|Publication number||USRE42916 E1|
|Application number||US 11/030,713|
|Publication date||Nov 15, 2011|
|Filing date||Jan 6, 2005|
|Priority date||Apr 27, 1993|
|Also published as||US5430342|
|Publication number||030713, 11030713, US RE42916 E1, US RE42916E1, US-E1-RE42916, USRE42916 E1, USRE42916E1|
|Inventors||William S. Watson|
|Original Assignee||Watson Industries, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (144), Non-Patent Citations (14), Classifications (12)|
|External Links: USPTO, USPTO Assignment, Espacenet|
1. Field of the Invention
This invention relates generally to angular rate sensors of the vibrating element type, and particularly to an angular rate tensor having a tingle integrated driving and sensing element.
2. Description of the Prior Art
U.S. Pat. No. 2,513,340 to Lyman discloses the use of flexure-sensitive Rochelle salt crystals as strain tensing elements connected to an axially rotating tuning-fork whose oscillations are magnetically induced. The Lyman '340 device measures rate of turn or change in orientation of a body to which the tuning-fork it attached, and represents an early example of the use of strain-sensitive piezoelectric type crystals in an angular gyroscope or rate sensing application.
Various types of angular rate tensors employing piezoelectric crystal elements (or transducers) that are electrically excited to induce vibration are known to the art.
The use of vibrating piezoelectric crystal elements in gyroscopes and angular rate tensing devices can be traced back at least to U.S. Pat. No. 2,716,893 to Birdsall, which discloses paired transducers mounted in diametric opposition on a rotor to provide two-axis angular rate or acceleration measurement with directional specificity obtained by phase difference calculations. The Birdsall '893 device provided the means for constructing mass-independent navigation and guidance gyroscopes, but did not result in practical systems for applications such as fixed-position north-seeking gyroscopes or navigational altitude and heading referencing until the development of suitable control and filtering circuits. Representative examples of operational embodiments for those applications are shown in U.S. Pat. Nos. 3,987,555 to Haagens and 4,444,053 to Rider.
In particular, angular rate sensors having dual drive and sensing elements disposed in a “tuning-fork” configuration are the primary subject of current development activity. Some vibrating element angular rate sensors of this type, and representative drive circuits and applications for those sensors, are disclosed in U.S. Pat. Nos. 4,479,098; 4,578,650; and 4,628,734 to Watson; U.S. Pat. No. 4,671,112 to Kimura; U.S. Pat. No. 5,038,613 to Takenaka; U.S. Pat. No. 5,014,554 to Terada, and U.S. Pat. No. 4,791,815 to Yamaguchi.
These vibrating element angular rate sensors are usually characterized by a pair of parallel drive elements attached to an intermediate bridge member, with a sensing element attached to the distal end of each drive element and oriented orthogonal to that corresponding drive element. One or both of the drive elements are electrically excited to induce flexure therein in order to energize the sensing elements, and cause them to vibrate back and forth in opposition to one another within an inertial plane at a resonant frequency.
Tuning-fork type sensors can be very labor intensive to fabricate due to the bonded and insulated joints that must be formed between the bridge member, drive elements, and sensing elements, and the need to properly orient the drive and sensing elements relative to one another. The joints and the construction of the bridge member can also lead to abnormalities and imperfections that will affect the accuracy of the angular rate sensor if not filtered or corrected electronically. These devices are also subject to damage from handling during fabrication and the high G-forces imparted on the elements due to shocks or rapid acceleration and deceleration.
Other types of angular rate sensors utilizing vibrating transducers are also known to the art. One representative example is the “cantilever” type configuration shown in U.S. Pat. No. 3,842,681 to Mumme, in which six paired transducers extend radially from a hub having a central axis of rotation. Two drive transducers are oriented with their planar faces parallel to the axis of rotation and normal to their angular velocity vector, and impart vibratory oscillations to the two remaining pairs of sensing transducers. The two pairs of sensing transducers are oriented orthogonal to one another, with their planar faces parallel to their angular velocity vectors and perpendicular to the axis of rotation.
However, the Mumme '681 device requires a very complicated suspension system that does not operate effectively, and the long warm-up time of several minutes necessary to establish predominance of the primary torsional oscillations over the lateral deflection vibrations has prevented development of a production model for angular rate sensing applications.
Composite rate sensing systems incorporating single or paired vibrating tuning-forks and vibrating cantilever structures with constrained seismic masses are also know. Representative examples of such systems are shown in U.S. Pat. Nos. 2,544,646 to Barnaby and 4,802,364 to Cage, as well as Great Britain Patent Specification No. 1,540,279 to Philpotts.
