RU2618496C1 - Acceleration sensor - Google Patents

Abstract

FIELD: physics, measurement equipment.

SUBSTANCE: invention refers to a measuring technique, namely to acceleration measurements. The acceleration sensor includes a base and a body with a cavity filled with rubbery environment that has no connection with the base, bend-operating bar with a strain gage, the ratio of the bar elasticity modulus E₁ and medium elasticity modulus E₂ satisfies the condition: E₁/E₂≥⋅5⋅10², while the bar is placed into the rubbery environment and is parallel to the base and equidistant from the housing walls.

EFFECT: invention provides increased in impact strength and reduced transverse sensitivity of the sensor.

3 cl, 4 dwg

Description

The invention relates to measuring technique, namely to measurements of accelerations.

The known acceleration sensor [SU No. 1174862, IPC G01P 15/12, publ. 08/23/1985], containing a base and a housing with a cavity filled with a dielectric fluid, an inertial mass and two sensing elements with strain gauges placed on them. The inertial mass (in the form of a ball) is installed in the guide support (in the form of protrusions on the housing), the axis of which coincides with the direction of the measured accelerations. Sensitive elements made in the form of flat elastic plates are located symmetrically on opposite sides of the inertial mass. In the presence of acceleration, the inertial mass, moving in the guide support, acts on the sensitive elements, causing their deformation, which is perceived and converted into an electrical signal by a strain gauge.

This acceleration sensor has liquid damping, which reduces superimposed oscillations on the information signal and relatively high basic sensitivity.

However, the disadvantage of this device is the initially stressed state of the plates. In the presence of shock loading, a transition from elastic to plastic deformation is possible, which leads to the failure of the sensor, and this, in turn, reduces impact strength.

Known acceleration sensor [RU No. 20144619, IPC ⁷ G01P 15/12, publ. 15.06.1994 g] comprising a base and a housing with a cavity filled rubbery medium having no connection with the base, with the strain gage ravine running on a bend, wherein the ratio of ravine modulus E _{1 of} the modulus of elasticity E ₂ of the medium satisfies the following condition: E ₁ / E ₂ ≥5⋅10 ² . One end of the beam is fixed cantilever in the wall of the housing. This device is considered as a prototype.

The cantilever fastening of the beam in the wall leads to a decrease in the impact strength of the sensor, since it is the place of sealing the beam in the housing that is a stress concentrator. In this case, the strain gauge located on the beam either directly enters the voltage concentration zone or is close to it, which increases the sensitivity of the sensor to the transverse component of the acceleration vector. In addition, one of the lead-out conductors passes through a significant part of the rubber-like medium, which introduces an asymmetry in the dynamics of its motion (restriction of movement in the lateral direction) during shock loading, and this also adversely affects the transverse sensitivity.

The disadvantage of the prototype is the lack of impact strength and a sufficiently large value of the transverse sensitivity.

The technical result to which the claimed invention is directed is to increase the impact strength and reduce the transverse sensitivity of the sensor.

The technical result is achieved in that in an acceleration sensor containing a base and a housing with a cavity filled with a rubber-like medium that has no connection with the base, a beam with a strain gauge working in bending, the ratio of the elastic modulus of the beam Ε ₁ to the elastic modulus of the medium E ₂ satisfies the condition: E ₁ / E ₂ ≥5⋅10 ² , according to the invention, the beam is placed in a rubber-like medium parallel to the base equidistant from the walls of the housing.

Placing the beam in a rubber-like medium equidistant from the walls of the housing has several advantages. On the one hand, the beam is protected by a rubber-like medium (in the case of an intense impact, the beam is displaced together with the rubber-like medium and is not deformed as intensively as when it is cantilevered (in the prototype), where it fails during the transition from elastic deformation of the beam). On the other hand, the beam limits the degree of strain gauge deformation and protects it from kink, in contrast to the prototype, where the point of attachment of the beam to the housing is a voltage concentrator. Thus, the impact strength of the proposed sensor is increased. When placing the beam closer to any wall of the body, the degree of its deformation will decrease - the beam will work to a lesser extent on bending and to a greater extent on radial displacement. The placement of the beam equidistant from the walls of the housing introduces symmetry in the dynamics of the beam in the presence of acceleration. The beam bends, the maximum of its deformation (stress) is proportional to acceleration and falls on its middle, that is, it captures almost the entire sensitive layer of the strain gauge. In the zone where the output conductors are located, the movement of the medium is minimal. Consequently, the stiffness of the conductors has a negligible effect on the dynamics of the medium and the beam. In contrast to the prototype, where in the case of a side impact during cantilever fastening, beam deformation occurs - the free end is shifted relative to the fixed end, the beam is bent - and the sensor generates a non-information signal. In the proposed sensor design with lateral impact, the deformation of the beam is minimal, which reduces the lateral sensitivity. The placement of the beam parallel to the base is due to the fact that when the beam is placed at any angle with respect to the base during a lateral (unmeasured) impact, it will deform, leading to an increase in lateral sensitivity, which is undesirable.

