INERTIAL NAVVIGATION SYSTEM.pptx

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1. AVIONICS 02/03 MODE III PHASE II INERTIAL NAVIGATION SYSTEMS BY woI(RTD) C N MAYABI INTRODUCTION

2. LESSON OBJECTIVE AT THE END THE OF THE LESSON,THE STUDENT SHOULD BE ABLE TO CORRECTLY;- EXPLAIN WHAT IS INERTIAL NAVIGATION SYSTEM. OPERATION PRINCIPLES INS IDENTIFY THE MAIN COMPONENTS OF INS BENEFITS INS

3. LESSON SCOPE ANALYSIS OF RNAV SYSTEMS. DEFINITION OF INS NAVIGATION. OPERATION PRINCIPLES INS MAIN COMPONENTS OF INS BENEFITS OF INS

4. INERTIAL NAVIGATION SYSTEM INTRODUCTION. DEFINITION . Inertial navigation system is an autonomous dead reckoning method of navigation, i.e it doe not require external inputs or references from ground stations.

5. Inertial navigation Inertial  navigation, which relies on knowing your initial position,  velocity, and attitude and thereafter measuring your attitude rates  and  accelerations. The operation of inertial navigation systems (INS)  depends upon Newton’s laws of classical mechanics. It is the only  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 accelerometers) and doubly integrate  the net acceleration to maintain an estimate of the position of the  host vehicle.

11. INERTIAL NAVIGATION SYSTEM There are many different designs of INS with different performance  characteristics, 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  techniques. In such systems, the inertial sensors are mounted on a  stable platform and mechanically isolated from the rotational  motion of the vehicle. 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 mechanical complexity  of platform systems by having the sensors attached rigidly, or  “strapped down”, to the body of the host vehicle. The potential  benefits of this approach are lower cost, reduced size, and greater  reliability compared with equivalent platform systems. The major  disadvantage is a substantial 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.

15. Accelerometers By attaching a mass to a spring, measuring its deflection, we get a simple accelerometer.

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/s 2

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/s 2

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 /s 2 =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/s 2 ,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.

23. PLATFORM NS-WE

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 .

29. Gyroscope

30. Gimbaled systems A gimbal is a rigid with rotation bearings for  isolating the inside of the frame from external  rotations about the bearing axes. At least three  gimbals are required to isolate a subsystem from  host vehicle rotations about three axes, typically  labeled roll, 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 stable platform on which  the inertial sensors are mounted.

32. How does gimbaled INS work The gyros of a type known as “integrating gyros” give an  output proportional to the angle through which they have  been rotated •

33. gimbaled INS Output of each gyro connected to a servo‐motor driving the  appropriate gimbal, thus keeping the  gimbalin  a constant  orientation in inertial  space The gyros also contain electrical torque generators which can  be used to create a fictitious input rate to the gyros

34. gimbaled INS Applications  of electrical input to the gyro torque generators  cause the  gimbal torque  motors/servos to null the difference  between the true gyro input rate and the electrically applied  bias rate. This forms a convenient means of cancelling out any  drift errors in the gyro.

35. Gimbaled INS example

36. Strapdown  INS Accelerometers  mounted directly to airframe  ( strapdown ) and measure “body”  acceleration

37. Strapdown   INS cont ---- Horizontal/vertical  accelerations computed  analytically using direction cosine matrix  (DCM) relating body coordinated and local  level navigation coordinates . DCM computed using  strapdown  body  mounted gyro outputs

38. SYSTEM DESCRIPTION The inertial navigation system can be considered to have three functions: Reference Processing Crew interface

39. REFERENCES The references are provided by: accelerometers gyroscopes.

40. 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.

41. 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.

42. 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.

43. CREW INTERFACE A complete inertial navigation system ( INS) contains: Inertial navigation unit (IRU) Control display unit (CDU) Mode selector unit (MSU)

44. 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

45. Q&A OK, what did I not make perfectly clear ?

46. LESSON OBJECTIVE AT THE END THE OF THE LESSON,THE STUDENT SHOULD BE ABLE TO CORRECTLY;- EXPLAIN WHAT IS INS WHOW INS WORK ADVANTAGES AND DISADVANTAGES OF INS

47. REFERENCE STUDENTS NOTES

48. TAKE HOME

49. Q1.Define what is ADS-B. Q2.Define what is TIS-B. Q3. Q6.Define what is FIS-B ?

50. LINK