CN104997515A - Plantar pressure distribution measurement device - Google Patents

Abstract

The invention relates to a plantar pressure distribution measurement device comprising a plantar three-dimension pressure measurement device body and a sensor system signal processor. Multiple capacitive pressure sensors for receiving plantar pressure information are arranged inside the plantar three-dimension pressure measurement device body. Each sensor includes a ring capacitor unit group and a strip capacitor unit group. The ring capacitor unit groups are used to measure the magnitude of tangential force and the magnitude of normal force, and the strip capacitor unit groups are used to measure the direction of tangential force. A disease complication monitoring and early warning system is established through plantar three-dimension pressure measurement to provide a reference basis for an expert-aided decision-making system and provide a reference basis for evaluation of the clinical therapeutic effect.

Description

A plantar pressure distribution measuring device

technical field

The invention belongs to the technical field of medical devices, and relates to a clinical medical treatment effect detection system, in particular to a plantar pressure distribution measurement device.

Background technique

The distribution of plantar pressure in the human body reflects the structure and function of the foot and the control of the entire body posture. Testing and analyzing plantar pressure can obtain the physiological, pathomechanical and functional parameters of the human body in various postures and movements, which is of great significance for clinical medical diagnosis, disease degree measurement, postoperative curative effect evaluation, biomechanics and rehabilitation research. Dynamic plantar pressure measurement is an important quantitative inspection and analysis method, and has broad application prospects. At present, in foreign countries, this technology has been used in the function and curative effect evaluation before and after artificial joint surgery, the inspection and follow-up of trunk and lower limb diseases, providing data for the design of prosthetics and artificial joints, the analysis and evaluation of rehabilitation training and physical training, and the diagnosis and treatment of diabetic feet. Early prediction and treatment, etc.

Foot ulcer is one of the serious complications of diabetes. Diabetic patients suffering from foot ulcer have significantly increased risk of amputation and death. Foot ulcers occur due to increased plantar pressure due to peripheral neuropathy and prolonged mechanical stress. Many foreign literatures have proved that the abnormal increase of dynamic plantar pressure is significantly related to the occurrence of diabetic plantar ulcers.

Existing plantar pressure data acquisition device is to adopt pressure sensor, but these pressure sensors all just collect the pressure on the vertical direction: what adopt as Chinese patent CN201110074892.6 is 10 film pressure sensors corresponding to plantar pressure distribution point; 3 adopts a matrix pressure sensor of 8 columns × 10 rows, and CN2012102984097 adopts a 40 by 40 piezoresistor matrix; but we know that in the process of walking, the force between the sole of the foot and the acting surface is also in the horizontal direction. Collecting the force in the vertical direction alone is not enough to reflect the force on the sole of the foot and the active surface.

Contents of the invention

In order to overcome the deficiencies of the prior art, the present invention provides a plantar pressure distribution measuring device for the prevention and monitoring of diabetic complications, through cleverly setting the capacitive pressure sensor structure, measuring the three-dimensional pressure of the plantar, and by adjusting the sensor The improvement of the plate structure eliminates the inter-dimensional coupling. Through the analysis of the plantar pressure, a disease complication monitoring and early warning system is established to provide a reference for the expert-aided decision-making system and the evaluation of clinical treatment effects.

The technical solution of the present invention is: a plantar pressure distribution measuring device, including a plantar three-dimensional pressure measuring device body and a sensor system signal processor, and a plurality of sensors for receiving plantar pressure information are arranged in the plantar three-dimensional pressure measuring device body. A capacitive pressure sensor, the capacitive pressure sensor includes a ring-shaped capacitor unit group and a strip-shaped capacitor unit group, the strip-shaped capacitor unit group is arranged at the four corners of the outer substrate of the ring-shaped capacitor unit group, and the ring-shaped capacitor unit group includes more than two pairs A ring capacitor unit pair, the ring capacitor unit pair includes two ring capacitor units, the strip capacitor unit group includes an X direction differential capacitor unit group and a Y direction differential capacitor unit group, and the X direction differential capacitor unit group Both the unit group and the Y-direction differential capacitor unit group include two or more capacitor unit modules that form differentials with each other. The capacitor unit module is a comb-shaped structure composed of more than two strip capacitor units. Each ring Both the capacitor unit and the strip capacitor unit include driving electrodes on the upper plate and sensing electrodes on the lower plate.

