JPH08184672A - Distance measuring apparatus - Google Patents

Abstract

PURPOSE: To improve the measuring accuracy and to automatically stopping an apparatus when a measurable distance is shortened by providing means for correcting a measuring distance in response to a laser beam emitting state. CONSTITUTION: The laser beam from a laser diode 11 is emitted to a vehicle 19, the reflected light is received by a photodiode 12, a received pulse RX and an emitting pulse TX are respectively input to set and reset terminals S, R of an RS flip-flop 14 via one-shot multivibrators 13a, 13b, a distance pulse DPO from the terminal Q is output, and input to a microcomputer 24. The output of a photodiode 21 which detects the beam intensity of the diode 11, amplified by an amplifier 22, detected and smoothed by a detector 12, and input to the microcomputer 24. The microcomputer 24 measures the pulse time width of the pulse DPO, and stores it in a memory. The relation of a correcting amount corresponding to the beam emitting level stored in the memory is read the amount is added to the pulse time of the measured DPO pulse, and converted to a correct correction distance.

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 using pulsed laser light, and more particularly to a distance measuring device that corrects a distance error due to a change in intensity of irradiation light.

[0002]

2. Description of the Related Art FIG. 5 is a diagram for explaining a method for measuring an inter-vehicle distance using laser light, and FIG. 5 (a) is a diagram for explaining the principle of distance measurement,
(B) is a figure which shows the state of an output pulse, (c) is a figure explaining the distance pulse detection method, (d) is a figure which shows the set timing of a flip-flop. Hereinafter, description will be given with reference to the drawings.

Reference numeral 11 denotes a laser diode which oscillates a laser beam, and a pulsed voltage (light emission signal) is applied at a constant cycle to generate pulsed light. 12 is a photodiode,
The pulsed laser light emitted from the laser diode 11 to the vehicle 19 receives the reflected light reflected by the vehicle 19 and outputs a light reception signal (see FIG. 5A). 13a,
Reference numeral 13b denotes a one-shot multivibrator, which emits a light emission signal from the laser diode 11 and the photodiode 1, respectively.
The light reception signal of 2 is input as the trigger signal. 14
Is an RS flip-flop, which is set by the output pulse of the one-shot multivibrator 13a (Q output high (H) level),
The output pulse of b is reset (Q output low (L) level) to generate a distance pulse having a width (time) corresponding to the distance to the measurement target (see FIG. 5C).

Next, a distance measuring method will be described. A pulsed voltage TX (light emission pulse TX) is applied to the laser diode 11 at a constant cycle, the laser diode 11 oscillates, and the light emission pulse is applied to the vehicle 19. Vehicle 1
The reflected light reflected from 9 is received by the photodiode 12 to generate a voltage RX (light receiving pulse RX). The light emission pulse TX and the light reception pulse RX are input to the one-shot multivibrators 13a and 13b, respectively, and the outputs thereof are input to the RS flip-flop 14. R-
The S-type flip-flop 14 is set by the output pulse of the one-shot multivibrator 13a (Q output H level)
Then, the output pulse of the one-shot multivibrator 13b is reset (Q output L level). as a result,
A distance pulse (pulse having a time width corresponding to the distance) DPO is output. The width of this distance pulse is from the own vehicle to the target vehicle 1
Since it is the time required for light to make a round trip to the distance up to 9,
The distance to the target vehicle can be calculated from the width of the distance pulse (see FIG. 5B).

[0005]

When measuring the distance from the distance pulse to the target vehicle, the one-shot multivibrator 13a triggers when the light emission pulse TX exceeds a certain reference voltage (OSM determination level). Therefore, even if the light emission pulse rises at the same timing, the timing at which the pulse is output from the one-shot multivibrator 13a differs depending on the magnitude of the light emission pulse. That is, there is a problem that a large light emission pulse TX1 outputs a pulse early and a small light emission pulse TX2 outputs a pulse with a delay, and a distance corresponding to the time t between them occurs as a measurement error.