Various “vibrating beam” angular rate sensors utilizing a plurality of vibrating transducers mounted on a rigid elastic core are also known to the art. These angular rate sensors provide separate transducers for driving and sensing, with the structural and physical properties of the core defining the flexural characteristics of the angular rate sensor and the vibrational modes of the transducers.
One representative example is shown in U.S. Pat. No. 3,520,195 to Tehon, which discloses an angular velocity sensing device having a central core or body with a square cross section, and a plurality of transducers bonded or soldered to each of its longitudinal surfaces. Each transducer has a pair of spaced-apart silver electrodes bonded or soldered to the outer surface opposing the central body through which the transducer can be electrically excited, or which will develop a voltage in response to flexure of the transducer induced by rotation of the central body about its longitudinal axis. A first pair of opposing transducers are energized to vibrate the central body at a resonant frequency, while the second pair of opposing transducers act as the sensing or read-out elements. Tehon '195 particularly discloses a hard or invariable metal rod such as stainless steel for the central body, and suggests that a central body having a circular or polyhedral cross section would also be operable.
Tehon '195 discloses a mounting structure in which the ends of the central body are clamped one resonant wavelength apart (defining an acoustic node located at the midpoint of the central body), and an alternate mounting structure in which the central body is directly supported at the natural acoustic nodes (one half resonant wavelength apart and inward from each end approximately 0.224-0.226 times the length of the central body) to eliminate the reflected acoustic energy created by clamping both ends. The Vyro ® inertial angular rate sensor produced by General Electric constituted a practical implementation of the nodal point mounting of the Tehon '195 device. Vibrating beam systems are typically used for measuring rotational accelerations and velocities, with a representative circuit for the dynamic system analysis of such a vibrating beam accelerometer being shown in U.S. Pat. No. 4,761,743 to Wittke.
Vibrating beam sensors of this type are subject to certain drawbacks. Since the core is a rigid elastic body, it is subject to mechanical fatigue and structural unreliability. The significant amount of tuning required by the system must be accomplished through electronic compensation. Since the same resonant driving and sensing frequencies are used to increase sensitivity, the system is very susceptible to bias error and scale factor shift caused by temperature changes. Thermal expansion of the beam will also cause the nodal points and resonant frequency of the system to shift physically. Attaching the transducers to a uniform shape beam will itself shift the location of the nodal points and affect the resonant frequency, thus requiring experimental evaluation or complex theoretical analysis to determine the true nodal points and resonant frequency to correct for discrepancies and variations as the angular rate sensor expands or contracts. Imperfections in the beam can cause twisting which will produce erroneous sensing signals. The amplitude of the output voltage from the sensing element is itself so minute that extremely high amplification is required, thereby increasing noise and temperature-related bias. Bondhig the transducers to the beam can result in misalignment and structural imperfections which interfere with performance, and the bonds tend to fatigue and deteriorate at different rates along the length of each transducer or relative to other transducers on the same beam, thereby interfering with the proper transmission of drive energy from the drive elements to the beam or the complete and uniform flexure of the sensing elements. The transducers are small relative to the physical size of the core, and the drive activation area for the system is therefore correspondingly limited. Additionally, the physical presence of the vibrating core makes the system susceptible to external magnetic fields which induce eddy currents that cause core vibrations in the sensitive direction.
Recent variants of the vibrating beam type angular rate sensor utilize metal cores having uniform triangular, square, or hexagonal cross sections, or a non-uniform quadrangular prismatic cross section. In practical embodiments using a core having a triangular cross section, a pair of transducers for driving and sensing are mounted on two adjacent longitudinal surfaces with a single drive detecting transducer mounted on the remaining longitudinal surface. The core is suspended near its nodal points from inverted U-shaped metal supports. Each longitudinal edge or ridgeline of the triangular core can be trimmed to raise the resonant frequency in one direction, and the drive and sensing frequencies can therefore be matched so that resonant frequencies in the X- and Y-directions are equal. Trimming all the ridgelines results in a core having a non-uniform hexagonal cross section. Systems of this general type are discussed in Japanese Patent Application Nos. 3-150,914; 2-223,818; 2-266,215; 2-266,601; 3-13,006; 3-34,613; and 59-51,517; and have been implemented in the Gyrostar ™ angular rate sensor by Mura Tech Manufacturing Company.
