CN112649128A - Sensing device and method for measuring three-dimensional contact stress - Google Patents
Sensing device and method for measuring three-dimensional contact stress Download PDFInfo
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- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
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- G01L1/14—Measuring force or stress, in general by measuring variations in capacitance or inductance of electrical elements, e.g. by measuring variations of frequency of electrical oscillators
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Abstract
The invention provides a sensing device for measuring three-dimensional contact stress, which sequentially comprises the following components in the signal direction: the sensor sequentially comprises an electrode substrate, an interdigital electrode array and a dielectric layer from bottom to top, the interdigital electrode array is fixed on the surface of the electrode substrate and clings to the dielectric layer, the interdigital electrode array is composed of a plurality of interdigital electrodes, and each interdigital electrode comprises a plurality of interdigital capacitor units which are uniformly arranged. The sensing device has simple and compact structure, high reliability, low cost and easy industrial production, and is beneficial to miniaturization, integration and flexibility. The invention also provides a method for measuring the three-dimensional contact stress, which has wide application range and various application scenes and provides a new idea for realizing the application scenes of flexible grabbing of the robot, wearable equipment and the like.
Description
Technical Field
The invention relates to the technical field of contact stress measurement, in particular to a sensing device and a sensing method for measuring three-dimensional contact stress.
Background
The contact stress sensing device is used as a sensing device for simulating a touch function in a robot, and when the contact stress sensing device is in contact with an object to be detected, the contact stress information vertical to the surface of the object to be detected can be obtained frequently, namely, the sensing of the normal dimensional stress of the object to be detected can be realized only. In the application of the actual robot to the fine-grip flexible wearing device, the information of the contact stress in the multi-dimensional direction is generally needed to be known. The method is limited by the limitation of the stress sensing dimension of the existing contact stress sensor, and the information of the contact stress in the multi-dimensional direction generally needs to adopt a plurality of stress sensors to capture the information of each contact stress component at the same time, which has high requirements on the structure, the installation position and the contact angle of the sensor. In addition, the contact stress sensor needs to have a certain flexibility characteristic when the contact object is fragile or a living body. Therefore, the sensing capability of the contact stress sensing device in the three-dimensional direction of the contact stress is improved, and the design of a novel sensing structure is the core requirement of future development of the contact stress sensing device.
Patent CN111751038A discloses a high-sensitivity capacitive flexible three-dimensional force touch sensor based on a bionic mushroom structure, which adopts a mushroom-type structure to form four capacitors that are spatially distributed, and has high detection sensitivity and response speed, but the structure is complex, the size is large, the cost is high, and the application range is narrow. Patent CN208736580U discloses a hybrid flexible touch sensor, which adopts a complementary structure of capacitance and resistance, and uses a resistance structure as an extended structure of the capacitance structure, so as to expand the measurement range of stress. However, the interdigital electrode of the sensor has a single form and a complex structure, so that the application scene of the sensor is single, and the miniaturization is not facilitated.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a sensing device and a sensing method for measuring three-dimensional contact stress, which can be applied to various scenes such as wearable scene, flexible grabbing scene and the like and are beneficial to miniaturization.
The invention provides a sensing device for measuring three-dimensional contact stress, which sequentially comprises the following components in the signal direction:
a signal generator generating an alternating signal;
a sensor receiving the alternating signal generated by the signal generator and producing a change in capacitance; the sensor sequentially comprises an electrode substrate, an interdigital electrode array and a dielectric layer from bottom to top, wherein the interdigital electrode array is fixed on the surface of the electrode substrate and clings to the dielectric layer, the interdigital electrode array is composed of a plurality of interdigital electrodes, and each interdigital electrode comprises a plurality of interdigital capacitor units which are uniformly arranged;
a conditioning circuit that receives a change in capacitance generated by the sensor and outputs the change in capacitance as voltage information;
and the upper computer receives the voltage information generated by the conditioning circuit and acquires the three-dimensional contact stress information according to the voltage information.
