JP2013076645A - Distance image generation apparatus and distance image generation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately perform range measurement even when a plurality of optical flying type distance image generation apparatuses simultaneously exist in the same photographing space when generating a distance image of the photographing space by an optical flying type distance image generation apparatus.SOLUTION: While fixing a light emission (ON) period of modulation light applied from a light source and a charge accumulation period in each unit accumulation part of a charge accumulation part, light emission and accumulation are controlled so that a period length is changed in each modulation period. The period length is changed by adding additional time different in each period to a predetermined fixed modulation period Ts. Electric charge acquired during the additional time is discharged.

Description

  The present invention relates to a distance image generation technique, and more particularly to a distance image generation technique using an optical time-of-flight distance image sensor.

  A distance image generation device (hereinafter referred to as an optical flight type distance image generation device) that uses a light time-of-flight distance image sensor to generate a distance image of an object in an imaging space with the distance from the sensor as a pixel value. ) In the optical flight type distance image generation device, the distance of the object is calculated for each pixel using the phase difference between the modulated light (ranging light) emitted from the light source and the reflected light of the modulated light from the object. The phase difference is calculated by converting the reflected light received by the imaging device prepared for each pixel into a charge amount corresponding to the light amount, and performing a predetermined calculation on the charge amount (for example, see Patent Document 1). .

  The optical flight-type distance image generation device calculates the distance value based on the reflected light received for each pixel as described above. However, for example, when there are multiple similar optical flight-type distance image generation devices in the same space, such as a road with a large amount of traffic, the distance measurement light of the other device interferes with the distance measurement light of its own device, resulting in erroneous measurement. A distance is generated.

  In order to solve the problem of erroneous ranging due to interference with ranging light from other devices, a timing control unit is provided outside the optical flight-type distance image generating device, and lighting control is performed in a time-sharing manner so that multiple ranging lights do not interfere with each other. There is a technique for performing (see, for example, Patent Document 2). In addition, there is a technique for avoiding interference by setting the modulation frequency of modulated light to be different for each optical flight-type distance image generation device (see, for example, Patent Document 3).

JP 2008-241435 A Japanese Patent No. 4300368 JP 2009-124398 A

  However, the technique described in Patent Document 2 requires an additional device called a timing control unit. In addition, since the distance measuring light is emitted in a time division manner, if the number of distance image generating devices to be controlled increases, the light emission time per unit decreases, and the distance accuracy and the frame rate decrease.

  In the technique described in Patent Document 3, fine frequency setting is required. Furthermore, since the equation for calculating the distance changes every time the frequency is changed, the distance calculation becomes complicated.

  The present invention has been made in view of the above circumstances. When a distance image of a shooting space is generated by an optical flight type distance image generation device, a plurality of optical flight type distance image generation devices exist in the same shooting space at the same time. Even if it is a case, it aims at ranging accurately.

  The present invention changes the period length for each modulation period while keeping the emission period (ON) period of modulated light emitted from the light source and the charge accumulation period in each unit accumulation part of the charge accumulation part. Controls light emission and accumulation. The length of the period is changed by adding an additional time different for each period to a predetermined fixed modulation period. Then, the charges acquired during the additional time are discarded.

  Specifically, a light source that irradiates modulated light to the imaging space, and a plurality of imaging elements that receive incident light including reflected light that is irradiated from the light source and reflected by an object in the imaging space and converts the incident light into charges. A light receiving means, a distance image generating means for generating a distance image in which the pixel value is a distance value and the number of pixels is the number of image pickup devices using the charge, a modulation period of the modulated light, and a charge of the light receiving means A distance image generating device including a control unit that controls accumulation, wherein each of the plurality of imaging elements is provided for each photoelectric conversion element that converts received incident light into electric charge, and for each of the photoelectric conversion elements. Charge accumulation means for accumulating the charge, the charge accumulation means comprising a plurality of distance measurement unit accumulation means for accumulating charges used by the distance image generation unit for distance value calculation, and the control means The modulation Additional time output means for outputting a different additional time for each modulation period, and by adding the additional time for each modulation period, the modulation period of the modulated light to be irradiated is changed for each one of the modulation periods And providing a distance image generating apparatus that controls the charge accumulation period in each distance measurement unit accumulating means to be the same in all cycles.

  A light source that emits modulated light to the imaging space; and a plurality of photoelectric conversion elements that receive incident light including reflected light that is irradiated from the light source and reflected by an object in the imaging space and converts the incident light into charges; and A plurality of unit accumulating means for accumulating the electric charge provided for each photoelectric conversion element and a distance value using the electric charge accumulated in the unit accumulating means used for the predetermined distance measurement among the plural unit accumulating means. A distance image generation method in a distance image generation device comprising: a distance image calculation means for calculating; an additional time generation step for generating an additional time to be added for each modulation period of the modulated light; and for each modulation period Adding the additional time to the modulation period to change the modulation period of the modulated light, and storing the charge obtained by converting the incident light received during the additional time in the unit storage means for disposal, Applicable A synchronization control step for accumulating charges acquired in a predetermined period other than time in a plurality of predetermined unit units for accumulating charges and the unit accumulating unit for accumulating charges at predetermined time intervals. And a distance value calculating step of calculating a distance value that is each pixel value of the distance image.

