JP5161938B2 - Spatial information detector - Google Patents

Description

  The present invention relates to a spatial information detection device that projects light into a target space, receives light from the target space, and detects spatial information about the target space from a change in the received light with respect to the projected light.

  Conventionally, light that has been modulated in intensity is projected into the target space, received from the target space, and present in the target space by determining the phase difference of the modulated component between the projected light and the received light. A technique for obtaining a distance to an object as spatial information is known (see, for example, Patent Document 1), and a reflected light component obtained by removing an ambient light component by a difference in received light amounts obtained at different phases of a modulation component is obtained. The technology required as spatial information is known. Here, since the reflected light component represents a change in light projection and reception, it corresponds to the presence or absence of an object in the target space, the reflectance of an object existing at a known distance, and the like.

Japanese National Patent Publication No. 10-508736

  By the way, this kind of spatial information detection device (hereinafter abbreviated as “detection device”) used for detecting spatial information projects a light whose intensity is modulated from a light source to a target space. When the detection devices of the bases try to detect spatial information about the common target space and the light projected from each detection device to the target space is mixed, it is distinguished from which detection device the light projected into the target space Can not be. In other words, each detection device cannot separate and detect the light projected by itself, which causes a problem that spatial information cannot be detected by each detection device.

  The present invention has been made in view of the above reasons, and its purpose is to independently detect the spatial information of each target space even when a plurality of vehicles share at least a part of the target space. It is an object of the present invention to provide a spatial information detection device that can be used.

  According to a first aspect of the present invention, there is provided a light emission source that projects light into a target space, and a light emission control unit that applies a modulation signal having a predetermined modulation frequency to the light emission source so as to modulate the intensity of light projected from the light emission source to the target space. , A light detection element having a photosensitive part that receives light from the target space and generates a charge according to the amount of light received, and a period that is synchronized with the phase interval defined in the modulation signal among the charges generated by the photosensitive part And an evaluation unit that detects spatial information of the target space from a change between the light projected from the light source using the generated charge and the light received by the light detection element, and the light emission control unit projects the light from the light source to the target space. The light emitting source is controlled to provide a light projecting period during which light is emitted and a rest period during which light is not projected, and the evaluation unit determines two types of charges generated by the light received by the light detection element during the rest period in the modulation signal. To compare the amount of charge in the phase interval of An interference determination unit for determining the presence or absence of a fluctuation component in the ambient light component, and the two types of modulation signals defined in the modulation signal so as to cancel out the fluctuation component in the phase interval among the ambient light components received by the light detection element When the difference in the charge amount in the phase interval is obtained and the interference determination unit determines that the difference between the integrated values is affected by the ambient light component, the difference is not adopted, and the difference is determined when the difference is equal to or less than the threshold value. It is characterized in that spatial information is detected using.

  According to this configuration, the difference between the charge amounts of two specific phase sections defined in the modulation signal among the charges generated by the light detection element is extracted so that the fluctuation component of the ambient light component is canceled out. Therefore, even if the light projected from another spatial information detection device is included in the ambient light component, it is possible to remove the influence of this light and detect the spatial information. In other words, even when a plurality of spatial information detection devices share at least part of the target space, the spatial information of the target space can be detected without being affected by other spatial information detection devices. it can.

  Furthermore, an ambient light component that receives light during a pause period in which light is projected intermittently by providing a light projection period during which light is projected from the light source to the target space and a pause period during which light is not projected is provided. Therefore, it is possible to determine the presence or absence of the fluctuation component in the environmental light component by removing the influence of the fluctuation component of the light projected from the light source to the target space. In other words, it is possible to easily determine whether other spatial information detection devices share the target space.

  According to a second aspect of the present invention, in the first aspect of the present invention, the modulation frequency of the modulation signal output from the light emission control unit can be selected from a plurality of types, and the interference determination unit detects the presence of a fluctuation component in the ambient light component. A frequency switching unit that changes the modulation frequency until it is not detected is provided.

  According to this configuration, it is not necessary to individually set the modulation frequency when using a plurality of spatial information detection devices, and the modulation frequency can be used easily and avoid interference with each other. Since it is automatically set, it becomes possible to detect spatial information without being affected by the ambient light component.

