Data processing: vehicles – navigation – and relative location – Relative location – Collision avoidance
Reexamination Certificate
2000-12-04
2002-11-12
Louis-Jacques, Jacques H. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Relative location
Collision avoidance
C701S300000, C701S120000, C701S122000, C340S947000, C340S961000, C342S029000, C342S032000, C342S064000, C342S065000
Reexamination Certificate
active
06480789
ABSTRACT:
FIELD OF THE PRESENT INVENTION
The present invention relates to an integrated positioning/proximity warning method and system thereof for vehicles, in which the information from the sensors of the positioning system and the ground proximity warning system are integrated to obtain improved performance of positioning and ground/water proximity warning functions; position data of near objects from an onboard object detection system is further incorporated to warn and avoid a potential collision hazard with the near objects.
BACKGROUND OF THE PRESENT INVENTION
Nowadays, there exist stand-alone operating positioning systems and ground proximity warning systems in civil aircraft. A positioning system is used to provide position, velocity, attitude, attitude rate information, and etc., for an aircraft flight control and management system. A ground proximity warning system is used to provide warning messages to prevent aircraft from inadvertently contacting with the ground or water.
Traditionally, positioning equipment in a civil aircraft generally employs an inertial navigation system and some radio navigation systems, such as a long range navigation system, a very-high-frequency omnidirectional range system, distance measurement equipment, tactical air navigation, and the newest global positioning system. Recently, integrated global positioning systems/inertial navigation systems have been the predominant navigation system in civil and military aircraft, replacing traditional navigation systems.
Generally speaking, an inertial navigation system comprises an onboard inertial measurement unit, a processor, and embedded software. The positioning solution is obtained by numerically solving Newton's equations of motion using measurements of vehicle specific forces and rotation rates obtained from onboard inertial sensors. The onboard inertial sensors consist of accelerometers and gyros, which, together with the associated hardware and electronics, comprise the inertial measurement unit.
The inertial navigation system may be mechanized in either a gimbaled or strapdown configuration. In a gimbaled inertial navigation system, the accelerometers and gyros are mounted on a gimbaled platform to isolate the sensors from the rotations of the vehicle, and to keep the measurements and navigation calculations in a stabilized navigation coordinated frame. Some possible navigation frames include earth centered inertial, earth centered earth fixed, locally level, with axes in the directions of north, east, down (of course, there is east, north, zenith or north, west, zenith, and locally level with a wander azimuth). In a strapdown inertial navigation system, the inertial sensors are rigidly mounted to the vehicle body frame, and a coordinate frame transformation matrix (analyzing platform) is used to transform the body-expressed acceleration to a navigation frame to perform the navigation computations in the stabilized navigation frame. Gimbaled inertial navigation systems can be more accurate and easier to calibrate than strapdown inertial navigation systems. Strapdown inertial navigation systems can be subjected to higher dynamic conditions (such as high turn rate maneuvers) which can stress inertial sensor performance. However, with the availability of newer gyros and accelerometers, strapdown inertial navigation systems are becoming the predominant mechanization, due to their low cost and reliability.
In principle, inertial navigation systems permit pure autonomous operation and output continuous position, velocity, and attitude vehicle data after initializing the starting position and initiating an alignment procedure. In addition to autonomous operation, other advantages of an inertial navigation system include the full navigation solution and wide bandwidth. However, an inertial navigation system is expensive and subjected to drift over an extended period of time. This error propagation characteristic is primarily caused by its inertial sensor error sources, such as gyro drift, accelerometer bias, and scale factor errors.
Generally, the accuracy of inertial navigation systems can be improved by employing highly accurate inertial sensors or by compensating with data from an external sensor.
The cost of developing and manufacturing inertial sensors increases as the level of accuracy improves. The advances in new inertial sensor technologies and electronic technologies have led to the availability of low cost inertial sensors, such as mechnical-electronis-micro-system inertial sensors. Mechnical-electronic-micro-system inertial sensors borrow processes from the semiconductor industry to fabricate tiny sensors and actuators on silicon chips. The precision of these new inertial sensors may be less than what conventional sensors achieve, but they have enormous cost, size, weight, thermal stability and wide dynamic range advantages over conventional inertial sensors.
The most obvious choice for implementing low cost, highly accurate, continuous positioning of a vehicle is to employ a low cost strapdown inertial system with the compensating of an external sensor. The global positioning system receiver is an ideal external sensor for an inertial navigation system.
The global positioning system is a space-based, worldwide, all-weather passive radio positioning and timing system which was developed and implemented over the course of the past two decades. The system was originally designed to provide precise position, velocity, and timing information on a global common grid system to an unlimited number of adequately equipped air, land, sea, and even space authorized users and civil users.
The global positioning system has three major operational segments:
Space Segment: The Space segment consists of a constellation of satellites (21 navigation satellites plus 3 active spares) in semi-synchronous orbit around the earth.
Control Segment: The control segment consists of one master ground control station and several other monitor stations with tracking antennas at accurately known positions throughout the earth.
User Segment: The User Segment is composed of the various kinds of end user with global positioning system receiving equipment.
The global positioning system user equipment comprises an antenna, a receiver, and associated electronics and displays, and receives signals from the global position system satellites to obtain a position, velocity, and time solution.
The global positioning system can provide Precise Positioning Service to authorized users, which is nominally within 15 meters Spherical Error Probable accuracy, and can provide Standard Position Service to civil users, which is limited to within roughly 100 meters (95% probability) by a number of error sources including ionospheric and troposheric effects and intentional degradation of the global positioning system signal, known as selective availability.
The global positioning system principle of operation is based on range triangulation. If the satellite position is known accurately via ephemeris data, the user can receive the satellite's transmitted signal and determine the signal propagation time. Since the signal travels at the speed of light, the user can calculate the measured range to the satellite. The actual range measurement (called the “pseudo range”) contains errors because of a bias in the user's clock relative to the global positioning system reference time. Because atomic clocks are utilized in the satellites, their errors are much smaller in magnitude than the users' clocks. Thus, for three-dimensional position determination, and also to calculate the clock bias, a minimum of four satellites is needed to obtain a solution to the navigation problem. The velocity can be obtained by various methods, which basically amount to time differencing the pseudo ranges over the measurement time interval.
As with any other measurement system, a global positioning system contains a number of error sources, such as the signal propagation errors and satellite errors, including selective availability. The user range error
American GNC Corporation
Chan Raymond Y.
David & Raymond Patent Group
Louis-Jacques Jacques H.
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