Education and demonstration – Vehicle operator instruction or testing – Flight vehicle
Reexamination Certificate
1999-03-30
2001-05-22
Harrison, Jessica J. (Department: 3713)
Education and demonstration
Vehicle operator instruction or testing
Flight vehicle
C434S037000, C434S029000, C345S952000
Reexamination Certificate
active
06234799
ABSTRACT:
FIELD OF THE PRESENT INVENTION
The present invention relates to an inertial measurement unit simulator, and more particularly to a real-time inertial measurement unit (IMU) simulator in response to inertial measurement simulation for global positioning system (GPS) guidance receivers/inertial navigation systems(INS). This invention was made with Government support under Contract No. F08635-98-6865. The Government has certain rights in the invention.
BACKGROUND OF THE PRESENT INVENTION
A typical integrated GPS/INS system is depicted as FIG.
1
. The GPS receiver and IMU are the two major parts in the integrated system. The GPS receiver receives RF signals from the GPS satellites while the IMU produces its own signals because of its self-contained characteristics. From the viewpoint of installed system testing, the simulation of a GPS receiver and an IMU is much different. Usually a real-time GPS satellite constellation RF simulator is used to generate the GPS satellite signals and inject them into the GPS receiver. But we cannot inject electronic signals into an IMU from outside.
A straightforward method for dynamic ground testing is the application of the flight motion tables that provide the motion of the aircraft or munitions during simulated flight in an installed system environment. With this method, the GPS receiver receives actual satellite RF signals and the IMU produces dynamic inertial measurement signals itself, for the integrated system is actually in motion. But this motion table method is not a viable solution. It needs a large set of testing equipment, its operational cost is high, its dynamic motion is limited, and its data acquisition during the simulation is not convenient. Therefore, the real-time computer simulation system for the dynamic ground testing of the installed system is desired.
SUMMARY OF THE PRESENT INVENTION
The main objective of the present invention is to develop and validate the software and hardware design of a real-time Inertial Measurement Unit (IMU) simulator. The IMU simulator is installed system test equipment. It supports the final integration of a developmental Guidance, Navigation, and Control (GNC) system into an aircraft or other vehicles. It assures testers that GNC avionics on board an aircraft work properly before and during a flight test. It helps debug on-board GNC avionics and verify the system performance. During the test, the IMU simulator receives real-time flight data from the 6DOF trajectory generator and produces IMU electronic signals according to the IMU measurement models and error models defined by the user. The simulated electronic signals are injected into the installed avionics system causing the on-board GNC system computer into “thinking” that the aircraft is really flying. The IMU simulator is useful equipment for ground testing of installed systems, laboratory hardware-in-the-loop dynamic simulation, and GNC system analysis and development. It has wide applications in both the military sector and the commercial world.
Another objective of the present invention is to provide a real-time inertial measurement unit simulator, wherein IMU models expressed in different coordinate systems have been developed. In the developed models, three coordinate systems are used: Earth-Centered Inertial coordinate system (denoted ECIZ), Earth-Centered Earth-Fixed coordinate system (denoted ECEF), and Navigation (or local geographical) coordinate system (denoted N). For different trajectory reference frames, the IMU measurement models have different mathematical forms. In order to build high accuracy IMU models, the gravity model of the earth was also included.
Another objective of the present invention is to provide a real-time inertial measurement unit simulator, wherein The IMU error modeling and simulation methods were investigated and the IMU error simulation methods were evaluated by the experimental system. In the software design for the error models, in addition to a generic error model, we also provide several error models for specific IMU sensors.
Another objective of the present invention is to provide a real-time inertial measurement unit simulator, wherein the proposed real-time IMU simulator is designed and realized on a high-performance PC computer. The PC's richness in software and hardware support makes it possible for us to have a variety of options in the configuration design of the IMU simulator. A modularized software design method is employed and the programs are organized in functional modules. The software is programmed mainly in the C/C++ language. The Matlab/Simulink software and the Labview software are used to test, simulate and evaluate the algorithm and software design for the IMU simulator.
Another objective of the present invention is to provide a real-time inertial measurement unit simulator, wherein a survey of current IMU electronics was made and based on the analysis results we found that though there are various types, the IMU output signals can be classified into the following four categories: (1) Analog signals, (2) Pulse signals, (3) Parallel digital signals or parallel standard bus emulation, and (4) Serial digital signals or serial standard bus emulation. According to the classification of the IMU output signals, a three-level hardware design was proposed and investigated.
Another objective of the present invention is to provide a real-time inertial measurement unit simulator, wherein the aims of the simulation were (1) to verify the correctness of the mathematical models, (2) to select a suitable computation algorithm, (3) to analyze the computation errors, and (4) to validate the fidelity of the simulated IMU signals. The simulation models are mainly programmed by using Matlab/Simulink software. The Matlab/Simulink program modules can be converted to the corresponding C language modules by a code generator in the Matlab/Simulink software. The verified simulation models are then used to validate the C/C++ program developed for the IMU simulator. Combining the use of Matlab/Simulink and Labview software, the simulation models can also generate real-time electronic signals. The generated real-time IMU signals can be displayed or can be injected into the INS system if it contains a DAC board and an injection connector.
Accordingly, in order to achieve the above objective, the following innovative technical features have been brought to our investigation.
The correct and accurate IMU measurement models are essential for the IMU simulator. The measurement models of the IMU are determined by the physical and kinematics principles of the inertial sensor. They describe the relationships between the ideal outputs of an IMU and the motion of the vehicle on which the IMU is installed. If a real IMU is installed in an aircraft or munition, it measures the vehicle's motion and produces measurement signals or data accordingly. An IMU simulator, however, must produce measurement signals or data, through a software model, according to the trajectory generated by the 6DOF flight simulator. Once the trajectory of a flight mission is defined, the 6DOF flight simulator can produce real-time flight states over the entire simulation period. A measurement model of the IMU simulator is required to produce ideal IMU outputs.
Generally, a trajectory generator consists of a full 6DOF kinematics model. It calculates a state vector consisting of several scalar variables to fully describe the trajectory of the simulated vehicle. Typically, the flight state variables include:
1. Time.
2. Translational position, velocity and acceleration.
3. Rotation matrix, angular velocity, and angular acceleration.
Because the flight trajectory or states can be expressed in different coordinate systems according to mission requirements or tester preference, we have to develop a suite of IMU measurement models expressed in different frames. In the developed models, three coordinate systems are used: Earth-Centered Inertial coordinate system (denoted ECIZ), Earth-Centered Earth-Fixed coordinate system (
American GNC Corporation
Chan Raymond Y.
David and Raymond Patent Group
Harris Chanda
Harrison Jessica J.
LandOfFree
Real-time IMU simulator does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Real-time IMU simulator, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Real-time IMU simulator will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2464727