Abstract:
An acceleration sensor includes a housing, a first seismic mass which is formed as a first asymmetrical rocker and is disposed in the housing via at least one first spring, a second seismic mass which is formed as a second asymmetrical rocker and is disposed in the housing via at least one second spring, and a sensor and evaluation unit which is designed to ascertain information regarding corresponding rotational movements of the first seismic mass and the second seismic mass in relation to the housing and to determine acceleration information with respect to an acceleration of the acceleration sensor, taking the ascertained information into account. In addition, a method for operating an acceleration sensor is disclosed. The rockers execute opposite rotational movements in response to the presence of an acceleration. A differential evaluation of the signals makes it possible to free the measuring signal of any existing interference signals.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an acceleration sensor and a method for operating an acceleration sensor. 
     BACKGROUND 
     A conventional acceleration sensor often takes the form of a capacitive acceleration sensor. The seismic mass of the capacitive acceleration sensor may be formed as an antisymmetric rocker. A micromechanical acceleration sensor having a seismic mass in the form of an antisymmetric rocker is described, for example, in European Patent Application Publication EP 0 773 443 A1. 
     Seismic masses in the form of rockers are also used for sensors to determine a tilt angle of a vehicle. A sensor of that kind for determining a tilt angle of a vehicle is described, for example, in European Patent Application Publication EP 0 244 581 A1. 
       FIGS. 1A to 1C  show, respectively, one cross-section and two plan views to illustrate a conventional acceleration sensor. 
     The capacitive acceleration sensor shown in cross-section in  FIG. 1A  is designed to detect an acceleration of the acceleration sensor oriented in a direction perpendicular to a wafer  10  (z-direction), and to determine a quantity corresponding to the acceleration. To that end, a seismic mass  12  formed as an antisymmetric rocker is adjustably disposed above wafer  10 . Seismic mass  12  is joined via two torsion springs  14  (see  FIG. 1B ) to an anchoring  16 , which is fixedly disposed on wafer  10 . Torsion springs  14 , not shown in  FIG. 1A , extend along a longitudinal axis  18 , around which seismic mass  12  in the form of a rocker is adjustable. 
     Seismic mass  12  includes a first electrode  20   a  situated on a first side of longitudinal axis  18 , and a second electrode  20   b situated on the second side of longitudinal axis  18 . Because of an additional mass  22 , second electrode  20   b  may have a larger mass than first electrode  20   a.    
     Counter-electrodes  24   a  and  24   b  to electrodes  20   a  and  20   b  of seismic mass  12  are applied fixedly on wafer  10 . The sensor principle of the acceleration sensor is thus based on a spring-mass system, in which movable seismic mass  12 , together with counter-electrodes  24   a  and  24   b  fixed in position on wafer  10 , form two plate-type capacitors. In this context, counter-electrodes  24   a  and  24   b , shown in plan view in  FIG. 1C , are disposed in such a way in relation to electrodes  20   a  and  20   b that the position of seismic mass  12  relative to wafer  10  is ascertainable by evaluation of a first capacitance between electrode  20   a  and associated first counter-electrode  24   a  and a second capacitance between electrode  20   b  and associated second counter-electrode  24   b.    
       FIG. 2  shows a cross-section through the conventional acceleration sensor of  FIGS. 1A to 1C  to illustrate its mode of operation. 
     If, as shown in  FIG. 2 , the acceleration sensor experiences an acceleration  26  in the z-direction, then, because of additional mass  22 , a force aimed in the direction of wafer  10  acts on second electrode  20   b . Therefore, due to acceleration  26 , seismic mass  12  in the form of a rocker is moved around the longitudinal axis (not sketched) in such a way that a first average distance dl between first electrode  20   a  and first counter-electrode  24   a  increases, and a second average distance d 2  between second electrode  20   b  and second counter-electrode  24   b  decreases. 
