JPH05323030A - Frequency detector, frequency followup method and doppler speedometer using the same - Google Patents

Abstract

PURPOSE:To equalize an input signal frequency and a BPF center frequency easily and quickly by arranging two band pass filters (BPF), a center frequency changing means and a detection means. CONSTITUTION:Input signal S is amplified 101 and inputted into a filter 102 for signals, a high frequency side BPF filter 104 and a low frequency side BPF 105. The signal via the BPF 102 is outputted as short wave signal with a waveform shaping device 103 to calculate the speed of an object to be measured with an external calculator. Signal via the BPFs 104 and 105 are converted into signals SF1 and SF2 with level detectors 106 and 107. With a level comparator 108, when ¦SF1-SF2¦ < set value N, the center frequency of the BPF 102 is regarded as coinciding with a signal S and when ¦SF1-SF2¦>N, it is regarded as deviated therefrom. The level comparator 109 performs a comparison in SF1-SF2<0. A control section 110 increases or decreases the center frequency of the BPFs 102, 104 and 105 simultaneously so as to correct the frequency deviation by information of the comparator 108 and 105 so that the center frequency of the BPF 102 coincides with the frequency of the signal S.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency detector for detecting the relationship between the frequency of an input signal and the center frequency of a band pass filter, and a method for making the center frequency of a band pass filter follow the frequency of an input signal. Regarding The present invention relates to a bandpass filter (in a signal processing of a speedometer for converting the speed of a moving object into a frequency of an electric signal to measure the speed, particularly a laser Doppler speedometer (hereinafter abbreviated as LDV) using a laser beam). (Hereinafter abbreviated as BPF), the present invention can be suitably applied to automatic center frequency tracking with respect to an input signal. At the same time, the present invention relates to a Doppler velocimeter using the same.

[0002]

2. Description of the Related Art In LDV signal processing, signal S /
Since N is bad, it is necessary to cut the noise of the signal through the BPF. However, since the frequency of the input signal changes according to the speed of the moving object, it is assumed that the center frequency of the internal BPF must be changed in accordance with the large change in the speed of the moving object. In order to automatically track the center frequency of the BPF, the center frequency of the BPF is swung from a low frequency to a high frequency or from a high frequency to a low frequency while inputting while searching for the best signal. The center frequency was adjusted to the signal.

[0003]

[Problems to be Solved by the Invention] However, B
In the search method in which the center frequency of the PF is changed from a low frequency to a high frequency or from a high frequency to a low frequency, it takes time to match the frequency of the input signal with the center frequency of the BPF. Further, it is more difficult to search and match the frequencies because it is difficult to distinguish a good signal when the level fluctuation of the input signal is large.

In view of the above-mentioned drawbacks of the conventional example, the present invention makes it possible to match the input signal frequency and the BPF center frequency easily and quickly without any problem even if a large level fluctuation of the input signal is met. An object is to provide a frequency detection device, a frequency tracking method, and a Doppler velocimeter using the same.

[0005]

In order to achieve the above-mentioned object, in the frequency detecting device of the present invention, at least two band pass filters, to which the detected signals are respectively input, with their center frequencies slightly shifted, Two bands
Center frequency changing means for simultaneously changing the respective center frequencies of the pass filters while maintaining a predetermined relationship,
Comparing the outputs of the two band pass filters while the frequency is changing by the frequency changing means, it is confirmed that the center frequency of the two band pass filters and the frequency of the signal have reached a predetermined relationship. And a detection means for detecting.

In the frequency tracking method of the present invention, the center frequency of the band pass filter for the signal is changed according to the frequency of the input signal, and the band pass filter for the signal is the center frequency. The input signal is input to one or more detection band pass filters, and one of the one or more detection band pass filters and the signal band pass filter is input. Detecting a frequency shift from the input signal by comparing at least two outputs of the one or more band pass filters for detection and the band pass filter for signals. By simultaneously changing the respective center frequencies in a predetermined relationship, the center frequency of the band pass filter for the signal is changed according to the frequency of the input signal. And in the manner to be of.

In the frequency tracking method of the present invention, the center frequency of the band pass filter for the signal is changed according to the frequency of the input signal, and the band pass filter for the signal is the center frequency. The input signal is input to at least two band pass filters for detection that are shifted to high and low, and the two detection band pass filters are set so that the output levels of the two band pass filters for detection are substantially equal to each other. By simultaneously changing the center frequencies of the band pass filter and the signal band pass filter in a predetermined relationship, the center frequency of the signal band pass filter is adjusted to the frequency of the input signal. I am trying to change it.

