JP2020112436A - Method for measuring viscoelastic characteristics of skin and apparatus using the same - Google Patents

Abstract

To provide a method capable of measuring viscoelastic characteristics of a skin in a short time by providing a simple-structured and small-sized pressure sensor unit easily mounted on a handy-type probe, and an apparatus using the method.SOLUTION: A hemispherical indenter is pushed in a surface of a skin; repulsive force that the indenter received from the skin with respect to a lapse time immediately thereafter, is measured by a simple-structure pressure sensor; by using the obtained measurement data, parameters when the viscoelastic characteristics of the skin are approximated by a stress relaxation function of a 3-element-type standard linear solid model are calculated, and a complex modulus of elasticity of the skin is measured from these parameters.SELECTED DRAWING: Figure 6

Description

The present invention mainly relates to a viscoelastic characteristic measuring method that can measure the viscoelastic characteristic of a relatively soft object such as skin and can be used as a handy type, and a device using the same.

The skin has a multi-layered structure consisting of epidermis and dermis, and the viscoelastic properties of each layer differ greatly, and the thickness of each layer and the structure of each layer also differ depending on the site, so the same site of the same person is measured. However, it is known that the obtained viscoelastic characteristics greatly differ depending on the measurement conditions such as the size of the measurement indenter, the indentation depth, and the measurement frequency.

Non-Patent Document 1 states that “human skin has a very thin and highly elastic corneocyte layer inside which highly elastic dermis and subcutaneous tissue are arranged. The multilayer structure of human skin is most simplified and the outermost layer is formed. It has a two-layer structure consisting of the stratum corneum and the deep subcutaneous tissue.Conventional studies have shown that the longitudinal elastic modulus of the stratum corneum is approximately 7.2 × 10-1MPa and the longitudinal elastic modulus of subcutaneous tissue is approximately 3.4 × 10-2MPa. It is known to exist.”

In addition, the conventional evaluation of the skin has been mainly performed with sensitive properties such as "elasticity", "hardness", "tension", and "smoothness", but the evaluation criteria for each are ambiguous. In Patent Document 1, mechanical characteristics of the skin, in particular, the hardness of the skin and the firmness of the skin, respectively, "skin hardness = elasticity value", a method of evaluating as "skin firmness = elasticity value / viscosity value" It is disclosed. That is, it indicates that the hardness of the skin and the firmness of the skin are represented by "skin hardness = storage elastic modulus" and "skin firmness = storage elastic modulus/loss elastic modulus", respectively, and this method is Although it seems to be effective as a universal evaluation standard of the skin, when trying to measure the storage elastic modulus or loss elastic modulus, that is, the complex elastic modulus of the skin, the conventional dynamic viscoelasticity measuring device has a large device, Since it is necessary to fix the sample to be measured, it is difficult to measure any part of the human body, and a measurement device that can measure the complex viscoelastic properties of the skin with a handy probe is desired. It is rare.

Hereinafter, about the dynamic viscoelastic property measurement method, stress relaxation measurement method, and contact impedance method, which have been widely performed in the past for widely measuring viscoelastic properties of relatively soft objects such as the living body such as skin, food, and rubber products. , Its outline and problems in using these measuring methods for measuring the viscoelastic properties of the skin will be described.

The dynamic viscoelasticity measurement method applies vibration strain γ ₀ (ω) at an angular frequency ω to an object, and the complex elastic modulus, which is the viscoelastic property of the object, is calculated from the amplitude ratio of the strain γ and the stress σ and the phase difference δ. E*(ω) = E'(ω)+j E''(ω) is measured, and E'(ω) and E''(ω) are called storage modulus and loss modulus, respectively. Is a function of the angular frequency ω. The dynamic viscoelasticity measurement method is widely used to measure the viscoelastic properties of objects from liquids to solids in the low frequency range below 1 Hz to high frequency ranges up to several 100 Hz.

In Patent Document 2, as a method for measuring the viscoelastic properties of the skin by the dynamic viscoelasticity measurement method, a cyclic force in the rotational or linear direction is applied to the measurement site of the skin, and the waveform of this cyclic force and the skin The method of measuring the mechanical properties of the skin by the waveform of stress is disclosed, from the obtained measurement data, the viscosity of the skin, elasticity, the waveform of the periodic force and the waveform phase difference of the stress from the skin (tan δ) , The maximum stress/maximum amplitude, the area of stress-strain Lissajous, etc. are shown to know the mechanical properties of the skin.

Further, Non-Patent Document 2, FIG. 1 is disclosed, "a typical measurement example of the skin viscoelasticity of each human site (forearm flexion side, palm, back, forehead, cheek, abdomen, back). The measurement frequency was 2 Hz, the amplitude was 2 mm, and the viscoelastic Lissajous diagram (hysteresis curve) showed different shapes depending on the site, which was in good agreement with the sensory value." In other words, the skin is pushed by a predetermined amount with an indenter that vibrates periodically, the displacement and repulsive force at that time are measured, and the amount of pushing and the vibration frequency are measured by the dynamic viscoelasticity measurement method that measures the amplitude ratio and phase difference. It has been shown that with proper selection, the viscoelastic properties of various parts of the skin can be measured.
In FIG. 1, the indentation amount is 2 mm and the indentation frequency is 2 Hz, but the measurement frequency is the frequency at which the area of the hysteresis curve in FIG. 1 is the maximum, that is, the loss of the measured viscoelastic body shows a maximum value. It is desirable to select the frequency.Specifically, for each measurement site, the frequency at which the loss elastic modulus E''(ω) obtained by changing the frequency by the dynamic viscoelasticity measurement method shows the maximum value is selected. The choice seems to be the most appropriate.

Further, in Patent Document 3, the electromagnetic force generated by the electromagnetic coil and the permanent magnet is applied to the surface of the viscoelastic body through a contact indenter, and the position of the contact indenter is detected by a position sensor, A viscoelastic body surface mechanical property measuring device for measuring the deformation process of the viscoelastic body surface and the recovery process of the viscoelastic body surface after removing electromagnetic force is disclosed. Specifically, a contact indenter is measured. The surface of the test object after removing the pressure of the contact indenter by applying it to the surface of the viscoelastic body, increasing the pressure of the contact indenter from zero to a predetermined target value in a short time, and suddenly decreasing it to zero after a given rest time. A method of calculating the elastic modulus and the viscous coefficient of a viscoelastic body by numerical analysis by measuring the relationship between the strain amount and the time is disclosed.

However, in Patent Document 3, “By measuring the relationship between the strain amount and time of the surface of the subject after removing the pressure of the contact indenter, the elastic modulus and viscosity of the viscoelastic body are calculated by numerical analysis.” , But it is not clear from the obtained measurement data what kind of procedure is specifically used to obtain the elastic modulus and viscosity of the object.

In addition, the contact impedance method compares the resonance frequency fr and the resonance resistance R in the unloaded state of the sensor oscillator that is configured by attaching a hemispherical contact at the antinode of the resonance oscillation of the piezoelectric oscillator or magnetostrictive oscillator. A method of measuring the viscoelastic characteristics of the object from the resonance frequency fr and the amount of change Δfr and ΔR of the resonance resistance R when the contactor is pressed against the object with a constant load. , A contact to which a vibration of a predetermined frequency is given, an oscillation circuit that measures a change in the frequency of the contact when the contact is brought into contact with the human skin surface, and a contact to a predetermined contact with the human skin surface. When pressed by pressure, it has a strain gauge that measures the reaction force received from the skin surface, and a skin characteristic measurement unit that measures the characteristics of the skin surface based on the measurement results of the oscillation circuit and the strain gauge. Disclosed is a skin characteristic measuring device 1 capable of measuring both the surface elasticity and the internal hardness of the skin simultaneously and at the same site on the skin surface. However, the skin characteristic measuring device disclosed in Patent Document 4 is disclosed. In, the viscoelastic property of human skin or food is simply measured as hardness or elasticity, and the viscoelastic property of skin is not measured.

