| As a new type of globoidal indexing cam, globoidal indexing cam mechanism with steel ball achieves "rotation to rotation" transmission through rolling steel ball, it can be used in CNC machine and automatic line to achieve high-speed and high-precision indexing motion, because it's spinning axis is not restrained and meshes at controlled point, it has advantages of high transmission efficiency, high speed, high precision and less residual vibration. It is meaningful for improving development level of equipment manufacturing industry of china. Under actual engineering conditions, for the purpose of improve indexing precision, moving stability and meshing efficiency, meshing characteristic of the mechanism is studied, and structure, force, preload, lubrication, kinetics and dynamics and fatigue life are analyzed, the study provides theoretical basis for optimization design, manufacture and application, the main research work done in the paper is as follows:Struction of globoidal indexing cam mechanism with steel ball is designed firstly, it is foundation of analyzing feature and optimizing parameters, and affects cost of manufacture and function, it mainly includes the section of raceway, indexing plate and part preventing steel ball separating from indexing plate. Taking example by bearing and ball screw, double-circle arc raceway can prevent lateral slip existing in ball screw drive, the ratio between radius of cam raceway and steel ball diameter is between 0.51 and 0.56, the mechanism can improve bearing capacity, decrease friction and EHL oil film is thicker. Ball seat in indexing plate adopts double-circle arc raceway for meshing at controllable point, retainer is used to prevent steel ball separating from indexing plate. At last, profile equation and meshing equation are deduced by the space meshing theory and rotating matrix operators, and pressure angle and it's influence factor are analyzed, pressure angle changes with cam angle, and with different motion rules the mechanism has different pressure angle. It is point contact between steel ball and cam raceway, so contact stress is large, contact strength should be checked in design for preventing intensive wear and fatigue failure, so force of the mechanism is analyzed firstly. Load is applied on steel ball in transmission, and pretightening force is applied on steel ball too because of pretightening, steel ball suffered resultant force. According to principle of independent role of force, force applied on steel ball by load and preload is analyzed firstly, then force of steel ball is composed, contact strength is checked.For continuous transmission and stability of motion in the process of working, the mechanism has contact ratio factor, several steel balls participate in meshing together, and the number of meshing steel ball changes periodically. Load is not equally distributed on each steel ball because principal curvature, normal and helix angle of cam raceway are different at different contact point. Applying hertz contact theory, deformation compatibility condition and torque balance principle, relationship of load distribution applied on each steel ball is deduced. It can be acquired by example that load is not equally distributed on each steel ball, and it is affected by structural parameters and cam motion law.In order to improve rigidity and bearing capacity of the mechanism, eliminate influence of manufacturing error, achieve transmission without clearance, globiodal indexing cam mechanism with steel ball works under preloading. Preload changes meshing point between steel ball and cam raceway, which changes the meshing character and meshing efficiency, even generates interference. Elastic deformation of the mechanism is generated by preload, and pretightening force has relationship not only with adjusting magnitude of preload, but also with rigidity of the mechanism. Theory of hertz contact, bending deformation of shaft and radial elastic deformation of bearing are used for analyzing the relationship between adjusting magnitude of preload and preload force. The calculation shows that relation between preload force and adjusting magnitude is non-linear, bending deformation of shaft is little enough to be ignored, in indexing period, pretightening force generated at each contact point is different and changes with cam angle. Actual pressure angle changes because preload changes engagement points of the mechanism. Compared with cam with single-circle arc raceway, pretightening force of cam with double-circle arc raceway is more continuous and pressure angle varies less, motion of the mechanism is more stable.Load and preload force are composed into resultant force applied on steel ball, then contact strength is checked. Calculation shows that contact stress changes with cam angle, contact stress between steel ball and cam raceway is larger than that between steel ball and ball seat, so it is proposed that contact between steel ball and cam raceway is checked only. Contact stress is analyzed when three kinds of motion law is adopted respectively, affected by inertial load contact stress in indexing period is large, and in dwelling period it is little.Globoidal indexing cam mechanism with steel ball transfers movement and power through steel ball, and