|Publication number||USRE32931 E|
|Application number||US 07/148,168|
|Publication date||May 30, 1989|
|Filing date||Jan 22, 1988|
|Priority date||Jan 23, 1984|
|Publication number||07148168, 148168, US RE32931 E, US RE32931E, US-E-RE32931, USRE32931 E, USRE32931E|
|Inventors||Juergen H. Staudte|
|Original Assignee||Piezoelectric Technology Investors, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (7), Referenced by (53), Classifications (6), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
.Iadd.This is a continuation of application Ser. No. 859,476, filed May 2, 1986, abandoned. .Iaddend.
The present application may be considered to be an improvement and an extension of the principles of a prior application entitled, "Angular Rate Sensor System," to Alsenz, et al., Ser. No. 06/321,964, filed on Nov. 16, 1981. The present application is assigned to the same assignee as is the prior copending application.
The present invention is also related to a copending application to Juptner, et al., entitled, "A Vibratory Angular Rate Sensing System," filed concurrently with the present application. The present application discloses a different configuration which substantially cancels all undesirable first and second harmonics of the output frequencies which represent noise.
The angular rate of motion of a craft is an essential input for all navigational and inertial guidance systems. Such systems are used conventionally for aircraft, spacecraft, ships, or missiles. The sensing of the angular rate of motion is presently accomplished by means of a gyroscope.
Gyroscopes, however, have various disadvantages. They must be built to extremely high accuracies and may have drift rates of fractions of a degree per hour. Due to the expense of building them, they are very costly; they are physically large and heavy. They must be frequently and precisely maintained, for the reason that critical movable elements, such as bearings, may change with time. They may also be damaged by even low levels of shock and vibration. This, in turn, may cause an increase of unknown size in the drift rate, occurring at unknown times.
Because gyroscopes are sensitive to the effects of shock and vibration, they frequently have heavy mounting configurations to protect them, which also are expensive.
It will accordingly be obvious that it is desirable to replace a gyroscope by some other device which is less expensive and which is capable of measuring angular rates, thereby measuring the attitude of a vehicle or craft. In accordance with the present invention, this is accomplished by a balanced resonant sensor. Such a sensor is represented, in accordance with the present invention, by a tuning fork. The tuning fork should be substantially mechanically temperaturestable, having low internal friction and following Hook's Law. According to Hook's Law, the strain set up with an elastic body is proportional to the stress to which the body is subjected by the applied load (the strain, however, must be within the elastic limit of the body), and the body will return to its original shape when the stress is removed.
Preferably, but not necessarily, the tuning fork consists of quartz. However, other piezoelectric materials may be used, such as synthetic crystals, for example, ethylene diamine tartrate (EDT), dipotassium tartrate (DKT) or ammonium dihydrogen phosphate (ADP). Non-piezoelectric materials may by used with an electromagnetic drive.
In accordance with the present invention there is provided a wafer of piezoelectric materials, preferably of Z-cut quartz. The wafer is cut to provide a frame having an opening within which are provided two pairs of tines. The two tines in each pair are parallel with each other and are interconnected by a stem. This vibratory structure is secured to the frame by a pair of suspension bridges disposed close to each other, integral with the frame and extending to the stem.
The first pair of tines is excited by a drive oscillator in such a manner that the two tines will move toward each other and, after an instant, away from each other. The other pair of tines represent the output tines, and they will vibrate due to an applied external force in such a manner that while one tine moves up, the other moves down, and vice versa.
The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawings.
FIG. 1 is a top plan view of a vibratory angular rate sensor system embodying the present invention;
FIG. 2 illustrates the trigonal crystalline orientation of a Z-cut quartz wafer;
FIG. 3 is a cross-sectional view taken along lines 3--3 of one of the first pair of tines and showing the drive electrodes as well as the drive oscillator;
FIG. 4 is a schematic view of the pair of electrodes of FIG. 3 and a drive oscillator;
FIG. 5 is a similar cross-sectional view to that of FIG. 3 but taken along lines 5--5 through one of the tines of the second pair of tines and showing two pairs of output electrodes; and
FIG. 6 is a schematic view of the pair of electrodes of FIG. 5 and an output circuit.
