Sensor box IMU with AHRS

The sensor box continuously measures angular velocities as well as the gravity vector and calculates its orientation in 3D space. On button press, the recorded process data are saved and transmitted via WLAN to a plant control system.

The sensor box was developed for the joint research project of RWE Nuclear and the Fraunhofer IGD. The sensor is used in a system that employs an industrial robot to decontaminate radioactively contaminated plant components of nuclear power plants.

to the press release from RWE Nuclear
to the press release from Fraunhofer IGD

The sensor box is attached to the component to be cleaned during the process and records its rotation in 3D space between successive cleaning processes. This ensures that the objects to be cleaned are fully covered by the high-pressure jet from all sides.

to the Fraunhofer IGD YouTube video

The sensor box was designed with protection class IP66 for the harsh environmental conditions of the decontamination chamber.

Thanks to the inductive Qi charging station, the sensor box is contactless and always ready for use.

Long-lasting gold caps serve as the energy storage and are housed very space-efficiently. The electronics find space in the gaps between the cells.

The small box contains the gold caps, the Qi module, the charge controller, the DC/DC converters, the button, two LED strips, as well as the gyroscope with accelerometer and a digital compass. The heart of the box is an ESP32, which provides sufficient computing power with a clock frequency of 240MHz.

Already in 1969 a Kalman filter was implemented for the first time on the Apollo mission to determine the rocket's attitude. In our project, an AHRS (Attitude Heading Reference System) with a Kalman filter is also used to combine the advantages of gyroscope and accelerometer and to enable the most precise determination possible of the absolute orientation in space.

The software was written in the low-level programming language C++ using the Visual Studio Code development environment. Using interrupts and the real-time operating system FreeRTOS, the compute-intensive and very time-critical processes are distributed across multiple CPU cores. Custom functions for computing with transformation matrices and quaternions save computing power and thus energy.

The robust Euromas housings made of polycarbonate were machined with a CNC milling machine and the magazine for the gold caps was printed with a 3D printer from PLA.

Wireless charging instead of contacts. Gold cap instead of Li-ion. Potting instead of wear. Combining the advantages of additive and subtractive manufacturing techniques. A good concept in close consultation with the customer.

Due to the short communication channels, less than a month passed from the preparation of the offer to the completion of the sensor box. Development, design, programming and manufacturing were carried out almost simultaneously and without additional interfaces by other external service providers.

In the charging cradle, red and green light indicate the current charge status. The window of the box fills accordingly.

In the charging cradle, the window of the box fills from bottom to top with green light according to the current charge level, displacing the red. During operation and the reference routine, the RGB LEDs pulse in the currently dominant axis color.

The engineering office Glaser thanks its clients for the excellent cooperation:

 TSE Wassmann

RWE Nuclear GmbH

Fraunhofer IGD