  According to a third aspect of the present invention, in the first or second aspect of the invention, the evaluation unit is an intermediate value corresponding to a phase difference between the light projected from the light emitting source into the target space and the light received by the light detection element. The target space is obtained by correcting the intermediate value obtained from the conversion table with a correction value determined according to the modulation frequency of the light projected from the light source to the target space. It is characterized in that a distance to an object existing in is obtained.

  According to this configuration, the conversion table in which the difference in the amount of charge output from the light detection element and the intermediate value corresponding to the phase difference between light transmission and reception are associated is used, and the intermediate value obtained from the conversion table is used as the modulation frequency. Since the correction is performed with the corresponding correction value, the same conversion table can be used even if the modulation frequency is different, and the product can be easily manufactured by sharing the data. Although it is possible to obtain the distance by calculation from the difference in the amount of charge output from the light detection element, an error due to device characteristics occurs when calculated using a theoretical formula, but a conversion table should be used. Thus, it is possible to set data in which an error due to the apparatus characteristic is folded, and as a result, it is possible to accurately obtain the distance to the object.

  According to the configuration of the present invention, the fluctuation component of the ambient light component is canceled out with respect to the difference between the charge amounts of the two specific types of phase sections defined in the modulation signal among the charges generated by the light detection element. Therefore, even if the light projected from another spatial information detection device is included in the ambient light component, it is possible to remove the influence of this light and detect the spatial information. In other words, even when a plurality of spatial information detection devices share at least part of the target space, the spatial information of the target space can be detected without being affected by other spatial information detection devices. It has the advantage of being able to.

  Furthermore, an ambient light component that receives light during a pause period in which light is projected intermittently by providing a light projection period during which light is projected from the light source to the target space and a pause period during which light is not projected is provided. Therefore, it is possible to determine the presence or absence of the fluctuation component in the environmental light component by removing the influence of the fluctuation component of the light projected from the light source to the target space. In other words, it is possible to easily determine whether other spatial information detection devices share the target space.

It is a block diagram which shows embodiment of this invention. It is operation | movement explanatory drawing same as the above. It is operation | movement explanatory drawing same as the above. It is operation | movement explanatory drawing same as the above.

  In the embodiment described below, a distance measuring device that measures the distance to an object existing in the target space is exemplified as a spatial information detection device (hereinafter, abbreviated as “detection device”). A distance measuring device described below generates a distance image in which a distance for each location in the target space is associated with each pixel by capturing an image of the target space. Note that the spatial information includes information obtained by removing environmental light components such as the reflectance of an object existing in the target space.

(Basic configuration of rangefinder)
A basic configuration of a distance measuring device as a detection device will be described. As shown in FIG. 1, the distance measuring device includes a light emitting source 2 that projects light into a target space, and a light detection element 1 that receives light from the target space and obtains an output that reflects the amount of received light. . The distance to the object Ob existing in the target space is the time from when light is projected from the light emission 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”). ) However, since the flight time is very short, the intensity of light projected from the light source 2 to the target space is modulated by giving the light source 2 a modulation signal having a predetermined modulation frequency from the light emission control unit 3. A technique is used in which a phase difference between light transmission and reception is obtained with respect to the modulation component, and this phase difference is converted into time of flight. That is, the light emission control unit 3 controls the light emission source 2 so that the intensity of light projected to the target space periodically changes at a constant period.

  Now, as shown in FIG. 2, the intensity of light radiated from the light source 2 to the space is modulated so as to have a sine waveform as shown in curve A, and the amount of light received by the light detecting element 1 is 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. That is, if the unit of the phase difference ψ is [rad], the distance to the object Ob is L [m], the speed of light is c [m / s], and the angular frequency of the intensity-modulated light is ω [rad / s], L = Ψ · c / 2ω.

