JPH0784046A - Distance measuring apparatus - Google Patents

Abstract

PURPOSE:To prevent outputting of a distance of an object unnecessary to be detected from being generated by providing deciding means for measuring a varied amount of a distance each time the distance is measured to decide invalid when the varied amount exceeds a predetermined value. CONSTITUTION:When a light pulse-emitted from transmitting means 1 is emitted to an object 6, it is reflected, and the reflected light is received by receiving means 2. Then, processing means 3 obtains a distance from a distance measuring apparatus and the object 6 from a reciprocating time of the light pulse. In this case, distance deciding means 36 compares a distance of this time with the previous distance each time the distance is measured and obtains its varied amount. As a result, when the amount exceeds a predetermined value, whether the state of the predetermined value or more is continued for a predetermined time or not is decided. When it is continued for the predetermined time, the distance of this case is output. On the other hand, when it is not continued for the predetermined time, the distance of the case is decided invalid, and the previous distance is output to output means 34.

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 which detects the presence or absence of an object by transmitting an electromagnetic wave and measures the distance to the object by the time between transmission and reception of the electromagnetic wave. The present invention relates to a distance measuring device that, when an object such as another vehicle appears temporarily, does not use the object that appears only temporarily as a distance measurement object to perform an appropriate distance measurement.

[0002]

2. Description of the Related Art As a distance measuring device of this type, a device disclosed in, for example, Japanese Patent Publication No. 3-30116 is known. FIG. 3 is a diagram showing a configuration of an example of a conventional device, and 1 is a transmission unit. The transmitting means 1 comprises a laser diode 11, a pulse driving device 12 for the laser diode 11, and a light transmitting lens 13. 2 is a receiving means. The receiving means 2 comprises a light receiving lens 21 and a light receiving element 22. Reference numeral 3 denotes a processing means. The processing means 3 measures the presence or absence of an object and the distance to the object according to the time from the light transmission of the transmission means 1 to the light reception of the reception means 2, and outputs the measured distance. . Reference numerals 4 and 5 are transparent covers made of glass or the like, which serve as a light transmitting window and a light receiving window, respectively. Further, 6 is an object to be detected.

Next, the operation of the conventional device thus constructed will be described. The pulse driving device 12 of the transmitting means 1 drives the laser diode 11 to emit pulsed light. The light emitted from the laser diode 11 is condensed by the light transmitting lens 13 and is emitted forward through the light transmitting window 4. If the object 6 is within the irradiation range, the irradiated light will be the object 6
Is received by the light receiving means 2 through the light receiving window 5. The light receiving means 2 collects this reflected light on the light receiving surface of the light receiving element 22 by the light receiving lens 21, and the light receiving element 22 converts the reflected light into an electric signal by photoelectric conversion. The processing means 3 detects this electric signal, measures the time from the pulse driving time from the laser diode of the light transmitting means 1 to the detection of the reflected light from the object 6, for example, by a high-speed counter or the like to measure the distance. The distance between the object and the object is calculated by the following equation 1. Distance = round trip time x speed of light / 2 (Equation 1)

[0004]

The distance measuring device of this type detects an object by irradiating the object with electromagnetic waves and receiving the reflected waves thereof. Even if a reflected wave from another object is received for a moment or rain, fog, or a reflected wave from graphite in the exhaust gas emitted from a vehicle ahead is detected, the light receiving means is intended for that purpose. It is impossible to determine whether it is a reflected wave from an object or a reflected wave from another object. Therefore, the processing means calculates the measured distance from the incident reflected wave and outputs incorrect distance data. The problem of incident reflected waves from other than the intended object always occurs when using this type of distance measuring device.

For example, if this type of distance measuring device is mounted on a vehicle and is used as a device for measuring the inter-vehicle distance to the preceding vehicle and issuing an alarm to keep the safe inter-vehicle distance, the own vehicle can detect the preceding vehicle ahead. While driving while detecting, when another car suddenly interrupts the same lane and immediately moves to another lane, it is only an instantaneous interruption, so even if the alarm is unnecessary in the driving situation, it will be incorrect. Will issue an alarm. Or, when encountering bad weather such as rain or fog, it becomes impossible to detect the distance to the preceding vehicle by detecting these objects,
There is also a case where a driver feels uncomfortable, for example, by detecting a transient object and determining that the distance between the preceding vehicle and the preceding vehicle is short, and suddenly reducing the speed of the vehicle. In this way, detecting unneeded objects and measuring the distance, and outputting the distance means that when this type of device is used as a sensor of a system for generating an alarm or controlling a vehicle, etc. It becomes an important issue regarding safety and reliability.

