JPH0585866B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION The present invention relates to a method and apparatus for measuring the loss coefficient of a string. As used herein, the term "string" refers to various types of fibers in the form of single wires, stranded wires, wire ropes, etc. stretched in the form of strings, various types of tapes (recording tapes, recording tapes, etc.), and the like. Conventional technology and its problems The recent competition to develop new materials has become a struggle for survival for companies, and in order to survive, companies must develop new materials with excellent properties, and in particular they are competing with each other to develop fibers that are stronger than steel. There is. In general, fibers and tapes are products themselves in the form of single wires, strands, or composite wire ropes, for example, when they are used for force transmission, and when fibers and tapes are used as fiber-reinforced composite materials FRP.
In some cases, it is commercialized as a product, but in any case, it has various properties that are superior to conventional fibers and tapes, etc.
A product with high added value is desired. In particular, when these components are incorporated as parts of devices that are designed to be lighter, thinner, and more compact, and also have high speed, high precision, and high reliability in response to recent technological innovations, they have a high vibration damping ability (i.e., a large loss coefficient). is required. However, to date, there has been no suitable method or apparatus for easily measuring the loss coefficients of these fibers, etc. over a wide frequency range and with high precision, and the need for data on loss coefficients is increasing. Here, conventional methods for measuring the loss coefficient of fibers, etc. are listed in the following table.

[Table] Among these conventional methods, methods (3) and (5), in which the loss coefficient is calculated from the resonance curve, have the disadvantage of large errors because it is difficult to accurately determine the bandwidth when the loss coefficient is small. . In addition, the above methods (2), (4) and
The problem with (5) is that the implementation device is complicated, and loss occurs due to the setup method, resulting in a loss coefficient that is larger than the actual one. Furthermore, the above method
(1) has the disadvantage that it can only measure low frequencies. SUMMARY OF THE INVENTION An object of the present invention is to provide a method and apparatus for measuring the loss coefficient of a string, which enables the measurement of the loss coefficient of a string easily, in a short period of time, with high precision, and over a wide frequency range. Means for Solving the Problems The object of the present invention is to make the string resonate in a non-contact manner by emitting sound waves at a resonant frequency from an electroacoustic transducer to a stretched string, and to generate a displacement amplitude of the string at the time of resonance. The maximum value of is measured by a non-contact displacement sensor at the antinode position of the resonance mode of the string, and after the resonance displacement amplitude maintains the maximum value constant, the sound wave emission is stopped, and the subsequent A method for measuring the loss coefficient of a string, characterized by determining the loss coefficient of the string from damped vibration behavior; an electroacoustic transducer installed so as to face the strings placed on the harp; a sound wave radiation area diaphragm device combined with the electroacoustic transducer so as to be directed toward the strings placed on the string; and a displacement of the strings. This is achieved by a string loss coefficient measuring device characterized by comprising a non-contact displacement sensor provided so as to face the measurement point. The electroacoustic transducer includes a speaker and the like, and the non-contact displacement sensor may be an eddy current type, an optical type, or the like, as appropriate. According to the present invention, the string is vibrated at approximately one point (the antinode position of the resonance mode) by non-contact vibration using an electroacoustic transducer.
Since the displacement amplitude of the string is also detected at a single point without contact by a non-contact displacement sensor, the resonance displacement amplitude of the string in a constant state before the sound wave emission is stopped is approximately the same on the plus and minus sides. Similarly, the envelope of the time waveform after the sound wave emission is stopped in this state has virtually the same shape on both the positive and negative sides, and this is expressed in a level ( ^dB converted value of string displacement) one-time diagram. An ideal attenuation straight line is obtained, and the slope of the straight line, that is, the amount of attenuation per unit time (d _B ) is defined as the attenuation degree D using the well-known formula D27.3o.
