JP2017173187A - Distance measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance measuring device whose ranging precision relative to a ranging object having low reflection rate is improved.SOLUTION: A distance measuring device 1 includes: a pixel arrangement section 401 having Fd for accumulating electrical charges related to intensity of each pixel G; a modulated light emission section 106 for emitting emission modulated light La toward an imaging range 6; a ranging section 102 for measuring a distance D to a ranging object 7 based on a phase difference φ between the emission modulated light La and reflection modulated light Lb reflected by the ranging object 7 to enter into the pixel G; and a modulated light control section 103 for controlling emission intensity of the emission modulated light La so that incident intensity of the reflection modulated light Lb to the pixel G becomes a reference value or more.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a distance measuring apparatus that performs distance measurement using a TOF (Time Of Flight) method.

  A distance measuring device that performs distance measurement using the TOF method is known (eg, Patent Document 1).

  Such a distance measuring device is, for example, an image sensor having a plurality of pixels distributed on a plane and a charge storage unit that stores charges with a charge amount related to the intensity of incident light on each pixel, and intensity-modulated. The modulated light emitting unit that emits the modulated light toward the imaging range of the imaging device, the emitted modulated light emitted by the modulated light emitting unit, and the emitted modulated light reflected by the distance measurement target in the imaging range to be reflected on the pixels of the imaging device A phase difference detection unit that detects the phase difference from the incident reflected modulated light based on the amount of charge in the charge storage unit, and a measurement that measures the distance to the distance measurement object based on the phase difference detected by the phase difference detection unit. And a distance portion.

JP 2008-89346 A

  In the image pickup device, an electronic element (such as a floating diffusion as a charge storage unit, an element such as a gate that distributes charges to the floating diffusion, or reads a charge amount from the floating diffusion) provided in each pixel is operated. There are variations. Accordingly, the readout value of the charge amount of the charge storage unit varies with respect to the reflected light having the same incident intensity. This variation is not much different between when the incident intensity is high and when the incident intensity is low, and is in a substantially constant range regardless of the incident intensity.

  When the incident intensity of the reflected light is low, the output value of the image sensor decreases, so that the proportion of variation in the output value increases accordingly. Therefore, the distance measurement accuracy of the distance measurement target having a low reflectance is lower than the distance measurement accuracy of the distance measurement object having a high reflectance.

  An object of the present invention is to provide a distance measuring device with improved distance measuring accuracy for a distance measuring object having a low reflectance.

The distance measuring device of the present invention is
An image sensor having a plurality of pixels distributed on a plane and a charge storage unit that stores charges with a charge amount related to the intensity of incident light on each pixel;
A modulated light emitting unit that emits intensity-modulated modulated light toward the imaging range of the imaging device;
The phase difference between the outgoing modulated light emitted from the modulated light emitting unit and the reflected modulated light reflected by the distance-measuring target in the imaging range and incident on the pixels of the imaging element is determined as the charge of the charge storage unit. A phase difference detector for detecting based on the quantity;
A distance measuring unit that measures a distance to the distance measuring object based on the phase difference detected by the phase difference detecting unit;
A modulation light control unit configured to control an emission intensity of the emission modulated light from the modulation light emission unit so that an incident intensity of the reflected modulation light in the pixel is equal to or higher than a reference value;

  According to the present invention, the emitted modulated light is emitted from the modulated light emitting unit with the emission intensity at which the incident intensity of the reflected modulated light in the pixel is equal to or higher than the reference value. As a result, the reflected modulated light from the distance measuring object having a low reflectance can also ensure a sufficient incident intensity and improve the distance measuring accuracy.

  In the distance measuring device of the present invention, the modulated light control unit detects an incident intensity of the reflected modulated light in the pixel, and based on the detected incident intensity, the incident intensity of the reflected modulated light in the pixel is equal to or higher than a reference value. The control process for emitting the output modulated light from the modulated light output unit with the output intensity controlled to the calculated output intensity is repeated, and in each control process, the detection target of the incident intensity in the pixel The reflected modulated light is preferably reflected modulated light derived from the outgoing modulated light emitted in the previous control process.

  According to this configuration, the emission intensity of the outgoing modulated light emitted in each control process is calculated based on the incident intensity of the reflected modulated light derived from the outgoing modulated light emitted in the previous control process. Therefore, in each control process, it is not necessary to exclusively emit the outgoing modulated light for detecting the incident intensity, and the time required for each control process can be shortened.

  In the distance measuring device according to the aspect of the invention, it is preferable that the modulated light control unit detects the incident intensity of the reflected modulated light incident on the pixel based on the charge amount of the charge storage unit.

  According to this configuration, the charge amount of the charge storage unit is shared by the phase difference detection by the phase difference detection unit and the incident intensity detection of the reflected modulated light incident on the pixel. Therefore, it is not necessary to emit the outgoing modulated light for detecting the incident intensity separately from the outgoing modulated light for detecting the phase difference, and the time required for each control process can be shortened.

