Abstract:
A two-position rotary actuator provides a latching or holding torque which can be adjusted by altering the magnetic properties of a selected pole member. The actuator also functions as a sector motor over a selected range of angular motion and provides failsafe operation which returns the actuator to a starting position when electrical power is removed.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to the field of actuators and more particularly to a rotary actuator in which a holding, or latching torque and return torque, may be set or varied. 
   BACKGROUND OF THE INVENTION 
   The prior art relating to electrically operated rotary actuators includes U.S. Pat. No. 6,518,685 for a Multi-Position Actuator or Sector Motor. Such an apparatus is essentially a three position actuator which includes three electromagnetic poles. An air gap of one or more of the electromagnetic poles is made different from an air gap of the remaining pole or poles in order to adjust operating characteristics of the actuator. The gap can be set for operation as a limited range actuator or as a continuous rotating device. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a two position rotary actuator in which the latching torque can be varied easily. 
   ANOTHER OBJECT of the present invention is to provide a bi-directional rotary actuator whose return torque to an initial position, when electrical power is removed, may be varied. 
   YET ANOTHER OBJECT of the present invention is to provide a rotary actuator which comprises a relatively small number of component parts resulting in reliable long term operation. 
   The foregoing objects and advantages of the invention will appear more clearly hereinafter. 
   In accordance with the present invention there is provided a two-position rotary actuator which includes three poles and which has a latching or holding torque which can be adjusted by altering magnetic properties of a selected one of the three poles. 
   The actuator also functions as a sector-motor over a selected range of angular motion. Failsafe operation is provided whereby the actuator returns to a starting position when electrical power is removed and return torque of the actuator may be adjusted by altering magnetic properties of a selected one of the three poles. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other important objects and advantages of the present invention will be apparent from the following detailed description of the invention taken in connection with the accompanying drawings in which: 
       FIG. 1  is a schematic view of a rotary actuator according to the present invention; 
       FIG. 2  is a plot of a graph showing a range of latching torque plotted against rotational position of the actuator; 
       FIG. 3  is a schematic view showing variation of air gap of one of the poles; 
       FIG. 4  is a schematic view of an actuator according to the invention in which the shape of the pole is varied; 
       FIG. 5  shows an actuator according to the invention which incorporates a screw adjustment; 
       FIG. 6  shows an actuator according to the invention which incorporates a permanent magnetic; 
       FIG. 7  shows an actuator whose armature is spaced close to a housing wall to provide added winding capability along with latching torque; 
       FIG. 8  shows a failsafe actuator with limited range; 
       FIG. 8A  is a plot of a graph showing the limited range of return torque of the actuator against rotational position of the failsafe actuator; 
       FIG. 9  shows a failsafe actuator with extended range which includes an angularly offset magnetic pole; and 
       FIG. 9A  is a plot of the extended range return torque for the unit in  FIG. 9 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to the drawings there is shown in  FIG. 1 , a rotary actuator  10  made in accordance with the present invention which includes a pair of poles  12 ,  14  positioned around a permanent magnet radially magnetized with north and south pole armature  16 . Surrounding the poles  12 ,  14  and the armature  16  is a housing  18 . The housing  18  preferably is made of soft iron. Poles  12 ,  14  are made of a magnetic material such as soft iron. The rotary actuator also includes a third pole  20 . The three poles  12 ,  14  and  20  generally are equally spaced within the housing  18 . The permanent magnet usually is neodymium, alnico or a similar material. 
   The rotary actuator  10  includes a pair of stops  22 ,  24  which, as shown in  FIG. 1 , are positioned typically at minus forty-five degrees (−45°) and plus forty-five degrees (+45°) from a zero degree (0°) position. As is shown in  FIG. 1 , the zero degree (0°) position is defined by the position of the third pole  20 . The stops  22 ,  24  engage a stop arm  26  which projects from the armature  16  and which limits motion of the armature  16 . The armature  16  is mounted on a bearing  17  for rotation relative to the housing  18 . The armature  16  includes a permanent magnet with radial north and south poles that interact with the stationary poles to produce rotation. 
