak hold circuit 63, and the peak hold circuit 63 inputs the maximum value of the output voltage V to the calculation unit 33.

A vehicle speed signal from a vehicle speed sensor (not shown) is also input to the arithmetic unit 33. Further, a fail lamp drive circuit 64 for indicating an abnormality is connected to the arithmetic unit 33, and when an abnormality in distance measurement or some abnormality occurs in the transmission / reception unit 31 due to the state of background light, as will be described later, the arithmetic unit 33. Fail lamp drive circuit 6
A drive signal is output to 4 to turn on the fail lamp 64a to notify the driver of the abnormality.

Next, the operation of the distance measuring device 1 thus constructed will be described. FIG. 5 is a flowchart showing the distance measurement processing repeatedly executed by the calculation unit 33, FIG. 6 is a graph showing the relationship between the monitor voltage and the limit of the detection distance that can be detected by the distance measuring device 1, and FIG. 2 is a timing chart showing

First, as shown in the flowchart of FIG. 5, a drive signal as a light emission trigger for causing the laser diode 39 to emit light is output to the light emission drive circuit 45 (S).
1000), and the laser diode 39 is caused to emit light (FIG. 7).
(See (A) and (B)). Corresponding to this light emission, the light receiving element 40 directly receives light and outputs a detection signal (in FIG. 7A).
Is output, and the light emission monitor circuit 54 outputs a predetermined threshold value Vth.
Is pulsed at and is input to the time measuring circuit 61 as a start pulse PA (in FIG. 7A).

Further, the laser light H reflected by an obstacle (not shown) is received by the light receiving lens 41 and converted into a voltage corresponding to the intensity at the point J side of the light receiving element 43, and the STC circuit 51, the variable gain amplifier. It is output from 53 (Fig. 7 (A)
Of the stop pulse PB (of FIG. 7A) after being pulsed by the comparator 57 with a predetermined threshold value COMP.
Is input to the time measuring circuit 61.

In the time measuring circuit 61, the time difference ΔT between the start pulse PA and the stop pulse PB is measured.
Note that, as shown in (7) of FIG. 7, the time measuring circuit 61 allows the time difference ΔT for each signal even if there are a plurality of reflected signals for one shot of the emitted laser light H.
1, ΔT2, ... Are detected.

Next, by determining the presence or absence of the output signal from the emission monitor circuit 54, the laser diode 39
In step S101, it is determined whether light is actually emitted.
0). If the laser diode 39 or the light emission drive circuit 45
The laser diode 39 does not emit light in response to the drive signal output in step S1000 due to the failure of step S1000, and the light receiving element 40 cannot detect the light emission. Therefore, the detection signal is output to the arithmetic unit 33 via the emission monitor circuit 54. If not (“NO” in S1010), the laser diode 3
9, the light-emission drive circuit 45, the light-receiving element 40, the light-emission monitor circuit 54, or the like has an abnormality, and the arithmetic unit 33 outputs a lighting drive signal to the fail-lamp drive circuit 64 to output the fail-lamp 64a. Is turned on (S1020), and the process ends.

The laser diode 39 emits light in response to the drive signal for light emission of the arithmetic unit 33, the light receiving element 40 detects this light emission, and the detection signal is input to the arithmetic unit 33 via the light emission monitor circuit 54. If (YES in S1010), it is then determined whether the monitor voltage obtained from the point I side of the light receiving element 43 is equal to or higher than the threshold voltage Vx (S).
1030). The total amount of light applied to the light receiving element 43,
That is, as the amount of background light increases, the amount of current flowing through the light receiving element 43 increases, so the monitor voltage decreases due to a voltage drop, and when the amount of light decreases, the monitor voltage increases.

Therefore, since the background light becomes stronger as the monitor voltage decreases, the reflected light of an object existing at a long distance becomes difficult to capture. That is, when the current flowing through the light receiving element 43 is i [A],
Shot noise current is [A] on the J point side of the light receiving element 43
Is expressed by the following equation.