Furthermore, in the contact impedance method, a resonator with a resonance frequency of several tens of kHz to several hundreds of kHz is generally used, but since the complex elastic modulus of the viscoelastic body changes greatly depending on the measurement frequency, the measurement data obtained by the contact impedance method is used. However, there is a problem in that the measurement frequency is always the measurement condition and the measurement data lacks universality.

Figure 2 shows a graph of stress relaxation characteristics showing the change in stress over time when a constant strain is applied to the viscoelastic body.Generally, in the measurement of stress relaxation characteristics, the characteristics of Figure 2 are shown in Figure 3. The method of approximation using the three-element type standard linear solid-state model shown is well known. In this case, E _e and E ₁ in FIGS. 2 and 3 are called permanent elastic modulus and relaxation elastic modulus, respectively, and τ in FIG. 2 is called relaxation time. The stress relaxation characteristic of Fig. 2 is expressed by the stress relaxation function of Equation 1, and η _t of the three-element type standard linear solid model of Fig. 3 is the viscosity, and the relationship between relaxation elastic modulus E ₁ and relaxation time τ and Equation 2 is is there.

When the stress relaxation characteristic of the viscoelastic body is expressed by Equation 1, the storage elastic modulus E′(ω) and loss elastic modulus E′(ω) of this viscoelastic body are given by Equation 3 and Equation 4, respectively. To be That is, if the parameters E _e , E ₁ , and τ of the stress relaxation function of Equation 1 are obtained, it is possible to obtain the same complex elastic modulus E*(ω) as that obtained by the dynamic viscoelasticity measurement method. 2, and Non-Patent Document 2, the viscosity of the skin, elasticity, phase difference (tan δ), maximum stress / maximum amplitude, the area of stress-strain Lissajous, can be determined, the mechanical properties of the skin You can know
Further, since the frequency f _{0 at} which the area of the hysteresis curve is maximum and the relaxation time τ have the relationship of Equation 5, if the relaxation time τ is obtained, from Equation 6, the area of the hysteresis curve is maximum. The frequency f ₀ can be obtained.

The dynamic viscoelasticity measurement method described above requires an excitation drive force generation device, a vibration displacement sensor, and a pressure sensor, which makes the device complicated and large, and also for controlling the drive frequency, drive force, and vibration width. Circuit and the phase detection circuit between the displacement sensor output and the pressure sensor output, etc. are required, and the cost is high, so it is especially difficult to incorporate it in the handy probe.

In addition, the conventional stress relaxation characteristic measurement method requires a long time to correctly measure the permanent elastic modulus E _e , and thus the measurement time becomes long, and in addition to the actual viscoelasticity of the skin, Since it is difficult to approximate the stress relaxation characteristics of the body with the three-element standard linear solid-state model shown in Figs. 2 and 3 over a wide elapsed time range, the viscoelastic characteristics of the skin can be determined from short-term measurement data. A method for approximating each parameter of the stress relaxation function of Equation 1 effective for evaluation is required.
Also in the stress relaxation characteristic measuring method, there is a demand for a load sensor that can be built in a small, handy probe.

JP-A 1-115342 JP 61-181436 JP 2004-85548 JP JP 2011-130805 JP

Hirokazu Shirato, et al.; “Development of artificial skin with skin texture”: The Japan Society of Mechanical Engineers, Vol. 73, No. 726, pp541-546 (2007-2). Umeya Junichiro; "Development and rheological analysis of skin viscoelasticity measuring instrument"; Journal of the Rheological Society of Japan Vol.23 No.4 pp197-206 (1995)

The present invention provides a small-sized pressure sensor unit that is easy to mount on a handy-type probe, has a simple structure, and provides long-term data from the measurement data of the stress relaxation characteristics of the skin obtained using this pressure sensor unit. Even within 2 seconds, the parameters of the stress relaxation function approximated by the three-element type standard linear solid model can be obtained, and from these parameters, the same complex elastic modulus as the characteristics obtained by the dynamic viscoelasticity measurement method can be obtained. A possible method for measuring the viscoelastic property of skin and an apparatus using the same are provided.

According to the invention,
On the surface of the skin, a means for pushing a substantially hemispherical indenter by a predetermined amount and holding it,
Means for measuring the repulsive force that the indenter receives from the skin with respect to the elapsed time from immediately after the indenter is pushed into the surface of the skin,
Using the measured data of the repulsion force with respect to the elapsed time, means for determining the parameters when the viscoelastic characteristics of the skin is approximated by the stress relaxation function of the three-element standard linear solid model,
From these parameters, means for obtaining frequency characteristics such as the complex elastic modulus of the viscoelastic body and the loss coefficient tan δ,
Using the viscoelastic properties of the skin obtained by the series of means, means for numerically displaying the elasticity and elasticity of the skin,
A viscoelastic property measuring method for skin and a device using the same are obtained.

Further, according to the present invention,
As a means for obtaining parameters when the viscoelastic properties of the skin are approximated by a stress relaxation function of a three-element standard linear solid model, a correction index to the data within 2 seconds from the measurement start of the repulsive force measurement data with respect to the elapsed time. A method for measuring the viscoelastic property of skin according to claim 1 characterized by applying a parameter estimation method for a function, and the method using the method are obtained.

Further, according to the present invention,
As a means for determining the parameters when the viscoelastic characteristics of the skin are approximated by a stress relaxation function of a three-element type standard linear solid model, from the measured data of the repulsive force with respect to the elapsed time, the repulsive force F ₀ immediately after indentation, and the measurement used after the start of within 0.2 seconds t ₁ and the repulsive force F ₁ at that time, and the measurement starting 2 seconds and the elapsed time t ₂ within the value of the repulsive force F ₂ at that time, satisfy these measurements Permanent elastic modulus E _e of the parameters of the stress relaxation function of the three-element standard linear solid model to be, relaxation elastic modulus E ₁ , and relaxation time τ of the skin according to claim 1, characterized by numerical calculation. A viscoelastic property measuring method and a device using the same can be obtained.

Further, according to the present invention,
As a means for measuring the repulsive force that the indenter receives from the skin, in the center of the rectangular elastic plate, a columnar indenter with a substantially hemispherical tip is formed perpendicular to the plate surface, and the rectangular elastic body is formed. A pressure sensor is used which is formed by forming strain gauges at four positions symmetrical with respect to a bisector in the width direction of the main surface of the plate and symmetrical with the position where the cylindrical indenter is formed. The method for measuring the viscoelastic property of the skin according to claim 2, and the device using the same are obtained.

According to the invention,
Using a pressure sensor that is easy to mount on a handy type probe, has a simple structure, and can be easily downsized, it has the same complex elastic modulus E*(ω) as that obtained by the dynamic viscoelasticity measurement method. It is possible to measure, and from the measurement data of the stress relaxation characteristics of the skin within 2 seconds at the longest, the parameter of the stress relaxation function approximated by the three-element standard linear solid model can be obtained, and the obtained parameters are used. Thus, it is possible to provide a method for measuring the viscoelastic property of skin and a device using the same.

Is a drawing described in Non-Patent Document 2 Is a graph showing changes in stress with time when a constant strain is applied to a viscoelastic body. Is an equivalent circuit of a three-element standard linear solid-state model used for analysis of stress relaxation characteristics Is a graph showing the modified exponential function Is a table for finding the partial sum for calculating the parameters of the modified exponential function Is a calculation example when the modified exponential parameter estimation method is applied to the measured data of stress relaxation characteristics. Is an example of calculation when the numerical calculation method is applied to the measured data of stress relaxation characteristics FIG. 1 is a cross-sectional view showing a structural example of a pressure sensor unit 1 used for a measurement probe of a skin viscoelasticity characteristic measuring apparatus of the present invention. FIG. 3 is a structural example of a strain gauge type pressure sensor used for a measurement probe of the skin viscoelasticity characteristic measuring apparatus of the present invention. FIG. 3 is a cross-sectional view showing a structural example of the tip portion of the measurement probe of the skin viscoelasticity characteristic measuring apparatus of the present invention. FIG. 4 is a cross-sectional view showing another structural example of the tip portion of the measurement probe of the skin viscoelasticity characteristic measuring apparatus of the present invention.

