WO2021074024A1

WO2021074024A1 - Acceleration sensor

Info

Publication number: WO2021074024A1
Application number: PCT/EP2020/078387
Authority: WO
Inventors: Flavio ROSA
Original assignee: Kistler Holding Ag
Priority date: 2019-10-14
Filing date: 2020-10-09
Publication date: 2021-04-22

Abstract

The invention relates to an acceleration sensor (1), wherein the acceleration sensor (1) has a seismic mass (2), a prestressing arrangement (3) and a measurement system (4); which seismic mass (2) exerts a force on the measurement system (4) in the event of an acceleration; wherein a longitudinal axis (X) runs centrally through the centre of the seismic mass (2); which measurement system (4) has two piezoelectric measurement elements (41) which are spatially spaced apart; which measurement elements (41) are arranged on both sides of the seismic mass (2) with respect to the longitudinal axis (X); which measurement elements (41) have surfaces; wherein an acceleration generates electrical polarization charges on the surfaces, wherein the acceleration sensor (1) has a number N of measurement systems (4); wherein the seismic mass (2) has a number N+1 of partial masses (21), which partial masses (21) are electrically insulated from one another; and wherein the number corresponds to N=3, 4, 5 or 6.

Description

Accelerometer

Technical area

The invention relates to a piezoelectric acceleration sensor according to the definition of the preamble of the independent claim.

State of the art

An acceleration is a directed physical quantity. An accelerometer picks up an acceleration component which corresponds to the acceleration component given by the orientation of the accelerometer.

An accelerometer is known from the document W017093100A1. The accelerometer has a piezoelectric system, a seismic mass and a pre-tensioning arrangement. When accelerating, the seismic mass exerts a force proportional to its acceleration on the piezoelectric system, which force generates piezoelectric polarization charges in the piezoelectric system's rule. The piezoelectric polarization charges can be tapped electrically as acceleration signals. The seismic mass has two mass elements from which the electrical polarization charges can be tapped. The acceleration sensor is set up to record the acceleration along a predetermined spatial direction. If there is an acceleration along a different spatial direction, the accelerometer only determines the acceleration component along the specified spatial direction. Accelerometers record at least one acceleration component of an acceleration along a spatial axis or around a spatial axis. An acceleration component corresponds to an acceleration along a spatial axis of a Cartesian coordinate system or an angular acceleration about a spatial axis. For this purpose, the acceleration sensor has a piezoelectric measuring system, which ideally has a sensitivity to the acceleration components to be determined, but is not sensitive to other acceleration components. The direction of the spatial axis is given by the properties and the alignment of the piezoelectric measuring system.

Piezoelectric crystals are generally cut along an axis of the crystal, so that piezoelectric measuring elements, which have at least one piezoelectric crystal, have a sensitivity to a force acting along a certain direction due to the piezoelectric effect. A distinction is made between four types of piezoelectric effect, analogous to the textbook "Piezoelectric Messtechnik"'by G. Gautschi, Springer-Verlag 1980: The longitudinal piezoelectric effect, in which one perpendicular to a first surface and a second surface the force acting on the piezoelectric Messele element generates an electrical polarization charge, or polarization charges for short, on the first surface and a polarization charge on the second surface; the transverse piezoelectric effect, in which a force acting perpendicular to a first surface and a second surface of the piezoelectric measuring element generates polarization charge on surfaces of the piezoelectric measuring element which are perpendicular to the first surface and the second surface; the piezoelectric longitudinal thrust effect, in which a thrust force acting parallel to the first upper surface between the first surface and the second upper surface generates polarization charges on the first surface and polarization charges on the second surface; and the piezoelectric transverse thrust effect, in which a thrust force acting parallel to the first surface between the first surface and the second surface generates polarization charges on surfaces of the piezoelectric measuring element which are perpendicular to the first surface and the second surface. The transversal and longitudinal piezoelectric shear effect is often referred to as the transversal and longitudinal piezoelectric shear effect.

If piezoelectric measuring elements in an acceleration sensor are biased against a seismic mass by means of a pretensioning device, a measuring element with a thrust effect is usually used, since a change in the magnitude of the bias does not generate a polarization charge which is incorrectly attributed to an acceleration would. A change in the preload can, for example, be caused by a change in the temperature of the acceleration sensor or the ambient pressure.

If several acceleration components are to be recorded, for example all three possible acceleration components of a linear acceleration, there are generally several acceleration sensors with piezoelectric measuring elements because of the advantages of using measuring elements with a piezoelectric thrust effect arranged perpendicular to one another with a thrust effect, each having its own seismic mass. The arrangement with several separate accelerometers requires a lot of space. Furthermore, each accelerometer has to be contacted with its own cable, which is complex. is. In this document, a linear acceleration is understood to mean an acceleration which acts along an axis in a Cartesian coordinate system without causing a change in direction.

An object of the invention is to provide a space-saving accelerometer which is directed to separately detect at least three acceleration components of an acceleration.

Presentation of the invention

The object is achieved by the features of the independent claims.

The invention relates to an accelerometer, the accelerometer having a seismic mass, a prestressing arrangement and a measuring system; which seismic mass exerts a force on the measuring system during acceleration; a longitudinal axis running centrally through the center of the seismic mass; which measuring system has two spatially spaced apart piezoelectric measuring elements; which measuring elements are arranged on both sides of the seismic mass with respect to the longitudinal axis; which measuring elements have surfaces; wherein an acceleration on the surfaces generates electrical polarization charges; wherein the accelerometer has a number N measuring systems; where the seismic mass has a number of N + 1 partial masses has which partial masses are electrically isolated from one another; and where the number corresponds to N = 3, 4, 5, or 6.

The accelerometer is preferably a directed to determine the acceleration in a number N = 3, 4, 5, or 6 acceleration components; wherein an acceleration component is an acceleration along a spatial axis of a Cartesian coordinate system or an angular acceleration about a spatial axis; acceleration components along at least three orthogonal spatial axes are indirect; wherein the longitudinal axis is one of the spatial axes; whereby one of the N measuring systems is sensitive to one of the N acceleration components.

In the present invention, the acceleration sensor has at least three piezoelectric measuring elements which each determine one of the at least three acceleration components along the orthogonal spatial axes.