Preferably, the electrode substrate in the sensor is made of a material with a dielectric constant larger than 0.8 and a dielectric loss smaller than 0.01.
Further, a plurality of interdigital capacitor units in the sensor are connected with each other through metal leads.
Further, the azimuth angles of adjacent interdigital capacitor units in the interdigital electrodes have fixed difference.
Preferably, the fixed difference of the azimuth angles of the adjacent interdigital capacitor units is 45 ° or 90 °.
Preferably, the dielectric layer in the sensor is made of an elastic material with a dielectric constant larger than 3.6.
The invention also provides a method for measuring three-dimensional contact stress, which comprises the following steps:
step S1, preparing a sensor for measuring three-dimensional contact stress, comprising:
step S11, providing an electrode substrate and a dielectric layer;
step S12, an interdigital electrode array is arranged between the electrode substrate and the dielectric layer, the interdigital electrode array is attached to the electrode substrate and clings to the surface of the dielectric layer, the interdigital electrode array is composed of a plurality of interdigital electrodes, and each interdigital electrode comprises a plurality of interdigital capacitor units which are uniformly arranged;
step S13, setting the interdigital width, the adjacent interdigital interval and the interdigital length of the interdigital capacitor unit according to the thickness of the dielectric layer;
step S2, a signal generator is connected to the input end of the sensor, the dielectric layer deforms under the contact stress, and the capacitance difference of the interdigital capacitor unit before and after the dielectric layer deforms is calculated according to the interdigital width, the adjacent interdigital interval and the interdigital length which are set in the step S13;
step S3, connecting the output end of the sensor to a conditioning circuit, and converting the capacitance difference of the interdigital capacitor unit before and after the dielectric layer is deformed into a voltage signal;
and step S4, connecting the conditioning circuit to an upper computer, and outputting the voltage signal into three-dimensional contact stress by the upper computer.
Further, the step S2 includes:
and step S21, constructing a solving model of the capacitance of the interdigital electrode, and acquiring the inherent capacitance of each interdigital capacitor unit before the dielectric layer is deformed according to the model.
And step S22, acquiring the equivalent capacitance of the interdigital capacitor unit in the sensor according to the inherent capacitance of the interdigital capacitor unit before the dielectric layer is deformed.
And step S23, calculating the capacitance difference between adjacent interdigital capacitor units in the interdigital electrode before and after the dielectric layer is deformed.
Further, the equivalent capacitance in step S22 is calculated according to the following formula:
in the formula, epsilonsIs the dielectric constant of the electrode substrate layer and is a dimensionless pure number; epsiloneffectIs the effective dielectric constant of the dielectric layer isA dimensionless pure number; c0The capacitance is the inherent capacitance of the interdigital capacitance unit before the dielectric layer is deformed; epsilon0Is a vacuum dielectric constant of ∈0＝8.854×10-12F/m; l is the length of the interdigital, w is the width of the interdigital, a is the spacing width of the interdigital, and L, w and a are both in mm; epsilonij(i, j ═ x, y, z) is the dielectric constant of the unit point of the dielectric layer in each direction of space, the x direction and the y direction are in the same plane and are mutually perpendicular, the x direction and the y direction are respectively parallel to two adjacent edges of the interdigital capacitor unit, and the z direction is the direction perpendicular to the plane of the x direction and the y direction; theta is an included angle between the interdigital capacitor unit and the y direction.
Further, the conversion relationship between the capacitance difference and the voltage signal in the step S3 is as follows:
wherein the proportionality coefficient K is 2 pi f.Vin·RfF is frequency in Hz; vinIs the excitation voltage in units of V; rfIs the gain of the conditioning circuit, in dB; c0The inherent capacitance of the interdigital capacitance unit is shown, v is the Poisson's ratio of the sample, alpha is the strain-dielectric constant, and u is the strain quantity.
