Distance measuring device

Abstract

To enhance distance resolution at a short distance without reducing distance resolution at a long distance in regard to distance measurement.SOLUTION: A control section: causes all projection elements to emit a first light-emission pulse P1f at the same first light-emission timing T1f respectively, and then controls a projection section to emit a second light-emission pulse P2f at a second light-emission timing T2f different from the timing at which at least some other projection elements emit so as to identify projection elements; and for each light-reception element, among a TOF measured distance obtained by TOF measurement on the basis of a first pulse response time ΔT1 and a stereo measured distance obtained by stereo measurement from an association between the projection element and light-reception element identified from the second light-emission timing T2f at which a second pulse response time ΔT2 is equal to a time difference between the first light-emission timing T1f and the light-emission timing, outputs TOF measured distance as a distance measurement result if the measured distance is equal to or greater than a predetermined distance threshold and outputs stereo measured distance as the distance measurement result if the measured distance is less than the predetermined distance threshold.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a distance measurement device that measures the distance to a measurement object by utilizing reflected light received from the measurement object. [Background technology]

[0002] Conventionally, optical distance measurement devices have been used to measure the distance to an object within a measurement target area using reflected light received from the object. These devices utilize the timing at which light reflected from the object is detected, i.e., the time of flight (TOF) of light traveling to and from the object. A known example of technology related to such optical distance measurement devices is the optical distance sensor disclosed in Patent Document 1 below. This optical distance sensor uses single photon avalanche diodes (SPADs) as light receiving elements. A detection signal is generated when a composite signal, which is the sum of output signals from multiple SPADs, exceeds a predetermined threshold. The measurement period between this generation and the start of detection is measured. Furthermore, by further considering timing information on the increase in the composite signal, multiple times at which multiple SPADs react to a single light emission and reception are obtained, thereby improving the light detection accuracy of the optical distance sensor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-158737 Summary of the Invention [Problem to be solved by the invention]

[0004] In TOF measurement using multiple SPADs, distance must be calculated based on the speed of light. However, because the speed of light is sufficiently fast, the distance measurement accuracy is theoretically limited to approximately 15 cm one way, even if the sampling interval is set to 1 GHz. Furthermore, even if faster sampling frequencies can be applied (custom) to a single SPAD at the research level, achieving a similar high sampling frequency is difficult with, for example, multiple SPADs arranged in an array. Therefore, in TOF distance measurement sensors that employ multiple SPADs, the sampling frequency constraint is the main factor determining the distance resolution. This results in a problem: while the distance resolution remains constant regardless of the measurement distance, it is difficult to improve the distance resolution at close ranges.

[0005] The present invention has been made to solve the above-mentioned problems, and its object is to provide a configuration that can improve distance resolution at short distances without reducing distance resolution at long distances in distance measurement. [Means for solving the problem]

[0006] In order to achieve the above object, the invention described in claim 1 of the claims is as follows: total For the measurement area each Emits a light pulse Multiple Light-emitting element With my child (21) , before Note measurement Reflected by objects within the target area And Ta The plurality of light emitting pulses transmitted by the plurality of light emitting elements respectively Multiple Receives light as a pulse Multiple Light reception Elements (31) and, The aforementioned Multiple light-emitting elements a control unit (11) for controlling the above; The aforementioned Multiple light receiving elements received by The aforementioned a measurement unit (40) that measures distance within the measurement target area based on a plurality of received light pulses; Equipped with picture, The control unit , the plurality of Light-emitting element To each of After emitting the first light pulse at the first light emission timing, Each of the plurality of light-emitting elements The second light pulse is emitted at the second light emission timing. the first light-emitting timing is the same for all of the plurality of light-projecting elements, and the second light-emitting timing is different between groups including at least one of the plurality of light-projecting elements; The measurement unit Multiple Light receiving element Group of For each (a) measuring a first time difference between the first light emission timing and a first light reception timing, and at the first light reception timing, the group of the plurality of light receiving elements receives a first light reception pulse corresponding to the first light emission pulse; (b) measuring a second time difference between the first light-receiving timing and a second light-receiving timing, wherein at the second light-receiving timing, the group of the plurality of light-receiving elements receives a second light-receiving pulse corresponding to the second light-emitting pulse; (c) based on the first time difference TOF (Time of Flight) Measurement distance Measure the (d) identifying a group of the plurality of light-projecting elements that emits the second light emission pulse at the second light emission timing, where the second time difference matches the time difference between the first light emission timing and the second light emission timing; (e) based on the projection angles of the light-projecting elements included in the specified group of the plurality of light-projecting elements and the light-receiving angles of the light-receiving elements included in the specified group of the plurality of light-receiving elements Stereo measurement distance Measure and (f) a criterion that is the TOF measurement distance or the stereo measurement distance; Measurement distance is specified Threshold Value or greater is In this case, the TOF measurement distance is Distance measurement The result is output as the reference measurement distance is the predetermined Threshold Less than the value is In this case, the stereo measurement distance is Distance measurement The resulting output R . The symbols in parentheses above indicate the correspondence with the specific means described in the embodiments to be described later. [Effects of the Invention]

