Electromagneto-mechanical actuator

Abstract

An electromagneto-mechanical actuator comprising a brushless D.C. torque motor capable of producing a torque proportional to the current fed to coil windings which are arranged as a stator, a permanent magnet being the rotor, these windings being severally arranged opposite the pole end faces of the magnet and being reversely wound so that the magnetomotive forces generated by these windings cancel out each other and thereby eliminate magnetic hysteresis. The pivotal movement of the rotor is converted to translational or rectilinear movement of an output drive element through a substantially frictionless band drive having no backlash. The actuator is preferably arranged in a closed servo loop so that the proportionality of its response can be utilized.

What is claimed is: 
     
       1. An electromagneto-mechanical actuator comprising, a torque motor including a rotor and a stator, and band drive means operatively associated with said motor and including a tensioned flexible resilient band having opposite end portions and an intermediate loop portion, a drum member arranged to pivot with said rotor about the pivotal axis of said rotor and having a cylindrical peripheral surface concentric with said axis, said band intermediate loop portion being wrapped around said surface and secured to said drum member against relative circumferential movement, a yoke member arranged for rectilinear movement along a line perpendicular to said axis, means securing one of said band end portions to said yoke member, means securing the other of said band end portions to said yoke member, and an output drive element extending from said yoke member. 
     
     
       2. An electromagneto-mechanical actuator according to claim 1 wherein said band intermediate loop portion includes a web part for attachment to said drum member, a central strip part extending between said web part and one of said band end portions and a pair of laterally spaced strip parts extending between said web part and the other of said band end portions, said central strip part projecting through the space between said pair of laterally spaced strip parts. 
     
     
       3. An electromagneto-mechanical actuator according to claim 2 wherein the transverse area of said central strip part is substantially equal to the sum of the transverse areas of said pair of laterally spaced strip parts. 
     
     
       4. An electromagneto-mechanical actuator according to claim 2 wherein said band intermediate loop portion and said band end portions are an integral element of substantially uniform thickness throughout its length and .[.each.]. .Iadd.the sum of the widths .Iaddend.of said laterally spaced strip parts .[.has.]. .Iadd.is .Iaddend.substantially .[.the same transverse.]. .Iadd.equal to the .Iaddend.width .[.as.]. .Iadd.of .Iaddend.said central strip part. 
     
     
       5. An electromagneto-mechanical actuator according to claim 2 which further comprises band securing means cooperating with said web part for securing said band to said drum member against relative circumferential movement, and band tensioning means cooperating with said web part for tensioning said band. 
     
     
       6. An electromagneto-mechanical actuator according to claim 5 wherein said drum member has a generally radial recess, said web part has a hole therethrough, and said band securing means comprises a stake extending through said hole and received in said recess. 
     
     
       7. An electromagneto-mechanical actuator according to claim 6 wherein said drum member has a groove recessed from said surface and said stake recess is at the base of said groove and internally threaded, said hand tensioning means comprises a block having an inner end face and an outer end face and a through hole extending between said end faces and projecting at least partially into said groove and arranged with said inner end face spaced from said base, said through hole being aligned with said hole in said web part, and said stake being a screw having a shank extending through said holes and threadedly engaged in said threaded recess and also having a head bearing against said outer end face, said web part extending along the walls of said groove and over said inner end face, whereby turning said screw adjusts the tension in said band. 
     
     
       8. An electromagneto-mechanical actuator according to claim 2 wherein said central and laterally spaced strip parts collectively wrap around said surface of said drum member circumferentially through only a single revolution whereby the remote unwrapped terminal portions of said parts leave said surface tangentially at substantially the same point. 
     
     
       9. An electromagneto-mechanical actuator according to claim 8 wherein said yoke member has a flat surface, said terminal portions are flat and substantially coplanar and lie against said flat surface. 
     
     
       10. An electromagneto-mechanical actuator according to claim 1 wherein said rotor includes a shaft and a permanent magnet mounted thereon for rotation therewith and having a first pole end face of one polarity and a second pole end face of the opposite polarity at a different circumferential location from said first pole end face, said stator including a first coil and a second coil, said first coil having an arcuate extent greater than the circumferential width of said first pole end face and spaced therefrom to provide therebetween a first constant air gap throughout an excursive range of circumferential movement of said first pole end face relative to said first coil, and said second coil having an arcuate extent greater than the circumferential width of said second pole end face and spaced therefrom to provide therebetween a second constant air gap throughout an excursive range of circumferential movement of said second pole end face relative to said second coil. 
     
     
       11. An electromagneto-mechanical actuator according to claim 10 wherein said stator includes a ring, said first and second coils are wound on different arcuate portions of said ring, and further comprises means for limiting the pivotal movement of said rotor about said axis to provide said excursive ranges. 
     
     
       12. An electromagneto-mechanical actuator according to claim 11 which further comprises a housing, and means securing said stator ring to said housing, said shaft being journaled at opposite ends on said housing and including a first section provided with an opening and a second section which provides said drum member, said magnet being a straight bar extending diametrically through said opening and being secured to said shaft. 
     
     
       13. An electromagneto-mechanical actuator according to claim 12 wherein said means for limiting the pivotal movement of said rotor comprises a pair of circumferentially spaced generally radially extending stop surfaces on said shaft and a pair of stop pins supported by said housing and severally arranged to abuttingly engage said stop surfaces. 
     
     
       14. An electromagneto-mechanical actuator according to claim 13 wherein said shaft includes a third section having a generally radial recess, a stop post mounted in said recess and having an exposed outer head part which provides said stop surfaces, and said stop pins being screws mounted on said housing for adjustment relative to said stop surfaces. 
     
     
       15. An electromagneto-mechanical actuator according to claim 12 wherein said output drive element is a rod rigidly connected to said yoke member and is guided on said housing to project therefrom.