Kinematic and Dynamic Characteristics Analysis of Bennett's Linkage

Bennett's linkage is a spatial fourlink linkage,and has an extensive application prospect in the deployable linkages.Its kinematic and dynamic characteristics analysis has a great significance in its synthesis and application. According to the geometrical conditions of Bennett 's linkage,the motion equations are established,and the expressions of angular displacement,angular velocity and angular acceleration of the followers and the displacement,velocity and acceleration of mass center of link are shown. Based on Lagrange's equation,the multi-rigid-body dynamic model of Bennett's linkage is established. In order to solve the reaction forces and moments of joint,screw theory and reciprocal screw method are combined to establish the computing method.The number of equations and unknown reaction forces and moments of joint are equal through adding link deformation equations. The influence of the included angle of adjacent axes on Bennett 's linkage 's kinematic characteristics,the dynamic characteristics and the reaction forces and moments of joint are analyzed.Results show that the included angle of adjacent axes has a great effect on velocity,acceleration,the reaction forces and moments of Bennett's linkage. The change of reaction forces and moments of joint are apparent near the singularity configuration.

Constraint and Mobility Change Analysis of Rubik’s Cube-inspired Reconfigurable Joints and Corresponding Parallel Mechanisms

The current research of reconfigurable parallel mechanism mainly focuses on the construction of reconfigurable joints.Compared with the method of changing the mobility by physical locking joints,the geometric constraint has good controllability,and the constructed parallel mechanism has more configurations and wider application range.This paper presents a reconfigurable axis(rA)joint inspired and evolved from Rubik’s Cubes,which have a unique feature of geometric and physical constraint of axes of joint.The effectiveness of the rA joint in the construction of the limb is analyzed,resulting in a change in mobility and topology of the parallel mechanism.The rA joint makes the angle among the three axes inside the groove changed arbitrarily.This change in mobility is completed by the case illustrated by a 3(rA)P(rA)reconfigurable parallel mechanism having variable mobility from 1 to 6 and having various special configurations including pure translations,pure rotations.The underlying principle of the metamorphosis of this rA joint is shown by investigating the dependence of the corresponding screw system comprising of line vectors,leading to evolution of the rA joint from two types of spherical joints to three types of variable Hooke joints and one revolute joint.The reconfigurable parallel mechanism alters its topology by rotating or locking the axis of rA joint to turn all limbs into different phases.The prototype of reconfigurable parallel mechanism is manufactured and all configurations are enumerated to verify the validity of the theoretical method by physical experiments.

INSTANTANEOUS KINEMATIC CHARACTERISTICS OF ASPECIAL 3-UPU PARALLEL MANIPULATOR

The instantaneous kinematics of a special 3-UPU parallel platform manipulator is discussed. First, the instantaneous motions of the 3-UPU manipulator in four kinds of positions and a special manipulator are studied by reciprocal screw theory. Then, the principal screws in one of four positions are obtained. It is shown that the moving platform has five degrees of freedom （DOF） in the initial position or after a translation along the z-axis; In the generic position, the mechanism only has three DOF, moreover the three DOF characteristics are different in different position. The instantaneous kinematic characteristics of alike 3-UPU mechanisms are very different in different position and special structure. The results presented are important to the use of alike 3-UPU parallel manipulator and contribute to the mechanism theory .