Distance measuring device and method

Abstract

To solve the problem that a position to be measured, depending on a distance to an object, and a distance image is distorted.SOLUTION: A three-dimensional distance measuring device includes: means (20) for generating a modulated waveform modulated by a plurality of frequencies hierarchically combined; means (3) for scanning and irradiating a measuring object with the modulated waveform; means (4) for receiving a reflected wave from the measuring object; means (23) for calculating a distance to the object by detecting a phase difference of each modulation frequency from the reflected wave; and means (27) for controlling timing of measurement of coordinates according to a result of measurement of coordinates already performed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a three-dimensional distance measuring device and method using an indirect ToF method. [Background technology]

[0002] LiDAR devices, which use laser light for detection and distance measurement, have been put into practical use as a means of detecting surrounding conditions in automotive ADAS (Advanced Driver Assistance Systems). By scanning the laser light in two dimensions (e.g., raster scanning) to measure distance, it is possible to create a distance image that shows the distance to an object. By recognizing the type and distance of an object, it is possible to realize functions such as automatic emergency braking.

[0003] LiDAR devices use the ToF (Time Of Flight) method to measure three-dimensional distances. There are two types of ToF methods: direct ToF and indirect ToF. The indirect ToF method irradiates a target with laser light and determines the distance by measuring the phase delay of the reflected wave.

[0004] As a method for measuring distance over a long distance with high accuracy using the indirect ToF method, for example, a method such as that described in Patent Document 1 has been realized. (1) Laser light is multiplex-modulated with high-frequency and low-frequency waveforms, and the distance is calculated from the measured values ​​of each frequency (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 64-69983 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the above-mentioned conventional example had a problem in that the measurement position shifted depending on the distance to the object, resulting in distortion of the distance image. The conventional distance measuring device performed measurements by scanning a laser beam. For example, measurement began at the left edge of the target area, and measurements were continued while shifting the position gradually to the right, scanning all the way to the right edge. For a close object, the laser beam reflected off the surface of the object at the expected position, and the reflected light returned. On the other hand, the reflected wave from a distant object arrived with a delay, so the received reflected light may be light that reflected off the object at a previous position (slightly to the left). In other words, the measurement result for a distant object measured a position slightly to the left of the object surface. Because the degree of position shift varied depending on the distance to the object, the distance image contained distortion in the surface direction. [Means for solving the problem]

[0007] In order to solve the above problems, a distance measuring device according to the present invention comprises: A means (20) for generating a modulation waveform modulated at a plurality of frequencies hierarchically combined; a means (3) for scanning and irradiating the modulated waveform onto a measurement object; a means (4) for receiving a reflected wave from the measurement object; a means (23) for detecting a phase difference between the respective modulation frequencies from the reflected waves and calculating a distance to an object; A three-dimensional distance measuring device comprising: means (27) for controlling the timing of coordinate measurement according to the results of previous coordinate measurements; Equipped with. [Effects of the Invention]

[0008] According to the present invention, it is possible to prevent displacement of the measurement position caused by the distance to the object, and therefore it is possible to obtain a distance image without distortion. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram showing the overall configuration of a distance measuring device according to a first embodiment. [Figure 2]A block diagram showing a schematic configuration of a waveform generating unit according to the first embodiment. [Figure 3] FIG. 1 is a block diagram showing a schematic configuration of a distance calculation unit according to a first embodiment. [Figure 4] Example of a distance image screen in Example 1 [Figure 5] Timing diagram of the data processing pipeline in Example 1 [Figure 6] 1 is a flowchart showing the flow of processing for creating a distance image according to the first embodiment. [Figure 7] FIG. 1 is a timing diagram showing an example of the operation of the measurement window position change process according to the first embodiment; [Figure 8] FIG. 10 is a block diagram showing the overall configuration of a distance measuring device according to a second embodiment. [Figure 9] Timing diagram of the data processing pipeline of Example 2 DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below based on preferred embodiments thereof with reference to the accompanying drawings. Note that the configurations shown in the following embodiments are merely examples, and the present invention is not limited to the configurations shown in the drawings. [Example]

[0011] In this embodiment, an example is described in which the measurement timing of a coordinate to be measured is changed according to the measured distance of the previous coordinate in an indirect ToF three-dimensional distance measuring device using a multiple modulation waveform. The position of the measurement period (hereinafter referred to as the "measurement window") of the primary modulated wave is determined from the approximate phase difference of the nearby coordinate (the previous coordinate). Data sampling and phase difference calculation are performed during the measurement window period, which is the data valid period of the primary modulated wave. The distance is calculated by combining this with the separately calculated phase difference of the secondary modulated wave.

