CN104977249A - Device for testing friction performance of skin - Google Patents

Abstract

The invention relates to a device for testing the friction performance of skin. The device comprises a testing piece and a sensing system signal processor, wherein the testing piece comprises a friction element and a sensor, the friction element is fixedly arranged on an upper PCB of the sensor, a lower PCB of the sensor is fixedly arranged on the device for testing the friction performance of skin, the sensor collects the positive pressure and the friction force and sends the positive pressure and the friction force to the sensing system signal processor, the sensor comprises an annular capacitor cell set and a strip-shaped capacitor cell set, the annular capacitor cell set is used for measuring the magnitude of tangential force and magnitude of force, and the strip-shaped capacitor cell set is used for measuring the direction of the tangential force. The device for testing the friction performance of skin provided by the invention tests by aiming at the skin of the upper limb of a human body, and the tested parts comprise the face, the forehead, the cheek, the rear parts of the ears, and the like, and the testing operation is flexible and convenient.

Description

Skin friction performance testing device

Technical Field

The invention belongs to the field of skin friction performance testing, and particularly relates to a skin friction performance testing device.

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 study of the friction and elasticity properties of human skin is closely related to a number of fields of application, such as dermatology, skin protection products, textile industry, manufacturing, etc. The elucidation of the friction and elasticity properties of human skin has an important role in the development of these fields of application. For example, the frictional properties of the skin surface may reflect the physical and chemical properties of the skin surface, and the frictional properties of the skin may reflect the histological properties of the skin, thereby determining physiological changes and pathological conditions of the skin, which is helpful for the research process of individual skin diseases.

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 friction performance testing device, which realizes skin testing on tiny parts of a human body, such as the forehead, the cheek, the back of 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 friction performance testing device comprises a friction performance testing device, the device 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 positive pressure and friction force and sends the positive pressure and the friction force to the sensing system signal processor, the sensor comprises a ring capacitor unit group and a strip capacitor unit group, the strip capacitor unit group is arranged at four corners of an outer substrate of the ring capacitor unit group, the ring capacitor unit group comprises more than two pairs of ring capacitor unit pairs, the ring capacitor unit pair comprises two ring capacitor units, the strip capacitor unit group comprises an X-direction differential capacitor unit group and a Y-direction differential capacitor unit group, and the X-direction differential capacitor unit group and the Y-direction differential capacitor unit group both comprise more than two capacitor unit modules which mutually form differential motions, the capacitor unit module is of a comb-tooth-shaped structure consisting of more than two strip-shaped capacitor units, and each ring-shaped capacitor unit and each strip-shaped capacitor unit respectively comprise a driving electrode of an upper polar plate and an induction electrode of a lower polar plate.

The skin friction performance testing device 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 performance testing device through the sensor fixing piece to move back and forth, and the friction element is made of a silicone material. The induction electrode and the driving electrode of each circular ring capacitor unit are opposite and same in shape, the driving electrode and the induction electrode of each strip capacitor unit are same in width, the length of the driving electrode of each strip capacitor unit is larger than that of the induction electrode, and left difference positions are reserved at two ends of the length of the driving electrode of each strip capacitor unit 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. Left difference position of the strip-shaped capacitor unit_{Left side of}Right difference position_{Right side}And is andwherein d is₀Is the thickness of the elastic medium, G is the shear modulus, τ, of the elastic medium_maxThe maximum stress value. The driving electrodes and the sensing electrodes of the strip-shaped capacitor units of the two groups of capacitor unit modules which mutually form the differential are provided with initial dislocation offsets along the width direction, and the dislocation offsets have the same size and opposite directions. The circular ring capacitor unit group comprises n concentric circular ring capacitor units,whereinWherein, a_{Flat plate}Length of parallel plate, r_{Round (T-shaped)}Is the width of the ring capacitor unit, a_{Round (T-shaped)}And the electrode distance between two adjacent circular capacitor units. The X-direction differential capacitance unit group and the Y-direction differential capacitance unit group both comprise m strip-shaped capacitance units,wherein, a_{Flat plate}Length of parallel plate, a_{Strip for packaging articles}Is the electrode spacing between two adjacent strip-shaped capacitor units, a₀The width of the strip-shaped capacitor unit. The width r of the concentric ring capacitor unit_{Round (T-shaped)}And the width a of the strip-shaped capacitor unit₀Equal; electrode spacing a of strip-shaped capacitor unit_{Strip for packaging articles}And the electrode spacing a of the circular ring capacitor unit_{Round (T-shaped)}Equal, 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. The drive electrodes of the ring capacitor unit group and the strip capacitor unit group are connected with the sensing system signal processor through an outgoing line, the induction electrode of each ring capacitor unit of the ring capacitor unit group is connected with the sensing system signal processor through an independent lead, and the induction electrodes of the capacitor unit modules of the X-direction differential capacitor unit group and the Y-direction differential capacitor unit group are connected with the sensing system signal processor through an outgoing line respectively. Intermediate converters are respectively arranged among the ring capacitor units, the capacitor unit modules 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 is used for testing 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 the convenience are realized, in addition, the sensor provided by the invention can be used for simultaneously measuring the normal force and the tangential force, the sensitivity is high, the utilization efficiency of the polar plate is high, the whole circular ring capacitor unit group contributes to the normal force, and the dynamic performance is better.

