CN104977250A - Skin care product quality evaluation system based on skin friction performance testing - Google Patents

Abstract

The invention relates to a skin care product quality evaluation system based on skin friction performance testing. The system comprises a friction performance testing device which comprises a testing piece and a sensing system signal processor; the testing piece comprises a friction element and a sensor; the friction element is fixed on an upper PCB of the sensor; a lower PCB of the sensor is fixed on the skin friction performance testing device; the sensor collects the values of positive pressure and friction force and sends the values to the sensing system signal processor; the sensor comprises an X-direction capacitor unit group and a Y-direction capacitor unit group; each of the X-direction capacitor unit group and the Y-direction capacitor unit group comprises capacitor unit modules; and each capacitor unit module is in a comb-tooth-shaped structure comprising more than two strip-shaped capacitor units. According to the skin care product quality evaluation system, the skin friction performance testing device is used for testing the skin on the upper limb of a human body; tested parts comprise the forehead, cheeks, retroauricular parts, and the like on the face; and the testing is flexible and convenient.

Description

Skin care product quality evaluation system based on skin friction performance test

Technical Field

The invention belongs to the field of skin friction performance tests, and particularly relates to a skin care product quality evaluation system based on the skin friction performance test.

Background

The skin is positioned on the surface of the human body and is the first line of defense of human health. The realization of many physiological functions of human skin depends on the mechanical properties of the skin, and the elastic properties of the skin are important parameters of the mechanical properties of the skin. Therefore, the research on the friction and elasticity of human skin has important significance for keeping the skin healthy and improving the life quality of people.

The skin care and cosmetic industries are rapidly developing in global markets, and the skin care and cosmetic industries can be quantitatively evaluated by applying the friction performance of the skin. Skin care or cosmetic products applied to the skin function to deliver nutrients and protective ingredients to the skin, store moisture, and evaporate moisture from the surface of the tissue skin to provide a smooth and moist feel to the skin, while also changing the viscosity, friction, and elastic properties of the skin.

However, most of the existing skin test devices can only test the skin of the upper limb part of the human body, the limitation of the test part is large, the test of the forehead, the cheek, the back of the ear and other parts of the face is restricted by the machine, the test precision is limited by the sensor, and the sensitivity is not high.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a skin care product quality evaluation system based on skin friction performance test, which realizes skin test on tiny parts of a human body, such as forehead, cheek, behind the ear and the like, by improving the structure of a skin tester, and improves the measurement precision by improving a force sensitive element.

The technical scheme of the invention is as follows: a skin care product quality evaluation system based on skin friction performance test comprises a friction performance test device, the device comprises a test piece and a sensing system signal processor, wherein the test piece comprises a friction element and a sensor, the friction element is fixed on an upper PCB of the sensor, a lower PCB of the sensor is fixed on the skin friction performance testing device, the sensor collects positive pressure and friction force and sends the positive pressure and the friction force to the sensing system signal processor, the sensor comprises an X-direction capacitor unit group and a Y-direction capacitor unit group, the X-direction capacitor unit group and the Y-direction capacitor unit group both comprise capacitor unit modules, the capacitor unit module is of a comb-tooth-shaped structure consisting of more than two strip-shaped capacitor units, each strip-shaped capacitor unit comprises a driving electrode of an upper polar plate and an induction electrode of a lower polar plate, and the capacitor unit module comprises more than two widths a.₀Length b₀A first strip-shaped capacitor unit group consisting of strip-shaped capacitor units and more than two widths ka₀Length b₀And the second strip-shaped capacitor unit group is formed by the strip-shaped capacitor units.

The skin care product quality evaluation system based on the skin friction performance test further comprises a transmission device, the transmission device comprises a sensor fixing piece, a lower PCB of the sensor is fixed at the upper end of the sensor fixing piece, the transmission device enables a friction element to penetrate through a rectangular hole in the top end of the skin friction test device through the sensor fixing piece to move back and forth, and the friction element is made of a silicone material. The width of the driving electrode and the width of the induction electrode of each strip-shaped capacitor unit are the same, the length of the driving electrode is greater than that of the induction electrode, and left difference positions are reserved at two ends of the length of the driving electrode respectively_{Left side of}And the right difference position_{Right side}，b_{0 drive}bb_{Feeling of 0}+_{Right side}+_{Left side of}Wherein b is_{0 drive}Length of the driving electrode of the strip-shaped capacitor unit, b_{Feeling of 0}The length of the induction electrode of the strip-shaped capacitance unit. The difference position_{Left side of}＝_{Right side}And is andwherein d is₀Is the thickness of the dielectric of the strip-shaped capacitor unit, G is the shear modulus of the elastic dielectric, tau_maxThe maximum stress value. The comb-shaped structure comprises more than 20 strip-shaped capacitor units and leads connected with the strip-shaped capacitor units in a one-to-one correspondence manner, and an electrode distance a is arranged between every two adjacent strip-shaped capacitor units . The parallel plate area S ═ M (a)₀+2a +ka₀)b₀A/2, wherein M is the number of strip-shaped capacitor units, b₀Is the length of the strip-shaped capacitor unit, a₀The width of the strip-shaped capacitor unit. And the strip-shaped capacitor unit leads of the first strip-shaped capacitor unit group and the second strip-shaped capacitor unit group are connected in parallel or independently connected to a sensing system signal processor. Width of the strip-shaped capacitor unitWherein d is₀E is the Young's modulus of the elastic medium, and G is the shear modulus of the elastic medium. Intermediate converters are respectively arranged between the first strip-shaped capacitor unit group and the sensing system signal processor, between the second strip-shaped capacitor unit group and the sensing system signal processor, and are used for setting transmission coefficients of voltage to capacitance or frequency to capacitance.