The same seismic mass acts on all measuring systems, whereby the accelerometer has a smaller spatial extent than the accelerometer, in which a separate seismic mass is used for each measuring system. The accelerometer is therefore space-saving and can also be used in applications in which little space is available for installing the accelerometer.

The measuring systems are prestressed with a prestressing arrangement in the direction of the longitudinal axis of the accelerometer. This has the advantage that the piezoelectric measuring elements are frictionally connected to their respective electrodes so that no gaps can form and the electrical and mechanical contact between the measuring element and the electrode is maintained even when the accelerometer is accelerated. The electrodes are part of the measuring system.

A measuring element is sensitive to a force along a spatial axis or to a torque about a spatial axis which the seismic mass exerts on the measuring element due to an acceleration component along a spatial axis of a Cartesian coordinate system or due to an angular acceleration component about a spatial axis .

As a result of the bias of the measuring elements, in addition to the compressive force, both a pushing force and a tensile force can be determined by a measuring element. A compressive force acts on the measuring element with a force, a tensile force relieves the measuring element with a force. If there is acceleration along the longitudinal axis, the measuring elements on one side of the seismic mass are acted upon with a force corresponding to the acceleration, while the measuring elements, which are arranged on the other side of the seismic mass, are relieved with the same force. Measuring elements of a measuring system are electrically connected in such a way that the respective polarization charges generated on a first surface and on the second surface have the same sign, i.e. add up. In the case of measuring elements which are sensitive to acceleration along the longitudinal axis or to angular acceleration around the transverse axis or around the vertical axis, this means that the measuring elements on one side of the seismic mass have a polarization direction opposite to the measuring elements with respect to the longitudinal axis the other side of the seismic mass exhibit. The measuring elements are thus arranged mirror-symmetrically with respect to the plane of the transverse axis and the longitudinal axis around the seismic mass.

This arrangement also has the advantage that a change in the bias voltage, which loads or relieves the measuring elements on both sides of the seismic mass with respect to the longitudinal axis, causes the polarization charges generated thereby to be eliminated. A change in the preload can be caused, for example, by a change in temperature of the acceleration sensor.

By using a common biasing arrangement for all at least three measuring systems, the acceleration sensor also has a smaller spatial extent than an acceleration sensor in which a separate biasing arrangement is provided for each of the measuring systems.

All polarization charges of the measuring elements are tapped, which makes it possible to check the consistency of the detected acceleration due to the same magnitude with opposite signs of the polarization charge on the first surface and the polarization charge on the second surface.

Brief description of the drawings

In the following, the invention is explained in more detail by way of example with reference to the figures. Show it

Fig. 1 is a partial view of an embodiment of the acceleration sensor loading,

FIG. 2 shows a further partial view of the embodiment from FIG

Fig. 1, FIG. 3 shows a further partial view of the embodiment from FIG

Fig. 1,

FIG. 4 shows a schematic partial view of the embodiment of the acceleration sensor from FIG. 1,

Fig. 5 is a partial view of a first electrode, web and

Contact element for use in the embodiment from FIG. 1,

Fig. 6 is a partial view of the second electrode, webs and con tact element for use in the embodiment of Fig. 1,

7 shows a partial view of a second electrode, web and contact element for use in the embodiment from FIG. 1 on one side of the seismic mass which faces a printed circuit board,

Fig. 8 is a partial view of a first electrode, web and

Contact element for use in the embodiment from FIG. 1 on one side of the seismic mass which faces a printed circuit board,

9 shows a schematic view of a measuring element,

Fig. 10 is a schematic view of a further Messele element,

11 is a schematic view of a further measuring element,

12 is a schematic view of a further measuring element, 13 shows a schematic view of a further measuring element,

14 shows a schematic view of a further measuring element,

15 shows a partial view of a further embodiment of the acceleration sensor,

FIG. 16 shows a partial view of the embodiment of the acceleration sensor from FIG. 15.

Ways of Carrying Out the Invention

Fig. 1 shows a section along the longitudinal axis X and a vertical axis Z through part of an embodiment of the accelerometer 1. The accelerometer 1 is set up the acceleration in a number N acceleration components Tx, Ty, Tz, Mx, My, Mz to be determined, an accelerometer 1 being shown as an example, which is set up to detect three acceleration components Tx, Ty, Tz, in which the number of acceleration components Tx, Ty, Tz, Mx, My, Mz N = 3 to be recorded is. Other embodiments of the acceleration sensor 1 are set up to detect N = 3, 4, 5, or 6 acceleration components. An acceleration component Tx, Ty, Tz, Mx, My, Mz is an acceleration along a spatial axis of a Cartesian coordinate system, or an angular acceleration around a spatial axis. The longitudinal axis X is one of these spatial axes. Further spatial axes are the transverse axis Y and the vertical axis Z. The accelerometer 1 in FIG. 1 has a seismic mass 2, a prestressing arrangement 3 and, for example, N = 3 measuring systems 4, which measuring systems 4 each have two spatially spaced piezoelectric measuring elements 41. One of the N measuring systems 4 is sensitive to one of the N acceleration components Tx, Ty, Tz, Mx, My, Mz.

The accelerometer 1 for N = 3 is described below. However, the description is also valid for embodiments of the accelerometer 1 which are sensitive to a number N = 4.5 or 6 acceleration components Tx, Ty, Tz, Mx, My, Mz. These forms of execution are also covered by the invention described.

A transverse axis Y is shown in the exploded view of FIG. Fig. 2 shows part of the embodiment of Fig. 1, wherein the biasing arrangement 3 is not shown for the sake of clarity. The measuring elements 41 are shown at a distance from the seismic mass 2 for a better overview. Longitudinal axis X, transverse axis Y and vertical axis Z form an orthogonal coordinate system.

