Polarized electromagnetic drive for a limited operating range of a control element

Claim 1

A polarized electromagnetic drive preferably for actuating a turning servo valve, comprising an electromagnetic field iron core having a central open area and a coil receiving recess defined in said core on each side of said open area, a rotatable armature drive shaft located in the open area of said core for rotation about an axis of rotation, an armature affixed to said drive shaft for rotation therewith having a pair of diametrically opposed armature portions radially extending relative to the axis of rotation with inner ends affixed to said shaft and outer ends extending outwardly from said shaft on respective opposite sides thereof, an actuating coil disposed in said coil receiving recess, said core having a leg portion spaced away from each side of each arm portion by an amount to define a large air gap between each side of each arm portion and each leg portion of said core, each leg portion having an end part extending outwardly from the associated leg portion and alongside the outer ends of said armature arm portions and being radially spaced relative to the axis of rotation from said outer ends by an amount to define a small air gap between each end part and the associated outer ends of said armature arm portions, said core having end pieces extending outwardly beyond each leg portion on each side of said leg portions and having a permanent magnet receiving recess defined therebetween, a permanent magnet in the permanent magnet receiving recess opposed to and spaced from each end of each arm portion, each end part being located intermediate a respective permanent magnet and one of said outer ends of said armature arm portions, the large and small air gaps formed between said armature and said core being such that force components of the large and small air gaps result in a total force having a range of linearity which is greater than the range of linearity of the individual force components, a lever arm affixed to said shaft, and spring means for biasing said lever arm to a centering position, said lever arm including an arm portion extending outwardly from each side of said shaft, said spring means including first and second springs biased against each side of each portion of said lever arm, screw means associated with at least one of said springs for varying the tension on said springs for varying the positioning of the center position of said lever arm.