The invention has the following positive effects: the skin friction performance testing device provided by the invention tests the skin of the upper limb part of a human body, the tested parts comprise the forehead, the cheek, the back of the ear and the like, the flexibility and convenience are realized, in addition, the sensitivity of the sensor provided by the invention is high, the force coupling is solved by reserving the difference positions at the two ends of the driving electrode, and the dynamic performance is better.

Drawings

Fig. 1 shows a stripe-shaped capacitor unit and its coordinate system according to an embodiment of the present invention.

Fig. 2 is a schematic diagram of a stripe-shaped capacitor unit according to an embodiment of the invention.

Fig. 3 is a schematic diagram of right-direction shift of a stripe-shaped capacitor unit according to an embodiment of the present invention.

Fig. 4 is a schematic diagram of left-shift of a stripe-shaped capacitor unit according to an embodiment of the present invention.

FIG. 5 shows an embodiment of the present invention having a width a₀And ka₀Capacitance versus force deflection plot of (a).

FIG. 6 is a diagram of a parallel plate three dimensional force pressure sensor configuration according to an embodiment of the present invention.

FIG. 7 is a signal diagram of a cell capacitor pair according to an embodiment of the present invention.

Fig. 8 is a skin friction performance testing apparatus according to an embodiment of the present invention.

Fig. 9 is a top view of a skin friction performance testing device according to an embodiment of the present invention.

Wherein, 1 friction element, 2 sensor, 3 upper cover, 4 sensor fixing piece, 5 travel switch, 6 stopper, 7 spout, 8 screw transmission structure, 9 motor, 10 data acquisition card, 11 outer wall.

Detailed Description

The following description of the embodiments with reference to the drawings is provided to describe the embodiments of the present invention, and the embodiments of the present invention, such as the shapes and configurations of the components, the mutual positions and connection relationships of the components, the functions and working principles of the components, the manufacturing processes and the operation and use methods, etc., will be further described in detail to help those skilled in the art to more completely, accurately and deeply understand the inventive concept and technical solutions of the present invention.

The main ideas of the invention are as follows: the skin feels just inversely proportional to the "degree of greasiness" the skin feels after the cosmetic is applied. That is, the higher the skin friction coefficient rises, the less greasy the skin feels. Because the cosmetics release nutrients and protective components to the skin, store moisture, resist evaporation of moisture from the skin surface, and utilize the relationship between changes in friction and skin feel due to hydration of cosmetics and emollients, the quality of the cosmetics and skin care products can be assessed.

Fig. 8 shows a skin friction test device of the present invention, which mainly comprises a test piece, a transmission device and a sensing system signal processor, wherein the test piece mainly comprises a friction element 1 and a sensor 2, the friction element 1 is made of silicone material, the sensor 2 comprises an upper PCB and a lower PCB, the friction element 1 is hemispherical, and a section of the friction element is fixed with the upper PCB of the sensor 2. The transmission device mainly comprises a motor 9, a thread transmission mechanism, a sliding groove 7, a sensor fixing part 4 and a travel switch 5, and a lower PCB of the sensor 2 is fixed on the sensor fixing part 4. The upper end of the sensor fixing part 4 penetrates through the rectangular through hole in the experimental device upper cover 3, the lower end of the sensor fixing part is clamped in the sliding groove 7 and can slide along the sliding groove 7, the two ends of the sliding groove 7 are provided with travel switches 5, and the travel of the sensor fixing part on the sliding groove 7 can be adjusted through the length of a stop block 6 arranged at the lower end of the sensor fixing part 4. The sensor fixing piece 4 is connected with a thread transmission structure 8, the thread transmission structure 8 is connected with a motor 9, and the motor 9 enables the sensor fixing piece 4 to slide on the sliding groove 7 through the thread transmission structure 8. The sensor 2 is connected to a data acquisition card 10 for transmitting the acquired signals to the data acquisition card 10. The reciprocating motion of the friction element 1 is realized by a travel switch 5, the reciprocating motion distance is 0-20 mm, and the reciprocating motion speed variation range is 0.2-1.0 mm/s.

Specifically, the upper end face of the friction element 1 is higher than the outer wall 11 of the skin friction test device, and in the skin friction test process, the outer wall 11 protruding from the test device is firstly utilized to compress the skin at the test position and keeps still, so that constant pressure can be kept between the friction element 1 and the test skin, and the pressure can be adjusted by adjusting the height of the sensor fixing part 4.

