JP4353086B2 - Safety confirmation device - Google Patents

Description

  The present invention relates to a safety confirmation device capable of confirming whether a monitored space is in the same safe state as before the start of monitoring.

  Conventionally, as this type of safety confirmation device, for example, in a factory, the monitoring target space is monitored using an image obtained by imaging the monitoring target space with an imaging means such as a CCD camera. There has been proposed a monitoring device that determines that the object is safe when there is no object (such as a person or a robot) (see, for example, Patent Document 1). Such a monitoring device is used by being mounted on, for example, a robot or an automated guided vehicle operating in a factory, or installed on a moving path of a robot or an automated guided vehicle in a factory. Used.

In the monitoring device disclosed in Patent Document 1 described above, a background image composed of an image obtained by previously imaging the monitoring target space by the imaging unit and an image obtained by imaging the monitoring target space by the imaging unit after the monitoring is started. To determine whether there is a safe state in which there is no obstacle object in the monitored space or in an unsafe state in which there is an obstacle object based on the difference image It has become.
JP-A-10-143665

  By the way, in the monitoring apparatus disclosed in the above-mentioned Patent Document 1, a general TV camera such as a CCD camera is used as an imaging unit, and an image obtained by imaging the monitoring target space by the imaging unit is a grayscale image. In addition, since only information about the brightness and darkness in the monitoring target space can be obtained, there are cases where an unsafe state cannot be detected due to the influence of sunlight, lighting, background, or the like.

  The present invention has been made in view of the above reasons, and its purpose is a safety confirmation device capable of confirming whether the monitored space is in a safe state without being affected by sunlight, lighting, background, or the like. Is to provide.

According to the first aspect of the present invention, a light-emitting source that irradiates the target space with intensity-modulated light whose intensity changes periodically, and a plurality of photosensitive units that generate electrical output according to the amount of received light are arranged to image the monitoring target space. The phase difference of the intensity-modulated light until the light irradiated from the light source to the monitoring target space is reflected by the object in the monitoring target space and received by each photosensitive part is converted into the distance to the object. An image generation unit that generates a distance image having a distance value as a pixel value, a background distance image storage unit that stores a distance image generated by the image generation unit before the monitoring of the monitoring target space as a background distance image, and a monitoring start Whether there is an object that did not exist before the start of monitoring by comparing the monitoring distance image consisting of the distance image generated by the image generation unit later with the background distance image stored in the background distance image storage unit Whether it is safe based on Anda state determination section for determining, the state determination unit, wherein the monitored space when the object that did not exist prior to the start monitoring the monitoring specific area monitored space exists is unsafe A safety confirmation device for determining that the state is in a state, wherein the state determination unit generates a warning output when the monitoring target space is determined to be in an unsafe state; and the image generation unit A shape estimation unit that estimates the shape and number of objects existing in the monitoring target space after the start of monitoring based on the output of the state, the state determination unit to the shape estimation unit when determined to be an unsafe state The unsafe level of the unsafe state is determined based on the combination of the shape and the number of the objects estimated in the above, and the alarm output unit outputs an alarm based on the unsafe level information given from the state determination unit. Change the alarm level It is characterized in. The object existing in the monitoring target space is a concept including a human body.

  According to the present invention, a safe state is based on whether there is an object that did not exist before the start of monitoring based on a distance image having a pixel value as a distance value to the object existing in the monitoring target space. Therefore, it is possible to confirm whether or not the monitoring target space is in a safe state without being affected by sunlight, lighting, or the background.

Further, according to this invention it can be determined that if the did not exist before starting the monitoring in the monitoring specific area object was present only in an unsafe state. That is, when an object that did not exist before the start of monitoring appears only in the area outside the monitoring specific area (when the difference image between the monitoring distance image and the background distance image changes), it is determined as a safe state. Therefore, it is determined that the state is unstable only when an object that does not exist before the start of monitoring appears in the monitoring specific area (when the difference image between the monitoring distance image and the background distance image changes). can do.

Furthermore, according to this invention, since the monitored space alarm output when it is determined to be in an unsafe condition occurs, the other to the monitored space when the monitored space is not safe state It is possible to prevent an object (for example, a human body, a robot, an automatic guided vehicle, etc.) from entering, and to prevent an accident from occurring in the monitoring target space.