steel ball meshes with cam and ball seat at the same time, motion of steel ball affects the failure mode, lubrication and meshing efficiency.Motion trajectories of steel ball center, contact point between steel ball and cam raceway and contact point between steel ball and ball seat are space spiral curve relative to cam axis, helical angle and intersection angle of the three helical curves are different and change with cam angle. lateral slip speed is calculated based on ball helical transmission theory, it changes with cam angle, and lateral slip speed of two contact point on steel ball is different, which deduces that steel ball rotates along section of cam raceway too. Steel ball dragged by cam raceway self-rotates and is wedged, self-rotation speed is undecided affected by relationship of frictional force between steel ball and cam raceway and that between steel ball and ball seat, self rotation speed is calculated supposing that steel ball rotates purely.For the research of high speed capacity, output property of the mechanism and motion of steel ball, kinematics simulation is studied applying virtual prototype technology. Profile surface of globoidal indexing cam with steel ball is undevelopable space surface, process of build of 3D models is complicated, point coordinate data of profile curve is generated by VC++ firstly,3D models is built using Pro/E, model data is imported into RecurDyn through format of Parasolid, and 3D models of other work parts are established in RecurDyn, the mechanism is assembled according to the position relationship, restrictions and loads are applied basing on motion relationship, and virtual prototype model is established, then kinetics simulation is carried out. In dwelling indexing period, angle acceleration of indexing plate waves slightly, which is residual oscillation of indexing plate, which affects indexing precision, in indexing period, the angle acceleration of indexing plate is not continuous, impact exists. Contact forces between steel ball and cam raceway are acquired by simulation, which proves that theory of load distribution is right, simulation also proves that lateral slid and wedge exist in the motion of steel ball.Though rolling transmission is achieved through rolling steel ball, friction property also is an important factor affected by lateral slid and wedge existing in ball helix transmission. Friction will leads to attrition and fatigue failure of steel ball and cam raceway, in high speed occasion, temperature raise caused by friction affects indexing precision and friction character, even makes the mechanism stuck. Lubrication between steel ball and cam raceway belongs to EHD, based on Hamrock-Dowson and Zheng Xuyun film thickness calculation formulae, the EHD film thickness formulae of globoidal indexing cam mechanism with steel ball between steel ball and cam raceway is deduced. Applying numerical calculation method, film thickness is analyzed and calculated when the modified constant velocity motion curve, modified trapezoidal acceleration motion curve and modified sine acceleration motion curve are adopted respectively. Analysis shows that oil film thickness varies in indexing period, affected by inertia load oil thickness is thick in former half of indexing period and is thin in latter half of indexing period. The influence of cam speed, load torque, ball diameter, indexing plate diameter and curvature ratio, on film thickness are also discussed, lubrication between steel ball and cam raceway is in boundary lubrication state judging by film thickness ratio, which provides theoretical basis for the lubrication design of globoidal indexing cam mechanism with steel ball.Globoidal indexing cam mechanism with steel ball should not only achieves indexing motion precisely and high speed, but also has high meshing efficiency. Based on the motion of steel balls, theoretical calculation equation of meshing efficiency of the mechanism is derived by analyzing power loss of the mechanism and the output power of indexing plate. Based on the features of loads, meshing efficiency and its influencing factors are analyzed, results show that meshing efficiency varies with the positions of contact points, friction coefficient and sliding velocity are primary influencing factors, and pretightening force, slide-roll ratio and cam motion rule are secondary factors. This research has guiding significance for design and manufacture of the mechanism.In globoidal indexing cam mechanism with steel ball, it is point contact between steel ball and cam raceway, between steel ball and ball seat in the indexing plate, so contact stress is large, sliding friction and rolling friction exist in working process, steel ball and cam raceway contact periodically, so fatigue life is an important factor in design. Referencing the calculation methods and empirical data of fatigue life of bearing and ball screw, the fatigue life formula of globoidal indexing cam with steel ball was calculated by using the life theory of Lundberg and Palmgren, the rated load and rated fatigue life formula was deduced. Fatigue life of globoidal indexing cam mechanism with steel ball is compensated using the international standards of bearing life on life.
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