Research And Design Of Constraint And Balance Mechanism Of 3-TPT Parallel Robot

With the rapid development and continuous progress of science and technology,robots have been widely used in industrial production,military and other fields.As a hot topic in the field of robot research,parallel robot has attracted the attention of many scholars in recent years,and its market prospect is widely valued.3-TPT parallel robot is a experimental prototype that is developed in Northeastern University,which is used to accomplish automatic grinding of local defect of the billets in the iron and steel.Its translational degrees of freedom is bound by constraints,which is composed of two layer identical compound parallelogram constraint in series.But it effects the workspace size,the pose error of the moving platform and exists the problems such as swing in the actual working process.Aiming at the deficiency of compound parallelogram constrain mechanism,a new type of constraint mechanism is designed to realize the degree of freedom restriction;At the same time,because of the great quality of moving platform and its subsidiary parts,if they are not balanced that will bring a great influence for motor drive motor selection and the overall motion performance of a robot.In order to realize that driving joints do not need to provide additional torque to overcome the gravity of the active component when the moving platform of parallel robot is in the arbitrary position,a balancing mechanism is designed to realize static balance of the moving platform of 3-TPT parallel robot.According to the 3-TPT parallel robot,this paper improved the 3-TPT parallel robot by means of theoretical analysis,simulation verification and experimental test,and the specific contents include:(1)The 3D model of virtual prototype of 3-TPT parallel robot is set up on the basis of structural analysis,including analysis of degree of freedom,calculation of kinematics positive/inverse solutions and Jacobian matrix,which lays the theoretical foundation for the design of constraint mechanism and balance mechanism.This paper analyzes the problems existing in the constraint mechanism and the advantages of realizing the static balance of the moving platform.(2)Constraint mechanism which contains a kind of 3-PRR structure is proposed,including drawing of schematic diagram,kinematic analysis and simulation analysis that changes of each component in the workspace and curvilinear path based on the closed loop vector method by utilizing matlab.(3)The common balance methods are summarized,combined with the structure characteristics of the robot,two kinds of balancing schemes are proposed.One is spring cam balance scheme,and the other is cylinder balance scheme which is used ultimately after overall consideration.(4)The 3-TPT parallel robot which has constraint mechanism and balance mechanism is analyzed,including complete machine interference detection and using Solid Works motion plugin to do the parallel robot kinematics simulation analysis.(5)The experimental platform of the pneumatic balance system is set up,and the parallel robot is operated along the set trajectory under two working conditions.The current output of the three groups of servo motors under each working condition is measured and recorded respectively,and the validity of the balancing mechanism is verified by comparing the experimental results.