Rotary sensors can help determine the position of a moveable body in relation to an axis. They are essential to the smooth running of car engines in the automotive industry, for example. In factories, goods and products are transported from one processing station to the next via conveyor belt. For the transfer from one belt to the next to run smoothly, it must take place precisely at a specific position, which means knowing the relative position of objects on the conveyor belts as they move towards each other. This can be determined from the angle of rotation, which refers to the position of a moveable body to an axis.

The polarization sensor measures the angle of rotation on a test board. At left is a shaft with integrated polarizing film. (© Fraunhofer IIS)

A new kind of sensor combines precision measurement with flexible handling, allowing it to be customized to specific measurement tasks. The sensor relies on optical measurement, utilizing the polarization effect. Under normal conditions, light oscillates in all possible directions, meaning it is not polarized in its original state. With the help of special polarizing films, it is possible to steer these oscillations in a defined uniform direction, either horizontally or vertically.

A good example of how polarizing films work is to be found in 3D glasses, which generate depth information because the viewer looks through lenses fitted with different polarizing filters for each eye. The researchers attach just such a polarization film to the test object — the drive shaft, for example — and direct a light beam at it. Polarized light is produced on the reverse side of the film. Should the drive shaft now rotate, the polarization vector rotates with it, thus serving as a kind of direction indicator.