  In the distance measuring device of the present invention, the modulated light emitting section deflects incident light incident from the light source that generates intensity-modulated modulated light, and directs the incident light as the emitted modulated light toward the imaging range. And the modulated light control unit is configured so that the modulated light emitted from the modulated light emission unit is emitted in a scanning cycle in which the imaging range is scanned with a constant scanning pattern in each control process. Further, the optical deflector is controlled, and the modulated light emitting unit is configured to output an outgoing phase of the outgoing modulated light emitted from the modulated light outgoing unit at each outgoing phase in the previous scanning cycle and a reflection modulation derived from the outgoing modulated light. It is preferable to detect a correspondence relationship with a pixel on which light is incident, and to control an emission phase of emission modulated light whose emission intensity is calculated for each pixel based on the correspondence relationship in the next scanning cycle.

  According to this configuration, in the next scanning cycle, the emission phase of the emission modulated light whose emission intensity is calculated for each pixel is controlled based on the correspondence detected based on the previous scanning cycle. Thereby, the outgoing modulated light having the outgoing intensity calculated in each control process can be accurately emitted to the corresponding distance measuring object in the imaging range.

The whole block diagram of a distance measuring device. The block diagram of the image pick-up element with which a camera is provided. The detailed block diagram of a pixel. 5 is a timing chart of outgoing modulated light and reflected modulated light. Explanatory drawing about the influence which the dispersion | variation in the element of a camera has on the ranging accuracy of a distance measuring device in relation to the incident intensity of reflected modulated light. The graph which shows the result of the experiment which investigated the influence which ranging value receives from the reflectance of a ranging object when a distance measuring device did not perform output intensity control. The block diagram of a distance measuring device. The flowchart of the distance measuring method which a distance measuring device implements. The figure which shows the relationship between the intensity division of reflected modulation light, and the dispersion | variation in the ranging by a distance measuring device.

  FIG. 1 is an overall configuration diagram of the distance measuring apparatus 1. The distance measuring device 1 includes a laser light source 2, an optical deflector 3, a camera 4, and a control device 5, and measures a distance D between the distance measuring device 1 and the distance measuring object 7 by the TOF method. The distance measuring device 1 emits an outgoing modulated light La as intensity-modulated modulated light toward an imaging range 6 of the camera 4 with a predetermined scanning pattern. When the distance measuring object 7 is present in the imaging range 6, the emitted modulated light La is reflected toward the distance measuring device 1 when irradiated on the distance measuring object 7, and the reflected light is derived from the emitted modulated light La. The reflected modulated light Lb is incident on the distance measuring device 1. The control device 5 measures the distance D between the distance measuring device 1 and the distance measuring object 7 based on the phase difference between the outgoing modulated light La and the reflected modulated light Lb.

  There may be a plurality of distance measuring objects 7 instead of only one in the imaging range 6. The distance measuring object 7 has various reflectances such as whitish and blackish. When the emission intensity Io of the outgoing modulated light La from the distance measuring device 1 is the same, the distance measuring object 7 having a lower reflectance and the distance measuring object 7 farther from the distance measuring device 1 are applied to the distance measuring device 1. The incident intensity Ii of the reflected modulated light Lb when incident becomes low. Of course, the reflected modulated light Lb derived from the emitted modulated light La is not generated for the emitted modulated light La that did not hit the distance measuring object 7.

  The control device 5 controls the laser light source 2, the optical deflector 3, and the camera 4 based on the input signals from the optical deflector 3 and the camera 4, and performs calculations such as calculation of the distance D.

  The laser light source 2 is controlled to be turned on and off by a control signal from the control device 5 and blinks at, for example, 10 MHz to generate laser light whose intensity is modulated. The laser light source 2 is also controlled by the control signal from the control device 5 so that the emission intensity of the laser light emitted at the time of lighting is controlled.

  The optical deflector 3 is a kind of MEMS (Micro Electro Mechanical Systems) device, and the structure itself is known. Regarding the detailed structure of the optical deflector 3, for example, Japanese Patent Application Laid-Open No. 2006-9050, Japanese Patent Application Laid-Open No. 2014-4155, Japanese Patent Application Laid-Open No. 2015-230326, and the like, which have been filed by the present applicant. Reference can be made to Japanese Unexamined Patent Publication No. 2015-219516.

  Briefly described, the optical deflector 3 reciprocally rotates a mirror portion (not shown) at first and second frequencies around first and second rotation axes that are substantially orthogonal to each other. In order to realize a raster scan described later, a relationship of first frequency> second frequency is set.

  The laser light emitted from the laser light source 2 and intensity-modulated hits a mirror portion that reciprocally rotates around the first and second rotation axes at the first and second frequencies, and is rotated around the first and second rotation axes. The direction is changed in the direction corresponding to the rotation angle of the mirror part. Then, the intensity-modulated emission modulated light La is emitted from the optical deflector 3 toward the imaging range 6.