[0032]

[Equation 1]

Here, q = 1.6 × 10 ⁻¹⁹ [C], B
Represents a band [Hz]. That is, as the current i flowing through the light receiving element 43 increases, the shot noise current is, that is, noise increases, and the reflected light becomes more difficult to detect. In particular, it becomes difficult to detect weak reflected light reflected from a distance, and it is understood that the distance measuring ability is deteriorated. The decrease in the measurement capability is shown in the measurement limit curve of FIG. 6, and it is shown that the distance cannot be measured due to noise above the measurement limit curve, that is, at a distance. Therefore, if the distance measurement on the distant side becomes impossible at a certain rate or more, the data becomes unreliable to the extent that the distance data cannot be used for various controls. By setting the threshold voltage Vx of the monitor voltage, it is determined that the normal distance measurement is performed when the threshold voltage is Vx or more, and the abnormal distance measurement is performed when the threshold voltage is less than the threshold voltage Vx.

Therefore, if the monitor voltage measured by the calculation unit 33 is lower than the threshold voltage Vx ("N" in S1030).
"O"), the fail lamp 64a is turned on as described above (S1020), the abnormal state is displayed, and the process ends. On the other hand, if the monitor voltage is equal to or higher than the threshold voltage Vx, it is determined to be normal (S1030), and then it is determined whether or not scanning of all predetermined areas is completed (S1040).
Each time the main distance measurement process is started, a drive signal from the calculation unit 33 is input to the scan mirror 35 via the motor drive unit 49 in a process (not shown), so that the mirror 47 swings. Scan at each angle. By repeating this scan, the laser light H is swept and irradiated in front of the vehicle over a predetermined angle in the horizontal plane. Whether the area over the predetermined angle is scanned once again after the distance output (described later) is performed last time is determined in step S1.
The determination is made at 040.

If scanning of all areas has not been completed ("NO" in S1040), once processing is completed, this processing is performed again with a different angle of the scan mirror 35 and repeated until scanning of all areas is completed. If the scanning of all areas is completed (“YES” in S1040),
It is determined whether or not distance data exists (S1050).
That is, it is determined whether the distance data is calculated by obtaining the time difference data from the time measuring circuit 61 in the scan of the entire area. If the time measurement circuit 6
If no data of the time difference is obtained from 1, the distance data is not calculated in the calculation unit 33 based on this time difference (“NO” in S1050), and the process is ended once again, and the whole process is restarted from the beginning. This process is repeated for the area.

On the other hand, when distance data is obtained (S
If “YES” at 1050), the distance data is grouped according to the distance (S1060). This "grouping according to distance" will be described. As mentioned above,
In the present embodiment, scanning type laser light emission is used.
Since the laser diode 39 is configured to emit light each time the mirror 47 swings by a predetermined angle, the irradiation direction of the laser light H is also set to be discontinuous at predetermined angles (for example, 0.5 degrees). Therefore, even if the distance data is originally based on the reflected wave from the same object, if the irradiation direction is different, it is distinguished as different distance data and is processed as it is as different data. Therefore, the subsequent processing is simplified by grouping adjacent distance data.

Next, the distance data for each group is output to another control device that requires this distance data (S1).
070). It should be noted that the distance data obtained from the time difference by the calculation unit 33 is the light receiving element 40 and the light emission monitor circuit 54.
Delay time of detection in the light receiving element 43, STC
Considering the detection delay time in the circuit 51, the variable gain amplifier 53, and the comparator 57, after converting into an accurate time difference corresponding to the distance, the accurate distance data is obtained from the time difference and the speed of light. It should be noted that the data does not have to be the distance data directly, but may be any physical quantity representing the distance, for example, the exact time difference itself. Since the time difference considering the delay time is proportional to the distance, it can be used instead of the distance itself. Such accurate distance data or accurate time difference may be calculated when the arithmetic unit 33 receives it from the time measuring circuit 61,
Before or immediately after the grouping in step S1060, data of all time differences may be collectively converted into a distance or a physical quantity representing the distance.

