The Motion And Loading Characteristics Study Of Planetary Roller Screws

The planetary roller screw pair has been widely used in precision linear transmission and heavy load applications in engineering applications such as precision CNC machine tools,medical equipment,special machinery,robotics technology,aviation industry,Weaponry,etc.due to its advantages of high load-bearing capacity,high precision,and long life,etc.The planetary roller screw is a new type of precision linear transmission device,which relies on the threaded transmission to transform the rotating motion of the screw into a straight and reciprocating motion of the nut.Through arranging a number of rollers around the screw evenly,the numbers of contacting of the thread pair are greatly increased in the transmission,which has the advantages of high transmission precision,large bearing capacity,long service life,etc.Taking the planetary roller screw as the research object,this paper explore the working principle of planetary roller screw,and studies its kinematics characteristics and bearing characteristics.In this thesis,the main contents are as below:(1)Based on the space helix theory,the mechanism study of the planetary roller screw is carried out,and the motion diagram of the mechanism is drawn,then demonstrates the working principle of the planetary roller screw deputy from the mathematical level.(2)According to working principle and mechanism analysis of the planetary roller screw,the geometrical shapes and mutual movement relations of each component are analyzed,and the calculation formulas for the design of geometry and working parameters are derived.(3)The kinematic relations among the components in the motion of the planetary roller screw are theoretically derived.Though studied on the axial motion speeds of the nuts under pure rolling and sliding of rollers and nuts,the result is gained that the speed is proportional to the number of screw heads,the pitch and the angular velocity of the screw.The kinematics analysis of the planetary roller screw pair was established by the virtual prototype,which verifies the correctness of the theoretical derivation formula.(4)Based on the Hertz contact theory,the elastoplastic contact model is established.The stress variation formula between contact pairs is derived theoretically and the factors of affecting the bearing capacity of the planetary roller screw are discussed.Through the reasonable simplification of the model and the use of computational mechanics,the correctness of analytical formulae is verified.(5)The theoretical study on the axial deformation of the screw under different support modes is carried out and then gained the variation rule of the axial deformation of the screw.The relationship between the screw strain and the support method was analyzed by computational mechanics.