Integrated Inertial Positioning Systems

Transcription

1 Integrated Inertial Positioning Systems Some facts, some editorial and some biased opinions

2 Inertial Tools - What instruments are currently in daily use for Survey? In our business Inertial navigation systems (INS) for land seismic, Vertical Reference Units (VRU s) for DP, USBL/SBL and Swath sonar attitude/heave corrections Surface heading sensors Spinning mass gyros as well as strap down Attitude Heading Reference Systems (AHRS) In other applications Inertial sensors - anti-lock brakes, anti skid, virtual reality headsets Analog Devices, Crossbow, Systron, Bosch, BAe and many others Inertial Navigation systems as (Tactical) short term positioning sensors - Northrop Grumman, Honeywell, Kearfott, BAe, Boeing, etc. High precision (Strategic) Inertial Navigation systems for long term positioning outages - Northrop Grumman, Honeywell, Thales navigation, etc.

3 Available How Long? In discussing this exciting new technology we must also understand that these tools have been around for a while, even in the seismic and survey business: Western Geophysical s W-INS ( we invariably needed SHORAN ) late 1970 s Shelltech/Itech land seismic use of INS for control (helicopter based Zupt s) Mid/late 1970 s Exxon/Honeywell s DP reference systems Riser and INS 1979 British Oceanics/Intersub INS for manned submersible construction positioning (used in place of the unreliable acoustic systems ) early 1980 s

4 Session Agenda A few definitions What is an inertial measurement unit (IMU)? Overview of inertial sensors Price versus performance Where is inertial technology going? Integrated Inertial Positioning Systems Loosely, tightly and deeply coupled Aiding Observations current and future Applications for Integrated Inertial Positioning Systems Current and near term products Commercial benefits of these systems

5 A few definitions An Inertial Sensor is a position, attitude or motion sensor whose reference are completely internal draft revision to IEEE Std 528 A Gyroscope is a sensor designed to illustrate the dynamics of a rotating body In Strapdown operations the inertial frame of reference is stored in the computer as opposed to being maintained mechanically by gimbals. Coordinate transformations and sensor compensation have to be completed within the strapdown computer. Bias - no input, but some level of output Angle random walk - white spectrum rate detection noise leads to an angle random walk (optical and coriolis gyros) Aiding - using external non inertial observations to minimize bias Scale Factor- an error in the assumed scale factor in the instrument output Schuler Oscillation/Period - 84 minutes just think about a pendulum centered at the earth s core and the IMU at the earth s surface

6 What does an IMU consist of?

7 How does this fit together? Accelerometers Navigation Computer Measure acceleration Compensate for accelerometer bias and SF Compensate for gravity Integrate Once-Velocity Twice-Distance Speed Distance Gyros Measure rotation rates Compensate for Gyro Bias, ARW, SF and acceleration sensitivities Compensate for Earth s rotation Heading

8 Overview of inertial sensors Inertial sensors come in many forms and are an excuse for infinite acronym generation. The two types of sensors within an IMU are: Gyroscopes - rate of rotation Accelerometers - linear acceleration Some examples are: Gyros Dynamically tuned, (DTG), Fiber Optic (FOG), Ring laser (RLG) Accels Vibrating Beam (VBA), Quartz Resonating (QRA), Pendulous Mass (PMA)

9 Gyro Technology Angular Rate Sensing technology principles: Spinning Mass - angular momentum Vibratory/Resonator - Coriolis Optical - Sagnac Micro Electro Mechanical Sensor(MEMS) primarily vibratory, some spinning mass, some optical Micro Optical Electro Mechanical Sensor (MOEMS) another variant

10 Current Gyro technology

11 More Gyro details Spinning Mass Honeywell, Northrop Grumman, Rockwell Pros Wide performance range to >100 /hr Very low noise - (specifically gas bearing) Cons Relatively high cost Long warm up Not well suited to strapdown applications Some types very fragile Vibratory/Resonant Watson, Systron Donner, Murata, BAe Pros Relatively small Minimum moving parts Cons Small scale factor Output noisy Rate gyro open loop Limited performance range (getting better though)

12 Pros and Cons Optical Pros Cons Honeywell, Northrop Grumman, (Fibresense), Ixsea, Sagem, etc. Rapid reaction and turn on(<1s) Ideally suited for strapdown operation No moving parts - very rugged Performance increases with size RLG is a high voltage device FOG very temperature sensitive Micro Electro Mech.Sensors (MEMS) Draper/Honeywell, JPL, BAe, AD, Bosch, etc. (only vibratory discussed) Pros Very small No moving parts Very low cost Cons Higher precision still under development Limited performance range (only for a while) Bias stability

13 FOG block Diag. Gyro Bias ( /hr) is usually proportional to length of fiber The longer the fiber - the better the FOG

14 RLG Block Diag. Gyro Bias ( /hr) is usually proportional to path length The longer the path length - the better the RLG Cervit block Path length control mirror Dither mechanism Anode Anode Optical beams Mirror Detector Cathode -Schematic of ring laser gyro. Input axis is perpendicular to the plane of page.

