Distance measuring device and distance measuring method

Abstract

To enable enhancing a frame rate, and alleviate an impact of a multipass.SOLUTION: A distance measuring device 100 comprises: a light emitting unit 103 that irradiates irradiation light toward a measurement object OBJ; a light reception unit 104 that outputs a light reception signal in accordance with a signal charge accumulated by an exposure; and a signal processing unit 105 that outputs a distance signal indicative of a distance up to the measurement object OBJ based on the light reception signal. The signal processing unit 105 is configured to calculate the distance, using a light reception signal in its entirety to be calculated from a first light reception signal obtained by the exposure of the light reception unit 104 in a first period of time including a rising of reflection light and a second light reception signal obtained by a long exposure in a second period of time including a falling of the reflection light, an amount of signals of one or more first measurement signals indicative of a ratio of an amount of signals of one or more light reception signals obtained by a short exposure in the first period of time to an amount of signals of the light reception signal in its entirety and an amount of second measurement signal indicative of a ratio of an amount of signal of the second light reception signal to the amount of signals of the light reception signal in its entirety.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a distance measuring device and a distance measuring method that measure distance using a TOF (Time Of Flight) method. [Background technology]

[0002] Patent Documents 1 and 2 propose a TOF distance measuring sensor and a distance measuring device that measure distance based on the time of flight of light reflected from an object. Generally, the measurement accuracy of TOF distance measuring devices deteriorates under conditions where multipath occurs, including both directly reflected light and indirectly reflected light. In response to this, Patent Documents 3 and 4, for example, propose distance measuring devices that reduce the effects of multipath. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2004-294420 [Patent Document 2] International Publication No. 2014 / 002415 [Patent Document 3] International Publication No. 2015 / 189311 [Patent Document 4] Patent Publication No. 2020-197422 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional techniques for reducing the effects of multipath have the problem that it is difficult to improve the frame rate. For example, in the distance measuring device of Patent Document 4, when it is determined that there is multipath, it is necessary to find unknown parameters required for correction by solving simultaneous equations using nonlinear estimation (repeated successive approximations), which makes it difficult to maintain the frame rate.

[0005] In view of the above-mentioned problems, an object of the present disclosure is to provide a ranging device and a ranging method that can improve the frame rate and reduce the influence of multipath. [Means for solving the problem]

[0006] In order to solve the above problem, a distance measuring device according to one aspect of the present disclosure includes an emission control unit that outputs an emission control signal, an exposure control unit that outputs an exposure control signal, an emission unit that irradiates an object to be measured with irradiation light in accordance with the emission control signal, a light receiving unit that performs exposure in accordance with the exposure control signal and outputs a light receiving signal corresponding to signal charges accumulated by the exposure, and a signal processing unit that outputs a distance signal indicating the distance to the object to be measured based on the light receiving signal. The light receiving unit performs long exposure, which is an exposure period equal to or longer than the irradiation period of the irradiation light, and short exposure, which is an exposure period shorter than the irradiation period of the irradiation light. The signal processing unit outputs a distance signal indicating the distance to the object to be measured based on the light receiving signal during a first period including the rise of reflected light from the object to be measured. is the sum of a plurality of signals obtained by the short exposure in each of a plurality of periods into which The signal processing unit calculates a total light receiving signal from the first light receiving signal and a second light receiving signal obtained by the long exposure in a second period after the first period and including a falling edge of the reflected light. are a plurality of signals obtained by the short exposure in each of a plurality of periods into which the The signal processing unit calculates one or more first measured signal amounts indicating a ratio of the signal amount of one or more received light signals, and calculates a second measured signal amount indicating a ratio of the signal amount of the second received light signal to the signal amount of all the received light signals. The signal processing unit also stores one or more first tables in which the distance to the measurement target is associated with one or more first reference signal amounts corresponding to the one or more first measured signal amounts measured in a multipath-controlled environment, and a second table in which the distance to the measurement target is associated with one or more second reference signal amounts corresponding to the one or more second measured signal amounts. The signal processing unit also calculates one or more first temporary distances from the one or more first measured signal amounts by referring to the one or more first tables, and calculates second temporary distances from the second measured signal amounts by referring to the second table. The signal processing unit also calculates a distance difference based on the one or more first temporary distances and the second temporary distances, determines the presence or absence of multipath by comparing the distance difference with a threshold, and calculates the distance by correcting the second temporary distance using the distance difference.

[0007] A distance measuring method according to one aspect of the present disclosure includes irradiating a measurement object with irradiation light from a light emitting unit, exposing the measurement object with a light receiving unit, outputting a light receiving signal corresponding to a signal charge accumulated by the exposure, and outputting a distance signal indicating the distance to the measurement object based on the light receiving signal. The light receiving unit performs long exposure, which is an exposure period equal to or longer than the irradiation period of the irradiation light, and short exposure, which is an exposure period shorter than the irradiation period of the irradiation light. In the distance measuring method, a first period including a rise of reflected light from the measurement object is detected. is the sum of a plurality of signals obtained by the short exposure in each of a plurality of periods into whichA total light receiving signal is calculated from a first light receiving signal and a second light receiving signal obtained by the long exposure in a second period after the first period and including a falling edge of the reflected light. are a plurality of signals obtained by the short exposure in each of a plurality of periods into which the One or more first measurement signal amounts indicating a ratio of the signal amount of one or more received light signals are calculated. In the distance measuring method, a second measurement signal amount indicating a ratio of the signal amount of the second received light signal to the signal amount of all the received light signals is calculated. The distance measuring method also includes one or more first tables in which the distance to the measurement target is associated with one or more first reference signal amounts corresponding to the one or more first measurement signal amounts measured in a multipath controlled environment, and a second table in which the distance to the measurement target is associated with a second reference signal amount corresponding to the second measurement signal amount. The distance measuring method also calculates one or more first temporary distances from the one or more first measurement signal amounts by referring to the one or more first tables, and calculates second temporary distances from the second measurement signal amounts by referring to the second table. The distance measuring method also calculates a distance difference based on the one or more first temporary distances and the second temporary distances, determines the presence or absence of multipath by comparing the distance difference with a threshold, and calculates the distance by correcting the second temporary distance using the distance difference. [Effects of the Invention]

[0008] According to the distance measuring device and the like according to the present disclosure, the frame rate can be improved and the influence of multipath can be reduced. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram showing an example of the configuration of a TOF distance measuring device according to the first embodiment. [Figure 2] FIG. 2 is a block diagram showing an example of the configuration of a signal processing unit in the first embodiment. [Figure 3] FIG. 3 is a diagram showing an example of a timing chart of the exposure operation in the first embodiment. [Figure 4] FIG. 4 is a diagram showing an example of a timing chart of the operation of the distance measuring device in one frame period according to the first embodiment. [Figure 5] FIG. 5 is a diagram showing another example of a timing chart of the operation of the distance measuring device in one frame period according to the first embodiment. [Figure 6] FIG. 6 is a graph showing an example of the signal amount in the first embodiment. [Figure 7] FIG. 7 is a flowchart showing an example of calculation of the provisional distance and the distance difference in the first embodiment. [Figure 8] FIG. 8 is a graph showing an example of the provisional distance and the distance difference in the first embodiment. [Figure 9]FIG. 9 is a graph showing another example of the provisional distance and the distance difference in the first embodiment. [Figure 10] FIG. 10 is a block diagram showing an example of the configuration of a signal processing unit in the second embodiment. [Figure 11] FIG. 11 is a block diagram showing an example of the configuration of a distance measuring device according to the third embodiment. [Figure 12] FIG. 12 is a block diagram showing an example of the configuration of a signal processing unit in the third embodiment. [Figure 13] FIG. 13 is a diagram showing an example of a timing chart of an exposure operation in the third embodiment. [Figure 14] FIG. 14 is a graph showing an example of the signal amount in the third embodiment. [Figure 15] FIG. 15 is a flowchart showing an example of calculation of the provisional distance and the distance difference in the third embodiment. [Figure 16] FIG. 16 is a graph showing an example of the provisional distance and the distance difference in the third embodiment. [Figure 17] FIG. 17 is a graph showing another example of the provisional distance and the distance difference in the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, distance measuring devices according to embodiments of the present disclosure will be described with reference to the drawings. Note that the following embodiments each illustrate a specific example of the present disclosure, and the numerical values, shapes, materials, components, arrangement positions and connection forms of the components are merely examples and do not limit the present disclosure.

[0011] (First embodiment) [1.1 Device configuration] Fig. 1 is a block diagram showing an example of the configuration of a TOF distance measuring device according to the first embodiment. As shown in Fig. 1, the distance measuring device 100 according to this embodiment includes a light emission control unit 101, an exposure control unit 102, a light emission unit 103, a light receiving unit 104, and a signal processing unit 105.