The phase difference ψ can be calculated using the received light amount of the curve B obtained at a plurality of timings of the curve A. For example, the received light amounts of curve B obtained at the timings when the phase interval in curve A is 0 to 90 degrees, 90 to 180 degrees, 180 to 270 degrees, and 270 to 360 degrees are respectively A0, A1, A2, and A3 (light reception). The light amounts A0, A1, A2, and A3 are indicated by hatching). That is, the received light amounts A0, A1, A2, and A3 in each phase section are integrated values of the phase width Tw of 90 degrees. Here, 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 while the received light amounts A0, A1, A2, A3 are obtained. And 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. Where A is the amplitude, B is the average value of the ambient light component and the reflected light component, ω is the angular frequency of the intensity modulated light (ω = 2πf; f is the modulation frequency), and δ is the initial phase. Here, it is assumed that the average value B can be regarded as constant during the period in which the received light amounts A0, A1, A2, and A3 of the four phase sections are obtained. From these conditions, the phase difference ψ can be expressed by the following equation, for example.
ψ = tan ⁻¹ (A2−A0) / (A1−A3)
The above equation changes the sign or the phase differs by 90 degrees depending on how the phase section to be integrated is taken (for example, in the above example, the phase width of one phase section is 90 degrees, but it may be 180 degrees). In any case, the phase difference ψ can be obtained by using the received light amounts A0, A1, A2, and A3 in the four phase sections.

  Since it is necessary to modulate the intensity of light projected into the target space with a modulation signal having a relatively high modulation frequency, a light source with a fast response speed is used as the light emission source 2. For example, a light emitting source 2 that uses a plurality of light emitting diodes arranged on one plane or a combination of a semiconductor laser and a diverging lens is used. A modulation signal for driving the light emission source 2 is output from the light emission control unit 3, and the intensity of light emitted from the light emission source 2 is modulated by the modulation signal. The light emission control unit 3 outputs, for example, a 10 MHz sine wave as a modulation signal. The waveform of the modulation signal may be a triangular wave, a sawtooth wave, or the like in addition to the sine wave.

  The light detection element 1 includes a plurality of photosensitive portions 11 regularly arranged. A light receiving optical system 5 is disposed in the light incident path to the photosensitive portion 11. The photosensitive unit 11 is a part where light from the target space is incident through the light receiving optical system 5 in the light detection element 1, and the photosensitive unit 11 generates an amount of 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 5 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 5 can be regarded as a conical field of view with a small apex angle set for each photosensitive portion 11 with the center of the light receiving optical system 5 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 5 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 5 is generally arranged so that the optical axis is orthogonal to the plane on which the photosensitive portions 11 are arranged, the center of the light receiving optical system 5 is the origin, and the vertical and horizontal directions of the plane on which the photosensitive portions 11 are arranged If an orthogonal coordinate system is set in which the optical axis of the light receiving optical system 5 is in the direction of three axes, the angles (so-called azimuth and elevation angles) 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 5 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 this configuration, as described above, in order to obtain the distance to the object Ob, the received light amounts A0, A1, A2 of the four phase sections synchronized with the intensity change of the light projected 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. Further, since the amount of charge generated in the photosensitive portion 11 is small in one cycle of the intensity change of light projected 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 accumulation units 13 for accumulating the charges generated in the respective photosensitive units 11 are provided, and the sensitivity for controlling the timing at which the charges generated by the photosensitive units 11 are accumulated in the charge accumulation unit 13 is provided. A control unit 12 is provided. The light emission control unit 3 controls this timing.

  The light detection element 1 used in this configuration is formed by arranging a plurality of (for example, 100 × 100) photosensitive portions 11 in a matrix and formed on a single semiconductor substrate. A vertical transfer unit, which is a CCD that transfers charges in the vertical direction along each column in the vertical direction of the photosensitive unit 11, is formed, and further, a CCD that receives charges from one end of the vertical transfer unit and transfers charges in the horizontal direction. The horizontal transfer part is formed. A transfer gate is provided between the photosensitive unit 11 and the vertical transfer unit.

  The photodetector 1 has the same configuration as an interline transfer (IT) type CCD image sensor, and the charge extraction unit 14 shown in FIG. 1 represents a function including a vertical transfer unit and a horizontal transfer unit. ing. The charge accumulating unit 13 represents a function of accumulating charges in a period until transfer is started in the vertical transfer unit.