Drawings

FIG. 1 is a diagram of an area analysis of concentric ring offset misalignment according to an embodiment of the present invention.

FIG. 2 is a graph of outer concentric ring misalignment versus outer diameter circle analysis for an embodiment of the present invention.

FIG. 3 is a plan layout view of a parallel plate capacitor according to an embodiment of the present invention.

Fig. 4 is a structural diagram of a driving electrode according to an embodiment of the present invention.

Fig. 5 is a rectangular coordinate system of a flat capacitor plate according to an embodiment of the present invention.

Fig. 6 is a diagram of two sets of circular capacitor sets according to an embodiment of the present invention.

FIG. 7 is an initial misalignment map of a differential stripe capacitor cell according to an embodiment of the present invention.

FIG. 8 is a graph illustrating the offset of the differential strip capacitor unit after being stressed according to the embodiment of the present invention.

FIG. 9 is a signal differential schematic of a cell capacitor pair according to an embodiment of the present invention.

Fig. 10 is a skin friction performance testing apparatus according to an embodiment of the present invention.

Fig. 11 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. 10 shows a skin friction test device according to the present invention, which mainly includes a test piece, a transmission device and a sensing system signal processor, wherein the test piece mainly includes a friction element 1 and a sensor 2, the friction element 1 is made of silicone material, the sensor 2 includes an upper PCB and a lower PCB, the friction element 1 is hemispherical, and a section of the friction element is fixed to 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 sensor comprises a circular ring capacitor unit group and strip capacitor unit groups, wherein the circular ring capacitor unit group is used for measuring the tangential force and the normal force, the strip capacitor unit groups are used for measuring the direction of the tangential force, and the strip capacitor unit groups are arranged at four corners outside the circular ring capacitor unit group of the substrate. The ring electric capacity unit group includes that ring electric capacity unit is right more than two sets of, ring electric capacity unit is right including two ring electric capacity units, strip electric capacity unit group includes X direction differential electric capacity unit group and Y direction differential electric capacity unit group, and X direction differential electric capacity unit group and Y direction differential electric capacity unit group all include the differential electric capacity unit module of mutual formation more than two, the electric capacity unit module adopts the broach structure of constituteing by the strip electric capacity unit more than two, and every ring electric capacity unit and strip electric capacity unit all include the drive electrode of upper polar plate and the induction electrode of bottom plate. The induction electrode and the driving electrode of each circular ring capacitor unit are opposite and same in shape, the driving electrode and the induction electrode of each strip capacitor unit are same in width, the length of the driving electrode of each strip capacitor unit is larger than that of the induction electrode, and left difference positions are reserved at two ends of the length of the driving electrode of each strip capacitor unit 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}Sensing for strip-shaped capacitive cellsElectrode length. Left difference position of the strip-shaped capacitor unit_{Left side of}Right difference position_{Right side}And is andwherein d is₀Is the thickness of the medium, G is the shear modulus, τ, of the elastic medium_ymaxThe maximum stress value. The driving electrodes and the sensing electrodes of the strip-shaped capacitor units of the two groups of capacitor unit modules which mutually form the differential are provided with initial dislocation offsets along the width direction, and the dislocation offsets have the same size and opposite directions. The ring capacitor unit group comprises n concentric ring capacitor unitsWherein, a_{Flat plate}Length of parallel plate, r_{Round (T-shaped)}Is the width of the ring capacitor unit, a_{Round (T-shaped)}And the electrode distance between two adjacent circular capacitor capacitors. The capacitor unit module adopts a comb-tooth structure, the X-direction differential capacitor unit group and the Y-direction differential capacitor unit group both comprise m strip-shaped capacitor units,wherein, a_{Flat plate}Length of parallel plate, a_{Strip for packaging articles}Is the electrode spacing between two adjacent strip-shaped capacitor units, a₀The width of the strip-shaped capacitor unit. The width r of the concentric ring capacitor unit_{Round (T-shaped)}And the width a of the strip-shaped capacitor unit₀Equal; electrode spacing a of strip-shaped capacitor unit_{Strip for packaging articles}And the electrode spacing a of the circular ring capacitor unit_{Round (T-shaped)}Equal, 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. The drive electrodes of the circular ring capacitor unit group and the strip capacitor unit group are connected with the sensing system signal processor through a leading-out wire, and the induction electrode of each circular ring capacitor unit of the circular ring capacitor unit group is independently led out from the sensing system signal processorAnd the induction electrodes of the capacitor unit modules of the X-direction differential capacitor unit group and the Y-direction differential capacitor unit group are respectively led out through an outgoing line and connected with a signal processor of the sensing system. Intermediate converters are respectively arranged among the ring capacitor units, the capacitor unit modules and the sensing system signal processor and are used for setting transmission coefficients of voltage or frequency to the capacitors.