  According to the present invention, when the distance image of the shooting space is generated by the optical flight-type distance image generation device, even if there are a plurality of optical flight-type distance image generation devices at the same time in the same shooting space, the accuracy is improved. Can measure well.

(A) is a block diagram of a general distance image generation device, (b) is a block diagram of an image sensor of a general distance image generation device. It is a timing chart of the control signal of a general distance image generation device. (A) is a block diagram of the distance image generation device of the embodiment of the present invention, (b) is a block diagram of the image sensor of the distance image generation device of the embodiment of the present invention. It is a timing chart of the control signal of the distance image generation device of the embodiment of the present invention. It is explanatory drawing for demonstrating that interference is prevented by the distance image generation apparatus of embodiment of this invention. It is a timing chart of the control signal of the other example of the distance image generation device of the embodiment of the present invention. It is a timing chart of the control signal of the other example of the distance image generation device of the embodiment of the present invention. (A) is explanatory drawing for demonstrating the additional time database of embodiment of this invention, (b) is explanatory drawing for demonstrating the pattern produced | generated by the pattern generation circuit of embodiment of this invention. It is. It is explanatory drawing for demonstrating the random addition time database of embodiment of this invention. (A) is a graph of the frequency spectrum of the modulated light when the additional time Tw is 0, and (b) is a graph of the frequency spectrum of the modulated light when performing frequency spreading according to the embodiment of the present invention. is there.

  Hereinafter, embodiments to which the present invention is applied will be described. Hereinafter, in all the drawings for explaining the embodiments of the present invention, those having the same function are denoted by the same reference numerals, and repeated explanation thereof is omitted.

  Prior to the description of the configuration of the optical time-of-flight distance image generation device (hereinafter referred to as a distance image generation device) of the present embodiment, the distance image generation device 101 using a general charge distribution type optical time-of-flight sensor is described. The configuration and the principle of distance image generation will be described.

  The optical time-of-flight range image sensor is a sensor configured with one image sensor as one pixel. The distance image generation apparatus 101 using this optical time-of-flight range image sensor receives optical reflected light using the optical time-of-flight (TOF) method by receiving reflected light of light irradiated on the target object 200. The distance image is generated by measuring the time and measuring the distance to the target object 200 based on the light flight time.

  As will be described later, the charge distribution method connects two or more charge storage capacitors to one photoelectric conversion element, and, for example, pulse light that periodically emits light (ON / OFF) (hereinafter, referred to in this specification). The pulsed light is referred to as “modulated light”.) Is synchronized and stored in two or more charge storage capacitors in synchronization with the modulation period and light emission time, and the distance is calculated based on these charges. In this charge distribution method, when calculating the distance value, the signal-to-noise ratio is increased by reading out and averaging the charges separated and accumulated at regular intervals. Therefore, the light distribution type optical time-of-flight distance image sensor can be used under unknown background light.

  FIG. 1A is a block diagram of the distance image generating apparatus 101. As shown in the figure, the distance image generation device 100 includes a light source 110, a light receiving unit 120, a distance image generation unit 130, and a control unit 140.

  The light source 110 irradiates the imaging space with the modulated light 151. As the light source 110, a device capable of high-speed modulation (high-speed blinking) such as an LED or a laser is used.

  The light receiving unit 120 receives the incident light 152 and converts it into electric charges. As illustrated in FIG. 1A, the light receiving unit 120 includes a plurality of imaging elements 121 corresponding to each pixel of the distance image generated by the distance image generating unit 130. The plurality of imaging elements 121 are regularly arranged in association with each pixel of the distance image generated by the distance image generation unit 130. FIG. 1A illustrates a 4 × 4 case.

  The incident light 152 incident on the light receiving unit 120 includes reflected light derived from the fact that the modulated light 151 emitted from the light source 110 is reflected by the object 200 in the imaging space, and light from an external light source such as natural light. It is the sum total with the background light derived from being reflected by the target object 200.

  This optical time-of-flight distance sensor employs the charge distribution method as described above. For this reason, each imaging element 121 includes a photoelectric conversion element 122 and a charge accumulation unit 123 as shown in FIG. The photoelectric conversion element 122 receives the incident light 152 and converts it into charges corresponding to the amount of received light. The charge storage unit 123 includes a plurality of unit storage units 124 that store the charges converted by the photoelectric conversion element 122.

  The charges converted by the photoelectric conversion element 122 are distributed and stored in the respective unit storage units 124 in accordance with instructions from the control unit 140. The distribution of charges to each unit storage unit 124 is performed in synchronization with the modulation period of the modulated light 151. The charges accumulated in each unit accumulation unit 124 are read according to an instruction from the control unit 140 and output to the distance image generation unit 130. Reading is performed at predetermined time intervals.

  Two or more unit accumulation units 124 are provided for each charge accumulation unit 123. As will be described later, when a distance image is generated using the charges accumulated in the unit accumulation unit 124, the phase difference (delay time) between the modulated light 151 and the incident light 152 is used. This is because, in order to calculate the delay time, two or more pieces of charge information acquired at different phases by delaying the start of acquisition at certain intervals are required.