[0007] In the invention of claim 1, the control unit causes each of the plurality of light-emitting elements to emit a first light-emitting pulse at a first light-emitting timing, and then causes each of the plurality of light-emitting elements to emit a second light-emitting pulse at a second light-emitting timing, the first light-emitting timing being the same for all of the plurality of light-emitting elements, and the second light-emitting timing being different between groups including at least one of the plurality of light-emitting elements; the measurement unit, for each group of the plurality of light-receiving elements, (a) measures a first time difference between the first light-emitting timing and a first light-receiving timing, at which the group of the plurality of light-receiving elements receives a first light-receiving pulse corresponding to the first light-emitting pulse, (b) measures a second time difference between the first light-receiving timing and a second light-receiving timing, at which the group of the plurality of light-receiving elements receives a second light-receiving pulse corresponding to the second light-emitting pulse, and (c) calculates a time of flight (TOF) based on the first time difference. (d) identifying a group of the plurality of light-projecting elements that emit the second light emission pulse at the second light-emitting timing where the second time difference matches the time difference between the first light-emitting timing and the second light-emitting timing; (e) measuring a stereo measurement distance based on the light-projecting angles of the light-projecting elements included in the identified group of the plurality of light-projecting elements and the light-receiving angles of the light-receiving elements included in the group of the plurality of light-receiving elements; and (f) outputting the TOF measurement distance as a distance measurement result when the TOF measurement distance or a reference measurement distance that is the stereo measurement distance is equal to or greater than a predetermined threshold, and outputting the stereo measurement distance as the distance measurement result when the reference measurement distance is less than the predetermined threshold.

[0008] This means: standard Measurement distance is specified Threshold When the value is less than the value, that is, when the distance is short, the distance resolution becomes higher in stereo measurement. Distance measurement The results are output, standard Measurement distance is specified Threshold When the value is greater than or equal to the value, that is, when the distance resolution does not decrease even at long distances, the TOF measurement Distance measurement The results are output. In particular, Multiple light-emitting elements ( Light projector ) The first light emitting pulse and the second light emitting pulse are emitted from Multiple light receiving elements (Light receiving part ) Since the timing of receiving light at the time of TOF measurement is utilized, TOF measurement and stereo measurement can be performed with one light projecting unit and one light receiving unit, without providing separate light projecting and receiving units for TOF measurement and stereo measurement. Therefore, a distance measurement device that can improve distance resolution at short distances without reducing distance resolution at long distances can be realized with one set of light projecting unit and light receiving unit.

[0009] In the invention of claim 2, Multiple The element is each The sensor is a SPAD (Single Photon Avalanche Diode), which has high response characteristics and allows for a small pixel size, thereby further increasing the distance resolution for distance measurement and improving the measurement accuracy.

[0010] In the invention of claim 3, the measurement unit Among the groups of multiple light receiving elements, The difference between the TOF measurement distance and the stereo measurement distance is given value End Included in the group that is Photodetector Distance measurement Do not output the results.

[0011] If there is a large difference between the TOF measurement distance and the stereo measurement distance, there is a high possibility that at least one of them is an incorrect measurement distance due to the influence of noise during measurement, etc. Therefore, when the difference between the TOF measurement distance and the stereo measurement distance is a predetermined value, value End Included in the group that is Regarding the light receiving element, since the TOF measurement distance and the stereo measurement distance are significantly different, by not outputting either measurement distance, it is possible to avoid erroneous results. Distance measurement The output of the results can be suppressed.

[0012] In the invention of claim 4, the measurement unit obtains information on the difference between the TOF measurement distance and the stereo measurement distance. Multiple Light receiving element Group of Output every time.

