Parallel robot as a kind of new structure robot,after half a century of development,has been deeply studied and widely used.Compared with serial robots,parallel robots have many advantages such as high precision,large stiffness,strong carrying capacity and easy control,which are widely used in aerospace,aviation,precision manufacturing and other advanced fields.The in-situ high-precision machining of complex surfaces and irregular holes with parallel robots as actuators is a new application scenario of parallel robots.In order to realize the machining of different types of workpieces by parallel robots,it is necessary to study the mechanism freedom and kinematics performance.Among them,the degree of freedom analysis of parallel robot is the most basic content.Kinematics analysis of parallel robot is to solve the position and velocity relationship between the input rod and the output end.It is one of the most basic tasks in kinematics analysis,and it is also the basis of studying other problems of parallel mechanism.The workspace of parallel robot is the basis of trajectory planning and an important measure of its motion performance.Therefore,it is of great significance to deeply study the basic theory of mechanism freedom,kinematics and workspace of parallel robot for practical engineering application.In this paper,a novel 5-DOF 4SPRR-SPR parallel robot used in in-situ intelligent manufacturing system is studied.The degree of freedom,kinematics and workspace are studied.The main research contents are as follows :(1)According to the 3D model of 4SPRR-SPR parallel robot,the mechanism configuration of the parallel robot is analyzed briefly.Based on screw theory and modified Kutzbach Grubler formula,the number and properties of degrees of freedom of the parallel robot are derived theoretically.Secondly,the velocity Jacobian matrix of the parallel robot is established,and five singular configurations of the parallel robot are obtained by solving the determinant of the Jacobian matrix.(2)Based on the idea of numerical calculation,the forward kinematics model of the parallel robot is established,and the adaptive particle swarm algorithm is used to solve the forward kinematics problem of the parallel robot by combining the two improved ideas of adaptive change of inertia weight and acceleration constant in the standard particle swarm algorithm.The forward kinematics problem of parallel robot is solved quickly by Matlab programming.(3)By measuring the main structural parameters of the parallel robot in UG and simplifying its model,the geometric relationship of each branch driving rod is analyzed by using the geometric vector method.The relationship between the position and attitude of the reference point on the end effector of the moving platform and the length of each driving rod is deduced,and the inverse kinematic position solution model of the parallel robot is established.The inverse kinematics problem of the parallel robot is solved quickly by Matlab programming.(4)According to the inverse kinematics model of the parallel robot and the hierarchical idea of the micro element in the workspace,and considering the constraint conditions such as the length of the rod,the rotation angle of the rotating pair,the rotation angle of the spherical pair,and the interference of the connecting rod,the limit boundary search method is used to solve the fixed attitude workspace and the achievable workspace of the parallel robot,and the workspace map of the parallel robot is plotted.At the same time,the influence of different structural parameters on the workspace size of the parallel robot is discussed,and its variation law is finally obtained.(5)Using ADAMS simulation software,the virtual prototype model of 4SPRR-SPR parallel robot is established by applying kinematic pair constraints and driving.Through Matlab programming simulation and ADAMS virtual prototype simulation,the variation trend of the driving rod length of each branch is compared and analyzed,and the correctness of the kinematic model of the parallel robot described in this paper is verified.In addition,taking the virtual prototype to simulate the machining of circular hole as an example,the variation rules of rod length,velocity and acceleration between each driving rod are obtained,which provides theoretical support for the actual trajectory planning. |