Distance measuring apparatus, and distance measuring method

Abstract

To provide a distance measuring apparatus capable of measuring the distance while reducing error in distance to an object even when noises such as stray light exist.SOLUTION: The distance measuring apparatus includes: 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 generates a received light signal based on the reflected light; and a controller that performs a series of processing based on the received light signal. The controller is configured to derive the measured distance value by measuring the distance from the distance measuring apparatus to the object based on the time from a point when the projected light is emitted until the signal level of the received light signal reaches a specified level or higher, acquire association information in which multiple measured distance values are associated with multiple actual distance values corresponding to each of the multiple measured distance values, and correct the measured distance value based on the association information when the measured distance value is less than or equal to a predetermined threshold.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] Conventionally, a distance measurement device that measures distance using a pulse wave is known. As one of the distance measurement devices, a transmission means for transmitting a pulse wave, a reception means for receiving a reflected wave generated by reflection of the pulse wave by a target, a time measurement means for measuring the required time from when the pulse wave is transmitted by the transmission means until the reflected wave is detected by the reception means, a pulse width measurement means for capturing the reception waveform of the reflected wave output from the reception means and measuring the pulse width of the reception waveform, a correction value calculation means for capturing the pulse width measured by the pulse width measurement means and calculating a correction value for the required time corresponding to the pulse width based on the input-output characteristics of the active region and the saturation region in the reception means, and a distance calculation means for correcting the required time measured by the time measurement means using the correction value calculated by the correction value calculation means and multiplying by the propagation speed of the pulse wave to calculate the distance to the target. A distance measurement device characterized by having these components is known (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

[0005] The present disclosure provides a distance measurement device and a distance measurement method that can reduce the error in the distance to an object and perform distance measurement even when noise such as stray light exists.

Means for Solving the Problem

[0006] One aspect of the present disclosure includes a light-emitting element that projects projection light, a light-receiving element that receives the reflected light reflected by an object from the projection light and generates a light-receiving signal based on the reflected light, and a controller that processes based on the light-receiving signal. The controller derives a measured distance value by measuring the distance to the object based on the time from the projection of the projection light until the signal level of the light-receiving signal becomes equal to or higher than a predetermined level, acquires association information in which a plurality of measured distance values and a plurality of actual distance values corresponding to each of the plurality of measured distance values are associated, and when the derived measured distance value is equal to or lower than a predetermined threshold value, corrects the derived measured distance value based on the association information. It is a distance measurement device.

[0007] One aspect of the present disclosure includes a step of projecting projection light, a step of receiving the reflected light reflected by an object from the projection light and generating a light-receiving signal based on the reflected light, a step of deriving a measured distance value by measuring the distance to the object based on the time from the projection of the projection light until the signal level of the light-receiving signal becomes equal to or higher than a predetermined level, a step of acquiring association information in which a plurality of measured distance values and a plurality of actual distance values corresponding to each of the plurality of measured distance values are associated, and a step of correcting the derived measured distance value based on the association information when the derived measured distance value is equal to or lower than a predetermined threshold value. It is a distance measurement method having

Advantages of the Invention

[0008] According to the present disclosure, even if there is noise such as stray light, it is possible to reduce the error in the distance to the object and perform distance measurement.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6A

Figure 6B

Figure 7A

Figure 7B

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, a more detailed description than necessary may be omitted. For example, a detailed description of well-known matters and a description of substantially the same configuration may be omitted. This is to avoid making the following description unnecessarily redundant and to facilitate the understanding of 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 it is not intended to limit the subject matter described in the claims by these.

[0011] (Process for arriving at the embodiments of the present disclosure) Assume that the distance measuring device of Patent Document 1 emits laser light and receives reflected light from an object to optically measure the distance. The distance measuring device of Patent Document 1 measures (calculates) the distance value from the distance measuring device to the object by measuring the time from the generation of the START signal that emits laser light to the generation of the STOP signal that detects the reflected light, and further corrects and outputs the distance value based on the pulse width of the received signal. In the distance measuring device of Patent Document 1, due to the influence of stray light existing inside the distance measuring device that occurs when laser light is emitted, a stray light component may be mixed as noise into the signal (received signal) processed by the light receiving circuit immediately after the emission. Also, as will be described later, other noises may be mixed in.