  Meanwhile, the sensitivity control unit 12 is controlled by the light emission control unit 3 so as to increase the sensitivity in the four phase sections respectively corresponding to the above-described received light amounts A0, A1, A2, A3, and the received light amounts A0, A1, A2, A3. Is accumulated in the charge accumulating unit 13. Here, since a configuration similar to that of an IT type CCD image sensor is adopted, a configuration for adjusting the amount of charge accumulated from the photosensitive portion 11 to the vertical transfer portion by controlling the transfer gate, and for each photosensitive portion 11 The function of the sensitivity control unit 12 is provided by using at least one of a configuration in which a waste electrode capable of discarding charges is provided to adjust the amount of charge discarded. That is, the transfer gate is controlled so that the charge passes from the photosensitive portion 11 to the vertical transfer portion in the phase interval corresponding to the desired received light quantity A0, A1, A2, A3, or the charges other than the desired phase interval are discarded. In this way, by controlling the voltage applied to the waste electrode, charges in only a desired phase interval are accumulated in the vertical transfer unit, and the accumulated charges are transferred.

  However, since the intensity of light incident on the photosensitive portion 11 of the light detection element 1 after being projected from the light source 2 into the target space and reflected by the object Ob is small, the received light amount A0, A1, A2, Even if the charge corresponding to A3 is accumulated in the charge accumulation unit 13 within one modulation period of the intensity-modulated light, a sufficient difference in the received light amounts A0, A1, A2, A3 cannot be obtained, and the distance Measurement accuracy is lowered. Therefore, in practice, charges generated corresponding to each section are accumulated in the charge accumulation unit 13 over a plurality of periods (for example, 30,000 periods) of intensity-modulated light, and then taken out from the light detection element 1 through the charge extraction unit 14. ing. The light emission control unit 3 controls the timing of extracting the charge through the charge extraction unit 14.

  Hereinafter, a period in which charges are accumulated in the charge accumulating unit 13 (that is, a period in which charges in the target section are generated in the photosensitive unit 11) is referred to as a light receiving period, and the charges accumulated in the charge accumulating unit 13 are A period of time taken out by the charge extraction unit 14 is referred to as a reading period.

  By the way, in the configuration example described above, when four adjacent photosensitive portions 11 are used as a set, the charge for each of the four phase intervals described above is accumulated in the four photosensitive portions 11 included in the set. It is possible to accumulate in the part 13. That is, if the sensitivity control units 12 corresponding to the four photosensitive units 11 in a set are controlled in association with the phase intervals corresponding to the received light amounts A0, A1, A2, and A3, four charge accumulations are performed. Charges corresponding to the received light amounts A0, A1, A2, and A3 are accumulated in the unit 13, respectively. With such an operation, it is possible to extract the received light amounts A0, A1, A2, and A3 of the four phase sections only by providing the light receiving period and the reading period once, and use information within a relatively short time. Thus, the distance of the object Ob can be obtained. However, since the four photosensitive portions 11 correspond to one direction of the target space, the resolution is reduced to a quarter compared to the case where one photosensitive portion 11 is associated with one direction of the target space. In addition, since the photosensitive portions 11 at different positions are associated with one direction of the target space, it is highly likely that each photosensitive portion 11 receives reflected light from different objects Ob, and erroneous measurement with respect to distance is likely to occur. .

  On the other hand, if one photosensitive unit 11 is associated with one direction of the target space, the resolution becomes high, so that the erroneous measurement of the distance to the stationary object Ob can be reduced, but the light receiving period and the reading period are four times. Since it is necessary one by one, erroneous measurement of the distance is likely to occur for the relatively moving object Ob. Therefore, in this configuration, there is a method of using two photosensitive portions 11 as a set and taking out the charges corresponding to the received light amounts A0, A1, A2, and A3 of the four sections by using the light receiving period and the reading period twice. Adopted. That is, the first time out of the two light receiving periods takes out the charge corresponding to the received light amounts A0 and A2, and the second time takes out the charge corresponding to the received light amounts A1 and A3.

  The light reception output output from the above-described light detection element 1 is given to the distance calculation unit 4 as an evaluation unit, and the distance calculation unit 4 charges corresponding to the received light amounts A0, A1, A2, and A3 in the above four phase sections. The light reception output corresponding to the quantity is received and applied to the above-described mathematical formula for obtaining the phase difference ψ, or by fitting to the conversion table corresponding to the mathematical formula, the phase difference ψ is obtained, and further from the phase difference ψ to the object Ob Find the distance. Since the distance calculation unit 4 obtains distances in a plurality of directions of the target space, it can obtain three-dimensional information about the target space, and can generate a distance image in which distance values are associated with pixel values. Of course, instead of the phase difference ψ, the distance may be obtained in the conversion table.

