JPH0455270B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention utilizes the Doppler effect of light to measure the rotational speed and rotational unevenness of rotating bodies such as audio equipment, information equipment, machine tools, etc. It is related to measuring instruments.

[Conventional technology]

The rotational unevenness of audio equipment such as recorder players, tape recorders, and VTRs is an important factor that affects the sound quality and image quality during recording, recording, and playback. decide.

Therefore, in such fields, measurement of rotational speed and rotational unevenness has become indispensable for inspection of these devices.

Generally, rotational unevenness is expressed by an index called wow/flatter W/F shown in equation (1).

W/F=ΔV/V×100=Δf/f×100(%)……(1
) Here, V: Rotational speed (m/min) ΔV: Rotational unevenness speed (m/min); Frequency according to the rotational speed, Δ: Frequency modulation amount Equation (1) is the rotational unevenness speed ΔV with respect to the rotational speed V. It is expressed as a percentage of the ratio of , and is usually evaluated for rotational unevenness speed of 0.2Hz or more as a frequency component.

The rotational speed V (m/min) must be determined in the form of the number of revolutions per minute N (rpm), and the number of revolutions N
The relationship between (rpm) and rotational speed V (m/min) is shown by equation (2).

N=V/2πr...(2) Here, r: radius of rotation (m) Figure 2 shows a rotational unevenness measuring device that uses a conventional non-contact optical speed sensor to measure rotational unevenness of a rotating body. This is a configuration diagram, in which 1 is a motor or a rotating body that is directly connected to a motor, etc., 2 is a laser device, and 3 is a rotating body that is directly connected to a motor or the like and rotates.
is a beam splitter that splits the laser beam from the laser device 2 into two; 4a, 4b, and 4c are mirrors for changing the direction of the laser beam; 5 is a lens for receiving the light scattered from the rotating body 1; 6 is a photodetector that converts received light into an electrical signal, 7 is an AC amplifier,
8 is a frequency tracker, 9 is a frequency-voltage converter (hereinafter referred to as an F-V converter) that converts the output frequency of the frequency tracker 8 into an analog voltage proportional to this frequency, and 10 is the output of the frequency tracker 8 A frequency counter 11 counts the pulse frequency, and a divider 11 inputs the output voltage of the F-V converter 9 via a discriminator (not shown).

In the rotational unevenness measuring device having the above configuration, the laser beam emitted from the laser device 2 is split into two by the beam splitter 3, and one laser beam is split into two by the mirror 4.
In b and 4c, the other laser beam changes its direction with a mirror 4a and irradiates the rotating body 1 so as to intersect the radius of rotation r (m), so that the scattered light of the rotating body 1 corresponding to each irradiation beam is The wavelength undergoes a so-called Doppler shift depending on the rotation speed V (m/min) at the rotation radius r (m) of the rotating body 1.

When the scattered light that has undergone the two positive and negative Doppler shifts is focused by a lens 5, guided to a photodetector 6, and converted into an electrical signal, this electrical signal contains a DC signal proportional to the intensity of the received light, and a DC signal proportional to the intensity of the received light. AC signal with Doppler frequency fd shown in equation (3) (hereinafter referred to as Doppler signal)
exists.

fd=2V/λ・sinψ/2 ...(3) where V: Rotation speed of rotating body at rotation radius r (m) λ: Wavelength of laser light ψ: Crossing angle of two irradiation beams At photodetector 6 The Doppler signal converted into an electrical signal is weak and has a low S/N, so it is not connected to the AC amplifier 7.
When the S/N is improved by the frequency tracker 8, a Doppler frequency d proportional to the rotational speed V at the rotation radius r (m) of the rotating body 1 as shown in equation (3) can be detected as a pulse signal. The rotational unevenness speed ΔV in the rotational speed V is detected as the frequency modulation amount Δrd in the Doppler frequency fd of the frequency tracker 8.

When the output signal of the frequency tracker 8, which is this frequency modulation signal, is input to the F-V converter 9, the output of the F-V converter 9 is a DC voltage E proportional to the Doppler frequency d and the DC voltage E. It becomes an analog signal in which both AC voltage ΔE, which increases and decreases in proportion to the magnitude of rotational unevenness, are superimposed at the center. The output of the F-V converter 9 is discriminated into a DC voltage E and an AC voltage ΔE by a discriminator (not shown), and is input to a divider 11.

On the other hand, the output signal of the frequency tracker 8 is also connected to a frequency counter 10, and is connected to the Doppler frequency
d is displayed as a count so that it can be read directly.

The divider 11 divides the alternating current voltage ΔE discriminated by the discriminator by the direct current voltage E, thereby extracting the uneven rotational speed ΔV component in comparison with the rotational speed V as shown in equation (1). Therefore, the rotational unevenness speed ΔV of the rotating body 1 is expressed as
It can be obtained as a flutter W/F.