After step S1070, the fail lamp 64a is turned off and output (S1080), and the process is terminated. After that, the scanning process for all the areas is newly started, and the distance measuring process described above is repeated.
In the present embodiment, as described above, the intensity of the background light is determined based on the value of the monitor voltage (S1030), and if the background light is too strong, particularly long-distance measurement data cannot be obtained. In step S1030, “NO”), the distance data is not obtained, and the fail lamp 64a is turned on to notify the driver that the distance cannot be accurately measured.

Therefore, abnormal distance data is not used for various controls, and abnormal control can be prevented in advance. In addition, by notifying the driver or the like that the distance data cannot be measured in this way, the driver or the like can know that the control accompanying the measurement of the distance measuring device 1 cannot be performed, so that the driver or the like is notified that various controls are not performed. It becomes clear and can prevent the driver etc. from being confused.

Further, the distance measuring device 1 of the present embodiment is
As a start pulse PA for the time measuring circuit 61,
Instead of using the drive signal for light emission given from the arithmetic unit 33 to the light emission drive circuit 45, the laser diode 3 is used.
The pulse output from the light emission monitor circuit 54 by the light reception of the light receiving element 40 provided close to 9 is used.

Therefore, as shown in FIG. 4, even if the delay time from the output of the drive signal to the emission of light greatly fluctuates due to the individual difference of the laser diode 39 and the light emission drive circuit 45 and the difference in temperature, the start pulse PA does not show at all. It does not affect. Moreover, the light receiving element 40 and the light emission monitor circuit 54
In comparison with the laser diode 39 and the light emission drive circuit 45, the individual difference in delay time or the change in delay time due to temperature is negligible.

Therefore, the time measuring circuit 61 can output the time difference accurately corresponding to the distance, and the arithmetic unit 33.
It is possible to obtain precise distance data with almost no error in the distance calculated in. In the present embodiment, the laser diode 39 and the light emission drive circuit 45 correspond to irradiation means, the configuration of FIG. 2 corresponds to reflected light detection means and background light intensity detection means, and the time measurement circuit 61 corresponds to time difference measurement means. Then, the calculation unit 33 corresponds to the distance calculation means. Further, in the distance measurement processing of FIG. 5 performed by the calculation unit 33, step S1030 corresponds to the processing as the distance measurement capability deterioration detection means and the distance measurement stop means, and S1020 corresponds to the processing as the alarm means.

[Others] The distance measuring device 1 of the present invention is not limited to the above-mentioned embodiment, and can be constructed in various modes without departing from the scope of the present invention.
For example, in the above-described embodiment, when the drive signal from the calculation unit 33 is input to the scan mirror 35 via the motor drive unit 49, the mirror 47 oscillates to scan a predetermined area so that the laser light is emitted. The H employs a so-called scan method in which the vehicle is swept and irradiated at a predetermined angle in front of the vehicle. However, the present invention is not limited to the scan method, and can be implemented in the fixed method as well.

In the case of this fixed system, the scan mirror 35 and the motor drive unit 49 are unnecessary, and the range of a predetermined angle (about the same as the predetermined angle swept and irradiated in the case of the scan system) from the laser diode 39 is unnecessary. Laser light will be emitted. Further, the light receiving element 40 may detect the laser light from the laser diode 39 via a reflecting mirror, or via a prism or an optical fiber, without directly receiving the laser light from the laser diode 39.
However, in order to eliminate various errors as much as possible, the light receiving element 40
It is preferable to directly detect the output light of the laser diode 39 at a position close to the laser diode 39.
In FIG. 1, the light receiving element 40 is arranged in a direction different from the optical path for irradiating the outside through the mirror 47 and the light emitting lens 37. The light receiving element 4 should be placed at a position that does not cause a shortage.
0 may be arranged to detect the light emission timing of the laser diode 39.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram illustrating a distance measuring device according to an embodiment.

