DE102019217505A1 - Inertial sensor with a substrate having a main extension plane and a seismic mass connected to the substrate via a spring arrangement - Google Patents

Abstract

An inertial sensor (1) is proposed with a substrate having a main extension plane (2) and a seismic mass (6) connected to the substrate via a spring arrangement (3), the seismic mass (6) being supported in this way by the spring arrangement (3) is that the seismic mass (6) can be excited to a linear oscillation and a torsional oscillation, wherein the linear oscillation runs along an X-direction (7) running parallel to the main extension plane (2) and an axis of rotation (10) of the rotary oscillation along a parallel to the main extension plane (2) and the Y-direction (8) running perpendicular to the X-direction (7), the spring arrangement (3) having a first and second spring (4, 5), the first and second spring (4, 5) each have a width (11) and a mutual spacing (12) in the X direction and the spacing (12) and the width (11) of the two springs are selected so that a resonance frequency of the linear oscillation is essentially equal to a resonance frequency of the torsional vibration.

Description

State of the art

The invention is based on an inertial sensor according to the preamble of claim 1.

Inertial sensors are known from the prior art in various embodiments. The basic physical principle of such sensors is that the inertial forces acting when the sensor is accelerated cause a deflection of one or more seismic masses.

For example, in the DE 10 2009 045 391 A1 proposed a micromechanical structure with a seismic mass which, when acceleration is applied, executes a movement parallel to the substrate, via which the acceleration can be detected. In the DE 10 2009 000 167 A1 describes a sensor arrangement with a seismic mass which is rotatably mounted by torsion springs and which has an asymmetrical mass distribution with respect to the axis of rotation. In the case of an acceleration acting perpendicular to the substrate, the torque generated by the asymmetry causes a rotation which serves to detect the acceleration. A disadvantage of such a structure, however, is that it has a more or less pronounced cross-sensitivity, that is to say that accelerations directed parallel to the substrate can also cause a rotation. The associated false signal is superimposed on the actual measurement signal and in this way falsifies the detection. In the DE 10 2012 223 016 A1 In this context, therefore, a special design of the suspension for a rotatably mounted mass is proposed, in which the springs have two sub-springs arranged one above the other, whereby the cross-sensitivity can be significantly reduced.

The one in the DE 10 2008 001 442 A1 proposed micromechanical component, the detection of two different acceleration directions is realized with a single seismic mass. One direction runs parallel to the substrate (X direction) and is detected by a corresponding X deflection of the seismic mass, while the second direction runs perpendicular to the substrate (Z direction) and is detected by a rotational movement of the seismic mass. With such combined XZ sensors, however, the problem arises that the two detection modes (rotation and linear movement) are far apart in the frequency range. This fact cannot be avoided when using a single torsion spring. The sensor has different transfer functions (frequency behavior) and correspondingly different sensitivities in the X and Z directions. One way of influencing the frequency behavior is, for example, the geometric design of the springs, in particular the choice of the spring width. In this way, however, an XZ sensor can only ever be optimized with respect to one of the two directions, so that an equalization of the two different frequency behavior is not possible in this way.

Disclosure of the invention

Against this background, it is an object of the present invention to provide an inertial sensor which has essentially the same resonance frequencies with respect to both oscillation modes (torsional oscillation and linear oscillation).

The inertial sensor according to the main claim has the advantage over the prior art that the special design of the suspension formed by the spring arrangement opens up additional scope for influencing the resonance frequency of the torsional vibration. The essence of the inventive concept is that the vibration behavior with respect to the rotary movement can be specifically influenced by a suitable choice of the distance between the two springs, without the vibration behavior of the linear movement being changed at the same time. In this way, the resonance frequencies of the two vibration modes can be matched to one another by simply adapting the micromechanical geometry.

To describe the geometric relationships, the main plane of extent of the substrate is taken as the basis as the X-Y plane of a coordinate system. The Z-direction perpendicular to this is also referred to below as the vertical direction and the mutual position of the various elements in relation to the Z-direction is described using the terms “top” and “bottom” without any relation to the direction of gravity being implied.

