WO2002059641A1

WO2002059641A1 - Distance measuring equipment and object detector

Info

Publication number: WO2002059641A1
Application number: PCT/JP2002/000471
Authority: WO
Inventors: Shigeki Nakase; Shigeyuki Nakamura; Tsuyoshi Ohta; Hiromi Shimano; Hiromichi Tozuka
Original assignee: Hamamatsu Photonics K.K.
Priority date: 2001-01-23
Filing date: 2002-01-23
Publication date: 2002-08-01
Also published as: JP4878080B2; JP2002214327A

Abstract

A projection optical system (11) comprises a light source (12) and a light intensity distribution correcting means, i.e. a projection lens (collimate lens) (13). The light source (12) is a laser diode (LD) outputting a light beam in response to a drive signal inputted from a laser diode drive circuit (LD drive circuit) (33). The projection lens (13) projects a light beam emitted from an LD (12) toward an object T being measured and corrects the light intensity distribution of a light beam emitted from the LD (12). The projection lens (13) corrects the light intensity distribution of a light beam emitted from the LD (12) such that the light intensity of the light beam in the vicinity of the optical axis is higher than the light intensity at the peripheral part thereof at a position separated by a specified distance from the projection lens (13). The projection lens (13) includes an aspherical lens part and a cylindrical lens part.

Description

Technical field of distance measurement device and object detection device

The present invention relates to a distance measurement device that measures a distance to a measurement target object, and an object detection device that uses the distance measurement device.

Background art

Conventionally, for example, as a vehicle detection device in the ETC (Electronic ToU Collection System), an irradiation optical system using a light source (laser diode, etc.) that generates irradiation light emitted outside, and a reflected light from the object to be measured are used. 2. Description of the Related Art There is known a distance measuring device including a detection optical system using a photodiode or the like for detection. This distance measuring device detects the presence or absence of an object to be measured in the detection direction based on the presence or absence of incident light, and calculates the distance to the object to be measured based on the time difference and phase difference between irradiation light and reflected light. To detect.

For example, Japanese Unexamined Patent Publication No. Hei 7-2525342 discloses a light projection optical system for projecting light emitted from a laser light source, and a light reflected from an object among light detected by a detection optical system. Detecting means for detecting the reflected light and outputting a detection signal; and calculating means for calculating a distance to the object by measuring a round trip time to the object based on a difference between the light projection timing and the detection timing. The disclosed distance measuring device is disclosed. In the distance measuring device disclosed in Japanese Patent Application Laid-Open No. Hei 7-253534, the light projecting optical system has a fly-eye lens, and the light from the laser light source is intensified by the fly-eye lens. The distribution is flattened and emitted, and errors due to the intensity distribution of the light emitted from the light source are reduced, and highly accurate distance measurement becomes possible.

Disclosure of the invention

As a result of the investigation and research by the present inventors, it has been found that the distance measuring device disclosed in Japanese Patent Application Laid-Open No. Hei 7-254642 has the following problems. JP In the distance measuring device disclosed in Japanese Patent Application Laid-Open No. Hei 7-252534, a fly-eye lens is used for a light projection optical system. However, since the emission intensity distribution of the laser light source is a Gaussian distribution (high near the optical axis and low near the periphery), the fly-eye lens only subdivides a light beam having a Gaussian emission intensity. However, it is difficult to flatten the emission intensity distribution of the entire luminous flux.

Even if the luminous intensity distribution of the entire luminous flux is flattened, if only part of the cylindrical object to be measured enters the irradiation range of the luminous flux emitted from the light source, the As the amount of light decreases, it becomes difficult to detect the reflected light flux itself, and the detection accuracy and accuracy may be inferior. In a cylindrical object to be measured, the light reflecting surface is a curved surface. Therefore, when a light beam is irradiated to the central part of the measured object, the irradiated light beam is specularly reflected, and the light intensity of the reflected light beam is high. When illuminated, the edge has a large angle of incidence, so scattering is large and the light intensity of the reflected light beam is sharply reduced. Further, since the emission intensity distribution of the laser light is a Gaussian distribution as described above, the light intensity itself at the periphery of the light beam is lower than the light intensity near the optical axis. For these reasons, when only the end of the object to be measured having a curved outer shape enters the irradiation range of the light beam, the light intensity of the reflected light beam is extremely low, and detection becomes difficult.

