Measurement system and measurement method

Abstract

To increase precision of counting of a rotating axle.SOLUTION: A measurement system includes an emission part of a first beam applied to a side surface, an upper surface, and a lower surface of a body of a vehicle and a second beam applied to a side surface of a wheel of a vehicle. When an angle formed by an emission direction of a first beam projected to a first plane along the surface of a road and a second plane vertical to a driving direction of a vehicle is set to φ1 when the first beam is applied to the side surface of a vehicle, an angle formed by an emission direction of a first beam projected to a third plane parallel with a driving direction and vertical to the first plane, and the second plane is set to φ1 when the first beam is applied to an upper surface or a lower surface of a body, an angle formed by a direction of a second beam projected to the first plane and the second plane is set to φ2, an angle formed by a direction of the first beam projected to the second plane and the first plane is set to θ1, and an angle formed by a direction of the second beam projected to the second plane and the first plane is set to θ2, |φ1|>0 is satisfied, and at least one of |φ2|>0 and |θ2|>0 is satisfied.SELECTED DRAWING: Figure 5

Description

Technical Field

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

Background Art

[0002] Conventionally, devices that measure the distance to an object or the velocity of an object using radar or laser have been proposed. For example, distance and velocity measurement apparatuses based on the Frequency Modulated Continuous Wave (FMCW) method have been developed. An FMCW measurement apparatus transmits an electromagnetic wave whose frequency is modulated at a constant period, and can measure distance and velocity based on the frequency difference between a transmitted wave and a reflected wave. When the electromagnetic wave is light such as visible light or infrared light, the FMCW measurement apparatus is called FMCW-LiDAR (Light Detection and Ranging) or laser radar. FMCW-LiDAR splits light whose frequency is modulated at a constant period into output light and reference light, generates interference light between the reflected light generated when the output light is reflected by an object and the reference light, and detects the interference light. Based on the frequency of the interference light, the distance to the object and the velocity of the object can be calculated.

[0003] Patent Documents 1 and 2 disclose measuring distance and velocity using an FMCW sensing apparatus. Patent Document 3 discloses a method of multiplexing a plurality of output signals on one detector using a plurality of delay lines in an FMCW laser radar that emits a plurality of light beams. Patent Document 4 discloses a method of counting rotating axles by measuring the rotational speed of wheels in a traveling vehicle using FMCW LiDAR.

Prior Art Literature

Patent Documents

[0004]

Patent Document 1

Patent Document 2

[0005] This disclosure provides sensing technology for improving the accuracy of counting rotating axles included in a moving vehicle. [Means for solving the problem]

[0006] A measurement system according to one aspect of the present disclosure includes: a first emission unit that emits a first beam for measuring the speed of a vehicle body, which is irradiated onto the side, top, or bottom surface of the vehicle body as the vehicle travels on a road; a second emission unit that emits a second beam for measuring the speed of a wheel, which is irradiated onto the side surface of a wheel of the vehicle; and a processing unit that generates first speed information at the irradiation point of the first beam and second speed information at the irradiation point of the second beam, and counts the rotating axles of the vehicle based on the first speed information and the second speed information. When the first beam is irradiated onto the side of the vehicle body, let φ1 be the angle between the exit direction of the first beam projected onto a first plane along the surface of the road and a second plane perpendicular to the direction of travel of the vehicle. When the first beam is irradiated onto the upper or lower surface of the vehicle body, let φ1 be the angle between the exit direction of the first beam projected onto a third plane parallel to the direction of travel and perpendicular to the first plane and the second plane. Let φ2 be the angle between the direction of the second beam projected onto the first plane and the second plane. Let θ1 be the angle between the direction of the first beam projected onto the second plane and the first plane. Let θ2 be the angle between the direction of the second beam projected onto the second plane and the first plane. Then, |φ1|>0 and at least one of |φ2|>0 and |θ2|>0 are satisfied.

[0007] The comprehensive or specific embodiments of this disclosure may be implemented by systems, apparatus, methods, integrated circuits, computer programs, or recording media such as computer-readable discs, or by any combination of systems, apparatus, methods, integrated circuits, computer programs, and recording media. Computer-readable recording media may include volatile recording media or non-volatile recording media such as CD-ROMs (Compact Disc - Read Only Memory). An apparatus may consist of one or more devices. If an apparatus consists of two or more devices, these two or more devices may be located in a single device or in two or more separate devices. In this specification and in the claims, “apparatus” may mean not only one device but also a system consisting of multiple devices. [Effects of the Invention]

[0008] According to one aspect of this disclosure, information on the vehicle's travel speed and the rotational speed of its wheels can be efficiently acquired. This improves the accuracy of counting the rotating axles included in a moving vehicle. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic block diagram showing an example of a sensor configuration using FMCW-LiDAR. [Figure 2A] Figure 2A schematically shows the time variation of the reference and reflected light frequencies when the vehicle is stationary. [Figure 2B] Figure 2B schematically shows the time evolution of the reference light and reflected light frequencies when a vehicle approaches the sensor. [Figure 3A] Figure 3A is a schematic side view showing an example of a vehicle being measured. [Figure 3B] Figure 3B is a schematic top view showing an example of a vehicle to be measured. [Figure 3C]FIG. 3C is a front view schematically showing an example of a vehicle to be measured. [Figure 3D] FIG. 3D is an enlarged view of one of the wheels. [Figure 4] FIG. 4 is a diagram schematically showing an example of temporal changes in measured speed and measured distance. [Figure 5] FIG. 5 is a diagram schematically showing a configuration example of a sensing system according to Embodiment 1 of the present disclosure. [Figure 6A] FIG. 6A is a diagram showing a first configuration example of a sensing system. [Figure 6B] FIG. 6B is a diagram showing a second configuration example of a sensing system. [Figure 7] FIG. 7 is a diagram showing an example of the arrangement of a first emission unit and a second emission unit. [Figure 8] FIG. 8 is a graph showing an example of the vehicle speed and the wheel rotation speed measured by the sensing system. [Figure 9] FIG. 9 is a diagram schematically showing the relationship between the position of an irradiation point of a first beam, the position of an irradiation point of a second beam on a vehicle, and the timing at which the speed of each irradiation point is measured. [Figure 10] FIG. 10 is a flowchart showing an example of the operation of a processing apparatus. [Figure 11] FIG. 11 is a flowchart showing details of the operation of determining whether a vehicle is present in step S1020. [Figure 12] FIG. 12 is a flowchart showing details of the operation of determining whether the rotation speed of a wheel has been measured in step S1060. [Figure 13] FIG. 13 is a flowchart showing details of the operation of step S1061. [Figure 14] FIG. 14 is a flowchart showing details of the operation of step S1070. [Figure 15] FIG. 15 is a diagram showing an example of temporal change in speed measured when a vehicle stops during measurement of wheel rotation speed. [Figure 16A]FIG. 16A is a diagram for explaining arrangement conditions of a second emission unit. [Figure 16B] FIG. 16B is a diagram for explaining arrangement conditions of a second emission unit. [Figure 17A] FIG. 17A is a diagram for explaining conditions to be satisfied by the position of an emission point of a first beam and the position of an emission point of a second beam. [Figure 17B] FIG. 17B is a diagram for explaining conditions to be satisfied by the position of an emission point of a first beam and the position of an emission point of a second beam. [Figure 18A] FIG. 18A is a diagram showing an example of conditions for emission angles of respective beams for allowing a first beam to irradiate a vehicle earlier than a second beam. [Figure 18B] FIG. 18B is a diagram showing another example of conditions for emission angles of respective beams for allowing a first beam to irradiate a vehicle earlier than a second beam. [Figure 19] FIG. 19 is a diagram showing an example of other conditions for allowing a first beam to irradiate a vehicle earlier than a second beam. [Figure 20A] FIG. 20A is a diagram showing an example of distance conditions from a road for a first emission unit and a second emission unit. [Figure 20B] FIG. 20B is a diagram showing another example of distance conditions from a road for a first emission unit and a second emission unit. [Figure 21A] FIG. 21A is a first diagram illustrating angle conditions for allowing a first beam to irradiate an upper portion of a vehicle more than a second beam does. [Figure 21B] FIG. 21B is a second diagram illustrating angle conditions for allowing a first beam to irradiate an upper portion of a vehicle more than a second beam does. [Figure 22] FIG. 22 is a diagram illustrating height conditions for a first emission unit and a second emission unit for allowing a first beam to irradiate an upper portion of a vehicle more than a second beam does. [Figure 23A] FIG. 23A is a diagram showing an example of distance conditions from a road for a first emission unit and a second emission unit for allowing a first beam to irradiate an upper portion of a vehicle more than a second beam does. [Figure 23B]Figure 23B shows another example of the distance conditions from the road to the first and second emitters so that the first beam is projected higher on the vehicle than the second beam. [Figure 24] Figure 24 is a schematic diagram showing the irradiation angles of the first beam and the second beam in a modified example 1 of Embodiment 1. [Figure 25] Figure 25 shows an example of the vehicle speed and wheel rotation speed measured in Modification 1 of Embodiment 1. [Figure 26] Figure 26 is a schematic diagram showing the irradiation angles of the first and second beams in a modified example 2 of Embodiment 1. [Figure 27] Figure 27 shows an example of the vehicle speed and wheel rotation speed measured in a modified example 2 of Embodiment 1. [Figure 28] Figure 28 is a schematic diagram showing the irradiation angles of the first and second beams in a modified example 3 of Embodiment 1. [Figure 29] Figure 29 shows an example of the vehicle speed and wheel rotation speed measured in modified example 3 of Embodiment 1. [Figure 30] Figure 30 is a schematic diagram showing the irradiation angles of the first and second beams in a modified example 4 of Embodiment 1. [Figure 31] Figure 31 shows an example of the vehicle speed and wheel rotation speed measured in Modification 4 of Embodiment 1. [Figure 32] Figure 32 is a schematic diagram showing the irradiation angles of the first and second beams in a modified example 5 of Embodiment 1. [Figure 33] Figure 33 shows an example of the vehicle speed and wheel rotation speed measured in modified example 5 of Embodiment 1. [Figure 34] Figure 34 is a schematic diagram showing the irradiation angles of the first and second beams in a modified example 6 of Embodiment 1. [Figure 35] Figure 35 shows an example of the vehicle speed and wheel rotation speed measured in modified example 6 of Embodiment 1. [Figure 36]Figure 36 is a schematic diagram showing the irradiation angles of the first and second beams in a modified example 7 of Embodiment 1. [Figure 37] Figure 37 shows an example of the vehicle speed and wheel rotation speed measured in modified example 7 of Embodiment 1. [Figure 38] Figure 38 is a schematic diagram showing the irradiation angles of the first and second beams in a modified example 8 of Embodiment 1. [Figure 39] Figure 39 shows an example of the vehicle speed and wheel rotation speed measured in modified example 8 of Embodiment 1. [Figure 40A] Figure 40A is a perspective view showing an example of the arrangement of the first and second injection units. [Figure 40B] Figure 40B is a front view showing an example of the arrangement of the first and second injection units. [Figure 41A] Figure 41A is a perspective view showing another example of the arrangement of the first and second injection units. [Figure 41B] Figure 41B is a front view showing another arrangement example of the first and second injection units. [Figure 41C] Figure 41C is a top view showing other arrangement examples of the first and second injection units. [Figure 42] Figure 42 is a schematic diagram showing an example of the arrangement of the first and second injection units in Embodiment 2. [Figure 43] Figure 43 shows an example of the vehicle speed and wheel rotation speed measured in Embodiment 2. [Figure 44] Figure 44 is a schematic diagram showing the irradiation angles of the first and second beams in a modified example 1 of Embodiment 2. [Figure 45] Figure 45 shows an example of the vehicle speed and wheel rotation speed measured in Modification 1 of Embodiment 2. [Figure 46] Figure 46 is a schematic diagram showing the irradiation angles of the first beam and the second beam in a modified example 2 of Embodiment 2. [Figure 47]Figure 47 shows an example of the vehicle speed and wheel rotation speed measured in a modified example 2 of Embodiment 2. [Figure 48] Figure 48 is a schematic diagram showing the irradiation angles of the first and second beams in a modified example 3 of Embodiment 2. [Figure 49] Figure 49 shows an example of the vehicle speed and wheel rotation speed measured in modified example 3 of Embodiment 2. [Figure 50A] Figure 50A is a perspective view showing an example of the arrangement of the first and second injection units. [Figure 50B] Figure 50B is a front view showing an example of the arrangement of the first and second ejection units. [Figure 51] Figure 51 is a schematic diagram showing the irradiation angles of the first and second beams in a modified example 4 of Embodiment 2. [Figure 52] Figure 52 shows an example of the vehicle speed and wheel rotation speed measured in modified example 4 of Embodiment 2. [Figure 53] Figure 53 is a schematic diagram showing the irradiation angles of the first and second beams in a modified example 5 of Embodiment 2. [Figure 54] Figure 54 shows an example of the vehicle speed and wheel rotation speed measured in modified example 5 of Embodiment 2. [Figure 55] Figure 55 is a schematic diagram showing the irradiation angles of the first and second beams in a modified example 6 of Embodiment 2. [Figure 56] Figure 56 shows an example of the vehicle speed and wheel rotation speed measured in modified example 6 of Embodiment 2. [Figure 57] Figure 57 is a schematic diagram showing the irradiation angles of the first and second beams in a modified example 7 of Embodiment 2. [Figure 58] Figure 58 shows an example of the velocity measured using the second beam in modified example 7 of Embodiment 2. [Figure 59A] Figure 59A is a perspective view showing an example of the arrangement of the first and second injection units. [Figure 59B]Figure 59B is a front view showing an example of the arrangement of the first and second ejection units. [Figure 60A] Figure 60A is a perspective view showing other arrangement examples of the first and second injection units. [Figure 60B] Figure 60B is a front view showing another arrangement example of the first and second injection units. [Figure 60C] Figure 60C is a top view showing other arrangement examples of the first and second injection units. [Modes for carrying out the invention]

[0010] In this disclosure, all or part of a circuit, unit, device, component, or part, or all or part of a functional block in a block diagram, may be implemented by one or more electronic circuits, including, for example, a semiconductor device, a semiconductor integrated circuit (IC), or a large-scale integration (LSI). The LSI or IC may be integrated on a single chip or may be composed of multiple chips combined. For example, functional blocks other than memory elements may be integrated on a single chip. Here, we refer to them as LSIs or ICs, but the name may change depending on the degree of integration, and they may also be called system LSIs, VLSIs (very large-scale integrations), or ULSIs (ultra-large-scale integrations). FPGAs (Field Programmable Gate Arrays) or RLDs (reconfigurable logic devices) that are programmed after the manufacture of the LSI, or that can reconfigure the junction relationships inside the LSI or set up the circuit compartments inside the LSI, can also be used for the same purpose.

[0011] Furthermore, the functions or operations of all or part of a circuit, unit, device, component, or part can be performed by software processing. In this case, the software is recorded on one or more non-temporary recording media such as ROMs, optical disks, or hard disk drives, and when the software is executed by a processor, the functions specified in the software are performed by the processor and peripheral devices. The system or device may include one or more non-temporary recording media on which the software is recorded, a processor, and necessary hardware devices, such as interfaces.

[0012] In this disclosure, "light" means electromagnetic waves including not only visible light (wavelengths of approximately 400 nm to 700 nm) but also ultraviolet light (wavelengths of approximately 10 nm to 400 nm) and infrared light (wavelengths of approximately 700 nm to 1 mm).

[0013] The following describes exemplary embodiments of this disclosure. The embodiments described below are either comprehensive or specific examples. The numerical values, shapes, components, arrangement and connection configurations of components, steps, and the order of steps shown in the following embodiments are examples only and are not intended to limit this disclosure. Furthermore, components in the following embodiments that are not described in the independent claim representing the highest-level concept are described as optional components. Also, the figures are schematic diagrams and not necessarily strictly illustrative. In addition, substantially identical components are denoted by the same reference numerals in the figures, and redundant explanations may be omitted or simplified.

[0014] <Insights discovered by the inventors> The ETC (Electronic Toll Collection) system is a system that allows vehicles to pay tolls on toll roads such as expressways without having to stop at toll booths. Tolls are categorized into several vehicle types, based on factors such as vehicle size and the number of axles (or the number of wheels rotating or in contact with the ground). Users set the appropriate vehicle type information in their onboard unit and then pay the toll.

[0015] Toll fees can vary depending on the number of rotating axles. Current ETC systems use a treadle-shaped axle detection sensor to count the number of rotating axles based on the number of wheels that come into contact with the sensor. In recent years, there has been an increase in large trucks equipped with a feature called a lift axle. Large trucks with three or more axles can use the lift axle function to raise some of the axles, lifting the wheels attached to those axles. This increases the pressure on the other wheels when the load weight is small, preventing the truck from slipping. Large trucks using the lift axle function have axles that do not rotate while driving. Therefore, ETC is required to accurately count the number of rotating axles among the multiple axles on the vehicle.