The plantar three-dimensional pressure measuring device body of the plantar pressure distribution measuring device of the present invention includes a recovery foam layer, a sensor layer, a substrate layer of elastic material, a lead wire layer and a hard backing plate from top to bottom, and the recovery foam layer is selected from polyurethane foam, Silicone foam or modified silicone is filled with inorganic short fibers, and the leads of the lead layer are connected to the signal processor of the sensing system in parallel or independently. 3 meters to 5 meters. The sensing electrode and the driving electrode of each ring-shaped capacitor unit are facing and have the same shape, the driving electrode and the sensing electrode of each strip-shaped capacitor unit have the same width, and the length of the driving electrode of the strip-shaped capacitor unit is greater than the length of the sensing electrode. The two ends of the drive electrode length of the strip capacitor unit are respectively reserved for left difference δ _left and right difference δ _right , b _{0 drive} = b _{0 sense} + δ _right + δ _left , where b _{0 drive} is the drive of the strip capacitor unit The electrode length, b ₀ is the sensing electrode length of the strip capacitor unit. The left differential bit δ _left of the strip capacitor unit = the right differential bit δ _right , and where d ₀ is the thickness of the elastic medium, G is the shear modulus of the elastic medium, and τ _max is the maximum stress value. The driving electrodes and the sensing electrodes of the strip capacitive units of the two groups of capacitive unit modules that form a differential with each other are provided with an initial dislocation offset along the width direction, and the dislocation offsets have the same magnitude and opposite directions. The ring capacitor unit group includes n concentric ring capacitor units, wherein Among them, a is the length of the _parallel plate, r is the width of the ring of the ring capacitor unit, and a _{δ circle is} the electrode spacing between two adjacent ring capacitor units. Both the X-direction differential capacitor unit group and the Y-direction differential capacitor unit group include m strip capacitor units, Among them, a _flat is the length of the parallel plate, a _{δ bar} is the electrode spacing between two adjacent strip capacitor units, and a ₀ is the width of the strip capacitor unit. The width r _circle of the concentric ring capacitance unit is equal to the width a ₀ of the strip capacitance unit; the strip capacitance unit electrode spacing a _{δ bar} is equal to the ring capacitance unit electrode spacing a _{δ circle} , and the strip capacitance unit width Among them, _d0 is the thickness of the elastic medium, E is the Young's modulus of the elastic medium, and G is the shear modulus of the elastic medium. The driving electrodes of the ring capacitor unit group and the strip capacitor unit group are connected to the signal processor of the sensing system through a lead wire, and the sensing electrodes of each ring capacitor unit of the ring capacitor unit group are connected to the sensing electrode separately. The sensor system signal processor is connected, 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 to the sensor system signal processor through a lead-out line. An intermediate converter is respectively arranged between the ring capacitor unit, the capacitor unit module and the signal processor of the sensing system, and the intermediate converter is used to set the transmission coefficient of voltage to capacitance or frequency to capacitance. The sensor system signal processor includes a multi-channel signal high-speed switching circuit, an A/D conversion circuit and a control circuit, and the high-speed switching circuit includes a three-stage switching circuit, and the output of the previous stage switching circuit is the input of the next stage switching circuit The signal is sent to the control circuit through the A/D conversion circuit at the last level of switching circuit.

The beneficial effects of the invention are: using the three-dimensional force pressure sensor, the three-dimensional force of the foot can be detected, and the three-dimensional pressure data of the sole can be used in the study of diabetic complications and foot ulcers. The measurement method is convenient and simple, and will not bring pain to the patient. The plantar data is used to predict foot ulcers and prevent the disease from getting worse. In addition, the sensor of the present invention can simultaneously measure normal force and tangential force, has high sensitivity, high plate utilization efficiency, and the entire ring capacitor unit group contributes to normal force, and has good dynamic performance.

Description of drawings

Fig. 1 is an analysis diagram of the offset dislocation area of concentric rings according to a specific embodiment of the present invention.

Fig. 2 is an analysis diagram of the outer diameter circle for the dislocation of the outer concentric ring according to the specific embodiment of the present invention.

Fig. 3 is a plan view of a parallel plate capacitor according to a specific embodiment of the present invention.

FIG. 4 is a structural diagram of a driving electrode according to a specific embodiment of the present invention.

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

Fig. 6 is a structural diagram of two ring-shaped capacitor groups according to a specific embodiment of the present invention.

FIG. 7 is an initial dislocation diagram of a differential strip capacitor unit according to a specific embodiment of the present invention.

Fig. 8 is a diagram showing the deflection of the differential strip capacitor unit under force in the specific embodiment of the present invention.

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

Fig. 10 is a structural diagram of a foot ulcer monitoring device according to a specific embodiment of the present invention.

Among them, 1 recovery foam layer, 2 sensor layer, 3 substrate layer, 4 lead layer, 5 backing board, 6 lead interface board.

Detailed ways

Referring to the accompanying drawings, through the description of the embodiments, the specific embodiments of the present invention include the shape, structure, mutual position and connection relationship of each part, the function and working principle of each part, and the manufacturing process of the various components involved. And the method of operation and use, etc., are described in further detail to help those skilled in the art have a more complete, accurate and in-depth understanding of the inventive concepts and technical solutions of the present invention.

The main idea of the present invention is: the clinical treatment effect evaluation system of the present invention includes two parts: the plantar three-dimensional pressure measuring device body and the sensor system signal processor. A flat capacitive pressure sensor, the signal processor of the sensing system is the control circuit used to collect the information of the plantar three-dimensional pressure measurement device body, to complete the collection, processing and sending of the plantar pressure information; finally, the signal is denoised, Increase the signal-to-noise ratio to make the collected signal reliable and effective.