Further, when the output of the irradiation laser beam decreases,
The output of the photodiode 12 decreases and the measurable distance also becomes shorter (since the amount of received light is inversely proportional to the fourth power of the measured distance). As a result, if the output of the irradiation laser light drops below a certain level, the measuring device becomes useless. For example, in the application to the inter-vehicle distance measuring device,
If the measurable distance is short in high-speed running, it is not useful, and it is necessary to stop the device or inform the user that the measurement is impossible.

It is an object of the present invention to improve the distance measuring accuracy of a distance measuring device and automatically stop the device when the measurable distance becomes short, or notify the user of that fact.

[0008]

In order to achieve the above object, the present invention provides an irradiating section for emitting and irradiating a pulse-shaped laser beam to a target object for distance measurement, and the laser beam reflected from the target object. A light receiving unit for receiving and outputting a light receiving pulse, and in a distance measuring device for measuring a distance to the target object from a time difference between the light emitting pulse and the light receiving pulse, a light emitting state of laser light of the irradiation unit. It has a correction means for correcting the measured distance according to the above.

Further, the emission state of the laser beam of the irradiation unit is detected by a second light receiving unit which is arranged in the vicinity of the irradiation unit and outputs a light emission state signal according to the received laser beam. It is a feature. Further, the emission state of the laser beam of the irradiation unit is detected by the voltage across the laser diode of the irradiation unit.

Further, it is provided with an irradiation unit which emits and irradiates a pulsed laser beam to a target object for distance measurement, and a light receiving unit which receives the laser beam reflected from the target object and outputs a light receiving pulse. From the time difference between the irradiation pulse and the light receiving pulse, in a distance measuring device that measures the distance to the target object, the emission state of the laser light of the irradiation unit,
A detection unit that detects that the intensity has dropped below a predetermined intensity,
When the detection unit detects a decrease in the emission intensity of the laser beam, the detection unit includes a stop unit that stops the control based on the distance measurement result.

Further, the detection means is provided in the vicinity of the irradiation section and outputs a second light receiving section for outputting an intensity signal corresponding to the received laser beam, and an intensity signal output from the second light receiving section. Is comprised of a comparison means for detecting that the voltage has dropped below the reference signal. Further, the detecting means comprises a second comparing means for detecting that the voltage across the laser diode of the irradiating section has dropped below a reference voltage.

Further, it is provided with an irradiation unit which emits and irradiates a pulsed laser beam to a target object for distance measurement, and a light receiving unit which receives the laser beam reflected from the target object and outputs a light receiving pulse. In the distance measuring device that measures the distance to the target object from the time difference between the light emitting pulse and the light receiving pulse, a detection unit that detects that the voltage across the laser diode of the irradiation unit has dropped below a reference voltage. And a notifying unit for notifying an abnormality of the device when the detecting unit detects that the voltage across the laser diode has dropped below a reference voltage.

[0013]

The pulsed laser light is emitted from the irradiation unit to the target object for distance measurement, and the light receiving unit receives the reflected light from the target object. Since the time between the irradiation pulse and the light receiving pulse is the time required for light to travel back and forth to the target object, the distance to the target object can be measured by measuring this time. The rising time of the irradiation pulse can be determined by detecting the time when the signal of the irradiation pulse exceeds the reference signal. However, since the irradiation pulse is not a perfect rectangular wave but has a rising curve, the time when the reference signal is exceeded fluctuates due to the emission state of the laser light of the irradiation section, that is, the pulse height, and distance measurement errors occur. Occurs. In order to correct this error, the correction means detects the light emission state of the laser light of the irradiation unit and corrects the distance according to the state.

Further, since the second light receiving section installed in the vicinity of the irradiation section receives the irradiation laser beam and outputs a signal corresponding to the intensity of the irradiation laser beam, the output signal of this light receiving section should be detected. Thus, the emission state of the laser light of the irradiation part can be known. Since the correction means detects the output signal of the light receiving unit and corrects the distance according to the magnitude of the output signal, correct distance measurement can be performed.

