Patent Application
20140224016
The invention relates to a method for detecting an output signal of a resonator micro-electronic gyro preferably of a micro-electromechanical system (MEMS) gyro comprising the steps of:
a) activating a vibrational in-plane movement of a first and a second resonator mass suspended for rotational vibration, and
b) providing an anti-phase vibration of the first and second vibrating mass by at least one mechanical coupling element flexibly connecting the first and the second resonator mass for anti-phase vibration.
The invention also relates to a resonator micro-electronic gyro comprising:
The term “gyro” is meant to be a general term that includes a gyroscope, that measures angles, as wall as a rotation rate gyro, that measures angular rates.
There is a wide range of MEMS devices for detecting angular rates e.g. U.S. Pat. No. 5,329,815 (Motorola), U.S. Pat. No. 5,025,346 (Univ. of California), EP 0 623 807 (GM) and U.S. Pat. No. 5,377,544 (Motorola).
U.S. Pat. No. 7,624,494 (Challoner et al.) discloses an inertial sensor that includes a mesoscaled disc resonator comprised of a micro-machined wafer with low coefficient of thermal expansion for sensing substantially in-plane vibration. A rigid support is coupled to the resonator at a central mounting point of the resonator by radial suspension beams. An excitation electrode is within an interior of the resonator to excite internal in-plane vibration of the resonator. At least one sensing electrode within the interior of the resonator is used for sensing the internal in-plane vibration of the resonator.
U.S. Pat. No. 6,062,082 (Guenther et al.) discloses a Coriolis rotation rate sensor, having a swinging structure that is movably suspended on a substrate (base) and can be deflected due to an acceleration effect. The sensor further has an arrangement for generating a planar rotational swinging movement of the swinging structure. An evaluating arrangement is provided for detecting a deflection of the swinging structure that is stipulated by Coriolis acceleration. The swinging structure is suspended so as to perform a planar rotational swinging movement. The problem of this structure is that there is a net reaction force acting on the base plate during the swinging of the mobile mass.
U.S. Pat. No. 6,629,460 (Challoner) discloses a resonator gyroscope comprising a resonator including two bodies, each with a center of mass and transverse inertia symmetry about an axis that are substantially coincident and each supported by one or more elastic elements. The bodies together form two differential rocking modes of vibration transverse to the axis with substantially equal frequencies. The two bodies transfer substantially no net momentum to the base plate when the resonator is excited. The gyro further includes a base plate affixed to the resonator by the one or more elastic elements.
The prior art is not satisfactory with respect to suppressing measurement disturbances. There is a need for lower environmental influences on the measurements to provide better sensitivity of the device.
It is an object of the invention to provide a micro-electromechanical system (MEMS) device for detecting rotation which has a low sensitivity to thermo-mechanical effects and to disturbing linear accelerations.
According to the invention, the above mentioned objectives are achieved by a method comprising the following steps:
Sx
out=({S21+}−μ{S11+})−({S21−}−μS11−}),
The differential detection of the invention avoids (or at least minimizes) the distorting effects of environmental influences and acceleration forces in z-direction. By means of the compensation factor μ it is possible to account for a difference in sensitivity of the two masses at a given level of rotation to be measured. The difference in sensitivity may result from different diameters (i.e. radial distance from the axis of vibration) of the two masses. If no compensation is necessary, the compensation factor is μ=1. If compensation is required, the compensation factor is different from 1. Typically, the compensation factor is in the range of 0.2-5 and more preferably in the range of 0.5-2.
It is an advantage of the invention that it may be implemented with a technology that is well established. In particular, the parts and circuits for generating and treating the electrical signals, e.g.
Two output signals:
While it is possible to use the invention for just one single output signal, it is preferable to detect rotation in the two axes x and y parallel to the plane of vibration of the masses. This means that two output signals Sxout, Syout are determined. In detail, there are additional steps namely:
Sy
out=({S22+}−μ{S12+})−({S22−}−μ{S12−}),
The compensation factor p is the same for both output signals.