  The outgoing modulated light La from the optical deflector 3 is imaged in a scanning cycle of a predetermined scanning pattern such as a raster scan, for example, as a result of reciprocal rotation around the first and second rotation axes of the mirror portion in the optical deflector 3. The range 6 is repeatedly scanned. Typically, the outgoing modulated light La reciprocates in the horizontal direction as the lateral direction of the imaging range 6 by reciprocating rotation of the mirror portion around the first rotation axis. Further, the imaging range 6 is reciprocated in the vertical direction as the vertical direction by the reciprocating rotation of the mirror portion around the second rotation axis.

  In the optical deflector 3, the reciprocating rotation of the mirror portion around the first and second rotation axes is performed by the first and second piezoelectric actuators that reciprocate the mirror portion around the first and second rotation axes. Is called. The control device 5 controls the driving voltage of the first and second piezoelectric actuators to control the scanning cycle of the outgoing modulated light La.

  When the distance measuring object 7 exists in the imaging range 6, the outgoing modulated light La is reflected by the distance measuring object 7, and after the reflection, the reflected modulated light Lb derived from the outgoing modulated light La becomes a distance measuring device. Return to 1. The reflected modulated light Lb that has returned enters the corresponding pixel G of the image sensor (image sensor) 400 (FIG. 2) of the camera 4.

  FIG. 2 is a configuration diagram of an image sensor 400 included in the camera 4. The imaging device 400 includes a pixel array unit 401, a row control unit 406, a column control unit 407, and an image processor 408 as main components.

  The pixel array unit 401 shown in FIG. 2 is shown in a front view, and has a plurality of pixels G (n, m) distributed in a lattice arrangement on the plane with a uniform density in the vertical and horizontal directions.

  Note that the pixel G in the pixel array unit 401 is represented by a row number n and a column number m. The pixel G (n, m) refers to the nth pixel G from the top and the mth pixel from the left in the front view of the pixel array unit 401. The pixel array unit 401 is composed of, for example, 126 × 126 pixels G. Hereinafter, when it is not necessary to distinguish individual pixels, the pixel G (n, m) is generically referred to as the pixel G, and (n, m) is omitted.

  Each pixel G has a left-side subpixel Po (subscript “o” means an odd number in front view), and the subpixel Po has an odd column number when the column number of the grid array including the subpixel is defined. And the right sub-pixel Pe (the subscript “e” means an even number).

  The row control unit 406 applies a control signal to the row control line 409 so that the pixels G of the pixel array unit 401 can be controlled for each row. The column controller 407 applies a control signal to the column control line 410 to control the pixels G of the pixel array unit 401 for each column. The image processor 408 controls the row control unit 406 and the column control unit 407 based on a control signal from the control device 5 (FIG. 1).

  FIG. 3 is a detailed configuration diagram of the pixel G. The pixel G is composed of a pair of two subpixels, a subpixel Po and a subpixel Pe.

  The subpixel Po includes PD, M1, M3, Fd1, Fd3, and two BMs. The sub-pixel Pe includes PD, M2, M4, Fd2, Fd4, and two BMs. Note that PD means a photodiode, M means a sorting switch, Fd means a floating diffusion as a charge storage unit, and BM means a transfer switch. M1 to M4 and BM are composed of FETs (field effect transistors).

  A control signal for controlling ON / OFF of M1 to M4 is supplied from the row control unit 406 to Tx1 to Tx4. A control signal for controlling on / off of the BM is supplied from the row control unit 406 to Bi. A set of lines Tx1 to Tx4 and Bi is included in each row control line 409 (FIG. 2).

  Ro is connected to the drains of all the BMs in the corresponding column (in the corresponding column, each column of Fd1 to Fd4 is distinguished). The column control unit 407 reads C1 to C4 as read values of the amount of charges accumulated in Fd1 to Fd4 of each pixel G via Ro. Ro is included in each column control line 410 (FIG. 2).

  The sub-pixel Po and the sub-pixel Pe are the same in overall operation except that the operation timings of M1 to M4 and BM as gates in the sub-pixel are different. Therefore, only the operation of the subpixel Po will be described.

  The PD generates a larger number of electrons as the intensity of incident light incident on the pixel G (the incident light includes background light and reflected modulated light Lb) is larger. Note that the amount of charge increases as the number of electrons increases. M1 and M3 are turned on and off in opposite phases by the applied voltages Tx1 and Tx3. That is, each on / off cycle is defined as one on / off cycle, and in each on / off cycle, the on period of M1 is the off period of M3, and the off period of M1 is the on period of M3. The blinking cycle of the laser light source 2 is sufficiently shorter than the time during which the reflected modulated light Lb passes through one pixel G in the scanning cycle described later. Accordingly, each pixel G may repeat the incidence of the reflected modulated light Lb a plurality of times during the passage of the reflected modulated light Lb, thereby increasing the amount of accumulated charge related to the incident intensity Ii of the reflected modulated light Lb. it can.

  In the ON period of M1 and M3, electrons generated by the PD are supplied to Fd1 and Fd3 and stored. In Fd1 and Fd3, charges having a charge amount related to the intensity of incident light incident on the pixel G (strictly, the subpixel Po or Pe) are accumulated. Ro is energized by the operation of a switch in the column control unit 407 at a predetermined readout timing, and the charge amounts of Fd1 and Fd3 of the subpixel Po to which the BM that is turned on at this time belong via the column control unit 407. Then, the read values C1 and C3 are read by the image processor 408. C1 and C3 are further sent from the image processor 408 to the control device 5 (FIG. 1).

