Limited angle electric rotary actuator

An electric rotary actuator for producing rotation through a limited angle to position magnetic heads of a magnetic disk file over selected information-bearing tracks on a disk, said actuator comprising:

• a stator (11) comprising a hollow magnetically permeable core (14),
• a plurality of axially extending, radially magnetized permanent magnets (13) circumferentially mounted around said core and separated by axially extending magnetic flux gaps (15) of uniform width, the outer cylindrical surface of said magnets constituting a plurality of circumferentially displaced magnetic pole faces of alternate polarity;
• an annular flux return means (20) surrounding said magnets and spaced therefrom to provide an annular magnetic flux gap (21), said flux return means having a plurality of axially extending slots (22), each circumferentially aligned with a respective one of said axially extending flux gaps;
• and
• a non-magnetic rotor concentrically disposed in the annular flux gap (21) and comprising a winding (30) including a plurality of substantially rectangular loop coils (31) that are curved out-of-plane and arranged edgewise in a substantially continuous cylindrical structure so that, throughout rotation within the limited angle, each pair of adjacent axially extending portions of adjacent coils (31) will be substantially opposite a respective one of the circumferentially displaced pole faces.