JP2006172210A - Distance image sensor for vehicle, and obstacle monitoring device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a distance image sensor for vehicles which has no dead zone near its attaching position and by which information on a distance to an object can be accurately acquired, and to provide an obstacle monitoring device using the sensor. <P>SOLUTION: The distance image sensor 10 for vehicles comprises a luminescence source 2 to emit a visible light which is modulated so that its intensity may change periodically, to an objective space outside the vehicle; a photo-detecting element 1 to capture an image of the objective space, in which a plurality of photosensitive parts 11 to generate an electric output according to the amount of light received are arranged; and an image generation part 4 to generate the distance image whose pixel value is defined as a distance value calculated by converting a phase difference of light irradiating the objective space from the luminescence source 2 to be reflected by an object in the objective space and received by each photosensitive part 11 into a distance to the object. The luminescence source 2 is composed of a backward light which is attached at the back of the vehicle and illuminates rearward of the vehicle at going back. An obstacle monitoring device 5 monitors an obstacle in the objective space behind the vehicle, based on the distance image behind the vehicle generated by the image generation part 4. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a vehicle distance image sensor that obtains distance information to an object outside a vehicle, and an obstacle monitoring device using the same.

Conventionally, as a sensor for obtaining distance information to an object outside the vehicle, the propagation time from sending an ultrasonic wave to the target space until receiving a reflected wave reflected by an object in the target space is calculated. An ultrasonic sensor that measures the distance to an object is provided. Such an ultrasonic sensor is used to detect a distance to an obstacle behind the vehicle and an obstacle ahead. In the obstacle monitoring apparatus that monitors an obstacle behind the vehicle, an ultrasonic sensor is attached to the rear part of the vehicle body, and an alarm is issued when the distance to the obstacle behind the vehicle becomes shorter than a predetermined distance. In the obstacle monitoring device that monitors obstacles in front of the vehicle, an ultrasonic sensor is attached to the front part of the vehicle body, and the distance between the obstacles in front of the vehicle, for example, another vehicle that travels ahead when traveling is measured. When the measurement results and the inter-vehicle distance result is shorter than a predetermined distance, an alarm signal is issued to cause the computer that controls the braking device to perform braking. Further, when parking, the distance to an object in front of the vehicle is measured, and an alarm is issued when the measurement result becomes shorter than a predetermined distance (see, for example, Patent Document 1).
JP-A-6-138226

  In the ultrasonic sensor described above, the distance to the object is detected by the ultrasonic sensor based on the ultrasonic wave propagation time, but the ultrasonic wave propagation direction is shifted by the wind or the sound speed changes relatively. Thus, there is a problem that a distance measurement error occurs, and such an obstacle monitoring device using an ultrasonic sensor has a problem that the measurement accuracy of the distance to the obstacle cannot be sufficiently obtained. In addition, since the sound speed changes depending on the temperature change, there is a problem that a measurement error due to the temperature change occurs. In addition, in the reflection type ultrasonic sensor that transmits and receives with one ultrasonic transducer, the reflected wave cannot be received until a predetermined time elapses after the ultrasonic wave is transmitted. There was a problem that a dead zone occurred in a range from the front surface of the acoustic wave transducer to a certain distance.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its object is to provide a vehicle distance image sensor that has no dead zone in the vicinity of the mounting position and can obtain accurate distance information to the target object. And it is providing the obstruction monitoring apparatus using the same.

  In order to achieve the above object, the invention of claim 1 generates a light source that irradiates a target space outside the vehicle with visible light modulated so that the intensity periodically changes, and an electric output corresponding to the amount of received light. A light detection element that images a target space by arranging a plurality of photosensitive parts, and light from the light emitted from the light source to the target space reflected by an object in the target space and received by each photosensitive part A distance image generating unit that generates a distance image having a pixel value as a distance value obtained by converting the phase difference of the above to a distance to an object, and a light source is attached to the vehicle and irradiates light outside the vehicle It consists of a lighting device.

  According to the present invention, the visible light modulated so that the intensity periodically changes from the light emitting source is irradiated to the target space outside the vehicle, and the light emitted from the light emitting source to the target space by the image generating unit is the target space. A distance image is generated with the pixel value as the distance value obtained by converting the phase difference of the light reflected by the object inside and received by each photosensitive unit into the distance to the object. Measurement error does not occur under the influence of air temperature and wind as in the case of obtaining distance information, accurate distance information can be obtained, and an undetectable dead zone near the sensor mounting position occurs There is an effect that there is nothing to do. Moreover, since the light source is composed of a vehicle lighting device that emits light to the outside of the vehicle, there is no need to add a new light source to obtain a distance image, and the vehicle lighting device is used as the light source of the distance image sensor. By using it also, the number of parts can be reduced and the cost can be reduced.

  Invention of Claim 2 is an obstacle monitoring apparatus, Comprising: The distance image sensor for vehicles of Claim 1, The said vehicle lighting apparatus is a reverse light, The distance of the vehicle rear produced | generated by the said distance image generation part An obstacle monitoring unit that monitors an obstacle in a target space behind the vehicle based on the image is provided.

  According to the present invention, accurate distance information to an object in the target space can be obtained by using the vehicular distance image sensor according to claim 1, and there is a dead zone that cannot be detected in the vicinity of the sensor mounting position. Since a backward light that does not occur and is turned on when the vehicle moves backward is used as a light source, a distance image in the target space behind the vehicle can be generated without adding a new light source. Moreover, since the obstacle monitoring unit monitors the obstacle in the target space based on the distance image behind the vehicle, it is possible to realize an obstacle monitoring device that can reliably ensure safety when reversing.

  A third aspect of the present invention is an obstacle monitoring apparatus, comprising the vehicle distance image sensor according to the first aspect, wherein the vehicle lighting device is a headlamp, and the front of the vehicle generated by the distance image generation unit is provided. An obstacle monitoring unit that monitors obstacles in the target space in front of the vehicle based on the distance image is provided.

  According to the present invention, accurate distance information to an object in the target space can be obtained by using the vehicular distance image sensor according to claim 1, and there is a dead zone that cannot be detected in the vicinity of the sensor mounting position. The headlight that does not occur at night or when traveling in tunnels is used as the light emission source, so that a distance image in the target space in front of the vehicle can be generated without adding a new light source. . In addition, since the inter-vehicle distance monitoring unit monitors the obstacle in the target space based on the distance image in front of the vehicle, an obstacle monitoring device that can ensure safety in front of the vehicle can be realized.

  According to the first aspect of the present invention, the visible light modulated so that the intensity periodically changes from the light emitting source is irradiated to the target space outside the vehicle, and the light emitted from the light emitting source to the target space by the image generation unit. Ultrasonic sensor generates a distance image with a pixel value as a distance value obtained by converting the phase difference of light from when the light is reflected by an object in the target space and received by each photosensitive unit to a distance to the object The measurement error does not occur under the influence of air temperature and wind as in the case of obtaining distance information using the sensor, accurate distance information can be obtained, and it cannot be detected near the sensor mounting position. There is an effect that a dead zone does not occur. Moreover, since the light source is composed of a vehicle lighting device that emits light to the outside of the vehicle, there is no need to add a new light source to obtain a distance image, and the vehicle lighting device is used as the light source of the distance image sensor. By using it also, the number of parts can be reduced and the cost can be reduced.

  According to the second aspect of the present invention, accurate distance information to the object in the target space can be obtained by using the vehicular distance image sensor according to the first aspect, and it cannot be detected in the vicinity of the sensor mounting position. No dead zone is generated, and a reversing lamp that is turned on when reversing is used as a light source, so that a distance image in the target space behind the vehicle can be generated without adding a new light source. Moreover, since the obstacle monitoring unit monitors the obstacle in the target space based on the distance image behind the vehicle, it is possible to realize an obstacle monitoring device that can reliably ensure safety when reversing.