The derivation and principle of the present invention, the shape, structure, mutual position and connection relationship of the parts, the function and operation principle of the parts, the manufacturing process and operation method, etc. will be described in further detail with reference to fig. 1-9.

1.1 capacitance formula and input-output characteristics thereof

The initial capacitance of the parallel plates 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> </mrow> <msub> <mi>d</mi> <mn>0</mn> </msub> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>1</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, a₀The initial facing area of the upper and lower polar plates. d₀Receive sigma_nIs excited to produce relative deformation_n＝_n/d₀＝σ_nAnd E, substituting the formula (1) to obtain the 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> <msub> <mi>A</mi> <mn>0</mn> </msub> <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> <msub> <mi>A</mi> <mn>0</mn> </msub> <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>2</mn> <mo>)</mo> </mrow> </mrow> </math>

1.2 Linearity and sensitivity under Normal stress

1.2.1 Normal Linearity

(2) In the formula F_nIn the denominator, therefore C_n＝f(F_n) The relationship of (a) is non-linear. Maximum value sigma in the range of conversion_nmaxIn comparison with the medium elastic constant E,_nis a very small quantity, i.e. in the denominator_n<<1, mixing(2) The formula is developed according to series, and high-order infinitesimal above quadratic is omitted, so that the formula can be simplified into the following steps:

<math> <mrow> <msub> <mi>C</mi> <mi>n</mi> </msub> <mo>=</mo> <msub> <mi>C</mi> <mn>0</mn> </msub> <mrow> <mo>(</mo> <mrow> <mn>1</mn> <mo>+</mo> <mi>&epsiv;</mi> </mrow> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>C</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> <mo>&CenterDot;</mo> <mi>E</mi> </mrow> </mfrac> </mrow> <mo>)</mo> </mrow> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>3</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.

1.2.2 sensitivity

Definition of sensitivity by Normal

According to the formula (2)

<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>4</mn> <mo>)</mo> </mrow> </mrow> </math>

The linear sensitivity can be obtained according to the formula (3),

S_n1＝C₀/AE＝_{0 r}/d₀E(5)

S_n2with F_nAnd is changed to F_nThe greater, S_n2The larger, the slightly non-linear over the entire conversion characteristic.

1.3 relationship between tangential displacement and effective area of circular ring capacitor

Analysis was performed for concentric ring capacitance pairs, as shown in FIG. 1, R₁Is the outer radius of the circle, R₂The radius of the inner circle, R equals the width of the ring, and equals the radius of the large outer circle R₁Inner circle radius R₂. Force F on a section of the drive electrode_xCausing a shear dislocation between the corresponding driving and sensing electrodes, and d_xThe displacement of the tangent plane and the dislocation area are S_{Inner part}And S_{Outer cover}The initial facing area of the electrode plate should be pi (R)₁ ²-R₂ ²). FIG. 2 is an analysis graph of capacitance of outer concentric ring versus outer diameter circle, where the distance between the centers of the two circles is d_xMoving the front and the backThe center of the circle and the intersection point of the two circles form a rhombus, and S can be calculated_{Outer cover}Area of (d):

in the above formula, there is d_x<<R₁To thereby obtain

By

Will be provided withAnd the high-order terms are omitted,

similarly, it can be known that S_{Inner part}＝2R₂d_xTherefore, the error area of the concentric ring capacitor is S-2R₁d_x+2R₂d_x。

1.4 capacitance Change of the Ring capacitive cell group under tangential stress τ excitation

The tangential stress tau does not change the geometric size parameter A of the polar plate₀To the thickness d of the medium₀Nor is it affected. However tau_xAnd τ_yThe spatial structure of the parallel plate capacitor is changed, and dislocation offset occurs between the upper and lower electrode plates facing in the forward direction. Dislocation deviation d of polar plate under action of tau_x. When tau is zero, the upper part of the ring capacitor unitThe lower electrodes are opposite, and the effective cross section between the upper and lower electrodesIn FIG. 2, at τ_xUnder the action of right direction, the upper polar plate is displaced to right relative to the lower polar plate_xThereby the effective area between the upper and lower polar plates is calculated when the capacitance is calculatedThe resulting capacitance is:

<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> <msubsup> <mi>&pi;R</mi> <mn>1</mn> <mn>2</mn> </msubsup> <mo>-</mo> <msubsup> <mi>&pi;R</mi> <mn>2</mn> <mn>2</mn> </msubsup> <mo>-</mo> <mn>2</mn> <msub> <mi>R</mi> <mn>1</mn> </msub> <msub> <mi>d</mi> <mi>x</mi> </msub> <mo>-</mo> <mn>2</mn> <msub> <mi>R</mi> <mn>2</mn> </msub> <msub> <mi>d</mi> <mi>x</mi> </msub> <mo>)</mo> </mrow> </mrow> <msub> <mi>d</mi> <mn>0</mn> </msub> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>6</mn> <mo>)</mo> </mrow> </mrow> </math>

according to shear Hooke's law

τ_x＝γ_x·G＝G·_x/d₀(7)

