Method of controlling a bi-directional stepping motor and a bi-directional stepping motor adapted to be controlled by this method

A stepping motor rotatable in both senses, comprising:

• a rotor comprising a permanent magnet producing a first magnetic field;
• a first coil for producing a second magnetic field and traversed by a first part of said first magnetic field;
• a second coil for producing a third magnetic field and traversed by a second part of said first magnetic field said first and second parts of a first magnetic field forming in said permanent magnet a resultant magnetic field;
• first means for applying said second magnetic field to said permanent magnet in a first direction;
• second means for applying said third magnetic field to said permanent magnet in a second direction symmetrical to said first direction relative to an axis of symmetry;
• and,
• positioning means for maintaining said rotor in or for returning said rotor to any one of a plurality of rest positions, said positioning means being arranged in such a manner that, in each of said rest positions, the resultant magnetic field formed in said permanent magnet by said first and second parts of the first magnetic field makes angle from about 20.degree. to about 70.degree. with said axis of symmetry.

A stepping motor rotatable in both senses, comprising:

• a rotor comprising a permanent magnet producing a first magnetic field;
• a first coil for producing a second magnetic field in response to a first current and traversed by a first part of said first magnetic field;
• a second coil for producing a third magnetic field in response to a second current and traversed by a second part of said first magnetic field, said first and second parts of the first magnetic field forming in said permanent magnet a first resultant field;
• first means for applying said second magnetic field to said permanent magnet in first direction;
• second means for applying said third magnetic field to said permanent magnet in a second direction symmetrical to said first direction relative to an axis of symmetry;
• positioning means for maintaining said rotor in or for returning said rotor to any one of a plurality of rest positions;
• and
• means for simultaneous supply of said currents to the coils each time said rotor must turn by one step, said currents being produced with the same sense during the entire duration of their supply to said coils and with intensities such that, at the beginning of said current supply and when the rotor occupies one of said rest positions, said first resultant field forms an angle having a value between about 110.degree. and about 160.degree. with a second resultant field produced in said permanent magnet by said second and third magnetic fields, said senses of said currents being furthermore such that said angle has a sense, when measured from the first resultant magnetic field towards the second resultant magnetic field, which is the sense in which the rotor should turn.