  According to the third aspect of the present invention, accurate distance information to the object in the target space can be obtained by using the vehicular distance image sensor according to the first aspect, and it cannot be detected in the vicinity of the sensor mounting position. A headlight that is turned on at night or when traveling in a tunnel is used as the light source, so that a distance image in the target space in front of the vehicle can be generated without adding a new light source. be able to. In addition, since the inter-vehicle distance monitoring unit monitors the obstacle in the target space based on the distance image in front of the vehicle, an obstacle monitoring device that can ensure safety in front of the vehicle can be realized.

(Embodiment 1)
In the following, an embodiment in which the vehicle distance image sensor according to the present invention is applied to an obstacle monitoring device for monitoring an obstacle in a target space behind the vehicle will be described. First, the basic configuration of the distance image sensor will be described with reference to FIG. Will be described with reference to FIG.

  As shown in FIG. 1, the distance image sensor 10 includes a light emitting source 2 that irradiates light to a target space, and receives light from the target space and obtains an electrical output having an output value that reflects the amount of received light. Device 1 is provided. The distance to the object Ob existing in the target space is the time from when light is irradiated from the light source 2 to the target space until the reflected light from the object Ob enters the light detection element 1 (referred to as “time of flight”). Ask for. However, since the flight time is very short, use the intensity-modulated light that is modulated so that the intensity of the light irradiating the target space changes periodically at a constant period, and use the phase when the intensity-modulated light is received. Ask for time. The technical idea of the present invention can be adopted not only in the configuration in which the distance image is generated by the time of flight, but also in the configuration in which the distance image is generated by the principle of triangulation method. However, the distance image sensor 10 having the configuration described below adopts the principle of triangulation because it can generate a distance image in a short time (almost real time) compared to the distance image sensor using the principle of triangulation. It is preferable to the distance image sensor.

  As shown in FIG. 3A, if the intensity of light radiated from the light source 2 into the space changes as shown by curve A, and the amount of received light received by the light detecting element 1 changes as shown by curve B, Since the phase difference ψ corresponds to the time of flight, the distance to the object Ob can be obtained by obtaining the phase difference ψ. Further, the phase difference ψ can be calculated using the received light quantity of the curve B obtained at a plurality of timings of the curve A. For example, it is assumed that the received light amounts of curve B obtained with the phases of curve A at 0, 90, 180, and 270 degrees are A0, A1, A2, and A3 (received light amounts A0, A1, A2,. A3 is indicated by hatching). However, the received light quantity A0, A1, A2, A3 in each phase is not an instantaneous value but a received light quantity integrated over a predetermined light receiving period Tw. Now, while obtaining the received light amounts A0, A1, A2, A3, the phase difference ψ does not change (that is, the distance to the object Ob does not change), and the reflectance of the object Ob does not change. To do. Further, it is assumed that the intensity of light emitted from the light emitting source 2 is modulated by a sine wave, and the intensity of light received by the light detection element 1 at time t is represented by A · sin (ωt + δ) + B. Here, A is the amplitude, B is the DC component (average value of the external light component and the reflected light component), ω is the angular frequency, and δ is the initial phase. The received light amounts A0, A1, A2, and A3 received by the light detection element 1 are instantaneous values, not integrated values of the light receiving period Tw, and time t = n / f (n = 0, 1, 2,. .., F is the modulation frequency), and the received light quantity A0 = A · sin (δ) + B, the received light quantity A0, A1, A2, A3 can be expressed as follows. The reflected light component means a component of light that is emitted from the light source 2 and is incident on the light detection element 1 after being reflected by the object Ob.

A0 = A · sin (δ) + B
A1 = A · sin (π / 2 + δ) + B
A2 = A · sin (π + δ) + B
A3 = A · sin (3π / 2 + δ) + B
In FIG. 3, since the phase difference is ψ, the initial phase δ (phase at time t = 0) of the waveform related to the amount of light received by the light detection element 1 is −ψ. That is, since δ = −ψ, A0 = −A · sin (ψ) + B, A1 = A · cos (ψ) + B, A2 = A · sin (ψ) + B, A3 = −A · cos (ψ) As a result, the relationship between each received light quantity A0, A1, A2, A3 and the phase difference ψ is expressed by the following equation.

ψ = tan ⁻¹ {(A2−A0) / (A1−A3)} (1)
In equation (1), the instantaneous values of the received light amounts A0, A1, A2, and A3 are used. However, even if the integrated values in the light receiving period Tw are used as the received light amounts A0, A1, A2, and A3, the phase difference in equation (1) ψ can be obtained.

  Further, when the intensity of light received by the light detection element 1 is A · cos (ωt + δ) + B, that is, at time t = n / f (n = 0, 1, 2,...) Synchronized with the modulation period. If the received light quantity is A0 = A · cos (δ) + B, the phase difference ψ can be obtained by the following equation.

ψ = tan ⁻¹ {(A1−A3) / (A0−A2)}
This relationship is a relationship in which the timing synchronized with the modulation period is shifted by 90 degrees. In addition, since the sign of the distance value is positive, if the sign is negative when the phase difference ψ is obtained, the order of the denominator in the parenthesis of tan ⁻¹ or each term of the numerator is changed, or An absolute value may be used.

  In the present embodiment, the light emission source 2 is attached to the rear part of the vehicle body 50, and is composed of a reverse lamp 51 for illuminating the rear of the vehicle and obtaining a rear view when the vehicle is reverse (see FIG. 2). The photodetecting element 1 is disposed in the vicinity. The light detection element 1 may be disposed inside the lamp body of the backward light 51. As the light source of the reversing lamp 51, for example, a light source in which a large number of light emitting diodes are arranged on a single plane is used in order to modulate the intensity of light applied to the target space. The light source 2 is driven by a modulation signal having a predetermined modulation frequency output from the control circuit unit 3, and the intensity of the light emitted from the light source 2 is modulated by the modulation signal. The control circuit unit 3 modulates the intensity of light emitted from the light source 2 with, for example, a 20 MHz sine wave. Here, since the control circuit unit 3 modulates the intensity of light emitted from the light source 2 with, for example, a 20 MHz sine wave, a change in the intensity of the irradiation light of the backward lamp 51 is detected by the human eye. No, the user does not feel uncomfortable. The light source of the reversing lamp 51 may be other than a light emitting diode, and any light source may be used as long as it emits visible light whose intensity is periodically changed, such as an incandescent bulb or an HID lamp. It may be used. Further, the intensity of the light emitted from the light source 2 may be modulated by a triangular wave, a sawtooth wave, or the like in addition to the modulation by a sine wave. In short, any configuration may be used as long as the intensity is modulated at a constant period. May be adopted.

  The light detection element 1 includes a plurality of photosensitive portions 11 regularly arranged. A light receiving optical system 19 is disposed on the light incident path to the photosensitive portion 11. The photosensitive part 11 is a part where light from the target space enters through the light receiving optical system 19 in the light detection element 1, and the photosensitive part 11 generates an amount of electric charge corresponding to the amount of received light. Further, the photosensitive portions 11 are arranged on the lattice points of the planar lattice, and are arranged in a matrix in which, for example, a plurality are arranged at equal intervals in the vertical direction (that is, the vertical direction) and the horizontal direction (that is, the horizontal direction). Is done.

  The light receiving optical system 19 associates the line-of-sight direction when viewing the target space from the light detection element 1 with each photosensitive portion 11. That is, the range in which light enters each photosensitive portion 11 through the light receiving optical system 19 can be regarded as a conical field of view having a small apex angle set for each photosensitive portion 11 with the center of the light receiving optical system 19 as the apex. . Therefore, if the reflected light emitted from the light source 2 and reflected by the object Ob existing in the target space is incident on the photosensitive portion 11, the optical axis of the light receiving optical system 19 is changed depending on the position of the photosensitive portion 11 that has received the reflected light. The direction in which the object Ob exists can be known as the reference direction.