As shown in Figure 10, it is the structural diagram of the plantar three-dimensional pressure measuring device of the present invention, and the measuring device includes a recovery foam layer, a sensor layer, a substrate layer, a lead layer, a pad layer and a lead interface board, and the bottom layer is a hard material The uppermost layer of the produced backing board is the recovery foam layer, the thickness of the foam is 20mm-30mm, and the recovery foam is made of polyurethane foam, organic silicon foam, modified organic silicon filled inorganic short fiber and other materials. The sensor layer is under the recovery foam layer, the substrate layer is under the sensor layer, and the lead layer is under the substrate layer. Arranging the sensors and leads on different layers can avoid mutual interference between the two. The sensor leads of the lead layer are connected to the lead interface board. . The substrate layer is an elastic matrix material, which can be a rubber material, and the capacitive pressure sensor layer. The pressure sensor layer is arranged between the substrate layer of elastic material and the recovery foam layer. Both the substrate layer of elastic material and the recovery foam layer are flexible materials, which can The pressure sensor plays a protective role to make the force uniform. The upper surface of the measuring device is rectangular, with a width of 45 cm to 1 meter and a length of 3 meters to 5 meters, which is convenient for the subject to walk on it. It can not only monitor the pressure changes when standing, but also monitor the pressure on the soles of the feet during normal walking. Variety.

The capacitive pressure sensor of the present invention includes a ring capacitor unit group and a strip capacitor unit group, the ring capacitor unit group is used to measure the size of the tangential force and the normal force, and the strip capacitor unit group is used to measure the shear force. In the direction of the force, the strip-shaped capacitor unit groups are arranged at four corners outside the ring-shaped capacitor unit group of the substrate. The ring capacitor unit group includes more than two groups of ring capacitor unit pairs, the ring capacitor unit pair includes two ring capacitor units, and the strip capacitor unit group includes an X direction differential capacitor unit group and a Y direction differential capacitor unit group. The capacitor unit group, the X-direction differential capacitor unit group and the Y-direction differential capacitor unit group all include two or more capacitor unit modules that form differentials with each other, and the capacitor unit modules are composed of more than two strip capacitor units. Comb-shaped structure, each ring capacitor unit and strip capacitor unit includes the driving electrode of the upper plate and the sensing electrode of the lower plate. The sensing electrode and the driving electrode of each ring-shaped capacitor unit are facing and have the same shape, the driving electrode and the sensing electrode of each strip-shaped capacitor unit have the same width, and the length of the driving electrode of the strip-shaped capacitor unit is greater than the length of the sensing electrode. The two ends of the drive electrode length of the strip capacitor unit are respectively reserved for left difference δ _left and right difference δ _right , b _{0 drive} = b _{0 sense} + δ _right + δ _left , where b _{0 drive} is the drive of the strip capacitor unit The electrode length, b ₀ is the sensing electrode length of the strip capacitor unit. The left differential bit δ _left of the strip capacitor unit = the right differential bit δ _right , and where d ₀ is the thickness of the medium, G is the shear modulus of the elastic medium, and τ _ymax is the maximum stress value. The driving electrodes and the sensing electrodes of the strip capacitive units of the two groups of capacitive unit modules that form a differential with each other are provided with an initial dislocation offset along the width direction, and the dislocation offsets have the same magnitude and opposite directions. The ring capacitor unit group includes n concentric ring capacitor units, wherein Among them, a _flat is the length of the parallel plate, r _circle is the width of the ring of the ring capacitor unit, and a _{δ circle} is the electrode spacing between two adjacent ring capacitors. The capacitor unit module adopts a comb-shaped structure, and the X-direction differential capacitor unit group and the Y-direction differential capacitor unit group both include m strip capacitor units, Among them, a _flat is the length of the parallel plate, a _{δ bar} is the electrode spacing between two adjacent strip capacitor units, and a ₀ is the width of the strip capacitor unit. The width r _circle of the concentric ring capacitance unit is equal to the width a ₀ of the strip capacitance unit; the strip capacitance unit electrode spacing a _{δ bar} is equal to the ring capacitance unit electrode spacing a _{δ circle} , and the strip capacitance unit width Among them, _d0 is the thickness of the medium, E is the Young's modulus of the elastic medium, and G is the shear modulus of the elastic medium. The driving electrodes of the ring capacitor unit group and the strip capacitor unit group are connected to the signal processor of the sensing system through a lead wire, and the sensing electrodes of each ring capacitor unit of the ring capacitor unit group are connected to the sensing electrode separately. The sensor system signal processor is connected, 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 connected to the sensor system signal processor through a lead-out line respectively. Intermediate converters are respectively arranged between the ring capacitor unit, the capacitor unit module and the sensor system signal processor, and the converters are used to set the transmission coefficient of voltage or frequency to capacitance.