  By the way, in the above equation for obtaining the phase difference ψ from the received light amounts A0, A1, A2, A3 of the four phase sections, the average value B is constant during the period in which the received light quantities A0, A1, A2, A3 of the four phase sections are obtained. This is based on the assumption that the ambient light component does not change within the time for obtaining the received light amounts A0, A1, A2, and A3 in the four phase sections. Therefore, the phase difference ψ cannot be obtained under conditions where the ambient light component varies within each phase interval. In the embodiment described below, the phase difference ψ can be obtained even when the ambient light component includes a fluctuation component that fluctuates within each phase interval.

(Embodiment)
In the present embodiment, as shown in FIG. 1, a case is assumed in which a plurality of ranging devices having the above-described configuration are arranged with at least a part of the target space in common. Each distance measuring device includes a light emission source 2, a light emission control unit 3, a light detection element 1, and a distance calculation unit 4. Further, the light emission control unit 3 in the present embodiment is configured such that a modulation frequency can be selected from a plurality of types, and the light emission control unit 3 is provided with a frequency selection unit 6 for selecting the modulation frequency. The frequency selection unit 6 is configured using a DIP switch or a rotary switch. Alternatively, a configuration may be adopted in which the frequency of the frequency selection unit 6 can be selected by a memory switch, and the contents of the memory switch can be changed using a support device such as a computer.

  In the present embodiment, it is assumed that the modulation frequencies of the distance measuring devices are fixedly set and the modulation frequencies are different from each other. For example, it is assumed that there are three distance measuring devices, and the modulation frequencies are set to 10 MHz, 12 MHz, and 15 MHz, respectively. In each distance measuring device, the received light amount output corresponding to the received light amount A0, A1, A2, A3 in a specific phase interval synchronized with the modulation signal is taken out from the light detecting element 1 and given to the distance calculation unit 4. The light receiving output of the charge amount corresponding to the received light amount A0, A2 is taken out in one reading period in the light detecting element 1, and the received light output of the charge amount corresponding to the received light amount A1, A3 in the other reading period. Take out.

  Since each distance measuring device extracts charges accumulated over a large number of periods of the modulation signal in the light receiving period, the light receiving output of the light detecting element 1 includes fluctuation components due to light projected from other distance measuring devices to the target space. It may be considered that all components are contained equally.

  For the sake of simplicity, assuming that two distance measuring devices with modulation frequencies of 10 MHz and 12 MHz operate in common with each other, both distance measuring devices are as shown in FIG. In addition, 12 MHz light (c) and 10 MHz light (d) are received simultaneously. In FIG. 3, the intensity of received light is shown to be almost equal, but actually the intensity of light is different in most cases. If a distance measuring device having a modulation frequency of 10 MHz receives light of two types of modulation frequencies at the same time, the received light amounts A0, A1, A2, and A3 in the respective phase sections corresponding to the curve D are represented by the positions corresponding to the curve C. Since the components of the phase section are added, the received light amounts A0, A1, A2, and A3 of each phase section corresponding to the curve D are calculated from the received light quantities obtained in each phase section if they are about several times the period of the modulation signal. It cannot be extracted.

  The problem described above is caused by the addition of the components in a part of the phase section of the curve C to the received light amounts A0, A1, A2, and A3 in each phase section of the curve D. In other words, the amount of light received in each phase interval is integrated, and it is long enough to add the components of all phases of curve C to the components corresponding to the amounts of light received A0, A1, A2, A3 in each phase interval of the curve D. If the integrated value of the period is obtained, the component of the curve C becomes substantially constant for any phase section of the curve D with the integrated value, and as a result, the component of the curve D can be extracted from the integrated value.

  The distance calculation unit 4 obtains the distance after performing such integration. However, when the integrated value for each phase section is obtained, the ambient light component is also integrated in addition to the reflected light component, so that the integrated value becomes a large value. For example, if digital signal processing is performed, the number of bits corresponding to the integrated value increases, and a memory or the like for storing the integrated value requires a large capacity. On the other hand, as described above, the values of the received light quantity differences A0-A2 and A1-A3 are used for the distance calculation. With such a difference, components that do not vary among the ambient light components are removed. Therefore, if this difference is integrated, the integrated value can be significantly reduced.

