KR20090107932A - Systems and methods for acceleration and rotational determination from an in-plane and out-of-plane mems device - Google Patents

Abstract

PURPOSE: A system and a method for determination of in-plane and out-of-plane acceleration and rotation using a MEMS sensor are provided to implement an inertial measuring unit using two inertia sensors, each of which senses the linear acceleration and rotation of two axes. CONSTITUTION: A method for determination of in-plane and out-of-plane acceleration and rotation using a MEMS sensor comprises a step of sensing out-of-plane linear acceleration of the MEMS sensor using a pair of first out-of-plane electrodes(106,108) and a pair of second out-of-plane electrodes(114,116), a step of sensing in-plane rotation of the MEMS sensor using the first out-of-plane electrodes and the second out-of-plane electrodes, a step of sensing in-plane linear acceleration of the MEMS sensor using first and second in-plane sensing computers, and a step of sensing out-of-plane rotation of the MEMS sensor is sensed the first and second in-plane sensing computers.

Description

SYSTEM AND METHOD FOR ACCELERATION AND ROTATION DETERMINATION IN IN-PLAN AND OUT- PLANE MEMS DEVICES {SYSTEMS AND METHODS FOR ACCELERATION AND ROTATIONAL DETERMINATION FROM AN IN-PLANE AND OUT-OF-PLANE MEMS DEVICE}

One embodiment of the present invention relates to a MEMS inertial sensor, and more particularly, to a MEMS inertial sensor for determining acceleration and rotation in an in-plane and out-of-plane direction.

This application is filed April 10, 2008 and is entitled "Systems And Methods For Acceleration And Rotational Determination From An In-plane And Out-of-plane MEMS Device," and is hereby incorporated by reference in its entirety. Claim priority from US Provisional Patent Application 61 / 043,974.

The Micro-Electro-Mechanical Systems (MEMS) inertial measurement unit includes three gyroscopes and three accelerometers to detect changes in attitude and acceleration. Typically, three gyroscopes and three accelerometers are mounted on separate orthogonal axes, each with its own set of control and readout electronics. In view of the fact that three gyroscopes and three accelerometers must be installed precisely, power is supplied to three gyroscopes and three accelerometers in terms of the relatively large processing capacity required to process information from six individual units. It is to be understood that there is an inherent cost in the assembly of MEMS inertial measurement units in terms of power requirements for supply. Many applications require savings in size, computational requirements, power requirements, and the cost of MEMS inertial measurement units. In view of these limitations, it would be beneficial to reduce the number of sensing devices in the MEMS inertial measurement unit.

Conventional MEMS gyroscopes can be used to determine angular rotation by measuring the force (turning force) of Coriolis applied to the resonant proof mass. Conventional MEMS gyroscopes include two silicon inertial masses suspended mechanically from a substrate that are mechanically connected to a generally glass substrate using one or more silicon bends. Multiple recesses etched into the substrate allow optional portions of the silicon structure to move back and forth freely within the interior of the device. In certain designs, a substrate may be provided above and below the silicon substrate to allow an inertial mass to fit between the two substrates. Patterns of metal traces formed on the substrate (s) can be used to deliver various electrical bias voltages and signal outputs to the device.

Many MEMS gyroscope drive systems generally include a number of drive elements that cause the inertial mass to oscillate back and forth along a drive axis perpendicular to the direction in which the forward force is sensed. In certain designs, for example, the drive element may comprise a plurality of interdigitated vertical comb fingers or tines that convert electrical energy into mechanical energy using electrostatic actuation. It may include. Such drive elements are hereby incorporated by reference in Tang et al., Incorporated herein by reference in their entirety and in US Pat. Nos. 5,025,346 and Johnson et al., Entitled " LATERALLY DRIVEN RESONANT MICROSTRUCTURES. DRIVE ELECTRODES ", US Patent No. 7,036,373. However, these MEMS devices operate in an open loop mode where acceleration and rotation (gyro) responses are coupled to and dependent on each other.

US Patent Application of Michael S. Sutton, filed May 11, 2007, entitled "MEMS TUNING FORK GYRO SENSITIVE TO RATE OF ROTATION ABOUT TWO AXES", incorporated herein by reference in its entirety. 11 / 747,629 discloses a MEMS device that can be used to sense rotation about two different axes orthogonal to the drive shaft. United States Patent Application of Supino et al., Filed Mar. 28, 2008, entitled "SYSTEMS AND METHODS FOR ACCELERATION AND ROTATIONAL DETERMINATION FROM AN OUT-OF-PLANE MEMS DEVICE", incorporated herein by reference in its entirety. 12 / 057,695 discloses a MEMS device usable to sense linear acceleration and rotation.

It is an object of one embodiment of the present invention to provide a MEMS inertial sensor for determining acceleration and rotation in in-plane and out-of-plane directions.

