Patent Publication Number: US-2023144666-A1

Title: Vibrating-mass sensor system

Description:
TECHNICAL FIELD 
     This disclosure relates generally to sensor systems, and more specifically to a vibrating-mass sensor system. 
     BACKGROUND 
     Vibrating mass sensors can be implemented for measuring a variety of inertial parameters, such as acceleration and rotation. As an example, a vibrating mass sensor can include a vibrating or pendulous mass that is electrostatically controlled to oscillate in response to a drive signal. The oscillatory motion of the vibrating mass can be monitored based on capacitance between sets of electrodes, such that off-axis motion of the vibrating mass that can correspond to effects of inertial motion (e.g., acceleration, rotation, etc.) can be monitored. The vibrating mass can thus be provided a force-rebalance signal to electrostatically force the vibrating mass to a substantially null position in the off axis direction. The amplitude of the force-rebalance signal required to null the vibrating mass to offset the inertial effects can thus correspond to a measurement of the inertial effects. 
     SUMMARY 
     One example includes a vibrating-mass sensor system. The system includes a sensor system comprising a vibrating mass and a housing. The housing includes a set of housing drive electrodes. The vibrating mass includes a set of mass drive electrodes that are capacitively coupled to the respective matching set of housing drive electrodes. The system also includes a sensor controller comprising a signal generator configured to generate a drive signal that is provided to one of the set of mass drive electrodes and the set of housing drive electrodes to provide for a periodic oscillatory motion of the vibrating mass. The signal generator includes a polarity reversal component configured to periodically reverse a polarity associated with the drive signal. The sensor controller can be further configured to calculate an inertial parameter of the vibrating mass system in response to the periodic oscillatory motion of the vibrating mass. 
     Another example includes a method for determining an inertial parameter in a vibrating-mass sensor system sensor. The method includes generating a drive signal and providing the drive signal to electrodes associated with the vibrating mass to provide for periodic oscillatory motion of a vibrating mass. The method also includes periodically reversing a polarity of the drive signal and measuring the periodic oscillatory motion of the vibrating mass. The method further includes generating a force-rebalance signal based on the measured periodic oscillatory motion of the vibrating mass, and calculating the inertial parameter based on an amplitude of the force-rebalance signal. 
     Another example includes a vibrating mass gyroscope system. The system includes a sensor system comprising a vibrating mass and a housing. The housing includes a set of housing drive electrodes. The vibrating mass includes a set of mass drive electrodes that are capacitively coupled to the respective matching set of housing drive electrodes. The system also includes a gyroscope controller comprising a signal generator configured to generate a drive signal comprising a DC voltage and an AC voltage. The drive signal can be provided to one of the set of mass drive electrodes and the set of housing drive electrodes to provide for a periodic oscillatory motion of the vibrating mass. The signal generator includes a polarity reversal component configured to periodically reverse a polarity associated with the DC voltage and the AC voltage. The sensor controller can be further configured to calculate an inertial parameter of the vibrating mass system in response to the periodic oscillatory motion of the vibrating mass. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates an example block diagram of a vibrating-mass sensor system. 
         FIG.  2    illustrates an example diagram of a signal generator. 
         FIG.  3    illustrates an example of a method for determining an inertial parameter in a vibrating-mass sensor system sensor. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure relates generally to sensor systems, and more specifically to a vibrating-mass sensor system. As an example, the vibrating-mass sensor system can correspond to a quad-mass gyroscope that includes a plurality of vibrating masses that oscillate orthogonally with respect to a sensitive axis. The vibrating-mass sensor system includes a sensor system that includes at least one vibrating mass and a housing. The vibrating mass includes a set of sensor electrodes and the housing includes a respective corresponding set of housing electrodes. The vibrating-mass sensor system also includes a sensor controller that includes a signal generator. The signal generator is configured to generate a drive signal that is provided to one of the sensor electrodes and the housing electrodes to provide for periodic oscillatory motion of the vibrating mass along a drive axis. As an example, the drive signal can include a DC voltage and an AC voltage. 
     The periodic oscillator motion of the vibrating mass is provided at a substantially equal frequency as the resonant frequency of the vibrating mass (e.g., via spring flexures). The DC voltage of the drive signal can be provided to tune the resonant frequency of the vibrating mass via a negative electrostatic spring force. However, providing the DC voltage as part of the drive signal can result in a build-up of charge on the electrodes. Over time, the charge buildup can result in errors (e.g., bias hook, scale-factor errors, bias drift, and/or bias walk) that can negatively affect operation of the vibrating-mass sensor system. 
