Electric stepper motor

Electric stepper motor having a stator part and a rotor part of substantially cylindrical shape, said stator part comprising at least two annular coils (6, 7) wound on respective annular cores (8), said cores (8) being arranged in parallel with each other and with a common axis which is the motor axis, said coils (6, 7) being separately fed AC current from an electronically controlled current source to magnetize alternatingly a number of flux-conducting elements comprised by said stator part and positioned successively along a direction of a circumference of a cylinder to form a series of flux gaps (36) with flux directions substantially along a circumferential direction between the elements, said elements (30, 35) being in engagement with said cores (8) of said coils (6, 7) to conduct magnetic flux therefrom and toward and through said flux gaps (36), and where said rotor part is constituted by a wheel which is arranged concentrically on an outside of said stator part, said wheel being equipped on a radial inside part with magnets (13) for interaction with magnetic fields of the stator part, said magnets (13) having only a small clearance to a radially outer surface of said stator part, and being arranged with a pole direction pointing radially and with alternatingly north pole and south pole toward the stator part in a circumferential direction, characterized in that

• a) the flux-conducting elements are generally T- and .GAMMA.-shaped profiles (30, 35) arranged with a lower end of each T-profile stem (24) between and engaging two neighboring ones of said cores (8) and a lower end of each .GAMMA.-profile stem (26) on an outside of and engaging one of the two annular cores (8),
• every profile stem (24, 26) extending outward in a radial direction past said coils (6, 7) and being uniformly distributed in circularly arranged rows between and on an axial outside of said coils (6, 7),
• top beams (25, 27) of the T-profiles (30) and the .GAMMA.-profiles (35) pointing in a direction parallel to said axis, the .GAMMA. top beams (27) pointing toward an opposite axial outside of said coils (6, 7), and each having a radially outer boundary surface lying substantially flush with an outer cylinder surface of the stator part,
• the profile stems (24, 26) being arranged in a shifted order from one circularly arranged row to the next such that each outer coil (6, 7) on its radial outside is covered in equal and uniformly distributed, successive sectors by alternatingly a .GAMMA.-profile top beam (27) and a T-profile top beam (25) with a circumferential flux gap (36) therebetween, and in such a manner that each axially inside coil is covered in a corresponding manner by top beams (25) having T-profiles (30) with stems (24) alternatingly on one axial side and the other axial side of the AC current coil, with the same circumferential flux gap also between these top beams (25),
• and top beams (25, 27) having .GAMMA.-profiles and T-profiles (35, 30) pointing toward each other in a direction parallel to said axis, being cut lengthwise to provide axial clearances (34) therebetween, and that,
• b) each magnet (13) in the rotor part has an extent in the circumferential direction which substantially corresponds to a circumferential center distance between two circumferentially neighboring top beams (25, 27) in an outer cylinder surface of the stator part, and lie in a close arrangement to constitute a magnet ring, the same number of such magnet rings as a number of coils (6, 7) in the stator part, being provided closely next to each other in a direction parallel to the axis, however, with each successive magnet (13) in the ring shifted in the circumferential direction one-half magnet sector in relation to the magnets (13) in a neighboring ring.