JPH083529B2 - Speed detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a speed detection device, and more particularly to a speed detection device for a moving object having a high speed and a large speed change.

[Conventional technology]

Conventionally, a speed detection device that detects the speed of a moving object normally emits a microwave to a moving object and calculates the speed from the Doppler shift amount of the frequency of the reflected wave. However, since the microwave has a spread due to diffraction depending on the wavelength and the emission diameter after being emitted, the microwave is widely spread at a place a little away from the emission source, and is irradiated to objects other than the target object. Therefore, the received reflected wave is a combination of reflections from objects having different speeds, and accurate measurement cannot be performed on a small moving object. Recently, in order to eliminate such a defect, a method has been used in which light as an electromagnetic wave having an extremely high frequency is used to reduce the spread due to diffraction and irradiate only a target object.

[Problems to be Solved by the Invention]

The conventional speed detection device using light described above has an advantage that the divergence angle is smaller than that of a device using microwaves and the like and that only the target can be irradiated, but it also has a disadvantage of half or less, which causes a change in speed. There is a drawback that it is difficult to detect the speed of a violent object.

That is, the frequency of the Doppler shift is obtained by multiplying the frequency of the wave by the ratio of the moving speed of the object and the speed of the wave (speed of light). Get higher Signal processing at such a high frequency is difficult, and although it has been put to practical use for low-speed moving objects, it is unsuitable for speed detection of high-speed moving objects.

On the other hand, in order to detect the velocity of a high-speed moving object, a method of modulating light (which can be handled by the frequency of the photodetector output in consideration of Doppler shift, that is, the modulation frequency) is also considered, but at present, There is an upper limit to the frequency of externally modulating light, and the amount of Doppler shift due to light modulated at this frequency becomes too small.In this case, it becomes difficult to detect the speed of an object at a slow speed, and therefore the speed is rapidly accelerated from a slow speed. It is not possible to detect the speed of a moving object every moment.

[Means for solving the problem]

The speed detecting device of the present invention includes a light source, an optical modulator that modulates the output light of the light source with a modulation signal to generate light modulated light, and sends the light modulated light to a moving object and reflects it. A transmitting / receiving optical system for receiving light, an optical detector for detecting reflected light received by the transmitting / receiving optical system, a sub-signal generator for outputting a sub-signal slightly different in frequency from the modulation signal, and the optical detection A mixer that mixes the output of the mixer and the output of the sub-signal generator to output a signal of the difference frequency, and measures the time between the zero-cross points of the output of the mixer with a clock pulse for measurement A pulse counter that outputs a count value that is a value for each of the zero-cross points, a reference signal generator that outputs the modulation signal and the measurement clock pulse, and the count value that the pulse counter outputs. For each zero-cross point While storing based on said count value to calculate the time between the zero-cross point formed by a storage circuit for obtaining a rate and velocity change of the moving object.

〔Example〕

 The present invention will now be described in detail with reference to the drawings.

FIG. 1 is a configuration diagram of an embodiment of the present invention. A light generating source 1 as a light source, an optical modulator 2 that modulates output light of the light generating source 1 with a modulation signal to generate light modulated light, A reference signal generator 3 for generating a modulated signal, a transmission / reception optical system 4 for transmitting the light-modulated light output from the light modulator 2 to a moving object 5 and receiving the reflected light, and a reflection received by the transmission / reception optical system 4. Photodetector 6 for detecting light, subsignal generator 8 for outputting a subsignal whose frequency is slightly different from that of the above-mentioned modulated signal, photodetector 6
Of the reference signal generator 3 together with the above-mentioned modulation signal, and the time between the zero-cross points of the mixer 7 and the output of the mixer 7 which mixes the output of the sub-signal generator 8 with the output of the sub-signal generator 8. A pulse counter 9 that measures with the output measurement clock pulse and outputs a count value that is the measured value for each of the zero cross points, and a measurement of the output of the mixer 7 counted by the pulse counter 9 for each zero cross point The memory circuit 10 is configured to store the count value of the clock pulse for use, calculate the time between the zero-cross points based on the count value, and obtain the speed and speed change of the moving object 5.

