Distance measuring device and distance measuring method

Abstract

This distance measuring device comprises: a light emitting element that projects projected light; a light receiving element that receives reflected light resulting from the projected light being reflected by an object, and that generates a light reception signal on the basis of the reflected light; and a controller. The controller: derives a measured distance value by measuring the distance from the distance measuring device to the object on the basis of the time from when the projected light was projected until the signal level of the light reception signal becomes equal to or higher than a predetermined level; acquires associated information in which a plurality of measured distance values and a plurality of actual distance values are associated with one another; and if a measured distance value is equal to or less than a threshold value, corrects the measured distance value on the basis of the associated information.

Description

Distance measuring device and distance measuring method

[0001] The present disclosure relates to a distance measurement device and a distance measurement method.

[0002] Distance measurement devices that measure distance using pulse waves are known, including a transmitting means for transmitting pulse waves, a receiving means for receiving a reflected wave generated when the pulse waves are reflected by a target, a time measuring means for measuring the time required from when the pulse waves are transmitted by the transmitting means to when the reflected wave is detected by the receiving means, a pulse width measuring means for receiving a received waveform of the reflected wave output by the receiving means and measuring a pulse width of the received waveform, a correction value calculating means for receiving the pulse width measured by the pulse width measuring means and calculating a correction value for the required time corresponding to the pulse width based on input / output characteristics of the receiving means in an active region and a saturated region, and a distance calculating means for correcting the required time measured by the time measuring means using the correction value calculated by the correction value calculating means and multiplying the corrected value by the propagation speed of the pulse waves to calculate the distance to the target (see Patent Document 1).

[0003] Japanese Patent Application Publication No. 8-179032

[0004] In the distance measurement device of Patent Document 1, when noise such as stray light is present, an error may occur in the distance to the target, and in this case, the accuracy of distance measurement (ranging) decreases.

[0005] The present disclosure provides a distance measurement device and a distance measurement method that can measure the distance to an object with reduced error even in the presence of noise such as stray light.

[0006] One aspect of the present disclosure is a distance measurement device comprising: a light-emitting element that emits projection light; a light-receiving element that receives reflected light from the projection light reflected by an object and generates a received light signal based on the reflected light; and a controller that processes the received light signal, wherein the controller derives a measured distance value by measuring the distance to the object based on the time from when the projection light is emitted until the signal level of the received light signal reaches a predetermined level or higher, obtains association information that associates multiple measured distance values ​​with multiple actual distance values ​​corresponding to each of the multiple measured distance values, and if the derived measured distance value is below a predetermined threshold, corrects the derived measured distance value based on the association information.

[0007] One aspect of the present disclosure is a distance measurement method comprising: projecting projection light; receiving reflected light of the projected light reflected by an object; generating a received light signal based on the reflected light; measuring the distance to the object based on the time from the projection of the projected light until the signal level of the received light signal reaches or exceeds a predetermined level, thereby deriving a measured distance value; obtaining association information that associates multiple measured distance values ​​with multiple actual distance values ​​corresponding to each of the multiple measured distance values; and, if the derived measured distance value is below a predetermined threshold, correcting the derived measured distance value based on the association information.

[0008] According to the present disclosure, even if noise such as stray light is present, distance measurement can be performed with reduced error in the distance to an object.

[0009] FIG. 1 is a perspective view of the appearance of a distance measurement device according to a first embodiment of the present disclosure; FIG. 2 is a longitudinal sectional view of the distance measurement device shown in FIG. 1; FIG. 3 is a block diagram showing an example of the functional configuration of the distance measurement device; FIG. 4 is a diagram showing an example of the detailed configuration of a correction unit; FIG. 5 is a diagram showing an example of the arrangement of mapping points based on each pre-measured distance value and each actual distance value on a two-dimensional plane; FIG. 6 is a diagram showing a first example of an approximation formula that approximates to pass through each mapping point on a two-dimensional plane; FIG. 7 is a diagram showing a second example of an approximation formula that approximates to pass through each mapping point on a two-dimensional plane;

[0010] Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed description than necessary may be omitted. For example, detailed descriptions of well-known matters or descriptions of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

[0011] (How the embodiments of the present disclosure were achieved) Assume that the distance measurement device of Patent Document 1 optically measures distance by emitting laser light and receiving reflected light from an object. The distance measurement device of Patent Document 1 measures (calculates) the distance from the distance measurement device to the object by measuring the time from the generation of a START signal when laser light is emitted to the generation of a STOP signal when reflected light is detected, and then corrects and outputs the distance value based on the pulse width of the received light signal. In the distance measurement device of Patent Document 1, due to the influence of stray light present inside the distance measurement device when laser light is emitted, stray light components may be mixed as noise into the signal (received light signal) processed by the light receiving circuit immediately after emission. In addition, other noise may also be mixed in, as described below.

[0012] 9 is a diagram showing a first example of the output (amplifier output) of the received light signal (or a signal obtained by amplifying the received light signal) and the output of the comparator. It can be seen that stray light and noise are more likely to be detected earlier than reflected light from an object. When stray light components or other noise are mixed into the received light signal as noise, the measured distance value (measured distance value) is not affected as long as the timing at which reflected light from an object is detected does not overlap with the stray light noise.