  The distance image generation unit 130 calculates the distance of the object 200 for each pixel using the delay time (phase difference) between the modulated light 151 and the incident light 152. Details of the calculation will be described later. The calculation of the distance image is performed every time the charge is read from the unit accumulation unit 124 in accordance with an instruction from the control unit 140. The distance image is generated by calculating the distance value of the shooting space corresponding to each pixel position. The generated distance image is output from, for example, an external output terminal (not shown).

  The control unit 140 controls the light source 110 and the light receiving unit 120 synchronously. The control unit 140 outputs control signals instructing the modulation (light emission) of the light source 110, the distribution of charges to each unit storage unit 124 in the light receiving unit 120, and the reading of the charges from each unit storage unit 124, respectively. Realize synchronous control. Hereinafter, the control signal for controlling the light emission of the light source 110 is a light emission signal TE, the control signal for controlling the distribution of charges to each unit storage unit 124 of the light receiving unit 120 is a gate signal TX, and the read timing from each unit storage unit 124 is set. A control signal to be controlled is called a read signal.

  Next, the timing of control signals output from the control unit 140 to the light source 110 and the light receiving unit 120 and the principle of distance image generation will be described. Here, a case where there are four unit accumulation units 124 is illustrated. The horizontal axis represents time, and the vertical axis represents ON / OFF of each signal.

  FIG. 2 is a timing chart of control signals output from the control unit 140 to the light source 110 and the light receiving unit 120. Here, a case where the light emission signal TE is a rectangular wave and the modulated light 151 is modulated by the rectangular wave and emits a pulse will be described as an example. The waveform used for modulation is not limited to a rectangular wave. A sine wave, a sawtooth wave, etc. may be sufficient.

  The top row is a timing chart of the light emission signal TE. The light emission signal TE is output as a rectangular wave having a cycle of Ts, an ON time of Ts / 2, and an OFF time of Ts / 2. The light source 110 repeats ON (light emission) / OFF (light emission stop) according to the light emission signal TE. Here, the light source 110 emits light during Ts / 2 when the light emission signal TE is ON, and stops light emission during Ts / 2 when the light emission signal TE is OFF.

  Here, the light reception timing of the reflected light of the modulated light 151 by the light receiving unit 120 is shown in the next stage. As shown in the figure, the reflected light reaches the light receiving unit 120 with a delay of time Td. This time Td is a delay (phase difference) caused by the flight time until the modulated light 151 is irradiated from the light source 110, reflected by the target object 200, and received by the light receiving unit 120. Hereinafter, it is called a delay time Td.

  The lower part is a timing chart of four gate signals TX1, TX2, TX3, and TX4 for instructing the timing for accumulating charges in each of the four unit accumulation units 124.

  These gate signals TX1, TX2, TX3, TX4 are output in synchronization with the light emission signal TE. Assuming that the period Ts of the light emission signal TE is equally divided into four, T1, T2, T3, and T4, respectively, the gate signal TX1 is a signal that synchronizes the light emission signal TE and the ON / OFF timing, and the gate signal. TX2, TX3, and TX4 are output as signals having a period Ts that are shifted from the gate signal TX1 by T1, T1 + T2, and T1 + T2 + T3, respectively. The gate signals TX2, TX3, TX4 are also turned ON for Ts / 2 and turned OFF for Ts / 2 every cycle Ts.

  In this way, by distributing charges according to the gate signals TX1, TX2, TX3, and TX4 that are shifted by the time obtained by dividing the period Ts of the light emission signal TE into four equal parts, the charge information C1 that is 0 degrees out of phase and the 90 degrees phase are changed. Charge information C2 that is shifted, charge information C3 that is 180 degrees out of phase, and charge information C4 that is 270 degrees out of phase are stored in each of the four unit storage units 124.

  Here, although not shown in the figure, the read signal is output at a predetermined time interval. In general, in order to obtain one distance image, it is necessary to accumulate charges for a time of about several ms. On the other hand, the modulation frequency of the light source 110 is several tens of MHz. Therefore, one modulation period Ts is about several tens of ns. For this reason, in order to obtain a distance image, a charge accumulation period Δt of several hundred to several hundred thousand cycles is required. A read signal is output at intervals of this charge accumulation period Δt. In accordance with the read signal, the light receiving unit 120 outputs the charge amounts C1, C2, C3, and C4 stored in the four unit storage units 124 to the distance image generation unit 130.

The distance image generation unit 130 calculates the distance value D using each of the charge amounts C1, C2, C3, and C4 received for each charge accumulation period Δt. As described above, the modulated light 151 and the incident light 152 have the delay time Td (phase difference φ) due to the flight time during which the light travels back and forth to the object 200. Since the speed of light c is known, the distance value D to the object can be obtained by the following equation (1) using the delay time Td and the period Ts.

The delay time Td (phase difference φ) is expressed by the following equation (2) using the charge amounts C1, C2, C3, and C4 accumulated in each unit accumulation unit 124.

  At this time, the component derived from the modulated light 151 in the incident light 152, that is, the charge due to the reflected light, is allocated to each unit storage unit 124 in an amount corresponding to the phase (delay time). Therefore, the amount of charge stored in each unit storage unit 124 is different. On the other hand, the electric charge due to the background light in the incident light 152 is equally allocated to each unit storage unit 124. Accordingly, the amount of charge accumulated in each unit accumulation unit 124 is substantially equal. Therefore, the background light is canceled by the above formula, and the phase difference of only the reflected light can be obtained.