The sensing device for measuring the three-dimensional contact stress provided by the invention uses the high-dielectric-elasticity material as the dielectric layer, can ensure the feasibility of three-dimensional contact stress measurement and the high flexibility of the sensing device, has the advantages of simple and compact structure, high reliability, low cost, easiness in industrial production and benefit for miniaturization, integration and flexibility. The invention also provides a method for measuring the three-dimensional contact stress, which is characterized in that the capacitance difference of the interdigital capacitor unit before and after the dielectric layer is deformed is solved, the relation between the capacitance difference and the output voltage is established, and the upper computer judges the stress information according to the voltage information. The method has wide application range and various application scenes, provides a new idea for realizing the application scenes of flexible grabbing of the robot, wearable equipment and the like, and overcomes the defects that the three-dimensional contact stress cannot be measured or the measurement effect of the three-dimensional contact stress is not ideal in the prior art.
Drawings
Fig. 1 is a schematic structural view of a sensing device for measuring three-dimensional contact stress according to the present invention.
Fig. 2 is a schematic diagram of the structure of the sensor of fig. 1.
Fig. 3 is a schematic structural diagram of the interdigital electrode array of type 1 × 2 in fig. 2.
Fig. 4 is a schematic structural diagram of the 1 × 4 interdigital electrode array in fig. 2.
Fig. 5 is a schematic structural diagram of the interdigital electrode array of type 64 × 4 in fig. 2.
Fig. 6 is a schematic layout of the interdigital capacitor cell.
Fig. 7 is a schematic diagram of a conditioning circuit configuration.
FIG. 8 is a schematic diagram of capacitance signal as a function of contact stress displayed on the human-computer interface.
Detailed Description
The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
As shown in fig. 1, the sensing device for measuring three-dimensional contact stress provided by the present invention sequentially includes a signal generator 10, a sensor 20, a conditioning circuit 30 and an upper computer 40 according to a signal direction, wherein the signal generator 10 generates an alternating signal and inputs the alternating signal to the sensor 20, the sensor 20 generates a capacitance change when being subjected to contact stress, the capacitance change is input to the conditioning circuit 30 to generate corresponding voltage information, the voltage information is input to the upper computer 40, and the upper computer 40 obtains information of three-dimensional contact stress according to the voltage information.
As shown in fig. 2, the sensor 20 includes, in order from bottom to top, an electrode substrate 21, an interdigital electrode array 22, and a dielectric layer 23, where the interdigital electrode array 22 is fixed on the surface of the electrode substrate 21 and clings to the dielectric layer 23.
The electrode base 21 may be formed as a thin film or sheet having a certain toughness using a material having a high dielectric constant E (>0.8) and a low dielectric loss tg (<0.01), such as at least one of ceramics, silicon, polyester (PET, LCP, etc.), polyketone, polyimide, or fluoropolymer, or a composite formed of these materials. In the present embodiment, the electrode substrate 21 is made of ceramic, polyethylene terephthalate (PET) or Polyimide (PI), wherein the tensile strength of PET is in the range of 1000-; the tensile strength range of the Polyimide (PI) is 2000-3000MPa, the elongation rate range is 50-100%, the dielectric constant range is 2-5, and the dielectric strength range is 200-400V.
The electrode substrate 21 serves as a carrier for the interdigital electrode array 22 and the dielectric layer 23, and serves as a fixed support for the sensor. On the other hand, the material properties of the electrode substrate 21 itself can block external interference, and facilitate flexibility, miniaturization, and integration.
The interdigital electrode array 22 is an n × m type electrode array, where n denotes the number of interdigital electrodes in the array, n is 1,2,3,4. For example, as shown in fig. 3, fig. 4 and fig. 5, fig. 3 shows a 1 × 2 interdigital electrode array, which includes 1 interdigital electrode, which includes 2 interdigital capacitor units; fig. 4 shows a 1 × 4 interdigital electrode array, which comprises 1 interdigital electrode, and the interdigital electrode comprises 4 interdigital capacitor units; fig. 5 shows a 64 × 4 interdigital electrode array, which includes 64 interdigital electrodes, and each interdigital electrode includes 4 interdigital capacitor units. It should be appreciated that in other embodiments, n and m may be selected using other suitable values.