The present invention has been made to solve such a problem. Even if the distance measuring device detects an object for an instantaneous time or receives a reflected wave due to other factors, an alarm or the like accompanying the distance measurement is generated. It is an object of the present invention to provide a distance measuring device capable of outputting an appropriate output according to the measured distance by determining whether or not the distance is valid so that the operation of To do.

[0007]

According to the present invention, an electromagnetic wave transmitting means, a receiving means for receiving a reflected wave from an object irradiated with the electromagnetic wave, and the presence or absence of the object from the round-trip time from the electromagnetic wave transmission to the reception are determined. In the distance measuring device having a processing means for detecting and measuring the distance to this object, the processing means is a determining means for determining whether or not the measured distance is valid, and the result of the determination is that it is valid. An object of the present invention is to solve the above-mentioned problems by a distance measuring device, which is provided with an output unit that outputs the measured distance and the distance that was valid last time if it is not valid.

Further, the electromagnetic wave transmitting means, the receiving means for receiving the reflected wave from the object irradiated with the electromagnetic wave, the presence / absence of the object is detected from the round trip time from the transmission of the electromagnetic wave to the reception, and the distance to the object is detected. In the distance measuring device having a processing means for measuring, the processing means is a command means for issuing a command to extend the measurement distance range when the measured distance is a very short distance, and when the measurement distance range is extended, When the distance is measured, the above problem is solved by a distance measuring device including a distance output unit that outputs a plurality of measured distances as effective distances.

Further, the electromagnetic wave transmitting means, the receiving means for receiving the reflected wave from the object irradiated with the electromagnetic wave, the presence or absence of the object is detected from the round-trip time from the transmission of the electromagnetic wave to the reception, and the distance to the object is detected. In a distance measuring device having a processing means for measuring the distance, it is determined that the measured distance is compared with a distance measured in the past, and the distance measured by this comparison means is shorter than a distance measured in the past by a predetermined value or more. Command means to issue a command to extend the measurement distance range when it is measured, and when the distance measurement range is extended, if another distance is measured, this distance is output as an effective distance and no other distance is measured. In this case, the above problem can be solved by a distance measuring device including a distance output unit that outputs a distance shorter than the predetermined value as an effective distance.

[0010]

According to the present invention, the reflected wave from the object in the irradiation range of the electromagnetic wave generated by the transmitting means is received, the round trip time of the electromagnetic wave between the distance measuring device and the object is measured, and the distance to the object is measured. taking measurement. When the reflected wave from the object is received,
It is converted into a distance for each reception, and it is determined whether or not this distance is valid. If valid, the distance measured at that time is output. If not valid, the previously valid distance is output. Here, in order to determine whether or not the measured distance is valid, as in claim 2, each time the distance is measured, the previous distance and the current distance are compared to obtain the amount of change. As a result, if the amount of change is equal to or more than the predetermined value, it is determined whether the state of being equal to or more than the predetermined value has continued for a predetermined time. If it continues for a predetermined time, the distance at that time is output. On the other hand, if it does not continue for the predetermined time, the distance at that time is not valid and the previous distance is output.

Further, in the invention of claim 3, when the measured distance is a very short distance, the command means extends the measurement distance range, and when another distance is measured when the measurement distance range is extended. Outputs a plurality of distances measured by the distance output means as effective distances. According to the invention of claim 4, the measured distance is compared with the distance measured in the past, and if the measured distance is shorter than the past distance by a predetermined value or more, the distance measuring range is extended by the command means, and the result is If another distance is measured, that distance is output from the distance output means, and if no other distance is detected, the first measured short distance is output.

