Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-02-08
2002-03-12
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
Reexamination Certificate
active
06356002
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to electrical slip rings, and more particularly, to an electrical slip ring having a higher circuit density than prior art. Advantageously, the present invention is directed to flat composite electrical slip ring in which the electrical rings are spaced in close proximity to each other.
BACKGROUND OF THE INVENTION
Electrical slip rings are well known devices for communicating electrical signals from one structural member to another where one of the structural members is rotatable with respect to the other. Such a slip ring apparatus, for example, may comprise a relatively stationary annular base member, which has a plurality of conductive rings extending annularly there around. One or more electrically conductive brushes are arranged on a relatively rotatable structural member to rotate about the stationary annular base member and each of the brushes is arranged to contact a surface of one of the conductive rings thereby forming a series of electrical connections between the two structural members.
A flat or “pancake” slip ring is such a device of minimal height or thickness for military or commercial environments where space for the slip ring is very limited. The conductive rings forming the slip ring base generally are formed from materials having a thickness from 0.003 to 0.040 inches with most such materials having a thickness in the range of 0.006 to 0.016 inches. Characteristically, the rings for such a slip ring base are approximately 0.015 to 0.020 inches in width. Spaces between the rings or the ring pitch are characteristically approximately of the same dimension.
A grooved plate process is the most common method of manufacturing pancake slip rings. In the grooved plate process, a grooved plate is prepared by rough machining a brass plate to approximately a “grooved plate” shape. The grooved plate is then annealed to minimize distortion during subsequent plastic curing and final machining. One side of the grooved plate is then machined to final “grooved plate” shape. Peaks correspond to the bottom of the future rings, and valleys correspond to the future insulation barriers between rings. The “grooved plate” is then plated with nickel and a gold strike. A lead wire is soldered or welded to individual ring features on the grooved plate. A glass cloth is then bonded to the plate to prevent leads from entering the valleys of the plate (the future barriers between rings). The plate and lead assembly is then loaded into a metal mold which contains features to provide for internal lead routing, lead exist positioning, and other rotor geometry requirements. The mold is vacuum cast with a liquid epoxy to completely fill the internal detail of the mold. At this point, the assembly is a single piece with a continuous plate on one or two sides with internal epoxy insulation. The final machining step turns the exposed surface of the plate to separate the plate into individual concentric rings separated from each other with epoxy (filling the former valleys in the plate). After the rings are separated, insulating barriers between the rings are machined to final dimensions. In addition, at this step the ring surface is machined to final dimension. The ring groove pattern may be V, U or double-V shaped. In addition to ring shape, the rings are machined to the required surface roughness. The rotor is then nickel plated and then plated with precious metal (usually gold or silver). This process is complex and the density of slip rings is limited by the machining requirements.
An electroformed rings process is another known process. A rotor and lead assembly is prepared by loading lead wire into a mold which contains features to provide for internal lead routing, lead exit positioning, and other rotor geometry requirements. The mold is cast with a liquid epoxy to completely fill the internal detail of the mold and encapsulate the lead wires. Grooves are machined which will contain the rings. Starter rings are prepared as follows. At the bottom of the ring groove, the lead wire conductor is exposed and prepared (generally by applying a fillet of conductive epoxy). The inside walls of the ring groove are coated with conductive plastic to form a continuous conductive starter ring for plating. The ring is electroformed by plating copper onto the starter ring using high build plating technology. High build plating technology or high buildup electroforming is a method of creating a thicker ring cross-section by plating up the starter ring, usually in a copper bath. The starter rings may be plated up with or without dielectric barriers between the rings. At this point, the assembly is a single piece with discrete rings and leads embedded in epoxy insulation. The final machining step will form final shape and texture of the rings and insulating barriers between the rings. The final rotor is nickel plated and then plated with precious metal (usually gold or silver). The disadvantages of the electroformed rings process include limited ring thickness buildup unless barriers are present. Extensive machining is required to create dielectric barriers which allow a buildup of thicker rings. Due to the lengthy times required to electroform the rings, plating solution can damage the slip ring materials, leak into loads embedded in the dielectric causing lead damage and electrical insulation failures. Dielectric materials can interfere with the electroforming process. Ring sides cannot be sealed with nickel allowing corrosion products to form and contaminate the electrical contacts. The contaminants will lead to contact failure and electrical shorts. This is the most significant drawbacks of conventional electroformed rings.
More recent requirements using an electrical slip ring assembly in a Forward Looking Infrared Radar (FLIR) platform have severe space requirements than can be accommodated by either of the grooved plate process or the electroformed rings process. The FLIR systems are used for surveillance, reconnaissance, rangefinder, targeting, and fire control applications. These FLIR platforms all impose severe requirements on the electrical slip ring, including a high circuit density in which many circuits are required and space for the slip ring is always limited. Another requirement is for high bandwidth and low noise for the digitized video signals that pass through the electrical slip ring assembly. Yet another requirement is for low temperature operations in which the electrical slip ring assembly can function over the temperature range of −54° C. to +60° C.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a flat composite electrical slip ring having a higher circuit density than prior art slip rings.
It is another object of the present invention to provide an electrical slip ring apparatus in which the electrical slip rings are not mechanically machined.
It is yet a further object of the present invention to provide an electrical slip ring which is reliable on the operation, easy to manufacture and cost effective.
These and other objects of the present invention are achieved using three related processes. These processes include double-sided printed circuit board technology, copper electroforming, and chemical machining. Using the present invention, double-sided copper clad glass reinforced epoxy laminate (FR
4
) is coated with a photosensitive polymer that is imaged using a photographic negative. Following exposure with an intense ultraviolet light source, the photosensitive polymer is then developed with solvent that selectively dissolves away unexposed areas of the resist. When the resist is removed, copper is exposed for subsequent etching.
The photo imaged material is then placed in a copper etchant that removes the exposed copper. Areas protected by the photoresist are unetched and form the interconnecting electrical passages on one side. Holes are subsequently drilled through the etched material to electrically connect the two sides. The connections are formed utilizing plated thro
Vaught Larry Dean
Witherspoon Barry Kent
Lowe Hauptman & Gilman & Berner LLP
Northrop Grumman Corporation
Perez Guillermo
Ramirez Nestor
LandOfFree
Electrical slip ring having a higher circuit density does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrical slip ring having a higher circuit density, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrical slip ring having a higher circuit density will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2872159