     To mitigate errors associated with charge buildup on the vibrating mass, the signal generator can be configured to reverse the polarity of the drive signal. As an example, the signal generator can reverse both the DC and AC voltages of the drive signal. The polarity reversal can be provided at each of predetermined time intervals, such as based on a period of the AC voltage. As an example, the AC voltage can have a frequency that is approximately equal to a resonant frequency of the vibrating mass. Thus, the signal generator can reverse the polarity of the drive signal at each of a predetermined number of periods of the AC voltage. Because the electrostatic force that drives the vibrating mass is based on a square of the voltage of the drive signal (e.g., the sum of the DC and AC voltages), then the reversal of the polarity of the drive signal (e.g., reversing the polarity of both the DC and AC voltages) will not affect the electrostatic driving force. As a result, capacitive charge buildup on the vibrating mass can be mitigated without affecting the driving force acting on the vibrating mass to provide the periodic oscillatory motion of the vibrating mass. 
       FIG.  1    illustrates an example block diagram of a vibrating-mass sensor system  100 . The vibrating-mass sensor system  100  can correspond to any of a variety of sensors (e.g., inertial sensors) that implement a vibrating mass to determine a measurable parameter (e.g., acceleration or rotation). As an example, the vibrating-mass sensor system  100  can correspond to a quad-mass gyroscope (QMG) that is configured to determine rotation about a sensitive axis. 
     In the example of  FIG.  1   , the vibrating-mass sensor system  100  includes a sensor system  102 . The sensor system  102  includes at least one vibrating mass  104  and a housing  106  that can correspond to the structural components accommodating the vibrating mass(es)  104 . For example, the vibrating mass(es)  104  can be mechanically coupled to the housing  106  via spring flexures, such that the vibrating mass(es)  104  can move relative to the housing  106 . In the example of  FIG.  1   , the vibrating mass(es)  104  include sets of mass electrodes  108  and the housing  106  includes sets of housing electrodes  110 . As an example, the respective sets of mass electrodes  108  and housing electrodes  110  can be capacitively coupled, such that a voltage applied to one of the mass electrodes or the housing electrodes can generate an electrostatic force to provide movement of the vibrating mass(es)  104  relative to the housing  106 . 
     The vibrating-mass sensor system  100  also includes a sensor controller  112 . The sensor controller  112  includes a processor  114 , a signal generator  116 , and a demodulator system  118 . The signal generator  116  is configured to generate a drive signal DRV that is provided to a set of drive electrodes of the mass and housing electrodes  108  and  110 , a force-rebalance signal FRB that is provided to a set of force-rebalance electrodes of the mass and housing electrodes  108  and  110 , and a quadrature rebalance signal QDR that is provided to a set of quadrature electrodes of the mass and housing electrodes  108  and  110 . As an example, the quadrature electrodes can be a dedicated set of electrodes, or can correspond to a combination of the drive and force-rebalance electrodes of the mass and housing electrodes  108  and  110 . As another example, the sensor controller  112  can be implemented in the digital domain, such that the drive signal DRV, the force-rebalance signal FRB, and the quadrature rebalance signal QDR can be generated digitally and can be converted to analog (e.g., via a digital-to-analog converter (DAC)) as analog signals provided to the sensor system  102 . 
     As described herein, all references to “drive signal DRV”, “force-rebalance signal FRB”, and “quadrature rebalance signal QDR” corresponds to at least one of each such drive signal DRV, force-rebalance signal FRB, and quadrature rebalance signal QDR, with respect to a respective at least one vibrating mass  104 . Thus, for a vibrating-mass sensor system  100  that includes multiple vibrating masses  104 , the signal generator  116  can generate a drive signal DRV, a force-rebalance signal FRB, and a quadrature rebalance signal QDR for each of the vibrating masses  104 . 