In the present invention, on the end face of the handy type measurement probe, the measurement probe equipped with a pressure sensor having a cylindrical indenter with a substantially hemispherical tip, which is configured to project at the time of measurement, is attached to an arbitrary portion of the body. Vertically pressed against the skin, the tip is pushed into the skin a predetermined amount of a substantially hemispherical cylindrical indenter, the change in the repulsive force from the skin with respect to the elapsed time immediately after the pressing is measured, and from this measurement data of the skin Seeking viscoelastic properties.
Since the repulsive force is proportional to the elastic modulus of the skin, the obtained measurement data will show the stress relaxation characteristics as shown in FIG. 2, and from the measurement data of the stress relaxation characteristics of FIG. Using the parameter estimation method, the parameters E _e , E ₁ , and τ of the stress relaxation function of Formula 1 are obtained in a short time.
The modified exponential function is generally a function expressed by Equation 7, where t is a time variable that takes a value of 0, 1, 2... And when a<0, 0<b<1, it becomes the function shown in FIG. The three unknown parameters K, a, and b of the modified exponential function can be obtained from the measurement data of stress relaxation characteristics by the following procedure 1 and procedure 2. When the three parameters K, a, and b of the modified exponential function are obtained, the procedure 3 allows the parameters E _e , E ₁ , and τ of the stress relaxation function of Expression 1 to be obtained.

(Procedure 1) As shown in FIG. 5, the measured values are divided into three groups of n pieces, and the sum of the data values of each group is defined as partial sums S ₁ , S ₂ , and S ₃ .
(Procedure 2) Using the partial sums S ₁ , S ₂ , and S ₃ of FIG. 5, the parameters b, a, and K of the modified exponential function are calculated from Equations 8, 9, and 10.

(Procedure 3) The equation 1 and the equation 5 are compared, and the parameters of the stress relaxation function of the equation 1 are obtained by the equations 11, 12, and 13.

However, Δt in Expression 13 is a coefficient for converting the time variable t that takes the values 0, 1, 2,... In Expression 7, into the real time, and is the measurement time for acquiring the stress relaxation characteristic data of FIG. It is the pitch.

FIG. 6 is a calculation example in the case of applying the parameter estimation method of the modified exponential function to the measurement data of the stress relaxation characteristics measured using the silicone rubber sample having the elastic modulus close to that of the skin, and the three figures are In addition, a calculation example in which the number of data n in one groove is set to n=5, n=10, and n=20 is shown in comparison with the actual measurement value. The title of each figure shows the time required for measurement given by the product of the value of n, the number of data used for calculation, and the measurement time pitch, and when n=5, n=10, n=20 It shows that the time required for each is 0.3 seconds, 0.6 seconds, and 1.2 seconds. Furthermore, in each figure, the parameters E _e , E ₁ , and τ of the obtained stress relaxation function of Equation 1 are shown. In FIG. 6, the units of E _e and E ₁ are Pa, and the unit of time t is s.

As described above, if the relaxation time τ is known, the frequency f _{0 at} which the area of the hysteresis curve becomes the maximum can be obtained, so n=5 obtained from the estimated value of the relaxation time τ obtained under each condition, The estimated values of f ₀ when n=10 and n=20 are 1.6 Hz, 0.8 Hz, and 0.4 Hz, respectively.
That is, as can be seen from FIG. 6, in the approximation method using the modified exponential function, the elapsed time region with good approximation accuracy changes depending on the number of data n in one group, and the parameters of the stress relaxation function of the obtained Equation 1 are obtained. The values of E _e , E ₁ , and τ are also changing. However, originally, the stress relaxation characteristics of the actual viscoelastic body such as the skin viscoelasticity can be approximated by the "3-element standard linear solid model" shown in Figs. 2 and 3 in a wide elapsed time range. Since it is difficult, by applying the parameter estimation method by the modified exponential function of the present invention, the approximation accuracy and the approximation limit by the number of data n of one group becomes clear, and the measurement target is limited to the skin, etc., By properly selecting the number n of data in one group, effective data regarding the viscoelastic properties of the skin can be obtained.

For example, according to the data shown in Fig. 1, the hysteresis between the applied strain and the generated stress is large at the vibration frequency of 2 Hz, and the loss elastic modulus E''(ω) is maximum near this frequency. It can be seen that the value is shown. When f ₀ =2Hz, the relaxation time τ becomes about 0.08 seconds from the relation of Equation 6. That is, in this case, it is considered that the approximation condition with high approximation accuracy near τ≈0.1 seconds is suitable. In the case of the silicone rubber sample shown in FIG. 6, τ=0.1 seconds when n=5, and it can be seen from FIG. 6 that the measured value and the calculated value are in good agreement until the elapsed time near 0.3 seconds. I understand.

In the present invention, further, from the measurement data of the stress relaxation characteristics of FIG. 2, as a method of obtaining the parameters E _e , E ₁ , τ of the stress relaxation function of Formula 1 in a short time, the repulsive force F ₀ immediately after the indentation, and the measurement used after the start of within 0.2 seconds t ₁ and the repulsive force F ₁ at that time, and the measurement starting 2 seconds and the elapsed time t ₂ within the value of the repulsive force F ₂ at that time, satisfy these measurements The permanent elastic modulus Ee, the relaxation elastic modulus E ₁ , and the relaxation time τ, which are the parameters of the stress relaxation function of the three-element type standard linear solid model, are obtained by numerical calculation.
This approximation method (hereinafter simply referred to as the numerical calculation method) is based on the measurement data of the stress relaxation characteristics shown in Fig. 2, E(t ₁ ) at t=t ₁ and E(t ₁ ) at t=t _2. (t ₂ ), and the initial value E ₀ =E(0)=E _e +E ₁ of the elastic modulus E are given to obtain the permanent elastic modulus E _e and the relaxation elastic modulus E ₁ .
From the above assumptions, Equations 14 and 15 are obtained, and from Equations 14 and 15, simultaneous equations of Equations 16 and 17 are obtained.

By solving the simultaneous equations of Formula 16 and Formula 17 by numerical calculation, the values of the stress relaxation number parameters E _e , E ₁ , and τ of Formula 1 can be obtained.

FIG. 7 is a calculation example in which a numerical calculation method is applied to the measurement data of stress relaxation characteristics measured using a silicone rubber sample having an elastic modulus similar to that of FIG. 6, and the three figures are respectively , E ₀ =4.42×10 ⁴ Pa, (1)t ₁ =0.1s, t ₂ =0.5s, (2)t ₁ =0.1s, t ₂ =1.0s, (3)t ₁ =0.1s, A calculation example when t ₂ =1.5 s is shown in comparison with the actual measurement value. The titles of the respective figures show the values of t ₁ and t ₂ , and in the respective figures, the parameters E _e , E ₁ , and τ of the obtained stress relaxation function of Equation 1 are shown.

