JPH11218484A - Method and device for viscoelasticity measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately and highly stably measure the viscoelastic characteristics of a viscoelastic body by sampling a displacement signal and a load signal simultaneously at a sampling period and converting them to each digital signal, and then executing processing after the conversion by computer software. SOLUTION: The both terminal parts of an elastic body test piece 11 are chucked by an upper chuck 12 and a lower chuck 13, the upper chuck 12 is positioned at a position corresponding to a load zero point-setting value, and at the same time a vibration rod 22 is vibrated in a vertical direction with an amplitude corresponding to a displacement amplitude setting value with a displacement point position as a center and at the same time a rod signal and a displacement signal outputted from a load cell amplifier 31 and a linearizer 42 are converted to a digital signal at a specific sampling section by A/D converters 32 and 43 in synchronization with a synchronization signal from a sinusoidal wave oscillator 56. A phase difference angle is directly measured on a time axis by an operation control circuit 33 based on the output of the A/D converters 32 and 43. The measurement result is outputted to an outputting device 71.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the viscoelastic properties of a viscoelastic body, for example, a vulcanized rubber, by a non-resonant forced vibration method of a tensile vibration or bending vibration method.

[0002]

2. Description of the Related Art For example, in recent years, a variety of performances such as maneuverability, stability, vibration riding comfort, and low fuel consumption have been recently developed in automobile tires in addition to durability such as tire wear, fatigue and destruction. Has been requested. In order to achieve such performance as expected, it is necessary to measure the viscoelastic properties of the rubber material with high accuracy.

Therefore, conventionally, a viscoelasticity measuring device such as a spectrometer has been used, and a strip-shaped elastic test piece made of, for example, vulcanized rubber, generally having a width of 4 m
m, a thickness of 2 mm, a length of 40 mm of the test piece is gripped at both ends, and one end of the test piece is subjected to, for example, a sine wave-like deformation by pulling. At the same time, the stress is detected based on, for example, the output of the load cell, and the waveforms of the detected signals are processed to obtain a dynamic storage modulus (E ′), a dynamic loss modulus (E ″), and a loss coefficient (tan δ). I want to ask.

[0004] Here, E 'is an elastic modulus calculated from the component of the stress (sine wave) in phase with the strain and the strain when considering the strain (sine wave), and E "is , Is the elastic modulus calculated from the component and the strain whose phase is advanced by 90 ° from the stress strain, and tan δ represents the degree of the viscoelastic material as an elastic material and the viscous material. , Tanδ = E ″ / E ′ (1), where δ represents the phase difference angle between strain and stress (see JIS K7198).

Further, E 'and E "are a real component and an imaginary component of the complex elastic modulus (E ^* ), respectively, and these parameters have the following relationship: E' = | ^{E * | cosδ ··· (2)} E "= | E * | sinδ ··· (3) | E * | 2 = E '2 + E" 2 ··· (4)

Among the above-mentioned parameters, in particular, tanδ
Is a numerical value indicating the viscoelastic property of a substance, and its measurement accuracy is greatly affected by the mechanical strength of the measurement device main body and is greatly affected by the measurement method. This tanδ
Conventionally, (1) a method of directly measuring tan δ from a strain signal waveform and a stress signal waveform, (2)
A method has been proposed in which E 'and E "are measured to determine tan δ, and (3) a method for directly measuring the phase difference angle δ between the stress waveform and the strain waveform.

[0007] The method of the above (1), as shown in FIG.
For example, the stress signal σ (t) detected based on the output of the load cell and the strain signal ε (t) detected based on the output of the displacement sensor are supplied to the multiplier 1 for analog multiplication. A signal proportional to cos δ is obtained by a so-called lock-in amplifier that supplies an output of the filter 1 to a low-pass filter 2 to remove an AC component, and tan δ is obtained based on the output of the low-pass filter 2.

