Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
2001-01-22
2002-06-18
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C701S214000, C340S398100, C340S450000
Reexamination Certificate
active
06408245
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
1. Field of the Present Invention
The present invention relates to a filtering mechanization method, and more particularly to a filtering mechanization method for integration of a Global Positioning System (GPS) receiver with an Inertial Measurement Unit (IMU) to produce highly accurate, highly reliable, and mixed GPS/IMU position, velocity, and attitude measurements of a carrier at affordable cost under high dynamic environments, heavy noise environments, and long-term (long-period) operation.
2. Description of Related Arts
The major function of a navigation system is designed to produce continuous position, velocity, and attitude measurements of a carrier, such as a vehicle, under dynamic environments. The attitude measurements usually include pitch, roll, and heading angle of the carrier.
In the past decade, a low cost inertial navigation system (INS) and GPS (Global Positioning System) receiver were commonly developed to determine the positioning measurements of a vehicle at affordable cost, such as position, velocity, etc.
An INS relies on three orthogonally mounted inertial angular rate sensors and three orthogonally mounted acceleration sensors to produce three-axis angular rate and acceleration measurements. Based on the carrier acceleration and angular rate measurements, the position, velocity, and attitude measurements of a carrier are obtained by numerically solving Newton's equations of motion. The three orthogonally mounted inertial angular rate sensors and three orthogonally mounted acceleration sensors with additional supporting mechanical structures and electronic devices are conventionally called an Inertial Measurement Unit (IMU). The conventional IMUs may be catalogued into Platform IMU and Strapdown IMU.
In the platform IMU, angular rate sensors and acceleration sensors are installed on a stabilized platform. Attitude measurements can be directly picked off from the platform structure. But attitude rate measurements cannot be directly obtained from the platform. Moreover, highly accurate feedback control loops must be designed to implement the platform IMU.
Compared with the platform IMU, in a strapdown IMU, the angular rate sensors and acceleration producers are directly strapped down to the carrier and move with the carrier. The output signals of the angular rate sensors and acceleration sensors are expressed in the carrier body frame. The attitude and attitude rate measurements can be obtained by means of a series of computations.
The INS, which uses a platform IMU, in general, is catalogued as a gimbaled inertial navigation system. The INS, which uses a strapdown IMU, in general, is catalogued as a strapdown inertial navigation system. In a gimbaled inertial navigation system, the angular rate sensors and acceleration sensors are mounted on a gimbaled platform to isolate the sensors from the rotations of the carrier so that the measurements and navigation calculations can be performed in a stabilized navigation coordinates frame. Generally, the motion of the carrier can be expressed in several navigation frames of reference, such as earth centered inertial (ECI), earth-centered earth-fixed (ECEF), and North-East-Down (NED), etc. In a strapdown inertial navigation system, the inertial sensors are rigidly mounted to the carrier body frame. In order to perform the navigation computation in the stabilized navigation frame, a coordinate frame transformation matrix is used and updated to transform the acceleration measurements from the body frame to the navigation frame.
In general, the navigation solution from the gimbaled inertial navigation system is more accurate than the one from the strapdown inertial navigation system. But, a gimbaled inertial navigation system is more complex and expensive than a strapdown inertial navigation system. The strapdown inertial navigation systems become the predominant mechanization due to their low cost and reliability.
An inertial navigation system provides the position, velocity, and attitude information of a carrier through a dead reckoning method. Inertial navigation systems, in principle, perform a self-contained operation and output continuous position, velocity, and attitude data of the carrier after initializing the starting position and initiating an alignment procedure.
In addition to the self-contained operation, other advantages of an inertial navigation system include the full navigation solution and wide bandwidth.
However, an inertial navigation system is expensive and is degraded with drift in output (position, velocity, and attitude) over an extended period of time. It means that the position and velocity errors increase with time. This error propagation characteristic is primarily caused by errors, such as, gyro drifts, accelerometer bias, misalignment, gravity disturbance, initial position and velocity errors, and scale factor errors.
Generally, the ways of improving the accuracy of inertial navigation systems include employing highly accurate inertial sensors and aiding the inertial navigation system using an external sensor. However, highly accurate inertial sensors are very expensive with big size and heavy weight.
A GPS receiver is a very ideal external source to aid an inertial navigation system. The GPS is a satellite-based, worldwide, all-weather radio positioning and timing system. The GPS system is originally designed to provide precise position, velocity, and timing information on a global common grid system to an unlimited number of adequately equipped users.
GPS receivers are designed for a user to exploit the advantages of the Global Positioning System. A conventional, single antenna GPS receiver supplies world-wide, highly accurate three dimensional position, velocity, and timing information, but not attitude information, by processing the so-called pseudo range and delta range measurements output from the code tracking loops and the carrier tracking loops in the GPS receiver, respectively. In a benign radio environment, the GPS signal propagation errors and GPS satellite errors, including the Selective Availability, serve as the bounds for positioning errors. However, the GPS signals may be intentionally or unintentionally jammed or spoofed, and the GPS receiver antenna may be obscured during carrier attitude maneuvering, and the performance degrades when the signal-to-noise ratio of the GPS signal is low and the carrier is undergoing highly dynamic maneuvers.
As both the cost and size of high performance GPS receivers are reduced in the past decade, a multiple-antenna GPS receiver was developed to provide both position and attitude solutions of a vehicle, using interferometric techniques. In principle, the attitude determination technology utilizes measurements of GPS carrier phase differences on the multiple-antenna to obtain highly accurate relative position measurements. Then, the relative position measurements are converted to the attitude solution. The advantages of this approach are long-term stability of the attitude solution and relatively low cost. However, this GPS position and attitude determination system still retains the characterization of low bandwidth which is susceptible to shading and jamming, requires at least 3 antennas configurations for a three-axis attitude solution, and requires antenna separation enough for high attitude resolution.
Because of the inherent drawbacks of a stand-alone inertial navigation system and a stand-alone GPS receiver, a stand-alone inertial navigation system or a stand-alone GPS receiver can not meet mission requirements under some constraints, such as low cost, long-term high accuracy, highly reliable, continuous high rate output, etc.
The mutual complementary characteristics of the stand-alone GPS receiver and the stand-alone inertial navigation system suggest that, in many applications, an integrated GPS/IMU system, combining the best positive properties of both systems, will provide superior accurate continuous navigation capability. This navigation capability is unattainable in either one of t
An Dong
Lin Ching-Fang
American GNC Corporation
Chan Raymond Y.
David and Raymond Patent Group
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