, удовлетворяющее условию:

позволяет повысить основную чувствительность датчика. При значении соотношения, меньшем 1,05, датчик потеряет работоспособность из-за возможного зажима балочки, вызванного различием температурных коэффициентов линейного расширения используемых материалов. При значении соотношения, большем 1,2, будет отсутствовать необходимая слабина выводных проводников, влияющая на динамику движения резиноподобной среды и балочки, что приведет к снижению основной чувствительности датчика, так как деформация резиноподобной среды будет в меньшей степени изгибать балочку.The practice of designing an acceleration sensor, the calculations and experimental testing showed that the ratio of the size L of the cavity in the plane of which the beam is located to its length

satisfying the condition:

allows you to increase the basic sensitivity of the sensor. If the ratio value is less than 1.05, the sensor will lose operability due to the possible clamping of the beam caused by the difference in the temperature coefficients of linear expansion of the materials used. When the ratio value is greater than 1.2, there will be no necessary slack in the output conductors, affecting the dynamics of the rubber-like medium and the beam, which will reduce the basic sensitivity of the sensor, since the deformation of the rubber-like medium will bend the beam to a lesser extent.

The presence in the claimed invention of signs that distinguish it from the prototype, allows it to be considered appropriate for the condition of "novelty."

New features that contain a distinctive part of the claims are not identified in technical solutions for a similar purpose. On this basis, we can conclude that the claimed invention meets the condition of "inventive step".

The invention is illustrated by drawings, where:

in FIG. 1 shows a general view of the sensor;

;in FIG. 2 shows the deformation of a rubber-like medium under the action of acceleration

;

in FIG. 3 shows an embodiment of an acceleration sensor with two strain gauges;

in FIG. 4 shows the electrical connection diagram of the strain gauges in the embodiment of the sensor with two strain gauges.

The device is as follows.

удовлетворяет условию:

. Отношение модулей упругостей Е₁/Е₂ непосредственно влияет на степень деформации балочки 4 и, следовательно, на чувствительность датчика. Снижение значения соотношения Е₁/Е₂ ведет к снижению чувствительности датчика (чем это отношение меньше, тем меньше деформируется балочка). Дальнейшее увеличение отношения модулей упругости (>5⋅10²) значительного вклада в чувствительность датчика не вносит.The proposed acceleration sensor (Fig. 1) contains a base 1 and a housing 2 with a cavity filled with a rubber-like medium 3 that is not connected with the base 1, and a beam 4 placed in a rubber-like medium 3 equidistant from the walls of the housing 2. The bending beam 4 is installed in parallel base 1 and is equipped with a strain gauge 5 having conclusions 6 connected to the measuring equipment. The elastic moduli of medium 3 and beam 4 satisfy the condition: E ₁ / E ₂ ≥5⋅10 ² , where E ₁ is the elastic modulus of beam 4, and E ₂ is the elastic modulus of rubber-like medium 3. Moreover, the ratio of the size L of the cavity in the plane of which beam 4 is located, to its length

satisfies the condition:

. The ratio of elastic moduli E ₁ / E ₂ directly affects the degree of deformation of the beam 4 and, therefore, the sensitivity of the sensor. Reducing the value of the ratio E ₁ / E ₂ leads to a decrease in the sensitivity of the sensor (the smaller this ratio, the less the beam is deformed). A further increase in the ratio of elastic moduli (> 5⋅10 ² ) does not significantly contribute to the sensitivity of the sensor.

The sensor operates as follows.

, направленного от основания 1 в тело датчика, в результате действия инерционных сил, деформируется резиноподобная среда, которая, в свою очередь, изгибает балочку (фиг. 2). Максимум деформации (напряжения) балочки 4 пропорционален ускорению

и приходится на ее середину, то есть захватывает практически весь чувствительный слой тензорезистора 5, повышая основную чувствительность датчика. При этом в зоне нахождения выходных проводников 6 движение минимально, а следовательно, их жесткость оказывает незначительное влияние на динамику среды 3 и балочки 4, снижая поперечную чувствительность.When exposed to measured acceleration

directed from the base 1 into the sensor body, as a result of inertial forces, a rubbery medium is deformed, which, in turn, bends the beam (Fig. 2). The maximum deformation (stress) of the beam 4 is proportional to the acceleration

and falls in its middle, that is, it captures almost the entire sensitive layer of the strain gauge 5, increasing the basic sensitivity of the sensor. Moreover, in the zone where the output conductors 6 are located, the movement is minimal, and therefore, their rigidity has a negligible effect on the dynamics of the medium 3 and beam 4, reducing the transverse sensitivity.

