4.4 Inertial Navigation System
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4.4 Inertial Navigation System
4.4.1 Basic Principle
The Inertial Navigation System (INS) is a system in which the navigation parameters including position, velocity, attitude and heading are solved, by using the Inertial
Measurement Units (IMU) to measure the angular velocity and linear acceleration
of the movable objects relative to the inertial reference system, and after making
the integral calculation, the movable objects can be guided for safe voyage, where
the IMU mainly includes the gyroscopes for the angular velocity measurement and
the accelerometers for the linear acceleration measurement. The inertia is a basic
property of matter, and matter always keeps the state of rest, or uniform motion in
a straight line, unless that state is changed by an external force. The principle of
the INS is based on the classic Newton’s law of mechanics. In 1687, Isaac Newton
published Three Laws of Motion:
every body continues in its state of rest, or of uniform motion in a straight line, unless it is
compelled to change that state by forces impressed upon it; the acceleration produced by a
particular force acting on a body is directly proportional to the magnitude of the force and
inversely proportional to the mass of the body; to every action there is always opposed an
equal reaction, or, the mutual actions of two bodies upon each other are always equal, and
directed to contrary parts.
Newton’s three laws of motion reveal the quantitative relationship of macromechanics in essence, which lays a theoretical foundation for the inertial navigation.
The inertial navigation is a navigation way of dead reckoning, in which by measuring
the heading angles and accelerations of the movable object, the current position is
deduced from the previously determined position, and thus the current position information of the movable object can be output continuously. The INS generally consists
of the gyroscopes, accelerometers, navigation computers and accessory circuit units.
The gyroscope is a kind of angular motion-sensing device, consisting of highspeed spinning rotor, inner ring frame, outer ring frame and fixed frame (as shown in
Fig. 4.2), and the rotor is mounted on the frames so that it can spin rapidly about an
axis which is free to alter in the direction. The orientation of the axis is not affected
by tilting of the mounting, so the gyroscopes can be used to provide stability or
keep a reference direction, with the performance of the stable-axis-directing and the
precession. The stable-axis-directing refers to the property that in the case of no
external force moment (torque), the direction of the spinning axis of the rotor remains
stable in the inertial space. As the external torque acts on the axis of the outer ring
frame, the gyroscope with high-speed spinning rotor will rotate around the axis of the
inner ring frame, and as the external torque acts on the axis of the inner ring frame, the
gyroscope will rotate around the axis of the outer ring frame. The precession refers to
the property that the direction of spinning angular velocity and that of external torque
is perpendicular to each other. There are many kinds of the gyroscopes. According to
the different number of the precession degree of freedom, the gyroscopes are divided
into single degree-of-freedom gyroscope and double degree-of-freedom gyroscope;
211
4.4 Inertial Navigation System
4.4.1 Basic Principle
The Inertial Navigation System (INS) is a system in which the navigation parameters including position, velocity, attitude and heading are solved, by using the Inertial
Measurement Units (IMU) to measure the angular velocity and linear acceleration
of the movable objects relative to the inertial reference system, and after making
the integral calculation, the movable objects can be guided for safe voyage, where
the IMU mainly includes the gyroscopes for the angular velocity measurement and
the accelerometers for the linear acceleration measurement. The inertia is a basic
property of matter, and matter always keeps the state of rest, or uniform motion in
a straight line, unless that state is changed by an external force. The principle of
the INS is based on the classic Newton’s law of mechanics. In 1687, Isaac Newton
published Three Laws of Motion:
every body continues in its state of rest, or of uniform motion in a straight line, unless it is
compelled to change that state by forces impressed upon it; the acceleration produced by a
particular force acting on a body is directly proportional to the magnitude of the force and
inversely proportional to the mass of the body; to every action there is always opposed an
equal reaction, or, the mutual actions of two bodies upon each other are always equal, and
directed to contrary parts.
Newton’s three laws of motion reveal the quantitative relationship of macromechanics in essence, which lays a theoretical foundation for the inertial navigation.
The inertial navigation is a navigation way of dead reckoning, in which by measuring
the heading angles and accelerations of the movable object, the current position is
deduced from the previously determined position, and thus the current position information of the movable object can be output continuously. The INS generally consists
of the gyroscopes, accelerometers, navigation computers and accessory circuit units.
The gyroscope is a kind of angular motion-sensing device, consisting of highspeed spinning rotor, inner ring frame, outer ring frame and fixed frame (as shown in
Fig. 4.2), and the rotor is mounted on the frames so that it can spin rapidly about an
axis which is free to alter in the direction. The orientation of the axis is not affected
by tilting of the mounting, so the gyroscopes can be used to provide stability or
keep a reference direction, with the performance of the stable-axis-directing and the
precession. The stable-axis-directing refers to the property that in the case of no
external force moment (torque), the direction of the spinning axis of the rotor remains
stable in the inertial space. As the external torque acts on the axis of the outer ring
frame, the gyroscope with high-speed spinning rotor will rotate around the axis of the
inner ring frame, and as the external torque acts on the axis of the inner ring frame, the
gyroscope will rotate around the axis of the outer ring frame. The precession refers to
the property that the direction of spinning angular velocity and that of external torque
is perpendicular to each other. There are many kinds of the gyroscopes. According to
the different number of the precession degree of freedom, the gyroscopes are divided
into single degree-of-freedom gyroscope and double degree-of-freedom gyroscope;