  FIG. 4 is a timing chart of the outgoing modulated light La and the reflected modulated light Lb. The scale on the horizontal axis is a value representing the passage of time by the phase of the outgoing modulated light La. The emitted modulated light La is light derived from the laser light emitted from the laser light source 2, and the level of the emitted modulated light La is Low when the laser light source 2 is turned off, and High (high) when the laser light source 2 is turned on. ). The light intensity corresponding to the high level during lighting is increased or decreased by increasing or decreasing the power supply current of the laser light source 2.

  The outgoing modulated light La is light having a periodic pulse waveform, and is a rectangular wave with a period = 100 ns (frequency = 10 MHz) and a duty ratio = 50%. In FIG. 4, the rising time of the outgoing modulated light La is represented by phase = 0 °. As for the reflected modulated light Lb, the outgoing modulated light La emitted from the distance measuring device 1 reaches the distance measuring object 7 (FIG. 1), is reflected by the distance measuring object 7, and returns to the distance measuring device 1. As a result, the phase of the reflected modulated light Lb is delayed from the outgoing modulated light La by the amount of time that flies twice as long as the distance D to the distance measuring object 7, and the outgoing modulated light La and the reflected modulated light Lb are delayed. A phase difference φ occurs between From the phase difference φ, the distance D between the distance measuring device 1 and the distance measuring object 7 can be measured.

  As described above, the image processor 408 (FIG. 2) can read the charge amounts of Fd1 to Fd4 for each pixel G via Bi and Ro. The image processor 408 can read the accumulated charge amount related to the incident intensity Ii of the reflected modulated light Lb incident on the pixel G from Fd1 to Fd4 of each pixel G. In FIG. 4, T <b> 1 to T <b> 4 indicate accumulation periods of charge amounts that the image processor 408 reads from each of the pixels G from Fd <b> 1 to Fd <b> 4.

  Although the start phase is different in the period from T1 to T4, the length of the period is set to be equal to 1/2 (= half period) of the period of the outgoing modulated light La. T1 is set to a period of phase 0 ° to 180 °. T2 is set to a period between 90 ° and 270 °. T3 is set to a period of 180 to 360 degrees. T4 is set to a period between phase 270 ° to 360 ° and phase 0 ° to 90 ° of the next cycle, in other words, phase 270 ° to 450 °. As a result, charges are accumulated in Fd1 to Fd4 with a charge amount corresponding to the incident intensity Ii of the reflected modulated light Lb incident on the subpixels corresponding to T1 to T4. The image processor 408 reads the charge amounts of the charges accumulated in T1 to T4 in each pixel G as read values C1 to C4.

The control device 5 calculates the phase difference φ by the following equation (1).
Formula (1): Phase difference φ = tan ⁻¹ {(C1−C3) / (C2−C4)}
In the above formula, “tan” means tangent, and “tan ⁻¹ ” means arc tangent. Each of C1 to C4 includes the accumulated charge amount due to the incident light derived from the background light, but the influence due to the incident light derived from the background light is removed from the difference C1-C3 and the difference C2-C4. Has been.

  Here, the ranging accuracy of the distance measuring apparatus 1 will be described. The incident intensity Ii of the reflected modulated light Lb in the camera 4 is detected based on C1 to C4, but is affected by the reflectance of the distance measuring object 7. In other words, even if the outgoing intensity Io of the outgoing modulated light La is equal and the distance D to the distance measuring object 7 is equal, the incident intensity Ii of the reflected modulated light Lb decreases as the reflectance of the distance measuring object 7 is lower.

  In addition, because of variations in the operation of the gate in the image sensor 400 of the camera 4, even when the incident intensity Ii of the reflected modulated light Lb is the same, the control device 5 passes each pixel G through the image processor 408 of the camera 4. Variations occur in C1 to C4 read from. Since these variations are constant regardless of the incident intensity Ii of the reflected modulated light Lb, the error rate (= (error / true value) × 100%) increases as the incident intensity Ii of the reflected modulated light Lb decreases. Tend to.

  FIG. 5 is an explanatory diagram showing the influence of the variation in the operation of the gate in the image sensor 400 on the distance measurement accuracy of the distance measuring device 1 in relation to the incident intensity Ii of the reflected modulated light Lb. In the characteristic extraction shown in FIG. 5, the distance measuring device 1 does not control the emission intensity Io of the emission modulated light La, and fixes the emission intensity Io to the standard value Iso (Io = Iso).

  In FIG. 5, the horizontal axis indicates C1-C3 as the difference between C1 and C3, and the vertical axis indicates C2-C4 as the difference between C2 and C4. In FIG. 5, W1 and W2 indicate variation ranges when the incident intensity Ii of the reflected modulated light Lb is low and high, respectively. The variations in C1 to C4 are affected by variations in the operation of each gate in the image sensor of the camera 4, and these variations are not related to the incident intensity Ii of the reflected modulated light Lb. Both are equal.