Further, since the voltage across the laser diode of the irradiation unit corresponds to the state of the irradiation unit, the emission state of the laser light of the irradiation unit can be known by detecting this voltage. Since the correction means detects the voltage across the laser diode of the irradiation unit and corrects the distance according to the voltage, correct distance measurement can be performed. Further, the detection means detects that the emission intensity of the laser light of the irradiation unit has dropped to a predetermined intensity or less. If the emission intensity decreases, the device becomes useless, and the stop means receives the detection signal of the detection means and stops the control based on the distance measurement result.

Further, the second light receiving section installed near the irradiation section receives the irradiation laser beam and outputs a signal corresponding to the intensity of the irradiation laser beam, and the comparison means outputs the second light receiving section. When the signal is compared with the reference signal and it is detected that the output signal is lower than the reference signal, the stop means stops the control based on the distance measurement result. Further, the second comparison means compares the voltage across the laser diode of the irradiation unit with the reference voltage,
When it detects that the voltage across both ends has dropped below the reference voltage,
The stop means stops the control based on the distance measurement result.

Further, the detection means detects that the voltage across the laser diode of the irradiation section has dropped to the reference voltage or lower and outputs a detection signal, and the notification means notifies the abnormality by this detection signal.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram for explaining an inter-vehicle distance correction circuit using laser light according to a first embodiment of the present invention, in which (a) is a configuration diagram,
(B) is a relationship diagram between a light emission level and a correction amount. Hereinafter, description will be given with reference to the drawings. Reference numeral 1 denotes a distance measuring unit, which receives a laser diode 11 to which a pulsed voltage is applied from a laser diode drive circuit 10 to generate pulsed light, and a reflected light obtained by reflecting pulsed light emitted from the laser diode 11 by a vehicle 19. When the terminal voltage of the photodiode 12 and the laser diode 11 is input, the laser diode 1
The one-shot multivibrator 13a that detects the rising of the applied voltage of 1 and the output of the photodiode 12 are input, and the one-shot multivibrator 13b that detects the rising of the output signal (voltage) and the input of the one-shot multivibrator 13a are set. (Q output is high (H) level) and reset by the input of the one-shot multivibrator 13b (Q output is low (L) level)
The R-S flip-flop 14 is configured to generate a high (H) level pulse between set and reset, that is, a distance pulse DPO having a time width corresponding to the distance to the measurement target.

Reference numeral 2 denotes a distance correction unit, which is a laser diode 11
Photodiode 21 for detecting the intensity of the pulsed light emitted from, resistor R21 for taking out the current flowing in photodiode 21 as a signal voltage, amplifier 22 for amplifying the output signal of photodiode 21, and detection of the output of amplifier 22. The distance to the vehicle 19 is calculated from the output pulse width of the detector 23 for smoothing and the RS flip-flop 14 and the emission level of the laser diode 11 (the output of the detector 23 received by the photodiode 21 is calculated. Microcomputer 2 for adding a predetermined correction amount to the distance pulse (DPO) as shown in FIG.
It is composed of 4.

Next, the distance measuring method and the correcting method will be described. The laser diode 11 is supplied with a pulsed voltage (light emission pulse TX) having a constant cycle, and the laser diode 1
1 oscillates and emits laser light, and the laser light is emitted from the vehicle 1
Irradiated to 9. The reflected light of the laser light reflected from the vehicle 19 is received by the photodiode 12 and received light pulse RX
Occurs. The light emitting pulse TX and the light receiving pulse RX are
One-shot multivibrator 13a, 13 respectively
b, and its output is the RS flip-flop 1
4 is input to the set terminal S and the reset terminal R. R-
The S-type flip-flop 14 is set by the output pulse of the one-shot multivibrator 13a (Q output is high (H)
The output pulse of the one-shot multivibrator 13b resets (the Q output becomes low (L) level). As a result, a distance pulse (pulse having a time width corresponding to the distance) DPO is output from the Q terminal. This distance pulse is input to the microcomputer 24.

