Distance image acquisition device and distance image acquisition method

Abstract

To reduce the effects of interference light and improve the accuracy of distance measurement.SOLUTION: A distance image capturing device comprises: a light receiving unit that includes a plurality of pixel circuits, each having a photoelectric conversion element, a charge storage unit and a transfer transistor, and a pixel drive circuit that causes the charge storage units to separately store the charges at a prescribed timing that is synchronized to the irradiation of optical pulses; a light source unit that irradiates the optical pulses; and a distance image processing unit that measures the distance to a subject as a measurement distance on the basis of the charges stored in each of the charge storage units. The distance image processing unit detects interference light on the basis of the difference between the maximum and minimum values of interference charge amounts that are stored in each of the charge storage units on an equal cycle as when optical pulses are irradiated and at the storage timing while no optical pluses are irradiated before measuring the distance, and when the interference light is detected, changes the optical pulse irradiation timing and the storage timing and measures the measurement distance.SELECTED DRAWING: Figure 1

Description

Technical Field

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[0001] The present invention relates to a distance image capturing device and a distance image capturing method.

Background Art

[0002] Utilizing the fact that the speed of light is known, a distance image capturing device using the Time of Flight (hereinafter referred to as "TOF") method that measures the distance between a measuring device and an object based on the flight time of light in space (measurement space) has been realized (for example, see Patent Document 1). In such a distance image capturing device, the delay time from the time when a light pulse, which is a pulsed near-infrared light, is irradiated until the light pulse reflected from the subject returns is obtained by accumulating the charges generated by a photoelectric conversion element in a plurality of charge accumulation units, and the distance to the subject is calculated using the delay time and the speed of light.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in a conventional distance image capturing device, for example, when a plurality of distance image capturing devices are used in close proximity, there are cases where the light pulses from other distance image capturing devices interfere and the distance to the subject cannot be accurately measured. Thus, in a conventional distance image capturing device, the accuracy of distance measurement may be reduced due to the influence of interference light.

[0005] The present invention has been made to solve the above problems, and an object thereof is to provide a distance image capturing device and a distance image capturing method that can reduce the influence of interference light and improve the accuracy of distance measurement.

Means for Solving the Problems

[0006] To solve the above problem, one aspect of the present invention provides a light receiving unit having a photoelectric conversion element that generates an electric charge corresponding to incident light, which is light incident from a measurement space that is the space to be measured; N (N≧3) charge storage units that store the charge at a predetermined integration period synchronized with the irradiation of an optical pulse; a plurality of pixel circuits each comprising a transfer transistor that transfers the charge from the photoelectric conversion element to each of the charge storage units; and a pixel driving circuit that, at a predetermined storage timing synchronized with the irradiation of the optical pulse, conducts the transfer transistors to each of the charge storage units to distribute and store the charge, and the measurement space The device comprises a light source unit that irradiates the light pulses, and a distance image processing unit that measures the distance to an object in the measurement space as the measurement distance based on the amount of charge accumulated in each of the charge storage units, wherein the distance image processing unit, before executing the integration cycle for measuring the distance, conducts the transfer transistors to the pixel driving circuit at the same period and storage timing as when the light pulses are irradiated, without irradiating the light pulses, and detects interference light based on the difference between the maximum and minimum values ​​of the interference charge amount accumulated in each of the charge storage units, and when interference light is detected, By randomly changing the aforementioned accumulation period, This distance image capturing device is characterized by measuring the measurement distance by changing the irradiation timing and storage timing of the light pulses.

[0007] Furthermore, in one aspect of the present invention, in the distance image acquisition device described above, the distance image processing unit, upon detecting interference light, changes the irradiation timing of the light pulse without changing the integration period, thereby changing the irradiation timing of the light pulse and the accumulation timing.

[0008] Furthermore, in one aspect of the present invention, in the distance image acquisition device described above, the distance image processing unit, upon detecting interference light, shifts the irradiation timing of the light pulses so that the interference light does not overlap with the accumulation timing, thereby changing the start timing of the integration cycle. Furthermore, in one aspect of the present invention, the distance image acquisition device described above is characterized in that the distance image processing unit alternately performs the process of shifting and changing the irradiation timing of the light pulse and the process of detecting the interference light without irradiating the light pulse until the interference light is no longer detected, thereby determining the irradiation timing of the light pulse.

[0009] Furthermore, in one aspect of the present invention, in the above-described distance image acquisition device, the distance image processing unit randomly changes the integration period when it detects interference light. By doing so, The irradiation timing and storage timing of the light pulses are changed. Then, by subtracting the uniform offset value, the measurement distance is measured. It is characterized by the following:

[0010] Furthermore, in one aspect of the present invention, the distance image acquisition device described above is characterized in that the distance image processing unit determines the presence of interference light when the difference between the maximum value and the minimum value is greater than or equal to a threshold.

[0011] Furthermore, in one aspect of the present invention, in the distance image acquisition device described above, the distance image processing unit measures the measurement distance without changing the integration period and the start timing of the integration period when interference light is not detected.

[0012] Furthermore, one aspect of the present invention includes a photoelectric conversion element that generates an electric charge corresponding to incident light, which is light incident from a measurement space that is the space to be measured; N (N≧3) charge storage units that store the charge at a predetermined integration period synchronized with the irradiation of an optical pulse; a plurality of pixel circuits each comprising a transfer transistor that transfers the charge from the photoelectric conversion element to each of the charge storage units; a pixel driving circuit that, at a predetermined storage timing synchronized with the irradiation of the optical pulse, conducts the transfer transistors to each of the charge storage units to distribute and store the charge; a light source unit that irradiates the measurement space with the optical pulse; and the charge storage units A distance image imaging apparatus comprising a distance image processing unit that measures the distance to an object in the measurement space as a measurement distance based on the amount of charge accumulated therein, a distance image imaging apparatus imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging apparatus distance imaging By randomly changing the aforementioned accumulation period, The distance image acquisition method is characterized by including a timing adjustment step of changing the irradiation timing of the light pulse and the accumulation timing to measure the measurement distance. [Effects of the Invention]

