A brief explanation of the bipolar motor

It’s pretty common for people to dismiss the mechanical majesty of Quartz watches due to invisible ‘magic’ that seems to occur in the integrated circuit. Sure, a fully mechanical watch is much more beautiful, and mind-boggling to imagine that horological theory, at one relatively recent point in time, did not even exist. It is hard enough to learn everything there is to know about how a mechanical watch functions, let alone conceive its conception. Quartz watches, because they are comparatively sterile, do not drop jaws or widen eyes in the same way. They are, however, equally amazing and, some might argue, their manipulation of the piezo-electric frequencies of a naturally occurring material make them even more beautiful than their mechanical counterparts, even if only in theory.

The bipolar motor is present in all quartz watches. It was designed by Lavet, has a fixed polarity rotor, surrounded by a varying polarity stator of soft iron.

The bipolar motor relies on the stator (made of a permeable alloy) being alternately magnetised by the current of a coil. The stator has special air gaps cut into the rim of the recess in which the rotor (a cobalt magnet that drives the gear train) sits.

The air gap around the rotor is designed to hold the rotor at a specific angle to the stator. When the coil receives an impulse of electricity from the Integrated Circuit (IC) it magnetises the stator for a number of milliseconds. The rotor then moves to align itself with the magnetic field. When the electric impulse is turned off, the rotor continues through 180 degrees and comes to rest in alignment with the air gaps. There it waits for the next impulse, which will be of different polarity to the last.

The Rotor only rotates in one direction thanks to the air gaps in the stator. The direction in which the current is passed from the IC, through the coil will determine the polarity of the magnetism. Through this mechanism, the wheels of a quartz watch are advanced one tooth at a time, translating into the movement of the hands every second, twenty seconds, thirty seconds or minute depending on the number of hands and the set-up of the circuit.

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