Abstract:
A solid core angular position resolver including stator coils and a coil-less rotor, the improvement wherein the rotor comprises a core having a substantially circular cylindrical configuration having on its surface a notch extending substantially helically over part of the surface of the cylindrical configuration.

Description:
The present invention relates to rotary electrical devices such as synchros and angular position transducers of the type known variously as resolvers, rotary inductors, rotary variable differential transducers, angular shaft position encoders, and the like. It particularly concerns such a device employing a solid rotor, i.e., one which has no electrical windings thereon. 
     THE PRIOR ART 
     Using an angular position resolver as an example, such a device has a rotor mounted on a rotatable shaft, which cooperates with a coil-wound stator to provide two sinusoidal voltage read-outs, the voltage magnitude relationship and phase relationship of which indicate the instantaneous angular position of the shaft over a range from 0 to 360 degrees of rotation. Coil-wound rotors (see e.g. Logue U.S. Pat. No. 5,404,101 and Chass U.S. Pat. No. 4,445,103) have been used in such devices, but they are difficult and expensive to manufacture, and often unreliable in use because the coils may develop electrical faults. 
     To overcome these problems, the art has developed a number of angular position resolvers with solid rotors, thus entirely eliminating the troublesome rotor windings. See Toida U.S. Pat. No. 4,255,682; Wyss U.S. Pat. No. 6,020,737; Huard U.S. Pat. No. 5,763,976; and Ishizaki U.S. Pat. No. 5,446,966. See also Carlen U.S. Pat. No. 5,160,886, and the prior art cited therein, for solid rotors which incorporate permanent magnets instead of windings. While these rotors achieve a degree of electrical simplification, a glance at the above-cited patents shows that they come in a variety of complex mechanical configurations, which can be costly to manufacture. 
     Accordingly, it is the principal object of this invention to provide a solid core rotor for a rotary electrical device which is simpler in its mechanical configuration and therefore more reliable in operation as well as less expensive to manufacture. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention contemplates a rotary electrical device which employs a plurality of stator coils and a coil-less (i.e. solid) rotor within the stator coils comprising a ferromagnetic core having a substantially circular cylindrical configuration. The cylindrical configuration has on its surface a notch extending substantially helically thereabout for a selected circumferential distance. The notch enables the otherwise cylindrical configuration to induce respective voltages in the stator coils, the voltage magnitude relationship and phase relationship of which indicate the angular position of the rotor. 
     In a preferred embodiment, the axial length of the notch is equal to the axial length of the electromagnetic stator core, and the circumferential width of the notch from edge to edge is substantially 180 degrees. In some embodiments the circumferential extent of each individual edge of the notch over the axial length of the cylindrical configuration is 180 degrees, but it may also be less than that. The core is preferably formed of a stack of individual metal circular discs in facing relationship lying substantially perpendicular to the axis of the cylindrical configuration to form a series of eddy-current-blocking laminations. Each disc preferably has a semicircular gap formed at its outer periphery, and the notch is formed by skewing the semicircular laminations relative to each other at a rotational angle calculated to distribute these gaps helically over the entire core length. Alternatively, the notch could be formed by machining away a helical area of the surface of the cylindrical body. 
     All of the described rotor configurations are mechanically simpler and easier to fabricate than any previously known solid core rotor, and therefore are more economical, while at the same time enjoying the same electrical advantages as other solid core rotors. 
    
    
     THE DRAWINGS 
     The invention thus briefly summarized will now be described in detail in connection with the following drawings: 
     FIG. 1 is an exploded perspective view of the mechanical assembly of a first embodiment of an angular position resolver in accordance with this invention. 
     FIG. 2 is a sectional view of the shaft and rotor of the resolver, taken along the lines  2 — 2  of FIG.  1 . 
     FIG. 3 is a plan view of a single lamination employed in the rotor of FIGS. 1 through 3. 
     FIG. 4 is a perspective view of the shaft and rotor of an alternate embodiment of the angular position resolver of this invention. 
     FIG. 5 is a sectional view of the shaft and rotor of the alternate embodiment, taken along the lines  5 — 5  of FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A resolver typically includes a stator structure  10  comprising two sensor coils  12  and  14  wound onto magnetic iron and enclosed within a hollow cylindrical casing  18 . An electrical cable  20  emerges from the casing  18 . 