Referring now to the drawing and particularly to FIG. 1, there is illustrated a vibratory angular rate sensor embodying the present invention. The sensor system includes a wafer 10 forming a mounting frame which preferably is a piece of Z-cut quartz. The crystalline orientation of the quartz is shown in FIG. 2. The mounting frame 10 is of rectangular configuration and has a rectangular central opening 11. The orientation of the wafer is shown adjacent to FIG. 1, illustrating the X, Y, and Z axes. Disposed within the opening 11 is a first pair of tines 12 and 13, arranged substantially parallel to each other. These tines 12, 13 represent the input or drive tines. A second pair of tines 14 and 15 are the output tines and are also disposed parallel to each other and have common axes with the respective tines 12, 13. The two pairs of tines 12, 13 and 14, 15 are interconnected by a stem or base 16.
The resonant system of the two pairs of tines 12, 13 and 14, 15 (the former being the input tines and the latter pair forming the output tines) is secured to the frame by four suspension bridges 17,18. The suspension bridges 17, 18 are integral with the frame 10 and are secured to the stem of base 16.
By way of example, the side of the frame 10 may have a length of 0.400 inch (in the X direction), the long side may have a length of 1.050 inch (in the Y direction) and the thickness (in the Z direction) may amount to 0.020 inch. However, it will be understood that other dimensions may be used for different materials or other purposes.
The tines 12, 13 may be energized by a pair of electrodes illustrated in FIG. 3. Thus, there are two pairs of electrodes 20, 21 and 22, 23. Each pair 20, 21 and 22, 23 is connected together and across a drive oscillator 25. (See FIG. 4). The electrodes 20, 21 extend in the Y direction, while the electrodes 22, 23 extend in the Z direction.
As illustrated in FIGS. 5 and 6, the output signal is derived at both the output tines 14, 15 by means of a first pair of output electrodes 26, 27 and a second pair of electrodes 28, 30. The output signals from both output tines 14 and 15 are connected in parellel. For convenience, only the output electrodes and output leads of one of the output tines have been illustrated. All of the output electrodes extend in the Y-Z direction. The output electrodes 26 and 30 are connected together, while the other electrodes 27 and 28 are also connected together and across an output circuit 32. This may be any conventional output circuit as well known in the art.
The structure of FIG. 1 may be chemically etched by means of photolithography from a suitable quartz wafer, or else it may be machined by a laser beam, ultrasonic machining, or other methods well known in the semiconductor art. The electrodes 20 to 23 and 26 to 30 may be obtained by gold-plating the respective tines and by removing unnecessary portions of the gold film, for example by a laser beam or by chemical etching.
The tines 12 and 13 resonate in the fundamental flexural mode in the X-Y plane. This is shown by arrows 35 in FIG. 1. The frequency in the X-Y plane is substantially lower than that in the Y-Z plane; that is, the plane in which the tines 14 and 15 vibrate. Hence the tines 14, 15 vibrate in opposite directions, up and down.
When the entire structure rotates about the Y axis and in the X-Y plane, the X-Y flexure plane vibration is conserved and therefore a flexure in the Y-Z plane is initiated. This motion is represented by the arrows .[.35.]. .Iadd.36 .Iaddend.in FIG. 1. The rotation in the X-Y plane may be caused by the angular motion of the vehicle carrying the system. As a result, the stem 16 is twisted due to the Coriolis force which acts normal to the plane of vibration of tines 12 and 13. This, in turn, causes an up-and-down motion of the output thines 14, 15 in opposition directions.