  According to the present invention, since the alarm level of the alarm output changes based on the combination of the shape and number of objects existing in the monitoring target space after the start of monitoring, the alarm is set according to the safety level of the monitoring target area. The level can be changed.

According to a second aspect of the present invention, in the first aspect of the invention, the state determination unit compares the monitoring distance image and the background distance image only for a specific area set in advance with respect to the monitoring target space. And

  According to the present invention, the processing speed of the state determination unit can be increased as compared with the case where the monitoring distance image and the background distance image are compared for all areas of the distance image related to the monitoring target space.

According to a third aspect of the present invention, in the second aspect of the invention, in addition to the function of the image generation unit to generate a distance image, the gray value that is the amount of light received by each of the photosensitive units is a pixel value, and each pixel is a distance image. A monitor device having a function of generating a gray image corresponding to a pixel on a one-to-one basis and displaying a gray image generated together with a distance image in the image generation unit before the monitoring of the monitoring target space is started. And a specific area setting means for setting the specific area in the grayscale image displayed on the screen.

  According to the present invention, since the specific area can be set in the grayscale image, the setting operation of the specific area is facilitated as compared with the case where the specific area is set in the distance image.

According to the first aspect of the invention, there is an effect that it is possible to confirm whether or not the monitoring target space is in a safe state without being affected by the illumination or background of the monitoring target space . In addition, there is an effect that it can be determined that an unsafe state exists only when an object that did not exist before the start of monitoring exists in the monitoring specific area. Further, when it is determined that the monitoring target space is in an unsafe state, an alarm output is generated. Therefore, when the monitoring target space is in an unsafe state, another object (for example, a human body, Robots, automatic guided vehicles, etc.) can be prevented from entering, and an accident can be prevented from occurring in the monitored space. Furthermore, since the alarm level of the alarm output changes based on the combination of the shape and number of objects existing in the monitoring target space after the start of monitoring, the alarm level is changed according to the safety level of the monitoring target area. There is an effect that can be made.

  Hereinafter, although the safety confirmation apparatus of this embodiment is demonstrated with reference to FIG. 1, first, the basic composition of the distance image sensor 10 used with the safety confirmation apparatus of this embodiment is demonstrated.

  The distance image sensor 10 includes a light emitting source 2 that irradiates light to a monitoring target space, and a light detection element 1 that receives light from the monitoring target space and obtains an output that reflects the amount of received light. The distance to the object Ob existing in the monitoring target space is the time from when the light is emitted from the light source 2 to the monitoring target space until the reflected light from the object Ob enters (arrives) the light detection element 1 (" Called "time of flight"). However, since the flight time is a very short time at the nanosecond level, intensity-modulated light that is modulated so that the intensity of the light irradiating the monitored space changes periodically at a fixed period is used to receive the intensity-modulated light. The time of flight is obtained using the phase when

That is, as shown in FIG. 2A, it is assumed that the intensity of light radiated from the light emitting source 2 to 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. For example, since the phase difference ψ corresponds to the flight time, 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 at the timings of curve 0 at a phase of 0 degree, 90 degrees, 180 degrees, and 270 degrees are A0, A1, A2, and A3 (received light quantities 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 (the average value of the external light component and the reflected light component), ω (= 2πf) 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 set to instantaneous values, not integrated values of the light receiving period Tw, and time t = n / f (n = 0, 1, 2, synchronized with the period of the modulation signal) ,..., Where f is the frequency of the modulation signal and the received light amount is A0 = A · sin (δ) + B, the received light amounts 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
Since the phase difference is ψ in FIG. 2, 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 the received light amounts A0, A1, A2, A3 and the phase difference ψ is expressed by the following equation.
ψ = tan ⁻¹ {(A2−A0) / (A1−A3)} (Formula 1)
Although the instantaneous values of the received light amounts A0, A1, A2, and A3 are used in Equation 1, the phase difference ψ can be obtained by using the integrated value in the light receiving period Tw as the received light amounts A0, A1, A2, and A3. Can do.

Further, when the intensity of light received by the light detection element 1 is A · cos (ωt + δ) + B, that is, time t = n / f (n = 0, 1, 2,...) Synchronized with the period of the modulation signal. If the received light quantity at 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 for synchronizing with the modulation signal 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.

