Dynamic Analysis of Intermittent-Motion Mechanisms Through the Combined Use of Gauss Principle and Logical Functions Pennestr` ı E. 1 , Valentini P.P. 1 , and Vita L. 1 Universit`a di Roma Tor Vergata Dipartimento di Ingegneria Meccanica, via del Politecnico, 1 00133 Roma - Italy pennestri@mec.uniroma2.it 1 Introduction Intermittent-motion mechanisms play an important role in modern technol- ogy. For instance they are key elements of many automatic machines. Scientific literature records different modelling analyses of this kind of mechanism (e.g. [1, 2]). Due to the widespread use of such devices, their analysis and design taking into account impact phenomena appears to be significant. The dynamic simulation of intermittent motion involves several issues. For example the presence of impact and sudden changes in velocity leads to the requirement of including transient mechanics. Several mathematical models of impact could be found in most of the investigations which deal with mechanism clearances. However in ratchet mechanisms the impact is an usual event whose presence does not depend on the clearances. The main contributions presented in this paper are: - an extension of the dynamic formulation proposed by Udwadia and Kalaba [3] to the analysis of impacts; - an engineering model for the analysis of the impact phenomena in ratchet mechanisms; - a procedure of optimal design of ratchet mechanism. 2 Brief summary of the Gauss-Udwadia-Kalaba dynamic formulation The main advantages of this formulation concern with the possibility of re- ducing the equations of motion to a system of ordinary differential equations (ODE), even in presence of redundant constraints or sudden topology changes. The numerical efficiency of this formulation has been discussed in the following bibliographical references [4, 7].