A slip ring is an electromechanical device that allows the transmission of power and
electrical signals from a stationary to a rotating structure. A slip ring can be used
in any electromechanical system that requires unrestrained, intermittent or continuous rotation
while transmitting power and / or data. It can improve mechanical performance, simplify
system operation and eliminate damage-prone wires dangling from movable joints.
Also called rotary electrical interfaces, rotating electrical connectors, collectors,
swivels, or electrical rotary joints, these rings are commonly found in slip ring motors,
electrical generators for alternating current systems and alternators and in packaging machinery,
cable reels, and wind turbines. They can be used on any rotating object to transfer power,
control circuits, or analog or digital signals including data such as those found on aerodrome
beacons, rotating tanks, power shovels, radio telescopes or heliostats.
A slip ring is a method of making an electrical connection through a rotating assembly. Formally,
it is an electric transmission device that allows energy flow between two electrical
rotating parts, such as in a motor.
Composition A slip ring is an electrical connector designed
to carry current or signals from a stationary wire into a rotating device. Typically, it
consists of a stationary graphite or metal contact which rubs on the outside diameter
of a rotating metal ring. As the metal ring turns, the electrical current or signal is
conducted through the stationary brush to the metal ring making the connection. Additional
ring/brush assemblies are stacked along the rotating axis if more than one electrical
circuit is needed. Either the brushes or the rings are stationary and the other component
rotates. This simple design has been used for decades as a rudimentary method of passing
current into a rotating device. Alternate names and uses
Some other names used for slip ring are collector ring, rotary electrical contact and electrical
slip ring. Some people also use the term commutator, however commutators are somewhat different
and are specialized for use on DC motors and generators. While commutators are segmented,
slip rings are continuous, and the terms are not interchangeable. Rotary transformers are
often used instead of slip rings in high speed or low friction environments.
A slip ring can be used within a rotary union to function concurrently with the device,
commonly referred to as a rotary joint. Slip rings do the same for electrical power and
signal that rotary unions do for fluid media. They are often integrated into rotary unions
to send power and data to and from rotating machinery in conjunction with the media that
the rotary union provides. Mercury-wetted slip rings, noted for their
low resistance and stable connection use a different principle which replaces the sliding
brush contact with a pool of liquid metal molecularly bonded to the contacts. During
rotation the liquid metal maintains the electrical connection between the stationary and rotating
contacts. However, the use of mercury poses safety concerns, as it is a toxic substance.
If a slip ring application involves food manufacturing or processing, pharmaceutical equipment, or
any other use where contamination could be a serious threat, the choice should be precious
metal contacts. Leakage of the mercury and the resultant contamination could be extremely
serious. The slip ring device is also limited by temperature, as mercury solidifies at approximately
-40 °C. A pancake slip ring has the conductors arranged
on a flat disc as concentric rings centered on the rotating shaft. This configuration
has greater weight and volume for the same circuits, greater capacitance and crosstalk,
greater brush wear and more readily collects wear debris on its vertical axis. However,
a pancake offers reduced axial length for the number of circuits, and so may be appropriate
in some applications. Slip rings are made in various sizes; one
device made for theatrical stage lighting had 100 conductors. The slip ring allows for
unlimited rotations of the connected object, whereas a slack cable can only be twisted
a few times before it will fail. References
External links Video depicting the interior of a slip ring
in motion