In the invention of claim 5, the measured distance is compared with the distance measured in the past, and when the measured distance is shorter than the past distance by a predetermined value or more, the distance measuring range is extended by the command means. As a result, if another distance is measured, that distance is output from the distance output means, and if no other distance is detected, it is counted whether the first measured short distance has continued a predetermined number of times, If it continues the number of times, the short distance is output. According to the invention of claim 6, the extension amount of the measurement distance range from the command means is determined based on the vehicle speed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Embodiment 1 In FIG. 1, reference numeral 1 denotes an electromagnetic wave transmitting means, which is composed of a laser diode 11, a pulse driving device 12 thereof, and a light transmitting lens 13 when pulsed light is used for the electromagnetic wave. Also, any electromagnetic wave other than pulsed light may be used as long as it is an electromagnetic wave that can be used for distance measurement. 2 is a receiving means, which comprises a light receiving lens 21 and a light receiving element 22. 3 is a processing means, which comprises a distance measuring means 35, a distance determining means 36, and a distance outputting means 34. The distance determining means 36 is composed of a storage means 31, a comparing means 32, and an adder 33. Reference numerals 4 and 5 denote transparent covers made of glass or the like, which serve as a light transmitting window and a light receiving window, respectively. 6 is an object to be detected.

Next, the operation will be described. When the light pulse-emitted by the transmitting means 1 hits the object 6, it is reflected, and the reflected light is received by the receiving means 2, and thereafter, the processing means 3
Then, the distance between the distance measuring device and the object is obtained by the above equation 1. Since these steps are similar to those of the conventional device, they will not be described in detail here, and the determination processing of the distance determination means 36 for determining whether or not the measured distance in the processing means 3 is valid will be described.

FIG. 2 is a flow chart showing this determination processing, and this processing is repeatedly executed every 100 (ms) period for measuring the distance. First, in step 1, the object 6
Is detected. If the object 6 is not detected, the distance cannot be measured, so the process proceeds to step 11. If the object 6 is detected, the process proceeds to step 2. In step 11, the counter value used to count the duration described later for determining the measured distance and the previous distance stored in the storage means 31 used to calculate the change amount of the distance are cleared and the processing is ended. To do.

If the object 6 is detected, the measured distance measured by the distance measuring means 35 is calculated in step 2, and the distance calculated in step 2 is substituted for the current distance in step 3. In step 4, the current distance and the previous distance are compared. If the current distance is equal to or greater than the previous distance, the process proceeds to step 5, otherwise the process proceeds to step 8. In step 5, the counter value (the counter value corresponding to a predetermined time for determining whether the measurement distance is valid or invalid) is cleared, and in step 6, the current distance is substituted for the previous distance. As a result, in step 7, the current distance is valid, the current distance is output to the output means 34, and the process ends.

If the current distance is smaller than the previous distance in step 4, the current distance is subtracted from the previous distance in step 8 to obtain the distance change amount. In step 9, the amount of change in distance obtained in step 8 is a distance constant X that is a predetermined value for determining whether or not the measured distance is valid.
The comparison means 32 compares whether or not the value is larger than (m). If the amount of change in distance is less than X (m), the process proceeds to steps 5, 6 and 7, and the process is terminated. If not, that is, if it is greater than or equal to X, the process proceeds to step 10.

In step 10, it is determined whether the counter value for counting the duration (predetermined time) of the state in which the change amount is X or more is less than Y. If less than Y, the counter is counted in step 12. The value is incremented by the adder 33. In this case, the distance change amount is X or more, but since the state is within the predetermined time, the current distance is not yet valid, and the previous distance (before the distance change becomes Xm or more Distance) is output as valid, and the process ends. If the counter value is Y or more, the process proceeds to steps 5, 6, and 7 to end the process. That is, in this case, the change in distance is equal to or larger than the predetermined value for the predetermined time, so it is determined to be valid and is substituted for the previous distance and output.

With the above processing, for example, as a result of another vehicle cutting in front of the own vehicle, the amount of change in distance becomes equal to or greater than the predetermined value Xm, and this state continues for a predetermined time (counter value Y) or more. For example, it is determined that the vehicle is a continuous interruption vehicle, and the interruption vehicle is set as an object for future distance measurement. On the other hand, if the interrupting vehicle appears for a moment in front of the own vehicle and immediately moves to another lane, it means that the state in which the amount of change in distance exceeds the predetermined value lasted for less than the predetermined time, so It will not be an object for distance measurement.

As described above, in the above-described embodiment, the measured distance is shortened in the direction of 100 (ms) or more by X (m) or more, and the state of being changed by X (m) or more is 10 or more.
By recognizing that it is within 0 (ms) × Y time, it is determined whether or not the measured distance is valid. In addition,
In the above embodiment, the measured distance is used for the determination, and the distance constant for determining the change amount of the distance is X (m),
Although the duration constant of the amount of change is Y, this value may be set according to the speed and accuracy for determining the measurement distance required by the system using the distance measuring device.