The present invention has been made in view of the above points, and provides a distance measurement device and an object detection device that can reliably detect a reflected light beam from an object to be measured and perform highly accurate distance measurement. The purpose is to do.

In order to achieve the above object, a distance measuring device according to the present invention comprises: a light projecting optical system for irradiating a light beam output from a light source toward an object to be measured; and a reflection light reflected by the object to be measured. A distance measuring device for measuring a distance to an object to be measured, wherein the light projecting optical system detects a light intensity near an optical axis of the light beam at a predetermined distance. This is characterized in that it also has a light intensity distribution correcting means for increasing the light intensity around the light beam. In the distance measuring device according to the present invention, since the light projecting optical system has the light intensity distribution correcting means, the light intensity distribution of the light beam output from the light source and applied to the object to be measured is represented by a peripheral portion of the light beam. Is higher than the light intensity near the optical axis of the light beam. As a result, when light at the periphery of the light beam enters the end of the measured object having a curved outer surface, the light intensity of the reflected light from the end of the measured object is changed from the light source. The light intensity distribution of the output luminous flux is higher than a Gaussian distribution or a flattened one. Therefore, even when only the end of the object to be measured having a curved outer surface enters the irradiation range of the light beam, the light intensity of the light beam reflected from the object to be measured increases, and this reflected light beam is Can be detected. As a result, the distance measurement device according to the present invention enables highly accurate distance measurement. When light is incident on the central part of the object to be measured having a curved outer surface, this light is substantially specularly reflected. ) Is incident on the center of the object to be measured, the light intensity of the reflected light beam is sufficient for detection.

Further, it is preferable that the light intensity distribution correcting means includes an aspherical lens portion and a cylindrical lens portion. As described above, since the light intensity distribution detecting means includes the aspherical lens portion and the cylindrical lens portion, the light near the optical axis of the light beam output from the light source spreads toward the peripheral portion of the light beam. become. Thus, the light intensity distribution correction means capable of increasing the light intensity at the peripheral portion of the light beam at a position separated by a predetermined distance from the light intensity near the optical axis of the light beam can be realized by combining the aspherical lens portion and the cylindrical lens portion. It can be realized with an extremely simple configuration. An object detection device according to the present invention is an object detection device including the above distance measurement device, wherein a plurality of light projecting optical systems are arranged in a direction intersecting the optical axis of the light beam. ¾¾

In the object detection device according to the present invention, the object to be measured having a curved outer surface invades a detection zone constituted by light beams output from a plurality of light-projecting optical systems arranged side by side. Even in the case of entering, the distance measurement can be performed with high accuracy, and the detection accuracy of the object to be measured can be improved.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a block diagram showing the configuration of the distance measuring device according to the present embodiment. FIG. 2A is a top view showing an example of a light projecting lens included in the distance measuring device according to the present embodiment.

FIG. 2B is a diagram illustrating an example of a light projecting lens included in the distance measuring device according to the present embodiment, as viewed from the emission side.

FIG. 2C is a bottom view showing an example of a light projecting lens included in the distance measuring device according to the present embodiment.

FIG. 2D is a diagram illustrating an example of a light projecting lens included in the distance measuring device according to the present embodiment, as viewed from the incident side.

FIG. 3 is an explanatory diagram showing a light intensity distribution of a light beam output from the light projecting optical system in the distance measuring device according to the present embodiment.

FIG. 4 is a characteristic diagram showing a light intensity distribution of a light beam output from the light projecting optical system in the distance measuring device according to the present embodiment.

