L.I.G.S. : Navigation
Land navigation complex
Strapdown INS development
Introducing the Integrated Inertial Instrument Technology
Aircraft Inertial Guidance System (Simplified) :-))
The real time SINS/DGPS aplication test
The LIGS/ U.of C. GPS-INS INTEGRATION project
Land navigation complex
Survey vehicle and GPS base station in Kananaskis country. Alberta, Canada.
Basing on the standard Russian INS we've made an Inertial Survey System for highly precise geodetic positioning and navigation. Such a system can be applied in GIS and PADS like systems both in autonomous mode and with GPS.
- Real-time navigation accuracy : over 1 m with 3 min ZUPT interval and 3 m with 10 min ZUPT interval;
- An original INS field azimuth misalignment calibration procedure allows to estimate the azimuth with 10" accuracy
- The system may be based on the customer's hardware with use of our algorithms.[go top]
Survey vehicle trajectory (white line) as projected on the city of Moscow aerial photography.
Moscow test in June 1999
The tests of the newly designed navigation complex were carried out in June, 1999 in Moscow. The challenge of the test was to estimate the trajectory in the urban area with frequent GPS constellation changes and satellites losses. In order to recover the GPS data gaps the strapdown INS was aplied.
Two Ashtech GG24 receivers were used for DGPS data processing.
In result we've obtained the accuracy of coordinates determination within 1 m. The tested complex destination is deodetic cadastrial survey in Russian Federation.
(same information and more photos in Russian)
Land geodetic surveying
Airborne precise navigation
The INS/GPS integration program has as a goal to create the navigation complex combined by the GPS receiver and inertial unit. The INS destination in the such a complex is to maintain the navigation task solution when the GPS information is not available because of the shading effect in the urban, mountain or forested areas and complex carrier evolution as well. The field tests of the complex combined by the standard strapdown INS (SINS), GPS/GLONASS receiver and barometric altimeter proved the real time accuracy better then 3 m SEP during 2 hours of running.[go top]
Strapdown INS development
The strapdown INS is most attractive for inexperienced user type of inertial hardware because its optimal cost/features rate. The inertial sensors (gyros and accelerometers) are actually available for very reasonable price. But in order to combine them into system a special knowledge is required. We posses such a knowledge and can help you to make your multi-purpose SINS based on your or our hardware.Regarding the specific applications and according the user requirements LIGS develops the inertial systems of the versatile type (gimbals and strapdown) with different kinds of sensors : floated gyros, DTG, laser-ring etc. The development of the new type of the SINS with laser-ring gyros is in progress under the leadership of the LIGS. The Lab has developed the original alignment and navigation software of the SINS that shall allows to reduce the cost of the system without accuracy loss.
The customer's hardware (sensors) can be used
Product costs comes from its application sphere
We can do your INS [go top]
The real time SINS/DGPS aplication test
A strapdown INS and real time radion linked differential GPS test was carried out in Moscow environ from December 12 to December 16. Two Ashtech GG24 receivers were used for base station and rover. The goal of the test was to estimate and calibrate in real time mode INS azimuth misalignment and accelerometers scale factors.
The first test serie consists in the ZUPT mode of vehicle motion. Each ZUPT was used for INS Shuler error calibration. A high accurate position information was provided by pseudo range DGPS radio link. At the CUPT (Coordinate Update Point), given the true value of the vehicle position with respect to the traverse starting point and the respective INS indication , it is possible to estimate the azimuth misalignment. The rest of traverse after CUPT with corrected azimuth is used to check the accuracy of the procedure. The INS coordinate error with corrected azimuth not exceeded 1.2 m CEP after 35 minuts of run.
The second test serie was for in motion (in flight) azimuth calibration. The option of this test was a carrier phase DGPS data that reduces a GPS noise to centimeter level. The applied technique requires a fast (60..80 km/h) speed of the test vehicle for 15...20 minutes. During this run the azimuth misalignment was calibrated and introduced into INS navigation algorithm. The suggested procedure allows to perform a highly accurate INS azimuth calibration (or even alignment) in flight, using the DGPS real-time differentila correction.
Introducing the Inertial Integrated Instrument technology
Futher tests in August 1999
The high cost of the inertial unit is a main obstacle to include it in the precise navigation complex for versatile areas of application. The standard inertial navigation system (INS) deals with precise gyro and accelerometer development. The trivial question which appears in the present consideration is: is it possible to use the simple inertial measurement unit (IMU) with rough sensors for the precise navigation? Faced this problem several companies worldwide are developing the low cost inertial devices which use the cheap compact sensors. This group of instruments is called motion sensors.Given the weak stand alone accuracy and poor run-to-run stability such devices are inapplicable as a sole system. Moreover, even the integration of motion sensor in the navigation complex as a supporting device demands to develop the non-traditional approaches and algorithms. The present paper introduces into the newly developed technology which promises to get the high real time accuracy with very low expenses for inertial unit.