     The changes in the capacitances of the two capacitors, formed of electrodes  20   a  and  20   b  and counter-electrodes  24   a  and  24   b , which correspond to the changes in distances d 1  and d 2 , may subsequently be evaluated to determine acceleration  26 . Since methods for evaluating changes in capacitance are known from the related art, they are not further discussed here. 
       FIG. 3  shows a cross-section through the conventional acceleration sensor of  FIGS. 1A to 1C  in the context of a mechanical stress exerted on the acceleration sensor. 
     In  FIG. 3 , a mechanical stress is acting upon wafer  10 , by which wafer  10  is bent asymmetrically along the y-axis. For example, first average distance dl between first electrode  20   a and first counter-electrode  24   a  changes due to the asymmetrical bending of wafer  10 . In the same way, second average distance d 2  between second electrode  20   b  and second counter-electrode  24   b  may increase or decrease under the influence of a mechanical stress. 
     Thus, in the case of the conventional acceleration sensor, a mechanical stress, which, for example, is produced via a force or via a pressure on at least one part of the acceleration sensor, particularly on a subunit of the housing, is able to bring about a change in the capacitance of the capacitors made up of electrodes  20   a  and  20   b  and counter-electrodes  24   a  and  24   b . As a rule, an evaluation unit (not shown) of the acceleration sensor is unable to distinguish the change in capacitance caused by an influence of stress from a change in capacitance triggered by an acceleration of the acceleration sensor. As a result, the acceleration sensor interprets a mechanical stress as an acceleration, and outputs a corresponding false message. This is also referred to as an offset of the measured acceleration caused by an influence on the housing. 
     It is desirable to have the possibility of operating an acceleration sensor in which the acceleration sensor is relatively insensitive to a mechanical stress exerted on the acceleration sensor. 
     SUMMARY 
     The present invention provides an acceleration sensor and a method for operating an acceleration sensor. 
     The present invention is based on the finding that it is possible to detect, as such, filter out and/or compensate for a change in the first position of the first seismic mass in relation to the housing caused by an effect of stress on the housing, by designing the sensor and evaluation unit to ascertain the information regarding corresponding rotational movements of the first seismic mass and the second seismic mass in relation to the housing and to determine acceleration information with respect to an acceleration of the acceleration sensor, taking the ascertained information into account. An acceleration of the acceleration sensor brings about corresponding rotational movements of the two seismic masses about the torsion axis of their springs. For example, the directions of the asymmetries of the two seismic masses are established in such a way that in response to an acceleration of the acceleration sensor, the first seismic mass is moved in a first direction of rotation and the second seismic mass is moved in a second direction of rotation differing from the first direction of rotation. The position of the first seismic mass thereby changes in relation to the second seismic mass. Preferably, the second direction of rotation may be counter to the first direction of rotation. In contrast, changes in the positions of the two seismic masses to be attributed to stress influences are erratic, in particular, the position of the first seismic mass in relation to the second seismic mass not changing. Therefore, the sensor and evaluation unit is able to detect, as such, changes which are not caused by acceleration, filter them out and/or compensate for them. 
     For instance, a bending of the housing brings about a change of at least one position of one of the two seismic masses in relation to the housing. However, since the sensor and evaluation unit is not designed exclusively to determine the acceleration information based on a change in position of the single seismic mass, it is also not susceptible to the faults which occur in the case of a conventional design of the sensor and evaluation unit and when the acceleration sensor is furnished with only one seismic mass. 
     In one possible specific embodiment, the sensor and evaluation unit compares a change in the first position of the first seismic mass to a change in the second position of the second seismic mass possibly occurring at the same time. However, as explained in greater detail hereinafter, the mode of operation of the sensor and evaluation unit is not limited to this specific embodiment. 
     Thus, the present invention permits an acceleration sensor which is considerably less sensitive to a mechanical stress. Consequently, it is possible to use an inexpensive type of housing for the acceleration sensor even if the inexpensive type of housing itself reacts more sensitively to the mechanical stress, since the acceleration sensor performs its function reliably, even in the event of a deformation of the housing. For example, it is thus possible to use a molded housing instead of a premold housing for an acceleration sensor. 