  As a result, the calculation accuracy of the phase difference φ calculated by the control device 5 from the above-described equation (1) is lower in W1 where the incident intensity Ii of the reflected modulated light Lb is lower. This means that the distance measurement accuracy decreases as the reflectance of the distance measurement object 7 is lower and as the distance D to the distance measurement object 7 is longer.

  FIG. 6 is a result of an experiment in which the distance measurement value is measured from the reflectance of the distance measurement object 7 when the distance measurement device 1 performs distance measurement with the emission intensity set to a uniform standard intensity without performing the emission intensity control. It is a graph which shows. In FIG. 6, the horizontal axis indicates the actual distance to the location of the distance measuring object 7, and the vertical axis indicates the distance measured by the distance measuring device 1.

  In this experiment, the emission intensity Io of the emission modulated light La in each scanning cycle is fixed to Iso as a standard value (Io = Iso). A well-known Munsell sheet was used as the distance measuring object 7. The variation of the distance measurement value by the distance measuring device 1 is expressed by Wb (“b” means black) when the reflectance = 12% of the Munsell sheet, and when the reflectance = 95% of the Munsell sheet, Wh ( "H" means white), and the two are compared.

  Five actual distances of 0.5 m, 1.0 m, 2.0 m, 3, 0 m, and 4.0 m were selected. At each selected distance, Wb> Wh at any distance. Further, both Wb and Wh increase as the selection distance increases. This is because the incident intensity Ii of the reflected modulated light Lb decreases as the distance D to the distance measuring object 7 increases. That is, the distance D to the distance measuring object 7 being far is equivalent to the low reflectance of the distance measuring object 7 with respect to the incident intensity Ii of the reflected modulated light Lb.

  The distance measuring device 1 controls both the ranging accuracy for the ranging object 7 having a low reflectance and the ranging accuracy for the far ranging object 7 by controlling the emission intensity Io of the emission modulated light La described below. Can be improved.

  FIG. 7 is a block diagram of the distance measuring device 1. The control device 5 includes a phase difference detection unit 101, a distance measurement unit 102, and a modulated light control unit 103. The laser light source 2 and the optical deflector 3 constitute a modulated light emitting unit 106. The control device 5 controls the emission intensity Io of the modulated output light La from the modulated light output unit 106 based on C1 to C4 from the camera 4. The output intensity Io of the output modulated light La is equal to the output intensity of the laser light from the laser light source 2, so what the control device 5 actually controls is the output intensity of the laser light from the laser light source 2.

  The control device 5 includes a CPU, a RAM, a ROM, a nonvolatile semiconductor memory, and an I / O port as a normal control device that executes a program (software) for general purposes. The control device 5 further includes an A / D converter and a D / A converter in accordance with an analog sensor or an analog actuator that is a control target of the control device 5 and that the distance measuring device 1 is equipped with. The phase difference detection unit 101, the distance measurement unit 102, and the modulated light control unit 103 are generated as the CPU of the control device 5 executes software related to the distance measurement method.

  FIG. 8 is a flowchart of a distance measuring method performed by the distance measuring apparatus 1. The distance measuring method is implemented by the control device 5 executing software installed in the ROM.

  In STEP 110, the modulated light control unit 103 performs a standard intensity scanning cycle. The standard intensity scanning cycle means that the emission intensity Io of the outgoing modulated light La from the distance measuring device 1 is fixed to Iso as a standard value (Io = Iso), and the outgoing modulated light La is scanned into the imaging range 6 such as a raster scan. This is a scanning cycle in which scanning is performed once with a constant scanning pattern.

  The intensity of the outgoing intensity Io of the outgoing modulated light La is controlled by increasing or decreasing the power supplied to the laser light source 2. The scanning of the outgoing modulated light La in the imaging range 6 is performed by the control device 5 controlling the voltage applied to the piezoelectric actuator of the optical deflector 3.

  In STEP 111, for each pixel G (n, m), the control device 5 (a) detects the incident intensity Ii of the reflected modulated light Lb, (b) measures the range 7 and (c) performs the next scan. The emission intensity Io of the emission modulated light La in the cycle is calculated. The process of “ranging the distance measuring object 7” in (b) is performed by the phase difference detecting unit 101 and the distance measuring unit 102. The processing of “detection of incident intensity Ii of reflected modulated light Lb” in (a) and “calculation of emission intensity Io of emitted modulated light La in the next scanning cycle” in (c) is performed by modulated light control unit 103. Do.

  Of the processes (a) to (c), the process of “ranging the distance measuring object 7” in (b) is stopped when the first STEP 111 is performed, and from the second and subsequent STEPs 111. To be implemented. That is, when STEP 111 is performed for the first time, the emission intensity Io of the emission modulated light La that is the origin of the reflected modulated light Lb in all the pixels G (n, m) is fixed to the standard value Iso. This is because there is a possibility that desired distance measurement accuracy cannot be obtained.

