Torque and ripple analyses of a small BLDC motor for a surgical device

A small brushless direct current (BLDC) motor is under consideration to operate small dental and surgical hand-pieces instead of low torque air turbines, due to high torque density compared to a size. Electromagnetic analyses were carried out numerically in order to improve the performance of a hand-piece motor such as torque output and torque ripple. Several case studies on the characteristics of electromagnetic torque outputs were carried out by increasing numbers of coil wires from 11 to 30 wound and the maximum motor torque was obtained with 20 wound wires at the electromagnetic angle of 90°. The stator slot made of Teflon was found to be better than steel in the magnetic flux density from a material comparison study. In an effort to reduce torque ripple of the motor, the changes in torque ripples for several slot shapes of a stator were evaluated by finite element analyses and compared. The slot with both circular holes and V-cut showed a best ripple performance that was 6.10%, compared to 7.80% of the current design.