Below in conjunction with accompanying drawing 1-10 derivation and principle of the present invention, to each part shape, structure, the mutual position between each part and connection relationship, the effect of each part and working principle, manufacturing process and operation and use method etc., make further Detailed explanation.

1.1 Capacitance formula and its input and output characteristics

The initial capacitance of the parallel plate is:

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, ε ₀ vacuum dielectric permittivity is 8.85PF/m, ε _r =2.5 is the relative permittivity of the dielectric, and A ₀ is the initial facing area of the upper and lower plates. d ₀ is stimulated by σ _n to produce relative deformation ε _n = δ _n /d ₀ = σ _n /E, which is substituted into (1) to obtain the input and output characteristics

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\frac{{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\frac{{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}{\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; E.</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

1.2 Linearity and sensitivity under normal stress

1.2.1 Normal linearity

In formula (2), F _n is in the denominator, so the relationship of C _n =f(F _n ) is nonlinear. Because the maximum value σ _nmax in the conversion range is compared with the elastic constant E of the medium, ε _n is a very small quantity, that is, ε _n <<1 in the denominator, expand the formula (2) by series and omit the quadratic power The higher-order infinitesimal of can be simplified as:

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; E.</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

It can be seen that the maximum relative error of normal linearity in the conversion characteristics of C _n and F _n is close to zero.

1.2.2 Sensitivity

According to the definition of normal sensitivity

And according to formula (2) then

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}{\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; E.</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

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

S _n1 ＝C ₀ /AE＝ε ₀ ε _r /d ₀ E (5)

S _n2 changes with F _n , the larger F _n is, the larger S _n2 is, showing a slight nonlinearity in the entire conversion characteristic.

1.3 Relationship between tangential displacement and effective area of ring capacitor

Analyze the capacitance pairs of concentric rings, as shown in Figure 1, R ₁ is the radius of the outer circle, R ₂ is the radius of the inner circle, r = width of the ring = large outer radius R ₁ - inner radius R ₂ . Give the driving electrode a force F _x on a tangential plane, resulting in a shear dislocation of the upper and lower corresponding driving electrodes and sensing electrodes, let d _x be the displacement of the tangential plane, the dislocation area is S _inside and S _outside , and the initial facing area of the electrode plate should be is π(R ₁ ² -R ₂ ² ). Figure 2 is an analysis diagram of the outer diameter circle of the outer concentric ring capacitor. The distance between the two centers before and after the movement is d _x . The intersection of the two centers and the two circles before and after the movement forms a rhombus, and the area _outside S can be calculated:

In the above formula, there is d _x <<R ₁ , so take

Depend on

Will $\mathrm{\&alpha;}=arcco\mathrm{the\; s}\frac{d_x}{2R_1}$ Taylor series expansion of , and omit higher-order terms, $\mathrm{\&alpha;}=\frac{\mathrm{\&pi;}}{2}-\frac{d_x}{2R_1}$

Similarly, it can _be known that S = 2R ₂ d _x , so the error area of the concentric ring capacitor is S = 2R ₁ d _x +2R ₂ d _x .

1.4 Capacitance change of ring capacitor unit group under tangential stress τ excitation

The tangential stress τ does not change the geometric dimension parameter A ₀ of the plate, nor does it affect the dielectric thickness d ₀ . However, τ _x and τ _y change the spatial structure of the parallel-plate capacitor, and a dislocation occurs between the upper and lower plates facing forward. The dislocation offset d _x of the plate under the action of τ. When τ is zero, the upper and lower electrodes of the ring capacitor unit are facing each other, and the effective section between the upper and lower electrodes In Figure 2, under the action of τ _x to the right, the upper plate has a rightward dislocation offset d _x relative to the lower plate, so that the effective area between the upper and lower plates when calculating the capacitance $A_{\mathrm{\&tau;}}={\mathrm{\&pi;R}}_1^2-{\mathrm{\&pi;R}}_2^2-2R_1{d}_x-2R_2{d}_x,$ The resulting capacitance is:

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; \&tau;</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; \&CenterDot;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&pi;R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&pi;R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

According to shear Hooke's law

τ _x = γ _x G = G δ _x /d ₀ (7)

Substitute (7) into (6) to get

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; \&tau;</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}{{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}\mathrm{<span\; class="notranslate">\; G</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

Equation (8) is the input-output characteristic under shear stress, C _τ has a linear relationship with τ _x , and its sensitivity

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; \&tau;</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 9</span>}<span\; class="notranslate">\; )</span>$

It can be seen from formula (9) that the tangential sensitivity is related to R ₁ -R ₂ , that is, the tangential sensitivity is inversely proportional to the width of the ring, and the smaller the width, the higher the sensitivity.