[0012] The light emission control unit 101 outputs a light emission control signal to the light emitting unit 103. In this embodiment, the light emission control signal is a pulse (light emission pulse).

[0013] The exposure control unit 102 outputs an exposure control signal to the light receiving unit 104. In this embodiment, the exposure control signal is a pulse (exposure pulse).

[0014] The light-emitting unit 103 emits irradiation light in accordance with a light-emitting control signal output from the light-emitting control unit 101. Here, if there is an object (including a living body such as a human) facing the light-emitting unit 103, this object becomes the measurement object OBJ. In this case, the light-emitting unit 103 will irradiate the irradiation light toward the measurement object OBJ in accordance with the light-emitting control signal.

[0015] The light-emitting unit 103 is composed of, for example, a light-emitting element, a diffuser, and a driver circuit. The light-emitting element is composed of a VCSEL (Vertical Cavity Surface Emitting Laser) or the like that emits near-infrared light with a central wavelength of about 940 nm. When the light-emitting control signal input from the light-emitting control unit 101 is at a high level, a voltage is applied to the light-emitting element via the driver circuit, and the light-emitting element emits irradiation light to the outside of the distance measuring device 100 through the diffuser.

[0016] The light receiving unit 104 is, for example, a solid-state image sensor, which performs exposure in accordance with an exposure control signal output from the exposure control unit 102 and outputs a light receiving signal corresponding to signal charges accumulated by the exposure. The light receiving unit 104 has a plurality of pixels arranged in a two-dimensional lattice, and when the exposure control signal input from the exposure control unit 102 is at a low level, each pixel is exposed to light incident from outside the distance measuring device 100, and the light is converted into signal charges and accumulated. Here, if a measurement object OBJ is present opposite the light receiving unit 104, and the light receiving unit 104 receives light reflected from the measurement object OBJ during exposure, the light receiving unit 104 will accumulate signal charges for each pixel corresponding to the amount of light reflected from the measurement object OBJ.

[0017] In this embodiment, the light receiving unit 104 is capable of accumulating multiple types of signal charges for each pixel. Furthermore, the light receiving unit 104 outputs multiple light receiving signals S0 to S3 and L1 to L2 based on the multiple types of signal charges. Here, the light receiving signals S0 to S3 are light receiving signals obtained by exposing the light receiving unit 104 when the exposure control unit 102 sets the exposure control signal to low level for a relatively short period of time. In other words, the light receiving signals S0 to S3 are light receiving signals obtained by short exposure. On the other hand, the light receiving signals L1 and L2 are light receiving signals obtained by exposing the light receiving unit 104 when the exposure control unit 102 sets the exposure control signal to low level for a relatively long period of time. In other words, the light receiving signals L1 to L2 are light receiving signals obtained by long exposure. The light receiving signals S0 to S3 and L1 to L2 will be described in detail in [1.2 Exposure Operation] below.

[0018] In this embodiment, the light receiving unit 104 is configured to perform long exposure, which is exposure for a period equal to or longer than the irradiation period of the irradiation light, and short exposure, which is exposure for a period shorter than the irradiation period of the irradiation light.

[0019] The signal processing unit 105 is configured with hardware such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). The signal processing unit 105 may also be software running on a processor such as a CPU (Central Processing Unit). The signal processing unit 105 outputs a distance signal ZO based on the input light receiving signals S0-S3 and L1-L2. The distance signal ZO is a signal that indicates the distance to the measurement object OBJ (in other words, the distance between the measurement object OBJ and the distance measuring device 100) when a measurement object OBJ exists opposite the distance measuring device 100. The distance signal ZO indicates the distance to the measurement object OBJ for each pixel.

[0020] The internal configuration of the signal processing unit 105 will now be further described with reference to Fig. 2. Fig. 2 is a block diagram showing an example configuration of the signal processing unit 105 in the first embodiment. The signal processing unit 105 includes a signal amount calculation unit 200, a provisional distance calculation unit 201, a distance difference calculation unit 202, and a distance correction unit 203.

[0021] The signal amount calculation unit 200 receives the received light signals S0-S3 and L1-L2 as inputs and outputs measurement signal amounts NS0-NS3 and NL. Here, the "measurement signal amount" refers to an amount that indicates the proportion of signal charge in a target exposure period to the total signal charge in the exposure period during which reflected light from the measurement object OBJ can be incident on the light receiving unit 104 (hereinafter also referred to as the "total exposure period"). In this embodiment, the total signal charge in the total exposure period is calculated by excluding signal charge due to ambient light that is not caused by irradiated light, known as background light. The method for calculating the measurement signal amounts NS0-NS3 and NL will be described in detail in [1.3 Operation of the signal processing unit] below.

[0022] The temporary distance calculation unit 201 holds tables TS0-TS3 of reference signal amounts RS0-RS3 and a table TL of reference signal amount RL, and outputs temporary distances ZS0-ZS3 and ZL using measurement signal amounts NS0-NS3 and NL as input. Tables TS0-TS3 and table TL are stored in a memory of the distance measuring device 100. Here, the "reference signal amount" refers to a measurement signal amount measured by gradually changing the distance to the measurement object OBJ, the irradiation timing of the irradiating light, or the exposure timing in a multipath-controlled environment before the distance measuring device 100 is actually put into operation (for example, during inspection before shipment), and is an experimental value. The "multipath-controlled environment" here refers to an environment in which there are no other reflecting objects around the measurement object OBJ and no multipath occurs, or an environment in which multipath occurs but its effect on signal measurement is so slight that it is virtually unaffected by multipath.

[0023] The "temporary distance" is the distance to the measurement object OBJ calculated from the measured signal intensity, assuming that no multipath exists. The calculation method of the temporary distances ZS0 to ZS3 and ZL will be described in detail in [1.3 Operation of the signal processing unit] below.

[0024] Distance difference calculation section 202 receives temporary distances ZS0 to ZS3 and ZL as input and outputs distance difference ZD. Here, "distance difference" is represented by a representative value of the differences between temporary distance ZL and temporary distances ZS0 to ZS3. In this embodiment, the representative value is the maximum value. The method for calculating distance difference ZD will be described in detail in [1.3 Operation of signal processing section] below.

[0025] Distance correction unit 203 receives the virtual distance ZL and the distance difference ZD as input and outputs a distance signal ZO. Here, the "distance signal" is a signal that indicates the distance to the measurement object OBJ, calculated after correcting for the effects of multipath. The method for calculating the distance signal ZO will be described in detail in [1.3 Operation of the signal processing unit] below.

[0026] In this embodiment, the light receiving unit 104 outputs four light receiving signals S0 to S3 by performing four short exposures, but this is not limited to this. For example, when the light receiving unit 104 performs n (n is a natural number) short exposures, it outputs n light receiving signals S0 to S3. n-1 In this case, the received light signals S0 to S n-1 are periods T10 to T11 obtained by dividing the first period T1 by n. n-1 In this case, the signal amount calculation unit 200 calculates the received light signals S0 to S n-1 , and L1 to L2 are used as inputs to measure signal quantities NS0 to NS n-1 , and NL. In this case, the temporary distance calculation unit 201 outputs the reference signal amounts RS0 to RS n-1 Tables TS0 to TS n-1 and a table TL of the reference signal amount RL, and the measured signal amounts NS0 to NS n-1 , and NL are used as inputs to calculate the provisional distance ZS0 to ZS n-1In this case, the distance difference calculation unit 202 outputs the provisional distances ZS0 to ZS n-1 , and ZL are input, and the distance difference ZD is output. In the following, unless otherwise specified, the case where n=4 will be described.

[0027] [1.2 Exposure operation] The exposure operation of the distance measuring device 100 in this embodiment will be described below. FIG. 3 is a diagram showing an example of a timing chart illustrating the exposure operation in the first embodiment. FIG. 3 shows an example of the exposure operation of the distance measuring device 100 in an environment where multipath interference may occur. In the diagram, "irradiated light" represents light emitted by the light-emitting unit 103 in accordance with a light emission control signal. In the diagram, "directly reflected light" represents reflected light that is received by the light-receiving unit 104 after being reflected by the measurement object OBJ without passing through another object. In the diagram, "indirectly reflected light" represents reflected light that is received by the light-receiving unit 104 after being reflected by other reflecting objects and the measurement object OBJ after being emitted by the light-emitting unit 103. The same applies to FIG. 13, which will be described later.