Substituting (7) into (6) 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> <mn>2</mn> <mrow> <mo>(</mo> <mrow> <msub> <mi>R</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>R</mi> <mn>2</mn> </msub> </mrow> <mo>)</mo> </mrow> <msub> <mi>d</mi> <mi>x</mi> </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> <mn>2</mn> <mrow> <mo>(</mo> <mrow> <msub> <mi>R</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>R</mi> <mn>2</mn> </msub> </mrow> <mo>)</mo> </mrow> <msub> <mi>F</mi> <mi>x</mi> </msub> </mrow> <mrow> <msub> <mi>A</mi> <mi>&tau;</mi> </msub> <mi>G</mi> </mrow> </mfrac> <mo>=</mo> <msub> <mi>C</mi> <mn>0</mn> </msub> <mo>-</mo> <mfrac> <mrow> <mn>2</mn> <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> <mi>G</mi> <mi>&pi;</mi> <mrow> <mo>(</mo> <mrow> <msub> <mi>R</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>R</mi> <mn>2</mn> </msub> </mrow> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>8</mn> <mo>)</mo> </mrow> </mrow> </math>

(8) The formula is the input-output characteristic under shear stress, C_τAnd τ_xIn a linear relationship, 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> <mi>&tau;</mi> </msub> </mrow> <mrow> <msub> <mi>dF</mi> <mi>x</mi> </msub> </mrow> </mfrac> <mo>=</mo> <mfrac> <mrow> <mn>2</mn> <msub> <mi>&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> </mrow> <mrow> <mi>G</mi> <mi>&pi;</mi> <mrow> <mo>(</mo> <msub> <mi>R</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>R</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>9</mn> <mo>)</mo> </mrow> </mrow> </math>

From equation (9), the tangential sensitivity and R can be seen₁-R₂In relation to this, the tangential sensitivity is inversely proportional to the width of the ring, the smaller the width the higher the sensitivity.

Design of 2-plate capacitor

2.1 design of Flat capacitors

See the electrode plan layout in FIG. 3 and the block diagram of the drive electrode in FIG. 4, at a 10X 10mm thickness²The circular ring type contact parallel plate three-dimensional pressure sensor on the substrate comprises a sensing system signal processor, a circular ring capacitance unit group and a strip capacitance unit group, wherein the circular ring capacitance unit group and the strip capacitance unit group are respectively connected with the sensing system signal processor, the circular ring capacitance unit group is used for measuring the tangential force and the normal force, the strip capacitance unit group is used for measuring the direction of the tangential force, and the strip capacitance unit group is arranged at four corners outside the circular ring capacitance unit group of the substrate. Therefore, the area of the parallel plates can be effectively used, the circular capacitor unit group is paved on the whole parallel plate, the circular capacitor unit group plays a role in measuring the three-dimensional force, and the strip-shaped capacitor unit group effectively utilizes the space at four corners of the parallel plate after the circular capacitor unit group is paved, and is used for measuring the direction of the three-dimensional force tangential force. The driving electrode and the induction electrode of the circular ring capacitor unit group are both composed of n concentric circular rings, and n is an even number, so that an n/2 circular ring capacitor unit pair is formed. The hatched portions represent the outer mold sections of the lost wax casting process, which geometry and dimensions should also be precise during mechanical forming.

Referring to the rectangular coordinate system of the plate capacitor of FIG. 5, the origin of the coordinate systemAt the origin of a concentric circle of the circular capacitor unit group, the X axis and the Y axis are respectively along the diagonal direction of the plate capacitor, the X-direction differential capacitor unit group comprises an X-direction differential capacitor unit group I and an X-direction differential capacitor unit group III, the X-direction differential capacitor unit group I and the X-direction differential capacitor unit group III are respectively positioned on the positive half shaft and the negative half shaft of the X axis and are symmetrical along the Y axis, the Y-direction differential capacitor unit group comprises a Y-direction differential capacitor unit group II and a Y-direction differential capacitor unit group IV, the Y-direction differential capacitor unit group II and the Y-direction differential capacitor unit group IV are respectively positioned on the positive half shaft and the negative half shaft of the Y axis and are symmetrical along the X axis, and the X-_xThe differential capacitor unit group II and the differential capacitor unit group IV form a pair tau_yA responsive differential capacitive cell combination.

The ring capacitor unit group comprises n concentric ring capacitor unitsWherein, a_{Flat plate}Length of parallel plate, r_{Round (T-shaped)}Is the width of the ring capacitor unit, a_{Round (T-shaped)}And the electrode distance between two adjacent circular capacitor capacitors. The capacitor unit module adopts a comb-tooth structure, the X-direction differential capacitor unit group and the Y-direction differential capacitor unit group both comprise m strip-shaped capacitor units,wherein, a_{Strip for packaging articles}An electrode distance a is arranged between two adjacent strip-shaped capacitor units₀The width of the strip-shaped capacitor unit. Width r of concentric ring capacitor unit_{Round (T-shaped)}And the width a of the strip-shaped capacitor unit₀Equal; electrode spacing a of strip-shaped capacitor unit_{Strip for packaging articles}And the distance a between the electrodes of the circular capacitor_{Round (T-shaped)}Equal, width of the strip-shaped capacitor unitWherein d is₀Medium thickness, E Young's modulus of elastic medium, G elasticityShear modulus of sexual media.