[0013] If the difference between the TOF measurement distance and the stereo measurement distance is small, the measurements are both correct and highly reliable. Distance measurementIf the difference between the TOF measurement distance and the stereo measurement distance is large, at least one of them is an incorrect measurement distance due to the influence of noise during measurement, and the result is unreliable. Distance measurement The result is likely to be output. In other words, the difference between the two is one of the two. Distance measurement This can be used to ensure the reliability of the results. Distance measurement The output destination that receives the result together with information about its reliability (information about the difference between the TOF measurement distance and the stereo measurement distance) can, for example, Distance measurement Only the results can be used, Distance measurement The usefulness of the results can be increased. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a block diagram showing a schematic configuration of a distance measurement device according to a first embodiment. [Figure 2] FIG. 2 is an explanatory diagram illustrating a schematic configuration of the VCSEL array of FIG. [Figure 3] FIG. 1 is an explanatory diagram illustrating distance measurement using a TOF measurement method. [Figure 4] FIG. 1 is an explanatory diagram illustrating distance measurement using a stereo measurement method. [Figure 5] 1 is an explanatory diagram illustrating the relationship between measurement distance and distance resolution for the TOF measurement method and the stereo measurement method. FIG. [Figure 6] FIG. 10 is an explanatory diagram illustrating measurement accuracy at close range in a stereo measurement method. [Figure 7]7(A) and 7(B) are explanatory diagrams illustrating the relationship between the first and second light emission timings, the first and second light reception timings, and the first and second pulse response times. FIG. 7(A) shows the light emission timing of the light-projecting element V11. FIG. 7(B) shows the light emission timing of the light-projecting element V12. FIG. 7(C) shows the light reception timing of the light reflected from the light emitted by the light-projecting element V11. FIG. 7(D) shows the light reception timing of the light reflected from the light emitted by the light-projecting element V12. FIG. 7(E) shows the light reception timing of the light reflected from the light emitted by the light-projecting element V11 at a distance measurement point farther away than that shown in FIG. 7(C). FIG. 7(F) shows the light reception timing of the light reflected from the light emitted by the light-projecting element V12 at a distance measurement point farther away than that shown in FIG. 7(D). [Figure 8] 10 is a flowchart illustrating a flow of a measurement process performed by a measurement unit. DETAILED DESCRIPTION OF THE INVENTION

[0015] [First embodiment] A first embodiment of a distance measurement device according to the present invention will be described below with reference to the drawings. A distance measurement device 10 according to this embodiment measures the distance to an object within a predetermined measurement target area using a TOF measurement distance result obtained by a TOF measurement method and a stereo measurement distance result obtained by a stereo measurement method. As shown in Fig. 1, this distance measurement device 10 is configured to include a control unit 11 that handles overall control, a light projecting unit 20 that projects a predetermined light emission pulse onto the predetermined measurement target area, a light receiving unit 30 that receives the light reflected by an object within the target area, and a measurement unit 40 that measures the distance to the object within the measurement target area based on the light receiving pulse received by the light receiving unit 30.

[0016] The control unit 11 is mainly composed of a microcomputer and has a CPU, a system bus, an input / output interface, etc., and constitutes an information processing device together with a storage unit consisting of a ROM, a RAM, a non-volatile memory, etc. The storage unit stores in advance programs related to the control of the light projecting unit 20 and the measuring unit 40, programs for executing control processing using the measurement results by the measuring unit 40, etc., so that they can be executed by the control unit 11.

[0017] The light-projecting unit 20 includes a VCSEL array 21 and a light source control unit 22 that controls each light-projecting element of the VCSEL array 21 in response to a light emission command from the control unit 11. As shown in Fig. 2, the VCSEL array 21 is configured such that a plurality of vertical cavity surface-emitting lasers, which are light-projecting elements (V11 to Vmn), are arranged in an array, and is controlled by the light source control unit 22 so as to be able to project a light emission pulse at a predetermined timing for each light-projecting element.

[0018] The light receiving unit 30 includes a SPAD array 31 and a signal processing unit 32 that processes output signals from the SPAD array 31 and outputs the signals to the measurement unit 40. The SPAD array 31 is configured by arranging a plurality of SPADs, which are used as light receiving elements with high response characteristics and small pixel size, in an array similar to the light projecting elements of the VCSEL array 21. The SPAD array 31 configured in this manner is arranged so that light emission pulses projected from the light projecting unit 20 are reflected by objects within the target area and received by each SPAD as light receiving pulses. The signal processing unit 32 is configured to process pulse signals output by each SPAD at the timing when it receives a light receiving pulse, and output the processed signals to the measurement unit 40.

[0019] The measurement unit 40 receives information from the control unit 11 regarding the timing of the light emission instruction given to the light-emitting unit 20 by the control unit 11 (hereinafter also referred to as light emission timing information), and receives a pulse signal for each SPAD from the signal processing unit 32 of the light-receiving unit 30, thereby performing measurement processing to measure the distance to an object within a specified measurement target area.

[0020] In the measurement process performed by the measurement unit 40 in this embodiment, the distance to an object within a predetermined measurement target area is measured using the TOF measurement distance result obtained by the TOF measurement method and the stereo measurement distance result obtained by the stereo measurement method.