And a plurality of interdigital capacitor units in each interdigital electrode are uniformly arranged according to a certain angle, and each interdigital capacitor unit is in the same plane. As shown in fig. 6, x and y in the figure represent two orientations of 90 °, and the azimuth angles of adjacent interdigital capacitor units have a fixed difference, which is 45 ° or 90 °, and θ in the figure represents the azimuth angle of the interdigital capacitor unit. Each interdigital capacitor unit comprises two metal lead wires, wherein one metal lead wire is connected with the same external measuring circuit, and the other metal lead wire is connected with the metal lead wires of other interdigital capacitor units. In addition, the ratio of the finger width w of the finger capacitor unit to the adjacent finger interval a is a fixed value, that is: w/a ═ c, where c is a constant. The thickness of the interdigital capacitor unit is 1-100nm, and the interdigital capacitor unit is made of one or more alloy materials such as copper, gold and silver.
The dielectric layer 23 shown in fig. 2 has good elastic characteristics, and satisfies a certain corresponding relationship between strain and stress in a certain deformation range, such as the linear relationship of hooke's law. The dielectric layer 23 is made of a material having a dielectric constant greater than 3.6, and can generate significant dielectric property change under a lower stress deformation condition, and may be made of polyisoprene, synthetic polyisoprene rubber, butadiene rubber, polychloroprene rubber, butyl rubber (including halogenated butyl rubber), styrene butadiene rubber, nitrile butadiene rubber (including hydrogenated nitrile butadiene rubber), ethylene propylene rubber series, epichlorohydrin rubber, polyacrylate, silicone rubber, fluorosilicone rubber (FVMQ), or a composite of the above materials. Meanwhile, in order to further improve the dielectric properties of the dielectric layer 23, highly conductive or high dielectric constant materials including, but not limited to, carbon black, carbon nanotubes, carbon fibers, graphene, metal nanowires, metal particles, ionic polymers, barium titanate, conductive polyurethane liquid metal, and the like, and composites thereof may be doped.
The invention does not limit the size of the electrode substrate 21, the interdigital electrode array 22 and the dielectric layer 23, and the size of the interdigital capacitor unit can be reduced to millimeter level or micron level according to the use environment, thereby facilitating the formation of the array structure.
As shown in fig. 7, the conditioning circuit 30 includes an amplifier and a phase-locked loop, and can convert a slight capacitance change into voltage information proportional to the capacitance change based on the phase-locked amplification principle, so as to improve the accuracy and applicability of the measurement.
If an external stimulus is applied to the interdigital electrodes, an electric field is generated in the vicinity of the interdigital electrodes, which penetrates the dielectric layer and may induce an electric potential shift within the dielectric layer to cancel the applied electric field. The electrical displacement changes the charge stored between the electrodes and thereby changes the capacitance between the electrodes, so that a measurement of the capacitance can be used in turn to infer the dielectric constant of the dielectric layer and its distribution.
Based on the principle, the method for measuring the three-dimensional contact stress provided by the invention comprises the following steps:
step S1, preparing a sensor for measuring three-dimensional contact stress, specifically including:
in step S11, an electrode substrate and a dielectric layer are provided, wherein the electrode substrate and the dielectric layer are made of the same material as described above.
And step S12, arranging an interdigital electrode array between the electrode substrate and the dielectric layer, wherein the interdigital electrode array is attached to the electrode substrate in a certain pattern form by deposition, etching and other processes and clings to the surface of the dielectric layer.
The dielectric layer is a strain induction layer of contact stress, and the thickness h of the dielectric layer satisfies the following conditions: and h, λ, a + w, wherein the spatial wavelength λ is the distance between adjacent electrodes of the same polarity, and the interdigital capacitance gradually increases and then reaches saturation as the thickness of the dielectric layer increases. Because the induction depth of the electric field is limited, when the thickness of the dielectric layer is larger than the induction depth of the electric field, the dielectric layer can be treated as a medium with infinite thickness, at the moment, the thickness of the medium is increased, the interdigital capacitance cannot be changed, and the maximum distance for detecting the output change generated by the sensor in the thickness direction does not exceed lambda.