  The specific contents of the “ranging of the distance measuring object 7” process of (b) will be described. The phase difference detection unit 101 reads C1 to C4 for each pixel G (n, m), applies the read C1 to C4 to the above equation (1), and outputs a phase difference for each pixel G (n, m). φ (n, m) is calculated.

The distance measuring unit 102 measures the distance D to the distance measuring object 7 based on the phase difference φ (n, m) calculated by the phase difference detecting unit 101. Thereby, the distance D to the distance measurement object is measured for each pixel G (n, m). The measurement of the distance D is based on the calculation by the following equation (2).
Formula (2): Distance D = (speed of light × 100 ns × phase difference φ (n, m)) / (360 ° × 2)
However, the unit of the phase difference φ is “°”.

  Next, the specific content of the “detection of the incident intensity Ii of the reflected modulated light Lb” in FIG. The modulated light control unit 103 detects the incident intensity Ii of the reflected modulated light Lb for each pixel G (n, m) based on C1 to C4 read for each pixel G (n, m). At this time, the reflected modulated light Lb to be detected for the incident intensity Ii is the reflected modulated light Lb derived from the outgoing modulated light La emitted in the previous scanning cycle. Here, the previous scanning cycle is not limited to the immediately preceding scanning cycle. The previous scanning cycle may be a scanning cycle a predetermined number of times before, or a plurality of scanning cycles performed before the present time may be collectively used as the previous scanning cycle.

  The incident light to each pixel G (n, m) includes background light in addition to the reflected modulated light Lb. Therefore, each of C1 to C4 has the incident intensity of the reflected modulated light Lb + background light. In order to detect the incident intensity Ii of the reflected modulated light Lb alone, for example, the incident intensity Ii is detected using a difference such as C1-C3, C2-C4, or (C1 + C2)-(C3 + C4).

  In the process (a), the correspondence detection process is also performed. Specifically, the correspondence relationship refers to each emission phase Oi in the scanning cycle and the pixel G (n, m) on which the reflected modulation light Lb derived from the emission modulation light La emitted at each emission phase Oi is incident. Is the correspondence relationship. Hereinafter, this correspondence is referred to as “Oi-G relationship”.

  The specific contents of the process of “calculation of the emission intensity Io of the emission modulated light La in the next scanning cycle” in (c) will be described.

  First, Ibi as a reference value of the incident intensity Ii of the reflected modulated light Lb will be described. FIG. 9 shows the relationship between the intensity classification of the reflected modulated light Lb and the variation in distance measurement by the distance measuring device 1. The control device 5 processes C1 to C4 with 8-bit discrete values of 0 to 255. Intensity categories 1 to 4 of the reflected modulated light Lb on the horizontal axis in FIG. 9 are obtained by segmenting the incident intensity Ii based on values of 0 to 255. The maximum value of the incident intensity Ii is 255 at the discrete value, and the minimum value of the incident intensity Ii is 0 at the discrete value.

  The intensity sections 1 to 4 are numbered in descending order of the incident intensity Ii, and the incident intensity Ii decreases in the order of the intensity sections 1, 2, 3, and 4. That is, the intensity category 1 is defined as the maximum intensity category of the incident intensity Ii, and the intensity category 4 is defined as the minimum intensity category of the incident intensity Ii.

  The intensity categories 1 to 4 are not obtained by equally dividing the above numerical range 0 to 255 by 64. The division ranges of the intensity divisions 1 to 4 are determined so that the emission intensity Io can be appropriately controlled. In the embodiment, the amount of division in the numerical range 0 to 255 is increased in the order of the division numbers of the strength categories 1 to 4, and the division amount is set so that the strength category 1 is the smallest and the strength category 4 is the largest. ing.

  Note that each of C1 to C4 has an incident intensity at which incident light including background light is incident on each pixel G (n, m) together with the reflected modulated light Lb. This is the intensity classification of the incident intensity Ii of the light Lb alone. That is, the sections 1 to 4 are divided based on, for example, the difference C1-C3 in order to exclude the incident intensity of the background light.

  The tolerance of the variation in distance measurement in the distance measurement device 1 is set to a value that differs depending on the distance measurement accuracy requested by the user or the like from the distance measurement device 1. For this distance measuring apparatus 1, it is assumed that 0.2 m is set as an allowable value of variation in distance measurement. FIG. 9 shows that if the incident intensity Ii of the reflected modulated light Lb is the intensity category 2, the distance measurement variation is 0.18 m, which is less than 2 m. Therefore, Ibi as the reference value of the incident intensity Ii of the reflected modulated light Lb is set to an intensity corresponding to the intensity category 2. Then, the output intensity Io of the output modulated light La is controlled so that the input intensity Ii of the reflected modulated light Lb incident on each pixel G satisfies Ii ≧ Ibi. In this way, distance measurement accuracy that satisfies the tolerance can be obtained.

