JPH07167954A - Distance measuring device - Google Patents

Abstract

PURPOSE:To decrease phase change associate with a gain change of a received electric signal and establish a high precision measurablity by varying the bias voltage of a photo-electron multiplying element according to a function of time from emission of photo-pulses which is measured by a clock means. CONSTITUTION:When a command signal 51 is fed from a calculation control part 1 to a timing control part 2, it 2 gives a timing signal 52a to a semiconductor laser driving part 3 so that pulse signal 53 is driven, and laser pulses are emitted from a source 4. The pulses are transmitted toward an object to be measured via a signal transmission lens 5. The laser pulses reflected thereby asre eceived by a light receiving element 7 through a signal reception lens 6, and photoelectric transducing takes place with an amplification factor which complies with a voltage signal 55 given from bias 8, followed by emission of a reception signal 5. The reception signal 54 is amplified 9, and an analog receive signal 56 is emitted. Then, the signal 56 is A/D converted 10 and another reception signal 60 is emitted. From the control part 2, a signal 58 is fed to a gate circuit 13, and with the feed of signal 52e, signals 59a, 59b are given from this gate circuit 13 to the A/D converter 10 and a memory 12.

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. More specifically, the distance to the object to be measured by emitting the optical pulse to the object to be measured and measuring the round-trip time of the optical pulse until the reflected light from the object to be measured is received. The present invention relates to a measuring device.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand in various fields to obtain distance information by mounting a distance measuring device on a moving object for the purpose of improving safety and automation. For example, a distance measuring device is mounted on a robot, an automobile, or a train to prevent collision of these moving objects, or a distance measuring device is mounted on a carrier vehicle used in a factory to control the stop position of the carrier vehicle. It is used to As such a distance measuring device, a device that emits a light pulse from a laser light source to a measurement target object, receives a light pulse reflected by the measurement target object, and measures the distance to the distance measurement target object is widely used. There is. Since it can measure the distance in a short time, it is often used especially as a sensor for preventing collision of a moving body or the like.

It is necessary to maintain accuracy in response to a large and rapidly changing measurement distance due to movement of an object to be measured, and a conventional optical pulse light receiving device having a gain control function in a received signal amplification circuit portion has been disclosed. Has been done. These are unnecessary objects other than the object to be measured, that is, from the time when the laser light pulse is generated (or the time measurement start time) for the purpose of not measuring the reflection / scattering signals from fog, rain, snow, smoke, dust, etc.
According to the function of time, the received signal amplification circuit section has a gain control function. Here, for the gain control function, an automatic gain control (AGC) circuit included in the reception signal amplification circuit unit is used. A gain control method that is generally widely used is STC (Sensitivity Time C
ontrol). This suppresses the reception sensitivity for a strong reflection signal from a short distance (a distance corresponding to a time when the laser light pulse is generated or a time measurement start time), and a long distance (a laser light pulse is generated). The reception sensitivity is increased as the time comes or the distance corresponding to a relatively long time from the time measurement start time).

As shown in FIG. 4, in the conventional example, when the operation control unit 101 outputs the command signal 151 to the timing control unit 102, the timing control unit 102 outputs the timing signal 152a to the semiconductor laser drive unit 103, The light source 104 is driven by the pulse signal 153 to emit a laser light pulse. Laser light pulse is the transmission lens 1
The laser light pulse transmitted to the measurement object (not shown) via 05 and reflected by the measurement object is received by the light receiving element 1.
It is received at 07. When the light receiving element 107 receives the laser light pulse, it photoelectrically converts it and outputs a reception signal 154. The reception signal 154 output from the light receiving element 107 is input to the reception signal amplification circuit unit 109, amplified, and output as an analog reception signal 156. At this time, the gain is increased by the STC operation of the timing signal 152c input to the reception signal amplification circuit unit 109. Next, when the analog reception signal 156 is input to the A / D converter 110, A is set with the reference voltage input from the A / D converter reference voltage generator 111 as a reference.
The digital reception signal 160 is output after being D / D converted.
The digital received signal 160 is output to the received signal storage unit 112, the operation control unit 101 then calculates time, the distance from the time to the measurement object is calculated, and the distance to the measurement object is displayed on the display unit 114. It was what was displayed.