Such systems have many of the structural drawbacks found in the Tehon '195 device since the piezoelectric crystals are still bonded to a rigid elastic core in the same manner as Tehon '195. While the ability to trim the ridgelines of the core can facilitate some mechanical tuning that is otherwise accomplished through electronic compensation, this mechanical tuning must be accomplished manually for each sensor produced. These sensor systems typically have a high Q-value and narrow operational bandwidth, making them unsuitable for many applications. Matching the driving and sensing frequencies does increase the sensitivity of the system by its Q-value, but also increases the sensitivity to temperature change and particularly to resonant or on-frequency vibrations. While one could compensate for having a lower Q-value by driving the system harder, there are practical limits posed by the capabilities of the drive circuit electronics and the fatigue properties of the bar. In addition, these sensors vibrate freely in the longitudinal direction parallel with the major axis of the core.
The concept of mounting a vibrating transducer on a rigid elastic core has also been extended to cores having a tuning-fork shape for use in devices such as acoustic resonators. Representative examples of such structures are shown in U.S. Pat. Nos. 4,178,526 and 4,472,654 to Nakamura.
U.S. Pat. Nos. 3,258,617 to Hart and 4,489,609 to Burdess each disclose a gyroscopic or inertial rotation measuring device having a matrix of electrodes adhered or disposed on the outer surfaces and extending around the edges of a piezoelectric beam, and operating in the shear mode with forced double resonance. Hart '617 further discloses a layered construction with a pair of electrodes extending partially into the interior of the beam from opposing sides. The particular locations and shapes of the electrodes in the matrix are complex and difficult to construct. In Hart '617, the piezoelectric device is mounted within an aperture in a collar disposed at the center of the beam to produce a center nodal point and forced vibrations or oscillations of equal magnitude on the opposing sides of the collar and ends of the beam. In Burdess '609, the piezoelectric device is fixedly mounted at opposing ends to produce two end nodal points and a center nodal point, with the forced vibrations or oscillations on each side of the center nodal point being equal in amplitude but opposite in direction. Each of these devices is subject to the drawbacks discussed above relating to the beam-type devices such as Tehon '195, and a configuration such as the Burdess '609 device is particularly susceptible to torsional vibration and noise.
Accelerometers and angular rate sensing devices employing piezoelectric crystals having either a unitary tall toroidal structure or composed of stacked disks for vibrating a seismic mass are also known. Representative examples of such devices are shown in U.S. Pat. Nos. 5,052,226 and 4,586,377 to Schmid, and U.S. Pat. Nos. 3,636,387; 3,614,487; and 3,482,121 to Hatschek.
Several types of systems for angular rate or acceleration sensing that utilize vibrating bodies energized by means other than piezoelectric crystal elements are also known to the art.
One type is the vibrating wire rate sensor, in which a thin metal wire suspended from fixed ends is vibrated at its primary resonant frequency in one plane using; a drive magnet which surrounds a portion of the wire. A signal magnet is oriented to detect vibrations in the plane perpendicular to the drive plane which are induced by Coriolis forces caused by rotation of the wire. The amplitude of those vibrations will be proportional to the rate of rotation, and the phase shift of the vibrations will indicate the direction of rotation. Representative examples of vibrating wire angular rate sensors are shown in U.S. Pat. No. 3,520,193 to Granroth and U.S. Pat. Nos. 3,515,003 and 3,504,554 to Taylor.
Because the vibrating wire is fixed at both ends, the system produces a significant amount of reflected acoustic energy, as well as transferring significant mechanical energy through the supports to the surrounding structure. At least a portion of this energy can be reflected back to the sensor in the perpendicular plane, and create an erroneous sensing signal. While the erroneous signal will cause a relatively constant bias error in a fixed acoustic environment, temperature fluctuations and acceleration of the system will induce changes in the environment and the bias error can become very unpredictable. Complex mounting systems can reduce but not eliminate these signal errors. Also, the vibrating wire system does not provide a natural nodal support when used for rate sensing, so random external vibrations can create significant noise affecting the integrity of the output signal.