[0013] According to the present invention, the effects of interference light can be reduced and the accuracy of distance measurement can be improved. [Brief explanation of the drawing]

[0014] [Figure 1] This is a block diagram showing an example of a distance image acquisition device according to the first embodiment. [Figure 2] This is a block diagram showing an example of a distance image sensor in the first embodiment. [Figure 3] This is a block diagram showing an example of a pixel circuit in the first embodiment. [Figure 4] It is a timing chart showing an example of the distance measurement process of the distance image capturing device according to the first embodiment. [Figure 5] It is a timing chart showing an example of the detection process of interference light of the distance image capturing device according to the first embodiment. [Figure 6] It is a timing chart showing an example of the timing adjustment process of the distance image capturing device according to the first embodiment. [Figure 7] It is a flowchart showing an example of the operation of the distance image capturing device according to the first embodiment. [Figure 8] It is a block diagram showing an example of the distance image capturing device according to the second embodiment. [Figure 9] It is a timing chart showing an example of the timing adjustment process of the distance image capturing device according to the second embodiment. [Figure 10] It is a flowchart showing an example of the operation of the distance image capturing device according to the second embodiment.

Embodiments for Carrying Out the Invention

[0015] Hereinafter, a distance image capturing device and a distance image capturing method according to an embodiment of the present invention will be described with reference to the drawings.

[0016] [First Embodiment] FIG. 1 is a block diagram showing an example of a distance image capturing device 1 according to the first embodiment. As shown in FIG. 1, the distance image capturing device 1 includes a light source unit 2, a light receiving unit 3, and a distance image processing unit 4. In FIG. 1, the subject S, which is an object for measuring the distance using the distance image capturing device 1, is also shown. The distance image capturing element is, for example, a distance image sensor 32 (described later) in the light receiving unit 3.

[0017] The light source unit 2, in accordance with control from the distance image processing unit 4, irradiates the space where the object S, whose distance is to be measured by the distance image acquisition device 1, is located with an optical pulse PO. The light source unit 2 is, for example, a surface-emitting semiconductor laser module such as a vertical cavity surface-emitting laser (VCSEL). Furthermore, the light source unit 2 includes a light source device 21 and a diffuser plate 22.

[0018] The light source device 21 is a light source that emits laser light in the near-infrared wavelength band (for example, a wavelength band of 850 nm to 940 nm) which becomes the optical pulse PO irradiated onto the subject S. The light source device 21 is, for example, a semiconductor laser light-emitting element. The light source device 21 emits pulsed laser light in response to control from the measurement control unit 44.

[0019] The diffuser plate 22 is an optical component that diffuses the near-infrared wavelength laser light emitted by the light source device 21 over a surface area that illuminates the subject S. The pulsed laser light diffused by the diffuser plate 22 is emitted as an optical pulse PO and irradiates the subject S.

[0020] The light-receiving unit 3 receives the reflected light RL of the light pulse PO reflected by the subject S whose distance is to be measured in the distance image capturing device 1, and outputs a pixel signal corresponding to the received reflected light RL. The light-receiving unit 3 comprises a lens 31 and a distance image sensor 32.

[0021] Lens 31 is an optical lens that guides the incident reflected light RL to the distance image sensor 32. Lens 31 emits the incident reflected light RL towards the distance image sensor 32, causing it to be received (incident) by the pixel circuit 321 located in the light-receiving area of ​​the distance image sensor 32.

[0022] The distance image sensor 32 is an image sensor used in the distance image acquisition device 1. The distance image sensor 32 comprises a plurality of pixel circuits 321 in a two-dimensional light-receiving area and a pixel driving circuit 322 that controls each of the pixel circuits 321.

[0023] The pixel circuit 321 includes one photoelectric conversion element (for example, the photoelectric conversion element PD described later), a plurality of charge storage units corresponding to this one photoelectric conversion element (for example, the charge storage units CS (CS1 to CS4) described later), and components that distribute charge to each charge storage unit.

[0024] The pixel driving circuit 322 conducts the transfer transistor G (described later) to each of the charge storage units CS (CS1 to CS4) at a predetermined storage timing synchronized with the irradiation of the light pulse PO, thereby distributing and storing the charge. Details of the distance image sensor 32, which includes the pixel circuit 321 and the pixel driving circuit 322, will be described later with reference to Figure 2.

[0025] The distance image sensor 32 distributes the charge generated by the photoelectric conversion element to its respective charge storage units in response to control from the measurement control unit 44. The distance image sensor 32 also outputs a pixel signal corresponding to the amount of charge distributed to the charge storage units. The distance image sensor 32 has multiple pixel circuits arranged in a two-dimensional matrix, and outputs a pixel signal for one frame corresponding to each pixel circuit.

[0026] Now, with reference to Figure 2, the detailed configuration of the distance image sensor 32 will be described. Figure 2 is a block diagram showing an example of a distance image sensor in this embodiment.

[0027] As shown in Figure 2, the distance image sensor 32 includes, for example, a light-receiving area 320 on which multiple pixel circuits 321 are arranged, and a pixel driving circuit 322. The pixel driving circuit 322 also includes a vertical scanning circuit 323 with distribution operation, a horizontal scanning circuit 324, a pixel signal processing circuit 325, and a control circuit 326.

[0028] The light-receiving region 320 is a region in which multiple pixel circuits 321 are arranged, and Figure 2 shows an example in which they are arranged in a two-dimensional matrix with 8 rows and 8 columns. The pixel circuit 321 stores charge equivalent to the amount of light received. The detailed configuration of the pixel circuit 321 will be described later with reference to Figure 3.

[0029] The control circuit 326 comprehensively controls the distance image sensor 32. For example, the control circuit 326 controls the operation of the components of the distance image sensor 32 in response to instructions from the measurement control unit 44 of the distance image processing unit 4. In addition, the control of the components of the distance image sensor 32 may be directly performed by the measurement control unit 44, in which case the control circuit 326 can be omitted.