On the other hand, the output of the photodiode 21 for detecting the light emission intensity of the laser diode 11 is amplified by the amplifier 22 and then detected and smoothed by the wave detector 23.
4 is input. In the microcomputer 24, the distance pulse DPO
Measure the pulse time width of. Further, the relationship of the correction amount corresponding to the light emission level of FIG. 1B stored in the memory inside the microcomputer 24 is read out, and this correction amount is added to the pulse time of the measured distance pulse DPO. Then, the corrected (added) pulse time is converted into a distance by the same method as the conventional one.

Next, the relationship between the light emission level and the correction amount will be described in detail. When the emission level of the laser diode 11 detected by the photodiode 21 is high (see FIG.
In (b), which corresponds to the light emission level 5, there is almost no measurement error in which the light emission pulse rises quickly (the time when the OSM determination level is exceeded is early), so the microcomputer 24 adds it to the pulse time of the distance pulse DPO. The correction amount is set to 0. Therefore, the corrected distance is the same as before correction.

When the light emission level of the laser diode 11 detected by the photodiode 21 is low (FIG. 1 (b))
(Corresponding to the light emission level 1), the rise time of the light emission pulse is late (the time when the OSM determination level is exceeded is late), and the set time to the RS flip-flop 14 is delayed as shown in FIG. As a result, a measurement error t occurs. Therefore, the correction amount added by the microcomputer 24 to the pulse time of the distance pulse DPO is set to +3.0. Therefore, the corrected distance is longer than the uncorrected distance (distance corresponding to the distance pulse DPO). Note that the correction amount +3.0 here is a relative value, and is actually stored in the memory of the microcomputer 24 in association with the light emission level and the pulse rise time delay t as the correction amount (time). Similarly, for the light emission levels 2, 3 and 4 with intermediate light emission levels, a correction amount corresponding to the light emission level is similarly read by the microcomputer 24 and added to the pulse time of the distance pulse DPO.

As described above, in this embodiment, the delay of the rising time of the light emission pulse, which fluctuates depending on the light emission intensity of the laser diode, is corrected according to the light emission intensity, so that the accuracy of distance measurement is improved. FIG. 2 is a diagram for explaining an inter-vehicle distance correction circuit using laser light according to a second embodiment of the present invention.
Is a configuration diagram, and (b) is a relationship diagram between a voltage level and a correction amount. Hereinafter, description will be given with reference to the drawings.

Reference numeral 1 is a distance measuring unit which is exactly the same as that of the first embodiment, and therefore its explanation is omitted. The same reference numerals as those in FIG. 1 indicate the same elements. Reference numeral 3 is a distance correction unit, which is a resistor R for dividing the voltage across the laser diode 11 and extracting it as a signal.
31, R32, a detector 33 for detecting and smoothing the output signal, and a distance from the output pulse width of the RS flip-flop 14 to the vehicle 19 is calculated, and a supply voltage level of the laser diode 11 (output of R32) Equivalent to)
2B, the microcomputer 34 is configured to add a predetermined correction amount to the time width pulse of the distance pulse (DPO). When the laser diode 11 deteriorates, the voltage across the laser diode 11 decreases.
Along with this, the current that flows decreases, and the brightness also decreases.

Next, the distance measuring method and the correcting method will be described. A pulsed voltage having a constant cycle is supplied to the laser diode 11, the laser diode 11 oscillates, emits laser light, and the laser light is applied to the vehicle 19. The reflected light of the laser light reflected from the vehicle 19 is received by the photodiode 12 and generates a light reception pulse RX. The light emission pulse TX and the light reception pulse RX are input to the one-shot multivibrators 13a and 13b, respectively, and the outputs thereof are set terminals S and S of the RS flip-flop 14.
It is input to the reset terminal R. The RS flip-flop 14 is set by the output pulse of the one-shot multivibrator 13a (Q output becomes high (H) level) and reset by the output pulse of the one-shot multivibrator 13b (Q output is low (L)). Will be a level). As a result, a distance pulse (pulse having a time width corresponding to the distance) DPO is output from the Q terminal. This distance pulse is input to the microcomputer 34.