The sensor according to the invention is sensitive to accelerations in the X direction in the following sense: With an applied X acceleration, the seismic mass is deflected in the negative X direction due to its inertia with respect to the substrate. This movement is made possible by the fact that the two springs of the spring arrangement (also referred to as double spring in the following) bend in the XY plane. The two springs preferably run at least partially or completely in the Y direction and curve in the X direction when they are bent. The stiffness of the spring arrangement against bending in the XY plane and thus the resonance frequency of the During this movement, linear oscillation is essentially determined by the width of the springs. The width of the springs is to be understood here as the extension in the X direction. In embodiments in which the springs additionally have sections that run at least partially in the Y direction, the width is to be understood in particular as the X dimension of the sections that run in the X direction. The concept according to the invention also explicitly allows the two springs to each include two or more sub-springs, the width of which can in particular also be different. In these embodiments, the spacing between the two springs and the widths of the partial springs are selected so that a resonance frequency of the linear oscillation is essentially equal to a resonance frequency of the torsional oscillation. For the detection of Z accelerations, the seismic mass has an asymmetrical mass distribution with respect to the axis of rotation, ie the axis of rotation in particular does not run through the center of gravity of the seismic mass. The axis of rotation is preferably arranged in the middle between the two springs with respect to the X direction.

In the rest position, i.e. without external accelerations, the seismic mass is preferably parallel to the X-Y plane. When accelerating in the Z direction, due to the mass asymmetry, a torque acts on the mass, so that it rotates around the axis of rotation, during which it tilts in relation to the X-Y plane. This movement is made possible by the fact that the two springs perform a bending in the Z direction or a combination of a bending in the Z direction and a torsional movement. The bending stiffness of the springs in the Z-direction generates a restoring force in the Z-direction, the restoring torque caused thereby being greater, the greater the lever length, which is formed by the distance between the springs, with the same flexural stiffness of the springs. In other words, this distance can be used to influence the elastic behavior of the spring arrangement formed by the two springs with respect to rotations and thus set the resonance frequency of the torsional vibration in a targeted manner. In this way, the spring spacing creates a further geometric parameter in addition to the spring width, via which the resonance frequency of the torsional vibration can be changed without simultaneously affecting the resonance frequency of the linear vibration.

According to the invention, the design of the spring arrangement is selected such that the resonance frequency of the linear oscillation is essentially the same as the resonance frequency of the torsional oscillation. The two resonance frequencies can, for example, be viewed as essentially the same if the deviation is a maximum of 1%, 2%, 5% or 10%. It is also conceivable to at least roughly equalize the two resonance frequencies through the design of the spring arrangement and to carry out a further fine adjustment, for example through the electrostatic effect of compensation electrodes, for a more precise adjustment.

According to a preferred embodiment, each of the two springs has an upper and a lower sub-spring, the upper and lower sub-springs each extending in the Y-direction and being spaced from one another in a Z-direction perpendicular to the main extension plane. According to a particularly preferred embodiment, the first and second springs are each designed such that a width of the upper part spring differs from a width of the lower part spring and / or the upper and lower part spring each have a height in the Z direction and a height of the upper one Part spring is different from a height of the lower part spring. Such a spring, also referred to below as an i-spring, thus comprises two sub-springs, the cross-sections of which have different dimensions. A spring arrangement that is formed from two spaced i-springs is also referred to below as a double i-spring. In particular, the height of the upper part spring can be greater than the height of the lower part spring. Furthermore, the upper part spring preferably has a width which is less than the width of the lower part spring. This design advantageously makes it possible to reduce the cross-sensitivity between linear and torsional vibration. Further details on the design of such an i-spring can be found in DE 10 2012 223 016 A1 described. According to the invention, the distance between the two springs forming the double i-spring and the widths of the partial springs are selected such that a resonance frequency of the linear oscillation is essentially equal to a resonance frequency of the torsional oscillation.

According to a preferred embodiment, each of the two springs is designed in a meandering shape and has at least two sections running in the Y direction, which are connected to one another by sections running at least partially in the X direction. This embodiment is also referred to below as a meander spring. According to a particularly preferred embodiment, the two springs each have at least three sections running in the Y direction, a first section having a connection point with the substrate which is arranged in the center of the first section with respect to the Y direction, the first section and a second section are connected to one another at the ends, the second section having a connection point with a third section which is arranged in the center of the second section with respect to the Y-direction. The first section is preferably with respect to the Y Direction in a central region of the first section connected to the substrate via an anchor point. The first and second sections are preferably connected to each other at the ends by short sections running in the X direction, and the second and third sections are preferably in turn connected to a section centered in relation to the Y direction and running in the X direction.

