JP2001174557A - All-weather optical range finder and range finding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an all-weather optical range finder and a range finding method providing high accuracy measuring results and reducing the load applying to the device. SOLUTION: This all-weather optical range finder 10 usable in rainy weather is provided with light projecting means LD, 12, 14 for sending a light P having a prescribed polarization property towards a measurement object OB, a removal means 30 provided on an optical path of a reflecting light from the measurement object OB and removing a light having a same polarization property with the polarization property sent out from the light projecting means LD, 12, 14, and a light receiving means PD, 20, 22 receiving the light transmitting through the removal means 30.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical distance meter for measuring a distance to an object and a distance measuring method.
In particular, the present invention relates to an all-weather optical distance meter that can be used even in rainy weather and a distance measuring method.

[0002]

2. Description of the Related Art As a device for measuring a distance to a measurement object in a non-contact manner, a laser beam is projected onto the measurement object, light reflected by the measurement object is received, and a time difference between the projection and the light reception is obtained. An optical rangefinder that calculates a distance is known.

[0003] However, such an optical distance meter has a drawback that the measurement accuracy is reduced in rainy weather. That is, in rainy weather, raindrops are present in the optical path along which the laser beam travels, and the light reflected and returned by the raindrops acts as noise, resulting in reduced measurement accuracy.

Therefore, for example, Japanese Patent Application Laid-Open No. Hei 10-253760
Japanese Patent Application Publication (hereinafter referred to as Document 1) discloses an optical distance meter that aims to improve the measurement accuracy by removing the influence of noise due to raindrops.

[0005]

That is, in the distance meter disclosed in Document 1, in order to prevent erroneous detection of a distance due to light reflected by raindrops, light reflected from both the object to be measured and rain is detected by a light receiving element. And converts the received light amount into a binary signal by comparing the received light amount with a predetermined threshold value. Then, a frequency distribution of the time difference between the projection and the light reception for each light projection is created from the binary signal based on a predetermined statistical processing algorithm, and the distance to the object to be measured is calculated based on the maximum frequency time difference. .

On the other hand, if the reflected light from the raindrop can be removed before the light-receiving element receives the reflected light from both the raindrop and the object to be measured, a highly accurate distance measurement can be performed. Thus, the amount of data to be analyzed is reduced, and the load on the device is reduced.

It is an object of the present invention to provide an all-weather optical distance meter and a distance measuring method capable of obtaining a highly accurate measurement result and reducing the load on the device.

[0008]

Means for Solving the Problems In order to achieve the above object, the present inventors have made intensive studies on the reflection characteristics of irradiation laser light by raindrops.

That is, as shown in FIG. 4 (a), a state in rainy weather is locally created using a shower, and a visible laser beam (wavelength λ = 632.8 nm) is irradiated during the shower to form water droplets. The reflected light reflected by was observed.

As a result, as shown in FIG. 4B, the area around the shower is divided into four areas, and the area (1)> the area (3)> the area (2) and the area (4) in this order. It was found that the intensity of the reflected light changed. Next, when the reflected light is observed through the polarizing plate, the reflected light observed in the region (1) and the region (3) maintains a state of linear polarization in the same predetermined direction as the polarization characteristic of the irradiation laser light. , Area (2)
Also, it was found that the reflected light observed in the region (4) did not maintain the polarization characteristics of the irradiation laser light, and changed by 90 degrees from the polarization direction of the irradiation laser light. Note that the angle θ defining the size of the region (2) and the region (4) is
About 60-90 degrees.

On the other hand, when a laser beam is similarly irradiated on paper, an iron plate, concrete, or the like other than water droplets and the reflected light is observed through a polarizing plate, the polarization characteristics of the irradiated laser light are hardly observed, and natural light and natural light are not observed. The same polarization characteristics were observed.

On the basis of these experimental results, the inventors have reached the following conclusions.