That is, σ (t) as shown in FIG.
And when, as shown in FIG. 6 (b) epsilon and (t) is multiplied by the multiplier 1, σ (t) · ε (t) = σ 0 sinωt · ε 0 cos (ωt -δ) = σ 0 · ε ₀ cosδ / 2− ｛σ ₀ · ε ₀ cos (2ωt−δ) / 2 ・ ・ ・ (5) where σ ₀ ; dynamic maximum stress ω = 2πf (where f is the vibration frequency) ε ₀ ; The dynamic maximum strain becomes as follows, and the vibration frequency is doubled as shown in FIG.
A waveform with an offset proportional to cos δ is obtained. Here, since the first term of the equation (5) is a DC component and the second term is a pure AC component, the cutoff frequency of the low-pass filter 2 is set to 2f, and the AC component of the second term is removed. , And obtain a signal proportional to cosδ, based on which tanδ
Is what you want.

The method (2) is a measurement method as defined by E 'and E "and is most generally employed in various conventional viscoelasticity measuring apparatuses. 7
As shown in the figure, the stress signal σ (t) is
, And the distortion signal ε (t) is supplied to the phase detector 5 and to the phase detector 6 via the 90 ° phase shifter 7. In this way, the phase detector 5 detects the phase of the stress signal σ (t) based on the strain signal ε (t), and obtains a stress waveform component in phase with the strain (output proportional to E ′). In the phase detector 6, the phase of the stress signal σ (t) is detected based on a sine wave signal ε ₉₀ (t) obtained by shifting the phase of the distortion signal ε (t) by 90 °. Then, a stress waveform component (output proportional to E ″) is obtained, and tan δ is obtained from the ratio of the output signals of the phase detectors 5 and 6.

In the above method (3), the dynamic components of the stress signal σ (t) and the strain signal ε (t) are extracted, and the points where the waveforms of both signals have the same phase (maximum value, minimum value). Value or zero point), the phase difference angle δ is directly measured and t
is to calculate anδ. For this reason, in an apparatus adopting such a measuring method, a stress signal σ as shown in FIG.
(t) and the distortion signal ε (t) as shown in FIG.
Are converted into rectangular waves as shown in FIGS. 8C and 8D, for example, by amplifying the signals by, for example, amplifiers having large gains. After obtaining the signal as shown in (e), this signal is integrated by an integrator to obtain an output proportional to δ.

[0011]

In the measurement of viscoelasticity, generally, the amplitude of a dynamic displacement (strain) is 20
The load (stress) measured by the load cell is as small as several gf to a few thousand near the Tg point (glass transition point of rubber at a low temperature) in a temperature spectrum. It is very wide, up to gf. Under these harsh conditions, as new materials are developed, more accurate measurements, such as tan
Accurate measurement of 0.001 or more in δ is required.

However, in the above-described conventional measuring methods, both the stress signal and the strain signal are subjected to signal processing by an electronic circuit (hardware) having a function corresponding to each measuring method to measure tan δ. Therefore, there is a problem that the accuracy cannot be sufficiently improved for the following reasons. In other words, to measure strain and stress with high accuracy and high stability over a wide dynamic range, there are limitations not only due to linearity but also due to circuit drift and the like. Although the phase difference is measured, a phase delay occurs due to the electronic circuit itself. Therefore, in particular, as in the measurement method (2), t ′ is indirectly derived from E ′, E ″.
When measuring anδ, the value of E ″ is two times greater than the value of E ′.
In the case of a low-loss material that is smaller than an order of magnitude, there is a problem in that the measurement accuracy limit of tan δ is determined by the measurement limit of E ″.

In general, in order to improve the measurement accuracy to some extent by hardware, a considerably expensive measurement circuit is required, which causes a problem that the cost is greatly increased. The various problems described above occur not only in the case of the tensile vibration method but also in the case where the viscoelastic characteristics are measured by the bending vibration method.

The present invention has been made in view of the above-mentioned conventional problems, and a first object of the present invention is to provide a viscoelasticity measurement capable of always measuring the viscoelasticity characteristics of a viscoelastic body with high accuracy and high stability. It seeks to provide a way.