The possibility of industrial implementation and practical feasibility of achieving the desired technical result when using the invention is illustrated by the following example.

Example.

мм, что удовлетворяло соотношению:

. Модуль упругости среды 3 составлял Е₂=5⋅10⁵ Па, а балочки - Е₁=10¹¹ Па, что удовлетворяло условию: E₁/E₂≥5⋅10². При воздействии измеряемого ускорения

, направленного от основания 1 в тело датчика, в результате действия инерционных сил деформировалась резиноподобная среда, которая, в свою очередь, изгибала балочку.The acceleration sensor contained a base 1 and a housing 2 with a cavity formed by a cylindrical hole with a diameter d and filled with a rubber-like medium 3 not connected with the base (EL-20 epoxy adhesive and PDI-3AK plasticizer). In medium 3, parallel to the base 1 and equidistant from the walls of the housing 2, a bending beam 4 was placed with a semiconductor strain transducer 5 placed on it and having terminals 6 connected to the measuring equipment. The size of the cavity L (diameter of the cavity d ), in the plane of which the beam 4 is located, was 3.8 mm, and the length of the beam 4 was equal to

mm, which satisfies the ratio:

. The elastic modulus of medium 3 was E ₂ = ⁵ =10 ⁵ Pa, and the beams - E ₁ = 10 ¹¹ Pa, which satisfied the condition: E ₁ / E ₂ ≥5⋅10 ² . When exposed to measured acceleration

directed from the base 1 into the sensor body, as a result of inertial forces, a rubbery medium deformed, which, in turn, bent the beam.

, соотношения модулей упругости среды и балочки Е₁/Е₂, которые показали следующее. Датчик с консольным закреплением балочки (по прототипу) разрушился при ударном ускорении до 10000 g. А датчик, выполненный по предлагаемой конструкции, выдержал ускорение более 30000 g, что подтвердило повышение ударной прочности предлагаемой конструкции. Основная чувствительность у прототипа составила порядка 0,8 мкОм/ (Ом⋅g), а поперечная чувствительность составила 5…15%. Основная чувствительность предлагаемого датчика составила порядка 1,0 мкОм / (Ом⋅g), а поперечная чувствительность не превысила 3%, что подтвердило снижение поперечной чувствительности датчика.The company conducted comparative experimental studies of the proposed design and the design of the sensor, made according to the prototype, with the above values of the dimensions of the cavity L and the beam

, the ratio of the elastic moduli of the medium and the beams E ₁ / E ₂ , which showed the following. The sensor with cantilever beam fixing (according to the prototype) collapsed during shock acceleration up to 10,000 g. And the sensor, made according to the proposed design, withstood the acceleration of more than 30,000 g, which confirmed the increase in impact strength of the proposed design. The main sensitivity of the prototype was about 0.8 μΩ / (Ohm⋅g), and the transverse sensitivity was 5 ... 15%. The main sensitivity of the proposed sensor was about 1.0 μOhm / (Ohm (g), and the transverse sensitivity did not exceed 3%, which confirmed a decrease in the transverse sensitivity of the sensor.

, удовлетворяющая условию:

, подтверждена экспериментом. Расчеты показывают, что при модуле упругости РПС Е₁=5⋅10⁵ Па, модуле упругости балочки 4 Е₂=10¹¹ Па, ее длине

мм и диаметре полости d=L=3,6 мм (

) нижняя (первая) частота

колебаний резиноподобной среды 3 совместно с балочкой 4 составляет 8,4 кГц, а механическое напряжение в центре балочки равно σ=213⋅10⁵ Па. Для той же балочки при d=L=6 мм (т.е при

) частота колебаний среды составила

кГц, σ=233⋅10⁵ Па. Высота заливки полости на коэффициент преобразования датчика (отношение величины измеряемого ускорения к механическому напряжению в центре балочки) и частоту

практически значимого влияния не оказывают. Представленные результаты показывают, что увеличение значения