Second Embodiment FIG. 3 shows the configuration of the second embodiment. Transmitting means 1 and receiving means 2
Is the same as that of the first embodiment. Further, although the light transmitting window 4 and the light receiving window 5 are not shown, they may be provided similarly to the first embodiment. Since the configuration of the processing means 3 is partially different from that of the first embodiment, the configuration of the processing means will be described including the parts different from the first embodiment. The processing means 3 includes a distance measuring means 35,
Depending on the distance output means 34 for outputting the distance measured by the means 35, the comparison means 32 for comparing the distance measured by the means 35 with a predetermined distance which is the closest distance, and the comparison result by the comparison means 32. And an instruction means 37 for instructing extension of the measurement range, and according to the instruction from this instruction means 37,
If necessary, the distance measuring means 35 extends the distance to be measured.

Next, the processing of the distance measuring device according to the second embodiment will be described with reference to FIG. This process measures the distance 1
It is repeatedly executed every 00 (ms) cycle. First, in step 21, after electromagnetic waves such as laser light are generated from the transmitting means, it is determined whether or not there is a received signal of a reflected wave from the object,
If there is no received signal, the distance cannot be measured, so the processing ends. If there is a received signal, the measured distance 1 to the object 7 measured by the distance measuring means 35 is calculated in step 22. In this example, the object 7 is rain, fog, or the like.
Next, in step 23, it is determined whether or not the measured distance 1 is the closest distance by comparing with the distance constant X (m) set in the comparison means 32. When the measured distance is larger than the distance constant X (m), the process proceeds to step 28, and the measured distance 1 is output to the distance output means 34.

When the measured distance is less than the distance constant X (m), the distance measuring means 35 extends the measuring range in step 24 based on the measured distance extension instruction from the instruction means 37. Specifically, at this point, it is difficult to distinguish whether the object 7 is an object that does not originally need to be detected, such as a rainy or transient object, or a vehicle that has actually cut into the front of the vehicle. . Therefore, in order to check whether there is any other object within the range measured by the distance measuring means 35, measurement is performed by measuring whether or not there is a received signal from another object within a predetermined time after measuring the object 7. The distance is extended. Based on this, in step 25, it is determined whether or not there is a received signal of a reflected wave from the object 6 other than the object 7, and if there is a received signal, the distance measuring means 35 measures the distance to the object 6 in step 26. Calculate 2.
In the second embodiment, the measured distance 2 is output by the distance output means 34 in step 27, and then step 28
Then, the measured distance 1, which is the distance to the object 7 existing within the shortest distance, is also output by the distance output means 18, and the process ends.

In the subsequent control, arbitrary processing may be performed such that the measurement distance 1 which is the closest distance is not adopted and the measurement distance 2 is adopted. Thus, in the second embodiment, the distance to the object is the distance constant X
In the case of the very short distance (m) or less, it is measured whether there is a received signal from another object within a predetermined time after the object measurement so as to extend the measurement distance range, and only the number of objects that can be measured is measured. The distance to each object is output as the effective distance. In the second embodiment, the extension measurement distance range instructed by the instruction means 37 is within a predetermined time. However, the measurement distance range is determined based on, for example, the vehicle speed of the vehicle using this distance measurement device. Good. Therefore, as shown in FIG. 3, the vehicle speed detection means 8 is connected to the command means 37, and the vehicle speed is input to the command means 37. And
For example, as the vehicle speed increases, the extension of the measurement distance range may be increased.

Third Embodiment A third embodiment will be described with reference to FIG. Also in the third embodiment, the transmitting means 1 and the receiving means 2 are the same as those in the first embodiment. Also,
Although the light transmitting window 4 and the light receiving window 5 are not shown, they may be provided as in the first embodiment. Since the configuration of the processing means 3 is partially different from that of the first and second embodiments, the configuration of the processing means will be described including the portions different from the above-described embodiments. Processing means 3
Is a distance measuring means 35, a distance output means 34 for outputting the distance measured by the means 35, a storage means 31 for storing a past distance, and a distance measured by the means 35 for the past distance. Comparison means 32 for comparison, command means 37 for commanding extension of the measurement range according to the comparison result by the comparison means 32, and distance to be measured by the distance measuring means 35 according to the command from the command means 37. Is extended but no other object can be detected, the adder 33 counts the number of times the object of the distance measured by the distance measuring means 35 is detected.