   An air gap  28  provided for the pole  20 , is different from air gaps  30 ,  32  provided for the poles  12 ,  14 . And the air gap difference results in a difference in magnetic behavior of the pole  20  relative to the magnetic behavior of the poles  12 ,  14 . The difference in magnetic behavior results in a latching torque during a de-energized state of the rotary actuator  10  as is shown in  FIG. 2  to stops  24  and  26 . The air gap  28  as shown in  FIG. 1  is larger than the air gaps  30 ,  32 . Alternatively, the air gap  28  may be made smaller than the air gaps  30 ,  32 , resulting in a latching torque to the zero (0°) position.  FIG. 2  shows a range of latching torque determined by the differences in magnetic behavior between pole  20  and poles  12  and  14 . For gap  28  larger than gaps  30  or  32 . 
   When the stop arm  26  contacts each of the stops  22 ,  24  there is a holding or latching torque present whose magnitude depends on difference in the magnetic behavior of the pole  20  relative to the poles  12  and  14 . If each of the poles  12 ,  14 ,  20  had exactly equal magnetic behavior with equal air gaps  28 ,  30 ,  32  there would be zero latching torque. A maximum latching torque is obtained when the gap  28  is a maximum or when pole  20  of  FIG. 1  is omitted. The omission of the pole  20  results in a non-symmetrical configuration of the poles  12 ,  14  relative to the armature  16 . 
   The latching torque may also be altered by altering shape of pole  34 , as is shown in  FIG. 4 , and/or by altering material of the pole or mounting a permanent magnet  36  to the pole  38 , as is shown in  FIG. 6 . 
   Applying electrical power to the coils  40 ,  42  on the poles  12 ,  14  produces a useful sector motor, by overcoming the latching or holding torque and driving the armature  16 , which may be connected to a load, through a range established by the stops  22 ,  24 . 
     FIG. 3  shows a pole  44  which has a relatively large air gap  46  or space between the end  48  of the pole  44  and the armature  16 . This air gap may be varied from the relatively large gap  46  as is shown to a relatively narrow gap  50  which is indicated schematically by the broken lines  52  in  FIG. 3  thereby increasing the latching torque or decreasing the hold torque accordingly. 
     FIG. 4  shows a pole  34 , according to the present invention, which has a cross-sectional area which increases from a relatively narrow portion relatively close the air gap  56 ) to a relatively wide portion  58  disposed relatively close to the housing  18 . 
     FIG. 5  shows a threaded pole member  60  which is made of a ferromagnetic material. The pole member  60  is threadably received in the housing  18  and rotation of the pole member  60  relative to the housing as shown by arrows  63 ,  65  and facilitates adjustment of the air gap  62  between the end  64  of the pole member  60  and the armature  16 . 
     FIG. 6  shows a pole member  38  which incorporates a permanent magnet  36  which is mounted on an end  66  of the pole member  38 . The pole member  38  may be made of a ferromagnetic material. 
     FIGS. 3–6  thus illustrate various pole member configurations of the present invention which provide a range of magnetic properties that differ from each other and also differ from the pole members  12  and  14 . 
     FIG. 7  shows spacing the armature assembly  68  close to the housing wall  70  to inherently produce a suitable gap  72 , different than gap  74  or  76  and to provide an increased winding capability on poles  78 ,  80  to provide more ampere turns which will increase the drive torque. 
     FIG. 8  illustrates the failsafe operation of the actuator  82 . When powered, the actuator  82  drives the stop arm  84  to the stop  86 . Removing the power returns the stop arm  84  to the stop  88 . The actuator  82  thus provides a failsafe mode.  FIG. 8A  also illustrates the useful range of the actuator which extends between the vertical marks  90 ,  92 , This range extends from approximately 10° to approximately 85°. As shown in  FIG. 8A , in broken lines the return or the latching torque may be changed by altering the magnetic properties of pole  94 . As is shown in  FIG. 9  the useful range of the actuator  86  may be extended 90° and beyond 90° by incorporating the pole  98  which is similar to the pole  28  shown in  FIG. 6 . The pole  98  is angularly offset to react against the armature magnet  100 . The return torque may be varied by altering the gap  102  by adjusting the position of the magnet  104  by rotating the adjustment screw  106 . The variation in return torque is illustrated by the variation illustrated by the solid line  108  and the broken line  110  in  FIG. 9A . The actuator  96  includes the stop arm  112  and the stops  114  and  116 . 
   The foregoing specific embodiments of the present invention as set forth in the specification herein are for illustrative purposes only. Various deviations and modifications may be made within the spirit and scope of this invention without departing from a main theme of invention delineated more specifically in claims that follow herein.