Numerical Analysis and Experimental Verification to Enhance the Assemble Process of an Array-type Permanent Magnet Sensor Using Steel Balls

Identifying the impeller type is essential for enabling torque sensing in conventional agitators. Previous studies have demonstrated that using arrays of permanent magnets with like poles facing each other allows for cost-effective, non-contact sensors. However, these configurations create strong repulsive forces, complicating assembly during sensor fabrication. This study addresses the issue of poor assemblability by introducing a high-permeability ferromagnetic ball between the magnets. This ball not only reduces repulsive forces but can also induce attractive forces, making assembly easier. We analyzed the effects of ball diameter, magnet thickness, and the number of magnets on the inter-magnetic force using ANSYS Maxwell. To validate the finite element method (FEM) results, we conducted experiments, which showed that the measured values closely matched the simulation results. This confirmed that the ferromagnetic ball significantly mitigates the repulsion between magnets, and in some cases, reverses the force to attraction. These findings are important for enhancing assemblability in automated mass production. Additionally, the study identified an optimal steel ball size that minimizes repulsion while facilitating sensor miniaturization, providing a practical solution for compact sensor design.