Next, the processing of the distance measuring apparatus according to the third embodiment will be described with reference to FIG. This process measures the distance 10
It is repeatedly executed every 0 (ms) cycle. First, in step 31, after electromagnetic waves such as laser light from the transmitting means 1 are generated,
It is determined whether there is a received signal of a reflected wave from the object. If there is no received signal, the distance cannot be measured, so the processing ends. If there is a received signal, the measured distance to the object (for example, the object 9) measured by the distance measuring means 35 is calculated in step 32. This distance is referred to as measurement distance 1. Next, in step 33, the distance difference between the measured distance 1 and the past distance stored in the storage means 31 is obtained by the formula: past distance-measured distance 1. Here, the distance measured in the previous distance measurement cycle is adopted as the past distance. Step 34
Then, the comparison means 32 compares whether or not the distance difference M is longer than the distance constant X (m) which is a predetermined distance. Here, the larger the numerical value of the distance difference M, the smaller the distance to the object (however, this object is not necessarily the same as the previously detected object) compared to the previous distance measurement. If M is shorter than the distance constant X (m) (small value), the value of the adder 33 that counts the number of continuous distances is cleared in step 41, and the measured distance 1 is measured in the past, that is, the previous measurement. The distance is stored in the storage unit 31 as the distance, the measured distance 1 is output to the distance output unit 34 in step 45, and the process is ended.

If the distance difference M is longer than the distance constant X (m) (the numerical value is large), the distance measuring means is generated in step 35 in response to the instruction from the instruction means 37 based on the past (previous) distance. 35 extends the measurement distance range,
It is measured whether or not there is a received signal from the object that approximates the past (previous) distance within a predetermined time after the measurement of the object 9. In steps 36 and 37, it is determined whether or not there is a received signal of a reflected wave from the object 6 that approximates the past (previous) measured distance.
That is, if there is a received signal, the distance to the object 6 is calculated by the distance measuring means 35 in step 37, so that it can be determined whether or not the distance to the object 6 is close to the past distance. When the distance to the object 6 which is approximate to the past distance is detected, this is set as the measurement distance 2, the measured distance 2 is stored in the storage means 31 as the past distance in step 38, and the measured distance 2 is measured in step 39. Output means 34
Is output, and the value of the adder 33 that counts the number of continuous distances is cleared in step 40, and the processing ends. Whether or not there is an object at a distance close to the past distance is determined by actually measuring the distance to that object, for example, the direction of the received reflected wave is approximate to the direction of the previously detected object. Or the strength of the received reflected wave is similar to the strength of the reflected wave from the object detected in the past.

On the other hand, if there is no received signal of a distance close to the past (previous) distance, the value of the adder 33 that counts the number of continuations of the measured distance 1 in step 42 is the count constant Y.
(Time) It is determined whether or not it is greater than. Count constant Y
If it is smaller than (times), the value of the adder 33 is incremented in step 43 and the process is terminated. Count constant Y
In the case of (times) or more, the measured distance 1 is stored as the past distance in the storage means 31 in step 44, the measured distance 1 is output from the distance output means 34 in step 35, and the processing is ended.
In this case, in many cases, another vehicle or the like is actually in the short distance of the own vehicle. As described above, in the third embodiment, when the measurement distance to the object is shorter than the past measurement distance by the distance constant X (m) or more, the object is extended so as to extend the measurement distance range based on the past measurement distance. Determine whether there is a received signal from an object that is close to the past measured distance at the time after measurement, if there is such a received signal, output the distance at that time as an effective output, if there is no measurement, If the initially measured distance continues for a predetermined number of cycles, the distance is output as an effective distance.

In the third embodiment, the extending measurement distance range is the past measurement distance. However, as shown in FIG. 5, the vehicle speed detecting means 8 for detecting the vehicle speed is connected to the command means 37 and is detected by this. The extension distance may be obtained according to the vehicle speed. For example, control may be performed such that the extension distance increases as the vehicle speed increases. In the third embodiment, when the distance difference M is larger than the distance constant X (m), if the measured distance 1 at that time does not eventually reach the count constant Y (times), the processing is terminated. However, even if the count constant Y (times) is not reached, this may be stored as a past distance and output from the distance output means 34. In each of the above embodiments, the distance measuring means 35 normally detects the actual preceding object even in bad weather such as rain and fog, but often receives reflected waves such as rain. The distance measuring device of the present invention is an effective countermeasure.