Systems and methods are disclosed for determining and / or sensing in-plane linear acceleration, in-plane rotation, out-of-plane linear acceleration, and out-of-plane rotation using Micro-Electro-Mechanical Systems (MEMS) inertial sensors. Exemplary embodiments include a first inertial mass and a second inertial mass aligned with an in-plane axis, a first out-of-plane electrode pair with the first inertial mass interposed therebetween, and a second with the second inertial mass interposed therebetween. A first in-plane sensing comb with a plurality of comb fingers interleaved with the out-of-plane electrode pair, opposing first inertial mass comb fingers, and a second plane with a plurality of comb interleaves with the opposing second inertial mass comb fingers It is equipped with a sense comb. The out-of-plane linear acceleration of the MEMS sensor may be sensed using the first out-of-plane electrode pair and the second out-of-plane electrode pair. In-plane rotation of the MEMS sensor may be sensed using the first out-of-plane electrode pair and the second out-of-plane electrode pair. In-plane linear acceleration of the MEMS sensor may be sensed using the first in-plane sensing comb and the second in-plane sensing comb. The out-of-plane rotation of the MEMS sensor may be sensed using the first in-plane sensing comb and the second in-plane sensing comb.

According to an embodiment of the present invention, since one inertial sensor detects linear acceleration of two axes and rotation of two axes, two inertial sensors are used instead of three gyroscopes and three accelerometers used in conventional inertial measurement units. It can be used to build one inertial measurement unit.

Embodiments of the inertial sensor 100 separate acceleration sensing and rotation sensing so that rotation and acceleration can be independently determined. 1 is a block diagram of a portion of one embodiment of an inertial sensor 100. An exemplary portion of the inertial sensor 100 can be used to sense either linear acceleration or rotation. Another portion of the inertial sensor 100 that senses rotation is described and illustrated below.

The illustrated portion of the inertial sensor 100 is interchanged with the first inertial mass 102 (also referred to as the left inertial mass 102) and the second inertial mass 104 (the right inertial mass 104). Can be). The left inertial mass 102 is between the first upper left sense (ULS) electrode 106 and the first lower left sense (LLS) electrode 108. In addition, the left inertial mass 102 is between the second ULS electrode 110 and the second LLS electrode 112. The right inertial mass 104 is between the upper right sense (URS) electrode 110 and the lower right sense (RLS) electrode 112. Also, the right inertial mass 104 is between the second URS electrode 118 and the second LRS electrode 120. The upper and lower sensing electrodes can be used to sense out-of-plane motion of the inertial sensor 100. Sense electrodes 106, 108, sense electrodes 110, 112, sense electrodes 114, 116 and sense electrodes 118, 120 are usable to sense out-of-plane motion of the corresponding inertial masses 102, 104. Form an electrode pair.

The left inertial mass 102 is separated from the ULS electrodes 106 and 110 by a gap G _ULS that defines capacitance dependent on the separation interval between the left inertial mass 102 and the ULS electrodes 106 and 110. Similarly, the left inertial mass 102 is separated from the LLS electrodes 108 and 112 by a gap G _LLS that defines a capacitance that depends on the separation gap between the left inertial mass 102 and the LLS electrodes 108 and 112. do. The variation in capacitance associated with the gaps G _ULS , G _LLS caused by out-of-plane linear acceleration or in-plane rotation is detectable.

The right inertial mass 104 is separated from the URS electrodes 114, 118 by a gap G _URS that defines a capacitance that depends on the separation interval between the right inertial mass 104 and the URS electrodes 114, 118. Similarly, the right inertial mass 104 is separated from the LRS electrodes 116, 120 by a gap G _LRS that defines a capacitance that depends on the separation interval between the right inertial mass 104 and the LRS electrodes 116, 120. do. The variation in capacitance associated with the gaps G _URS and G _LRS caused by out-of-plane linear acceleration or in-plane rotational motion is detectable.

The inertial masses 120 and 104 are drive electrodes (not shown in FIG. 1) that impart "back-and-forth" motion to the inertial masses 102 and 104 as an alternating current (AC) voltage is applied to the drive electrodes. Is connected capacitively). The drive electrode causes the inertial masses 102 and 104 to vibrate while resonating back and forth along the drive axis (X axis shown). The drive axis and the Y axis define the in-plane motion of the inertial masses 102 and 104. During the half period of the resonant motion, the relative direction of motion of the left inertial mass 102 as indicated by the direction vector 122a is opposite to the direction of motion of the right inertial mass 104 as indicated by the direction vector 122b. Thus, the inertial masses 102, 104 are shown as being far from each other in FIG. 1. During the next half period of the resonant motion, the inertial masses 102, 104 move towards each other. The inertial masses 102 and 104 resonate with opposite motions out of phase by 180 degrees. It will be appreciated that embodiments of the inertial sensor 100 may be implemented in a MEMS based device having drive electrodes of various configurations.

The inertial sensor 100 includes at least one in-plane sensing electrode 124 capacitively coupled to the inertial mass 102 to sense in-plane motion of the inertial mass 102. At least one in-plane sensing electrode 126 is capacitively coupled to the inertial mass 104 to sense in-plane motion of the inertial mass 104. In-plane sensing electrodes 124, 126, which may be interchangeably referred to herein as in-plane sensing combs, comprise a pair of comb fingers 128 usable to sense movement of inertial masses 102, 104 in the Y-axis direction. do. A comb finger pair 128 is shown having a comb finger of the in-plane sensing electrode 124 interleaved with each other and a comb finger of the inertial mass 102. Movement along the Y axis causes a variation in the gap G _CLS between the comb fingers such that the capacitance of the comb finger varies in a detectable manner. Similarly, interleaved comb fingers (not shown) of in-plane sensing electrode 126 and inertial mass 104 sense motion along the Y axis corresponding to variations in gap G _CRS .