The seismic mass 2 is preferably designed to be cylindrical along the longitudinal axis X and has a number N + 1, four partial masses 21 in the embodiment shown in FIG. The longitudinal axis X runs centrally through the center of the seismic mass 2. The partial masses 21 extend along the longitudinal axis X from one end face 24 of the cylindrical seismic mass 2 to another end face 24 of the seismic mass 2. The partial masses 21 accordingly have two each End faces, which each form part of the end face 24 of the seismic mass 2 and which are largely aligned parallel to one another and along the Longitudinal axis X are spaced. In the embodiment shown in FIGS. 1 and 2, the partial masses 21 have the shape of a segment of a circle in a section along the transverse axis Y and the vertical axis Z, as shown in FIG. The circle segments are spaced from one another. FIG. 3 shows a further partial view of the embodiment of the acceleration sensor 1 from FIG. 1.

The partial masses 21 are electrically isolated from one another by an insulator 22. The insulator 22 is arranged between the partial masses 21. Between the partial masses 21 an electrically insulating material is angeord net as an insulator 22, for example Kapton, Teflon, PVC, polyethylene, polypropylene, rubber, air, aluminum oxide, silicon oxide, glass, nitrogen, electrically insulating gas mixtures or noble gases or similar materials. Vacuum is also possible as an insulator 22.

The specific resistance of the insulator 22 is at least 10 ⁹ W mm ² / m (Q = ohms, mm = millimeters, m = meters). This ensures that the individual partial masses 21 can be used to conduct polarization charges without the polarization charges being able to flow off to another partial mass 21.

The partial mass 21 is preferably made of an electrically conductive pure metal or a metal alloy.

The insulator 22 preferably has a modulus of elasticity of at least 100 GPa (GPa = 10 ⁹ Pascal) and a shear modulus of at least 50 GPa. The insulator 22 is materially or non-positively connected to the partial masses 21. This has the advantage that the by virtue of partial masses 21 arranged rigidly relative to one another, even in the case of extreme accelerations outside the acceleration area defined by the amount of the pretensioning force, they cannot move relative to one another.

A measuring system 4 is set up to determine an acceleration Tx, Ty, Tz along a spatial axis X, Y, Z or an angular acceleration Mx, My, Mz about a spatial axis X, Y, Z. For this purpose, the measuring system 4 has two piezoelectric measuring elements 41, which are arranged on both sides of the seismic mass 2 with respect to the longitudinal axis X. In addition, the measuring system 4 has first electrodes 47 and second electrodes 48, which are set up to absorb the polarization charges of a measuring element 41 that occur during an acceleration or angular acceleration of the accelerometer 1.

The measuring elements 41 are plate-shaped and parallel to the end faces 24 of the seismic masses 2. The measuring elements 41 each have a first surface 42 and a second surface 43. The opposite largest areas of the plate-shaped measuring elements 41 are identified as the first surface 42 and the second surface 43. The first surface 42 is largely parallel to the second surface 43. The first surface 42 is largely parallel to the transverse axis Y and largely parallel to the vertical axis Z. The measuring elements 41 have an extension along the transverse axis Y and the vertical axis Z, which is equal to or less than the extent of the end faces 24 of the seismic mass 2 along the transverse axis Y and the vertical axis Z is Ver. As a result, a force which the seismic mass 2 exerts on the measuring elements 41 acts evenly on the entire first or second surface 42, 43 of the measuring element 41, which prevents the measuring element 41 from breaking due to the uneven application of force. In a plane along the transverse axis Y and the vertical axis Z, the measuring elements 41 preferably have a square or octagonal cross section. This enables a plurality of measuring elements 41 to be stacked with respect to the longitudinal axis X in such a way that all edges of a measuring element 41 lie in one plane with all corresponding edges of the other measuring elements 41. This he allows a uniform force on all Messelemen te 41 of the stack.

Of course, in one embodiment of the acceleration sensor 1, a measuring element 41 can also have a different cross section in the plane along the transverse axis Y and the vertical axis Z, for example a circular cross section.

If the accelerometer 1 experiences an acceleration, then due to the inertia of the seismic mass 2, a force K proportional to the acceleration acts on the measuring elements 41. If a force K proportional to the acceleration acts on a measuring element 41, the first upper surface 42 of the measuring element 41 generates a polarization charge and generates a polarization charge on the second surface 43 of the same measuring element 41. The polarization charge of the first surface 42 and the second surface 43 have opposite electrical polarity, one surface has a positive polarization charge and one surface has a negative polarization charge. The respective first surfaces 42 of the measuring elements 41 of a measuring system 4 are connected in an electrically conductive manner. All polarization charges generated on the first surfaces 42 of a measuring system 4 can be tapped as an acceleration signal. Since the measuring elements 41 of a measuring system 4 are arranged on both sides of the seismic mass 2, they are electrically connected in such a way that, when a force K is acted by the seismic mass 2 on which the measuring system 4 is sensitive, the measuring element 41 on one side of the seismic mass Ground 2 and the measuring element 41 on the other side of the seismic mass 2, the respective polarization charges generated on the first surface 42 of the measuring elements 41 have the same sign and on the second surface 43 of the measuring elements 41 have the same sign, i.e. add up.

For each measuring system 4, the first electrode 47, which is in contact with the first surface 42 of the measuring element 41 on one side of the seismic mass 2 with respect to the longitudinal axis X, is electrically conductively connected to the first electrode 47, which is shown in FIG Contact with the first surface 42 of the measuring element 41 on the other side of the seismic mass 2 is. The first electrodes 47 and the second electrodes 48 are part of the measuring system 4.

The first electrodes 47 are each connected to a contact element 46 via a web 44. The contact element 46 is in electrically conductive and mechanical contact with one of the N + 1 partial masses 21 of the seismic mass 2. Web 44, contact element 46 and electrode are advantageously made in one piece. The web 44 protrudes laterally with respect to the transverse axis Y beyond the cross section of the measuring elements 41 and is located there in the direction of the seismic mass 2. bent long along the longitudinal axis X, extends to the next end face 24 of the seismic mass 2, and is bent towards the contact element 46, as can be seen from FIG. 2.

4 schematically shows the electrodes, the webs 44, the contact elements 46 and the partial masses 21.

The electrically conductively connected to one of the first electrode 47 contact element 46 contacts exactly one partial mass 21 and is electrically isolated from all other partial masses 21 of the seismic mass 2. For this, the contact element 46 along the transverse axis Y and the vertical axis Z is preferred a cross section which corresponds at least to the intersection between the cross section of the partial mass 21 in this plane and of the measuring element 41 in this plane. An embodiment of a contact element 46, a web 44 and a first electrode 47 is shown in FIG.

