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    • 专利摘要:
    DOUBLE AND TRIPLE SHAFT INERIAL SENSORS AND INERIAL DETECTION METHODS An inertial sensor comprising: a frame; a test piece suspended from the frame; a pair of first resonant elements electrically coupled to the test mass, or to an intermediate component mechanically coupled to the test mass, each first resonant element coupled to one side opposite the test mass to the other, the first resonant elements being substantially identical to each other and having substantially identical electrostatic coupling with the test mass when the sensor is not accelerating; in which the first resonant elements and the test mass are substantially located in one plane, and in which the movement of the test mass in relation to the first resonant elements orthogonal to the plane, changes the electrostatic coupling between the test mass and the first elements resonants; drive means coupled to the first resonant elements to vibrate each of the first resonant elements; and a sensor array for detecting a change in the resonant frequency of each of the first resonant elements; and processing medium to sum up the changes of each of the first resonant elements to provide a measure of the acceleration of the test mass (...).
    公开号:BR112015004404B1
    申请号:R112015004404-2
    申请日:2013-09-04
    公开日:2021-01-26
    发明作者:Ashwin Arunkumar Seshia；Pradyumna Thiruvenkatanathan；Xudong Zou
    申请人:Cambridge Enterprise Limited；
    IPC主号:
    专利说明:

    FIELD OF THE INVENTION
    [0001] The present invention relates to inertial sensors and inertial detection methods using microscopic mechanical inertial sensors. Specifically, the information refers to inertial sensors that can be readily manufactured and are capable of detecting in two or three orthogonal directions using only a single suspended test mass. BACKGROUND OF THE INVENTION
    [0002] Oscillators based on lightly damped microscopic mechanical resonators are well known for their ability to produce stable, low-noise frequency outputs. While these characteristics make them valuable in communication systems as stable timing / frequency references, they are also attractive for use as sensors. A resonant sensor, by definition, is an oscillator whose output frequency is a function of an input measurement result. In other words, the output of a resonant sensor corresponds to the change in resonant frequency of a mechanical microstructure that becomes tuned according to a change in a physical / chemical quantity to be measured. The almost digital nature of the output signal in such sensors, together with the high sensitivity and stability of the output signals of altered frequency, has resulted in widespread use of such micro-machined resonant sensors for various applications ranging from biomolecular and chemical diagnostics, high precision force, mass, tension and even load detection.
    [0003] As a specific case of resonant sensors, there has been a greater interest in recent years in the development of high precision micro-machined resonant micro-accelerometers “all-silicon”. See, for example: US5969249; US4851080; US2011 / 0056294; CN101303365. This interest was sparked due to the recent growth in demand for miniature high-precision motion sensors within the aerospace, automotive and even consumer electronics markets. The resonant micro-accelerometers manufactured using silicon micro-machining techniques have some significant advantages, the largest of which is the economy. These resonant silicon micro-accelerometers not only enhance enhanced sensitivity and resolution compared to their counterparts based on traditional capacitive detection with similar device footprint, but have also been shown to provide enhanced dynamic range making the same ideal candidates for potential application in various motion detection applications within the identified markets.
    [0004] However, most of these sensors still remain uniaxial or biaxial, consequently limiting their functionality and practical applicability to those applications that do not require sophisticated three-dimensional (3D) motion control. Although orthogonally oriented, uniaxial resonant micro-accelerometers can potentially be used for accurate, three-dimensional altered frequency movement / acceleration reading, such implementations correspondingly increase the cost, size and energy requirements of the device.
    [0005] An objective of the present invention is to provide a resonant micro machined silicon accelerometer that allows reading of two and three-dimensional acceleration using only a single suspended test mass. SUMMARY OF THE INVENTION
    [0006] The invention is defined in the attached independent claims, to which reference must be made. Optional features are presented in the dependent claims.
    [0007] In a first aspect of the invention, an inertial sensor is provided comprising: a frame; a test piece suspended from the frame; a pair of first resonant elements electrically coupled to the test mass, or to an intermediate component mechanically coupled to the test mass, each first resonant element coupled to one side opposite the test mass to the other, the first resonant elements being substantially identical to each other and having substantially identical electrostatic coupling with the test mass when the sensor is not accelerating; in which the first resonant elements and the test mass are substantially located in one plane, and in which the movement of the test mass in relation to the first resonant elements orthogonal to the plane, changes the electrostatic coupling between the test mass and the first elements resonants; drive means coupled to the first resonant elements to vibrate each of the first resonant elements; and a sensor array for detecting a change in the resonant frequency of each of the first resonant elements; and processing means to sum up the changes of each of the first resonant elements to provide a measure of acceleration of the test mass parallel to a first axis, the first axis being orthogonal to the plane.