The loss coefficient η can be determined from η (o: resonant frequency). The method and apparatus of the present invention can also be applied to loss coefficient measurement of higher-order resonance modes by setting the measurement point on the string at one of the antinode positions. The measurable frequency range depends on the frequency characteristics of the electroacoustic transducer and the mass, elasticity, length, tensile strength, tension, etc. of the string, but is approximately 20Hz~
Approximately 5KHz. Embodiment Hereinafter, an embodiment of the method of the present invention will be described with reference to the drawings together with an example of the apparatus of the present invention. First, string 1, whose loss coefficient is to be measured, is placed between a pair of strings 2 and 3, which have a small contact area between the friction coefficient and the strings.
Stretch it between. One of the harp pillars 2 is attached to a harp pillar support block 6, and the other harp pillar 3 is attached to a harp pillar support block 7. The block 6 is erected on a base 8, and the block 7 is erected on a slide 9. The slide 9 is slidably attached to the base 8 and can be fixed at a suitable position with fixing means (not shown).
In the illustrated device, the relative distance between the pair of harp pillars 2 and 3 is adjusted by sliding the slide base 9. To string the strings 1 onto the pair of strings 2 and 3, one end of the strings 1 is fixed to the stopper 4 on the fixed frame 10 erected on the base 8 at a position outside the block 6, and then
Fixed frame 1 erected on slide stand 9 at the outer position of
This is done by fixing the other end of the string to the stopper 5 on top of the string. The fixed frame 10 has an arc shape with the contact point between the strings 1 and the harp post 2 as the center of the circle, and the stopper 4 is connected to the frame 10 via the fixing member 11. The metal fitting 11 can be moved along the arc on the frame 10 and fixed at an appropriate position. Further, the fixed frame 15 has an arc shape with the contact point between the string 1 and the harp post 3 as the center of the circle, and the stopper 5
is connected to the frame 15 via the load sensor 12, the connecting fitting 14, and the tension load section 13 in this order. The load sensor 12 may be a mechanical load cell such as a spring balance, or a load cell such as an electric load cell using a strain gauge or the like. The tension loading section 13 can be slid on the fixed frame 15 along its arc and fixed at an appropriate position. For the tension load section 13, a string winding and tensioning device used in various stringed instruments or other suitable means may be used. The tensioning of the string 1 will be explained in more detail as follows. In the initial state in which both ends of the string 1 are first fixed to the stoppers 4 and 5, the string 1 is arranged so as to lightly touch the strings 2 and 3 and stretched in a substantially horizontal state. Next, while looking at the load sensor 12, the string 1 is
Apply a predetermined tension to the Furthermore, the fixing metal fitting 11 is slid on the fixing frame 10 from approximately the same horizontal position as the string 1 to a certain angle, and then fixed. Similarly, the tension loading section 13 is slid on the fixed frame 15 from approximately the same horizontal position as the string 1 to a certain angle, and then fixed. Thus, the tension of the string 1 between the harp pillars will be the same as the reading of the load sensor 12. A speaker 16 is placed between the harp pillars 2 and 3 as an electroacoustic transducer, and placed on a base 8 with a cushioning material 17 such as a rubber sheet interposed therebetween as required. Further, the electroacoustic transducer 16 is provided with a diaphragm device 18 that narrows down the radiation area of the sound wave in order to increase the excitation force when forcing the string to vibrate, and to bring the vibration closer to one point. In this case, the speaker 16
By adjusting the installation position of the diaphragm device 18
intersects the central axis of string 1 at the antinode of its resonance mode. Further, an eddy current type non-contact displacement sensor 20 is arranged facing the intersection 19 of the central axis and the string 1 as a displacement measurement point. Note that if string 1 is a non-conductor, measurement point 19
Provide a conductor by pasting aluminum foil on the Next, pluck the stretched string 1 with your fingernail, and the displacement sensor 2
Catch the vibration displacement of the string at 0, amplify the sensor output with amplifier A1, and then use the spectrum analyzer.
