Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2001-07-20
2002-11-12
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S357490
Reexamination Certificate
active
06480152
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
1. Field of the Present Invention
The present invention relates to a motion measurement system, and more particularly to an integrated Global Positioning System (GPS)/Inertial Measurement Unit (IMU) micro system, which can produce highly accurate, digital angular rate, acceleration, position, velocity, and attitude measurements of a carrier under a variety of environment.
2. Description of Related Arts
In the past decade, an IMU or GPS receiver is commonly employed to determine the motion measurement of a carrier.
An IMU is a key part of an inertial navigation system (INS). Generally, an INS consists of an IMU, a microprocessor and associated embedded navigation software. The components of the IMU include the inertial sensors (angular rate producer and acceleration producer, traditionally called gyros and accelerometers or angular rate sensor and acceleration sensor) and the associated hardware and electronics. Based on the carrier acceleration and rotation rate measurements obtained from the onboard inertial sensors, the position, velocity, and attitude measurements of a carrier are obtained by numerically solving Newton's equations of motion through the microprocessor.
In principle, an IMU relies on three orthogonally mounted inertial angular rate producers and three orthogonally mounted acceleration producers to produce three-axis angular rate and acceleration measurement signals. The three orthogonally mounted inertial angular rate producers and three orthogonally mounted acceleration producers with additional supporting mechanical structure 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 producers and acceleration producers 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, highly accurate feedback control loops are required to implement the platform IMU.
Compared with the platform IMU, in a strapdown IMU, angular rate producers and acceleration producers are directly strapped down with the carrier and move with the carrier. The output signals of the strapdown angular rate producers and acceleration producers are angular rate and acceleration measurements expressed in the carrier body frame. The attitude measurements can be obtained by means of a series of computations.
A conventional IMU uses a variety of inertial angular rate producers and acceleration producers. Conventional inertial angular rate producers include iron spinning wheel gyros and optical gyros, such as 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 acceleration producers include Pulsed Integrating Pendulous Accelerometer (PIPA), Pendulous Integrating Gyro Accelerometer (PIGA), etc.
The inertial navigation system, which uses a platform IMU, in general, is catalogued as a gimbaled inertial navigation system. The inertial navigation system which uses a strapdown IMU is, in general, catalogued as a strapdown inertial navigation system. In a gimbaled inertial navigation system, the angular rate producer and acceleration producer 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 coordinated 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), locally level with axes in the directions of north-east-down (NED) or east-north-up (ENU) or north-west-up (NWU), and locally level with a wander azimuth. 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 established and updated in a high rate to transform the acceleration measurements from the body frame to the navigation frame.
In general, the motion measurements from the gimbaled inertial navigation system are more accurate than the ones from the strapdown inertial navigation system. Moreover, the gimbaled inertial navigation system is easier to be calibrated than 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, reliability, and small size.
An inertial navigation system is based on the output of inertial angular rate producer and acceleration producer of an IMU to provide the position, velocity, and attitude information of a carrier through a deadreckoning method. Inertial navigation systems, in principle, permit self-contained operation and output continuous position, velocity, and attitude data of a carrier after loading the starting position and performing an initial 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 errors, velocity errors, and attitude errors increase with time. This error propagation characteristic is primarily caused by many error sources, such as, gyro drift, accelerometer bias, misalignment, gravity disturbance, initial position and velocity errors, and scale factor errors.
Generally, the ways of improving accuracy of inertial navigation systems include employing highly accurate inertial sensors and aiding the inertial navigation system using an external sensor.
However, current highly accurate inertial sensors are very expensive with big size and heavy weight.
A GPS receiver has been commonly used to aid an inertial navigation system recently. 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.
A specific GPS receiver is the key for a user to access 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 so-called pseudo range and range rate measurements 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 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 can provide both position and attitude solution of a carrier, using interferometric techniques. This 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 attitude measurement sy
An Dong
Lin Ching-Fang
American GNC Corporation
Chan Raymond Y.
David & Raymond Patent Group
Phan Dao
LandOfFree
Integrated GPS/IMU method and microsystem thereof does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Integrated GPS/IMU method and microsystem thereof, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Integrated GPS/IMU method and microsystem thereof will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2933963