2 illustrates sensing electrodes 106 and 108, sensing electrodes 110 and 112, sensing electrodes 114 and 116, sensing electrodes 118 and 120, and upper electrodes of sensing electrodes 124 and 126 mated out of plane. Top view of an exemplary embodiment of an inertial sensor 100 that is shown. In this exemplary embodiment, four in-plane sense electrodes 130, 132, 134, 136 corresponding to the in-plane sense electrode 124 described above are shown. In-plane sensing electrodes 130, 132, 134, 136 have comb fingers interleaved with corresponding comb fingers of inertial mass 102 to form a plurality of comb finger pairs 128. Also shown are four in-plane sensing electrodes 138, 140, 142, 144 corresponding to the in-plane sensing electrode 126 described above. The in-plane sensing electrodes 138, 140, 142, 144 also have a comb finger interleaved with the corresponding comb finger of the inertial mass 104 to form a plurality of comb finger pairs 128.

The in-plane sensing electrodes 130, 132, 134, 136, 138, 140, 142, 144 shown conceptually show only four finger pairs 128. In a practical configuration, the in-plane sensing electrodes 130, 132, 134, 136, 138, 140, 142, 144 may have more comb finger pairs 128. Also, for conceptual illustration, in-plane sensing electrodes 130, 132, 134, 136, 138, 140, 142, 144 are shown as relatively large electrodes. Various embodiments include four illustrated in-plane sensing electrodes 130, 132, 134, and 136 capacitively coupled to an inertial mass 102 and four illustrated in-plane capacitively coupled to an inertial mass 104. It may have more or fewer than the sensing electrodes 138, 140, 142, 144. In addition, all of the various in-plane electrodes produced may be relatively smaller than those shown.

In addition, embodiments of the inertial sensor 100 may include other sensing electrodes not shown in the drawings for the sake of brevity. For example, pick-off sensing electrodes can be included to sense motor motion induced in the inertial masses 102 and 104.

3 is a top view of an exemplary embodiment of an inertial 100 sensor showing drive electrode 146 interleaved and capacitively coupled to a comb of inertial mass 102. The drive electrode 146 induces the above-described motor movement of the inertial masses 102 and 104.

4 shows four out-of-plane electrode pairs (sensing electrodes 106 and 108, sensing electrodes 110 and 112, sensing electrodes 114 and 116) having two inertial masses 102 and 104, respectively, an upper electrode and a lower electrode. , Sensing electrodes 118, 120), and in-plane sensing electrodes 130, 134, 138, 142 are side views of an exemplary embodiment of the inertial sensor 100. Also shown are drive electrodes 146 inside the inertial masses 102 and 104.

5 is a conceptual diagram illustrating in-plane gyro detection. Rotation as shown (relative to FIG. 1, relative to the Y axis) induces movement in and out of the inertial mass 102, 104 relative to the page (Z axis, see FIG. 1). As described below, the plurality of out-of-plane sensing electrode pairs sense the shown rotation of the inertial sensor 100.

6 is a conceptual diagram illustrating out-of-plane gyro detection. Rotation as shown (relative to FIG. 1, relative to the Z axis) induces motion (along FIG. 1, along the Y axis) in the inertial masses 102, 104. As described below, the plurality of out-of-plane sensing electrode pairs sense the shown rotation of the inertial sensor 100.

7 is a conceptual diagram illustrating out-of-plane linear acceleration sensing. Linear acceleration as shown (see FIG. 1 along the Z axis) induces movement in the opposite direction in the inertial masses 102 and 104 (also along FIG. 1 along the Z axis). One or more in-plane sensing electrode pairs sense the shown rotation of the inertial sensor 100 as described below.

8 is a conceptual diagram illustrating in-plane linear acceleration sensing. Linear acceleration (shown along the Y axis, see FIG. 1) as shown is a motion with a smaller magnitude in the opposite direction relative to the motion of the inertial sensor 100 on the inertial masses 102, 104 (also along the Y axis, FIG. 1). Induction). One or more in-plane sensing electrode pairs sense the illustrated acceleration of the inertial sensor 100 as described below.

9 and 10 show examples of some of other embodiments of inertial sensors 100 that measure the rotational speed about two orthogonal axes. Some of the embodiments of inertial sensor 100 include two tuning fork inertial masses 24 and 26, a motor charge amplifier 44, a sense charge amplifier 50, a processing device 54, and an output device ( 56). Inertial masses 24 and 26 are disposed on top of the substrate that includes out-of-plane turning force sensing electrodes 40 and 42 that are sensitive to out-of-plane inertial mass motion. The sensor 20 also includes two in-plane anti-force sensing electrodes 63 comprising a plurality of interleaved comb fingers sensitive to in-plane inertial mass motion. The motor driver element 60 is electrically connected to the drive comb 62. The motor charge amplifier 44 is electrically connected to the plurality of sense combs 64.

The inertial masses 24 and 26 are driven to resonate and oscillate in the X axis direction. The inertial masses 24, 26 are driven to vibrate out of phase by the motor driver element 60. On opposite sides of the inertial masses 24, 26 are fingers (combs) interleaved with the fingers of the drive sensing comb 64. The motor charge amplifier 44 is a processing device that generates a motor driver signal transmitted to the motor drive comb 62 through the motor driver element 60 to ensure that the inertial masses 24, 26 are driven at a mechanical resonant frequency. The motor signal is output to 54.

