How does gyroscopic navigation work

The PIGA device is essentially a rate gyro, constrained by the electrical torque motor, used to measure acceleration and speed by integrating the acceleration over time. It is also used to measure distance travelled by integrating the speed over time. This second integration was initially accomplished by mechanical integrators but is now performed electronically.

Stabilised Platform and Inertial Navigation. Inertial navigation systems are based on a stabilised reference platform consisting of three orthogonal gyroscopes which maintain a fixed reference orientation in space, independent of any motion of the vehicle in which they are mounted. The quality of the INS output is highly dependent on the quality of the input. Random inaccuracies of the input are solved by the use of a smoothing filter using the internal sensors: if no acceleration or course change is detected, the velocity input has to be constant and the position differences as well.

In general, the used filter technique is Kalman filtering. A single outlier or artificial jump in the measured position or velocity is easily detected and removed. In this way, an INS also becomes an excellent device for integrity monitoring. Such an input integrity check is necessary because an undetected gross error, like a single outlier, influences the track for a while. Gross error detection is done with respect to the expected level of inaccuracy of the input as specified by, for example, a standard deviation.

If the given standard deviation and the real quality of the data do not match the results could possibly be very unreliable. An example: if the velocity input is poorer than anticipated, the changes in position do not match the velocity enough.

The software could conclude that this is due to a position outlier and the position input is rejected. The poor quality velocity input is now able to influence the interpolated positions even more, resulting in an incorrect track.

If the position input is suddenly accepted again, the track is corrected to the real position. Such a strong jump in input to an autopilot in a busy shipping track could have serious consequences, for which the INS could incorrectly be blamed. However, if the quality of the input matches the stated accuracy the integrity monitoring algorithms in the filters are generally of high quality.

In that case, the user strongly benefits from the filter of the INS as it prevents gross errors and reduces the effect of inaccuracies in the input. Pitfalls The filter in an INS works with accurate time stamps, giving it an opportunity to also benefit from data that arrives late. The improvement of a previous position or velocity still helps in calculating the next position or velocity. It is even possible to forecast the track. In practice, this means that an INS can estimate its output data in real-time, even before the measurements of that moment have been processed.

As always, such an advanced solution is vulnerable. If the timing of the input signal is incorrect or inaccurate, a first consequence is that the forecasts are affected, and a second consequence is that the wrong sensor might be rejected, with potential consequences as stated above. To reduce this risk, the implementation of an INS needs to be done in close co-operation with the manufacturers of the positioning, velocity and timing sensors.

As long as there are regular position updates, the accuracy of the output position is of a constant quality and better than the input. When position aiding stops, position errors build up in time. And then to appreciate the strengths and weaknesses of INS, you also need to know about drift. An inertial navigation system comprises two-distinct parts; the first is the IMU inertial measurement unit —sometimes called the IRU inertial reference unit. Read on…. Accelerometers are one of the sensor types used in most inertial navigation systems.

As you can guess from their name, they measure acceleration, not velocity. Gyros are one of the sensor types used in most inertial navigation systems INS. Using the measurements taken from three accelerometers and three gyros, the OxTS inertial navigation system keeps track of where it is in three-dimensional space.

Dead reckoning is the name of this process. Like everything, inertial navigation has its strengths and weaknesses. Or, the alignment process can be speeded up with data supplied from a GPS or other systems, and even manual entry.

This alignment of position and orientation is an iterative process, each relying on the progress of the other. Of the many different designs of INS, each with different performance characteristics, there are two main categories used in aircraft: stabilised platform and strap-down. This platform is driven by gyros two or three to always maintain its alignment with these axes regardless of any movement of the aircraft.

Analogue feeds can be taken directly from the accelerometers and gyros that are in direct proportion to acceleration, and changes in velocity and direction. Stabilised platforms have some disadvantages. Gyros are usually mounted in three gimbals on bearings; this allows the aircraft and gimbals to rotate around the gyros without moving the platform.

However, when two of the three gimbals align, and are effectively operating around the same axis, they can become locked together and be directly affected by movement around the remaining third axis.

The solution is to complicate the system further by adding a fourth motorised gimbal, which is continuously driven to avoid alignment with the other three.