Mechanical Design And Theoretical Research Of The Over-constrained 5-dof Hybrid Manipulators

The over-constrainted parallel mechanisms(PMs)with two translational degree of freedoms(DOFs)and one rotational DOF(2T1R)and PMs with two rotational DOFs and one translational DOF(2R1T)owning simple structures have gained much attention.Over-constrained 5-DOF hybrid manipulators constructed on the basis of lower-mobility parallel mechanisms(PMs),especially the 3-DOF over-constrained PMs,present a compromise between the good flexibility,large workspace of serial robots and the high stiffness,high loading of PMs.Hybrid manipulators have been widely used in complex space surfaces machining.Aiming at the machining tasks in the field of aerospace,automobile and shipping,mechanical design and theoretical research of the over-constrained 5-DOF hybrid manipulators will be carried out.The main contents are as follows:Constraint force/torque analysis of the typical limbs of the lower-mobility PMs is done by means of screw theory method.And limbs are divided into different types according to their planar and spatial movement characteristics.As the 2R1T PMs with two continuous rotational axes have better motion decoupling,the kimematic models of this type 2R1T PMs are easier.For example,the analytical solutions of the kinematics can be established.Therefore,the relations between rotational axes of the rotational DOFs and constraint force/torque of the limbs are analyzed.The conditions of rigid body rotating around two axes are researched,which can be used to obtain the effects of limbs arrangement acting on the joints.The 3PRR planar PM is picked out from the obtained 2T1R planar PMs by means of type synthesis method.And structure modifications are carried out,for example,by adding one PRR limb changes the 3PRR planar PM into an actuation redundancy planar PM.After that,splitting the moving platform(MP)into two parts make the planar PM into a kinematically redundant planar PM.So the metamorphic property of the 3-DOF kinematically redundant planar PM can be used to research not only kinematic redundancy but also actuation redundancy,which enhances the research applications of the robot.A novel 5-DOF hybrid manipulator is constructed on the basis of 2PRR~2+R planar PM.Systematic and comprehensive theoretical analysis,including kinematic,dynamic and stiffness,are researched.Basing on dexterity indice of the MP,dimention optimization of the planar PM,the structure topological optimization of the limb and mechanical design of the whole robot are accomplished,respectively.After that,the prototype of the 5-DOF hybrid manipulator is processing and manufacturing.According to the position of rotational axes of 2R1T PMs,2R1T PMs can be divided into three types.The principles of constructing 5-DOF hybrid manipulators are given,then a 5-DOF hybrid manipulator(2RPU/UPR+R+P)based on 2RPU/UPR PM with two continuous rotational axes is obtained.To simplify the structural model of the obtained hybrid manipulator,an equivalent model method according to the properties of rotational axes is proposed.A serial equivalent model P-RPRR of the 2RPU/UPR+R+P hybrid manipulator is established using this method.After that,the inverse and forward position,velocity and acceleration of the hybrid manipulator are analyzed by menas of the serial equivalent model.Based on the kinematic model,the dynamic,stiffness and simulation verification are analyzed and carried out.An actuation force stability indice is proposed,and then combining force transmission and rotational ability indices,the dimension optimization of the 2RPU/UPR PM is performed.At last,the mechanical design on the basis of theoretical results is done and the prototype of the 2RPU/UPR+R+P 5-DOF hybrid manipulator is processing and manufacturing.Mounting a 2-DOF AC head onto the MP of the 2R1T position type 2UPU/SP PM,a novel 5-DOF 2UPU/SP+RR hybrid manipulator is obtained.The properties of two rotational axes of the 2UPU/SP are analyzed,and the results show that this PM has two ordered continuous rotational axes.The kinematic and dynamic models of the 2UPU/SP PM are established,and simulation verification also is performed.Comprehensive consideration the motion/force transmission indice and the size of workspace,the key physical dimensions of the 2UPU/SP PM are determined.At last,according to two different limbs,two 3-D models of the 2UPU/SP+RR hybrid manipulator are established,and several modular configurations of the hybrid manipulator are given.Comparison analysis of different types of 5-DOF hybrid manipulators is researched.And taking the 2RPU/UPR+R+P 5-DOF hybrid manipulator as an example,some experiments are performed.Five-axis control system of the 5-DOF hybrid manipulator is established on the basis of Spanish FAGOR CNC8070 system.Force loading platform of the 2RPU/UPR PM is constructed,which is used for performing the comparison experiments of the lateral stiffness of the 2RPU/UPR PM.Using genetic algorithm method,the home position errors of the limbs are identified,and the experiments of processing the workpieces with spherical surface are carried out.