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

[0013] FIG. 10 is a diagram showing a second example of the amplifier output and the output of the comparator. When the object is near the distance measuring device, stray light and other noise are superimposed as noise on the reflected light from the object, and the amount of received light changes (increases or decreases) compared to the state without stray light. Therefore, the timing at which the level of the received signal based on the amount of received light becomes the slice level of the comparator is shifted by Δ time with respect to the ideal waveform that is not affected by stray light and 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 measuring device of Patent Document 1, an error (measurement error) may occur in the measured distance value due to the shift in the generation timing of the STOP signal caused by such stray light components and other noises. That is, a deviation occurs between the measured distance value and the actual distance. In the example of FIG. 10, it is assumed that the object is measured to be closer than it actually is.

[0015] Furthermore, when the distance measuring device emits laser light, inductive noise may also be generated due to a large current flowing inside the device during laser emission. Inductive noise includes, for example, electrical or magnetic noise. This is because a large current flows when the light emitting element emits laser light. 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 measuring device and a distance measuring method that can reduce the error in the distance to an object and perform distance measurement even in the presence of noise such as stray light will be described.

[0017] (Embodiment) <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 a cross-sectional view taken along line A-A in the distance measuring device 1 shown in Fig. 1.

[0018] The distance measuring device 1 is, for example, a LiDAR (Light Detection And Ranging) device. The distance measuring device 1 optically measures the distance to an object to be measured (distance measurement) using light such as laser light. The distance measuring device 1 uses light in a scanner method to perform two-dimensional scanning (scanning) for object detection and distance measurement.

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

[0020] The fixed part 100 has a substantially rectangular parallelepiped shape. The rotating part 300 is connected to the upper surface of the fixed part 100 and has a cylindrical shape that rotates about an axis perpendicular to the upper surface with the rotation axis C. The outer cover part 10 has a substantially cylindrical shape and covers the rotating part 300 from above. The outer cover part 10 has a wavelength window 11 formed using a wavelength selection member on at least a part 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 wavelength (frequency) components in the visible region. The wavelength selection member has a role of blocking disturbing light such as natural light and electric lights, for example.

[0021] For convenience of explanation, as shown in FIG. 1, an axis perpendicular to the upper surface (or bottom surface) of the fixed part 100 is defined as the Z-axis. An axis perpendicular to the Z-axis is defined as the X-axis. An axis perpendicular to the Z-axis and the X-axis is defined as the Y-axis. Also, for convenience of explanation, the positive direction of the Z-axis may be referred to as "up", the negative direction of the Z-axis may be referred to as "down", and the direction away from the Z-axis in the X-axis direction or the Y-axis direction may be referred to as "sideways". Note that these expressions regarding directions are used for convenience of explanation and are not intended to limit the posture during actual use of the structure. For example, the distance measurement device 1 shown in FIG. 1 may be used with the top and bottom reversed. Also, the cross-sectional view A-A shown in FIG. 2 corresponds to a cross-sectional view of 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 a housing surface of a predetermined device, etc.).

[0023] The rotating part 300 rotates about the central axis in the height direction (Z-axis) of the cylinder as the rotation axis C. As the rotating part 300 rotates, the optical axis of the projection light (hereinafter referred to as projection light 3A) projected laterally from a part of the side surface of the rotating part 300 rotates about the rotation axis C. Accordingly, the projection light 3A and the region where distance measurement is possible with the projection light 3A (hereinafter referred to as the distance measurement region) also rotate. As will be described later, the distance measurement device 1 measures the distance to an object existing in the distance measurement region based on the time difference (Time of Flight (TOF)) between the timing when the projection light 3A is projected and the timing when the light (hereinafter referred to as reflected light 3B) reflected by the object in the distance measurement region is received. When the rotating part 300 makes one full rotation about the rotation axis C, the distance measurement device 1 can measure the distances to the objects existing in the distance measurement region of 360 degrees in the lateral circumferential direction.