The first surface 42 of a measuring element 41 on one side of the seismic mass 2 is, as shown schematically in FIG. 4, that is, the web 44 via the electrode 47, 48, which is in electrical contact with the first surface 42 , the contact element 46 is electrically conductively connected to a partial mass 21. The first surface 42 of a measuring element 41 on another side of the seismic mass 2 is electrically connected via the electrode 47, 48, which is in electrical contact with the first surface 42, the web 44, the contact element 46 with the same partial mass 21 , with which the first surface 42 of the Messele element 41 on one side of the seismic mass 2 is connected. The generated polarization charge of the first upper surfaces 42 of the measuring elements 41 in each case one of the N measuring systems 4 can thus be tapped off as an acceleration signal at each one of the N + 1 partial masses 21.

The respective second surfaces 43 of the measuring elements 41 of all measuring systems 4 are preferably connected to one another in an electrically conductive manner. All polarization charges generated on the second surfaces 43 of all measuring systems 4 can be tapped off as the sum of the polarization charges. The second electrode 48 of the measuring system 4 is in electrically conductive contact with the second surface 43 of a measuring element 41 of a measuring system 4. The second electrodes 48, which are in contact with the second surface 43 of the measuring element 41 on one side of the seismic mass 2 with respect to the longitudinal axis X are connected to the second electrodes 48 of the Messelemen te 41 of all measuring systems 4 on the same side of the seismic mass 2 and to all second electrodes 48 on the other side of the seismic mass 2 in an electrically conductive manner. The electrodes are made of an electrically conductive material and are plate-shaped and essentially have the same or larger cross-section with respect to the transverse axis Y and the vertical axis Z as the measuring element 41.

The second electrodes 48 are each electrically conductively connected via a web 44 to the next second electrodes 48 with respect to the longitudinal axis X, which are arranged on the same side of the seismic mass 2 with respect to the longitudinal axis X, as shown in FIG . The second electrode 48 closest to the seismic mass 2 with respect to the longitudinal axis X is connected to a contact element 46 in an electrically conductive manner via a web 44. The contact element 46 is in electrically conductive and mechanical contact with one of the N + 1 partial masses 21 of the seismic mass 2nd web 44, Contact element 46 and electrodes are advantageously made in one piece. The web 44 protrudes laterally with respect to the transverse axis beyond the cross section of the measuring elements 41 and is bent there along the longitudinal axis X, then extends along the longitudinal axis X to the next electrodes and is then bent towards the next electrode, as shown in FIG.

2 and 6 can be seen. If a second electrode 48 is arranged closest to a contact element 46 with respect to the longitudinal axis X, the web 44 extends along the longitudinal axis X to the contact element 46 and is then bent towards the contact element 46. FIG. 4 schematically shows the electrodes, the webs 44, the contact elements 46 and the partial masses 21.

The electrically conductive connected to the second electrodes 48 contact element 46 contacts exactly one partial mass 21 and is electrically isolated from all other partial masses 21 of the seismic mass 2. For this, the contact element 46 has a cross section along the transverse axis and the vertical axis Z preferably a cross section which corresponds to the intersection between the cross section of the partial mass 21 in this plane and the measuring element 41 in this plane. An embodiment of a contact element 46, a web 44 and a second electrode 48 is shown in FIG. 6 GE.

The second surfaces 43 of all measuring elements 41 on one side of the seismic mass 2 are thus electrically conductively connected via the second electrodes 48, which are in electrical contact with the second surfaces 43, webs 44 and the contact element 46 with a partial mass 21 . The second surfaces 43 of all measuring elements 41 on the other their side of seismic mass 2 are connected in an electrically conductive manner to the same partial mass 21 via the second electrodes 48, which are in electrical contact with the second surfaces 43, webs 44 and the contact element 46. The generated polarization charge of the second surfaces 43 of the measuring elements 41 of all N measuring systems 4 can thus be tapped at one of the N + 1 partial masses 21.

A check for consistency now includes a comparison of the sum of the polarization charges tapped as acceleration signals of the first electrodes 47 of the N measuring systems 4 with the tapped polarization charges of the second electrodes 48 of the N measuring systems 4. Are they the same in terms of amount and have the same value has an opposite sign, the acquisition of the acceleration components Tx, Ty, Tz, Mx, My, Mz is consistent. This type of consistency check is advantageous because the polarization charge of the second upper surfaces 43 of the measuring systems 4 is not tapped individually. To check the consistency of the detection of the acceleration component Tx, Ty, Tz, Mx, My, Mz, the summed polarization charge of the second surfaces 43, which can be tapped on a single signal conductor 5, is sufficient. If the polarization charges on the second surfaces 43 of the measuring systems 4 were tapped individually, then N signal conductors 5 would be required. Equality exists when the sum of the polarization charges of the first electrodes 47 of the N measuring systems 4 deviates by less than 10% from the tapped polarization charges of the second electrodes 48 of the N measuring systems 4.

Between the contact element 46 and the electrode 47, 48, which is arranged closest from the seismic mass 2 with respect to the longitudinal axis X, there is generally a Mechanical contact with the contact element 46, an Isolierele element 49 is arranged, which electrically isolates the contact element 46 from the electrode. The insulating element 49 is largely dimensioned in the same way as a measuring element 41. The insulating element 49 is made of an electrically insulating mate rial, the specific resistance of the insulating relementes 49 is at least 10 ⁹ W mm ² / m. The Isolie relement 49 is made of Kapton, Teflon, PVC, Po lyethylene, polypropylene, rubber, aluminum oxide, silicon oxide, glass, etc., for example.

The first electrodes 47 and the second electrodes 48 are preferably made of an electrically conductive pure metal or a metal alloy, for example copper, gold, silver, stainless steel, etc.

The first electrodes 47 and the second electrodes 48 are plate-shaped made of an electrically conductive material and essentially have the same or larger cross-section with respect to the transverse axis and the vertical axis Z as the measuring element 41. The electrode has a thickness with respect to the longitudinal axis X of at least 0.05 mm and a maximum of 0.50 mm.

