JPH07260937A - Distance measuring device - Google Patents

Abstract

PURPOSE:To keep measurement accuracy, while ensuring the safety of eyes for optical pulses, by controlling a pulse generator so as to reduce pulse width according to a decrease in a distance up to an object. CONSTITUTION:Concurrently with the start of distance measurement, a microcomputer 1 sets the pulse width T of pulse light at minimum pulse width Tmin capable of maintaining mean transmission power for the safety of eyes at a short distance, and outputs a pulse width control signal S2 to a pulse generator 2 for performing distance measurement. When a measured distance value D is less than a minimum distance Dmin within a detection range, the pulse width Tmin is kept unchanged. When the value D exceeds a maximum distance Dmax within the detection range, the microcomputer 1 sets pulse width at maximum pulse width Tmax safe for eyes at a short distance. When the value Dmax is not exceeded, the microcomputer 1 sets pulse width Tcal between a minimum value Tmin and a maximum value Tmax corresponding to a roughly measured distance Dcal for performing detailed measurement. Thus, pulse width is narrowed for the safety of eyes at a short distance and pertinently set, unless otherwise required, thereby maintaining good distance measurement accuracy.

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 present invention relates to a distance measuring device using a laser radar, which is mainly mounted on a traveling body such as a vehicle.

[0002]

2. Description of the Related Art A conventional distance measuring device mounted on a traveling body such as a vehicle detects the presence of an object within a certain distance range from a measured distance, for example, an object such as a car, using a laser radar. In addition, the distance to the object was measured. When a laser radar is used to detect an object such as for a vehicle, in order to secure the reflected light power capable of detecting the object, the transmitted light power needs to be larger as the object is farther away, while the human Since it is dangerous to hit the laser beam on the eyes, it is necessary to prevent the transmission light power from being output unnecessarily so as not to damage the eyes. Therefore, in the conventional device, the traveling speed of the mounted vehicle is detected, and when the traveling speed is less than a certain value, the output of the laser light is reduced, or the power supply to the distance measuring device is stopped so that the laser light is not transmitted. I tried to ensure the safety of my eyes.

[0003]

SUMMARY OF THE INVENTION In the above prior art,
Regardless of whether the object is in front of the vehicle or not, the laser light output was reduced when the vehicle's running speed decreased, so the range where humans could be actually harmed by the laser light The transmission light power of the laser radar was reduced even though I was not there. For this reason, the range of detectable distance is short, and it may be said that it is unnecessarily limited, or the distance to the object cannot be measured because the transmitted light is weak, or measurement with poor accuracy is forced. There was such a problem. Even when the power supply to the distance measuring device is stopped when the traveling speed of the vehicle becomes low, there is a problem that the same measurement cannot be performed or measurement with low accuracy is forced.

In view of such a situation, the present invention ensures the safety of the eyes, does not reduce the output of the laser beam unless necessary for that purpose, and maintains the distance measurement with good accuracy. The purpose is to provide a device.

[0005]

According to a first aspect of the present invention, there is provided a pulse generator for generating a lighting drive pulse, and a pulse having a pulse width defined by the lighting drive pulse upon receiving the lighting drive pulse. Light source means for emitting light, transmitting means for transmitting the pulsed light, receiving means for receiving the pulsed light that has been transmitted and reflected back from the target object, and outputs a reception signal, and the target signal based on the reception signal The detection calculation means is provided for calculating the distance to the object by detecting the object and measuring the round-trip time of the pulsed light from the output of the pulsed light to the output of the reception signal. In the distance measuring device, the pulse generator is for generating a lighting drive pulse having a variable pulse width, and a pulse width control signal for controlling the pulse width of the lighting drive pulse is supplied. Comprising a pulse width control means for force, it said pulse width control means, the shorter the distance calculated by said detection calculating means is for controlling the pulse generator 2 so as to reduce the pulse width.