On the other hand, the pulsed supply voltage to the laser diode 11 is divided by the resistors R31 and R32, and a signal is taken out from the connecting portion. The wave is detected and smoothed by the wave detector 33 and input to the microcomputer 34. The microcomputer 34 measures the pulse time width of the distance pulse DPO. Further, the relationship of the correction amount corresponding to the voltage level of FIG. 2B stored in the memory inside the microcomputer 34 is read out, and this correction amount is added to the pulse time of the measured distance pulse DPO. Then, the corrected (added) pulse time is converted into a distance by the same method as the conventional one. Note that the relationship between the voltage level and the correction amount is exactly the same as in the first embodiment except that the light emission level in the first embodiment is read as the voltage level, and therefore the description thereof is omitted.

As described above, in the present embodiment, the delay of the rising time of the voltage pulse, which fluctuates depending on the supply voltage to the laser diode, is corrected according to the supply voltage, so that the accuracy of distance measurement is improved. FIG. 3 is a block diagram showing a third embodiment of the present invention. Hereinafter, description will be given with reference to the drawings.

Reference numeral 4 denotes an abnormality detecting section, which is a laser diode 11
The photodiode 41 that detects the intensity of the laser light emitted from the photodiode, the resistor R41 for extracting the current flowing through the photodiode 41 as a signal voltage, the output signal of the photodiode 41, that is, the signal voltage extracted by the resistor R41 is amplified. The amplifier 42, a detector 43 for detecting and smoothing the output of the amplifier 42, and a comparator 45 for comparing the output of the detector 43 with the reference signal VR4. Reference numeral 9 is a power switch of the apparatus, and 91 is a display unit.

Next, the abnormality detecting operation will be described. The output of the photodiode 41 for detecting the emission intensity of the laser diode 11 is amplified by the amplifier 42, detected by the detector 43, and then compared with the reference voltage VR4 by the comparator 45. The comparator 45 outputs a high level (H) when the output of the amplifier 42 becomes lower than the reference voltage VR4. When the output of the comparator 45 becomes H, the power switch 9 of the device
Is cut off. In addition, a message or the like for notifying the abnormality is displayed on the display unit 91.

As described above, in the present embodiment, if the measurable distance is reduced and the reliability of the measurement is reduced, the distance measuring device is stopped and the fact is displayed. FIG. 4 is a block diagram showing a fourth embodiment of the present invention. Hereinafter, description will be given with reference to the drawings. Reference numeral 5 denotes an abnormality detection unit, which divides the voltage supplied to the laser diode 11 and takes out as a signal, resistors R51 and R5.
2. A detector 53 for detecting and smoothing the output signal, and a comparator 55 for comparing the output signal of the detector 53 with the reference signal VR5. 9 is the power switch of this device,
Reference numeral 91 is a display unit.

Next, the abnormality detecting operation will be described. The voltage across the laser diode 11 is divided by the resistors R51 and R52, and a signal is taken out from the connecting portion. This output signal (divided voltage) is detected and smoothed by the detector 53,
The comparator 55 compares it with the reference voltage VR5. The comparator 55 outputs a high level (H) when the output signal becomes lower than the reference voltage VR5. When the output of the comparator 55 becomes H, the power switch 9 of the device is cut off. In addition, a message or the like for notifying the abnormality is displayed on the display unit 91.

As described above, in the present embodiment, when the measurable distance decreases and the reliability of the measurement decreases, the distance measuring device is stopped and the fact is displayed. In the present embodiment, the H output of the comparator 55 activates the alarm device and displays an abnormality, but it is also possible to use the abnormality detection signal to take other measures corresponding to the abnormality.