[0030] The vertical scanning circuit 323 controls the pixel circuits 321 arranged in the light-receiving area 320 row by row in response to control from the control circuit 326. The vertical scanning circuit 323 causes the pixel signal processing circuit 325 to output a voltage signal corresponding to the amount of charge stored in each of the charge storage units CS of the pixel circuits 321. In this case, the vertical scanning circuit 323 distributes and stores the charge converted by the photoelectric conversion element in each of the charge storage units of the pixel circuits 321.

[0031] The pixel signal processing circuit 325 performs predetermined signal processing (for example, noise suppression processing or A / D conversion processing) on ​​the voltage signals output from the pixel circuits 321 of each row, in response to control from the control circuit 326.

[0032] The horizontal scanning circuit 324 is a circuit that sequentially outputs the signals output from the pixel signal processing circuit 325 in a time series, in response to control from the control circuit 326. As a result, pixel signals corresponding to the amount of charge accumulated for one frame are sequentially output to the distance image processing unit 4. In the following description, it is assumed that the pixel signal processing circuit 325 performs A / D conversion processing and that the pixel signals are digital signals.

[0033] Next, referring to Figure 3, the configuration of the pixel circuit 321 located within the light-receiving area 320 of the distance image sensor 32 will be described. Figure 3 is a block diagram showing an example of the pixel circuit 321 in this embodiment. Note that the pixel circuit 321 shown in Figure 3 is an example configuration equipped with four pixel signal readout units RU (RU1 to RU4).

[0034] As shown in Figure 3, the pixel circuit 321 comprises one photoelectric conversion element PD, a charge discharge transistor GD, and four pixel signal readout units RU (RU1 to RU4) that output voltage signals from their corresponding output terminals O (O1 to O4). Each of the pixel signal readout units RU comprises a transfer transistor G, a floating diffusion FD, a charge storage capacitor C, a reset transistor RT, a source follower transistor SF, and a selection transistor SL. The floating diffusion FD and the charge storage capacitor C constitute a charge storage unit CS.

[0035] In the pixel circuit 321 shown in Figure 3, the pixel signal readout unit RU1, which outputs a voltage signal from the output terminal O1, comprises a transfer transistor G1, a floating diffusion transistor FD1, a charge storage capacitor C1, a reset transistor RT1, a source follower transistor SF1, and a selection transistor SL1. In the pixel signal readout unit RU1, the floating diffusion transistor FD1 and the charge storage capacitor C1 constitute a charge storage unit CS1. Pixel signal readout units RU2 to RU4 have a similar configuration.

[0036] The photoelectric conversion element (PD) is an embedded photodiode that converts incident light into electricity to generate an electric charge corresponding to the incident light, and stores the generated charge. In this embodiment, the incident light is introduced from the space being measured.

[0037] In the pixel circuit 321, the photoelectric conversion element PD converts incident light into electricity to generate charge, which is then distributed to each of the four charge storage units CS (CS1 to CS4). The voltage signals corresponding to the amount of charge distributed are then output to the pixel signal processing circuit 325.

[0038] Furthermore, the configuration of the pixel circuit arranged in the distance image sensor 32 is not limited to the configuration with four pixel signal readout units RU (RU1 to RU4) as shown in Figure 3, but may also be a pixel circuit with one or more pixel signal readout units RU.

[0039] Furthermore, in driving the pixel circuit 321, an optical pulse PO is irradiated at irradiation time To, and the reflected light RL is received by the distance image sensor 32 after a delay time Td. The pixel driving circuit 322, under control by the measurement control unit 44, synchronizes with the irradiation of the optical pulse PO and distributes the charge generated in the photoelectric conversion element PD to the transfer transistors G (G1, G2, G3, G4) by supplying accumulation drive signals TX1 to TX4 at their respective timings, thereby accumulating the charge in the charge accumulation units CS1, CS2, CS3, and CS4 in that order.

[0040] The pixel driving circuit 322 controls the reset transistor RT and the selection transistor SL respectively using the driving signals RST and SEL, converts the charge stored in the charge storage unit CS into an electrical signal using the source follower transistor SF, and outputs the generated electrical signal to the distance calculation unit 43 via the output terminal O.

[0041] Furthermore, the pixel driving circuit 322, under the control of the measurement control unit 44, discharges the charge generated in the photoelectric conversion element PD by sending it to the power supply VDD via the driving signal RSTD (erasing the charge).

[0042] Returning to the explanation of Figure 1, the distance image processing unit 4 controls the distance image acquisition device 1 and calculates the distance to the subject S. Based on the amount of charge accumulated in each of the charge storage units CS, the distance image processing unit 4 measures the distance to the subject S in the measurement space as the measured distance. Furthermore, the distance image processing unit 4 includes an interference light detection unit 41, a timing adjustment unit 42, a distance calculation unit 43, and a measurement control unit 44.

[0043] The distance calculation unit 43, in response to the control of the measurement control unit 44, outputs distance information (quantized as gradation) calculated from the distance image imaging device 1 (each pixel) to the subject S based on the pixel signal (voltage value corresponding to the amount of accumulated charge) output from the distance image sensor 32.

[0044] The distance calculation unit 43 calculates the delay time Td from the time the optical pulse PO is irradiated until the reflected light RL is received, based on the amount of charge accumulated in the multiple charge storage units CS. The distance calculation unit 43 calculates the distance from the distance image acquisition device 1 to the subject S according to the calculated delay time Td.

[0045] The measurement control unit 44 controls the timing of outputting various control signals required for distance measurement, thereby controlling the calculations in the distance calculation unit 43. These various control signals include, for example, signals that control the irradiation of the light pulse PO, signals that distribute the reflected light RL to multiple charge storage units (storage drive signal TX that operates the transfer transistor G described later), and signals that control the number of distributions per frame. The number of distributions is the number of times the process of distributing the charge generated by the incident light from the photoelectric conversion element PD to the charge storage unit CS via the transfer transistor G is repeated.

[0046] The measurement control unit 44 irradiates the light source unit 2 with an optical pulse PO at an integration cycle, and acquires the amount of charge in the charge storage unit CS, which is stored by distributing the charge, from the light receiving unit 3 at a predetermined accumulation timing synchronized with the irradiation of the optical pulse PO. The measurement control unit 44 instructs the distance calculation unit 43 to calculate the measurement distance using the amount of charge stored in each of the charge storage units CS acquired from the light receiving unit 3. Here, the integration cycle is a predetermined cycle synchronized with the optical pulse PO, and is repeated the number of distribution cycles in one frame during distance measurement.