15 Accelerometer Technology Linear acceleration sensing technologies: Pendulous/Translational Mass displacement/rebalance Electrical Restraint Rotational Restraint Elastic Restraint Resonant Element Frequency Vibrating String Vibrating Beam Double Ended Tuning Fork

16 Current Accelerometer Technology

17 More accel. details Force Rebalance Accels - Honeywell Q-Flex, Northrop Grumman A4, Kearfott Mod VII Pros Highly Reliable - relatively low cost Wide bandwidth Low bias error Cons Analog output self heating under changing acceleration Power consumption Pendulous Rebalance Accels. Pros Reliable, rugged, small Well understood error model Pendulous Integrating Gyro Accel. (PIGA) as good as it gets used for ICBM and general missile guidance Cons PIGA - Cost Resonant Element Accel. Sundstrand, Allied Signal Adkem Pros Digital output Low power Cons Not good in high shock environment Detailed calibration required

18 Sensor Advances - MEMS Wafer thick gyros - 400µm Critical assembly process for MEMS Assembly issues being worked on to make a low cost, mass produced instrument. Noise is the challenge I-O have low noise, low G product VectorSeis

19 MEMS DoD Development Program A low cost, high G MEMS and guidance effort is underway for a DoD joint forces program. This effort has the following goals: Phase 1 <75 /hr, >10,000G, <8 cubic inches This phase should have been delivered 3 vendors selected 2 delivered 4 months ago Phase 2 <10 /hr, >20,000G, <4 cubic inches This phase should be delivered this/next year 2 vendors selected one ready to deliver Phase 3 <0.5 /hr desired (<1 /hr acceptable), >20,000G launch survivable, <2 cubic inches volume. DoD s cost expectation for this IMU is <$1,200 Should have been delivered in 2006 may not be needed due to deeply coupled Phase 2. Deeply coupled L1 and L2/Lm, WAAS, SAASM GPS receiver should be incorporated as an option to Phase 2/3

20 So how good is a good INS? Once the sensors (just discussed) have been combined to make an Inertial Measurement Unit software has to be added to turn the raw rate (incremental rate -?) and the raw acceleration (incremental velocity - V) data into something useful as a: Attitude Heading Reference System (AHRS), or an Inertial Navigation System (INS) The performance of an INS is usually rated in terms of its position error growth rate once the INS is navigating in free inertial mode (no aiding). The USAF define INS in the following manner: INS Classification Position Error Growth Rate Heading Errors Low > 2nm/hr >0.2 Medium 0.5 to 2nm/hr 0.05 to 0.2 Precision <0.5nm/hr <0.05 Following a standard ground alignment at 50 or lower latitude USAF SNU84-1

21 Cost versus Performance PRICE $K 160 Department of State Controlled Technology Dept. of Commerce Controlled? Primarily for internationally sourced IMU's only IMAR.003º $155K 20cm RLG Thales Totem.001º Thales $100K 30cm RLG T24.003º $130K Kearfott 24cm RLG LN º? $90K 1200m? FOG 80 LN º $80K Northrop 18cm RLG PHINS.003º $80K Ixsea 1200m FOG CIMU.0035 $80K Honeywell 6" path RLG Sigma 10.05º SAGEM $65K 10cm RLG 60 Octans 0.01º $60K Ixsea 700m FOG (AHRS only) 40 T16.01º $100K Kearfott 18cm RLG T90 1º $39K Tamam 20 LN200 1º $22K Northrop 200m FOG BOEING 3º $20K MEMS BIAS STAB º/hr

22 Where is this technology going?

23 Maturity of technology Draper Laboratory s view on the state of current development. The suggestion is that most technologies are now mature except for MEMS gyros.

24 Export Control The fastest way to go to jail (without passing go) will be to flaunt the export controls associated with this technology. The International Traffic in Arms Regulations (ITAR) and the Arms Export Control Act (AECA) are the governing law that is overseen through the Directorate of Defense Trade Controls (DDTC within the U.S. Department of State (remember Colin Powell). Simply put (to me by the DDTC) if you screw up, it will be you, not the company, that goes to jail. DDTC is responsible for all licensing issues if the commodity is controlled by State. To get a commodity under the more understanding Dept. of Commerce control a Commodity Jurisdiction has to be filed with the D.o.State. Most US manufactured and high end international IMU s will fall under the control of the DDTC Do not listen to the vendors when they say don t worry about this talk to your own export attorney and get their advice.