[0013] 10 is a diagram showing a second example of the amplifier output and the comparator output. When an object is near the distance measurement device, stray light and other noise are superimposed on the reflected light from the object, causing the amount of received light to change (increase or decrease) compared to when there is no stray light. As a result, the timing at which the level of the light reception signal based on the amount of received light reaches the slice level of the comparator is shifted by Δ time from an ideal waveform that is not affected by stray light or other noise.

[0014] Fig. 11 is a diagram showing the relationship between the measured distance value and the actual distance to the object. Fig. 12 is a diagram showing the relationship between the measured distance value and the measurement error. In the distance measurement device of Patent Document 1, an error (measurement error) can occur in the measured distance value due to a shift in the timing of generation of the STOP signal caused by such stray light components and other noise. In other words, a discrepancy occurs between the measured distance value and the actual distance. In the example of Fig. 10, the distance is measured assuming that the object is closer than it actually is.

[0015] Furthermore, when a distance measurement device emits laser light, a large current flows inside the device during laser light emission, which can generate induced noise. The induced noise includes, for example, electrical or magnetic noise. This is because a large current flows when a light-emitting element emits laser light. The electrical or magnetic noise can be mixed into the received light signal as a signal component (see FIG. 9). In this case, similar to stray light, it affects the measured distance value.

[0016] In the following embodiments, a distance measurement device and a distance measurement method that can measure the distance to an object with reduced error even when noise such as stray light is present will be described.

[0017] (Embodiments) <Physical Configuration of Distance Measuring Device> Fig. 1 is an external perspective view of a distance measuring device 1 according to embodiment 1. Fig. 2 is a longitudinal sectional view of the distance measuring device according to embodiment 1. Fig. 2 corresponds to the AA sectional view of the distance measuring device 1 shown in Fig. 1.

[0018] The distance measurement device 1 is, for example, a LiDAR (Light Detection and Ranging) device. The distance measurement device 1 optically measures the distance to a measurement target object using light such as laser light. The distance measurement device 1 uses a scanner system to perform two-dimensional scanning using light to detect and measure the distance to the object.

[0019] As shown in FIGS. 1 and 2, the distance measurement device 1 includes a fixed part 100, a rotating part 300, and an outer cover part 10.

[0020] The fixed unit 100 has a substantially rectangular parallelepiped shape. The rotating unit 300 is connected to the upper surface of the fixed unit 100 and has a cylindrical shape that rotates around a rotation axis C that is perpendicular to the upper surface. The outer cover unit 10 has a substantially cylindrical shape and covers the rotating unit 300 from above. The outer cover unit 10 has a wavelength window 11 formed using a wavelength selection member on at least a portion of its side surface. The wavelength selection member is a material that transmits light of a predetermined wavelength (frequency) component used for distance measurement and blocks light of a wavelength (frequency) component in the visible range. The wavelength selection member has the role of blocking ambient light, such as natural light and electric light.

[0021] For ease of explanation, as shown in FIG. 1, the axis perpendicular to the top surface (or bottom surface) of the fixed unit 100 is referred to as the Z axis. The axis perpendicular to the Z axis is referred to as the X axis. The axis perpendicular to the Z axis and the X axis is referred to as the Y axis. For ease of explanation, the positive direction of the Z axis may be referred to as "up," the negative direction of the Z axis as "down," and the direction away from the Z axis in the X axis direction or the Y axis direction as "sideways." Note that these directional expressions are used for ease of explanation and are not intended to limit the orientation of the structure during actual use. For example, the distance measurement device 1 shown in FIG. 1 may be used upside down. The A-A cross-sectional view shown in FIG. 2 corresponds to a cross-sectional view in the YZ plane.

[0022] The bottom surface of the fixed part 100 may be fixedly installed on a predetermined plane (for example, a floor surface or the surface of a housing of a predetermined device).

[0023] The rotating unit 300 rotates around a rotation axis C, which is the central axis in the height direction (Z axis) of the cylinder. As the rotating unit 300 rotates, the optical axis of projection light (hereinafter referred to as projection light 3A) projected laterally from a portion of the side surface of the rotating unit 300 rotates around the rotation axis C. Accordingly, the projection light 3A and the area where distance measurement can be performed using the projection light 3A (hereinafter referred to as the distance measurement area) also rotate. As described below, the distance measurement device 1 measures the distance to an object in the distance measurement area based on the time difference (Time of Flight (TOF)) between the timing at which the projection light 3A is projected and the timing at which light reflected from the projection light 3A by an object in the distance measurement area (hereinafter referred to as reflected light 3B) is received. As the rotating unit 300 rotates around the rotation axis C, the distance measurement device 1 can measure the distance to an object in a 360-degree horizontal distance measurement area.

[0024] The fixed unit 100 includes a substrate 101, a light-emitting element 102, a light-receiving element 103, a condenser lens 104, a collimator lens 105, a coil 106, and a photointerrupter 107. The rotating unit 300 includes a rotating member 301, a magnet 302, and a reflecting mirror 303.

