Laser scanning device, laser scanning method, and laser scanning program

Abstract

To increase the scanning density of laser scanning at a low cost.SOLUTION: A laser scanning device 100 comprises a horizontal rotation unit 113 that determines the range of laser scanning, and control means that controls the rotation of the horizontal rotation unit 113, and the device performs the laser scanning while rotating the horizontal rotation unit 113 to perform scanning of laser scanning light in a vertical angle direction at a specific interval. The control means causes the horizontal rotation unit 113 to perform a plurality of times of repetitive rotations within overlapping angle ranges to perform a plurality of times of laser scanning for overlapping laser scanning ranges. The rotation starting positions in the plurality of times of rotations of the horizontal rotation unit 113 are sequentially shifted, and the shift corresponds to a distance shorter than the specific interval.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the technology of laser scanning. [Background technology]

[0002] A known laser scanning device has a structure in which a rotating body is rotated and laser scanning light is emitted from the rotating body (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-47068 Summary of the Invention [Problem to be solved by the invention]

[0004] Since laser scanning is performed radially, the farther away you go, the wider the laser scan pitch (the distance between adjacent scan beams). This means that the scan density decreases over distance. Possible ways to avoid this problem are to slow down the scan speed (method 1) or shorten the interval between scan beam emissions (method 2).

[0005] The first method involves rotating the optical system, slowing down the rotation while keeping the scanning light emission interval the same. In this case, the rotation is performed by a motor, but slowing down the motor's rotation causes unevenness in the rotation to become apparent. This unevenness in rotation has a negative effect on the accuracy of angle measurement.

[0006] One possible way to reduce the rotational irregularities is to devise a motor drive method or gear structure, but this would be costly. The second method, shortening the interval between scan light emissions, would be problematic in that it would increase the cost and size of the light-emitting part.

[0007] In this context, an object of the present invention is to provide a technology for increasing the scan density of laser scanning at low cost. [Means for solving the problem]

[0008] The present invention includes a rotating body that determines the range of the laser scan; Another rotating body that rotates around a rotation axis in a direction perpendicular to the rotation axis of the rotating body; a control means for controlling the rotation of the rotating body; 、 Equipped with the rotating body rotates horizontally, the other rotating body rotates vertically, and the other rotating body rotates vertically while emitting pulses of laser scanning light in a vertical angle direction, thereby performing scanning with the laser scanning light; The laser scanning is performed while rotating the rotating body, The aforementioned A laser scanning device in which scanning with laser scanning light is performed at specific intervals, and the control means causes the rotating body to perform multiple repeated rotations in overlapping angle ranges to perform multiple laser scans on overlapping laser scanning ranges, the start positions of the rotations for the multiple rotations being sequentially shifted, and the shift corresponds to a distance shorter than the specific interval.

[0009] In the present invention, when the number of repetitions is M (M is a natural number of 2 or more) and the angle range corresponding to the specific interval is Δθ, an aspect in which the angle range corresponding to the deviation is Δθ / M can be given.

[0011] The present invention provides A laser scanning device is used that includes a rotating body that determines the range of the laser scan and another rotating body that rotates around a rotation axis that is perpendicular to the rotation axis of the rotating body. 1. A laser scanning method, comprising: the rotating body rotates horizontally, the other rotating body rotates vertically, and the other rotating body rotates vertically while emitting pulses of laser scanning light in a vertical angle direction, thereby performing scanning with the laser scanning light; The laser scanning is performed while rotating the rotating body, The aforementioned The laser scanning light is scanned at a specific interval, and the rotating body is caused to rotate repeatedly multiple times in overlapping angle ranges to perform multiple laser scans on overlapping laser scanning ranges, and the starting positions of the rotations for the multiple rotations are sequentially shifted, and the shift can also be understood as a laser scanning method corresponding to a distance shorter than the specific interval.

[0012] The present invention provides A laser scanning program to be read and executed by a computer that controls laser scanning using a laser scanning device including a rotating body that determines a range of laser scanning and another rotating body that rotates around a rotation axis that is perpendicular to the rotation axis of the rotating body, the rotating body rotates horizontally, the other rotating body rotates vertically, and the other rotating body rotates vertically while emitting pulses of laser scanning light in a vertical angle direction, thereby performing scanning with the laser scanning light; The computer performs the laser scanning while rotating the rotating body, The aforementionedA control is performed to scan with laser scanning light at a specific interval, and in this control, the rotating body is caused to rotate repeatedly multiple times in overlapping angle ranges to perform multiple laser scans on overlapping laser scan ranges, and the start positions of the rotations for the multiple rotations are sequentially shifted, and the shift can also be understood as a laser scanning program corresponding to a distance shorter than the specific interval. [Effects of the Invention]

[0013] According to the present invention, the scanning density of laser scanning can be increased at low cost. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is an external view of a laser scanning device. [Figure 2] FIG. 1 is a block diagram of a laser scanning device. [Figure 3] FIG. 1 is an image diagram showing the state of beam arrangement in laser scanning. [Figure 4] FIG. 1 is an image diagram showing the state of beam arrangement in laser scanning. [Figure 5] FIG. 2 is a circuit block diagram of a circuit that controls the timing of scanning. [Figure 6] FIG. 1 is an image diagram showing the state of beam arrangement in laser scanning. [Figure 7] FIG. 10 is a diagram showing the timing of control of horizontal rotation. [Figure 8] FIG. 1 is an image diagram showing the state of beam arrangement in laser scanning. [Figure 9] FIG. 1 is an image diagram showing the state of beam arrangement in laser scanning. [Figure 10] FIG. 1 is a conceptual diagram showing an overview of laser scanning. [Figure 11] 10 is a flowchart illustrating an example of a processing procedure. DETAILED DESCRIPTION OF THE INVENTION

[0015] (overview) 1 shows the appearance of a laser scanning device (laser scanner) 100. Laser scanning device 100 includes a tripod 111, a base unit 112 fixed to the top of tripod 111, a horizontal rotation unit 113 which is a rotation body capable of horizontal rotation on base unit 112, and a vertical rotation unit 114 which is a rotation body capable of vertical rotation relative to horizontal rotation unit 113.