[0016] The inventors have devised a method for identifying rotating axles on a moving object non-contactually using FMCW LiDAR technology, and disclosed it in Patent Document 4. In the method described in Patent Document 4, a light beam is obliquely shone onto the side of the wheel to measure the rotational speed of the wheel, and the number of rotating axles can be counted based on the measurement result. In this disclosure, a method is devised to more accurately count the number of rotating axles even when the vehicle speed (hereinafter sometimes referred to as "driving speed" or "vehicle speed") changes due to the vehicle accelerating or decelerating during measurement. When the vehicle accelerates or decelerates during measurement, the time change of the measured speed of the rotating wheels behaves differently from the time change when the vehicle speed is constant, making it difficult to distinguish between individual wheel segments. For this reason, there is a need for a method that can correctly acquire speed information due to wheel rotation and accurately count axles even when speed changes occur due to the acceleration or deceleration of the vehicle.

[0017] Therefore, in the embodiments of the present disclosure described below, we propose a method for generating wheel rotation speed information that is free from the effects of vehicle acceleration and deceleration by acquiring vehicle speed information along with wheel rotation speed information. This makes it possible to measure wheel rotation speed with high accuracy and to count the number of axles on a vehicle more accurately.

[0018] The measurement system according to the embodiments of this disclosure is a system that generates wheel speed information of a vehicle traveling on a road using FMCW technology such as FMCW-LiDAR. Such a system may be referred to as a "sensing system" in this specification. The measurement system according to the embodiments of this disclosure comprises a first emission unit that emits a first beam for measuring the speed of a vehicle body, which is projected onto the side, top, or bottom of the vehicle body traveling on a road, and a second emission unit that emits a second beam for measuring the speed of a wheel, which is projected onto the side of the wheel of the vehicle. The measurement system may further include a processing unit that generates first speed information at the point of projection of the first beam and second speed information at the point of projection of the second beam, and counts the rotating axle based on the first speed information and the second speed information.

[0019] The first emission unit is the part or component that emits the first beam. The second emission unit is the part or component that emits the second beam. The measurement system may comprise one or more light sources, one or more interference optics, and one or more photodetectors, as will be described in detail later. The measurement system may comprise a first LiDAR unit including the first emission unit and a second LiDAR unit including the second emission unit. In this case, each of the first LiDAR unit and the second LiDAR unit may comprise a light source, an interference optics, and a photodetector. Alternatively, the measurement system may comprise a single LiDAR unit including the first and second emission units. In this case, the single LiDAR unit may comprise a light source, an interference optics, and a photodetector, in addition to an optical splitter that splits the light from the light source and directs it to the first and second emission units. Details of these configurations will be described later.

[0020] Here, the angles φ1, φ2, θ1, and θ2 are defined as follows. • φ1: (a) When the first beam is projected onto the side of the vehicle body, the angle between the direction of emission of the first beam projected onto a first plane along the road surface and a second plane perpendicular to the vehicle's direction of travel, or (b) When the first beam is projected onto the top or bottom of the vehicle body, the angle between the direction of emission of the first beam projected onto a third plane parallel to the direction of travel and perpendicular to the first plane and the second plane. • φ2: The angle between the direction of the second beam projected onto the first plane and the second plane. • θ1: The angle between the direction of the first beam projected onto the second plane and the first plane. ·θ2: The angle between the direction of the second beam projected onto the second plane and the first plane. At this time, the first and second ejection sections are arranged such that |φ1|>0 and at least one of |φ2|>0 and |θ2|>0. |φ1|, |φ2|, and |θ2| are the absolute values ​​of φ1, φ2, and θ2, respectively.

[0021] With this configuration, the effects of vehicle acceleration and deceleration can be removed from the wheel rotation speed information (i.e., second speed information) obtained by the irradiation of the second beam, based on the vehicle speed information (i.e., first speed information) obtained by the irradiation of the first beam. This makes it possible to count the number of rotating axles more accurately. Details of the angle conditions mentioned above will be described later.

[0022] <How to identify a rotating wheel> Before describing the details of embodiments of this disclosure, an example of a method for non-contact identification of rotating wheels on a vehicle using FMCW LiDAR technology will be described. The method described below is similar to the method disclosed by the inventors in Patent Document 4. The entirety of the disclosure in Patent Document 4 is incorporated herein by reference.

[0023] Figure 1 is a schematic block diagram showing an example configuration of a sensor 110 using FMCW-LiDAR. Figure 1 shows a vehicle 10 to be measured. The vehicle 10 shown in Figure 1 includes a body 12 having two axles, and four wheels 14 attached to those axles. The wheels 14 include metal wheels and rubber tires mounted on those wheels.

[0024] The sensor 110 shown in Figure 1 comprises a light source 20, an interference optical system 30, a photodetector 40, a beam shaper 50, a processing circuit 60, and a memory 62. The white arrows shown in Figure 1 represent the direction of travel of the vehicle 10. The thick line arrows shown in Figure 1 represent the flow of light. The thin line arrows shown in Figure 1 represent the flow of signals. The sensor 110 can be installed, for example, next to the lane in which the vehicle 10 travels, or at a gate above the lane.

[0025] The light source 20 can change its frequency in response to control from the processing circuit 60. The light source 20 emits laser light 20L0. The frequency can be modulated with a constant time period, such as a triangular wave or a sawtooth wave. This period is called the modulation period. The modulation period of the frequency can be, for example, 1 μs to 10 msec. The modulation amplitude of the frequency can be, for example, 100 MHz to 1 THz. The wavelength of the laser light can be, for example, included in the near-infrared wavelength range of 700 nm to 2000 nm. Since the amount of near-infrared light in sunlight is less than the amount of visible light, using near-infrared light as the laser light 20L0 can reduce the influence of sunlight as noise. Alternatively, the wavelength of the laser light 20L0 may be included in the visible light wavelength range of 400 nm to 700 nm, or it may be included in the ultraviolet wavelength range.

[0026] The interference optical system 30 includes a first fiber splitter 32, a second fiber splitter 34, and an optical circulator 36. The first fiber splitter 32 separates the laser light 20L0 emitted from the light source 20 into a reference light 20L1 and an output light 20L2. The first fiber splitter 32 inputs the reference light 20L1 to the second fiber splitter 34 and the output light 20L2 to the optical circulator 36. The optical circulator 36 inputs the output light 20L2 to the beam shaper 50. The optical circulator 36 inputs the reflected light 20L3 generated by irradiating the side of the vehicle 10 with the output light 20L2 to the second fiber splitter 34. The second fiber splitter 34 inputs the interference light 20L4, obtained by superimposing and interfering the reference light 20L1 and the reflected light 20L3, to the photodetector 40.

[0027] The photodetector 40 detects interference light 20L4. The photodetector 40 includes one or more photodetectors. The photodetectors output an electrical signal corresponding to the intensity of the detected light.

[0028] The beam shaper 50 shapes the irradiation spot of the output light 20L2 and emits the output light 20L2 toward the vehicle 10. The side of the vehicle 10 is illuminated by the output light 20L2 output from the beam shaper 50. The side of the vehicle 10 includes the side of the body 12 and the side of the wheels 14. Even if the direction of the output light 20L2 is fixed, as the vehicle 10 moves, the side of the vehicle 10 is scanned by the output light 20L2. The beam shaper 50 inputs the reflected light 20L3 generated on the side of the vehicle 10 into the interference optical system 30. The beam shaper 50 is located in the optical path of the output light 20L2 and the reflected light 20L3 between the interference optical system 30 and the vehicle 10.

[0029] The beam shaper 50 may include, for example, a collimating lens 52 that reduces the spread of the output light 20L2. The collimating lens 52 adjusts the illumination spot diameter of the output light 20L2 to be smaller than the diameter of the wheel 14 of the vehicle 10. Output light 20L2 having such an illumination spot diameter can illuminate the vehicle body 12 and the wheel 14 separately. The collimating lens 52 may also adjust the illumination spot diameter of the output light 20L2 to be smaller than the cross-sectional height of the tire. This cross-sectional height is equal to half the value obtained by subtracting the inner diameter of the tire from the outer diameter of the tire. Output light 20L2 having such an illumination spot diameter can illuminate only the tire of the wheel 14 with the output light 20L2. Part of the wheel 14 may be cut out for design reasons. In such cases, the sensor 110 may be configured to illuminate only the tire of the wheel 14 with the output light 20L2. The collimating lens 52 adjusts the spot diameter of the output light 20L2 to be smaller than the shortest distance between two adjacent wheels 14. Output light 20L2 with such a spot diameter can individually measure the rotation speed of multiple wheels 14.

[0030] The processing circuit 60 controls the operation of the light source 20 and the photodetector 40. The processing circuit 60 processes the signal output from the photodetector 40 using FMCW-LiDAR technology. Through signal processing, the processing circuit 60 can count the number of rotating axles in the vehicle 10.

[0031] The computer program executed by the processing circuit 60 is stored in memory 62, such as ROM or RAM (Random Access Memory). The processing circuit 60 and memory 62 may be integrated on a single circuit board or provided on separate circuit boards. The functions of the processing circuit 60 may also be distributed across multiple circuits. Part or all of the processing circuit 60 may be installed in a remote location away from other components of the sensor 110, and may control the operation of the light source 20 and the photodetector 40 and process the signals output from the photodetector 40 via a wired or wireless communication network.

[0032] Next, with reference to Figures 2A and 2B, the principle of distance and velocity measurement using FMCW-LiDAR technology will be briefly explained. FMCW-LiDAR technology enables the realization of a measurement device that is highly vibration-resistant, achieves both a wide dynamic range and high spatial resolution for distance, and is capable of measuring the distance and velocity of moving objects.

[0033] Figure 2A schematically shows the time variation of the frequencies of the reference light 20L1 and the reflected light 20L3 when the vehicle 10 is stationary. The solid line represents the reference light, and the dashed line represents the reflected light. The frequency of the reference light 20L1 shown in Figure 2A repeats the time variation of a triangular wave. That is, the frequency of the reference light 20L1 increases linearly during one period, and then decreases linearly by the amount of the increase. The frequency of the reflected light 20L3 is shifted along the time axis by the amount of time it takes for the output light 20L2 to be emitted from the sensor 110, reflected by the vehicle 10, and returned as reflected light 20L3, compared to the frequency of the reference light 20L1. As a result, the interference light 20L4, which is formed when the reference light 20L1 and the reflected light 20L3 are superimposed and interfere, has a frequency corresponding to the difference between the frequency of the reflected light 20L3 and the frequency of the reference light 20L1. The double arrows shown in Figure 2A represent the difference in the frequencies of the two. The photodetector 40 outputs an electrical signal indicating the intensity of the interference light 20L4. This signal is called a beat signal. The frequency of the beat signal, i.e., the beat frequency, is equal to the difference between the above frequencies. The processing circuit 60 can generate data relating to the distance from the sensor 110 to the vehicle 10 from the beat frequency.

[0034] Figure 2B schematically shows the time evolution of the frequencies of reference light 20L1 and reflected light 20L3 when vehicle 10 is approaching sensor 110. When vehicle 10 approaches, due to Doppler shift, the frequency of reflected light 20L3 shifts in the increasing direction along the frequency axis compared to when vehicle 10 is stationary. The amount by which the frequency of reflected light 20L3 shifts depends on the component obtained by projecting the velocity vector at the illuminated part of vehicle 10 in the direction of reflected light 20L3. The beat frequency differs between the up-chirp period, in which the frequencies of reference light 20L1 and reflected light 20L3 increase linearly, and the down-chirp period, in which they decrease linearly. In the example shown in Figure 2B, the beat frequency during the down-chirp period, in which both frequencies decrease linearly, is higher than the beat frequency during the up-chirp period, in which both frequencies increase linearly. Based on this difference in beat frequencies, the processing circuit 60 can calculate the component of the velocity of the illuminated point on vehicle 10 in the direction toward sensor 110.

[0035] Next, with reference to Figures 3A to 3D, an example of how a moving vehicle 10 is illuminated by the output light 20L2 will be explained. In this example, the vehicle 10 being measured is a large truck. Note that the type of vehicle 10 is not particularly limited; any vehicle with wheels, such as a passenger car, motorcycle, or light truck, is acceptable.

[0036] The vehicle 10 shown in Figure 3A includes a body 12 having five axles and 10 wheels 14 mounted on those axles. Figures 3A, 3B, and 3C are schematic side, top, and front views of an example of the vehicle 10, respectively. Figure 3D is an enlarged view of one of the wheels 14 of the vehicle 10 shown in Figure 3A. In the wheel 14 shown in Figure 3D, the inner circle represents the wheel 14a and the outer ring represents the tire 14b.

[0037] Figures 3A to 3D show mutually orthogonal X, Y, and Z axes for the sake of clarity. The direction opposite to the direction of travel of the vehicle 10 is defined as the +X direction, the direction perpendicular to the road surface and away from the road surface is defined as the +Y direction, and the direction to the left in the direction of travel is defined as the +Z direction. Note that this coordinate system is introduced for the sake of explanation and does not limit the position and orientation of the vehicle 10 and sensor 110.

[0038] The white arrows shown in Figures 3A and 3B represent the direction of travel of the vehicle 10. The thick arrow in Figure 3A represents the position and direction in which the moving vehicle 10 is scanned by the output light 20L2. Of the two thick arrows shown in Figures 3B and 3C, the arrow pointing from the sensor 110 to the vehicle 10 represents the output light 20L2, and the arrow pointing from the vehicle 10 to the sensor 110 represents the reflected light 20L3. The angle φ shown in Figure 3B represents the angle between the output light 20L2 projected onto the XZ plane and the YZ plane perpendicular to the direction of travel of the vehicle 10. The angle θ shown in Figure 3C represents the angle between the output light 20L2 projected onto the YZ plane and the XZ plane parallel to the road surface. The white arrow in Figure 3D represents the direction of the rotational speed of the wheel 14 at position P.

[0039] The angles φ and θ can be both positive and negative. When the output light 20L2 is emitted from the front at an angle toward the side of the vehicle 10, the angle φ is positive. Conversely, when the output light 20L2 is emitted from the rear at an angle toward the side of the vehicle 10, the angle φ is negative. Also, when the output light 20L2 is emitted from above at an angle toward the side of the vehicle 10, the angle θ is positive. Conversely, when the output light 20L2 is emitted from below at an angle toward the side of the vehicle 10, the angle θ is negative.

[0040] If the absolute value of the vehicle 10's travel speed is V, then the vehicle 10's travel speed vector is expressed as (-V, 0, 0). In the example shown in Figure 3D, let R be the maximum radius of the wheel 14, r be the straight-line distance from the center of the wheel 14 to position P, and A be the angle at which this line rotates from the X-axis. In the XY coordinate system with the center of the wheel 14 as the origin, the X and Y components of position P are expressed as x = r × cosA and y = r × sinA, respectively. Since the absolute value of the rotational speed of the outermost part of the wheel 14 is equal to the absolute value of the travel speed V, the absolute value of the rotational speed of the wheel 14 at position P is V × r / R. The rotational speed vector at position P is expressed as (-V × r / R × sinA, V × r / R × cosA, 0) = (-(y / R)V, (x / R)V, 0).

[0041] The velocity vector V1 at the vehicle body 12 or the non-rotating wheel 14 is equal to the travel velocity vector and is expressed by the following equation (1).

number

[0042] The velocity vector V2 at the rotating wheel 14 is the resultant velocity vector of the travel velocity vector and the rotation velocity vector, and is expressed by the following equation (2).

number

[0043] On the other hand, the unit vector N parallel to the direction of the reflected light 20L3 is expressed by the following equation (3).

number

[0044] The X component on the right-hand side of equation (3) can be derived by projecting the unit vector N onto the X-axis in the example shown in Figure 3B. The Y component on the right-hand side of equation (3) can be derived by projecting the unit vector N onto the Y-axis in the example shown in Figure 3C. The Z component on the right-hand side of equation (3) can be derived from the fact that the magnitude of the unit vector N is 1 and that it is a positive component.

[0045] The speed measured by the sensor 110 is the component obtained by projecting the velocity vector in the illuminated portion of the vehicle 10 in the direction of the reflected light 20L3. In other words, the measured speed is obtained by the dot product of the velocity vector in that portion of the vehicle 10 and the unit vector N.

[0046] When the output light 20L2 is directed toward the vehicle body 12 or the non-rotating wheels 14, the measured speed v1 is obtained by the dot product of the velocity vector V1 and the unit vector N, and is expressed by the following equation (4).

number

[0047] Since the angle φ is known, if the angle φ ≠ 0°, the vehicle speed V can be calculated by dividing the measured speed v1 by sinφ.

[0048] On the other hand, when the output light 20L2 is directed toward the rotating wheel 14, the measured speed v2 is obtained by the dot product of the velocity vector V2 and the unit vector N, and is expressed by the following equation (5).

number

[0049] The measured speed v2 is the measured speed v1 plus the first term on the right-hand side, which is due to the rotational speed. The first term depends on the X and Y components of position P.

[0050] When the emission angles of the output light 20L2 are θ=0° and φ=0°, the measured speeds v1 and v2 are zero. If at least one of the emission angles θ and φ of the output light 20L2 is not zero, the measured speeds v1 and v2 can be different from each other. If both the emission angles θ and φ of the output light 20L2 are not zero, the absolute value of the difference between the measured speeds v1 and v2 can be even larger than when only one of the emission angles θ and φ is not zero.