     The drive signal DRV can include a DC voltage and an AC voltage. The AC voltage can have a frequency that is approximately equal to the resonant frequency of the vibrating mass(es)  104 . The DC voltage can be provided to tune the resonant frequency of the vibrating mass(es)  104  via a negative electrostatic spring force, and to provide for demodulation of the drive signal at the frequency of the AC voltage, as opposed to twice the frequency of the AC voltage. Therefore, in response to the drive signal DRV being provided to the drive electrodes of the mass and housing electrodes  108  and  110 , each of the vibrating mass(es)  104  can be driven via the electrostatic force in a periodic oscillatory motion at a frequency that is approximately equal to the frequency of the AC voltage. In the example of the vibrating-mass sensor system  100  being arranged as a QMG gyroscope, the vibrating-mass sensor system  100  can include four vibrating masses  104 , with each of the vibrating masses  104  being driven along a given axis and with two of the four vibrating masses  104  being 180° out-of-phase of the other two vibrating masses  104 . 
     In response to the application of the drive signals DRV, pickoff signals PO are provided from the sensor system  102  (e.g., from the mass and housing electrodes  108  and  110 ) to the demodulator system  118 . As an example, the pickoff signals PO can correspond to amplitude-modulated pickoff signals that are capacitively coupled to the mass and housing electrodes  108  and  110  in response to motion of the vibrating mass(es)  104 . The pickoff signals PO can thus be demodulated via the demodulator system  118  to determine an appropriate magnitude of the respective force-rebalance signals FRB, such as to maintain the periodic oscillatory motion of the vibrating mass(es)  104  and to maintain the vibrating mass(es)  104  in the null position in the sense axis, respectively. 
     Thus, the processor  114  can calculate the magnitude of the force-rebalance signals FRB in a manner that is indicative of the measurable inertial parameter of the sensor system  102 . As an example, a magnitude of the force-rebalance signals FRB, and thus the electrostatic force, that is required to maintain the vibrating mass(es)  104  at the null position along the sense axis can correspond to the measurable inertial parameter (e.g., a rate of rotation of the sensor system  102  about the input axis). Therefore, the magnitude of the force-rebalance signals FRB can be implemented by the processor  114  to calculate the measurable inertial parameter. Accordingly, the sensor controller  112  can provide the measurement of the inertial parameter (e.g., angular rate of rotation about the input axis) as an output signal MP. 
     As an example, fabrication and electronic variations can result in changes in the separation of the resonant frequencies of the drive axis and the sense axis of each of the vibrating mass(es)  104  due to variation of spring stiffness and mass of the vibrating mass(es)  104 . As a result of such frequency separation, a remodulation phase-error can couple quadrature effects into the sense axis, and thus affect the magnitude of the generated force-rebalance signal FRB. Because the magnitude of the force-rebalance signal FRB can correspond to the measurable inertial parameter, such quadrature coupling can create errors in the calculation of the output signal MP. Accordingly, demodulator system  118  can measure the quadrature from the pickoff signals PO, such as based on comparing a quadrature signal received from the pickoff signals PO with a quadrature reference signal, as described in greater detail herein. The signal generator  116  can thus generate the quadrature rebalance signal(s) QDR with respect to the mass and housing electrodes  108  and  110  to substantially mitigate the quadrature motion, and thus the quadrature coupling into the force-rebalance signal FRB. 
     As described above, the drive signal DRV includes both a DC voltage and an AC voltage, such that the drive signal DRV is a sum of the AC and DC voltages. As also described above, the DC voltage is provided to tune the resonant frequency of the vibrating mass(es)  104  via a negative electrostatic spring force, such that any small difference between the resonant frequency of the vibrating mass(es)  104  and the frequency of the AC voltage can be mitigated. However, providing the DC voltage as part of the drive signal DRV can result in a build-up of charge on the mass and/or housing electrodes  108  and  110 . Over time, the charge buildup can result in errors (e.g., bias hook and/or bias walk) that can negatively affect operation of the vibrating-mass sensor system  100 . For example, such bias errors can provide errors in the generation of the force-rebalance signal FRB, and thus errors in the measurement of the inertial parameter MP. 