[0016] The vertical rotation unit 114 includes an optical unit 115 that emits and receives laser scanning light. Pulses of laser scanning light are emitted from the optical unit 115. This pulse emission occurs along a direction (plane) perpendicular to the rotation axis (axis extending horizontally) of the vertical rotation unit 114 while the vertical rotation unit 114 is rotating. In this case, pulses of laser scanning light are emitted from the optical unit 115 along the vertical angle direction.

[0017] Laser scanning is performed by emitting pulses of laser scanning light from optical unit 115 and receiving the light reflected from the target object while horizontal rotation unit 113 is rotating horizontally and vertical rotation unit 114 is rotating vertically. In this example, vertical rotation is performed at a relatively high speed, and horizontal rotation is performed at a relatively low speed.

[0018] That is, by emitting pulses of laser scanning light from the optical unit 115 while rotating the vertical rotation unit 114 vertically, a scan along the vertical angle direction (a vertical scan) is performed, and at the same time, the horizontal rotation unit 113 rotates horizontally, so that the scan line along this vertical angle direction (scanning line) moves so as to be shifted along the horizontal angle direction. Note that, since horizontal rotation is also performed simultaneously with vertical rotation, the scan along the vertical angle direction is not completely along the vertical direction, but is performed along a line that is slightly oblique. Note that if the horizontal rotation unit 113 does not rotate, the scan along the vertical angle direction would be along the vertical direction.

[0019] Motors are used to rotate the horizontal rotation unit 113 and the vertical rotation unit 114. The horizontal rotation angle of the horizontal rotation unit 113 and the vertical rotation angle of the vertical rotation unit 114 are precisely measured by encoders.

[0020] The laser scanning light is a single pulse of distance measurement light, and one laser scanning light measures the distance to the scanning point, which is the reflection point where the laser scanning light hits. The position of the scanning point relative to the laser scanning device 100 is calculated from this measured distance and the direction of the laser scanning light.

[0021] If the exterior orientation parameters (position and orientation) of the laser 100 in the absolute coordinate system are known, the position of the scan point in the absolute coordinate system can be determined. The absolute coordinate system is a coordinate system used in maps and GNSS. In the absolute coordinate system, a position is described by, for example, latitude, longitude, and altitude.

[0022] The laser scan point cloud output from the laser scanning device 100 can be in the form of outputting distance and direction data for each point (each scan point). It is also possible for the laser scanning device 100 to calculate the position of each point in a specific coordinate system and output the three-dimensional coordinate position of each point as point cloud data. The laser scan point cloud data also includes information on the brightness (intensity of reflected light) of each scan point.

[0023] An optical system 116 of a camera 110 (see FIG. 2) is arranged in front of the horizontal rotation unit 113. This camera 110 can capture an image of the laser scan target. The exterior orientation parameters (position and attitude) of the camera 110 in the laser scanning device 100 are known, and the image captured by the camera 110 can be associated with the laser scan point cloud. For example, a point cloud image can be obtained in which the laser scan point cloud is superimposed on the image captured by the camera 110.

[0024] The density of the laser scan is set and adjusted by adjusting the horizontal and vertical rotation speeds and the interval between laser scan beams. Note that the farther away the object is, the wider the interval between the laser scan beams (the interval between the centers of the laser scan points) and the larger the cross-sectional area of ​​the laser scan beam.

[0025] The optical axis of the optical unit 115 is the optical axis of the laser scanning light. This optical axis is understood to be the direction of the center of the beam of the laser scanning light. The extension of this optical axis is the laser scanning point, i.e., the point of the reflection center of the laser scanning light.

[0026] 2 is a block diagram of the laser scanning device 100. The laser scanning device 100 includes a light emitting unit 101, a light receiving unit 102, a distance measuring unit 103, a direction obtaining unit 104, a light emission control unit 105, a drive control unit 106, a scan condition setting unit 107, a communication unit 108, a touch panel display 109, a camera 110, and a position calculation unit 111.

[0027] The laser scanning device 100 includes a computer including a CPU, which implements some or all of the functions of the direction acquisition unit 104, light emission control unit 105, drive control unit 106, scan condition setting unit 107, and position calculation unit 111. Some of these functional units may be configured with dedicated electronic circuits. As will be described later, in this embodiment, part of the drive control unit 106 is configured with a dedicated electronic circuit having the configuration shown in FIG. 5.

[0028] The light-emitting unit 101 has a light-emitting element that emits laser scanning light, an optical system related to light emission, and peripheral circuits. The light-receiving unit 102 has a light-receiving element that receives laser scanning light, an optical system related to light reception, and peripheral circuits.

[0029] The distance measuring unit 103 calculates the distance from the laser scanning device 100 to the reflection point of the laser scanning light. In this example, a reference optical path is provided inside the laser scanning device 100. The laser scanning light output from the light emitting element is split into two, one of which is irradiated onto the target from the optical unit 115 as laser scanning light, and the other is guided to the reference optical path as reference light.