In-plane anti-force sensing electrode to allow detection of fluctuations in capacitance with respect to in-plane motion of the inertial masses 24, 26 in the Y-axis direction induced by rotation about the Z axis (direction perpendicular to the motor motion). 63 is asymmetrical from the motor drive comb 62 and drive sense comb 64 of the inertial mass 24.

In the first embodiment, both inertial masses 24 and 26 are electrically connected to the charge amplifier 50 for outputting a voltage signal to the processing device 54. The output voltage signal is received by the processing device 54. The voltage signal applied to the in-plane turning force electrode 63 is modulated at a first frequency, and the voltage signal applied to the out-of-plane turning force electrodes 40 and 42 is modulated at a second frequency different from the first frequency. Processing device 54 includes a demodulator that demodulates all modulated frequencies. The modulation frequency can be removed far from the mechanical resonance of the sensor 20. After the processing device 54 demodulates the received signal according to the first frequency, the processing device 54 analyzes the demodulated signal to determine if a rotational speed has occurred about the Z axis. Processing device 54 then demodulates the received signal at the modulated second frequency to determine the rotational speed about the Y axis. The determined rotation speed value is output through the output device 56.

11 shows another example system 70 for sensing the rotational speed about two separate axes. The system 70 includes the same motor driver element 60, inertial masses 24 and 26, electrodes 40a and 42a and combs 62 and 64 as in FIG. System 70 includes a processing device 54 that receives signals from electrodes 40a and 42a and from in-plane sensing comb 63. In this example, inertial masses 24 and 26 are biased to a predefined voltage, such as ground. In one embodiment, the separate processing devices 54 are two separate devices for determining the rotation speed value for each rotation axis. The determined rotation speed value is output through the output device 56.

12 is a conceptual side view of one embodiment of an inertial sensor 100. Here, the inertial masses 102, 104 are shown aligned with respect to each other along the X axis. The bend 302 supports the left inertial mass 102 between the gaps G _ULS , G _LLS . The bend 304 supports the right inertial mass 104 between the gaps G _URS , G _LRS . Flexures 302 and 304 are attached to anchor 306. In other embodiments anchor 306 may be attached to upper substrate 310 or attached to both substrates 308, 310, but anchor 306 is attached to lower substrate 308 in this exemplary embodiment. The bends 302, 304 are flexible members having properties similar to springs such that the inertial masses 102, 104 resonate when the inertial masses 102, 104 are driven by drive electrodes (not shown).

In other embodiments, anchor 306 may be attached to upper substrate 310. Some embodiments may employ a plurality of bends to connect the inertial masses 102, 104 to the various anchor points in the MEMS device. In some embodiments, the bends 302 and 304 may be connected to different anchors.

In an exemplary embodiment of the inertial sensor 100, the inertial masses 102, 104 may be suspended such that the gaps G _ULS , G _LLS and the gaps G _URS , G _LRS are equal to each other. Thus, the upper and lower capacitances associated with the inertial masses 102 and 104 and the out-of-plane electrodes shown are substantially the same (relative to each other). For example, assuming that the surface area and other properties of the electrodes 206, 214, 228, and 236 are substantially the same, the capacitance between the electrode 206 and the left inertial mass 102, the electrode 214 and the left inertial mass The capacitance between 102, the capacitance between the electrode 228 and the right inertial mass 104, and the capacitance between the electrode 236 and the right inertial mass 104 are substantially the same. In other embodiments, the capacitances may be different from one another.

Linear acceleration in the direction along the Z axis shown causes the inertial masses 102, 104 to move at substantially the same speed and / or distance in the same direction. This movement is referred to herein as the movement in the "common mode". The common mode motion of the inertial masses 102, 104 traverses substantially the same fluctuations and gaps G _LLS , G _LRS in the electrode-inertial mass capacitance of the out-of-plane electrode pair across the gap G _ULS , G _URS . The same variation occurs in the electrode-inertial mass capacitance of the out-of-plane electrode pair. That is, if the upper and lower gaps (G _URS , G _LRS , G _ULS , G _LLS ) are assumed to be the same (ie, equilibrium), the variation of the out-of-plane electrode pair across the gaps G _ULS , G _URS The magnitude of the capacitance and the variation of the capacitance of the out-of-plane electrode pair across the gaps G _LLS and G _LRS are substantially the same. Although the gaps G _ULS , G _LLS , G _URS , G _LRS are not equilibrium, the upper capacitance is substantially the same since the forces for moving the inertial masses 102, 104 that provide a variation in capacitance are substantially the same. And the lower capacitance fluctuates substantially the same amount. Linear acceleration can be determined from the sensed common mode variation in capacitance.

Also, rotation in the direction around the Y axis shown causes the inertial masses 102, 104 to move at substantially the same speed and / or distance in the Z direction in the opposite direction. This movement is referred to herein as the movement in a " differential mode. &Quot; The differential mode motion of the inertial masses 102 and 104 is generated by the turning force. The differential mode motion (in the opposite direction) of the inertial masses 102, 104 is a substantially equal magnitude of variation in the electrode-inertial mass capacitance of the electrode pair across the gap G _ULS , G _LRS , and the gap G _LLS , G _LLS ) produces substantially the same magnitude of variation in the electrode-inertial mass capacitance of the electrode pair. Rotation can be determined from the sensed differential mode variation in capacitance.