    [0008] Any change in the electrostatic coupling between the test mass and a resonant element results in a change in the effective stiffness of that resonant element, which changes the resonant frequency of the resonant element. In this context, "detecting a change in the resonant frequency" should be understood as including both, directly detecting a change in the resonant frequency and indirectly detecting a change in the resonant frequency by detecting a change in another aspect of the resonant response of the resonant element.
    [0009] By adding the changes in the resonant frequency any contribution is removed from the movement in the plane of the test mass towards or away from the resonant elements, so that acceleration outside the plane can be decoupled and determined. As each of the first resonant elements is mounted on opposite sides of the test mass, any movement in the plane will result in a change of equal magnitude, but in the opposite direction in each resonant element. Preferably, the test mass and the resonant elements are configured in such a way that the movement of the tangential test mass to the first resonant elements does not alter the electrostatic coupling. For example, the sides of the test mass to which the first resonant elements are attached can be uniform in thickness and extend parallel to the tangential direction, in addition to the first resonant elements in the tangential direction.
    [0010] Any suitable resonant elements can be used, such as double-ended tuning tuning resonators.
    [0011] The sensor can also comprise a second resonant element coupled to the test mass, the second resonant element configured to allow the detection of acceleration parallel to a second axis, orthogonal to the first axis; wherein the drive means is coupled to the second resonant element to vibrate the second resonant element, and the sensor assembly detects a change in the resonant frequency of the second resonant element. The second resonant element is preferably mechanically coupled to the test mass.
    [0012] The inertial sensor can also comprise a third resonant element coupled to the test mass, the third resonant element configured to allow the detection of acceleration parallel to a third axis, where the third axis is orthogonal to the first axis and the second axis ; wherein the drive means is coupled to the third resonant element to vibrate the third resonant element, and the sensor assembly detects a change in the resonant frequency of the third resonant element. The third resonant element is preferably mechanically coupled to the test mass.
    [0013] The second and third resonant elements allow acceleration in the plane of the test mass to be measured. The combination of the first, second and third resonant elements provides a rail-axis accelerometer using only a single suspended test mass.
    [0014] The sensor can comprise a pair of third resonant elements, each third resonant element positioned on the opposite side of the test mass to the other, the third resonant elements being identical to each other, and a pair of second resonant elements, each second element resonant positioned on the opposite side of the test mass to the other, the second resonant elements being identical to each other. By providing identical pairs of resonant elements, a differential reading can be used so that frequency fluctuations resulting from environmental factors such as temperature and pressure variations, can be eliminated from the measurement of acceleration in the plane.
    [0015] In addition, a common mode reading from one or both pairs of seconds and third resonant elements can provide an output that is indicative of temperature with a rejection of first order variations in frequency due to acceleration. Taking the sum (common mode) and difference (differential) readings, a multi-parameter sensor is provided. The ability to determine temperature, or changes in temperature, is of interest in many applications in which accelerometers are used. Temperature measurement can also be used in combination with the acceleration reading to provide a more accurate determination of the acceleration. The relationship between resonant frequency and temperature can have second order or higher order terms and the temperature measurement can be used to calculate any second order or higher order terms, which are then considered when calculating the acceleration from the detected resonant frequency changes.
    [0016] The inertial sensor can also comprise a mechanical stage between the test mass and the frame, the mechanical stage configured to decouple the movement of the test mass in two orthogonal directions in the plane, in which the second or third resonant elements, or both, the second and third resonant elements, are mechanically coupled to the mechanical stage. This allows for reduced cross-axis sensitivity and, as a consequence, simpler processing of the outputs from the sensor.
    [0017] The inertial sensor may also comprise a fourth resonant element, in which the fourth resonant element is substantially identical to the first resonant elements and is not electrically coupled to the test mass. The fourth resonant element, or a pair of fourth resonant elements, can be used to provide a differential reading with the first pair of resonant elements, to eliminate environmental factors such as temperature and pressure, by measuring out-of-plane acceleration.
    [0018] The inertial sensor can also comprise at least one amplification lever coupled between the test mass or mechanical stage between one end of the first, second or third resonant elements. The amplification lever is designed to be a force amplifier when coupled to the second and third resonant elements to increase the inertial force communicated to the resonant elements for a given induced acceleration, and as a consequence to increase the device's scale factor. The frame, the test mass and the resonant elements can all be formed from machined silicon.
    [0019] The invention provides a micro machined silicon resonant accelerometer that offers the main advantages of improved sensitivity and dynamic range as in the case of most resonant accelerometers reported to date, but also allows a three-dimensional altered frequency acceleration reading, with improved transverse axis rejection, using only a single suspended test mass. Such an implementation allows a reduction in the costs of manufacturing such sensors, and allows a reduction in the size and consequently in the occupied space of the device - another essential determining factor of installation costs in various applications, especially within consumer electronics.