[0030] The laser scanning light reflected from the object and taken in by the optical unit 115 and the reference light propagating through the above-mentioned reference optical path are combined and input to the light receiving unit 102. The laser scanning light and the reference light have different propagation distances, and the reference light is detected first by the light receiving element, and then the laser scanning light is detected by the light receiving element.

[0031] Looking at the output waveform of the light receiving element, the detected waveform of the reference light is output first, followed by the detected waveform of the laser scanning light after a time lag. The distance to the reflection point of the laser scanning light is calculated from the phase difference (time difference) between these two waveforms. Note that it is also possible to calculate the distance from the flight time of the laser scanning light.

[0032] The direction acquisition unit 104 acquires the direction of the optical axis of the laser scanning light. The direction of the optical axis is obtained by measuring the horizontal angle and the vertical angle. The direction acquisition unit 104 has a horizontal angle detection unit 104a and a vertical angle detection unit 104b.

[0033] The horizontal angle detection unit 104a detects the horizontal rotation angle of the horizontal rotation unit 113. Horizontal rotation is rotation around the vertical axis. The angle is detected by an encoder. The encoder used here has a detection accuracy of, for example, 10 arcseconds or less. For example, an encoder with a resolution of 17 bits will have an angular resolution of just under 10 arcseconds. An angular resolution of 10 arcseconds corresponds to approximately 5 mm at a horizontal distance of 100 m.

[0034] The vertical angle detection unit 104b detects the vertical rotation angle of the vertical rotation unit 114. Vertical rotation is rotation around the horizontal direction as the rotation axis. The angle is detected by an encoder. The performance of the encoder is the same as that for the horizontal rotation angle.

[0035] By measuring the horizontal rotation angle of the horizontal rotation unit 113 and the vertical rotation angle of the vertical rotation unit 115, the direction of the optical axis of the laser scanning light as seen from the laser scanning device 100, that is, the direction of the scanning point, can be determined.

[0036] The light emission control unit 105 controls the emission timing of the laser scanning light from the light emitting unit 101. Details of this control are explained below. Laser scanning is performed by emitting pulses of laser scanning light from the optical unit 105 and receiving the reflected light from the optical unit 115 while rotating the horizontal rotation unit 113 horizontally and rotating the vertical rotation unit 114 vertically.

[0037] Figure 3 is an image diagram showing the arrangement of laser scanning light in conventional technology. Figure 3 shows a case where laser light with a horizontally elongated elliptical beam cross section is emitted in dots. In the case of Figure 3, the laser scanning light is emitted in dots while scanning vertically from top to bottom or bottom to top, and the scanning rows (scan lines) are repeated from row n to row n+1 to ... while shifting the rows horizontally, thereby performing laser scanning. Here, the effective range of the beam is defined as the range where the intensity is half of its peak.

[0038] It should be noted that while the vertical scan is being performed, the horizontal rotation unit 113 continues to rotate slowly. Therefore, to be precise, the vertical scan is performed along a slightly oblique line. In other words, the scanning line of the vertical scan is slightly oblique. This slightly oblique vertical scan is performed while being shifted horizontally.

[0039] As mentioned above, the spacing between scan points increases as the distance increases. For example, at a distance of 150 m, the spacing between scan points in the vertical direction (up and down) is approximately 80 mm. Of course, this depends on the specifications of the laser scanning device, but the lower the cost of the laser scanning device, the more pronounced the problem of spacing between scan points becomes.

[0040] Consider the case where a reflective prism measuring 40 mm x 40 mm is to be measured. In this case, the reflective prism may be located between adjacent scanning beams in the vertical direction, resulting in a possibility that an effective reflection cannot be obtained. Furthermore, even if a reflection is obtained, the number of measurement points in the vertical direction may be insufficient due to the beam divergence, making it impossible to obtain the required positioning accuracy. This is not limited to the case of a reflective prism, but can be pointed out similarly for any object requiring precise positioning.

[0041] For precise positioning of a reflecting prism, it is necessary to obtain a large number of measurement points (scan points), such as 5 x 5 points or more, from the reflecting prism and obtain the average or center of gravity position to achieve positioning accuracy. In the above case, the required accuracy cannot be obtained.

[0042] Therefore, in this embodiment, the timing of vertical scanning is shifted between the nth column and the (n+1)th column. An example is shown in Figure 4. In this case, the vertical scanning interval is the same, but the position of the scan point, i.e., the timing of light emission, is shifted between the nth column and the (n+1)th column. Note that n is a natural number starting from 1.

[0043] That is, although the pulse intervals of the emitted pulsed laser scanning light are the same, when comparing the nth and n+1th columns, the positions (phases) of the laser scanning light irradiated in dots in the vertical direction are shifted. By adjusting this shift, when viewed in a vertical arrangement, it is possible to achieve a state in which each beam of the n+1th column of laser scanning light is positioned in the gap between each beam of the nth column of laser scanning light.

[0044] Looking at it from another perspective, when viewed in the vertical angle direction, the light emission positions of each beam of laser scanning light in the (n+1)th column are positioned in the gaps between the light emission positions of each beam of laser scanning light in the nth column. As a result, when considering two columns, the nth column and the (n+1)th column, the gaps between the light emission positions of the nth column are filled in and interpolated by the light emission in the (n+1)th column.