[0012] <Example of distance image (Fig. 4)> First, an example of a distance image screen in this embodiment will be described using Fig. 4. Reference numeral 200 denotes the distance image screen. Coordinates of distance measurements are arranged in a grid pattern, such as 207 to 209, and each coordinate is colored according to distance. The user can know the distance to an object by looking at the color of the object on the screen.

[0013] Distance image 200 is created by raster scanning in the two-dimensional X and Y directions. 201 to 203 are raster lines indicating the horizontal scanning position. After measurement of raster line 201 is completed, measurement of raster line 202 is performed, followed by measurement of raster line 203, and so on, with sequential scanning in the vertical direction. In raster line 201, 204 to 206 are distance measurement cycles, which are measurement periods for measuring the distance to one coordinate. The distance measurement cycle is common to the entire screen. 207 to 209 are coordinate centers indicating the center position of the distance measurement cycle, and the distance value measured during the distance measurement cycle is treated as the distance value of the point at this coordinate center.

[0014] If the relationship between the actual measurement position and the coordinate center position shifts depending on the distance to the object, distortion occurs in the plane direction of the range image. In this embodiment, processing is performed to prevent this position shift.

[0015] <Configuration of distance measuring device (Figs. 1-3)> Next, the configuration of the distance measuring device in this embodiment will be described.

[0016] FIG. 1 is a block diagram showing a schematic configuration of a distance measuring device.

[0017] Reference numeral 1 denotes the main body of the distance measuring device, which performs three-dimensional distance measurement using the indirect ToF method. Reference numeral 2 denotes the object to be measured. The distance measuring device 1 irradiates the object to be measured 2 with laser light and measures the phase difference of the reflected light to measure the distance.

[0018] In distance measuring device 1, reference numeral 3 denotes an irradiating unit that irradiates laser light. Reference numeral 4 denotes a light receiving unit that receives the laser light. Reference numeral 5 denotes a scanning system drive unit that moves the irradiation direction of irradiating unit 3 so as to scan in two dimensions. Reference numeral 6 denotes a control unit that controls the process from irradiating laser light, receiving reflected light, and obtaining and outputting a distance image.

[0019] In the irradiation unit 3, 10 denotes a D / A converter that converts digital data indicating the irradiation waveform output from the control unit 6 into an analog signal. 11 denotes a laser diode that emits laser light in accordance with the analog signal. 12 denotes an irradiation optical system that is composed of a lens optical system for irradiating the laser light.

[0020] In the light receiving unit 4, 13 is a light receiving optical system, which is composed of a lens optical system for receiving the reflected laser light. 14 is a photosensor, which converts the reflected laser light into an electrical signal. 15 is an A / D converter, which converts the electrical signal of the reflected light into digital data.

[0021] In the scanning system driver 5, 16 is an X-axis driver that scans the laser light output from the irradiation unit in the X-axis direction. X-axis driver 16 is composed of, for example, a polygon mirror. 17 is a Y-axis driver that scans the laser light output from the irradiation unit in the Y-axis direction.

[0022] In the control unit 6, reference numeral 20 denotes an overall control unit that creates a distance image and controls the entire distance measuring device 1. Overall control of the device includes, for example, power supply, distance measurement, on / off image output, and user interface control. The overall control unit 20 is composed of a CPU, memory, various control LSIs, switches, a user interface, etc. Reference numeral 21 denotes a waveform generation unit that generates a modulation waveform for modulating the laser light output from the irradiation unit 3. Reference numeral 22 denotes a measurement window control unit that controls the extraction and output of only the data used for distance calculation from the measured data. The extraction range of the measurement window control unit 22 is controlled by a measurement timing control unit 27 (described below). Reference numeral 23 denotes a distance calculation unit that calculates the distance of the irradiated coordinates from the waveforms of the measurement light and reflected light. Reference numeral 24 denotes a distance measurement result memory that stores the calculated distance values. Reference numeral 25 denotes a distance image creation unit that creates a distance image based on the distance values ​​for each coordinate. It also performs three-dimensional point cloud processing such as outlier removal and distortion correction. Reference numeral 26 denotes an output control unit that outputs the distance image. For example, it is configured with a communication interface such as USB, Ethernet, or WiFi. 28 is a coordinate control unit that outputs the coordinate position where measurement is performed so that two-dimensional scanning can be performed in the horizontal and vertical directions. 29 is a scan control unit that controls the scan system drive unit 5 so that laser light can be irradiated in the direction of the coordinate position where measurement is performed. 27 is a measurement timing control unit that determines and outputs the measurement period for data used in distance calculation. The measurement timing control unit 27 receives an approximate phase difference from the distance calculation unit 23, determines the position of the measurement window accordingly, and outputs a signal indicating the position to the measurement window control unit 22.

