| The lower-mobility parallel
mechanism (PM) has fewer than six degrees of freedom (DoFs) and requires
fewer links, joints and actuators than its 6-DoF counterpart. Hence, the
use of the lower-mobility PMmay save much cost in those applications requiring
less mobility. In this paper, the type synthesis of symmetrical lower-mobility
PMs is performed systematically using the constraint-synthesis method. First,
some important theoretical fundamentals of type synthesis of lower-mobility
PMs are investigated, including a classification of symmetry of lower-mobility
PMs, the identification of instantaneous mechanisms and input selection
method. Moreover, the difficult problem of how to correctly apply the general
Grübler-Kutzbach criterion to lower-mobility PMs is solved. A mobility
analysis of PMs with a closed loop in the limbs is also presented to demonstrate
the validity. The type synthesis of 5-DoF and 4-DoF PMs is then dealt with
in detail. Enumerations of novel 5-DoF and 4-DoF PMs are presented. The
characteristics of constraint and structure of 5-DoF and 4-DoF PMs are also
proposed. In addition, some novel 3-DoF PMs are presented. |