  The four charges acquired according to the gate signals TX1, TX2, TX3, and TX4 may be acquired simultaneously or may be acquired over a plurality of frames. Any distance may be used as long as the distance is calculated from the charge information of at least two different phases.

The amplitude amount B of the modulated light component of the modulated light 151 reflected by the target object 200 is obtained by the following equation (3).

In general, the average value A of the charges distributed to the four charge storage units 123 according to the following equation (4) is used as the pixel value of the luminance image.

  As described above, the distance image generating apparatus 101 can obtain the distance image and the luminance image at the same time.

  Next, the distance image generation device 100 of this embodiment will be described. FIG. 3A is a functional block diagram of the distance image generating apparatus 100 of the present embodiment. The distance image generation device 100 of the present embodiment basically has the same configuration as the distance image generation device 101. That is, the light source 110, the light receiving unit 120, the distance image generation unit 130, and the control unit 140 are provided.

  The light receiving unit 120 of this embodiment also includes a plurality of image sensors 121. Each image sensor 121 is regularly arranged in association with each pixel of the distance image generated by the distance image generation unit 130. The distance image generation unit 130 generates a distance image having the number of pixels of the image sensor 121.

  As shown in FIG. 3B, the image sensor 121 according to the present embodiment also includes a photoelectric conversion element 122 that converts incident light 152 into electric charges and a plurality of unit accumulation units 124, as in the image sensor 121 of the distance image generation device 101. And a charge accumulating portion 123 for accumulating charges.

  Each of these units has basically the same function as the configuration of the same name of the conventional distance image generation device 101.

  However, the distance image generation device 100 according to the present embodiment is capable of high-precision measurement without interference even when there is a distance image generation device that uses a plurality of optical flight distance sensors in the same space at the same time. Do the distance. In the distance image generating apparatus 100 of the present embodiment, the emission (ON) period of the modulated light 151 emitted from the light source 110 and the charge accumulation timing and period in each unit accumulation unit 124 of the charge accumulation unit 123 are constant as in the conventional case. However, the length of the period is changed for each modulation period, that is, for each light emission of the light source 110. The length of the period is changed by adding an additional time Tw that is different for each period to a predetermined fixed modulation period Ts.

  In order to realize this, the control unit 140 of the distance image generating apparatus 100 according to the present embodiment includes an additional time output unit 144 that outputs an additional time Tw that differs for each period. In addition, the control unit 140 of the present embodiment uses the additional time Tw to generate a light emission signal 141 that controls the light emission (ON / OFF) of the light source 110, and the light receiving unit 120 using the additional time Tw. A storage control unit 142 that generates a gate signal for controlling charge storage in the charge storage unit 123, and a read control unit 143 that controls reading from each unit storage unit 124.

  Note that the plurality of unit storage units 124 included in the charge storage unit 123 of the present embodiment includes a distance measurement unit storage unit 125 that uses the accumulated charge to generate a distance image in the distance image generation unit 130, and the accumulated charge. Is used as the discard unit storage unit 126 that is not used for distance image generation but is discarded. This figure illustrates the case where there are four ranging unit storage units 125 and one discard unit storage unit 126.

  Similar to the unit storage unit 124 of the conventional distance image generation apparatus 101, the charge measurement information of different phases is stored in the four distance measurement unit storage units 125. That is, according to the gate signals TX1, TX2, TX3, and TX4 that are shifted by four equal intervals of the period Ts of the light emission signal TE, the charge information C1 that is 0 degrees out of phase, the charge information C2 that is 90 degrees out of phase, and 180 degrees Charge information C3 with a phase shift and charge information C4 with a phase shift of 270 degrees are stored in each of the four distance measurement unit storage units 125.

  The distance image generation unit 130 uses the charge information stored in the distance measurement unit storage unit 125 to calculate the distance value by the method described in the conventional distance image generation device 101. In order to calculate the distance value D, it is sufficient if there are two or more pieces of charge information having different phases. The two or more pieces of charge information may be acquired at the same time or may be acquired over a plurality of frames. Therefore, the number of ranging unit accumulating units 125 may be two or more like the distance image generating apparatus 101, and is determined by the structure and specifications of the image sensor 121.

  On the other hand, charges are accumulated in the discard unit accumulating unit 126 at a time including the additional time Tw. The charges accumulated in the discard unit accumulation unit 126 are not used for calculating the distance. The charge stored in the discard unit storage unit 126 may be configured to be discarded after reading, or may be configured to be discarded at a predetermined time interval.

  The additional time output unit 144 calculates the additional time Tw in software using a CPU or a microcomputer, and outputs the calculated time to the light emission control unit 141, the accumulation control unit 142, and the read control unit 143. The additional time output unit 144 may be realized by a circuit such as an FPGA (Field Programmable Gate Array). The additional time Tw is calculated in the range of about 100 ns to 10 μs, for example.

