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 decontaminates radioactively contaminated plant parts from nuclear power plants using an industrial robot.

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 consecutive cleaning processes. This ensures that the objects to be cleaned are fully covered from all sides by a high-pressure jet.

to the YouTube video from Fraunhofer IGD

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

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

Long-lived gold caps serve as the energy storage and are housed very space‑efficiently. The electronics are placed in the free spaces between the cells.

The small box contains the gold caps, the Qi module, the charge controller, the DC/DC converters, the push button, two LED strips, 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 240 MHz.

As early as 1969, a Kalman filter was implemented for 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 of absolute attitude possible.

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 computationally intensive and time-critical processes are distributed across multiple CPU cores. Custom functions for calculations with transformation matrices and quaternions save processing 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 3D-printed from PLA.

Wireless charging instead of contacts. Gold cap instead of Li‑Ion. Potting instead of wear. The combination of the advantages of additive and subtractive manufacturing techniques. A good concept developed 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 production were implemented 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 in this process.

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

The engineering firm Glaser thanks the clients for the excellent cooperation:

 TSE Wassmann

RWE Nuclear GmbH

Fraunhofer IGD