When a magnetic encoder ring rotates at high speed, the magnetic material inside it experiences eddy current losses and hysteresis losses due to the alternating magnetic field. These losses not only reduce the encoder's efficiency but can also cause localized overheating, affecting its long-term operational stability. To effectively reduce these losses, a multi-dimensional approach is needed, encompassing material selection, structural design, process optimization, and magnetic field control, to achieve a balance between performance and reliability.
Regarding material selection, choosing soft magnetic materials with low coercivity and high permeability is fundamental to reducing hysteresis losses. Silicon steel sheets, due to their excellent magnetic properties, are commonly used in magnetic encoder rings. Their narrow hysteresis loop results in low domain turning resistance in an alternating magnetic field, significantly reducing hysteresis losses. Furthermore, high-permeability materials such as permalloy, through optimized crystal structures, further reduce the energy consumption for domain turning. For eddy current losses, high-resistivity conductor materials, such as copper or aluminum, should be selected to reduce the generation of induced currents. Meanwhile, the use of bonded magnet technology, by adding high-resistivity powder (such as alumina) to increase the overall resistivity of the material, can effectively suppress eddy current effects, but a balance must be struck between magnetic properties and resistivity.
Structural design optimization is a key aspect of reducing losses. For the magnetic part of the magnetic encoder ring, using a stacked or segmented structure can significantly reduce eddy current losses. A stacked structure divides the magnetic material into multiple thin sheets, with each layer isolated by an insulating layer, increasing the eddy current path length and thus reducing losses. A segmented structure divides the magnet into several segments along the circumference, reducing the induced current loop area of a single magnet segment and further suppressing eddy currents. Furthermore, optimizing the magnetic pole distribution design, such as using a non-uniform magnetic pole arrangement, can improve the uniformity of the magnetic field distribution and reduce eddy current concentration caused by excessively strong local magnetic fields.
Process optimization has a direct impact on reducing losses. In the manufacturing process of the magnetic encoder ring, using ultra-thin silicon steel sheets (e.g., below 0.1 mm) can significantly reduce eddy current losses. Ultrathin sheets reduce losses by shortening the eddy current path through reduced sheet thickness, but their improvement on hysteresis losses is limited. Furthermore, optimizing the material's crystal structure through heat treatment processes can increase permeability and reduce coercivity, further reducing hysteresis losses. For bonded magnets, the binder content and distribution uniformity must be controlled to ensure synergistic optimization of material resistivity and magnetic properties.
Magnetic field control technology provides a dynamic adjustment method for loss reduction. By optimizing the magnetic field excitation waveform, such as replacing square waves with sine waves, the width of the hysteresis loop can be reduced, thereby lowering hysteresis losses. Additionally, using pulsed magnetic fields or magnetic field modulation techniques, by controlling the frequency and amplitude of magnetic field changes, minimizes eddy current losses over different time periods. In magnetic encoder ring applications, combining sensors to monitor magnetic field strength and frequency in real time and dynamically adjusting excitation parameters allows for precise loss control.
Magnetic circuit design optimization is a systematic solution for reducing losses. By increasing the length and cross-sectional area of the magnetic circuit, the magnetic flux density can be reduced, thereby reducing hysteresis losses. Meanwhile, a segmented magnetic circuit design, dividing the magnetic circuit into multiple independent loops, reduces magnetic leakage and improves magnetic field uniformity, further reducing losses. Furthermore, optimizing the distance between the magnetic encoder ring and the reading head ensures efficient magnetic field transmission in the air gap, reducing additional losses caused by magnetic field attenuation.
Shielding and isolation technologies provide further protection against losses. In the conductor section of the magnetic encoder ring, a magnetic shielding layer (such as high-permeability materials like iron or nickel) reduces interference from external magnetic fields, thereby reducing eddy current losses. The shielding layer can be a coating, thin film, or multilayer composite to suit different application scenarios. In addition, insulating the conductor, such as by applying an insulating coating, reduces localized overheating caused by eddy currents, improving equipment reliability.
Reducing eddy current and hysteresis losses during high-speed rotation of the magnetic encoder ring requires coordinated optimization from multiple dimensions, including materials, structure, process, magnetic field control, and shielding. By selecting low-loss materials, optimizing structural design, improving manufacturing processes, dynamically adjusting magnetic field parameters, and adopting shielding technology, the efficiency and reliability of the magnetic encoder ring can be significantly improved, meeting the performance requirements of high-speed rotation scenarios.