Further, in the invention described in claim 2, a pulse generator for generating a lighting drive pulse, and receiving the lighting drive pulse, emits pulsed light having a pulse width determined by the lighting drive pulse. Light source means, transmitting means for transmitting the pulsed light, receiving means for receiving the pulsed light that has been transmitted and reflected back from the object, outputs a reception signal, and detects the object by the reception signal. At the same time, the vehicle is equipped with a detection calculation unit that calculates the distance to the object by measuring the round-trip time of the pulsed light from the output of the pulsed light to the output of the reception signal. In the mounted distance measuring device, the pulse generator generates a lighting drive pulse having a variable pulse width, and a speedometer for measuring a traveling speed of the traveling body and the lighting drive pulse are used. And a pulse width control means for outputting a pulse width control signal for variably controlling the pulse width of the pulse, wherein the pulse width control means reduces the pulse width as the traveling speed measured by the speedometer is slower. To control the pulse generator.

[0007]

According to the first aspect of the present invention, the pulsed light transmitted and reflected from the object is received, it is detected that the object exists within a certain distance range, and the distance to the object is measured. It As the measured distance becomes shorter, the pulse width of the pulsed light becomes smaller. Alternatively, in the invention according to claim 2, the smaller the traveling speed of the traveling body, the smaller the pulse width of the pulsed light.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. The microcomputer 1 is a CPU that outputs a measurement start signal S1 and a pulse width control signal S2 to the pulse generator 2 and calculates a distance. The pulse generator 2 outputs a laser diode drive pulse signal S3 to drive the driver 3 and causes the laser diode 4 to emit pulsed light. The light-transmitting convex lens 5 collects the emitted pulsed light and transmits it to the object, and the light-receiving convex lens 6 receives the light reflected from the object.

The light receiving element 7 is installed in the vicinity of the front of the laser diode 4, receives a part of the pulsed light to be transmitted and photoelectrically converts it, and the light receiving element 8 is installed at the condensing position of the light receiving convex lens 6 and receives the pulse. Photoelectric conversion of light. Amplifier circuit 9,
Reference numeral 10 is a circuit for amplifying the signals output from the light receiving elements 7 and 8, respectively, and the threshold detectors 11 and 12 are provided.
Is a circuit that further digitizes it into a pulse signal. A signal START indicating a transmission timing is input from the threshold detector 11 to the flip-flop 13, and a signal STOP indicating a reception timing is input from the threshold detector 12.

The counter 14 is a circuit that counts the number of pulses from the pulse generator 15 while the flip-flop 13 is set, and the microcomputer 1 measures the round-trip time based on the pulse number signal output from the counter 14. , Calculate the distance to the object. Then, the measurement start signal S1 output to the pulse generator 2 based on the calculated distance
To control.

Next, the operation will be described. The microcomputer 1 uses the measurement start signal S1 and the pulse width control signal S
2 is output to the pulse generator 2. The pulse generator 2 outputs the laser diode drive pulse signal S3 to the driver 3 in accordance with the pulse width control signal S2 to drive it, and the laser diode 4 emits pulsed light. The pulse width of the pulsed light can be set to any width by the pulse width control signal S2, but the pulse width of the first one pulse is the narrowest in a predetermined setting range, as will be described later. It is a thing. The pulsed light is directly applied to the light receiving element 7 and directly to the light receiving element 8
Through the light-transmitting convex lens 5, is reflected by the object, and enters through the light-receiving convex lens 6. By using the light receiving element 7, the delay time correction of the transmission timing in the electric circuit is performed.

The signal START is output from the threshold detector 11 by the light incident on the light receiving element 7, and the flip-flop 13 is set. The signal S from the threshold detector 12 is generated by the light incident on the light receiving element 8.
The TOP outputs and resets the flip-flop 13. The number of pulses while the flip-flop 13 is set is counted by the counter 14, the round trip time is measured based on the number of pulses, and the distance to the object is calculated.

The pulsed light does not enter the light receiving element 8 and the signal STOP is output from the threshold detector 12 within a fixed time.
Is not output, the round-trip time is not measured, it is determined that the object does not exist within the predetermined distance range, and the flip-flop 13 is reset. Based on the calculated distance, the microcomputer 1 determines a pulse width control signal S2 so that the pulse width of the pulsed light corresponds to the distance measurement value and outputs it to the pulse generator 2, and also outputs a measurement start signal S1 to the pulse generator. Two
Output to. The operation of transmitting / receiving the pulsed light is repeated.