  This embodiment utilizes such characteristics, and the distance calculation unit 4 uses the frequency difference of the modulation frequency of each detection device (that is, the period difference when the fluctuation period of the ambient light component is known). For the specified integration time, the integrated value of the difference (A0-A2) and (A1-A3) in the received light quantity is obtained, and the distance is obtained using this integrated value. The integration time is preferably set to one cycle (or an integer multiple cycle) of the beat component determined by the frequency difference between the modulation frequencies of the detection devices. That is, since the frequency difference between the curve C component and the curve D component is relatively small, a beat component corresponding to the frequency difference between the two components occurs. If the integrated value is obtained with the cycle of the beat component, the beat component is removed. If one cycle of the beat component determined by the frequency difference of the modulation frequency is set as the integration time, the influence of the mutual modulation frequency is canceled out. Thus, the ambient light component can be removed.

As described above, assuming that the modulation frequencies of the three detection devices are set to 10 MHz, 12 MHz, and 15 MHz, respectively, and the distance is obtained in the detection device of 10 MHz, the frequency difference is a beat of 2 MHz and 5 MHz, respectively. Ingredients will be produced. Therefore, the ambient light component can be removed by setting the integration time as the time at which the integer multiple cycles of the beat components coincide. At the frequency described above, one cycle of each beat component is 5 × 10 ⁻⁷ s and 2 × 10 ⁻⁷ s, respectively. Therefore, the minimum time in which the integer multiple cycles coincide is 1 μs. Therefore, if the integration time is set to 1 μs or an integral multiple thereof, the distance can be obtained by canceling the influence of light projected from other detection devices while using three detection devices.

  By the way, if the integration time is sufficiently long, the influence of the error represented by the vibration change in the beat component period on the integrated value is small. Therefore, the above condition (integration time is set to an integral multiple period of each beat component). If the integration time is sufficiently long, the occurrence of an error can be ignored even if the condition of matching is not completely satisfied. For example, it has been confirmed that if the integration time is 30,000 cycles of the modulation signal, it does not have to coincide with an integral multiple cycle of each beat component.

  In addition, since the modulation frequency of the detection device sharing the target space is known, a period for obtaining each received light amount A0, A1, A2, A3 is set at an appropriate time interval according to the modulation frequency of each detection device. By doing so, it is possible to cancel out the components that fluctuate within the phase interval among the ambient light components simply by obtaining the difference (A0-A2) and (A1-A3) in the received light amount.

  By using the integrated values of the differences (A0−A2) and (A1−A3) obtained as described above, the light projected from the light source 2 to the target space and the photosensitive portions 11 of the light detection element 1 are used. The phase difference ψ with the reflected light component of the received light can be obtained. If the unit of the phase difference ψ is radians, the distance L to the object Ob can be expressed as L = Lm · ψ / 2π. However, when the modulation frequency is f and the luminous flux is c [m / s], Lm = c / 2f. In short, according to the above-described principle, the distance that reciprocates in one cycle time of the modulation signal is the maximum measurable distance Lm, and when the phase difference ψ is 2π, it is considered to correspond to the maximum distance Lm. By obtaining the ratio of the phase difference ψ, the distance L to the object Ob that reflects the light can be obtained.

  Although it is possible to obtain the distance L by the theoretical formula as described above, in reality, an error occurs with respect to the value of the theoretical formula depending on the arrangement and characteristics of each member. In addition, the error generally varies with distance. Therefore, the distance obtained by the theoretical formula needs to be corrected. Although it is possible to provide a data table in which such correction values are associated with distances, if a data table is provided, it is more efficient to perform the operation itself with the data table. Therefore, in the present embodiment, a conversion table for obtaining a value corresponding to the distance from the set of differences (A0−A2) and (A1−A3) is used as the data table.

  Here, as described above, since the distance L changes depending on the maximum measurable distance Lm, when the modulation frequency is switched by the frequency selection unit 6, a different conversion table is required. Although it is possible to provide a plurality of conversion tables according to the modulation frequencies that can be selected in this way, it takes time to register the conversion table data, and the semiconductor memory that constitutes the conversion table is used. A large capacity is required.

