Data processing: measuring – calibrating – or testing – Measurement system – Accelerometer
Reexamination Certificate
1999-09-20
2002-10-29
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Accelerometer
C701S011000
Reexamination Certificate
active
06473713
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
1. Field of the Present Invention
The present invention relates to a processing method for motion measurement, and more particularly to a processing method for a motion inertial measurement unit, wherein output signals of an angular rate producer and acceleration producer, such as an angular rate device array and an acceleration device array, or an angular rate and acceleration simulator, are processed to obtain highly accurate attitude and heading measurements of a carrier under dynamic environments.
2. Description of Related Arts
Generally, conventional methods for determining the motion of a carrier are to employ inertial angular rate devices and acceleration devices, such as gyros and accelerometers, radio positioning systems, and hybrid systems.
In principle, inertial motion measurement methods depend on three orthogonally mounted inertial rate sensors and three orthogonally mounted accelerometers to obtain three-axis rate and acceleration measurement signals. The three orthogonally mounted inertial rate sensors and three orthogonally mounted accelerometers with additional supporting mechanical structure and electronics devices are conventionally called an Inertial Measurement Unit (IMU). The existing IMUs may be cataloged into Platform IMU and Strapdown IMU.
In the Platform IMU, rate sensor and accelerometers are installed on a stabilized platform. Attitude measurements can be directly picked off from the platform structure. But attitude rate measurements can not be directly obtained from the platform. Moreover, there are highly accurate feedback controlling loops associated with the platform.
Compared with the platform IMU, in the strapdown IMU, rate sensors and accelerometers are directly fixed in the carrier and move with the carrier. The output signals of strapdown rate sensors and accelerometers are expressed in the carrier body frame. The attitude and attitude rate measurements can be obtained by means of a series of computations.
Conventional inertial rate sensors include Floated Integrating Gyros (FIG), Dynamically Tuned Gyros (DTG), Ring Laser Gyros (RLG), Fiber-Optic Gyros (FOG), Electrostatic Gyros (ESG), Josephson Junction Gyros (JJG), Hemisperical Resonating Gyros (HRG), etc.
Conventional accelerometer includes Pulsed Integrating Pendulous Accelerometer (PIPA), Pendulous Integrating Gyro Accelerometer (PIGA), etc.
The processing methods in conventional IMUs vary with types of gyros and accelerometers used in the IMUs. Because conventional gyros and accelerometers have big size, large power consumption, and moving mass, complex feedback controlling loops are required to obtain stable motion measurements. For example, dynamic-tuned gyros and accelerometers need force-rebalance loops to create a moving mass idle position. There are often pulse modulation force-rebalance circuits associated with dynamic-tuned gyros and accelerometer based IMUs.
New horizons are opening up for inertial sensor device technologies. MEMS (MicroElectronicMechanicalSystem) inertial sensors offer tremendous cost, size, reliability improvements for guidance, navigation, and control systems, compared with conventional inertial sensors. It is well-known that the silicon revolution began over three decades ago, with the introduction of the first integrated circuit. The integrated circuit has changed virtually every aspect of our lives. The hallmark of the integrated circuit industry over the past three decades has been the exponential increase in the number of transistors incorporated onto a single piece of silicon. This rapid advance in the number of transistors per chip leads to integrated circuits with continuously increasing capability and performance. As time has progressed, large, expensive, complex systems have been replaced by small, high performance, inexpensive integrated circuits. While the growth in the functionality of microelectronic circuits has been truly phenomenal, for the most part, this growth has been limited to the processing power of the chip.
MEMS, or, as stated more simply, micromachines, are considered the next logical step in the silicon revolution. It is believed that this coming step will be different, and more important than simply packing more transistors onto silicon. The hallmark of the next thirty years of the silicon revolution will be the incorporation of new types of functionality onto the chip structures, which will enable the chip to, not only think, but to sense, act, and communicate as well.
Prolific MEMS angular rate sensor approaches have been developed to meet the need for inexpensive yet reliable angular rate sensors in fields ranging from automotive to consumer electronics. Single input axis MEMS angular rate sensors are based on either translational resonance, such as tuning forks, or structural mode resonance, such as vibrating rings. Moreover, Dual Input Axis MEMS Angular Rate Sensors may be based on angular resonance of a rotating rigid rotor suspended by torsional springs. The inherent symmetry of the circular design allows angular rate measurement about two axes simultaneously. Preferred MEMS angular rate sensors are mostly based on an electronically-driven tuning fork method. Such MEMS gyros operate in accordance with the dynamic theory (Coriolis Effect) that when an angular rate is applied to a translating body, a Coriolis force is generated. When this angular rate is applied, the axis of an oscillating tuning fork, its tines receive a Coriolis force, which then produces torsional forces about the sensor axis. These forces are proportional to the applied angular rate, which then can be measured capacitively, as shown in FIG.
16
.
MEMS devices can be fabricated by bulk micromachining (chemical etching) single crystal silicon or by surface micromachining layers of ploysilicon. Surface micromachined devices are typically a few microns to 10 microns thick while bulk machining produces devices 100 to 500 microns thick. Angular rate sensors created with surface machining have very low masses and are presently not sensitive enough for military applications but are useful for automotive applications. Bulk machining produces devices with far greater mass but it is a much more expensive technology. Allied Signal produces bulk machined inertial sensors. The advantage of surface machining is the low cost and the ease of incorporating the electronics close to the sensor.
FIG. 17
depicts the basis of the Charles Stark Draper Laboratory design based on an electronically-driven tuning fork method. The MEMS angular rate sensor measures angular rate voltage signals by picking-off a signal generated by an electromechanical oscillating mass as it deviates from its plane of oscillation under the Coriolis force effect when submitted to a rotation about an axis perpendicular to the plane of oscillation. Two vibrating proof masses are attached by springs to each other and to the surrounding stationary material. The vibrating (dither) proof masses are driven in opposite directions by electrostatic comb drive motors to maintain lateral in-plane oscillation. The dither motion is in the plane of the wafer. When an angular rate is applied to the MEMS device about the input axis (which is in the plane of the tines), the proof masses are caused to oscillate out of plane by a Coriolis force due to Coriolis effect. The resulting out-of-plane up and down oscillation motion amplitude, proportional to the input angular rate, is detected and measured by capacitive pickoff plates underneath the proof masses. The device can either be designed for closed loop or open loop operation. Running the device closed loop adds more complexity but less cross coupling and better linearity. The comb drives move the masses out of phase with respect to each other. The masses will then respond in opposite directions to the Corilois force.
Several MEMS accelerometers incorporate piezoresistive bridges such as those used in early micromechnical pressure gauges. More accurate accelerometers are the force rebalance type that uses closed-loop capacitive sen
Lin Ching-Fang
McCall Hiram
American GNC Corporation
Chan Raymond Y.
Charioui Mohamed
David & Raymond Patent Group
Hoff Marc S.
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