Another type of system employs magnetostrictive forces to induce flexure in an isotropic elastic body, with the Villari effect producing an output signal detectable by sensing magnets or electromotive devices. U.S. Pat. Nos. 2,455,939 to Meredith; 2817,779 to Barnaby; 2,974,530 to Jaouen; 3,177,727 to Douglas; 3,127,775 to Hansen; and 3,182,512 to Jones disclose a wide variety of angular velocity measuring devices in which resonant vibrations are induced in a magnetostrictive bodies (including bars, rods, tubes, hollow cylinders, and tuning-forks) by placing the bodies in a permanent or constant magnetic field, and then applying an alternating current to excite the bodies (or magnetically responsive elements attached to the bodies.) Flexure or vibration of the bodies within the magnetic field combined with movement of the bodies out of their inertial or vibratory plane produces variations in the magnetic flux lines within opposing parts of the body that are proportional to the angular velocity of the system. Jaouen '530 discloses several embodiments, including cylindrical rods having fixed ends mounted within a base, a tuning-fork structure, and a single cylindrical rod suspended at its nodal points. In this latter embodiment, the rod is either suspended by crossed wires passing through perpendicularly bored holes at the nodal points, or by spring steel needles welded at the nodal points, to permit two degrees of freedom perpendicular to the longitudinal axis.
Due to their cumbersome physical structures and the limitations imposed by their drive or sense signal processing circuitry, the vibrating wire and magnetostrictive systems described above are generally disfavored for modern rate sensing applications as compared to vibrating piezoceramic crystal element systems.
It is therefore one object of this invention to design an angular rate sensor and associated signal processing circuitry employing a vibrating piezoceramic element having a basic geometric shape (such as a rectangular bar) and substantially uniform construction which is suspended at its natural acoustic nodal points and mounted to achieve a predetermined level of vibrational “stiffness” in each of the planes orthogonal to the mode of driven vibration.
It is a related object of this invention to design the above angular rate sensor so that it utilizes a solid unitary piezoelectric device that does not require mechanical tuning, provides a lower intrinsic Q-value, increases rate sensing sensitivity compared with conventional angular rate sensors of the tuning-fork or vibrating beam types, is relatively insensitive to frequency changes, affords greater available bandwidth, and has negligible susceptibility to external magnetic fields.
It is further an object of this invention to design the above angular rate sensor to facilitate using independent drive and sensing frequencies, thus permitting a drive frequency high enough to substantially eliminate systemic noise (with the vibrational envelope rolling off at approximately one half the drive frequency), and so that baseline signals may be adjusted out.
It is yet another object of this invention to design the above angular rate sensor such that the effective length of the sensing element could be doubled without exceeding the physical parameters of a corresponding tuning-fork type sensor, thereby providing a fifth power (or three thousand percent) increase in sensitivity, along with substantial increases in drive activation area and stability compared with vibrating beam systems.
It is a further object of this invention to design the above angular rate sensor so that it may be fabricated using relatively inexpensive-and readily available materials and components, is constructed in a manner that reduces the potential for misalignment and other physical defects to occur during manufacturing, and will mitigate against structural fatigue and deterioration in operation due to a unitary structure.
It is a distinct object of this invention to design a particular embodiment of the above angular rate sensor in which the signal processing circuit provides for partially shared driving and sensing functions to thereby reduce system noise, eliminate the need to compensate for capacitance of the piezoelectric device, and reduce the number of electrical connections and manufacturing steps needed.
It is a unique object of this invention to design a further embodiment of the above angular rate sensor in which the signal processing circuit provides for totally isolated driving and sensing functions to further reduce system noise, and accomplish fully independent drive sensing and rate sensing.
Briefly described, the angular rate sensing system of this invention comprises a vibratory sensing element and a signal processing circuit which serves both driving and angular rate discriminating functions. The vibratory sensing element is preferably a single rectangular bar fabricated from two layers of piezoceramic material divided by a center electrode, with one or more outer electrodes scored onto one planar conductive face of the vibratory sensing element parallel with the center electrode, and a plurality of outer electrodes scored onto the opposing planar conductive face. The vibratory sensing element is polarized to a p-morph configuration, and vibrates in one dimension oriented normal to the physical plane of the electrodes.
The vibratory sensing element is preferably suspended at its natural acoustic nodes to vibrate freely without reflected energy, using any suitable mounting structure such as two parallel crossed filaments spaced one half wavelength apart, or four inwardly angled support arms that provide predetermined and potentially differing degrees of lateral and longitudinal stiffness. This latter mounting assembly permits flexure for thermal expansion and torsional freedom proximate to the vibratory sensing element.
Various embodiments of the driving and sensing signal processing circuit incorporate an automatic gain control, first and second operational amplifiers each with negative feedback loops, and signal conditioning components including a phase shifting means, demodulator, and low pass filter. The signal processing circuit may constitute totally shared, partially shared, or totally isolated driving and sensing functions, with the corresponding vibratory sensing element having a dual-pair, single-pair, or single-triple outer electrode configuration, respectively. A separate tuning module may also be utilized with a principal embodiment of the signal processing circuit.
