|
The trend
in servo motor and servo system designs requires manufacturers of couplings,
as well as other components to focus their design and performance attributes.
Servo motors have become smaller, with lower inertia, greater torque and
greater performance and duty cycle capabilities.
These
changes and others require different balance of coupling attributes. How
well each attribute is balanced among other design attributes of the servo
coupling is important to system performance and reliability.
Some
of the design attributes considered in the design of the new ServoClass
couplings are:
•
Zero backlash
• Torsional stiffness
• Inertia
• Torque
• RPM
• Misalignment
• Coupling reaction force
• Shaft mounting arrangement
• Assembly and construction
• Dimensions and weight
• Total cost, performance & reliability attributes
Zero Backlash - the Benchmark
Zero
backlash is a "benchmark" attribute in the selection of a coupling
for a servo drive system. Next are "torsional stiffness" and
"inertia".
A coupling with too much inertia can detrimentally affect the performance
of the servo motor system.
Other attributes are important and must be considered.
The coupling must have an integral clamp-type hub mounting in order to
provide zero backlash mounting.
The clamping design should be as compact as possible so that it does not
increase the inertia of the coupling.
Additionally, the design of the clamp hub can also affect the torsional
stiffness of the coupling.
Balanced Coupling Attributes
Very high coupling torsional stiffness is often interpreted as
providing "better" mechanical position response. However, VERY
high torsional stiffness is often unnecessary and may sacrifice other
coupling attributes needed for long-term system performance and reliability.
Likewise, a coupling selected for its "soft" torsional stiffness
and "vibration" damping can be a poor choice for a servo drive
system. "Ringing" may occur while the system attempts to compensate
or hunt for the true position. And "electronic damping" may
decrease system performance. The torsional stiffness of the driven equipment
must be considered.
Excessive torsional stiffness often means misalignment capabilities will
be reduced and misalignment reaction forces increased.
There is no practical escape. The important coupling design attributes
must be balanced against the value of the others.
The design of ServoClass® couplings also minimizes coupling
reaction load while transmitting torque.
ServoClass® Couplings - a "Balanced Design"
By design, ServoClass couplings substantially reduce reaction
loads, even those generated by torque transmission.
SC Series ServoClass® couplings utilize two flexible, stainless
steel disc mounted to a lightweight, high-strength aluminum center member
and precision mounting hubs. The lightweight, small diameter ServoClass
coupling provides very low inertia, another important attribute, along
with torsional stiffness in avoiding system resonance and increasing system
performance.
As an example, a ServoClass® coupling is compared to another
coupling with similar torque, misalignment capacity and dimensions. The
same servo motor and linear ball screw are used in the application comparison.
Data concerning the motor inertia, coupling inertia, torsional stiffness,
actuator load, lead screw diameter, pitch, system gain, etc. are entered
into a 2 Mass Natural Frequency calculation to determine whether there
may be a system resonance problem.
Comparison results showed the older design alternative coupling produced
a natural frequency of 229 Hz. The system natural frequency was 880 Hz.
The design attributes of the ServoClass coupling placed the system natural
frequency far beyond the typical resonance range of 150-350 Hz.
The new ServoClass® coupling is a valued component for
many servo drive systems, SMT (Surface Mount Technology) and positioning
control applications.
For more detailed
information please download the
ServoClass PDF catalog
|