2 Design of plate capacitor

2.1 Design of the plate capacitor

Refer to the layout of the electrodes in Figure 3 and the structural diagram of the driving electrodes in Figure 4, a ring-type contact parallel plate three-dimensional pressure sensor on a 10×10mm ² substrate, the sensor includes a ring-shaped capacitance unit group and a strip Capacitor unit group, ring capacitor unit group is used to measure the size of tangential force and normal force, strip capacitor unit group is used to measure the direction of tangential force, strip capacitor unit group is set outside the substrate ring capacitor unit group the four corners. In this way, the area of the parallel plate can be effectively used. The ring capacitor unit group covers the entire parallel plate, and it works when measuring the three-dimensional force. The strip capacitor unit group effectively uses the parallel plate after the ring capacitor unit group is laid. The space of the four corners is used to measure the direction of the tangential force of the three-dimensional force. Both the driving electrodes and the sensing electrodes of the ring capacitor unit group are composed of n concentric rings, and n is an even number, then n/2 ring capacitor unit pairs are formed. The hatched part represents the section of the outer mold of the lost wax casting process, and its geometry and size should also be kept accurate during mechanical forming.

Referring to the Cartesian coordinate system of the plate capacitor in Figure 5, the origin of the coordinate system is at the origin of the concentric circles of the ring capacitor unit group, the x-axis and the y-axis are respectively along the diagonal direction of the plate capacitor, and the differential capacitor unit group in the X direction includes the X direction Differential capacitor unit group I and X-direction differential capacitor unit group III, X-direction differential capacitor unit group I and X-direction differential capacitor unit group III are respectively located on the positive and negative semi-axes of the x-axis and are symmetrical along the y-axis. The differential capacitor unit group includes the Y-direction differential capacitor unit group II and the Y-direction differential capacitor unit group IV, and the Y-direction differential capacitor unit group II and the Y-direction differential capacitor unit group IV are respectively located on the positive and negative half axes of the y-axis And it is symmetrical along the x-axis, the X-direction differential capacitance unit group I and the X-direction differential capacitance unit group III form a differential capacitance unit combination that responds to τ _x , and the Y-direction differential capacitance unit group II and the Y-direction differential capacitance unit group Capacitive cell group IV forms a differential capacitive cell combination that responds to _τy .

The ring capacitor unit group includes n concentric ring capacitor units, where Among them, a _flat is the length of the parallel plate, r _circle is the width of the ring of the ring capacitor unit, and a _{δ circle} is the electrode spacing between two adjacent ring capacitors. The capacitor unit module adopts a comb-shaped structure, and the X-direction differential capacitor unit group and the Y-direction differential capacitor unit group both include m strip capacitor units. Wherein, a _{δ bar} is the electrode spacing between two adjacent bar-shaped capacitive units, and a ₀ is the width of the bar-shaped capacitive unit. The width r _circle of the concentric ring capacitance unit is equal to the width a ₀ of the strip capacitance unit; the strip capacitance unit electrode spacing a _{δ bar} is equal to the ring capacitance electrode spacing a _{δ circle} , and the width of the strip capacitance unit Among them, _d0 is the thickness of the medium, E is the Young's modulus of the elastic medium, and G is the shear modulus of the elastic medium.

2.2 Excitation signal and coordinate system

The ring capacitor unit is placed in the Cartesian coordinate system shown in Figure 5, and the three-dimensional excitation is applied to the outer surface of the capacitor plate, and the contact force generated has three direction components of Fx, Fy and Fz, and the effects of Fx and Fy The direction is along the X axis and the Y axis, and the action direction of Fz is along the OZ axis. Direction, normal and tangential stress are all a kind of stress tensor, the response of capacitance can be output from the lead wire of the electrode; normal stress σ _n =Fn/A, where is the normal force-bearing surface of the pole plate, Fn=Fz is the normal component; paired _tangential stress τcut= _Fcut /A is generated on the surfaces of both sides.

According to Hooke's law in elastic mechanics, σ _n and τ _x , τ _y will cause the corresponding deformation of the elastic body. in,

${\mathrm{<span\; class="notranslate">\; \&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}{\mathrm{<span\; class="notranslate">\; A</span>}}$

In the formula, E is the Young's modulus GN/m ² of the elastic medium, G is the shear modulus GN/m ² of the elastic medium, δn is the normal displacement of the elastic medium (unit: μm), and δx and δy are The relative dislocation (unit: μm) of the upper and lower plates of the ring capacitor unit is determined by the direction of the coordinate axis.

2.3 Calculation of normal force and tangential force

Select the nth ring capacitor unit and the n/2th ring capacitor unit, and calculate the composition equations by establishing the ring capacitor unit, as shown in Figure 6. After the electrode plate is subjected to normal and tangential excitation, the output capacitance of the nth ring capacitor unit is C ₁ , the output capacitance of n/2 ring capacitor units is C ₂ , and the tangential displacement is d _x , The normal capacitance distance is d _n , S ₁₀ is the initial facing area of the outer ring, and S ₂₀ is the initial facing area of the inner ring.