     In addition, the present invention makes it possible to compensate for surface charge effects which may occur due to the different potentials of the various materials of housing components, electrodes and/or a rocker. This ensures that the surface charge effects cannot contribute to a corruption of the acceleration information determined with respect to the acceleration of the acceleration sensor, as is customarily often the case. 
     In one advantageous specific embodiment, the torsion axis of the first spring subdivides the first seismic mass into a first partial mass on a first side of the torsion axis of the first spring and into a second partial mass on a second side of the torsion axis of the first spring, the second partial mass being lighter than the first partial mass; the torsion axis of the second spring subdivides the second seismic mass into a third partial mass on a first side of the torsion axis of the second spring and into a fourth partial mass on a second side of the torsion axis of the second spring, the fourth partial mass being heavier than the third partial mass. For example, the additional mass of the first partial mass in relation to the second partial mass and/or the additional mass of the fourth partial mass in relation to the third partial mass is able to be realized by a larger patterning of the first partial mass and/or the fourth partial mass out of a micromechanical functional layer and/or by an additional coating of the first partial mass and/or the fourth partial mass. Thus, it is possible to inexpensively produce the acceleration sensor having the first antisymmetric rocker and the second antisymmetric rocker. 
     Advantageously, the first seismic mass includes a first electrode situated on the first side of the torsion axis of the first spring and a second electrode situated on the second side of the torsion axis of the first spring, and the second seismic mass includes a third electrode situated on the first side of the torsion axis of the second spring and a fourth electrode situated on the second side of the torsion axis of the second spring, the sensor and evaluation unit including four counter-electrodes which are fixedly disposed in relation to the housing. Thus, the sensor and evaluation unit may be produced easily and cost-effectively using standard methods. 
     For example, the sensor and evaluation unit is designed in such a way that a first capacitance between the first electrode and an associated first counter-electrode of the four counter-electrodes and a fourth capacitance between the fourth electrode and an associated fourth counter-electrode of the four counter-electrodes are interconnected to form a first sum, and a second capacitance between the second electrode and an associated second counter-electrode of the four counter-electrodes and a third capacitance between the third electrode and an associated third counter-electrode of the four counter-electrodes are interconnected to form a second sum. Furthermore, the sensor and evaluation unit may additionally be designed to ascertain a difference between the first sum and the second sum, and to determine the acceleration information regarding he acceleration of the acceleration sensor based on the difference ascertained. In this manner, changes in the first position and/or the second position brought about by stress influences may be offset reliably and with little work expenditure. 
     In particular, the torsion axis of the first spring may lie on the torsion axis of the second spring. The acceleration sensor therefore has a very symmetrical design. Given this symmetrization, surface charge effects between a substrate, the electrodes and the two antisymmetric rockers have almost no influence any longer on the sensor performance. 
     In one advantageous further development, the first seismic mass and the second seismic mass are formed in such a way and disposed in at least one position relative to each other such that at least one end section of the first seismic mass directed away from the torsion axis of the first spring extends into at least one interspace defined by the second seismic mass. In this case, the two seismic masses in the form of asymmetrical rockers in the acceleration sensor are so interlaced that an asymmetrical bending of the substrate is able to be offset in reliable fashion. In this context, it is especially advantageous if, in addition, the electrodes are interconnected in the manner described above. 
     For example, the first seismic mass includes a first comb-like section having at least one tooth and the second seismic mass includes a second comb-like section having at least two teeth, the first seismic mass in at least one position being disposed relative to the second seismic mass in such a way that the at least one tooth of the first comb-like section extends into the at least one interspace between the at least two teeth of the second comb-like section. The construction of the two seismic masses described here has a very symmetrical design. In addition, this is advantageous in terms of the surface charge effects already described above. 
     Furthermore, the first seismic mass may include at least one third comb-like section and the second seismic mass may include at least one fourth comb-like section. Such a formation of the seismic masses additionally reduces the effects of asymmetrical deformations of the housing. 