Further, for example, the technique disclosed in Japanese Patent Publication No. 3-1626 has a variable gain amplifying means, controls the gain as a function of time, and switches the gain with a switch.

[0006]

However, in the prior art, only the received signal amplifying section bears the STC function. Therefore, by changing the gain, the signal amplitude of the received electric signal due to the received laser light pulse signal from the object to be measured changes, and its phase changes in the delay direction as the amplitude increases. When the phase changes, an error occurs in the time measurement corresponding to the phase change of the received electric signal. When an error occurs in the time measurement, an error occurs in the distance measurement calculated based on the measured time. Thus S
There is a problem in that an error in the distance measurement value, which occurs when the TC function is borne by only the reception signal amplification unit, cannot be avoided.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a distance measuring device with high distance measuring accuracy by reducing the phase change associated with the gain change of the received electric signal due to the STC function.

[0008]

In order to solve the above-mentioned problems, the present invention according to claim 1 emits a light pulse when a timing control means for outputting a light emission timing signal and the light emission timing signal is input. A light emitting means, a light receiving means having a photoelectric element for receiving the light pulse emitted from the light emitting means and reflected by an object to be measured and outputting a light reception signal, and a variable amplifier, and the variable reception signal amplification factor Reception signal amplification means for amplifying the received light signal and outputting an analog reception signal; and A / D conversion means having a reference voltage generator for converting the analog reception signal into a digital reception signal at a set reference voltage, Time measuring means for measuring the time after the light pulse is emitted, and an object to be measured based on the time measured from the time when the light pulse is emitted until the light receiving is received by the time measuring means. The variable amplifier is configured to change the reception signal amplification factor according to a function of time after the optical pulse measured by the timing means is emitted, and the analog reception signal In the distance measuring device for amplifying, the photoelectric element is constituted by a photomultiplier element with a variable multiplication factor, and the bias voltage of the photoelectron multiplier element is measured by the time measuring means of the time from the emission of the optical pulse. It is changed according to a function.

The reference voltage generator is a variable reference voltage generator capable of changing the reference voltage, and the A / D conversion means emits the optical pulse measured by the timing means by the variable reference voltage generator. It is desirable to convert the analog reception signal into the digital reception signal with reference to the reference voltage changed according to a function of time after the reception.

According to a third aspect of the present invention, there is provided a timing control means for outputting a light emission timing signal as a light emission timing signal, a light emitting means for emitting a light pulse when the light emission timing signal is input, and the light emitting means. The light receiving means having a photoelectric element for receiving the light pulse emitted and reflected by the object to be measured and outputting a light receiving signal, and a variable amplifier, amplifying the light receiving signal with a variable reception signal amplification factor and analog receiving Comparing means for comparing the analog received signal with a threshold value generated by the threshold value generating means, which has a reception signal amplifying means for outputting a signal and a threshold value generating means, and the optical pulse is emitted. From the above, the time measuring means for measuring the time until the analog reception signal exceeds the threshold value, and the time measuring means for measuring from the time the light pulse is emitted to the time it is received And a calculation means for calculating the distance to the object to be measured based on the time, wherein the variable amplifier calculates the reception signal amplification factor according to a function of time after the optical pulse measured by the time measuring means is radiated. In the distance measuring device that changes and amplifies the analog reception signal, the photoelectric element is configured by a photomultiplier element with a variable multiplication factor, and the optical pulse measured by the timing means is a bias voltage of the photoelectron multiplier element. It is changed according to the function of time after being emitted.