The reflected light from the water droplet observed in the region (3) maintains the polarization characteristics of the irradiation laser light, while the reflection light from an object other than the water droplet changes the polarization characteristics of the irradiation laser light. Without maintaining, it has the same polarization characteristics as natural light. Therefore, before the reflected light mixed with the reflected light from the object to be measured and the reflected light from the rain is received by the light receiving sensor in rainy weather, the rain having the same polarization characteristic as the irradiation laser light is utilized by utilizing the difference in the light reflection characteristics. It has been concluded that if the reflected light from the object can be removed in advance, it is possible to detect only the reflected light from the object to be measured.

Based on this conclusion, various trials and errors have been made to remove reflected light due to rain having the same polarization characteristics as the irradiation laser light, and as a result, the present invention has the following configuration.

The all-weather optical rangefinder of the present invention comprises (1)
An all-weather optical distance meter that can be used even in rainy weather, wherein (2) light emitting means for transmitting light having a predetermined polarization characteristic toward a measurement target; Removing means for removing light having the same polarization characteristic as that of the light sent from the light projecting means; and (4) removing the light transmitted through the removing means. Light receiving means for receiving light.

In this all-weather optical rangefinder, light having predetermined polarization characteristics is transmitted toward the object to be measured by the light projecting means. Then, the transmitted light is reflected by the object to be measured. Here, the reflected light from the object to be measured has a different polarization characteristic from the light transmitted from the light projecting means, and has the same polarization characteristic as natural light. Therefore, of the reflected light from the object to be measured, light having the same polarization characteristic as that of the transmitted light is removed by the removing means, and the remaining light passes through the removing means and is received by the light receiving means. . Then, the distance to the object to be measured is obtained based on the light received by the light receiving means.

Here, when it is raining, the light emitted from the light projecting means is reflected not only by the object to be measured but also by raindrops existing in the optical path along which the light travels. The reflected light from the raindrop maintains the polarization characteristics of the light sent from the light projecting means. Therefore, while the reflected light from the raindrop is removed by the removing means, a part of the reflected light from the measurement target is
As described above, the light passes through the removing means and is received by the light receiving means. Then, the distance to the object to be measured is obtained based on the light received by the light receiving means.

As described above, the all-weather optical rangefinder of the present invention removes, on the optical path of the reflected light from the object to be measured, light having the same polarization characteristic as the light transmitted from the light projecting means. The removal of light reflected from raindrops in advance by utilizing the difference in light reflection characteristics between the measurement target and the raindrop, and receiving a part of the reflection light from the measurement target. it can. Therefore, the amount of data to be analyzed is reduced, so that the load on the apparatus can be reduced, and highly accurate distance measurement can be performed not only in fine weather but also in rainy weather.

Further, in the all-weather optical rangefinder of the present invention, the light projecting means may include a laser oscillator that generates linearly polarized pulse light in a predetermined direction. With this configuration, the pulse light generated from the laser oscillator has a linear polarization characteristic in a predetermined direction. The reflected light from the measurement target has a different polarization characteristic from the pulsed light generated from the laser oscillator, and has the same polarization characteristic as natural light. On the other hand, the reflected light from the raindrop maintains the same linear polarization characteristic in a predetermined direction as the pulsed light generated from the laser oscillator.

Further, the distance measuring method according to the present invention transmits light having a specific polarization component toward an object to be measured, and removes a specific polarization component from light directly reflected from the object to be measured.
The remaining light component from which a specific polarization component has been removed is received, and the distance to the measurement object is determined based on the timing of transmission and reception.

In this method, when light having a specific polarization component is transmitted toward the object to be measured, the light is reflected by the object to be measured, and the reflected light changes its polarization characteristic and has the same polarization characteristic as natural light. Become like Here, if raindrops exist in the optical path in which the transmitted light travels, the raindrops also reflect the light. The reflected light from the raindrop becomes light having a specific polarization component that maintains the polarization characteristics of the transmitted light. Then, a specific polarization component is removed from the reflected light directly from the measurement object, and the remaining light components are received. At that time, the reflected light from the raindrop having the specific polarization component is also removed. As a result, by determining the distance based on the timing of transmission and light reception, highly accurate distance measurement can be performed not only in fine weather but also in rainy weather.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of an all-weather optical distance meter and a distance measuring method according to the present invention will be described below with reference to the accompanying drawings. Note that the same components are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 1 is a block diagram showing the configuration of an all-weather optical distance meter (hereinafter, also referred to as a “distance meter”) according to an embodiment of the present invention, and FIG. 2 explains the principle of distance measurement of the distance meter. FIG.