Also in FIG. 7, as in the case of the approximation method by the modified exponential function method shown in FIG. 6, in the approximation by the numerical calculation method, at times t ₁ and t ₂ for obtaining the simultaneous equations of Equation 16 and Equation 17, Depending on the selection method, the elapsed time region with good approximation accuracy changes, and the values of the parameters E _e , E ₁ , and τ of the obtained stress relaxation function of Equation 1 also change. However, by applying the parameter estimation method of the stress relaxation function by the numerical calculation method of the present invention, it becomes clear that the elapsed time region with good approximation accuracy changes depending on how to select the times t ₁ and t ₂ , and the measurement target is changed. with limited like the skin, by choosing the time t ₁ and t ₂ properly, it is possible to obtain effective data relating to viscoelastic properties of the skin. Also in FIG. 7, the units of E _e and E ₁ are Pa and the unit of time t is s.

From the description of FIG. 1 and the results of FIG. 6 and FIG. 7 described above, in the method for measuring the viscoelastic property of the skin of the present invention, if the measurement data within 2 seconds from the start of the measurement is used, the viscoelastic property of the skin is correctly measured. It turns out that it can be measured.

FIG. 8 is a cross-sectional view showing a structural example of the pressure sensor unit 1 used in the measurement probe of the skin viscoelastic characteristic measuring apparatus of the present invention. Vertically, the tip end shape is attached with a cylindrical indenter 3 having a substantially hemispherical shape, and a plurality of strain gauges 4 are attached to at least one surface of the rectangular elastic plate 2 to provide a strain gauge type pressure sensor 5 Is formed. Both ends of the rectangular elastic body plate 2 of the strain gauge type pressure sensor 5 are fixed near the roots of the legs of the substantially U-shaped sensor holder 6, and between the rectangular elastic body plate 2 and the bottom of the sensor holder 6. Has a minute gap 7 formed therein. The space between the minute gaps 7 serves to prevent an excessive force from acting on the cylindrical indenter 3 and the bending amount of the rectangular elastic plate 2 becoming too large.
In FIG. 8, when a load is applied to the tip of the cylindrical indenter 3, the rectangular elastic plate 2 bends, and a voltage proportional to this bending can be detected by the strain gauge pressure sensor 5.

FIG. 9 is a structural example of the strain gauge type pressure sensor 5 used in the pressure sensor unit 1 shown in FIG. 8, and is a plan layout view when four strain gauges are formed on the surface of the rectangular elastic plate 2. Is shown. In FIG. 9, four strain gauges 41, 42, 43, 44 are formed at four positions symmetrical with respect to the bisector in the width direction of the rectangular elastic plate 2 and symmetrical with the position of the cylindrical indenter 3. Has been done.
By arranging the four strain gauges as shown in FIG. 9, if a force is applied to the tip of the cylindrical indenter 3 to incline the cylindrical indenter 3 in the longitudinal direction of the rectangular elastic plate 2, When the output voltage of the strain gauges 41 and 42 increases, the output voltage of the strain gauges 43 and 44 decreases, and conversely, when the output voltage of the strain gauges 41 and 42 decreases, the output voltage of the strain gauges 43 and 44 increases. As a result, even when a force that tilts the cylindrical indenter 3 in the longitudinal direction of the rectangular elastic plate 2 is applied, the length of the cylindrical indenter 3 is calculated by obtaining the sum of the output voltages of the four strain gauges. The load component in the depth direction can be correctly detected.

Further, when a force that tilts the cylindrical indenter 3 in the width direction of the rectangular elastic plate 2 is applied to the tip of the cylindrical indenter 3, when the output voltage of the strain gauges 41 and 43 increases, the strain gauges 42 and 44 become When the output voltage decreases and conversely the output voltage of the strain gauges 41 and 43 decreases, the output voltage of the strain gauges 42 and 44 increases. As a result, even when a force that tilts the cylindrical indenter 3 in the width direction of the rectangular elastic plate 2 is applied, by calculating the sum of the output voltages of the four strain gauges, the load in the longitudinal direction of the cylindrical indenter 3 is obtained. The component can be detected correctly.
According to the effects described above, four strain gauges are arranged as shown in FIG. 9, and the sum of the output voltages of the four strain gauges is obtained to correctly detect the load component in the longitudinal direction of the cylindrical indenter 3. be able to.

FIG. 10 is a cross-sectional view showing a structural example when the pressure sensor unit 1 is incorporated in the tip of a measurement probe. The pressure sensor unit 1 includes a pressure sensor unit holder 8 having an opening 10 at the tip thereof, and the tip of the cylindrical indenter 3 of the pressure sensor unit 1 from the opening 10 by a predetermined amount from the end surface 9 of the probe tip. It is fixed so that it only protrudes. Since the end surface 9 of the pressure sensor holder 8 is processed to be flat, when the measurement probe is brought into vertical contact with the skin, the skin is pushed by the protruding amount of the cylindrical indenter 3, and the measurement probe is moved at a normal speed. By contacting the skin, the cylindrical indenter 3 can be pushed into the skin almost instantly.

FIG. 11 is a cross-sectional view showing another structural example of the skin viscoelasticity measurement probe using the pressure sensor unit 1 used in the skin viscoelasticity characteristic measuring apparatus of the present invention, (a) is a standby for measurement. In the state, the tip of the cylindrical indenter 3 is recessed from the end surface 9 of the sensor unit holder 8 of the measurement probe, and (b) shows the tip of the cylindrical indenter 3 in the state of measurement is the sensor unit of the measurement probe. It projects from the end surface 9 of the holder 8 by a predetermined amount. In FIG. 11, the pressure sensor unit 1 is joined to a movable shaft 12 of a direct-acting electromagnetic solenoid 11, and a coil spring 13 acts so as to recess the cylindrical indenter 3 during standby, and at the time of measurement, the electromagnetic By energizing the solenoid 11, the drive shaft 12 moves downward as shown in FIG. 11(b), and the tip of the cylindrical indenter 3 projects from the end surface 9 of the measurement probe by a predetermined amount.
By driving the electromagnetic solenoid 11 in a state where the measurement probe is in vertical contact with the skin, it is possible to project the cylindrical indenter 3 in a state where the probe is held in a more correct position, which is more accurate. Can be measured.

As described above, in the present invention, from the measured data of the stress relaxation characteristics, as a method of estimating the parameters of the stress relaxation function of the three-element type standard linear solid model, (a) when using the parameter estimation method of the modified exponential function, three elements (B) Repulsive force F ₀ immediately after indentation, elapsed time t ₁ within 0.2 seconds from the start of measurement, repulsive force F _{1 at} that time, and start of measurement Although the method of obtaining by numerical calculation using the elapsed time t ₂ within 2 seconds and the repulsive force F ₂ at that time was explained, other methods such as the general least square method are applied to obtain Is also good.

Further, although the present invention is mainly used for measuring the viscoelastic properties of the skin, it goes without saying that the device of the present invention may be used for measuring the viscoelastic properties of relatively soft objects such as rubber and food. That is.

Further, in the description of the pressure sensor unit of the present invention, the case where the cylindrical indenter having a substantially hemispherical tip is used has been described, but the shape of the columnar portion may be a prism having a square cross section.

1: Pressure sensor unit
2: Rectangular elastic plate
3: Cylindrical indenter
4,41,42,43,44: Strain gauge
5: strain gauge type pressure sensor
6: Sensor holder
7: Minute gap
8: Sensor unit holder
9: Probe end face
10: opening

The present invention mainly relates to a viscoelastic characteristic measuring method that can measure the viscoelastic characteristic of a relatively soft object such as skin and can be used as a handy type, and a device using the same.

The skin has a multi-layered structure consisting of epidermis and dermis, and the viscoelastic properties of each layer differ greatly, and the thickness of each layer and the structure of each layer also differ depending on the site, so the same site of the same person is measured. However, it is known that the obtained viscoelastic characteristics greatly differ depending on the measurement conditions such as the size of the measurement indenter, the indentation depth, and the measurement frequency.