[0024] The fixed part 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 photo interrupter 107. The rotating part 300 includes a rotating member 301, a magnet 302, and a reflecting mirror 303.

[0025] A hollow motor 402 (see FIG. 3) is formed by the coil 106 of the fixed part 100 and the magnet 302 of the rotating part 300, and the rotating part 300 rotates about the rotation axis C by driving this motor 402.

[0026] The substrate 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 substrate 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 projected from the light emitting element 102 into substantially parallel light and outputs it upward.

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

[0030] The reflected light 3B obtained by reflecting the projected light 3A by an object passes through the wavelength window 11 of the outer cover portion 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 it downward.

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

[0033] The rotating member 301 includes a plurality of ribs 311 at regular intervals. For example, the rotating member is annular and ribs are present at regular intervals in the circumferential direction. The photo interrupter 107 is arranged so as to be able to detect the passage of one rib 311. By detecting and counting the passage of one rib 311 using the photo interrupter 107, the controller 600, which will be described later, can detect the rotation angle (rotation position) of the rotating member 301 (that is, the rotating portion 300). Therefore, the photo interrupter 107 and the rib 311 can constitute a rotation angle detector 403 (see FIG. 3), which will be described later.

[0034] Note that a part of the projected light 3A projected by the light emitting element 102 and reflected by the reflecting mirror 303, or unintended light, stays inside the distance measuring device 1 without passing through the wavelength window 11. The light staying inside can be received by the light receiving element 103 as stray light 3C. The stray light 3C received by the light receiving element 103 can be superimposed on the received signal. Further, when the light emitting element 102 projects light, a large current flows instantaneously, so that noise 3D due to, for example, electromagnetic induction can be generated. The noise 3D includes electrical or magnetic noise. This noise 3D can also be superimposed on the received signal.

[0035] <Functional configuration of distance measuring device> FIG. 3 is a block diagram showing a functional configuration example of the distance measuring device 1 according to Embodiment 1.

[0036] The distance measuring 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 in 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 outside the controller 600.

[0037] The light emitting element 102 is formed of, for example, a laser diode. The light emitting element 102 receives a pulse signal for instructing light emission by the light emitting element 102 from the distance measurement control unit 610. The light emitting element 102 projects pulsed projected light 3A corresponding to 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 formed of, for example, a photodiode. The light receiving element 103 receives the reflected light 3B and outputs a received signal corresponding to the received level.

[0039] Comparator 401 receives a light reception signal from the light receiving element 103. The comparator 401 outputs a pulse signal (also referred to as a light reception pulse signal) according to the signal level of the light reception signal. The light reception pulse signal becomes a predetermined High level during a period when the level of the light reception signal is equal to or higher than a predetermined comparator threshold value (comparator slice level), and becomes a predetermined GND level during a period when the level of the light reception signal is lower than the comparator threshold value. The High level is greater than the GND level. In FIG. 3, the output of the light reception pulse signal is expressed as STOP (STOP signal).

[0040] The motor 402 applies a driving force for rotating the rotating part 300 to the rotating part 300. The rotation angle detector 403 detects the rotation angle of the rotating part 300. This rotation angle indicates an angle with respect to a predetermined reference angle.

[0041] TDC 500 receives a START signal from the distance measurement control unit 610. The input timing of this START signal corresponds to the light projection timing of the projected light 3A by the light emitting element 102. TDC 500 receives a STOP signal from the comparator 401. The input timing of the STOP signal corresponds to the light reception timing of the reflected light 3B by the light receiving element 103, and more specifically, corresponds to the timing when the light reception pulse signal is generated. TDC 500 outputs TOF (time of flight) information based on the START signal and the STOP signal. TDC 500 may output information on the pulse width of the light reception 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 constituted by various integrated circuits (for example, LSI (Large Scale Integration), FPGA (Field Programmable Gate Array)). The controller 600 realizes various functions by executing a program held in a memory disposed inside or outside the controller 600. The controller 600 has, as various functional units, a distance measurement control unit 610, a distance calculation unit 620, a correction unit 630, a motor control unit 640, etc.