     The advantages described in the paragraphs above are also ensured in the case of a corresponding method for operating an acceleration sensor. 
     Further features and advantages of the present invention are explained in the following with reference to the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A to 1C  show one cross-section and two plan views to illustrate a conventional acceleration sensor. 
         FIG. 2  shows a cross-section through the conventional acceleration sensor of  FIGS. 1A to 1C  to illustrate its mode of operation. 
         FIG. 3  shows a cross-section through the conventional acceleration sensor of  FIGS. 1A to 1C  in the case of a mechanical stress exerted on the acceleration sensor. 
         FIGS. 4A to 4C  show one cross-section and two plan views to illustrate a first specific embodiment of the acceleration sensor. 
         FIG. 5  shows a cross-section through the acceleration sensor of  FIGS. 4A to 4C  to illustrate its mode of operation. 
         FIG. 6  shows a cross-section through the acceleration sensor of  FIGS. 4A to 4C  in the case of a mechanical stress exerted on the acceleration sensor. 
         FIGS. 7A and 7B  show plan views to illustrate a second specific embodiment of the acceleration sensor. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 4A to 4C  show one cross-section and two plan views to illustrate a first specific embodiment of the acceleration sensor. 
     The schematically rendered acceleration sensor has a first seismic mass  50  and a second seismic mass  52 . First seismic mass  50  is joined via at least one spring  54  (see  FIG. 4B ) to at least one anchoring  56 , which is fixedly disposed on a base substrate  58 . Correspondingly, at least one further spring  54  joins second seismic mass  52  to at least one anchoring  56  attached to base substrate  58 . The two seismic masses  50  and  52  may also be joined via at least two springs  54  to at least one anchoring  56  in common. 
     The at least two springs  54  may take the form of torsion springs. For example, springs  54  may run along a common longitudinal axis, referred to hereinafter as axis of rotation  60 . However, it is stressed here that the present invention is not limited to springs  54  which lie on one common axis of rotation  60 . In the present invention, the at least one spring  54  of first seismic mass  50  may also have a different torsion axis than the at least one spring  54  of second seismic mass  52 . Moreover, the number of springs  54  and anchorings  56 , as well as the placement of seismic masses  50  and  52  relative to springs  54  and anchorings  56  are not restricted to the specific embodiment described here. 
     The two seismic masses  50  and  52  are disposed in the acceleration sensor in such a way that, provided the acceleration sensor experiences no acceleration, they are in their initial positions in relation to base substrate  58 . For example, the two seismic masses  50  and  52  in their initial positions are disposed parallel to each other. In particular, the two seismic masses  50  and  52  in their initial positions may lie in one common plane, which advantageously is aligned parallel to base substrate  58 . This facilitates the production of the acceleration sensor, since in this case, seismic masses  50  and  52  are patternable in their initial positions out of one micromechanical functional layer, advantageously together with springs  54 . It is therefore not necessary to adjust seismic masses  50  and  52 . Axis of rotation  60  subdivides first seismic mass  50  into a first partial mass  50   a  and a second partial mass  50   b , first partial mass  50   a  located on a first side of axis of rotation  60  having a larger mass than second partial mass  50   b  located on a second side of axis of rotation  60 . Because of the different masses of the two partial masses  50   a  and  50   b , first seismic mass  50  is in the form of an antisymmetric rocker which is disposed so as to be adjustable about axis of rotation  60  in relation to base substrate  58 . 
     Second seismic mass  52  is also in the form of an antisymmetric rocker, axis of rotation  60  subdividing second seismic mass  52  into a third partial mass  52   a  and a fourth partial mass  52   b . Third partial mass  52   a  located on the first side of axis of rotation  60  has a smaller mass than second partial mass  52   b  situated on the second side of axis of rotation  60 . A “rocking movement” of second seismic mass  52  is understood to be a rotation of second seismic mass  52  about axis of rotation  60 . 