As shown in FIG. 1, the distance meter 10 is roughly divided into a light projecting unit, a light receiving unit, a polarizing plate as a removing unit, a signal processing unit, and an arithmetic control unit.

The light emitting means is a light emitting element L such as a semiconductor laser.
D and a laser driver 1 for driving the light emitting element LD
2 and a light projecting lens 14 for transmitting the pulse light P projected from the light emitting element LD to the measurement object OB. The laser driver 12 drives the light emitting element LD so as to project the pulse light P synchronized with a predetermined measurement cycle τ during the measurement period T specified by the control signal STR from the controller 40. The light emitting element LD is a laser oscillator that emits a pulse light P having a predetermined polarization characteristic. In the present embodiment, the light emitting element LD emits linearly polarized light composed of vertically polarized components. Note that a polarizing plate may be arranged near the light projecting lens 14 in order to make the polarization direction completely uniform.

The light receiving means includes a receiving lens 20 for incident and a light receiving element PD such as a photodiode, the reflected light I _t from the measurement object OB on the light-receiving element PD, the light receiving elements P
Amplifies the photoelectric conversion signal output from D and outputs a detection signal S _PD
The amplifier 22 is provided as an output.

The polarizing plate 30 removes light having the same polarization as the polarization characteristics of the pulse light P projected by the light emitting element LD. In the present embodiment, the polarization direction of the pulse light P projected by the light emitting element LD is used. Only the horizontal polarization component inclined by 90 degrees from the light is transmitted. The polarizing plate 30 is disposed on the optical path of the reflected light I _t from the measurement object OB to a vicinity of the light receiving lens 20.

The signal processing means includes a predetermined threshold voltage V specified by a threshold setting signal D _TH output from the controller 40.
A threshold setting circuit 42 for generating a _TH, includes a comparator 44 for converting the detection signal S _PD into a binary signal C _PD compares the detection signal S _PD and the threshold voltage V _TH, the.

The arithmetic and control means includes a controller 40 comprising a microcomputer system or the like having arithmetic and control functions. The controller 40 controls the laser driver 12 and the threshold setting circuit 42,
The binary signal C _PD output from the comparator 44 is processed to determine the distance L to the measurement object OB.

The above-mentioned light projecting means LD, 12, 14, light receiving means PD, 20, 22, polarizing plate 30 as removing means,
All of the signal processing means 42 and 44 and the arithmetic control means 40 are covered by a protective case 46 made of ABS resin, and waterproof measures which are problematic in rainy weather are taken.

Next, the principle of distance measurement of the distance meter 10 will be described with reference to FIGS.

As shown in FIG. 2A, the pulse light P projected from the light projecting means is linearly polarized light composed of a polarized component in a predetermined direction, here, a vertical direction.

The pulse light P is applied to the object OB to be measured.
Is reflected by Reflected light I _t from the object to be measured OB
Has a polarization characteristic different from that of the pulse light P of linearly polarized light in the vertical direction projected from the light projecting means as shown in FIG.
The polarization state is different and has the same polarization characteristics as natural light.
Therefore, part of the reflected light I _t from the measurement object OB is received by the light receiving means is transmitted through the polarizer 30 that transmits only the polarization component in the horizontal direction inclined 90 degrees from the polarization direction of the pulsed light P .

[0034] only the reflected light I _t from the measurement object OB is at the time of fine weather as described above returns to the distance meter 10, but in addition to the reflected light I _t from the measurement object OB at the time of rainy weather, the pulse beam P reflected light I _r from the raindrops present in the optical path of travel
Will also come back. Reflected light I _r from the raindrops, 2
The pulse light P projected from the light projecting means as shown in FIG.
Is maintained, and the light becomes linearly polarized light composed of a polarization component in the vertical direction. Therefore, the reflected light I from the raindrop
_r is removed by the polarizing plate 30 that transmits only the polarization component in the horizontal direction.