[0025] The coil 106 of the fixed part 100 and the magnet 302 of the rotating part 300 form a hollow motor 402 (see FIG. 3). When the motor 402 is driven, the rotating part 300 rotates around the rotation axis C.

[0026] The board 101 is, for example, a printed circuit board (PCB). A comparator 401, a TDC 500, and a controller 600 (see FIG. 3), which will be described later, are mounted on the board 101. Note that TDC is an abbreviation for Time to Digital Converter.

[0027] The light emitting element 102 is arranged along the rotation axis C and projects the projection light 3A upward.

[0028] The collimator lens 105 corrects the projection light 3A emitted from the light emitting element 102 to be approximately parallel light and outputs it upward.

[0029] The reflecting mirror 303 is provided on the rotating member 301 so as to reflect the parallel light projected upward from the light emitting element 102 and corrected by the collimator lens 105 in the horizontal direction (direction along the XY plane). Because the reflecting mirror 303 rotates together with the rotating member 301, the projected light is projected (scanned) over time in a 360-degree circle around the rotation axis C in a direction (horizontal direction) perpendicular to the rotation axis C. The projected light 3A reflected by the reflecting mirror 303 passes through the wavelength window 11 of the outer cover unit 10 and is projected onto the distance measurement area.

[0030] The reflected light 3B, which is the projected light 3A reflected by the object, passes through the wavelength window 11 of the outer cover part 10 and is reflected downward by the reflecting mirror 303.

[0031] The condenser lens 104 condenses the reflected light 3B reflected downward by the reflecting mirror 303 and outputs the condensed light downward.

[0032] The light receiving element 103 receives the reflected light 3 B condensed by the condenser lens 104 .

[0033] The rotating member 301 has a plurality of ribs 311 spaced at regular intervals. For example, the rotating member is annular, with the ribs spaced at regular intervals around the circumference. The photointerrupter 107 is positioned so as to detect the passage of one rib 311. By using the photointerrupter 107 to detect and count the passage of one rib 311, a controller 600 (described later) can detect the rotation angle (rotation position) of the rotating member 301 (i.e., the rotating unit 300). Therefore, the photointerrupter 107 and the ribs 311 can form a rotation angle detector 403 (see FIG. 3 ) (described later).

[0034] Note that a portion of the projected light 3A projected by the light-emitting element 102 and reflected by the reflecting mirror 303, as well as unintended light, remains inside the distance measurement device 1 without passing through the wavelength window 11. The light that remains inside may be received by the light-receiving element 103 as stray light 3C. The stray light 3C received by the light-receiving element 103 may be superimposed on the light-receiving signal. Furthermore, when the light-emitting element 102 projects light, a large current flows instantaneously, which may generate noise 3D due to, for example, electromagnetic induction. The noise 3D includes electrical or magnetic noise. This noise 3D may also be superimposed on the light-receiving signal.

[0035] <Functional Configuration of Distance Measuring Device> FIG. 3 is a block diagram showing an example of the functional configuration of the distance measuring device 1 according to the first embodiment.

[0036] The distance measurement device 1 includes a light emitting element 102, a light receiving element 103, a comparator 401, a TDC 500, a motor 402, a rotation angle detector 403, and a controller 600. The controller 600 has functions as a distance measurement control unit 610, a distance calculation unit 620, a correction unit 630, and a motor control unit 640. Note that at least one of the comparator 401 and the TDC 500 may be included within the controller 600, or at least one of the distance measurement control unit 610, the distance calculation unit 620, the correction unit 630, and the motor control unit 640 may be located outside the controller 600.

[0037] The light emitting element 102 is formed of, for example, a laser diode. A pulse signal instructing the light emitting element 102 to emit light is input to the light emitting element 102 from the distance measurement control unit 610. The light emitting element 102 projects projection light 3A of a pulse wave in accordance with the input pulse signal (also referred to as an input pulse signal). In Fig. 3, the input of the input pulse signal is expressed as START (START signal).

[0038] The light receiving element 103 is configured by, for example, a photodiode, and receives the reflected light 3B and outputs a light receiving signal according to the light receiving level.

[0039] The comparator 401 receives a light-receiving signal from the light-receiving element 103. The comparator 401 outputs a pulse signal (also referred to as a light-receiving pulse signal) according to the signal level of the light-receiving signal. The light-receiving pulse signal is at a predetermined high level while the level of the light-receiving signal is equal to or greater than a predetermined comparator threshold (comparator slice level), and is at a predetermined ground level while the level of the light-receiving signal is less than the comparator threshold. The high level is greater than the ground level. In FIG. 3, the output of the light-receiving pulse signal is expressed as STOP (STOP signal).

[0040] The motor 402 provides the rotation unit 300 with a driving force that rotates the rotation unit 300. The rotation angle detector 403 detects the rotation angle of the rotation unit 300. This rotation angle indicates an angle relative to a predetermined reference angle.

[0041] The TDC 500 receives a START signal from the distance measurement control unit 610. The input timing of this START signal corresponds to the timing of projection of the projected light 3A by the light-emitting element 102. The TDC 500 receives a STOP signal from the comparator 401. The input timing of the STOP signal corresponds to the timing of reception of the reflected light 3B by the light-receiving element 103, and more specifically, corresponds to the timing of generation of a light-receiving pulse signal. The TDC 500 outputs information on the time of flight (TOF) of light based on the START signal and the STOP signal. The TDC 500 may also output information on the pulse width of the light-receiving signal.