[0023] 2 is a block diagram showing a schematic configuration of the waveform generating unit 21. The waveform generating unit 21 generates two sine waves of frequencies that are hierarchically combined, and modulates them to generate a modulated waveform.

[0024] For example, the sine wave to be generated has a primary modulating wave of 49 MHz and a secondary modulating wave of 1 MHz. "Hierarchical" means that the primary modulating wave has a frequency that is an integer multiple (49 times in this case) of the secondary modulating wave. The secondary modulating wave is used to measure a rough distance, and the primary modulating wave increases the accuracy of the distance measurement. To achieve this, an integer number of waves of the primary modulating wave are included in one cycle of the secondary modulating wave. The modulation frequency is not limited to two waves; three or more waves can be combined hierarchically. For example, in the case of three waves, if they are layered at a multiplier of 7, 49 MHz, 7 MHz, and 1 MHz can be used.

[0025] Reference numeral 40 denotes a first waveform generator, which generates the waveform of the primary modulation wave (49 MHz). Reference numeral 41 denotes a second waveform generator, which generates the waveform of the secondary modulation wave (1 MHz). Waveform generators 40 and 41 store sine wave waveform data in advance in internal memory and generate waveforms by sequentially reading it out in accordance with the timing. Reference numeral 42 denotes a modulator, which amplitude-modulates the primary modulation wave with the secondary modulation wave and sequentially outputs the waveform data. Here, to measure the waveform phase, calculations must be performed using a period of at least one cycle of the waveform. Since the secondary modulation wave is 1 MHz, the ranging cycle is set to, for example, every 1 us.

[0026] FIG. 3 is a block diagram showing the schematic configuration of the distance calculation unit 23. 50 is a phase difference detection unit for the primary modulated wave. In the phase difference detection unit 50 for the primary modulated wave, 53 is a discrete Fourier transform unit (hereinafter referred to as DFT unit) that performs a discrete Fourier transform on the irradiated waveform and converts it into frequency domain data. 54 is a phase calculation unit that calculates the phase of the waveform from the frequency domain data. Similarly, in the block for the reflected waveform, 55 is a DFT unit and 56 is a phase calculation unit. 57 is a phase difference calculation unit that calculates the phase difference between the irradiated waveform and the reflected waveform. 51 is a phase difference detection unit for the secondary modulated wave. As with the phase difference detection unit 50 for the primary modulated wave, 58 is a DFT unit for the irradiated waveform and 59 is a phase calculation unit. 60 is a DFT unit for the reflected waveform and 61 is a phase calculation unit. 62 is a phase difference calculation unit. 52 is a distance calculation unit that calculates a distance value using the phase difference between the primary modulated wave and the secondary modulated wave.

[0027] The flow of calculation processing by the distance calculation unit 23 will be described below.

[0028] Discrete Fourier transform units 53, 55, 58, and 60 perform a discrete Fourier transform on the input waveform. The data is converted into frequency space data, and frequency parameters of the waveform of the target frequency (primary modulating wave, secondary modulating wave) are extracted. A known algorithm can be used for the discrete Fourier transform calculation. A complex vector X+iY is obtained as a result of the calculation. The absolute value of the complex vector represents the amplitude of the waveform, and the angle represents the phase of the waveform.