As mentioned above, embodiments of the inertial sensor 100 provide a separation between acceleration sensing and rotation sensing such that rotation and acceleration are independently sensed and determined. In a preferred embodiment, the quadrature force, which is a phase 90 degrees away from the turning force, is also separated from the acceleration and turning force. Thus, linear acceleration, in order to maintain the position of the inertial masses 102, 104 in a fixed position such that the capacitance associated with the corresponding electrode pair across the gaps G _ULS , G _LLS , G _URS , G _LRS is substantially matched The rebalance force for the turning force and / or the orthogonal force is applied separately to the electrode pair. Thus, if an unbalance between the positions of the inertial masses 102, 104 occurs (detectable from variations in the electrode-inertial mass capacitance of the electrode pair across the gaps G _ULS , G _LLS , G _URS , G _LRS ) The rebalancing forces the masses of inertial masses 102 and 104 to center themselves.

The forward rebalance force is applied to the inertial mass 102 by the selected electrode pair. The forward force rebalance force is also applied to the inertial mass 104 by another selected electrode pair. The applied forward force rebalancing forces the inertial masses 102 and 104 to center themselves during the rotation of the inertial sensor 100. The amount of forward rebalance that is required corresponds to the amount of rotation. Similarly, the applied linear acceleration rebalance forces center the inertial masses 102 and 104 themselves during the linear acceleration of the inertial sensor 100. The magnitude of the linear acceleration rebalance force required corresponds to the linear acceleration amount. Since the linear acceleration rebalance force is provided by the direct current (DC) voltage applied to the selected electrode pair, the linear acceleration rebalance force can be distinguished from the forward rebalance force. That is, since linear acceleration (inducing time-varying acceleration in the Z axis) is different from rotation (inducing a modulated force at the drive frequencies of the inertial masses 102, 104), linear acceleration rebalance and forward rebalance Can be determined individually.

13 is a conceptual side view of one embodiment of an inertial sensor 100 having an applied initialization rebalance force 402 shown as a vector 402. The selected out-of-plane electrode can be operated to apply an initial rebalancing force to the corresponding inertial masses 102, 104. Therefore, the gaps G _ULS , G _LLS , G _URS , and G _LRS may be set equal to each other or to a desired value.

For example, as conceptually shown in FIG. 13, while manufacturing the inertial sensor 100, the left inertial mass 102 has its own designed ideal location 404 (predetermined herein) between the out-of-plane electrodes. May be interchanged with location 404). Here, the left inertial mass 102 is shown in the non-ideal position 406 such that the gaps G _ULS , G _LLS are not substantially equal. The non-ideal position 406 of the left inertial mass 102 may be acceptable from a manufacturing point of view but may be sufficiently different from the ideal position 404 as a result of design and / or manufacturing tolerances such that linear acceleration and / or rotational motion Inaccuracy can be provided in the detection of. An initial rebalancing force, shown as a vector 402, is applied by one or more selected out-of-plane electrodes to reposition the left inertial mass 102 to or very close to the designed ideal position 404. The initial rebalance force may be the same or different depending on the amount of initial rebalance required to place the inertial mass in an ideal position. Preferably, the initial rebalance force is generated from the DC bias applied to the selected electrode. The initial rebalance force may be determined before use of the inertial sensor 100, such as by post-fabrication bench testing.

14 is a conceptual side view of one embodiment of an inertial sensor 100 having an applied linear acceleration represented by an acceleration vector 502 (corresponding to movement in the negative Z axis direction). Inertial forces (shown as vectors 504) are applied to the inertial masses 102, 104. Thus, the inertial masses 102 and 104 are moved toward the upper substrate 310 during the acceleration period. The bends 302, 304 will operate to return the inertial masses 102, 104 to their initial position (see FIG. 12) when acceleration stops.

The aforementioned common mode motion of the inertial masses 102, 104 is substantially at the electrode-inertial mass capacitance of the electrode pair across the gap G _ULS , G _LLS and the pair of electrodes across the gap G _URS , G _LRS . Each produces the same variation. That is, the magnitude of the changed electrode-inertial mass capacitance of the electrode pair across the gaps G _ULS , G _URS and the magnitude of the varied electrode-inertial mass capacitance of the electrode pair across the gaps G _LLS , G _LRS Substantially the same. In response to the motion of the inertial masses 102 and 104, a linear acceleration rebalance force may be applied through the selected electrode pair to reposition the inertial masses 102 and 104 back to their original or predetermined positions. Linear acceleration can be determined from the amount of applied linear acceleration rebalance force and / or from the sensed common mode variation in capacitance.

15 is a conceptual side view of one embodiment of an inertial sensor 100 having an applied rotation represented by a rotation vector 602 (corresponding to a rotational motion about the Y axis). When the inertial masses 102, 104 move outwards (see vectors 114, 116), an inertial force, shown as vectors 604, 606, is applied to the inertial masses 102, 104, respectively. Thus, during this portion of the motor drive cycle, the inertial mass 102 is moved towards the upper substrate 310 during the rotational period, and the inertial mass 104 is moved towards the lower substrate 308 during the rotational period. During the next portion of the motor drive cycle, when the inertial masses 102 and 104 move inward, the aforementioned inertial forces applied to the inertial masses 102 and 104 reverse (or change direction). The bends 302, 304 will operate to return the inertial masses 102, 104 to their initial position (see FIG. 12) when rotation stops.