  Control by the control unit 140 in the distance image generating apparatus 100 of the present embodiment having the above configuration will be described using a timing chart showing the output timing of each control signal. FIG. 4 is a timing chart of control signals by the control unit 140 of this embodiment. Here, as in the conventional example shown in FIG. 2, the case where the light emission signal TE is a rectangular wave and the modulated light 151 is modulated by this rectangular wave and emits pulses will be described as an example. In this embodiment as well, the waveform used for modulation is not limited to a rectangular wave. A sine wave, a sawtooth wave, etc. may be sufficient. Further, here, as shown in FIG. 3, a case where there are four ranging unit accumulating units 125 and one discard unit accumulating unit 126 will be described as an example.

  The top row is a timing chart of the light emission signal TE. As shown in this figure, when the light emission control unit 141 of this embodiment receives the additional time Tw from the additional time output unit 144, the additional time Tw received in the OFF signal of the light emission signal that is an ON / OFF signal of the period Ts. And output as a light emission signal TE. That is, the light emission signal TE is a control signal having a cycle of (Ts + Tw), an ON period of Ts / 2, and an OFF period of Ts / 2 + Tw. Hereinafter, Ts is referred to as a set period, and (Ts + Tw) is referred to as an effective period.

  In accordance with the light emission signal TE, the light source 110 of the present embodiment emits light (ON) for Ts / 2 and stops (OFF) light emission for (Ts / 2 + Tw) every effective period (Ts + Tw). The light emission period is constant regardless of the period, and the light emission stop period changes for each period. During the additional time Tw, the light source 110 does not emit the modulated light 151.

  Here, the light receiving timing of the reflected light of the modulated light 151 by the light receiving unit 120 is shown in the next stage. As shown in the figure, also in this embodiment, the reflected light reaches the light receiving unit 120 with a delay of the delay time Td. This delay time Td is a delay caused by the flight time from when the modulated light 151 is irradiated from the light source 110, reflected by the target object 200, and received by the light receiving unit 120.

  The lower stage shows four gate signals TX1, TX2, TX3, TX4 for instructing the timing for storing charges in each of the four distance measuring unit storage units 125, and the discard gate for instructing the timing for storing charges in the discard unit storage unit 126. Signal TX5 is shown.

  As shown in the figure, the accumulation control unit 142 according to the present embodiment outputs these gate signals TX1, TX2, TX3, TX4, and TX5 in synchronization with the light emission signal TE, as in the conventional example.

  The gate signals TX1, TX2, TX3, and TX4 for the ranging unit accumulating unit 125 are the same as those in the conventional example. That is, assuming that the times obtained by dividing the set period Ts into four equal parts are T1, T2, T3, and T4, respectively, TX1 is output to be ON for Ts / 2 from the timing when the light emission signal TE is ON, and TX2, TX3 , TX4 are output so as to be ON for Ts / 2 from the time delayed from the timing at which the light emission signal TE is turned ON in order of T1, T1 + T2, and T1 + T2 + T3. These are the same throughout the entire period regardless of the additional time Tw. With these gate signals TX1, TX2, TX3, and TX4, charge information of four different phases (0 degree, 90 degrees, 180 degrees, and 270 degrees) C1 is stored in each distance measurement unit accumulation unit 125 over the entire period, as in the past. , C2, C3, C4 are accumulated.

  The discard gate signal TX5 is generated and output as a signal having a cycle of (Ts + Tw) like the other gate signals. However, the discard gate signal TX5 is generated and output during one period (Ts + Tw) so that any of the gate signals TX1, TX2, TX3, and TX4 of the ranging unit accumulating unit 125 is not ON. . The discard unit accumulation unit 126 accumulates charges during a period in which no charge is accumulated in any of the distance measurement unit accumulation units 125, including the period of the additional time Tw. Here, the gate signal TX5 is generated and output so as to be ON for the additional time Tw. Then, charges are accumulated in the discard unit accumulation unit 126 during that time.

  The read signal is output at a predetermined time interval Δt as in the conventional example, although not shown here. The time interval Δt is an interval in which charges necessary for obtaining one distance image are accumulated, and is determined in advance. In accordance with the read signal, the light receiving unit 120 outputs the charge amounts C1, C2, C3, and C4 stored in the four unit storage units 124 to the distance image generation unit 130.

  The distance image generation unit 130 calculates the distance value D using the equations (1) and (2) as in the conventional example, using the respective charge amounts C1, C2, C3, and C4 received for each charge accumulation period Δt. To do.

  It will be described that the distance image generating apparatus 100 configured as described above can prevent interference with other distance image generating apparatuses in the same shooting space. FIG. 5 is a diagram for explaining that interference is prevented. Here, the effective period by Ts and Tw of the two distance image generation devices A and B and the light emission timing of the light source 110 are shown.

  When the light sources 110 of the distance image generation devices A and B irradiate the same space, the modulated light 151 emitted from the distance image generation device A also enters the distance image generation device B. However, as shown in this figure, since the emission timing of the modulated light 151 of the distance image generation device A is shifted from the emission timing of the distance image generation device B, the charge accumulation timing in the light receiving unit 120 of the distance image generation device B. And no interference occurs.

As described above, in order to obtain one distance image, it is necessary to accumulate light for several ms (10 ⁻³ seconds). On the other hand, the period Ts of the modulated light is about several tens to 100 ns (10 ⁻⁹ seconds). Accordingly, after accumulating thousands to tens of thousands of cycles, the data is read by the reading unit, and the distance value is calculated. Therefore, the modulated light 151 of another distance image generation device that is not synchronized is regarded as noise (DC light) by being repeated thousands to tens of thousands of times, and is canceled as described above.