It should be noted that the Y-Z flexural frequency is higher than the X-Y flexural frequency. Stated another way, a torque is felt by the stem 16. This, in turn, initiates or drives an Y-Z flexure in output tines 14, 15. This is so because the frequency is substantially similar to that of the tuning fork consisting of tines 12, 13. The X-Y flexure in tines 12 and 13 is piezoelectrically driven by the input electrodes 20 to 23 of FIG. 3. On the other hand, the Y-Z flexure caused by a rotation about the axis Y in tines 14, 15 is picked up piezoelectrically by the output electrodes 26 to 30 of FIG. 5.
The bridges 17, 18 have an X-Z flexural frequency which is substantially that of the flexural frequency of the tines 12, 13.
The electrodes and shielding connections for the input and output circuits are preferably made from the bridges 17, 18. It should be noted that the frequency and balance of the two pairs of tines 12, 13 and 14, 15 are adjusted by adding or removing material, such as a gold film, at the free ends of the tines on the appropriate sides. This may be effected by chemical etching or by a laser beam.
The rate sensors of the prior art depend on the flexural frequency of the drive tines being substantially the same as the torsional frequency of the entire system. According to the present invention, the drive frequency of the angular rate sensor and the structural torisonal frequency are not the same. Therefore, large displacements of the stem 16 are not necessary. The displacement of the stem 16 is extremely small relative to that of the pickup or output tines 14, 15. This is due to the Q multiplication of the displacement of the tines with respect to the entire structure. It will now be understood that the vibration of the angular rate sensor is easily isolated from the mounting frame 10 and hence from the environment.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US2544646 *||Jun 16, 1948||Mar 13, 1951||Sperry Corp||Angular velocity measuring instrument|
|US3127775 *||Oct 28, 1960||Apr 7, 1964||Gyrex Corp||Vibratory rate gyroscope|
|US3141100 *||Jun 21, 1962||Jul 14, 1964||Avco Corp||Piezoelectric resonance device|
|US4654663 *||Nov 16, 1981||Mar 31, 1987||Piezoelectric Technology Investors, Ltd.||Angular rate sensor system|
|GB611011A *||Title not available|
|GB861436A *||Title not available|
|JPS5521679A *||Title not available|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US5193391 *||Nov 14, 1990||Mar 16, 1993||Cage Donald R||Controlled vibration angular rate sensor|
|US5331852 *||Dec 16, 1991||Jul 26, 1994||The Charles Stark Draper Laboratory, Inc.||Electromagnetic rebalanced micromechanical transducer|
|US5349855 *||Apr 7, 1992||Sep 27, 1994||The Charles Stark Draper Laboratory, Inc.||Comb drive micromechanical tuning fork gyro|
|US5357817 *||Apr 19, 1990||Oct 25, 1994||Charles Stark Draper Laboratory, Inc.||Wide bandwidth stable member without angular accelerometers|
|US5361036 *||Aug 12, 1993||Nov 1, 1994||Rockwell International Corporation||Complex digital demodulator employing Chebychev-approximation derived synthetic sinusoid generation|
|US5388458 *||Nov 24, 1992||Feb 14, 1995||The Charles Stark Draper Laboratory, Inc.||Quartz resonant gyroscope or quartz resonant tuning fork gyroscope|
|US5396144 *||Aug 2, 1993||Mar 7, 1995||New S.D., Inc.||Rotation rate sensor with center mounted tuning fork|
|US5408119 *||Oct 17, 1990||Apr 18, 1995||The Charles Stark Draper Laboratory, Inc.||Monolithic micromechanical vibrating string accelerometer with trimmable resonant frequency|