The measurement principle of the sensor of the invention is detailed below: FIGS. 4-6 are block diagrams of the plates of the pressure sensor of the present invention, the sensor including an X-squareTo electric capacity unit group and Y direction electric capacity unit group, X direction electric capacity unit group and Y direction electric capacity unit group all include electric capacity unit module, electric capacity unit module adopts the comb-tooth structure of constituteing by the strip electric capacity unit more than two, and every strip electric capacity unit includes the drive electrode of upper polar plate and the response electrode of bottom plate. The capacitance unit module comprises more than two widths a₀Length b₀A first strip capacitor unit group consisting of strip capacitor units and more than two widths ka₀Length b₀And the second strip capacitor unit group is formed by the strip capacitor units. The width of the driving electrode and the width of the induction electrode of each strip-shaped capacitor unit are the same, the length of the driving electrode is greater than that of the induction electrode, and left difference positions are reserved at two ends of the length of the driving electrode respectively_{Left side of}And the right difference position_{Right side}，b_{0 drive}＝b_{Feeling of 0}+_{Right side}+_{Left side of}Wherein b is_{0 drive}Length of the driving electrode of the strip-shaped capacitor unit, b_{Feeling of 0}The length of the induction electrode of the strip-shaped capacitance unit. The difference position_{Left side of}＝_{Right side}And is andwherein d is₀Is the thickness of the medium, G is the shear modulus, τ, of the elastic medium_maxThe maximum stress value. The comb-shaped structure comprises more than 20 strip-shaped capacitor units and leads connected with the strip-shaped capacitor units in a one-to-one correspondence manner, and an electrode distance a is arranged between every two adjacent strip-shaped capacitor units . The parallel plate area S ═ M (a)₀+2a +ka₀)b₀A/2, wherein M is the number of strip-shaped capacitor units, b₀Is the length of the strip-shaped capacitor unit, a₀The width of the strip-shaped capacitor unit. And the strip-shaped capacitor unit leads of the first strip-shaped capacitor unit group and the second strip-shaped capacitor unit group are connected in parallel or independently connected to a sensing system signal processor. Width of the strip-shaped capacitor unitWherein d is₀Is the dielectric thickness, E is the Young's modulus of the elastic dielectric, G is the elasticityShear modulus of the media. And intermediate converters are arranged between the first strip-shaped capacitor unit group and the sensing system signal processor, between the second strip-shaped capacitor unit group and the sensing system signal processor, and are used for setting transmission coefficients of voltage to capacitance or frequency to capacitance.

1. Conversion characteristics of strip-shaped capacitor unit

(1) Excitation signal and coordinate system

The strip-shaped capacitor unit is arranged in a rectangular coordinate system shown in figure 1, and the length b of the plane of the polar plate is₀Width a₀Thickness d of medium₀. The three-dimensional excitation is applied to the outer surface of the capacitor plate, and the generated contact type acting force has three directional components of Fx, Fy and Fz, the acting directions of the Fx and the Fy are along the X axis and the Y axis, and the acting direction of the Fz is along the OZ axisThe direction, normal direction and tangential direction stress are both stress tensors, and capacitance response can be output from the space between leads of the electrodes; normal stress sigma_NFn/A, wherein A ═ a₀·b₀The pole plate is a normal force bearing surface, and Fn is a normal component; generating paired tangential stresses tau on both side surfaces_x＝Fx/A，τ_y＝Fy/A。

According to Hooke's law, σ, in elastic mechanics_nAnd τ_x，τ_yA corresponding deformation of the elastomer will occur. Wherein,

<math> <mrow> <msub> <mi>&sigma;</mi> <mi>n</mi> </msub> <mo>=</mo> <mi>E</mi> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>n</mi> </msub> <mo>=</mo> <mi>E</mi> <mo>&CenterDot;</mo> <msub> <mi>&delta;</mi> <mi>n</mi> </msub> <mo>/</mo> <msub> <mi>d</mi> <mn>0</mn> </msub> <mo>=</mo> <mfrac> <msub> <mi>F</mi> <mi>n</mi> </msub> <mi>A</mi> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow> </math>

<math> <mrow> <mo>&PlusMinus;</mo> <msub> <mi>&tau;</mi> <mi>x</mi> </msub> <mo>=</mo> <mo>&PlusMinus;</mo> <msub> <mi>&gamma;</mi> <mi>x</mi> </msub> <mo>&CenterDot;</mo> <mi>G</mi> <mo>=</mo> <mo>&PlusMinus;</mo> <mi>G</mi> <mo>&CenterDot;</mo> <msub> <mi>&delta;</mi> <mi>x</mi> </msub> <mo>/</mo> <msub> <mi>d</mi> <mn>0</mn> </msub> <mo>=</mo> <mo>&PlusMinus;</mo> <mfrac> <msub> <mi>F</mi> <mi>x</mi> </msub> <mi>A</mi> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow> </math>

<math> <mrow> <mo>&PlusMinus;</mo> <msub> <mi>&tau;</mi> <mi>y</mi> </msub> <mo>=</mo> <mo>&PlusMinus;</mo> <msub> <mi>&gamma;</mi> <mi>y</mi> </msub> <mo>&CenterDot;</mo> <mi>G</mi> <mo>=</mo> <mo>&PlusMinus;</mo> <mi>G</mi> <mo>&CenterDot;</mo> <msub> <mi>&delta;</mi> <mi>y</mi> </msub> <mo>/</mo> <msub> <mi>d</mi> <mn>0</mn> </msub> <mo>=</mo> <mo>&PlusMinus;</mo> <mfrac> <msub> <mi>F</mi> <mi>y</mi> </msub> <mi>A</mi> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>3</mn> <mo>)</mo> </mrow> </mrow> </math>

wherein E is the Young's modulus (unit: GN/m) of the elastic medium²) G is the shear modulus of the elastic medium (unit: GN/m²) And n is the normal displacement of the elastic medium (unit: μ m) and x and y are relative offsets of the upper and lower plates of the capacitor (unit: μ m) with signs determined by the coordinate axis orientation.