Thus, in step S13, the finger width w, the adjacent finger interval a, and the finger length L of the finger capacitor unit in the finger electrode array are set according to the thickness h of the dielectric layer. Typically, the finger width w and the spacing a between adjacent fingers are equal in size, and the sum of the lengths is equal to the dielectric layer thickness h. The interdigital length L is the most important parameter for determining the overall size of the interdigital electrode and the sensor, and is also a key parameter for determining the size of an electric field generated by the interdigital electrode, the size of L is set according to the size requirement of the sensor and the number of capacitor units, if the length of the sensor is A and the width of the sensor is B, M interdigital capacitors are arranged in the length direction, N interdigital capacitors are arranged in the width direction, ML is less than or equal to A, and NL is less than or equal to B. Wherein the units of the parameters h, lambda, a, w, L, A and B are all mm.
And step S2, connecting a signal generator to the input end of the sensor, enabling the dielectric layer to deform under the contact stress, and acquiring the capacitance difference delta C of the interdigital capacitor unit before and after the dielectric layer deforms according to the interdigital width w, the adjacent interdigital interval a and the interdigital length L which are set in the step S1.
The signal generator generates a sweep frequency alternating signal of 10Hz-250GHz, the alternating signal is used as a carrier wave to enable the dielectric layer to be influenced by external contact stress to deform, and the spatial position and the dipole orientation of each unit point in the material change, so that the dielectric constant changes. When the dielectric characteristics of the dielectric layer and the stress deformation have a corresponding relationship, such as a linear corresponding relationship, the contact stress borne by the dielectric layer can be represented by measuring the capacitance change delta C of the interdigital electrode before and after the deformation of the dielectric layer. Step S2 specifically includes:
step S21, constructing a solving model of the capacitance of the interdigital electrode, and acquiring the inherent capacitance C of each interdigital capacitance unit according to the model0kAnd k denotes a serial number k of the interdigital capacitor unit, which is 1,2, 3. The capacitance solving model of the interdigital electrode is as follows:
in the formula, epsilon0Is a vacuum dielectric constant of ∈0＝8.854×10-12F/m, L is the length of the interdigital and the unit is mm; w is the interdigital width and the unit is mm; and a is the spacing width of the fingers and has the unit of mm.
Relative strain u of isotropic dielectric layerijAnd the dielectric constant epsilon of the dielectric layer in the ij (i, j ═ x, y, z) directionijThe following linear relationship exists, the x-axis direction and the y-axis direction are in the same plane and perpendicular to each other, the x-axis direction and the y-axis direction are respectively parallel to two adjacent edges of the interdigital capacitor unit, and the z-axis direction is a direction perpendicular to the plane of the x-axis direction and the y-axis direction:
εij＝εδij+α1uij+α2ullδij (2)
wherein ε is the dielectric constant of the dielectric layer before deformation, and is a dimensionless pure number; alpha is alpha1And a2Is the strain-dielectric coefficient, is a dimensionless pure number,
δijis a function of kronecker, i.e.
Coefficient of volume change ull＝uxx+uyy+uzzIs the sum of the coefficients of volume change in the x, y and z directions, e.g. if the dielectric layer only produces a thickness change Δ h in the z direction
h is the original thickness of the dielectric layer.
When the dielectric layer is deformed under the action of stress, the dielectric layer material is changed into anisotropic material, and the dielectric properties of the dielectric layer material can be defined by three directions of x, y and z and the dielectric constants epsilon corresponding to the three directionsijTo indicate.
