Electrical generator or motor structure – Non-dynamoelectric – Thermal or pyromagnetic
Reexamination Certificate
1999-10-15
2001-09-04
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Thermal or pyromagnetic
C310S328000, C310S329000, C073S504120, C073S514290, C073S514360
Reexamination Certificate
active
06285111
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an apparatus and method for determining the rate of angular rotation of a moving body and, in particular, to alignment of the dither motion and the Coriolis acceleration sensing direction in a sensor adapted to be formed, i.e. micromachined, from a silicon substrate.
REFERENCE TO RELATED APPLICATIONS
Reference is made to the following commonly assigned patents:
1) entitled “Monolithic Accelerometer,” U.S. Pat. No. 5,165,279 issued on Nov. 24, 1992, in the name of Brian L. Norling;
2) entitled “Accelerometer With Co-Planar Push-Pull Force Transducers,” U.S. Pat. No. 5,005,413 issued on Apr. 9, 1991, in the name of Mitch Novack;
3) entitled “Coriolis Inertial Rate and Acceleration Sensor,” U.S. Pat. No. 5,168,756 issued on Dec. 8, 1992, in the name of Rand H. Hulsing II;
4) entitled “Torque Coil Stress Isolator,” U.S. Pat. No. 5,111,694 issued on May 12, 1992, in the name of Steven Foote;
5) entitled “Micromachined Rate And Acceleration Sensor,” U.S. Pat. No. 5,627,314 issued on May 6, 1997, in the name of Rand H. Hulsing II;
6) entitled “Micromachined Rate And Acceleration Sensor,” U.S. Pat. No. 5,557,046 issued on Sep. 17, 1996, in the name of Rand H. Hulsing II;
7) entitled “Micromachined Rate And Acceleration Sensor Having Vibrating Beams,” U.S. Pat. No. 5,331,854 issued on Jul. 26, 1994, in the name of Rand H. Hulsing II;
8) entitled “Micromachined Rate And Acceleration Sensor,” U.S. Pat. No. 5,241,861 issued on Sep. 7, 1993, in the name of Rand H. Hulsing II;
9) entitled “Micromachined Rate And Acceleration Sensor,” U.S. application Ser. No. 08/893,721 filed Jul. 10, 1997, in the name of Rand H. Hulsing II; and
10) entitled “Micromachined Rate And Acceleration Sensor,” U.S. application Ser. No. 08/786,185 filed Jan. 20, 1997, in the name of Rand H. Hulsing II;
11) entitled “Low Vibration Link,” U.S. application Ser. No. 09/016,186 filed Jan. 30, 1998, in the name of Rand H. Hulsing II
all of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The rate of rotation of a moving body about an axis may be determined by mounting an accelerometer on a frame and dithering it, with the accelerometer's sensitive axis and the direction of motion of the frame both normal to the rate axis about which rotation is to be measured. For example, consider a set of orthogonal axes X, Y and Z oriented with respect to the moving body. Periodic movement of the accelerometer along the Y axis of the moving body with its sensitive axis aligned with the Z axis results in the accelerometer experiencing a Coriolis acceleration directed along the Z axis as the moving body rotates about the X axis. A Coriolis acceleration is that perpendicular acceleration developed while the body is moving in a straight line, while the frame on which it is mounted rotates. This acceleration acting on the accelerometer is proportional to the velocity of the moving sensor body along the Y axis and its angular rate of rotation about the X axis. An output signal from the accelerometer thus includes a DC or slowly changing component or force signal F representing the linear acceleration of the body along the Z axis, and a periodic component or rotational signal &OHgr; representing the Coriolis acceleration resulting from rotation of the body about the X axis.
The amplitude of that Coriolis component can be produced by vibrating the accelerometer, causing it to dither back and forth along a line perpendicular to the input axis of the accelerometer. Then, if the frame on which the accelerometer is mounted is rotating, the Coriolis acceleration component of the accelerometer's output signal will be increased proportional to the dither velocity. If the dither amplitude and frequency are held constant, then the Coriolis acceleration is proportional to the rotation rate of the frame.
The linear acceleration component and the rotational component representing the Coriolis acceleration may be readily separated by using two accelerometers mounted in back-to-back relationship to each other and processing their out put signals by sum and difference techniques. In U.S. Pat. No. 4,510,802, assigned to the assignee of this invention, two accelerometers are mounted upon a parallelogram with their input axes pointing in opposite directions. An electromagnetic D'Arsonval coil is mounted on one side of the parallelogram structure and is energized with a periodically varying current to vibrate the accelerometers back and forth in a direction substantially normal to their sensitive or input axis. The coil causes the parallelogram structure to vibrate, dithering the accelerometers back and forth. By taking the difference between the two accelerometer outputs, the linear components of acceleration are summed. By taking the sum of the two outputs, the linear components cancel and only the Coriolis or rotational components remain.
U.S. Pat. No. 4,590,801, commonly assigned to the assignee of this invention, describes the processing of the output signals of two accelerometers mounted for periodic, dithering motion to obtain the rotational rate signal &OHgr; and the force or acceleration signal F representing the change in velocity, i.e. acceleration of the moving body, along the Z axis. U.S. Pat. No. 4,510,802, commonly assigned to the assignee of this invention, describes a control pulse generator, which generates and applies a sinusoidal signal of a frequency &ohgr; to the D'Arsonval coil to vibrate the parallelogram structure and thus the first and second accelerometer structures mounted thereon, with a dithering motion of the same frequency &ohgr;. The accelerometer output signals are applied to a processing circuit, which sums the accelerometer output signals to reinforce the linear components indicative of acceleration. The linear components are integrated over the time period T of the frequency &ohgr; corresponding to the dither frequency to provide the force signal F, which represents the change in velocity, i.e. acceleration, along the Z axis. The accelerometer output signals are also summed, whereby their linear components cancel and their Coriolis components are reinforced to provide a signal indicative of frame rotation. That difference signal is multiplied by a zero mean periodic function sgnc &ohgr;t. The resulting signal is integrated over a period T of the frequency &ohgr; by a sample and hold circuit to provide the signal &OHgr; representing the rate of rotation of the frame.
The D'Arsonval coil is driven by a sinusoidal signal of the same frequency &ohgr; which corresponded to the period T in which the linear acceleration and Coriolis component signals were integrated. In particular, the pulse generator applies a series of pulses at the frequency &ohgr; to a sine wave generator, which produces the substantially sinusoidal voltage signal to be applied to the D'Arsonval coil. A pair of pick-off coils produce a feedback signal indicative of the motion imparted to the accelerometers. That feedback signal is summed with the input sinusoidal voltage by a summing junction, whose output is applied to a high gain amplifier. the output of that amplifier in turn is applied to the D'Arsonval type drive coil. The torque output of the D'Arsonval coil interacts with the dynamics of the parallelogram structure to produce the vibrating or dither motion. In accordance with well known servo theory, the gain of the amplifier is set high so that the voltage applied to the summing junction and the feedback voltage are forced to be substantially equal and the motion of the mechanism will substantially follow the drive voltage applied to the summing junction.
U.S. Pat. No. 4,881,408 describes the use of vibrating beam force transducers in accelerometers. In U.S. Pat. No. 4,372,173, the force transducer takes the form of a double-ended tuning fork fabricated from crystalline quartz. The transducer comprises a pair of side-by-side beams which are connected to common mounting structures at their ends. Electrodes are deposited on the beams and a drive
Allied-Signal
Mullins Burton
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