Further, a second object of the present invention is to provide a viscoelasticity measuring apparatus capable of implementing the above measuring method with a simple and inexpensive configuration.

[0016]

In order to achieve the first object, in the viscoelasticity measuring method according to the present invention, the elastic body test piece is subjected to non-resonant forcible vibration at a constant vibration frequency.
A displacement amount due to the vibration and a load acting on the elastic body test piece are detected by a displacement sensor and a load cell, respectively. Based on the displacement signal from the displacement sensor and the load signal from the load cell, the viscoelastic characteristics of the elastic body test piece are measured. In measuring the displacement signal, an analog / digital conversion step of simultaneously sampling the displacement signal and the load signal at a predetermined sampling cycle and converting them into digital signals, respectively, based on the digital signal of the displacement signal, A zero cross point detecting step of detecting a cross point and detecting a zero cross point of the load signal based on the digital signal of the load signal; and the displacement signal detected in the zero cross point detecting step. The difference between the zero crossing point of the load signal and the zero crossing point of the load signal is calculated, and the zero crossing point is calculated. The difference of the point, on the basis of the sampling period and the vibration frequency and is characterized in that it comprises a calculation step of calculating a phase difference angle of the displacement signal and the load signal.

In one embodiment of the present invention, the zero crossing point detecting step includes a smoothing process for removing a noise component from each of the digital signal of the displacement signal and the digital signal of the load signal, and the smoothing process. The maximum value and the minimum value of the digitized digital signal are obtained, a zero point detection process of detecting the average value thereof as a zero point, and digital signals of several points before and after the sign changes with respect to the detected zero point are obtained. Each of the extracted digital signals is subjected to interpolation processing for interpolating the digital signal, and a corresponding zero-cross point is detected from the interpolated digital signal.

In this way, each zero-cross point can be detected more accurately, and therefore, the phase difference angle can be determined more accurately.

Further, in order to achieve the second object,
According to the present invention, the elastic body test piece is subjected to non-resonant forced vibration at a constant vibration frequency by a vibrator, and a displacement amount due to the vibration and a load acting on the elastic body test piece are detected by a displacement sensor and a load cell, respectively. In a viscoelasticity measuring device for measuring a viscoelastic characteristic of the elastic test piece based on a displacement signal from the displacement sensor and a load signal from a load cell, a first analog for sampling the displacement signal and converting it into a digital signal / Digital conversion means, second analog / digital conversion means for sampling the load signal and converting it into a digital signal, the vibrator, the first analog / digital conversion means, and the second analog / digital Controlling the operation of each of the conversion means, the first analog / digital conversion means and the second Calculation control means for calculating the phase difference angle between the displacement signal and the load signal based on each digital signal from the analog / digital conversion means, and the displacement control signal and the load signal are calculated by the calculation control means. Are controlled by controlling the operations of the first analog / digital conversion means and the second analog / digital conversion means so that the signals are simultaneously sampled at predetermined sampling periods and converted into digital signals. Based on the digital signal from the digital conversion means, while detecting the zero cross point of the displacement signal,
A zero cross point of the load signal is detected based on a digital signal from the second analog / digital conversion means, and a zero cross point of the detected displacement signal and a zero cross point of the load signal are detected. The phase difference angle is calculated on the basis of the difference between the phase difference, the sampling period, and the vibration frequency.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of a main part of an embodiment of a viscoelasticity measuring device for performing a viscoelasticity measuring method according to the present invention. This viscoelasticity measuring device has an upper chuck 12 and a lower chuck 13 for detachably chucking both ends of an elastic body test piece 11 respectively. The upper chuck 12 is provided with a rod 1 extending inside a cylindrical slide screw 14 movable in a vertical direction.
5 is connected to a load cell 16 provided above the slide screw 14. A gear 17 is screwed into the slide screw 14, and a gear 19 attached to an output shaft of a pulse motor 18 is meshed with the gear 17, and the gear 17 is driven in the forward and reverse directions through the gear 19 by driving the pulse motor 18. By rotating, the upper chuck 1 is integrated with the slide screw 14.
2. The rod 15 and the load cell 16 are moved vertically. In addition, a lower limit sensor 20 for detecting the lower limit position of the slide screw 14 is provided near the movement path of the slide screw 14 in order to position the upper chuck 12 at the chucking position of the elastic test piece 11.