  Therefore, in the present embodiment, one type of conversion table is provided regardless of the modulation frequency, an intermediate value corresponding to the phase difference is obtained from the set of differences (A0-A2) and (A1-A3), and this intermediate value is modulated. A technique for obtaining the distance by correcting with a correction value corresponding to the frequency is adopted. For example, if a value corresponding to (c · ψ / 4π) is obtained as an intermediate value and a coefficient corresponding to (1 / f) is used as a correction value, the distance L to the object Ob is calculated by multiplying the intermediate value by the coefficient. Can be sought. Here, errors due to the arrangement and characteristics of each member are folded into an intermediate value. Alternatively, a value corresponding to the phase difference ψ can be obtained as an intermediate value, and (c / 4π · f) can be used as a correction value. The intermediate value and the correction value can be selected as appropriate.

  As described above, if an intermediate value is obtained from a set of differences (A0−A2) and (A1−A3) and the intermediate value is corrected according to the modulation frequency, the conversion table depends on the modulation frequency. Thus, only one type need be prepared, and the labor of registering data is reduced, and the capacity of the semiconductor memory used for the conversion table is also reduced.

  By the way, in the above-described configuration, the modulation frequency of each detection device is fixedly set in the frequency selection unit 6, but a configuration is adopted in which the modulation frequency of each detection device is automatically changed over time. Also good. The basic configuration is the same as the configuration described above, except that a frequency switching unit (not shown) that automatically changes the modulation frequency with the passage of time is provided instead of the frequency selection unit 6.

  The frequency switching unit automates the selection of the modulation frequency in the frequency selection unit 6 and automatically selects the modulation frequency as time elapses. The only difference is that the selection operation is linked to the timer function. Other operations are the same as those described above. In addition, since the modulation frequency automatically changes with time, there is no need to set the modulation frequency. It is desirable that the time for changing the modulation frequency is longer than the integration time described in the above configuration. This is because if the modulation frequency changes in the middle of the integration time, it cannot be guaranteed that the influence of the light projected from other detection devices will be almost canceled. Further, it is desirable that the timing for changing the modulation frequency varies among the detection devices. Thus, if the timing which changes a modulation frequency differs, the probability that a modulation frequency becomes equal in the several detection apparatus which makes the object space common can be reduced.

  Further, if the modulation frequency is changed irregularly in the frequency switching section, the probability that the modulation frequencies are equal in a plurality of detection devices can be reduced even when the timing for changing the modulation frequency is not shifted.

  As described as the basic configuration, the light detection element 1 reads out charges corresponding to the received light amounts A0, A1, A2, and A3 in two phase sections in one reading period. Therefore, in order to read out charges in the four phase sections, two light receiving periods and two reading periods are required. In other words, the distance can be measured by alternately repeating the light receiving period and the reading period and providing the light receiving period and the reading period twice. In addition, since no light projection from the light source 2 is required during the readout period, the readout period is matched with a pause period during which no light is emitted from the light source 2 and the light reception period is projected from the light source 2 to the target space. It is desirable to match with the floodlighting period. In short, it is desirable that the light receiving period and the reading period defined for the operation of the light detection element 1 are made to coincide with the light projecting period and the rest period defined for the operation of the light emitting source 2, respectively.

  For example, as shown in FIG. 4, the light receiving period T02 for generating charges corresponding to the received light amounts A0 and A2 coincides with the light projecting period of the light source 2, and the light receiving period for generating charges corresponding to the received light amounts A1 and A3. T13 also coincides with the light projection period of the light source 2. Further, the readout period Td corresponding to each of the light receiving periods T02 and T13 coincides with the rest period of the light emitting source 2.

  As described above, the light receiving periods T02 and T13 and the reading period Td are normally repeated alternately. However, as shown in FIG. 4, in this embodiment, the light receiving period Te that does not coincide with the light projecting period is appropriately set. It is provided at the timing. In other words, the light detection element 1 is provided with a readout period Td for reading out the charges generated during the light receiving period Te as in the light receiving periods T02 and T13, but the light emitting source 2 does not project light from the light emitting source 2 during the light receiving period Te. The operation is different from the operation in the light receiving periods T02 and T13 in that the rest period is reached. Therefore, in the light emitting source 2, in addition to the period corresponding to the reading period Td, the period corresponding to the light receiving period Te is also a pause period. In the light receiving period Te, the light emitting source 2 of the detection device does not project light, so that the light detecting element 1 receives only the ambient light component in the light receiving period Te. As is apparent from the operation of the basic configuration, if the ambient light component does not substantially vary, the difference between the received light amounts of two different phase sections in the pause period is ideally zero. “Substantially not changing” includes the case where the ambient light component changes in a short period, but the amount of change is canceled out by the integrated value in the integrated time. Therefore, it is possible to determine whether or not the ambient light component affects the distance measurement result by comparing the amount of received light in the two phase sections.

