The lavet type stepping motor has widespread use as a drive in electro-mechanical

Electromechanics

In engineering, electromechanics combines the sciences of electromagnetism, of electrical engineering and mechanics. Mechanical engineering in this context refers to the larger discipline which includes chemical engineering, and other related disciplines. Electrical engineering in this context...

 clock

Clock

A clock is an instrument used to indicate, keep, and co-ordinate time. The word clock is derived ultimately from the Celtic words clagan and clocca meaning "bell". A silent instrument missing such a mechanism has traditionally been known as a timepiece...

s and is a special kind of single-phase stepping motor. Through miniaturization it can be used in wristwatches and requires very little power, making a battery last for many years. The French engineer Marius Lavet is known as the inventor for this kind of drives and described it 1936 in his patent application FR823395.

Like other single-phase motors the lavet motor is only able to turn in one direction, which depends on the geometry of its stator

Stator

The stator is the stationary part of a rotor system, found in an electric generator, electric motor and biological rotors.Depending on the configuration of a spinning electromotive device the stator may act as the field magnet, interacting with the armature to create motion, or it may act as the...

. The rotor

Rotor

Rotor may refer to:*A rotating part of a mechanical device, for example in an electric motor, generator, alternator or pump.In engineering:...

 is a permanent magnet

Magnet

A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...

.
Essential for the movement of the lavet motor are the cogging points of the rotor. Its position deviates between energized stator coil and currentless stator coil. In some way this effect serves as a delayed phase like in shaded-pole motor

Shaded-pole motor

A shaded-pole motor is a type of AC single-phase induction motor. It is basically a small squirrel cage motor in which the auxiliary winding is composed of a copper ring surrounding a portion of each pole. This auxiliary winding is called a shading coil. Currents in this coil delay the phase of ...

 and defines the rotational direction. The cogging points with no current are caused by reluctant force

Magnetic reluctance

Magnetic reluctance, or magnetic resistance, is a concept used in the analysis of magnetic circuits. It is analogous to resistance in an electrical circuit, but rather than dissipating magnetic energy it stores magnetic energy...

.

Movement of the common two step lavet motor:

(a) currentless stator, north pole of rotos points to the upper left

(b) energized stator, rotor moves clockwise and north pole points to the right afterwards

(c) after energization of the stator has declined, rotor moves further until north pole points downright

(d) stator energized in opposite direction, rotor moves clockwise and north pole points to the left

(a') after energization of the stator has declined, rotor moves to its initial position (a)

To make a lavet motor turn the current thru its stator coil must change direction each step (bipolar) followed by a short interval without current while the rotor move to its reluctant position.

Aside from clock drives there are many variations of Lavet's concept. One example are types of dashboard

Dashboard

A dashboard is a control panel placed in front of the driver of an automobile, housing instrumentation and controls for operation of the vehicle....

instruments in cars.