 Next, the operation of the embodiment shown in FIG. 1 will be described.

The light 101 emitted from the light source 1 is modulated by the sine wave modulation output signal 102 output from the reference signal generator 3, and emitted from the optical modulator 2 as amplitude-modulated light 103.

The amplitude-modulated light-modulated light 103 is emitted as output light 109 by the transmission / reception optical system 4 and hits the moving object 5 to be reflected. The reflected light 104, whose modulation frequency has changed due to the Doppler shift proportional to the velocity of the moving object 5 at the time of reflection, is received by the transmission / reception optical system 4, enters the photodetector 6, and is reflected by the modulation frequency of the reflected light 104. The detection signal 105 is output and input to the mixer 7.

The mixer 7 mixes the detection signal 105 with the sub-signal 106 from the sub-signal generator 8 which generates a signal 106 having a frequency difference of several KHz, which is slightly different from the reference signal generator 3, and calculates the difference between the two signals. The frequency difference frequency signal 107 is output.

The difference frequency signal 107 is thus the sub-signal 106- (modulation signal
The frequency is 102 + Doppler shift). However, in the present embodiment, the frequency of the sub-signal 106 is set to be higher than the frequency of the modulated signal 102, but the setting may be reversed, as a matter of course.

This difference frequency signal 107 is supplied to the pulse counter 9. This difference frequency signal is a sine wave signal of approximately several KHz, and the pulse counter 9 measures the time for each zero cross point of this difference frequency signal with the measurement clock pulse 108 obtained from the reference signal generator 3, The count value of the measurement clock pulse 108 obtained for each zero-cross point is supplied to the memory circuit 10.

2 (a) is an explanatory diagram of pulse counting between pulse points between zero cross points in the embodiment of FIG. 1, and FIG. 2 (b) is storage of pulse counting between zero cross points in the embodiment of FIG. It is explanatory drawing of a content.

As shown in FIG. 2 (a), in the present embodiment, the points t _m and t _{n at} which the difference frequency signal 107 cuts the zero line with a positive slope is used as a zero cross point, but this also applies to a negative slope. Of course, it does not matter if all the zero-cross points are used.

The time between the zero-cross points t _m and t _n is the measurement clock pulse.
You can easily tell from the count of 108.

The memory circuit 10 stores the pulse count value (count value) for each zero-cross point provided from the pulse counter 9, and determines the time for each zero-cross point based on this. The time between these zero-cross points is obviously the moving object 5
Changes according to the speed of, and changes corresponding to the change in speed. The storage circuit 10 also uses this relationship to calculate the velocity of the moving object 5 and the change in velocity for each zero-cross point.

In FIG. 2 (b), n1, n2 and n3 indicate the pulse measurement numbers between the zero cross points t _{0 to} t ₁ , t _{1 to} t ₂ and t _{2 to} t ₃ , respectively. The time between the zero cross points is the reciprocal of the instantaneous frequency of the difference frequency signal 107. This time is constant if the moving object 5 that reflects light is stationary, but if it is moving,
For example, the frequency of the difference frequency signal becomes lower (the time between the zero cross points becomes longer as the moving speed increases, and the pulse measurement number n increases). Change.

Although FIG. 2 (b) is exaggerated for the sake of clarity, it is not such a big change in reality. In the present embodiment, the time between the zero cross points is on the order of 0.1 millisecond, data corresponding to the instantaneous speed for each time between the zero cross points is stored in the storage circuit 10, and the moving object 5 whose speed changes drastically changes. Also, since the speed is measured every moment, it is also possible to obtain the position information every moment by further processing the data.

FIG. 3A is a characteristic diagram showing an example of the number of counting pulses in the memory circuit 10 of the embodiment of FIG. 1, and shows an example of the number of measuring pulses of a moving object at each zero-cross point.

Further, FIG. 3 (b) is a characteristic diagram of the calculated speed of the moving object obtained corresponding to the number of measured pulses in FIG. 3 (a), and FIG. 3 (c) is the calculated speed of FIG. 3 (b). It is a characteristic diagram of the position of the moving object obtained based on.

Next, this embodiment will be described with reference to specific numerical examples.

