JPH087262B2 - Doppler signal tuning method for measuring the moving speed and length of the DUT using the laser Doppler method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for tuning a Doppler signal generated on the basis of scattered light scattered by an object to be measured in measuring the moving speed and length of the object by a laser Doppler method. is there.

[0002]

2. Description of the Related Art The inventors of the present invention have previously developed the measurement of the moving speed and length of an object to be measured by the laser Doppler method. As shown in FIG. 1, the measuring principle is such that a laser light a from a laser light source 2 such as a He-Ne laser is divided into two by a beam splitter 11, and one of them is used as a laser light a. Mira-12
When the object to be measured (for example, a running body such as a rope) 1 is irradiated with the laser light a reflected by the object 1 at a crossing angle φ, the scattered light b scattered by the object to be measured 1 is generated by a condenser lens or the like. The sensor (photoelectric converter) 3 receives the light through the optical system 13 and the heterodyne detection is performed, and the sensor 3 outputs the electric signal A in which the Doppler signal d is superimposed on the pedestal signal B as shown in FIG. It is the one.

The Doppler frequency fD of this Doppler signal is expressed by the following equation. fD = 2v / λ sin φ / 2 · cos Δθ f _D : Doppler frequency v: moving speed of the measured object λ: laser wavelength (632.8 nm) φ: beam crossing angle Δθ: beam normal Deviation angle from right angle of DUT Since the Doppler frequency fD is proportional to the moving speed v of the DUT 1 as in the above equation, if the Doppler signal d is taken out and processed by the processing unit 4, Of course, the length of the DUT 1 can be measured by time-integrating the moving speed v.

The frequency of the Doppler signal d is 100 to 500 times the frequency of the pedestal signal B, depending on the scattering state of the surface of the DUT 1, and the level of the Doppler signal d is pedestal signal B. 1/1 level
It is 0 to 1/50. Further, as is clear from the above equation, the frequency of the Doppler signal d is proportional to the moving speed of the DUT 1.

In order to extract the Doppler signal d having the above characteristics from the electric signal A, conventionally, the Doppler signal d is tuned by a bandpass filter system or a PLL system.

The bandpass filter method includes a method of using one bandpass filter and a method of using two or more bandpass filters for different pass frequency bands. In the former method, the pass band of one band pass filter is changed from the low frequency band to the high frequency band of the electric signal A, the electric signal is passed in each band, and all the passed electric signals are scanned by the CPU. Then, the Doppler signal d is extracted by synchronizing with a signal whose frequency is equal to or higher than a predetermined frequency and whose level is maximum. The latter method
The electric signal A passed through each bandpass filter is sent to the CPU
The scanning is performed in order to obtain the Doppler signal d by synchronizing with a signal whose frequency is equal to or higher than a predetermined frequency and whose level is maximum.

In the PLL system, the Doppler signal d contained in the electric signal A is followed by a loop and synchronized with the Doppler signal d to take out the Doppler signal d.

[0008]

Among the tuning methods described above, the method using a bandpass filter has the following problems. ． Since it is not possible to find the maximum level electric signal without scanning all the electric signals that have passed through the band pass filter, it takes a long time to achieve tuning and the response speed is slow. ． Since the signal is tuned to the signal whose frequency is equal to or higher than the predetermined frequency and whose level is the maximum, when the frequency of the pedestal signal B is lower than the operating frequency band of the processing unit 4, the pedestal signal B is not tuned. When the moving speed of the device under test 1 increases and the frequency of the pedestal signal B also increases, and the frequency enters the operating frequency band of the processing unit 4, the pedestal signal B having a high level and a high frequency may be tuned. , Doppler signal d cannot be taken out.

[0009]. In order to solve the above-mentioned problems, conventionally, in anticipation that the frequency of the pedestal signal B increases in proportion to the moving speed of the DUT 1, a high-pass filter for removing the pedestal signal B of the increased frequency. Was put in the measuring section 4. However, this is preferable when the moving speed of the DUT 1 is fast, but when the moving speed sharply decreases and the frequency of the Doppler signal B also decreases, the Doppler signal B having the decreased frequency is also removed by the high-pass filter, A new problem occurs that the Doppler signal d cannot be tuned.

In the PLL system, since it takes time for the loop to reach a steady state in synchronization with the Doppler signal d, the response speed is slow.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a Doppler signal tuning method which has a fast response speed to a Doppler signal and can be tuned quickly.

[0012]

The present invention, as shown in FIG.
Laser light a is emitted from the laser light source 2 to the DUT 1, and scattered light b from the DUT 1 is received by the sensor 3,
The sensor 3 outputs an electric signal A as shown in FIG.
An object to be measured by a laser Doppler system in which a processing unit 4 extracts a Doppler signal d from the electric signal A, processes the Doppler signal d, and measures the moving speed, length, etc. of the object to be measured 1. In measuring the moving speed, length, etc., the electric signal A is passed through two or more band pass filters 5 having different pass frequency bands shown in FIG. 2, and the level of each electric signal A passing through each filter 5 is shown. The comparator 6 of No. 2 compares the electric signal A with the threshold value or more and outputs only the electric signal A with the threshold value or more, and the priority encoder 7 shown in FIG. The electrical signal A having the highest frequency is determined, and the electrical signal A having the same frequency as the determined electrical signal A is taken as the Doppler signal d from the electrical signals A that have passed through the band pass filter 5. In which was set to put out.