Ring-shaped coupling element:
The method of claim 1 or 2, wherein the coupling element is provided in the form of a ring-shaped elastic structure with radial beams connecting the ring-shaped structure to the two masses. Alternatively, other designs can be used such as Z-shaped or S-shaped spring elements.
A resonator micro-electronic gyro, preferably a micro-electromechanical system (MEMS) gyro using the method of the invention comprises:
Sx
out=(S21+−μS11+)−(S21−−μS11−),
It is to be noted that the term “calculator” is not to be understood in a limited way. A calculator according to the invention may be a general purpose calculator device as well as an application specific electronic circuit that is capable of doing the required differentiation of the signals.
According to a preferred embodiment, the device for determining two output signals Sxout, Syout has
Sy
out=({S22+}−μ{S12+})−({S22−}−μ{S12−})
Ring-Shaped Outer Mass:
According to a preferred embodiment of the invention the second mass has the shape of a ring and the first mass is concentrically suspended within the second mass. The ring is a closed body with a central opening for the second mass. Both masses perform a rotational vibration about a common geometric axis. The direction of the vibration axis is in z-direction and is defined orthogonal to the plane in which the movement of vibration takes place.
Most preferably, the ring has a rotationally symmetric shape. Typically the shape is that of a circular ring-plate. But it is also possible to use a ring having polygonal (e.g. octagonal or square) shape, which requires more area on the substrate. Instead of providing a closed ring, it is also possible to design the second mass in a more complex shape (having e.g. several separated ring segments).
Circular Shape of First Mass:
The first mass, which is suspended within the second mass, has preferably the shape of a circular disk (disk-shape). When both masses are circular (disk or ring) the surface area needed on the substrate is minimal and the symmetry within the plane of vibration is optimal. This embodiment is best when two output signals Sxout and Syout are to be determined. However, the inner mass may also have the shape of a ring plate.
Coupling Element:
Preferably, the coupling element (or each of the two or more coupling elements) is fixed on an anchor and is suspending the two masses. Therefore, the coupling element is also the suspension element for each of the masses. Coupling elements and suspension elements may also be embodied by two different mechanical structures.
In general, for reasons of symmetry, each mass is suspended on at least two suspension elements. Preferably, there are four suspension elements for each mass. The suspension elements are flexible and allow a rotational vibration of the mass within the x-y-plane (plane parallel to the substrate of the device). They are also resilient to allow for an out-of-plane swinging of the mass (depending on the exerted Coriolis force).
The mechanical coupling element is designed so as to allow anti-phase vibration of the masses. In-phase vibrations should be damped or suppressed by the coupling element. This is achieved e.g. by beam that is stiffly connected at each of its ends to each one of the two masses and that is attached at its centre (or generally speaking: in its middle part) to an anchor post of the substrate in such a way that an in-plane bending force (exerted by the vibrating inner mass on the coupling element) can be transmitted or propagated across the anchor from one end of the beam to its other end (to the outer mass).
Anchor:
Preferably, each of said anchors is arranged in a free space between the two masses and is supporting the coupling element in a middle area. When several (e.g. four) separate coupling elements are used, this means that there may be one single anchor point for each coupling beam. The anchor points of the different anchors may be arranged on a circle at equal angular distance from each other. It is also possible to have two separate anchor points for each of the coupling elements.
Shape of Coupling Element:
There is a variety of designs that may be used for implementing the coupling elements. When the distance between the two masses is sufficiently large for providing the required resilience of the elements, the coupling elements may be straight beams. Preferably, the coupling element is curved. It may then have an Z- or S-shape. However, it may also have a more complicated shape. The coupling element may also have a central part that is straight and two end parts that have the shape of a fork, the two prongs of the fork being connected to the mass (Y-shape).