The threshold value generating means is a variable threshold value generating means capable of changing the threshold value, and the comparing means is the optical pulse measured by the clocking means by the variable threshold value generating means. It is preferred to compare the analog received signal with the threshold value modified according to a function of the time since the radiation.

[0012]

According to the first aspect of the present invention, the optical pulse emitted and reflected by the object to be measured is received by the photomultiplier element, the received signal amplification factor of the received signal amplifying means and the bias voltage of the photoelectron multiplier element. And change as a function of time since the light pulse was emitted. In the invention described in claim 3, the reference voltage of the A / D conversion means or the threshold value for the comparison means changes according to a function of time after the light pulse is emitted.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. The arithmetic control unit 1 is a CPU that outputs a command signal 51 to the timing control unit 2. The timing control unit 2 uses the command signal 51
Is input, timing signals 52 (52a, 52b, 5
2c, 52d, 52e, 52f) and a sampling clock signal 58. The semiconductor laser drive unit 3 is a semiconductor laser which receives the timing signal 52a and outputs a pulse signal 53, and the light source 4 is driven by the pulse signal 53 to emit a laser light pulse.

The transmitting lens 5 transmits an optical pulse of laser light to the object to be measured (not shown) at a predetermined beam divergence angle, and the receiving lens 6 receives the laser pulse reflected from the object to be measured (not shown). Optical system for collecting and receiving light, light receiving element 7
Is an AP that photoelectrically converts the received laser light pulse with an amplification factor according to the applied bias voltage and outputs a reception signal 54.
D (avalanche photodiode). AP
The D bias circuit 8 is a circuit which receives the timing signal 52b and outputs a bias voltage signal 55 for varying the multiplication factor by applying a variable bias voltage to the light receiving element 7 according to the timing signal 52b.

The reception signal amplification circuit section 9 receives the reception signal 54, amplifies it by the timing signal 52c with a variable amplification factor, increases the gain, and outputs the analog reception signal 56, the A / D converter 10. Is an A / D converter reference voltage generator 11 that outputs an analog reception signal 56 to be input, and a reference voltage signal 57 that is variable according to a timing signal 52d.
It is a circuit that receives the reference voltage signal 57 output from the device and outputs the digital reception signal 60 to the reception signal storage unit 12 with the set reference voltage as a reference.

The reception signal storage unit 12 receives the digital reception signal 60 and stores it as reception signal level data, and the gate circuit 13 receives the sampling clock signal 58 output from the timing control unit 2 and the timing signal 52e. The sampling clock signal 59 (59) is stored in the A / D converter 10 and the reception signal storage unit 12 at the instant
a, 59b). The arithmetic control unit 1
After the timing signal 52f is input, the reception signal level data signal 61 is sequentially received from the reception signal storage unit 12, the distance is calculated from the memory address (= light traveling time) at which the reception signal level shows a peak, and the distance data signal 62 is obtained. Display 1
Output to 4. The display unit 14 is a display device that displays distance data.

Next, the basic distance measuring operation will be described with reference to FIG. When the command signal 51 is output from the arithmetic and control unit 1 to the timing control unit 2, the timing control unit 2 operates as shown in FIG.
The timing signal 52a shown as the rising edge in (a) is output to the semiconductor laser drive unit 3, and the pulse signal 5a is output.
3 is driven and a laser light pulse is emitted from the light source 4 (FIG. 3B). The laser light pulse is transmitted toward the measurement object (not shown) via the transmission lens 5. The laser light pulse reflected by the measuring object (not shown) is received by the light receiving element 7 through the reception level 6. When the light receiving element 7 receives the laser light pulse, it photoelectrically converts it with an amplification factor by the bias voltage according to the bias voltage signal 55 from the APD bias circuit 8 and outputs a reception signal 54 shown in FIG. At this time, the bias voltage signal 55 is ST which will be described in detail after the timing signal 52b input to the APD bias circuit 8.
The bias voltage is changed by the C operation, and the bias voltage approaches the breakdown voltage as shown in FIG.