(2) Capacitance formula and input-output characteristics thereof

The initial capacitance of a rectangular parallel plate capacitor is:

<math> <mrow> <msub> <mi>C</mi> <mn>0</mn> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> <mo>&CenterDot;</mo> <msub> <mi>a</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>b</mi> <mn>0</mn> </msub> </mrow> <msub> <mi>d</mi> <mn>0</mn> </msub> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>4</mn> <mo>)</mo> </mrow> </mrow> </math>

in the formula,₀the electric constant of the vacuum medium is 8.85PF/m,_r2.5 is the relative permittivity of the dielectric. d₀Receive sigma_nIs excited to produce relative deformation_n＝_n/d₀＝σ_nE, substituting into (4) to obtain input/output characteristics

<math> <mrow> <msub> <mi>C</mi> <mi>n</mi> </msub> <mo>=</mo> <msub> <mi>&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> <mfrac> <mrow> <msub> <mi>a</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>b</mi> <mn>0</mn> </msub> </mrow> <mrow> <msub> <mi>d</mi> <mn>0</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <msub> <mi>&epsiv;</mi> <mi>n</mi> </msub> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>=</mo> <msub> <mi>&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> <mfrac> <mrow> <msub> <mi>a</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>b</mi> <mn>0</mn> </msub> </mrow> <mrow> <msub> <mi>d</mi> <mn>0</mn> </msub> <mrow> <mo>(</mo> <mrow> <mn>1</mn> <mo>-</mo> <mfrac> <msub> <mi>F</mi> <mi>n</mi> </msub> <mrow> <mi>A</mi> <mi>E</mi> </mrow> </mfrac> </mrow> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>5</mn> <mo>)</mo> </mrow> </mrow> </math>

(3) Linearity and sensitivity under normal stress

a. Degree of normal linearity

In the formula (5), F_nIn the denominator, therefore C_n＝f（F_n) Is non-linear due to the maximum value σ in the conversion range_nmaxIn comparison with the medium elastic constant E,_nis a very small quantity, i.e. in the denominator_n<<1, expanding (5) in series while omitting higher order infinitesimal more than the square: (5) The formula can be simplified as follows:

<math> <mrow> <msub> <mi>C</mi> <mi>n</mi> </msub> <mo>=</mo> <msub> <mi>C</mi> <mn>0</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mi>&epsiv;</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>C</mi> <mn>0</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mfrac> <msub> <mi>F</mi> <mi>n</mi> </msub> <mrow> <mi>A</mi> <mo>&CenterDot;</mo> <mi>E</mi> </mrow> </mfrac> <mo>)</mo> </mrow> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>6</mn> <mo>)</mo> </mrow> </mrow> </math>

can be seen in C_nAnd F_nThe maximum relative error of the normal linearity in the conversion characteristic of (a) is close to zero.

b. Sensitivity of the probe

Definition of sensitivity by Normal

The linear sensitivity can be obtained according to the formula (6),

S_n1＝C₀/AE＝_{0 r}/d₀E (7)

and according to the formula (5)

<math> <mrow> <msub> <mi>S</mi> <mrow> <mi>n</mi> <mn>2</mn> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>dC</mi> <mi>n</mi> </msub> </mrow> <mrow> <msub> <mi>dF</mi> <mi>n</mi> </msub> </mrow> </mfrac> <mo>=</mo> <msub> <mi>C</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <mfrac> <mn>1</mn> <mrow> <mn>1</mn> <mo>-</mo> <mn>2</mn> <mi>&epsiv;</mi> </mrow> </mfrac> <mo>=</mo> <msub> <mi>C</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <mfrac> <mn>1</mn> <mrow> <mn>1</mn> <mo>-</mo> <mn>2</mn> <mfrac> <msub> <mi>F</mi> <mi>n</mi> </msub> <mrow> <mi>A</mi> <mo>&CenterDot;</mo> <mi>E</mi> </mrow> </mfrac> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>8</mn> <mo>)</mo> </mrow> </mrow> </math>

S_n2With F_nAnd is changed to F_nThe greater, S_n2The larger, the slightly non-linear over the entire conversion characteristic.

(4) Tangential stress tau_xAnd τ_yCapacitance change under excitation

Tangential stress tau_xAnd τ_yWithout changing the geometric parameters b of the plates₀And a₀To the thickness b of the medium₀Nor is it affected. However tau_xAnd τ_yThe space structure of the strip-shaped capacitor unit is changed, and dislocation offset occurs between the upper and lower electrode plates facing in the forward direction. Taking OX direction as an example, the plate is at tau_xOffset under action_x。

In FIG. 2 when τ is_xIs zero, a_{0 is on}＝a_{0 is lower}Are aligned, effective cross-section A between the substrates_τ＝a₀·b₀(ii) a In FIG. 3, at τ_xUnder the action of right direction, the upper polar plate produces right dislocation offset relative to the lower polar plate_xThereby making the upper and lower electrode platesEffective area A in calculating capacitance_τ＝(a₀＝_x)·b₀(ii) a In FIG. 4, when τ is_xIn the left direction, the offset_xThen to the left and A_τ＝(a₀＝_x)·b₀，τ_xThe reduction in effective area is the same in the left and right directions, resulting in a capacitance of:

<math> <mrow> <msub> <mi>C</mi> <mrow> <mi>&tau;</mi> <mi>x</mi> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>a</mi> <mn>0</mn> </msub> <mo>-</mo> <msub> <mi>&delta;</mi> <mi>x</mi> </msub> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <msub> <mi>b</mi> <mn>0</mn> </msub> </mrow> <msub> <mi>d</mi> <mn>0</mn> </msub> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>9</mn> <mo>)</mo> </mrow> </mrow> </math>

according to shearing Hooke's law

τ_x＝γ_x·G＝G·_x/d₀ (10)

Substituting (10) into (9) to obtain

<math> <mrow> <msub> <mi>C</mi> <mrow> <mi>&tau;</mi> <mi>x</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>C</mi> <mn>0</mn> </msub> <mo>-</mo> <mfrac> <mrow> <msub> <mi>&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> <mo>&CenterDot;</mo> <msub> <mi>&delta;</mi> <mi>x</mi> </msub> <mo>&CenterDot;</mo> <msub> <mi>b</mi> <mn>0</mn> </msub> </mrow> <msub> <mi>d</mi> <mn>0</mn> </msub> </mfrac> <mo>=</mo> <msub> <mi>C</mi> <mn>0</mn> </msub> <mo>-</mo> <mfrac> <mrow> <msub> <mi>&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> <mo>&CenterDot;</mo> <msub> <mi>b</mi> <mn>0</mn> </msub> <msub> <mi>&tau;</mi> <mi>x</mi> </msub> </mrow> <mi>G</mi> </mfrac> <mo>=</mo> <msub> <mi>C</mi> <mn>0</mn> </msub> <mo>-</mo> <mfrac> <mrow> <msub> <mi>&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> <msub> <mi>F</mi> <mi>x</mi> </msub> </mrow> <mrow> <msub> <mi>Ga</mi> <mn>0</mn> </msub> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>11</mn> <mo>)</mo> </mrow> </mrow> </math>

(11) The formula is the input-output characteristic under shear stress, C_τAnd τ_xIn a linear relationship.