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 10</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&pi;R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&pi;R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 20</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; S</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&pi;r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&pi;r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

Will (10)-(11) get:

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; *</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; *</span>\frac{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}$

set in the formula $\frac{R_1+R_2}{r_1+r_2}=K,$ but $d_{\mathrm{no}}=\frac{\mathrm{\&epsiv;}(S_{10}-{\mathrm{KS}}_{20})}{C_1-{\mathrm{KC}}_2}$

according to $d_{\mathrm{no}}=d_0-\mathrm{\&Delta;}d=d_0(1-\frac{f_{\mathrm{no}}}{\mathrm{E.}\&CenterDot;S_0})$

It can be seen that: $f_{\mathrm{no}}=\frac{(d_{\mathrm{no}}-d_0)\mathrm{E.}\&Center\; Dot;S_0}{d_0}$

Combine the above (10)*C ₂ -(11)*C ₁ to get:

${\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 10</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 20</span>}}}{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; ;</span>$

Depend on $\mathrm{\&gamma;}=\frac{\mathrm{\&tau;}}{G}=\frac{f_{\mathrm{\&tau;}}}{G\&Center\; Dot;S_0}=\frac{d_x}{d_0}=\frac{C_2{S}_{10}-C_1{S}_{20}}{d_{0}2C_2(R_1+R_2)-d_{0}2C_1(r_1+r_2)},$ So F _τ is

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 10</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 20</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}$

2.4 Determine the direction of tangential force

2.4.1 Strip capacitor unit group structure and parameter design

In order to realize that the tangential response between τ _x and τ _y does not affect each other, a difference δ ₀ is reserved at both ends of the driving electrode length, so b _{0 driving} = b _{0 bottom} + 2·δ ₀ , where at the two ends of b _{0 driving} Length reservation should theoretically guarantee Its calculated value is ${10}^{-5}\&times;\frac{70\&times;{10}^3}{2.4\&times;{10}^6}=2.9\&times;{10}^{-8}m={10}^{-2}um<<1um,$ Therefore, in the process, it should be ensured that b _{0 drive} - b _{0 bottom} ≥ 0.01mm. In order to realize that τ _x and τ _y do not affect the normal capacitance response, the driving electrodes and the sensing electrodes of each strip capacitor unit are arranged with a certain offset in the planar arrangement to eliminate the mutual influence through differential.

As shown in Figure 4, the four dotted boxes in the figure are the references of the sensing electrodes on the lower plate. Taking the position of the sensing electrodes on the lower PCB substrate as a reference, the layout of the driving electrodes on the upper PCB substrate should be based on the PCB substrate The edge line is the reference. Each strip capacitor unit includes the driving electrode of the upper plate and the sensing electrode of the lower plate, assuming that the width of each strip capacitor unit is a ₀ , and the groove width between the two capacitor units is a _δ , then each The pitch of the strip capacitor units is a ₀ +a _δ . In this way, it can be guaranteed that τ _x and τ _y will not affect the normal capacitance response when calculating the output response of the normal capacitance. The distance between them and the geometric reference line is δ ₀ (0.1mm), so as to ensure that the differential capacitance unit group I in the X direction and the differential capacitance unit group III in the X direction only produce a differential capacitance output response to τ _x , while the Y The direction differential capacitance unit group II and the Y direction differential capacitance unit group IV only produce a differential capacitance response to τ _y , an initial misalignment offset δ _xo is set, and its value should ensure that Its calculated value is similar to δ ₀ , and its initial dislocation offset is set to δ _xo = δ _yo = 0.01mm to ensure that the four capacitor units can generate two sets of differential capacitor pairs under the tangential excitation of τ _x and τ _y .

In Fig. ₇ , the dimensions a ₀ , b ₀ , and d ₀ of a pair of capacitors _CL and _{C R} are the same, and the initial dislocation offset δ ₀ is also the same. , while the sharp angle of δ ₀ on the upper layer of capacitor C _R on the right points to -OX. When τ _x =0, That is, the capacitance corresponding to the shaded part in the figure. On this basis, if a dislocation offset of ±δ _x is generated under -F _x excitation, the effect of capacitance increase and decrease as shown in Figure 8 is formed,

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; b</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&PlusMinus;</span>{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; d</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; )</span>$

In Figure 8, the differential capacitance of C _L and C _R will produce ±δ _x and ±ΔC _τ responses to the same τ _x , The size of δ ₀ should satisfy It is desirable to take δ ₀ =10μm, thus, formula (11) can be modified as

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; \&tau;</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; \&tau;</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}{{\mathrm{<span\; class="notranslate">\; Ga</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; )</span>$

In the formula, is the initial capacitance when the shear stress is zero, formula (13) is the input and output characteristics of the shear stress, C _τx and F _x have a linear relationship, and its sensitivity

It can be seen from formula (13) that the smaller a ₀ is, the greater the sensitivity of the tangential stress response is, so the capacitor unit of the present invention adopts a strip capacitor unit group composed of multiple strip capacitors.