[0051] Next, with reference to Figure 4, an example of the time variation of measured speed and measured distance will be described. Figure 4 is a schematic diagram showing an example of the time variation of measured speed and measured distance. The dashed lines in Figure 4 represent the front and rear ends of the vehicle 10. The broken lines in Figure 4 represent both ends of the wheel 14 that are scanned by the output light 20L2. In the vehicle 10 shown in Figure 4, the fourth axle from the front of the five axles is raised by the lift axle function. Therefore, the wheel 14 attached to the fourth axle is floating and does not rotate while driving.

[0052] In the example shown in Figure 4, the emission angle of the output light 20L2 is θ>0° and φ=0°, and the output light 20L2 passes near the center of the wheel 14. The output light 20L2 intersects the road surface at an oblique angle and perpendicular to the direction of travel of the vehicle 10.

[0053] The measured speed shown in Figure 4 is zero for the vehicle body 12 and the fourth non-rotating wheel 14 from the front, and increases linearly from negative to positive for the other wheels 14. The time change of this measured speed can be explained by equations (4) and (5). In this example, since φ=0°, from equation (4), the measured speed of the vehicle body 12 and the non-rotating wheel 14 is zero. Also, from equation (5), the measured speed of the rotating wheel 14 is V(x / R)sinθ. In the example shown in Figure 4, x / R increases linearly from -1 to 1 with the passage of time. Of the wheels 14, the rotational speed of the front part is measured as a negative value, and the rotational speed of the rear part is measured as a positive value. The rotational speed of the wheel 14 changes from a minimum speed of -Vsinθ to a maximum speed of Vsinθ. The difference between the measured speed of the rotating wheel 14 and the measured speed of the vehicle body 12 or the non-rotating wheel 14 is clear. Therefore, based on the difference in these measured speeds, it is possible to detect rotating wheels and count their number.

[0054] The measurement distance shown in Figure 4 represents the distance from the sensor 110 to the vehicle 10 when the vehicle 10 is illuminated by the output light 20L2. When the vehicle 10 is not illuminated by the output light 20L2, the measurement distance represents the distance from the sensor 110 to an object located far away. In reality, the measurement distances for the vehicle body 12 and the wheels 14 are different, but in Figure 4, for simplicity, the measurement distances for the vehicle body 12 and the wheels 14 are assumed to be constant.

[0055] As shown in Figure 4, there is a clear difference in the measured distance depending on whether the vehicle 10 is illuminated by the output light 20L2 or not. Therefore, based on the measured distance shown in Figure 4, the vehicle 10 can be detected and its number counted. When multiple vehicles 10 are traveling at a narrow distance between them, the measured speed alone may not be able to distinguish whether the rotating wheels 14 correspond to one vehicle 10 or two vehicles 10. Even in such cases, by considering both the measured speed and the measured distance, the number of rotating axles on a single vehicle 10 can be accurately counted.

[0056] In the example in Figure 4, φ=0°, but φ≠0° is also acceptable. That is, the output light 20L2 may intersect not only obliquely with respect to the road surface, but also obliquely with respect to the direction of travel of the vehicle 10. With such a configuration, as can be seen from equations (4) and (5) above, the difference between the measured speeds v1 and v2 becomes larger, making it easier to detect the rotating axle.

[0057] The above method allows for the identification of rotating wheels and the counting of the number of rotating axles in a moving vehicle. However, as mentioned above, if the vehicle accelerates or decelerates during measurement, the measured speed associated with the wheel rotation will differ from that when the vehicle speed is constant, making it difficult to identify the rotating wheels or axles. The following describes in detail an embodiment that solves this problem.

[0058] <Embodiment 1> Figure 5 is a schematic diagram showing an example configuration of a sensing system 100 according to an exemplary embodiment 1 of the present disclosure. The sensing system 100 shown in Figure 5 is an example of a measurement system based on FMCW-LiDAR technology. The sensing system 100 measures the speed of a moving vehicle and the rotational speed of the vehicle's wheels, and counts the number of rotating axles included in the vehicle based on these measurement results. In this specification, "measurement of rotational speed" is not limited to measuring the rotational speed (i.e., the number of rotations or rotation angle per unit time) itself, but also includes measuring the speed of a measurement point accompanying the rotation, and measuring the component of the speed of the measurement point in the direction toward the sensor. A "measurement point" is a point to which a light beam emitted from the sensor is irradiated, and is also referred to as an "irradiation point".

[0059] The sensing system 100 shown in Figure 5 comprises a first sensor 111, a second sensor 112, a processing unit 120, a storage device 130, and an output device 140. The first sensor 111 and the second sensor 112 are sensors for measuring distance and speed using FMCW-LiDAR technology. The first sensor 111 is used to measure the speed of the vehicle and the distance to the vehicle. The second sensor 112 is used to measure the rotational speed of the wheels included in the vehicle measured by the first sensor 111 and the distance to the wheels.

[0060] The processing unit 120 may be a computer including one or more processors and one or more memories. By executing computer programs stored in the memories, the processors can perform various processes described later. The processing unit 120 is connected to the first sensor 111 and the second sensor 112.

[0061] The storage device 130 is a device that includes any storage medium, such as a semiconductor storage medium or a magnetic storage medium. The storage device 130 is connected to the processing unit 120 and stores various data generated by the processing unit 120 during the processing process.

[0062] The output device 140 includes, for example, a communication device and outputs the processing results from the processing device 120 to a higher-level system. The output device 140 may also include a display device that displays the processing results from the processing device 120.

[0063] The higher-level system is a computer system connected to the output device 140 by wire or wirelessly. The higher-level system records the number of axles of each vehicle traveling on the road and manages tolls. The higher-level system can be implemented, for example, by a server computer on the cloud. The output device 140 and the higher-level system may communicate via a network such as the Internet.

[0064] Each of the first sensor 111 and the second sensor 112 may be an FMCW-type LiDAR unit having a light-emitting section (hereinafter simply referred to as "emitting section") that emits a light beam. The first sensor 111 includes a first emitting section that emits a first beam for measuring the speed of the vehicle body. The second sensor 112 includes a second emitting section that emits a second beam for measuring the speed of the vehicle's wheels. Each of the first sensor 111 and the second sensor 112 may have a configuration similar to, for example, the light source 20, interference optical system 30, photodetector 40, and beam shaper 50 in the sensor 110 shown in Figure 1. Alternatively, the first sensor 111 and the second sensor 112 may be configured as a single LiDAR unit having two emitting sections. In that case, the LiDAR unit may be configured to include one light source 20, one photodetector 40, and one interference optical system 30 as shown in Figure 1, with light being split from the interference optical system 30 to two output sections via an optical splitter.

[0065] Figures 6A and 6B show examples of the configuration of the sensing system 100. Figure 6A shows a first configuration example of the sensing system 100. Figure 6B shows a second configuration example of the sensing system 100. Figures 6A and 6B show the rear of the vehicle 10 to be measured. In these figures, thick arrows indicate the flow of light, and thin arrows indicate the flow of signals.

[0066] In the example shown in Figure 6A, each of the first sensor 111 and the second sensor 112 is configured as a LiDAR unit including a light source 20, an interference optical system 30, a photodetector 40, and a beam shaper 50. The configuration and function of the light source 20, the interference optical system 30, the photodetector 40, and the beam shaper 50 are as described with reference to Figure 1. In this example, the processing unit 120 controls the light source 20 and the photodetector 40 in each of the first sensor 111 and the second sensor 112. The light source 20 emits laser light with a periodically fluctuating frequency in response to a control signal input from the processing unit 120. The interference optical system 30 separates the laser light emitted from the light source 20 into output light and reference light, and generates interference light between the reflected light from an object and the reference light. The photodetector 40 receives the interference light and outputs an electrical signal, i.e., a beat signal, corresponding to the intensity of the interference light. The processing unit 120 generates distance information and speed information (i.e., first speed information) of the vehicle body 10 based on the beat signal output from the photodetector 40 of the first sensor 111. The processing unit 120 also generates distance information and speed information (i.e., second speed information) of the wheels of the vehicle 10 based on the beat signal output from the photodetector 40 of the second sensor 112. Based on this distance information and speed information, the processing unit 120 can generate information indicating the number of rotating axles in the vehicle 10. Processing circuits that perform some of the functions of the processing unit 120 may be included in each of the first sensor 111 and the second sensor 112. Such processing circuits may be configured to generate distance information and speed information based on the signal output from the photodetector 40. For example, each of the first sensor 111 and the second sensor 112 may have a configuration similar to that of the LiDAR sensor 110 shown in Figure 1. In that case, the processing unit 120 may be configured to count the number of rotating axles in the vehicle 10 based on the distance information and speed information output from the processing circuits of the first sensor 111 and the second sensor 112, respectively. In that case, the combination of the processing unit 120 and the processing circuits of each sensor functions as a "processing unit that generates first speed information and second speed information, and counts the rotating axles of the vehicle based on the first speed information and second speed information."

[0067] In the example shown in Figure 6B, a single LiDAR unit 114 is provided as a component corresponding to the first sensor 111 and the second sensor 112 shown in Figures 5 and 6A. The LiDAR unit 114 comprises one light source 20, one photodetector 40, and one interference optical system 30, as well as an optical splitter 70, two optical fibers 42, and two beam shapers 50. The thick ring-shaped line in Figure 6B schematically shows that the lengths of the two optical fibers 42 are different due to the winding of the optical fibers 42. The two beam shapers 50 can be positioned at different locations and in different orientations. In the example in Figure 6B, light from the optical circulator 36 in the interference optical system 30 is split by the optical splitter 70 and input to two optical fibers 42 of different lengths. The light propagating through the two optical fibers 42 is collimated by the respective beam shapers 50 and emitted toward the vehicle 10 as the first beam and the second beam. The reflected light from the first beam and the reflected light from the second beam are incident on the corresponding optical fiber 42, pass through the optical circulator 36 and the second fiber splitter 34, and are input to the photodetector 40. The photodetector 40 detects the interference light between the reflected light from the first beam and the reference light, and the interference light between the reflected light from the second beam and the reference light, and outputs electrical signals including beat signals corresponding to the first beam and beat signals corresponding to the second beam. Because the lengths of the two optical fibers 42 are different, a frequency difference occurs between the beat signal corresponding to the first beam and the beat signal corresponding to the second beam. The processing unit 120 detects the frequency of each beat signal by performing processing such as a Fourier transform on the signals output from the photodetector 40. Based on the frequency of each beat signal, the processing unit 120 can generate distance information and velocity information at the irradiation point of the first beam, and distance information and velocity information at the irradiation point of the second beam. Based on that distance information and velocity information, the processing unit 120 can generate information indicating the number of rotating axles in the vehicle 10. Furthermore, the LiDAR unit 114 may include processing circuits that perform some of the functions of the processing unit 120. Such processing circuits may be configured to generate distance information and velocity information based on the signal output from the photodetector 40.In that case, the processing unit 120 may be configured to perform a process of counting the number of rotating axles in the vehicle 10 based on the distance information and speed information output from the processing circuit.

[0068] In this specification, “emission unit” refers to the part or component of a LiDAR unit from which a light beam is emitted toward the outside space. In the examples in Figures 6A and 6B, each of the two beam shapers 50 corresponds to an emission unit. The sensing system 100 includes a first emission unit that emits a first beam for measuring the speed of the vehicle body 10, and a second emission unit that emits a second beam for measuring the rotational speed of the wheels of the vehicle 10. The first and second emission units are fixed facing the direction in which the vehicle 10 to be measured is passing.

[0069] Although Figures 6A and 6B depict the first and second beams irradiating perpendicularly to the side of the vehicle 10, in reality, the first and second beams are irradiated obliquely to the side of the vehicle 10. In this embodiment, the first beam is irradiated obliquely to the side of the vehicle body of the vehicle 10, and the second beam is irradiated obliquely to the side of the wheel of the vehicle 10. The emission direction of the first beam and the emission direction of the second beam are different from each other.

[0070] Figure 7 shows an example of the arrangement of the first emission unit 111a and the second emission unit 112a. Part (a) of Figure 7 shows the side of the vehicle 10 to be measured. Part (b) of Figure 7 shows the front of the vehicle 10. Part (c) of Figure 7 shows the top of the vehicle 10. In Figure 7, the direction of travel of the vehicle 10 is indicated by a white arrow, the positions of the first emission unit 111a and the second emission unit 112a are indicated by stars, and the first beam and the second beam are indicated by thick arrows. Part (a) of Figure 7 shows the irradiation point 111b of the first beam emitted from the first emission unit 111a and the irradiation point 112b of the second beam emitted from the second emission unit 112a. In the following description, the coordinate system consisting of mutually orthogonal x, y, and z axes shown in Figure 7 will be used. In Figure 7 and subsequent figures, the direction of travel of vehicle 10 is defined as the positive x-axis, the vertically upward direction as the positive y-axis, and the rightward direction of vehicle 10 as the positive z-axis. Here, "direction of travel" refers to the direction in which the road on which vehicle 10 travels extends. The road extends linearly within the measurement area, and the direction parallel to that road corresponds to the "direction of travel." Although vehicle 10 does not necessarily travel parallel to the direction in which the road extends, in this specification, regardless of the actual orientation of vehicle 10, the direction in which vehicle 10 is traveling that is parallel to the road is defined as the "direction of travel." For simplicity, in the following explanation, it will be assumed that vehicle 10 is traveling parallel to the road.

[0071] As shown in part (a) of Figure 7, the irradiation point 111b of the first beam is positioned at a height that irradiates the upper part of the side of the vehicle body 10, and the first beam does not irradiate the wheels. On the other hand, the irradiation point 112b of the second beam is positioned at a height that irradiates the wheels of the vehicle 10. As the vehicle 10 moves, the first beam scans the side of the vehicle body 10 from the front to the rear. As the vehicle 10 moves, the second beam sequentially scans the front of the side of the vehicle body 10, the side of the front wheels, the part of the side of the vehicle body between the front and rear wheels, the side of the rear wheels, and the rear of the side of the vehicle body.

[0072] In this embodiment, the first emission unit 111a is positioned higher than the second emission unit 112a so that the irradiation point 111b of the first beam is not on the wheel, and the irradiation point 112b of the second beam is on the wheel. As shown in part (b) of Figure 7, the first emission unit 111a is positioned on the side of the vehicle 10 to be measured, higher than the wheel. The first emission unit 111a emits the first beam toward the side of the vehicle body of the vehicle 10. The second emission unit 112a is positioned on the side of the vehicle 10 and emits the second beam from diagonally above toward the side of the wheel of the vehicle 10.

[0073] Here, the plane along the surface of the road (hereinafter also referred to as the "road surface") 90 on which the vehicle 10 travels is defined as the first plane P1, and the plane perpendicular to the direction of travel of the vehicle 10 is defined as the second plane P2. Assuming the road surface is approximately planar, the first plane P1 is parallel to the road surface. The first plane P1 is parallel to the xz plane and corresponds to the horizontal plane. The second plane P2 is parallel to the yz plane and corresponds to the vertical plane that crosses the road. The angles φ1, φ2, θ1, and θ2 are defined as follows. • φ1: The angle between the direction of the first beam projected onto the first plane P1 and the second plane P2. • φ2: The angle between the direction of the second beam projected onto the first plane P1 and the second plane P2. ·θ1: The angle between the direction of the first beam projected onto the second plane P2 and the first plane P1. ·θ2: The angle between the direction of the second beam projected onto the second plane P2 and the first plane P1. φ1 and φ2 take positive values ​​when they are inclined toward the direction of travel of the vehicle 10 (i.e., the +x direction) with respect to the second plane P2. θ1 and θ2 take positive values ​​when they are inclined toward the upward side (i.e., the +y direction) with respect to the first plane P1.

[0074] In this embodiment, φ1 > 0 and θ1 = 0. That is, the first emission unit 111a emits the first beam in a direction parallel to the first plane P1 (i.e., the horizontal plane) and obliquely incident on the side of the vehicle body from the front side of the vehicle 10. Also in this embodiment, φ2 = 0 and θ2 > 0. That is, the second emission unit 112a emits the second beam in a direction parallel to the second plane P2 (i.e., perpendicular to the direction of travel) and obliquely incident on the side of the wheel from above.

[0075] Figure 8 is a graph showing an example of the speed of the vehicle 10 and the rotational speed of its wheels as measured by the sensing system 100. The upper part of Figure 8 shows an example of the time change of the measured speed at the irradiation point 111b of the first beam. The lower part of Figure 8 shows an example of the time change of the measured speed at the irradiation point 112b of the second beam. The first beam is irradiated onto the body of the vehicle 10, but not onto the wheels. Therefore, as shown in the upper part of Figure 8, the measured speed at the irradiation point 111b of the first beam remains at a nearly constant value while the first beam is irradiating the vehicle body. Here, the measured speed at the irradiation point 111b of the first beam is the component of the vehicle body's speed that is directed toward the first emission unit 111a. On the other hand, the second beam is irradiated onto the body and wheels of the vehicle 10. The measured speed at the irradiation point 112b of the second beam is the component of the vehicle body's or wheels' speed that is directed toward the second emission unit 112a. In this embodiment, since φ2=0 and θ2>0, the measured speed of the vehicle body is almost zero in the measurement using the second beam, and only the y-direction component of the velocity at the illumination point 112b on the side of the wheel is substantially measured. Therefore, in this embodiment, the measured speed data shown in Figure 8 is obtained.