According to a preferred embodiment, the two springs are each formed by a spring bar, each of the two spring bars in particular having a height in the Z direction that is greater than a width in the X direction. Each of the two spring bars is preferably connected to the substrate in a central region, while the two ends are connected to the seismic mass. This embodiment corresponds essentially to the double i-spring described above, but the springs are each formed only by a bar, that is to say do not have a second partial spring.

According to a preferred embodiment, the distance and the width of the two springs are selected such that a frequency behavior of the linear oscillation is essentially the same as a frequency behavior of the torsional oscillation. In other words, the dynamic behavior with respect to the linear oscillation is described by a first transfer function (i.e. by the mathematical relationship between the frequency of the drive signal and the resulting oscillation frequency), the dynamic behavior with respect to the torsional oscillation is described by a second transfer function and the course corresponds to the first transfer function essentially the course of the second transfer function. In particular, in such a case, both the resonance frequencies and the sensitivities with regard to the two oscillation modes are essentially identical. An adaptation of the frequency behavior is made possible by the geometric design of the sensor, in particular by the choice of the width and the spacing of the springs.

According to a preferred embodiment, the spring arrangement is surrounded by the seismic mass with respect to the main plane of extent. The spring arrangement is completely surrounded by the seismic mass, in particular with regard to the X-Y plane, the mass preferably forming a frame structure which completely surrounds the spring arrangement with regard to the X-Y plane. The seismic mass preferably has a recess in its inner region and the spring arrangement is arranged in this recess, the two springs of the spring arrangement preferably being connected on the one hand to an inner edge of the recess and on the other hand to the anchor point also arranged in the recess.

According to a preferred embodiment, the first and second springs are connected to the substrate via a common anchor point. Alternatively, it is conceivable to connect the two springs to the substrate via two separate anchor points.

Figure list

• 1 shows an embodiment of the inertial sensor according to the invention, in which the spring arrangement is formed by a double i-spring.
• 2 shows an embodiment of the inertial sensor according to the invention, in which the spring arrangement is formed by a double meander spring.
• 3 shows a schematic representation of the cross section of an i-spring.
• 4th shows a schematic representation of the shape of a meander spring.

Embodiments of the invention

In 1 is an embodiment of the inertial sensor according to the invention 1 shown in a top view. The horizontal direction of the plane of the sheet corresponds to the X direction 7th while the vertical of the Y direction 8th corresponds to. The one from both directions 7th , 8th The spanned XY plane corresponds to the main extension plane 2 of the substrate of the sensor 1 . The sensor 1 exhibits a seismic mass 6th on that about one out of two in the X direction 7th spaced springs 4th , 5 formed spring arrangement 3 is vibrantly connected to the substrate. In the illustrated embodiment, the spring arrangement is 3 a so-called double i-spring, in which each of the two springs 4th , 5 made of two vertical sub-springs arranged one above the other 13th , 14th exists, with which the cross-sensitivity of the sensor 1 can be significantly reduced (for vertical expansion i-springs see 3 ; the special design and functionality of the i-springs is also in the DE 10 2012 223 016 A1 described). The feathers 4th , 5 or their respective sub-springs 13th , 14th have the form of bar springs with an anchor point in their central area 22nd are connected and the ends of which are connected to the seismic mass 6th connected so that the seismic mass 6th is mounted elastically in this way with respect to the substrate. The two feathers 4th , 5 point in the X direction 7th a distance 12th and grab both at the centrally located anchor point 22nd on, but embodiments with two or more anchor points are also conceivable. The spring arrangement 3 is from the crowd 6th with respect to the XY plane 2 completely surrounded, ie the mass 6th forms a frame structure that holds the spring assembly 3 with respect to the XY plane 2 completely surrounds. In other words, the crowd points 6th in its interior a recess and the spring arrangement 3 is arranged in this recess, with the springs 4th , 5 on the one hand with an inner edge of the recess and on the other hand with the anchor point also arranged in the recess 22nd are connected.