[0028] First, the light-emission control unit 101 sets the light-emission control signal to a high level for a certain period of time, causing the light-emitting unit 103 to emit irradiation light for a period T. Hereinafter, this period will also be referred to as the "first period T1." After a period corresponding to the distance to the measurement object OBJ has elapsed since the light-emitting unit 103 began emitting irradiation light, the directly reflected light reaches the light-receiving unit 104. After a further delay, the indirectly reflected light that has passed through the measurement object OBJ and one or more other objects reaches the light-receiving unit 104. For simplicity's sake, the changes in the light intensity of the directly reflected light and the indirectly reflected light are represented by trapezoids, but this is not necessarily the case. In addition to the directly reflected light and the indirectly reflected light, ambient light not resulting from the irradiation light, known as background light, also enters the light-receiving unit 104.

[0029] Next, in four periods, each delayed by a period T / 4 from the rising edge of the light emission control signal, the exposure control unit 102 sets the exposure control signal to a low level for the period T / 4, causing the light receiving unit 104 to expose to reflected light. These operations are called short exposures. The light receiving signals obtained by these four short exposures are called light receiving signals S0 to S3, respectively.

[0030] Specifically, the light receiving signal obtained by short exposure in the first period T10 of the four periods included in the first period T1 is light receiving signal S0, the light receiving signal obtained by short exposure in the second period T11 is light receiving signal S1, the light receiving signal obtained by short exposure in the third period T12 is light receiving signal S2, and the light receiving signal obtained by short exposure in the last period T13 is light receiving signal S3.

[0031] In other words, the light receiving signals S0 to S3 are first light receiving signals obtained by exposing the light receiving unit 104 during a first period T1 that includes the rising edge of reflected light from the measurement object OBJ. The light receiving signals S0 to S3 are also one or more light receiving signals obtained by short exposure during the first period T1. In yet other words, the light receiving signals S0 to S3 are multiple light receiving signals obtained by short exposure during each of multiple periods T10 to T13 that are obtained by dividing the first period T1. Here, the first light receiving signal is the sum of the multiple light receiving signals S0 to S3.

[0032] Next, after a first period T1 has elapsed since the rise of the light-emission control signal, the exposure control unit 102 sets the exposure control signal to a low level for a period T, thereby exposing the light-receiving unit 104 to reflected light. Hereinafter, this period will also be referred to as the "second period T2." Then, after a period xT has elapsed since the rise of the light-emission control signal, during which the incidence of reflected light becomes negligible, the exposure control unit 102 performs another exposure for a period T. Hereinafter, this period will also be referred to as the "third period T3." These operations are referred to as long exposures, and the light-receiving signals obtained by the two long exposures in the second period T2 and the third period T3 are referred to as light-receiving signals L1 and L2, respectively. Light-receiving signal L2 indicates a light-receiving signal resulting from background light. Note that the long exposure may also be realized by four consecutive short exposures.

[0033] In other words, the light receiving signal L1 is a second light receiving signal obtained by long exposure in the second period T2 after the first period T1 and including the falling edge of the reflected light, and the light receiving signal L2 is a third light receiving signal obtained by long exposure in the third period T3 including only background light.

[0034] The period T, which is the length of each of the first period T1 to the third period T3, is determined according to the range of the measurement distance of the distance measuring device 100, as shown in the following formula 1-1. max " is the upper limit of the measurement distance, and "c" is the speed of light (approximately 3 x 10 8 [m / s]).

[0035]

number

[0036] 4 is a diagram showing an example of a timing chart of the operation of one frame period of the distance measuring device 100 in the first embodiment. Here, one frame period is made up of an exposure repetition period, a readout period, and a signal processing period.

[0037] First, during the exposure repetition period, the short exposure and long exposure shown in Fig. 3 are repeated together with irradiation of the irradiated light to accumulate a sufficient amount of signal charge for distance measurement. In this embodiment, the series of steps shown in Fig. 3 is counted as one order, and is repeated, for example, several thousand times during the exposure repetition period in one frame. As a result, the signal charge required to measure the distance to the measurement object OBJ is accumulated in each pixel in the light receiving unit 104.

[0038] Next, during the readout period, the signal charges accumulated in the light receiving unit 104 are read out line by line (lines 1 to y) and pixel by pixel (P1 to Px) as light receiving signals S0 to S3 and L1 to L2. Here, the light receiving unit 104 has x columns and y rows of pixels. During the signal processing period, the signal processing unit 105 performs signal processing on the light receiving signals S0 to S3 and L1 to L2 read out in the immediately preceding frame, thereby outputting the distance signal ZO in parallel with the exposure repetition period.

[0039] Note that the exposures for the light receiving signals S0 to S3 and L1 to L2 do not necessarily have to be performed consecutively in this order; for example, each exposure may be repeated individually, as shown in FIG. 5. FIG. 5 is a diagram showing another example of a timing chart of the operation of one frame period of the distance measuring device 100 in the first embodiment. That is, in the example shown in FIG. 5, the exposure repetition period is divided into a short exposure repetition period and a long exposure repetition period. In the short exposure repetition period, short exposure is repeated for the light receiving signal S0, and then similarly short exposure is repeated for the light receiving signals S1, S2, and S3. In the long exposure repetition period, long exposure is repeated for the light receiving signal L1, and then long exposure is repeated for the light receiving signal L2. In the example shown in FIG. 5, as in the example shown in FIG. 4, during the readout period, the signal charges accumulated in the light receiving unit 104 are read out line by line (lines 1 to y) and pixel by pixel (P1 to Px) as the light receiving signals S0 to S3 and L1 to L2.

[0040] [1.3 Operation of the signal processing section] The following describes the operation of each component of the signal processing unit 105. First, the signal amount calculation unit 200 calculates the measured signal amounts NS0 to NS3 and NL based on the following formulas 1-2 and 1-3. That is, here, n=4 is substituted into each of formulas 1-2 and 1-3.

[0041] In the following formula 1-2, "i" is an integer between 0 and n-1. The term "-L2 / n" in the numerator of formula 1-2 means removing the amount of background light incident during the short exposure period. In this embodiment, the short exposure period is 1 / n of the long exposure period, so the light receiving signal L2 is also 1 / n. Similarly, the term "-L2" in the numerator of formula 1-3 means removing the amount of background light incident during the long exposure period. Furthermore, "-2×L2" in the denominator of each of formulas 1-2 and 1-3 means removing the amount of background light incident during the entire exposure period (the first period T1 and the second period T2). The same applies to formulas 2-1 and 2-2 described below.

[0042] That is, the signal amount calculation unit 200 calculates the first received light signal (received light signals S0 to S n-1 The total light receiving signal is calculated from the second light receiving signal (light receiving signal L1) and the total light receiving signal (light receiving signals S0 to S1). n-1 1 or more first measured signal amounts (measured signal amounts NS0 to NS- n-1 ) is calculated.

[0043] Furthermore, the signal amount calculation section 200 calculates a second measured signal amount (measured signal amount NL) that indicates the ratio of the signal amount of the second received light signal to the signal amount of all received light signals.

[0044] In addition, in this embodiment, the signal amount calculation unit 200 subtracts the third light receiving signal (light receiving signal L2) from the first light receiving signal, the second light receiving signal, and the total light receiving signal, and then calculates one or more first measurement signal amounts and second measurement signal amounts.

[0045] In addition, the aforementioned reference signal amounts RS0 to RS n-1 is one or more first measurement signal quantities (measurement signal quantities NS0 to NS- n-1 ) is a first reference signal amount of 1 or more corresponding to the second measured signal amount (measured signal amount NL) measured in a multipath controlled environment.

[0046]

number

[0047] Next, the temporary distance calculation unit 201 calculates temporary distances ZS0 to ZS3 by comparing the measured signal amounts NS0 to NS3 with the reference signal amounts RS0 to RS3 stored in the tables TS0 to TS3, respectively. The temporary distance calculation unit 201 also calculates temporary distance ZL by comparing the measured signal amount NL with the reference signal amount RL stored in the table TL.

[0048] Fig. 6 is a graph showing an example of signal amounts in the first embodiment. In Fig. 6, the vertical axis represents signal amount, and the horizontal axis represents distance to the measurement object OBJ. The solid lines in Fig. 6 represent reference signal amounts RS0 to RS3 and RL measured for each distance to the measurement object OBJ in a multipath controlled environment. The dotted lines in Fig. 6 represent measured signal amounts NS0 to NS3 and NL measured for each distance to the measurement object OBJ under certain conditions where multipath occurs. The same applies to Figs. 8 and 9 described below.

[0049] In this way, the signal intensity changes depending on whether or not there is an effect of multipath, even if the measurement object OBJ is at the same distance from the distance measuring device 100. Note that the tables TS0 to TS3 and TL may be expressed by approximate values ​​such as polynomials or broken lines, rather than by actual measured values.

[0050] Taking the above characteristics into consideration, the temporary distance calculation unit 201 calculates the temporary distances ZL and ZS0 to ZS3 according to the procedure shown in steps 1 and 2 of Fig. 7. Fig. 7 is a flowchart showing an example of calculation of the temporary distance and the distance difference in the first embodiment.

