Study On The Contact Stiffness Of Mechanical Pair And Dynamic Characteristic Of Conjugate Cam

Conjugate cam is widely used in various kinds of automatic machines like light machinery,textile machinery,packing machinery, printing machinery,combustion engines,to realize all kinds of complex movements.It has features like small rotational inertia and unbalanced inertial forces,good dynamic performance,little wear and tear and long useful life.The joint clearances and nonlinear stiffness in the conjugate cam mechanisms is a challenge to theoretical analysis and yet are among the most important factors that must be considered when designing and manufacturing a conjugate cam system.The subject draws the attention of many researchers in the past couple of years,not only in the field of mechanism dynamics,but also in multibody dynamics.In this thesis,the contact stiffness in the revolute joint and cam couple of conjugate cam is discussed based on the theory of contact mechanics and elastic mechanics.By introducing some appropriate assumptions of approximate elastic model,a modified contact formula is presented,which proposes a corresponding solution to the failure of the Hertz theory in dealing with the contact between concave and convex.In addition,a contact model considering the effects of lubrication and friction is established.Besides the stiffness,this thesis also discusses the influence of dimension tolerance to the clearance of cam couple,with the calculating formula for impact factors of the clearance being introduced. At the end of the thesis,a dynamic model of the conjugate cam in the combing machine with clearances is developed through modeling the contact problem as a spring/damper model to analyze the dynamic properties in different clearances.Introducing the variable stiffness into the simulation of a conjugate cam system with clearance explores a new way to make the simulation model close to the practice.And proposing an analysis of the clearance influenced by dimension tolerance provides a theory basis to optimize the tolerance allocation.This study has profound theory and application value in system designing and dynamics behavior predicting.