Therefore, in step S22, according to the intrinsic capacitance of the interdigital capacitor unit, the equivalent capacitance C of the interdigital capacitor unit is obtained when the sensor uses the isotropic material as the substrate and the surface is closely covered with the anisotropic dielectric layer materialθEquivalent capacitance CθCalculated according to the following formula:
wherein theta is the included angle between the interdigital capacitor unit and the y-axis direction, epsilonsIs the dielectric constant of the electrode substrate layer and is a dimensionless pure number; epsiloneffectIs the effective dielectric constant of the dielectric layer, is a dimensionless pure number; epsilonijAnd (i, j ═ x, y, z) is the dielectric constant of the dielectric layer unit point in all spatial directions. For isotropic dielectric layer materials,. epsiloneffect＝ε。
When the dielectric layer material deforms to become an anisotropic material, the dielectric constant is expressed by a second-order tensor, that is:
after the dielectric layer is deformed, the equivalent capacitance calculation formula of the interdigital capacitor unit is as follows:
where γ is the strain amplitude and is a dimensionless pure number.
If the dielectric layer is deformed only by the positive stress, the equivalent capacitance calculation formula is:
after obtaining the equivalent capacitance of each interdigital capacitor unit after the dielectric layer is deformed, step S23 is performed to calculate the capacitance difference Δ C between adjacent interdigital capacitor units before and after the dielectric layer is deformed.
According to the arrangement condition of the interdigital capacitor units, the two conditions can be divided into the following two conditions:
1) as shown in fig. 3, when two identical interdigital capacitor units are perpendicular to each other and are deformed by stress, a conditioning circuit is used for subtracting, and the capacitance difference of the two interdigital capacitor units is obtained as follows:
wherein u is1And u2Respectively the relative strain in the direction of stress application and the strain perpendicular to the direction of stress application.
2) As shown in FIG. 4, when four identical interdigital capacitor units are arranged in a matrix at 45 DEG intervals, the capacitors after being deformed by stress are respectively C1、C2、C3、C4And then the capacitance difference between the interdigital capacitance units is as follows:
in particular, when two identical interdigital capacitor units are perpendicular to each other and arranged in an x-y plane, one interdigital capacitor has an angle of 0 DEG with respect to the y-axis, and the capacitance is C0°＝C⊥(ii) a The included angle between the other interdigital capacitor and the y axis is 90 degrees, and the capacitor is C90°＝Cp. Under uniaxial stress, the correspondence of the stress action direction becomes u1The transverse direction perpendicular to the direction of application of the stress is changed to u2. The capacitance difference of the two interdigital capacitor units is as follows:
step S3, connecting the output end of the sensor to a conditioning circuit, and converting the capacitance difference Delta C of the interdigital capacitor unit before and after the dielectric layer is deformed into a voltage signal Vout。
Output voltage V of external circuit of sensoroutThe following proportional relationship exists with the capacitance difference Δ C:
proportionality coefficient K2 pi f.Vin·RfF is the external excitation, i.e. the frequency provided by the signal generator, in Hz; vinIs the excitation voltage provided by the signal generator, and the unit is V; rfIs the gain of the conditioning circuit, in dB; c0The inherent capacitance of the interdigital capacitance unit is shown, v is the Poisson's ratio of the sample, alpha is the strain-dielectric constant, and u is the strain quantity.
Specifically, when stress is measured using a single interdigital capacitive cell sensor, C in formula (9) is setpFrom CdAlternative, CdRepresenting the capacitance of the dielectric layer without deformation corresponding to the virtual interdigital capacitance, and having no relative strain, wherein the capacitance differences Δ C and VoutThe method comprises the following steps:
when four same interdigital capacitor units are arranged in a matrix at intervals of 45 degrees, the output voltage V of each group of sensorsout1And Vout2Variation u corresponding to main phase1-u2The relationship between is:
simultaneously solving a formula (12) to obtain the output voltage value V of each group of sensorsout1And Vout2。
And finally, step S4, the conditioning circuit is connected to an upper computer, a program built in the upper computer outputs the voltage signal into three-dimensional contact stress, and the result is displayed through a human-computer interaction interface. Specifically, the upper computer built-in program corresponds the voltage difference parallel to the dielectric layer and the voltage difference perpendicular to the dielectric layer to the contact stress one by one, and the decomposed forces are synthesized to obtain the three-dimensional contact stress information. The capacitance of the dielectric layer displayed on the human-computer interface is changed along with the contact stress, and the situation is shown in figure 8.