[0076] Figure 9 schematically shows the relationship between the position of the irradiation point 111b of the first beam, the position of the irradiation point 112b of the second beam, and the timing of the measurement of the velocities of the irradiation points 111b and 112b on the vehicle 10. In this embodiment, φ1 > 0 and φ2 = 0, and the first emission unit 111a and the second emission unit 112a are located in close proximity in the direction of travel of the vehicle 10. The first emission unit 111a and the second emission unit 112a are arranged so that the first beam is irradiated to the rear side of the vehicle 10 than the second beam. Therefore, the first beam from the first emission unit 111a irradiates the vehicle 10 before the second beam from the second emission unit 112a, and the measurement of the vehicle 10's velocities by the second beam begins first.

[0077] Here, Δx is the distance in the x-direction between the irradiation point of the first beam and the irradiation point of the second beam on the vehicle 10, L is the total length of the vehicle 10, and the vehicle 10 is assumed to be traveling at a constant speed V during the measurement. In this case, the speed measurement of the vehicle 10 by the first beam and the second beam continues for a time L / V, and the speed measurement by the first beam starts and ends earlier by Δx / V than the speed measurement by the second beam. The processing unit 120 takes this time difference into account to determine the speed of each wheel on the vehicle 10 and counts the rotating axles.

[0078] In reality, the vehicle 10 may accelerate or decelerate during measurement, so the actual measured speed may show a different time variation than the graph shown in Figure 9. Also, due to misalignment of the ejection units 111a and 112a and deviations in the direction of travel of the vehicle 10, the measured speed often does not actually become 0 even during periods when it should be 0. For this reason, the processing unit 120 may perform processing such as treating the measured speed as 0 if it is below a threshold close to 0. The threshold can be determined based on statistical values ​​such as the variance or standard deviation of the acquired data.

[0079] In this embodiment, φ2=0, but φ2>0 or φ2<0 is also possible. That is, the second emission unit 112a may emit the second beam from the front or rear side of the vehicle 10 toward the wheels. Also, φ1<0 is also possible. That is, the first emission unit 111a may emit the first beam from the rear side of the vehicle 10 toward the vehicle body. However, if the first emission unit 111a and the second emission unit 112a are arranged in close proximity, the first emission unit 111a and the second emission unit 112a may be arranged to satisfy the condition φ1>φ2. By satisfying this condition, the degree of freedom in the arrangement design to ensure that the first beam irradiates the vehicle 10 before the second beam is increased.

[0080] Thus, in this embodiment, the first beam from the first emission unit 111a is irradiated onto the vehicle 10 to be measured before the second beam from the second emission unit 112a. In other words, information on the speed of the vehicle 10's body is acquired before information on the rotational speed of the wheels. As a result, after identifying the vehicle 10 to be measured based on the information on the vehicle's body speed, the rotational speed of each wheel included in that vehicle 10 can be measured. With this configuration, the rotating wheels or axles included in the vehicle 10 can be identified with high accuracy.

[0081] In this embodiment, the first beam is irradiated onto the side of the vehicle 10, but as in other embodiments described later, the first beam may be irradiated onto the top or bottom surface of the vehicle 10. The conditions for the first beam from the first emission unit 111a to irradiate the vehicle 10 to be measured before the second beam from the second emission unit 112a are (1) or (2) below. (1) When the first beam is shone onto a plane perpendicular to the road surface or horizontal plane and parallel to the direction of travel of the vehicle, i.e., a plane approximating the side of the vehicle, the shone position is defined as the first spot, and when the second beam is shone onto a plane, the shone position is defined as the second spot, in which case the first spot is located further rearward in the direction of travel of the vehicle than the second spot. (2) When the first beam is shone onto a plane parallel to the road surface or horizontal plane, i.e., a plane approximating the top or bottom surface of the vehicle, the shone position is defined as the first spot, and when the second beam is shone onto a plane approximating the side surface of the vehicle, the shone position is defined as the second spot, the first spot is located further rearward in the direction of travel of the vehicle than the second spot.

[0082] Condition (1) indicates that when both the first and second beams are directed to the side of the vehicle, the first beam is directed further rear of the vehicle than the second beam. Condition (2) indicates that when the first beam is directed to the top or bottom of the vehicle and the second beam is directed to the side of the vehicle, the first beam is directed further rear of the vehicle than the second beam. The first and second emission units 111a and 112a may be arranged to satisfy either condition (1) or (2) above. This makes it easier to identify the vehicle being measured and to detect the rotating wheels or axles on that vehicle.

[0083] Next, a specific example of the operation of the sensing system 100 according to this embodiment will be described.

[0084] Figure 10 is a flowchart illustrating an example of the operation of the processing unit 120 in the sensing system 100. The processing unit 120 starts operation in accordance with an operation start signal input from an input means (not shown). The input means may be an input device such as an external computer. The processing unit 120 performs the operations from steps S1010 to S1080 shown in Figure 10. The operation of each step will be described below.

[0085] <Step S1010> The processing unit 120 determines whether or not an operation termination signal has been input from the input means. If an operation termination signal has been input, the processing unit 120 terminates its operation. If no operation termination signal has been input, the process proceeds to step S1020.

[0086] <Step S1020> The processing unit 120 determines the presence or absence of a vehicle based on the measurement results using the first beam. The processing unit 120 determines that a vehicle is present if the distance measured using the first beam is shorter than the distance measured when no vehicle is present. If a vehicle is determined to be present, the process proceeds to step S1060. If no vehicle is determined to be present, the process proceeds to step S1030. Details of the operation for determining the presence or absence of a vehicle will be described later with reference to Figure 11.

[0087] <Step S1030> The processing unit 120 determines whether the number of axles recorded in the storage device 130 is greater than 0. The number of axles is recorded in the storage device 130 when a rotating axle is counted in step S1080, which will be described later. If the recorded number of axles is greater than 0, the process proceeds to step S1040. If the recorded number of axles is 0, the process returns to step S1010.

[0088] <Step S1040> The processing unit 120 outputs the number of axles recorded in the storage device 130 to the output device 140. The output device 140 transmits the recorded number of axles as the number of axles of the vehicle that passed immediately before to the higher-level system.

[0089] <Step S1050> The processing unit 120 resets the number of axles recorded in the storage device 130 to 0. After the operation of step S1050, the process returns to step S1010.

[0090] <Step S1060> If the processing unit 120 determines in step S1020 that a vehicle is present, it proceeds to step S1060. In step S1060, the processing unit 120 determines whether or not the rotational speed of the wheels has been measured based on the results of speed measurements using the first beam and the second beam. If the vehicle speed measured using the first beam is greater than 0 and the rotational speed of the wheels measured using the second beam is greater than 0, or if the rotational speed had been continuously measured up to that point, the processing unit 120 determines that the rotational speed of the wheels has been measured. If the processing unit 120 determines that the rotational speed of the wheels has been measured, it records the rotational speed information of the wheels in the storage device 130. On the other hand, if the processing unit 120 determines that the rotational speed is no longer being measured, it records rotation end information in the storage device 130 indicating that the section of time for the rotating wheels has ended. If the rotational speed has been measured, it returns to step S1010. If the rotational speed has not been measured, it proceeds to step S1070. Details of the operation for determining whether or not the rotational speed has been measured will be described later with reference to Figure 12.

[0091] <Step S1070> The processing unit 120 determines whether the wheel measurement interval has ended based on whether rotation speed information and rotation end information have been recorded in the storage device 130. Here, it is determined whether the wheel rotation speed was measured immediately before and whether that measurement has ended. If it is determined that the wheel rotation speed measurement interval has ended, the process proceeds to step S1080. If it is determined that the wheel rotation speed measurement interval has not ended, the process returns to step S1010. Details of the operation for determining whether the wheel rotation speed measurement interval has ended will be described later with reference to Figure 14.

[0092] <Step S1080> When the processing unit 120 determines that the measurement interval for the rotational speed of the wheels has ended, it adds 1 to the number of axles and records it in the storage device 130. In other words, the processing unit 120 counts 1 each time a rotating axle is detected and stores the counted number of axles in the storage device 130. After the operation of step S1080, the process returns to step S1010.

[0093] By repeating the operations from step S1010 to step S1080, the processing unit 120 can detect and count the rotating axles included in the vehicle being measured.

[0094] Next, with reference to Figure 11, the details of the operation in step S1020 will be described.

[0095] Figure 11 is a flowchart detailing the operation to determine the presence or absence of a vehicle in step S1020. Step S1020 includes steps S1021 to S1024 shown in Figure 11. The operation of each step will be described below.

[0096] <Step S1021> The processing unit 120 determines whether or not the distance to the vehicle has been measured based on the distance measurement result using the first beam. Specifically, the processing unit 120 determines that the distance to the vehicle has been measured if the distance measured using the first beam is within a predetermined range that is shorter than the distance measured when there is no vehicle. The processing unit 120 determines that the distance to the vehicle has not been measured if the distance measured using the first beam is about the same as the distance measured when there is no vehicle. When the processing unit 120 determines that the distance to the vehicle has been measured, it associates that distance with the time and stores it in the storage device 130. If the distance to the vehicle has been measured, the process proceeds to step S1023. If the distance to the vehicle has not been measured, the process proceeds to step S1022.

[0097] <Step S1022> The processing unit 120 reads the most recent time when the distance to the vehicle was measured from the storage device 130 and determines whether the difference between that time and the current time falls within a predetermined margin. The margin is a value corresponding to the time difference Δx / V shown in Figure 9. Δx is a fixed value determined by the position and orientation of the first emission unit 111a and the second emission unit 112a. The speed V can be calculated based on the results of speed measurement by the first beam. Alternatively, the average vehicle speed that is assumed in advance can be set as V. If the difference between the most recent time when the distance to the vehicle was measured and the current time is within the margin, the process proceeds to step S1023. If the difference between the most recent time when the distance to the vehicle was measured and the current time exceeds the margin, the process proceeds to step S1024.

[0098] <Step S1023> The processing unit 120 determines that a vehicle is within the measurement range of the sensing system 100 and proceeds to step S1060.

[0099] <Step S1024> The processing unit 120 determines that there is no vehicle within the measurement range of the sensing system 100 and proceeds to step S1030.

[0100] Next, with reference to Figure 12, the details of the operation in step S1060 will be described.

[0101] Figure 12 is a flowchart detailing the operation to determine whether or not the wheel rotation speed was measured in step S1060. Step S1060 includes the operations of steps S1061 to S1069 shown in Figure 12. The operation of each step will be described below.

[0102] <Step S1061> The processing unit 120 determines whether or not the speed of the vehicle being measured has been measured, based on the speed measured using the first beam. In other words, the processing unit 120 determines whether or not the vehicle being measured is moving. If the vehicle's speed has been measured, the process proceeds to step S1062. If the vehicle's speed has not been measured, the process proceeds to step S1066. Details of the method for determining whether or not the vehicle is moving will be described later with reference to Figure 13.

[0103] <Step S1062> The processing unit 120 determines whether the absolute value of the rotational speed measured using the second beam is greater than a threshold. The threshold is a predetermined value close to 0 and can be determined based on statistical values ​​such as the variance or standard deviation of the acquired rotational speed data. If the absolute value of the measured rotational speed is greater than the threshold, the process proceeds to step S1064. If the absolute value of the measured rotational speed is less than or equal to the threshold, the process proceeds to step S1063.

[0104] <Step S1063> The processing unit 120 determines, based on the rotational speed information stored in the storage device 130, whether the absolute value of the rotational speed obtained in any of the most recent predetermined number of consecutive measurements (e.g., 1, 2, 3, etc.) is greater than the threshold value. If the absolute value of the rotational speed obtained in any of the most recent predetermined number of measurements is greater than the threshold value, the process proceeds to step S1064. If the absolute values ​​of the rotational speed obtained in all of the most recent predetermined number of measurements are less than or equal to the threshold value, the process proceeds to step S1066.

[0105] <Step S1064> The processing unit 120 stores the rotational speed value measured using the second beam in the storage device 130.

[0106] In this embodiment, the second beam emits the second beam perpendicular to the vehicle's direction of travel, so the velocity component in the same direction as the travel direction is not measured. On the other hand, since the emission direction of the second beam has an angle greater than 0 with respect to a plane parallel to the road surface (i.e., the horizontal plane), the vertical velocity component can be measured. That is, when measuring the rotational speed of a wheel using the second beam, the value corresponding to the vertical component of the velocity vector associated with the rotation of the wheel at the position where the second beam is irradiated is measured. Therefore, as shown in the lower part of Figure 8, in the time interval where there is no vertical component of velocity due to rotation, i.e., the time interval when the second beam is irradiated onto the body of the vehicle, the measured speed is substantially 0. A single rotating wheel has a downward velocity component in its front half and an upward velocity component in its rear half. In the example in Figure 8, the downward velocity component is measured as a negative value, and the upward velocity component as a positive value. In this embodiment, the vertical component of the velocity of a single rotating wheel measured using the second beam becomes zero at a moment because its sign reverses from negative to positive during the measurement of one wheel. Even when the vertical component of the velocity is zero, which is within the wheel's range, the process in step S1063 is introduced in the example in Figure 12 to determine that it is a single rotating wheel's range. As a result, if the magnitude of the velocity measured by the second beam in the previous one or more measurements exceeds a threshold close to zero, the measured velocity by the second beam in the current measurement is recorded in step S1064 as the velocity value within the rotating wheel's range, even if it is below the threshold (for example, almost zero).

[0107] <Step S1065> The processing unit 120 determines that the rotational speed has been measured and returns to step S1010.

[0108] <Step S1066> The processing unit 120 refers to the storage device 130 to determine whether the end of the rotating wheel section has been recorded. The end of the rotating wheel section is recorded in step S1068, which will be described later. If the end of the rotating wheel section has been recorded, the process proceeds to step S1069. If the end of the rotating wheel section has not been recorded, the process proceeds to step S1067.

[0109] <Step S1067> The processing unit 120 reads the rotational speed measurements obtained so far using the second beam from the storage device 130 and determines whether the time change of the rotational speed measurements matches the pattern of the end of the section of the rotating vehicle. For example, the processing unit 120 determines whether the rotational speed measurements obtained from one or more previous measurements show a pattern in which the value changes from a value exceeding the threshold (i.e., a value greater than 0) to the current measurement (e.g., approximately 0). Alternatively, the processing unit 120 may determine whether the time change of the rotational speed measurements obtained from multiple measurements immediately preceding the current measurement changes from a negative value to a positive value and then to approximately 0, as shown in Figure 8. Note that if the second beam is emitted from below the vehicle diagonally upward toward the wheels (i.e., θ2 < 0), it may be determined whether the time change of the rotational speed measurements changes from a positive value to a negative value and then to approximately 0. If the time change of the measured rotational speed matches the pattern of the end of the section of the rotating wheel, the process proceeds to step S1068. If the time variation of the measured rotational speed does not match the pattern of the end of the section of the rotating wheel, proceed to step S1069.

[0110] In this embodiment, the time variation of the rotational speed, as shown in Figure 8, is pre-recorded in the storage device 130 as a time variation pattern of the wheel's rotational speed measured using the second beam. This allows the processing device 120 to correctly determine the timing of the end of the rotational section of the wheel and to identify a state in which wheel rotation is not detected.

[0111] <Step S1068> The processing unit 120 records the end of the section in which the rotating wheel has passed in the storage device 130. At this time, the processing unit 120 erases the record of the rotation speed of the wheel immediately preceding the record.

[0112] <Step S1069> The processing unit 120 determines that the rotational speed was not measured in this measurement and proceeds to step S1070.

[0113] Next, the operation of step S1061 will be described in more detail with reference to Figure 13.

[0114] Figure 13 is a flowchart detailing the operation of step S1061. Step S1061 includes the operations of steps S1161 to S1164 shown in Figure 13. The processing unit 120 determines whether the speed of the vehicle being measured has been measured, that is, whether the vehicle is moving, based on the speed value measured using the first beam. The operation of each step is described below.

[0115] <Step S1161> The processing unit 120 determines whether the velocity measured using the first beam is greater than a threshold. The threshold is a predetermined value close to 0 and can be determined based on statistical values ​​such as the variance or standard deviation of the acquired velocity data. If the measured velocity is greater than the threshold, the process proceeds to step S1162. If the measured velocity is less than or equal to the threshold, the process proceeds to step S1163.

[0116] <Step S1162> The processing unit 120 determines that the vehicle's speed has been measured, that is, that the vehicle being measured is moving, and proceeds to step S1062.

[0117] <Step S1163> The processing unit 120 reads from the storage device 130 the most recent time when the vehicle's measured speed exceeded the threshold, and determines whether the difference between that time and the current time falls within a predetermined margin. The margin is a value corresponding to the time difference Δx / V shown in Figure 9. If the difference between the most recent time when the vehicle's measured speed exceeded the threshold and the current time is within the margin, the process proceeds to step S1162. If the difference between the most recent time when the vehicle's measured speed exceeded the threshold and the current time exceeds the margin, the process proceeds to step S1164.