    [0020] In another aspect, the invention provides a method of measuring off-plane acceleration using a micro machined flat inertial sensor, the inertial sensor comprising: a frame; a test piece suspended from the frame; a pair of first resonant elements electrically coupled to the test mass, each first resonant element coupled to an opposite side of the test mass to the other, the first resonant elements being substantially identical to each other and having electrostatic coupling substantially identical to the test mass when the sensor is not accelerating; where the first resonant elements and the test mass are located substantially on a plane, and where the movement of the test mass in relation to the first resonant elements orthogonal to the plane alters the electrostatic coupling between the test mass and the first resonant elements ; and drive means coupled to the first resonant elements to vibrate each of the first resonant elements; the method comprising: detecting a change in the resonant frequency of each of the first resonant elements; and adding the changes of each of the first resonant elements to provide a measure of the acceleration of the test mass parallel to the first axis, the first axis being orthogonal to the plane.
    [0021] In a further aspect, the invention provides an inertial sensor comprising: a frame; a mechanical stage suspended from the frame, a test mass suspended from the mechanical stage, the mechanical operative stage for decoupling movement of the test mass in two orthogonal directions; a first resonant element coupled to a first portion of the mechanical stage, the first portion of the mechanical stage free to move parallel to a first axis; a second resonant element coupled to a second portion of the mechanical stage, the second portion of the mechanical stage free to move parallel to a second axis, the second axis being orthogonal to the first axis; drive means coupled to the resonant elements to vibrate each of the resonant elements; and a sensor array for detecting a change in the resonant frequency of each of the first and second resonant elements.
    [0022] The combination of a stage that decouples the X and Y axis movement from the test mass with resonant acceleration detection provides an effective and accurate dual-axis accelerometer, inexpensive using only a single suspended test mass.
    [0023] The inertial sensor can also comprise at least one amplification lever, such as a mechanical force amplification lever, coupled between the mechanical stage and one of the first and second resonant elements.
    [0024] The inertial sensor may comprise a pair of first resonant elements, each of the first resonant elements disposed on opposite sides of the mechanical stage and being substantially identical to each other. The inertial sensor may comprise a pair of second resonant elements, each of the second resonant elements disposed on opposite sides of the mechanical stage and being substantially identical to each other. By providing identical pairs of resonant elements, a differential reading can be used so that frequency fluctuations resulting from environmental factors, such as temperature and pressure variations, can be eliminated from the measurement of acceleration in the plane. In addition, a common mode reading from one or two pairs of seconds and third resonant elements can provide an output that is indicative of temperature, with a rejection of first order variations in frequency due to acceleration. Taking both readings, sum (common mode) and difference (differential), a multi-parameter sensor is provided.
    [0025] The initial sensor can also include at least a third resonant element electronically coupled to the test mass or mechanical stage, in which the acceleration of the test mass in a direction orthogonal to the first and the second axis changes the electrostatic coupling between the third resonant element and the test mass or mechanical stage. Any change in electrostatic coupling resulting from acceleration along the first or second axis can be calculated from the signal resulting from the first and second resonant elements, or can be canceled using a pair of opposing mounted third resonant elements, according to the first aspect of the invention.
    [0026] The frame, specimen and resonant elements can all be formed from machined silicon.
    [0027] In a further aspect of the invention, an inertial sensor is provided comprising: a frame; a test piece suspended from the frame; a pair of first resonant elements coupled to the test mass, or to an intermediate component coupled to the test mass, each first resonant element coupled to an opposite side of the test mass to the other, the first resonant elements being substantially identical to each other and having substantially identical coupling with the test mass when the sensor is not accelerating; wherein a movement of the specimen towards or away from the first resulting elements alters the effective stiffness of the first resonant elements; drive means coupled to the first resonant elements to vibrate each of the first resonant elements; a sensor assembly to detect a change in the resonant frequency or effective stiffness of each of the first resonant elements; and processing means to sum up the changes of each of the first resonant elements to provide a measure of the temperature.
    [0028] The processing medium can be configured to provide a difference between the changes of each of the first resonant elements to provide a measure of the acceleration in one direction. Preferably, the test mass and the resonant elements are configured in such a way that the movement of the tangential test mass to the first resonant elements does not alter the electrostatic coupling.
    [0029] The processing medium may comprise a mixer that has an input connected to the sensor assembly and an output connected to a first filter and a second filter, the first filter configured to provide an output that is a sum of the changes of each one of the first resonant elements to provide the temperature measurement, the second filter configured to provide an output that is a difference between the changes of each of the first resonant elements to provide the acceleration measurement in one direction.