[0045] For example, the above-mentioned deviation between the first and second rows is set to half the pulse interval (half a phase difference period). In this case, when considered in the vertical angle direction, the intermediate positions of the gaps between the irradiation positions (scan points) of the laser scanning light in the first row are filled by the irradiation positions of the laser scanning light in the second row. In other words, when considered in the vertical angle direction, the gaps between the emission positions of the laser scanning light in the first rotation are interpolated by the emission positions of the laser scanning light in the second rotation.

[0046] The same concept can be applied to three or more rows. For example, the above-mentioned shift (phase difference) between the first, second, and third rows is set to 1 / 3 of the pulse interval. In this case, when considered in the vertical angle direction, the gap in the irradiation position of the laser scanning light for the first row is interpolated by the irradiation positions of the laser scanning light for the second and third rows. In other words, when considered in the vertical angle direction, the gap in the emission position of the laser scanning light for the first rotation is interpolated by the emission positions of the laser scanning light for the second and third rotations.

[0047] FIG. 5 shows a circuit block diagram for performing the above-described processing. The circuit in FIG. 5 is an example of the scan control unit 105. In this example, an encoder that detects the vertical rotation angle of the vertical rotation unit 114 outputs two types of data: V-angle encoder data, which is angle information on the vertical angle, and index data, which is output once per vertical rotation. The index data is output, for example, when the optical unit 115 is oriented in a direction in which a laser scan point cloud cannot be obtained. Examples of directions in which this laser scan point cloud cannot be obtained include a downward vertical direction and a direction in which the optical axis of the laser scan light interferes with the horizontal rotation unit 113.

[0048] In the configuration of Figure 5, V-angle encoder data is input to a flip-flop (FF) circuit. The V-angle encoder is an example of the vertical angle detection unit 104b in Figure 2, and in this case also serves as a means for generating a periodic signal that controls light emission in the light-emitting unit 101. The FF circuits are provided in multiple stages and generate multiple delayed V-angle encoder data. These multi-stage FF circuits generate V-angle encoder data with slight phase shifts. Each V-angle encoder data is a periodic signal with the same frequency but with a phase shift.

[0049] One of these V-angle encoder data is selected by a multiplexer (MUX), and based on the selected encoder data, the timing of supplying a drive voltage to a laser diode (LD), which is a light-emitting element of the light-emitting unit 101, is determined. The V-angle encoder data is a periodic signal obtained in accordance with the rotation of the vertical rotating unit 114, which rotates at a constant speed, and the light-emitting element emits light periodically in accordance with this periodic signal, thereby performing pulse emission.

[0050] Furthermore, the CPU included in the laser scanning device 100 calculates the vertical angle (V angle) based on the V angle encoder data.

[0051] For example, the interval between light emissions (interval between pulsed emissions) in the light emitting unit 102 is Δt, the FF circuit has four stages, and the delay (phase difference) in one stage of the FF circuit is Δt / 4. In this case, in the multiplexer (MUX), the output from the FF circuit to be selected is shifted by one stage each time an index signal is input.

[0052] That is, in the rotation control of the vertical rotation unit 114, at the nth rotation the output of the first stage FF circuit is selected and light emission control is performed based on that, at the n+1th rotation the output of the second stage FF circuit is selected and light emission control is performed based on that, at the n+2th rotation the output of the third stage FF circuit is selected and light emission control is performed based on that, at the n+3rd rotation the output of the fourth stage FF circuit is selected and light emission control is performed based on that, at the n+4th rotation the output of the first stage FF circuit is selected and light emission control is performed based on that, and so on.

[0053] In this case, the timing of light emission is shifted by Δt / 4 between the nth rotation and the n+1th rotation, even though the pulse frequency is the same. Similarly, the timing of light emission is shifted by Δt / 4 between the n+1th rotation and the n+2th rotation, even though the pulse frequency is the same. In other words, the alignment of adjacent vertical scan points is shifted by a distance of (scan point spacing) / 4 in the vertical direction.

[0054] In the above example, if the light emission interval is Δt and the outputs of the first and third stage FF circuits are selected for each index, the light emission timing will be shifted by Δt / 2 between the nth rotation and the n+1th rotation at the same pulse frequency. The scan pattern in this case is shown in Figure 4.

[0055] With this method, when viewed in one vertical column (a column extending in the vertical direction), the spacing between scan points does not narrow. However, when viewed in two adjacent vertical columns, the spacing remains the same, but the scan points are shifted in the vertical direction (vertical angle direction). Therefore, when viewed in multiple vertical columns, the scan density in the vertical direction (vertical angle direction) can be increased.

[0056] In the above case, scanning must be performed under the same conditions at the nth rotation and the n+1th rotation, except for the difference in light emission timing.

[0057] The above can be generalized as follows: If n and m are natural numbers starting from 1, the timing of pulse emission during the nth rotation is determined by the first periodic signal, the first periodic signal to the (m+1)th periodic signal each have the same frequency but are phase-shifted, the timing of pulse emission during the (n+m)th rotation is determined by the (m+1)th periodic signal, and if the period (emission interval) of the pulse emission is T, the phase difference between the mth periodic signal and the (m+1)th periodic signal is T / (m+1).

[0058] For example, if n=1 and m=1, the timing of pulse emission during the first rotation is determined by the first periodic signal, and the first to second periodic signals have the same frequency but are phase-shifted; the timing of pulse emission during the second rotation is determined by the second periodic signal, and the phase difference between the first and second periodic signals is T, where T is the period of the pulse emission.

