Planar linkages: Structural influence on mechanical advantage and function generation

There are many merit indexes to tell whether a mechanism is a good one or poor one; mechanical advantage, transmission angle and mathematically more rigorous Jacobian matrix are some of the indexes. When a selection has to be made out of all the distinct linkages Jacobian approach is tedious and time consuming. Hence a quick and simple method is necessary. This paper is an attempt in this direction. It is shown that the structural parallelism that exists between the links of a kinematic chain has a definite influence on their relative displacements. By properly matching the links, i.e., by selecting correctly the input and output links greater mechanical advantage can be obtained and also functions can be generated more accurately. This concept helps in selecting the best possible chain from a large group of distinct chains with the same number of links and degree-of-freedom (d.o.f). Assigning dimensions systematically to the links of such a chain leads to best performance. All the merit indexes proposed earlier are dimension-based where as the present one is strictly structural.