Electric motor

An electric motor for reciprocating an object in a straight line along a rod having a predetermined length, the electric motor comprising:

• a housing;
• a rotor part including a rotor shaft rotatably mounted inside the housing via a bearing and axially coupled to the rod to reciprocate in a straight line along the rod when rotating, and a plurality of magnets mounted in a circumferential direction of the rotor shaft;
• and
• a stator part including at least one stator core including a closed loop-shaped yoke part embedded in the housing to surround a circumference of the rotor part and a plurality of slot parts extending from the yoke part toward the rotor part, and a coil wound around at least one slot part among the plurality of slot parts,
• wherein the stator core includes a plurality of first slot parts in which coils are wound and a plurality of second slot parts in which the coils are not wound,
• wherein the plurality of first slot parts are disposed to surround a first arc part corresponding to an angle of θ among an entire circumference of a virtual circle connecting the ends of the plurality of first slot parts and the plurality of second slot parts,
• wherein the plurality of second slot parts are disposed to surround a second arc part corresponding to an angle of 2π-θ among the entire circumference of the virtual circle excluding the first arc part,
• wherein the angle of θ is greater than the angle of 2π-θ,
• wherein each of the plurality of second slot parts is extended from the yoke part to the rotor shaft by a predetermined length so as to have a shorter length than the plurality of first slot parts,
• wherein the plurality of first slot parts are disposed to a position closer to an upper surface of the housing,
• wherein the plurality of second slot parts are disposed to a position closer to a lower surface of the housing,
• wherein the rotor shaft is disposed to be located at an eccentric position closer to the lower surface of the housing than to the upper surface of the housing from the center of the housing,
• wherein the object is fixed to the upper surface of the housing,
• wherein the rotor shaft is positioned at a position close to a bottom surface of a space including the object,
• wherein the plurality of first slot parts include:
• a first set of first slot parts is formed of a first teeth having a first length;
• a second set of first slot parts is formed as a second teeth having a second length that is shorter than the first length;
• and
• a third set of first slot parts is formed as a third teeth having a third length,
• wherein the first set of first slot parts is positioned between the second set of first slot parts, and the third set of first slot parts is positioned between the second set of first slot parts and the plurality of second slot parts,
• wherein the first teeth, the second teeth and the third teeth have a length longer than teeth of the plurality of second slot parts, and
• wherein the first set of first slot parts and the plurality of second slot parts are disposed to be positioned on an opposite side with respect to a center point of the virtual circle.