On the other hand, the lower chuck 13 is connected to a vibrating rod 22 of a vibrator 21. In this embodiment, the vibrator 21 has a holding coil 23 for holding the vibrating rod 22 at a predetermined neutral position (zero displacement point position), and a vibrating device for vertically vibrating around the zero displacement position. A vibration coil 24, and the displacement of the vibration rod 22 is detected by a displacement sensor probe 25. Displacement sensor probe 25
Uses an optical fiber sensor having a light source 26, an optical fiber 27, a light receiving element (not shown) and a preamplifier 28 in this embodiment, and transmits the light from the light source 26 to the optical fiber 27.
The light is projected on the lower end surface of the vibrating rod 22 via the optical fiber 27, the reflected light is received by the light receiving element via the optical fiber 27, and the output is supplied to the preamplifier 28. The lower end surface of the vibrating rod 22 is preferably subjected to reflection processing.

The output (load signal) of the load cell 16 is amplified by a load cell amplifier 31 and then amplified by an A / D converter 32.
Then, the signal is converted into a digital signal of, for example, 12 bits or more and supplied to the arithmetic and control circuit 33. The pulse motor 18 is selectively driven in forward and reverse directions by a pulse motor driver 35. For this reason, the forward rotation pulse (CW) and the reverse rotation pulse (CCW) from the pulse oscillator 36 are selectively supplied to the pulse motor driver 35 via the switch circuits 37 and 38, respectively. The switch circuit 37 receives the load zero point set value (Fmin, for example, 160 gf) from the arithmetic control circuit 33 and the load cell amplifier 31.
The control is performed on the basis of the output of the differential amplifier 39 which receives the load signal from the lower limit sensor 20 as an input, and the switch circuit 38 controls based on the output of the lower limit sensor 20. In this embodiment, the range of the load cell amplifier 31 is switched via the range switching circuit 40 based on the output of the differential amplifier 39.

The output (displacement signal) of the preamplifier 28 of the displacement sensor probe 25 is
Then, for example, as shown in FIG. 2A, the signal is amplified, and the output is amplified by the linearizer 42, for example, as shown in FIG.
After converting the displacement amount and the output so as to be proportional, the A / D converter 43 converts the displacement into a digital signal of, for example, 12 bits or more, and supplies the digital signal to the arithmetic control circuit 33. Note that the sampling of the load signal by the A / D converter 32 and the sampling of the displacement signal by the A / D converter 43 are synchronized with a synchronizing signal from a sine wave oscillator described later that drives the excitation coil 24 of the exciter 21. Then, in a predetermined sampling interval, Δδ / 2πf (where Δδ / 2πf
.delta. is the accuracy of .delta. to be measured, and f is a sampling pulse of a constant cycle equal to or less than the output frequency of the sine wave oscillator).

Next, the drive system of the vibrator 21 will be described. A DC current is supplied from the DC power amplifier 51 to the holding coil 23 based on the zero displacement set value (for example, 400 μm) from the arithmetic and control circuit 33, and the vibration rod 22
At a predetermined zero displacement position. For this reason, the predetermined displacement zero point set value from the arithmetic control circuit 33 and the displacement signal from the linearizer 42 are supplied to the differential amplifier 5
2, the output of the differential amplifier 52 is supplied to the DC power amplifier 51, and the feedback control is performed so that the vibration rod 22 is maintained at the predetermined displacement zero point position.

