Patent ID: 7941043

Claim:
An automatic focal point control apparatus to move a lens barrel mounted in a camera linearly back and forth, the apparatus comprising: a base fixed in the camera, the base comprising a cylindrical projection which extends from a top surface thereof and into which a lower part of the lens barrel is inserted; a bobbin inserted into the cylindrical projection on the base, the bobbin comprising a plurality of electromagnets around which coils are wound and which are arranged at regular intervals along an outer circumference of the bobbin; a rotation body comprising a support ring, which is rotatably connected by screws to the outer circumference of the lens barrel, and a ring-shaped permanent magnet which is fixed onto an outer surface of the support ring and which has a plurality of N poles and an equal number of poles alternately arranged on an outer surface at regular intervals; and a housing detachably mounted on the base, the housing comprising a space part formed thereinside to house the bobbin, rotation body and lens barrel, and a through hole formed therein side so that light and images are projected onto the lens barrel, wherein, if each pair of electromagnets facing each other from among the plurality of electromagnets is continuously driven and the rotation body is made to rotate by the magnetic field generated by the plurality of electromagnets so that the lens barrel is driven linearly back and forth along an axis, and wherein the permanent magnet of the rotation body has four N poles and four S poles alternatively arranged at regular intervals and the bobbin has four electromagnets.