And its sensitivity

<math> <mrow> <msub> <mi>S</mi> <mrow> <mi>&tau;</mi> <mi>x</mi> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>dC</mi> <mrow> <mi>&tau;</mi> <mi>x</mi> </mrow> </msub> </mrow> <mrow> <msub> <mi>dF</mi> <mi>x</mi> </msub> </mrow> </mfrac> <mo>=</mo> <mfrac> <mrow> <msub> <mi>&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> </mrow> <mrow> <msub> <mi>Ga</mi> <mn>0</mn> </msub> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>12</mn> <mo>)</mo> </mrow> </mrow> </math>

Analyses similar to equations (9) - (12) are equally applicable to τ_yAnd C_τyThe characteristic and technical index of (1) are merely long side b of the strip-shaped capacitor unit₀Should be arranged in the direction of the OX axis and its short side a₀In the OY direction.

2. Contact parallel plate capacitor design

(1) Planar design of parallel plate capacitor

Set original index normal maximum contact stress sigma_nmax200Kpa, if the normal force A is square 10X 10mm²Then maximum normal force F_zmaxIs σ_nmaxA ═ 20N. Tangential maximum contact stress τ_max70Kp, and the stressed cloth distribution surfaces of the tangential stress are all 10 multiplied by 10mm²The maximum tangential force component F_xmax＝F_ymax＝τ_max·A＝7N。

The structural changes of the strip-shaped capacitor units shown in fig. 3 and 4 are only to illustrate the capacitor output and the tangential stress±τ_xThe capacitance increment is negative in the input relation, so that the initial capacitance structure is not suitable for being used for +/-T_xA response of increasing or decreasing capacitance is obtained. Therefore, the invention adjusts the initial structure of the upper and lower electrode plates of the strip-shaped capacitor unit, and the width is a₀And ka₀The strip-shaped capacitor units form a pair of capacitor unit pairs (C)_LAnd C_R) As shown in detail in fig. 5.

In FIG. 5, capacitor cell C_LAnd C_RElectrode size b₀、d₀Are all the same, and have a width of₀One is ka₀Where k is a constant, preferably an integer greater than 1. When tau is_xWhen equal to 0, C_L＝C₀，C_R＝kC₀On the basis of this as in F_xUnder excitation to produce_xWill result in the offset effect shown in fig. 3 or 4.

<math> <mrow> <msub> <mi>C</mi> <mi>L</mi> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> <mo>&CenterDot;</mo> <msub> <mi>b</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>a</mi> <mn>0</mn> </msub> <mo>-</mo> <msub> <mi>&delta;</mi> <mi>x</mi> </msub> <mo>)</mo> </mrow> </mrow> <msub> <mi>d</mi> <mn>0</mn> </msub> </mfrac> <mo>=</mo> <msub> <mi>C</mi> <mn>0</mn> </msub> <mo>-</mo> <mfrac> <mrow> <msub> <mi>&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> <mo>&CenterDot;</mo> <msub> <mi>b</mi> <mn>0</mn> </msub> <msub> <mi>&tau;</mi> <mi>x</mi> </msub> </mrow> <mi>G</mi> </mfrac> <mo>=</mo> <msub> <mi>C</mi> <mn>0</mn> </msub> <mo>-</mo> <mfrac> <mrow> <msub> <mi>&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> <msub> <mi>F</mi> <mi>c</mi> </msub> </mrow> <mrow> <msub> <mi>Ga</mi> <mn>0</mn> </msub> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>13</mn> <mo>)</mo> </mrow> </mrow> </math>

<math> <mrow> <msub> <mi>C</mi> <mi>R</mi> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> <mo>&CenterDot;</mo> <msub> <mi>b</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>Ka</mi> <mn>0</mn> </msub> <mo>-</mo> <msub> <mi>&delta;</mi> <mi>x</mi> </msub> <mo>)</mo> </mrow> </mrow> <msub> <mi>d</mi> <mn>0</mn> </msub> </mfrac> <mo>=</mo> <msub> <mi>kC</mi> <mn>0</mn> </msub> <mo>-</mo> <mfrac> <mrow> <msub> <mi>&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> <mo>&CenterDot;</mo> <msub> <mi>b</mi> <mn>0</mn> </msub> <msub> <mi>&tau;</mi> <mi>x</mi> </msub> </mrow> <mi>G</mi> </mfrac> <mo>=</mo> <msub> <mi>kC</mi> <mn>0</mn> </msub> <mo>-</mo> <mfrac> <mrow> <msub> <mi>&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> <msub> <mi>F</mi> <mi>x</mi> </msub> </mrow> <mrow> <msub> <mi>Ga</mi> <mn>0</mn> </msub> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>14</mn> <mo>)</mo> </mrow> </mrow> </math>

C_LAnd C_RThe capacitor unit pairs are positioned at the same T_xWill generate_xAnd Δ C_τIn response to (2).