[0059] Furthermore, for example, if n=1 and m=3, the timing of pulse emission during the first rotation is determined by the first periodic signal, and the first to fourth periodic signals have the same frequency but are phase-shifted, and the timing of pulse emission during the fourth rotation is determined by the fourth periodic signal, and when the period of pulse emission is T, the phase difference between the fourth and third periodic signals is T / 4.

[0060] For example, in addition to the above method, by increasing the scan density in the horizontal direction, the scan density in the two-dimensional plane can be increased as shown in Fig. 6. The control for increasing the scan density in the horizontal direction is realized by the horizontal rotation drive control unit 106a, which will be described later.

[0061] Figure 5 shows an example of a circuit that determines the timing of light emission based on angle data measured by an encoder. Another method for determining the timing of light emission is to use a reference clock signal for light emission control. In this case, when light is emitted, angle data at that time is obtained. The technique shown in Figure 5 can also be applied to this method.

[0062] In this case, the reference clock signal for light emission control is input to multiple FF circuits to obtain reference clock signals with phase shifts in multiple stages. Then, as in the case of Figure 5, the output of the FF circuit is selected based on the index data output from the V-angle encoder for each rotation. In this case, the same effect as above can be obtained.

[0063] The drive control unit 106 controls the horizontal rotation of the horizontal rotation unit 113 and the vertical rotation of the vertical rotation unit 114. The drive control unit 106 has a horizontal rotation drive control unit 106a and a vertical rotation drive control unit 106b. The horizontal rotation drive control unit 106a controls the drive of a motor for performing horizontal rotation. The vertical rotation drive control unit 106b controls the drive of a motor for performing vertical rotation of the vertical rotation unit 114.

[0064] The horizontal rotation drive control unit 106a also performs the following control. In laser scanning, a specific range may be repeatedly scanned. For example, a reflective prism may be searched for by laser scanning with a low scanning density, and then a high-density laser scan focused on the reflective prism may be performed to precisely determine the position of the reflective prism.

[0065] In this case, the laser scan is performed multiple times over a narrow range, aiming at the reflecting prism. In such a case, the horizontal rotation drive control unit 106a performs the following control.

[0066] Now, let's assume that a certain range is scanned twice. For example, suppose that a range of horizontal angles between 40° and 45° is scanned twice. The horizontal angle is measured clockwise from a vertically upward perspective, with north being 0°.

[0067] First, a first laser scan is performed. That is, laser scan is performed while rotating the vertical rotation unit 114 vertically and rotating the horizontal rotation unit at a horizontal angle in the range of 40° to 45°. At this time, the method for improving the scan density in the vertical angle direction described in relation to FIG. 5 may be used in combination.

[0068] Next, a second laser scan is performed. The second laser scan returns to the horizontal angle position where the first scan started and starts from there. In this embodiment, the laser does not return to the exact same position, but returns to a slightly shifted position and starts the laser scan from there. The second scan frequency is the same as the first. Also, the overall scan range shifts slightly by the amount of the shift, but the first and second laser scans overlap for the most part.

[0069] This is shown in Figure 7. Figure 7 shows the case where the start position (horizontal angle position) of the first horizontal laser scan and the start position (horizontal angle position) of the second horizontal laser scan are shifted. The first and second laser scans overlap, but by shifting the start position, gaps between adjacent laser scan beams in the first scan are filled by the laser scan beams in the second scan. Note that apart from the start position, the first and second laser scans are performed under the same conditions.

[0070] Figure 7 shows the case where the horizontal angle position at which the first laser scan starts is θ1, the horizontal angle position at which the second laser scan starts is θ2, the horizontal scan interval is Δθ, and θ1 < θ2, so θ2 = (θ1 + Δθ / 2).

[0071] In this case, the horizontal angle position of the vertical scan line of the first laser scan light is shifted by Δθ / 2 from the horizontal angle position of the vertical scan line of the second laser scan light. Since the spacing between the laser scan lights in the horizontal angle direction (vertical laser scan lights) is Δθ, the second laser scan is performed in the horizontal angle direction to fill in the gaps in the first laser scan.

[0072] As a result, overlapping the first and second laser scans in the horizontal angle direction results in twice the scan density compared to performing only one laser scan.

[0073] Using the same principle, if the horizontal angle position at which the first laser scan begins is θ1, the horizontal angle position at which the second laser scan begins is θ2, and the horizontal angle position at which the third laser scan begins is θ3, and the interval between scans in the horizontal direction is Δθ, then θ1 < θ2 < θ3, and the angle by which each scan is sequentially shifted is Δθ / 3. In this case, by performing three laser scans from the first to third with θ2 = (θ1 + Δθ / 3) and θ3 = (θ2 + Δθ / 3), the scan density in the horizontal angle direction is three times that of performing only one laser scan.

[0074] To generalize, if the number of laser scans repeated in the horizontal angle direction is M, and the interval between scans in the horizontal direction is Δθ, then M laser scans are repeatedly performed on the same object while sequentially shifting the starting position by an angle difference of Δθ / M. This increases the scan density in the horizontal direction by M times. Note that M is a natural number greater than or equal to 2. Also, since M>2, the shift angle is smaller than Δθ.

[0075] M is selected so that the laser scanning light beams overlap to a minimum extent. For example, suppose that at a certain distance, in one laser scan, the laser scanning light beams do not overlap in the horizontal direction, leaving gaps. In this case, M is selected so that the laser scanning light beams overlap to a minimum extent. By doing this, a state in which no gaps occur in the laser scanning light can be achieved after the M laser scans.

