WO2017122637A1 - Rangefinder and rangefinding method - Google Patents

Abstract

One configuration of a rangefinder according to the present disclosure is provided with an optical device (116), a light receiving unit (120), and a calculating unit (134). The optical device (116) outputs an output light. The output light is configured such that the oscillation frequency of the light emission amount periodically changes in response to a signal that has a periodically changing frequency. The light receiving unit (120) detects reflected light, which is the output light of the optical device (116) reflecting from a target object (10). The calculating unit (134) calculates the distance to the object (10) on the basis of the difference in frequency between the output light and the reflected light.

Description

Ranging device and ranging method Cross reference of related applications

This application claims the priority of Japanese Patent Application No. 2016-003526 filed in Japan on January 12, 2016, the entire disclosure of which is incorporated herein by reference.

The present disclosure relates to a distance measuring apparatus and a distance measuring method for measuring a distance by changing a light amount of an optical device.

Examples of the distance measuring device include an ultrasonic device, a millimeter wave device, and a laser light device. As the distance measurement method, there are a TOF (Time Of Flight) method, an FMCW (Frequency Modulated Continuous Wave) method, and the like. The TOF method is a method of measuring a distance by measuring a time until a transmitted signal is reflected by an object and returns. The FMCW method is a method for measuring a distance by measuring a frequency difference between a transmitted FM modulated signal wave and an FM modulated signal wave reflected back from an object. For example, Patent Document 1 describes an automobile radar device using the FMCW method.

Japanese Patent Laid-Open No. 11-271430

The distance measuring apparatus according to an embodiment of the present disclosure includes an optical device, a light receiving unit, and a calculation unit. The optical device outputs light whose frequency of vibration of light quantity changes according to a signal whose frequency changes. The light receiving unit detects reflected light that is reflected from the object by the output light of the optical device. The calculation unit calculates the distance to the object from the frequency difference between the output light and the reflected light. The optical device may be an LED. The optical device may be a car headlight.

The distance measuring method according to an embodiment of the present disclosure uses an optical device that outputs light having a fixed wavelength. In the distance measuring method, a signal whose frequency changes periodically is generated. The optical device outputs output light in which the frequency of vibration of the light amount changes according to the signal. The reflected light reflected from the object is detected by the output light of the optical device. The distance to the object is measured from the frequency difference between the output light and the reflected light.

It is a figure explaining the ranging apparatus and ranging method concerning this embodiment. It is a figure explaining the chirp signal which the signal generation part shown in Drawing 1 generates. It is a figure explaining the control signal which AMP shown in FIG. 1 outputs. It is a figure explaining the synthetic wave obtained by integration processing when a subject is near. It is a figure explaining the waveform after the Fourier-transform by the FFT process part shown in FIG. 1 when a target object is near. It is a figure which shows the waveform which expanded the zero vicinity of the waveform shown to FIG. 3B. It is a figure explaining the synthetic wave obtained by integration processing when a subject is far. It is a figure explaining the waveform after the Fourier-transform by the FFT process part shown in FIG. 1 when a target object is near. It is a figure which shows the waveform which expanded the zero vicinity of the waveform shown to FIG. 4B. It is a figure explaining the chirp signal which the signal generation part shown in Drawing 1 generates. It is a figure explaining the relationship between the distance to a target object, and a frequency difference.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating understanding, and do not limit the present disclosure unless otherwise specified. In the present specification and drawings, elements having substantially the same functions and configurations are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present disclosure are not illustrated. To do.

The present inventor has come up with the following problems from the viewpoint of the distance measuring device in the above-described conventional technology.

The ultrasonic device has a shorter distance measurement range than the millimeter wave device and the laser light device. The ultrasonic device has low ranging accuracy when the relative speed is high as compared with the millimeter wave device and the laser beam device. Ultrasonic devices have poor directivity compared to millimeter wave devices and laser light devices, and are not suitable for distance measurement in a minute region.

Millimeter wave devices are expensive because they handle high frequencies compared to ultrasonic devices and optical devices. Millimeter-wave devices have a higher degree of circuit design difficulty than ultrasonic devices and optical devices. Millimeter-wave devices have laws and regulations in each country depending on the frequency, and must be handled strictly.

Laser light device includes a semiconductor laser (laser diode: LD). The wavelength (frequency) of the LD is variable depending on the amount of control current. The LD can use the FMCW method as a ranging method. An LD is an excellent device, but is generally an expensive device. *

The present inventor has come to mind that the prior art has the following problems from the viewpoint of the ranging method.

The TOF (Time Of Flight) method measures the distance by measuring the time difference between the transmitted wave and the reflected wave. In the TOF method, an AD converter with a high sampling rate corresponding to the distance measurement accuracy is required. For example, in order to obtain an accuracy of 10 cm by the TOF method, an AD converter capable of sampling at 1.6 GHz or more is required. The upper limit sampling rate of a generally available AD converter is several hundred MHz. Some AD converters with sampling rates exceeding 1 GHz are produced only for special applications. The distance measuring accuracy of the distance measuring device of the TOF method is limited by the sampling rate of the AD converter.