[0021] In the TOF measurement method, as shown in Fig. 3, the distance (TOF measurement distance) is measured for each light-receiving element according to the time difference (hereinafter also referred to as the first pulse response time ΔT1) between the emission timing at which a light-emitting pulse is emitted from a light-emitting element and the light-receiving timing at which a light-receiving pulse, which is reflected light generated in response to the emission pulse, is received by the light-receiving element. Note that in the TOF measurement method, the distance resolution for distance measurement depends on the sampling time performance of the light-receiving unit 30, and as shown by the solid line D1 in Fig. 5, the distance resolution is constant regardless of whether the measurement distance Z is close or far.

[0022] In the stereo measurement method (active stereo measurement method), as shown in Figure 4, the projection angle α and acceptance angle β are calculated by identifying and linking the light-emitting element that emitted the light-emitting pulse corresponding to the light-receiving pulse received by the light-receiving element, and the distance to the object (distance measurement point) (stereo measurement distance) is measured by triangulation based on these projection angle α and acceptance angle β and the parallax, which is known from the design. Therefore, in the stereo measurement method, the distance resolution for distance measurement is basically determined by the design parameters (number of pixels, pixel size, projection field of view and light-receiving field of view per pixel, etc.) of the light-receiving unit 30 and the light-emitting unit 20 and the measurement distance Z, and the distance resolution becomes higher as the distance becomes shorter, as shown by the dashed line D2 in Figure 5. Note that for convenience, the optical system, such as lenses, is not shown in Figure 4.

[0023] For example, if the VCSEL array 21 has a projection field of view (horizontal) of 90° and 200 horizontal elements, and the SPAD array 31 has a reception field of view (horizontal) of 90° and 200 horizontal elements, and the horizontal parallax is 15 cm, the distance resolution at a distance of 1 m for the stereo measurement method is calculated as follows:

[0024] Since the projection field of view (horizontal) is 90° and there are 200 horizontal elements, the accuracy of the projected light beam is 0.45°. Also, since the receiving field of view (horizontal) is 90° and there are 200 horizontal elements, the accuracy of the received light beam is 0.45°. As shown in the example of Figure 6, if we consider a distance measuring point 1 m that corresponds to the center in the horizontal direction between the light projecting element and the light receiving element, the parallax is 15 cm, and therefore the projection angle α can be calculated from Pythagoras' theorem as follows: α=tan -1 (1 / 0.075)=85.7° Therefore, distance Zmax is the distance when projection angle α = 85.7° + (0.45° / 2), and thus, using Pythagoras' theorem, distance Zmax = 1.05 m can be calculated. Similarly, distance Zmin is the distance when projection angle α = 85.7° - (0.45° / 2), and thus, using Pythagoras' theorem, distance Zmin = 0.95 m can be calculated. Therefore, the distance accuracy (distance Zmax - distance Zmin) is approximately 10 cm, which is higher than the measurement accuracy of approximately 15 cm achieved with the TOF measurement method using high-speed sampling at 1 GHz described above, and it can be seen that the closer the distance, the higher the measurement accuracy.

[0025] For this reason, in this embodiment, the control unit 11 controls the light-projecting unit 20 to emit a first light-emitting pulse at the same first light-emitting timing from all the light-projecting elements in the VCSEL array 21, and then emits a second light-emitting pulse for each of the light-projecting elements at a second light-emitting timing different from that of at least some of the other light-projecting elements so that the light-projecting element can be identified. The first light-emitting pulse is a light-emitting pulse for TOF measurement, and the second light-emitting pulse is a light-emitting pulse for stereo measurement.

[0026] Specifically, for example, after a predetermined time has elapsed since all the light-emitting elements (V11 to Vmn) have emitted first light-emitting pulses at the same first light-emitting timing, the light-emitting elements in the first row (V11, V21, V31...Vm1) are first made to emit second light-emitting pulses. After a predetermined time (e.g., 10 ns) has elapsed since the light-emitting elements in the first row emitted light, the light-emitting elements in the second row (V12, V22, V32...Vm2) are made to emit second light-emitting pulses. Subsequently, after the predetermined time has elapsed since the light-emitting elements in the second row emitted light, the light-emitting elements in the third row (V13, V23, V33...Vm3) are made to emit second light-emitting pulses. In this way, the light-emitting timing (second light-emitting timing) is shifted by a predetermined time unit for each row, and all the light-emitting elements are made to emit second light-emitting pulses.

[0027] As described above, by shifting the second light emission timing for each column of the VCSEL array 21 (each predetermined light emission group), it is possible to identify the light-emitting element that emitted the light emission pulse corresponding to the light-receiving pulse received by the light-receiving element by utilizing the timing of the output signal output from the signal processing unit 32 of the light-receiving unit 30 to the measurement unit 40.