Non-Patent Document 1 states that “human skin has a very thin and highly elastic corneocyte layer inside which highly elastic dermis and subcutaneous tissue are arranged. The multilayer structure of human skin is most simplified and the outermost layer is formed. It has a two-layer structure consisting of the stratum corneum and the deep subcutaneous tissue.Conventional studies have shown that the longitudinal elastic modulus of the stratum corneum is approximately 7.2 × 10-1MPa and the longitudinal elastic modulus of subcutaneous tissue is approximately 3.4 × 10-2MPa. It is known to exist.”

In addition, the conventional evaluation of the skin has been performed mainly with sensitive properties such as "elasticity", "hardness", "tightness", and "smoothness", but the respective evaluation criteria are ambiguous. In Patent Document 1, mechanical characteristics of the skin, in particular, the hardness of the skin and the firmness of the skin, respectively, "skin hardness = elasticity value", a method of evaluating as "skin firmness = elasticity value / viscosity value" It is disclosed. That is, it indicates that the hardness of the skin and the firmness of the skin are represented by "skin hardness = storage elastic modulus" and "skin firmness = storage elastic modulus/loss elastic modulus", respectively, and this method is Although it seems to be effective as a universal evaluation standard of the skin, when trying to measure the storage elastic modulus or loss elastic modulus, that is, the complex elastic modulus of the skin, the conventional dynamic viscoelasticity measuring device has a large device, Since it is necessary to fix the sample to be measured, it is difficult to measure any part of the human body, and a measurement device that can measure the complex viscoelastic properties of the skin with a handy probe is desired. It is rare.

Hereinafter, about the dynamic viscoelastic property measurement method, stress relaxation measurement method, and contact impedance method, which have been widely performed in the past for widely measuring viscoelastic properties of relatively soft objects such as the living body such as skin, food, and rubber products. , Its outline and problems in using these measuring methods for measuring the viscoelastic properties of the skin will be described.

The dynamic viscoelasticity measurement method applies vibration strain γ ₀ (ω) at an angular frequency ω to an object, and from the amplitude ratio of the strain γ and stress σ and the phase difference δ, the complex elastic modulus, which is the viscoelastic property of the object E*(ω) = E'(ω)+j E''(ω) is measured, and E'(ω) and E''(ω) are called storage modulus and loss modulus, respectively. Is a function of the angular frequency ω. The dynamic viscoelasticity measurement method is widely used to measure the viscoelastic properties of objects from liquids to solids in the low frequency range below 1 Hz to high frequency ranges up to several 100 Hz.

In Patent Document 2, as a method for measuring the viscoelastic properties of the skin by the dynamic viscoelasticity measurement method, a cyclic force in the rotational or linear direction is applied to the measurement site of the skin, and the waveform of this cyclic force and the skin The method of measuring the mechanical properties of the skin by the waveform of stress is disclosed, from the obtained measurement data, the viscosity of the skin, elasticity, the waveform of the periodic force and the waveform phase difference of the stress from the skin (tan δ) , The maximum stress/maximum amplitude, the area of stress-strain Lissajous, etc. are shown to know the mechanical properties of the skin.

Further, Non-Patent Document 2, FIG. 1 is disclosed, "a typical measurement example of the skin viscoelasticity of each human site (forearm flexion side, palm, back, forehead, cheek, abdomen, back). The measurement frequency was 2 Hz, the amplitude was 2 mm, and the viscoelastic Lissajous diagram (hysteresis curve) showed different shapes depending on the site, which was in good agreement with the sensory value." In other words, the skin is pushed by a predetermined amount with an indenter that vibrates periodically, the displacement and repulsive force at that time are measured, and the amount of pushing and the vibration frequency are measured by the dynamic viscoelasticity measurement method that measures the amplitude ratio and phase difference. It has been shown that with proper selection, the viscoelastic properties of various parts of the skin can be measured.
In FIG. 1, the indentation amount is 2 mm and the indentation frequency is 2 Hz, but the measurement frequency is the frequency at which the area of the hysteresis curve in FIG. 1 is the maximum, that is, the loss of the measured viscoelastic body shows a maximum value. It is desirable to select the frequency.Specifically, for each measurement site, the frequency at which the loss elastic modulus E''(ω) obtained by changing the frequency by the dynamic viscoelasticity measurement method shows the maximum value is selected. The choice seems to be the most appropriate.

Further, in Patent Document 3, the electromagnetic force generated by the electromagnetic coil and the permanent magnet is applied to the surface of the viscoelastic body through a contact indenter, and the position of the contact indenter is detected by a position sensor, A viscoelastic body surface mechanical property measuring device for measuring the deformation process of the viscoelastic body surface and the recovery process of the viscoelastic body surface after removing electromagnetic force is disclosed. Specifically, a contact indenter is measured. The surface of the test object after removing the pressure of the contact indenter by applying it to the surface of the viscoelastic body, increasing the pressure of the contact indenter from zero to a predetermined target value in a short time, and suddenly decreasing it to zero after a given rest time. A method of calculating the elastic modulus and the viscous coefficient of a viscoelastic body by numerical analysis by measuring the relationship between the strain amount and the time is disclosed.

However, in Patent Document 3, “By measuring the relationship between the strain amount and time of the surface of the subject after removing the pressure of the contact indenter, the elastic modulus and viscosity of the viscoelastic body are calculated by numerical analysis.” , But it is not clear from the obtained measurement data what kind of procedure is specifically used to obtain the elastic modulus and viscosity of the object.

In addition, the contact impedance method compares the resonance frequency fr and the resonance resistance R in the unloaded state of the sensor vibrator that is configured by mounting a hemispherical contact at the antinode of the resonance vibration of the piezoelectric vibrator or magnetostrictive vibrator. A method of measuring the viscoelastic characteristics of the object from the resonance frequency fr and the amount of change Δfr and ΔR of the resonance resistance R when the contactor is pressed against the object with a constant load. , A contact to which a vibration of a predetermined frequency is given, an oscillation circuit that measures a change in the frequency of the contact when the contact is brought into contact with the human skin surface, and a contact to a predetermined contact with the human skin surface. When pressed by pressure, it has a strain gauge that measures the reaction force received from the skin surface, and a skin characteristic measurement unit that measures the characteristics of the skin surface based on the measurement results of the oscillation circuit and the strain gauge. A skin characteristic measuring device 1 capable of measuring both the surface elasticity and the internal hardness of the skin at the same time and at the same site on the skin surface is disclosed. However, the skin characteristic measuring device disclosed in Patent Document 4 is disclosed. In, the viscoelastic property of human skin or food is simply measured as hardness or elasticity, and the viscoelastic property of skin is not measured.

Furthermore, in the contact impedance method, a resonator with a resonance frequency of several tens of kHz to several hundreds of kHz is generally used, but since the complex elastic modulus of the viscoelastic body changes greatly depending on the measurement frequency, the measurement data obtained by the contact impedance method is used. However, there is a problem in that the measurement frequency is always the measurement condition and the measurement data lacks universality.

Figure 2 shows a graph of stress relaxation characteristics showing the change in stress over time when a constant strain is applied to the viscoelastic body.Generally, in the measurement of stress relaxation characteristics, the characteristics of Figure 2 are shown in Figure 3. The method of approximation using the three-element type standard linear solid-state model shown is well known. In this case, E _e and E ₁ in FIGS. 2 and 3 are called permanent elastic modulus and relaxation elastic modulus, respectively, and τ in FIG. 2 is called relaxation time. The stress relaxation characteristic of Fig. 2 is expressed by the stress relaxation function of Equation 1, and η _t of the three-element type standard linear solid model of Fig. 3 is the viscosity, and the relationship between relaxation elastic modulus E ₁ and relaxation time τ and Equation 2 is is there.