Thus, equation (11) can be modified to

<math> <mrow> <msub> <mi>C</mi> <mrow> <mi>&tau;</mi> <mi>x</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>C</mi> <mrow> <mi>&tau;</mi> <mn>0</mn> </mrow> </msub> <mo>-</mo> <mfrac> <mrow> <msub> <mi>&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> </mrow> <mrow> <msub> <mi>Ga</mi> <mn>0</mn> </msub> </mrow> </mfrac> <msub> <mi>F</mi> <mi>x</mi> </msub> </mrow> </math>

In the formula,the initial capacitance when the shear stress is zero, the above formula is the shear stress input-output characteristic, C_τxAnd F_xIs a linear relationship, and the sensitivity thereof

See the electrode plan layout of FIG. 6, at a 10X 10mm²The center of the substrate is divided into four quadrants, namely an upper right first quadrant I, an upper left second quadrant II, a lower left third quadrant III and a lower right fourth quadrant IV, wherein the quadrants I and III are opposite to tau_xThe capacitor units responding to the combination, and quadrants II and IV are corresponding to tau_yA combination of responsive capacitive cells. The peripheral line is 10X 10mm²The hatched parts represent the cross sections of the outer molds of the lost wax casting process. And taking the position of the induction electrode on the lower PCB substrate as a reference, and arranging the driving electrode on the upper PCB substrate by taking the edge line of the PCB substrate as a reference. The four dotted line boxes in the figure are the reference of the induction electrode on the lower polar plate, and the difference between the induction electrode and the geometric reference line is set₀(0.1mm)。

The capacitance unit module adopts a comb structure, the capacitance unit module adopts a comb-shaped structure consisting of more than two strip-shaped capacitance units, and each strip-shaped capacitance unit comprises a driving electrode of an upper polar plate and an induction electrode of a lower polar plate. From the formula (12) a₀The smaller the sensitivity of the tangential stress response, the greater the single cell is elongated. Let each strip-shaped capacitor unit have a width₀The width of the slot between two strip capacitors is a The pitch of each strip-shaped capacitor unit is ka₀+a₀+2a . To make full use of the planar space of a square substrate, M (ka)₀+a₀+2a )b₀The surface area of a square substrate is approximately equal to 1 in 2, M is the number of strip capacitors, and then M (ka) is obtained₀+a₀+2a ) 20mm, wherein the groove width a It should not be too large, otherwise it is not favorable to use the effective planar space on the substrate, and it should not be too small, and it should be constrained by the lost wax casting process. For normal sensitivity S_nAnd tangential sensitivity S_τEquality, according to equations (7) and (12), let a₀·G＝d₀E, when d₀When k is 0.1mm and k is 1.5, M can be determined.

To realize tau_xAnd τ_yTangential response does not mutually influence, and difference positions are reserved at two ends of the length of a driving electrode of the strip-shaped capacitor unit₀Thus b is_{0 drive}＝b_{0 bottom}+2·₀Wherein in b_{0 drive}The length reservation difference of two ends should be theoretically ensuredCalculated value thereof is <math> <mrow> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>5</mn> </mrow> </msup> <mo>&times;</mo> <mfrac> <mrow> <mn>70</mn> <mo>&times;</mo> <msup> <mn>10</mn> <mn>3</mn> </msup> </mrow> <mrow> <mn>2.4</mn> <mo>&times;</mo> <msup> <mn>10</mn> <mn>6</mn> </msup> </mrow> </mfrac> <mo>=</mo> <mn>2.9</mn> <mo>&times;</mo> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>8</mn> </mrow> </msup> <mi>m</mi> <mo>=</mo> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>2</mn> </mrow> </msup> <mi>u</mi> <mi>m</mi> <mo>&lt;</mo> <mo>&lt;</mo> <mn>1</mn> <mi>u</mi> <mi>m</mi> <mo>,</mo> </mrow> </math> Therefore, it should be ensured in terms of process b_{0 drive}－b_{0 bottom}≥0.01mm。

To realize tau_xAnd τ_yDoes not have any influence on normal capacitance response and has the width of a₀And ka₀The strip-shaped capacitor units form a pair of capacitor unit pairs (C)_LAnd C_R) And performing public calculation to eliminate mutual influence. Guarantee of tau_xGenerating pairs tau in I, III quadrant capacitance unit_xAnd the capacitance response of the unit generates the counter tau in the II and IV quadrants_yTo ensure that the capacitive cells in the four quadrants are at τ_xAnd τ_yTwo groups of differential capacitance pairs can be generated under tangential excitation.

(2) Calculation of normal and tangential forces

Let the width be a in FIG. 6₀When the strip-shaped capacitor unit is subjected to a tangential force tau_xGenerating a tangential displacement d_xThe output capacitance value is C₁Width of ka₀When the strip-shaped capacitor unit is subjected to a tangential force tau_xGenerating a tangential displacement d_xThe output capacitance value is C₂Then, there are:

<math> <mrow> <msub> <mi>C</mi> <mn>1</mn> </msub> <mo>=</mo> <mfrac> <mrow> <mi>&epsiv;</mi> <mrow> <mo>(</mo> <msub> <mi>a</mi> <mn>0</mn> </msub> <mo>-</mo> <msub> <mi>d</mi> <mi>x</mi> </msub> <mo>)</mo> </mrow> <msub> <mi>b</mi> <mn>0</mn> </msub> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> <mo>=</mo> <mfrac> <mrow> <msub> <mi>&epsiv;a</mi> <mn>0</mn> </msub> <msub> <mi>b</mi> <mn>0</mn> </msub> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> <mo>-</mo> <mfrac> <mrow> <msub> <mi>&epsiv;b</mi> <mn>0</mn> </msub> <msub> <mi>d</mi> <mi>x</mi> </msub> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>15</mn> <mo>)</mo> </mrow> </mrow> </math>