[0076] This effect will be explained from another perspective below. Figure 8 shows the distribution of the laser scanning light beam in the horizontal direction at a certain distance. Here, the horizontal dimension is displayed based on the angle of view from the viewpoint. Note that at a distance of 100 m, an angle of 10 arcseconds corresponds to a distance of approximately 5 mm.

[0077] In Figure 8, the cross-sectional shape of the laser scan beam is an ellipse with its major axis in the horizontal direction, and the horizontal length of the beam cross section at the distance of interest is 40 arcseconds. The laser scan beams are arranged horizontally at intervals of Δθ = 80 arcseconds. In this case, there is a gap between adjacent laser scan beams in the horizontal direction. Note that Figure 8 also shows a state in which the beams are positioned closely together in the vertical direction (vertical angle direction).

[0078] In this case, for example, the angle by which the scan start position is shifted is set to Δθ / 2 = 40 seconds. If Fig. 8 is the first laser scan, then the angular position of the second laser scan will be shifted by 40 seconds, as shown in Fig. 9, and the gap in the horizontal direction in the first laser scan will be filled as shown in Fig. 9.

[0079] Using the same principle, if Δθ is set to 20 seconds and a third laser scan is performed, it becomes possible to perform a laser scan that further fills in gaps in the horizontal direction. The lower limit of Δθ is determined by the positioning accuracy of the horizontal angle of the horizontal rotation unit 113. A pattern where θ1 > θ2 is also possible.

[0080] The scan condition setting unit 107 sets various conditions related to the laser scan. For example, the scan condition setting unit 107 sets the laser scan mode to increase the scan density in the vertical angle direction, the laser scan mode to increase the scan density in the horizontal angle direction, or the laser scan mode that combines both methods.

[0081] The communication device 108 communicates with external devices. The communication is performed using, for example, a wireless LAN standard. Wired, mobile phone line, or optical communication is also possible. The touch panel display 109 functions as a UI (user interface) for the laser scanning device 100. Various operations and settings of the laser scanning device 100 are performed using the touch panel display 109. In addition, various information related to the operation of the laser scanning device 100 is displayed on the touch panel display 109.

[0082] The camera 110 is a digital camera. The camera 110 is capable of capturing still images and videos. The position calculation unit 111 calculates the position of each laser scan point. The position of the laser scan point is calculated based on the distance from the optical origin of the laser scanning device 100 to the laser scan point and the direction of the laser scan point. The calculation of the positions of the laser scan points may be performed on an external PC or server. For example, an absolute coordinate system is used as the coordinate system for describing the position of each point. In this case, the exterior orientation parameters of the laser scanning device 100 in the absolute coordinate system must be known.

[0083] (Example of processing) An example of laser scanning using the laser scanning device 100 will be described below. Fig. 10 is a conceptual diagram showing the situation at the site where laser scanning is performed. First, prior to processing, the laser scanning device 100 and the target reflecting prisms 300 and 301 are installed.

[0084] Here, a case will be described in which the position of the laser scanning device 100 is unknown, the reflecting prisms 300 and 301 are installed at known positions, and the position and attitude of the laser scanning device 100 are determined by the resection method. The number of reflecting prisms is not limited to two and may be three or more. Instead of reflecting prisms, other types of reflecting targets using retroreflective beads or retroreflectors may also be used.

[0085] After determining the position and orientation of the laser scanning device 100, the laser scanning device 100 is used to perform a laser scan of a survey target such as a building 400. This is a normal operation, so a description thereof will be omitted here.

[0086] Conversely to the above case, it is also possible to measure the positions of the reflecting prisms 300 and 301 when the position of the laser scanning device 100 is known and the positions of the reflecting prisms 300 and 301 are unknown.

[0087] An example of the processing procedure is shown in Figure 11. A program for executing the processing shown in Figure 11 is stored in an appropriate storage medium and executed by a computer built into the laser scanning device 100. It is also possible to perform the processing of Figure 11 on an external computer and control the laser scanning device 100 from outside.

[0088] When the process starts, first, the first laser scanning conditions are set (step S101). The first laser scanning is performed over a wide range (for example, the entire circumference) including the reflecting prisms 300 and 301.

[0089] The first laser scan is performed at a relatively low scan density as long as it can capture the reflecting prisms 300 and 301. For example, the scan density for the first laser scan is set under conditions where about four points of incidence are expected on the reflecting prisms 300 and 301. For example, the scan conditions may be such that two points of incidence are expected in the horizontal angle direction and two points in the vertical angle direction on the reflecting prisms 300 and 301.

[0090] Although there is a little less leeway, it is also possible to have scan conditions where one point of incidence in the horizontal angle direction and two points of incidence in the vertical angle direction are expected, or scan conditions where two points of incidence in the horizontal angle direction and one point of incidence in the vertical angle direction are expected.

[0091] Increasing the scan density of the first laser scan makes it possible to capture the reflecting prisms 300 and 301 more reliably, but it also increases the time and power required for scanning. Taking this into consideration, the conditions for the first laser scan are set.

[0092] Next, a first laser scan is performed using the laser scanning device 100 (step S102). Next, points where the intensity of reflected light is equal to or greater than a predetermined threshold are extracted from the laser scan point cloud (laser scan data) obtained by the first laser scan. This allows detection of reflected light from the reflecting prisms 300, 301 (step S103). Because the reflected light from the prisms has an extremely high intensity, setting the extremely high reflected light as the threshold makes it possible to distinguish it from other structures. In this way, the direction and distance of the reflecting prisms 300, 301 as seen from the laser scanning device 100 are obtained.

[0093] If the reflected light is too strong and the light receiving unit 102 receives too much light, the distance information cannot be obtained accurately, and approximate distance information containing an error is obtained.