[0047] The interference light detection unit 41 conducts each of the transfer transistors G to the pixel driving circuit 322 at the same (equivalent) period and accumulation timing as when the optical pulse PO is irradiated, but without irradiating with the optical pulse PO, before the accumulation period for measuring distance by the measurement control unit 44 described above. The interference light detection unit 41 detects interference light based on the difference between the maximum and minimum values ​​of the interference charge amount accumulated in each of the charge accumulation units CS without irradiating with the optical pulse PO.

[0048] The interference light detection unit 41 determines, for example, that interference light is present if the difference between the maximum and minimum values ​​of the interference charge is greater than or equal to a predetermined threshold. The interference light detection unit 41 also determines, for example, that there is no interference light if the difference between the maximum and minimum values ​​of the interference charge is less than a predetermined threshold.

[0049] The timing adjustment unit 42 changes the irradiation timing and accumulation timing of the optical pulse PO when the interference light detection unit 41 detects interference light. In other words, the timing adjustment unit 42 changes the control timing by the measurement control unit 44 when the interference light detection unit 41 detects interference light.

[0050] When the interference light detection unit 41 detects interference light, the timing adjustment unit 42 changes the irradiation timing of the optical pulse PO without changing the integration period, thereby changing the irradiation timing and accumulation timing of the optical pulse PO. Specifically, when the distance image processing unit 4 detects interference light, it shifts the irradiation timing of the optical pulse PO so that the interference light does not overlap with the accumulation timing, thereby changing the start timing of the integration period.

[0051] By changing the start timing of the integration cycle using the timing adjustment unit 42, the measurement control unit 44, when the interference light detection unit 41 detects interference light, executes control to change the start timing of the integration cycle so that the interference light does not overlap, and causes the distance calculation unit 43 to calculate the measured distance.

[0052] Furthermore, the distance image processing unit 4 (measurement control unit 44) measures the distance without changing the integration period or the start timing of the integration period if the interference light detection unit 41 does not detect interference light. In other words, the timing adjustment unit 42 does not perform the timing adjustment described above if the interference light detection unit 41 does not detect interference light.

[0053] Next, the operation of the distance image acquisition device 1 according to this embodiment will be described with reference to the drawings. First, referring to Figures 1 to 3, the basic operation of the distance measurement device 1 will be explained.

[0054] In driving the pixel circuit 321 of the distance image acquisition device 1, an optical pulse PO is irradiated at irradiation time To, and the reflected light RL is received by the distance image sensor 32 after a delay time Td. The vertical scanning circuit 323, in synchronization with the irradiation of the optical pulse PO, distributes the charge generated in the photoelectric conversion element PD to the charge storage units CS1, CS2, CS3, and CS4 in that order, and stores it in each of them.

[0055] At this time, the vertical scanning circuit 323 turns on the transfer transistor G1, which is located on the transfer path that transfers charge from the photoelectric conversion element PD to the charge storage unit CS1, (conducting state). As a result, the charge photoelectrically converted by the photoelectric conversion element PD is stored in the charge storage unit CS1 via the transfer transistor G1. Subsequently, the vertical scanning circuit 323 turns off the transfer transistor G1 (non-conducting state). As a result, the transfer of charge to the charge storage unit CS1 is stopped. In this way, the vertical scanning circuit 323 stores charge in the charge storage unit CS1. The same applies to the charge storage units CS2 to CS4.

[0056] During the charge storage period in which charge is distributed to the charge storage unit CS, the storage drive signals TX1 to TX4 are each supplied to the transfer transistors G1 to G4, respectively, and the storage cycle is repeated.

[0057] Then, charge corresponding to the incident light is transferred from the photoelectric conversion element PD to the charge storage units CS1 to CS4, respectively, via the transfer transistors G1 to G4. Multiple storage cycles are repeated during the charge storage period. As a result, charge is accumulated in each of the charge storage units CS1 to CS4 during each storage cycle of the charge storage period.

[0058] Furthermore, when the vertical scanning circuit 323 repeats the storage cycle of each of the charge storage units CS1 to CS4, after the transfer (redistribution) of charge to the charge storage unit CS4 is completed, it turns on the charge discharge transistor GD provided on the discharge path that discharges charge from the photoelectric conversion element PD.

[0059] As a result, the charge discharge transistor GD discards the charge generated in the photoelectric conversion element PD after the previous charge storage cycle of the charge storage unit CS4 before the storage cycle for the charge storage unit CS1 begins (i.e., it resets the photoelectric conversion element PD).

[0060] The vertical scanning circuit 323 then sequentially outputs voltage signals from each of the pixel circuits 321 arranged within the light-receiving area 320 to the pixel signal processing circuit 325, in units of rows (horizontal arrangement) of the pixel circuits 321. The pixel signal processing circuit 325 then performs signal processing, such as A / D conversion, on each of the input voltage signals and outputs them to the horizontal scanning circuit 324. The horizontal scanning circuit 324 outputs the voltage signals, after signal processing, to the distance calculation unit 43 sequentially in the order of the rows of light-receiving areas 320.

[0061] As described above, the accumulation of charge in the charge storage unit CS by the vertical scanning circuit 323 and the discarding of charge photoelectrically converted by the photoelectric conversion element PD are repeatedly performed over one frame. As a result, a charge equivalent to the amount of light received by the distance image imaging device 1 during a predetermined time interval is accumulated in each of the charge storage units CS. The horizontal scanning circuit 324 outputs an electrical signal equivalent to the amount of charge accumulated in each of the charge storage units CS for one frame to the distance calculation unit 43.

[0062] The distance calculation unit 43 calculates the delay time Td based on the charge amounts Q1 to Q4 stored in each of the charge storage units CS. The distance calculation unit 43 calculates the round-trip distance to the subject S by multiplying the calculated delay time Td by the speed of light (velocity). Then, the distance calculation unit 43 calculates the distance to the subject S by dividing the round-trip distance calculated above by half.