[0028] For example, as illustrated in FIG. 7(A), a case is assumed in which a first light-emitting pulse P1f(11) is emitted from the light-projecting element V11 at a first light-emitting timing T1f, and then a second light-emitting pulse P2f(11) is emitted at a second light-emitting timing T2f(1); and as illustrated in FIG. 7(B), a case is assumed in which a first light-emitting pulse P1f(12) is emitted from the light-projecting element V12 at the same first light-emitting timing T1f as the light-projecting element V11, and then a second light-emitting pulse P2f(12) is emitted at a second light-emitting timing T2f(2) after the predetermined time has elapsed since the second light-emitting timing T2f(1).

[0029] In this case, the light receiving element that receives the reflected light of the first light emission pulse P1f(11) and the second light emission pulse P2f(11) receives a first received light pulse P1r(11) as reflected light of the first light emission pulse P1f(11) at a light receiving timing (hereinafter also referred to as a first light receiving timing) T1r(1) that is delayed from the first light emission timing T1f in accordance with the measured distance, as shown in Fig. 7(C). The time difference between the first light emission timing T1f and the first light receiving timing T1r(1) is the first pulse response time ΔT1(1).

[0030] 7(C), the same light receiving element receives a second received light pulse P2r(11) as reflected light of the second emitted light pulse P2f(11) at a second received light timing T2r(1) after the first received light timing T1r(1). The time difference between the first received light timing T1r(1) and the second received light timing T2r(1) (hereinafter also referred to as the second pulse response time ΔT2) is equal to the time difference between the first emitted light timing T1f(1) and the second emitted light timing T2f(1).

[0031] 7(D), at the light receiving element that receives the reflected light of the first light emission pulse P1f(12) and the second light emission pulse P2f(12), a first received light pulse P1r(12) is received as reflected light of the first light emission pulse P1f(12) at a first received light timing T1r(2) that is delayed from the first light emission timing T1f in accordance with the measured distance. The time difference between the first light emission timing T1f and the first received light timing T1r(2) is the first pulse response time ΔT1(2).

[0032] 7(D), the same light receiving element receives a second received light pulse P2r(12) as reflected light of the second emitted light pulse P2f(12) at a second received light timing T2r(2) after the first received light timing T1r(2). The second pulse response time ΔT2(2), which is the time difference between the first received light timing T1r(2) and the second received light timing T2r(2), is equal to the time difference between the first emitted light timing T1f(2) and the second emitted light timing T2f(2).

[0033] In addition, in Figures 7(C) and 7(D), it is assumed that the measured distance to the ranging point where the light emission pulses (first light emission pulse P1f(11) and second light emission pulse P2f(11)) from the light-emitting element V11 are reflected and the measured distance to the ranging point where the light emission pulses (first light emission pulse P1f(12) and second light emission pulse P2f(12)) from the light-emitting element V12 are reflected are the same measured distance Zm.

[0034] Therefore, when light emitting pulses are emitted from the light emitting element V11 as described above to distance measurement points at measurement distance Zn that is farther than measurement distance Zm, as shown in Figure 7(E), a first light receiving pulse P1r(11) is received at a first light receiving timing T1r(1) that is delayed from the first light emitting timing T1f according to the measurement distance Zn, and a second light receiving pulse P2r(11) is received at the subsequent second light receiving timing T2r(1).

[0035] Similarly, when light emitting pulses are emitted from the light emitting element V12 to the distance measurement points of the measurement distance Zn as described above, as shown in Figure 7(F), a first light receiving pulse P1r(12) is received at a first light receiving timing T1r(2) that is delayed from the first light emitting timing T1f according to the measurement distance Zn, and a second light receiving pulse P2r(12) is received at the subsequent second light receiving timing T2r(2).

[0036] Because the measurement distances Zm and Zn are different, the first pulse response time ΔT1(1) in FIG. 7(C) is different from the first pulse response time ΔT1(1) in FIG. 7(E), and the first pulse response time ΔT1(2) in FIG. 7(D) is different from the first pulse response time ΔT1(2) in FIG. 7(F). On the other hand, even if the measurement distances Zm and Zn are different, the second pulse response time ΔT2(1) in FIG. 7(C) is the same as the second pulse response time ΔT2(1) in FIG. 7(E) because the reflected light of two light-emitting pulses from the same light-emitting element V11 is sequentially received. Similarly, the second pulse response time ΔT2(2) in FIG. 7(D) is the same as the second pulse response time ΔT2(2) in FIG. 7(F) because the reflected light of two light-emitting pulses from the same light-emitting element V12 is sequentially received. In this way, the second pulse response time ΔT2 of each of the light-receiving elements that receive pulsed light from the light-emitting element having the same second light-emitting timing T2f is the same value.

