Servo Coupling0 pages

www.ruland.com
Oldham coupling: high parallel
misalignment capability
What to look for in a Servo Coupling
Selecting a coupling for a servo application
can be a complex process. It involves many
different performance factors, including:
torque, shaft misalignment, stiffness, rpm,
space requirements, and others, that all
must be satisfied for the coupling to work
properly. Before selecting a coupling, it
is helpful to know the specifics of these
issues for the application for which the
coupling is to be used. Many different
types of servo couplings exist with their
own individual strong and weak points.
This article is designed to introduce end
users to the different types of couplings
available for servo applications. It also
helps the user select the proper coupling
for their application by highlighting the
factors that should be considered in the
decision making process and how they
relate to the different product offerings
available.
Choosing the most appropriate
type of coupling to use in
servo applications can be confusing.
William Hewitson,
Director of Manufacturing
and Engineering with the
Ruland Manufacturing Company
in the US, examines the
pros and cons of the various
technologies. Beam coupling: a good general
purpose choice
Beam Couplings
Beam type couplings are manufactured
from a single piece of material, usually
aluminum, and utilize a system of spiral
cuts to accommodate misalignment and
transmit torque.
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Single beam couplings are an economical
option that are best utilized in lower torque
applications, especially in connections to
encoders and other light instrumentation.
Multiple beam couplings, which usually
consist of 2 or 3 overlapping beams, attack
the problem of low torsional rigidity.
They generally have good performance
characteristics and are an economical
choice. For many applications, beam
couplings are a good place to start.
The single piece design allows the coupling
to transmit torque with zero backlash and
no maintenance required. Two basic
variations on this theme exist: a single
beam style and a multiple beam style. The
single beam style has one long continuous
cut that usually consists of multiple complete
rotations. This results in a coupling that is
very flexible and yields light bearing loads.
It is able to accommodate all types of
misalignment, but works best with angular
misalignment and axial motion. Parallel
misalignment capabilities are reduced
because the single beam is required to bend
in two different directions at the same time,
creating larger stresses in the coupling that
could cause premature failure.
Although the long single beam allows the
coupling to bend easily under misalignment
conditions, it has the same affect on the
rigidity of the coupling under torsional
loads. The relatively large amount of
windup under torsional loads adversely
affects the accuracy of the coupling and
reduces its overall performance.