The received signal 54 output from the light receiving element 7 is input to the received signal amplifier circuit section 9, amplified, and output as an analog received signal 56. At this time, the gain of the reception signal amplification circuit unit 9 is increased as shown in FIG. 3E by the STC operation started from the time when the timing signal 52c is input.

Next, when the analog reception signal 56 is input to the A / D converter 10, it is A / D converted with the reference voltage as a reference and the digital reception signal 60 is output. At this time A /
The timing signal 52d is supplied to the D converter reference voltage generator 11.
By the STC operation starting from the time when the input is made, the reference voltage decreases as time passes, as shown in FIG.

The sampling clock signal 58 output from the timing control unit 2 is always input to the gate circuit 13, and the sampling clock signals 59a and 59b from the gate circuit 13 are A / A from the moment the gate is opened by the input of the timing signal 52e. It is output to the D converter 10 and the reception signal storage unit 12.

The A / D converter 10 and the reception signal storage unit 12 receive the sampling clock signals 59a and 59b, respectively, and start the A / D conversion operation or the reception signal storage operation, respectively. In the reception signal storage section 12, the operation of sequentially updating the address by the sampling clock signal 59b is also performed. The A / D converter 10 A / D converts the analog reception signal 56 at the sampling clock cycle from the time when the sampling clock signal 59a is input, and outputs the digital reception signal 60 to the reception signal storage unit 12. The reception signal storage unit 12 receives the digital reception signal 60 and receives the digital reception signal 6 at the sampling clock cycle from the time when the sampling clock signal 59b is input.
0 is stored as the received signal level.

Here, the STC operation will be described in detail. In addition to outputting the timing signal 52a from the timing controller 2 to the semiconductor laser driver 3, the timing signal 52b to the APD bias circuit 8, the timing signal 52c to the received signal amplifier circuit 9, and the reference voltage generator for the A / D converter. 11
The timing signal 52d is output to. Then, the APD so that the timing signals 52b, 52c, and 52d have predetermined time characteristics from the time when they are input, respectively.
In the bias circuit 8, the bias voltage signal 55 causes the AP
The bias voltage of D is brought close to the breakdown voltage and accordingly the amplification factor of photoelectric conversion is increased, and the reception signal amplification circuit unit 9
Then, the amplification factor is increased to increase the gain, and the A / D converter reference voltage generator 11 uses the reference voltage signal 57 to convert the A / D signal.
The reference voltage of the converter 10 is lowered (Figs. 3 (d), (e),
(F)). Therefore, the STC function operates so that a received signal of a small level can be detected with high resolution. By the operation of this STC function, the following two effects (a) and (b) occur simultaneously due to the predetermined time characteristic. (A) By bringing the APD bias voltage close to the breakdown voltage, the multiplication factor of the APD is increased, the capacitance between the terminals of the APD is reduced, the reception frequency band is expanded, and the phase delay of the reception signal is reduced. (B) By increasing the gain in the reception signal amplification circuit section 9, the delay of the phase of the reception signal becomes large. Since both (a) and (b) are contradictory events related to the phase, the both suppress the phase change extremely small, and the change in the reception signal transmission time caused by the phase change becomes extremely small or cancels. To be done.

Now, the operation will be described again. When a predetermined time elapses in the timing control unit 2, the timing control unit 2 outputs the timing signal 52 'shown as the falling edge in FIG. 3A, and the signal 52e' closes the gate circuit 13 (see FIG. 3 (g)), the output of the sampling clock signal 59 from the gate circuit 13 is stopped, and the A / D conversion operation in the A / D converter 10 and the storage operation in the reception signal storage unit 12 are completed.

On the other hand, by the output of the timing signal 52 ', the operation of bringing the APD bias voltage closer to the breakdown voltage by the signal 52b', the operation of increasing the gain in the received signal amplifying circuit section 9 by the signal 52c ', and the signal 52d'. At A /
The operation of lowering the reference voltage of the A / D converter 10 in the D converter reference voltage generating section 11, that is, a series of STC function operations ends. The signal 52a 'generated by the output of the timing signal 52' this time has no influence on the semiconductor laser driving unit 3.

