Monitoring sensor and method for adjusting monitoring sensor

Abstract

A monitoring sensor comprising: a light-emission unit; a scanning unit configured so as to periodically scan the surrounds by using light emitted from the light-emission unit; and a light-reception unit that receives reflected light which is emitted light that has been reflected by the surrounds. The scanning unit has: an optical member that refracts or reflects the emitted light and the reflected light; a beam spring 30 that supports the optical member; and an actuator 32 that displaces the beam spring. The beam spring 30 has formed therein machining areas 72 that can be laser machined to increase or decrease the mass of the constituent material.

Description

Technical Field

[0001] The present invention relates to a monitoring sensor.

Background Art

[0002] In recent years, the development of driving assistance systems and autonomous driving systems for automobiles has been rapidly progressing. In such systems, sensors that constantly monitor the positions and speeds of other vehicles around the host vehicle are important in order to determine the behavior of the host vehicle. As such a sensor, LiDAR (Light Detection and Ranging or Laser Imaging Detection and Ranging) using a laser has been devised to detect and identify objects around the vehicle (see, for example, Patent Document 1).

[0003] A general LiDAR is a sensor that emits non-visible light (infrared laser light) in front of it and acquires information such as the distance to an object and the shape of the object based on the emitted light and the reflected light.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, the above-described LiDAR includes a scanning mechanism for irradiating a target wide range with laser light. This scanning mechanism drives the beam by resonating a beam spring having a beam structure using the resonance frequency. Therefore, if there are variations in the mass and shape of the beam spring, the resonance frequency will vary, which will affect the performance of the LiDAR.

[0006] The present invention has been made in view of such circumstances, and one of its exemplary purposes is to provide a new technology for improving the scanning accuracy of a scanning unit provided in a monitoring sensor.

Means for Solving the Problems

[0007] In order to solve the above problems, a monitoring sensor according to an aspect of the present invention includes a light emitting unit, a scanning unit configured to periodically scan the surroundings with emitted light emitted from the light emitting unit, and a light receiving unit that receives reflected light, which is the emitted light reflected by the surroundings. The scanning unit includes an optical member that refracts or reflects the emitted light and the reflected light, a beam spring that supports the optical member, and an actuator that displaces the beam spring. The beam spring has a processed region that can be laser processed to increase or decrease the mass of the constituent material.

[0008] According to this aspect, the mass of the beam spring can be easily adjusted. Therefore, it is possible to adjust the resonance frequency when the beam spring is displaced to a desired range, and the scanning accuracy of the scanning unit provided in the monitoring sensor can be improved.

[0009] The processed region may be a thin portion with holes formed by laser processing. Thereby, the mass of the beam spring can be easily reduced.

[0010] The processed region may be subjected to a polishing treatment or a non-plating treatment so as to facilitate joining of a metal piece by laser welding. Thereby, the mass of the beam spring can be easily increased.

[0011] Another aspect of the present invention is a method for adjusting a monitoring sensor. This method includes a light emitting unit, a scanning unit configured to periodically scan the surroundings with the emitted light emitted from the light emitting unit, and a light receiving unit that receives the reflected light which is the emitted light reflected by the surroundings. The scanning unit includes an optical member that refracts or reflects the emitted light and the reflected light, a beam spring that supports the optical member, and an actuator that displaces the beam spring. The adjustment process includes an adjustment step for adjusting the monitoring sensor having these components, and the adjustment step includes a laser processing step for increasing or decreasing the mass of the material constituting the beam spring.

[0012] According to this aspect, the mass of the beam spring can be easily adjusted. Therefore, it is possible to adjust the resonance frequency when the beam spring is displaced to a desired range, and the scanning accuracy of the scanning unit included in the monitoring sensor can be improved.

[0013] The laser processing step may be a step of making holes in the beam spring. Thereby, the mass of the beam spring can be easily reduced.

[0014] The laser processing step may be a step of joining a metal piece to the beam spring by laser welding. Thereby, the mass of the beam spring can be easily increased.

[0015] In addition, any combination of the above components, and those obtained by converting the expression of the present invention between a method, an apparatus, a system, etc. are also effective as aspects of the present invention.

Effects of the Invention

[0016] According to the present invention, the scanning accuracy of the scanning unit included in the monitoring sensor can be improved.

Brief Description of the Drawings

[0017]

Figure 1

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Figure 6

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted as appropriate. Also, the configurations described below are examples and do not limit the scope of the present invention in any way.

[0019] (First Embodiment) First, LiDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging) using light, which is a type of monitoring sensor for vehicles, will be described. FIG. 1 is a diagram showing the appearance of the LiDAR. FIG. 2 is a cross-sectional view taken along the line A-A of FIG. 1.