  In other words, like the standard intensity scanning cycle of STEP 110, when the outgoing modulated light La is emitted at the outgoing intensity Io = Iso, the reflected modulated light Lb derived from the outgoing modulated light La is in the intensity categories 3 and 4. There is a distance measuring object 7 having a low reflectance and a distance measuring object 7 in the distance. For such a distance measuring object 7, when the next outgoing modulated light La is emitted, the outgoing intensity Io of the outgoing modulated light La is changed to Ito as an increased adjustment value of the outgoing intensity Io by an appropriate amount. Will be emitted. As a result, the incident intensity Ii of the reflected modulated light Lb incident after the next outgoing modulated light La is reflected and incident on the distance measuring object 7 is ensured to be equal to or higher than Ibi corresponding to the intensity category 2.

  It should be noted that the reflected modulated light Lb derived from the outgoing modulated light La is still in the intensity categories 3 and 4 even though the adjustment value Ito is set to be larger than the outgoing intensity Io in the previous scanning cycle in the previous scanning cycle. In this case, when the next outgoing modulated light La is emitted, the outgoing intensity Io is changed to Ito as the readjustment value further increased, and the outgoing modulated light La is emitted.

  Further, when the outgoing modulated light La is emitted at the outgoing intensity Io = Iso or Ito (this Ito is Ito in the previous scanning cycle), the reflected modulated light Lb derived from the outgoing modulated light La is divided into intensity categories 1 and 2. Suppose that there is a distance measuring object 7 having a high reflectance and a nearby distance measuring object 7. For such a distance measuring object 7, when the next outgoing modulated light La is emitted, the outgoing intensity Io is the same value as the previous scanning cycle (the outgoing intensity Io is the same as the previous value. The emission modulated light La is emitted as an “adjustment value”. As a result, the incident intensity Ii of the reflected modulated light Lb derived from the emitted modulated light La emitted with the adjusted emission intensity Io set to the same value as the previous scanning cycle is the intensity category 1 in the next scanning cycle. , 2 comes to fit.

  Note that, when the outgoing modulated light La is emitted at the outgoing intensity Io = Iso or Ito (this Ito is Ito in the previous scanning cycle), the reflected modulated light Lb derived from the outgoing modulated light La is in the intensity category 1. With respect to the distance measuring object 7 having a high reflectance and the nearby distance measuring object 7, the incident intensity Ii of the reflected modulated light Lb derived from the emitted modulated light La is determined as the intensity classification when the next emitted modulated light La is emitted. The emission intensity Io of the emission modulated light La in the next scanning cycle can be lowered from the standard value Iso or the previous Ito so that the intensity division is from 1 to 2. In this case, there is an advantage that the amount of heat generated by the laser light source 2 is suppressed and the saturation of the charge amount in Fd1 to Fd4 is suppressed.

  Based on the above, in the process of (c), the reflected modulated light Lb derived from the emission intensity Io of the emitted modulated light La emitted from the modulated light emitting unit 106 in the next scanning cycle (adjusted intensity scanning cycle of STEP 112) is Ito (n as an adjustment value of the output intensity Io of the output modulated light La so that the corresponding pixel G (n, m) is incident at the incident intensity Ii of the intensity category 2 in which Ibi or more is secured as a reference value. , M). Thus, Oi-Ito (n, m) as a further correspondence is created based on Oi-G (n, m).

  In STEP 112, the modulated light control unit 103 performs an adjustment intensity scanning cycle. The adjustment intensity scanning cycle in STEP 112 corresponds to the next scanning cycle in the process (c) in STEP 111. In STEP 112, the modulated light control unit 103 uses the correspondence relationship of Oi-Ito (n, m) created in the process (c) of STEP 111 and outputs the output phase Oi at each output phase Oi of the adjustment intensity scanning cycle. Ito (n, m) with respect to is obtained, and the emitted modulated light La is emitted from the modulated light emitting unit 106 with the obtained Ito (n, m). Also in the adjustment intensity scanning cycle, similarly to the standard scanning cycle of STEP 110, the outgoing modulated light La scans the imaging range 6 once with a scanning pattern such as a raster scan.

  In STEP 113, the control device 5 checks whether or not there is an instruction to end the distance measurement. If there is an instruction, the distance measuring process is terminated, and if not, the process returns to STEP 111. The instruction to end the distance measurement is generated, for example, when the user operates a predetermined operation unit of the distance measuring device 1. The control device 5 repeats STEPs 111 and 112 (hereinafter, the processes of STEPs 111 and 112 are collectively referred to as “control process”) until an instruction to end the distance measurement process is given.

  In the repetition of the control process, the emission intensity Io of the outgoing modulated light La emitted in the current control process in each control process is changed to the incident intensity Ii of the reflected modulated light Lb derived from the outgoing modulated light La emitted in the previous control process. Based on the control. Thereby, the effort of emitting the outgoing modulated light La for detecting the incident intensity Ii used by the modulated light control unit 103 separately from the outgoing modulated light La for ranging used by the phase difference detecting unit 101 and the distance measuring unit 102 Is omitted, and the entire distance measurement process can be simplified.