     For example, the additional mass of first partial mass  50   a  in relation to second partial mass  50   b  and/or the additional mass of fourth partial mass  52   b  in relation to third partial mass  52   a  is determined by a larger patterning of first partial mass  50   a  and/or of fourth partial mass  52   b  out of a micromechanical functional layer. As an alternative or as an addition to that, the unequal mass distribution may also be realized by an additional coating of first partial mass  50   a  and/or of fourth partial mass  52   b.    
     Partial masses  50   a ,  50   b ,  52   a  and  52   b  are formed at least partially as electrodes. However, for the sake of better clarity, the areas of partial masses  50   a ,  50   b ,  52   a  and  52   b acting as electrodes are not marked in  FIGS. 4A to 4C . 
     Preferably, the area of a first electrode of first partial mass  50   a  is equal to an area of a second electrode of second partial mass  50   b . Correspondingly, second seismic mass  52  may also be formed in such a way that an area of a third electrode of third partial mass  52   a  is equal to an area of a fourth electrode of fourth partial mass  52   b . In addition to this, the area of the third electrode may be equal to the area of the first electrode. The advantages of forming the four electrodes with equal area are discussed in greater detail below. 
     In addition, at least one of seismic masses  50  or  52  may be formed in such a way that at least one of its electrodes is made up of at least two electrode regions disposed separate from each other. For example, the third and the fourth electrode each include two electrode regions disposed separate from each other. In this case, the area of the electrode is understood to be the sum of the areas of the at least two electrode regions. 
     In the case of the specific embodiment of the acceleration sensor described here, the two seismic masses  50  and  52  are in the form of two interlaced rockers. For example, two interlaced rockers is understood to mean that the two seismic masses  50  and  52  are formed in such a way and, in at least one position, are disposed relative to each other such that at least one end section  62  of second partial mass  50   b  of first seismic mass  50  directed away from axis of rotation  60  extends into at least one interspace  64  which is defined by fourth partial mass  52   b  of second seismic mass  52 . The at least one position of the two seismic masses  50  and  52  is preferably the initial position of the two seismic masses  50  and  52 . 
     For example, first partial mass  50   a  has a maximum width b 1  which is greater than a maximum width b 3  of third partial mass  52   a , the two widths b 1  and b 3  being oriented in a direction perpendicular to axis of rotation  60 . Correspondingly, fourth partial mass  52   b  may have a maximum width b 4  which runs perpendicular to axis of rotation  60  and is greater than maximum width b 2  of second partial mass  50   b  perpendicular to axis of rotation  60 . 
     In the case of the specific embodiment described here, entire second partial mass  50   b  of first seismic mass  50  extends into interspace  64  defined by fourth partial mass  52   b  of second seismic mass  52 . Thus, in at least one position, the lateral faces of second partial mass  50   b  of first seismic mass  50  are framed two-dimensionally by the inner surfaces of fourth partial mass  52   b  of second seismic mass  52 , which define interspace  64 , and axis of rotation  60 . 
     The formation of the two seismic masses  50  and  52  may also be described such that first seismic mass  50  is comb-like with one tooth and second seismic mass  52  is comb-like with two teeth. First seismic mass  50  is made up of a connecting part running parallel to the x-axis and the tooth aligned in the y-direction. Correspondingly, second seismic mass  52  includes a connecting part directed along the x-axis and the two teeth running in a direction perpendicular to the connecting part. In at least one position of the two seismic masses  50  and  52 , the tooth of first seismic mass  50  extends into an interspace between the at least two teeth of second seismic mass  52 . 
     It is pointed out here that the specific embodiment of  FIG. 4B  may also be modified by providing first seismic mass  50  with at least two teeth and second seismic mass  52  with two or more teeth. In this instance, in at least one position, several teeth of first seismic mass  50  may also extend into at least two interspaces between the teeth of second seismic mass  52 . In this case, the number of springs  54  and anchorings  56  is adjusted accordingly. The advantages of such a modification are discussed below. 