[0029] The phase calculation units 54, 56, 69, and 61 calculate the phase of the waveform from the above complex vector. The phase of the waveform is found by calculating the arctangent of the complex vector (Equation (1)). The arctangent calculation is performed using, for example, a known CORDIC algorithm. The phase ph is given by ph=arctan(Y / X) Equation (1)

[0030] The phase difference calculation units 57 and 62 calculate the phase difference phdif between the irradiated wave and the reflected wave (Equation (2)), where ph_t is the phase of the irradiated wave, and ph_r is the phase of the reflected wave. phdif=ph_r-ph_t Formula (2)

[0031] Distance calculation section 52 calculates distance from the phase difference of each modulated wave. If the phase difference of the primary modulated wave is phdif_m and the phase difference of the secondary modulated wave is phdif_s, the overall phase difference pdif_t can be found as shown in equation (3). phdif_t=phdif_s+phdif_m Formula (3)

[0032] Finally, the distance value dst can be calculated using equation (4), where c is the speed of light. dst=c×phdif_t Equation (4)

[0033] By performing the above calculations, the distance value dst can be calculated from the data string of the measured waveform.

[0034] <Explanation of the data processing pipeline (Figure 5)> Figure 5 is a timing diagram showing the flow of the data processing pipeline that processes measurement data. The position of the measurement window is determined during the first period of the ranging cycle, and discrete Fourier transform processing of the primary modulated wave is performed during the measurement window. During the ranging cycle for the next coordinate, processing is performed to calculate the distance from the phase difference of each modulated wave.

[0035] In the figure, 110 to 114 are distance measurement periods, and distance measurements are performed for coordinates arranged on a raster line. 120 is the waveform of the secondary modulated wave in the irradiation waveform output from the irradiation unit 3. 121 is the waveform of the secondary modulated wave in the reflected waveform input to the light receiving unit 4. 122 to 126 indicate waveforms in each distance measurement period. 140 is the waveform of the primary modulated wave in the reflected waveform input to the light receiving unit 4. 141 to 145 indicate the positions of the measurement windows, which are the measurement periods for the primary modulated wave in each distance measurement period. 141 to 143 are measurement windows set to the "rear," and 144 to 145 are measurement windows set to the "center." 150 indicates the processing timing for the discrete Fourier transform calculation of the secondary modulated wave. 151 indicates the processing timing for rough distance determination. At processing timing 151, phase calculation units 59 and 61 of the secondary modulated wave and phase difference calculation unit 62 operate in parallel, and after the phase difference of the secondary modulated wave is calculated, approximate distance determination processing is performed. 152 indicates the processing timing of the discrete Fourier transform calculation of the primary modulated wave. 153 indicates the processing timing of the distance calculation. At processing timing 153, phase calculation units 54 and 56 of the primary modulated wave and phase difference calculation unit 57 operate in parallel, and after the phase difference of the primary modulated wave is calculated, distance calculation processing is performed.

[0036] As an operational example, the flow of measurement during the ranging period 111 will be described. First, the approximate phase difference 154 of the immediately preceding coordinate is referenced. Next, during the approximate distance determination period 155 of the ranging period 111, the position of the measurement window (period 156 in this case) is determined based on the approximate phase difference 154 and set in the measurement window control unit 22. If the approximate phase difference is large, the measurement window is set to the rear, and if it is small, it is set to the center. During period 156, a discrete Fourier transform of the primary modulated wave is performed under the control of the measurement window control unit 22. Meanwhile, during the ranging period 111, a discrete Fourier transform 157 of the secondary modulated wave is performed in parallel. During the next ranging period 112, the distance calculation unit 23 calculates the distance during the distance calculation period 158 and stores the result in the ranging result memory 24. Measurement processing after the ranging period 112 is also performed using the same pipeline control.

[0037] By carrying out the above pipeline control, distance measurement for each coordinate can be carried out.

[0038] <Distance image creation process (Fig. 6)> 6 is a flowchart showing the process from measuring the distance to each coordinate to creating a distance image, and the series of processes up to creating a distance image will be explained using this figure. The process is performed by the CPU in the overall control unit 20 and each block in the control unit 6 in cooperation with each other.

[0039] In the figure, in step S200, the coordinate position to be measured is initialized in the coordinate control unit 28. The coordinate position is set to the origin (upper left) of the screen. In step S201, the approximate phase difference of the previous coordinate is read from the distance calculation unit 23.