<math> <mrow> <msub> <mi>C</mi> <mn>2</mn> </msub> <mo>=</mo> <mfrac> <mrow> <mi>&epsiv;</mi> <mrow> <mo>(</mo> <msub> <mi>ka</mi> <mn>0</mn> </msub> <mo>-</mo> <msub> <mi>d</mi> <mi>x</mi> </msub> <mo>)</mo> </mrow> <msub> <mi>b</mi> <mn>0</mn> </msub> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> <mo>=</mo> <mfrac> <mrow> <msub> <mi>&epsiv;ka</mi> <mn>0</mn> </msub> <msub> <mi>b</mi> <mn>0</mn> </msub> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> <mo>-</mo> <mfrac> <mrow> <msub> <mi>&epsiv;b</mi> <mn>0</mn> </msub> <msub> <mi>d</mi> <mi>x</mi> </msub> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>16</mn> <mo>)</mo> </mrow> </mrow> </math>

obtained from (15) to (16):

<math> <mrow> <msub> <mi>C</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>C</mi> <mn>2</mn> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>&epsiv;a</mi> <mn>0</mn> </msub> <msub> <mi>b</mi> <mn>0</mn> </msub> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> <mo>-</mo> <mfrac> <mrow> <msub> <mi>&epsiv;ka</mi> <mn>0</mn> </msub> <msub> <mi>b</mi> <mn>0</mn> </msub> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> </mrow> </math> and calculating to obtain:

<math> <mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>&epsiv;a</mi> <mn>0</mn> </msub> <msub> <mi>b</mi> <mn>0</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>k</mi> <mo>)</mo> </mrow> </mrow> <mrow> <msub> <mi>C</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>C</mi> <mn>2</mn> </msub> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>17</mn> <mo>)</mo> </mrow> </mrow> </math>

from (15) × k- (16):

<math> <mrow> <msub> <mi>kC</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>C</mi> <mn>2</mn> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>&epsiv;d</mi> <mi>x</mi> </msub> <msub> <mi>b</mi> <mn>0</mn> </msub> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> <mo>-</mo> <mfrac> <mrow> <msub> <mi>&epsiv;kd</mi> <mi>x</mi> </msub> <msub> <mi>b</mi> <mn>0</mn> </msub> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> <mo>=</mo> <mfrac> <mrow> <msub> <mi>&epsiv;d</mi> <mi>x</mi> </msub> <msub> <mi>b</mi> <mn>0</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>k</mi> <mo>)</mo> </mrow> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> <mo>,</mo> </mrow> </math> substituting (17) into the above formula, one can obtain:

$d_x=\frac{a_0({\mathrm{kC}}_1-C_2)}{C_1-C_2}---\left(18\right)$

according to <math> <mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> <mo>=</mo> <msub> <mi>d</mi> <mn>0</mn> </msub> <mo>-</mo> <mi>&Delta;</mi> <mi>d</mi> <mo>=</mo> <msub> <mi>d</mi> <mn>0</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mfrac> <msub> <mi>F</mi> <mi>n</mi> </msub> <mrow> <mi>E</mi> <mo>&CenterDot;</mo> <msub> <mi>S</mi> <mn>0</mn> </msub> </mrow> </mfrac> <mo>)</mo> </mrow> </mrow> </math>

Therefore, the following steps are carried out: <math> <mrow> <msub> <mi>F</mi> <mi>n</mi> </msub> <mo>=</mo> <mfrac> <mrow> <mo>(</mo> <msub> <mi>d</mi> <mi>n</mi> </msub> <mo>-</mo> <msub> <mi>d</mi> <mn>0</mn> </msub> <mo>)</mo> <mi>E</mi> <mo>&CenterDot;</mo> <msub> <mi>S</mi> <mn>0</mn> </msub> </mrow> <msub> <mi>d</mi> <mn>0</mn> </msub> </mfrac> </mrow> </math>

by <math> <mrow> <mfrac> <msub> <mi>d</mi> <mi>x</mi> </msub> <msub> <mi>d</mi> <mn>0</mn> </msub> </mfrac> <mo>=</mo> <mi>&gamma;</mi> <mo>=</mo> <mfrac> <mi>&tau;</mi> <mi>G</mi> </mfrac> <mo>=</mo> <mfrac> <msub> <mi>F</mi> <mi>&tau;</mi> </msub> <mrow> <mi>G</mi> <mo>&CenterDot;</mo> <msub> <mi>S</mi> <mn>0</mn> </msub> </mrow> </mfrac> <mo>,</mo> </mrow> </math> Therefore, it is not only easy to use <math> <mrow> <msub> <mi>F</mi> <mrow> <mi>&tau;</mi> <mi>x</mi> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>GS</mi> <mn>0</mn> </msub> <msub> <mi>d</mi> <mi>x</mi> </msub> </mrow> <msub> <mi>d</mi> <mn>0</mn> </msub> </mfrac> <mo>.</mo> </mrow> </math>

In the above formula, either the normal excitation F_nOr tangential excitation F_yAll are not to O_τAn influence is produced. I.e. automatically eliminating sigma_nAnd τ_yFor tau_xBecause the equivalent and signed capacitance changes are automatically cancelled in all operations where the signals contain a subtraction. And F_yAnd F_xTo sigma_nCan pass through the upper electrode at b₀Directionally increasing geometric length 2₀And (4) eliminating. In the same way, F can be obtained_τy。

(4) Choice of main material and its characteristic parameters

Plate spacing d of comb-shaped parallel plate capacitor₀The inner spaces of the upper and lower substrates except for the copper foil electrodes were all PDMS (polydimethylsiloxane) super-elastic insulating media filled by a lost wax casting method, which was 0.1 mm. Its mechanical and physical parameters are Young's modulus E equal to 6.2MPa, shear elastic modulus G equal to 4.1MPa, and relative dielectric constant when medium is polarized_γ2.5. Since E and G of the medium are much smaller than the elastic modulus E of copper_{Copper (Cu)}103 GPa. Therefore, the deformation of the internal medium of the capacitor in a stress state is far larger than that of the polar plate.