The angular rate sensor system of this invention is shown in
In each of the embodiments discussed herein, the vibratory sensing element 12 comprises a generally uniform rectangular prismatic bar having a length L measured along the longitudinal axis, width W measured along the transverse or lateral axis, and thickness T measured in the direction or mode of vibration V as shown in
As has been shown in the art, for a uniform rectangular bar vibrated in the vibrational direction V perpendicular to its thickness T, the two natural acoustic nodal points for such a uniform rectangular bar will lie along lines N, N′ extending perpendicular to the longitudinal axis (or within planes perpendicular to the longitudinal axis bisecting the vibratory sensing element 12 at the midpoint along the thickness T thereof) measured inward from each opposing end 16, 18 a distance of 0.2247 times the length L of the vibratory sensing element 12 (or L/(2+60½)).
One or both of the outer conductive layers 30, 32 of each vibratory sensing element 12 is scored or etched to form a plurality of electrodes E1-E4 as discussed in further detail below. This scoring or etching may be accomplished by any conventional means, such as manual scoring using a diamond-tipped scribe or cutting wheel, to create a linear score line 76 extending entirely through the conductive layers 30, 32 and forming a gap, groove, or channel having a width of approximately 0.005″ between the adjacent electrodes E1-E4. The vibratory sensing element 12 further defines four edgewise faces other than the outer conductive layers 30, 32 disposed around the perimeter surface of the vibratory sensing element 12 along its thickness T and parallel with the vibrational direction V, each of those four edgewise faces of the perimeter surface being generally free of electrodes adhered thereto or defined thereby, with the exception of the exposed portions of the center or base electrode 20 which extends outwardly toward and adjacent to each of the four edgewise faces of the perimeter surface.
The vibratory sensing element 12 is preferably convened to a poly- or p-morph for proper functioning as an angular rate sensing device by grounding the base electrode 20 and electrically stimulating the outer conductive layers 30, 32 at approximately 800 Vdc while the vibratory sensing element 12 is immersed in an oil bath, thereby repolarizing the layers of vibratory sensing dement element 12 as shown by the positive and negative charge signs in
Referring particularly to
A plurality of electrically conductive leads 40-48 are attached to the vibratory sensing element 12 in the manner described below, with each of the leads 40-48 in turn being electrically connected to one of a plurality of terminals 50-58 defined by the frame member 36 or integrated into and electrically connected to one or more of the electronic circuits 14.
Referring particularly to
The vibratory sensing element 12 is then mounted or suspended by adhering, bonding, or attaching each support arm 64 to the one of the two opposing edgewise faces of the vibratory sensing element 12 such that the fold lines 72 or a portion of the distal ends 74 of the support arms 64 are aligned with and along the lines N, N′ representing the nodal points of the vibratory sensing element 12 so as to maximize or optimize the ability of the vibratory sensing element 12 to freely vibrate in the direction or mode of vibration V at its resonant frequence.
Adjusting factors such as the composition, thickness, flexibility, and rigidity of the materials used to fabricate the plate members 60, 62, the length of the support arms 64, and the relative angles α, β formed between the support arms 64 and the plate members 60, 62 or vibratory sensing element 12 will affect the “stiffness” or resistance to linear vibration of the vibratory sensing element 12 in either the longitudinal S or lateral S′ directions normal to the mode of vibration V. It may be appreciated that adjusting or varying the relative angles α, β formed between the support arms 64 and the plate members 60, 62 or vibratory sensing element 12 (absent other compensating modifications) will have an opposite effect on the stiffness of the mounting assembly in the longitudinal S and lateral S′ directions, with an increase in the lateral S′ stiffness resulting in a decrease in longitudinal S stiffness, and vice versa. The magnitude of the effect of these angular adjustments will normally be proportional to the sine or cosine of the relevant angle α, β, such that the longitudinal S and lateral S′ stiffness of the mounting assembly may be optimized for particular applications. Relative angles α, β between the support arms 64 and the plate members 60, 62 of 45° have proven suitable for the embodiments of the angular rate sensing system discussed herein. In addition, the thickness and pliability of the metal or material from which the support arms 64 are fabricated will affect the longitudinal S and lateral S′ stiffness of the mounting assembly, and a balance can effectively be drawn to optimize or weigh off the maximum g-forces to which the angular rate sensor system 10 will be subjected against the maximum desirable “softness” of the overall mounting assembly, thus permitting the mounting assembly to be adequately soft so there is no input from vibrations in the sensing range but the support arms 64 will not shear, crack, or flex unduly during rapid acceleration or deceleration.