     In the example of  FIG.  1   , the signal generator  116  includes a polarity reversal component (“POLARITY REVERSE”)  120 . The polarity reversal component  120  is configured to periodically reverse the polarity of the drive signal DRV to mitigate errors associated with charge buildup on the vibrating mass(es)  104 . As an example, the polarity reversal component  120  can reverse both the DC and AC voltages of the drive signal DRV concurrently, such as by reversing a sign of the DC voltage and by implementing a 180° phase-shift of the AC voltage. For example, the polarity reversal of the drive signal DRV can be provided at each of predetermined time intervals, such as based on an integer multiple of the period of the AC voltage. Thus, the polarity reversal component  120  can reverse the polarity of the drive signal DRV at each of a predetermined number of periods of the AC voltage. As described in greater detail herein, because the electrostatic force that drives the vibrating mass(es)  104  is based on a square of the voltage of the drive signal DRV (e.g., the sum of the DC and AC voltages), then the reversal of the polarity of the drive signal DRV (e.g., reversing the polarity of both the DC and AC voltages) does not affect the electrostatic driving force. As a result, capacitive charge buildup on the vibrating mass(es)  104  can be mitigated without affecting the driving force acting on the vibrating mass(es)  104  to provide the periodic oscillatory motion of the vibrating mass(es)  104 . Accordingly, bias errors resulting from the capacitive charge buildup can be mitigated. 
       FIG.  2    illustrates an example diagram of a signal generator  200 . The signal generator  200  can correspond to the signal generator  116  in the example of  FIG.  1   . Therefore, reference is to be made to the example of  FIG.  1    in the following description of the example of  FIG.  2   . As an example, the signal generator  200  can correspond to hardware, software, firmware, or a combination thereof. For example, the signal generator  200  can be implemented on or as part of an integrated circuit (IC) chip, a processor, an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or any of a variety of devices. 
     The signal generator  200  includes an AC voltage generator  202  and a DC voltage generator  204 . The AC voltage generator  202  is configured to generate an AC voltage V AC  that can have a frequency that is approximately equal to the resonant frequency of the vibrating mass(es)  104  of the vibrating-mass sensor system  100 . The DC voltage generator  204  is configured to generate a DC voltage V DC . As an example, the AC voltage V AC  can have an amplitude that is lower than the amplitude of the DC voltage V DC . For example, the AC voltage V AC  can be less than one voltage (e.g., approximately 0.1 volts) and the DC voltage V DC  can be greater than three volts (e.g., approximately 5 volts). In the example of  FIG.  2   , the DC voltage V DC  and the AC voltage V AC  are added together via a summation component  206  to generate the drive signal DRV. The drive signal DRV is demonstrated as being provided to electrodes  208 , which can correspond to the mass and/or housing electrodes  108  and  110 . 
     The signal generator  200  also includes a force-rebalance signal generator (“FORCE-REBALANCE GENERATOR”)  210  and a quadrature rebalance signal generator (“QUADRATURE REBALANCE GENERATOR”)  212 . The force-rebalance signal generator  210  is configured to generate the force-rebalance signal FRB and the quadrature rebalance signal generator  212  is configured to generate the quadrature rebalance signal QDR. As described above, the force-rebalance signal FRB is generated in response to the pickoff signals PO, such that the force-rebalance signal FRB is generated to have an amplitude to generate a sufficient force to rebalance the vibrating mass(es)  104  (e.g., along an axis orthogonal to the drive axis for a QMG gyroscope). 
     As also described above, the quadrature rebalance signal QDR is generated to have an amplitude to generate a sufficient force to rebalance quadrature effects acting upon the vibrating mass(es)  104 . In the example of  FIG.  2   , the signal generator  200  also includes a quadrature reference signal generator (“QUADRATURE REFERENCE GENERATOR”)  214  that is configured to generate a predetermined quadrature reference signal. The demodulator system  118  can receive a quadrature signal as part of the pickoff signals PO that corresponds to measured quadrature from the vibrating mass(es)  104 . The processor  114  can thus compare the received quadrature signal with the quadrature reference signal to determine a difference. Therefore, the quadrature rebalance signal generator  212  can generate the quadrature rebalance signal that is provided to the mass and/or housing electrodes  108  and  110  to provide quadrature rebalance of the vibrating mass(es)  104  to compensate for the difference between the quadrature signal and the quadrature reference signal. 
     In the example of  FIG.  2   , the signal generator  200  further includes a polarity reversal component (“POLARITY REVERSAL COMPONENT”)  216 . The polarity reversal component  216  is configured to provide a reversal signal REV to each of the AC voltage generator  202  and the DC voltage generator  204 . Therefore, the reversal signal REV can command the AC voltage generator  202  and the DC voltage generator  204  to periodically reverse the polarity of the AC voltage V AC  and the DC voltage V DC , respectively. In the example of  FIG.  2   , the polarity reversal component  216  receives a clock signal CLK that can provide predetermined timing to the polarity reversal of the AC voltage V AC  and the DC voltage V DC . As described above, the predetermined timing can correspond to an integer multiple of the period of the AC voltage V AC . 