  Since the light receiving optical system 19 is generally arranged so that the optical axis is orthogonal to the plane on which the photosensitive portion 11 is arranged, the center of the light receiving optical system 19 is the origin, and the vertical and horizontal directions of the plane on which the photosensitive portion 11 is arranged If an orthogonal coordinate system is set in which the optical axis of the light receiving optical system 19 is in the direction of the three axes, the angles (so-called azimuth and elevation) when the position of the object Ob existing in the target space is expressed in spherical coordinates are set. This corresponds to the photosensitive portion 11. The light receiving optical system 19 can also be arranged so that the optical axis intersects at an angle other than 90 degrees with respect to the plane on which the photosensitive portions 11 are arranged.

  In the present embodiment, as described above, in order to obtain the distance to the object Ob, the received light amounts A0, A1, A2, and the like at the timing of four points synchronized with the intensity change of the light irradiated from the light source 2 to the target space. We are seeking A3. Therefore, it is necessary to control the timing to obtain the desired received light amount A0, A1, A2, A3. In addition, since the amount of charge generated in the photosensitive portion 11 is small in one cycle of intensity change of light irradiated from the light source 2 to the target space, it is desirable to accumulate the charge over a plurality of cycles. Therefore, as shown in FIG. 1, a plurality of charge accumulating units 13 for accumulating charges generated in the respective photosensitive units 11 are provided, and a plurality of sensitivity control units 12 for adjusting the sensitivity of the respective photosensitive units 11 are provided. Yes.

  In each sensitivity control unit 12, the sensitivity of the photosensitive unit 11 corresponding to the sensitivity control unit 12 is increased at any one of the four points described above, and in the photosensitive unit 11 with increased sensitivity, the received light amount A0, Since charges corresponding to A1, A2, and A3 are mainly generated, charges corresponding to the received light amounts A0, A1, A2, and A3 can be accumulated in the charge accumulating unit 13 corresponding to the photosensitive unit 11.

  Hereinafter, as a specific configuration of the sensitivity control unit 12, a technique for adjusting a ratio of charges given to the charge accumulating unit 13 among charges generated by the photosensitive unit 11, and a part that substantially functions as the photosensitive unit 11 will be described. The technology to change the area. The technique for adjusting the ratio of charges given to the charge accumulating unit 13 includes a technique for adjusting the passing rate from the photosensitive unit 11 to the charge accumulating unit 13, a technique for adjusting a discard rate for discarding charges from the photosensitive unit 11, There is a technique for adjusting both the passing rate and the discarding rate.

  In the technique of adjusting the pass rate and the discard rate in the sensitivity control unit 12, as shown in FIG. 4, a gate electrode 12a is provided between the photosensitive unit 11 and the charge accumulation unit 13, and the pass voltage applied to the gate electrode 12a. Is changed to control the movement of charges from the photosensitive portion 11 to the charge accumulating portion 13 (that is, the passing rate). Further, by providing the charge discarding part 12c and changing the discarding voltage applied to the disposal electrode 12b attached to the charge discarding part 12c, the movement of the charge from the photosensitive part 11 to the charge discarding part 12c (that is, the discard rate) is changed. Control. The charge accumulating units 13 are provided so as to correspond one-to-one for each photosensitive unit 11, and the charge discarding units 12c are provided so as to correspond to the plurality of photosensitive units 11 so as to correspond one-to-many. In the illustrated example, all of the photosensitive portions 11 of the photodetecting element 1 share a set of discarding electrode 12b and charge discarding portion 12c.

  In order to control the sensitivity, it is conceivable to control only the pass rate from the photosensitive unit 11 to the charge accumulating unit 13 without discarding the charge from the photosensitive unit 11. Since charges remain in the unit 11 for a while, unnecessary residual charges out of the charges generated in the photosensitive unit 11 are mixed as noise components in the used charges (hereinafter referred to as signal charges). Therefore, in order to prevent the residual charge from being mixed into the signal charge, not only the passing voltage applied to the gate electrode 12a but also the discard voltage applied to the discard electrode 12b is controlled.

  In order to control the sensitivity using the gate electrode 12a and the waste electrode 12b, the charge generated in the photosensitive portion 11 can pass through the charge accumulating portion 13 by keeping the passing voltage applied to the gate electrode 12a constant. In addition, a waste voltage is applied to the waste electrode 12b so that the charge moves from the photosensitive part 11 to the charge discarding part 12c except for a period in which the charge used for the signal charge among the charges generated by the photosensitive part 11 is generated. In short, the signal charge is not discarded to the charge discarding unit 12c only during the period in which the charge used as the signal charge is generated in the photosensitive unit 11, and the signal charge is discarded to the charge discarding unit 12c in the other period. Only the charges generated during the period to be used are accumulated in the charge accumulation unit 13.

  Now, it is assumed that the intensity of light emitted from the light source 2 to the space is modulated by the modulation signal as shown in FIG. The charge accumulation unit 13 accumulates charges corresponding to the received light amounts A0, A1, A2, and A3 in a specific section synchronized with the modulation signal in a plurality of periods (tens of thousands to hundreds of thousands) of the modulation signal. The accumulated signal charge is taken out for each charge accumulation, and the charge in the next section is accumulated. For example, when charges corresponding to the received light quantity A0 are accumulated for tens of thousands of cycles of the modulation signal, the signal charges corresponding to the received light quantity A0 are once taken out to the outside, and thereafter, the charges corresponding to the received light quantity A1 are converted to tens of thousands of modulation signals. Accumulate about the period.

  FIG. 5 shows a state in which charges corresponding to the received light quantity A0 are accumulated. As shown in FIG. 5B, the passing voltage applied to the gate electrode 12a is kept constant. Further, as the charge corresponding to the received light quantity A0, the charge generated by the photosensitive portion 11 in the interval where the phase of the modulation signal is 0 to 90 degrees is employed. That is, a waste voltage is applied to the waste electrode 12b so that the charge generated by the photosensitive portion 11 is an unnecessary charge in the section where the phase of the modulation signal is 90 to 360 degrees as shown in FIG. This control makes it possible to accumulate signal charges corresponding to the received light amount A0 in a desired section in the charge accumulation unit 13 as shown in FIG. The processing shown in FIG. 5 is performed for tens of thousands to hundreds of thousands of cycles of the modulation signal, and the signal charge obtained in the charge accumulating unit 13 during this period is taken out by the charge extracting unit 14 as a received light output corresponding to the received light quantity A0. .

  The electric charge extracted from the electric charge extraction unit 14 is given to the image generation unit 4 as an image signal. In the image generation unit 4, the distance to the object Ob in the target space is determined based on the above-described equation (1). , A1, A2, and A3. That is, the image generation unit 4 calculates the distance to the object Ob in each direction corresponding to each photosensitive unit 11, and calculates the three-dimensional information of the target space. By using this three-dimensional information, it is possible to generate a distance image in which the pixel values of the pixels matching each direction of the target space are distance values.

  In the above-described control, a passing voltage that is a constant voltage is applied to the gate electrode 12a during the period in which the discarding voltage is applied to the discarding electrode 12b, but the magnitude relationship between the discarding voltage and the passing voltage is appropriately determined. If set, it is possible to prevent signal charges from being almost integrated during a period in which unnecessary charges are discarded. The reason why charges are accumulated for tens of thousands to hundreds of thousands of cycles of the modulation signal is to increase the sensitivity by increasing the amount of charges to be accumulated, and if the modulation signal is set to 20 MHz, for example, 30 Even if signal charges are taken out at a frame / second, integration of several hundred thousand cycles or more is possible.

