Synthesis of function-generation mechanisms using variable length driving links

In this paper, a design method is proposed to solve function-generation problems for four-bar linkages without any limitation on the number of precision positions, using variable length driving links. A single degree-of-freedom (DOF) linkage mechanism, comprising the original four-bar linkage, a ternary link, a roller link, and a guiding slot in a fixed link, is employed to make the length of driving link variable while being driven by a power source. A new function-generation design process is also proposed. An nth-degree polynomial is utilized to design the contour of the guiding slot. Three examples are provided to verify the effectiveness of this technique, and the structural errors show significant improvement in all examples, compared to the conventional three precision-point solution.

Research highlights
► A design method is proposed for exact function-generation problems of four-bar linkages using variable length driving links.
► A guiding slot in a fixed link is employed to make the length of driving link variable while being driven by a power source.
► A new function-generation design process is also proposed.