The aforementioned differential mode motion of inertial masses 102 and 104 results in a detectable variation in the electrode-inertial mass capacitance of the electrode pair across the gaps G _ULS , G _LLS , G _URS , G _LRS . The magnitude of the varied electrode-inertial mass capacitance of the electrode pair across the gap G _ULS , G _LRS and the magnitude of the varied electrode-inertial mass capacitance of the electrode pair across the gap G _LLS , G _URS The same (assuming initial equilibrium of gaps G _URS , G _LRS , G _ULS , G _LLS ). In response to the movement of the inertial masses 102 and 104, a forward force rebalance force may be applied through the selected electrode pair to relocate the inertial masses 102 and 104 to their original or predetermined positions. Rotation can be determined from the applied forward force rebalance force and / or from the sensed differential mode variation in capacitance.

FIG. 16 shows applied and sensed voltages for some of the embodiments of the inertial sensor 100 shown in FIG. 1. The voltages V _ULS , V _LLS applied by the electrode pairs 106, 108 and the voltages V _URS , V _LRS applied by the electrode pairs 110, 112 partially correspond to linear acceleration rebalance forces. .

The applied voltage has three components that provide three functions: linear acceleration rebalance, rotation sense bias, and acceleration sense pickoff. The applied upper left sense plate voltage V _ULS may be defined by Equation 1 below.

Here, V _SB is a sense bias voltage (DC bias voltage) applied for rotation sensing. V _A is the linear acceleration rebalance force voltage applied. V _p is the applied AC pickoff voltage for acceleration sensing. And ω _p is the frequency of the applied AC pickoff voltage V _p . The current i _SPO arises from an unbalance at the position of the inertial masses 102, 104.

The applied lower left sense plate voltage (V _LLS ), the applied upper right sense plate voltage (V _URS ), and the applied lower right sense plate voltage (V _LRS ) are defined by the following equations (2), (3) and (4), respectively. Can be.

Amplifier system 702 is communicatively coupled to detect voltage and / or current from inertial masses 102 and 104. The output of the amplifier system 702 corresponds to the sensed pickoff voltage V _SPO . V _SPO may be defined by Equation 5 below.

Where V _Ω is the V _SPO portion proportional to the rotational motion, V _Q is the orthogonal component of V _Ω , V _CM is the V _SPO portion proportional to the common mode motion (generated by linear acceleration), and ω _pm is The motor frequency applied.

17 shows the applied voltage and sense voltage for some of one embodiment of inertial sensor 100. The aforementioned applied voltages V _ULS , V _LLS , corresponding to the linear acceleration rebalance forces applied to the inertial mass 102 by the electrodes 208, 216 and to the inertial mass 104 by the electrodes 226, 234. V _URS , V _LRS ). Other embodiments may apply a linear acceleration rebalance force using differently selected electrodes. In some embodiments, electrodes 208, 216, 226, 234 can be used to inject a current (or voltage) used for sensed common mode motion and / or differential mode motion of inertial masses 102, 104.

Electrode pairs 210 and 218 provide a forward force rebalance force to inertial mass 102. Similarly, electrode pairs 224, 232 provide a forward force rebalance force to inertial mass 104. Preferably, the forward force rebalance force applied to the inertial mass 102 has the same magnitude in the opposite direction as the forward force rebalance force applied to the inertial mass 104. Other embodiments may apply a forward force rebalancing force using differently selected electrodes.

The forward force rebalance force corresponding to V _CUL applied by the electrode 210 may be defined by Equation 6 below.

Where V _COR is the forward voltage and ω _m t / 2 is the half frequency of the motor frequency of the inertial masses 102 and 104.

A forward force rebalance force corresponding to V _CLL applied by electrode 218, a forward force rebalance force corresponding to V _CUR applied by electrode 224, and a V _CLR applied by electrode 232. The forward rebalance can be defined by Equations 7, 8 and 9, respectively.

Some embodiments may apply an optional orthogonal rebalance force through the optional electrodes 206, 214, 218, and 236. The orthogonal rebalance force is proportional to the induced motor motion of the inertial masses 102 and 104. In the exemplary embodiment shown in Figures 12-17, four electrodes are shown (at each end of inertial masses 102, 104) used for the application of the orthogonal rebalance force. In another embodiment, one electrode pair may be used to apply an orthogonal rebalance force for each of the inertial masses 102 and 104. A pair of orthogonal rebalance electrodes can be disposed in a suitable position with respect to the inertial masses 102, 104. In other embodiments, the orthogonal rebalance electrode is optional or not used.

18 shows applied and sensed voltages for another embodiment of inertial sensor 100. Electrodes 208, 216, 226, 234 are connected to pickoff amplifier systems 902, 904, 906, 908, respectively, to sense or pick off voltage at the corresponding electrode. This embodiment allows compensation of parasitic signals injected into the inertial masses 102 and 104, which can generate undesirable applied parasitic forces. That is, since the frequency of the parasitic term is higher than (ω _p + ω _m / 2), the parasitic coupling effect between the rotational force and the linear acceleration force may be reduced.