[0118] <Step S1164> The processing unit 120 determines that the vehicle speed was not measured and proceeds to step S1066.

[0119] Next, with reference to Figure 14, the operation in step S1070 shown in Figure 10 will be described in more detail.

[0120] Figure 14 is a flowchart detailing the operation of step S1070. Step S1070 includes steps S1071 to S1074 shown in Figure 14. The operation of each step will be described below.

[0121] <Step S1071> The processing unit 120 refers to the storage device 130 to determine whether information indicating the end of a section of the rotating wheel has been recorded. This information is recorded in step S1068 shown in Figure 12. If this information has been recorded, the process proceeds to step S1074. If this information has not been recorded, the process proceeds to step S1072.

[0122] <Step S1072> The processing unit 120 refers to the storage device 130 and determines whether there is a record of the rotational speed measured using the second beam in one or more measurements prior to the current measurement. If there is a record of a previously measured rotational speed, the process proceeds to step S1073. If there is no record of a previously measured rotational speed, the process proceeds to step S1074.

[0123] <Step S1073> The processing unit 120 determines that the section of the rotating wheel is continuing, that is, the section of the rotating wheel has not ended, and proceeds to step S1010.

[0124] <Step S1074> The processing unit 120 determines that the section of the rotating wheel has ended and proceeds to step S1080.

[0125] In the above operation, the vehicle may accelerate or decelerate while the wheel rotation speed is being measured. For example, the vehicle may stop while the wheel rotation speed is being measured. Figure 15 shows an example of the time change of the measured speed when the vehicle stops while the wheel rotation speed is being measured. The upper part of Figure 15 shows an example of the speed measured by the first beam. The lower part of Figure 15 shows an example of the speed measured by the second beam. In this example, the measured value of the vehicle's speed by the first beam remains constant for a period of time, then decreases monotonically with deceleration until it becomes 0. Subsequently, as the vehicle accelerates, the measured speed increases and becomes constant again. When the wheel rotation speed by the second beam is measured during a time interval in which the vehicle's running speed decreases to 0 and then accelerates, the measured value shown in the lower part of Figure 15 is obtained. When the vehicle is stopped, the rotation of the wheels stops, so the vertical component of the speed at the irradiation point of the second beam becomes 0, and the measured speed by the second beam becomes 0. When accelerating after a period of zero speed, the vertical component of the wheel speed increases, and therefore the absolute value of the speed measured by the second beam also increases. As shown in the example in Figure 15, even if there is a time period in which the rotational speed of the wheels becomes zero due to the vehicle stopping, in order to detect this as a single wheel section, the process of step S1067 shown in Figure 12 is introduced in this embodiment. As a result, even if the wheel speed is not detected by the measurement with the second beam, it is determined that the measurement section for the rotational speed of one wheel continues until the time change pattern of the speed at the end of the wheel rotational speed measurement section is detected. Therefore, even if the vehicle performs actions involving acceleration or deceleration, such as stopping, during measurement, the measurement section for the rotational speed of one wheel can be accurately detected.

[0126] Next, we will explain an example of the arrangement conditions for the second beam emitter that measures the rotational speed of the wheels.

[0127] Figures 16A and 16B are diagrams illustrating the arrangement conditions of the second beam emitter. Figure 16A schematically shows the positional relationship between the angle θ2 between the emission direction of the second beam emitted from the second beam emitter 112a and a plane parallel to the road surface, and the vehicle 10 in the lane 92. In this embodiment, the emission direction of the second beam is inclined downward from the horizontal, and the angle θ2 is positive. When the vehicle 10 being measured is traveling on the side of the lane 92 closer to the second beam emitter 112a, the second beam is irradiated onto a higher position on the vehicle 10. Conversely, when the vehicle 10 is traveling on the side of the lane 92 further from the second beam emitter 112a, the second beam is irradiated onto a lower position on the vehicle 10, as shown by the dotted line.

[0128] Figure 16B schematically shows the conditions under which the angle θ2 of the second beam can measure the rotational speed of the wheels of all vehicles traveling within the lane 92. Let h be the diameter (i.e., height) of the smallest wheel among the wheels of the vehicle being measured. In this case, the second beam is positioned such that it is irradiated at a height less than h on the side of the wheel 14n closest to the second beam emitter 112a on the lane 92, and at a height higher than the point of contact between the side of the wheel 14f furthest from the second beam emitter 112a and the road surface. For example, consider the case where the lane width is 3 m, the minimum wheel height h is 0.5 m, and the vehicle width is 1.5 m. In this case, the side of the wheel 14f furthest from the second beam emitter 112a is 1.5 m from the side of the wheel 14n closest to the second beam emitter 112a. At this time, the position and orientation of the second ejection unit 112a are determined such that the angle θ2 is smaller than the following angle.

number

[0129] By determining the angle θ2 as described above, the second beam will illuminate the wheels regardless of the vehicle's position within the lane. Therefore, the wheel rotation speed can be measured stably regardless of the vehicle's position within the lane.

[0130] Next, the arrangement of the first ejection unit for measuring the vehicle's body speed and the second ejection unit for measuring the wheel speed will be explained in more detail.

[0131] In this embodiment, as shown in steps S1020 and S1060 in Figure 10, assuming that the vehicle to be measured is located at the irradiation position of the first beam, the second beam is irradiated onto the wheels to measure the rotational speed of the wheels. That is, as shown in Figure 9, after detecting the presence of the vehicle 10 by measurement with the first beam from the first emission unit 111a, the rotational speed of the wheels is measured by measurement with the second beam from the second emission unit 112a. Therefore, the time at which the first beam begins to irradiate the moving vehicle 10 is before the time at which the second beam begins to irradiate the vehicle 10. The conditions for satisfying this condition are exemplified below.

[0132] Figures 17A and 17B illustrate the conditions that the positions of the exit points for the first beam and the second beam must satisfy. In the example in Figure 17A, both φ1 and φ2 are positive values, and φ1 is greater than φ2. In the example in Figure 17B, both φ1 and φ2 are negative values, and the absolute value of φ1|| is greater than the absolute value of φ2|||. Figures 17A and 17B illustrate two possible locations for the second exit unit 112a. As shown in these figures, the irradiation point 111b of the first beam from the first exit unit 111a must be located closer to the front of the vehicle in the direction of travel (i.e., closer to the rear of the vehicle) than the irradiation point 112b of the second beam from the second exit unit 112a. To satisfy this condition, the second emission unit 112a is positioned on the travel direction side (i.e., the forward direction side) of the vertical plane P4 that passes through the irradiation point 111b of the first beam and is inclined by an angle φ2 from the second plane P2.

[0133] The positions of the irradiation points of the first and second beams depend on the angles φ1 and φ2, the positions (or x-coordinates) of the first and second emission units 111a and 112a in their respective directions of travel, and the distances (or z-coordinates) of the first and second emission units 111a and 112a from the road. The following are examples of conditions regarding the angles φ1 and φ2, the positions of the first and second emission units 111a and 112a in their directions of travel, and the distances of the first and second emission units 111a and 112a from the road.

[0134] Figures 18A and 18B show examples of the conditions for the exit angles of each beam so that the first beam illuminates the vehicle before the second beam. The sign of the angle between the exit direction of the first and second beams and the yz plane perpendicular to the vehicle's travel direction (x direction) is considered positive on the side of the vehicle's travel direction. The first and second exit sections 111a and 112a can be arranged such that the angle φ1 between the exit direction of the first beam and the yz plane is greater than the angle φ2 between the exit direction of the second beam and the yz plane. Figure 18A shows an example where both φ1 and φ2 are positive and satisfy φ1>φ2>0. Figure 18B shows an example where both φ1 and φ2 are negative and satisfy 0>φ1>φ2. Thus, the first and second exit sections 111a and 112a can be arranged to satisfy φ2>φ1. In these figures, the positions of the first emission section 111a and the second emission section 112a coincide, but in reality, their positions may differ. By satisfying the angle conditions shown in Figure 18A or Figure 18B, the degree of freedom in the positions of the first emission section 111a and the second emission section 112a is increased, making it easier to satisfy the condition that the first beam illuminates the vehicle before the second beam.

[0135] Figure 19 shows an example of other conditions for the first beam to illuminate the vehicle before the second beam. In the example in Figure 19, the first emitter 111a is located in front of the vehicle in the direction of travel (i.e., behind the vehicle) than the second emitter 112a. By arranging the first emitter 111a and the second emitter 112a to satisfy this condition, the degree of freedom in the angle and position of the first emitter 111a and the second emitter 112a is increased, making it easier to satisfy the condition that the first beam illuminates the vehicle before the second beam, even when φ2 > φ1.

[0136] Figures 20A and 20B show examples of conditions for the distance from the road to the first discharge section 111a and the second discharge section 112a. Here, the distance from the road means the distance from a plane that passes through the centerline in the width direction of the road and is perpendicular to the surface of the road. In the example in Figure 20A, both φ1 and φ2 are positive, and the distance L1 from the road to the first discharge section 111a is longer than the distance L2 from the road to the second discharge section 112a. That is, in this example, φ1 > 0, and the first discharge section 111a is further from the plane that passes through the centerline in the width direction of the road and is perpendicular to the surface of the road than the second discharge section 112a. In the example in Figure 20B, both φ1 and φ2 are negative, and the distance L1 from the road to the first discharge section 111a is shorter than the distance L2 from the road to the second discharge section 112a. In other words, in this example, φ1 < 0, and the first emission unit 111a is closer to a plane perpendicular to the road surface passing through the center line in the width direction of the road than the second emission unit 112a. By satisfying the distance conditions shown in Figure 20A or Figure 20B, the degrees of freedom for the angle and position of the first emission unit 111a and the second emission unit 112a are increased, making it easier to satisfy the condition that the first beam is irradiated onto the vehicle before the second beam.

[0137] The first and second emission units 111a and 112a are positioned such that, in addition to satisfying the condition that the first beam illuminates the vehicle before the second beam, the first beam illuminates the vehicle higher than the second beam. The positions of the illumination points of the first and second beams depend on the angles θ1 and θ2, the distance (or y-coordinate) of the first and second emission units 111a and 112a from the road surface, and the distance (or z-coordinate) of the first and second emission units 111a and 112a from the road. The following are examples of the conditions under which the first beam illuminates the vehicle higher than the second beam.

[0138] Figures 21A and 21B illustrate the angular conditions required for the first beam to illuminate the upper part of the vehicle more than the second beam. The angle θ1 between the emission direction of the first beam from the first emission unit 111a and a plane parallel to the road surface, and the angle θ2 between the emission direction of the second beam from the second emission unit 112a and a plane parallel to the road surface, take positive values ​​when they spread upward. In the example of Figure 21A, angles θ1 and θ2 are both positive, satisfying θ1 < θ2. In the example of Figure 21B, angles θ1 and θ2 are both negative, satisfying θ1 < θ2. Thus, the first emission unit 111a and the second emission unit 112a can be arranged to satisfy θ2 > θ1. By arranging them in this way, the degree of freedom of the positions of the first emission unit 111a and the second emission unit 112a is increased, making it easier to satisfy the condition that the first beam illuminates the upper part of the vehicle more than the second beam.

[0139] Figure 22 illustrates the height conditions of the first and second emitters for the first beam to illuminate the upper part of the vehicle more than the second beam. In the example in Figure 22, the distance (i.e., height) H1 of the first emitter 111a from the road surface is greater than the distance H2 of the second emitter 112a from the road surface. By satisfying this condition, even if θ1 > θ2, as shown in Figure 22, the first beam is more likely to illuminate the upper part of the vehicle more than the second beam. In other words, by positioning the first emitter 111a further from the road surface (i.e., higher) than the second emitter 121a, the degrees of freedom for the angle and position of the first emitter 111a and the second emitter 112a are increased, making it easier to satisfy the condition for the first beam to illuminate the upper part of the vehicle more than the second beam.

[0140] Figures 23A and 23B show examples of conditions for the distances of the first and second emitters 111a and 112a from the road so that the first beam illuminates the upper part of the vehicle more than the second beam. In the example in Figure 23A, both θ1 and θ2 are positive, and the distance D1 of the first emitter 111a from the road is shorter than the distance D2 of the second emitter 112a from the road. That is, in this example, θ1 > 0, and the first emitter 111a is closer to a plane passing through the centerline in the width direction of the road and perpendicular to the surface of the road than the second emitter 112a. In the example in Figure 23B, both θ1 and θ2 are negative, and the distance D1 of the first emitter 111a from the road is longer than the distance D2D of the second emitter 112a from the road. In other words, in this example, θ1 < 0, and the first emission unit 111a is further from the plane passing through the centerline in the width direction of the road and perpendicular to the road surface than the second emission unit 112a. By satisfying the distance conditions shown in Figure 23A or Figure 23B, the degrees of freedom for the angle and position of the first emission unit 111a and the second emission unit 112a are increased, making it easier to satisfy the condition that the first beam illuminates the upper part of the vehicle more than the second beam.

[0141] As described above, the sensing system 100 in this embodiment can count the rotating axles by measuring the vehicle's travel speed and the wheel rotation speed, and identifying the rotating wheels within a single vehicle. By measuring both the vehicle's travel speed and the wheel rotation speed, it is possible to distinguish between speed changes due to rotation and speed changes due to acceleration / deceleration, even when it is difficult to distinguish between speed changes due to rotation and speed changes due to acceleration / deceleration based solely on the measurement results of the wheel speed sensor. This allows for more reliable counting of rotating axles. Furthermore, by utilizing the vehicle speed measurement results, it is possible to detect when the vehicle is stopped during measurement. Therefore, if the wheel speed becomes 0 during measurement, it is possible to avoid false detections such as counting one wheel multiple times, and to accurately count the axles.

[0142] <Modified form of Embodiment 1> Next, a modified example of Embodiment 1 will be described.

[0143] In Embodiment 1, the angles of the first beam and the second beam satisfy φ1>0, φ2=0, θ1=0, and θ2>0. Not limited to these conditions, the first emission unit 111a and the second emission unit 112a can be arranged to satisfy the following (i) and (ii). (i) |φ1| > 0 (ii) Satisfying at least one of |φ2|>0 and |θ2|>0

[0144] The following are examples of modifications that satisfy the above conditions (i) and (ii). Each of the following modifications has the same configuration as Embodiment 1, except that the irradiation angles of the first beam and the second beam are different.

[0145] (Modification 1 of Embodiment 1) Figure 24 is a schematic diagram showing the irradiation angles of the first and second beams in Modification 1 of Embodiment 1. The irradiation angle of the first beam satisfies φ1>0 and θ1>0, and the irradiation angle of the second beam satisfies φ2=0 and θ2>0. This modification differs from Embodiment 1 in that θ1>0 is used instead of θ1=0.

[0146] Figure 25 shows an example of the vehicle speed and wheel rotation speed measured in Modification 1 of Embodiment 1. Since the angle θ1 of the first beam with respect to the plane parallel to the road surface does not affect the measurement of the vehicle speed, the measured speed is the same as in the example in Figure 8. Therefore, the operation of the sensing system 100 is the same as in Embodiment 1. Note that if θ1 > 0, the speed measured by the first beam may differ from the case where θ1 = 0, but in Figure 25, for simplicity, the measured speed is shown on the same scale as in the example in Figure 8. This point is also the same in subsequent figures.

[0147] (Modification 2 of Embodiment 1) Figure 26 is a schematic diagram showing the irradiation angles of the first and second beams in Modification 2 of Embodiment 1. Similar to Modification 1, the irradiation angle of the first beam satisfies φ1>0 and θ1>0, and the irradiation angle of the second beam satisfies φ2=0 and θ2>0. In this modification, as shown in part (a) of Figure 26, the irradiation point 112b of the second beam is at a lower position than the irradiation point 112b in Embodiment 1 and Modification 1. The second beam does not irradiate the vehicle body, but only the wheels.

[0148] Figure 27 shows an example of the vehicle speed and wheel rotation speed measured in Modification 2 of Embodiment 1. In this modification, the position of the irradiation point 112b of the second beam is low, and the second beam is irradiated only on the wheels. Therefore, in measurements using the second beam, the vehicle speed is not measured, and only the wheel speed is measured. However, since φ2=0 in Embodiment 1 and Modification 1, the time change of the measured speed shown in Figure 27 is the same as in Embodiment 1 and Modification 1. In Modification 2, the operation of the sensing system 100 is the same as in Embodiment 1.

[0149] In the modified example 2, θ1 may also be 0. In that case, the operation of the sensing system 100 is the same as in embodiment 1.

[0150] (Modification 3 of Embodiment 1) Figure 28 is a schematic diagram showing the irradiation angles of the first and second beams in Modification 3 of Embodiment 1. The irradiation angle of the first beam is φ1>0, θ1=0, as in Embodiment 1. The irradiation angle of the second beam is φ2>0, θ2>0.

