Design And Basic Theory Analysis Of A Novel Five-Axis Gantry Hybrid Machine Tool

The slender structural parts are widely used in aerospace,railway transportation,national defense industry and other fields.Aiming at high speed machining of slender structural parts,the machine tool should satisfy the requirements of high stiffness to weight ratio,high response velocity and high machining precision.This paper presents a novel gantry hybrid machine tool(HMT for short)whose main mechanism is a new hybrid mechanism.The main contents of this paper are summarized as follows:The configuration of the novel gantry five-axis HMT is designed.The three-dimensional translations and two-dimensional rotations motion mode of this HMT are analyzed using screw theory.The selection method of driving joints are presented.The motion singularity is analyzed and the parameter design conditions are presented to decrease motion singularity.The kinematics of the novel gantry five-axis HMT is analyzed.The inverse kinematics of this HMT is solved using vector algebra method.The inputs of all driving parts are obtained when the position of the machine tool tip and the orientation of the moving platform are known.The first order influence coefficient matrix i.e.Jacobian matrix and two order influence coefficient matrix,i.e.Hessian matrix are obtained using influence coefficient method.The dynamics of the novel gantry five-axis HMT is analyzed.The dynamics model of the HMT is established considering the virtual energy of the system using the principle of virtual work.A numerical example is given and the simulation of mechanism dynamics is implemented using ADAMS software.The simulation results testify the validity of the analytic model.An example is given for drilling a slender structural part.The variation laws of driving forces of the HMT is obtained.The static stiffness of the 2-UPS+2-RPU parallel mechanism of the HMT is analyzed.The elastic deformations of the limbs is analyzed under the action of the limb's constraint wrenches(including the constraint screws)using small deformation superposition principle.The stiffness matrix of the limb's constraint wrenches is defined.The relationship between external loads and the deformation of the position and orientation of the moving platform is set up through the static equilibrium and the relationship between the deformation of the limbs and the deformation of the moving platform.The matrices of flexibility and stiffness are obtained.It is found that the constraint force/torques have a major influence on the stiffness and elastic deformation of limited-DOF over-constraint parallel mechanisms.The elastic deformation are mainly in the axial direction of the constraint force/torques.The model of the novel gantry five-axis HMT is analyzed.The modals at five typical locations of the gantry five-axis HMT are analyzed using ANSYS Workbench software.The first six order natural frequencies and vibration types are determined.The low order vibration laws of the HMT are analyzed.The weaknesses of the HMT structure are determined.It provides a reference for optimum design for this HMT.The two-axis rotation capacity of the HMT are about ±40°.solving the processing problems for the slender structural patrs are solved.The results have important application value.