2.4.2 Calculation of tangential stress direction

C _Ⅰ to C _Ⅱ and C _Ⅲ to C _Ⅳ can realize two pairs of differential combinations, as shown in Figure 9, the signal differential diagram of the unit capacitance pair, after differential technology processing, the total response of the differential output

${\mathrm{<span\; class="notranslate">\; o</span>}}_{\mathrm{<span\; class="notranslate">\; \&tau;</span>}\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; mK\&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; .</span>{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}{{\mathrm{<span\; class="notranslate">\; a</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; G</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}$

In the formula, neither the normal excitation F _n nor the tangential excitation F _y has any influence on O _τ , that is, the coupling or interference of σ _n and τ _y on the total output of τ _x is automatically eliminated. Because in any operation involving subtraction in the signal, the equivalent and coincident capacitance changes are automatically eliminated. The interference of F _y and F _x on σ _n can be eliminated by increasing the geometric length 2δ ₀ of the upper electrode in the b ₀ direction.

In the same way, $o_{\mathrm{\&tau;}\mathrm{the\; y}}=\frac{2{\mathrm{mK\&epsiv;}}_0\&Center\; Dot;{\mathrm{\&epsiv;}}_r}{a_{0}G}{f}_{\mathrm{the\; y}};$

The direction of the tangential force is calculated from the values of O _τx and O _τy .

2.4 Selection of main materials and their characteristic parameters

The distance between the plates of the parallel plate capacitor is d ₀ =0.1mm, and the inner space of the upper and lower substrates is filled with PDMS (polydimethylsiloxane) superelastic insulating medium except for the copper foil electrode by the lost wax casting method. Its mechanical and physical characteristic parameters are Young's modulus E=6.2MPa, while its shear elastic modulus is G=4.1MPa, and the relative dielectric constant ε _γ =2.5 when the medium is polarized. Since the E and G of the medium are much smaller than the elastic modulus of copper E _copper = 103GPa, the deformation of the internal medium of the capacitor under stress is much greater than that of the plate.

2.5 Electrode lead design

Both the driving electrodes and the sensing electrodes need to be equipped with lead wires. Considering that each driving electrode is grounded at the signal level, the driving electrodes only need to share the same lead wire. The driving electrodes of the ring capacitor unit group and the strip capacitor unit group are connected to the signal processor of the sensing system through a lead wire, and each ring of the ring capacitor unit group is connected to the signal processor of the sensor system by a separate lead wire, The sensor system signal processor calculates according to the free combination of the output values of each ring, and then calculates the average to obtain the size of the tangential force and the normal force. In the case of low precision requirements, the ring capacitor unit group Only two optimal rings can be selected to lead out two leads, and d _x and d _n can be obtained through these two rings, so as to obtain the magnitude of the tangential force and the magnitude of the normal force; the differential capacitor unit group in the X direction and The differential capacitor unit groups in the Y direction are connected to the signal processor of the sensor system through a lead wire respectively, and are used for calculating the direction of the tangential force. An intermediate converter is arranged between the signal processor of the sensing system and the capacitor unit, and the converter is used to set the transmission coefficient of the voltage or frequency to the capacitor. At least 7 pins of the entire capacitor assembly are led out from the side of the planar package, so that the outer surface of the top and bottom of the entire assembly can be conveniently contacted with the measurement object.

Under the support of new materials and new technology, the invention completes the design of a novel three-dimensional force-sensitive capacitor combination. On the force-bearing surface of 10×10mm ² , whether it is normal or tangential, the stress can be transmitted to the medium more uniformly. There is only one external force in the contact between the space force and the sensor surface, and the information of the normal direction F _n can be obtained by summing the capacitance, that is, the entire electrode plate contributes to the calculation of F _n , and at the same time, the information of F _x and F _y can be obtained Information, so as to completely describe a three-dimensional force, according to the design parameters, the normal sensitivity and tangential sensitivity and the maximum linear error of a conversion can be improved.

Capacitive pressure sensors are evenly arranged in a matrix between the substrate layer and the recovery foam layer. The capacitive plates are connected to the signal processor of the sensor system through circuit leads. The signal processor of the sensor system includes a multi-channel signal high-speed switching circuit, A/D Conversion circuit and control circuit. In order to save A/D conversion circuit, one A/D conversion circuit is used to complete the measurement of multiple pressure sensors. The multi-channel signal high-speed switching circuit and control circuit are the key to the design of the system. The switching speed affects the short-term The amount of data tested during the walk. The acquisition circuit designed in the present invention switches signals of 256 sensors at the same time. After local shaping, the control system from the control circuit is switched in three stages. The first stage uses 32 8-way switchers to work in parallel to output 32-way signals, and the 32-way signals enter the second-level switcher, using 4 8-way switchers. The switches work in parallel to obtain 4 signals, which enter the third-stage switcher, obtain 1 signal, and enter the A/D conversion circuit. The A/D conversion circuit reads the data into the computer for temporary storage during the conversion process, and saves all the data in the computer after reading.

