US Patent 9638202 Centrifugal pump apparatus

A centrifugal blood pump apparatus includes a plurality of permanent magnets (17) in an impeller (10) in a blood chamber (7), a plurality of coils (20) in a motor chamber (8), and a magnetic element (18) in each of the coils (20). The magnetic elements (18) are made shorter than the coils (20) to lower attractive force between the magnetic elements (18) and the permanent magnets (17) in the impeller (10), to set a large gap between the magnetic elements (18) and the permanent magnets (17). As a result, axial attractive force and negative rigidity can be lowered while required torque is satisfied.