  As described above, the charge discarding unit 12c including the disposal electrode 12b is provided, and unnecessary charges that are not used as signal charges among the charges generated in the photosensitive unit 11 are actively discarded to the charge discarding unit 12c. In the unit 11, most of the charge generated in the photosensitive unit 11 during the period when no signal charge is given to the charge accumulating unit 13 is discarded as unnecessary charge, and mixing of noise components into the signal charge is greatly suppressed. The

  In the above-described example, a period in which the discard voltage is not applied by providing a period in which the discard voltage is applied to the discard electrode 12b and a period in which the discard voltage is not applied to the discard electrode 12b in the period in which the passing voltage that is a constant voltage is applied to the gate electrode 12a. In FIG. 6, the charge generated in the photosensitive portion 11 is used as the signal charge. As shown in FIG. 6, the period for applying the passing voltage to the gate electrode 12a and the period for applying the discard voltage to the discard electrode 12b do not overlap. You may control as follows.

  FIG. 6 shows the operation when signal charges corresponding to the received light quantity A0 are integrated. FIG. 6A shows a modulation signal for modulating the intensity of light emitted to the space from the light emitting source 2, and the gate electrode 12a has a timing corresponding to the received light amount A0 as shown in FIG. 6B. Apply the passing voltage with. The period during which the passing voltage is applied to the gate electrode 12a is set from 0 degrees in the phase of the modulation signal to a certain period (0 to 90 degrees in the illustrated example). During this period, the charge from the photosensitive portion 11 to the charge accumulation portion 13 is transferred. It becomes possible to move. On the other hand, as shown in FIG. 6C, a discard voltage is applied to the waste electrode 12b in a period other than the period in which the signal charge corresponding to the received light amount A0 is accumulated in the charge accumulation unit 13, and in the period other than the period in which the signal charge is accumulated. The charges generated in the photosensitive unit 11 are discarded as unnecessary charges in the charge discarding unit 12c. Such control makes it possible to extract signal charges corresponding to the received light amount A0 as shown in FIG.

  In the control shown in FIG. 6, the period during which the passing voltage is applied to the gate electrode 12a is different from the period during which the discarding voltage is applied to the discard electrode 12b. Therefore, as in the control example shown in FIG. The magnitude of the passing voltage and the discarding voltage can be controlled independently without considering the magnitude relationship with the discarding voltage. As a result, the passing voltage and the discarding voltage can be easily controlled, and the photosensitive unit 11 receives light. Control of the sensitivity, which is the ratio of taking in the signal charge with respect to the light quantity, is facilitated, and control of the ratio of discarding unnecessary charges out of the charges generated in the photosensitive portion 11 is facilitated. Further, in the control example shown in FIG. 6, the period in which the signal charges are accumulated in the charge accumulation unit 13 is defined by the passing voltage applied to the gate electrode 12a, so the period in which the discard voltage is applied to the discard electrode 12b is shortened. For example, it is possible to apply the waste voltage to the waste electrode 12b only during a predetermined period immediately before applying the pass voltage to the gate electrode 12a.

  When the control shown in FIG. 6 is performed, the charge generated in the photosensitive unit 11 is discarded as an unnecessary charge in the period when the charge generated in the photosensitive unit 11 is not accumulated as the signal charge in the charge accumulating unit 13. Mixing of noise components into is greatly suppressed.

  As an example of controlling the passing voltage and the discarding voltage, as shown in FIG. 7, the discarding voltage applied to the discarding electrode 12b is maintained at a constant voltage so that a part of the charge generated in the photosensitive portion 11 is always discarded. May be. In the control example of FIG. 7, a period in which the pass voltage is applied to the gate electrode 12 a and a period in which the pass voltage is not applied are provided, and a period in which the pass voltage is applied is a period in which signal charges are accumulated in the charge accumulation unit 13.

  FIG. 7 shows an operation when signal charges corresponding to the received light quantity A0 are integrated. FIG. 7A shows a modulation signal that modulates the intensity of light emitted to the space from the light emitting source 2, and the gate electrode 12a provided in the charge accumulating unit 13 has a structure as shown in FIG. A passing voltage is applied during a period corresponding to the received light amount A0, and the charge generated in the photosensitive unit 11 is accumulated in the charge accumulating unit 13 as a signal charge corresponding to the received light amount A0. That is, the period during which the pass voltage is applied to the gate electrode 12a is set from 0 degree to a certain period (0 to 90 degrees in the illustrated example) in the phase of the modulation signal. Charge transfer is possible. On the other hand, as shown in FIG. 7C, a constant voltage discard voltage, which is a DC voltage, is always applied to the waste electrode 12b, and a part of the charge generated in the photosensitive portion 11 is always used as an unnecessary charge. Discard to 12c. In the above control, since the passing voltage is applied to the gate electrode 12a only during the period in which the signal charge is accumulated in the charge accumulation unit 13, the signal charge corresponding to the received light amount A0 is taken out as shown in FIG. Is possible.

  In the control shown in FIG. 7, a constant voltage discarding voltage is applied to the disposal electrode 12b regardless of whether or not a passing voltage is applied to the gate electrode 12a. Unnecessary charges that have not been accumulated as signal charges in the accumulation unit 13 are discarded as discard charges in the charge discard unit 12c. Here, the signal charge is continuously discarded from the photosensitive portion 11 to the charge discarding portion 12c even during a period in which a part of the charge generated in the photosensitive portion 11 is accumulated in the charge accumulating portion 13 as a signal charge. In order to properly integrate the voltage in the charge accumulation unit 13, it is necessary to consider the magnitude relationship between the passing voltage and the discard voltage. However, since the discard voltage is a constant voltage and is always applied to the discard electrode 12b, in practice, only the passing voltage needs to be controlled, and the control itself is easy.

  The photodetecting element 1 including the sensitivity control unit 12 illustrated in FIG. 4 can be realized by a CCD image sensor including an overflow drain. Any charge transfer method may be used in the CCD image sensor, and any of an interline transfer (IT) method, a frame transfer (FT) method, and a frame interline transfer (FIT) method may be used.

  FIG. 8 shows the configuration of an interline transfer type CCD image sensor having a vertical overflow drain. The illustrated example is a two-dimensional image sensor in which a plurality of photodiodes 41 serving as the photosensitive portions 11 are arranged in a horizontal direction and a vertical direction (3 × 4 in the figure), and the photodiodes 41 arranged in the vertical direction are arranged. A vertical transfer register 42 made of a CCD is provided on the right side of each column, and a horizontal transfer register 43 made of a CCD is provided below the area where the photodiodes 41 and the vertical transfer registers 42 are arranged. The vertical transfer register 42 includes two transfer electrodes 42 a and 42 b for each photodiode 41, and the horizontal transfer register 43 includes two transfer electrodes 43 a and 43 b for each vertical transfer register 42.

  The photodiode 41, the vertical transfer register 42, and the horizontal transfer register 43 are formed on one semiconductor substrate 40, and the photodiode 41, the vertical transfer register 42, and the horizontal transfer register 43 are formed on the main surface of the semiconductor substrate 40. An overflow electrode 44 which is an aluminum electrode is provided so as to directly contact the semiconductor substrate 40 without going through an insulating film over the entire circumference of the semiconductor substrate 40 so as to surround the whole. If an appropriate disposal voltage that is positive with respect to the semiconductor substrate 40 is applied to the overflow electrode 44, electrons (charges) generated by the photodiode 41 are discarded through the overflow electrode 44. The overflow electrode 44 functions as the discard electrode 12b because a discard voltage is applied when discarding unnecessary charges among the charges generated in the photodiode 41 which is the photosensitive portion 11, and the power supply for applying the discard voltage to the overflow electrode 44 Functions as a charge discarding unit 12c that discards electrons (charges) generated in the photosensitive unit 11. The surface of the semiconductor substrate 40 is covered with a light shielding film 46 (see FIG. 9) except for a portion corresponding to the photodiode 41.