[0151] Figure 29 shows an example of the vehicle speed and wheel rotation speed measured by the sensing system 100 of Modification 3. In this modification, because the angle φ2 of the second beam is not 0, the measurement using the second beam measures a speed that is a combination of the vehicle speed and the wheel speed. The irradiation point 112b of the second beam can be located on both the vehicle body and the wheels, as shown in Figure 28. Therefore, as shown in the lower part of Figure 29, the vehicle speed is measured in the section where the second beam is irradiated onto the vehicle body, and the speed measured in the section where the second beam is irradiated onto the wheels is a speed that is the vehicle speed plus values ​​corresponding to both the horizontal and vertical components of the wheel speed. Similar to Embodiment 1, in the section where the second beam is irradiated onto the wheels, the vertical component of the wheel rotation speed shows a time change in which the sign changes during the measurement period of the wheels, so that the time change pattern of the measured speed shown in the lower part of Figure 29 is obtained. In the example shown in Figure 28, the position of the irradiation point 112b of the second beam is approximately in the center of the wheel's vertical width, and the wheel's velocity has almost a vertical component. Therefore, the horizontal component of the wheel's rotational velocity is approximately zero.

[0152] In Embodiment 1, the processing device 120 could determine the presence or absence of wheel rotation speed in step S1060 shown in Figure 10 based solely on the measurement value obtained by measurement using the second beam. In contrast, in this modified example, the processing device 120 determines the presence or absence of wheel rotation speed using both the measurement value obtained by measurement using the first beam and the measurement value obtained by measurement using the second beam. The measurement value obtained by measurement using the first beam corresponds to the magnitude of the component in the direction toward the first ejection unit 111a of the vehicle's travel speed vector being measured. When this measurement value is A and the vehicle's speed is V, the following relationship holds.

number

number

[0153] Therefore, the processing unit 120 can calculate the vehicle speed component B included in the measured value obtained by measurement using the second beam using the following formula.

number

[0154] The processing unit 120 can determine the wheel rotation speed by subtracting the vehicle speed component B from the speed obtained by measurement using the second beam. Based on the rotation speed determined in this way, the processing unit 120 executes the process shown in step S1060 in Figure 10, more specifically, steps S1062 to S1064 and S1067 in Figure 12.

[0155] (Modification 4 of Embodiment 1) Figure 30 is a schematic diagram showing the irradiation angles of the first and second beams in Modification 4 of Embodiment 1. The irradiation angle of the first beam satisfies φ1>0 and θ1>0, and the irradiation angle of the second beam satisfies φ2>0 and θ2>0. The configuration of this modification is the same as the configuration of Modification 3, except that θ1>0.

[0156] Figure 31 shows an example of the vehicle speed and wheel rotation speed measured in Modification 4. The angle θ1 of the first beam with respect to a plane parallel to the road surface or a horizontal plane does not affect the measurement of the vehicle speed. Also, the irradiation angle of the second beam is the same as the irradiation angle in Modification 3. Therefore, the measured speed shown in Figure 31 is the same as the measured speed shown in Figure 29. The operation of the sensing system 100 in this modification is the same as the operation in Modification 3.

[0157] (Modification 5 of Embodiment 1) Figure 32 is a schematic diagram showing the irradiation angles of the first and second beams in Modification 5 of Embodiment 1. The irradiation angle of the first beam satisfies φ1>0 and θ1>0, similar to Modification 4, and the irradiation angle of the second beam satisfies φ2>0 and θ2>0. In this modification, as shown in part (a) of Figure 32, the irradiation point 112b of the second beam is located lower than the bottom of the vehicle body. Therefore, the second beam does not irradiate the vehicle body, but only the wheels. Except for this point, the configuration of this modification is the same as the configuration of Modification 4.

[0158] Figure 33 shows an example of the vehicle speed and wheel rotation speed measured in Modification 5. The speed measured by the first beam is the same as in Modification 4. In this modification, the irradiation point 112b of the second beam is not located on the vehicle body, but only on the side of the wheel. Therefore, in measurements using the second beam, as shown in the lower part of Figure 33, measurement values ​​are obtained only during the period when the second beam is irradiating the side of the wheel. In this modification, since φ2 > 0, the speed measured using the second beam includes a component of the vehicle speed. The measured speed includes the vehicle speed component and the horizontal and vertical components of the wheel rotation speed. Therefore, the measured speed is like the measured speed in Modification 4 shown in the lower part of Figure 31, but extracted only for the section in which the wheel speed is measured. In the first half of the period in which the wheel speed is measured, the measured speed is the sum of the vehicle speed, the vertical component of the rotation speed measured as a negative value, and the horizontal component of the rotation speed measured as a negative value. After the second irradiation point 112b passes the center of the wheel, the vehicle speed is measured as the sum of the vertical component of the rotational speed measured as a positive value and the horizontal component of the rotational speed measured as a negative value. The horizontal component of the wheel's rotational speed is in the same direction as the vehicle's direction of travel at the top of the wheel and in the opposite direction at the bottom of the wheel. When the wheel is rotating at a constant speed, the horizontal component of the rotational speed measured at the same height is constant. The speed measured by the second beam becomes 0 at the end of the wheel section. Thus, in the measurement by the second beam, the speed is measured only at the wheel section and the measured speed has fluctuations. This point is the same as in Embodiment 1 and Modification 1 of Embodiment 1. Therefore, the operation of the sensing system 100 in this modification is the same as in Embodiment 1.

[0159] In this modified example, θ1 may also be 0. The operation is the same when θ1=0.

[0160] (Modification 6 of Embodiment 1) Figure 34 is a schematic diagram showing the irradiation angles of the first and second beams in a modified example 6 of Embodiment 1. In this modified example, the irradiation angle of the first beam satisfies φ1>0 and θ1=0, and the irradiation angle of the second beam satisfies φ2>0 and θ2=0.

[0161] Figure 35 shows an example of the vehicle speed and wheel rotation speed measured in Modification 6. The angle θ1 between the emission direction of the first beam and a plane parallel to the road surface or a horizontal plane does not affect the measurement of the vehicle speed; therefore, the speed measured by the first beam shown in the upper part of Figure 35 is the same as the speed measured in the upper part of Figure 8. The emission direction of the second beam makes an angle of φ2 with respect to a plane perpendicular to the direction of travel of the vehicle being measured, but the angle with respect to a plane parallel to the road surface or a horizontal plane is 0. Since φ2 is not 0, the measurement by the second beam measures the sum of the vehicle's speed component moving in the direction of travel and the component of the wheel's rotation speed in the direction of travel. In the example of Figure 34, the second beam is irradiated to a position above the center of the wheel's vertical width. Since θ2 is 0, the vertical speed component of the wheel's rotation is not measured, and since φ2 is not 0, the horizontal component of the wheel's rotation speed is measured. As shown in the lower part of Figure 35, in measurements using the second beam, the vehicle speed is measured while the second beam is shining on the vehicle body. While the second beam is shining on the top of the wheels, in addition to the vehicle speed, the horizontal component of the wheel rotation speed is measured. In this modified example, since the second beam is shining above the center of the wheel's vertical range, the direction of wheel rotation is the same as the direction of vehicle travel. Therefore, the sign of the measured horizontal component of wheel speed is the same as the sign of the vehicle speed.

[0162] The second beam may be directed below the center of the wheel's vertical range. In this case, the direction of the horizontal component of the wheel's rotational velocity will be opposite to the direction of the vehicle's travel, and the sign of the measured wheel velocity will be opposite to the sign of the vehicle's velocity.

[0163] In this modified example, the measurement from the second beam includes both the vehicle speed component and the wheel rotation speed component. Therefore, similar to Modified Example 3, the processing unit 120 extracts the wheel rotation speed component by subtracting the vehicle speed component from the measurement from the second beam, based on the measurement from the first beam. Based on the wheel rotation speed component obtained in this way, the operations of step S1060 shown in Figure 10, and steps S1062 to S1064 and S1067 shown in Figure 12 are performed.

[0164] In this modified example, the time variation pattern of the measured wheel rotation speed differs from that of the examples described above. In the examples described above, the vertical component of the wheel speed is measured, so the measured wheel rotation speed exhibits a time pattern that includes a steep speed change at the start of the wheel section, a linear speed change over the section in which the second beam is irradiated onto the wheel, and a steep speed change at the end of the wheel section. In contrast, in this modified example, the horizontal component of the speed associated with the rotation of the wheel is measured, so there is no speed change in the wheel measurement section, and the measured wheel rotation speed exhibits a time pattern that includes a steep speed change at the start of the wheel section, followed by a constant speed, and then a steep change at the end of the wheel section. In the example shown in Figure 12, in step S1067, the processing unit 120 determines the end of the wheel rotation speed measurement section based on the time pattern of the speed measured using the second beam. In contrast, in this modified example, the processing unit 120 extracts the wheel rotation speed component based on the vehicle speed measured using the first beam, and then determines the end of the wheel rotation speed measurement section when it detects a steep drop in rotation speed as shown in the lower part of Figure 35. Note that if φ2 is negative, the sign of the measured speed shown in the lower part of Figure 35 is reversed. In that case, the processing unit 120 extracts the wheel rotation speed component based on the vehicle speed measured using the first beam, and then determines the end of the wheel rotation speed measurement section when it detects a steep rise in rotation speed.

[0165] (Modification 7 of Embodiment 1) Figure 36 is a schematic diagram showing the irradiation angles of the first and second beams in Modification 7 of Embodiment 1. The irradiation angles of the first beam are φ1>0 and θ1>0, and the irradiation angles of the second beam are φ2>0 and θ2=0. This modification is the same as Modification 6 except that θ1>0.

[0166] Figure 37 shows an example of the vehicle speed and wheel rotation speed measured in Modification 7. The angle θ1 of the first beam with respect to a plane parallel to the road surface or a horizontal plane does not affect the measurement of the vehicle speed. Therefore, the measured speed shown in the upper part of Figure 37 is the same as the measured speed shown in the upper part of Figure 35. Note that if θ1 > 0, the measured speed by the first beam may be lower than when θ1 = 0, but for simplicity, the measured speed in Figure 37 is shown on the same scale as in Figure 35. Since the irradiation angle of the second beam is the same as in Modification 6, the measured speed shown in the lower part of Figure 37 is the same as the measured speed shown in the lower part of Figure 35. Therefore, the operation of the sensing system 100 in this modification is the same as in Modification 6.

[0167] (Modification 8 of Embodiment 1) Figure 38 is a schematic diagram showing the irradiation angles of the first and second beams in Modification 8 of Embodiment 1. In this modification, similar to Modification 7, the irradiation angle of the first beam satisfies φ1>0 and θ1>0, and the irradiation angle of the second beam satisfies φ2>0 and θ2=0. In this modification, as shown in part (a) of Figure 38, the irradiation point 112b of the second beam is at a lower position than the irradiation point 112b in Modification 7. The second beam does not irradiate the vehicle body, but only the wheels.

[0168] Figure 39 shows an example of the vehicle speed and wheel rotation speed measured in Modification 8. In this modification, the position of the irradiation point 112b of the second beam is low, and the second beam is irradiated only on the side of the wheel. Therefore, the vehicle speed is not measured when using the second beam, and only the wheel speed is measured. Since φ2 > 0, the measured speed includes the vehicle speed component. Also, since θ2 = 0, the vertical component of the wheel speed is not measured, and only the horizontal component is measured. In the example in Figure 38, the irradiation position of the second beam is located below the wheel. Below the wheel, the wheel moves in the opposite direction to the direction of travel, so the horizontal component of the rotation speed has the opposite sign to the travel speed. The speed measured using the second beam is the sum of the vehicle speed component and the horizontal component of the rotation speed, which is measured with the opposite sign, and therefore shows the time change as shown in Figure 39. Speed ​​is not measured outside the wheel section, and the measured value is 0. In the lower example of Figure 39, speed is measured only at the wheel, but since the measured speed component is the horizontal component, there is no numerical fluctuation with a change in sign like the vertical component.

[0169] The operation of the sensing system 100 in this modified example is generally the same as in Embodiment 1. However, the operation of step S1067 shown in Figure 12 differs from that of Embodiment 1. In Embodiment 1, in step S1067, the processing unit 120 determines the end of the wheel rotation speed measurement section based on the time change pattern of the velocity measured using the second beam. In contrast, in this modified example, after extracting the wheel rotation speed component based on the vehicle speed measured using the first beam, the processing unit determines the end of the rotation speed measurement section when it detects a steep drop in rotation speed, as shown in the lower part of Figure 39. Note that if φ2 is negative, the sign of the measured velocity shown in the lower part of Figure 39 is reversed. In that case, after extracting the wheel rotation speed component based on the vehicle speed measured using the first beam, the processing unit 120 determines the end of the wheel rotation speed measurement section when it detects a steep rise in rotation speed.

[0170] Note that θ1 may also be 0. The operation of the processing unit 120 is the same even when θ1 is 0.

[0171] (Example of application to ETC 1) Next, we will describe an example of an installation method when installing the sensing system in Embodiment 1 and its modified examples 1 to 8 at an ETC toll booth.

[0172] Figures 40A and 40B show examples of the arrangement of the first emission unit 111a and the second emission unit 112a. In Embodiment 1 and its modifications 1 to 8, the first emission unit 111a and the second emission unit 112a can be installed in a housing 96 mounted on an island 94 that divides the lanes, as shown in Figure 40A. Figure 40A illustrates the emission direction of the first beam 111c emitted from the first emission unit 111a and the emission direction of the second beam 112c emitted from the second emission unit 112a. In this example, the first emission unit 111a and the second emission unit 112a are arranged vertically side by side in a housing 96 mounted on an island 94. The first emission unit 111a is positioned higher than the second emission unit 112a.

[0173] Figures 41A to 41C show other arrangement examples of the first ejection unit 111a and the second ejection unit 112a. In this example, the first ejection unit 111a and the second ejection unit 112a are arranged side by side along the direction of travel of the vehicle 10 in a housing 96 installed on an island 94. As shown in Figure 41C, the first ejection unit 111a is located further rearward than the second ejection unit 112a in the vehicle 10.

[0174] In the examples shown in Figures 40A and 40B, and in the examples shown in Figures 41A to 41C, the first emission unit 111a emits the first beam 111c in a direction parallel to the road surface and incident at an oblique rearward angle to the side of the vehicle 10. The second emission unit 112a emits the second beam 112c in a direction parallel to a plane perpendicular to the direction of travel of the vehicle 10 and incident at an oblique downward angle to the side of the wheel of the vehicle 10. This arrangement is the same as the arrangement in Embodiment 1. Not limited to the arrangement in Embodiment 1, an arrangement similar to the arrangements in Modifications 1 to 8 of Embodiment 1 may also be applied.

[0175] <Embodiment 2> Next, a sensing system according to Embodiment 2 of this disclosure will be described.

[0176] In Embodiment 1 and its modifications 1 to 8, the first emission unit 111a and the second emission unit 112a are both positioned to the side of the vehicle being measured and emit a light beam toward the side of the vehicle. In contrast, in this embodiment, the first emission unit 111a is positioned above the vehicle being measured and emits a first beam toward the upper surface of the vehicle. The second emission unit 112a is positioned to the side of the vehicle and emits a second beam toward the side of the vehicle. The configuration of the sensing system 100 in this embodiment is the same as that of Embodiment 1, except for the arrangement of the first emission unit 111a.

[0177] Figure 42 is a schematic diagram showing an example of the arrangement of the first emission unit 111a and the second emission unit 112a in Embodiment 2. In this embodiment, as shown in part (a) of Figure 42, the first emission unit 111a is installed above the vehicle 10 and emits a first beam diagonally downward toward the upper surface of the vehicle 10. When the first beam is irradiated toward the upper surface of the vehicle 10, for example, the hood or roof, the angle between the direction of the first beam projected onto a third plane P3 (i.e., the xy plane) perpendicular to the road surface and parallel to the direction of travel and the second plane P2 (or vertical line) perpendicular to the direction of travel is defined as φ1. φ1 takes a positive value when it is tilted toward the direction of travel (i.e., toward the front of the vehicle). The angle φ1 can be set to a value greater than -π / 2 (-90°) and less than π / 2 (90°) (except 0). In the example shown in Figure 42, φ1 > 0, but φ1 < 0 is also acceptable. The arrangement of the second emission unit 112a and the emission direction and irradiation position of the second beam are the same as in Embodiment 1.

[0178] Angle φ1 forms an angle of (π / 2-φ1) with the first plane P1 (or horizontal plane) parallel to the road surface. That is, as illustrated in Figure 42, the angle θ1 of the first beam, which is irradiated from the first emission unit 111a located above the vehicle 10 toward the upper surface of the vehicle 10, with respect to the first plane P1 (or horizontal plane) is (π / 2-φ1). For this reason, in this embodiment, φ1 is considered, while θ1 is left unspecified.

[0179] Part (b) of Figure 42 shows the front of the vehicle 10. Part (b) of Figure 42 illustrates the position of the first emission unit 111a, the emission direction of the first beam, the position to which the first beam is irradiated, the position of the second emission unit 112a, and the emission direction of the second beam. The first emission unit 111a is located above the vehicle 10 to be measured, and the first beam is irradiated to the center of the upper part of the vehicle body of the vehicle 10 in the vehicle width direction. Note that the irradiation position of the first beam can be anywhere on the upper surface of the vehicle 10, and does not necessarily have to be the center in the vehicle width direction. The first sensor 111 emits the first beam from the first emission unit 111a toward the vehicle 10. The emission angle is at an angle of φ1 with the second plane P2 perpendicular to the direction of travel. Here, if we let ψ1 be the angle between the third plane P3, which is parallel to the direction of travel and perpendicular to the first plane P1 (or the road surface or horizontal plane), and the direction of emission of the first beam, then ψ1 is 0. As shown in the modified examples described later, ψ1 may be a value other than 0. The second emission unit 112a is installed on the side of the vehicle 10 and emits the second beam toward the vehicle 10. The direction of the second beam makes an angle of θ2 with respect to the plane P1 which is parallel to the road surface on which the vehicle 10 travels.