  In the present embodiment, an interference determination unit (not shown) that performs the above-described determination is provided in the distance calculation unit 4, and the interference determination unit integrates two phase sections that differ by 180 degrees in the light receiving period Te. A difference (A0-A2) of (integrated value obtained by integration time) is obtained, and this difference is compared with a threshold value to determine whether or not the difference of the integrated value is affected by the ambient light component. When the interference determination unit determines that the difference between the integrated values is affected by the ambient light component, the distance calculation unit 4 uses the difference only when the difference is equal to or less than the threshold. Ask for. The accuracy of the distance obtained by such an operation is guaranteed.

  Further, when adopting a configuration in which the frequency switching unit is provided and the selection of the modulation frequency in the frequency selection unit 6 is automated as described above, the determination of the interference determination unit is performed instead of selecting the modulation frequency over time. It is desirable to select the modulation frequency according to the result. In this configuration, when the interference determination unit determines that it is affected by the ambient light component, the frequency selection unit 6 is instructed to change the modulation frequency, and the interference determination unit is not affected by the ambient light component. A search is automatically made for a modulation frequency that can be determined. Therefore, since the modulation frequency that is not affected by the ambient light component is automatically determined, it can be ensured that setting of the modulation frequency does not take time and is not affected by the ambient light component.

  In the above configuration, the same configuration as that of the IT type CCD image sensor is adopted, but the same configuration as the frame transfer (FT) method and the frame interline transfer (FIT) method is adopted. Is also possible. In addition, when an IT system configuration is adopted for the charge transfer, the sensitivity control unit 12 discards the charge and controls the gate unit that transfers the charge from the photosensitive unit 11 to the charge extraction unit (vertical transfer unit). It is also possible to adopt a configuration that does this.

DESCRIPTION OF SYMBOLS 1 Light detection element 2 Light emission source 3 Light emission control part 4 Distance calculating part (evaluation part)
6 Frequency selection part 11 Photosensitive part

Claims (3)

  A light source that projects light into the target space, a light emission control unit that gives a modulation signal of a predetermined modulation frequency to the light source so as to modulate the intensity of light projected from the light source into the target space, and light from the target space A light-emitting source using a light detection element having a photosensitive part that receives light and generates a charge corresponding to the amount of received light, and a charge generated in the period synchronized with the phase interval defined in the modulation signal among the charges generated in the photosensitive part And an evaluation unit that detects spatial information of the target space from a change between the light projected from the light and the light received by the light detection element, and the light emission control unit includes a light projection period and a light projection from the light source to the target space. The light emitting source is controlled to provide a non-lighting pause period, and the evaluation unit determines the charge amounts of the two types of phase sections defined in the modulation signal among the charges generated by the light received by the light detection element during the pause period. By comparing it to the ambient light component And an interference determination unit that determines whether or not there is a fluctuation component, and charges in two types of phase sections defined in the modulation signal so as to cancel out the fluctuation components in the phase section among the environmental light components received by the photodetector. When the difference of the amount is obtained, and the interference determination unit determines that the difference of the integrated value is affected by the ambient light component, the difference is not adopted, and when the difference is equal to or less than the threshold, the difference is used. A spatial information detection apparatus characterized by detecting information.   A frequency switching unit that can select a modulation frequency of the modulation signal output from the light emission control unit from a plurality of types and changes the modulation frequency until the interference determination unit does not detect the presence of a fluctuation component in the ambient light component; The spatial information detection device according to claim 1.   The evaluation unit has a conversion table in which an intermediate value corresponding to a phase difference between light projected from the light emission source to a target space and light received by the light detection element is associated with the difference, and from the conversion table The distance to an object existing in the target space is obtained by correcting the obtained intermediate value with a correction value determined according to a modulation frequency of light projected from the light source to the target space. The spatial information detection device according to 1 or 2.

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