The FMCW system is a system that measures the distance by measuring the frequency difference between the transmitted wave and the reflected wave. The FMCW method is capable of highly accurate distance measurement, and is used in various modules as a general distance measurement method. Since the FMCW method uses an FM modulated wave, a device that outputs a signal having a fixed frequency cannot be used.

LEDs (Light Emitting Diodes) are cheaper than millimeter wave devices and LDs. An LED has a longer reachable distance of emitted light than an ultrasonic device. LED does not have any national regulations on frequency. In the LED, the frequency of light emitted is fixed according to the characteristics of the element used. Devices that output at a fixed frequency cannot use the FMCW method.

FIG. 1 is a diagram illustrating a distance measuring device and a distance measuring method according to an example of a plurality of embodiments. The waveform graph shown in FIG. 1 is an image. Waveform graphs are described in detail in FIGS. FIG. 2 is a diagram for explaining the chirp signal.

The transmission system of the distance measuring apparatus 100 will be described. The signal generator 110 generates a chirp signal whose frequency changes periodically as shown in FIG. 2A. The chirp signal generated by the signal generator 110 is a digital signal. Similar to the FMCW system, this chirp signal is a signal whose frequency increases (up chirp) with time and then decreases with time (down chirp). FIG. 2A illustrates a chirp signal only when up-chirping. A DA converter (DAC; Digital-to-Analog-Converter) 112 converts a chirp signal, which is a digital signal, into an analog signal. The DAC 112 outputs an analog signal to an amplifier (AMP) 114. The AMP 114 amplifies the analog signal output from the DAC 112. The amplified analog signal becomes a control signal as shown in FIG. 2B. The control signal is a signal in which the frequency of current vibration changes periodically. In FIG. 2B, the vertical axis represents current and the horizontal axis represents time. The AMP 114 supplies this control signal to the LED 116 that is an example of an optical device.

In the optical device of the present disclosure, the frequency of the output light is fixed. Hereinafter, the light output from the optical device may be referred to as output light. The LED 116 is an example of an optical device. The LED 116 outputs light having a fixed wavelength. In other words, the LED 116 outputs light having a specific frequency. The amount of light emitted from the LED 116 changes according to the amount of current. The amount of light emitted from the LED 116 changes according to the change in the amount of current in the control signal. The light emitted from the LED 116 periodically changes in frequency in the oscillation of the light emission amount. The waveform of the output light corresponds to that obtained by replacing the vertical axis in FIG. The light output from the LED 116 becomes an amplitude-modulated wave whose light emission amount changes periodically. The object 10 reflects the output light emitted from the LED 116. Hereinafter, the output light reflected by the object 10 may be referred to as reflected light.

The receiving system of the distance measuring device 100 will be described. The distance measuring device 100 detects reflected light by the light receiving unit 120. The light receiving unit 120 includes, for example, a photodiode. The light receiving unit 120 emits a detection signal corresponding to the detected amount of reflected light. The detection signal is, for example, a signal whose voltage value or current amount changes according to the amount of light emission. The waveform of the detection signal changes in voltage value or current amount according to the change in the amount of reflected light to be detected. The reflected light received by the light receiving unit 120 is delayed in time from the output light by the propagation time required for reciprocal propagation to the object 10. The light receiving unit 120 outputs a detection signal having a waveform delayed from the output light by the propagation time to an AGC circuit (AGC; Automatic Gain Control) 122 at the next stage.

The AGC 122 automatically adjusts the gain according to the signal and controls the output level. The AGC 122 may adjust the output level to be constant. The AGC 122 amplifies the detection signal in accordance with a gain corresponding to the amount of light attenuated until the output light of the LED 116 is reflected by the object 10 and detected by the light receiving unit 120. An analog signal having a waveform delayed in time corresponding to the control signal shown in FIG. 2B is obtained.

The AD converter (ADC: Analog-to-Digital Converter) 124 converts the signal amplified by the AGC 122 into a digital signal. The ADC 124 outputs a digital signal having a waveform delayed in time corresponding to the chirp signal shown in FIG. 2A.

The mixer (MX) 126 performs digital integration processing on the digital signal output from the ADC 124 and the chirp signal generated by the signal generator 110. These two signals are chirp signals that increase or decrease in frequency. The frequency difference between the two signals changes due to the time delay from the chirp signal. The MX 126 outputs a signal mainly including a frequency component corresponding to a frequency difference between two digital signals. Hereinafter, the output signal from the MX 126 may be referred to as a synthesized wave.

The filter 128 removes a frequency component unnecessary for distance measurement, and outputs a signal to the FFT processing unit 132 at the next stage. The filter 128 can mainly remove high frequency. The FFT processing unit 132 performs Fourier transform on the output signal of the filter 128 and outputs the result to the calculation unit 134. In the Fourier-transformed waveform, a peak appears in the frequency component corresponding to the frequency difference. The computing unit 134 detects this peak and converts it into a distance from the distance measuring device 100 to the object 10. The computing unit 134 can calculate the distance to the object 10 from the frequency difference between the output light and the reflected light.