[0051] In STEP 1, the temporary distance calculation unit 201 calculates the temporary distance ZL using a function called DISTANCE(Tx, Nx). "x" represents Si or L. Here, DISTANCE(Tx, Nx) is a function that searches table Tx for a reference signal amount Rx whose signal amount is closest to the measured signal amount Nx, and returns the distance corresponding to that reference signal amount Rx. That is, in STEP 1, the temporary distance calculation unit 201 searches table TL for a reference signal amount RL whose signal amount is closest to the measured signal amount NL, and calculates the distance corresponding to that reference signal amount RL as the temporary distance ZL.

[0052] In STEP 2, the temporary distance calculation unit 201 searches the table TSi for a reference signal amount RSi whose signal amount is closest to the measured signal amount NSi, and calculates the distance corresponding to the reference signal amount RSi as the temporary distance ZSi.

[0053] However, i is an integer between 0 and 3, and the temporary distance calculation unit 201 invalidates the temporary distance ZSi when the measured signal amount NSi is 0. Furthermore, when there are multiple reference signal amounts RSi in the table TSi whose signal amounts are closest to the measured signal amount NSi, the maximum distance among the multiple distances corresponding to the reference signal amount RSi is selected as the temporary distance ZSi.

[0054] It should be noted that by using the signal amount as the index of the tables TS0 to TS3 and TL and the distance as the value to be stored, it is possible to calculate the tentative distance at high speed.

[0055] In this way, the temporary distance calculation unit 201 calculates the distance to the measurement object OBJ and one or more first reference signal amounts (reference signal amounts RS0 to RS n-1 ) and one or more first tables (TS0 to TS n-1 ) and a second table (TL) in which the distance to the measurement object OBJ is associated with the second reference signal amount (RL). The temporary distance calculation unit 201 then refers to one or more first tables to calculate one or more first temporary distances (temporary distances ZS0 to ZS1) from one or more first measurement signal amounts. n-1 ) Further, the temporary distance calculation unit 201 calculates a second temporary distance (temporary distance ZL) from the second measured signal amount by referring to a second table.

[0056] Next, in STEP 3 of FIG. 7, the distance difference calculation unit 202 calculates MAX i=0~3 The distance difference ZD is calculated using a function called (ZL-ZSi). That is, the distance difference calculation unit 202 calculates the distance difference ZD using the following formula 1-4. In formula 1-4, MAX(a,b,c,d) is a function that returns the maximum value from a, b, c, and d (excluding invalid values). Also, here, n=4 is substituted into formula 1-4.

[0057]

number

[0058] Below, a description will be given of a specific example of calculation of the temporary distances ZL and ZSi by the temporary distance calculation unit 201 and calculation of the distance difference ZD by the distance difference calculation unit 202. Fig. 8 is a graph showing an example of the temporary distances ZL and ZSi and the distance difference ZD in the first embodiment.

[0059] First, assume that the true value of the distance to the measurement object OBJ (i.e., the actual distance) is ZT1, and that under conditions where a certain amount of multipath occurs, the measured signal amount NL is a signal amount a1. In this case, the temporary distance calculation unit 201 calculates the distance at which the reference signal amount RL is closest to a signal amount a1 as the temporary distance ZL. Next, because the measured signal amounts NS0 and NS1 are both 0, the temporary distance calculation unit 201 invalidates the temporary distances ZS0 and ZS1. Furthermore, because the measured signal amount NS2 is a signal amount b1, the temporary distance calculation unit 201 calculates the distance at which the reference signal amount RS2 is closest to b1 as the temporary distance ZS2. Similarly, because the measured signal amount NS3 is a signal amount c1, the temporary distance calculation unit 201 calculates the distance at which the reference signal amount RS3 is closest to c1 as the temporary distance ZS3. However, since there are many corresponding distances, the temporary distance calculation unit 201 determines the maximum distance among them as the temporary distance ZS3.

[0060] Since ZL-ZS2>ZL-ZS3, distance difference calculation unit 202 calculates distance difference ZD as ZL-ZS2 based on equation 1-4. Note that in this example, temporary distances ZS0 and ZS1 are invalid values, so distance difference calculation unit 202 does not consider ZL-ZS0 and ZL-ZS1 when calculating distance difference ZD.

[0061] 9 is a graph showing another example of the tentative distances ZL and ZSi and the distance difference ZD in the first embodiment. Note that (b) of FIG. 9 is an enlarged view of the section X in (a) of FIG. 9.

[0062] First, assume that the true value of the distance to the measurement object OBJ is ZT2, and that under conditions where a certain amount of multipath occurs, the measured signal amount NL is a signal amount a2. In this case, the temporary distance calculation unit 201 calculates the distance at which the reference signal amount RL is closest to a signal amount a2 as the temporary distance ZL. Next, because the measured signal amount NS0 is a signal amount of 0, the temporary distance calculation unit 201 invalidates the temporary distance ZS0. Furthermore, because the measured signal amount NS1 is a signal amount b2, the temporary distance calculation unit 201 calculates the distance at which the reference signal amount RS1 is closest to b2 as the temporary distance ZS1. Similarly, because the measured signal amount NS2 is a signal amount c2, the temporary distance calculation unit 201 calculates the distance at which the reference signal amount RS2 is closest to c2 as the temporary distance ZS2. Furthermore, since the measured signal level NS3 is the signal level d2, the temporary distance calculation unit 201 calculates the distance at which the reference signal level RS3 is closest to the signal level d2 as the temporary distance ZS3. However, since there are many corresponding distances, the temporary distance calculation unit 201 determines the largest distance among them as the temporary distance ZS3.

[0063] Then, since ZL-ZS1>ZL-ZS2>ZL-ZS3, distance difference calculation unit 202 calculates distance difference ZD as ZL-ZS1 based on equation 1-4. Note that in this example, since temporary distance ZS0 is an invalid value, distance difference calculation unit 202 does not consider ZL-ZS0 when calculating distance difference ZD.

[0064] The distance correction unit 203 compares the distance difference ZD with a threshold value α to determine whether or not there is a multipath effect. Specifically, if the distance difference ZD is equal to or less than the threshold value α, the distance correction unit 203 determines that there is no multipath effect. In this case, the distance correction unit 203 calculates a distance signal ZO using the following equation 1-5, in other words, calculates the distance to the measurement object OBJ. In this case, the temporary distance ZL is calculated as the distance signal ZO. On the other hand, if the distance difference ZD is greater than the threshold value α, the distance correction unit 203 determines that there is a multipath effect. In this case, the distance correction unit 203 calculates the distance signal ZO using the following equation 1-6. Note that in the following equation 1-6, "β" is a preset adjustment coefficient for determining the degree of distance correction. In this case, the distance signal ZO is calculated by subtracting a distance corresponding to the difference between the distance difference ZD and the threshold value α from the temporary distance ZL.

[0065]

number

[0066] In this way, the signal processing unit 105 detects one or more first measured signal amounts (measured signal amounts NS0 to NS- n-1 ) and a second measurement signal amount (measurement signal amount NL), and one or more first reference signal amounts (reference signal amounts RS0 to RS n-1 ) and a second reference signal amount (reference signal amount RL) to calculate the distance to the measurement object OBJ.

[0067] Furthermore, the distance difference calculation unit 202 calculates one or more first temporary distances (temporary distances ZS0 to ZS n-1 ) and the second temporary distance (temporary distance ZL), and determines whether or not there is a multipath by comparing the distance difference ZD with a threshold α. The distance difference calculation unit 202 also corrects the second temporary distance using the calculated distance difference ZD to calculate the distance.

[0068] In this embodiment, the one or more first temporary distances are a plurality of first temporary distances, and the distance difference calculation unit 202 calculates the difference between each of the plurality of first temporary distances and the second temporary distance (ZL-ZS0, ZL-ZS1, ..., ZL-ZS n-1 ) and the maximum value is taken as the distance difference ZD.

[0069] Through the above operations, the distance measuring device 100 can calculate the distance to the measurement object OBJ using the light receiving signal that is least affected by multipath among the light receiving signals S0 to S3 as a reference. Here, the "light receiving signal that is least affected by multipath" refers to a light receiving signal that does not contain signal charge due to indirectly reflected light, or a light receiving signal that contains signal charge due to indirectly reflected light but has the smallest signal charge.

[0070] [1.4 Effects, etc.] The distance measuring device 100 in this embodiment can correct distance measurement errors caused by the effects of multipath simply by comparing the measurement signal amount obtained by short exposure and long exposure at multiple timings with the reference signal amount stored in a table and performing simple calculations, and can achieve distance measurements with reduced effects of multipath at an inexpensive and practical frame rate.