FIG. 2 is a configuration explanatory view showing details of a light receiving circuit in the distance measuring device.

FIG. 3 is a configuration explanatory view showing details of an emission monitor circuit in the distance measuring device.

FIG. 4 is a timing chart showing a delay of light emission of a laser diode with respect to a drive signal to a light emission drive circuit.

FIG. 5 is a flowchart showing a distance measurement process repeatedly executed by a calculation unit of the distance measurement device.

FIG. 6 is a graph showing the relationship between the monitor voltage and the limit of the detection distance.

FIG. 7 is a timing chart showing various signals when a distance is measured by the distance measuring device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Distance measuring device, 31 ... Transceiver, 33 ... Arithmetic unit, 3
3a ... A / D converter 35 ... Scan mirror, 37 ... Light emitting lens, 39 ... Laser diode 40 ... Light receiving element, 41 ... Light receiving lens, 43 ... Light receiving element,
44 ... Light receiving circuit 44a, 44b ... Load resistance, 44c ... 8V power supply, 45 ...
Light emission drive circuit 47 ... Mirror, 49 ... Motor drive unit, 51 ... STC circuit 53 ... Variable gain amplifier, 54 ... Emission monitor circuit, 55
... D / A converter 57 ... Comparator, 61 ... Time measuring circuit, 63 ... Peak hold circuit 64 ... Fail lamp drive circuit, 64a ... Fail lamp, 71 ... 8V power supply 73 ... Noise removing resistor, 75 ... Charge supply capacitor block 77 ... Load resistance, 79 ... Amplifier circuit block, 79a,
79c ... Capacitor, 79b, 79d ... Amplifier, 79e
… Inverter

Claims (7)

[Claims] 1. An irradiating means for irradiating light, a reflected light detecting means for detecting reflected light which is the light radiated by the irradiating means reflected from a reflector, and the irradiating means irradiates the light. A time difference measuring means for measuring a time difference from the time when the reflected light detecting means detects the reflected light, and a distance to the reflector or a physical quantity representing the distance based on the time difference measured by the time difference measuring means. In the distance measuring device including the distance calculating means, the background light intensity detecting means for detecting the intensity of the background light, and the distance measuring ability according to the degree of the background light detected by the background light intensity detecting means. A distance measuring device comprising: a distance measuring capability deterioration detecting means for detecting deterioration. 2. The distance measuring device according to claim 1, wherein the reflected light detecting means also serves as the background light intensity detecting means. 3. A circuit in which the reflected light detecting means is arranged in series in the order of a load resistance, a light receiving element for flowing a current of a current amount according to the intensity of light, and a load resistance, and a predetermined constant voltage is applied. 3. The intensity of the background light is detected based on the voltage on the other end side of the light receiving element while detecting the reflected light based on the voltage change on the one end side of the light receiving element. Distance measuring device. 4. The reflected light detecting means detects the reflected light based on a voltage change on the low potential side of the light receiving element, and the lower the voltage based on the voltage on the high potential side of the light receiving element, the lower the voltage. The distance measuring device according to claim 3, wherein the background light is detected to be strong. 5. An alarm unit is further provided for issuing an alarm when it is determined that the degree of distance measurement capability deterioration detected by the distance measurement capability deterioration detection unit is larger than a predetermined state. The distance measuring device according to any one of claims 1 to 4. 6. The distance measuring device according to claim 5, wherein the alarm by the alarm means is lighting of a lamp for notifying the abnormality or ringing of a buzzer for notifying the abnormality. 7. The processing of the distance calculating means is stopped when it is determined that the degree of the distance measuring ability decrease detected by the distance measuring ability decrease detecting means is larger than a predetermined state. A distance measuring stop means is provided, and the distance measuring stop means is provided.
The distance measuring device as described.