[0013]

In the present invention, the output levels of the individual electric signals A having different frequency bands that have passed through the two or more band pass filters 5 having different passing frequency bands are compared with the threshold value, and the electric signals having the threshold value or more are compared. Take out only A.

Next, in the priority encoder 7, the electric signal A having the highest frequency is judged from among the electric signals A above the threshold value. Therefore, the electric signal A judged here is the threshold value. The electric signal is at the above level and in the frequency band farthest from the frequency of the pedestal signal B.

Further, the electronic switching circuit 8 is switched by the control signal outputted from the priority encoder 7, and the electric signal A which has passed through the band pass filter 5 is judged by the priority encoder 7. Signal A
An electric signal A having the same frequency as is extracted as a Doppler signal d. Therefore, even if there is a pedestal signal B having a large level and a high frequency, or if there are two or more Doppler signals d having a predetermined level or more, regardless of the pedestal signal B, and two or more Doppler signals d. Among them, the Doppler signal d having a level equal to or higher than a predetermined threshold and having the highest frequency is reliably and quickly selected.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a principle diagram of a method for measuring the moving speed and length of an object to be measured by the laser Doppler method. In this measuring method, laser light a output from a laser light source 2 such as a semiconductor laser is applied to a DUT 1 through a beam splitter 11 and is branched by a beam splitter 11 to a mirror. The laser light a reflected by -12 is applied to the DUT 1 at a crossing angle φ.

The scattered light b scattered from the DUT 1 is shown in FIG.
As described above, the light is received by the sensor 3 through the condenser lens 10, and the electric signal A of FIG. 3 having a level corresponding to the light receiving level is output from the sensor 3. A Doppler signal d is superimposed on the pedestal signal B on the electric signal A. This electrical signal A
2 is amplified by the amplifier 9 of FIG. 2 and is input to the processing unit 4. The processing unit 4 extracts the Doppler signal d from the electric signal A, processes the Doppler signal d, and moves the moving speed v of the DUT 1. Or the object to be measured 1 based on this speed v
Or ask for the length of.

In order to tune and select the Doppler signal d from the electric signal A in the present invention, the electric signal A amplified by the amplifier 9 is passed through the band pass filters 5 having different pass frequency bands as shown in FIG. The electric signal A in the frequency band of is taken out. The individual electric signals A taken out are compared in the comparator 5 with a preset threshold value, and only the electric signal A having a higher level than the threshold value is outputted from the comparator 5.

The output electrical signal A is input to the priority encoder 7 to determine the input signal having the largest weight (the highest frequency in the present invention), and the priority encoder according to the determined electrical signal. The control signal e is output from the terminal 7.

This control signal e is input to the electronic switching circuit 8 of FIG. 2, and the switching circuit 8 is switched from each bandpass filter.
The electric signal A having the same frequency as that of the electric signal A determined by the priority encoder 7 among the electric signals A input to is output from the switching circuit 8 as a Doppler signal d.

[0021]

According to the present invention, when the Doppler signal d is taken out, it is not necessary to scan a large number of electric signals A having different frequency bands that have passed through the band pass filter 5 to search for a high level electric signal. , The response speed of tuning becomes faster, and the Doppler signal d can be selected quickly. By the way, in the past, it took 100m to get the tuning done.
Although it was about sec, according to the present invention, it is about 10 μsec. Moreover, since it is not necessary to insert a high-pass filter in the processing unit 4, the problem in the case where a high-pass filter is inserted is eliminated.

[Brief description of drawings]

FIG. 1 is a principle diagram of a method of measuring a moving speed, a length and the like of an object to be measured by a laser Doppler method.

FIG. 2 is an explanatory diagram showing an example of a tuning method of the present invention.

FIG. 3 is an explanatory diagram of a Doppler signal according to the present invention.

[Explanation of symbols]

 1 DUT 2 Laser light source 3 Sensor 4 Processing unit 5 Bandpass filter a Laser light b Scattered light d Doppler signal A Electrical signal

Claims (1)

[Claims] 1. A laser light a from a laser light source 2 to an object to be measured 1.
And the scattered light b from the DUT 1 is received by the sensor 3, the electric signal A is output from the sensor 3, and the processing unit 4 extracts the Doppler signal d from the electric signal A, When the Doppler signal d is processed to measure the moving speed, length, etc. of the DUT 1, the electric signal A is passed in the measurement of the moving speed, length, etc. of the DUT by the laser Doppler method. Passing through two or more band pass filters 5 having different frequency bands, comparing the level of each electric signal A passing through each filter 5 with a threshold value, outputting only the electric signal A above the threshold value, The electric signal A having the highest frequency among the electric signals A equal to or higher than the threshold value is determined and passed through the band pass filter 5.
A Doppler signal tuning method in measurement of speed, length, etc. by the laser Doppler method, wherein an electric signal having the same frequency as the judged electric signal A is taken out as a Doppler signal d from among the above.