[0037] That is, because the second pulse response time ΔT2 is the same for each column (each predetermined light-emitting group) of the VCSEL array 21, it is possible to identify the column of the VCSEL array 21 to which the light-projecting element that emitted the light-emitting pulse corresponding to the light-receiving pulse received by that light-receiving element belongs from the second pulse response time ΔT2. Therefore, the measurement unit 40, which acquires light-emitting timing information including the first light-receiving timing T1r and the second light-receiving timing T2r for each light-receiving element from the control unit 11, can identify the light-projecting element for each light-receiving element from the second light-emitting timing T2f at which the second pulse response time ΔT2 is equal to the difference from the first light-emitting timing T1f. Then, the stereo measurement distance can be measured based on the projection angle α and the light-receiving angle β calculated by linking the identified light-projecting element with the light-receiving element (see FIG. 4).

[0038] Then, since the TOF measurement distance can be measured for each light receiving element according to the first pulse response time ΔT1 (see Figure 3), the measurement process performed by the measurement unit 40 measures the distance to an object (each ranging point) within a specified measurement target area based on the TOF measurement distance measured for each light receiving element and the stereo measurement distance.

[0039] Hereinafter, the measurement process and the like performed by the measurement unit 40 in this embodiment will be described in detail with reference to the flowchart shown in FIG. When measurement processing is started in the measurement unit 40 in response to a predetermined operation or the like, each light-projecting element of the VCSEL array 21 of the light-projecting unit 20 enters a state in which it can emit light, and each light-receiving element of the SPAD array 31 of the light-receiving unit 30 enters a state in which it can receive light. Then, in response to a light-emitting instruction from the control unit 11, each light-projecting element emits a first light-emitting pulse P1f at a first light-emitting timing T1f, and then emits a second light-emitting pulse P2f at a second light-emitting timing T2f that differs for each column (each group) (S101 in FIG. 8). As a result, in the light-receiving unit 30, the first light-receiving timing T1r at which the first light-receiving pulse P1r is received and the second light-receiving timing T2r at which the second light-receiving pulse P2r is received are processed by the signal processing unit 32 for each light-receiving element, and output to the measurement unit 40 (S103).

[0040] In the measurement unit 40, when the first light receiving timing T1r and second light receiving timing T2r for each light receiving element output from the signal processing unit 32 of the light receiving unit 30 as described above are acquired, the measurement distance for each light receiving element is measured using the light emission timing information (first light emission timing T1f and second light emission timing T2f for each light receiving element) acquired from the control unit 11.

[0041] First, the TOF measurement process shown in step S105 is performed, and the TOF measurement distance is measured for each light receiving element based on the first pulse response time ΔT1, which is the difference between the first light emission timing T1f and the first light reception timing T1r.

[0042] Next, stereo measurement shown in step S107 is performed. In this process, for each light-receiving element, a row of light-emitting elements that emitted a light-emitting pulse corresponding to the light-receiving pulse received by that light-receiving element is identified based on the second pulse response time ΔT2 (the time difference between the first light-receiving timing T1r and the second light-receiving timing T2r). Then, the stereo measurement distance is measured based on the projection angle α and the reception angle β calculated by linking the identified light-emitting element with the light-receiving element.

[0043] As described above, once the TOF measurement distance and the stereo measurement distance are measured for each light receiving element, a measurement result deletion process shown in step S109 is performed to delete measurement distances that are likely to be erroneous. Specifically, if the difference between the TOF measurement distance and the stereo measurement distance is greater than or equal to a predetermined distance difference, it is determined that at least one of the TOF measurement distances is likely to be erroneous due to noise or other factors during measurement, and the TOF measurement distance and the stereo measurement distance are deleted. In this way, for light receiving elements where the difference between the TOF measurement distance and the stereo measurement distance is greater than or equal to the predetermined distance difference, the TOF measurement distance and the stereo measurement distance are determined to be significantly different, and neither measurement distance is output, thereby preventing the output of erroneous measurement distance results. Note that if the measurement distance becomes long, the second light receiving pulse P2r may no longer be received, resulting in the stereo measurement distance not being measured. In such cases, the TOF measurement distance may be used as the measurement distance result without deletion.

[0044] Then, a measurement result selection and examination process shown in step S111 is performed, and either the TOF measurement distance or the stereo measurement distance is selected as the correct measurement result for each light receiving element. As can be seen from Fig. 5, the stereo measurement distance has a higher distance resolution at short distances and the TOF measurement distance has a higher distance resolution at long distances. Therefore, the distance (boundary point) at which the distance resolution of the TOF measurement distance and the distance resolution of the stereo measurement distance are designed to be equal is set as a predetermined distance threshold Zth. If the measured distance is equal to or greater than the predetermined distance threshold Zth, the TOF measurement distance is selected as the measured distance result, and if the measured distance is less than the predetermined distance threshold Zth, the stereo measurement distance is selected as the measured distance result, thereby improving the distance measurement accuracy.