FIG. 3 is a diagram for explaining the case where the object is close (22.5 m). FIG. 3A is an example of a synthetic wave obtained by integration processing. FIG. 3B shows a waveform after Fourier transform by the FFT processing unit 132. FIG. 3C is a waveform obtained by enlarging the vicinity of zero of the waveform shown in FIG. 3B. FIG. 4 is a diagram for explaining a case where the object is far (90 m). FIG. 4A is an example of a composite wave obtained by integration processing. FIG. 4B shows a waveform after Fourier transform by the FFT processing unit 132. FIG. 4C is a waveform obtained by enlarging the vicinity of zero of the waveform shown in FIG. 4B.

The synthesized wave has a frequency difference according to the time delay between the output light and the reflected light. The beat component corresponding to the frequency difference is included as a low frequency component in the synthesized wave. As can be seen by comparing FIG. 3A and FIG. 4A, the frequency of the beat component is relatively low when the object is relatively close, and the frequency of the beat component is relatively high when the object is relatively far. Become. In the examples of FIGS. 3B and 3C, it can be seen that a signal peak is detected in the vicinity of 0.015 MHz. In the example of FIGS. 4B and 4C, a signal peak is detected in the vicinity of 0.06 MHz.

Explain the relationship between the distance to the object and the frequency difference. As shown in FIG. 5A, the type of the chirp signal generated by the signal generator 110 is a linear chirp signal. The frequency change is assumed to be 10 MHz / 100 μsec. In this case, as shown in FIG. 5B, the relationship between the distance to the object and the frequency difference is such that the frequency difference increases proportionally as the distance increases. That is, the frequency difference detected by the calculation unit 134 can be converted into a distance to the object 10.

As described above, the distance measuring device 100 uses the LED 116 that outputs light of a fixed wavelength to periodically change the frequency in the oscillation of the light emission amount. By doing so, a frequency difference (beat component) corresponding to the distance to the object is generated between the output light of the LED 116 and the reflected light from which the output light is reflected by the object. The distance measuring device 100 can perform highly accurate distance measurement equivalent to the FMCW method by converting this frequency difference into distance. The distance measuring device 100 can also obtain the relative velocity with respect to the object 10 by calculating the Doppler shift from the frequency difference between the up-chirp and the down-chirp.

Since the distance measuring device 100 does not need to change the frequency of light, the distance measuring device 100 can perform distance measurement with an accuracy equivalent to the FMCW method using an LED. Since the LED is used, the cost of the distance measuring device can be reduced.

When the above-mentioned distance measuring device is mounted on a vehicle, an optical device used for automobile lighting may be used for the distance measuring device. Automobile lights include headlights, reverse lights, vehicle width lights, tail lights, rear number lights, front fog lights, rear fog lights, rear under lights, daytime running lamps, side markers, and turning lamps. Increasingly, power-saving and highly durable LEDs are used for automobile lights. By performing the above-described control using such lighting LEDs, distance measurement can be performed without adding a distance measurement device. As the optical device, one or more of a plurality of types of lamps can be used. When a plurality of LED spheres are used for one lamp, some of the spheres may be controlled as described above. If the vibration of the light amount is made high speed, it becomes difficult for humans to perceive a change in the light amount of the lamps.

As mentioned above, although embodiment was described referring an accompanying drawing, it cannot be overemphasized that this indication is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present disclosure. Understood.

The present disclosure can be used as a distance measuring device and a distance measuring method for measuring a distance by changing a light amount of an optical device.

DESCRIPTION OF SYMBOLS 10 ... Object, 100 ... Distance measuring device, 110 ... Signal generation part, 112 ... DAC, 114 ... AMP, 116 ... LED, 120 ... Light receiving part, 122 ... AGC, 124 ... ADC, 126 ... MX, 128 ... Filter, 132... FFT processing unit, 134.

Claims (6)

1. An optical device that outputs light in which the frequency of vibration of the amount of light changes according to a signal whose frequency changes;
   A light receiving unit for detecting reflected light reflected from an object by the output light of the optical device;
   A distance measuring apparatus comprising: an arithmetic unit that calculates a distance to the object from a frequency difference between the output light and reflected light.
2. The distance measuring device according to claim 1, wherein the optical device includes an LED.
3. A signal generation unit for generating a signal whose frequency changes periodically;
   The distance measuring apparatus according to claim 1, wherein the optical device outputs light in which a frequency of vibration of light quantity periodically changes according to a signal of the signal generation unit.
4. The distance measuring device according to claim 1, wherein the type of the signal is a linear chirp signal.
5. 2. The distance measuring device according to claim 1, wherein the optical device is at least one of automobile lights.
6. In a distance measuring method using an optical device that outputs light of a fixed wavelength,
   Generating a signal whose frequency changes periodically;
   The optical device outputs light whose frequency of vibration of the amount of light changes according to the signal;
   Detecting the reflected light reflected from the object by the output light of the optical device;
   Measuring a distance from the frequency difference between the output light and the reflected light to the object.

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