DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] In order to keep an electrically adequately conductive plate floating between capacitor plates which are aligned horizontally and provided vertically one above the other, without any dedicated electrical connection, at least two mutually insulated capacitor plates are required above the plate to be held floating, between which plates a suitable electric potential difference is applied. If, underneath the plate, there are likewise two capacitor plates with a potential difference applied between them, the force exerted by the upper capacitor plates on the plate and directed upward (because it is always an attracting force) is to a certain extent compensated by a force which is directed downward and is exerted on the plate by the lower capacitor plates. Given suitable selection and readjustment of the potential differences, the plate can be kept floating within close limits.

[0033] A simple model, which does not take into account tilting of the held plate, is intended to clarify the fact that, in principle, the required voltages can be determined by calculation as a function of the relevant physical and geometric variables, without requiring any further inventive step. If the number of upper capacitor plates is equal to the number of lower capacitor plates and all capacitor plates have the same area, the electric potential of the floating plate is:

U _p =[( d/ 2− z ) ( U ₁₁ +U ₁₂ +. . . U _1n )+( d/ 2+ z ) ( U ₂₁ +U ₂₂ +. . . +U _2n )+ Q ( d ² /4− z ² )/( Aε ₀ )]/( nd )

[0034] where:

[0035] d is the air gap between the capacitor plates,

[0036] z is the distance of the plate from its central position between the capacitor plates in the upward direction,

[0037] U _1i is the electric potential applied to the ith lower capacitor plate,

[0038] U _2i is the electric potential applied to the ith upper capacitor plate,

[0039] Q is the electric charge present on the plate,

[0040] A is the area of a capacitor plate,

[0041] ε ₀ is the electric field constant (absolute dielectric constant) and

[0042] n is the number of upper and lower capacitor plates.

[0043] Here, the thickness of the floating plate has been ignored.

[0044] The force exerted on the floating plate by the ith lower capacitor plate is then:

F _1i =( U _1i −U _p ) ² ·Aε ₀ /( d/ 2+ z ) ²

[0045] the force exerted on the floating plate by the ith upper capacitor plate is correspondingly:

F _2i =( U _2i −U _p ) ² ·Aε ₀ /( d/ 2+ z ) ²

[0046] the resulting overall force upward acting on the plate is equal to the sum of all F _2i reduced by the sum of all F _1i .

[0047] In order to be able to prevent tilting of the floating plate, the angular rate sensor according to the invention has, at the top and bottom in each case, at least three electrodes functioning as capacitor plates.

[0048] The always attracting electrostatic forces pull a floating plate into the interior of the capacitor formed by the electrodes, so that the area in which the plate and the electrodes overlap in the vertical direction of view is always the greatest. This is the basis for the drive with which the rotational element is set rotating. The rotational element is configured in such a way that it has different radial dimensions in successive segments. As a result, during a rotational movement of the rotational element, the area of the overlap with a specific pair of electrodes varies. Driving the electrodes cyclically and with subdivision into phases, using applied potentials, makes it possible to exert an attractive force on the rotational element in each case in the direction of the same direction of rotation and in this way to generate a rotational movement.

[0049] FIG. 1 shows in plan view the configuration of three electrodes in three circular ring sectors located rotationally symmetrically in relation to a 120° angle.

[0050] FIG. 2 shows a matching form of the rotational element in plan view. The rotational element here is a ring having three broadenings or broadened segments 5 provided rotationally symmetrically in relation to a 120° angle. These broadenings or broadened segments are formed by the radial dimensions in three segments of the ring differing from the remaining width of the ring. These broadenings are used to drive the ring through the use of electrodes fitted above and below and having a form as illustrated in plan view in FIG. 1 .

[0051] FIG. 3 shows an alternative configuration of the electrodes with a subdivision into four segments. For reasons of optimizing the drive, however, triple symmetries are preferred, in which the smallest angle of the rotational symmetry is an integer fraction of 360° which can be divided by three (120° [÷3], 60° [÷], 40° [÷9], 30° [÷12], 24° [÷15], 20° [÷18]).