[0063] Figure 4 is a timing chart diagram showing an example of the distance measurement process of the distance image acquisition device 1 according to this embodiment. Here, we will describe the distance measurement process in the absence of interference light.

[0064] In Figure 4, waveforms W1 to W8, from top to bottom, represent, respectively, the irradiation timing signal L of the optical pulse PO, the incident timing signal Lr of the reflected light RL, the incident timing signal Li of the interference light, the conduction timing of the transfer transistors G (G1 to G4), and the conduction timing of the charge discharge transistor GD. The horizontal axis represents time.

[0065] In Figure 4, the period Ta represents the time from the start of irradiation with the light pulse PO to the start of conduction of the transfer transistor G1. The period T represents the emission period (integrated period).

[0066] The example shown in Figure 4 illustrates a case where reflected light RL is incident on transfer transistors G1 (waveform W4) and G2 (waveform W5). Furthermore, for example, as shown by the dashed line in waveform W3, when interference light is incident on transfer transistor G3 (waveform W6) and transfer transistor G4 (waveform W7), charge accumulates not only in charge storage units CS1 and CS2, but also in charge storage units CS3 and CS4. As a result, the distance measurement accuracy of conventional distance image acquisition devices decreases.

[0067] In contrast, the distance image acquisition device 1 according to this embodiment detects the presence or absence of interference light by conducting the transfer transistors G (G1 to G4) without irradiating with optical pulse PO, as shown in Figure 5, before measuring the distance at the timing shown in Figure 4.

[0068] It should be noted that the interfering light referred to here is, for example, light pulses from other distance image capturing devices 1, such as when multiple distance image capturing devices 1 are used in close proximity, and is assumed to be light (interfering light) that is incident periodically with a period equivalent to that of the distance image capturing device 1.

[0069] Figure 5 is a timing chart diagram showing an example of the interference light detection process of the distance image acquisition device 1 according to this embodiment. In Figure 5, waveforms W11 to W18 are, from top to bottom, the same as waveforms W1 to W8 shown in Figure 4 above. The horizontal axis represents time.

[0070] In the example shown in Figure 5, similar to the example shown in Figure 4, interference light is incident on transfer transistor G3 (waveform W6) and transfer transistor G4 (waveform W7), and charge is accumulated in charge storage units CS3 and CS4. As a result, the difference between the maximum value (charge amount Q3 or Q4) and the minimum value (charge amount Q1 or Q2) of the interference charge amount becomes greater than or equal to a predetermined threshold, and the interference light detection unit 41 determines that interference light is present.

[0071] Figure 6 is a timing chart diagram showing an example of the timing adjustment process of the distance image acquisition device 1 according to this embodiment. In Figure 6, waveforms W21 to W28 are, from top to bottom, the same as waveforms W1 to W8 shown in Figure 4 above. The horizontal axis represents time.

[0072] The example shown in Figure 6 illustrates the timing adjustment process when interference light is detected by the interference light detection process shown in Figure 5. As shown in Figure 6, the timing adjustment unit 42 changes the start timing of the integration cycle by shifting the irradiation timing of the optical pulse PO so that the interference light does not overlap with the accumulation timing.

[0073] In the example shown in Figure 6, the timing adjustment unit 42 shifts the timing of the start of irradiation of the optical pulse PO without changing the period Ta and the integration period T, so that the incidence timing of the interference light (signal Li) coincides with the off period (drain period) of the charge discharge transistor GD (waveforms W23 and W28).

[0074] The timing adjustment unit 42 may also determine the timing of the start of irradiation of the optical pulse PO (the start timing of the integration period T) by alternately performing the following processes: shifting and changing the timing of the start of irradiation of the optical pulse PO (the start timing of the integration period T), and detecting interference light by the interference light detection unit 41 without irradiating with the optical pulse PO, until the difference between the maximum and minimum values ​​of the interference charge amount falls below a threshold.

[0075] Figure 7 is a flowchart showing an example of the operation of the distance image acquisition device 1 according to this embodiment.

[0076] As shown in Figure 7, the distance image acquisition device 1 first conducts each of the transfer transistors G to the pixel drive circuit 322 without irradiating with the light pulse PO, and with the same period and accumulation timing as when the light pulse PO is irradiated (step S101). The interference light detection unit 41 of the distance image acquisition device 1 turns on the transfer transistors G (G1 to G4) in sequence, for example, as shown in Figure 5.

[0077] Next, the interference light detection unit 41 determines whether the difference between the maximum and minimum values ​​of the interference charge is greater than or equal to a threshold (step S102). The interference light detection unit 41 detects the presence or absence of interference light based on whether the difference between the maximum and minimum values ​​of the interference charge is greater than or equal to a threshold. If the difference between the maximum and minimum values ​​of the interference charge is greater than or equal to a threshold (step S102: YES), the interference light detection unit 41 proceeds to step S103. If the difference between the maximum and minimum values ​​of the interference charge is less than a threshold (step S102: NO), the interference light detection unit 41 proceeds to step S105.

[0078] In step S103, the distance image acquisition device 1 determines that interference light is present and changes the start timing of the integration cycle by shifting the irradiation timing of the optical pulse PO so that the interference light does not overlap with the accumulation timing. The interference light detection unit 41 determines that interference light is present, and the timing adjustment unit 42 of the distance image acquisition device 1 changes the start timing of the integration cycle by shifting the irradiation timing of the optical pulse PO, for example, as shown in Figure 6.

[0079] Next, the distance image acquisition device 1 measures the distance by changing the irradiation timing and accumulation timing of the light pulse PO according to the accumulation period of the changed start timing (step S104). The measurement control unit 44 controls the irradiation timing and accumulation timing of the light pulse PO by changing them, for example, as shown in Figure 6, and the distance calculation unit 43 obtains the charge amounts Q1 to Q4 accumulated in each of the charge accumulation units CS and calculates the delay time Td using the charge amounts Q1 to Q4 accumulated in each of the charge accumulation units CS. The distance calculation unit 43 calculates the round-trip distance to the subject S by multiplying the calculated delay time Td by the speed of light (velocity). After the processing in step S104, the distance image acquisition device 1 terminates the process.