    [0030] In a still further aspect of the invention, a method of measuring acceleration and temperature using a single inertial sensor is provided, the inertial sensor comprising: a frame; a test piece suspended from the frame; a pair of first resonant elements coupled to the specimen or an intermediate component coupled to the specimen, each of the first resonant element coupled to one side opposite the specimen to the other, the first resonant elements being substantially identical to each other and having substantially identical coupling with the test mass when the sensor is not accelerating; in which the movement of the test mass towards or away from the first resonant elements alters the effective stiffness of the first resonant elements; drive means coupled to the first resonant elements to vibrate each of the first resonant elements; and a sensor assembly to detect a change in the resonant frequency of each of the first resonant elements, the method comprising the steps of: adding the changes in resonant frequency of the first resonant elements to provide a temperature measurement; and calculating a difference in the resonant frequency changes of the first resonant elements to provide a measure of the acceleration.
    [0031] It should be evident that the features described in relation to one aspect of the invention can also be used in other aspects of the invention. BRIEF DESCRIPTION OF THE DRAWINGS
    [0032] Modalities of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic perspective view of a dual-axis accelerator according to the invention; Figure 2 is a plan, schematic view of a dual-axis accelerator of the type shown in Figure 1, additionally incorporating micro power amplification levers and illustrating activation and detection electrodes; Figure 3 is a schematic plan view of a triple-axis accelerometer according to the invention; Figure 4 is a schematic illustration of the drive and detection electronics that can be used with the triple-axis accelerometer shown in Figure 3; Figure 5 illustrates the processing electronics used to derive a Z axis acceleration using the accelerometer illustrated in Figure 3; and Figure 6 is a schematic illustration of a sensor providing a single axis acceleration measurement and a temperature measurement, according to the invention. DETAILED DESCRIPTION
    [0033] Figure 1 is a schematic illustration of a dual axis inertial sensor according to an embodiment of the invention. The sensor comprises a single suspended silicon test mass held within a dual axis stage. The double axis stage comprises four platforms 14 which are coupled to the test mass 10 at each corner of the test mass, by means of flexures 12. The platforms 14 are coupled to a surrounding frame 20 by means of flexures 16. The stage is designed in such a way that it allows decoupled, but symmetrical movement of the suspended test mass on both X and Y axes, with reduced mechanical interference between the two axes. The stage is designed to limit the movement of platforms 14 to a degree of freedom, that is, along the X or Y axis, as shown, while allowing the suspended mass of evidence within the stage to move with two degrees of freedom, that is, along both X and Y axes. This allows decoupled outputs to be connected to platforms 14 to transduce the acceleration of the test mass in each of the two orthogonal axes. The suspension flexures 12, 14 are designed to be structurally identical along both X and Y axes, to have equal effective stiffness along both axes. This symmetry reduces the mechanical interference between the X and Y axes, and also allows for identical dual axis sensitivity. The sensor in Figure 1 is advantageously manufactured entirely from a single semiconductor wafer, such as a silicon wafer over insulator (SOI) and can be manufactured using conventional MEMS fabrication techniques, such as micro surface machining and engraving.
    [0034] Platforms 14 are individually mechanically coupled to vibratory double-ended tuning resonators 22. Each resonator 22 is oriented perpendicular to the platform 14 to which it is connected. The acceleration of the test mass results in tension in the resonators, changing their resonant frequency. The X and Y accelerations are decoupled by the stage to provide separate X and Y outputs.
    [0035] In the modality illustrated in Figure 1, identical resonators 22 are fixed on diametrically opposite sides of the test mass 10, along the two axes in the sensitivity plane (illustrated by the dotted lines in Figure 1). Any movement of the test mass is consequently converted to an equal magnitude of voltage in each of the opposing resonators, but of opposite polarity. In other words, one resonator is subjected to an axial tensile stress while the other is subjected to an axial compressive stress. Consequently, the voltage induced in each of the tuning fork resonators results in a change in their resonant frequency in an equal magnitude, but in an opposite direction. A differential measurement from the two diametrically opposed resonators can then be used to provide a first order common mode cancellation of any frequency fluctuations that arise from environmental variations, such as temperature and pressure fluctuations. A more detailed description of the electrical processing of the outputs from the resonators is provided with reference to Figure 4.
    [0036] Figure 1 is just an example of a mechanical stage model that can be used in conjunction with resonators according to Figure 1. Any suitable flexural-based mechanical stage can be used according to the present invention if it effectively decouples the movement of the specimen along two orthogonal axes.