[0094] In addition, in the first laser scan, there is also a method of reducing the output of the laser scanning light or using a neutral density filter to reduce the intensity of the input light so that the light receiving unit 102 is not saturated by the strong reflected light from the reflecting prism.

[0095] The reflecting surfaces of the reflecting prisms 300 and 301 are mirror surfaces with high reflectivity, so the reflected light is stronger than the light reflected from other objects. This can be utilized to identify the reflection from the reflecting prisms 300 and 301. In this case, it is also possible to use a method of identifying the reflecting prisms 300 and 301 through image recognition using images captured by the camera 110.

[0096] Once the reflecting prisms 301, 301 are detected, conditions for a second laser scan specialized for precise positioning of the reflecting prisms 300, 301 are set (step S104). In this process, conditions for the second laser scan are set using one or both of the mode for increasing the scan density in the vertical angle direction described with reference to Figures 4 and 6 and the mode for increasing the scan density in the horizontal angle direction described with reference to Figures 8 and 9, with the scan density being higher than that of the first laser scan.

[0097] An example of the second laser scanning conditions will be described below. Here, the second laser scanning conditions for the reflecting prism 300 will be described. In this case, first, the laser scanning density required at that position is calculated from the distance from the laser scanning device 100 of the reflecting prism 300 obtained in step S103.

[0098] For example, suppose that the reflecting prism 300 is 50 mm square and you want to secure 10 × 10 (100 points in total) scan points there. On the other hand, suppose that the scan density in the vertical angle direction (vertical direction) at the position of the reflecting prism 300 is 2 points / 50 mm.

[0099] In this case, the above objective is achieved by increasing the vertical scanning density by five times to 10 points / 50 mm. Therefore, the method described in relation to Figure 4 is used to increase the scanning point density in the vertical direction by five times.

[0100] Here, let us assume that the scan interval in the vertical rotation is Δt. In this case, the FF circuit in Figure 5 is used to shift the scan start time of the (n+1)th vertical rotation by Δt / 5 from the start time of the nth rotation.

[0101] In this way, adjacent rows of vertical scan points are offset in the direction of vertical rotation (vertical direction) by a distance of 1 / 5 of the scan interval, resulting in a 5-fold increase in scan density in the direction of vertical rotation (vertical direction) when viewed in five vertical rows.

[0102] On the other hand, suppose the horizontal scan density is 2 points / 50 mm, i.e., the interval between scan points is 25 mm. To increase this density by five times, selective (local) laser scans are performed five times, aimed at the reflecting prism 300. In this case, the interval between the scan points finally obtained in the horizontal direction is set to 5 mm using the method described with reference to FIGS. 7 to 9.

[0103] That is, if the above scan interval of 25 mm converted to an angle is α, and the starting horizontal angular position of the first second laser scan is θ, then the starting horizontal angular position of the second second laser scan is θ+α / 5, the starting horizontal angular position of the third second laser scan is θ+2α / 5, the starting horizontal angular position of the fourth second laser scan is θ+3α / 5, and the starting horizontal angular position of the fifth second laser scan is θ+4α / 5. This results in a final scan density in the horizontal angle direction of 10 points / 50 mm.

[0104] In reality, the scan density in the vertical direction does not increase when viewed in one vertical row (one row in the vertical direction). Therefore, taking this into consideration, the scan density in the horizontal direction is set higher so that the target scan density can be achieved.

[0105] The above-mentioned setting of the scan density in the vertical angle direction and the setting of the scan density in the horizontal angle direction are determined taking into consideration the interval between the scan beams, the shape of the scan beam, and the required scan density.

[0106] Here, an example has been described in which the conditions for the second laser scan on the reflecting prism 300 are set. Similarly, the conditions for the second laser scan on the reflecting prism 301 are set.

[0107] After the conditions for the second laser scan are set, the second laser scan is performed (step S105). In the second laser scan, a laser scan with higher density than the first laser scan is performed.

[0108] After the second laser scan is performed, the reflecting prisms 300 and 301 are precisely positioned based on the results. For example, suppose 10 x 10 scan points are obtained from the reflecting prism. In this case, the position of the reflecting prism is calculated from the average of a total of 100 positioning points. Alternatively, the position of the reflecting prism is calculated from the weighted average of 100 points that take into account the reflection intensity.

[0109] (superiority) For example, the circuit configuration in Figure 5 can be realized at low cost using an FPGA. The control in Figure 9 can be achieved by preparing software, and does not require new hardware. Overall, the basic specifications of the laser scanning device can be used as is, and the scanning density can be increased at low cost.

[0110] (others) A laser scanning device having two rotation axes can also be configured so that vertical rotation occurs at a relatively slow speed and horizontal rotation occurs at a relatively high speed. In this case, it is possible to apply the method described with reference to Figure 4 to drive the horizontal rotation unit, and the method described with reference to Figures 7 to 9 to drive the vertical rotation unit.

[0111] The laser scanning device 100 can also be applied to a laser scanning device with a structure in which it is tilted 90 degrees to the side. In this case, the horizontal rotation unit 113 rotates vertically, and the vertical rotation unit 114 rotates horizontally. For example, this type of laser scanning device is available as a device mounted on a moving object. The tilt angle is not limited to 90 degrees, but can also be 45 degrees or 60 degrees.