  FIG. 9 shows a portion of the CCD image sensor shown in FIG. 8 that is related to one photodiode 41. An n-type semiconductor is used for the semiconductor substrate 40, and a well region 31 made of a p-type semiconductor is formed in a region straddling the photodiode 41 and the vertical transfer register 42 on the main surface of the semiconductor substrate 40. The well region 31 is formed so that the thickness dimension of the region corresponding to the vertical transfer register 42 is larger than the region corresponding to the photodiode 41. An n + -type semiconductor layer 32 is provided in a region corresponding to the photodiode 41 in the well region 31, and the photodiode 41 is formed by a pn junction between the well region 31 and the n + -type semiconductor layer 32. A surface layer 33 made of a p + type semiconductor is stacked on the surface of the photodiode 41. The surface layer 33 is provided for the purpose of controlling the vicinity of the surface of the n + -type semiconductor layer 32 so as not to be a passage path for charges when the charge generated by the photodiode 41 is moved to the vertical transfer register 42. Such a structure is known as a buried photodiode.

An accumulation transfer layer 34 made of an n-type semiconductor is overlaid in a region corresponding to the vertical transfer register 42 in the well region 31. The surface of the accumulation / transfer layer 34 and the surface of the surface layer 33 are substantially flush with each other, and the thickness dimension of the accumulation / transfer layer 34 is larger than the thickness dimension of the surface layer 33. The accumulation transfer layer 34 is in contact with the surface layer 33, but a separation layer 35 made of a p + type semiconductor having the same impurity concentration as that of the surface layer 33 is interposed between the storage layer 34 and the n + type semiconductor layer 32. Transfer electrodes 42 a and 42 b are disposed on the surface of the accumulation transfer layer 34 via an insulating film 45. Two transfer electrodes 42a and 42b are provided for each photodiode 41, and one of the two transfer electrodes 42a and 42b is formed wider than the other in the vertical direction. Specifically, as shown in FIG. 10, of the two transfer electrodes 42a and 42b corresponding to one photodiode 41, the narrow transfer electrode 42b is formed in a flat plate shape, and the wide transfer electrode 42a. Are arranged on the same plane as the narrow transfer electrode 42b and disposed between the pair of transfer electrodes 42b, and from both ends in the vertical direction (left and right direction in FIG. 10) of the flat plate portion. And a curved portion that extends and overlaps the transfer electrode 42b. Here, the insulating film 45 is formed of SiO ₂ , the transfer electrodes 42 a and 42 b are formed of polysilicon, and the transfer electrodes 42 a and 42 b are insulated from each other through the insulating film 45. Further, the surface of the light detection element 1 is covered with a light shielding film 46 except for a portion where light is incident on the photodiode 41. In the well region 31, the region corresponding to the vertical transfer register 42 and the storage transfer layer 34 are formed over the entire length of the vertical transfer register 42. Therefore, the storage transfer layer 34 has a wide transfer electrode 42a and a narrow transfer electrode 42b. And are alternately arranged.

  In the light detection element 1 described above, the photodiode 41 corresponds to the photosensitive portion 11, the transfer electrode 42 a corresponds to the passing electrode 12 a, the overflow electrode 44 corresponds to the discard electrode 12 b, and the vertical transfer register 42 corresponds to the charge accumulation portion 13. And functions as a part of the charge extraction unit 14. Further, the horizontal transfer register 43 also becomes a part of the charge extraction unit 14. That is, if light enters the photodiode 41, a charge is generated, and the ratio of the charge generated as a signal charge to the vertical transfer register 42 among the charges generated by the photodiode 41 is equal to the passing voltage applied to the transfer electrode 42a and the overflow. It can be determined according to the relationship with the waste voltage applied to the electrode 44. When a pass voltage is applied to the transfer electrode 42a, a potential well is formed in the storage transfer layer 34, and the depth of the potential well can be controlled by controlling the pass voltage. Therefore, by controlling the depth of the potential well and the time during which the passing voltage is applied, the ratio of charges delivered from the photodiode 41 to the vertical transfer register 42 can be adjusted. Further, if the discard voltage applied to the overflow electrode 44 is controlled, the potential gradient between the photodiode 41 and the semiconductor substrate 40 can be controlled. Therefore, if the potential gradient and the time for applying the discard voltage are controlled. The rate of charge delivered to the vertical transfer register 42 can be adjusted. The control voltage and the discard voltage may be controlled as in the control examples shown in FIGS.

  The signal charges delivered from the photodiode 41 to the vertical transfer register 42 are signals corresponding to the received light amounts A0, A1, A2, and A3 of each one of the four received light amounts A0, A1, A2, and A3 described above. It is read each time charge is accumulated. For example, when a signal charge corresponding to the received light quantity A0 is accumulated in a potential well formed corresponding to each photodiode 41, the signal charge is read, and then a signal charge corresponding to the received light quantity A1 is accumulated in the potential well. Then, the operation of reading the signal charge again is repeated. Note that the period during which signal charges corresponding to the received light amounts A0, A1, A2, and A3 are accumulated is set to be equal.

  Of the control examples described above, in the control example shown in FIG. 5, the charge (electrons) generated by the photosensitive unit 11 (photodiode 41) is always delivered to the charge accumulation unit 13 (vertical transfer register 42). Therefore, the charges accumulated in the charge accumulating unit 13 include not only the charges generated during the period in which the target received light amounts A0, A1, A2, and A3 are obtained, but also the charges generated during periods other than the target. It will be. Now, in the sensitivity control unit 12, the sensitivity in the period for generating the charges corresponding to the received light amounts A0, A1, A2, A3 is α, the sensitivity in the other periods is β, and the photosensitive unit 11 is a charge proportional to the received light amount. Is generated. Under this condition, the charge accumulating unit 13 that accumulates charges corresponding to the received light amount A0 is proportional to αA0 + β (A1 + A2 + A3) + βAx (Ax is a received light amount other than the period during which the received light amounts A0, A1, A2, and A3 are obtained). Charges proportional to αA2 + β (A0 + A1 + A3) + βAx are accumulated in the charge accumulation unit 13 that accumulates charges and accumulates charges corresponding to the received light amount A2. As described above, when obtaining the phase difference ψ, (A2−A0) is obtained, and when a value corresponding to (A2−A0) is obtained from the charge accumulated in the charge accumulation unit 13, (α−β) ( Similarly, since the value corresponding to (A1-A3) is (α-β) (A1-A3), (A2-A0) / (A1-A3) Theoretically the same value is obtained regardless of the presence or absence, and the obtained phase difference ψ is the same value even if charges are mixed.

  In the configuration example described above, a CCD image sensor is used for the photodetecting element 1, and sensitivity control is performed by controlling at least one of the amount of charge passed through the charge accumulating unit 13 and the amount of charge discarded into the charge discarding unit 12c. Although the example which comprises the part 12 was shown, the sensitivity control part 12 shown below changes the area (substantially light reception area) of the area | region which produces | generates the electric charge which can be utilized in the photosensitive part 11. FIG.

  Hereinafter, a specific structural example of the light detection element 1 will be described. The photodetecting element 1 shown in FIG. 11 has a plurality of (for example, 100 × 100) photosensitive portions 11 arranged in a matrix, and is formed on, for example, a single semiconductor substrate. One photosensitive portion 11 has a configuration in which a plurality (five in the figure) of control electrodes 23 are arranged on a semiconductor layer 21 to which impurities are added via an insulating film 22 made of an oxide film. In the illustrated example, the direction in which the electrodes are arranged (left-right direction) is the vertical direction, and when taking out the charge generated by the photosensitive portion 11 (using electrons in this embodiment), the charge is transferred in the vertical direction by the vertical transfer register. After that, the data is transferred in the horizontal direction using a horizontal transfer register. That is, the charge extraction unit 14 is configured by the vertical transfer register and the horizontal transfer register. As the configuration of the vertical transfer register and the horizontal transfer register, the same configuration as the interline transfer (IT) method, the frame transfer (FT) method, and the frame interline transfer (FIT) method in the CCD image sensor can be adopted.