  For this reason, according to the present embodiment, even if there are a plurality of distance image generation devices in the same imaging space, erroneous distance measurement can be avoided without interfering with each other.

  The distance image generation device 100 according to the present embodiment includes a CPU, a memory, and a storage device, and implements the functions of the image generation unit 130 and the control unit 140 by executing a program stored in the storage device.

  As described above, the distance image generating apparatus 100 according to the present embodiment includes the light source 110 that irradiates the imaging space with the modulated light, and the incident light that includes the reflected light that is emitted from the light source and reflected by the object in the imaging space. A light receiving unit (light receiving unit 120) including a plurality of imaging elements 121 that receive light and convert it into charges, and generate a distance image in which the pixel value is a distance value and the number of pixels is the number of imaging elements, using the charge. A distance image generating unit (distance image generating unit 130); and a control unit (control unit 140) for controlling a modulation period of the modulated light and charge accumulation in the light receiving unit. Each of the photoelectric conversion elements 122 for converting the received incident light into charges, and charge storage means (charge storage unit 123) for storing the charges provided for each of the photoelectric conversion elements. The storage unit (charge storage unit 123) includes a plurality of distance measurement unit storage units (range measurement unit storage unit 125) for storing charges used by the distance image generation unit for calculating distance values, and the control unit (control unit 140). ) Includes additional time output means (additional time output unit 144) for outputting different additional times for each modulation period of the modulated light, and adding the different additional times for each modulation period to thereby modulate the irradiation The light modulation period is changed for each one of the modulation periods, and the charge accumulation period in the ranging unit accumulating unit (ranging unit accumulating unit 125) is controlled to be the same in all periods. .

  The modulated light is pulsed light that repeats light emission and emission stop, and the charge storage unit (charge storage unit 123) further includes one discard unit storage unit (discard unit storage unit 126) that stores charges to be discarded. The control means (control unit 140) includes a light emission control means (light emission control unit 141) for changing the modulation period of the modulated light by adding the additional time to the light emission stop period of the modulated light, and the addition Accumulation control means (accumulation control unit 142) for controlling to accumulate charges obtained from incident light received in time in the discard unit accumulation means.

  As described above, in this embodiment, the light emission period is constant regardless of the period, but the light emission stop period is changed for each period, and the light emission period is randomized as a whole. On the other hand, the charge accumulation period in the distance measurement unit accumulation unit 125 used for calculating the distance value is constant for each period.

  That is, in the present embodiment, the light emission period of the modulated light 151 emitted from the light source 110 and the charge accumulation period of the distance measurement unit accumulation unit 125 of the light receiving unit 120 are distances using a conventional time-of-flight distance sensor. The same as those of the image generation apparatus. For this reason, the distance value using the reflected light of the modulated light from the light source 110 can be obtained with high accuracy by the same distance calculation as before. Further, the light emission time of the light source 110 is shortened, and the accuracy of the calculated distance value is not lowered.

  Furthermore, a random cycle is realized by adding a different additional time Tw for each cycle. This additional time Tw is 100 ns to several μs, which is sufficiently shorter than the accumulation time (several ms) required to acquire one image. For this reason, by adding the additional time Tw, the frame rate does not extremely decrease.

  On the other hand, in the present embodiment, the modulation period of the modulated light 151 is changed for each period to be random. Therefore, the possibility of synchronizing with the modulated light of another distance image generation device in the same imaging space is extremely low. Accordingly, it is possible to suppress the possibility of erroneous distance measurement due to interference between the distance image generation apparatuses.

  Therefore, according to the present embodiment, when the distance image generating device generates a distance image of the shooting space, even if there are a plurality of distance image generating devices in the same shooting space at the same time, complicated processing is performed. Ranging can be performed with high accuracy without being performed.

  In the above-described embodiment, the case where five unit accumulation units 124 are provided, four of which are ranging unit accumulation units 125 and one is a discard unit accumulation unit 126 has been described as an example. The number of unit storage units 124 of the charge storage unit 123 is not limited to this. The number of unit storage units 124 may be any number as long as it is two or more. Regardless of the number of unit storage units 124, one unit storage unit 124 among them is a discard unit storage unit 126 for storing discarded charges, and the rest is a distance measurement unit storage unit 125. The distance measurement unit storage unit 125 can obtain the same effect by controlling to store charges in the same manner as when the additional time Tw is not added to the emission and charge storage.

  For example, there may be three unit accumulating units 124, two of which may be distance measurement unit accumulating units 125 and the other one may be a discard unit accumulating unit 126. An example of a timing chart of the control signal output by the control unit 140 in this case is shown in FIG.

  In this case, the light emission signal TE by the light emission control unit 141 is the same as that in the above embodiment. That is, an additional time Tw is added to a predetermined period Ts, and the signal is output as a signal of the period (Ts + Tw). At this time, every (Ts + Tw) time, the modulated light 151 is generated as a signal for turning on for Ts / 2 and turning off for Ts / 2 + Tw.