       FIG. 4C  shows a plan view of counter-electrodes  66   a ,  66   b ,  68   a and  68   b  of the four electrodes of the two seismic masses  50  and  52 , the counter-electrodes being fixedly disposed on base substrate  58 . First counter-electrode  66   a  and the first electrode of first seismic mass  50  form a first capacitor having capacitance C 1 A. Correspondingly, second counter-electrode  66   b  cooperates with the second electrode of first seismic mass  50  as a second capacitor having capacitance C 1 B. The third electrode of second seismic mass  52  and third counter-electrode  68   a  form a third capacitor having capacitance C 2 A. In addition, the acceleration sensor includes a fourth capacitor made up of the fourth electrode of second seismic mass  52  and fourth counter-electrode  68   b  having capacitance C 2 B. 
     Preferably, the positioning of counter-electrodes  66   a ,  66   b ,  68   a  and  68   b  corresponds to the positioning of the four electrodes of the two seismic masses  50  and  52 . For instance, third counter-electrode  68   a  may include two separate electrode areas, situated between which is first counter-electrode  66   a . Correspondingly, fourth counter-electrode  68   b  may also be subdivided into two separate electrode areas, between which is second counter-electrode  66   b . However, it is stressed here that the formation of counter-electrodes  66   a ,  66   b ,  68   a  and  68   b is not limited to the exemplary embodiment of  FIG. 4C . For example, third counter-electrode  68   a  and/or fourth counter-electrode  68   b  may each also take the form of a contiguous electrode area. It is advantageous to form counter-electrodes  66   a ,  66   b ,  68   a  and  68   b  with equal total areas, as explained in greater detail below. 
     As already explained above, first seismic mass  50  may also be formed as a comb having at least two teeth, and second seismic mass  52  may be formed as a comb having two or more teeth. In this case, counter-electrodes  66   a ,  66   b ,  68   a  and  68   b  may be adapted to the formation and the placement of the four electrodes accordingly. 
     Advantageously, the capacitors having capacitances C 1 A and C 2 B are interconnected in such a way that a first sum C 1 A+C 2 B of capacitances C 1 A and C 2 B is calculated. Correspondingly, the capacitors having capacitances C 1 B and C 2 A may also be interconnected with each other in such a way that a second sum C 1 B+C 2 A of capacitances C 1 B and C 2 A is calculable. In addition, it is advantageous to design the electronics of the acceleration sensor in such a way that a difference Δ ges  is ascertained between first sum C 1 A+C 2 B and second sum C 1 B+C 2 A, where:
 
Δ ges =(C1A+C2B)−(C1B+C2A)   [Equation 1].
 
     In this case, the acceleration which the acceleration sensor experiences may be determined by an evaluation unit based on the difference Δ ges . Since possibilities for determining the acceleration, while taking the difference Δ ges  into consideration, are known from the related art, it is not further discussed here. 
       FIG. 5  shows a cross-section through the acceleration sensor of  FIGS. 4A to 4C  to illustrate its mode of operation. 
     If the acceleration sensor undergoes an acceleration with an acceleration component  69  which runs perpendicular to base substrate  58  and in a direction from base substrate  58  to the two seismic masses  50  and  52  (in positive z-direction), then, because of their opposite asymmetrical Mass distributions relative to each other, the two seismic masses  50  and  52  in the form of rockers are moved in opposite directions of rotation  70  and  72  out of their initial positions about the axis of rotation (not sketched). That is to say, given such an acceleration component  69 , heavier partial masses  50   a  and  52   b , which lie on different sides of the axis of rotation, come closer to base substrate  58 . Lighter partial masses  50   b  and  52   a  move away from base substrate  58 . The two seismic masses  50  and  52  thus execute corresponding rotational movements. 
     Naturally, the functioning method of the acceleration sensor described in the paragraph above is also ensured if the two seismic masses  50  and  52  are mounted so as to be movable about different axes of rotation. 