[0180] Part (c) of Figure 42 shows the top surface of the vehicle 10. The white arrow indicates the direction of travel of the vehicle 10. Part (c) of Figure 42 shows the position to which the first beam emitted from the first emission unit 111a irradiates, and the position and emission direction of the second emission unit 112a. The second emission unit 112a emits the second beam from the side of the vehicle 10 toward the side of the vehicle 10. The emission direction of the second beam is perpendicular to the direction of travel of the vehicle 10. That is, the angle φ2 that the emission direction of the second beam makes with respect to a second plane P2 perpendicular to the direction of travel of the vehicle 10 is 0. The position of the second emission unit 112a, the emission direction of the second beam, and the irradiation position of the second beam shown in Figure 42 are the same as the configuration of Embodiment 1 shown in Figure 7.

[0181] Figure 43 shows an example of the vehicle speed and wheel rotation speed measured by the sensing system 100 in this embodiment. In the measurement using the first beam in this embodiment, the vehicle speed is measured while the vehicle is passing under the first emission unit 111a and the first beam is irradiating the vehicle. The upper part of Figure 43 schematically shows the vehicle speed data measured when the vehicle is passing under the first emission unit 111a at a constant speed. Note that the measured vehicle speed may fluctuate depending on the shape of the upper surface of the vehicle 10, for example, the undulations, but in Figure 43, for simplicity, such fluctuations are ignored. This point is also the same in the following figures. The lower part of Figure 43 shows an example of the time change of the speed obtained in the measurement using the second beam. The speed measured using the second beam is the same as in the example of Embodiment 1 shown in the lower part of Figure 8.

[0182] The positions of the irradiation points for the first beam and the second beam are determined by the respective positions of the first and second emission units 111a and 112a, and the respective emission directions of the first and second beams. Based on the measured speed at each of the irradiation points for the first and second beams, the processing unit 120 counts the rotating axles included in the vehicle being measured. The counting method is the same as the method in Embodiment 1 shown in Figure 10.

[0183] According to this embodiment, the first emission unit 111a is installed above the vehicle, the first beam irradiates the upper surface of the vehicle, and the speed at the irradiated point is measured as the vehicle's speed. As a result, regardless of the shape of the vehicle, the first beam irradiates the vehicle body along its entire length, allowing for more reliable measurement of the vehicle's speed along its entire length.

[0184] In this embodiment as well, similar to the modification 2 of Embodiment 1, the second emission unit 112a may be arranged so that the second beam is not irradiated onto the vehicle body but only onto the wheels. Even in this case, the measurement results from the second beam remain substantially unchanged.

[0185] In this embodiment, the definition of angle φ1 differs from Embodiment 1 and its modifications 1 to 8, but the relationship between φ1 and φ2 described with reference to Figures 17A to 20B applies directly to this embodiment and the modifications described later. In this embodiment, the first beam is irradiated onto the upper surface of the vehicle body, but the first beam may also be irradiated onto the lower surface of the vehicle body. When the first beam is irradiated onto the upper or lower surface of the vehicle body, φ1 is defined as the angle between the emission direction of the first beam, which is projected onto a third plane P3 parallel to the direction of travel and perpendicular to the road surface, and a second plane P2 perpendicular to the direction of travel. The first emission unit 111a and the second emission unit 112a can be arranged so as to satisfy the conditions described with reference to Figures 17A to 20B with respect to the φ1 defined in this way and the angle φ2 between the emission direction of the second beam and the second plane P2.

[0186] <Modified form of Embodiment 2> Next, a modified example of Embodiment 2 will be described.

[0187] In Embodiment 2, the angles of the first beam and the second beam satisfy φ1 > 0, φ2 = 0, and θ2 > 0. Not limited to these conditions, the first discharge unit 111a and the second discharge unit 112a can be arranged to satisfy the following (i) and (ii). (i) |φ1| > 0 (ii) Satisfying at least one of |φ2|>0 and |θ2|>0 Here, φ1 is defined differently from the definitions in Embodiment 1 and its various modifications, and is the angle between the exit direction of the first beam, which is projected onto a plane parallel to the direction of travel and perpendicular to the road surface (or horizontal plane), and a vertical line perpendicular to the road surface or a plane perpendicular to the direction of travel. The definitions of φ2 and θ2 are the same as those in Embodiment 1 and its various modifications.

[0188] The following are examples of modifications that satisfy the above conditions (i) and (ii). Each of the following modifications has the same configuration as Embodiment 2, except that the irradiation angles of the first beam and the second beam are different.

[0189] (Modification 1 of Embodiment 2) Figure 44 is a schematic diagram showing the irradiation angles of the first and second beams in a modified example 1 of Embodiment 2. The irradiation angle of the first beam satisfies φ1>0, and θ1=π / 2-φ1. Unlike Embodiment 1, when the emission direction of the first beam is projected onto a plane P2 perpendicular to the vehicle's direction of travel, it forms an angle of ψ1(>0) with respect to a plane P3 parallel to the direction of travel and perpendicular to the road surface. Here, ψ1 takes a positive value when it is tilted toward the side where the second emission unit 112a is located. The irradiation angle of the second beam satisfies φ2=0 and θ2>0, and is the same as in Embodiment 2.

[0190] Figure 45 shows an example of the vehicle speed and wheel rotation speed measured in Modification 1 of Embodiment 2. Since the angle ψ1 > 0 does not affect the measurement of the vehicle speed, the time change of the measured speed shown in Figure 45 is the same as in the example shown in Figure 43. For this reason, the operation in this modification is the same as the operation in Embodiment 2.

[0191] Since the angle ψ1 does not affect the measurement of the vehicle's speed, the explanation of ψ1 will be omitted in the following modifications. When the first beam is shone on the upper surface of the vehicle 10, ψ1 can take on any value.

[0192] In this modified example, as in Modification 2 of Embodiment 1, the second emission unit 112a may be arranged so that the second beam is not irradiated onto the vehicle body but only onto the wheels. Even in this case, the measurement results from the second beam remain substantially unchanged.

[0193] (Modification 2 of Embodiment 2) Figure 46 is a schematic diagram showing the irradiation angles of the first and second beams in Modification 2 of Embodiment 2. In this example, the irradiation angle of the first beam satisfies φ1>0 and θ1=0, and the irradiation angle of the second beam satisfies φ2>0 and θ2>0. The difference from Embodiment 2 is that φ2>0. The configuration of this second beam is the same as in Modification 3 of Embodiment 1.

[0194] Figure 47 shows an example of the vehicle speed and wheel rotation speed measured in Modification 2 of Embodiment 2. The vehicle speed and wheel rotation speed measured in this modification show the same time evolution as in Modification 3 of Embodiment 1 shown in Figure 29. Therefore, the operation of the sensing system 100 in this modification is the same as the operation in Modification 3 of Embodiment 1. In this modification, ψ1 > 0 is also possible, and in that case as well, the vehicle speed measured using the first beam is the same except that the level of the measured value may change depending on the magnitude of ψ1.

[0195] In this modified example, the second emission unit 112a may be arranged so that the second beam is not irradiated onto the vehicle body but only onto the wheels. In that case, the measurement results from the second beam are the same as those in Modified Example 5 of Embodiment 1 shown in Figure 33, and the operation is also the same as the operation in Modified Example 5 of Embodiment 1.

[0196] (Modification 3 of Embodiment 2) Figure 48 is a schematic diagram showing the irradiation angles of the first and second beams in Modification 3 of Embodiment 2. In this modification, the irradiation angle of the first beam satisfies φ1>0 and θ1=0, and the irradiation angle of the second beam satisfies φ2>0 and θ2=0. It differs from Modification 2 of Embodiment 2 in that θ2=0. The configuration of this second beam is the same as the configuration in Modification 6 of Embodiment 1 shown in Figure 34.

[0197] Figure 49 shows an example of the vehicle speed and wheel rotation speed measured in Modification 3 of Embodiment 2. The vehicle speed and wheel rotation speed measured in this modification show the same time evolution as in Modification 6 of Embodiment 1 shown in Figure 35. Therefore, the operation of the sensing system 100 in this modification is the same as the operation in Modification 6 of Embodiment 1. In this modification, ψ1 > 0 is also possible, and in that case as well, the vehicle speed measured using the first beam is the same except that the level of the measured value may change depending on the magnitude of ψ1.

[0198] Also in this modification, the second emission unit 112a may be arranged such that the second beam is not irradiated onto the vehicle body but is irradiated only onto the wheels. In this case, the measurement result obtained by the second beam is the same as the measurement result in modification 8 of embodiment 1 shown in FIG. 39, and the operation is also the same as the operation in modification 8 of embodiment 1.

[0199] (Example of Application to ETC 2) Next, an example of an installation method when the sensing system 100 according to embodiment 2 and modifications 1 to 3 thereof is installed at an ETC tollgate will be described.

[0200] FIG. 50A and FIG. 50B are diagrams showing an arrangement example of the first emission unit 111a and the second emission unit 112a. As shown in these figures, the first emission unit 111a according to embodiment 2 and modifications 1 to 3 thereof can be arranged in a housing 97 installed downward from a gate 95 straddling a lane. The second emission unit 112a according to embodiment 2 and modifications 1 to 3 thereof can be arranged in a housing 96 installed on an island 94.

[0201] In the examples of FIG. 50A and FIG. 50B, the first emission unit 111a irradiates the first beam obliquely downward from above the vehicle 10 onto the upper surface of the traveling vehicle 10. The second emission unit 112a irradiates the second beam obliquely downward from the side of the vehicle 10 onto the side surface of the wheel of the traveling vehicle 10. This arrangement is the same as the arrangement in embodiment 2. Not limited to the arrangement of embodiment 2, arrangements similar to those in modifications 1 to 3 of embodiment 2 may also be applied.

[0202] (Modification 4 of Embodiment 2) FIG. 51 is a schematic diagram showing irradiation angles of the first beam and the second beam in modification 4 of embodiment 2. In this modification, the second emission unit 112a is installed above the vehicle 10 to be measured, and emits the second beam downward. The second beam is irradiated onto the wheel side surface of the vehicle 10 from above the vehicle 10. The irradiation angles of the first beam satisfy φ1>0 and ψ1=0. The irradiation angles of the second beam satisfy φ2=0 and θ2>0. These conditions are the same as the conditions of embodiment 2.

[0203] FIG. 52 is a diagram illustrating an example of vehicle speed and wheel rotational speed measured in Modification 4 of Embodiment 2. The vehicle speed and wheel rotational speed measured in the present modification exhibit the same time variation as in the case of Embodiment 2 illustrated in FIG. 43. Therefore, the operation of the sensing system 100 in the present modification is the same as the operation in Embodiment 2. In the present modification, ψ1 may be greater than 0, and even in that case, the operation is the same except that the level of the measured value of the vehicle speed measured using the first beam can vary depending on the magnitude of ψ1.

[0204] (Modification 5 of Embodiment 2) FIG. 53 is a schematic diagram illustrating irradiation angles of the first beam and the second beam in Modification 5 of Embodiment 2. The irradiation angle of the first beam satisfies φ1>0 and ψ1=0, and the irradiation angle of the second beam satisfies φ2=0 and θ2>0. This condition is the same as the condition in Modification 4 of Embodiment 2. In the present modification, unlike the example of FIG. 51, the irradiation point of the second beam is located at a position lower than the vehicle body, so the second beam is not irradiated onto the vehicle body, but is irradiated only onto the wheels.

[0205] FIG. 54 is a diagram illustrating an example of vehicle speed and wheel rotational speed measured in Modification 5 of Embodiment 2. In the present modification, the position of the irradiation point 112b of the second beam is low, so the second beam is irradiated only onto the wheels. Therefore, in measurement using the second beam, the speed of the vehicle body is not measured, only the speed of the wheels is measured. When φ2 is 0, the second beam is perpendicular to the traveling direction, so measurement using the second beam does not measure the speed in the traveling direction, that is, the vehicle speed. Therefore, the time variation of the speed obtained by measurement using the second beam in the present modification is the same as in the case of Modification 4 of Embodiment 2 illustrated in FIG. 52. The operation of the sensing system 100 in the present modification is the same as the operation in Modification 4 of Embodiment 2. Also in the present modification, ψ1 may be greater than 0, and even in that case, the measured speed value and operation do not substantially change.

[0206] (Modification 6 of Embodiment 2) Figure 55 is a schematic diagram showing the irradiation angles of the first and second beams in Modification 6 of Embodiment 2. This modification differs from the configuration of Modification 4 shown in Figure 51 in that φ2 > 0. The first emission unit 111a and the second emission unit 112a are both installed above the vehicle 10 to be measured, and emit the first and second beams downward, respectively. The first beam irradiates the upper surface of the vehicle 10. The second beam irradiates the sides of the wheels of the vehicle 10 from above. The irradiation angle of the first beam is φ1 > 0, ψ1 = 0. The irradiation angle of the second beam is φ2 > 0, θ2 > 0, and these conditions are the same as those in Modification 2 of Embodiment 2 shown in Figure 46.

[0207] Figure 56 shows an example of the vehicle speed and wheel rotation speed measured in Modification 6 of Embodiment 2. The measured speed shown in Figure 56 is the same as the measured speed in Modification 2 of Embodiment 2 shown in Figure 47. Therefore, the operation of the sensing system 100 in this modification is the same as the operation in Modification 2 of Embodiment 2. In this modification as well, ψ1 > 0 may also be the case, and in that case as well, the measured speed value and operation remain substantially unchanged.

[0208] As shown in modifications 4 to 6 of Embodiment 2, when the first emission unit 111a and the second emission unit 112a are provided above the vehicle 10, the first emission unit 111a may be positioned such that the irradiation position of the first beam is not located on the side of the vehicle. For example, the first emission unit 111a may be positioned on the upper part of the vehicle 10, and within the range of the vehicle width of the vehicle 10 when viewed from the front of the vehicle 10. Such an arrangement makes it easier to satisfy the condition that the irradiation position of the first beam on the vehicle is not on the wheels, and the irradiation position of the second beam on the vehicle is located on the wheels.

[0209] (Modification 7 of Embodiment 2) Figure 57 is a schematic diagram showing the irradiation angles of the first and second beams in Modification 7 of Embodiment 2. In this modification, similar to the example in Figure 55, the irradiation angle of the first beam satisfies φ1>0 and ψ1=0, and the irradiation angle of the second beam satisfies φ2>0 and θ2>0. As shown in part (a) of Figure 57, the irradiation position of the second beam is lower than the vehicle body, unlike the example in Figure 55. Therefore, in measurements using the second beam, only the wheel speed is measured.

[0210] Figure 58 shows an example of speed measured using the second beam in Modification 7 of Embodiment 2. In this modification, the second beam is not irradiated onto the vehicle body, but only onto the side of the wheel. Therefore, as shown in the lower part of Figure 58, speed is measured only during the period when the second beam is irradiated onto the side of the wheel.

[0211] Although the speed is measured only during the period when the beam is irradiated onto the wheel, since φ2 > 0, the measured speed includes the vehicle's speed component. Therefore, a speed measurement result is obtained that is similar to extracting only the wheel section of the measured speed obtained in Modification 6 of Embodiment 2 shown in the lower part of Figure 56. In the first half of the wheel section, the speed measured is the sum of the vehicle's speed and the vertical and horizontal components of the rotational speed, which are measured as negative values. After the irradiation point of the second beam passes the center of the wheel, the vertical component of the rotational speed, which is measured as a positive value, and the horizontal component of the rotational speed, which is measured as a negative value, are added to the vehicle 10's speed. The measured speed becomes 0 at the same time as the end of the wheel section. The pattern in which the speed is measured only in the wheel section, as shown in the lower part of Figure 58, and the measured speed fluctuates, is the same as the example shown in Figure 33. Therefore, the operation of the sensing system 100 is the same as the operation in Modification 5 of Embodiment 1 shown in Figure 33. In this modification as well, ψ1 > 0 is also acceptable, and in that case, the measured speed and operation remain substantially unchanged.

[0212] (Example of application to ETC 3) Next, we will describe an example of an installation method when the sensing system 100 in modified examples 4 to 7 of Embodiment 2 is installed at an ETC toll booth.

[0213] In modifications 4 to 7 of Embodiment 2, both the first ejection unit 111a and the second ejection unit 112a are installed above the vehicle. Therefore, there is no need to provide an area on the side of the vehicle for installing the second ejection unit 112a. In most current ETC systems, vehicles travel in lanes separated by a median strip called an island. By installing both the first ejection unit 111a and the second ejection unit 112a above the vehicle, the island can be eliminated, the gap between lanes can be eliminated or narrowed, and the space efficiency of the toll booth can be improved.