[0043] The distance measurement control unit 610 controls the distance measurement by the distance measurement device 1, and controls, for example, the TDC500 and the distance calculation unit 620. The distance measurement control unit 610 acquires the rotation angle information from the rotation angle detector 403. When the acquired rotation angle is a predetermined rotation angle or is included in a predetermined angle range, the distance measurement control unit 610 sends a START signal to the light emitting element 102 and the TDC500. Thereby, the light emitting element 102 can project the projection light 3A in a desired direction or a range of desired directions around the distance measurement device 1.

[0044] The distance calculation unit 620 acquires the TOF and pulse width information from the TDC500. The distance calculation unit 620 calculates, for example, 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. 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 the information of the measured distance value X from the distance calculation unit 620, and derives (for example, calculates) a distance value obtained by correcting the measured distance value X (also referred to as a corrected distance value Y). The correction unit 630 outputs the information of the corrected distance value Y to an external device or a storage device. Details of the method for correcting the measured distance value X by the correction unit 630 will be described later.

[0046] Further, the distance calculation unit 620 may specify 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 measured distance value X among the two-dimensional positions, and correct the two-dimensional position by specifying the two-dimensional position based on the corrected distance value Y and the rotation angle. The correction unit 630 may output the 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 for controlling the motor 402 to the motor 402.

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

[0049] The correction unit 630 includes a memory 631, a memory selector 632, and an arithmetic unit 633. The memory 631 includes, for example, a RAM or a ROM, and may include other storage devices. The memory 631 holds association information in which each measured distance value X and each corrected distance value Y are associated. The memory 631 may hold a plurality of association information. Note that the association information is also information in which a pre-measured distance value and a plurality of actual distance values corresponding to each of the plurality of measured distance values are measured and associated in advance, as will be described later. The association information is represented by, for example, polynomial information which is information regarding a polynomial. In the present embodiment, mainly an example in which the association information is polynomial information will be illustrated and described.

[0050] The polynomial has, for example, a plurality of coefficients. For example, when the polynomial is represented by a quadratic equation, if the measured distance value is "X" and the corrected distance value is "Y", then Y = aX 2 + bX + c. The polynomial information held in the memory 631 includes at least a set of values for x, a, b, and c. Here, "x" is a boundary value described later, and "a", "b", and "c" are coefficients of the polynomial. When the set of x, a, b, and c is described in the form of {x, a, b, c}, as an example, x = x 1 , a = a 1 , b = b 1 , c = c 1 In the case of, {x 1 , a 1,b 1 ,c 1} is expressed. In FIG. 4, as an example, in the memory 631, {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) of polynomial information is held. Further, the polynomial information may include not only information on coefficients in the polynomial but also the expression itself in a state where the coefficients in the polynomial are specifically set (for example, Y = a 1 X 2 +b 1 X+c 1 ).

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

[0052] The calculator 633 sets, as a polynomial for correction, the polynomial corresponding to the polynomial information selected by the memory selector 632. Thus, for example, when the polynomial information I2 is selected, the polynomial Y = aX 2 +bX+c is set as Y = a 2 X 2 +b 2 X+c 2Set it. The arithmetic unit 633 corrects the value of the measured distance value X based on the set polynomial to obtain the value of the corrected distance value Y. Further, when measuring a plurality of objects around the distance measuring device 1, the memory selector 632 selects polynomial information from the memory 631 a plurality of times based on the obtained measured distance value X, acquires the polynomial information from the memory 631, switches it, and sets it in the arithmetic unit 633.