The plate members 60, 62 are fixedly or securely mounted in a frame or housing (not shown) suitable to protect the plate members 60, 62, support arms 64, vibratory sensing element 12, and the associated leads 40-48 and electrical components from potential damage caused by impact or rapid acceleration and deceleration.
Referring particularly to
The drive and sensing signal processing circuit 14 of
Output 102 of the AGC 100 is similarly connected through capacitor 106 to the non-inverting input 122 of a first operational amplifier (op amp) 108, the output 126 of which is in turn is connected to the input 104 of the AGC 100. A resistor 110 and ground connection 112 are disposed between the capacitor 106 and the non-inverting input 122 of the first op amp 108. Resistor 114 is connected between the output 126 and the inverting input 124 of the first op amp 108 forming a resistance type negative feedback loop to control the gain of the first op amp 108. A second resistor 116 and ground connection 118 are disposed between the capacitor 106 and first resistor 110 and the non-inverting input 122 of the first op amp 108.
Interposed between the inverting input 124 of the first op amp 106 and the vibratory sensing element 12 is a bank of four resistors 120, each resistor 120 being connected to one of the first through fourth outer electrodes E1, E2, E3, E4. Disposed between each resistor 120 and the corresponding electrode E1-E4 is a connection to a resistor 128 and ground connection 130.
Two outer electrodes E2, E3 located alternately on opposite faces of the vibratory sensing element 12 are connected through respective resistors 132, 134 to the non-inverting input 138 of a second op amp 136. The remaining two diametrically opposed outer electrodes E1, E4 of the vibratory sensing element 12 are connected through respective resistors 144, 146 to the inverting input 140 of the second op amp 136. The connections between the electrodes E1-E4 and the second op amp 136 are each interposed between the associated resistor 128 and the corresponding resistor 120.
The resistors 120 may be adjusted in ratio to one another in order to compensate for variations in the signals for the vibratory sensing element 12 to cancel unbalanced vibrational responses for the drive portion of the drive and sensing signal processing circuit 14. Similarly, resistors 132, 134, 144, and 146 may be adjusted in ratio to one another in order to cancel unbalanced vibrational responses for the sensing portion of the drive and sensing signal processing circuit 14.
The output 142 from the second op amp 136 is in turn connected through capacitor 148 back to the inverting input 140 of the second op amp 136 forming a capacitance type negative feedback loop to control the gain of the second op amp 136, and the non-inverting input 138 of the second op amp 136 is connected through capacitor 150 to ground connection 152.
As such, the inverting inputs 124, 140 of the first and second op amps 108, 136 provide a 180° phase shift to the respective outputs 126, 142, with the non-inverting inputs 122, 138 being in phase with the outputs 126, 142. It should be noted that the normal collector (Vcc) and emitter (Vcc) power supply terminals for each of the first and second op amps 108, 136 have been omitted from FIGS. 5 and 7-9.
The automatic gain control 100 and operational amplifiers 108, 136 may be of any type commonly utilized for these purposes, representative examples being discussed in U.S. Pat. No. 4,479,098. Suitable values for the various resistance and capacitance components for the tuning module of
R132, 134, 144, 146
C106, 148, 150
In the dual-pair electrode embodiment the first and third electrodes E1, E3 confront, overlap, and are aligned with one another across the vibratory sensing element 12, and the second and fourth electrodes E2, E4 are similarly disposed confronting, overlapping, and aligned with one another across the vibratory sensing element 12.
Referring particularly to
The drive and sensing signal processing circuit 14 of
Input 204 of the AOC 200 is connected to the output 212 of first op amp 206, with the output 202 of the AGC 200 being connected back through capacitor 246 to the non-inverting input 208 of the first op amp 206. A resistor 248 and ground connection 250 are disposed between the capacitor 246 and the non-inverting input 208 of the first op amp 206.
Resistor 254 is connected between the output 212 and the inverting input 210 of the first op amp 206 forming a resistance type negative feedback loop to control the gain of the first op amp 206.
The second and third electrodes E2, E3 of the vibratory sensing element 12 are connected together and to the inverting input 210 of the first op amp 206 through resistor 242, while the first and fourth electrodes E1, E4 are similarly connected together and to the inverting input 210 of the first op amp 206 through resistor 244.
The second and third electrodes E2, E3 are similarly connected to the inverting input 218 of a second op amp 214 through resistor 228, while the first and fourth electrodes E1, E4 are connected together and to the non-inverting input 216 of the second op amp 214 through resistor 258.