2.2 excitation Signal and coordinate System

The circular-ring capacitor unit is placed in a rectangular coordinate system shown in fig. 5, 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 Fx and Fy are along the X axis and the Y axis, and the acting direction of Fz is along the OZ axis, namelyThe direction, normal direction and tangential direction stress are both stress tensors, and the response of capacitance can be output from the lead wires of the electrodes; normal stress sigma_nFn/A, whereinThe pole plate is a normal force bearing surface, and Fn is a normal component; generating paired tangential stresses tau on both side surfaces_{Cutting machine}＝F_{Cutting machine}/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> </mrow> </math>

wherein E is the Young's modulus GN/m of the elastic medium²G is the shear modulus GN/m of the elastic medium²N is the normal displacement (unit: mum) of the elastic medium, x and y are the relative dislocation (unit: mum) of the upper and lower electrode plates of the circular ring capacitor unit, and the sign of the displacement is determined by the orientation of the coordinate axis.

2.3 calculation of Normal and tangential force magnitudes

And selecting the nth ring capacitor unit and the nth/2 ring capacitor unit, and calculating a composition equation set by establishing the ring capacitor units, as shown in fig. 6. After the electrode plate is subjected to normal and tangential excitation, the output capacitance of the nth circular ring capacitance unit is set as C₁N/2 ring capacitor units with output capacitance of C₂Tangential displacement of d_xNormal capacitance pole distance of d_n，S₁₀Is the initial facing area of the outer ring, S₂₀Is the initial facing area of the inner ring.

<math> <mrow> <msub> <mi>C</mi> <mn>1</mn> </msub> <mo>=</mo> <mfrac> <mrow> <mi>&epsiv;</mi> <mrow> <mo>(</mo> <msub> <mi>S</mi> <mn>10</mn> </msub> <mo>-</mo> <mi>S</mi> <mn>1</mn> <mo>)</mo> </mrow> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> <mo>=</mo> <mfrac> <mrow> <mi>&epsiv;</mi> <mrow> <mo>(</mo> <msubsup> <mi>&pi;R</mi> <mn>1</mn> <mn>2</mn> </msubsup> <mo>-</mo> <msubsup> <mi>&pi;R</mi> <mn>2</mn> <mn>2</mn> </msubsup> <mo>)</mo> </mrow> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> <mo>-</mo> <mfrac> <mrow> <mi>&epsiv;</mi> <mrow> <mo>(</mo> <mn>2</mn> <msub> <mi>R</mi> <mn>1</mn> </msub> <msub> <mi>d</mi> <mi>x</mi> </msub> <mo>+</mo> <mn>2</mn> <msub> <mi>R</mi> <mn>2</mn> </msub> <msub> <mi>d</mi> <mi>x</mi> </msub> <mo>)</mo> </mrow> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> </mrow> </math> ①

<math> <mrow> <msub> <mi>C</mi> <mn>2</mn> </msub> <mo>=</mo> <mfrac> <mrow> <mi>&epsiv;</mi> <mrow> <mo>(</mo> <msub> <mi>S</mi> <mn>20</mn> </msub> <mo>-</mo> <mi>S</mi> <mn>2</mn> <mo>)</mo> </mrow> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> <mo>=</mo> <mfrac> <mrow> <mi>&epsiv;</mi> <mrow> <mo>(</mo> <msubsup> <mi>&pi;r</mi> <mn>1</mn> <mn>2</mn> </msubsup> <mo>-</mo> <msubsup> <mi>&pi;r</mi> <mn>2</mn> <mn>2</mn> </msubsup> <mo>)</mo> </mrow> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> <mo>-</mo> <mfrac> <mrow> <mi>&epsiv;</mi> <mrow> <mo>(</mo> <mn>2</mn> <msub> <mi>r</mi> <mn>1</mn> </msub> <msub> <mi>d</mi> <mi>x</mi> </msub> <mo>+</mo> <mn>2</mn> <msub> <mi>r</mi> <mn>2</mn> </msub> <msub> <mi>d</mi> <mi>x</mi> </msub> <mo>)</mo> </mrow> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> </mrow> </math> ②

Will be (r-c)Obtaining:

<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>R</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>R</mi> <mn>2</mn> </msub> </mrow> <mrow> <msub> <mi>r</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>r</mi> <mn>2</mn> </msub> </mrow> </mfrac> <mo>=</mo> <mfrac> <mrow> <mi>&epsiv;</mi> <mi>&pi;</mi> <mrow> <mo>(</mo> <msubsup> <mi>R</mi> <mn>1</mn> <mn>2</mn> </msubsup> <mo>-</mo> <msubsup> <mi>R</mi> <mn>2</mn> <mn>2</mn> </msubsup> <mo>)</mo> </mrow> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> <mo>-</mo> <mfrac> <mrow> <msub> <mi>R</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>R</mi> <mn>2</mn> </msub> </mrow> <mrow> <msub> <mi>r</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>r</mi> <mn>2</mn> </msub> </mrow> </mfrac> <mo>*</mo> <mfrac> <mrow> <mi>&epsiv;</mi> <mi>&pi;</mi> <mrow> <mo>(</mo> <msubsup> <mi>r</mi> <mn>1</mn> <mn>2</mn> </msubsup> <mo>-</mo> <msubsup> <mi>r</mi> <mn>2</mn> <mn>2</mn> </msubsup> <mo>)</mo> </mrow> </mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> </mfrac> </mrow> </math>