The invention provides a novel method for measuring three-dimensional contact stress, and the dielectric constant epsilon of a dielectric layer of a sensoreffectChanges along with the deformation of the dielectric material caused by the external contact stress to establish the effective dielectric constant epsiloneffectThe relation between the change delta C of different interdigital capacitance units in the interdigital electrode structure is obtained, then the signal of the stress deformation of the dielectric layer is transmitted to a conditioning circuit, and the small capacitance change value delta C is converted into a voltage V which is in direct proportion to the change delta C through the conditioning circuitoutThe delta C is output to an upper computer, and the output voltage V can be displayed on a human-computer interfaceoutAnd further judging the stress information. The interdigital electrode provided by the method has various forms, wide application range and various application scenes, is beneficial to miniaturization, integration and flexibility, and the sensing device based on the method has the advantages of simple and compact structure, high reliability, low cost and easiness in industrial production, and provides application scenes such as flexible grabbing of a robot, wearable equipment and the likeA new idea is provided.
The above embodiments are merely preferred embodiments of the present invention, which are not intended to limit the scope of the present invention, and various changes may be made in the above embodiments of the present invention. All simple and equivalent changes and modifications made according to the claims and the content of the specification of the present application fall within the scope of the claims of the present patent application. The invention has not been described in detail in order to avoid obscuring the invention.
Claims (10)
1. A sensing device for measuring three-dimensional contact stress is characterized by sequentially comprising the following components along the signal trend:
a signal generator generating an alternating signal;
a sensor receiving the alternating signal generated by the signal generator and producing a change in capacitance; the sensor sequentially comprises an electrode substrate, an interdigital electrode array and a dielectric layer from bottom to top, wherein the interdigital electrode array is fixed on the surface of the electrode substrate and clings to the dielectric layer, the interdigital electrode array is composed of a plurality of interdigital electrodes, and each interdigital electrode comprises a plurality of interdigital capacitor units which are uniformly arranged;
a conditioning circuit that receives a change in capacitance generated by the sensor and outputs the change in capacitance as voltage information;
and the upper computer receives the voltage information generated by the conditioning circuit and acquires the three-dimensional contact stress information according to the voltage information.
2. The sensing device for measuring three-dimensional contact stress according to claim 1, wherein the electrode substrate in the sensor is made of a material with a dielectric constant greater than 0.8 and a dielectric loss less than 0.01.
3. The sensing device for measuring three-dimensional contact stress according to claim 1, wherein a plurality of interdigital capacitive elements in the sensor are connected to each other by metal leads.
4. The sensing device for measuring three-dimensional contact stress according to claim 3, wherein the azimuthal angles of adjacent interdigital capacitor units in the interdigital electrode have a fixed difference.
5. The sensing device for measuring three-dimensional contact stress according to claim 4, wherein the fixed difference of the azimuthal angles of the adjacent interdigital capacitor units is 45 ° or 90 °.
6. The sensing device for measuring three-dimensional contact stress according to claim 1, wherein the dielectric layer in the sensor is made of an elastic material with a dielectric constant greater than 3.6.
7. A method of measuring three-dimensional contact stress, comprising:
step S1, preparing a sensor for measuring three-dimensional contact stress, comprising:
step S11, providing an electrode substrate and a dielectric layer;
step S12, an interdigital electrode array is arranged between the electrode substrate and the dielectric layer, the interdigital electrode array is attached to the electrode substrate and clings to the surface of the dielectric layer, the interdigital electrode array is composed of a plurality of interdigital electrodes, and each interdigital electrode comprises a plurality of interdigital capacitor units which are uniformly arranged;
step S13, setting the interdigital width, the adjacent interdigital interval and the interdigital length of the interdigital capacitor unit according to the thickness of the dielectric layer;
step S2, a signal generator is connected to the input end of the sensor, the dielectric layer deforms under the contact stress, and the capacitance difference of the interdigital capacitor unit before and after the dielectric layer deforms is calculated according to the interdigital width, the adjacent interdigital interval and the interdigital length which are set in the step S13;
step S3, connecting the output end of the sensor to a conditioning circuit, and converting the capacitance difference of the interdigital capacitor unit before and after the dielectric layer is deformed into a voltage signal;
and step S4, connecting the conditioning circuit to an upper computer, and outputting the voltage signal into three-dimensional contact stress by the upper computer.