Disposed between the pair of electrodes E2, E3 is a connection through resistor 234 to ground connection 236, and similarly disposed between the pair of electrodes E1, E4 is a connection through resistor 238 to ground connection 240.
The output 220 from the second op amp 214 is in mm connected through resistor 252 back to the inverting input 218 of the second op amp 214 forming a resistance type negative feedback loop to control the gain of the second op amp 214, and the non-inverting input 216 of the second op amp 214 is connected through resistor 230 to ground connection 232.
The output 220 from the second op amp 214 is further connected to the input of a 90° phase shift means 222, whose output is in turn connected to a demodulator 224. One output from the demodulator 224 is connected to the input of a low pass filter 226, while the remaining output from the demodulator 224 is connected to the output 202 of the AGC 200 and through capacitor 246 to the non-inverting input 208 of the first op amp 206. The output from the low pass filter 226 provides an output signal at the signal processing circuit output 256.
In this shared driving and sensing embodiment of the signal processing circuit 14, the four outer electrodes E1-E4 each detect the same angular rate, but with corresponding opposite signs. The average of the output signals from each of the outer electrodes E1-E4 corresponds to the driving motion and the first op amp 206 utilizes that average signal to generate the drive signal. The difference between the output signals from the pairs of outer electrodes E1-E4 is used by the second op amp 214 to produce an output signal whose amplitude is proportional to the angular rate of the vibratory sensing element 12.
As with the principal embodiment of the signal processing circuit 14, this shared driving and sensing embodiment may be easily constructed from staple components, and is substantially free from fatigue limitations. The signal processing circuit 14 is relatively insensitive to frequency changes, has a greater available bandwidth than previous tuning fork or vibrating beam type angular rate sensors, and has negligible magnetic sensitivity. It should be noted that signal processing is initiated with a minute signal that roust be amplified significantly and shifted 90°, thereby permitting sources of error and drift to arise in the output signal. It may also be necessary in some applications to compensate for the capacitance of the particular piezoceramic material from which the vibratory sensing element 12 is fabricated in order to maintain drive resonance. Cross talk between the sense and drive signals can occur and will be temperature variable, with noise and bias change resulting from that cross talk. The resistance will usually lower the level of the output signal considerably, and the signal processing circuit 14 may therefore be subject to noise and component drift. Some noise and drift could be alleviated by substituting an integrator circuit or differential integrator for the differential amplifier to initially process the sensing signal, which reduces noise at higher frequencies and produces an output signal having a stable 90° phase shift.
Referring particularly to
The drive and sensing signal processing circuit 14 of
Input 304 of the AGC 300 is connected to the output 312 of first op amp 306, with the output 312 of the first op amp 306 being connected back through resistor 346 to the inverting input 310 of the first op amp 306 to form a resistance type negative feedback loop to control the gain of the first op amp 306. The non-inverting input 308 of the first op amp 306 is connected directly to ground connection 350.
The second electrode FE2 is connected to the inverting input 310 of the first op amp 306 through resistor 342, while the third electrode E3 is similarly connected to the inverting input 310 of the first op amp 306 through resistor 344.
The second electrode E2 is connected through resistor 328 to the inverting input 318 of second op amp 314, while the third electrode E3 is similarly connected through resistor 356 to the non-inverting input 316 of the second op amp 314.
Disposed between the second electrode F2 and resistor 342 is a connection through resistor 334 to ground connection 336, and similarly disposed between the third electrode E3 and resistor 344 is a connection through resistor 338 to ground connection 340. Disposed between the inverting input 316 of the second op amp 314 and resistor 356 is a connection through resistor 330 to ground connection 332. The center electrode Ec is connected directly to ground connection 352. As previously noted with respect to the circuit shown in
The output 320 from the second op amp 314 is in turn connected through resistor 348 back to the non-inverting input 318 of the second op amp 314 forming a resistance type negative feedback loop to control the gain of the second op amp 314. The output 320 from the second op amp 314 is further connected to the input of a 90° phase shift means 322, whose output is in turn connected to demodulator 324. One output from demodulator 324 is connected to the input of low pass filter 326, while the remaining output from demodulator 324 is connected to the input 304 of the AGC 300 and the output 312 of the first op amp 306. The output from the low pass filter 326 provides an output signal at the signal processing circuit output 354.