  That is, when the photosensitive portions 11 arranged in the vertical direction share the continuous semiconductor layer 21 and the semiconductor layer 21 is used as a vertical transfer register, the semiconductor layer 21 is used as both the photosensitive portion 11 and the charge transfer path. The structure allows the charge to be transferred in the vertical direction in the same manner as the FT type CCD image sensor, and if the charge is transferred from the photosensitive portion 11 to the vertical transfer register via the transfer gate, the IT type or FIT Charges can be transferred in the same manner as a CCD image sensor of the type.

  As described above, the semiconductor layer 21 is doped with impurities, the main surface of the semiconductor layer 21 is covered with the insulating film 22 made of an oxide film, and a plurality of control electrodes 23 are formed on the semiconductor layer 21 via the insulating film 22. Is arranged. This light detection element 1 has a structure known as a MIS element, but a normal MIS element is that a plurality of (five in the illustrated example) control electrodes 23 are provided in a region functioning as one light detection element 1. Is different. A material is selected for the insulating film 22 and the control electrode 23 so that light having the same wavelength as the light emitted from the light source 2 to the target space can be transmitted. When light enters the semiconductor layer 21 through the insulating film 22, the semiconductor layer 21. A charge is generated inside the. The conductivity type of the semiconductor layer 21 in the illustrated example is n-type, and electrons e are used as charges generated by light irradiation. FIG. 11 shows only a region corresponding to one photosensitive portion 11, and a plurality of regions having the structure of FIG. 11 are arranged on the semiconductor substrate (not shown) as described above, and charge extraction is performed. A structure to be part 14 is provided. The vertical transfer register provided as the charge extraction unit 14 is assumed to transfer charges in the left-right direction in FIG. 11, but it is also possible to adopt a configuration in which charges are transferred in a direction orthogonal to the plane in FIG. is there. In addition, when transferring charges in the horizontal direction in the figure, it is desirable to set the width dimension of the control electrode 23 in the horizontal direction to about 1 μm.

  In the light detection element 1 having this structure, when a positive control voltage + V is applied to the control electrode 23, a potential well (depletion layer) 24 that accumulates electrons e in a portion corresponding to the control electrode 23 is formed in the semiconductor layer 21. The That is, when light is applied to the semiconductor layer 21 with a control voltage applied to the control electrode 23 so as to form the potential well 24 in the semiconductor layer 21, a part of the electrons e generated in the vicinity of the potential well 24. Are captured in the potential well 24 and accumulated in the potential well 24, and the remaining electrons e disappear due to recombination in the deep part of the semiconductor layer 21. Further, the electrons e generated at a location away from the potential well 24 are also extinguished by recombination in the deep part of the semiconductor layer 21.

  Since the potential well 24 is formed at a portion corresponding to the control electrode 23 to which the control voltage is applied, the potential well 24 along the main surface of the semiconductor layer 21 is changed by changing the number of the control electrodes 23 to which the control voltage is applied. (In other words, the area of a region that generates a charge that can be used on the light receiving surface) can be changed. That is, changing the number of control electrodes 23 to which the control voltage is applied means adjusting sensitivity in the sensitivity control unit 12. For example, when the control voltage + V is applied to the three control electrodes 23 as shown in FIG. 11A and when the control voltage + V is applied to the one control electrode 23 as shown in FIG. Since the area occupied by the potential well 24 on the light receiving surface changes, the area of the potential well 24 is larger in the state of FIG. 11A, so that the same amount of light is obtained compared to the state of FIG. As a result, the ratio of the charge that can be used increases and the sensitivity of the photosensitive portion 11 is substantially increased. Thus, it can be said that the photosensitive portion 11 and the sensitivity control portion 12 are constituted by the semiconductor layer 21, the insulating film 22, and the control electrode 23. The potential well 24 functions as the charge accumulation unit 13 because it holds charges generated by light irradiation.

  As described above, in order to extract charges from the potential well 24, the same technique as that of the CCD image sensor is employed. For example, when the photosensitive portion 11 is used as a vertical transfer register, after the electrons e are accumulated in the potential well 24, a control voltage having a different application pattern from that at the time of charge accumulation is applied to the control electrode 23. The accumulated electrons e can be transferred in one direction (for example, in the right direction in the figure). Alternatively, it is possible to adopt a configuration in which charges are transferred from the photosensitive portion 11 via a transfer gate to a vertical transfer register provided separately from the photosensitive portion 11. Charge is transferred from the vertical transfer register to the horizontal transfer register, and the charge transferred to the horizontal transfer register is taken out of the photodetector 1 from an electrode (not shown) provided on the semiconductor substrate.

  The sensitivity control unit 12 in the configuration shown in FIG. 11 switches the sensitivity of the photosensitive unit 11 into two levels, high and low, by switching the area for generating available charges into two levels, that is, the received light quantity A0, A1, A2, The sensitivity corresponding to any one of A3 is set to high sensitivity only during a period when the photosensitive portion 11 is to be generated (the area for generating charges is increased), and the sensitivity is set to be low during other periods. The period of high sensitivity and the period of low sensitivity are set in synchronization with the modulation signal that drives the light emitting source 2. Specifically, in a specific section (specific phase section) synchronized with the modulation signal, the charge generation area is increased to accumulate the charge generated by the photosensitive portion 11, and in other sections other than the specific section. The charge generated by the photosensitive portion 11 is accumulated by reducing the area for generating the charge. That is, in the photosensitive portion 11, the function of accumulating charges and the function of accumulating are realized alternately. Here, accumulation means collecting electric charges, and accumulation means holding electric charges. In other words, in the configuration shown in FIG. 11, by changing the size (area) of the charge accumulating unit 13 provided in the photosensitive unit 11, the integration rate of charges generated in the photosensitive unit 11 during the period of accumulating charges. The charge accumulation rate generated in the photosensitive portion 11 is reduced during the period in which charges are accumulated.

  In addition, after the charges are accumulated in the potential well 24 over a plurality of periods of the modulation signal, the charges are extracted to the outside of the light detection element 1 through the charge extraction unit 14. Charges are accumulated over a plurality of periods of the modulation signal because the period during which the photosensitive unit 11 generates usable charges within one period of the modulation signal is short (for example, if the frequency of the modulation signal is 20 MHz). This is because less than a quarter of 50 ns is generated. That is, by integrating charges for a plurality of periods of the modulation signal, signal charges (charges corresponding to light emitted from the light emission source 2) and unnecessary charges (mainly generated in the external light component and the light detection element 1). The charge corresponding to the shot noise) can be made large, and a large SN ratio can be obtained.

  By the way, if the charges corresponding to the received light amounts A0, A1, A2, and A3 of the four sections necessary for obtaining the phase difference ψ are generated by one photosensitive portion 11, the resolution in the line-of-sight direction is increased. There arises a problem that the time difference for obtaining the charges corresponding to the received light amounts A0, A1, A2, A3 becomes large. On the other hand, if the charges corresponding to the received light amounts A0, A1, A2, A3 are generated by the four photosensitive portions 11, respectively, the time difference for obtaining the charges corresponding to the received light amounts A0, A1, A2, A3 becomes small. However, a shift occurs in the line-of-sight direction for obtaining the charges in the four sections, and the resolution in the line-of-sight direction decreases. Therefore, a configuration in which two types of charges corresponding to the received light amounts A0, A1, A2, and A3 are generated by using two photosensitive portions 11 within one cycle of the modulation signal may be employed. That is, two photosensitive portions 11 may be used as a set, and light from the same line-of-sight direction may be incident on the two photosensitive portions 11 in the set.

