Synthesis of three dimensional steering crank mechanisms

The task of this paper is an analysis of opportunities provided by the approximate cinematic synthesis of three - dimensional straight -l ine steering mechanism when regarding it as a flat one, with the specific task shown as an example: designing of looper mechanism for chain stitch sewing machine. For solving the objectives set by this paper, classical analytical methods applicable in the theory of machines and mechanisms were used (closed vector paths method) as well as analytical geometry methods; weighted difference method was also used for approximate synthesis of the mechanism. In addition to the above, the determination of mechanism performance values was done through the method of the best approximation of the specified function. Three - dimensional five - link looper mechanism was viewed as a flat four - link one. For performing the synthesis in two ways it was shown that the partial declination of the pathway traced out by the driven link of the three dimensional five - link element is insufficient and does not exceed hundredth of a millimeter when compared with the similar part of the pathway traced out by four - link element, which proves the sufficient accuracy of the approximate method. As a result of the work carried out the practicality of the given method was proven as well as the reasonability of its use in design practice when creating new three - dimensional mechanisms for consumer industry.