|US5408877 *||Mar 16, 1992||Apr 25, 1995||The Charles Stark Draper Laboratory, Inc.||Micromechanical gyroscopic transducer with improved drive and sense capabilities|
|US5426970 *||Aug 2, 1993||Jun 27, 1995||New Sd, Inc.||Rotation rate sensor with built in test circuit|
|US5444641 *||Sep 24, 1993||Aug 22, 1995||Rockwell International Corporation||Admittance-parameter estimator for a piezoelectric resonator in an oscillator circuit|
|US5459432 *||Jan 20, 1995||Oct 17, 1995||Rockwell International Corporation||Use of a chopper and a sigma-delta modulator for downconverting and digitizing an analog signal including information modulated by a carrier|
|US5471396 *||Mar 24, 1995||Nov 28, 1995||Rockwell International Corporation||Estimator of amplitude and frequency of a noisy-biased sinusoid from short bursts of samples|
|US5473945 *||Aug 6, 1993||Dec 12, 1995||The Charles Stark Draper Laboratory, Inc.||Micromechanical angular accelerometer with auxiliary linear accelerometer|
|US5476008 *||Jul 25, 1994||Dec 19, 1995||Rockwell International Corporation||Rate-sensing tuning fork design|
|US5487015 *||Sep 13, 1993||Jan 23, 1996||Rockwell International Corporation||Self-oscillating driver circuit for a quartz resonator of an angular rate sensor|
|US5496436 *||Jun 15, 1994||Mar 5, 1996||The Charles Stark Draper Laboratory, Inc.||Comb drive micromechanical tuning fork gyro fabrication method|
|US5505084 *||Mar 14, 1994||Apr 9, 1996||The Charles Stark Draper Laboratory, Inc.||Micromechanical tuning fork angular rate sensor|
|US5507911||Apr 14, 1995||Apr 16, 1996||The Charles Stark Draper Laboratory, Inc.||Monolithic micromechanical vibrating string accelerometer with trimmable resonant frequency|
|US5515724 *||Apr 20, 1995||May 14, 1996||The Charles Stark Draper Laboratory, Inc.||Micromechanical gyroscopic transducer with improved drive and sense capabilities|
|US5535902 *||May 22, 1995||Jul 16, 1996||The Charles Stark Draper Laboratory, Inc.||Gimballed vibrating wheel gyroscope|
|US5555765 *||Nov 14, 1994||Sep 17, 1996||The Charles Stark Draper Laboratory, Inc.||Gimballed vibrating wheel gyroscope|
|US5576976 *||Sep 7, 1993||Nov 19, 1996||Rockwell International Corporation||Amplitude detection and automatic gain control of a sparsely sampled sinusoid by adjustment of a notch filter|
|US5581035 *||Aug 29, 1994||Dec 3, 1996||The Charles Stark Draper Laboratory, Inc.||Micromechanical sensor with a guard band electrode|
|US5585561 *||Aug 11, 1994||Dec 17, 1996||New S.D., Inc.||Rotation rate sensor with closed ended tuning fork|
|US5605598 *||May 13, 1994||Feb 25, 1997||The Charles Stark Draper Laboratory Inc.||Monolithic micromechanical vibrating beam accelerometer with trimmable resonant frequency|
|US5635639 *||Jun 7, 1995||Jun 3, 1997||The Charles Stark Draper Laboratory, Inc.||Micromechanical tuning fork angular rate sensor|
|US5635739 *||Apr 25, 1995||Jun 3, 1997||The Charles Stark Draper Laboratory, Inc.||Micromechanical angular accelerometer with auxiliary linear accelerometer|
|US5646348||Sep 5, 1995||Jul 8, 1997||The Charles Stark Draper Laboratory, Inc.||Micromechanical sensor with a guard band electrode and fabrication technique therefor|
|US5650568||May 12, 1995||Jul 22, 1997||The Charles Stark Draper Laboratory, Inc.||Gimballed vibrating wheel gyroscope having strain relief features|
|US5725729 *||Aug 15, 1996||Mar 10, 1998||The Charles Stark Draper Laboratory, Inc.||Process for micromechanical fabrication|