    [0037] Different resonator topologies can be used instead of the double-ended tuning tuning resonators, shown in Figure 1. Any suitable resonant element providing an indicative acceleration output of the test mass, based on a change in the resonant behavior of the elements resonant, can be used.
    [0038] Additionally, power amplification levers can be coupled between the stage and the resonators to increase the effort applied on the resonators. Figure 2 is a schematic plan view of a dual-axis sensor of the type shown in Figure 1, with force amplification levers positioned between platforms 14 and resonators 22. Figure 2 also illustrates the drive and detection electrodes used for activate the resonators and detect an output.
    [0039] The micro levers 24 are positioned between the platforms 14 and the resonant elements 22 and revolve around fulcrums 26. Each fulcrum 26 is positioned so as to increase the effort on the resonant element 22. Levers of this type are described in more detail in US5969249, the contents of which are incorporated by reference.
    [0040] Figure 2 also shows that each of the resonant elements includes a pair of coupling electrodes 28. Activation and detection electrodes 30, 32 are positioned adjacent to the coupling electrodes 28. A trigger signal can be applied to each element resonant through the drive electrode 30 and an output signal detected by the detection electrode 32. This arrangement is shown in more detail in Figure 4. Alternatively, additional transduction electrodes can be positioned to allow for improved transduction of the resonant elements.
    [0041] The dual axis accelerometer, shown in Figures 1 and 2, can be used as part of a triple axis accelerometer model, as shown in Figure 3. In Figure 3, the same reference numerals are used to indicate elements identical to those shown in Figure 2. The embodiment illustrated in Figure 3 incorporates two additional pairs of mechanically identical tuning fork resonators 40 and 42 and 50 and 52. Each of the first resonators 40, 42 is electrostatically coupled to the platform 14 and diametrically opposite positions. The first resonators include capacitive coupling plates 44 for capacitively coupling the two platforms 14 (shown by the dotted arrows) and the drive electrodes 46. As an alternative to the configuration shown in Figure 3, resonators 40, 42 could be electrostatically coupled to the test mass more properly than to platform 14. The other pair of resonators 50, 52 is not electrically coupled to the test mass or to stage 14 since the same voltage CD is applied to resonators 50, 52 and the mass of proof and platform. Resonators 50 and 52 are identical in construction to the first pair of resonators 40, 42 including capacitive coupling plates, and are positioned close to the first pair of resonators 40, 42 so that they are subjected to substantially the same environmental conditions. In the example shown in Figure 3 they are positioned between the platform 14 and the test mass 10, in a similar way to the first pair of resonators 40, 42.
    [0042] Any induced acceleration of the test mass along the Z axis will shift the test mass and consequently the platforms 14 by a distance, the magnitude of which depends on the stiffness offered by the stage along the Z axis. test mass or platforms 14 changes the capacitive area between the first pair of resonators 40, 42 and platforms 14, resulting in a variation in their operating resonant frequencies.
    [0043] The magnitude of the change in resonant frequency is dependent on the change in the capacitive coupling area. The electrically decoupled pair of resonators 50, 52 experiences no frequency variation as a result of displacement of the test mass along the Z axis. The decoupled pair of resonators 50, 52 can be used to cancel any variation in resonant frequency that is due to environmental factors, such as variations in temperature and pressure.
    [0044] By measuring the sum of the frequency changes experienced by the coupled resonators 40 and 42 and, then, performing a differential calculation with the summed output of the resonators 50 and 52, a direct measurement of the displacement of the stage along the Z axis can be obtained, which can be used to determine the acceleration along the Z axis. Simultaneous measurements of the variations in the parallel plate capacitor formed between the test mass and the substrate silicon layer could be used to provide the acceleration polarity . Alternative mechanical arrangements such as capacitive Z axis acceleration detection techniques based on combined drive can be used in conjunction with the resonant reading mechanism to provide polarity information in the case of specific manufacturing processes where the underlying substrate is etched.
    [0045] Of course, any displacement along the X axis also results in a capacitive gap modulation between the coupled resonant elements 40, 42 and the platform 14. Furthermore, provided that the capacitive coupling gaps are designed to be identical , any fluctuation in frequency, which arises from a movement of the stage along the X axis, will be of the same magnitude, but of opposite polarity for the resonant elements 40 and 42. Consequently, the sum of the resonator outputs 40 and 42, results in a cancellation of any variation as a result of movement on the X axis. Thus, unlike the direct differential measurement of the resonant frequencies of the axially coupled resonators to monitor the acceleration along the X and Y axes, the measurement of the Z axis is obtained by monitoring addition of the resonant frequency changes of the electrically coupled resonators 40 and 42. Subtracting any frequency changes obtained at starting from the sum of the signals from the unattached resonators 50 and 52 can then be used to correct any unwanted environmental factors.