When the stress relaxation characteristic of the viscoelastic body is expressed by Equation 1, the storage elastic modulus E′(ω) and loss elastic modulus E′(ω) of this viscoelastic body are given by Equation 3 and Equation 4, respectively. To be That is, if the parameters E _e , E ₁ , and τ of the stress relaxation function of Equation 1 are obtained, it is possible to obtain the same complex elastic modulus E*(ω) as that obtained by the dynamic viscoelasticity measurement method. 2, and Non-Patent Document 2, the viscosity of the skin, elasticity, phase difference (tan δ), maximum stress / maximum amplitude, the area of stress-strain Lissajous, can be determined, the mechanical properties of the skin You can know
Further, since the frequency f _{0 at} which the area of the hysteresis curve is maximum and the relaxation time τ have the relationship of Equation 5, if the relaxation time τ is obtained, from Equation 6, the area of the hysteresis curve is maximum. The frequency f ₀ can be obtained.

The dynamic viscoelasticity measurement method described above requires an excitation drive force generation device, a vibration displacement sensor, and a pressure sensor, which makes the device complicated and large, and also for controlling the drive frequency, drive force, and vibration width. Circuit and the phase detection circuit between the displacement sensor output and the pressure sensor output, etc. are required, and the cost is high, so it is especially difficult to incorporate it in the handy probe.

In addition, the conventional stress relaxation characteristic measurement method requires a long time to correctly measure the permanent elastic modulus E _e , and thus the measurement time becomes long, and in addition to the actual viscoelasticity of the skin, Since it is difficult to approximate the stress relaxation characteristics of the body with the three-element standard linear solid-state model shown in Figs. 2 and 3 over a wide elapsed time range, the viscoelastic characteristics of the skin can be determined from short-term measurement data. A method for approximating each parameter of the stress relaxation function of Equation 1 effective for evaluation is required.
Also in the stress relaxation characteristic measuring method, there is a demand for a load sensor that can be built in a small, handy probe.

JP-A 1-115342 JP 61-181436 JP 2004-85548 JP JP 2011-130805 JP

Hirokazu Shirato, et al.; “Development of artificial skin with skin texture”: The Japan Society of Mechanical Engineers, Vol. 73, No. 726, pp541-546 (2007-2). Umeya Junichiro; "Development and rheological analysis of skin viscoelasticity measuring instrument"; Journal of the Rheological Society of Japan Vol.23 No.4 pp197-206 (1995)

The present invention provides a small-sized pressure sensor unit that is easy to mount on a handy-type probe, has a simple structure, and provides long-term data from the measurement data of the stress relaxation characteristics of the skin obtained using this pressure sensor unit. Even within 2 seconds, the parameters of the stress relaxation function approximated by the three-element type standard linear solid model can be obtained, and from these parameters, the same complex elastic modulus as the characteristics obtained by the dynamic viscoelasticity measurement method can be obtained. A possible method for measuring the viscoelastic property of skin and an apparatus using the same are provided.

According to the invention,
On the surface of the skin, a means for pushing a substantially hemispherical indenter by a predetermined amount and holding it,
Means for measuring the repulsive force that the indenter receives from the skin with respect to the elapsed time from immediately after the indenter is pushed into the surface of the skin,
Using the measured data of the repulsion force with respect to the elapsed time, means for determining the parameters when the viscoelastic characteristics of the skin is approximated by the stress relaxation function of the three-element standard linear solid model,
From these parameters, means for obtaining frequency characteristics such as the complex elastic modulus of the viscoelastic body and the loss coefficient tan δ,
Using the viscoelastic properties of the skin obtained by the series of means, means for numerically displaying the elasticity and elasticity of the skin,
A viscoelastic property measuring method for skin and a device using the same are obtained.

Further, according to the present invention,
As a means for obtaining parameters when the viscoelastic properties of the skin are approximated by a stress relaxation function of a three-element standard linear solid model, a correction index to the data within 2 seconds from the measurement start of the repulsive force measurement data with respect to the elapsed time. A method for measuring the viscoelastic property of skin according to claim 1 characterized by applying a parameter estimation method for a function, and the method using the method are obtained.

Further, according to the present invention,
As a means for determining the parameters when the viscoelastic characteristics of the skin are approximated by a stress relaxation function of a three-element type standard linear solid model, from the measured data of the repulsive force with respect to the elapsed time, the repulsive force F ₀ immediately after indentation, and the measurement used after the start of within 0.2 seconds t ₁ and the repulsive force F ₁ at that time, and the measurement starting 2 seconds and the elapsed time t ₂ within the value of the repulsive force F ₂ at that time, satisfy these measurements Permanent elastic modulus E _e of the parameters of the stress relaxation function of the three-element standard linear solid model to be, relaxation elastic modulus E ₁ , and relaxation time τ of the skin according to claim 1, characterized by numerical calculation. A viscoelastic property measuring method and a device using the same can be obtained.

Further, according to the present invention,
As a means for measuring the repulsive force that the indenter receives from the skin, in the center of the rectangular elastic plate, a columnar indenter with a substantially hemispherical tip is formed perpendicular to the plate surface, and the rectangular elastic body is formed. A pressure sensor is used which is formed by forming strain gauges at four positions symmetrical with respect to a bisector in the width direction of the main surface of the plate and symmetrical with the position where the cylindrical indenter is formed. The method for measuring the viscoelastic property of the skin according to claim 2, and the device using the same are obtained.

According to the invention,
Using a pressure sensor that is easy to mount on a handy type probe, has a simple structure, and can be easily downsized, it has the same complex elastic modulus E*(ω) as that obtained by the dynamic viscoelasticity measurement method. It is possible to measure, and from the measurement data of the stress relaxation characteristics of the skin within 2 seconds at the longest, the parameter of the stress relaxation function approximated by the three-element standard linear solid model can be obtained, and the obtained parameters are used. Thus, it is possible to provide a method for measuring the viscoelastic property of skin and a device using the same.

Is a drawing described in Non-Patent Document 2 Is a graph showing changes in stress with time when a constant strain is applied to a viscoelastic body. Is an equivalent circuit of a three-element standard linear solid-state model used for analysis of stress relaxation characteristics Is a graph showing the modified exponential function Is a table for finding the partial sum for calculating the parameters of the modified exponential function Is a calculation example when the modified exponential parameter estimation method is applied to the measured data of stress relaxation characteristics. Is an example of calculation when the numerical calculation method is applied to the measured data of stress relaxation characteristics FIG. 1 is a cross-sectional view showing a structural example of a pressure sensor unit 1 used for a measurement probe of a skin viscoelasticity characteristic measuring apparatus of the present invention. FIG. 3 is a structural example of a strain gauge type pressure sensor used for a measurement probe of the skin viscoelasticity characteristic measuring apparatus of the present invention. FIG. 3 is a cross-sectional view showing a structural example of the tip portion of the measurement probe of the skin viscoelasticity characteristic measuring apparatus of the present invention. FIG. 4 is a cross-sectional view showing another structural example of the tip portion of the measurement probe of the skin viscoelasticity characteristic measuring apparatus of the present invention.

In the present invention, on the end face of the handy type measurement probe, the measurement probe equipped with a pressure sensor having a cylindrical indenter with a substantially hemispherical tip, which is configured to project at the time of measurement, is attached to an arbitrary portion of the body. Vertically pressed against the skin, the tip is pushed into the skin a predetermined amount of a substantially hemispherical cylindrical indenter, the change in the repulsive force from the skin with respect to the elapsed time immediately after the pressing is measured, and from this measurement data of the skin Seeking viscoelastic properties.
Since the repulsive force is proportional to the elastic modulus of the skin, the obtained measurement data will show the stress relaxation characteristics as shown in FIG. 2, and from the measurement data of the stress relaxation characteristics of FIG. The parameter E _e , E ₁ , and τ of the stress relaxation function of Equation 1 are obtained in a short time using the “parameter estimation method”.
The modified exponential function is generally a function expressed by Equation 7, where t is a time variable that takes a value of 0, 1, 2... And when a<0, 0<b<1, it becomes the function shown in FIG. The three unknown parameters K, a, and b of the modified exponential function can be obtained from the measurement data of stress relaxation characteristics by the following procedure 1 and procedure 2. When the three parameters K, a, and b of the modified exponential function are obtained, the procedure 3 allows the parameters E _e , E ₁ , and τ of the stress relaxation function of Expression 1 to be obtained.