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

[0054] In order to generate the polynomial information held in the memory 631, the following processing is performed in advance. For example, the distance measuring device 1 measures an arbitrary object, and while changing the distance from the distance measuring device 1 to the object, measures the distance to the object according to the TOF method by the distance measuring device 1 as described above, thereby deriving a plurality of measured distance values. Since this measured distance value is a measured distance value measured in advance (previously), it is also referred to as a pre-measured distance value. Further, the distance measuring device 1 acquires information in which the actual distance (real distance) to the object is measured by a method other than the TOF method. For example, the actual distance is measured by actually measuring the distance from the distance measuring device 1 to the object with a measuring instrument by the measurer or measuring it with another sensor. The measured actual distance information is input to the distance measuring device 1 by, for example, a communication device or an input device (for example, a key, a button) of the distance measuring device 1.

[0055] The controller 600 maps each pre-measured distance value from the distance measuring device 1 to the object measured in advance and each real distance value to the same object at the same position measured in advance on a two-dimensional plane.

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

[0057] In a two-dimensional plane, one mapping point mp is arranged 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). In contrast, in reality, the pre-measured distance value may include a measurement error. Therefore, some of the mapping points mp are not arranged on the straight line indicating the ideal value. Such an error is more likely to occur as the pre-measured distance value is smaller, that is, in the short-distance region where the distance from the distance measurement device 1 is closer.

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

[0059] The correction unit 630 generates an approximation formula approximated to pass through each mapping point mp in the two-dimensional plane. The approximation formula is represented by, for example, a polynomial. The approximation formula approximated to pass through each mapping point mp may be represented by a plurality of approximation formulas. For example, in FIG. 6A, the characteristics of the shape formed by the set of mapping points mp are significantly different between the range where the pre-measured distance value is equal to or less than x1 and the 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 (that is, the side closer to the distance measurement device 1), the set of mapping points mp is quadratic, and in the range where the pre-measured distance value is greater than x1 (that is, 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, for example, by the administrator inputting through an input device, or may determine the value of x1 by calculation based on the position of the mapping point mp or the positional relationship between the positions of the mapping points mp. In such a case, by using different approximation formulas for the range where the pre-measured distance value is equal to or less than x1 and the range where the pre-measured distance value is greater than x1, the measurement error included in the measurement distance value can be efficiently reduced. A point that serves as a boundary for changing an approximation formula such as x1 is also referred to as a boundary value.

[0060] Also, in FIG. 6A, near the maximum value of the pre-measured distance value, within the range below the maximum value, the mapping points mp form a predetermined shape, and in the range exceeding the maximum value, the mapping points mp themselves do not exist. Therefore, the correction unit 630 also uses 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 formula 1 for 0 < pre-measured distance value ≤ x 1 and generates approximation formula 2 for x 1 < pre-measured distance value ≤ x 2 . Approximation formula 1 is represented by a quadratic formula (ax 2 + bx + c) as in FIG. 4, and the specific coefficients of "a", "b", and "c" are in the form of (a 1 , b 1 , c 1 ). Similarly, approximation formula 2 has specific coefficients of "a", "b", and "c" in the form of (a 2 , b 2 , c 2 ). The correction unit 630 calculates each approximation formula, for example, by a known linear approximation or non-linear approximation method according to the positions of the mapping points mp included in the respective pre-measured distance value ranges. For example, the correction unit 630 performs curve fitting to obtain an approximation curve. The polynomial information regarding the polynomial representing each generated approximation formula is held in the above-described memory 631. The polynomial information is held, for example, in the form of a set {x, a, b, c} of the boundary value and the coefficients of the polynomial as shown in FIG. 4.

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

[0062] Also in FIG. 6B, the method of generating the approximation formula is the same as in FIG. 6A, but there are three boundary values of x 1 , x 2 , and x 3 , and there are also three approximation formulas. The correction unit 630 generates approximation formula 1 for 0 < pre-measured distance value ≤ x 1 and generates approximation formula 2 for x 1 < pre-measured distance value ≤ x2 Generate approximation formula 2 for, and x 2 <Pre-measured distance value ≤ x 3 Generate approximation formula 3 for. The approximation formula 3 has specific coefficients of "a", "b", and "c" as (a 3 , b 3 , c 3 ). As shown in FIG. 6B, since the approximation formula 3 has a linear shape, it can be expressed by a linear formula, and the value of coefficient a 3 is 0.