[0020] The LiDAR 10 shown in FIG. 1 includes a sensor unit 12, a housing 14 that covers the sensor unit 12, and a light-transmitting cover 15 made of a material through which the light emitted from the sensor unit 12 passes. As shown in FIG. 2, the sensor unit 12 includes a light-emitting unit 16, a scanning unit 18 configured to periodically scan the surroundings with the emitted light emitted from the light-emitting unit 16, and a light-receiving unit 20 that receives the reflected light, which is the emitted light reflected by the surroundings. The light-emitting unit 16 is, for example, a laser light source that emits infrared light. Also, the light-receiving unit 20 is, for example, a photodetector such as a photodiode.

[0021] The scanning unit 18 includes a light-emitting lens 22 that refracts light and emits it to the periphery, a light-receiving lens 24 that receives and refracts the reflected light from the periphery, a lens holder 26 that holds the light-emitting lens 22 and the light-receiving lens 24, and a beam spring 30 that supports the lens holder 26 and is fixed so as to swing with respect to a base plate 28 that forms a part of the housing 14. The beam spring 30 is a pair of plate-shaped metal members having spring properties. The beam spring 30 is periodically amplitude-modulated (displaced) by a scanning actuator 32, and accordingly, the lens holder 26 vibrates in the direction of the arrow. Note that the optical member may be not only the aforementioned lens but also a reflecting member that reflects the emitted light or the reflected light.

[0022] As a result, the light emitted from the light-emitting unit 16 disposed on the rear focal plane of the light-emitting lens 22 scans forward while being parallelized. Also, when a part of the scanned light is reflected by an object and enters the light-receiving lens 24, the light is detected by being focused on the light-receiving unit 20 disposed on the rear focal plane of the light-receiving lens 24. Then, the LiDAR 10 can scan forward one-dimensionally as the lens holder 26 reciprocates linearly as shown by the arrow, and obtain information on the direction in which the object exists and the distance to the object. Note that the sensor unit 12 shown in FIG. 1 describes the case of one-dimensional scanning, but two-dimensional scanning may be realized by combining a plurality of beam springs.

[0023] As described above, the LiDAR 10 according to the present embodiment drives the lens holder 26 corresponding to the beam by resonating the beam spring 30 that constitutes the sensor unit 12 having a beam structure, using the resonance frequency. The resonance frequency f is represented by f = (k / m) 1 / 2 and varies depending on the shape of the beam spring 30 (which affects the spring constant k) and the mass (m). Therefore, depending on the processing accuracy of the beam spring, the resonance frequency may vary from the desired value. Thus, as a result of intensive studies by the inventor of the present application, several methods for reducing the variation in the resonance frequency have been conceived.

[0024] (First Embodiment) In this embodiment, an example of adjusting the resonance frequency unique to the beam spring will be described. FIG. 3(a) is a schematic diagram of the beam spring before adjustment according to the first embodiment, and FIG. 3(b) is a schematic diagram of the beam spring after adjustment according to the first embodiment.

[0025] The beam spring 30 shown in FIG. 3(a) is configured to vibrate with an amplitude (displacement) at the resonance frequency f while being fixed to the base plate 28. However, depending on the processing accuracy, the thickness of the beam spring 30 may deviate from the ideal value t by Δt. In this case, the resonance frequency f’ is f’=(k / (m + Δm)) 1 / 2 and a deviation occurs with respect to the ideal resonance frequency f.

[0026] Therefore, the beam spring 30 shown in FIG. 3(a) is formed with a processing region 72 that can be laser processed to increase or decrease the mass of the constituent material. The processing region 72 is a thin-walled portion with holes formed by laser processing or laser welding. As a result, as shown in FIG. 3(b), it becomes easier to form holes 74 in the processing region 72 by laser processing or laser welding. That is, the mass of the beam spring 30 can be easily adjusted. Therefore, it becomes possible to adjust the resonance frequency f when the beam spring 30 vibrates within a desired range, and the scanning accuracy by the scanning unit provided in the monitoring sensor can be improved. Further, when the processing region 72 of this embodiment is a thin-walled portion with holes formed by laser processing or laser welding, the mass of the beam spring 30 can be easily reduced.

[0027] Note that the number of processing regions 72 may be one or more. If knowledge of how the resonance frequency changes when holes are formed in which processing region 72 is obtained in advance, even when there is a large variation in the resonance frequency, appropriate hole formation by laser processing or laser welding can be performed quickly.

[0028] FIG. 4 is a schematic diagram after adjustment according to another example of the beam spring according to the first embodiment. The processed region 76 of the beam spring 30 shown in FIG. 4 is subjected to a polishing treatment or a non-plating treatment (treatment for not plating) so as to facilitate joining of the metal piece 78 by laser processing (more specifically, laser welding). Thereby, the mass of the beam spring 30 can be easily increased, and it can be adjusted to an appropriate resonance frequency.

[0029] Note that it is preferable to prepare metal pieces of a plurality of weights and sizes. If knowledge of how the resonance frequency changes when each metal piece is joined to the processed region 76 in advance is obtained, even when there is a large variation in the resonance frequency, appropriate joining of the metal piece by laser welding can be performed quickly.