  In the repetition of the control process, the distance measurement object 7 that did not exist in the imaging range 6 in the previous control process appears in the current control process, or the measurement target that exists in the imaging range 6 in the previous control process. The distance object 7 may disappear in the current control process. STEPs 111 and 112 are repeatedly performed during the distance measurement period, and appropriate Ito (n, m) is determined for each pixel G (n, m) in each control process. Thereby, ranging of the ranging object 7 in the imaging range 6 can be performed with a predetermined accuracy without any trouble with respect to the appearance and disappearance of the ranging object 7 during the ranging period.

  Further, since the distance measurement object 7 moves in the imaging range 6, the pixel G to which the reflected modulated light Lb from the distance measurement object 7 is incident in the previous control process and the pixel G that is incident in the current control process are There may be differences. When the distance to the distance measuring object 7 is changed and the distance measuring object 7 is farther, the incident intensity Ii of the reflected modulated light Lb from the distance measuring object 7 is reflected from the distance measuring object 7 having a low reflectance. It decreases similarly to the incident intensity Ii of the light Lb. STEPs 111 and 112 are repeatedly performed during the distance measurement period, and appropriate Ito (n, m) is determined for each pixel G (n, m) in each control process. Thereby, the distance measurement of the distance measurement object 7 in the imaging range 6 can be performed with a predetermined accuracy without any trouble with respect to the movement of the distance measurement object 7 and the change in reflectance during the distance measurement period.

  Although the embodiments of the present invention have been described, the present invention is not limited to the embodiments and includes various aspects other than the embodiments.

  In the embodiment, the charge accumulation unit is formed by floating diffusion, but the charge accumulation unit can be configured by other capacitive elements.

  In the embodiment, one pixel G includes two subpixels Po and Pe. However, the pixel G without a subpixel may be a single pixel G. In that case, the charges Fd1 to Fd4 are distributed from one PD, and the charges accumulated in each phase period of 0 to 90 °, 90 ° to 180 °, 180 ° to 270 °, and 270 ° to 360 °, respectively. Are read as C1 to C4.

  In the embodiment, the emission intensity Io of the emission modulation light La in the next scanning cycle is controlled so that the incident intensity Ii of the reflection modulation light Lb derived from the emission modulation light La is in the intensity category 2 to which Ibi as a reference value belongs. ing. In the present invention, it is sufficient that the incident intensity of the reflected modulated light in the pixel is equal to or higher than the reference value. Therefore, the output intensity Io of the output modulated light La in the next scanning cycle is set so that the incident intensity Ii of the reflected modulated light Lb derived from the output modulated light La belongs to the intensity section 1 as an intensity section higher than the intensity section 2. It can also be controlled.

DESCRIPTION OF SYMBOLS 1 ... Distance measuring device, 2 ... Laser light source, 3 ... Optical deflector, 5 ... Control device, 6 ... Imaging range, 7 ... Distance measuring object, 101 ... Position Phase difference detecting unit, 102... Distance measuring unit, 103... Modulated light control unit, 106.

Claims (4)

An image sensor having a plurality of pixels distributed on a plane and a charge storage unit that stores charges with a charge amount related to the intensity of incident light on each pixel;
A modulated light emitting unit that emits intensity-modulated modulated light toward the imaging range of the imaging device;
The phase difference between the outgoing modulated light emitted from the modulated light emitting unit and the reflected modulated light reflected by the distance-measuring target in the imaging range and incident on the pixels of the imaging element is determined as the charge of the charge storage unit. A phase difference detector for detecting based on the quantity;
A distance measuring unit that measures a distance to the distance measuring object based on the phase difference detected by the phase difference detecting unit;
A distance measurement comprising: a modulation light control unit that controls an emission intensity of the emission modulated light from the modulation light emission unit so that an incident intensity of the reflected modulation light in the pixel is equal to or higher than a reference value. apparatus. The distance measuring device according to claim 1,
The modulated light control unit detects an incident intensity of the reflected modulated light at the pixel, calculates an emission intensity at which the incident intensity of the reflected modulated light at the pixel is a reference value or more based on the detected incident intensity, Repeat the control process of emitting the output modulated light from the modulated light output unit with the output intensity controlled to the calculated output intensity,
In each control process, the reflected modulated light to be detected for incident intensity in the pixel is reflected modulated light derived from the outgoing modulated light emitted in the previous control process. The distance measuring device according to claim 2,
The distance measuring device, wherein the modulated light control unit detects an incident intensity of reflected modulated light incident on the pixel based on a charge amount of the charge storage unit. The distance measuring device according to claim 2,
The modulated light emitting unit includes a light source that generates intensity-modulated modulated light, and an optical deflector that deflects incident light incident from the light source and emits the emitted modulated light as the emitted modulated light toward the imaging range. And
The modulated light control unit controls the optical deflector so that the modulated output light from the modulated light emitting unit is emitted in a scanning cycle in which the imaging range is scanned with a constant scanning pattern in each control process,
The modulated light emitting unit has a correspondence relationship between an emission phase of the emitted modulated light emitted from the modulated light emitting unit at each emission phase in the previous scanning cycle and a pixel on which the reflected modulated light derived from the emitted modulated light is incident. A distance measuring apparatus that detects and controls the emission phase of the emission modulated light whose emission intensity is calculated for each pixel based on the correspondence in the next scanning cycle.