FIG. 5A is a top view showing an example of a light projecting lens included in the distance measuring device according to the present embodiment.

FIG. 5B is a diagram illustrating an example of a light projecting lens included in the distance measuring device according to the present embodiment, as viewed from the emission side.

FIG. 5C is a bottom view showing an example of a light projecting lens included in the distance measuring device according to the present embodiment.

FIG. 6A is a top view showing an example of a light projecting lens included in the distance measuring device according to the present embodiment.

FIG. 6B is a diagram illustrating an example of a light projecting lens included in the distance measuring device according to the present embodiment, as viewed from the emission side. FIG. 6C is a bottom view showing an example of a light projecting lens included in the distance measuring device according to the present embodiment.

FIG. 7 is a schematic perspective view showing the configuration of the object detection device according to the present embodiment. FIG. 8 is an explanatory diagram showing a light intensity distribution of a light beam output from the light projecting optical system in the object detection device according to the present embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of a distance measuring device according to the present invention will be described in detail with reference to the drawings. In the description, the same elements or elements having the same functions will be denoted by the same reference symbols, without redundant description.

First, a configuration of a distance measuring device according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing the configuration of the distance measuring device according to the present embodiment. The distance measuring device 1 includes a light projecting optical system 11 for irradiating the measured object T with a light beam, a detecting optical system 21 for detecting a reflected light beam reflected by the measured object T, It comprises a light projection optical system 11 and a signal processing system 31 for processing various electric signals input / output to / from the detection optical system 21.

The light projecting optical system 11 has a light source 12 and a light projecting lens (collimating lens) 13 as a light intensity distribution correcting means. The light source 12 is a laser diode (LD) that generates and outputs a luminous flux according to the drive signal input from the laser diode drive circuit (LD drive circuit) 33. The light intensity distribution of the light beam output from the light source (hereinafter referred to as LD) 12 is a Gaussian distribution (the light intensity near the optical axis of the light beam is higher than the light intensity around the light beam). The light projecting lens 13 emits the light beam output from the LD 12 toward the object T to be measured, and corrects the light intensity distribution of the light beam output from the LD 12. The light projecting lens 13 makes the light intensity at the periphery of the light beam higher than the light intensity near the optical axis of the light beam output from the LD 12 at a position away from the light projecting lens 13 by a predetermined distance. . In the present embodiment, the light projecting lens 13 is positioned at a distance of about 5 m from the light projecting lens It is designed so that the ratio of the light intensity near the optical axis to the light intensity around the light beam is about 1: 2.

Next, the configuration of the light projecting lens 13 will be described with reference to FIGS. FIG. 2A is a top view showing an example of the light projecting lens 13, FIG. 2B is a view seen from the emission side, FIG. 2C is a bottom view, and FIG. 2D is a view seen from the incidence side. The projection lens 13 includes an aspheric lens portion 14 and a cylindrical lens portion 15, and the aspheric lens portion 14 and the cylindrical lens portion 15 are integrally formed. . The light projecting lens 13 has the aspheric lens part 14 positioned on the incident (LD 12) side of the light projecting lens 13 and the cylindrical lens part 15 positioned on the emitting (measurement object T) side. It is arranged in the state where it was made to be. The exit surface of the cylindrical lens portion 15 is concavely curved to have a cylindrical side surface. The light projecting lens 13 may be provided with the cylindrical lens portion 15 positioned on the incident side of the light projecting lens 13 and the aspherical lens portion 14 positioned on the light emitting side.

The light beam output from the LD 12 enters the light projecting lens 13, and is collimated by the aspheric lens portion 14 of the light projecting lens 13. The width of the collimated light beam is set to about 50 mm. Then, the cylindrical lens portion 15 of the light projecting lens 13 causes light near the optical axis of the light beam to spread toward the peripheral portion of the light beam. As a result, as shown in FIG. 3, the light intensity distribution of the light beam output from the LD 12 becomes higher from the Gaussian distribution than the light intensity near the optical axis of the light beam. It becomes an intensity distribution.

