'3D' Hall sensor can calculate the exact position of an object
11 June 2013
New Hall sensors developed by Fraunhofer researchers are making the process of position measurement even more precise and free from interference.
Magnetic field sensors are used to measure the position of machine parts and products with zero contact and zero wear – a modern car has around 100 of these sensors monitoring safety belt buckles and door locks, registering pedal positions, or as part of ABS, EPS, and engine control systems.
While being cost-effective and robust, these conventional sensors only measure the magnitude of the magnetic field perpendicular to the chip surface and the measurement is imprecise and susceptible to interference.
Michael Hackner, Hans-Peter Hohe, and Markus Stahl-Offergeld from the Fraunhofer Institute for Integrated Circuits IIS decided they wanted to improve on this and set about developing a 3D Hall sensor.
“First we connected up several sensors on a chip in order to improve the measuring accuracy of the individual sensors,” says Markus Stahl-Offergeld. “Next we arranged several of these sensors to measure the three-dimensional magnetic field at one point. The result was our pixel cells.”
The 3D Hall sensor is capable of measuring all three spatial axes of a magnetic field and calculating the exact position of an object. The chip contains a designated sensor for each of the three magnetic axes, and these are placed together in the pixel cell, attaining a resolution of just a few micro-Teslas, depending on the measurement speed.
Also integrated in the chip are the evaluation circuit and a coil, which enable self-testing and calibration. “In spite of its complexity, the 'HallinOne' magnetic sensor can be manufactured using standard semiconductor fabrication processes – and that makes it cost-effective,” says Hans-Peter Hohe.
“Our next goal is to develop a sensor for five-axis position measurement,” says Michael Hackner. “This will allow us to detect more mechanical degrees of freedom simultaneously, including translational and rotary movements by the magnet in all directions. It already works in laboratory tests, but the system still needs some adjustments before it is ready for real-life applications.”