[0063] Note that the amount of light of the reflected light 3B changes according to the reflectivity of the object, the signal level of the received light signal also changes, and the generation timing of the STOP signal may change. Also, since the pulse width of the received light pulse signal changes according to the amount of light of the reflected light 4B, the generation timing of the STOP signal may change. Therefore, the correction unit 630 may generate an approximation formula and polynomial information for each object, for example, taking into account the reflectivity of the object to be measured. Note that the amount of light (light intensity) of the projected light 3A by the light emitting element 102 may be constant.

[0064] In this way, the correction unit 630 may define a plurality of distance regions in which each pre-measured distance value is divided by each boundary value, and generate an approximation formula for each distance region, and may hold polynomial information corresponding to the approximation formula in the memory 631 for each distance region.

[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.

[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 the corrected distance value Y. For example, when 0 < X ≤ x 1 is satisfied, the correction unit 630 selects approximation formula 1 and derives (for example, calculates) the corrected distance value Y from the measured distance value X based on approximation formula 1. For example, when x 1 < X ≤ x 2 is satisfied, the correction unit 630 selects approximation formula 2 and derives (for example, calculates) the corrected distance value Y from the measured distance value X based on approximation formula 2.

[0067] Specifically, in the correction unit 630, the boundary values ​​and the coefficients of the polynomial are stored in the form of a set {x, a, b, c} in the memory 631 as shown in FIG. <X≦x 1 If this is satisfied, the {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 approximation 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 the approximation formula 2 indicated by the polynomial information I2. That is, when the measured distance value X is equal to any of the boundary values ​​x, the memory selector 632 selects the polynomial information including the 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 is x 2 <X≦x 3 If the above equation is satisfied, the approximation formula 3 is selected, and the corrected distance value Y is derived (for example, calculated) from the measured distance value X based on the approximation formula 3. 2 <X≦x 3 If this is satisfied, the {x 3 ,a 3 ,b3 , c 3 Select the polynomial information I3 that is {}. The arithmetic unit 633 calculates the corrected distance value Y from the measured distance value X according to the approximation formula 3 indicated by the polynomial information I3.

[0070] In this way, the correction unit 630 selects one piece of polynomial information from the polynomial information held for each distance range based on the input measured distance value X, and can derive the corrected distance value Y from the measured distance value X according to the polynomial (approximation formula) indicated by the polynomial information.

[0071] Note that the approximation formula and the polynomial may be represented by an n-th order formula (n is an integer of 3 or more) instead of a quadratic formula. In this case, the number of coefficients of the n-th order formula is larger than that of the quadratic formula.

[0072] Next, the distance range of the measured distance value X for which correction is performed by the correction unit 630 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 value. When an object to be measured exists in the short distance range, the reflected light 3B reflected by the object is received in a relatively short time from the projection of the projection light 3A. Therefore, stray light 3C caused by the projection of the light emitting element 102 and noise 3D caused by a large current at the time of light emission are superimposed on the received signal, and it is easy to affect the generation timing of the STOP signal. The predetermined threshold value of 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 originally desired to be received and the reflected light 3B that is originally desired to be received. That is, the predetermined threshold value may be the same value as, for example, the boundary value x1 or the boundary value x2, which is a relatively small boundary value. In this way, by correcting the measured distance value X when the measured distance value X is equal to or less than the predetermined threshold value, the measurement error can be efficiently reduced.