Further, in the Doppler velocimeter of the present invention, first detecting means for detecting the light from the object to be inspected which is irradiated with the velocity measuring light beam and generating the Doppler signal according to the speed of the object to be inspected, A signal band-pass filter for filtering the Doppler signal, and one or a plurality of detection band-filters to which the input signal is input and the signal band-pass filter is shifted in center frequency.
A pass filter and the one or more detection bands
Second detection means for detecting a frequency shift from the input signal by comparing output signals from at least two of the pass filter and the signal band pass filter, and the detection of the second detection means Depending on the result, the center frequency of each of the one or more detection band pass filters and the signal band pass filter is simultaneously changed in a predetermined relationship to simultaneously change the band pass filter for the signal. Center frequency changing means for changing the center frequency of the filter according to the frequency of the input signal, and an output unit for generating an output signal according to the speed of the object to be inspected by the output of the signal band pass filter are provided. ing.

[0009]

Embodiments will be described below with reference to the drawings.

FIG. 1 is a schematic view of an essential part of an optical system of a laser Doppler velocimeter according to an embodiment of the present invention. In the figure, 1A is a laser Doppler speedometer main body. Reference numeral 1 is a laser diode, 2 is a collimator lens, 7 is an object to be measured, and 10 is a diffraction grating. 21 has a curvature of 15.57.
mm biconvex lens with a thickness of 3.6 mm, 22a and 22b are plano-convex lens groups with a curvature of 15.57 mm and a thickness of 5.6 mm, and the focal lengths f of the biconvex lens and the plano-convex lens group are both about 15 mm.
Is. The distances a and b satisfy the relationship of a + b = 2f. The distance a is set to about 10 mm in order to increase the working distance b, and the working distance b is set to about 20 mm. Reference numeral 8 is a condenser lens, and 9 is a photodetector. Further, 7a is the velocity measuring direction of the object to be measured.

The laser beam 3 generated from the laser diode 1 is strictly collimated by the collimator lens 2. The laser beam from the laser diode 1 having a wavelength λ of about 0.68 μm becomes a parallel light beam 3 having a diameter of 1.2 mmφ by the collimator lens 2 and is incident perpendicularly to the grating arrangement direction of the transmission type diffraction grating 10 having a grating pitch of 3.2 μm. Then, the ± 1st-order diffracted lights 5a and 5b are reflected at the diffraction angle θ = 12.
Emitted at °. When the light beams 5a and 5b enter the biconvex lens 21 having the focal length f, the light beams 13a and 13b as shown in the figure are obtained. When the light beams 13a and 13b are incident on the plano-convex lens groups 22a and 22b that are separated by 2f, the parallel light beams 14a and 14 are again generated.
b is obtained, and the measured object 7 is irradiated with a spot diameter of 1.2 mmφ at an angle equal to the diffraction angle θ from the diffraction grating. The plano-convex lens group 22
a, 22b and the condensing lens 8 make the photodetector 9 efficient
The photodetector 9 outputs the output signal S containing the Doppler signal shown in the equation (1).

F = 2V / d (1) If the wavelength λ of the laser diode 1 changes, θ changes corresponding to dsin θ = λ, but the Doppler signal does not change. Further, in this device, the position of the two-beam spot can be fixed. That is, DUT 7
1 is set to the arrangement shown in FIG. 1, since the positions of the two light flux spots do not move on the object to be measured, the positional deviation between the spots does not occur and the proper crossing state is always maintained.

Further, since a <b, b becomes relatively long, the working distance can be increased, and the degree of freedom in installing the speedometer is increased.

FIG. 2 shows a block diagram of the configuration of the signal processing unit of this apparatus.

In FIG. 2, an input signal S in which the velocity of a moving object is converted into an electrical frequency is passed through an amplifier 101, a signal BPF 102 (center frequency F0), a high frequency side BPF 104 (center frequency F1), and a low frequency. BP on the side
Input to three filters of F105 (center frequency F2) (where F1 / F0 = F0 / F2 is set). The signal that has passed through the signal BPF 102 is processed by the waveform shaper 103 and output as a rectangular wave signal. This output signal is sent to an external calculator (not shown), where the speed of the DUT 7 is calculated. BPF104 and BPF10
The signals passed through 5 are level detectors 106 and 107, respectively.
Entered in. A signal S _F1 , which passes through the level detectors 106 and 107 and indicates the level (amplitude value) of each input signal,
S _F2 and the level comparator 108 outputs | S _F1 −S _F2
| <N is compared. A signal indicating the result of this comparison is output to the control unit 110. Signals S _F1 and S _F2
If the absolute value of the level difference is less than the preset allowable value N, it can be considered that the center frequency of the signal BPF 102 matches the input signal S, and if it is greater than N, it can be considered that there is a deviation. Next, in the level comparator 109, S
_F1- S _F2 <0 is compared. A signal indicating this result is output to the control unit 110. S _F2 rather than S _F1
Is larger than the input signal S, the signal BPF 102
The center frequency of is shifted to the high frequency side with respect to the frequency of the signal S, and if S _F1 is larger than S _F2 , then the signal BPF1
The center frequency of 02 is shifted to the low frequency side with respect to the frequency of the signal S. Therefore, the level comparators 108, 1
From the information from 09, the control unit 110 waits until the frequency match is recognized in the direction of correcting the frequency shift.
The center frequencies of the two BPFs 102, 104 and 105 are simultaneously UP or DOWN to follow the frequencies. This allows the center frequency of the BPF 102 to always match the frequency of the signal S. Here, the frequency change is such that, for example, the ratio of the center frequencies of the three BPFs 102, 104, 105 to each other always changes while maintaining a preset value.

