Patent ID: 7202578

Claim:
An electromagnetic drive device comprising a drive part arranged to be reciprocated in a stroke direction and possessing a circular or oval cross section, said drive part having a permanent magnet arrangement magnetized athwart the stroke direction, such arrangement consisting essentially of two pairs of oppositely magnetized magnet portions arranged sequentially in the stroke direction and being arranged in the intermediate space of a yoke arrangement with pole pieces provided in the direction of magnetization on opposite sides of the drive part, wherein the yoke arrangement consists essentially of two pairs of pole pieces delimiting the intermediate space and which are joined together by two yoke regions extending essentially in parallelism to the stroke direction, at least one of the yoke regions being surrounded by a coil able to conduct current for performing a stroke and each pair of pole pieces is provided with a pair of oppositely magnetized magnet portions of the permanent magnet arrangements, and wherein each pair of magnet portions includes an inner magnet portion and an oppositely magnetized outer magnet portion, said inner magnet portions facing one another to form a common magnetic pole in a center portion of said drive part, and said outer magnet portions forming an opposite magnetic pole at each end portion of said drive part.