عنوان مقاله [English]
In this paper, by using the theory of linear transformations, we investigate the type synthesis of 4-DOF parallel mechanisms performing different motion patterns are investigated. Most of the applications in various fields require limited movement and less than 6 degrees of freedom. The parallel mechanism with 4 degrees of freedom has many applications in different areas, such as
industry and, medicine. Thus, the type synthesis of these mechanisms are is of paramount importance. This theory, which is one of the motion criteria, is applied to determine the degrees of freedom, and then synthesize the limbs of mechanisms. Unlike the classical theories of motion, in the case of parallel mechanisms and mechanisms with closed chains, this approach leads to promising and remarkable results. In this paper, 4-DOF parallel mechanisms performing three rotational DOFs and one translational DOF (3R1T), two rotational DOFs and two translational DOFs (2R2T), and three translational DOFs and one rotational DOF (3T1R) are synthesized. These mechanisms belong to a group of complex mechanisms which have closed chains in the structure of their limbs. The parallelogram loop is considered to synthesizes these complex mechanisms which helps to achieved mechanisms with lower motion decoupling. After synthesizing and obtaining the appropriate degrees of freedom and motion patterns, the mechanism with less kinematic complexities is selected, and then analyzed via the screw theory. Using the screw theory, without complex derivative of inverse kinematic problems, Jacobian mechanism can be obtained. In this analysis, the degrees of freedom and motion patterns of each mechanism are tested and the Jacobian matrix related to each one is obtained. Using the screw theory, Jacobian matrix of all mechanisms are is obtained. The results indicate that the mechanisms have the appropriate degrees of freedom and motion patterns, and thus, the theory of linear transformations works properly. Moreover, the Jacobian matrices for these mechanisms have acceptable motion decoupling which implies the non-complexity in the velocity equations of these mechanisms.