(5) Electrode lead design

Both the driving electrodes and the sensing electrodes need to be provided with lead-out wires, and considering that each driving electrode is grounded on a signal level, four groups of driving electrodes only need to share one lead-out wire. The induction electrodes of the four first strip-shaped capacitor unit groups and the four induction electrodes of the second strip-shaped capacitor unit groups need to use respective independent outgoing lines, so that the whole capacitor assembly has at least 5 pins which are led out from the side surface of the planar package,the four induction electrodes refer to the width a in the X direction₀And a width of ka₀And a width in the Y direction of a₀And a width of ka₀So that the top and bottom outer surfaces of the entire assembly can be easily brought into contact with the measurement object. The invention completes the design of a novel three-dimensional force-sensitive capacitor combination under the support of a new material and a new process, and the design is 10 multiplied by 10mm²The stress surface can transmit the stress to the medium more uniformly in the normal direction or the tangential direction. The four unit capacitors are distributed in two pairs. In the contact of space force and the surface of the sensor, the external force is only 1, the capacitance response is 4, the whole electrode plate contributes to solving Fn, and simultaneously, two pairs of capacitors are combined to form a system, and F can be obtained_xAnd F_yThereby completely describing a three-dimensional force.

The invention has been described above with reference to the accompanying drawings, it is obvious that the invention is not limited to the specific implementation in the above-described manner, and it is within the scope of the invention to apply the inventive concept and solution to other applications without substantial modification.

Claims (9)

1. The skin care product quality evaluation system based on the skin friction performance test is characterized by comprising a friction performance test device, the device comprises a test piece and a sensing system signal processor, the test piece comprises a friction element and a sensor, the friction element is fixed on an upper PCB of the sensor, a lower PCB of the sensor is fixed on the skin friction performance test device, the sensor collects positive pressure and friction force and sends the positive pressure and the friction force to the sensing system signal processor, the sensor comprises an X-direction capacitor unit group and a Y-direction capacitor unit group, and the X-direction capacitor unit group and the Y-direction capacitor unit group are connected with the sensing system signal processor through the X-direction capacitor unit group and the Y-Each capacitor unit module comprises a capacitor unit module which is a comb-shaped structure consisting of more than two strip-shaped capacitor units, each strip-shaped capacitor unit comprises a driving electrode of an upper polar plate and an induction electrode of a lower polar plate, and each capacitor unit module comprises more than two width a₀Length b₀A first strip-shaped capacitor unit group consisting of strip-shaped capacitor units and more than two widths ka₀Length b₀And the second strip-shaped capacitor unit group is formed by the strip-shaped capacitor units.

2. The skin care product quality assessment system according to claim 1, further comprising an actuator, wherein the actuator comprises a sensor fixing member, the lower PCB of the sensor is fixed on the upper end of the sensor fixing member, the actuator moves the friction member back and forth through the rectangular hole at the top end of the skin friction test device via the sensor fixing member, and the friction member is made of silicone material.

3. The skin care product quality evaluation system of claim 1, wherein the width of the driving electrode and the width of the sensing electrode of each strip-shaped capacitor unit are the same, the length of the driving electrode is greater than the length of the sensing electrode, and a left difference position is reserved at each end of the length of the driving electrode_{Left side of}And the right difference position_{Right side}，b_{0 drive}＝b_{Feeling of 0}+_{Right side}+_{Left side of}Wherein b is_{0 drive}Length of the driving electrode of the strip-shaped capacitor unit, b_{Feeling of 0}The length of the induction electrode of the strip-shaped capacitance unit.

4. The skin care product quality assessment system according to claim 3, wherein said poor location_{Left side of}＝_{Right side}And is andwherein d is₀Is the thickness of the dielectric of the strip-shaped capacitor unit, G is the shear modulus of the elastic dielectric, tau_maxThe maximum stress value.

5. The system for evaluating the quality of skin care products according to claim 1, wherein said comb-like structure comprises more than 20 strip-like capacitor units, leads connected with the strip-like capacitor units in a one-to-one correspondence manner, and an electrode spacing a is provided between two adjacent strip-like capacitor units 。

6. The skin care product quality assessment system according to claim 5, wherein said parallel plate area S = M (a)₀+2a +ka₀）b₀A/2, wherein M is the number of strip-shaped capacitor units, b₀Is the length of the strip-shaped capacitor unit, a₀The width of the strip-shaped capacitor unit.

7. The skin care product quality assessment system according to claim 2, wherein the strip-shaped capacitor unit leads of the first strip-shaped capacitor unit group and the second strip-shaped capacitor unit group are connected in parallel or independently to the sensing system signal processor.

8. The skin care product quality assessment system according to claim 2, wherein the width of said strip-shaped capacitive unitWherein d is₀E is the Young's modulus of the elastic medium, and G is the shear modulus of the elastic medium.

9. The skin care product quality assessment system according to claim 2, wherein intermediate converters are respectively arranged between the first strip-shaped capacitor cell group and the sensing system signal processor, and the intermediate converters are used for setting transmission coefficients of voltage to capacitance or frequency to capacitance.