Construction of this partially shared driving and sensing embodiment is simplified compared to the dual-pair electrode embodiment, since one less manufacturing step is involved to fabricate the electrodes E1-E3 on the vibratory sensing element 12,, and one less lead is physically attached to the vibratory sensing element 12. The partial isolation of the driving and sensing functions in this embodiment greatly reduces system noise and eliminates the need to compensate for capacitance of the piezoelectric material. While only half the force is available to drive the vibratory sensing element 12, the high Q-value of the piezoceramic material and vibratory sensing element 12 as a whole normally permit the use of a relatively low voltage drive signal, and a higher drive voltage can be used to compensate for the reduction in drive area. The output signal is similarly reduced by half, thereby requiring amplification, and this may increase the effect of some noise and bias components. Finally, the symmetry of the vibratory sensing element 12 is disturbed, which may be a consideration in some applications.
Referring particularly to
The drive and sensing signal processing circuit 14 of
The input 404 of the AGC 400 is connected to the output 412 of first op amp 406, with the output 412 of the first op amp 406 being connected back through resistor 432 to the inverting input 410 of the first op amp 406 to form a resistance type negative feedback loop to control the gain of the first op amp 406. The non-inverting input 408 of the first op amp 406 is connected directly to ground connection 436.
The fourth electrode E4 is connected directly to the inverting input 410 of first op amp 406. The second electrode E2 is connected directly to the inverting input 418 of the second op amp 414, while the third electrode E3 is similarly connected directly to the non-inverting input 416 of the second op amp 414. The center electrode Ec is connected directly to ground connection 434.
Disposed between the fourth electrode E4 and the non-inverting input 416 of the second op amp 414 is a connection through capacitor 426 to ground connection 428. The output 420 from the second op amp 414 is in turn connected through resistor capacitor 430 back to the non-inverting input 418 of the second op amp 414 forming a capacitance type negative feedback loop to control the gain of the second op amp 414. As previously noted with respect to the circuit shown in
The output 420 from the second op amp 414 is further connected to the input of demodulator 422. One output from demodulator 422 is connected to the input of low pass filter 424, while the remaining output from demodulator 422 is connected to the input 404 of the AGC 400 and the output 412 of the first op amp 406. The output from the low pass filter 424 provides an output signal at the signal processing circuit output 438.
It may be appreciated that one could readily interchange the second and fourth electrodes E2, E4 within this totally isolated embodiment. This embodiment requires fewer components than the partially shared driving and sensing embodiment discussed above, however an additional manufacturing step is required in fabricating the vibratory sensing element 12, and a fifth lead must be physically connected to the vibratory sensing element 12. This totally isolated embodiment permits sensing to be accomplished freely with the lowest noise, and drive sensing is fully independent from angular rate sensing. The symmetry of the vibratory sensing element 12 is further diminished, however the wide separation between drive and sense resonance under normal operating conditions should render any consideration of symmetry non-critical or inconsequential.
It may be appreciated that each of the embodiments of the angular rate sensor system 10 fabricated according to the guidelines set forth above will have a characteristic Q-value associated therewith, which will be further affected by the particular nature and physical properties of the materials utilized in constructing each embodiment. It is understood that through the selection of appropriate and suitable materials for specified applications, and the tuning or adjustment of the associated drive and sensing signal processing circuit 14, the sensing frequency for the angular rate sensor system 10 may be related to and optimized for the particular characteriztic Q-value associated with that system 10.
While the preferred embodiments of the above angular rate sensor system 10 have been described in detail with reference to the attached drawing Figures, it is understood that various changes and adaptations may be made in the angular rate sensor system 10 without departing from the spirit and scope of the appended claims.
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|GB1540279A *||Title not available|
|GB2206415B *||Title not available|
|GB2223309A||Title not available|
|JP4118515B2||Title not available|
|JPH046472A||Title not available|
|JPH0334613A||Title not available|
|JPH0438513A||Title not available|
|JPH0534162A||Title not available|
|JPH02128117A||Title not available|
|JPH02298812A||Title not available|
|JPH04118515A||Title not available|
|JPH06222120A||Title not available|
|JPS63292017A||Title not available|
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|10||Fujishima, Satoru; Nakamura, Takeshi; and Katsumi Fujimoto. "Piezoelectric Vibratory Gyroscope Using Flexural Vibration of A Triangular Bar."|
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|U.S. Classification||310/316.01, 310/352, 73/504.14, 310/332, 310/351, 310/318|
|International Classification||H01L41/08, G01C19/5642|
|Cooperative Classification||H01L2924/01039, H01L2224/48091, G01C19/5642|