in the above formula $\frac{R_1+R_2}{r_1+r_2}=K,$ Then <math> <mrow> <msub> <mi>d</mi> <mi>n</mi> </msub> <mo>=</mo> <mfrac> <mrow> <mi>&epsiv;</mi> <mrow> <mo>(</mo> <msub> <mi>S</mi> <mn>10</mn> </msub> <mo>-</mo> <msub> <mi>KS</mi> <mn>20</mn> </msub> <mo>)</mo> </mrow> </mrow> <mrow> <msub> <mi>C</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>KC</mi> <mn>2</mn> </msub> </mrow> </mfrac> </mrow> </math>

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>

will be described in the above₂-②*C₁Obtaining:

$d_x=\frac{C_2{S}_{10}-C_1{S}_{20}}{2C_2(R_1+R_2)-2C_1(r_1+r_2)};$

by <math> <mrow> <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> <mfrac> <msub> <mi>d</mi> <mi>x</mi> </msub> <msub> <mi>d</mi> <mn>0</mn> </msub> </mfrac> <mo>=</mo> <mfrac> <mrow> <msub> <mi>C</mi> <mn>2</mn> </msub> <msub> <mi>S</mi> <mn>10</mn> </msub> <mo>-</mo> <msub> <mi>C</mi> <mn>1</mn> </msub> <msub> <mi>S</mi> <mn>20</mn> </msub> </mrow> <mrow> <msub> <mi>d</mi> <mn>0</mn> </msub> <mn>2</mn> <msub> <mi>C</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <msub> <mi>R</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>R</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> <mo>-</mo> <msub> <mi>d</mi> <mn>0</mn> </msub> <mn>2</mn> <msub> <mi>C</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <msub> <mi>r</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>r</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> </mrow> </mfrac> <mo>,</mo> </mrow> </math> So F_τIs composed of

<math> <mrow> <msub> <mi>F</mi> <mi>&tau;</mi> </msub> <mo>=</mo> <mfrac> <mrow> <mo>(</mo> <msub> <mi>C</mi> <mn>2</mn> </msub> <msub> <mi>S</mi> <mn>10</mn> </msub> <mo>-</mo> <msub> <mi>C</mi> <mn>1</mn> </msub> <msub> <mi>S</mi> <mn>20</mn> </msub> <mo>)</mo> <mo>&CenterDot;</mo> <mi>G</mi> <mo>&CenterDot;</mo> <msub> <mi>S</mi> <mn>0</mn> </msub> </mrow> <mrow> <msub> <mi>d</mi> <mn>0</mn> </msub> <mn>2</mn> <msub> <mi>C</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <msub> <mi>R</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>R</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> <mo>-</mo> <msub> <mi>d</mi> <mn>0</mn> </msub> <mn>2</mn> <msub> <mi>C</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <msub> <mi>r</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>r</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> </mrow> </mfrac> </mrow> </math>

2.4 determination of the direction of tangential force

2.4.1 strip-shaped capacitor unit group structure and parameter design

To realize tau_xAnd τ_yTangential response does not mutually influence, and difference positions are reserved at two ends of the length of the driving electrode₀Thus b is_{0 drive}＝b_{0 bottom}+2·₀Wherein in b_{0 drive}The length reservation of the two ends should be ensured theoreticallyCalculated 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}Not less than 0.01 mm. To realize tau_xAnd τ_yThe drive electrode and the induction electrode of each strip-shaped capacitor unit are arranged on the plane without influencing the normal capacitance response, and certain dislocation offset is set for eliminating mutual difference through differential motionInfluence.

As shown in fig. 4, four dotted line boxes in the figure are taken as the reference of the sensing electrode on the lower plate, and the position of the sensing electrode on the lower PCB substrate is taken as a reference, then the arrangement of the driving electrode on the upper PCB substrate should be taken as the reference of the edge line of the PCB substrate. 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 width of each strip-shaped capacitor unit is set to be a₀The width of the groove between two strip-shaped capacitor units is a The pitch of each strip-shaped capacitor unit is a₀+a . Thus ensuring tau already when calculating the normal capacitance output response_xAnd τ_yThe normal capacitance response is not affected. All of them are different from the geometric reference line₀(0.1mm) to ensure that the X-direction differential capacitance unit group I and the X-direction differential capacitance unit group III only generate a pair tau_xThe Y-direction differential capacitance unit group II and the Y-direction differential capacitance unit group IV only generate a pair tau_ySetting an initial misalignment offset_xoThe value of which should be guaranteedCalculated value thereof and₀similarly, the initial misalignment offsets are all set_xo＝_yo0.01mm to ensure that four capacitor units are at tau_xAnd τ_yTwo groups of differential capacitance pairs can be generated under tangential excitation.