[0042] The controller 600 may be configured to include an MPU (Micro Processing Unit), a CPU (Central Processing Unit), a DSP (Digital Signal Processor), etc. The controller 600 may be configured with various integrated circuits (e.g., an LSI (Large Scale Integration), an FPGA (Field Programmable Gate Array)). The controller 600 realizes various functions by executing programs stored in a memory located inside or outside the controller 600. The controller 600 has various functional units such as a distance measurement control unit 610, a distance calculation unit 620, a correction unit 630, and a motor control unit 640.

[0043] The distance measurement control unit 610 controls distance measurement by the distance measurement device 1, and controls, for example, the TDC 500 and the distance calculation unit 620. The distance measurement control unit 610 acquires rotation angle information from the rotation angle detector 403. If the acquired rotation angle is a predetermined rotation angle or falls within a predetermined angle range, the distance measurement control unit 610 sends a START signal to the light emitting element 102 and the TDC 500. This allows the light emitting element 102 to project the projection light 3A in a desired direction or in a range of desired directions around the distance measurement device 1.

[0044] The distance calculation unit 620 acquires information on the TOF and pulse width from the TDC 500. The distance calculation unit 620 calculates the distance from the distance measurement device 1 to an object by converting the TOF into a distance based on the acquired TOF and the speed of light, for example. This distance is a distance value measured according to the TOF, and is also referred to as a measured distance value.

[0045] The correction unit 630 acquires information on the measured distance value X from the distance calculation unit 620, and derives (for example, calculates) a distance value (also referred to as a corrected distance value Y) obtained by correcting the measured distance value X. The correction unit 630 outputs information on the corrected distance value Y to an external device or a storage device. The method of correcting the measured distance value X by the correction unit 630 will be described in detail later.

[0046] Furthermore, the distance calculation unit 620 may identify the two-dimensional position of the object based on the measured distance value X and the obtained rotation angle. The correction unit 630 may correct the two-dimensional position by correcting the measured distance value X of the two-dimensional position and identifying the two-dimensional position based on the corrected distance value Y and the rotation angle. The correction unit 630 may output information on the corrected two-dimensional position to an external device or a storage device.

[0047] The motor control unit 640 outputs a motor control signal to the motor 402 to control the motor 402 .

[0048] FIG. 4 is a diagram showing an example of the detailed configuration of the correction unit 630.

[0049] The correction unit 630 includes a memory 631, a memory selector 632, and a calculator 633. The memory 631 includes, for example, a RAM or a ROM, and may also include other storage devices. The memory 631 stores association information that associates each measured distance value X with each corrected distance value Y. The memory 631 may store multiple pieces of association information. Note that, as will be described later, the association information is also information in which a pre-measured distance value and multiple actual distance values ​​corresponding to each of the multiple measured distance values ​​are measured and associated in advance. The association information is represented by, for example, polynomial information, which is information related to a polynomial. In this embodiment, the association information is mainly described as polynomial information.

[0050] For example, when the polynomial is expressed as a quadratic expression, where the measured distance value is "X" and the corrected distance value is "Y", Y=aX ２ +bX+c. The polynomial information stored in the memory 631 includes a set of values ​​for at least x, a, b, and c. Here, "x" is a boundary value, which will be described later, and "a," "b," and "c" are coefficients of the polynomial. When the set of x, a, b, and c is written in the form of {x, a, b, c}, for example, x=x １ , a=a １ , b=b １ , c=c １ If x １ , a １ , b １ , c １In FIG. 4, for example, the memory 631 stores {x １ , a １ , b １ , c １} (also referred to as polynomial information I1), {x ２ , a ２ , b ２ , c ２} (also referred to as polynomial information I2), {x １ , a １ , b １ , c １} (also referred to as polynomial information I3), ..., {x ｎ , a ｎ , b ｎ , c ｎ} (also referred to as polynomial information In). The polynomial information includes not only information on the coefficients in the polynomial, but also the formula itself in which the coefficients in the polynomial are specifically set (for example, Y=a １ X ２ +b １ X+c １ ) may be included.

[0051] Memory selector 632 selects, from memory 631, polynomial information corresponding to the measured distance value X input to correction unit 630, and based on the polynomial information, determines a polynomial to be used for calculation by calculator 633. When there are multiple polynomials in memory 631, memory selector 632 selects polynomial information corresponding to the measured distance value X input to correction unit 630 from the multiple pieces of polynomial information held in memory 631, and determines the polynomial to be used for calculation by calculator 633.

[0052] The calculator 633 sets the polynomial corresponding to the polynomial information selected by the memory selector 632 as the polynomial to be used for correction. Therefore, for example, when the polynomial information I2 is selected, the polynomial Y=aX ２ +bX+c, where Y=a ２ X ２ +b ２ X+c ２The calculator 633 corrects the measured distance value X based on the set polynomial to obtain the corrected distance value Y. When measuring the distances to multiple objects around the distance measurement device 1, the memory selector 632 selects polynomial information from the memory 631 multiple times based on the obtained measured distance value X, acquires the polynomial information from the memory 631, switches between them, and sets it in the calculator 633.

