The Contact-impact Force Model Of Coated Revolute Joints With Clearance And Its Application

Revolute joint is one of the most common kinematic pairs widely used in mechanical engineering,but the clearance in its structure is inevitable,which could lead to many unexpected problems such as exciting the nonlinear characteristics of deployable mechanisms,non-periodic motion,a lower positional accuracy and service life.Thus,the clearance in revolute joints,inner impact,friction,lubrication and other nonlinear factors can affect the dynamic behaviors of multi-body mechanical system significantly.The contact surface of revolute joint is coated by some anti-friction and wear-resisting coating to improve behaviors of the whole system under some extreme operating conditions,which has been used regularly in engineering.However,few studies on mechanical behaviors of coating/substrate under load is published considering structure characteristics of revolute joints,which restricts the simulation accuracy and control level of these related mechanical systems.To solve this problem,in this paper the relationships between contact force and deformation of coated sleeve under static and impact loads are investigated,respectively.And the main tasks have been completed as follows:Models utilized to calculate the contact force of pin-elastic half space and pin-single elastic layer sleeve were developed based on non-conformal contact method and Winkler elastic foundation model,respectively.It proves that the Winkler foundation model has a high accuracy to calculate the contact force of clearance joints with a small radial clearance.Then a modified double elastic contact force model applicable to static load was proposed based on Winkler elastic foundation model and Hertz assumption of ellipsoidal pressure distribution,thereafter the validity of the new model was examined.The contact-impact process between pin and coated sleeve was simulated via explicit dynamic finite element method,which proved there was energy dissipation during that process.Then,a double elastic layer contact-impact force model considering energy dissipation was proposed based on the modified double elastic layer model after deriving the damping force equation according to the relationships between work and energy during the impact process.The validity of the contact-impact model was also verified.At last,the double elastic layer contact-impact force model was integrated to the multi-body system dynamic equation,and a crank-slider mechanism was utilized as a sample to analyse the kinematic and dynamic behaviors of mechanism with coated clearance joint.Results show that clearance is the main reason for remarkable deviation of kinematic and dynamic behaviors between imperfect and ideal joints.And effects on dynamic characteristics of the mechanism by coating were revealed through many aspects synthetically.The anti-friction and wear-resisting functions of coating can avoid a bigger clearance due to pairs wear for long time operating revolute joints.And a small equivalent elastic module and restitution coefficient of coating/substrate system could improve the performance of multi-body mechanical system with clearance revolute joints.