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Parallel kinematics offer a high potential for increasing performance of machines for handling and assembly. Due
to greater stiffness and reduced moving masses compared to typical serial kinematics, higher accelerations and
thus lower cycle times can be achieved, which is an essential benchmark for high performance in handling and
assembly.
However, there are some challenges left to be able to fully exploit the potential of such machines. Some of
these challenges are inherent to parallel kinematics, like a low ratio between work and installation space or a
considerably changing structural elasticity as a function of the position in work space. Other difficulties arise
from high accelerations, which lead to high dynamic loads inducing significant vibrations.
While it is essential to cope with the challenges of parallel kinematics in the design-process, smart structures
technologies lend themselves as means to face some of these challenges. In this paper a 4-degree of freedom
parallel mechanism based on a triglide structure is presented. This machine was designed in a way to overcome the
problem of low ratio between work and installation space, by allowing for a change of the structure's configuration
with the purpose of increasing the work space. Furthermore, an active vibration suppression was designed and
incorporated using rods with embedded piezoceramic actuators. The design of these smart structural parts is
discussed and experimental results regarding the vibration suppression are shown.
Adaptive joints are another smart structures technology, which can be used to increase the performance of
parallel kinematics. The adaptiveness of such joints is reflected in their ability to change their friction attributes,
whereas they can be used on one hand to suppress vibrations and on the other hand to change the degrees of
freedom (DOF). The vibration suppression is achieved by increasing structural damping at the end of a trajectory
and by maintaining low friction conditions otherwise. The additional feature to alter the DOF is realized by
increasing friction to the point where clamping happens. This can be used to support the change in the machines
configuration of parallel kinematics. Two kinds of adaptive joints are presented, both utilizing piezoceramic
actuators. The first kind features an adjustable clearance of the slide bearing that provides low friction for high
clearance conditions and great friction for reduced clearance. The second kind offers the possibility to reduce
the friction by moving the rubbing surfaces dynamically. For both joints experimental results are shown.
The paper closes with an outlook on ongoing research in the field of parallel robots for handling and assembly
with an emphasis on smart structures technologies.
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