  As described above, in order to modulate the intensity of the light irradiating the monitoring target space, the light source 2 includes, for example, a structure in which a large number of light emitting diodes are arranged on one plane, or a combination of a semiconductor laser and a diverging lens. Etc. are used. 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. 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. 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 is acceptable 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 monitoring 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 charge corresponding to the amount of received light. In addition, 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 (ie, the vertical direction) and the horizontal direction (ie, the horizontal direction). Is done.

  The light receiving optical system 19 associates the line-of-sight direction when viewing the monitoring 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 angle (so-called azimuth and elevation angle) when the position of the object Ob existing in the monitored space is expressed in spherical coordinates is set. It corresponds to each 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, and A2 are synchronized at four timings synchronized with the intensity change of the light emitted from the light source 2 to the monitoring target space. , 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 the intensity change of light irradiated from the light source 2 to the target space, it is desirable to accumulate the charges 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. As a technique for adjusting the ratio of charges given to the charge accumulating unit 13, a technique for adjusting a passing rate of charges from the photosensitive unit 11 to the charge accumulating unit 13 and a technique for adjusting a discard rate for discarding charges from the photosensitive unit 11. And a technique for adjusting both the passing rate and the discarding rate.

  In the technique of adjusting the passing rate and the discard rate in the sensitivity control unit 12, as shown in FIG. 3, a gate electrode 12a is provided between the photosensitive unit 11 and the charge accumulating unit 13, and the passing 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 may be possible to control only the charge passage rate from the photosensitive unit 11 to the charge accumulating unit 13 without discarding the charge from the photosensitive unit 11, but the charge must be discarded. For example, since charges remain in the photosensitive portion 11 for a while, unnecessary residual charges among the charges generated in the photosensitive portion 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 the modulation signal. Accumulate about the period.

  FIG. 4 shows a state where charges corresponding to the received light quantity A0 are accumulated, and the passing voltage applied to the gate electrode 12a is kept constant as shown in FIG. 4B. 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 in the photosensitive portion 11 is an unnecessary charge in a 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 quantity A0 in a desired section in the charge accumulation unit 13 as shown in FIG. The processing shown in FIG. 4 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 monitoring target space is expressed by the received light amount A 0, using Equation 1 described above. It is calculated from the received light output corresponding to 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 monitoring 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 in each direction of the monitoring 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. 5, the charge generated in the photosensitive portion 11 is used as a signal charge. However, as shown in FIG. 5, the period for applying the pass 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. 5 shows an operation when signal charges corresponding to the received light quantity A0 are integrated. FIG. 5A shows a modulation signal that modulates the intensity of light emitted to the space from the light source 2, and the gate electrode 12a has a timing corresponding to the received light amount A0 as shown in FIG. 5B. 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. 5C, a waste 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 take out signal charges corresponding to the received light amount A0 as shown in FIG.

  In the control shown in FIG. 5, the period during which the pass voltage is applied to the gate electrode 12a is different from the period during which the waste voltage is applied to the discard electrode 12b. Therefore, as shown in the control example 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. 5, the period in which the signal charge is 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.

  If the control shown in FIG. 5 is performed, the charge generated in the photosensitive portion 11 is discarded as an unnecessary charge during the period when the charge generated in the photosensitive portion 11 is not accumulated in the charge accumulating portion 13 as a signal charge. Mixing of noise components into is greatly suppressed.

  As an example of control of the pass voltage and the discard voltage, as shown in FIG. 6, the discard voltage applied to the discard 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. 6, a period in which the passing voltage is applied to the gate electrode 12 a and a period in which the passing voltage is not applied are provided, and a period in which the passing voltage is applied is a period in which signal charges are accumulated in the charge accumulation unit 13.

  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 irradiated 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. 6C, 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 by the photosensitive portion 11 is always used as an unnecessary charge. Discard to 12c. In the control described above, the passing voltage is applied to the gate electrode 12a only during the period in which the signal charge is accumulated in the charge accumulating unit 13, so that the signal charge corresponding to the received light quantity A0 is taken out as shown in FIG. Is possible.

