Uploaded byJames Titcomb
PHINS for DP applications
The document discusses inertial navigation systems (INS) and their use in dynamic positioning (DP) applications. An INS uses gyroscopes and accelerometers to continuously calculate position without external references. While INS drift over time, integrating additional sensors like acoustic positioning, Doppler velocity logs, and GPS can significantly improve accuracy through data fusion. The document examines how pairing an INS with acoustic positioning systems can provide reliable, high-accuracy positioning even if individual sensors fail or are unavailable. It suggests INS combined with acoustic loggers is sufficient redundancy and accuracy for many DP applications.
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PHINS for DP applications
- 1. PHINS for DPApplications Jim Titcomb North Sea Spring Seminars 2013
- 2. 2 PHINS & ROVINS– Inertial Products What is an Inertial Navigation System (INS)? An instrument (electronic + sensors) which is using its initial state (position) and internal motion sensors (gyroscopes + accelerometers) to measure and calculate its subsequent positions in space with high accuracy, stability and update rate
- 3. 3 INS Introduction Whatmakes an INS good.. or not? Internal sensors (gyroscopes & accelerometers) are never perfect, bias and scale factors accumulate over time Navigation is mostly about Gyroscopes Gross figures: Accelerometers errors are not heavily involved in the position drift – 4m – Schuller period Gyroscope are heavily involved in the drift – 400 m Conclusions A good INS requires good gyro’s IXBLUE manufactures FOG (Fiber Optic Gyroscope) and controls the whole process A range of FOG’s (FOG90, FOG120, FOG180…) for a range of INS
- 4. 4 What's in anINS? 3 “FOG” gyrometers monitor rotation and speed in X, Y & Z axis 3 accelerometers measure acceleration (>> speed >> motion) in 3 axis Powerful electronic / firmware package PHINS “knows” in real time its motion in space . Firmware (Kalman filter) calculates its position in real time + heading, pitch, roll, heave, etc… All integrated small, lean, powerful! (PHINS 6000 example)
- 5. 5 The problem withINS The best sensors are still not perfect, accumulating small errors vs. time makes the system drift on the long term External sensors (aiding) are required to bound drift within acceptable limits. PHINS & ROVINS includes interfaces for most common external sensors GPS DVL (Doppler Velocity Log) Pressure sensor Acoustic positioning references (USBL, LBL) …and all IXBLUE products! IXBLUE INS are fully integrated Inertial Positioning solutions designed for ease of installation & operation, flexible enough to fit most requirements, with no specialist engineer to install / operate.
- 6. 6 iXBlue underwater positioningsolutions the benefits of data fusion Data Fusion Use various and different technologies to measure the same parameter Blend (fuse all this data (Kalman filter) in order to correlate it and obtain a better result A simple example GPS + INS (PHINS, GAPS) 0 0,5 1 1,5 2 2,5 3 0 20 40 60 80 100 time t (s) positionaccuracy(m) PHINS pure inertial drift (0.0002 x t^2 m) Averaging of DGPS data (3 / sqrt(t) m) PHINS+DGPS
- 7. 7PHINS & ROVINS:Inertial Navigation System Robust to Acoustic navigation solution Acoustic positioning can be poor, low update rate, or out of range. INS + USBL combination / data fusion provides continued high quality positioning: Actual USBL data (Hipap) @ 2400 meters water depth 0 0,5 1 1,5 2 2,5 3 3,5 4
- 8. 8PHINS & ROVINS:Inertial Navigation System Robust to Acoustic navigation solution Acoustic positioning can be poor, low update rate, or out of range. PHINS + USBL combination / data fusion provides continued high quality positioning: Using PHINS + USBL in extreme shallow water. RESON / ADUS 2007 Données de positionnement PHINS et GAPS 0 5 10 15 20 25 30 5 10 15 20 25 30 35 X (m) Y(m) Phins Gaps Données de positionnement PHINS et GAPS 5 10 15 20 25 30 35 0 5 10 15 20 25 30 X (m) Y(m) Phins Gaps 10 15 20 25 30 35 40 5 10 15 20 25 X (m) Y(m) Données de positionnement PHINS et GAPS 0 5 10 15 20 25 30 5 10 15 20 25 30 35 X (m) Y(m) Phins Gaps Données de positionnement PHINS et GAPS 5 10 15 20 25 30 35 0 5 10 15 20 25 30 X (m) Y(m) Phins Gaps 10 15 20 25 30 35 40 5 10 15 20 25 X (m) Y(m)
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- 11. 11 DP-PHINS What isit? Time Signals Time and Position For Initialisation Only Time stamped beacon positions and heading Processed Positions Enhanced Position Acoustic Positions
- 12. 12 DP- PHINS, Features Relative to Global co-ordinate transforms. Unlimited number of beacons Flexible Expandable Future Sensors Taught Wire Fan Beam Radascan Etc. Etc.