     As described above, the electrostatic force that drives the vibrating mass(es)  104  is based on a square of a drive voltage V DR v corresponding to the drive signal DRV. The drive voltage V DRV  can be expressed as follows: 
         V   DRV   =V   AC   +V   DC   Equation 1
 
         V   DRV ( t )= V   AC  cos(2π f   AC   t )+ V   DC   Equation 2
 
     Where: f AC t is the resonant frequency of the vibrating mass(es)  104 . 
     The electrostatic force F DRV  can thus be expressed as: 
         F   DRV ( t )= V   DRV   2   Equation 3
 
         F   DRV ( t )= V   DC   2 +2* V   DC   *V   AC  cos(2π f   AC   t )+ V   AC   2  cos 2 (2π f   AC   t )  Equation 4
 
     Applying trigonometric identity to the cosine squared term of Equation 4 results in the following expression: 
         F   DRV ( t )=( V   DC   2   +V   AC   2 /2)+2* V   DC   *V   AC  cos(2π f   AC   t )+ V   AC   2 /2 cos(2π f   AC   t )  Equation 5
 
     The first term of Equation 5 represents the DC voltage that results from the squaring of the sum of the DC voltage V DC  and the AC voltage V AC . The second term of Equation 5 represents the driving force for the vibrating mass(es)  104 , and the third term of Equation 5 is the second harmonic of the driving frequency. 
     Based on the squaring of the AC and DC voltages V AC  and V DC  in the expression of Equation 5 as affecting the driving force F DRV (t), then the reversal of the polarity of the DC voltage V DC  and the AC voltage V AC  of the drive signal DRV does not affect the electrostatic driving force F DRV (t). As a result, capacitive charge buildup on the vibrating mass(es)  104  can be mitigated without affecting the driving force F DRV (t) acting on the vibrating mass(es)  104  to provide the periodic oscillatory motion of the vibrating mass(es)  104 . Accordingly, bias errors resulting from the capacitive charge buildup can be mitigated. 
     Furthermore, in the example of  FIG.  2   , the polarity reversal component  216  provides the reversal signal REV to the quadrature reference signal generator  214 . The reversal signal REV can thus command the quadrature reference signal generator  214  to reverse the sign of the quadrature reference signal at the same periodic interval as the AC voltage V AC  and the DC voltage V DC . In this manner, the processor  114  can properly compare the quadrature signal with the quadrature reference signal, such that the quadrature rebalance signal generator  212  can generate the quadrature rebalance signal QDR to properly accommodate the quadrature effects acting on the vibrating mass(es)  104 . 
     In view of the foregoing structural and functional features described above, methods in accordance with various aspects of the present disclosure will be better appreciated with reference to  FIG.  3   . While, for purposes of simplicity of explanation, the method of  FIG.  3    is shown and described as executing serially, it is to be understood and appreciated that the present disclosure is not limited by the illustrated orders, as some aspects could, in accordance with the present disclosure, occur in different orders and/or concurrently with other aspects from that shown and described herein. Moreover, not all illustrated features may be required to implement method in accordance with an aspect of the present disclosure. 
       FIG.  3    illustrates an example of a method  300  for determining an inertial parameter in a vibrating-mass sensor system sensor (e.g., the vibrating-mass sensor system  100 ). At  302 , a drive signal (e.g., the drive signal DRV) is generated. At  304 , the drive signal is provided to electrodes (e.g., the mass and/or housing electrodes  108  and  110 ) associated with a vibrating mass (e.g., the vibrating mass  104 ) to provide for periodic oscillatory motion of the vibrating mass. At  306 , a polarity of the drive signal is periodically reversed. At  308 , the periodic oscillatory motion of the vibrating mass is measured. At  310 , a force-rebalance signal (e.g., the force-rebalance signal FRB) is generated based on the measured periodic oscillatory motion of the vibrating mass. At  312 , the inertial parameter (e.g., the measurable inertial parameter MP) is calculated based on an amplitude of the force-rebalance signal. 
     What have been described above are examples of the disclosure. It is, of course, not possible to describe every conceivable combination of components or method for purposes of describing the disclosure, but one of ordinary skill in the art will recognize that many further combinations and permutations of the disclosure are possible. Accordingly, the disclosure is intended to embrace all such alterations, modifications, and variations that fall within the scope of this application, including the appended claims.