The one about the spring assembly 3 stored seismic mass 6th can perform two different types of deflection. On the one hand it causes an acceleration of the sensor 1 in X direction 7th one also parallel to the X axis 7th running linear movement 36 the seismic mass 6th . Does the sensor move? 1 in the positive X direction 7th becomes the seismic mass 6th due to their inertia relative to the accelerated substrate in the negative X-direction 7th postponed. The shift is here by means of comb electrodes that are fixed to the substrate 25th , 27 detected that with several, firmly with the mass 6th connected electrodes 26th interlock. With one by an X-shift 36 caused change in the distances between the electrodes 25th , 26th , 27 the capacitance of the electrode arrangement changes 25th , 26th , 27 so that the shift 36 a measurement becomes accessible, for example, via a differential method. The sensor shown 1 is also sensitive to accelerations in the Z direction 9 showing a tilting of the crowd 7th cause. To this end is the crowd 6th As shown asymmetrically with respect to the suspension 3 designed. In the case of a Z acceleration, this is due to the inertia of the left side of the mass 6th caused torque is much greater than that of the right-hand side, so that there is a total torque through which the mass 6th a twisting motion 37 around the axis of rotation 10 learns so that the crowd 6th opposite the XY plane 2 in the Z direction 9 tilted. To detect this tilt 37 are among the crowd 6th Electrodes fixed to the substrate 23 , 24 arranged along with the seismic mass 6th also form a capacitive system, over which the rotary movement 37 can be converted into an electrical signal.

The spring arrangement 3 enables both types of deflection through the following deformations: With an X deflection 36 the springs bend 4th , 5 in X direction 7th , ie the spring constant of the suspension 3 with regard to this linear deflection is due to the bending stiffness of the springs 4th , 5 and thus primarily through the width of the nib 12th certainly. When turning 37 the springs bend 4th , 5 on the other hand in the Z-direction 9 . The associated restoring torque is in addition to the spring stiffness in the Z direction 9 determined by the lever length, by the distance 12th of the two springs is formed. The spring rate of the suspension 3 regarding rotations 37 is therefore essentially due to the distance 12th of the two springs 4th , 5 determined, being the distance 12th on the other hand, there is little or no influence on the elastic behavior in the case of X deflections 36 Has.

Because of the elastic behavior with linear or rotary movements 36 , 37 the frequency behavior of linear and / or torsional vibrations is also determined, the facts just described provide the possibility of adjusting the two frequency behavior by a suitable choice of the spring spacing 12th and the width of the nib 11 to influence in a targeted manner. In particular, it is possible in this way to design the spring arrangement accordingly 3 achieve that the frequency behavior and thus the sensitivity with regard to the two oscillation modes is essentially the same.

At the in 2 illustrated embodiment of the inertial sensor according to the invention 1 the structure is analogous to that in 1 , however, here is the spring arrangement 3 by a double meander spring 3 educated. The double meander spring 3 again includes two springs 4th , 5 , which are designed as meander springs, ie the springs 4th , 5 have several sections that alternate in the X and Y directions 7th , 8th run away. The course of the meander spring on the right in the drawing 5 is in 4th pictured. The meander spring on the left in the drawing 4th lies with respect to the axis of rotation 10 mirror symmetrical to it.

In the 3 the cross-section of an i-spring is shown. Two such i-springs 4, 5 form the double i-spring 3 with which the seismic mass 6th in the embodiment 1 is elastically mounted. The cross section shown corresponds to a section parallel to the XZ plane, ie the horizontal direction of the plane of the sheet corresponds to the X direction here 7th and the vertical of the Z direction 9 . The term “i-spring” expresses the fact that the cross-section of the spring resembles an “i” turned upside down. The i-spring 4, 5 comprises two sub-springs 13th , 14th whose cross-sections have different dimensions 15th , 16 , 17th , 18th exhibit. In particular, here is the height 17th the upper part spring 13th greater than the height 18th the lower part of the spring 14th . Furthermore, the upper part of the spring 13th a width 15th on that is less than the width 16 the lower part of the spring 14th . This design advantageously makes it possible to reduce the cross-sensitivity between linear and torsional vibration. Alternatively, it is also possible that each of the two springs 4th , 5 can only be formed by a single bar spring, for example the cross-sectional shape of the upper part of the spring shown 13th may have, but without additionally a lower part spring 14th to include. Such a spring can also be found in the in 1 depicted way be connected with substrate and seimsic mass.