As shown in FIG. 4, the beam shape S of the light beam emitted from the light projecting lens 13 has a substantially rectangular shape when viewed in a plane perpendicular to the optical axis L of the light beam. Further, as shown in the figure, the light intensity distribution 0 ぃ 0 ₂ along two mutually perpendicular straight lines passing through the optical axis L of the light beam is smaller than the light intensity near the optical axis L of the light beam. The distribution of light intensity is high. The ratio of the light intensity near the optical axis L of the light beam to the light intensity around the light beam is about 1: 2 as described above. The light intensity distribution is not necessarily the distribution described above. 〇i and distribution o ₂ need not be the same, and distribution or distribution o ₂ may be unidirectional depending on the application.

Instead of using the light projecting lens 13 shown in FIGS. 2A to 2D, light projecting lenses 16 and 18 as shown in FIGS. 5A to 5C and 6A to 6C may be used. FIGS. 5A to 5C and FIGS. 6A to 6C are diagrams showing an example of the light projecting lenses 16 and 18 as in FIGS. 2A to 2D. FIGS. 5A and 6A are top views, FIGS. 5B and 6B are views from the emission side, and FIGS. 5C and 6C are bottom views. The light projecting lens 16 shown in FIGS. 5A to 5C includes an aspheric lens part 14 and a cylindrical aspheric lens part 17 as shown. The light projecting lens 16 is disposed with the aspheric lens part 14 positioned on the incident side of the light projecting lens 13 and the cylindrical aspheric lens part 17 positioned on the output side. The light projecting lens 18 shown in FIGS. 6A to 6C includes an aspheric lens part 14 and a roof prism 19. The light projecting lens 13 is disposed with the aspheric lens part 14 positioned on the incident side of the light projecting lens 13 and the roof prism 19 positioned on the light emitting side.

Referring again to FIG. The detection optical system 21 includes a lens 22 and a photodetector 23. The lens 22 causes the reflected light flux, which is reflected and returned from the object T to be measured, of the light flux emitted through the light projecting lens 13 to be incident on the photodetector 23. The photodetector 23 is a photodiode (PD) that outputs a signal obtained by performing photoelectric conversion corresponding to the incident reflected light beam to the amplifier 34.

Signal processing system 3 1 includes a pulse generator circuit 3 2, an LD driving circuit 3 3, an amplifier 3 4, a comparator _35, a clock generation circuit 3 6, and the time difference measuring circuit 3 7, distance output section 3 Includes 8 and. The pulse generation circuit 32 generates a pulse signal of a predetermined cycle and outputs the pulse signal to the LD drive circuit 33 and the time difference measurement circuit 37. The LD drive circuit 33 operates with the pulse signal input from the pulse generation circuit 32 as a lighting trigger, and outputs a drive signal to the LD 12.

The amplifier 34 converts the electric output input from the photodetector (hereinafter referred to as PD) 23 into The amplified output is output to the comparator 35 as an analog output. The comparator 35 converts the analog output from the amplifier 34 into a pulse output of a digital square wave, and converts the output to the time difference measurement circuit 37.

The time difference measurement circuit 37 is composed of a pulse signal from the pulse generation circuit 32 and a comparator.

Based on the output from 35, the time difference between the projection timing of the light beam from LD 12 and the incident timing of the reflected light beam at PD 23, that is, the light beam output from LD 12 is the object to be measured. Measure the time until the reflected light flux is reflected at T and enters the PD 23 (the reciprocating flight time of the light flux). The clock signal from the clock generation circuit 36 is input to the time difference measurement circuit 37, and the time difference measurement circuit 37 determines the input timing of the pulse signal (for example, the rising timing of the pulse signal) from the comparator 3. The clock signal up to the output timing of 5 (for example, the rising edge of the output of the comparator 35) is counted, and the number of counted clock signals is multiplied by the period of the clock signal, whereby the reciprocation of the luminous flux described above is performed. Measure and calculate flight time.

