Design for an electrostatic motor to drive a quartz watch

Abstract

In this thesis the design possibilities to replace a Lavet-type motor with an electrostatic motor are investigated. At the moment, almost all quartz watches use a Lavet type of motor. Two electrostatic conceptual designs are made by Timex and Accutron. An electrostatic motor for the watch application looks promising due to the more efficient scaling of force compared to magnetic, and since the current design consists of an intricate and, relative to the rest of the movement, bulky coil of wires. Various designs were devised and then analysed. The concepts were selected based on ease of manufacture and potential losses, resulting in the two best designs. In the investigation, various mechanisms for losses in the concepts are calculated, and the concepts are compared to each other. The most promising concepts to replace a Lavet type motor are a ratchet comb design and a top drive. A quartz motor designer can choose different parameter sets to get a high efficiency or a low surface area of the actuator. The ratchet comb and top drive design have approximately the same efficiency or better as the current Lavet motor, and the size is approximated to be between 3−20 mm2 where the Lavet motor uses a surface of around 80 mm2.