The Systron Donner's MotionPAK™ is a "solid-state" six degree of freedom inertial sensing system used for measuring linear accelerations and angular rates in instrumentation and control applications.
It is a highly reliable, compact, and fully self-contained motion measurement package. It uses three orthogonally mounted "solid-state" micromachined quartz angular rate sensors, and three high performance linear servo accelerometers mounted in a compact, rugged package, with internal power regulation and signal conditioning electronics.
Given the fact that the applied here calculation schemes and algorithms are absolutely original and have not much concern with anything we have done before in sphere of strapdown inertial navigation, we believe that we probably can introduce a new category in the inertial tools terminology. The Integrated Inertial Instrument (I.I.I. or simply "Triple I") - is a combination of the cheap motion sensor with poor stand-alone performances and an advanced sophisticated software which provides a powerful integration of this unit in the navigation complex for a real-time high accurate positioning and angular attitude determination.
For this test we had a lucky chance to put the "Triple I" system side by side with I-21, precise gimbal Russian INS. So, the highly accurate aircraft attitude data was available for the entire flight. The two Trimble 4000SE receivers provided the double differential GPS data that was used as a reference for position and velocity calculation.
Velocity indication of "Triple I" in pure inertial mode and DGPS
The comparative analysis of plots shows that the "Triple I" pure inertial errors are about 100 m/sec, that is not very bad for such rough sensors. To achieve such error level the effective calibration procedure was required. However, the long term in run stability of gyro drift biases is certainly an achievment of the manufacturer.
After the first correction step (so called platform correction) the accuracy of velocity increases up to 0.7 m/sec (RMS), The final correction gives the error 0.1 m/sec and 0.2 m for velocity (up) andcoordinate respectively(below)
In order to confirm the real time attitude accuracy of the the pitch, roll and heading indication of the INS I-21 was used as a primary standard. The plots below shows the correspondence of the respective "Triple I" and INS data on the level of 30 arc min (RMS). In order to fulfill the in flight calibration of the vertical gyro drift rate the magnetic compass was applied for the heading correction. The achieved accuracy is the result of the aplied data processing procedure which allows to compensate the long term inertial sensors errors by GPS, whereas the short term indications are good enough as accepted from MotionPAK real time measurements.
The important task of the inertial system in the navigation complex concerns to the prediction property of the "Triple I" system in case of real time GPS data losses. The special prediction algorithm was designed and tested for GPS losses recovery. The simulation result of the 60 sec GPS data gap are shown on the plots (left) The coordinate error during this gap does not exceed 15 m. Same time the attitude angles error remained within 30..40 arc min boundaries. The good prediction property of such a system is a consequence of the Schuler mode of error behaviour organisation which allows to use the long term calibration values of sensor errors only, whereas the high level of short term errors is rteduced by the Schuler loop smoothing. New test of the "Triple I" technology were carried out in August 1999 at the University of Calgary (Dept. of Geomatics Eng., Dr. Gerard Lachapelle and Dr. Elizabeth Cannon group). 9 test runs in the Calgary downtown had as a goal to improve the forecasting capacity of the software and investigate the Ashtech GPS/GLONASS GG-24 receiver performances for the Motion PAK/GPS integration. The detailed report of thes tests is coming soon.
Aircraft Inertial Guidance System Simplified
Got from Lee Toma's Web Site.
"We are not sure who the author of the following article is, however we feel that the article is one of the best, clearly defined descriptions of the magic that resides withing the aircraft's black boxes."
The aircraft knows where it is at all times. It knows this because it knows where it isn't. By subtracting where it is from where it isn't, or where it isn't from where it is (whichever is the greater), it obtains a difference, or deviation. The Inertial Guidance System uses deviations to generate error signal commands which instruct the aircraft to move from a position where it is to a position where it isn't, arriving at a position where it wasn't, or now is. Consequently, the position where it is, is now the position where it wasn't; thus, it follows logically that the position where it was is the position where it isn't.
In the event that the position where the aircraft now is, is not the position where it wasn't, the Inertial Guidance System has acquired a variation. Variations are caused by external factors, the discussions of which are beyond the scope of this report.
A variation is the difference between where the aircraft is and where the aircraft wasn't. If the variation is considered to be a factor of significant magnitude, a correction may be applied by the use of the autopilot system. However, use of this correction requires that the aircraft now knows where it was because the variation has modified some of the information which the aircraft has, so it is sure where it isn't.
Nevertheless, the aircraft is sure where it isn't (within reason) and it knows where it was. It now subtracts where it should be from where it isn't, where it ought to be from where it wasn't (or vice versa) and intergrates the difference with the product of where it shouldn't be and where it was; thus obtaining the difference between its deviation and its variation, which is variable constant called "error".