The reciprocating flight time of the light beam measured and calculated by the time difference measurement circuit 37 is output to the distance output unit 38 as time information. The distance output unit 38 calculates the distance from the distance measuring device 1 to the measured object T based on the time information from the time difference measurement circuit 37, and outputs the distance as distance information.

As described above, in the distance measuring device 1 according to the present embodiment, since the light projecting optical system 11 has the light projecting lens 13, the light is output from the LD 12 and irradiates the object T to be measured. The light intensity distribution of the light beam is such that the light intensity at the periphery of the light beam is higher than the light intensity near the optical axis of the light beam. Thus, for example, when light at the periphery of the luminous flux enters the end of the measured object T whose outer shape is a curved surface as shown in FIG. 3, the end of the measured object T The light intensity of the reflected light beam from the light source is higher than that of the light beam output from the light source whose light intensity distribution is Gaussian distribution or flattened. It becomes. Therefore, even when the end of the object to be measured τ having a curved outer shape slightly enters the irradiation range (detection area) of the light beam, the object to be measured is

The light intensity of the reflected light beam from Τ increases, and the light intensity necessary for detecting the reflected light beam at the PD 23 (detection optical system 21) is obtained.The reflected light beam is transmitted to the PD 23 (detection optical system 21). It can be detected properly. As a result, according to the distance measurement device 1 of the present embodiment, highly accurate distance measurement can be performed. When light is incident on the central part of the object to be measured ある having a curved outer surface, the light is substantially specularly reflected. Therefore, for example, light near the optical axis of the light flux (light intensity is lower than that of the peripheral part of the light flux). (Low) is incident on the central part of the object to be measured τ, the light intensity of the reflected light flux is an intensity necessary for detection. By the way, as a technique for increasing the light intensity of the reflected light flux, it is conceivable to increase the output of the LD 12. By increasing the output of the LD 12, the light intensity not only near the optical axis of the light beam but also at the periphery is increased, and the light intensity of the reflected light beam from the end of the object to be measured, which has a curved outer shape, is also increased. Become. As described above, increasing the output of the LD 12 causes deterioration of the life of the LD 12 earlier. In addition, lasers are classified into safety classes “1”, “2”, “3Α”, “3Β”, and “4” according to the Japanese Industrial Standards (JIS). In order to obtain the necessary light intensity for detection of the laser beam, it is necessary to use an LD 12 of class 3 mm, which causes a problem in terms of safety. However, according to the distance measuring device 1 according to the present embodiment, even when the LD 12 having a class 1 output is used, the reflected light beam can be appropriately detected by the PD 23 (detection optical system 21). In addition, there will be no problems regarding early deterioration of LD 12, safety, etc. In addition, it is possible to reduce the cost of the LD 12 itself, such as lowering the running cost due to lower power consumption.

The light projecting lens 13 includes an aspherical lens portion 14 and a cylindrical lens portion 15 so that light near the optical axis of the light beam output from the LD 12 spreads toward the peripheral portion of the light beam. become. This makes it possible to increase the light intensity at the periphery of the light beam at a position separated by a predetermined distance from the light intensity near the optical axis of the light beam. 3 (light intensity distribution correcting means) can be realized with an extremely simple configuration of a combination of the aspherical lens portion 14 and the cylindrical lens portion 15.

Next, an object detection device using the above-described distance measurement device 1 will be described with reference to FIGS. FIG. 7 is a schematic perspective view showing the configuration of the object detection device according to the embodiment of the present invention, and FIG. 8 is a diagram showing the light intensity of the light beam output from the light projecting optical system in the object detection device according to this embodiment. It is explanatory drawing which shows distribution. The object detection device shown in FIG. 7 is a vehicle detection device used for ETC and the like.