[0071] As described above, the distance measuring device 100 in the first embodiment includes an emission control unit 101 that outputs an emission control signal, an exposure control unit 102 that outputs an exposure control signal, an emission unit 103 that irradiates the measurement object OBJ with irradiation light in accordance with the emission control signal, a light receiving unit 104 that performs exposure in accordance with the exposure control signal and outputs a light receiving signal corresponding to signal charges accumulated by the exposure, and a signal processing unit 105 that outputs a distance signal ZO indicating the distance to the measurement object OBJ based on the light receiving signal. The light receiving unit 104 performs long exposure, which is exposure for a period equal to or longer than the irradiation period of the irradiation light, and short exposure, which is exposure for a period shorter than the irradiation period of the irradiation light. The signal processing unit 105 processes a first light receiving signal (light receiving signals S0 to S1) obtained by exposure of the light receiving unit 104 in a first period T1 that includes the rise of reflected light from the measurement object OBJ. n-1), and a second light receiving signal (light receiving signal L1) obtained by long exposure in a second period T2 after the first period T1 and including the falling edge of the reflected light, and n-1 and light receiving signal L1). The signal processing unit 105 also calculates the ratio of one or more light receiving signals (light receiving signals S0 to S1) obtained by short exposure in the first period T1 to the signal amount of all light receiving signals. n-1 ) n-1 ) and the signal processing unit 105 calculates a second measured signal amount (measured signal amount NL) that indicates the ratio of the signal amount of the second received light signal to the signal amount of all received light signals. The signal processing unit 105 then calculates one or more first measured signal amounts and one or more second measured signal amounts, and one or more first reference signal amounts (reference signal amounts RS0 to RS10) that correspond to the one or more first measured signal amounts and one or more second measured signal amounts measured in a multipath controlled environment, respectively. n-1 ) and a second reference signal amount (reference signal amount RL) to calculate the distance.

[0072] This makes it possible to improve the frame rate and reduce the influence of multipath. That is, the distance measuring device 100 can calculate the distance based on the received light signal that is relatively less affected by multipath by a simple calculation of comparing one or more first measurement signal amounts and second measurement signal amounts with one or more first reference signal amounts and second reference signal amounts. Therefore, it is not necessary to perform a relatively heavy calculation such as nonlinear estimation as in the distance measuring device of Patent Document 4, and the frame rate can be improved.

[0073] Also, for example, one or more received light signals S0 to S n-1 are the multiple periods T10 to T1 obtained by dividing the first period T1. n-1 The first light receiving signal may be a plurality of light receiving signals S0 to S1 obtained by short exposure in each of the first and second light receiving signals. n-1 may be the sum of

[0074] According to this, a plurality of light receiving signals S0 to S n-1In either case, the received signal is relatively less affected by multipath, making it easier to reduce the effects of multipath.

[0075] Furthermore, for example, the light receiving unit 104 may further output a third received light signal (received light signal L2) obtained from a long exposure in a third period T3 including only background light. Then, the signal processing unit 105 (signal amount calculation unit 200) may calculate one or more first measurement signal amounts and second measurement signal amounts by subtracting the third received light signal from the first received light signal, the second received light signal, and the total received light signal.

[0076] This allows the accuracy of calculating one or more first measurement signal quantities and second measurement signal quantities to be improved by removing the influence of background light, which is disturbance light not caused by the irradiated light, and as a result, the accuracy of distance measurement to be improved.

[0077] Also, for example, the signal processing unit 105 (temporary distance calculation unit 201) calculates the distance to the measurement object OBJ and one or more first reference signal amounts (reference signal amounts RS0 to RS n-1 ) and one or more first tables (TS0 to TS n-1 ), and a second table (TL) in which the distance to the measurement object OBJ is associated with the second reference signal amount (RL). The signal processing unit 105 (temporary distance calculation unit 201) then refers to one or more first tables to calculate one or more first temporary distances (temporary distances ZS0 to ZS1) from one or more first measurement signal amounts. n-1 Alternatively, the signal processing unit 105 (temporary distance calculation unit 201) may calculate the second temporary distance (temporary distance ZL) from the second measured signal amount by referring to a second table.

[0078] This allows one or more first temporary distances and one or more second temporary distances to be calculated through a simple process of referencing one or more first tables and one or more second tables that have been prepared in advance, thereby reducing the processing load on the distance measuring device 100.

[0079] Furthermore, for example, the signal processing unit 105 (distance difference calculation unit 202) calculates one or more first temporary distances (temporary distances ZS0 to ZSn-1 ) and the second tentative distance (tentative distance ZL), and then the presence or absence of multipath may be determined by comparing the distance difference ZD with a threshold α.

[0080] According to this, the presence or absence of multipath can be determined by the simple process of comparing the distance difference ZD with the threshold value α, so that the processing load of the distance measuring device 100 can be reduced.

[0081] Furthermore, for example, the signal processing unit 105 (distance difference calculation unit 202) may calculate the distance by correcting the second temporary distance (temporary distance ZL) using the calculated distance difference ZD.

[0082] According to this, the reliability of distance measurement can be improved by making appropriate adjustments taking into account that the first measurement signal amount, which is one or more and is referenced when calculating the distance difference ZD, is based on the signal charge of the light receiving signal during the short exposure period and therefore has a smaller S / N ratio compared to the signal charge of the light receiving signal during the long exposure period.

[0083] Also, for example, one or more first temporary distances (temporary distances ZS0 to ZS n-1 ) are a plurality of first temporary distances, and the signal processing unit 105 (distance difference calculation unit 202) calculates the difference (ZL-ZS0, ZL-ZS1, ..., ZL-ZS) between each of the plurality of first temporary distances and the second temporary distance (temporary distance ZL). n-1 ) and the maximum value may be used as the distance difference ZD.

[0084] This makes it possible to improve the accuracy of distance measurement by referencing the first temporary distance that is considered to have the maximum distance difference ZD, that is, the distance that is closest to the true value ZT of the distance to the measurement object OBJ.

[0085] The distance measurement method in the first embodiment involves irradiating the measurement object OBJ with irradiation light from the light-emitting unit 103, exposing the light-receiving unit 104, outputting a light-receiving signal corresponding to the signal charge accumulated by the exposure, and outputting a distance signal ZO indicating the distance to the measurement object OBJ based on the light-receiving signal. The light-receiving unit 104 performs long exposure, which is exposure for a period equal to or longer than the irradiation period of the irradiation light, and short exposure, which is exposure for a period shorter than the irradiation period of the irradiation light. In the distance measurement method, a first light-receiving signal (light-receiving signals S0 to S1) obtained by exposure of the light-receiving unit 104 in a first period T1 including the rise of reflected light from the measurement object OBJ is output as a distance signal ZO. n-1 ), and a second light receiving signal (light receiving signal L1) obtained by long exposure in a second period T2 after the first period T1 and including the falling edge of the reflected light, and n-1 and light receiving signal L1). In addition, in the distance measurement method, the ratio of one or more light receiving signals (light receiving signals S0 to S1) obtained by short exposure in the first period T1 to the signal amount of all light receiving signals is calculated. n-1 ) n-1 ) is calculated. In addition, the distance measuring method calculates a second measured signal amount (measured signal amount NL) that indicates the ratio of the signal amount of the second received light signal to the signal amount of all received light signals. Then, the distance measuring method calculates one or more first reference signal amounts (reference signal amounts RS0 to RS10) that correspond to one or more first measured signal amounts and one or more second measured signal amounts, respectively, measured in a multipath controlled environment. n-1 ) and a second reference signal amount (reference signal amount RL) to calculate the distance.

[0086] This makes it possible to improve the frame rate and reduce the influence of multipath. That is, the distance measuring method can calculate the distance based on the received light signal that is relatively less affected by multipath by a simple calculation of comparing one or more first measurement signal amounts and second measurement signal amounts with one or more first reference signal amounts and second reference signal amounts. Therefore, it is not necessary to perform a relatively heavy calculation such as nonlinear estimation as in the distance measuring device of Patent Document 4, and therefore the frame rate can be improved.

[0087] (Second embodiment) [2.1 Device Configuration] The TOF distance measuring device 100 of this embodiment has the same configuration as the first embodiment, as shown in Fig. 1. However, the distance measuring device 100 of this embodiment differs from the first embodiment in the configuration of the signal processing unit 105. Below, a description of the points in common with the first embodiment will be omitted, and the description will focus on the points that are different from the first embodiment.

[0088] 10 is a block diagram showing the internal configuration of the signal processing unit 105 in this embodiment. As in the first embodiment, the signal processing unit 105 includes a signal amount calculation unit 200, a tentative distance calculation unit 201, a distance difference calculation unit 202, and a distance correction unit 203. The signal processing unit 105 of this embodiment further includes a received light signal smoothing unit 301 and a distance difference smoothing unit 305. The signal processing unit 105 of this embodiment also includes line memories 300, 303, 304, and 307, and selectors 302 and 306.