Further, the arithmetic control unit 1 receives the signal 52f 'resulting from the output of the timing signal 52f, and receives the received signal storage unit 12
Receives a series of received signal level data and its address stored by using the sampling clock signal 59 as a trigger, as a received signal level signal 61, judges a measurement object from the received received signal level data, and judges the received signal level. The time is calculated from the address giving the data, and the distance from the time to the measurement object is calculated.

The arithmetic control unit 1 outputs the calculated distance to the display unit 14 as a distance data signal 62. The display unit 14 displays the distance to the measurement target. Hereinafter, the above series of operations is repeated at regular intervals.

In the above basic distance measuring operation, since the change in the transmission time of the received signal becomes extremely small, the accuracy of the time calculated from the received signal waveform data stored in the received signal storage section 12 and its address increases. However, it is possible to measure distance with high accuracy.

In this embodiment, even if the reference voltage output from the A / D converter reference voltage generator 11 is fixed, the analog received signal 56 output from the received signal amplifier circuit 9 is received.
Since both of the reception signals 54 output from the light receiving element 7 are changed by the timing signals 52b and 52c, there is no problem.

Next, another embodiment of the present invention will be described with reference to FIG. A detailed description of the same or similar points as in the embodiment will be omitted. The arithmetic control unit 1 sends a command signal 5 to the time measuring circuit unit 21.
It is a CPU that outputs 1. When the command signal 51 is input, the time measuring circuit section 21 receives the timing signals 52 (52a, 5a, 5a).
2b, 52c, 52g). The semiconductor laser drive unit 3 is a semiconductor laser which receives the timing signal 52a and outputs a pulse signal 53, and the light source 4 is driven by the pulse signal 53 to emit a laser light pulse.

The transmitting lens 5 transmits the laser light pulse toward the measurement object (not shown) at a predetermined beam divergence angle, and the reception lens 6 collects the laser light pulse reflected by the measurement object (not shown). Optical system for receiving and receiving light 7
Is an AP that photoelectrically converts the received laser light pulse with an amplification factor according to the applied bias voltage and outputs a reception signal 54.
D (avalanche photodiode). AP
The D bias circuit 8 is a circuit which receives the timing signal 52b and outputs a bias voltage signal 55 for varying the multiplication factor by applying a variable bias voltage to the light receiving element 7 according to the timing signal 52b.

The reception signal amplifying circuit section 9 is a circuit which receives the reception signal 54, amplifies it with a timing signal 52c at a variable amplification rate, increases the gain, and outputs an analog reception signal 56.

The comparator 22 inputs the analog received signal 5
6 is received from the threshold value signal 71 output from the comparator threshold value generating section 23 which outputs a variable threshold value signal 71 in accordance with the timing signal 52g, and is compared with the set threshold value to input exceeding 6 When there is a received signal detection signal 7
2 is a circuit that outputs 2 to the time measuring circuit unit 21. The time measuring circuit unit 21 receives the received signal detection signal 72, measures time, and outputs the obtained time data to the arithmetic control unit 1 as the time data signal 73. The arithmetic control unit 1 outputs the time data signal 73. Received and calculated distance, distance data signal 6
2 is output to the display unit 14. The display unit 14 is a display device that displays distance data.

Next, the basic distance measuring operation will be described. When a command signal 51 is input from the arithmetic and control unit 1 to the time measuring circuit unit 21, a timing signal 52a is output to the semiconductor laser drive unit 3, a pulse signal 53 is driven, and a laser light pulse is emitted from the light source 4. The laser light pulse is transmitted toward the measurement object (not shown) via the transmission lens 5.