- 13. 13 DP-PHINS, Why? INSimproves USBL USBL improve INS We still have a single point of failure INS will drift quickly if the acoustics fail. 3m in 2 min, 20m in 5 min. 0.6Nmi in an hour. INS can make USBL almost as good as GPS (depending on depth). Adding INS with USBL alone does not increase redundancy. What else is available?
- 14. 14 What about LBL? At Least three ranges are required for LBL positioning.
- 15. 15 Pure LBL Withonly two ranges positioning is not possible There are two possible locations which match the received ranges.
- 16. 16 INS aided byLBL Station keeping with only two ranges is possible with INS and LBL combined. The system must be initialised to the correct position first. The two ranges will constrain the INS drift. Positioning accuracy is directly related to the range measurement accuracy.
- 17. 17 INS LBL Accuracyand Geometry Accuracy of results is dependant on a combination of geometry and range measurement accuracy If the beacons are “in line” with the vessel results will be poor. But accuracy will be good if there is a high “Angle of cut”
- 18. 18 INS Velocity Aiding INS measures rotation rate and acceleration. First integration produces heading and velocity Second integration produces position USBL aids INS at the second integration level DVL aids INS at the First integration level. INS aiding data is used to estimate errors. The errors are fed back in to the calculation in order to correct at a low level. Aiding at the first integration level has more effect than aiding at the second integration level.
- 19. 19 Effect of VelocityAiding INS free inertial specification is based on time. The more time, the greater the drift. DVL aided INS specification is based on distance travelled. If you don’t move the error can’t grow (as much).
- 20. 20 The problem withDVL Deep water. DVL is only available in water depths up to around 1,000m. In deeper water DVL update rate will be slow. Remember DVL aids INS at a more fundamental level than other sensors. The INS only needs a velocity aiding input infrequently in order to correctly estimate the error on the sensors. DVL Update Rate Error, % distance travelled. Drift speed m/h 1S 0.03% 0.18 2S 0.13% 0.82 3S 0.26% 1.67 4S 0.27% 1.77 6S 0.32% 2.08 8s 0.30% 1.98
- 21. 21 Acoustic Aiding Examples- Recap ROV on Seabed. 850m water depth Well calibrated USBL About as good as it gets with USBL Standard Deviation X Y Position USBL 1.03 0.86 1.34
- 22. 22 INS Aided withUSBL - Recap Spikes in USBL rejected Automatically. Much higher update rate. Smoother positioning. Reduced spread of positions. 5 X improvement with INS Standard Deviation X Y USBL 1.03 0.86 1.34 INS 0.16 0.2 0.26
- 23. 23 INS Aided withUSBL & DVL DVL update only every 3 seconds Positioning now better than high accuracy GPS even in 850m 17 x Better than raw acoustics. Standard Deviation X Y USBL 1.03 0.86 1.34 INS 0.16 0.2 0.26 With DVL 0.05 0.06 0.07
- 24. 24 What if welose acoustics? DVL update only every 3 seconds Positioning now better than high accuracy GPS even in 850m Standard Deviation X Y USBL 1.03 0.86 1.34 INS 0.16 0.2 0.26 With DVL 0.05 0.06 0.07 INS DVL 0.04 0.02 0.05
- 25. 25 Conclusions INS isa proven technology on Land, Under water, in Space, why not in DP? INS has a long track record, Modern FOG based systems bring extreme robustness and reliability. INS can produce heading and attitude data as well as positioning. INS Should not be aided just by GPS for DP applications. INS can make your acoustics as good as high accuracy GPS. The biggest benefits can be obtained by combining aiding sensors. With the addition of DVL, INS can now be considered a stand alone PME for a significant period of time.
- 26. 26 Nautronix Cooperation NASDrill RS925SBL / LBL Overview Premier DP acoustic positioning reference for deepwater operations Uses Nautronix ADS2 signalling for robust and reliable operation in extreme acoustic noise High level of system redundancy (hardware and acoustics) Independent SBL only, LBL only or combined SBL/LBL operation Compatible with all major DP systems Now with PHINS Inertial Navigation
- 27. 27 Nautronix Cooperation NASDrill RS925SBL / LBL Overview Proven performance since 1998 with operation in water depths down to 5,830m. Fast position update (SBL <2 seconds) High Accuracy:- SBL only = 0.15% slant range LBL only = 1m irrespective of water depth SBL/LBL combined = 2.5m @ 3,500msw Allows for integration with: NASNet® DPR NASeBOP
- 28. 28 Nautronix Cooperation NASDrill RS925– Stability • Standard deviation on the calibration was 1.7m RMS • Spread of position data very small, approx 5m • Highlights suitability of RS925 as reliable position reference input for DP systems which demand regular, stable & accurate position data. • Meets Rig Positioning requirements in deep water on acoustics alone The following results were taken during calibration of the NASDrill RS925 system on board the Deepwater Discovery in 2,870m water. 5m radius
- 29. 29 Nautronix Cooperation NASDrill RS925Position Accuracy - INS Interface between NASDrill RS925 and PHINS created Single PHINS (no redundancy): Non-redundant RS925/PHINS configuration. Provided in addition to standard RS925 output(s) to DP
- 30. 30 Nautronix Cooperation NASDrill RS925Position Accuracy - INS Interface between NASDrill RS925 and PHINS created Dual PHINS (full redundancy): Dual redundant RS925/PHINS configuration. Provided in addition to standard RS925 output(s) to DP
- 31. 31 Nautronix Cooperation NASDrill RS925PHINS Testing Initial integration tests completed RS925 SBL simulated data fed into PHINS Simulated SBL data configured to have a noise level of 4.5 m RMS. Equivalent to a SBL system operating in 3000m depth of water, with a noise level of 0.15% slant range SBL position output compared to SBL aided PHINS output...
