The quartz crystal, cut and finished in the shape of a tuning fork, is responsible for delivering a intervallic voltage, drawn from its piezoelectric frequency, to the circuit, but how the circuit chooses to use that voltage is a different matter.
The load, or drain, on the battery increases with the introduction of mechanical friction. Powering the circuit doesn’t really require all that much energy. The battery is just doing what it would do naturally and allowing power to flow all around it. Imagine the battery like a human body. When the body is standing still it can be said to be doing nothing, but blood still flows and its heart still beats. Assuming the body has a finite energy resource it can maintain this static pose until power runs out. Now if you ask that body to physically push something (for the sake of this example, let’s say a boulder), the energy will deplete faster, the body’s lifespan will decrease and it will burn out. That’s the problem faced by the battery.
When allowing power to flow around the circuit and through the quartz crystal, the battery is barely flexing its muscles. As soon as the wheels come into play, powered of course by the bipolar motor as previously discussed, the friction of driving the train asks an awful lot of the power source.
In a Quartz Watch that has a seconds hand an impulse is needed every second. However, for watches with no seconds hand, such a load can be reduced. It is not necessary for the Lavet motor to convert electric impulse into mechanical movement EVERY SINGLE SECOND, and so the impulse is ‘chopped’ into larger chunks, pulsing maybe once every 20, 30 or even 60 seconds in order to reduce the strain on the battery.
Here’s a neat little definition for you:
The length of the impulse is varied (chopped) according to the load on the motor, optimising power consumption. Basically, the watch only uses power when necessary. It is common for more power to be released during the date change phase of a quartz watch as it takes slightly more energy to power the movement during this period. This whole process is controlled by the Integrated Circuit (the IC), which reacts to the feedback it receives from the movement and distributes power accordingly.
The stator is made of a permeable soft iron that does not hold on to magnetism. I is magnetised by the coil, which passes an electric current through it. The current is reversed with every impulse, meaning the polarity of the stator alternates, affecting the rotor, which sits in a gap in the middle of the stator. The Rotor is a cobalt disc, which is always strongly magnetised. The rotor pivots in jewelled bearings and drives the train. It is moved itself by the stator which, thanks to ‘air gaps’ cut into the walls of the hole in which the rotor sits, positions the rotor correctly so that each impulse will turn it in the right way and prevent it from every flipping backwards.
The coil creates a temporary magnetic field in the stator when current is applied. The polarity depends on the direction of the current.
The coil, under influence from the Integrated Circuit (IC), alternates the polarity of the stator so that the rotor, which sits in the cut out of the stator, can rotate and thus drive the gear train of the watch.
The stator is made of a soft permeable alloy, which conducts the alternating magnetic field from the coil to the rotor. The shape and slots in the stator hold the rotor in the correct position, ready for the next impulse.
The Rotor is a cobalt magnet disc, pressed on to a pinion. This magnet rotates in the stator and drives the train.
The bipolar motor, designed by Lavet, has a fixed polarity rotor (Green/Red disc in above picture), surrounded by a varying polarity stator of soft iron (Silver bit in above picture).
The bipolar motor relies on the stator made of a permeable alloy, being alternately magnetised by the current of a coil (Orange bit in above picture). 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 aligned 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.
To understand how the Quartz watch works, you need to the basic principles behind the timekeeping element of the watch, then get your head around how these principles translate into mechanics.
First things first, what is a Quartz Watch? A Quartz Watch is so named because of the sliver of genuine quartz crystal that, remarkably, plays the same role as the hairspring would in a mechanical watch. When a quartz crystal is properly cut (normally in the shape of a tuning fork) and mounted, it can be made to distort in an electric field by applying a voltage to an electrode near or on the crystal, distorting the crystal. This property is known as piezoelectricity. When the field is removed, the quartz will generate an electric field as it returns to its previous shape, and this can generate a voltage. The result is that a quartz crystal behaves like a circuit composed of an inductor, capacitor and resistor, with a precise resonant frequency.
This frequency (32,768 Hz) is equal to 2 to the power of 15 cycles per second. The frequency is ideal due to the fact that it can be stepped down cleanly to 2, thus allowing the wheels in the watch to easily translate that impulse into one tick per second.
Now you understand how the quartz crystal acts as a timekeeping element, we can move on to the motor that receives the impulse from the Integrated Circuit, which is under the instruction of the quartz crystal itself.