     The rotational movements of the two seismic masses  50  and  52  in opposite directions of rotation  70  and  72  produce changes in signal Δ ges  of capacitances C 1 A, C 1 B, C 2 A and C 2 B of the four capacitors of the acceleration sensor. Thus, a value corresponding to acceleration component  69  may be determined based on signal Δ ges . 
     Similarly, an acceleration component which runs perpendicular to base substrate  58  and in a direction from the two seismic masses  50  and  52  to base substrate  58  (in negative z-direction) brings about a change in signal Δ ges . Therefore, the acceleration sensor described here is also able to determine a quantity for an acceleration component in the negative z-direction. 
       FIG. 6  shows a cross-section through the acceleration sensor of  FIGS. 4A to 4C  in the context of a mechanical stress exerted on the acceleration sensor. 
     In  FIG. 6 , a mechanical stress, by which base substrate  58  is bent asymmetrically along the y-axis, is acting upon the acceleration sensor. Due to the asymmetrical bending of base substrate  58  along the y-axis, for example, the distances between the first electrode and first counter-electrode  66   a , as well as the third electrode and third counter-electrode  68   a change. The asymmetrical bending of base substrate  58  brings about a change in capacitances C 1 A and C 2 A accordingly. 
     Especially given equality of area of the first electrode and the third electrode, as well as of first counter-electrode  66   a and third counter-electrode  68   a , it is ensured that capacitances C 1 A and C 2 A each change by an equal differential capacitance Δ C . Capacitances C 1 A and C 2 A of the first and third capacitors are thus made up of a stress-free initial capacitance C 1 A 0  or C 2 A 0  prior to the occurrence of the mechanical stress and differential capacitance Δ C , where:
 
C1A=C1A0+Δ C   [Equation 2]
 
and
 
C2A=C2A0+Δ C   [Equation 3].
 
     First sum C 1 A+C 2 B and second sum C 1 B+C 2 A calculated according to the procedure described above likewise change by differential capacitance Δ C , where:
 
C1A+C2B=C1A0+Δ C +C2B0  [Equation 4]
 
and
 
C1B+C2A=C1B0+C2A0+Δ C .  [Equation 5].
 
     However, in calculating difference Δ ges , differential capacitance Δ C  cancels out again.
 
Δ ges =(C1A+C2B)−(C1B+C2A)=(C1A0+C2B0)−(C1B0+C2AO)  [Equation 6].
 
     Therefore, the bending of base substrate  58  along the y-axis brings about no change in difference Δ ges . In this manner, it is ensured that the asymmetrical bending of base substrate  58  along the y-axis has no influence on an acceleration component in the z-direction ascertained by the acceleration sensor. 
     Since the asymmetrical bending of base substrate  58  does not lead to corresponding rotational movements of the two seismic masses  50  and  52 , it thus also causes no change in difference Δ ges . Therefore, a non-occurring acceleration of the acceleration sensor, based on the asymmetrical bending of base substrate  58 , is prevented from being output as a false measured value. 
     In the exemplary embodiment of  FIG. 4C , counter-electrodes  66   a ,  66   b ,  68   a  and  68   b  (as well as the electrodes) are segmented in the x-direction. In this manner, as described above, it is possible to fully compensate for asymmetrical bendings of base substrate  58  along the y-axis. Asymmetrical bendings along the x-axis are likewise sharply limited in their effects due to the three-fold segmentation in the x-direction. 
     At this point, it is particularly stressed that the specific embodiment of the acceleration sensor described in the paragraphs above is not limited to a segmentation in the x-direction. Depending upon the influence on the housing, it may also prove to be advantageous to carry out the segmentation in the y-direction, or in any other direction especially adapted to the housing. 
     Advantageously, the suspension of springs  54  is symmetrical for both rockers, in order to improve reliable compensation of a substrate bending. Furthermore, springs  54  may be formed in an analogous manner with respect to their coupling to the at least one anchoring  56 . This additionally improves the compensation for a bending of the substrate. 