(Procedure 1) As shown in FIG. 5, the measured values are divided into three groups of n pieces, and the sum of the data values of each group is defined as partial sums S ₁ , S ₂ , and S ₃ .
(Procedure 2) Using the partial sums S ₁ , S ₂ , and S ₃ of FIG. 5, the parameters b, a, and K of the modified exponential function are calculated from Equations 8, 9, and 10.

(Procedure 3) The equation 1 and the equation 5 are compared, and the parameters of the stress relaxation function of the equation 1 are obtained by the equations 11, 12, and 13.

However, Δt in Expression 13 is a coefficient for converting the time variable t that takes the values 0, 1, 2,... In Expression 7, into the real time, and is the measurement time for acquiring the stress relaxation characteristic data of FIG. It is the pitch.

FIG. 6 is a calculation example in the case of applying the parameter estimation method of the modified exponential function to the measurement data of the stress relaxation characteristics measured using the silicone rubber sample having the elastic modulus close to that of the skin, and the three figures are In addition, a calculation example in which the number of data n in one groove is set to n=5, n=10, and n=20 is shown in comparison with the actual measurement value. The title of each figure shows the time required for measurement given by the product of the value of n, the number of data used for calculation, and the measurement time pitch, and when n=5, n=10, n=20 It shows that the time required for each is 0.3 seconds, 0.6 seconds, and 1.2 seconds. Furthermore, in each figure, the parameters E _e , E ₁ , and τ of the obtained stress relaxation function of Equation 1 are shown. In FIG. 6, the units of E _e and E ₁ are Pa, and the unit of time t is s.

As described above, if the relaxation time τ is known, the frequency f _{0 at} which the area of the hysteresis curve becomes the maximum can be obtained, so n=5 obtained from the estimated value of the relaxation time τ obtained under each condition, The estimated values of f ₀ when n=10 and n=20 are 1.6 Hz, 0.8 Hz, and 0.4 Hz, respectively.
That is, as can be seen from FIG. 6, in the approximation method using the modified exponential function, the elapsed time region with good approximation accuracy changes depending on the number of data n in one group, and the parameters of the stress relaxation function of the obtained Equation 1 are obtained. The values of E _e , E ₁ , and τ are also changing. However, originally, the stress relaxation characteristics of the actual viscoelastic body such as the viscoelastic characteristics of the skin can be approximated by the "3-element type standard linear solid model" shown in Figs. 2 and 3 in a wide elapsed time range. Since it is difficult, by applying the parameter estimation method by the modified exponential function of the present invention, the approximation accuracy and the approximation limit by the number n of data in one group becomes clear, and the measurement target is limited to the skin, etc., By properly selecting the number n of data in one group, effective data regarding the viscoelastic properties of the skin can be obtained.

For example, according to the data shown in Fig. 1, the hysteresis between the applied strain and the generated stress is large at the vibration frequency of 2 Hz, and the loss elastic modulus E''(ω) is maximum near this frequency. It can be seen that the value is shown. When f ₀ =2Hz, the relaxation time τ becomes about 0.08 seconds from the relation of Equation 6. That is, in this case, it is considered that the approximation condition with high approximation accuracy near τ≈0.1 seconds is suitable. In the case of the silicone rubber sample shown in FIG. 6, τ=0.1 seconds when n=5, and it can be seen from FIG. 6 that the measured value and the calculated value are in good agreement until the elapsed time near 0.3 seconds. I understand.

In the present invention, further, from the measurement data of the stress relaxation characteristics of FIG. 2, as a method of obtaining the parameters E _e , E ₁ , τ of the stress relaxation function of Formula 1 in a short time, the repulsive force F ₀ immediately after the indentation, and the measurement used after the start of within 0.2 seconds t ₁ and the repulsive force F ₁ at that time, and the measurement starting 2 seconds and the elapsed time t ₂ within the value of the repulsive force F ₂ at that time, satisfy these measurements The permanent elastic modulus Ee, the relaxation elastic modulus E ₁ , and the relaxation time τ, which are the parameters of the stress relaxation function of the three-element type standard linear solid model, are obtained by numerical calculation.
This approximation method (hereinafter simply referred to as the numerical calculation method) is based on the measurement data of the stress relaxation characteristics shown in Fig. 2, E(t ₁ ) at t=t ₁ and E(t ₁ ) at t=t _2. (t ₂ ), and the initial value E ₀ =E(0)=E _e +E ₁ of the elastic modulus E are given to obtain the permanent elastic modulus E _e and the relaxation elastic modulus E ₁ .
From the above assumptions, Equations 14 and 15 are obtained, and from Equations 14 and 15, simultaneous equations of Equations 16 and 17 are obtained.

By solving the simultaneous equations of Formula 16 and Formula 17 by numerical calculation, the values of the stress relaxation number parameters E _e , E ₁ , and τ of Formula 1 can be obtained.

FIG. 7 is a calculation example in which a numerical calculation method is applied to the measurement data of stress relaxation characteristics measured using a silicone rubber sample having an elastic modulus similar to that of FIG. 6, and the three figures are respectively , E ₀ =4.42×10 ⁴ Pa, (1)t ₁ =0.1s, t ₂ =0.5s, (2)t ₁ =0.1s, t ₂ =1.0s, (3)t ₁ =0.1s, A calculation example when t ₂ =1.5 s is shown in comparison with the actual measurement value. The titles of the respective figures show the values of t ₁ and t ₂ , and in the respective figures, the parameters E _e , E ₁ , and τ of the obtained stress relaxation function of Equation 1 are shown.

Also in FIG. 7, as in the case of the approximation method by the modified exponential function method shown in FIG. 6, in the approximation by the numerical calculation method, at times t ₁ and t ₂ for obtaining the simultaneous equations of Equation 16 and Equation 17, Depending on the selection method, the elapsed time region with good approximation accuracy changes, and the values of the parameters E _e , E ₁ , and τ of the obtained stress relaxation function of Equation 1 also change. However, by applying the parameter estimation method of the stress relaxation function by the numerical calculation method of the present invention, it becomes clear that the elapsed time region with good approximation accuracy changes depending on how to select the times t ₁ and t ₂ , and the measurement target is changed. with limited like the skin, by choosing the time t ₁ and t ₂ properly, it is possible to obtain effective data relating to viscoelastic properties of the skin. Also in FIG. 7, the units of E _e and E ₁ are Pa and the unit of time t is s.

From the description of FIG. 1 and the results of FIG. 6 and FIG. 7 described above, in the method for measuring the viscoelastic property of the skin of the present invention, if the measurement data within 2 seconds from the start of the measurement is used, the viscoelastic property of the skin is correctly measured. It turns out that it can be measured.

FIG. 8 is a cross-sectional view showing a structural example of the pressure sensor unit 1 used in the measurement probe of the skin viscoelastic characteristic measuring apparatus of the present invention. Vertically, the tip end shape is attached with a cylindrical indenter 3 having a substantially hemispherical shape, and a plurality of strain gauges 4 are attached to at least one surface of the rectangular elastic plate 2 to provide a strain gauge type pressure sensor 5 Is formed. Both ends of the rectangular elastic body plate 2 of the strain gauge type pressure sensor 5 are fixed near the roots of the legs of the substantially U-shaped sensor holder 6, and between the rectangular elastic body plate 2 and the bottom of the sensor holder 6. Has a minute gap 7 formed therein. The space between the minute gaps 7 serves to prevent an excessive force from acting on the cylindrical indenter 3 and the bending amount of the rectangular elastic plate 2 becoming too large.
In FIG. 8, when a load is applied to the tip of the cylindrical indenter 3, the rectangular elastic plate 2 bends, and a voltage proportional to this bending can be detected by the strain gauge pressure sensor 5.