[0074] Further, even when the measured distance value X is included in the long-distance region, specifically, even when the measured distance value X is greater than a predetermined threshold value, the correction unit 630 may correct the measured distance value X. When an object to be measured exists in the short-distance region, the reflected light 3B reflected by the object is received from the projection of the projection light 3A for a relatively long time. Even when a certain amount of time has elapsed from the light emission timing of the light emitting element 130, there may be stray light 3C or noise. In contrast, when the measured distance value X is greater than a predetermined threshold value, the distance measuring device 1 corrects the measured distance value X, so that the measurement error can be reduced without depending on the distance between the distance measuring device 1 and the object.

[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 the approximation formula (polynomial) by the correction unit 630, the corrected distance value Y becomes a value 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 is in a state where the measurement error is close to 0 whether the corrected distance value Y is in a distance region with a small value or in a distance region with a large value. Thus, 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 measuring device 1 of the present embodiment includes a correction unit 630 that holds information on 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 holds quadratic approximation formulas for the short-distance region and the long-distance region in the distance measurement region, respectively. As an example, the short-distance region is a region in the range of 0 ≦ X < x1. In this case, the correction unit 630 sets the approximation formula 1. As an example, the long-distance region is a region in the range of x1 ≦ X < x2. In this case, the correction unit 630 sets the approximation formula 2. Further, the distance measurement region is divided into N regions of three or more. As an example, the Nth region is X n-1 ≦ X < X nIt is an area within the range, and in this case, the correction unit 630 may set the approximate formula n. The correction unit 630 switches the coefficients of the approximate formula set according to the measured distance value X, performs an operation using the approximate formula, corrects the measured distance value X, and outputs a corrected distance value Y. Thereby, the distance measuring device 1 can reduce the error of the measured distance value (measured distance value).

[0078] Note that in this embodiment, it is exemplified that the correction unit 630 executes preparatory operations such as the association between each pre-measured distance value and each actually measured distance value, the mapping onto a two-dimensional plane, the generation of an approximate formula, and the retention of polynomial information in the memory 631, but it is not limited thereto. For example, an external server may execute these preparatory operations. In this case, when it is time to actually correct the measured distance value X, the polynomial information may be acquired from the external server via a communication device or the like, and the memory 631 may hold it at least temporarily. Also, the polynomial information may be directly set in the arithmetic unit 633 without being held in the memory 631. Therefore, the controller 600 acquires association information in which a plurality of measured distance values and a plurality of actual distance values corresponding to each of the plurality of measured distance values are measured in advance and associated, from the memory 631, an external server, or the like.

[0079] As described above, various embodiments have been described with reference to the drawings, but it goes without saying that the present invention is not limited to such examples. It is obvious that a person skilled in the art can conceive of various modification examples or correction examples within the scope described in the claims, and it is naturally understood that those also belong to the technical scope of the present invention. Also, within the scope not departing from the gist of the invention, the components in the above embodiments may be arbitrarily combined.

[0080] <Summary of this Embodiment> As described above, the present disclosure describes at least the following matters. In the parentheses, the corresponding components and the like in the above-described embodiment are exemplified, but it is not limited thereto.

[0081] (Item 1) A light-emitting element (light-emitting element 102) that projects projection light (projection light 3A), a light-receiving element (light-receiving element 103) that receives reflected light (reflected light 3B) reflected by an object from the projection light and generates a light-receiving signal based on the reflected light, and a controller (controller 600) that processes based on the light-receiving signal. The controller derives a measured distance value (measured distance value X) by measuring the distance to the object based on the time from the projection of the projection light until the signal level of the light-receiving signal becomes a predetermined level or higher, acquires association information in which a plurality of measured distance values (pre-measured distance values) and a plurality of actual distance values corresponding to each of the plurality of measured distance values are associated, when the derived measured distance value is equal to or less than a predetermined threshold value, corrects the derived measured distance value based on the association information. A distance measurement device (distance measurement device 1).

[0082] The reflected light may be received by the light-receiving element with stray light (stray light 3C) superimposed thereon. Also, when the light-emitting element projects light, noise (noise 3D) such as electrical or magnetic noise may be generated due to a large current or the like. Therefore, the measured distance value may include a measurement error caused by stray light or noise. The measurement error is likely to be included when the measured distance value is equal to or less than a predetermined threshold value, that is, when the object is present at a short distance from the distance measurement device. Even in this case, the distance measurement device can reduce the measurement error and perform distance measurement by correcting the measured distance value of the object to be measured in consideration of the relationship between the previously obtained measured distance value and the actual distance value.