  In the control shown in FIG. 6, 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. 3 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. 7 shows a 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 column of the 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. 8) except for the portion corresponding to the photodiode 41.

For the CCD image sensor shown in FIG. 7, a portion related to one photodiode 41 is cut out and shown in FIG. 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 layer is laminated 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 charge passage path 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 layer having an impurity concentration equal to 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. 9, 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. Is a flat plate portion arranged on the same plane as the narrow transfer electrode 42b and disposed between the pair of transfer electrodes 42b, and from both ends of the flat plate portion in the vertical direction (left-right direction in FIG. 9). 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 photodetector 1 described above, the photodiode 41 corresponds to the photosensitive portion 11, the transfer electrode 42 a corresponds to the gate 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 passing 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 amount 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 amount 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.

  By the way, in the control example shown in FIG. 4 among the control examples described above, 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 the 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 of configuring the unit 12 has been shown, the sensitivity control unit 12 of the light detection element 1 shown below changes the area (substantial light receiving area) of a region that generates a charge that can be used in the photosensitive unit 11. is there.

  Hereinafter, a specific structural example of the light detection element 1 will be described. The light detection element 1 shown in FIG. 10 has a plurality of (for example, 100 × 100) photosensitive portions 11 arranged in a matrix, and is formed on a single semiconductor substrate, for example. 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 control electrodes 23 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. 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 irradiated to the monitoring target space from the light emitting source 2 is transmitted, and when the light enters the semiconductor layer 21 through the insulating film 22, the semiconductor layer Electric charges are generated inside 21. 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. 10 shows only a region corresponding to one photosensitive portion 11, and a plurality of regions having the structure shown in FIG. 10 are arranged on the semiconductor substrate (not shown) and the 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. 10, but it is also possible to adopt a configuration in which charges are transferred in a direction orthogonal to the plane in FIG. 10. 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 a control voltage + V is applied to three control electrodes 23 as shown in FIG. 10A, and when a control voltage + V is applied to one control electrode 23 as shown in FIG. 10B. Since the area occupied by the potential well 24 on the light receiving surface changes and the area of the potential well 24 is larger in the state of FIG. 10A, the area of the potential well 24 is larger than that of 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. 10 switches the sensitivity of the photosensitive unit 11 to two levels, high and low, by switching the area for generating available charges to 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. 10, by changing the size (area) of the charge accumulating unit 13 provided in the photosensitive unit 11, the integration rate of the charges generated by the photosensitive unit 11 during the charge accumulation period. 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 for which the photosensitive unit 11 can generate 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. In other words, by reducing the time difference for generating the charges corresponding to the received light amounts A0, A1, A2, and A3, the distance detection accuracy is kept relatively high even for the object Ob moving in the monitoring target space. be able to. 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. 10, an example in which five control electrodes 23 are provided for one photosensitive portion 11 is shown. However, the two control electrodes 23 on both sides are charged by the photosensitive portion 11 (electrons e). In this case, a potential barrier is formed to prevent the charge from flowing out to the adjacent photosensitive portion 11 while the two photosensitive portions 11 are used as pixels. Between the potential wells 24 of the portions 11, potential barriers are formed in any one of the photosensitive portions 11, so it is sufficient to provide three control electrodes 23 for each photosensitive portion 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 pixels.

  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 monitoring 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. However, in order to reduce the incidence of external light components on the light detection element 1 when generating a distance image, the target space is irradiated with infrared light from the light source 2 and an infrared transmission filter is disposed in front of the light detection element 1. Therefore, the grayscale image becomes a grayscale image with respect to infrared rays.

  Next, the overall configuration of a safety confirmation device using the above-described distance image sensor 10 will be described.

  As shown in FIG. 1, the safety confirmation device according to the present embodiment includes a distance between the above-described distance image sensor 10 and the monitoring target space generated by the image generation unit 4 of the distance image sensor 10 before starting monitoring of the monitoring target space. A background distance image storage unit 5 including a memory for storing an image as a background distance image, and a monitoring distance image including a distance image of a monitoring target space generated by the image generation unit 4 after the start of monitoring and a background distance image storage unit 5 are stored. A state determination unit 6 that determines whether or not a safe state is based on whether or not there is an object that did not exist before the start of monitoring in the monitoring target space by comparing the background distance image that has been set; An alarm output unit 7 that generates an alarm output when the state determination unit 6 determines that the monitored space is in an unsafe state. Note that the functions of the image generation unit 4, the state determination unit 6, the alarm output unit 7, the shape estimation unit 8, which will be described later, and the like are realized by executing appropriate programs on the microcomputer.