[0112] The invention disclosed in this specification can also be applied to structures other than the laser scanning device having a rotating unit that rotates on two axes as shown in Fig. 1. For example, a structure in which vertical rotating unit 114 does not rotate and a scanning optical system using a polygon mirror or a galvanometer mirror, or an electronic scanning optical system using semiconductor devices is used in place of vertical rotating unit 114 is conceivable. In this case, the invention disclosed in this specification can be applied to driving horizontal rotating unit 113.

[0113] Some laser scanning devices installed on a moving body have a structure with only one rotating part. This laser scanning device only performs laser scanning along a specific surface, but as the moving body moves, laser scanning over a wide area can be performed. The invention disclosed in this specification can be applied to driving the rotating part of a laser scanning device with such a structure.

[0114] The method of generating a signal that determines the timing of the second pulse emission from a signal that determines the timing of the first pulse emission, as illustrated in FIG. 5, and the method of generating a signal that determines the timing of the nth pulse emission are simple and useful, but other methods may also be adopted.

[0115] For example, a first signal generating circuit is provided that generates a signal with a predetermined phase difference to determine the timing of the first pulse emission, a second signal generating circuit is provided that generates a signal that determines the timing of the second pulse emission, and an nth signal generating circuit is provided that generates a signal that determines the timing of the nth pulse emission. Then, as in the case described with reference to Fig. 5, signals that are shifted by a predetermined phase difference are selected for each rotation to obtain a scan beam pattern such as that shown in Fig. 4.

[0116] The technique described with reference to FIGS. 7 to 9 can be applied to full-circle scanning using the laser scanning device 100 to increase the scan density of the full-circle scanning. In this case, the normal full-circle scanning is repeated two or more times. In this case, the horizontal rotation unit 113 is rotated 360° multiple times, but the start position of the nth rotation and the start position of the n+1th rotation are shifted. The shifting method is the same as that described with reference to FIGS. 7 to 9.

[0117] For example, to double the scan density in the horizontal angle direction, the horizontal rotation unit 113 is rotated twice. At this time, the start angle position for the first time and the start angle position for the second time are shifted by an angle corresponding to half the interval between scan points in the horizontal angle direction (interval between light emission positions).

[0118] For example, to triple the scan density in the horizontal angle direction, the horizontal rotation unit 113 is rotated three times. At this time, the start angle position for the first rotation and the start angle position for the second rotation are shifted by an angle corresponding to 1 / 3 of the interval between scan points in the horizontal angle direction. Also, the start angle position for the second rotation and the start angle position for the third rotation are shifted by an angle corresponding to 1 / 3 of the interval between scan points in the horizontal angle direction.

[0119] This method requires a longer time for scanning, but can increase the scanning density in the horizontal angle direction. [Explanation of symbols]

[0120] 100...laser scanning device, 111...tripod, 112...base unit, 113...horizontal rotation unit, 114...vertical rotation unit, 115...optical unit for emitting and receiving laser scanning light, 116...camera optical system, 300...reflecting prism, 301...reflecting prism, 400...building to be laser scanned.

Claims

1. a rotating body that determines the range of the laser scan; Another rotating body that rotates around a rotation axis in a direction perpendicular to the rotation axis of the rotating body; a control means for controlling the rotation of the rotating body; Equipped with The rotating body rotates horizontally, The other rotating body rotates vertically, the other rotating body rotates vertically while emitting pulses of laser scanning light in a vertical angle direction, thereby performing scanning with the laser scanning light; The laser scanning is performed while rotating the rotating body, so that the laser scanning light is scanned at specific intervals; the control means causes the rotating body to perform a plurality of repeated rotations in overlapping angular ranges to perform a plurality of laser scans in overlapping laser scan ranges; The start positions of the rotations in the plurality of rotations are sequentially shifted, A laser scanning device, wherein the offset corresponds to a distance less than the specified interval.

2. The number of repetitions is M (M is a natural number equal to or greater than 2), The angle range corresponding to the specific interval is defined as Δθ In this case, 2. The laser scanning device according to claim 1, wherein the angular range corresponding to the deviation is Δθ / M.

3. A rotating body that determines the range of laser scanning; Another rotating body that rotates around a rotation axis in a direction perpendicular to the rotation axis of the rotating body; A laser scanning method using a laser scanning device comprising: The rotating body rotates horizontally, The other rotating body rotates vertically, the other rotating body rotates vertically while emitting pulses of laser scanning light in a vertical angle direction, thereby performing scanning with the laser scanning light; The laser scanning is performed while rotating the rotating body, so that the laser scanning light is scanned at specific intervals; rotating the rotor multiple times through overlapping angular ranges to perform multiple laser scans over overlapping laser scan ranges; The start positions of the rotations in the plurality of rotations are sequentially shifted, A laser scanning method, wherein the deviation corresponds to a distance shorter than the specified interval.

4. A rotating body that determines the range of the laser scan; Another rotating body that rotates around a rotation axis in a direction perpendicular to the rotation axis of the rotating body; A laser scanning program that is read and executed by a computer that controls laser scanning using a laser scanning device comprising: The rotating body rotates horizontally, The other rotating body rotates vertically, the other rotating body rotates vertically while emitting pulses of laser scanning light in a vertical angle direction, thereby performing scanning with the laser scanning light; To the computer performing the laser scanning while rotating the rotating body, thereby controlling the laser scanning light to be scanned at specific intervals; In the control, the rotating body is caused to rotate repeatedly multiple times in overlapping angular ranges to perform multiple laser scans in overlapping laser scan ranges; The start positions of the rotations in the plurality of rotations are sequentially shifted, A laser scanning program in which the deviation corresponds to a distance shorter than the specified interval.

Images