- 32. 32 Nautronix Cooperation NASDrill RS925SBL 3000m Easting (m) 547044 547046 547048 547050 547052 547054 547056 547058 547060 547062 547064 1 13 25 37 49 61 73 85 97 109 121 133 145 157 169 181 193 205 217 229 241 253 265 277 289 301 313 325 337 349 361 373 385 397 409 421 433 445 457 469 481 493 Easting(m) Time RS925 SBL Phins Output
- 33. 33 Nautronix Cooperation NASDrill RS925SBL 3000m Northing (m) 6341538 6341540 6341542 6341544 6341546 6341548 6341550 6341552 6341554 6341556 6341558 1 13 25 37 49 61 73 85 97 109 121 133 145 157 169 181 193 205 217 229 241 253 265 277 289 301 313 325 337 349 361 373 385 397 409 421 433 445 457 469 481 493 Northing(m) Time RS925 SBL Phins Output
- 34. 34 Nautronix Cooperation NASDrill RS925/PHINSTest Results SBL raw position data with a noise level of 4.5m RMS (3000m depth equivalent) PHINS output data with a noise level of 1.6m RMS Approximately three fold increase in precision (as is typical of various acoustically aided INS systems) Above are static tests with simulated data. Dynamic results are expected to be very similar, with a slight increase in accuracy expected
- 35. 35 Nautronix Cooperation Summary NASNet® DPR & PHINS: PHINS used to enable sparse array positioning capability from a standard NASNet ® deployed field Increase in accuracy of less importance, due to existing capability of NASNet ® BLBL • NASDrill RS925 & PHINS: PHINS used to significantly increase the precision of SBL. Providing a higher accuracy, higher update rate, input to DP Sparse array capability of less importance, due to the deployment of beacons dedicated for the drill rig/vessel – risk of no acoustic return extremely low
Editor's Notes
- #4 Of course, no sensor is perfect and errors will always crepe in to a n inertial solution. Bias and Scale factor errors accumulate over time leading to a drift in the calculated position over time. The longer we try to navigate on inertial only data the further the navigation results deviate from reality.The majority of the errors in an inertial calculate are due to gyroscope errors, in general the higher quality the gyroscopes the better will be the navigation accuracy. Therefore we find that a good INS requires good gyroscopes. IXBLUE manufactures fibre optic gyroscopes, we control the whole process, from the manufacture of the fibre itself and the optical components that are essential for the measurement of the optical parameters.IXBLUE manufacture a range of Fibre optic gyroscopes, the FOG90 used in our ROVINS and OCTANS products, the FOG 120 used in PHINS and Hydrins, the FOG180 used in our military product MARINS. And the FOG210 used in our space products STARINS.A FOG 90 based INS typically has a free inertial drift rate of 6m in two minutes, the PHINS with it’s FOG120 has a free inertial drift rate of roughly half that 3.2m in two minutes, (that's 0.6Nmi per hour). Where as the Maris is an order of magnitude better than that at 1Nmi in 24 hours.
- #5 PHINS is fast becoming the standard instrument for high accuracy ROV navigation , here we see a PHINS 6000, the standard unit for ROV use. Inside we can see the three cans holding the fibre coils with the accelerometers mounted in the centre of each coil. Between the coils is the electronics stack including optical sources and components, interface cards and main signal processing card.A Kalman filter is implemented to fuse the inertial measurements with external aiding data.
- #6 As described earlier, no inertial sensor is perfect, errors will accumulate over time. The kalman filter implemented within IXBLUE inertial products is able to take external aiding data and fuse that data with the inertial measruements in order to calculate the current position.A large buffer within the Kalman filter allows the use of old data within the position calculation so long as the age of the data is known. Typically in the offshore environment, the INS will be initialised on deck with GPS, then when the ROV is deployed aiding will switch over to USBL or LBL, and as the vehicle gets closer to the seabed, Doppler Velocity Log becomes available.The PHINS contains a very accurate real time clock, if necessary the PHINS can operate entirely on it’s own clock, but normally a GPS time signal (ZDA) is used to tie the PHINS time to GPS time. This allows the age of time stamped data to be properly taken in to account in the Kalman filter.PHINS is a fully self contained system, all calculations are done within the subsea unit with no surface equipment required. PHINS is as well suited to AUV operation as it is to ROV operations and no link to the surface is required.