The laser light pulse reflected by the object to be measured (not shown) is received by the light receiving element 7 through the receiving lens 6. When the light receiving element 7 receives the laser light pulse, the APD
The received signal 54 is output after photoelectric conversion with an amplification factor according to the bias voltage according to the bias voltage signal 55 from the bias circuit 8. At this time, the bias voltage signal 55 is changed by the STC operation described in detail after the timing signal 52b input to the APD bias circuit 8, and the bias voltage changes so as to approach the breakdown voltage (FIG. 3 (d)).

The reception signal 54 output from the light receiving element 7 is input to the reception signal amplification circuit section 9 and amplified, and the analog reception signal 56 is output. At this time, the gain is increased by the STC operation of the timing signal 52c input to the reception signal amplification circuit unit 9 (FIG. 3 (e)).

Then, the analog reception signal 56 is sent to the comparator 22.
When the analog input signal 56 exceeds the threshold signal 71 for the first time, the received signal detection signal is compared with the threshold value set by the threshold signal 71 from the comparator threshold value generator 23. 72 is output. At this time, the threshold is lowered by the STC operation of the timing signal 52g input to the comparator threshold generator 23 (FIG. 3).
(H).

At the same time when the timing signal 52a is output, the reception signal detection signal 72 can be input to the time measuring circuit section 21 and the time measurement is started. The obtained time data is input to the arithmetic control unit 1 as the time data signal 73, the arithmetic control unit 1 calculates the distance, and the distance data is displayed on the display unit 14.

Here, the STC operation will be described in detail. In addition to outputting the timing signal 52a from the timing controller 2 to the semiconductor laser driver 3, the timing signal 52b to the APD bias circuit 8, the timing signal 52c to the received signal amplifier circuit 9, and the timing to the comparator threshold value generator 23. The signal 52g is output. And timing signal 5
In the APD bias circuit 8, the bias voltage signal 55 causes the bias voltage of the APD to approach the breakdown voltage so that 2b, 52c, and 52d each have a predetermined time characteristic from the input time. , The reception signal amplification circuit section 9 increases the amplification factor to increase the gain, and the comparator threshold generation section 2
In 3, the threshold value is lowered by the threshold signal 71 (FIGS. 3D, 3E and 3H). Therefore, the STC function that can detect even a received signal of a small lens operates. By this operation of the STC function, the bias voltage of the APD is brought close to the breakdown voltage, and the amplification factor of the reception signal amplification circuit section 9 is increased to increase the gain. The changes will also be very small or offset.

Now, the operation will be described again. When a predetermined time has elapsed in the timing control unit 2, the timing control unit 2 outputs timing signals 52b ', 52c',
52g 'outputs and the operation of bringing the APD bias voltage close to the breakdown voltage, the operation of increasing the gain in the received signal amplification circuit section 9, the operation of lowering the threshold value in the comparator threshold value generating section 23, that is, a series of The STC function operation of is ended. The timing signals 52b ', 52c',
The output of 52 g'has no influence on the semiconductor laser driving section 3.

In addition, the arithmetic control unit 1 waits for the input of the time data signal 73 from the time when the command signal 51 is output,
By inputting the time data signal 73, the distance from that time to the measurement object is calculated. Hereinafter, the above series of operations is repeated at regular intervals.

In the above basic distance measuring operation, since the change in the transmission time of the received signal becomes extremely small, the accuracy of the time measured by the time measuring circuit unit 21 increases, and the distance measurement with high accuracy becomes possible. .

In this embodiment, even if the threshold value output from the comparator threshold value generating section 23 is fixed, the analog reception signal 56 output from the reception signal amplifying circuit section 9 and the light receiving element 7 are output. There is no problem because both of the reception signals 54 are changed by the timing signals 52b and 52c.