In the 4th is the shape of the right meander spring 5 out 2 with respect to the X and Y directions 7th , 8th shown. The feather 5 is at the connection point 33 with the centrally located anchor point 22nd connected while the ends 32 with that through the seismic mass 6th formed frame structure are connected. The meander spring 5 includes three in the Y direction 8th running sections 28 , 29 , 30th going through in the X direction 7th running sections 31 , 35 are connected to each other. The first part 28 is in the middle 34 with the anchor point 22nd connected. The first and second part 28 , 29 are each at the ends by the short ones in the X-direction 7th extending sections connected to each other and the second and third sections 29 , 30th are in turn with a centrally attached, in the X direction 7th trending segment 35 connected.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102009045391 A1 [0003]
• DE 102009000167 A1 [0003]
• DE 102012223016 A1 [0003, 0011, 0017]
• DE 102008001442 A1 [0004]

Claims (9)

Inertial sensor (1) with a substrate having a main extension plane (2) and a seismic mass (6) connected to the substrate via a spring arrangement (3), the seismic mass (6) being supported by the spring arrangement (3) in such a way that the seismic mass (6) can be excited to a linear oscillation and a torsional oscillation, wherein the linear oscillation runs along an X-direction (7) running parallel to the main extension plane (2) and an axis of rotation (10) of the rotary oscillation along a parallel to the main extension plane (2) and the Y-direction (8) which is perpendicular to the X-direction (7), characterized in that the spring arrangement (3) has a first and second spring (4, 5), the first and second springs (4, 5 ) each have a width (11) and a mutual spacing (12) in the X direction and the spacing (12) and the width (11) of the two springs are selected so that a resonance frequency of the linear oscillation in Is essentially equal to a resonance frequency of the torsional vibration. Inertial sensor (1) Claim 1 , each of the two springs (4, 5) each having an upper and a lower part spring (13, 14), the upper and lower part spring (13, 14) each extending in the Y direction (8) and in one on the Main extension plane (2) perpendicular Z-direction (9) are spaced from one another. Inertial sensor (1) Claim 2 , wherein the first and second springs (4, 5) are each designed such that a width (15) of the upper part spring (13) is different from a width (16) of the lower part spring (14) and / or the upper and lower part Partial spring (13, 14) each have a height (17, 18) in the Z direction (9) and a height (17) of the upper partial spring (13) is different from a height (18) of the lower partial spring (14). Inertial sensor (1) Claim 1 , wherein each of the two springs (4, 5) is designed in a meandering manner and has at least two sections (28, 29, 30) running in the Y direction (8) which are separated by sections (31 , 35) are connected to each other. Inertial sensor (1) Claim 4 , wherein the two springs (4, 5) each have at least three sections (28, 29, 30) running in the Y direction (8), a first section (28) having a connection point (34) with the substrate which, with respect to the Y-direction (8) is arranged in the middle of the first section (28), the first section (29) and a second section (30) being connected to one another at the ends (31), the second section (29) has a connection point with a third section (30) which is arranged with respect to the Y-direction (8) in the middle of the second section (29). Inertial sensor (1) Claim 1 , the two springs (4, 5) each being formed by a cantilever, each of the two cantilevers in particular having a height in the Z direction (9) which is greater than a width in the X direction (7). Inertial sensor (1) according to one of the preceding claims, wherein the distance (12) and the width (11) of the two springs (4, 5) are selected so that a frequency behavior of the linear oscillation is essentially the same as a frequency behavior of the torsional oscillation. Inertial sensor (1) according to one of the preceding claims, the spring arrangement (3) being surrounded by the seismic mass (6) with respect to the main extension plane (2). Inertial sensor (1) according to one of the preceding claims, wherein the first and second springs (4, 5) are connected to the substrate via a common anchor point (22).

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