Permanent magnetic chuck

Claim 1

A permanent magnetic chuck comprising: a workpiece holding plate having an attractive surface and a bottom surface, said holding plate having first permanent magnets with a high coercive force disposed along said bottom surface in a first direction each of said permanent magnents having a magnetic isolator adjacent to said permanent magnet disposed along said attractive surface said holding plate also having magnetic pole pieces which alternate with said permanent magnets, the poles of adjacent first permanent magnets which face each other being in an imposed magnetic relationship with each other, said isolator and magnetic pole pieces are respectively constructed as layers of a plurality of thin magnetic layers and a plurality of thin nonmagnetic layers each of which is disposed alternatively with each of said magnet layers; a sliding magnet member in which disk-shaped second permanent magnets with a high coercive force are disposed, in round holes provided in said member at the same pitch as the pitch of said first permanent magnets in said workpiece holding plate, said second permanent magnets being so disposed that the magnetic lines of flux are at right angles relative to said workpiece holding plate and that the magnetic poles of adjacent second permanet magnets are oppositely directed, said sliding magnet member being slidably made into contact with the bottom surface of said workpiece holding plate; a sliding mechanism for causing said sliding magnet member to slide by one pitch of said second permanent magnet in said first direction; and a bottom plate disposed in contact with the bottom surface of said sliding magnet member, said bottom plate and said first and second permanent magnets of said workpiece holding plate and sliding magnet member establishing magnetic circuits.