JPH0483156A - Vibration measuring device for sheet material - Google Patents

Abstract

PURPOSE:To precisely know the whole characteristic of a sheet by emitting a receiving laser beam to a sheet material, and measuring a Doppler shift received by the laser beam. CONSTITUTION:A signal as outputting a pulse is outputted to a laser body 19 from a power source 17, and the time t1 of this time is also inputted to a time measuring device 20. The laser pulse from the body 19 vibrates a sheet 16 in a point A, this vibration propagates in the sheet and reaches a point B, and gives a Doppler shift to laser beams 7-9 radiating the point B. The Doppler shift is converted to an electric signal by a converter device 3, and the time t2 of this time is inputted. In this case, when the time of the vibration propagating in the sheet 16 is compared with the time until the vibration reaches the point B to give the Doppler shift to the laser, and this signal is inputted to the device 20, the time of the vibration propagating in the sheet 16 is far late, so that t2-t1 can be regarded as the propagation time of the vibration propagating in the sheet.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention vibrates a sheet-like object with pulsed laser light,
The present invention relates to a device for measuring vibrations of a sheet-like object by measuring the vibrations using a laser Doppler vibrometer.

<Conventional technology> Sheet-like objects such as paper and plastic films (hereinafter referred to as
It is well known that the elastic modulus of a sheet can be determined by propagating an ultrasonic pulse through the sheet (simply referred to as a sheet) and measuring its propagation speed. A pulse transmitting vibrator and a receiving vibrator are placed a certain distance apart, and the propagation speed of the vibrations is measured.

■Also. It is also known to non-contactly measure the vibration of a speaker's diaphragm using the laser Doppler effect.

<Problems to be Solved by the Invention> By the way, it is well known that when a piece of paper is vibrated, longitudinal waves are related to the tensile strength of the paper, and transverse waves are related to the tear strength of the paper. However, since the method (2) above does not directly measure the vibration of the paper, it is almost impossible to measure the vibration mode of the paper (the direction of vibration such as longitudinal waves, transverse waves, and temporal changes in vibration). Furthermore, method (2) only measures vibrations in the direction perpendicular to the surface of the paper cone, and is not intended to determine the general characteristics of the paper.

The present invention has been made to solve the problems of the prior art described above, and involves emitting a pulsed laser beam to a sheet-like object to vibrate the sheet, emitting a receiving laser beam to the sheet, and vibrating the sheet. Measures the Doppler shift received by the receiving laser beam and detects longitudinal and transverse waves.

Measure vibration modes (vibration directions) such as bending waves.

The purpose is to accurately know the general characteristics of paper.

Means for Solving the Problems> In order to solve the problems of the prior art described above, the present invention provides means for vibrating a sheet-like object by emitting an elliptical or laser beam at regular intervals, and a means for vibrating a sheet-like object by emitting laser light at regular intervals; The present invention is characterized by being equipped with a laser Doppler vibration measurement device that emits light, measures the Doppler shift that the laser light undergoes, and outputs the instantaneous velocity of vibration.

Effect> When a pulsed laser beam is emitted to a sheet-like object, the sheet-like object vibrates. By emitting laser light from any direction toward the sheet and measuring the Doppler shift, it is possible to determine the speed of propagation through the sheet and the direction of vibration, making it possible to comprehensively judge the characteristics of a single sheet. Become.

<Example> A vibration measuring device for a sheet-like object according to the present invention will be described below with reference to nine drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, ■ is the optical system of the laser Doppler device, which measures the Doppler shift of the laser using a laser light source, ultrasonic modulation, photodiode, etc. 2 is a lens for focusing the laser beam; 3 is a conversion device that electrically processes the Doppler shift of the laser and outputs an instantaneous vibration velocity; these 1, 2.3 are generally commercially available. 5 is an output laser beam, 10 is a mirror 7, 8.9 is a beam distributed by the mirror 10, and 7 is a beam that is incident on the sheet 16 from the lateral (X) direction at an angle of 02 via the mirror 12. 8 is a beam arranged to be incident from the longitudinal (Y) direction at an angle of θ through the mirror 13, and 9 is a beam which is also incident through the mirror 11 in the perpendicular (Z) direction to the sheet surface. This is a beam that is made to enter from. Note that the incident direction of the beam is not limited to the illustrated example, and by changing the position and angle of the mirror, the beam can be incident on the sheet 16 from any direction and at any angle. 19
is the laser main body, which is supported by a support device (not shown). Reference numeral 17 represents a power source for starting the laser main body 19 to output laser pulses, and reference numeral 20 represents a time measuring device having an oscilloscope, into which the outputs from the pulse power source 17 and the converter 3 are input.

In the above configuration, now from the 4IR source 17 the laser book #
A signal such as a pulse output is outputted to the time measuring device 19, and at the same time, the current time rWJtt is inputted to the time measuring device 20. The laser pulse from the laser body 19 vibrates the sheet 16 at point A.