  The state determination unit 6 generates a difference image (an image having a difference for each corresponding pixel as a pixel value) between the monitoring distance image and the background distance image (that is, generates a difference image from distance images at different times). When the number of pixels whose distance value exceeds the predetermined value in the monitoring specific area of the difference image is equal to or less than the threshold value, it is determined that the monitor is in a safe state (the monitoring target space is in the same state as before the monitoring start), and the threshold value is exceeded. If it is, it is determined that the state is unsafe (the object Ob that does not exist before the start of monitoring exists in the monitoring target space).

  On the other hand, the alarm output generated in the alarm output unit 7 to which the determination result in the state determination unit 6 is given is given to controlled devices such as a robot, an automatic guided vehicle, and an alarm device, for example. In the case of a robot or automatic guided vehicle that the control target device moves from outside the monitoring target space into the monitoring target space and returns to or crosses the monitoring target space, an alarm output is received. What is necessary is just to comprise so that a control object apparatus may temporarily stop a movement out of the monitoring object space. Note that the timing at which the control target device such as the robot or the automatic guided vehicle resumes movement is canceled by the alarm output unit 7 when the state determination unit 6 determines that the movement is safe, for example. Thus, the movement may be resumed when the alarm output from the alarm output unit 7 is lost. When the device to be controlled is an alarm device (for example, a buzzer, a lamp, an audio output device, etc.), the alarm device may be provided in the safety confirmation device. It may be installed in a disaster prevention center that manages safety in the factory. Here, if an alarm device is installed in the vicinity of the safety confirmation device or the safety confirmation device, for example, a person who did not exist in the monitoring target space before the start of monitoring is regarded as an object Ob, resulting in an alarm. When a device issues a report, it is possible to take immediate action by a person who has entered the monitored space, and robots or unmanned carriers that did not exist in the monitored space before the start of monitoring When it is regarded as Ob and the alarm device issues a warning, it is possible to quickly deal with a person outside the monitoring target space.

  Therefore, in the safety confirmation device according to the present embodiment, whether there is an object that did not exist before the start of monitoring based on a distance image having a pixel value as a distance value to the object Ob existing in the monitoring target space. Therefore, it is possible to check whether the monitoring target space is in a safe state without being affected by sunlight, lighting, background, or the like. Further, for example, the state determination unit 6 may determine that the monitoring target space is in an unsafe state when an object that did not exist before the start of monitoring exists in the monitoring specific area of the monitoring target space. Only when an object that did not exist before the start of monitoring exists in the monitoring specific area, it can be determined that the unsafe state exists. In other words, when a difference image appears only in an area outside the monitoring specific area, it is determined that the state is safe. Therefore, for example, when an automated guided vehicle travels in a factory, setting the traveling area of the automated guided vehicle as a monitoring specific area makes it unstable only when a difference image changes in that area. It can be judged that it is a bad state. Further, when the state determination unit 6 determines that the monitoring target space is in an unsafe state, an alarm output is generated from the alarm output unit 7, so that the monitoring target space is moved to the monitoring target space when the monitoring target space is in an unsafe state. It is possible to prevent other objects (for example, human bodies, robots, automatic guided vehicles, etc.) from entering, and it is possible to prevent an accident from occurring in the monitoring target space.

  By the way, the safety confirmation device of the present embodiment estimates the shape of the object Ob that did not exist in the monitoring target space before the start of monitoring based on the distance image generated by the image generation unit 4. And an unsafe level of an unsafe state based on the shape of the object Ob estimated by the shape estimation unit 8 by the state determination unit 6 (the unsafe level becomes a higher value as the safety is lower). Judgment is possible. Accordingly, when the state determination unit 6 determines that the state is unsafe, information on the unsafe level is given to the alarm output unit 7, and the alarm output unit 7 is based on the information on the unsafe level received from the state determination unit 6. If the alarm level of the alarm output is changed, the alarm level of the alarm output changes based on the combination of the shape and number of the objects Ob existing in the monitoring target space after the start of monitoring. The alarm level can be changed according to the level of the characteristics. Note that, for example, the above-described control target device includes an alarm device including a plurality of lamps having different output lights (for example, a lamp having a red output light, an orange lamp having an output light, and a lamp having a blue output light). In the case of an alarm device), an output light lamp associated in advance according to the alarm level may be turned on. Further, if the control target device is an automatic guided vehicle or a movable robot, for example, the movement speed may be reduced or the movement may be stopped according to the alarm level.