25 What type of sensor do you need to buy/integrate? As can be seen from the previous charts IMU s are available in many flavors. The one underlying suggestion I would make is to: Only buy the sensor with the performance you really need Do not over specify the performance requirements of your sensor or it will cost significantly more than it should. OR?

26 Free Inertial Drift $100K buys apx. 20 meters for 20 minutes free inertial. This level of inertial performance is not needed if the IMU errors can be bounded with some form of external aiding hence the need for Integrated Inertial Positioning Systems.

27 System Integration Coupling? A very basic Loosely Coupled system the INS and aiding system provide position and velocity into the Kalman filter. Example GPS/INS GPS would provide Position and Velocity INS would provide position and velocity INS Aiding Nav Systems Kalman Filter Tightly Coupled the IMU and aiding system provide raw observations that are modeled within the Kalman filter. Example GPS/INS GPS would provide code and phase observations, the IMU provides rate and acceleration observations. IMU Aiding Nav Systems Kalman Filter

28 Deeply Coupled Deeply Coupled the IMU and aiding system provide raw observations that are modeled within the Kalman. The solution provides feedback into both the IMU and the aiding observations. Example GPS/INS GPS would provide code and phase observations, the IMU provides rate and acceleration observations. IMU Aiding Nav Systems Kalman Filter The GPS receiver is controlled to window onto expected arrivals of SV data. Significantly improves the signal to noise performance of the GPS system. Currently in use for anti jamming and blocking of GPS signals in defense applications. Just imagine what a deeply coupled acoustic line of position/ins solution would do for ROV positioning? Improving the SNR of the system!

29 Why spend effort on better coupling? Assuming life was good and GPS was very visible a loosely coupled solution will work well why would we need such a system (GPS/INS)? High update rate position with precision attitude information (LIDAR, Photogrammetry etc.) Now we start to require GPS observations in a crowded urban area (road survey) the GPS solution fails, no position or velocity my loosely coupled GPS/INS solution starts to fail. The same is true for land survey under canopy. With some visibility, a loosely coupled system should provide a solution as long as the GPS system provides a position and velocity. Once the canopy thickens such that only occasionally data is available from some SV s then a tightly or deeply coupled solution will provide a valid solution much longer.

30 In Offshore Applications ROV Long Baseline construction survey tasks To go to work a LBL array has to be deployed and calibrated takes time and equipment, usually on the critical path. The ROV then positions itself within this array to complete the subsea construction tasks. The conventional LBL solution could be integrated with an IMU to get a higher update rate and precision attitude info. This may have some value. But if if this integration is taken one step further we will be able to offer significant savings to offshore operations. What if we could reduce the number of beacons in the array and position the ROV with just a tightly coupled INS/Line of Position (with respect to a seabed mounted transponder) solution? Deeply coupled would be even better as we could extend our acoustic range as we improve our SNR due to driving the acoustic transceiver.

31 Aiding Observations what is available? Many aiding observations are used to bound the error growth of IMU s. A few of the normal and not so normal observations are listed below some from air, land and marine (I am sure I have left many out): Conventional: GPS Zero Velocity Update - Zupt Doppler velocity sensors/logs (airborne radar and underwater acoustic) Altimeters (RF and acoustic) Depth sensors Pedometers Not so conventional: Distance Measuring Indicators Range/Range systems (RF and acoustics) Half Gauge (Rail tracking indicator) Terrain matching matching to existing terrain data Vision relative position and velocity from CCD or SIT images (already working) Stripe laser illuminated imagery very high definition=resolution observations (near to working) Swath Sonar - relative position/velocity from image processing of sonar data (working today) Terrain Mapping establishing the environment around the system and noting changes as they occur (prototypes working at MIT allowing navigation around halls

32 Commercial Benefits Let s take a look at just a few examples of integrated solutions to try and understand why these systems will make inroads into our business over the next few months/years: Marine Construction Dynamic Positioning Land Seismic Stake Out under Canopy A list of No brainer uses As you will see all of these applications of an integrated solution are affordable through real operational savings. The benefits are not just better data, higher update rate, more reliable solutions The incentives are real dollar savings through the life of projects