    [0046] Figure 4 illustrates a reading electronics modality that can be used in conjunction with the triple axis accelerometer shown in Figure 3.
    [0047] The reading electronics required for X-axis and Y-axis accelerations are identical and thus only the X-axis reading will be described in detail. Each resonant element 22 is driven by an alternating voltage applied to electrode 30. The oscillation frequency of resonator 22 is read from electrode 32. Sustained oscillations are maintained using an oscillator circuit with automatic gain control, which returns to the drive electrode 30. The oscillator circuit includes a trans-resistance amplifier 33, a bandpass filter 35 and a comparator 37.
    [0048] The mixer 55 is used to provide a sum and difference of the outputs from the diametrically opposed resonators 22. The output from the mixer 55 passes through a low pass filter 57 to provide the difference signal, which is a output proportional to X-axis acceleration.
    [0049] As described above, an identical configuration is used to provide the output of the Y axis, and identical reference numerals have been used to label the electronic components for the Y axis.
    [0050] A high-pass filter can also be connected to mixer 55 at any of the X-axis and Y-axis outputs to provide a temperature measurement. Figure 4 shows a high-pass filter 59, connected only to the Y-axis output. The high-pass filter 59 removes the difference signal from the mixer output 55 leaving only the sum signal (also referred to as common mode output) . In the common mode output, frequency changes due to acceleration are canceled leaving an output predominantly sensitive to environmental factors, the most significant of which is temperature. In this way, a single, machined silicon sensor can provide both acceleration and temperature outputs. The temperature measurement from the high-pass filter 59 can also be used to refine the acceleration measurement from the low-pass filter 57, since the acceleration measurement is still sensitive to any second order component of the frequency relationship resonant and temperature.
    [0051] The activation and detection arrangement for the Z axis resonant elements is similar to that of the X and Y resonant elements. A trigger signal is applied to the drive electrodes 46, 60 and the output read from the detection electrodes 48 , 62, positioned at the base of the resonant elements. An oscillator circuit, including a trans-resistance amplifier, a bandpass filter and an automatic gain control / comparator element, is used to sustain the oscillation of the resonant elements 40, 42 and 50, 52.
    [0052] Figure 5 illustrates the signal processing for Z axis acceleration, more clearly. The mixer 70 is used to provide the sum and difference of the outputs of the electrically coupled resonators 40, 42. The output from the mixer 70 is subsequently filtered in high pass mode by the filter 72 to provide the sum signal. Similarly, the outputs from the unbound resonators 50, 52 are added and subtracted by the mixer 80 and filtered in high pass mode by the filter 82. The mixer 90 is used to provide a sum and difference signal from the filter outputs 72 and filter 82. This output is filtered by the low-pass filter 92 to provide a frequency output proportional to the Z-axis acceleration. Additional detection electrodes can also be incorporated to facilitate the larger transduction area for each of the resonators, to reduce consequently the resistance related to the movement and to improve the limited resolution of electronic noise of the oscillator.
    [0053] The sensitivity of the sensor in Figures 3 and 4 to the acceleration of the Z axis depends on the stiffness of the resonant elements and the flexures of the test mass. Any displacement of the double axis / test mass stage by a distance (Z) along the Z axis due to an az acceleration results in an electrostatic modulation of the rigidity of each of the resonators that are electro-elastically coupled to the test mass. This can be expressed as:

    [0054] Where ΔV represents the potential difference between the stage and each of the resonators; ε0 denotes the permittivity of air; l, the length of the capacitive coupling plates between the resonator and the dual axis stage platforms; h, the thickness of the platform; Mz and Kz represent the effective mass and stiffness of the test mass along the Z axis eg, the capacitive coupling gap before any induced displacement of the double axis / test mass stage. The relative shift in the resonant frequency of each tuning fork resonator is then given by:

    [0055] Where k refers to the stiffness of the tuning fork in the operation mode. As the output corresponds to the summed component of the frequency shifts that arise from two structurally identical resonators subtracted by the sum of the frequency shifts that arise from two tuning forks that remain electrically decoupled from the movement of the test mass, the net sensitivity along the Z axis can be expressed as:

    [0056] The scale factor of the device, along the X and Y axes, can be written as a proportion of the nominal differential frequency shift between the two tuning forks, resonant force sensors designed to read acceleration along the X axes and Y. This can be expressed as:

    [0057] Where Ai represents the net expansion factor of the mechanical force levers along the two orthogonal axes;
    Li, the tuning fork resonator along the sensitive axes; And, Young's modulus, the thickness of the tuning fork resonator; wi the width of the tuning fork resonator; M is the test mass subjected to acceleration along the X and Y axes; aa acceleration input along the order i axis.