приводит к повышению коэффициента преобразования всего на 9%, а первая частота снижается в 3,3 раза. Последнее весьма нежелательно для датчиков ударных ускорений.The validity of the choice of the values of L and

satisfying the condition:

, confirmed by experiment. Calculations show that with the elasticity modulus of the RPS E ₁ = 5⋅10 ⁵ Pa, the elastic modulus of the beam 4 E ₂ = 10 ¹¹ Pa, its length

mm and cavity diameter d = L = 3.6 mm (

) lower (first) frequency

oscillations of the rubber-like medium 3 together with the beam 4 is 8.4 kHz, and the mechanical stress in the center of the beam is σ = 213⋅10 ⁵ Pa. For the same beam at d = L = 6 mm (i.e., at

) the oscillation frequency of the medium was

kHz, σ = 233⋅10 ⁵ Pa. The height of the cavity filling by the sensor conversion coefficient (the ratio of the measured acceleration to the mechanical stress in the center of the beam) and the frequency

have practically no significant effect. The presented results show that an increase in the value

leads to an increase in the conversion coefficient by only 9%, and the first frequency decreases by 3.3 times. The latter is highly undesirable for shock acceleration sensors.

To further increase the basic sensitivity of the sensor and reduce the lateral sensitivity to levels less than 2.5%, an embodiment of the sensor with two strain gauges 5 is possible (Fig. 3). For this, a second cavity is introduced into the housing 2, which is identical to the first (one of the walls of both cavities is common) with a similar strain gauge 5 on the beam 4. The beams 4 in the cavities are mounted coaxially and rotated 180 ° relative to each other relative to the longitudinal axis. The gage tensors TP 1 and TP 2 (Fig. 4) are electrically connected in a half-bridge circuit.

, тензорезисторы 5 на балочках 4 испытывают деформацию различных знаков (один тензорезистор работает на растяжение, другой - на сжатие), в результате чего они будут вырабатывать сигналы разных полярностей, что в соединении тензорезисторов по полумостовой схеме дает удвоение коэффициента преобразования, увеличивая основную чувствительность датчика. При действии же ускорения в поперечном направлении сигналы, как правило, однополярны, а полумостовое соединение тензорезисторов синфазные помехи вычитает, снижая поперечную чувствительность датчика. Предложенная конструкция экспериментально опробована. Она работоспособна при пиковом ударном ускорении до 5⋅10⁵ м/с², при этом поперечная чувствительность составила менее 2,5%, а собственная частота

≈10 кГц.In this embodiment, the sensor in the presence of acceleration

, the strain gages 5 on the beams 4 undergo deformation of various signs (one strain gage works in tension, the other in compression), as a result of which they will produce signals of different polarities, which in the connection of the strain gages in a half-bridge circuit will double the conversion coefficient, increasing the basic sensitivity of the sensor. Under the action of acceleration in the transverse direction, the signals are usually unipolar, and the half-bridge connection of the strain gages subtracts common-mode noise, reducing the transverse sensitivity of the sensor. The proposed design has been experimentally tested. It is operational at peak shock acceleration up to 5⋅10 ⁵ m / s ² , while the transverse sensitivity was less than 2.5%, and the natural frequency

≈10 kHz.

So, the presented information indicates the fulfillment of the following set of conditions when using the claimed invention:

- a tool embodying the claimed invention in its implementation, is intended to measure accelerations;

- providing increased impact strength and basic sensitivity while reducing the transverse sensitivity of the sensor;

- for the claimed device in the form in which it is described in the claims, the possibility of its implementation using the means and methods described in the application and known prior to the priority date is confirmed.

Therefore, the claimed invention meets the condition of "industrial applicability".

Claims (3)

1. An acceleration sensor containing a base and a housing with a cavity filled with a rubber-like medium that is not connected to the base, a beam with a strain gauge operating in bending, the ratio of the elastic modulus of the beam Ε ₁ to the medium elastic modulus E ₂ satisfies the condition: Ε ₁ / Ε ₂ ≥5⋅10 ² , characterized in that the beam is placed in a rubber-like medium parallel to the base equidistant from the walls of the housing. 2. The acceleration sensor according to claim 1, characterized in that the ratio of the size L of the cavity in the plane of which the beam is located to its length l satisfies the condition: L / l = 1.05 ... 1.2. 3. Acceleration sensor according to paragraphs. 1 and 2, characterized in that a second cavity is additionally introduced into the housing, which is identical to the first with a similar strain gage on the beam, the beams in the cavities are mounted coaxially and rotated 180 ° relative to each other relative to the longitudinal axis, the beam resistance gages are electrically connected according to a half-bridge circuit.

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