8. The method for measuring three-dimensional contact stress according to claim 7, wherein said step S2 comprises:
step S21, constructing a solving model of the capacitance of the interdigital electrode, and acquiring the inherent capacitance of each interdigital capacitor unit before the dielectric layer is deformed according to the model;
step S22, acquiring the equivalent capacitance of the interdigital capacitor unit in the sensor according to the inherent capacitance of the interdigital capacitor unit before the dielectric layer is deformed;
and step S23, calculating the capacitance difference between adjacent interdigital capacitor units in the interdigital electrode before and after the dielectric layer is deformed.
9. The method for measuring three-dimensional contact stress according to claim 8, wherein the equivalent capacitance in step S22 is calculated according to the following formula:
in the formula, epsilonsIs the dielectric constant of the electrode substrate layer and is a dimensionless pure number; epsiloneffectIs the effective dielectric constant of the dielectric layer, is a dimensionless pure number; c0The capacitance is the inherent capacitance of the interdigital capacitance unit before the dielectric layer is deformed; epsilon0Is a vacuum dielectric constant of ∈0＝8.854×10-12F/m; l is the length of the interdigital, w is the width of the interdigital, a is the spacing width of the interdigital, and L, w and a are both in mm; epsilonij(i, j ═ x, y, z) is the dielectric constant of the unit point of the dielectric layer in each direction of space, the x direction and the y direction are in the same plane and are mutually perpendicular, the x direction and the y direction are respectively parallel to two adjacent edges of the interdigital capacitor unit, and the z direction is the direction perpendicular to the plane of the x direction and the y direction; theta is an included angle between the interdigital capacitor unit and the y direction.
10. The method for measuring three-dimensional contact stress according to claim 8, wherein the conversion relationship between the capacitance difference and the voltage signal in step S3 is:
wherein the proportionality coefficient K is 2 pi f.Vin·RfF is frequency in Hz; vinIs the excitation voltage in units of V; rfIs the gain of the conditioning circuit, in dB; c0The inherent capacitance of the interdigital capacitance unit is shown, v is the Poisson's ratio of the sample, alpha is the strain-dielectric constant, and u is the strain quantity.
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| CN113776699A (en) * | 2021-09-18 | 2021-12-10 | 太原理工大学 | Positive pressure insensitive interdigital capacitive strain sensor and preparation method thereof |
| CN114397057A (en) * | 2021-12-14 | 2022-04-26 | 中国科学院深圳先进技术研究院 | Underwater contact pressure and water depth monitoring integrated sensor |
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| CN114838860A (en) * | 2022-04-15 | 2022-08-02 | 合肥工业大学 | Flexible multidimensional contact stress sensor and preparation method thereof |
| CN115791917A (en) * | 2022-11-10 | 2023-03-14 | 中国科学院长春应用化学研究所 | Method for dividing circular equal-area units and application of method in interdigital electrode distribution |
| EP4246110A1 (en) * | 2022-03-16 | 2023-09-20 | Benecke-Kaliko AG | Capacitive pressure sensor |
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| CN113776699A (en) * | 2021-09-18 | 2021-12-10 | 太原理工大学 | Positive pressure insensitive interdigital capacitive strain sensor and preparation method thereof |
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| CN114397057A (en) * | 2021-12-14 | 2022-04-26 | 中国科学院深圳先进技术研究院 | Underwater contact pressure and water depth monitoring integrated sensor |
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