|
The evaluation of transmission performance plays a very
improtant role in the design of mechanisms. It offers valuable
criteria for designers to choose better parameters and to
construct mechanisms with high quality of transmission. There
are two ways in the evaluation of motion and force transmission
of a mechanism, i.e., quantitative analysis and qualitative
analysis. The former is to measure the transmission quantity
between the output and input of the mechanism, and can be
described as velocity or force ratio; the latter is to indicate
the transmission quality when transmitted force/torque is acted
on the output and input links, and can be classified as
transmissivity and manipulability. All of those transmission
phenomena can be characterized by the concept of transmission
wrench screw (TWS). In general, transmission quality is more
improtant than transmission quantity in single-DOF mechanisms.
For a single- DOF single-loop linkage, if the TWS can be
uniquely determined, then transmissivity and manipulability
indices can be clearly defined based on the effectiveness of
power transmission. For those linkages whose TWS is not unique,
however, we can only obtain the measurements of transmissivity
and manipulability based on the closeness to the special
configurations. More- over, those transmission criteria
developed are also extensible to evaluate the transmission
quality of multi-loop mechanisms. In multi-DOF mechanisms such
as robots and manipulators, it seems that the measure of
transmission quantity is as improtant as that of transmission
quality. Here, transmission performance of serial and parallel
manipulators are studied. Based on the TWS matrix and virtual
coefficient matrix, the analysis of transmission quality and
the measure of transmission quantity are modeled by a similar
form. Some indices applicable to indicate the kinematic
performance of manipulators are thus developed.
|