Getting the right spin

May 14, 2014
The polarization sensor that measures the angle of rotation mounted on the test board. On the left: A shaft with integrated polarizing film. Credit: Fraunhofer IIS

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. Fraunhofer researchers have developed a new kind of sensor that combines precision measurement with flexible handling, allowing it to be customized to specific measurement tasks. The scientists will be presenting their prototype at the Sensor + Test trade show in Nürnberg from June 3 to 5.

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. Rotation angles are also important within the , where they provide information for engine feedback systems, for example, in which the rotational speed of the drive shaft must be precisely set. The angle of rotation is measured using special sensors. There are currently two types of such rotation angle sensors on the market, working according to either magnetic or optical measuring principles. Magnetic sensors are very durable and dirt resistant, giving them an advantage in harsh environments. They are, however not as precise as . These in turn are not very flexible to use since they must be precisely mounted in a fixed position on the object being measured.

Researchers at the Fraunhofer Institute for Integrated Circuits IIS in Erlangen have now developed a new rotational angle sensor that combines the advantages of both solutions into one. "While our sensor also relies on optical measurement, its functional principle is completely different to other products currently available on the market," says Dr. Norbert Weber, group manager at the IIS. The researchers' development utilizes 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.

Sensor can be fitted flexibly

The read-out module is then mounted in such a way that it is located in the beam of light. Several wire grids – small microstructures – are arranged in a matrix on the sensor chip. These lattices can be produced as part of the normal CMOS chip manufacturing process without any additional effort. The angular position of the shaft is calculated when the polarized light strikes the lattices. "In order to obtain a definite measurement of the angular position of a shaft, we need at least three grids that are each structured in different directions. Depending on the measuring task we can also add further grids, thus adapting the chip to suit the specific requirements of customers while increasing measurement accuracy, "explains Weber. With this design, the Erlanger researchers are not able to attain 100 percent of the precision of conventional optical sensors, but their sensor is significantly more robust and can be positioned relatively flexibly. "The chip does not even have to sit directly on the optical axis – the only thing that matters is that it is located within the ," says Weber. Another advantage is that even if the shaft wobbles slightly, the result will not be affected as long as the beam is wide enough. At the SENSOR + TEST 2014 trade fair, researchers from Erlangen will present their solution on an exhibit which demonstrates rotation angle measurement on a hollow shaft. The measurement results are then displayed as a graph on the monitor.

Explore further: 3-D Magnetic field measurement

Related Stories

3-D Magnetic field measurement

June 11, 2013

Magnetic field sensors are a contact- and wear-free means of measuring the position of machine parts and products. A new generation of Hall sensors is now making the process even more precise and free of interference.

Magnetic Sensor That Brooks No Interference

June 3, 2008

Sensors accurately register the slightest temperature fluctuations, the tiniest changes to a magnetic field, or barely perceptible air currents. In some cases, however, there are limits to their accuracy – for instance ...

NXP launches new angular sensor compliant with SENT standard

March 12, 2014

NXP Semiconductors today announced the release of the KMA215, a programmable angle sensor with digital output, which is compliant with the most recent Single Edge Nibble Transmission (SAE J2716 JAN2010 SENT) standard. The ...

Racing car with electric drive

April 26, 2013

Drive technology has an electric future – of this Fraunhofer research scientists are in no doubt. At the Sensor + Test measurement fair in Nuremberg from May 14 -16, they will use an electric racing car to present novel ...

Researchers build acoustic tractor beam

May 8, 2014

( —A team of researchers with members from the U.K., Scotland and the U.S. has built a functioning acoustic tractor beam in a lab—one that is able to pull objects of centimeter size. In their paper published ...

Recommended for you

Newest solar cells underperform in cloudy countries

August 22, 2017

To determine how efficient new solar cells convert sunlight into electricity, small sample cells are tested under ideal conditions. However, the reported efficiency is not very representative of the actual annual yield when ...

Google to serve next version of Android as 'Oreo"

August 22, 2017

An upcoming update to Google's Android software finally has a delectable name. The next version will be known as Oreo, extending Google's tradition of naming each version after a sweet treat.

Forget oil, Russia goes crazy for cryptocurrency

August 16, 2017

Standing in a warehouse in a Moscow suburb, Dmitry Marinichev tries to speak over the deafening hum of hundreds of computers stacked on shelves hard at work mining for crypto money.

Researchers clarify mystery about proposed battery material

August 15, 2017

Battery researchers agree that one of the most promising possibilities for future battery technology is the lithium-air (or lithium-oxygen) battery, which could provide three times as much power for a given weight as today's ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.