[0080] Furthermore, in step S105, the distance image acquisition device 1 determines that interference light is present and measures the measurement distance at the initial integration period. The measurement control unit 44 controls the irradiation timing and accumulation timing of the light pulse PO, for example, as shown in Figure 4, and the distance calculation unit 43 obtains the charge amounts Q1 to Q4 accumulated in each of the charge accumulation units CS, and calculates the delay time Td using the charge amounts Q1 to Q4 accumulated in each of the charge accumulation units CS. The distance calculation unit 43 calculates the round-trip distance to the subject S by multiplying the calculated delay time Td by the speed of light (velocity). After processing in step S105, the distance image acquisition device 1 terminates processing.

[0081] As described above, the distance image imaging device 1 according to this embodiment comprises a light receiving unit 3, a light source unit 2, and a distance image processing unit 4. The light receiving unit 3 has a plurality of pixel circuits 321 and a pixel driving circuit 322. The plurality of pixel circuits 321 comprises a photoelectric conversion element PD, N (N≧3) charge storage units CS, and a transfer transistor G. The photoelectric conversion element PD generates charge corresponding to the incident light, which is light incident from the measurement space, which is the space to be measured. The N (N≧3) charge storage units CS store charge at a predetermined integration period synchronized with the irradiation of the light pulse. The transfer transistor G transfers charge from the photoelectric conversion element PD to each of the charge storage units CS. The pixel driving circuit 322 conducts the transfer transistor G to each of the charge storage units CS at a predetermined storage timing synchronized with the irradiation of the light pulse PO, thereby distributing and storing the charge. The light source unit 2 irradiates the measurement space with the light pulse PO. The distance image processing unit 4 measures the distance to the subject S in the measurement space as the measurement distance based on the amount of charge accumulated in each of the charge storage units CS. Furthermore, before executing the integration cycle for measuring the distance, the distance image processing unit 4 conducts each of the transfer transistors G in the pixel driving circuit 322 without irradiating with the light pulse PO, but at the same period and accumulation timing as when the light pulse PO is irradiated, and detects interference light based on the difference between the maximum and minimum values ​​of the interference charge amount accumulated in each of the charge storage units CS. When interference light is detected, the distance image processing unit 4 changes the irradiation timing and accumulation timing of the light pulse PO and measures the measurement distance.

[0082] As a result, the distance image acquisition device 1 according to this embodiment can reduce the influence of interference light and improve the accuracy of distance measurement by changing the irradiation timing and accumulation timing of the optical pulse PO when interference light is detected.

[0083] Furthermore, in this embodiment, when the distance image processing unit 4 detects interference light, it changes the irradiation timing of the optical pulse PO without changing the integration period, thereby changing the irradiation timing and accumulation timing of the optical pulse PO. That is, when the distance image processing unit 4 detects interference light, it shifts the irradiation timing of the optical pulse PO so that the interference light does not overlap with the accumulation timing, thereby changing the start timing of the integration period.

[0084] As a result, the distance image acquisition device 1 according to this embodiment can appropriately reduce the influence of interference light by a simple method, for example, by shifting the irradiation timing of the optical pulse PO so that interference light does not overlap with the accumulation timing, as shown in Figure 6.

[0085] Furthermore, in this embodiment, the distance image processing unit 4 determines that interference light is present when the difference between the maximum and minimum values ​​of the interference charge is greater than or equal to a threshold. As a result, the distance image acquisition device 1 according to this embodiment can appropriately detect interference light using a simple method.

[0086] Furthermore, in this embodiment, if interference light is not detected, the distance image processing unit 4 measures the measurement distance without changing the integration period or the start timing of the integration period. As a result, the distance image acquisition device 1 according to this embodiment can appropriately reduce the influence of interference light.

[0087] Furthermore, in this embodiment, the timing adjustment unit 42 may alternately perform the following processes until the difference between the maximum and minimum values ​​of the interference charge amount falls below a threshold: a process to shift and change the timing of the start of irradiation of the optical pulse PO (the start timing of the integration period T); and a process to detect interference light by the interference light detection unit 41 without irradiating with the optical pulse PO.

[0088] As a result, the distance image acquisition device 1 according to this embodiment can appropriately determine the timing of the start of irradiation of the optical pulse PO (the start timing of the integration period T) so that interference light does not overlap with the accumulation timing.

[0089] Furthermore, the distance image acquisition method according to this embodiment is a distance image acquisition method for a distance image acquisition device 1 comprising the light receiving unit 3, the light source unit 2, and the distance image processing unit 4 described above, and includes an interference light detection step and a timing adjustment step. In the interference light detection step, the distance image processing unit 4, before executing the integration cycle for measuring distance, conducts each of the transfer transistors G to the pixel driving circuit 322 without irradiating with an optical pulse PO, and at the same period and accumulation timing as when the optical pulse PO is irradiated, and detects interference light based on the difference between the maximum and minimum values ​​of the interference charge amount accumulated in each of the charge accumulation units CS. In the timing adjustment step, when the distance image processing unit 4 detects interference light, it changes the irradiation timing and accumulation timing of the optical pulse PO and measures the measurement distance.

[0090] As a result, the distance image acquisition method according to this embodiment achieves the same effects as the distance image acquisition device 1 described above, reducing the influence of interference light and improving the accuracy of distance measurement.

[0091] [Second Embodiment] Next, with reference to the drawings, a distance image acquisition device 1a according to a second embodiment will be described.

[0092] Figure 8 is a block diagram showing an example of a distance image acquisition device 1a according to the second embodiment. As shown in Figure 8, the distance image acquisition device 1a comprises a light source unit 2, a light receiving unit 3, and a distance image processing unit 4a.

[0093] In Figure 8, components identical to those shown in Figure 1 are given the same reference numerals, and their explanations are omitted. Also, as in Figure 1, Figure 8 shows the subject S, which is the object whose distance is measured using the distance image acquisition device 1a.