Now, the frequency of the modulation signal of the reference signal generator 3 is 100 MHz, the frequency of the sub signal of the sub signal generator 8 is 100.005 MHz, the speed of the moving object 5 is 1000 m / S, and the light speed is 300000 Km / S. −100000000 = 5000
Hz, and one cycle time = 200 μS.

When the moving object 5 speed is 1000m / S, the Doppler shift = 1000m / S ÷ 300000000m / S × 100000000Hz = 333.333333Hz The reflected wave modulation frequency when the speed is 1000m / S, when the speed of the moving object 5 is 1000m / S. Is 100000333.33333Hz Difference frequency = 100005000Hz-100000333.33333Hz = 4666.666666Hz One cycle time = 214.286μS 100MHz or 21428 or 21429 counts with 10nS clocks Difference from the count at speed 0 is 1428 or 1429 counts Consider resolution And at 2m / S, Doppler shift = 2m / S ÷ 300000000m / S × 100000000Hz = .66666Hz When the speed is 2m / S, the modulation frequency of the reflected wave is 100000000.66666Hz, the difference frequency = 100005000Hz-100000000.66666Hz = 4999.33333Hz 1 cycle Time = 200.0267 μS 100 MHz, that is, 20002 or 20003 counts with a clock every 10 nS, and it can be distinguished from the case of speed 0. That is, a resolution of 2 m / S can be obtained.

〔The invention's effect〕

As described above, the present invention does not directly measure the Doppler shift frequency due to reflection from a moving object, but a difference frequency that is easy to measure by using a side signal having an appropriate frequency difference and a reflected signal including Doppler shift. A signal is obtained, and at that time, the time between the zero cross points of the difference frequency signal is set to an optimum time according to the speed change of the moving object, and the time between all the zero cross points is stored as the count value of the pulses of the reference frequency. By doing so, there is an effect that it is possible to measure the speed change of a high-speed moving object moment by moment, accurately and faithfully corresponding to the speed change.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the speed detecting device of the present invention, FIG. 2 (a) is an explanatory view of pulse counting between zero cross points in the embodiment of FIG. 1, and FIG. 2 (b) is FIG. 3 is an explanatory diagram of stored contents of pulse count between zero cross points in the embodiment of FIG. 1, FIG. 3A is a characteristic diagram showing an example of the number of counted pulses in the memory circuit 10 of the embodiment of FIG. FIG. 3 (b) is a characteristic diagram of the calculated speed of the moving object obtained corresponding to the number of measured pulses in FIG. 3 (a), and FIG. 3 (c) is obtained based on the calculated speed of FIG. 3 (b). It is a characteristic view of the position of the moving object to be generated. 1 ... Light source, 2 ... Optical modulator, 3 ... Reference signal generator, 4 ... Transmission / reception optical system, 5 ... Moving object, 6 ... Photodetector, 7 ... Mixer, 8 ... ... Sub-signal generator, 9 ... Pulse counter, 10 ... Storage circuit, 101 ... Optical, 102 ... Modulated signal, 103 ... Optically modulated light, 104 ... Reflected light, 105 ... Detection signal, 106 …… Sub signal, 107 …… Difference frequency signal, 108 …… Measuring clock pulse, 109 …… Output light.

Claims (1)

[Claims] 1. A light generating source, an optical modulator that modulates the output light of the light generating source with a modulation signal to generate light modulated light, and the light modulated light is sent to a moving object and the reflected light is received. A transmitting / receiving optical system, an optical detector for detecting reflected light received by the transmitting / receiving optical system, a sub-signal generator for outputting a sub-signal slightly different in frequency from the modulated signal, and an output of the photo-detector Is a measurement value obtained by measuring the time between the mixer and the output of the sub-signal generator by outputting a signal of the difference frequency and the zero-cross point of the output of the mixer with a measurement clock pulse. A pulse counter that outputs a count value for each of the zero-cross points, a reference signal generator that outputs the modulation signal and the measurement clock pulse, and the count value output by the pulse counter between the zero-cross points. Remembering each Speed detecting apparatus characterized by based on the serial count value to calculate the time between the zero crossing point comprising a storage circuit for obtaining a rate and velocity change of the moving object.