The distance measuring device described above is mounted on a vehicle,
If you use it for a device that measures the inter-vehicle distance to the preceding vehicle and warns you to keep a safe inter-vehicle distance, when your vehicle is traveling while detecting the preceding vehicle in front, other vehicles in the same lane If you move to another lane immediately, if you momentarily detect an object other than the preceding vehicle, or if you only detect a transient object, or if it is bad weather such as rain or fog However, it is possible to accurately detect the distance to the preceding vehicle. On the other hand, when the alarm is unnecessary, it is possible to improve the safety and reliability of the system without erroneously issuing the alarm. Furthermore, since such a determination is performed by the processing device, no special device for comparing and storing distances or counting time is required, and it can be realized by software processing of the processing device that measures the distance. The device can be made compact and inexpensive.

[0031]

As described above, according to the present invention,
Unnecessary output of the distance to an object that does not need to know the distance can be suppressed, and an unnecessary alarm is issued in the control after the distance measurement that accompanies detecting the distance to the object that does not need to know the distance. Can be eliminated and proper distance measurement can be performed.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a distance measuring device according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing a processing procedure according to the first embodiment of the present invention.

FIG. 3 is a configuration diagram showing a distance measuring device according to a second embodiment of the present invention.

FIG. 4 is a flowchart showing a processing procedure according to a second embodiment of the present invention.

FIG. 5 is a configuration diagram showing a distance measuring device according to a third embodiment of the present invention.

FIG. 6 is a flowchart showing a processing procedure according to a third embodiment of the present invention.

FIG. 7 is a configuration diagram showing a conventional distance measuring device.

[Explanation of symbols]

 1 transmitting means 2 receiving means 3 processing means 31 storage means 32 comparing means 34 distance outputting means 35 distance measuring means 36 distance determining means 37 commanding means 6, 7, 9 detected object

Claims (6)

[Claims] 1. An electromagnetic wave transmitting means, a receiving means for receiving a reflected wave from an object irradiated with this electromagnetic wave, the presence / absence of the object is detected from the round-trip time from the transmission of the electromagnetic wave to the reception, and the distance to this object is also detected. In the distance measuring device having a processing means for measuring, the processing means is a determining means for determining whether or not the measured distance is valid, and the result of the determination is that if the measured distance is valid, the measured distance is also valid. If not, the distance measuring device is provided with an output means for outputting the previously effective distance. 2. The determination means measures the amount of change in the distance each time the distance is measured, and when the amount of change exceeds a predetermined value and the state of exceeding the predetermined value is within a predetermined time. The distance measuring device according to claim 1, which is determined to be invalid. 3. An electromagnetic wave transmitting means, a receiving means for receiving a reflected wave from an object irradiated with the electromagnetic wave, the presence / absence of the object is detected from the round-trip time from the transmission of the electromagnetic wave to the reception, and the distance to the object is detected. In the distance measuring device having a processing means for measuring, the processing means is a command means for issuing a command to extend the measurement distance range when the measured distance is a very short distance, and when the measurement distance range is extended, A distance measuring device comprising a distance output means for outputting a plurality of measured distances as effective distances when the distances are measured. 4. An electromagnetic wave transmitting means, a receiving means for receiving a reflected wave from an object irradiated with this electromagnetic wave, the presence / absence of the object is detected from the round-trip time from the transmission of the electromagnetic wave to the reception, and the distance to the object is detected. In a distance measuring device having a processing means for measuring the distance, a comparison means for comparing the measured distance with a distance measured in the past, and the distance measured by this comparison means is shorter than a distance measured in the past by a predetermined value or more. Command means to issue a command to extend the measurement distance range when it is determined, and when the distance measurement range is extended and another distance is measured, this distance is output as an effective distance and the other distance A distance measuring device comprising: a distance output means for outputting a distance shorter than the predetermined value as an effective distance when the distance is not measured. 5. The processing means according to claim 4, further comprising means for measuring whether or not a distance shorter than a predetermined value by a predetermined value or more continues for a predetermined number of times, when no other distance is measured. A distance measuring device that outputs a distance shorter than the predetermined value by the distance output means when it is determined by this means that the distance continues for a predetermined number of times. 6. The method according to claim 3 or 4,
The commanding means is a distance measuring device that determines the extending measurement distance range based on the speed of the vehicle.