[0053] Next, a specific procedure for correction will be described.

[0054] The following processing is performed in advance to generate the polynomial information stored in the memory 631. For example, the distance measurement device 1 derives multiple measured distance values ​​by measuring the distance to an arbitrary object according to the TOF method using the distance measurement device 1 as described above while changing the distance from the distance measurement device 1 to the object. Since these measured distance values ​​are measured in advance, they are also referred to as pre-measured distance values. The distance measurement device 1 also acquires information on the actual distance (real distance) to the object measured by a method other than the TOF method. For example, the actual distance is measured by having a person actually measure the distance from the distance measurement device 1 to the object using a tape measure or another sensor. Information on the measured real distance is input to the distance measurement device 1, for example, via a communication device or input device (e.g., a key or button) of the distance measurement device 1.

[0055] The controller 600 maps each pre-measured distance value from the distance measurement device 1 to an object and each pre-measured actual distance value to the same object at the same position onto a two-dimensional plane.

[0056] 5 is a diagram showing an example of the arrangement of mapping points mp on a two-dimensional plane based on each pre-measured distance value and each actual distance value. In the two-dimensional plane of Fig. 5, the horizontal axis represents the pre-measured distance value and the vertical axis represents the actual distance value. The mapping points are an example of corresponding points determined by each pre-measured distance value measured in advance and a plurality of actual distance values ​​corresponding to each pre-measured distance value.

[0057] On a two-dimensional plane, one mapping point (mp) is positioned based on the pre-measured distance value and the actual distance to the same object at the same position. Ideally, the pre-measured distance value and the actual distance value to the same object at the same position should be the same value. Therefore, the ideal value of the set of mapping points (mp) indicating the relationship between each pre-measured distance value and each actual distance value is a straight line passing through the origin of the two-dimensional plane (two-dimensional coordinates). However, in reality, the pre-measured distance value may contain measurement errors. Therefore, some of the mapping points (mp) are not positioned on the straight line indicating the ideal value. Such errors are more likely to occur the smaller the pre-measured distance value, i.e., the closer the distance from the distance measurement device 1 is to the short-distance region.

[0058] FIG. 6A is a diagram showing a first example of an approximation formula that is approximated so as to pass through each mapping point mp on a two-dimensional plane.

[0059] The correction unit 630 generates an approximation equation that approximates the shape of the set of mapping points (mp) on a two-dimensional plane. The approximation equation may be expressed by, for example, a polynomial. The approximation equation that approximates the shape of the set of mapping points (mp) may be expressed by multiple approximations. For example, in FIG. 6A , the shape characteristics of the set of mapping points (mp) significantly differ between a range where the pre-measured distance value is equal to or less than x1 and a range where the pre-measured distance value is greater than x1. Specifically, in the range where the pre-measured distance value is equal to or less than x1 (i.e., the side closer to the distance measurement device 1), the set of mapping points (mp) is quadratic, whereas in the range where the pre-measured distance value is greater than x1 (i.e., the side farther from the distance measurement device 1), the set of mapping points (mp) is linear. The correction unit 630 may determine the value of x1 by having an administrator input the value via an input device, for example, or may determine the value of x1 by calculation based on the positions of the mapping points (mp) or the positional relationship between the positions of the mapping points (mp). In such a case, the measurement error contained in the measured distance value can be efficiently reduced by using different approximate expressions for correction in the range where the pre-measured distance value is equal to or less than x1 and in the range where the pre-measured distance value is greater than x1. The boundary point where the approximate expression such as x1 is changed is also called the boundary value.

[0060] 6A, in the vicinity of the maximum value of the pre-measured distance value, the mapping points mp form a predetermined shape in the range below the maximum value, and no mapping points mp exist in the range above the maximum value. Therefore, the correction unit 630 also sets the maximum value of the pre-measured distance value as a boundary value. Note that there may be three or more boundary values. The correction unit 630 generates the same number of approximation formulas as the number of boundary values. For example, in the case of FIG. 6A, the correction unit 630 generates approximation formulas in the range 0<pre-measured distance value≦x １ Generate an approximate equation 1 for x １ <Preliminary measurement distance value≦x ２ Approximation formula 2 is generated for the following. Approximation formula 1 is a quadratic formula (ax ２ +bx+c), and the specific coefficients of "a", "b", and "c" are (a １ , b １ , c １ Similarly, the approximate formula 2 is expressed in the form of (a) where the specific coefficients of "a", "b", and "c" are ２ , b ２ , c ２ ) format. The correction unit 630 calculates each approximation equation by, for example, a known linear approximation or nonlinear approximation method according to the position of each mapping point mp included in the range of each pre-measured distance value. For example, the correction unit 630 performs curve fitting to obtain an approximate curve. Polynomial information regarding polynomials representing the generated approximation equations is stored in the above-mentioned memory 631. The polynomial information is stored in the format of, for example, a set {x, a, b, c} of boundary values ​​and coefficients of the polynomials, as shown in FIG. 4 .