In the actual use process, the pressure detection device is laid flat on the ground, and the subject walks with a normal gait or stands still on it. The measuring instrument collects three dynamic plantar pressures and three static plantar pressures respectively. The plantar pressure is compared, and the average pressure of the eight areas of the plantar are analyzed through three tests, the heel, the arch of the foot, the first metatarsal head, the second metatarsal head, the third to fifth metatarsal heads, the first toe, and the second toe , The 3rd to 5th toe, the data of the plantar pressure test provide a reference for analysis, diagnosis and establishment of an expert-aided decision-making system, and provide a reference for the evaluation of clinical treatment effects. The present invention has been exemplarily described above in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited by the above methods, as long as various insubstantial improvements are adopted in the method concept and technical solutions of the present invention, or there is no improvement Directly applying the conception and technical solutions of the present invention to other occasions falls within the protection scope of the present invention. The protection scope of the present invention should be determined by the protection scope defined in the claims.

Claims (10)

1. A plantar pressure distribution measuring device is characterized by comprising a plantar three-dimensional pressure measuring device body and a sensing system signal processor, wherein a plurality of capacitance pressure sensors for receiving plantar pressure information are arranged in the plantar three-dimensional pressure measuring device body, each capacitance pressure sensor comprises a circular ring capacitance unit group and a strip-shaped capacitance unit group, the strip-shaped capacitance unit groups are arranged at four corners of an outer base plate of the circular ring capacitance unit group, each circular ring capacitance unit group comprises more than two pairs of circular ring capacitance units, each circular ring capacitance unit pair comprises two circular ring capacitance units, each strip-shaped capacitance unit group comprises an X-direction differential capacitance unit group and a Y-direction differential capacitance unit group, each X-direction differential capacitance unit group and each Y-direction differential capacitance unit group respectively comprise more than two capacitance unit modules which mutually form a differential, and each capacitance unit module is of a comb-tooth-shaped structure consisting of more than two strip-shaped capacitance units, each ring capacitor unit and each strip capacitor unit respectively comprise a driving electrode of an upper polar plate and an induction electrode of a lower polar plate.

2. The plantar pressure distribution measuring device according to claim 1, wherein the plantar three-dimensional pressure measuring device body comprises a recovery foam layer, a sensor layer, a substrate layer made of an elastic material, a lead layer and a hard base plate from top to bottom, the recovery foam layer is made of polyurethane foam, organic silicon foam or modified organic silicon filled inorganic short fibers, leads of the lead layer are connected to a sensing system signal processor in a parallel or independent mode, the upper surface of the plantar three-dimensional pressure measuring device is rectangular, the width of the plantar three-dimensional pressure measuring device is 45 cm-1 m, and the length of the plantar three-dimensional pressure measuring device is 3 m-5 m.

3. The plantar pressure distribution measuring device according to 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 drive electrode of the strip-shaped capacitor unit, v_{Feeling of 0}The length of the induction electrode of the strip-shaped capacitance unit.

4. The plantar pressure distribution measuring device according to claim 3, wherein the left differential 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 plantar pressure distribution measuring device according to claim 2, characterized in that the driving electrodes and the sensing electrodes of the two groups of strip-shaped capacitive units forming a differential capacitive unit module with each other are provided with initial offset along the width direction, and the offset is the same in size and opposite in direction.

6. The plantar pressure distribution measuring device according to claim 2, wherein the circular ring capacitance unit group includes n concentric circular ring capacitance 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 plantar pressure distribution measuring device according to claim 2, wherein the X-direction differential capacitance unit group and the Y-direction differential capacitance unit group each include 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 plantar pressure distribution measuring device according to claim 2, wherein the pressure measuring unit is a pressure measuring unitWidth r of center 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.

9. The plantar pressure distribution measuring device according to claim 2, wherein the driving electrodes of the circular ring capacitor unit groups and the strip capacitor unit groups are connected with a sensing system signal processor through a lead wire, the sensing electrode individual lead wire of each circular ring capacitor unit of the circular ring capacitor unit groups is connected with the sensing system signal processor, and the sensing electrodes of the capacitor unit modules of the X-direction differential capacitor unit groups and the Y-direction differential capacitor unit groups are respectively connected with the sensing system signal processor through a lead wire.

10. The plantar pressure distribution measuring device according to claim 2, characterized in that intermediate converters are respectively provided between the circular ring capacitance unit, the capacitance unit module and the sensor system signal processor, the intermediate converters are used for setting transmission coefficients of voltage to capacitance or frequency to capacitance, the sensor system signal processor comprises a multi-channel signal high-speed switching circuit, an A/D conversion circuit and a control circuit, the high-speed switching circuit comprises three stages of switching circuits, the output of the previous stage of switching circuit is the input signal of the next stage of switching circuit, and the last stage of switching circuit is sent to the control circuit through the A/D conversion circuit.