The prestressing arrangement 3 prestresses the measuring elements 41 of a piezoelectric measuring system 4 against the seismic mass 2. Such a bias prevents the piezoelectric measuring elements 41 from slipping against one another with respect to the vertical axis Z and with respect to the transverse axis. The preload arrangement is also advantageous in order to avoid gaps between the measuring elements 41 with respect to the longitudinal axis X. Gaps are to be avoided, as otherwise the existing during acceleration and from seismic mass 2 The force K exerted on the measuring elements 41 is not transmitted uniformly to the measuring element 41. In this case, the exerted force K would not be fully recorded and the measurement of the acceleration would be incorrect.

The prestressing arrangement 3 prestresses the measuring elements 41 against the seismic mass 2 with a prestressing force. This pretensioning force is greater than the force K which the seismic mass 2 exerts on the measuring elements 41 along the longitudinal axis X when the acceleration is present. An acceleration along the longitudinal axis X acts on the measuring elements 41 arranged under the prestressing force on one side of the seismic mass 2 with an additional force K corresponding to the acceleration, while the measuring elements 41 arranged under the prestressing force on the other side of the seismic mass 2 be relieved with the corresponding force K. This relieving force K must not exceed the pre-tensioning force.

The measuring elements 41 of the piezoelectric measuring systems 4 are electrically insulated from the prestressing arrangement 3 by an insulating element 49. The insulating member 49 is arranged between the electrode which is closest to the bias arrangement 3 and the bias arrangement 3. The electrode is in contact with the measuring element 41 closest to the pretensioning arrangement 3. The insulating element 49 is largely dimensioned to be the same as a measuring element 41. The insulating element 49 is made of an electrically insulating material, the specific resistance of the insulating element 49 being at least 10 ⁹ W mm ² / m. The Isolierele element 49 is, for example, made of Kapton, Teflon, PVC, polyethylene len, polypropylene, rubber, aluminum oxide, silicon oxide, glass, etc.

In the embodiment shown in FIG. 1, the prestressing arrangement 3 has a cup-shaped prestressing sleeve 31 and a lid-shaped prestressing element 32. The cup-shaped prestressing sleeve 31 has a bottom which is largely parallel to the surfaces of the measuring elements 41 is arranged, and a cylindrical wall which is largely along the longitudinal axis X is arranged with egg ner cylinder axis. The measuring systems 4, insulating elements 49, electrodes and the seismic mass 2 are arranged with respect to the longitudinal axis X within the prestressing sleeve 31, preferably centrally with respect to the vertical axis Z and the transverse axis Y. The pot-shaped pretensioning sleeve 31 is connected at its open end with respect to the longitudinal axis X to the cover-shaped pretensioning element 32 in a materially, non-positively or positively locking manner. As a result of the connection of the prestressing sleeve 31 and the prestressing element 32, a prestressing force is exerted on the measuring systems 4, insulating elements 49, electrodes and the seismic mass 2. The pretensioning arrangement 3 is made for the most part from an electrically conductive material. The prestressing arrangement 3 largely encloses the N measuring systems 4.

The biasing arrangement 3 is connected to a defined potential, for example the ground potential, often also called ground potential. This has the advantage that the prestressing arrangement 3 shields the measuring systems 4 arranged in its interior from external interference. The pretensioning arrangement 3 cannot be charged with electrical charge either, for example through frictional electricity, also called the triboelectric effect. For example there are disturbances in the determination of the force K by electromagnetic waves or electrical charging of the prestressing arrangement 3 prevents ver.

The connection of prestressing sleeve 31 and prestressing element 32 is hermetically sealed against gases and liquids, for example by a suitable seal or, in the case of a material connection, by an adhesive or a weld. Hermetically tight is understood to mean a seal which has an air leak rate of less than 10 ^-3 Pa-m ³ / s. This has the advantage that the usually hygroscopic piezoelectric crystals are protected from moisture. Moisture within the Vorspanna arrangement 3 reduces the resistance between the electrodes, which are electrically isolated from one another and from the prestressing arrangement 3, and thereby reduces the determinable polarization charge.

In the embodiment shown in FIG. 1, the polarization charge generated on the first surfaces 42 at the respective partial mass 21 is tapped. For this purpose, a printed circuit board 55 is arranged on one side of the seismic mass 2 with respect to the longitudinal axis X between the biasing arrangement 3 and insulating element 49, which insulating element 49 electrically insulates the biasing arrangement 3 from the Messelemen 41. The printed circuit board 55 is made of an electrically insulating material and has N + 1 conductor tracks 56 on the side facing the seismic mass 2. The N + 1 conductor tracks 56 are set up to make contact with N + 1 contact elements 46. The contact element 46, which makes electrically conductive contact with the conductor track 56, is the same as the contact element 46 from FIGS. 5 and 6, which has the partial mesh. se 21 of the seismic mass 2 contacted electrically. The contact element 46 is arranged with respect to the longitudinal axis X between the printed circuit board 55 and the insulating element 49, which insulating element 49 electrically insulates the prestressing arrangement 3 from the measuring elements 41.

A contact element 46 in electrical contact with one of the N + 1 conductor tracks 56 is connected in an electrically conductive manner to the closest second electrode 48 via a web 44, as shown in FIG. 7. The generated polarization charge of all second surfaces 43 of all Messelemen te 41 can be tapped electrically at a partial mass 21. The corresponding partial mass 21 is electrically connected via the contact element 46, wel Ches the partial mass 21, via webs 44 between the second electrodes 48 and via the web 44 between the contact element 46, which makes electrically conductive contact with the conductor track 56, and the next second electrode 48 is electrically conductively connected to conductor track 56.

Each contact element 46 in electrical contact with one of the N + 1 conductor tracks 56 is connected in an electrically conductive manner via a web 44 to each of the closest first electrodes 47, as shown in FIG. 8. As a result, the polarization charge generated on the first surfaces 42 of the measuring elements 41 can be tapped electrically from one measuring system and from one partial mass 21. The corresponding partial mass 21 is via the contact element 46, which makes electrically conductive contact with the partial mass 21, via webs 44 between the first electrode 47, which is arranged on the same side of the seismic mass 2 as the circuit board 55, and via the web 44 between the Contact element 46, which the Conductor 56 electrically conductively contacted, and the next th first electrode 47 connected to the conductor 56 electrically lei tend.