[0094] The distance image processing unit 4a controls the distance image acquisition device 1a and calculates the distance to the subject S. Based on the amount of charge accumulated in each of the charge accumulation units CS, the distance image processing unit 4a measures the distance to the subject S in the measurement space as the measurement distance. For example, when interference light is detected, the distance image processing unit 4a randomly changes the integration period to change the irradiation timing and accumulation timing of the light pulse PO. Furthermore, the distance image processing unit 4a includes an interference light detection unit 41, a timing adjustment unit 42a, a distance calculation unit 43, and a measurement control unit 44.

[0095] When interference light is detected, the timing adjustment unit 42a randomly changes the integration period to alter the irradiation timing and accumulation timing of the optical pulse PO.

[0096] Now, with reference to Figure 9, the timing adjustment process of the distance image acquisition device 1a according to this embodiment will be described. Figure 9 is a timing chart diagram showing an example of the timing adjustment process for the distance image acquisition device according to this embodiment.

[0097] In Figure 9, waveforms W31 to W38 are, from top to bottom, the same as waveforms W1 to W8 shown in Figure 4 above. The horizontal axis represents time.

[0098] The example shown in Figure 9 illustrates a modified timing adjustment process when interference light is detected by the interference light detection process shown in Figure 5. As shown in Figure 9, the timing adjustment unit 42a changes the irradiation timing and accumulation timing of the optical pulse PO by randomly changing the integration period.

[0099] In the example shown in Figure 9, the timing adjustment unit 42a randomly changes the integration period, for example, to integration period T1, integration period T2, and integration period T3 (see waveforms W31 to W38).

[0100] Figure 10 is a flowchart showing an example of the operation of the distance image acquisition device 1a according to this embodiment.

[0101] In Figure 10, the processes in steps S201 and S202 are the same as those in steps S101 and S102 shown in Figure 7 above, so their explanation is omitted here. In step S202, the interference light detection unit 41 proceeds to step S203 if the difference between the maximum and minimum values ​​of the interference charge is greater than or equal to a threshold (step S202: YES). Also, the interference light detection unit 41 proceeds to step S205 if the difference between the maximum and minimum values ​​of the interference charge is less than a threshold (step S202: NO).

[0102] In step S203, the distance image acquisition device 1a determines that interference light is present and randomly changes the integration period. The interference light detection unit 41 determines that interference light is present, and the timing adjustment unit 42a of the distance image acquisition device 1a changes the start timing of the integration period by randomly changing the integration period, for example, as shown in Figure 9.

[0103] Next, the distance image acquisition device 1a measures the distance by changing the irradiation timing and accumulation timing of the light pulse PO according to a randomly changed accumulation period (step S204). The measurement control unit 44 controls the irradiation timing and accumulation timing of the light pulse PO by changing them, for example, as shown in Figure 9, and the distance calculation unit 43 obtains the charge amounts Q1 to Q4 accumulated in each of the charge accumulation units CS and calculates the delay time Td using the charge amounts Q1 to Q4 accumulated in each of the charge accumulation units CS. The distance calculation unit 43 calculates the round-trip distance to the subject S by multiplying the calculated delay time Td by the speed of light (velocity). After the processing in step S204, the distance image acquisition device 1a terminates its processing.

[0104] Furthermore, since the process in step S205 is the same as the process in step S105 shown in Figure 7 above, its explanation will be omitted here.

[0105] As described above, the distance image acquisition device 1a according to this embodiment includes a distance image processing unit 4a. When interference light is detected, the distance image processing unit 4a randomly changes the integration period to change the irradiation timing and accumulation timing of the optical pulse PO.

[0106] As a result, the distance image imaging device 1a according to this embodiment randomly changes the integration period, causing interference light to be incident on transfer transistors G1 to G4 at random timings. Therefore, by increasing the number of distribution cycles (the number of times the charge distribution process is repeated) of the distance image imaging device 1a according to this embodiment, the amount of charge due to the incident interference light is made uniform for the charge amounts Q1 to Q4 accumulated in each of the charge storage units CS. Thus, the distance image imaging device 1a according to this embodiment can eliminate the effect of interference light by subtracting the uniformized offset value. In other words, the distance image imaging device 1a according to this embodiment can reduce the effect of interference light and improve the accuracy of distance measurement.

[0107] It should be noted that the present invention is not limited to the embodiments described above, and can be modified without departing from the spirit of the invention. For example, in each of the embodiments described above, the pixel circuit 321 is shown to have four charge storage units CS (CS1, CS2, CS3, CS4), but it is not limited to this, and may have three or more N charge storage units CS.

[0108] Furthermore, although the above embodiments describe an example in which the distance image processing unit 4(4a) is located inside the distance image capturing device 1(1a), the invention is not limited to this, and the distance image processing unit 4(4a) may be located outside the distance image capturing device 1(1a).

[0109] Furthermore, in each of the embodiments described above, the photoelectric conversion element PD was described as an embedded photodiode that converts incident light photoelectrically to generate charge and stores the generated charge, but it is not limited to this, and the structure of the photoelectric conversion element PD can be arbitrary. The photoelectric conversion element PD may be, for example, a PN photodiode with a structure in which a P-type semiconductor and an N-type semiconductor are joined, or a PIN photodiode with a structure in which an I-type semiconductor is sandwiched between a P-type semiconductor and an N-type semiconductor. Moreover, the photoelectric conversion element PD is not limited to a photodiode, but may be, for example, a photogate type photoelectric conversion element.

[0110] Furthermore, each component of the distance image acquisition device 1(1a) described above has a computer system inside. The processing in each component of the distance image acquisition device 1(1a) described above may be performed by recording a program for realizing the functions of each component of the distance image acquisition device 1(1a) onto a computer-readable recording medium, loading the program recorded on this recording medium into the computer system, and executing it. Here, "loading the program recorded on the recording medium into the computer system and executing it" includes installing the program into the computer system. Here, "computer system" includes hardware such as the OS and peripheral devices.

[0111] Furthermore, "computer system" may include multiple computer devices connected via a network, including communication lines such as the Internet, WAN, LAN, and dedicated lines. "Computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Thus, the recording medium storing the program may be a non-transient recording medium such as a CD-ROM.