[0061] 6B is a diagram showing a second example of an approximation formula that is approximated so as to pass through each mapping point mp on a two-dimensional plane. In FIG. 6B, differences from FIG. 6A will be mainly described.

[0062] In FIG. 6B, the method for generating the approximation formula is the same as in FIG. 6A, but the boundary value is x １ , x ２ , x ３ There are three approximate expressions: 0<preliminary measured distance value≦x １ Generate an approximate equation 1 for x １ <Preliminary measurement distance value≦x ２ Generate an approximate equation 2 for x２ <Preliminary measurement distance value≦x ３ Approximation formula 3 is generated for the following: Approximation formula 3 is generated for the following: ３ , b ３ , c ３ ) As shown in FIG. 6B, the approximate formula 3 has a linear shape and can be expressed as a linear formula. ３ The value of is 0.

[0063] The amount of reflected light 3B varies depending on the reflectivity of the object, which in turn changes the signal level of the received light signal, potentially changing the timing at which the STOP signal is generated. Furthermore, the pulse width of the received light pulse signal varies depending on the amount of reflected light 4B, which in turn changes the timing at which the STOP signal is generated. Therefore, the correction unit 630 may take the reflectivity of the object being measured into account and generate the approximation equation and polynomial information for each object, for example. The amount of light (light intensity) of projected light 3A from the light-emitting element 102 may be constant.

[0064] In this way, the correction unit 630 may define multiple distance regions in which each pre-measured distance value is divided by each boundary value, and may generate an approximate equation for each distance region, or may store polynomial information corresponding to the approximate equation for each distance region in memory 631.

[0065] FIG. 7A is a diagram showing a first example of the relationship between the measured distance value X and the corrected distance value Y. In FIG.

[0066] The correction unit 630 selects an approximation formula to be used for correction based on the measured distance value X, and corrects the measured distance value X using the selected approximation formula to obtain a corrected distance value Y. For example, the correction unit 630 may select an approximation formula to be used for correction based on the measured distance value X, and may correct the measured distance value X using the selected approximation formula to obtain a corrected distance value Y. １ If x satisfies the above equation, the correction unit 630 selects the approximate expression 1 and derives (e.g., calculates) the corrected distance value Y from the measured distance value X based on the approximate expression 1. For example, the correction unit 630 １ <X≦x ２ If the above equation is satisfied, approximate expression 2 is selected, and the corrected distance value Y is derived (for example, calculated) from the measured distance value X based on approximate expression 2.

[0067] Specifically, in the correction unit 630, boundary values ​​and coefficients of polynomials are stored in the memory 631 in the form of sets {x, a, b, c} as shown in FIG. １ If the formula satisfies the approximation formula 1, {x １ , a １ , b １ , c １}. The calculator 633 calculates the corrected distance value Y from the measured distance value X according to the approximate formula 1 indicated by the polynomial information I1. Similarly, the memory selector 632 selects the polynomial information I1 such that x １ <X≦x ２ If this is satisfied, the {x ２ , a ２ , b ２ , c ２}. The calculator 633 calculates the corrected distance value Y from the measured distance value X according to approximate equation 2 indicated by the polynomial information I2. That is, when the measured distance value X is equal to any one of the boundary values ​​x, the memory selector 632 selects polynomial information including that boundary value x. When the measured distance value X is different from any of the boundary values ​​x, the memory selector 632 selects, for example, polynomial information including a boundary value x that is greater than the measured distance value X and closest to the measured distance value X. Note that when the measured distance value X is different from any of the boundary values ​​x, the memory selector 632 may select polynomial information including a boundary value x that is smaller than the measured distance value X and closest to the measured distance value X.

[0068] Fig. 7B is a diagram showing a second example of the relationship between the measured distance value X and the corrected distance value Y. In Fig. 7B, differences from Fig. 7A will be mainly described.

[0069] The correction unit 630 calculates x ２ <X≦x ３ satisfies the following equation: approximation formula 3 is selected, and the corrected distance value Y is derived (for example, calculated) from the measured distance value X based on approximation formula 3. Specifically, in the correction unit 630, the memory selector 632 selects x ２ <X≦x ３ If this is satisfied, the {x ３ , a ３ , b ３ , c ３}. The calculator 633 calculates the corrected distance value Y from the measured distance value X according to the approximate equation 3 indicated by the polynomial information I3.

[0070] In this way, the correction unit 630 can select one piece of polynomial information from the polynomial information stored for each distance region based on the input measured distance value X, and derive the corrected distance value Y from the measured distance value X according to the polynomial (approximate equation) indicated by the polynomial information.

[0071] The approximation formula or polynomial may be expressed as an n-th degree formula (n is an integer equal to or greater than 3) instead of a quadratic formula. In this case, the number of coefficients in the n-th degree formula will be greater than in the case of a quadratic formula.

[0072] Next, the distance range of the measured distance value X for which correction by the correction unit 630 is performed will be described.