[0089] [2.2 Exposure Operation] The exposure operation in this embodiment is the same as that in Embodiment 1. That is, during the readout period, the distance measuring device 100 reads out the signal charges accumulated in the light receiving unit 104 as light receiving signals S0 to S3 and L1 to L2 for each line (1 to y lines) and for each pixel (P1 to Px).

[0090] [2.3 Operation of the signal processing section] The operation of the signal processing unit 105 in this embodiment will be described below. As shown in Fig. 10, the received light signals S0 to S3 pass through a line memory 300, are delayed line by line, and then input to a received light signal smoothing unit 301 as five lines of received light signals. The received light signal smoothing unit 301 is configured with an edge-preserving smoothing filter (here, a 5 x 5 pixel bilateral filter), smoothes the received light signals S0 to S3 while maintaining edge information to a certain extent, and outputs the smoothed signals as received light signals S0_FLT to S3_FLT. Furthermore, the received light signals L1 to L2 are input to the signal amount calculation unit 200 via a line memory 303 to match the line-by-line delay with the received light signals S0_FLT to S3_FLT. Note that pixel-by-pixel delays are not shown in Fig. 10.

[0091] The selector 302 selects the signals to be input to the signal amount calculation unit 200 from the light receiving signals S0 to S3 and the smoothed light receiving signals S0_FLT to S3_FLT. That is, when the input parameter SEL_S is "0," the selector 302 selects the light receiving signals S0 to S3. In this case, the light receiving signals S0 to S3 input to the signal amount calculation unit 200 are equivalent to those in the first embodiment. On the other hand, when the parameter SEL_S is "1," the selector 302 selects the smoothed light receiving signals S0_FLT to S3_FLT. In this case, the smoothed light receiving signals S0_FLT to S3_FLT are input to the signal amount calculation unit 200, improving the S / N ratios of the measurement signal amounts NS0 to NS3 and NL. The parameter SEL_S may be set in advance, for example, when the distance measuring device 100 is used, or may be set appropriately by the user.

[0092] It should be noted that compared to the light receiving signals L1 to L2, the light receiving signals S0 to S3 have a shorter exposure period and tend to have a relatively lower S / N ratio. For this reason, in this embodiment, only the light receiving signals S0 to S3 are smoothed, but the light receiving signals L1 to L2 may also be smoothed. In this case, a light receiving signal smoothing unit and a selector may be further provided after the line memory 303.

[0093] The distance difference ZD calculated by the distance difference calculation unit 202 passes through a line memory 304, is delayed by a line unit, and then input to a distance difference smoothing unit 305 as a distance difference for five lines. The distance difference smoothing unit 305 is configured with an edge-preserving smoothing filter (here, a 5×5 pixel bilateral filter), smoothes the distance difference ZD while maintaining edge information to a certain extent, and outputs the smoothed distance difference ZD_FLT. Furthermore, the temporary distance ZL is input to the distance correction unit 203 via a line memory 307 to match the distance difference ZD_FLT with the line-unit delay.

[0094] The selector 306 selects the signal to be input to the distance correction unit 203 from the distance difference ZD and the smoothed distance difference ZD_FLT. That is, when the parameter SEL_ZD is "0," the selector 306 selects the distance difference ZD. In this case, the distance difference ZD input to the distance correction unit 203 is the same as in the first embodiment. On the other hand, when the parameter SEL_ZD is "1," the selector 306 selects the smoothed distance difference ZD_FLT. In this case, the smoothed distance difference ZD_FLT is input to the distance correction unit 203, improving the S / N ratio of the distance signal ZO. The parameter SEL_ZD may be set in advance, for example, when the distance measuring device 100 is used, or may be set appropriately by the user.

[0095] [2.4 Effects, etc.] As with the first embodiment, the distance measuring device 100 of this embodiment can correct distance measurement errors due to the effects of multipath by simply comparing the measurement signal amounts obtained by short exposure and long exposure at multiple timings with the reference signal amounts stored in a table and performing simple calculations. This allows distance measurements with reduced multipath effects to be achieved inexpensively and at a practical frame rate. Furthermore, the distance measuring device 100 of this embodiment can eliminate the decrease in S / N caused by the short exposure period compared to the first embodiment by smoothing the received light signals S0 to S3. Furthermore, the distance measuring device 100 of this embodiment can improve the S / N of the distance signal ZO without losing edge information of the distance compared to the first embodiment by smoothing the distance difference ZD.

[0096] As described above, in the distance measuring device 100 according to the second embodiment, the light receiving unit 104 includes a plurality of pixels arranged in a two-dimensional lattice pattern. The signal processing unit 105 smooths each of the plurality of pixels using adjacent pixels (i.e., using the light receiving signal smoothing unit 301) to generate one or more light receiving signals (light receiving signals S0 to S1). n-1 ) based on one or more first measurement signal quantities (measurement signal quantities NS0 to NS n-1 ) is calculated.

[0097] This can eliminate the decrease in S / N caused by a short exposure period of one or more received light signals, and improve the accuracy of distance measurement.

[0098] Furthermore, for example, the signal processing unit 105 may smooth the distance difference ZD using pixels adjacent to each of the plurality of pixels (that is, using the distance difference smoothing unit 305).

[0099] This makes it possible to improve the S / N ratio of the distance signal ZO without losing edge information of the distance, thereby improving the accuracy of distance measurement.

[0100] (Third embodiment) [3.1 Device configuration] Fig. 11 is a block diagram showing an example of the configuration of a TOF distance measuring device 1100 according to the third embodiment. As shown in Fig. 11, the distance measuring device 1100 according to this embodiment includes a light receiving unit 1104, a signal processing unit 1105, and, similarly to the first embodiment, an emission control unit 101, an exposure control unit 102, and an emission unit 103. Below, a description of the points in common with the first embodiment will be omitted, and the description will focus on the points that are different from the first embodiment.

[0101] The light receiving unit 1104 is, for example, a solid-state image sensor having multiple pixels arranged in a two-dimensional grid. When the exposure control signal input from the exposure control unit 102 is at a low level, the light receiving unit 1104 exposes each pixel to light incident from outside the distance measuring device 1100, converts the light into signal charges, and accumulates the signal charges. If a measurement object OBJ faces the light receiving unit 1104, the light receiving unit 1104 receives light reflected from the measurement object OBJ during exposure, and accumulates signal charges for each pixel according to the amount of light reflected from the measurement object OBJ. The light receiving unit 1104 is also capable of accumulating multiple types of signal charges for each pixel. Furthermore, the light receiving unit 1104 outputs multiple light receiving signals S0 and L0-L2 based on the multiple types of signal charges. Here, the light receiving signal L0, like the light receiving signals L1-L2, is a light receiving signal obtained by long exposure. The light receiving signals S0 and L0-L2 will be described in detail in [3.2 Exposure Operation] below.

[0102] The signal processing unit 1105 is configured with hardware such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). The signal processing unit 1105 may also be software that runs on a processor such as a CPU (Central Processing Unit). The signal processing unit 1105 receives the light reception signals S0 and L0 to L2 as inputs and outputs a distance signal ZO.

[0103] 12 is a block diagram showing an example of the configuration of the signal processing unit 1105 in the third embodiment. The signal processing unit 1105 includes a signal amount calculation unit 1200, a temporary distance calculation unit 1201, a distance difference calculation unit 1202, and a distance correction unit 203, similar to the first embodiment.

[0104] The signal amount calculation unit 1200 receives the received light signals S0 and L0 to L2 as inputs and outputs the measured signal amounts NS0 and NL. The method for calculating the measured signal amounts NS0 and NL will be described in detail in [3.3 Operation of the signal processing unit] below.

[0105] The temporary distance calculation unit 1201 holds a table TS0 of reference signal levels RS0 and a table TL of reference signal levels RL, and outputs temporary distances ZS0 and ZL using the measured signal levels NS0 and NL as inputs. The method for calculating the temporary distances ZS0 and ZL will be described in detail in [3.3 Operation of the signal processing unit] below.

[0106] Distance difference calculation section 1202 receives tentative distances ZS0 and ZL as inputs and outputs distance difference ZD. The method of calculating distance difference ZD will be described in detail in [3.3 Operation of signal processing section] below.

[0107] Distance correction unit 203 receives the tentative distance ZL and the distance difference ZD as input and outputs a distance signal ZO. The method of calculating the distance signal ZO will be described in detail in [3.3 Operation of the signal processing unit] below.

[0108] [3.2 Exposure Operation] The following describes the exposure operation of the distance measuring device 1100 in this embodiment. Fig. 13 is a diagram showing an example of a timing chart of the exposure operation in the third embodiment.

