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INERTIAL NAVVIGATION SYSTEM.pptx
1.
2. LESSON OBJECTIVE
AT THE END THE OF THE LESSON,THE
STUDENT SHOULD BE ABLE TO CORRECTLY;-
1. EXPLAIN WHAT IS INERTIAL
NAVIGATION SYSTEM.
2. OPERATION PRINCIPLES INS
3. IDENTIFY THE MAIN COMPONENTS OF
INS
4. BENEFITS INS
3. LESSON SCOPE
1.ANALYSIS OF RNAV SYSTEMS.
1. DEFINITION OF INS NAVIGATION.
2. OPERATION PRINCIPLES INS
3. MAIN COMPONENTS OF INS
4. BENEFITS OF INS
5. Inertial navigation
Inertial navigation, which relies on knowing
your initial position, velocity, and attitude a
nd thereafter measuring your attitude rates
and accelerations. The operation of inertial
navigation systems (INS) depends upon Ne
wton’s laws of classical mechanics. It is the o
nly form of navigation that does not rely on
external references.
6. INERTIAL NAVIGATION SYSTEM
• Inertial Navigation Systems, unlike other navigation
systems, do not depend on external (radio)
measurements. Instead an INS keeps track of its
position by accurately measuring acceleration
(accelerometers) and rotation (gyroscopes). It
therefore works in remote areas where there are no
ground based navaids available.
7. INERTIAL NAVIGATION SYSTEM
• An inertial navigation system (INS) is a navigation aid
that uses a computer, motion sensors
(accelerometers) and rotation sensors (gyroscopes) to
continuously calculate via dead reckoning the
position, orientation, and velocity (direction and
speed of movement) of a moving object without the
need for external references.
8. INERTIAL NAVIGATION SYSTEM
•Initially, the INS gets its position from pilot input
at the gate, or in more recent systems from GPS,
sometimes even during flight. By measuring all
the accelerations and rotations and integrating
them into speed and direction the position is
tracked. In doing this, the INS has to correct for
the rotation of the earth and the related Coriolis
force.
9. INERTIAL NAVIGATION SYSTEM
• Inertial navigation is a self-contained navigation technique in which
measurements provided by accelerometers and gyroscopes are used
to track the position and orientation of an object relative to a known
starting point, orientation and velocity. Inertial measurement units
(IMUs) typically contain three orthogonal rate-gyroscopes and three
orthogonal accelerometers, measuring angular velocity and linear
acceleration respectively. By processing signals from these devices it
is possible to track the position and orientation of a device(aircraft)
10. INERTIAL NAVIGATION SYSTEM
An INS consists of the following:
• An inertial measurement unit(IMU)
•Instrument support electronics
•Navigation computers (one or more) calculate the
gravitational acceleration (not measured by acce
lerometers) and doubly integrate the net acceler
ation to maintain an estimate of the position of th
e host vehicle.
11. INERTIAL NAVIGATION SYSTEM
There are many different designs of INS with different performance ch
aracteristics, but they fall generally into two categories: –
gimbaled or stabilized platform techniques, and – strapdown
12. INERTIAL NAVIGATION SYSTEM
The original applications of INS technology used stable platform techni
ques. In such systems, the inertial sensors are mounted on a stable pla
tform and mechanically isolated from the rotational motion of the vehi
cle. Platform systems are still in use, particularly for those applications
requiring very accurate estimates of navigation data, such as ships and
submarines.
13. INERTIAL NAVIGATION SYSTEM
Modern systems have removed most of the mech
anical complexity of platform systems by having t
he sensors attached rigidly, or “strapped down”, t
o the body of the host vehicle. The potential ben
efits of this approach are lower cost, reduced size,
and greater reliability compared with equivalent
platform systems. The major disadvantage is a su
bstantial increase in computing complexity.
14. INERTIAL NAVIGATION PRINCIPLES
•The primary sensors used in the system are
accelerometers and gyroscopes (gyro) to
determine the motion of the aircraft.These
sensors provide reference outputs that are
processed to develop navigation data.
16. accelerometer
• The accelerometer device is formed with a mass and two springs
within a housing.Newton second law of motion states that a body at
rest (or in motion)tends to stay at rest (or in motion)unless acted
upon by outside force.Moving the accelerometer to the right causes
a relative movement of mass to the left.If the applied force is
maintained, the mass returns to neutral position.
• Attaching an electrical pickup to the accelerometer creates a
transducer that can measure the amount of relative movement of the
mass.The relative movement is direct proportion to the acceleration
being applied to the device expressed in m/s2
17. accelerometer
•When the accelerometer is moved to the
left,or brought to rest, the relative
movement of mass is to the right.The mass
continues in its existing state of rest unless
the applied force changes, this is the
property of inertia.
18. accelerometer
•Attaching an electrical pickup to the
accelerometer creates a transducer that can
measure the amount of relative movement
of the mass.The relative movement is direct
proportion to the acceleration being applied
to the device expressed in m/s2
19. Accelerometer cont----
•If this electrical output is mathematically
integrated effectively means we are
multiplying the acceleration output by
time,this can be expressed as:
Timexacceleration=sxm/s2=m/s=velocity
20. Accelerometer cont----
If again the velocity output is intergrated
which means multiplying the output by time:
Time x velocity= sx m/s=m=distance.