This vibration propagates through the sheet and reaches point B, and the laser beam irradiating point B undergoes a Doppler shift due to this vibration. The Doppler shift is converted into an electrical signal by the converter 3, and the time t2 at that time is input. In this case, when comparing the time it takes for the vibration to propagate through the sheet 16 and the time it takes for the vibration to reach point B, the laser undergoes a Doppler shift, and the signal is input to the time measuring device 20, the vibration propagates through the sheet. Since time is much slower, t2t1 can be regarded as the propagation speed of the vibration propagating through the sheet.

Doppler shift occurs only in the direction of the laser beam, that is, for longitudinal waves, Doppler shift occurs only for light in the direction that passes through mirror 13, and for transverse waves, Doppler shift occurs only for light in the direction that passes through mirror 12. does not occur, and for waves perpendicular to the sheet surface, the Doppler shift is large in the direction of the laser beam passing through mirror 11, and small in the direction of passing through mirror 12.13. Therefore, the direction of vibration can be determined by examining which direction the Doppler shift is large.

Here, the vibration velocity Jf is VL (im wave), Vs (III
wave), and Vv (wave perpendicular to the sheet), the speed that gives a Doppler shift to the beam incident in the Y direction is VL
CO5θ, and that in the X direction is Vscosθ2+Z
In the direction vT roars.

FIG. 2 shows MD using copy paper as the measurement sheet in FIG. (Hachine direct
The waveform observation results of a laser Doppler velocimeter are shown in oscilloscope waveforms when vibrations propagating in the direction perpendicular to the paper surface are measured (in the direction of the fibers of the paper).

The output of the YAG laser is 120mJ, and the emission time is 500mJ.
nS, multimode, beam diameter 3mm.

The measurement range is 31.64xlO'm/5ec-V. In the figure, the voltage level a indicates the noise component when the laser is not emitted, and the level b indicates the level when vibration occurs due to laser irradiation.
Vibration occurs at point d after 0 μs.

In addition, vibrations caused by laser pulses include bending waves.

Longitudinal waves and transverse waves are also generated, and the longitudinal waves cause the laser on the receiving side to
The transverse wave can be measured by making it incident from the X direction at a predetermined angle θθ2.

Further, the laser beam diameter, the distance from the paper to the emission port, the distance from the laser emission position to the detection position, etc. shall be adjusted as appropriate depending on the paper quality.

Note that by changing the position of the measurement point, it is possible to measure the speed more accurately based on the change.

Furthermore, by changing the distance from the laser emission position to the detection position using the same paper, it is possible to measure wave attenuation from changes in the magnitude of the Doppler shift.

By the way, when the sheet is irradiated with laser light.

According to the applicant's experiments, although it depends on the thickness and type of the sheet, in the case of high-quality paper, 60% of the laser beam is reflected from the surface, and most of the remaining light is transmitted through the paper and absorbed by the sheet. Only about 2% of people do so. Even in newspapers, which tend to be easily absorbed by the Hindu religion, only about 10% of them are at most.

Therefore, in order to measure vibrations by applying sufficiently large vibrations to paper, a laser with high power is required. In that case,
This is uneconomical and poses a major safety problem.

FIG. 3 is a sectional view showing the effective use of laser light from the laser main body 19.

20 and 21 are the first parts arranged to sandwich the sheet 16 in a non-contact manner. a second concave reflector, and a first concave reflector 2
0 has a hole 22 formed above through which the laser beam enters.

According to the above configuration, the laser light incident through the hole 22 is reflected or transmitted in each direction by the sheet, but these lights are reflected by the spherical reflector 20, 21 and return to the sheet.

In this case, since the reflector is a spherical surface, this reflected light is focused on the position where the laser first struck. The light reflected here and the light further reflected or transmitted by the sheet perform the same operation. Therefore, the result is the same as if a laser with higher power was used for the sheet.

As a result, the power supply for the pulsed laser and the cooling device for the laser can be downsized, making it possible to downsize the entire device and making it easy to incorporate it into an analysis device.

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, a pulsed laser beam is emitted to a sheet-like object to vibrate the sheet, and a receiving laser beam is emitted to the sheet. Then, the Doppler shift received by the receiving laser beam is measured, and vibration modes (vibration directions) such as m-waves, transverse waves, and bending waves are detected.
Since the vibration direction and the temporal change in vibration can be measured without contact, the characteristics of the sheet can be judged comprehensively and accurately.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram showing one embodiment of the present invention. FIG. 2 is a diagram showing an example of a waveform generated by a laser, and FIG. 3 is a sectional view showing the effective use of the laser. 1... Laser Doppler device, 2... Lens, 3...
・Conversion device, 5, 7, 8.9...Laser light, 10.1
1゜12.13...Mirror 16...Sheet, 17.
...Laser pulse power supply, 19...Laser body, 20.
・・Time measurement L″-Chair leap diagram

Claims (1)

[Claims] means for emitting a laser beam at regular intervals to vibrate a sheet-like object; emitting a receiving laser beam to the sheet-like object and measuring the Doppler shift that the laser beam undergoes;
A vibration measuring device for a sheet-like object, characterized by being equipped with a laser Doppler vibration measuring device that outputs the instantaneous velocity of vibration.