According to a further variant, the coupling element has the form of a ring-shaped elastic structure with radial beams connecting the ring-shaped structure with the two masses.
Therefore, there is just one (complex) coupling element instead of several individual coupling elements. This has the advantage that the anti-phase vibration mode of the masses is strongly supported and other in-plane vibration modes are suppressed.
The radial beams may be straight or curved. They may also have a fork-shape, the prongs of the fork being connected to one of the masses.
The ring-shaped elastic structure may be fixed to at least three, preferably four, anchor posts. In between the anchor posts the ring can deflect from its circular shape when the masses vibrate. The ring-shaped structure is connected to the two masses e.g. by radially extending beams (with respect to the centre of the ring). The connection points of the beams to the ring-shaped elastic structure are angularly displaced with respect to the anchor points of the ring-shaped structure. The connection points may be in the middle between two neighbouring anchor points.
Electrodes:
When viewed from the centre of the masses the positive sensing electrodes of the two masses are in the same sector (e.g. in the same quarter). In an analogous way the negative sensing electrodes of the masses are in a common sector (e.g. in a quarter displaced with respect to the quarter of the positive sensing electrodes). The sensing electrodes in each case define a capacity that varies depending on the out-of-plane movement of the masses. One electrode layer is arranged on the main surface of the vibrating mass and the other electrode layer may be on a fixed element above and face to face to the moving electrode.
There may be four pairs of sensing electrode layers for each of the two masses (2 positive and 2 negative sensing electrodes). However, there may be less (when detecting just one Coriolis rotation axis) or more (e.g. 6) electrode pairs.
Geometry of Mobile Mass:
The geometry of the mobile mass is selected in such a way that the actuated vibration frequency of the inner and the outer mass is the same. When a certain Coriolis acceleration is exerted on the two vibrating masses, they will usually react with different out-of-plane amplitudes. (Note that an angular rate generates a Coriolis acceleration.) It is advantageous to take measures so that the amplitudes are not too much different.
One preferred measure is to construct the suspending elements of the inner mass differently from those of the outer mass so that the inner mass has substantially the same output amplitude as the outer mass.
Another measure is to suspend the inner mass in such a way that it has a higher in-plane vibration amplitude than the outer mass so that in the end the out-of-plane swinging amplitude of the two masses is of the same (or at least similar) magnitude .
Activating Means:
The vibration of the mobile masses is generated by activating electrodes. They may have a comb-like structure. The fingers of the comb may be oriented parallel to the direction of movement. Such electrode structures are known in the prior art. For instance, circumferentially oriented activation electrodes of the invention may have a structure as shown in
It is to be noted that due to the different radial extension of the inner and the outer mass the tangential velocities at the periphery of masses are different and, as a consequence, the Coriolis accelerations are different. For compensating this difference a different gain is introduced between the sensing electrodes of the outer and the inner mass. Alternatively, the activation control may be made such that the amplitudes of the vibrations of the masses are different so that the tangential velocity is the same.
The geometry of the mobile mass is selected in such a way that the actuated vibration frequency of the inner mass and the outer mass is identical.
The accompanying drawings further illustrate the invention and serve to explain the preferred embodiments in combination with the detailed specification:
Generally speaking, like reference numerals refer to identical parts.
The two masses are mechanically connected by four Z-shaped coupling elements 4, 5, 6, 7. All of them are identical. The following description, therefore, only refers to the coupling element 4.
The coupling element 4 is supported on a post 8.1 (anchor point) of the substrate. The post 8.1 acts as a dot-like anchor for the coupling element 4. It supports the coupling element 4 at a certain distance above the substrate and in the centre of the coupling element 4. A first end 4.1 of the coupling element 4 is fixed to the inner mass 1 and a second end 4.2 is fixed to the outer mass 2. When the inner mass 1 is displaced clockwise from its still-position, the coupling element 4 is bent and transfers a momentum to the outer mass 2, which rotates the outer mass 2 counter-clockwise. This means that the two masses are mechanically coupled to perform anti-phase in-plane vibrations.