  When the shape estimation unit 8 estimates the shape of the object Ob using the distance image, the object Ob is first extracted using the distance image. In order to automatically extract the object Ob, for example, after differential processing is performed on the distance image, binarization is performed to extract a region corresponding to the edge of the object Ob, and the object Ob is extracted from the extracted regions. And a candidate area of the object Ob, and further evaluate whether the candidate area is a group (for example, the distance difference in the three-dimensional space between two adjacent candidate areas is If it is equal to or less than the prescribed value, both candidate areas are regarded as areas included in one continuous object Ob), and further, using the number of pixels surrounded by a group of areas (that is, a connected area) and a distance value What is necessary is just to evaluate the magnitude | size of the object Ob (if it is the same object Ob, the number of pixels is in inverse proportion to the square of distance). Alternatively, when the object Ob moves, the distance value of the distance image is differentiated and binarized, and if the difference between the binarized images obtained from the distance images at different times is taken, the moved object Ob is extracted. can do. Furthermore, if the above-mentioned difference image is differentiated and binarized in order to separate the object Ob of interest from the background, it becomes easy to extract a region where the object Ob exists.

  The shape estimation unit 8 extracts a region where the object Ob exists by the method described above, then estimates the shape and number of the object Ob using a known template matching technique, and sends the estimation result to the state determination unit 6. give. On the other hand, based on the estimation result given from the shape estimation unit 8, the state determination unit 6, for example, detects that the object Ob that exists in the monitoring target space after the start of monitoring and does not exist before the start of monitoring is a person or an automated guided vehicle. If it is either one, it is determined that the greater the number is, the higher the unsafe level is, and the object Ob that is not present before the start of monitoring and is present in the monitoring target space after the start of monitoring is between the automatic guided vehicle and the person. In some cases, it is determined that the unsafe level is higher than when either one is present. In short, the state determination unit 6 determines the unsafe level based on the combination of the shape and number of objects estimated by the shape estimation unit 8.

  By the way, the state determination unit 6 divides the monitoring target space into a plurality of monitoring areas in the distance image in advance, and assigns a warning level to each monitoring area. The warning level information weighted to the monitoring area where the object Ob that does not exist is output to the warning output unit 7, and the warning output unit 7 outputs the warning level of the warning output based on the warning level information. If, for example, the alarm output unit 7 decreases the alarm level as the alarm level of the monitoring area where the object Ob that did not exist before the start of monitoring is lower, the alarm output unit 7 increases the alarm. By raising the level, a more appropriate warning output is generated from the warning output unit 7 compared to the case where the warning level is the same throughout the range image. Theft is possible.

  Further, as is clear from the above description, the image generation unit 4 of the distance image sensor 10 has a function of generating a distance image, and a gray value that is a received light amount of each photosensitive unit 11 as a pixel value, and each pixel is a distance image. However, in the safety confirmation apparatus according to the present embodiment, the user can check the space to be monitored in the grayscale image (on the grayscale image screen). The user can set in advance a specific area that is a target for determining whether the state is safe or unsafe. That is, in the configuration shown in FIG. 1, in order for the user to set the specific area from the grayscale image, the grayscale image generated by the image generation unit 4 is displayed, and the monitor device 9a displays the grayscale image. And a position specifying device 9b including a pointing device such as a mouse for setting the specific area in the grayscale image. In the present embodiment, the monitor device 9a and the position specifying device 9b constitute specific area setting means for setting a specific area in a grayscale image.

  Here, in the state determination unit 6, when a specific area is set in advance for the monitoring target space, the monitoring distance image and the background distance image are compared only for the specific area. Compared with the case where the monitoring distance image and the background distance image are compared for all areas of the distance image related to space, the processing speed of the state determination unit 6 can be increased.