[0040] In step S202, the phase difference values ​​are ranked according to their degree. A ranking table (not shown) is created in advance, in which distance values ​​in the measurement range are divided into multiple ranks according to their degree and associated with measurement window positions. This table is used to identify which rank the measured phase difference falls into. The ranking table is prepared with entries in which distance values ​​are converted to phase differences, and identification is performed by comparing these entries. In this embodiment, identification is performed using two ranks: "short distance" and "long distance." For example, if the measurement range is 0 to 100 m, 0 to 50 m is ranked as "short distance" and 50 to 100 m is ranked as "long distance." The number of divisions into ranks corresponding to the degree of distance and the width of each rank (whether linear or nonlinear, for example) can be arbitrary.

[0041] In step S203, the position of the measurement window is set according to the rank. The measurement window position is read by referring to the ranking table described above and set in the measurement window control unit 22. In this embodiment, the position is set to the center position (144 in FIG. 5) for "short distance" and to the rear position (141 in FIG. 5) for "long distance."

[0042] In step S204, after waiting for the measurement window period, a discrete Fourier transform is performed to extract the primary modulated wave. In step S205, the distance is calculated from the phase difference between the primary modulated wave and the secondary modulated wave. In step S206, the calculated distance value is stored in the distance measurement result memory 24. In step S207, the coordinate position to be measured is updated. The coordinate setting is moved to the position immediately to the right of the coordinate where measurement was completed. If the coordinate was the last coordinate (the rightmost coordinate) of the raster line, it is set to the first coordinate (the leftmost coordinate) of the next raster line. In step S208, it is determined whether measurement of the entire screen has been completed. If completed, proceed to step S209; if not, proceed to step S201. In step S209, a distance image is created and the process ends. In this step, 3D point cloud processing such as outlier removal, distance value interpolation, and distortion correction is performed, and the distance image is created by coloring according to the distance value. If the distance image is to be provided as a video, return to step S200, initialize the coordinate position, and start measurement again.

[0043] By the above processing, distance measurements can be performed for each coordinate and a distance image can be created.

[0044] <Example of measurement window position change process (Fig. 7)> FIG. 7 is a timing diagram showing an example of the operation of the measurement window position change process.

[0045] The upper half of the figure shows the distance relationship between the distance measuring device and the object to be measured. The lower half of the figure shows the correspondence between the internal signals of the distance measuring device. It shows the relationship between the waveforms of the emitted wave and the reflected wave according to the distance to the object, and the approximate distance determination. Since the distance measuring device performs measurements within the field of view while scanning the laser light, in the upper half of the figure, the movement of the figure from left to right corresponds to the movement of the coordinate position on the screen from left to right. In the lower half of the figure, the movement of the figure from left to right corresponds to the passage of time in the scanning process.

[0046] In the top half of the figure, 100 is the position of the object. At 101, the object is far away, and at 103, it is close. At 102, there is a boundary where the distance changes suddenly from far to close.

[0047] In the lower half of the figure, 110 to 114 are distance measurement cycles, each measuring the distance to coordinates aligned on a raster line. 120 is the waveform of the secondary modulated wave in the irradiation waveform output from the irradiation unit 3. 121 is the waveform of the secondary modulated wave in the reflected waveform input to the light receiving unit 4. 122 to 126 indicate waveforms in each distance measurement cycle. 130 is the approximate distance determination process and its results performed by the measurement timing control unit 27. The distance level is ranked by referring to the measurement result of the immediately preceding coordinate. 131 to 135 indicate the determination results in each distance measurement cycle. 140 is the waveform of the primary modulated wave in the reflected waveform input to the light receiving unit 4. 141 to 145 indicate the position of the measurement window in each distance measurement cycle.

[0048] As an example of operation, the flow when measurement is performed in distance measurement cycle 111 will be described. In distance measurement cycle 111, the reflected wave of the secondary modulated wave is measured as the shape of 122. As indicated by the corresponding circle, the delay (=phase difference) is large. Approximate distance determination 133 determines this as a "long distance" and moves the measurement window period to position 143 later in the distance measurement cycle. This measurement window is used for measurement in distance measurement cycle 112.