[0214] Figures 59A and 59B show examples of the arrangement of the first emission unit 111a and the second emission unit 112a. In this example, both the first emission unit 111a and the second emission unit 112a are installed in a housing 97 that extends downward from a gate 95 that straddles the lane. Figures 59A and 59B illustrate the emission direction of the first beam 111c and the emission direction of the second beam 112c. In each of the modifications 4 to 7 of Embodiment 2, the first emission unit 111a and the second emission unit 112a can be installed in the housing 97 provided on the gate 95 in this manner. The second emission unit 112a is installed outside the center of the lane in the width direction of the lane in order to irradiate the side of the wheel with the second beam 112c. In the examples shown in Figures 59A and 59B, the housing 97 is installed closer to the inside of the area corresponding to the lane width of the gate 95 that straddles the lane, but the housing 97 may be installed beyond the width of the gate 95 in the lane width direction. The second ejection section 112a may be installed in a position that crosses the lane in the lane width direction, for example, above the lane adjacent to that lane.

[0215] Figures 60A to 60C show other arrangement examples of the first ejection unit 111a and the second ejection unit 112a. In this example, the first ejection unit 111a and the second ejection unit 112a are installed at the first gate 95A and the second gate 95B, respectively, which are located at different positions on the lane. As shown in Figures 60A and 60C, the first ejection unit 111a is installed in the first housing 97A located at the first gate 95A on the near side (i.e., the rear side of the vehicle) in the direction of travel of the vehicle 10. The second ejection unit 112a is installed in the second housing 97B located at the second gate 95B on the far side (i.e., the front side of the vehicle) in the direction of travel of the vehicle 10. In each of the modifications 4 to 7 of Embodiment 2, the first ejection unit 111a and the second ejection unit 112a may be installed at the first gate 95A and the second gate 95B, as in this example.

[0216] (Other variations) In Embodiment 2 and its various modifications, the first emission unit 111a is provided above the vehicle to be measured, but it may also be provided below the vehicle. For example, the first emission unit 111a may be installed on the road surface. In that case, the first emission unit 111a may be arranged to emit the first beam toward the underside of the vehicle. Even in such a configuration, the vehicle speed can be measured as long as the angle φ1 between the second plane perpendicular to the vehicle's direction of travel and the emission direction of the first beam projected onto a third plane parallel to the direction of travel and perpendicular to the road surface is not zero.

[0217] In Embodiment 1 and its various modifications, and in Embodiment 2 and its various modifications, the first sensor 111 and the second sensor 112 perform measurements by irradiating a light beam from a laser, but other light sources may be used. Alternatively, the first sensor 111 and the second sensor 112 may perform measurements by emitting radio waves and detecting the radio waves reflected by the object.

[0218] As described above, in the embodiments of this disclosure, as explained with reference to Figure 9, the first emission unit 111a and the second emission unit 112a are arranged such that the time at which the second beam begins to irradiate the vehicle to be measured is later than the time at which the first beam begins to irradiate the vehicle to be measured. However, the first emission unit 111a and the second emission unit 112a may be arranged such that the irradiation position of the first beam and the irradiation position of the second beam on the surface of the vehicle are as close as possible. In the case where the irradiation position of the first beam and the irradiation position of the second beam are different on the top (or bottom) surface and the side surface of the vehicle, as in Embodiment 2, the first emission unit 111a and the second emission unit 112a may be arranged such that the irradiation position of the first beam and the irradiation position of the second beam are as close as possible on the longitudinal axis of the vehicle.

[0219] In Embodiment 1 and its various modifications, and in Embodiment 2 and its various modifications, the first beam is directed diagonally onto the vehicle body from the front to the rear. However, as shown in Figure 17B, the first beam may also be directed diagonally onto the vehicle body from the rear to the front. Even in this case, it is still possible to measure the speed of the vehicle body.

[0220] Furthermore, in Embodiment 1 and its various modifications, and in Embodiment 2 and its various modifications, the second beam is emitted downwards. However, as shown in Figure 21B, the second beam may be emitted upwards. Even in this case, it is still possible to measure the speed of the wheels.

[0221] The first sensor 111 and the second sensor 112 may each be equipped with a light source 20 and an interference optical system 30, as shown in Figure 6A, or they may be equipped with one interference optical system 30 that splits light from one light source, as shown in Figure 6B. Alternatively, the two sensors may be realized by a configuration that splits light from one light source and directs it to two interference optical systems.

[0222] Each of the first sensor 111 and the second sensor 112 is not limited to a configuration in which each includes a single emission unit, and each of the first sensor 111 and the second sensor 112 may have a plurality of emission units and be configured to emit a plurality of parallel beams from the plurality of emission units.

[0223] [Supplementary Note] Based on the description of the above embodiments, the following technology is disclosed.

[0224] (Technology 1) a first emission unit that emits a first beam for measuring the speed of a vehicle body, the first beam being irradiated onto a side surface, an upper surface, or a lower surface of the vehicle body of a vehicle traveling on a road; a second emission unit that emits a second beam for measuring the speed of a wheel of the vehicle, the second beam being irradiated onto a side surface of the wheel of the vehicle; a processing device that generates first speed information at an irradiation point of the first beam and second speed information at an irradiation point of the second beam, and counts rotating axles of the vehicle based on the first speed information and the second speed information; a measurement system comprising: when the first beam is irradiated onto the side surface of the vehicle body, letting φ1 be the angle formed between an emission direction of the first beam projected onto a first plane along a surface of the road and a second plane perpendicular to a traveling direction of the vehicle, when the first beam is irradiated onto the upper surface or the lower surface of the vehicle body, letting φ1 be the angle formed between an emission direction of the first beam projected onto a third plane parallel to the traveling direction and perpendicular to the first plane and the second plane, letting φ2 be the angle formed between a direction of the second beam projected onto the first plane and the second plane, letting θ1 be the angle formed between a direction of the first beam projected onto the second plane and the first plane, and letting θ2 be the angle formed between a direction of the second beam projected onto the second plane and the first plane, |φ1|>0 is satisfied, and at least one of |φ2|>0 and |θ2|>0 is satisfied, the measurement system.

[0225] This configuration allows for more accurate counting of the rotating axles in a moving vehicle.

[0226] (Technology 2) A measurement system as described in Technical 1, satisfying |φ2|=0 and |θ2|>0.

[0227] This configuration eliminates the vehicle's speed component from the speed measured by the second beam, making it easier to measure the rotational speed of the wheels.

[0228] (Technology 3) The measurement system according to Art 1 or 2, wherein the first emission unit and the second emission unit are arranged such that the first beam is directed to the rearward side of the vehicle than the second beam.

[0229] This configuration allows for the acquisition of vehicle speed information before wheel speed information. Therefore, the accuracy of axle counting can be improved.

[0230] (Technology 4) φ1 and φ2 take positive values ​​when they are inclined toward the direction of travel of the vehicle with respect to the second plane. Satisfying φ1 > φ2, A measurement system as described in any of the technologies 1 to 3.

[0231] This configuration increases the design flexibility for the placement of the first and second emission units, which are used to illuminate the vehicle with the first beam before the second beam.

[0232] (Technology 5) The measurement system according to any one of the technologies 1 to 4, wherein the first ejection unit is located further rearward than the second ejection unit when viewed from the moving vehicle.

[0233] This configuration allows for greater design flexibility in the arrangement and angle of the first and second emission units, which are used to illuminate the vehicle with the first beam before the second beam.

[0234] (Technology 6) φ1 and φ2 take positive values ​​when they are inclined toward the direction of travel of the vehicle with respect to the second plane. Satisfying φ1 > 0, The first ejection unit is further from the plane passing through the center line in the width direction of the road and perpendicular to the surface of the road than the second ejection unit. A measurement system as described in any of the technologies 1 to 5.

[0235] This configuration allows for greater design flexibility in the arrangement and angle of the first and second emission units, which are used to illuminate the vehicle with the first beam before the second beam.

[0236] (Technology 7) φ1 and φ2 take positive values ​​when they are inclined toward the direction of travel of the vehicle with respect to the second plane. Satisfying φ1 < 0, The first ejection unit is closer to a plane that passes through the center line in the width direction of the road and is perpendicular to the surface of the road than the second ejection unit. A measurement system as described in any of the technologies 1 to 5.

[0237] This configuration allows for greater design flexibility in the arrangement and angle of the first and second emission units, which are used to illuminate the vehicle with the first beam before the second beam.

[0238] (Technology 8) The measurement system according to any one of the technologies 1 to 7, wherein the first emission unit and the second emission unit are arranged such that the first beam is irradiated to a higher position on the vehicle than the second beam.

[0239] This configuration makes it easier to position the first and second emission units so that the first beam illuminates the vehicle body but not the wheels, and the second beam illuminates the wheels.

[0240] (Technology 9) θ1 and θ2 take positive values ​​when they are inclined upward with respect to the first plane. Satisfying θ2 > θ1, A measurement system as described in any of the technologies 1 through 8.

[0241] This configuration increases the design flexibility for arranging the first and second emission units to direct the first beam to a higher position on the vehicle than the second beam.

[0242] (Technology 10) The measurement system according to any one of the technologies 1 to 9, wherein the first ejection unit is further from the road surface than the second ejection unit.

[0243] This configuration allows for greater design flexibility in the arrangement and angle of the first and second emission units, enabling the first beam to be directed at a higher position on the vehicle than the second beam.

[0244] (Technology 11) θ1 and θ2 take positive values ​​when they are inclined upward with respect to the first plane. Satisfying θ1 > 0, The first ejection unit is closer to a plane that passes through the center line in the width direction of the road and is perpendicular to the surface of the road than the second ejection unit. A measurement system described in any of the techniques 1 through 10.

[0245] This configuration allows for greater design flexibility in the arrangement and angle of the first and second emission units, enabling the first beam to be directed at a higher position on the vehicle than the second beam.

[0246] (Technology 12) θ1 and θ2 take positive values ​​when they are inclined upward with respect to the first plane. Satisfying θ1 < 0, The first ejection unit is further from the plane passing through the center line in the width direction of the road and perpendicular to the surface of the road than the second ejection unit. A measurement system described in any of the techniques 1 through 10.

[0247] This configuration allows for greater design flexibility in the arrangement and angle of the first and second emission units, enabling the first beam to be directed at a higher position on the vehicle than the second beam.

[0248] (Technology 13) A measurement method for obtaining information regarding the speed of a vehicle traveling on a road, A first beam for measuring the speed of the vehicle body is shone onto the side, top, or bottom of the vehicle body. A second beam for measuring the speed of the vehicle's wheels is shone onto the side of the wheel, To generate first velocity information at the irradiation point of the first beam and second velocity information at the irradiation point of the second beam, Based on the first speed information and the second speed information, the number of rotating axles of the vehicle is counted, Includes, When the first beam is irradiated onto the side of the vehicle body, the angle between the emission direction of the first beam projected onto a first plane along the surface of the road and a second plane perpendicular to the direction of travel of the vehicle is defined as φ1. When the first beam is projected onto the upper or lower surface of the vehicle body, the angle between the emission direction of the first beam, which is projected onto a third plane parallel to the direction of travel and perpendicular to the first plane, and the second plane is defined as φ1. Let φ2 be the angle between the direction of the second beam projected onto the first plane and the second plane. Let θ1 be the angle between the direction of the first beam projected onto the second plane and the first plane. If we let θ2 be the angle between the direction of the second beam projected onto the second plane and the first plane, |φ1|>0 satisfies, and Satisfying at least one of |φ2|>0 and |θ2|>0, Measurement method.

[0249] (Technology 14) The method according to Technology 13, wherein the first beam is directed to the rear side of the vehicle than the second beam.

[0250] (Technology 15) The measurement method according to Art 13 or 14, wherein the first beam is irradiated to a higher position on the vehicle than the second beam. [Industrial applicability]

[0251] The technology disclosed herein can be used, for example, in devices or systems for detecting the rotating axles of moving vehicles in traffic infrastructure such as ETC systems that utilize FMCW-LiDAR. [Explanation of Symbols]

[0252] 10 vehicles 12 car bodies 14 wheels 20 light source 30 Interferometric Optics 40 Photodetectors 50. Beam shaping unit (light emission section) 60 Processing Circuits 62 memory 90 Road surface 92 lanes 94 Island Gate 95 96, 97 cabinet 100 Sensing Systems 110 Sensor 111 First Sensor 111a Launch point of the first beam 111b Irradiation point of the first beam 112 Second Sensor 112a Launch point of the second beam 112b Irradiation point of the second beam 114 LiDAR units 120 Processing Units 130 Storage device 140 Output device

Claims

1. A first emission unit emits a first beam that is projected onto the side, top, or bottom of a vehicle traveling on a road to measure the speed of the vehicle, A second emission unit emits a second beam that is irradiated onto the side of the wheel of the vehicle and used to measure the speed of the wheel, A processing device that generates first velocity information at the irradiation point of the first beam and second velocity information at the irradiation point of the second beam, and counts the rotating axles of the vehicle based on the first velocity information and the second velocity information, A measurement system comprising, When the first beam is projected onto the side of the vehicle body, the angle between the emission direction of the first beam projected onto a first plane along the surface of the road and a second plane perpendicular to the direction of travel of the vehicle is defined as φ1. When the first beam is irradiated onto the upper or lower surface of the vehicle body, the angle between the emission direction of the first beam, which is projected onto a third plane parallel to the direction of travel and perpendicular to the first plane, and the second plane is defined as φ1. Let φ2 be the angle between the direction of the second beam projected onto the first plane and the second plane. Let θ1 be the angle between the direction of the first beam projected onto the second plane and the first plane. If we let θ2 be the angle between the direction of the second beam projected onto the second plane and the first plane, |φ1| > 0 satisfies, Satisfying at least one of |φ2| > 0 and |θ2| > 0, Measurement system.

2. The measurement system according to claim 1, satisfying |φ2| = 0 and |θ2| > 0.

3. The measurement system according to claim 1 or 2, wherein the first emission unit and the second emission unit are arranged such that the first beam is irradiated to the rear side of the vehicle than the second beam.

4. φ1 and φ2 take positive values ​​when they are inclined toward the direction of travel of the vehicle with respect to the second plane. Satisfying φ1 > φ2, The measurement system according to claim 3.

5. The measurement system according to claim 3, wherein the first ejection unit is located further rearward than the second ejection unit when viewed from the moving vehicle.

6. φ1 and φ2 take positive values ​​when they are inclined toward the direction of travel of the vehicle with respect to the second plane. Satisfying φ1 > 0, The first ejection unit is further from the plane passing through the center line in the width direction of the road and perpendicular to the surface of the road than the second ejection unit. The measurement system according to claim 3.

7. φ1 and φ2 take positive values ​​when they are inclined toward the direction of travel of the vehicle with respect to the second plane. Satisfying φ1 < 0, The first ejection unit is closer to a plane that passes through the center line in the width direction of the road and is perpendicular to the surface of the road than the second ejection unit. The measurement system according to claim 3.

8. The measurement system according to claim 1 or 2, wherein the first emission unit and the second emission unit are arranged such that the first beam is irradiated to a higher position on the vehicle than the second beam.

9. θ1 and θ2 take positive values ​​when they are inclined upward with respect to the first plane. Satisfying θ2 > θ1, The measurement system according to claim 8.

10. The measurement system according to claim 8, wherein the first discharge unit is further from the road surface than the second discharge unit.

11. θ1 and θ2 take positive values ​​when they are inclined upward with respect to the first plane. Satisfying θ1 > 0, The first ejection unit is closer to a plane that passes through the center line in the width direction of the road and is perpendicular to the surface of the road than the second ejection unit. The measurement system according to claim 8.

12. θ1 and θ2 take positive values ​​when they are inclined upward with respect to the first plane. Satisfying θ1 < 0, The first ejection unit is further from the plane passing through the center line in the width direction of the road and perpendicular to the surface of the road than the second ejection unit. The measurement system according to claim 8.

13. A measurement method for obtaining information regarding the speed of a vehicle traveling on a road, A first beam for measuring the speed of the vehicle body is shone onto the side, top, or bottom of the vehicle body. A second beam for measuring the speed of the vehicle's wheels is shone onto the side of the wheel, To generate first velocity information at the irradiation point of the first beam and second velocity information at the irradiation point of the second beam, Based on the first speed information and the second speed information, the number of rotating axles of the vehicle is counted, Includes, When the first beam is projected onto the side of the vehicle body, the angle between the emission direction of the first beam projected onto a first plane along the surface of the road and a second plane perpendicular to the direction of travel of the vehicle is defined as φ1. When the first beam is irradiated onto the upper or lower surface of the vehicle body, the angle between the emission direction of the first beam, which is projected onto a third plane parallel to the direction of travel and perpendicular to the first plane, and the second plane is defined as φ1. Let φ2 be the angle between the direction of the second beam projected onto the first plane and the second plane. Let θ1 be the angle between the direction of the first beam projected onto the second plane and the first plane. If we let θ2 be the angle between the direction of the second beam projected onto the second plane and the first plane, |φ1| > 0 satisfies, Satisfying at least one of |φ2| > 0 and |θ2| > 0, Measurement method.

14. The method according to claim 13, wherein the first beam is irradiated to the rear side of the vehicle than the second beam.

15. The measurement method according to claim 13 or 14, wherein the first beam is irradiated to a higher position on the vehicle than the second beam.

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