The pretensioning arrangement 3 is designed as a closed housing with an opening 33. The partial masses 21 are connected in an electrically conductive manner to a signal cable 9 through the opening 33.

In FIG. 1, the N + 1 conductor tracks 56 are electrically conductively connected to a signal cable 9, which signal cable 9 has N + 1 signal conductors 5 isolated from one another. The signal cable 9 is passed through an opening 33 in the Vorspannanord 3 voltage.

The signal conductors 5 of the signal cable 9 are set up to derive acceleration signals from the partial masses 21 electrically.

A sealing element 57 is arranged between the signal cable 9 and the prestressing arrangement 3. The housing is hermetically sealed. The opening 33 is hermetically sealed in a gas-tight manner around the signal cable 9.

The printed circuit board 55 can also be dispensed with. In this case, an electrical signal conductor 5 is electrically conductive frictionally sig, cohesively or positively connected to each partial mass 21. The resulting N + l signal conductors 5 are bundled together to form a signal cable 9, which signal cable 9 is guided through an opening 33 in the biasing arrangement 3. The signal conductors 5 can alternatively also be connected in an electrically conductive manner to a web 44 or an electrode 47, 48. The signal cable 9 advantageously has N + 1 electrical signal conductors 5 and a potential conductor 8 with a defined electrical potential. The electrical signal conductor's 5 are directly or indirectly connected to the masses 21 electrically conductive and mechanically. The potential conductor 8 is directly or indirectly connected to the Vorspanna arrangement 3 in an electrically conductive and mechanical manner. The potential conductor 8 largely encloses the signal conductor 5. The potential conductor 8 has the same electrical potential as the prestressing arrangement 3. As a result, the signal conductors 5 of the signal cable 9 are equally protected from electromagnetic interference as are the measuring elements 41 within the prestressing arrangement 3.

The measuring systems 4 are arranged in different proximity to the seismic mass 2. A first measuring system 4 has the smallest distance from seismic mass 2. An Nth measuring system 4 has the greatest distance from seismic mass 2. The numbering of the measuring systems 4 increases as the distance from the seismic mass 2 increases. Measurement elements 41 which are arranged closest to seismic mass 2 with respect to longitudinal axis X accordingly belong to first measurement system 4. Measurement elements 41 which are furthest away from seismic mass 2 belong to the Nth measurement system 4 and, as already described, an insulating element 49 is arranged in the first measuring system 4. The first surface 42 of the measuring elements 41 of the first measuring system 4 and of each measuring system 4 with an odd number is oriented towards the seismic mass 2. The first surface 42 of the measuring elements 41 with an even number is oriented away from the seismic mass 2. Between two facing second Surfaces 43 of two measuring elements 41, arranged directly next to one another with respect to the longitudinal axis X, of different measuring systems 4, a second electrode 48 is arranged in contact with the two second surfaces 43. Between two facing first surfaces 42 of two measuring elements 41 of different measuring systems 4 arranged directly next to one another with respect to the longitudinal axis X, a first electrode 47 is arranged in each case in contact with one of the first surfaces 42 and between the two first electrodes 47 directly next to one another with respect to the longitudinal axis X is arranged measuring elements 41, an insulating element 49 is net angeord. Measuring elements 41 of two measuring systems 4 are arranged directly next to one another if the number of the measuring systems 4 differs by the number 1. Polarization charges on adjoining first surfaces 42 of different measuring systems 4 are thus electrically isolated from one another. The polarization charges on the first surfaces 42 of the measuring systems can be tapped individually at the partial mass 21 which is electrically connected to the first electrode 47.

The measuring elements 41 are arranged mirror-symmetrically with respect to the longitudinal axis X on both sides of the seismic mass 2 with respect to a plane perpendicular to the longitudinal axis X.

The measuring element 41 has at least one piezoelectric crystal element 45. A piezoelectric crystal element 45 is made of a piezoelectric crystal. A piezoelectric crystal is, for example, quartz, tourmaline, gallium orthophosphate, crystals from the CGG group, lithium niobate, lithium tantalate, etc.

A measuring element 41 for determining an acceleration component Tx along the longitudinal axis X is shown in FIG. 9 shown schematically and comprises a crystal, which has the longitudinal piezoelectric effect and is sensitive to forces along the longitudinal axis X is. Polarization charges are generated on the upper surfaces perpendicular to the longitudinal axis X when the acceleration is present.

A measuring element 41 for determining an acceleration component Ty along the transverse axis is shown schematically in FIG. 10 and comprises a crystal which has the longitudinal piezoelectric thrust effect and is sensitive to thrust forces which act on the surfaces perpendicular to the longitudinal axis X and along the transverse axis are aligned. When the acceleration is present, polarization charges are generated on the surfaces perpendicular to the longitudinal axis X.

A measuring element 41 for determining an acceleration component Tz along the vertical axis Z is shown schematically in FIG. 11 and comprises a crystal which has the longitudinal piezoelectric thrust effect and is sensitive to thrust forces which act on the surfaces perpendicular to the longitudinal axis X and along the vertical axis Z are aligned. When the acceleration is present, polarization charges are generated on the surfaces perpendicular to the longitudinal axis X.

A measuring element 41 for determining an acceleration component My about the transverse axis Z is shown schematically in FIG. 12 and comprises two symmetrical crystal elements 45 which each have the longitudinal piezoelectric effect. The crystal elements 45 are aligned opposite sets in their polarization and separated along the transverse axis. An angular acceleration around the transverse axis se generates a loading force K on one of the crystal elements 45 and a relieving force K on the other crystal element 45 of the measuring element 41. Polarization charges are generated on the surfaces perpendicular to the longitudinal axis X when the acceleration is present. Due to the opposite alignment, polarization charges of the same type on the first surface 42 of the measuring element 41 and opposite polarization charges of the same type on the second surface 43 of the measuring element 41 can still be tapped when there is an angular acceleration about the transverse axis. The measuring element 41 for determining an acceleration component My about the transverse axis is shown schematically in FIG. 12.