    [0058] It should be evident that the modality in Figure 4 is just an example of an accelerometer according to the invention. It is also possible to provide an accelerometer that operates on the same principles using, among other things, a differently shaped test mass, a different flexural construction for the stage plane, different positions for the fourth resonant elements, different types of resonant element , different positions for the activation and detection electrodes for each resonant element and different oscillator circuits.
    [0059] It should also be evident that the idea of providing a temperature measurement from the common mode output of a pair of resonant elements coupled to the opposite sides of a single specimen can be applied to a single axis accelerometer model or double-axis, in the same manner as described with reference to Figure 4.
    [0060] Figure 6 is a schematic illustration of a single axis accelerometer with simultaneous temperature detection. A silicon test mass 110 is suspended from a frame by means of flexures 116. A pair of resonant elements 122 is mounted on opposite sides of the test mass, each of which is mechanically coupled to the test mass by means of micro levers power amplifier 124. The resonant elements 122 are driven by an alternating voltage applied to electrode 130. The oscillation frequency of each resonator 122 is read from the corresponding electrode 132. Sustained oscillations are maintained using an oscillator circuit with control of automatic gain, which feeds back to the drive electrode 130. The oscillator circuit includes a trans-resistance amplifier 133, a bandpass filter 135 and a comparator 137, as described with reference to Figure 4.
    [0061] The mixer 155 is used to provide the sum and difference of the outputs from the opposing resonant elements 122. The output from the mixer 155 passes through a low-pass filter 157 to provide the difference signal. Any change in the resonant frequency due to the movement of the test mass 110 on the sensitivity axis will be the same for each resonant element, but of opposite polarity. Changes in the resonant frequency due to temperature changes will be the same for the two resonant elements and the same polarity. Thus the difference signal will provide an output that is proportional to the acceleration. A 159 high pass filter is also connected to the mixer. The high pass filter 159 removes the difference signal from the mixer output 155 leaving only the added output. At the added output, frequency changes due to acceleration are canceled leaving a temperature sensitive output.
    [0062] In this way, a single machined silicon sensor can provide both acceleration and temperature outputs. As described with reference to Figure 4, the temperature measurement from the high-pass filter 159 can also be used to refine the acceleration measurement from the low-pass filter 157, since the acceleration measurement is still sensitive to any component. second order of the relationship between the resonant frequency and the temperature.
    [0063] In the embodiment of Figure 8, the resonant elements 122 are mounted on opposite sides of the test mass, individually mechanically coupled to the test mass by means of force amplification micro levers 124. However, it must be evident that the resonant elements can be electrostatically coupled to the specimen as an alternative. In the case of electrostatic coupling, displacement amplifiers can be used instead of the force amplification micro levers 124.
    权利要求:
    Claims (15)
    [0001]
    1. Inertial sensor comprising: a frame (20); a test piece (10) suspended from the frame; a pair of first resonant elements (40, 42) electrically coupled to the test mass (10), or to an intermediate component (14) mechanically coupled to the test mass, each first resonant element (40, 42) coupled to an opposite side from the test mass to the other, the first resonant elements being identical to each other and having identical electrostatic coupling with the test mass when the sensor is not accelerating; characterized by the fact that the first resonant elements and the test mass are located on a plane, and in which the movement of the test mass in relation to the first resonant elements orthogonal to the plane, alter the electrostatic coupling between the test mass and the first resonant elements; drive means (46) coupled to the first resonant elements to vibrate each of the first resonant elements; and a sensor assembly (48) for detecting a change in the resonant frequency of each of the first resonant elements; and processing means (33, 35, 37, 70) to sum up the changes of each of the first resonant elements to provide a measure of acceleration of the test mass parallel to a first axis, the first axis being orthogonal to the plane.
    [0002]
    2. Inertial sensor, according to claim 1, characterized by the fact that it additionally comprises a second resonant element (22) coupled to the test mass (10), the second resonant element configured to allow the detection of acceleration parallel to a second axis , orthogonal to the first axis; wherein the drive means (30) is coupled to the second resonant element to vibrate the second resonant element, and the sensor assembly (32) detects a change in the resonant frequency of the second resonant element.
    [0003]
    Inertial sensor according to claim 2, characterized in that the second resonant element (22) is preferably mechanically coupled to the test mass.
    [0004]
    4. Inertial sensor, according to claim 2 or 3, characterized by the fact that it additionally comprises a third resonant element (22) coupled to the test mass (10), the third resonant element configured to allow the detection of acceleration parallel to a third axis, where the third axis is orthogonal to the first axis and the second axis; wherein the drive means is coupled to the third resonant element to vibrate the third resonant element, and the sensor assembly detects a change in the resonant frequency of the third resonant element.