[0049] Furthermore, when measurement is performed in the ranging cycle 113, the reflected wave of the secondary modulated wave is measured as the shape 125. As indicated by the corresponding circle, the delay (=phase difference) is small. The approximate distance determination 133 determines this as a "short distance" and moves the period of the measurement window to the center 145 of the ranging cycle. This measurement window is used for measurement in the ranging cycle 114.

[0050] An exception to this is when measuring a boundary position where the distance to the object changes significantly. This occurs during distance measurement cycle 112. In this case, the distance to the object changes significantly within the distance measurement cycle, so the phase of the secondary modulated wave also differs significantly between the first and second halves. As a result, even if the phase difference is calculated, an accurate distance cannot be calculated. The distance value of the boundary position is interpolated during the distance image creation process, which is a later process. For example, it can be calculated by interpolating from the top, bottom, left, and right coordinates.

[0051] By controlling the position of the measurement window as described above, it is possible to perform measurements without positional deviation due to distance.

[0052] As described above, according to this embodiment, it is possible to prevent displacement of the measurement position caused by the distance to the object, and therefore it is possible to obtain a distortion-free distance image by three-dimensional distance measurement.

[0053] The present invention is not limited to the above-mentioned conventional examples, but can be widely applied.

[0054] In this embodiment, the approximate phase difference of the immediately preceding coordinates is used to determine the position of the measurement window, but the distance value that is the final result of the calculation may also be used.

[0055] The nearby coordinates to be referenced are not limited to the immediately preceding coordinates. In this embodiment, the measurement result of the immediately preceding coordinates (coordinates adjacent to the left) is used as the nearby coordinates, but the measurement result of the coordinate directly above may also be used. This can be achieved by reading the measurement result of the coordinate directly above from the measurement result memory 24. Alternatively, a plurality of nearby coordinates may be used to determine the coordinate by combining the coordinate to the left and the coordinate directly above, etc. [Example]

[0056] In the three-dimensional distance measuring device of this embodiment, the sampled A / D data is temporarily stored in a buffer memory, and the position of the measurement window is controlled using the data in the buffer memory. After the position of the measurement window is determined from the approximate phase difference of the previous coordinate, the data corresponding to the measurement window is read from the buffer memory and the distance is calculated.

[0057] <Configuration of distance measuring device (Fig. 8)> Figure 8 is a block diagram showing the schematic configuration of the distance measuring device of this embodiment. Elements that are the same as those in the previous embodiment are given the same numbers, and their explanations will be omitted. In the distance measuring device of this embodiment, a measurement data memory for storing sampled measurement data has been newly added.

[0058] In the figure, reference numeral 30 denotes a measurement data memory. It stores the irradiated waveform generated by the waveform generating unit 21 and the waveform of the reflected wave received by the light receiving unit 4. Upon request from the measurement window control unit 22, it extracts and outputs data on the irradiated waveform and the reflected waveform for a specified period.

[0059] <Explanation of the data processing pipeline (Figure 9)> Figure 9 is a timing diagram showing the flow of the data processing pipeline in this embodiment, and the flow of timing control will be explained using this diagram. During the distance measurement cycle for a given coordinate, sampled measurement data is temporarily stored in measurement data memory 30. During the next distance measurement cycle, the position of the measurement window is determined from the approximate phase difference of the previous coordinate, and data corresponding to the measurement window is read from measurement data memory 30 to calculate the distance.

[0060] 5 of the previous embodiment are given the same numbers, and a description thereof will be omitted. In the figure, reference numeral 160 indicates the timing at which measurement data is stored in the measurement data memory 30.

[0061] As an operational example, the flow of measurement during a ranging cycle 111 will be described. First, during the measurement cycle 111 for the coordinate in question, buffering 162 of the measurement data is performed. In parallel, a discrete Fourier transform 161 of the secondary modulated wave of the immediately preceding coordinate is performed. During the next ranging cycle 112, the position of the measurement window is determined during an approximate distance determination period 164. During period 165, measurement data for the period corresponding to the measurement window is read from the measurement data memory 30, and a discrete Fourier transform of the primary modulated wave is performed. Furthermore, during the next ranging cycle 113, the distance calculation unit 23 calculates the distance during a distance calculation period 158, and the result is stored in the ranging result memory 24. Measurement processing after the ranging cycle 112 is also performed using similar pipeline control.

[0062] By using the above timing control, the position of the measurement window can be controlled even when a buffer memory is used.