A measuring element 41 for determining an acceleration component Mz about the vertical axis Z is shown schematically in FIG. 13 and comprises two symmetrical crystal elements 45 which each have the longitudinal piezoelectric effect. The crystal elements 45 are oppositely aligned in their polarization and separated along the vertical axis Z ent. An angular acceleration about the vertical axis Z generates a loading force K on one of the crystal elements 45 and a relieving force K on the other crystal element 45 of the measuring element 41. Due to the opposite orientation, polarization charges of the same type on the first surface 42 of the measuring element 41 and polarization charges of the opposite type on the second surface 43 of the measuring element 41 can also be tapped when an acceleration is present. A measuring element 41 for determining an acceleration component Mx about the longitudinal axis XZ is shown schematically in FIG. 14 and comprises at least two symmetrical crystal elements 45 which each have the longitudinal piezoelectric thrust effect. The crystal elements 45 are largely tangential to their polarization about the longitudinal axis X, ie along the direction of rotation about the longitudinal axis X, aligned. An angular acceleration about the longitudinal axis X generates a thrust along the direction of rotation about the longitudinal axis X between the first surface 42 and the second surface 43 of the measuring element 41, each crystal element 45 experiencing a thrust largely along its polarization direction. Polarization charges are generated on the surfaces perpendicular to the longitudinal axis X when there is an angular acceleration around the longitudinal axis X. Due to the alignment along the direction of rotation about the longitudinal axis X, polarization charges of the same type on the first surface 42 of the measuring element 41 and polarization charges of the same type on the second surface 43 of the measuring element 41 can also be tapped when acceleration is present.

The acceleration sensor 1 advantageously has a compensation device for temperature compensation. The temperature-dependent linear expansion along the longitudinal axis X of the prestressing arrangement 3 and the measuring elements 41 differs because the linear expansion coefficient of the metallic prestressing arrangement 3 is generally greater than the linear expansion coefficient of the measuring elements 41 Vorspannanord voltage 3 exerts on the measuring elements 41. A change in the Clamping force changes the sensitivity of the measuring elements 41. The sensitivity is the relationship between the force K acting and the polarization charge generated. This is disadvantageous because the generated polarization charge is used to deduce the force K acting on the measuring elements 41 due to an acceleration Tx, Ty, Tz, Mx, My, Mz by means of the seismic mass 2. The compensation device consists of the combination of the seismic mass 2 and the prestressing arrangement 3, the material of the seismic mass 2 and the prestressing arrangement 3 being selected so that the material of the seismic mass 2 has a greater coefficient of linear expansion than the material of the prestressing arrangement 3 . The length of the seismic mass 2 with respect to the longitudinal axis X is adapted in such a way that the combined length expansion of the measuring elements 41, electrodes 47, 48, insulating elements 49 and seismic mass 2 arranged along the length of the longitudinal axis X is equal to the length expansion of the prestressing arrangement 3 therein From section with respect to the longitudinal axis X is. When the temperature of the accelerometer 1 changes, the pre-tensioning force of the measuring elements 41 remains largely constant. Of course, instead of adjusting the length of the seismic mass 2, a length compensation element (not shown) can also be arranged at a suitable point, for example between insulating element 49 and biasing arrangement 3. The length compensation element is made of a material with a greater coefficient of linear expansion than the material of the pre-tensioning arrangement 3. The expansion of the length compensation element along the vertical axis Z and the transverse axis Y is equal to the insulating element 49 and the thickness of the length compensation element along the longitudinal axis X is adapted so that the combined length expansion of the lengthwise Axis X arranged measuring elements 41, electrodes 47, 48, Iso lierelemente 49, seismic mass 2 and Längenausgleichsele element equal to the length extension of the prestressing arrangement 3 in this section with respect to the longitudinal axis X is.

Advantageously, the length and the choice of material of the seismic mass 2 is chosen such that the combined length expansion of the seismic mass 2 and the N piezoelectric measuring systems 4 and existing insulating elements 49 do not exceed 10% of the length expansion of the prestressing arrangement 3 deviates over a temperature range of at least 50 K in the direction of the longitudinal axis X.

A further embodiment of the acceleration sensor 1 is shown in FIG. In this embodiment, the accelerometer 1 is set up to record N = 6 acceleration components Tx, Ty, Tz, Mx, My, Mz. The seismic mass 2 accordingly has N + 1 = 7 partial masses 21. 15 shows a further partial view of the acceleration sensor 1, which accordingly has N = 7 measuring systems 4. The acceleration components Tx, Ty, Tz, Mx,

My, Mz are, for example, an acceleration component each Tx, Ty, Tz along the longitudinal axis X, the transverse axis Y and the vertical axis Z, as well as an acceleration component each Mx, My, Mz around the longitudinal axis X, around the transverse axis Y and around the vertical axis Z.

Further embodiments are possible which combine various features of the embodiments disclosed in this document with one another where possible. List of reference symbols

1 accelerometer

2 Seismic mass

3 bias arrangement

4 measuring system

5 signal conductors

8 potential conductors

9 signal cables

21 partial mass

22 isolator

24 face

31 preload sleeve

32 preload element

33 opening

41 measuring element

42 First surface

43 Second surface

44 bridge

45 crystal element

46 contact element

47 first electrode

48 second electrode

49 insulating element

55 PCB

56 conductor tracks

57 Sealing element

K force

Mx acceleration component around the longitudinal axis

My acceleration component around the transverse axis

Mz acceleration component around the vertical axis

Tx acceleration component along the longitudinal axis Ty component of acceleration along the transverse axis

Tz acceleration component along the vertical axis

X longitudinal axis Y transverse axis Z vertical axis

Claims

1. Accelerometer (1) wherein the accelerometer (1) has a seismic mass (2), a Vorspannanord voltage (3) and a measuring system (4); which seismic mass (2) exerts a force on the measuring system (4) during acceleration; a longitudinal axis (X) running centrally through the center of the seismic mass (2); wel Ches measuring system (4) has two spatially spaced piezoelectric measuring elements (41); which Messelemen te (41) with respect to the longitudinal axis (X) on both sides of the seis mix mass (2) are arranged; which Messelemen te (41) have surfaces; an acceleration generating electrical polarization charges on the surfaces, characterized in that the acceleration sensor (1) has a number N measuring systems (4); that the seismic mass (2) has a number N + 1 partial masses (21), which partial masses (21) are electrically isolated from one another; and that the number N = 3, 4, 5, or 6 corresponds.