[0045] Once the measurement results to be output for each light receiving element have been selected as described above, the selected measurement results are output for each light receiving element in the measurement result output shown in step S113, and this measurement process ends.

[0046] As described above, in the distance measurement device 10 according to this embodiment, the control unit 11 controls the light-projecting unit 20 to emit a first light emission pulse P1f from all light-projecting elements at the same first light emission timing T1f, and then to emit a second light emission pulse P2f at a second light emission timing T2f different from at least some of the other light-projecting elements so that the light-projecting element can be identified. For each light-receiving element, the measurement unit 40 outputs the TOF measurement distance as a measured distance result if the measured distance is equal to or greater than a predetermined distance threshold Zth, and outputs the stereo measurement distance as a measured distance result if the measured distance is less than the predetermined distance threshold Zth.

[0047] As a result, when the measurement distance is less than a predetermined distance threshold Zth, i.e., at a short distance, a measurement distance result by stereo measurement in which the distance resolution increases as the distance becomes shorter is output, and when the measurement distance is equal to or greater than the predetermined distance threshold Zth, i.e., at a long distance, a measurement distance result by TOF measurement in which the distance resolution does not decrease even at long distances is output. In particular, by utilizing the timing at which the light-receiving unit 30 receives the first emission pulse P1f and the second emission pulse P2f emitted from the light-projecting unit 20, TOF measurement and stereo measurement can be performed with one light-projecting unit 20 and one light-receiving unit 30, without providing separate light-projecting and receiving units for TOF measurement and stereo measurement. Therefore, a distance measurement device 10 that can increase distance resolution at short distances without decreasing distance resolution at long distances can be realized with one set of light-projecting unit 20 and light-receiving unit 30.

[0048] In addition, in this embodiment, the light receiving element is a SPAD (Single Photon Avalanche Diode), and since a SPAD has high response characteristics and can have a small pixel size, it is possible to further increase the distance resolution for distance measurement and improve the measurement accuracy. Note that the light receiving unit 30 is not limited to being configured to include a SPAD array 31 in which SPADs are arranged in an array, and may be configured so that multiple other light receiving elements are arranged in the same manner as the light projecting elements of the light projecting unit, depending on the usage environment of the distance measurement device 10, etc.

[0049] In particular, in this embodiment, if the difference between the TOF measurement distance and the stereo measurement distance is greater than a predetermined distance difference, the measurement unit 40 erases the TOF measurement distance and the stereo measurement distance (S109) and does not output the measurement result for that light receiving element.

[0050] In this way, for light receiving elements where the difference between the TOF measurement distance and the stereo measurement distance is greater than a predetermined distance difference, the TOF measurement distance and the stereo measurement distance are considered to be significantly different, and neither measurement distance is output, thereby preventing the output of erroneous measurement distance results.

[0051] As a modification of this embodiment, the measurement unit 40 may output information on the difference between the TOF measurement distance and the stereo measurement distance for each light receiving element as information on the reliability of the measurement distance result.

[0052] When the difference between the TOF measurement distance and the stereo measurement distance is small, it is highly likely that each measurement was performed correctly and a highly reliable measurement distance result is output.On the other hand, when the difference between the TOF measurement distance and the stereo measurement distance is large, it is highly likely that at least one of the measurement distances is an incorrect measurement distance due to the influence of noise during measurement, etc., and therefore a less reliable measurement distance result is output.

[0053] For example, if a light-receiving element receives an interference light pulse from a light source other than the light-projecting unit 20 before the first received light pulse P1r, the first pulse response time ΔT1 and the second pulse response time ΔT2 will not be measured correctly, resulting in an incorrect measured distance in both measurement methods. Also, if a light-receiving element receives an interference light pulse between the first received light pulse P1r and the second received light pulse P2r, the second pulse response time ΔT2 will not be measured correctly, resulting in an incorrect measured distance in the stereo measurement method. Also, if light-projecting pulses from different light-projecting elements become mixed after reflection and are received by the same light-receiving element, at least one of the measurement methods will result in an incorrect measured distance.

[0054] For this reason, in a modification of this embodiment, the difference between the two is used as the credibility of one of the measured distance results, which is the measured distance result. As a result, an output destination that acquires the measured distance result together with information on its credibility (information on the difference between the TOF measured distance and the stereo measured distance) can use only the measured distance result with high credibility, for example, thereby increasing the utility value of the measured distance result.

[0055] The present invention is not limited to the above-described embodiments, and may be embodied as follows, for example. (1) The light-projecting unit 20 is not limited to being configured to include a VCSEL array 21 in which a plurality of vertical-cavity surface-emitting lasers are arranged in an array, but may also be configured to include other light-projecting means capable of controlling the light emission timing for each light-projecting element, such as an LED array in which a plurality of LEDs are arranged in an array.