     The purpose of the resolver is to sense the angular position of a rotating shaft  26 . Toward that end, a solid (i.e., coil-less) rotor generally designated  28  is made of ferromagnetic metal and staked to the shaft in order to rotate therewith, and the shaft passes through a central opening  30  in the housing  18  and the coils  12  and  14  contained therein. The shaft  26  is located so that the rotor  28  remains within the opening  30 , and also inside the stator coils  12  and  14 , while rotating with the shaft  26 . 
     The mode of operation of a solid core resolver (i.e., one with a coil-less rotor) is understood in the art. A sinusoidal input voltage to the stator coils  12  and  14  interacts magnetically with the material of the rotor  28  to induce sinusoidal output voltages in the coils. The coils are in quadrature, that is, they are physically located 90 degrees apart, so that these output voltages are out of phase with each other. The rotor  28  has a shape which departs from its overall cylindrical configuration, and that causes the voltage magnitude relationship and phase relationship between the output voltages to vary as a function of the angular position of the rotor, which in turn depends on the angular position of the shaft  26 . Thus, the voltage magnitude relationship and phase relationship between the respective output voltages appearing on the stator coils indicate the angular position of the shaft  26 . If desired, this shaft position indication can then be digitally encoded using known analog-to-digital circuitry. 
     In accordance with the present invention, the departure from cylindricity of the shape of the rotor  28  arises from its novel method of construction, which will now be described in detail. 
     Rotor  28  is a body substantially in the shape of a right circular cylinder, and is formed of a stack of individual laminations  28 A, B, C etc. Each individual lamination is made of ferromagnetic material and is in the form of a thin, flat toroidal disc  29  having a central opening  31 , and it is those central openings through which the shaft  26  passes. Each disc has a 180-degree gap  33  formed at its outer periphery, so that half of the disc is a semi-circle  29 A of larger diameter, and the other half is a semi-circle  29 B of smaller diameter. These gaps  33  combine to form a notch having edges  32  and  34 . The individual laminations  28 A, B, C, etc., are stacked in face-to-face relationship and skewed progressively relatively to each other so that the notch formed by all the gaps  33  wraps helically about the rotor core  28  over the entire rotor core length. The confronting faces of the individual laminations  28 A, B, C, etc. are coated with a thin layer of shellac or similar material to limit eddy currents, as is well known in the electrical art. 
     The progressive skewing or relative rotation of the laminations  28  is such as to cause the notch edges  32  and  34  to be substantially parallel to each other, and to wrap substantially helically around the cylindrical body of the rotor  28 , so that the space between those edges  32 ,  34  is in effect a helical notch having a width defined by the distance between the edges  32  and  34 , measured around the circumference of the cylindrical body of the rotor  28 . The length of the helical notch  32 ,  34  in the axial direction of the cylindrical rotor  28  is preferably equal to the entire axial length of the rotor (i.e., from the top of the first lamination  28 A through the bottom of the last lamination  28 C). 
     In the embodiment of FIGS. 1 through 3, the width of the notch between edges  32  and  34  is 180 degrees, measured about the circumference of the cylindrical rotor  28 ; and the rotor  28  is long enough in the axial direction so that the extent to which either edge  32  or  34  wraps circumferentially about the cylindrical rotor  28  over its entire axial length is also 180 degrees. 
     The embodiment of FIGS. 4 and 5 is similar in most respects to that of FIGS. 1 through 3, but the notch dimensions are somewhat different. In this second embodiment, notch edges  132  and  134  respectively are once again formed on a cylindrical rotor designated  128  formed of laminations  128 A, B, C etc., and the rotor is staked to a rotating shaft  126  so as to rotate therewith. The rotor  128  cooperates electrically with the stator  10  in the same way described above. Here again, the width of the helical notch between the edges  132  and  134 , measured circumferentially about the cylindrical rotor, is 180 degrees; and the axial length of the notch is equal to the entire axial length of the rotor  128  from the top of the first lamination  128 A to the bottom of the last lamination  128 B. 
     But in this embodiment, the extent to which any one edge  132  or  134  wraps circumferentially about the rotor over its entire axial length is less than 180 degrees. This variation appears to produce acceptable electrical results, just as the embodiment of FIGS. 1 through 3 does. 
     As an alternative to the skewed lamination technique described above, in either of these two described embodiments the helical notch can be formed by starting with either a solid or a laminated cylindrical body, and then machining away the material which occupies the space where the helical notch is desired. 
     Any of the described embodiments are both simpler and less expensive to manufacture than prior art solid rotors for resolvers and other types of rotary electrical equipment. In addition, the rotor structures disclosed herein are rugged and relatively resistant to malfunctions. 
     The above-described embodiments are merely illustrative, and the scope of protection to which the invention is entitled is defined in the following claims.