Robust, high precision encoded magnetic measuring systems based on magnetic strong field sensors

• Applicant: Professor Dr.-Ing. Marc Christopher Wurz
• Subject Area: Measurement Systems
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 539322758

Magnetic coded measurement systems for capturing position or angle are now indispensable in numerous industrial sectors. These systems have proven themselves over measurement systems based on optical or inductive principles in machine tools and semiconductor manufacturing machines. The measurement systems consist of a sensor head in combination with a planar or rotary measuring scale made of a magnetic material. A magnetic pole pattern is encoded on the scale to enable both incremental and absolute distance or angle measurement. The requirements for higher robustness and high accuracy with corresponding cost-effectiveness cannot be achieved with the current generation of measuring scales based on polymer-bonded magnets or sintered magnets. In this transfer project, the previous experiences of the DFG projects "MagDat" are to be combined with the potential of gas flow-sputtered hard magnetic layers made of SmCo. The deposition process patented by Fraunhofer IST enables the production of robust magnetic layers with reproducibly good magnetic properties. These layers offer high measurement accuracy as well as high mechanical, chemical, and thermal robustness. However, for the existing SmCo sputtered layers, only a stray field strength of 5 kA/m could be achieved, which currently limits them to "weak-field operation". While this operation is suitable for measurement systems with very high accuracy requirements, it is extremely susceptible to variations in the sensor-surface distance. Therefore, weak-field sensor systems are used in highly precise and high-priced machines. Increasing the stray field strength of the magnetic layers would enable sensor operation in the "strong-field" mode. In this mode, the sensor is saturated and less susceptible to distance variations. This would allow less expensive machines to benefit from the robustness of magnetic measurement systems while maintaining high accuracy. The general aim of the project is therefore to develop a mechanically and thermally robust magnetic measurement system that enables strong-field operation. Specifically, this requires coding on the dimensioning that generates a stray field of >25 kA/m at a sensor distance of >250 µm and a pole pitch of 0.5 mm. Firstly, the deposited layers will be optimized in terms of their magnetic properties by varying the deposition parameters. Secondly, different post-treatment methods for the thin films will be used to create a microstructure that is advantageous for magnetization. In addition, the magnetization process itself will be optimized. For this purpose, powerful application-specific write heads will be developed, and the use of various coding strategies, including thermally assisted ones, will be analyzed.

• DFG Programme: Research Grants (Transfer Project)
• Application Partner: ITK Dr. Kassen GmbH
• Cooperation Partner: Dr. Ralf Bandorf