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

[0084] Thereby, the distance measurement device can reduce the measurement error and perform distance measurement not only when the object is present at a short distance but also when the object is present at a long distance.

[0085] (Item 3) An approximation formula is generated so as to pass through corresponding points (mapping points mp) determined by the plurality of measured distance values and the plurality of actual distance values measured in advance. The association information includes polynomial information regarding the polynomial indicating the approximation formula. The distance measuring device according to item 1 or 2.

[0086] Thereby, the distance measuring device can easily correct the measured distance value of the object to be measured by using a polynomial through calculation, reduce the measurement error, and perform distance measurement.

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

[0088] Thereby, the distance measuring device can correct the measured distance value by using different association information for each distance region.

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

[0090] Thereby, when the distance measuring device measures a plurality of objects and obtains measured distance values in different measurement regions, it can switch the association information and correct each of the plurality of measured distance values.

[0091] (Item 6) A step of projecting projection light. A step of receiving the reflected light reflected by the object from the projection light and generating a reception signal based on the reflected light. Deriving a measured distance value by 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; Obtaining association information in which a plurality of measured distance values and a plurality of actual distance values corresponding to each of the plurality of measured distance values are associated; When the derived measured distance value is equal to or less than a predetermined threshold value, correcting the derived measured distance value based on the association information; A distance measurement method comprising the steps of:

[0092] Thereby, the same effect as in Item 1 can be obtained.

Industrial Applicability

[0093] The present disclosure is useful for a distance measurement device, a distance measurement method, etc. that can reduce the measurement error of the distance to an object and perform distance measurement even in the presence of noise such as stray light.

Explanation of Signs

[0094] 1 Distance measurement 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 Condensing lens 105 Collimator lens 106 Coil 107 Photointerrupter 300 Rotating part 301 Rotating member 302 Magnet 303 Reflecting mirror 311 Rib 401 Comparator 402 Motor 403 Rotation angle detector 500 TDC 600 Controller 610 Distance Measurement Control Unit 620 Distance Calculation Unit 630 Correction Unit 631 Memory 632 Memory Selector 633 Arithmetic Unit 640 Motor Control Unit

Claims

1. A light emitting element that projects projection light, a light receiving element that receives the reflected light reflected by an object from the projection light and generates a light reception signal based on the reflected light, and a controller that processes based on the light reception signal, wherein the controller derives a measured distance value by measuring the distance to the object based on the time from the projection of the projection light until the signal level of the light reception signal becomes equal to or higher than a predetermined level, acquires association information in which a plurality of measured distance values and a plurality of actual distance values corresponding to each of the plurality of measured distance values are associated, and corrects the derived measured distance value based on the association information when the derived measured distance value is equal to or less than a predetermined threshold value, a distance measurement device.

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

3. An approximation formula approximated so as to pass through corresponding points determined by the plurality of measured distance values and the plurality of actual distance values measured in advance is generated, wherein the association information includes polynomial information regarding a polynomial indicating the approximation formula, The distance measurement device according to claim 1 or 2.

4. 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 determined for each distance region and stored in the memory, The distance measurement device according to claim 1 or 2.

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

6. a step of projecting projection light, a step of receiving the reflected light reflected by an object from the projection light and generating a light reception signal based on the reflected light, a step of deriving a measured distance value by measuring the distance to the object based on the time from the projection of the projection light until the signal level of the light reception signal becomes equal to or higher than a predetermined level, a step of acquiring association information in which a plurality of measured distance values and a plurality of actual distance values corresponding to each of the plurality of measured distance values are associated, and a step of correcting the derived measured distance value based on the association information when the derived measured distance value is equal to or less than a predetermined threshold value, a distance measurement method.

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