[0109] First, the light-emission control unit 101 sets the light-emission control signal to high level for a certain period of time, causing the light-emitting unit 103 to emit irradiation light for a period T. After a period corresponding to the distance to the measurement object OBJ has elapsed since the light-emitting unit 103 started emitting the irradiation light, the directly reflected light reaches the light-receiving unit 1104. After a further delay, the indirectly reflected light that has passed through the measurement object OBJ and one or more other objects reaches the light-receiving unit 1104. Note that for simplicity of illustration, the changes in the light intensity of the directly reflected light and the indirectly reflected light are shown as trapezoids, but this is not limited to this. In addition to the directly reflected light and the indirectly reflected light, ambient light that is not caused by the irradiation light, known as background light, also enters the light-receiving unit 1104.

[0110] Next, after a period T / 2 has elapsed since the rise of the light emission control signal, the exposure control unit 102 sets the exposure control signal to a low level for a period T / 4, causing the light receiving unit 1104 to expose to reflected light. The light receiving signal obtained by this short exposure is designated as light receiving signal S0. In other words, in this embodiment, unlike the first embodiment, short exposure is performed only once, for a period T10, in the first period T1.

[0111] Next, at the rising edge of the light emission control signal and after a period T has elapsed since the rising edge, the exposure control unit 102 sets the exposure control signal to low level for the period T, thereby exposing the light receiving unit 1104 to reflected light. Then, after a period xT has elapsed since the rising edge of the light emission control signal, during which the incidence of reflected light becomes negligible, the exposure control unit 102 performs another exposure for the period T. The light receiving signals obtained by these three long exposures are referred to as light receiving signals L0 to L2, respectively. Light receiving signal L2 represents a light receiving signal resulting from background light.

[0112] Note that these exposure operations are repeated in one frame period in the same manner as in the first embodiment in order to accumulate sufficient signal charges.

[0113] [3.3 Operation of the signal processing section] The operation of each component of the signal processing unit 1105 in this embodiment will be described below. First, the signal amount calculation unit 1200 calculates the measured signal amounts NS0 and NL based on the following formulas 2-1 and 2-2.

[0114]

number

[0115] Next, the temporary distance calculation unit 1201 calculates the temporary distance ZS0 by comparing the measured signal level NS0 with the reference signal level RS0 stored in the table TS0. The temporary distance calculation unit 1201 also calculates the temporary distance ZL by comparing the measured signal level NL with the reference signal level RL stored in the table TL.

[0116] Fig. 14 is a graph showing an example of signal intensity in the third embodiment. In Fig. 14, the vertical axis represents signal intensity, and the horizontal axis represents distance to the measurement object OBJ. The solid lines in Fig. 14 represent reference signal intensity RS0 and RL measured for each distance to the measurement object OBJ in a multipath-controlled environment. The dotted lines in Fig. 14 represent measured signal intensity NS0 and NL measured for each distance to the measurement object OBJ under certain multipath conditions.

[0117] In this way, the signal intensity changes depending on whether or not there is an effect of multipath, even if the measurement object OBJ is at the same distance from the distance measuring device 1100. Note that the tables TS0 and TL may be expressed by approximate values ​​such as polynomials or broken lines, rather than by actual measured values.

[0118] Taking the above characteristics into consideration, the temporary distance calculation unit 1201 calculates the temporary distances ZL and ZS0 according to the procedure shown in steps 1 and 2 of Fig. 15. Fig. 15 is a flowchart showing an example of calculation of the temporary distance and the distance difference in the third embodiment.

[0119] In STEP 1, the temporary distance calculation unit 1201 calculates the temporary distance ZL using a function called DISTANCE(Tx, Nx), where "x" represents S0 or L. That is, in STEP 1, the temporary distance calculation unit 1201 searches the table TL for a reference signal amount RL whose signal amount is closest to the measured signal amount NL, and calculates the distance corresponding to the reference signal amount RL as the temporary distance ZL.

[0120] In STEP 2, the temporary distance calculation unit 1201 searches table TS0 for the reference signal amount RS0 whose signal amount is closest to the measured signal amount NS0, and calculates the distance corresponding to that reference signal amount RS0 as the temporary distance ZS0. However, if the measured signal amount NS0 is 0, the temporary distance calculation unit 1201 invalidates the temporary distance ZS0. Furthermore, if there are multiple reference signal amounts RS0 whose signal amounts are closest to the measured signal amount NS0 in table TS0, the temporary distance calculation unit 1201 selects the largest distance among the multiple distances corresponding to the reference signal amount RS0 as the temporary distance ZS0. Note that by using the signal amount as the index of tables TS0 and TL and the distance as the stored value, it is possible to calculate the temporary distance quickly.

[0121] Next, in STEP 3 of Fig. 15, the distance difference calculation unit 1202 calculates the distance difference ZD using a function called MAX(ZL-ZS0,0). That is, if the temporary distance ZS0 is an invalid value, the distance difference calculation unit 1202 sets the distance difference ZD to 0, and if the temporary distance ZS0 is not an invalid value, it calculates ZD using the following formula 2-3. Here, in formula 2-3, MAX(a,b) is a function that returns the maximum value of a and b.

[0122]

number

[0123] Below, a description will be given of a specific example of calculation of the temporary distances ZL and ZS0 by the temporary distance calculation unit 1201 and calculation of the distance difference ZD by the distance difference calculation unit 1202. Fig. 16 is a graph showing an example of the temporary distances ZL and ZS0 and the distance difference ZD in the third embodiment.

[0124] First, assume that the true value of the distance to the measurement target OBJ is ZT3, and under the condition that a certain multipath occurs, the measured signal amount NL becomes the signal amount a3. In this case, the provisional distance calculation unit 1201 calculates the provisional distance ZL as the distance at which the reference signal amount RL is closest to the signal amount a3. Next, since the measured signal amount NS0 becomes the signal amount b3, the provisional distance calculation unit 1201 calculates the provisional distance ZS0 as the distance at which the reference signal amount RS0 is closest to the signal amount b3. Therefore, the distance difference calculation unit 1202 calculates the distance difference ZD as ZL - ZS0.

[0125] FIG. 17 is a graph showing another example of the provisional distances ZL, ZS0, and the distance difference ZD in the third embodiment. First, assume that the true value of the distance to the measurement target OBJ is ZT4, and under the condition that a certain multipath occurs, the measured signal amount NL becomes the signal amount a4. In this case, the provisional distance calculation unit 1201 calculates the provisional distance ZL as the distance at which the reference signal amount RL is closest to the signal amount a4. Next, since the measured signal amount NS0 becomes the signal amount b4 and there are a plurality of distances at which the reference signal amount RS0 is closest to the signal amount b4, the provisional distance calculation unit 1201 calculates the maximum distance among them as the provisional distance ZS0. Therefore, since ZL < ZS0, the distance difference calculation unit 1202 calculates the distance difference ZD as 0.

[0126] Similar to the first embodiment, the distance correction unit 203 calculates the distance signal ZO in which the influence of the multipath is corrected by Equations 1-5 and 1-6. However, as in the example shown in FIG. 17, depending on the true value ZT4 of the distance to the measurement target OBJ, even in a situation where it is affected by the multipath, the distance difference calculation unit 1202 calculates the distance difference ZD as 0. In this case, the distance correction is not performed.

[0127] [3.4 Effects, etc.] The distance measuring device 1100 of this embodiment can correct distance measurement errors due to the influence of multipath only by comparing the measurement signal amount obtained by short exposure at a single timing and long exposure at multiple timings with the reference signal amount stored in a table and by performing simple calculations, and can achieve distance measurement with reduced influence of multipath within a predetermined distance range at low cost and at a practical frame rate. Furthermore, since the number of tables of reference signal amount is reduced compared to the first embodiment, the manufacturing cost of the signal processing unit 1105 can be reduced.

[0128] As described above, in the distance measuring device 1100 of the third embodiment, one or more light receiving signals (here, one light receiving signal S0) are one or more signals (here, one signal) obtained by short exposure in one or more periods (here, one period) included in the first period T1. The first light receiving signal (light receiving signal L0) is a light receiving signal obtained by long exposure in the first period T1.