  On the other hand, the accumulation control unit 142 generates two gate signals TX1 and TX2 that instruct the charge accumulation timing of the two distance measurement unit accumulation units 125, and a discard gate signal TX5 that instructs accumulation in the discard unit accumulation unit 126. Generate and output.

  The gate signals TX1 and TX2 are generated as signals that are shifted by an effective period (Ts + Tw), an ON period of Ts / 2, and the ON timing, for example, by dividing the set period Ts into two equal parts. Here, a case where the gate signal TX1 is a signal synchronized with the light emission signal TE and the gate signal TX2 is a signal whose ON start timing is shifted from the light emission signal TE and the gate signal TX1 by Ts / 2 is illustrated. Also in this case, the ON periods of the gate signals TX1 and TX2 within the set period Ts are the same over the entire period.

  The discard gate signal TX5 is generated so that the period is an effective period (Ts + Tw) and is ON during a period in which neither of the gate signals TX1 and TX2 is ON. Here, it is generated as a signal that is ON for Tw.

  As a result, the two ranging unit accumulating units 125 accumulate charge information having different start timings, that is, charge information C1 and C2, which are charge information whose accumulation start times are shifted by a time equal to the period Ts. Then, charges for the additional time Tw are accumulated in the discard unit accumulation unit 126. The distance image generation unit 130 calculates the delay time Td from the ratio using the charges C1 and C2, and calculates the distance value D using the delay time Td.

  Further, the number of unit accumulating units 124 may be two. An example of a timing chart of each control signal output by the control unit 140 when there are two unit storage units 124, one of which is the distance measurement unit storage unit 125 and the other of which is the discard unit storage unit 126. Shown in

  In this case, the light emission signal TE is the same as that in the above embodiment. That is, an additional time Tw is added to a predetermined period Ts, and the signal is output as a signal of the period (Ts + Tw). At this time, every (Ts + Tw) time, the modulated light 151 is generated as a signal for turning on for Ts / 2 and turning off for Ts / 2 + Tw.

  On the other hand, among the gate signals generated by the accumulation control unit 142, the gate signal that is the control signal for the distance measurement unit accumulation unit 125 is output as a signal having a cycle of (Ts + Tw) and an ON period of Ts / 2. The discard gate signal is output as a signal having a cycle of (Ts + Tw) and an ON period of (Ts / 2 + Tw). The ON period of the discard gate signal is set to be ON while the gate signal for the distance measurement unit accumulation unit 125 is OFF. Also in this case, the ON period within the set period Ts of the gate signal TX1 is the same over the entire period.

  In this case, only one piece of charge information required for ranging and acquired with a delay at regular intervals can be acquired per cycle. For this reason, when there are two unit accumulating units 124, a plurality of frames are used to acquire charge information with different acquisition timings necessary for distance value calculation. For example, when the distance value D is calculated using four different pieces of charge information as in the above-described embodiment, charge information having different phases is acquired using four frames. Further, as described with reference to FIG. 6, when the distance value D is calculated using two charge amounts having different acquisition timings, the accumulation start time is set for each time obtained by dividing the period Ts into two equal parts using two frames. Acquire the shifted charge information.

  In the above embodiment, the additional time output unit 144 that generates the additional time Tw is not particularly limited. Although the case where it implement | achieved as software by CPU and a microcomputer, and implement | achieved as a circuit using FPGA etc. was mentioned as an example, the structure of the additional time output part 144 is not restricted to this. Any means may be used as long as a different additional time Tw can be generated for each period.

  The additional time output unit 144 may be realized by a random time generation circuit, for example. The random time generation circuit is configured using, for example, a pseudo random number generation circuit. Using this pseudo-random number generation circuit, the additional time Tw is generated in the range of about 100 ns to 10 μs.

  Further, the additional time output unit 144 may be configured by a pattern generation circuit, for example. The pattern generation circuit is a circuit that generates an output order as a pattern. In this case, a predetermined number of additional times Tw are generated in advance and stored as an additional time database. The additional time Tw to be held is, for example, about 1000 from 1 to 1000. According to the pattern (order) generated by the pattern generation circuit, the additional time output unit 144 extracts from the additional time database and outputs it as the additional time Tw.

  An example of the additional time database 301 is shown in FIG. An example of the pattern 302 generated by the pattern generation circuit is shown in FIG. The additional time output unit 144 sequentially extracts the additional time Tw corresponding to the number (No.) of the pattern 302 generated by the pattern generation circuit from the additional time database 301 and outputs it as the additional time Tw for each cycle.

  Further, the additional time output unit 144 may be configured to register the additional time Tw randomly generated in advance as the random additional time database 311 and sequentially output it for each period. At this time, an example of the additional time Tw registered as the random additional time database 311 is shown in FIG. The additional time output unit 144 extracts the additional time Tw in order from the random additional time database 311 for each cycle, and outputs it as the additional time Tw.

  By generating the additional time at random in advance and registering it in the database, a circuit for generating random time and a circuit for generating a pattern become unnecessary. Therefore, the configuration becomes simple and the processing time can be shortened.

  Further, by registering in advance as the random addition time database 311, it is possible to further reduce the possibility of setting Tw that is likely to cause interference.

  Further, the additional time output unit 144 may be realized by a frequency spread control circuit that controls the modulation frequency distribution of the modulated light 151 to be constant.