A DC current whose amplitude changes in a sinusoidal manner is supplied from the DC power amplifier 55 to the excitation coil 24 to reciprocate the excitation rod 22 at a predetermined frequency and amplitude around the zero displacement position. Make it vibrate. Therefore, a DC signal (sine wave signal) whose amplitude changes in a sine wave form is supplied to the DC power amplifier 55 from the sine wave oscillator 56 via the switch circuit 57, and the frequency of the output of the sine wave oscillator 56 and The amplitude is calculated by the arithmetic control circuit 33.
Are controlled based on the frequency setting value (for example, 1 to 100 Hz) and the displacement amplitude setting value (for example, 20 to 400 μm). The sine wave oscillator 5
The amplitude of the sine wave signal from 6 is fed back to the differential amplifier 58 by the feedback of the displacement signal from the linearizer 42 to detect the difference from the amplitude of the displacement zero point set value from the arithmetic and control circuit 33. The signal is converted into a voltage signal by the amplitude / voltage converter 59, and the operation control circuit 33 is
Is detected, and control is performed so that the difference becomes zero, that is, the actual amplitude becomes an amplitude corresponding to the displacement amplitude set value. The sine wave oscillator 56 supplies a synchronization signal to the arithmetic control circuit 33 in order to generate sampling pulses for the A / D converters 32 and 43.

The above-described sine wave oscillator 56 is controlled to start and stop under the control of the cycle counter 61. The cycle counter 61 counts the measurement cycle (cycle) of the vibration of the excitation coil 24 based on the output of the differential amplifier 58. 10 cycles), and after the start of the sine wave oscillator 56, the drive of the sine wave oscillator 56 is stopped when the count value of the measurement cycle reaches the set value.

Also, in order to position the upper chuck 12 so that the output of the load cell 16 becomes the load zero point set value from the operation control circuit 33, the differential amplifier 65 sets the displacement zero point set value from the operation control circuit 33 to the position. , Linearizer 4
2 is detected, and the difference between the difference signal and the displacement amplitude set value from the arithmetic and control circuit 33 is detected by the differential amplifier 6.
6, the output of the differential amplifier 66 is supplied to the DC power amplifier 55 through the switch circuit 57, thereby driving the exciting coil 24 and moving the exciting rod 22 from the zero displacement position to the displacement amplitude. Position at the top dead center position corresponding to the set value.

With the above structure, both ends of the elastic body test piece 11 are chucked to the upper chuck 12 and the lower chuck 13, and the upper chuck 12 is positioned at a position corresponding to the set value of the load zero point, and the vibrating rod is set. 22 is positioned at a position corresponding to the displacement zero point set value, and in this state, the load cell amplifier 31 is vibrated in the vertical direction with the amplitude corresponding to the displacement amplitude set value centering on the displacement zero point position. And the displacement signal output from the linearizer 42 are synchronized by the A / D converters 32 and 43 with the synchronizing signal from the sine wave oscillator 56 at predetermined sampling intervals in a predetermined sampling interval. At the same time, the signals are sampled and converted into digital signals, and the arithmetic and control circuit 3 In directly measured the phase difference angle δ on the time axis, and outputs the measurement result to the output device 71 such as a display or a printer.

The operation of this embodiment will be described below. Before starting the measurement, it is assumed that the switch circuit 37 is off and the switch circuit 38 is on, and the switch circuit 57 is connected to the differential amplifier 66 side. First,
The pulse motor 18 is rotated in reverse by the CCW pulse from the pulse oscillator 36 via the pulse motor driver 35, and the slide screw 14 is lowered. Thereafter, when the lower limit sensor 20 detects the slide screw 14, the switch circuit 38 is turned off, and the upper chuck 12 is positioned at the chucking position. In this state, both ends of the sample elastic body test piece 11 are
Chucking.

After that, based on the outputs of the differential amplifiers 65 and 66, the vibrating rod 22 is positioned from the zero displacement position to the top dead center position corresponding to the displacement amplitude set value, and in that state the switch circuit 37 is turned on. The pulse oscillator 36
The pulse motor 18 is rotated forward through the pulse motor driver 35 by the CW pulse from the
In the differential amplifier 39 until the load zero point set value and the load signal from the load cell amplifier 31 become equal, and the switch circuit 37 is turned off. This allows
A constant static load (tensile force) or static elongation at a set value of zero load point is applied to the elastic body test piece 11 so that the elastic body test piece 11
Buckling (slack) does not occur when dynamic elongation deformation is applied to Note that the range of the load cell amplifier 31 is switched by the range switching circuit 40 so as to be narrow during the above-mentioned zero load point positioning operation and wide during the subsequent measurement.