Because the coupling element is fixed on the post 8.1 it has also the function of flexibly suspending the masses 1, 2. So the masses can perform a vibrational movement around the centre C of the two masses 1, 2. The two ends 4.1, 4.2 of the coupling element 4 are like springs, allowing the masses 1, 2 to perform in-plane rotations and an out-of-plane swinging.
The Z-shaped coupling element 4 is a bent beam with a length L that is longer than the radial space 9.1 between the masses (L>R4 −R1). The length of each one part (between the post 8.1 and the connection to the inner and outer mass 1, 2, respectively, may be 1-1.5 times the radial extension of the radial space 9.1. Therefore, it is possible to adapt the resilience of the arms of the Z-shaped coupling element in a sufficiently broad range so as to control the amplitudes of the masses 1, 2 in the x-y-plane and out of the x-y-plane. The two ends 4.1, 4.2 may have the same or different shapes and lengths and the anchor post 8.1 may be displaced out of the centre of the Z-shaped coupling element 4. The cross-section of the coupling element is preferably constant along the length of the bent beam. However, it may also vary to make one of the arms stiffer than the other one.
For each mass 1, 2 there are four activation electrode structures A11+, A11−, A12+, A12− for the first mass 1, and A21+, A21−, A22+, A22− for the second mass 2. Their position is symmetrical with respect to the x- and y-axis. In the present embodiment the activation electrode structures A12+, A12− and A22+, A22− are aligned along the x-axis while the other activation electrode structures are aligned along the y-axis. The activation electrode structures A11+, A11−, A12+, A12− of the inner mass 1 are arranged at the outer periphery of the inner mass 1, namely in the radial range between R1 and R2. And the activation electrode structures A21+, A21−, A22+, A22− of the outer mass 2 are arranged at the inner periphery of the ring-shaped outer mass 2, namely in the radial range between R3 and R4. (It is also possible to consider the activation electrodes for the external mass at the periphery outside, and the electrodes for the inner mass may be in the inner centre part.) In the azimuthal direction the activation electrode structures are between the four free areas 9.1, 9.2, 9.3, 9.4. Each activation electrode structure may e.g. occupy an azimuthal range of 50-70°, while the remaining 40-20° are taken by the free areas 9.1, 9.2, 9.3, 9.4. Between the activation electrode structures A11+, A11−, A12+, A12− of the inner mass 1 and the activation electrode structures A21+, A21−, A22+, A22− of the outer mass 2 there is a small radial gap 10 corresponding to the difference between R2 and R3.
The activation electrode structure may have a comb-like constitution as known in the prior art (not shown in the Figures). They generate the anti-phase vibration of the masses 1, 2 in the x-y-plane.
On each mass 1, 2 there are four sensing electrodes, S11+, S11−, S12+, S12− on the inner mass 1 and S21+, S21−, S22+, S22− on the outer mass 2. Each of them may occupy a quarter of the surface of the respective mass 1, 2. They are electrically isolated from each other by small radially oriented gaps 11.1, . . . 11.4 and 12.1, . . . 12.4. In the present embodiment the gaps 11.1, . . . 11.4 of the inner mass 1 and the gaps 12.1, . . . 12.4 of the outer mass 2 are in line with each other. So the sensing electrodes, which are occupying the azimuthal area between the gaps 12.1, . . . , 12.4 are in line with each other. To be clear, the sensing electrodes S11+ and S21+ are in line with each other on the positive branch of the y-axis. The sensing electrodes S11− and S21− are positioned mirror symmetrically to the sensing electrodes S11+, S21+ on the negative branch of the y-axis. In an analogous manner, the sensing electrodes S12+ and S22+ are in line with each other on the positive branch of the x-axis and the sensing electrodes S12− and S22− are in line with each other on the negative branch of the x-axis.
