| Just as there are a number of advantages
associated with compliant mechanisms, there are also several challenges
and disadvantages for some applications. Perhaps the largest challenge
is the relative difficulty in analyzing and designing compliant mechanisms.
Knowledge of mechanism analysis methods and the deflection of flexible
members is required. The combination of the two bodies of knowledge in
compliant mechanisms requires not only an understanding of both, but also
an understanding of the interactions of the two in a complex system. Since
many of the flexible members undergo large deflections, linearized beam
equations are no longer valid. Nonlinear equations must be used that account
for the geometric nonlinearities caused by large deflections. Because of
these difficulties, many compliant mechanisms in the past were designed
by trial and error approaches. Such methods are only applicable for very
simple systems that perform relatively simple tasks, and are often not
cost efficient for many potential applications. Theory has been developed
to simplify the analysis and design of compliant mechanisms and the limitations
are not as great as they once were. Even considering these advances, however,
compliant mechanism analysis and design is typically more difficult than
for rigid-body mechanisms. |
Energy stored in flexible elements was discussed
above as an advantage since it can be used to simplify mechanisms that
incorporate springs, to obtain specified force-deflection relationships,
and to store energy that is transferred or transformed by the mechanism.
However, in some applications having energy stored in flexible members
is a disadvantage. For example, if a mechanism's function is to transfer
energy from the input to an output, not all of the energy is transferred
since some is stored in the mechanism.
Fatigue analysis is typically a more vital issue for compliant mechanisms
than for their rigid-body counterparts. Since compliant members are often
loaded cyclically when a compliant mechanism is used, it is important to
design those members such that they will have sufficient fatigue life to
perform their prescribed functions.
The motion from the deflection of compliant links are also limited by the
strength of the deflecting members. Obviously a compliant link cannot produce
a continuous rotational motion such as that possible with a pin joint.
While these challenges may be overcome, it is important that the difficulties
and limitations of compliant mechanisms are understood. Such knowledge
is helpful in determining which applications will benefit the most by utilizing
compliant mechanism technology. |