After the positioning of the load cell 16 to the zero load position is completed, the switch circuit 57 is connected to the sine wave oscillator 56, and the operation control circuit 3
Under the control of 3, the sine wave oscillator 56 is started by the cycle counter 61, and a sine wave DC current having a set frequency and a set amplitude is supplied from the DC power amplifier 55 to the exciting coil 24 to oscillate the exciting rod 22. While the A / D converter 3
2 and 43 are taken into the arithmetic and control circuit 33 to measure the phase difference angle δ. During this measurement period, the difference between the set value of the displacement zero point and the displacement signal from the linearizer 42 is detected by the differential amplifier 52, and the shaker is applied via the DC power amplifier 51 so that the difference becomes zero. 21 holding coils 23
To control the vibrating rod 22 to be maintained at the set displacement zero point position, as well as the differential amplifier 58, the amplitude / voltage converter 59, and the differential amplifier 60.
Thus, the output amplitude of the sine wave oscillator 56 is controlled so that the elastic body test piece 11 vibrates at the set amplitude. Thereafter, when the cycle counter 61 counts the set number of measurement cycles, the driving of the sine wave oscillator 56 is stopped, the measurement of the elastic body test piece 11 is completed, and the measurement of the next elastic body test piece is performed. Prepare.

In FIG. 1, the pulse oscillator 36, the switch circuits 37, 38, 57 and the differential amplifiers 39, 52, 5
8, 60, 65, 66, linearizer 42, amplitude / voltage converter 59, and cycle counter 61, for convenience,
Although shown separately from the arithmetic control circuit 33, those functions are realized by software in the arithmetic control circuit 33.

Next, the measurement processing of the phase difference angle δ in the arithmetic and control circuit 33 based on the outputs of the A / D converters 32 and 43 will be described with reference to the flowchart shown in FIG. First, in step S1, the A / D converter 32,
At 43, a load signal and a displacement signal which are simultaneously sampled at a predetermined sampling period in a predetermined sampling section and converted into digital signals are read. Here, a load signal (F) as shown in FIG. 4A is output from the load cell amplifier 31, and a displacement signal (L) as shown in FIG. 4B is output from the linearizer 42. Therefore, in this embodiment, the sections t (F ₀ ) ₊ , t (F ₀ ) ₋ , t (L) including the average value are included in one cycle of each signal based on the synchronization signal from the sine wave oscillator 56. ₀ ) ₊ , t (L ₀ )
_- a section that contains the maximum value Fmax, the Lmax, and the minimum value Fmi
A sampling section T including sections n and Lmin is set, and in each of the sampling sections T, the load signal (F) and the displacement signal (L) are simultaneously sampled at a constant sampling cycle and A / D converted.

After that, in step S2, when it is confirmed that each signal has been read for one cycle or more, step S3
In the above, the read load signal and displacement signal are respectively subjected to filter processing for smoothing to remove noise components. This filtering process is performed, for example, in each sampling interval T by using a 2-4th order polynomial fitting method (Savitzky Golay
), Smoothing and numerical detection of each point are performed simultaneously.

Thereafter, in step S4, the maximum value, minimum value and average value of each signal waveform are obtained. Here, the maximum value (Fmax, Lmax) and the minimum value (Fmin, Lmin)
Is obtained by first-differentiating each signal waveform and detecting a zero-crossing point from a signal obtained by smoothing the signal. The average value (F
₀ , L ₀ ) is obtained by calculating F ₀ = (Fmax + Fmin) / 2 L ₀ = (Lmax + Lmin) / 2 from the detected maximum value and minimum value. These average values are each set to the zero point of each signal waveform.