[0073] The correction unit 630 corrects the measured distance value X at least when the measured distance value X is included in the short distance range, specifically when the measured distance value X is equal to or less than a predetermined threshold. When a measurement target object is present in the short distance range, the reflected light 3B reflected by the object is received relatively quickly after the projected light 3A is emitted. Therefore, stray light 3C resulting from light emission by the light-emitting element 102 and noise 3D resulting from a large current during light emission are superimposed on the received light signal, which easily affects the timing of the STOP signal generation. The predetermined threshold for the measured distance value X may be, for example, a value near the boundary between the stray light 3C and noise components that are not intended to be received and the reflected light 3B that is intended to be received. In other words, the predetermined threshold may be the same value as, for example, a relatively small boundary value, such as boundary value x1 or boundary value x2. Thus, by correcting the measured distance value X when the measured distance value X is equal to or less than a predetermined threshold, measurement errors can be efficiently reduced.

[0074] Furthermore, the correction unit 630 may correct the measured distance value X even when the measured distance value X is included in the long distance range, specifically when the measured distance value X is greater than a predetermined threshold. If the object to be measured is present in the short distance range, the reflected light 3B reflected by the object will be received a relatively long time after the projection of the projected light 3A. Even if a certain amount of time has passed since the light-emitting element 130 emitted light, stray light 3C or noise may still be present. In contrast, the distance measurement device 1 can reduce measurement errors regardless of the distance between the distance measurement device 1 and the object by correcting the measured distance value X even when the measured distance value X is greater than a predetermined threshold.

[0075] FIG. 8 is a diagram showing an example of the relationship between the corrected distance value Y and the measurement error.

[0076] By correcting the measured distance value X using an approximation formula (polynomial), the corrected distance value Y becomes closer to the actual distance to the object than the measured distance value X. Therefore, as shown in Fig. 8, the corrected distance value Y has a measurement error close to 0 whether the corrected distance value Y is in a distance range with a small value or a distance range with a large value. Therefore, it can be said that the correction unit 630 can reduce the measurement error by correcting the measured distance value X.

[0077] As described above, the distance measurement device 1 of this embodiment includes a correction unit 630 that stores information about an approximation formula in the form of a polynomial in advance and corrects the measured distance value X. As an example, the correction unit 630 stores quadratic approximation formulas for the short distance area and the long distance area of ​​the distance measurement area. As an example, the short distance area is an area in the range of 0≦X<x1, and in this case, the correction unit 630 sets approximation formula 1. As an example, the long distance area is an area in the range of x1≦X<x2, and in this case, the correction unit 630 sets approximation formula 2. Furthermore, the distance measurement area is divided into N areas, which are three or more areas, and as an example, the Nth area is set to X<x<x<2. ｎ－１ ≦X<X ｎIn this case, the correction unit 630 may set an approximate formula n. The correction unit 630 switches the coefficient of the approximate formula set according to the measured distance value X, performs calculations using the approximate formula, corrects the measured distance value X, and outputs a corrected distance value Y. This allows the distance measurement device 1 to reduce errors in the measured distance value (measured distance value).

[0078] In the present embodiment, the correction unit 630 performs the advance preparations, such as associating each pre-measured distance value with each actual distance value, mapping the pre-measured distance value onto a two-dimensional plane, generating an approximation equation, and storing polynomial information in the memory 631. However, this is not limited to this. For example, an external server may perform these advance preparations. In this case, when it is time to actually correct the measured distance value X, the polynomial information may be obtained from the external server via a communication device or the like, and the memory 631 may store it at least temporarily. Alternatively, the polynomial information may not be stored in the memory 631, but may be set directly in the calculator 633. Therefore, the controller 600 obtains, from the memory 631 or an external server, association information in which multiple measured distance values ​​and multiple actual distance values ​​corresponding to each of the multiple measured distance values ​​are measured and associated in advance.

[0079] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present disclosure is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure. Furthermore, the components of the above-described embodiments may be combined in any manner without departing from the spirit of the invention.

[0080] <Outline of the Present Embodiment> As described above, the present disclosure describes at least the following matters. Note that, in parentheses, examples of components corresponding to the above-described embodiment are shown, but the present disclosure is not limited to these.

[0081] (Item 1) A distance measurement device (distance measurement device 1) comprising: a light-emitting element (light-emitting element 102) that emits projection light (projection light 3A); a light-receiving element (light-receiving element 103) that receives reflected light (reflected light 3B) from the projection light reflected by an object and generates a light-receiving signal based on the reflected light; and a controller (controller 600) that processes the light-receiving signal, wherein the controller: derives a measured distance value (measured distance value X) by measuring the distance to the object based on the time from when the projection light is emitted until the signal level of the light-receiving signal becomes equal to or higher than a predetermined level; acquires association information that associates a plurality of measured distance values ​​(pre-measured distance values) with a plurality of actual distance values ​​corresponding to each of the plurality of measured distance values; and, if the derived measured distance value is equal to or lower than a predetermined threshold, corrects the derived measured distance value based on the association information.

[0082] The reflected light may be received by the light-receiving element with stray light (stray light 3C) superimposed on it. Furthermore, when light is projected by the light-emitting element, electrical or magnetic noise (noise 3D) may occur due to a large current, etc. Therefore, the measured distance value may contain measurement errors due to stray light or noise. Measurement errors are likely to be included when the measured distance value is equal to or less than a predetermined threshold, i.e., when the object is located close to the distance measurement device. Even in this case, the distance measurement device can reduce measurement errors and measure the distance by taking into account the relationship between the previously obtained measured distance value and the actual distance value and correcting the measured distance value of the object to be measured.