As described above, the distance meter 10 uses the polarizing plate 30 that removes light having the same polarization characteristic as that of the pulsed light P projected by the light projecting means. by utilizing the difference in light reflection characteristics removed beforehand reflected light I _r from raindrops, but to reduce and improve the measurement accuracy of the distance according to the total of 10 load.

Next, a distance measuring method according to an embodiment of the present invention using the above-mentioned all-weather optical distance meter 10 will be described with reference to FIGS.

First, the control signal S from the controller 40 to the laser driver 12 over a predetermined measurement period T
TR is output, and the light emitting element LD is driven to oscillate a linearly polarized pulse light P composed of a vertically polarized component synchronized with a predetermined measurement period τ. This pulse light P is transmitted to the light projecting lens 1
After passing through 4, the light is transmitted toward the object OB while maintaining the polarization characteristics. A projection timing signal LD synchronized with the projection timing of the pulse light P from the laser driver 12
_ON is output to the controller 40 to notify the actual measurement period τ.

The pulse light P transmitted from the light emitting element LD is
The light travels straight toward the measurement object OB without changing the polarization characteristics, is directly reflected by the measurement object OB, and a part of the light directly returns to the distance meter 10. Reflected light I _t which is reflected by the measurement object OB has different polarization characteristics from the pulse light P in the vertical direction of the linearly polarized light transmitted from the light projecting means, have the same polarization characteristics as natural light polarization state disjointed.

[0039] Then, a direct reflected light I _t from the distance meter measuring object has returned to 10 OB to be incident on the polarizing plate 30 to remove the vertical polarization component, 90 degrees from the polarization direction of the pulsed light P Only the polarized light component in the horizontal direction that is inclined only is transmitted. Then, the light transmitted through the polarizing plate 30 is received by the light receiving element PD via the light receiving lens 20.

The light signal received by the light receiving element PD is converted into an electric signal and output to the amplifier 22.
And amplifies this electric signal and outputs it to the comparator 44 as a detection signal _SPD . The threshold voltage V _TH output from the threshold setting circuit 42 based on the threshold setting signal D _TH of the controller 40 is input to the comparator 44.

Then, the threshold voltage V
By comparing _TH with the detection signal S _PD , the detection signal S
Converting the _PD into a binary signal C _PD. Binary signal C _PD is defined, a rectangular signal which becomes logical "H" in synchronism with the generation timing of the signal component S _r corresponding to the reflected light I _t as shown in FIG.

The binary signal C output from the comparator 44
_{The PD} is input to the controller 40, and the controller 40 obtains a time difference δt between transmission and reception based on the projection timing signal LD _ON and the binary signal C _PD to obtain the measurement object O.
The distance L to B is calculated. This operation is performed using the control signal ST
The actual measurement period τ over the measurement period T defined by R
Each time, the distance L to the measurement object OB is calculated. Then, the average value is calculated as the distance L to the actual measurement object OB.
Output as

Here, the distance meter 10 according to the present embodiment is
In the distance measurement method used, it is
There is a sign. That is, when it rains, the light is transmitted from the light emitting element LD.
Pulsed light P exists in the optical path on which the pulsed light P travels.
Is reflected by the raindrops, and some of the reflected light
Return to total 10. Reflected light I from this raindrop_rIs
The polarization characteristic of the pulse light P sent from the optical means is maintained,
This is linearly polarized light composed of a polarization component in a perpendicular direction. But
The reflected light from raindrops I_rIs the horizontal polarization component
Can be removed by the polarizing plate 30 which transmits only
You. On the other hand, the direct reflected light I from the measurement object OB_tIs
As described above, the pulse light P transmitted from the light projecting means is polarized.
The light characteristics are different, the polarization state is different and the same polarization as natural light
Has optical properties. Therefore, it is measured by the polarizing plate 30.
Reflected light I directly from the object OB _tOut of the horizontal
A light-receiving lens that transmits only light components and transmits the transmitted light components
After passing through 20, the light is received by the light receiving element PD. And sending
Obtain the time difference δt of the light reception and determine the distance L to the object OB.
Is calculated.