In FIG. 7, a pair of capacitors C_LAnd C_RElectrode size a₀、b₀、d₀All are the same, initial misalignment offset₀Also the same, the difference being the left capacitor C_LUpper layer of₀The point of the tip is pointed at + OX, and the capacitor C on the right_RUpper layer of₀The sharp corners point to-OX. When tau is_xWhen the content is equal to 0, the content,i.e. the capacitance corresponding to the shaded part of the figure. On the basis thereof, e.g. in-F_xProducing ± -c under excitation_xOffset ofTo form the capacitance increasing and decreasing effect as shown in FIG. 8,

<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> <mn>0</mn> </msub> <mo>&PlusMinus;</mo> <msub> <mi>&delta;</mi> <mi>x</mi> </msub> <mo>)</mo> </mrow> </mrow> <msub> <mi>d</mi> <mn>0</mn> </msub> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>10</mn> <mo>)</mo> </mrow> </mrow> </math>

in FIG. 8, C_LAnd C_RDifferential capacitor pair_xWill produce ± +/-_xAnd. + -. Δ C_τIn response to (2) the response of (c), ₀should be of a size thatIs convenient to use₀10 μm, whereby equation (8) can be modified

<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>&PlusMinus;</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> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>11</mn> <mo>)</mo> </mrow> </mrow> </math>

In the formula,the initial capacitance when the shear stress is zero, and the formula (11) is the shear stress input-output characteristic, C_τxAnd F_xIs a linear relationship, and the sensitivity thereof

A is shown in formula (11)₀The smaller the sensitivity of tangential stress response is, the larger the sensitivity of tangential stress response is, so that the capacitor unit adopts a strip-shaped capacitor unit group consisting of a plurality of strip-shaped capacitors.

2.4.2 tangential stress Direction calculation

C_ⅠTo C_ⅡAnd C_ⅢTo C_ⅣTwo pairs of differential combinations can be realized, such as the signal differential diagram of the cell capacitor pair of FIG. 9, processed by differential techniques, the total response of the differential output

<math> <mrow> <msub> <mi>O</mi> <mrow> <mi>&tau;</mi> <mi>x</mi> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <mn>2</mn> <msub> <mi>mK&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> </mrow> <mrow> <msub> <mi>a</mi> <mn>0</mn> </msub> <mi>G</mi> </mrow> </mfrac> <msub> <mi>F</mi> <mi>x</mi> </msub> </mrow> </math>

In which either the normal excitation F_nOr tangential excitation F_yAll are not to O_τEffecting, i.e. automatically cancelling, sigma_nAnd τ_yFor tau_xOr interference of the total output. Because the equivalent and congruent capacitance changes are automatically eliminated in all operations in which the signals contain 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, the method for preparing the composite material, <math> <mrow> <msub> <mi>O</mi> <mrow> <mi>&tau;</mi> <mi>y</mi> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <mn>2</mn> <msub> <mi>mK&epsiv;</mi> <mn>0</mn> </msub> <mo>&CenterDot;</mo> <msub> <mi>&epsiv;</mi> <mi>r</mi> </msub> </mrow> <mrow> <msub> <mi>a</mi> <mn>0</mn> </msub> <mi>G</mi> </mrow> </mfrac> <msub> <mi>F</mi> <mi>y</mi> </msub> <mo>;</mo> </mrow> </math>

according to O_τxAnd O_τyThe value of (c) calculates the direction of the tangential force.

2.4 selection of the principal materials and their characteristic parameters

The cross-sectional view of the parallel plate capacitor structure is similar to a sandwich structure as shown in FIG. 10. As can be seen from fig. 10, 1 is the upper PCB substrate, 2 is the lower PCB substrate, 3 is the driving electrode,4 is an induction electrode, and 5 is an elastic medium. Distance d between the plates₀The 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)}The deformation of the internal dielectric of the capacitor in a stress state is far larger than that of the polar plate because the internal dielectric of the capacitor is 103 GPa.

2.5 electrode lead design

Both the driving electrodes and the sensing electrodes need to be provided with lead-out lines, and considering that the respective driving electrodes are grounded in signal level, the driving electrodes need only share the same lead-out line. The driving electrodes of the ring capacitor unit group and the strip capacitor unit group are connected with a sensing system signal processor through an outgoing line, each ring independent lead of the ring capacitor unit group is connected with the sensing system signal processor, the sensing system signal processor calculates according to the output value free combination of each ring, then averaging is carried out to obtain the size of the tangential force and the size of the normal force, under the condition that the precision requirement is not high, the ring capacitor unit group can only select two optimal rings to lead out 2 leads, and d is obtained through the two rings_xAnd d_nSo as to obtain the magnitude of the tangential force and the magnitude of the normal force; the X-direction differential capacitance unit group and the Y-direction differential capacitance unit group are respectively led out through an outgoing line to be connected with the sensing system signal processor and used for calculating the direction of the tangential force. An intermediate converter is arranged between the sensing system signal processor and the capacitor unit and is used for setting the transmission coefficient of voltage or frequency to the capacitor. The entire capacitor assembly has at least 7 pins leading out from the side of the planar package so that the top and bottom outer surfaces of the entire assembly can be conveniently contacted 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. At 10X 10mm²Stress surface ofThe stress can be transferred to the medium more uniformly in the normal direction or the tangential direction. In the contact of space force and the sensor surface, the external force is only 1, and the information of the normal Fn can be obtained by summing the capacitance, namely the whole electrode plate contributes to the Fn calculation, and F can be obtained_xAnd F_yThe three-dimensional force can be completely described, and the normal sensitivity, the tangential sensitivity and the maximum linear error of one-time conversion can be improved according to design parameters.