Next, in step S5, the phase difference angle δ
On the time axis, in order to accurately detect at the zero point having the largest change rate with respect to the time axis, the sampling value of each signal is sequentially scanned starting from the sampling start point, and the point at which the sign changes with respect to the above-mentioned zero point Are respectively detected.

Thereafter, in step S6, in order to exactly determine the zero crossing point, sampling values of several points before and after the zero point detected for each signal waveform are extracted.
These measurement points are linearly regression-analyzed and interpolated between sampling periods to accurately determine a zero crossing point.

Next, in step S7, step S
After calculating the difference between the zero cross points of the respective signal waveforms determined in step 6, the phase difference angle δ is calculated based on the difference and the sampling period.
Is calculated (Δt).

Thereafter, in step S8, based on Δt obtained in step S7 and the frequency set value f of the sine wave oscillator 56, the phase difference angle δ is calculated by δ = 2πf · Δt, Output.

It should be noted that the present invention is not limited to the above-described embodiment, and that various changes or modifications are possible. For example, in the above-described embodiment, since the maximum value and the minimum value of each signal waveform are obtained in step S4 in FIG. 3, the values, the width (w), the thickness (d), and the load of the elastic test piece 11 are determined. Upper and lower chucks 12, 1 at zero point
Based on the distance between the _{3 (l 0), σ 0} = {(Fmax + Fmin) / 2} / (w × d) ε 0 = {(Lmax + Lmin) / 2} / l dynamic maximum stress by ₀ sigma ₀ and the dynamic maximum strain ε ₀ , and based on these σ ₀ and ε ₀ , the absolute value of the complex elastic modulus is obtained by | E ^* | = σ ₀ / ε ₀ , and based on the complex elastic modulus, From the above equations (1), (2) and (3), tan
δ, E ′ and E ″ can also be determined.

[0041]

As described above, according to the viscoelasticity measuring method according to the first aspect, the displacement signal and the load signal are simultaneously sampled at a predetermined sampling cycle, converted into digital signals, and converted into digital signals. Each zero-cross point is detected based on the difference, and the phase difference angle is calculated based on the difference between the two zero-cross points, the sampling period, and the vibration frequency. The processing after the conversion can be executed by software of a computer to directly calculate the phase difference angle on the time axis. Therefore, the viscoelastic properties of the viscoelastic body can always be measured with high accuracy and high stability.

According to the viscoelasticity measuring method of the present invention, when detecting the zero-cross point, the digital signals of the displacement signal and the load signal are smoothed to remove noise components, and the smoothing is performed. Based on the maximum value and the minimum value of each digital signal obtained, their average value is detected as a zero point, and further, digital signals of several points before and after the sign changing with respect to those zero points are extracted and interpolated, respectively. Since the processing is performed to detect the corresponding zero-cross points, the respective zero-cross points can be detected more accurately, and the phase difference angle can be obtained more accurately.

Furthermore, according to the viscoelasticity measuring device of the third aspect, the first and second analog / digital conversion means for converting the displacement signal and the load signal into digital signals, respectively, and the first and second analog / digital conversion means. Arithmetic and control means for processing a digital signal from the analog / digital conversion means, wherein the arithmetic and control means controls the first and second analog / digital conversion means to sample the displacement signal and the load signal by predetermined sampling. Sampling at the same time at the same time, converting them into digital signals, detecting the respective zero-cross points based on the digital signals, and calculating the phase difference angle based on the difference between the two zero-cross points, the sampling period, and the vibration frequency. The processing after converting the displacement signal and the load signal into digital signals, respectively, is performed. It can be calculated directly the phase difference angle on the time axis by performing the software over data. Therefore, the viscoelastic properties of the viscoelastic body can always be measured with high accuracy and high stability with a simple and inexpensive configuration without causing problems such as circuit drift and phase delay of the circuit itself.

[Brief description of the drawings]

FIG. 1 shows a configuration of a main part of an embodiment of a viscoelasticity measuring apparatus for performing a viscoelasticity measuring method according to the present invention.

FIG. 2 is a diagram for explaining operations of a displacement sensor amplifier and a linearizer shown in FIG.