As described above, the distance meter 1 according to this embodiment is
In 0, the optical path of the reflected light I _t from the measurement object OB,
Since the polarizing plate 30 is provided to remove light having the same polarization characteristic as that of the pulse light P sent from the light projecting means, the raindrop is made using the difference between the light reflection characteristics of the measurement object OB and the raindrop. it can be removed in advance reflected light I _r from. Therefore, it is possible to reduce the amount of data to be analyzed and reduce the load on the apparatus, and to measure the distance L to the measurement object OB with high measurement accuracy not only in fine weather but also in rainy weather. Can be.

Further, in such distance measuring method in the present embodiment, and it sends toward the pulse light P having a vertical polarization component in the measuring object OB, the direct reflected light I _t and raindrops from the measurement object OB polarizer direct reflected light I _r from 30
To be incident on, and at the same time to remove the vertical polarization component of the reflected light I _t from the measurement object OB, to remove the reflected light I _r from the raindrops with a vertical polarization component, receiving the remaining light component can do. Then, it is possible to determine the distance L to the measurement object OB based on the timing of the transmission and the light reception. Thus, the measurement object O
By utilizing the difference in light reflection characteristics between B and raindrops, the distance L to the measurement object OB can be measured with high measurement accuracy not only in fine weather but also in rainy weather.

[0046]

According to the present invention, on the optical path of the reflected light from the object to be measured, there is provided a removing means for removing light having the same polarization characteristic as that of the light transmitted from the light projecting means. Therefore, the reflected light from the raindrop can be removed in advance by using the difference between the light reflection characteristics of the measurement object and the raindrop. As a result, it is possible to reduce the amount of data to be analyzed and reduce the load on the device, and to obtain highly accurate measurement results not only in fine weather but also in rainy weather. It becomes possible to provide a range finder.

According to the present invention, when a specific polarized light component is removed from the reflected light directly from the object to be measured, the direct reflected light from the raindrop having the specific polarized light component is also removed, The remaining light component of the reflected light directly from the measurement object can be received. Then, the distance to the object to be measured can be determined based on the timing of the transmission and the light reception. As described above, by utilizing the difference between the light reflection characteristics of the measurement target and the raindrop, a distance measurement method capable of measuring the distance to the measurement target with high measurement accuracy not only in fine weather but also in rainy weather is proposed. Provision is possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an all-weather optical distance meter according to an embodiment of the present invention.

FIGS. 2A to 2C are explanatory diagrams for explaining the principle of distance measurement of the all-weather optical distance meter according to the embodiment;

FIG. 3 is an explanatory diagram for explaining the operation of the all-weather optical distance meter according to the embodiment;

FIGS. 4A and 4B are explanatory diagrams for explaining a state of an experiment for examining a reflection characteristic of irradiated laser light by raindrops.

[Explanation of symbols]

10: all-weather optical distance meter, 12: laser driver,
14: light projecting lens, 20: light receiving lens, 22: amplifier,
30: polarizing plate, P: pulsed light, OB: object to be measured, LD
... Light emitting element, PD ... Light receiving element.

Claims (3)

[Claims] 1. An all-weather optical distance meter that can be used even in rainy weather, comprising: a light projecting means for transmitting light having a predetermined polarization characteristic toward a measurement target; Removing means for removing light having the same polarization characteristic as that of the light emitted from the light projecting means, and receiving light transmitted through the removing means. An all-weather optical rangefinder. 2. The all-weather optical rangefinder according to claim 1, wherein the light projecting means includes a laser oscillator that generates linearly polarized pulse light in a predetermined direction. 3. Transmitting light having a specific polarization component toward the measurement target, removing the specific polarization component from light directly reflected from the measurement target, and removing the specific polarization component. Receiving the remaining light component, and determining a distance to the object to be measured based on the timing of the transmission and the light reception.