[0112] Furthermore, the recording medium also includes internal or external recording media accessible from the distribution server for distributing the program. The program may be divided into multiple parts, downloaded at different times, and then combined in each configuration of the distance image acquisition device 1(1a), and different distribution servers may distribute each of the divided programs. Additionally, "computer-readable recording media" includes volatile memory (RAM) within computer systems that act as servers or clients when a program is transmitted over a network, which retains the program for a certain period of time. Moreover, the program may be intended to implement only a part of the functions described above. Furthermore, the program may be a so-called differential file (differential program) that can implement the functions described above in combination with a program already recorded in the computer system.

[0113] Furthermore, some or all of the above-mentioned functions may be implemented as integrated circuits such as LSIs (Large Scale Integrations). Each of the above-mentioned functions may be implemented as an individual processor, or some or all of them may be integrated into a single processor. In addition, the method of implementing integrated circuits is not limited to LSIs; they may also be implemented using dedicated circuits or general-purpose processors. Furthermore, if advances in semiconductor technology lead to the emergence of integrated circuit technologies that can replace LSIs, integrated circuits using such technologies may be used. [Explanation of Symbols]

[0114] 1, 1a... Distance image acquisition device 2...Light source section 3...Light receiving section 4, 4a... Distance image processing unit 21...Light source device 22... Diffuser 31... Lens 32... Distance image sensor 41... Interferometric light detection unit 42, 42a... Timing adjustment section 43...Distance calculation section 44...Measurement Control Unit 320…Light receiving area 321...Pixel circuit 322...Pixel driving circuit 323…Vertical scanning circuit 324... Horizontal scanning circuit 325...Pixel signal processing circuit 326...Control circuit CS, CS1, CS2, CS3, CS4...Charge storage section FD, FD1, FD2, FD3, FD4… Floating Diffusion G, G1, G2, G3, G4… Transfer transistors GD…Charge Emission Transistor ML... Microlens PD…Photoelectric converter PO... Light pulse RT1, RT2, RT3, RT4… Reset transistors S…Subject SF, SF1, SF2, SF3, SF4… Source follower transistors SL, SL1, SL2, SL3, SL4… Selective transistors

Claims

1. A light receiving unit having a photoelectric conversion element that generates an electric charge corresponding to incident light, which is light incident from a measurement space that is the space to be measured; a plurality of pixel circuits each comprising a photoelectric conversion element that generates an electric charge corresponding to incident light, which is light incident from a measurement space that is the space to be measured; N (N≧3) charge storage units that store the electric charge at a predetermined integration period synchronized with the irradiation of an electric pulse; and a pixel driving circuit that conducts the charge to each of the charge storage units by conducting the transfer transistors to each of the charge storage units at a predetermined storage timing synchronized with the irradiation of an electric pulse, thereby distributing and storing the electric charge. A light source unit that irradiates the measurement space with the light pulse, A distance image processing unit measures the distance to an object in the measurement space as the measurement distance based on the amount of charge accumulated in each of the charge storage units. Equipped with, The distance image processing unit, Before executing the integration cycle for measuring the distance, without irradiating with the light pulse, and with the same period and storage timing as when the light pulse is irradiated, the transfer transistors in the pixel driving circuit are connected, and interference light is detected based on the difference between the maximum and minimum values ​​of the interference charge amount stored in each of the charge storage units. When the aforementioned interference light is detected, the irradiation timing of the light pulse and the accumulation timing are changed by randomly changing the integration period, thereby measuring the measurement distance. A distance image acquisition device characterized by the following features.

2. The distance image processing unit, When the aforementioned interference light is detected, the irradiation timing of the light pulse and the accumulation timing are changed by randomly changing the integration period, and the measurement distance is measured by subtracting the uniform offset value. The distance image capturing device according to feature 1.

3. The distance image processing unit determines that interference light is present if the difference between the maximum value and the minimum value is greater than or equal to a threshold. A distance image capturing device according to claim 1 or 2.

4. The distance image processing unit measures the measurement distance without changing the integration period or the start timing of the integration period if it does not detect the interference light. A distance image capturing device according to claim 1 or 2.

5. A distance image imaging apparatus and distance image imaging method comprising: a photoelectric conversion element that generates an electric charge corresponding to incident light, which is light incident from a measurement space that is the space to be measured; a plurality of pixel circuits each having N (N≧3) charge storage units that store the charge at a predetermined integration period synchronized with the irradiation of an optical pulse; a light receiving unit having a pixel driving circuit that conducts the transfer transistors to each of the charge storage units at a predetermined storage timing synchronized with the irradiation of the optical pulse to distribute and store the charge; a light source unit that irradiates the measurement space with the optical pulse; and a distance image processing unit that measures the distance to an object present in the measurement space as the measurement distance based on the amount of charge stored in each of the charge storage units, wherein the apparatus and distance image imaging method comprises: a photoelectric conversion element that generates an electric charge corresponding to incident light, which is light incident from a measurement space that is the space to be measured; N (N≧3) charge storage units that store the charge at a predetermined integration period synchronized with the irradiation of an optical pulse; a plurality of pixel circuits each having a transfer transistor that transfers the charge from the photoelectric conversion element to each of the charge storage units; a light receiving unit that distributes and stores the charge by conducting each of the transfer transistors to each of the charge storage units at a predetermined storage timing synchronized with the irradiation of an optical pulse; a light source unit that irradiates the measurement space with the optical pulse; and a distance image processing unit that measures the distance to an object present in the measurement space as the measurement distance based on the amount of charge stored in each of the charge storage units, wherein the apparatus and distance image imaging apparatus and distance image imaging method The distance image processing unit, before executing the integration cycle for measuring the distance, performs an interference light detection step in which it connects each of the transfer transistors to the pixel driving circuit at the same period and storage timing as when the light pulse is irradiated, without irradiating the light pulse, and detects interference light based on the difference between the maximum and minimum values ​​of the interference charge amount stored in each of the charge storage units. When the distance image processing unit detects the interference light, it randomly changes the integration period to change the irradiation timing of the light pulse and the accumulation timing, thereby performing a timing adjustment step to measure the measurement distance. A distance image acquisition method characterized by including the following.

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