GNC Solutions
Guidance, Navigation & Control
DriftLess+ technology:

The DriftLess+ technology is an improved version of the initial DriftLess technology invented & patented by
TNO.
This technology allows the estimation and subsequent compensation of the offsets (biases) of any type of sensor that measures a vector quantity.
Examples of such sensors are: accelerometers, gyroscopes, magnetometers, gravimeters etc.

In many cases, the offsets on the output of these sensors pose a serious problem. Especially when the outputs of the sensors are numerically integrated, unknown offsets may be disastrous.
A patent application for this new DriftLess+ technology is being prepared.

The basic operation of the technology is depicted in the figure on the right. Two sensor units are used. Each sensor unit has one or more sensing axes. In general, each sensor unit has three sensing axes (x, y and z), but the concept also works for units having only two sensing axes or even only one sensing axis.
Both sensor units are rotated by some rotation mechanism, controlled by a processing unit. Both sensor units measure the same input quantity x̅ (the line above the x denoting its a vector quantity).
The sensor output signals s̅1 and s̅2 are processed by the processing unit. This processing unit estimates the offsets and compensates for it, resulting in the corrected sensor output y̅.
More detailed information about the basic operation of the DriftLess technology can be
found in a paper. Another paper describes the benefits of this technology in a INS/GPS integrated navigation system.

Using the improved DriftLess+ technology, the offsets of the sensors are estimated. This is done continuously during operational use. If the offsets change, for instance due to sensor temperature changes, the changing offset is immediately estimated and compensated for. The result is that the offsets are virtually completely eliminated, leaving only a small remainder.

This technology can be used in several different ways. Besides the configuration shown above, it is also possible to use the DriftLess+ technology as an add-on to a system with an existing sensor. If the existing sensor suffices except for an unknown fluctuating bias, the DriftLess+ technology can be used as an add-on that estimates the bias of the existing sensor. Subsequently, the sensor can be compensated for the unknown bias. The bias correction can be done outside the DriftLess+ unit (as shown in the figure) or inside the unit. In the latter case, the unit is placed in line with the signal flow of the existing sensor.
Other combination are also possible, and besides the shown full-3D configurations (requiring two mechanical rotation axes), 2D-configurations and 1D-configurations are also possible (requiring only one mechanical rotation axis).