|US5760305||Feb 20, 1996||Jun 2, 1998||The Charles Stark Draper Laboratory, Inc.||Monolithic micromechanical vibrating beam accelerometer with trimmable resonant frequency|
|US5767405||Jan 11, 1996||Jun 16, 1998||The Charles Stark Draper Laboratory, Inc.||Comb-drive micromechanical tuning fork gyroscope with piezoelectric readout|
|US5783973||Feb 24, 1997||Jul 21, 1998||The Charles Stark Draper Laboratory, Inc.||Temperature insensitive silicon oscillator and precision voltage reference formed therefrom|
|US5817942 *||Feb 28, 1996||Oct 6, 1998||The Charles Stark Draper Laboratory, Inc.||Capacitive in-plane accelerometer|
|US5892153 *||Nov 21, 1996||Apr 6, 1999||The Charles Stark Draper Laboratory, Inc.||Guard bands which control out-of-plane sensitivities in tuning fork gyroscopes and other sensors|
|US5893054 *||Sep 7, 1993||Apr 6, 1999||Boeing North American, Inc.||Amplitude detection and automatic gain control of a sparsely sampled sinusoid by computation including a hilbert transform|
|US5911156||Feb 24, 1997||Jun 8, 1999||The Charles Stark Draper Laboratory, Inc.||Split electrode to minimize charge transients, motor amplitude mismatch errors, and sensitivity to vertical translation in tuning fork gyros and other devices|
|US5952574||Apr 29, 1997||Sep 14, 1999||The Charles Stark Draper Laboratory, Inc.||Trenches to reduce charging effects and to control out-of-plane sensitivities in tuning fork gyroscopes and other sensors|
|US5969250||Jan 21, 1998||Oct 19, 1999||The Charles Stark Draper Laboratory, Inc.||Micromechanical accelerometer having a peripherally suspended proof mass|
|US6230563||May 28, 1999||May 15, 2001||Integrated Micro Instruments, Inc.||Dual-mass vibratory rate gyroscope with suppressed translational acceleration response and quadrature-error correction capability|
|US6532817||Apr 27, 1999||Mar 18, 2003||Matsushita Electric Industrial Co., Ltd.||Angular velocity sensor and process for manufacturing the same|
|US6564636||Aug 22, 2001||May 20, 2003||Honeywell International Inc.||Wide band digital phase locked loop (PLL) with a half-frequency output|
|US6691550||Oct 16, 2001||Feb 17, 2004||Honeywell International, Inc.||Estimator for determining resonant frequency and Q|
|US6725169||Mar 7, 2002||Apr 20, 2004||Honeywell International Inc.||Methods and apparatus for automatic gain control|
|US6823733||Nov 4, 2002||Nov 30, 2004||Matsushita Electric Industrial Co., Ltd.||Z-axis vibration gyroscope|
|US7051590||Jun 13, 2000||May 30, 2006||Analog Devices Imi, Inc.||Structure for attenuation or cancellation of quadrature error|
|US7138288 *||Mar 25, 2004||Nov 21, 2006||Citizen Watch Co., Ltd.||Method for manufacturing small crystal resonator|
|US8187902||Jul 9, 2008||May 29, 2012||The Charles Stark Draper Laboratory, Inc.||High performance sensors and methods for forming the same|
|US20040083812 *||Nov 4, 2002||May 6, 2004||Toshihiko Ichinose||Z-axis vibration gyroscope|
|US20040191944 *||Mar 25, 2004||Sep 30, 2004||Akihiro Shioji||Method for manufacturing samll crystal resonator|
|US20100005884 *||Jan 14, 2010||Weinberg Marc S||High Performance Sensors and Methods for Forming the Same|
|USRE34006 *||Jan 11, 1991||Jul 28, 1992||Angular rate sensor|
|U.S. Classification||73/504.16, 310/370, 310/329|
|Jun 16, 1989||SULP||Surcharge for late payment|
|Jun 16, 1990||FPAY||Fee payment|
Year of fee payment: 4
|Sep 24, 1992||FPAY||Fee payment|
Year of fee payment: 8
|Dec 24, 1996||FPAY||Fee payment|
Year of fee payment: 12