33 Marine Construction What are the issues for the marine construction survey community? Boat time, Boat time, Boat time Any operational gain that can be made to reduce the amount of vessel/spread time consumed specifically for the survey aspects of marine construction tasks will go straight into savings for the end customer do these customers really care? The marine construction survey community need to be able to reduce vessel/spread time while completing tasks similar to the following: Metrology providing repeatable, reliable positioning data while consuming minimal ROV/spread time. A local, relative positioning problem well suited to an aided inertial solution. Local field development positioning - 300mx300m subsea infrastructure relative installation significantly reduce the operational time currently consumed to deploy and calibrate large LBL arrays, reduce the LBL beacon count significantly. Wide area deepwater absolute positioning 3,000mx 3,000m field wide control with significantly reduced acoustic observation sets. Vessel/ROV spread consumption reduced due to less hardware deployed on the seabed. Such an application would be deepwater permanent suction mooring installations. Deepwater pipeline as built survey improve the survey deliverable from USBL systems by aiding with an inertial observation set no need for LBL.

34 Marine Construction Example OR Using an example of a project that has multiple frame sets including an array installation and calibration at 4 locations: Each location: 5 Far field transponders, 6 Near field transponders 2.8 boat/rov spread days per location for deployment/calibration, 4 locations $65K/day complete spread rate - 4(2.8x65) = $728K If proven aided inertial tools are available Each location: 2 near filed transponders (absolute array orientation taken care of with good IMU), 1.3 boat/rov spread days per location, 4 locations $65K/day complete spread rate 4(1.3x65) = $338K A very conservative estimate of savings = $390K on a single job this savings would nearly pay for the system development

35 The DP IMU/ERA Case Riser Operating in Non Bi-Stable Mode Patented in 1979, not used since Class 2 and 3 DP Requires 3 independent ref systems from 2 different Operating principles. IMU Riser Model Including: Riser Angle Tension Mud Weight Slip Joint Position Today in deep water we only have two systems to choose from - GPS and Acoustics. The numbers work for this solution as well.

36 The $ Benefit for DP Operators Graceful disconnect/ shut down of operations $1,000,000/incident Short term DGPS outage Slow down acoustic update Assist the Multi-user problem Extend battery Life $Operator penalty or disconnect $To work or not, penalty $45,000/year Additional reference sensor $100, 000 or penalty saving DP model smoothing Less fuel consumption $Does the client care? Less wear and tear $1,000,000/repair incident (Seal failure * recent example) Heading, pitch, roll, heave $40,000 + $50,000

37 Land Seismic Stake Out Under Canopy This is one of the sectors where aided inertial systems have been trying to find a home for the past several years. What are the issues for the land seismic community? When seismic acquisition moves into wooded or forested areas the canopy starts to impact the reception of the direct GPS signals as well as the radio link for RTK. The primary system will consist of a very good IMU bounding it s error through the use of Zupt s. Occasional RTK GPS may be available, but in many cases the days survey is completed with just the IMU and Zupt s. These systems deliver sub 1m post processed accuracy with good initial calibrations and good closing RTK calibrations.

38 Land Seismic Stake Out Under Canopy OR Survey time to stake out under canopy requires cutting of the canopy to allow for conventional optical survey tools to be used. Using backpack based inertial instruments significantly reduces the amount of time taken to survey locations. Conventional cutting and surveying will achieve perhaps a mile a day or less under canopy Inertial based systems allow between 3 to 4 miles per day (4 times conventional production), and in some instances up to 8 miles per day. Cost per mile $1,000/mile, line miles on an average (no such thing) 3D land survey will be (a line every.25 miles 10x10 mile survey) 400 line miles. Other very significant issues are: Environmental issues minimal cutting (low impact seismic) is being specified more often Safety issues significant issues associated with HS&E

39 Some more examples of No Brainers Some of the current issues facing the survey and positioning community that will benefit from Integrated Inertial Positioning Systems: EM or 4C/D seabed station installations Large numbers of nodes that require precise installation in deep water. Currently primary options are very large LBL arrays as USBL cannot provide the accuracy required. A combined DVL, LOP, Depth and IMU solution will subtracts days from the deployment and calibration of such systems Metrology/Spool piece measurement Some valiant efforts (CDL Subsea7) to use systems. The introduction of a proven and fully accepted capability would reduce many hours from each measurement set. Just taking a look at some of the west African field development should pay for the development and proving of such a solution. Acoustic Pollution Slow down update rates, make acoustic bandwidth available through the use of less acoustic channels, DP, construction, ROV tracking and seafloor positioning will all benefit significantly with even a loosely coupled IMU in the loop. No need for massive, commercially confusing, pseudo ranging Seabed GPS systems.