Research On Structural Synthesis Methods And Application Of Task-based Generalized Parallel Mechanisms

The traditional parallel mechanisms(PMs)suffer from the shortcomings of small workspace and low task specificity,which become one of the key factors limiting its widespread application in industries,logistics,services,etc.Increasing the workspace of the parallel mechanism,especially the orientational workspace,and improving the task specificity of the PMs have become hot technical topics for PM research.The generalized parallel mechanism(GPM)no longer follows the structure of the traditional PM,so that it can overcome the shortcomings of the traditional PM and retain its advantages.It is an important way to improve the performance of the mechanism and promote the widespread application of the PM.Since the structural synthesis methods of the traditional PM are no longer suitable for designing GPM,the structural methods based on the screw theory and Lie group theory are proposed.Considering the requirement of large orientational workspace,an improved method based on the traditional constraint synthesis method is proposed,by adding a procedure that constructing articulated moving platform(AMP)with relatively independent rotational axes,and a procedure that identifying the passive degree of freedom(DOF)using the modified mobility formula and constructing redundant kinematic chains.A mathematical model of GPM based on closed-loop kinematic chain is built depending on the set mapping.Further,a method and process for the structural synthesis of GPM based on a closed-loop kinematic chain is presented.The sufficient and necessary condition of planar decoupled pure rotational DOF is deduced,and the synthesis topology framework and mathematical model of GPM based on fixed closed-loop chain are established,and then the synthesis process of GPM based on fixed closed-loop chain is proposed.Aiming at the application requirements of the 3 DOF 1T2 R PM with large 2D rotational angles,a class of 1T2 R GPMs with high 2D rotational performance is designed by using the proposed improved constraint synthesis method.Combined with a two DOF base slide,a class of 5-axis cooperative mechanisms with 2D large rotational angles is constructed,which can be used in 5-axis machine tools and multi-direction 3D printer.The high rotation performance of the GPMs is proved by kinematic analysis,and the reason for the high rotational performance is explained by decoupling research.In response to the application requirements of PMs with large multi-dimensional rotational angles and specific translational DOF,a class of 4-DOF 1T3 R,2T2R,3T1 R GPMs and a class of 5-DOF 3T2 R,2T3R GPMs are synthesized,using the synthesis method of GPM that based on closed-loop kinematic chain.The GPMs that designed by the high-output planar closed-loop kinematic chains and their derivative space closed-loop chain are proposed,so that the designed mechanism has both the high-output performance of the planar closed-loop kinematic chain and the performance advantages of the PM itself.In order to design mechanisms for multi-dimensional large rotational angles and tasks of grasping,assembling,sorting,etc.,a 3T3 R GPM with 3D large rotational angles and a class of planar 3+1 DOF,spatial 6+1 DOF GPMs with integrated end-effectors are constructed relying on the synthesis method that based on the fixed closed-loop chain.The workspace performance of this type of GPMs is analyzed,and the multi-dimension high rotational capabilities are proved,and the effectiveness of the synthesis method is also proved.Two prototypes are built,which verifies the gripping characteristics and DOF of this type of mechanisms,and proves the validity of the synthesis method.Further,aiming at the task requirements of grabbing,assembling,sorting and carrying for large working space,high carrying capacity,high precision and high task adaptability in the fields of industry,service industry and disaster rescue,a 2-UU-UPU generalized parallel dexterous hand finger is designed depending on the motion function of human fingers,and the structure evolution of 3-UU parallel mechanism based on the theory of Lie group.The operation modes of the dexterous hand and the in-hand manipulation characteristics for the object are analyzed.The workspace of fingers is presented,and the performance evaluation index and analysis method for the relationship between the object size and input-output of the generalized parallel dexterous hand is proposed.The force transmission capability of the dexterous finger is developed and a prototype is built.In order to further improve the task adaptability of the generalized parallel dexterous hand,based on the characteristics of the 3-[P][S] PMs,a kind of 2-DOF parallel dexterous hand fingers is proposed,and a palm with a pair of symmetrical double slider mechanisms is designed,so as to construct a multi-mode generalized parallel dexterous hand.The operation mode is analyzed,and it is proved that the proposed hands have stronger task adaptability.The properties of the rotational DOF of the dexterous hands after holding the object in different modes are analyzed.The size of the finger workspace of the proposed dexterous hands is compared with that of the traditional anthropomorphic dexterous hand,which proves the large workspace performance of the fingers of this kind of multi-mode dexterous hands.The relationship between the maneuverability of dexterous hand and the size of the object is analyzed.