Research On Some Foundation Issues Of 3-DOF Hybrid Redundant Driving Mechanism

Hybrid driving mechanism can realize flexible trajectory at the output of moving platform,which adopts two kinds of driving modes at the same time,i.e.constant speed motor and servo motor.Hybrid driving mechanism has solved the contradiction between high bearing capacity and flexibility theoretically,which is one of the main branches of modern mechanisms.Hybrid driving mechanism can make up for the shortcoming of less flexibility of traditional high-power rigid machines and the high cost and insufficient power of fully flexible mechanism.It is an intelligent mechanism between modern real-time controllable fully flexible mechanism and traditional rigid completely uncontrollable mechanism.At present,the research content of the mechanism is mainly about the kinematics,dynamics,control system and its applications.At the same time,the configuration studied is limited to 2-DOF or 3-DOF planar mechanism of five-bar or seven-bar.However,it is subject to the technical bottleneck of lacking of newly spatial mechanism configuration,which cannot expand to the space area.Currently,there is no literature on the spatial multi-DOF linkage hybrid driving mechanism for reference,and the research work of the spatial hybrid driving mechanism is stagnant.The hvbrid driving mechanism has its unique advantages is suited to the fields,which demand of certain flexibility such as production line,factory and medical rehabilitation fields.Therefore,the study of hybrid driving spatial mechanism has important theoretical significance and practical value.Based on the theory of hybrid driving mechanisms,the paper analyzes the reason why the configuration studied stays in the plane area in present.A new type of reconfigurable mechnism named HRDM is proposed,which integrate the characteristics of hybrid driving mechanism and redundant driving mechanism together,through a limb called the hybrid redundant drive limb(HRDL for short).A systematic theoretical study of this new mechanism is carried out in this paper.A novel 3-DOF HRDM mechanism as 3-PSS/6R was studied,about the kinematics foundation,trajectory planning,dynamic model,control strategy,experiment and control system are studied.The main content of this paper is as follows.(1)A kind of reconfigurable hybrid redundant driving mechanism(HRDM for short)is proposed.The freedom of the kind of mechanism is determined by the intermediate limb called HRDL,which is the key subassembly under force of the whole mechanism under the working condition.The HRDL is driven by both the constant speed motor and the servo motor,among which the constant speed motor is the main power source of the whole mechanism.The servo motor accurately compensates the trajectory of the moving platform by adjusting the input torque.(2)The degrees of freedom of 3-PSS/6R HRDM is analyzed,and the kinematics model is established.Based on the model,the workspace of 3-PSS/6R is analyzed,and the atlas of workspace is obtained.The correctness of the kinematics model is verified using ADAMS software.The driving motor runs smoothly and the movement of the mechanism is control able.(3)Based on the principle of virtual displacement,the static balance equation of the HRDM is established,and the relation between input drive and generalized force is obtained.Considering the influence of gravity on the static force of the mechanism,a new static equilibrium equation is established by considering the influence of gravity of each component on the static force of the mechanism.The links are disassembled from the kinematic pairs using disassembling link method,and the forces of each kinematic pair are analyzed using virtual work principle.(4)The stiffness of the mechanism directly determines the dynamic performance of the mechanism,and it is the basis of kinematics analysis of the mechanism.The stiffness model of the mechanism is established and verified using finite element method.The vibration characteristics,vibration mode,strain and deformation of the mechanism are obtained.The weak links existing in HRDM structure are obtained,which provide theoretical support for the structure designing of the type mechanism.(5)The dynamic model of the mechanism is established using Lagrange method.The HRDL can not only increase the stiffness of mechanism,but also provide the main source of power for the moving platform.In the designing structure of the mechanism,the strength of HRDL should be increased.While the rest limbs can drived by small power servo motor,which beared a very small force.The HRDL is drived by an uncontrollable constant speed motor,which provides the main power with repeated movement.By optimizing the driving torque of the servo motor,it can obviously reduce the force of the symmetrical branched-chain.Therefore,HRDM mechanism can be optimized by controlling method.(6)A modular reconfigurable open control system architecture is proposed to meet the requirements of experimental for a type of n-DOF HRDM based on the reconfigurable theory.Then,a feedback linearization control strategy based on neural network compensation is proposed,as a control system of the 3-PSS/6R mechanism.Finally,the trajectory of the mechanism is verified by experiments.