[0056] (2) The control unit 11 is not limited to controlling the light-projecting unit 20 to change the second light-emitting timing T2f for each column in predetermined time units and sequentially emit the second light-emitting pulses P2f. For example, the control unit 11 may control the light-projecting unit 20 to change the second light-emitting timing T2f for each row in predetermined time units and sequentially emit the second light-emitting pulses P2f, or may control the light-projecting unit 20 to change the second light-emitting timing T2f for each predetermined group in predetermined time units and sequentially emit the second light-emitting pulses P2f. Furthermore, the control unit 11 may control the light-projecting unit 20 to change the second light-emitting timing T2f for each light-projecting element in predetermined time units and sequentially emit the second light-emitting pulses P2f.

[0057] (3) The configuration is not limited to receiving the first received light pulse P1r and the second received light pulse P2r at one light receiving unit 30, but may be such that the first received light pulse P1r for TOF measurement is received at the light receiving unit 30, and the second received light pulse P2r for stereo measurement is received at another light receiving unit different from the light receiving unit 30. In this case, the parallax between the light projecting unit 20 and the other light receiving unit can be increased without being restricted by the measurement accuracy of the TOF measurement distance, thereby improving the measurement accuracy of the stereo measurement distance.

[0058] (4) The present invention can be applied to a device that measures the distance to an object within a specified monitoring area, but is not limited to this. For example, the present invention may be applied to a device that measures the distance to an object that moves relative to the object when installed on a moving body.

[0059] 10...Distance measuring device 11...Control unit 20...Light projecting unit 21...VCSEL array (multiple light-emitting elements) 30…Light receiving section 31...SPAD array (multiple light receiving elements) 40...Measuring unit T1f…First flash timing T2f…Second flash timing T1r: First light receiving timing T2r: Second light receiving timing P1f...First light emitting pulse P2f: Second light emitting pulse P1r: First received light pulse P2r: Second light receiving pulse Zth: distance threshold ΔT1: First pulse response time ΔT2: Second pulse response time

Claims

1. A plurality of light-emitting elements each emitting a light pulse onto a measurement target area; a plurality of light-receiving elements that receive, as a plurality of light-receiving pulses, the plurality of light-emitting pulses transmitted by the plurality of light-projecting elements that are reflected by an object within the measurement target area; a control unit that controls the plurality of light-emitting elements; a measurement unit that measures distances within the measurement target area based on the plurality of light-receiving pulses received by the plurality of light-receiving elements; Equipped with the control unit causes each of the plurality of light-projecting elements to emit a first light-emitting pulse at a first light-emitting timing, and then causes each of the plurality of light-projecting elements to emit a second light-emitting pulse at a second light-emitting timing, the first light-emitting timing being the same for all of the plurality of light-projecting elements, and the second light-emitting timing being different between groups including at least one of the plurality of light-projecting elements, The measurement unit, for each group of the plurality of light receiving elements, (a) measuring a first time difference between the first light emission timing and a first light reception timing, and at the first light reception timing, the group of the plurality of light receiving elements receives a first light reception pulse corresponding to the first light emission pulse; (b) measuring a second time difference between the first light-receiving timing and the second light-receiving timing, and at the second light-receiving timing, the group of the plurality of light-receiving elements receives a second light-receiving pulse corresponding to the second light-emitting pulse; (c) measuring a time-of-flight (TOF) distance based on the first time difference; (d) identifying a group of the plurality of light-projecting elements that emits the second light-emitting pulse at the second light-emitting timing, where the second time difference matches the time difference between the first light-emitting timing and the second light-emitting timing; (e) measuring a stereo measurement distance based on the projection angles of the light-projecting elements included in the specified group of the plurality of light-projecting elements and the light-receiving angles of the light-receiving elements included in the specified group of the plurality of light-receiving elements; (f) when the TOF measurement distance or the reference measurement distance, which is the stereo measurement distance, is equal to or greater than a predetermined threshold, outputting the TOF measurement distance as a distance measurement result, and when the reference measurement distance is less than the predetermined threshold, outputting the stereo measurement distance as the distance measurement result. Distance measuring device.

2. Each of the plurality of light receiving elements is a SPAD (Single Photon Avalanche Diode). The distance measurement device according to claim 1 .

3. The measurement unit does not output the distance measurement result for the light receiving elements included in a group of the plurality of light receiving elements in which a difference between the TOF measurement distance and the stereo measurement distance is equal to or greater than a predetermined value. The distance measurement device according to claim 1 .

4. The measurement unit outputs information about a difference between the TOF measurement distance and the stereo measurement distance for each group of the plurality of light receiving elements. The distance measurement device according to claim 1 .

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