[0063] As described above, this embodiment can achieve the same effects as the previous embodiment. Furthermore, this embodiment also has the advantage of enabling more flexible applications because it uses data stored in the buffer memory for calculations, thereby increasing the degree of freedom in arranging the calculation timing. For example, even if the modulation frequency is increased from two waves to multiple frequencies, the final distance value that takes into account the influence of each frequency can be used, thereby improving the accuracy of determining the position of the measurement window. When modulating with three frequencies, 1 MHz, 7 MHz, and 49 MHz, information on the phase difference of the intermediate frequency of 7 MHz can be taken into account. The position of the measurement window can also be set to overlap the next ranging cycle, or the measurement windows can be set to overlap each other.

[0064] The present invention is not limited to the above-mentioned conventional examples, but can be widely applied.

[0065] An example of pipeline control was explained in Figure 9, but the processing timing can be set freely as long as the interdependence of each element is satisfied. The discrete Fourier transform processing of the secondary modulated wave can thin out the amount of data used within a range that satisfies the Nyquist frequency of the secondary modulated wave. This shortens the processing time and allows for the timing of executing the subsequent rough distance determination period and the discrete Fourier transform period of the primary modulated wave to be advanced. [Explanation of symbols]

[0066] 1 Rangefinder body 2. Measurement object 3. Irradiation unit 4 Light receiving section 5. Scanning system drive unit 6 Control Unit 10 D / A converter 11 Laser diode 12 Irradiation optical system 13 Light receiving optical system 14 Photo sensor 15 A / D converter 16 X-axis drive unit 17 Y-axis drive unit 21 Waveform generator 22 Measurement window control section 23 Distance calculation unit 24 Distance measurement result memory 25 Range image creation unit 26 Output control section 27 Measurement timing control section 28 Coordinate control section 29 Scanning control section 20 Overall control unit 40, 41 Waveform generator 42 Modulator 50 Phase difference detector for primary modulation wave 51 Phase difference detector for secondary modulation wave 52 Distance calculation section 53, 55, 58, 60 Discrete Fourier Transform Section 54, 56, 59, 61 Phase calculation section 57, 62 Phase difference calculation section

Claims

1. A means (20) for generating a modulated waveform modulated at a plurality of frequencies hierarchically combined; a means (3) for scanning and irradiating the modulated waveform onto a measurement object; A means (4) for receiving a reflected wave from the measurement object; a means (23) for detecting a phase difference between the respective modulation frequencies from the reflected waves and calculating a distance to an object; A three-dimensional distance measuring device comprising: a means (27) for controlling the timing of coordinate measurement according to the results of coordinate measurements already performed; A distance measuring device comprising:

2. 2. The distance measuring device according to claim 1, wherein said timing control means refers to the results of previous measurements of nearby coordinates.

3. The distance measuring device according to claim 1 or 2, characterized in that the timing control means controls the measurement period of the primary modulated wave used in the distance calculation means, and controls it so that it is positioned later than the measurement period of the coordinate depending on the degree to which the distance of the referenced coordinate becomes farther.

4. 4. The distance measuring device according to claim 3, further comprising a memory means for storing data received by said light receiving means, wherein said distance calculation means reads data from said memory means from a position corresponding to said measurement period to calculate the distance.

5. generating a modulation waveform modulated at a plurality of frequencies hierarchically combined; scanning and irradiating the modulated waveform onto a measurement object; receiving a reflected wave from the measurement object; a step of detecting a phase difference between each of the modulation frequencies from the reflected wave and calculating a distance to the target; A three-dimensional distance measuring method comprising: a step of controlling the timing of coordinate measurement according to the results of coordinate measurements already performed; A distance measuring method comprising:

6. 6. The distance measuring method according to claim 5, wherein said timing control step refers to the results of measurements of nearby coordinates that have already been performed.

7. The distance measurement method according to claim 5 or 6, characterized in that the timing control step controls the measurement period of the primary modulated wave used in the distance calculation step, and controls it so that it is positioned later than the measurement period of the coordinate depending on how far the distance of the referenced coordinate becomes.

8. The distance measuring method according to claim 7, further comprising a storage step for storing data received in the light receiving step, wherein the distance calculation step reads data from a position corresponding to the measurement period in the storage step to calculate the distance.

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