  By adopting this configuration, the resolution in the line-of-sight direction can be made relatively high, and the time difference for generating charges corresponding to the received light amounts A0, A1, A2, and A3 can be reduced. That is, by reducing the time difference for generating the charges corresponding to the received light amounts A0, A1, A2, and A3, the distance detection accuracy of the object Ob moving in the target space can be kept relatively high. Can do. In this configuration, the resolution in the line-of-sight direction is lower than that in the case where the charge corresponding to the four types of received light amounts A0, A1, A2, and A3 is generated by one photosensitive unit 11, but the resolution in the line-of-sight direction is as follows. This can be improved by downsizing the photosensitive unit 11 or designing the light receiving optical system 19.

  The operation will be specifically described below. In the example shown in FIG. 11, an example in which five control electrodes 23 are provided for one photosensitive portion 11 is shown. However, two control electrodes 23 on both sides are charged (electrons e) by the photosensitive portion 11. In the case where two photosensitive portions 11 are used as a pair, the adjacent photosensitive portions are formed. Since any one of the photosensitive portions 11 forms a barrier between the 11 potential wells 24, it is sufficient to provide three photosensitive electrodes 11 for each of the photosensitive portions 11. With this configuration, the occupation area per one photosensitive portion 11 is reduced, and it is possible to suppress a decrease in resolution in the line-of-sight direction while using the two photosensitive portions 11 as a set.

  In the configuration example of the distance image sensor 10 described above, four sections corresponding to the received light amounts A0, A1, A2, and A3 are set so that the phase interval is 90 degrees within one period of the modulation signal. However, if the phase with respect to the modulation signal is known, the four sections can be set at appropriate intervals other than 90 degrees. However, the formula for obtaining the phase difference ψ differs if the interval is different. Also, the period of taking out the charge corresponding to the received light quantity of the four sections is within one period of the modulation signal as long as the reflectance and the external light component of the object Ob do not change and the phase difference ψ does not change. It is not essential to take out signal charges in four sections. Furthermore, when there is an influence of disturbance light such as sunlight or illumination light, it is desirable to dispose an optical filter that transmits only the wavelength of light emitted from the light source 2 in front of the photosensitive portion 11.

  Incidentally, since the distance image sensor 10 described above generates an amount of electric charge corresponding to the amount of received light in each photosensitive portion 11, each of the received light amounts A0, A1, A2, A3 reflects the brightness of the object Ob. That is, the DC component B obtained from the received light amounts A0, A1, A2, A3 corresponds to the density value in the grayscale image. In other words, when the received light amounts A0, A1, A2, and A3 at the respective photosensitive portions 11 are used, it is possible to obtain the density value of the object Ob in addition to obtaining the distance to the object Ob. In addition, since the distance and the density value of the object Ob are obtained using the photosensitive portion 11 at the same position, it is possible to obtain both the density value and the distance value information for the same position. Therefore, the image generation unit 4 of the present embodiment generates a grayscale image together with the distance image, and generates a distance image and a grayscale image from the same photosensitive unit 11. Therefore, the image generation unit 4 can obtain the distance value and the density value at substantially the same time for the same position in the target space. Since the average value of received light amounts A0, A1, A2, A3 (that is, DC component B) is used as the density value, the influence of the intensity-modulated light from the light source 2 can be removed.

  Next, the overall configuration of the obstacle monitoring apparatus using the above-described distance image sensor 10 will be described. As shown in FIG. 1, the obstacle monitoring apparatus according to the present embodiment includes the above-described distance image sensor 10, the obstacle monitoring unit 5, and an alarm output unit 6.

  Here, in the present embodiment, the light emitting source 2 is constituted by the backward light 51, and the backward light 51 is turned off during forward movement. Therefore, the light detection element 1 receives only the external light component, and image generation is performed. The unit 4 generates only a gray image. On the other hand, when the gear is switched to reverse during reverse, the reverse lamp 51 is lit and modulated by the control circuit unit 3 so that the intensity of the irradiation light of the reverse lamp 51 changes periodically. A distance image having a pixel value as a distance value obtained by converting the phase difference of the light from the reflected light 51 reflected by the object in the target space and received by the photosensitive unit 11 into the distance to the object, and the light and shade Both images are generated.

  The obstacle monitoring unit 5 monitors obstacles in the target space behind the vehicle based on the distance image generated by the image generation unit 4. For example, there is a pixel whose pixel value is shorter than a predetermined safe distance. For example, it is determined that the distance to the obstacle in the target space is shorter than the safe distance (that is, it is very close to the obstacle), and an alarm signal is output.

  The alarm output unit 6 includes a buzzer for generating an alarm sound. When an alarm signal is input from the obstacle monitoring unit 5, the alarm output unit 6 generates an alarm sound and notifies the driver that the vehicle is approaching the obstacle. The alarm output unit 6 may be configured by a voice output device that transmits an alarm by voice, a lamp that emits an alarm by light, or the like. When the obstacle monitoring unit 5 detects the approach of an obstacle, the alarm output unit 6 By issuing an alarm, it is possible to prevent the vehicle body 50 from coming into contact with an obstacle.

  Further, since the obstacle monitoring unit 5 generates an alarm signal when the distance to the obstacle is shorter than a predetermined safety distance, the object is within a predetermined safety distance from the vehicle body 50 regardless of the size of the object. If there is, a warning signal is generated. From the distance image generated by the image generation unit 4, an aggregate of pixels whose pixel values (that is, distance values) are shorter than a predetermined safe distance is extracted. When the area exceeds a predetermined threshold, an alarm signal may be generated, and an alarm can be output only when an object of a certain size is approached.

  As described above, in the present embodiment, the light source 2 that irradiates the target space outside the vehicle with the visible light modulated so that the intensity periodically changes, and a plurality of electric outputs that generate electric outputs according to the amount of received light. The light detection element 1 that images the target space with the photosensitive units 11 arranged, and the light from the light emitted from the light source 2 to the target space reflected by the object in the target space and received by each photosensitive unit 11 A distance image sensor 10 including a distance image that generates a distance image having a pixel value as a distance value obtained by converting the phase difference of the pixel into a distance to the object is used to determine the distance value to the object in the target space as a pixel value. As a distance image is obtained, measurement error does not occur under the influence of air temperature and wind as in the case of obtaining distance information using an ultrasonic sensor, and it is detected in the vicinity of the sensor mounting position. An impossible dead zone does not occur. In addition, since the vehicle lighting device (reverse light 51) that is required to be attached to the vehicle body 50 is used as the light emission source 2, there is no need to attach a new light source to the vehicle body 50, and the reverse light 51 is connected to the distance image sensor 10. By sharing the light-emitting source 2, the cost can be reduced by sharing parts.

  Since the image generation unit 4 generates both the distance image and the grayscale image of the target space, the vehicle can be displayed by displaying the generated grayscale image on a display device (not shown) installed in the vehicle interior. It is also possible to monitor the back of the.

(Embodiment 2)
Hereinafter, an embodiment in which the vehicle distance image sensor according to the present invention is applied to an obstacle monitoring apparatus that monitors an obstacle ahead of the vehicle will be described.

  The inter-vehicle distance monitoring device according to the present embodiment includes a distance image sensor 10, an obstacle monitoring unit 5, and an alarm output unit 6 as in the first embodiment (see FIG. 1). Since the distance image sensor 10 is common to the first embodiment, the same components are denoted by the same reference numerals and description thereof is omitted.