    [0005]
    Inertial sensor according to claim 4, characterized in that the third resonant element (22) is mechanically coupled to the test mass (10).
    [0006]
    6. Inertial sensor, according to claim 4 or 5, characterized by the fact that it comprises a pair of third resonant elements (22), each third resonant element positioned on an opposite side of the test mass to the other, the third resonant elements being identical to each other.
    [0007]
    7. Inertial sensor, according to claim 6, characterized in that the output in both a common mode and a differential mode is read from the pair of third resonant elements (22), the common mode output providing a measure of the temperature and differential output providing an acceleration measurement.
    [0008]
    Inertial sensor according to any one of claims 2 to 7, characterized in that it comprises a pair of second resonant elements (22), each second resonant element positioned on one side opposite the test mass to the other, the second elements resonants being identical to each other.
    [0009]
    9. Inertial sensor, according to any of the preceding claims, characterized by the fact that it additionally comprises a mechanical stage between the test mass and the frame, the mechanical stage configured to decouple the movement of the test mass in two orthogonal directions in the plane , in which the second or third resonant elements, or both, the second and third resonant elements, are mechanically coupled to the mechanical stage.
    [0010]
    10. Inertial sensor, according to any of the preceding claims, characterized by the fact that it additionally comprises a fourth resonant element, in which the fourth resonant element is identical to the first resonant elements and is not electrically coupled to the test mass.
    [0011]
    11. Inertial sensor, according to any one of the preceding claims, characterized in that it additionally comprises at least one amplification lever coupled between the test mass or mechanical stage and one of the first, second and third resonant elements to mechanically amplify the communicated strength.
    [0012]
    12. Inertial sensor according to any one of the preceding claims, characterized by the fact that one or more of the resonant elements is a double-ended tuning fork resonator.
    [0013]
    13. Inertial sensor, according to any of the preceding claims, characterized by the fact that the frame, the test mass and the resonant elements can all be formed from machined silicon.
    [0014]
    14. Method of measuring out-of-plane acceleration using a micro machined flat inertial sensor as defined in claim 1, the inertial sensor comprising: a frame; a test piece suspended from the frame; a pair of first resonant elements electrically coupled to the specimen, each first resonant element coupled to an opposite side of the specimen to the other, the first resonant elements being identical to each other and having identical electrostatic coupling to the specimen when the sensor it is not accelerating; where the first resonant elements and the test mass are located on a plane, and where the movement of the test mass in relation to the first resonant elements orthogonal to the plane alters the electrostatic coupling between the test mass and the first resonant elements; and drive means coupled to the first resonant elements to vibrate each of the first resonant elements; the method characterized by the fact that it understands the steps of: detecting a change in the resonant frequency of each of the first resonant elements; and adding the changes of each of the first resonant elements to provide a measure of the acceleration of the test mass parallel to the first axis, the first axis being orthogonal to the plane.
    [0015]
    15. Method according to claim 14, characterized in that the inertial sensor comprises an additional resonant element, in which the additional resonant element is identical to the first resonant element and is not electrically coupled to the test mass, the method comprising additionally the steps of: measuring a change in the resonant frequency or a change in effective stiffness of the additional resonant element, and modifying the measure of acceleration of the test mass parallel to the first axis based on the change in the resonant frequency of the additional resonant element.
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    同族专利:
    公开号 | 公开日
    SA515370337B1|2016-04-14|
    WO2014037695A2|2014-03-13|
    CA2883200A1|2014-03-13|
    CA2883200C|2021-11-23|
    GB2505875A|2014-03-19|
    EP2893362B1|2017-01-18|
    BR112015004404A8|2019-08-20|
    US9310391B2|2016-04-12|
    CN104781677B|2017-09-12|
    BR112015004404A2|2017-07-04|
    US20150226762A1|2015-08-13|
    CN104781677A|2015-07-15|
    EP2893362A2|2015-07-15|
    WO2014037695A3|2014-12-31|
    SA515360107B1|2016-01-14|
    GB201215750D0|2012-10-17|
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    法律状态:
    2018-11-21| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|
    2020-02-11| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|
    2020-11-17| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|
    2021-01-26| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 04/09/2013, OBSERVADAS AS CONDICOES LEGAIS. |
    优先权:
    申请号 | 申请日 | 专利标题
    GB1215750.9|2012-09-04|
    GB1215750.9A|GB2505875A|2012-09-04|2012-09-04|Dual and triple axis inertial sensors and methods of inertial sensing|
    PCT/GB2013/000375|WO2014037695A2|2012-09-04|2013-09-04|Dual and triple axis inertial sensors and methods of inertial sensing|
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