[0034]

As described above, according to the present invention,
Since the error due to the light emitting state of the laser diode is corrected, the accuracy of distance measurement is improved. Also, when the light emitting state deteriorates, the operation of the device is stopped and a notification is given.
It is possible to prevent continuous measurement with low reliability.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an inter-vehicle distance correction circuit using laser light according to a first embodiment of the present invention, in which (a) is a configuration diagram and (b) is a relationship diagram between a light emission level and a correction amount.

2A and 2B are views for explaining an inter-vehicle distance correction circuit using laser light according to a second embodiment of the present invention, FIG. 2A is a configuration diagram, and FIG. 2B is a relationship diagram between a voltage level and a correction amount.

FIG. 3 is a configuration diagram of a laser light abnormality detection circuit according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram of a laser light abnormality detection circuit according to a fourth embodiment of the present invention.

5A and 5B are diagrams showing a method of measuring an inter-vehicle distance by a laser beam, FIG. 5A is a diagram illustrating a principle of distance measurement, FIG. 5B is a diagram showing a state of an output pulse, and FIG. 5C is a distance pulse detection method. FIG. 6D is a diagram illustrating the set timing of the flip-flop.

[Explanation of symbols]

 11 ... Laser diode 12, 21, 41 ... Photodiode 22, 42 ... Amplifier 23, 33 ... Detector 24, 34 ... Microcomputer 45, 55 ... Comparator 13a, 13b ...・ One-shot multivibrator 14 ・ ・ ・ RS flip-flop

Claims (7)

[Claims] 1. An irradiation unit that emits and irradiates a pulsed laser beam to a target object for distance measurement, and a light receiving unit that receives the laser beam reflected from the target object and outputs a received light pulse. A distance measuring device that measures a distance to the target object from a time difference between the light emitting pulse and the light receiving pulse, and has a correcting unit that corrects the measured distance according to a light emitting state of a laser beam of the irradiation unit. A distance measuring device characterized by the above. 2. The light emitting state of the laser beam of the irradiation unit is detected by a second light receiving unit which is arranged in the vicinity of the irradiation unit and outputs a light emission state signal according to the received laser beam. The distance measuring device according to claim 1, which is characterized in that. 3. The distance measuring device according to claim 1, wherein the emission state of the laser light of the irradiation unit is detected by the voltage across the laser diode of the irradiation unit. 4. An irradiation unit that emits and irradiates a pulsed laser beam to a target object for distance measurement, and a light receiving unit that receives the laser beam reflected from the target object and outputs a received light pulse. A distance measuring device that measures a distance to the target object from a time difference between the irradiation pulse and the light receiving pulse, a detection unit that detects that the emission state of the laser light of the irradiation unit has decreased to a predetermined intensity or less. And a stop unit that stops the control based on the distance measurement result when the detection unit detects a decrease in the emission intensity of the laser light. 5. The second light receiving section, which is arranged in the vicinity of the irradiation section and outputs an intensity signal corresponding to the received laser beam, and the intensity signal output from the second light receiving section. 5. Comparing means for detecting that the voltage has dropped below the reference signal.
The described distance measuring device. 6. The distance measuring device according to claim 4, wherein the detecting means comprises second comparing means for detecting that the voltage across the laser diode of the irradiation unit has dropped below a reference voltage. apparatus. 7. An irradiation unit that emits and irradiates a pulsed laser beam to a target object for distance measurement, and a light receiving unit that receives the laser beam reflected from the target object and outputs a received light pulse. A distance measuring device that measures the distance to the target object from the time difference between the light emitting pulse and the light receiving pulse, and a detecting unit that detects that the voltage across the laser diode of the irradiation unit has dropped below a reference voltage. A distance measuring device, comprising: an informing device that informs an abnormality of the device when the detecting device detects that the voltage across the laser diode has dropped below a reference voltage.