FIG. 2 shows the width of the pulse signal transmitted by the pulsed light. FIG. 2A shows a case of a wide transmission pulse signal in which an object is at a long distance, and FIG. 2B shows a case of a narrow transmission pulse signal in which an object is at a short distance. When the widths of the respective transmission pulse signals are Ta, Tb, the periods of the transmission pulse signals are τa, τb, and the average transmission powers Ia, Ib, τa = τb, Ta> Tb, Ia> Ib. It is sufficient that Ia> Ib, so Ta, T
The relationships among b, τa, and τb do not necessarily have to be as described above.

The flowchart shown in FIG. 3 shows a processing procedure in the microcomputer 1 for controlling the pulse width of the pulsed light. In step ST1, a series of distance measuring operations starts. In step ST2, the microcomputer 1 sets the pulse width to Tmin and outputs the pulse width control signal S2 to the pulse generator 2. Tmin is the minimum set pulse width that ensures eye safety for people at close range.

In step ST3, the pulse width Tmi
Distance measurement is performed with n pulsed light, and in step ST4,
It is checked whether or not the distance measurement value Dcal obtained in step ST3 is smaller than the minimum distance Dmin of the detection range. Distance measurement value Dc
When al is smaller than the minimum distance Dmin of the detection range,
If it is larger, the process proceeds to step ST6.
Proceed to. In step ST5, the obtained distance measurement value Dc
Since al is smaller than the distance Dmin, the pulse width is Tmi in order to maintain the average transmission power that is eye-safe.
Leave as n and do not change.

In step ST6, it is checked whether the obtained distance measurement value Dcal exceeds the maximum distance Dmax in the detection range. When the distance measurement value Dcal exceeds the distance Dmax, the process proceeds to step ST7. Distance measurement value Dcal is distance Dm
When it does not exceed ax, the process proceeds to step ST8. In step ST7, the pulse width is Tmax. In step ST8, a pulse width Tcal corresponding to the measurement value Dcal roughly measured in step ST3 is set.
Tcal is the minimum value Tmin and the maximum value Tmax of the pulse width.
It is a value between and. The maximum value Tmax corresponds to the maximum distance of the set distance measuring range in this embodiment, and does not exceed half of the repetition cycle of the pulse train.

In step ST9, step ST
5, pulse light is emitted with the pulse widths Tmin, Tmax, and Tcal set in step ST7 or step ST8, respectively, and the distance is precisely measured. In step ST10, the average value of all measured values is calculated. It ends at step ST11.

FIG. 4 shows the relationship between the pulse width T and the distance D to the object. The minimum distance of the detection range of the distance measuring device of this embodiment is Dmin, and the maximum distance is Dmax. As for the pulse width T, the average transmission power shown in FIGS. 2 (a) and 2 (b) corresponds to the longest distance in the set distance measuring range, and Tmax, which is safe for the eyes at a long distance, has a maximum value, and Tmax at a short distance. Tmin, which is eye-safe, is the minimum value. Tmin
A narrower pulse width is meaningless as it only reduces the measurement accuracy.

In the present embodiment, when the distance is short, the pulse width is narrowed and reduced to suppress the increase in energy of a series of light pulses, and eye safety can be secured.

Next, another embodiment will be described with reference to FIGS. The present embodiment is different from the above-described embodiment only in that a speedometer 16 for measuring the speed of the traveling body is added, and therefore detailed description thereof will be omitted.

The flow of this embodiment will be described with reference to FIG.
In step ST11, a series of distance measuring operations starts. In step ST12, the speed information is read from the speedometer 16. In step ST13, it is checked whether or not the speed V is lower than a predetermined minimum speed Vmin. When the read speed Vobs is smaller than the set minimum speed Vmin, the process proceeds to step ST14, and when it is larger, the process proceeds to step ST15. In step ST14, since the read speed Vobs is smaller than the set minimum speed Vmin, the pulse width is set to Tmin so as not to exceed the average transmission power that is safe for the eyes. In step ST15, the corresponding pulse width Tcal is calculated from the read speed Vobs. In step ST16, it is checked whether the calculated pulse width Tcal exceeds Tmax. When the calculated pulse width Tcal exceeds Tmax, the process proceeds to step ST17. Calculated pulse width Tca
When l does not exceed Tmax, the process proceeds to step ST18.

