3D Static Magnetic Field Analysis of Torque and Rotor Shaft Attraction Force of Narrow-Gap Stepping Motors for Driving the Hands of a Wristwatch

Abstract

In this study, a three-dimensional static magnetic field analysis was conducted on a narrow-gap stepping motor for driving the hands of a wristwatch. The purpose of this analysis was to design a stepping motor with a low power consumption, by calculating the holding and detent torques and rotor shaft attraction force in two cases, namely a rotor with no eccentricity and a rotor with 5µm eccentricity. We analyzed why existing stepping motors are constrained to a gap width of 300µm. We further confirmed that the rotor shaft attraction force, which is derived from the rotor eccentricity, increases rapidly with the decrease in gap width, which in turn has a negative impact on the stepping motor. In the future, we intend to study the movement of a wristwatch comprising a metal wheel bearing, to design a stepping motor with a narrow gap, and subsequently reduce the power consumption.