[0129] This means that the signal processing unit 1105 needs to refer to fewer received light signals, and therefore the reference signal amount used for comparison with the measured signal amount based on the received light signal can also be reduced, resulting in a reduction in memory capacity and a reduction in the manufacturing cost of the signal processing unit 1105. [Industrial Applicability]

[0130] The distance measuring device according to the present disclosure can perform distance measurement at a high frame rate with reduced effects of multipath, and is therefore useful for three-dimensional measurement in indoor transport robots, for example. [Explanation of symbols]

[0131] 100, 1100 range finder 101 Light emission control unit 102 Exposure control unit 103 Light-emitting part 104, 1104 Light receiving section 105, 1105 Signal processing section 200, 1200 Signal amount calculation section 201, 1201 Temporary distance calculation unit 202, 1202 distance difference calculation unit 203 Distance correction unit 301 Received light signal smoothing unit 305 Distance difference smoothing section 300, 303, 304, 307 line memory 302,306 Selector

Claims

1. a light emission control unit that outputs a light emission control signal; an exposure control unit that outputs an exposure control signal; a light emitting unit that irradiates irradiation light toward a measurement object in accordance with the light emission control signal; a light receiving section that performs exposure in accordance with the exposure control signal and outputs a light receiving signal corresponding to signal charges accumulated by the exposure; a signal processing unit that outputs a distance signal indicating the distance to the measurement object based on the light receiving signal, the light receiving unit performs a long exposure, which is an exposure for a period equal to or longer than the irradiation period of the irradiation light, and a short exposure, which is an exposure for a period shorter than the irradiation period of the irradiation light, the signal processing unit calculates a total light receiving signal from a first light receiving signal that is a sum of a plurality of signals obtained by the short exposure in each of a plurality of periods obtained by dividing a first period including a rising edge of the reflected light from the measurement object, and a second light receiving signal that is obtained by the long exposure in a second period that follows the first period and includes a falling edge of the reflected light, calculating one or more first measurement signal amounts indicating a ratio of the signal amount of one or more light receiving signals, which are a plurality of signals obtained by the short exposure in each of a plurality of periods obtained by dividing the first period, to the signal amount of the total light receiving signals; calculating a second measurement signal amount indicating a ratio of the signal amount of the second received light signal to the signal amount of all the received light signals; the signal processing unit holds one or more first tables in which the distance to the measurement object is associated with one or more first reference signal amounts corresponding to the one or more first measured signal amounts measured in a multipath controlled environment, and a second table in which the distance to the measurement object is associated with a second reference signal amount corresponding to the second measured signal amount, the signal processing unit calculates one or more first temporary distances from the one or more first measured signal amounts by referring to the one or more first tables, and calculates one or more second temporary distances from the one or more second measured signal amounts by referring to the second table; calculating a distance difference based on the one or more first temporary distances and the second temporary distance, determining whether or not a multipath exists by comparing the distance difference with a threshold, and correcting the second temporary distance using the distance difference to calculate the distance; Ranging device.

2. A light emission control unit that outputs a light emission control signal; an exposure control unit that outputs an exposure control signal; a light emitting unit that irradiates irradiation light toward a measurement object in accordance with the light emission control signal; a light receiving section that performs exposure in accordance with the exposure control signal and outputs a light receiving signal corresponding to signal charges accumulated by the exposure; a signal processing unit that outputs a distance signal indicating the distance to the measurement object based on the light receiving signal, the light receiving unit performs a long exposure, which is an exposure for a period equal to or longer than the irradiation period of the irradiation light, and a short exposure, which is an exposure for a period shorter than the irradiation period of the irradiation light, the signal processing unit calculates a total light receiving signal from a first light receiving signal that is a light receiving signal obtained by the long exposure in a first period that includes a rising edge of the reflected light from the measurement object, and a second light receiving signal that is obtained by the long exposure in a second period that follows the first period and includes a falling edge of the reflected light; calculating one or more first measurement signal amounts indicating a ratio of the signal amount of one or more light receiving signals, which are one or more signals obtained by the short exposure in one or more periods included in the first period, to the signal amount of all the light receiving signals; calculating a second measurement signal amount indicating a ratio of the signal amount of the second received light signal to the signal amount of all the received light signals; the signal processing unit holds one or more first tables in which the distance to the measurement object is associated with one or more first reference signal amounts corresponding to the one or more first measured signal amounts measured in a multipath controlled environment, and a second table in which the distance to the measurement object is associated with a second reference signal amount corresponding to the second measured signal amount, the signal processing unit calculates one or more first temporary distances from the one or more first measured signal amounts by referring to the one or more first tables, and calculates one or more second temporary distances from the one or more second measured signal amounts by referring to the second table; calculating a distance difference based on the one or more first temporary distances and the second temporary distance, determining whether or not a multipath exists by comparing the distance difference with a threshold, and correcting the second temporary distance using the distance difference to calculate the distance; Ranging device.

3. the light receiving unit further outputs a third light receiving signal obtained from the long exposure in a third period including only background light; the signal processing unit subtracts the third light receiving signal from the first light receiving signal, the second light receiving signal, and the total light receiving signal, and then calculates the one or more first measurement signal amounts and the second measurement signal amount; 3. A distance measuring device according to claim 1 or 2.

4. the light receiving unit includes a plurality of pixels arranged in a two-dimensional grid pattern, the signal processing unit calculates the one or more first measurement signal amounts based on the one or more light receiving signals obtained by smoothing each of the plurality of pixels using adjacent pixels; The distance measuring device according to any one of claims 1 to 3.

5. The one or more first temporary distances are a plurality of first temporary distances, the signal processing unit calculates a difference between each of the plurality of first temporary distances and the second temporary distance, and determines the maximum value of the differences as the distance difference; The distance measuring device according to any one of claims 1 to 4.

6. the light receiving section is composed of a plurality of pixels arranged in a two-dimensional grid pattern, the signal processing unit smoothes the distance difference using pixels adjacent to each of the plurality of pixels; The distance measuring device according to any one of claims 1 to 5.

7. The light emitting unit emits light toward the object to be measured, The light receiving section is exposed to light, and a light receiving signal corresponding to the signal charge accumulated by the exposure is output. a distance measuring method for outputting a distance signal indicating a distance to the measurement target based on the light receiving signal, the light receiving unit performs a long exposure, which is an exposure for a period equal to or longer than the irradiation period of the irradiation light, and a short exposure, which is an exposure for a period shorter than the irradiation period of the irradiation light, a first light receiving signal that is the sum of a plurality of signals obtained by the short exposure in each of a plurality of periods obtained by dividing a first period including a rising edge of the reflected light from the measurement object, and a second light receiving signal that is obtained by the long exposure in a second period that follows the first period and includes a falling edge of the reflected light; calculating one or more first measurement signal amounts indicating a ratio of the signal amount of one or more light receiving signals, which are a plurality of signals obtained by the short exposure in each of a plurality of periods obtained by dividing the first period, to the signal amount of the total light receiving signals; calculating a second measurement signal amount indicating a ratio of the signal amount of the second received light signal to the signal amount of all the received light signals; one or more first tables in which the distance to the measurement object is associated with one or more first reference signal amounts corresponding to the one or more first measurement signal amounts measured in a multipath controlled environment, and a second table in which the distance to the measurement object is associated with one or more second reference signal amounts corresponding to the second measurement signal amounts, calculating one or more first temporary distances from the one or more first measured signal amounts by referring to the one or more first tables, and calculating one or more second temporary distances from the one or more second measured signal amounts by referring to the second table; calculating a distance difference based on the one or more first temporary distances and the second temporary distance, determining whether or not a multipath exists by comparing the distance difference with a threshold, and correcting the second temporary distance using the distance difference to calculate the distance; Distance measurement method.

8. Irradiating light from a light emitting unit toward a measurement object, The light receiving section is exposed to light, and a light receiving signal corresponding to the signal charge accumulated by the exposure is output. a distance measuring method for outputting a distance signal indicating a distance to the measurement target based on the light receiving signal, the light receiving unit performs a long exposure, which is an exposure for a period equal to or longer than the irradiation period of the irradiation light, and a short exposure, which is an exposure for a period shorter than the irradiation period of the irradiation light, a first light receiving signal obtained by the long exposure in a first period including a rising edge of the reflected light from the measurement object, and a second light receiving signal obtained by the long exposure in a second period after the first period including a falling edge of the reflected light; calculating one or more first measurement signal amounts indicating a ratio of the signal amount of one or more light receiving signals, which are one or more signals obtained by the short exposure in one or more periods included in the first period, to the signal amount of all the light receiving signals; calculating a second measurement signal amount indicating a ratio of the signal amount of the second received light signal to the signal amount of all the received light signals; one or more first tables in which the distance to the measurement object is associated with one or more first reference signal amounts corresponding to the one or more first measurement signal amounts measured in a multipath controlled environment, and a second table in which the distance to the measurement object is associated with one or more second reference signal amounts corresponding to the second measurement signal amounts, calculating one or more first temporary distances from the one or more first measured signal amounts by referring to the one or more first tables, and calculating one or more second temporary distances from the one or more second measured signal amounts by referring to the second table; calculating a distance difference based on the one or more first temporary distances and the second temporary distance, determining whether or not a multipath exists by comparing the distance difference with a threshold, and correcting the second temporary distance using the distance difference to calculate the distance; Distance measurement method.

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