[0052] In order to ensure the centring of the floating rotational element, it is advantageous if the electrodes are divided up into two concentric circular rings, as illustrated in plan view in FIG. 4 . An annular rotational element can be pulled into a position concentric with the electrodes through the use of mutually different electric potentials on the inner and the outer electrodes. This stabilizes the position of the axis of rotation.

[0053] FIG. 5 shows a schematically simplified cross section of an angular rate sensor. The rotational element 3 is kept floating between the electrodes 4 . The electrodes 4 are fitted to a substrate 1 or a semiconductor chip and to a cover 2 or a second substrate, which is connected to the first, for example through the use of wafer bonding.

[0054] FIG. 6 shows an alternative configuration of an annular rotational element in plan view. Here, the different configuration in individual segments is not formed by a broadening of the ring but by cut-outs 6 in the ring, of which three are shown as an example in FIG. 6 . This configuration has the advantage that, because of the greater annular area as compared with the exemplary embodiment according to FIG. 2 , and therefore the greater area of the overlap with the electrodes, better stabilization of the position of the rotational element is possible. Furthermore, the broader ring is mechanically more stable and has a greater moment of inertia.

[0055] As soon as a cut-out 6 in the rotational element 3 begins to overlap with an electrode 4 in the vertical direction of view, the potential applied to this electrode is switched to the potential on the rotational element or to float. This means that the area of the overlap of cut-out and electrode can be enlarged without any restoring force occurring. The electrodes adjacent to the relevant cut-out have a high potential difference applied to them, in order to produce a torque acting on the rotational element.

[0056] FIGS. 7 to 9 explain the drive principle. For this purpose, in a side view in each case three lower electrodes U ₁₁ , U ₁₂ , U ₁₃ and three upper electrodes U ₂₁ , U ₂₂ , U ₂₃ are shown, between which a ring-like rotational element 3 provided with broadenings 5 is provided. Let the illustrated edge of the rotational element move to the right in this example, so that the broadening 5 of the rotational element 3 shown on the left-hand side in FIG. 7 comes firstly between the electrodes U ₁₁ and U ₂₁ , then between the electrodes U ₁₂ and U ₂₂ and then between the electrodes U ₁₃ and U ₂₃ in the course of the rotation, while the broadening 5 shown on the right-hand side disappears behind the plane of the drawing and moves to the left at the rear.

[0057] The electrodes between which a broadening 5 of the rotational element is currently pulled are set to the potential U _p of the rotational element, while potential differences are applied to the pairs of electrodes in front and behind it. In the illustrated example, for the configuration in FIG. 7 , the result is the following relations between the potentials:

U ₁₁ =U ₂₁ =U _p , U ₁₂ >U _p , U ₁₃ <U _p , U ₂₂ >U _p , U ₂₃ <U _p ;

[0058] for the configuration in FIG. 8 :

U ₁₂ =U ₂₂ =U _p , U ₁₁ >U _p , U ₁₃ <U _p , U ₂₁ >U _p , U ₂₃ <U _p ; and

[0059] for the configuration in FIG. 9 :

U ₁₃ =U ₂₃ =U _p , U ₁₁ >U _p , U ₁₂ <U _p , U ₂₁ >U _p , U ₂₂ <U _p .

[0060] A Coriolis force which occurs is detected by evaluating the electrical voltages which have to be applied to the electrodes in order to keep the rotational element in its plane of rotation. As long as the angular rate sensor remains aligned horizontally, the compensation of gravitation and rectilinear accelerations requires equally large electrostatic forces at all electrode positions. A Coriolis force arising from tilting of the angular rate sensor appears as a torque which can be compensated only through the use of forces of different magnitudes and therefore only through the use of different potentials on the electrodes. The required potential differences can be determined, and the magnitude of the Coriolis force can be determined from these. One advantage as compared with resonant structures is that in this case no effects of the suspension of the rotational element on the resonant frequencies of the drive and the Coriolis oscillation need to be taken into account.