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 (10)

1. The utility model provides a skin friction performance testing arrangement, a serial communication port, including friction performance testing arrangement, the device is including testing piece and sensing system signal processor, and the testing piece includes friction element and sensor, and friction element fixes on the last PCB board of sensor, and the lower PCB board of sensor is fixed on skin friction performance testing arrangement, and the sensor gathers positive pressure and frictional force and sends for sensing system signal processor, and the sensor includes ring electric capacity unit group and strip electric capacity unit group, strip electric capacity unit group sets up the four corners at ring electric capacity unit group outer base plate, and the ring electric capacity unit group includes that the ring electric capacity unit is right more than two pairs, ring electric capacity unit pair includes two ring electric capacity units, strip electric capacity unit group includes X direction differential electric capacity unit group and Y direction differential electric capacity unit group, and X direction differential electric capacity unit group and Y direction differential electric capacity unit group all include the electric capacity unit pair that forms differential more than two each other The capacitor unit module is of a comb-tooth-shaped structure consisting of more than two strip-shaped capacitor units, and each ring-shaped capacitor unit and each strip-shaped capacitor unit respectively comprise a driving electrode of an upper polar plate and an induction electrode of a lower polar plate.

2. The skin friction performance testing device of claim 1, further comprising a transmission device, wherein the transmission device comprises a sensor fixing member, the lower PCB of the sensor is fixed at the upper end of the sensor fixing member, the transmission device enables the friction element to move back and forth through the rectangular hole at the top end of the skin friction testing device through the sensor fixing member, and the friction element is made of silicone material.

3. The skin friction performance testing device of claim 2, wherein the sensing electrode and the driving electrode of each circular ring capacitor unit are opposite and have the same shape, the driving electrode and the sensing electrode of each strip capacitor unit have the same width, the length of the driving electrode of each strip capacitor unit is greater than that of the sensing electrode, and left difference positions are reserved at two ends of the length of the driving electrode of each strip capacitor unit 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.

4. The skin friction performance testing device of claim 3, wherein the left difference position of the strip-shaped capacitor unit_{Left side of}Right difference position_{Right side}And is andwherein d is₀Is the thickness of the elastic medium, G is the shear modulus, τ, of the elastic medium_maxThe maximum stress value.

5. The skin friction performance testing device of claim 2, wherein the driving electrodes and the sensing electrodes of the two strip-shaped capacitor units forming the differential capacitor unit module are provided with initial offset along the width direction, and the offset is the same in size and opposite in direction.

6. The skin friction performance testing device of claim 2, wherein the circular ring capacitor unit group comprises n concentric circular ring capacitor units, whereinWherein, a_{Flat plate}Length of parallel plate, r_{Round (T-shaped)}Is the width of the ring capacitor unit, a_{Round (T-shaped)}The electrode distance between two adjacent circular capacitor units.

7. The skin friction performance testing device according to claim 2, wherein each of the X-direction differential capacitance unit group and the Y-direction differential capacitance unit group includes m strip-shaped capacitance units,wherein, a_{Flat plate}Length of parallel plate, a_{Strip for packaging articles}Is the electrode spacing between two adjacent strip-shaped capacitor units, a₀The width of the strip-shaped capacitor unit.

8. The skin friction performance testing device of claim 2, wherein the width r of the concentric ring capacitor unit_{Round (T-shaped)}And the width a of the strip-shaped capacitor unit₀Equal; electrode spacing a of strip-shaped capacitor unit_{Strip for packaging articles}And the circleAnnular capacitor unit electrode spacing a_{Round (T-shaped)}Equal, 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.

9. The skin friction performance testing device of claim 2, wherein the driving electrodes of the circular ring capacitor unit group and the strip capacitor unit group are connected with the sensing system signal processor through a leading line, the sensing electrode of each circular ring capacitor unit of the circular ring capacitor unit group is separately connected with the sensing system signal processor through a leading line, and the sensing electrodes of the capacitor unit modules of the X-direction differential capacitor unit group and the Y-direction differential capacitor unit group are respectively connected with the sensing system signal processor through a leading line.

10. The skin friction performance testing device of claim 2, wherein intermediate converters are respectively arranged between the circular ring capacitor unit, the capacitor unit module and the sensing system signal processor, and are used for setting transmission coefficients of voltage to capacitance or frequency to capacitance.