  FIG. 10A shows the frequency spectrum of the modulated light 151 emitted from the light source 110 when the additional time Tw is zero. In FIG. 10A, the horizontal axis represents frequency [Hz] and the vertical axis represents spectrum intensity [dB]. For example, as shown in the timing chart of FIG. 2, when the additional time Tw is 0, that is, when the modulation of the modulated light 151 is constant and the light source 110 emits light periodically, the frequency spectrum is assumed to be Ts. Has a steep peak at a frequency of 1 / Ts. For example, when the additional time Tw is constant, the light emission cycle of the light source is (Ts + Tw), and thus has a peak at a frequency of 1 / (Ts + Tw).

  FIG. 10B shows a frequency spectrum of the modulated light 151 emitted from the light source 110 when frequency spreading is performed. In FIG. 10B, the horizontal axis represents frequency [Hz] and the vertical axis represents spectrum intensity [dB]. By adding the additional time Tw to the period Ts, the peak of the frequency spectrum moves to the lower frequency side than the frequency 1 / Ts.

  The frequency spread control circuit according to the modification of the present embodiment sets the spread spectrum unit time, and determines and outputs the additional time Tw so as to satisfy the frequency spectrum shown in FIG. 8 for each spread spectrum unit time. The spread spectrum unit time is set to a time sufficiently shorter than the light accumulation time.

  DESCRIPTION OF SYMBOLS 100: Distance image generation apparatus, 101: Distance image generation apparatus, 101: Distance image generation apparatus, 110: Light source, 120: Light-receiving part, 121: Image sensor, 122: Photoelectric conversion element, 123: Charge storage part, 124: Unit Accumulator, 125: Ranging unit accumulator, 126: Discarding unit accumulator, 130: Distance image generator, 140: Controller, 141: Light emission controller, 142: Accumulator controller, 143: Read controller, 144: Additional time output unit, 151: modulated light, 152: incident light, 200: target object, 200: object, 301: additional time database, 302: pattern, 311: random additional time database

Claims (7)

A light source that irradiates the imaging space with modulated light; and a light receiving means that includes a plurality of imaging elements that receive incident light including reflected light that is irradiated from the light source and reflected by an object in the imaging space, and converts the incident light into charges. A distance image generating unit that generates a distance image having a pixel value that is a distance value and the number of pixels is the number of image pickup devices using the charge, and controls a modulation period of the modulated light and charge accumulation in the light receiving unit. A distance image generating device comprising a control means,
Each of the plurality of image sensors is
A photoelectric conversion element that converts received incident light into electric charge;
Charge accumulation means for accumulating the charge, provided for each photoelectric conversion element,
The charge storage means includes a plurality of distance measurement unit storage means for storing charges used by the distance image generation unit for calculating distance values
The control means includes additional time output means for outputting a different additional time for each modulation period of the modulated light, and the modulation period of the modulated light to be irradiated is determined by adding the additional time for each modulation period. A distance image generating apparatus characterized by changing the modulation period for each period and controlling the accumulation period of electric charges in each ranging unit accumulating unit to be the same in all periods. The distance image generating device according to claim 1,
The modulated light is pulsed light that repeats light emission and light emission stop,
The charge storage means further comprises one discard unit storage means for storing charges to be discarded,
The control means includes
Light emission control means for changing the modulation period of the modulated light by adding the additional time to the emission stop period of the modulated light;
And a storage control means for controlling the charge obtained from the incident light received during the additional time to be stored in the discard unit storage means. The distance image generating device according to claim 1 or 2,
The distance image generating device, wherein the additional time output means randomly generates and outputs the additional time. The distance image generating device according to claim 1 or 2,
The distance image generating device, wherein the additional time output means outputs the additional time in a predetermined order from a plurality of different additional times. The distance image generating device according to claim 1 or 2,
The distance image generating apparatus according to claim 1, wherein the additional time output means includes additional time storage means for storing a plurality of different additional times in a predetermined order, and sequentially outputs from the additional time storage means for each period. The distance image generating device according to claim 1 or 2,
The distance image generating device characterized in that the additional time output means determines and outputs the additional time so that the frequency distribution of the modulated light becomes constant every predetermined unit time. A light source that irradiates modulated light to the imaging space, a plurality of photoelectric conversion elements that receive incident light including reflected light that is irradiated from the light source and reflected by an object in the imaging space, and converts the incident light into charges, and the photoelectric conversion A plurality of unit accumulating means for accumulating the electric charge provided for each element, and a distance value is calculated using the electric charge accumulated in the unit accumulating means used for the predetermined distance measurement among the plurality of unit accumulating means. A distance image generation method in a distance image generation device comprising a distance image calculation means,
An additional time generation step of generating an additional time to be added for each modulation period of the modulated light;
For each modulation period, the additional period is added to the modulation period to change the modulation period of the modulated light, and the charge obtained by converting incident light received during the additional period is stored in a unit for disposal. A synchronization control step of accumulating charges in the means and accumulating charges acquired in a predetermined period other than the additional time in a plurality of predetermined unit accumulating means for charge accumulation,
A distance value calculating step of reading a charge accumulated in the unit for storing charges at a predetermined time interval and calculating a distance value that is each pixel value of the distance image. Method.

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