[0083] (Item 2) The distance measurement device according to item 1, wherein the controller corrects the derived measured distance value based on the association information when the measured distance value is equal to or greater than the threshold value.

[0084] This allows the distance measurement device to measure distances with reduced measurement errors not only when the object is located at a short distance but also when the object is located at a long distance.

[0085] (Item 3) The distance measurement device according to item 1 or 2, wherein an approximation equation is generated so as to pass through corresponding points (mapping points mp) determined by the plurality of measured distance values ​​measured in advance and the plurality of actual distance values, and the association information includes polynomial information relating to a polynomial representing the approximation equation.

[0086] This allows the distance measurement device to easily correct the measured distance value of the object to be measured by calculation using a polynomial, thereby enabling distance measurement with reduced measurement error.

[0087] (Item 4) The distance measurement device according to item 1 or 2, further comprising a memory (memory 631), wherein the plurality of measured distance values ​​measured in advance are divided into a plurality of distance regions, and the association information is determined for each of the distance regions and stored in the memory.

[0088] This allows the distance measurement device to correct the measured distance value using association information that differs for each distance region.

[0089] (Item 5) The distance measurement device according to item 4, wherein the controller retrieves the association information from the memory and switches the association information based on the derived measured distance value.

[0090] As a result, when measuring a plurality of objects, if the distance measurement device obtains measured distance values ​​for different measurement areas, it can switch the association information and correct each of the plurality of measured distance values.

[0091] (Item 6) A distance measurement method comprising: projecting projection light; receiving reflected light of the projected light reflected by an object and generating a received light signal based on the reflected light; measuring the distance to the object based on the time from the projection of the projected light until the signal level of the received light signal becomes equal to or higher than a predetermined level, thereby deriving a measured distance value; acquiring association information that associates a plurality of measured distance values ​​with a plurality of actual distance values ​​corresponding to each of the plurality of measured distance values; and, if the derived measured distance value is equal to or lower than a predetermined threshold, correcting the derived measured distance value based on the association information.

[0092] This allows the distance measurement method to achieve the same effect as in item 1.

[0093] This disclosure is based on a Japanese patent application (Patent Application No. 2023-202863) filed on November 30, 2023, the contents of which are incorporated herein by reference.

[0094] The present disclosure is useful for a distance measurement device and a distance measurement method that can measure the distance to an object with reduced measurement error even in the presence of noise such as stray light.

[0095] REFERENCE SIGNS LIST 1 Distance measuring device 3A Projected light 3B Reflected light 3C Stray light 3D Noise 10 Outer cover part 11 Wavelength window 100 Fixed part 101 Substrate 102 Light emitting element 103 Light receiving element 104 Condenser lens 105 Collimator lens 106 Coil 107 Photointerrupter 300 Rotating part 301 Rotating member 302 Magnet 303 Reflector 311 Rib 401 Comparator 402 Motor 403 Rotation angle detector 500 TDC 600 Controller 610 Distance measurement control part 620 Distance calculation part 630 Correction part 631 Memory 632 Memory selector 633 Calculator 640 Motor control part

Claims

1. A distance measuring device comprising: a light-emitting element that projects a projection light; a light-receiving element that receives light reflected from an object from the projection light and generates a received light signal based on the reflected light; and a controller that processes the received light signal, wherein the controller derives a measured distance value by measuring the distance to the object based on the time from when the projection light is projected to when the signal level of the received light signal becomes equal to or higher than a predetermined level, obtains association information that associates a plurality of measured distance values ​​with a plurality of actual distance values ​​corresponding to each of the plurality of measured distance values, and if the derived measured distance value is equal to or lower than a predetermined threshold, corrects the derived measured distance value based on the association information.

2. The distance measurement device according to claim 1, wherein the controller corrects the derived measured distance value based on the association information when the derived measured distance value is equal to or greater than the threshold value.

3. A distance measuring device as described in claim 1 or 2, wherein an approximation equation is generated that is approximated to pass through corresponding points determined by the multiple measured distance values ​​and the multiple actual distance values ​​measured in advance, and the association information includes polynomial information regarding a polynomial that represents the approximation equation.

4. A distance measuring device as described in claim 1 or 2, further comprising a memory, wherein the plurality of measured distance values ​​measured in advance are divided into a plurality of distance regions, and the association information is defined for each of the distance regions and stored in the memory.

5. The distance measuring device according to claim 4, wherein the controller retrieves the association information from the memory and switches the association information based on the derived measured distance value.

6. A distance measurement method comprising: projecting a projection light; receiving light reflected by an object from the projection light, and generating a received light signal based on the reflected light; measuring the distance to the object based on the time from the projection of the projection light to the time when the signal level of the received light signal becomes equal to or higher than a predetermined level, thereby deriving a measured distance value; obtaining association information that associates a plurality of measured distance values ​​with a plurality of actual distance values ​​corresponding to each of the plurality of measured distance values; and, if the derived measured distance value is equal to or lower than a predetermined threshold value, correcting the derived measured distance value based on the association information.

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