Amplifier system 902 outputs signal V _ULSP . Amplifier systems 904, 906 and 908 output signals V _LLSP , V _URSP and V _LRSP , respectively. The rotational output V _RATE can be derived from the output of the amplifier system 902, 904, 906, 908 according to Equation 10 below.

19 is a block diagram illustrating an example implementation of a processing system 1002 coupled to a portion of one embodiment of an inertial sensor 100. In an exemplary embodiment, the processing system is a digital signal processing (DSP) electronic system. Processing system 1002 may be implemented as an analog system, as a digital system, or as a combination thereof, depending on the particular application, and may be implemented as software, hardware or a combination of hardware and software.

Amplifier system 702 provides the sensed pickoff voltage V _SPO to processing system 1002. Demodulators 1004, 1006, 1008 demodulate V _SPO by stripping off the AC portion of V _SPO . The 90 degree clock applied to the demodulator 1004 and the 0 degree clock applied to the demodulator 1006 correspond to motor signals multiplied in different phases (90 degree phase and 0 degree phase, respectively).

The low pass filter 1010 processes the output of the demodulator 1004 and outputs a forward force output signal to a proportional-integral-derivative (PID) controller 1012. The low pass filter 1014 and the PID controller 1016 process the output of the demodulator 1006 and output an orthogonal output signal. The low pass filter 1018 and the PID controller 1020 process the output of the demodulator 1008 and output an acceleration output signal corresponding to the common mode unbalance in capacitance. The output signal is used to generate the outputs V _ULS , V _LLS , V _URS , V _LRS corresponding to the aforementioned linear acceleration rebalance forces, and the outputs V _CUL , V _CLL , V corresponding to the aforementioned deflection rebalance forces. _CUR , V _CLR ).

Embodiments of the inertial sensor 100 that can be used to detect and determine linear acceleration and rotation can be included as an inertial measurement unit. Since one inertial sensor 100 senses linear acceleration in two axes and rotation in two axes, if properly oriented, two inertial sensors (not three gyroscopes and three accelerometers used in conventional inertial measurement units) 100) can be used to build one inertial measurement unit.

As described above, although the preferred embodiment of the present invention has been illustrated and described, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely with reference to the following claims.

Preferred and other embodiments have been described above with reference to the following drawings:

1 is a conceptual perspective view of an electrode and an inertial mass for a portion of one embodiment of an inertial sensor;

2 is a top view of one exemplary embodiment of an inertial sensor;

3 is a top view of an exemplary embodiment of an inertial sensor illustrating a drive electrode having a comb interleaved with two inertial masses.

4 is a side view of an exemplary embodiment of an inertial sensor;

5 is a conceptual diagram illustrating in-plane gyro sensing;

6 is a conceptual diagram illustrating out-of-plane gyro sensing;

7 is a conceptual diagram illustrating out-of-plane linear acceleration sensing;

8 is a conceptual diagram illustrating in-plane linear acceleration sensing;

9 shows a top view of a portion of an embodiment of an inertial sensor;

10 shows a partial cross-sectional view of the system of FIG. 9;

11 shows another exemplary system 70 for sensing the rotational speed about two separate axes;

12 is a conceptual side view of a portion of one embodiment of an inertial sensor;

FIG. 13 is a conceptual side view of a portion of one embodiment of an inertial sensor with applied reset rebalance force; FIG.

14 is a conceptual side view of a portion of one embodiment of an inertial sensor 100 with applied linear acceleration;

15 is a conceptual side view of a portion of one embodiment of an inertial sensor 100 with applied rotation;

16 shows applied and sensed voltages for some of one embodiment of an inertial sensor;

17 and 18 show the sensing voltage and sensing voltage before embodiments of the inertial sensor; And,

19 is a block diagram illustrating an example implementation of a digital signal processing system coupled to one embodiment of an inertial sensor.

<Explanation of symbols for the main parts of the drawings>

100: inertial sensor

102: left inertial mass

104: right inertia mass

106, 108, 114, 116: electrode

702: amplifier system

1002: processing system

1010, 1014, 1018: low pass filter

1012, 1016, 1020: PID controller

Claims (10)

