1. Field of the Present Invention
The present invention relates to an orientation measurement method and system, and more particularly to an orientation measurement method and system with three-axes acceleration producers and an Earth""s magnetic detector and a Digital Signal Processing (DSP) technique, which can produce highly accurate, digital, attitude, and heading measurements of a static platform, such as pitch, roll, and heading, and the local Earth""s magnetic field vector measurements.
2. Description of Related Arts
Conventionally, the system that can provide attitude and heading measurements of a static platform includes: an inertial measurement unit (IMU) that can provide attitude, and heading measurements; a vertical gyro that can provide pitch and roll measurements; directional gyro that can provide heading measurements; a compass that can provide heading measurement; a tilt sensor that can provide pitch and roll angle measurements.
The principle that the IMU determines the attitude and heading measurements of the static platform depends on the so-called self-alignment capability, which uses gravity acceleration to compute a local level-plane, and the Earth rate vector to determine heading direction. It is well known that Gravity acceleration is a strong signal. Unfortunately, the Earth rate vector is a very weak signal. For example, modern aircraft are capable of angular rates exceeding 400 deg/sec or nearly one hundred thousand times the Earth""s rotation rate of 15 deg/hr. Furthermore, the horizontal component of the Earth rate is a function of latitude areas, and decreases substantially as latitude increases. For example, at 45 degrees latitude, the north Earth rate decreases to 10.6 degrees/hr, while at 70 degrees latitude, the value is only 5.13 degrees/hr. As latitude approaches 90 degrees, the north Earth rate vanishes and heading becomes undefined. Because of the small magnitude of the Earth rate, the heading is always more difficult to acquire than are pitch and roll for a low cost, low quality IMU. For example, an IMU with 1 deg/hr angular rate producers is typically capable of approximately 5 degrees initial heading at mid-latitude areas.
The magnetic compass has been used for centuries. Today, the balanced needle compass and the gimbaled compass are variations of the early magnetic compass. However, these compasses have big size and low accuracy and slow response time.
Therefore, conventional orientation systems commonly have the following features: high cost; large bulk (volume, mass, large weight); high power consumption; limited lifetime, and; long turn-on time. These present deficiencies of conventional orientation measurement systems prohibit them from use in the emerging commercial applications, such as phased array antennas for mobile communications, automotive navigation, and handheld equipment.
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. One of the benefits of the silicon revolution is today""s powerful digital signal processor. 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.
As in the previous silicon revolution, a new sensor revolution is coming. MEMS (MicroElectronicMechanicalSystem), or, as stated more simply, micromachines, are considered the next logical revolution after the silicon revolution. It is believed that this coming revolution will be different, and more important than simply packing more transistors onto silicon. The hallmark of the next thirty years of the silicon revolution including MEMS 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.
MEMS accelerometers are one of the results of the MEMS sensor techniques. Several MEMS accelerometers incorporate piezoresistive bridges such as those used in early micromechanical pressure gauges. More accurate accelerometers are the force rebalance type that use closed-loop capacitive sensing and electrostatic forcing. For example, a type of micromechanical accelerometer is a monolithic silicon structure consisting of a torsional pendulum with capacitive readout and electrostatic torquer. Another type of MEMS accelerometer has interdigitated polysilicon capacitive structure fabricated with an on-chip BiMOS process to include a precision voltage reference, local oscillators, amplifiers, demodulators, force rebalance loop and self-test functions. MEMS based magnetic sensors are also under development and test.
It is still very challenging to design an orientation measurement system for a small platform with limitations of power budget, size, and weight. Digital Signal Processing (DSP) is one of the most advanced technologies that will be a driving force for science and engineering in the twenty-first century. The method and system of the present invention addresses the need of an orientation measurement system for a small platform with limitations of power budget, size, and weight using MEMS and DSP technologies.
A main objective of the present invention is to provide a digital signal processing method and system thereof for producing precision orientation measurements, which employs MEMS based accelerometers and magnetic sensors with the powerful DSP device and algorithms to achieve a miniaturized orientation measurement system.
Another objective of the present invention is to provide a digital signal processing method and system thereof for precision orientation measurements and local Earth""s magnetic field vector measurements, which can achieve a stabilized, highly accurate orientation measurement with increased system flexibility and reduced time of circuit and control design.
Another objective of the present invention is to provide a digital signal processing method and system thereof for precision orientation measurements and local Earth""s magnetic field vector measurements, wherein MEMS accelerometer, micro magnetoresistance sensor, and Digital Signal Processor (DSP), as well as analog signal conditioning and Analog/digital circuitry, are integrated to deliver orientation measurement solutions to stabilisation, orientation and alignment requirements of many commercial platforms.
Another objective of the present invention is to provide a digital signal processing method and system thereof for precision orientation measurements and local Earth""s magnetic field vector measurements, wherein MEMS accelerators measure gravity accelerations about the body axes of the platform; the low-level gravity acceleration analog signals from the MEMS accelerometer are converted into a digital output, which are digitally processed to obtain orientation information, to provide superior performance to alternative analog techniques.
Another objective of the present invention is to provide a digital signal processing method and system thereof for precision orientation measurements and local Earth""s magnetic field vector measurements, wherein the magnetometer detects the components of the earth""s magnetic field vector about the body axes of the platform, which are digitized and transformed into the components of the earth""s magnetic field vector in the level-plane. The components of the earth""s magnetic field vector in the level-plane are proportional to the sine and cosine of the platform magnetic heading angle, which magnetic heading is derived based on.
Another objective of the present invention is to provide a digital signal processing method and system thereof for precision orientation measurements and local Earth""s magnetic field vector measurements, wherein MEMS accelerometer""s faster response and settling than traditional liquid tilt sensors, up to 100 hz response, are exploited to achieve orientation measurements without xe2x80x9csloshxe2x80x9d or leaking problems associated with traditional liquid tilt sensors.
Another objective of the present invention is to provide a digital signal processing method and system thereof for precision orientation measurements of a platform and local Earth""s magnetic field vector measurements, wherein a velocity producer is further incorporated to compensate the platform motion acceleration to deal with the platform motion.
The orientation measurement systems can offer many advantages, such as shock and vibration resistance, software compensation for stray field effects, which can be used for navigation, survey, research, training, construction, entertainment, pointing and leveling applications.