The vehicle detection device (object detection device) 41 is installed on the vehicle entry side of the tollgate island 51, and a plurality of distance measurement devices 1 are provided at predetermined intervals (for example, 4 mm pitch) (for example, 38 ch) It is juxtaposed. As shown in FIG. 7, the distance measuring device 1 is in the vehicle vertical direction in a direction intersecting (for example, orthogonally) with the optical axis of the light beam emitted from the light projecting optical system 11 of the distance measuring device 1. It is juxtaposed in the direction. The vehicle detection device 41 irradiates a light beam from the plurality of distance measuring devices 1 arranged in parallel in an area, and the reflected light beam is incident on the distance measuring device 1, whereby the reciprocating flight time of the light beam is measured. It detects whether or not the vehicle is present based on the round-trip flight time (time information).

By the way, as shown in FIG. 7, when the vehicle to be measured T is, for example, a towing vehicle, the towing drive vehicle V1 and the towing vehicle V2 are connected by a towing rod V3. ing. Such towing vehicles are generally treated as one vehicle in total for toll payment. Aluminum or iron cylindrical pipe material (diameter of about 40 mm) may be used as towbar V3.

As shown in Fig. 8, the light intensity distribution of the light beam emitted from the light projecting optical system 11 of each distance measuring device 1 is such that the light intensity around each light beam is smaller than the light intensity near the optical axis of the light beam. Also has a high intensity distribution. For this reason, when the end of the towbar V3 (cylindrical pipe material) is irradiated with a light beam, the light intensity of the reflected light beam from the end of the towbar V3 is the light intensity of the light beam output from the light source. If the distribution is gaseous or flat It is higher than Therefore, even when the end of the tow rod V3 is slightly intruding into the detection area of the distance measuring device 1 (the irradiation range of the light beam from the light emitting optical system 11), The light intensity of the reflected light beam is increased, and a light intensity necessary for detecting the reflected light beam by the distance measuring device 1 is obtained. As a result, according to the vehicle detection device 41 of the present embodiment, highly accurate distance measurement can be performed, and the towing vehicle can be correctly detected as one vehicle.

The present invention is not limited to the above-described embodiment, and the light projecting lens 13 also has a light intensity distribution of the light beam at a position away from the light projecting lens 13 by a predetermined distance than the light intensity near the optical axis. The configuration is not limited to the configuration described above as long as the light intensity distribution in the peripheral portion is increased. Note that the value of the “predetermined distance” described above is appropriately set in consideration of the detection range of the distance measuring device 1.

Further, the distance measurement device according to the present invention can be applied to an object detection device other than the above-described vehicle detection device. The object detection device according to the present invention is particularly suitable for detecting an object to be measured having a curved surface portion.

The distance measuring device according to the present embodiment measures the distance based on the time until the light beam emitted from the light projecting optical system is reflected by the object to be measured and returns, and the reflected light beam is detected by the detection optical system. The measurement target is based on the phase difference between the light beam emitted from the light projection optical system and the reflected light beam detected by the detection optical system. Configured to measure distance to object

Industrial applicability

INDUSTRIAL APPLICATION This invention can be utilized for the vehicle detection apparatus in ETC.

Claims

The scope of the claims

1. A light projection optical system for irradiating a light beam output from a light source toward the object to be measured, and a detection optical system for detecting a light beam reflected by the object to be measured, A distance measuring device for measuring a distance to a target object, wherein the light projecting optical system measures a light intensity at a peripheral portion of the light beam more than a light intensity near an optical axis of the light beam at a position separated by a predetermined distance. A distance measuring device comprising light intensity distribution correcting means for increasing the height.

2. The distance measuring device according to claim 1, wherein the light intensity distribution correcting means includes an aspherical lens portion and a cylindrical lens portion.

3. An object detection device provided with the distance measurement device according to claim 1 or claim 2, wherein a plurality of the light projecting optical systems are arranged in a direction intersecting an optical axis of the light beam. An object detection device, which is provided.