Design And Analysis Of Parallel Mechanism With Rod Moving Platform

The parallel mechanisms(PMs)have received wide attention and research in recent years,due to their excellent performance of high speed,high stiffness,high precision and high carrying capacity compared with the series counterpart.However,the traditional parallel mechanisms suffer from a problem of limited rotational capability due to the serious interference between limbs,which limits their application in industry.In order to obtained parallel mechanisms with large rotational angles,this paper presents a type of parallel mechanisms with rod moving platform(PM-RMP),which connected with the limbs by revolute joints.It is demonstrated that the PM-RMP possesses high rotational capability in the condition of the same dimension parameters,which indicates a more applicable in industry.A class of 2-5 degree of freedom(DOF)PM-RPM is synthesized based on the Lie group theory.To obtain large rotational angles,the end of each limb is connected with the rod moving platform by revolute joints and then connected to the universal joints to reduce the interference between platform and limbs.A 5-DOF PM-RPM is analyzed by means of the structural features and advantages of the symmetrical PM.The inverse kinematics of this mechanism is calculated based on the bar length constraint condition and the orientation workspace is obtained.The optimal design for it is conducted by means of the genetic algorithm,by which the maximum rotational angle is presented in the invariable dimension parameters.The proposed PM-RPM is used to be a guide device in a pedicle screw implanting mechanism(PSIM)to overcome the disadvantage of lower rotational angles of the traditional guide mechanisms.The 2-DOF PM-RPM is selected as the end-effector of the PSIM.A double-layer double-parallelogram mechanism with two translational DOF is proposed as the feed mechanism to complete the guide task of the pedicle screw implanting procedure.The PSIM is a hybrid mechanism by connecting a parallel body part and a feed mechanism in series.The forward and inverse kinematics of the PSIM are presented,based on which the forward and inverse workspaces are obtained and compared.The Jacobian of this mechanism is presented to analyze the singularities and the relationship between input and output parameters,which is the foundation of the control research.In the basis of the Jacobian,the dexterity and the static stiffness are analyzed.The optimal designs are conducted for these two PMs by means of the genetic algorithm and a model is built using the optimal data.The obtained model is imported to Adams to do the trajectory simulation.The dynamic model of the hybrid mechanism is established based on the Lagrange equation and the dynamics is analyzed.The result illustrates that the PM-RPM possesses high rotational capability,which overcome the disadvantage of the traditional PMs and has potential application value in industry.