[0030] Thus, in the present embodiment, the adjustment step for adjusting the scanning unit of the LiDAR 10 includes a laser processing step for increasing or decreasing the mass of the material constituting the beam spring.

[0031] (Second Embodiment) In the present embodiment, an adjustment actuator for adjusting the resonance frequency is driven by feedback control based on information obtained from an accelerometer provided in the beam spring. FIG. 5 is a schematic diagram of the beam spring according to the second embodiment.

[0032] In the beam spring 80 shown in FIG. 5, an accelerometer 82 is provided on one surface on the tip side of a long plate-shaped plate portion 80a corresponding to the leg portion of the beam structure, and an adjustment actuator 84 is provided on the other surface. Note that the positions where the accelerometer 82 and the adjustment actuator 84 are provided correspond to the position of the antinode 85 of the resonance mode when the beam spring 80 is driven.

[0033] Note that the actuator may be provided on one surface of the plate portion 80a, and the accelerometer may be provided on the other surface of the plate portion 80a. The accelerometer 82 is, for example, a piezoelectric element using a single crystal of quartz or barium titanate. As the adjustment actuator 84, an active type piezo element, a voice coil, or a passive type oil damper is used.

[0034] FIG. 6 is a block diagram of a resonance adjustment unit according to the second embodiment. As shown in FIG. 6, the resonance adjustment unit 86 includes a control unit 88 that controls the movement of the adjustment actuator 84 so as to adjust the resonance frequency of the beam spring 80 based on the acceleration signal acquired from the accelerometer 82. The control unit 88 includes a charge amplifier 90 that integrates the acceleration signal acquired from the accelerometer 82 to generate a velocity signal, and a control signal generation unit 92 that generates a control signal for controlling the adjustment actuator 84 so that the resonance frequency approaches a desired value based on the generated velocity signal. Further, the control unit 88 may include arithmetic processing devices and storage devices such as a CPU, a ROM, and a RAM as necessary.

[0035] As described above, in the LiDAR 10 according to the present embodiment, in a normal operation of driving the scanning actuator 32, the vibration caused by the resonance generated in the beam spring 80 is detected by the accelerometer, and the adjustment actuator 84 is driven by the control signal calculated based on the acceleration signal, so that the resonance frequency of the beam spring 80 is adjusted and the scanning accuracy of the LiDAR 10 is improved.

[0036] Note that the beam spring according to the present embodiment may be driven by feedforward control based on a control signal calculated based on the acceleration signal acquired from the accelerometer 82. Thereby, even when the initial beam spring deviates from the desired resonance frequency due to a mass error or a shape tolerance and resonates, the scanning accuracy by the scanning unit can be improved by the feedforward control.

[0037] As described above, the present invention has been described with reference to the above-described embodiments. However, the present invention is not limited to the above-described embodiments, and the present invention also includes combinations and replacements of the configurations of the respective embodiments as appropriate. Further, it is possible to appropriately rearrange the combinations and processing orders in each embodiment based on the knowledge of those skilled in the art, and to add various design changes and other modifications to the embodiments. Embodiments to which such modifications are added may also be included in the scope of the present invention.

Industrial Applicability

[0038] The present invention can be used for monitoring sensors.

Explanation of Signs

[0039] 10 LiDAR, 12 sensor unit, 16 light emitting unit, 18 scanning unit, 20 light receiving unit, 22 light emitting lens, 24 light receiving lens, 26 lens holder, 28 base plate, 30 beam spring, 32 scanning actuator, 72 processed area, 74 hole, 76 processed area, 78 metal piece, 80 beam spring, 80a plate portion, 84 adjustment actuator, 86 resonance adjustment unit, 88 control unit, 90 charge amplifier, 92 control signal generation unit.

Claims

1. A light-emitting unit, a scanning unit configured to periodically scan the periphery with the emitted light emitted from the light-emitting unit, and a light-receiving unit that receives the reflected light that is the emitted light reflected by the periphery, and the scanning unit includes an optical member that refracts or reflects the emitted light and the reflected light, a beam spring that supports the optical member, and an actuator that displaces the beam spring, the beam spring has a machinable region that can be laser-processed to reduce the mass of the material constituting the displaced portion of the beam spring, the machinable region is a thin-walled portion with holes formed by the laser processing, and is a monitoring sensor.

2. A light-emitting unit, a scanning unit configured to periodically scan the periphery with the emitted light emitted from the light-emitting unit, and a light-receiving unit that receives the reflected light that is the emitted light reflected by the periphery, and the scanning unit includes an optical member that refracts or reflects the emitted light and the reflected light, a beam spring that supports the optical member, and an actuator that displaces the beam spring, and includes an adjustment step of adjusting the monitoring sensor, the adjustment step includes a laser processing step for reducing the mass of the material constituting the displaced portion of the beam spring, the laser processing step is a step of making holes in the beam spring, and is a method for adjusting the monitoring sensor.

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