FIG. 3 is a flowchart showing a process of measuring a phase difference angle δ in the arithmetic and control circuit shown in FIG. 1;

FIG. 4 is a waveform diagram showing a load signal and a displacement signal output from the load cell amplifier and the linearizer shown in FIG. 1, respectively.

FIG. 5 is a block diagram showing an example of a conventional viscoelasticity measuring device.

FIG. 6 is a signal waveform diagram for explaining the operation.

FIG. 7 is a block diagram showing another example of a conventional viscoelasticity measuring device.

FIG. 8 is a signal waveform diagram for explaining still another example of the conventional viscoelasticity measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Elastic body test piece 12 Upper chuck 13 Lower chuck 16 Load cell 18 Pulse motor 20 Lower limit sensor 21 Vibrator 22 Vibrating rod 23 Holding coil 24 Vibrating coil 25 Displacement sensor probe 31 Load cell amplifier 32, 43 A / D converter 33 Operation control circuit 35 Pulse motor driver 41 Displacement sensor amplifier 51, 55 DC power amplifier 56 Sine wave oscillator 71 Output device

Continued on the front page (72) Inventor Kiyoshi Watanabe Japan

Claims (3)

[Claims] 1. A displacement sensor and a load cell respectively detect a displacement amount due to the vibration and a load acting on the elastic body test piece while non-resonantly forcibly vibrating the elastic body test piece at a constant vibration frequency. In measuring the viscoelastic characteristics of the elastic test piece based on the displacement signal from the load cell and the load signal from the load cell, the displacement signal and the load signal are simultaneously sampled at a predetermined sampling cycle and converted into digital signals, respectively. An analog / digital conversion step; detecting a zero cross point of the displacement signal based on the digital signal of the displacement signal, and detecting a zero cross point of the load signal based on the digital signal of the load signal A zero-crossing point detection step to be performed, and zero of the displacement signal detected in the zero-crossing point detection step. Calculating the difference between the cross point and the zero cross point of the load signal, and calculating the phase difference between the displacement signal and the load signal based on the difference between the zero cross points, the sampling period and the vibration frequency; A calculating step of calculating an angle. 2. The viscoelasticity measuring method according to claim 1, wherein the zero-cross point detecting step is a smoothing process for removing a noise component from each of the digital signal of the displacement signal and the digital signal of the load signal. And zero point detection processing for obtaining the maximum value and the minimum value of the digital signal subjected to the smoothing processing and detecting the average value thereof as a zero point, and several points before and after the sign changes with respect to the detected zero point. And performing an interpolation process for interpolating the digital signal, and detecting a corresponding zero-cross point from the interpolated digital signal. 3. A displacement sensor and a load cell respectively detect a displacement amount due to the vibration and a load acting on the elastic body test piece while the elastic body test piece is non-resonantly forcibly vibrated at a constant vibration frequency by a vibrator. A viscoelasticity measuring device for measuring a viscoelastic characteristic of the elastic test piece based on a displacement signal from the displacement sensor and a load signal from a load cell, wherein the displacement signal is sampled and converted into a digital signal; Analog / digital conversion means; second analog / digital conversion means for sampling the load signal to convert it into a digital signal; the vibrator, the first analog / digital conversion means, and the second analog / digital conversion means The operation of each of the digital conversion means is controlled, and the first analog / digital conversion means and the second Calculation control means for calculating the phase difference angle between the displacement signal and the load signal based on each digital signal from the analog / digital conversion means. The calculation control means allows the displacement signal and the load signal to be calculated. Are controlled by controlling the operations of the first analog / digital conversion means and the second analog / digital conversion means so that the signals are simultaneously sampled at predetermined sampling periods and converted into digital signals. A zero cross point of the displacement signal is detected based on a digital signal from the digital conversion means, and a zero cross point of the load signal is detected based on a digital signal from the second analog / digital conversion means. The difference between the zero cross point of the detected displacement signal and the zero cross point of the load signal, The viscoelasticity measuring device is configured to calculate the phase difference angle based on the sampling cycle and the vibration frequency.