[Problem that the invention seeks to solve]

The conventional rotational unevenness measuring device described above determines the rotational unevenness of the rotating body 1 as a frequency modulation component of the laser Doppler frequency d obtained by irradiating the rotating body 1 with a laser beam. However, the scattered light reflected from the rotating body 1 includes, in addition to the above-mentioned Doppler frequency d, a luminance modulation component corresponding to the rotational frequency that periodically changes every rotation depending on the surface condition of the rotating body 1.

Therefore, the Doppler signal becomes a signal subjected to brightness modulation having the above-mentioned rotation frequency, and is subjected to so-called amplitude modulation.

Now, the Doppler signal is ed(t)=A(t)Sin(2πfd・t)
Then, the amplitude A(t) is given by the following equation.

A(t)=A{1+ _∞ 〓 ⁿ⁼¹ m _o・COS (2πnf _n・t)} ……(4) Here, A: Amplitude m _o : Nth-order amplitude modulation rate _n : Rotation frequency n: Order Therefore, the Doppler signal ed(t) is: ed(t)=A(t)・Sin(2πfd・t)=A{1+ _∞ 〓 〓 ⁿ⁼¹ m _o・Cos(2πnf _n・t)}・Sin(2πf _d・t)……(5
) As is clear from the theory of amplitude modulation, Equation (5) is based on the sidewave component fd±
It has fm, fd±2fm, ..., fd±nfm, .... Therefore, in the conventional rotational unevenness measuring device, wave measurement components due to the amplitude modulation are included in the spectrum fm, 2fm, 3fm,... nfm position, and this pseudo rotational unevenness signal has the problem of acting as noise in a form superimposed on the original rotational unevenness signal, which is a frequency modulation signal of the Doppler frequency.

The present invention was made to solve this problem, and by eliminating the amplitude modulation of the Doppler signal, which is amplitude-modulated in accordance with the rotational frequency depending on the surface condition of the rotating body 1, the rotational unevenness signal is The purpose of this invention is to obtain a rotational unevenness measuring device that synchronizes the rotational frequency and removes noise.

[Means for solving problems]

The rotational unevenness measuring device according to the present invention is provided with a limit amplifier after the AC amplifier 7 to keep the amplitude of the Doppler signal constant.

[Effect]

In this invention, a limit amplifier is provided to suppress the amplitude of the Doppler signal, which is amplitude-modulated by reflected light that changes periodically with each rotation depending on the surface condition of the rotating body 1, to a constant level, thereby suppressing the rotational unevenness signal. Removes noise synchronized with the rotation frequency included in the rotation frequency.

〔Example〕

FIG. 1 is a block diagram of a rotational unevenness measuring device showing one embodiment of the present invention, and will be described below with reference to the drawings.

In the figure, 1 to 11 are the same as those in the conventional example, and 14 is a limit amplifier that makes the amplitude of the Doppler signal constant.

In the rotational unevenness measuring device having the above configuration, the Doppler signal that is the output signal of the AC amplifier 7 is a signal that has undergone amplitude modulation at the rotational frequency m of the rotating body 1, as shown in equation (5), doppler frequency
Wave measurement components fd±fm, fd±2fm, ... centered on d
..., fd±nfm, .... Here, AC amplifier 7
After that, by providing a limit amplifier 14 that keeps the amplitude of the Doppler signal constant, amplitude modulation of the Doppler signal is eliminated. Becomes a measuring instrument.

〔Effect of the invention〕

As described above, according to the present invention, by providing a limit amplifier that suppresses the amplitude of the Doppler signal to a constant value, amplitude modulation of the Doppler signal, which is subjected to amplitude modulation in accordance with the rotational frequency depending on the surface condition of the rotating body 1, is eliminated. It is possible to provide a rotational unevenness measuring device that removes noise synchronized with the rotational frequency included in the rotational unevenness signal.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a rotational unevenness measuring device showing an embodiment of the present invention, and FIG. 2 is a configuration diagram of a conventional rotational unevenness measuring device. In the figure, 19 is a limit amplifier. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A laser that outputs light of a specific wavelength, a beam splitter that splits the output beam of the laser into two, and a plurality of mirrors that receive the split laser beam and irradiate it onto a rotating body so as to cross each other;
a lens that receives the scattered light that has undergone a Doppler shift according to the speed of the rotating body for each of the two irradiation beams; a photodetector that electrically converts the scattered light that includes the Doppler signal received by the lens; an AC amplifier that amplifies the output of the photodetector; a frequency tracker that detects a Doppler frequency containing a frequency modulation component from the amplified signal; and a frequency tracker that detects the Doppler frequency that is the output signal of the frequency tracker in proportion to the Doppler frequency. a frequency-voltage converter that converts it into an analog voltage; a DC voltage proportional to the Doppler frequency output from the frequency-voltage converter; In the rotational unevenness measuring device, the rotational unevenness measuring device is equipped with a means for inputting a moving alternating current voltage and extracting the rotational unevenness speed of the rotating body in a ratio relation to the rotational speed, the output end of the alternating current amplifier and the input end of the frequency tracker. A rotational unevenness measuring device characterized by comprising a limit amplifier provided between the two doppler signals, which is amplified by the alternating current amplifier, and constants the amplitude of the Doppler signal which is amplitude-modulated by the surface condition of the rotating body.