The first inertial mass 102 and the second inertial mass 104 aligned with the in-plane axis, the first out-of-plane electrode pairs 106 and 108 with the first inertial mass interposed therebetween, and the second inertial mass A first in-plane sensing comb 124 having a second out-of-plane electrode pair 114, 116 disposed therebetween, a plurality of comb fingers 128 interleaved with opposing first inertial mass comb fingers, and opposing first A method of sensing linear acceleration and rotation of a MEMS sensor 100 having a second in-plane sensing comb 126 having a plurality of comb fingers 128 interleaved with a two inertial mass comb finger, Sensing out-of-plane linear acceleration of the MEMS sensor using the first out-of-plane electrode pair and the second out-of-plane electrode pair; Detecting in-plane rotation of the MEMS sensor using the first out-of-plane electrode pair and the second out-of-plane electrode pair; Sensing in-plane linear acceleration of the MEMS sensor using the first in-plane sensing comb and the second in-plane sensing comb; And Sensing out-of-plane rotation of the MEMS sensor using the first in-plane sensing comb and the second in-plane sensing comb; Linear acceleration and rotation detection method comprising a. The method of claim 1, Detecting the out-of-plane linear acceleration and the in-plane linear acceleration from the common mode motion of the first and second inertial masses; And Sensing the out-of-plane rotational acceleration and the in-plane rotation from the differential mode motion of the first and second inertial masses; Linear acceleration and rotation detection method comprising a. The method of claim 1, Detecting the out-of-plane linear acceleration of the MEMS sensor by using the first out-of-plane electrode pair and the second out-of-plane electrode pair, Sensing out-of-plane linear acceleration of the first inertial mass using the first out-of-plane electrode pair; And Sensing out-of-plane linear acceleration of the second inertial mass using the second out-of-plane electrode pair; Linear acceleration and rotation detection method comprising a. The method of claim 1, Detecting in-plane rotation of the MEMS sensor using the first out-of-plane electrode pair and the second out-of-plane electrode pair, Sensing in-plane rotation of the first inertial mass using the first out-of-plane electrode pair; And Sensing in-plane rotation of the second inertial mass using the second out-of-plane electrode pair; Linear acceleration and rotation detection method comprising a. The method of claim 1, Detecting in-plane linear acceleration of the MEMS sensor using the first in-plane sensing comb and the second in-plane sensing comb, Sensing in-plane linear acceleration of the first inertial mass using the first in-plane sensing comb; And Sensing in-plane linear acceleration of the second inertial mass using the second in-plane sensing comb; Linear acceleration and rotation detection method comprising a. The method of claim 1, Detecting the out-of-plane rotation of the MEMS sensor using the first in-plane sensing comb and the second in-plane sensing comb, Sensing out-of-plane rotation of the first inertial mass using the first in-plane sensing comb; And Sensing out-of-plane rotation of the second inertial mass using the second in-plane sensing comb; Linear acceleration and rotation detection method comprising a. The method of claim 1, Applying a first orthogonal rebalance force to the first inertial mass using a third out-of-plane electrode pair; And Applying a second orthogonal rebalance force to the second inertial mass using a fourth out-of-plane electrode pair; Linear acceleration and rotation detection method further comprising. A first inertial mass 102 having a plurality of in-plane comb fingers 128 and a first drive comb 146, the first drive comb configured to drive the first inertial mass in an oscillating motion along an in-plane axis ; A second inertial mass 104 aligned with the first inertial mass along the in-plane axis, the second inertial mass 104 having a plurality of in-plane comb fingers 128 and a second drive comb 146-the second drive comb being the second; Configured to drive an inertial mass along an in-plane axis in an opposite oscillating movement substantially 180 degrees out of phase from the oscillating movement of the first inertial mass; The first inertial mass disposed between and configured to sense a first out-of-plane motion of the first inertial mass corresponding to an in-plane rotation of the MEMS sensor and corresponding to an out-of-plane linear acceleration of the MEMS sensor First out-of-plane electrode pairs 106 and 108 configured to sense a second out-of-plane motion of the first inertial mass; The second inertial mass disposed between and configured to sense the first out-of-plane motion of the second inertial mass corresponding to in-plane rotation of the MEMS sensor, A second out-of-plane electrode pair (114, 116) configured to sense the second out-of-plane motion of the corresponding second inertial mass; And a plurality of comb fingers interleaved with opposing comb fingers of said first inertial mass, and configured to sense in-plane motion of said first inertial mass corresponding to out-of-plane rotation of said first inertial mass; A first in-plane sensing comb (124) configured to sense in-plane motion of the first inertial mass corresponding to in-plane linear acceleration of the first inertial mass; And A plurality of comb fingers interleaved with the opposing comb fingers of the second inertial mass, configured to sense out-of-plane rotation of the second inertial mass, and configured to sense in-plane linear acceleration of the second inertial mass Second in-plane sensing comb 126; MEMS sensor 100 for determining the linear acceleration and rotation comprising a. The method of claim 8, Coupled to at least one of the first and second out-of-plane electrode pairs, and configured to determine a first capacitance between the top of the out-of-plane electrode pairs and between the bottom of the out-of-plane electrode pairs. A processing device (1002) configured to determine a second capacitance and configured to determine an initialization rebalance force applied to the first inertial mass; MEMS sensor for determining the linear acceleration and rotation further comprising. The method of claim 8, An amplifier system (702) coupled to the first inertial mass and the second inertial mass and configured to generate a pickoff voltage signal; A first low pass filter (1010) coupled to the amplifier system and configured to pass a first portion of the pickoff voltage signal; A first proportional-integral-derivative (PID) controller (1012) coupled to the first low pass filter and configured to output a forward force rebalance signal in accordance with the first portion of the pickoff voltage signal; A second low pass filter (1014) coupled to the amplifier system and configured to pass a second portion of the pickoff voltage signal; A second PID controller (1016) coupled to the second low pass filter and configured to output an orthogonal rebalance signal in accordance with the second portion of the pickoff voltage signal; A third low pass filter (1014) coupled to the amplifier system and configured to pass a third portion of the pickoff voltage signal; And A third PID controller (1020) coupled to the second low pass filter and configured to output an acceleration rebalance signal in accordance with the third portion of the pickoff voltage signal; MEMS sensor for determining the linear acceleration and rotation further comprising.

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