Many of the
more than 5,000 Moog Components Group slip ring designs are available
for use in their existing configuration, or they may be modified
to meet your specific requirements. New designs can also be created
to meet the most demanding specification. Our engineers are experienced
in a wide range of slip ring applications. We utilize resources
such as the Anvil computer-aided design (CAD) system. And, a very
active in-house quality circle program solicits the best inputs
from all of our many skilled craftspeople, from start to finish.
This section is designed to guide you through the process of specifying
a slip ring. We've outlined below the major considerations that
a slip ring engineer will need to know about your application.
Basic
Slip Ring Design
Throughout
this section you will see the terms 'slip ring capsule' and
'slip ring separates'. The term 'separate' indicates an individual
rotor/brush block combination. The term 'capsule' is used to
denote a
self contained unit consisting of a rotor, stator and
its own integral ball bearings. There are two basic slip ring
configurations to consider based on space allocation in your
system: the more common drum approach where each ring is adjacent
to the next along the centerline, somewhat like the threads
on a bolt, and the pancake approach where the rings are concentric
with one another like the groves on a phonograph record. The
pancake approach is used when length is at a premium but diameter
is less restrictive.
Defining
the Mechanical Envelope
The
envelope is, of course, largely dictated by the space available
in the system. The slip ring engineer should be given the maximum
space available in the system so all existing candidate designs
can be considered. It is imperative that the space required
for the slip ring be specified in the early stages of the system
design and that it be consistent with the structural and electrical
demands.
Defining
System Interface Requirements
The
slip ring engineer will need to know these system interface
considerations:
-
Is a
bore required through the slip ring for routing coolant plumbing,
hydraulic lines, pneumatic lines, waveguides, etc? In such
applications, the slip ring actually mounts concentric with
these lines in the system.
-
How will
the slip ring attach to the system? It is never advisable
to hard mount both the rotor and the stator to the system
since the slip ring bearings may overload if there is any
misalignment between them and the system bearings.
-
How should
the electrical connections to the slip ring be made? Is it
desirable to have connectors integral with the slip ring on
both the rotor and stator, or would flying leads on one or
the other ends be desirable? And if flying leads are preferred,
should they exit the rotor in a radial or axial direction,
and what length should the leads be?
Defining
Electrical Requirements
The
current specified enables the slip ring engineer to propose
a unit with the appropriate cross-sectional area of the rings,
brushes and lead wires. The specified voltage dictates the spacing
between adjacent rings and brushes. It is helpful in achieving
the most cost effective and smallest practical envelope not
to rate all circuits at the maximum level. For example, if you
need 20 circuits total, three of which must carry ten amps,
designate three for high current. Don't go for 100% functional
interchangeability by specifying that all 20 be able to carry
ten amps. And, if the ten amps is a surge current with a continuous
current of only two amps, tell us that, too. There is no reason
for you to pay for ten amps continuous capacity when you only
need two. Be aware that voltage surges and spikes are the major
cause of system slip ring failures. Poly-Scientific uses a very
conservative approach to circuit design, however, it is not
uncommon in some power supply systems to see voltage spikes
ten or more times the normal operating voltage. We strongly
recommend surge protection on all power supplies. Most smaller
slip rings will satisfactorily conduct signals to 1 MHz or 500
Kilobits. Special slip rings can be used to pass broadband signals
from dc to 1 gigahertz and data rates of 500 megabits or even
higher. Cross-talk, insertion loss and bit error rate information
can be provided if data rates, formats and impedance's are defined.
Defining
Mechanical Requirements
-
Operating
speeds (rpm's). Almost any slip ring can operate successfully
at speeds to 100 RPM although many applications only require
operation at a few rpm. But slip rings are also routinely
used to instrument jet turbine engines operating at speeds
in excess of 20,000 RPM. The operating speed in conjunction
with the diameter dictates the surface speed of the brush
relative to the ring and hence the internal design approach
and material selection.
-
What
rotational life is necessary for your application? Will the
unit oscillate or rotate at a continuous speed?
Defining
the Environment
The
environment in which the slip ring must survive is a key factor.
Operating temperature is important in specifying the proper
lubricant. And if the slip ring will operate exposed to the
elements or to a hostile environment, integral seals must be
included in the design. Any unusual shock or vibration should
also be specified.
Many
of the slip ring designs and manufacturing processes described
are proprietary and are covered under one or more U.S., European
or Japanese patents. The information provided is intended to
assist the system engineer in initial discussions and is not
intended as a specification.