In summary we started by measuring
acceleration and we able to to derive velocity
and distance information by applying the
mathematical process of intergration
21. Accelerometer cont-----
By measuring acceleration ,velocity and
distance information were derived .Consider
a body accelerating at 5m/s2,after ten
seconds the velocity of the body will be
50m/s.If the body now travels at a constant
velocity of 50m/s for ten seconds ,it will have
changed position by 500m.
22. Accelerometer cont-----
•This acceleromter is providing useful velocity and
distance information ,but only measured in one
direction.In practice two accelerometers are
mounted on a platform at right angles to each other
whereby the acceleration,velocity and distance
information are measured in any lateral
direction.The plat form is aligned with a true north
whereby the two accelerometers are directed N-S
and W-E respectively.
24. INERTIAL NAVIGATION SYSTEM
• A minimum of two accelerometers are used, one referenced to north,
and the other referenced to east. In older units, they are mounted on
a gyro-stabilized platform. This averts the introduction of errors that
may result from acceleration due to gravity.
• An INS uses complex calculation made by an INS computer to convert
applied forces into location information. An interface control head is
used to enter starting location position data while the aircraft is
stationary on the ground.
25. INERTIAL NAVIGATION SYSTEM
• The system derives attitude, velocity, and direction information from
measurement of the aircraft’s accelerations given a known starting
point. The location of the aircraft is continuously updated through
calculations based on the forces experienced by INS accelerometers.
26. INERTIAL NAVIGATION SYSTEM
• An INS uses complex calculation made by an INS computer to convert
applied forces into location information. An interface control head is
used to enter starting location position data while the aircraft is
stationary on the ground.
27. INERTIAL NAVIGATION SYSTEM
•This is called initializing. [Figure 11-155]
From then on, all motion of the aircraft is
sensed by the built-in accelerometers and
run through the computer. Feedback and
correction loops are used to correct for
accumulated error as flight time progresses.
28. Gyroscope
A gyroscope is a device used to measure or
maintain an angular position. It works using the
principles of angular momentum. The gyroscope
is made up of a spinning wheel or disc, as well as
(in some cases) many other moving parts. It helps
with navigation, and plays a part in such things as
a gyrocompass and artificial horizon.
30. Gimbaled systems
A gimbal is a rigid with rotation bearings for isola
ting the inside of the frame from external rotatio
ns about the bearing axes. At least three gimbals
are required to isolate a subsystem from host veh
icle rotations about three axes, typically labeled r
oll, pitch, and yaw axes.
31. Gimbaled systems
The gimbals in an INS are mounted inside
one another. Gimbals and torque servos
are used to null out the rotation of stabl
e platform on which the inertial sensors
are mounted.
32. How does gimbaled INS work
The gyros of a type known as “integrating gyr
os” give an output proportional to the angle
through which they have been rotated •
33. gimbaled INS
Output of each gyro connected to a servo‐m
otor driving the appropriate gimbal, thus kee
ping the gimbalin a constant orientation in in
ertial space
The gyros also contain electrical torque gener
ators which can be used to create a fictitious
input rate to the gyros
34. gimbaled INS
•Applications of electrical input to the gyro t
orque generators cause the gimbal
torque motors/servos to null the difference
between the true gyro input rate and the el
ectrically applied bias rate. This forms a con
venient means of cancelling out any drift er
rors in the gyro.
38. Strapdown INS cont----
•Horizontal/vertical accelerations computed anal
ytically using direction cosine matrix (DCM) relat
ing body coordinated and local level navigation c
oordinates.
•DCM computed using strapdown body mounted
gyro outputs
39. SYSTEM DESCRIPTION
•The inertial navigation system can be considered
to have three functions:
-Reference
-Processing
-Crew interface
41. accelerometers
• The accelerometers senses acceleration and a closed
servomechanism feedback signal proportional to the
acceleration is then amplified and demodulated. This
feedback signal is applied to coils to restrain the pendulum
at a null position. The feedback required to maintain the null
position is proportional to the sensed acceleration. This
becomes the accelerometer’s output signal.
42. GYROS
• The original inertial navigation systems used
electromechanical gyros, these were subsquently replaced
by more reliable and accurate technology, the ring laser
gyro(RLG).
• The ring laser gyro use interference of laser beam within
an optic path ,or ring to detect rotational displacement.
• An IRU contains three such devices for measuring changes
in pitch, roll and azimuth.
• The angular rate becomes the gyro output.
43. INERTIAL SIGNAL PROCESSING
• The acceleration and angular rate outputs from the IRU are
transmitted to navigation processor.
• Acceleration is measured as a linear function in each of the three
aircraft axes,normal,lateral and longitudinal. Attitude is measured as
an angular rate in pitch,roll and yaw.
• These outputs are resolved and combined with air data inputs to
provide navigation data, eg latitude,longitude,true heading,distance
to next waypoint,ground speed,wind speed and wind direction.
• The processor performs these navigation calculations using outputs
fron accelerometers and gyros.
44. CREW INTERFACE
•A complete inertial navigation system (INS)
contains:
-Inertial navigation unit (IRU)
-Control display unit (CDU)
-Mode selector unit (MSU)
45. CREW INTERFACE cont----
• The CDU is the crew’s interface with the system, it is used to enter
data in IRU, eg present position during the alignment process
47. LESSON OBJECTIVE
AT THE END THE OF THE LESSON,THE
STUDENT SHOULD BE ABLE TO CORRECTLY;-
1. EXPLAIN WHAT IS INS
2. WHOW INS WORK
3. ADVANTAGES AND DISADVANTAGES OF
INS