A method of detecting the frequency shift will be described with reference to FIG. FIG. 3 shows three BPFs 102 and 10.
4, 105 pass frequency characteristics (CF0, CF respectively)
1, CF2), where the horizontal axis represents frequency (logarithmic display) and the vertical axis represents the relative value of the output level of the passing signal. In the filter whose center frequency is set as shown in FIG. 3, the input signal S (frequency F0
And S0 are the same), the levels of CF1 and CF2 are equal, so | S _F1 −S _F2 | is almost 0.
Therefore, the level comparator 108 outputs that | S _F1 −S _F2 | is smaller than N. When the signal S is on the low frequency side like the frequency S1, the levels of CF1 and CF2 are largely deviated, and CF2 is always CF.
Since it is greater than 1, the value of | S _F1 −S _F2 | exceeds the appropriately set value N, and the value of S _F1 −S _F2 becomes less than 0. Therefore, from the level comparator 108, | S _F1 −S _F2 |
When a signal that S is greater than N is output and a signal that S _F1 −S _F2 is less than 0 is output from the level comparator 109, the center frequency F0 of the BPF 102 is deviated to the high frequency side with respect to the signal S. I understand. Conversely, when the signal S is on the high frequency side like the frequency S2, CF1 and CF
The level of 2 is greatly deviated, and CF1 is CF
Must be greater than 2. Therefore, when the level comparator 108 outputs a signal that | S _F1 −S _F2 | is greater than N and the level comparator 109 outputs a signal that S _F1 −S _F2 is greater than 0, the center frequency of the BPF 102 is It can be seen that F0 is shifted to the low frequency side with respect to the signal S.

FIG. 4 is a flow chart of control of the automatic frequency tracking system. In the level comparison of 121, it is compared whether or not the absolute value of the level difference between S _F1 and S _F2 is larger than a certain value N, and if it is not larger, the processing is ended as it is. Comparing the magnitude of the level of the S _F1 and S _F2 proceeds to the 122 level comparison is greater than a value N, S _F1
If is small, proceed to 123 and DOWN the center frequency to 1
Return to 21. If S _F2 is small, the flow proceeds to 124, the center frequency is increased, and the flow returns to 121. This is repeated until the absolute value of the level difference between S _F1 and S _F2 becomes smaller than N. This control can be executed by software using a CPU or only by hardware using a logic circuit.

In the above embodiment, the BPFs 104 and 1 for detection are used.
Although the pair of center frequencies of 05 are provided on both sides in frequency with respect to the signal BPF 102, another BPF for detection may be provided further outside thereof. Hereinafter, such an embodiment will be described.

FIG. 5 is a block diagram showing the configuration of a signal processing unit according to another embodiment. The optical system portion and the like are the same as those in the above-described embodiment, and the same members as those in FIG. 2 are given the same reference numerals.
The difference from FIG. 2 is that members 111 to 116 are added. In the figure, 111 is a BPF having a center frequency on the higher frequency side of the BPF 104, and 112 is the BPF 105.
BPF with a center frequency on the lower frequency side than 11
Reference numerals 3 and 114 are level detectors for detecting the output level of the signal, and 115 and 116 are level comparators. A control method in the signal processing unit will be described with reference to FIG. 6 showing a control flowchart of the control unit 110. First 1
At 25, the output from the level comparator 115, here the output signal carrying the result of the comparison of whether the sum of the levels of S _F1 and S _F2 is greater than a predetermined value M, is received. If the level sum is larger than the predetermined value, BPF 104, 10
5, it is judged that the process can be performed according to the flow of FIG.
Proceed to step 121. Steps 121, 122, 123, 12
4 is the same as the above-mentioned embodiment. One value M
If it becomes smaller, it is judged that the processing is difficult with the flow of FIG.
At 6, the center frequency is adjusted by comparing the levels S _F3 and S _F4 of the outputs of the level detectors 113 and 114. That signal indicating whether the difference is less than S _F3 -S _F4 is 0 by the level comparator 116 is sent to the control unit 110 proceeds to 123 smaller than S _F3 -S _F4 is 0, the center frequency of each BPF DOWN To do. If S _F3 −S _F4 is greater than 0, proceed to 124, and set the center frequency of each BPF to U.
P. This is continued until the level sum of S _F1 and S _F2 becomes larger than the predetermined value M.