Analyze the frequency with SA and display it on the CRT to find the resonant frequency. Once the resonant frequency is known in this way, the oscillator OS connected to the speaker 16 via the amplifier A2
Set the frequency to be Δ (frequency resolution when Fourier analysis is performed with a spectrum analyzer) lower than the obtained resonance frequency, emit a sound wave from the speaker 16, excite the string 1, and measure the displacement amplitude at this time. While looking at the output level of the recorder LR (the value obtained by converting the string displacement into _dB ), gradually increase the oscillator frequency and search for the frequency at which the output level becomes maximum. Note that the time waveform of the displacement amplitude or the power level may be used instead of the output level of the level recorder. The frequency at which the output level of the level recorder LR becomes maximum is the resonance frequency, and when the maximum value is maintained at a constant state CS as shown in Figure 3, the recording paper of the level recorder LR is fed at a constant speed, and the oscillator Turn off the OS to stop sound wave emission. After that, record the damping behavior of string 1 on the recording paper as shown by line L in Figure 3,
The loss coefficient of the string is determined from this attenuation curve L. The constant state displacement of the measurement point 19 on the string 1 before stopping the sound wave emission is approximately equal on the plus side and the minus side as shown in Figure 2, and when the sound wave emission is stopped in this state as described above, the time waveform changes. The envelope curve has the same shape on both the plus and minus sides, and the attenuation curve _L in FIG. (d _B /sec), the loss coefficient η of string 1 can be obtained from the following equation. D27.3oη (o: resonant frequency) The resonant frequency o is known by the frequency counter c connected to the oscillator OS. Also, once the resonant frequency o is known, the formula for calculating the resonant frequency of a string fixed at both ends (the following formula)
If necessary, the mass ρo per unit length of the stretched string can be calculated from

[C] (i=positive integer, l=chord length, T=tension) Note that BPF in FIG. 1 is a bandpass filter. The embodiment described above employs a non-contact sine wave excitation method, but in the contact-based impact excitation method (for example, by plucking the string with a fingernail), the time waveform of the damped vibration of the string is shown in Figure 4. As shown in Figure 5, the attenuation curve recorded by the level recorder is not the same on the plus side and the minus side, as shown in Figure 5.
Since it is not a straight line and there are multiple attenuation degrees, the correct loss coefficient cannot be determined. FIG. 6 shows another mode of tensioning the string 1,
In this case, a weight W is used. Effects of the Invention As described above, the present invention can be applied to strings made of various materials easily, in a short time, over a wide frequency range, and by a non-contact excitation method using an electroacoustic transducer. A method and method for measuring the loss coefficient of a string, in which the loss in the vibrating part is small due to vibration, and the loss coefficient can be measured with high precision, and also enables the measurement of the loss coefficient of higher-order resonance modes. A simple and easy-to-handle device can be provided.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an example of the apparatus of the present invention for carrying out the method of the present invention, Fig. 2 is a one-time diagram of string vibration displacement in the present invention, and Fig. 3 is a level corresponding to Fig. 2.
d _B one-hour diagram, Figure 4 is a one-hour diagram of string vibration displacement when using the contact impact excitation method, Figure 5 is a level d _B one-time diagram corresponding to Figure 4, and Figure 6 The figure is a schematic diagram showing another example of string installation. 1... Strings, 2, 3... Harp pillar, 16... Speaker (electroacoustic transducer), 18... Aperture device, 20...
Non-contact displacement sensor.

Claims (1)

[Claims] 1. A sound wave at a resonant frequency is emitted from an electroacoustic transducer to a stretched string to cause the string to resonate without contact, and the maximum value of the displacement amplitude of the string at the time of resonance is determined as the resonance of the string. Measurement is performed using a non-contact displacement sensor at the antinode position of the mode, and after the resonance displacement amplitude maintains the maximum value constant, the sound wave emission is stopped, and the loss of the string is determined from the subsequent damped vibration behavior of the string. A method for measuring a loss coefficient of a string, characterized by determining a coefficient. 2. A pair of harp pillars for which the relative distance for stringing strings can be adjusted; an electroacoustic transducer installed so as to face the strings strung between the harp pillars; A string loss characterized by comprising: a sound wave radiation area diaphragm device combined with the electroacoustic transducer such that the electroacoustic transducer has a non-contact type displacement sensor disposed to face a string displacement measurement point; Coefficient measuring device.