The electric permanent magnet chuck is mainly composed of a main magnet, a secondary magnet, an excitation coil and a control module. The main magnet is generally using high-coercivity neodymium magnet, even in a strong magnetic field, the magnetism of the neodymium magnet would not be changed. The secondary magnet generally selects low-coercivity AlNiCo magnet. Under the magnetic field excited by the pulse current, the magnetism and the magnetization direction of the AlNiCo magnet are relatively easy to be changed, thereby changing the magnetism of the entire chuck. The excitation coil is mainly used to generate a pulsed magnetic field when lifting and unloading the steel, and to change the magnetism and magnetization direction of the AlNiCo magnet.
Referring to Figures A and B, the magnetic polarity of the main magnet 2 remains unchanged all the time. When the secondary magnet 5 is positively magnetized by the excitation coil 4, the direction of the magnetic polarity of the main magnet 2 and the secondary magnet 5 stay the same, the suction force of the magnetic chuck is the largest at this time. The magnetic field lines pass through the external magnetic pole 1 and the internal magnetic pole 3 to penetrate the steel plate 6, presenting magnetic adsorption. When the secondary magnet 5 is reversely magnetized by the excitation coil 4, the magnetic polarities of the main magnet 2 and the secondary magnet 5 are opposite, causing the external magnetic lines of force cancel out, so no magnetic force lines penetrate the steel plate. The magnetic chuck is not magnetic to the steel plate and cannot be adsorbed to the steel plate in this case.