[0043]

The optical pulse emitted by the distance measuring device of the present invention and reflected by the object to be measured is received by the photomultiplier, and the received signal amplification factor of the received signal amplifying means is
In addition to the amplification factor due to the bias voltage of the photomultiplier element, either the reference voltage of the A / D conversion means or the threshold value for the comparison means is operated by the STC operation according to a function of time after the light pulse is emitted. Be changed. The change in the phase due to the change in the received signal amplification factor of the received signal amplifying means and the change in the phase due to the change in the bias voltage of the photomultiplier element are changes in the opposite directions, and the change in the combined phase decreases. Or by being offset, ST of the received electric signal
The phase change accompanying the gain change due to the C function is reduced, and a distance measuring device with high distance measuring accuracy can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a block diagram of another embodiment of the present invention.

FIG. 3 is a time chart of the operation in each embodiment of the present invention.

FIG. 4 is a block diagram of a conventional example.

[Explanation of symbols]

 1 ... Calculation control unit 2 ... Timing control unit 3 ... Semiconductor laser drive unit 4 ... Light source 5 ... Transmission lens 6 ... Reception lens 7 ... Light receiving element 8 ... APD bias circuit 9 ... Reception signal amplification circuit section 10 ... A / D converter 11 ... A / D converter reference voltage generation section 12 ... Reception Signal storage unit 13 ... Gate circuit 14 ... Display unit 22 ... Comparator 23 ... Comparator threshold value generation unit

Claims (4)

[Claims] 1. A timing control means for outputting a light emission timing signal, a light emitting means for emitting a light pulse when the light emission timing signal is input, and a light pulse for receiving the light pulse emitted from the light emitting means and reflected by an object to be measured. A light receiving means having a photoelectric element for outputting a light receiving signal and a variable amplifier, a received signal amplifying means for amplifying the light receiving signal with a variable received signal amplification factor and outputting an analog received signal, and a reference voltage generating means. And an A / D conversion means for converting the analog reception signal into a digital reception signal at a set reference voltage, a time measuring means for measuring a time after the light pulse is emitted, and the time measuring means. A variable amplifier for calculating the distance to the object to be measured based on the time measured from the emission of the optical pulse to the reception of the optical pulse; In a distance measuring device that amplifies the analog reception signal by changing the reception signal amplification factor according to a function of time after the optical pulse measured by a stage is radiated, a photoelectric multiplication element in which the photoelectric element is variable And a bias voltage of the photoelectron multiplying element is changed according to a function of time after the light pulse measured by the time measuring means is emitted. 2. The reference voltage generator is a variable reference voltage generator capable of changing the reference voltage, and the A / D conversion means includes the optical pulse measured by the timing means by the variable reference voltage generator. 2. The distance measuring device according to claim 1, wherein the analog reception signal is converted into the digital reception signal with reference to the reference voltage changed according to a function of time after the radiation. 3. A timing control means for outputting a light emission timing signal, a light emitting means for emitting a light pulse when the light emission timing signal is input, and a light pulse for receiving the light pulse emitted from the light emitting means and reflected by an object to be measured. A light receiving means having a photoelectric element for outputting a light receiving signal and a variable amplifier, receiving signal amplifying means for amplifying the light receiving signal at a variable received signal amplification factor and outputting an analog received signal, and a threshold value Comparing means for comparing the analog received signal with a threshold value generated by the threshold value generating means; and the analog received signal exceeding the threshold value after the light pulse is emitted. To calculate the distance to the object to be measured based on the time measured from the time when the light pulse is emitted to the time when the light pulse is received. In the distance measuring device, the variable amplifier amplifies the analog reception signal by changing the reception signal amplification factor according to a function of time after the light pulse measured by the timing means is emitted. The photoelectric element is constituted by a photomultiplier element with variable multiplication factor, and the bias voltage of the photomultiplier element is changed according to a function of time after the light pulse measured by the timing means is emitted. Characteristic distance measuring device. 4. The threshold value generating means is a variable threshold value generating means capable of changing the threshold value, and the comparing means is the variable threshold value generating means measured by the clocking means. 4. The distance measuring device according to claim 3, wherein the analog reception signal is compared with the threshold value changed as a function of time after the light pulse is emitted.