A
case conditions, components in the slip
ring don’t overheat and the case temperature does not pose a burn risk, the
slip ring design can be acceptable.
For data, all sliding contacts generate
some electrical resistance variation as
they rotate. The degree of variation
depends on many variables such as
the sliding contact selected, speed,
temperature, and contact force. Effects
of this resistance variation will depend
on the overall circuit of which the slip
ring is a part of. The design of the slip
ring’s sliding contact should consider
the data bandwidth required as well as
the circuit’s tolerance to variations. For
critical applications, experts recommend
using many contacts for each channel
to minimize the resistance variations.
Slip Rings
FREQUENTLY ASKED QUESTIONS
Q: What are slip rings?
A: A slip ring is an electrical connec-
tion designed to pass the flow of current from a stationary device to a rotating one. This electromechanical device
is also known as a rotary electrical connector or rotary electrical joint. Electrical
slip rings are free to rotate without limitations, unlike cables which twist and
eventually break.
Q: Where are they used?
A: Typical applications include revolv-
ing automation or control systems such
as turntables, index tables, and robots.
Wind turbines, semiconductor processing, printing plastic molding, CT and
MRI medical scanners, satellite communications, beverage processing, and industrial washers are also common slip
ring applications.
Q: How do they work?
A: Electrical slip rings work by holding
a sliding contact (brush) against a ring
(conductor ring). One part, typically the
brush, is stationary while the other, typically the conductor ring, rotates. Leadwires to the brush and conductor ring
terminate internally and provide electrical connections to devices on either side
of the slip ring.
In general, conductor rings are mounted on the rotor and terminated with
leadwires that run axially through the
rotor to one end. Brushes are secured
by a brush holder that is mounted to
the housing. A set of ball bearings
inside the housing supports the rotor. A
cover and endcaps enclose the device.
Structural components like the housing, rotor, cover, and endcaps are made
of metallic and non-metallic materials
selected based on application requireSponsored by Deublin
ments such as temperature, weight,
size, ruggedness, and cost.
Electrical components — the brush,
conductor ring, and electrical connectors — are made of highly conductive
materials. They’re selected based on
requirements such as current density,
voltage drop, rotational speed, temperature, resistance variation, bandwidth,
and characteristic impedance.
Q: So are there different types of
slip rings?
A: Yes. The underlying design that governs sliding contact between brushes and conductor rings is the most critical aspect of an electrical slip ring. The
specific requirement for each application dictates the most-appropriate sliding contact technology.
Power is generally transmitted through
composite brushes of a carbon-graphite
base and may have other metals such
as copper or silver to increase current
density. These are similar to composite
brushes typically used in motors.
Data communication, signals, and
other sensitive voltages, on the other
hand, are generally transmitted through
precious-metal wire brushes contacting a precious-metal conductor ring
surface. For specific cases that require
high bandwidth and extreme reliability
of the data, multiple contacts (such as
Deublin’s Poly-filament brushes) provide
dependable data transmission.
Hybrid slip rings handle both power
and data transmission. In these cases,
good RF design techniques ensure electromagnetic interference (EMI) does not
compromise data integrity. Engineers
must separate power and data channels
and ensure proper shielding of the slip
ring as well as adjacent cabling.
Q: Are there other design
Pneumatic connections can also be
integrated with the electrical hardware
into a single package when space is
limited.
Q: What are typical sizes?
A: Slip rings can typically range in size
from under one inch to several feet in
diameter. In general, the goal is to minimize the size of the conductor rings.
This reduces the equivalent linear distance traveled for each revolution and
minimizes wear of the sliding contacts. This extends the life compared
to designs with a larger conductor ring.
However, larger sizes often permit media like fluids to pass through the center
via hose or tubing. Slip rings can mount
with a flange, threaded rotor, or slip fit
over a shaft or into a shaft cavity. Electrical connection options include leadwires, electrical connectors, and terminal blocks.
Q: Are there limits to power and
data transmission?
A: For power, there are many tradeoffs
to consider. It is generally not so much
the power being used at the load that
affects a slip ring’s ability to meet the requirement, but rather the voltage drop
across the slip ring along with the actual current flow. Voltage drop affects the
actual voltage available at the load as
well as the total power being dissipated
in the slip ring. Dissipated power converts to heat and will affect the unit’s
operating temperature. If, under worst-
concerns?
A: EMI should always be a concern
when designs include a slip ring. Even
dc signals have transient voltages when
they are switched on and off. Thus,
good RF design techniques are recommended. Shielding sensitive signals as
much as possible throughout the physical electrical path is always best. Connecting the shields through a sliding
contact from the rotor to the stator is
a must to get good EMI shielding from
the physical braiding. Separation between channels is an important design
consideration as well.
Environmental characteristics are
also important. For example, ingress
protection levels will dictate the sealing
requirements of all components. Shock
and vibration will affect the sliding
contact technology that is used and
the position of the contacts to assure
electrical continuity is maintained under
those conditions.
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Rotating Unions for
Every Application
When you need a rotating union solution for your
application, count on the experts – DEUBLIN.
OEM or maintenance. Custom design or
replacement. DEUBLIN offers both stock
items, or unions engineered to your unique
requirements. And you can count on the cost
savings generated by precision engineering,
and the highest quality components.
For solutions to your numerous applications
call DEUBLIN at 1-847-689-8600.
Q: Are slip rings available in
standard or custom versions?
A: Off-the-shelf slip rings are good for
basic installations, but there are many
unique and critical applications that demand a tailored slip ring designed to
meet performance requirements and
exceed the expected life from the user.
For instance, Deublin develops many
slip rings tailor-made to customers’ demanding applications. Features include
extreme temperature resistance, small
packaging, integrated slip rings and rotary unions, and unique electrical connection methods, as just a few examples. 
Request the new 56-page catalog featuring
hundreds of rotating unions, along with complete
specification and application information.
ONLINE ORDERING AVAILABLE
NOW OFFERING ELECTRICAL SLIP RINGS
Phone: 1-847-689-8600
Email: customerservice@deublin.com
Web: www.deublin.com