Each of the sensing electrodes on the masses 1, 2 has a mating electrode on a fixed carrier element (not shown) so as to form an electrical capacity that varies depending on the deviation of the masses from their still position.
The detection circuit is connected to the sensing electrodes for detecting the out-of-plane swinging movement of the masses 1, 2 by calculating the following differential signals:
The activation electrode structure and the circuit are not shown in detail. It is well known to the person skilled in the art (see e.g. U.S. Pat. No. 6,062,082, U.S. Pat. No. 5,377,544, WO 2007/003501 for activation electrode structures and WO 2005/066584, for the circuitry).
A flexible coupling ring 26, which is concentric with the inner and the outer mass 21, 22, is placed in between the inner anchor points 24.1, 24.3, 24.5, 24.7 and the outer anchor points 24.2, 24.4, 24.6, 24.8. The coupling ring 26 is supported at a distance from the anchor points 24.1, . . . 24.8 and at the same time above the substrate of the device by short radial arms 27.1, . . . 27.8, the length L of the radial arms being smaller than half of (or preferably smaller than a quarter of) the radial extension of the free area 23 (see distance in
In the middle between two neighbouring pairs of anchor points 24.1/24.2 and 24.3/24.4 there are two radial beams 28.1, 28.2 for connecting the outer and the inner mass respectively to the coupling ring 26. There are three similar radial beam structures 28.3/28.4, 28.5/28.6, 28.7/28.8 azimuthally displaced by 90° with respect to the first radial beam structure 28.1/28.2.
Whereas the radial beams 28.1, 28.2 may be straight and directly connected to the masses 21, 22, the present embodiment shows a different solution. The radial beam 27.1 has at its inner end a prong with two arms 29.1, 29.2 that are oriented transversely to the radial beam 28.1 and that are connected to the outer periphery of the ring-shaped mass 21 at a lateral distance from the virtual intersection of the axis of the radial beam 28.1 and the periphery of the mass 21. The radial beam 28.1 and the arms 29.1, 29.2 form a Y-shaped connection between the coupling ring 26 and the inner mass 21. In a similar way the outer mass 22 is connected to the coupling ring 26. As can be seen from
Sx
out=({S21+}−μ{S11+})−({S21−}−μ{S11−})
Sy
out=({S22+}−μ{S12+})−({S22−}−μ{S12−})
The invention is not limited to the embodiments shown above. It may be an additional feature to provide a part of each sensing electrode for a quadratic compensation electrode. Such an additional electrode may be used to inject a signal that is proportional to the activation amplitude.
It is possible to use the detection scheme of the invention for just one axis. In such a simplified structure only two sensing electrodes are needed. They are diametrically opposed to each other with respect to the center axis C of the vibrating mass. They may also occupy more area than just a quarter of the top face of the mass.
It is to be noted that the signal
S
—3={S21+}+{S11+}+{S21−}+{S11−}+{S22+}+{S12+}+{S22−}+{S12−}
represents the linear acceleration along the z-axis (Szout). This signal may be evaluated and outputted.
A good geometric symmetry of the masses and supports with respect to the central axis and to the x- and y-axis of the masses makes sure that imbalance of the swinging masses is avoided.
Preferably, the design of the masses and the coupling elements is such that the vibrational frequencies of the masses is substantially higher (i.e. more than double) than the frequency of any environmental disturbing signal. This facilitates the gyro operation. A typical activation frequency higher than the highest mechanical environment perturbation frequency may be at least 3 KHz. A preferred frequency range is 3-12 KHz. For the sensing frequency a frequency shift of 5 to 10% from the activation frequency may be used.
In summary, the invention provides a technical solution to minimize the environmental influence on a Coriolis rotation detection device.
| Number | Date | Country | Kind |
|---|---|---|---|
| EP 11 290 426.3 | Sep 2011 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2012/001984 | 9/20/2012 | WO | 00 | 3/20/2014 |