In addition, one BPF for detection, for example, BP
The level detector 107 may be configured to receive only the signal from the signal BPF instead of the F104, and control may be performed by comparing with the level of the signal BPF. In this case, when the signal frequency becomes lower than the center frequency of the BPF 102, the value of S _F1 −S _F2 becomes
It becomes a substantially constant negative value regardless of the value of the difference in the center frequency of the PF 102. Therefore, the level comparator 109 sets a value whose absolute value is a little smaller than the constant negative value (for example, L <0) as a comparison reference value that changes to 0, and outputs a signal indicating the comparison result indicating whether S _F1 −S _F2 <L. Is transmitted to the control unit 110. In addition, the level comparator 108 is | S _F1 −S _F2 −
The comparison result of whether L | <N may be transmitted to the control unit 110. The control unit controls the center frequency of the BPF as described above based on the comparison result. In this case, the signal frequency and the center frequency of the BPF 102 may not be completely matched in some cases, but in that case as well, it is possible to match the substantially matched frequencies.

[0021]

As described above, according to the present invention, the deviation of the center frequency of the input signal and the center frequency of the signal BPF and the direction of the deviation can be known at a time, and the frequency tracking can be speeded up.
Since the levels of the two filters are compared, it is possible to detect the frequency shift even when the signal level changes.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical system of a laser Doppler velocimeter according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a signal processing system of this embodiment.

FIG. 3 is an explanatory diagram of filter characteristics and frequency shift detection.

FIG. 4 is a flowchart of control of automatic frequency tracking.

FIG. 5 is a block diagram showing a signal processing system according to another embodiment of the present invention.

6 is a flowchart of control of automatic frequency tracking in the apparatus of FIG.

[Explanation of symbols]

101 Amplifier 102 Signal band pass filter 103 Waveform shaper 104 High frequency side control band pass filter 105 Low frequency side control band pass filter 106 Level detector 107 Level detector 108 Level comparator 109 Level comparator 110 Control unit

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Makoto Takamiya 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (4)

[Claims] 1. The signals to be detected are respectively input,
At least two band pass filters whose center frequencies are slightly shifted, center frequency changing means for simultaneously changing the center frequencies of the two band pass filters while maintaining a predetermined relationship, and the frequency changing means Detecting means for detecting that the center frequency of the two band pass filters and the frequency of the signal have reached a predetermined relationship by comparing the outputs of the two band pass filters while the frequency is changing. And a frequency detecting device. 2. A method for changing the center frequency of a band pass filter for a signal according to the frequency of an input signal, wherein one or a plurality of the band pass filters for the signal are shifted in center frequency. The input signal to a detection band pass filter and comparing at least two outputs of the one or more detection band pass filters and the signal band pass filter. By detecting the frequency deviation from the input signal by
While performing the detection, the center frequency of each of the one or more detection band pass filters and the signal band pass filter is simultaneously changed in a predetermined relationship to obtain the signal band pass filter. A frequency tracking method characterized in that the center frequency of a pass filter is changed according to the frequency of an input signal. 3. A method of changing the center frequency of a band pass filter for a signal in accordance with the frequency of an input signal, wherein the band pass filter for the signal is at least two in which the center frequency is shifted to high or low. The input signal is input to one detection band pass filter, and the two detection band pass filters and signals are input so that the output levels of the two detection band pass filters are substantially equal. The center frequencies of the band pass filters for signals are simultaneously changed in a predetermined relationship to change the center frequencies of the band pass filters for the signal in accordance with the frequency of the input signal. Frequency tracking method. 4. A first detecting means for detecting light from an object to be inspected, which is irradiated with a speed measurement light beam, and generating a Doppler signal according to the speed of the object to be inspected, and for filtering the Doppler signal. A signal band pass filter, the input signal being input and the signal band pass filter
The pass filter is one or a plurality of detection band pass filters whose center frequencies are shifted, and at least one of the one or a plurality of detection band pass filters and the signal band pass filter. Second detection means for detecting a frequency shift from the input signal by comparing output signals from two, and the one or a plurality of bandpasses for detection according to the detection result of the second detection means. A center frequency that changes the center frequency of the signal and the band pass filter for the signal simultaneously in a predetermined relationship to change the center frequency of the band pass filter for the signal according to the frequency of the input signal And a changing unit and an output unit for generating an output signal according to the speed of the object to be inspected by the output of the signal band pass filter. Doppler velocity meter and butterflies.