FIG. 9 is a structural example of the strain gauge type pressure sensor 5 used in the pressure sensor unit 1 shown in FIG. 8, and is a plan layout view when four strain gauges are formed on the surface of the rectangular elastic plate 2. Is shown. In FIG. 9, four strain gauges 41, 42, 43, 44 are formed at four positions symmetrical with respect to the bisector in the width direction of the rectangular elastic plate 2 and symmetrical with the position of the cylindrical indenter 3. Has been done.
By arranging the four strain gauges as shown in FIG. 9, if a force is applied to the tip of the cylindrical indenter 3 to incline the cylindrical indenter 3 in the longitudinal direction of the rectangular elastic plate 2, When the output voltage of the strain gauges 41 and 42 increases, the output voltage of the strain gauges 43 and 44 decreases, and conversely, when the output voltage of the strain gauges 41 and 42 decreases, the output voltage of the strain gauges 43 and 44 increases. As a result, even when a force that tilts the cylindrical indenter 3 in the longitudinal direction of the rectangular elastic plate 2 is applied, the length of the cylindrical indenter 3 is calculated by obtaining the sum of the output voltages of the four strain gauges. The load component in the depth direction can be correctly detected.

Further, when a force that tilts the cylindrical indenter 3 in the width direction of the rectangular elastic plate 2 is applied to the tip of the cylindrical indenter 3, when the output voltage of the strain gauges 41 and 43 increases, the strain gauges 42 and 44 become When the output voltage decreases and conversely the output voltage of the strain gauges 41 and 43 decreases, the output voltage of the strain gauges 42 and 44 increases. As a result, even when a force that tilts the cylindrical indenter 3 in the width direction of the rectangular elastic plate 2 is applied, by calculating the sum of the output voltages of the four strain gauges, the load in the longitudinal direction of the cylindrical indenter 3 is obtained. The component can be detected correctly.
According to the effects described above, four strain gauges are arranged as shown in FIG. 9, and the sum of the output voltages of the four strain gauges is obtained to correctly detect the load component in the longitudinal direction of the cylindrical indenter 3. be able to.

FIG. 10 is a cross-sectional view showing a structural example when the pressure sensor unit 1 is incorporated in the tip of a measurement probe. The pressure sensor unit 1 includes a pressure sensor unit holder 8 having an opening 10 at the tip thereof, and the tip of the cylindrical indenter 3 of the pressure sensor unit 1 from the opening 10 by a predetermined amount from the end surface 9 of the probe tip. It is fixed so that it only protrudes. Since the end surface 9 of the pressure sensor holder 8 is processed to be flat, when the measurement probe is brought into vertical contact with the skin, the skin is pushed by the protruding amount of the cylindrical indenter 3, and the measurement probe is moved at a normal speed. By contacting the skin, the cylindrical indenter 3 can be pushed into the skin almost instantly.

FIG. 11 is a cross-sectional view showing another structural example of the skin viscoelasticity measurement probe using the pressure sensor unit 1 used in the skin viscoelasticity characteristic measuring apparatus of the present invention, (a) is a standby for measurement. In the state, the tip of the cylindrical indenter 3 is recessed from the end surface 9 of the sensor unit holder 8 of the measurement probe, and (b) shows the tip of the cylindrical indenter 3 in the state of measurement is the sensor unit of the measurement probe. It projects from the end surface 9 of the holder 8 by a predetermined amount. In FIG. 11, the pressure sensor unit 1 is joined to a movable shaft 12 of a direct-acting electromagnetic solenoid 11, and a coil spring 13 acts so as to recess the cylindrical indenter 3 during standby, and at the time of measurement, the electromagnetic By energizing the solenoid 11, the drive shaft 12 moves downward as shown in FIG. 11(b), and the tip of the cylindrical indenter 3 projects from the end surface 9 of the measurement probe by a predetermined amount.
By driving the electromagnetic solenoid 11 in a state where the measurement probe is in vertical contact with the skin, it is possible to project the cylindrical indenter 3 in a state where the probe is held in a more correct position, which is more accurate. Can be measured.

As described above, in the present invention, from the measured data of the stress relaxation characteristics, as a method of estimating the parameters of the stress relaxation function of the three-element type standard linear solid model, (a) when using the parameter estimation method of the modified exponential function, three elements (B) Repulsive force F ₀ immediately after indentation, elapsed time t ₁ within 0.2 seconds from the start of measurement, repulsive force F _{1 at} that time, and start of measurement Although the method of obtaining by numerical calculation using the elapsed time t ₂ within 2 seconds and the repulsive force F ₂ at that time was explained, other methods such as the general least square method are applied to obtain Is also good.

Further, although the present invention is mainly used for measuring the viscoelastic properties of the skin, it goes without saying that the device of the present invention may be used for measuring the viscoelastic properties of relatively soft objects such as rubber and food. That is.

Further, in the description of the pressure sensor unit of the present invention, the case where a cylindrical indenter having a substantially hemispherical tip is used has been described, but the shape of the columnar portion may be a prism having a square cross section.

1: Pressure sensor unit
2: Rectangular elastic plate
3: Cylindrical indenter
4,41,42,43,44: Strain gauge
5: strain gauge type pressure sensor
6: Sensor holder
7: Minute gap
8: Sensor unit holder
9: Probe end face
10: opening

Claims (4)

On the surface of the skin, a means for pushing a substantially hemispherical indenter by a predetermined amount and holding it,
Means for measuring the repulsive force that the indenter receives from the skin with respect to the elapsed time from immediately after the indenter is pushed into the surface of the skin,
Using the measured data of the repulsion force with respect to the elapsed time, means for determining the parameters when the viscoelastic characteristics of the skin is approximated by the stress relaxation function of the three-element standard linear solid model,
From these parameters, means for obtaining frequency characteristics such as the complex elastic modulus of the viscoelastic body and the loss coefficient tan δ,
Using the viscoelastic properties of the skin obtained by the series of means, means for numerically displaying the elasticity and elasticity of the skin,
And a device using the same As a means for obtaining parameters when the viscoelastic properties of the skin are approximated by a stress relaxation function of a three-element standard linear solid model, a correction index to the data within 2 seconds from the measurement start of the repulsive force measurement data with respect to the elapsed time. A method for measuring the viscoelastic property of skin according to claim 1, characterized by applying a parameter estimation method for a function, and a device using the same As a means for determining the parameters when the viscoelastic characteristics of the skin are approximated by a stress relaxation function of a three-element type standard linear solid model, from the measured data of the repulsive force with respect to the elapsed time, the repulsive force F ₀ immediately after indentation, and the measurement used after the start of within 0.2 seconds t ₁ and the repulsive force F ₁ at that time, and the measurement starting 2 seconds and the elapsed time t ₂ within the value of the repulsive force F ₂ at that time, satisfy these measurements Permanent elastic modulus E _e of the parameters of the stress relaxation function of the three-element standard linear solid model to be, relaxation elastic modulus E ₁ , and relaxation time τ of the skin according to claim 1, characterized by numerical calculation. Viscoelastic property measuring method and apparatus using the same As a means for measuring the repulsive force that the indenter receives from the skin, in the center of the rectangular elastic plate, a columnar indenter with a substantially hemispherical tip is formed perpendicular to the plate surface, and the rectangular elastic body is formed. A pressure sensor is used which is formed by forming strain gauges at four positions symmetrical with respect to a bisector in the width direction of the main surface of the plate and symmetrical with the position where the cylindrical indenter is formed. A method for measuring the viscoelastic property of skin according to claim 2, and a device using the same