2. Accelerometer (1) according to the preceding claim, characterized in that the acceleration sensor (1) is set up to determine the acceleration in a number N acceleration components (Tx, Ty, Tz, Mx, My, Mz); wherein an acceleration component (Tx, Ty, Tz, Mx, My, Mz) is an acceleration along a rough machine (X, Y, Z) of a Cartesian coordinate system or an angular acceleration about a spatial axis (X, Y, Z); wherein the longitudinal axis (X) is one of the spatial axes (X, Y, Z); whereby one of the N measuring systems (4) is linked to one of the N Acceleration components (Tx, Ty, Tz, Mx, My, Mz) are sensitive; that the measuring elements (41) have a first surface (42) and a second surface (43); and that the first surface (42) is parallel to the second upper surface (43).

3. accelerometer (1) according to claim 2, characterized in that the first surfaces (42) of the measuring elements (41) of the measuring system (4) are electrically connected; and that the polarization charge generated on the first surfaces (42) of the measuring elements (41) of one of the N measuring systems (4) can be tapped as an acceleration signal at one of the N + 1 partial masses (21).

4. accelerometer (1) according to claim 3, characterized in that the second surfaces (43) of the measuring elements (41) of all piezoelectric measuring systems (4) are connected to one another in an electrically conductive manner; and that the generated polarization charge of all second surfaces (43) of all measuring elements (41) can be tapped electrically at a partial mass (21).

5. acceleration sensor (1) according to the preceding claim, characterized in that the measuring systems (4) are arranged in different proximity to the seismic mass (2); that a first measuring system (4) has the smallest distance to the seismic mass (2); that an N-th measuring system (4) has the greatest distance from the seismic mass (2); that the numbering of the measuring systems (4) increases with increasing distance from the seismic mass (2); that an insulating element (49) is arranged between the seismic mass (2) and the first measuring system (4); that the first surface (42) of the measuring elements (41) of the first measuring system (4) and each measuring system (4) with an odd number to the seismic mass (2) is orientated towards; that the first surface (42) of the Messelemen te (41) is aligned with an even number away from the seismic mass (2); that between two facing second surfaces (43) of two measuring elements (41) of different measuring systems (4) arranged directly next to one another with respect to the longitudinal axis (X) a second electrode (48) is arranged in contact with the two second surfaces (43) ; that between two facing first surfaces (42) of two measuring elements (41) of different measuring systems (4) arranged directly next to one another with respect to the longitudinal axis (X) each have a first electrode (47) in contact with one of the first surfaces (42 ) is arranged and that between the measuring elements (41) arranged directly next to one another with respect to the longitudinal axis (X) in the case of the first electrodes (47), an insulating element (49) is arranged; and that measuring elements (41) of two measuring systems (4) are arranged directly next to one another when the number of the measuring systems (4) differs by the number 1.

6. Accelerometer (1) according to one of the preceding claims, characterized in that the biasing arrangement (3) biases the measuring elements (41) of a piezoelectric measuring system (4) against the seismic mass (2).

7. acceleration sensor (1) according to the preceding claim, characterized in that the measuring elements (41) of the piezoelectric measuring systems (4) are electrically isolated from the prestressing arrangement (3) by an insulating element (49).

8. Accelerometer (1) according to one of the preceding

Claims, characterized in that the measuring element (41) has at least one piezoelectric crystal element (45); that a piezoelectric crystal element (45) is made from a piezoelectric crystal.

9. Accelerometer (1) according to one of the preceding claims, characterized in that the prestressing arrangement (3) largely encloses the N measuring systems (4); and that the biasing arrangement (3) is connected to a defined potential.

10. Accelerometer (1) according to one of the preceding claims, characterized in that the acceleration sensor (1) has a compensation device for temperature compensation.

11. Accelerometer (1) according to the preceding claim, characterized in that the combined length expansion of the seismic mass (2) and the piezoe lectric measuring systems (4) and existing Isolierelemen te (49) not more than 10% of the linear expansion Prestressing arrangement (3) deviates in the direction of the longitudinal axis (X) over a temperature range of at least 50 K.

12. Accelerometer (1) according to one of the preceding claims, characterized in that the Teilmas sen (21) are electrically isolated from one another by an insulator (22); that the insulator (22) is arranged between the part masses (21); that the insulator (22) has a modulus of elasticity of at least 100 GPa and a shear modulus of at least 50 GPa; that the insulator (22) with the partial masses (21) cohesively or non-positively connected is; and that the insulator (22) is an electrically insulating material with a specific resistance of at least 10 ⁹ W mm ² / m.

13. Accelerometer (1) according to claim 9, characterized in that the biasing arrangement (3) is designed as a closed housing GE with an opening (33); that the partial masses (21) are electrically conductively connected to a signal cable (9) through the opening (33); that between the signal cable (9) and pretensioning arrangement (3)

Sealing element (57) is arranged; and that the pre-tensioning arrangement (3) is hermetically sealed.

14. Accelerometer (1) according to the preceding claim, characterized in that the signal cable (9) has N + 1 electrical signal conductors (5) and a Potentiallei ter (8) with a defined electrical potential; that the electrical signal conductors (5) are electrically and mechanically connected directly or indirectly to the partial masses (21); that the potential conductor (8) is connected directly or indirectly to the prestressing arrangement (3) electrically and mechanically; that the potential conductor (8) largely encloses the signal conductor (5); and that the electrical signal conductors (5) are set up to electrically derive acceleration signals from the partial masses (21).

15. A method for checking acceleration signals of an accelerometer (1) according to one of claims 4 to 14, characterized in that the sum of the polarization charges tapped as acceleration signals of the first electrodes of the N measuring systems with the tapped polarization charges of the second electrodes of the N measuring systems is compared; and that for amount moderate equality and opposite sign acceleration signals is consistent.