  In this embodiment, the light emission source 2 is composed of a headlamp 52 that is attached to the front part of the vehicle body and illuminates the front (see FIG. 12), and the light detection element 1 is disposed in the vicinity of the left and right headlamps 52. is doing. The light detection element 1 may be disposed inside the lamp body of the headlamp 52. When the headlamp 52 is turned off, the light detection element 1 receives only an external light component, and the image generation unit 4 generates only a grayscale image. On the other hand, when the headlamp 52 is turned on in order to ensure forward visibility at night or when traveling in a tunnel, or to improve visibility from other vehicles or passersby during the daytime, the control circuit unit 3 causes the headlamp to be turned on. Since the intensity of the irradiation light 52 is modulated so as to periodically change, the irradiation light from the headlamp 52 is reflected by the object in the target space and received by the photosensitive unit 11 by the image generation unit 4. Both a distance image and a grayscale image having a distance value obtained by converting the phase difference of the light up to the distance to the object as a pixel value are generated.

  Here, as the light source of the headlamp 52, in order to modulate the intensity of visible light irradiated to the target space, for example, it is preferable to use a plurality of light emitting diodes arranged on one plane. The light emission source 2 is driven by a modulation signal having a predetermined modulation frequency output from the control circuit unit 3, and the intensity of the light emitted from the light emission source 2 is modulated by the modulation signal. In the control circuit unit 3, for example, the intensity of light emitted from the light source 2 is modulated by a sine wave of 20 MHz, so that a change in intensity of the irradiation light of the headlamp 52 is not perceived by human eyes. The user does not feel uncomfortable. The light source of the headlamp 52 may be other than a light emitting diode, and any light source may be used as long as it emits visible light modulated so that the intensity changes periodically, such as an incandescent bulb or an HID lamp. It may be used. Further, the intensity of the light emitted from the light source 2 may be modulated by a triangular wave, a sawtooth wave, or the like in addition to the modulation by a sine wave. In short, any configuration may be used as long as the intensity is modulated at a constant period. May be adopted.

  The obstacle monitoring unit 5 monitors an obstacle in the target space in front of the vehicle based on the distance image generated by the image generation unit 4. For example, there is a pixel whose pixel value is shorter than a predetermined safe distance. For example, it is determined that the distance to the obstacle in the target space is shorter than the safe distance (that is, it is very close to the obstacle), and an alarm signal is output.

  The alarm output unit 6 includes a buzzer that generates an alarm sound. When an alarm signal is input from the obstacle monitoring unit 5, the alarm output unit 6 generates an alarm sound to notify the driver that the distance from the obstacle is short. . The alarm output unit 6 may be configured by a sound output device that transmits a warning by voice, a lamp that emits a warning by light, or the like.

  Here, the obstacle monitoring unit 5 obtains vehicle speed information from a vehicle speed sensor (not shown), and sets the safety distance longer as the vehicle speed increases. That is, the safety distance is set so that the time until it comes into contact with the obstacle is about several seconds. Thus, during high speed traveling, the safety distance is set to a relatively long distance of 10 m or more, and when the distance to another vehicle traveling ahead (the distance between the vehicles) becomes shorter than the safety distance, the alarm output unit 6 warns. A signal is output and an alarm is generated from the alarm output unit 6, and the driver can be urged to increase the inter-vehicle distance from the preceding vehicle. Also, when driving at low speeds such as when parking, the safety distance is set to a relatively short distance of about 1 m, and when the distance to the obstacle ahead is shorter than the safety distance, the alarm output unit 6 outputs an alarm signal, An alarm is generated from the alarm output unit 6, and contact with obstacles ahead can be prevented.

  The obstacle monitoring unit 5 outputs an alarm signal when there is a pixel whose pixel value is shorter than a predetermined safe distance, so that the object is placed in a space within the safe distance from the vehicle body 50 regardless of the size of the object. If there is, an alarm signal is output, but from the distance image generated by the image generation unit 4, an aggregate of pixels whose pixel values (that is, distance values) are shorter than the safe distance is extracted, and the area of the aggregate When the value exceeds a predetermined threshold value, an alarm signal may be output, and the alarm signal can be output only when an object of a certain size is approached.

  In the present embodiment, as described in the first embodiment, the light source 2 that irradiates the target space outside the vehicle with the visible light modulated so that the intensity periodically changes, and the electric output corresponding to the received light amount are generated. A plurality of photosensitive units 11 arranged to image the target space, and light emitted from the light source 2 to the target space is reflected by an object in the target space and received by each photosensitive unit 11. The distance to the object in the target space using the distance image sensor 10 provided with the image generation unit 4 that generates a distance image having a pixel value as a distance value obtained by converting the phase difference of the light up to the distance to the object Since a distance image with pixel values is obtained, measurement errors do not occur under the influence of air temperature and wind as in the case of using an ultrasonic sensor, and detection is not possible near the sensor mounting position. There is no possible dead zone. In addition, since the vehicle lighting device (headlight 52) that is required to be attached to the vehicle body 50 is used as the light emission source 2, there is no need to attach a new light source to the vehicle body 50, and the headlight 52 is displayed as a distance image. By sharing the light-emitting source 2 of the sensor 10, it is possible to reduce costs by sharing parts.

  In each of the above-described embodiments, the visible light is emitted from the light emission source 2, and the detection result of the distance value is easily influenced by the external light component. In the time zone in which the sense of distance is difficult to grasp, there is almost no influence of the external light component, so that it is possible to accurately detect the distance information to the object in the target space.

  In addition, since the image generation unit 4 generates both the distance image and the grayscale image of the target space, the generated grayscale image is displayed on a display device (not shown) installed in the vehicle interior, so that the vehicle It is also possible to monitor the front of the.

It is a block diagram which shows Embodiment 1 of this invention. It is explanatory drawing explaining the state which attached the same to the vehicle. (A)-(c) is operation | movement explanatory drawing same as the above. It is a block diagram which shows the structural example of the sensitivity control part in the same as the above. (A)-(d) is explanatory drawing which shows the operation example same as the above. (A)-(d) is explanatory drawing which shows the other operation example same as the above. (A)-(d) is explanatory drawing which shows the other operation example of the same as the above. It is a top view which shows the structural example of the photon detection element used for the same as the above. It is a principal part disassembled perspective view of the photon detection element shown in FIG. FIG. 10 is a sectional view taken along line AA in FIG. 9. It is operation | movement explanatory drawing of the principal part of the photon detection element used for the same as the above. It is explanatory drawing explaining the state which attached Embodiment 2 of this invention to the vehicle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light detection element 2 Light emission source 4 Image generation part 5 Obstacle monitoring part 10 Vehicle distance image sensor 11 Photosensitive part

Claims (3)

  A light source that irradiates a target space outside the vehicle with visible light modulated so that the intensity changes periodically, and a plurality of photosensitive units that generate an electrical output according to the amount of received light are arranged to image the target space Distance obtained by converting a light detection element and a phase difference of light from light emitted from the light emitting source to the target space to be reflected by the object in the target space and received by each photosensitive unit into a distance to the object A distance image generation unit that generates a distance image having a value as a pixel value, and the light emission source is a vehicle lighting device that is attached to the vehicle and irradiates light outside the vehicle. Distance image sensor for vehicles.   The vehicle distance image sensor according to claim 1, wherein the vehicle lighting device is a backward light, and an obstacle in a target space behind the vehicle based on a distance image behind the vehicle generated by the distance image generation unit. An obstacle monitoring device comprising an obstacle monitoring unit for monitoring the obstacle.   The vehicle distance image sensor according to claim 1, wherein the vehicle lighting device is a headlamp, and an obstacle in a target space in front of the vehicle based on a distance image in front of the vehicle generated by the distance image generation unit. An obstacle monitoring apparatus comprising an obstacle monitoring unit for monitoring an object.

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