In step ST18, step ST
14, pulse light is emitted with the pulse width Tmin, Tmax, or Tcal set in step ST17, or step ST16, respectively, and the distance is measured. It ends at step ST19.

In the present embodiment, during a low speed operation in which a person is likely to be in front of a short distance, the pulse width is narrowed and reduced to prevent the energy of a series of light pulses from increasing and to ensure eye safety. be able to.

[0025]

According to the invention described in claim 1, the pulse width of the pulsed light becomes smaller as the distance becomes shorter while maintaining the intensity of the light so as to maintain the measurement accuracy. Output becomes smaller. Therefore, even if the detected object is a human being, the safety of the eyes can be ensured without being affected by the optical pulse, and the distance measurement can be maintained with good accuracy. According to the invention described in claim 2, when the traveling speed of the traveling body is small, the pulse width of the pulsed light becomes small while maintaining the intensity of the light so as to maintain the measurement accuracy. Output becomes smaller. Therefore, even if the detected object is a human being, the safety of the eyes can be ensured without being affected by the optical pulse, and the distance measurement can be maintained with good accuracy.

[Brief description of drawings]

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

FIG. 2 is a relationship diagram showing a relationship between a transmission pulse signal and an average transmission power according to an embodiment of the present invention.

FIG. 3 is a flowchart of a microcomputer according to an embodiment of the present invention.

FIG. 4 is a relationship diagram showing a relationship between a distance to an object and a pulse width according to an embodiment of the present invention.

FIG. 5 is a block diagram showing another embodiment of the present invention.

FIG. 6 is a flowchart of a microcomputer according to another embodiment of the present invention.

[Explanation of symbols]

 1 ... Microcomputer 2 ... Pulse generator 3 ... Driver 4 ... Laser diode 5 ... Convex lens for light transmission 6 ... Convex lens for light reception 7, 8 ... ..Reception element 9,10 ... Amplification circuit 11,12 ... Threshold detector 13 ... Flip-flop 14 ... Counter 15 ... Pulse generator 16 ... Velocity meter

Claims (2)

[Claims] 1. A pulse generator for generating a lighting drive pulse, a light source means for receiving the lighting drive pulse and emitting a pulsed light having a pulse width defined by the lighting drive pulse, and the pulsed light. Transmitting means for transmitting to the object, receiving means for receiving the pulsed light transmitted and reflected back from the object, and outputting a reception signal, and detecting the object by the reception signal, the pulse In the distance measuring device comprising a detection calculation unit that calculates the distance to the object by measuring the round-trip time of the pulsed light from the output of light to the output of the received signal, the pulse generation And a pulse width control means for outputting a pulse width control signal for controlling the pulse width of the lighting drive pulse. The distance measuring device, characterized in that the pulse width control means controls the pulse generator 2 so that the pulse width is reduced as the distance calculated by the detection calculation means is shorter. 2. A pulse generator for generating a lighting drive pulse, a light source means for receiving the lighting drive pulse and emitting a pulsed light having a pulse width defined by the lighting drive pulse, and transmitting the pulsed light. And transmitting means for receiving the pulsed light transmitted and reflected back from the object,
By receiving means for outputting a reception signal, and detecting the object by the reception signal, by measuring the round-trip time of the pulsed light from the output of the pulsed light until the reception signal is output, In a distance measuring device mounted on a traveling body, comprising a detection calculation unit for calculating a distance to the object, the pulse generator generates a lighting drive pulse having a variable pulse width, A speedometer for measuring the running speed of the body, and a pulse width control means for outputting a pulse width control signal for variably controlling the pulse width of the lighting drive pulse, wherein the pulse width control means is the speedometer. A distance measuring device, wherein the pulse generator is controlled so that the pulse width is reduced as the measured traveling speed becomes slower.