     With the aid of the following figures, it is explained how effects of an asymmetrical bending along the x-axis are able to be further limited by an increased segmentation. Already above, the acceleration sensor having a first seismic mass  50  formed as a comb with at least two teeth and having a second seismic mass  52  formed as a comb with two or more teeth is indicated as an example for an increased segmentation. In the same way, depending upon the area requirement and properties of the rocker suspension, it may prove advantageous, instead of a double rocker, to use a multi-rocker. An example for a multi-rocker is described with the aid of the following paragraphs. 
       FIGS. 7A and 7B  show plan views to illustrate a second specific embodiment of the acceleration sensor. 
     The two seismic masses  80  and  82  of the acceleration sensor shown schematically in  FIGS. 7A and 7B  are mounted in a manner allowing rotation about the axis of rotation by way of springs  54  already described, having anchorings  56  fixedly attached to the base substrate (not sketched) The axis of rotation subdivides first seismic mass  80  into a first partial mass  80   a  and a second partial mass  80   b , and second seismic mass  82  into a third partial mass  82   a  and a fourth partial mass  82   b . First partial mass  80   a  and third partial mass  82   a  are situated on a first side of the axis of rotation, and second partial mass  80   b  and fourth partial mass  82   b  are situated on a second side of the axis of- rotation. 
     In the exemplary embodiment shown, second partial mass  80   b  of first seismic mass  80  has three end sections  84  directed away from the axis of rotation, which extend into interspaces  86  defined by fourth partial mass  82   b . In particular, the two seismic masses  80  and  82  may be formed in such a way relative to each other that the lateral faces of second partial mass  80   b  are framed by the inner surfaces of fourth partial mass  82   b  which bound a total inside space, and the axis of rotation. 
     This may also be described such that second partial mass  80   b includes a first comb-like section having a connecting part and three teeth, and fourth partial mass  82   b  includes a second comb-like section having a connecting part and four teeth. The three teeth of the first comb-like section, which are aligned parallel to the y-axis, extend into the three interspaces between the four teeth of the second comb-like section which run parallel to the y-axis. The two connecting parts are aligned parallel to the x-axis. 
     First partial mass  80   a  likewise includes a third comb-like section having a connecting part and three teeth, an additional mass  88  being attached to the middle tooth of the third comb-like section. Additional mass  88  and the connecting part are aligned parallel to the x-axis, while the three teeth run along the y-axis. Third partial mass  82   a  has two comb-like sections  90  having one connecting part and two teeth each. The two outer teeth of the third comb-like section of first partial mass  80   a  in each case extend into an interspace between the two teeth of the two further comb-like sections  90  of third partial mass  82   a.    
     Corresponding to the procedure described above, subunits of partial masses  80   a ,  80   b ,  82   a  and  82   b  are used as electrodes. Interacting counter-electrodes  92   a ,  92   b ,  94   a  and  94   b  are fixedly disposed in relation to the base substrate. The interconnection of the capacitors made up of the electrodes and counter-electrodes  92   a ,  92   b ,  94   a  and  94   b  corresponds to the example described above. Since the interaction of the capacitors for ascertaining an acceleration acting on the acceleration sensor is thus obvious for one skilled in the art, it is not further discussed here. 
     Due to the increased segmentation of the electrodes and counter-electrodes  92   a ,  92   b ,  94   a  and  94   b , the effects of an asymmetrical bending along the x-axis are additionally minimized. In a further refinement of the specific embodiment described here, the number of segmentations of the electrodes and counter-electrodes  92   a ,  92   b ,  94   a  and  94   b  may be additionally increased. 
     In the specific embodiments of the acceleration sensor described above, the two seismic masses  50  and  52  or  80  and  82  are formed as two interlaced rockers. However, it is stressed here that the present invention is not restricted to interlaced rockers as seismic masses  50  and  52  or  80  and  82 . Instead, seismic masses  50  and  52  or  80  and  82  may also be disposed separate and set apart from each other.