Measuring and testing – Speed – velocity – or acceleration – Acceleration determination utilizing inertial element
Reexamination Certificate
2002-04-29
2004-03-09
Moller, Richard A. (Department: 2856)
Measuring and testing
Speed, velocity, or acceleration
Acceleration determination utilizing inertial element
C073S504040, C073S514180, C073S504160
Reexamination Certificate
active
06701786
ABSTRACT:
BACKGROUND
1. Technical Field of the Invention
The present invention relates to an apparatus and methods for determining the acceleration and rate of angular rotation of a moving body, and in particular, one which is adapted to be formed, for example through micromachining, from a silicon substrate.
2. Description of the Prior Art
A variety of methods and systems are known for determining the acceleration and rate of angular rotation of a moving body. Such methods and systems have found their way in a diverse range of applications, one of which is military. However, the use of tactical grade inertia measuring units has been limited by their cost to high-priced systems such as military aircraft, missiles, and other special markets. The cost of inertia measuring units is dominated by the expensive discrete gyroscopes and discrete accelerometers and attendant electronics used to drive and convert these signals for use in computer systems.
Other problems with inertial measuring units are high power consumption and large package size. The problems of high power consumption and large package size further limit applications to larger equipment boxes in equipment racks. For example, a hockey puck sized tactical grade navigator is not known in the prior art.
Still other problems with the prior art, discussed below in more detail, include a limitation in rate bias accuracy caused by modulation of the accelerometer due to coupling from the dither motion which causes phase angle sensitivity of the rate data. A further limitation in rate bias accuracy is caused by modulation of the accelerometer due to coupling of external vibration components coupling into the rate data.
Exemplary rate and acceleration sensors, components of such sensors, and methods of forming the same are described in the following patents all of which are assigned to the assignee of this disclosure: U.S. Pat. Nos. 5,005,413; 5,168,756; 5,319,976; 5,331,242; 5,331,854; 5,341,682; 5,367,217; 5,456,110; 5,456,111; 5,557,046; 5,627,314; 6,079,271; 6,098,462; and 6,276,203.
By way of background, 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 Coriolis 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 output signals using summed difference techniques. In U.S. Pat. No. 4,510,802, assigned to the assignee of the present 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 axes. 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 the present 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 the present 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 a well known in the art 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 doubleended tuning fork fabricated from crystalline quartz. The transducer comprises a pair of side-by-side beams which are connected to c
L-3 Communications Corporation
Moller Richard A.
Proskauer Rose LLP
LandOfFree
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