Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2001-01-04
2003-03-11
Freay, Charles G. (Department: 3746)
Metal working
Method of mechanical manufacture
Electrical device making
C029S598000, C029S596000, C029S732000, C029S736000
Reexamination Certificate
active
06530142
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to laminated parts for use in electric motors and generators. More particularly, the present invention relates to electric motor or generator stators and rotors having stacked laminae and the methods and machines, i.e., progressive dies and controllers therefor, used in the manufacture of such laminated parts.
The manufacture of stators and rotors employing stacked laminae is well known in the art. Typically, the laminae are blanked from continuous strip stock and then stacked and bound together to form the stator or rotor. Progressive die assemblies for producing stator or rotor laminations wherein a strip of lamination material is fed through a sequence of punching steps to progressively form the laminae are also well known.
Rotor laminae generally include a plurality of skewed conductor slots which are formed around the periphery of the rotor stack in arcuately spaced relation to one another by rotationally indexing the laminae with respect to the rotor stack axis. Indexing involves rotating the rotor stack and the last produced lamina relative to each other by a predetermined rotational increment so that, when the laminae are combined in a stack, the rotor conductor bar slots defined by adjacent conductor slots are skewed or slanted relative to the stack axis. Stator stacks, on the other hand, include winding slots around the inner periphery of the stack which extend parallel to the stack axis, without skew, and are shaped to receive the stator windings. Although relatively rare, inside-out motors are often used in fan motor designs and utilize inner cores manufactured with straight slots to be used with outer cores having skewed slots, in which case it would be the outer core laminations which are rotated relative to each other to produce the skew angle.
In addition to producing a skew angle, as discussed above, the relative rotation of a lamina and the lamina stack onto which the lamina will be placed can be used to overcome the negative effects created by thickness inconsistencies in the strip stock from which the laminae are blanked. The strip stock used to manufacture lamina stacks may have thickness inconsistencies wherein one side of the strip stock is thicker than the other side. If laminae punched from the strip stock are stacked without rotation, the lamination stack produced will not have a uniform height around its entire perimeter because the stacking of the individual laminae will additively compound the thickness inconsistencies present in the strip stock on one side of the stack. A stack having a substantially uniform height can be produced, however, by rotating individual laminae relative to the lamina stack to equally distribute the thickness inconsistencies about the stack axis. The inconsistencies thereby cancel each other out in a known process often referred to as gamma correction.
In response to these problems, an autorotation system to compensate for nonuniform stock thickness was developed which both rotates and interlocks the stacked laminae. This system compensates for variations in lamina thickness while properly skewing the conductor slots of rotor laminae, as described in U.S. Pat. Nos. 4,619,028; 4,738,020; 5,087,849 and 5,123,155, all assigned to the assignee of the present invention and the disclosures of which are expressly incorporated herein by reference. In the systems disclosed in the aforementioned patents, the choke barrel holding the lamination stack is automatically rotated before each lamina is blanked from the strip stock and the lamina's circumferentially disposed tabs are interlocked with the slots of the uppermost lamina of the incomplete lamination stack within the barrel.
In the apparatus and method disclosed in the aforementioned patents, the individual laminae are typically rotated through an angle which is the sum of 180° to provide for gamma correction plus a smaller incremental amount necessary to provide the proper skew angle. Although the laminae may be rotated through other angles, the angle, without including the incremental rotation necessary to produce the skew angle, must be at least 360°/(number of interlock tabs) to permit the use of interlocking tabs and slots.
The use of an AC or DC servomotor and a controller allows the operator of the die assembly to rapidly and easily alter the rotational amounts to produce different skew angles or to alter the angle through which the laminae are rotated to correct for thickness inconsistencies. The controller computes a single angle through which the choke barrel must be rotated to provide for both gamma correction and a proper skew angle. The use of a servometor to rotate a choke barrel for such purposes, however, places a limit on the number of strokes per minute of the die assembly because it requires the use of a relatively large, and relatively slow, servo drive unit which has the capacity to handle the inertial loads involved in rotating the choke barrel through such large angles between each stroke of the die assembly as well as to be sufficiently accurate. Typical achievable rates are 275 to 300 strokes/minute. Notably, the life of the servomotor in such a system is not particularly long; in addition to providing the desired skew angle, the motor must also provide the necessary gamma correction. A faster indexing system, which also extends servomotor life, is desirable.
Mechanical indexers which utilize a camming assembly such as a roller cam to provide indexed rotational movements to rotate the choke barrel are also known and may be used to provide for gamma correction while allowing the die assembly to operate at significantly higher rates, e.g., in the range of 400 to 500 strokes/minute, than a comparable servo drive assembly. Indexers of the type used for rotating choke barrels in stamping die apparatuses are manufactured by the Ferguson Company, 11820 Lackland Road, St. Louis, Mo. 67146. Mechanical indexers used for gamma correction lack the flexibility of servo drive systems, however, since the angle at which they rotate the choke barrel cannot be easily adjusted.
A mechanical system has also been developed to provide for the incremental indexing of laminae to provide a proper skew angle and U.S. Pat. No. 3,203,077 provides one example. Although such a mechanical system provides for some adjustment of the amount of rotational indexing necessary for a skew angle, the adjustment of mechanical indexing systems is not as flexible or convenient as the adjustment of a servo drive motor which is regulated by a controller.
A system which utilizes a modified roller cam assembly to provide a mechanical indexer in conjunction with a system for providing an incremental rotational movement for producing a skew angle is disclosed by U.S. Pat. No. 5,163,217. The disclosed system, however, cannot employ a standard “off the shelf” roller cam assembly thereby increasing the cost of the system. The disclosed system also employs a plurality of small rollers which are in frictional contact between an input roller and an output disk. The use of such frictionally engaged surfaces to transmit rotational movements is more subject to slippage than an arrangement involving the transfer of rotational movement by positively locking gear teeth.
A system which utilizes a differential device having an output shaft which is coupled to the rotary choke barrel of a die stamping apparatus, an input shaft which is driven by a mechanical indexer to impart gamma correction with each press cycle, and a housing or casing incrementally rotated by a servomotor to impart a fixed amount of skew angle with each press cycle, is disclosed in U.S. Pat. No. 4,615,207. The differential device thus serves as a phase adjuster which combines the gamma correction and the skew angle. A rotary cam switch is attached to the press crank and, with each cycle of the press, provides a timing signal to a control circuit which actuates the servomotor, causing it to rotate through a small, fixed angle. The output shaft of the servomotor is provided
Baker & Daniels
Freay Charles G.
L. H. Carbide Corporation
Sayoc Emmanuel
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