Numerical and experimental analysis of non-circular gears and cam-follower systems as function generators

The paper shows an analysis of two mechanisms that are typically used as function generators. The former consists of a pair of non-circular gears, which drives a slider-crank mechanism, the latter is a cam-follower system. Both mechanisms are designed to obtain a specific motion law. In this paper the proposed application is to generate a pulsating blood flow during cardiopulmonary by-pass for cardiac surgery. The prescribed motion law can be obtained by a volumetric pump, which can be used to modulate the blood flow in external circulation machines. The reciprocating motion consists of a quick forward stroke, corresponding to the Systolic phase, and a slow return stroke, corresponding to the Diastolic phase. The study has been focused on specific transmission characteristics that are related to a mechanical blood pumping design. In particular, experimental tests have been analyzed to understand benefits and drawbacks for using non-circular gears and polynomial cams in pure mechanical transmissions with limited motion regulation but with specific prescribed motion law. The contribution of the paper can be recognized in comparing numerically and experimentally a traditional cam transmission with a non-circular gear solution to show proper operation feasibility for both solutions without using complex control equipment, even for a robust/reliable demanding application like a blood pumping system. (C) 2007 Elsevier Ltd. All rights reserved.