  In addition, since the specific area can be set in the grayscale image, for users who are not familiar with the distance image, the specific area is set as compared with the case where the specific area is set in the distance image before the start of monitoring. In particular, when a state where the object Ob does not exist in the monitoring target space is defined as a safe state, the setting of the specific area becomes easier than when the specific area is specified in the distance image.

  Specifically, the setting of the specific area is performed by the following procedure, for example. When the specific area is set, a rectangular area of a prescribed size is automatically displayed on the screen of the monitor device 9a, and the user uses the position specifying device 9b to locate the rectangular area near the desired position. Move to (drag with mouse). Next, the upper left corner of the rectangular area is adjusted (dragged) to a desired position, and the upper left position of the rectangular area is determined (click button is pressed). Thereafter, the lower right corner of the rectangular area is adjusted to a desired position (dragging to enlarge or reduce the rectangular area), and the lower right position of the rectangular area is determined (pressing the click button). By such an operation, that is, by specifying two points of the specific area on the gray image on the monitor screen 9a, the rectangular specific area can be set on the screen of the monitor device 9a. Note that the shape of the specific area set on the grayscale image on the grayscale image is not limited to a rectangle based on the two-point instruction, but may be an arbitrary shape based on the multipoint instruction.

It is a block diagram which shows embodiment of this invention. It 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. It is explanatory drawing which shows the operation example same as the above. It is explanatory drawing which shows the other operation example same as the above. It is explanatory drawing which shows the other example of an operation 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. It is the sectional view on the AA line of FIG. It is operation | movement explanatory drawing of the principal part of the photon detection element used for the same as the above.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photodetector 2 Light emission source 3 Control circuit part 4 Image generation part 5 Background distance image memory | storage part 6 State judgment part 7 Alarm output part 8 Shape estimation part 9a Monitor apparatus 9b Position designation apparatus 10 Distance image sensor 11 Photosensitive part 19 Light reception optical System Ob Object

Claims (3)

A light source that irradiates the target space with intensity-modulated light whose intensity changes periodically, a light detection element that images a monitoring target space by arranging a plurality of photosensitive units that generate electrical output according to the amount of received light, and light emission The pixel value is a distance value obtained by converting the phase difference of the intensity-modulated light until the light irradiated from the source to the monitoring target space is reflected by the object in the monitoring target space and received by each photosensitive unit into the distance to the object. An image generation unit that generates a distance image, a background distance image storage unit that stores a distance image generated by the image generation unit before starting monitoring of the monitoring target space as a background distance image, and an image generation unit that starts after monitoring starts A safe state based on whether or not there is an object that did not exist before the start of monitoring by comparing the monitoring distance image consisting of the distance image and the background distance image stored in the background distance image storage unit Status judgment to judge whether or not It has a section, a determining that the state determination section, the monitored space when the object that did not exist prior to the start monitoring the monitoring specific area of the monitored space is present is in an unsafe condition A safety confirmation device,
An alarm output unit that generates an alarm output when the state determination unit determines that the monitoring target space is in an unsafe state, and exists in the monitoring target space after starting monitoring based on the output of the image generation unit A shape estimation unit that estimates the shape and number of objects to be performed, and the state determination unit combines the shape and number of objects estimated by the shape estimation unit when it is determined to be an unsafe state. A safety confirmation is characterized in that an unsafe level of an unsafe state is determined based on the alarm output unit, and the alarm output unit changes the alarm level of the alarm output based on the unsafe level information given from the state determination unit. apparatus. Wherein the state determination section, the safety confirmation device according to claim 1, wherein that you make a comparison of the monitoring distance image and the background range image only predetermined specific area with regard between the monitored air. In addition to the function of generating the distance image by the image generating unit, the function of generating a gray image corresponding to each pixel of the distance image on a one-to-one basis using the gray value that is the amount of light received by each photosensitive unit as a pixel value. And a monitor device that displays a grayscale image generated together with the distance image in the image generation unit before the monitoring of the monitoring target space is started, and the specific area is set in the grayscale image displayed on the monitor device. The safety confirmation device according to claim 2, further comprising a specific area setting unit .

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