Research On The Type Synthesis Of Lower-mobility Generalized Decoupling Parallel Mechanism With Three Rotational Degree Of Freedom

With the promotion and development of the strategic initiative INDUSTRIE 4.0 and “Made in China 2025” plan,it makes a higher demand for the robotic technology and high-tech production equipment.As an important branch of mechanism,parallel mechanisms have a bright prospect of application and are widely used in the field of robot and production equipment because of their superiority in stiffness,intensity,and load capacity.The introduction and research of decoupled parallel mechanisms make great change for parallel mechanism.The decoupled parallel mechanisms obtain the merits of general parallel mechanisms.In addition,it has better performance in dynamic and higher efficiency in control system when compared with general parallel mechanisms.In this paper,the 3RnT lower-mobility parallel mechanism is taken as the research object,and the method of decoupled parallel mechanism type synthesis is studied which enriches the configuration of decoupled parallel mechanisms.The research provides a theoretic foundation and new design approach for type synthesis of decoupled parallel mechanism.The main contents of this paper are as follows:Analyze the characteristics of the output parameters in translational decoupled parallel mechanism.Based on the analysis result and combined with the previous definition of decoupled mechanism,a new concept of generalized decoupling is proposed which gives restrictions on the output parameters of parallel mechanism.The output parameters are analyzed according to the definition of generalized parallel mechanism,and the concept of cardinal limb is presented.It provides a theoretic foundation for the following type synthesis of generalized parallel mechanism.Do research on the characteristics of combined kinematic pairs,and the conditions for limbs' single DOF motion are studied including single rotational DOF motion and single translational DOF motion,the concept of motion unit is proposed.Based on the aforementioned research results,the requirements for limbs' revolute pairs to be coaxial with the revolute pairs all the time is discussed,and a new method is presented to evaluate the coaxial case for revolute pairs.The arrangement of motion unit in a limb is discussed including the rotation unit and the translation unit.The requirements of actuators for limbs is analyzed basing on the feature of generalized parallel mechanism.A new method for type synthesis of the generalized parallel mechanism is presented,which provides a new design approach for generalized parallel mechanism.Type synthesis method of the generalized parallel mechanism is applied to synthesis the three DOF rotational generalized decoupling parallel mechanisms,3R1 T generalized decoupling parallel mechanism,and 3R2 T generalized decoupling parallel mechanism.Firstly,the output parameters of parallel mechanisms are chose.Secondly,allot the mobility of each limb in the parallel mechanisms.Secondly,the cases of the combination for different coaxial revolute pairs are discussed.Then,type synthesis the structure of limbs,and the full structure of each kind of limb can be obtained.As a result,a large number of generalized decoupling parallel mechanisms are gained which proves the feasibility of the newly proposed theory and method for generalized decoupling parallel mechanisms.